A kind of HRB500E earthquake-resistant steel bar and its preparation method

Abstract

The present application relates to a HRB500E earthquake-resistant steel bar and a preparation method thereof, belonging to the technical field of earthquake-resistant steel bar production. The chemical composition of the steel bar comprises: C: 0.20 wt%-0.25 wt%, Si: 0.50 wt%-0.75 wt%, Mn: 1.20 wt%-1.40 wt%, P: ≤0.030 wt%, S: ≤0.030 wt%, V: 0.05 wt%-0.08 wt%, Fe; the metallographic structure of the steel bar is: ferrite and pearlite. The preparation method of HRB500E earthquake-resistant steel bars provided in the present application eliminates the heating step of the heating furnace, and is optimized from the aspects of composition control, continuous casting billet drawing speed control, direct rolling insulation roller conveying control, start rolling temperature, finishing rolling entrance temperature, wire drawing temperature, air cooling process, roller speed, etc. The produced HRB500E earthquake-resistant steel bars have excellent organizational properties, mechanical properties, and earthquake-resistant properties, with performance parameters Rp0.2≥520Mpa, tensile strength Rm≥700Mpa, elongation≥18%, Agt≥9%, strength-to-yield ratio≥1.25, and yield-to-yield ratio≤1.2.

Description

Technical Field

[0001] The present application relates to the field of earthquake-resistant steel bars, and in particular to a HRB500E earthquake-resistant steel bar and a preparation method thereof. Background Art

[0002] With the development of direct rolling production technology without heating, the application degree of "hot charging and hot delivery" of continuous casting billets and "continuous casting and direct rolling" technology has become a new indicator to measure the level of steel production technology.

[0003] At present, HRB500E steel bars produced by the heat-free direct rolling production technology not only have insufficient plasticity and toughness, but also have large fluctuations in product performance, resulting in some products being unable to meet earthquake resistance requirements. Summary of the invention

[0004] The present application provides a HRB500E earthquake-resistant steel bar and a preparation method thereof, so as to solve the technical problems that the HRB500E earthquake-resistant steel bar prepared by the existing heating-free direct rolling production technology has insufficient plasticity and toughness and large fluctuations in the yield strength of the product.

[0005] In a first aspect, the present application provides a HRB500E earthquake-resistant steel bar, the chemical composition of which comprises:

[0006] C: 0.20 wt% - 0.25 wt%, Si: 0.50 wt% - 0.75 wt%, Mn: 1.20 wt% - 1.40 wt%, P: ≤ 0.030 wt%, S: ≤ 0.030 wt%, V: 0.05 wt% - 0.08 wt%, Fe.

[0007] Optionally, the metallographic structure of the steel bar is ferrite and pearlite.

[0008] Optionally, the ferrite content is 35 volume %-55 volume %.

[0009] Optionally, the average diameter of the ferrite grains is 9.5 μm-10 μm.

[0010] Optionally, the content of pearlite is 45 volume %-65 volume %.

[0011] Optionally, the average diameter of the pearlite grains is 20 μm-50 μm.

[0012] In a second aspect, the present application provides a method for preparing HRB500E earthquake-resistant steel bars, which is used to prepare the HRB500E earthquake-resistant steel bars described in any one of the first aspects, and the method comprises:

[0013] Under the condition of a set billet drawing speed, continuously casting the molten steel containing the chemical composition to obtain a billet;

[0014] Under the set rolling start temperature condition, the ingot is conveyed to the rolling mill for rough rolling;

[0015] Under the set finishing rolling temperature condition, finishing rolling is performed on the rough-rolled ingot to obtain a steel strip;

[0016] Under the set spinning temperature condition, the strip steel is subjected to spinning treatment to obtain steel bars;

[0017] The steel bars are air-cooled under the conditions of a set first-section roller speed, a set final cooling temperature, and a set overlap point temperature.

[0018] Optionally, the setting value of the casting speed is not less than 3.0 m / min; and\or

[0019] The set rolling temperature is set to be 950°C-980°C.

[0020] Optionally, the set finishing temperature is 860°C-880°C; and\or

[0021] The set spinning temperature is between 910°C and 930°C.

