Casehardening lock parts , how hot, how long?

[Rolf]

Plan to case harden the 1772 Lock.
1.How hot does it have to be?
2.How long do you bake the parts?
3.Any spesial requirements for a mild steel frizzen?
4.Can you case harded silver solder/brazed parts?

Best regards
Rolf

[Mark Elliott]

How hot depends on whether you are hardening for color or hardness.   When pack casehardening 1018 for hardness,  I heat to 1600 and hold for 90 minutes, then quench in room temp water(agitated brine would be better).  If you want color and not hardness (or case depth), then you can go down in the 1400's.    Silver solder will not survive such temperatures.   Brazing won't survive the higher end of the temperature range.   I wouldn't try to harden any soldered or brazed parts.  You are going to have to weld such parts.   You are going to have to make a special crucible for heating the lock plate to allow you to dump it in the quench vertically.    The little parts can be heated in a standard crucible. 

[44-henry]

Keep in mind that parts will warp when you quench if not properly blocked for support. As for times at 1425 F one hour in a carburizing mix would yield about .003-.004 inches case depth. If you up the temperature to 1600 you could get as much as .016". Keep in mind that these depths assume an efficient carburizing compound, Kasenite is one and there are others, plain wood charcoal is not a very efficient mix, though it improves a bit when bone is added.

I have always been curious about brazing and case hardening. Copper or hard silver brazing might withstand the process as the melting temp is well above the lower carburizing temps, though the shock of quenching might break the bond. It would be an interesting experiment.

[David Rase]

I have been color case hardening parts using a 2 to 1 ratio of wood to bone charcoal at 1500 degrees Fahrenheit for one hour with excellent results.  Careful placement of the parts in my bottom drop crucible helps prevent warp age.  I did color harden at 1450 one time with good results, more blues.
David 
 

[smart dog]

Hi Rolf,
Dave Rase gives good advice (as always).  Much depends on your objectives.  If you are going to polish parts bright and are not concerned with colors, I would increase the heat to 1550-1575, heat soak the parts 90 minutes-2 hours, and quench in a big barrel of room temperature water.  Dave's mix of bone and wood charcoal is ideal. For a mild steel frizzen, the case needs to be deep so you may want to heat soak it longer but definitely heat it to 1575.  You can go higher but 1575 will do the job nicely.  I would be very nervous carburizing brazed or soldered joints unless they can be clamped together when in the pack or the solder is not there to really hold them together just to add insurance they don't loosen.  Tempering after hardening is critical unless the parts were all mild steel that cannot through harden during the process. If there is risk they could through harden you need to temper the parts. I would suggest 575-600 degrees F (300-315 degrees C) for 1 hour for all of the parts except the frizzen.  For the frizzen 375-400 degrees F (190  - 200 degrees C) for one hour should work well.  You may want to heat just the toe of the frizzen to blue with a torch later to make sure it is not too brittle. Let everything just air cool when tempering, no quench.

dave

[FlintFan]

I would disagree about soaking and quenching at such high temperatures.  It is simply not needed, and there is a much higher chance of warping and cracking at quench with such high temps. It is much preferable to use longer heat soaks at lower temps. You will achieve the same results with fewer possible problems.  One of the biggest misconceptions surrounding heat treatment is that you must have temps in the 1500-1600 degree range to achieve hardness.  That is simply not the case.  Here is a chart to guide you.

[smart dog]

Hi Flintfan,
I have no misconceptions about lower temps enabling hardening.  My advice is based on experience.

dave

[SingleMalt]

If I remember correctly, Taylor posted something about this.  A PM to him wouldn't be a bad idea either.

That said, I've used Kasenite when it was available, and just followed the directions with excellent results.  You do get some color, but it's a mottled gray, not pretty blues and browns.  After polishing, there's some mottling present, but faint.

[David Rase]

Thanks Smartdog for bringing up the information about tempering.  I completely forgot to mention tempering in my earlier response.  It is definitely an important step.  Not only is tempering critical to relieve the stresses and brittleness, but it has been my experience that every time I temper a change in the vividness of the colors occurs as well.  One other thing I might add is it has been my experience that I need to remove the scale on the face of the frizzen in order to get it to spark.  I have an 8" CBN wheel that I use to just lightly remove the outer glass layer (color) on the face of the frizzen.
David

[FlintFan]

Hi Flintfan,
I have no misconceptions about lower temps enabling hardening.  My advice is based on experience.

dave

Mine too. Just pointing out there is a much lower chance of something going wrong by holding at 1450 for 4-5 hours instead of 1575 for 1 1/2-2 hours. After seeing the amazing work that Rolf has put into his locks, I would be sick to my stomach seeing him have a quench failure after all that hard work. 

