Case hardening

[andyhigham]

I think this will work
I want to case harden a top hat shaped hub, not the whole hub just the top of the "brim" and the outer surface of the cylindrical part.
I thought of using a cut down food can, place the hub in the bottom and layer Kasenit equivalent on top then place it in the furnace.
My worry is the tin plating on the food can, will it react badly with the Kasenit?

[chris vine]

Hi Andy,

That sounds like a tricky problem you are setting yourself!!

Can you make the part from silver steel and then harden and temper the whole thing. Not so hard that it is brittle, but perhaps to a dark straw colour? It would still be pretty hard wearing and at least you would know what you had!

I have found that when case hardening thin parts (mind you, you don't say how thin it is), that the casehardening can go right through and then the whole thing is brittle as glass...

Chris.

[andyhigham]

These are the parts top right and bottom left in the first photo 65mm dia 5mm thick

[Roger]

I don't think you need to bake it in a tin, you can just apply the Kasenit to the rim. You could protect the areas you don't want hardened with Tippex, get it all red hot and then dip the end in the kasenit. You can heat it again and dip it again and then quench it.

[abby]

A fireclay wash would be more effective or packing the area to remain unhardened with fire-clay , there is very little tin on a tin-can and in fact many cans have no tin on the inside.
I prefer to use a piece of steel pipe or RHS with the Kasenit well packed around the job and allow at least 15 minutes in the furnace at bright red heat before tipping into cold water.
Dan.

[andyhigham]

What temperature is bright red heat? As I have fitted temperature control to my furnace I may as well use it

[RGR 60130]

I was taught to case harden stuff on a fire brick, bringing the job up to bright red then spooning Kasenit over and heating some more to burn the carbon in, repeating and turning over as required then quenching. Some areas will receive more than others but it seems to work ok.

For jobs requiring partial hardening then some planning is required. A simple example is a pivot pin where the ends are a smaller diameter and aren't required to be hardened. The whole pin is subjected to the burning in process but not quenched. The ends are then turned down to the required size. After this the pin is re-heated and quenched. That will leave the centre portion hard and the ends soft.

Unfortunately for Andy his components are already made so this technique can't be applied. However, it may help someone else.

A fire clay wash may indeed make a good mask. I will be interested to learn how it works out. Good luck.

Reg

[andyhigham]

Ok I (almost) followed the instructions with the case hardening compound-Beta No1
I packed fireclay around the parts and applied a good layer of compound
2017-07-28_07-19-12 by Sigma Projects, on Flickr

2017-07-28_07-18-47 by Sigma Projects, on Flickr
Then placed them in the furnace at 700 deg C for 4 hours (instructions 600-700), I then broke off the fireclay and put them back in the furnace to ensure they were still at 700 deg C. I then quenched in oil, The result is still soft parts. WTF have I done wrong?

[gwr14xx]

Do you know what spec steel you used? Most free cutting steels are not easily case hardened.

Eddie.

[andyhigham]

I believe it is EN3B.
I think I will put it together as it is and see how it performs over a few months

[nonort]

I have some practical knowledge of Kasnit powder. and have had mixed results. The hardened skin tends to be thousandths of an inch thick on low carbon steels EN8 etc do harden deeper but not much. Leaded steels don't seem to harden at all I presume this is due to the lead leaching to the surface and stopping the carbon attaching to the surface.

[abby]

Andy I don't think the temperature is high enough , effectively you are changing the surface to carbon steel ( of unknown carbon content ).
The prolonged soak at 700°C is probably enough to allow carbon infusion into the steel but will the required crystaline change occur at this temperature ?
If I am hardening any type of carbon steel I heat to cherry red ...............about 850°C , then quench in cold water.
Dan.

[andyhigham]

I suppose it wont hurt to try 850 degrees

[Roger]

Have you got a scrap of the material you can try an experiment with?

[92220]

As Dan says, you are not getting the parts hot enough to start with, and for case hardening you should quench in cold water. That will give you a glass hard skin with a soft steel core. That is the idea of case hardening. For a tempered surface you would normally use high carbon steel (silver steel) and harden and temper. Quenching in oil should only be done after getting the skin hard. One problem with tempering is that case hardening only gives you a hard skin of between 0.0005" and 0.005" thick. Trying to temper to a specific hardness is not easy. You say you think you have used EN3B. That makes me think you are not sure what you have used so do as Roger says, case harden a test piece at 850C and quench in water. If the skin is glass hard you just have to re-harden your parts at the higher temperature. If it doesn't harden you know you have used leaded steel and it cannot be case hardened.

Bob.

[daveburrage]

A company I used to work for case hardened gears etc. The gears were wax coated then the wax stripped from the areas to remain soft. It went in a copper plate bath. Then the wax was fully removed. The copper plated areas remained soft. This was with a carbon rich gas hardenning process, but I suspect it would probably work with kasenit.

regards

Dave Burrage

[andyhigham]

Today I warmed the furnace up to 850 degC, put the parts in and left them for 1/2 hour then quenched in oil. Still soft. Its on hold now for a couple of weeks due to work and bike racing

[Roger]

How sure are you that the furnace is achieving the stated temperature? 850C is bright Red, heading towards Orange.

[andyhigham]

It was nicely bright red, I double checked it with an infra red thermometer, within 4 degrees

[Roger]

It doesn't sound like there's much left to be wrong then.
I'd be interested to see how a scrap of the material behaves if you did it the crude way, ie heating it bright red and stirring it round in the Kasenit, then repeat a few times and quench. The Kasenit flares and glows in the flame, so you can tell it's the right stuff.