Patent ID: 6478898
Filing Date: 2002-11-12
Classification: C21D,C22C

Abstract:
A method of producing a tool steel comprises; preparing a steel having a chemical composition such that it contains, by mass percent, C: 0.25 to 0.45%, Si: 0.10 to 1.00%, Mn: 0.20 to 1.00%, Ni: 0.50 to 2.00%, Cr: 2.80 to 4.20%, Mo: 1.00 to 2.00%, V: 0.10 to 1.00% and Al: 0.005 to 0.10%, with the balance being Fe and impurities, and that the content of P among the impurities is not more than 0.015%, that of S is not more than 0.005% and that of N is not more than 0.015%; quenching the steel from a temperature of 900 to 1050Â° C. to obtain a hardness H such that the hardness index K defined below by the formula (1) becomes between 0.20 to 0.95; and then tempering the quenched steel at a temperature of 550 to 640Â° C.;K=(Hâˆ’H2)/(H1âˆ’H2)â€ƒâ€ƒ(1) whereH1: Vickers hardness found on a standard sample with 10 mm thickness which is heated to a temperature of the Ac3 transformation point plus 50Â° C., and quenched into water; H2: Vickers hardness found on a standard sample with 10 mm thickness which is heated to a temperature of the Ac3 transformation point plus 50Â° C., and cooled to room temperature over 20 hours.