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:

Time, temperature, quench, suitable steel.
Time, temperature, quench, suitable steel.

  1. Mixed steel / wrong steel being heat treated.
  2. Decarburization on the surface.
  3. Failure to heat it above the austenitizing temperature.
  4. Failure to hold it for sufficient soaking time. (This can be especially problematic  with induction processes)
  5. 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.