A low-cost 420mpa grade h-beam steel and a method of manufacturing the same

Abstract

The application relates to a low-cost 420MPa H-shaped steel and a preparation method thereof, and belongs to the technical field of H-shaped steel micro-alloying, and aims to solve the problem of high production cost of the existing high-strength H-shaped steel. The low-cost 420MPa H-shaped steel has the following chemical components in percentage by weight: C 0.10-0.20%, Si 0.20-0.40%, Mn 1.20-1.60%, V 0.03-0.10%, N 0.005-0.05%, P <=0.01%, S <=0.01%, and V / N>4; and the balance is Fe and inevitable impurities. The H-shaped steel prepared by the application has the following properties: yield strength >=420MPa, tensile strength >=550MPa, elongation >=25%, and impact energy >=150J; the H-shaped steel has good mechanical property stability and plasticity and toughness, and the preparation cost is low.

Description

Technical Field

[0001] This invention relates to the field of H-beam microalloying technology, and in particular to a low-cost 420MPa grade H-beam and its preparation method. Background Technology

[0002] Steel structure buildings have lower carbon emissions than concrete structure buildings, and using hot-rolled H-beams and angle steel to replace traditional concrete T-beams will be an important way to achieve dual carbon targets.

[0003] Hot-rolled H-beams have optimized cross-sectional dimensions. Compared with I-beams, they have a larger section modulus, which can save 10-15% of metal consumption under the same load conditions. They also have excellent mechanical properties and superior performance. Therefore, hot-rolled H-beams are widely used in large buildings, large bridges, offshore platforms, and other applications, and have promising prospects.

[0004] In terms of the types of steel used in steel structures, Q235 and Q355 account for more than 80% of the steel used in my country's steel structures, while Q390 and Q420 account for less than 10%. The development of high-strength steel grades above Q390 has been slow in recent years. One of the main reasons for this is the high cost of high-strength steel grades used in steel structures. Therefore, how to reduce the production cost while ensuring that hot-rolled H-beams meet the performance requirements has become one of the urgent problems for steel companies to solve. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a low-cost 420MPa grade H-beam and its preparation method to solve the problem of high production cost of existing high-strength H-beams.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] A low-cost 420MPa grade H-beam has the following chemical composition by weight percentage: C 0.10-0.20%, Si 0.20-0.40%, Mn 1.20-1.60%, V 0.03-0.10%, N 0.005-0.05%, P≤0.01%, S≤0.01%, V / N>4; the balance being Fe and unavoidable impurities.

[0008] Furthermore, the microstructure of the H-beam is ferrite and pearlite, wherein the volume fraction of ferrite is 77.2-81.6% and the volume fraction of pearlite is 22.8-18.4%.

[0009] Furthermore, the average grain size of the ferrite is <25μm.

[0010] A low-cost method for preparing 420MPa grade H-beams, comprising the following steps:

[0011] S1: Converter smelting, the proportion of raw materials is determined according to the content of each component in the composition ratio, the raw materials are smelted in the converter, and deoxidation treatment is carried out using manganese-aluminum alloy during the steel tapping process;

[0012] S2: LF refining, LF furnace for white slag desulfurization and refining of molten steel;

[0013] S3: Continuous casting, using a special-shaped billet continuous casting machine for continuous casting, adopting protective or semi-protective casting, superheat ≤25℃, using a weak cooling regime and constant casting speed operation to obtain continuously cast billets;

[0014] S4: Stacking and slow cooling. After the continuous casting billet is cut, it is promptly removed from the production line and stacked for slow cooling. The slow cooling time is >48 hours.

[0015] S5: Semi-continuous rolling, which involves heating the continuously cast billet and then performing semi-continuous rolling on it. Semi-continuous rolling includes two stages: roughing and finishing rolling, to obtain the rolled billet.

[0016] S6: Slow cooling on a cooling bed. The billet is slowly cooled on a cooling bed. The temperature of the cooling track is ≥400℃. After the temperature of the billet drops to 200~300℃, it is straightened by a straightening machine.

[0017] S7: Fine finishing, the straightened steel billet is finely finished to obtain the low-cost 420MPa grade H-beam.

[0018] Furthermore, in step S2, manganese ferronitride and ferrovanadium are added sequentially during the LF refining process, with an interval of 5 to 20 minutes between the addition of the two additives, and argon is gently blown for 10 to 25 minutes after the alloy is added.

[0019] Furthermore, the weak cooling process is as follows: before entering the straightening machine, the target temperature of the web of the billet is ≥900℃, and the target temperature of the flange of the billet is ≥800℃.

[0020] Furthermore, in step S3, the constant pulling speed is 0.6 m / min to 1.0 m / min.

[0021] Furthermore, in step S5, the heating temperature is 1200℃~1250℃, and the rolling speed is 0.5~1m / sec.

