What alloys is cast iron made of? The term cast iron, production and use of cast iron, properties of cast iron

alloy resulting in industrial materials

The concept of cast iron, the history of its discovery and consumption, cast iron production, stages of cast iron production, countries where cast iron is sold, general characteristics of cast iron, the occurrence of cast iron in nature, cast iron minerals, cast iron compounds, methods of extracting cast iron from solid materials, cast iron processing, industrial processes for processing cast iron , properties of cast iron, areas of application of cast iron, cast iron and environmental problems associated with it, main sources of environmental pollution from cast iron, diseases resulting from cast iron poisoning, quantitative determination of cast iron, world reserves of cast iron, mining of iron ores in the world, cost of cast iron in the world markets, interesting facts about cast iron

Expand contents

Collapse content

Cast iron is the definition

Cast iron is a large vessel, a pot made of cast iron, later also made of aluminum alloy, round in shape, for stewing and cooking in a Russian oven. A special feature of cast iron is its shape, which follows the shape of a traditional clay stove pot: narrowed at the bottom, widening towards the top and tapering again towards the neck. This shape allows cast iron to be placed in the oven and removed from the oven using a special tool - a grip, which is an open metal ring on a long wooden handle.

Cast iron is an alloy of Fe (base) with C (usually 2 4%), containing permanent impurities (Si, Mn, S, P), and sometimes alloying elements (Cr, Ni, V, Al, etc.). Typically fragile. It is obtained from iron ore materials in blast furnaces.

Cast iron is the first smelting from which, by reheating and pressing under a strong hammer, is mined. White cast iron, hard and brittle; gray and black, soft.

Cast iron balls

Cast iron is a general designation for various forms of iron, primarily gray cast iron and ingots (immediately after leaving the BLAST FURNACE). This includes a range of alloys of iron with carbon and silicon, the carbon content ranging from 1.7 to 4.5%.

Cast iron is an alloy of iron with carbon (from 1.5 to 4%), usually contains, in addition, in small quantities impurities of silicon, manganese, phosphorus and; obtained from iron ores by blast furnace.

Cast iron is an alloy of iron with a large amount of carbon and other elements. The bulk of cast iron is processed into.

Production of cast iron, steel, and rolled products

Cast iron is an alloy of iron with carbon (and other elements). The carbon content in cast iron is at least 2.14% (the point of limiting solubility of carbon in austenite on the phase diagram): less - steel. Carbon imparts hardness to iron alloys, reducing ductility and toughness. Carbon in cast iron can be contained in the form of cementite and graphite. Depending on the shape of graphite and the amount of cementite, white, gray, malleable and high-strength cast irons are distinguished. Cast irons contain permanent impurities (Si, Mn, S, P), and in some cases also alloying elements (Cr, Ni, V, Al, etc.). As a rule, cast iron is brittle.

Cast iron is cheap engineering material with good casting properties. It is a raw material for steel smelting. Pig iron is obtained from iron ore using fuel and fluxes.

Cast iron is iron smelted from ore mixed with carbon, more brittle and less malleable than steel . Round shaped vessel, metal pot.

Cast iron is an alloy of iron (base) with carbon (2-4.5%), containing permanent impurities (manganese up to 1.5%, silicon up to 4.5%, sulfur up to 0.08%, phosphorus up to 1.8%), and sometimes and alloying elements (chrome, etc.). Typically fragile.

Cast iron is iron, containing some carbon, obtained by smelting iron ore in a blast furnace, is more brittle and less malleable than steel. A pot, a vessel made of something like this.

Cast iron is an alloy of iron with carbon and some other elements, more brittle and less malleable than steel. A round-shaped vessel made of such an alloy.

Cast iron is a hard brittle alloy of iron and carbon with a content of the latter from 2 to 5%; tensile strength 8 12 kg/mm2; smelted in blast furnaces directly from iron ore in the form of a semi-finished product) used for casting or reworking.

Cast iron is an iron alloy in which the percentage of carbon ranges from 2.14 to 6.67. The popularity of this material is due to the fact that it is inexpensive and has excellent casting properties. The main use of pig iron is as a raw material for steel production. In addition, adding alloying elements to cast iron can quite significantly change its properties, reducing the inherent brittleness of this material and even making it similar to carbon steels. The raw material for smelting cast iron is iron, i.e. iron ore. To put it very simply, the process looks something like this: reduced iron from the oxides in which it is present in the ore is melted by air supply, resulting in a chemical reaction with carbon - the formation of cast iron.

Cast iron is one of the few alloys that allows you to maintain the temperature of the contents for a long time. Cast iron teapots are convenient to use as teapots. You can prepare tea for a long conversation without fear that during the conversation the prepared tea will cool down and be tasteless. The material of such teapots is absolutely harmless to humans and has long been used as a material for the manufacture of kitchen utensils. It is not recommended to use such a kettle to heat water for tea, since the inside is coated with enamel during manufacture, which can become deformed due to high temperatures.

History of the discovery and consumption of cast iron

Iron had industrial uses already before our era. In ancient times it was obtained in a plastic state in forges. The slag was separated by squeezing it out of sponge iron with hammer blows. As iron production technology progressed, the temperature at which the process was carried out gradually increased. The metal and slag began to melt; it became possible to separate them much more completely.

But at the same time, the content of carbon and other impurities in the metal increased, and the metal became brittle and inflexible. This is how cast iron appeared. Later they learned to process cast iron; a two-stage method of producing iron from ore was born. In principle, it continues to this day: the modern scheme for producing steel consists of a blast furnace process, during which cast iron is obtained from ore, and steelmaking, which leads to a decrease in the amount of carbon and other impurities in the metal.

The history of cast iron, how work on cast iron products occurs, smelting in blast furnaces, and the appearance of cast iron itself

The modern high level of metallurgical production is based on theoretical research and discoveries made in various fields, and on rich practical experience. A significant share in this process belongs to Russian scientists. For example, Russian scientists were the first to widely use it for blast furnace smelting.

Cast iron was obtained in commercial quantities even before our era when smelting iron by the Sumerians, Chinese, Romans... Cast iron was considered as a less expensive by-product. But they soon found a use for it. This is how cast iron frying pans and cauldrons appeared. And in ordinary centuries, cast iron has already become the main material in the manufacture of utensils for cooking. A copper cauldron, of course, heats up faster than a cast iron one, but copper costs many times more. In addition, copper is easily oxidized, and its oxides are very harmful to health. Therefore, the spiritual part of such dishes was covered with the thinnest layer, which quickly wore out during use and felt the need for constant renewal. Operating costs were added to the purchase of utensils. Cast iron did not ask for any operating costs.

Nowadays there are fewer and fewer wood-burning stoves left, a whole cast iron stove is becoming exotic, and many have only noticed the grip in the movies. But cast-iron frying pans, stewpans, cauldrons, duckling and goose pans, and various baking shapes are still produced. Grill pans, previously unknown to our fellow citizens, were born - a square shape, with a hilly bottom. So, despite all the technical innovations and zigzags of culinary fashion, cast iron does not intend to give up its position.

This cutting of cast iron just gives me goosebumps, but it turns out quite well

Malleable cast iron is produced by long-term annealing of white cast iron, which results in the formation of flake-shaped graphite. The metal base of such cast iron is ferrite and, less commonly, pearlite. Malleable cast iron got its name due to its increased ductility and viscosity (despite the fact that it is not subject to pressure treatment). Malleable cast iron has increased tensile strength and increased impact resistance. Parts of complex shapes are made from malleable cast iron: car rear axle housings, brake pads, tees, angles, etc.

The design of the Police Bridge was very successful and was approved as a “model”. Some time later, cast iron blocks were prepared for the entire series of bridges across the Moika. The Alexandrovsky plant also took part in projects for the construction of other bridges in the capital. So in 1814, side planks, railings and other details were cast for the Bloody Bridge, and in 1816 for the Kissing Bridge at the Moscow Outpost.

Steel bathtubs last about 15 years. The disadvantages of these baths are the volume when drawing water, taking a shower, taking a bath; they also do not maintain the water temperature well, that is, the water in these baths quickly becomes cool. Acrylic bathtubs have a drawback - scratches quickly appear, despite the fact that they can be polished, but after 6 - 7 years the acrylic bathtub loses its original appearance and becomes unpleasant to the touch.

