What is made from high-strength cast iron

:

Ministry of Education and Science of the Russian Federation

Federal state budgetary educational institution of higher professional education

"Volgograd State Technical University"

Department of Machinery and Foundry Technology

SEMESTER WORK

BY COURSE _________________________________

HIGH STRENGTH NOBULAR CAST IRON

Completed:

Student of group TM-429

Bondarenko A.A.

Checked:

________________

Volgograd, 2012

1. Properties of high-strength cast iron4

2. Application of high-strength cast iron5

3. Production of high-strength cast iron... 5

4. Classification of cast iron..6

5. Iron-graphite phase diagram ..7

6. Graphitization process ..8

7. Structure and properties of cast iron .. 10

8. The influence of graphite on the mechanical properties of castings11

9. Positive aspects of having .11 graphite

10. List of sources used13

Introduction

Cast iron is an iron-carbon alloy containing more than 2.14% C and hardening to form a eutectic called ledeburite. Cast iron differs from steel in composition (higher carbon content), better casting qualities, and low plastic deformation. Cast iron is cheaper than steel.

Due to the combination of high casting properties (fluidity, melting point), sufficient strength and wear resistance, as well as relative cheapness, cast iron has become widespread in mechanical engineering. They are used for the production of high-quality castings of complex shapes.

Depending on the form in which carbon is present in these alloys, white, gray, high-strength and malleable cast irons are distinguished.

Classification of cast irons

  Cast iron differs from steel: in composition - a higher content of carbon and impurities; in technological properties - higher casting properties, low ability to plastic deformation, almost not used in welded structures.

Depending on the state of carbon in cast iron, there are:

• white cast iron - carbon in a bound state in the form of cementite, when fractured it has a white color and a metallic sheen;
• gray cast iron - all or most of the carbon is in a free state in the form of graphite, and no more than 0.8% of carbon is in a bound state. Due to the large amount of graphite, its fracture has a gray color;
• half - part of the carbon is in a free state in the form of graphite, but at least 2% of the carbon is in the form of cementite. Little used in technology.

Structure, properties

From an examination of the structures of cast iron, it can be concluded that their metallic base is similar to the structure of eutectoid or sub-eutectoid steel or technical iron. They differ from steel only in the presence of graphite inclusions, which determine the special properties of cast iron.

Depending on the form of graphite and the conditions of its formation, the following groups of cast iron are distinguished: gray - with lamellar graphite; high-strength - with spherical graphite; malleable - with flake graphite.

Diagrams of cast iron microstructures depending on the metal base and the shape of graphite inclusions are presented in Figure 3.

Figure 3 - Diagrams of cast iron microstructures depending on the metal base and the shape of graphite inclusions

The most widely used are cast irons with a carbon content of 2.43.8%. The higher the carbon content, the more graphite is formed and the lower its mechanical properties, therefore, the amount of carbon should not exceed 3.8%. At the same time, to ensure high casting properties (good fluidity), carbon must be at least 2.4%.

Source: https://studfile.net/preview/2623670/

Ductile Iron (Digital Iron) | Agency Lite++

High-strength cast iron with nodular graphite has high physical and mechanical properties, which is due to the spherical shape of graphite. Such graphite formations weaken the cross-section of the casting to the least extent, giving it high strength and ductility. The mechanical properties of cast iron are regulated by GOST 7293-85 and are presented in table. 1.

GOST includes eight grades of cast iron. The letters HF indicate the name of cast iron - high-strength cast iron, subsequent numbers indicate the minimum permissible value of tensile strength in kgf/mm2.

The strength and performance characteristics of the material of ductile iron castings can be varied over a wide range without compromising casting and technological performance.

Table 1. Mechanical properties of cast iron in the cast state or after heat treatment

Cast iron grade	Tensile strength σВ, MPa (kgf/mm2)	Conditional yield strength σ02, MPa (kgf/mm2)	Relative elongation, δ, %	Brinell hardness, HB
no less
HF 35	350 (35)	220 (22)	22	140-170
HF 40	400 (40)	250 (25)	15	140-202
HF 45	450 (45)	310 (31)	10	140-225
HF 50	500 (50)	320 (32)	7	153-245
HF 60	600 (60)	370 (37)	3	192-277
HF 70	700 (70)	420 (42)	2	228-302
HF 80	800 (80)	480 (48)	2	248-351
HF 100	1000 (100)	700 (70)	2	270-360

Mechanical properties of ductile iron compared to steel:

• The tensile strength is the same or more.
• Higher ratio of yield strength to ultimate strength - 0.65-0.80 (for steel - 0.55-0.60).
• High wear resistance.
• Higher damping capacity.
• Less sensitivity to stress concentrators.

According to the microstructure, ductile iron is divided into ferritic, ferrite-perlite, pearlite, pearlite-cementite-ferrite and austenite.

There are also high-strength cast iron with troostite, troostitoferrite, martensite, pearlite-cementite and other structures. Ferritic and austenitic cast irons are distinguished by high plastic properties (relative elongation 5–35%, impact strength 2–20 kgf • m/cm2). Austenitic cast irons include Nomag and Niresist cast irons with different nickel contents. Tall fur. the properties of austenitic cast iron do not change up to a temperature of 600°C.

Such cast irons are especially promising when used at low temperatures (down to a temperature of 250°C). Pearlitic and troostite cast irons are characterized by high strength (tensile strength 60-140 kgf/mm2) with relatively low plastic properties (relative elongation - 2.0-6%, impact strength 2.0-6.0 kgf • m/cm2) . Nickel, copper, chromium, manganese and tin contribute to the formation of a pearlite structure.

