Mark Clifford

I am making musical steel 'tongue' drums and am using mild, low carbon steel [CR4] and I need to harden the steel to get it to ring or 'sing'. Some say you cannot harden mild steel, some say you can case harden mild steel. If I heat to dull red and quench in water will this harden the mild steel? Is it better to quench in oil as this adds carbon in the process? When using homemade case-hardening compounds - flour/salt/carbon do you put the paste onto cool metal? One site said apply to hot metal but I couldn't get it to stick and if I do manage to cover the area to be hardened I can't see if the metal is heated to dull red! I just need to harden the steel then temper it to 'straw' colour [for visual effect and to counteract brittleness] so it doesn't have to be to 'tool work' standard. The discs I am working on are about the size of a small car wheel using 2mm mild steel. I aim to experiment with small strips to test for filing and brittleness [presuming that means it has hardened]. Glad to hear any views/ideas.