O1 heat treat: austenitize, quench & temper chart
O1 is a spring / tool 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 O1 heat-treat schedule
Austenitize: 1450–1500°F (1475°F recommended), hold 10 min once to temperature. A controlled oven or kiln beats forge colour for hitting this window repeatably.
Quench: Parks AAA. Also acceptable: Parks 50, Duratherm 48, Canola oil. Never use Water, Brine. Medium oil works for O1 due to high hardenability. Fast oil is acceptable but not required.
Cryo (optional): Small hardness increase with cold treatment; matching drop in toughness.
Temper: 2 passes of 2 h at 400°F for the recommended edge (~60–61 HRC). Temper twice for 2 hours. Up to 450°F does not embrittle.
O1 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) | 61–62 HRC |
| 400°F (204°C) | 60–61 HRC |
| 450°F (232°C) | 59–60 HRC |
Target hardness for O1 by knife type
| Use | Recommended HRC |
|---|---|
| Kitchen | 61–62 HRC |
| EDC | 60–61 HRC |
| Hunter | 59–60 HRC |
| Hard-use chopper | 59–60 HRC |
Forging O1
Forge-friendly. O1 is beginner-popular for its forgiving heat treat window.
Most common mistake
Austenitizing at 1550°F reduces toughness. Stay at or below 1500°F.
FAQ
What temperature do you austenitize O1?
1450–1500°F, with 1475°F recommended, held 10 min once the steel is fully up to temperature.
What is the best quench for O1?
Parks AAA. Parks 50, Duratherm 48, Canola oil also work. Never Water, Brine. Medium oil works for O1 due to high hardenability. Fast oil is acceptable but not required.
What HRC does O1 reach?
59–62 HRC across the usable tempering range; about 61–62 HRC for a kitchen knife. Temper at 400°F for ~60–61 HRC.
How do you temper O1?
2 passes of 2 h at 400°F for the recommended edge. See the chart above to pick a different tempering temperature for a harder or tougher blade.
Can you forge O1?
Forge-friendly. O1 is beginner-popular for its forgiving heat treat window.
What you need to heat-treat O1
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 1475°F austenitizing temperature — the single biggest factor in repeatable hardness.
- Quench in Parks AAA 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 O1; 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.