home Endocrinology How to distinguish cast iron from steel at home without special tools. Description of the composition of the cast iron alloy and its difference from steel

How to distinguish cast iron from steel at home without special tools. Description of the composition of the cast iron alloy and its difference from steel

Question: March 28, 2009
What is the difference between cast iron and steel, and why?

Answer:
Oddly enough, but, despite the abundance of specialized literature on this topic, we are often asked the following question: How does cast iron differ from steel? In short and in general terms, it can be said that the composition of cast iron differs from steel in a higher carbon content, in technological properties - better casting qualities and low plastic deformation capacity. Cast iron is generally cheaper than steel.
And if in more detail, then - read the classics, dear! Many volumes are devoted to materials science and metallurgy of ferrous alloys. As an example, I cite an excerpt from the fundamental work of Gulyaev A.P. "Metal":
“Steel is an iron-carbon alloy containing less than 2.14% carbon. However, the specified limit (2.14% C) applies only to double iron-carbon alloys or alloys containing a relatively small number of impurities. The question of the boundary between steels and cast irons in high-alloy iron-carbon alloys, i.e. containing even more elements other than iron and carbon is debatable.
In the light of modern technology, alloys based on iron are known and have recently become widespread, in which carbon is very small and even a harmful element; however, such alloys are also referred to as steels. In order to avoid terminological confusion, it is customary to consider alloys in which iron is more than 50% as steels (cast iron) and not to call them alloys, but to refer to alloys containing less than 50% iron. It's not scientifically rigorous, but it's technically clear."

Many people know about such material as cast iron and its strength characteristics. Today we will deepen this knowledge and find out what cast iron is, what it consists of, what types it happens and how it is produced.

Compound

What is cast iron? It is an alloy of iron, carbon and various impurities, thanks to which it acquires the necessary properties. The material must contain at least 2.14% carbon. Otherwise, it will be steel, not cast iron. It is thanks to carbon that cast iron has increased hardness. At the same time, this element reduces the ductility and malleability of the material, making it brittle.

In addition to carbon, the composition of cast iron without fail includes: manganese, silicon, phosphorus and sulfur. Some brands also add additional additives to give the material specific properties. Commonly used alloying elements include chromium, vanadium, nickel and aluminium.

The material has a density of 7.2 g/cm 3 . For metals and their alloys, this is a fairly high figure. Cast iron is well suited for the production of all kinds of products by casting. In this regard, it surpasses all iron alloys except for some steel grades.

The melting point of cast iron is 1200 degrees. For steel, this figure is 250-300 degrees higher. The reason for this lies in the increased content of carbon in cast iron, which causes less close bonds between iron atoms. During the smelting of cast iron and its subsequent crystallization, carbon does not have time to fully penetrate into the structure of iron. Therefore, the material is brittle. The structure of cast iron does not allow it to be used for the production of products that are constantly subjected to dynamic loads. But what cast iron is ideal for is for parts that must have increased strength.

Receipt

Obtaining cast iron is a very costly and material-intensive process. To get one ton of alloy, you need 550 kg of coke and 900 liters of water. As for the ore, its amount depends on the content of iron in it. As a rule, ore with a mass fraction of iron of at least 70% is used. The processing of less rich ores is not economically feasible.

Before going to the smelter, the material is enriched. Pig iron production in 98% of cases takes place in blast furnaces.

The technological process includes several stages. First, ore is loaded into the blast furnace, which includes magnetic iron ore (a compound of two- and three-valent iron oxide). Ores containing hydrous iron oxide or its salts can also be used. In addition to raw materials, coking coals are placed in the furnace, which are necessary to create and maintain a high temperature. Combustion products of coals as iron reducing agents are also involved in chemical reactions.

Additionally, a flux is supplied to the furnace, which plays the role of a catalyst. It accelerates the process of melting rocks and releasing iron. It is important to note that before entering the furnace, the ore must undergo special processing. Since small parts melt better, it is pre-crushed in a crushing plant. The ore is then washed to get rid of non-metal impurities. Then the raw material is dried and fired in kilns. Thanks to roasting, sulfur and other foreign elements are removed from it.

