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  • dumb metal question

    I am new to the sport and want to start fabbing carts and tables. What is the difference between cold rolled and hot rolled steel? What do I need to be looking for? Sorry for the basic question, I just have no idea.
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  • #2
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    • #3
      The short answer s Hot Rolled Steel (HRS) in plate , round stock and square stock. It welds and forms easy...most always has a mill scale on it. Cold rolled is clean and has square corners on plate, and is more subject to cracking, so I'm told, however, I have never seen any of my CRS jobs crack.
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      • #4
        Here's a little practical advice on the differences:

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        --- RJL ----------------------------------------------

        Ordinarily I'm insane, but I have lucid moments when I'm merely stupid.
        -------------------------
        DialArc 250 (1974), Idealarc 250 (1971), SyncroWave 250 w/Coolmate 3, SP-175+, TA 161STL,
        Lincwelder AC180C (circa 1952), Victor & Smith's O/A, Dayton (Miller) spot welder, 1200 sq.ft. of garage filled with crap and a kid that can actually run the stuff +++

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        • #5
          If I could make a somewhat related suggestion, as you are researching metal types/grades/alloys I suggest looking at the Esab site and read through the O/A handbook online, specifically the section on the various fumes created when welding grinding and cutting metals. A lot of the stuff that gets airborn when working with metal is some nasty stuff. Its good to know the potential hazards so you can take appropriate measures to protect yourself, like when welding on galvanized steel!

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          • #6
            Originally posted by Rocky D View Post
            The short answer s Hot Rolled Steel (HRS) in plate , round stock and square stock. It welds and forms easy...most always has a mill scale on it. Cold rolled is clean and has square corners on plate, and is more subject to cracking, so I'm told, however, I have never seen any of my CRS jobs crack.
            I've heard too that for machining purposes, CR material is not as stable because of internal stresses. Never experienced it, though.

            Dave
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            • #7
              We have a piece of 1" x 1/8" cold rolled that we needed to form into about an 8" diameter curve. That stuff was really tough and hard to form for its size.
              --- RJL ----------------------------------------------

              Ordinarily I'm insane, but I have lucid moments when I'm merely stupid.
              -------------------------
              DialArc 250 (1974), Idealarc 250 (1971), SyncroWave 250 w/Coolmate 3, SP-175+, TA 161STL,
              Lincwelder AC180C (circa 1952), Victor & Smith's O/A, Dayton (Miller) spot welder, 1200 sq.ft. of garage filled with crap and a kid that can actually run the stuff +++

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              • #8
                Rolled my friends......Rolled!

                There's no real difference in metalurigical make-up.
                {as far as welding is concerned}.

                Understanding the workings of a steel-Mill helps.
                Have you even seen footage of a steel-Mill?
                Hot-rolled is rolled to nominal sise. The process is complete
                and there is still enough heat left in the metal to insure it is nearly
                stress free. The rolling is the sorce of the heat that keeps it hot.

                http://www.youtube.com/watch?v=6xnKm...FC6B&index=179
                http://www.youtube.com/watch?v=BqLtM...FC6B&index=178

                Just as the hammering in "Forge-Welding" does. The friction and
                compression / compaction of the process creates Heat.
                This is why the scale is presant, from the cooling back below the
                ?M? temorature. Can't retain those names.
                It's also why Hot-Rolled is usually a few thou smaller than nominal dimention.

                Cold rolled is "re-rolled" after haveing been allowed to cool.
                This re-rolling is why the scale is gone, and why C.R.S. is closer to
                real nominal sise. It is why it's also a poor choise for manufactueing
                parts from, where considerable material is to be machined away.
                The "stesses" are highest near the surface, but they are ballanced stresses.
                Both sides have metal in a state of stress thats fairly equall.
                If you try to shave off say 20% off one side then the stress on the other
                side is now free to relax and distort the part.

                Welding also releases those stresses in the HAZ, and a bit further.
                The work may need to be surface heated on the contracted side in order
                to restore st8'ness & flatness.

                An earlier term for CRS was "machine-steel".
                The whole Idea was to mill a selection of steel, in sises that were
                very close to nominal sise. And consistantly srt8 and flat as possible.
                You ordered these products to be cut to lenght and used pretty-much
                as-is. Maybe holes added. (incidently drill a row of holes along one side
                of CRS and see what happens).

                Want to fabricate? Choose Hot-Rolled! OR.
                Do like us tool-makers used to do. At the end of a run of heat-treating.
                Just after the tool-steel has been pulled for drawing. Lay all your CRS
                blanks in the oven and let them hit just barely dark-cherry red.
                Turn the oven off and collect your perfect parts in the morning.

                They will be best-case. No scale, nice and flat, pretty, nominal sise.
                and above all-else "STREE-FREE".
                vg

                Please take this and some of the repeat welding questions, and make a sticky.
                This is allot of typing about the third time now..........fweew!
                Last edited by vicegrip; 06-06-2009, 12:39 PM.
                sigpicViceGrip
                Negative people have a problem for every solution

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                • #9
                  Originally posted by Rocky D View Post
                  Cold rolled is clean and has square corners on plate, and is more subject to cracking, so I'm told, however, I have never seen any of my CRS jobs crack.

                  "and is more subject to cracking"
                  Bunk.......more prone to distrorting. Less tolerant of "cold-welds".
                  The welds may crack, the CRS will not.
                  Not enough carbon in it to sneeze at.

                  Cheers
                  VG
                  sigpicViceGrip
                  Negative people have a problem for every solution

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                  • #10
                    Absolutely NOT a dumb question !!

                    Originally posted by G22inSC View Post
                    I am new to the sport and want to start fabbing carts and tables. What is the difference between cold rolled and hot rolled steel? What do I need to be looking for? Sorry for the basic question, I just have no idea.

                    Absolutely NOT a dumb question !!

                    It's one of the best questions to start with !!
                    sigpicViceGrip
                    Negative people have a problem for every solution

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                    • #11
                      Phil

                      You are a walking steel encyclopedia. Thanks for the info. It wasn't a question I would have asked but your replies got my mind going on a bunch of ideas and answers as to what happened to the part I though was going to come out straight

                      Thanks

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