Abstract: A low alloy steel ingot contains from 0.15 to 0.30% of C, from 0.03 to 0.2% of Si, from 0.5 to 2.0% of Mn, from 0.1 to 1.3% of Ni, from 1.5 to 3.5% of Cr, from 0.1 to 1.0% of Mo, and more than 0.15 to 0.35% of V, and optionally Ni, with a balance being Fe and unavoidable impurities. Performing quality heat treatment including a quenching step and a tempering step to the low alloy steel ingot to obtain a material, which has a grain size number of from 3 to 7 and is free from pro-eutectoid ferrite in a metallographic structure thereof, and which has a tensile strength of from 760 to 860 MPa and a fracture appearance transition temperature of not higher than 40° C.

Abstract: A low alloy steel ingot contains from 0.15 to 0.30% of C, from 0.03 to 0.2% of Si, from 0.5 to 2.0% of Mn, from 0.1 to 1.3% of Ni, from 1.5 to 3.5% of Cr, from 0.1 to 1.0% of Mo, and more than 0.15 to 0.35% of V, and optionally Ni, with a balance being Fe and unavoidable impurities. Performing quality heat treatment including a quenching step and a tempering step to the low alloy steel ingot to obtain a material, which has a grain size number of from 3 to 7 and is free from pro-eutectoid ferrite in a metallographic structure thereof, and which has a tensile strength of from 760 to 860 MPa and a fracture appearance transition temperature of not higher than 40 ° C.

Abstract: In a turbine blade, for a snapper cover provided on the top blade portion of the effective blade portion of the turbine blade and a snapper cover provided on the top blade portion of the effective blade portion of a turbine blade neighboring to the above-described turbine blade, contact surfaces composed of plural side-surfaces are formed in a crank shape, respectively. In these surfaces constituting the contact surfaces, a contact-friction surface of the snapper cover which is brought into contact with a contact-friction surface of the other snapper cover has a positive angle of inclination in the rotation direction of the effective blade portion. According to this structure, there is provided a turbine blade in which the contact surfaces of the snapper cover and the neighboring snapper cover are maintained in the contact-state during the driving of the turbine, and the same vibration mode as that in the rotational direction of the effective blade portion can be sufficiently controlled.

Abstract: A steam turbine rotor having a combination of at least one of a high pressure rotor, an intermediate pressure rotor and a low pressure rotor, which are each formed from a metal material of different chemical composition and welded together by means of welding.