780 MPa级冷成型用热连轧回火钢板的工业化生产

 抗拉强度780 MPa级冷成型用热连轧高强钢在工程起重机和混凝土泵车上得到了广泛使用。为进一步改善此种高强钢的力学性能与使用性能，对其热轧卷开平后的横切钢板在热连轧带钢热处理线进行回火热处理。对回火钢板的力学性能、焊接性能、压型性能和显微组织进行检验与分析。结果表明：热轧钢板经回火热处理后，钢板强度和硬度有明显提高，冲击韧性与伸长率略有降低，横向与纵向力学性能差异减小；焊后失强率降低，焊接接头力学性能得到改善；压型性能得到极大改善。在微观结构上，回火后钢板的组织类型无显著改变，但部分铁素体晶粒长大、粗化，回火后铁素体中位错密度降低，近等轴位错胞状结构增多，而固溶Ti、Nb、Mo元素以（Ti,Nb,Mo）C形式继续析出，产生沉淀硬化。

Industrial Production of 780 MPa Grade Tempering Steel Plates for Cold Forming and for Hot-Strip Rolling

Leveled steel plates were taken from hot-rolled strip steel with tensile strength of 780 MPa, which had been?widely?used?in building cranes and concrete pump trucks by cold forming. In the present work, the plates were tempered on a production line, and their mechanical properties, welding performance, cold forming property and microstructures were investigated. The results show that the strength and hardness of the steel increased significantly after the tempering, while the impact toughness and elongation rate decreased slightly. The difference between the mechanical properties in transverse direction and these in longitudinal direction decreased due to the tempering. The mechanical properties of the welded joints were improved showing reduced strength-loss after welding. The cold forming performance was also greatly improved. No significant change in phase constituents was observed due to the tempering, however, some ferrites grains were coarsened and their dislocation density decreased associated with increasing of cellular dislocation. Increased precipitates containing Ti, Nb, Mo were observed, resulting in the precipitation hardening.