Hot-Rolled vs. Cold-Rolled Steel

Hot-rolled and cold-rolled are not exactly types of steel, rather they indicate how the steel was "finished" during its manufacture. You can obtain a number of steels in both hot-rolled and cold-rolled. Hot-rolled is more blacksmith friendly for 2 reasons: primarily price - it is a lot less expensive as compared to cold rolled; when drawing cold rolled out to a fine point, you have to be careful that work with with sufficient heat in the bar, or the tip will split.

Both hot-rolled and cold-rolled start out the same way. They start as massive billets of orange hot steel. Then they are passed through a series of rollers that take them down to their final size. Here is where the two steels differ. Hot-rolled is processed HOT all the way down to its final size. Cold-rolled is processed HOT almost to the end, but it is allowed to cool before going through the last sets of rollers. The rolling to final dimension is done COLD. Next it is passes through a pickle/acid bath which removes the mill scale from the surface. Finally it passes through an oil wipe which leaves a film of oil on the steel to prevent rusting.

You can identify hot-rolled steel by the following caricaturistics: it will have a layer of gray mill scale on its surface; the corners will have a slight radius; the sizing will not be as exact as cold-rolled, i.e. cold-rolled will be closer to the nominal size; hot-rolled may have some rust forming on it, depending on where it has been stored.

Cold-rolled steel will have the following caricaturistics: it will be bright and shiny with a film of oil on it; generally there should be no sign of rust; the corners of the bars will be sharper, have less of a radius than hot-rolled steel; it will have been rolled to a tighter tollerance when it comes to sizing.

Since the cold-rolled is squeezed down to its final size cold, it will have been work hardened. You can actually feel the difference. Take 2 bars of the same size and same lenght, say 5/16" square, 24" long. The cold-rolled bar will be stiffer, the hot-rolled bar will flex a little more.

At this time, 1/4" square can only be located as cold-rolled steel. Apparently the steel mills feel that there is not enough of a market to manufacture 1/4" square as hot-rolled.

-- AlbinDrzewianowski - 15 Apr 2009