Which cast iron is called white

White cast iron

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White cast iron is a type of cast iron that has a white color when fractured and a characteristic metallic sheen. It contains carbon in the form of cementite. The presence of graphite in white cast iron is not visually detectable and is determined only chemically.

Unalloyed and alloyed white cast iron have different chemical compositions. Alloying of white cast iron is carried out in order to increase its wear resistance. For these purposes, carbide-forming elements are used - chromium, tungsten, molybdenum, etc.

Features of producing white cast iron

In the process of producing white cast iron of a given structure, it is necessary to suppress the graphitization process during the entire time of crystallization of the liquid mass. In this case, both the competent selection of source materials and adherence to the technology for cooling cast iron in the mold are important.

When castings are made from unalloyed cast iron in wet sand molds, there is a need to maintain the proportion of carbon and silicon: C (Si + log R) < 4.5. The cross-sectional area of ​​the casting divided by the perimeter of the section is called the reduced thickness and is denoted in this case as R.

The high content of cementite in white cast iron seriously complicates their use as structural materials, since they are brittle and extremely difficult to machine.

On the other hand, white cast iron castings are characterized by corrosion resistance, resistance to high temperatures and open fire, and wear resistance. To maintain the above qualities, their composition must be as homogeneous as possible. The more carbides contained in white cast iron, the greater its hardness.

If coagulation of carbides occurs due to non-compliance with technology, the hardness of cast iron is significantly reduced. White cast iron with a martensitic structure has the maximum hardness.

Alloying elements of white cast iron

The hardness of white cast iron is most strongly influenced by carbon, which, in fact, determines the amount of carbides. The remaining elements that affect its hardness are arranged in the following order (in descending order): nickel, phosphorus, manganese, chromium, molybdenum, vanadium, silicon, copper, titanium, sulfur.

Elements such as Ni, Mn, Cr are directly involved in the formation of the martensite-carbide structure. If their total content is approximately equal to the proportion of carbon, the white iron casting has maximum hardness.

White cast iron is characterized by the absence of a direct relationship between hardness and wear resistance; in this case these are different qualities.

Wear resistance is a defining characteristic, and its best indicators are found in white cast iron with a special structure of the metal mass, in which carbides and phosphides are arranged in the form of separate uniform inclusions or a graphically regular grid.

White cast iron has found wide application in the production of machine parts, equipment and mechanisms operating under conditions of increased abrasive wear and in the absence of lubrication.

Alloyed white cast iron, in addition to heat resistance and corrosion resistance, also has electrical resistance.

These characteristics are determined by the structure of its metallic mass, which can be carbide-pearlite, carbide-austenitic, and contain alloyed ferrite.

In other words, the quality of casting directly depends on the composition of alloying elements and their concentration. In most cases, chromium is the main alloying element that forms chromium and iron carbides and binds carbon.

High chromium white cast iron

High-chromium white cast iron is characterized by maximum resistance to corrosion due to the formation of oxide films on its surface. In addition, chromium and iron carbides are characterized by a high electrode potential, comparable to the potential of chromium ferrite, the second component of the metallic mass of white cast iron. High-chromium white cast iron retains its corrosive properties in alkaline and saline solutions, sulfuric and nitric acid.

The process of complex alloying of white cast iron is fraught with coagulation of carbides under high temperature conditions. The presence of chromium in it increases the temperature resistance of carbides and helps slow down diffusion processes. If high-chromium white cast iron is additionally alloyed with elements such as Ni and Mo, its mechanical characteristics are further enhanced, and its strength approaches that of heat-resistant steel.

In areas where such qualities of cast iron as corrosion resistance and high electrical resistance are in demand, alloyed white cast iron is used.

White stainless and heat-resistant cast iron

In industry today, stainless white cast iron of the X28 and X34 grades is widely used. In addition to corrosion resistance, parts made from it have the ability to maintain their original dimensions during prolonged and cyclic heating. The improved characteristics of cast iron of these grades are due to additional alloying with the following elements:

N – 0.1%; Ti – 0.5%;

Cu – 0.5-2.0%.

White cast iron with high resistivity

Cast iron grade X34 is used for cast heaters capable of operating at temperatures of 800-900 ˚C. This type of white cast iron is called sormite and is distinguished by the following percentage of alloying elements:

carbon – 2.5-3.5%; silicon – 2.0-2.5%; manganese – 1.0-1.5%;

nickel – 3.0-5.0%.

Its resistivity is characterized by the following indicators: p = 1.4/1.5 ohm * m/mm2, σв = 35 kg/mm2; σben = 70 kg/mm2; HRC 48-50.

White cast iron castings are annealed to relieve internal stress and stabilize dimensions. The annealing temperature depends on the resistance of the carbides and in the case of white cast iron it rises to 850 ˚C. Heating and cooling processes should be slow for all grades of alloy cast iron. The result is durable parts that are much less prone to cracking.

See also:

Source: https://www.autowelding.ru/publ/1/1/belyj_chugun/4-1-0-532

The concept of cast iron, its features and nuances of use

Cast iron firmly entered our lives many years ago. It is relatively easy to produce and widely used in various fields. To have a clear understanding of this material, you need to know its features, disadvantages, advantages, chemical composition, properties, structure of cast iron and its alloys, their production and scope of application.

So, let's find out which iron-carbon alloys are called cast irons.

Concept

Cast iron is an iron-carbon alloy containing carbon, that is, it means a material that consists of an alloy of iron and carbon. The percentage of carbon in cast iron is more than 2.14%. The latter element can be included in cast iron in the form of graphite or cementite.

This video talks about the features of cast iron:

There are white and gray cast iron.

• The carbon in white cast iron is in the form of iron carbide. If you break it, you can see a white tint. White cast iron is not used in its pure form. It is added to the process of producing malleable iron.
• At a fracture, gray cast iron has a silvery tint. This type of cast iron has a wide range of uses. It lends itself well to processing with cutters.

In addition, cast irons are high-strength, malleable and with special properties.

• High-strength cast iron is used to increase the strength of the product. The mechanical properties of such cast iron allow this to be done perfectly. High-strength cast iron is obtained from gray cast iron by adding magnesium to the mass.
• Ductile iron is a type of gray iron. The name does not mean that this cast iron is easily forged. It has increased plasticity properties. It is obtained by annealing white cast iron.
• There is also a distinction between half cast iron. Some of the carbon in it is in the form of graphite, and the remaining part is in the form of cementite.

