Modeling the effect of austenite deformation on the bainite structure parameters in low carbon microalloyed steels

Abstract

A modeling approach to calculate the kinetics of non-isothermal bainite formation in low carbon microalloyed steels is presented. The model development is based on experimental data obtained by means of deformation dilatometry and electron back scattering diffraction. It is suggested that the misorientations inherited from the plastically deformed austenite make a significant contribution to the misorientation distribution in the final microstructure. Taking the inheritance phenomenon into consideration, the model allows prediction of the transformation kinetics and the effective grain size of bainitic microstructure as a function of the austenite deformation level and the cooling rate.

Effect of ausforming and cooling condition on the orientation relationship in martensite and bainite of low carbon steels

“…Previously it was shown, that ausforming disturbs linearity of martensite [27] and bainite [28] crystallites usual for microstructures transformed from non-deformed austenite. In case of bainite, in particular, such an apparent bending appears because orientations of successively nucleated small subunits depend on corresponding local orientations of curved austenite lattice [29,30]. That is why the OR keeps approximately the same all along the interphase boundary.…”

Modeling of Microstructure and Mechanical Properties of Hot Rolled Steels

“…Kinetics of the martensite transformation is calculated using an empirical model from literature [4]. The bainite transformation model based on previously developed approaches [5] is briefly described below.…”

“…= is the volume of the element having a rectangular parallelepiped form; B B w ; l are its sizes determined by the equations: k ; k ; k ; k are empirical parameters.An average value of the bainite packet size is estimated as: primary elements total number[5]. In quantifying of granular (GB) and lath (conventional) (CB) morphology bainite volume fractions, it is supposed that transition to formation of the later takes place under the condition: value of the transformation driving force (empirical parameter).…”

Modeling Bainitic Transformations during Press Hardening

“…Tensile stresses also increase both the length and width of the bainite sub-units significantly [ 11 , 12 , 13 ]. On the other hand, deformation of the austenite prior to bainitic transformation leads to much finer bainite [ 14 ], shorter incubation time [ 1 ] and higher strength [ 15 ]. Moreover, there occurs a transformation-induced anisotropic eigenstrain at the same direction of the applied stress [ 8 , 11 ].…”

“…There is a long controversy whether the bainitic transformation kinetics should be described by a diffusion-controlled model or a diffusionless (autocatalytic-nucleation controlled) model, see [ 22 ] and references therein. According to the controversy different models exist, which describe the (stress and pre-strain free) austenite to bainite transformation [ 14 , 23 , 24 , 25 , 26 ]. Various kinetic models exist [ 9 , 27 , 28 , 29 ], which use mean-field descriptions of free energies of austenite and bainitic ferrite, with or without the contribution of mechanical energy, which is formulated as the product between the stress and the “shape strain”.…”