A Kinetic Model to Predict the Rate of Austenitization During Continuous Heating of Electric Steels

摘要

The effects of heating and cooling rates on ferrite, pearlite/austenite/ferrite, bainite, martensite transformation temperatures (Ac_1, Ac_3, Ar_1, Ar_3, B_s, B_f and M_s) are of paramount importance for processing modern advanced high strength (AHSS) and other types of steels in fast continuous hot rolling/annealing/galvanizing processing lines. Complex chemical compositions of these steels are also important since they also magnify the effects of heating/cooling rates on the transformation temperatures. These temperatures and continuous cooling transformation diagrams can be calculated from the chemical composition of the steel and its austenite grain size for cooling treatments using commercially available programs such as JMatPro [1],Most thermo-mechanical processes and heat treatments of steels require a strict control of the temperature. For instance, intercritical annealing for production of dual phase steels requires heat treatments at high temperatures within the austenite+ferrite ( ) phase field (Ac_1 < T < Ac_3). In this case, the annealing temperature controls the volume fraction of austenite that transforms to ferrite, pearlite, bainite and/or martensite [2-6]. Severe ductility losses at high temperatures during hot rolling in steels [7] are often associated to formation of strain-induced ferrite films (-5-20 μm thick) at temperatures between Ar_3 and Ae_3 transformation temperatures [8-11]. In addition, Yada [11] reported that ferrite was formed during the deformation even above Ae_3 with para-equilibrium.