Pretty simple, really. Clean the bolt with lacquer thinner, first. If they are galvanized, I throw them in muriatic acid (outdoors, downwind!) to strip the zinc. After rinse, it can go straight to the phosphoric bath.
I put phosphoric acid in an old glass cake pan or bowl, and leave soak a day or two. The metal turns brown or purple when you get it right. Its about like gun bluing, you are just trying to get the phosphorus to slip between the iron crystals and take up valence bonds where water would like to join the party.
Thats the same thing chromium does in stainless steel, and both results are more brittle than good old iron. The acid method doesnt go that deep, so the bolt keeps its strength better, and can be unscrewed without using anti-seize.
I dont use stainless bolts where I expect a lot of bending force or chafing, and especilly where there is a long section of thread needed. It always gets nasty and wont come apart. Stainless is especially bad where thermal cycling goes on. Thats why air-fuel ratio sensors almost always require throwing the stainless steel exhaust manifolds away, when the sensor needs replacement on modern vehicles.
On my ocean sailboats, I used bronze hardware instead of stainless, for all underwater or deck mounting (where salt water would pool during long days on the same tack). Stainless just rusted and snapped off in salt water.
I'm not much on metallurgy, I just learned some things the hard way, sometimes a long way offshore.