Steel and cast iron - how do the metals differ? Become. General classification. Differences from cast iron

Among the metals produced in one technological process Some of the most common ones stand out - steel and cast iron. Despite the fact that one is made as a result of alteration of the other, these metals differ significantly from each other, both in their composition and in their use in the economy.

How steel is made

Steel is an iron-carbon alloy in which the carbon content does not exceed 3.4 percent. The usual indicator is within 0,1-2,14 % . It reduces the plastic characteristics of steel, while making it harder and stronger. Alloyed and highly alloyed contain more than 45% iron. The elasticity of steel determines its demand for the creation of engineering products, primarily power springs and springs, shock absorbers, suspensions, braces and other elastic parts.

Regardless of the forms and operating conditions of the elastic parts of machines, mechanisms and devices, they have a common remarkable quality. It lies in the fact that, despite the large shock, periodic and static loads they have no residual deformation.

Steels are classified according to their purpose, chemical composition, structure and quality. There are many categories of appointments, including the following:

Instrumental.
Structural.
Stainless.
Heat resistant.
Resistant to ultra-low temperatures.

Steels can vary in their carbon content, from low-carbon, in which it is up to 0.25%, to high-carbon with 0.6-2%. Alloyed ones can contain from 4 to 11 or more percent of the corresponding additives. Depending on the content of various impurities, they are classified into steels with ordinary qualities, high-quality and those with especially high qualities.

In its production, the main thing is to reduce to the required level the content of sulfur and phosphorus, which make the metal brittle and brittle. In this case, they apply different ways, carbon oxidation, which can be open-hearth, converter and electrothermal. The open-hearth method requires a lot of thermal energy, which is released when gas or fuel oil is burned. Arc or induction furnaces are heated using electricity. The converter version does not require an external heat source. Here, molten pig iron is usually separated from impurities by blowing oxygen through it.

The raw materials for steel production are metal, pig iron, and additives that form slag and provide steel alloying. The smelting process itself can be carried out in different options. It happens that it begins in an open-hearth furnace and ends in an electric one. Or, in order to obtain steel that is resistant to corrosion, after melting in an electric furnace, it is poured into a converter. In it, it is purged with oxygen and argon to minimize carbon content. Steel melts at a temperature 1450-1520 °C.

How to get cast iron

An alloy of iron and carbon can also be called cast iron. However, unlike steel, it must contain at least 2.14% carbon, which gives this very hard material high brittleness. At the same time, it becomes less ductile and viscous. Depending on the content of cementite and graphite in it, cast iron can be called white, gray, malleable and high-strength.

The first one contains 4.3-6.67% carbon. It is light gray at the break. It is used primarily to produce malleable cast iron using annealing technology. Cast iron is called gray because of the gray color of its fracture due to the presence of graphite in lamellar form and the presence of silicon. As a result of prolonged annealing of white cast iron, malleable cast iron is obtained. It has increased ductility and toughness, impact resistance and greater strength. Complex parts for machines and mechanisms are made from it. It is marked with the letters “K” and “H”, after which numbers are placed indicating the tensile strength and relative elongation.

High-strength cast iron is distinguished by the presence of spheroidal graphite, which prevents stress concentration and weakening of the metal base. A laser is used to strengthen it, which makes it possible to obtain critical machine parts of increased strength. For industrial needs, there are various classifications of pig iron, anti-friction, alloy and graphite-containing cast iron. Its melting point is between 1,150 and 1,200 °C.

Cast iron has proven itself universal, inexpensive and durable material. Complex and massive parts of machines and mechanisms, as well as unique artistic products are made from it. Cast iron decorations and monuments decorate many cities around the world. Fences skillfully made from it have served people for centuries. ancient buildings, steps in them, plumbing and sewer pipes. Cast iron hatches cover communication wells on the streets of many settlements. Baths, sinks and sinks, heating radiators made from this material are reliable and durable. Crankshafts and cylinder blocks of internal combustion engines, brake discs and other automobile parts are cast from cast iron. Typically, cast iron parts undergo additional machining after casting.

