Patent ID: 6174132
Filing Date: 2001-01-16
Classification: B23K,C21D,F01D

Abstract:
A steam turbine comprising a rotor shaft, moving blades which are assembled on said rotor shaft, fixed blades which guide inflow of steam to said moving blades, and an inner casing which holds said fixed blades; the steam flowing into a first stage of said moving blades at a temperature of 610-660.degree. C. and under a pressure of at least 250 kg/cm.sup.2 ; wherein:said rotor shaft and, at least, first stage of said moving blades and first stage of said fixed blades are made of high-strength martensitic steel of fully-tempered martensitic structure which exhibits a 10.sup.5 -hour creep rupture strength of at least 15 kg/mm.sup.2 at a temperature corresponding to the inflowing steam temperature of the first stage of the moving blades, and which contains 9-13 weight % of Cr; and said inner casing is made of martensitic cast steel which exhibits a 10.sup.5 -hour creep rupture strength of at least 10 kg/mm.sup.2 at a temperature corresponding to said inflowing steam temperature of the first-stage of the moving blades, and which contains 8-12 weight % of Cr; wherein:said rotor shaft has a distance (L) of at least 5000 mm between centers of bearings in which it is journaled, and a minimum diameter (D) of at least 600 mm at its parts which correspond to said fixed blades, a ratio (L/D) between the distance (L) and the diameter (D) being 8.0-9.0,the diameters of those parts of said rotor shaft on which said moving blades are assembled are larger than diameters of those parts of said rotor shaft which correspond to said fixed blades; and widths of the moving blade assembling parts of said rotor shaft in an axial direction of said rotor shaft are stepwise larger on the downstream side than on the upstream side, and their ratios to the lengths of said moving blades decrease from said upstream side toward said downstream side within a range of 0.6-1.0; andsaid moving blades are arranged including at least 7 stages, and they have lengths of 35-210 mm in a region from an upstream side of the steam flow to a downstream side thereof; ratios between the lengths of said moving blades of the respectively adjacent stages are at most 1.2, and they increase gradually toward the downstream side; and said lengths of said moving blades are larger on said downstream side than on the upstream side.