SPHEROIDIZING HEAT TREATMENT METHOD FOR HIGH CARBONN CHROMIUMMMOLYBDENUM BEARING STEEL

摘要

PURPOSE:To perfectly spherodize metal carbides in the structure of a high carbon Cr-Mo bearing steel by repeatedly annealing the steel under specific conditions. CONSTITUTION:A high carbon Cr-Mo steel contg. C; 0.80-1.20%, Si; 0.10-0.80%, Mn2.0%, Cr; 1-2% and Mo; 0.1-1.0% is refined in a high frequency furnace or the like and cast into an ingot. The ingot is forged and drawn to a bearing round bar of uniform pearlite structure. The bar is then heated to a temp. from the Acid point (742 deg.C of the steel to the Acie point (776 deg.C), held for about 1hr, slowly cooled from the Arib point (710 deg.C) to the Arie point (660 deg.C) at a very slow cooling rate of 10 deg.C/hr, and held at 650 deg.C for 1hr. The annealing is repeated 4 times or more. By the treatment metal carbides in the structure are spheroidized and become few spherical carbides of large diameter, and hence the wear resistance and hardenability of the bearing steel are enhanced.