焊后热处理对高氮奥氏体不锈钢搅拌摩擦焊接头组织及性能的影响

Effect of Post-welded Heat Treatment on the Microstructures and Mechanical Properties of Friction Stir Welded Joint of High-nitrogen Austenitic Stainless Steel

对高氮奥氏体不锈钢进行搅拌摩擦焊接。焊接过程中没有出现氮元素的损失及其他相的生成。对焊接接头进行焊后热处理,以得到具有不同组织差异性的搅拌摩擦焊接头。微观组织分析表明:在焊态的接头中,焊核区晶粒细化且含有大量的小角度晶界,母材区与焊核之间存在明显的组织差异;热处理态接头中,焊核区的晶粒尺寸略小于母材,各种特征晶界的比例分数都与母材基本相当,接头内组织差异性减小。力学性能分析表明:大的组织差异使焊接接头呈现出典型的高匹配特征,屈服强度、抗拉强度明显升高,伸长率有所降低。较小组织差异的接头匹配模式发生变化,进而导致力学性能发生明显改变,屈服强度、抗拉强度降低,伸长率恢复到母材水平。

Friction stir welding is applied to a high-nitrogen austenitic stainless steel. Loss of nitrogen and other precipitates are not found during the process of friction stir welding. In the as-welded joint, the nugget zone is consisted of fine grains with high fraction of low angle boundaries. Significant differences of microstructure are observed along the transverse direction of as-welded joint. Further, the post-weld heat treatment joint is shown an effectively weaken difference. The differences of microstructure have a significant impact to the mechanical property. In the as-welded, the distribution of different microstructures leads to overmatching characteristic with higher strength but lower ductile. In the post-weld heat treatment joint, the strength matching mode is changed. The elongation of the joint is increased companied with enhanced strength.