I went and looked at a picture of one, and it seems to have a bead blasted finish to it. If it does, then that is your problem. There have been various threads overyears at various forums concening how to keep bead blasted finishes from rusting....with various results. A brief explanation into steel metallurgy explains why it happens.
The two most important elements present in stainless steel are carbon and chromium. When heated to critical temperature, they combine at a ratio of 1% carbon to 10% chromium. These are the chromium carbides and have nothing to do with keeping a knife stainless.
Whatever chromium remains that has not combined with the carbon is referred to as "free Chromium". This chromium forms a layer at the SURFACE of the steel and is what keeps the steel rust resistant. It's interesting stuff, since it is also self repairing, i.e. if you scratch the steel or remove some of the chromium while sharpening,the chromium migrates to fill in the "gap". On the surface.......the layer is measured in molecules as far as thickness goes. One of the problems with bead blasting is that the beads often penetrate into the steel to a depth where the chromium refuses to migrate to. That, or the beadblasting has so increased the surface area of the steel, that there isn't enough chromium to effectively coat the surfaceto prevent oxidation....which is what rusting is). When the "inner surface"of the steel is exposed to moisture, the steel rusts, just as normal carbon steel will rust.
I thoroughly despise beadblasted finishes. They are a copout in the manufacturing process, since you don't have to worry so much about surface appearance....the beads blast the finish down smooth. And they stain and rust. As you have found out; often quickly.
