Vanadium-niobium microalloyed Q460B angle steel and preparation method thereof

Abstract

The invention discloses vanadium-niobium microalloyed Q460B angle steel and a preparation method thereof, and belongs to the technical field of hot-rolled section steel. The problems that existing Q460B angle steel is high in production cost; and a large amount of Nb element is used in the Q460B angle steel, so that the Q460B angle steel is easy to crack, and the Nb element is not used for preparing the angle steel. The vanadium-niobium microalloyed Q460B angle steel comprises the following components in percentage by mass: 0.15 to 0.2 percent of C, 0.20 to 0.45 percent of Si, 1.40 to 1.60 percent of Mn, 0.03 to 0.08 percent of V, 0.01 to 0.045 percent of Nb, less than or equal to 0.02 percent of N, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S and the balance of Fe and inevitable impurities. According to the method, under the condition that a small amount of alloy elements are added, the mechanical property meets the mechanical property requirement specified by the standard, and low-cost and high-production-efficiency production of the 460 MPa grade angle steel is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled steel sections and relates to a vanadium-niobium microalloyed Q460B angle steel and a preparation method thereof. Background Art

[0002] Angle steel is widely used in various building structures and engineering structures, such as beams, bridges, transmission towers, lifting and transportation machinery, ships, etc. At present, the output of angle steel in my country has reached more than 10 million tons, most of which are concentrated in the Q235 strength level. In the fields of construction, large machinery, etc., using Q390 and above high-strength steel to replace Q235 strength steel can effectively reduce the weight of the product, reduce the amount of steel used, and effectively reduce the carbon emissions of steel product production. Therefore, the quality upgrade of steel products is of great practical significance to the development of industry.

[0003] At present, most of the angle steel produced in my country is Q235, Q345 and Q420, with low strength grade and few optional types. The high cost is one of the important reasons for the difficulty in promotion. Usually, the organizational state of the material can be improved by adding an appropriate amount of microalloying elements to meet its final mechanical properties. At present, the research on the production and application of vanadium microalloyed steel in China has been relatively comprehensive. However, in previous studies, in order to obtain good comprehensive mechanical properties, more expensive alloying elements such as Cr, Ni, Mo, Nb were often added, which was costly and had a low cost performance ratio. At the same time, adding more Nb elements can easily cause cracking of angle steel, so Nb elements are basically not used in the preparation of angle steel.

[0004] Therefore, how to reduce the process production cost while ensuring that the angle steel has good comprehensive mechanical properties such as high strength and toughness has become one of the urgent problems to be solved by steel companies. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a vanadium-niobium microalloyed Q460B angle steel and a preparation method thereof, so as to at least solve one of the following problems existing in the existing Q460B angle steel: 1. The production cost of Q460B angle steel is high; 2. The Nb element is used in large quantities in Q460B angle steel, which easily causes cracking of Q460B angle steel and is not used in the preparation of angle steel.

[0006] The purpose of the present invention is mainly achieved through the following technical solutions:

[0007] A vanadium-niobium microalloyed Q460B angle steel, the components of which are calculated by mass percentage: C: 0.15-0.2%, Si: 0.20-0.45%, Mn: 1.40-1.60%, V: 0.03-0.08%, Nb: 0.01-0.045%, N≤0.02%, P≤0.02%, S≤0.01%, and the balance is Fe and unavoidable impurities.

[0008] Furthermore, in the vanadium-niobium microalloyed Q460B angle steel, the mass ratio of V+Nb to N (V+Nb) / N is 3-5:1.

[0009] Furthermore, in the vanadium-niobium microalloyed Q460B angle steel, the mass ratio of V to Nb V / Nb is 2.1-3.5:1.

[0010] Furthermore, the microstructure of the vanadium-niobium microalloyed Q460B angle steel is ferrite, pearlite and dispersed second phase particles.

[0011] Furthermore, the volume content of the ferrite is 60% to 80%, the average grain size of the ferrite is ≤7 μm, and the average size of the second phase particles is <60 nm.

[0012] The present invention also provides a method for preparing vanadium-niobium microalloyed Q460B angle steel, which is used to prepare the above-mentioned vanadium-niobium microalloyed Q460B angle steel, including converter smelting-LF refining-continuous casting-continuous casting billet heating-semi-continuous rolling-cooling bed slow cooling;

[0013] The converter does not perform vacuum degassing after steel is tapped.

[0014] Furthermore, during the LF refining process, the vanadium-nitrogen alloy and the ferroniobium alloy are added to the LF refining furnace in sequence; the time interval between adding the vanadium-nitrogen alloy and the ferroniobium alloy is 12-17 minutes.

[0015] Furthermore, during the continuous casting process, the superheat is controlled to be no greater than 20° C. and the casting speed is 0.8-1.3 m / min.

[0016] Furthermore, during the continuous casting billet heating process, the continuous casting billet is heated from room temperature to 1200-1280° C. in a heating furnace at a heating rate not higher than 10° C. / s, and the time in the furnace is ≥180 min.

