Low-temperature-resistant hot-rolled h-beam and manufacturing method therefor

Abstract

A low-temperature-resistant hot-rolled H-beam and a manufacturing method therefor. Said H-beam comprises the chemical components in percentage by weight: C: 0.10-0.13; Si≤0.25; Mn: 0.8-1.0; V: 0.07-0.11; P≤0.01; S≤0.005; Nb: 0.005-0.015; Al: 0.008-0.015; N: 0.08-0.012; O≤0.003; and RE: 0.008-0.015, wherein As+Sn+Zn+Ca+Mg+S≤0.03, and the balance is Fe and inevitable impurities. By means of online structure control and microalloying process design, in view of the characteristics of reciprocating rolling for H-beams, industrial production for large-sized high-strength and high-toughness H-beam products is achieved, and the requirements of transverse impact toughness are met.

Description

A low-temperature resistant hot-rolled H-shaped steel and its preparation method

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 2024101256682, filed on January 30, 2024, entitled “A low-temperature resistant hot-rolled H-beam and its preparation method”, which is hereby incorporated by reference. Technical Field

[0003] The present invention relates to the technical field of smelting and rolling of building structural steel, and in particular to a low-temperature resistant hot-rolled H-shaped steel and a preparation method thereof. Background Art

[0004] Oil and natural gas resources are abundant and offer significant development potential. With the establishment of the Polar Silk Road, polar ocean oil reserves are increasingly being recognized by various countries. Marine equipment, such as floating vessels, and offshore oil platforms, are expanding into more complex deep-sea and polar regions, placing increasingly stringent demands on equipment construction quality. Consequently, demand for hot-rolled H-beams used in marine equipment and engineering projects is increasing, while also placing higher demands on comprehensive performance in low-temperature environments. Currently, impact toughness requirements for hot-rolled H-beams used worldwide are primarily along the rolling direction. Due to the complex shape and microstructure of H-beams, and the significant microstructure variations along the transverse direction of the flange, specific requirements for transverse impact resistance are generally not specified. However, with the increasing quality and quantity of projects under complex environmental conditions, platform structures are becoming more complex. While maintaining strength and toughness, higher requirements are being placed on transverse impact toughness. Consequently, some standards and projects are promoting the use of profiles with excellent transverse impact toughness. Due to the complexity of the H-beam cross-section, the production and preparation of H-beams is more difficult by controlling the metal flow and temperature during the rolling process to achieve simultaneous improvement of the transverse and longitudinal impact toughness.

[0005] For medium and large-sized H-beams, special-shaped billets are often used for rolling. In addition, the application of microalloying in the field of H-beam preparation makes it more difficult to ensure the structure. In addition, the presence of manganese sulfide content has a significant impact on transverse impact toughness. Therefore, many factors combined ultimately affect transverse impact toughness. Especially for industrial mass production, stable and uniform control of transverse impact toughness at -40°C is also a huge challenge. The disclosed patent provides corresponding technical ideas based on different preparation conditions to ensure the stability of the transverse impact toughness of steel.

[0006] Patent application CN1421286A discloses a method for rolling niobium-containing H-beams. This method utilizes the principles of metal physical metallurgy to adjust and optimize conventional process conditions. It employs controlled rolling in the recrystallization zone and the non-recrystallization zone, controlling the deformation amount per pass to nucleate ferrite in the deformation zone, resulting in fine ferrite grains. This uniformly refines the metallographic structure and produces H-beams with high strength, high toughness, and good weldability. The resulting H-beams have a tensile strength of 490-610 MPa and a transverse impact energy of 34-98 J at -20°C. This invention imposes stringent control conditions on the deformation temperature and deformation amount, which also increases the load on the rolling mill. Adjusting the reduction in real time is extremely difficult, significantly impacting product performance. Controlling volatility is also extremely difficult, resulting in a significant reduction in product qualification rates.

[0007] Patent CN 103556055B discloses a hot-rolled H-beam for offshore natural gas production platform structures and its production method. This invention provides hot-rolled H-beam for offshore natural gas production platform structures. The composition of the hot-rolled H-beam, calculated by weight, is as follows: C: 0.10-0.17, Si: 0.10-0.40, Mn: 1.00-1.60, P ≤ 0.025, S ≤ 0.015, Nb: 0.02-0.05, Ti ≤ 0.025, with the remainder being iron and unavoidable impurities. The mechanical properties, -20°C transverse and longitudinal impact energy, and surface quality of the hot-rolled H-beam for offshore natural gas production platform structures fully meet the technical requirements for H-beams used in offshore natural gas production platform structures. The invention primarily utilizes a Nb and Ti composite microalloying composition design. Due to the Nb and Ti composite microalloying mechanism, the rolling forces during actual rolling are relatively high, placing high demands on the rolling equipment.

