Soften. Harden. Stress relieve. Choose wisely.

Depends on the material and application. Aluminum 6061: arrives pre-heat-treated to T6 temper — no additional heat treatment unless welding creates heat-affected zones needing re-T6. Stainless 304/316L: typically used as-supplied unless aging (17-4 PH) is required. Steel 1018: as-supplied fine for most uses. Steel 4140: pre-hardened or through-hardened depending on strength needed. Tool steels: require heat treatment to achieve tool hardness. Always check the material datasheet for recommended temper and heat treatment.

Quench-hardening (for carbon and alloy steels): heat to austenite temperature (~820 °C for most steels), quench rapidly in oil or water. Martensitic transformation creates hard, brittle material that must be tempered to useful properties. Age-hardening / precipitation hardening (for 17-4 PH, Inconel 718, 7075 aluminum): solution treat at high temperature, then age at lower temperature for hours. Precipitates form in the microstructure, blocking dislocation motion and strengthening the material.

Annealing softens the material and relieves residual stress. Specify annealing when: (1) Material was cold-worked and needs to be reformed. (2) Welding created significant residual stress that would cause distortion after machining. (3) You need to machine a hardened material (first anneal, then machine, then re-harden). (4) Dimensional stability in high-precision parts where residual stress would cause slow distortion over months.

Simple stress relief or annealing: typically $1–5 per kg, often included in machining cost on small parts. Quench and temper on steel: $5–20 per kg. Precipitation hardening (17-4 PH, Inconel 718): $10–30 per kg. Case hardening (carburizing, nitriding): $15–40 per kg. Specialty treatments (cryogenic treatment, plasma nitriding, PVD-hardening): $30–80 per kg. Cost varies significantly by quantity, size, and temperature required.

Yes — especially quench hardening, where rapid cooling creates internal stresses. Typical distortion: 0.05–0.3% per dimension after quench hardening. Counteract by: (1) Machining slightly oversized before heat treatment, then grinding to final. (2) Using lower-distortion heat treatment processes (nitriding, air-hardening steels). (3) Stress-relieving before final machining. (4) Designing parts with symmetric cross-sections to minimize differential cooling. For precision parts, plan on grinding allowance of 0.2–0.5 mm per surface.

Standard: AMS 2750 (pyrometry for aerospace), AMS 2759 (steel heat treatment), AMS 2770 (aluminum), ASM 2774 (Inconel). For aerospace critical heat treatment, work is performed by AMS 2750-qualified partners with documented pyrometry records. Documentation package includes: process records (time, temperature, atmosphere), hardness verification, material certificates, and (on request) chamber thermocouple records.