A high-strength and high-toughness angle steel with uniform cross-sectional performance and its production process

Abstract

The present invention relates to the technical field of steel for steel structures, and particularly to a high-strength and high-toughness angle steel with uniform cross-sectional properties and its production process. A high-strength and high-toughness angle steel with uniform cross-sectional properties, the chemical composition is by mass percentage: C: 0.14% - 0.17%, Si: 0.20% - 0.40%, Mn: 1.35% - 1.70%, P ≤ 0.010%, S ≤ 0.010%, N: 0.70% - 1.20%, V: 0.07% - 0.18%, Ti: 0.005% - 0.010%, N: 0.015% - 0.026%, wherein C / N ≤ 8.0, Ti / V ≤ 0.12, Mn / Ni ≤ 2.2, and the balance is Fe and inevitable impurities. The angle steel prepared by the present invention has a yield strength ≥ 550 MPa, a low-temperature impact energy at -60 °C ≥ 60 J, and the difference in cross-sectional yield strength is within 20 MPa.

Description

Technical Field

[0001] The present invention relates to the technical field of steel for steel structures, and particularly to a high-strength and high-toughness angle steel with uniform cross-sectional properties and its production process. Background Art

[0002] The rapid development of the steel structure industry and the power industry has put forward requirements for angle steel used in transmission towers, such as high strength, high toughness, and easy weldability. It is very urgent to develop and research high-strength and high-quality grade angle steel for transmission towers. Traditional tower angle steel mainly adopts C-Mn steel alloy design, with a yield strength below 345 MPa, and the quality grades are mainly A and B. Due to the angle steel being rolled in a pass, restricted by the shape of the angle steel, rolling conditions, and equipment conditions, it is impossible to perform large reduction rolling in the non-recrystallization zone of austenite during production, and only multi-pass light reduction rolling can be carried out in the recrystallization zone of austenite. The single-pass deformation amount and the cumulative deformation amount during rolling are both relatively small, and it is difficult to refine the coarse original austenite grains, resulting in a significant decrease in strength and toughness. In addition, due to the angle steel being rolled in a pass, its cross-sectional properties are very uneven. Usually, the strength of the edge is high, and the strength at the connection of the two edges is low, with a strength difference greater than 35 MPa, and this difference becomes more obvious as the size of the angle steel increases and the strength requirement increases.

[0003] The patent "Hot-rolled weathering angle steel with a yield of 420 MPa for transmission towers and its production method" (publication number: CN109487164A) introduces a production process for hot-rolled weathering angle steel with a yield of 420 MPa. By adding 0.05 - 0.15% V and 0.0100 - 0.0150% N, the strength of the steel is improved, but the grade of the angle steel produced is Q420, with relatively low strength. The patent "A Q460 grade hot-rolled angle steel and its preparation method" (publication number: CN111411304A) discloses a Q460 grade hot-rolled angle steel and its preparation method, but the grade of the angle steel produced is Q460, with relatively low strength, and it improves the low-temperature impact energy at 0 °C, which is not applicable to extremely cold regions at lower temperatures. The patent "A hot-rolled angle steel resistant to high and low temperatures and its preparation method" (publication number: CN111926262A) discloses that by adding 0.042 - 0.070% V and 0.015 - 0.026% Mo, the strength of the steel is improved, and its yield strength reaches the 500 MPa level, unable to meet the requirements for higher strength. The patent "An anti-severe cold high-strength hot-rolled angle steel and its production method" (publication number: CN102676921A) introduces a method for improving the strength and low-temperature impact toughness of angle steel through V+Nb complex microalloying. Its yield strength reaches the 550 MPa level, but it improves the low-temperature impact energy at -40 °C and cannot meet the requirements for higher toughness. In terms of the uniformity of the cross-sectional properties of angle steel, there is basically no relevant research in China.

