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. For forged square bars with edge length 100 - 250 mm, the highest permitted level of carbon equivalent is 0.52%.
S355 in forged execution is standardised in SS-EN 10250 - 2. The (discontinued) SS-designation is 2172. Tibnor prescribes that Charpy-V impact toughness shall be at least 27 Joule at -40°C while delivery performance is normalized (+ N). The bars are finished by rough milling with an edge-length tolerance of +3/-0 mm per side. Height-of-arc straightness is better than 0.002 times bar length.
The minimum prescribed level of yield strength from tensile testing of forged and milled S355 is 285 or 275 MPa (depending on dimension) along with tensile strength in the range 450 - 630 MPa and an elongation of 16% or better. Following SS-EN 10250 - 2, the sampling location is halfway between the surface and centre.
In the event that the application requires a part with 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).