The main difference is that SS490 has a minimum tensile strength of 490 MPa, while SS400 has a minimum tensile strength of 400 MPa. SS490 is a higher-strength steel, while SS400 is a more common, general-purpose structural steel that is versatile and has better weldability. Both are defined under the Japanese Industrial Standards (JIS) G 3101 for general structural steel, and their "SS" designation stands for "Steel Structure".
Chemical composition(%)
| Grade | C | Mn | P | S |
| SS400 | - | - | 0.050 max | 0.050 max |
| SS490 | - | - | 0.050 max | 0.050 max |
Mechanical properties
| Grade | Yield strength MPa in different thickness mm | Tensile strength MPa | |||
| ≤16 | 16-40 | 40-100 | >100 | - | |
| SS400 | 245 | 235 | 215 | 205 | 400-510 |
| SS490 | 285 | 275 | 255 | 245 | 490-610 |
