Tensile strength loss with heat
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  1. #1
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    Default Tensile strength loss with heat

    What temperature will steel loose tensile strength? Let me explain. I use a moly coating for transmission gears to reduce friction on racing motorcycles. Part of the instructions are to bake the coated gears at 400F for 1 hour. I decided to apply it to the rear drive chain so I thoroughly degreased a new chain and coated the pins, rollers and side plates. My plan was to place the chain in my gas barbecue grill to do the baking process, checking the temp with an infrared thermometer. Long story- short, I got side tracked. Two hours later. I checked the temperature and the chain was 650F. The factory tensile strength is 11,500. Will 650F weaken the chain that I should order a new one? Hope not.

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    I'd scrap the chain, as 650F is enough to reduce the temper. Even if it was still at the original strength, you likely have remaining oil in the links that's now carbonized, making it abrasive to some degree. Much cheaper to buy and treat a new chain than have the old one break in use and damage the bike or you.

    If you try the treatment again, use an electric toaster oven that you've checked with a thermometer for accurate temperature control. That way you'll have a proper cure without overheating.

    As an example of how excess heat can effect temper and steel strength, look for the chart "Hardness vs. Tempering Temperature for Various Steels" near the bottom of this link: Tidewater Blacksmiths Guild - Heat-Treating Tool Steels

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    Chain was thoroughly degreased and ultrasonically cleaned so any residual oil was very minimal. Good idea about using a toaster oven. So, probably a next time with a new chain. That was a special heavy duty chain made especially for racing. Still I wonder how much tensile strength is lost, if any.

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    David

    If the chain is a "special", find out what steel it is made of.

    Side plates will be different from pins and rollers, but inquire. SPECIFICATIONS matter!

    Otherwise it's all just a guess.

    This statement rings true. When Heated Carbon Steel becomes Non-Magnetic at 1420F.



    Until you get up there, nothing much happens to steel that isn't good for it. Some "hardening" might be lost to the "tempering", But I'm not sure roller chain relies on hardening for it's strength. Wear resistance of the pins maybe, but they aren't so hard that the ends can't be staked.

    I would run that chain.

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    Yup, gotta scrap that chain, get a new one. Watch out with toaster ovens, sometimes they keep climbing -- the control isn't real good.

    Its been decades since I rode, but the hot tip back then was to boil the chain in candle wax then hang it up to dry.

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    Quote Originally Posted by David Hidaka View Post
    ... moly coating for transmission gears to reduce friction on racing motorcycles. Part of the instructions are to bake the coated gears at 400F for 1 hour. I decided to apply it to the rear drive chain ....

    Wait. Chain not equal to gears. Does your bike have a front drive chain? If so, it's a Rokon.

    Always wanted one.

    Throw the chain away.

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    You can see the same size / type material and what the effect on strength is at differing tempering temperatures in this mass effect data

    4142.jpg

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    Quote Originally Posted by johnoder View Post
    You can see the same size / type material and what the effect on strength is at differing tempering temperatures in this mass effect data

    4142.jpg
    Note carefully those tempering temperatures.

    650 doesn't appear on the page that I see.

    Now OPERATION at 650 degrees is a different discussion.

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    Quote Originally Posted by CalG View Post
    Note carefully those tempering temperatures.
    650 doesn't appear on the page that I see.
    You got me wondering if my eyes are going, Cal. I'm seeing tempering temperature on the lower left graph going down to 400° F. Depending upon the original temper, 650°F could drop the tensile 20% and the yield 10%. If the original tempering temperature was 600° F, then the effect was not so much.

    If the stuff is 4142.

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    Quote Originally Posted by bosleyjr View Post
    You got me wondering if my eyes are going, Cal. I'm seeing tempering temperature on the lower left graph going down to 400° F. Depending upon the original temper, 650°F could drop the tensile 20% and the yield 10%. If the original tempering temperature was 600° F, then the effect was not so much.

    If the stuff is 4142.

    Thanks for the second pass. I can barely read the graph on page one. I read now the lower heat numbers. But it sure looks like 650 degrees is in the "doesn't really matter" zone.

    I was looking at the "mass effect data" because my eyes are going, and I could read the text with my "readers" on and the page blown up as much as it could be by hitting (control +) a couple of times. Those heat numbers are high.

    As I stated. Give up something, maybe gain somewhere else.
    Next step is the cryostat... then the ball peener, followed by the LASER ;-)

    I would not hesitate to use that chain.

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    how did you measure the temp. and can you be sure it was not higher in the meantime?

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    Quote Originally Posted by dian View Post
    how did you measure the temp. and can you be sure it was not higher in the meantime?
    Nor evenly distributed....scrap that chain.

    400f might be doable with hot oil (no, not the VO-5 treatment....)

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    Quote Originally Posted by digger doug View Post
    ...400f might be doable with hot oil (no, not the VO-5 treatment....)
    That's a good idea.

    I've never used it for tempering, but I use one of those "Fry-Daddy" electric deep fryers when I need to re-oil sintered bronze bushings after machining. Good temperature control, and they come with a basket.

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    Quote Originally Posted by jancollc View Post
    That's a good idea.

    I've never used it for tempering, but I use one of those "Fry-Daddy" electric deep fryers when I need to re-oil sintered bronze bushings after machining. Good temperature control, and they come with a basket.
    That's a hell of an idea.

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    We can't say for sure what temp (or temper change) may have happened to the chain, but isn't loss of control a risk if the chain breaks while on the throttle? I wouldn't be so worried if it was a car part, but you're sort of exposed on a bike if the wheel locks up or some other non-optimal event occurs.

    Racing costs money, appease the speed gods and get an new chain...

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    Quote Originally Posted by bosleyjr View Post
    You got me wondering if my eyes are going, Cal. I'm seeing tempering temperature on the lower left graph going down to 400° F. Depending upon the original temper, 650°F could drop the tensile 20% and the yield 10%. If the original tempering temperature was 600° F, then the effect was not so much.

    If the stuff is 4142.
    There is a very strange quirk in the physics of tempering. Plain carbon and alloy steels have a memory. If heated below their original tempering temperature there is no appreciable drop in hardness.

    In this case the OP could infer the original tempering temp by determining the original surface hardness. Rc60 would say temper around 350 F. Rc30 would say temper around 900F. I'm leaning toward these being boat anchor material at this juncture.

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    Quote Originally Posted by Milland View Post
    Racing costs money, appease the speed gods and get an new chain...
    Chains are actually some of the least expensive parts for race bikes.

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    Yeah, your chain and rollers are softer now, scrap it.

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    Scrap the chain - 650F is in the blue brittleness range. The pins will be brittle when tempered at that temperature for an length of time.

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    Quote Originally Posted by Dave G. View Post
    Scrap the chain - 650F is in the blue brittleness range. The pins will be brittle when tempered at that temperature for an length of time.
    I get the impression the OP did not like the advice he heard and has gone away.


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