On the Role of Chromium in Dynamic Transformation of Austenite

Abstract

The effect of Chromium (Cr) on the dynamic transformation (DT) of austenite to ferrite at temperatures up to 430 °C above Ae3 was studied in a medium-carbon low-alloy steel.Hot compression tests were performed using Gleeble 3800 ® thermomechanical simulator followed by microstructural examinations using electron microscopy (FESEM-EBSD).Driving force calculation using austenite flow stress and ferrite yield stress on an inverse absolute temperature graph indicated that Cr increases the driving force for the transformation of austenite to ferrite; however, when the influence of stress and thermodynamic analysis are taken into account, it was observed that Cr increases the barrier energy and therefore, emerges as a barrier to the transformation. An analysis,

Influence of Process Parameters on Microstructure Evolution During Hot Deformation of a Eutectic High-Entropy Alloy (EHEA)

“…Recent studies on hot deformation of low carbon steels have shown that under the influence of stress and temperature, it is the pipe diffusion mechanism that is enhanced compared to lattice diffusion resulting in the dynamic transformation of austenite to ferrite. [49,50] Similar observations were made for weld cracking of Ni superalloys where, under applied stress, grain boundary diffusion or pipe diffusion was observed to be the dominant mechanism compared to lattice diffusion. [51] To quantify the contributions from lattice and pipe diffusion in the deformation process of the investigated EHEA, their diffusion coefficients were determined as a function of the applied strain rate by an analytical method using the flow curve data and activation energy.…”

The Effect of Retained Work Hardening on the Driving Force for Dynamic Transformation

“…for 0.25 s -1 and 0.5 s -1 , respectively. As expected, the amount of ferrite increases as the strain rate decreases due to larger diffusion distances of the alloying elements 18 .…”

“…Although the first deformation driving force values perfectly align with the observations in the literature 16 , the calculated driving forces in the second deformation employing strain rates of 0.25 s -1 and 0.50 s -1 were significantly lower than the total energy barrier (224 J/mol and 229 J/mol, respectively). Note that DT has been previously shown to take place every pass during rolling, and the interpass time affects the volume fraction of DT ferrite 18 ; thus, in the present work, it seems that the retained work hardening in between deformation plays a significant role in supplying a retained driving force to re-initiate DT in the second deformation. More specifically, the experiments with strain rates of 0.25 s -1 and 0.5 s -1 require additional driving forces of at least 41 J/mol and 36 J/mol, respectively, to initiate dynamic phase transformation, as displayed in Since the interpass time is 5 s, the 2 nd deformation starts after 7 s, which takes about 1.2 s to complete.…”

“…The MATLAB ® was developed using Levenberg-Marquardt algorithm and considering the degree of polynomial 'n' higher than 8 th order. The details of the analysis technique could be found in the following references 1,[16][17][18][19][20][21] . The first and second minima in each curve of Fig.…”

Microstructure Evolution, Mechanical Properties and Deformation Behavior of an Additively Manufactured Maraging Steel

“…Thus, an increase in the strain hardening rate is expected. The double differentiation method [34][35][36][37] was applied to the true stress-strain curves of Figure 10a to detect the change in the hardening rate during deformation. This technique is commonly utilized in hot deformation studies to track the evolution of microstructures and fluctuations in strain hardening rate [21,22].…”