Comparison of Quenching Processes for Hardening a Coil Spring

Intensive quenching has been proposed as a new or underused technology for heat treatment of steel parts that offers the capability of improved product performance due to highly compressive surface residual stresses. However, the science behind intensive quenching has not been well documented in terms of evolution of microstructure and stress. Using the heat treat simulation software, DANTE™, conventional oil quenching and intensive quenching of an automotive coil spring made from 9260 steel are compared to examine differences between the two quenching methods. From these analyses, both methods are predicted to produce nearly the same metallurgical phases and amounts thereof. However, there is a significant difference between the processes with respect to the temperature history and the timing of austenite decomposition on the surface versus in the part core. This large difference in the timing of martensite formation during intensive quenching is responsible for the achievement of high compressive surface stresses in this part.