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 to 62 HRC

555759616365+

Cobalt Special (CoSP) is a stainless steel from Takefu Special Steel, which calls it a super high-grade stainless steel for cutlery, made by a special remelting method that gives a uniform composition and a fine dispersion of carbides. Takefu lists 1.05% carbon, 16.00% chromium, 1.50% molybdenum, 0.25% vanadium, 0.25% tungsten and 2.50% cobalt, and a hardness of 60 HRC or more.

Takefu credits the tungsten with tempering resistance, the molybdenum with corrosion resistance, the vanadium with a finer microstructure, and the cobalt with strengthening the matrix and helping the edge last. Stainless, in the Japan Stainless Steel Association's words, rusts less rather than never, so dry the knife after washing.

We list Cobalt Special knives from Yu Kurosaki and Myojin Riki.

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

Typical values from third-party sources.

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
Element	Composition	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.

Frequently asked questions

What is Cobalt Special (CoSP) steel?

Cobalt Special (CoSP) is Takefu's stainless blade steel for cutlery: Takefu's page describes it as super high-grade and made by a special remelting process that gives a uniform composition and finely dispersed carbides.

Takefu's table gives 1.05% carbon, 16.00% chromium, 1.50% molybdenum, 0.25% vanadium, 0.25% tungsten and 2.50% cobalt, with a hardness of HRC 60 or more. In Takefu's description, tungsten improves tempering resistance, molybdenum adds corrosion resistance, vanadium gives a finer microstructure, and cobalt strengthens the matrix and helps keep a long-lasting edge. Its 16.00% chromium is above the JSSA's 10.5% minimum for stainless, which the JSSA says strictly means rusts less; wash and dry the knife after use.

Published by K&S Education Desk; staff review pending