齿轮钢20CrNiMo轧材表面裂纹缺陷原因分析

针对规格不小于?80 mm的齿轮钢20CrNiMo轧材探伤合格率低,轧材表面存在裂纹缺陷问题,对轧材裂纹缺陷进行分析,可知这可能是铸坯裂纹缺陷造成的。为了验证这一观点及查找出确切原因,便于提供解决方法,首先对铸坯表面进行抛丸检查,未发现裂纹缺陷;其次将存在裂纹的铸坯轧制成材的缺陷与轧材表面裂纹缺陷通过金相显微镜进行对比分析,发现裂纹形貌及周围脱碳程度存在差异,分析认为轧材裂纹不是由铸坯缺陷导致的;最后将铸坯开坯后方坯直接挑出缓冷后抛丸检查,发现表面存在严重划伤和凹坑缺陷,划伤缺陷形貌和周围脱碳程度与轧材裂纹相似。结果表明:轧材裂纹及翘皮缺陷是由铸坯开坯过程中产生的划伤和凹坑缺陷导致的,不是由铸坯裂纹缺陷导致的。

Cause analysis of surface crack defects of gear steel 20CrNiMo rolled product

For the gear steel 20CrNiMo rolled material with specification of more than ?80 mm,it was found that the defect detection rate was low. Moreover,the problem of crack defects on the surface of rolled product was also observed.Based on the analysis of crack defects of the rolled products,the cracks were possibly caused by the crack defects in the billet. In order to verify this point of view and find out the exact reason so as to provide solutions,the shot blasting inspection of billet surface was firstly conducted,and no crack defect was observed. Secondly,the defects of the rolled product prepared from billet with cracks and the surface cracks of rolled product were compared and analyzed by metallographic microscope. It was found that the crack morphology and decarburization degree around were different,which indicated that the cracks on rolled product were not caused by the defects of the billet. Finally,the surface of cast billet was found to be seriously scratched and pitted by blasting the billet after slow cooling and be similar to that of the rolling cracks. The results showed that the cracks and warping defects were caused by scratches and pits in the process of casting but not caused by crack defects of the billet.