What is the process to determine how hard a components surface should be, but more importantly how do you determine how deep the the hardness should travel?
A sample with a perpenicular cut to the case surface is done, polished and a micro hardeness test is done from the surface toward the inside of the part. The case thickness is the depth from the surface to the depth where the hardness id equall 50RC.
Selecting hardness values for a part usually is trial-and-error and experiential rather than done from first principles. Some common surface hardness values are 60 HRC for gear teeth, 50 HRC to 60 HRC for splines, 50 HRC for journal bearings and seal surfaces. Fatigue strength is the driver for hardness depth. Typical values are ~ 1 mm to 50 HRC for gears, and depth to 45 HRC of ~ 5 mm for shafts.
