Tempering

Tempering is a post-quench heat treatment that reheats hardened steel to a controlled temperature below the critical range, then cools it to reduce brittleness, relieve residual stress, and retain a functional hardness level. It balances hardness and toughness for machined components.

In a CNC cell, tempering is part of a heat-treat route for quenched steel components like shafts, inserts, fixtures, and structural parts. The part is reheated to a precisely controlled temperature, held for the required soak time, then air-cooled per alloy procedure. This reduces brittleness and residual stress from quenching while preserving usable hardness. For production, rough machining is done in softer stock, followed by hardening and tempering, then final machining to avoid distortion-driven scrap. Tempering is critical for parts that must survive impact, cyclic load, or tool contact—trading some hardness for increased toughness and fatigue resistance. Lower temperatures retain hardness for tooling; higher temperatures boost toughness for functional parts. The sequence matters: if finish features are cut before tempering, heat can shift dimensions, so shops leave stock allowance and finish after the last temper cycle for tighter tolerance control.