| 摘要 |
PURPOSE:To develop a low-alloy steel excellent in stress corrosion cracking resistance and suitable for steam turbine material, by adding specific alloy contents to an Ni-Cr-Mo low-alloy steel and also by limiting respective contents of Si, Mn, and P to specific ranges. CONSTITUTION:The low-alloy steel used as a material for steam turbines driven by high-temp. and high-pressure steam has a composition containing, by weight, <=0.40% C, <=0.15% Si, <=0.60% Mn, <=0.010% P, <=0.030% S, 0.50-4.00% Ni 0.50-2.50% Cr, 0.25-4.00% Mo, and <=0.30% V, satisfying the compositional relations in Si+Mn+2P<=0.75%, and further containing either or both of 0.001-0.50%, in total, of at least one element among Al, Ti, Nb, W, B, and Ce and 0.003-0.015% Sn. Moreover, the above steel is an Ni-Cr-Mo low-alloy steel excellent in stress corrosion cracking resistance having a structure in which old austenite grain size is regulated to >=4 by ASTM grain size number.
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