355mpa super-thick high-toughness low-alloy hot-rolled coil and method of manufacturing the same

Abstract

This invention provides a 355MPa extra-thick high-toughness low-alloy hot-rolled coil and its manufacturing method. The manufacturing method includes the following steps: continuous casting of molten steel to obtain a slab; heating the slab and then rolling it to obtain the extra-thick high-toughness low-alloy hot-rolled coil; the chemical composition of the molten steel, by mass fraction, includes: 0.05wt% ≤ C ≤ 0.08wt%, 0.10wt% ≤ Si ≤ 0.30wt%, 1.05wt% ≤ Mn ≤ 1.30wt%, P ≤ 0.020wt%, S... ≤0.005wt%, 0.018wt%≤Als≤0.050wt%, 0.025wt%≤Ti≤0.038wt%, 0.020wt%≤Nb≤0.035wt%, N≤0.0055wt%, B≤0.0008wt%, Cr≤0.30wt%; the remainder is iron and other unavoidable impurities; this invention breaks through the thickness limit of conventional hot-rolled wire coil production, and obtains a material that meets the requirements of high dimensional accuracy, few inclusions and high low-temperature toughness.

Description

Technical Field

[0001] This invention belongs to the field of metal rolling, specifically relating to a 355MPa extra-thick, high-toughness low-alloy hot-rolled coil and its manufacturing method. Background Technology

[0002] The market capacity for 25-30mm extra-thick 355Mpa strength grade hot-rolled high-strength steel coils is large. They are mainly used for infrastructure pile pipes in major projects and are processed by spiral welding. The use environment of extra-thick hot-rolled coils (thickness of 25-30mm) is complex and they need to meet high-quality standards such as low inclusions, high transverse and longitudinal impact toughness, and no surface defects. The requirements for the quality of steel coil materials are high.

[0003] Conventional hot rolling, as one of the main rolling processes, offers higher production efficiency and greater precision in material dimensional control compared to medium plate rolling, making it the primary production method for major steel products. However, conventional hot-rolled products are limited in thickness and width. Most conventional hot-rolled coil production lines were originally designed to produce coils up to 25mm in thickness, and the quality of products with extreme thicknesses is unstable, resulting in low dimensional accuracy for extra-thick hot-rolled coils.

[0004] Therefore, it is necessary to provide a method for manufacturing 355MPa extra-thick, high-toughness, low-alloy hot-rolled coils to alleviate or solve the above problems. Summary of the Invention

[0005] To address the technical problem of unstable quality in the production of 355MPa strength-grade hot-rolled coils with a thickness of 25mm or more using conventional hot-rolling technology, this invention provides a method for manufacturing 355MPa extra-thick, high-toughness, low-alloy hot-rolled coils, comprising the following steps:

[0006] The molten steel is continuously cast to obtain a slab, which is then heated and rolled to obtain the extra-thick, high-toughness, low-alloy hot-rolled coil. The chemical composition of the molten steel, by mass fraction, includes: 0.05wt%≤C≤0.08wt%, 0.10wt%≤Si≤0.30wt%, 1.05wt%≤Mn≤1.30wt%, P≤0.020wt%, S≤0.005wt%, 0.018wt%≤Als≤0.050wt%, 0.025wt%≤Ti≤0.038wt%, 0.020wt%≤Nb≤0.035wt%, N≤0.0055wt%, B≤0.0008wt%, Cr≤0.30wt%; the remainder is iron and other unavoidable impurities.

[0007] The thickness of the extra-thick, high-toughness, low-alloy hot-rolled coil is not less than 25 mm;

[0008] During the continuous casting process, the casting superheat is 10-25℃, the casting speed is 1.10-1.30m / min, and the dynamic light pressure at the end of solidification is 4.5mm.

[0009] Furthermore, the rolling process includes primary rolling and finishing rolling, wherein the entry temperature of the primary rolling does not exceed 980°C, and the temperature of the finishing rolling is 820–850°C.

[0010] Furthermore, the reduction rate during the finishing rolling process is not less than 50%.

