Info on Case Hardening

[Long John]

Well friends,

I am part way with this new hunting rifle and I have been thinking about this business of case hardening of the lock.  I have case hardened screw heads and triggers before with Kasenit but a whole lock will require some things that I will have to get or build.  If you don't mind, can you answer a couple of questions for me?

1. I have gathered that the parts must be inside an enclosure that is packed with charcoal.  Is there any reason that a schedule 40 2.5 " ID 6 inch nipple with end caps wouldn't work?  What do you all use for a hardening enclosure? Does the lid have to be air-tight?  Will crushed charcoal briquettes or lump charcoal or should I get some special type of charcoal?

2.  How hot does the enclosure have to be and for how long.  Would red hot in a wood fire be hot enough?  Should I have enough wood for an hour? 2 hours? 15 minutes?  Is a furnace necessary?  If so, what temperature should it be able to attain?

3.  Which of the parts do you case harden?  I am using a Chambers lock that has been assembled already so the internals and frizzen are already heat treated.  So if you were me would you just case harden the hammer, flashpan and lock plate?

4.  I have heard that you all bolt the lock plate to a bar of steel to prevent warping.  Do you use the existing screw holes and bolt it flat to another piece of steel?  It seems that would prevent the carbon from gaining access to the part of the lock plate that is flush with the steel stiffener plate or do you put spacers between the lock plate and the anti-warping plate?   How big is the plate you use to prevent lock plate warping?

That's it for now, I think, although there might be others as I begin to think this whole thing through.

Thanks for taking the time to reply.

Best Regards,

John Cholin

[rich pierce]

What are you building, Long John?  We gotta know.  What lock?

All I know about case hardening is that a wood fire is not hot enough w/o a chimney action- a breech pin encased in a steel pipe packed with wood charcoal in the coals of a very hot open fire did not get it done for me.  I got dull colors but no hardness.

[T*O*F]

John,
Case hardening is for putting a hard exterior on iron parts, or soft steel parts with no carbon in them.  Kasenite, charcoal, bone, etc all provide the carbon to do this.

Most modern locks are cast from steel which does contain carbon, thus there is no need to add any.  If you heat them to critical temperature and then quench them, they will harden all the way thru.  Then you need to temper them back to the hardness you desire.

To harden a lockplate, put a piece of black iron wire thru one of the screw holes near the center of the plate, so that when suspended it hangs as near horizontal as possible.  Make sure it is already engraved and polished.  Heat it with a slight carburizing flame from an oxy/acetyl torch.  Lick the flame over the plate on the backside so the whole plate comes up to temp evenly.  WATCH CLOSELY.  Just before scale starts to form, it will look like a small dark bubble is going to appear.  Immediately dip it straight into a coffee can full of water with 1/2" of oil floating on top.  Rapidly dip it up and down about 15 times and then let it hang in the water until totally cool.  The plate should not warp at all.

Depending on the ambient temperature of the oil/water, you will get colors from blue-black to light gray.  The colder the dip, the deeper the color.  Do the file test and you should find the plate is hardened all the way thru.

I repeat, case hardening only adds carbon where it is lacking and is not necessary where it is present.  Thus the part only needs to be hardened, not case hardened.

[Jim Kibler]

Most commercial lock plates, cocks, top Jaws etc. are cast from 8620 steel.  With only 0.20% carbon nominal they are not going to harden significantly by simply heating and quenching.  8620 fully hard will only reach an absolute maximum of approximately 40-45 HRC.  In practice, a quenched lockplate will probably be less than this.  Although this will help with wear resistance and durability, it is no substitute for proper case hardening or carburizing.  In carburizing, additional carbon is introduced to the surface of the part allowing it to transform to a much harder state.  Typical cases would be in the range of 60 HRC.  This provides parts which are very durable and work very well together since they are hard and slick.  I've been carburizing all of my locks and wouldn't use one any other way.

[J.D.]

Weren't there a coupla tutorials on case hardening, and color case hardening on the old board? Since this subject comes up from time to time, is it possible to resurrect the tutorials from the old board, or does someone need to search the old archives to repost in the tutorials of this board?

With that thought, I volunteer to dig up some of those old threads.

I used the same basic set-up as in Acer's post in the old archives. The difference was that I used four bricks set on edge in a square, three bricks high. The ends of the bricks were placed close together to prevent a too high draft, which translates to too high heat. The contraption was placed on a piece of sheet metal to prevent discoloring the concrete, otherwise pretty much the same set-up.

http://americanlongrifles.org/old_board/index.php?topic=9724.0

And this one, but unfortunately, the links no longer work.
http://americanlongrifles.org/old_board/index.php?topic=34.0

http://americanlongrifles.org/old_board/index.php?topic=5967.0

Maybe someone who has saved those tutorials can re-post them with information and photos?

