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Hardness for Sear Surfaces

Discussion in 'Gunsmithing and Repairs' started by Johnm1, Jul 12, 2020.

  1. Johnm1

    Johnm1 Member

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    Thanks for the encouragement. I do need to temper my enthusiasm with my limited skills. Especially in diagnosis. I believe everything I have done to the little .25 could have been avoided had I diagnosed the real problem initially. I saw that the pin on the back of the trigger wasn't making enough contact to reliably trigger the sear. Assuming that surface was worn I went down the path of adding material to that surface. I believe that had I replaced the pivot pin the problem would have been resolved.

    When I'm done, I plan to put what I have learned about each firearm in writing. Not for the Gunsmith audience, but for the person who wants to know how his gun works. Because I won't have gained enough knowledge to be a gunsmith resource these would just give a general outline of function and what I have learned about weak points. The little H&R just doesn't have enough written about it. I suspect because there just weren't that many made and the audience isn't there.

    I have done/are doing similar things with a Savage 1907 pistol in .380 and a Marlin 1892 in .32 Colt that I'm still working on. I have learned a lot that isn't written about them that I'd like to share.
     
  2. Blue68f100

    Blue68f100 Member

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    You can get a PID controller kit for ~ $25 on ebay. Then all you need to do is set your desire temp and let it do it's thing. As to hooking up to the kilm, it all depends if yours 220v 1ph as I expect due to current draw. Just put the solid state relay (SCR) on 1 of the power lines. Need to have a SCR rated to take the full current load, to keep from burning them up. Most have a auto tune feature that should get you close enough on your control temp. I normally self tune after the auto tune to minimize and temp swings, I like ±1° F control if I can get it. Most all cases I can but depends on the accuracy of the sensor being used.
     
  3. Johnm1

    Johnm1 Member

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    Not the case here. It is 110 volt, small, and definitely meant for the jewel's market. Although I don't mind spending a few dollars for temperature control the thermocouple/thermometer due to arrive on Monday do not have an output. I may not be able to control the temperature well enough just by monitoring it and manually adjusting. But when the thermocouple/thermometer arrive on Monday I'll test to see if I can.
     
  4. Blue68f100

    Blue68f100 Member

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    Most on/off type thermometers have a on/off span of ~25F, some more, some less. With a PID it ramps up and shuts off and coast to temp (slightly over shoot) then starts cycling the output to maintain temp. Depending on response of the heat less than a sec cycle time. For real high temp it takes a special TC, I believe a type K will cover your needs. I've use Platinum/Platinum Rd for extreme high temp, these are very expensive.
     
  5. Johnm1

    Johnm1 Member

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    We will have to see what both the kiln and the thermocouple/thermometer are capable of doing. If the equipment is capable of measuring temperature accurately and the kiln responds quickly enough, it will be me making those adjustments, not the PID loop. I'm not sure any of this is going to work but won't know until after Monday when the thermocouple/thermometer arrive and I can test.

    Thanks for the information.
     
  6. David Hoback

    David Hoback Member

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    His jewelers Kiln already has presets. To use a PID would be rewiring his kiln, and he would STILL need a thermocouple. Using a PID is for building your own Kiln.

    John, all you need is a thermocouple. I’m guessing your kiln has maybe 4...5 “presets” for temp control, right?
     
  7. Blue68f100

    Blue68f100 Member

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    Not necessarily, If he set the onboard controller to max he could control the power on/off to the Kiln.

    The only Kiln I seen had a cone that was installed to control the temp, but this was for porcelain/ceramic. It melted and shutoff the kiln when temp was reached for a period.
     
  8. Johnm1

    Johnm1 Member

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    Actually it has 7 presets. Low, high, and off have distinct places they 'lock in'. There are not stops between 2 and high. The placard on the unit indicates that 4 is 1200 degrees and not to exceed 1900 degrees. At this point all I know is that it heats and gets to a temperature and then the heating coils cycle on and off. I cannot find anything on the internet about the kiln or even the company that made it. I'll have to figure a way to mount the thermocouple through the lid or side. The circular opening is less than 2" in diameter, so the thermocouple will take a substantial portion of the available volume. The unit is probably older than I am. Lord knows if this is going to work. Here are some photographs of the unit.

    IMG_2223.JPG
    IMG_2224.JPG
    IMG_2225.JPG
    IMG_2226.JPG
     
  9. Blue68f100

    Blue68f100 Member

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    A type K is good for ~2450F, these can be just exposed wire ends connected to being a SS sheath, 1/16" and up. Most are around 24ga wire so it's fairly small, the glass insulation takes most of the space up. I have a special welder for making them up. All I need is just the wire, I twist them together and strike a ark to melt them into a small ball. In a pinch you can just twist them together tight ( smash with a hammer to make tight) and use as it.
     