[0022] Furthermore, in step S5, the roughing is a continuous rolling process without temperature measurement, and the roughing is divided into no less than 3 passes. The initial rolling temperature is 1120-1160℃, the total reduction is 50%-60%, and the reduction per pass is 17%-25%.

[0023] Furthermore, in step S5, the finishing rolling is a discontinuous rolling process, the finishing rolling is no less than 3 passes, the total reduction is 35% to 40%, the single pass reduction is 10% to 15%, and the final rolling temperature is 800℃ to 850℃.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0025] 1. This invention saves costs and simplifies the process of steel composition control by adding only a small amount of V, Mn, and N, without adding other expensive alloying elements. Compared with the traditional production process that requires the addition of a large amount of expensive microalloying elements such as Ni, Cr, and Nb, it reduces production costs, simplifies the production process, and is suitable for industrial production applications.

[0026] 2. This invention optimizes the continuous casting and rolling processes, thereby achieving mechanical properties that meet the requirements of the standard with the addition of a small amount of alloying elements. It enables low-cost production of 420MPa grade hot-rolled H-beams. Furthermore, the rolling processes used in this invention have low equipment requirements and are suitable for widespread use by enterprises.

[0027] 3. The H-beams prepared by this invention have a yield strength ≥420MPa, tensile strength ≥550MPa, elongation ≥25%, and impact energy ≥150J; they possess good mechanical property stability and ductility, and the product quality is stable and exceeds the national standard requirements of GB / T 1591-2018 for low alloy high strength structural steel, while also having a lower cost.

[0028] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0029] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0030] Figure 1 The image shows the microstructure of the 420MPa grade H-beam steel sample in Example 1.

[0031] Figure 2 The image shows the microstructure of the 420MPa grade H-beam steel sample in Example 2.

[0032] Figure 3 The image shows the microstructure of the 420MPa grade H-beam steel sample in Example 3.

[0033] Figure 4 The image shows the microstructure of the H-beam sample from Comparative Example 1.

[0034] Figure 5 The image shows the microstructure of the H-beam steel sample from Comparative Example 2. Detailed Implementation

[0035] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form 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 intended to limit the scope of the present invention.

[0036] This invention provides a low-cost 420MPa grade H-beam steel with the following chemical composition by weight percentage: C 0.10-0.20%, Si 0.20-0.40%, Mn 1.20-1.60%, V 0.03-0.10%, N 0.005-0.05%, P≤0.01%, S≤0.01%, V / N>4; the balance being Fe and unavoidable impurities.

[0037] The rationale for limiting the composition of the low-cost 420MPa grade H-beam and its preparation method in this invention will be explained below. Hereinafter, only the mass percentage of the composition will be expressed as %.

[0038] C: In steel, C improves the steel’s properties by forming solid solution structures and carbides. Increasing the C content can enhance the steel’s strength, hardness, and wear resistance, but excessive C content can also seriously deteriorate the steel’s plasticity and toughness. Therefore, in this invention, the C content is controlled at 0.10 to 0.20% to ensure that the steel has good plasticity and toughness while maintaining its strength.

[0039] Si is a commonly used deoxidizer in steelmaking. It is usually dissolved in ferrite and austenite in steel and has a strong solid solution strengthening effect, which has a significant effect on improving the strength of steel. However, if the Si content is too high, it will seriously deteriorate the plasticity and toughness of steel, increase the cold brittleness of steel, and affect the safety performance of steel. Excessive Si content will also deteriorate the weldability of steel. Therefore, in this invention, the Si content is controlled at 0.20% to 0.40%.

[0040] Mn is a commonly used deoxidizer and desulfurizer in steel. Mn reacts with sulfur in steel to form MnS, which has a higher melting point. This can prevent the formation of FeS and thus prevent hot brittleness, thereby improving the hot working properties of steel. Mn is 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, thereby eliminating sulfur that is harmful to the properties of steel. However, if the Mn content is too high, it will significantly increase the carbon equivalent and impair the plasticity and toughness of the steel. Therefore, the Mn content in this invention is controlled at 1.20% to 1.60%.

[0041] V: V combines with C and N elements in steel to form 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. At the same time, V is relatively expensive. Taking all factors into consideration, the V content in this invention is controlled at 0.03% to 0.10%.

[0042] Nitrogen (N): Normally, nitrogen (N) in steel is a harmful element that causes aging embrittlement. Therefore, in traditional steelmaking, vacuum degassing and refining processes are used to remove N from steel. However, by adding vitamin C (V), it can be transformed into a beneficial element. Adding N to V-containing steel can significantly refine ferrite grains by refining the original austenite grains and promoting V precipitation, thereby increasing the nucleation density and nucleation sites of ferrite after phase transformation. When the N content is low, most of the V added to the steel exists in solid solution form and cannot fully exert the precipitation strengthening effect of V. Adding an appropriate amount of N can promote the precipitation strengthening effect of V in the steel by forming VN precipitates, thereby effectively improving the strength and ductility of the steel. At the same time, since the precipitation strengthening effect of N on V can reduce the addition of V while ensuring the mechanical properties of the steel, it can effectively reduce costs. In this invention, N and V elements work synergistically to form VN precipitates to improve the strength and ductility of the steel. Taking all factors into consideration, the N content in this invention is controlled at 0.005% to 0.05%.

