JIS G3136 — Rolled steel for building structures
Grades
SN400A, SN400B, SN400C, SN490A, SN490B, SN490C, SN490Y, SN520B, SN520C
Chemical composition and mechanical properties
| Grade | Chemical composition | Mechanical properties |
|---|---|---|
| SN400A | C≤0.24, P≤0.050, S≤0.050, Ceq≤0.36 | Rm 400-510 MPa, Rp0.2 ≥235 MPa, A≥18%, yield strength ratio ≤0.80 |
| SN400B | C≤0.20, Mn 0.60-1.40, P≤0.030, S≤0.030, Ceq≤0.36 | Rm 400-510 MPa, Rp0.2 ≥235 MPa, A≥18%, Akv≥27J at 0℃, yield strength ratio≤0.80 |
| SN400C | C≤0.18, Mn 0.60-1.40, P≤0.025, S≤0.020, Ceq≤0.36 | Rm 400-510 MPa, Rp0.2 ≥235 MPa, A≥18%, Akv≥27J at 0℃, yield strength ratio≤0.80 |
Application scope
JIS G3136 specifies rolled steel for building structures, including the SN400 to SN520 series and grades A, B, and C, covering steel plates and sections, specifically designed for seismic design of buildings. The standard controls yield strength ratio, carbon equivalent, and properties in the thickness direction. Grades B and C also specify impact toughness to ensure plastic deformation capacity and weld quality, making it suitable for welded or bolted load-bearing components in seismic zones.
Typical applications
Primarily used in steel structures of high-rise and super high-rise buildings, beams, columns, and joints of seismic-resistant frames, large-span buildings, and heavy-duty factories—load-bearing components requiring seismic performance. Grade C exhibits thickness-direction properties, making it suitable for important joints and thick plate connections. With its controlled yield-to-tensile ratio and good plasticity and weldability, it can achieve stable plastic energy dissipation under strong earthquakes, making it a dedicated steel for seismic-resistant building structures.
