Heat Treatment Guide

Soften. Harden.
Stress relieve.
Choose wisely.

Annealing, normalizing, quenching, tempering, aging, case hardening. Each treatment targets specific material behaviors. This guide explains when to specify each and what hardness or property changes to expect.

Material Properties Get Quote

01 · Treatment families

Every heat treatment, categorized.

Softening treatments

Reduce hardness, restore ductility, or relieve internal stress.

Annealing

Hold at high temp then slow cool in furnace. Maximum softening. Used before heavy machining, cold forming, or welding.

Normalizing

Heat above critical, air cool. Uniform fine-grain microstructure. Used for stress relief on forgings, welds.

Stress Relief

Heat to 500–650 °C (below transformation), slow cool. Reduces residual stress without changing microstructure.

Process Annealing

Intermediate anneal during heavy cold working to restore ductility and allow further deformation.

Hardening treatments

Increase strength and hardness through microstructural transformation.

Quench Hardening

Heat to austenite (815–900 °C for steels), quench in oil/water/air. Creates martensite — hard and brittle. Always followed by tempering.

Tempering

Post-quench reheat to 150–600 °C. Reduces brittleness, sets final hardness. Temperature determines final hardness (low temp = hard; high temp = softer).

Precipitation / Age Hardening

Solution anneal + low-temperature age. For precipitation-hardenable alloys: 17-4 PH, 2024 Al, 7075 Al, Inconel 718, Ti-6Al-4V.

Cryogenic Treatment

Cool to -196 °C in liquid nitrogen. Transforms retained austenite to martensite in tool steels. Improves wear resistance, dimensional stability.

Surface treatments

Harden surface while maintaining tough core — best of both worlds.

Carburizing

Pack or gas carburize at 870–925 °C. Carbon diffuses into surface layer. Case hardness 58–62 HRC, core remains tough.

Nitriding

Gas or salt-bath nitride at 500–570 °C. Nitrogen forms hard surface nitrides. 65+ HRC with minimal distortion.

Carbonitriding

Combined C+N diffusion. Intermediate between carburizing and nitriding. Faster than pure nitriding.

Induction Hardening

Local surface hardening via induction coil. Ideal for selective hardening (bearing areas, gear teeth) without full-part hardening.

02 · Common specifications

Typical heat treatments by material.

Material	Standard Treatment	Result
Al 6061	T6 (mill supplied)	276 MPa yield, 95 HB
Al 7075	T6 (mill supplied)	503 MPa yield, 150 HB
Al 2024	T3 or T4 (mill supplied)	324 MPa yield
Steel 4140	Q&T to 28–32 HRC typical	655 MPa yield
Steel 4340	Q&T to 32 HRC typical	860 MPa yield
Tool Steel D2	Through-hardened 60–62 HRC	Maximum wear resistance
Tool Steel H13	Hardened 50 HRC, double tempered	Hot-work tool properties
Stainless 17-4 PH	H900 aging	1,170 MPa yield, 40 HRC
Stainless 15-5 PH	H1025 aging	1,000 MPa yield
Stainless 304/316L	Solution annealed (mill supplied)	No additional HT needed
Inconel 718	Solution + double age	1,036 MPa yield, 45 HRC
Ti-6Al-4V	Mill annealed or STA	828–965 MPa yield

FAQ

Heat treatment questions.

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.

Soften. Harden.Stress relieve.Choose wisely.