[0008] Patent application CN110938778A relates to a low-temperature-resistant hot-rolled H-beam for marine engineering and its preparation method. The chemical composition of the H-beam, by weight percentage, includes: C: 0.040-0.070; Si: 0.015-0.30; Mn: 1.20-1.50; P ≤ 0.015; S ≤ 0.010; Nb: 0.02-0.040; Ti: 0.008-0.025; Ni: 0.10-0.50, Al: 0.015-0.050; B: 0.0001-0.0008; As+Sn+Cu+Zn≤0.04; N ≤ 0.0040; T.[O] ≤ 0.0015. The remainder is Fe and unavoidable impurities. This invention utilizes composite microalloying for controlled rolling and cooling, enabling the mass production of products with varying shapes and specifications. This approach meets the needs of producing small batches of various steel sections for low-temperature marine engineering projects. However, the project utilizes an ultra-low carbon content design, resulting in high production costs. Consequently, the economic viability of industrial mass production is limited.

[0009] In summary, it is necessary to specially design the smelting and rolling process and heating equipment for H-shaped steel rolled from special-shaped billets, so that it can not only meet the smelting requirements and reduce the rolling load, but also ensure that the microstructure after rolling has high transverse impact toughness under certain low temperature conditions and improves uniformity. Summary of the Invention

[0010] To meet the demands of marine equipment and marine engineering construction in diverse regions and harsh and complex environments, the present invention provides a method for preparing large-scale, low-temperature-resistant, hot-rolled H-steel based on profiled blank rolling, which exhibits excellent comprehensive impact toughness. The technical solutions of the present invention are as follows:

[0011] The present invention provides a large-size, low-temperature-resistant, hot-rolled H-shaped steel with good transverse impact toughness and a preparation method thereof. The chemical composition of the H-shaped steel is as follows by weight: C: 0.10-0.13; Si: ≤0.25; Mn: 0.8-1.0; V: 0.07-0.11; P≤0.01; S≤0.005; Nb: 0.005-0.015; Al: 0.008-0.015; N: 0.08-0.012; O≤0.003; RE: 0.008-0.015; As+Sn+Zn+Ca+Mg+S≤0.03, with the remainder being iron (Fe) and unavoidable impurities. The production process mainly includes converter smelting, LF refining, continuous casting and hot rolling forming, online soaking treatment using a dedicated electromagnetic induction heating device, and online controlled cooling.

[0012] The high-strength, tough, and low-temperature-resistant hot-rolled H-shaped steel has a yield strength of ≥420 MPa, a tensile strength of ≥500 MPa, an elongation of ≥19%, a -50°C transverse impact energy of ≥120 J, and Z-direction performance: a section shrinkage of ≥50%.

[0013] Preferably, the RE comprises lanthanum and / or cerium.

[0014] The design principles of the main chemical elements in the high-strength hot-rolled H-beam of the present invention are as follows:

[0015] Carbon: To meet the mechanical property requirements of large-sized, low-temperature-resistant, hot-rolled H-beams with excellent transverse impact toughness, ultrafine ferrite and lamellar pearlite structures are achieved, with a grain size of 8 or higher. Given the low compression ratio of thick H-beams, excessively high carbon content can easily produce abnormal structures such as widmanstattenite and variant pearlite. To prevent the occurrence of peritectic steel reactions during the smelting process, avoid the peritectic zone, and improve the surface quality of the ingot, while ensuring a yield strength of over 420 MPa, the carbon content is controlled within the range of 0.10-0.13%, based on the comprehensive strength and toughness requirements.

[0016] Manganese: In steel, it increases hardenability, stabilizes austenite, exerts a solid solution strengthening effect, and significantly improves yield strength. Large-size H-beams exhibit varying deformation and structural transformations in different locations. Excessive Mn can easily lead to severe segregation, resulting in significant performance variations. To ensure the strength of marine steel while reducing segregation and improving microstructure uniformity between the center and edges, a Mn content of 0.8-1.0% is recommended.

[0017] Phosphorus: Although high phosphorus content can easily improve corrosion resistance, excessive phosphorus content can easily lead to deterioration of low-temperature resistance at brittle grain boundaries. Therefore, the lower the phosphorus content, the better the effect, which can improve low-temperature toughness. P should be controlled below 0.01%.