History of the use of cast iron in ancient China

Iron that consists of more than 3% carbon is called cast iron. Compared to iron, it has a significantly lower melting point and is well suited for. In the Ancients, mass production of such metal was established. It was relatively cheap, so cast iron tools were available to almost everyone. Almost all ancient agricultural tools were made of so-called white cast iron. It is characterized by high abrasion resistance, hardness and brittleness. This led to the fact that when hitting a stone, the hoe could simply crack. Archaeologists have found many coins from the Han, Song and Qing dynasties. They came to the conclusion that due to a shortage of copper, the traditional metal for manufacturing, it was necessary to use white cast iron. If this alloy was cast in special ceramic molds and left to cool slowly for several days, a metal called gray cast iron was obtained.

At that time they were also able to produce malleable cast iron with a carbon content of no more than 1%. Scientists suggest that “black” malleable cast iron was obtained by annealing at temperatures above 900 degrees for several days. Arrowheads, swords, scissors, tips for wooden shovels and other items were made from it. The mechanical properties of this metal were significantly superior to white cast iron.

Many examples of cast iron products from Ancient China have survived to this day. Perhaps the most unusual is the tomb, carved into the rock around 100 BC. In order to reliably close the entrance, its walls were filled with a continuous layer of cast iron. This metal was also used to make statues of various sizes, bells, the ringing tone of which depended on the number of bubbles in the cast iron, anchors and chains, cannons, and kitchen utensils.

Cast iron was first invented in China in the 4th century BC and was poured into molds to make ploughshares and pots as well as weapons and pagodas. In the west, where it did not become available until the end of the 14th century, its earliest use included cannon and firing. Henry began casting guns in England. Soon, English iron workers using blast furnaces developed the technique of producing cast iron cannons, which, while heavier than prevailing bronze cannons, were much cheaper and enabled England to arm its navy better. Heath ironworkers continued to produce cast irons until the 1760s, and weaponry was one of the main uses of irons after the Restoration.

With its relatively low melting point, good fluidity, casting ability, excellent machinability, deformation resistance and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes, machines and parts

History of Russian cast iron

The most popular metal used in interior design and construction is steel. With the help of steel beams, in particular, residential buildings and various buildings intended for production or administration are erected.

Unfortunately, cast iron, which is now used for the manufacture of pipes, drain grates and spare parts for vehicles, has been consigned to oblivion.

Russian cast iron production has been developing for five centuries. One of the main Ural crafts since the seventeenth century has been iron casting. The foundry, whose workshop was engaged in cast iron, became a symbol of the Urals. Cast iron was used in the creation of landscape gardening ensembles and in architecture. Craftsmen created beautiful products from cast iron: fences, benches, lamp posts, fireplace grilles and window grilles, stove doors, gazebos, stair railings and much more. Cast iron grilles with cast gates with openwork elements were very popular, and balconies and bas-reliefs made of cast iron added sophistication to palaces and apartment buildings.

Several centuries later, cast iron ceased its triumphal march as the basis of decoration and in the twentieth century began to be considered a “rough” metal, which found use only for the manufacture of various structures. At the same time, it was widely used in construction, for example, for the manufacture of reinforcing mesh in reinforced concrete products and pipeline parts.

At this time, cast iron is being used again. Railings for balconies and openwork grilles, statues, benches, gazebos and twisted lamp posts are again made from cast iron; Foundry Mechanical Plant LLC again fulfills construction orders. The active use of cast iron is noted in interiors. Nowadays, fireplace grates, brackets for decorative lanterns and flower pots are again popular. Perceiving cast iron as something heavy and rough, we are sometimes amazed by its airiness and lightness when we see the openwork weaving of a cast-iron fence.

Start of iron foundry

People have never been particularly interested in the history of cast iron, although its importance is difficult to overestimate. Only a relatively narrow circle knows what role this seemingly inconspicuous material played in the development of productive forces in different eras, but everyone knows that cast iron and the steel produced from it in oxygen converters are the basis of modern engineering and technology. Among structural materials, they are, of course, in first place and will not give it up for a long time, despite the increasingly widespread use of polymer and ceramic materials.

Already today the number of iron-based alloys has exceeded 10 thousand.

Analyzing European languages ​​in the field of iron foundry, sometimes you come to interesting observations. For example, a billet for further remelting is called “pig” in Russian and Ukrainian, that is, “pig”. Likewise, in English it is called “Pig Iron”, that is, literally “pig iron”. This was due to the fact that pig casting, unlike shaped casting, was trusted to students and journeymen, considering this type of casting to be the most primitive and unprestigious. In most European languages, the term for cast iron is derived from the root term assigned to the base material of iron-carbon alloys, iron, and means “cast iron.”

So, in English, the term “Iron” - “iron” corresponds to the term “Cast Iron” - “cast iron”; in German, the term “Eisen” - “iron” corresponds to the designation “Gusseisen” - “cast iron”; in Swedish “jarn” means “iron”, “gjutjarn” means “cast iron”. The same is true in Turkish, Finnish, Modern Greek and other languages. However, in French the name of cast iron “fonte” is associated with the concept “fondre” - melt, cast; in Russian, cast iron is denoted by the term “cast iron”, in Ukrainian it is clearly a derivative of the Russian “chavun”, which sound foreign (and in fact they are), and at first glance have nothing to do with the term “iron”.

How could it happen that the most characteristic difference between cast iron and other alloys - its production exclusively in a cast state - did not find a domestic designation, instead of which a foreign word began to be used. Where did the word “cast iron” come to us and what does it mean?

Cast iron as a foundry material was invented and mastered in China many centuries before the new era, as evidenced by the four-shot cast iron cannon cast in the fifth century BC. e. and cast iron castings that still exist, the largest of which is considered to be the “lion”, about 6 m high and 5.4 m long. According to literary data, the appearance of cast iron in China dates back at least to the 6th century. BC e. In contrast to these data, B.B. Gulyaev believes that casting iron was mastered only 600 years ago.

The vast Mongol Empire, which arose as a result of the predatory campaigns of Genghis Khan and his first successors, greatly facilitated familiarization with the cultural achievements of the Chinese, residents of the Middle and East.

Comparison of the dates of the Tatar invasion and their establishment in Eastern Europe and the southeastern parts of Europe (the first half of the 13th century), as well as the dates of the travels of the first European scout ambassadors to the Tatars - Plano de Carpini (1246), Ascelina (1247), Marco Polo and others, with the time of the “invention” of gunpowder (late 13th century) and cast iron (2nd half of the 14th century) by Europeans, clearly shows the mutual connection of these seemingly disparate and seemingly completely independent historical facts .

Ancient Rus' had direct connections with the Golden Horde, in the capital of which many Russians lived, who had separate trade and craft rows there and even a separate diocese, and was in more favorable conditions than Western countries for the development of Chinese and Khorezm achievements in the field of technology. Therefore, it is logical that the Russian word - cast iron - comes from the Tajik word “chuyan” (in Tatar “chuen”). This term for both Tajiks and Tatars was brought from outside, namely from the Chinese, for whom the term “chu” (“zhu”) corresponds to the verb “to cast”, and the term “gong” is equivalent to the name “foundry” (production). Two Chinese characters: the left one “zhu” means “to pour”, the right one “gong” means “to do, production”.

V. Yakovlev points out that in some languages ​​the term for cast iron is also derived from the term assigned to iron, but in combination with different adjectives. Thus, in Chinese, the synonym for the word “cast iron” - (shengte) can be literally translated as “living iron” or as “raw”, “unfamiliar”, “unusual” iron. The same can be observed in Japanese, Danish, Hindi and other languages.

But in another group of languages ​​the term for cast iron was not formed in the same way as in previous cases. These languages ​​include Russian, Tajik, Turkmen, Kyrgyz, Afghan and, probably, a number of others. In terms of sound similarity, the Afghan term for cast iron is closest to the Russian word “cast iron”. In Afghani (cast iron) - and means cast iron. “Cast iron” in Turkmen and Kyrgyz is “choyun”, and in Tajik it is “chuyan”. One gets the impression that the Russian term “cast iron” is of Central Asian, not Chinese, origin. But this does not mean that the peoples of our country became acquainted with cast iron through the mediation of the peoples of Central Asia.

Confirmation that the Russians borrowed the name cast iron from the Tatars and Chinese through Central Asian merchants can be seen in the fact that in the census books of clerks Yuri Telepnev and Afanasy Fonvizin for the Tula and Kashira factories of 1645-1676 we have a confusion of unidentified technical terms “cast " and "cast iron" iron.

