Stainless Stainless Steel

"Stainless" means stain-resistant, not stain-proof. In kitchen use, the steel can still discolour or pit if exposed to acidic environments — citrus, vinegar, or salt water — for extended periods. Wash and wipe dry after every use, and avoid leaving the blade soaking in water. With basic care, a stainless knife is very low-maintenance and a great everyday choice. Takefu Special Steel, Japan 🇯🇵

COSP (Cobalt Special) コバルトスペシャル鋼

Hardness

60–62 HRC

555759616365+

Takefu Special Steel's Cobalt Special steel, often referred to as Cobalt Steel, is a premium high-performance steel known for its exceptional edge retention and hardness. This steel incorporates a significant amount of cobalt in its composition, enhancing its wear resistance and strength. The addition of cobalt, along with other elements like carbon, chromium, and molybdenum, allows the steel to achieve a high level of hardness without compromising its toughness. Cobalt Special steel is designed to maintain a sharp edge for extended periods, even under rigorous use, making it highly valued for crafting high-end kitchen knives and cutting tools.
Makers such as Mojin and Kurosaki have some excellent COSP offerings.

Compare with

COSP (Cobalt Special)

—

16.0% 12.0% 8.0% 4.0% 0

1.05%

16.0%

0.25%

1.5%

0.25%

2.5%

C — Carbon Cr — Chromium V — Vanadium Mo — Molybdenum W — Tungsten Co — Cobalt

Hardness 60–62 HRC

555759616365+

Steel

COSP (Cobalt Special)

What's in COSP (Cobalt Special)

What each element does in your knife.

COSP (Cobalt Special) element composition and spec ranges
Element	Spec range	What it does in your knife
CrChromium	15.0–17.0%	Raises corrosion resistance; at roughly 13%+ free chromium the steel qualifies as stainless. Also improves hardenability and wear.
CoCobalt	2.0–3.0%	Allows higher hardening temperatures for more hardness and wear resistance, and strengthens the steel matrix.
MoMolybdenum	1.0–2.0%	Improves hardenability and toughness, boosts corrosion resistance, and helps the steel hold hardness under heat.
CCarbon	0.95–1.15%	The primary hardening element. More carbon means a harder edge that holds longer — but past a point it trades away toughness and rust resistance.
SiSilicon	0.6–0.7%	Strengthens the steel matrix and acts as a deoxidiser, improving hardness and resistance to oxidation.
MnManganese	0.3–0.5%	Aids hardenability and strength and acts as a deoxidiser in smelting. Too much can reduce toughness.
VVanadium	0.2–0.3%	Forms extremely hard vanadium carbides for superior edge retention, and refines the grain for a finer, tougher edge.
WTungsten	0.2–0.3%	Forms hard carbides for wear resistance and edge stability, and keeps the steel hard even at elevated temperatures.
NiNickel	0.25%	Improves toughness and ductility without sacrificing hardness, and adds a small boost to corrosion resistance.
PPhosphorus	0.03%	An impurity from smelting. Even small amounts promote brittleness, so steelmakers keep it as low as possible.
SSulfur	0.01%	An impurity that reduces toughness and promotes brittleness; only ever added deliberately in free-machining steels.

Composition from zknives (K&S steel dataset) reference material. These ranges come from the K&S steel composition dataset, which is derived from zknives; maker figures are cited separately only when they are used on the page.