METHOD FOR REDUCING DEFORMATION AND IMPROVING FATIGUE STRENGTH IN CARBURIZATION HARDENING OF STEEL-MADE PARTS

摘要

PURPOSE: To reduce the deformation due to hardening and improve the fatigue strength by executing nitriding treatment following carburization and then hardening treatment to retain a large quantity of austenite on the surface layer to restrain the development of hardened strain and, thereafter, executing work- hardening to the retained austenite. ;CONSTITUTION: A material to be treated is carburized at 870-900°C, and successively, while adding gaseous ammonia of an amt. of 1-6vol% to the furnace atmosphere, the temp. is lowered to 600-730°C, and after holding it for 10-60min, the hardening is executed. By this method, the deformation of hardening and the inner oxidation are prevented. The adjustment of the retained austenite quality and the stability are executed mainly by the added ammonia and a prescribed retained austenite quantity is controlled to exist at ≤100μm below the surface layer. Further, the retained austenite is uniformly work-hardened and the surface is flattened by executing the operation in trial after combining one pair of gears already hardened or by colliding high speed fluid on the surface at a speed of 500-1000m/s.;COPYRIGHT: (C)1995,JPO