Influence of Intercritical Annealing Temperature on Mechanical Properties and Microstructure of 0.23%C Low Alloy Steel
The influence of intercritical annealing temperature on the microstructure and mechanical properties of an 0.23%C low alloy steel was undertaken in this work. The as-received steel was normalised and afterwards annealed in the (α+γ) region at 730OC, 750OC, 770OC and 790OC followed by quenching in hot water at about 50OC.Mechanical testing (tensile, impact and hardness) of the annealed samples were conducted at room temperature. The fracture surfaces of the impact test samples were examined using the scanning electron microscope (SEM). Micros structural evolution of the samples was also examined with an optical microscope. The results showed that all the evaluated mechanical properties were improved by intercritical annealing, with the samples treated at 790OC possessing the optimum combination of properties. The ultimate tensile strength (UTS), yield strength (YS), impact strength (IS), total elongation (TEL) and hardness of these samples improved by 2.7%, 13.7%, 19.7% and 31.05% respectively over the normalised sample. The microstructure photographs of the intercritically annealed samples revealed duplex structures of predominantly martensite in a ferrite matrix with little dispersions of either carbide or retained austenite, which is a typical characteristic of conventional dual phase steel.