Cold-rolled vs. hot-rolled mild steel?

Date 08-29-2003 12:53

Hi Folks:

What are the differences between hot-rolled and cold-rolled mild steel? I *think* I know a few, which I'll list below, but I'm sure there's plenty more that I don't know. Please add to these or correct any misconceptions I may have. Thanks!

Hot rolled:
1) Generally has mill-scale on the surface.
2) Cheaper than cold-rolled.
3) Generally has less accurate dimensions (say for square or rectangular solid stock) than cold-rolled.
4) What else?

Cold rolled:
1) Generally has a smooth shining finish.
2) A little more expensive than hot-rolled.
3) Generally has a more accurate dimensions (say for square or rectangular solid stock) than hot-rolled.
4) What else?

Thanks!
Dave

By CHGuilford (****)

Date 08-29-2003 13:10

Most "hot rolled" we deal with is actually an ASTM A36 type of steel. The "cold rolled" we use comes with a 1011, 1018, 1020 or other grade designation of steel. The physical properties vary a bit between the actual alloys but are similar as far as weldability. We don't normally get into other types of bars so I can't tell you about them.

Chet Guilford

By G.S.Crisi (****)

Date 08-29-2003 14:06

Apart from the differences you mention, all of them correct, there`s another one to consider.
Hot rolled steel has been shaped at high temperature (say 1000 degrees C, you convert to F) and after rolling it was left to cool down naturally to room temperature. The cooling takes place into the steel mill building, so we can assume (at least approximately) that it cooled down in still air. So, in the great majority of cases, it`s not necessary to stress relief the hot rolled product. The applicable ASTM standards will state the few cases when the stress relief is necessary, usually for thicker products.
On the other hand, the cold rolled steel shows a high degree of residual internal stress produced by the operation, and are ususally subjected to stress relief after the rolling is complete.
Giovanni S. Crisi
Sao Paulo - Brazil