Special Features

The peculiarity of cast iron lies in the process of its production. The average melting point of different types of cast iron is 1200ºC. This value is 300 degrees less than that of steel. This is due to the very high carbon content. Carbon and iron atoms do not have a very close connection with each other.

https://www.youtube.com/watch?v=Wj3yX7R9dE4

When the smelting process takes place, carbon cannot be completely incorporated into the iron lattice. As a result, cast iron takes on the property of brittleness. It cannot be used for the manufacture of parts that will be subject to constant load.

Cast iron is a ferrous metallurgy material. Its characteristics are often compared to steel. Products made of steel or cast iron are widely used in our lives. Their use is justified. After comparing the characteristics, we can say the following about these two materials:

• The cost of cast iron products is lower than the cost of steel ones.
• Materials vary in color. Cast iron is a dark matte material, while steel is light and shiny.
• Cast iron is easier to cast than steel. But steel is easier to weld and forge.
• Cast iron is less durable than steel.
• Cast iron is lighter in weight than steel.
• Steel has a higher carbon content than steel.

Advantages and disadvantages

Cast iron, like any material, has positive and negative sides.

The advantages of cast iron include:

• Carbon in cast iron can be in different states. Therefore, this material can be of two types (gray and white).
• Certain types of cast iron have increased strength, so cast iron is sometimes placed on the same line as steel.
• Cast iron can maintain temperature for quite a long time. That is, when heated, the heat is evenly distributed throughout the material and remains in it for a long time.
• In terms of environmental friendliness, cast iron is a clean material. Therefore, it is often used to make dishes in which food is subsequently prepared.
• Cast iron is resistant to acid-base conditions.
• Cast iron has good hygiene.
• The material has a fairly long service life. It has been noticed that the longer cast iron is used, the better its quality.
• Cast iron is a durable material.
• Cast iron is a harmless material. It is not capable of causing even slight harm to the body.

The disadvantages of cast iron include:

• Cast iron will rust if it is exposed to water for a short time.
• Cast iron is an expensive material. However, this minus is justified. Cast iron is very high quality, practical and reliable. Items made from it are also high quality and durable.
• Gray cast iron is characterized by low ductility.
• White cast iron is characterized by brittleness. It is mainly used for smelting.

Properties and characteristics

Cast iron has the following properties:

1. Physical . These characteristics include: specific gravity, coefficient of linear expansion, actual shrinkage. Specific gravity varies depending on the carbon content of the material.
2. Thermal . The thermal conductivity of a material is usually calculated using the displacement rule. For solid cast iron, the volumetric heat capacity is 1 cal/cm3*oC. If cast iron is liquid, then it is approximately 1.5 cal/cm3*oC.
3. Mechanical . These properties depend on the base itself, as well as on the size and shape of the graphite. Gray cast iron with a pearlite base is considered the most durable, and the most ductile is with a ferritic base. The maximum reduction in strength is observed with the “plate” shape of graphite, and the minimum – with the “ball” shape.
4. Hydrodynamic . Viscosity in cast iron varies depending on the presence of manganese and sulfur. It also increases sharply when the temperature of cast iron passes the point where solidification begins.
5. Technological. Cast iron has excellent casting properties, resistance to wear and vibration.
6. Chemical . According to the electrode potential (in decreasing order), the structural components of cast iron are arranged in the following form: cementite - phosphide eutectic - ferrite.

Differences between cast iron and steel in chemical composition and properties

The properties of cast iron are affected by special impurities.

• Thus, the addition of sulfur can significantly reduce fluidity and reduce refractoriness.
• The addition of phosphorus simultaneously makes it possible to create a product of complex shape, but does not give it increased strength.
• The silicon impurity makes the melting point not so high and significantly improves the casting properties. Different percentages of silicon create different types of cast iron, from pure white to ferritic.
• Manganese worsens casting and technological properties, but increases strength and hardness.

In addition to the mentioned impurities, cast iron may also contain other components. Then such materials will be called alloyed. The most common materials added to cast iron are titanium, chromium, aluminum, nickel and copper.

Next, you will find out what elements are included in the chemical composition of cast iron.

The video below will show you how to weld cast iron using electric welding:

If we consider cast iron as a structural material, then it is a metal cavity with graphite inclusions. The structure of cast iron is mainly pearlite, ledeburite and ductile graphite. Moreover, for each type of cast iron these elements predominate in different proportions or are absent altogether.

According to the structure of cast iron there are:

• perlite,
• ferritic and
• ferritic-pearlitic.

Graphite is present in this material in one of the forms:

• Globular. Graphite takes on this shape when magnesium is added. The spherical shape of graphite is characteristic of high-strength cast irons.
• Plastic. Graphite is similar to the shape of petals. In this form, graphite is present in ordinary cast iron. This cast iron has increased ductility properties.
• Flaky. Graphite acquires this shape by annealing white cast iron. Graphite is found in flake form in malleable cast iron.
• Vermicular. The named form of graphite is found in gray cast iron. It was developed specifically to improve ductility and other properties.

Metal production

Cast iron is produced in special blast furnaces. The main raw material for producing cast iron is iron ore. The technological process consists of reducing the iron oxides of the ore and obtaining another material as a result - cast iron. The following fuels are used to make cast iron: coke, natural gas and thermal anthracite.

Once the ore is reduced, the iron is in a solid form. Next, it is lowered into a special part of the furnace (steam), where carbon is dissolved in the iron. The output is liquid cast iron, which falls into the lower part of the furnace.

The price of cast iron (per 1 kg) depends on the amount of carbon in it, the presence of additional impurities and alloying components. Approximately the price of a ton of cast iron will be 8,000 rubles.

Cast iron is common in many areas.

• It is used for the production of parts in mechanical engineering. Engine blocks and crankshafts are mainly made from cast iron. The latter require advanced cast iron, to which special graphite additives are added. Due to the resistance of cast iron to friction, it is used to make excellent quality brake pads.
• Cast iron can operate smoothly even at extremely low temperatures. Therefore, it is often used in the production of machine parts that will have to work in harsh climatic conditions.
• Cast iron has proven itself well in the metallurgical field. It is valued for its relatively low price and excellent casting properties. Products made from cast iron are characterized by excellent strength and wear resistance.
• A large variety of plumbing products are made from cast iron. These include sinks, radiators, sinks and various pipes. Cast iron bathtubs and heating radiators are especially famous. Some of them still serve in apartments today, although they were purchased many years ago. Cast iron products retain their original appearance and do not require restoration.
• Thanks to its good casting properties, cast iron produces real works of art. It is often used in the manufacture of artistic products. For example, such as beautiful openwork gates or architectural monuments.

