Effects of Heavy Warm Deformation on Microstructure and Mechanical Properties of a Medium Carbon Ferritic-Pearlitic Steel

Abstract

The study of medium-carbon steel (0.36% C) with deformation induced spheroidized cementite produced by heavy warm deformation (HWD) was carried out as a potential substitution of conventional quenching and tempering (QT) or soft annealing (SA). After austenite deformation the HWD samples were cooled and heavily deformed (e∼1.6) at the temperatures below the γ-α transformation with a subsequent simulated coiling. To estimate the treatment sensitivity the effect of the heating due to the heavy deformation on the mechanical properties was studied using both isothermal and adiabatic processing routes. The mechanical properties after the various treatments show that the strength-ductility relation after HWD and QT are superior to that after CC or SA. The reason is in the presence of lamellar pearlite in the microstructure after CC and also partially after SA that deteriorates the reduction of area. A similar effect is observed after the adiabatic HWD treatment: the deformation heating at high HWD temperatures may lead to partial pearlite-austenite-pearlite transformation, which results in some lamellar pearlite in the final microstructure. HWD at 670°C with subsequent coiling simulation allows to get a microstructure with dispersed spheroidized cementite distributed homogeneously in fine grained ferritic matrix with an average grain size of 2 μm and an amount of high angle grain boundaries (HAGB) of about 65%. The features of ferrite and cementite after both HWD and QT have some important resemblances: fine homogeneous distributed cementite and fairly high amount of HAGB. As a result, the mechanical properties of the HWD samples are well comparable to those after QT.