Cast iron with pearlite and troostite structures is characterized by high wear resistance; cast iron with troostite and troostitoferrite structures obtained by isothermal hardening. [1]

Roughly speaking: ductile iron has the mechanical properties of steel (sometimes surpassing them) and the casting properties of gray cast iron (high fluidity, lack of tendency to crack, etc.). All this provides prerequisites for the widespread use of ductile iron castings in industry. So, in particular, the service life of metallurgical molds made of ductile iron is 1.5-2.5 times longer than molds made of gray cast iron.

Interesting is the experience of the Czech company KASI, which mastered large-scale (the largest in Europe) production of manhole hatches made of ductile iron on AFL HWS, while the mass of the hatch was reduced by almost 50% compared to hatches made of gray cast iron. Since the 80s of the last century, the Moscow Vodopribor plant has also been producing manhole hatches from ductile iron on an AFL chill mold (with a vertical connector), using synthetic cast iron; the mass of the hatch is also significantly reduced.

Ductile iron is used to produce parts for rolling and forging equipment; mining and crushing and grinding equipment; turbine parts; gear housings; gear parts and material handling machinery.

The lower specific gravity and significantly higher fluidity of ductile iron compared to steel makes it possible to use ductile iron castings in the automotive industry with high efficiency instead of steel castings, which leads to a reduction in the weight of the car and an increase in its power. Crankshafts, gears, crankcases, etc. are produced from ductile iron.

Centrifugally cast ductile iron pipes occupy a significant place in the production of large-diameter pipes operating under high pressure. The production of fittings for subways and tunnels from ductile iron made it possible to significantly reduce their weight.

The use of cast iron in the machine tool industry has made it possible to design complex cast parts for machines and heavy engineering equipment weighing more than 150 tons (die holders for injection pressing machines, cylinders and frames of forging presses, pistons and other parts), to reduce the weight of cast parts while maintaining sufficient rigidity.

CShG is an ideal material for a variety of hand tools (spanners, clamps, gauges, etc.). In the parts of paper-making machines, ChShG provides a significant technical and economic effect (for example, due to the fact that the elastic modulus of ChShG is 60% higher compared to ChPG, the weight of the pressing and drying rolls of the machines is reduced).

ChShG is a common material for shut-off and control valves operating in gas and liquid media (acid, saline and alkaline). For example, a batch of ball valve plugs for the Siberia-Western Europe main gas pipeline with a diameter of 1420 mm was cast abroad from cast iron.

Initially, these plugs were made from steel forgings with a diameter of 2440 mm and a weight of 17 tons each. [4]

The patent for high-strength nodular cast iron No. 2485760 dated 10/25/1949 was received by Keith D. Millis. Since the fifties of the last century, industrial production of ductile iron castings began all over the world.

In recent years, the first places in terms of production volumes of ductile iron castings have been shared by Japan and the USA, as the most technologically developed countries.

Today, in most industrialized countries, the volume of production of ductile iron castings among iron-carbon alloys ranks second after gray cast iron.

A scientific school in the field of ductile iron research in Ukraine began to form in the mid-sixties of the last century on the basis of the Institute of Casting Problems of the National Academy of Sciences of the Ukrainian SSR (now FTIMS NAS of Ukraine). The issues of production of castings from ductile iron were dealt with at different times by such prominent scientists as: Voloshchenko M.V., Vashchenko K.I., Gorshkov A.A., Sidletsky O.G., Shumikhin V.S., Sheiko A.A., Levchenko Yu.N., Litovka V.I. and many others.

The largest mass production of ductile iron castings using the method of in-mold modification for automotive and tractor engineering was established in the seventies and eighties of the last century at the Kupyansky plant "Tsentrolit" (Kharkov region). Unfortunately, today this plant no longer exists.

Literature

1. Encyclopedia of Inorganic Materials. In 2 volumes, volume 1. Kyiv, “Higher School”, 1977.
2. Mogilev V.K., Lev O.I. Foundryman's Handbook. M.: Mechanical Engineering, 1988. – 272 p.
3. Handbook on iron casting./Edited by Doctor of Technical Sciences. N.G. Girshovich. – 3rd ed. reworked and additional L.: Mechanical Engineering, 1978 – 758 p.
4. Castings from cast iron with spherical and vermicular graphite/Zakharchenko E.V., Levchenko Yu.N., Gorenko V.G., Varenik P.A. – Kyiv: Naukova Dumka, 1986 – 248 p.

Source: https://on-v.com.ua/novosti/texnologii-i-nauka/vysokoprochnyj-chugun-s-sharovidnym-gra/

Gray malleable high-strength cast iron

The reliability and durability of a product in modern mechanical engineering largely depends on the properties of the structural materials used. Over 80% of mechanical engineering parts of various weights and complexity are made from iron-based alloys. Depending on the carbon content, iron-based alloys are divided into steels and cast irons .

Unlike steel, in cast iron, under certain conditions, part of the carbon is released in the form of graphite rosettes. In the cross-section of such a socket, only individual plates are visible. Therefore, isolated inclusions of graphite are noticeable on a polished section of cast iron. The structure of the matrix is ​​most often ferrite-pearlite or pearlite. This type of cast iron is called gray.

Typically, gray cast iron contains between 2.5% and 3.6% carbon. It contains silicon and manganese in certain quantities. Sulfur and phosphorus are constantly present as impurities.

The strength of cast iron is determined by the presence of plate-shaped graphite in its structure. Such graphite inclusions significantly weaken the matrix. Under the influence of load, stress arises in the metal with the highest concentration at the ends of graphite inclusions. Microcracks appear in these places. Gray cast iron has relatively low strength and breaks without plastic deformation.

Cast iron is a casting alloy.

