大厚度电子束焊接接头厚度方向的组织差异性

利用K110型电子束焊机焊接50 mm厚的304不锈钢板,并对焊接接头深度方向的微观组织及硬度进行分析. 结果表明,利用电子束焊接方法能够一次性焊透50 mm厚不锈钢板,得到成形良好的焊接接头. 焊缝深宽比较大,约为18:1. 焊缝组织由奥氏体和铁素体组成. 从焊缝上表面到深约39 mm处,铁素体形态依次为网状,板条状/骨架状和树枝状分布于奥氏体枝晶间或晶界处. 在焊缝的下层,亚稳的胞状奥氏体将取代稳定铁素体相作为初生相直接从熔体中析出. 沿焊缝中心深度方向,接头的凝固模式由primary ferrite with second-phase austenite,FA转变成primary austenite with second-phase ferrite,AF模式,晶粒尺寸减小,硬度呈波动性增加趋势.

Microstructure difference analysis of large thickness welded joint with EBW

50 mm thick 304 stainless steel plates were welded using K110 electron beam welding (EBW) machine with high voltage vacuum. Microstructure and hardness along the weld center line were tested with optical microscope, scanning electron microscope and microhardness tester. The results show that complete defect free butt joints could be obtained by one pass with electron beam welding. The weld depth-to-width ratio reached as high as 18:1. From the top to the depth of 39 mm, ferrite distributed in austenite grain boundaries or between dendrites with net, lathy/skeletal and equiaxed dendrite morphologies. At the weld bottom, the cellular metastable austenite would precipitate directly as primary phase from the melt, replacing stable ferrite. The weld microstructure consisted of austenite and ferrite. Solidification mode of the weld transformed from FA to AF mode along the weld center line because of the increasing cooling rate. The grain size reduced and the hardness in weld center fluctuated but grew along the weld depth direction.