Aogami Super, the King of Carbon

The top of the blue-paper family

All of the famous traditional Japanese knife steels, the white-paper (Shirogami) and blue-paper (Aogami) families, come from one place: the Yasugi specialty steel works in Shimane Prefecture, on the Sea of Japan coast near the old tatara iron-sand smelting country. For most of the modern era these steels were sold under the Hitachi Metals name; after the company was acquired and renamed in 2023, the maker is now called Proterial, and the Yasugi Speciality Steel (YSS) branding continues. When smiths and retailers say "Hitachi Blue Super," they mean this steel; the paperwork just says Proterial now.

The paper names are literal. The mill historically wrapped billets of each grade in colored paper so warehouses and blacksmiths could tell them apart: white paper for the purest simple carbon steel, blue paper for the tungsten-and-chromium enhanced version. Aogami Super was developed later than Blue #1 and Blue #2 as the flagship of the line, the answer to a simple question: how far can a traditional forge-weldable carbon steel be pushed before it stops behaving like a traditional steel at all?

The answer is: quite far. Aogami Super raises carbon to roughly 1.40-1.50%, raises tungsten to roughly 2.00-2.50%, and adds two elements that no other steel in the white or blue families carries: molybdenum and vanadium. Vanadium in particular forms extremely hard carbides and helps pin grain growth during forging, which is part of why a well-made AS blade can be pushed to hardness levels that would make lesser carbon steels crumble at the apex.

One important framing before we go further: Aogami Super is not a stainless steel, not a powder steel, and not a modern "super steel" in the marketing sense. It is a traditional ingot carbon steel, forge-weldable to soft iron or stainless cladding in the classic Japanese manner, that happens to sit at the extreme performance end of that tradition. That is exactly what makes it special. It delivers a level of edge retention that gets within sight of modern powder metallurgy steels while keeping the fine, simple-steel edge feel that carbon steel lovers refuse to give up.

Aogami Super vs Blue #1 and Blue #2

Published mill specifications for the three blue-paper grades line up like this. For the full family story, see our Aogami reference page.

Element	Blue #2	Blue #1	Aogami Super
Carbon (C)	1.05-1.15%	1.25-1.35%	1.40-1.50%
Tungsten (W)	1.00-1.50%	1.50-2.00%	2.00-2.50%
Chromium (Cr)	0.20-0.50%	0.30-0.50%	0.30-0.50%
Molybdenum (Mo)	None	None	0.30-0.50%
Vanadium (V)	None	None	0.30-0.50%
Typical blade HRC	62-64	63-65	64-66

What each addition buys. The extra carbon raises attainable hardness and carbide volume. Tungsten forms tungsten carbides that are far harder than plain iron carbides; they are the abrasion-resistant particles that keep an AS edge cutting long after a white-steel edge has dulled. Molybdenum adds hardenability and a measure of resistance to softening. Vanadium forms the hardest carbides in the mix and, just as importantly, refines grain during heat treatment, which is why a properly made AS blade holds a surprisingly fine, stable apex despite all that carbide.

What it does not buy. Chromium at half a percent is a rounding error next to the 13%+ a stainless steel carries. Aogami Super rusts. It patinas. It demands the same wipe-and-dry discipline as every other carbon steel, and only slightly less urgently than Shirogami.

How it actually performs

Trait	Rating	Reality check
Edge retention	Exceptional (for carbon steel)	The best in the traditional carbon-steel world. Holds a working edge noticeably longer than Blue #2, and far longer than White #2. Modern high-vanadium powder steels can still outlast it in pure abrasion tests.
Attainable sharpness	Excellent	Takes a screaming, fine-grained edge. Slightly less of the glassy "pure steel" feel than white steel because of the carbide load, but very close.
Toughness	Low to moderate	At 64-66 HRC this is not a steel for twisting, prying, or frozen food. Vanadium grain refinement helps, and many users find good AS more stable than Blue #1, but thin edges can still chip on bones and hard boards.
Corrosion resistance	Poor (it is carbon steel)	Marginally better than white steel thanks to the small chromium content. It will patina within days of normal use and will rust if left wet.
Ease of sharpening	Moderate	Easy compared to powder stainless steels, slow compared to White #2 or Blue #2. Tungsten and vanadium carbides resist abrasion on softer stones.

The honest summary: Aogami Super trades away some of carbon steel's two classic virtues, effortless sharpening and high toughness at moderate hardness, to maximize the third, edge life. Whether that trade is worth it depends entirely on how you cook and how often you enjoy visiting your stones.

Why few smiths truly master it

Every serious conversation about Aogami Super arrives at the same point: the steel is only as good as its heat treatment, and its heat treatment is unforgiving. Three things make it harder to handle in the forge than Blue #2 or the white steels.

The working window is narrow. With 1.40-1.50% carbon plus heavy carbide formers, AS is sensitive to overheating. Push the forge or the hardening temperature too far and grain coarsens, carbides grow, and the finished edge becomes brittle and crumbly no matter what the hardness tester says. Traditional smiths judge much of this by color and feel, and the margin between "fully hardened" and "quietly ruined" is smaller here than in any other steel in the Yasugi carbon lineup.

