Gas quenching of carburized aero‑engine gearbox gears
Gears in a geared-turbofan gearbox carry extreme loads at high speed, so their case hardness, core properties and geometry are tightly specified. High-pressure gas quenching is cleaner and more controllable than oil — but only if the quench is designed for the part.
One model, from carbon profile to final shape.
The work was carried out as the doctoral research of our founder, Bartosz Iżowski, PhD, at Rzeszów University of Technology.
The challenge
Carburizing gives a hard, wear-resistant case over a tough core. The quench that follows decides whether that case reaches its hardness — and how much the gear moves while it does. In a gas quench, the heat-transfer coefficient varies over the part surface with gas pressure, velocity and the part’s orientation in the furnace. Thin and thick sections cool at different rates, the high-carbon case transforms later than the core, and the result is a combination of residual stress and distortion that is hard to predict by experience alone.
The approach
The process was modelled as a coupled thermal–metallurgical–mechanical problem:
- Carbon diffusion during carburizing, giving the carbon profile through the case.
- Heat transfer in the quench, with surface heat-transfer coefficients representing gas pressure and flow conditions.
- Phase transformation kinetics dependent on local carbon content and cooling rate.
- Stress and strain evolution, including transformation strains, to predict residual stress and distortion.
What it enables
With a calibrated model, quench pressure, gas flow and part fixturing can be compared virtually. Hardness, case depth, residual stress and distortion are predicted for each variant, so trials are used to confirm a chosen route rather than to search for one.
Why it matters for you
The same methodology applies to carburized and through-hardened gears, shafts and bearing components in aerospace, rotorcraft and defense drivetrains — in gas, oil or polymer quenchants.
Gears moving after heat treatment?
Send us the drawing and the heat-treatment route. Under NDA, we will tell you what a model can predict.