Effect of Grain Size and Residual Strain on the Dynamic Transformation of Austenite under Plate Rolling Conditions

Abstract

When austenite is deformed within the austenite phase field, that is, above the equilibrium transformation temperature Ae 3 , it partially transforms dynamically into ferrite. Here, rough rolling simulations are conducted at 1100 C on an X70 steel to study the influence of grain size and residual strain on this type of transformation. Three simulated roughing passes are applied with pass strains of 0.4 at a strain rate of 1.0 s À1 . The resulting stress-strain curves are recorded and analyzed. The volume fractions of ferrite and martensite (prior austenite) are determined on quenched samples by means of metallographic techniques. It is observed that dynamic transformation took place during the first roughing pass and that the volume fraction of transformed ferrite increases with the cumulative strain. Both the critical strain to the onset of dynamic transformation as well as the grain size decrease with pass number.

Dynamic Phase Transformation Behavior of a Nb-microalloyed Steel during Roughing Passes at Temperatures above the Ae3

“…These values demonstrate that the rate of peak stress increase during cooling can be significantly affected by the occurrence of DT once the volume fraction of ferrite reached above 5%. This observation is consistent with the results of an earlier work of the present authors [13][14][15].…”

“…Note that the samples were strained to 0.3 during each pass applied at a strain rate of 1 s −1 . A strain higher than the critical stains for the onset of DT [9][10][11][12][13][14][15] was selected so as to allow for DT to take place. Water spray quenching after R1, R3, and R5 were performed at minimum rate of 500 • C/s using the Gleeble high flow quenching system.…”

“…More recently, Rodrigues et al [13][14][15], investigated the phenomenon of DT under various industrial plate rolling simulation conditions. They found that the application of roughing passes under isothermal conditions can lead to the presence of around 8% of transformed ferrite after deformation.…”

Simulation of Microstructure Evolution in Ultra‐Heavy Plates Rolling Process Based on Abaqus Secondary Development

“…Recrystallization and grain growth evolutions during ultra‐heavy plate rolling processes have important influence on the rolling process and the microstructure of the steel plate. Through appropriate alloying design and deformation process control, the austenite after recrystallization has proper microstructure state like refined grain size and uniform distribution . Then after phase transformation the satisfactory microstructure and performance can be obtained.…”

“…Through appropriate alloying design and deformation process control, the austenite after recrystallization has proper microstructure state like refined grain size and uniform distribution. [7,8] Then after phase transformation the satisfactory microstructure and performance can be obtained. The real-time observation of recrystallization by experiment is hamstrung due to the complexity, especially recrystallization is affected by a variety of factors during the hot rolling process.…”