EFFECTS OF CR, MO, W, MN AND NI ON TOUGHN ESS OF 2.25CR-MO-V ROTOR STEEL

The effect of Cr, Mo, W, Mn and Ni contents on the toughness of a 2.25 Cr-Mo-V based bainitic steel was investigated and microstructural fact ors which affect the toughness of this steel were discussed. Fracture appearance transition temperature (FATT) is decreased remarkably with the increase of Cr, Mo and/or Ni contents whereas the FATT is increase d with the addition of Mo in excess of 1.5% or with the addition of W. Mn exerts no significant effect on the FATT. Cr addition refines the bainitic microstructure by lowering the bainite start temperature (Bs) and improves the toughness. Ni addition also contributes to the impro vement of toughness by increasing stacking fault energy which makes cr oss slip easier. The decrease in toughness with the addition of Mo ove r 1.5% may be attributed to the high precipitation density of coarse p articles of M6C in the matrix. In addition, it is demonstrated that th e toughness of the 2.25Cr-Mo-V steels is superior to that of the conve ntional 1Cr-Mo-V steel.