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. PM / Powder Steel Powder Metallurgy (PM)
A modern steel-making process where the alloy is atomised into a fine powder and then compressed under high pressure before sintering. This creates an exceptionally uniform carbide distribution — far finer and more even than conventionally cast steel. The result is a blade that achieves higher hardness without sacrificing toughness, holds a keener edge for longer, and is more resistant to chipping. PM steels are generally considered a step up in performance, though they can be harder to sharpen on coarse stones. Hitachi Special Steel, Japan 🇯🇵
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. PM / Powder Steel Powder Metallurgy (PM)
A modern steel-making process where the alloy is atomised into a fine powder and then compressed under high pressure before sintering. This creates an exceptionally uniform carbide distribution — far finer and more even than conventionally cast steel. The result is a blade that achieves higher hardness without sacrificing toughness, holds a keener edge for longer, and is more resistant to chipping. PM steels are generally considered a step up in performance, though they can be harder to sharpen on coarse stones. Hitachi Special Steel, Japan 🇯🇵
HAP-40 粉末ハイス鋼 HAP40
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.
64–68
HRC
555759616365+
HAP-40 steel is a high-speed tool steel known for its exceptional edge retention and durability, ideal for kitchen knives. It achieves high hardness, up to 68 HRC, allowing it to maintain sharpness through extensive use. Comprising a mix of carbon, chromium, and other elements like tungsten and vanadium, it offers a balance of hardness and toughness, reducing chipping risks. While its superior wear resistance ensures long-term performance, sharpening HAP-40 steel may require advanced tools due to its hardness. This steel appeals to those who prioritize cutting efficiency and minimal maintenance in their culinary tools.
Composition
HAP-40 Element Composition
Compare with
HAP-40
—
8.0%
6.0%
4.0%
2.0%
0
C
1.3%
Cr
4.0%
V
3.0%
Mo
4.8%
W
6.0%
Co
8.0%
C — Carbon
Cr — Chromium
V — Vanadium
Mo — Molybdenum
W — Tungsten
Co — Cobalt
Hardness
64–68 HRC
555759616365+