Herberstein testifies that in Rus', already under Vasily III, cast iron cannonballs were cast, and under Ivan the Terrible, cast iron bells and cannons were cast, which means that by this time iron foundry in Rus' already had a long-term practice and went through a period of development and establishment.

The Chinese origin of the word “cast iron” is also proven by Professor L. M. Marienbach. He believes that the Russian name for cast iron comes from the Chinese word "zhugong" (must be "zhutsauogong"), which in Russian means "foundry worker", or from the Chinese word "zhugendi" (must be "zhuchandi"), which -Russian means “cast”.

In both assumptions, Chinese words were selected that were close in sound similarity and denoted terms from the field of cast iron production. If we select words only by sound similarity, then in Chinese the word for a stick or staff sounds nothing more than “zhugun”. A direct connection in sound between the Chinese and Russian terms for cast iron cannot be detected. In addition to direct acquaintance with iron casting in the Great Bulgars and Sarai Berke, the Moscow government used the services of Western European specialists, and contrary to the opinion of V. Knabbe, cast iron in Rus' appeared not in the 17th century, but much earlier. Thus, the work describes that from the works of the famous ancient scientist Aristotle, it can be assumed that he knew cast iron 2300 years before the present day. Four centuries later, the Roman scientist Pliny the Elder reported that sometimes “iron, when melted, becomes liquid like water, and then breaks like a sponge.” These are already clear signs of cast iron. (Although in many sources these signs were interpreted differently.)

The outstanding Russian foundry worker N.N. Rubtsov directly writes: “Be that as it may, we have several cast iron castings dating back to the 5th-6th centuries. BC e. In museums there are many examples of cast iron dating back to a period more than a thousand years before the Middle Ages, which is considered the time of the discovery of cast iron.”

Cast iron casting was widespread BC. e. in China, irrefutable evidence of which is the cast iron castings that still exist to this day. The largest of these is a cast iron lion, about 6 m high and more than 5 m long, which stands near the Tien-jin-Pukou railway near Chien-zhou and is probably the largest of the cast-iron statues, the casting is dated 974 AD. e. About the same monument, A. M. Petrichenko and E. A. Sukhodolskaya write that they themselves examined this unique casting in detail and were convinced that the form of the Lion Tsar was poured in one go (or with short breaks, during which the cast iron in the mold did not had time to harden).

According to literary data, the appearance of cast iron in China dates back at least to the 6th century. BC e. It is interesting to note that the Scythians, who inhabited the territory of our country from the 8th century BC. e until the end of the 2nd century AD. e. There was no cast iron. The Scythians did not go further and cast.

According to the American magazine Modern Casting, 600 BC. e. In China, the first cast iron casting was cast - a tripod (weighing 600), and in 233 BC. e. The first cast iron shares were cast there.

It is known that the inhabitants of Fergana in the 2nd century. BC e. learned how to cast iron from fugitives from the Chinese troops. In 115 BC. e. The Chinese government monopolized the entire iron industry; there are numerous indications that one of the main uses of iron was the production of vats for evaporating salt from sea water and, as far as one can go back centuries, these vats were always made of cast iron.

Of all the countries known in the ancient world, only in China was iron reduced from ore with coal, and in all others with charcoal.

The ore used contained from 0.5 to 1% P, so that the pig iron obtained from this ore should not contain more than 1% P. The castings contained from 5 to 7% P, with an additional amount being obtained from coal. Thus, the Chinese learned to produce an alloy close to phosphide eutectic, that is, a metal with a melting point approximately 100° lower than bronze. This explains the relatively wide distribution of cast iron castings in China in ancient times and the, at first glance, surprising fact that neither Fergana, nor Russia, conquered by Batu, who had the opportunity to get acquainted with the Chinese experience, could develop this production at home, because they didn’t have a suitable one. Therefore, the development of iron foundry production began again in the Middle Ages, when 1) the invention of more powerful blowing devices made it possible to move to higher furnaces for the production of iron, in which cast iron was obtained due to the carburization of reduced iron, at first unexpectedly for the metallurgists of that time; 2) when the demand for cast iron cannonballs and then for cast iron cannons created a stable demand and, therefore, a solid economic basis for young production.

Interesting data is provided by A. M. Petrichenko, a great expert in artistic and coin casting, who writes that an exception to the rule should be the casting and participation in the monetary circulation of China of cast iron coins, which were widely used during the period of the Five Kingdoms (907-960 AD. ) and especially during the Song era (960-1279 AD). In some regions, in order to save copper, only cast iron coins were in circulation, but there was also a ban on their export abroad.

In foreign and domestic literature, the prevailing opinion is that the reason for the emergence of iron casting in China was the presence of high-phosphorus ores and the use of special phosphorus additives by ancient Chinese foundries.

Even a short excursion into the history of metallurgy in China is enough to convince us that this is not the only and not the main reason for the early appearance of cast iron in China. The main reason that the Chinese were the first in the world and more than 1500 years earlier than the Europeans to learn how to mine ores, smelt iron and make iron castings is the remarkable success of the Chinese in the field of bronze smelting and the construction of furnaces at the time of the advent of iron.

Some researchers attribute the first castings to the “Warring States” period, others reasonably believe that the Chinese knew how to make cast iron castings back in the “Spring and Autumn” era (722-481 BC). In fact, China began its Iron Age, as Li Heng-de testifies, not by mining raw iron and forging products from it, but by smelting cast iron and making iron castings. This is one of the features of the original development of Chinese foundry production. If there is still no convincing evidence about the use of forged iron products in the “Spring and Autumn” era, then there is a lot of completely reliable data about the production of cast iron castings during this period.

In China, already in 513 (BC), a large cast-iron ritual vessel was made, on which one of the then vaults (a kind of criminal vault) was cast. But the first cast iron castings were primarily implements and tools for agricultural purposes. The ancient chronicles of China provide irrefutable evidence of the use of iron (cast iron) agricultural tools back in the 7th century. BC e., which led to a sharp increase in field yields.

A. M. Petrichenko directly points out that the Chinese, more than 1500 years earlier than the Europeans, learned to smelt cast iron and make complex cast iron castings. By the period of the “Warring States” (403-221 BC), i.e. by the time of the appearance of cast iron die casting in China, Chinese foundry workers had perfected the technique of smelting cast iron. By this time they had reached a high level in the manufacture of foundry molds. Moreover, to produce cast money and other castings, the foundry workers of that time used mainly semi-permanent fireclay molds. The halves of such forms were made using metal (bronze) models or molds.

Of course, casting iron money was a very progressive process for several reasons.

Fourthly, it is unlikely that cast iron can be smelted from ore at home by a person who does not master the art of metallurgy, who does not have prepared ore, fluxes and reducing agents, the recipe of which was almost always kept secret and passed on from father to son.

China is the country of the most ancient literature on foundry production. Apparently, the first book on casting technology was the book “Kao Gong Di”, widely known in China, written more than 2000 years ago. This book outlines not only methods for producing castings, but also a detailed description of alloys for various products (swords, bells, household utensils, etc.), their composition and melting methods. Similar information about various casting methods is available in later sources.

More than four hundred years ago, Song Ying-hsing's book "Original Inventions" was first published, which gives brief descriptions of many of the most characteristic casting processes that have survived from ancient times. This book is well illustrated; it has been reprinted many times.

It is interesting to note that in our country, on the territory of the Odessa region, near the village. Nikolaevka, Belyaevsky district, in 1964, A.I. Melyukova found three fragments of cast iron boilers, which are the most ancient cast iron products not only in the entire European part of the former USSR. The fragments were found at a settlement of the Greco-barbarian type in undisturbed layers in different places and at a significant depth - 0.7-1 m. This layer contained a large number of products of the ancient era, reliably dated to the 4th-3rd centuries. BC e. The fragments, like any deformed cast iron, had an irregular shape measuring 94x140-110x160 and 95x130 mm, with a wall thickness of 3-7 mm. Etching revealed in all sections the cast structure of hypereutectic white cast iron with the structure of ledeburite, primary cementite and a small amount of graphite. The authors explain the reason for the chilling of cast iron by the low silicon content, and the almost complete absence of manganese indicates that the cast iron was smelted without the use of fluxes.

Chemical and spectral analyzes proved that the fragments belonged to the same boiler and were made of ore, apparently a type of brown iron ore, which was often used by ancient metallurgists to obtain iron.

