Low-carbon-equivalent HRB400E reinforcing steel bar and preparation method thereof

Abstract

The invention provides a low-carbon equivalent HRB400E steel bar and a preparation method thereof. The steel bar comprises the following chemical components in percentage by mass: 0.22%-0.25% of C, 0.35%-0.45% of Si, 0.70%-0.80% of Mn, less than or equal to 0.040% of P, less than or equal to 0.040% of S, 0.03%-0.040% of V, 0.005%-0.02% of Cr, 0.012%-0.018% of N and the balance of Fe and trace elements. And the carbon equivalent Ceq of the HRB400E steel bar is greater than or equal to 0.34% and less than or equal to 0.39%. The mass percentage content of silicon and manganese in the low-carbon equivalent HRB400E reinforcing steel bar is at a relatively low level, and microalloyed vanadium and chromium with proper mass percentage content are matched, so that the cost of the reinforcing steel bar can be reduced on the whole, the mechanical property of the HRB400E reinforcing steel bar can be relatively ideal, meanwhile, the low-carbon equivalent HRB400E reinforcing steel bar has relatively low carbon equivalent of 0.34-0.39%, and the service life of the low-carbon equivalent HRB400E reinforcing steel bar is prolonged. And the HRB400E reinforcing steel bar can have better welding performance at the same time.

Description

Technical Field

[0001] The present application belongs to the field of steel technology, and specifically relates to a low-carbon equivalent HRB400E steel bar and a preparation method thereof. Background Art

[0002] With the increasing requirements for building structural safety and earthquake resistance, traditional building steel bars have deficiencies in earthquake resistance. Therefore, high-strength, high-performance earthquake-resistant steel bars such as HRB400E have gradually become the mainstream of the market. In addition, with the rapid development of national infrastructure construction, such as the increase in post-disaster reconstruction, bridges, highways, high-rise buildings and other projects, the demand for high-strength earthquake-resistant steel bars is also increasing. These factors have jointly promoted the research and development and widespread application of HRB400E steel bars.

[0003] HRB400E steel bars mainly improve the strength and toughness of steel bars by increasing the content of alloy elements, such as vanadium-nitrogen alloying, but this will also increase the production cost of steel bars and excessive consumption of alloy resources, which is not conducive to the sustainable development of the economy and society. On the other hand, as hot-rolled ribbed steel bars are used in infrastructure construction, engineering and construction, the welding performance of steel bars is of great concern. Summary of the invention

[0004] The present application provides a low-carbon equivalent HRB400E steel bar and a preparation method thereof, aiming to provide a low-carbon equivalent HRB400E steel bar that can reduce alloy content and reduce cost while improving the quality of the steel bar.

[0005] In a first aspect, the present application provides a low-carbon equivalent HRB400E steel bar, comprising the following chemical composition in percentage by mass: C: 0.22% to 0.25%, Si: 0.35% to 0.45%, Mn: 0.70% to 0.80%, P≤0.040%, S≤0.040%, V: 0.03% to 0.040%, Cr: 0.005% to 0.02%, N: 0.012% to 0.018%, and the rest are Fe and trace elements; the carbon equivalent Ceq of the HRB400E steel bar satisfies: 0.34%≤Ceq≤0.39%.

[0006] Carbon equivalent Ceq=C+Mn / 6+(Cr+V+Mo) / 5+(Cu+Ni) / 15, where C, Mn, Cr, V, Mo, Cu and Ni refer to the mass percentages of C, Mn, Cr, V, Mo, Cu and Ni respectively.

[0007] In a feasible implementation manner of the first aspect of the present application, the sum of the mass percentage of Si and the mass percentage of Mn is W Si+Mn Satisfy: 1.1% ≤ W Si+Mn ≤1.25%.

[0008] In a feasible implementation manner of the first aspect of the present application, the sum of the mass percentage of V and the mass percentage of Cr is W v+Cr Satisfy: 0.04% ≤ W v+Cr ≤0.05%.

