30Mn2热轧棒材表面裂纹缺陷原因分析

针对30Mn2热轧棒材表面出现裂纹缺陷的问题，取样进行了成分、性能、显微组织及能谱分析。结果表明，材料的成分及性能均符合设计要求，裂纹内存在较大的残留气泡及夹杂物，基体存在由P偏析导致的带状组织即鬼线组织，夹杂物包含保护渣成分。结晶器卷渣是导致轧材出现纵向裂纹的主要原因。通过更换保护渣及优化加入方式等，避免了30Mn2轧材表面裂纹和鬼线组织等缺陷的再次产生。

Cause Analysis of Surface Crack Defect of 30Mn2 Hot Rolled Bar

Aiming at the surface crack defects of 30Mn2 hot rolled bar, the sample was taken in defect position and the composition, properties, microstructure and energy spectrum were analyzed. The results showed that the material composition and performance met the design requirements, large bubbles and inclusions existed in crack inside, matrix existed in banded structure caused by phosphorus segregation （the ghost line structure）, and inclusions contained slag composition. Crystallizer slag entrapment is the main cause resulted in appearing longitudinal crack in rolled bar. Through replacing protection slag and optimizing adding way, the emergence of the rolled 30Mn2 steel surface defects again such as cracks and ghost line structure was avoided.