[0011] Furthermore, the step of continuously casting molten steel to obtain a slab, and then heating the slab and rolling it to obtain the extra-thick, high-toughness, low-alloy hot-rolled coil further includes the following step: the extra-thick, high-toughness, low-alloy hot-rolled coil is obtained by rolling after the rolling process, and the rolling temperature is 550-610℃.

[0012] Furthermore, in the step of obtaining the extra-thick, high-toughness, low-alloy hot-rolled coil by rolling after heating the slab, the furnace exit temperature of the slab after heating is 1170-1220℃.

[0013] Furthermore, the preparation of the molten steel includes the following steps:

[0014] After desulfurization treatment, the molten iron is fed into a converter, and the steel is tapped from the converter and refined by LF to obtain the molten steel; wherein the sulfur content of the molten iron fed into the converter is not higher than 0.005%.

[0015] Furthermore, in the step of feeding the molten iron into the converter after desulfurization treatment, the iron content of the molten iron fed into the converter is not less than 75%, and the carbon content of the molten steel produced from the converter is 0.03% to 0.06%, and the phosphorus content does not exceed 0.015%.

[0016] Furthermore, the slag basicity R2 in the LF refining process is controlled to be 4-6, the Ca content in the molten steel is controlled to be 15-30ppm, the mixture is stirred slightly for 6-10 minutes, and the steel is then poured out of the station at a suitable temperature.

[0017] This invention provides a 355 MPa extra-thick, high-toughness, low-alloy hot-rolled coil, which is produced by the manufacturing method described in any of the above claims.

[0018] Furthermore, the microstructure of the extra-thick, high-toughness, low-alloy hot-rolled coil includes ferrite, bainite, and pearlite, and the core grain size of the extra-thick, high-toughness, low-alloy hot-rolled coil is grade 9.5, while the surface grain size is grade 11.

[0019] Compared with the prior art, the present invention has at least the following advantages:

[0020] The applicant found that conventional technologies are often limited by the uniformity of cooling temperature during the continuous casting and rolling process of extra-thick hot-rolled coils, making it difficult to break through the 25mm production limit while maintaining stable product quality.

[0021] Based on the above, the present invention precisely controls the composition of molten steel, with the following effects:

[0022] This invention controls the carbon content to be between 0.05 wt% and 0.08 wt%. Carbon is a major alloying element in steel, directly affecting its strength and hardness. Within this carbon content range, the hardness and strength of the molten steel are moderate, which is beneficial for obtaining good mechanical and processing properties of hot-rolled coils. However, carbon in molten steel forms carbides during cooling. The formation of these carbides requires heat absorption, thus slowing down the cooling rate of the molten steel. When the carbon content of the molten steel is in the range of 0.05 wt% to 0.08 wt%, the formation of carbides has a significant impact on the uniformity of cooling temperature. High-carbon-content molten steel has a relatively low cooling rate, which is beneficial for maintaining higher temperature stability, but may also lead to increased cooling non-uniformity, especially in areas with faster cooling rates.

[0023] This invention controls the silicon content to be between 0.10 wt% and 0.30 wt%. Silicon helps reduce defects such as inclusions and bubbles in hot-rolled coils, improving the internal quality of the product. Silicon primarily affects the uniformity of cooling temperature by influencing the thermal conductivity of molten steel.

[0024] This invention controls the manganese content within the range of 1.05wt% to 1.30wt%, which plays a role in solid solution strengthening, deoxidation, and desulfurization, increasing the strength and toughness of the steel and improving its corrosion resistance, thereby enhancing the overall mechanical properties and corrosion resistance of hot-rolled coil products. Manganese primarily affects the microstructure and properties of molten steel after cooling by altering its microstructure and phase transformation behavior, thus indirectly affecting the uniformity of cooling temperature.

[0025] This invention controls the acid-soluble aluminum content to between 0.018 wt% and 0.050 wt%, which helps refine grains, improve strength and toughness, and has a significant impact on the purity and inclusion morphology of molten steel. Acid-soluble aluminum mainly improves the uniformity of cooling temperature by reducing the oxygen content and the number of inclusions in molten steel.

