Steel casting is a specialized form of casting involving various types of steel cast to either final/net or near-net shape. Steel castings are used when iron castings cannot deliver enough strength or shock resistance.Oberg, p. 1332

Examples of items that are steel castings include: hydroelectric turbine wheels, forging presses, gears, railroad truck frames, valve bodies, pump casings, mining machinery, marine equipment, turbocharger turbines and engine cylinder blocks.

Steel castings are categorized into two general groups: carbon steels and alloy steels.

Steel castability Steel is more difficult to cast than iron. It has a higher melting point and greater shrinkage rate, which requires consideration during mold design. Risers should be given more capacity to draw from as the metal cools and shrinks. Attention should be paid to the thickness of mold cavities, as thinner areas will cool quicker than thicker areas, which can create internal stress points that can lead to fracture.

Molten steel is also less fluid than molten iron, making it more difficult to pour and fill intricate gaps in a mold cavity. Molten steel is also more likely to react with internal mold surfaces, making for more unpredictable results.

Machinability Cast parts often require machining to achieve accurate tolerances and desired surface finishes. Carbon steel is the easiest type of steel to machine. High-carbon steel can be more time-consuming to cut or grind, and will wear tools faster. Low-carbon steel can get gummy, making it difficult to work with. Generally, the presence of alloys used to increase mechanical performance often makes machining more difficult.

Damping ability Casting is often a valuable means to creating intricate parts used in machine applications where vibration is often a factor. Cast steel typically has a lower damping ability than cast iron, which can lead to excess vibration and noise in the form of ringing or squealing.

Impact and wear resistance Most steels offer a good balance of strength and ductility, which makes them extremely tough. This allows them to withstand significant stress and strain without fracturing. Steel can also be fairly wear-resistant. Alloy additions can increase both impact and wear resistance.

Steel casting alloys

Alloy steel castings are broken down into two categories: low-alloy steels and high-alloy steels. Low-alloy steels contain less than 8% alloying content and high-alloy steels have 8% or more.

This is a table of some steel casting alloys:

+ Heat resistant steel castings per ASTM A297-1981Oberg, p. 1334 Grade Nominal alloy composition (%wt) Tensile strength, minimum Yield strength to 0.2%, minimum Elongation, minimum, from (%) (ksi) (MPa) (ksi) (MPa) HC 28 Cr 55 380 - - - HD 28 Cr, 5 Ni 75 515 35 240 8 HF 19 Cr, 9 Ni 70 485 35 240 25 HH 25 Cr, 12 Ni 75 515 35 240 10 HI 28 Cr, 15 Ni 70 485 35 240 10 HK 25 Cr, 20 Ni 65 450 35 240 10 HL 29 Cr, 20 Ni 65 450 35 240 10 HN 20 Cr, 25 Ni 63 435 - - 8 HP 26 Cr, 35 Ni 62.5 430 34 235 4.5 HT 15 Cr, 35 Ni 65 450 - - 4 HU 19 Cr, 39 Ni 65 450 - - 4 HW 12 Cr, 60 Ni 60 415 - - - HX 17 Cr, 66 Ni 60 415 - - -

+ Corrosion resistant steel castings per ASTM A743-1981aOberg, p. 1335 Grade Nominal alloy composition (%wt) Tensile strength, minimum Yield strength to 0.2%, minimum Elongation, minimum, from (%) (ksi) (MPa) (ksi) (MPa) CF-8 9 Cr, 9 Ni 70 485 30 205 35 CG-12 22 Cr, 12 Ni 70 485 28 195 35 CF-20 19 Cr, 9 Ni 70 485 30 205 30 CF-8M 19 Cr, 10 Ni, with Mo 70 485 30 205 30 CF-8C 19 Cr, 10 Ni, with Nb 70 485 30 205 30 CF-16 & CF-16Fa 19 Cr, 9 Ni, free machining 70 485 30 205 25 CH-10 & CH-20 25 Cr, 12 Ni 70 485 30 205 30 CK-20 25 Cr, 20 Ni 65 450 28 195 30 CE-30 29 Cr, 9 Ni 80 550 40 275 10 CA-15 & CA-15M 12 Cr 90 620 65 450 18 CB-30 20 Cr 65 450 30 205 - CC-50 28 Cr 55 380 - - - CA-40 12 Cr 100 690 70 485 15 CF-3 19 Cr, 9 Ni 70 485 30 205 35 CF-3M 19 Cr, 10 Ni, with Mo 70 485 30 205 30 CG6MMN Cr-Ni-Mn-Mo 75 515 35 240 30 CG-8M 19 Cr, 11 Ni, with Mo 75 520 35 240 25 CN-7M 20 Cr, 29 Ni, with Co & Mo 62 425 25 170 35 CN-7MS 19 Cr, 24 Ni, with Co & Mo 70 485 30 205 35 CW-12M Ni, Mo & Cr 72 495 46 315 4 CY-40 Ni, Cr & Fe 70 485 28 195 30 CA-6NM 12 Cr, 4 Ni 110 775 80 550 15 CD-4MCu 25 Cr, 5 Ni, 3 Cu, 2 Mo 100 690 70 485 16 CA-6N 11 Cr, 7 Ni 140 965 135 930 15

Terminology In present-day vocabulary, the term cast steel is almost always used in its sense referring to steel castings. Between the late 19th and mid 20th centuries, this was not always true, which is worth understanding if one is reading historical documents; see cast steel for details.

References

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