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Steel casting

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Steel casting is a specialized form of casting involving various types of steel. Steel castings are used when cast irons cannot deliver enough strength or shock resistance.[1]

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.[1]

Steel castings are categorized into two general groups: carbon steels and alloy steels.[1]

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[2]

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 make 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.[3]

Steel casting alloys

Alloy steel castings are broken down into two categories: low-alloy steels and high-alloy steels.[4] Low-alloy steels contain less than 8% alloying content and high-alloy steels have 8% or more.[4]

This is a table of some steel casting alloys:

Heat resistant steel castings per ASTM A297-1981[4]
Grade Nominal alloy composition (%wt) Tensile strength, minimum Yield strength to 0.2%, minimum Elongation, minimum, from 2 in, 51 mm (%)
(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 A743-1981a[5]
Grade Nominal alloy composition (%wt) Tensile strength, minimum Yield strength to 0.2%, minimum Elongation, minimum, from 2 in, 51 mm (%)
(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

References

Notes

  1. ^ a b c Oberg, p. 1332
  2. ^ "Machining Cast Iron Components | Modern Casting | AFS". www.afsinc.org. Retrieved 2016-07-07.
  3. ^ "Understanding Material Specifications for Steel Castings | AFS". www.afsinc.org. Retrieved 2016-07-07.
  4. ^ a b c Oberg, p. 1334
  5. ^ Oberg, p. 1335

Bibliography

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