4140 Heat Treat Questions

I am going to be heat treating some 4140 parts soon in a non-controlled environment ht oven, and I have some questions, mainly regarding decarb and scale. It seems that the best ways are obviously either a controlled oxygen purged environment or a molten salt bath. I have read about using stainless foil or anti scale compound, but I have some concerns.

With the foil, my main concern is, how I will remove the part from the envelope fast enough to quench. My first idea was, open the oven, cut the bag, remove the part, and then quench. To me it seems that it may be quite a pain to do all that fast and effectively (without the bag getting caught on the tongs, etc). My second idea was, open the oven, remove the bag with the part in it, hold it over a 'ladle' so to speak, cut the bag to let the part fall in the ladle and immediately quench. It seems that this would be much faster, although I would need another person helping.

How well do the various anti scale compounds work? I have found powder and paste. I have also seen people use borax as well.

I am hoping some of you guys have experience with this and can offer some tips and advice to make this go as smooth as possible haha

Decarb is exposure time based. If mine, I would assume it was okay to open door after expiry of soak time, rip off stainless (part stays in or is returned to being in), and close door for five minutes or so before going for quench on the naked part

If you wrap with stainless foil, you can put a small piece of paper in with the part. The paper will burn off consuming the oxygen inside the foil. I have done this when annealing a file to make a knife blank.

How big are the parts you are heat treating? Will they be in the oven long enough to scale? You're only bringing then to critical temperature and then quenching.

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If you do this and then oil quench will you not have what most would call scale even assuming you don't use up the time?
I've always accepted it as a given in 4140 series steel. Can it be done clean and new looking?
That would save some work.
Bob

I started using tin cans to hold my parts for initial heat treating. Find a couple that can telescope together to make an enclosure large enough to hold my part. Add some paper inside to burn up and burn off the oxygen in the cans. Once the time is up, i quickly dump the thing on a plate and remove the part for quenching. I've found there are times the paper isn't completely burned upside when I dump it. The cans need to fit snug on the lip of the inner inside down can to the outers bottom so oxygen doesn't continue to get in. The parts are still going be darkened from the heat, but scaling has been reduced for me using this method. Mostly the cans last one time, maybe two. They then get so thin they're about like paper.

Most of my heat treating is with D2 and O1, but I'd think the same results would be had with other alloys. Most of my parts are polished after tempering and the process outlined above has shown improvement in the reduced scaling from when I first started heat treating. I use two ovens for my heat treating.

I read once another thing is to use a can, add in some cast iron chips, layer in the part and cover it with more chips. Supposedly the chips give up iron during the process. Not something I've tried in spite of having a few bags of chips for that end.

Regards
Bob

Foil wrapping and most other anti-scale containers really don't work the best for direct quenching because of the time delay in removing the parts. Brownells sells a couple of coatings that should be good. ATP SUPPLY COMPANY, INC ANTI SCALE COATING | Brownells

I use Keep-Bryte, but it doesn't seem to be made any longer. The ATP-641 sold by Brownells is recommended by at least one heat-treating book author. If I were starting from scratch, that is probably what I would go with.

RWO

4140 is normally austenized at around 1500F +_. At that temperature there are a number of coatings that can be applied to prevent decarb. The process is preheat the part to around 500-600F, coat the part liberally with the coating, usually a powder, and return it to the furnace. No bags to open. Only problem is the coating getting into quench oil.

Tom

Thanks for all the answers everyone, I might go with the ATP-641 after researching it some. That seems like it would work pretty good for my needs