[0009] In a feasible implementation manner of the first aspect of the present application, the microstructure of the low carbon equivalent HRB400E steel bar is ferrite+pearlite; the volume fraction of ferrite is 67-76%, and the volume fraction of pearlite is 23-33%.

[0010] In a feasible implementation manner of the first aspect of the present application, the average grain size of the low carbon equivalent HRB400E steel bar is 6.52 μm to 11.37 μm.

[0011] In a feasible implementation manner of the first aspect of the present application, the yield strength of the low carbon equivalent HRB400E steel bar is 430Mpa~450Mpa; the tensile strength of the low carbon equivalent HRB400E steel bar is 570Mpa~600Mpa; the strength-to-yield ratio of the low carbon equivalent HRB400E steel bar is 1.3~1.4, and can be optionally 1.31~1.35.

[0012] In a feasible implementation manner of the first aspect of the present application, the elongation of the low-carbon equivalent HRB400E steel bar is 19% to 25%; the maximum force elongation of the low-carbon equivalent HRB400E steel bar is 13% to 20%.

[0013] The second aspect of the present application provides a method for preparing a low carbon equivalent HRB400E steel bar, comprising:

[0014] Obtaining raw materials with a predetermined mass percentage of chemical composition, smelting, and casting to obtain steel billets;

[0015] The steel billet is heated, taken out of the furnace, rolled, and cooled to obtain low carbon equivalent HRB400E steel bars; the low carbon equivalent HRB400E steel bars include the following chemical composition in mass percentage: C: 0.22% to 0.25%, Si: 0.35% to 0.45%, Mn: 0.70% to 0.80%, P≤0.040%, S≤0.040%, V: 0.03% to 0.040%, Cr: 0.005% to 0.02%, N: 0.012% to 0.018%, and the rest are Fe and trace elements; the carbon equivalent Ceq of the HRB400E steel bars satisfies: 0.34%≤Ceq≤0.39%.

[0016] In a feasible implementation manner of the second aspect of the present application, in the steps of heating the steel billet, taking out of the furnace, rolling, and cooling to obtain low-carbon equivalent HRB400E steel bars, the heating temperature is ≤1180°C, and the heating time is 40 to 80 minutes; the steel tapping temperature is 950°C to 1000°C, and can be optionally 955°C to 980°C.

[0017] In a feasible implementation manner of the second aspect of the present application, in the steps of heating, taking out of the furnace, rolling and cooling the steel billet to obtain low carbon equivalent HRB400E steel bars, the rolling includes rough rolling, intermediate rolling and finishing rolling.

[0018] In a feasible implementation manner of the second aspect of the present application, in the steps of heating, taking out of the furnace, rolling and cooling the steel billet to obtain low-carbon equivalent HRB400E steel bars, after the steel billet is taken out of the furnace, it is continuously rolled by 19 horizontal and vertical staggered rolling mills, and the rolling includes 6 rough rolling processors, 6 intermediate rolling processors and 7 finishing rolling processors.

[0019] In a feasible implementation manner of the second aspect of the present application, in the steps of heating, taking out of the furnace, rolling and cooling the steel billet to obtain low carbon equivalent HRB400E steel bars, the starting rolling temperature of the rough rolling process is 930°C to 980°C.

[0020] In a feasible implementation manner of the second aspect of the present application, in the steps of heating, taking out of the furnace, rolling and cooling the steel billet to obtain low carbon equivalent HRB400E steel bars, the temperature of the cooling bed on the steel bars is controlled to be 810°C to 850°C, and the cooling rate is 2.0°C / s to 4.0°C / s.

[0021] In a feasible implementation manner of the second aspect of the present application, in the steps of obtaining raw materials with a predetermined mass percentage of chemical composition, smelting, and casting to obtain a steel billet, the size of the steel billet is 165mm×165mm×12000mm or 165mm×165mm×9000mm.

