Case Hardening – can’t even harden a washer !

[C WParticipant @cw29454]

Hi all,

 

I have a gear I bought from HPC I would like to harden, and some hardening powder obtained from eBay here: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=330577934005

Before I attempted hardening my gear I thought I would test the whole process on something less important. First thing to hand was a washer, not zinc plated just plain old mild steel, tested and cleaned with a file, confirmed soft. (Also tried on a mild steel bracket I had laying about, same result)

So I heated it up with a MAPP gas torch, started with heating till it was red, (have subsequently tried up to orange in colour), dunked it in the compound, let cool, heated again, quenched, repeated three times, still as soft as a mars bar.

Everywhere I read suggest the process is dead easy, finish can’t be touched by a file, temperatures aren’t that critical, it’s even in black and white in the “Hardening, Tempering & Heat Treatment” book by Tubal Cain.

What am I doing wrong, are mild steel washers un-hardenable ?

Edited By C W on 28/06/2011 01:07:20

Edited By C W on 28/06/2011 01:10:37

[C WParticipant @cw29454]

[adyParticipant @ady]

You may be annealing it, most of these things talk about a yellow “straw” colour when I read about it.

Cherry was when you wanted to soften a hard metal for reshaping.

 

The temperatures appeared to be quite critical, going too high softens(anneals) metal.

150 degrees more than what you need and you can ruin a job kinda thing.

 

I’ve never done this myself btw, memory/booktheory only.

 

I recall someone making a motorbike part which was always wearing out.

So they heated it and and plunged it and it never needed replacing again so when you get it right you’ve got a very handy asset there but a fair amount of messing and experimenting about will probbly be needed.

 

case hardening

 

Edited By ady on 28/06/2011 07:55:39

[Roderick JenkinsParticipant @roderickjenkins93242]

C W,

 

Are you sure the washer isn’t plated or passivated, this could act as a barrier to carbon diffusion? My method is to heat the the piece up to red and then to dunk it in the hardening compound. The powder sticks to the hot piece in a thick cake. Then heat up the piece to bright red (cherry is the usual description but cooked carrots is a better description IMHO). The carbon from the compound then diffuses into the surface of the steel – this takesa bit of time so give it a minute or two at this temperature. Now dunk into cold water. Only the surface will be hard, to the depth that the carbon has diffused. A file should glide off but the washer will still bend because the core is soft.

 

ady,

 

The straw colour describes the appearance of the metal when it is at the correct temperature for tempering. You shouldn’t need to do this for case hardening, which is the major advantage of this method: the piece remains tough but the surface is dead hard and therefore wear resistant.

 

It is a straightforward process. I would try it on small piece of steel rod with a turned surface.

 

Rod

 

[mickParticipant @mick65121]

I haven’t tried any of the new range of case hardening powders, but using the old type of powdered bone we burnt the carbon into the steel after every emersion in the powder, then after three visits to the powder, quench, letting the part cool after dipping, in my view won’t achieve anything.

 

[C WParticipant @cw29454]

The instructions received with the compound seem to differ from what you guys are saying. There is no mention of prolonged heating of the object after dipping it in the compound. The only reheating mentioned is before you quench it. Also the compound doesn’t stick to the object, certianly doesn’t form a “thick cake”. If I could get it to stick heating after dipping makes more sense, after all a washer doesn’t stay hot for long when just left in the compound.

 

The washer didn’t look plated or passivated, was rusty when I picked it out of the box. Also I used the a file to clean it up before starting. I will obtain some different steel today and give it another try.

 

Do you guys just eyeball the temperature or it there a more accurate method I should know about ?

Edited By C W on 28/06/2011 09:49:22

[VersabossParticipant @versaboss]

Ady, I’m sorry to say your ‘answer’ does not give much help to our friend C W.

Tempering colors have nothing to do with case hardening.

C w, from your description it seems you did not heat the washers with the hardening powder sticking to it.. Heck, a bad sentence I know. So another try:

– Heat the washer to red (or yellow, or cherry, or whatever you call that color)

– dunk it tn the powder

– heat again; let the molten powder flow around the part

– repeat if necessary

– drop the still red hot part in cold water

– test with the old file

if it still is soft, then something’s wrong with your powder or your washer is stainless steel

Greetings, Hansrudolf

[VersabossParticipant @versaboss]

C W, just saw your answer which arrived when I was typing. Seems you really have a strange type of hardening powder. Maybe this works only with a larger lump of steel; your washer stays not hot more than a few seconds I suppose (ok you wrote that too…).

I think I cannot help much in that case (nice pun, however…)

Greetings, Hansrudolf

[Chris CourtneyParticipant @chriscourtney72250]

Case hardening powder consists of a source or carbon plus an activator. There are lots of different “recipes”, but I seem to remember Barium Carbonate being used at one stage. The principle is that if the low carbon steel component is covered in the powder and held at an elevated temperature then carbon will gradually diffuse into the surface layer of the steel. This diffusion is a very slow process. The higher the temperature, the faster the diffusion takes place. Industrially it used to be done by packing the components in a box with the case hardening powder and heating for many hours. Once sufficient carbon had been absorbed, the components would then be quenched to develop the hardness in the surface layer. (There are other industrial case hardening methods, such as liquid and gas carburizing).