It resists the hammer. Smiths consistently describe AS as harder to move under the hammer than Blue #2, with a higher risk of cracking during forging and straightening. Forge-welding it to cladding, iron or stainless, adds another failure point that the simpler steels tolerate more gracefully.

The payoff only shows at the extreme. An AS blade hardened to a cautious 61-62 HRC gives up most of its advantage over well-treated Blue #2 while keeping all of its extra cost and sharpening resistance. The steel only makes sense when a smith has the confidence to run it at 64-66 HRC and the skill to keep it stable there. That is precisely the regime where inexperienced heat treatment falls apart, which is why the AS knives with great reputations cluster around a small number of workshops that have forged this steel for decades.

This is worth remembering when you shop: the name on the steel matters less than the name on the forge. A masterfully treated Blue #2 blade will outperform a mediocre Aogami Super blade every single day of the week.

Who forges Aogami Super

Because of everything above, AS is a signature steel rather than a commodity steel. A few names to know, all covered in our maker library:

• Moritaka: the smithy most closely identified with Aogami Super in enthusiast circles. Nearly the entire Moritaka kitchen line is hand-forged AS with a rustic kurouchi finish, and their gyuto and nakiri are many people's first taste of what this steel can do.
• Miki Hamono: the small family forge in Banshu Miki (Hyogo) offers stainless-clad Aogami Super santoku and gyuto, hardened to reportedly around 65 HRC. The stainless jacket leaves only the exposed core edge reactive, a friendly way to live with AS.
• Mcusta Zanmai: the Beyond line pairs an Aogami Super core at 62-63 HRC with stainless cladding and modern Seki precision grinding. It is the polished, production-grade take on AS, as opposed to the hand-forged rustic school.
• Tosa smiths: the free-forging smiths of Kochi work mostly in Blue #2 and white steel, but a number of Tosa workshops also offer Aogami Super versions of their kurouchi knives, typically at very fair prices for what the steel costs.

You will also see AS honyaki and high-end custom work from small independent smithies across Japan. The pattern holds everywhere: AS appears where a workshop is confident enough in its forge work to charge for it.

AS vs Blue #2, White #2, SG2

	Aogami Super	Blue #2	White #2	SG2 / R2
Type	Ingot carbon steel	Ingot carbon steel	Ingot carbon steel	Powder metallurgy stainless
Typical HRC	64-66	62-64	61-63	62-64
Edge retention	Best of the carbon steels	Very good	Moderate	Excellent, comparable to AS or better in abrasive work
Ease of sharpening	Moderate, slower on soft stones	Easy	Easiest, the benchmark feel	Slow, harder carbides
Rust care	Required, patinas fast	Required, patinas fast	Required, most urgent	Not required, stainless
Character	Maximum-performance traditional steel	The sweet-spot carbon steel	The purist's sharpening steel	The low-maintenance high performer

AS vs Blue #2: AS holds its edge meaningfully longer and runs a point or two harder, but Blue #2 is easier to sharpen, a little tougher at its typical hardness, cheaper, and far more forgiving of both smith and owner. For most cooks moving into carbon steel, Blue #2 is the smarter first step; AS is the upgrade you buy once you know you love the maintenance ritual.

AS vs White #2: two different philosophies. White #2 (Shirogami) is prized for the purity of its sharpening feel and the ease of raising a perfect edge; AS is prized for how long that edge survives contact with a cutting board. Sakai single-bevel tradition leans white; modern enthusiast double-bevels lean blue.

AS vs SG2: this is the real modern rivalry, and we cover the stainless side in depth on our SG2 / R2 page. SG2 matches or exceeds AS edge retention in most kitchen use and never rusts, but many sharpeners find its edge feel slightly more "carbide-y" and its feedback on stones less rewarding. AS deburrs more cleanly, takes a keener low-angle edge more easily, and develops a patina with a story. If you want zero-thought maintenance, SG2 wins. If sharpening is part of why you own Japanese knives, AS wins.

Sharpening and patina care

On the stones

AS sharpens like carbon steel with a tax. The matrix abrades willingly, but the tungsten and vanadium carbides push back, so expect sessions to run noticeably longer than with White #2 or Blue #2 on the same stones. Practical advice:

• Use quality synthetic stones with hard, fast-cutting abrasive. A 1000-grit medium stone and a 3000-6000 finisher cover almost everything; see our whetstone sharpening guide for the full routine.
• Deburr patiently. At 64-66 HRC the burr is small and crisp, but leaving it behind wastes the entire point of the steel.
• Respect the hardness with your angles. Around 15 degrees per side is a sensible floor for general kitchen work; chasing extreme low angles invites microchipping.
• Skip the honing rod, especially grooved steel rods. At this hardness, stropping or a few light passes on a fine stone is the correct touch-up.