[0043] In this invention, V / N > 4 to ensure that V can completely bind to free N elements.

[0044] P: A harmful element that is detrimental to the plasticity and toughness of steel and should be avoided as much as possible. Therefore, the content of P in this invention is ≤0.01%.

[0045] S: A harmful element that forms sulfide inclusions, thereby impairing the performance of steel. It should be avoided as much as possible. Therefore, the content of S in this invention is ≤0.01%.

[0046] Preferably, the present invention provides a low-cost 420MPa grade H-beam steel, the chemical composition of which, by weight percentage, is: C 0.14-0.19%, Si 0.32-0.34%, Mn 1.35-1.58%, V 0.061-0.084%, N 0.0088-0.02%, P≤0.01%, S≤0.01%, V / N>4; the balance being Fe and unavoidable impurities.

[0047] This invention also provides a method for preparing low-cost 420MPa grade H-beams, comprising the following steps:

[0048] S1: Converter smelting, the proportion of raw materials is determined according to the content of each component in the composition ratio, the raw materials are smelted in the converter, and deoxidation treatment is carried out using manganese-aluminum alloy during the steel tapping process;

[0049] S2: LF refining, LF furnace for white slag desulfurization and refining of molten steel;

[0050] S3: Continuous casting, using a special-shaped billet continuous casting machine for continuous casting, adopting protective or semi-protective casting, superheat ≤25℃, using a weak cooling regime and constant casting speed operation to obtain continuously cast billets;

[0051] S4: Stacking and slow cooling. After the continuous casting billet is cut, it is promptly removed from the production line and stacked for slow cooling. The slow cooling time is >48 hours.

[0052] S5: Semi-continuous rolling, which involves heating the continuously cast billet and then performing semi-continuous rolling on it. Semi-continuous rolling includes two stages: roughing and finishing rolling, to obtain the rolled billet.

[0053] S6: Slow cooling on a cooling bed. The billet is slowly cooled on a cooling bed. The temperature of the cooling track is ≥400℃. After the temperature of the billet drops to 200~300℃, it is straightened by a straightening machine.

[0054] S7: Fine finishing, the straightened steel billet is finely finished to obtain the low-cost 420MPa grade H-beam.

[0055] Specifically, in step S1, the proportion of raw materials is determined according to the content of each component in the composition ratio. The raw materials are then smelted in a converter, followed by slag removal and tapping to obtain molten steel. During the tapping process, manganese-aluminum alloy is used for deoxidation treatment, ferrosilicon is added, and top slag is added for slag washing. The entire smelting process uses a top-bottom blowing method. Because nitrogen is chemically inert, it has less corrosive effect on the converter and is less costly. At the same time, nitrogen can dissolve in trace amounts in molten steel, increasing the N content and providing alloying elements for the subsequent VN microalloying of this invention. Therefore, nitrogen is used as the bottom blowing gas. To ensure the N content in the molten steel, vacuum degassing is not performed after tapping from the converter.

[0056] Specifically, in step S2, the steel liquid is desulfurized and refined using white slag produced in an LF furnace. To ensure more complete desulfurization, the desulfurization time is >15 min, and the S content in the molten steel is controlled to be ≤0.006%. Ferromanganese nitride and ferrovanadium are added sequentially, with an interval of 5–20 min between the two additives. After the alloy is added, soft argon blowing is performed for 10–25 min. It should be noted that after increasing the N content in the steel through bottom blowing nitrogen in step S1, ferromanganese nitride is used as an additive for N and Mn, and ferrovanadium is used as an additive for V. Ferromanganese nitride has a high content of main elements, low content of harmful impurities such as P, relatively high N utilization rate after being added to the melt, and requires a small amount.

[0057] Specifically, in step S3, a direct-reading spectrometer is used for compositional analysis during continuous casting to ensure that the composition of the cast billet is within the range specified in this invention. Continuous casting is performed using a shaped billet continuous casting machine, employing protective or semi-protective casting with a superheat of ≤25℃; a weak cooling regime is used, with the target temperature of the billet web ≥900℃ and the target temperature of the billet flange ≥800℃ before entering the straightening machine; a constant casting speed of 0.6m / min~1.0m / min is used to obtain the continuously cast billet.

[0058] Specifically, in step S5, the continuously cast billet is heated to a temperature of 1200℃~1250℃ and held for ≥60min. After the continuously cast billet is taken out of the furnace, it is subjected to semi-continuous rolling, which includes two stages: rough rolling and finish rolling, with a rolling speed of 0.5~1m / sec.

