Influence of Induction versus Furnace Tempering Process on Mechanical Properties of Alloy Steel

Tempering, an important step in the heat treatment of steel alloys, can be carried out through different methods, with primary consideration of heating rate and soak periods. Furnace tempering relies on convection and conduction to heat the steel from surface to core. Steel can also be tempered through induction heating, for which the steel is heated from eddy currents flowing through the material and the Joule heating effect. Therefore, induction tempering operations typically result in more rapid heating and shorter times compared to furnace tempering. Heating rate and soak time are known to influence the microstructure and mechanical properties of the tempered steel, so these must be factored into the recipe plan. The Holloman-Jaffe relationship remains an industry standard in steel heat treating, but limitations of the relationship are not always addressed. The goals of this project are to improve the way heat treaters optimize tempering times and temperatures and to determine if the tempering process is fundamentally different for longer-time low temperature vs shorter-time higher temperature tempering. The material parameter, C, represents material differences in response to the tempering process. We also consider methods for determining C, and the impact of this value on the resulting recipe prediction.