Patina and rust

An AS blade in regular use turns gray, then blue-gray, then develops the mottled personal patina that carbon-steel owners treasure. That oxide layer is mildly protective and completely normal. Red or orange rust is not; it means water sat on the steel. The rules are the same as for every reactive blade, and our patina guide covers them in depth:

• Wipe the blade during use, especially after acidic ingredients like onions, citrus, and tomatoes.
• Wash by hand and dry completely the moment you finish. Never the dishwasher, never the drying rack.
• Oil lightly (camellia or food-safe mineral oil) before any storage longer than a few days.
• If red rust appears, remove it early with a rust eraser or fine polish; do not let it pit.

Stainless-clad AS knives, like the Miki Hamono and Zanmai Beyond lines above, reduce the reactive surface to the few millimeters of exposed core at the edge. They still need drying, but the margin for error is much wider.

Myths worth retiring

"Aogami Super is semi-stainless." No. Half a percent of chromium does almost nothing for corrosion resistance. AS is fully reactive carbon steel and will rust as enthusiastically as any other if neglected. The only semi-stainless thing about many AS knives is their stainless cladding.

"AS is always better than Blue #2." Only when the heat treatment is right. The steel's advantages exist at the hard, precise end of its envelope; a timid or botched treatment produces an expensive knife that performs like a worse Blue #2. Buy the smith, then the steel.

"That much hardness means it shatters." Exaggerated. AS at 64-66 HRC is less tough than softer steels and thin edges will chip on abuse, but the molybdenum and vanadium refine the grain enough that well-made AS is a dependable daily kitchen steel. Treat it like a scalpel, not a cleaver, and it holds up for decades.

"The king of carbon is the best steel for everyone." The nickname describes its position in the carbon-steel hierarchy, not a universal recommendation. If you will not commit to wiping and drying, a stainless steel will serve you better, and there is no shame in that.

Aogami Super, quick answers

What is Aogami Super steel?

Aogami Super (青紙スーパー, Blue Paper Super, AS) is the highest-alloy carbon steel in the blue-paper family from the Yasugi specialty steel works, historically sold under Hitachi Metals and today under Proterial. It combines roughly 1.40-1.50% carbon with tungsten, chromium, molybdenum, and vanadium, and hardens to about 64-66 HRC in skilled hands. It is widely regarded as the best-performing traditional carbon steel for kitchen knives.

What is the difference between Aogami Super and Blue #2?

Aogami Super carries more carbon and tungsten than Blue #2 and adds molybdenum and vanadium, which Blue #2 lacks entirely. In practice AS runs 1-2 HRC points harder, holds an edge noticeably longer, and costs more, while Blue #2 is easier to sharpen, more forgiving to forge, and slightly tougher at its typical hardness. Blue #2 is the sensible entry point; AS is the specialist's upgrade.

Does Aogami Super rust?

Yes. Aogami Super is a reactive carbon steel. Its small chromium content slows corrosion only marginally, so it will patina within days of normal use and will rust if left wet or stored damp. Wipe it during use, dry it immediately after washing, and oil it before long storage. Stainless-clad AS knives limit the reactive area to the exposed edge.

Aogami Super vs SG2: which is better?

They are close in edge retention, so the choice is really about maintenance and feel. SG2 is a powder metallurgy stainless steel that needs no rust care; Aogami Super is a reactive carbon steel that sharpens with better feedback, deburrs more cleanly, and takes a very keen edge more easily. Pick SG2 for convenience, AS for the traditional carbon-steel experience with maximum edge life.

What hardness does Aogami Super reach?

Mill literature indicates the steel can exceed 66-67 HRC in laboratory conditions, but finished knives are typically hardened to 64-66 HRC, balancing edge life against chipping risk. Some stainless-clad production lines run it slightly softer, around 62-63 HRC, for extra stability.

Is Aogami Super good for beginners?

Usually not as a first Japanese knife. It combines the maintenance demands of carbon steel with slower sharpening and a chip-prone hardness level. A stainless steel, or an easier carbon steel like White #2 or Blue #2, teaches the same habits with more forgiveness. AS rewards owners who already keep their knives dry and their stones flat.

Why is it called "blue paper" steel?

The Yasugi mill historically wrapped each steel grade in a different color of paper to identify billets: white paper for the simple carbon grades, blue for the tungsten-alloyed grades. "Super" marks the top grade of the blue line. The steel itself is not blue, though a used AS blade often develops a handsome blue-gray patina.

What this page is built on

Composition figures and hardness ranges reflect published mill specifications and the sources below. Where only vendor-reported numbers exist, we say "reportedly."

• Proterial Ltd. (formerly Hitachi Metals), Yasugi Speciality Steel product literature for the high-class cutlery steel series
• Hitachi Metals high-class cutlery steels technical brochure (YSS grades)
• Knife Steel Nerds metallurgical articles by Dr. Larrin Thomas
• zKnives knife steel composition database
• Sakai Ichimonji Mitsuhide steel reference articles
• Moritaka Hamono company materials
• Miki Hamono Seisakusho company materials and dealer specifications
• Mcusta Zanmai official Beyond series product documentation