Surface hardening of workpieces by arc remelting - esp. cast iron camshafts, where local remelting is followed by slow cooling to prevent cracking and martensite formation

摘要

The workpieces are made of cast iron contg. carbon; and a path on the surface is melted by an energy beam, esp. an arc. Cooling then proceeds by the transfer of heat to the workpiece below the surface; and this cooling is retarded so that the austenite below the surface zone solidifying as ledeburite does not cool so fast that martensite is formed. The workpiece is pref. preheated so that after arc melting, the temp. of the workpiece underneath the molten zone is just below the lower transformation point A1. In conventional surface hardening, martensite is formed below the surface ledeburite, thus resulting in stresses which lead to cracks, e.g. on the surfaces of hardened cams. The process prevents the formation of martensite.