What is the difference between hot rolled steel and cold rolled steel?
Each metal has its own advantages and uses. For example, certain types of steel are very suitable for household appliances, while other types of steel are suitable for use in the automotive or shipbuilding industry, gas tanks, and construction.
In addition, the grades of materials with the same chemical composition may have different qualities depending on the manufacturing method. Hot-rolled steel and cold-rolled steel are examples. So, how to choose hot-rolled steel or cold-rolled steel?
Hot rolled steel
Hot processing is more widely used because it requires less energy, and is usually used for compression molding, such as rolling, extrusion, forging, etc. Hot rolling takes place at a temperature higher than the recrystallization temperature of the material, raising the temperature of the billet to above 1000°C, and then sending it to the rolling machinery. Continuous rolling can obtain the required metal sheet (3 mm and above) or profile.
Compared with cold-rolled steel, hot-rolled steel can be mass-produced, and its market price remains at a relatively low level. After the steel cools at room temperature, the microstructure of the material is changed, thereby increasing the ductility and toughness.
However, hot-rolled steel shrinks slightly during the cooling process, causing the metal to withstand internal stress, resulting in uneven and distorted dimensional measurements. The dimensional tolerance of the material can vary between 2-5%. Hot-rolled steel has a scaly surface, which is an oxide formed at high temperatures, so it is easy to identify hot-rolled products by touching the surface.
Uses of hot-rolled steel
When the precision is not high, hot-rolled steel is a good choice, and its huge price advantage is more important than precision. Some common uses of hot rolled steel are: building construction, pipes, truck frames, doors and shelves, railroad tracks, tram parts, etc.
Cold rolled steel
Cold working is a metal forming method, which has many advantages compared with hot working. Technically speaking, cold working includes cold rolling and cold drawing. The former is used for sheet metal manufacturing, and the latter can be used for rectangular and round steel bars.
In contrast to hot rolling, the metal temperature during cold rolling is lower than its recrystallization temperature. If low carbon steel is used, the metal can be rolled to a thickness of 0.5-3 mm; if stainless steel is used, the metal can be rolled to a thickness of 0.5-5 mm. During the rolling process, oil is used to cool the material and also acts as a lubricant. If there is no oil film, the material will wear and deform. Therefore, cold-rolled steel can be identified by oily and smooth surface.
The main advantages of cold working are: accurate finished product size, smooth surface, higher strength performance.
Uses of cold-rolled steel
Although cold-rolled steel is more expensive than hot-rolled steel, the above advantages make it useful in many scenarios. Since the surface is already smooth enough, the finished product does not require a lot of extra surface finishing. Cold rolled/cold drawn steel uses include: metal furniture, structural parts, household appliances, water heaters, metal containers, fan blades, pans, computer cabinets, etc.