What makes them different

Steel and cast iron are materials widely used in industry, transport and construction. Outwardly they are very similar.

However, there are these main differences between them:

Steel is final products steelmaking, and cast iron is the raw material for it.
Steel has higher strength and hardness than brittle cast iron.
It contains much less carbon than cast iron.
Steel is heavier than cast iron and has a higher melting point.
Steel can be processed by cutting, rolling, forging, etc.; cast iron products are mainly cast.
Cast iron products are porous and have a thermal conductivity significantly lower than steel
New steel parts have a silver shine, cast iron matte and black.
To give steel special properties, it can be hardened; this is not done with cast iron.

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 represents rock, which 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 fracture grey colour and 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 chemical compound with iron, have a fracture White color. 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 applied in all fields 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 sheet metal, as well as into forgings 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- become improved quality 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.

Structural alloy steel is used to produce critical machine parts and various metal constructions. For improvement 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 11Х and 13Х - for files, razor knives, surgical and engraving instruments;

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

For the manufacture of cutting tool 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.

Instructions

You can identify cast iron by the density of the product. Weigh the object and then determine how much water it displaces. This way you will calculate its density and draw a conclusion about the material. The fact is that the density of the main steel grades lies in the range of 7.7 - 7.9 grams/cm^3, while the density of the most common gray cast iron does not exceed 7.2 grams/cm^3. But this method is unreliable, since there is also white cast iron, the density of which varies between 7.6 and 7.8 grams/cm^3. Therefore, it can only be used if you are firmly convinced that the product is made of either steel or gray cast iron.

You can use a magnet. It sticks to it worse than to steel. But this method cannot be called accurate, since some types of alloy steels with a high nickel content almost do not attract a magnet.

Therefore, it is more reliable to use one of the following methods: determine cast iron using the type of sawdust or shavings formed, as well as using grinder. Take a finely cut file and run it over the surface of the product several times. Try to collect the tiny sawdust that forms on a sheet of paper. Fold the paper in half and rub vigorously. If it is cast iron, then the paper will be noticeably stained; if it is steel, there will be practically no marks left.

You can also drill the product a little with a thin drill (of course, not from the front side, but in a place that is not obvious). This produces a small amount of chips. According to her appearance and properties, you can accurately determine what material the part is made of. If it is cast iron, the shavings will literally crumble in your fingers, turning into dust. If it's steel, the shavings will look like a coiled spring and may even scratch your fingers if you try to break them.

Finally, you can judge a material by the size, shape and color of the sparks produced when a sander is passed along the edge of the product. The higher the carbon content, the brighter and stronger the sheaf of light yellow sparks will be. And the carbon content is much higher than in steel.

If in doubt, it is better to use pieces of cast iron and steel as standards and compare the shape and properties of sawdust (shavings), as well as the type of sparks produced, with what is obtained when processing these samples.

In our lives we often have to deal with the use of various products from cast iron, which in its structure is a rather brittle alloy, but with good thermal conductivity. In accordance with this, the question often arises: how to cook it, because cast iron, due to its high content of carbon, sulfur and phosphorus, belongs to the group of poorly weldable metals?

Instructions

Having omitted the subtleties of the chemical composition of cast iron, chemical and other processes occurring during welding, let's still figure it out: how to weld? Our industry produces gray and white cast iron, which are very different in their characteristics. Accordingly, the welding methods are different for them. Here it is necessary to remember that welding cast iron products that long time were exposed to high temperatures of 300 degrees and above, as well as products that worked for a long time in direct contact with various oils, is practically impossible.

The most acceptable method of welding cast iron in our households is welding using an electric welding machine. So, when electric welding, make a V-shaped cut on the edges being welded and thoroughly clean them of oil, rust and dirt with a brush.

Purchase electrodes coated with UONI-13/45 (welding with these electrodes is carried out at direct current of reverse polarity).

Apply the welding seam separate sections(broken down), this will help you avoid uneven heating of the part (separately directed sections of the weld should be no more than 10 cm). When welding products with a thickness of more than 5 mm, do not forget to reinforce the seam to a length equal to the thickness of the part being welded.

