| 摘要 |
PURPOSE:To increase reliability against fracture at high temp. and to provide high toughness at room temp., by constituting by use of a martensitic steel in which creep rupture strength and impact value are increased by specifying Cr equivalent as well as respective compositional ranges of components. CONSTITUTION:The titled stacking bolt is formed of the martensitic alloy steel having a 100,000hr creep rupture strength at 450 deg.C of >=45kg/mm<2> and a 20 deg.C V notch Charpy impact value of >=5kg-m/cm<2>. In order to obtain the above high creep rupture strength, the steel composition is regulated so that it consists of, by weight ratio, 0.5-0.2% C, <=1% Si, <=1.5% Mn, 1-2.5% Ni, 8-15% Cr, 1.0-3.5% Mo, 0.05-0.30% V, 0.05-0.20% Nb and Ta independently or in combination, <=0.1% N, and >=75% Fe. Further, it is preferable that Cr equivalent is regulated to about 10 or below. The above steel is subjected to total tempering to be formed into martensitic structure. By use of this steel, embrittlement of stacking bolts for gas turbine during use can be minimized.
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