[0026] Other trace elements (such as Ti, Nb, N, B, Cr, etc.):

[0027] These trace elements typically exist in steel in the form of solid solutions or compounds. They have little impact on the cooling process of molten steel, but they play a role in refining grains, improving strength and toughness. Within a given content range, these trace elements mainly affect the uniformity of cooling temperature indirectly by influencing the microstructure and phase transformation behavior of molten steel.

[0028] The interactions between these elements collectively affect the cooling temperature uniformity of the hot rolling production line. Furthermore, based on the mechanism by which these elements influence uniformity, the cooling environment must meet stringent requirements to produce consistently high-quality, extra-thick hot-rolled coils. Therefore, providing a cooling process compatible with these elements is crucial.

[0029] In this invention, during the continuous casting process, the casting superheat is controlled at 10-25℃, the casting speed is controlled at 1.10-1.30m / min, and the dynamic light pressure at the end of solidification is controlled at 4.5mm.

[0030] In the continuous casting process, the use of specific casting superheat, casting speed, and dynamic light reduction parameters at the end of solidification has a significant and beneficial impact on the production limit of thickness in hot rolling production lines and the quality stability (such as mechanical properties) of products.

[0031] Improving the production limit of thickness: Controlling the casting superheat within the range of 10-25℃ helps the molten steel solidify quickly and uniformly in the crystallizer, forming a stable billet shell. This helps the continuous casting machine improve the thickness production limit of the hot rolling line while maintaining high quality.

[0032] Appropriate casting speed (1.10-1.30 m / min) and dynamic light reduction at the end of solidification (4.5 mm) can ensure the stability of molten steel during solidification, reduce problems such as uneven billet thickness or cracks caused by excessive casting speed or insufficient reduction, and thus further improve the thickness production limit of hot rolling production lines.

[0033] Improving Mechanical Properties: Precise control of casting superheat helps reduce defects such as inclusions and bubbles in molten steel, improving its purity and density, and forming a uniform and dense microstructure. This, in turn, helps improve the mechanical properties of hot-rolled coils, such as tensile strength, yield strength, and impact toughness. Appropriate casting speed and dynamic light pressure at the end of solidification ensure the uniformity of molten steel during solidification, reducing fluctuations in mechanical properties caused by uneven solidification.

[0034] In summary, this invention, through the coordinated control of the chemical composition of the hot-rolled coil and the continuous casting parameters, maximizes the uniformity of cooling temperature during the continuous casting and hot rolling processes. While ensuring product quality, it breaks through the 25mm production limit and produces a 355MPa extra-thick, high-toughness, low-alloy hot-rolled steel coil with a thickness greater than 25mm. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0036] Figure 1 (a) is a surface metallographic diagram of the extra-thick, high-toughness, low-alloy hot-rolled coil obtained in Example 1 of the present invention; Figure 1 (b) is a metallographic diagram of the core of the extra-thick, high-toughness, low-alloy hot-rolled coil prepared in Example 1 of the present invention.

[0037] Figure 2 (a) is a surface metallographic diagram of the extra-thick, high-toughness, low-alloy hot-rolled coil obtained in Example 2 of the present invention; Figure 2 (b) is a metallographic diagram of the core of the extra-thick, high-toughness, low-alloy hot-rolled coil obtained in Example 2 of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0040] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of the invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of the present invention.

[0041] To address the technical problems encountered in the aforementioned commonly used technologies, this invention provides a method for manufacturing a 355MPa extra-thick, high-toughness, low-alloy hot-rolled coil, comprising the following steps:

[0042] The molten steel is continuously cast to obtain a slab, which is then heated and rolled to obtain the extra-thick, high-toughness, low-alloy hot-rolled coil. The chemical composition of the molten steel, by mass fraction, includes: 0.05wt%≤C≤0.08wt%, 0.10wt%≤Si≤0.30wt%, 1.05wt%≤Mn≤1.30wt%, P≤0.020wt%, S≤0.005wt%, 0.018wt%≤Als≤0.050wt%, 0.025wt%≤Ti≤0.038wt%, 0.020wt%≤Nb≤0.035wt%, N≤0.0055wt%, B≤0.0008wt%, Cr≤0.30wt%; the remainder being iron and other unavoidable impurities.