[0022] In a feasible implementation manner of the second aspect of the present application, in the step of obtaining a raw material with a predetermined mass percentage of chemical composition, smelting, and casting to obtain a steel billet, the smelting includes converter smelting and LF refining, wherein the converter smelting includes controlling the ladle bottom blowing argon gas flow rate at 50-100 Nm 3 / h, ferrosilicon and silicon-manganese alloy are added 1 minute after steel is tapped, vanadium-nitrogen or vanadium-containing pig iron and ferroniobium are added with the steel flow after half of the ferrosilicon and silicon-manganese alloy are added, and the addition is completed before the slag rod is thrown.

[0023] In a feasible implementation manner of the second aspect of the present application, in the step of obtaining a raw material with a predetermined mass percentage of chemical composition, smelting, and casting to obtain a steel billet, the smelting includes converter smelting and LF refining, wherein the LF refining includes controlling the ladle bottom blowing argon / nitrogen flow rate at 100-300 Nm 3 / h, add lime and slagging agent to control the binary basicity of the refined final slag to 2.5-3.5 to obtain refined molten steel.

[0024] In a feasible implementation manner of the second aspect of the present application, in the steps of obtaining raw materials with a predetermined mass percentage of chemical composition, smelting, and casting to obtain a steel billet, the physical and chemical properties of the protective slag used in the crystallizer during the casting process include: viscosity 0.15 poise to 0.26 poise at 1300°C, melting temperature 1070°C to 1110°C, and the protective slag includes the following mass percentage compositions: SiO2: 28% to 37%, CaO: 22%-27%, K2O+Na2O: 8%-14%, F: 5%-9%, C solid: 8%-12%, and the rest are iron and trace elements.

[0025] In a feasible implementation manner of the second aspect of the present application, in the steps of obtaining raw materials with a predetermined mass percentage of chemical composition, smelting, and casting to obtain steel billets, the molten steel is subjected to secondary strong cooling in the crystallizer during the casting process, the water flow rates on the wide and narrow sides of the crystallizer are both 150t / h to 170t / h, and the specific water volume of the secondary cooling water is 1.4L / kg to 1.6L / kg. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is an electron microscope image of the organizational structure of the low carbon equivalent HRB400E hot-rolled ribbed steel bar in Example 1.

[0027] Figure 2 This is the electron microscope image of the organizational structure of HRB400E hot-rolled ribbed steel bar in comparative example 1 DETAILED DESCRIPTION

[0028] In order to make the invention purpose, technical scheme and beneficial technical effect of the present application clearer, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application, not for limiting the present application.

[0029] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range. In addition, although not explicitly stated, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.

[0030] In the description herein, when a composition is described as containing, comprising or including specific components, or when a process is described as containing, comprising or including specific process steps, it is expected that the composition of the present application also consists essentially of or consists of the components, and the process of the present application also consists essentially of or consists of the process steps.

[0031] The use of the terms "including," "comprising," "containing," and "having" should generally be interpreted as open ended and non-limiting unless expressly stated otherwise.

[0032] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number itself, and the “multiple” in “one or more” means more than two.

[0033] The above-mentioned summary of the invention of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0034] The inventors found that HRB400E steel bars are usually composed of C, Si, Mn, Cr, V, P, S, N, Fe and other trace elements. After the introduction of GB / T 1499.2-2018, the composition, performance and metallographic requirements were further standardized, and new requirements were put forward for the production process, metallographic structure and strength level of steel bars. In order to meet the standards, most steel mills use Nb, V, Cr and other micro-alloys to strengthen hot-rolled ribbed steel bars, and the alloy cost is still high.

