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How did manganese help Robert Mushet improve Bessemer steel casting?

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manufacturing — steel Molten steel being poured into a ladle from an electric arc furnace, 1940s.

Robert Mushet significantly improved the Bessemer process by introducing an alloy of carbon, manganese, and iron—often referred to as spiegeleisen—after the air-blowing stage was complete.12

This addition served two critical functions:
* Restoration and Neutralization: It restored the necessary carbon content to the steel while neutralizing the detrimental effects of remaining impurities, particularly sulfur.1
* Improved Workability: By removing sulfur and oxygen, manganese prevented "hot shortness," a condition that causes metal to crack or fail during hot working. Consequently, Mushet’s discovery allowed the steel to better withstand the stresses of rolling and forging at high temperatures.34

By addressing these metallurgical challenges, Mushet’s contribution helped transform the Bessemer process into a reliable method for the mass production of high-quality steel.1