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Thread: The best heat treatment for Böhler K720 (~O2)

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    Senior Member gregg71's Avatar
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    Default The best heat treatment for Böhler K720 (~O2)

    Hi All,

    what do you experiences, what is the ideal quenching temperature for K720 or O2 steel to make razor? I have tried from 790 C (tempering 2x180 C). Not bad but a little bit soft and the edge is sensitive. Shaving well but maybe there is a better solution.

    I made braking tests and saw this steel has bigger grain sizes than O1. This is the reason why I choosed the lowest temperature.

    Thanks in advance for your help!
    Last edited by gregg71; 09-28-2016 at 09:09 AM.
    gregg

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    Senior Member blabbermouth Substance's Avatar
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    Bruno uses O2 a lot and may be able to add some useful info.
    I use O1 but my HT is 815C into 60c canola oil then 2 X 205C temp cycles
    No true HT tester but my RC files tell me it is in the 60RC range
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    to shave another day.

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    aka shooter74743 ScottGoodman's Avatar
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    I get my O2 from Bruno & was told to HT just as O1. It's worked fine for me.

    I HT by color & gas. Bruno is the guru on O2, Mike Blue may chime in too...you will never go wrong listening to either.
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    Senior Member gregg71's Avatar
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    Thank you guys for the quick answers. All information useful to me. I am waiting for the gurus.
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    gregg

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    aka shooter74743 ScottGoodman's Avatar
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    http://www.cashenblades.com/steel/o1.html

    I look at this guys site from time to time, good smith. Here is his info on O-1, IMO it's spot on for O-2. I use Parks 50 for my quench:

    O1 is one of the most commonly available tool steels and has been an industry standard for many decades. It possesses a high dimensional stability during heat treatment and is not particularly vulnerable to decarburization. O1 is a fairly deep hardening steel when quenched in oil and it is for this reason that it has too often been incorrectly recommended as a good beginner steel for knifemakers. While it will harden very easily, it is a richer alloy that requires more involved heating and soak times to unlock its full potential in the hardening operation. O1 can cost as much as three times the price as a simple high carbon blade steel which can easily reach their full potential in heat treatment with the simpler equipment most bladesmiths possess, thus making it the less economically prudent choice for many bladesmiths. If you have only a forge to heat treat with why pay extra for a steel that you may not get 100% out of? If however you have the equipment to soak at precise temperature for extended periods, O1 will most likely outperform any of the simpler steels in cutting applications.

    Recommended Working Sequence For O1

    Forging: Start forging at 1800 to 1950 °F (980 to 1065 °C). Do not forge below 1550 °F (845 °C)

    Normalizing: Heat to 1600 °F (870 °C). cool from temperature in still air.

    Annealing: Heat to 1400 to 1450 °F (760 to 790 °C). Use lower temperature for small sections and higher tem*perature for large sections. Cool at a maximum rate of 40 °F (22 °C) per hour. The maximum rate is not critical after cooling to below 1000 °F (540 °C). Typical annealed hardness, 183 to 212 HB

    Grinding or Machining

    Stress Relieving (optional): Heat to 1200 to 1250 °F (620 to 650 °C) Cool in air

    Hardening: Aus*tenitize at 1450 to 1500 °F (790 to 815 °C) for 10 to 30 min, then quench in oil. Quenched hardness, 63 to 65 HRC

    Tempering: Temper at 350 to 500 °F (175 to 260 °C)

    Polish

    The following tempering guidelines apply to O1 that has been soaked at temperature for a proper amount of time to achieve maximum hardness. Knifemakers using other methods will have to adjust the resulting hardness numbers downward for the same temperatures.



    Tempering Temperature Rockwell Hardness

    oC oF HRC

    149 300 65
    177 350 64-65
    204 400 62-63
    232 450 60-61
    260 500 59-60
    288 550 57-58
    316 600 55-57
    343 650 54-55

    *The above information is based upon personal experience and testing along with data from ASM International, Carpenter Steel and Crucible Service Centers.
    Northeastern Texas & Southeastern Oklahoma Mentor/Helper...PM me if I can assist you.
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    Admin & Forum fixer Bruno's Avatar
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    790 is borderline too low. I do 820 with a 5 min soak once it is at temperature. Quench in warm oil an temper for an hour and a half at 200 Celsius.

    That gives me splendid edges.

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    Thanks, Bruno! Than I will try to raise the temperature.
    gregg

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    Thanks, Bruno. It looks like we will be getting O2 over here in the future without having to buy a huge sheet from Bestar in Georgia and waiting to have it shipped from Germany. The damascus makers are psyched.

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    aka shooter74743 ScottGoodman's Avatar
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    Quote Originally Posted by JDM61 View Post
    Thanks, Bruno. It looks like we will be getting O2 over here in the future without having to buy a huge sheet from Bestar in Georgia and waiting to have it shipped from Germany. The damascus makers are psyched.
    WHo's going to make it or import it?
    Northeastern Texas & Southeastern Oklahoma Mentor/Helper...PM me if I can assist you.
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    Quote Originally Posted by ScottGoodman View Post
    WHo's going to make it or import it?
    a certain Italian-American gentleman from New Jersey

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