  10. Johnm1

    Johnm1 Member

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    Here is the thermocouple/thermometer I have on the way. It will arrive on Monday.

    http://www.meter-depot.com/k-type-thermometer-w-high-temperature-ceramic-probe-furnace-kiln-cr-7/

    Thermocouple.JPG

    Scientific K-type Thermometer DM6801A+ With High Temperature K-Type Sensor CR-2 Measures -500 to 1999.0 °F (-50.0 to 1300.0 °C)

    This is a brand new, high quality K-type thermometer for high temperature measurements. It has one input for K-type thermocouples and can display the temperature up to 1999 degree F or 1300 degree C.
     
  11. Jim Watson

    Jim Watson Member

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    Suggest you heat some odd pieces of steel and not make your gun part the first job.
     
  12. Johnm1

    Johnm1 Member

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    Sage advice. I'll have to test the kiln for temperature and see if I can keep it at a steady temperature using the dial controls. If I can't, this will be all for nothing. David is sending me some tool steel scraps so I can practice both shaping and hardening. I'm not sure I have the skills to shape the tool steel, even though it is annealed, and create the shape I need. I think I will be able to, but I have to know first. So a lot can happen to kill this brilliant idea.

    Someone(s) had suggest mild steel and Kasenit for surface hardening. If this experiment fails, there will be another thread on Kasenit.
     
  13. Jim Watson

    Jim Watson Member

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    I mentioned your project to FLG.
    He suggested the Stressproof steel sold by Brownells. Use as is.
     
  14. Johnm1

    Johnm1 Member

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    I did a search on Brownells website and couldn't find anything with the word 'Stressproof'. I did find stressproof steel under the heading of stressproof at McMaster-Carr.

    High-Strength Easy-to-Machine 1144 Carbon Steel Rods
    8888k101p1-j01-digital@halfx_637062404234677299.png

    • Yield Strength: 100,000 psi
    • Hardness:
      Inch sizes: Rockwell C25 (Hard)
      Metric sizes: Rockwell C15 (Medium)
    • Heat Treatable: Yes
    • Max. Hardness After Heat Treatment: Not Rated
    Often called Stressproof, these rods are stress-relieved to minimize warping during machining. Containing more carbon and manganese than other easy-to-machine carbon steels, 1144 offers higher yield strength and hardness, even without further heat treatment. Use it to fabricate parts that require stress resistance.

    So, is a C25 hard enough for a sear surface?
     
  15. Johnm1

    Johnm1 Member

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    There is a version of 1144 that reaches a Rockwell C of 30. https://www.mcmaster.com/stress-proof-steel/

    Ultra-Strength Easy-to-Machine 1144 Carbon Steel Rods

    Apparently 1144 can be hardened but I haven't found much on it. McMaster-Carr indicates it is not rated but MatWeb indicates hardening temperatures but no resulting hardness.

    MatWeb http://www.matweb.com/search/datasheet.aspx?MatGUID=8d6de85fc0204269879cc4a481425738
    AISI 1144 Steel, oil quenched 845°C (1550°F), 540°C (1000°F) temper, 13 mm (0.5 in.) round

    The suggestion is that it can be used without hardening.
     
  16. Johnm1

    Johnm1 Member

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    Well, I tested the kiln and thermostat/thermocouple today. Keep in mind that the kiln is really a jewelers melting furnace. It is meant to reach certain temperatures without much concern if it over reaches. It is able to reach 1750 degrees and I can easily keep it within 10 degrees of the target temperature by adjusting the rheostat every couple of minutes. I may be able to tighten that range by increasing temperatures more slowly like I will have to do pre-heating the steel. Most of the pre-heat instructions limit temperature rise to 400 degrees an hour.

    Will a plus minus of 10 degrees be sufficient for the hardening process?
     
  17. Blue68f100

    Blue68f100 Member

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    Should be fine. What you don't want is to over shoot greatly. Over shooting is a bad thing, it can drive the carbon out and the steel will not harden. Under shooting nothing really happens since the steel did not get hot enough to get the phase change (grain structure) needed to harden.
     
  18. Johnm1

    Johnm1 Member

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    Thank you Blue. I can easily keep from overshooting by no more than 5 degrees. Like I said, I may well be able to stabilize the temperatures by increasing temperatures slower. The unit turns the heating element on/off I assume based on the voltage modified by a thermocouple in the unit. No way to really tell as old as the unit is. But I assume if I increase the temperature slowly the amount of time the heating elements are on will decrease and so will the temperature swing.

    I had to repair some of the insulation inside the unit and I still have to figure out how to seal the hole that the thermocouple goes through. That in and of itself should stabilize the temperature inside the unit and limit the heat loss and as such the temperature swings. I was able to reach 1200 degrees in 45 minutes and it took less than 15 minutes to go from 1200 to 1750 degrees. So, I'll have to watch myself on the annealing process after I shape the piece.

