Modeling of the Steel Microstructure Gained after the Application of an Ultra-Fast Heat Treatment

The current work elucidates the phase transformation and carbide dissolution during rapid heating followed by short austenization and quenching to room temperature. For this work, dilatometry experiments were carried out in medium carbon low alloy steel containing chromium and molybdenum (42CrMo4).The thermal cycle of the sample was analyzed with the use of Thermocalc  and Dictra. The simulation results indicate that the high heating rate and short austenization time limits diffusion and the alloying elements segregate at the interfaces between carbides and ferrite. In addition, the segregation of alloying elements at the interfaces in conjunction with the rapid heating rate and the short dwelling time leads to incomplete dissolution of carbides and the formation of austenite with varying sizes and different carbon content, which in some cases reaches 1% wt; this of course can be of significance as it affects phase transformations and lead in retaining the austenite during quenching. The carbide morphology, size and type could be revealed only after Transmission Electron Microscopy (TEM) analysis. The microstructure consists of bainite, martensite and undissolved carbides confirming the results of simulation. Further investigation in the effect of chemical composition and size of austenite during bainitic and martensitic transformation is necessary and thorough study on the effect of the alloying elements on the transformations mentioned above.