8740/8620 heat treat process inquiry
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  1. #1
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    Default 8740/8620 heat treat process inquiry

    I have a part that needs heat treat, I originally sent it out but it came back as the heat treater could not get to it in time. It is now on me to get the parts done in time for the hard drop-dead timeframe. The part is just shy of a 6" OD ring that is 5" long, the ID at the smallest is 4.5" The thickest cross section is 1.35". There are .1 fillets on the two internal corners to reduce the chance of cracking. I need to harden the piece to about 50hRc just on the ID of the two opposing sides. I was hoping that someone out there would have some experience with heat treating this type of material. I have one piece that is 8740, the second piece was made from 8620. The second piece is just a spare in case the first develops problems. There is .025" that needs to come off the ID to bring the part to size. So question, who has or can recommend a process to HT these parts to the appx 50hRc? I am going to be borrowing time on a local oven that is an controlled HT oven, there is oil for quenching, water for quenching if I need it.

    gauge-1.jpggauge-2.jpggauge-3.jpg

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    I would try another heat treater before attempting it myself. Bodycote has a lot of facilities. One in Los Angeles. Pack hardening may take several attempts to get it acceptable. In the end you will not get the depth of the case that someone who does for a living gets.

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    Just my guess. The heat treater didn't send them back because he didn't have the time..

    He sent them back because "This isn't going to be my fault"..

    25 thou.. You made scrap. That shit is going to twist up like a pretzel.
    You *might* be lucky.. but odds are that you won't..

    In something like that I'd give it .100" all around maybe more, and I would make a basic donut.
    Keep the wall thickness consistent. This isn't a little tiny thing, and its TUBE shaped, and
    its LONG.. I would have sent it back too.

    Make some new ones quick, I will 98.734% guarantee you that if you heat treat the ones you have,
    you won't be able to clean them up.. They will pretzel out of size.

    Sounds like you found a smart heat treater.. Not a 100% honest one, but smart. Though I do give him/her?
    credit for letting you down easy. They could have just said what I did... And you didn't want to hear that,
    I wouldn't have.

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    Quote Originally Posted by Bobw View Post
    Just my guess. The heat treater didn't send them back because he didn't have the time..

    He sent them back because "This isn't going to be my fault"..

    25 thou.. You made scrap. That shit is going to twist up like a pretzel.
    You *might* be lucky.. but odds are that you won't..

    In something like that I'd give it .100" all around maybe more, and I would make a basic donut.
    Keep the wall thickness consistent. This isn't a little tiny thing, and its TUBE shaped, and
    its LONG.. I would have sent it back too.

    Make some new ones quick, I will 98.734% guarantee you that if you heat treat the ones you have,
    you won't be able to clean them up.. They will pretzel out of size.

    Sounds like you found a smart heat treater.. Not a 100% honest one, but smart. Though I do give him/her?
    credit for letting you down easy. They could have just said what I did... And you didn't want to hear that,
    I wouldn't have.
    Well if it’s 8620 sounds like he will be case hardening it.

    Seems like you aren’t going to get that thick of a case.

    How about getting closer to size and carbonitriding


    I have some parts that I want to case harden around here aswell and I had good luck on some samples but haven’t done to many tests.

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    The 8740 is a direct hardening (quench and temper) steel, the 8620 is a carburizing steel- The part looks pretty symmetrical, so I would not expect much warp, but it is going to probably shrink a bit. You are in CA- PM me if you need a heat treater. Those are small enough to mail or UPS. On the 8620 one, you are going to have to specify a case depth. If you are .025 small now, I would imagine you would want .030-0.40 case. Getting 50 Rc should not be a problem for either one.

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    I only saw 8620, sorry. Would expect 8740 to be direct hardening, confirmed by Dan. Some direct hardening allows are tricky, no experience or knowledge on this one.

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    Two totally different materials, too much left in the bore, no specs/strange specs on hardness, and can't find a heat treater in a state that has dozens, wants to do it himself ?

