Size change from heat treatment, as distinct from warping. Martensite takes up more volume than the annealed structure, so hardened parts typically grow on the order of 0.001 inch per inch, while tempering shrinks them slightly back. Later transformation of retained austenite causes more growth in service, which upsets gauges, bearing fits and press fits.
Rings grew 0.0012 on the OD in hardening, so take that out of the grind stock on the next lot.
Also heard as
- size change
- heat treat growth
Related terms
Distortion
Unwanted change in shape or size of a part during heat treatment, such as bowing, warping or ovality.
Retained austenite
Austenite that fails to transform during the quench and survives at room temperature inside hardened steel.
Sub-zero treatment
Chilling hardened steel well below room temperature to turn retained austenite into martensite.
Tempering
Reheating hardened steel below its lower critical temperature to trade some hardness for toughness.