Optimization of Heat Treatment Parameters to Improve Hardness of High Carbon Steel Using Taguchi’s Orthogonal Array Approach

Abstract

EN31 is a high carbon steel, used in manufacturing bearings, punches and gauges because of its better hardness. Heat treatment is one of the major process adopted to improve microstructural and mechanical properties of high carbon steels. The present investigation aims to improve hardness of EN31 high carbon steel through heat treatment. Parameters considered during this investigation were austenization temperature, soaking time, temper temperature and temper time. Microstructure examination was carried out to confirm the phases of heat treated EN31. Taguchi’s orthogonal approach was adopted to minimize the number of experimental runs. Influence of each parameter on the hardness was analyzed. The levels of each parameter were identified that maximize the hardness through S/N ratio. Identified optimal levels of parameters are 900 °C austenization temperature, 30 min soaking time, 150 °C temper temperature and 10 min temper time. A regression model for hardness has been established. Analysis of variance test was used to identify the significant parameters. Finally, the results were validated through confirmation experiments.