Effects of electromagnetic induction on growth kinetics of case hardened layers

Abstract

Induction heating using medium or high frequency currents has been proposed as a means of achieving improved layer growth kinetics during case hardening. Experimental research on the carburising of 21TiMnCr12 (18HGT) steel in natural gas by induction heating with medium frequency currents (2000 Hz) has demonstrated significant process acceleration. A model of the carburising process has been derived by statistical processing of the experimental data from a designed experimental programme. The diffusion coefficients and the adsorption rate constants in these processing conditions were derived using the Popov methodology, based on criteria solution of Fick’s second law. The diffusion coefficient and adsorption rate constant values obtained were approximately two orders of magnitude higher than those obtained for conventional processing in resistance furnaces (∼10−5 versus ∼10−7 cm2 s−1). The form of the iso-property fields (constant values of the total case hardened depth for different values of the heat and time process parameters) calculated from the mathematical model demonstrates the highly accelerated kinetics obtained during induction carburising.