[0004] In summary, the prior art cannot simultaneously meet the service requirements of high strength (yield strength ≥ 550 MPa), high toughness (-60 °C impact energy ≥ 60 J), and uniform cross-sectional properties for angle steel. There is an urgent need for a high-strength and high-toughness angle steel with uniform cross-sectional properties to meet the service requirements. Summary of the Invention

[0005] In view of the above analysis, the embodiments of the present invention aim to provide a high-strength and high-toughness angle steel with uniform cross-sectional properties and its production process to solve the problem that the prior art cannot simultaneously meet the service requirements of high strength, high toughness, and uniform cross-sectional properties for angle steel.

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

[0007] On the one hand, the present invention provides a high-strength and high-toughness angle steel with uniform cross-sectional properties. The chemical components in the angle steel are calculated by mass percentage: C: 0.14% - 0.17%, Si: 0.20% - 0.40%, Mn: 1.35% - 1.70%, P ≤ 0.010%, S ≤ 0.010%, N: 0.70% - 1.20%, V: 0.07% - 0.18%, Ti: 0.005% - 0.010%, N: 0.015% - 0.026%, where C / N ≤ 8.0, Ti / V ≤ 0.12, Mn / Ni ≤ 2.2, and the balance is Fe and unavoidable impurities.

[0008] Further, the chemical components in the angle steel are calculated by mass percentage as follows: C: 0.142% - 0.153%, Si: 0.22% - 0.28%, Mn: 1.36% - 1.47%, P ≤ 0.009%, S ≤ 0.008%, Ni: 0.73% - 0.86%, V: 0.077% - 0.093%, Ti: 0.0055% - 0.0077%, N: 0.0155% - 0.0176%, where C / N ≤ 6.8, Ti / V ≤ 0.11, Mn / Ni ≤ 2.0, and the balance is Fe and unavoidable impurities.

[0009] Further, the chemical components in the angle steel are calculated by mass percentage as follows: C: 0.160% - 0.168%, Si: 0.30% - 0.37%, Mn: 1.52% - 1.63%, P ≤ 0.008%, S ≤ 0.007%, Ni: 0.92% - 1.10%, V: 0.107% - 0.135%, Ti: 0.0081% - 0.0093%, N: 0.0182% - 0.0246%, where C / N ≤ 7.6, Ti / V ≤ 0.10, Mn / Ni ≤ 1.8, and the balance is Fe and unavoidable impurities.

[0010] Further, the width of the side of the angle steel is greater than 300 mm, and the thickness of the side is greater than 20 mm.

[0011] Furthermore, the microstructure of the angle steel is ferrite F and pearlite P, and the volume fraction ratio of the ferrite F to the pearlite P is 3:1 to 5:1.

[0012] Furthermore, the volume fraction ratio of the ferrite F to the pearlite P in the microstructure of the angle steel is 4.4:1.

[0013] On the other hand, the present invention also provides a production process for high-strength and high-toughness angle steel with uniform cross-sectional properties, which is used for the above-mentioned angle steel and includes the following steps:

[0014] S1. Electric furnace smelting: Ensure argon blowing throughout the tapping process, and transfer to the LF refining furnace after argon blowing;

[0015] S2. Secondary refining: Add VN16 alloy powder in the middle stage of refining, and blow argon throughout the refining period;

[0016] S3. Continuous casting: Use long nozzle argon sealing for protective casting during continuous casting, and control the superheat of molten steel so that the superheat at the start of casting furnace ≤ 34°C and the superheat at the continuous casting furnace ≤ 25°C;

[0017] S4. Blooming;

[0018] S5. Rolling.

[0019] Furthermore, in the step S1, the tapping temperature ≥ 1620°C, and the argon blowing time > 3 min.

[0020] Furthermore, in the step S2, the refining temperature is 1560 - 1600°C.

[0021] Furthermore, in the step S4, the rolling start temperature ≤ 1050°C, and the finishing rolling temperature ≤ 1000°C; in the step S5, the billet heating temperature is 1150 - 1200°C, the rolling start temperature is 1100°C - 1180°C, and the finishing rolling temperature is 880 - 980°C.

