1. The SS400 Grade in JIS G3101
SS400 is the most widely used structural carbon steel grade in Japan, defined in JIS G3101 for general structure applications. The designation SS means structural steel and the number 400 refers to the minimum tensile strength of 400 MPa. The grade is produced as hot rolled plates, bars and sections including H-beams, and it is recognized internationally as a general purpose structural material for buildings, bridges and machinery.
2. Mechanical Properties
The yield strength of SS400 depends on the product thickness. For thickness up to 16 mm the minimum yield strength is 245 MPa, for 16 to 40 mm it is 235 MPa and for 40 to 100 mm it is 215 MPa, while the tensile strength is 400 to 510 MPa across the range. The elongation requirement is 17 to 21 percent depending on thickness and test piece. These values are verified by tensile testing on each heat and reported on the mill certificate.
| Thickness | Min Yield MPa | Tensile MPa |
| Up to 16 mm | 245 | 400 - 510 |
| 16 - 40 mm | 235 | 400 - 510 |
| 40 - 100 mm | 215 | 400 - 510 |
3. H-Beam Section Range
SS400 H-beams are hot rolled in the standard H section series with depths from about 100 mm up to 400 mm and beyond, in web and flange thickness combinations that cover light to heavy duty frames. The H shape gives a high section modulus in both directions, so the beam resists bending and column buckling efficiently. Sections are produced to the dimensional tolerances of the applicable standard and supplied in lengths of 6 to 12 m or cut to order.
4. Fabrication Properties
SS400 is a low carbon steel with excellent weldability, and no preheat is normally required for thin sections in ordinary workshop conditions. The beam can be cut, drilled, bolted and welded with standard equipment and consumables, and it can be hot-dip galvanized for outdoor service. Because the grade has no special toughness requirement, it is selected for general structures at normal temperatures rather than for low temperature or impact loaded applications.
5. Typical Applications
Frames and columns of low and medium rise buildings.
Mezzanine floors, platforms and machine bases.
Bridge secondary members and approach structures.
Agricultural and industrial storage buildings.
General fabrication, racks and support structures.
Frequently Asked Questions
Q: What does SS400 mean in JIS G3101? SS stands for structural steel and 400 is the minimum tensile strength in MPa, so SS400 is a general structure steel with at least 400 MPa tensile strength.
Q: Is SS400 equivalent to ASTM A36? Both are general purpose carbon structural steels with similar strength levels, and they are often accepted as equivalents for design purposes with the approval of the engineer.
Q: What is the yield strength of SS400? The yield strength is 245 MPa minimum for thickness up to 16 mm and reduces to 235 MPa and 215 MPa for thicker material.
Q: Can SS400 H-beams be welded easily? Yes, SS400 is a low carbon steel with excellent weldability, and ordinary structural welding procedures apply without special preheat for thin sections.
Q: Is SS400 suitable for low temperature service? The grade has no guaranteed Charpy impact value, so for low temperature or impact loaded structures a fine grain grade such as S355NL or an equivalent toughness tested steel should be selected.