Metallurgy/17-4 PH H900
I have 1150 Pcs to machine out of 17-4 PH H900 the part requires a hole of .033 ( in ) Dia X .500 Deep and another Hole .065 Dia X 1.550 Deep Should I be machining these features in a heatreat condition OTHER than the H900 and then heatreat to the H900 condition after Machining ??
There are two things to consider before making a decision. Hardness which affects the machinability is lower in the solution annealed condition, namely after annealing at around 1900 F, than in the H900 condition. As a rule of thumb, the typical hardness in the solution annealed condition of 36 HRC increases to about 44 HRC after the H900 aging. If this hardness increase is not much in view of your machining capabilities, then it would be better to drill the holes after the H900 treatment.
If you conclude that the higher hardness in the H900 condition would mean a lot to your drilling tools, then drilling may be done in the solution annealed condition (before H900 aging) as long as it can be ensured that the holes' dimension would remain within the allowed tolerance after the contraction caused by the H900 aging. The magnitude of contraction after aging of the 17-4PH grade is 0.0004-0.0008 inch per inch.