We have long thought that stainless steel (which contains chromium to prevent rust) was the product of modern metallurgy, but new evidence suggests that the ancient Persians made a version. primitive stainless steel from 1,000 years ago. Archaeologists are extremely surprised when they discover this special metal in the Chahak region.
New research is published on Journal of Archaeological Science Conclusion: The ancient Persians smelted steel alloys with chromium in the 11th century AD. Most likely, this steel was used to make swords, knives, armor and many other items. Phosphorus is also present in the alloy, which makes this metal sample brittle.
“This steel forged and forged in Chahak contains 1% to 2% chromium and 2% phosphorus”, Said Rahil Alipour, an archaeologist working at University College London and lead author of the study.
Microscopic image shows a round piece of steel stuck in slag.
Up to this point, both archaeologists and historians believe that chromium-phase steel is a modern man’s invention. Stainless steel as we see it today, developed in the 20th century, contains much more chromium (containing about 11% chromium) than steel of the ancient Persians. Prof Alipour said that the ancient Persian chromium “has no rust properties”.
However, the new research “provides the oldest evidence of the addition of the element chromium, most likely chromite, to be intentionally added to the metal-making process – resulting in a steel containing a limited amount of chromium“.
Researchers made their way to Chahak – an archaeological site in southern Iran – with instructions from a translation of the medieval Persian manuscript. Chahak was once the most important steel smelter in antiquity, and is also the only archaeological site in Iran that bears evidence of the practice of calcining a mixture of metal in a closed furnace for steel. After this mixture cools, the metal crucible is broken down to get steel. This technique occurs in many different cultures, including humans Viking.
“Usually, pot-fired steel is a very high quality steel. It contains no impurities and is great for weapons, armor and other tools“, Researcher Alipour said.
A piece of slag attached to the fragment comes from a crucible of metal mixture.
The research-oriented ancient manuscript, written by Persian scholar Abu-Rayhan Biruni, dates from the 10th or 11th century AD. The manuscript’s title is “al-Jamahir fi Marifah al-Jawahir“, mean “Summary to understand gemstones“, Which is a guide to forging steel by heating combinations of many metals; Among the ingredients, Abu-Rayhan Biruni wrote about a mysterious compound named “rusakhtaj” (does that mean “scorched objects“), The scientists analyzed that this was chromite sand.
In the Chahak archaeological site, the researchers found traces of charcoal remaining in the slag. Carbon dating shows that charcoal dates between the 10th and 12th centuries AD. Using electron scanning technique on slag, they discovered traces of chromite. And finally, the steel molecules present in the slag indicate that the Chahak region steel contains between 1% and 2% chromium.
“Chahak region steel is the only steel made according to the ancient heating method that contains chromium – an essential element in modern steel production, such as steel tool or stainless steel making.“, Professor Alipour explained. “Chahak region chromium steel will have the same properties as today’s tool steel, and the chromium content in the steel will increase hardness and strength, which are important for tool making.“.
We can see objects made of Persian steel appear in museums around the world, we also know that fired steel has been used in the manufacture of weapons, armor, ornaments that bring prestige to the wearer and many other tools. The name Chahak also appears in many historical texts, associated with valuable swords and knives. According to the records, the swords of the Chahak region were sold for a very high price but since they were very brittle, the value of the swords soon plummeted.
The slag composition analysis also found the element phosphorus; The smith adds it to the metal mixture to reduce the melting point of the metal, but in addition the phosphorus makes the finished product brittle.
A large piece of steel is stuck in the slag.
Anyway, the new discovery points to an important aspect: the tradition of forging steel was only available to the Persians. According to the study’s author, the element chromium present in Chahak steel could become an identifiable feature, allowing researchers to later distinguish it from artifacts from other regions.
“There is archaeological evidence showing that calcination and forging of steel have been found in centers located in India, Sri-Lanka, Turkmenistan and Uzbekistan, but no steel contains chromium. Thus, chromium is a major ingredient in Chahak steel, unlike any steel forging industry in ancient cultures.“.
Researchers want to collaborate with experts from museums around the world, to expand their research, find more objects also made of chromium steel for comparison and analysis.