A 9% Cr steel containing cobalt and boron, X13CrMoCoVNbNB9-2-1, has been manufactured by electroslag remelting (ESR) to evaluate its performance and to compare its creep strength and microstructure to a forging made from electroslag hot-topping ingot. The evaluation results confirm that it is possible to produce rotor forgings with homogeneous composition and good properties by the ESR process. The results of creep rupture tests up to 5000 h indicate that the creep strength of the forging made from ESR ingot is similar to that of the forging produced by the electroslag hot-topping process. Martensitic lath microstructures with high density dislocations and the precipitations of M 23 C 6 , VX, NbX and M2X are observed after the quality heat treatments at the center portion of both forgings. There is no large difference in the martensitic lath widths, distributions, and sizes of those particles between both trial forgings.

10CrMoWVNbN (X 12 CrMoWVNbN 10 1 1) steel trial forgings has been manufactured to clarify the effect of austenitizing temperature on the creep rupture strength and microstructure. From the results of creep rupture tests up to 30,000 hours, higher austenitizing temperature improves the rupture strength without large degradation of the rupture ductility. The microstructural investigations demonstrate that the prior austenite grain size and the precipitation behavior of fine M2X particles are presumed to contribute to the improvement of creep rupture strength.