[0043] The thickness of the extra-thick, high-toughness, low-alloy hot-rolled coil is not less than 25 mm. For example, the thickness of the extra-thick, high-toughness, low-alloy hot-rolled coil can be 28 mm.

[0044] 355MPa refers to the yield strength of the material.

[0045] For example, the mass fraction of carbon in this invention can be 0.060 wt% to 0.070 wt%; the mass fraction of carbon in this invention can be 0.05 wt% to 0.07 wt%; the mass fraction of carbon in this invention can be 0.06 wt% to 0.08 wt%.

[0046] For example, the mass fraction of silicon in this invention can be 0.18 wt% to 0.21 wt%; the mass fraction of silicon in this invention can be 0.18 to 0.30; the mass fraction of silicon in this invention can be 0.10 wt% to 0.21 wt%.

[0047] For example, the mass fraction of manganese in this invention can be 1.10 wt% to 1.20 wt%.

[0048] For example, the mass fraction of phosphorus in this invention can be ≤0.0112wt%.

[0049] For example, the mass fraction of sulfur in this invention can be ≤0.0022wt%;

[0050] For example, the mass fraction of acid-soluble aluminum in this invention can be 0.02-0.03 wt%; the mass fraction of acid-soluble aluminum in this invention can be 0.02 wt%-0.05 wt%; the mass fraction of acid-soluble aluminum in this invention can be 0.018 wt%-0.013 wt%.

[0051] For example, the mass fraction of titanium in this invention can be 0.028 wt% to 0.032 wt%; the mass fraction of titanium in this invention can be 0.028 wt% to 0.038 wt%; the mass fraction of titanium in this invention can be 0.025 wt% to 0.032 wt%;

[0052] For example, the mass fraction of niobium in this invention can be 0.019 wt% to 0.022 wt%; the mass fraction of niobium in this invention can be 0.02 wt% to 0.022 wt%.

[0053] For example, the mass fraction of nitrogen in this invention can be 0.0045 wt% to 0.0052 wt%; the mass fraction of nitrogen in this invention can be 0.0045 wt% to 0.0055 wt%.

[0054] For example, the mass fraction of boron in this invention can be ≤0.0005wt%.

[0055] In some embodiments, the preparation of the molten steel includes the steps of:

[0056] S1. After desulfurization treatment, the molten iron is fed into a converter, and the steel is produced by LF refining.

[0057] The main steps of steelmaking are: desulfurization treatment → primary refining in a top and bottom blown converter → LF refining → (casting at the station).

[0058] Specifically, after desulfurization, molten iron is obtained and fed into the converter. After primary refining in the top and bottom blown converter, molten steel is obtained and then refined in the LF to obtain the molten steel in step S1.

[0059] In some embodiments, the desulfurization treatment includes KR desulfurization treatment, wherein the sulfur content of the molten iron entering the converter after KR desulfurization treatment is controlled to be no higher than 0.005%, and the iron-to-roll ratio of the molten iron entering the converter can be no less than 75.

[0060] For example, the ratio of molten iron to molten iron entering the converter can be 75%-85%.

[0061] In some embodiments, the temperature of the molten iron entering the converter can be 1280–1350°C.

[0062] In some embodiments, the carbon content of the molten steel tapped from the converter is not less than 0.03% and the phosphorus content is not more than 0.015%, and the slag-blocking and slag-retaining tapping operation can be adopted.

[0063] The slag basicity R2 in the LF refining process is controlled to be 4-6, the steel composition is adjusted appropriately, calcium treatment is performed to modify inclusions, the Ca content in the steel is controlled to be 15-30ppm, micro-stirring is performed for 6-10 minutes, and the steel is poured out at a suitable temperature.

[0064] In some embodiments, the interval between the LF molten steel leaving the station and the start of continuous casting can be controlled to be 25-35 minutes.