[0035] At the same time, the carbon equivalent in carbon steel is one of the main factors affecting strength and weldability. A simple method to judge weldability is the carbon equivalent identification method. The so-called carbon equivalent refers to the content of alloy elements (including carbon) in steel converted into the equivalent content of carbon according to their role. It can be used as a reference indicator for evaluating the weldability of steel. Therefore, in order to ensure the performance of steel bars, they should also have a lower carbon equivalent to have better welding performance.

[0036] The inventors conducted in-depth research and, after a large amount of experimental research and demonstration, provided in this application a reasonable configuration of various elements such as Si, Mn, V and Cr, medium silicon, low manganese, low vanadium and chromium microalloying, and low carbon equivalent, and obtained a low-cost, low-carbon equivalent HRB400E steel bar with good mechanical properties and welding properties.

[0037] The present application provides a low-carbon equivalent HRB400E steel bar and a preparation method thereof, aiming to provide a low-carbon equivalent HRB400E steel bar that can reduce alloy content and reduce cost while improving the quality of the steel bar.

[0038] In the implementation manner of the first aspect of the present application, a low carbon equivalent HRB400E steel bar is provided, comprising the following chemical composition in percentage by mass: C: 0.22% to 0.25%, Si: 0.35% to 0.45%, Mn: 0.70% to 0.80%, P≤0.040%, S≤0.040%, V: 0.03% to 0.040%, Cr: 0.005% to 0.02%, N: 0.012% to 0.018%, and the rest are Fe and trace elements; the carbon equivalent Ceq of the HRB400E steel bar satisfies: 0.34%≤Ceq≤0.39%.

[0039] In the low carbon equivalent HRB400E steel bar of the present application, Si: 0.35% to 0.45%, Mn: 0.70% to 0.80%, V: 0.03% to 0.040%, Cr: 0.005% to 0.02%, the mass percentage of silicon and manganese is at a relatively low level, and is strengthened with appropriate mass percentages of micro-alloyed vanadium and chromium, which is beneficial to reducing the cost of the steel bar as a whole and can make the mechanical properties of the HRB400E steel bar more ideal. At the same time, it has a low carbon equivalent of 0.34% to 0.39%, which can make the HRB400E steel bar have better welding performance.

[0040] Carbon equivalent Ceq=C+Mn / 6+(Cr+V+Mo) / 5+(Cu+Ni) / 15, where C, Mn, Cr, V, Mo, Cu and Ni refer to the mass percentages of C, Mn, Cr, V, Mo, Cu and Ni respectively.

[0041] In some embodiments, the sum of the mass percentage of Si and the mass percentage of Mn is Si+Mn Satisfy: 1.1% ≤ W Si+Mn ≤1.25%.

[0042] The mass percentage of silicon and manganese has a certain impact on the cost and performance of HRB400E steel bars. When the mass percentage of silicon and manganese in the steel bars of this application is controlled within the above range, the alloy cost can be effectively reduced by more than 10 yuan / ton of steel, and it has a cost advantage when the price of silicon-manganese alloy increases. However, when the mass percentage of silicon and manganese is too low, it will affect the strength, plasticity and toughness of the steel bars, and may increase the processing cost, be easy to break, and affect the life of the steel bars.

[0043] In some embodiments, the sum of the mass percentage of V and the mass percentage of Cr is v+Cr Satisfy: 0.04% ≤ W v+Cr ≤0.05%.

[0044] In the present application, V and Cr elements mainly affect the strength of the steel bar by microalloying, and can affect the mechanical properties, welding performance and cost of the steel bar together with Si and Mn elements. In the present application, the content of silicon and manganese elements is relatively low, and when combined with the appropriate mass percentage of V and Cr elements, especially the mass percentage within the above range, the cost of the steel bar can still be low, and it has relatively ideal mechanical properties and welding strength. If the content of V and Cr elements is too high, it increases the cost and may affect the welding performance, making the welded joint prone to cracks. If the content is too low in the present application, it may be difficult to give full play to the strengthening effect of alloying, resulting in insufficient strength of the steel.