[0059] The roughing process consists of no fewer than three passes. The initial rolling temperature is 1120-1160℃, with a total reduction of 50%-60% and a single pass reduction of 17%-25%. During the multi-pass roughing process, temperature is not measured and the rolling is continuous. Temperature is measured after the roughing process is completed, and the finishing rolling begins when the temperature drops to 900-980℃. The finishing rolling is a non-continuous process with no fewer than three passes. The total reduction is 35%-40%, and the single pass reduction is 10%-15%. The final rolling temperature is 800℃-850℃ to ensure the mechanical properties of the billet.

[0060] Specifically, in step S6, the billet is cooled slowly and centrally on a cooling bed, with the cooling track temperature ≥400℃, to prevent the cooling rate from being too fast and affecting the final properties of the steel; after the billet temperature drops to 200-300℃, it is promptly sent to a straightening machine for straightening.

[0061] This invention ensures excellent comprehensive mechanical properties of the material through a rational design of V and N alloying elements. It improves the material's strength through precipitation strengthening and grain refinement. A certain amount of undissolved V(C,N) particles pins to the austenite grain boundaries, preventing further austenite grain growth and thus refining the grains. Simultaneously, the dispersed V(C,N) particles after air cooling after rolling exert a strong precipitation strengthening effect, thereby improving the steel's strength. Setting the final rolling temperature to 800℃~850℃ effectively promotes the refinement of precipitated V(C,N) particles, resulting in even better precipitation strengthening. This invention, through rational composition and rolling process design, effectively improves the strength and toughness of the steel.

[0062] The microstructure of the steel prepared by the above method consists of ferrite and pearlite, with a ferrite volume fraction of 77.2-81.6% and a pearlite volume fraction of 22.8-18.4%. The average ferrite grain size is <25μm. Ferrite possesses good plasticity and toughness, but its strength and hardness are relatively low. Compared with ferrite, pearlite has significantly improved strength and hardness, but its plasticity and toughness are significantly reduced. The steel of this invention uses ferrite as the matrix, ensuring that the material has good plasticity and toughness. At the same time, through the grain-refining effect of V (C, N), the ferrite grains are refined, thereby improving its strength. In this invention, pearlite is uniformly distributed in the ferrite matrix, which improves the strength and hardness of the material while ensuring good plasticity and toughness.

[0063] The H-beams prepared by this invention have a yield strength ≥420 MPa (e.g., 456–461 MPa), tensile strength ≥550 MPa (e.g., 586–601 MPa), elongation ≥25% (e.g., 27.0–28.7%), and impact energy ≥150 J (e.g., 151–167 J). They possess good mechanical property stability and ductility, and the product quality is stable and exceeds the national standard requirements of GB / T 1591-2018 for low-alloy high-strength structural steel, while also having a lower cost.

[0064] Example 1

[0065] The H-beam of this embodiment comprises, by weight percentage: C 0.14%, Si 0.32%, Mn 1.35%, V 0.061%, N 0.0088%, P≤0.01%, S≤0.006%, V / N=6.9, with the balance being Fe and unavoidable impurities.

[0066] The H-beams of this embodiment are prepared through the following steps:

[0067] S1: Converter smelting, the proportion of raw materials is determined according to the content of each component in the composition ratio, the raw materials are smelted in the converter, and after the raw materials are smelted in the converter, the slag is blocked and the steel is tapped to obtain molten steel;

[0068] During the tapping process, manganese-aluminum alloy (Mn 30wt%) is used for deoxidation treatment, ferrosilicon (Si 70wt%) is added, and top slag is added for slag washing. No vacuum degassing treatment is performed after tapping from the converter.

[0069] S2: LF refining, LF furnace for white slag desulfurization and refining of molten steel;

[0070] To achieve more complete desulfurization, the desulfurization time was 20 minutes, and the S content in the molten steel was controlled to be ≤0.006%. Ferromanganese nitride (Mn 75wt%) and ferrovanadium (V 50wt%) were added in sequence, with a 15-minute interval between the addition of the two additives. After the alloy was added, argon was blown softly for 20 minutes.

[0071] The LF refining station outlet temperature is 1615℃, and the calcium-aluminum wire is 217m.

[0072] S3: Continuous casting, using a special-shaped billet continuous casting machine for continuous casting, adopting protective or semi-protective casting, superheat ≤25℃, using a weak cooling regime and constant casting speed operation to obtain continuously cast billets;

[0073] The superheat was 17℃, a weak cooling regime was adopted, and before entering the straightening machine, the target temperature of the billet web was measured to be 931℃ and the target temperature of the billet flange was measured to be 856℃. A constant drawing speed of 0.8m / min was adopted.

[0074] S4: Stacking and slow cooling. After the continuous casting billet is cut, it is promptly taken off the production line and stacked for slow cooling. The slow cooling time is 61 hours.

[0075] S5: Semi-continuous rolling, which involves heating the continuously cast billet and then performing semi-continuous rolling on it. Semi-continuous rolling includes two stages: roughing and finishing rolling, to obtain the rolled billet.

