Case Hardening Experiments Mod-Up

[vtsteam]

For this Mod-Up the goal is to come up with useful case hardening materials and methods for the hobbyist workshop. A method that uses commonly available, safe materials that produce repeatable results, in a reasonable time, is the hoped for goal. Actual experimentation, and results, rather than theoretical arguments, opinion, and hearsay (of which there seems to be a great quantity online) are the purposes of this Mod-Up.

Anyone can join, but I hope that there will be contributions results (and pics if useful) of actually testing rather than just procedural theories. And for any experimenter no matter if those ideas don't work, or do work out, either result is equally welcome!  Thank you, thank you!

Since this is a Mod-up, to put some very slight urgency to the matter, this thread will be closed, June 9, 2015.

Finally one stong caution. Some of the commonly used commercial or DIY suggested ingredients, the ferri and ferro cyanides can under certain conditions of heat or acidity produce cyanide gas, which is deadly. Online discussions disagree on what those conditions are, just as online discussions seem to disagree on most points re. case hardening. I personally intend to steer clear of them in this Mod-Up. In fact the desired result is a usable case, using commony avaiable materials that are reasonably safe.

Anyone want to join me trying out smelly concoctions and setting them on fire for the greater good? Thanks in advance if you do! 

[lordedmond]

I have seen this method used but a now passed over model engineer but not used it as we do not have a coal fire

He used to wrap the part in question in old cotton rags seal them in a tin ( small parts in a Bruno baccy tin) put them in the fire before going to bed this gave them a long hot cook in the embers , these were retrieved next day befor his boss slung them of with the ashes, he then heated them up to red heat and quenched in water .

Now I think that this method gave a shallow case but as it was for the motion work on loco,s it was ok , his reason to harden them was it gave a fine finish when polished up and a small amount of corrosion resistance

If it's not the info you want then delete this post
My self I used a kasenite but dip the part in water then into the compound then heat to red and quench, a point often missed is that a heat up to red and a slow cool will soften the case ,but reheat and quench will restore it
Stuart

[vtsteam]

Stuart, not a problem, that's good info to try if someone wants to. 

I've got a similar direction I'd like to try in conjunction with charcoal making. One of the oft-stated theories is that cabon monoxide, rather than just carbon itself is the causative agent in closed vessel case hardening. Some say that pure carbon in the form of charcoal is not very effective in comparison with hooves, horns, leather scraps, etc. My guess is that these (and perhaps rags) may pyrolise to carbon, and the pyrolisis itself is important.

During wood pyrolysis, lots of carbon monoxide is evolved. So I thought I'd try putting those two things, charcoal making and hardening case together to see what happens.

One of the interesting questions to me is just how much oxygen is needed to produce the (supposedly) necessary carbon monoxide. Is an absolutely sealed container with nearly pure carbon perhaps too poor in oxygen to produce enough carbon monoxide for a case? Or is the carbon monoxide not the right transfer agent -- perhaps something other in say hooves, or rags is responsible. Anyway, trying things out is the real way to solve these kinds of puzzles.

I also would like to try Andrew's sugar suggestion.

[awemawson]

Crushed bone and charcoal has been used also historically for case hardening, packed in an iron box and left sometimes for days, in a furnace.

[NormanV]

I once read somewhere that they used to wrap it in leather inside a sealed metal box and then heated it to red heat.

[awemawson]

I believe that practically any source of carbon will work, and the various additives are to speed up the absorption process. I've heard of all sorts of weird concoctions being used, but with the exception of the Kasenit look-a-likes, the thing in common is heating for a long time in a sealed atmosphere to minimise oxidation.

[vtsteam]

These are some of the theories commonly presented. Anybody want to actually try out a paricular method? and check results?

The sugar version I'll try today. Doesn't mean someone else shouldn't do the same material, since it is almost guaranteed that different people will use different procedures, and I'm guessing those can produce different results....

[Lew_Merrick_PE]

The method we used in the tool & die shop where I apprenticed was to pack the parts in a (terra-cotta) ceramic "bowl" (more like a fully-bottomed cylinder) using bone mean and molasses as the pack.  This was covered with a slightly larger "bowl" (ditto) that was set into a coke forge on "dull-red" heat and left for 10-12 hours of "soak."  We then let the container cool before disassembling it and removing the parts.  We then fired up the parts to a "medium-red" and quenched them (usually Puget Sound salt-water).

We got consistent .080/.060 inch casing this way.  I last did this in the late-1980's.

[Manxmodder]

I believe that practically any source of carbon will work, and the various additives are to speed up the absorption process. I've heard of all sorts of weird concoctions being used, but with the exception of the Kasenit look-a-likes, the thing in common is heating for a long time in a sealed atmosphere to minimise oxidation.