[0018] Sulfur: Sulfur reacts with Mn to form MnS inclusions. Excessive sulfur content can easily lead to the formation of more sulfides such as MnS, which can create a large number of long MnS inclusions in different parts of complex cross-section steels. This reduces transverse low-temperature toughness, reduces cross-sectional shrinkage, and indirectly reduces the Z-axis properties of the steel. Therefore, S should be strictly controlled to ≤ 0.005%.

[0019] Aluminum: It improves steel cleanliness and acts as a strong deoxidizing element. It forms a large amount of AlN with nitrogen, which refines the grain size during rolling. This helps keep the oxygen content in the steel low, reducing the likelihood of large oxide inclusions. Furthermore, the AlN precipitates formed by aluminum and nitrogen in the steel refine the grain size, thereby increasing the steel's strength. However, excessive Al content can increase casting difficulty, leading to nozzle buildup and eyelet formation. Therefore, the aluminum content is controlled within a range of 0.008% to 0.015% in this invention.

[0020] Rare earth: RE in steel mainly purifies the steel, deteriorates inclusions, and reduces pitting and intergranular corrosion. In order to control the shape of MnS and avoid the presence of a large number of long strips of MnS inclusions, which affect the uniformity of the transverse structure and thus reduce impact toughness, a certain amount of RE elements are selected to improve the shape of MnS. RE rare earth elements are a composite added element. Considering factors such as economy and cost performance, the present invention mainly uses lanthanum and / or cerium series elements to play the role of spheroidizing inclusions. Considering that too much RE rare earth elements will affect other properties of steel, it is necessary to add an appropriate amount, so the selection range is RE: 0.008~0.015%.

[0021] Vanadium: As a strong carbonitride-forming element, V (C, N) contributes to precipitation strengthening. Furthermore, V (C, N) nanoparticles serve as nucleation sites for ferrite and pearlite, contributing to grain refinement and austenite refinement. Due to the low C content and high N content in the present invention, V precipitation is minimal. Therefore, V primarily exists as VN during rolling and post-rolling cooling, enhancing precipitation strengthening. VN is primarily added to steel via alloying. To achieve a yield strength of 420 MPa for low-temperature-resistant sections, the V content is controlled between 0.07 and 0.11%.

[0022] Nitrogen: A certain concentration of nitrogen in steel combines with vanadium to form VN second-phase particles, which exert a precipitation strengthening effect and significantly improve strength. However, too high a nitrogen content can easily induce surface defects such as transverse cracks and corner cracks on the ingot surface. Low nitrogen content results in fewer VN particles, poor precipitation strengthening, and substandard strength. The present invention requires a nitrogen content of 0.08-0.012%.

[0023] Oxygen: Oxygen easily forms large oxide inclusions with elements such as Al, Mg, and Ca. At the same time, controlling the oxygen content to a lower level will lead to a significant increase in cost. Therefore, in order to ensure that the strength is improved while the transverse impact toughness and plasticity of the steel are improved, the present invention comprehensively considers controlling the oxygen content to ≤0.003%.

[0024] The present invention provides a method for preparing low-temperature resistant hot-rolled H-shaped steel, comprising the following steps:

[0025] 1) smelting;

[0026] 2) Rolling: Electromagnetic heating devices are respectively provided at the entrance and exit of the finishing mill; a cooling system is provided after the electromagnetic heating device at the exit of the finishing mill.

[0027] Preferably, the step 1) includes:

[0028] Hot metal pretreatment: The sulfur content of hot metal entering the furnace should be ≤0.006%, and the arsenic content of hot metal should be less than 60ppm;

[0029] Converter smelting: the final slag basicity is controlled within the range of 2.8-3.8, the slag material is added 3 minutes before the end point, and the final gun pressure time is ≥1 minute until the injection is completed;

[0030] During the tapping process, aluminum-manganese iron is used for deoxidation, with the addition amount of aluminum-manganese iron being 1.2-2.3 kg / t steel. Metallic manganese, low-phosphorus and low-carbon silicon-manganese, vanadium-nitrogen, and ferroniobium are used for alloying. The target composition value is controlled. After tapping, 3-6 kg / t of lime is added. The tapping time is not less than 3 minutes.

