AUS-8, AUS-10 and Other Japanese Workhorses

Between a knife from a twenty-euro block and a Hattori at 600 euros lies the range that covers roughly everything people actually cut with. Japanese metallurgy fills it densely, but almost nobody writes about these grades: they are not exotic, and they are awkward to sell through a legend.

A reference point for calibration. A cheap supermarket knife is around 52 HRC. European knives — Sabatier, Güde, Zwilling, Wüsthof, Messermeister — use softer steels with low carbon but good toughness, and in a professional European kitchen they are trued on a steel every day or several times a day. Anything below 56 HRC is pointless to compare with Japanese knives.

AUS-8 and AUS-8A

AUS-8 gives 57–58 HRC, AUS-8A 57–59 HRC. It is often called a “molybdenum-vanadium steel,” and in its properties it is close to the steel the best German knives are made from.

It is a good steel: decent rust resistance, an affordable price, predictable behaviour. Its main virtue is rarely printed on the box — it sharpens easily. A knife at 57 HRC is trued in a minute and back in service, and in a kitchen where people cut every day that is worth more than a few extra months of edge retention.

AUS-10

The next grade in the same family, and it keeps different company. AUS-10 sits alongside Austrian Böhler N690, French Z100CD17, Swedish Sandvik 12C27, German X102CrMo17 and Russian 95Kh18 — a family of stainless steels close in composition and properties, related to 440C. Japanese VG-10 belongs to the same company, only with more molybdenum and chromium.

Cromova 18

A single-brand steel: Yoshikin puts it only in Global knives. The name reads letter by letter — Cr, Mo, Va: chromium, molybdenum, vanadium. The composition is not published; all that is known is the 18% chromium.

Hardness 56–58 HRC. For a Japanese steel that is low, and that is the whole point: Global is the best-known Japanese maker of chef’s knives, and it uses relatively soft steel. In exchange the steel is tougher than German X50CrMoV15, resists rust very well and sharpens easily. A knife held in the hand eight hours straight is designed for repairability, not for a record.

The budget floor

• Daido 1K6 — 57–58 HRC, relatively soft, found in inexpensive lines such as Kai Wasabi.
• 6A/1K6 — 56 ± 1 HRC. A very clean stainless with high chromium content, which is why it resists corrosion well; it has more carbon than the really simple steels, so it holds an edge more respectably.
• SK-5 from JFE Steel — a wide range, 57–65 HRC, but in kitchen knives it is usually hardened to around 60.
• S55C, also JFE — 58–61 HRC.

The tool-steel corner: SKD11 and SLD Magic

SKD11 is a Japanese tool steel from Hitachi, identical to American D2 and also known as SLD and DC11. Hardness 60–64 HRC: Yoshikane hardens it to 64, other makers to 62.

It resists rust, but not remarkably. It takes a very keen edge — and chips willingly, meaning bits of the edge fly off during work. Often that is the result of too acute a sharpening angle: tool and high-speed steels should not be given a thin angle at all, and 22–24 degrees is considered sensible for SKD11.

SLD Magic is Hitachi’s answer to that tendency to chip, an upgrade of ordinary SLD. It hardens to 60–62 HRC; Tadafusa uses it in its S line at 62 HRC. The steel is considered especially good for the kitchen, but it is rare: poor availability and a high price.

Where the workhorses end

ATS-34 is the Japanese version of American 154CM, also from Hitachi, 60–61 HRC. A high-quality stainless with very high wear resistance, which can be brittle at high hardness.

It does not appear in production kitchen knives for a simple reason: cost. Small batches are made by individual smiths, they are hard to find, and kitchen knives start at 300 euros. For slightly more money there are better steels — which describes the position of ATS-34 today rather precisely.

Who needs all this

Practically everyone who cooks.

Look at how a professional kitchen works. There is no single knife there: for hygiene and to save washing time, each type of product has its own knife, outwardly indistinguishable from the rest, marked something like “RF” for raw fish or “RV” for raw vegetables. That is seven or eight knives per cook, and only a mentally unwell restaurant owner would buy them in a luxury version.

For a knife picked up twenty times a day, recovering quickly matters more than going dull slowly.

Steel at 57–58 HRC is a deliberate trade, not a saving. You give up months of edge retention and get a knife that sharpens in a minute, does not fear the sink, survives a fall onto tile and causes no panic if someone carries it off to the next station. If after a knife like that you really do find something missing, you already know exactly what it is — and that is when it makes sense to look at powder steels and carbon.