Q235B钢板冷弯裂纹成因分析

Formation Cause Analysis on Cold Bending Cracks in Q235B Steel Plate

某厚度为8mm的Q235B钢板在冷弯塑性变形超过90°后,反向弯曲调整角度时,在弯角处出现由内侧向外侧扩展的裂纹,为分析裂纹成因,对开裂钢板进行了断口分析、力学性能测试、金相检验、显微硬度测试以及电子背散射衍射分析。结果表明:由于Q235B钢板基体中含有超视场尺寸的长条状和链状夹杂物,钢板冲击韧度偏低,钢板正弯后在弯角处存在一定程度的加工硬化和弯角内侧形成的晶体结构变化,使得钢板处于反弯韧性和塑性力学性能劣化的状态,从而导致钢板在反向弯曲调整时在弯角内侧以脆性解理方式开裂。

A Q235B steel plate with thickness of 8 mm was bent more than 90° during room temperature plastic deformation process, and cracks initiated in the inboard and propagated to the outboard of the steel plate at the bending comer when bent back. In order to find the reason for cracks occurring, fracture surface observation, mechanical properties test, metallographic examination, micro-hardness test and EBSD analysis had been done. The results indicated that the over length inclusions in the steel plate, bad ductility reflected by the impacting value, the working hardening and crystal change induced by the normal bending, worsened the mechanical properties of the bending comer of the steel plate and caused it to crack with the formation of cleavage during the contrary flexure.