In contrast to conventional quenching processes in liquids, the quenching intensity and characteristics
of high-pressure gas quenching can be adjusted by variation of the gas velocity and pressure. The local
quenching intensity and hence the resulting hardness or distortion are not only depending on the
quenching parameters but are also influenced by the batch built and the part itself. The traditional
approach until now was to determine the optimum quenching parameters by performing several
expensive and time-consuming test trials.
To improve the process development a digital quenching simulation model that combines the fields of
computational fluid dynamics (CFD) and heat treatment process simulation was developed. It was
found that the gas flow and hence the quenching properties depend on both local (geometry of parts,
carrier, and chamber) as well as global influencing factors (fan characteristics, system pressure and
hydraulic resistances). Therefore, a CFD model that includes all these factors was realized. The
approach includes a heat transfer analysis to determine the local heat exchange coefficients on the
component level. By connecting the CFD and heat treatment simulation the local quenching
characteristics are used to compute the temperature history of the quenched part. Based on a thermo-
metallurgical heat treatment simulation the computed local cooling curves and metallurgical phase
compositions are used to accurately predict the part properties like microstructure and hardness.
Hardness results for different batch positions, batch setups or tray systems can now be computed
enabling an efficient virtual development of the gas quenching process. This method has been
successfully validated and applied for spindles to homogenize the heat transfer on the part and in the
batch resulting in constant core hardness over the part. The simulation can also be used to identify
causes of inhomogeneous distortion within batches by identifying unfavorable flow configurations.
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