Metal treatment – Stock – Ferrous
Reexamination Certificate
2000-11-29
2004-11-23
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Ferrous
C148S334000, C420S104000, C420S105000, C420S106000, C420S108000, C420S114000
Reexamination Certificate
active
06821360
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to heat-resisting steel. More particularly, the present invention relates to heat-resisting materials suitable for use in applications where high heat resistance and good mechanical strength are required, such as steam turbine rotors.
2. Background Art
Formerly, low alloy heat resistant steel such as 1Cr-1Mo-0.25V steel, and high-chromium heat resistant steel such as 12Cr-1Mo-VNbN steel were extensively used to produce components of thermal power plants, which are required to withstand high temperatures. In recent years, however, higher steam temperatures have rapidly come to be used during the operation of thermal power plants, so that the use of high-chromium heat resistant steel, which is superior to low alloy heat resistant steel in strength and environmental resistance, has increased. It has become possible to construct plants having higher performance through the use of such high-strength steel.
Thermal power plants now tend to be required to have both high thermal efficiency and excellent profitability. It is therefore becoming essential for components of the plants to have mechanical properties and workability that are equal to or better than those of conventional ones, and, in addition, to be excellent in profitability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide heat-resisting steel that is stable even in high steam temperature environments and that has excellent profitability.
We made studies to develop low alloy heat resistant steel having high-temperature strength comparable to that of high-chromium heat resistant steel, and, as a result, finally attained the present invention.
A first heat-resisting steel according to the present invention comprises 0.15-0.30 wt. % C, 0.05-0.3 wt. % Si, 0.01-0.7 wt. % Mn, 1.8-2.5 wt. % Cr, 0.15-0.23 wt. % V, 1.5-2.5 wt. % W, 0.01-0.02 wt. % Ti, 0.01-0.08 wt. % Nb, 0.005-0.03 wt. % N, 0.001-0.015 wt. % B, and Fe and unavoidable impurities as the remainder.
A second heat-resisting steel according to the present invention comprises 0.15-0.30 wt. % C, 0.05-0.3 wt. % Si, 0.01-0.7 wt. % Mn, 1.8-2.5 wt. % Cr, 0.15-0.23 wt. % V, 1.5-2.5 wt. % W, 0.3-0.8 wt. % Mo, 0.01-0.02 wt. % Ti, 0.01-0.08 wt. % Nb, 0.005-0.03 wt. % N, 0.001-0.015 wt. % B, and Fe and unavoidable impurities as the remainder.
A third heat-resisting steel according to the present invention is the above first or second heat-resisting steel in which all of Nb and a part of Fe are replaced with V and/or Ti to make the V content 0.23 (exclusive)-0.35 wt. %, and the Ti content 0.02 (exclusive)-0.03 wt. %, the heat-resisting steel thus containing no Nb other than that existing as the impurity.
A fourth heat-resisting steel according to the present invention is the above first or second heat-resisting steel in which all of Nb and Ti, and a part of Fe are replaced with V to make the V content 0.23 (exclusive)-0.35 wt. %, the heat-resisting steel thus containing no Nb and Ti other than those existing as the impurities.
A fifth heat-resisting steel according to the present invention is the above third or fourth heat-resisting steel in which a part of Fe is replaced with Ni to make the Ni content 0.1-3.0 wt. %.
A sixth heat-resisting steel according to the present invention is the above third or fourth heat-resisting steel in which a part of Fe is replaced with Cu to make the Cu content 0.1-3.0 wt. %.
A seventh heat-resisting steel according to the present invention is obtained by subjecting any of the above first to sixth heat-resisting steels to a heat treatment comprising the steps of normalizing the heat-resisting steel, and oil-cooling the normalized heat-resisting steel to a temperature of 300° C. or lower.
An eighth heat-resisting steel according to the present invention is any of the above first to seventh heat-resisting steels, useful for producing steam turbine rotors.
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British Search Report dated May 31, 2002, for application No. GB0029247.4.
Ishii Ryuichi
Tsuda Yoichi
Yamada Masayuki
Foley & Lardner LLP
Ip Sikyin
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