Why parts distort
Distortion comes from two forces: thermal stress (sections cooling unevenly) and the phase change from austenite to martensite, which expands in volume.
Thin, long or asymmetric shapes warp most easily because heat leaves the part unevenly.
Residual stress locked in by prior forming or machining is “released” as warping once the part is heated.
How we reduce distortion
- Stress-relieve before hardening to release forming stresses.
- Heat uniformly and slowly enough to limit internal temperature gradients.
- Choose the right quenchant—oil or polymer instead of water—to soften thermal shock.
- Use jigs/fixtures or press-quenching for flat parts that must stay flat.
- Lay parts on the belt/tray so they do not pile or overlap.
What if a part already warped
Slightly warped parts can sometimes be straightened while still warm after tempering—carefully, to avoid cracking.
For tight-tolerance work, leave a machining allowance and grind/turn to size after hardening.
The best fix is designing the process together up front; we assess it from your geometry and required tolerances.
FAQ
How much do dimensions change?+
It depends on grade, geometry and quench method—usually small, a fraction of a millimetre. Tight-tolerance parts should allow stock for post-grinding.
Can you straighten parts after hardening?+
Sometimes, especially while warm, but there is a crack risk. Planning an allowance up front is safer.
How is distortion controlled in bulk fastener lots?+
With a belt furnace for uniform temperature, controlled quenching, and dimensional sampling every lot.