[0017] Furthermore, the semi-continuous rolling includes blooming rolling and finishing rolling;

[0018] The rolling temperature is 1100-1160℃, the rolling speed is not more than 2.5m / s, and the rolling is not less than 5 times;

[0019] The starting rolling temperature of the finishing rolling is 900-1000℃, the rolling speed is ≤2m / s, and the final rolling temperature of the finishing rolling is 750-850℃.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. The present invention only adds a small amount of V, Nb, Mn, and N, without adding other expensive alloying elements, thereby saving costs and simplifying the process of regulating the composition of molten steel. Compared with the production process in which a large amount of expensive micro-alloying elements such as Ni, Cr, and Ti need to be added in traditional production, the present invention reduces production costs, simplifies the production process, and is suitable for industrial production applications.

[0022] 2. The preparation method of the present invention ensures the mechanical properties and surface quality of the angle steel by continuous casting of special-shaped billets and controlling the drawing speed, and ensures the surface quality of the steel and avoids the generation of cracks in the core and corners by controlling the rolling speed of the semi-continuous rolling mill; thereby achieving mechanical properties that meet the mechanical properties requirements specified in the standard by adding a small amount of alloy elements, and achieving low-cost and high-efficiency production of 460MPa grade angle steel; at the same time, a semi-continuous casting rolling process is adopted, which can achieve rapid preparation of large-size and thick-size angle steels compared to the rolling method of traditional ordinary two-roll or three-roll steel rolling mills, with a specification of not less than ∠140mm and not more than ∠200mm, and a thickness of not less than 10mm.

[0023] 3. The present invention introduces part of niobium element on the basis of vanadium microalloying. Since the complete use of Nb element will lead to excessive reduction in plastic toughness and forming performance, it is easy to cause corner cracking when preparing large-sized angle steels, but the complete use of V element will increase the cost because of the relatively expensive price of V. The present invention adds part of Nb element on the basis of V microalloyed steel. This part of the addition not only leads to grain refinement and increased strength by introducing alloy elements that can pin grain boundaries, but also can reduce the use of part of V element and reduce costs.

[0024] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be achieved and obtained through the contents particularly pointed out in the description and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0026] Figure 1 It is the metallographic photograph of the Q460B grade angle steel in Example 1;

[0027] Figure 2 It is a metallographic photograph of the Q460B grade angle steel in Example 2;

[0028] Figure 3It is the metallographic photograph of the Q460B grade angle steel in Example 3;

[0029] Figure 4 This is a metallographic photograph of the Q460B grade angle steel in Comparative Example 1;

[0030] Figure 5 This is a metallographic photograph of a crack at a certain location of the Q460B grade angle steel in Comparative Example 1;

[0031] Figure 6 This is a metallographic photograph of a crack at a certain location in the Q460B grade angle steel in comparative example 3. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0033] The invention discloses a vanadium-niobium microalloyed Q460B angle steel, the components of which are calculated by mass percentage: C 0.15-0.2%, Si 0.20-0.45%, Mn 1.40-1.60%, V 0.03-0.08%, Nb 0.01-0.045%, N≤0.02%, P≤0.02%, S≤0.01%, and the balance is Fe and unavoidable impurities.

[0034] The reasons for limiting the composition of the Q460B angle steel in the present invention are explained below, and only % is used to represent the mass percentage in the composition.

[0035] C: It improves the performance of steel by forming solid solution structure and carbide in steel. The increase of C content can enhance the strength and hardness of steel and increase the wear resistance of steel, but too high C content will also seriously deteriorate the plasticity and toughness of steel. The C content of the present invention is controlled at 0.15-0.2%, which ensures that the steel has good plasticity and toughness while ensuring the strength of the steel.

[0036] Si: It is a commonly used deoxidizer in steelmaking. It is usually dissolved in ferrite and austenite in steel. It has a strong solid solution strengthening effect and has a significant effect on improving the strength of steel. When the Si content is too high, the plasticity and toughness of the steel will be seriously deteriorated, the cold brittleness tendency of the steel will be increased, and the safety performance of the steel will be affected. At the same time, too high Si content will deteriorate the welding performance of the steel. Therefore, the Si content in the present invention is controlled at 0.20% to 0.45%.

[0037] Mn: It is a commonly used deoxidizer and desulfurizer in steel. Mn reacts with S in steel to generate MnS with a higher melting point, thereby preventing the hot brittleness caused by the formation of FeS, thereby improving the hot processing performance of steel. Mn is solid-dissolved in ferrite and austenite, and has a strong solid solution strengthening effect. Adding an appropriate amount of Mn can effectively improve the strength and hardness of the material, and generate MnS to eliminate S that is harmful to the performance of steel; but if the Mn content is too high, the carbon equivalent will be significantly increased, which will harm the plasticity and toughness of the steel. Therefore, the Mn content in the present invention is controlled at 1.40% to 1.60%.

[0038] V: V combines with C and N elements in steel to generate V(C,N). V(C,N) has precipitation strengthening effect and can also refine grains and improve the mechanical properties of steel. However, too high V content will also harm the plasticity and toughness of steel, and V is relatively expensive. Taking all factors into consideration, the V content in the present invention is controlled at 0.03% to 0.08%.

