Case Hardening

[Anthony KnightsParticipant @anthonyknights16741]

Quote from my dad’s book “THE HANDYMAN AND HOME MECHANIC” (reprinted 1948)

“…..it is necessary to heat the metal in contact with the carbon to a very high temperature. This can easily be done by enclosing the material to be treated in a piece of gas barrel charged with bone dust, scraps of leather etc”

 

Question:- I have a solid fuel Central Heating boiler which can get to a bright red heat. If I made a suitable container from steel tubing, with end caps and packed the object to be hardened inside with either charcoal or anthracite dust, would this work?

[Anthony KnightsParticipant @anthonyknights16741]

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Anthony, you could try it on a piece of scrap and see, however I would sugest you have at least one cap vented to stop any gases inside bulding up pressure and blowing  your boiler apart. You will probabley be better off getting some proper case hardening compond

 

Regards Nick.

 

P.S. don’t tell your insurance company I siad it was Ok if it goes pear shaped.

Edited By Nicholas Farr on 09/01/2011 01:47:13

[Stewart HartParticipant @stewarthart90345]

That would work we use to case harden in vessels sealed with clay, packed with charcoal something rich in carbon,

 

But it’s a lot easier to use one of the case hardening powders available I think Chronos stock it for one. Just heat the job up to cherry red bury it in the powder, let it cool, then burn the powder that stick to it off taking the job up to cherry red bury it in the powder repeat burn off, job done.

 

Stew 

[MikeParticipant @mike89748]

I think those scraps of leather mentioned in Anthony’s post are to produce a purely cosmetic effect. It is how gunmakers produced that random pattern of blues and browns, known in the trade as “colour hardening”, found on some shotgun actions. The use of bone charcoal is supposed to produce a particularly attractive shade of dark blue, and was said to be the secret of the blue on Colt firearms.

[colin hawesParticipant @colinhawes85982]

Hi Anthony, the method you use largely determines the depth of case.  I have successfully done a case deep enough for heavily loaded ball bearing races, about 2″ diameter that had to be ground ,using a tobacco tin & lid with the job packed in charcoal (ex bonfire) and a piece of an old leather belt .It was the second attempt because I had not properly sealed the lid with clay (from the garden) the first time.I cant remember how long it was kept at red heat but I think it should be an hour for every 10 thou of case depth required. 

[Sam StonesParticipant @samstones42903]

Anthony,

 

Not knowing the size of the mild steel (MS) part which you intend to case harden, it’s difficult to ascertain what would be most appropriate.

 

That said, I feel sure that Stewart would have gone on to mention that you need to quench the part in clean water or oil after final `soaking’ of the MS part in the case-hardening compound.

 

I’ve had plenty of good results using case-hardening compound. Was it called Kasenit? There was none of the mess associated with burning leather etc. Then again, the parts I made were relatively small

 

After `soaking’, the newly formed high carbon `skin’ needs to be hardened and tempered just like normal high carbon steel, eg. silver steel and gauge plate.

 

I found that it was unnecessary to remove the powdery coating of compound. This would fall away during the initial quench from cherry red, leaving a pleasing (to me at least) mid gray colour.

 

Just to add to this, the procedure being used when I began my toolmaking apprenticeship in 1950, involved carefully lowering the clean AND VERY DRY mild steel parts into a bath of molten cyanide, set at around 950 degrees C.

 

Failure to dry the parts properly could result in a violent reaction from the cyanide bath.

 

I’m not sure if the cyanide needed charging with extra carbon, since we had one chap who did all of the hardening himself.

 

However, I don’t recommend this latter process for the home enthusiast for very obvious reasons.

 

Good luck.

 

Sam  

[KWILParticipant @kwil]

Cyanide hardening produced a very nice blue/grey patterning which is still visible on parts thus treated 56 years ago!

[Aestus57Participant @aestus5782081]

Just as an aside, this little story may be of interest….

 

I know nothing about Cyanide hardening but my Dad who was a very accomplished engineer did. When he passed away some 40 odd years ago, I found a bottle of cyanide crystals in the workshop and as a lad of only 14 years I had no idea of what to do with them. My mother was very worried about having them in the workshop so despatched me to the local Police station with them for advice. The look on the desk sergeants face when I placed the bottle on the counter was something to be seen!! He took one look at the label and jumped back at least 6ft. I was then questioned very thoroughly about how I came to have them and what they were used for. Luckily they disposed of them and we heard nothing more about them.!!

 

 

[Speedy Builder5Participant @speedybuilder5]

I have just read the rear cover of Model Engineer (Thursday Dec 19 1946.. 6pence) – those were the days. 

There is an advert for FLUXITE soldering past which says it can be used for case hardening and tempering steel.  I wonder how that worked,  and would it work with todays composition ?

[Anthony KnightsParticipant @anthonyknights16741]

I had intended making the end caps (or plugs) on the end of the container a fairly tight push fit in order to prevent unwanted explosions, but the suggestion about sealing with clay seems a better idea. There is loads of it in my garden.

