Vicker's had a multiple quenching technique in the say 1880s where they heated a piece of metal to say 950F, cooled it, heated it again to say 750F and cooled it. I can find the particulars if anyone is interested. They were addressing the tensile issue. Something similar for cogs where the end result was case colours of 1/32. Is that a typical case colour depth?

Kind Regards,

Raimey
rs