铁素体不锈钢搅拌摩擦焊工艺及缺陷形成机理

采用钨铼合金搅拌工具对T4003铁素体不锈钢进行搅拌摩擦焊接工艺试验，研究搅拌摩擦焊缝成形、接头组织特征及缺陷形成机理.结果表明，不同旋转速度下随焊接速度增加，轴向压力呈单调增加趋势；当转速为150，250 r/min时，可获得无缺陷致密焊缝；当转速为350 r/min时，靠近前进侧的焊缝区出现孔洞缺陷，随着焊接速度和轴向压力不断增加，焊接缺陷有减少趋势.焊接接头焊核区发生了相变和明显淬硬现象，组织为细小等轴铁素体和低碳马氏体，焊缝具有明显不均匀硬度分布.提出了一种焊缝热塑性金属平衡流动模型分析其缺陷形成机理.

Investigation on friction stir welding process of ferritic stainless steel and mechanism of defect formation

Friction stir welding was performed on joining T4003 ferritic stainless steel by using a tungsten rhenium (W-Re) alloy tool. The weld formation, microstructural characteristics, and mechanism of defect formation in the weld were examined. It was showed that the axial pressure of tool monotonously increased with the increasing of welding speed under different rotational speeds. Defect-free welds were successfully produced at rotational speeds of 150 and 250 r/min. However, wormhole defects were produced near the advancing side of the stir zone in the welded joints at the rotational speed of 350 r/min. This phenomenon tended to decrease with the increasing of the tool axial pressure and welding speed. A phase transformation and significantly harden occurred in the stir zone of the welded joint, and the microstructure in this region changed to very fine grains consisting of duplex structure of equiaxed ferrite and low carbon martensite. An uneven hardness distribution in the weld was observed. Moreover, a balanced-flow model of weld metal was proposed, and employed to analyze the mechanism of defect formation in the weld.