Dependence of solvus temperature of the laves phase on (Mo+W+Re) contents in high Cr ferritic steels

The solvus temperatures of the Laves phase were investigated in heat resistant 10Cr ferritic steels containing 2.3-4.7 mass% (Mo+W) and 0-1.7 mass% Re. The measured solvus data was approximately represented as a solvus curve in the pseudo-binary system of Fe-W (+Mo). The solvus temperatures increased with increasing content of Mo+ W in the steels, for example, 1 020 K for 2.3 mass% (Mo+W) steel, 1 130 K for 3.7 mass% (Mo+W) and 1 145 K for 4.7 mass% (Mo+W) steel. It was suggested from the measured solvus curve that the Laves phase precipitated at 923 K granularly in a 2 mass% W steel, but finely in a 4.5 mass% W steel. On the other hand, the solvus temperature did not change with the Re addition up to 1.7 mass%.