Basic knowledge of deformed steel

Rebar is commonly known as rebar, also known as fine-grained hot-rolled rebar; The first letter of "Fine" is added after the English abbreviation of hot-rolled ribbed steel bar. For example: HRBF335, HRBF400, HRBF500. The applicable grades of seismic structures with higher requirements are: add E after the existing grades (for example: HRB400E, HRBF400E). 1、 The deformed steel bar is commonly known as steel bar, also known as fine-grained hot-rolled steel bar; The first letter of "Fine" is added after the English abbreviation of hot-rolled ribbed steel bar. For example: HRBF335, HRBF400, HRBF500. The applicable grades of seismic structures with higher requirements are: add E after the existing grades (for example: HRB400E, HRBF400E).
2、 Category (1) Performance classification: according to the executive standard of deformed steel bars in China (G B1499.2-2007), the deformed steel bars are divided into three grades according to the strength grade (yield point/tensile strength); (2) The deformed steel bars are classified according to their uses, such as ordinary steel bars for reinforced concrete, pre-stressed steel bars, heat-treated steel bars for concrete, etc. (3) According to appearance, it is divided into ribbed reinforcement and plain round reinforcement.
The difference between deformed steel bar and plain round steel bar is that the deformed steel bar and plain round steel bar have longitudinal ribs and transverse ribs on the surface, usually with two longitudinal ribs and transverse ribs evenly distributed along the length direction. The deformed steel belongs to the small section steel, which is mainly used for the skeleton of reinforced concrete building components. In use, certain mechanical strength, bending deformation performance and process welding performance are required. The raw steel billet for the production of deformed steel bars is carbon structural steel or low alloy structural steel which has been killed and melted, and the finished steel bars are delivered in hot rolled, normalized or hot rolled condition.
Main producing areas: North China, East China, Northeast China, such as Shougang, Tangshan Iron and Steel, Xuangang, Chenggang, Xinxing Cast Iron and Steel, Jianlong, Xilin, Beitai, Fushang, Shagang, Jingye Iron and Steel, Hebei Iron and Steel, etc.
Specification requirements of deformed steel bars shall be listed in the import and export trade contract. Generally, it shall include the standard grade (type code), nominal diameter of reinforcement, nominal weight (mass), specified length and the tolerance of the above indicators. Chinese standards recommend the series of deformed steel bars with nominal diameters of 6, 8, 10, 12, 16, 20, 25, 32, 40, and 50 mm. The supply length is divided into fixed length and double length. The selection range of length of deformed steel bars exported from China is 6~12m, and that of deformed steel bars produced in Japan is 3.5~10m; If there is no requirement specified in the contract, the domestic domestic screw thread steel is usually fixed to a length of 9m and 12m.
3、 It is widely used in building, bridge, road and other civil engineering construction. 1) Surface quality. The surface quality of deformed steel bars is specified in the relevant standards, and the ends shall be cut straight, the surface shall be free of cracks, scabs and folds, and there shall be no harmful defects in use. 2) Allowable value of overall dimension deviation. The requirements for the bending of deformed steel bars and the geometric shape of reinforcement are specified in the relevant standards. As specified in Chinese standards, the bending of straight bar reinforcement shall not affect normal use, and the total bending shall not be greater than 0.4% of the total length of reinforcement.
4、 Technical standard GB1499.2-2007 (Steel for Reinforced Concrete Part 2: Hot Rolled Ribbed Steel) GB1499.2-2007/XG1-2009 Steel for Reinforced Concrete Part 2: Hot Rolled Ribbed Steel National Standard No. 1 Amendment; GB700-2006 (carbon structural steel); GB/T 2101-2008 (General provisions for acceptance, packaging, marking and quality certificate of section steel); GB1499.1 ～ GB1499.3 (steel bars for concrete); JIS G3112-87 (98) (bar steel for reinforced concrete); JISG3191-66 (94) (Shape, size, weight and tolerance of hot-rolled bar steel and coil bar steel); BS4449-97 (Hot rolled steel bars for concrete structures).