During welding, do not forget to allow the separately deposited areas to cool to 60-80 degrees. When welding cast iron using studs, do the following: using a drill (in a checkerboard pattern), drill holes in the prepared edges (not through ones!), cut the threads and screw them into them low-carbon steel studs (the angle of the edges of the parts being welded should be 90 degrees).

Insert pins of larger diameter into the groove. Perform welding with electrodes with a protective alloying coating of grade E42 (42A) or E50 (50A) at constant or alternating current, while the thickness of the electrode is selected depending on the thickness of the product being welded.
Perform the welding itself by scalding the studs with a circular seam and only after that, in short sections, fill the space between the scalded studs and the cutting itself. There are other methods of welding cast iron, but we’ll talk about them later.

Video on the topic

The debate continues with unabated fervor about whether it is possible to brew cast iron? How reliable will such welding be? The experience of inquisitive and persistent “homemade” people shows that it is quite possible to eliminate a crack in a cauldron or repair stove grates using gas or electric welding.

You will need

Gas-burner or electric welding machine, filler rods, electrodes.

Instructions

Use gas welding - one of the most reliable welding methods cast iron A. Gas welding makes it possible to obtain a deposit with maximum properties similar to the base one.
Do gas welding cast iron or better yet with preheating. Pre-clean the edges of the material to be welded from dirt with a wire brush, remove all traces of oil.
Use as filler rods cast iron rods 40-70 cm long. The diameter of the rod should be equal to half the thickness of the main one.

note

When welding cast iron, it is necessary to swap the welding cables - from the ground to the holder, and from the holder to the ground.

Helpful advice

You can also solder cast iron using a gas welding torch, using borax - as an oxidizing agent - and non-ferrous metals - brass, bronze, copper.

Cast iron is an alloy of iron with a small amount of carbon. Sometimes alloying additives are also introduced into this composition, giving it higher consumer qualities. This metal is the primary material for ferrous metallurgy. It is used not only in steel production and mechanical engineering, but also for the manufacture of artistic products.

Cast iron and steel products from the metallurgical industry are used both in everyday life and in production. Both materials are unique alloys of iron and carbon. Everyone knows that iron is mined from the depths of the earth in huge quantities. But it is impossible to use it in its pure form; this element is too soft and therefore unsuitable for the manufacture of high-strength products. Therefore, for industrial, construction and household purposes, it is not iron in its pure form that is used, but its derivatives - cast iron and steel. What is the difference between steel and cast iron?

Cast iron and steel are alloys of iron and carbon.

Their difference is manifested in many qualities, and the commonality of elements during production does not give the material identical characteristics.

Gradation of steel and cast iron

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Steel

To produce steel, iron is alloyed with carbon and various impurities. Required condition is the carbon content is no more than 2% (it increases strength), and the iron content is no less than 45%. The remainder consists of alloying binding components (chromium, molybdenum, nickel, etc.). Chromium increases the strength of steel, its hardness and wear resistance. Nickel increases strength, toughness and hardness, improves its anti-corrosion qualities and hardenability. Silicon adds strength, hardness and elasticity to steel and reduces its toughness. Manganese improves weldability and hardenability. Metallurgists distinguish different types become. They are classified depending on the volume of the remaining elements. For example, a content of more than 11% alloy metals produces high-alloy steel. There is also:

Low alloy steel - up to 4%.
Medium alloy steel - up to 11%.

Based on the amount of carbon, steel is classified into:

low-carbon metal - up to 0.25% C;
medium carbon metal - up to 0.55% C;
high-carbon metal - up to 2% C.

The composition of non-metallic elements (phosphides, sulfides) classifies the metal into:

regular;
quality;
high quality;
especially high quality steel.

As a result, all types of steel are a strong, wear-resistant and deformation-resistant alloy with a melting point from 1450 to 1520 °C.

