TMCP高强贝氏体钢板拉伸断裂机制研究

Study on Tensile Fracture Mechanism of TMCP High Strength Bainitic Steel

TMCP型F620船板钢的拉伸伸长率达15%时未出现分层断裂。但随着颈缩的发展,在断裂前瞬间发生分层。对钢板及拉伸断口分层裂纹进行光学显微镜(OM)观察,未发现明显偏析及异常夹杂物等缺陷。对拉伸断口分层面进行扫描电镜(SEM)观察,发现分层面具有明显的低塑性解理断裂特征。利用X射线衍射(XRD)对形变前后的试样进行织构分析,发现<111>//拉伸方向的织构被加强。通过电子背散射衍射(EBSD)分析形变组织,发现晶界分布状态发生了改变。Z向短棒拉伸试验证明厚度方向具有良好的塑性。上述结果表明,拉伸断口分层是TMCP贝氏体钢板特有的特征,并非性能降低所致。

In the tensile test of F620 grade shipbuilding steel produced by thermomechanically controlled process(TMCP),the laminate fracture didn 't occurred when the elongation was 15%,while occurred instantaneously before fracture. Based on optical microscopy(OM) observation on the laminated crack,no harmful defects,such as obvious segregation bands and abnormal inclusions were found. According to scanning electron microscopy(SEM) observation on the laminated surface,the ‘laminate'had features of cleavage fracture. Meanwhile,the texture in< 111 > parallel to the tensile direction measured by X-ray diffraction(XRD) was strengthened.Based on electron backscatter diffraction(EBSD) analysis,it was found that the grain boundary distribution changed. The steel plates had good plasticity in the direction of thickness measured by short bar tensile test in Z direction. These observations indicated that the laminated fracture was the characteristic of bainitic steel,and not attributed to decrease of mechanical properties.