We are looking at one disc made in Stainless steel for machines with plastic or aluminium armour, and another disc made of a steel called H13 for Hardox and Titanium machines. We have various treatments we could do on the part once it is machined

The exact details of the 6x refers to impact toughness in a Chappy C-Notch test, (ft-lbs) where D2 comes out with around 20ft-lbs and S7 around 120 ft-lbs. H13 is up at 145 ft-lbs.

When looking at Rockwell hardness:

D2 = 63
S7 = 58
H13 = 52

There is a distinct trade off between Impact Toughness, Hardness and wear resistance. H13 has the highest toughness, but the lowest harness. D2 is the opposite and S7 sits in the middle. The disc needs to be hard so it doesn't deform but if it cant take the shock loadings of a hit then its just going to snap. This is just one very expensive balancing act.