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Thread: 4140 HARDNESS

  1. #1
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    Default 4140 HARDNESS

    I bought some 4140 today at a steel merchants who specialize in machining steels

    Anyway, the guy on the desk said 4140 comes in black and bright which I did not know .

    He wandered down a huge warehouse with rows of steel and found some 3/4" 4140 , it is marked a blue colour which is the correct 4140 colour code going by the interalloy chart .

    I tried a file test on the 4140 and its not as hard as I thought it would be . I also filed a few grade 8 and unbrako bolts as a comparison and they file down about the same as the 4140 does .

    I think he gave me black 4140 as it has a rough finish .

    Mike

  2. #2
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    The data sheet suggests that it is machinable in the hardened condition

    4140-high-tensile-steel.pdf

    Michael

  3. #3
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    Default

    You could check with Interlloy, I've bought 4140 from them previously, and as supplied it machines nicely, when you've finished machining it's pretty easy to harden and temper as well...

  4. #4
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    The shiny stuff only means it has been ground or peeled and polished...

    It all comes out of the rollers as black...

    All the 4140 I have bought is bright since not much elese is available locally and around 35HRC.. You can heat it up and quench it to get upwards of something like 50HRC.. Been awhile since I tested it so only going by memory here..
    Gold, the colour of choice for the discerning person.

  5. #5
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    Default OK

    OK thanks for the replies

    I should have mentioned that I am more concerned about the tensile strength , it's ability to withstand stretching , as I am making studs 18" long . I guess the surface hardness is of little consequence in my case . I will be threading it 3/4" BSW on both ends . Yes the stuff I got today is the raw product, it hasn't been polished or cold rolled . Mike

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    Default more info

    Ok this info tells the story , I found this on a web site


    4140 Mechanical Properties

    4140 Hot Rolled:

    • Typical Tensile Strength: 89 KSI
    • Typical Yield Strength: 62 KSI

    4140 Cold Rolled:

    • Typical Tensile Strength: 102 KSI
    • Typical Yield Strength: 90 KSI

    4140 HT Oil Quenched & Tempered:

    • Typical Tensile Strength: 153 KSI
    • Typical Yield Strength: 131 KSI




    http://www.speedymetals.com/information/Material43.html

  7. #7
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    Default MORE INFO

    A close up look at the hardening process


    https://www.youtube.com/watch?v=ClIPVcBj5xQ

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    I think you will find its not quite as simple as that for the properties of the material. The term or name 4140 only gives you a hint as to what the material properties actually are, that it should have a certain percentage of this and that.

    But the actual properties, for that particular piece of bar stock will have come from the steel mill with a certification showing a chemical breakdown of how that particular batch ended up and also its actual tensile strength etc.

    Different batches will show different properties, and simply saying its 4140 does not provide the whole story, granted some of this is not important for various jobs, but for some it is paramount that it meets a minimum standard and having the certification paperwork is the only way to know.

    The supplier can and will provide this info if you ask them for it, and it's a huge eye opener when you get to see what the variation of a particular material can be. Every piece of material is traceable back to the steel mill and the batch it came from.
    It's Ripping Time!!!

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    Most 4140 supplied is aus is quenched and tempered, I assume that is what you have been supplied. When you machine it take a decent cut to get under the black skin, it is pretty harsh on tooling.

  10. #10
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    Default Not sure

    Quote Originally Posted by snapatap View Post
    Most 4140 supplied is aus is quenched and tempered, I assume that is what you have been supplied. When you machine it take a decent cut to get under the black skin, it is pretty harsh on tooling.
    I'm not convinced the stuff I have has been quenched and tempered . The file bites into it easily , just like mild steel . I think hardened 4140 should exhibit at least some surface hardness - that is it should have a surface that is harder than mild steel is ?

    Mike

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    Default

    May be you just have a good file.

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    Quote Originally Posted by pipeclay View Post
    May be you just have a good file.
    Wouldn't think so, 35 Rc should file quite ok, it's only when you get above 55 to 60 or so that the file will start skating.

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    Don't think too hard about my reply,think more about the post I replied to.

  14. #14
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    According to the data sheet I posted in #2, in the T condition hardness is around HB 250 to 300 - approximately 24 to 32 RC. (101 to 107 RB)
    By comparison, 1022 carbon steel (hot rolled) is around HB 150 or RB 80 (Just off the RC scale)
    So - 4140 is harder but not horribly so (and a metal file is around RC 60).
    As Pipeclay suggests, with a good file the difference may be minor.

    Michael

  15. #15
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    I did a file test on some 4140qt at work and it files the same as 1020. You will know if it is annealed when you machine it. Annealed 4140 is very gummy (worse than 1020) and you will struggle to get a good finish. 4140 QT will machine very well and you will get a really good finish easily. I doubt they would have sold you annealed 4140.

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