[0031] LF refining: Bottom argon blowing and stirring are carried out throughout the refining process, and the refining soft argon blowing lasts for more than 15 minutes. After entering the station, aluminum wire ≥50 meters is fed, and the ladle enters the LF furnace for argon blowing and smelting for 7-12 minutes. Before refining soft argon blowing, high calcium wire 80-100m / furnace is fed for calcification treatment;

[0032] Special-shaped continuous casting billet casting: The continuous casting process uses a casting plug package with a nozzle immersion depth of 60-75mm; the casting superheat is controlled to be less than 25℃, and the continuous casting speed is 0.85-1.0m / min;

[0033] The continuous casting billet is slowly cooled.

[0034] Preferably, the step 2) includes: the soaking temperature of the heating furnace during the rolling process is 1220-1260°C, and the time the billet is in the furnace is 240-360 min; the rough rolling speed is ≥2.5 m / s; the vertical roll reduction rate in the finishing stage is controlled to be not less than 12%, and the reduction rate of the remaining passes is not less than 18%; the finishing rolling start temperature is 930-950°C, and the finishing rolling final temperature is 780-850°C; the compression ratio of the last finishing pass is 8%-12%, and the rolling mill is controlled to be below 1.6 m / s for reduced speed rolling; the yield strength difference between the upper and lower flanges is controlled to be 10-15 MPa.

[0035] Preferably, the electromagnetic heating device includes several heating units arranged in sequence, and the heating unit includes a sub-heating unit symmetrically arranged on the outside of the flange of the H-shaped steel, and the sub-heating unit covers the upper and lower flanges and at least part of the web for temperature compensation heating.

[0036] Preferably, when the rolled piece enters and when the rolling passes are an even number, the electromagnetic heating device at the entrance of the finishing mill is operated to reduce the temperature difference between the upper and lower flanges caused by the rough rolling process;

[0037] When finishing the last pass of finishing rolling, operate the electromagnetic heating device at the outlet of the finishing mill.

[0038] Preferably, at the end of the last pass of finishing rolling, or when the rolling passes are an odd number, a cooling system at the outlet of the finishing mill is used for cooling to obtain the required inter-pass temperature or phase transition temperature.

[0039] Preferably, the number of rolling passes in the finishing rolling process is less than or equal to 7.

[0040] Specifically, the present invention provides a method for producing hot-rolled H-beams with excellent transverse impact toughness, comprising the following steps: hot metal pretreatment (KR desulfurization) → smelting in a 120-ton converter → argon blowing in a ladle → LF refining → casting of special-shaped continuous casting slabs → slow cooling in a slow cooling pit for the continuous casting slabs → heating in a heating furnace → rough rolling → reversible rolling (TM) → inter-stand cooling → electromagnetic induction online rapid heat treatment → intensive slow cooling on a cooling bed → straightening in a straightener → finishing treatment of the finished product. This process primarily achieves stable and improved transverse impact toughness by controlling the shape of MnS and improving the microstructure through subsequent online heat treatment.

[0041] (1) Smelting process: High-quality low-sulfur molten iron and scrap steel are put into the converter for smelting. The raw materials entering the furnace meet the requirements of molten iron sulfur content ≤ 0.006%, molten iron arsenic content less than 60ppm, and high-quality internally adjusted scrap steel is used for scrap steel; the final slag basicity is controlled within the range of 2.8-3.8, the slag is added 3 minutes before the end point, and the end gun pressure time is ≥ 1 minute; the bottom blowing adopts Ar gas blowing throughout the process. Aluminum manganese iron is used for deoxidation during the steel discharge process, and the amount of aluminum manganese iron added is 1.2-2.3kg / t steel. The insufficient part is added during refining. Metallic manganese, low-phosphorus and low-carbon silicon manganese (P content is less than or equal to 0.06%, S content is less than or equal to 0.02%), vanadium nitrogen, and niobium iron are used for alloying, and the target composition value is controlled. 3-6kg / t of lime is added after the steel is discharged. The steel tapping time is not less than 3 minutes. Bottom argon is blown and stirred throughout the refining process. Before leaving the furnace, soft blowing is performed at a pressure of 0.2-0.25 MPa to ensure inclusions float, and the refining soft argon blowing period is maintained for at least 15 minutes. Upon entering the furnace, ≥50 meters of aluminum wire is fed to control the aluminum content and minimize subsequent aluminum additions. The ladle enters the LF furnace for argon blowing for 7-12 minutes. Before refining soft argon blowing, 80-100 meters of high-calcium wire is fed per furnace for calcification. The continuous casting process uses a dedicated stopper rod ladle, with a nozzle immersion depth of 60-75 mm. Mild cooling is used for the secondary cooling process (this is a conventional technique in the field), and the continuous casting speed is 0.85-1.0 m / min. A mold slag specifically designed for peritectic steel is used, and the thickness of the liquid slag layer is measured during the process to ensure it exceeds the mold amplitude. The tundish is protected with carbonized rice husks to ensure good liquid surface coverage. The ingots are slowly cooled in the slow cooling pit, and the surface of the ingots is inspected and cleaned if any surface cracks are found. Among them, the special protective slag for peritectic steel is a conventional general protective slag used by those skilled in the art.

