A Physics-Based Low-Pressure Carburizing Model for 16MnCr5 with Case-Depth Comparisons and Parameter Identifiability

Low-pressure carburizing (LPC) models can support recipe screening, but numerical agreement must be separated from experimental validation and calibration. A one-dimensional model using concentration-dependent Ågren diffusivity, a prescribed boost carbon flux, zero-flux diffusion windows, a carbide reservoir and a non-isothermal tail is compared with four industrial trials on 16MnCr5 at 940–950 °C. Numerical verification includes an analytical solution, grid refinement and an independent COMSOL implementation. With no parameter fitted to this campaign, depths at 0.36 wt.% C are 894 and 866 µm for two free-surface trials, compared with hardness-based CHD550 values of 1036 and 907 µm measured at HV0.3: point deviations of −13.7% and −4.6%. A joint flux fit gives residuals of −4.9% and +5.2%; two-point leave-one-out transfer gives +10.6% and −9.6%. These are conditional deviations, not uncertainty-inclusive accuracy bounds. An empirical hardness bridge changes the uncalibrated depths by about 11%, and the available hardness traverses do not support statistical confidence intervals. The primary experimental limitation is the absence of measured carbon profiles: comparison is restricted to depth criteria, and predicted surface concentrations remain unverified. Flux and diffusivity sensitivities are nearly collinear for the two schedules. A single bore observation is 36% shallower than a free-surface observation from another trial, with unresolved load, quench and laboratory effects. Nominal gas-supply calculations suggest scope for flow-reduction experiments but disagree with cylinder weighing and do not establish transfer efficiency. The practical application is preliminary recipe screening and selection of informative follow-up measurements within the studied conditions; broader accuracy, concentration-profile validation and geometry corrections require further experiments.