By the early part of the 1700s, steel was being used to make some parts of firearms (e.g.) lock springs, frizzens etc., as well as the tools to make firearms. In Europe, England and Germany were two major sources of steel during this period. The next development in steel making was due to an English clock maker and the technology he developed was crucible steel. We will study the process in this post.
The process of making crucible steel is actually much older -- as early as 300 BC, there were several places in southern India making a type of crucible steel called "wootz steel". This steel was exported to the middle-east, where it was encountered by Europeans during the crusades and was labelled by them as "damascus steel". The source of iron ore for the Indian steel was an area in South India, where the iron ore came with small amounts of vanadium and other rare earths. As a result of these trace elements, wootz steel has carbon nanotubes in it, contributing to its superior ability to hold an edge. Unfortunately, by the 1700s, with the rise of British power in India, the secrets of its production died with the blacksmiths. However, we have several earlier descriptions of many travelers to India (Arabs, Persians, French, English, Scottish etc.) from which we know that they were definitely using a crucible process.
Over in England, Benjamin Huntsman was in the business of making clocks, tools and locks in Doncaster, in the early 1720s. Later on, he also practiced as a surgeon and an oculist. Like most people in the clock making trade, he bought most of his steel from German sources. However, he found that this steel was not always good enough for springs and pendulums for his clocks, where consistency in the steel is the key to accuracy. Therefore, he performed several experiments to try and find a more uniform steel production process. Since he needed a large amount of suitable fuel for his steel furnace, he moved his business from Doncaster to Sheffield in 1740, because of the better availability of coke and coal in Sheffield. He continued his experiments in secret in Sheffield for many years and gradually re-discovered the crucible steel process. Essentially, his process consists of melting the iron in a clay crucible, adding a precise amount of carbon. The carbon distributes evenly throughout the molten steel, resulting in a more consistent product. The molten steel is then poured out into a mold to harden. Since the steel is poured out into a mold, it is sometimes called "cast steel" as well. However, unlike cast iron, this steel is flexible enough that it can be heated and forged by a hammer as well, or even welded.
The process starts off by using a crucible made of clay, to which is added wrought iron bars and powdered charcoal. The amount of charcoal added to the crucible is calculated based on the amount of wrought iron. A flux consisting of ordinary glass pieces is also added to the crucible. The crucible lid is then sealed and it is heated in a furnace. Since the glass has a lower melting point than the iron, it melts first and forms a liquid in the bottom of the crucible. After a few hours, the iron starts to melt and absorbs some of the carbon from the powdered charcoal as it becomes a liquid. Since iron is denser than glass, the liquid iron sinks past the liquid glass to the bottom of the crucible. Any oxygen is released in the form of carbon monoxide gas, which bubbles out through the layer of liquid glass. In a few hours, the iron is fully melted into a liquid and absorbs enough carbon to transform to steel. The liquid steel is at the bottom of the crucible, with a layer of liquid glass above it. The liquid glass seals the steel and prevents any oxygen or excess charcoal carbon from being absorbed by the molten steel. At this point, a worker, called a "puller-out", (sometimes, it was two people) reaches down into the furnace and pulls out the crucible pot. The crucible pot can be left to cool until the metal turns solid, at which point, the glass layer is broken with a hammer and the steel ingot underneath is retrieved. Alternatively, immediately after pulling the crucible from the furnace, another worker, called a "teemer", can open the crucible lid and pour the liquid steel into a mold, with another worker using a tool to dam the glass slag floating in the crucible on top of the steel. The steel has to be poured into the mold quickly (in under two minutes or so) and then a lid is placed on the top of the mold, to limit the amount of oxygen combining with the cooling steel. In about five minutes, the steel becomes solid enough inside the mold. If the steel ingot is to be sold to someone else, then the mold is allowed to cool for several hours before being opened. However, if the foundry has its own forging shop, then the mold is broken after 5 minutes and the still hot ingot is carried off to a hammer to be forged into the final shape, as it is still soft enough to be easily shaped (incidentally, this is the origin of the English saying, "strike while the iron is hot"). The crucible can be re-used a few times before it has to be disposed off, because it weakens due to the intense heat and erosion, every time it is used.
The "puller-out" and "teemer" had to be strong men, to lift and handle the crucible, since the weight of the steel alone in a single crucible was usually around 20 to 45 kg. (45 to 100 lbs.). The mold was typically about 50-100 cm. (about 20 to 40 inches) in length and square in cross section. It was made of two halves, held together by rings. The hole on top of the mold typically had a width of only 7.5 cm. (about 3 inches). The mold was deliberately kept narrow so that the molten steel cannot be exposed to much oxygen as it is poured into the mold. A good teemer could pour molten metal from the crucible through this narrow hole of the mold in under 2 minutes, without any splashing or spilling. Teemers were trained to do this by making them pour cold lead pellets into molds, until they could do it perfectly, before they were allowed to handle hot steel.
