Hot Bluing

ghostdncr said:
I have absolutely zero scientific evidence to back this up, but it seems that pieces I've treated with it have considerably more resistance to corrosion than similar untreated parts
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Seems hardened parts are more rust resistant than unhardened.
Probably some science behind that....
 
rgray said:
Seems hardened parts are more rust resistant than unhardened.
Probably some science behind that....
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Can't speak to other processes but with rust bluing, you coat the steel with a chemical that promotes rust and leave it there for an extended period. Then after lite brushing (carding) the part is immersed in boiling water which turns the rust black. You do this repeatedly (I do it 4 times) alternating between rusting periods and dunking in boiling water until the part refuses to rust any further even when coated with the rust promoting chemical. At that point all the oxygen in the steel has already turned to iron oxide (rust) and the boiling water has turned it into a rich blue/black durable coating so it's not possible to rust any further. I rust blued my smokeless muzzle loader and it still looks great after being dragged thru swamps for days in the pouring rain and banging up against tree stands. It's a great system even for the first timer.
 
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RJSakowski said:
Heat bluing as the OP is describing will take the piece to more than 600ºF and destroy any temper.
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Sorry, that is not correct. To get a nice blue color, like for bluing watch and clock hands, 575°F works for me. Anything over that temp and you lose the rich blue color. And my tempering chart has a range from 400° to 1200°F for tempering various steels. Meaning, 600° F is not going to destroy the temper, maybe change it? Actually 600° F is on the low side for tempering many steels. And of course, this can be further discussed in more detail because of the wide range of steel types and hardness desired…Dave
 
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Dave, you are indeed correct. I misspoke. I was thinking about grinding an edge on hardened steel. and "if it's blue, you've lost the tool". I also had not considered the various alloys on my statement.

The color that I have always drawn to for a spring temper is a blue and I should have recalled that. I have also tempered springs in a molten lead bath and lead has a melting point of around 620ºF so clearly 600ºF won't destroy the temper.
 
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