Agree with you, Andrew, any source of carbon will permeate into the steel. Once it is in there the steel  can be treated in the normal way the carbon steel is hardened.

When I was a little lad the local blacksmith/farrier used to gather up all the horse hoof trimmings whenever he shod a horse.

These and old leather pieces along with the item to be hardened were packed into metal boxes and sealed with fire clay. He then put the boxes in the forge and left them at bright red allowing the steel pieces to absorb a case of carbon. The longer the metal is in contact with the carbon at red heat the greater the depth of case carburising becomes.........OZ.

Edit to add: A mate who does a lot of gun smithing tells me that carburising parts using small leather pieces gives the component a mottled finish often seen on older gun parts.

[vtsteam]

Okay back to experiments, which is what this Mod-Up is actually about....

I removed the scale from 5 pieces of 1/2" x 3/32" from a ten foot length of ordinary hot rolled steel. I added a beveled end as a pseudo cuting edge and labelled them C for Control, S for Sugar, A for Air, and 1 and 2 for other trials.

C would not be heated at all. 
S would be an attempt to case harden with sugar
A would be another control which was heat treated the same as S, but would not receive sugar.

Here's the setup. A MAPP torch, cup of granulated cane sugar, and a container of water to plunge the pieces into.

Please notice I am going to use controls and the same stock and method throughout. That is important to avoid jumping to conclusions from a trial of any material by itself. I personally think that the failure to do that is responsible for many errors of opinion on the Internet.

[vtsteam]

The  first trial, done mainy out of curiosity was the sugar coated trial.

The strip of steel was heated to cherry red (my estimate) and plunged into the sugar. The sugar carmelized into a pool immediately, boiling off steam, and darkening quickly to near black. There was flame above the sugar for a short time. When the bubbling had settled down a bit and I judged the coating would stay on the metal, but before it hardened in the cup - about 30 sec. I removed it.

[vtsteam]

Here's the coating:

[vtsteam]

I then heated it to cherry red again and plunged it into the water. Result: the metal was hardened and I was able to scratch strip C with it. I was quite pleased! Gosh, sugar works to harden ordinary hot rolled steel !!!

So, next to test the control, I heated strip A (with no sugar) to cherry red and plunged that into the cold water. Result: that, too was hardened and I was able to scratch strip C with it. Well, so much for the first conclusion!

Well, which was harder S, or A?

Scratching them against eachother, it seemed that A would scratch S slightly but not the reverse. Well this was too much, I wanted to make sure, so I sharpened both on a fine stone to give clearer results, and repeated the same case hardening method with each to hopefully increase case depth, and give a better indication.

The result: A definitely scratched S, while S only removed discoloration, but did not scratch into A. And not only that, but clamping C (the unheated control) in a vise and using A as a chisel, I was easily able to cut right into the unhardened control piece. You can see the notch made above A in this photo, and also the deep scratches it made on S. 



I also found it possible for a file to remove a small amount of metal from S, but not at all from A.

Conclusion, simply heating and plunging these particular steel pieces into cold water makes a harder tool than using sugar does. If I had done this experiment without a control, I might have assumed sugar was responsible for case hardening this steel.

In fact it appears it may inhibit hardening.

[vtsteam]

As a followup experiment to determine whether possibly a carbeurizing flame in the MAPP gas torch somehow case hardened piece A, or whether the material was itself hardenable, I ground the cutting edge back on the grinder and repeated the scratch experiment on C and S. No change. So my conclusion is that this steel is hardened all the way through, and therefore a hardenable material.

It is interesting that the sugar treatment seems to have reduced the degree of hardness.

[Bluechip]

[1] Please note I know nothing about the subject.

[2] If you had some carbonising material ie. sugar and applied a flame I see no reason for the carbon to go into the steel.  I would assume it would be CO₂. in fairly short order.

Dave

[vtsteam]

And as one more experiment today, I stripped the zinc coating off of a piece of 3/8" dia threaded rod, in hopes that it wasn't a hardenable material. I heated it to cherry red, plunged it and it would not scratch either A or S. Both those samples would cut into it. So not hard.

It did seem slightly harder than C, but not by much -- light scratches. The untreated end would not scratch C at all. So, let's call it very slightly hardenable.

I did the sugar procedure on it, and it reverted to the full soft state, not even scratching C. So again, using this sugar case hardening procedure is counterproductive.

[vtsteam]

Might be true Dave. What is unexpected is that it actually seems to pull carbon out of the surface.

[awemawson]

Well the POWS got through the wire - read Paul Brickhills book !

[vtsteam]

Andrew I didn't conjecture about different procedures and materials used by other people. That's the point. Small alterations in details sometimes can make big differences in results. I pointed out the importance of individual method to start with, and still encourage others to try with sugar, including you if you want. A test only takes a few minurtes to do.

