The Difference Between Hot Rolled Stainless Steel and Cold Rolled Stainless Steel?
Well that depends on what part of the train you’re looking at. If you’re looking at the tracks, you’re seeing hot rolled steel. If you’re looking at a railroad car, you’re likely looking at cold rolled steel.
Stainless steel hot rolled steel and cold rolled steel are two of the final processes in stainless steel fabrication. While both processes involve manipulating steel, they are based on different temperatures; different methods and the final products are very different. Even the appearance is different: hot-rolled metal has a rougher finish and is usually a blue-gray color, while cold-rolled metal is smooth and gray.
Now let’s look at the processes in a little more detail. Hot rolling, a process that occurs above the recrystallization temperature of the metal, produces a metal that has a rougher surface finished. Hot rolled steel is used for products such as railroad tracks.
Cold rolling is a process that’s done with the metal below its recrystallization temperature (usually at room temperature), which increases the metal’s strength. Cold rolled metal is used for the railroad cars themselves. Cold metal, which has a smoother finish, is also used for such things as cars and appliances.
Simply put, hot rolled steel is steel that has been heated high enough for the metal to begin to soften. After the metal is rolled, it is heat treated to strengthen it.
Cold rolled steel has simply been pounded with special hammers without having external heat applied to it. Cold rolled steel can also be rolled or stretched, as long as it is done at the same low temperature – usually room temperature. Rolling and stretching the steel in this way causes a permanent increase in the hardness of the stainless steel, as well as it strength. When forces such as hammering, stretching or rolling are applied to the stainless steel, it causes changes in the composition that enhance certain features of the steel. It’s imperative that the temperature of the steel be below a certain range, because at higher temperatures, those desired features will be eliminated.
Hot rolled metal is generally done in large operations or smaller ones. Large projects are done by feeding large pieces of metal into rolling mills at the proper temperature. Smaller operations involve starting the materials at room temperature and heating them. The material has to stay about the recrystallization temperature while it’s being worked. If the temperature drops too much, the metal worker has to reheat it. Cold rolling can produce different shapes as long as they are relatively uniform and small but it does require a series of shaping operations.
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