Dynamic Transformation of a Low Carbon Steel at Temperatures above the Ae3

Abstract

The dynamic transformation of austenite was studied in a 0.06%C low carbon steel by deforming to strains of 0.25–5.0 at strain rates of 0.04 and 0.4 s–1 over the temperature range 877–917°C. All these temperatures are at or above the conventional Ae3. Two critical strains were detected, the first (about e=0.2) was for the formation of strain-induced ferrite; the second (about e=1.5) was the critical strain for the reverse transformation, which was gradual and only observed in specimens deformed at the lower strain rate. After deformation, the strain-induced ferrite was stable for about 60 s of isothermal holding. However, after this time, the reverse transformation began to take place, approaching saturation in about 240 s. The influence of strain, strain rate and temperature on the dynamic transformation is described. The results indicate that reverse transformation is unlikely to take place in the finishing stands of strip mills due to the high strain rates and short interpass times involved. It is also suggested that conventional phase diagrams do not apply to austenite undergoing deformation in rolling mills.