Japanese Knife Steel: White Steel, Blue Steel, and Super Blue — The Iron-Carbon-Chromium Trinity

Yasuki City, Shimane Prefecture — Hitachi Metals (Proterial) standardised the Shirogami/Aogami classification system in the 20th century

Japanese kitchen knife steel is classified within a precise metallurgical hierarchy developed and standardised by Hitachi Metals (now Proterial) under the Yasuki steel brand, with Shirogami (White Steel), Aogami (Blue Steel), and Aogami Super (Super Blue Steel) representing the three primary grades used by Japanese blacksmiths for professional kitchen knives. Understanding these steels is essential for professional Japanese chefs who select, maintain, and sharpen their knives according to the specific properties of each alloy. Shirogami (White Steel) — so named for the white tissue paper wrapping on the billets — is a high-purity carbon steel with minimal alloying elements beyond iron and carbon. Shirogami #1 has approximately 1.25–1.35% carbon (the highest purity); Shirogami #2 has slightly less carbon at 1.05–1.15%. The purity of White Steel allows exceptionally fine edge geometry and extreme sharpness — a well-sharpened Shirogami blade can achieve a kasumi (mist) finish on wet stones that is visually striking and tactilely extraordinary. However, White Steel is reactive to acids and moisture, patinas rapidly, and requires diligent maintenance to prevent corrosion. Aogami (Blue Steel) — wrapped in blue tissue — adds tungsten (1.0–2.0%) and chromium (0.20–0.50%) to a carbon steel base similar to Shirogami, with carbon content at 1.0–1.5%. These additions significantly improve edge retention and toughness compared to White Steel while maintaining a comparable level of maximum sharpness. Blue Steel knives hold their edge through more extended work sessions, making them preferred for professional kitchens where continuous resharpening is impractical. Aogami Super (Super Blue) is further alloyed with molybdenum and vanadium in addition to tungsten and chromium, achieving very high hardness (62–65 HRC) and exceptional wear resistance — the longest edge retention in the Yasuki line. Super Blue is the choice for high-wear cuts (dense root vegetables, repeated fine julienne), but its hardness makes it slightly more brittle and more difficult to sharpen without advanced technique. Professional chefs in Japan often own multiple knives in different steels, choosing by task: White Steel yanagiba for sashimi presentation (maximum sharpness, infrequent use), Blue or Super Blue usuba for sustained vegetable prep, and stainless steel for acidic preparations where reactivity would stain fish or fruit.

Not applicable — metallurgical entry; relevance is tactile: White Steel sharpness produces thinner cuts with less cellular damage, affecting texture and moisture retention in delicate proteins