Thermal and Metallurgical Effects Associated with Gas Carburized and Induction Hardened Components

Dimensional distortion occurs due to the thermal and transformation stresses formed during the heat treatment processes. Taguchi and Factorial design of experiment concepts were applied to optimize the operating variables involved in the gas carburising and induction hardening processes so as to minimize the geometrical distortions. Experimental data obtained for the materials EN353, EN351, AISI 4140, and AISI 9255 were analyzed by Response graph method and Signal to Noise method. Even though, EN 351 and EN 353 are having the same carbon percentage, EN 353 gives minimal dimensional and volume changes because of the presence of three alloying elements namely cobalt, molybdenum and nickel. Analysis by variance (ANOVA) results indicated that the furnace temperature and quenching time in the gas carburising process were the variables which had more influence on distortion. The percentage deviations between the experimental and predicted results for the runout and helix variations were in the range of 7 to 10%.