    No wonder the first guy passed.

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    8740 is direct hardening as Dan had said. The 8620 is just a test piece to see how the carburizing will compare to the heat treat for cost per process. This is not the first time that I have had to make a gauge like this last minute out of this material. I was curious what the cost comparison would be to carburize to a case depth of roughly .05-.065, versus the cost to quench to desired 50hRc.

    The gauge just needs to be hardened to match the part that it is used against and I don't post specifics on my parts for a reason (things such as specs for surface finish, heat treat, dimension, etc) they are between the person I am doing the work for and myself. Even the drawing that I post has been modified enough to preserve the NDA. Unless I get approval to release "through inquiry" specifics about the parts I keep it to myself. Nothing like loosing work because I breech an NDA indirectly to satisfy the forums.


    @Dan From Oakland: If the shipping time up and back wasn't a problem I would just send it up to you. I need this finish ground and out the door by Wed. I will keep you in mind as down here by me there doesn't seem to be anyone that can do quick turn around, or will do one off parts without breaking the budget. This isn't the first time I am facing this type of issue, finding heat treaters that can do and know what they are doing in the area. The last time I sent parts out to one of the quick turn around places I got un-tempered parts back. Those parts went in the scrap bin after I tried to grind the first part. I am going to look for an oven at some point, but for now I just don't have the room.

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    Sshep71, your wording makes me skeptical that you can heat treat this yourself. Your material says the part will be quench and tempered. Quenching is always the same. Heat the part to austenizing temp (1450-1650F)and rapidly cool in water or oil. This sets the microstructure. I would recommend checking as-quenched hardness to evaluate the adequacy of the quench.

    The second process is tempering where ductility provided and hardness is achieved.
    Rc50? You have to think about how and where you will measure this. The ends seem to be the likely place, but only if you know your quench was good. 500F would be a good place to start.

    In any event you will need to introduce the part into the quench axially and either move the part or the quenchant axially to the part to minimize distortion. Press quenching can eliminate a lot of distortion also This is where you restrain the part from distorting before it is lowered in the quench but still allowing the quenchant flow through it.

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    To the OP- I was simply going to point you to our heat treater, not process your parts. Good luck with the job.

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    Quote Originally Posted by SShep71 View Post
    not the first time that I have had to make a gauge like this last minute.....
    .

    The gauge just needs to be hardened to match the part that it is used against
    .....
    I need this finish ground and out the door by Wed.
    So remove the guesswork. If it is dimensionally STABLE, as-had?

    Finish grind it, Allow a micron or three for plating, and hard-chrome the sumbich. Or Cobalt.

    You said "gauge". More than once.

    Measuring device. Not structurally loaded or movement-wear component.

    How much TIME do you need this b**h to buy for you to give you time to do it over a better way than "Wednesday"?

    You think hard chrome on Ordnance steel is overly fragile?

    See chamber & bore, "Avtomat Kalashnikova".

    About as close to idiot-proof as ever was.. even with worser and worser idiots involved every passing year.

    Not ALL of them on the field of battle...

    Go figure there was ever any sort of "patent" on that...


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    a gage? why this steel? because you had it around? with 0.6% carbon you might try a marquench, but 8740 might even be hard to get to 50 hrc if is happens to be on the low side of the specs.

    both of your steels are being used for case hardening.

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    How long does hard chrome plating take? If that's an option, grind or turn the parts a little oversize, get them plated, then grind to spec.

    Hell, since I'm going full-tard here, what about turning oversize, epoxying some 1095 shim stock in the bores, then grind that? McM 1095 shim is RC48 min, so some .025" cut to a butt length, take .005" a side to finish diameter.

    Then tell the customer "That's the way it came from the heat-treaters".



    [Dammit, I have Termite on block because I only have a few decades left to live so prefer to avoid his language buggery. But this time I figured he might dribble out something of use, and yup, he mentioned hard chrome first. Oh well, I can claim the shim hack for myself...]

  14. Likes Dan from Oakland liked this post

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