355MPa extra-thick high-toughness low-alloy hot-rolled coil and manufacturing method thereof

Abstract

The invention provides a 355MPa extra-thick high-toughness low-alloy hot-rolled coil and a manufacturing method thereof.The manufacturing method comprises the steps that molten steel is subjected to continuous casting to obtain a plate blank, and the plate blank is heated and then subjected to rolling treatment to obtain the extra-thick high-toughness low-alloy hot-rolled coil; the molten steel comprises the following chemical components in percentage by mass: not less than 0.05 wt% and not more than 0.08 wt% of C, not less than 0.10 t% and not more than 0.30 wt% of Si, not less than 1.05 wt% and not more than 1.30 wt% of Mn, not more than 0.020 wt% of P, not more than 0.005 wt% of S, not less than 0.018 wt% and not more than 0.050 wt% of Als, not less than 0.025 wt% and not more than 0.038 wt% of Ti, not less than 0.020 wt% and not more than 0.035 wt% of Nb, not more than 0.0055 wt% of N, not more than 0.0008 wt% of B and not more than 0.30 wt% of Cr. And the balance of iron and other inevitable impurities. The production thickness limit of a conventional hot-rolled wire coil plate is broken through, and the material which is high in size precision, few in inclusions and high in low-temperature toughness is obtained.

Description

Technical Field

[0001] The invention belongs to the field of metal rolling, and in particular relates to a 355MPa ultra-thick high-toughness low-alloy hot-rolled coil and a manufacturing method thereof. Background Art

[0002] The market capacity of 25-30mm extra-thick specification 355Mpa strength level hot-rolled high-strength steel coils is large. It is mainly used for pile pipes of major engineering infrastructure and is processed by spiral welding. The use environment of extra-thick hot-rolled coils (thickness is 25-30mm) is complex. It needs to meet high quality standards such as few material inclusions, high transverse and longitudinal impact toughness, and no surface defects, and has high requirements on the quality of the steel coil material.

[0003] Conventional hot rolling is one of the main rolling process forms. Compared with medium plate rolling, it has high production efficiency and high material size control accuracy. It is the main production method for the current major steel products. However, conventional hot-rolled products are limited in thickness and width. The original design capacity of the main conventional hot-rolled coil production line is only up to 25mm thickness specifications, and the quality of extreme thickness products is unstable, and the dimensional accuracy of the extra-thick hot-rolled coils produced is low.

[0004] Based on this, it is necessary to provide a method for manufacturing 355MPa ultra-thick specification high-toughness low-alloy hot-rolled coils to alleviate or solve the above problems. Summary of the invention

[0005] In order to solve the technical problem of unstable product quality of 355MPa strength grade hot rolled coils with a thickness of more than 25mm produced by the above conventional hot rolling technology, the present invention provides a method for manufacturing 355MPa ultra-thick high-toughness low-alloy hot rolled coils, comprising the steps of:

[0006] The molten steel is continuously cast to obtain a slab, and the slab is heated and then rolled to obtain the ultra-thick high-toughness low-alloy hot-rolled coil; the chemical composition of the molten steel includes, by mass fraction: 0.05wt%≤C≤0.08wt%, 0.10t%≤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 rest is iron and other inevitable impurities;

[0007] The thickness of the ultra-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° C., the casting speed is 1.10-1.30 m / min, and the dynamic light pressure is 4.5 mm at the end of solidification.

[0009] Furthermore, the rolling process includes initial rolling and finishing rolling, the rolling temperature of the initial rolling does not exceed 980°C, and the temperature of the finishing rolling is 820-850°C.

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

[0011] Furthermore, the step of continuously casting the 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 also includes: after the rolling treatment, the extra-thick high-toughness low-alloy hot-rolled coil is obtained, and the coiling temperature is 550-610°C.

[0012] Furthermore, in the step of heating the slab and subjecting it to rolling treatment to obtain the ultra-thick high-toughness low-alloy hot-rolled coil, the furnace temperature of the heated slab is 1170-1220°C.

