There are only a handful of things to check when your steel parts fail to respond to quench and temper heat treatment.
Here’s my list in decreasing probability order:
- Mixed steel / wrong steel being heat treated.
- Decarburization on the surface.
- Failure to heat it above the austenitizing temperature.
- Failure to hold it for sufficient soaking time. (This can be especially problematic with induction processes)
- Failure to quench fast enough.
So someone could say “Well you didn’t mention that the steel had a microstructure that interfered with the process and is preventing us from getting the hardness required.”
To them I would say “Please see items 3 and 4 above.”
Photo credit Da Wei Induction Heating Machine Inc.