 

Case hardening with a gas torch works surprisingly well, but the case layer is very thin. Roderick Jenkin’s advice is quite correct. Heat the component and dunk into the powder to cover it, then heat to the “cooked carrot” colour (I like the description, it describes it perfectly!). A few minutes should give you a few microns of case depth. Re-dip into the powder and continue heating if the surface starts to become uncovered. Don’t repeatedly heat and quench, it won’t achieve anything. To harden the component, quench into cold water from the carrot colour at the end of the process.

 

If it isn’t hard enough, just repeat the process for longer. I’ve found case hardening like this is effective and easily done, but you do have to give time for the carbon to diffuse into the steel.

 

Chris

 

[Ramon WilsonParticipant @ramonwilson3]

Hi CW,

 

My experience with case hardening as opposed to through hardening is somewhat limited – mainly to carrying it out at home but on occasion at work. The method you are using is okay in principle but I feel you need to refine a little.

 

Firstly though continue as you are by doing test pieces until you are really satisfied -gears are expensive

 

The mild steel washer should have hardened. You do need to get the part hot enough to absorb the compound – if as you say it cools rapidly this is not likely to happen. A better way on small objects is to place it with some compound in a small container that can be heated to the required temperature – a good bright red breaking into orange heat – don’t be confused by the ‘yellow’ given off by compound. Give this a good ‘soak’ at this heat then allow to cool. You do need adequate heat for this.

Break off all the residue and reheat the part to an even bright red heat then plunge rapidly into clean cold water. If you have done it correctly you will hear a sharp crack as the part hardens.

You can go straight from the heating stage into the water but the key to success is definitely plunging it quickly into clean cold water. Unlike through hardening it is not usual to temper so you do not have to worry about various colours and temperatures.

If you decide to heat the compound as above make sure you have plenty of ventilation it does make for a smelly and fume ridden workshop

 

The surface finish will have a greyish mottled appearance – well at least it did with original Kasenit.

 

Hope this is of help, keep us informed how you get on

 

Regards – Ramon

[Michael Cox 1Participant @michaelcox1]

Hi CW,

 

Like you I have a container of case hardening compound that does not stick to the surface when you dunk the hot piece into it.

 

I believe there are two types of case hardening compounds on the market. One type, Kasenite and its clones, is based on alkali metal ferrocyanides. These melt and stick to the surface of the hot metal and carbon from the ferrocyanide diffuses into the hot surface. Once the powder has stuck to the surface it can be further heated with a torch to maintain a high temperature.

 

The other type, that you and I have, is simply powdered charcoal with perhaps an acivator (barium carbonate?). Like you I have had little success using this product to case harden small parts by the heat, dunk in powder. repeat a few times and then finally quench. Partly I think this is because with small parts like washers there is so little retained heat in the component when you dip it in the powder and it cools rapidly in contact with the powder. There is thus little time for the carbon to diffuse into the surface whilst the component is hot. Maybe it would work better for large components where there is much more retained heat and they would not cool so quickly. All the components that I have tried to case harden have been small so I don’t know whether this is true.

 

I have used the compound by sealing the components and powder in a copper tube with pinched of ends and then heating in a furnace to bright red heat. This works well and the components after quenching are very hard. Having said that I can get the same result using just powdered wood charcoal mixed with a little sodium bicarbonate (ratio about 20 parts charcoal to 1 part sodium bicarbonate) as activater, by this process. These ingredients cost very little.

 

Kasenite seems to be in very short supply and none of the usual model engineeering supplies stockists (eg Chronos, RDG etc.) list the product. Maybe it is available from specialist suppliers like gunsmiths. This may be because it is thought to be poisonous. Whilst cyanides are very toxic ferrocyanides are relatively benign. Potassium ferrocyanide is frequently add at a low level (circa 1%) to table salt as an anticaking agent.

 

I hope this information helps

 

Mike

[chris stephensParticipant @chrisstephens63393]

Hi Guys,

Good old LBSC used to give, more or less, the following instructions for case hardening, heat the part to carrot colour, dunk in powder then re-heat in flame till the flame colour from the powder has burnt away, repeat if thought necessary and then quench.

With small parts, like a washer, quenching must be done very quickly, it must still be carrot colour as it enters the water, any cooler and you are more likely to anneal instead of harden.

chriStephens

[Clive HartlandParticipant @clivehartland94829]

I think Micheal has it by soak heating in a container. I would use a piece of steel tube and put it on a lager piece of steel and fill the tube with hardener and then put in the washer or component.

Heat the tube and soak heat it for five or ten minutes and then tip straight into water.

In any case I would do the gear in the same way by immersion in the hardening compound and do a soak heat as stated above.