[0039] Nb: Similar to V, Nb can combine with C and N in steel to form carbonitrides, which can form a high-strength solid solution in steel, thereby improving the strength and toughness of the steel. It can also refine the grains and improve the performance of the steel through the action of carbonitrides. Since Nb is relatively cheap compared to V, the present invention adds a small amount of Nb to control the cost while improving the mechanical properties of the steel. Taking all factors into consideration, the content of Nb in the present invention is controlled at 0.01-0.045%.

[0040] N: Generally, N in steel is a harmful element that will cause aging embrittlement of steel. Therefore, vacuum degassing and refining processes are used to remove N in steel in traditional steelmaking. However, it can be converted into a beneficial element by adding V and Nb. Adding N to V and Nb-containing steel can significantly refine the ferrite grains by refining the original austenite grains, promoting the precipitation of V and Nb, and thus increasing the nucleation density and nucleation position of ferrite after phase transformation. When the N content is low, most of the V and Nb added to the steel exist in the steel in the form of solid solution, and the precipitation strengthening effect of V and Nb cannot be fully exerted. After adding an appropriate amount of N element, it can be strengthened by forming VN and NbV precipitates are formed to promote precipitation strengthening, effectively improve the strength of the steel, and improve the plasticity and toughness of the steel; at the same time, due to the promotion of the precipitation strengthening effect of N on V and Nb, the addition of V and Nb can be reduced while ensuring the mechanical properties of the steel, effectively reducing the cost. Taking into account the addition amounts of V and Nb, the addition ratio of V+Nb and N in the present invention should be 3-5:1 to ensure that N is fully utilized. At the same time, in order to ensure that the steel has good plasticity and toughness and forming properties, the addition amount of Nb also needs to be considered, and the addition ratio of V to Nb should be 2.1-3.5:1; taking into account comprehensively, the content of N in the present invention is controlled to be ≤0.02%.

[0041] P: a harmful element, which is harmful to the plasticity and toughness of steel and should be avoided as much as possible. Therefore, the content of P in the present invention is ≤0.02%.

[0042] S: a harmful element, which forms sulfide inclusions and thus harms the performance of steel, and should be avoided as much as possible. Therefore, the content of S in the present invention is ≤0.01%.

[0043] The mass ratio of V+Nb to N in the vanadium-niobium microalloyed Q460B angle steel is 3-5:1, and the mass ratio of V to Nb is 2.1-3.5:1.

[0044] Preferably, a vanadium-niobium microalloyed Q460B angle steel has the following components by mass percentage: C: 0.16-0.18%, Si: 0.21-0.35%, Mn: 1.40-1.60%, V: 0.034-0.067%, Nb: 0.012-0.029%, N: 0.011-0.02%, P≤0.01%, S≤0.006%, and the balance is Fe and unavoidable impurities.

[0045] Preferably, in the vanadium-niobium microalloyed Q460B angle steel, the mass ratio of V+Nb to N is 4.18-4.74:1, and the mass ratio of V to Nb is 2.1-2.83:1.

[0046] On the other hand, the present invention also provides a method for preparing vanadium-niobium microalloyed Q460B angle steel, the preparation method comprising the following steps:

[0047] Step S1: Converter smelting

[0048] According to the chemical composition of the above-mentioned vanadium-niobium microalloyed Q460B angle steel, converter smelting is carried out, molten iron or scrap steel is added as raw material in converter smelting, and silicon and manganese are then added to adjust the alloy composition. Due to the decarbonization of the converter, supplementary blowing is required;

[0049] The top-bottom combined blowing method is used throughout the smelting process. Since nitrogen is chemically inactive, it has less erosion on the converter and has a lower cost. At the same time, nitrogen can be dissolved in molten steel in trace amounts to increase the nitrogen content and provide alloying elements for the subsequent VN microalloy of the present invention. Therefore, nitrogen is used as the bottom blowing gas.

[0050] After smelting in the converter, the slag is tapped to obtain molten steel. During the tapping process, manganese-aluminum alloy (Mn mass fraction is about 30%) is used for deoxidation treatment, ferrosilicon (Si mass fraction is about 70%) is added, and top slag is added for slag washing. In order to ensure the N content in the molten steel, vacuum degassing treatment is not performed after tapping from the converter.

[0051] S2: LF Refining

[0052] The LF furnace is used to make white slag for desulfurization and refine the molten steel. In order to make the desulfurization more complete, the desulfurization time is greater than 15 minutes, and the S in the molten steel is controlled to be ≤ 0.006%. The vanadium-nitrogen alloy and the ferroniobium alloy are added in the LF refining furnace in sequence to adjust the alloy composition. The time interval for adding the vanadium-nitrogen alloy and the ferroniobium alloy is 12-17 minutes. After adding the vanadium-nitrogen alloy and the ferroniobium alloy, argon is soft-blown to ensure that the soft-blowing time is ≥ 10 minutes.