Also I'm sure my own sample S will cut wire if made into a tool. It just wasn't the sugar that caused it to harden. And a better cutter could be made of A. I'd guess Mr. Brickhill loses no credence as a result. But I won't be using this particular method with sugar to case harden anything.

I have thought of giving sugar one more try at least, this time in a tool wrap to exclude oxygen. If that fails then I give up on it.

[vtsteam]

One other thing I just thought of re. The Great Escape. When you plunge the hot steel into the sugar you get a great volume of very strong smelling white smoke, very identifiably sugar -- like burning marshmallows, and flames. Then reheating it to red heat burns off all the remaining carbon producing even more fumes.

If I were trying to escape notice in using sugar, I'd use a sealed container method, not an open one. I doubt they'd have considered using an open method at all, under those circumstances. I haven't read the book, so I can't say what was reported there, though.

[SwarfnStuff]

For what it's worth,
     I recalled reading somewhere that case hardening could be done in old sump oil. Easy to get some from my mechanic friend then recalling that it was supposed to be the carbon in the oil I ground some charcoal in a pestle & mortar, tossed it into the oil and left it for a few days. I had made a pair of mini bottle jacks from some scrap steel and thought they were good candidates. So, heated them to as red as my propane torch would get them and dropped them into the old oil. No hardening evident after trying the scratch test but hey! they had a nice black finish that looked good. (Now, this black finish bit I recall from blacksmithing class in junior tech school.)

 After reading the earlier posts perhaps I should have re-heated and quenched??

    Also tried sugar on some scrap but apart from the sweet smell nada. This thread will be interesting to follow. John B   

[SwarfnStuff]

Another thought VT, you were wondering about trying to combine charcoal making and hardening -  later in the post you also wondered if the charcoal may be too pure in carbon to exude the monoxide. My thinking would be to try the steel in with whatever wood you were going to carbonise in the not fully sealed container (just need to exclude air ingress but allow pressure to escape. End of safety reminder.  ) and there should be plenty of CO amongst the other fumes.

[Eugene]

Steve,

What your experiment demonstrated was the effect of "flame hardening" rather than case hardening. If you heat a bit of medium carbon steel to cherry red and quench it, it will produce a hardening effect, wether or no you have an external carbon source such as sugar. The process takes a couple of minutes.

"Case hardening" was traditionally applied to low carbon steels where an external carbon source was provided in the form of charcoal, the classical usage being in gun making. The advantage in using the mild steel was that it could be filed, drilled, ground, and engraved in the soft easily worked state, and then hardened to give wear resistance afterwards. The process takes hours rather than minutes, to allow for absorption of the carbon into the surface layer, quite a slow business. I'd guess all your sugar did was to make it more difficult to judge the colour changes, there wouldn't be enough time for a significant degree of absorption.

I've only done case hardening to produce the traditional colouring effect that is seen on gun actions, and I used the old style method of placing the parts together with charcoal into an iron box which went into a home made (and distinctly dodgy ) muffle. Getting the colours right is a bit of an art and is typically surrounded by a "bodyguard of lies", but the hardening effect is quite easy to obtain, it's depth depending on the soak time.

I think you'll be fine with home made wood charcoal if it's reasonably graded in size; small enough to contact the parts but big enough to allow the oxygen from the air to be present in good quantities. The oxygen isn't used up as the process continues, it merely has to be present to begin with.

I have some printed work on this iron box method; if you like I could scan it and send it to you. Let me know. Brownells in the US supply materials for the colour case process and may well have some info online; worth a shot.

In the far off days when I was alive, we used to copper plate steel parts in selective areas prior to them being hardened. The coating acted as a barrier to the carbon and left those areas soft. Only The Gubbernmint could afford it!

Eug

[vtsteam]

What your experiment demonstrated was the effect of "flame hardening" rather than case hardening. If you heat a bit of medium carbon steel to cherry red and quench it, it will produce a hardening effect, wether or no you have an external carbon source such as sugar. The process takes a couple of minutes.

Eugene, I would say that the experiment so far demonstrated conventional hardening on the first sample steel, since it contained enough carbon throughout to harden, using a conventional method. And no "flame" or case hardening of the second.

JohnB, exactly what I was intending to try. I've made charcoal through a number of different methods over the years. There are plenty of variables to play with.

Please anybody jump in here with your own experiments -- using whatever appeals to you. We have only my photographed experimental results so far. Somebody with an acet torch could do the soot and heat method,, oil method, etc. As I've said before, method is as important as ingredients -- small differences can produce different results for different people. That's the point of documenting what you try.

[vtsteam]

Continuing with the last experiment with sugar, I cut a piece of .002" stainless steel tool wrap and sharpened the non-hardenable steel threaded rod: