520M is an M-Steel®, so-named because, through treatment of the melt with calcium, improved machinability is achieved without detriment to strength, toughness or weldability. The steel is micro-alloyed via a small addition of vanadium.
In relation to chemical analysis, 520M is similar to S355J2 which is standardised in SS-EN 10025 - 2 and for which the (discontinued) SS-designations are 2172 and 2174. However, 520M has a higher yield strength thanks to the vanadium addition. The Charpy-V impact toughness is equivalent to or better than S355J2 (27 Joule or better at -20°C and for smaller diameters -40°C). 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.
520M has good weldability with a carbon equivalent between 0.45 and 0.54% depending on diameter. Welding without preheat is normally quite feasible unless parts are very large. Machinability is excellent especially in comparison with that of S355J2.
If the application requires that the part has a wear-resistant surface, 520M 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).