Surface hardening of high carbon steels - which are induction heated and then quenched in fluidised bed or stream of particles, which may be heated for isothermal quenching

摘要

Surface of a steel workpiece is heated by induction and then immediately quenched via particles, which pref. form either a fluidised bed or a stream of particles impinging on the hot piece. Particles may be heated to achieve isothermal quenching of the surface of the piece. Process may either be discontinuous, where the piece and an induction coil are immersed in a vessel in which particles are fluidised after the heating coil has been switched off; or continuous, where the piece travels through an induction coil and then through a fluidised bed. Particles used in the bed are pref. fluisided by a stream of protective or inert gas. Surface induction hardening of steels is normally restricted to pieces contg. max. 0.4% C, because quenching, e.g. in water, tends to cause cracks in steels contg. over 0.4% C. With the invention, steels of 0.4-1.0% C can be surface hardened to 64Rc without cracking.