STEEL COMPOSITIONS AND METHODS OF PROCESSING FOR PRODUCING COLD-FORMED AND CARBURIZED COMPONENTS WITH FINE-GRAINED MICROSTRUCTURES

摘要

Steel compositions and processes are described that provide optimum resistance to austenite grain coarsening in cold-formed and carburized components for automotive and machine structural applications. The steel compositions include, in weight percent, 0.1-0.3 % C, 150-220 ppm N and a grain refining addition selected from the group consisting of Al, V plus Al and Nb plus Al, the balance comprising iron and other alloying elements typically found in carburizing grades of steel. The steels are processed by reheating to a temperature in the vicinity of a solution temperature of the least soluable species of grain refining precipitate and then hot worked. The hot-worked steel is cooled at an accelerated rate to 500 °C and then subcritically annealed, cold formed in at least one operation with intermediate anneals, subcritically annealed after the last cold-forming operation, and carburized, quenched and tempered (6).