Hey Alessandro, thank you so much for taking the time to write us a review.
If the blades can get a patina, that means that they can also rust. How fast? That depends on your use and moisture that is left on the blades. Even some ingredients can increase the speed at which the patina will be developed. That doesn't mean that the blade is made out of low quality steel. Some of the best Japanese traditional steels develop patina (or rust, if you don't take good care of them) and are still considered one of the best on the market.
The good news is that the rust can be easily removed. Use a rough sponge and polish the blades until there is no more rust on them. Then apply a thin layer of oil to prevent further oxidation. You can read more about patina here: https://sharpedgeshop.com/blogs/knives-101/what-is-patina-good-or-bad-on-your-knife?_pos=1&_psq=patina&_ss=e&_v=1.0
Please let us know if there is anything we can do to improve your overall experience with purchasing this item.
All the best,
Urban