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

[0014] The molten iron is desulfurized and then fed into a converter, and 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 molten iron ratio of the molten iron feeding into the converter is not less than 75%, the carbon content of the molten steel tapped 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 is controlled to be 4-6, the Ca content in the molten steel is controlled to be 15-30ppm, micro-stirring is performed for 6-10 minutes, and the steel is cast at a suitable temperature.

[0017] The present invention provides a 355Mpa ultra-thick high-toughness low-alloy hot-rolled coil, which is produced by any one of the manufacturing methods described above.

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

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

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

[0021] Based on the above, the present invention accurately controls the composition of molten steel, and the effects are as follows:

[0022] The present invention controls the carbon content to be between 0.05wt% and 0.08wt%. Carbon is the main alloying element in steel and directly affects the strength and hardness of steel. Within the carbon content within this range, the hardness and strength of the molten steel are moderate, which is conducive to obtaining good mechanical properties and processing properties of hot-rolled coil products. However, the carbon element in the molten steel will form carbides during the cooling process. The formation of these carbides requires the absorption of heat, thereby slowing down the cooling rate of the molten steel. When the carbon content of the molten steel is within the range of 0.05wt% to 0.08wt%, the formation of carbides has a more significant effect on the uniformity of the cooling temperature. The cooling rate of the molten steel with a high carbon content is relatively low, which is conducive to maintaining a higher temperature stability, but may also lead to an increase in cooling unevenness, especially in areas with a faster cooling rate.

[0023] The present invention controls the silicon content to 0.10wt% to 0.30wt%, and the silicon helps to reduce defects such as inclusions and bubbles in hot rolled coil products and improve the internal quality of the products. The silicon element mainly indirectly affects the uniformity of cooling temperature by affecting the thermal conductivity of molten steel.

[0024] The present invention controls the manganese content within the range of 1.05wt% to 1.30wt%, which plays the role of solid solution strengthening and deoxidation and desulfurization, can increase the strength and toughness of steel, improve the corrosion resistance of steel, and improve the overall mechanical properties and corrosion resistance of hot-rolled coil products. Manganese elements mainly affect the organization and properties after cooling by changing the microstructure and phase change behavior of molten steel, and thus indirectly affect the uniformity of cooling temperature.

[0025] The present invention controls the acid-soluble aluminum content to 0.018wt% to 0.050wt%, which helps to refine the grains, improve the strength and toughness and other properties, and has an important influence on the purity of molten steel and the morphology of inclusions. 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 usually exist in steel in the form of solid solutions or compounds, and have little effect on the cooling process of molten steel, but they play a role in refining grains, improving strength and toughness, etc. Within a given content range, these trace elements mainly indirectly affect the cooling temperature uniformity by affecting the microstructure and phase change behavior of molten steel.

[0028] The above elements interact with each other and jointly affect the cooling temperature uniformity of the hot rolling production line. At the same time, based on the influence mechanism of the elements on uniformity, the cooling environment must meet strict requirements in order to produce extra-thick hot-rolled coils with stable quality. Therefore, it is very important to provide a cooling process that is compatible with the elements:

[0029] In the present invention, during the continuous casting process, the casting superheat is controlled to be 10-25° C., the casting speed is controlled to be 1.10-1.30 m / min, and the dynamic soft pressure reduction at the end of solidification is controlled to be 4.5 mm.

[0030] During the continuous casting process, the use of specific casting superheat, casting speed and dynamic soft reduction parameters at the end of solidification has a significant beneficial effect on the production limit of the hot rolling production line thickness and the quality stability of the product (such as mechanical properties).

[0031] Improvement of the production limit of thickness: Controlling the casting superheat within the range of 10-25°C helps the molten steel to solidify quickly and evenly in the crystallizer to form a stable billet shell. This helps the continuous casting machine to improve the thickness production limit of the hot rolling production line while maintaining high quality.