Are you choosing a bath? Don't know which is better, cast iron or steel? Then this video will help you:

Source: http://stroyres.net/metallicheskie/vidyi/chyornyie/chugun/ponyatie-osobennosti.html

White cast iron: properties, application, structure and features

Initially, cast iron technology was first mastered in China back in the 10th century, after which it became widespread in other countries of the world. The basis of cast iron is an alloy of iron with carbon and other components.

A distinctive feature is that cast iron contains more than 2% carbon in the form of cementite, which is not found in other metals.

A prominent representative of such an alloy is white cast iron, which is used in mechanical engineering for the manufacture of parts, in industry and in everyday life.

Appearance

The alloy has a white color when fractured and a characteristic metallic luster. The structure of white cast iron is fine-grained.

Properties

In comparison with other metals, iron-carbon alloy has the following characteristics and properties:

• high fragility;
• increased hardness;
• high resistivity;
• low casting properties;
• low machinability;
• good heat resistance;
• high shrinkage (up to 2%) and poor filling of molds;
• low impact resistance;
• high wear resistance.

The metal mass has great corrosion resistance in hydrochloric or nitric acid. If there are free carbides in the structure, then corrosion will occur when cast iron is placed in sulfuric acid.

White cast irons, which contain a lower percentage of carbon, are considered more resistant to high temperatures. Due to the increased mechanical strength and toughness that appear when exposed to high temperatures, the formation of cracks in castings is minimized.

Compound

Iron-carbon alloy is considered a cheaper material compared to steel. White cast iron contains iron and carbon, which are in a chemically bonded state. Excess carbon, which is not present in the solid solution of iron, is contained in a combined state in the form of iron carbides (cementite), and in alloyed cast iron in the form of special carbides.

Kinds

Depending on the amount of carbon content in white cast iron is divided into the following types:

1. Hypoeutectic contains from 2.14% to 4.3% carbon and, after complete cooling, acquires the structure of pearlite, secondary cementite and ledeburite.
2. Eutectic contains 4.3% carbon and has a structure in the form of a light background of cementite, which is dotted with dark pearlite grains.
3. Hypereutectic has from 4.3% to 6.67% carbon in its composition.

Application

Based on the above properties, we can conclude that it makes no sense to practice thermal and mechanical treatment of white cast iron. The alloy found its main application only in the form of casting. Consequently, white cast iron obtains its best properties only if all casting conditions are met. This processing method is actively used if it is necessary to produce massive products that must have high surface hardness.

In addition, white cast iron is annealed, resulting in malleable cast iron, which is used for the production of thin-walled castings, for example:

• automobile parts;
• products for agriculture;
• parts for tractors, combines, etc.

The alloy is also used for the manufacture of plates with a ribbed or smooth surface, and is also actively used for the production of steel and gray cast iron.

The use of white cast iron in agriculture as a structural metal is quite limited. Most often, iron-carbon alloy is used for the manufacture of parts for hydraulic machines, sand throwers and other mechanisms that can operate under conditions of increased abrasive wear.

Bleached cast irons

This alloy is considered a type of white cast iron. It is possible to achieve a chill of 12-30 mm by rapidly cooling the surface of the iron-carbon alloy. Material structure: the surface part is made of white, gray cast iron in the core. Wheels, balls for mills, and rolling rolls are made from this material, which are mounted in machines for processing sheet metal.

Alloying elements of the alloy

Specially introduced alloying substances added to the composition of white cast iron can impart greater wear resistance and strength, corrosion resistance and heat resistance. Depending on the amount of added substances, the following types of cast iron are distinguished:

• low alloy alloy (up to 2.5% excipients);
• medium alloyed (from 2.5% to 10%);
• highly alloyed (more than 10%).

Alloying elements can be added to the alloy:

• chromium;
• sulfur;
• nickel;
• copper;
• molybdenum;
• titanium;
• vanadium,
• silicon;
• aluminum;
• manganese.

Alloyed white cast iron has improved properties and is often used for casting turbines, blades, mills, parts for cement and conventional furnaces, pumping machine blades, etc. The iron-carbon alloy is processed in two furnaces, which allows the material to be brought to a certain chemical composition:

• in a cupola;
• in electric melting furnaces.

Castings made of white cast iron are annealed in furnaces to stabilize the required dimensions and relieve internal stress. The annealing temperature can increase to 850 degrees. The heating and cooling process must be done slowly.

The marking or designation of white cast iron with impurities begins with the letter H. Which alloying elements are contained in the alloy can be determined by the subsequent letters of the marking. The name may contain numbers that indicate the amount in percentage terms of additional substances that are contained in white cast iron. If the marking contains the designation Ш, this means that the alloy structure contains spherical graphite.

Types of annealing

To form white cast iron, industry uses rapid cooling of the alloy. Today, the following main types of carbon alloy annealing are actively used:

• softening annealing is used primarily to increase the ferrite content of cast iron;
• annealing to relieve internal stresses and minimize phase transformations;
• graphitizing annealing, as a result of which it is possible to obtain malleable cast iron;
• normalization at a temperature of 850-960 degrees, resulting in graphite and perlite, and also increases wear resistance and strength.

Additional information

Today it has been proven that there is no direct relationship between wear resistance and hardness of a carbon alloy. Only due to the structure, namely the arrangement of carbides and phosphides in the form of a regular network or in the form of uniform inclusions, increased wear resistance is achieved.

The strength of white cast iron is most strongly influenced by the amount of carbon, and the hardness depends on the carbides. The greatest strength and hardness are those cast irons that have a martensitic structure.

Source: https://FB.ru/article/365393/belyiy-chugun-svoystva-primenenie-struktura-i-osobennosti

Composition of white cast iron

The carbon in white cast iron has a bound form. (Fe3C). Its quantitative content in this alloy determines the following types of white cast iron:

• hypoeutectic white cast iron. This cast iron is characterized by a carbon content of 2.14% to 4.3%. After complete cooling, the structure of this cast iron is the structure of perlite, ledeburite (perlite and cementite), as well as secondary cementite;
• eutectic white cast iron. The main characteristic of this alloy is the carbon content of 4.3%;
• hypereutectic white cast iron differs from the two previous types by its increased content of carbon in its composition - from 4.35% to 6.67%.

