Case Hardening

Hello, I have some parts made out of mild steel which I would like to surface harden just to avoid nicks and dents in them in general workshop handling and to attain some wear resistance.

I have done some reading on the subject but I would like some advice before I attempt anything.

I understand that I will have to heat the parts to a high temperature in a carbon rich material. I have read about Kasenit for carburizing material but I wouldn't know where to find that or something similar locally. I have some fine graphite powder (like talc) was wondering if it would make for a good case hardening material.

Chris

Chris,Make your own mixture by chopping up an old leather shoe and some charcoal. Place in a metal box and get it hot and soak for a while and then tip staright into some salty water. You will get some discoloration. but it will be surface hard. No doubt others will come in with ideas. Kasenit is good if you can find some.

Hi Clive thanks for the tip. By charcoal, would the bbq type do? And regarding heat, how hot should one go, does it need to be red?

Chris, Kasenit has long gone but there are some other alternative compounds available form some of our usual suppliers if you dig around.

However it depends on what you want to harden, how big, how many, how thick a case to do you want/need ? If you want to go ahead and without getting into too much detail you need a suitable heat source that can sustain the temperature at 750 deg C for a lengthy period - a small furnace is best. A container to pack the work in, an old tin will work but a thicker walled one is better, you need to be able to seal the top while its "cooking"

Yes BBQ charcoal will work but better if you can get bone charcoal or as Clive suggests some leather charcoal or mix of both. Carbon penetration is generally assumed to be 3-5 thou per hour depending on the compound and temperature.

If your items are small and you go for the kasenit type compound you can use a large gas torch and a makeshift hearth, the case is thin but will offer a fair degree of wear resistance and protection from dings.

Hope this helps a little

John

For the kasenit process holding it at red hart for several minutes will do the job, the longer the better but 2 or 3 mins will usually suffice 

Edited By JohnF on 04/12/2019 20:15:59

Chris I think Blackgates sell a case hardening compound

Roy

Early American firearms such as the Sharps rifles have mottled colour patterns due to their being case hardened using bonemeal....the parts were packed in the bonemeal, leaving no air spaces, inside iron tubes and brought to red heat.

I've just bought some Beta Case Hardening compound from EKP supplies on eBay. Has anyone used this?

https://www.ebay.co.uk/itm/Case-Hardening-Powder-250g-Model-engineering-metal-working-Quality-UK-Product/332822906445?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

I've not used it yet, and like you, I've not done this before. I have purchased a MAP gas torch and bottle to use...and still need to get some refractory bricks. Well, that's my plan anyway.

Ian

Blackgates, EKP and a number of others sell case hardening compounds. They are probably all a mixture of ground charcoal, sodium ferrocyanide and barium carbonate. Which is pretty much what Kasenit was. Quicker than pack carburizing and they produce a good case.

Case hardening is a time sensitive process. The longer you hold the part at temperature during case hardening the deeper the case will be. The compounds like Kasenit or Cherry Red will give a very shallow case due the short time the metal is exposed to the compound.

I have very good results with that same stuff from ebay.

I really wouldn't bother making my own!

Jim

This is why you repeat the process several times to get a deeper case if needed, each time it takes in more carbon.

Not sure if case hardening will offer much protection against dings and dents but will stop the item being scratched so easily.

Thanks for all the replies, much appreciated. First thing I'm going to need is to get a proper gas torch and some fire bricks, think those will help concentrate the heat better as the parts are quite thick at 2 inches.

Good morning all,

Not sure case hardening is really about absorbing carbon into the surface layer of the parent at all. My understanding is that it is actually a nitriding process, which is why you don't need to quench the treated part to get a hard finish layer. Or do you need the carbon to capture the nitrogen into solution?

So bone meal has nitrogen in it, as does anything cyanide flavoured, but simple barbecue charcoal isn't (I think) going to do the whole chemical/metallurgical/structural alteration.

Any metallurgists?

Best rgds to all

Simon

Wikipedia has a reasonable description of the case-hardening process and mentions in passing the similar processes of nitriding and boriding amongst other similar surface treatments for low carbon steels.

John

I've always quenched after case hardening, does not do anything if you don't as it is just a higher carbon steel layer on the outside so needs to be hardened by heating and quenching just like any other high carbon steel. The instructions I have for my Beta powder also say to quench.

I was always told to heat, then place in powder, reheat and finally quench. No need to temper as the soft core means the part is not brittle.

Edited By JasonB on 05/12/2019 12:09:36

My dad was a master weighing machine maker and repairer. Weighing machines have steel knife-edge bearings that rotate on either hardened steel or agate V-blocks. He mostly used agates.

He would use cast steel blanks and file them to the required sized knife-edge before hardening them. This was an apparently primitive process where he would hold the bearing with spring pliers, knife-edge down and horizontal, in the flame of a Bunsen burner, until it was red hot. He then dipped it in Kasenit, shovelled are little more onto the edge, and returned it to the flame to get it red hot again. This was repeated 2 or 3 times when he then plunged it into cold water and stirred it around until cold. When tested with a file it was always glass hard, and lasted many years in service.

I know nothing on this subject but what is the difference in the end product between case hardening using a carbon compound or quenching in oil which I believe is another method of hardening..?

Ron, quenching in oil (or brine or water) will only harden a metal if it has a high enough carbon content such as silver steel or gauge plate. If you did it with normal EN1A or EN3 then it would do nothing except make the part dirty.

Case hardening increases the carbon content of the metals surface which can then be hardened but it is only the surface so ideal for wear surfaces and as the core will retain the properties of the original metal it will have been easier to machine and won't be as brittle as a fully hardened item. Once you have increased the carbon content then you heat and quench as you would the higher carbon steels so oil, brine or water will all work

Ah I see, thanks Jason.

So are there two methods for case hardening? If I understood correctly some are saying to heat the part enclosed and let it soak, and then there is another process where I heat the part and dip it in case hardening material multiple times and then quench. Is this right?