After the furnace is fully loaded, the second stage of production begins. When the burners are started, the coke gradually heats up the feedstock. This releases carbon, which reacts with oxygen and forms an oxide. The latter takes an active part in the reduction of iron from the compounds in the ore. The more gas accumulates in the furnace, the slower the reaction proceeds. When the desired proportion is reached, the reaction stops altogether. Excess gases further serve as fuel to maintain the required temperature in the furnace. This method has several strengths. Firstly, it allows you to reduce fuel costs, which reduces the cost of the production process. And, secondly, combustion products do not enter the atmosphere, polluting it, but continue to participate in production.

Excess carbon is mixed with the melt and absorbed by iron. This is how cast iron is made. Impurities that have not melted float to the surface of the mixture and are removed. They are called slag. Slag finds use in the production of certain materials. When all excess particles are removed from the melt, special additives are added to it.

Varieties

What is cast iron and how it is obtained, we have already found out, now we will deal with the classification of this material. In the way described above, conversion and foundry iron is obtained.

Pig iron is used in the production of steel via the BOF route. This type is characterized by a low content of silicon and manganese in the alloy. Foundry iron is used in the production of all kinds of products. It is divided into five types, each of which will be considered separately.

White

This alloy is distinguished by the content of excess carbon in the form of carbide or cementite. The name of this species was given for the white color at the fault. The carbon content of such cast iron is typically greater than 3%. White cast iron is highly brittle and brittle, so it is used to a limited extent. This type is used for the production of parts of a simple configuration that perform static functions and do not carry heavy loads.

By adding alloying additives to the composition of white cast iron, it is possible to increase the technical parameters of the material. For this purpose, chromium or nickel is most often used, less often vanadium or aluminum. A brand with this kind of additives was called "sormite". It is used in various devices as a heating element. "Sormite" has a high resistivity, and works well at temperatures not higher than 900 degrees. The most common use of white cast iron is in the production of domestic bathtubs.

Grey

This is the most common type of cast iron. It has found application in various areas of the national economy. In gray cast iron, carbon is present in the form of pearlite, graphite, or ferrite pearlite. In such an alloy, the carbon content is about 2.5%. As for cast iron, this material has high strength, so it is used in the manufacture of parts that receive cyclic loading. Gray cast iron is used to make bushings, brackets, gears and industrial equipment cases.

Thanks to graphite, gray cast iron reduces friction and improves the performance of lubricants. Therefore, parts made of gray cast iron have a high resistance to this type of wear. When operating in particularly aggressive environments, additional additives are introduced into the material, which make it possible to level the negative impact. These include: molybdenum, nickel, chromium, boron, copper and antimony. These elements protect gray cast iron from corrosion. In addition, some of them increase the graphitization of free carbon in the alloy. This creates a protective barrier that prevents damaging elements from reaching the surface of the cast iron.

half-hearted

An intermediate material between the first two varieties is half cast iron. The carbon contained in it is presented in the form of graphite and carbide in approximately equal proportions. In addition, small amounts of leadburite (no more than 3%) and cementite (no more than 1%) may be present in such an alloy. The total carbon content of cast iron ranges from 3.5 to 4.2%. This variety is used for the production of parts that are operated in conditions of constant friction. These include automotive brake pads, as well as rolls for grinding machines. All kinds of additives are added to the alloy to further increase wear resistance.