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Cast iron

Iron production also involves the fusion of iron and carbon. The main difference between cast iron and steel is the content of the latter in the mixture. It should be more than 2%. In addition, the mixture contains impurities: silicon, manganese, phosphorus, sulfur and alloying metals. Cast iron is more brittle than steel and breaks without visible deformation. Carbon in the metal is represented by graphite or cementite, while the volume and shape of the element determine the types of alloy:

White cast iron, in which all the carbon is represented by cementite. When broken, this material is white, very hard, but at the same time fragile. It is easy to process and is used to produce the malleable variety.
Gray - carbon is represented by graphite, which gives the material plasticity. Soft, easy to cut, with a low melting point.
Malleable, 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, the excessive brittleness and hardness characteristic of white cast iron are greatly reduced. Malleable cast iron cannot be forged, and the name only indicates its ductility.
Ductile iron containing nodular graphite formed during the process of crystallization.

The amount of carbon in the alloy determines its melting point (the higher the content of the element, the lower the temperature and the higher the fluidity when heated). Therefore, cast iron is a fluid, non-plastic, brittle and difficult to process material with a melting point of 1150 to 1250 °C.

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Corrosion resistance

Both alloys are susceptible to corrosion, and improper use will accelerate this process.

Cast iron becomes covered with dry rust during use. This is the so-called chemical corrosion. Wet (electrochemical) corrosion affects cast iron more slowly than steel. Initially, the conclusion suggests itself that the anti-corrosion characteristics of cast iron are much higher. In fact, both of these alloys are susceptible to corrosion equally, it’s just that for cast iron products the process takes longer due to thick walls. This, for example, can explain the difference in the service life of boilers: steel - from 5 to 15 years, cast iron - from 30 years.

In 1913, Harry Brearley made a discovery in the field of metallurgy. He discovered that steel with a high chromium content had good resistance to acid corrosion. This is how stainless steel was born. It also has its own gradation:

Corrosion-resistant steel has resistance to corrosion in elementary industrial and living conditions(oil and gas, light industry, engineering industry, surgical instruments, household stainless steel utensils).
Heat-resistant steel is resistant to high temperatures and aggressive environments (chemical industry).
Heat-resistant steel has increased mechanical strength at high temperatures.

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Thermal shock and shock resistance

Cast iron and steel are often used in the manufacture of heating boilers. In this case, the issue of resistance to thermal shocks becomes especially important. If a cast iron boiler gets into an uncooled cold water, it may crack. Thermal shock is not dangerous for steel products. Steel is more elastic and tolerates temperature differences well. But big and frequent temperature changes in steel they contribute to the appearance of “tired” zones and, as a result, cracks in places that are weakened by welding.

Good ductility makes steel products resistant to mechanical damage. The fragility of cast iron inevitably leads to the formation of cracks due to impacts or distortions.

Gray cast iron has a more uniform structure, increased ductility and anti-corrosion properties, and is able to withstand large temperature changes.

Cast iron is less durable and hard than steel.
Steel is heavier and has a higher melting point.
The lower carbon content of steel, unlike cast iron, makes it easier to process (cook, cut, forge).
For a similar reason, cast iron products are produced only by casting, while steel products can be forged and welded.
Products made of steel are less porous than those made of cast iron, and therefore their thermal conductivity is much higher.
Products made of cast iron are usually black in color and have a matte surface, while those made of steel are light-colored with a shiny surface.

Cast iron and steel - two types of iron-carbon compounds - are widely used in a wide variety of industries. But sometimes it becomes necessary to distinguish cast iron from steel, for example, during repairs, because these alloys have different properties and, accordingly, require different treatment.

Methods for determining cast iron

You can use a magnet. It sticks to cast iron worse than to steel. But this method cannot be called accurate, since some types of alloy steels with a high nickel content almost do not attract a magnet.

Therefore, it is more reliable to use one of the following methods: determine cast iron using the type of sawdust or shavings formed, as well as using a grinding machine. Take a finely cut file and run it over the surface of the product several times. Try to collect the tiny sawdust that forms on a sheet of paper. Fold the paper in half and rub vigorously. If it is cast iron, then the paper will be noticeably stained; if it is steel, there will be practically no marks left.

