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Tempering temperature and color chart
A freshly hardened blade is glass-hard and just as brittle — it will chip or snap. Tempering reheats it to a moderate temperature to relieve stress and convert some of the brittle martensite, trading a little hardness for a lot of toughness. The temperature you choose sets that trade-off.
The temper-color (oxide) chart
On clean, bare carbon steel, a thin oxide layer forms as you heat, and its color tracks the surface temperature. Smiths have used these colors for centuries to judge tempering by eye:
| Oxide color | Approx. temp | Typical use |
|---|---|---|
| Pale / faint straw | ~350°F (176°C) | Harder edges, razors, scrapers |
| Straw | ~400°F (204°C) | Many knife edges |
| Dark straw / bronze | ~465°F (240°C) | Tougher knives, chisels |
| Purple | ~520°F (271°C) | Springs, tougher tools |
| Blue | ~570°F (299°C) | Springs, high-toughness/low-hardness |
The oxide-color chart only holds for plain and low-alloy carbon steels with a clean surface, and the colors shift with lighting and alloy content. Alloy and stainless steels temper to very different hardnesses at the same temperature, and many need higher temper ranges entirely. For repeatable results, temper to a number in a thermostatically controlled oven — not to a color.
Typical knife tempering
Most carbon-steel kitchen and EDC blades are tempered around 350–450°F to land in the high-50s to low-60s HRC. Lower temper = harder, better edge retention, less tough; higher temper = tougher, more forgiving, slightly softer. Always temper at least twice, with a full cool to room temperature between cycles, so freshly formed martensite from the first cycle also gets tempered.
Match the temper to the steel, not a generic chart. The right temperature depends on the specific alloy and the hardness you're targeting. A published heat-treat recipe for your exact steel beats any one-size chart — and many air-hardening and stainless steels behave nothing like the oxide-color table above.
Temper gives you the recipe for your steel
Pick your steel and target hardness and Temper returns the austenitizing and tempering temperatures, cycle counts, and expected HRC — drawn from published metallurgy, not shop lore. Free to download.
Sources
- Larrin Thomas, Knife Steel Nerds (heat-treatment metallurgy and hardness data)
- Steel manufacturer heat-treatment datasheets (per-alloy temper response)
Oxide-color temperatures are approximate and apply to plain carbon steel only. Always follow your steel's published heat-treat data.