Low-cost hot-rolled weather-resistant steel plate for container and preparation method thereof

Abstract

The invention discloses a low-cost hot-rolled weather-resistant steel plate for a container and a preparation method of the low-cost hot-rolled weather-resistant steel plate and belongs to the technical field of hot continuous rolling plate strip production. The hot-rolled weather-resistant steel plate comprises the following chemical components in percentage by weight: 0.06 to 0.08 percent of C, 0.20 to 0.30 percent of Si, 0.55 to 0.65 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.008 percent of S, 0.30 to 0.40 percent of Cr, 0.20 to 0.30 percent of Cu, 0.050 to 0.065 percent of Ti, 0.010 to 0.045 percent of Als, less than or equal to 0.0050 percent of N and the balance of Fe and impurities. According to the invention, Ti microalloying component design is combined with reasonable production process design, so that stable production and structure property control of thin products are ensured, and the problem that the alloy cost and the production cost of the existing hot-rolled weather-resistant steel plate are relatively high can be effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled plate and strip production, and specifically relates to a low-cost hot-rolled weathering steel plate for containers and a preparation method thereof. Background Art

[0002] Weathering steel is a type of low-alloy steel with good corrosion resistance in the atmosphere. Through a large amount of research at home and abroad, it is now generally believed that after long-term exposure to the atmosphere, a layer of dense and well-adhesive oxidation products will be generated on the surface of weathering steel to isolate the steel matrix from external corrosive substances, thereby significantly improving the corrosion resistance of weathering steel.

[0003] In order to achieve cost reduction, efficiency improvement and lightweight application, the container manufacturing industry has continuously upgraded its requirements for weathering steel for containers. It not only requires the material to have high strength to achieve high-strength thinning, but also requires the material to have a low production cost to reduce procurement costs, thereby further increasing profits.

[0004] CN109338212A discloses a thin-gauge weathering steel and method with a yield strength ≥550MPa produced by a short process. Precious metal elements Ni (0.15-0.40%) and Nb (0.02-0.06%) are added to the steel, and the Mn element content is relatively high (0.7-1.3%), resulting in a higher alloy cost for the product.

[0005] CN115976396A discloses a high-strength, corrosion-resistant hot-rolled steel strip Q550NQR1 for containers and a production method thereof. Precious metal Ni elements (0.20-0.35%) are added to the steel, and the content of Mn (0.75-0.80%), Cr (0.50-0.55%), and Cu (0.35-0.50%) elements is relatively high, which significantly increases the alloy cost of the product.

[0006] CN115679190A discloses a hot-rolled weathering steel plate and a manufacturing method thereof. Precious metal elements such as Ni (0.12-0.20%) and Nb (0.01-0.02%) are added to the steel, and the contents of Ca (0.001-0.006%) and B (0.0005-0.003%) need to be controlled. The alloy composition of the product is complex. Laminar cooling adopts two-stage cooling. The cooling rate of the first stage after rolling is ≥50°C / s, the intermediate cooling temperature is 630-670°C and the cooling is controlled for 3-5s, and then the cooling is performed at a cooling rate of 5-15°C / s. The cooling process is complex and the operation is difficult. Summary of the invention

[0007] The technical problem to be solved by the present invention is the high alloy cost and production cost of the existing hot-rolled weathering steel plates.

[0008] The technical solution adopted by the present invention to solve the technical problem is: the present invention provides a low-cost hot-rolled weathering steel plate for containers, the chemical composition of the hot-rolled weathering steel plate is as follows by weight percentage: C 0.06-0.08%, Si 0.20-0.30%, Mn0.55-0.65%, P≤0.020%, S≤0.008%, Cr 0.30-0.40%, Cu 0.20-0.30%, Ti 0.050-0.065%, Als0.010-0.045%, N≤0.0050%, and the balance is Fe and unavoidable impurities.

[0009] The yield strength of the hot-rolled weathering steel plate is ≥550MPa, the tensile strength is ≥600MPa, the elongation after fracture is ≥22%, and the 180° bending test D=a.