[0045] In some embodiments, the microstructure of the low carbon equivalent HRB400E steel bar is ferrite+pearlite; the volume fraction of ferrite is 67-76%, and the volume fraction of pearlite is 24-33%.

[0046] In this application, the ferrite + pearlite has a suitable volume fraction so that the low carbon equivalent HRB400E steel bar has a suitable organizational structure. The higher ferrite content helps to improve the welding performance of the steel bar and reduce defects such as cracks and lack of fusion generated during the welding process. The low carbon equivalent HRB400E steel bar has good mechanical properties, welding strength and cold bending performance.

[0047] In some embodiments, the average grain size of the low carbon equivalent HRB400E steel bar is 6.52 μm to 11.37 μm, and optionally 7 μm to 10 μm.

[0048] The low carbon equivalent HRB400E steel bar in this application has a suitable average grain size as shown in the above range, which can balance the requirements of strength, toughness, weldability and cold bending performance of the material to meet the needs of different engineering applications. If the average grain size of the HRB400E steel bar is too large, it will increase the difficulty of welding, and it is easy to crack or break during the processing, and the mechanical properties will decrease.

[0049] In some embodiments, the yield strength of the low carbon equivalent HRB400E steel bar is 430Mpa to 450Mpa; the tensile strength of the low carbon equivalent HRB400E steel bar is 570Mpa to 600Mpa; the strength-to-yield ratio of the low carbon equivalent HRB400E steel bar is 1.3 to 1.4, and can be optionally 1.31 to 1.35.

[0050] On the basis of having good yield strength and tensile strength, the HRB400E steel bar of the present application has a small strength-to-yield ratio and strong toughness, can better withstand external impact and deformation resistance, and is more conducive to improving welding performance.

[0051] In some embodiments, the elongation of the low carbon equivalent HRB400E steel bar is 19% to 25%; the maximum force elongation of the low carbon equivalent HRB400E steel bar is 13% to 20%.

[0052] In an embodiment of the second aspect of the present application, a method for preparing a low carbon equivalent HRB400E steel bar is provided, comprising:

[0053] Obtaining raw materials with a predetermined mass percentage of chemical composition, smelting, and casting to obtain steel billets;

[0054] The steel billet is heated, taken out of the furnace, rolled, and cooled to obtain low carbon equivalent HRB400E steel bars; the low carbon equivalent HRB400E steel bars include the following chemical composition in mass percentage: C: 0.22% to 0.25%, Si: 0.35% to 0.45%, Mn: 0.70% to 0.80%, P≤0.040%, S≤0.040%, V: 0.03% to 0.040%, Cr: 0.005% to 0.02%, N: 0.012% to 0.018%, and the rest are Fe and trace elements; the carbon equivalent Ceq of the HRB400E steel bars satisfies: 0.34%≤Ceq≤0.39%.

[0055] In some embodiments, in the steps of heating the steel billet, taking out of the furnace, rolling, and cooling to obtain low carbon equivalent HRB400E steel bars, the heating temperature is ≤1180°C, and the heating time is 40 to 80 minutes; the steel tapping temperature is 950°C to 1000°C, and can be optionally 955°C to 980°C.

[0056] In some embodiments, in the step of heating the steel billet, taking out of the furnace, rolling, and cooling to obtain low carbon equivalent HRB400E steel bars, the rolling includes rough rolling, intermediate rolling, and finish rolling.

[0057] In some embodiments, in the steps of heating, taking out of the furnace, rolling, and cooling the steel billet to obtain low-carbon equivalent HRB400E steel bars, the steel billet is continuously rolled by 19 horizontal and vertical staggered rolling mills after it is taken out of the furnace, and the rolling includes 6 rough rolling processors, 6 intermediate rolling processors, and 7 finishing rolling processors.

[0058] In some embodiments, in the step of heating, taking out of the furnace, rolling, and cooling the steel billet to obtain low carbon equivalent HRB400E steel bars, the starting rolling temperature of the rough rolling process is 930°C to 980°C.

