Heat treat affecting black oxide?

thetree · Jan 25, 2011

We have a small CRESS brand toolroom heat treating furnace. When we heat treat A-2, we do it in foil. During the air quench, we simply wait for the glow to leave the bag, then pop it open to let air get to it. On smaller items, we will let them quench in the bag. We are having problems with our black oxide not getting black on items we heat treat in house. If we send it out to our normal vendors, it is not a problem, the stuff gets black as night. When we do it in house, it just turns a greyish color. I would like some suggestions on getting rid of this problem. Thanks in advance

m37 · Jan 25, 2011

you have a thin oxide film that formed from the heat treating that is preventing
the black oxide from working
your vendors probably etch it in a dilute acid solution and rinse

mike

JRIowa · Jan 25, 2011

Normal heat treat vendor or black oxide vendor. Heat treating in an atmospheric furnace would solve the problem. $$$$

We used to double wrap a lot of our mold parts. They'd come out with just a light gold tone. Either try that or a light bead blast before black oxide.
JR

Modelman · Jan 25, 2011

My A-2 comes back from a commercial heat treat shop the light gold color.

When bagging to do it yourself, don't forget to wrap a piece of paper inside the foil, so it burns and consumes the oxygen that is inside the foil wrap. I would suspect the paper will leave a mark if it touches the steel, so make sure it's either on the backside of the part, or separated by an extra layer of foil.

Dennis

thetree · Jan 25, 2011

Bead blast doesnt seem to work, however we use a very light media. I will try one using the paper. Is there a temperature at which this oxide layer will not form? I need to know the temperature that it is safe to open the foil. Thanks for all the help

m37 · Jan 25, 2011

brain wasn't fully on this morning im used to hot bluing things
I realized you might be cold bluing

You are still going to to get some scale
as JRIowa said atmosphere furnace is the way to fix that $$$$

Glass beading can be good
but the beads will be contaminated with dirt and oil from previously blasted parts
and the lube they use to keep the beads from clumping together
that gets pounded into the surface
degrease with acetone
a-2 has about 5% chrome may not work well with a cold blue
that much chrome could cause problems with hot blue

with some of the cold blues heating parts to 150-180f before application helps + multiple applications
mike

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