[jim]

I agree with the good Doctor. We need alot more information to help you with this. Like what Temperature, Time in Hrs, Carbon. Also what was the Temper and Material also what Hardness were you looking for and what Hardness and Case depth have you been getting in the past.

[Richard Howell]

I run several heats of 8620 material through 12 Batch furnaces. The difference in case depth and hardness verries by +/- one HRC surface hardness and +/- 0.005 in case depth. We control the incoming hardenability for repeatability.

Look at the core hardness from lot to lot. The core hardness is primarly controlled by the chemistry of the incoming heat. A large veriation would indicate that the incoming material has a wide chemistry and the hardenability is not being controlled. Also, the variation from furnace to furnace would indicate a quench issue with one of the furnaces.

A raise in tempering temperature should have resulted in a drop in the surface hardness of 2 points HRC from the as quenched hardness. What is the as quenched hardness? Does it vary from heat lot to heat lot? My as quenched surface hardness on a carburize cycle is HRC 64 to 65. My temper drops that hardness to HRC 60 to 61.

You need to collect and analyze the data to understand the changes.

[The Heat Treat Doctor]

Perhaps the attached article on the Shim Stock method will be of some value. I find that it is extremely reliable and a fairly easy procedure. Just be sure that your shim extends all the way into the furnace - a common error that plays havoc with results!