[0010] The thickness of the hot-rolled weathering steel plate is 1.5 to 6.0 mm.

[0011] The metallographic structure of the hot-rolled weathering steel plate is polygonal ferrite + a small amount of pearlite; the volume fraction thereof is 90-95% polygonal ferrite and 5-10% pearlite.

[0012] The present invention also provides a method for preparing the above-mentioned low-cost hot-rolled weathering steel plate for containers: smelting slabs according to the chemical composition of the hot-rolled weathering steel plates, and then heating, rough rolling, finish rolling, laminar cooling and coiling the slabs in sequence to obtain the low-cost hot-rolled weathering steel plates for containers.

[0013] Furthermore, the slab is heated by hot delivery and hot loading, the heating temperature is 1240-1280° C., and the heating time is 130-230 min.

[0014] Furthermore, the rough rolling process is performed through 6 rough rolling passes, and the deformation amount of each pass is ≥ 18%;

[0015] When the finished product thickness δ is 1.5≤δ<2.5mm, the intermediate billet thickness is controlled to be 38~42mm;

[0016] When the finished product thickness δ is 2.5≤δ≤6.0mm, the intermediate billet thickness is controlled to be 42-46mm.

[0017] Furthermore, the finishing rolling process is performed through 7 finishing rolling passes;

[0018] When the finished product thickness δ is 1.5≤δ<2.5mm, the final rolling temperature is controlled to be 860~900℃;

[0019] When the finished product thickness δ is 2.5≤δ≤6.0mm, the final rolling temperature is controlled to be 840~880℃.

[0020] Furthermore, the laminar flow process adopts a front-stage cooling mode, and the cooling rate is ≥40°C / s.

[0021] Furthermore, when the finished product thickness δ is 1.5≤δ<2.5mm, the coiling temperature is controlled to be 600-640°C.

[0022] Furthermore, when the finished product thickness δ is 2.5≤δ≤6.0 mm, the coiling temperature is controlled to be 580-620°C.

[0023] The beneficial effects of the present invention are as follows: the present invention effectively reduces the alloy cost by not adding the Ni element, and at the same time ensures the performance and avoids the occurrence of "copper brittleness" defects through a reasonable heating system design; exerts the effects of fine grain strengthening and precipitation strengthening through Ti microalloying, and regulates the microstructure and performance in combination with a controlled rolling and controlled cooling process, so that the product achieves high strength and excellent plasticity without adding precious metal elements such as Nb and reducing the Mn element content; and ensures the stable production of thin-gauge products and the control of microstructure and performance through a reasonable production process design.

[0024] The present invention adopts Ti microalloying composition design, does not add precious alloys, and reduces the alloy cost of steel; the production method of the product is simple and the production cost is low, the thickness is 1.5-6.0 mm, the metallographic structure is polygonal ferrite (90-95%) + a small amount of pearlite (5-10%), the yield strength is ≥550MPa, the tensile strength is ≥600MPa, the elongation after fracture is ≥22%, and the 180° bending test D=a, and the product can be applied to the field of container manufacturing to achieve good lightweight application and cost reduction effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the metallographic structure diagram of the low-cost hot-rolled weathering steel plate for containers prepared in Example 1. DETAILED DESCRIPTION

[0026] The technical solution of the present invention can be specifically implemented in the following manner.

[0027] The chemical composition of the hot-rolled weathering steel plate for low-cost containers is as follows by weight: C 0.06-0.08%, Si0.20-0.30%, Mn 0.55-0.65%, P≤0.020%, S≤0.008%, Cr 0.30-0.40%, Cu 0.20-0.30%, Ti0.050-0.065%, Als 0.010-0.045%, N≤0.0050%, and the balance is Fe and unavoidable impurities.

[0028] The composition design principle of the low-cost hot-rolled weathering steel plate for containers according to the present invention is as follows.

