Buying metals can be confusing. Most of the time, our customers know which form (Bar, Plate, Tube, Sheet, Channel, etc.) they need but not always which type of metal. While it is pretty easy to tell the difference between two dissimilar metals like Aluminum and Brass, it can be a little harder to differentiate between iron alloys that have been Hot Rolled from those that have been Cold Finished.
what is hot, rolled steel?
The basic definition: stock that has been passed through a pair of metal rollers while keeping the temperature of the stock well above its recrystallization temperature. This means that the metal is heated until it is hot enough to scale (over 1700 degrees Fahrenheit) and then forced through a set of rollers, taking whatever shape that the rollers allow the metal to take. This process is not quick, and the surface takes on a characteristic bluish-grey finish from the oxidation that occurs when the hot steel cools in the open air of the mill.
things to keep in mind about hot rolled steel
- The characteristic bluish-grey tint is caused by mill scale.
Mill scale does not tint consistently—the colors can fluctuate across a single piece—so it is best to not rely on an even coating of mill scale to supply the color for your form.
- If you plan on coloring any piece of Hot Rolled, you must first expose the base metal by grinding away its shell of oxidation. In order to color hot rolled forms, you must use a coloring agent that will chemically react with the metal itself. The bluish mill scale is inert and must be removed in order to cause any coloring agent’s chemical reaction.
how does hot rolled differ from cold finished?
- Cold-Finished is stock that has been rolled at room temperature. During this rolling process, the stock is doused in oil, which keeps the final product unoxidized, keeping the surface smooth and the natural grey color of the actual steel. Hot Rolled is formed at much higher temperatures and is not bathed in oil, allowing for more flexibility in forming the metal, but also allowing for greater corrosion.
- Most forms of Hot Rolled are more flexible than Cold Finished. While this isn’t usually noticeable in most forms, you can see a difference in some of the smaller sizes. If you are looking for steel with high structural integrity, Cold-Finished might be a better choice.
- At the corners and edges, Hot Rolled may appear to be a little rounded, with dimensions that might be less exact than Cold-Finished.
We hope that this section has been informative. We carry all of the standard forms and sizes of most metal products.. Please visit metalsforasteel.com to see all of our Hot Rolled Steel Inventory. If you are looking for a particular piece of metal that you haven’t been able to find anywhere, please email us and one of our metal specialists will get right back to you.