Q355B钢板拉伸断口分层原因及改善措施

Causes and improvement measures of delamination of tensile fracture of Q355B steel plate

采用宏观观察、化学成分分析、拉伸试验、热酸蚀检验、金相检验、扫描电镜及能谱分析等方法,分析了Q355B钢板拉伸断口出现分层的原因。结果表明:Q355B钢板拉伸断口出现分层的主要原因是连铸坯厚度中心处存在缩孔、疏松、偏析和夹杂物缺陷,导致钢板产生中心裂纹,在拉伸试验过程中,裂纹处产生应力集中,随着变形量的不断增加,裂纹不断扩展,最终出现断口分层现象;在适当调整连铸坯浇注及钢板轧制工艺参数(如过热度、二次冷却速率、拉坯速率、道次压下率和轧制温度等)后,采用电磁搅拌和轻压下技术,以及轧后缓冷等措施,Q355B钢板拉伸断口不合格率由6.82%降低至0.84%,并稳定在1%以下。

By means of macroscopic observation,chemical composition analysis,tensile test,thermal acid etching inspection,metallographic inspection,scanning electron microscope and energy spectrum analysis,the reasons for the delamination of tensile fracture of Q355B steel plate were analyzed.The results showed that the main reason for the delamination of tensile fracture of Q355B steel plate was that there were shrinkage holes,porosity,segregation and inclusion defects in the center continuously cast product thickness,which led to the central micro crack in the steel plate.During the tensile test process,stress concentration occurred at the crack,as the amount of deformation continued to increase,the micro cracks continued to expand,and finally the fracture delamination was occurred.In the appropriate adjustment of continuously cast products casting and steel plate rolling process parameters(such as superheat degree,secondary cooling rate,billet drawing speed,pass reduction rate,rolling temperature),electromagnetic stirring and light reduction technology,and slow cooling measures after rolling were adopted,the failure rate of Q355B steel plate tensile fracture was reduced from 6.82%to 0.84%,and stabilized below 1%.