Drawing of CCCT diagrams by static deformation and consideration deformation effect on martensite and bainite transformation in NiCrMoV steel

In this article, three Compression Continuous Cooling Transformation (CCCT) diagrams of NiCrMoV steel were considered that indicate induced transformations by compression during continuous cooling of austenite. CCCT diagrams of this steel were compared with its Continuous Cooling Transformation (CCT) diagram. In comparison, it was deduced that in all three CCCT, Md and Bd have increased, the probable nose of bainite has shifted to left and the bainite area has increased. The phenomenon of enhancing Md and Bd in CCCT was justified by thermodynamical and metallurgical concepts. Thermodynamical consideration indicated that the induced stress at higher temperatures results in to increasing mechanical driving force and decreasing total free energy of transformation. Metallurgical considerations specified that if the deformation temperature is selected so that the strength of austenite after deformation increases, the essential shear for martensite transformation (MT) and bainite transformation (BT) will get more difficult; therefore, Md and Bd decrease. But if during or after deformation, recrystallization or full recovery process is onset, the structure of austenite gets softer and so the essential shear for MT and BT gets easier and Md and Bd increase. In addition, it was characterized that by deformation accompanying dynamic recrystallization (DRX) or static recrystallization (SRX), the grains get finer, thus in finer grains, nucleation of bainite gets easier than nucleation of martensite. Thus, bainite becomes more preferable than martensite. So the probable nose of bainite in CCCT diagrams shifts to left relative to CCT and the bainite area increases.