[0042] (2) Rolling process: The billet first enters a step-beam heating furnace for heating to obtain an austenite grain structure of appropriate size. After rough rolling and finishing rolling, the billet is rolled into a product. The rolling process is controlled by rolling and cooling. The heating furnace soaking temperature during the rolling process is 1220-1260℃, and the billet time in the furnace is 240-360min; the rough rolling BD rolling speed is ≥2.5m / s. The rolling load of the vertical roller is controlled during the finishing rolling stage. The vertical roller reduction rate of the last pass shall not be less than 12%, and the remaining passes shall not be less than 18%. The compression ratio is guaranteed during the rough rolling stage. The intermediate billet undergoes sufficient recrystallization to increase the austenite nucleation rate and refine the austenite structure. The finishing rolling start temperature is 930-950℃, the cooling water between the finishing rolling stands is fully turned on, and the finishing rolling final rolling temperature is 780-850℃. To ensure controlled final rolling temperature, the final finishing pass achieves a reduction ratio of 8% to 12%, while the mill is controlled at a reduced speed below 1.6 m / s. A cooling system at the finishing mill exit maintains the desired interpass temperature, facilitating the precipitation strengthening of the vanadium-containing carbonitrides that subsequently precipitate. It should be noted that due to the large thickness of the thick-gauge flanges and the significant temperature difference between the upper and lower flanges, the final microstructure transformation is significantly affected by external factors. Therefore, a special in-line heat treatment setup (see Figure 1 for a diagram of the heat treatment apparatus) is designed for normalizing after the final finishing pass to ensure uniform microstructure. This ensures a uniform transverse phase transformation between the upper and lower flanges, resulting in a more uniform microstructure. This improves transverse impact toughness and maintains high consistency, enhancing stability. This consistent microstructure ensures consistent Z-direction performance of the flanges, ensuring structural stability and system safety for applications such as offshore equipment steel structures, offshore oil platforms in polar environments, and steel structures in extremely cold regions.

[0043] The present invention realizes the industrial production of large-scale high-strength and tough H-beam products through online structure control and microalloying process design, combined with the characteristics of H-beam reciprocating rolling, to meet the requirements of transverse impact toughness.

[0044] Compared with other inventions, the advantages of the technical solution of the present invention are:

[0045] 1. The present invention adopts low-cost VN alloying + fine rolling process microstructure refinement control to achieve matrix microstructure grain size refinement to above level 9; the composition design does not contain Ni element, meeting the low-cost composition design requirements while ensuring significant improvement in the comprehensive low-temperature resistance in the transverse and longitudinal directions.

[0046] 2. The present invention controls the sulfur content during the smelting process and strictly controls the Mn / S ratio, ultimately achieving a lower number of strip inclusions with smaller sizes, refining the grain size of the transverse structure, and significantly improving the transverse impact toughness at -50°C.

[0047] 3. The present invention combines the characteristics of rolling large-size H-beams with different compression ratios of 16-50 mm, adopts a VN microalloying composition design suitable for temperature-controlled rolling, and increases the amount and size of VN precipitation by controlling the N content during the LF refining process. At the same time, combined with Nb recrystallization control, it meets the -50°C strength and toughness requirements of products of different specifications, thereby obtaining low-temperature resistant hot-rolled H-beams with stable performance on a general hot-rolled H-beam mill.

[0048] 4. The rolling process of the present invention adopts specially designed online soaking equipment and cooling equipment before and after the finishing mill to perform stable uniformity control. Temperature compensation heating is carried out in time according to the size of the rolled piece and the temperature change, which significantly reduces the temperature difference between the upper and lower flanges. The temperature difference is controlled below 10°C, and the grain size difference of the upper and lower flanges is met at a level below 0.5, achieving uniform consistency of the upper and lower flange structures, and ultimately achieving a significant improvement in the lateral impact toughness, thereby refining the structure.