It should be noted that, as an independent industry, foundry separated from metallurgical production only at the end of the 19th - beginning of the 20th centuries with the advent of small furnaces (cupola furnaces) capable of melting metal, providing sufficient overheating and providing molten cast iron with sufficient fluidity and other casting properties. It was then that when casting cast iron they stopped using only the metal of the first melt, and cast iron itself became a widespread structural material. But the foundation for this was laid by the ancient masters of China, Uzbekistan, and Volga Bulgaria.

Cast iron casting was widespread BC. e. in China, irrefutable evidence of which is the cast iron castings and cast iron molds that still exist to this day. Scythian tribes that inhabited the territory of our country from the 8th century BC. e. until the end of the 2nd century AD. e., they didn’t know iron casting. The ancient chronicles of China provide irrefutable evidence of the use of iron (cast iron) agricultural tools back in the 7th century. BC e. In fact, China began its Iron Age not by mining raw iron and forging products from it, but by smelting cast iron and making iron castings. This is one of the features of the original development of Chinese foundry production. The main reason that the Chinese were the first in the world and more than 1500 years earlier than the Europeans to learn how to mine ores, smelt iron and make iron castings is the remarkable success of the Chinese in the field of bronze smelting and the construction of furnaces at the time of the advent of iron.

Iron production

Cast iron is an alloy of iron and carbon containing more than 2% C. Ore freed from waste rock is a chemical compound of metal with other elements. In order to obtain metal from ore, certain chemical reactions must be carried out. At the same time, elements connected to the metal are affected by substances that have less affinity with it than with other elements. Since in iron ores iron is usually combined with oxygen, reduction processes must be carried out to obtain this metal. In its pure form, iron is used in technology in very small quantities. Basically, only in mechanical engineering alloys of iron and carbon are required. One of these alloys is cast iron.

Pig iron is smelted from iron ore in blast furnaces. These furnaces have the form of towers (shaft furnaces). The internal parts of the blast furnace are lined with refractory fireclay bricks. The charge, i.e. ore, fuel and flux are fed from the hopper by lift 1 into the charging apparatus of the top 2, from where it enters the internal cavity of the furnace. The furnace has a shaft 4, a steam chamber 5, shoulders 8, a hearth 9, the bottom of which is called the flange. molten cast iron is produced through a hole - a cast iron tap hole, above which there is a slag tap hole through which liquid slag is released. The air required to produce cast iron is blown under pressure in a heated state (up to 1200°C) into tuyeres 7 (12-18 pcs.), passing through an annular pipe 6 located above the air pressure at the tuyeres up to 350 kn/m2 (3, 5 kg/cm2). The blast furnace (“top”) gas is discharged through pipes 3 into cleaning devices, since it is subsequently used as fuel for the needs of blast furnace production and other purposes.

Cast iron has become widespread as a structural material in mechanical engineering, metallurgical and other industries due to a number of advantages over many materials, the main ones being low cost and good casting properties. Products made from it have sufficiently high strength and wear resistance when operating under friction and are characterized by less sensitivity to stress concentrators than steel.

In white cast iron, all carbon is bound into the chemical compound iron carbide Fe3C - cementite. In gray cast iron, a significant part of the carbon is in a structurally free state in the form of graphite. While gray cast iron lends itself well to machining, white cast iron has very high hardness and cannot be processed with a cutting tool. Therefore, white cast irons are used extremely rarely for the manufacture of products; they are used mainly in the form of an intermediate product to obtain malleable cast irons. The production of white or gray cast iron depends on the composition and cooling rate.

In the production of cast iron, the fuel used is:

Thermoanthracite;

Natural gas

Cast iron is smelted in blast furnaces, which are vertical metal shafts lined inside with refractory bricks with a high alumina content. Liquid cast iron is released into ladles, from where it is poured into molds or mixers (mixing containers, where the alloy is stored for some time in a liquid state). The cast iron produced in furnaces is divided into foundry and conversion. Foundry cast irons are used for the production of iron castings, while pig irons are used for the production of steel. To cast products, cast iron is melted in cupola furnaces, flame and electric furnaces. Liquid cast iron, molten at a temperature of 1380-1420° C, is released through a tap hole into refractory-lined casting ladles for casting cast iron into molds made from molding material with bonds.

In recent years, progressive methods of casting iron have been used: under pressure, centrifugally into shell molds. Cast iron poured into a mold remains in it until it completely transforms into a solid state, first expanding and subsequently shrinking by about 1%. Die casting is carried out in special installations consisting of a boiler with molten metal, split molds, a pressure mechanism and opening of the molds. Centrifugal casting is based on the principle of centrifugal forces acting on metal poured into a rotating mold. In this way, various products can be cast - pipes, rings, bushings, solid and bimetallic.

Domestic scientists and practitioners have developed a method for ingotless rolling of thin cast iron sheets. Cast iron, molten in cupola furnaces, is rolled into a strip between the rolls, followed by annealing for 2-3 hours at a temperature of 980-1050 ° C. Under these conditions, the cast iron sheet acquires some plasticity, allowing holes to be punched in it, cut with scissors, bent and etc.

The production of ferrous metals from iron ore is a complex process that can be roughly divided into two stages. At the first stage, pig iron is obtained, and at the second, it is processed into steel. Considering that students are already familiar with the basics of metallurgical processes from high school, below we will consider only the basic principles of iron and steel technology. Cast iron is an alloy of iron with carbon 2... 6.67%; in addition, the alloy may contain silicon, manganese, sulfur, phosphorus, etc. The starting materials for the production of cast iron are iron ores, fuel and fluxes.

Brown iron ore

Spar ReSOz iron ores containing 30...70% iron and waste rock from various natural chemical compounds SiO2, Al2Oz, etc., and harmful impurities (sulfur, phosphorus).

The fuel is coke, a product of dry distillation (without access of air) of coking coal. Fluxes (fluxes) - limestones, dolomites, quartz, sandstones - are used to lower the melting point of waste rock and convert it and fuel ash into slag. The main method of producing cast iron from ores at present is the blast furnace process, which consists of reducing iron from ores (oxides) at high temperature and separating it from the gangue ore.

Pig iron is smelted in blast furnaces with a volume of up to 5000 m3, into which ore, coke and fluxes are loaded in alternating layers, which descend down the furnace under the influence of its own mass. In the lower part of the furnace - the hearth, through the holes - tuyeres, heated air is supplied under pressure, necessary to maintain the combustion of the fuel. Coke, burning in the upper part of the hearth, forms CO2, C+O2 = CO2, which rises up the furnace and, meeting hot coke on its way, turns into carbon monoxide: CO2-f-:-f-C=2CO. Carbon monoxide reduces iron oxides to pure iron in the following order: Fe2O3, F3O4, FeO, HFe. This process can be represented by the following reactions: 3F9Q3 + CO = 2F3O4 + CO2; 2Fe3O4+2CO=6FeO+2CO; 6FeO+6CO = 6Fe+6CO2. At the bottom of the furnace, some of the reduced iron combines with carbon to form iron carbide Fe3C (carburization of iron). Then the carburized metal melts, which flows into the blast furnace hearth, while the saturation of iron with carbon continues. As a result of melting, not only iron is restored, but also other elements found in the ore, Si, Mn, P, which, as well as part of the sulfur in the form of FeS, pass into cast iron. Molten slag also flows into the furnace and floats above the cast iron, since its density is less than cast iron.

Molten cast iron and slag are periodically released through special holes - cast iron and slag tapholes, first the slag, and then the cast iron. Progressive processes in the development of blast furnace production include improving the preparation of the charge through crushing, thorough washing, sorting and beneficiation of iron ores, which is carried out, for example, by magnetic separation. The production of sinter by sintering fine ore into larger pieces is being widely developed. blast furnaces reached 5 thousand m3, which ensured an improvement in the utilization rate of useful volume and a reduction in fuel consumption per 1 ton of pig iron.

According to IISI, world production of pig iron in 2002 for 42 leading countries of the world amounted to about 600 million tons. Compared to 2001, pig iron production increased by 5.5%.

High alloy cast iron

Cast iron is the name given to iron-carbon alloys (which also contain varying amounts of impurities and alloying elements) that harden to form eutectic. Therefore, unlike steel, cast iron cannot acquire a single-phase structure (for example, austenitic) during heat treatment. According to the state diagram of Fe-C alloys (Fig. 1), the cast iron region covers alloys containing over 2.11% C. In practice, 2% C is generally accepted as the specified limiting carbon content. With an increase in the content of alloying elements, this limit is usually , shifts towards lower carbon concentrations. Thus, many high-chromium, high-silicon (for example, ferrosilides), high-aluminum iron alloys contain a significant amount of eutectic and are conventionally considered cast iron, despite the very low carbon content.

