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Thread: Softening *HARD* steel?

  1. #1
    Happy Camper hcpookie's Avatar
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    Default Softening *HARD* steel?

    I made an attempt to start my home-built Saiga-12 muzzle brake last night. I didn't get very far.

    About 5 years ago, right when I first bought my mini-mill, I purchased a bunch of bar stock and round stock from a salvage metal yard. The steel had surface rust on it when I bought it.

    I chucked up one of the round ingots for the brake. The ingots are about 5" long, and measure 1.25" OD. I didn't realize that even after 5 years, the surface rust had not progressed.

    Using my trusty carbide cutters, I began facing the ingot to true it up. That's as far as I got. After the rust layer was removed, the nice shiny steel laughed at the carbie cutter that was trying to cut into it. All I managed to do was create a thin hair-like shaving that got orange-hot because the cutter wasn't doing anything but scraping, making heat.
    Sparks were flying! The 316 stainless steel I use to make pistons is like butter compared to this stuff!

    The metal looks more silvery than the "grey-white" I normally see on the softer 1018? that I usually cut on.

    The cuts are concentric and some of the ingots appear to have a centering dimple on the ends.

    I'm guessing something like the 4340 that I have? It looks closer to 4340 than any other steel I have in the shop. What could this be from? I have a whole bunch of ingots that I am not going to be able to use for anything but paper weights, considering how tough they are. Perhaps an automotive axle that was cut up...? Is it even suitable for machining? It could make some mighty fine rifle bolts...

    I'm afraid if it is 4300 steel (or worse) then I'm probably out of luck, because my tools simply can't handle this stuff. And that's too bad, because I have a bunch of it. I also have some HUGE rounds, one that is 8" diameter x about 8" tall. And quite a few 4" rounds.

    Any thoughts on how to make this easier to digest on the lathe? Different cutters perhaps?

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    pbdeh pbdeh's Avatar
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    Is it hard chromed shafting? If it is, the surface will just eat carbide tooling. The method I use to machine it is to take a deep enough cut to get under the surface
    approx. .100- .125". If it is just really hard steel I heat it cherry and then bury it in sand for the night - annnealing it enough to machine.

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    tired of idiots vz58's Avatar
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    If its 4130 you should still be able to turn it with carbide, I do it often. Now if its that hard try to anneal it like said above.

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    Where's my lathe? ashhoe's Avatar
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    Yup. Dig a big hole and line it with palm leaves. Stick a dead pig in it and add more leaves. Heat it as hot as you can get it and chuck them around the pig. Cover with sand and crack a few cold ones, poof, softened steel and dinner.
    member # 575

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    Gunco Veteran Lt762x39's Avatar
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    Pookie,

    Your steel might be inconell (not sure of the spelling ) but its way hard I remember seeing a speed and feed setting in tool post (CNC ) program. I would as an alternitive consider getting some diamond tipped tools (inserts the triangle shaped ones with a metalic mirror looking tip( borpax or cbn (artificial diamond) )
    those tools will cut anything except a diamond) Like this
    http://www1.mscdirect.com/CGI/GSDRVS...00000034852517
    or this one http://www1.mscdirect.com/CGI/GSDRVS...00000034852649

    this site covers your problem as a topic
    http://www.sciencedirect.com/science...46b4dcbbcef7eb

    another article about hard material cutting
    http://www.mmsonline.com/articles/010203.html

    and one more article
    http://ezinearticles.com/?Troublesho...ning&id=772036

    hope this helps

  6. #6
    Gunco Member FordGalaxy's Avatar
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    Default Annealing

    First its not inconel, inconel and monel are high heat corosion resisant alloys and it would not have rust on them.

    Carbide will cut most hardened tool steel and if the feed is consistant it leaves a nice shiney finish the catch is your machine has to have enough power to cut it and you need a fairly large radius on your cutter. Most tool steel can be annealed by heating to a red heat and very slowly letting it cool. I've done files in the BBQ by packing the coals around them and taking them out the next day. For pieces the size you describe your going to need a bucket of dry sand.
    Once you get the piece hot enough bury it in the dry sand you'll need about 4" all around the part to insulate it. and check it with a file the next day.
    The slower the cool the better.

    There are a few tool steels that requre more effort to soften but they're not to common.

    Even soft it's going to be hard on your tooling.
    have fun
    Ford

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    Happy Camper hcpookie's Avatar
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    Thanks for the info. I'm debating whether or not to use this or just let it be and buy more steel.

    Lt762x39 I can't get those MSC links to work, I get a "try your search again" page. Do you have part numbers?

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    Gunco Rookie MetalMan52's Avatar
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    The BIG problem with purchasing stock form a salvage yard is that they usually don't know what the hell they have. To them steel is steel, it pays the same. It is word of mouth and if the guy that sold it don't really know what he has, the myth gets perpetuated. When we buy metal from the local scrap yard we call it "mystery metal" and only use it for non critical applications no matter what the guy claims.
    If you happen to get some of the steels that are used in the upper 50 to low 60 Rockwell C range your carbide will not hold up to them. If your steel is case hardened or nitrided and you are taking relatively light cuts it will eat carbide alive.
    I wouldn't think that a muzzle brake wouldn't have to be made from all that great of a grade of steel. It would seem that 0-1, 4140 or even a case hardened steel would hold up just fine.
    Pat

  9. #9
    Gunco Veteran Lt762x39's Avatar
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    Pookie,

    In your search enter the search terms "CBN inserts" and you will get 8 pages of 30 items. And for the holders type in" insert holders" (lathe tools) and for end mills with replaceable inserts type in "indexable milling" Hope that helps ya Pookie.......

  10. #10
    Indian Admin Winn R's Avatar
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    Quote Originally Posted by MetalMan52
    If your steel is case hardened or nitrided and you are taking relatively light cuts it will eat carbide alive.
    Pat
    I was making some light cuts on a bolt and destroyed three good end mills before I gave up. Could it have been this?
    There is no nonsense so errant that it cannot be made the creed of the vast majority by adequate governmental action. -- Bertrand Russell


    "Never attribute to malice that which can be adequately explained by stupidity." Robert J. Hanlon

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