[0076] The continuous casting billet is heated to 1220℃, held for 70 minutes, and rolled immediately after being taken out of the furnace.

[0077] The rolling speed is 0.8 m / sec;

[0078] The roughing process consists of four passes. The initial rolling temperature is 1141℃, with a total reduction of 55% and a single pass reduction of 18%. The four passes of roughing are continuous without temperature measurement. Temperature measurement is performed after the roughing process is completed, and finishing rolling begins when the temperature drops to 953℃. The finishing process is discontinuous, consisting of four passes with a total reduction of 38% and a single pass reduction of 14%. The final rolling temperature is 832℃.

[0079] S6: Slow cooling on a cooling bed. The billet is slowly cooled on a cooling bed. The temperature of the cooling track is 432℃. After the billet temperature drops to 267℃, it is straightened by a straightening machine.

[0080] S7: Fine finishing, the straightened steel billet is finely finished to obtain a low-cost 420MPa grade H-beam with a specification of 300mm×300mm, a spoke thickness of 28mm, and a flange thickness of 30mm.

[0081] Example 2

[0082] The H-beam of this embodiment comprises, by weight percentage: C 0.17%, Si 0.34%, Mn 1.58%, V 0.071%, N 0.012%, P≤0.01%, S≤0.006%, V / N=5.9, with the balance being Fe and unavoidable impurities.

[0083] The H-beams of this embodiment are prepared through the following steps:

[0084] S1: Converter smelting, the proportion of raw materials is determined according to the content of each component in the composition ratio, the raw materials are smelted in the converter, and after the raw materials are smelted in the converter, the slag is blocked and the steel is tapped to obtain molten steel;

[0085] During the tapping process, manganese-aluminum alloy (Mn 30wt%) is used for deoxidation treatment, ferrosilicon (Si 70wt%) is added, and top slag is added for slag washing. No vacuum degassing treatment is performed after tapping from the converter.

[0086] S2: LF refining, LF furnace for white slag desulfurization and refining of molten steel;

[0087] To achieve more complete desulfurization, the desulfurization time should be >25 min and the S content in the molten steel should be controlled to ≤0.006%.

[0088] Add manganese nitride ferronitride (Mn 75 wt%) and ferrovanadium (V 50 wt%) in sequence, with an 18-minute interval between the addition of the two additives. After adding the alloy, gently blow argon for 20 minutes.

[0089] The LF refining station outlet temperature is 1607℃, and the calcium-aluminum wire is 226m long.

[0090] S3: Continuous casting, using a special-shaped billet continuous casting machine for continuous casting, adopting protective or semi-protective casting, superheat ≤25℃, using a weak cooling regime and constant casting speed operation to obtain continuously cast billets;

[0091] The superheat was 20℃, a weak cooling regime was adopted, and before entering the straightening machine, the target temperature of the billet web was measured to be 917℃ and the target temperature of the billet flange was measured to be 842℃. A constant drawing speed of 0.7m / min was adopted.

[0092] S4: Stacking and slow cooling. After the continuous casting billet is cut, it is promptly removed from the production line and stacked for slow cooling. The slow cooling time is 57 hours.

[0093] S5: Semi-continuous rolling, which involves heating the continuously cast billet and then performing semi-continuous rolling on it. Semi-continuous rolling includes two stages: roughing and finishing rolling, to obtain the rolled billet.

[0094] The continuous casting billet is heated to 1230℃, held for 65 minutes, and rolled immediately after being taken out of the furnace.

[0095] The rolling speed is 0.9 m / sec;

[0096] The roughing process consists of four passes. The initial rolling temperature is 1143℃, with a total reduction of 57% and a single pass reduction of 21%. The four passes of roughing are continuous without temperature measurement. Temperature measurement is performed after the roughing process is completed, and finishing rolling begins when the temperature drops to 962℃. The finishing process is discontinuous, consisting of four passes with a total reduction of 36% and a single pass reduction of 11%. The final rolling temperature is 845℃.

[0097] S6: Slow cooling on the cooling bed. The billet is slowly cooled on the cooling bed. The temperature of the cooling track is 451℃. After the temperature of the billet drops to 281℃, it is straightened by the straightening machine.

[0098] S7: Fine finishing, the straightened steel billet is finely finished to obtain a low-cost 420MPa grade H-beam with a specification of 300mm×300mm, a spoke thickness of 31mm, and a flange thickness of 32mm.

[0099] Example 3

[0100] The H-beam of this embodiment comprises, by weight percentage: C 0.19%, Si 0.33%, Mn 1.46%, V 0.084%, N 0.02%, P≤0.01%, S≤0.006%, V / N=4.2, with the balance being Fe and unavoidable impurities.

