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Case Hardening

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PeterB09/10/2009 15:48:23
14 forum posts

I'm soon going to be doing some case-hardening of mild steel IC engine components.  Before I go out and buy a large tin of Kasenite, or similar, it occurs to me that I have a large supply of fine coal-dust.  Could I use that instead or would it cause unforeseen problems? 
 
Regards, Peter B. 
Michael Cox 109/10/2009 16:27:59
555 forum posts
27 photos
Hi Peter,
The use of coaldust is not recommended. It has a high sulphur content that will adversely affect the case hardening. Fine powdered charcoal will work ok especially if mixed with sodium bicarbonate (baking soda). A 90% charcoal dust with 10 % sodium bicarbonate works well for pack carbonising.
Regards
Mike
PeterB09/10/2009 20:14:15
14 forum posts
Mike,
 
Thanks a lot for the prompt and valuable advice which I shall follow to the letter...
 
Peter
Michael Malleson23/10/2009 10:39:54
62 forum posts
2 photos
Hi Peter B. Any organic carbon-rich material will do so long as you areconfident it is free of things like sulphur (see Mike Cox above) . The old blacksmiths used to use things like hoof-parings, chicken s--t, and shredded leather. Best done outside !! Best of luck, Mike.
JohnF24/10/2009 15:53:39
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1243 forum posts
202 photos
Hi Peter,
 
Although you can use the materials suggested i.e. any carbon rich material--chrcoal made from leather, wood, bone etc you need activators added to get good results[bicarbonate of soda is one] As already pointed out coal dust is a no no!
 
I harden quite a lot of small components and would highly recomend Kasnit or similar to get good consistant results.
 
I f you want a thick case and are soaking the components for several hours then be aware of grain growth in the core--you need to do a multi heat treatment to relieve this then finally harden the component.
Regards John.
ColH25/10/2009 00:15:57
28 forum posts
Hi Stephen
 
Can you please run through the multi heat treatment process?
 
thanks  ColH
JohnF01/11/2009 11:36:07
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1243 forum posts
202 photos
Hi Peter,
 
A quick run down on the process is a s follows: -
 
1. Pack all your components in suitable a container with at leat 1/2" of charcoal between them
2. Heat to 900deg C and hold at this temp for the requiered time--pentration is .005" per hour so you need 4 hours for a .020" case.  Is it duering this time the grain growth occurs in the core due to being at an elevated temp for a long period
3. To resolve this--allow to cool--still in the box
4. reheat to the upper critical temp for the core, 830deg C--assuming the core is .02%C and quench in oil--you will now have a tough refined core and a hard but coarse grain case
5. Now heat again to the upper critical temp for the case--720deg C [case will be .09%C] and quench--this will give you a very hard and fine grain case.
6. Temper to your required hardness or just stress releive at say 150degC then finish by grinding polishing etc.
 
This is a quick run down on the prefered process but if you don't need a thick case to allow for finishing you can cut corners and not fefine the case--grain growth will be less or minimal if you are producing only a .005" case for instance. There is a lot more to the tech side [some a bit misty now] but this works well.
 
If my memory is good we used a set of books called Chapmans Workshop Practice some 40+ years ago at Tech School which had a lot of info regarding the above and Im sure there are more books available.
 
Good luck!      Regards John.
PS if you want to speak to me please snd me your phone number
 

Edited By Stephen John Fawcett on 01/11/2009 11:36:25

Ian S C01/11/2009 12:17:18
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7468 forum posts
230 photos
Workshop Technology part one W.A.J.Chapman p43 about a page on case-hardening.A few little differences,your (4)900degC (5)770degC (6)Temper at 200degC or more depending on required hardness.There is a paragraph on superficial hardening using cyanide salts etc,When I was at school in the early 60s we had salt bath facilities,but we wern't allowed to do any hardening ourselves even then(we broke most of todays OSH regs every time we went into the workshop),I'v got Chapman 1&3,if I can i'm looking for 2.IAN S C
mgj01/11/2009 12:21:23
1017 forum posts
14 photos
Forgive me, but I thought certain steels were not heat treatable so the ability or requirement to refine the core would depend on what the item was made of in the first place.
 
The 40 carbons, to use the old terminology, sure, but if its a low carbon mild, and especially a freecutting mild, one can certainly case harden, but refining the core might prove a tad more difficult? 
 
My metallurgy in that field was always a bit limited, but I think that is right?

Edited By meyrick griffith-jones on 01/11/2009 12:24:42

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