Material choice is the first and highest-leverage engineering decision on any spare part. Get it right and the part outlasts the machine; get it wrong and no amount of machining precision will rescue it. This guide is the shorthand our engineers use to match material family to duty.
SEC. 01
Mechanical duty
- Grey iron (GG25/GG30) — damping and machinability, low tensile.
- Ductile iron (GGG50/GGG60) — strength + impact, general-purpose engineering.
- Carbon steel (C45) — strong, machinable, weldable.
- Alloy steel (42CrMo, 40Cr) — high fatigue and induction-hardening capability.
- Case-hardening steel (20CrMnTi) — surface hard, tough core, gear teeth.
SEC. 02
Corrosion duty
- 304 stainless — food, water, indoor architectural.
- 316 stainless — mild marine, chloride-bearing chemistry.
- Monel 400 — seawater, hydrofluoric acid, reducing environments.
- Inconel 625 — chloride pitting, elevated temperature, sour service.
- Nickel 200 — caustic soda, reducing chemistry.
SEC. 03
Thermal duty
- Carbon steel — safe to ~400 °C.
- Cr-Mo alloy (P22/P91) — power piping to ~600 °C.
- Inconel 625/718 — turbine and exhaust to 900 °C+.
Key Takeaways
- Match the family to the dominant duty (mechanical, corrosion or thermal).
- Cast iron is the most economical machinable blank for general engineering.
- Nickel alloys are the answer for chloride and reducing-acid corrosion.
- Alloy + heat treatment always beats a stronger raw material with no heat treatment.