[0022] Compared with the prior art, the present invention can at least achieve one of the following beneficial effects:

[0023] 1. The yield strength of the high-strength and high-toughness angle steel with uniform cross-sectional properties described in the present invention is not less than 550 MPa, the low-temperature impact energy at -60°C is not less than 60 J, and the difference in cross-sectional yield strength is within 20 MPa, solving the problem that the angle steel cannot simultaneously meet the usage requirements of high strength, high toughness, and uniform cross-sectional properties.

[0024] 2. For the problem of uneven cross-sectional properties caused by the large differences in deformation and cooling rates between the edges of the angle steel and the connection of its two sides during the rolling process, through the optimization of chemical composition and the characteristic of slower cooling rate at the connection of its two sides, the precipitation strengthening effect of the second phase at the connection is stronger than that at the edges, compensating for the insufficient strength at the connection, enhancing the uniformity of its cross-sectional properties, effectively reducing the consumption of vanadium, saving vanadium resources and reducing production costs.

[0025] 3. The production of the high-strength and high-toughness angle steel with uniform cross-sectional properties according to the present invention makes full use of the characteristic of high N content in electric furnace steel, combined with the addition of VN16 alloy powder, which can effectively ensure the recovery rates of vanadium and nitrogen, with a simple process, and finish rolling at 880 - 980 °C, having a small load on the rolling mill and effectively ensuring the service life of the rolling mill; at the same time, by adding VN16 alloy powder, it promotes the precipitation of V in austenite, not only increasing the precipitation strengthening effect, but also having a fine grain strengthening effect, significantly improving the low-temperature impact toughness.

[0026] 4. The high-strength and high-toughness angle steel with uniform cross-sectional properties according to the present invention can adopt the same smelting and rolling processes as traditional angle steel, without the need for special production equipment such as controlled cooling.

[0027] 5. The angle steel provided by the present invention can meet the requirements of high strength, high toughness, easy weldability, etc. for angle steel used in transmission towers put forward by the rapid development of the steel structure industry and the power industry, and can be used as angle steel for high-strength and high-quality grade towers.

[0028] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained from the content specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings are only for the purpose of showing specific embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference signs represent the same components.

[0030] Figure 1 It is the microstructure diagram of the angle steel in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The following will specifically describe the preferred embodiments of the present invention in conjunction with the drawings, where the drawings form a part of this application and are used together with the embodiments of the present invention to explain the principle of the present invention, not for limiting the scope of the present invention.

[0032] The present invention provides a high-strength and high-toughness angle steel with uniform cross-sectional properties. The chemical components in the angle steel are as follows by mass percentage: C: 0.14% - 0.17%, Si: 0.20% - 0.40%, Mn: 1.35% - 1.70%, P ≤ 0.010%, S ≤ 0.010%, N: 0.70% - 1.20%, V: 0.07% - 0.18%, Ti: 0.005% - 0.010%, N: 0.015% - 0.026%, where C / N ≤ 8.0, Ti / V ≤ 0.12, Mn / Ni ≤ 2.2, and the balance is Fe and unavoidable impurities.

[0033] Specifically, in the above-mentioned high-strength and high-toughness angle steel with uniform cross-sectional properties, the functions and ratios of each element are as follows:

[0034] C is an effective element to improve the strength of steel. In order to obtain the required strength, the C content needs to be above 0.14%, but when its content exceeds 0.17%, the low-temperature toughness of the steel will be significantly reduced. Therefore, its range is specified as 0.14 - 0.17%.

[0035] Si is a deoxidizing element and also a solid-solution strengthening element. On the one hand, it can ensure the deoxidation effect, and on the other hand, Si can improve the strength of the material. In order to ensure the deoxidation effect and the required strength, the Si content needs to be above 0.20%, but when its content exceeds 0.40%, the toughness and weldability of the steel will become poor. Therefore, in order to ensure the strength, toughness and weldability of the angle steel, the present invention specifies the range of Si as 0.20 - 0.40%.