[0059] In some embodiments, in the step of heating, unloading, rolling, and cooling the steel billet to obtain low carbon equivalent HRB400E steel bars, the temperature of the cooling bed on the steel bars is controlled to be 810°C to 850°C, and the cooling rate is 2.0°C / s to 4.0°C / s.

[0060] In some embodiments, in the steps of obtaining raw materials with a predetermined mass percentage of chemical composition, smelting, and casting to obtain a steel billet, the size of the steel billet is 165mm×165mm×12000mm or 165mm×165mm×9000mm.

[0061] In some embodiments, in the step of obtaining a raw material with a predetermined mass percentage of chemical composition, smelting, and casting to obtain a steel billet, the smelting includes converter smelting and LF refining, wherein the converter smelting includes controlling the flow rate of argon gas at the bottom of the ladle to be 50-100 Nm 3 / h, ferrosilicon and silicon-manganese alloy are added 1 minute after steel is tapped, vanadium-nitrogen or vanadium-containing pig iron and ferroniobium are added with the steel flow after half of the ferrosilicon and silicon-manganese alloy are added, and the addition is completed before the slag rod is thrown.

[0062] In some embodiments, in the step of obtaining a raw material with a predetermined mass percentage of chemical composition, smelting, and casting to obtain a steel billet, the smelting includes converter smelting and LF refining, wherein the LF refining includes controlling the ladle bottom blowing argon / nitrogen flow rate at 100-300 Nm 3 / h, add lime and slagging agent to control the binary basicity of the refined final slag to 2.5-3.5 to obtain refined molten steel.

[0063] In some embodiments, in the steps of obtaining raw materials with a predetermined mass percentage of chemical composition, smelting, and casting to obtain a steel billet, the physical and chemical properties of the protective slag used in the crystallizer during the casting process include: viscosity of 0.15 poise to 0.26 poise at 1300°C, melting temperature of 1070°C to 1110°C, and the protective slag includes the following mass percentage compositions: SiO2: 28% to 37%, CaO: 22%-27%, K2O+Na2O: 8%-14%, F: 5%-9%, C solid: 8%-12%, and the rest are iron and trace elements.

[0064] In some embodiments, in the steps of obtaining raw materials with a predetermined mass percentage of chemical composition, smelting, and casting to obtain steel billets, the molten steel is subjected to secondary strong cooling in the crystallizer during the casting process, the water flow rates on the wide and narrow sides of the crystallizer are both 150 t / h to 170 t / h, and the specific water volume of the secondary cooling water is 1.4 L / kg to 1.6 L / kg.

[0065] The low carbon equivalent HRB400E steel bar in this application is combined with the appropriate preparation process in some of the above embodiments, so that the low carbon equivalent HRB400E steel bar has better organizational structure, mechanical properties, welding properties and cold bending properties.

[0066] Example

[0067] The following examples more specifically describe the disclosure of the present application, which are intended for illustrative purposes only, as it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0068] The present invention is further described below by means of specific examples and comparative examples.

[0069] Example 1

[0070] A preparation method of low carbon equivalent HRB400E hot-rolled ribbed steel bar, comprising: blast furnace molten iron → converter smelting → LF refining → billet continuous casting → heating furnace heating → rough rolling → intermediate rolling → finishing rolling → controlled cooling → multiple length shearing → cooling on a cooling bed → cold shearing to length → finishing → packaging → weighing → warehousing;

