ZDP-189: A Steel That’s Hard to Sharpen and Easy to Ruin

ZDP-189 is a Japanese powder steel from Hitachi with an extremely high content of carbon and chromium: 3% carbon and 20% chromium. Besides these, the composition includes molybdenum, vanadium, tungsten, manganese and silicon. The maker does not disclose the exact recipe.

For comparison: anything with 0.05% to 2.1% carbon counts as carbon steel. ZDP-189 goes past the upper bound of that range — and still manages to be stainless. Hence the hardness: 64–67 HRC, with some makers quenching to 65 and even 67.

Three names for one steel

It is easy to run into this steel without recognising it.

• MC66 is the Henckels designation. MC stands for Micro Carbide, 66 for the target Rockwell hardness. A company representative in Tokyo confirmed that MC66 and ZDP-189 are identical. Twin Cermax and Miyabi 7000MC knives are made in Japan, so there is not much German about them beyond the lettering.
• Cowry-X is a powder steel from Daido Special Steel with the same 3% carbon and 20% chromium, at 64–65 HRC. The difference is that ZDP-189 contains molybdenum, tungsten and vanadium, and Cowry-X does not.

In lists of “Western steels”, MC66 is often filed as German. That is precisely the sort of error such articles exist to correct.

What it can do

In terms of the balance between hardness and strength, ZDP-189 is one of the peaks of knife metallurgy, and on a short list of the best steels for a kitchen knife it stands next to Aogami. Edge retention is very high, and the claimed impact toughness is too.

How high can be estimated from a rough rule: every two points of HRC roughly doubles the time a knife stays sharp. A knife at 52 HRC — the hardness of cheap knives from a block — is sharp for about a week. A knife at 62 HRC lasts about a year under regular use. What 66 HRC means on that scale, anyone can work out for themselves, but the working out will stay theoretical: the knife usually reaches the end of that period chipped rather than still sharp.

What it cannot do

Here it is worth being honest, including about the contradictions in the descriptions.

ZDP-189 is described at once as having very high impact toughness and as relatively prone to chipping because of its extreme hardness. Both claims come from spec sheets and reviews, and they sit together badly. General metallurgy leans towards the second: 20% chromium at 3% carbon means a very large volume of carbide, and chromium carbides are softer than vanadium carbides and coarser. Plenty of carbide means poorer crack resistance, that is, an edge that chips more readily.

Second: the steel is very hard to sharpen compared with others. That follows directly from the same thing — the abrasive is grinding away exactly those hard inclusions you bought the steel for.

How to ruin it

There are not many ways, and all of them are domestic.

Overheating. Steel ground on a dry wheel without water cooling loses hardness — this happens at the factory and it happens in the workshop of the man who has taken it on to “sharpen it properly”. Formally the blade still carries an expensive grade name; in fact you now own a knife with ruined heat treatment, and there is no getting it back.

Too acute an angle. Tool and high-speed steels dislike a narrow grind: for the class-related SKD11, 22–24 degrees is considered sensible. Bringing a very hard steel down to a thin edge is technically possible, and it will even cut — until the first bone, avocado stone or glass board.

Lateral load. A hard edge does not bend, it breaks off. A chip at 66 HRC is not a “touch it up on the steel” matter, it is several sessions on proper stones.

A steel that is hard to sharpen is worth buying only if you know exactly what you will be sharpening it with.

What it costs

A lot. ZDP-189 is a very expensive alloy, and knives made from it are priced to match. The order of magnitude can be judged from its relative: kitchen knives in Cowry-X are made, in effect, by one maker — Hattori — and the series starts at around 600 euros.

Who needs it

Not a cook. A cook in a real kitchen does not work with a knife that must not be dropped, whose handle must not get wet and which is easy to steal. In a professional setting there are many knives, they are identical, marked by product type, and they are touched up on a steel ten times a shift — in a practised motion, without a thought.

ZDP-189 is for someone who finds the object itself interesting. It is a domestic luxury, and its purpose is to give the owner pleasure, not to earn money. Put that way, the purchase makes perfect sense, is honest and deceives nobody. The other framing does deceive — the one where ZDP-189 is bought in order to “finally stop sharpening”.