[0036] Mn is an alloying element that plays a major role in the phase transformation strengthening and solid-solution strengthening mechanisms of microalloyed steel. In the present invention, in order to obtain the required strength, the Mn content needs to be above 1.35%, but when its content exceeds 1.70%, the low-temperature toughness and weldability of the steel will be reduced. Therefore, the range of Mn is specified as 1.35 - 1.70%.

[0037] P is an impurity element in steel. The less the P content, the better the performance of the angle steel in the present invention. Therefore, P is limited to ≤ 0.010%.

[0038] S is an inevitable harmful element in steel, which will form MnS inclusions and reduce the toughness and weldability of the steel. Therefore, its content should be reduced as much as possible, and its content is controlled below 0.01%.

[0039] Ni is an important element in the angle steel of the present invention. It can reduce the surface activity of the steel, improve the low-temperature toughness and corrosion resistance of the steel. To achieve the protection effect, the Ni content should be above 0.70%. However, considering the cost, the upper limit should be controlled at 1.20%. In addition, the contents of Ni and Mn need to satisfy Mn / Ni ≤ 2.2. Mn / Ni ≤ 2.2 is an important control factor in the present invention. The main reason is that the increase of Mn will promote the formation of granular bainite in the structure, resulting in the disappearance of the toughness improvement effect brought by the Ni element.

[0040] V is a key microalloying element in the angle steel of the present invention. V precipitates in austenite, which can refine austenite grains. At the same time, the interfacial energy between these particles and ferrite is small, promoting the nucleation of ferrite and playing a role in inducing intragranular ferrite nucleation and refining ferrite grains. In addition, it precipitates dispersively in ferrite, playing a precipitation strengthening role and further improving the strength of the angle steel. When the vanadium content is lower than 0.07%, the minimum strength requirement of the present invention cannot be met. At the same time, considering the cost, the upper limit should be controlled at 0.18%.

[0041] Ti is a key microalloying element in the angle steel of the present invention and also a precipitation strengthening element in microalloyed steel. It can form very stable TiN particles in the high-temperature zone, which can effectively prevent the growth of austenite grains. To achieve this purpose, the minimum Ti content should be controlled at 0.005%. However, too high Ti content will make the TiN particles in the steel coarse, reducing the low-temperature toughness of the steel. Therefore, the present invention stipulates the range of Ti as 0.005% - 0.010%. At the same time, Ti / V ≤ 0.12 should be strictly controlled. This is mainly because the combination of Ti and N will reduce the N content in the steel, thus affecting the precipitation of V in austenite and ferrite.

[0042] N is a key microalloying element in the angle steel of the present invention. N can combine with V and Ti in the steel to form second-phase particles and precipitate. Moreover, increasing nitrogen in the steel can control the precipitation of V in austenite, change the distribution of V that plays a role in fine-grain strengthening and precipitation strengthening, and can play the process route of V's fine-grain strengthening role, replacing part of the precipitation strengthening effect with fine-grain strengthening, improving the plasticity and toughness of the matrix without changing the strength. Moreover, the increase of nitrogen promotes the precipitation of V, thus reducing the dosage of V and playing a role in reducing costs. However, too high N content will increase the aging brittleness of the steel and reduce the low-temperature toughness of the steel. Therefore, combined with the contents of V and Ti, the N content should be controlled at 0.015% - 0.026%. In addition, the contents of N and C need to satisfy C / N ≤ 8.0, which is an important control factor in the present invention. This is mainly because when the N content is small, the remaining V will combine with C and precipitate, instead reducing the strength of the steel.