[0022] Optionally, the set value of the first-section roller speed is 0.6m / s-0.7m / s, the set value of the final cooling temperature is 660℃-680℃, and the set value of the overlap point temperature is not greater than 680℃.

[0023] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0024] The method provided in the embodiment of the present application eliminates the heating step of the heating furnace and is optimized from the aspect of chemical composition design. By adding a proper amount of Mn element, the strength, hardness and hardenability of steel are improved, the hot processing performance of steel is improved, the strength and strength-to-yield ratio of the material are improved by adding a proper amount of C element, the elastic limit, yield point and tensile strength of steel are improved by adding a proper amount of Si element, and the grain size of the structure is refined by adding a proper amount of V element to improve the strength and toughness. The HRB500E earthquake-resistant steel bars produced by the designed composition of the present application have the characteristics of excellent plasticity and toughness, and the product yield strength fluctuation is less than 50MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0027] Figure 1 A schematic diagram of a process for preparing HRB500E earthquake-resistant steel bars provided in an embodiment of the present application; DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0029] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0030] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0031] In this application, unless otherwise specified, directional words such as "upper" and "lower" used refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the specification of this application, the terms "include", "comprising", etc. mean "including but not limited to".

[0032] In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that there can be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "multiple" refers to two or more. "At least one", "the following at least one (individual)" or similar expressions refer to any combination of these items, including any combination of single (individual) or plural (individual). For example, "at least one (individual) of a, b, or c", or "at least one (individual) of a, b, and c", can all represent: a, b, c, ab (i.e. a and b), ac, bc or abc, wherein a, b, c can be single or multiple respectively.

[0033] In a first aspect, the present application provides a HRB500E earthquake-resistant steel bar, the chemical composition of which comprises:

[0034] C: 0.20 wt% - 0.25 wt%, Si: 0.50 wt% - 0.75 wt%, Mn: 1.20 wt% - 1.40 wt%, P: ≤ 0.030 wt%, S: ≤ 0.030 wt%, V: 0.05 wt% - 0.08 wt%, Fe.

[0035] In this embodiment, the role of C is to improve the strength and strength-to-yield ratio of the material, but the plasticity and impact toughness will be reduced. The reason for controlling the mass fraction of C to 0.20%-0.25% is to obtain appropriate strength and strength-to-yield ratio. The disadvantage of taking a mass fraction that is too large is that the standard requirements are not met, and the disadvantage of taking a mass fraction that is too small is that the strength and strength-to-yield ratio are insufficient.

[0036] In this embodiment, the role of Si is to improve the elastic limit, yield point and tensile strength of the steel, but it will reduce the welding performance of the steel. The reason for controlling the mass fraction of Si to 0.50%-0.75% is to obtain a suitable yield point and ensure welding performance. The disadvantage of taking the mass fraction too large is that the welding performance is reduced, and the disadvantage of taking the mass fraction too small is that the strength is insufficient;

[0037] In this embodiment, the role of Mn is to improve the strength, hardness and hardenability of steel and improve the hot working performance of steel, but it will weaken the corrosion resistance of steel and reduce the welding performance. The reason for controlling the mass fraction of Mn to 1.20%-1.40% is to obtain appropriate strength, hardness and welding performance. The disadvantage of taking the mass fraction too large is poor welding performance, and the disadvantage of taking the mass fraction too small is insufficient strength and hardness;

[0038] In general, P and S are harmful elements in steel. P increases the cold brittleness of steel, deteriorates welding performance, reduces plasticity, and deteriorates cold bending performance. S makes steel hot brittle and reduces ductility and toughness. Therefore, the lower the P and S in steel, the better, but too low requirements will increase equipment and cost investment.

[0039] The role of V is to refine the grain size and improve the strength and toughness. The carbonitride formed by vanadium, carbon and nitrogen can improve the resistance to hydrogen corrosion under high temperature and high pressure. The reason for controlling the mass fraction of V to 0.05%-0.08% is to obtain the appropriate grain size and strength. The disadvantage of taking too large a mass fraction is that the strength is too high and the strength-to-yield ratio is insufficient, while the disadvantage of taking too small a mass fraction is that the strength is insufficient.

