LOW-YIELD-RATIO HIGH-STRENGTH HOT-ROLLED STEEL PLATE WITH EXCELLENT LOW-TEMPERATURE TOUGHNESS AND PROCESS FOR PRODUCING SAME

摘要

A low yield ratio and high-strength hot rolled steel sheet having a composition containing, on a mass percent basis, 0.03% to 0.10% C, 0.10% to 0.50% Si, 1.4% to 2.2% Mn, 0.005 % to 0.10% Al, 0.02% to 0.10% Nb, 0.001% to 0.030% Ti, 0.05% to 0.50% Mo, 0.05% to 0.50% Cr, and 0.01% to 0.50% Ni, in which Moeq preferably satisfies the range of 1.4% to 2.2%; and a microstructure including a main phase that contains bainitic ferrite having an average grain size of 10 μm or less and a secondary phase that contains massive martensite having an aspect ratio of less than 5.0 in an area ratio of 1.4% to 15%.

主权项

1. A hot rolled steel sheet comprising a composition containing, on a mass percent basis:
0.03% to 0.10% C; 0.10% to 0.50% Si; 1.4% to 2.2% Mn; 0.025% or less P; 0.005% or less S; 0.005% to 0.10% Al; 0.02% to 0.10% Nb; 0.001% to 0.030% Ti; 0.05% to 0.50% Mo; 0.05% to 0.50% Cr; 0.01% to 0.50% Ni; and the balance comprising Fe and incidental impurities; and a microstructure including a main phase that contains bainitic ferrite and a secondary phase that contains massive martensite having an aspect ratio of less than 5.0 in an area ratio of 1.4% to 15%, wherein the average grain size of the bainitic ferrite is 10 μm or less.