高强钢拉伸样断口中心分层渐进失效分析

Progressive failure analysis for center lamellar cleavage fracture of tensile specimens of high strength structure steel HG70C

为探讨高强钢热轧板带在力学性能检验中出现严重的拉伸样断口中心分层现象,结合HG70C钢试验设计不同拉伸应力级别的试样,并通过金相检测和电镜观察拉伸样断口截面中心偏析带组织和裂纹的演变,从微观上分析拉伸样断口芯部分层的渐进过程,为改善钢材拉伸性能建立了实验依据。研究表明,中心偏析带颈缩阶段由于承受三向拉应力作用,导致珠光体带组织被拉长变细,并沿Z向扩展;分层断口裂纹是在应力加载过程中逐步产生的,当载荷超过屈服强度时,在芯部区域存在的大量铌钛夹杂物边缘处诱发微裂纹,随着拉伸应力的增大,微裂纹相互连接,形成裂纹孔洞贯通平台,最终产生层状分离断口。

Serious centerline de-lamination fracture appeared in mechanical property test of hot rolled strip of high-strength structure steel. To address this, this paper tested specimens at different stress levels, studied the evolution of centerline macro segregation bands and cracks of the test specimens by Optical Micrograph and Scanning Electron Microscope （SEM-EDS）, and analyzed progressive failure for center lamination fracture. Furthermore, this study described the cracking mechanism of de-lamination tensile fracture, and established the foundation for improving the tensile fracture of high strength structure steel HGTOC. The results of the study showed that the pearlite colonies elongated in the tensile direction and extended in Z direction. The void nucleation was generated around the inclusions in abundance located in the center area. And then the void grew, coalesced and eventually extended to form Iamellar cleavage fracture with stress increasing.