Bessemers and Open Hearth Steelmaking

Before the mid 1850s, steelmaking was an inefficient and expensive process. At the time, steel was produced in small crucibles around the size of a small vase.¹ It was not commercially viable to produce large quantities of structural steel, so many industry applications simply used iron instead. But iron was a softer material than steel, causing it to degrade more quickly under intense pressure, like that which would occur in railway lines. Because of this, many people sought ways to mass produce high-quality structural steel.

Henry Bessemer was the first person to successfully develop an inexpensive process to mass produce steel. The English inventor developed this process while seeking to improve the ironmaking process for weapons manufacturing.² In Bessemer’s own words, the process “consists in the decarbonization or partial decarbonization and refinement of the crude iron which is obtained in a fluid state from the blast furnaces in which the iron ore is usually smelted."³ By acting directly on molten iron, one can cut the costs of transporting and melting of solid iron.

A Bessemer Converter

The Bessemer Process

There are two key characteristics of the Bessemer process. The first is the size of the converters. As opposed to the steel crucibles that came before, Bessemer converters are large cylindrical structures around 20 feet tall that are mounted so that they can be rotated, and the molten metal dumped out. The sheer size of the converters allows them to produce significantly more steel than previous steel production.

The second characteristic of the Bessemer process is the way it removes impurities from the metal. The Bessemer process will “blow or force into and among the fluid metal numerous small jets of atmospheric air... and thereby to keep up the required temperature during the process.”⁴ These jets of air oxidize the metal, removing impurities that exist in the iron. A side effect of this is that the oxidization also helps to heat the metal, keeping it molten and reducing the need for external fuel sources.

Because the Bessemer process was rather simple to use, it did not require skilled laborers to operate the machines. By removing the need for skilled workers to produce steel, one could make more steel for cheaper labor costs. Production using the Bessemer process was also much faster. Three to five tons of steel could be produced in around ten to twenty minutes, a process that used to take a day or more.⁵

Despite these benefits to the Bessemer process, there were drawbacks to the system. One of the biggest drawbacks was the entire absence of power to manipulate beyond very narrow limits, "for the reason that, when a heat is blown, the sources of heat are exhausted, and the steel must be put into ingots before it becomes too cold. If it be overblown, the excess of [oxides] cannot be eliminated; if it be underblown, or if it be a cold heat, there is no means of increasing the temperature.”⁶ Another quirk of the bessemer process is that it required iron with a low phosphorous content to work effectively. Upon hearing about the Gilchrist–Thomas process, which allowed iron with a higher phosphorous content to be used in Bessemer converters by lining the converters with lime, Carnegie adopted this process in many of his converters.

Open Hearth Furnaces

The Gilchrist-Thomas process, while effective in Bessemer converters, had the side effect of needing to reline the converter more often. However, Bessemer converters were not where the Gilchrist-Thomas process truly flourished. The process worked significantly better in Siemens open hearth furnaces. Open hearth furnaces were slow and required skilled laborers, but the steel produced was of higher quality than steel from Bessemer converters.⁷ This prompted Carnegie to invest in installing more open-hearth furnaces in his plants.

Carnegie’s shift in focus to open-hearth furnaces was a boon to skilled laborers. Their talents were once again required with these furnaces, which gave them a much better negotiating position during labor disputes.⁸