The cooling conditions of cast iron after filling the mold have a decisive influence on the formation of its structure. In thin sections of the casting, where the cooling rate during the crystallization period is high, a white cast iron . Carbon in it is in the form of cementite, graphite is absent. In the remaining sections, a gray cast iron structure is formed.

The chemical composition also affects the structure. As the content of manganese and sulfur increases, the chill zone increases. An increase in the content of graphitizing elements - carbon and silicon - reduces the tendency of cast iron to whiten.

To obtain castings with specified properties, it is necessary in each specific case to take into account both the chemical composition and the cooling rate of the cast iron in the mold.

Gray cast iron

Despite its relatively low mechanical properties, gray cast iron is widely used. Because it is easy to process, has increased damping capacity, as well as anti-friction properties. Because the graphite of cast iron holds the lubricant and itself serves as a lubricant. The mating cast iron parts move easily relative to each other.

Gray cast iron with small additions of chromium and nickel acquires good elastic properties. A piston ring made of such cast iron, after removing the load, returns to its original dimensions.

Gray cast iron has high fluidity. At real pouring temperatures, the length of a spiral cast iron sample is almost twice as long as a steel one, which makes it possible to produce castings of complex configurations.

Gray cast iron is characterized by low volumetric shrinkage during crystallization, allowing in many cases to dispense with installation and profit.

The most common unit for smelting gray cast iron is a cupola with a dripper, in which metal accumulates, as well as its composition and temperature are averaged. To reduce the tendency of cast iron to chill, it is modified by introducing silicon-containing additives into the liquid metal.

Modification allows you to equalize the properties of the metal in different sections of the casting. This can be seen from the example of measuring the hardness of cast iron. Unmodified and modified.

The chill depth on a wedge sample of modified cast iron is significantly less than that of unmodified cast iron. The shape of graphite inclusions also changes as a result of modification.

In addition to cupola furnaces, electric furnaces . They allow metal to be smelted at a higher temperature, which is important for subsequent, out-of-furnace processing of cast iron. Molds for producing castings from gray cast iron are made by compacting the molding sand in flasks. Cores are installed into the mold cavity to perform the internal configuration of the casting.

In mass production, automatic flaskless molding lines , including installation of cores using a core layer.

The metal of the mold is also poured automatically. Gray cast iron castings are made not only in sand molds, but also in metal ones. To produce castings shaped like bodies of rotation, the centrifugal casting method is widely used. At the same time, labor productivity increases, molding materials are not consumed, and there is no gating system.

Gray cast iron is a generally recognized construction material. It is used for the manufacture of various parts operating under conditions of static loads, vibration, and increased friction.

Malleable iron

It is known that such car parts as wheel hubs and differential housings experience dynamic loads. Can cast iron be used to make them? It is possible if its plasticity is significantly increased. Malleable cast iron has this property , in which the graphite has a flake-like rather than a lamellar shape. Compared to gray cast iron, ductile iron has a lower concentration of graphitizing elements - carbon and silicon.

Malleable cast iron is superior to gray cast iron in terms of strength and ductility. Changes in the chemical composition have led to a decrease in fluidity and an increase in shrinkage during solidification, which requires the installation of profits even on small castings. The production of malleable iron usually uses the duplex process.

Cast iron is smelted into a cut, then transported in a transfer ladle and poured into an electric induction furnace, where it is heated before pouring to increase fluidity.

The technological process for producing castings from malleable cast iron is similar to producing castings from gray cast iron. Automatic molding lines are becoming increasingly common. Metal is poured into molds on a conveyor belt. The castings produced must have a white cast iron structure throughout their entire cross-section.

To obtain the structure of malleable cast iron, they are subjected to graphitizing annealing in thermal furnaces. During the holding period, white cast iron cementite decomposes and flake-shaped graphite inclusions are formed. After heat treatment, the castings are straightened on special presses.

The need to use long-term heat treatment and straightening significantly increases the complexity of manufacturing parts made of malleable cast iron. The forged steel blank of an engine camshaft is noticeably different from the finished part.

The cast billet is much closer in configuration to it, which greatly reduces the complexity of machining. The same applies to crankshafts, critical parts. To replace forged blanks with cast ones, an alloy is needed that would combine the mechanical properties of steel with the technological and operational properties of cast iron.

Ductile iron

High-strength cast iron has such properties which, during crystallization, spherical graphite inclusions are formed. Compared to gray cast iron, high-strength cast iron is characterized by a higher content of carbon and silicon. As well as a low concentration of sulfur. The mechanical properties of cast iron are determined by testing samples specially manufactured in accordance with GOST.

In ductile iron, the nodular graphite, less than the flake graphite in gray, weakens the matrix and significantly reduces the stress concentration under load.

The strength of cast iron with spherical graphite is close to steel. Castings made from high-strength cast iron can be processed just as well as those made from gray cast iron. At the same time, the required accuracy and surface cleanliness are achieved.

Ductile iron has high airtightness . Cylinders of gas engine compressors are made from it, which can withstand pressures of up to 100 atmospheres during testing.

At the same time, high-strength cast iron is prone to the formation of shrinkage cavities , which requires the installation of profits to feed massive parts of the castings.

For the smelting of high-strength cast iron, induction crucible furnaces are widely used, in which cast iron of the desired composition and temperature sufficient for subsequent modification is obtained.

Magnesium, cerium, and yttrium are used as modifiers in the form of pure metals or alloys. To prevent rapid floating and increase the time of contact with the melt, the modifier is covered with steel sheets. The metal is then released from the furnace into a ladle.

This technology increases the absorption of modifiers in cast iron and ensures process stability.

