Steam turbine rotor shaft

Claim 1

A steam turbine rotor shaft comprising a shaft formed of forged and precipitation-hardened austenite steel consisting essentially, by weight, of 0.01-0.10% C, not more than 1.0% Si, not more than 2.0% Mn, 12-16% Cr, 24-27% Ni, 0.5-1.5% Mo, 1-2.5% Ti, 0.2-0.4% Al, 0.1-0.4% V and the balance substantially Fe, said austenite steel having as a whole austenite structure having a γ' phase precipitated therein, and a metal member of better bearing characteristics than such forged austenite steel provided on an outer surface of a bearing portion of a journal section of said shaft, said metal member comprising a plurality of layers of build-up welding applied directly to said shaft including a first layer formed by use of a welding rod of a Ni base alloy consisting essentially, by weight, of 0.01-0.1% C, 0.5-3.5% Mn, 0.2-1.0% Si, 0.2-1.0% Cu, 60-75% Ni, 0.2-1.0% Al, 1.5-3.0% Ti, 10-20% Cr, 0.5-1.5% Nb and the balance substantially Fe, while a second layer and succeeding layers are formed by use of welding rods of low alloy steel consisting essentially, by weight, of not more than 0.1% C, not more than 1.0% Si, not more than 2.0% Mn, 0.3-3.0% Cr, nor more than 2.0% Mo and the balance substantially Fe such that a surface of said metal member to be in contact with a bearing is formed of low alloy steel containing Cr of 0.3-3.0 weight percent.