[0101] The H-beams of this embodiment are prepared through the following steps:

[0102] S1: Converter smelting, the proportion of raw materials is determined according to the content of each component in the composition ratio, the raw materials are smelted in the converter, and after the raw materials are smelted in the converter, the slag is blocked and the steel is tapped to obtain molten steel;

[0103] During the tapping process, manganese-aluminum alloy (Mn 30wt%) is used for deoxidation treatment, ferrosilicon (Si 70wt%) is added, and top slag is added for slag washing. No vacuum degassing treatment is performed after tapping from the converter.

[0104] S2: LF refining, LF furnace for white slag desulfurization and refining of molten steel;

[0105] To achieve more complete desulfurization, the desulfurization time should be >25 min and the S content in the molten steel should be controlled to ≤0.006%.

[0106] Add manganese nitride ferronitride (Mn 75 wt%) and ferrovanadium (V 50 wt%) in sequence, with a 10-minute interval between the addition of the two additives. After adding the alloy, gently blow argon for 18 minutes.

[0107] The LF refining station outlet temperature is 1610℃, and the calcium-aluminum wire is 220m long;

[0108] S3: Continuous casting, using a special-shaped billet continuous casting machine for continuous casting, adopting protective or semi-protective casting, superheat ≤25℃, using a weak cooling regime and constant casting speed operation to obtain continuously cast billets;

[0109] The superheat was 18℃, a weak cooling regime was adopted, and before entering the straightening machine, the target temperature of the billet web was measured to be 925℃ and the target temperature of the billet flange was measured to be 858℃. A constant drawing speed of 1.0m / min was adopted.

[0110] S4: Stacking and slow cooling. After the continuous casting billet is cut, it is promptly removed from the production line and stacked for slow cooling. The slow cooling time is 66 hours.

[0111] S5: Semi-continuous rolling, which involves heating the continuously cast billet and then performing semi-continuous rolling on it. Semi-continuous rolling includes two stages: roughing and finishing rolling, to obtain the rolled billet.

[0112] The continuous casting billet is heated to 1250℃, held for 80 minutes, and rolled immediately after being taken out of the furnace.

[0113] The rolling speed is 1.0 m / sec;

[0114] The roughing process consists of four passes. The initial rolling temperature is 1156℃, with a total reduction of 58% and a single pass reduction of 20%. The four passes of roughing are continuous without temperature measurement. Temperature measurement is performed after the roughing process is completed, and finishing rolling begins when the temperature drops to 956℃. The finishing process is discontinuous, consisting of four passes with a total reduction of 40% and a single pass reduction of 15%. The final rolling temperature is 836℃.

[0115] S6: Slow cooling on the cooling bed. The billet is slowly cooled on the cooling bed. The temperature of the cooling track is 460℃. After the temperature of the billet drops to 276℃, it is straightened by the straightening machine.

[0116] S7: Fine finishing, the straightened steel billet is finely finished to obtain a low-cost 420MPa grade H-beam with a specification of 300mm×300mm, a spoke thickness of 29mm, and a flange thickness of 31mm.

[0117] Comparative Example 1

[0118] The H-beams in this comparative example have the following composition by weight percentage: C 0.18%, Si 0.31%, Mn 1.50%, V 0.16%, N 0.009%, P≤0.01%, S≤0.006%, V / N=17.7, with the balance being Fe and unavoidable impurities.

[0119] The preparation method and process parameters of the H-beams in this comparative example are the same as those in Example 1.

[0120] Comparative Example 2

[0121] The H-beams in this comparative example have the same composition as those in Example 1.

[0122] The preparation method of this comparative example includes the following steps:

[0123] S1: Converter smelting, the proportion of raw materials is determined according to the content of each component in the composition ratio, the raw materials are smelted in the converter, and after the raw materials are smelted in the converter, the slag is blocked and the steel is tapped to obtain molten steel;

[0124] During the tapping process, manganese-aluminum alloy (Mn 30wt%) is used for deoxidation treatment, ferrosilicon (Si 70wt%) is added, and top slag is added for slag washing. No vacuum degassing treatment is performed after tapping from the converter.

[0125] S2: LF refining, LF furnace for white slag desulfurization and refining of molten steel;

[0126] To achieve more complete desulfurization, the desulfurization time was 20 minutes, and the S content in the molten steel was controlled to be ≤0.006%. Ferromanganese nitride (Mn 75wt%) and ferrovanadium (V 50wt%) were added in sequence, with a 15-minute interval between the addition of the two additives. After the alloy was added, argon was blown softly for 20 minutes.

[0127] S3: Continuous casting, using a special-shaped billet continuous casting machine for continuous casting, adopting protective or semi-protective casting, superheat ≤25℃, using a weak cooling regime and constant casting speed operation to obtain continuously cast billets;

[0128] The superheat was 17℃, a weak cooling regime was adopted, and before entering the straightening machine, the target temperature of the billet web was measured to be 921℃ and the target temperature of the billet flange was measured to be 851℃. A constant drawing speed of 0.8m / min was adopted.