To reduce the tendency of cast iron to chill, it is additionally modified with ferrosilicon. Molds for large mass castings are mainly made on large shaking tables.

The molds are assembled and poured on a special platform. During the crystallization of high-strength cast iron under the influence of modifiers in the melt, multiple branching of graphite plates and the formation of spherical inclusions occurs. If the amount of modifier is insufficient or its uneven distribution in cast iron, ordinary flake graphite can form.

To stabilize the structure and ensure uniformity of the physical and mechanical properties of high-strength cast iron, large castings of complex shape are subjected to heat treatment. For example, normalization.

After machining, the parts are sent to the inspection area. Critical parts undergo flaw detection. Replacing a number of steel parts that experience high shock loads and pressure during operation with parts made of high-strength cast iron significantly reduces the cost of production of certain types of engineering products.

About 50% of crankshafts for engines for various purposes are made from high-strength cast iron. The operational and casting properties of cast iron have ensured their widespread use in various branches of mechanical engineering. More than two-thirds of the cast billets used by industry in our country are obtained from them.  

Source: https://kovkapro.com/metalloobrabotka-obschie-svedeniya/chugun-seryy-kovkiy-vysokoprochnyy/

Ductile iron pipes properties and applications

What do we know about cast iron:

• It is a primary product of iron ore processing and a raw material for steel production, differing from it in its high carbon content;
• Cast iron, unlike black steel (devoid of alloying additives - chromium, nickel and molybdenum), is resistant to corrosion. It compares favorably with stainless steels in its low cost;
• At the same time, it is inferior to steel in ductility and toughness: the presence of carbon makes the metal brittle.

It is curious: in the absence of an abrasive cutting tool, experienced mechanics often broke off sections of gray cast iron pipes, having previously cut them in a circle with a chisel.

In 1949, American inventor Keith Millis received a patent for an unusual form of cast iron. The essence of the modification was to add a small amount of magnesium to the melt.

As a result, graphite (one of the forms of carbon), contained in cast iron and determining its properties, underwent a curious transformation: its particles acquired a spherical shape instead of the usual flat one.

Form of graphite in gray cast iron and ductile iron.

High-strength cast iron with nodular graphite was strikingly different from gray: while maintaining resistance to corrosion, it became viscous, malleable, ductile and acquired the highest mechanical strength. At the same time, the cost of metal increased very slightly.

Application and installation method

Traditionally, cast iron pipes have been used in two areas:

1. During the construction of sewer systems. The resistance of cast iron to corrosion was very useful here: the aggressiveness of domestic and industrial wastewater made it impossible to use stronger steel;
2. During the construction of main water pipelines. Groundwater and dissolved oxygen in water are almost as destructive to steel as sewage.

This, however, does not prevent the cast-iron water supply system of Peterhof, restored after the Great Patriotic War, from serving for six decades.

The method of installing socket connections depended on the application:

• The sewerage was embossed with cable (organic fiber impregnated with oil or bitumen) and sealed with cement-sand mortar;
• The sockets of water pipes were filled with sulfur, lead or stamped with lead tape. Sulfur was, however, also used during sewer installation, but much less frequently.

It is clear that high-strength cast iron quickly made room for its predecessor. Currently, it is used both in the public sector and in the construction of oil and gas pipelines.

The installation method is still determined by the area of ​​application:

• Ductile iron pipes for sewerage use the same socket joints, but no longer for hammering, but equipped with rubber seals;

Please note: for diameters up to 250 mm, clamps and levers are used for joining.
For large sizes, loading equipment is used for installation.

Large diameter pipelines are installed using special equipment.

• VChShG pipe for water supply and heating mains can be connected with both sockets and flanges. Paronite and, somewhat less frequently, silicone are used as gasket materials;
• High-pressure oil and gas pipelines are installed using welded joints; fortunately, high-strength (as well as gray) cast iron is perfectly welded with special electrodes.

What else is useful to know about LTK products?

1. The nominal diameter of the products varies from 80 to 1000 millimeters;
2. The standard pipe length is 6 meters;
3. All products of the Lipetsk plant are manufactured only and exclusively for socket joints with a rubber seal. In this case, the manufacturer uses three types of locks, differing in the operating pressure range:

Compound	Working pressure, MPa	Diameter, mm
Tyton	3,0 — 6,4	80-1000
R.J.	2,5 — 8,8	80-500
R.J.S.	1,6-3,2	600-1000

1. Locks allow you to install pipes not only on one longitudinal axis, but also with a deviation from a straight line of 1.5 - 5 angular degrees without the use of fittings and without violating the tightness;
2. Despite the corrosion resistance, the products are additionally equipped with protective coatings. It makes sense to dwell on them in a little more detail.

External covering

It consists of two layers:

1. Zinc metal;
2. Bituminous varnish.

The coating is interesting because it is capable of self-healing. How does this happen? The fact is that zinc forms a galvanic couple with iron and alloys based on it, including ductile iron.

If the zinc layer is damaged, the exposed cast iron acts as a cathode, and the galvanized surface of the pipeline acts as an anode. The migration of zinc ions gradually restores the protective layer.

Self-healing protective coating.

Moreover, when laid in the ground, an extremely durable and practically insoluble layer of zinc oxides, salts and hydrates is formed on the surface of the pipeline.

External coating with bitumen varnish preserves ion exchange processes with the environment; the process of slow, extremely prolonged corrosion does not lead to the destruction of walls, but to the formation of a dense layer of corrosion products that performs protective functions.

The outer shell is capable of performing its functions in an extremely aggressive environment.

Inner coating

All Svobodny Sokol products are ductile iron pipes with CPP. What is CPP? This is a cement-sand coating, again protecting the walls from the aggressive effects of the transported environment.

The manufacturer emphasizes that the coating provides passive and active protection. Passive means primitive mechanical protection against abrasive wear and direct contact with an aggressive environment.

The active one consists in the gradual saturation of the pores of the protective layer with cement hydration products, primarily calcium hydroxide. This, in turn, provokes the transformation of the iron in the surface layer into Fe2O3 oxide, which is kept from destruction by the cement-sand coating and prevents further corrosion of the walls.

CPP has a number of additional useful properties:

• despite the relative roughness, it reduces the hydraulic resistance of pipes, preventing the formation of deposits;
• is self-healing under conditions of transportation of the aquatic environment. When cracks occur and the coating is moistened, the same hydration of cement with the formation of calcium hydroxide and carbonate contributes to their gradual filling.

Regulations

We will leave foreign standards regulating the quality of imported products behind the scenes and focus on domestic regulatory documentation.

A rather funny picture emerged with her:

1. a significant part of sellers refer to GOST 9583-75 as the main document;
2. however, the only manufacturer - the notorious LTK "Svobodny Sokol" - does not mention it in the list of regulatory documents; but it includes technical specifications TU 1461-037-50254094-2008.

Let's try to clarify the picture and study both documents.

GOST

It regulates the production of pressure cast iron pipes using semi-continuous and centrifugal casting.

For the convenience of the reader, we will highlight only the main points of the standard:

• All pipes are produced with sockets;

VChShG pipe 100 mm with a socket for an O-ring seal.

• The minimum nominal diameter is 65 mm, the maximum is 1000 mm;

Please note: there is a clear discrepancy here with the LTK product range, starting with a diameter of 80 mm.

• The length of the pipes varies from 2 to 10 meters, which also raises certain doubts about the compliance of LTK products with this GOST;
• Finally, the main thing: products must be made from, hold your breath, dear reader, gray cast iron containing no more than 0.12% sulfur and no more than 0.7% phosphorus. Not a word about ductile iron.

The conclusion is obvious: the compliance of any domestic ductile iron pipe with this standard is nothing more than a fiction.

THAT

The author of the technical specifications will seem familiar to us: this is a certain Lipetsk enterprise “Svobodny Sokol”. Needless to say, the technical conditions he issued are strictly followed!

However, this document will bring us several interesting discoveries:

• The specifications provide for the presence of not only sockets, but also flanges. There is no mention of them on the company's home page;

Products with flanges are not mentioned on the company’s website, but are provided for in technical specifications.

• Only water and sewerage are mentioned as areas of application. On the main page, a similar list includes oil and gas pipelines and heating mains with operating temperatures up to +120C;
• Pipes can be supplied without a zinc outer coating, protected with bitumen varnish or polymer resin;
• Examples of symbols include both a 150 mm ductile iron pipe, 6 meters long, and a pipe with a diameter of 300 mm and a length of 5500 mm. Despite the fact that the only standard size produced is directly indicated on the company’s website - 6000 mm.

Conclusion

Despite all the oddities of the regulatory documentation, pipes made of high-strength cast iron are one of the most attractive solutions for laying water supply and sewerage systems at great depths or in conditions of probable ground movement.

Source: https://samstroy.com/%D1%82%D1%80%D1%83%D0%B1%D1%8B-%D0%B8%D0%B7-%D0%B2%D1%8B%D1 %81%D0%BE%D0%BA%D0%BE%D0%BF%D1%80%D0%BE%D1%87%D0%BD%D0%BE%D0%B3%D0%BE-%D1% 87%D1%83%D0%B3%D1%83%D0%BD%D0%B0-%D1%81%D0%B2%D0%BE%D0%B9%D1%81/

Malleable cast iron: marking according to GOST, properties and application

Cast iron is an alloy of iron and carbon obtained by processing iron ore in blast furnaces. feature – high carbon content – ​​more than 2.14%. The carbon in ductile iron has a flaky shape.  

Production Features

An alloy of iron and carbon, which takes the form of graphite flakes in the metal structure, is called malleable cast iron. It is obtained by long-term heat treatment of white cast iron blanks. Under the influence of annealing, the structure of the metal changes, cementite in it turns into graphite. This process is called graphitization. After heat treatment, the alloy changes its mechanical characteristics - strength and hardness decrease, and the material becomes plastic.

Annealing technology includes 5 stages:

1. Slow heating of the workpiece for 20–25 hours to a temperature of 950–1000 ºС.
2. The first stage of graphitization. Exposure at a temperature of 950–1000 ºС for 15–20 hours.
3. Slow cooling to a temperature of 740–720 ºС, operation time 6–12 hours.
4. The second stage of graphitization is a long exposure of the workpiece at a temperature of 720 ºС or a gradual decrease in temperature from 760 to 720 ºС. The duration of this operation is about 30 hours.
5. Complete cooling of the part.

There are four annealing methods to impart the required properties to an iron casting. They differ in stage No. 4 (temperature range from 760–720 ºС). The remaining annealing stages are the same.

1. Rapid cooling to a temperature below critical - 720 ºС and holding at this temperature for 30 hours.
2. Slow cooling over 30 hours, in the critical temperature range from 760–720 ºС.
3. Step cooling in the temperature range from 760 to 720 ºС.
4. Technology of alternate heating above 760 ºС and cooling below 720 ºС.

Soviet scientists developed a method that made it possible to reduce the annealing time to 10–15 hours. Its essence is to harden parts in oil before heat treatment.

Types of malleable cast iron

Annealing technology and the composition of the metal microstructure determine what kind of malleable cast iron will be obtained - pearlitic or ferritic class. There is an intermediate ferrite-pearlite class.

