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A36 HRS strength kept when heated

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  • A36 HRS strength kept when heated

    Hi Group,

    I need to make a bumper brace like the original, it's the long narrow back piece to mount the chrome bumper too on a old car. I have 1.25" x.25" flat stock A36 HRS and I need to heat a section up in the center to give it a cup shape on the .25 width for 12" and want to keep the metal strength after this is done, because I will be putting a bend at the end of this cupped area and don't want to have the cupped area be soft.
    I have a plan to us my press with a die set to do this, I plan on taking it to a dull orange color unless someone advises differently and then just air cooling.

    So the question is, heat it then let it air cool, water quench it to cool, or another method to keep the hardness of the metal. and is temp a consideration that I need to be aware of?

    Click image for larger version  Name:	IMG_20171018_204533931.jpg Views:	0 Size:	2.16 MB ID:	1876919Click image for larger version  Name:	IMG_20171018_204513267.jpg Views:	0 Size:	2.25 MB ID:	1876920Click image for larger version  Name:	IMG_20171018_204619129.jpg Views:	0 Size:	2.42 MB ID:	1876921
    As you can maybe see, the center is the part that I'm speaking about. This is pics of 2 different parts.

    TX
    Mr fixit for the family
    Chris
    Last edited by Mr Fixit; 05-22-2020, 04:53 PM.

  • #2
    I've spent most of my life working with A36. It doesn't have enough carbon to harden noticeably -- between 0.2 and 0.25 percent is what the spec calls for IIRC. Its the closest thing you'll get to wrought iron normally. So it doesn't matter if or how you heat and quench it. On parts like yours I just go orange-hot, the color of carrots. And then just let it cool in still air. It won't harden even if you dunk it in brine.

    For punched holes or vibratory stress it is recommended not to quench it. Most codes specify drilled holes in fact. Welding, no special prep or care is required. Its just cheap mild steel designed for welding. A36 doesn't have any hardness, never will, it cuts like butter.

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    • #3
      Yeah, gooey butter. My cheap plasma cutter cuts through 1/2" like tin foil. I just made a hook spanner wrench for one of my "keyless" chucks. The chuck really gets tight sometimes. Or maybe I'm getting weak. But my larger one doesn't do that (yet).

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      • #4
        Hi NCF and CCWKen,

        Thanks for the quick response, as I'm planning on working in the shop on this project this weekend.

        So before I sign off, do any of you think that A36 is the wrong material for the job? The originals as you can kind of see in the pictures are the same dimensions as my material and they do bend easy as you might see with the primed one which is twisted and not the same shape on both ends. I'm going to make another set for another car and will be using the originals in the pictures as patterns, but with better shape and consistency. I'm not going for harder just wanted to keep the same strength after the shaping.

        Any suggestions I'm certainly open to.

        TX
        Mr fixit for the family
        Chris

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        • #5
          Instead of heating it I would cold bend it in the press bend a little move it bend a little more. If you bend too much bend it back. That’s how I would do it.

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          • #6
            The strength won't change much, if any. After all, they build buildings with it so it ain't all bad.

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            • #7
              Hi Guys,

              True temper, I need to put a dish in the center the .25" width for 12" long I'm not sure my 20 ton press can do that cold, or could it? Iv'e taken a piece of 1.25" pipe and made a bottom die and then a piece of 1" round stock for the top die, I was going to do it hot to get the dish shape I needed.

              What say you?

              TX
              Mr fixit for the family
              Chris

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              • #8
                A36 is probably good enough. For sure modern steel mill practice is better than the originals. If I remember right, the minimum tensile strength of A36 is around 55,000 PSI, I forgot what they yield is. I've used it for offroad 4x4 bumpers and winches.

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                • #9
                  I appreciate the confirmation NCF, Thanks.

                  TX
                  Mr fixit for the family
                  Chris

                  Comment


                  • #10
                    Originally posted by nickel-city-fab View Post
                    A36 is probably good enough. For sure modern steel mill practice is better than the originals. If I remember right, the minimum tensile strength of A36 is around 55,000 PSI, I forgot what they yield is. I've used it for offroad 4x4 bumpers and winches.
                    Minimum yield strength is 36,000 PSI, hence A36. Tensile strength is specified as being between 58,000 PSI and 80,000 PSI.

                    As others have said, it's a very common structural steel. It's cheap, easily welded, readily punched, sheared, drilled, etc. If you have an application where strength to weight ratio, hardness, etc. are important than obviously it's not the right choice. But for bumper brace? Perfectly suitable, IMO.

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                    • #11
                      I agree heating wont hurt it but I would still bend it cold. Your press should handle it no problem.

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