[ZZII 527]

An update on the heat-treating front: Yesterday, I tempered the 42mm plate, which seems to be some type of tool steel, and managed to get a significant increase in hardness, although my first attempt was too brittle. I will try again when I get another sample, but in the mean time I tested the 56mm plates too. Unfortunately, they are definitely NOT tool steel and will not harden much without adding carbon. Some data:

56mm carrier before heat treatment: HRA 46.1, 46.5, 46.5
56mm carrier, 950C for 15 minutes, oil quenched: HRA 49.3, 49.9, 49.4
56mm carrier, 950C for 15 minutes, water quenched: HRA 57.1, 57.9, 58.5 (about a C16)

It's a slight improvement, but not the C40 we are looking for or even the C23 of the shaft. Case hardening is still an option, but not an easy one. I suspect the solution will be an entirely new plate made of something harder and with a tighter fit for the shaft. I will probably shift my focus to this avenue now, although hardening is still an easy solution for the tool-steel 42mm carrier.

Good luck all!