[0040] In some embodiments, the metallographic structure of the steel bar is ferrite and pearlite.

[0041] The advantage of having a ferrite and pearlite structure is that a good match of strength and plasticity can be obtained.

[0042] In some embodiments, the ferrite content is 35 volume %-55 volume %.

[0043] The benefit of controlling the structure to 35 volume % to 55 volume % of ferrite is that good plasticity is obtained.

[0044] In some embodiments, the average diameter of the ferrite grains is 9.5 μm-10 μm.

[0045] The benefit of the average diameter of the ferrite grains being 9.5 μm to 10 μm is that suitable strength and strength-to-yield ratio are obtained.

[0046] In some embodiments, the pearlite content is 45 volume % to 65 volume %.

[0047] The advantage of a pearlite content of 45 volume % to 65 volume % is that suitable strength can be obtained.

[0048] In some embodiments, the average diameter of the pearlite grains is 20 μm-50 μm.

[0049] The advantage of having an average grain diameter of pearlite of 20 μm to 50 μm is that a good match between strength and plasticity is obtained.

[0050] In a second aspect, the present application provides a method for preparing HRB500E earthquake-resistant steel bars, which is used to prepare the HRB500E earthquake-resistant steel bars described in any one of the first aspects, and the method comprises:

[0051] Under the condition of a set billet drawing speed, continuously casting the molten steel containing the chemical composition to obtain a billet;

[0052] Under the set rolling start temperature condition, the ingot is conveyed to the rolling mill for rough rolling;

[0053] Under the set finishing rolling temperature condition, finishing rolling is performed on the rough-rolled ingot to obtain a steel strip;

[0054] Under the set spinning temperature condition, the strip steel is subjected to spinning treatment to obtain steel bars;

[0055] The steel bars are air-cooled under the conditions of a set first-section roller speed, a set final cooling temperature, and a set overlap point temperature.

[0056] In this embodiment, the production process of HRB500E earthquake-resistant steel bars is: molten iron → converter smelting → alloy addition → LF refining → continuous casting into small square billets → direct rolling roller conveying → controlled rolling → controlled cooling, wherein alloy is added at the end of the converter, continuous casting adopts full protection pouring, and the overheating does not exceed 35°C. Insulated transportation to the rolling mill is: the high-speed continuous casting billet coming out of the casting machine is insulated between the straightening machine and the hydraulic shear, between the hydraulic shear and the fixed length, and on the waiting position of the transport roller. An automatic steelmaking system is set up, and the continuous casting billet is collected and climbed and turned through the steel rolling area according to the time interval of high-speed wire or high-bar rolling. The insulation roller and the direct rolling insulation roller are merged from the heating furnace to the furnace discharge roller, and sent to the rolling mill for direct rolling, so that the temperature of the head, middle and tail of the continuous casting billet is uniform when entering the rolling mill, and the temperature difference is controlled within 30°C. In the air cooling stage, fans 1# and 2# are turned on at 100%, and fan 3# is turned on at 80%.

[0057] In some embodiments, the setting of the drawing speed is not less than 3.0 m / min; and\or

[0058] The set rolling temperature is set to be 950°C-980°C.

[0059] When the pulling speed is lower than 3.0m / min, the temperature difference between the head and tail of the ingot will be too large, thus failing to meet the setting requirements of the start rolling temperature. The advantage of setting the start rolling temperature to 950℃-980℃ is to refine the austenite grains and avoid overloading the primary rolling equipment.

[0060] In some embodiments, the set finishing temperature is 860°C-880°C; and\or

[0061] The set spinning temperature is between 910°C and 930°C.

[0062] The advantages of the finishing rolling temperature of 860℃-880℃ and the spinning temperature of 910℃-930℃ are to refine the austenite grains and avoid overloading the finishing rolling equipment.

[0063] In some embodiments, the set value of the first roller speed is 0.6m / s-0.7m / s, the set value of the final cooling temperature is 660℃-680℃, and the set overlap point temperature is not greater than 680℃.

[0064] The speed of the first roller is controlled at 0.6m / s-0.7m / s, which has the advantage of reducing overlap and ensuring uniform cooling.

