Differentially carburizing.

[Bennett]

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Edited April 28, 2011 by Bennett

[Greg Thomas Obach]

i haven't read to much about it... .. my thinking was that its the gas ( carbon rich ) that was best to carburize the steel... but if your controlling it locally.. it would be by intimate contact with the carbon media that would be at work...

 

i have seen people use casenit and it looked real simple... .. thought that was somekind of cyanide

 

 

also... i wonder how many normalize cycles it would take to disperse the carbon rich areas..... being that this is a alloy steel... some of the elements may retard the speed of carb migration.. ... or not

 

 

Greg

[Bennett]

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Edited April 28, 2011 by Bennett

[Greg Thomas Obach]

sounds like a neat experiment...

i'd give it a go ...

 

and i think your right ...those are very good steels... just need a bit more carb to be great for knives

 

just a thought... if you could make another coupon.... quench it in water right after the carburize treatment... and crack off the end to see the grain...... then do the quench cycles on the remaining large piece and crack off a piece each time... maybe we could see the effect? and note if the carbon rich area thins out..

 

 

Greg

[Bennett]

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Edited April 28, 2011 by Bennett

[Bennett]

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Edited April 28, 2011 by Bennett

[kb0fhp]

Nicely done Jerry... You did something called pack carburizing. You can also do something similar with charcoal, cast iron chips, a bit of carbonate. You can also add various stop off compounds - Avion and Condursal are two good ones. They won't spall during carburizing.

 

Now regarding the etchant, I would suggest nital (2% nitric acid in methanol) - it will show the carburized case if not tempered as white, and the non martensitic areas as a deep gray. Only need about 10 seconds or so, then wash with water. You might also want to use a clamp when polishing so you maintain a sharp edge....

 

Your estimate of the case depth followed nicely the time at temperature...nice when the science and applied work out together....

Edited November 18, 2008 by kb0fhp

[Bennett]

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Edited April 28, 2011 by Bennett

[kb0fhp]

Thanks Doc.

 

I tried some more techniques, like masking the blade where I did not want extra carbon and packing the whole vessal. I just didn't want to ramble on.

 

I love 4340. I thinks it's the best low alloy, carbon steel, but a little light on the carbon. This technique should make it useful for cutlery.

 

Don't forget to use this during hardening also. Keeps the decarb down and some of the carburized area will diffuse a bit. Don't worry about insulating the edge from the quenchant. 4340 is almost air hardening. It was born to make martensite.

 

Thanks for the tips. How nasty is the stuff with barium in it? The MSDS looks pretty scary.

 

Very nasty - don't do it, unless you want your yard classified as a superfund site

[Bennett]

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Edited April 28, 2011 by Bennett

[Greg H.]

Cool. if you are just case hardening, (carburizing the whole part), leave out the sugar. The sugar helps keep it in place when just doing spot areas. I find the sea salt works better than the table salt. Don't know why that is exactly. I also reground the dry ingredients in the mortar and pestal. The finer, the better. More surface area to cover the steel.

 

Just a couple of thoughts:

 

Most table salt has iodide added to it that could be affecting the process.

Sea salt usually has slightly higher levels of magnesium chloride, calcium chloride, and potassium chloride that ordinary table salt has little of ( if any ).

 

If you get a chance you might try non-iodized table salt and perhaps rock salt, and post the results, as it might help narrow down the factor that makes sea salt better.