Heat treatment of 17-4 PH after machining

[corbeau]

Hi all,

My machinist has been machining 17-4 PH in an as-received DHT1150 condition. He has expressed concerns about how hot the pieces get during machining.

Is it necessary/recommended to redo the full heat treatment (anneal + DHT1150) after machining? Or just redo the DHT1150 process? Or is material performance similar after machining if the metal is already in the heat treated condition?

 

[EdStainless]

First figure out if there has been any damage.
Micros and microhardness should tell you that.
If it has been over heated then the entire HT will need to be done over.

Then find a new machinist, There should be no way to get anywhere close to 1150F.

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

 

[RolMec]

Perhaps of interest as far as it concerns the workers experience:

http://www.practicalmachinist.com/vb/cnc-machining/milling-problem-17-4-ph-stainless-275120/

As to the machining process: How much temperature is "hot"? Was there no coolant applied?

Roland Heilmann
Lpz FRG

 

[WKTaylor]

corbeau...

Machining PH-CRES without lubricant-cooling is ill-advised since distortion due to gross over-heating while machining will be 'built-into' your part.

Temperatures above service temp for this alloy/temper MAY be of metallurgical concerns; however, effect on corrosion resistance may be a more pressing concern.

Machining lubricant-fluids have a significant coolant aspect so temperature due to cutter-friction can be drastically reduced.

See SAE MS1008 Lubricants, Industrial Oils and Related Products Type M (Metal Removal Fluids) Specification

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
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[mfgenggear]

Hi Corbeau

first off all rough machining should be done prior to heat treat.
second cond. 1150 is equivalent to 30 HRc hardness approx. it is the correct hardness for machining.
and should be easily machined. ( feeds and speeds and correct coolant) there is no need for subsequent heat treating)
how ever a post stress relieve prior to finished machining. is all-ways helpful.

make sure the shop is using the correct machining procedures

 

[WKTaylor]

MMPDS-10 states the following up-front... and the 'great reason for rough machining to within ~0.2" of finished dimensions before precipitation hardening...

Manufacturing Considerations — 17-4PH is readily forged, machined, welded, and brazed. Machining
requires the same precautions as the austenitic stainless steels except that work-hardening is not a problem.
Best machinability is exhibited by Conditions H1150 and H1150M. A dimensional contraction of 0.0004 to
0.0006 and 0.0008 to 0.0010 in./in. occurs upon hardening to the H900 and H1150 conditions, respectively.
This fact should be considered before finish machining prior to aging treatment.

NOTE. IF a lot of machining is done after PHT, and part is structurally critical, then I always recommend a final stress relief HT operation, when HT above 150-KSI [~H1025 or lower].. especially when HT to 170-KSI or higher [H925, or lower].

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]