Case Hardening Compound

case-hardening-001Just 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.

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


  • bone charcoal
  • potassium ferrocyanide

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


…..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.

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.

About Nigel 225 Articles
Have been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

1 Comment

  1. Try using the old gunsmiths trick, fruit stones heated till they change to charcoal, smash with a hammer till a fine powder then use as casnit.
    Different fruits will give different colours.
    The best bit is its free.

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