Difference between Hot Rolled Steel and Cold Rolled Steel

Hot-rolled steel and cold-rolled steel are the two main processing methods in steel production, and they differ significantly in many aspects. Here is a detailed comparison of hot-rolled steel versus cold-rolled steel:

1. Production process

Hot rolled steel: Hot rolled steel is rolled through a rolling mill at high temperatures (usually above 1000°C). At high temperatures, steel becomes more plastic and can be formed into desired shapes more easily. During the hot rolling process, a layer of iron oxide scale will be produced on the surface of the steel, which needs to be removed in subsequent processing. Hot rolling usually uses large ingots and large rolling reductions. The production pace is fast and the output is large, creating conditions for large-scale production.

Cold rolled steel: Cold rolled steel is rolled at room temperature. Cold-rolled steel has higher precision and surface quality because it is rolled at lower temperatures. However, due to the poor plasticity of steel during cold rolling, it is usually necessary to perform hot rolling treatment first, and then cool the hot-rolled steel before cold rolling. The production process of cold-rolled steel includes pickling, rolling, annealing and surface treatment.

2. Mechanical properties

Hot-rolled steel: Since the steel has experienced high temperature and plastic deformation during the hot-rolling process, its internal structure and structure are relatively loose. Therefore, the strength and hardness of hot-rolled steel are relatively low, but the elongation and toughness are high. This makes hot-rolled steel more suitable for applications requiring higher plasticity and toughness, such as building structures, bridges, etc.

Cold-rolled steel: The rolling temperature of cold-rolled steel is lower, and the internal structure and structure of the steel are tighter, so its strength and hardness are higher, and the elongation and toughness are lower. This makes cold-rolled steel more suitable for applications requiring higher strength and stiffness, such as automobile manufacturing, machinery manufacturing, etc.

3. Appearance and surface quality

Hot-rolled steel: The appearance color is usually black or dark gray. The surface may have an oxide layer or a black layer of iron tetroxide, and the surface quality is relatively poor.

Cold-rolled steel: Due to the surface finishing performed during the cold-rolling process, cold-rolled steel generally has a better surface quality than hot-rolled steel, with a bright surface, a smoother surface finish, and tighter dimensional tolerances.

4. Application areas

Hot-rolled steel: Hot-rolled steel is widely used in construction, bridges, ships, petrochemicals and other fields because of its good plasticity and toughness. Especially in the construction field, hot-rolled steel is widely used in beams, columns, floors and other parts of reinforced concrete structures.

Cold-rolled steel: Due to its high strength and good surface quality, cold-rolled steel is mainly used to manufacture products with high precision and surface requirements, such as automobile bodies, home appliance casings, precision instruments, etc.

5. Cost

Because the production process of hot-rolled steel is relatively simple and the production efficiency and output are high, its cost is usually lower than that of cold-rolled steel. The cost of cold-rolled steel is relatively high due to the complex production process and high requirements for materials and equipment.

In summary, there are significant differences between hot-rolled steel and cold-rolled steel in terms of production process, mechanical properties, appearance and surface quality, application fields, and cost. In actual applications, the appropriate steel type should be selected according to specific needs and scenarios to ensure the safety and reliability of the project.