• BarqsHasBite@lemmy.world
    37·
    15 days ago

    Comment from imgur:

    Hardening the gears… pretty awesome. Oil cools the metal slightly slower than water so it helps avoid stress damage from the cooling process, but ends up a little bit less hard overall. The fire looks dramatic but it’s actually safer than steam from a water quench. We don’t have such good footage but the same technique was used for tanks in world war 2, which just looks bananas.

    Never underestimate thermal strain. So if that’s the reason, yeah.

    • ramble81@lemm.ee
      4·
      15 days ago

      So the slower the cooling, the less stress damags, but I’m sure there’s a curve where something like air cooling would damage it in a different way? I wonder what the best rate of cooling and medium is to facilitate it.

    • beastlykings@sh.itjust.works
      2·
      15 days ago

      Pulling from memory here, but doesn’t the oil also add carbon to the steel? Or affect the outer chemistry somehow? Aside from just cooling at a different rate

      • Pulptastic@midwest.socialEnglish
        9·
        15 days ago

        It could add a little but not significant. Not enough to counteract the decarburization from annealing in an air fired oven.

        Carburizing surrounds the metal with a carbon source and heats it for hours to get sufficient hard layer thickness. That typically is done in the anneal cycle before the quench shown in the video. High temperature austenitic steel has higher solubility of carbon and a proper quench will produce a fine mix of martensite and carbides. Tempering will precipitate more fine carbides in the martensite and reduce hardness a bit to prevent brittle failure. Sometimes the surface is then peened to build a thin surface layer of compressive stress to prevent crack initiation.