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Old 06-24-2007, 07:52 PM   #1 (permalink)
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Hot Roll VS. Cold Roll

Steel.......


Whats the differance between Hot Roll and Cold Roll?


Which is stronger?


Which is better for chassis tabs and mounts?


Thanks
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Old 06-24-2007, 09:47 PM   #2 (permalink)
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assuming they are or the same alloy, the cold rolled will be, but in realilty it isn't going to make a difference unless you use a higher strength welding electrode (80ksi would be a safe bet), but the heat from the welding of the tabs will reverse the effects the cold rolling has.

Cold rolled will have tiny bit better abrasion resistance, but when it comes down to it unless you can get a deal on cold rolled (unless you need a high quality finish) its not really worth the extra cost vs the same alloyof the hot rolled variety.
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Old 06-24-2007, 10:21 PM   #3 (permalink)
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Cold Roll has a lot better dimensional tolerances. Its also better for welding because it doesn't have the slag on it from when it cools down after forming.
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Old 06-24-2007, 10:59 PM   #4 (permalink)
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A good example is pipe and other mild steel..... pipe is hot rolled and other mild steel is cold rolled.... pipe is weaker....
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Old 06-24-2007, 11:02 PM   #5 (permalink)
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cold rolled is great but getting hard to find in over like .134, military is getting anything thicker than that for the hummers.
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Old 06-25-2007, 10:39 AM   #6 (permalink)
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As stated above, alloy is everything.

CR has great dimensional tolerances and edges sharp enough to cut your hand on, it is great to work with but pricey.

I've recently started using Hot Rolled P&O (pickled and oiled) in places I used to use Cold Roll.

For comparisson I was buying CR 1018 for $80 for a 6" x .188 x 12'bar.

I recently bought a sheet of HR P&O 1012 (nearly the same UTS and Yield strenght, better elongation at break) the sheet was 4'x12' and I had it sheared into strips ranging from 1 1/2 to 6" wide. It was $350 for the sheet including cut charge. The finish is not as good as CR, but is monumentally better than normal HR steel from the farm material yard. It is also seeming to be comparable in strength, but I don't have enough testing or or seat time on the parts to say for sure yet.
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Old 06-26-2007, 04:02 PM   #7 (permalink)
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Cold rolled breaks when bent.
Hot rolled bends.
Worked in a machine shop long time ago. Things that got bent were hot rolled for this reason.
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Old 06-28-2007, 10:34 AM   #8 (permalink)
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Quote:
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Cold rolled breaks when bent.
Hot rolled bends.
Worked in a machine shop long time ago. Things that got bent were hot rolled for this reason.
I work in a sheet metal shop, where 95% of our work is on forming and formed pieces...

its all 1018 CRS...

I think you need to re-think your generalization...
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Old 06-28-2007, 05:56 PM   #9 (permalink)
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Depends on thickness and bend radius, but cold roll will break (assuming same alloy) before HR will in tight bends, as cold rolling and bending have the same effect on the steel.
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Old 06-29-2007, 04:46 PM   #10 (permalink)
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most of the hot rolled is 1010 or 1012. most of the cold rolled is 1018
1010 hot rolled bar is 47ksi ultimate strength and 26ksi yield
1018 cold rolled is 64ksi ultimate and 54ksi yield.
Without the coldwork (like near a weld) the 1018 is 58ksi ultimate and 32ksi yield.
so even in the HAZ near a weld the cold rolled is still 23% stronger (yield strength) than the typical hot rolled..

Youcan tell pretty easily forming the stuff that the cold rolled is stronger than the hot rolled.
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Old 06-29-2007, 06:14 PM   #11 (permalink)
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The difference between HR and CR is the CR has undergone a significant amount of yielding under the recrystalization temperature. Yield strength decreases as temperature increases. The people that roll the material take advantage of this by heating the material to minimize the effort required to roll the material into shape. This temperature happens to be above the recrystalization temperature so there is no yeild strength increase. It is "hot" when they roll it. Hence the name Hot Roll. The cost associated with the larger machines required to overcome the yield strength of the steel at lower temperatures (CR), increases the price of the flat bar/shee/plate.

For the steels in this discussion, there is a significant amount of yielding before failure (ductility) and when you yield them, the yield strength increases. That is where CR's relative strength increase over HR comes from. You can take a piece of HR and bend it back and forth and you might notice that it takes more effort to yield the material after a bend or two. The yield strength is increasing. Often the location of the yielding will migrate to areas that haven't been "cold worked". CR's yield point is closer to its Ultimate Tensile Strength than HR. HR is more apt to bending without cracking because it hasn't gone through the available plastic deformation (yeilding) that CR has.

If you take a piece of CR and heat it to red, you now effectively have a piece of HR. So, as stated before, if you weld a piece of CR, the weld strength is the same as a piece of HR. Fortunately, if you are using the piece of CR as a shock tab, the material outside of the HAZ (the bolt hole) still has the qualities of CR.
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