A Brief Story of Steel
The story of steel starts right back to around 4000BC , but the real production of steel did not start until 1300-1400BC; in Eastern Africa, and later by the Spartans who were known to have produced steel in large quantities.
How did the Ancient blacksmiths make their steel? Well, they started by heating an iron bar until it arrived at a specific colour, and then hammered the iron, forcing out the impurities (carbon). If you watch a blacksmith at work, you will see the impurities in the form of sparks.
In the ancient world, steel was a precious product, and could only be made by hand. The secrets of making swords and knives were passed down from generation to generation. A typical “recipe” for sword making would be as follows:
- Heat the iron until the colour of the setting Sun.
- Hammer the iron flat.
- Heat the iron again, and make a cut half way down the length of iron.
- Fold the iron (2 layers) and beat into shape.
- Heat the iron again, and repeat (3) and (4) ten times.
- Heat the steel and twist it.
- Beat it once again into shape.
- Heat it for the last time and “quench” it in urine.
The sword blade is ready!
You may be surprised that urine was used, but in one historical account only urine of a red headed boy could be used! And this process left the most incredible “etched” designs on the blade.
Up until the 19th century, the manufacture of steel relied almost exclusively on the skill of the blacksmith; meaning that it could not be used in engineering or construction, as it could not be massed produced.
This is why all the metal bridges of the 19th century were made from iron.
In 1879 the then longest bridge in the world collapsed (The Tay Bridge Disaster), causing the death of 75 people. It was later found that although iron resisted extremely well under compression, it was very bad under tension.
If you conduct a tension test on an iron bar, it will snap clean, and the snap being where there is the greatest concentration of carbon.
In the late 1800’s the production of steel could be massed produced by the invention of the Bessemer Converter. This was like a very large iron bucket full of molten iron. With air being pumped into the base of the bucket. The air (containing oxygen) would combine with the carbon in the iron and would produce carbon dioxide.
The idea was brilliant, but it failed for a very simple reason. To make good steel required a carbon content of 1%, and there was no accurate means of knowing when the Bessemer converter had obtained this value. However a metallurgist called Sidney Gilchrist Thomas came to the rescue with a very simple solution. He suggested that all the carbon should be extracted from the iron, and then the 1% carbon content added afterwards. It worked, and over night Great Britain became the worlds greatest producer of steel, which in turn fired the Industrial Revolution to even greater heights, and opened the door to the modern era.