Inconel-690 alloy is a new high-chromium nickel-base alloy, designed to be used for steam generator tubes for advanced PWR. It has serious solidification segregation and poor hot workability due to its high chromium content. Metallograph-microprobe method was used to study the solidification process and segregation of this alloy and the influence of P, S, Ti and Al on it. It was found that Inconel-690 alloy has a rather high final solidification temperature, so the poor hot workability did not resulted from the low melting point phase. In the solidification process, there was a segregation layer of Cr, S and P in the front area of the solidification interface. In the final solidification region, brittle phase α' - Cr would be expected. Trace elements S and P segregated very seriously due to their very small solubility in γ solid solution. The segregation of Cr increased with the increase of S content. Eutectic (γ + CrS) would be expected in the final solidification region at 1310 ℃ when S was 0.039%. The segregation degree of P was less than hat of S, But P profoundly promoted the segregation of S and hence Cr. As a positive dendritic segregation element, Ti reduced the segregation of Cr and S because itself segregated in the front area of the solidification interface. Cr changed from positive dendritic segregation into negative dendritic segregation because of the addition of 1.0%Ti. The influence of Al on the solidification segregation was not obvious. The high temperature ductility of Inconel-690 alloy can be improved by limiting S ＜ 0.003%, P 0.0008% and further by adding 0.30%Ti.
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