The Secret of Damascus Swords

Damascus steel swords were legendary due to their high hardness and strength, as well as their “near-eternal” blade. They could cut silk as well as break stone. Sultan Saladin impressed Richard the Lionheart at a sword show. Sultan, slender, light and the dull blue of Damascus steel, was able to sink into a soft pillow of feathers.

Blacksmiths and metalworkers have searched for centuries for the secret that made them the bloodiest and most coveted weapons. However, it took centuries to master the technology of making Damascus steel.

Today, in the most advanced laboratories in the world, we obtain steels that combine that almost eternal hardness and strength, recreating the structure of that mythical material, the forging of which the Christians of the Crusades attributed to Lucifer himself.

Katanas, Toledo steel and Damascus steel

Like the secret forging processes of Japanese samurai katana or Spanish Toledo steel known throughout Europe in the Middle Ages, the production of Damascus steel has been passed down from generation to generation of metallurgists for centuries. These methods are now lost, but this may change.

A recent scientific publication by the prestigious Max-Planck-Institut für Eisenforschung (MPIE) in Düsseldorf shows that by imitating the principles of Damascus steel production, the properties of more modern steels can be surpassed, but using only cheap and readily available raw materials. .

The secret of its internal structure

The use of iron by humans has changed the world. And steel is basically an alloy of iron and carbon.

The first iron-based materials, known as tinned steels, appeared in India around 200 B.C. And. V. These steels were obtained by forging sponge iron mixed with carbon from various natural sources.

At the same time, Chinese metallurgists were developing something similar to iron casting. However, the high carbon content made this material incredibly brittle and therefore almost useless.

Looking inside Damascus steel, we found that when it was forged, a hierarchy of microstructures was created, in which ductile layers (easily deformable) alternated with hard layers (more brittle), which led to mechanical properties far superior to Damascus steels from other steels.

Diffusion processes during their production have made the sheets very plastic, allowing changes and transformations, but at the same time incredibly hard.

However, for over 1,000 years, the cost of producing these steels meant that their use was limited to very specific applications that required a very sharp edge, such as knives, razors, and swords. It was also used to make small, intricate parts such as clock springs.

In the late 19th century, with the invention of modern steelmaking technologies such as the Bessemer process, people were able to produce steels similar to the structural materials we know today.

Modern steel production process

The 21st century has already brought a number of advances in this area. As two examples, we can take 3D printing and new heat treatments such as quenching and separation (hardening and separation or Q&P), two manufacturing methods currently being studied at the IMDEA Institute of Materials.

The main goal of current research is to create microstructures in mild steel sheets that not only exhibit improved mechanical properties, but also exhibit application-related properties such as fatigue, fracture and impact resistance, as well as formability and weldability.

More recently, IMDEA Materials has also begun active research into carbon steel 3D printing for structural applications. The focus is on the processing of parts with a variety of properties suitable for the end use of complex steel parts.

Return to the lessons of the past

Although this type of research is at the forefront of today’s steel production, in a sense we are still playing catch-up with the metallurgists of the past.

In the MPIE publication cited above, metallurgists were able to replicate the hierarchical structural manufacturing process thousands of years ago by alternating ductile and hard layers.

The researchers were able to produce a steel capable of withstanding 2,000 MPa but with a strain of 25%, much higher than any current technique.

To put this achievement into perspective, the strongest steels (known as maring), which are currently used in the aerospace industry, can reach 2500-2600 MPa, but with the disadvantage of a low level of deformation (4-5%). This level is much lower than when using Damascus steel, and the result is a strong but brittle material that can break under load or impact.

Meanwhile, the steels produced by Q&P showed improved ductility by about 14%, but at the expense of the strength shown by the steels. maringreaching about 1,500-1,600 MPa.

In another recent work published in Nature MPIE scientists, also based on the development of hierarchical microstructure such as Damascus swords, have obtained even better results. But this latest publication has used all the artillery that materials science allows us: a lot of alloying elements (rare and more expensive) and the most modern 3D printing technology.

However, the real achievement of MIPE research is the results obtained solely on the basis of non-critical alloying elements in combination with traditional forging and heat treatment technologies.

Advanced tools based on artificial intelligence and machine learning will gradually replace trial and error in steel design and production. But, at all times, that the arrogance of progress does not prevent us from seeing the genius of those who preceded us, and all that they can teach us.

José Manuel Torralba, Professor, Carlos III University of Madrid, IMDEA MATERIALS, and Ilchat Sabirov, Senior Research Fellow, IMDEA MATERIALS

This article was originally published on The Conversation. Read the original.

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