Cyanide, being a compound of Nitrogen and and Carbon would supply the neccesary carbon for hardening, but personally, it’s not something I would like to try, even assuming one could obtain supplies of it without being raided by the anti-terrorist squad.

My original query was prompted by reading the book which used to belong to my Dad (part of which I quoted ) and also by the fact that I have ready made furnace (AKA central heating boiler) and that the coalman usually manages to deliver at least half a bag of anthracite dust with every load of smokeless fuel. I have to admit I am trying to save money.

Before retiring , I managed to buy a small lathe and mill/drill machine and set up a basic workshop. I also took government advice and “Saved for My Old Age”. What they didn’t tell me was that as soon as I started to draw on this money along comes HMRC wanting their 20%. I am now hard pressed to afford basic materials, let alone luxuries like “Kasenit” or brazing rods.
.

 

 

 

 

[mariano diazParticipant @marianodiaz48581]

 

   on my book Cyanide pellets , are the best for low production case hardening, that is what

  we were using when we where apprentices, latter on commercial powders like Hardite,

or Kasenite , come about , but there is nothing wrong with using Cyanide, If you take the right precautions

 

[TerrydParticipant @terryd72465]

Hi all,

 

sorry to go OT but I thought this might amuse:

 

Many years ago, while between jobs I taught as an ‘unqualified instructor’ of Metalwork in a rag-tag, back street, boys secondary modern school (that dates me) in an industrial area of the West Midlands.  The lads were poor, tough and unruly but were generally good hearted rascals.

 

One day the Head decided to investigate some large crates that had stood in the cloakroom for many years, certainly from before his time.  He discovered two brand new potters wheels, a kiln to match, which the art teacher was overjoyed with as it was not the best resourced school in the area.  In the final package he found a large cardboard  box labelled ‘case hardening powder’.  On opening he found a container with the inscription ‘Cyanide – poison’.  Fortunately the many generations of schoolboys had not been too inquisitive.  I hate to think what might have happened to the population of Dudley had they been otherwise!  I politely declined his offer to use the crystals in the metal workshop.

 

Terry

[Gordon WParticipant @gordonw]

Years ago a factory I worked for used molten Cyanide for hardening small parts, very effective. Spent cyanide was tipped down a hole in the yard, to save money. One day the molten bath blew up, water on the parts, un-trained operator. The works manager rushed out, handed out large round pills, antidote for cyanide poisoning he said. Found out later they were polo mints.

[Ian S CParticipant @iansc]

At Tech in Dunedin (NZ) back in the early 60s, we had a large, industrial size Cyanide bath in the workshop, us kids were kept well away, but could observe the prosess through the large windows. it must have penitrated far enough, it left the tap wrench I had made in a brittle state, and when it was tried it broke, enough to make one say bother. Ian S C

[JohnFParticipant @johnf59703]

Hi Anthony, have a look at this link to a post I sent some time ago regarding case hardening–might be of interest.

Regarding cyanide–unless you have the corret equipment and expert knowlege keep away from it. We usedthis method in industry but you have special furnaces with fume venting and protective equipment–OK if you use properly but definatly not for DIY home use!!!

Coal dust is no good–use charcoal of some description and preferably with “accelerators” added to make the material disolve the carbon better. Penetration is about .005″ per hour

Regars John

http://www.model-engineer.co.uk/forums/postings.asp?th=32838

[WALLACEParticipant @wallace]

Is there much distortion ? sometime, I’d like to make up a dickson style tool holder to fit a universal head on a cutter grinder.

Mild steel would probably be more than adequate – but it would be nice to make something that is as tough as the commercial items !

W.

[Sam StonesParticipant @samstones42903]

I fully support John Fawcett’s comments about cyanide heat treatment. It can be full of hazzards for both professionals and amateurs, as the following example shows.

The `hardening shop’ I hinted at in my earlier posting on this subject, was a small room next door to our toolroom. It was accessed through a personal door in one corner of the toolroom. As a young apprentice, I could never comprehend that next door to the hardening shop was a fairly large work area know as the drug-store. It must have been the most significant fire risk area of the whole factory, since it was stocked with open bins of finely powdered coal, sulphur, and various other industrial chemicals. These chemicals were openly weighed into bins, which in turn were elevated along conveyors. There were bails of natural rubber too, ready to be cut up and fed to two-roll mills and large Banbury mixers.

Back in the hardening shop were a couple of gas-heated cyanide baths measuring some 18″ deep by about 9″ diameter. There was also a small electric furnace for hardening HSS. I think it was normally heated to about 1250-1300C. For quenching, there was a bath of hot water, and standing on the floor was a rather large tank of oil which measured about 4′ high and 4′ diameter. Allowing for the volume of any items to be quenched, the oil tank was kept topped up to within an inch or so of the rim.

It became necessary to harden several cylindrical mould inserts. At a guess, these steel inserts measured about 14″ long and 6″ diameter. The actual mould cavity was by way of a hole down the centre of the inserts. This through-hole measured perhaps 1.7″ diameter. In order to lower these inserts into the cyanide bath, the wise ones in charge made up a hook and had it bolted to the platform of one of those hand pumped stacker-trucks. The idea being that the mould inserts could be lifted from the cyanide bath and then lowered into the oil.