Ferritic class of cast iron

Using the technology described above, malleable ferritic cast iron is obtained. The microstructure of such an alloy is ferrite (iron) with rounded, isolated graphite inclusions. At the fracture, the ferritic alloy part is black and velvety.

Ferritic-pearlitic cast iron

A metal with a pearlite-ferritic structure, in which a smaller amount of carbon has been graphitized and the pearlite component has been preserved.

The production of pearlitic-ferritic malleable cast iron is carried out by increasing the content of alloying elements in the metal, which prevent graphitization. These include Mn, Cr, Mo, but most often manganese. And a decrease in the content of carbon and silicon - elements that contribute to the graphitization of perlite.

To obtain pearlitic-ferritic malleable cast iron, the holding time in annealing stage No. 3 should be reduced and cooling should be accelerated.

Pearlitic class of cast iron

To obtain a pearlite structure, castings are covered with powder from a mixture of iron ore and metal scale. Under the influence of high temperature and oxidized iron ore, the metal surface is gradually decarbonized. Workpieces made from this alloy appear silver or white when broken.

This metal has an uneven structure and macrostructure. In the center of the ingot there is more pearlite component. Closer to the edges, the amount of annealing carbon decreases and the amount of ferrite increases.

To obtain an alloy with high mechanical characteristics, you need to use white cast iron with a low carbon content - no more than 3%.

Properties of Ductile Iron

The heat treatment mode and the content of alloying elements, carbon and silicon determine the mechanical characteristics of the annealed metal.

Pearlitic cast irons are characterized by high tensile strength, hardness, wear resistance, anti-friction properties, and anti-corrosion resistance. But these materials have low elongation values ​​and, as a consequence, low ductility.

Malleable cast irons of the ferritic class have lower tensile strength, lower hardness and higher elongation. They have less strength, but higher ductility.

The alloy in question compares favorably with steels and gray cast iron in the following indicators:

• the ratio of yield strength to ultimate strength is higher than that of steel, reaching 0.6-0.8 for pearlitic alloy;
• the pearlitic class alloy in question is superior to gray cast iron and even high-strength structural steels in hardness and strength (630 N/mm2);
• The ferritic malleable alloy's elongation value is 10 times higher than that of gray cast iron, which indicates its high ductility.

In addition, annealed metal has a high internal friction, which allows it to quickly dampen vibrations, good anti-friction properties and low sensitivity to cuts.

When alloyed with the elements: Mn, Ti, Cr, Cu, the metal acquires high wear resistance. When chromium and nickel are added to the cast iron melt, heat resistance is added to increased wear resistance.

Ductile iron marking

Labeling rules are prescribed in Marking is prescribed in GOST 1215-79. There are 11 stamps in total. The group is designated by the letters KCH, to which two meanings are added. The first is equal to the ultimate tensile strength. The second number indicates the elongation expressed as a percentage.

Marking KCH 45-7 means: malleable cast iron with mechanical characteristics: tensile strength 441 kgf/mm², with relative elongation - 7%. 

Grade of malleable cast iron of ferritic and pearlitic class	Temporary tensile strength, MPa (kgf/mm²), not less	Relative elongation, %, not less	Brinell hardness HB
CC 30-6	294 (30)	6	100-163
CC 33-8	323 (33)	8	100-163
CC 35-10	333 (35)	10	100-163
CC 37-12	362 (37)	12	110-163
CC 45-7	441 (45)	7*	150-207
CC 50-5	490 (50)	5*	170-230
CC 55-4	539 (55)	4*	192-241
CC 60-3	588 (60)	3	200-269
CC 65-3	637 (65)	3	212-269
CC 70-2	686 (70)	2	241-285
CC 80-1.5	784 (80)	1,5	270-320

* By agreement between the manufacturer and the consumer, a reduction of 1% is allowed.

Application

The material has a lower cost compared to steel and comparable strength properties.

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Parts with a wall thickness from 3 to 40 mm are made from malleable cast iron.

Ductile cast iron is used to make parts that operate under conditions of bending, twisting, impact, and other alternating dynamic loads, pressure up to 20 kg/cm2, vibration, and increased friction of parts against each other.

Used in mechanical engineering, construction, automotive, agricultural equipment and other industrial sectors:

• Agriculture and automotive industry: production of gears, couplings, chain links, sprockets, hubs of agricultural machinery. Axle housings, crankshafts, gearbox housings, brake pads and other parts produced by automobile manufacturers.
• Car manufacturing and shipbuilding: production of air brake elements, brackets, clutches, bearings.
• Energy: production of terminals, wire holders, insulator hooks.
• Construction: fittings, valves, gate valves, pneumatic valves.
• Textile industry: chain links for equipment drives, gears, bearings.

One of the most common industrial materials is malleable cast iron. The metal is suitable for the manufacture of highly loaded machine parts and mechanisms in modern industry.

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

Where is ductile iron used?

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An alloy of iron and carbon is called cast iron. We will devote the article to malleable cast iron. The latter is contained in the alloy structure either in the form of graphite or cementite. In addition to the above components, cast iron contains impurities based on the following chemicals - silicon, manganese, etc.

Alloying components can be added to cast iron alloys, which have a significant impact on their technical parameters.

Cast iron is used in the production of products by casting, for example, machine tool housings, which operate under small static and dynamic, including multidirectional loads.

Unlike steel, cast iron has good casting parameters and a low price. In addition, this raw material is better processed on metal-cutting equipment than most steel alloys. But, on the other hand, cast iron alloys, regardless of type, are welded with certain difficulties. In addition, cast iron has low parameters of strength, hardness, and brittleness.

Types of cast iron

The grade of a cast iron alloy is determined by the amount of carbon and other substances in its composition.