The presence of eutectic in the structure of cast iron determines its use exclusively as a casting alloy (work on rolling cast iron, especially high-strength cast iron with nodular graphite, has given some positive results, but has not found industrial application; rolling low-carbon, low-silicon white cast iron is promising).

Cast iron is less strong and more brittle than steel, but is cheaper than steel and casts well into molds. Therefore, cast iron is widely used for the manufacture of cast parts. Carbon in cast iron can be contained in the form of cementite (Fe 3 C) or graphite. Cementite is light in color, has great hardness and is difficult to machine. Graphite, on the contrary, is dark in color and quite soft. Depending on which form of carbon predominates in the structure, there are two main types of cast iron: white and gray.

Based on the degree of eutecticity, cast iron is divided into hypoeutectic, eutectic and hypereutectic (see Fig. 1). It is wrongly accepted to equate the degree of eutecticity of cast iron with the degree of “saturation”. The latter applies to both cast iron and steel and reflects only the ratio of the carbon content in the alloy to the eutectic or, taking into account the influence of silicon and phosphorus on the shift of the eutectic point to the left.

Cast iron is considered eutectic when the carbon equivalent is 4.2-4.3%.

Based on the content of additional components, cast iron is divided into unalloyed, low-alloyed, medium- and high-alloyed. Cast iron is considered unalloyed if it contains up to 3.5-4% Si, up to 1.5-2% Mn, up to 0.3% P, up to 0.2-0.25% S and up to 0.1% of elements such as Cr, Ni, Cu. In low-alloy cast iron, the content of each of the listed alloying elements usually does not exceed 1.0-1.5%, in medium-alloyed cast iron it can reach 7%, and in high-alloyed cast iron it exceeds 7-10%. Additives of hundredths and even thousandths of a percent of elements such as magnesium, nitrogen, boron, bismuth are considered alloying (microalloying, modification).

According to the degree of graphitization, cast iron is divided into white (practically not graphitized), bleached or half-grafitized (partially graphitized) and gray (largely or completely graphitized). Malleable is the name given to cast iron obtained from white cast iron by graphitizing it in the solid state during heat treatment.

White cast iron is an alloy in which all or virtually all of the excess carbon not in solid solution in the iron is present in the form of cementite Fe 3 C (or special carbides in alloyed cast iron). In unalloyed cast iron, cementite is a metastable phase that can decompose to form iron and graphite. In the figure above, the metastable equilibrium lines (cementite system) PSK, ES, ECF and CD are shown solid, and the stable equilibrium lines (graphite system) P`S`K`, E`S`, E`C`F` and C`D ` —- dotted (in the physical chemistry of metals the reverse order of designation is accepted).

In incompletely graphitized gray cast iron, the eutectoid transformation occurs not in a stable (graphite) but in a metastable (cementite) system, and austenite does not transform into a ferrite-graphite eutectoid, but into a ferrite-cementite mixture - pearlite. Moreover, the presence of pearlitic cementite and even a small amount of secondary cementite (precipitating from austenite during its cooling in accordance with the metastable equilibrium line ES in the figure above) is not a sign of chilling of gray cast iron.

In industrial practice, cases are most often observed when the eutectoid transformation occurs partly in stable and partly in metastable systems. The resulting pearlitic-ferritic cast iron has properties approaching those of pearlitic or ferritic gray cast iron, depending on the percentage of ferrite and pearlite in the structure of the metal base.

When white cast iron is annealed onto malleable graphite, it is released in the form of more compact inclusions, as a result of which the metal acquires certain plastic properties (hence the name of this type of cast iron). Like gray cast iron, malleable cast iron can be fully or partially graphitized and is divided respectively into ferritic, ferritic-pearlitic and pearlitic. There should be no ledeburite or secondary cementite in malleable cast iron (with the exception of individual isolated, so-called “residual” carbides). Half ductile cast iron has not found industrial application.

At the end of the forties, a method was invented for modifying cast iron with magnesium, cerium (and now also with yttrium and a number of other elements), in which graphite inclusions acquire a spherical or similar shape. This alloy is actually a type of gray cast iron, but due to the acquisition of a number of specific properties (a combination of high strength and ductility, increased impact strength), it is classified separately under the name “high-strength” cast iron (DC) or nodular cast iron (SG). Depending on the modifier used, it is also called magnesium or cerium cast iron. In foreign literature it is often called “ductile” cast iron. High-strength cast iron is also divided into pearlitic, pearlitic-ferritic and ferritic. In industry, bleached nodular cast iron is also used.

Often modification with magnesium or cerium leads to almost complete whitening of cast iron. After graphitizing annealing, spherical graphite inclusions are formed in the metal. This material is actually a type of malleable cast iron. However, due to a number of specific features (short annealing time due to the high silicon content in the metal and the absence of an incubation period), it is classified in the same group with high-strength cast iron.

Thus, significantly graphitized cast iron is conventionally divided into gray (SG), malleable (CC) and high-strength (HF), although in some cases it is very difficult to draw a boundary between them.

Gray, ductile and ductile iron are classified according to their mechanical properties. According to the general classification, the following division is accepted:

Based on special properties, cast iron is divided into wear-resistant, anti-friction, corrosion-resistant, heat-resistant, and non-magnetic.

Based on hardness, cast iron is divided into:

Soft cast iron< HB149

Medium hardness HB149-197

Increased hardness HB 197-269

Solid > HB269

Based on strength, cast iron is divided into:

Ordinary strength< 20 кГ/мм 2

Increased strength = 20-38 kg/mm ​​2

High strength > 38kg/mm ​​2

In white cast iron, almost all the carbon is contained in a bound state in the form of cementite. Such cast iron has a light gray color when broken, is very hard, almost impossible to machine, and therefore is not used for the manufacture of parts, but is used for conversion into steel and for the manufacture of parts from malleable cast iron. This type of cast iron is also called pig iron.

Gray cast iron has a dark gray color when broken, is soft, can be easily machined with tools, and is therefore widely used in mechanical engineering. The melting point of gray cast iron is 1100–1250° C. The more carbon in cast iron, the lower the melting point. The main amount of carbon in gray cast iron is contained in the form of graphite, evenly distributed among the grains of the base alloy.

Gray cast iron, compared to white cast iron, contains more silicon and less manganese, since silicon promotes the graphitization of carbon in cast iron, and manganese, on the contrary, causes the formation of fixed carbon - cementite.

Approximate composition of gray cast iron: 3-3.6% carbon; 1.6-2.5% silicon; 0.5-1% manganese; 0.05-0.12% sulfur; 0.1-0.8% phosphorus. Sulfur is a harmful impurity in cast iron, making it difficult to weld and reducing its strength; it increases the viscosity of cast iron in the molten state and increases its casting shrinkage.

Phosphorus makes cast iron more melting and improves its weldability, but at the same time increases brittleness and hardness. Therefore, the content of sulfur and phosphorus in cast iron should not exceed the specified limits.

According to GOST 1412-54, the grade of gray cast iron is designated by the letters SCh and two numbers, of which the first indicates the average value of tensile strength in kgf/mm 2, and the second - the same for bending. For example, gray cast iron of the SCh12-28, SCh15-32, SCh18-36, etc. grades is produced. The most durable is the SCh38-60 cast iron. The Brinell hardness for gray cast iron SCh12-28 ranges from 143 to 229, for cast iron SCh38-60 - from 207 to 262.

Malleable cast iron, in terms of mechanical properties, occupies an intermediate position between cast iron and steel; it differs from gray cast iron in being more tough and less brittle. To obtain parts from malleable cast iron, they are cast from white cast iron and then subjected to heat treatment, for example, long-term annealing or “simmering” in sand at 800-850 ° C. In this case, free carbon is released in the form of small rounded particles arranged in the form of separate clusters ( flakes) between iron crystals. At temperatures above 900-950° C, carbon turns into cementite and the part loses the properties of malleable cast iron. Therefore, after welding, parts must again be subjected to a full cycle of heat treatment to obtain a ductile cast iron structure in the weld and heat-affected zone.

Malleable cast iron according to GOST 1215-59 is designated by the letters KCH and two numbers: the first indicates the tensile strength in kgf/mm 2, and the second indicates the elongation in percent, for example KCH35-4.

