HT atmosphere protection

[Jerrod Miller]

Just wanted to share a little something that people may be interested in. This is a product that we use at work to prevent carbon pick-up during carburization/case hardening. This is applied to surfaces that are to be welded or machined after heat treat to prevent those surfaces from picking up carbon. Obviously this should work the other-way around and prevent de-carburization/scaling. It isn't overly cheap (we buy a lot of it and still pay just under $50/1gal. tub), but it is designed for this application and works well. At some point I will snag an "empty" pail from a garbage can, scrape what I can out, apply it to a blade and show before and after pics. But don't hold your breath on that. If someone wants to try it sooner than I get around to it I thought I should share.

[Miles Hebbard]

Now that looks interesting!!!

[Jerrod Miller]

So I got curious and since I was running a really long heat over the weekend (I didn't do the math but it should be about 40 hours, peaking at a soak of 1800 for 2 hours) I grabbed a chunk of 1050, coated half of it and added it to the heat. It is an electric oven, but with these temps and times we should see a ton of scale; at least on the uncoated side. Before and after pics will come tomorrow (if I have time).

[Jerrod Miller]

OK that test was a bit severe. I'll have to go back and so something a little more reasonable. Actually came out to a 32 hours cycle with a decent ramp up and slow cool down. Here are the pictures.

Original part:

 

Half coated:

 

After heat treat:

 

After 3 minute shot blast:

 

You can't really tell in the last picture, but there is definitely an improvement with the paste. Less scale still stuck to the part. At some point I'll get around to doing a more reasonable test as related to blades. Ultra thin coats, short temperature exposure times, normalize vs quench. Some day...

[Miles Hebbard]

That will be cool, I've been coating with a thin layer of potters slip, applied with my finger tips, and it makes a differance, I reckon anything that keeps oxygen off the steel will work...

[Jan Ysselstein]

Jerrod,

 

Thanks for posting this, it is an interesting topic to all of us I am sure. Until recently, stopping carbon from getting absorbed during heat treatment was not a problem....now we see carbon being added on the fly. My problem is, the carbon leaving the steel..so like Miles, I have made slips containing graphite and slowed the carbon loss a little..that ceramic quickly becomes porous and oxygen/CO2 passes right through. I am still working with graphite.

It would be nice if there were a standard test various knife makers could use ( or design ) to evaluate various compositions for blocking carbon migration entering or leaving the metal.

 

Jan

Edited June 10, 2014 by Jan Ysselstein

[Wick Ellerbe]

ATP-641 works great in an electric HT oven when below 1600°, but just OK when much above. Most comes off in the quench, hot water removes any left.