冷轧双相钢HC420/780DP冲压开裂原因分析及改进

Analysis and improvement of stamping cracking reason for cold-rolled dual-phase steel HC420/780DP

针对采用冷轧双相钢HC420/780DP冲压某车型前纵梁加强件过程中易出现开裂现象的问题,通过对材料性能、显微组织、断口形貌与冲压工艺进行分析可知,材料带状组织及针状马氏体的存在、屈强比偏高均对冲压变形产生不利影响,裂纹产生与成形复杂程度、模具圆角半径、板料成形方向及压边力等有关。通过在连铸过程中铸坯凝固末端实施轻压下与在冷轧过程中提高板料退火温度实现了材料显微组织与力学性能的优化,结合冲压工艺,利用改变落料方向发挥板料轧制成形优势与降低压边力,提高了成形过程中的材料流动性,开裂问题得到了有效解决,开裂率由75%降至0.5%以内。

Aiming at the cracking problem in the stamping process of the front longitudinal beam reinforcement part of a certain type of vehicle with cold-rolled dual-phase steel HC420/780 DP,based on analysis of material properties,microstructure,fracture morphology and stamping process,it is found that the existence of banded structure and acicular martensite,and high yield ratio have negative effects on stamping deformation. The formation of crack is related to the forming complexity,die fillet radius,sheet metal forming direction and blank holder force. The optimization of microstructure and mechanical properties of the material was realized by implementing light reduction at the solidification end during continuous casting process and increasing the annealing temperature of the sheet metal during cold rolling process. Combining with the stamping process,changing the blanking direction gives full play to the advantages of sheet rolling forming and reduces the blank holding force,which improves the material fluidity in the forming process,the cracking problem is effectively solved,and the cracking rate is reduced from 75% to less than 0. 5%.