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Heat Treating Results

Discussion in 'Heat Treating' started by krash-bang, Oct 18, 2016.

  1. krash-bang

    krash-bang Active Member

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    Hi everyone,

    I just finished heat treating a couple of blades using my Evenheat kiln. I'm still getting used to the unit and to the process itself. I have a few questions about my results that I would like to run by you.

    I heated the blades to 1950F and held them there for about an hour as per the recipe I had. I had the blades double wrapped in stainless steel foil. After quenching with aluminium plates, I noticed that the tool wrap was sticking to the blades. Some of it was really easy to remove but for some spots, I had to use a knife to scrape the foil off the blade. Also, and this is what's bugging me, where the foil stuck to the blade there were some discoloration where the foil stuck and where it wasn't touching the blade.

    [​IMG]

    [​IMG]


    When I started cleaning up my blades, I noticed some streaking on the blade as it got shinier. Almost as if water had dripped on it then dried off. I tried sanding it off by hand at first with increasingly coarser grit then I went to the grinder with a 320 belt and I tried not taking too much off but those streaks seem to go quite deep. I still can see the streaks in the blade but they're getting fainter, I think if I go deep enough they'll dissappear. However, my blade is getting thin and I haven't started on the other side yet.

    I'm wondering if those streaks aren't like a light hamon caused by some difference in the speed at wich the blade quenched since the foil was stuck to the blade and the little streaks are where the foil wasn't touching the blade.

    My plan right now it to grind that off but I'm a little worried that I'll end up with my blades too thin. The other option it to start over but I really hate that option having put so much effort into these.

    Any ideas on how to avoid the tool wrap sticking to the blades and if this ever happened to you, is there a quick fix (I know, I'm dreaming) to get those streaks off my blades?

    Thanks
     
  2. John Noon

    John Noon Well-Known Member

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    Only reason for sticking that I am aware of is using a lower temperature rated foil wrap
    309 foil wrap temperature 2240F
    321 foil wrap temperature 2000F

    Looks like you had something on the blades?
    Did you place a piece of paper inside the envelope to burn of the oxygen?
     
  3. dancom

    dancom Dust Maker Best Shop Tool

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    Hi Serge,

    I am not sure what steel you are using, but I'll assume something like 154CM. The hold time seems a bit long. Not sure if that would have any ill effects. I would normally hold at soak temp for around 15 to 30 minutes for blades.

    When I was using foil in the past there was always some minor oxidization patterns on the surface of the steel. Normally these would sand out quite easily. In some cases a rainbow effect appears on the steel (see photo). Again, light sanding removed this as it was only on the surface. The foil I used was 304 and never had any major issues. What kind of pressure are you applying with the plates? I used about 20 or 30 lbs. Not like cranking the vise down on it like I see some guys doing. Enough to contact and draw the heat out.

    You can see an area top of the ricasso where the foil left some impression. This CPM154, 15 minutes in the oven at 1050°C in a 304 foil envelope. I recall the envelope ballooned a little, meaning it was well sealed.
    [​IMG]

    I did a few hardenings with a small scrap of tissue inside the envelope and many without. The only difference I could see was a char mark where the tissue burned so I stopped doing that. The oxygen inside the envelope is limited and once consumed there should be no more coming in.

    Nowadays, I do the heat treat after profiling and grind the bevels after heat treat. That way surface crap is all ground away. And if plate quenching, the two main surfaces are fully and evenly in contact with the plates.

    So far I have failed at several attempts to create any kind hamon with air hardened steel. It's just way too slow.

    I guess at this stage you're best to keep cleaning up the blades. Do you have a picture of what it looks like after some grinding? Are the lines working through the steel? Are they different shades of grey, light /dark? etc. Maybe there is something is the steel itself?

    Dan
     
  4. John Noon

    John Noon Well-Known Member

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    Maximum temperatures for Foil wrap,

    304 is 1800°F
    321 is 2000°F
    309 is 2240°F

    not important anymore for this thread just add on info for future searches
     
  5. krash-bang

    krash-bang Active Member

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    It was two layers of 309 foil wrap with no paper inside. Some say it's good while others say it doesn't matter so I tried without.
     
  6. dancom

    dancom Dust Maker Best Shop Tool

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    Thanks John,

    I never had any issues with 304 tool wrap around the 1080°C mark. 304 melts above 1400°C. My rationale was if it isn't melting, it's still doing its job.

    I asked Ray Rogers this exact question a few years back and replied "if it ain't broke, don't fix it."

    :whistling

    Dan
     
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  7. krash-bang

    krash-bang Active Member

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    The steel was CPM 154. All the blades I ever sent Rob came back like the one in your picture and you're right, it's easy to clean up. I was sort of expecting a similar result as the recipe I was using is was the one he sent me with the kiln. I've never had any issues with his heat treat so I figured I'd try that.

    I used a couple of 25lb barbellss as weight on the plates.

    It seemed to me that the foil was up tight against the blade when they came out of the oven. I noticed because my previous attempt had ballooned my envelope. I had used a piece of paper inside the enveloppe, maybe too big. Anyway my seal broke and the blade came out black. This is why I tried double wrapping and no paper.

    I'll get a picture when I start on the other side when it shows real bad. The discoloration seems to go into the steel, I'll try to measure how much I'll have to take off on the other side.
     
  8. John Noon

    John Noon Well-Known Member

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    I learned it does not take much paper, a full wrap of paper covered the blade in carbon. Of course carbon is an insulator or something because after plate quench they were soft. Pretty sure it only takes a tiny bit of paper to work properly, next time trying just a thumb sized chunk.
    Have read mention of a small wood chip as well but never tried.
    Next day or so I will be doing 154CM and probably foil wrapped since the anti-scaling paint I bought seems to blow off in the furnace. Any weirdness and I will post pictures.

    Found your answer. posting with tags for future searches. On the second post near the end, another one mentions the nice hues and stuff do not have to be removed for tooling like cutters as it holds lubricant.

    Sounds like a good reason to keep the color on the knife beside looking nice it is functional.
     
    Last edited: Oct 19, 2016
  9. John Noon

    John Noon Well-Known Member

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    Why does the Tool Wrap stick to a tool, die or part after heat treating?
    At higher temperatures the Tool Wrap may adhere or weld to the piece during hardening. This is usually caused by excessively tight wrapping, uneven support of the work surface such as a heat treating basket or mesh, or oil or residue left on the metal surface. Alternatively, if the part is “clean”, loosely wrapped and smooth work support surfaces are used and this still results in sticking, a liberal dusting of aluminum oxide or magnesium oxide eliminates this problem. Again, it is strongly recommended that before using this material for the first time that a limited amount of experimental work be undertaken.
     
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  10. krash-bang

    krash-bang Active Member

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    I'll have to admit that my wrapping was quite tight, no more then a 1/4" slack on both sides, a little more at the ends. I cleaned the blades with acetone before wrapping.
     
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  11. krash-bang

    krash-bang Active Member

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    I started on the other side this morning. Took a before pic.

    [​IMG]

    The lighter parts is where the foil was up against the blade and the darker areas are where the foil wasn't touching.

    I started with 400 grit then went to 600 until no more scratches from previous grit and you can see it when you hold it against the light. It shows more as you go finer in grit.

    [​IMG]

    I'll go to the grinder like I did on the other side then finish by hand. I just hope my blade doesn't get too thin.
     

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