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

Abstract

A high-strength martensite heat resisting steel which has long-time creep rupture strength required for steam temperature condition of 600-630° C. and toughness at room temperature, and which is suitable for use as a material of a steam turbine rotor shaft and as large-sized forged steel with an improvement of hot forgeability. A method of producing the steel and applications of the steel are also provided. The high-strength martensite heat resisting steel contains 0.05-0.20% by mass of C, 0.1% or less of Si, 0.05-0.6% of Mn, 0.1-0.6% of Ni, 9.0-12.0% of Cr, 0.20-0.65% of Mo, 2.0-3.0% of W, 0.1-0.3% of V, 2.0% or less of Co, 0.02-0.20% of Nb, 0.015% or less of B, 0.01-0.10% of N, and 0.015% or less of Al, (W / Mo) being 4.0-10.0.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a novel high-strength martensite heat resisting steel which has superior creep rupture strength at high temperatures of 600-630° C. and which is suitable for use as large-sized forged steel, and to a method of producing the novel steel. Also, the present invention relates to a rotor shaft of a steam turbine, a method of producing the rotor shaft, a rotor blade and a stator nozzle of the steam turbine, and a steam turbine power plant.[0003]2. Description of the Related Art[0004]Materials having superior high-temperature strength are required for various members of a steam turbine which are exposed to high temperatures. In reply to such requirement, a practically used material of a steam turbine rotor shaft has been changed from CrMoV steel to 12Cr steel, i.e., ferrite-base heat resisting steel having superior high-temperature strength. The steam turbine rotor shaft is required to have not...

AI Technical Summary

Benefits of technology

[0006]An object of the present invention is to provide a high-strength martensite heat resisting steel which has long-time creep rupture strength required for steam temperature condition of 600-630° C. and toughness at room temperature, and which is suitable for use as a material of a steam turbine rotor shaft and as large-sized forged steel with an improvement of hot forgeability, and to a method of producing that steel. Another object of the present invention is to provide a steam turbine rotor shaft and a method of producing it, a steam turbine rotor blade and a method of producing it, a steam turbine stator nozzle and a method of producing it, as well as a steam turbine and a steam turbine power plant, including the method of producing the steam turbine, in which the turbine blade in a stage using steam to cool the rotor has a larger height by increasing the high-temperature tensile strength, and higher thermal efficiency is ensured.

Problems solved by technology

If the toughness at room temperature is low, there is a risk that the rotor shaft may cause brittle rupture at the start of the steam turbine.

Meanwhile, steam turbines have recently been improved with intent to realize higher efficiency and larger capacity, but a thermal power plant operating at steam temperature of 650° C. is not yet realized.

The reasons reside in not only the state of the art that the high-temperature material technology for the entire plant is still insufficient, but also the problem of reduction in the material cost which is necessitated from a market trend toward a lower cost.

The above-described materials of the turbine rotor shaft adapted for steam temperature of 600° C. or above are relatively high in cost.

A primary one of factors pushing up the cost is poor productivity.

In producing a large-sized forged product, however, B noticeably reduces productivity because of increasing forging resistance and narrowing a forgeable temperature range.

Thus, the production cost is increased.

Images