5、 Chemical composition Brand Chemical composition, 100% C Si Mn P S CeqHRB400 0.25 0.80 1.60 0.045 0.045 0.54HRB500 0.25 0.80 1.60 0.045 0.045 0.55 (1) Composition inspection 1) Inspection method: The commonly used standard inspection methods for the inspection and analysis of the above chemical components are as follows: GB/T223, JISG1211? 1215, BS1837, BS Manual 19, etc. 2) Composition index: The main indicators for assessing the composition content of deformed steel bars are: C, Mn, P, S, Si, etc. The content varies with the grade, and the approximate range is: C (0.10~0.40%), Mn<1.80%, P<0.050%, S<0.050%, Si (0.60~1.00%). (2) The surface of surface quality reinforcement shall be free of cracks, scabs and folds. Bumps are allowed on the surface of the reinforcement, but they shall not exceed the height of the transverse rib. The depth and height of other defects on the surface of the reinforcement shall not exceed the allowable deviation of the size of the location. (3) Dimension profile 1) The nominal diameter range and the recommended diameter range of reinforcement are 6~50mm, and the standard recommended nominal diameter of reinforcement is 6, 8, 10, 12, 16, 20, 25, 32, 40, 50mm. 2) Allowable deviation of surface shape and size of ribbed reinforcement included angle between transverse rib and reinforcement axis β It shall not be less than 45 degrees. When the included angle is not more than 70 degrees, the direction of the reinforcement relative to the transverse rib on both sides shall be opposite; The nominal spacing l of transverse ribs shall not be greater than 0.7 times of the nominal diameter of reinforcement; The included angle between the side of transverse rib and the surface of reinforcement α Not less than 45 degrees; The sum of the clearance between the ends of transverse ribs on two adjacent sides of the reinforcement (including the width of longitudinal ribs, transferred from the rolling house) shall not be greater than 20% of the nominal perimeter of the reinforcement; When the nominal diameter of reinforcement is not more than 12mm, the relative rib area shall not be less than 0.055; When the nominal diameter is 14mm and 16mm, the relative rib area shall not be less than 0.060; When the nominal diameter is greater than 16 mm, the relative rib area shall not be less than 0.065. Refer to Appendix C for the calculation of relative rib area. Ribbed reinforcement is usually with or without longitudinal ribs;
3) Length and allowable deviation a. The length of reinforcement is usually delivered according to the fixed length, and the specific delivery length shall be indicated in the contract; Rebar can be delivered in coils. Each coil should be one rebar, and 5% of the number of coils per batch (two coils if less than two coils) is allowed to be composed of two rebars. The coil weight and diameter shall be determined by both parties through negotiation. B. Allowable deviation of length: the allowable deviation of length when the reinforcement is delivered according to the fixed length shall not be greater than ± 25mm; When the minimum length is required, the deviation is 50mm; When the maximum length is required, the deviation is - 50mm. C. Bending degree and end, bending degree of straight bar reinforcement shall not affect normal use, and the total bending degree shall not be greater than 0.4% of the total length of reinforcement; The end of reinforcement shall be cut straight, and local deformation shall not affect the use.
6、 Performance inspection 1) Performance index: the inspection items for assessing the mechanical properties of deformed steel bars include tensile test (tensile strength, yield strength, elongation) and bending test (one-time bending and reverse bending). See Table 6-7-7 for specific indicators. 2) Test method: ① Tensile test method: Common standard test methods include GB/T228.1-2010, JISZ2201, JIS SZ2241, ASTMA370 ГОСТ 1497, BS18, etc.; ② Bending test method: common standard test methods include GB/T232-88, YB/T5126-2003, JISZ2248, ASTME290 ГОСТ 1401 9, etc. 3) Bending performance After bending 180 degrees of the bending center diameter specified in the following table, the surface of the bending part of the reinforcement shall not produce cracks. 4) The reverse bending performance can be tested according to the requirements of the Demander. The diameter of the bending center of the reverse bending test is increased by one reinforcement diameter compared with the bending test. First bend 90 degrees in the forward direction, then bend 20 degrees in the reverse direction. After the reverse bending test, there shall be no cracks on the surface of the bending part of the reinforcement.