    Here are the hardening instructions for the 3V tool steel. I do not have the capacity for the hardest option as my kiln is limited to below 1900 degrees. I have bolded and minimized the font for the two 'harder' options for 3V steel. I can get to the 'Maximum Toughness' temperatures though it approaches the limit of the temperatures I'm able to reach.

    Hardening
    Preheating: 1500-1550°F (816-845°C), equalize.
    Austenitizing (High Heat): Heat rapidly from the preheat.

    For Maximum Wear Resistance: Furnace or Salt Bath: 2000-2050°F (1093-1121°C)
    Soak for 20 minutes minimum at temperature.


    For Balanced Wear & Toughness:
    Furnace or Salt Bath: 1950°F (1066°C)
    Soak for 20 minutes minimum at temperature


    For Maximum Toughness:
    Furnace or Salt Bath: 1875-1900°F (1024-1038°C)
    Soak for 45 minutes minimum at temperature

    Quenching: Air, pressurized gas, warm oil, or salt. For pressurized gas, the furnace should have a minimum quench pressure of 4 bars. For oil, quench until black, about 900°F (482°C), then cool in still air to 150-125°F (66-51°C), then cool in still air to 150-125°F (66-51°C). For salt maintained at 1000-1100°F (538-593°C), equalize in the salt, then cool in still air to 150-125°F (66-51°C).

    Tempering: Temper immediately after quenching. Typical temperature range is 1000-1100°F (524-593°C). Do not temper below 950°F (510°C). Hold at temperature for 1 hour per inch of thickness, 2 hours minimum, then air cool to ambient temperature. Double tempering is required. Triple tempering is recommended when austenitized at 2000°F (1093°C) or above and when tooling will be wire EDM'd from a solid block after heat treatment.

    Annealing
    Annealing must be performed after hot working and before rehardening.
    Heat at a rate not exceeding 400°F per hour (222°C per hour) to 1600-1650°F (871-899°C), and hold at temperature for 1 hour per inch of maximum thickness; 2 hours minimum. Then cool slowly with the furnace at a rate not exceeding 50°F per hour (28°C per hour) to 1000°F (538°C). Continue cooling to ambient temperature in the furnace or in air. The resultant hardness should be approximately 241 HBW.
     
  19. beag_nut

    beag_nut Member

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    Wow.
    All those steps are going to make you an expert at heat-treating. And you are doing only one piece? I tend to agree with those who have recommended case-hardening, which simply takes one can of compound and about 15 minutes of work. The sear surface only needs to be hard for a few thousandths; once mated the rubbing parts will not go more than simple polishing, during use. Too bad we don't have a reader of this forum who actually worked in a firearms factory, to tell us how it was done in-house.
    I wish you good luck. Plus, it will be a great way to pass time during the present health situation.
     
  20. Johnm1

    Johnm1 Member

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    I don't disagree that this is overkill especially for a Single part. There is something to be said for the process and learning how to do it. I may well end up with a surface hardened piece. But I'd like to know if I can do it.
     
  21. BBBBill

    BBBBill Member

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    The original question was about surface hardness. That was a "thing" on older guns, but current stuff is pretty much through hardened. Different alloys...
     
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  22. David Hoback

    David Hoback Member

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    John...as with many things, there are a bunch of voices telling you things when they HAVE NO CLUE WHAT THEY ARE TALKING ABOUT!

    But with your finding on your kiln, the 3V won’t work. 1750 won’t harden it correctly. You can get away doing S7 and A2 with that kiln. Or several carbon steels, as they Austenitize at around 1450-1500F.

    Let me know if you still want these pieces of 3V. I have it all packaged & ready to go.
     
  23. Johnm1

    Johnm1 Member

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    David,

    The kiln is rated for 1900 degrees. I picked 1750 to test how well I could monitor/adjust the temperature. The least hard state of the3V steel, the one titled 'For Maximum Toughness' can be hardened between 1875 and 1900 according the Hudson. I had planned to keep it below the 1900 but above the 1875. Now if you know that won't work, then it doesn't make sense to send the material and I can find something from one of the local suppliers I'm sure.

    Bill is correct. My original question was "what is the hardness of sear surfaces". It kind of morphed into hardening the entire piece. Mostly to see if I could do it with what I have. It certainly won't be efficient but you never know when you might need a hardened piece and at least I'll have some experience.
     
  24. David Hoback

    David Hoback Member

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    I misunderstood you John. I thought you meant your kiln will ONLY reach 1750. As long as it will reach 1900, you can Austenitize 3V.

    Yes, I wasn’t referring to Bill. He didn’t say anything out of sorts. Was in reference to the back ground noise, LOL. Unfortunately it’s what happens on public forums. Ok, like I said I already have it all packaged up.. so I’ll get it shipped this week. Cheers!
     
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  25. Johnm1

    Johnm1 Member

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    Thanks Dave.
     
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