Abstract: The invention is of a heat resisting martensitic steel comprising, by weight, 0.05 to 0.30% C, not more than 0.50% Si, not more than 0.60% Mn, 8.0 to 13.0% Cr, 0.5 to 3.0% Ni, 1.0 to 3.0% Mo, 0.1 to 1.5% W, 0.5 to 4% Co, 0.05 to 0.35% V, 0.02 to 0.30% in total of one or two elements selected from the group consisting of Nb and Ta, and 0.02 to 0.10% N, wherein a value of the square of a difference between the Ni amount and the Co amount, and the Ni amount are not more than values determined by a straight line drawn on a point A (1.0, 2.7%) and a point B (2.5, 1.0%) in the orthogonal coordinates shown in the attached drawing of FIG. 2 which represents a relationship between the above square value and the Ni amount, and an amount ratio of Mo/(Mo+0.5 W) is not less than 0.5. The heat resisting steel is suitably used in various components of a gas turbine.

Abstract: To provide a rotor material preferable for a steam turbine of which main steam temperature is 675° C. or more, particularly exceeding 700° C., and a steam turbine plant having a rotor formed by the material, the invention provides a steam turbine plant including a very-high-pressure turbine of which steam inlet temperature is 675 to 725° C. and steam outlet temperature is 650° C. or less, a high-pressure turbine, and a medium-low-pressure turbine, wherein a rotor of the very-high-pressure turbine is formed from a forged material of NiFe-base alloy containing: 14 to 18 weight % Cr, 15 to 45 weight % Fe, 1.0 to 2.0 weight % Al, 1.0 to 1.8 weight % Ti, C and N of which the sum is 0.05 or less weight %, and Nb in the range specified by the formula: 3.5−(Fe weight %)/20<(Nb weight %)<4.5−(Fe weight %)/20.