[0043] To further improve the comprehensive performance of the above angle steel, the composition of the above angle steel can be further adjusted. Exemplarily, the chemical components in the angle steel are by mass percentage: C: 0.142% - 0.153%, Si: 0.22% - 0.28%, Mn: 1.36% - 1.47%, P ≤ 0.009%, S ≤ 0.008%, Ni: 0.73% - 0.86%, V: 0.077% - 0.093%, Ti: 0.0055% - 0.0077%, N: 0.0155% - 0.0176%, where C / N ≤ 6.8, Ti / V ≤ 0.11, Mn / Ni ≤ 2.0, and the balance is Fe and unavoidable impurities.

[0044] Further, the chemical components in the angle steel are by mass percentage: C: 0.160% - 0.168%, Si: 0.30% - 0.37%, Mn: 1.52% - 1.63%, P ≤ 0.008%, S ≤ 0.007%, Ni: 0.92% - 1.10%, V: 0.107% - 0.135%, Ti: 0.0081% - 0.0093%, N: 0.0182% - 0.0246%, where C / N ≤ 7.6, Ti / V ≤ 0.10, Mn / Ni ≤ 1.8, and the balance is Fe and unavoidable impurities.

[0045] It should be noted that the side width of the above angle steel is greater than 300 mm, and the side thickness is greater than 20 mm.

[0046] It should be noted that the microstructure of the above angle steel is mainly ferrite F and pearlite P, and the volume fraction ratio of the ferrite F to the pearlite P is 3:1 - 5:1.

[0047] Further, the volume fraction ratio of ferrite F to pearlite P in the microstructure of the angle steel is 4.4:1.

[0048] In the present invention, the microstructure of the angle steel is mainly ferrite and pearlite. Since the angle steel is a section steel, the deformation amount and cooling rate of each part are different during the rolling process, so the proportion of ferrite and pearlite in different parts is different. There is more pearlite at the edge, and less pearlite at the connection of the two sides. When produced according to ordinary components, the strength of the edge is much higher than that of the connection. However, after adopting vanadium-nitrogen microalloying, through the optimization of chemical components and the characteristic of slower cooling rate at the connection of the two sides itself, the precipitation strengthening effect of the second phase at the connection is stronger than that at the edge, making up for the insufficient strength at the connection, and finally making the strength of each part of the angle steel in the present invention relatively uniform.

[0049] The present invention also provides a production process for a high-strength and high-toughness angle steel with uniform cross-sectional performance for preparing the above angle steel, including the following steps:

[0050] S1. Electric furnace smelting: During the tapping process, ensure argon blowing throughout, and transfer to the LF refining furnace after argon blowing;

[0051] S2. Secondary refining: Add VN16 alloy powder in the middle stage of refining, and blow argon throughout the refining period;

[0052] S3. Continuous casting: Use long nozzle argon sealing protection casting during continuous casting, and control the superheat of molten steel as follows: the superheat at the start of casting furnace ≤ 34°C, and the superheat at the continuous casting furnace ≤ 25°C;

[0053] S4. Blooming;

[0054] S5. Rolling.

[0055] It should be noted that in step S1, the tapping temperature T ≥ 1620°C, and the argon blowing time > 3 min to prevent steel oxidation.

[0056] It should be noted that in step S2, the refining temperature in the refining furnace is 1560 - 1600°C. Specifically, taking advantage of the high N content in electric furnace steel and the characteristic that the cooling at the connection of the two sides of the angle steel is slower than that of the edge, adopt the V-N microalloying technology to improve the cross-sectional performance difference of the angle steel; the LF refining time is 30 - 40 min. Add VN16 alloy powder in the middle stage of refining to prevent local supersaturation of nitrogen, improve the recovery rate, and blow argon throughout the refining period to improve the recovery rate of vanadium and nitrogen in the steel. Adding VN16 alloy powder too early will cause local supersaturation of nitrogen and is likely to generate nitrogen volatilization, while adding it too late will result in insufficient dissolution of VN16 alloy powder, leading to uneven steel composition. At the same time, using VN16 alloy powder can ensure that the recovery rates of V and N are above 90%, while using other addition methods, such as ferroniobium, ferrovanadium nitride, etc., cannot ensure the recovery rates of V and N. Specifically, the addition amount of VN16 alloy powder is 0.97 - 2 kg / t.

