On the influence of alloying elements on the bainite reaction in low alloysteels during continuous cooling

The CCT diagrams of a class of Fe-(0.1-0.6)C-(0.4-2.0)Si-(0.4-2.0) Mn-(0.5- 2.0)Cr-(0.0-0.8)Mo steels are predicted by an artificial neural network (AN N) model. The results indicate that an increase in carbon concentration (C wt%) gives rise to a decrease in bainite start (BS) temperature. The rate o f decrease depends also on cooling rate. Additions of Si, Mn, Cr and Mo all decrease the bainite start temperature. The dependencies for different all oying elements vary: 32, 100-120, 100-130, and 70-150 degrees C per wt% of Si, Mn, Cr and Mo, respectively. Mn shifts the whole bainite transformation region to the far right-hand side of the CCT diagram, while C, Cr, and Mo have considerable, and Si has minor effects on the incubation period of bai nite. Mn and Cr significantly decrease the MS temperature, while Si only ha s a minor influence. When Mo < 0.5 wt% it has a minor influence, whilst whe n Mo > 0.5 wt%, it increases MS temperature. Quasi-isochronal and quasi-iso thermal methods have been used to analyze the influence of the proportion o f Mo to C upon the BS and incubation period. Attempts, for qualitative expl anations using the shear and diffusion mechanism, as well as a certain amou nt of thermodynamic analysis, have been made to interpret the influence of alloying elements on the nucleation of the bainite reaction. The results su pport that bainite reaction takes place utilizing a diffusion-controlled me chanism. (C) 2000 Kluwer Academic Publishers.