You can also drill the product a little with a thin drill (of course, not from the front side, but in a place that is not obvious). This produces a small amount of chips. By its appearance and properties, you can accurately determine what material the part is made of. If it is cast iron, the shavings will literally crumble in your fingers, turning into dust. If it's steel, the shavings will look like a coiled spring and may even scratch your fingers if you try to break them.

What is the qualitative difference between steel and cast iron?

Gradation of steel and cast iron
- Steel
- Cast iron
Corrosion resistance

Cast iron and steel are alloys of iron and carbon.

Their difference is manifested in many qualities, and the commonality of elements during production does not give the material identical characteristics.

Gradation of steel and cast iron

Return to contents

Steel production scheme.

To produce steel, iron is alloyed with carbon and various impurities. A prerequisite is that the carbon content is no more than 2% (it increases strength), and the iron content is no less than 45%. The remainder consists of alloying binding components (chromium, molybdenum, nickel, etc.). Chromium increases the strength of steel, its hardness and wear resistance. Nickel increases strength, toughness and hardness. increases its anti-corrosion qualities and hardenability. Silicon adds strength, hardness and elasticity to steel and reduces its toughness. Manganese improves weldability and hardenability. Metallurgists distinguish different types of steel. They are classified depending on the volume of the remaining elements. For example, a content of more than 11% alloy metals produces high-alloy steel. There is also:

Low alloy steel – up to 4%.
Medium alloy steel – up to 11%.

Mechanical properties of steel.

Based on the amount of carbon, steel is classified into:

low-carbon metal – up to 0.25% C;
medium carbon metal – up to 0.55% C;
high-carbon metal – up to 2% C.

The composition of non-metallic elements (phosphides, sulfides) classifies the metal into:

regular;
quality;
high quality;
especially high quality steel.

As a result, all types of steel are a strong, wear-resistant and deformation-resistant alloy with a melting point from 1450 to 1520 °C.

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White cast iron, in which all the carbon is represented by cementite. When broken, this material is white, very hard, but at the same time fragile. It is easy to process and is used to produce the malleable variety.
Gray – carbon is represented by graphite, which gives the material plasticity. Soft, easy to cut, with a low melting point.
Malleable, 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, the excessive brittleness and hardness characteristic of white cast iron are greatly reduced. Malleable cast iron cannot be forged, and the name only indicates its ductility.
Ductile iron containing nodular graphite formed during the process of crystallization.

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Corrosion resistance

Both alloys are susceptible to corrosion, and improper use will accelerate this process.

Preparation of cast iron from ore.

Cast iron becomes covered with dry rust during use. This is the so-called chemical corrosion. Wet (electrochemical) corrosion affects cast iron more slowly than steel. Initially, the conclusion suggests itself that the anti-corrosion characteristics of cast iron are much higher. In fact, both of these alloys are susceptible to corrosion to the same extent; it’s just that for cast iron products, due to thick walls, the process takes longer. This, for example, can explain the difference in the service life of boilers: steel - from 5 to 15 years, cast iron - from 30 years.

Corrosion-resistant steel is resistant to corrosion in basic industrial and domestic conditions (oil and gas, light industry, engineering industry, surgical instruments, household stainless steel utensils).
Heat-resistant steel is resistant to high temperatures and aggressive environments (chemical industry).
Heat-resistant steel has increased mechanical strength at high temperatures.

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Thermal shock and shock resistance

Comparative indicators of cast iron and steel.

Cast iron and steel are often used in the manufacture of heating boilers. In this case, the issue of resistance to thermal shocks becomes especially important. If cold water gets into a cast iron boiler that has not cooled down, it may crack. Thermal shock is not dangerous for steel products. Steel is more elastic and tolerates temperature differences well. But large and frequent temperature changes in steel contribute to the appearance of “tired” zones and, as a result, cracks in places that are weakened by welding.

Good ductility makes steel products resistant to mechanical damage. The fragility of cast iron inevitably leads to the formation of cracks due to impacts or distortions.

