While both are general-purpose structural grades, their specified limits differ. Q235B (GB) emphasizes yield strength (235 MPa min), while SS400 (JIS) emphasizes tensile strength (400 MPa min). Consequently:
Carbon: Typically slightly higher in SS400 to achieve higher tensile strength.
Manganese: Often higher in SS400 for solid solution strengthening.
Phosphorus & Sulfur: Limits are comparable, usually max 0.045-0.050% for each, but stricter for higher quality grades (e.g., Q235C/D, SS400 with specific impact requirements).