Patent ID: 6863749
Filing Date: 2005-03-08
Classification: C21D

Abstract:
1. A method for improving the toughness of a high-strength steel containing in % by weight about 0.09% to 0.17% C, 0.005% to 0.05% Al, and more than about 60 ppm N, comprising the steps of: (a) casting said steel to provide a hot, solidified steel shape; (b) cooling the hot solidified steel shape in a thermally controlled environment from a temperature near a solidification temperature of the steel at a rate of 1° C./second or less to a temperature in excess of an equilibrium solution temperature for AlN in austenite for a sufficient amount of time to effect the dissolution of coarse AlN precipitates in a microstructure of said hot solidified steel shape; and (c) further cooling the hot solidified steel shape to room temperature or to a primary hot-rolling temperature.