This approach allows us to distinguish the following types of this material:

• white;
• gray (GOST 1412);
• malleable (GOST 1215);
• high-strength (GOST 7293).

White cast iron

In this alloy, carbon is collected in the form of cementite. This grade of material is wear-resistant and has good hardness parameters. At the same time, it is quite poorly processed on metal-cutting equipment.

White cast iron structure

White cast iron is divided into the following groups:

• hypoeutectic with carbon concentration from 2.14% to 4.3%;
• eutectic - 4.3%;
• hypereutectic from 4.3% to 6.67%.

In other grades of cast iron, the carbon is in the form of graphite.

Features of the production of malleable cast iron

The production of KCh cast iron has a number of subtleties that are determined by casting characteristics and other properties.

Ductile iron production

Cast iron of the BC grade, which is the main product of malleable iron, does not have very good casting parameters. In particular, it has reduced fluidity, a large amount of shrinkage during cooling, and it is prone to the formation of various casting defects.

These are the reasons why during production it is necessary to overheat the metal and take measures to combat casting defects. The production of malleable cast iron can be carried out with the obligatory consideration of shrinkage and changes in the dimensions of the workpieces during simmering. Thin workpieces have maximum shrinkage, thick ones have minimal shrinkage.

The simmering operation is performed at 1350 - 1450 degrees Celsius.

Annealing (simmering) is a basic step in the production of cast iron. It is produced in separate workshops called languid. The preparations are placed in pots made of steel or cast iron alloys of different grades for simmering. Up to 300 castings can be placed in a pot, based on the fact that up to 1,500 kg should be per cubic meter.

Malleable cast iron gains its greatest strength in pots made from white cast iron with chromium additions and a minimum amount of phosphorus. The consumption of pots is measured by weight; it can range from 4 to 15% of the weight of the workpieces. That is why increasing their durability plays a big role in determining the cost of finished malleable cast iron.

To avoid warping of the finished castings, placing the blanks in pots must be done with special care. They are laid as tightly as possible; to enhance the effect, the workpieces are sprinkled with sand or ore. These materials protect the workpieces from deformation and excess oxidation.

Electric furnaces are used to produce malleable cast iron. This is due to the fact that during the simmering process it must be possible to regulate the temperature, a sharp rise during heating and a rapid decrease at the stage of its graphitization. In addition, it will not be superfluous to be able to adjust the air mixture in the oven.

Most of the furnaces used to produce malleable cast iron are muffle furnaces. That is, the products of fuel combustion do not come into contact with the pots in which the workpieces are placed.

Castings made from malleable iron go through a cleaning operation several times, and after annealing, feeders are removed and straightened. The first cleaning is carried out to remove residual molding sands. For cleaning, sandblasting equipment or special tumbling drums are used. Removal of feeder residues occurs using emery cloth.

Malleable cast iron defects

The most common defects in malleable cast iron are the following:

• shrinkage cavities;
• underfilling;
• cracks, etc.

Some defects cannot be corrected by further heat treatment. It should be noted that the production of malleable cast iron requires strict compliance with all GOST requirements, technological rules and regulations. Only in this case can we talk about obtaining high-quality malleable cast iron, which can be used to replace other, expensive materials - steel, non-ferrous metals.

Main characteristics of the metal

The key parameters of cast iron are determined by the amount of carbon, which has the form of graphite, and the presence of silicon. Pearlitic malleable cast iron alloy contains two more constituent elements - chromium and manganese.

Characteristics of Ductile Iron

The difference in the structure of malleable cast iron is also reflected in the final properties of products obtained from it. For example, workpieces made from ferritic cast iron have lower hardness than those made from pearlitic material, but at the same time the former have increased ductility. Graphite in the form of flakes provides high strength parameters to finished parts with relatively good ductility.

Products made of KCh cast iron can be deformed at room temperature and humidity. It was this property that determined the name of this material – malleable. In fact, this is a conditional name and does not mean that finished parts are obtained from it using forging equipment. Casting is used to produce products.

The main property of this material is that there is no stress in it.

Microstructure of ductile iron

The mechanical properties of ductile cast iron are between gray cast iron and steel. That is, cast iron of this type has high fluidity, resistance to wear, corrosion, and aggressive substances. In addition, this material has high strength properties. Thus, a part with a wall thickness of 7–8 mm can withstand working pressure of up to 40 atm. This allows it to be used for the manufacture of pipeline fittings for gas and water.

We must not forget that at low temperatures, cast iron becomes very brittle and is very susceptible to impact.

Properties of malleable cast irons

The basic property of the KCh cast iron alloy is that it contains carbon inclusions in different forms, which determines its strength and ductility.

Cast iron with a low amount of carbon (decarbonized), in fact, is the only material from structural cast iron alloys that is well welded and is used to produce welded metal structures. For welding, either gas protection or butt technology is used.

This grade of cast iron lends itself to pressing, embossing and quite simply fills voids and gaps. Parts made from a malleable ferritic cast iron alloy are subjected to cold processing, while parts made from pearlitic alloy are heated.

The cast iron used in production is made from a white cast iron alloy by annealing it. The structure obtained after performing this operation may have a ferritic or pearlitic form.

One of the advantages of a malleable cast iron alloy is that it has uniform cross-sectional properties; in addition, it is well processed on turning-milling machines.

The main physical and technical parameters of a malleable cast iron alloy are standardized in GOST 1215-79. The marking of this material is based on permissible tensile and elongation values. The hardness of the material is determined by the structure, and the strength parameters and ductility are determined by the presence of graphite.

