Cast iron: cast iron properties, marking and designation

Cast iron – These are iron-carbon alloys. The percentage of carbon (C) in such a material is at least 2%. The maximum percentage of carbon usually does not exceed 6.67%. In some cases, with an increase in the alloying impurity content, the percentage of carbon content shifts downward, in which case the material is designated as  cast iron, but with some modification. High-chromium, high-aluminum, and high-silicon alloys are prime examples.

Properties of cast iron

Main properties of cast iron – these are good casting qualities, brittleness (significantly higher than that of steels) and hardness. Properties of cast iron may vary depending on its components. Cast iron contains the following elements:

• Si – silicon, in the composition of less than 4.3%, is the second most important element after carbon, gives the material softness and improves its fluidity, thereby increasing casting properties;
• Mn - manganese, in the composition of alloys no more than 2%, helps to increase the strength of the metal;
• S – sulfur, content less than 0.7%, causes “red brittleness”, worsens the fluidity of the alloy and its casting characteristics;
• P – phosphorus, content less than 1.2%, causes “cold brittleness”, which manifests itself in the form of cracks when cooling castings, the component worsens the mechanical properties of the alloy;
• C – carbon, the main component of cast iron, which gives it its basic qualities; depending on the content, type and form of this component, cast iron is divided into grades.

Cast iron has a number of the following mechanical properties, listed in the table. Other parameters—melting point, density, relative elongation, viscosity, and hardness—vary significantly for each individual alloy grade.

Cast iron grades

There are some different types, which in turn have separately developed grades of cast iron, which are given in the table.

Foundry iron:

• L1, L2, L3, L4, L5,
• L6, LR1, LR2, LR3, LR4,
• LR5, LR6, LR7.

Pig iron:

• P1, P2, PVC1, PVC2, PVC3,
• PL1, PL2, PF1, PF2, PF3.

Grey cast iron:

• SCh10, SCh15, SCh20, SCh25, SCh30,
• SCH35.

Malleable cast iron:

• KCh30-6, KCh33-8, KCh35-10, KCh37-12, KCh45-7,
• KCh50-5, KCh55-4, KCh60-3, KCh65-3, KCh70-2, KCh80-1.5.

Low-alloy cast iron:

• CHN2X, CHN3KHMDSH, CHNMSH, CHNKHMD, CHNKHMDSH,
• ChNHT, ChS5, ChS5Sh, ChH1, ChH2,
• ЧХ3, ЧХ3Т, ЧЮХШ.

High-alloy cast iron:

• ChG6S3Sh, ChG7X4, ChG8D3, ChN11G7Sh, ChN15D3Sh,
• ChN15D7, ChN19H3Sh, ChN20D2Sh, ChN4H2, ChS13,
• ChS15, ChS15M4, ChS17, ChS17M3, ChH16,
• ChH16M2, ChH22, ChH22S, ChH28, ChH28D2,
• ChH28P, ChH32, ChH9N5, ChYu22Sh, ChYu30,
• ЧЮ6С5, ЧЮ7Х2.

Antifriction cast iron:

• AChV-1, AChV-2, AChK-1, AChK-2, AChS-1,
• ASF-2, ASF-3, ASF-4, ASF-5, ASF-6.

High nickel cast iron:

• L-Ni35, L-NiCr20-2, L-NiCr20-3, L-NiCr30-3, L-NiCuCr15-6-2,
• L-NiCuCr15-6-3, L-NiMn13-7, L-NiSiCr20-5-3, L-NiSiCr30-5-5, S-Ni22,
• S-Ni35, S-NiCr20-2, S-NiCr20-3, S-NiCr30-1, S-NiCr30-3,
• S-NiCr35-3, S-NiMn13-7, S-NiMn23-4, S-NiSiCr20-5-2, S-NiSiCr30-5-5.

Nodular cast iron:

• HF100, HF35, HF40, HF45, HF50,
• HF60, HF70, HF80.

Cast iron with vermicular graphite for castings:

• ChVG30, ChVG35, ChVG40, ChVG45.

Designation of cast iron grade

Designation of cast iron grade There are a number of established GOST designation rules. These include a letter designation indicating the primary nature or purpose of the metal: KCh – malleable, VCh – high-strength, SCh – gray, P – pig iron, L – foundry. The following basic cast iron designations are also accepted:

• PL1, PL2 – conversion for castings;
• P1, P2 – conversion;
• PVK1, PVK2, PVK3 – high-quality conversion;
• PF1, PF2, PF3 – phosphorus steel;
• СЧ – with lamellar graphite (it is important to know that the digital designation following the letters indicates the value of the tensile strength, measured in kgf/mm);
• АЧ – antifriction;
• AChS – antifriction gray cast iron;
• ACHV – high-strength antifriction;
• HF – with spheroidal graphite (digital designation after the letter designation indicates tensile strength);
• Ch – alloyed cast iron, distinguished by special properties.