On Sunday, July 15, 2018 at 1:57:55 PM UTC-4, Ken Grunke wrote:
Does anyone know what type of stainless steel is generally used for common butterknives? They seem to have the same temper as carbon spring steel, as I can't bend them. Looking for guidelines on heat treating, as I want to hot-forge the handles to make jaw harps, and might have to restore the blade's temper for springiness of the tongue.

It's 18-8 austenitic stainless steel -- the cheap generic, uncertified version of 304 stainless.

It cannot be hardened except by cold-working. Kitchen flatware (table knives, forks, etc.) are cold-forged, stamped, or coined, depending on their quality. Those are all cold-working processes that work-harden the hell out of 304 stainless.

As soon as you heat them to around 400 deg. F, they start to lose their strength and hardness. At 900 deg. F, they become quite soft. They can't be re-hardened except by cold-working them again.

As Jim says, "springiness" has nothing to do with hardness. It's the same whether the stainless (or any steel) is dead soft or fully hardened.

It's not quite that simple, though, as hardness DOES determine how far you can bend them before they're bent permanently. Their stiffness, or springiness, doesn't change, but how much you can "spring" them does vary with their hardness.

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Ed Huntress