Determination of heat transfer coefficient during quenching of an alloy steel by in-situ plant testing

For accurate phase transformation modeling during quenching, characterizing the heat transfer process specific to the quenchant / steel combination which will take into account the bath condition, circulation levels etc., is required. This in turn, requires the description of the surface heat flux or heat transfer coefficient as a boundary condition. This work reports the development of equipment for determining the heat transfer coefficient during quenching of alloy steels in the plant. The equipment comprises of a portable furnace for deployment at the plant near the quench tank, a hand held unit with an alloy steel probe attached to the end of the unit instrumented with thermocouple and data logger. The equipment is designed to record the temperature of the probe during immersion quenching under plant conditions. The cooling curve thus obtained is input to the software for computing the heat transfer coefficient as a function of the surface temperature of the probe. A finite element based software coupling inverse heat transfer with austenite decomposition developed as a part of this research work is used in conjunction with the equipment for analyzing the cooling curve. The equipment was extensively tested in both laboratory and industries for various steel/quenchant combinations. This paper reports a set of results obtained with quenching of 100Cr6 grade steel in two different industrial quenchants in a heat treating plant manufacturing bearings. Copyright © 2012 ASM International® All rights reserved.