High-strength heat resisting cast steel, method of producing the steel, and applications of the steel

Abstract

A high-strength heat resisting cast steel which has high creep rupture strength at temperatures of 620° C. or above, high toughness, and good weldability. A method of producing the steel, a steam turbine casing, a main steam valve casing, and a steam control valve casing, each casing being made of that steel, as well as a steam turbine power plant using those components are also provided. The high-strength heat resisting cast steel contains 0.06-0.16% by mass of C, 0.1-1% of Si, 0.1-1% of Mn, 8-12% of Cr, 0.1-1.0% of Ni, 0.7% or less of Mo, 1.9-3.0% of W, 0.05-0.3% of V, 0.01-0.15% of one or more of Nb, Ta and Zr in total, 0.1-2% of Co, 0.01-0.08% of N, and 0.0005-0.01% of B, the balance being Fe and unavoidable impurities.

1 . A steam turbine casing made of a high-strength heat resisting cast steel containing 0.06-0.16% by mass of C, 0.1-1% of Si, 0.1-1% of Mn, 10.0-11.0% of Cr, 0.1-1.0% of Ni, 0.7% or less of Mo, 2.0-2.5% of W, 0.05-0.3% of V, 0.01-0.15% of one or more of Nb, Ta and Zr in total, 0.2-1.2% of Co, 0.01-0.08% of N, and 0.0005-0.01% of B, and 0.0005-0.03% by mass of AI and 0.004-0.01% of O as well as at least one of 1.5% by mass or less of Re, 0.5% or less of Nd, and 1.0% or less of Sr, the balance being Fe and unavoidable impurities, and
 wherein in orthogonal coordinates expressed by the relationship between [W/(Mo+0.5W)] and (Co/W), values of [W/(Mo+0.5W)] and (Co/W) are not larger than the values represented by linear lines interconnecting a coordinate point A (1.1, 0.90), a coordinate point B (1.5, 0.55), and a coordinate point C (1.8, 0.55).   
     
     
         2 . A steam turbine comprising a rotor shaft including implanted rotor blades, an inner casing including stator nozzles implanted corresponding to said rotor blades and covering said rotor shaft including said implanted rotor blades, and an outer casing covering said inner casing,
 wherein said inner casing is constituted by the steam turbine casing according to  claim 1 .   
     
     
         3 . A main steam valve for controlling supply and stop of main steam obtained by a boiler with respect to a steam turbine,
 wherein a casing of said main steam valve is made of the high-strength heat resisting cast steel according to  claim 1 .   
     
     
         4 . A steam control valve for controlling a supply amount of main steam obtained by a boiler through a main steam valve which controls supply and stop of the main steam with respect to a steam turbine,
 wherein a casing of said steam control valve is made of the high-strength heat resisting cast steel according to  claim 1 .   
     
     
         5 . A steam turbine power plant including any of a set of a high-pressure steam turbine, an intermediate-pressure steam turbine, and two low-pressure steam turbines connected in tandem, and a set of a high- and intermediate-pressure integral steam turbine and a low-pressure steam turbine,
 wherein at least one of said high-pressure steam turbine, said intermediate-pressure steam turbine, and said high- and intermediate-pressure integral steam turbine is constituted by the steam turbine according to  claim 2 .   
     
     
         6 . A steam turbine power plant including any of a set of a high-pressure steam turbine, an intermediate-pressure steam turbine, and two low-pressure steam turbines connected in tandem, and a set of a high- and intermediate-pressure integral steam turbine and a low-pressure steam turbine, said power plant further including a main steam valve for controlling supply and stop of main steam obtained by a boiler and a steam control valve for controlling a supply amount of the main steam through a main steam valve,
 wherein at least one of said main steam valve and said steam control valve is constituted by the main steam valve and the steam control valve according to  claim 3 .