Malleable

This alloy is a kind of white cast iron, which is subjected to special firing in order to graphitize free carbon. Compared to steel, such cast iron has improved damping properties. In addition, it is not as sensitive to notches and performs well at low temperatures. In such cast iron, the mass fraction of carbon is not more than 3.5%. In the alloy, it is presented in the form of ferrite, granular pearlite containing inclusions of graphite or ferrite pearlite. Malleable cast iron, like half cast iron, is mainly used in the production of parts operating under conditions of continuous friction. To improve the performance of the material, magnesium, tellurium and boron are added to the alloy.

high strength

This type of cast iron is obtained due to the formation of spherical graphite inclusions in the metal lattice. Because of this, the metal base of the crystal lattice is weakened, and the alloy acquires improved mechanical properties. The formation of nodular graphite occurs due to the introduction of magnesium, yttrium, calcium and cerium into the material. Ductile iron is close in its parameters to high-carbon steel. It lends itself well to casting and can completely replace steel parts of mechanisms. Due to its high thermal conductivity, this material can be used for the manufacture of pipelines and heating appliances.

Industry difficulties

Today, cast iron casting has dubious prospects. The fact is that due to the high level of costs and the large amount of waste, industrialists are increasingly abandoning cast iron in favor of cheaper substitutes. Thanks to the rapid development of science, it has long been possible to obtain better materials at lower costs. A serious role in this matter is played by the protection of the environment, which does not accept the use of blast furnaces. It will take years, if not decades, to fully convert iron smelting to electric furnaces. Why so long? Because it is very expensive, and not every state can afford it. Therefore, it remains only to wait until the mass production of new alloys is established. Of course, it will not be possible to completely stop the industrial use of cast iron in the near future. But it is obvious that the scale of its production will fall every year. This trend started 5-7 years ago.

Conclusion

Having dealt with the question: “What is cast iron?”, We can draw several conclusions. First, cast iron is an alloy of iron, carbon and additives. Secondly, it has six kinds. Thirdly, cast iron is a very useful and versatile material, so for a long time its expensive production was expedient. Fourthly, today cast iron is already considered a relic of the past, and is gradually losing its position to more reliable and cheaper materials.

Modernity is iron. Those who understand know that the word "iron" refers to iron-carbon alloys - steel and cast iron. It would seem that two completely different materials and they are very easy to distinguish. However, given the wide range of their species and brands, it is difficult to determine the fine line of difference in the chemical composition of some of them. It is important to have additional skills in order to know the answer to the question: what is the difference between cast iron and steel?

Cast iron

Characteristics:

Rough, having a gray matte color.
Melting at 1000-1600˚С, depending on the composition (for industrial ones, on average - 1000-1200˚С, white and pig irons are melted at higher temperatures).
Density: 7200-7600 kg/m 3 .
540 J/(kg˚C).
High hardness: 400-650HB.
Low ductility, very crumbly when exposed to pressure; malleable ductile cast iron δ=6-12% has the highest elongation values.
Low strength: 100-200 MPa, for malleable it reaches 300-370 MPa, for some high-strength grades - 600-800 MPa.
It is modeled using heat treatment, but rarely and with great care, since it is characterized by a cracking process.
It is alloyed with the help of auxiliary chemical elements, however, a significant degree of alloying further complicates the technological processing.
It is characterized by satisfactory weldability, good machinability, excellent casting properties. Forging and stamping is not subject.
Good wear resistance and corrosion resistance.

Cast iron is a material for body parts, blocks, machine components made by casting. It is the main charge component for

Steel

An iron-carbon alloy containing carbon in an amount of not more than 2.14% and iron - not less than 45% is called steel. Its main characteristics:

Smooth, has a silvery color with a characteristic sheen.
Melting within 1450˚С.
The density is from 7700 to 7900 kg/m 3 .
Heat capacity at room temperature: 462 J/(kg˚C).
Low hardness, on average 120-250 HB.
Excellent ductility: the elongation coefficient δ for various grades ranges from 5-35%, for most - δ≥20-40%.
Average values of tensile strength for structural materials - 300-450 MPa; for especially strong alloyed - 600-800 MPa.
It lends itself well to the correction of properties with the help of thermal and chemical-thermal treatment.
It is actively doped with various chemical elements in order to change properties and purpose.
Qualitatively high rates of weldability, workability by pressure and cutting.
It is characterized by low rates of corrosion resistance.

