| 摘要 |
PURPOSE:To provide low alloy steel excelling in resistance to embrittlement at high temp. and having superior toughness by limiting the content of P, Sb, Sn, As, and O as impurities to a specific range in Mn-Ni-Cr-Mo-V steel having a specific composition. CONSTITUTION:The low alloy steel consists of, by weight, 0.06-0.35% C, <=0.10% Si, 0.20-0.50% Mn, 3.25-4.00% Ni, 1.00-2.00% Cr, 0.25-0.50% Mo, 0.07-0.15% V, and the balance Fe with inevitable impurities. In this composition, the inevitable impurities, i.e., P, Sb, Sn, As, and O are incorporated in relations satisfying, by ppm, (10P+5Sb+4Sn+As)X10<-2=0.625XO+25. This low alloy steel is suitable for use as material for low pressure turbine rotors and the like and has superior resistance to embrittlement after long-period driving even if steam temp. rises. Moreover, it has such excellent properties as high strength, high toughness, highly reliable resistance to brittle fracture, and the like.
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