In addition, this alloy is also divided into ordinary, bleached, and alloyed.

The internal structure of white cast iron is represented by alloys of two chemical elements - iron and carbon. Despite the fact that the production of white cast iron is carried out under fairly high temperature conditions, it retains a fine-grained structure, which, in turn, gives that characteristic white color on the fracture of a part made of this cast iron.

It is worth noting that the structure of a hypoeutectic alloy always contains cementite, the percentage of which can reach 100%. However, this situation is more typical for a eutectic metal. But the hypereutectic type of white cast iron consists of eutectic and primary cementite.

A representative of such alloys is bleached cast iron, which is based on gray or high-strength cast iron. The surface layer of this cast iron contains a high percentage of ledeburite and perlite. Bleaching to a depth of up to 30 mm is carried out by rapid cooling. In this way, it is achieved that the cast iron is white on top, but contains an ordinary gray alloy inside.

Cast iron may also contain alloyed elements such as chromium, nickel, aluminum and others. Depending on the amount of alloying elements contained in cast iron, there are the following types of alloys:

• low-alloy, containing a maximum of 2.5% alloying additives;
• medium alloyed, in which the percentage of alloyed additives can be 10%;
• highly alloyed, which contain 10% or more alloyed elements.

Properties of white cast iron

As mentioned above, cast iron is distinguished by its strength and fragility at the same time. However, this combination of qualities gives it many unique properties that make cast iron an indispensable material for use in many areas of human activity.

Among these qualities are the following:

• high hardness;
• high resistivity;
• high wear resistance;
• resistance to high temperatures on the material;
• resistance to corrosion, as well as various types of acids.

It is worth noting that white cast iron, which has a lower percentage of carbon, is more resistant to high temperatures. This property is used to reduce the number of cracks in castings.

However, nothing is perfect. Despite its many advantages and uniqueness, cast iron also has some disadvantages:

• low casting properties;
• fragile;
• castings and parts made of white cast iron are difficult to process;
• large shrinkage, sometimes reaching 2%;
• low resistance to impacts;
• poor weldability.

Application of white cast iron

Due to the fact that ordinary white cast iron is difficult to mechanically and thermally treat, its scope of application is quite limited. As a rule, for the manufacture of products it is used in the form of unprocessed or partially processed castings.

However, the alloy is still used for the manufacture of dimensional products of simple configuration, as well as components and assemblies that are constantly exposed to abrasive materials. In this regard, it has found its application in mechanical engineering, machine tool building, and shipbuilding.

Thus, white cast iron is used for the manufacture of housings and parts of machine tools and rolling mills, balls for mills, drive and support wheels. It is also a raw material for the production of some parts for cars and trucks, tractors, combines, as well as various large agricultural machinery.

Alloying elements, as already mentioned above, can significantly improve the alloy, endowing it with specially specified properties. This allows the use of white cast iron to produce slabs with different surface shapes.

It is worth noting that white cast iron is the raw material from which malleable grades of iron-carbon cast iron and steel alloys are made.

Source: http://mining-prom.ru/rud/zhelez/belyy-chugun/

Cast iron: production process, classification and marking

In the age of rapid development of the metallurgical industry and production, cast iron plays a key role. Let's figure out what kind of material this is, how it appeared, how it is produced, what properties it has, what types of classification of cast iron exist, and how it is used in various fields of industry.

Definition

Cast iron is a mixture of 2.14% carbon with iron, obtained by thermal heating in blast furnaces to 1200 degrees Celsius. With the help of the sixth element of the periodic table, iron in the form of an alloy acquires increased hardness, losing ductility and malleability, making the material brittle.

In addition to carbon, to obtain special parameters, elements such as Si, Mg, P, S are added to the metal matrix. Alloying agents are also widely used - Cr, V, Ni, Al.

Story

The technology for making cast iron came to us from China, where cast iron money circulated back in the 10th century AD. The descendants of the Mongols already prepared boilers from this alloy in the 13th century.

On the battlefields of the Hundred Years' War, artillery pieces and ammunition cast from this solid solution were used for the first time. In Russia, its widespread use in the manufacture of weapons was established in the 16th century after the appearance of the blast furnace.

In this regard, the Ural Iron Foundry was built in 1701, which became the beginning of a folk craft called “Kasli casting”.

Since the 18th century, Great Britain has been the world's leading iron producer. Thanks to Wilkinson's new technology, by the mid-19th century this country produced half the world's total.

Manufacturing technology did not stand still, which allowed the United States to take the lead at the end of the 19th century.

At that time, rails, water and sewer pipes, fireplaces, and such complex engineering structures as bridges began to be made from this alloy.

Iron production process

The production of cast iron is carried out in blast furnaces. This process is quite energy-intensive and costly production. 4 main groups of ores are used as raw materials:

• Hematite iron ore, consisting of iron anhydrite oxide, holds 70% (Fe) and 30% (O);
• Magnetite iron ore contains 72.4% (Fe), and 27.6% (O);
• Brown iron ore contains 59.8% elemental iron;
• Siderite iron ore, contains 48.3% (Fe).

The technological process takes place in several stages

First, during the preparation process, iron ore containing iron oxides (FeO and Fe2O3) of at least 40% of the total mass is crushed. Then, by crushing, screening, averaging, washing, enrichment and roasting, they get rid of non-metallic impurities - S, P, As, and increase the mass fraction of the base metal in the ore.

At the end of the preparatory stage, all components are loaded into the oven.

A blast furnace is a continuously operating metallurgical equipment in the form of a shaft, weighing 30 thousand tons. The blast furnace consists of 5 elements: the upper part in the shape of a cylinder - the furnace, the wide conical part - the shaft, the wide part - the steam chamber, the narrowed part - the shoulders and the lower part - the hearth. All components are produced from above through the furnace, and the finished product and slag come out separately from below from the furnace.

Simultaneously with the ore, coking coals are placed into the blast furnace to act as fuel. During the thermal decomposition of coals, carbon compounds are formed that act as a reducing agent. Fluxes are added to speed up the process of releasing metal from the ore. Typically these are rocks containing oxides of calcium and magnesium.

