NM500耐磨钢切割裂纹分析及控制措施

Analysis and control measures of flame cutting cracks on NM500 abrasion-resistant steel

针对耐磨钢NM500钢板火焰切割后出现头尾纵裂纹及边部横裂纹的现象,利用金相显微镜、扫描电镜等手段对表面裂纹、裂纹断面进行观察分析。结果表明:在钢板头部或者尾部宽度1/2或1/4处存在贯穿整个厚度方向的纵裂纹,并有(Nb,Ti)(N,C)夹杂物;在钢板边部厚度中心,存在平行于轧向不连续分布的横裂纹,且有主要为xCaO·yAl2O3夹杂和(Ca,Mg,Al)xOy复合夹杂。火焰切割后,在夹杂物和残余应力的共同作用下导致钢板上产生氢致延迟裂纹。通过优化冶炼工艺,控制夹杂物含量和降低H含量,改进精整工艺,采用带温切割,切割后边部保温或堆垛等措施来降低残余应力,可以有效地避免或减少切割裂纹。

Head and tail longitudinal cracks and edge transverse cracks of NM500 abrasion-resistant steel plate after flame cutting were investigated by optical microscopy,electron scanning microscopy and energy spectroscopy.The results show that longitudinal cracks penetrate the whole thickness direction and(Nb,Ti)(N,C)inclusions exist at the head or tail and 1/2 or 1/4 of the width.Transverse cracks distribute discontinuously and parallel to the rolling direction at the center thickness of the edge,primarily with xCaO·yAl2O3and(Ca,Mg,Al)xOy complex inclusions.Hydrogen-induced delayed cracking is caused by the combined action of inclusions and residual stress after flame cutting.Cutting cracks can be effectively avoided or reduced by optimizing steelmaking process to control inclusions and reduce hydrogen content,improving finishing process to retain certain temperature prior to cutting,and reducing residual stress by stacking and slow cooling immediately after cutting.