Carbon Steel
Carbon Steel
Carbon steel is reactive — it will rust quickly if not properly cared for. Always wash immediately after use, dry thoroughly, and apply a thin coat of food-safe oil (camellia, mineral) before storage. Over time it develops a patina that offers some natural protection and, for many users, becomes part of the knife's character. Rewarding to use, but not recommended if you want a "wash and forget" knife. Hitachi Special Steel, Japan 🇯🇵
Carbon steel is reactive — it will rust quickly if not properly cared for. Always wash immediately after use, dry thoroughly, and apply a thin coat of food-safe oil (camellia, mineral) before storage. Over time it develops a patina that offers some natural protection and, for many users, becomes part of the knife's character. Rewarding to use, but not recommended if you want a "wash and forget" knife. Hitachi Special Steel, Japan 🇯🇵
Blue 1 / Aogami #1 青一鋼
Hardness
Rockwell C Hardness(HRC) measures how resistant a steel is to permanent deformation. For kitchen knives:
55–58 HRC — Soft. Easy to sharpen and forgiving of rough use, but dulls faster. Typical of most German knives.
59–61 HRC — Balanced. Good edge retention with manageable sharpening. Common in mid-range Japanese knives.
62–64 HRC — Hard. Excellent edge retention, holds a very fine edge. Requires more care and a fine stone to sharpen.
65+ HRC — Very hard. Exceptional edge longevity but more brittle — more prone to chipping if used roughly.
Higher is not always better — it depends on how you use and maintain your knife.
55–58 HRC — Soft. Easy to sharpen and forgiving of rough use, but dulls faster. Typical of most German knives.
59–61 HRC — Balanced. Good edge retention with manageable sharpening. Common in mid-range Japanese knives.
62–64 HRC — Hard. Excellent edge retention, holds a very fine edge. Requires more care and a fine stone to sharpen.
65+ HRC — Very hard. Exceptional edge longevity but more brittle — more prone to chipping if used roughly.
Higher is not always better — it depends on how you use and maintain your knife.
61–64
HRC
555759616365+
Blue Steel No.1, also known as Aogami #1 or Yasugi #1 Blue Steel, is a premium high carbon steel from Hitachi Metals Ltd, celebrated for its exceptional edge retention and toughness. This steel is an upgrade from Blue Steel No.2, enriched with higher carbon and tungsten content, making it a favorite for high-grade Japanese traditional single-bevel knives. It's known for being easy to sharpen, achieving a very fine edge that lasts. Despite its susceptibility to rust, with proper care and maintenance, including regular wiping and drying, it can develop a protective patina that minimizes rusting. Blue Steel No.1 is highly regarded among knife makers for its ability to achieve a mirror finish and maintain a sharp edge over extended periods, offering an outstanding balance of performance and durability.
Composition
Blue 1 / Aogami #1 Element Composition
Compare with
Blue 1 / Aogami #1
—
1.75%
1.3%
0.9%
0.4%
0
C
1.3%
Cr
0.4%
W
1.75%
Mn
0.25%
Si
0.15%
P
0.025%
S
0.004%
C — Carbon
Cr — Chromium
W — Tungsten
Mn — Manganese
Si — Silicon
P — Phosphorus
S — Sulfur
Hardness
61–64 HRC
555759616365+
Blue 1 / Aogami #1 Composition
What's in Blue 1 / Aogami #1
What each element does in your knife.
| Element | Spec range | What it does in your knife |
|---|---|---|
| WTungsten | 1.5–2.0% | Forms hard carbides for wear resistance and edge stability, and keeps the steel hard even at elevated temperatures. |
| CCarbon | 1.25–1.35% | 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 | 0.3–0.5% | Raises corrosion resistance; at roughly 13%+ free chromium the steel qualifies as stainless. Also improves hardenability and wear. |
| MnManganese | 0.2–0.3% | Aids hardenability and strength and acts as a deoxidiser in smelting. Too much can reduce toughness. |
| SiSilicon | 0.1–0.2% | Strengthens the steel matrix and acts as a deoxidiser, improving hardness and resistance to oxidation. |
| PPhosphorus | 0.025% | An impurity from smelting. Even small amounts promote brittleness, so steelmakers keep it as low as possible. |
| SSulfur | 0.004% | 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
Will a carbon steel knife rust, and how do I look after it?
Reviewed by James Zhang · Last updated 29 May 2026
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