We had a call that a customer rejected an alloy steel part because the hardness was too low,
despite a certification from the heat treater that the hardness was correct.

So what went wrong?

Well, when we got all the details, heat treatment had been performed on six inch diameter bar
stock. The hardness was certified on the bar surface.

The final customer tested hardness on the surface of the disc shaped part at what would be the
center of the original bar. The thickness of the disc was only two inches.

The result is that the bar surface (OD) was correct hardness but due to the larger mass and thickness, its center was
not what was expected.

The solution was to heat treat the part in its disc shape that had much less mass so that all
surfaces of the part achieved the expected hardness.