8670 heat treat: austenitize, quench & temper chart
8670 is a simple carbon knife steel. Here is the full heat-treat schedule — austenitizing temperature, quench, cryo and a tempering-temperature chart mapping each temper to final HRC — with every number cited to the source, not guessed.
The 8670 heat-treat schedule
Austenitize: 1475–1525°F (1500°F recommended), hold 10 min once to temperature. A controlled oven or kiln beats forge colour for hitting this window repeatably.
Quench: Parks 50. Also acceptable: Duratherm 48, Parks AAA. Never use Water, Brine. Fast oil quench. 8670 is nickel-alloyed for toughness — Aldo's 8670M is a popular bowie / chopper steel.
Cryo (optional): Optional; not tested in Larrin's nickel-steels article.
Temper: 2 passes of 1.5 h at 375°F for the recommended edge (~59–60 HRC). Temper twice for 1–2 hours. 8670 shows a large jump in toughness between 300°F and 350°F — do not temper below 350°F.
8670 tempering-temperature chart
Two-hour temper (×2), HRC after cryo where used. Pick the tempering temperature for the hardness your knife needs:
| Tempering temperature | Resulting hardness |
|---|---|
| 350°F (177°C) | 60–61 HRC |
| 375°F (191°C) | 59–60 HRC |
| 400°F (204°C) | 58–59 HRC |
Target hardness for 8670 by knife type
| Use | Recommended HRC |
|---|---|
| Kitchen | 60–61 HRC |
| EDC | 59–60 HRC |
| Hunter | 58–59 HRC |
| Hard-use chopper | 58–59 HRC |
Forging 8670
Forge-friendly with care. Nickel content increases hardenability — fast oil quench still recommended.
Most common mistake
Do not temper below 350°F — big toughness drop. Above 400°F was not tested in Larrin's article.
FAQ
What temperature do you austenitize 8670?
1475–1525°F, with 1500°F recommended, held 10 min once the steel is fully up to temperature.
What is the best quench for 8670?
Parks 50. Duratherm 48, Parks AAA also work. Never Water, Brine. Fast oil quench. 8670 is nickel-alloyed for toughness — Aldo's 8670M is a popular bowie / chopper steel.
What HRC does 8670 reach?
58–61 HRC across the usable tempering range; about 60–61 HRC for a kitchen knife. Temper at 375°F for ~59–60 HRC.
How do you temper 8670?
2 passes of 1.5 h at 375°F for the recommended edge. See the chart above to pick a different tempering temperature for a harder or tougher blade.
Can you forge 8670?
Forge-friendly with care. Nickel content increases hardenability — fast oil quench still recommended.
What you need to heat-treat 8670
Repeatable hardness comes from controlling temperature and quench speed — eyeballing colour is how blades end up soft or cracked.
- A heat-treat oven or kiln holds the 1500°F austenitizing temperature — the single biggest factor in repeatable hardness.
- Quench in Parks 50 for the cited as-quenched hardness.
- Verify the result with a Rockwell hardness tester or hardness files — don't trust the schedule blind.
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Sources
Heat-treat schedules are the cited published values for 8670; every furnace, quench and blade geometry varies, so verify against your own hardness testing. Getting steel to non-magnetic is not the same as reaching austenitizing temperature — use a controlled oven or kiln for repeatable results.