浅谈氢含量对圆棒端部开裂的影响

Discussion on the Effect of Hydrogen Content on End Cracking of Bars

宝武杰富意特钢有限公司中棒未过RH的200方45钢放量生产的圆棒,经过冷剪分段后打捆入库,在库内堆放2~3 d后,出现批量性45钢端部开裂现象。端部开裂的圆棒返修处理,修磨后的圆棒出现二次、三次开裂现象,端部裂纹深度0.1~5 mm,存在较大的质量管控风险。通过对45钢炼钢工艺分析,发现过RH的45钢在任何温度下剪切均不开裂,不过RH的45钢在200~300℃下剪切端部存在开裂缺陷;通过对比圆棒各规格剪切残留应力分布情况,发现大规格剪切后端部残留应力大,端部开裂率偏高,由此得出,圆棒端部开裂受残留氢量及残留应力影响。为了解决圆棒端部开裂问题,采用高温剪切方式对圆棒进行分段,高温剪切圆棒硬度小,可大幅度降低圆棒所受的剪切应力,且高温剪切后圆棒存在一个缓冷过程,能将残留氢去除,有效解决未过RH的45钢端部开裂问题。

Baowu JFE produced 200 square meters of steel 45 without RH treatment in bulk.The bars were cold cut and segmented before being bundled and stored in the warehouse.After being stacked for 2-3 days,end cracks appeared in the batch of the steel.The bars with end cracks were repaired,and the polished,and still the bars showed secondary and tertiary cracks.The depth of end cracks was about 0.1mm-5mm,posing a significant quality control risk.By analyzing the steelmaking process of the steel,it was found that the steel with RH treatment did not crack during shearing at any temperature,but there were cracking defects at the sheared ends of the steel without RH treatment at 200℃-300℃;By comparing the distribution of shear residual stress in various diameters of bars,it was found that the residual stress at the rear end of large diameters is high,and the occurrence rate of end cracking is significantly higher.This indicates that the end cracking of bars is affected by residual hydrogen content and residual stress.To solve the problem of end cracking of rods,high-temperature shear is used to segment the bars.The hardness of high-temperature bars is small when shearing,which can significantly reduce the shear stress on the bars.And after high-temperature shearing,there is a slow cooling process in the bars,which can remove residual hydrogen.This method effectively solves the problem of end cracking of the steel that has not had RH treatment.