[0053] It should be noted that the addition of vanadium-nitrogen alloy is mainly to improve the strength and toughness of steel; nitrogen in vanadium-nitrogen alloy can form carbonitrides with vanadium, and these carbonitrides play a role of precipitation strengthening in steel, increasing the strength of steel; in addition, nitrogen can also refine the grains of steel and improve the toughness of steel; the addition of vanadium-nitrogen alloy can also optimize the precipitation state of vanadium and increase the precipitation strengthening effect of vanadium. Therefore, vanadium-nitrogen alloy is usually added in the early stage so that its strengthening effect can be fully exerted in the subsequent smelting process. The addition of niobium-iron alloy is to further improve the performance of steel, especially in improving the corrosion resistance and high temperature performance of steel. Niobium reacts with carbon and nitrogen in steel to form stable niobium carbide and niobium nitride. These compounds are evenly distributed at the grain boundaries of steel, which can prevent the grain growth of steel at high temperature, thereby improving the strength and toughness of steel; niobium can also improve the corrosion resistance of steel and prevent the precipitation of chromium carbide at the grain boundaries of steel; since these effects of niobium are crucial to the performance of the final steel, it is usually added after vanadium-nitrogen alloy to ensure that niobium can fully react with molten steel in the later stages of the smelting process to form the required compounds. First add vanadium nitrogen alloy to take advantage of its strengthening effect, and then add an appropriate amount of niobium iron alloy to improve the corrosion resistance and high temperature performance of the steel. This order of addition helps to optimize the entire smelting process and produce angle steel with better performance.

[0054] S3: Continuous Casting

[0055] A composite continuous casting machine for special-shaped billets is used for continuous casting, and protective or semi-protective pouring is adopted. Through a weak cooling system and constant pulling speed operation, a continuous casting billet is obtained. In order to ensure that there is no serious segregation inside the continuous casting billet, the overheat is controlled to be no more than 20°C and the pulling speed is 0.8-1.3m / min.

[0056] S4: Continuous casting heating

[0057] The continuous casting billet is heated; the composition of the continuous casting billet is measured by a spectrometer before being placed in the heating furnace to ensure that the composition is correct; the continuous casting billet is heated from room temperature to 1200-1280°C in the heating furnace at a heating rate not higher than 10°C / s, and the furnace time is ≥180min to ensure that the alloy elements can be fully dissolved.

[0058] S5: Semi-continuous rolling

[0059] Semi-continuous rolling includes two stages: slab rolling and finish rolling. Slab rolling uses reciprocating rolling, that is, the continuous casting slab is rolled as soon as it comes out of the heating furnace. The starting rolling temperature is 1100-1160℃, the rolling speed is not more than 2.5m / s to avoid the generation of cracks in the slab, and the rolling is not less than 5 passes. After the slab rolling is completed, the temperature is measured, and finish rolling begins after the temperature drops to 900-1000℃. The finish rolling uses 5-9 universal rolling mills for continuous rolling. To ensure the surface quality of the angle steel, the rolling speed is ensured to be ≤2m / s, and the final rolling temperature is 750-850℃.

[0060] S6: Slow cooling on cooling bed

[0061] The billet after finish rolling is slowly and centrally cooled on a cooling bed, with the cooling track temperature ≥400°C, to prevent stress concentration caused by excessive cooling and thus affect the final performance of the steel; after the billet temperature is reduced to 200-300°C, it is promptly straightened and fine-trimmed by a straightener, and air-cooled to room temperature to obtain Q460B angle steel.

[0062] In the production of traditional Q460B angle steel, the addition of a large amount of microalloying elements will lead to a decrease in the toughness of the material. At the same time, the residual N element and stress concentration will increase the probability of cracking, which is not conducive to the preparation of angle steel. The present invention adopts V-Nb microalloying, optimizes the configuration of alloy elements, and then completely combines the N element in the steel, preventing the N element from causing cracking of the steel. The present invention introduces part of the niobium element on the basis of vanadium microalloying. Since the complete use of the Nb element will lead to excessive reduction in plastic toughness and forming performance, it is easy to cause corner cracking when preparing large-sized angle steel, but the complete use of the V element will increase the cost because the price of V is relatively expensive. The present invention adds part of the Nb element on the basis of V microalloyed steel. This part of the addition not only leads to grain refinement and increased strength by introducing alloy elements that can pin the grain boundaries, but also reduces the application of part of the V element, thereby reducing costs.

[0063] The present invention ensures that the material has excellent comprehensive mechanical properties through reasonable design of V, Nb, and N alloy element composition, improves the strength of the material through precipitation strengthening and grain refinement, and a certain amount of undissolved (V, Nb) (C, N) will be pinned to the austenite grain boundary to prevent the continued growth of austenite grains, thereby playing a role in grain refinement. At the same time, the air-cooled (V, Nb) (C, N) after rolling is dispersed in the steel, thereby playing a strong precipitation strengthening role, thereby improving the strength of the steel. The final rolling temperature is set at 750°C to 850°C, which can effectively promote the refinement of the precipitated (V, Nb) (C, N) particles, thereby playing a better precipitation strengthening role. Through reasonable composition design and rolling process design, the strength and plastic toughness of the steel are effectively improved. The angle steel contains dispersedly distributed vanadium carbonitride and niobium carbonitride as strengthening phases, and the sizes of these two strengthening phases are both less than 60nm, and the strengthening phase plays a solid solution strengthening role in the steel.

