A knifemaker friend offered me the use of his heat-treat oven to treat my bent-flat receiver.

I would appreciate advise from those who did it before:

1. DId you use the standard 4130 steel procedure - 1600F, oil quench, 700F drawdown for 1 hour?
Or, something else?

2. Did you do any hardness testing before, after quench, and after tempering? I have a cheap durometer, and can get my hands on a proper crush tester.

3. Did you treat the rails separately, and weld them on later?

4. If I weld the rails on before the treatment, will my spot weld joints survive the oven?

TIA,
LT

If you try to heat treat the entire receiver it will warp.

Just do the ejector and axis pin holes

I was gonna ask kinda the same question also today. In this thread: www.ak47.net/forums/topic.html?b=4&f=51&t=79779

mg34ss states (second to the last post): "You cannot quench 4130 in oil. It cools it too slowly and the steel will mush, 4130 requires a violent water quench." and "You should not anneal it at all"

In the article: "From Soup to Nuts Part V: Final Assembly and Finishing by Rob Summerhill", The oil method is used with the 4130 flat (at least on the rails). www.surplusrifle.com/shooting2005/souptonuts2/index.asp

Which method do you builders use?

I'm not an expert, but the following is the sum total of my knowledge and experiance to date, and what seems to me to be the preferred methods to receive the desired results.

Don't oil quench, it seems to me that there is just enough advice oput there that you'll have a difficult time getting a finish to adhere as the metal's "pores" are "open" and will slam shut upon quenching, trapping oil within the metal. These "pores" then open up later when you get the weapon warm from rapid fire, and cause the finish to slough off.
Not to mention theh fun of the oil/ATF fluid bursting into flames when you jam a cherry red peice of metal in it. Whee!

Heat treat rails first, a kiln is ideal for this, quench in a solution of 1lb rock salt, 4 gals tepid water and 6 oz dish soap. Heat the rails to 1600F, IMMEDIATELY quench.

Heat the Hammer pivot pin and trigger pivot pin holes on either side with a MAPP gas torch, it's best to use a welder's crayon to see when you've achieved 1500F. Quench as above.


An excerpt from an article I found here....IIRC by an ARFCOMmer-

Heat the part or the hole to its critical temperature.  Only attempt ONE hole at a time – it is difficult keeping multiple pivot holes at the critical temperature.  The rule of thumb is that the part loses its magnetism when the critical temp is reached – this is true, but difficult to do without having three hands.  Another option is to get some Templaq from Brownell’s – it melts at a very specific temperature.  Welding crayons can do the same thing.  Instead, I use a simple color chart that attempts to determine the temp by the glowing color of the metal.  Here is what I go by: Faint Red 950-1050º F Dark Red 1150-1250º F Dark Cherry 1175-1275º F Cherry Red 1300-1400º F Bright Cherry 1475-1575º F Dark Orange 1650-1750º F Orange 1750-1850º F Yellow 1800-1900º F Yellow/white Over 2000º F Since the critical temp of 4130 is 1475 degrees, heat the part until it is glowing a nice cherry red.  Practice on scrap and try to not do this in direct sunlight so you can see the color.

Remove the scale from all metal surfaces.

Spot weld your rails in place.

Once the rails are in place, do ALL of your fitting and mock assembly. Once this is accomplished, take the receivers, and put 'em in Mommy's oven. Crank the heat to  550/600F (Most kitchen stoves only go to 550F) and maintain for 1- 1 1/2 hours, then reduce the heat by 50F every 45 minutes thereafter, once to 0F on the dial, let 'em sit til morning and the heat is fully dissapated. Your recievers will be "blued" in appearance (That's the oils in the metal being drawn to the surface and oxidizing) they are now tempered to approximately 40-50 range of Rockwell hardness.


Another excerpt-

Temper the part carefully with the MAPP torch.  Since we want FAR lower temperatures this time, the item should never glow.  Once again, you can use Templaq or welding crayons, but the cheap and simple way to just observe the part.  As the metal heats, oxides form on its surface, giving a decent estimation of temperature. Here’s a chart: Pale Yellow 350º F Straw Yellow 400º F Yellow/Brown 450º F Red 500º F Violet 550º F Dark Blue 600º F Light Blue 650º F Blue/Gray 700º F Gray 750º F So, shoot for a violet/blue color.  If the blue disappears, its still OK just don’t go much higher than that.  Once again, practice on scrap before you try this on your receiver.

Heat to 1600F, quench in water by 1550F. Draw down at 600F for 2 hrs (For my oven) Ends up 42-43 Rockwell. The receiver will most likely warp unless you clamp a bunch together. The first one I did was a 1.6mm receiver and it still twisted a little. Lately I've been just treating the holes. I can't see any advantage for a full heat treat on a 1.6mm, and I don't like bringing that kind of stuff to work.

Thank you all for excellent advise.
I wonder how the commercial makers prevent their receivers from warping during the heat-treat?
LT

Linear, I built a salt pot (actually stainlessandalloly.com did it) to Austemper the 4130 just like the soviets.  I'm going for distorion free lower bainite at 42-45RC, no scale, no loss of critical metal thickness due to scale, no decarburization, much stronger and longer lasting.  

I re-heat threat the ejector to 50RC witha  simple torch heat to salmon red 1600F and water quench.  Isolate the receiver via copper plates, get them at onlinemetals.com for example.

Researched on my own, worked with many heat treat guru's, professors at U of M, knife makers, and scientists to get this plan going.

4130 is best tempered above 750F to avoid "tempered martensite embrittlement"  or 500FE. 500 is the lower bound.  

Warp comes from phase transformation, uneven cooling contractions, and not quenching tip down.

Felt or perceived stiffness will be increased along with strength, fatigue, elasticity, and reliability.  True elastic modulus wont increase, but hard steel resists even tiny plastic deformations at low displacments making it feel stiff.

Edit:

Austempering in this case will eliiminate most of the warping.  The other key steps include at least one normalization step (austenetize and air cool, make sure its sealed in stainelss foil).  between normalization steps straighten out any warping.  Then go on to Austemper - no regual temper is needed. And quench like the swordmakers, tip down.  

Twisted - this is precisely the advise I was looking for.
I am continually amazed at the depth of knowledge on this board.
Thank you!

For what it's worth, here's what I do. Clamp the receiver to a 3/4" x 3/4" angle iron. Heat the hammer and trigger pin holes (one at a time) with a MAPP gas torch to cherry red. Youonly need to heat the area around the holes. In this case, less is better. Quench in a 5 gallon bucket of water. Remove any scale and reheat to blue. Allow to air cool. Once you have done this to all four holes and the TIP of the ejector you are finished. Crude but effective (WECSOG). BTW: I tried heating a receiver in the oven and it warped so badly it was unuseable. Live and learn. I'm glad the flats only cost $13.00.

if the sides of the receiver warp here is an idea. Take two 1/4 inch plates and hole saw or mill a 1 inch hole in them both. sandwich the receiver side between the plates exposing the rivet hole to be hardened in the 1" holes in the thick plates.  This way you will only heat up the 1 inch area to the glowing color and when you dunk it in the water it will not warp because it is sandwiched in.