Grain-Refining ability of ultra-rapid annealing for low-carbon steel: Severe plastic deformation

Abstract

To study the grain-refinement ability of ultra-rapid annealing (URA), heating rates from 0.3 °C/s up to 1200 °C/s with conventional annealing and URA in the intercritical temperature range were performed on severely deformed low-carbon steel. The results show that recrystallization in conventional annealing is completed below the critical temperature of Ac1 without grain refinement. URA up to 730 °C at a heating rate of 200 °C/s causes grain refinement due to full interaction between the recrystallization and phase transformation. URAs up to 730 °C with heating rates of 600 °C/s and 1000 °C/s lead to partial grain refinement and no grain refinement, respectively. During annealing with a heating rate of 1200 °C/s, the temperature should reach 760 °C for the occurrence of recrystallization leading to grain refinement. The sample URAed at 600 °C/s up to 730 °C shows the maximum hardness due to fine grains being partially formed.