[0071] Obtain raw materials with a predetermined mass percentage of chemical composition, smelt, and cast to obtain a steel billet; the smelting includes converter smelting and LF refining, wherein the converter smelting includes controlling the ladle bottom blowing argon flow rate at 80Nm 3 / h, ferrosilicon and silicon-manganese alloy are added 1 minute after steel is tapped, vanadium nitrogen or vanadium-containing pig iron and ferroniobium are added with the steel flow after half of ferrosilicon and silicon-manganese alloy are added, and the addition is completed before the slag rod is thrown. LF refining includes controlling the argon / nitrogen flow rate of the ladle bottom blowing at 120Nm 3 / h, add lime and slagging agent, the refining time is 30min, and the binary basicity of the refined final slag is controlled to be 2.6 to obtain refined molten steel; the refined molten steel is cast, and the physical and chemical properties of the protective slag used in the crystallizer during the casting process include: viscosity 0.2 poise at 1300℃, melting temperature 1080℃, and the protective slag includes the composition of mass percentage: SiO2: 30%, CaO: 25%), K2O+Na2O: 10%, F: 6%, C solid: 10%, and the rest are iron and trace elements; during the casting process, the molten steel is subjected to secondary strong cooling at the crystallizer, and the water flow rate of the wide and narrow sides of the crystallizer is 160t / h; the specific water volume of the secondary cooling water is: 1.5L / kg.

[0072] The raw materials with the chemical composition of the predetermined mass percentage are obtained, smelted and cast to obtain the steel billet; the square billet is transported to the heating furnace for heating and taken out of the furnace. The steel tapping temperature is measured at the exit of the 6# frame. After the steel billet is taken out of the furnace, it is continuously rolled by 19 horizontal and vertical staggered rolling mills, including 6 rough rolling mills, 6 medium rolling mills and 7 finishing rolling mills. The rolling specifications are ∮12mm~∮32mm. The steel bars are cooled by air cooling on the cooling bed. The produced rebars are sampled and inspected, and then sheared, packaged and stored to obtain low carbon equivalent HRB400E steel bars.

[0073] Compared with Example 1, the different parameters in the preparation process of Examples 2 to 4 and Comparative Example 1 are shown in Tables 1 to 3.

[0074] The composition parameters of low carbon equivalent HRB400E hot rolled ribbed steel bar products are shown in Tables 1 and 2.

[0075] Table 1:

[0076]

[0077] Table 2:

[0078]

[0079] The technical parameters of the preparation process of the low carbon equivalent HRB400E hot-rolled ribbed steel bar products in each embodiment and comparative example are shown in Table 3.

[0080] Table 3:

[0081]

[0082]

[0083] The performance of the HRB400E hot-rolled ribbed steel bars obtained in each embodiment and comparative example was tested, and the test results are shown in Table 4 below.

[0084] Table 4:

[0085]

[0086] From the data in the table, it can be seen that the HRB400E hot-rolled ribbed steel bars produced in Examples 1 to 4 of the present application have good surface quality, mechanical properties, and cold bending properties, and ceq is ≤0.39%, with the characteristics of low carbon equivalent, the organizational structure is ferrite + pearlite, and has a suitable grain size range, which fully meets the requirements of GB / T 1499.2-2018, and a low-cost, low-carbon equivalent HRB400E steel bar with good mechanical properties and welding performance is obtained. Among them, Examples 1 to 4 have more reasonable chemical composition, organizational structure and preparation process, and the comprehensive performance is more ideal. Comparative Example 1 HRB400E hot-rolled ribbed steel bar has a high carbon equivalent, a high strength-to-yield ratio, and a large surplus. It is easy to produce unfavorable organizations such as bainite and martensite when the ambient temperature is low.

[0087] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A low carbon equivalent HRB400E steel bar, characterized in that: The chemical composition includes the following mass percentages: C: 0.22% to 0.25%, Si: 0.35% to 0.45%, Mn: 0.70% to 0.80%, P≤0.040%, S≤0.040%, V: 0.03% to 0.040%, Cr: 0.005% to 0.02%, N: 0.012% to 0.018%, and the rest are Fe and trace elements; The carbon equivalent Ceq of the HRB400E steel bar satisfies: 0.34%≤Ceq≤0.39%.