[0064] The microstructure of the steel prepared by the above preparation method is ferrite, pearlite and dispersed second phase particles, and the second phase particles mainly include (V, Nb)(C, N); the volume content of ferrite in the microstructure is 60% to 80% (for example, 67.4 to 73.5%), the average grain size of ferrite is ≤7μm (for example, 5.4 to 6.8μm), and the average size of the second phase particles is <60nm (for example, 26 to 31nm). The ferrite content of 60% to 80% can ensure that the angle steel has good plasticity and toughness while ensuring its mechanical properties; the steel of the present invention uses ferrite as the matrix, which ensures that the material has good plasticity and toughness. At the same time, through the grain refinement effect of (V, Nb)(C, N), the ferrite grains are refined to improve its strength, and its grain size is ≥8 levels; in the present invention, pearlite is evenly distributed in the ferrite matrix, which improves the hardness of the material while also ensuring good plasticity and toughness.

[0065] The Q460B angle steel prepared by the present invention has a yield strength of ≥510Mpa (for example, 511-543Mpa), a tensile strength of ≥640MPa (for example, 642-658Mpa), an elongation of ≥22% (for example, 22.1-23.6%), and an impact energy of ≥105J (for example, 108-121J); it has good mechanical property stability and plastic toughness, and the product quality is stable and higher than the national standard requirements of GB / T 1591-2018 low-alloy high-strength structural steel, and the cost is low.

[0066] The Q460B angle steel prepared by the present invention is an equilateral angle steel. Due to the use of a semi-continuous casting rolling process, compared with the rolling method of a traditional ordinary two-roll or three-roll steel rolling mill, it can achieve rapid preparation of large-size and thick-size angle steels, with a specification of not less than ∠140 and not more than ∠200, and a thickness of not less than 10 mm.

[0067] The advantages of precise control of the composition and process parameters of the steel of the present invention will be demonstrated below with specific examples and comparative examples.

[0068] Example 1

[0069] The Q460B angle steel in this embodiment has the following components by mass percentage: C: 0.17%, Si: 0.21%, Mn: 1.40%, V: 0.067%, Nb: 0.026%, N: 0.02%, P≤0.01%, S≤0.006%, and the remainder is Fe and unavoidable impurities.

[0070] The mass ratio of V+Nb to N is 4.65:1, and the mass ratio of V:Nb is 2.58:1.

[0071] The Q460B angle steel of this implementation is prepared by the following steps:

[0072] Step S1: Converter smelting

[0073] According to the chemical composition of the above-mentioned vanadium-niobium microalloyed Q460B angle steel, converter smelting is carried out, molten iron or scrap steel is added as raw material in converter smelting, and silicon and manganese are then added to adjust the alloy composition. Due to the decarbonization of the converter, supplementary blowing is required;

[0074] The top-bottom combined blowing method is used throughout the smelting process. Since nitrogen is chemically inactive, it has less erosion on the converter and has a lower cost. At the same time, nitrogen can be dissolved in molten steel in trace amounts to increase the nitrogen content and provide alloying elements for the subsequent VN microalloy of the present invention. Therefore, nitrogen is used as the bottom blowing gas.

[0075] After smelting in the converter, the slag is tapped to obtain molten steel. During the tapping process, manganese-aluminum alloy (Mn mass fraction is about 30%) is used for deoxidation treatment, ferrosilicon (Si mass fraction is about 70%) is added, and top slag is added for slag washing. In order to ensure the N content in the molten steel, vacuum degassing treatment is not performed after tapping from the converter.

[0076] S2: LF Refining

[0077] The LF furnace is used to make white slag for desulfurization and refine the molten steel. In order to make the desulfurization more complete, the desulfurization time is greater than 15 minutes, and the S content in the molten steel is controlled to be ≤ 0.006%. 100 kg of vanadium-nitrogen alloy and 45 kg of ferroniobium alloy are added in the LF refining furnace in sequence to adjust the alloy composition. The time interval between adding the vanadium-nitrogen alloy and the ferroniobium alloy is 15 minutes. After adding the vanadium-nitrogen alloy and the ferroniobium alloy, argon is soft-blown to ensure a soft-blowing time of 20 minutes.

[0078] S3: Continuous Casting

[0079] A composite continuous casting machine for profiled billets is used for continuous casting, and protective or semi-protective pouring is adopted. Through a weak cooling system and constant pulling speed operation, a continuous casting billet is obtained; wherein the superheat is 18°C ​​and the pulling speed is 1.1m / min.

[0080] S4: Continuous casting heating

[0081] The continuous casting billet is heated; the composition of the continuous casting billet is measured by a spectrometer before being placed in the heating furnace to ensure that the composition is correct; the continuous casting billet is heated from room temperature to 1250°C in the heating furnace at a heating rate of 8°C / s, and the furnace time is 220 minutes to ensure that the alloy elements can be fully dissolved.

