Quenching Process Improvement Through Modeling

Computer modeling offers an excellent method to investigate heat treatment processes, especially processes that have quality issues, that are open to use of different alloys, or that are under development.[1-4] A recent presentation from Karlsruhe Institute of Technology[5] was an excellent example of this, where three variations of a novel tube quenching process showed experimental evidence that two of the processes resulted in tubes with cracks on the bore while the third process produced crack-free parts. Interested in investigating this in more detail using computer modeling, a study was initiated to investigate additional process variations to better understand the effect of quenching conditions on stresses and microstructural evolution in the part. With a goal of producing martensite and residual compressive stress in the bore of a 4140 steel tube, a matrix of hardening processes was developed and executed. Models examined heat transfer and also microstructural evolution, i.e. phase transformation kinetics. Results showed that the timing and rate of martensite formation, and bainite kinetics had a significant effect on both the in-process stress state and the residual stress state.