2. The low carbon equivalent HRB400E steel bar according to claim 1, characterized in that: The sum of the mass percentage of Si and the mass percentage of Mn is W Si+Mn Satisfy: 1.1% ≤ W Si+Mn ≤1.25%.

3. The low carbon equivalent HRB400E steel bar according to claim 1, characterized in that: The sum of the mass percentage of the V and the mass percentage of the Cr is W v+Cr Satisfy: 0.04% ≤ W v+Cr ≤0.05%.

4. The low carbon equivalent HRB400E steel bar according to claim 1, characterized in that: The microstructure of the low carbon equivalent HRB400E steel bar is ferrite+pearlite; the volume fraction of ferrite is 67-76%, and the volume fraction of pearlite is 24-33%.

5. The low carbon equivalent HRB400E steel bar according to claim 1, characterized in that: The average grain size of the low carbon equivalent HRB400E steel bar is 6.52 μm to 11.37 μm, and can be optionally 7 μm to 10 μm.

6. The low carbon equivalent HRB400E steel bar according to claim 1, characterized in that: The yield strength of the low-carbon equivalent HRB400E steel bar is 430Mpa-450Mpa; the tensile strength of the low-carbon equivalent HRB400E steel bar is 570Mpa-600Mpa; and the strength-to-yield ratio of the low-carbon equivalent HRB400E steel bar is 1.3-1.

4.

7. The low carbon equivalent HRB400E steel bar according to claim 1, characterized in that: The elongation of the low-carbon equivalent HRB400E steel bar is 19% to 25%; the maximum force elongation of the low-carbon equivalent HRB400E steel bar is 13% to 20%.

8. A method for preparing low carbon equivalent HRB400E steel bar, characterized in that: include: Obtaining raw materials with a predetermined mass percentage of chemical composition, smelting, and casting to obtain steel billets; The steel billet is heated, taken out of the furnace, rolled, and cooled to obtain a low-carbon equivalent HRB400E steel bar; the low-carbon equivalent HRB400E steel bar comprises the following chemical composition in percentage by mass: C: 0.22% to 0.25%, Si: 0.35% to 0.45%, Mn: 0.70% to 0.80%, P≤0.040%, S≤0.040%, V: 0.03% to 0.040%, Cr: 0.005% to 0.02%, N: 0.012% to 0.018%, and the rest are Fe and trace elements; the carbon equivalent Ceq of the HRB400E steel bar satisfies: 0.34%≤Ceq≤0.39%.

9. The method for preparing low carbon equivalent HRB400E steel bar according to claim 8, characterized in that: In the step of heating the steel billet, taking out of the furnace, rolling and cooling to obtain low carbon equivalent HRB400E steel bars, the heating temperature is ≤1180°C, the heating time is 40-80min; the steel tapping temperature is 950°C-1000°C, and can be optionally 955°C-980°C.

10. The method for preparing low carbon equivalent HRB400E steel bar according to claim 8, characterized in that: In the step of heating the steel billet, taking out of the furnace, rolling and cooling to obtain low carbon equivalent HRB400E steel bars, the starting rolling temperature of the rough rolling treatment during the rolling is 930°C to 980°C.

11. The method for preparing low carbon equivalent HRB400E steel bar according to claim 8, characterized in that: In the step of heating, taking out of the furnace, rolling and cooling the steel billet to obtain low carbon equivalent HRB400E steel bars, the temperature of the cooling bed on the steel bars is controlled to be 810°C to 850°C, and the cooling rate is 2.0°C / s to 4.0°C / s, and can be optionally 2.0°C / s to 3.0°C / s.

12. The method for preparing low carbon equivalent HRB400E steel bars according to any one of claims 8 to 13, characterized in that: In the steps of obtaining raw materials with a predetermined mass percentage of chemical composition, smelting, and casting to obtain a steel billet, the size of the steel billet is 165mm×165mm×12000mm or 165mm×165mm×9000mm.

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