How does manganese prevent steel from breaking during hot rolling or forging?

Manganese prevents steel from breaking during hot rolling or forging by acting as a desulfurizer.12

In the absence of manganese, sulfur in steel forms low-melting iron sulfide, which concentrates at the crystalline grain boundaries of the metal. This condition, known as "hot shortness," renders the steel unable to withstand the stresses of hot working, causing it to break or fracture during processes like forging or rolling.12

When manganese is added to the steel, it reacts with the sulfur because it has a greater chemical affinity for it than iron does. This reaction converts the low-melting iron sulfide into stable, high-melting manganese sulfide particles. By removing sulfur from the grain boundaries in this way, manganese ensures the structural integrity of the metal during high-temperature processing.12