Steel is the main structural alloy in modern metallurgy, mechanical engineering, instrument making and technology.

We determine the origin by the type of part

Having considered the detailed characteristics of these alloys, you can confidently use the knowledge of how cast iron differs from steel. Having a metal object in front of you, doubting its origin, it is rational to immediately recall the main distinctive technological properties. So cast iron is a casting material. It is used to produce simple dishes, massive pipes, bodies of machine tools, engines, large objects of a simple configuration. Parts of all sizes and complexity are made from steel, since forging, stamping, drawing, rolling and other methods are used for this. Thus, if there is a question about the origin of reinforcement, there can be no doubt - this is steel. If you are interested in the origin of a massive cauldron - this is cast iron. If you need to find out what the engine housing or crankshaft is made of, you should resort to other recognition options, since both options are possible.

Color features and fragility analysis

In order to know how to distinguish cast iron from steel by eye, you need to remember the main visual differences. Cast iron has a matte gray color and a rougher outer texture. Steel is characterized by its special silvery lustrous tint and minimal roughness.

Also important knowledge on how to distinguish cast iron from steel visually is information about the ductility of these materials. If the investigated workpieces or metal objects are not of serious value, you can test them for strength and ductility by applying impact force. Brittle cast iron will crumble into pieces, while steel will only deform. With more serious loads aimed at crushing, cast iron crumbs will turn out to be small in various shapes, and pieces of steel will be large, of the correct configuration.

Cutting and drilling

How to distinguish cast iron from steel at home? It is necessary to get fine dust or chips out of it. Since steel has high ductility, its chips also have a tortuous character. Cast iron, on the other hand, crumbles; when drilling, small chips of fracture are formed along with dust.

To obtain dust, you can use a file or rasp and slightly sharpen the edge of the part of interest. Consider the resulting fine shavings on your hand or on a white sheet of paper. Cast iron contains carbon in large quantities in the form of graphite inclusions. Therefore, when rubbing its dust, a black graphite “trace” remains. In steels, carbon is in a bound state, so the mechanical effect on dust does not give any visible results.

Heat up and sparkle

How to distinguish cast iron from steel? You need to operate with the necessary equipment and a little patience.

In the first case, you can resort to heating, for example, with a blowtorch, initially dressed in special protective clothing and observing safety rules at work. The temperature must be raised before the metal begins to melt. It has already been said that the melting point of cast iron is higher than that of steel. However, this applies mainly to white and relatively all industrial grades - they contain carbon in an amount of not more than 4.3% and melt already at 1000-1200˚С. Thus, it can be melted much faster.

A cognitive method of obtaining information about how cast iron differs from steel is to use an experimental sample on a grinding machine or under a sharp circle of a grinding machine. The analysis is carried out according to the characteristics of the sparks. Cast iron is characterized by dim red sparks, and steel is characterized by bright blinding short rays with a white-yellow tint.

How does it sound

An interesting feature is how to distinguish cast iron from steel by sound. The two alloys sound different. It is not at all necessary to produce musical accompaniment on existing experimental objects. But it is necessary to have both samples or to have an experienced ear in this matter. Steel is characterized by a higher density, which is reflected in its sound. When hitting it with a metal object, the sound is much more sonorous than in the same situation with cast iron.

In order to know how cast iron differs from steel, you need to have a little knowledge about these materials and some experience. After all, an experienced professional in the field of forging, grinding, milling, drilling, turning, heat treatment or welding, a metallurgist or a technician can easily distinguish them from each other, evaluating only visually or by touch.

Ferrous metallurgy products are widely used in many sectors of the national economy, and ferrous metal is always in demand in construction and engineering. Metallurgy has been successfully developing for a long time, thanks to its high technical potential. The most commonly used in production and in everyday life are cast iron and steel products.

Cast iron and steel both belong to the group of ferrous metals, these materials are alloys of iron and carbon that are unique in their properties. What are the differences between steel and cast iron, their main properties and characteristics?

