Partial Stress Relief of HS Alloys steels

[WKTaylor]

Help.. I am fully aware of stress relief procedures for high strength alloy steels (IE: part of AMS2759/2 for instance). However, recently, I was presented with a "generic" partial stress relief process [350F--400F] for use with HS aerospace steels (180--300KSI, IE: 4330M, 4340M, 300M, etc), as part of an overhaul process for HS parts [IE: landing gear, flap tracks, etc]. The obvious benefit is avoiding damage to platings and minimal affects on residual stress mechanisms [IE: shot-peening and hole cold-working]. HOWEVER... I can find no specs, tech data, literature, etc, justifying the benefits of this process. To me, this just sounds like prophylactic hydrogen embrittlement relief [IE: same as ASM2759/9]: but I'm informed that this is NOT the intent of this procedure... and that real stress relief is occuring. Anyone have ref info/data/etc on "partial stress relief" procedures?????


Regards, Wil Taylor

 

[unclesyd]

This procedure was used at one time to keep parts from distorting due to machining and prior to a full stress relief. The parts were keep out of the "Blue Brittle Range (400°F-700°F). I haven't seen it done lately. I never understood how one would determine that stress relief was occuring. Stress relieving as "mcguire" pointed out in a previous post is nothing more than controlled creep. There some heat treatments that call for a tempering temperature of 350°F, not for the alloys in your case.

I think all these alloys are in the

"Aerospace Structural Metals Handbook"

http://www.cll.purdue.edu/extendeduniversity/selfdirected/ir/index.cfm?ir=aero

This is a very expensive set of handbooks but have everything allowed with Aerospace Metals. Check around to see if can get to a copy.

You might be able to find a heat treating book at the

http://www.asminternational.com

 

[unclesyd]

Correction on URL
This if for the Aerospace Structural Metal Handbook

http://www.cll.purdue.edu/extendeduniversity/selfdirected/ir/index.cfm?ir=aero

This for a book Structural Alloys Handbook

http://www.cll.purdue.edu/extendeduniversity/selfdirected/ir/index.cfm?ir=alloy

What is not covered in one is covered in the other

 

[WKTaylor]

unclesyd... Thanks for Your comments.

I purposefully reviewed the CINDAS-ASMH**, numerous heat treating specs, ASM handbooks, library reports on HSA steel, etc... before asking this question. All have no significant references to a low temp stress relief. Stress relief is invariably defined as being 50F below the KNOWN (or if unknown, spec-minimum) temering temperature.

I did find references to hydrogen re-embrittlement of HSA steel, due to the inevitable porosity of platings and oreganic coatings (after many years of service)... implying that a hydorgen relief bake during overhaul would be beneficial, similar to AMS2759/9. But in some cases this was considerd a theoretical problem... not warrented by inservice problem/failure data.

Regards, Wil taylor

CINDAS-ASMH*** provides excellent metallurgy info + mechanical values... definite companion to MIL-HDBK-5.

Regards, Wil Taylor

 

[Miper]

Wil,
When did you get back to Eng-Tips? The guys would love to hear from you on the "mental challenge" thread you started last year. So sorry about your mother. Welcome back.

Miper

 

[TVP]

For background information on stress relieving, consult ASM HANDBOOK Volume 4 Heat Treating. The Larson-Miller equation has been used to describe the time-temperature relation for stress relief:

Thermal effect = T (log t + 20)10^-3

Low temperature stress relieving is frequently performed on components fabricated from high strength steel alloys, especially those that are formed. Cold wound/coiled springs are the items with which I have the most experience. Standards such as SAE J217 and J230 have a requirement for the springs to be stress relieved at a temperature of 230-260 C for 30 minutes. I am sure there are some SAE aerospace standards that are similar. Raytheon has a standard (BS25526) that has similar requirements. The old military standard MIL-S-6715 had a requirement for stress relief of 250 F for 1 hour.

In general, springs fabricated from patented & cold drawn steel wire (music wire) are stress relieved at 190-230 C, oil tempered carbon springs at 260-400 C, and oil tempered alloy springs at 315-425 C. I could not find any standards that cover this type of treatment, mainly because there are no universally-used standards for mechanical springs. However, all spring design handbooks discuss this topic.