Patent ID: 8932416
Filing Date: 2015-01-13
Classification: B21D,C21D,C22C,Y02P

Abstract:
1. A die-quenched part comprising: A high-strength steel sheet consisting of 0.1 to 0.4 mass % of C, 0.2 to 3 mass % of Si, 0.1 to 5 mass % of Cr, 0.1 to 0.5 mass % of Mo, optional adding 0.0005 to 0.005 mass % of B, and the remainder of substantially Fe and unavoidable impurities, the high-strength steel sheet having a range of Ac3 transformation temperature from 858 to 980° C., wherein the prior-austenite grain size of the high-strength steel sheet is 10 μm or smaller, wherein the die-quenched part has a microstructure of martensite wherein carbide particles are finely dispersed over an entire region including prior-austenite grain boundaries, and a dispersion coefficient of carbide particles is 0.02 or more, the dispersion coefficient of carbide particles being expressed by the following formula (1): where d is a mean diameter in nm of the finely dispersed carbide particles and L is a mean spacing of particles in nm, wherein the die-quenched part is formed by heating a high-strength steel sheet up to an austenite region and then hot stamping and cooling inside a mold so that the dispersion coefficient of carbide particles of the die-quenched part becomes 0.02 or more.