Steel and its main characteristics

Steel is deformed alloy of iron and carbon, which is always a maximum of 2%, as well as other elements. Carbon is an important component, since it gives strength to iron alloys, as well as hardness, due to this, softness and ductility are reduced. Alloying elements are often added to the alloy, which ultimately gives alloyed and high-alloyed steel, when the composition is not less than 45% iron and not more than 2% carbon, the remaining 53% are additives.

Steel is the most important material in many industries, it is used in construction, and as the technical and economic level of the country grows, so does the scale of steel production. In ancient times, craftsmen used crucible melting to produce cast steel, and such a process was inefficient and laborious, but the steel was of high quality.

Over time, the processes of obtaining steel changed, the crucible was replaced by Bessemer and open-hearth method obtaining steel, which made it possible to establish mass production of cast steel. Then they began to smelt steel in electric furnaces, after which the oxygen-converter process was introduced, it made it possible to obtain especially pure metal. From the number and types of binding components, steel can be:

low alloy
medium alloyed
Highly alloyed

Depending on the carbon content it happens:

low carbon
medium carbon
High carbon.

The composition of the metal often includes non-metallic compounds - oxides, phosphides, sulfides, their content differs on the quality of steel, there is a certain quality classification.

Steel density is 7700-7900 kg/m3, and the general characteristics of steel are made up of such indicators as strength, hardness, wear resistance and suitability for various types of processing. Compared to cast iron, steel has greater ductility, strength and hardness. Due to its ductility, it is easy to process, the steel has a higher thermal conductivity, and its quality is improved by hardening.

Elements such as nickel, chromium and molybdenum are alloying components, each of which gives the steel its own characteristics. Thanks to chromium, steel becomes stronger and harder, and its wear resistance increases. Nickel also imparts strength, as well as toughness and hardness, increases its anti-corrosion properties and hardenability. Silicon reduces toughness, while manganese improves weldability and annealing.

All existing types of steel have melting point from 1450 to 1520оС and are strong wear-resistant and deformation-resistant metal alloys.

Cast iron and its main characteristics

The basis for the production of cast iron is also iron and carbon, but unlike steel, it contains more carbon, as well as other impurities in the form of alloying metals. It is brittle and breaks without visible deformation. Carbon here acts as graphite or cementite, and due to the content of other elements cast iron is divided into the following varieties:

The melting temperature of cast iron depends on the carbon content in it, the more it is in the composition of the alloy, the lower the temperature, and also its fluidity increases when heated. This makes the metal non-plastic fluid, as well as brittle and difficult to machine. Its melting point is from 1160 to 1250оС.

The anti-corrosion properties of cast iron are higher because it undergoes dry rusting during use, this is called chemical corrosion. Wet corrosion also attacks cast iron more slowly than steel. These qualities led to the fact that a discovery was made in metallurgy - steel with a high chromium content began to be smelted. This is where stainless steel came from.

We draw a conclusion

Based on their many characteristics, the following can be said about cast iron and steel, what is their difference:

It can be concluded that steel and cast iron are united by the content of carbon and iron in them, but their characteristics are different and each of the alloys has its own characteristics.

Steel and its main characteristics

low alloy
medium alloyed
Highly alloyed

Depending on the carbon content it happens:

low carbon
medium carbon
High carbon.

The composition of the metal often includes non-metallic compounds - oxides, phosphides, sulfides, their content differs on the quality of steel, there is a certain quality classification.

The density of steel is 7700-7900 kg / m 3, and the general characteristics of steel are made up of such indicators as strength, hardness, wear resistance and suitability for various types of processing. Compared to cast iron, steel has greater ductility, strength and hardness. Due to its ductility, it is easy to process, the steel has a higher thermal conductivity, and its quality is improved by hardening.

All existing types of steel have melting point from 1450 to 1520 o C and are strong wear-resistant and deformation-resistant metal alloys.

Cast iron and its main characteristics