Flame hardening S7
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  1. #1
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    Default Flame hardening S7

    not worth sharing
    Last edited by macds; 01-30-2021 at 01:05 PM.

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    Quote Originally Posted by macds View Post
    Wanted to put this out, especially after reading paper from various steel companies, and the few forum posts I could find.
    Had to make up a splined shaft for a man lift, runs the 4wd.
    Decided to go with S7 over run of the mill stuff.
    My biggest obstacle was how to make it hard (at least on the outside).
    A few things I read talked about decarb, high temp wrap, vacuum furnace....
    This was an emergency job, no time for that.

    So, being a round part (1.5" dia) I stuck it in the lathe at 80 rpm, and let it chew with the torch.
    Initially nice and slow to bring it up, then white flame tip once it started to red up.

    Then switched up to a hotter, but not short blue cone until bright orange, almost yellow. This took almost 40-45 minutes on a 1.5" dia x9.5" long part.
    Once i saw consistent carbon flaking on the surface (like O1), I went a little further, maybe 5 minutes, then killed the oxygen and did an acetylene carbon soak on the part until the acetylene stopped burning off.

    Let the lathe run with the part spinning to cool off in still air for a good hour, then did a surface oil quench at around 400C.
    Keep in mind that im primarily after surface hardness on this part, while retaining sponginess at the core.

    Couple hours later after a nice spinning air cool, part is nice and straight dimensionally, and a file wont touch the skin.

    Did I just make the most shatterable shaft known to man, should i bead blast it and draw it down (i think i SHOULD until a straw colour), or do you think it will be ok?

    Curious if anyone else has done similar with S7, just to compare notes.
    The part you made needs to be somewhat hard and very TOUGH. You have made it very hard. I think there is little doubt you should draw it down by tempering to at least a deep yellow. Leaving it fully hard means it lacks toughness and is at risk of breaking. I do not see any downside to tempering.

    I have not flame hardened and tempered S7 specifically. But, I’ve made hundreds of parts in O1 and A2. The principles are the same. Too much hardness equals too little toughness. I virtually never skip tempering except in the rare case that toughness is unimportant and max hardness is needed.

    Denis

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    Just a slightly contrarian opinion. If it was another tool steel I'd fully agree. Since this is a shock resisting tool steel it's designed to resist fracturing. Drawing the hardness down would also reduce wear resistance, I'd assume, so it would be a matter of juggling what would be the biggest threat to the part in service. I don't have a firm opinion.

    If it were another variety of oil hardening steel that might have been an advantageous process. That is, the transition from soft to hard is dependent on the rate of cooling. Cooling it slower than the critical rate is annealing, and faster becomes hardening. So in this particular case, cooling just the splines to produce hardening while allowing latent heat to slow the interior might have produced the desired hard surface/tougher interior.

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    I agree that S7 has good shock resistance. But for some reason, if you look at the steel manufacturer’s or supplier’s use recommendations for S7, every one recommends double tempering.

    Crucible Selector - CRUCIBLE S7

    Is there an argument for not tempering?

    Denis

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    An advantage of S7 is that it is pretty good at through hardening especially given the length of soak reported. Not that less would have been better metallurgically. There’s probably a small hardness differential. Whether that suits the purpose or not is up for analysis based on your calculations for the part. I do think it is risky to harden steel without tempering it; though the tempering might be such as to barely lower hardness, if that is important to you.
    Read the steel suppliers charts. They seldom guess.i

    When you designed the replacement part, how did 4140 prehard compare?

    How did the original part fail?

    smt

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    If they are concern with torque and strength, 4340 would have been a better candidate. Have used 4140/42 heat treated before with excellent results, along with either induction hardening or flame hardening. At least, heat treating by this method will produce a good surface hardness but will leave you with a somewhat softer core hardness without sacrificing strength.

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    Hi All:
    Am I the only one who's terrified of what is being advocated here?

    Here's a snip from the original post with my emphasis added:
    "Had to make up a splined shaft for a man lift, runs the 4wd."...
    "
    A few things I read talked about decarb, high temp wrap, vacuum furnace....
    This was an emergency job,
    no time for that."
    "Did I just make the most shatterable shaft known to man, should i bead blast it and draw it down (i think i SHOULD until a straw colour),
    or do you think it will be ok?"

    I'd be scared to death of liability exposure, not only for doing the job this way, but also for talking about it on the forum.
    If that manlift suffers a failure or even has an accident unrelated to the repair and a smart lawyer ever gets wind of this, the OP is in a world of hurt, even if by some miracle, he ultimately escapes with exoneration.

    I'm not a doomsayer by any stretch, nor am I terrified of my own shadow, but I'd walk away from this job, forgo the bit of cash I didn't earn and be grateful I can still sleep at night without fear.