[0029] Carbon: Carbon is an effective strengthening element in steel. It can be dissolved into the matrix to play a role in solid solution strengthening, and can combine with titanium to form carbide precipitation particles, which play a role in fine grain strengthening and precipitation strengthening. Therefore, increasing the carbon content is beneficial to improving strength. However, too high a carbon content will increase the carbon equivalent of the steel and reduce weldability; at the same time, it is easy to form a segregation band in the center of the steel plate, and when the cooling rate is high, it is easy to form a martensitic structure at the segregation band, resulting in reduced bending performance, impact performance, and forming performance. Therefore, the value range of C in the present invention is set to 0.06-0.08%.

[0030] Silicon: Silicon can be dissolved in ferrite and austenite to increase the hardness and strength of steel, which is beneficial to refine the rust layer structure and reduce the overall corrosion rate of steel. However, too high a content will reduce the plasticity and toughness of the steel and make it difficult to remove scale during rolling. Therefore, the value range of Si in the present invention is set to 0.20-0.30%.

[0031] Manganese: Manganese has a strong solid solution strengthening effect, can significantly reduce the phase transition temperature of steel, refine the microstructure of steel, and is an important strengthening element. However, when the manganese content is too high, the continuous casting process is prone to cracks in the ingot, and may cause component segregation in the core of the steel plate, resulting in reduced bending performance, impact performance, and forming performance, while increasing production costs. Therefore, the value range of Mn in the present invention is set to 0.55-0.65%.

[0032] Phosphorus: Although phosphorus has a strong solid solution strengthening effect and can effectively improve the atmospheric corrosion resistance of steel with low cost, excessive phosphorus content will significantly reduce the plasticity and low-temperature toughness of steel. Therefore, the value range of P in the present invention is set to P≤0.020%.

[0033] Sulfur: Sulfur will have an adverse effect on the structure and properties of steel plates. Too high a sulfur content will increase the hot brittleness tendency of steel. At the same time, sulfur will form sulfide inclusions that deteriorate the properties of steel. Therefore, the value range of S in the present invention is set to S≤0.008%.

[0034] Chromium: Chromium has a significant effect on improving the passivation ability of steel, and can promote the formation of a dense passivation film or protective rust layer on the steel surface. Its enrichment in the rust layer can effectively improve the selective permeability of the rust layer to corrosive media; however, too high a chromium content will increase production costs, and at a high cooling rate, it is easy to cause martensite structure to be produced, which reduces the plasticity and toughness of the steel. Therefore, the value range of Cr in the present invention is set to 0.30-0.40%.

[0035] Copper: Copper added to steel is conducive to forming a dense, well-adhesive amorphous oxide (hydrocarbon oxide) protective layer on the surface of the steel, which has a significant corrosion resistance effect; in addition, copper and sulfur form insoluble sulfides, thereby offsetting the harmful effects of S on the corrosion resistance of steel; however, when the copper content is too high, due to the low melting point of copper, which is lower than the heating temperature of the steel billet, the precipitated copper is in liquid and aggregates at the austenite grain boundary. When the precipitated copper content reaches a certain level, it is easy to produce cracks during heating or hot rolling, that is, "copper brittleness" defects; in addition, according to the calculation formula of the atmospheric corrosion resistance index I, too little or too much copper content will reduce the calculated value of I. Therefore, the value range of Cu in the present invention is set to 0.20-0.30%.

[0036] Titanium and nitrogen: Titanium combined with carbon and nitrogen can form tiny carbonitrides to pin grain boundaries, delay recrystallization, inhibit the growth of austenite grains, and produce fine grain strengthening and precipitation strengthening effects; increasing the titanium content can increase the volume fraction of its carbonitrides and enhance the fine grain strengthening and precipitation strengthening effects; increasing the nitrogen content in the steel is conducive to promoting the precipitation of the second phase of titanium; but too high a titanium or nitrogen content is likely to form large-sized TiN, resulting in reduced bending performance, impact performance, and forming performance, and too high a nitrogen content will increase the aging tendency and cold brittleness and hot brittleness of the steel, and damage the welding performance and cold bending performance of the steel; therefore, the value range of Ti in the present invention is set to 0.050-0.65%, and the value range of N is set to ≤0.0050%.

