Q550D拉伸分层原因分析

Cause analysis of layered fracture in tensile test of Q550D steel

利用光学显微镜(OM)和扫描电子显微镜(SEM),对低合金高强钢Q550D的典型拉伸分层断口进行了微观分析。结果表明:组织为贝氏体+铁素体+颗粒状碳化物,存在一定程度的带状分布。试样拉伸变形过程中,大尺寸碳化物处的位错塞积导致萌发微裂纹和孔洞,试样出现缩颈后产生垂直拉应力导致裂纹扩展,组织的带状分布进一步促进了裂纹的扩展,最终形成宏观断口分层。

The microstructure analysis of typical layered fracture in tensile test of low alloy high strength steel Q550 D was conducted by means of optical microscope(OM) and scanning electron microscopy(SEM). The results showed that the microstructure was composed of bainite, ferrite and granular carbide with certain zonal distribution. In the process of tensile deformation of sample, the dislocation pileup located at large carbide particles led to the origination of microcracks and pores. When the necking down formation occurred on the sample, the crack propagation was caused due to the tensile stress which perpendicular to the tensile axis. The zonal distribution of microstructure further promoted the crack propagation, and the macroscopic layered fracture was finally formed.