Author Topic: Case hardening 4140 steel  (Read 6860 times)

Offline smart dog

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Case hardening 4140 steel
« on: September 18, 2018, 04:22:44 PM »
Hi,
I have a chambered flint breech that was machined from 4140 steel.  My original intent was to color case harden it like many English breeches from the early 19th century.  Does 4140 have too much carbon such that there is a risk of through hardening?  I will brown the barrel and I can rust blue the breech for contrast as an alternative to the color casing if that is unwise.

dave
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Offline JPK

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Re: Case hardening 4140 steel
« Reply #1 on: September 18, 2018, 06:58:21 PM »
4140 can be safely color cased hardened by lowering the temperature at quench to 1375 degrees. The critical temperature for 4140 is 1575 so by quenching at below this will not harden the piece except for the high carbon surface. Draw at 375 immediately to reduce stresses.   
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Offline L. Akers

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Re: Case hardening 4140 steel
« Reply #2 on: September 18, 2018, 07:04:13 PM »
I have found that more colors can be obtained if the quench is done in a column of bubbles in the quench medium.  I use a bait bucket aerator to supply bubbles.  Keep the item moving within the bubble column until cool.

Offline jerrywh

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« Last Edit: September 18, 2018, 07:30:34 PM by jerrywh »
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Offline 45-110

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Re: Case hardening 4140 steel
« Reply #4 on: September 18, 2018, 09:02:05 PM »
one thing you could do is to leave a nut screwed on the breech threads during the heat treat and quench process to lessen the chance of embrittlement.
kw

greybeard

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Re: Case hardening 4140 steel
« Reply #5 on: September 18, 2018, 10:07:42 PM »
Paint the threads with a saturate  solution of copper sulfate mix and the carbon cannot penetrate the steel.    Mr Bivins. Muzzle Blast .
     Bob

Offline Rwnblack

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Re: Case hardening 4140 steel
« Reply #6 on: September 18, 2018, 10:42:18 PM »
I have casehardened a number of parts and actions for BPCR without any problems.  I did have to use a bit higher temp than iron to get nice colours.  Usually I heat pieces at 720 But 4140 I have been going to 760.  I drop the temp to 620 C over 30 minutes before I quench.  I use a 2:1 wood to bone char mix.  Sorry for being in C, my furnace is an old lab unit that work was tossing and it is in metric.

Offline smart dog

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Re: Case hardening 4140 steel
« Reply #7 on: September 18, 2018, 11:09:27 PM »
Hi,
Thanks everyone.  I will follow advice given.  I am hardening for color not performance so lower temps are in order.  Rwnblack, I have a programmable oven so I can program any regime.  I will coat the threads and heat to 1400 (760) for 1 hour and then reduce the temp to 1150 for 30 minutes and quench.  I have both bone and wood charcoal.  L. Akers, when I quench, I tip my rectangular container over with the lid still on. The lid falls off into the quench in front of the pack and creates a lot of bubbles.  Seems to work pretty well for vivid colors.

dave
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Offline JCKelly

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Re: Case hardening 4140 steel
« Reply #8 on: September 30, 2018, 01:27:06 AM »
One more thing youi might want to think about, if you have a family

Get a decent insurance policy to take care of them just in case that breech happens to leave its appointed station in the rifle.

Tons of 4140 are hardened through each year. A Ruger single shot has a cast 4140 receiver hardened to about Rockwell C  40; many smokeless revolver
frames are also heat treated thus - but not case hardened.

One would be very hard pressed to find any industrial application where 4140 is case hardened and used in Lethal Service.


I am continually amazed at those who so disrespect the power of explosives

Offline smart dog

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Re: Case hardening 4140 steel
« Reply #9 on: September 30, 2018, 02:17:57 AM »
Hi JC,
Your last comment seems offensive to me.  I asked the question about case hardening 4140 steel to get advice and received some. Now you contradict that advice and complain you are amazed at folks who disrespect the power of explosives. Just explain your reasons without the attitude and chip on your shoulder.

dave 
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Offline JCKelly

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Re: Case hardening 4140 steel
« Reply #10 on: September 30, 2018, 06:01:36 AM »
I appologize for being offensive.

The thing about steel, and gunpowder of any sort, is that things occasionally go wrong. When that happens - and I am aware of a number of such events - then the steel barrel/breech will burst in some manner. If it bulges and splits a bit one may be injured, but the thing must show some ductilty when it fails. Or, if it just shatters, ones wounds may be severe.

I hear people speak of "Tensile Strength, "Hardness" & cetera. What matters in a metal for a reasonably safe barrel i that it be tough, above all else.
That is,  it must bend or tear a little when it comes apart, and not just break like a file does.

I say "when" it comes apart, and not "if" because there are so many ways to get into trouble with a gun that accidents do happen. When something does go wrong, which no one expects, it is good to survive with only the need for fresh clothing. Loading with the ball off the powder some distance can ring the muzzle loading barrel, or it can shatter it. In a modern centerfire rifle one nasty problem is when one decides to go for light loads in his, say .30-'06. So the guy loads with a greatly reduced chgarge of rifle powder (here I am talking smokeless). For reasons I do not understand, but I think some Army artillery guys know, this reduced charge gets presssure waves bounching back & forth & where they meet the rifle disintegrates. There ws one on display in Clarkston Michigan at the Flint & Frizzen shop. Think the shooter survived OK but the rifle is a mess.

That was a digression. ANyway, it is good, normal practice to caseharden steels that are low in carbon content. Century or so ago that meant wrought iron. Then for early cartridge guns it meant low carbon steel. Low being, say, 0.20%carb or or less, nominally. "Medium carbon steels", say about 0.40% carbon can get very hard all the way through if they see a normal case hardening heat treatment.

I guess it can be done by somone who knows their business, and this would involve heating up to rather low temperatures in the 1300-something F range. Me I'd distinctly rather not be present when someone brings out his beautifully color hardened Ruger or 1911 to pop off a few rounds.

Think the first thing I wrote about steel and muzzle loaders was for the Buckskin Report, probably early 1980'. John Baird was the only one preaching  design/metals gun safe manufacturing back then, that has not and will not change. At that time some fine fellows were selling breeches investmentcast of high carbon steel, specifically 1095. Never heard of anyone getting hurt by them but damnifIknow why.  No, no no I'd not color harden one. Neither would I use one in any condition. This is the stuff from which files, and in Ancient Times, star drills (for concrete) were made.

43 years employed as a metallurgist I have analyzed many, many machine failures. Along the way a few muzzle loading failurs that changed the shooters' lives. One was, finally, the reason Douglas Barrel Company stopped advertising muzzle loading barrels in the mid-1980s.

Just don't harden your 4140 breech.

It is not easly to communicate this to muzzle loading shooters. I have tried close to four decades now. Hence the chip. Sorry to be offensive but that is the way it is. And it will continue to be so.

Offline bob in the woods

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Re: Case hardening 4140 steel
« Reply #11 on: September 30, 2018, 06:45:16 AM »
This may be out of place, but forgive me for asking.  Modern reproductions of colour case actions [ Sharps, 1873 Win etc ] are coloured via different means [ acid bath ?? ] which doesn't affect the properties of the steel. Is this a process which one could use on 4140 ?   

Offline 44-henry

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Re: Case hardening 4140 steel
« Reply #12 on: September 30, 2018, 12:11:57 PM »
Many reproductions are color case hardened using molten potassium cyanide which the parts are submerged/dipped in followed by a quench, none use acids to my understanding and you certainly would not want to mix them into this process or you would have the makings of a gas chamber.