[0037] Aluminum: Aluminum is added to steel to deoxidize and improve the quality of steel. However, if the aluminum content is too high, its nitrogen oxides are easily precipitated at the austenite grain boundaries, causing cracks in the casting. Therefore, the value range of Als in the present invention is set to 0.010-0.045%.

[0038] The preparation method of the above-mentioned low-cost hot-rolled weathering steel plate for container is to smelt the composition of the low-cost hot-rolled weathering steel plate for container as described above into slab, and then heat, rough roll, finish roll, laminar cool and coil the slab in sequence to obtain the low-cost hot-rolled weathering steel plate for container.

[0039] The functions and mechanisms of the main processes in the method for preparing the low-cost hot-rolled weathering steel plate for containers described in the present invention are as follows.

[0040] Further specifically, in the heating step, the slab is heated in a regenerative heating furnace. The purpose of heating the slab is to homogenize the as-cast structure and component segregation, and to dissolve the alloy elements. The low-cost hot-rolled weathering steel plate for containers according to the present invention has many types of alloy elements and a high content, and the precipitate solution temperature of Ti is relatively high, so the heating process requires sufficient temperature and time; in addition, since the temperature of thin-gauge steel plates drops rapidly during hot rolling, and the low-cost hot-rolled weathering steel plates for containers according to the present invention have a high strength, it is easy to cause a large rolling load during the finishing rolling process, so it is necessary to increase the heating temperature; but too high a heating temperature and too long a heating time will lead to coarse austenite grains, as well as problems such as burning, overheating, and overburning; at the same time, compared with traditional weathering steel, in order to reduce the alloy cost, a certain amount of Cu is added to the low-cost hot-rolled weathering steel plate for containers according to the present invention without adding Ni, and a Ni-containing copper-rich phase cannot be formed to reduce the chance of formation of a liquid copper-rich phase, so too long a heating time will lead to "copper brittleness" defects. Therefore, in the present invention, in the heating step, the casting is required to be hot transported and hot loaded, the heating temperature is set to 1240-1280° C., and the heating time is 130-230 min.

[0041] Further specific to the rough rolling step, the rough rolling needs to achieve sufficient deformation to ensure austenite recrystallization, refine austenite grains, and prevent the appearance of mixed crystal structure. If the thickness of the intermediate billet is too small, the deformation of the finishing rolling may be insufficient; if the thickness of the intermediate billet is too large, the deformation of the rough rolling may be insufficient, and at the same time, it will promote the strain-induced phase transformation precipitation during the finishing rolling process and after the finishing rolling, resulting in the consumption of Ti elements, etc., thereby weakening the supersaturated precipitation in the coiling stage, resulting in a reduction in the final precipitation strengthening effect; in addition, when the thickness of the finished product is small, the temperature drop of the strip during the finishing rolling process is faster, and the thickness of the intermediate billet can be appropriately reduced to avoid excessive finishing load while ensuring sufficient finishing deformation. Therefore, the present invention sets the rough rolling step to undergo 6 rough rolling passes, and the deformation of each pass is ≥18%; when the thickness of the finished product is 1.5~<2.5mm, the thickness of the intermediate billet is 38~42mm; when the thickness of the finished product is 2.5~6.0mm, the thickness of the intermediate billet is 42~46mm.

[0042] To be more specific, in the finishing step, if the final rolling temperature is too low, there is a risk of rolling in the two-phase region in the last few stands of finishing rolling, especially because the temperature of the strip in the width direction is different, and its edge temperature is often lower. As the thickness of the strip decreases, the temperature of the strip edge is faster during the finishing rolling process. When the strip is rolled in the last few stands of finishing rolling, the temperature is easily reduced to the austenite-ferrite two-phase region, resulting in mixed crystal structure and poor product comprehensive performance; if the final rolling temperature is too high, the deformation of the non-recrystallized zone rolled in the last few stands of finishing rolling is insufficient, which is not conducive to the final organization refinement. Therefore, in the present invention, it is set that after 7 passes of finishing rolling in the finishing step, when the finished product thickness is 1.5~<2.5mm, the final rolling temperature is 860~900℃; when the finished product thickness is 2.5~6.0mm, the final rolling temperature is 840~880℃.

