Just paint the thing as we used to do day in and day out. You could strip it totally and have it done as a REME Armourers Base workshops did it but to achieve what? And if you blue it, it ain't real blue. Just prepare it, degrease it and paint it with a heat resisting paint then put it in a large oven to cure. It ain't going into action any time soon. It's just got to look the part. Just my humble opinion of course.