[0057] Blowing argon throughout in step S2 helps to homogenize the chemical composition of the molten steel, remove harmful gases such as N and H, and deoxidize.

[0058] It should be noted that in step S3, use long nozzle argon sealing protection casting during continuous casting to reduce the temperature loss of the steel flow and make the molten steel temperature more uniform. Control the superheat of molten steel as follows: the superheat at the start of casting furnace ≤ 34°C, and the superheat at the continuous casting furnace ≤ 25°C. Controlling the appropriate superheat during continuous casting can increase the equiaxed crystal zone of the casting billet, make the structure of the casting billet dense, and is beneficial to reducing the central segregation and porosity of the casting billet, thereby optimizing the quality and output of the casting billet. If the superheat of the continuous casting molten steel is too large, the central segregation of the casting billet will be aggravated, and it is easy to induce breakout accidents.

[0059] It should be noted that in step S4, the ingot is subjected to blooming rolling. The starting rolling temperature is ≤1050°C, and the finishing rolling temperature is ≤1000°C. After rolling, it is air-cooled. Exemplarily, the starting rolling temperature is 1033°C, and the finishing rolling temperature is 945°C.

[0060] It should be noted that in step S5, the heating temperature of the hot-rolled steel billet is 1150 - 1200°C, and the heating time in the furnace shall not exceed 3 hours. Excessive time is likely to cause defects such as overheating, burning, decarburization, and oxidation. The starting rolling temperature is 1100°C - 1180°C, the finishing rolling temperature is 880 - 980°C, and after rolling, it is air-cooled. Controlled rolling is carried out in the austenite recrystallization zone, which requires a lower rolling force for the rolling mill, with a small load, being beneficial to protecting the rolling mill. Exemplarily, the heating temperature of the hot-rolled steel billet is 1188°C, the heating time in the furnace is 2.6 h, the starting rolling temperature is 1142°C, and the finishing rolling temperature is 968°C.

[0061] The yield strength of the angle steel prepared by the present invention is ≥550 Mpa (such as 559 - 582 MPa), the tensile strength is ≥670 MPa (such as 670 - 705 MPa), the elongation is ≥25% (such as 26 - 29%), the low-temperature impact energy at -60°C is >60 J (such as 68 - 104 J), and the difference in cross-sectional yield strength is within 20 MPa.

[0062] Next, specific examples and comparative examples will be used to demonstrate the advantages of precise control of the elemental chemical composition, content, and preparation process parameters of the present invention.

[0063] The various angle steels of Examples 1 - 4 and Comparative Examples 1 - 4 are all industrially produced. The chemical compositions of the angle steels in each example and comparative example are shown in Table 1. The angle steel is smelted in a 70-ton electric furnace and undergoes the technological processes of electric furnace smelting, ladle furnace refining, continuous casting, blooming, and rolling. Example 1 and Comparative Example 1 are made into 300×30 mm, Example 2 and Comparative Example 2 are made into 320×26 mm, Example 3 and Comparative Example 3 are made into 320×32 mm, and Example 4 and Comparative Example 4 are made into 360×24 mm equal-angle steels. The production process and its technical parameter control are as follows:

[0064] Electric furnace smelting: Smelted in a 70-ton electric furnace, the tapping temperature is 1630 ± 10°C. During tapping, ensure full argon blowing throughout the process, and transfer to the LF furnace after 3 minutes of argon blowing.

[0065] Ladle furnace refining: The refining temperature is 1580 ± 5°C. Add VN16 alloy powder in the middle stage of refining. The amount of the added alloy powder is 1.4 - 2.0 kg / ton. Argon is blown throughout the refining period, and large-argon-volume stirring that exposes the molten steel is strictly prohibited.

