Application of central composite design in investigating the effect of heat treatment process on mechanical properties of AISI 440C martensitic stainless steel

The influences of heat treating processes with specific hardening sequences on mechanical properties of the AISI 440C martensitic stainless steel were experimentally investigated. The central composite design (CCD) was used to carry out all experiments by varying process times with particular hardening sequences. Analysis of variance (ANOVA) was used to determine whether there were any statistically significant factors of heat treating process affecting hardness and impact toughness of the heat-treated steel. The results showed that the quenching time and holding time were statistically significant whereas the two-factor interaction were not sufficient at the level of significance of 0.05 based on ANOVA result of hardness. Based on ANOVA result of impact toughness, the most statistically significant factor in predicting impact toughness was the quenching time.