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Posted: 9/12/2004 9:06:25 PM EDT
[#1]
OK , here's the deal. 4130 will not harden without a VIOLENT quench. Toss it in the furnace and get it bright orange. When it gets there, just pop it out and into cold water. You have about 1 second to get it from the furnase to the water. This is important. Longer than that, and it will remain soft. Another hint. Get the furnace hot, then put it in. It has to be in the furnace for as short a time as possible as oxide scale will built up on it wicked fast. The only way to get that off is sandblasting. I have done four receivers this way with acceptable results. Have the quench water right in front of the furnace door and do it fast. DO NOT USE OIL!!! It might catch fire, you will never get it out of the pores in the metal and it will screw up an oxide or park job you might want to do, and it will be dead soft. Use water.
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Posted: 9/13/2004 6:33:44 PM EDT
[#2]
Thank you, MG34.
Now, of course, as you have taken the time to offfer your experience, I am going to look the part of the typical newbie know-it-all a__hole and describe ANOTHER method I have found, which is used by a MilSpec Aerospace manufacturer. They heat to ~1500-1600 deg F (which reaches the bright orange you referenced), and then quench in oil. (I'm curious about your experience. Oil really made a mess, eh? I'm used to quenching in oil when doing some of my hideous amateur forgings, and the flame, smoke, etc. don't bug me. Did you attempt any kind of degreasing step?) In their case, the furnace does have an inert atmosphere, so they "soak" their parts (admittedly much thicker than an AK rcvr) for ~30 minutes. Immediately after the quench, the part is dried off and tempered at a lower temperatore for about an hour, with the tempering heat dependent on the Rockwell hardness required by the print. Higher temperings give a lower hardness. You can get 4130 to be quite hard, but it is of course embrittled then. Seems to be we would be shooting for Rc ~ 30-35, which would be ~1000 deg F, and again 10 minutes or so would be enough owing to the thinness of the rcvr. Finally, at the conclusion of tempering, the part is allowed to cool in still ambient air, is descaled, degreased, and sent to the next operation. Having said all that, I'm liking your approach for all the reasons you mentioned (rapid oxidation, etc.) that I will face because I only have amateur equipment. Perhaps I'll cut the boogered-up piece in two and try both methods to see where I end up. Thanks again!!! |
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Posted: 9/14/2004 2:18:43 AM EDT
[#3]
I'm useing crude equipment too. I have a programable PID temerature controler in my shop and its on my park tank, not on my furnase. A half hour soak will distroy your receiver. You will loose half the thickness of the sheet metal to scale. All those ideas you have are about thick section parts and do not apply to sheet metal receivers. You have some scrap. Try my process on some scrap. Try yours as well. Get some cheap black oxide solution and see how it works on the treated scrap metal. ( It won't work on oil quenched parts, even after sandblasting ) I didn't temper. My receivers didn't seem to need it. I have no cracks and little wear after 1000 rnds. thru my RPK. 800 to 900 degrees was the tempering temp I remember. 2 or 3 minutes would be plenty of time. Remember the longer times are used to equilize the temp. in a thick section part. You do not need the time, only to reach the temp. Remember also, the 1400 degree sheet metal can cool 400 degrees in 5 or 6 seconds exposure to room temerature air, effectivly anneling the part to dead soft. I've done it both ways, stick to water.
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Posted: 9/14/2004 8:56:07 PM EDT
[#4]
Can't figger out how to post the pics, but you were right -- your way looks fine and has made a tough piece, mine is wrecked and soft.
Thanks for saving me the dough on the real thing. |
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Posted: 9/15/2004 5:34:45 AM EDT
[#5]
I heard that!!!! Great thread !!!!!! +1
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Posted: 9/15/2004 4:35:59 PM EDT
[#6]
I feel a little priveliged to be in the presense of these guys...
I am hoping that some of that knowledge will rub-off on me... have Thanks Guys! |
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Posted: 9/16/2004 3:57:17 AM EDT
[#7]
I built about 8 really cool home made receivers. What I need to point out is that I distroyed about 25 receivers working out the process. I'm a pic posting impared person too. Like to show you my RPK.
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Posted: 9/19/2004 3:36:03 AM EDT
[#8]
Good conversation. If you handle picture posting like you do steel we all would be
drooling and bowing to your RPK. |
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