Yesterday I mentioned the steel Sawyer rifles inventoried within the batteries of the Department of the Gulf. We usually associate bronze and iron (cast or wrought) with Civil War artillery. The majority of cannons used in the war were constructed of those metals. Indeed, the use of steel cannons on a large scale was a post-Civil War trend. But a small number of weapons with wartime vintage might be described as “steel.” In addition to European sources, several northern gunmakers turned to the metal for experimental and small production batches. But it is important to understand that not all steels are alike. While steel in name, some of the metal used in the 1860s did not exhibit the properties of the steel we use (everywhere) today.
Steel itself was known in ancient times and isn’t some recent invention. As you probably learned in the classroom at some point, steel is an alloy of iron. Most naturally occurring iron is found as an ore, or compound. Iron easily bonds with oxygen, forming iron-oxides (such as rust). As with many metals, mankind developed smelting processes to remove the oxygen and produce strong metals. For iron, the most common practice was/is to heat the ore to a liquid state, then introduce carbon to displace oxygen. Two issues faced the steelmaker of old. Iron melts at around 2,500° Fahrenheit, much higher than some other common metals. Furthermore, before melting as the iron temperature raises the oxidation increases. In other words, if not carefully controlled the steel maker creates more work just by heating the metal.
The second of these two issues separated grades of iron from steel. Normal smelting required large amounts of carbon, such as charcoal or coke. This resulted in an alloy which was high in carbon content. In the Civil War era metal produced through the common process was known as pig iron, which was roughly 3.5 to 5% carbon depending on the exact procedure used. But metalworkers had long known the lower the carbon content the stronger the metal. Closer to the Civil War, Ordnance Department tests confirmed gun metal with lower carbon content stood up better in proofing. The Ordnance Manual of 1861 described steel as:
… a compound of iron and carbon, in which the proportion of the later is 5 to 1 per cent., and even less, in some kinds. Steel may be distinguished from iron by its fine grain; its susceptibility of hardening by immersing it, when hot, in cold water; and with certainty by the action of diluted nitric acid, which leaves a black spot on steel….
Metal workers could refine the high-carbon irons into steel, but the process was time consuming and resource expensive. Wootz and Damascus steel making processes required carefully controlled heating and cooling cycles (and unknowingly producing carbon “nanotubes” that strengthened the metal, according to some). While producing strong weapons and tools, this process was far too expensive for common use and could not be adapted for cannon production.
By the 19th century methods known as “puddling steel” and “blister steel” emerged. The puddling process involved, for simplicity’s sake, bringing the iron to a boil. Then impurities and carbon burned off leaving a “ball” of purer iron within the puddle of the furnace.
Metalworkers used this process to produce puddled iron with relatively low carbon content, but as the Ordnance Manual noted, could be used to produce steel:
If, in the operation of puddling, the process be stopped at a particular time determined by indications given by the metal to an experienced eye, an iron is obtained of greater hardness and strength than ordinary iron, to which the name semi-steel, or puddled steel, has been applied. The principal difficulty in its manufacture is that of obtaining uniformity in the product, homogeneity and solidity throughout the entire mass. It is much improved by reheating and hammering under a heavy hammer.
The product had high, for its day, tenacity and could be worked into artillery, at least to the size of field pieces. But as noted, the process required the trained, subjective eye of the metal worker. The product could be used to make cannons.
Blister steel, sometimes called cementation, involved, again for simplicity, baking the iron within a furnace. As described in the Manual, blister steel was:
… prepared by the direct combination of iron and carbon. For this purpose, the iron in bars is put in layers alternating with powdered charcoal, in a close furnace, and exposed for 7 or 8 days to a heat of about 70° Wedgewood [10,177° Fahrenheit], and then suffered to cool for as many days more. The bars on being taken out are covered with blisters, have aquired a brittle quality, and exhibit in the fracture a uniform crystalline appearance.
This may sound contrary to the refining task, but with the cementation process, carbon was actually re-introduced to the iron in order to clear out impurities and oxygen. Then the carbon was burned off. The trick was to know when to remove the heat to have just the right level of carbon mix.
A video from Ric Furrer provides a lesson in blister steel production:
Around the four minute mark they show the blisters which give this process its name. Notice also the “spark” test of steel vs. wrought iron. As alluded to in the video, blister steel was an intermediate step to sheer steel. So part two:
This worked great to produce tools and small weapons. But it was not practical for artillery. So yet another process was used to produce cast steel:
Cast steel is made by breaking blistered steel into small pieces and melting it in close crucibles, from which it is poured into iron molds; the ingot is then reduced to a bar by hammering or rolling, as described under the head of malleable iron, these operation being performed with great care. Cast steel is the finest kind of steel and best adapted for most purposes….
Several northern steel works used this process before the Civil War. And at the start of hostilities these turned to military production. But, as the descriptions indicate, steel working remained much more expensive than simple iron casting or even wrought iron techniques. As such, even with the superior qualities of steel, costs inhibited its use as cannon metal.
The steel furnaces of Singer, Nimick & Company in Pittsburgh produced cast steel 3-inch ordnance pattern rifles. A.M. Sawyer’s 6-pdr rifles were cast steel, likely produced by the Putnam Machine Company of Fitchburg, Massachusetts. Norman Wiard’s rifles, in both 2.9- and 3.67-inch caliber, were probably produced at a foundry in or near New York City. However Wiard’s guns have been classified as “semi-steel” and may have used the puddling process instead of blistering.
All of these steel making processes were, even at the time of the Civil War, obsolete. Englishman Henry Bessemer patented his more efficient and economical process in 1855. Bessemer took on the task of improving steel making in an effort to provide cannons that would withstand a new rifling scheme he’d patented. So one might say the Bessemer process was born from a need to improve artillery. At the end of the Civil War, two Bessemer works existed in the north. Neither were involved in artillery production, or military contracts as far as I can tell. But perhaps of interest to the “what might have been” crowd, Confederate naval papers include a plan for a Bessemer plant.
Yes, fuel for much speculation.