低合金钢制方管焊后斜向裂纹的原因分析与改进措施

Cause Analysis and Improvement of Inclined Crack in Low Alloy Steel Square Pipe after Welding

针对Q355B低合金热轧钢带弯折制方管焊接后出现斜向裂纹问题,选择7.75 mm问题钢带为研究对象,进行化学成分、力学性能、布氏硬度、金相组织等检验分析。结果表明,母材钢带各项指标均符合标准要求。分析认为纵剪剪切质量不高,剪切时边部出现了小裂口,卷管应力造成裂纹扩展是造成焊后裂纹的主要原因。实际生产中选择合适纵剪刀具,定期维护保养,避免刀具锈蚀、磨损等应力集中缺陷对钢带边部剪切质量的影响,同时根据钢带厚度及力学性能,合理布局剪切垫板,调节至合理高度,优化剪切工艺,可有效避免该类焊后裂纹问题。

In view of the actual problem of oblique crack of Q355B low alloy hot rolled steel strip after bending square pipe welding,the 7.75 mm problem steel strip was selected as the research object.The chemical composition,mechanical properties,Brinell hardness,metallostructure and other inspection and analysis were carried out.The results show that all indexes of the base metal steel strip meet the standard requirements.The analysis shows that the cutting quality of longitudinal shear is not high,there are small cracks at the edge of shear,and the crack propagation caused by coil stress is the main reason for the crack after welding.In actual production,proper longitudinal scissors are selected and maintained regularly to avoid the influence of stress concentration defects such as tool rust and wear on the shear quality of steel strip edge.At the same time,according to the thickness and mechanical properties of steel strip,reasonable layout of shear plate,adjusting to a reasonable height and optimizing the shear process can effectively avoid the problem of post-welding cracks.