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  #11  
Old 04-18-2010, 01:17 AM
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Originally Posted by AJinNZ View Post
You would use an oil or water quench on carbon steel.
Mild steel wont harden due to the very low or non-existant carbon content.

The case hardening process allows enough carbon to get into the metal surface to create a harder shell. The longer it has to be in contact with the carbon source, the deeper the case.

The unknown part is I havent done this before so it is all 'try and see'.

Thanks Cutter. I will find out in the morning.
So you do this process to increase the carbon content in the pieces you are trying to harden, correct? I assume the carbon comes from what ever you are burning in the forge (coal for example)? Does this process harden them as well? Or will you have to go through another step?
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  #12  
Old 04-18-2010, 01:53 AM
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Correct, yes.

Coal wont work as it has too many impurities in it, so I am using charcoal. Even then one of my books suggests a method for driving off unwanted gasses, but I didnt go into that much detail.
Bone dust, hooves and charred leather were also traditional sources of carbon.
A gunsmith mate used to have me file up bone for him to colour case harden parts. Although they came out hard he couldnt get the colour he wanted.


Once the required depth of case has been created, the steel is re-heated to cherry red and quenched in either oil or water. I will use oil just to be careful and avoid any cracking.
The case is then brittle hard. Heat again and quench at the colour/temp you want the finished article to be at.
Once done right ( If all goes to plan ) you will have a hard shelled exterior tempered to the level you need and a soft mild steel core.
For this gizmo it is the only way to make the cams resist damage while being done up.
Ideally I would make new ones from better steel, but without a working set of cams in the first place and a reliable chuck it would be like going in circles.

The first try didnt work anyway.
The case was incredibly thin as to be useless. The forge heating though was effective in that I had no scale formation, so a small win.

I cleaned up the cams again and went for round two.

I got the electric kiln going and put them in there for a long bake. I will go over and turn the thing off at about 1 a.m

Will post some pics of that later tonight.
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  #13  
Old 04-18-2010, 07:42 AM
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Some pics of the kiln process

1. is the kiln itself. Has a max temp of 1000 degrees celcius
For the carbon pack stage it needs to be held at 913 to 940 degrees. I decided 920ish would be OK.

It took almost 5 hours for the thing to come up to final temp.

2. The cams in cold before I turned anything on.

3. A pic taken through the side peep hole. The cams started turning pale red at around 700 degrees.

4. The hot cams in the tin with charcoal on the bottom and just before I covered them with more charcoal.
I reached into the kiln with pliers and a welding glove on. I knew 900 was hot but had no real concept of HOW hot. I now know it is hot enough to make a welding glove start to smoke in under 3 seconds.

5. Tin full of charcoal and 3 well covered hot cams with its lid on. The initial heat made the lid warp a bit and it popped off, so I got it back out ( more smoking leather ) and replaced it and put it back with a couple chunks of heavy scrap steel to keep it in place.

A small flame was coming out from under the lid for a little bit which had me concerned as I dont think an electric kiln and flames would get along too well, but it didnt last long.
I kept a close eye on things for the first hour, but assumed that after the air in the tin had been driven out/consumed and the carbon monoxide was being produced that there was very little chance of fire.

I have a copy of Machinery's Handbook 1953 that has been excellent for all kinds of things. One of the best books I have.

In 1/2 an hour it will have been in at full temp for 6 hours and i will turn it off and leave it alone to cool slowly. Tomorrow I will be able to see what I got out of it all.
No matter what happens though it sure is funner than hell farting round with this stuff.
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  #14  
Old 04-19-2010, 07:05 AM
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I got the tin out this morning. Even though it had been a good few hours it was still pretty hot in the kiln. Everything had returned to a normal colour though.

The tin holding the cams and charcoal was totally destroyed by the heat. It just fell apart when I tried to open the lid and it had fused itself to the ceramic spacers under it and to the scrap steel on top used to keep the lid tight. ( pic 1 and 2 )

Next time I will have to make a thick steel box and probably seal the lid with kaowool or something.

Even the 2 bits of scrap steel had fused together. ( pic 2 )

When I checked the kiln last night before turning it off, there was a lazy pale blue flame coming out the peep hole, almost like burning alcohol kinda flame.
The charcoal around the outer edge of the tin had turned to ash so I assume that it had burned as the tin had failed. The charcoal where the cams were buried in the middle still looked like ordinary charcoal.

When removed the cams had a crusty black sorta scale on that was pretty hard when cold. Some parts were well stuck to the metal and others flaked off easily. It polished up to look just like steel and for a while I wondered if this was actually the case I had tried for and here it was ruined.
As it was cracked and wrinkled I wire wheeled it off and heated them one at a time to pale red and quenched in linseed oil.

As the kiln was still warm I re-set it to 220 degrees for a 'sorta hard' temper and left them in it for 1 1/2 hours or so.
Got them out and quenched again in the oil and then cleaned them up.

The finished article is pic 3.

A test with a file shows it is harder than before.

Using them on the lathe will show if they are OK, if not I will re-harden and temper to a higher level, but I dont think I will need it.
If I look closely I can make out a sort of marbled pattern on the surface of the steel which I assume is where the charcoal was touching it, so it has definitely changed.

Next time I case harden anything I will try adding the yellow prussic stuff ( I hope I remember that right ) and see how much difference it makes.

Thanks for the encouragement and advice fellas.
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  #15  
Old 04-19-2010, 12:40 PM
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Well, that sounds good. I hope they do the job now, AJ.
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  #16  
Old 04-20-2010, 12:03 AM
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Interesting, AJ. I knew about Kasenit but, never knew you could do it with charcoal. What else do you use the kiln for? I always thought they'd be nice for melting aluminum for casting.


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  #17  
Old 04-20-2010, 12:26 AM
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I got the kiln because it had only been used a couple of times and was 1/3 the price of new.

It was one of those things I thought would be handy to have so I couldnt help myself.
The plan for it is to use it for tempering steel springs, small tools, blades etc.
Being able to set a temperature was the big thing, rather than rely on my estimate of a colour change for tempering parts that need to be done right.....like lathe cams for example.
Would like to play around with some glass as well.

Aluminium melts at 660 degrees, so well within the scope of this kiln. I dont know how much electricity it chewed through though.
For melting metal I would prefer gas. The fella who made the kiln sold me a pile of firebricks and some bits he didnt want, so that was to be the start of a gas setup.
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  #18  
Old 04-24-2010, 10:11 PM
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Originally Posted by AJinNZ View Post

Using them on the lathe will show if they are OK, if not I will re-harden and temper to a higher level, but I dont think I will need it.
Aaaaaaa Jaaaaaa - aaaaaaay,




enquiring minds & all that, want to knoooooowwww ooooooh?

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  #19  
Old 04-25-2010, 01:52 AM
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Default Case Hardening

Here is a link to a How to Case Harden Video if any of you guys are interested in the process. Its a great way for the home shop hobby type to heat treat.
Its fast easy and don't require high dollar equipment.

The video is by Cherry Red but there are other brands of compound available that is cheaper then Cherry Red

How to Case Harden Video
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  #20  
Old 04-25-2010, 07:48 AM
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LOL

Sorry Cutter.

I havent even been in the shop since the heat treating. Been getting my ceiling framed in and batts installed before the weather turns.

Gimme a day or so and I will get back out there for the final test.
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