Patent ID: 8286455
Filing Date: 2012-10-16
Classification: C21D

Abstract:
1. A transformable metal surface hardening method comprising the steps of: rotating a nearly cylindrical pressurizing tool at a high speed and pressing a bottom surface thereof slightly into the surface of an object to be hardened with a specific pressure so as to generate local frictional heat between said pressurizing tool and said object, wherein said object to be hardened has a base material including at least 30% of a perlite structure; causing transformation to a fine martensitic structure in a portion of said object to be hardened that receives the frictional heat; and moving said pressurizing tool at a specific speed when the surface of the object in the vicinity of said pressurizing tool starts to soften because of the frictional heat; wherein said frictional heat provides an input heat quantity amounting to the melting temperature of said object multiplied by 0.5 (Kelvin) or larger and said object has a surface temperature of 850 to 1,050° C.