Damascus steel

Two steels with the same name

The word “Damascus” covers two very different things:

• Pattern-welded steel: layers of different steels are forge-welded together, folded, twisted and recombined. The pattern comes from these layers. This is the Damascus I forge.
• Wootz (crucible Damascus, “bulat” in Russian): a steel melted in a crucible in South and Central Asia. Its pattern grows from within the steel, without any welding.

Both look as if they were flowing; technically they have nothing in common.

From ore to iron

Iron ore is never pure iron but a chemical compound, usually an iron oxide. In nature, metallic iron occurs almost only in meteorites, and even there as an alloy of iron and nickel. The few iron objects from the Bronze Age, such as Tutankhamun’s dagger, are meteoritic.

Iron was first smelted from ore in Anatolia from around 2000 BC, in tiny quantities at first. It only became common from around 1200 BC, with the Iron Age.

This was done in a bloomery. Iron melts at 1538 °C; a bloomery reaches roughly 1100 to 1300 °C. So the iron never becomes liquid: carbon monoxide from the charcoal strips the oxygen from the ore, the slag melts and runs off. What remains is the bloom, a spongy, porous lump of iron full of slag, soft in some places and already as hard as steel in others. Molten steel being poured into moulds, as in the films, did not come out of these furnaces.

So the bloom is consolidated while hot: hammered, the slag squeezed out, folded and forge-welded, again and again, until a usable piece of iron emerges. A blade, however, needs steel. From about 0.3 to 0.4% carbon, iron can be hardened; knife steels usually have 0.6 to 1% or more. Often the furnace already supplied this carbon, as parts of the bloom are steely, and smiths sorted the pieces. Or they carburised the iron afterwards in the glowing charcoal.

The same principle exists in Japan. In the tatara furnace, iron sand is smelted with charcoal; the result is the kera, a porous mass of iron and steel. Its best part is tamahagane. In Shimane this is still done today: around 10 tonnes of iron sand and 12 tonnes of charcoal yield a kera of about 3 tonnes after roughly 72 hours.

Iron and steel together: pattern welding

For centuries, steel was precious. Many blades and tools therefore had a body of soft iron with a steel edge welded on. This saves steel, and the tough iron holds the blade together.

The decorative pattern is something else. Smiths twisted rods of different iron, welded them side by side and made them into the core of a sword blade. This is documented from the 3rd century AD at the latest, for instance in the bog finds of Nydam, and was at its height from the 5th to the 8th century. The light contrast usually came from phosphorus-rich iron, not from steel. Materials testing shows that the pattern did not make a sword stronger. It was decoration and a sign of status.

From the 9th and 10th centuries, such blades disappeared. They were replaced by swords made of a few pieces, or a single piece, of steel.

Wootz: the other Damascus

Wootz is a melted steel. Iron and carbon (charcoal, plant matter or cast iron) were heated in a sealed clay crucible until everything was liquid. The result was a small ingot of very high-carbon steel, around 1.5% carbon. It was made in South India and Sri Lanka, probably as early as the last centuries BC, and is securely documented from the 9th century in Central Asia (Merv, Akhsiket).

The pattern forms without any folding. As it solidifies, the steel grows in tree-like crystals, and tiny amounts of vanadium or molybdenum collect between them. When the ingot is then forged many times at a comparatively low heat, hard iron carbides line up along these traces: light bands in darker steel.

The famous sabres in museums mostly date from the 16th to the 18th century. Where the name “Damascus” comes from is disputed: from the trading city of Damascus, or from the comparison with patterned damask fabric.

Here the legend is half true: the making of such blades died out in the 19th century. Only in the 1990s did the metallurgist John Verhoeven and the smith Alfred Pendray manage to reproduce them and explain how the pattern forms.

Never lost

Pattern-welded steel was never “lost”, even if that story is often told, usually by someone who has just “rediscovered” it. In Indonesia the keris, with its layered pattern (pamor), has been forged without interruption for centuries. In Japan, folded blade steel shows its grain (hada). In 19th-century Europe, gunmakers, above all in Liège but also in Paris and England, made barrels from twisted iron and steel ribbons, wound round a mandrel and welded: Damascus barrels. Pattern names such as “damas crollé” date from that time. Only around 1900 did barrels of cast steel replace them.

In the USA, the knifemaker Bill Moran brought Damascus back to knifemakers’ attention in 1973. Since then it has been part of knifemaking for good.

