Simulation of the growth of austenite during continuous heating in low carbon iron alloys

Abstract

The growth of austenite from martensite or carbon-supersaturated ferrite matrix during continuous heating, which accompanies carbon diffusion in the growing austenite, was studied by DICTRA and linearized gradient approximation extended to include soft impingement of diffusion fields in the matrix. While the austenite growth is controlled by carbon diffusion in ferrite at an early stage, it is controlled by diffusion in austenite at the intermediate and late stages. At a low heating rate, the austenite-finish temperature A f is almost equal to the Ae 3 temperature of the alloy, whereas at a high heating rate, A f exceeds the Ae 3 to a progressively larger extent with the increasing heating rate and matrix grain size. At a very high heating rate, i.e., 10 5 -10 6°C /s, the mobility of a/c interface is likely to have a significant influence on the growth of austenite, and the untransformed ferrite matrix is transformed in a massive mode. These results are in accordance with the earlier observation of austenite formation during rapid heating in a low carbon iron alloy.

‘Flash’ Annealing in a Cold‐Rolled Low Carbon Steel Alloyed With Cr, Mn, Mo, and Nb: Part I ‐ Continuous Phase Transformations

“…Of particular interest is the finding that the austenite transformation in a hypereutectoid steel with initial martensitic microstructure happens in martensitic (diffusionless) mechanism at heating rates above 3500 °C s −1 . The anisothermal formation of austenite was kinetically described for different initial microstructures by Rödel and Spies (ferrite‐cementite) and Enomoto and Hayashi (martensite). However, neither of these theoretical studies clearly defines the transition temperatures nor provide experimental evidence of such.…”

The Effect of Heating Rate on the Microstructure of a Soft-Annealed Medium Carbon Steel

“…The works of Rödel and Spies and Enomoto and Hayashi on initial ferrite‐pearlite or martensitic microstructures, respectively, have provided a kinetic description of the process of austenite formation during continuous heating. However, the effect of the heating rate on austenite formation has not been kinetically described in a spheroidized ferrite‐cementite mixture.…”

A simulation study of pearlite-to-austenite transformation kinetics in rapidly heated hot-rolled low carbon steel

“…Austenite formation in the inter-critical region has been extensively studied [19][20][21]. Austenite growth in the given steel can be controlled by controlling the carbon diffusion in ferrite [22]. Austenite formation takes place in three basic steps: dissolution of pearlite into austenite (Step-I), growth of austenite into pro-eutectoid ferrite (Step-II), homogenization of the austenite formed (Step-III) [23].…”