Steel Designation Myth -vs- Fact | Problem Solving | Forum

Lynn as Wayne says the difference between hot rolled and cold rolled is the mechanical processing. But ... most cold rolled MILD steel is 1018/1020, while most hot rolled mild steel is A36 or 44W here in Canada. The 36 or 44 refer to strength rather than carbon content. A big myth on blacksmith internet sites is that there are no chemistry specs for A36. There are chemistry specs but they are looser tolerances than the specs for 1018, and the maximum allowable carbon is .26% carbon vs .23% for 1018. due to tolerances though you could probably have 1018 with higher carbon than A36.

Lee,

Thanks for the links - I've bookmarked them. For some reason I've had a hard time finding steel analysis charts when I've Googled.

I think of SAE steel designations like gun "calibers." I though I understood them until I heard that you could fire .38 ammunition from a .357, but not the other way around. And compared a .22 shell to a .223. Then I realized the numbers are names that tell you something about the diameter, but they aren't specs. The steel designations are much the same way.

Rashelle;16083 wrote: Lynn, Once we heat it doesn't that make it the equivalent of hot rolled? Even if it started out as cold. Shouldn't the only difference at that point be the slight sizing difference? Maybe if there is slight scale on the hot rolled but not on the cold along with the cold being slightly larger diameter and a smoother surface, thus does not corrode as fast?

Not quite, cold roll is not the hot roll bar fed trough an additional roll, it is a completely different mix of steel, similar but different. Common hot roll A36 is a strength designation and common cold roll 1018,1020 etc are mix recipes. I am sure if someone tried hard enough they could find cold roll A36 or hot roll 1018 but not common in central Ca.

I have my doubts about cold-rolled lacking flaws because the "mix" is different. I've got no special knowledge about this, but can't imagine much that could go into a steel furnace and not fully mix with the melt. And my understanding is that all steel produced in the U.S. is remelted scrap. Since the chemistry is tighter on 1018/1020 than on A-36, there may be fewer engine blocks and dental implements included, but I doubt they're eliminated altogether.

Since cold-rolled is a premium product, perhaps the mills are more careful about things like cold shuts from billet tops (if everything isn't continuous cast these days). And maybe the the additional stress of cold rolling makes some flaws apparent that would be hidden in hot rolled until after it's shipped.

Or maybe it's just that flaws in modern steel are rare enough that we tend to remember them, and we find flaws in hot-rolled more often because we work hot-rolled more often.