[0049] 5. The inter-stand and post-rolling cooling systems of the present invention utilize a real-time rolling parameter model to cool the entire flange area with cooling water, reducing the temperature difference to less than 10°C and ensuring that the final rolling temperature is controlled within a range of 780-850°C. The yield strength difference between the upper and lower flanges is controlled within a range of 10-15 MPa, and the transverse impact energy is stably controlled at above 120 J, meeting the requirements for uniform performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG1 is a schematic diagram of an online heating and cooling device before and after the finishing rolling process of the present invention;

[0051] FIG2 is a schematic diagram of the overall online electromagnetic heating device of the present invention;

[0052] FIG3 is a schematic front view of an online electromagnetic heating device according to the present invention;

[0053] FIG4 is a microstructure diagram of the hot-rolled low-temperature resistant H-beam involved in Example 2;

[0054] Reference numerals:

[0055] 1. H-shaped steel rolled piece, 2. Upper flange, 3. Lower flange, 4. Induction heating coil, 5. Roller for rolling piece transport, 6. Cooling water pipe on the outer side of the flange. DETAILED DESCRIPTION

[0056] The present invention will be further described below with reference to specific embodiments.

[0057] To achieve uniform microstructure and improve transverse impact toughness of the upper and lower flanges, this invention designs an online heating and cooling device. The process and equipment layout are shown in Figure 1. An online electromagnetic heating device is installed at the entrance and exit of the finishing mill. The electromagnetic heating device comprises several sequentially arranged heating units, each of which includes sub-heating units symmetrically positioned outside the flanges of the H-beam. These sub-heating units cover the upper and lower flanges and at least a portion of the web, providing temperature compensation heating. Each sub-heating unit comprises an induction heating coil 4, which provides timely temperature compensation heating based on changes in the workpiece temperature. This heating device features an instant heating function. Based on PLC feedback, it activates when the temperature difference between the workpiece flanges (He 2 and the upper and lower flanges (3) in Figure 3) exceeds 10°C, thereby reducing the temperature difference. In the pre-mill heating zone I, the electromagnetic induction device is activated at the entrance of the workpiece (I) and during even-numbered passes, depending on the temperature, gradually reducing the significant temperature difference between the upper and lower flanges caused by the roughing process. In post-mill heating zone II, an electromagnetic induction device is combined with a cooling system consisting of a workpiece transport roller 5 and cooling water pipes on the outer flanges. This system controls the microstructure uniformity and refinement during the phase transformation process, ensuring a grain size difference of less than 0.5 between the upper and lower flanges, ultimately achieving a significant improvement in transverse impact toughness. This process is adjusted to the size of the H-beam workpiece 1 to meet the required temperature control range. In particular, precise cooling control of the wire rod temperature is performed during the final pass of the rolling process to stabilize temperature variations across different parts of the workpiece during rolling, ensuring transverse temperature uniformity across the entire workpiece. This system reduces the cross-sectional temperature difference between the upper and lower flanges to within 10°C, while also minimizing the temperature difference between the flange and web, improving the overall performance stability and uniformity of the H-beam. Combined with a microalloying design, this equipment achieves the required transverse impact toughness of the final hot-rolled H-beam, ensuring a transverse impact energy of ≥120 J at -50°C, a low ductile-brittle transition temperature, and a stable Z-axis reduction of area of ​​≥50%.

[0058] The present invention realizes the industrial production of large-scale high-strength and tough H-beam products through online structure control and microalloying process design, combined with the characteristics of H-beam reciprocating rolling, to meet the requirements of transverse impact toughness.

[0059] The present invention is described in detail below:

[0060] Table 1 is a list of chemical compositions of various embodiments and comparative examples of the present invention;

[0061] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0062] Table 3 is a table of performance tests of various embodiments and comparative examples of the present invention.

[0063] Each embodiment of the present invention is produced according to the following steps:

