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氮对提高焊缝的耐点腐蚀性能具有有利的影响。当同时含有钼时,其效果增加。一般认为,铬和钼对提高耐点腐蚀性能效果是显著的。但是,铬和钼在焊缝金属中会发生严重的偏析。按照电子探针显微分析的结果,在r基体中的钼含量至少要比在δ-铁素体中低50％;当焊缝金属是纯奥氏体时,钼集中在枝晶间的区域,而在枝干中心部分则钼贫化。因此,在焊缝金属中添加大量的钼,不能得到象在薄板和中厚板情况下同样显著的预期效果。在焊缝金属中存在各种不同的点蚀源,例如:r基体、r晶界以及r基体-δ-铁素体相界面。蚀点一经发生,就优先在铬、钼贫化的r基体上长大和传播,而其铬、钼的贫化又是由于结晶时的偏析引起,尤其是由于沿着网格状枝晶和枝状晶胞的枝干发生的偏析引起。r基体的点蚀能够通过增加氮在该基体中的含量来抑制。达到这一目的的最有效方法是在焊缝金属中填加锰。实际上,添加的锰作为一种奥氏体形成元素而在结晶过程中在r基体中偏析,而锰的偏析又进一步提高了氮在r基体中的溶解度。值得指出的是:添加一定量的铌对氮含量高达0.45％的高氮奥氏体不锈钢焊缝金属的耐点腐蚀性能具有颇为良好的作用。
Nitrogen has a beneficial effect on improving the pitting corrosion resistance of the weld. When containing molybdenum, the effect is increased. It is generally believed that the effect of chromium and molybdenum on improving the resistance to pitting corrosion is remarkable. However, chromium and molybdenum severely segregate in the weld metal. According to the results of electron probe microanalysis, the molybdenum content in the r matrix is at least 50% lower than in the δ-ferrite; when the weld metal is pure austenite, the molybdenum is concentrated in the interdendritic region , While in the central part of the branch molybdenum depleted. Therefore, adding a large amount of molybdenum to the weld metal can not achieve the same remarkable expected effect as in the case of a thin plate and a medium plate. There are various sources of pitting corrosion in the weld metal, such as: r matrix, r grain boundary, and r matrix-δ-ferrite phase interface. As soon as the eclipse point occurs, it grows and propagates preferentially on the chromium-molybdenum-depleted r matrix, whereas the depletion of chromium and molybdenum is due to segregation during crystallization, especially due to dendrites and dendrites Segregation of the cell stems caused by segregation. Pitting of the r matrix can be suppressed by increasing the content of nitrogen in the matrix. The most effective way to do this is to fill the weld metal with manganese. In fact, the added manganese as an austenite-forming element segregates in the r matrix during crystallization, and the segregation of manganese further increases the solubility of nitrogen in the r matrix. It is worth noting that the addition of a certain amount of niobium has a good effect on the pitting corrosion resistance of high nitrogen austenitic stainless steel weld metal with nitrogen content up to 0.45%.