×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

17-4 wide hardness spread after aging
3

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?

RE: 17-4 wide hardness spread after aging

This is a known fact that for same heat treatment even if the tensile and yield are within spec the hardness can vary in a range of 10RC. If you look at MIL-HDBK-5J you will see that the spec only ask for minimum yield and tensile properties there is no requirement for minimum hardness.

RE: 17-4 wide hardness spread after aging

On top of what was mentioned, converted hardness values adds another level of variability versus direct hardness measurement using HRC scale.

RE: 17-4 wide hardness spread after aging

2
The only way that re-aging could raise the properties is a) if your original age was not hot enough (below 900F) or b)if your original age was too short of a time.
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

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: 17-4 wide hardness spread after aging

There was no mention of the heat treat specification used (if any). I checked AMS 2759/3 and the hardness range for 17-4PH H900 is Rc 40-47. The H900 aging set temp is 890-910 degF and the aging time is 60-75 minutes. Additional aging is permitted only if the part hardness exceeds the required maximum. Regarding metengr's comment about variation in conversion of hardness values, AMS 2759/3 table 7 lists a minimum tensile strength requirement of 190ksi for 17-4PH condition H900.

RE: 17-4 wide hardness spread after aging

(OP)
My previous experience has been consistent with EdStainless's statement: that with our hardness results the original age must have been too cold or too short. But in this case we run monthly TUS (±10°F) and weekly SAT on the aging furnace and are very confident the logged temperature of 900°F for 1 hour was what the parts actually saw.

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

Based on what you presented there is nothing strange only a case for re-evaluation of your in-house process controls.

RE: 17-4 wide hardness spread after aging

It was clear to me the solution heat treatment issue: the bar was not completely transformed to martensite due to either too low annealing temperature, or in-sufficient oooling. Re-aging won't solve your problem.
Further, it was not due to too high solution temperature (ferrite formed), in which case even re-solution will unlikely solve your problem.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources