Heat Bluing

Does anyone have any experience with heat bluing 440C stainless steel? I want to do an art piece, heat treat it, mirror polish it and then heat blue it. The problem is I don't have information on the exact temperature that the bluing appears at.

I would like to do this in a kiln or oven instead of using a torch because I would like the entire piece to heat up at the same rate to get an even shade across the thick and thin areas. Any ideas?



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george
www.tichbourneknives.com
sales@tichbourneknives.com


 
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George, I hope the piece that you are doing isn't very large. Stainless has 4 times the distortion of carbon steel. As it is with most steels, the temp. will be slightly different for the different grades of 440 to get a certain color. What I would do is start out with a sample piece of the steel that I was going to use and put it in the oven at about 325 deg. as a safe temp. to start. Turn the oven up 25 deg. every 30 min. until the desired color is reached. If possible, cool at a very slow rate to reduce warpage due to the different parts cooling at different rates. I hope this helps. I do know that the heat color is very thin and needs to be protected from every thing.

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Ray Kirk
www.tah-usa.net/raker
 
You are right about the warpage and cooling problems Ray. There is no room for error here and repeated checking until I get the right temp is out of the question. Once the blade is in the oven it will have to stay there until the cooling cycle is over. That is why I have to have a very good idea of the bluing temperature before starting. I would guess that it is in the 700-900 degree area but that is just that, a guess.

This knife will be carved from 5/8" 440C and will take about 60 hours to complete so there is no room for screwups.

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george
www.tichbourneknives.com
sales@tichbourneknives.com


 
George, I was thinking of using a sample piece of the 440 for the temp. test. I know that at 450 deg., 52100 is blue and at 500 deg., it is kinda purple. That is the max temp. that I heat treat. The SS shouldn't be a lot different since it is still an oxidizing temp that causes the color.
It shouldn't take a very big piece to test. One work of caution, CLEAN, VERY, VERY, VERY, GOOD. Any thing on the steel will cause a variation in the color. For tempering it isn't too bad, but I etched a piece of damascus that had my finger print on it and it looked like superman had squeezed it and left his mark. I redid the piece. If I knew exactly how it happened, I might try to make some finger print similated damascus. I really don't think the bluing temp will be as high as you think but then again, I don't know for sure either.

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Ray Kirk
www.tah-usa.net/raker
 
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