Science and steel

by Jason Crawford · June 22, 2019 · 1 min read

In my research on the history of steel, I discovered a new data point on the question of the importance of science to the early Industrial Revolution.

Specifically, Henry Bessemer, in developing his revolutionary process for the refining of cast iron into steel, relied on explicit knowledge of chemistry. Quoting The Epic of Steel (emphasis added):

Bessemer’s new theory was in principle very simple. Pig iron as produced in the blast furnace, contains an excessive amount of carbon—about 4 per cent—and certain other elements, such as silicon, phosphorous, and sulphur, all of which tend to make iron brittle. To convert the iron into steel, the carbon content is reduced through oxidation usually to less than 1 per cent, and the other elements are at the same time largely burned out. Bessemer knew that carbon in molten iron united very readily with oxygen. Why not reduce the carbon content in pig iron and remove the other elements by means of oxygen from a strong blast of air?

How did Bessemer know this, in 1855? In an earlier chapter, the same book describes the development of the science of metallurgy, including this passage:

The fact that varying percentages of carbon caused the differences in hardness of wrought iron, cast iron and steel, gained recognition slowly. Bergmann made some headway in 1781 but he confused carbon, which he isolated, with phlogiston [a non-existent substance held by a mistaken theory to be responsible for combustion], and he held stubbornly to the phlogiston theory. His views were combated by Vandermonde, Berthollet, and Monge who claimed in a report to the Académies des Sciences in 1786 that carbon was the element which all were seeking as the cause of the differences between iron and steel. This theory was proven by Clouet in 1798 and by Pepys in 1815, both of whom succeeded in making steel by heating iron and a diamond together. Then, in 1827, Karsten in Germany isolated the carbide from soft steel and showed it to be a compound of iron and carbon.

So carbon had been identified as the hardening element in iron by the early 1800s, and the fact of oxygen as a reactive element was a known part of chemistry by this time as well, setting the stage for Bessemer’s experiments in the mid-1800s.

Relevant books

The Epic of Steel