A teemer at work. Public domain image.
In the beginning, Huntsman remelted a mixture of blister steel and wrought iron, instead of just wrought iron, in his crucibles, and he kept improving the process over several years. He realized very early on, that his steel could be used for other purposes besides clock springs and tried to interest other local manufacturers of cutlery and tools to use his steels, but they were not interested, since his steel was harder than everyone else's steel. Therefore, he exported his steel to France, where it was very well received. Pretty soon, the Sheffield cutlery manufacturers began to lose market share to superior products from French manufacturers and as a result, they actually tried to obtain a government order to force Huntsman to stop exporting his steel! Due to their efforts, Huntsman even contemplated moving his factory elsewhere. Luckily, cooler heads prevailed and the Sheffield manufacturers abandoned their attempts to sabotage his business and started buying from him instead and the demand for his steel went up tremendously. He established a larger steel factory in 1770 and the city of Sheffield started becoming famous for its steel. Within 100 years of his discovery, the city of Sheffield was producing about 40% of the steel produced in Europe!
Click on the image to enlarge.
Huntsman worked in secret and never patented his process, so other companies elsewhere also tried manufacturing crucible steel. However, they could not duplicate the Huntsman process immediately for a few reasons.
The first reason was the crucible -- it had to be able to withstand high temperatures and therefore, it needed to be made of a special type of fire-clay. By some lucky chance, the place where Huntsman went to dig his clay from, in the north western part of Sheffield town, happened to be one of the few places in England where this special type of clay existed. We now call this type of clay as "Stannington clay". When people in other parts of England, Europe and the United States tried to duplicate the process, their attempts failed because their clay pots could not withstand the intense heat of molten steel. It took other people a few decades to figure out that the type of clay used was crucial to the process.
The second reason was the flux that he used -- his secret was broken glass. The glass melts before the steel does and coats the surface of the molten steel ingot. As legend has it, this secret was finally discovered by one of his competitors, using industrial espionage tactics. The story goes that a person by the name of Samuel Walker had a rival foundry at Grenoside, on the northern part of Sheffield. One cold winter night, Walker disguised himself as a poor beggar and showed up outside Huntsman's factory, pretending to be ill and begged to be let inside for shelter and warmth. The workers took pity on him and led him to a corner of the factory floor to sleep in. Walker pretended to sleep, but what he was actually doing was carefully watching the whole process of making the steel. He observed the workers breaking green glass bottles and putting them in the crucibles. About three months later, Walker's factory in Grenoside was also making crucible steel. Whether the story about the disguised beggar is true or not, it is definitely true that Samuel Walker did exist and he did learn details of Hunstman's secret process somehow. Samuel Walker is recorded to have built his rival factory for making steel in 1750, although he did not expand his factory until 1771, indicating that his original furnace had only limited success. Perhaps he didn't figure out the other secrets, such as the clay, until many years later. Other people in Sheffield also started making cast steel, once they had figured out Huntsman's secrets and Sheffield became the first "Steel city" in the world.
The following three videos show some experiments made by a couple of geeks (one is Niels Provos, who is well known in computer security circles and now works in Google):
In the United States, steel was mainly imported from England during this period. The Remington company was one of the first to start offering crucible steel barrels for firearms in the late 1820s. In 1845, Samuel Remington appeared before the Ordnance Trial Board, to persuade them to use Remington steel barrels for military firearms.
By the time of the Civil War, both Remington and Colt were supplying crucible steel barrels, while most of the other manufacturers were still making wrought iron barrels only. Both companies stamped "cast steel" on their barrels, to show that they were of a superior quality. It must be noted though that wrought iron barrels were still cheaper than cast steel at this stage, so both companies also offered wrought iron barrels for sale as well. From a catalog dating from 1871, Remington is listed as offering both cast steel barrels and iron barrels of different grades. During this time, Remington's "cast steel barrels weighing 6 lbs. or less" are listed at a price of $5.00 each, whereas the price of their "iron barrels weighing 7 lbs. or less" are listed at $3.00 each.
The invention of the Bessemer steel process dropped the price of steel even more and was really responsible for many other firearm manufacturers to switch from wrought iron to steel. We will study that process in the next post.