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  • 1.  Relative fatigue strengths of 17-7PH and 15-5PH stainless steel

    Posted 04-20-2022 14:27
    I'm looking to evaluate the two alloys mentioned above. similar HT (180-200ksi UTS)
    Is there any additional information available outside the ASM handbook, volume 19?
    Which of these two alloys works best (higher fatigue life)in a non- high temperature environment under variable cyclical loads with fmin/fmax ratio ranging between -0.5 and 0.0.
    Info or resource is appreciated.

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    Chip Haynes
    Structures Technical Fellow
    Aviation Partners Boeing
    Edgewood WA
    2062294943
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    Data Ecosystem - Global Materials Platform


  • 2.  RE: Relative fatigue strengths of 17-7PH and 15-5PH stainless steel

    Posted 04-21-2022 07:45
    Hi Chip,
    17-4 PH and 15-5 PH are actually very close. 15-5PH is the "little brother" of 17-4PH with slightly less chrome and higher Nickel in order to minimize the formation of the delta phase which is detrimental for fatigue. This could be very important for welding, and has its advantage for additive manufacturing.
    Thus, it is easier to have thicker products in 15-5PH without cracking. 15-5PH toughness in the transverse direction is better, and crack growth rate lower linked to the finer and cleaner microstructure.
    Corrosion resistance is similar.
    You can find the properties of both materials in the Mil-handbook 5 (superseded by MMPDS-01), but you can still find it here:
    http://everyspec.com/MIL-HDBK/MIL-HDBK-0001-0099/MIL_HDBK_5H_1804/

    Hope this helps.



    ------------------------------
    Nihad Ben Salah
    President
    NBS- M&P Consulting
    Canada
    https://www.nbsmpconsult.com/en/home
    ------------------------------

    Data Ecosystem - Global Materials Platform


  • 3.  RE: Relative fatigue strengths of 17-7PH and 15-5PH stainless steel

    Posted 04-24-2022 19:23
    Hello, Chip et al.
    * Regarding the preference between 15-5PH and 17-7PH - it would depend on the configuration and application of the component;
    * Both alloys have good properties and characteristics, as do 17-4PH and 13-8 Molly.
    * 13-8 Molly is a stronger alloy if you need higher strength, but it is a bit more expensive.
    * Perhaps contacting Carpenter Technology in PA or ARMCO Steel in OH would help selecting the most optimal alloy, considering formability, weldability, machinability, HT distortion, cost…
    * Important to note that the specifying the apptopriste tempering temperature is as important as the alloy selection itself - it typically ranges between 900F and 1100F in 25-50 degrees intervals.
    * The lower end of the range assures higher UTS (ultimate tensile strength) and low RA and EL (reduction of area and elongation), thus poor fatigue properties.
    * The higher end of the range provides decreased UTS and higher RA and EL, thus much better fatigue characteristics.
    * Also, would be good to know if your application is high-cycle fatigue (over 100,000 cycles or low-cycle fatigue (below 100,000 cycles).
    * 15-5PH would probably be better than 17-7PH for low-cycle fatigue.
    * Puzzled by your min/max stress (-0.5/0.0)?
    * If that is indeed correct, and there is no tensile stress - there is no concern for fatigue.
    * Tensile stress is needed to initiate a fatigue crack and propagate it to catastrophic failure.
    * Ultimate stress analyses for compressive yielding and column stability analysis in case of long slender components would be sufficient.
    * Typically fatigue curves are constructed for:
    R=-1 (fully reversed tension/compression of the same magnitude, like -1/+1);
    R=0 (zero-to-tension, like 0/+1);
    R=.33 (one-third tension to full tension, like 0.33/1.);
    * The noted range (-0.5/0.0) would result in an infinite R-ratio? Never seen that in fatigue analyses.
    * May want to double check; if indeed there is no tensile stress - fatigue analysis wouldn’t be a critical consideration.

    ** Good Luck, Chip!

    Best regards.

    -Jack.


    Sent from my iPhone


    Data Ecosystem - Global Materials Platform


  • 4.  RE: Relative fatigue strengths of 17-7PH and 15-5PH stainless steel

    FASM
    Posted 04-24-2022 19:54
    In LCF, plastic deformation renders stress ratio relatively unimportant. After a few cycles, it's balanced tension-compression.

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    John Grubb
    New Kensington PA
    (724) 448-5272
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    Data Ecosystem - Global Materials Platform


  • 5.  RE: Relative fatigue strengths of 17-7PH and 15-5PH stainless steel

    Posted 04-22-2022 07:14
    Another source you might try is the data library from Crucible Industries. (http://www.crucible.com/products.aspx)  They manufacture both materials and have extensive information available.

    Neville W. Sachs, P.E.
    Neville W. Sachs, P.E., PLLC

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    NEVILLE SACHS
    Neville W. Sachs, P.E., PLLC
    Camillus NY
    (315) 436-1257
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    Data Ecosystem - Global Materials Platform


  • 6.  RE: Relative fatigue strengths of 17-7PH and 15-5PH stainless steel

    Posted 04-22-2022 08:38
    Hi Chip, Sorry I just noticed that your question was on 17-7 not 17-4.
    My answer was a comparison between 17-4 and 15-5 PH, but it is not completely useless. The Mil-hdbk 5 gives info on 17-7PH too.
    17-7 is different from 15-5PH at different levels because it is semi-austenic while 15-5 is martensitic. Thus it is more stable at high temperature. It has relatively higher UTS but lower YS than 15-5PH for the heat treatment conditions at which they are usually used, which should be considered for fatigue strength.
    Finally, I noticed that you are interested by the heat treat conditions for UTS180-200 ksi. This is not a recommended condition for most of the PH steels for applications where Stress Corrosion Cracking resistance is a concern since this resistance is only achievable for low tempering temperatures (usually H900). Only 13-8Mo PH could have this resistance at fairly high tempering temperature (H1000).
    Hope this helps.


    ------------------------------
    Nihad Ben Salah
    President
    NBS- M&P Consulting
    Canada
    https://www.nbsmpconsult.com/en/home
    ------------------------------

    Data Ecosystem - Global Materials Platform


  • 7.  RE: Relative fatigue strengths of 17-7PH and 15-5PH stainless steel

    Posted 04-22-2022 16:52
    Thank you for the additional information.

    ------------------------------
    Chip Haynes
    Structures Technical Fellow
    Aviation Partners Boeing
    Edgewood WA
    2062294943
    ------------------------------

    Data Ecosystem - Global Materials Platform


  • 8.  RE: Relative fatigue strengths of 17-7PH and 15-5PH stainless steel

    Posted 04-22-2022 16:54
    Thanks for the link!

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    Chip Haynes
    Structures Technical Fellow
    Aviation Partners Boeing
    Edgewood WA
    2062294943
    ------------------------------

    Data Ecosystem - Global Materials Platform


  • 9.  RE: Relative fatigue strengths of 17-7PH and 15-5PH stainless steel

    FASM
    Posted 04-24-2022 15:38
    Check your library for the Aerospace Structural Metals Handbook (now out of print). It has chapters on both alloys. You also can try CINDAS ( https://cindasdata.com/ ). 
     The real answer to your question may lie in what product form you're contemplating. 17-7 is best as sheet, while 15-5 is better suited to plates, bars, forgings, and castings.
    --
    John Grubb



    Data Ecosystem - Global Materials Platform