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Heat treating
Heat treating is a controlled cycle of heating, holding and cooling that changes a metal's properties rather than its surface finish. Through hardening quenches and tempers steels like 4140 to 28–50 HRC. Case hardening, such as carburizing, puts a hard 58–62 HRC skin over a tough core. Stress relieving, annealing and aging stabilize, soften or strengthen parts after machining or forming.
- Applies to
- Carbon, alloy and tool steels, stainless steels, powder metal steels, spring wire, heat-treatable aluminum and titanium
- Adds
- 5 days
- Cost
- Low
Specs
| Through hardening (quench and temper) | 4140: 28–50 HRC by temper; 1045: thin sections to about 50–55 HRC |
|---|---|
| Carburizing | 1018, 8620, 12L14: case 58–62 HRC, 0.010–0.060 in (0.25–1.5 mm) deep |
| Carbonitriding | Low-carbon steels: thin case 0.003–0.020 in (0.08–0.5 mm) |
| Nitriding | 4140 and tool steels: case 0.005–0.025 in (0.13–0.64 mm), about 500–600 HV on 4140, minimal distortion |
| Induction hardening | 1045 and 4140 shafts and teeth: surface 50–60 HRC, 0.040–0.200 in (1–5 mm) deep |
| Stress relief | Steel 1,000–1,200 °F (540–650 °C); music wire springs 450–500 °F (230–260 °C); stainless springs 600–800 °F (315–425 °C) |
| Precipitation hardening | 17-4 PH: H900 to H1150; 6061 and 7075: solution treat and age to T6 |
| Annealing | Softens for forming or machining and restores ductility after cold work |
Call out on the drawing
- AMS 2759 (steel: /1 carbon and low-alloy, /3 PH stainless, /7 carburizing)
- AMS 2770 (aluminum)
- AMS 2801 (titanium)
- ASTM E18 (Rockwell hardness testing)
- AIAG CQI-9 (automotive heat treat system assessment)
Materials it suits
Questions
Through hardening vs case hardening?
Through hardening quenches the whole section, so strength and hardness run deep; it needs a medium-carbon or alloy steel such as 1045 or 4140. Case hardening adds carbon or nitrogen to the surface of low-carbon or alloy steel for a hard, wear-resistant skin over a tough core. Use case hardening for gears, pins and cams that see surface wear and impact.
Should I machine before or after heat treating?
Machine to near final size before hardening, then grind, hard turn or EDM critical features afterward. Parts up to about 32 HRC, such as 4140 pre-hard, can be machined complete. Leave about 0.005–0.010 in (0.13–0.25 mm) of grind stock per side on features that must hold tight tolerances after hardening.
How much do parts distort in heat treatment?
It depends on geometry, steel and quench. Oil and water quenching can bow long shafts and move bores by thousandths of an inch; nitriding and precipitation aging distort least. Uniform sections, symmetric features and a stress relief before final machining reduce movement.
How is heat treatment called out on a drawing?
State the material, process and result with a tolerance, for example '4140, quench and temper to 32–36 HRC' or 'carburize 0.030–0.045 in effective case depth at 50 HRC, surface 58–62 HRC'. Add the governing spec, such as AMS 2759/1, and where hardness is tested.
Price it with this finish.
The builder adds lot charges, per-part cost and lead time for the finish you pick.