Alloyed cast iron has special properties - acid resistance, high strength under impact loads, etc. Cast iron obtains these properties as a result of alloying with chromium and nickel.

Modified cast iron is produced from gray cast iron by introducing special additives into liquid cast iron, called modifiers - silicocalcium, ferrosilicon, silicoaluminum, etc. The amount of modifiers introduced does not exceed 0.1 - 0.5%, and the temperature of the liquid cast iron must not be lower than 1400° WITH.

During modification, the composition of cast iron remains almost unchanged, but the graphite grains take on a fine-plate, slightly swirled appearance and are located isolated from each other. This makes the structure of cast iron homogeneous, dense, and increases its strength, wear and corrosion resistance.

According to GOST 1412-54, modified cast iron is designated in the same way as gray, but with the addition of the letter M, for example: MSCh2848.

High-strength and ultra-strong cast irons have spherical graphite. This is achieved by introducing pure magnesium or its alloys with copper and ferrosilicon into liquid cast iron at 1400° C, followed by modification with silicocalcium or ferrosilicon. Heavy-duty cast iron has a tensile strength of 50-65 kgf/mm 2 (with bending 80-120 kgf/mm 2) and a relative elongation of 1.5-3%.

Mechanical and technological properties: Cast iron is a kind of composite material, the mechanical and operational properties of which depend on the characteristics of the metal base (strength, ductility, hardness, etc.), as well as the shape, size, quantity and distribution of graphite inclusions. In this case, in some cases, either graphite or a metal base is decisive. For example, the elastic modulus of cast iron depends critically on the shape and size of graphite inclusions, and hardness is mainly determined by the properties of the metal base. Properties such as tensile strength, impact strength, and long-term strength depend both on the properties of the metal base and on the shape or size and number of graphite inclusions.

Obtaining a particular structure of cast iron in castings depends on many factors: the chemical composition of the cast iron, the type of charge materials, the technology of smelting and out-of-furnace metal processing, the rate of crystallization and cooling of the melt in the mold, and therefore the thickness of the casting wall, the thermophysical properties of the mold material, etc. The structure of the metal base of cast iron can also be changed by heat treatment of castings, the general patterns of influence of which are similar to those arising during heat treatment of carbon steel, and the features are associated with accompanying changes in the metal base by graphitization processes.

Among the elements of the chemical composition, C and Si determine the formation of the structure of cast iron, and for a given casting technology, the reduced size of the casting wall R np characterizes its cooling rate - the ratio of the cross-sectional area of ​​the wall to the perimeter).

Along with Si, Al is of great importance as a graphitizing element, which sometimes partially or completely replaces Si. This improves the properties of cast iron, especially ductility. The most favorable combination of strength, toughness and ductility characteristics is achieved in aluminum cast irons when they contain Si< 1,0 %.

Based on the influence of small additions of other elements on the structure of cast iron and, consequently, the properties of the additives, they can be divided into three groups.

The first group of elements (Ni, Co, Cu), similar to Si, has a graphitizing effect and contributes to the grinding of graphite precipitates. At the same time, these elements stimulate the production of more dispersed pearlite needles and. martensitic structures even with relatively slow cooling.

The second group of elements (Cr, Mo, W, V, etc.), in contrast to the first, prevents graphitization with an intensity proportional to the concentration. When the content exceeds their solubility limit in cementite or ferrite, they form special carbides.

The third group of elements includes Ti, Zr, Ce, Ca, Mg, B, etc. These elements are characterized by high chemical activity and are almost entirely consumed in the formation of refractory carbides, sulfides, oxides, nitrides, which can serve as nuclei in the process of subsequent crystallization and increase the dispersion of the metal base. Moreover, the elements of this group Mg, Ca, Ce and other rare earth metals (REM) are included in alloys for modifying cast iron in order to obtain vermicular or spherical graphite.

Magnetic properties of cast irons. In accordance with the requirements for parts, cast iron can be used as a ferromagnetic (soft magnetic) or paramagnetic material.

Magnetic properties, to a greater extent than any other, depend on the structure of the metal, which determines the division of magnetic properties into primary and secondary. The primary ones include induction, saturation (4ll), permeability in strong fields and magnetic transformation temperature. These properties depend on the quantity and composition of ferromagnetic phases and do not depend on their shape and distribution. Secondary properties include hysteresis characteristics: induction, saturation and permeability in weak and medium fields, coercive force, residual magnetism. Secondary properties depend little on the composition of the phases and are determined mainly by the shape and distribution of structural components.

The main ferromagnetic components of cast iron are ferrite and cementite, characterized by the following data.

Cementite is a harder magnetic component, therefore gray rather than white cast iron is always used as a soft magnetic material. Graphitization leads to a sharp decrease in H c and an intense increase in U max, especially during the decomposition of the last carbide residues. In this case, the influence of graphite, like other non-magnetic phases, also depends on the shape and size of inclusions. The most favorable in this regard is the globular form. Therefore, ductile and high-strength cast iron are characterized by higher induction and magnetic permeability and lower coercive force than gray cast iron with the same matrix.

The enlargement of eutectic and ferrite grains and a decrease in the amount of pearlite have the same effect. Therefore, tempering after hardening helps to improve the soft magnetic properties.

Non-magnetic (paramagnetic) cast irons are used in cases where it is necessary to minimize power losses (oil switch covers, transformer end boxes, pressure rings on electric machines, etc.) or when minimal distortion of the magnetic field is necessary (stands for magnets, etc.). P.). In the first case, along with low magnetic permeability, high electrical resistance is required; Cast iron satisfies this requirement even to a greater extent than non-ferrous alloys. In the second case, a particularly low magnetic permeability is required. Therefore, in some cases it is not possible to replace non-ferrous alloys with austenitic cast irons for the second group of castings.

Depending on the composition, austenitic non-magnetic cast irons are distinguished:

Nickel type niresist with varying amounts of chromium;

Nickel-manganese type Nomag with varying amounts of copper and aluminum, superior to the first cast irons

The groups are non-magnetic, but inferior to them in heat resistance, heat resistance and corrosion resistance;

Manganese with varying amounts of copper and aluminum, which are the cheapest, but have lower strength and physical properties.

Ferritic high-alloy aluminum cast irons, characterized by particularly low magnetic permeability, are also of interest.

The influence of the type of cast iron on its density: The highest density is characterized by white cast iron, which does not contain free graphite inclusions, and some alloy cast iron (chrome, nickel, chromium-nickel). In gray cast iron, the density is usually greater, the higher the strength of the cast iron.

High-strength cast iron, all other things being equal (the same content of silicon, pearlite and graphite), is characterized by a higher density than cast iron with flake graphite. However, in many cases this density may actually be lower than that of gray cast irons due to the higher carbon and silicon content or greater ferritization of the matrix.

Austenitic cast irons are also characterized by higher density due to their denser structure, especially when alloyed with nickel and copper, the density of which is greater than that of iron.

When alloyed with manganese, the density of austenite decreases slightly. The density of ferritic silicon and aluminum cast irons is even lower.

Brief designations:
σ in	- temporary tensile strength (tensile strength), MPa		ε	- relative settlement at the appearance of the first crack, %
σ 0.05	- elastic limit, MPa		J to	- ultimate torsional strength, maximum shear stress, MPa
σ 0.2	- conditional yield strength, MPa		σ izg	- ultimate bending strength, MPa
δ5,δ 4,δ 10	- relative elongation after rupture, %		σ -1	- endurance limit during bending test with a symmetric loading cycle, MPa
σ compress0.05 And σ compress	- compressive yield strength, MPa		J-1	- endurance limit during torsion test with a symmetrical loading cycle, MPa
ν	- relative shift, %		n	- number of loading cycles
s in	- short-term strength limit, MPa		R And ρ	- electrical resistivity, Ohm m
ψ	- relative narrowing, %		E	- normal modulus of elasticity, GPa
KCU And KCV	- impact strength, determined on a sample with concentrators of the types U and V, respectively, J/cm 2		T	- temperature at which properties were obtained, degrees
s T	- proportionality limit (yield strength for permanent deformation), MPa		l And λ	- thermal conductivity coefficient (heat capacity of the material), W/(m °C)
HB	- Brinell hardness		C	- specific heat capacity of the material (range 20 o - T), [J/(kg deg)]
H.V.	- Vickers hardness		p n And r	- density kg/m 3
HRC uh	- Rockwell hardness, scale C		A	- coefficient of thermal (linear) expansion (range 20 o - T), 1/°С
HRB	- Rockwell hardness, scale B		σ t T	- long-term strength limit, MPa
HSD	- Shore hardness		G	- modulus of elasticity during torsional shear, GPa

Carbon in cast iron can be contained in the form of cementite (Fe3C) or graphite. Cementite is light in color, has great hardness and is difficult to machine. Graphite, on the contrary, is dark in color and quite soft. Depending on which form of carbon predominates in the structure, they distinguish: white, gray, malleable and high-strength cast iron. Cast irons contain permanent impurities (Si, Mn, S, P), and in some cases also alloying elements (Cr, Ni, V, Al, etc.).

