8670 knife steel

8670 came to knifemaking from industrial band-saw blades, and it never lost the day job’s virtues: it bends before it breaks, it costs less than almost anything else worth forging, and it forgives the kind of heat-treat sins that ruin fussier steels. Its nickel content puts its toughness in the same conversation as 5160 and 15N20, and it does that at a higher working hardness than 5160 usually runs. What it will not do is hold a slicing edge like an alloyed steel — 8670 is the tough, cheap, honest end of the spectrum, and it does not pretend otherwise.

8670 FAQ

Is 8670 a good knife steel?

For choppers, camp knives, machetes and first knives — genuinely excellent. Impact toughness testing puts it among the toughest common knife steels at working hardness, matched only by the 5160/15N20 class. For fine slicers it is the wrong tool: with no vanadium carbides its wear resistance is low, and an alloyed steel will out-cut it several times over.

How tough is 8670 really?

Knife Steel Nerds measured roughly 27 ft-lbs at 59.7 HRC — and around 50 ft-lbs on an earlier batch — which is elite territory; most stainless steels manage single digits. The ~0.85% nickel is doing the work, letting 8670 hold that toughness at a hardness where plainer steels have already gone brittle. Fine grain helps too; see grain structure and refinement.

How do you heat treat 8670?

Austenitize at 1500°F with a 10–15 minute soak — the tested sweet spot; 1475–1550°F all works, but 1450°F costs hardness and 1600°F costs toughness. Quench in Parks 50 or AAA — both produce full hardness. Temper twice at 300–450°F: the tradeoff is linear across that whole range with no embrittlement trough, which makes dialing a target hardness unusually predictable. Around 400°F lands near 58–60 HRC.

Can you heat treat 8670 in a forge?

Yes — it is one of the friendliest steels for it. Its nickel and chromium give it enough hardenability that a slight miss on temperature still hardens fine, unlike shallow-hardening steels that punish every degree. Magnet-plus-a-shade works; a kiln just makes it repeatable. Walkthrough in our heat treating guide.

8670 or 1084 for a first knife?

Either succeeds; they fail differently. 1084 is the classic teaching steel and the better damascus layer, while 8670 is tougher at the same hardness and cheaper per bar — and its forgiveness in the quench is comparable. If your first knife is a camp blade that will get batoned, 8670 is the better parent. See our 1084 page for the other side of the argument.

Does 8670 rust?

Yes. The nickel is for toughness, not stain resistance — treat it exactly like a carbon steel: oil after use, and let a working patina build.