不锈钢焊接件不等强度激光冲击与应力腐蚀试验研究

Improving stress corrosion cracking resistance of stainless steel welded joints by laser shock peening

针对不锈钢焊接接头应力及组织分布不均匀,容易导致应力腐蚀开裂的问题,采用不等强度激光冲击波对316奥氏体不锈钢焊接接头进行处理。通过应力腐蚀试验、残余应力测试及微观组织分析,研究了激光冲击强化对焊接接头应力腐蚀抗性的影响及其作用机理。试验结果表明:激光冲击强化将焊接件的应力腐蚀断裂时间提高了33.48%。激光冲击波的作用,在焊接接头部位引入了高数值的残余压应力,一方面消除了热影响导致的残余拉应力,同时抵消了拉伸工作载荷的作用,降低局部应力梯度,从而延缓表面钝化膜的破裂;另一方面,激光冲击使焊接接头不同区域之间的微观组织均匀和细化,提高了微裂纹萌生的条件,降低了金属发生阳极溶解的可能性。两种因素的共同作用,使得不锈钢焊接接头的抗应力腐蚀性能显著增强。

Because the distribution of temperature field was not uniform during the processing of welding, the stress, micro- structure and performances in different regions in the welded joints were different. And there ware residual tensile stress whieh might cause to stress corrosion cracking （SCC）. The 316 austenitic stainless steel welded joints were treated by laser shock pee- ning. In order to protect the welded joints from stress corrosion cracking, the laser shock waves were designed with different strengths in the weld, heat affected zone （HAZ） and the matrix. Under a constant temperature of 90 ℃, the performance of stress corrosion cracking of 316 stainless steel was studied in FeC13 solution. The welded specimens cracked within 112 h. After laser shock peening the crack time was increased by 33. 48%. The mechanisms were analyzed from residual stress tests and mi- crostructure observation. It was found that the residual tensile stress was eliminated in HAZ. There were residual compressive stress and the stress gradient was reduced from 54.7 MPa/mm to 11.7 MPa/mm which were beneficial for protecting weldments against SCC. On the other hand, the microstrueture and mechanical property of the welded joints after laser shock peening became uniform. The grain refining would delay crack initiation and propagation. All in all, the residual compressive stress and uniform mierostructure caused by laser shock peening would protect the welded joints against stress corrosion cracking.