October 12, 2022
A strip of steel used as a major structural material in concrete works. According to the shape of the circular section of light circular steel bar and ribbed deformation steel bar, according to the production process of hot rolled steel bar, heat treatment steel bar, cold rolled ribbed steel bar and so on. Its specification is expressed in diameter (mm).
The hot rolled steel bar is made of carbon structural steel or low alloy structural steel billet by hot rolling, which is one of the most used steel varieties in civil construction engineering. Hot rolled steel bar has a considerable strength, can meet the structural deformation, absorption of seismic energy, molding and connection required good plasticity, toughness, weldability and concrete bonding. The light round steel bar in hot rolled steel bar is mainly Q235 carbon structural steel, the specification is 5.5 ~ 9mm, mostly rolled into wire rod, mainly used as the raw material of small and medium-sized beam, plate component stirrup, main reinforcement and cold drawn low carbon steel wire. Ribbed deformed steel bar commonly known as threaded steel, rolled by low alloy structural steel, nominal diameter of 8 ~ 50mm, mostly used as the main reinforcement of concrete structure; After cold drawing can also be used as the main reinforcement of prestressed concrete structure. Various countries have different classification standards for hot rolled steel bars. According to the strength index, hot rolled steel bars are divided into four grades (Ⅰ, Ⅱ, Ⅲ, Ⅳ) in China. In addition, the finished rolled steel bar without welding performance requirements is also a kind of hot rolled steel bar.
(1) Class Ⅰ steel bar. In the strength index, the yield point and compressive strength are 235MPa and 370MPa respectively, and the specification is 8 ~ 20mm. With Q235 carbon structural steel rolled into straight round steel bar, its plasticity, toughness, easy to bend forming, easy to welding, suitable for small and medium-sized concrete structure of the main reinforcement, stirrup and steel and wood structure, etc..
(2)Ⅱ, Ⅲ grade reinforcement. In the strength index, the yield point and compressive strength of the Ⅱ grade steel bar are 335MPa and 510MPa, the Ⅲ grade steel bar is 400MPa and 570MPa, the specification is 8 ~ 40mm, with low alloy structural steel sedation steel (Ⅱ grade steel bar can also be used for semi-sedation steel) rolling. The surface of the steel bar is equipped with two longitudinal ribs and transverse ribs (also called crescent ribs) that are evenly distributed along the length to enhance the bond between the steel bar and the concrete. For the convenience of identification and management, the steel bar surface is rolled with strength grade, specification and other marks. Ⅱ, Ⅲ reinforced high strength, good plasticity, suitable for the main force of reinforced concrete structure, and also can be used after cold drawn for prestressed reinforcement, in order to improve the comprehensive performance of Ⅱ, Ⅲ grade steel, meet the requirement of aseismatic structure and improving Ⅲ grade steel welding performance, developed into 400 mpa grade steel varieties in China, and has been incorporated into the national standard, Named as "high quality hot rolled ribbed steel bar", its main technical conditions are: carbon equivalent ≤ 0.50%; Reduce carbon and sulfur content; Stipulating the upper limit value of yield point and the minimum yield ratio; Increase back bending performance test, etc.
(3) Grade Ⅳ reinforcement bar. Strength index, yield point and compressive strength are 540MPa and 835MPa, specifications for 8 ~ 32mm, rolled with low carbon alloy steel. The surface of the steel bar is the contour of the equal height rib, which can be used as the prestressed steel of the building structure. Because of its low strength in hot rolling state, it needs to be cold drawn before use. Of cold drawn steel bar are "age-hardening" phenomenon, namely, after months of natural aging or after artificial heat ageing, the yield of reinforced and there will be a short step, its value is slightly higher than the cold tensile stress, tensile strength increased slightly, there is a decrease in the elongation and impact toughness, so cold drawn to ensure that regulations of tensile stress at the same time, must control the elongation cannot too big, In order to avoid the yield point of the steel bar is too close to the tensile strength, resulting in brittle steel bar or lack of failure warning. The steel bars of grade Ⅳ have high carbon content and poor welding performance, and the welded joints are easy to appear hardening structure and brittle fracture. Therefore, countries tend to stop using, or can not be welded, or try to reduce the use, most have been replaced by prestressed steel wire and steel strand.
(4) fine rolled thread steel bar. There is no longitudinal rib on the surface, and the transverse rib is trapezoidal threaded steel bar. The rolling precision of the steel bar is higher than that of the general hot rolled steel bar. The steel bar can be lengthened by the inner thread sleeve and the special nut can be used as the prestressed anchor. The steel bar has no welding performance requirements, its yield point can be as high as 750MPa, and does not need to be cold drawn. It can be used in large prestressed concrete structures and bridge structures.
Heat treatment Rebar Tempered soxhlet rebar is made of medium carbon low alloy structural steel hot rolled rebar after quenching and tempering. It has high strength and toughness. According to its appearance, it can be divided into two kinds: with longitudinal rib and without longitudinal rib. It is one of the important varieties of prestressed high strength steel. The HEAT-TREATED STEEL BARS ARE SUPPLIED IN THE FORM OF DISKS. In order to ensure self-straightening after opening, the diameter of the disks should not be less than 250 times the diameter of the steel bars, so that the stress of the steel bars in the disks is within the elastic limit. There is no obvious yield point of heat-treated steel bar. Generally, only tensile strength and elongation are tested. Special equipment should be used to open the market. Do not use electric welding cutting, also can not be used for welding and spot welding, so as not to cause electric lighting resulting in steel strength reduction or brittle break. As other high strength steels, heat-treated rebar has high sensitivity to stress corrosion. Therefore, it is necessary to avoid the occurrence of rain, chloride or acid media etching, scoring, water accumulation in prestressed channels and unsatisfactory grouting in the process of transportation, storage and use, so as to prevent the brittle fracture or hysteretic fracture of rebar under low stress. Compared with ordinary prestressed steel wire, heat-treated steel bar has the advantages of good bond performance with concrete, low stress relaxation rate and convenient construction. It is mainly used in prestressed concrete sleeper and some industrial and civil buildings in China.
