690镍基合金焊接结晶裂纹形成机理分析

Solidification cracking mechanism of 690 nickeil-based alloy surfacing metal

采用横向可调拘束试验方法研究了690镍基合金焊带堆焊金属的结晶裂纹形成机理。结果表明,690镍基合金焊接结晶裂纹的形成与晶界(及亚晶界)偏析密切相关,Nb元素在其中有着重要影响:富Ni,Nb低熔点共晶相在晶界(及亚晶界)的偏析,导致堆焊金属的实际结晶温度降低,晶界(及亚晶界)处塑性储备减小、形貌被改善,促使结晶过程中裂纹萌生并沿平直晶界(及亚晶界)扩展。另外,Mn元素可通过抑制Nb元素在晶界的偏析,削弱Nb的上述不利作用,增强690镍基合金抵抗结晶裂纹的能力。

Trans-varestraint test was used to investigate the solidification cracking mechanism of 690 nickel-based alloy surfacing metal. Results show that, the solidification cracking susceptibility of 690 nickel-based alloy surfacing metal is closely correlated with the segregation process during welding, which is greatly influenced by Nb. The solidification temperature of 690 nickel-based alloy surfacing metal falls when the Ni, Nb-rich phases segregate on the grain boundary or subgrain boundary, which induces that the ductility decreases and the appearance is fined. Then, cracking initiates and expands along the finer grain boundary or subgrain boundary during the solidification process. Furthermore, in 690 nickel-based alloy surfacing metal, Mn weakens the negative influence of Nb on solidification cracking resistance to some extent by restraining the segregation effect of Nb, and then the cracking resistance is improved.