Mean field model of phase transformations in steels during cooling, which predicts evolution of carbon concentration in the austenite

The objectives of the paper were twofold. The first was exploring possibility of fast and reliable modelling of phase transformations during cooling of steels, accounting for the evolution of the carbon concentration in the austenite. Existing discrete models require long computing times and their application to optimization of industrial processes is limited. Therefore, a model based on the modified JMAK equation was proposed. Control of the carbon concentration in the austenite during ferritic and bainitic transformations allowed to predict incomplete austenite transformation and occurrence of the retained austenite. Moreover, prediction of the onset of pearlitic transformation after the bainitic was possible. The model was validated by comparison the predictions with the results of physical simulations. Numerical simulations for various industrial processes were performed. Problem of the difference in the incubation time between isothermal and constant cooling rate tests was raised.

Thermo-Elasto-Plastic Analysis of Pearlitic Transformation Plasticity under Combined Bending-Tensile Loading

In a previous study, we showed the anisotropy of plastic strain due to the pearlitic transformation and proposed a hydrostatic pressure-dependent constitutive equation to describe this phenomenon. In the present study, we assess the validity of this model using a bending-tensile loading system to experimentally and numerically analyze and characterize the pearlitic transformation plasticity. First, the maximum bending deflections due to the austenite-pearlite transformation were measured under different loadings and then transformation-plasticity coefficients were determined. Furthermore, as was done for bending-tensile loading tests, the pearlitic transformation plasticity was simulated using Abaqus Standard under the same austenitization and loading conditions as in experiments, and the calculated results for pearlitic-transformation plastic deformation are compared with the experimental results. The results show that the transformation plastic deflection due to the pearlitic transformation decreases with increasing applied tensile stress. In addition, this behavior can be described by a hydrostatic pressure-dependent model in large-deformation theory.

Experimental Investigation of Transformation Plastic Behavior under Tensile-Compressive-Torsional Stress in Steel

A tensile/compressive-torsional biaxial testing system was employed and tensile/ compressive-torsional tests were performed for the hollow specimen, which was loaded and the austenized specimen was cooled so that pealrite transformation accompanied by transformation plasticity occurred and axial and torsional strain were measured. Furthermore, the elastic-plastic constitutive equation due to phase transformation based on the hydrostatic pressure dependent model was proposed, and the validity of this equation was discussed experimentally. The test results showed the transformation plasticity coefficient due to pearlitic transformation of S45C depends on the loading direction, and these behaviour can be appropriately expressed by the hydrostatic pressure dependent model than the isotropic model.

Effects of Ce or Nb Addition on Nucleation of Pearlite in High Carbon Steel

The high-carbon steel was micro-alloying by Ce and Nb respectively, and the effect of micro-alloying on the nucleation of pearlite was reported in the present work. The results show that the pearlite could nucleate in rare earth sulfide inclusions and Nb-containing precipitates. The formation of NbC caused the C-depleted zone, promote the formation of proeutectoid ferrite of the pearlite. And the strain energy caused by rare earth sulfide inclusions will provide activation energies for pearlitic transformation. The inclusion and precipitates will increase the rate of nucleation of pearlite and refined the microstructures of pearlitic steel.