17-4 wide hardness spread after aging
17-4 wide hardness spread after aging
(OP)
My company has aged at 900° for 1 hour some small pieces of 17-4 material (120 pieces of 1.9" long bolts that weigh 0.022 lb each). Our customer says these parts were machined from the same bar as the two previous orders we processed, where the hardness results were as expected.
On the current order, the hardness came out at 36-37 HRC (converted from HR15N), below the expected hardness of 40-47 HRC for the H900 condition. We re-aged for a second hour and then had hardness of 38-49 HRC. We tried a third hour at 900°, with no change in the hardness.
Any idea what could cause this wide hardness spread with both soft and hard parts?
On the current order, the hardness came out at 36-37 HRC (converted from HR15N), below the expected hardness of 40-47 HRC for the H900 condition. We re-aged for a second hour and then had hardness of 38-49 HRC. We tried a third hour at 900°, with no change in the hardness.
Any idea what could cause this wide hardness spread with both soft and hard parts?





RE: 17-4 wide hardness spread after aging
RE: 17-4 wide hardness spread after aging
RE: 17-4 wide hardness spread after aging
There are only a couple of sources of scatter, either the two things above or a variation in the annealing temperature.
If you want to check material re-anneal a couple of them and then age them. I would do this to a couple of the softer ones and a couple of the harder ones. 1900F x 30min, cool to room temp, 900F x 45min
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P.E. Metallurgy, Plymouth Tube
RE: 17-4 wide hardness spread after aging
RE: 17-4 wide hardness spread after aging
We re-solutioned the order, re-aged it (in the same aging furnace) and now hardness (testing the same 5 pieces that previously were 38-49 HRC) is 45-46 HRC equivalent on all 5 tested pieces.
It is very strange.
RE: 17-4 wide hardness spread after aging
RE: 17-4 wide hardness spread after aging
Further, it was not due to too high solution temperature (ferrite formed), in which case even re-solution will unlikely solve your problem.