980 MPa级DH钢开发阶段铸坯开裂的分析与改善

Analysis and improvement of slab cracking in development stage of 980MPa grade DH steel

汽车结构日益复杂,需要具有高强度、高延伸性能的先进高强钢材料。DH钢是在传统DP钢基础上开发而来,在保持强度的同时,其成形性能更优,但铸坯开裂成为制约品种开发的关键问题。通过低倍检验、成分检测、金相分析等表征方法研究了DH钢铸坯开裂的原因。结果表明,柱状晶体粗大、中心偏析严重、芯部裂纹等内部质量问题是开裂的直接原因,存在内部裂纹的铸坯经过加热后,在冷却过程中裂纹会快速扩展。热模拟试验表明,铸坯表面微裂纹脱碳严重不会造成铸坯发生开裂。通过开发专用保护渣、优化铸机设备精度、减小铸坯过程温降,实现了连浇1500 t以上,铸坯回退比例从7.0%降至0.2%,铸坯开裂发生率从1.74%降至0.11%以下。研究结果可为解决该类成分体系的铸坯开裂、断坯问题提供参考。

The increasing complexity of automobile structures requires advanced high-strength steel materials with high strength and high elongation.DH steel is developed on the basis of traditional DP steel,which has better formability while maintaining strength,but slab cracking has become a key problem restricting the development of varieties.The causes of slab cracking of DH steel were studied by means of macroscopic examination,composition detection and metallographic analysis.The results show that the internal quality problems such as coarse columnar crystals,serious central segregation and central cracks are the direct causes of cracking.The cracks will expand rapidly during the cooling process of the slab with internal cracks after heating.The thermal simulation test shows that the serious decarburization of the micro-cracks on the surface of the slab will not cause the slab to crack.By developing special mold powder,optimizing the accuracy of casting machine and reducing the temperature drop of slab process,the continuous casting of more than 1500twas realized,the slab retreat ratio was reduced from 7.0%to 0.2%,and the slab cracking rate was reduced from 1.74%to below 0.11%.The research results can provide reference for solving the problems of slab cracking and slab breaking in this kind of composition system.