[0065] This invention specifically designs the chemical composition of extra-thick hot-rolled coils. The interaction between elements jointly affects the cooling temperature uniformity of the hot rolling production line. At the same time, based on the mechanism of the influence of elements on uniformity, the cooling environment must meet stringent requirements to produce extra-thick hot-rolled coils with stable quality. Therefore, it is crucial to provide a cooling process that is compatible with the elements: In the continuous casting process of this invention, the casting superheat is controlled at 10-25℃, the casting speed is controlled at 1.10-1.30m / min, and the dynamic light pressure at the end of solidification is 4.5mm.

[0066] Specific parameters for casting superheat, casting speed, and dynamic light reduction at the end of solidification during continuous casting have a significant and beneficial impact on the production limits of hot-rolled coil thickness and the quality stability (such as mechanical properties) of the product. Precise control of these parameters helps optimize the production process, improve product quality and performance stability, thereby meeting market demand for high-quality hot-rolled coils.

[0067] By precisely controlling various parameters in the continuous casting process, the production flow of the hot rolling line can be optimized. For example, stable billet shell formation helps reduce rolling force fluctuations during hot rolling and improves rolling efficiency. At the same time, reasonable casting speed and light reduction parameters also help reduce billet center segregation and billet microstructure, protect continuous casting equipment, reduce continuous casting machine downtime, improve equipment utilization, and thus further increase the capacity of the hot rolling line.

[0068] By precisely controlling various parameters during the continuous casting process, a high degree of consistency in hot-rolled coil products can be ensured across different batches. This helps reduce product quality variations caused by fluctuations in production conditions, thereby increasing customer satisfaction and trust.

[0069] Due to the optimization of element design and continuous casting process, the slab obtained in this application has a center segregation and center porosity grade of no more than C1.5.

[0070] In the step of obtaining the extra-thick, high-toughness, low-alloy hot-rolled coil by rolling after heating the slab, the furnace exit temperature of the slab after heating is 1180-1220℃.

[0071] In some embodiments, the heated billet may be subjected to descaling, rolling and coiling in sequence.

[0072] The rolling process includes rough rolling and finish rolling. The entry temperature of the rough rolling does not exceed 980℃, and the temperature of the finish rolling is 820-850℃. This ensures the formation of the material microstructure, avoids grain coarsening, and results in a fine-grained microstructure of the rolled material, forming a certain proportion of bainite, pearlite, and ferrite.

[0073] For example, the initial rolling temperature can be 930–980°C.

[0074] In some embodiments, the reduction rate during the finishing rolling process is not less than 50%.

[0075] For example, the reduction rate during the finishing rolling process can be 50% to 55%.

[0076] In some embodiments, the cooling method for the finished steel plate can be ultra-fast cooling + laminar flow cooling, and the cooling rate can be 25-30° / s.

[0077] In some embodiments, the finishing rolling speed can be 1.75 to 2.50 m / min.

[0078] The step of obtaining the extra-thick, high-toughness, low-alloy hot-rolled coil by continuous casting of molten steel and heating the slab further includes the following step: the extra-thick, high-toughness, low-alloy hot-rolled coil is obtained by rolling after the rolling process, and the rolling temperature is 550-610℃.

[0079] An extra-thick, high-toughness, low-alloy hot-rolled coil is produced by any one of the above-mentioned continuous casting and rolling methods.

[0080] The microstructure of the extra-thick, high-toughness, low-alloy hot-rolled coil includes ferrite, bainite, and pearlite. The core grain size of the extra-thick, high-toughness, low-alloy hot-rolled coil is grade 9.5, and the surface grain size is grade 11.

[0081] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided:

[0082] Example 1:

[0083] This embodiment provides a manufacturing method for producing 28mm high-toughness low-alloy hot-rolled coils, the specific implementation process of which includes:

[0084] Composition of molten steel in the tundish: C: 0.065wt%, Si: 0.183wt%, Mn: 1.15wt%, P: 0.0112wt%, S: 0.0022wt%, Als: 0.0296wt%, Ti: 0.0285wt%, Nb: 0.0215wt%, Ca: 0.0018%, N: 0.0045wt%, B: 0.0005wt%. The remainder is iron and unavoidable elements.