[jerrywh]

I have been heat treating for over30 years and taught many others how to do it. The different soak temp between 1450 and 1550 is pretty trivial but it does make some difference. Using plain CLEAN wood charcoal will produce good colors but the inclusion of about ½ bone charcoal will enhanced them. The water quench must be clean, fresh and cool or cold. Dave Race does as good as I have ever seen. The soak temp of 1450 or cooler will produce more colors but will be somewhat softer however hard enough. Tempering is a must and if tempered at about 400° for at least 1 hour will greatly enhance the colors. Some commercial heat treaters will soak at 1500° for about an hour and then allow the parts to cool down in the oven to 1250° and then quench. This does not produce a good hard surface bit will produce great looking colors for presentation purposes. I will add that Dave Race has a lot of experience. I have known him for over 20 year and when he says something it is from experience and he has done it all and it’ not just talk. He is a great gun maker and a highly talented man.

[JCKelly]

Metallurgist, mostly modern industrial stuff but know a tad about case hardening gun stuff.

I like FlintFan's chart. Yup, harden from a lower temperature, get less warpage & cracking

Use charcoal mixed with bone charcoal, as jerryw says, to get colors. The Art of color hardening was detailed by Oscar L. Gaddy in The Double Gun Journal, Vol. 7, Issue 4, 1996 and Vol. 8, Issue 1, 1997

Old original wrought iron frizzens were not, in my observation, carburized. They had a steel face forge welded or brazed on, then the whole thing heat treated.

I think military flintlocks and good British guns had the face welded on. Lots of guns used copper brazing.

Here is one example of a late commercial flint lock Dillin-

What shows as a dark line in the photo is a copper braze line, which attaches the frizzen's steel face to a forged wrought iron body
This rifle is in The Kentucky Rifle, Dillin, 1924. On pages 83-84, rifle #3, Plates 93 & 94, St. John collection. Made late in the flintlock period, possibly in Susquehanna County

[RJD-VT]

Hi everybody, I have been reading this forum for years but finally joined so I can stop acting like a tick on a moose.   
Anyway, lots of good advice posted above so I thought I would just point out some good pic’s  Dr. Marshall took of Jud Brennan case hardening a homemade lock with charred bone. Many of you have probably seen these
but if not, it might be worth a look.  http://judsonbrennan.blogspot.com/2017/05/
Dr. Marshall also briefly explains Juds technique.
Bob D.

[FALout]

How do you “support” the lock plate to keep it from warping?

[David Rase]

How do you “support” the lock plate to keep it from warping?

It's all in how it hits the water.  If your lock plate hits the water on the flat surface like a pancake you will get warp age.  If your lock plate goes in edge first chances of warp age is greatly reduced.  Some people bolt a bar to the backside of the lock using a spacer between the bar and the lock plate to help prevent warp age.  The lock I just case color hardened last week went in nose edge first and was as just flat after the quench as it was before heating.
David

[Rwnblack]

I agree with modest temperatures but haven’t had issues with warpage unless I went very high in temp.  My oven is in metric but I typically caseharden at 720 to 750 C.  I have gone as high as 900 but that is too high.  For frizens where I am more concerned about hardness I will go up to 800 C.  I draw the temper by soaking the part in heavy duty oil (diesel motor oil), wrap in tin foil and heat in my furnace at about 310 C.  Colours darken and add more browns in during tempering but that is okay.  I typically use a 2:1 wood to bone charcoal with some wheat charcoal added for good measure. I arrange the parts and wire them up so they fall pointy end in first.

[Rolf]

I'll be using a thermostat controlled heat treating oven.
Why not soak at 1700 fahreheit  for 2 hours, the lower to 1500 fahreheit for 2 hours, the quench in brine.  Lowering the temp before quenching should reduce warping, while still getting a deeper caseing.



