M390 heat treat: austenitize, quench & temper chart
M390 is a powder metallurgy 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 M390 heat-treat schedule
Austenitize: 2050–2150°F (2100°F recommended), hold 20 min once to temperature. A controlled oven or kiln beats forge colour for hitting this window repeatably.
Quench: Plate quench. Never use Water, Brine, Parks 50, Duratherm 48, Parks AAA, Canola oil. Plate quench between aluminum plates. M390 / 20CV / 204P are nearly identical; same schedule applies.
Cryo (recommended): LN₂ 30–60 min. Stay near 2100°F peak — 2150°F gives excess retained austenite. Straight from the quench into cryo, then temper.
Temper: 2 passes of 2 h at 400°F for the recommended edge (~60–61 HRC). Temper twice for 2 hours. M390 has a secondary-hardening bump near 500°F — but the lower-temper range gives better corrosion resistance.
M390 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 |
| 500°F (260°C) | 61–62 HRC |
Target hardness for M390 by knife type
| Use | Recommended HRC |
|---|---|
| Kitchen | 60–61 HRC |
| EDC | 60–61 HRC |
| Hunter | 59–60 HRC |
| Hard-use chopper | 58–59 HRC |
Most common mistake
2150°F gives excess retained austenite; stay at 2100°F. Secondary hardening at ~500°F drops corrosion resistance — keep tempers in the 350–400°F band unless edge retention is the only goal.
FAQ
What temperature do you austenitize M390?
2050–2150°F, with 2100°F recommended, held 20 min once the steel is fully up to temperature.
What is the best quench for M390?
Plate quench. Never Water, Brine, Parks 50, Duratherm 48, Parks AAA, Canola oil. Plate quench between aluminum plates. M390 / 20CV / 204P are nearly identical; same schedule applies.
What HRC does M390 reach?
58–62 HRC across the usable tempering range; about 60–61 HRC for a kitchen knife. Temper at 400°F for ~60–61 HRC.
How do you temper M390?
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 M390?
M390 is best heat-treated in a controlled oven or kiln rather than forged by colour — its austenitizing window and quench are too tight to hit reliably by eye.
What you need to heat-treat M390
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 2100°F austenitizing temperature — the single biggest factor in repeatable hardness.
- Air-hardening steel plate-quenches between aluminium quench plates — no oil bath needed.
- Verify the result with a Rockwell hardness tester or hardness files — don't trust the schedule blind.
- Wrap in stainless tool-wrap foil to stop decarb and scale at high austenitizing temperatures.
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Sources
Heat-treat schedules are the cited published values for M390; 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.