[0043] To be more specific, in the laminar cooling step, the front-stage cooling mode is adopted and the cooling rate is controlled to be ≥40°C / s, which can achieve a larger degree of supercooling and thus refine the final structure. The use of a larger cooling rate can improve the core banded structure to a certain extent, while increasing the precipitation driving force of the Ti element, thereby precipitating fine and dispersed second phase particles to enhance the precipitation strengthening effect.

[0044] To be more specific, in the coiling step, if the coiling temperature is too low, the cooling rate during the cooling process will be too high, resulting in the formation of martensite structure, resulting in reduced plasticity and toughness, and at the same time, the diffusion rate of Ti and C elements will be slowed down, resulting in their precipitation being blocked, resulting in reduced precipitation strengthening effect; if the coiling temperature is too high, the grains and second phase particles will be coarse, resulting in reduced strength, plasticity and toughness. Therefore, in the present invention, when the thickness of the finished product is 1.5 to <2.5 mm, the coiling temperature is set to 600 to 640°C; when the thickness of the finished product is 2.5 to 6.0 mm, the coiling temperature is set to 580 to 620°C.

[0045] The technical solution and effects of the present invention are further illustrated below through practical examples.

[0046] Example

[0047] The yield strength, tensile strength and elongation after fracture of the hot-rolled weathering steel plate described in this embodiment are tested according to "Tensile Test of Metallic Materials Part 1: Room Temperature Test Method" (GB / T 228.1); the bending performance is tested according to "Bending Test Method for Metallic Materials" (GB / T 232).

[0048] The present invention provides three groups of embodiments 1 to 3 for preparing low-cost hot-rolled weathering steel plates for containers by the method of the present invention, and the weathering steel and its preparation method described in the existing public technology are used as comparative examples 1 to 3; wherein, comparative example 1 specifically refers to embodiment 1 in "Thin-gauge weathering steel with yield strength ≥550MPa produced by short process and method" (CN109338212A), comparative example 2 specifically refers to embodiment 2 in "A hot-rolled steel strip Q550NQR1 for high-strength corrosion-resistant containers and its production method" (CN115976396A), and comparative example 3 specifically refers to embodiment 1 in "A hot-rolled weathering steel plate and its manufacturing method" (CN115679190A).

[0049] The chemical compositions of the hot-rolled weathering steels of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1, with the remainder being Fe and unavoidable impurities.

[0050] Table 1 Chemical composition (by mass percentage, %)

[0051] category Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 C 0.07 0.08 0.08 0.04 0.07 0.052 Si 0.27 0.27 0.28 0.15 0.28 0.172 Mn 0.60 0.58 0.60 1.20 0.77 0.49 P 0.012 0.014 0.013 0.018 0.013 0.0047 S 0.003 0.004 0.005 0.005 0.004 0.0022 Cr 0.33 0.31 0.34 0.35 0.51 0.344 Ni - - - 0.20 0.28 0.124 Cu 0.24 0.23 0.24 0.15 0.41 0.215 Nb - - - 0.02 - 0.012 Ti 0.058 0.060 0.065 0.060 0.060 0.044 B - - - - - 0.0024 Als 0.042 0.045 0.043 0.050 0.26 - Al - - - - - 0.039 O - - - - 0.0032 - N 0.0041 0.0030 0.044 0.007 0.0045 0.0033 Ca - - - - - 0.0015

[0052] Example 1

[0053] The composition shown in Table 1 is smelted into slabs by conventional methods, and the smelted slabs are further processed, and heating, rough rolling, finishing rolling, laminar cooling and coiling are performed in sequence. The specific processing technology is as follows: the heating temperature is 1275°C, and the heating time is 200min; after 6 rough rolling passes, the deformation of each pass is 18%, 23%, 24%, 26%, 24%, 26%, and the thickness of the intermediate slab is 40mm; after 7 finishing rolling passes, the final rolling temperature is 880-900°C; the front cooling mode is adopted, the cooling rate is 65°C / s, and the coiling temperature is 610-630°C.

