The steel bars with a diameter of 6.5 to 9 mm are rolled into wire rods; the diameters of 10 to 40 mm are generally 6 to 12 meters long. Hot-rolled steel bar should have a certain strength, namely the yield point and tensile strength, which is the main basis for structural design. At the same time, in order to meet the requirements of structural deformation, absorption of seismic energy, and processing and forming, hot-rolled steel bars should also have good plasticity, toughness, weldability, and adhesion between steel bars and concrete. China's hot-rolled steel bars can be divided into four levels according to their strength:
Grade I steels have a strength rating of 24/38 kg and are light steel bars rolled with plain steel, semi-killed steel or boiling steel No. 3 plain carbon steel. It belongs to low-strength steel, has good plasticity, high elongation (δ5 is more than 25%), easy to bend forming, easy to weld and so on. Its scope of use is very wide, and it can be used as the main stressed steel reinforcement for small and medium-sized reinforced concrete structures, stirrups of components, and tie rods for steel and wood structures. Rod reinforcement can also be used as a raw material for cold drawn low carbon steel wire and double reinforcing steel.
Grade II steel and grade III steel are rolled with low-alloy killed steel or semi-killed steel. Silicon and manganese are used as solid solution strengthening elements. Grade II steel strength level is 34 (32)/52 (50) kg; Grade III steel is 38/58 kg grade, its strength is higher, plasticity is better, and welding performance is ideal. The surface of the steel bar is rolled with lengthened longitudinal bars and evenly distributed transverse ribs, which can strengthen the bond between the steel bars and the concrete. The use of II and III steel bars as the stressed steel bars for reinforced concrete structures can save 40 to 50% of steel compared to the use of Grade I steel bars. Therefore, it is widely used in large and medium-sized reinforced concrete structures, such as bridges, dams, port engineering, and main reinforcements of building structures. Grade II and III steel bars can also be used as prestressed steel bars for building structures after cold drawing.
Grade IV rebars have a strength rating of 55/85 kg and are rolled with medium-carbon, low-alloy killed steels, with silicon and manganese as the main alloying elements, and vanadium or titanium as solid solution and precipitation strengthening elements. Strengthens its strength while ensuring its plasticity and toughness. Grade IV steel bars are also rolled with longitudinal and transverse ribs, which are the main prestressed reinforcements for building construction. Grade IV steel bars shall be cold-drawn by the construction unit before use, with a cold drawing stress of 750 megapascals to increase the yield point and give full play to the steel's inherent potential to save steel. The cold-drawn steel bars do not have a pronounced yield point. Therefore, the design is based on the cold tension stress statistics (cold drawing design strength). However, after several months of natural aging or artificial aging, the cold-pulled steel bar will have a short yielding step. Its value is slightly higher than the cold tensile stress, and the steel tends to be hardened. This phenomenon is called "age hardening. ". Therefore, when cold-rolled steel bar to ensure the provisions of the cold-drawn stress at the same time, it is necessary to control the cold-stretching rate is not too large, so as to avoid the steel becomes brittle. The carbon content of Grade IV rebar is high, and the process of flash-preheat-flash welding or post-weld heat treatment is generally used in the welding process to ensure that the welding head, including the heat affected zone, does not generate hardened microstructure and prevent brittle fracture. . Grade IV rebars are generally 12 mm in diameter and are widely used in prestressed concrete slab members and bundled configurations for large prestressed building components (such as roof trusses, crane girders, etc.). When hot-rolled grade IV steel bars are used as prestressed steel bars, cold drawing and welding are still required, and their strength is still low, and further improvement is needed.
Finished rolled steel bars In order to solve the problems of connection and anchorage of large-diameter, high-strength prestressed steel bars, we have developed successfully rolled steel bars. It is directly rolled out on the surface of the steel bar without longitudinal reinforcement and the transverse ribs are trapezoidal screw fasteners in the shape of the reinforcement, can be connected to the sleeve length, with a special nut as an anchor. This kind of steel bar has been used successfully in large-scale prestressed concrete structures, bridge structures, etc.
Grade I steels have a strength rating of 24/38 kg and are light steel bars rolled with plain steel, semi-killed steel or boiling steel No. 3 plain carbon steel. It belongs to low-strength steel, has good plasticity, high elongation (δ5 is more than 25%), easy to bend forming, easy to weld and so on. Its scope of use is very wide, and it can be used as the main stressed steel reinforcement for small and medium-sized reinforced concrete structures, stirrups of components, and tie rods for steel and wood structures. Rod reinforcement can also be used as a raw material for cold drawn low carbon steel wire and double reinforcing steel.
Grade II steel and grade III steel are rolled with low-alloy killed steel or semi-killed steel. Silicon and manganese are used as solid solution strengthening elements. Grade II steel strength level is 34 (32)/52 (50) kg; Grade III steel is 38/58 kg grade, its strength is higher, plasticity is better, and welding performance is ideal. The surface of the steel bar is rolled with lengthened longitudinal bars and evenly distributed transverse ribs, which can strengthen the bond between the steel bars and the concrete. The use of II and III steel bars as the stressed steel bars for reinforced concrete structures can save 40 to 50% of steel compared to the use of Grade I steel bars. Therefore, it is widely used in large and medium-sized reinforced concrete structures, such as bridges, dams, port engineering, and main reinforcements of building structures. Grade II and III steel bars can also be used as prestressed steel bars for building structures after cold drawing.
Grade IV rebars have a strength rating of 55/85 kg and are rolled with medium-carbon, low-alloy killed steels, with silicon and manganese as the main alloying elements, and vanadium or titanium as solid solution and precipitation strengthening elements. Strengthens its strength while ensuring its plasticity and toughness. Grade IV steel bars are also rolled with longitudinal and transverse ribs, which are the main prestressed reinforcements for building construction. Grade IV steel bars shall be cold-drawn by the construction unit before use, with a cold drawing stress of 750 megapascals to increase the yield point and give full play to the steel's inherent potential to save steel. The cold-drawn steel bars do not have a pronounced yield point. Therefore, the design is based on the cold tension stress statistics (cold drawing design strength). However, after several months of natural aging or artificial aging, the cold-pulled steel bar will have a short yielding step. Its value is slightly higher than the cold tensile stress, and the steel tends to be hardened. This phenomenon is called "age hardening. ". Therefore, when cold-rolled steel bar to ensure the provisions of the cold-drawn stress at the same time, it is necessary to control the cold-stretching rate is not too large, so as to avoid the steel becomes brittle. The carbon content of Grade IV rebar is high, and the process of flash-preheat-flash welding or post-weld heat treatment is generally used in the welding process to ensure that the welding head, including the heat affected zone, does not generate hardened microstructure and prevent brittle fracture. . Grade IV rebars are generally 12 mm in diameter and are widely used in prestressed concrete slab members and bundled configurations for large prestressed building components (such as roof trusses, crane girders, etc.). When hot-rolled grade IV steel bars are used as prestressed steel bars, cold drawing and welding are still required, and their strength is still low, and further improvement is needed.
Finished rolled steel bars In order to solve the problems of connection and anchorage of large-diameter, high-strength prestressed steel bars, we have developed successfully rolled steel bars. It is directly rolled out on the surface of the steel bar without longitudinal reinforcement and the transverse ribs are trapezoidal screw fasteners in the shape of the reinforcement, can be connected to the sleeve length, with a special nut as an anchor. This kind of steel bar has been used successfully in large-scale prestressed concrete structures, bridge structures, etc.
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