Dynamic transformation behavior of a deformed high carbon steel at temperatures above the Ae3

Abstract

The dynamic transformation behavior of deformed austenite was studied in a 0.79%C high carbon steel over the temperature range 743-823°C. The experiments were carried out in torsion under an atmosphere of argon and 5% H2. All these temperatures are above the orthoequilibrium Ae 3 temperature of the steel. Strains of 0.25-4 were applied at a strain rate of 4 s-1. The experimental parameters were varied in order to determine the effects of strain and temperature on the formation of strain-induced ferrite and cementite. The critical strain for dynamic transformation was about 0.20. The volume fractions of the transformed phases increased with strain and decreased with temperature. The observed ferrite structures are Widmanstätten in nature and appear to have formed displacively. The carbon diffusion times required for formation of the observed spheroidal cementite particles were calculated; these are consistent with the occurrence of interstitial diffusion during deformation. Similar calculations indicate that substitutional diffusion does not play a role during dynamic transformation. © 2013 ISIJ.