冷轧制桶用钢扩径开裂研究

Study on Diameter Expansion Cracking of Cold Rolled Steel for Barrel-Making

针对A钢厂CSP+BAF流程生产的冷轧制桶用钢客户加工使用过程中焊缝扩径开裂问题,通过金相显微镜、SEM对比分析了焊缝处热影响区及母材微观形貌及金相组织。结果表明,热影响区组织相比母材组织晶粒细小、无明显方向性、位错密集、韧窝较浅,热影响区呈现脆性断裂形貌,母材呈现塑性断裂形貌。通过调整焊接参数,降低焊接电流速度、提高焊接时间、降低焊后冷却速度,焊缝处扩径开裂得到一定程度的控制,但不能完全消除。进一步对比行业中其他钢企制桶用钢成分控制,对比分析碳当量及冷裂纹敏感指数,进一步优化该钢厂冷轧制桶用钢成分,降低Mn含量,提高Si、Cr含量,在保证产品强度的同时降低碳当量及冷裂纹敏感指数,最终焊缝扩径开裂问题得到有效解决。

In order to solve the problem of weld seam enlargement cracking in cold rolled steel for barrel-making produced by CSP+BAF process in A steel plant,the microstructure and metallographic structure of heat affected zone(HAZ)at weld seam and base metal were compared and analyzed by metallographic microscope and SEM.The results show that the microstructure of the grain size in the HAZ is smaller,there is no obvious direction,the dislocation is dense,the dimple is shallow.The heat-affected zone exhibits brittle fracture morphology,and the base material exhibits plastic fracture morphology.By adjusting the welding parameters,reducing the welding current speed,increasing the welding time,reducing the cooling rate after welding,enlargement cracking at weld seam can be controlled to a certain extent,but it can not be eliminated completely.By comparing the steel composition control of other steel enterprises in the industry,comparing and analyzing the carbon equivalent and cold crack sensitivity index,the steel composition of cold rolled steel for barrel-making of this steel mill was optimized,the Mn content was reduced,and the content of Si and Cr were increased to reduce the carbon equivalent and cold crack sensitivity index while ensuring the product strength.The problem of weld seam enlargement cracking is finally solved effectively.