Modern steel changes everything

Around 1740, Benjamin Huntsman in Sheffield developed a way of melting steel in a crucible: clean and even, ideal for knives and springs. From 1856, Henry Bessemer’s process made steel a mass product, and other processes followed. Since then, steel has contained hardly any slag. Folding and forge-welding therefore no longer make it cleaner or better. Every weld is, if anything, a potential flaw, and the carbon spreads out between the layers during forging.

Stainless steel has no single inventor. In 1904 the Frenchman Léon Guillet studied alloys of iron and chromium without recognising their resistance to rust. In 1911 the German Philipp Monnartz explained from what chromium content steel becomes resistant, and in 1913 Harry Brearley in Sheffield made the first stainless steel for industry, soon used for cutlery. Today, steel counts as stainless from 10.5% chromium; knife steels usually have 12 to 14% or more. For around three thousand years before that, not a single blade was stainless.

Stainless means rust-resistant, though, not rust-proof. The chromium forms a thin, self-healing protective layer on the surface, and for that it has to be dissolved in the steel, not locked up in carbides.

Conventionally made steels with a lot of carbon and chromium, such as 440C, form large chromium carbides as they solidify. These make a very fine, acute edge harder to achieve and reduce toughness. There are fine-grained stainless steels too, such as the razor-blade steels AEB-L and 12C27. For highly alloyed steels, powder metallurgy solved the problem (from 1970): liquid steel is atomised into fine powder, each grain solidifies almost instantly, and the carbides stay tiny and evenly spread. The powder is then pressed back into solid steel under pressure and heat. Incidentally, the “CPM” in names such as CPM S30V stands for “Crucible Particle Metallurgy”: Crucible is the manufacturer’s name and has nothing to do with crucible steel.

Why I still forge Damascus

Because every pattern is unique, like a fingerprint. Because the technique is well over a thousand years old. And because it is beautiful. Not because Damascus cuts better: a well-made Damascus blade is exactly as good as the steels and the heat treatment it is made of, no better and no worse.

The pattern comes from combining two steels that colour differently when etched: the nickel-bearing steel stays bright, the carbon steel turns dark. This is how a billet takes shape in my workshop:

The steels I use

• Damascus, standard mix: XC75 and 15N20. Both have around 0.75% carbon and harden together; the nickel in 15N20 stays bright after etching.
• Higher-performance Damascus: O2 (1.2842) and 15N20.
• Japanese blade shapes: 1080 and 1.1645 in equal parts, averaging about 0.9% carbon.
• Kitchen knives: plain carbon steels, ApexUltra or stainless steels. For stainless I often use AEB-L and CPM MagnaCut, as well as M390 and CPM S30V, and a basic 420 where rust resistance matters above all.
• Folding and outdoor knives: from D2 to CPM S90V, plus stainless Damascus.

Harder is not better

The quality of a blade is often judged by its hardness, in Rockwell (HRC): the harder, the better. I disagree. Hardness has to suit how a knife is used, looked after and sharpened.

An example: a kitchen knife in Maxamet, a powder steel made by Carpenter, can be hardened to around 68 to 70 HRC. With professional heat treatment that is no problem, and in a test rig the edge stays sharp for a very long time, at 68 HRC about twice as long as 440C. In the kitchen, though, such a knife is delicate. Harder steels are less tough: the edge tends to chip rather than just roll. And it can only be resharpened with diamond or CBN abrasives, with plenty of time and experience. Little benefit, many drawbacks – like a Bugatti Veyron as an everyday city car: technically outstanding, out of place in practice.

How long a blade stays sharp does not depend on hardness alone either, but just as much on the amount and type of carbides in the steel. Two steels of the same hardness can differ several-fold.

Common myths

• “Damascus is harder and sharper.” It is as good as its steels and its heat treatment.
• “The secret of Damascus is lost.” That only applies to wootz, and it has been forged again since the 1990s. Pattern-welded steel was never lost.
• “More layers are better.” The number of layers determines the pattern, not the quality.
• “Folding cleans the steel.” For a slag-rich bloom, yes; for modern steel, no.
• “Harder is better.” See above.
• “A hard blade bends less.” How far a blade flexes depends on its thickness, not its hardness. Harder steel can simply be bent further before it takes a set – and is more likely to snap than bend.
• “Stainless never rusts.” Stainless means rust-resistant.

Sources

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