Heat treatment of AK based receivers

Greetings,


I've undertaken my first gun build. It's a Yugo RPK from a parts kit. Instead of building with a store bought receiver, I plan on bending from a flat. So far I've bent a flat up from AK builder 1.5mm RPK flat with the AK builder bend dies. I've yet to weld on rails, or drill front trunions. According to most: a torch to the fire control group pin holes is enough, but I'd much rather have a fully hardened example. I want it to last.

A few years back, I was gifted a kiln (one of three in the garage) I'm in the process of retrofitting a proper PID/Thermocouple to it.


My question is about metallurgy and hardening/tempering. I get a lot of different sources on what temp and times to use. The steel is 4130. Has anyone on here done this? Dispite the low cost, I'd rather not mess a couple of flats up! I want also to be safe about it.



I was planning on doing it like this: Full Heat Treat of AK Receivers - YouTube


I guess I just want more science behind the procedure. Not sure on the brine used, but I was planning on using used motor oil. Heat treat is all new to me, I would usually outsource this.

That video looks like how NOT to do it. To prevent warping, quench vertically, No paint stirrers and no plastic buckets. You plunge it in and move it up and down moving to colder quenchant each stroke. Don't use witches brew recipes, do it per the manufacturer. Brines are not table salt they are usually soda ash. It's a saturated solution to raise the boiling point. The draw should be 450F for 1 hour.

If you've not yet purchased the temp controllers, suggest you check out Auber Instruments. Used their timer and PID controller for a large Cerakote cure oven after losing time/frustration with eBay crap that came with Chimercan instructions for setting parameters. Reasonably priced with good support.

Austenitize at 1600F for 30 minutes in a protected atmosphere/stainless bag for best results to prevent surface decarburization.

tobnpr said:

If you've not yet purchased the temp controllers, suggest you check out Auber Instruments. Used their timer and PID controller for a large Cerakote cure oven after losing time/frustration with eBay crap that came with Chimercan instructions for setting parameters. Reasonably priced with good support.

Click to expand...

I went with a Ebay PID, which I already regret. It came with a "Fotek" SSR: which I'm glad I learned is a fake and could have very well burned down my garage. Bought a proper 25 amp rated triac ssr from automation direct.

UL warns of solid state relay with counterfeit UL Recognition Mark (Release 13PN-52) | UL

tdmidget said:

That video looks like how NOT to do it. To prevent warping, quench vertically, No paint stirrers and no plastic buckets. You plunge it in and move it up and down moving to colder quenchant each stroke. Don't use witches brew recipes, do it per the manufacturer. Brines are not table salt they are usually soda ash. It's a saturated solution to raise the boiling point. The draw should be 450F for 1 hour.

Click to expand...

This is the info I'm looking for!

So 1600 in a stainless bag for 30 min, quench (from cold oven)

450 for an hour, let cool in kiln?

Yep. From the "Heat Treating Databook" and mfrs recommendations.

Monomer said:

in kiln?

Click to expand...

A "kiln"... recycled from those goods intended for ceramics .. has its differences from "the usual suspects" among heat-treat furnaces.

You might want to research that.

Plenty of info on it, PM and otherwise.

Monarchist said:

A "kiln"... recycled from those goods intended for ceramics .. has its differences from "the usual suspects" among heat-treat furnaces.

You might want to research that.

Plenty of info on it, PM and otherwise.

Click to expand...

I should work just fine for what I'm doing. It'll have a temp controller and thermocouple.

As a bonus, the wife can use it for ceramics still.



Not to worried about a little scale. My only fear is warping.

tdmidget said:

That video looks like how NOT to do it. To prevent warping, quench vertically, No paint stirrers and no plastic buckets. You plunge it in and move it up and down moving to colder quenchant each stroke. Don't use witches brew recipes, do it per the manufacturer. Brines are not table salt they are usually soda ash. It's a saturated solution to raise the boiling point. The draw should be 450F for 1 hour.

Click to expand...

Are you sure about this Draw temp? Most other sources goto 700 degrees. Granted, most of these sources are other AK builders and not heat treat specialists. Please; do educate me on this and point me in the right direction. I'm less afraid of messing up, and more afraid of not learning from this project. I took this project on to push myself a bit, as I'm not getting it at work for once.

According to this: https://www.secowarwick.com/wp-content/uploads/2017/03/HeatTreatingDataEBook.2011.pdf - Tempering/Draw temps vary "to desired hardness" - How hard should a receiver be?


I'm thinking of using an anti-scaling chemical instead of an SS bag. Has anyone ever use such a product? Knife makers seem to like it: ATP SUPPLY COMPANY, INC ANTI SCALE COATING | Brownells

Mostly because I would have to cut the bag and remove the part to quench, and I'm not going to have time for that before dropping below quench temps.

Monomer said:

Are you sure about this Draw temp? Most other sources goto 700 degrees.

Click to expand...

5deg F. Embrittlement in Steels | World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools - BROWNELLS

short answer is you stay below 500 or go above 700.

450 it is!

I'm glad I asked on here. A lot of what comes up in google has no backing.