Unfortunately, when it came time to quench the first heated insert, the stacker truck could not be pumped up high enough to lift the insert over the edge of the oil tank. It was therefore necessary to rapidly transfer the red-hot insert from the hook of the stacker truck to a steel wire hoist above the oil tank, the hoist in turn being secured to the steel roof truss. The hoist consisted of two pulleys around which were several turns of twisted wire. The transfer went well, and the insert was lifted up and over the edge of the bath of oil.

Then the real drama began. The hoist hadn’t been used for many years, and as the insert was being lowered into the oil bath, the hoist wire spun around and jammed. This was a perfect situation for a massive fire because, with the red-hot insert half in and half out of the oil, ignition was almost instantaneous. Burning oil began to pour over the sides of the tank, and there was panic. Somehow, they managed to free the hoist and totally submerge the insert, but flames began to leap towards the roof, as sand and all sorts of other stuff was used to try to quell the blaze. Finally, the fire was brought under control. The drug-store didn’t ignite, and the excitement ended with a toolroom full of smoke and several red faces.

I think the remaining inserts were sent away to be hardened, and why Kasenit is my preference for case-hardening.

 

Regards,

 

Sam

Edited By Sam Stones on 21/01/2011 06:00:01

[KWILParticipant @kwil]

UK source of genuine Kasenit?

Edited By KWIL on 21/01/2011 10:49:41

[mgjParticipant @mgj]

I’m a little puzzled why one would want to temper a case hardened surface after quenching?

 

There doesn’t seem a lot of point in getting all that carbon in there, getting it all hot enough to make it austenitic and then quenching to martensite (which is darned hard), and then converting it back to something softer, especially when the load is being carried on a soft matrix to which carbon is not added, and brittleness is therefore not a problem.

 

[Sam StonesParticipant @samstones42903]

To temper or not to temper case-hardened mild steel, is a very interesting question mgj.

Surely it will not only depend upon the shape and thickness distribution of the part, but also upon its purpose? A solid lump of MS will no doubt be less likely to fail, than a part with varying thickness. I certainly wouldn’t venture into case-hardening a part whose reliability was important, without seriously considering the need for tempering.

Having replaced certain instrument parts which varied in thickness, and choosing to go via the case-hardened mild steel route, the question of final brittleness was always a consideration.

I tend to view the case (skin?) of a case-hardened (even nitrided) part as being a little like a pie crust, which will craze and even collapse under external stresses. So, for the sake of an extra bit of safety, would you chance it?

 

Regards,

 

Sam

[mgjParticipant @mgj]

Well yes and no.

 

Point 1 is of course that one wants a wear resistant outer skin, so it wants to be as hard as possible. It is not there to carry a load – thesubstrate does that.

 

Metallurgucally as we know, its not (generally) possible to have something very hard, and not have it brittle.

 

So that means one has to introduce carbon into the outer layers (there are several ways), of a relatively low carbon substrate, (which in general terms will not respond to heat treatment) because basically high carbon = brittle. And then you quench which locks the outer layer in a hard state, and ones choice of substrate (often mild) provides the unbrittle load bearing material, which will take shock loads etc, and should be very resistant to the intrusion of cracks (even more so if the guy who machined it used a nose radius on his tooling.)

 

So far so good – but what if one wants to toughen the base material – ie machine it while soft, case harden, and then regain mechanical properties by toughening. It can be done by controlled heating and grain imporvement, but it is NOT tempering, and its not done at the same temperatures, and the alloys used are chosen for their toughenabilty or heat treatability, and temperatures which will not interfere with the quenched case.

 

So I ask the question again – why temper the outer case, when the whole object is to get it as hard as possible. You have the iron carbide there, you quench to lock it in the marensitic form, to provide the wear resistant properties, why is why one has case hardened – so why disperse it?

 

 

Isn’t nitriding a toughening process? More than a case hardening process?

 

I also accept that there are specific instances involving highly specialised alloys, but in general terms, I think my point is correct.

 

 

 

 

 

 

Edited By mgj on 02/02/2011 02:09:12

[TendorParticipant @tendor]

 

Folk might like to look here

http://hazard.com/msds/f2/brq/brqbk.html

to see the ingredient of Kasenit. It is Potassium Ferrocyanide.

 

KASENIT CO INC -- KASENIT SURFACE HARDENING COMPOUND NO.1 AND -- 

=============  Composition/Information on Ingredients  =============

> >Ingred Name:POTASSIUM FERROCYANIDE (YELLOW PRUSSIATE OF SODA)

[Ian S CParticipant @iansc]

Quoting of the can of Kasnit No., 1 surface hardening compound for case hardening iron and steel. Kasenit compounds are highly refined, non poisonous, non inflammable, and non explosive. Ian S C

[Martin WParticipant @martinw]

Ian

 

That confirms what the data sheet says, in the link above, that there is effectively no hazard with this stuff. Just a recommendation to use in a well ventilated workshop. Extreme use might give a sore throat or runny eyes but that’s about all.

 

Cheers

 

Martin

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