[Ian Pratt]

  Rich, wondering about the procedure you used, the coals of a wood fire should work quite well. It works well using a steel can as a "crucible", possibly the contents of your steel pipe were not at a high enough temp for long enough or were quenched when too cool?
   John, to answer some of your questions, plain hardwood charcoal works great for case hardening. You do not want a completely air tight container, a loose cover is fine. I routinely use steel cans, for example a tuna fish can for small parts, screws,  set triggers etc. Bigger can for bigger stuff. I set a piece of thin sheet steel over the top as a lid.
   The wood fire method can be used, you can also use a forge but requires more attention. Build up a good sized coke fire, pull the top half of it apart, set a steel plate in there to act as a buffer and put your steel can on it, then rebuild the fire over it.  I have a pretty good handle on the heat I need but I still keep a few sticks of sheet brass handy to check myself, if they melt when pushed through the fire next to my steel can, back off the air.
  However you do it you need to start your timer after the contents of the can come up to temperature. An hour would be plenty long for what you want to do to a lock plate. Bolting your lock plate to a piece of 1/4" steel with some steel spacers in between would be a good idea

[rich pierce]

Not sure, Ian, what went wrong.  The capped pipe I used was beyond red toward orange hot.  I emptied and dunked it pretty quick.  Maybe it wasn't long enough at critical temp.  Maybe the thick water pipe took a lot of time to heat up inside, etc.  I dunno.  I used home-made hardwood charcoal for packing.  Had coals burning well and then stuffed them in a can and covered with a lid to stop the burning.  Maybe too much carbon was gone.  Anyhow, will try again sometime.

[44-henry]

This process is a whole lot easier with a small furnace and pyrometer that you can buy or build yourself. A lot of what you need also depends on whether you are trying for colors or just want to surface harden your parts. I use bone and wood charcoal that I purchase from Brownells, but there are cheaper sources for the same stuff. I've found that a 50/50 mix of wood to bone held for 1-2 hours at 1400 degrees gives a good case and nice colors if you do your part. Some say that better colors show up at lower temperatures (some even advocate going around 1200 degrees) but if you are not at the critical temperature all you are doing is coloring the surface, not casehardening it. You definitely want to block the lockplate and it is also a good idea to temper it following the quench at about 400 degrees for one hour.

[J.D.]

Rich,
I, too, tried a wood fire, as a heat source, with no luck.

Lump charcoal from Waly World works much better as a heat source and works well enough for carburization. Break the charcoal for the crucible into pea sized pieces and smaller. The first parts I hardened came out with a black sooty coating, but the second batch came out clean. The charcoal used in the crucible for the second batch was placed in a 1 lb coffee can, covered with a sheet metal lid, and baked until the any remaining  incompletely charred wood had, indeed, been charred. The rebaked charcoal, used in the crucible, didn't coat the parts with soot.

Pour an inch and a half of charcoal in the bottom, rap the side of the crucible to settle the charcoal, place the parts in the crucible and surround them  with charcoal. Rap the side of the crucible after each addition of charcoal. fill the crucible with at least 1 1/2 inch of charcoal on top, settle, add more charcoal, and cover with a loose fitting lid.

The crucible in my experiments was the bottom half of an empty 1 # propane bottle. The lid was nothing more than a square piece of sheet metal with the corners bent down.

I found a pair of pick-up tongs with about 28 inch reins, for $8.50 at a junk shop, to handle the hot crucible. The long reins are nice to keep my pinkies cool, not to mention that I couldn't make 'em for the price paid.

Since I have only case hardened small parts, I can't comment on what is required to block a lockplate to prevent warping.

Good luck, and God Bless,
J.D.

[Dphariss]

John,
Case hardening is for putting a hard exterior on iron parts, or soft steel parts with no carbon in them.  Kasenite, charcoal, bone, etc all provide the carbon to do this.

Most modern locks are cast from steel which does contain carbon, thus there is no need to add any.  If you heat them to critical temperature and then quench them, they will harden all the way thru.  Then you need to temper them back to the hardness you desire.

To harden a lockplate, put a piece of black iron wire thru one of the screw holes near the center of the plate, so that when suspended it hangs as near horizontal as possible.  Make sure it is already engraved and polished.  Heat it with a slight carburizing flame from an oxy/acetyl torch.  Lick the flame over the plate on the backside so the whole plate comes up to temp evenly.  WATCH CLOSELY.  Just before scale starts to form, it will look like a small dark bubble is going to appear.  Immediately dip it straight into a coffee can full of water with 1/2" of oil floating on top.  Rapidly dip it up and down about 15 times and then let it hang in the water until totally cool.  The plate should not warp at all.

Depending on the ambient temperature of the oil/water, you will get colors from blue-black to light gray.  The colder the dip, the deeper the color.  Do the file test and you should find the plate is hardened all the way thru.

I repeat, case hardening only adds carbon where it is lacking and is not necessary where it is present.  Thus the part only needs to be hardened, not case hardened.

Unless you want a hard surface and a soft interior when using steels with a high quench temperature like 4140.
4140 and some other carbon steels can be casehardened with or without colors.
Increasing the carbon level at the surface reduces the critical temperature and will allow casehardening *some* through hardening steels by quenching below the base metals critical temperature.
Requires careful temp control.