After the loading stage is completed, the smelting process begins, where the loaded components are converted into an alloy, slag and gas. The physicochemical reactions occurring in this case can be characterized as reduction-oxidation, since the reduction of iron oxides and the oxidation of the reducing agent occurs.

Processes occurring in the furnace

The processes occurring in a blast furnace can be described by the following chemical equations:

When coke is heated, elemental carbon is released, which forms carbon dioxide with oxygen.

C + O2 = CO2 + energy release

CO2, when heated, is further oxidized to carbon monoxide, and reduces elemental iron from its oxides in the ore.

CO2 + C = 2CO

Fe2O3 + 3 CO = 2Fe + 3 CO2

After the reduction reaction, the metal is saturated with carbon, and when it reaches 1150-1200°C, it flows in the form of a metal compound into the furnace. From the remains of empty ore and fluxes, waste is formed - slag, which is continuously removed.

Cast iron parameters

Density - 7.2 g/cm3. The melting point is 1200 °C. The fragility and low ductility of the alloy is due to the following factors:

1. Increased bond length between Fe atoms due to increased carbon content;
2. Incomplete introduction of carbon atoms into the structure of the iron matrix due to the low melting point compared to steel.

It is for these reasons that this solid metal solution has found wide application in the production of parts with high strength. However, it is not suitable for products subject to loads that change rapidly over time.

Classification of cast irons

There are several types of classification of cast iron.

1. Based on elemental carbon content they are divided into:
   • hypoeutectic (2.14-4.3%);
   • eutectic (4.3%);
   • hypereutectic (4.3-6.67%).
2. By type of carbon and fracture color:
   • White (C > 3%, in carbide form). Its use is limited to the production of products that are not subject to heavy loads due to its significant fragility. But when adding alloying additives containing chromium, nickel, vanadium, aluminum, its performance parameters increase;
   • Gray (C -2.5%, in the form of perlite) has good wear resistance and reduces friction. Used in the manufacture of industrial equipment parts subject to cyclic loads. When adding special additives containing Mo, Ni, Cr, B, Cb, Sb, resistance improves when used in aggressive environments;
   • Half (C – 3.5-4.2%, in the form of graphite and carbide and the presence of trace amounts of cementite and ledeburite). This type has found its application in the production of products subject to constant friction.
3. According to physical parameters, according to GOST 1412-54 and 1215-59, cast iron grades are distinguished:
   • Malleable (CC), is its white variety after special firing. At the same time, the proportion of carbon is at the level of 3.5%, and it is presented in the form of Fe2O3 or granular pearlite, with graphite inclusions. Mg, Te, B are usually added as additives to increase friction resistance. It should be noted that this brand is never forged, in the literal sense of the word;
   • High-strength (HF), is formed by interspersing spherical carbon inclusions into a metal lattice and introducing magnesium, calcium, selenium, and yttrium into the composition. Characterized by improved mechanical, thermally conductive plastic parameters.
4. By specific properties:
   • Wear-resistant;
   • Antifriction;
   • Corrosion resistant;
   • Heat resistant;
   • Non-magnetic.
5. According to the Brinell hardness scale:
   • Soft (HB less than 149);
   • Moderate hardness (HB 149-197);
   • Improved hardness (HB 197-269);
   • Hard (HB more than 269).
6. According to the value of temporary tensile strength:
   • Ordinary strength (less than 20 kgf/mm2);
   • Improved strength (20-38 kgf/mm2);
   • Maximum strength (more than 38 kgf/mm2).
7. According to magnetic characteristics:
   • Ferromagnetic - having magnetic properties, due to the high content of ferrite and cementite in the metal matrix;
   • Vapor-magnetic – having low magnetic permeability, containing additives of chromium, copper and aluminum.

Marking

According to GOST, all existing brands are designated by 2 letters and 2 numbers, with the numbers reflecting the values ​​of tensile strength (kgf/mm2) and elongation (%). For example, the numbers in the KCh-30-6 brand show a temporary resistance of 30 kgf/mm2 and a relative elongation of 6%.

By introducing special additives into the composition, the composition of the alloy is modified. Then the letter M is added to the brand name.

Areas of use

The use of different grades of cast iron depends on the metallurgical compound and its performance characteristics.

The white type is used in the production of heating elements and household sanitary ware (baths, sinks), and is also a raw material for the production of malleable varieties of solid solutions.

Gray - is part of various engine components for the engineering industry.

Malleable – in the manufacture of brake pads and parts for industrial grinding equipment. In addition, it has wide application in the textile industry in casting complex shaped spare parts for machinery. KCh is used in the manufacture of kitchen utensils, interior elements, street lamps, and railings for stairs.

The high-strength grade is used in the production of pipes, fittings for water supply, sewerage, and oil production. In addition, sectional radiators are made from it, used in central heating systems of residential buildings and administrative buildings.

Electrical panels and other components of electrical equipment are made from the ferromagnetic type, while its non-magnetic type, on the contrary, is used as an electrical insulating material.

Pig iron is used in huge quantities as a raw material in steel foundries.

Interesting Facts

According to Professor Marienbach, cast iron got its name from the Chinese word “zhugun”, which means “foundry worker”.

Cast iron cookware has long been used around the world and is very convenient for preparing various types of food.

An integral attribute of Russian folk tales is the oven, in which, in a cast iron pot - a vessel of a certain shape and cast from a given alloy, the heroes cooked the main dish - jacket potatoes.

The best pancakes are made in a cast iron skillet.

Before the advent of electric irons, housewives used heavy cast iron irons with perfectly smooth soles, heating them until red hot over a fire source.

The next stage was coal cast-iron irons, whose design resembled small stoves. To heat them, birch charcoal was placed inside. This iron even had a pipe to obtain the necessary traction.

The sewer manholes for inspection wells known to us from childhood were round in shape, cast from cast iron and were first made one hundred and fifty years ago.

Pig iron production worldwide in 2015 amounted to more than 898 million tons, which is 3% less than in 2008.