7、 Identification of true and false deformed steel bars' At present, the disqualification factors of fake and inferior hot-rolled ribbed steel bars (commonly known as deformed steel bars) in the steel market are mainly as follows: 1. The actual size is about one specification smaller than the nominal size. The dealers purchase the goods by actual weight and deliver the goods by theoretical weight to earn the amount of metal and gain profits. 2. The strength is low. 3. The unqualified rate of chemical composition is high. The main reason is that the raw materials of the small rolling mill are unqualified, and the deformed steel bars are rolled with home-made steel billets. When purchasing deformed steel bars, first of all, from the perspective of the appearance size, the vernier gauge can be used to simply measure whether the actual size is about one specification or more smaller than the indicated size (generally, the deformed steel bars are rolled with specification marks, and transferred from the home of steel rolling) (for example, the standard inner diameter of Ø 12 deformed steel bars is 11.5 ± 0.4mm, while the inner diameter of fake deformed steel bars is mostly about 10mm). At the same time, some fake and inferior deformed steel bars deceive people's vision by flattening, so the end face of steel bars is flat and elliptical, while the end face of normal steel bars should be basically circular; Secondly, in terms of surface quality, the fake and inferior deformed steel bars are rolled with earth billets, and their surface quality is poor, often with defects such as scabs, and have overall roughness. At the same time, due to insufficient heating temperature and rolling speed, the surface color of some small rolling plants is red; Third, most of the regular steel products are packaged in large bundles when they are delivered from the factory. The bundled steel products are hung with metal labels corresponding to the real products, indicating the manufacturer, steel grade, batch number, specification and inspection code. However, due to the poor production conditions, there is no large lifting equipment for the fake and inferior steel bars. Most of them are packed in small bundles (about ten bundles) or in bulk, without metal labels and quality assurance. Of course, to avoid buying fake and inferior steel bars at all, it is better to buy them from the direct agent of famous manufacturers, especially the famous steel bars in the province ("Minguang" brand deformed steel bars of Sangang), which are not only of stable quality, but also easy to handle even if there is a dispute. Experienced people can also identify other chemical components through sparks. It is suggested that when purchasing deformed steel, users must purchase regular steel at regular steel business units or business sites, obtain steel quality certificates and conduct acceptance. Those with quality doubts can go to professional inspection institutions for quality consultation and testing.
8、 The production process deformed steel bar is the steel bar with ribs on the surface, also known as ribbed steel bar, usually with two longitudinal ribs and transverse ribs evenly distributed along the length direction. The shape of transverse rib is spiral, herringbone and crescent. It is expressed in millimeters of nominal diameter. The nominal diameter of ribbed reinforcement is equivalent to the nominal diameter of plain round reinforcement with equal cross section. The nominal diameter of reinforcement is 8-50 mm, and the recommended diameters are 8, 12, 16, 20, 25, 32 and 40 mm. Ribbed reinforcement mainly bears tensile stress in concrete. Due to the role of the rib, the ribbed steel bar has a greater bonding capacity with the concrete, so it can better bear the role of external forces. Ribbed reinforcement is widely used in various building structures, especially large, heavy, light thin-walled and high-rise building structures.
The deformed steel bar is produced by small rolling mill. The main types of small rolling mill are continuous, semi-continuous and horizontal. At present, most of the newly built and in use full-continuous small mills in the world. Nowadays, the popular steel bar rolling mills include the universal high-speed rolling steel bar rolling mill and the 4-cut high yield steel bar rolling mill.
The billets used for continuous small rolling mill are generally continuous casting billets, with side length of 130~160mm, length of 6~12m and unit weight of 1.5~3t. The rolling lines are mostly arranged in the form of horizontal and vertical interchanges to realize the whole line of non-twist rolling. There are 18, 20, 22 and 24 small rolling mills according to different blank specifications and finished product sizes, and 18 are the mainstream. At present, new processes such as walking beam heating furnace, high-pressure water descaling, low temperature rolling and endless rolling are mostly used for bar rolling. Rough rolling and intermediate rolling are developed to adapt to large billets and improve rolling accuracy. The finishing mill is mainly used to improve accuracy and speed (up to 18m/s). The product specification is generally ф 10-40mm, also available ф 6-32mm or ф 12-50mm. The steel produced is low, medium and high carbon steel and low alloy steel which are widely needed in the market; The maximum rolling speed is 18m/s. The production process is as follows:
Walking beam heating furnace → roughing mill → intermediate mill → finishing mill → water cooling device → cooling bed → cold shear → automatic counting device → baling machine → unloading bench
Calculation formula of theoretical weight of deformed steel bar: outer diameter Х external diameter Х 0.00617=kg/m