[0066] Continuous casting: The superheat of the molten steel is controlled such that the superheat of the starting casting furnace is ≤34°C, and the superheat of the continuous casting furnace is ≤25°C.

[0067] Blooming: The continuous casting billet is subjected to primary rolling blooming. The starting rolling temperature is 1033 °C, the final rolling temperature is 945 ± 20 °C, and it is air-cooled after rolling.

[0068] Rolling: The heating temperature of the steel billet is 1178 ± 20 °C, the heating time in the furnace is 2.6 h, the starting rolling temperature is 1142 °C, the final rolling temperature is 968 °C, and it is air-cooled after rolling.

[0069] Table 1 Chemical compositions (wt%) of angle steels in examples and comparative examples

[0070]

[0071]

[0072] As can be seen from Table 1, for the 4 test steels produced by the method of the present invention, their chemical compositions all meet the required ranges described in the present invention. Among them, the ratios of C / N, Ti / V, and Mn / Ni also all meet the requirements of the present invention; the Ti / V ratio in Comparative Example 1 does not meet the requirements of the present invention; the C / N ratio in Comparative Example 2 does not meet the requirements of the present invention; the contents of V and N in Comparative Example 3 do not meet the requirements of the present invention, and the C / N and Ti / V ratios do not meet the requirements of the present invention; the contents of C and Ni and the Mn / Ni ratio in Comparative Example 4 do not meet the requirements of the present invention.

[0073] Samples are taken from each of the examples and comparative examples. The sampling locations are at the 1 / 3 position of the angle steel side and the connection of the two sides. According to the provisions of GB / T 228-2010 "Metallic materials - Tensile testing at ambient temperature", room temperature tensile tests are carried out on a WE-300 hydraulic tensile testing machine, and according to the provisions of GB / T 229-2007 "Metallic materials - Charpy V-notch impact test", low-temperature impact tests are carried out on a JBN-300C impact testing machine to measure the fracture impact absorption work of the test steel at -60 °C. The results are shown in Table 2.

[0074] Table 2 Mechanical properties of angle steels in examples and comparative examples

[0075]

[0076]

[0077] As can be seen from Table 2, for the equal-angle steels of 300×30 mm, 320×26 mm, 320×32 mm, and 360×24 mm rolled from the steels of Examples 1 to 4, the yield strengths are all greater than 550 MPa, the low-temperature impact work at -60 °C is all greater than 60 J, and the differences in cross-sectional yield strengths are all within 20 MPa. However, the yield strengths and the differences in cross-sectional yield strengths of the angle steels rolled from the steels of Comparative Example 1 and Comparative Example 3 cannot meet the requirements, and the low-temperature impact work at -60 °C and the differences in cross-sectional yield strengths of Comparative Example 2 and Comparative Example 4 cannot meet the requirements.

