Cold and hot steel????

I thought I would open a new thread on this... Since it was one of my questions...

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Originally Posted by everlastsupport

Just be aware the bed rails are normally cold steel. Works fine for most projects.

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What is the difference cold rolled and hot rolled steel??? I see suppliers offer both.

Oh and BTW I do have a handful of them in the scrap metal drum.

Hot rolled = last processing steps are performed when it is hot, at oxidizing temperatures. It has no internal stresses, but is covered with "mill scale" (a thick layer of Iron oxides.) To TIG or MIG weld to it, you will get the best results by first removing the mill scale. Otherwise, the thick oxide layer will make it difficult to observe the puddle and get good, uniform penetration. Storing it outside won't really "hurt" it very much, due to the mill scale.

Cold rolled = last processing steps are performed after it has cooled down below oxidizing temperatures. Typically this includes grinding off the "mill scale", leaving behind a shiny, bright bare steel surface. Sometimes processing includes further cold work, which means it can have internal stresses. (So it's dimensions can change as the stresses "relax" after it is machined or cut.) The bare, unoxidized surfaces are "ready to go" with beautiful TIG or MIG welds with no grinding required before welding. (Just remove any dirt or oils from the surface.) As rust will quickly form on the bare steel surfaces if you let it get wet, it should be stored in a dry environment to keep it from rusting.

Thanks... Is there any difference in welding the 2??? Besides the hot rolled needs aggressive cleaning??? Are the strengths about the same???

http://www.spaco.org/hrvscr.htm this will tell you difference

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Originally Posted by Rodsmachineshop

http://www.spaco.org/hrvscr.htm this will tell you difference

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Thanks for the link... Looks like they are similar but hot rolled usually has more carbon and there is a mid grade called P & O.

I had a general idea of what the hot and cold referred to and defaulted to Wikipedia as a reference. This article is interesting and has some visuals, and actually refers to the Spaco.org website:
http://en.wikipedia.org/wiki/Rolling_(metalworking)

"Hot" and "cold" refer to whether the final rolling process (shaping the steel to final dimensions) occurs above or below the re-crystalization temperature of the metal. This Wiki article conflicts with its own reference by saying hot rolled is more expensive than cold- gotta keep the realism filters in place even with Wiki, I guess.

Also, cold rolled steel is usually stronger because it gets work hardened. Work hardening is the same reason why stainless steel can be a pain in the azz to machine. In fact, 300 series stainless steel can be work hardened to a spring temper.