Manganese is a key alloying element in H-beams, present at 0.5-1.65%. It enhances tensile strength and hardenability by forming solid solutions with iron, strengthening the metal matrix. Manganese also counteracts sulfur's harmful effects: sulfur forms brittle iron sulfides, but manganese reacts with sulfur to create manganese sulfides, which are less brittle and distributed evenly, reducing hot shortness during rolling. Higher manganese levels (1.0-1.65%) in high-strength grades boost strength without significant ductility loss, making them suitable for heavy loads. However, excess manganese can increase brittleness, so levels are tightly controlled per standards to maintain a balance of strength and toughness.