锅炉钢20g和20K埋弧焊接头冷弯开裂的研究

An Investigation into the Cracking of SAW Joints of 20g and 20K Boiler Steels Due to Cold Beading

本文通过锅炉钢20g和20K埋弧焊接头冷弯试件断口的金相分析,认为冷弯开裂主要是在接头熔合区附近,由于焊接热的作用,在接头的熔合区产生结晶裂纹和液化裂纹,冷弯时导致这些显微裂纹的扩展。经分析和试验表明:母材的含碳、硫和磷量是影响20g和20K钢热裂敏感性的重要冶金因素,而线能量大小则是冷弯开裂的外界因素。只有严格控制母材的含硫、磷量小于0.02％以下,含碳量小于0.2％以下,才能提高冷弯合格率。针对板厚为12～14mm的20g和20K钢,根据研究结果给出了可以提高这两种钢冷弯合格率的埋弧焊最佳工艺规范参数。

In this paper, through the fracture and metallographic examination of the cold bent specimens with submerged arc welding ( SAW ) joints of 20g and 20K boiler steels, it is shown that the cold bending cracking mainly originates from the bond zone of the joint. Because of the effects of arc heat solidification, cracks and liquation cracks take place in the bond zone of the joint and these micro-cracks extend to break during bending. Based on experimental results and systematical analysis, it is suggested that the contents of carbon, sulphur and phosphorus in the base metal are important metallurgical factors influencing heat crack sensitivity of 20g and 20K steels. The energy input affecting cold bending cracking is only an aditional external factor. Only if the sum of the contents of sulphur and phosphorus are less than 0.02% and the content of carbon is less than 0.2% in the base metal, could the qualified ratio of cold bending be risen. According to this investigation, the optimum welding condition parameters are given with which the qualified ratio of SAW joints with cold bending can be risen for 20g and 20K steels of 12-14mm in thickness.