White cast iron- a type of cast iron in which carbon in a bound state is in the form of cementite, when fractured it has a white color and a metallic sheen. In the structure of such cast iron there are no visible inclusions of graphite and only a small part of it (0.03-0.30%) is detected by subtle methods of chemical analysis or visually at high magnifications. White iron castings are wear-resistant, relatively heat-resistant and corrosion-resistant. The strength of white cast iron decreases, and the hardness increases with increasing carbon content.

White cast iron is very hard, almost impossible to machine, and therefore is not used for making parts, but is used for conversion into steel and for making parts from malleable cast iron. This type of cast iron is also called pig iron.

Gray cast iron– an alloy of iron, silicon (from 1.2-3.5%) and carbon, also containing permanent impurities of Mn, P, S. In the structure of such cast irons, most or all of the carbon is in the form of plate-shaped graphite. The fracture of such cast iron is gray in color due to the presence of graphite. A separate variety (group of grades) of gray cast iron is high-strength cast iron with globular (spherical) graphite, which is achieved by modifying it with magnesium (Mg), cerium (Ce) or other elements.

Gray cast iron is characterized by high casting properties (low crystallization temperature, fluidity in the liquid state, low shrinkage) and serves as the main material for casting. It is widely used in mechanical engineering for casting machine beds and mechanisms, pistons, and cylinders.

High fragility inherent Gray cast iron, due to the presence of graphite in its structure, makes it impossible to use it for parts that work mainly in tension or bending; Cast irons are used only for “compression” work.

Gray cast iron is marked with the letters SCh, after which the guaranteed tensile strength value in kg/mm² is indicated, for example SCh30. High-strength cast irons are marked with the letters HF , after which the strength and, through a dash, the relative elongation in percent are indicated, for example VC60-2.

Malleable iron– the conventional name for soft and viscous cast iron, obtained from white cast iron by casting and further heat treatment. Long annealing is used, as a result of which cementite decomposes with the formation of graphite, that is, the process of graphitization, and therefore such annealing is called graphitizing.

Malleable cast iron, like gray cast iron, consists of a steel base and contains carbon in the form of graphite, but the graphite inclusions in ductile iron are different from those in ordinary gray cast iron. The difference is that the graphite inclusions in malleable cast iron are arranged in the form of flakes, which are obtained during annealing, and are isolated from each other, as a result of which the metal base is less separated, and the cast iron has some viscosity and ductility. Because of its flaky shape and the method of production (annealing), the graphite in malleable iron is often called annealing carbon. Malleable cast iron got its name due to its increased ductility and viscosity (although it is not subject to pressure treatment).

Malleable cast iron has increased tensile strength and high impact resistance. Parts of complex shapes are made from malleable cast iron: car rear axle housings, brake pads, tees, angles, etc.

Malleable cast iron is marked with two letters and two numbers, for example KCH 370-12. The letters KCH mean malleable cast iron, the first number is the tensile strength (in MPa), the second number is the relative elongation (in percent), characterizing the ductility of cast iron.

Ductile iron– cast iron having graphite inclusions of spheroidal shape. Spheroidal graphite has a lower surface-to-volume ratio, which determines the greatest continuity of the metal base, and therefore the strength of cast iron.

High-strength cast iron is most often used for the manufacture of critical products in mechanical engineering, as well as for the production of high-strength pipes (water supply, drainage, gas and oil pipelines). Products and pipes made from high-strength cast iron are distinguished by high strength, durability, and high performance properties.

Cast iron is an alloy of iron and carbon, containing carbon from 2.14 to 6.67%. Along with carbon, cast iron contains silicon (Si), manganese (Mn), sulfur (S) and phosphorus (P). The content of sulfur (S) and phosphorus (P) in cast iron is higher than in steel. Alloying additives are introduced into special (alloyed) cast irons - nickel (Ni), molybdenum (Mo), vanadium (V), chromium (Cr), etc.

Cast iron is divided:

• by structure- to white, gray and malleable;
• by chemical composition- into alloyed and unalloyed.

White cast iron is one in which most of the carbon is chemically combined with iron in the form of cementite Fe 3 C. Cementite is light in color and has great hardness and brittleness. Therefore, white cast iron also has a light gray, almost white color when fractured, is very hard, cannot be machined, and is therefore of limited use as a structural material. White cast irons are used to produce malleable cast irons. Gray cast iron is cast iron in which most of the carbon is in a free state in the form of graphite. Gray cast iron is soft, easy to machine with cutting tools, and has a dark gray color when broken. The melting point of gray cast iron is 1100-1250°C.

The more carbon there is in cast iron, the lower its melting point and the higher its fluidity.

Silicon reduces the solubility of carbon in iron, promotes the decomposition of cementite with the release of free graphite. When welding, oxidation of silicon occurs; silicon oxides have a melting point higher than the metal being welded, and thereby complicate the welding process.

Manganese binds carbon and prevents the release of graphite. In this way, it promotes the bleaching of cast iron. Manganese forms sulfur compounds (MnS), insoluble in liquid and solid cast iron and easily removed from the metal into slag. When the manganese content exceeds 1.5%, cast iron deteriorates.

Sulfur in cast iron it is a harmful impurity; it makes welding difficult, reduces strength and promotes the formation of hot cracks. Sulfur forms a chemical compound with iron - iron sulfide, prevents the release of graphite and promotes the bleaching of cast iron. The upper limit of sulfur content in cast iron is 0.15%. To reduce the harmful effects of sulfur in cast iron, the manganese content should be three times higher.

Phosphorus in cast iron it increases fluidity and improves its weldability, but at the same time lowers the solidification temperature, increases brittleness and hardness. The phosphorus content in gray cast iron should not exceed 0.3%.

According to GOST 1412-79 brand gray cast iron denoted by the letters SCh and two numbers, of which the first indicates the value of the tensile strength of cast iron in MN/m 2, and the second - the same in bending.

Malleable iron produced from white cast iron by heat treatment - long-term exposure at a temperature of 800-850°C. In this case, the carbon in the cast iron is released in the form of flakes of free carbon located between the crystals of pure iron. Depending on the mode, malleable cast iron with a ferritic or pearlitic structure is obtained. When ductile cast iron is heated above 900°C, depending on the cooling rate, graphite can disintegrate and form a chemical compound with iron - (Fe 3 C), and the part loses the properties of ductile cast iron. This makes it difficult to weld ductile cast iron, since in order to obtain the original structure of ductile cast iron, it must be subjected to a full cycle after welding.

Malleable iron denoted by the letters KCh and two numbers: the first - indicates the temporary tensile strength, MN/m, the second - ,%.

Alloy cast irons have special impurities Cr, Ni, due to which their acid resistance, strength under impact loads, etc. are increased.

Ductile iron obtained from gray cast iron by special treatment - introducing pure magnesium (Mg) or its alloys into liquid cast iron at a temperature not lower than 1400°C. The graphite in ductile iron has a spheroidal shape.

Weldability of cast iron

Cast iron is a difficult alloy to weld. Difficulties in welding cast iron are due to its chemical composition, structure and mechanical properties. When welding cast iron, the following properties must be taken into account: fluidity, so welding is performed only in the lower position; small, characterized by the occurrence of significant internal stresses and hardening structures during the welding process, which often lead to the formation of cracks; intense carbon burnout, which leads to porosity of the weld; in the molten state, cast iron oxidizes to form refractory oxides, the melting point of which is higher than that of cast iron. Welding cast iron is used mainly to correct casting defects, to repair worn and damaged parts during operation and in the manufacture of welded structures.

Ferrous metals include cast iron and steel, which are alloys of iron and carbon, which also contain silicon, manganese, sulfur and other elements.

