Effect of Si on Precipitation Behavior of Nb-Laves Phase and Amount of Nb in Solid Solution at Elevated Temperature in High Purity 17%Cr-0.5%Nb Steels

Abstract

The effect of Si was investigated on the precipitation behavior and the amount of Nb in solid solution at temperature ranging from 1073 to 1173 K in high purity 17Cr-0.5Nb steels. Adding Si promoted the precipitation of the Nb Laves phase and then decreased the solubility of Nb in steels. The Nb Laves phase which was composed of Fe, Cr and Nb could be expressed as (Fe, Cr)2Nb in a 0.002 mass% Si steel. On the other hand, in a 0.5 mass% Si steel the Nb Laves phase which was composed of Fe, Si, Cr and Nb could be expressed as (Fe, Si, Cr)2Nb. Based on calculations from the experimental results assuming the Laves phase is Fe2Nb, the standard free energy change of the Fe2Nb precipitation reaction was about −61 k J/mol for a 0.002 mass% Si steel.