"Case hardening" compounds are intended for use on more or less "mild" steel components
Markus will fill us in on the exact "specifications", I have a big "Casenit" tin and the instructions are for use on "mild steel" . It will only harden an outer layer of the component
Clutch pushrods need to be hard throughout (at the ends) which is why the steel of choice is "silver steel" or drillrod
The entire end does not need to be through hard,
If it is cased all over then the pressure plate / clutch lever will be pushing against a hard surface because the end will also be hard and will see no difference between a cased end and a fully hardened end provided that they are hardened to the same level.
The depth of hardening depends totally on how long you soak. Leave them in it for long enough and you can get through hardening of thin sections.
You can use these compounds on any grade of steel although the lower the carbon content the better it works.
the higher the carbon content the longer you need to soak in the salts and of course eventually you get to a point where the cost of holding the part at temperature is greater than the cost of using a higher strength grade of steel in the first place. Or if you are not careful and overheat end up with recrystalization and large grain growth which is not good.
The only real difference between using a cased rod and a through hardened rod is that the cased rod needs to be cased all the way back to the point where it exits the mainshaft or it might bend.
Usually you case an item that is hard to fabricate so that you can machine it while soft & easy to do then harden it latter.
