N690 has both nickel and cobalt in it, something we don't often see in stainless steels.
Anyway, nickel has a long history in saw steels for making saws tough and resharpenable.
Up here in the Northwest woods we have tons of L6 nickel steel saws, and they make great knives that take a beating, hold an edge and sharpen easily.
S30V's big advantage comes from particle metallurgy, which allows the steel maker to keep the alloys homogenously distributed and keep the impurities out.
For those not familiar with smelting steel, the various alloys in steel all have different specific gravities, meaning, they weigh more or less for a given volume.
This means that some alloys tend to either float on top of steel or sink to the bottom, sort of like oil and water.
The steel makers in the past have attempted to get around this by constantly agitating the molten steel until the time comes to pour it into ingots.
Still, in those few seconds it takes the steel to go from liquid to glowing semi-solid, the alloys have already begun to stratify so that the steel does not have a uniform distribution of alloys all the way through.
For this reason, many metallurgists have dreamed of a future when they could mix molten metals in the zero gravity of space.
However, in today's world of super-metals, the metallurgists have learned new tricks, among them, particle metallurgy, which allows the maker to mix the allows as fine particles and then press them together under heat and pressure, without the steel ever attaining a true liquid state where the alloys would have the opportunity to stratify.
Crucible Particle Metallurgy (CPM) makes S30V using the above method.
Other makers have developed other strategies.
For example Timken-Latrobe, maker of BG-42, and Hitachi, maker of the very similar ATS-34, have developed double vacuum melts with electric arcs, in which they pour and role the highly agitated liquid metal, and keep rolling it as it cools, all in a huge vacuum facility.
Their methods produce very homogenous steels.
After all, they use BG-42 as bearing steel in the most advanced jet engines.
They have to really trust its properties.
I don't know the smelting details of N690, but given the outrageous complexity and sophistication of the alloy mixture, and knowing the reputation the Italians have with metal, I suspect they have as good a means of dealing with stratification as does Timken-Latrobe, Hitachi, or CPM (maker of S30V).
I'd like to know more about it, though, just out of curiosity.