Agreed, you don't want the steel too hot. Just nicely warmed up. Going over with a heat gun will make the paint sprayed on go off a bit quicker without it burning straight away of evaporating. I would have used a heat gun after painting too, just to aid drying but you have to use a very gentle heat from quite far away, to not only prevent paint being burnt off but to stop debris blowing on it.
i lay the spray can or paint and the items which need paint in the living room to warm up and then after painting and initial drying, i lay these in the living room again for hardening. A bit difficult when the parts are bigger or the wife is not in a too good mood….
Heating up steel parts with a gas torch normally just makes water condense on it. Paint doesn't dry because cold air in this country is normally associated with winter ,which is wet and so cold air is normally full of water, so the solvent in the paint has no where to go. Warming the part helps with adhesion,but doesn't make a huge difference in drying time. Putting parts in a make shift box and heating the air up in it helps. A dehumidifier also helps......
I used one of those cheap heaters that glow bright orange - they radiate the heat so that the material is warmed rather than the air. Even a small one is capable of warming large body panels to the temperature ideal for painting.
It's also the only way I've found to feel toasty working in the garage - tried a couple of fan heaters which made no difference. One small radiant heater and I'm cosy.
To prevent problems with condensation when painting I also use a radiant heater to heat the object before and after painting.
The evaporation of the solvent cools the object you are painting which causes condensation while the paint is being applied and is drying, which is what I think causes microblisters later, the radiant heater prevents this.
For this reason its no good painting in the cold and then taking the object to a warm place to dry, its too late.
It also helps the paint to dry and you to feel warm better than any other type of heater I've experienced.
I'm no expert, maybe a proper painter can confirm or otherwise.