海工用低合金高强钢厚板的组织与力学性能

Microstructure and mechanical properties of high strength low alloy thick steel plates for offshore engineering

采用TMCP后600℃回火的工艺生产了厚度为80 mm的420 MPa级高强度低合金宽厚板,利用光学显微镜、扫描电镜、电子背散射衍射、透射电镜、力学性能检测等手段,研究了其组织性能随厚度方向的变化规律。结果表明,TMCP钢板的晶粒尺寸分布在6~10μm,组织主要为粒状贝氏体及块状铁素体,且表面处以贝氏体为主,心部以铁素体及碳化物为主;钢板600℃回火后在铁素体晶界有较多渗碳体析出,Nb、Ti元素的碳化物存在复合析出的现象。力学性能测试结果表明,宽厚板表面处的屈服强度可达542 MPa,而心部处的屈服强度为384 MPa。样品断裂方式以微孔聚集性断裂为主,且微孔多在铁素体板条间及夹杂物处形成。各强化机制对屈服强度的贡献中,细晶强化、析出强化占主导地位。

A 420 MPa grade high strength low alloy heavy plates with a thickness of 80 mm were produced by the process of TMCP plus tempering at 600℃.The microstructure and mechanical properties along the thickness direction were analyzed by using optical microscopy,scanning electron microscopy,transmission electron microscopy,electron back-scattered diffraction and mechanical tests.The results show that a fine-grained structure with an average grain size of 6-10μm can be obtained by TMCP.After tempering,the microstructure near the surface of the plate is dominated by bainite,while the core is mainly characterized by aggregated carbides and ferrite.After tempering at 600℃,cementite precipitates on the ferrite grain boundary,and compound precipitation of carbides of Nb and Ti elements is found.Tensile tests show a decrease in yield strengths from 542 MPa on the surface to 384 MPa at the core.The fracture model of the plate is dominated by micro-hole coalescence fracture.Micro-holes are mostly formed between ferritic laths and near inclusions.The grain refinement strengthening and precipitation strengthening dominate the contribution of each strengthening mechanism to the yield strength.