4140 welding

whaqt would be the correct procedure to weld up a crack in hardened 4140 on a rifle receiver? I'm asking for another person, glad its not
my problem.
Karl
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On Fri, 24 May 2013 16:51:42 -0500, Karl Townsend

Receiver in 4140? Are you sure?
Where is the crack? Behind or along the locking lugs?
How did the crack happen?
Its pretty important to know. As to the welding...you are probably going to have to anneal the receiver after welding..then reheat treat..if the crack is in a loaded area.
Gouge with a Dremal tool, preheat to 400-500 F, weld with Cronatig 340T or similar
Gunner
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What's the typical hardness of a non-case-hardened bolt rifle's reciever made of some sort of medium carbon steel? :)
Are you sure they're heat treated? <shrug>
Spark test it. :) Is it -really- 4140? How hard is it now?
Alvin in AZ
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On Fri, 24 May 2013 23:55:02 +0000 (UTC), snipped-for-privacy@Example.com wrote:

http://www.rifleshootermag.com/2011/12/29/guide-to-gun-metal/
http://www.practicalmachinist.com/vb/gunsmithing/best-grade-steel-rifle-receiver-194959/
http://answers.yahoo.com/question/index?qid 081222171619AAz4xfJ
RC 35-45

Yes. Common Gun Metals Carbon Steels
1020 and 1520Common, plain or cold-rolled steel. Youll find it in trigger guards, floorplates, sights, sling swivels and other steel hardware. 4140Ordnance steel or chrome-moly steel, it has 0.4 percent carbon and is really strong while still being cost-effective to machine. Youll find this in barrels, bolts receivers and high-stress items like muzzle brakes. 4150The same as ordnance steel but with the carbon content upped to 0.5 percent. 4150 holds up better to serious abuse, and its found primarily in mil-spec AR-15 barrels. 41V45A chrome-moly variant, it has a dash of vanadium in it. This is an alloy selected to produce hammer-forged barrels. 8620This is a full-up alloy of nickel, chromium, molybdenum, with 0.2 percent carbon. Cast receivers are made of this alloy because it fills the mold well, machines cleanly and ends up very tough and strong.
Stainless Steels
316Also known as marine grade stainless, as it resists corrosion well because of added molybdenum but is not easy to harden. Used in trigger guards and floorplates. 17-4An alloy with 17 percent chromium and 4 percent nickel. 17-4 (or a close kin) is readily hardened and is used in barrels, bolts and receivers.
Aluminum Alloys
6061Aircraft aluminum, selected in that application for its light weight and ease of fabrication into complex parts. Floorplates on hunting rifles, scope rings and some handguards and buffer tubes on AR-15 rifles are made of 6061. 7075Much stronger than 6061, its the alloy used in AR-15 upper and lower receivers, some mil-spec brands of buffer tubes and some railed handguards. In mil-spec parlance, it is known as 7057-T6; the last part designates the type of heat treatment it receives.

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On Fri, 24 May 2013 23:55:02 +0000 (UTC), snipped-for-privacy@Example.com wrote:

At one time I converted quite a few short (Argentina?) Mauser actions and did Rockwell them to see what I was working with - 55,000 - 60,000 psi. Based on how easy they were to drill I would reckon that many Springfield and early Winchester M70 receivers are in about the same range.
I also "recovered" a number of M1 Carbines that had been demilitarized by being cut in half with a cutting torch by trimming the ends and welding them back together. they were only 30 cal. carbine but never had one fail.
Many years ago P.O. Ackley investigated the thrust of a brass cartridge case against the bolt face. It turns out that when a cartridge is fired the case walls expand against the chamber walls and actual thrust against the bolt face is much less than expected from only considering chamber pressure.
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wrote:

Positve on the 4140. its the trunion on an M2HB. The guy has two cracks. One in the top cover he's already welded and another through the rivet holes along the bottom of the trunion - lot of force here.
You get a pile of parts from a de militarized kit, and then build a weapon. So, no clue on cause of trouble.
Karl

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Use 8018 and preheat, peening etc. If the crack is safety sensitive, I would junk the rifle.
i
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Ignoramus5200 wrote:

You don't junk an M2HB Iggy, you do everything humanly and inhumanly possible to preserve it.
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wrote:

Its obvious he doesent know what it is..or what its worth in real dollars.
http://en.wikipedia.org/wiki/M2_Browning
http://www.usord.com/weapons/m2hb
$6500-8500 at very low end of the scale..up to $12k
Not something you toss in the scrap bin
Gunner
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wrote:

I watched your ex-Governator's new movie yesterday and had a blast. They were firing an old Vickers gun at the cartel guys who had come to town to kill them. The air was filled with a lovely pink mist. <g> https://en.wikipedia.org/wiki/Vickers_machine_gun
The other metal-containing movie was Parker, with Jason Statham. It's another two-thumbs-up movie.
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Larry Jaques wrote:

Er, I'm in Texas.

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wrote:

Sorry, I thot I saw Gunner at the helm of that message. Shrub never did movies. <bseg>

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On Fri, 24 May 2013 19:30:47 -0500, Karl Townsend

Then my suggestion should work. Is it cracking in the weld..or is it cracking along side the weld? He didnt anneal then reheat treat afterwards did he?
Should reheat treat afterwards. The HAZ is probably causing him problems and needs to be annealed then the whole piece needs to be reheat treated.
Probably best to have a commercial heat treater do the reheat after the repair. Their quality control is better then a guy with a small oven in his garage. Including the argon flood.
Gunner

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On Fri, 24 May 2013 19:30:47 -0500, Karl Townsend

Can he send it back for a less-cracked version, or did his welding screw up that possibility?
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On Sat, 25 May 2013 16:41:45 -0700, Larry Jaques

LOL..send it back where? The US Government?
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wrote:

The "You get a pile of parts from a de militarized kit" part seemed to be a mail order type thing, I deducted. And that meant he might be able to swap 'em out.
Karl, what's the real story?
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There are sources all over. MANY forums dedicated to rebuilding weapons from parts kits or even scratch. Watching there for an individual selling is the best deal, but often a pig'n'poke on qualtiy or completeness. The eBay of weapons is GunBroker.com Also several vendors, APEX, Numrich gun parts, Sarco, What a country, dozens more. A HUGE number of garage size CNC shop businesses supply nearly any part you can dream up. "The Kid" is one of them.
There is near zero inventory and rip off pricing in this entire field right now. This is all due to the world's best gun salesman, the Moron in Chief, threatening to close down everything. The scare is subsiding but prices are still considerably higher that last year.
Karl
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On Sun, 26 May 2013 09:41:00 -0500, Karl Townsend

IOW, no vendor/no swap. That's a Roger, Over.

Yeah, I was considering a move from 9mm up to .45 but the cost of ammo to restock was too scary to consider, IF I could find it.
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On Sun, 26 May 2013 10:48:21 -0700, Larry Jaques

You dont handload??????? Why the fuck not?
Gunner
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wrote:

I don't shoot a whole lot (3+ year ROI on a reloading station) and 9mm was always really cheap. See any $50 reloading presses any more? If so, a .45 looks good. Ping me offline.
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