Most stainless steel knife blades are made from fairly soft steels. Its the presense of Chromium that makes them " stainless" more than anything else. Some stainless steel blades can be stained after they are heated up to cherry red, and then hit with acid stains. Whether your particular knife blade can stained would need to be tested. The blade can always be repolished to its bright finish, unless the chrome is affected by the acid.
As for bending brass: Brass can work harden, as well as be hardened by heating it red hot, and letting it cool slowly. To anneal(soften) brass, you need to heat it up red hot, and quickly drop it into water. If you are making any kind of radical bend( up to or past 90 degrees) you probably will be served best by making the bend in stages, and annealing the brass after each stage. You can sometime bend small piece while they are heated to that red heat color, where the metal is " maleable". But, Brass cools very rapidly in air, or in any liquid, and that can induce cracks, or break parts off.
When hardening a brass part, you want to keep the heat on the part and slowly reduce the heat, either by backing the flame slowly away from the brass piece, or by reducing the size of the flame mechanically by cutting back on the fuel/oxygen source.
When annealing the brass, you want the piece as close to water as you can, so there is no time for the piece to cool before it hits the water. For instance when annealing the necks on cartridge casings, most people put the casings in a contained of water, up to the case neck, and then simply tip the cases over when they are red hot, to anneal them.