[0054] The low-cost hot-rolled weathering steel plate for container is obtained, and its specific properties are shown in Table 2; the metallographic structure is composed of polygonal ferrite (92%) + pearlite (8%), such as Figure 1 shown.

[0055] Example 2

[0056] The composition shown in Table 1 is smelted into slabs by conventional methods, and the smelted slabs are further processed, and heating, rough rolling, finishing rolling, laminar cooling and coiling are performed in sequence. The specific processing technology is as follows: the heating temperature is 1260°C, and the heating time is 188min; after 6 rough rolling passes, the deformation of each pass is 18%, 22%, 23%, 25%, 25%, 20% respectively, and the intermediate billet thickness is 44mm; after 7 finishing rolling passes, the final rolling temperature is 860-880°C; the front cooling mode is adopted, the cooling rate is 50°C / s, and the coiling temperature is 580-610°C.

[0057] A low-cost hot-rolled weathering steel plate for containers was obtained, and its specific properties are shown in Table 2; the metallographic structure consists of polygonal ferrite (96%) + pearlite (4%).

[0058] Example 3

[0059] The composition shown in Table 1 is smelted into slabs by conventional methods, and the smelted slabs are further processed, and heating, rough rolling, finishing rolling, laminar cooling and coiling are performed in sequence. The specific processing technology is as follows: the heating temperature is 1255°C, and the heating time is 179min; after 6 rough rolling passes, the deformation of each pass is 18%, 23%, 22%, 25%, 25%, 21% respectively, and the intermediate billet thickness is 44mm; after 7 finishing rolling passes, the final rolling temperature is 850-880°C; the front cooling mode is adopted, the cooling rate is 45°C / s, and the coiling temperature is 600-620°C.

[0060] A low-cost hot-rolled weathering steel plate for containers was obtained, and its specific properties are shown in Table 2; the metallographic structure consists of polygonal ferrite (93%) + pearlite (7%).

[0061] Comparative Example 1

[0062] According to the composition shown in Table 1, thin slab continuous casting is carried out after conventional smelting, the temperature of molten steel in the tundish is controlled at 1545-1555℃, the thickness of thin slab is controlled at 70mm, and the casting machine pulling speed is 3.7m / min; the thin slab is heated evenly, the furnace temperature is controlled at 1180℃, and the furnace time is 40min; two consecutive descaling passes are carried out, and the distance from the nozzle of the upper manifold to the surface of the thin slab in the first and second descaling passes is controlled to be 55-70mm respectively; seven finishing rolling passes are carried out, and the final rolling temperature is controlled at 910℃; the automatic control function of the tail roll gap of the strip steel is put into use in the finishing rolling unit; the correction coefficient of the predicted rolling force of the F7 frame head is adjusted to 0.90, and the correction delay is 100 milliseconds; the short stroke of the side guide plate head of the finishing rolling frame F1-F4 is controlled At positive 45-55mm, the short stroke in the middle and tail is reduced to positive 10-15mm; the rolling reduction rate of the F7 stand is controlled at 8%; when the tail of the strip reaches the F7 stand, the running speed of the strip is controlled at 6-9.8m / s; laminar cooling to the coiling temperature, it adopts the method of opening a header every other header for sparse spray cooling; the nozzles on each side of the laminar flow are controlled to open for spray cooling after the strip head runs for more than 3 meters; during this period, the hysteresis rate of the first group of laminar rollers is controlled at 45%, and then gradually reduced at an equal rate until the hysteresis rate of the last group of rollers is 25%; coiling is carried out, and the coiling temperature is controlled to be 580℃; the coiling tension control is divided into three stages: the first stage adopts constant tension control, that is, at 45N / mm 2 A force value is selected within the range for winding; the second stage adopts constant torque control. When the coil diameter reaches 1.2m during the winding process, the tension begins to be gradually reduced until it is reduced to 30-35N / mm at the end of the second stage.2 The third stage adopts tail tension reduction control. The coiling tension starts to decrease after the F1 frame throws steel and gradually decreases to 20N / mm when the F7 frame throws steel. 2 ; for leveling.

