Effect of billet microstructure and deformation on austenite grain growth in forging heating of a medium-carbon microalloyed steel

We prepared samples with different ferrite-pearlite characteristics and deformation by heat treatment and Gleeble thermocompression respectively. Then, the different samples are rapidly heated to 1200 degrees C for 60 s to study the austenite grain growth. The study results show that the ferrite-pearlite characteristics has little effect on austenite grain growth. With the mean austenite grain size (MAGS) of billet microstructure increasing from 14 mu m to 56 mu m, the MAGS after heating only increases from 47 mu m to 56 mu m. With the cooling rate of billet samples increasing from 0.1 degrees C/s to 1.0 degrees C/s, the MAGS after heating has basically no change. However, the deformation of billet samples has significant effect on the austenite grain growth. With the deformation at 1150 degrees C increasing from 10% to 50%, the MAGS after heating decreases from 63 mu m to 31 mu m. In the meanwhile, the mean distance between element segregation bands decreases from 115 mu m to 33 mu m, and the mean width of element segregation bands decreases from 70 mu m to 20 mu m. Electron probe microanalysis shows that the segregation region has higher Si, Cr, Mn and V contents, which generate stronger solute drag effect on austenite grain boundaries. Deformation can crush the as-cast grains and make the segregation bands fine and dispersed, further refining the austenite grains after heating. (C) 2021 Elsevier B.V. All rights reserved.