Mn strengthens ferrite, especially in low alloy general structural steel, the solid solution strengthening effect is better;

Mn reduces ΔGγ→a, shifts the austenite isothermal transformation curve to the right and improves steel hardenability;

Mn is an austenite-forming element that lowers the temperature of A1 steel, promotes grain growth, and improves the steel's overheating sensitivity;

Mn contributes to the segregation of harmful elements at the grain boundary and increases the tendency of steel to temper brittleness;

Mn greatly reduces the temperature Ms of the steel, thereby increasing the AR in the hardened steel;

Mn plays a big role in the expansion of the γ region and has an infinite solid solution with γ-Fe, therefore, with a large Mn content in steel, austenite can be obtained at room temperature.

Mn and S easily form MnS, so it can reduce or eliminate the hot embrittlement of steel.

Mn and O easily form MnO, so it is the best deoxidizer.