[0065] The temperature of the lap joint is controlled to be no greater than 680°C, which has the benefit of ensuring that the phase change of the lap joint is complete.

[0066] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0067] Embodiment 1:

[0068] The chemical composition used in this embodiment is: C: 0.25 wt%, Si: 0.75 wt%, Mn: 1.40 wt%, V: 0.08 wt%, and the balance is Fe and unavoidable impurities. Figure 1 As shown, alloy is added at the end of the converter, continuous casting adopts full protection pouring, overheating does not exceed 35℃, and insulation and transportation control is as follows: the high-speed continuous casting billet coming out of the casting machine is insulated between the straightening machine and the hydraulic shear, between the hydraulic shear and the fixed length, and on the waiting position of the transport roller. An automatic steelmaking system is set up, and the continuous casting billet is collected and climbed and turned through the insulation roller and the direct rolling insulation roller in the rolling area according to the time interval of high-speed wire or high-bar rolling, and then merged into the furnace discharge roller from the heating furnace and sent to the rolling mill for direct rolling. The rolling temperature is 978℃, the finishing rolling temperature is 878℃, the wire laying temperature is 928℃, and the air cooling process is as follows: fans 1# and 2# are turned on at 100%, 3# fan is turned on at 80%, the speed of the first roller is 0.65m / s, the final cooling temperature is controlled at 675℃, and the maximum temperature of the overlap point is 675℃. The mechanical properties are shown in Table 1.

[0069] Embodiment 2:

[0070] The chemical composition used in this embodiment is: C: 0.23 wt%, Si: 0.62 wt%, Mn: 1.30 wt%, V: 0.065 wt%, and the balance is Fe and unavoidable impurities. Figure 1As shown, alloy is added at the end of the converter, continuous casting adopts full protection pouring, overheating does not exceed 35℃, and insulation and transportation control is as follows: the high-speed continuous casting billet coming out of the casting machine is insulated between the straightening machine and the hydraulic shear, between the hydraulic shear and the fixed length, and on the waiting position of the transport roller. An automatic steelmaking system is set up, and the continuous casting billet is collected and climbed and turned through the insulation roller and the direct rolling insulation roller in the rolling area according to the time interval of high-speed wire or high-bar rolling, and then merged into the furnace discharge roller from the heating furnace and sent to the rolling mill for direct rolling. The starting rolling temperature is 966℃, the finishing rolling temperature is 871℃, the wire laying temperature is 921℃, and the air cooling process is: fans 1# and 2# are turned on at 100%, and fan 3# is turned on at 80%. The speed of the first roller is 0.65m / s, the final cooling temperature is controlled at 670℃, and the maximum temperature of the overlap point is 671℃. The mechanical properties are shown in Table 1.

[0071] Embodiment 3:

[0072] The chemical composition used in this embodiment is: C: 0.20 wt%, Si: 0.50 wt%, Mn: 1.20 wt%, V: 0.05 wt%, and the balance is Fe and unavoidable impurities. Figure 1 As shown, alloy is added at the end of the converter, continuous casting adopts full protection pouring, overheating does not exceed 35℃, and insulation and transportation control is as follows: the high-speed continuous casting billet coming out of the casting machine is insulated between the straightening machine and the hydraulic shear, between the hydraulic shear and the fixed length, and on the waiting position of the transport roller. An automatic steelmaking system is set up, and the continuous casting billet is collected and climbed and turned through the insulation roller and the direct rolling insulation roller in the rolling area according to the time interval of high-speed wire or high-bar rolling, and then merged into the furnace discharge roller from the heating furnace and sent to the rolling mill for direct rolling. The opening rolling temperature is 955℃, the finishing rolling temperature is 861℃, the wire laying temperature is 912℃, and the air cooling process is as follows: fans 1# and 2# are turned on at 100%, and fan 3# is turned on at 80%, the speed of the first roller is 0.65m / s, the final cooling temperature is controlled at 662℃, and the maximum temperature of the overlap point is 665℃. The mechanical properties are shown in Table 1.

[0073] Related experimental test methods:

[0074] Metallographic structure inspection method: GB / T13298, metal microstructure inspection method.

