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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。
Tensile strength 780 MPa cold forming hot rolling high strength steel in engineering cranes and concrete pump truck has been widely used. In order to further improve the mechanical properties and serviceability of this kind of high strength steel, the hot rolled coils were tempered at the hot strip after the hot rolled coil was opened. The mechanical properties of tempering steel, welding performance, pressure-type properties and microstructure inspection and analysis. The results show that the strength and hardness of the hot-rolled steel sheet are obviously enhanced after tempering, the impact toughness and elongation are slightly reduced, the difference between the transverse and longitudinal mechanical properties is reduced, the loss ratio after welding is decreased, the mechanical properties of the welded joint Have been improved; press-type performance has been greatly improved. On the microstructure, there is no significant change in the microstructure of the steel after tempering, but some ferrite grains grow, coarsening and tempering ferrites dislocation density decreased near the axial dislocation cell structure increased, The solid solution Ti, Nb, Mo elements (Ti, Nb, Mo) C form of precipitation continued precipitation hardening.