[0085] The molten iron undergoes KR desulfurization treatment, and the sulfur content of the molten iron entering the converter is 0.002%. The molten iron entering the converter is at 1310℃, the iron ratio is 82%, and the primary refining is carried out in a top and bottom blowing converter. The final control of the steel output is C: 0.04% and P: 0.010%, and the slag-blocking and slag-retaining operation is adopted for steel tapping.

[0086] For LF refining white slag operation, the slag basicity R2 is controlled at 5.0, the steel composition is adjusted appropriately, calcium treatment is performed to modify inclusions, the Ca content of the steel is 0.0015%~0.0030%, and it is stirred slightly for 8 minutes before being poured out of the station at the appropriate temperature.

[0087] The time from LF molten steel leaving the station to continuous casting is controlled within 25 minutes, the casting superheat is 18℃, the casting speed is controlled at 1.15m / min, and the dynamic light reduction at the end of solidification is 4.5mm, resulting in a 230mm thick slab. The slab exhibits center segregation, center porosity (C1.0), and no intermediate cracks or triangular cracks. After casting, the slab is placed in the reheating furnace after a 15-hour interval to improve quality such as segregation.

[0088] The cast billet is heated and then descaled, primary rolled, finish rolled, and coiled to obtain an extra-thick, high-toughness, low-alloy hot-rolled coil. Heating temperature: 1170-1220℃; primary rolling inlet temperature: 972℃; finish rolling temperature: 820℃~850℃; finish rolling start speed: 1.85m / min; after finish rolling, ultra-fast cooling + laminar flow cooling is performed at a cooling rate of 25° / s; CT coiling temperature: 606℃.

[0089] Example 2:

[0090] This embodiment provides a method for producing 28mm high-toughness low-alloy hot-rolled coils, the specific implementation process of which includes:

[0091] Composition of S1 ladle steel: C: 0.062wt%, Si: 0.203wt%, Mn: 1.23wt%, P: 0.008wt%, S: 0.0020wt%, Als: 0.0266wt%, Ti: 0.0315wt%, Nb: 0.0195wt%, Ca: 0.0022%, N: 0.0052wt%, B: 0.0004wt%. The remainder is iron and unavoidable elements.

[0092] The molten iron undergoes KR desulfurization treatment, and the sulfur content of the molten iron entering the converter is 0.005%. The molten iron entering the converter is at 1280℃, the iron ratio is 85%, and the primary refining is carried out in a top and bottom combined blowing converter. The final control of the steel output is C: 0.04% and P: 0.007%, and the slag-blocking and slag-retaining operation is adopted for steel tapping.

[0093] For LF refining white slag operation, the slag basicity R2 is controlled at 4.8, the steel composition is adjusted appropriately, calcium treatment is performed to modify inclusions, the Ca content of the steel is retained at 0.0022%, and it is stirred slightly for 10 minutes before being poured out of the station at the appropriate temperature.

[0094] The time from LF molten steel leaving the station to continuous casting is controlled within 28 minutes, with a casting superheat of 15°C and a casting speed of 1.20 m / min. A dynamic light reduction of 4.5 mm is applied at the end of solidification to obtain a 230 mm thick slab. The slab exhibits center segregation, center porosity (C1.0), and is free of intermediate cracks and triangular cracks. After casting, the slab is placed in the reheating furnace after a 13-hour interval to improve quality, including addressing segregation issues.

[0095] The cast billet is heated and then descaled, primary rolled, finish rolled, and coiled to obtain an extra-thick, high-toughness, low-alloy hot-rolled coil. Heating temperature: 1180-1220℃; primary rolling inlet temperature: 952℃; finish rolling temperature: 820℃~850℃; finish rolling start speed: 1.85m / min; after finish rolling, ultra-fast cooling + laminar flow cooling is performed at a cooling rate of 28° / s; CT coiling temperature: 555℃.

[0096] Analysis example 1

[0097] The mechanical property data of the extra-thick hot-rolled coils obtained in Examples 1 and 2 are shown in Table 1:

[0098] Table 1: Mechanical Performance Data

[0099]

[0100] The impact energy properties of the extra-thick hot-rolled coils obtained in Examples 1 and 2 are shown in Table 2:

[0101] Table 2: Impact Energy Test Data

[0102]

[0103]

[0104] The metallographic information of the extra-thick hot-rolled coils obtained in Examples 1 and 2 is shown in Table 3:

[0105] Table 3: Metallographic Structure Information

[0106]

[0107] The surface metallographic structure of the extra-thick hot-rolled coil obtained in Example 1 is shown in the figure below. Figure 1 As shown in (a), the metallographic structure of the core is as follows: Figure 1 As shown in (b).