Conclusion

Having examined in detail the questions posed above, we can conclude:

1. Cast iron is an alloy of iron and carbon with the addition of special modifiers;
2. For its production, various types of ores are mined, subjected to preliminary preparation and enrichment;
3. Smelting takes place in a blast furnace, which operates continuously and represents a whole metallurgical complex of equipment;
4. Depending on the amount and forms of dissolved carbon in the metal matrix, all alloys are divided into different types and have different properties;
5. The use of various grades of cast iron directly depends on its physical and chemical parameters of the resulting alloy;
6. Despite the availability of new types of materials, cast iron cookware is still in demand among many housewives and cooks;
7. Ancient coal cast iron irons were a small stove and heated with coal, which made the ironing process very tedious and a fire hazard;
8. The production of cast iron is quite an energy-intensive and financially expensive business, so at present its volume is invariably declining throughout the world, as other modern, wear-resistant and cheap-to-manufacture composite materials are replacing it.

Source: https://SoproMats.ru/materialyi/metallyi/chugun/

Types of produced white cast iron

Depending on the crystalline structure, as well as the presence and ratio of the constituent elements, white cast iron is divided into:

• ordinary;
• alloy;
• heat resistant;
• stainless.

A separate type is cast iron alloys with high electrical resistivity.

The internal structure of ordinary white cast iron contains carbon in the form of cementite grains. The amount of carbon affects the melting point and, depending on this, cast iron is divided into:

1. hypoeutectic with a lower melting point, carbon not more than 4.3%;
2. eutectic with a carbon content of 4.3%;
3. hypereutectic - more than 4.35% and can reach - 6.3%.

The effect of cast iron bleaching is achieved by rapidly cooling the casting, which as a result is heterogeneous in composition. The top layer, up to 30 mm thick, becomes white, and the rest of the core is ordinary gray cast iron.

Advantages and disadvantages 

Like all cast iron alloys, white ones are distinguished by great strength combined with brittleness under strong mechanical shocks. Among the main positive qualities of white cast iron are:

• high hardness;
• high resistivity;
• wear resistance;
• increased corrosion resistance.

An important quality of white cast iron is considered to be very good resistance to high temperatures, which is used to reduce the number of cracks in initial castings.

The main disadvantages include such qualities as:

• fragility and the possibility of destruction under mechanical stress;
• low casting qualities and poor mold filling;
• the likelihood of internal cracks forming during casting;
• complex and low-quality mechanical processing.

Formation of defects during welding due to the rapid burnout of carbon and the formation of pores.

Application area

Ordinary white cast iron is used very limitedly, since it is poorly applicable to mechanical and heat treatment. For the production of products it is often used in the form of unprocessed or partially processed castings.

The alloy is most widely used in the manufacture of large parts of simple configuration. These are housings and parts of machine tools and rolling mills, balls for mills, drive and support wheels. In addition, white cast iron is used for the manufacture of assembly units that are constantly exposed to abrasive materials.

An important point is the use of ordinary cast iron as a raw material for the manufacture of malleable grades of iron-carbon cast iron and steel alloys.

Alloying of white cast iron

The presence of alloying additives in the alloy greatly changes its physical properties, which significantly expand its scope of application. Very common substances are used as alloying elements in metallurgy.

To increase hardness, the following can be added to an iron-carbon cast iron alloy: nickel, phosphorus, manganese, chromium, vanadium, silicon, copper, titanium and sulfur.

In the event that the amount of alloying additives is approximately equal to the carbon content, cast iron acquires the maximum possible hardness.

Wear resistance, as a physical characteristic of white cast iron, is considered regardless of its hardness. Its increase is achieved by changing the structure of the metal by adding carbides and phosphides in the form of evenly distributed inclusions. The quality of casting parts directly depends on the chemical composition of the alloys and the amount of alloying elements.

Depending on the percentage of alloying impurities, white cast iron is divided into:

• low alloyed up to 2.5%;
• medium alloyed up to 10%;
• highly alloyed.

Already finished cast iron castings are subjected to additional temperature treatment (annealing), as a result of which the internal stresses of the metal are relieved and the external dimensions are stabilized. The annealing temperature of white alloy cast iron is about 850°C.

The heating and cooling process occurs slowly to prevent the formation of internal cracks and other defects.

Alloy cast iron alloys are widely used in production:

• parts of industrial equipment and machine tools;
• components and parts of cars, tractors and agricultural machinery;
• rolling stock; pipes, pumps, boilers;
• household and household products.

This is due to the improved qualities of the metals compared to ordinary white cast iron.

Stainless alloys

To increase the resistance of white cast iron to corrosion, large amounts of chromium are added to it. This leads to the formation of an oxide film on the surface and further cessation of oxygen access. In addition, high-chromium white cast iron becomes resistant to alkaline solutions, sulfuric and nitric acid.

Additionally, the process of alloying with chromium prevents the possibility of coagulation of carbides when the alloy is heated strongly. This allows you to obtain high-quality welded joints of parts made of white cast iron. If nickel and molybdenum are added along with chromium during the alloying process, the resulting stainless alloy can be compared in strength to the best heat-resistant steels, which are much more expensive.

Chromium-containing white cast iron is used in cases of severe operating conditions, the presence of alkalis and oxidizing agents, and the need for high electrical resistance.

White heat-resistant cast iron

To obtain a cast iron alloy capable of maintaining its original dimensions during cyclic heating to high temperatures, in addition to chromium, the following is added to it:

• up to 2.0% copper;
• 0.5% titanium;
• 0.1% nickel.

Moreover, the metal belongs to the group of stainless white cast iron and can be used in many industries.

High resistivity alloys

These types of white cast iron are used for the manufacture of cast heaters for electric furnaces and dryers operating at temperatures up to 900°C. To obtain the alloy, add to it:

• 3.0-5.0% nickel;
• 2.5-3.5% carbon;
• 2.0-2.5% silicon;
• 1.0-1.5% manganese.

Such white cast iron with high resistivity is called sormite and is used for the manufacture of electric heaters of various powers.

White cast iron cannot be called a very common alloy due to technical difficulties in its mechanical and heat treatment. However, the creation of alloyed alloys significantly expands the scope of application of this material as a result of a fundamental change in its physical and chemical properties.

Moreover, the alloying process does not require the use of rare and very expensive additives. Therefore, the use of white cast iron for the manufacture of products and workpieces will expand.

Source: https://prompriem.ru/chugun/belyj.html

Malleable cast iron: what it is, properties and applications, marking of cast iron grades

Malleable cast iron is obtained by prolonged thermal annealing of white cast iron blanks. As a result of heat treatment, cementite decomposes into iron and carbon in the form of graphite of a compact flake shape.

