Semi-Stainless Semi-Stainless Steel

Semi-stainless steels sit between carbon and full stainless. They will rust if left wet or neglected, but under normal use they tend to develop a patina — a dark, protective layer — rather than forming aggressive surface rust. Rinse and wipe dry after use and you will rarely have issues. Much more forgiving than true carbon steel, while still offering excellent cutting performance. Hitachi Special Steel, Japan 🇯🇵

SKD SKD合金工具鋼

Hardness

62–64 HRC

555759616365+

SKD short for SKD12 also known as A2 tool steel, with about 1% of Carbon content, and only 4.5% of Chromium. It can be treated to about 63 to 64.

The SKD very much behaves like carbon steel in terms of taking a very keen edge, the food release and also super easy to sharpen; yet without the need of high maintenance. As a result it is very popular amongst professional chefs.

Yoshikane is the noteable compnay that loves the SKD.

Compare with

SKD

—

5.0% 3.8% 2.5% 1.3% 0

1.0%

5.0%

0.35%

1.0%

0.7%

0.4%

0.03%

0.25%

0.5%

C — Carbon Cr — Chromium V — Vanadium Mo — Molybdenum Mn — Manganese Si — Silicon P — Phosphorus S — Sulfur Cu — Copper Ni — Nickel

Hardness 62–64 HRC

555759616365+

Steel

SKD

What's in SKD

What each element does in your knife.

SKD element composition and spec ranges
Element	Spec range	What it does in your knife
CCarbon	0.95–1.05%	The primary hardening element. More carbon means a harder edge that holds longer — but past a point it trades away toughness and rust resistance.
CrChromium	4.5–5.5%	Raises corrosion resistance; at roughly 13%+ free chromium the steel qualifies as stainless. Also improves hardenability and wear.
MoMolybdenum	0.8–1.2%	Improves hardenability and toughness, boosts corrosion resistance, and helps the steel hold hardness under heat.
VVanadium	0.2–0.5%	Forms extremely hard vanadium carbides for superior edge retention, and refines the grain for a finer, tougher edge.
MnManganese	0.6–0.9%	Aids hardenability and strength and acts as a deoxidiser in smelting. Too much can reduce toughness.
SiSilicon	0.4%	Strengthens the steel matrix and acts as a deoxidiser, improving hardness and resistance to oxidation.

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 SKD steel used for in Japanese knives?

SKD steel is a high-carbon, mid-chromium tool steel used in Japanese knives to deliver carbon-steel-like edge sharpness and ease of sharpening without the high maintenance requirements of traditional carbon steel.

This steel contains 1.0% carbon and 5.0% chromium, allowing it to be hardened to an HRC of 62–64 while maintaining a balance between edge retention and corrosion resistance. It is currently available in the K&S catalog through the Hatsukokoro x Yoshikane collaboration, with popular in-stock options including mid-range to upper-mid-range models such as the SKD Nashiji Honesuki 150mm, the SKD Nashiji Gyuto 240mm, and the SKD Nashiji Sujihiki 270mm. These knives are best suited for professional chefs or serious home cooks who want a keen edge and simple sharpening process but prefer not to deal with the rusting issues common to pure carbon steels.

Reviewed by K&S Staff · Last updated 18 July 2026