Cyanide color case hardening is an actual carburizing process, but the colors achieved are quite different than those achieved with the traditional wood and bone packed process. The depth of the case is also generally quite shallow, though this has more to do with the time the parts are allowed to remain in contact with the cyanide.

At one time I did do some experiments combining potassium cyanide with wood and bone charcoal for color case hardening. I think this was done quite often in at least the 19th century, and it does yield some different colors. I quit doing it due to the dangers associated with the cyanide and the disposal afterwards.

Offline smart dog

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Re: Case hardening 4140 steel
« Reply #13 on: September 30, 2018, 02:20:53 PM »
Hi JC,
Thank you for that reply.  That is the kind of information I was seeking in my original post and because of my concern about failure due to brittleness after case hardening (which might even through harden 4140 steel if not done correctly). I asked that question because I absolutely understand the power of explosives and the risks of unintended events. If I didn't, I would not have asked the question.

dave
"The main accomplishment of modern economics is to make astrology look good."

Offline 44-henry

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Re: Case hardening 4140 steel
« Reply #14 on: September 30, 2018, 02:54:51 PM »
One thing to keep in mind is just because the part has been casehardened does not mean it cannot be tempered afterwards. I do this regularly with CCH parts both to enhance the appearance and reduce the hardness/brittleness of the part.

Offline bob in the woods

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Re: Case hardening 4140 steel
« Reply #15 on: September 30, 2018, 03:31:15 PM »
Thanks for that 44-Henry.  My follow up question was going to be about tempering/ annealing  and if it would affect the colours.  If the purpose of the exercise is colour only, then it seems a good option .

Offline smart dog

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Re: Case hardening 4140 steel
« Reply #16 on: September 30, 2018, 04:48:20 PM »
Hi,
I case harden parts all the time and I always temper them because the part is usually steel, often steel that could through harden. Unless it is a frizzen, I usually bring the temper up to about 490 for 1 hour. That deepens the bronze colors such that the color case has darker blues and browns, which is my preference.  If it is a tumbler or sear, I temper at 600 degrees, if a frizzen at 375-400 degrees.

dave
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Offline JCKelly

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Re: Case hardening 4140 steel
« Reply #17 on: September 30, 2018, 06:45:05 PM »
Do not color harden or otherwise case harden your 4140 breech parts.

If you temper them high enough for a safe part, say about 1100F, the colors will be long gone.


Offline smart dog

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Re: Case hardening 4140 steel
« Reply #18 on: September 30, 2018, 06:52:45 PM »
Hi JC,
After your post I changed my mind and am not going to case harden the breech.  The case was just cosmetic to produce colors as that 4140 steel is pretty darn tough.  There was a huge difference when I filed the hook into it compared to when I  file those from standard breech plugs.  What I will do is simply rust blue the breech, which is also authentic for British sporting guns of the time and will contrast with the brown on the barrel.

dave 
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Offline jerrywh

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Re: Case hardening 4140 steel
« Reply #19 on: September 30, 2018, 08:10:01 PM »
 If you heat a piece of 4140 to 1500°F and quench it.  It will be harder than normal. But if you than hit it with a hammer you will find that you cannot break it. That is because it does not have enough carbon in it to get very hard. It is tough but not very hard. JC is referring to modern Rugers. We are talking about Black powder. A classic example of Apples to Oranges.
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Offline Pennsylvania Dutchman

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Re: Case hardening 4140 steel
« Reply #20 on: September 30, 2018, 09:23:58 PM »
4140 will thru harden to RC58-59, which if you hardened a breech plug that hard, you can easily break the tang off with a hammer. It would need to be quenched in oil at 1575-1600F to harden. Casehardening at 1350F would not harden it. I made a lot of tooling for Eaton Aeroquip that I machined from 4140, 41L42, and 4145. I hardened and tempered it in the shop to RC 44-46 and finished machining. It was hard all the way thru.
Mark
« Last Edit: October 02, 2018, 03:25:54 AM by Pennsylvania Dutchman »
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