[0082] S5: Semi-continuous rolling

[0083] The slab rolling adopts reciprocating rolling, that is, the continuous casting slab is rolled as soon as it comes out of the heating furnace, and a two-roller reversible rolling mill is used for slab rolling. The starting rolling temperature is 1150℃, the rolling speed is 1.8m / s, and 6 reciprocating rolling passes are performed. After the slab rolling is completed, the temperature is measured, and the finishing rolling begins after the temperature drops to 900-1000℃. The finishing rolling uses 9 universal rolling mills for continuous rolling, with a total rolling speed of 1.5m / s, and the final rolling temperature is measured to be 760℃.

[0084] S6: Slow cooling on cooling bed

[0085] The billet after finish rolling is slowly cooled on a cooling bed with a cooling track temperature of 432°C to prevent excessive cooling from affecting the final performance of the steel. After the billet temperature drops to 267°C, it is straightened and fine-finished in a straightener and air-cooled to room temperature to obtain a Q460B angle steel with a specification of 200mm×200mm and a thickness of 16mm.

[0086] Example 2

[0087] The Q460B angle steel in this embodiment has the following components by mass percentage: C: 0.16%, Si: 0.35%, Mn: 1.49%, V: 0.034%, Nb: 0.012%, N: 0.011%, P≤0.01%, S≤0.006%, and the remainder is Fe and unavoidable impurities.

[0088] The mass ratio of V+Nb to N is 4.18:1, and the mass ratio of V to Nb is 2.83:1.

[0089] The Q460B angle steel of this implementation is prepared by the following steps:

[0090] Step S1: Converter smelting

[0091] According to the chemical composition of the above-mentioned vanadium-niobium microalloyed Q460B angle steel, converter smelting is carried out, molten iron or scrap steel is added as raw material in converter smelting, silicon and manganese are added to adjust the alloy composition, and supplementary blowing is required due to the decarbonization of the converter;

[0092] The top-bottom combined blowing method is used throughout the smelting process. Since nitrogen is chemically inactive, it has less erosion on the converter and has a lower cost. At the same time, nitrogen can be dissolved in molten steel in trace amounts to increase the nitrogen content and provide alloying elements for the subsequent VN microalloy of the present invention. Therefore, nitrogen is used as the bottom blowing gas.

[0093] After smelting in the converter, the slag is tapped to obtain molten steel. During the tapping process, manganese-aluminum alloy (Mn mass fraction is about 30%) is used for deoxidation treatment, ferrosilicon (Si mass fraction is about 70%) is added, and top slag is added for slag washing. In order to ensure the N content in the molten steel, vacuum degassing treatment is not performed after tapping from the converter.

[0094] S2: LF Refining

[0095] The LF furnace is used to make white slag for desulfurization and refine the molten steel. In order to make the desulfurization more complete, the desulfurization time is greater than 15 minutes, and the S in the molten steel is controlled to be ≤ 0.006%. 80 kg of vanadium-nitrogen alloy and 36 kg of ferroniobium alloy are added in the LF refining furnace in sequence to adjust the alloy composition. The time interval between adding the vanadium-nitrogen alloy and the ferroniobium alloy is 12 minutes. After adding the vanadium-nitrogen alloy and the ferroniobium alloy, argon is soft-blown for 30 minutes.

[0096] S3: Continuous Casting

[0097] A composite continuous casting machine for profiled billets is used for continuous casting, and protective or semi-protective pouring is adopted. Through a weak cooling system and constant pulling speed operation, a continuous casting billet is obtained; wherein the superheat is 20°C and the pulling speed is 1.4m / min.

[0098] S4: Continuous casting heating

[0099] The continuous casting billet is heated; the composition of the continuous casting billet is measured by a spectrometer before being placed in the heating furnace to ensure that the composition is correct; the continuous casting billet is heated from room temperature to 1270°C in the heating furnace at a heating rate of 7°C / s, and the furnace time is 310 minutes to ensure that the alloy elements can be fully dissolved.

[0100] S5: Semi-continuous rolling

[0101] The slab rolling adopts reciprocating rolling, that is, the continuous casting slab is rolled as soon as it comes out of the heating furnace, and a two-roller reversible rolling mill is used for slab rolling. The starting rolling temperature is 1160℃, the rolling speed is 1.9m / s, and 6 reciprocating rolling passes are performed. The temperature is measured after the slab rolling is completed, and the finishing rolling starts after the temperature reaches 980℃. The finishing rolling uses 9 universal rolling mills for continuous rolling, with a total rolling speed of 1.8m / s, and the final rolling temperature is measured to be 780℃.

[0102] S6: Slow cooling on cooling bed

[0103] The billet after finish rolling is slowly cooled on a cooling bed with a cooling track temperature of 400°C to prevent the final performance of the steel from being affected by excessive cooling. After the billet temperature is reduced to 283°C, it is straightened and fine-finished in a straightener in a timely manner and air-cooled to room temperature to obtain a Q460B angle steel with a specification of 200mm×200mm and a thickness of 16mm.

