Case Hardening Compound

Just bought some case hardening compound from EKP Supplies. I want it for a cylinder that I have machined and would like to try and harden the inner surface.

I bought 250g for around £14.00 maybe a tad expensive, but if it is anything like the Kasenit of the past then it will last for ages.

As you can see the case hardening is a consistent grey coloured granular powder.

The first job that needed case hardening were the surfaces of the sliding beams for my steam engine turned gas engine. This image shows the 2 sets of upper and lower beams laying on the furnace hearth (an easy to make hearth using stove bricks) ready to be heated up to 850-900°C.

I put some of the case hardening compound into a ceramic dish that I have and then placed each of the heated parts into the compound in turn and moved them around in the powder. There is quite a lot of fumes from this and I would recommend good ventilation.

I covered the parts in the dish with a metal plate to both keep the heat in for longer and to reduce any chance of the material combusting – which apparently it can.

I repeated the process of heating the parts up to a cherry red and placing them into the case hardening 3 times. The parts took on a crust of black carbon and the powder changed to a much deeper black carbon looking mix where it was heated by the parts.

Once I felt happy with the length of time in the case hardening I finally heated the parts up and quenched them in cold water.

The cleaned and assembled parts on the engine (transitional engine). Some more work to do to get these to a final finish, but cleaning the surfaces gave me a good feel about the hardening of the mild steel parts. I will have to run some tests to see if I can determine how much harder the resultant parts are and will give you feedback on their endurance on this engine.

Alternative Case Hardening Compound

The Case Hardening is marked as Beta 1 – made me wonder how much the team have tried different formulas and whether you could in fact make your own. So a quick search for recipes threw up the following options:

• carbon rich compounds – diffusion of carbon into the steel matrix
• additive that prevents the carbon from oxidising

Some online recipes:

First a sophisticated list

• 13 parts hardwood charcoal (barbecue charcoal)
• 3 parts barium carbonate
• 2 parts sodium carbonate
• 1 part calcium carbonate

or

• bone charcoal
• potassium ferrocyanide

apparently bone charcoal does not have residual acids that wood charcoal has

or

…..need some more ideas of mixtures – preferably ones that meet basic health and safety requirements

My next problem is whether to buy or make a small high temperature oven that could heat the part and hold it there for 10 minutes or so.

Examples of Case Hardening

Small Homemade Planishing Hammer – the head was turned and milled from a piece of hexagonal mild steel. The slot was drilled 9.5mm and then open up into an elongated slot using a 10mm slot drill. Quite an easy machining task when using mild steel.
Mild steel is not really sensible for the hammer head faces and so I decided to case harden them.