Best regards
Rolf

[James Wilson Everett]

Guys,

I do not case harden for color, only for hardness.  The mix I use is 1/3 hardwood charcoal, 1/3 bone charcoal, 1/3 leather charcoal.  This is a mix that I was able to document from the 18th c period, but now I cannot remember the source.  The bone charcoal starts from bone meal that you can buy at a garden supply.  I cook it outside in a metal pot with a lid (stinks).  At one time I dumped the lock parts & charcoal mix directly into brine.  Quite a mistake!  It really dirties the brine mix and I also got a steam scald on my wrists above my gloves (ouch).  Also, you do risk a lot of warpage as you cannot control how the parts enter the brine.  Now, I cook the parts in the charcoal, allow to cool, reheat each part and then individually quench.  This way I can better control the quench temperature and how the part enters the brine.  For a larger part such as the lock plate, just plunge it straight down into the brine, tail first.  Do not swirl the part in the brine, just straight in without stirring or swirling.  Parts done this way have very little warpage and have a grey surface color.  As a bonus the brine remains rather clean for re-use.

Jim

[jerrywh]

  Just a warning here, If you soak at 1700° or higher the surface begins to get a grainy look like small bumps on the surface.  I recommend staying around 1500° . If you have gold inlays you cannot go over 1550° or the gold will alloy with the steel.
   This lock is case hardened and polished back. The gold is only .003 thick. Case hardening this stuff is a bit tricky. 

[yulzari]

All good stuff. Just to slightly de mystify all this :

[kutter]

When I worked at one of the big guy Restoration shops in the 90's..
1435F was the temp.
Quench was pre-heated to 90F
No aggitation, no additives and used only once then dumped.
No blocking or anti-warping plates added to the parts.
BUT the position in the box during HT and the direction they hit the quench was critical so as not to warp.
That's what worked and got the results. Probably 100 other ways to get good results w/o getting problems.
Too many variables in that work to say one way or another is the only way.

Brazed parts went through just fine w/o any damage to the braze fix or other problems.
I used to send occasional parts with a braze fix on them (hammer, screw heads half soled, ect) to Case Color Co in Ohio (Don Menk)
back when he was still in the biz. Never any problem with him doing them either.

I had one customer that insisted his restored SxS be re-CCH by a now gone but well known artisan of the trade. I'm sure many would
recognize the name but it's not important.
In talking to him about sending along the parts for CCH, I casually mentioned that the top tang screw had been repaired (half soled) with a braze fix so as not worry if he saw the yellow metal line,,that it was in fact braze and not hard solder. (Hard solder would come apart in the CCH process, )
Well, after a long pause, he then lit in to me about how I could have damaged his CCH equipment if that one part had gone through there,,an on and on.
I repeated that it was brazed,,not silver soldered.
Didn't make any difference he said, it would contaminate the whole thing.

He agreed to do the work, ... 'don't send any brazed parts'.


But we never seemed to get a long much after that,,never had that gun guy bond thing going.

[JCKelly]

Yulzari that is a wonderful video, illustrates stuff more clearly than just words. I am keeping it in my files.

Here, by the way, is how they did things in 1589:

"In The Thirteenth Book of Natural Magick, 1589, G.B. Della Porta describes “ways whereby iron may be made extream hard”. To harden files he says:

Take Ox hoofs, and put them into an Oven to dry, that they may be powdered fine; mingle well one part of this with as much common Salt, beaten Glass, and Chimney-soot, and beat them together, and lay them up for your use in a wooden Vessel hanging in the smoak; for the salt will melt with any moisture of the place or Air. The powder being prepared, make your iron like to a file; then cut it chequerwise, and crossways, with a sharp edged tool: having made the iron tender and soft, as I said, then make an iron chest fit to lay up your files in, and put them into it, strewing on the powder by course, that they may be covered all over: then put on the cover, and lute well the chinks with clay and straw, that the smoak of the powder may not breath out; and then lay a heap of burning coals all over it, that it may be red-hot about an hour: when you think the powder to be burnt and consumed, take the chest out from the coals with iron pinchers, and plunge the files into very cold water, and so they will become extream hard. This is the usual temper for files; for we fear not if the files should be wrested by cold waters."

This four-centuries old process is metallurgically entirely correct. The chimney soot, of course, is a nearly pure source of carbon to carburize or case harden the surface. “Ox hoofs”, provide nitrogen which, along with the carbon, further improves sliding wear resistance. Salt and glass melt the whole mess together to provide intimate contact with the surface, and “activate” the surface to make it easier for the iron to absorb carbon. This is really 21st Century stuff!  Even today the “usual temper for files” is just as they come from the quench, with no further reheat/temper/draw.

In Ancient Times (1974 - 1990?) Nicholson file quenched into salt water from about 1440F and sold the files just as-quenched, no tempering at all

I learned a bit working with those guys.