Quench hardening is the process of heating finished or pre-finished steel parts to a specific temperature in order to reach a phase transformation of steel to austenite (austenitization) followed by quenching in oil, water or brine to induce desired metallurgical properties. During this process, both macroscopic quantities such as temperature and heat duty and microscopic variables, such as austenite grain size, determine the quality of the quenched product. In this paper, we propose a novel model-based approach for optimizing the energy input to an austenitization furnace system by capturing the essential physics at both the aforementioned length scales. The model predicts the energy consumption of the system, the part temperature distribution and the austenite grain size distribution as a function of the processing time and processing conditions. An optimization scheme is proposed to minimize the furnace energy consumption without compromising the part heating requirements and product quality. (C) 2017 Elsevier Ltd. All rights reserved.