[0075] Mechanical properties testing method: GB / T18900, test methods for steel for reinforced concrete.

[0076] Related experiments and effect data:

[0077] Table 1

[0078] Steel Type <![CDATA[R el ,MPA]]> Rm,MPa A5％ Agt,% <![CDATA[Rm / R el ]]> <![CDATA[R o el / R el ]]> Example 1 585 780 24.0 13.5 1.33 1.17 Example 2 575 760 25.0 13.0 1.32 1.15 Example 3 535 720 25.5 13.0 1.35 1.07

[0079] The present invention reasonably designs chemical composition, continuous casting speed, heat-insulating conveying roller, rolling, air cooling and other processes, so that the temperature of the head, middle and tail of the continuous casting billet of the heating-free HRB500E earthquake-resistant steel bar is uniform when entering the rolling mill, the temperature difference is controlled within 30°C, the start rolling temperature can meet the conventional process requirements, the product yield strength fluctuates within 50MPa, and the comprehensive performance is stably controlled in a narrow range, while achieving the purpose of energy saving and consumption reduction. The high-strength earthquake-resistant steel bar HRB500E produced by the present invention has a ferrite+pearlite structure, a ferrite grain size of 9.5-10.5, Rp0.2≥520Mpa, a tensile strength Rm≥700Mpa, an elongation≥18%, Agt≥9%, a strength-yield ratio≥1.25, and a yield-yield ratio≤1.2.

[0080] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing HRB500E earthquake-resistant steel bars, characterized in that: The method comprises: Under the set billet drawing speed condition, the molten steel is continuously cast to obtain a billet; Under the set rolling start temperature condition, the ingot is conveyed to the rolling mill for rough rolling; Under the set finishing rolling temperature condition, finishing rolling is performed on the rough-rolled ingot to obtain a steel strip; Under the set spinning temperature condition, the strip steel is subjected to spinning treatment to obtain steel bars; Under the conditions of setting the first roller speed, setting the final cooling temperature and setting the overlap point temperature, the steel bar is air-cooled; the setting billet drawing speed is not less than 3.0 m / min; the setting start rolling temperature is 950°C-980°C; the setting finish rolling temperature is 860°C-880°C; the setting wire laying temperature is 910°C-930°C; the setting first roller speed is 0.6 m / s-0.7 m / s, the setting final cooling temperature is 660°C-680°C, and the setting overlap point temperature is not more than 680°C; The continuous casting adopts full protection pouring, and the overheating degree does not exceed 35°C; the heat preservation and transportation to the rolling mill are as follows: the high-speed continuous casting billet from the casting machine is heat-insulated between the straightening machine and the hydraulic shear, between the hydraulic shear and the fixed length, and on the waiting position of the transport roller. An automatic steel-making system is set up, and the continuous casting billet is collected, climbed, turned, and heat-insulated rollers and direct rolling heat-insulated rollers in the rolling area according to the time interval of high-speed wire or high-bar rolling, and then merged into the furnace-out roller from the heating furnace, and sent to the rolling mill for direct rolling; The chemical composition of the steel bar is: C: 0.20 wt%-0.25 wt%, Si: 0.50 wt%-0.75 wt%, Mn: 1.20 wt%-1.40 wt%, P: ≤0.030 wt%, S: ≤0.030 wt%, V: 0.05 wt%-0.08 wt%, and the balance is Fe and inevitable impurities.

2. The HRB500E earthquake-resistant steel bar prepared by the preparation method according to claim 1 is characterized in that: The metallographic structure of the steel bar is ferrite and pearlite.

3. The HRB500E earthquake-resistant steel bar according to claim 2, characterized in that: The content of ferrite is 35 volume %-55 volume %.

4. The HRB500E earthquake-resistant steel bar according to claim 2, characterized in that: The average diameter of the ferrite grains is 9.5 μm-10 μm.

5. The HRB500E earthquake-resistant steel bar according to claim 2, characterized in that: The content of the pearlite is 45 volume % to 65 volume %.

6. The HRB500E earthquake-resistant steel bar according to claim 2, characterized in that: The average diameter of the pearlite grains is 20 μm to 50 μm.

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