[0129] S4: Stacking and slow cooling. After the continuous casting billet is cut, it is promptly removed from the production line and stacked for slow cooling. The slow cooling time is 47 hours.

[0130] S5: Semi-continuous rolling, which involves heating the continuously cast billet and then performing semi-continuous rolling on it. Semi-continuous rolling includes two stages: roughing and finishing rolling, to obtain the rolled billet.

[0131] The continuous casting billet is heated to 1220℃, held for 60 minutes, and rolled immediately after being taken out of the furnace.

[0132] The rolling speed is 1.0 m / sec;

[0133] The roughing process consists of four passes. The initial rolling temperature is 1103℃, with a total reduction of 47% and a single pass reduction of 18%. The four passes of roughing are continuous without temperature measurement. Temperature measurement is performed after the roughing process is completed, and finishing rolling begins when the temperature drops to 907℃. Finishing is a non-continuous rolling process with four passes. The total reduction is 37%, the single pass reduction is 12%, and the final rolling temperature is 803℃.

[0134] S6: Slow cooling on the cooling bed. The billet is slowly cooled on the cooling bed. The temperature of the cooling track is 414℃. After the temperature of the billet drops to 281℃, it is straightened by the straightening machine.

[0135] S7: Fine finishing, the straightened steel billet is finely finished to obtain an H-beam with a specification of 300mm×300mm, a spoke thickness of 30mm, and a flange thickness of 31mm.

[0136] Comparative Example 3

[0137] The H-beams in this comparative example are composed of the following components by weight percentage: C 0.10%, Si 0.35%, Mn 1.50%, P 0.035%, S 0.025%, Cu 0.25%, Cr 0.45%, Ni 0.30%, Nb 0.028%, with the balance being Fe and unavoidable impurities.

[0138] The preparation method of the H-beam in this comparative example includes the following steps:

[0139] Step S1: The molten iron is sent to the desulfurization station. After desulfurization, the sulfur content in the molten iron is guaranteed to be ≤0.020wt%.

[0140] Step S2: Converter smelting: Alloying is carried out using ferrosilicon manganese, medium-carbon ferromanganese, copper granules, nickel plates, medium-carbon ferrochrome, and ferroniobium, with the alloy composition controlled within the middle limit. Copper granules and nickel plates are added with the furnace charge, and the remaining alloys are added in batches when the molten steel reaches one-quarter of its charge and when it reaches three-quarters of its charge. Aluminum manganese ferrooxidizer is added at a rate of 2.5 kg / t.

[0141] Step S3: Continuous casting: The tundish baking temperature is 1100℃, the crystallizer is aligned with the arc, and full-process protective pouring is used. The secondary cooling is weak cooling, the crystallizer uses non-sinusoidal vibration, the tundish uses low-carbon alkaline covering agent, the amount of covering agent added is 1.5kg / t steel, the liquidus temperature is 1517.8℃, the tundish superheat is controlled at 25℃, the billet size is 165mm×200mm, and the casting speed is 1.0m / min.

[0142] Step S4: The heating furnace has a homogenization temperature of 1250℃ and the billet is in the furnace for 160 minutes; the final rolling temperature is 910℃ on the outer flange and the rolled material is naturally cooled on the cooling bed. The specifications of the rolled material are H175×90×5×8.

[0143] Table 1 shows the mechanical properties and cost of the H-beams in the embodiments and comparative examples of the present invention; Table 2 shows the microstructure of the H-beams in the embodiments and comparative examples of the present invention.

[0144] Table 1 Mechanical properties of H-beams in the examples and comparative examples

[0145]

[0146] Table 2 shows the microstructure parameters of the H-beams in the examples and comparative examples.

[0147]

[0148] As shown in Table 1, the embodiments of the present invention have a yield strength of 456-461 MPa, a tensile strength of 586-601 MPa, an elongation of 27.0-28.7%, and an impact energy of 151-167 J; they possess good mechanical property stability, and the product quality is stable and all exceed the national standard requirements of GB / T 1591-2018 for low alloy high strength structural steel.

[0149] As shown in Table 2, the microstructure of the present invention in the hot-rolled state is ferrite + pearlite, wherein the volume fraction of ferrite ranges from 77.2% to 81.6% and the volume fraction of pearlite ranges from 22.8% to 18.4%.

[0150] The V content of Comparative Example 1 exceeds the requirements of this invention. Its grain size is smaller than that of Examples 1-3, and its strength is slightly greater than that of Examples 1-3. However, due to the excessive addition of V, its elongation is only 17.3%, and its impact energy is 127J. While its plasticity and toughness are greatly affected, its strength has not increased significantly. Moreover, the addition of more V elements leads to a rapid increase in cost.

[0151] The rolling temperature of Comparative Example 2 was lower than that of Examples 1-3, and its strength was significantly reduced compared to Examples 1-3. The grain size was significantly larger. The lower final rolling temperature affected the dispersion distribution of V(C,N), which severely affected the grain refinement effect.