Clive

[C WParticipant @cw29454]

Wow, you guys have really been a help.

 

It’s starting to look like I am going to have to seal it up and drop it in somewhere hot for a while. This is a bit of a problem as I have an blow lamp, even and oxy set but no furnace. More questions now, sorry:

 

Will the little clay chiminea I have in the back yard do the job or won’t it get anywhere near the right temperature ?

 

Also how long ? I am guessing the longer the deeper the hard layer. Is ten minutes as suggested by Clive a minimum ?

 

Does anyone have a source for the sticky hardening compound ?

 

And finally, how many time can I re-use this stuff ? Obviously I don’t want to test it to death.

 

Out of interest I contacted the eBay seller and he said “I bought the powder originally from Chronos. It referred to the powder orginaly as ethernite.”

 

Cam.

 

P.S. The washer I tested it on was an M10 mud guard washer, so it held it’s heat for a little while but only in the order of seconds. And quenching was done with it still carrot red hot.

Edited By C W on 28/06/2011 18:28:01

[Roderick JenkinsParticipant @roderickjenkins93242]

CW,

 

I’d have a go at laying the washer on a thin bed (1mm) of hardening powder and then put a similar layer on top. Get it carroty hot for a couple of minutes and then pick it up and quench it. If necessary you can re-heat after you take it out of its powder bed, the carbon should already have diffused into the steel surface.

 

How disappointing that we can’t seem to get the good stuff anymore. Fortunately (for me!) I have a little stash of Kasenit that should see me out.

 

Good luck

 

Rod

[Sub MandrelParticipant @submandrel]

A technique I have seen described is to use a tin box, packed with charcoal (ideally bone charcoal as this contains more nitrogen and has a nitriding effect as well as carburising). Pack item(s) in tin with charcoal, seal it, and place in a hot fire for a few hours. Break out, heat to carrot and quench. Apparently this gives a good deep case, but few of us have open fires (and even those of us with one don’t have it roaring away this week!)

 

Neil

[Ramon WilsonParticipant @ramonwilson3]

CW, Hi,

 

As long as the ‘container’ has sufficient compound to cover the part it does not have to be ‘sealed’. Depending on how tight the ends are folding over the ends of pipe may, may prove a bit ‘explosive’

 

I’m not sure about a chimea but a charcoal barbie fire would do providing the whole container was at a uniform heat.

 

I was first shown this by a well revered ME who would do all his small cutting tools in a small steel ‘box’ pushed in his fire. He was one of the old school you could say – long gone but fondly remembered

 

Providing your ‘blowlamp’ has sufficient power to heat the whole object a good bright red heat for a few minutes that should more than suffice. I would think an oxy flame might prove a bit localised .

 

As has been mentioned several times rapid quenching is essential.

 

I have only used Kasenit and heated in this fashion not much is reuseable – where the part is heated then rolled in the powder – reheated and rolled again etc the residue can be used again.

 

No one has mentioned the ‘crack’ as it quenches – something ‘Lenny’ was at pains to stress – I merely pass it on

 

Keep doing the test pieces – you’ll get there in the end.

 

Regards – Ramon

[C WParticipant @cw29454]

Just tried washer No2 in a little container with enough powder to coat it, and blow torched it for 5 minutes or so. Result was no different unfortunately Suspect I didn’t get it/keep it hot enough. Off tomorrow to buy some BBQ Charcoal I think, will report back.

[Clive HartlandParticipant @clivehartland94829]

I have used shoe leather chopped up in little pieces and this hardened a cylinder pawl for a pistol beautifully with a nice colour and the file bounced off it!

I have now locked up my tin of Kasenit just in case a person fancies it!

 

Clive

[Roderick JenkinsParticipant @roderickjenkins93242]

So, Clive’s leather worked OK and they used to use powdered horn. Start saving your toenails chaps

[AndyPParticipant @andyp13730]

I have a tin of case hardening powder bought from Blackgates at a show in the last 3 or so years, it behaves like the “sticky” variety described here and everything I have done with it has been hard – no connection etc.

Andy

[C WParticipant @cw29454]

Don’t suppose you remember where it came from Andy P ?

[AndyPParticipant @andyp13730]

CW

Blackgates

Andy

[C WParticipant @cw29454]

Phoned Blackgates and a very nice lady went and checked the case hardening compound, and she confirmed it is the type that sticks, duly ordered ! 11GBP plus VAT plus P+P for 400g. Thanks AndyP.

 

Meanwhile after buying some of the worse BBQ briquettes I have even seen from Pound Stretchers (you know the saying “There’s no smoke without fire” will if it comes from Pound Stretchers there is a very strong chance there will be and lots of it), I am back on track. Got 8 bricks, a little steel mesh and an 80mm computer fan keeping my washer just toasty. Going to try for an hour and see.

 

Cam.

Edited By C W on 29/06/2011 16:10:03

[C WParticipant @cw29454]

In progress

 

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