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Heat Treating O-1 - Not sure if it went so well!

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  • Heat Treating O-1 - Not sure if it went so well!

    Related to my profile-cutter post (https://bbs.homeshopmachinist.net/fo...ter-for-delrin) I'm looking for feedback on my broken heat treated O-1 profile tool. The attached picture shows the broken 5/8" x 1" x 5-1/2" long O-1 cutter. I believe that it failed (cutting Delrin) because of improper geometry. But, I'm wondering if anyone has any feedback regarding the crystalline-looking area exposed where the tool broke. Does anyone spot any issues with my heat treating?

    After machining, the part was heated slowly (in a digitally-controlled PID heat-treat oven) from ambient temperature up to 1200 degree Fahrenheit (60 minute ramp time). It was the heated to 1450 over the next 30 minutes and then held at 1450 for 15 minutes. It was then quenched in 11-second quenching oil from McMaster-Carr and tempered for 2 hours at 350 degrees.

    Not sure if there are any defects in the heat treating and am interested if anyone spots something in the photo. Specifically, is this what it should look like after a failure?

    There were two potential process shortcomings:

    1) My tempering oven is my heat treat oven so the piece sat in the warm quenching oil for approximately 90 minutes while the oven cooled down enough to reset and use as a tempering oven; and

    2) There was a tremendous amount of scale formed on the part which I understand is carbon which I'm guessing would weaken the part. I've rectified this issue by ordering some Brownells anti-scale coating for the next cutter. (https://www.brownells.com/gunsmith-t...076-49084.aspx)

    Again, any thoughts on how I might improve my heat treating?







    Picture above shows similarly shaped (and also failed!) profile cutter. This is what the side view of the broken O-1 cutter looked like before the break.


  • #2
    Was it straw colored after tempering? 350 doesn't seem hot enough for tempering, more like 500.

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    • #3
      I have made a few punches for punching machines out of O 1. Using only a Bernzomatic torch.. 5 minutes to harden and temper... can't recall any breakage.

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      • #4
        I've broken a couple of bits of O1 because I didn't temper it afterwards. Snapped in a heart beat. Maybe try 300deg in your toaster oven?

        Not sure about this either, but I seem to recall reading somewhere that the piece should go in the tempering oven straight after quenching and not be allowed to cool to RT. Don't know about that, but might be worth looking into.

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        • #5
          2 hours tempering time?
          The usual formula is 1 hr per inch of thickness.

          My other thought is the HT oven used for tempering... I use my kitchen oven because those lower temperatures are iffy in an oven meant to go well above.

          In my experience, cooling to room temperature never negatively affects my results. Perhaps clean thoroughly before HT and encase in SS foil with a slip of paper? That's what I do. The paper consumes the oxygen by burning up and very little scale results.

          Seems to be off if delrin snapped it. Heat build-up on O1 is a big problem... but with delrin?? It sounds like the tempering didn't take. Very very hard = brittle. Most likely the case here.
          Last edited by MyrtleLake; 09-21-2020, 02:54 PM.

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          • #6
            Just looked it up...
            Lathe tools 200-220 Celcius
            = 395-430 Fahrenheit

            Too low a temper?
            Last edited by MyrtleLake; 09-21-2020, 03:04 PM.

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            • #7
              X2 I would have tempered in the kitchen oven at about 400 - 450 F for an hour, directly after quenching. Make sure to clean off *all* of the oil first if you are married....

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              • #8
                It should be 1500 Degrees F., not 1450. It probably didn't form the Austenite correctly. Everything else looks about right. You want to keep it in the quenching oil at least till it gets below 200 F., Hold it vertically, and move it up and down to keep from having hot spots in the quenching medium.

                A broken part will always look crystalline to some extent.
                Last edited by Toolguy; 09-21-2020, 03:23 PM.
                Kansas City area

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                • #9
                  The large grain structure needs to be reduced through normalizing. Rough rule of thumb is normalize three times before quenching. See slide 18:
                  https://www.slideshare.net/thiru1mec...ansformation-1

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                  • #10
                    Looks like really coarse grain structure. Most often result of overheating the material at some point.
                    Assuming you didnt grossly overheat the part where did you buy the material? Known manufacturer or just O-1?

                    Normalization should help as previously mentioned but I wouldnt expect this coarse looking result from decent supplier.
                    Location: Helsinki, Finland, Europe

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                    • #11
                      Originally posted by MattiJ View Post
                      Looks like really coarse grain structure. Most often result of overheating the material at some point.
                      Assuming you didnt grossly overheat the part where did you buy the material? Known manufacturer or just O-1?

                      Normalization should help as previously mentioned but I wouldnt expect this coarse looking result from decent supplier.
                      I’m with you on this one matti. Process looks good but what I see is an overheated large grain structure.

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                      • #12
                        Grain size is way large, personally I'm looking at that ramp and soak time. O1 doesn't need much of either, and heating for too long like that can do some funky things. Now, soak time is needed for larger pieces, but for anything below about 1/2" at it's thickest you can pop in a preheated furnace, bring it up to temp and quench immediately.

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                        • #13
                          I believe that normalizing is only an issue if the item were forged. For stock annealed O-1 that you cut, machine and file straight to heat and quench then temper.

                          And yeah, light straw needs to be more like 400F to 420F 450F gives more like a medium brown.... at least it does from my toaster oven.
                          Chilliwack BC, Canada

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                          • #14
                            As has been said, tempering temps are probably too low - where did you get 350 from? I say probably as the amount of tempering achieved is a function of both time and temp, you'd have to look up a chart. You can sit at a low temp and get a temper normally associated with a high colour, but it takes a long time. There's about zero chance sitting in the warm oil effected things

                            I've seen normalizing make a big difference but not in my experience with new O1. If re purposing something, like say a file, its pretty much required.

                            I've made many tools over years, and while I've got the PID controlled oven so can do things that way, I don't find that long process necessary for an O1 tool. Heat at the bench for a 5 minutes, plunge into a can of old oil, polish up a bit and very slowly heat until you get the desired colour. It may be a few percent less than perfect but i'm working again in 15 minutes, and scale is a minimal issue. My point of mentioning this is that its not that fussy if you get the basics right; decent quality known steel, get up to the right temp,. quench and temper to the right temp. I retry at the bench getting it up to a pale yellow, say 450F.
                            in Toronto Ontario - where are you?

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                            • #15
                              Originally posted by 754 View Post
                              I have made a few punches for punching machines out of O 1. Using only a Bernzomatic torch.. 5 minutes to harden and temper... can't recall any breakage.
                              A propane torch will work for smaller parts but it becomes difficult to impossible to evenly heat and hold the temp on larger parts. Sounds like the OP reached maximum hardness of the 01 but didn't draw it back. Uneven quench maybe?? I always temper the part in the oven at 350 deg. for about an hour until I get that straw color.

                              JL................

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