Steel sheets and strips

Abstract From the Canadian patent

A medium-hard to hard thin steel sheet and a strip cut or stamped therefrom, both having an increased fatigue strength, are prepared by cold rolling a soft steel sheet carburizing or carbo-nitriding the soft thinned sheet until a medium-hard to hard thin steel sheet is obtained and subjecting the resulting sheet or strip cut or stamped therefrom to a threepart heat treatment, which heat treatment involves first and second different austenizing operations each followed by an, identical two-step cooling operation and a third lesser, reheating and cooling operation.