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When I was working in a powder-coat plant, the peak temp in the oven was 450 F, took about 20 minutes for the trim parts to run around the horseshoe-shaped conveyor track in the oven. Gave enough time to get the substrate heated up to temperature. If the surface of the powder fuses but the metal underneath isn't up to temperature, the stuff just peels off. Powder coating is great for aluminum, not so hot for steel. The reason being that there are always pores for moisture to get through, when rust starts, there's no way to get at it. So the coating bubbles, delaminates and generally looks doggy. Only way to fix it is to strip the whole coating off, treat the rust and recoat. Same deal with abrasion damage, something likely with a bike, no touchups.
Two-part urethanes are commonly used for auto paints, I can get pints from the local distributor. NAPA also carries some stuff. The deal with those is that you have to buy ALL the bits and pieces needed from the same outfit, auto paints are typically systems. So you have to buy paint and hardener, diluent, primer and maybe clearcoat if used, all from the same company. It all adds up. Accurate measuring and mixing is a must, too. Upside is that all you need is a spray gun, no furnace. The overspray isn't good to breathe, so some sort of mask with filtering is needed. With the system I last used, by the time all the stuff was added, that pint eventually became close to a gallon of ready to spray solution.
Stan