A柱加强板热冲压延迟开裂机理

针对某车型超高强度硼钢A柱加强板热冲压成形后小翻边易发生延迟开裂的问题,进行了变薄率、化学成分、断面硬度、残余应力和断裂面扫描电镜等试验,对延迟开裂的原因进行了详细地讨论,并提出了改进措施。研究结果表明,开裂面呈韧窝形态,翻边圆角处发生氢脆现象。小翻边部位在热冲压时圆角处的应力集中导致镀层开裂,且放置一段时间后氢原子积聚形成氢分子易从开裂的镀层间隙处释放,形成该零件的延迟开裂。通过增加露点控制以有效降低氢的导入,可以避免氢脆的发生。

Mechanism of delayed fracture for A-pillar in hot stamping

For the delayed fracture of flanging after hot stamping of ultra high strength boron steel A-pillar,experiments of thickness thinning rate,chemical composition,section hardness,residual stress and SEM observation were conducted,and the causes were discussed and the improvement measures were suggested.The results show that the crack surface is in dimple shape and the hydrogen embrittlement phenomenon occurs at the flanging fillet.Furthermore,the stress concentration at the flanging fillet during hot stamping leads to coating cracking,and it produces the delayed fracture of part because the gathered hydrogen atoms forming hydrogen molecules are easy to release from the coating gap after the part which is placed a period of time.Thus,the hydrogen embrittlement can be avoided by increasing dew point to deduce the introduction of hydrogen effectively.