1993 Volume 79 Issue 8 Pages 980-987
The effect of Cr, Mo, W, Mn and Ni contents on the toughness of a 2.25Cr-Mo-V based bainitic steel was investigated and microstructural factors 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 increased 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 improvement of toughness by increasing stacking fault energy which makes cross slip easier. The decrease in toughness with the addition of Mo over 1.5% may be attributed to the high precipitation density of coarse particles of M6C in the matrix. In addition, it is demonstrated that the toughness of the 2.25Cr-Mo-V steels is superior to that of the conventional 1Cr-Mo-V steel.