Material with such graphite inclusions is characterized by high strength parameters, ductility and resistance to impact loads.

Types of cast iron

Cast iron is an alloy of iron and carbon, where the content of the latter is more than 2.14%. The composition of such an alloy may also include other elements. Their content determines many parameters and properties of the material.

The iron-carbon alloy contains cementite, graphite and graphite with cementite. Cementite is a compound of carbon and iron with the composition Fe3C. Graphite is one of the allotropic modifications of carbon with a layered structure.

Depending on the content of these compounds, the color of the product changes. When cementite predominates, the material acquires a light sheen. This is where the name “white” came from.

Graphite has a dark color, which it imparts to castings. It is the structure of graphite inclusions that determines the plastic properties of the material.

Based on this, the alloy is divided into:

• grey;
• malleable;
• high strength;
• special purpose.

The first type of materials includes an alloy of iron and carbon in the graphite modification of flake, lamellar or globular shape. It has high casting properties. Thanks to them, it is often used to produce parts of complex shapes.

At the same time, the fragility of the alloy limits its use in products subject to tension or bending. An alloy with globular graphite is characterized by high strength properties. It is classified as one of the subspecies of gray cast iron.

The formation of graphite of the specified form is achieved thanks to the addition of magnesium and cerium. Other forms are obtained due to different cooling rates.

Malleable cast iron contains carbon in the concentration range from 2.4–2.8%. In addition, the alloy may contain: silicon, manganese, sulfur and phosphorus. These elements influence the final properties of products.

Features of the production of malleable cast iron

Shape of graphite inclusions and metal base.

To obtain malleable cast iron, it is necessary to follow a technology based on thermal annealing of workpieces at a certain temperature. As a result of this process, cementite and austenite decompose. Thus, carbon is obtained that crystallizes in flocculent graphite.

Austenite is iron with a face-centered lattice. This modification is high temperature. In iron-carbon steels it can form at temperatures above 727 degrees, and in pure iron at 910 degrees.

The final process of graphite formation occurs at lower temperatures - in the range of 720-760 degrees. It is carbon in this modification that determines such characteristics as the ductility and strength of malleable cast iron.

The method involves heat treatment of malleable cast iron in two stages. First, the material is exposed to temperatures up to 1000 degrees. Holding castings under these conditions leads to the decomposition of ledeburite into graphite and austenite.

After annealing at high temperature, the product is cooled to 720-760 degrees. As a result, pearlite is formed, which further decomposes into ferrite and graphite.

Melting of material for the production of cast iron is carried out in cupola furnaces, flame and electric furnaces. Sometimes this process is carried out in combination furnaces. The original castings may contain varying amounts of carbon.

When producing a ferritic alloy, it is necessary to use workpieces with a lower carbon concentration. Such products have a high melting point and therefore require an increased superheating temperature.

Typically, two furnaces are used for smelting in this situation. Melting occurs in the cupola furnace, and overheating occurs in the electric arc furnace. The described smelting technology is called the duplex process.

For the production of pearlitic alloy, workpieces with a high “C” content are used. A cupola furnace is sufficient to melt such material.

A feature of the production of molds for castings is the increased shrinkage of the white alloy. Because of this process, it becomes necessary to install side profits at each local thickening of the casting. This avoids the formation of shells.

In order to increase the cooling rate of thicker parts of the casting, metal coolers are used.

The influence of carbon and silicon on the structure of cast iron and the dependence of the structure on the thickness of cast iron.

The name of this material is due only to its higher plastic properties. In fact, it cannot be forged. This type of alloy is used in the same way as its other types.

The advantage of malleable cast iron, compared to white cast iron, is its high corrosion resistance. In terms of this property, the material ranks higher than carbon steels. In mechanical properties it is inferior to steel, but superior to white cast iron.

Types of malleable cast iron

Depending on the production process, malleable cast iron is either ferritic or pearlitic. In the first case, production is carried out in a neutral environment. This material has a ferritic structure with residual annealing carbon.

The composition of the alloy before heat treatment includes 2.2-2.99 percent carbon, as well as additives of other elements, the content of which does not exceed one percent. A decrease in the “C” concentration is accompanied by an increase in the strength characteristics of the material. However, its casting properties are reduced.

This material is widely used in the manufacture of parts for machines and agricultural equipment, where resistance to constant loads and stresses is required.

This alloy has lower plastic properties. In this regard, it is used in tasks that do not require resistance to severe plastic and chemical loads.

Properties of malleable cast irons

Malleable cast iron has mechanical properties that depend on the silicon-carbon content in the graphite allotropic modification. For white-core material, chromium and manganese also have an effect.

The difference in the structure of products also determines the difference in properties. Thus, the black-core alloy is characterized by greater ductility, but lower hardness than the pearlite type.

The high strength characteristics of these alloys are provided by flake-shaped graphite. Despite their name, these products cannot be forged. They are made by casting parts into specified shapes.

The main advantage of a malleable alloy is the uniformity of properties across the cross-section of the material, as well as the absence of stress.

In terms of other characteristics they differ:

• good fluidity during casting;
• absorption of vibrations;
• high wear resistance;
• good corrosion resistance to moisture and many aggressive chemical compounds;
• high resistance to shock loads.

Product marking

Ductile iron grades begin with the letters “KCH” followed by numbers. The first numbers correspond to a tenfold reduction in the tensile strength of the material. The second pair is an indicator of relative elongation.

According to accepted standards, malleable cast irons have eleven types of marking. 4 grades correspond to ferritic, and 7 grades correspond to pearlitic.

Areas of use of the material

Mechanical properties and chemical composition of cast iron.

The use of malleable cast iron was found in mechanical engineering, automotive industry, in the production of railway cars, and in the manufacture of agricultural equipment.

The best properties for the noted applications are the pearlite type. However, despite the higher characteristics, black-heart alloy is more often used. This is due to lower production costs.

Only for the manufacture of parts subject to high loads, white-core material is used. Such products include springs, engine parts, etc.

Bottom line

Malleable cast irons have found wide application in various areas of human activity due to their high strength properties and good corrosion resistance.

They are used for the manufacture of various parts that must withstand significant constant and periodic loads.

