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KOMPAX is an acronym for the Swedish “komprimerad axel” which is essentially cold-drawn rounds in grade S355J2C +C. 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 in cold-drawn execution is standardised in SS-EN 10277 - 2. The (discontinued) SS-designation is 2172. The minimum prescribed level of yield strength for steel S355J2C varies depending on diameter over the range 490 - 375 MPa. The interval for tensile strength decreases and the minimum allowed elongation in a tensile test increases somewhat as the bar diameter increases. There is no guarantee for impact toughness.
The diameter tolerance for S355J2C rounds in cold drawn execution is good, h9 as defined in ISO 286 - 2 or better. Furthermore, straightness is considerably better than for hot-rolled round bars and the maximum height of arc is 0.001 times bar length.
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).