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The Difference Between Hot Rolled & Pickled Steel

Steel began to be mass produced in the United States for use in the construction of railroads. The mass production of steel has evolved over the years, and there are many steps in the manufacturing process. Pickled steel and hot-rolled steel are not different types of steel, but different steps in the steel-making process that relate to the finished surface. There is also cold-rolled steel, which is different from hot-rolled steel because it is processed at a low temperature to prevent the formation of iron oxide scales.

Hot-Rolled Steel
- Hot-rolled steel is produced when steel manufacturers heat the metal and press it through industrial rollers that manipulate the metal according to certain specifications. The hot metal is more malleable, and thus easier to work with. Manufacturers use hot-rolling to achieve uniform surface, thickness and mechanical properties. Hot-rolled steel is used in the production of the following grades of steel: commercial steel, drawing steel, structural quality steel and medium/high strength low alloy steel.
Cold-Rolled Steel
- Cold-rolled steel is produced when steel that has been created during hot-rolling is allowed to cool before it is rolled into its final shape. Cold-rolled steel is available in fewer shapes and sizes than hot-rolled steel because the durability of steel is affected when it gets manipulated at room temperature. When the steel is hammered or shaped at room temperature it can harden at the site of impact and begin to crack. Unlike hot-rolled steel, cold-rolled steel does not require pickling to prevent oxidation.
Scales
- Scales are formations that occur on the surface of heated steel when the iron in the steel reacts with the air and oxidizes. Scales make the steel susceptible to accelerated corrosion and can cause skidding on cold-rolling equipment, which result in dangerous mill wrecks. To remove them, manufacturers employ a two-step process. First is scale-breaking. The steel is passed through a series of large and small rolls that pound the scales. Scales begin to crack, which is important for the second part of the scale removal process: pickling.
Pickled Steel
- After the steel passes through the scale-breaking rollers, it gets pickled. The steel is submerged into three separate hydrochloric acid baths of increasing strength, from weakest to strongest. Scale breaking is vital to the pickling process because the cracks created in the scales allows these acids to penetrate more deeply. The pickling process can be sped up by increasing the temperature of the acid, but only to a certain degree. If heated too much the acid evaporates and forms harmful vapors. After pickling, the steel is rinsed of the acid and lubricated with oil to prevent further oxidization.

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