Depending on the tasks, either ferritic or pearlitic type of material can be used. Each of them has its own advantages and disadvantages, described in this article.

Source: https://tutsvarka.ru/kovka/kovkij-chugun

Composition and types of white cast iron

White cast iron consists of the so-called cementite eutectic. In this regard, it is divided into three categories:

• Hypoeutectic. These are alloys in which carbon does not exceed 4.3% of the total composition. It is obtained after complete cooling. As a result, it acquires the characteristic structure of such elements as pearlite, secondary cementite and ledeburite.
• Eutectic. Their carbon content is 4.3%.
• Hypereutectic white cast iron. exceeds 4.35% and can reach 6.67%.

In addition to the above classification, it is divided into ordinary, bleached and alloyed.

The internal structure of white cast iron is an alloy of two elements: iron and carbon. Despite high-temperature production, it retains a fine-grained structure. Therefore, if you break a part made of such metal, a characteristic white color will be observed.

In addition, in the structure of a hypoeutectic alloy, for example, hard grades, in addition to pearlite and secondary cementite, cementite is always present. Its percentage can approach 100%. This is typical for a eutectic metal.

For the third type, the structure is a composition of eutectic (Ep) and primary cementite.

One of the varieties of such alloys is the so-called bleached cast iron. Its basis, that is, the core, is gray or high-strength cast iron. The surface layer contains a high percentage of elements such as ledeburite and perlite. The whitening effect up to 30 mm deep is achieved using the rapid cooling method. As a result, the surface layer is white, and then the casting consists of an ordinary gray alloy.

White cast iron structure

Depending on the percentage of alloyed additives, the following types of metal are distinguished:

• low-alloyed (they contain no more than 2.5% alloying elements);
• moderately alloyed (the percentage of such elements reaches 10%);
• highly alloyed (in them the amount of alloying additives exceeds 10%).

Quite common elements are used as alloying additives. The alloyed white cast iron obtained in this way acquires new, predetermined properties.

Marking of white cast iron

To mark white cast iron, letters of the Russian alphabet and numbers are used. If it contains impurities, then the marking begins with the letter “H”. The composition of the available alloying additives can be determined by the following letters P, PL, PF, PVK.

They indicate the presence of silicon. If the resulting metal has increased wear resistance, then its marking will begin with the letter “I”, for example ICHH, ICH.

For example, the presence of the designation “Ш” in the marking means that the alloy structure contains spherical graphite.

The numbers indicate the amount of additional substances present in white cast iron.

Brand CHN20D2ХШ is deciphered as follows. This is a heat-resistant high-alloy metal. It contains the following elements: nickel - 20%, copper - 2%, chromium - 1%. The remaining elements are iron, carbon, and spherical graphite.

What is white cast iron?

Among the brands of cast iron, white cast iron occupies a special place. Although, like all other types of cast iron, it contains carbon components, the amount of graphite compared to other types is much less, only about 0.3%. This property gives it a characteristic white shine and a distinctive grayish-white color at the fracture.

Types and composition of white cast iron

The classification of the material is carried out mainly according to two criteria - the physical structure of the metal and the composition of its components.

If we take a classification by composition, then we analyze the cementite eutectic - the internal structure of the material; it largely depends on the constituent chemical elements, namely carbon.

There are three categories of materials in this classification:

• A material in which the proportion of carbon does not exceed 4.3% is called hypoeutectic. This structure is formed after complete cooling. In turn, this category is divided into materials having a structure such as pearlite, ledeburite and secondary cementite;
• With a carbon content of 4.3%, the material belongs to the category of eutectic cast iron;
• Hypereutectic material contains from 4.3 to 6.6% carbon.

The second classification divides white cast iron into ordinary, bleached and alloyed.

Ordinary white cast iron is an alloy of two components - iron and carbon. In cross-section, it has a fine-grained structure; even despite high-temperature processing, this structure remains unchanged.

The class of white cast iron also includes bleached cast iron. The peculiarity of this alloy is that the basis for it is high-strength gray cast iron, and the surface layer, which includes a large amount of ledeburite and pearlite, gives it a characteristic white color. This effect is achieved by rapid cooling of the workpiece; the bleaching depth can reach 30 mm.

Alloyed types of white cast iron are divided into low, medium and high alloy grades. This division depends on the content of alloying components in the metal. In percentage terms it looks like this:

• Up to 2.5% additives – low-alloy grades of cast iron;
• from 2.5 to 10% – medium alloy white cast iron;
• over 10% – high-alloy white cast iron.

Adding alloying additives to the composition makes it possible to obtain a material with predetermined qualities and parameters. It should be noted that the additives used are the usual, most common additives used in metallurgy for the smelting of grade steels and cast irons.

Material properties, advantages and disadvantages

Like other types of cast iron, white cast iron has advantages and disadvantages characteristic of the entire type. Like other types of alloys, it has increased strength, but at the same time it also has increased fragility; it is very afraid of impacts.

The strengths of white cast iron include:

• excellent mechanical strength;
• increased resistivity;
• high wear resistance;
• ability to withstand high temperatures, including temperature changes;
• resistance to corrosion, including a large number of organic and inorganic compounds.

Alas, like most metals of this class, white cast iron is characterized by the following disadvantages:

• It makes castings poorly - during filling of molds it forms internal cavities and cracks, which significantly reduce the strength of the casting;
• the material has increased fragility - a sharp blow is enough for the workpiece to crack;
• the material is very poorly processed, it is poorly cut, milled, drilled and welded;
• alloy workpieces are subject to large shrinkage during cooling, it can reach 2%;

It is worth noting that this brand of cast iron does not weld well - when heated, microcracks form at the welding site, reducing the mechanical strength of the weld. In addition, such microscopic cavities increase even more as the workpiece cools.

Application area of ​​white cast iron

High strength and the ability to retain shape at high temperatures have determined the use of the material in such industries as machine tool building, mechanical engineering, the production of machines and mechanisms for maritime transport, structural elements of machine tools, engines, and construction machines.

Alloyed types of cast iron are used in the automotive industry; individual engine parts are made from it. Alloyed white cast iron is indispensable in the mechanisms of mining machines.

The high strength has found its application in the form of rolling rolls for machines producing paper and cardboard. Mills, drive wheels and pulleys, balls for crushing crushed stone are all made of white cast iron.

Source: https://1nerudnyi.ru/belyj-chugun-10/