Tempering of martensite with retained austenite

  1. Hi,

    What changes will happen to retained austenite in a martensite matrix during tempering of martensite in an alloy steel @740 C-760 C (ie, below Ac1 temperature)?Will retained austenite transform to martensite (untempered) during tempering or retained austenite will stay as it is during tempering??Is there any possibility for a transformation from retained austenite to pearlite/bainite during tempering??I am confused:confused:Any help would be highly appreciated.

    PS:I am not looking for a cryogenic treatment to transform all retained austenite to martensite and further tempering solution to this problem.

    Thanks
     
    Last edited: Oct 26, 2012
  2. jcsd
  3. :uhh:,119 views,no reply (right or wrong)so far.I never thought that this was a much complicated question!:rofl:
     
    Last edited: Oct 27, 2012
  4. During heating, as in tempering, the retained austenite may form pearlite but will NOT form martensite. Martensite formation is diffusionless and shear-dominated, and therefore some combination of quenching and/or deformation is needed. In short, it is not possible to 'heat' a phase and convert it to Martensite. Or Bainite, for that matter since it too requires a fast quenching rate to form, although not as severe a rate as martensite.
     
  5. Astronuc

    Staff: Mentor

    Is one referring to martensitic steels, or alloy steels in general.

    Martempering occurs at rather low temperatures. A steel could be quenched into the martensite region then brough up into a temperature to promote bainite.

    Here is some information from various sources:

    The effect of tempering depends on the alloy composition, soak time (time at temperature), and quench rate.
    http://www.azom.com/article.aspx?ArticleID=313

    Some steels are deliberately austenitic, ferritic or martensitic, or some combination, e.g., duplex. Their processing will depend on composition, e.g., content of carbon and elements that promote stabilization of one of the microstructures, e.g., austenite.


    Tempering Processes/Technology - ASM International
    http://www.asminternational.org/pdf/spotlights/tempering.pdf

    Austenitic and Ferritic Stainless Steels in Practical Applications: Part One
    http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&NM=156

    Martensitic Stainless Steels
    http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&NM=199


    From: ASM Handbook Volume 4, Heat Treating (ASM International), Published: 1990, pp. 152-163
    http://www.asminternational.org/por...a7e0e64e18110VgnVCM100000701e010aRCRD#details


    Austempering process description.
    http://www.advancedcast.com/austempering-process.htm

    The austempering process
    http://www.appliedprocess.com/process
    Examples
    http://www.appliedprocess.com/adi
    http://www.appliedprocess.com/as

    Marbain process
    http://www.fisherbartonsp.com/products/products.php

    Some other information
    http://www.msm.cam.ac.uk/phase-trans/2005/Stainless_steels/stainless.html


    A practical application: Bainite and austempered ductile iron combined in high-strength steel
    http://www.asminternational.org/por...toid=86f6ba653fcda310VgnVCM100000621e010aRCRD
     
    Last edited: Nov 14, 2012
  6. Thanks Bavid and Astronuc for the reply. That means, during tempering cycle (ie, heating), retained austenite will not transform to martensite(ie, no possibility for lattice shear and the temperature is well above Ms temp.). Still the possibility of Austenite decomposition to ferrite and carbide during tempering heating cycle depends on tempering temperature and holding (soaking) time. The martensite will get tempered during tempering cycle. During cooling, below Ms Temperature, the remaining conditioned retained austenite (if it is available, much of carbon depleted from retained austenite during tempering thus Ms Temperature of alloy further raised) will transform to hard and brittle martensite. So, I think, I need one more tempering cycle to temper the secondary martensite.
     
    Last edited: Oct 30, 2012
  7. If it is plain carbon steel, Austenite is way too unstable to exist at the tempering temperature. I obviously do not know the tempering time you are using, but if you steel is plain carbon, you can very quickly convert ALL of the retained austenite to ferrite+pearlite, so when you quench for another cycle it is possible that there is no austenite left to form the 'secondary martensite' you mention.
     
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