Gray cast iron has a more uniform structure, increased ductility and anti-corrosion properties, and is able to withstand large temperature changes.

Cast iron is less durable and hard than steel.
Steel is heavier and has a higher melting point.
The lower carbon content of steel, unlike cast iron, makes it easier to process (cook, cut, forge).
For a similar reason, cast iron products are produced only by casting, while steel products can be forged and welded.
Products made of steel are less porous than those made of cast iron, and therefore their thermal conductivity is much higher.
Products made of cast iron are usually black in color and have a matte surface, while those made of steel are light-colored with a shiny surface.

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According to the density of the product. It is necessary to weigh the object and determine how much water it will displace. The density of steel lies in the range of 7.7-7.9 g/cm³, gray cast iron - does not exceed 7.2 g/cm³. This method is not particularly reliable because white cast iron has a density between 7.6 and 7.8 g/cm³.
Using a magnet. Cast iron is less magnetic than steel. The disadvantage of this method is that steels with a high nickel content practically do not attract a magnet.
The most accurate way is to determine the cast iron using a grinding machine and the type of chips produced. You should take a file with a fine notch and run it over the surface of the object several times. The resulting sawdust must be collected on paper, folded in half and rubbed vigorously. Cast iron will noticeably stain paper, steel will leave virtually no marks.

You can draw conclusions about the material by the size, shape and color of the sparks that appear during grinding. The more carbon, the brighter and stronger the sheaf of light yellow sparks will be. As we already know, cast iron contains more carbon than steel. Also, when drilling a product with a thin drill, you can determine the material by the type of chips. Cast iron shavings will literally turn into dust before your eyes, steel shavings will take on the appearance of a coiled spring.

What is the visual difference between cast iron and steel?

October 21, 2016

An uninformed person believes that the main structural material of modern times is iron. Anyone who understands knows that under the word “iron9raquo; This refers to iron-carbon alloys - steel and cast iron. It would seem that two are absolutely different materials and they are very easy to distinguish. However, given the wide range of their types and brands, there is a fine line of difference in chemical composition some of them are difficult to identify. 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?

Rough, matte gray in color.
Melting at 1000-1600˚С depending on the composition (for industrial ones on average - 1000-1200˚С, white and pig iron melt at higher temperatures).
Density: 7200-7600 kg/m3.
Specific heat capacity: 540 J/(kg˚C).
High hardness: 400-650HB.
Low ductility, very crumbles when exposed to pressure; highest values ductile high-strength cast iron has a relative elongation of δ=6-12%.
Low strength: 100-200 MPa, for malleable its value reaches 300-370 MPa, for some brands of high-strength - 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, but a significant degree of alloying further complicates the processing processes.
It is characterized by satisfactory weldability, good machinability, and excellent casting properties. Cannot be forged or stamped.
Good wear resistance and corrosion resistance.

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

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 reflection.
Melting within 1450˚С.
Density ranges from 7700 to 7900 kg/m3.
Heat capacity at room temperature: 462 J/(kg˚С).
Low hardness, on average 120-250 HB.
Excellent ductility: the relative elongation coefficient δ for different brands ranges from 5-35%, for most - δ9ge; 20-40%.
Average values of tensile strength for structural materials are 300-450 MPa; for especially strong alloyed ones - 600-800 MPa.
It lends itself well to correction of properties using thermal and chemical-thermal treatment.
Actively doped with various chemical elements for the purpose of changing properties and purpose.
Qualitatively high indicators of weldability, machinability and cutting.
Characterized by low corrosion resistance.

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

Determining origin by type of part

Having examined 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 remember the main distinctive technological properties. So, cast iron is a casting material. It is used to produce simple dishes, massive pipes, housings of machine tools, engines, and large objects of simple configuration. Parts of all sizes and complexity are made from steel, as forging, stamping, drawing, rolling and other methods of metal forming are used for this purpose. Thus, if there is a question about the origin of the reinforcement, there can be no doubt - it is steel. If you are interested in the origin of a massive cauldron, it 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 is characterized by a matte gray color and a rougher external texture. Steel is characterized by its special silvery shiny hue 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 workpieces or metal objects being examined do not have 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 crushing loads, cast iron crumbs will turn out to be of small, varied shapes, and pieces of steel will be large, with the correct configuration.

