Temperability
Temperability is the ability of a steel to harden to a useful depth during quenching, describing how readily martensite forms through the cross-section. In practice, higher temperability means a thicker section can achieve a more uniform hardened core after quench, reducing the risk of a hard skin with a soft core.
On the shop floor, temperability drives critical decisions about stock allowance, roughing sequence, and heat-treat scheduling. When a shaft, die, gear blank, or fixture plate exceeds the effective hardening depth of the selected steel, the quench can leave a soft core even though the outer surface meets hardness spec. That hidden softness leads to inconsistent cutting forces, delayed size change, and dimensional drift that undermines CNC tolerances. Steels with better temperability—like 4140 or 4340—are preferred for thick or complex sections because they harden more uniformly through the cross-section. The safe sequence is to rough machine in the softer condition, heat treat, temper, and then finish machine critical features after the final thermal cycle. During inspection, controlling part temperature and allowing normalization before measuring prevents thermal expansion from skewing results.
Is temperability the same as tempering?
No. Temperability is a material property that describes how deeply a steel hardens through the cross-section during quenching. Tempering is a separate heat-treatment step performed after quenching to reduce brittleness and improve toughness.
Why does temperability matter for CNC tolerances?
Because final size and shape depend on whether the entire section hardens consistently and then stabilizes during tempering. Non-uniform hardening creates different residual stresses across the part, which drives warp and dimensional drift during machining and inspection.
Which process sequence is safest for precision parts?
Rough machine in the softer condition, heat treat, temper, and then finish machine critical features after the final thermal cycle. This ensures final tolerances are cut on a stabilized part rather than one still moving from stress redistribution.