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Dislocations in FCC and BCC iron due to C interstitials

  1. Apr 7, 2013 #1
    I was just wondering why is it that the strengthening effect of interstitial carbon is different in FCC and BCC iron alloys. I can't figure this one out on my own so I thought I'd come to the place where the smart people hang out.

    Any opinions?
     
  2. jcsd
  3. Apr 8, 2013 #2

    Astronuc

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  4. Apr 8, 2013 #3
    What I meant to ask was which one would result in a more strengthened iron, C interstitials on BCC or FCC?
     
  5. Apr 9, 2013 #4
    I'm pretty sure that ferritic steels have higher yield stresses than austenitic steels anyway, so adding C would only increase it.
     
  6. Jun 2, 2013 #5
    "Plastic deformation proceeds in metals by a process known as 'slip', that is, by one layer or plane of atoms gliding over another (the motion of the dislocations).
    All metals of similar crystal structure slip on the same crystallographic planes and in the same crystallographic directions. Slip occurs when the shear stress resolved along these planes reaches a certain value —the critical resolved shear stress.
    This is a property of the material and does not depend upon the structure. The process of slip is facilitated by
    the presence of the metallic bond, since there is no need to break direct bonds between individual atoms as there is in co-valent or electro-valent structures." (Higgins, 1993)

    The carbon effect
    The carbon form an intertitial solid solution with Fe. These carbon in the solution tend to impede or stop the movement of the dislocation, so that a higher stress is required to allow the movement of dislocations, i.e., plastically deform the metal.

    So, if the phase austenite has a higher solubility limit for carbon (2.0%), it will be more resistant.
    Frequently ferrite phase is compared with Fe pure, cause it can absorb only 0.02%.
    And solid solutions are stronger than pure metals.
     
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