Dan

[Long John]

Friends,

I want to thank you all for the information you have provided.  I think I now have enough info to start assembling the equipment I need to pull this off. 

As for the rifle, Rich, it is a 54 caliber hunting rifle that is loosely styled after RCA 53 and RCA 52.  It is my illusion of what one of William Antes' rifles would have looked like before he built # 53.   I am using a light-weight, Getz 47 inch long swamped barrel and a modestly restyled Chambers Deluxe Golden Age lock.  I probably should have just used the gunmaker's lock but I had this one and I was able to get it to fit the rifle, I think.  The patch box will be a wooden slider, of course.  The carving on the cheek side will be a Christian Springs design very similar to RCA 53.  However, I plan to put more engraving on this one than RCA 53 has. 

The plan is to have this one finished this spring.  I know the judges at the Fair will savage it like they do all the rifles I build.  I don't care anymore - I just build the best I can.  I have determined that the wrist on this rifle is in an exact 3 to 5 ratio with the length of my hatchet handle so I won't get whacked for non-conforming proportions again!  As it is, based upon my squirrel rifle last year I actually have some one that wants me to build them a rifle!

I'll take a picture and post it ASAP.

I also have a project I am calling the 'Spike Buck' that I am itching to get going on.  Hopefully I will get some free time over the Christmas Celebration to work on rifles!

Best Regards,

John Cholin

[rich pierce]

I love #53 if it's the Antes with the CS style cheek carving and daisy patchbox etc.  I see it as the precursor of the Bucks County guns.

[J.D.]

Those are nice choices to build. A friend has a close copy of 52 that holds and points very well. I suspect that you will be pleased with those designs.

There isn't any magic in case hardening any part, so go for it. I do suggest making an experimental plate, to include screw holes and tumbler hole, to experiment with blocking prior to hardening the lockplate.

If, by chance, the lockplate does warp, put it back into the crucible and return it to the fire. Anneal by letting it cool slowly in the crucible. Leave the crucible in the fire and allow the fire to go out, for a full anneal. The carbon rich environment of the crucible will prevent scaling of the lockplate. Annealing will prevent breaking the plate in an attempt to straighten it.

Once the plate is straight, block it better, and repeat the process.

God Bless,
J.D.

[TPH]

If the link works, you may find this from the Archives useful?

http://americanlongrifles.org/old_board/index.php?topic=34.0

[Greg Field]

Please pardon my ignorance, as exposed by these questions.

I have been trying to visualize the blocking of the lock plate. Am I correct that one would block it using stand-offs between the lock plate and the block and that these standoffs would at least partially cover the metal surrounding the holes through which the screws extend that fasten everything? If the stand-offs block the carbon agent from touching the metal around the holes, wouldn't those stand-offs prevent the carbon from entering the metal in those areas? Isn't the area around the hole for the sear mechanism precisely what needs hardening most? If all this is so, how then does one prevent warping while getting the hardness in this one critical area.

Again, not questioning that it happens; just trying to understand.

Thanks

[Jim Kibler]

Please pardon my ignorance, as exposed by these questions.

I have been trying to visualize the blocking of the lock plate. Am I correct that one would block it using stand-offs between the lock plate and the block and that these standoffs would at least partially cover the metal surrounding the holes through which the screws extend that fasten everything? If the stand-offs block the carbon agent from touching the metal around the holes, wouldn't those stand-offs prevent the carbon from entering the metal in those areas? Isn't the area around the hole for the sear mechanism precisely what needs hardening most? If all this is so, how then does one prevent warping while getting the hardness in this one critical area.

Again, not questioning that it happens; just trying to understand.

Thanks

A stand-off will prevent the area it is contacting from absorbing as much carbon as surrounding areas.  Keep the stand-offs fairly small.  I don't think the plate area behind the sear is a high wear area.  There really isn't much force pushing the sear towards the plate.  I've never worried about this small area that isn't as completely carburized as other areas.  If you can be sure the plate will enter the quench on edge or front / tail first you can get away without blocking the plate.  I've used this approach with modern gas carburizing furnaces.  If quenching from a pack, it will be hard to control how the plate enters the quench.

[Greg Field]

Thanks. And sorry but I meant to say "tumbler" but instead said "sear." It seems lik you want maximum hardness on the hole between tumbler and cock and on the plate around the tumbler hole. Do you avoid using a standoff at the tumbler hole?

Thanks again.

[Jim Kibler]

Thanks. And sorry but I meant to say "tumbler" but instead said "sear." It seems lik you want maximum hardness on the hole between tumbler and cock and on the plate around the tumbler hole. Do you avoid using a standoff at the tumbler hole?

Thanks again.

I wouldn't use a stand-off on the tumbler hole.  In my experience if it's attached to a plate in a couple places it's sufficient.

[Greg Field]

OK. That's what I needed to know. Thanks for taking the time to respond.