Thanks for the comments,
by Niobium steel I mean the following steel:
Lohman's 1.4153.03 (niolox) Stainless Niobium tool steel. I'm told the niobium is a carbide former which produces much smaller carbides than Chrome. Because of the niobium, the chrome does not have the tendency to produce that much chromecarbides, which is why you don't need that much chrome in the steel to get it really rust resistant. The other benifit is that because of the lesser chromecarbides the steel has a very fine grain stucture and is more flexible and won't chip that easily. the steel is developed for the food processing industry.
I'm no metallurgist so I hope I have explained it the right way.
On a more practical level, there are quit some makers here in Europe who use the steel, and they all report a better performanc than ATS 34 or RWL 34. I have a testknife that I'm using at this moment, and it looks veeeeeery promising.