Solidification and segregation behavior of corrosion resistant alloy 945A with high level of Ni and Nb
By employing JmaPro thermodynamic calculations in conjunction with optical microscopy,scanning e-lectron microscopy,and electron probe microanalysis,the types of precipitated phases,characteristics of the as-cast microstructure,and element segregation behaviors of corrosion resistant alloy 945A with high level of nick-el and niobium were investigated.The results indicate that during the non-equilibrium solidification process of the 945A alloy,M2O3-type oxides,MC-type carbides,γ matrix,MN-type nitrides,Laves phase and η phase were sequentially precipitated in the liquid phase.The as-cast microstructure of the electroslag ingot exhibited a typical solidified structure with significant contrast differences,and there was an enrichment of needle-shaped phases near the large precipitated phases in the interdendritic regions.Severe element segregation was observed in the alloy,with Cr,Fe,and Al elements segregating towards the dendrite core,and the degree of negative segregation follows the order:KCr＞KFe＞KAl.Nb,Mo.Ti elements were enriched in the interdendritic re-gions,and the degree of positive segregation was KNb＞KMo＞KTi.Due to the segregation of Ni,Nb,and Ti near the large precipitated phases,the precipitation of needle-shaped η-Ni3(Ti,Nb)was facilitated.The segre-gation of Nb,Mo,and Ti in the interdendritic regions at the end of solidification led to the distribution of non-metallic inclusions such as MgO.Al2O3+(Ti,Nb)N,(Nb,Ti)(C,N)+M23C6.
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