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

[0033] Improve mechanical properties: Precise control of casting superheat helps reduce defects such as inclusions and bubbles in molten steel, improves the purity and density of steel, forms a uniform and dense microstructure, and thus helps improve the mechanical properties of hot-rolled coil products, such as tensile strength, yield strength and impact toughness. Appropriate casting speed and dynamic light pressure at the end of solidification can ensure the uniformity of molten steel during solidification and reduce fluctuations in mechanical properties caused by uneven solidification.

[0034] In summary, the present invention coordinates the chemical composition of the hot-rolled coil and the continuous casting parameter regulation to ensure the uniformity of the cooling temperature during the continuous casting and hot rolling process to the greatest extent, while ensuring product quality and breaking through the production limit of 25 mm, and produces a 355 MPa ultra-thick specification high-toughness low-alloy hot-rolled steel coil with a thickness greater than 25 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

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

[0037] Figure 2 (a) is a surface metallographic structure diagram of the ultra-thick high-toughness low-alloy hot-rolled coil prepared in Example 2 of the present invention; Figure 2 (b) is the core metallographic structure diagram of the ultra-thick high-toughness low-alloy hot-rolled coil prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0040] When numerical ranges are given in the embodiments, it should be understood that unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention are familiar to those skilled in the art and the description of the present invention, and any method, device and material of the prior art similar or equivalent to the method, device and material in the embodiments of the present invention can also be used to implement the present invention.

[0041] In order to solve the technical problems faced by the above-mentioned conventional technologies, the present invention provides a method for manufacturing a 355MPa ultra-thick high-toughness low-alloy hot-rolled coil, comprising the steps of:

[0042] The molten steel is continuously cast to obtain a slab, 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 comprises, by mass fraction: 0.05wt%≤C≤0.08wt%, 0.10t%≤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 rest is iron and other inevitable impurities.

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

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

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

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

[0047] For example, the mass fraction of manganese in the present invention may be 1.10 wt% to 1.20 wt%;

[0048] Exemplarily, the mass fraction of phosphorus in the present invention may be ≤0.0112wt%;

[0049] Exemplarily, the mass fraction of sulfur in the present invention may be ≤0.0022wt%;

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

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

[0052] For example, the mass fraction of the niobium element in the present invention may be 0.019wt% to 0.022wt%; the mass fraction of the niobium element in the present invention may be 0.02wt% to 0.022wt%;

[0053] Exemplarily, the mass fraction of nitrogen in the present invention may be 0.0045 wt % to 0.0052 wt %; the mass fraction of nitrogen in the present invention may be 0.0045 wt % to 0.0055 wt %;

[0054] Exemplarily, the mass fraction of the boron element in the present invention may be ≤0.0005 wt %.

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

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

[0057] The smelting of molten steel mainly includes the following steps: desulfurization treatment → top and bottom double-blowing converter primary smelting → LF refining → (out-station casting).

[0058] Specifically, after desulfurization treatment, molten iron for converter is obtained, after primary refining in top and bottom combined blowing converter, molten steel for converter tapping is obtained, and after LF refining, molten steel in step S1 is obtained.

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

[0060] Exemplarily, the molten iron ratio of the molten iron entering the converter may be 75%-85%.

[0061] In some embodiments, the temperature of the molten iron entering the converter may 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 a slag blocking and slag retaining tapping operation can be adopted.

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

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

[0065] The present invention carries out targeted design of the chemical composition in the extra-thick hot-rolled coil. The elements interact with each other and jointly affect the cooling temperature uniformity of the hot rolling production line. At the same time, based on the influence mechanism of the elements on uniformity, the cooling environment must meet strict requirements in order to produce extra-thick hot-rolled coils with stable quality. Therefore, it is very important to provide a cooling process that is compatible with the elements: During the continuous casting process of the present invention, the casting superheat is controlled at 10-25°C, 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] The use of specific casting superheat, casting speed and dynamic soft reduction parameters at the end of solidification during continuous casting has a significant positive impact on the production limit of the hot rolling production line thickness and the quality stability of the product (such as mechanical properties). Precise control of these parameters helps to optimize the production process, improve product quality and performance stability, thereby meeting the market demand for high-quality hot rolled coil products.