[0104] Example 3

[0105] The Q460B angle steel in this embodiment has the following components by mass percentage: C: 0.18%, Si: 0.25%, Mn: 1.60%, V: 0.061%, Nb: 0.029%, N: 0.019%, P≤0.01%, S≤0.006%, and the remainder is Fe and unavoidable impurities.

[0106] The mass ratio of V+Nb to N is 4.74:1, and the mass ratio of V:Nb is 2.1:1.

[0107] The Q460B angle steel of this implementation is prepared by the following steps:

[0108] Step S1: Converter smelting

[0109] According to the chemical composition of the above-mentioned vanadium-niobium microalloyed Q460B angle steel, converter smelting is carried out, molten iron or scrap steel is added as raw material in converter smelting, silicon and manganese are added to adjust the alloy composition, and supplementary blowing is required due to the decarbonization of the converter;

[0110] The top-bottom combined blowing method is used throughout the smelting process. Since nitrogen is chemically inactive, it has less erosion on the converter and has a lower cost. At the same time, nitrogen can be dissolved in molten steel in trace amounts to increase the nitrogen content and provide alloying elements for the subsequent VN microalloy of the present invention. Therefore, nitrogen is used as the bottom blowing gas.

[0111] After smelting in the converter, the slag is tapped to obtain molten steel. During the tapping process, manganese-aluminum alloy (Mn mass fraction is about 30%) is used for deoxidation treatment, ferrosilicon (Si mass fraction is about 70%) is added, and top slag is added for slag washing. In order to ensure the N content in the molten steel, vacuum degassing treatment is not performed after tapping from the converter.

[0112] S2: LF Refining

[0113] The LF furnace is used to make white slag for desulfurization and refine the molten steel. In order to make the desulfurization more complete, the desulfurization time is greater than 15 minutes, and the S content in the molten steel is controlled to be ≤ 0.006%. 100 kg of vanadium-nitrogen alloy and 45 kg of ferroniobium alloy are added in the LF refining furnace in sequence to adjust the alloy composition. The time interval between adding the vanadium-nitrogen alloy and the ferroniobium alloy is 16 minutes. After adding the vanadium-nitrogen alloy and the ferroniobium alloy, argon is soft-blown to ensure a soft-blowing time of 20 minutes.

[0114] S3: Continuous Casting

[0115] A composite continuous casting machine for profiled billets is used for continuous casting, and protective or semi-protective pouring is adopted. Through a weak cooling system and constant pulling speed operation, a continuous casting billet is obtained; wherein the superheat is 18°C ​​and the pulling speed is 1.1m / min.

[0116] S4: Continuous casting heating

[0117] The continuous casting billet is heated; the composition of the continuous casting billet is measured by a spectrometer before being placed in the heating furnace to ensure that the composition is correct; the continuous casting billet is heated from room temperature to 1280°C in the heating furnace at a heating rate of 7°C / s and the furnace time is 250 minutes to ensure that the alloy elements can be fully dissolved.

[0118] S5: Semi-continuous rolling

[0119] The slab rolling adopts reciprocating rolling, that is, the continuous casting slab is rolled as soon as it comes out of the heating furnace, and a two-roller reversible rolling mill is used for slab rolling. The starting rolling temperature is 1150℃, the rolling speed is 1.8m / s, and the reciprocating rolling is performed for 5 passes. The temperature is measured after the slab rolling is completed, and the finishing rolling starts after the temperature reaches 920℃. The finishing rolling uses 6 universal rolling mills for continuous rolling, with a total rolling speed of 1.6m / s, and the final rolling temperature is measured to be 770℃.

[0120] S6: Slow cooling on cooling bed

[0121] The billet after finish rolling is slowly cooled on a cooling bed with a cooling track temperature of 420°C to prevent excessive cooling from affecting the final performance of the steel. After the billet temperature drops to 270°C, it is straightened and fine-finished in a straightener and air-cooled to room temperature to obtain a Q460B angle steel with a specification of 200mm×200mm and a thickness of 18mm.

[0122] Comparative Example 1

[0123] The Q460B angle steel of this comparative example is prepared according to the method in CN 111411304A, and its components are as follows by mass percentage: C: 0.18%, Si: 0.41%, Mn: 1.46%, V: 0.055%, N: 0.014%, P≤0.01%, S≤0.006%, and the remainder is Fe and unavoidable impurities.

[0124] The preparation method and process parameters of the Q460B angle steel in this comparative example are in accordance with the method in CN 111411304A, which is continuous rolling, and the rolling is carried out according to the rolling mill sequence of 850 / 750 / 650I / 650II / 65 and the temperature is controlled.

[0125] Comparative Example 2

[0126] The composition of the Q460B angle steel in this comparative example is the same as that in Example 1.

[0127] The preparation method of Q460B angle steel in this comparative example is similar to that in Example 1, except that this comparative example uses the rolling method of a conventional ordinary two-roll or three-roll steel section mill, and uses a two-roll reversible rolling mill for bloom rolling and finish rolling. The bloom rolling adopts 5 passes and the finish rolling adopts 9 passes.

