How does manganese affect the properties of Q355 I-beams?

Q355 I-beams (Chinese standard) contain 1.20-1.70% manganese, which strengthens the ferrite matrix by forming solid solutions and refining grain structure. This increases yield strength (355 MPa minimum) and tensile strength (470-630 MPa) while improving hot workability during rolling. Manganese also counteracts sulfur's harmful effects by forming manganese sulfides, preventing "hot shortness" (brittleness at high temperatures). Unlike higher-carbon alloys, Q355 retains good weldability due to manganese's ability to stabilize the microstructure, making it ideal for heavy-duty applications like crane girders and offshore platforms. Excessive manganese (>1.7%) is avoided to prevent cold brittleness in low-temperature environments.