S355 is a low-carbon structural steel with good weldability which in effect means that welding without pre-heating is usually feasible unless the parts involved are very large. The highest permitted level of carbon equivalent is in the range 0.45 - 0.47% depending on edge length.
S355 is standardised in SS-EN 10025 - 2. The (discontinued) SS-designation is 2172. The number 355 relates to the minimum level of yield strength in MPa for the smallest dimensions while J2 prescribes that Charpy-V impact toughness shall be at least 27 Joule at -20°C. The bar that is stored has the addition + AR that indicates that the bars are as-hot-rolled with edge-length tolerance in accord with SS-EN 10059. Height-of-arc straightness for regular straightened bars is better than 0.004 times bar length.
The minimum prescribed level of yield strength for steel S355 varies depending on edge length over the range 355 - 295 MPa. The interval for tensile strength and the minimum allowed elongation in a tensile test decrease somewhat as the edge length increases.
If the application requires that the part has a wear-resistant surface, S355 responds well to both case hardening and nitriding. Furthermore, its strength can be increased via quenching and tempering provided cooling during hardening is fast enough (in water or polymer quenchant).