A: The grade is like an "identity card" for steel, representing its chemical composition and mechanical properties.

Q235B: "Q" represents yield strength, "235" means the yield strength is not less than 235 MPa, and "B" is the quality grade, indicating specific impact toughness requirements at 0°C.

SS400: Japanese standard, "SS" represents ordinary structural steel, and "400" means the tensile strength is not less than 400 MPa.

304: A common stainless steel grade, representing that it contains approximately 18% chromium and 8% nickel, possessing good corrosion resistance and machinability.