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What makes a grade 8 bolt a grade 8 bolt?

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  • What makes a grade 8 bolt a grade 8 bolt?

    IIRC a grade 8 is about 175ksi tensile. What are they made out of and what kind of HT profile do they undergo?

    Anyone care to share?

    Clutch

  • #2
    According to the Chinese 6 little lines on the head and that is it.

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    • #3
      Bolt

      One item--- Money
      JRW

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      • #4
        one reference I have states:

        "medium carbon alloy steel, quenched and tempered, minimum tensile strength 150,000 psi."

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        • #5
          Like KVom says, the SAE/ASTM bolt standards specify a tensile strength, heat treatment, and rough carbon content, but not the specific alloy:

          Grade 0-1-2: 74,000 psi Low Carbon Steel
          Grade 3: 100,000 psi Medium Carbon Steel
          Grade 5: 120,000 psi Medium Carbon Steel Heat Treated
          Grade 6: 133,000 psi Medium Carbon Steel Tempered
          Grade 7: 133,000 psi Medium Carbon Alloy Steel
          Grade 8: 150,000 psi Medium Carbon Alloy Steel

          Grade 8's machine a lot like 4140 Pre-Hard, and have similar Rockwell Hardness and Tensile Strength, so the "medium carbon alloy steel" is probably very similar.
          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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          • #6
            Note the difference between carbon steel and alloy steel. Carbon steel has only iron and carbon as the significant constituents unless otherwise specified (ie. leaded steel). Alloy steel is alloyed with other metals to achieve the desired properties and may contain very significant quantities of several different metals other than iron.
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              Originally posted by lazlo
              Grade 8: 150,000 psi Medium Carbon Alloy Steel

              Grade 8's machine a lot like 4140 Pre-Hard, and have similar Rockwell Hardness and Tensile Strength, so the "medium carbon alloy steel" is probably very similar.
              4140 = Chromoly. It's very likely that your Grade 8 bolts are Chromoly, since it's one one of the most common alloys that can meet the 150 K Psi tensile strength requirement.
              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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              • #8
                Originally posted by Evan
                Note the difference between carbon steel and alloy steel.

                So is "carbon alloy steel" "carbon steel" or "alloy steel" or something else ?
                I'm an abstract poet and I didn't even think I was.

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                • #9
                  Originally posted by SmoggyTurnip
                  So is "carbon alloy steel" "carbon steel" or "alloy steel" or something else ?
                  Well, steel can be alloyed with constituents, not including a high carbon content. Stainless steel, for instance could be a low carbon composition.

                  Roughly speaking, the "carbon" parts suggests to you that it can be hardened, and the "alloy" suggests additional characteristics such as heat strength, work hardenability, corrosion resistance or other things.
                  .
                  "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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                  • #10
                    Originally posted by SmoggyTurnip
                    So is "carbon alloy steel" "carbon steel" or "alloy steel" or something else ?
                    A medium carbon low-alloy steel will usually have around 0.4-0.45% carbon (taking it into the 'medium carbon' range as it is > 0.25%) but will also usually have less then 8% of the alloying element (making it 'low-alloy').

                    For example, our EN19 grade (equivalent to your 4140) is a 'medium carbon low-alloy steel', having a composition of:

                    C. 0.40% / Si.0.25% / Mn. 0.70% / Cr. 1.20% / Mo. 0.30%

                    where the Chromium and Molybdenum are the main alloying elements.

                    Plain medium carbon steel (our EN8/your 1045) would have the same carbon/silicon/manganese content (Si. & Mn. are essentially process aids for steelmaking), but no other alloying elements.

                    Does this help or is it still as clear as mud?

                    Peter

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                    • #11
                      Originally posted by SmoggyTurnip
                      So is "carbon alloy steel" "carbon steel" or "alloy steel" or something else ?
                      Carbon steel is steel with varying amount of carbon. Alloy steel has an alloying agent, usually Chromium and Molybdenum.

                      So like I said: 4140 = Chromoly = carbon alloy steel. So the Grade 8 bolts are most likely Chromoly.

                      The bolt maker is free to use any alloying agent they want to meet the Grade 8 spec (and in my experience, ultra-premium bolts like Unbrakos are far stronger than "normal" Grade 8 bolts), but Chromoly is the most cost effective alloy, and therefore the most likely.
                      "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                      • #12
                        If you need bolts to spec, buy em from an industrial supplier that sells to spec. (and get a receipt, ISO 90XX, etc)

                        If not, buy from the local hardware store to suit you needs.
                        Just got my head together
                        now my body's falling apart

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                        • #13
                          Lin, I think he's trying to figure out what kind of stock a Grade 8 bolt would make.

                          Grade 8's machine a little worse than 4140 Pre Hard.
                          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                          • #14
                            OK, fair call Rob.
                            But why bother with "grade XX" fasteners?
                            Chuck it up and see how it cuts.

                            Unless you have to follow an audit trail, or a moral trail ("would I hang my harness on this?")

                            Frankly I've often wondered about this "grade xx" bolt/screw I've seen here from US members.
                            Can you enlighten me?
                            Just got my head together
                            now my body's falling apart

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                            • #15
                              Originally posted by Swarf&Sparks
                              Frankly I've often wondered about this "grade xx" bolt/screw I've seen here from US members.
                              Can you enlighten me?
                              People are looking for cheap turning stock.
                              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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