Hardenability
How deep into a section the hardened structure forms on quenching — the reason heavy forgings use alloy rather than carbon steel.
Carbon decides maximum hardness; alloying elements such as chromium, molybdenum and nickel decide how far from the surface that hardness is reached. A 300 mm C45 shaft is hard at the skin and soft in the middle; the same shaft in 42CrMo4 or 34CrNiMo6 transforms through. Specifying a property class without stating the ruling section is the most common cause of a forging that tests fine at the surface and fails at the core.
Related terms
Where this applies
forged-shafts
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