It must be understood that the properties of the material are affected not only by the shape, but also by the amount of graphite contained in the alloy. Malleable cast iron reaches its maximum strength characteristics in the presence of fine pearlite and a small amount of graphite. The maximum ductility and toughness of cast iron of this class is achieved in the presence of ferrite and the same amount of graphite.

Scope of application

Malleable cast iron has found its application in mechanical engineering for the production of machine tools, individual car parts, structures and mechanisms used in railway transport, etc.

Most often, ferrite castings are used, which are somewhat cheaper than all others. Perlite castings are used for the manufacture of parts that are used for products and assemblies operating under increased loads.

Malleable cast iron is used to produce castings with a thin wall; its size can range from 3 to 40 mm.

Source: https://moy-instrument.ru/masteru/gde-primenyaetsya-vysokoprochnyj-chugun.html

Malleable iron

An alloy of iron and carbon is called cast iron. We will devote the article to malleable cast iron. The latter is contained in the alloy structure either in the form of graphite or cementite. In addition to the above components, cast iron contains impurities based on the following chemicals - silicon, manganese, etc.

Cast iron

Alloying components can be added to cast iron alloys, which have a significant impact on their technical parameters.

Cast iron is used in the production of products by casting, for example, machine tool housings, which operate under small static and dynamic, including multidirectional loads.

Iron casting

Unlike steel, cast iron has good casting parameters and a low price. In addition, this raw material is better processed on metal-cutting equipment than most steel alloys. But, on the other hand, cast iron alloys, regardless of type, are welded with certain difficulties. In addition, cast iron has low parameters of strength, hardness, and brittleness.

Advantages of high-strength nodular cast iron

For more than fifty years, ductile iron (ductile iron) pipes have been very popular throughout the world due to their high quality, reasonable price and durability.

Ductile iron pipes

According to regulatory documents according to GOST, the service life of such pipes is more than 100 years. Today, ductile iron products are the most promising in their industry; they have virtually no equal.

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Application area of ​​ductile graphite cast iron

High-strength nodular cast iron is a rare combination of physical and mechanical characteristics, obtained by modifying graphite particles in cast iron. This compound was obtained by adding magnesium to the alloy.

Ductile iron has a very wide range of mechanical and operational properties, which are regulated by GOST. Such cast iron products are widely used in various fields of industry, but the main share of their production is made up of cast pipes. Cast iron pipes are laid for water supply and sewerage, used for pumping oil, gas, etc.

Pipes made of ductile iron can withstand heavy loads and are not affected by the environment: cast iron does not break and joints do not crack. The advantage of ductile iron according to GOST is:

• Strength;
• Plastic;
• Durability;
• Ease of installation.

Ductile nodular cast iron

Cast iron pipes are used for:

• Extending the service life of utility networks;
• Reducing costs and reducing costs.

The VChShG 100 pipe, according to GOST standards, has a small diameter and is used for drilling rigs and water supply installations. Ductile iron sewer pipe is used when laying a sewerage system.

This pipeline is coated on the outside with a protective layer of zinc and bitumen varnish, and on the inside with a cement-sand coating (CSC).

This coating has good hydraulic properties, excellent energy saving indicators, and also ensures compliance with all sanitary and epidemiological standards in accordance with GOST when transporting drinking water.

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The meaning and method of applying cement-sand coating

The cement-sand coating (CSC) method is used in industrial areas, residential areas and places where there are underground communications to save money during the reconstruction of damaged pipelines.

During operation of a pipeline that has been treated with CPP, a hydrophilic ball is formed, thanks to which leaks are sealed and all defects in the pipe are removed. According to GOST standards, the pipeline restoration technology by applying CPP is used for the following purposes:

• Preventing the formation of plaque inside the pipe;
• Prevention of corrosion formation;
• Sealing joints;
• Increased service life.

Installation of ductile iron pipes

Cement-sand coating (CSC) is a solution of cement and sand, which is applied to the inside of the pipeline by centrifugal spraying. An important advantage of this method of protection is the low cost of materials (sand and cement).

The cement-sand coating method (CSC) is regulated by GOST and is used when rehabilitating old and worn-out pipelines. Such work significantly saves time and financial costs compared to laying new pipes.

CPP is also applied to new cast iron pipes for utility, agricultural and industrial applications. Due to its microbiological properties, CPP serves as the best material for water supply systems.

During installation, cast iron pipes are built up gradually, observing all the conditions of the design documentation.

Cast iron pipes do not require significant installation effort and are easy to use.

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Cast iron products from “Free Falcon”

A large monopolist in the production of cast iron products from ductile iron is the Svobodny Sokol plant in Lipetsk. Today, the enterprise includes 19 workshops with modern and developed infrastructure, producing more than 800 thousand tons of cast iron per year.

Factory Free Falcon

The products of the Svobodny Sokol plant have the following distinctive characteristics:

• The cast iron pipes produced by LMZ Svobodny Sokol are intended for the public sector;
• The products have high strength;
• In the field of drinking water supply, Svobodny Sokol is the only manufacturer of ductile iron pipes in Russia;
• When manufacturing products, the Svobodny Sokol plant adheres to all standards and requirements of GOST;
• Cast iron pipes are certified in compliance with all conditions according to international standards.

Today, LMZ “Svobodny Sokol” is a modern enterprise that is equipped with specialized equipment from well-known global manufacturers, which makes it possible to supply products not only to the regions of Russia and the CIS countries, but also to Europe and Asia.

Over many years, experience in using ductile iron has proven that it is a unique and impeccable alloy, which has no equal in strength and anti-corrosion resistance.

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Production of cast iron pipes VChShG

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Source: http://VseOTrubax.com/materialy/chugunnye/dostoinstva-vysokoprochnogo-chuguna-s-sharovidnym-grafitom.html