    I'm not a lawyer but here's what I see:
    The OP knew or should have known that it was for an application in which a failure could conceivably cause harm.
    The OP chose to violate the accepted heat treat protocol for this material (that he chose without any engineering justification), even knowing this is a potentially critical component and knowing what the correct HT protocol is.
    The OP knew his heat treat of the material made its properties unknown, and even speculated as to the potential failure mode, but chose to sell it to the customer anyway.

    I for one am convinced a lawyer would have a field day with a confession like this.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    The part was consequently double drawn.

    Marcus, I do appreciate the legal concern.

    I apologize for sharing information and upsetting anyone.

    OP will be removed.

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    What Marcus said- in addition a technical based comment: 1st off, S7 is a through hardening air quench tool steel. Why did you attempt to add additional carbon by sooting the surface with the acetylene flame?

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    Hi macds:
    I'm not in the least upset about the post; I'm just concerned you may have unknowingly bitten a monster on the ass.

    We all know about the infamous lawsuit where the moron cut off his own dick (or whatever) with the lawn mower when he and his buddy tried to use it as a hedge trimmer and the maker of the lawnmower got the blame.
    In a legal climate as fucked up as that, the liability you expose yourself to even when you are trying to help someone out of a jam is an ever present threat to everything you've spent years to build up.

    I've never knocked up against this directly (Thank God) but I have a buddy who got absolutely raped over a motorcycle part (steering component) that was postured to have been a contributing factor in a fatal accident.

    He didn't even make the part...he just ground off the bits that were no longer needed and polished the thing (it was a triple tree for a Harley) to make it pretty so it could be chromed.
    I don't know if it was even a legitimate contributor to the wreck, but he just got jumped on, and this was way back in the 70's.
    It's a lot worse now.

    So be careful out there boys and girls...there be assholes in suits with law degrees about, and they will hurt you if they can, all so they can make a pile.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    The OP most likely has a working mind and probably thought of the possibility that his part might fail and what the consequances might be. He also probably realizes that he could get hurt running his lathe and mill and "those who play with fire get burnt." So, if someone asks a simple question, I don't think it is up to us to jump down his throat. Answer the question. If we routinely just pillory someone for asking a question, the folks with a question will be put off on asking and so will not. Is that a better situation?

    Perhaps a mild cautionary statement is in order, but making one assumes we are more aware of risks than the OP. How do we know that? The key question was "should I temper the part?" The answer is unequivocally "yes" and he followed that advice.

    I hope he comes back after using the part for a while to let us know how it worked out.

    Denis

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    Hi Denis:
    I thought that WAS a mild cautionary statement...I certainly hope I did not convey censure or anything like that.

    However, in the desire that so many of us have to help out, we can and do hang our asses out sometimes, and don't even really realize it.

    Maybe the OP's method worked a treat and I'm fulla shit....maybe...I hope so!
    Maybe it'll go a million miles with never a hiccup.
    I cannot say...nobody can say...not with any certainty.

    Here's another cautionary tale:
    Eons ago, I built some parts for an experiment with fruit flies to go up in the space shuttle.
    The guy who ordered the stuff was a local scientist who made his name doing research on starfish embryos.

    He related a story about a big engineering firm in Montreal, contracted to design and build an aquarium for him that was also going up on the shuttle.
    Well they built some of the parts out of aluminum, didn't anticipate what the corrosion products might do, and killed all the critters.
    Twenty million dollars worth of experiment in the toilet...the shitshow that ensued apparently was epic.
    That engineering firm no longer exists.

    Stories like these are why I care.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by implmex View Post
    Hi macds:
    I'm not in the least upset about the post; I'm just concerned you may have unknowingly bitten a monster on the ass.

    We all know about the infamous lawsuit where the moron cut off his own dick (or whatever) with the lawn mower when he and his buddy tried to use it as a hedge trimmer and the maker of the lawnmower got the blame.
    In a legal climate as fucked up as that, the liability you expose yourself to even when you are trying to help someone out of a jam is an ever present threat to everything you've spent years to build up.

    I've never knocked up against this directly (Thank God) but I have a buddy who got absolutely raped over a motorcycle part (steering component) that was postured to have been a contributing factor in a fatal accident.

    He didn't even make the part...he just ground off the bits that were no longer needed and polished the thing (it was a triple tree for a Harley) to make it pretty so it could be chromed.
    I don't know if it was even a legitimate contributor to the wreck, but he just got jumped on, and this was way back in the 70's.
    It's a lot worse now.

    So be careful out there boys and girls...there be assholes in suits with law degrees about, and they will hurt you if they can, all so they can make a pile.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    Chrome plating = hydrogen embrittlement. Part must be cooked to drive out the hydrogen after plating.

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    Quote Originally Posted by implmex View Post
    Hi All:
    Am I the only one who's terrified of what is being advocated here?

