Patent ID: 6146472
Filing Date: 2000-11-14
Classification: C21D,C22C,C23C,Y02P

Abstract:
A method of making a carburizing steel exhibiting optimum core toughness properties and good austenite grain coarsening resistance which is suitable for the manufacture of automotive and machine structural components, comprising the steps of:a. providing a steel comprising in % by weight: 0.10-0.40 C, 0.018-0.064 Nb, 0.024-0.066 Al, and 80-220 ppm N, the balance being substantially iron and other alloying elements found in common carburizing grades of steel;b. conducting a solution pretreatment that comprises reheating the steel at a temperature near or above a solution temperature of the least soluble species of grain-refining precipitate in the steel, hot rolling at high temperatures, and accelerated cooling to 500.degree. C.;c. subcritical annealing at temperatures in the range from 650.degree. C. to the A.sub.Cl ;d. carburizing at elevated temperatures for an extended period of time, quenching; ande. tempering at temperatures below about 250.degree. C.