[0108] The surface metallographic structure of the extra-thick hot-rolled coil obtained in Example 2 is shown in the figure below. Figure 2 As shown in (a), the metallographic structure of the core is as follows: Figure 2 As shown in (b).

[0109] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for manufacturing an extra-thick, high-toughness, low-alloy hot-rolled coil with a strength of 355 MPa, characterized in that, Including the following steps: The slab is obtained by continuous casting of molten steel, and the slab is heated and then rolled to obtain the extra-thick, high-toughness, low-alloy hot-rolled coil. The chemical composition of the molten steel, by mass fraction, includes: 0.06wt%≤C≤0.07wt%, 0.10wt%≤Si≤0.30wt%, 1.05wt%≤Mn≤1.30wt%, P≤0.020wt%, S≤0.005wt%, 0.018wt%≤Als≤0.050wt%, 0.025wt%≤Ti≤0.038wt%, 0.019wt%≤Nb≤0.022wt%, N≤0.0055wt%, 0.0004wt%≤B≤0.0008wt%, Cr≤0.30wt%; the remainder being iron and other unavoidable impurities. The thickness of the extra-thick, high-toughness, low-alloy hot-rolled coil is not less than 28 mm; During the continuous casting process, the casting superheat is 10-25℃, the casting speed is 1.10-1.30m / min, and the dynamic light pressure at the end of solidification is 4.5mm.

2. The manufacturing method according to claim 1, characterized in that, The rolling process includes primary rolling and finishing rolling. The entry temperature of the primary rolling is no more than 980°C, and the temperature of the finishing rolling is 820~850°C.

3. The manufacturing method according to claim 2, characterized in that, The reduction rate during the finishing rolling process shall not be less than 50%.

4. The manufacturing method according to claim 1, characterized in that, The step of obtaining the extra-thick, high-toughness, low-alloy hot-rolled coil by continuously casting molten steel and heating the slab further includes the following step: the extra-thick, high-toughness, low-alloy hot-rolled coil is obtained by rolling after the rolling process, and the rolling temperature is 550-610℃.

5. The manufacturing method according to claim 1, characterized in that, In the step of obtaining the extra-thick, high-toughness, low-alloy hot-rolled coil by rolling after heating the slab, the furnace exit temperature of the slab after heating is 1170-1220℃.

6. The manufacturing method according to any one of claims 1 to 5, characterized in that, The preparation of the molten steel includes the following steps: After desulfurization treatment, the molten iron is fed into a converter, and the steel is produced by LF refining. The sulfur content of the molten iron fed into the converter is not higher than 0.005%.

7. The manufacturing method according to claim 6, characterized in that, In the step of feeding the molten iron into the converter after desulfurization treatment, the iron content of the molten iron fed into the converter is not less than 75%, and the carbon content of the molten steel produced from the converter is 0.03% to 0.06%, and the phosphorus content does not exceed 0.015%.

8. The manufacturing method according to claim 6, characterized in that, The slag basicity R2 in the LF refining process is controlled to be 4-6, the Ca content in the molten steel is controlled to be 15-30ppm, the mixture is stirred slightly for 6-10 minutes, and the steel is poured out of the station at a suitable temperature.

9. A 355MPa extra-thick, high-toughness, low-alloy hot-rolled coil, characterized in that, It is produced by the manufacturing method described in any one of claims 1 to 8.

10. The 355MPa extra-thick, high-toughness, low-alloy hot-rolled coil according to claim 9, characterized in that, The microstructure of the extra-thick, high-toughness, low-alloy hot-rolled coil includes ferrite, bainite, and pearlite. The core grain size of the extra-thick, high-toughness, low-alloy hot-rolled coil is grade 9.5, and the surface grain size is grade 11.

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