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Soak time for heat treating steel

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  • #31
    [QUOTE=dian;n1932171]oh, i completely forgot induction hardening.

    sometimes things happen that actually "should" not happen. its a special case with heating rates up to 1000°c/second and extremely fast quenching (cycle times can be as short as 5 seconds). not too many steels get induction hardened (4140, 4340, 1541 among others) and im led to believe that they somehow (!) lend themselves particularly well to this prozess.

    three things happen:

    - austenizing temp. increases by 100-300°c which considerably accelerates diffusion
    - extremely fine austenite grains form under these cicumstances facilitating transformation to martensite
    - retained austenite dereases dramaticaly at these cooling rates.

    which result in a hardness even several hrc points higher than conventional heat treat.

    besides, induction hardening is not really hardening, its rather heat treat, in the sence that the parts usually dont get tempered. you dont expect hrc 60 from the process, so that martensite transformation doesnt have to be "complete". its also important in which state the steel procesed: pherodized, annealed, normalized or hadened&tempered austenize/harden differently in ascending order.

    maybe somebody can explain better why it works.[/QUOTE

    Daang it!!!

    You mage me turn on the electric oven, Most folks dont kwow what 23-24k looks like .

    I do. "{ JR


    • #32
      Originally posted by JRouche View Post

      Yes. Wanna know why?

      You can heat it fast, it wiill burn.

      I can run the oven at 1600-2300df 24/7. JR

      -P.S> An electric oven at 2300 dregress is not sometyhin you play with.

      2200degress willmcook the meat on your arm in seconds,

      2300 of dry heat will fry yer skim. Dont do that .. I nhave gloves, and I always dis-arm the heatwer.


      • #33
        [QUOTE=dian;n1932380] yes, its all well and clear until parts start failing. then its not anymore.

        Man do I have some customer fail stories! Not for this thread though as I've diluted it enough. Vehicle recalls, big equipment breakages etc.


        • #34
          In a similar vein regarding HSLA steels, and yes there is an upper limit on hardness for each amount of alloying. Large truck frames are made of HSLA steel, and their strength does not depend on being forged, rolled, etc. Rather their strength depends on the trace alloy amount and heat treatment. Usually with a fairly low amount of carbon. This is why they are assembled with rivets (cold riveting with hydraulic) instead of welding -- there are very specific regulations about welding on a semi truck frame, in most cases the truck must be scrapped because it will no longer pass safety if it has been welded on.
          25 miles north of Buffalo NY, USA


          • #35
            you correctly say "trace alloy elements". while without those, often exotic (niobium, zirkonium) additions the precipitation strenghening would not be possible, the point is their tiny amounts and making them work by very specific and very controlled thermomechanical rolling and cooling strategies, often to achieve a bainitic structure. these simultaniously result in highest grain refinement (4µ austenite grains) and grain elongation/orientation. (grain boundary strenghtening is the only strenghtening mechanism that yields higher strenght and higher toughness.)

            often the processing equipment is not available (e.g. accelerated cooling), so the mill switches to additional alloying (e.g. molybdenum in truck frames), thereby partially defeating the purpose. of course there are many types of hsla steels and many are weldable.

            if you are interested i can see what i have bookmarked on this topic.
            Last edited by dian; 03-12-2021, 12:16 PM.