[0152] Comparative Example 3, which describes the composition and preparation method of CN105401075A, reveals that this composition contains several expensive alloying elements such as Nb, Ni, and Cr, making it more expensive than the embodiments of this invention. Furthermore, its yield strength is lower than that of this invention.

[0153] Ferrite possesses good plasticity and toughness, but its strength and hardness are relatively low. Compared to ferrite, pearlite has significantly improved strength and hardness, but its plasticity and toughness are significantly reduced. The H-beam of this invention uses ferrite as the matrix, ensuring good plasticity and toughness. Simultaneously, the grain-refining effect of V (C, N) further refines the ferrite grains, thereby improving its strength. In this invention, pearlite is uniformly distributed within the ferrite matrix, enhancing the material's strength and hardness while maintaining good plasticity and toughness.

[0154] This invention ensures excellent comprehensive mechanical properties of the material through a rational design of V and N alloying elements. Precipitation strengthening and grain refinement enhance the material's strength and improve the steel's ductility and toughness. A well-planned production system enables rapid industrial production, ensuring product compliance with national standards while maintaining low costs. This facilitates guidance for industrial production and promotes widespread industrial adoption.

[0155] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-cost method for preparing 420MPa grade H-beams, characterized in that, The low-cost 420MPa grade H-shaped steel has chemical components in weight percentage as follows: C 0.10~0.20%, Si 0.20~0.34%, Mn 1.35~1.46%, V 0.03~0.084%, N 0.005~0.0088%, P≤0.01%, S≤0.006%, 4<V / N<5.9; the balance is Fe and unavoidable impurities; The preparation method comprises the following steps: S1: converter smelting: determining the ratio of raw materials according to the content of each component in the component ratio, carrying out converter smelting on the raw materials, and performing deoxidation treatment with manganese-aluminum alloy during the tapping process; top-bottom combined blowing is adopted throughout the smelting process, and nitrogen is used as the bottom blowing gas; S2: LF refining: LF furnace makes white slag to desulfurize and refine molten steel; the desulfurization time is > 15min, and S in molten steel is controlled to be ≤ 0.006%; S3: continuous casting: carrying out continuous casting with a beam blank caster, adopting protective or semi-protective pouring, controlling superheat degree ≤ 25°C, and adopting a weak cooling system and constant pulling speed operation to obtain a continuous casting billet; S4: stacking slow cooling: after cutting, the continuous casting billet is discharged from the production line in time for stacking slow cooling, and the slow cooling time is > 48h; S5: semi-continuous rolling: heating the continuous casting billet, and performing semi-continuous rolling on the continuous casting billet, wherein the semi-continuous rolling comprises two stages of rough rolling and finish rolling to obtain a rolled billet; S6: slow cooling on cooling bed: performing slow cooling on the rolled billet on a cooling bed, the temperature of the cooling rail is ≥ 400°C, and when the temperature of the rolled billet drops to 200~300°C, the rolled billet enters a straightener for straightening; S7: finishing: performing finishing treatment on the straightened billet to obtain the low-cost 420MPa grade H-shaped steel; In step S2, two additives, namely nitrided ferromanganese and ferrovanadium, are added successively in the LF refining process, the interval between the addition of the two additives is 5~20min, and soft argon blowing is performed for 10~25 min after the alloy is added; In step S3, the weak cooling system is: before entering the withdrawal and straightening machine, the target temperature of the casting billet web is ≥ 900°C, and the target temperature of the casting billet flange is ≥ 800°C; In step S3, the constant pulling speed is 0.6 m / min ~0.8 m / min; In step S5, the heating temperature is 1200°C ~ 1250°C, and the rolling speed is 0.5~1m / sec; In step S5, the rough rolling is continuous rolling without temperature measurement, the rough rolling is divided into no less than 3 passes, the rough rolling starting temperature is 1120~1160°C, the total reduction is 50%~60%, and the reduction per single pass is 17%~25%; In step S5, the finish rolling is discontinuous rolling, the finish rolling is no less than 3 passes, the total reduction is 35%~40%, the reduction per single pass is 10%~15%, and the finishing temperature is 800°C ~ 850°C.

2. A low-cost 420MPa grade H-beam, characterized in that, Prepared by the preparation method according to claim 1, the chemical compositions in terms of weight percentage are: C 0.10~0.20%, Si 0.20~0.34%, Mn 1.35~1.46%, V 0.03~0.084%, N 0.005~0.0088%, P≤0.01%, S≤0.006%, 4<V / N<5.9; the balance is Fe and unavoidable impurities, and the microstructure of the H-shaped steel is ferrite and pearlite.

3. The 420MPa grade H-beam according to claim 2, characterized in that, Wherein the volume fraction of ferrite is 77.2-81.6%, and the volume fraction of pearlite is 22.8-18.4%.

4. The 420MPa grade H-beam according to claim 2, characterized in that, The average grain size of the ferrite is <25μm.

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