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AK-47 » Build It Yourself Full Receiver Heat Treating

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22zSteve Member Joined: Feb 2008 UT, USA Posts: 61 Feedback: 0-0-0

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Message Posted: 8/30/2008 4:01:05 AM

[Last Edit: 5/8/2010 9:40:46 PM by 22zSt

This was a reply to another thread but I figured Why not let everyone read it. I will try to be as thorough as I possibly can. I realize heat treating terms are confusing and it seems everyone uses alot of the terms interchangably. I will however up my info with other sources as I find them and see fit. OK, lets go. Austenitizing: Forming austenite in carbon steel by heating to the austenitizing Temperature. 4130 is 1600deg. This is the initial heating of the steel. Some good I Soak: Time at desired temp to allow structural change. A half hour is probably sufficient for a reciever. My kiln will start clicking on and off, thinking it is up to temp about 1 hour before everything inside is actually up to temp. I say this to remind every one to make sure you know what the temperature really is. It is easy to unde if you are not carefull. Do some testing with Pyrometric cones Quench: Rapid cooling through the critical zone to create desired properties. For our purposes it is usually done in water or oil. I have never used water, but I am curious how it would work in a jig. Tempering: Also called Drawing, it is raising the austenetized and quenched steel to a temperature that draws the hardness back, increasing toughness and reducing brittleness. 700deg will give a hardness of around 41 on the Rockwell C scale, Which is suppose to be around spec for a 4130 reciever. I have heard of guys doing i their kitchen oven at 500deg or so and getting around 45-47Rc, I guarantee your ejector wont dent at this range. Tempering will also require a 30 to 45 minute soa Also it is best to let it cool to room temp before tempering. After tempering remove from oven and cool at room temerature, There is no need to cool slowly. Heat Treat Terms (Update 12-2-08) Over The Thanksgiving holiday I quenched a receiver in soapy water and Tempered at 550F in the kitchen oven, It seemed to come out fine. With hardness tester we will just have to report after a few thousand rounds. OK That is the order it is done, Austenitize, Soak, Quench,and Temper. Now lets talk about Oxidation, At elevated temperatures you will completely destroy a receiv it isnt protected from oxygen. One way to do this is to use a controled atmosphere oven. This is an oven that has a constant flow of inert gas perging the chamber. suppose with a little research This could be rigged up to any heat treat oven. There are also things like neutral salt baths where Molton salt is used to submerge the This is not even in the scope of our needs. The best method I believe is the perged foil wrap. Stainless Foil is used to completely envelop the receiver. Use gloves cuts like a razor. Leave enough to get three folds on all 3 sides, I use a piece 12"x 18" and lay the reciever longways. Crimp each fold real good. and Just before yo the last end perge the bag with inert gas,(Mig,Tig welding gas, Argon is best) I believe these gasses are heavier than air so hold the open end up, make sure you un your wire feed mechanism or you will fill your reciever with wire. Turn on the welder and poke the stinger in and filler up. Your guess is as good as mine as to how to perge, I just do it untill I say to myself "Man that has to be full". To be honest you may not even need to perge it. The amount of oxygen in a receiver might not excessive oxidation but if you have gas available I would do it. I have never done it, but putting somthing like paper or apiece of wood will burn up the oxygen. Ive wondered if the extra carbon could cause some form of Carburizing. Another Stainless Foil Link, And Another OK This first picture is of the jig and its first receiver. As you can see I used washers to hold every thing together. and while the receiver didnt warp, there were som slight deformations (waves) where the bolts squose so tight. The jig is a piece of mild steel 1/4 X 1 1/4 strap with long nuts tac welded to the top. If your receiver h stepdown rails you may have to mill the edges of the jig. The jig slides right in between the top and bottom rails. Also make sure you have finished fitting your trunnions, magazine, Saftey selector, and trim the ejector, because they dont file nearly as well after heat treating.

1/28/2011 6:39 PM

Full Receiver Heat Treating - AR15.COM

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This next pic is of the clamping frame I built for the jig. It does 2 things. The first thing it does is puts even pressure along the entire top edge of the receiver instea just under the washers as in the last pic. It also covers the receiver therefore holding more heat in during the transfer to quench. It takes time to razer knife the foil and get it in the oil (although I have gotten pretty fast at it), and if you take too long it can cool too slowly through the critical point. So the extra steel helps hold th heat in. And it works very well. You will also notice in the next pic that I left openings in the bottom. These are to alow oil flow during quenching. It also made it ea build. It is just 3 pieces of strap welded across. It is also wider than the reciever at the bottom by about 1/16" That way the only place it touches the receiver is alon top at the rails. One more thing I would recomend is design it so that all the bolts have exposed nuts that can be cut or ground off when they gauld and sieze. I wa

1/28/2011 6:39 PM

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lucky with the first one that used 5/16" bolts into the long nuts. When I built the clamping frame I had 1/4" treads tapped in the side of the thing and I had one seiz what fun that was. So bolts and nuts from then on. Also use #8 hard if you use 1/4". I had a 1/4" mush bolt brake just before I put it in the oven. Had to unwrap r etc. what a pain. You should be safe with 5/16" mush bolts, that is what I used on the first job. When things get red hot they tend to relax a bit, so the bolts need to snug (1/4"#8 - 12 ft-lb 5/16"#2 - 13 ft-lb) Let me also add, that by using the clamping frame you dont even need the long nuts on the jig.

The receiver in these pictures is for demonstration, it should actually have the rails installed.

