EFFECTS OF CR, MO, W, MN AND NI ON CREEP- PROPERTIES OF 2.25CR-MO-V ROTOR STEEL

The effect of Cr, Mo, W, Mn and Ni contents on the creep properties of a 2.25Cr-Mo-V based bainitic steel was investigated and microstructur al factors which affect the creep rupture strength were discussed. The creep rupture strength is decreased by increasing Cr, Mn and Ni conte nts although it is slightly increased with the addition of W. The effe ct of Mo is very small. Addition of Ni in excess of 1.8% decreases the creep rupture strength remarkably. Preferable precipitation of Cr23C6 and Cr7C3 due to the increase of Cr content suppresses the precipitat ion Of V4C3, and decreases the creep rupture strength. Ni and/or Mn ad dition decreases the creep rupture strength because the stacking fault energy which makes cross slip easier is increased. No further improve ment of creep rupture strength due to solid solution strengthening is expected by the addition of Mo in excess of 0.8%. W contributes to the increase in creep rupture strength through solid solution strengtheni ng effect. In addition, it is concluded that the creep rupture strengt h of the 2.25Cr-Mo-V steels equals or exceeds that of the conventional 1Cr-Mo-V steels.