高强大梁用钢折弯起皮开裂原因分析

Cause Analysis on Peeling and Cracking of High Strength Beam Steel during Bending

针对汽车大梁用热轧高强钢板在辊压折弯过程中发生的起皮开裂,采用金相显微镜和扫描电子显微镜对开裂件进行了分析。结果表明,在开裂部位近表层分布大量连续点状或带状夹杂物,夹杂物含有O、Al和Ti元素;钢板表层脱碳层金相组织为粗大等轴铁素体。分析认为,硬性夹杂物TiO_(2)和Al_(2)O_(3)破坏了产品基体的连续性,氧化脱碳组织降低了表层的塑性,在折弯过程中含夹杂物的基体首先发生破裂,同时使上方表层变形量增加,超出了其承受范围形成起皮开裂。通过采取中间包预吹氩技术,防止开浇初期钢水二次氧化产生氧化物夹杂,使钢板折弯层状开裂问题得到了解决。

The cracked part is analyzed with metallographic microscope and scanning electron microscope aiming at the peeling and cracking of hot rolled high strength beam steel plate during the process of bending.The results showed that many continuous punctiform or banded inclusions containing O,Al and Ti elements were distributed close to the surface layer at cracking;metallographic microstructure of decarburized layer on surface layer of steel plate was coarse equiaxed ferrite.The analysis suggests that hard inclusions,TiO_(2)and Al_(2)O_(3)destroy the continuity of product matrix and plasticity of surface layer is reduced by microstructures of oxidation and decarbonization,the matrix with inclusions fractures firstly in bending process,which makes the deformation of upper surface layer increase and it is out of tolerance range so that peeling and cracking are formed.The problem of lamellar cracking during bending for steel plate is solved by adopting the technology of pre-blowing argon in tundish to prevent oxide inclusion caused by secondary oxidation of molten steel at the initial stage of pouring.