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One last thing, If you build a heat treat oven (Kiln) make sure it is big enough! These foil wrapped receivers get kinda big when all the clamping accesories and foil add up. I say that because mine is just barely big enough. I have to put it kitty corner diagonally and have to be carefull not to short out the elements and not hit t thermocouple. But I cant complain it does a great job. Here is a link to building a heat treat oven. You can Buy one as well. Well that about sums it up untill I some questions. I hope it has helped and I would love to here of all your progress and successes. Happy AK building, Steve

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buckmeister Member Joined: Apr 2005 TX, USA

Posted: 8/30/2008 10:24:13 AM Sticky! This needs a pin! Add the "how to build a kiln", sources, and it is perfect.

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buckmeister

Dakoma

Posted: 10/4/2008 8:39:29 PM

Member Joined: Sep 2008

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To build a electric heat treat oven.Hmm ! seems I saw one on British Blades.com Forums .Would have posted details but not sure how to work controls here yet,hope someone can .Nice fixtures by the way.You have had good results with this method?

TN, USA Posts: 2 Feedback: 0-0-0

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maxpowers

Posted: 1/3/2009 2:00:08 PM

Member Joined: Feb 2008

do the rec warp during the ramp cycle or during the quench

NJ, USA Posts: 19 Feedback: 0-0-0

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22zSteve

Posted: 1/3/2009 5:58:47 PM

Member Joined: Feb 2008 UT, USA

Originally Posted By maxpowers: do the rec warp during the ramp cycle or during the quench

Posts: 168 Feedback: 0-0-0 There is NO warping, if a jig is properly used. However it has been my experiance that warping in thin materials happens mostly during the quench. Hope This helps. Happy Ak Building, Steve

User Info Posted: 3/3/2009 10:02:50 PM

toy Member Joined: May 2003 PA, USA

What is the proper procedure for quenching in order to prevent warping? Do you drop it in the oil / water fast or slow? ( I have read of some who submerge the receiver about 1 inch per second) Do you place the reciever in vertically or horizontally? Do you stir or agitate? Or just hold it still? Thanks

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doylek

Posted: 4/23/2009 2:23:04 PM

Member Joined: Apr 2009 WA, USA Posts: 2 Feedback: 0-0-0

To avoid warping you want to cool the metal evenly so put the receiver in your quenchant as quick as possible. Use salt water or something else (liquid soap was mentioned before and i think that should work) if you use water. Introducing the hot receiver to the water causes hydrogen gas to accumulate on the surface which in turn causes non uniform cooling and possible warping. The salt/soap breaks up the bubbles quicker and allows the metal to cool more evenly and faster. When I treated mine I did not make a jig as labeled above and it turned out fine. Anything that you bent will relax if you don't have a jig to hold it in place. I didnt use a jig because it introduces too many variables that may or may not be an issue. If the receiver cools quicker than the inside jig, your part will be out of spec because it will cool to the size that the expanded jig is in. The expansion from the jig may be negligible but I didnt want to take the chance.

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twistedneck Member Joined: Mar 2005 MI, USA Posts: 208 Feedback: 0-0-0

Posted: 5/27/2009 7:12:17 AM

[Last Edit: 5/27/2009 7:20:51 AM by twistedneck]

22zsteve, Nice Jig for the quench, that is the best one i've seen. Jigs like that are normally only used during intensive quenching when you have extreme agitation. Most of the time you can get around warping by a combination of pre stress relieving and even immersion. actaully it would be ideal to normalize these before heat treatement to get rid of bending and welding stresses, however heating up to 1600F and air cooling would cause too much decarburization. Also be very careful tempring 4130 at 550F oven temp. its going to be about 47Rc hardness, that is super hard but OK. the only other issue is tempered martensite embrittlement also called 500FE (500 Fahrenheit Embrittlement, or blue embrittlement) - since that is about the blue oxide temperature for 4130. 750F to 800F is more like what the soviets would have used to hit 32-36 Rc. And that link to eng-tips.com is a very good resource. I worked with NickE one of the mods there for the last two years before our company started shrinking due to this auto industry slump. however its my experience that you dont need anywhere near 30min soak time at 1600F+ - the decarb will be too great. with thin sheet you only need just a few seconds at that temp since it takes a while to achive it in a convection kiln. unless you plan to use molten salt? I did not like how foil worked out. it slows down the quench so much that the properties were compromised due to slow quench. As for how quckly to immerse these in quench fluid? a lot of heat treat places will have them fall of a conveyor right into the quench. usually they fall in a vertical orientation. if you want to make a banana, try quenching it horizontally, i've done that a few times. all swordmakers will tell you vertical is the only way to go unless you are trying to get a curved blade - i.e katana.

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rbthntr64 Member

Posted: 9/30/2009 10:54:28 AM What material did you make the jig out of? What kind of weld wire did you use to weld it up?

1/28/2011 6:39 PM

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Team Member Joined: Jun 2004 MO, USA Posts: 971 Feedback: 0-0-0

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ibreel

Posted: 8/9/2010 9:55:10 PM

Member Joined: Jan 2010 KS, USA

Another way to create an oxygen free environment within your foil wrap is to put some wood chips inside the wrap with the receiver. The heat within the kiln will be high enough to make the chips smolder as long as there is oxygen within the wrap. The wood chips will stop combustion after all of the oxygen has been consumed. This will create an oxygen free environment during heat treating. I know this was mentioned above but, it is a good way to create an oxygen free wrap. I have never tried it on an AK receiver, but I use this technique when heat treating knives. The same principals apply.

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hodgescl

Posted: 1/14/2011 12:29:17 AM

Member Joined: Nov 2008 VA, USA

have any of yall thought about using an oil for the quench instead of a water based solution? it has a higher vapor temp. so you could avoid a "vapor sheild" which could compromise the quench? just throwing that out there, thats why oil is often used in blade making.

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