[0064] 1) After molten iron is charged to the furnace and smelted in the converter, it is then fed to the LF furnace for composition and inclusion control. The incoming raw materials are strictly controlled to maintain a sulfur content of ≤0.006% and an arsenic content of less than 60 ppm. The final slag basicity is controlled within the range of 2.8-3.8, with slag addition completed 3 minutes before the finish line and a lance pressure of ≤1 minute. Argon is used throughout the bottom blowing process. During the tapping process, 1.2-2.3 kg / t of ferro-aluminum manganese is added for deoxidation, with additional additions during refining. 3-6 kg / t of lime is added after tapping. The tapping time is 3-5 minutes. Argon is blown bottom throughout the refining process for agitation. Before tapping, low-pressure soft blowing is used to float all inclusions. Soft argon blowing is performed for 15-20 minutes during refining. After entering the furnace, 50-100 meters of aluminum wire is fed to meet the required aluminum content in the steel. Upon entering the LF furnace, 80-100 meters of high-calcium wire is fed per ladle for calcification. The continuous casting process uses a dedicated stopper rod package, with the nozzle immersed to a depth of 60-75mm. A weak cooling mode is used for the secondary cooling process, and the continuous casting speed is 0.85-1.0m / min. A mold slag specifically designed for peritectic steel is used. The tundish is protected by well-carbonized rice husks covering the liquid surface. The ingots are slowly cooled in a slow cooling pit, and the surface of the ingots is inspected and cleaned for defects.

[0065] The final continuous casting process produces a beam blank, which is divided into three types based on flange thickness. The residual elements in the molten iron are strictly controlled to a value of As+Sn+Zn+Pb+Ca+Mg ≤ 0.03. During the casting process, the casting superheat is controlled to be less than 25°C. The casting speed is set to a constant value between 0.85 and 1.0 m / min, and the straightening temperature is not less than 860°C.

[0066] 2) In the rolling process, the billet is reheated in a furnace at a controlled temperature of 1220-1260°C for 240-360 minutes before being removed from the furnace for rolling. Controlled rolling and cooling processes are implemented during the rolling process. The roughing (BD) process consists of fewer than nine passes, with a rolling speed of ≥2.5 m / s. The finishing (TM) process consists of fewer than seven passes. During the finishing process, the vertical roll load is controlled, with a vertical roll reduction of no less than 12% in the final pass and no less than 18% in the remaining passes. The starting temperature for finishing rolling is 930-950°C, and the final temperature for finishing rolling is controlled between 780-850°C. The reduction ratio for the final finishing pass is 8%-12%, with the mill controlled at a reduced speed of less than 1.6 m / s. In the front-of-mill heating zone I, an electromagnetic induction device is activated at the entry of the workpiece 1 and during even-numbered passes, depending on the temperature, to gradually reduce the significant temperature difference between the upper and lower flanges caused by the roughing process. After the last pass of finishing rolling, a special online heat treatment setup is designed (see Figure 1 for the heat treatment device diagram) for heating treatment, and then cooling equipment is used for cooling in the last pass or odd-numbered passes to obtain the required inter-pass temperature or phase change temperature, ultimately meeting the uniformity control needs of the organization, improving the lateral impact toughness to maintain a high degree of consistency, and improving stability. At the same time, the consistency of the flange Z-direction performance under uniform organizational conditions is guaranteed, ensuring the structural stability and system safety when using the product under special environments. The cooling track of the cooling bed maintains a temperature above 300°C, and the product is concentrated and slowly cooled on the cooling bed for more than 15 minutes. When the product temperature drops below 200°C, it enters the straightening machine for straightening.

[0067] 3) Finishing process: the surface and size of the product are finished after it comes off the production line; during the finishing process, samples are taken to analyze product performance.

[0068] Table 1 Chemical composition of various embodiments of the present invention and comparative examples (wt.%)

[0069] The main refining process parameters are shown in Table 2

[0070] Table 2 Refining process parameters

[0071] The specific process parameters of the continuous casting process are shown in Table 3.

[0072] Table 3 Continuous casting process parameters

[0073] Table 4 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0074] Table 4 Rolling process parameters

[0075] The performance tests of the embodiments of the present invention and the comparative examples are shown in Table 5.

[0076] Table 5: Mechanical properties record of rolled products

[0077] Product samples from the patented embodiments were sampled for performance testing. Mechanical performance testing was performed at a point one-third of the way from the edge to the center of the H-beam flange, according to EN ISO 377-1, "Mechanical Properties Test Specimens — Sampling Location and Preparation." Yield strength, tensile strength, and elongation were tested according to EN ISO 6892-1, "Metallic Materials — Room Temperature Tensile Test Methods." Impact energy testing was conducted according to ISO 148-1, "Metallic Materials — Charpy Pendulum Impact Test." Comparison of mechanical properties with those in the embodiments revealed that H-beam flanges produced using this patented method outperformed existing patented products and exhibited excellent Z-axis performance.

[0078] In addition, any content not described in detail in the present invention may adopt conventional technical knowledge in this field.

