What will be the reaction of photohydrogenation of stainless steel in annealing furnace

What will be the reaction of photohydrogenation of stainless steel in annealing furnace?

I want to know how you only add hydrogen? As we all know, there are two gases in the annealing furnace, one is nitrogen and the other is hydrogen, which come from the same gas - ammonia. During normal operation of the annealing furnace, the two gases have their own division of labor. Nitrogen is an inert gas, which is filled in the furnace tube to prevent oxygen from entering the tube and causing oxidation to the products, Hydrogen is a reducing gas, which is burned at both ends of the furnace tube, mainly to reduce the places with slight oxidation on the product surface. When only hydrogen exists in the furnace tube, the product will be oxidized first, and then the surface will be reduced. After the product comes out, you will see that the surface is a layer of silver white, and there will be an oxide layer below it, and the silver white on the surface is very easy to fall off, leaving only the original black after falling off.