Patent ID: 8177925
Filing Date: 2012-05-15
Classification: B21B,B21C,C21D,C22C,Y10S,Y10T

Abstract:
1. A high-tensile steel plate comprising 0.02% to 0. 1% C, at most 0.6% Si, 1.6% to 2.5% Mn, 0.1% to 0.7% Ni, 0.01% to 0.1% Nb, 0.005% to 0.03% Ti, at most 0.1% sol. Al, 0.001% to 0.006% N, 0% to 0.0025% B, 0% to 0.6% Cu, 0% to 0.8% Cr, 0% to 0.6% Mo, 0% to 0.1% V, 0% to 0.006% Ca, 0% to 0.006% Mg, 0% to 0.03% a rare earth element, at most 0.015% P, and at most 0.003% S, the balance consisting of Fe and impurities, said high-tensile steel plate having: a carbon equivalent Pcm in Expression (1) in the range from 0.180% to 0.220%; a surface hardness of at most Vickers hardness of 285; a ratio of a martensite austenite constituent in the surface layer of at most 10%; a ratio of a mixed structure of ferrite and bainite on the inner side beyond the surface layer of at least 90%; a ratio of the bainite in the mixed structure of at least 10%, a lath of the bainite having a thickness of at most 1 μm and a length of at most 20 μm; and a segregation ratio as the ratio of the Mn concentration of a center segregation part to the Mn concentration of a part in a depth equal to ¼ of the thickness of the plate from the surface of at most 1.3.  where the element symbols represent the % by mass of the respective elements.