Cut and drill

How to distinguish cast iron from steel at home? It is necessary to obtain fine dust or shavings from it. Since steel has high ductility, its chips also have a tortuous character. Cast iron crumbles, and when drilling, small chips 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. Examine the resulting fine shavings on your hand or a white sheet of paper. Cast iron contains large amounts of carbon 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 mechanical influence on dust does not give any visible results.

Heat and sparkle

How to distinguish cast iron from steel? Need to operate necessary equipment and a little patience.

In the first case, you can resort to heating, for example, using a blowtorch, initially wearing special protective clothing and following safety rules at work. The temperature must be increased 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 pig iron. Regarding all industrial grades, they contain carbon in an amount of no more than 4.3% and melt at 1000-1200˚C. Thus, it can be melted much faster.

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

What does it sound like

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 using existing experimental facilities. But it is necessary to have both samples or have an experienced ear in this matter. Steel is characterized by a higher density, which is reflected in its sound. When you hit it with a metal object, the sound is much louder 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 technician can easily distinguish them from each other, assessing them only visually or by touch.

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How to distinguish between cast iron and cast steel

The difference between cast iron scrap and steel scrap is not only in the chemical composition, but also visual. To test the difference you will need grinding wheel, a piece of metal, a blowtorch, a protective mask and gloves

Physical properties of cast iron and cast steel

You can distinguish metals by their appearance. Cast iron is rough and matte gray in color, while cast steel is smooth and silvery gray in color.

Spark test

You will need two small pieces of each metal. Press the sanding wheel against the edge of each metal and note the color of the sparks that form. Steel will create shiny white sparks, while cast iron will generate dull red sparks.

Crushing test

Take a small piece from each metal and try to crush it. You will find that cast iron will break randomly, while cast steel will break into long, smooth, thin pieces with little or no effort.

Melting test

For this test you will need a small piece of each metal to melt. Put on your protective gear and melt the metal blowtorch. The more carbon in a metal, the harder the metal becomes. You will see that the cast iron melts faster and turns red. Cast steel takes longer to melt and turns white when melted.

Fragility test

Drop a thin slab of each metal and drop it onto the ground with some force. Cast iron will break into many pieces, while steel will not break, or will break into two pieces. This is because cast iron is more brittle than steel.

Find an inconspicuous place on the part and go over the metal several times with a needle file or a small file. Rub the resulting sawdust between your fingers. Regular cast iron will leave a distinctive graphite black color on the skin.
It will be even clearer if you rub sawdust between sheets of white paper. Steel filings will not stain paper.

You can determine whether the material in front of you is cast iron or steel experimentally: by the color and shape of the spark.
Turn on grinding machine and take two parts or blanks that are known to you: steel and cast iron. Shoot sparks from them one by one and compare. After that, go through the same detail about the part you doubt. Draw a conclusion based on the greatest analogy with the samples.
Sparks that occur when grinding steel are tiny molten particles of metal that fly tangentially to the circumference of the wheel at the point of contact with the workpiece.
If there is carbon in the metal, the hot particles, in contact with air, are oxidized, the carbon turns into carbon dioxide. In this case, very numerous sparks with short rays are formed.
Cast iron will spark a bright straw color.

Take a drill and insert a small diameter drill into it. Determine a secluded place on the part and drill a little.
Firstly, the process of drilling a cast iron part is different from drilling in steel. To better feel the difference, do similar drilling on samples of cast iron and steel that you know.
Secondly, when drilling cast iron, almost no chips are formed. And if it does form, it is very short and it can easily be ground into dust with your fingers. The steel shavings are twisted like wire, and you can’t break them with your fingers.
You can also check the type of metal by processing lathe– for cast iron, the shavings will be coarse dust.

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