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

[0068] By precisely controlling various parameters during the continuous casting process, it is possible to ensure that hot rolled coil products have a high degree of consistency between different batches. This helps to reduce product quality differences caused by fluctuations in production conditions and improve customer satisfaction and trust.

[0069] Due to the element design and continuous casting process optimization, the level of center segregation and center porosity of the slab produced in this application does not exceed C1.5.

[0070] In the step of heating the slab and subjecting it to rolling treatment to obtain the extra-thick high-toughness low-alloy hot-rolled coil, the furnace temperature of the heated slab is 1180-1220°C.

[0071] In some embodiments, the heated ingot may be descaled, rolled and coiled in sequence.

[0072] The rolling process includes initial rolling and finishing rolling, wherein the initial rolling temperature does not exceed 980° C., and the finishing rolling temperature is 820-850° C. The formation of the material structure is ensured, the coarsening of the grains is avoided, the microstructure of the rolled material has fine grains, and a certain proportion of bainite, pearlite and ferrite is formed.

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

[0074] In some embodiments, the reduction ratio during the finish rolling is not less than 50%.

[0075] For example, the reduction ratio during the finish rolling process may be 50% to 55%.

[0076] In some embodiments, the cooling method of the steel plate after finish rolling can be ultra-fast cooling + laminar cooling, and the cooling rate can be 25-30° / s.

[0077] In some embodiments, the finishing rolling start speed may be 1.75-2.50 m / min.

[0078] The step of continuously casting molten steel to obtain a slab, heating the slab and rolling it to obtain the extra-thick high-toughness low-alloy hot-rolled coil also includes: after the rolling treatment, the extra-thick high-toughness low-alloy hot-rolled coil is obtained by coiling, and the coiling temperature is 550-610°C.

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

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

[0081] In order to facilitate those skilled in the art to further understand the present invention, examples are given below:

[0082] Embodiment 1:

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

[0084] The composition of the molten steel in the tundish is: 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%, and the rest is iron and unavoidable elements.

[0085] The molten iron is subjected to KR desulfurization treatment, and the S content of the molten iron entering the converter is 0.002%; the molten iron entering the converter is 1310℃, the molten iron ratio is 82%, and the top and bottom double-blowing converter is used for primary smelting. The end point control of steel tapping is C: 0.04%, P: 0.010%, etc., and the slag blocking and slag retaining steel tapping operation is adopted.

[0086] LF refining white slag operation, slag basicity R2 is controlled at 5.0, molten steel composition is adjusted appropriately, calcium treatment is carried out to modify inclusions, molten steel Ca content is 0.0015% ~ 0.0030%, micro-stirring is carried out for 8 minutes, and the casting is carried out 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 soft pressure at the end of solidification is 4.5mm, and a 230mm thick ingot is obtained. The center segregation and center porosity of the slab are C1.0, without middle cracks, triangular cracks, etc. After the slab is cast, it is put into the heating furnace at an interval of 15h to improve the quality of the slab such as segregation.

[0088] After heating, the ingot is descaled, rolled, finished and coiled to obtain a super thick, high toughness, low alloy hot rolled coil. The heating furnace temperature is 1170-1220℃, the rolling temperature is 972℃, the finishing temperature is 820℃~850℃, the finishing rolling speed is 1.85m / min, and after finishing rolling, ultra-fast cooling + laminar cooling is performed, the cooling rate is 25° / s, and the CT coiling temperature is 606℃.

[0089] Embodiment 2:

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

[0091] S1. Composition of molten steel in the middle package: 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 rest are iron and unavoidable elements.

[0092] The molten iron is subjected to KR desulfurization treatment, and the S content of the molten iron entering the converter is 0.005%; the molten iron entering the converter is 1280℃, the molten iron ratio is 85%, and the top and bottom double-blowing converter is used for primary smelting. The end point control of steel tapping is C: 0.04%, P: 0.007%, etc., and the slag blocking and slag retaining steel tapping operation is adopted.

[0093] LF refining white slag operation, slag basicity R2 is controlled at 4.8, molten steel composition is adjusted appropriately, calcium treatment is carried out to modify inclusions, the Ca content of the molten steel is retained at 0.0022%, micro-stirring is carried out for 10 minutes, and the casting is carried out at the appropriate temperature.

