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From Reclaimed Metal

Discussion in 'Heat Treating' started by 4MDesigns, Dec 11, 2016.

  1. 4MDesigns

    4MDesigns New Member

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    Hello fellow makers and fellow beginners. This is my first venture in to knife making. I was given an old circular saw blade and decided to try and make a knife or three from it to start learning some of the process. I'll post pics of start to finish when it's done but I have a question for right now, and I couldn't find my answers searching here or google.

    This sawblade was most likely tempered steel. Based on how it resists being drilled and grinding. I'm done profiling it and I did an acceptable bevel (thin steel limits me from the size I'd like on this one) so before I attempt to go any further
    (tl;dr)
    I need to know if this has to be heat treated and if the process differs from that of stock steel. It didn't get annealed and it didn't get overly hot when I was cutting it out.

    Thanks
     
  2. dancom

    dancom Dust Maker Best Shop Tool

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    Dave,

    Generally hardened steel like saw blades will have to be annealed before working it. You really don't want to cut, drill or grind hardened steel as you will kill bits, kill blades and burn belts. Really, a frustrating waste.

    You want to soften or anneal the hardened steel before machining it. A typical example of annealing is to heat the steel in a forge or kiln until it is very hot and then cool it very slowly to make it workable. Make it red hot, 850 (1500°F) and then cool over a long period of time, say 15 to 24 hours. To slow the rate of cooling, most makers use a bucket of vermiculite or ashes for super-slow cooling. Remember the cooling can and should take hours. Once cooled, the steel will in a workable condition.

    I use my heat treatment oven, heat to critical and then switch it off and let the insulated fire bricks of the oven slow the cooling.

    Dan
     
  3. John Noon

    John Noon Well-Known Member

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    Circular saw blades can be a wide variety of steels from what I have found from 1080, 80crv2 and 75cr1 being the only ones worth heat treating for a knife. There are a couple more that escape me right now.

    Some are a very low carbon with lots of alloys for hardening but are not great for knives.
    Saws while hard to drill will be tempered back to high 40's or low 50's Rockwell C so as not to fracture during use. Heavy use like cold cutting concrete and steel will be the better steel over Chinese supplied home use skill saw.


    If you use a heat treating schedule for 1080 and get similar hardness you are on the right track. You may temper after and get unexpected results so testing is a good idea.
     
  4. 4MDesigns

    4MDesigns New Member

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    Good info, thank you. I didn't anneal it and so it did eat some carbide dremel bits, some cutting discs, and probably made a dent in the bench grinder and belt sander I ended up using to do the last parts. The dremel was taking so long that I waited a day to get on a band saw and finish the rough outline. My question originally was - if I didn't anneal it - do I have to heat treat it now? But I think I need to investigate the type of steel it could be to see if it's worth more time for treating, and additions like a bolster or if it will just be a cheap example/prototype sort of thing. I'd eventually like to take this shape to some stock steel but I'd want it thicker. I'll still finish it to some degree and post, I'm 60% done now anyway.
     
  5. John Noon

    John Noon Well-Known Member

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    Circular saw blades do to the work environment need to be tempered much softer than you would typically want for a knife so in reality it is best too anneal, work, normalize then quench and temper.
     
  6. Mythtaken

    Mythtaken Staff Member CKM Staff

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    I'm arriving late to the party, but yes, you do need to heat treat. Just by cutting, drilling, and grinding, you've introduced a lot of stress into the metal. You need to run it through a heat treat cycle to remove that stress.

    The saw blade may or may not be suitable steel for a knife, but as John has said, even if it is good steel, it has been heat treated to be a saw blade rather than a knife blade.
     
  7. 4MDesigns

    4MDesigns New Member

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    Thanks. I haven't had time to do anything with it yet. I'll see if I can figure out more about the metal, and take some more time to treat it (if it's worth it). Or I'll just slap a handle on it and keep it as an example/prototype of a shape I'd like to make from proper stock some day.
     
  8. John Noon

    John Noon Well-Known Member

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    Found out today 8670 is used in carbide tipped metal cutting saws
     
  9. 4MDesigns

    4MDesigns New Member

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    That could be alright as a knife, but certainly requires treating. Interesting. And I do believe this particular table saw blade has carbide tips.
     

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