EVALUATION OF THE INFLUENCE OF INTERCRITICAL TREATMENT VARIABLES ON THE TRANSFORMATION BEHAVIOUR OF A CARBON STEEL

Abstract

This research study was focused on determining the intercritical treatment conditions for optimized martensite and ferrite formation for enhanced strength and plasticity in plain carbon steels. As-received plain carbon steel of predetermined composition was used as rest material. Ferrite/pearlite structure was produced for use as initial microstructure before cold rolling to achieve varied degrees of deformations. Intercritical anneals at 740⁰C, 760⁰C, and 780⁰C for various holding times before quenching in water was subsequently performed on the samples. The transformation behaviour was studied with the aid of optical microscopy and hardness curves obtained by plotting hardness values against log of soaking time. From the results it is observed that the structural evolution when intercritical annealing is carried out at 740⁰C and 760⁰C, is characterized by one mode and four transformation stages; while two transformation modes consisting of five and three transformation stages, were observed when treatment is carried out at 780⁰C. Schematic models were used to explain the mechanism of each stage of transformation observed.