[0078] As described above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any change or replacement that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A high-strength and high-toughness angle steel with uniform cross-sectional performance, characterized in that, In the angle steel, the chemical components are in mass percentage: C: 0.14% - 0.17%, Si: 0.37% - 0.40%, Mn: 1.36% - 1.42%, P ≤ 0.010%, S ≤ 0.010%, Ni: 0.70% - 0.98%, V: 0.07% - 0.18%, Ti: 0.0055% - 0.009%, N: 0.015% - 0.02%, where Mn / Ni ≤ 2.2, and the balance is Fe and unavoidable impurities; The contents of C and N satisfy 7.5 ≤ C / N ≤ 8; The contents of Ti and V satisfy 0.07 ≤ Ti / V ≤ 0.08; The production process of the high-strength and high-toughness angle steel with uniform cross-sectional properties includes the following steps: S1. Electric furnace smelting: Ensure full argon blowing during the tapping process, and transfer to the LF refining furnace after argon blowing; S2. Secondary refining: Add VN16 alloy powder in the middle stage of refining, and blow argon throughout the refining period; S3. Continuous casting: Use long nozzle argon sealing for casting during the continuous casting process, and control the superheat of molten steel as follows: the superheat at the start of casting furnace ≤ 34°C, and the superheat at the continuous casting furnace ≤ 25°C; S4. Blooming; S5. Rolling; In step S1, the tapping temperature ≥ 1620°C, and the argon blowing time > 3 min; In step S2, the refining temperature is 1560 - 1600°C; In step S4, the starting rolling temperature ≤ 1050°C, and the final rolling temperature ≤ 1000°C; In step S5, the heating temperature of the steel billet is 1150 - 1200°C, the starting rolling temperature is 1100°C - 1180°C, and the final rolling temperature is 880 - 980°C; The microstructure of the angle steel is ferrite F and pearlite P, and the volume fraction ratio of ferrite F to pearlite P is 3:1 - 5:1; The width of the side of the angle steel is greater than 300 mm, and the thickness of the side is greater than 20 mm; The high-strength and high-toughness angle steel with uniform cross-sectional properties has a yield strength ≥ 550 Mpa, a tensile strength ≥ 670 MPa, a low-temperature impact energy at -60°C > 60 J, and the difference in cross-sectional yield strength is within 20 MPa.

2. The angle steel according to claim 1, wherein In the angle steel, the chemical components are in mass percentage: C: 0.142% - 0.153%, Si: 0.37% - 0.40%, Mn: 1.36% - 1.42%, P ≤ 0.009%, S ≤ 0.008%, Ni: 0.73% - 0.86%, V: 0.077% - 0.093%, Ti: 0.0055% - 0.0077%, N: 0.0155% - 0.0176%, where 7.5 ≤ C / N ≤ 8, 0.07 ≤ Ti / V ≤ 0.08, Mn / Ni ≤ 2.0, and the balance is Fe and unavoidable impurities.

3. The angle steel according to claim 1, characterized in that The chemical components of the angle steel are as follows by mass percentage: C: 0.160% - 0.168%, Si: 0.37% - 0.40%, Mn: 1.36% - 1.42%, P ≤ 0.008%, S ≤ 0.007%, Ni: 0.92% - 0.98%, V: 0.107% - 0.135%, Ti: 0.0081% - 0.009%, N: 0.0182% - 0.02%, where 7.5 ≤ C / N ≤ 8, 0.07 ≤ Ti / V ≤ 0.08, Mn / Ni ≤ 1.8, and the balance is Fe and inevitable impurities.

4. The angle steel according to claim 1, characterized in that, The volume fraction ratio of ferrite F to pearlite P in the microstructure of the angle steel is 4.4∶1.

5. A production process of a high-strength and high-toughness angle steel with uniform cross-sectional performance, which is used to prepare the angle steel described in any one of claims 1-4, characterized in that, It includes the following steps: S1. Electric furnace smelting: Ensure argon blowing throughout the tapping process, and transfer to the LF refining furnace after argon blowing. S2. Secondary refining: Add VN16 alloy powder in the middle stage of refining, and blow argon throughout the refining period. S3. Continuous casting: Use a long nozzle with argon sealing for protective casting during continuous casting, and control the superheat of the molten steel as follows: the superheat at the start of casting ≤ 34°C, and the superheat during continuous casting ≤ 25°C. S4. Blooming. S5. Rolling.

6. The production process of the angle steel according to claim 5, characterized in that, In the step S1, the tapping temperature is 1620 - 1640°C, and the argon blowing time > 3 min.

7. The production process of the angle steel according to claim 6, characterized in that, In the step S2, the refining temperature is 1575 - 1585°C.

8. The production process of the angle steel according to claim 7, characterized in that, In the step S4, the starting rolling temperature ≤ 1033°C, and the final rolling temperature is 925 - 965°C. In the step S5, the heating temperature of the steel billet is 1158 - 1198°C, the starting rolling temperature is 1100°C - 1142°C, and the final rolling temperature is 880 - 968°C.

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