[0079] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. A low temperature resistant hot rolled H-beam, characterized in that: The chemical composition of the low-temperature resistant hot-rolled H-shaped steel comprises, by weight percentage, the following: C: 0.10-0.13; Si: ≤0.25; Mn: 0.8-1.0; V: 0.07-0.11; P≤0.01; S≤0.005; Nb: 0.005-0.015; Al: 0.008-0.015; N: 0.08-0.012; O≤0.003; RE: 0.008-0.015; wherein As+Sn+Zn+Ca+Mg+S≤0.03, and the rest are iron Fe and unavoidable impurities.

2. The low temperature resistant hot rolled H-beam according to claim 1, characterized in that: The yield strength of the low-temperature resistant hot-rolled H-shaped steel is ≥420 MPa, the tensile strength is ≥500 MPa, the elongation is ≥19%, the transverse impact energy at -50°C is ≥120 J, and the Z-direction performance is: the section shrinkage is ≥50%.

3. The low temperature resistant hot rolled H-beam according to claim 1, characterized in that: The RE includes lanthanum and / or cerium.

4. A method for preparing low-temperature resistant hot-rolled H-beam, comprising the following steps: 1) smelting; 2) Rolling: Electromagnetic heating devices are respectively provided at the entrance and exit of the finishing mill; a cooling system is provided after the electromagnetic heating device at the exit of the finishing mill.

5. The preparation method according to claim 4, characterized in that The step 1) includes: Hot metal pretreatment: The sulfur content of hot metal entering the furnace should be ≤0.006%, and the arsenic content of hot metal should be less than 60ppm; Converter smelting: the final slag basicity is controlled within the range of 2.8-3.8, the slag material is added 3 minutes before the end point, and the final gun pressure time is ≥1 minute until the injection is completed; During the tapping process, aluminum-manganese iron is used for deoxidation, with the addition amount of aluminum-manganese iron being 1.2-2.3 kg / t steel. Metallic manganese, low-phosphorus and low-carbon silicon-manganese, vanadium-nitrogen, and ferroniobium are used for alloying. The target composition value is controlled. After tapping, 3-6 kg / t of lime is added. The tapping time is not less than 3 minutes. LF refining: Bottom argon blowing and stirring are carried out throughout the refining process, and the refining soft argon blowing lasts for more than 15 minutes. After entering the station, aluminum wire ≥50 meters is fed, and the ladle enters the LF furnace for argon blowing and smelting for 7-12 minutes. Before refining soft argon blowing, high calcium wire 80-100m / furnace is fed for calcification treatment; Special-shaped continuous casting billet casting: The continuous casting process uses a casting plug package with a nozzle immersion depth of 60-75mm; the casting superheat is controlled to be less than 25℃, and the continuous casting speed is 0.85-1.0m / min; The continuous casting billet is slowly cooled.

6. The preparation method according to claim 4, characterized in that The step 2) includes: during the rolling process, the soaking temperature of the heating furnace is 1220-1260° C., and the time the cast billet is in the furnace is 240-360 minutes; the rough rolling speed is ≥2.5 m / s; in the finishing rolling stage, the vertical roll reduction rate in the last pass is controlled to be not less than 12%, and the reduction rate in the remaining passes is not less than 18%; the finishing rolling start temperature is 930-950° C., and the finishing rolling final temperature is 780-850° C.; the reduction ratio in the last finishing pass is 8%-12%, and the rolling mill is controlled to be below 1.6 m / s for reduced speed rolling; and the yield strength difference between the upper and lower flanges is controlled to be 10-15 MPa.

7. The preparation method according to claim 4, characterized in that The electromagnetic heating device includes a plurality of heating units arranged in sequence, wherein the heating unit includes a sub-heating unit symmetrically arranged on the outside of the flange of the H-shaped steel, and the sub-heating unit covers the upper and lower flanges and at least part of the web for temperature compensation heating.

8. The preparation method according to claim 4, characterized in that When the rolled piece enters and the rolling passes are even, the electromagnetic heating device at the entrance of the finishing mill is operated to reduce the temperature difference between the upper and lower flanges caused by the rough rolling process; When finishing the last pass of finishing rolling, operate the electromagnetic heating device at the outlet of the finishing mill.

9. The preparation method according to claim 4, characterized in that When the last pass of finishing rolling is completed, or when the rolling passes are an odd number, the cooling system at the outlet of the finishing mill is used for cooling to obtain the required inter-pass temperature or phase change temperature.

10. The preparation method according to claim 7 or 8, characterized in that: The number of rolling passes in the finishing rolling process is less than or equal to 7.

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