[0094] The time from LF molten steel leaving the station to continuous casting was controlled at 28 minutes, the casting superheat was 15°C, the casting speed was controlled at 1.20m / min, and the dynamic soft pressure at the end of solidification was 4.5mm, and a 230mm thick ingot was obtained. The center segregation and center looseness of the slab were C1.0, without middle cracks, triangular cracks, etc. After the slab was cast, it was put into the heating furnace at an interval of 13h to improve the quality of the slab such as segregation.

[0095] After heating, the ingot is descaled, rolled, finished and coiled to obtain a super thick, high toughness, low alloy hot rolled coil. The heating furnace temperature is 1180-1220℃, the rolling temperature is 952℃, the finishing temperature is 820℃~850℃, the finishing rolling speed is 1.85m / min, and after finishing rolling, ultra-fast cooling + laminar cooling is performed, the cooling rate is 28° / s, and the CT coiling temperature is 555℃.

[0096] Analysis example 1

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

[0098] Table 1: Mechanical properties data

[0099]

[0100] The impact energy performance of the extra-thick hot-rolled coils obtained in Example 1 and Example 2 is shown in Table 2:

[0101] Table 2: Impact energy test data

[0102]

[0103]

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

[0105] Table 3: Metallographic structure information table

[0106]

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

[0108] The surface metallographic structure of the extra thick hot rolled coil obtained in Example 2 is shown in FIG. Figure 2 (a) shows the core metallographic structure diagram. Figure 2 (b) as shown.

[0109] The above technical solutions of the present invention are only preferred embodiments of the present invention, and the patent scope of the present invention is not limited thereto. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for manufacturing a 355MPa ultra-thick high-toughness low-alloy hot-rolled coil, characterized in that: Includes steps: The molten steel is continuously cast to obtain a slab, and the slab is heated and then rolled to obtain the ultra-thick, high-toughness, low-alloy hot-rolled coil; The chemical composition of the molten steel includes, by mass fraction, 0.05wt%≤C≤0.08wt%, 0.10t%≤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 rest is iron and other unavoidable impurities; The thickness of the ultra-thick high-toughness low-alloy hot-rolled coil is not less than 25 mm; During the continuous casting process, the casting superheat is 10-25° C., the casting speed is 1.10-1.30 m / min, and the dynamic light pressure is 4.5 mm at the end of solidification.

2. The manufacturing method according to claim 1, characterized in that: The rolling process includes initial rolling and finishing rolling. The rolling temperature of the initial rolling does not exceed 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 ratio during the finish rolling process is not less than 50%.

4. The manufacturing method according to claim 1, characterized in that: The step of continuously casting the molten steel to obtain a slab, heating the slab and rolling it to obtain the extra-thick high-toughness low-alloy hot-rolled coil also includes: after the rolling treatment, the extra-thick high-toughness low-alloy hot-rolled coil is obtained, and the coiling temperature is 550-610°C.

5. The manufacturing method according to claim 1, characterized in that: In the step of heating the slab and subjecting it to rolling treatment to obtain the extra-thick high-toughness low-alloy hot-rolled coil, the furnace temperature of the heated slab is 1170-1220°C.

6. The manufacturing method according to any one of claims 1 to 5, characterized in that: The preparation of the molten steel comprises the steps of: The molten iron is desulfurized and then fed into a converter, and 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%.

7. The manufacturing method according to claim 6, characterized in that: In the step of feeding the molten iron into the converter after desulfurization, the molten iron ratio of the molten iron into the converter is not less than 75%, the carbon content of the molten steel tapped 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 is controlled to be 4-6, the Ca content in the molten steel is controlled to be 15-30ppm, micro-stirring is performed for 6-10 minutes, and the steel is cast at a suitable temperature.

9. A 355Mpa ultra-thick high-toughness low-alloy hot-rolled coil, characterized in that: The product is produced by the production method according to any one of claims 1 to 8.

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

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