[0063] The obtained thin-gauge weathering steel has a yield strength ≥550MPa, and its specific properties are shown in Table 2.

[0064] Comparative Example 2

[0065] According to the composition shown in Table 1, self-produced scrap steel + desulfurized hot metal are used, and the refined S content is less than 0.013%, which creates conditions for refining and rapid desulfurization to the required value; then converter smelting is carried out, the converter tapping temperature is controlled at 1630-1650°C, single slag process is used for smelting, low-carbon ferromanganese and micro-carbon aluminum-iron alloy are used for deoxidation and alloying, and the converter slag layer thickness is less than 40mm; the smelting time is 40-45 minutes, and the tapping time is more than 5 minutes. In order to stabilize the production sequence, this steel is produced with copper plate and nickel plate alloy are added in the converter; currently, due to the heavy weight of the raw copper plate in storage and the narrow control requirements for Cu content, copper plates are used in production with scrap oxygen lance copper heads; the amount of lime added in the refining process is 8-10kg / t steel, the refining soft blowing time is 5-10 minutes, and the superheat of the molten steel is 22-28℃; deoxidized aluminum is added once in the refining process to ensure that the inclusions have sufficient time to float; during continuous casting, special protective slag for weathering steel is used, which contains: SiO231.06%, CaO 32.85%, Al2O34.88%, Na2O 8.48%, K2O0.28%; density 0.75g / ml, melting point 1101℃, viscosity 1.49Poise, middle package temperature 1550~1560℃, except for the tail billet, the furnace temperature meets the requirements of the trial production plan (990~1000℃), the middle package composition meets the trial production standard requirements, and the average pulling speed is 4.0~4.1m / min; the atmosphere in the heating furnace is strictly controlled to be a reducing atmosphere, and the heating section heating rate is controlled to 12~15℃ / min, the furnace outlet temperature should be controlled between 1089℃ to reduce the enrichment of copper at the grain boundary and the surface of the billet; in order to uniform the plate shape and properties, refine the austenite grains and avoid mixed crystals, the continuous rolling mill F1 rolling reduction is 55%, the F2 rolling reduction is 47%, the final rolling temperature is set to 890℃, the cooling adopts front concentrated laminar cooling, the cooling water temperature is 24~28℃, and the coiling temperature is 583℃.

[0066] 700MPa grade CSP short process hot-rolled high weather-resistant container steel was produced. Its specific properties are shown in Table 2. The metallographic structure is ferrite + pearlite.

[0067] Comparative Example 3

[0068] According to the composition shown in Table 1, steelmaking and casting were carried out in a 500kg vacuum induction furnace in the laboratory. During the steelmaking process, LF refining process was adopted, and the alloy was fine-tuned according to the target composition; the heating furnace was a reducing atmosphere, the ingot was heated, and the ingot discharge temperature was controlled at 1254℃; the hot rolling controlled the end temperature of rough rolling to 1095℃, and the cumulative reduction rate of the rough rolling stage was 87.86%; the start temperature of finishing rolling was controlled to 999℃, and the end temperature of finishing rolling was controlled to 874℃; two-stage cooling was adopted, the first cooling rate after rolling was 51℃ / s, the intermediate stop cooling temperature was 664℃, and air cooling was performed for 3s, and then cooled to 568℃ at a cooling rate of 10.9℃ / s for coiling; air cooling was performed to room temperature.

[0069] The hot-rolled weathering steel plate was obtained, and its specific properties are shown in Table 2. The metallographic structure is ferrite.

