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  • Metal Hardning process.

    Anyone have advice or experience on how to harden mild steel for my projects? I do not have a need yet, just want to be able to do it.
    It's not an optical illusion...it just looks like one

  • #2
    Al,

    I once had a professional blacksmith teach me the basics of tempering. It is pretty much a hands on type of thing. I can make and temper a cold chisel pretty good, but I'm not sure about trying to explain it here. What type of things are you looking to do? Maybe I can touch on some of the basics if this is what you had in mind. Let me know.
    Arbo & Thor (The Junkyard Dog)
    The Next Loud Noise You Hear Is Me!

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    • #3
      The basic process is to heat the steel to a minimum temperature then cool it fast enough to lock it into a particular grain structure. This makes an extremely hard but brittle steel that must then be tempered by bringing it back up to a tempering temperature. The temperatures depend on the type of steel and the desired final hardness. You can quench in oil, air, or water depending on the rate of cooling that is required...

      There is a minimum carbon content required for through hardening steel. For example 1018/1020 type steels can only be case hardened because they don't have enough carbon content to through harden.

      This is also why the alloy steels require extra steps for welding. They can be locally heat treated during the welding process, leaving hard, brittle sections.

      Try searching the internet for info. There are good explanations there and in books like Machinery's Handbook.

      The cold chisel is a good example. You heat the shank and edge then quench the edge end. Pull the chisel out of the quench and watch the edge change colors as the heat from the unquenched section soaks out to the edge. When it gets to the correct color (associated with the tempering temperature) then quench it again.

      Heat treating is both an art and science. Have Fun!
      Bill C
      "The more I learn about welding the more I find there is to learn..."

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      • #4
        Arbo,
        I would like to know about the basics of tempering. What it does to metal, how to control it and test it. There must be a couple of links on the subject.

        How a knife edge is tempered while the body is made softer to support the edge. General knowledge stuff is what I need.
        It's not an optical illusion...it just looks like one

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        • #5
          Thanks BillC,
          I give that a try. I knew there were some easy experiments.

          I found a link, it was quite informative:
          http://easyweb.easynet.co.uk/~chrish/t-ht.htm
          It's not an optical illusion...it just looks like one

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          • #6
            Originally posted by BillC
            <<SNIP>>
            There is a minimum carbon content required for through hardening steel. For example 1018/1020 type steels can only be case hardened because they don't have enough carbon content to through harden.
            <<SNIP>>
            Just to clarify, case hardening involves adding carbon to the surface of the steel. The increased carbon content of the case is what allows the otherwise low carbon steel to be hardened.
            Bill C
            "The more I learn about welding the more I find there is to learn..."

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            • #7
              Originally posted by Al T.
              Thanks BillC,
              I give that a try. I knew there were some easy experiments.

              I found a link, it was quite informative:
              http://easyweb.easynet.co.uk/~chrish/t-ht.htm
              You are welcome, Al! I read through the link and while its not all perfectly technically correct, it certainly is close enough.

              If you want something relatively cheap to play with buy some old automotive leaf springs from the local junkyard. Leaf springs have a high carbon content and should be easily hardenable. They are great material for homemade knives.

              They are probably too hard to play with as purchased, so you can anneal them by heating them up (red) and letting them cool slowly. After you cut and machine them you can harden and temper them.
              Bill C
              "The more I learn about welding the more I find there is to learn..."

              Comment


              • #8
                I foud a usefull site that give the proper tempretures hardening/annealing and more for lots of metals

                http://www.suppliersonline.com/Resea...erty/step1.asp

                I have a friend who makes Axe's and swords for SCA and other rennasance activities..

                Latey he's been making Axes from 4340 and quenching them in Olive oil.. Aparently it's been working well. His new ones will take a big chunk out of a mild steel blade without nicking the edge much at all.

                Not much welding involved but it's still interesting metal work.
                Scott Schering
                http://www.pontiacs.org

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                • #9
                  For case hardening, there is a product made in granular form, comes in a can, that you heat up your part to a cherry, dip it in and heat it again, then cool it in oil or water. You keep repeating the process till you achieve the hardness you want. BillC is right, it is an art form. As with welding, it takes lots of practice. If you are doing knife blades, you have to be careful...it can be so brittle it will snap on ya.

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                  • #10
                    G'Day Al,

                    Your original question was about hardening MILD STEEL.

                    Yes, you can harden mild steel. It's very easy and quite effective. Just heat it to cherry red and quench immediately in cold water.

                    No need for any tempering because it's not hard enough to be brittle, but it is a lot harder, tougher than before. It's not tool steel quality, but I sure have found it useful. Particularly good for the edges of earth digging tools.

                    Try it on one end of a piece of 1/8" mild steel flat and then compare filing and bending to the other end to feel the differnce.

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                    • #11
                      Thankyou for all the advice and links. I think I'm dangerous now. I'll keep everyone updated as my projects march on.
                      Last edited by Al T.; 01-13-2003, 01:55 PM.
                      It's not an optical illusion...it just looks like one

                      Comment


                      • #12
                        case hardening

                        I've done some amateur blacksmithing. To case harden, I heat low carbon steel to yellow heat using a reducing fire, then rub off the scale with an abrasive stone and dip the hot tool in finely powdered potassium ferrocyanide and return it to the fire. Repeat three times, then quench in acidic water. The scale blows off in the water, leaving a silvery white surface. This case hardened layer is very thin, like an eggshell, but harder than a file. High carbon steel is so cheap and plentiful in junkyards that this process really isn't worth the trouble.
                        There was a man in my area who forge welded cast iron pieces to the tips of plowshares. I still use a little 2 bottom with these tips, which have long outlasted the steel shares.
                        chasin' the $

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                        • #13
                          case hardening

                          Heat to yellow heat in a reducing fire, then rub off the scale with an abrasive stone then dip in powdered potassium ferrocyanide. Repeat process three times, then quench in acidic water. Upon quenching, the scale will blow off, leaving a silvery white surface. This layer is as thin as an eggshell but harder than a file. My grandfather used to hire a man to weld cast iron tips on plowshares, and these tips long outlasted the tough steel shares. I still plow with a little two bottom today.
                          chasin' the $

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                          • #14
                            tempering

                            Flynsparx:

                            A lot of Asian manufactured tools are made of decent steel that is sold in the annealed condition for some reason. I once bought a Chinese copy M14 rifle like this. I also bought a bunch of Chinese pocketknives that were the same. Hit 'em with a grinding wheel and look at the sparks.
                            chasin' the $

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