Production Process:
The production process of hot-rolled rebars involves heating the steel slab to a high temperature (generally above 1000°C) and then processing it through a rolling mill. In this high temperature environment, the steel has excellent plasticity and can be easily stretched and formed. Hot rolled products usually have a rough surface, which provides some adhesion. The production process of hot-rolled rebars is simple, low-cost, and suitable for large-scale production.

In contrast, cold-rolled rebars are bars that have already been processed to a hot-rolled state and then further processed at room temperature. Through the cold rolling process, the diameter of the rebar can be reduced while the strength and hardness are increased. Since room temperature processing is used during the cold rolling process, higher precision and better surface finish can be achieved. Cold-rolled rebars often require more equipment investment and operation, and the production cost is relatively high.

Differences in physical properties:
Hot-rolled rebars, processed at high temperatures, generally have good toughness and plasticity. These properties make hot-rolled rebars less likely to break when subjected to large impacts or stretching, and therefore, they are widely used in many construction projects. According to national standards, the yield strength of hot-rolled rebars is generally between 300-500MPa, but the specific values will vary depending on different models and usage requirements.

Cold rolled rebars have undergone cold working treatment, so their strength is much higher than that of hot rolled rebars. The yield strength of cold-rolled rebars is generally between 400-600 MPa, and can even reach over 700 MPa. In addition, the elongation of cold-rolled rebars is relatively low, so cold-rolled rebars are more suitable in some high-demand projects.

Differences in Appearance and Size:
Hot-rolled rebars typically have a rougher surface due to the presence of scale and other impurities formed during high-temperature processing. However, this rough surface can provide better adhesion of concrete and help enhance the integrity of the structure. Hot rolled rebars are usually available in a wide range of diameters, from 6mm to 40mm.

Cold-rolled rebars have a higher surface finish, a more precise diameter, and can be made smaller. Common diameters range from 5mm to 16mm. This size advantage makes cold-rolled rebars more flexible in some specific projects, especially where high strength and small diameter are required.

The differences between cold-rolled and hot-rolled rebar lie primarily in processing technology, material properties, and application scenarios.
Cold rolling is carried out at room temperature, while hot rolling requires high-temperature heating. This temperature difference leads to significant differences in hardness, toughness, surface quality, etc. between the two.

The temperature of the cold rolling process is usually controlled at room temperature. The steel billet is deformed through mechanical pressure and directly rolled into rebar. Due to the low temperature, the grains inside the steel are crushed, the structure is denser, and the material has higher hardness and strength. Cold-rolled rebar has a smooth surface, high dimensional accuracy, and the error can be controlled at the millimeter level. It is suitable for scenarios with strict requirements on surface flatness, such as precision mechanical parts and decorative building materials. However, the cold rolling process will make the steel brittle, reduce its impact toughness, and make it prone to cracking when bent, so annealing treatment is required before processing.

Hot rolling requires heating the steel billet to above 1100℃. The high temperature softens the steel and makes it easier to shape during rolling. After rolling, the rebar cools naturally and the internal grains are rearranged to form a coarse and uniform structure with better toughness than cold-rolled steel. The surface of hot-rolled rebar has oxide scale, slight bumps and color differences, and the dimensional error is usually more than 5 mm, but it has good impact resistance and can withstand repeated bending. Hot-rolled products are commonly used in beam and column steel bars and bridge supports at construction sites, and their cost is about 30% lower than that of cold-rolled products.

In terms of material properties, the yield strength of cold-rolled rebar can reach over 500MPa, which is about 20% higher than that of hot-rolled, but the elongation is only two-thirds of that of hot-rolled products. If both are immersed in salt water for corrosion testing, cold-rolled steel rusts 40% slower than hot-rolled steel due to the protection of the dense oxide layer on the surface. Things to note during construction: arc welding is required for cold-rolled rebar welding, as ordinary arc welding is prone to burn-through; the oxide scale must be removed before welding hot-rolled rebar, otherwise the weld strength will be reduced by 15%.

The choice between cold-rolling and hot-rolling depends on specific needs.

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