Dear Jake,
Thanks a lot for your quick answer and the suggestions.
Now I used the Times tool (with 100) and the Int tool. Then the Raster To Polygon tool worked.
But after this in the polygon layer there were the fields: FID, shape, ID and Gridcode. I suppose that gridcode is equivalent to the former field value (in the raster layer), but am not sure. Should the tool not maintain the original field value?
Regards,
Matthias