[0070] Table 2 Performance test results

[0071] category Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Thickness / mm 1.5 4.5 6.0 4.0 4.5 1.5 Yield strength / MPa 564 569 574 570 585 466 Tensile strength / MPa 628 625 642 635 645 608 Elongation after break / % 25.0 28.0 30.0 22.0 25.5 23.8 180° bending test D=a qualified D=a qualified D=a qualified D=1.5aPass - D=0Pass

[0072] In combination with the preparation methods of the embodiments and comparative examples, according to the chemical composition in Table 1 and the performance test results of the embodiments and comparative examples obtained in Table 2, it can be seen that: the mechanical properties of comparative examples 1 and 2 are equivalent to those of embodiments 1 to 3, the strength of comparative example 3 is lower, and the comparative example adds precious metal elements Ni and Nb, and the content of Mn, Cr, and Cu elements is relatively high, which significantly increases the alloy cost of the product; at the same time, comparative example 3 needs to control the content of Ca and B elements, the alloy composition of the product is complex, and laminar cooling adopts two-stage cooling, and its cooling process is complex and difficult to operate; according to the embodiments produced by the alloy composition and key process parameters provided by the present invention, the alloy cost is low and the production method is simple, and the product has high strength and high plasticity, and has good comprehensive performance and application prospects.

Claims

1. Low-cost hot-rolled weathering steel plate for containers, characterized by: The chemical composition of the hot-rolled weathering steel plate is C 0.06-0.08%, Si 0.20-0.30%, Mn 0.55-0.65%, P≤0.020%, S≤0.008%, Cr 0.30-0.40%, Cu 0.20-0.30%, Ti 0.050-0.065%, Als 0.010-0.045%, N≤0.0050% by weight, and the balance is Fe and unavoidable impurities.

2. The low-cost hot-rolled weathering steel plate for container according to claim 1, characterized in that: The yield strength of the hot-rolled weathering steel plate is ≥550MPa, the tensile strength is ≥600MPa, the elongation after fracture is ≥22%, and the 180° bending test D=a.

3. The low-cost hot-rolled weathering steel plate for container according to claim 1, characterized in that: The thickness of the hot-rolled weathering steel plate is 1.5 to 6.0 mm.

4. The low-cost hot-rolled weathering steel plate for container according to claim 1, characterized in that: The metallographic structure of the hot-rolled weathering steel plate is polygonal ferrite + a small amount of pearlite; The volume fraction is 90-95% polygonal ferrite and 5-10% pearlite.

5. The method for preparing a low-cost hot-rolled weathering steel plate for a container according to any one of claims 1 to 4, characterized in that: The slab is smelted according to the chemical composition of the hot-rolled weathering steel plate, and then the slab is heated, roughly rolled, finely rolled, laminar cooled and coiled in sequence to obtain the hot-rolled weathering steel plate for low-cost containers.

6. The method for preparing low-cost hot-rolled weathering steel plate for container according to claim 5, characterized in that: The slab is heated by hot delivery and hot loading, the heating temperature is 1240-1280° C., and the heating time is 130-230 min.

7. The method for preparing low-cost hot-rolled weathering steel plate for container according to claim 5, characterized in that: The rough rolling process is performed by 6 rough rolling passes, and the deformation amount of each pass is ≥18%; When the finished product thickness δ is 1.5≤δ<2.5mm, the intermediate billet thickness is controlled to be 38~42mm; When the finished product thickness δ is 2.5≤δ≤6.0mm, the intermediate billet thickness is controlled to be 42-46mm.

8. The method for preparing low-cost hot-rolled weathering steel plate for container according to claim 5, characterized in that: The finishing rolling process is performed through 7 passes of finishing rolling; When the finished product thickness δ is 1.5≤δ<2.5mm, the final rolling temperature is controlled to be 860~900℃; When the finished product thickness δ is 2.5≤δ≤6.0mm, the final rolling temperature is controlled to be 840~880℃.

9. The method for preparing a low-cost hot-rolled weathering steel plate for a container according to claim 5, characterized in that: The laminar flow process adopts a front-stage cooling mode, and the cooling rate is ≥40°C / s.

10. The method for preparing low-cost hot-rolled weathering steel plate for container according to claim 5, characterized in that: When the finished product thickness δ is 1.5≤δ<2.5mm, the coiling temperature is controlled to be 600~640℃; When the finished product thickness δ is 2.5≤δ≤6.0mm, the coiling temperature is controlled to be 580~620℃.

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