Dimensional movement from heat treating, split into size change (uniform growth or shrinkage from phase volume changes) and shape change (bend, twist, out-of-round or dishing from uneven heating and cooling, residual stress and sagging). Controls include symmetric design, stress relief before hardening, fixturing, press quenching, marquenching, uniform agitation and gas quenching. Distortion drives grind stock and straightening, so it is usually the costliest heat-treat problem.
Distortion on the ring gears is 0.006 out of flat, put the next lot on the press quench.
Much distortion is baked in before the furnace: machining stress, asymmetric features and how parts are racked matter as much as the quench.
Also heard as
- movement
- warpage
- warp
Related terms
Growth
The increase in a part's size after hardening, caused mainly by austenite turning into bulkier martensite.
Potato chip
Shop name for a thin, flat part that warps into a dished or wavy shape during the quench.
Marquenching
Quenching steel into hot oil or salt just above Ms, holding to even out temperature, then air cooling.
Agitation
Forced movement of quenchant around parts by pumps, propellers or nozzles to speed up and even out cooling.
Stress relieving
Heating a part below its transformation range to relax residual stress from welding, machining or forming.