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 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. 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.