低膨胀高温合金焊缝金属凝固行为的模拟预测

Modeling and prediction of solidification behavior of low-expansion superalloy welds

为研究低膨胀高温合金的焊缝结晶裂纹倾向,利用改进的M F模型进行焊接凝固过程溶质再分布的模拟。自行编制了QBasic程序,利用该程序计算了三种低膨胀高温合金焊缝的凝固反应顺序和形成共晶组分的种类与数量。结果表明,GH903和GH907合金在初始凝固后首先发生L→(γ+NbC)共晶反应,然后以次共晶反应L→(γ+Laves)结束凝固,最终凝固组分由γ/NbC和γ/Laves两类共晶组分构成。而GH909合金在初始凝固后只发生L→(γ+Laves)反应,且最终γ/Laves共晶生成量大,因此结晶裂纹敏感性高于GH903和GH907合金。改变碳含量能够影响GH909合金的凝固路径,但是仅靠提高碳含量改善焊接性的作用有限。

In order to predict the tendency of low-expansion superalloys on weld solidification cracking, the modified M-F model was used to simulate solute redistribution in weld solidification. Basic procedures were developed and the solidification reaction sequence, type and amount of eutectic product were calculated for superalloys with different compositions. It is shown that the primary solidification is followed by eutectic-type L &rarr (γ + NbC) reaction and L &rarr (γ + Laves) reaction sequentially for weld metals of GH903 and GH907, hence the terminal eutectic constituent is made up of γ/NbC and γ/Laves. While for GH909 weld only reaction L &rarr (γ + Laves) occurs after primary solidification and more terminal γ/Laves eutectic forms than the other two alloys. Thus the tendency of GH909 to weld solidification cracking is higher than that of GH903 and GH907. Varying carbon content of GH909 can change its solidification path, but the effectiveness of improving weldability only by increasing carbon content is limited.