| 摘要 |
PURPOSE:A heat resistant steel especially suitable for the casing of the steam turbine for a large steam power plant, obtained by specifying the content of P, Sb, Sn and As among inevitable impurities in steel containing C, Cr, Mo, V, Al and B respectively in a predetermined ratio and a value obtained by adding Al to said content. CONSTITUTION:Heat resistant steel contains, on a wt. basis, 0.05-0.2% C, 0.5- 2.0% Cr, 0.5-2.0% Mo, 0.05-0.5% V, 0.002-0.1% Al and 0.0002-0.0030% B and comprises the remainder of Fe and inevitable impurities. In this case, it is an essential condition that a value obtained by adding the X value and the Al value represented by formulae to the content (ppm) of P, Sb, Sn and As among the aforementioned inevitable impurities is 2,920 deg. or less. This heat resistant steel is adapted to the main body of the aforementioned casing, a main steam closure valve and a heating valve. This heat resistant steel generates no crack in stress removing annealing after welding and further has characteristics such that crack propagation speed is slow in said uses.
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