The purpose of this study is to determine the optimal design parameters of the heat treatment process (HTP) in the context of the multi-response surface optimization. An aim is to improve quality characteristics in the HTP by simultaneously optimizing hardness, stain yield and roundness via pre-heat and heat chamber heaters, number of vacuum, gas fan speed in quenching chamber and partial gas pressure. Taguchi orthogonal design and desirability function approach are applied to form the path of steepest ascent. Influential parameters from the hunting search and ant colony optimization metaheuristics are integrated to seek the optimum. The results proved that the hybrid approach based on the hunting search optimization mechanism was successfully applied in the study. The confirmation tests based on the predicted optimal results were verified and carried out to show considerable improvement. © (2012) Trans Tech Publications, Switzerland