    Here's a snip from the original post with my emphasis added:
    "Had to make up a splined shaft for a man lift, runs the 4wd."...
    "
    A few things I read talked about decarb, high temp wrap, vacuum furnace....
    This was an emergency job,
    no time for that."
    "Did I just make the most shatterable shaft known to man, should i bead blast it and draw it down (i think i SHOULD until a straw colour),
    or do you think it will be ok?"

    I'd be scared to death of liability exposure, not only for doing the job this way, but also for talking about it on the forum.
    If that manlift suffers a failure or even has an accident unrelated to the repair and a smart lawyer ever gets wind of this, the OP is in a world of hurt, even if by some miracle, he ultimately escapes with exoneration.

    I'm not a doomsayer by any stretch, nor am I terrified of my own shadow, but I'd walk away from this job, forgo the bit of cash I didn't earn and be grateful I can still sleep at night without fear.

    I'm not a lawyer but here's what I see:
    The OP knew or should have known that it was for an application in which a failure could conceivably cause harm.
    The OP chose to violate the accepted heat treat protocol for this material (that he chose without any engineering justification), even knowing this is a potentially critical component and knowing what the correct HT protocol is.
    The OP knew his heat treat of the material made its properties unknown, and even speculated as to the potential failure mode, but chose to sell it to the customer anyway.

    I for one am convinced a lawyer would have a field day with a confession like this.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    I’m with you, Marcus. I spent my entire career responsible for safety related components. You don’t even have to be responsible for a failure to lose in court. Especially if you are in Bumfuk, Iowa.

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    Just out of thinking out loud, I was under the impression that hydraulic cylinders on man lifts have burst hose check valve things ( excuse description hydraulics is something I try to stay clear of, age induced fear)
    If the pipe bursts you don’t plummet to your death, the last one I rode was 150’ up and I swear it scared the shit out of me, harness or no harness it’s a long way down before half a day at the undertakers, plenty of time for my life to flash before me
    If the spline is the pto running the pump, and it shears, pump stops?, if elevated the arm doesn’t drop does it?, when the one I was on engine stopped we just lowered the basket as normal, couldn’t raise it but lowering was ok
    However I appreciate the liability concern, parts like that are normally fully inspected, NDT, bombed, stared at with squinting eye, tapped on desk, etc
    Mark

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    I don't think much of your suggestion to do S7 this way. Take a look at 6150 and heat treat.
    Roger

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    Hi again All:
    OK, one last point to make and then I promise I'll shut up on the subject:

    You do all know that when engineers make recommendations they get paid big bucks to assume the liability exposure.
    They're also covered by liability insurance and have the additional cover of their degrees and their professional associations.
    Ask an engineer (if you know any) how much they would charge to do an engineering assessment on a project like this and certify their recommendation with their PEng stamp on the drawing.
    Do you think you would get away under ten grand?

    Why on earth would you assume that risk...AND FOR FREE???
    Yeah yeah, I know, we do it all the time...but SHOULD we?

    That's the essence of this last point I want to make; never mind how badly you'd feel if God forbid, your guesses cost a life.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by implmex View Post
    Hi All:
    Am I the only one who's terrified of what is being advocated here?

    Here's a snip from the original post with my emphasis added:
    "Had to make up a splined shaft for a man lift, runs the 4wd."...
    "
    A few things I read talked about decarb, high temp wrap, vacuum furnace....
    This was an emergency job,
    no time for that."
    "Did I just make the most shatterable shaft known to man, should i bead blast it and draw it down (i think i SHOULD until a straw colour),
    or do you think it will be ok?"

    I'd be scared to death of liability exposure, not only for doing the job this way, but also for talking about it on the forum.
    If that manlift suffers a failure or even has an accident unrelated to the repair and a smart lawyer ever gets wind of this, the OP is in a world of hurt, even if by some miracle, he ultimately escapes with exoneration.

    I'm not a doomsayer by any stretch, nor am I terrified of my own shadow, but I'd walk away from this job, forgo the bit of cash I didn't earn and be grateful I can still sleep at night without fear.

    I'm not a lawyer but here's what I see:
    The OP knew or should have known that it was for an application in which a failure could conceivably cause harm.
    The OP chose to violate the accepted heat treat protocol for this material (that he chose without any engineering justification), even knowing this is a potentially critical component and knowing what the correct HT protocol is.
    The OP knew his heat treat of the material made its properties unknown, and even speculated as to the potential failure mode, but chose to sell it to the customer anyway.

    I for one am convinced a lawyer would have a field day with a confession like this.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    its the 4wd, not the lift part... cool your panties.

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    Hi Woodchuck:
    Panties are cool.
    Clean too!
    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by woodchuckNJ View Post
    its the 4wd, not the lift part... cool your panties.
    What would you know about ?:
    1. machining
    2. heat treating
    3. material selection
    4. running a machine shop


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