Originally posted by JSmith:
from what I understand heat treating is not a surface treatment. heat treating will affect the entire shaft.
A surface treatment would be something like nitriding or carburizing which hardens the surface of the metal to produce a hard wear resistant surface while the base metal remains unaffected so it retains its original strength and durability.
Dude, I heat treat shiz all day long, it's my job, as I design axles! The rear shafts on the new Hummer 2 are mine!
Depending on what frequency and current you put through the coil that goes around the part you are heat treating (induction coil hardening) you can control the depth of the heat treatment. You do NOT want something through hardened, i.e. the whole x-section is the same hardness, as that takes away from the fatigue strength of the part. I can assure you that cams are not through hardened, so they have a "shell" of varying hardness (softer as you get deeper), up to a point and then from there on in it will be essentially all the same hardness to the center of the part. This technique is used on axle shafts, cams, conrods etc.
Nitriding and carburizing are as you said, a surfacing hardening treatment that has an extremely thin shell that is significantly harder than the core of the part. They use this treatment on diff cases a lot, especially helical cases, like the Quaife.
