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 - 0.52% depending on diameter.
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 stocked has either the addition + AR which shows that the delivery version is hot rolled or + N which indicates normalized condition. Diameter tolerances are according to SS-EN 10060. The straightness (arrow height) for a normal direction bar must be better than 0.004 times the length of the bar.
The minimum prescribed level of yield strength for steel S355 varies depending on diameter over the range 355 - 275 MPa. The interval for tensile strength and the minimum allowed elongation in a tensile test decrease somewhat as the diameter 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).