Cast iron- an iron-carbon alloy in which the carbon content exceeds 2%. It also contains silicon, manganese, phosphorus and sulfur. Pig iron is smelted in blast furnaces from iron ores. The starting materials for its production, in addition to ore, are fuel and fluxes.

Iron ore is a rock that contains iron compounds and impurities of other elements. Cast iron is obtained from red, brown and magnetic iron ores.

Coal coke is mainly used as fuel. Fluxes are used to separate waste rock (silica, calcium, manganese oxides) from iron ore, which, contributing to the formation of slag, has a harmful effect on the iron smelting process.

IN cast iron carbon is contained in a free state in the form of graphite or in a bound state in the form of iron carbide or cementite.

Cast irons, in which carbon is in the form of graphite, have a gray color when fractured and a coarse-grained structure. They are well processed by cutting tools, have high casting qualities, a relatively low melting point (1100-1200°C), low shrinkage (1%) and are used for the manufacture of many machine parts and mechanisms. These cast irons are called gray or cast irons.

Cast iron, in which carbon is contained only in the form of a chemical compound with iron, have a white color when fractured. They are difficult to machine with cutting tools and are usually used to make steel. These cast irons are called white or pig iron.

In addition to white and gray cast iron, the so-called malleable cast iron is also used for casting parts in tractor, automobile and other industries, which is obtained from white cast iron by special annealing (simmering) in special heating furnaces at a temperature of 950-1000°C. At the same time, excessive brittleness and hardness characteristic of white cast iron are greatly reduced. Malleable cast iron, like gray cast iron, cannot be forged, and the name “malleable” only indicates its significant ductility.

To increase strength, cast irons are alloyed, i.e., nickel, chromium, molybdenum, copper and other elements (alloyed cast iron) are introduced into their composition, and they are also modified, i.e. add magnesium, aluminum, calcium, silicon (modified cast iron).

The following grades of cast iron are most widely used: gray cast iron castings: SCh-10, SCh-15, SCh-18, SCh-20, etc. (GOST 1412-79); malleable iron castings: KCh30-6, KCh33-8, KCh35-10, KCh37-12, etc. (GOST 1215-79).

The letters and numbers of cast iron grades indicate: SCh - gray cast iron, KCH - malleable cast iron. The numbers after the letters for gray cast iron indicate the tensile strength.

Steel- an alloy of iron and carbon containing no more than 2% carbon. Compared to cast iron, steel has significantly higher physical and mechanical properties. It is characterized by high strength, is well processed by cutting, it can be forged, rolled, and hardened. In addition, steel is fluid in the molten state; various castings are made from it. Therefore, it is widely used in all areas of the national economy, especially in mechanical engineering.

Steel obtained from pig iron by remelting it and removing excess carbon, silicon, manganese and other impurities and smelted in open hearths, electric furnaces and converters.

The most common method for producing ordinary types of steel is open-hearth, and for the smelting of high-quality steels, electric melting is used.

Steel, smelted from cast iron at metallurgical plants, in the form of ingots is supplied to rolling, forging or pressing shops, where it is processed into shaped and rolled sheets, as well as into forgings of various shapes and sizes.

All currently used steels are classified according to the following criteria:

by chemical composition - carbon, alloyed;

in terms of quality - steel of ordinary quality, high-quality, high-quality;

by purpose - structural, instrumental.

Carbon steel widely used in industry. The main component that determines its mechanical and other properties is carbon. Increasing the carbon content of steel increases strength and hardness, but reduces toughness and makes it more brittle.

Depending on the purpose, carbon steel is divided into structural and tool.

Carbon structural steels are divided into ordinary quality steel (GOST 380-78) and high-quality steel (GOST 1050-74). Depending on the conditions and degree of deoxidation, a distinction is made between calm steels (sp), semi-quiet steels (ps) and boiling steels (kp).

Ordinary quality steel marked with the letters St (steel) and the numbers 1, 2, 3.....6 (St0, St1, St2, etc.). The higher this number, the more carbon it contains.

Depending on their purpose, these steels are divided into three groups:

group A- steels supplied according to mechanical properties without specifying their chemical composition (St0, St1kp, St2ps, St1sp, St2kp, St2sp, St3kp, etc.);

group B- steels with a guaranteed chemical composition (BSt0, BSt1kp, BSt1sp, BSt2kp, etc.);

group B- high quality steels with guaranteed chemical composition and mechanical properties (VSt2, VSt3, VSt4, VSt5).

The numbers indicating the steel grade show the average carbon content in the steel in hundredths of a percent (for example, grade 45 steel contains an average of 0.45% carbon).

Low-carbon steel grades 05, 08, 10, 20, 25 are used for lightly loaded parts, the manufacture of which involves welding and stamping.

Axles, shafts, gears and other parts are made from medium-carbon steel grades 40, 45, 50, 55.

High-carbon steels are used to make spiral springs, cables and other critical parts.

Quality tool steel is designated by the letter U, followed by a number indicating the carbon content in tenths of a percent, for example U7, U8, U10, etc.

High-quality tool steel contains less harmful impurities (sulfur, phosphorus) than high-quality steel. It is marked in the same way as a high-quality one, but with the addition of the letter A, for example U7A, U8A, etc.

Tool carbon steel is used for the manufacture of various tools (percussion, cutting, measuring, etc.).

Composition of alloy steel in addition to carbon, elements are introduced that improve its properties. These elements include: chromium, nickel, silicon, tungsten, manganese, vanadium, cobalt, etc.

Depending on the alloying elements introduced, steels are divided into chromium, nickel, silicon, chromium-nickel, chromium-vanadium, etc.

Alloying elements impart the necessary properties to steel depending on its purpose. Let's consider what effect they have on the properties of steel.

Chromium helps to increase the strength of steel, its hardness and wear resistance. Nickel increases the strength, toughness and hardness of steel, increases its corrosion resistance and hardenability. Silicon, with a content of more than 0.8%, increases the strength, hardness and elasticity of steel, while reducing its toughness. Manganese increases the hardness and strength of steel, improves its weldability and hardenability.

Alloy steel according to the number of alloying elements introduced into it, it is classified into low-alloyed (up to 5% of alloying elements), medium-alloyed (from 5 to 10%) and high-alloyed (over 10%).

According to their purpose, alloy steel, like carbon steel, is divided into structural and instrumental.

Alloying elements introduced into the steel according to the standard have the following designations:

• X - chrome,
• B - tungsten,
• M - molybdenum,
• F - vanadium,
• K - cobalt,
• G - manganese,
• T - titanium,
• C - silicon,
• N - nickel,
• D - copper,
• Yu - aluminum,
• R - boron,
• A - nitrogen.

High quality steel denoted by adding the letter A at the end of the marking.

Alloy steel marked with a combination of numbers and letters.

The first two numbers indicate the average carbon content in hundredths of a percent, the letters indicate alloying elements, and the numbers following the letters indicate the percentage content of these elements in the steel.

Thus, grade 40X denotes chromium steel containing 0.4% carbon and 1% chromium;

12ХНЗА - chromium-nickel steel containing about 0.12% carbon, 1% chromium and 3% nickel, etc.

Critical machine parts and various metal structures are made from structural alloy steel. To improve the mechanical properties, parts made of this steel are subjected to heat treatment.

Structural alloy steels include:

• chromium (15X, 20X, 30X, etc.),
• chrome vanadium (15HF, 20HF, 40HF),
• chromium-silicon (33ХС, 38ХС, 40ХС),
• chromium-nickel (12ХН2, 12ХНЗА, etc.).

Tool alloy steel is wear-resistant compared to carbon steel; it is annealed deeper, provides increased toughness in the hardened state and is less prone to deformation and cracks during hardening.

The cutting properties of alloy steels are approximately the same as carbon steels, because they have low heat resistance, equal to 200-250°C.

The purpose of some grades of alloy tool steels is as follows:

9ХС steel is used for the manufacture of dies, drills, reamers, cutters, combs and taps;

steel 11X and 13X - for files, razor knives, surgical and engraving instruments;

HVG steel - for long taps, reamers and other tools.

For the manufacture of cutting tools, high-speed steel is used, which is so named for its high cutting properties.

Due to the presence of tungsten and vanadium in its composition, this steel has high heat resistance and red resistance, i.e., the ability to maintain high hardness and wear resistance at elevated temperatures.

A tool made of high-speed steel, heating up to 550-600°C during the cutting process, does not lose its cutting properties.