The toughness record-holder that kitchen artisans rarely reach for, a WWII-era nickel-chrome-moly steel built to absorb punishment rather than win sharpness contests.
8670
For the Newcomer
8670 is a low-alloy steel from the 86xx family, developed during World War II when the United States needed to conserve nickel and other strategic alloying elements while still producing tough, reliable blades. It holds a remarkable distinction: of all commonly available knife steels, 8670 ranks at the absolute top for measured toughness in Larrin Thomas's testing at Knife Steel Nerds. A blade in 8670 can absorb extraordinary impact before chipping or breaking. The practical tradeoff for kitchen use is that its edge does not stay sharp for long. Without the high-carbide structure needed for wear resistance, the edge dulls faster than steels with more carbon and alloying elements. Artisan kitchen knife makers rarely choose it, but when they do, the result is a remarkably forgiving blade that comes back to sharp easily and survives abuse that would chip other steels.
About this composition
Why 8670 tops the toughness charts. The AISI 86xx alloy series was engineered during WWII to maximize mechanical toughness while conserving strategic elements. 8670's A metallic element that, added in small amounts, makes steel tougher and more resistant to cracking. addition (0.40 to 0.70%) is the key variable: nickel promotes a fine, tough The hard crystal structure that forms when steel is quenched; it is what gives a blade its hardness and holds its edge. structure and significantly raises the energy required to propagate fractures. Larrin Thomas's testing has confirmed 8670 ranks as the toughest commonly-available forging steel, ahead of 5160 (second), L6, and all other high-toughness competitors tested.
The edge retention penalty. Alpha Knife Supply's internal rating gives 8670 a toughness score of 100/100 and an edge-holding score of 27/100, among the lowest of all knife steels they stock. With few hard Microscopic hard particles within steel that resist wear; fewer of them means the edge dulls faster but sharpens more easily., the martensite matrix itself is the edge: tough and resilient, but not wear-resistant.
Compared to 15N20. Both share similar toughness profiles but serve different roles. 15N20's nickel (2%) is higher and chosen for its etch-brightening property in Damascus billets. 8670's lower nickel (around 0.55% typical) does not brighten dramatically in acid etch, so it is used as a mono-steel for performance.
Performance Deep Dive
Toughness: Record-holder, the toughest commonly-available forging steel.
Larrin Thomas's testing places 8670 at the absolute top. Beyond roughly 62 Rockwell C, the standard hardness scale for blade steel. Most kitchen knives fall between about 56 and 66., even 8670's exceptional toughness begins to decline as high hardness introduces brittleness.
Edge retention: Modest, among the lowest of any kitchen steel.
Corrosion resistance: None; full carbon steel care required.
At 0.40 to 0.60% chromium it sits far below the stainless threshold.
Ease of sharpening: Effortless; no hard carbides means quick restoration.
Any whetstone cuts efficiently, and a CrO₂ strop noticeably extends the edge. Full technique is in the care section.
Forging character: Well-regarded by bladesmiths.
Low alloy makes it predictable under the hammer; it normalizes cleanly and heat-treats without complexity.
Research Notes
8670 artisan kitchen knife production is extremely limited. The examples in the makers list represent the most consistently findable producers, and all URLs require manual verification before final publication. Most 8670 work in the blade world goes to choppers, outdoor knives, and survival blades where impact resistance is the priority; kitchen production is a niche application. The full reactive-carbon care routine is in the care section.
In the Kitchen
8670 makes sense for the cook who breaks things: the heavy-prep workhorse user who would rather a knife stay intact than stay maximally sharp. Pair it with a thick Western chef's knife or cleaver profile. Hone often, accept the sharpening cadence, and treat it as a carbon steel. Develop a patina through normal use.
Composition
| Element | % | Role |
|---|---|---|
| Carbon (C) | 0.7 | Primary hardening; elevated for 59 to 62 HRC while preserving forgeability (range 0.65–0.75) |
| Chromium (Cr) | 0.5 | Hardenability; minimal corrosion contribution (range 0.40–0.60) |
| Nickel (Ni) | 0.55 | The critical toughness element; promotes grain-boundary energy absorption before fracture (range 0.40–0.70) |
| Molybdenum (Mo) | 0.2 | Hardenability; secondary strength; part of the WWII alloy conservation formula (range 0.15–0.25) |
| Manganese (Mn) | 0.85 | Hardenability (range 0.75–1.00) |
| Silicon (Si) | 0.25 | Deoxidizer (range 0.15–0.35) |
Steel family: Conventional ingot-cast AISI 86xx nickel-chromium-molybdenum low-alloy series. WWII-era American engineering to conserve strategic alloying elements while producing tough, reliable blades. No powder metallurgy version is commercially available. Larrin Thomas's Knife Steel Nerds testing has confirmed it ranks as the toughest commonly-available forging steel.
Artisan Makers
| Maker | Knife | Style | Price | Link |
|---|---|---|---|---|
| Ry Smith Knives | 6.5" Hand-Forged Chef's Knife (8670, Stabilized Mango Wood, Ancient Bogwood bolster) | Western chef, hand-forged | $200 | rysmithknives.com |
| Josh Hults | 8670 Chef Knife 8" (Box Elder Handle) | ABS Journeyman Smith, Western chef, S-grind | $533 | arkansasknifeshop.com |
| BladeGallery / Epicurean Edge | Forged Chef's Knife, 5-2/3", African Blackwood Handle (one-of-a-kind) | Western chef, custom one-off | $335 | epicedge.com |