520MW+ is an M-Steel® in which treatment of the melt with calcium is supplemented with an addition of sulphur to further promote machinability which is even better than offered by 520M. This is achieved without significant detriment to strength or toughness. The steel is micro-alloyed via a small addition of vanadium.
Apart from the sulphur addition, the chemical analysis of 520MW+ is similar to that for S355J2 which is standardised in SS-EN 10025 - 2 and for which the (discontinued) SS-designations are 2172 and 2174. However, 520MW+ has a higher yield strength thanks to the vanadium addition. The Charpy-V impact toughness is equivalent to S355J2 (27 Joule or better at -20°C) for diameters up to 90mm. The execution of the bars is as-hot-rolled with diameter tolerance in accord with
SS-EN 10060. Height-of-arc straightness for regular straightened bars is better than 0.004 times bar length. Tibnor stocks some 520MW+ dimensions in peeled execution in which case the diameter tolerance is h12 and straightness (height of arc) is at most 0,0015 times bar length.
The weldability of 520MW+ is limited as a consequence of the high sulphur content. However, machinability is excellent especially in comparison with that of S355J2.
If the application requires that the part has a wear-resistant surface, 520MW+ 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 (preferably in water or polymer quenchant).