[0128] Comparative Example 3

[0129] The Q460B angle steel in this comparative example has the following components by mass percentage: C: 0.14%, Si: 0.51%, Mn: 1.40%, Cu: 0.41%, P: 0.07%, Cr: 0.55%, Ni: 0.45%, Nb: 0.041%, and S≤0.020%. It is a niobium micro-alloyed angle steel; the preparation method of the Q460B angle steel in this comparative example is the same as that in Example 1.

[0130] Table 1 shows the mechanical properties and costs of the Q460B angle steels of the embodiments of the present invention and the comparative examples; Table 2 shows the organizational structure of the Q460B angle steels of the embodiments of the present invention and the comparative examples.

[0131] Table 1 Mechanical properties of Q460B angle steel of embodiment and comparative example

[0132]

[0133] Table 2 shows the microstructure parameters of Q460B angle steel of the embodiment and comparative example.

[0134]

[0135]

[0136] The composition and preparation method parameters of the angle steel in Example 1 meet the requirements of the present invention. A large proportion of V and Nb elements are added, resulting in the best strength of this embodiment. At the same time, the grain size of this embodiment is relatively small. Since the amount of V and Nb elements added is large, the second phase particles are fully separated, so the number of second phase particles is the largest and the size is relatively small.

[0137] The angle steel composition and preparation method process parameters of Example 2 meet the requirements of the present invention. A relatively small proportion of V and Nb elements are added. By comparing this example with Comparative Example 1, it can be seen that in Comparative Example 1, due to the continuous rolling process used, the process has high production efficiency, but due to problems such as instability of continuous rolling, cracks and other problems are prone to occur during the production process. At the same time, in this comparative example, a relatively large amount of V is used, so the production cost is higher than that of Example 2 in which some Nb is mixed and added.

[0138] In Comparative Example 2, the composition of the angle steel meets the requirements of the present invention, but the traditional rolling method of a common two-roll or three-roll steel section mill is adopted in the preparation process, and a two-roll mill is used for both rough rolling and finishing rolling. Although this method can ensure the surface quality and performance of the product, the backward method leads to low production efficiency.

[0139] In Comparative Example 3, since niobium microalloying is used without adding V, the strong precipitation strengthening effect of the Nb element easily leads to segregation and cracking.

[0140] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A vanadium-niobium microalloyed Q460B angle steel, characterized in that: The components are calculated by mass percentage as follows: C: 0.15-0.2%, Si: 0.20-0.45%, Mn: 1.40-1.60%, V: 0.03-0.08%, Nb: 0.01-0.045%, N≤0.02%, P≤0.02%, S≤0.01%, and the balance is Fe and unavoidable impurities.

2. The vanadium-niobium microalloyed Q460B angle steel according to claim 1, characterized in that: In the vanadium-niobium microalloyed Q460B angle steel, the mass ratio of V+Nb to N (V+Nb) / N is 3-5:

1.

3. The vanadium-niobium microalloyed Q460B angle steel according to claim 2, characterized in that: In the vanadium-niobium microalloyed Q460B angle steel, the mass ratio of V to Nb (V / Nb) is 2.1-3.5:

1.

4. The vanadium-niobium microalloyed Q460B angle steel according to claim 1, characterized in that: The microstructure of the vanadium-niobium microalloyed Q460B angle steel is ferrite, pearlite and dispersed second phase particles.

5. The vanadium-niobium microalloyed Q460B angle steel according to claim 4, characterized in that: The volume content of the ferrite is 60% to 80%, the average grain size of the ferrite is ≤7μm, and the average size of the second phase particles is <60nm.

6. A method for preparing vanadium-niobium microalloyed Q460B angle steel, used for preparing the vanadium-niobium microalloyed Q460B angle steel according to any one of claims 1 to 5, characterized in that: Including converter smelting - LF refining - continuous casting - continuous casting billet heating - semi-continuous rolling - cooling bed slow cooling; The converter does not perform vacuum degassing after steel is tapped.

7. The preparation method according to claim 6, characterized in that: During the LF refining process, the vanadium-nitrogen alloy and the ferroniobium alloy are added to the LF refining furnace in sequence; the time interval between adding the vanadium-nitrogen alloy and the ferroniobium alloy is 12-17 minutes.

8. The preparation method according to claim 7, characterized in that: During the continuous casting process, the superheat is controlled to be no greater than 20° C. and the casting speed is 0.8-1.3 m / min.

9. The preparation method according to claim 8, characterized in that: During the continuous casting billet heating process, the continuous casting billet is heated from room temperature to 1200-1280° C. in a heating furnace at a heating rate not higher than 10° C. / s, and the time in the furnace is ≥180 min.

10. The preparation method according to claim 9, characterized in that: The semi-continuous rolling includes blooming rolling and finishing rolling; The rolling temperature is 1100-1160℃, the rolling speed is not more than 2.5m / s, and the rolling is not less than 5 times; The starting rolling temperature of the finishing rolling is 900-1000℃, the rolling speed is ≤2m / s, and the final rolling temperature of the finishing rolling is 750-850℃.

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