A high-strength hot-rolled coil for thin and wide commercial vehicle tank and a manufacturing method thereof

Abstract

The invention relates to a high-strength steel for hot-rolled commercial vehicle tank body, which comprises the following components by weight percentage: C: ≤0.100%, Si: ≤0.30%, Mn: ≤1.40, S: ≤0.005%, P: ≤0.008%, Al: ≥0.015%, Nb: 0.010-0.040%, Ti: 0.050-0.090%, N: ≤0.0040%, B≥0.0015%, and the rest is Fe and other inevitable impurities. The present invention also relates to a method for preparing a high-strength steel for hot-rolled commercial vehicle tank bodies, comprising molten iron pretreatment, converter refining, continuous casting process, rough rolling and finishing rolling, controlled cooling, coiling, and hood annealing. The method makes full use of reasonable rolling temperature design, reasonable distribution of rolling force, reasonable edge shielding design, reasonable hood annealing and other processes in the above steps, so that the obtained high-strength steel has a width of 2000 mm and a thickness of 2.0 mm, and at the same time, the tensile strength is ≥570 MPa, the yield strength is ≥520 MPa, the elongation is ≥25%, the unevenness is ≤3 mm / m, the plate shape is good, and it meets the production requirements of commercial vehicle tank bodies.

Description

Technical Field

[0001] The invention relates to the technical field of steel materials, and in particular to a high-strength hot-rolled coil for a thin and wide commercial vehicle tank body and a manufacturing method thereof. Background Art

[0002] The automobile industry is an important force in promoting a new round of scientific and technological revolution and industrial transformation, an important support for building a strong manufacturing country, and an important pillar of the national economy. In recent years, energy shortages and environmental pollution have become prominent issues restricting the sustainable development of my country's automobile industry. As a result, automobile lightweighting has become an important research field for major car manufacturers and steel mills. As the main medium of the road transportation industry, commercial vehicles only account for 10.9% of my country's automobile ownership, but they produce 56% of road traffic carbon emissions. The lightweighting of commercial vehicles has become an irreversible trend.

[0003] Research on automobile lightweight technology has become a major mainstream in the field of modern automobile design and manufacturing. The Automobile Lightweight Technology Innovation Strategic Alliance established by the my country Society of Automotive Engineering, together with domestic steel companies, OEMs, universities and other enterprises and institutions, has started the preparation of the National Key Laboratory of Automobile Lightweight. Since the body accounts for more than 60% of the entire automobile design and manufacturing cost, and in the field of commercial vehicles, especially commercial modified vehicles, the steel used for automobile beams, tanks, and compartments accounts for more than 70% of the steel used for the body, the top priority of commercial vehicle lightweighting is the integrated preparation control and application of beams, tanks and compartments. In the past two decades, international research on the lightweighting of commercial vehicles has been in full swing. The three main paths for the development of lightweight commercial vehicle bodies are lightweight material technology, lightweight structural design and optimization technology, and new manufacturing and forming process technology. These three paths complement each other. To achieve the lightweighting of commercial vehicles, it is necessary to adopt a method that combines lightweight material replacement, structural optimization design, and manufacturing and forming technology to ensure that commercial vehicles can minimize the weight of the main components of the body under high-intensity loads.

[0004] With the promulgation of the newly revised GB1589-2016 "External Dimensions, Load and Mass Limits of Automobiles, Trailers and Automobile Trains", the overloading and over-limit phenomena of vehicles will be strictly controlled. At present, commercial tank car processing companies mainly purchase high-strength tank steel with a width of 1500mm and a thickness of ≥3mm. Under the current background of lightweight commercial vehicles, the defects of low equipment production efficiency, low personnel work efficiency, increased working hours due to many welds when welding tanks, and insufficient aesthetics are highlighted. The main problems are as follows:

[0005] 1) Thicker tank bodies increase vehicle weight and fuel consumption. The mainstream tank steel on the market is currently concentrated in the 3.0-3.5mm thickness range. Compared with the 2mm thick tank steel of this patent invention, the thickness has increased by more than 50%, resulting in a 10%-15% increase in tank body weight, increased fuel consumption, and a heavy burden on customers.

[0006] 2) The width of mainstream tank steel is 1500mm or less. For example, welding a conventional 6m tank requires four pieces of welding, which increases the working hours. At the same time, the aesthetics is greatly reduced due to the increase in welds. At the same time, it leads to low production efficiency and increased process costs.

[0007] 3) A steel company has developed high-strength tank steel with a width of 1800mm or more, but cannot guarantee the unevenness of the steel plate. The tank steel has extremely high unevenness requirements due to its special forming and welding methods (≤5mm / m. The wide high-strength tank steel produced in the same way as ordinary high-strength steel cannot meet the unevenness requirements).

[0008] Meanwhile, Chinese patent document CN111041379A discloses a steel plate for making a vehicle-mounted concrete tank and a production method thereof, wherein the chemical composition is C: 0.06-0.08%, Si: 0.10-0.20%, Mn: 1.75-1.85%, P≤0.018%, S≤0.008%, Nb: 0.060-0.070%, V: 0.015-0.030%, Ti: 0.080-0.110%, Als: 0.030-0.050%, and the balance is Fe and unavoidable impurity elements. This invention belongs to conventional tank steel, does not have the appearance of wide and thin specifications, and the lightweight effect of the whole vehicle after the tank steel is applied is not obvious, and does not have strong market competitiveness. Chinese patent document CN112108527A discloses a plate shape control method for hot-rolled high-strength mixing tank steel. The limit specifications in the test example are 6.0*1900 and 5.0*1800, which obviously do not meet the requirements of wide and thin specifications. At the same time, because the weight reduction is not obvious, it does not have the significance of large-scale promotion.

[0009] Nowadays, traditional high-strength tank steel can no longer meet the lightweight needs of commercial vehicles. The market urgently needs to find tank steel with wider width and better plate flatness to improve the production efficiency of tank truck manufacturers. Summary of the invention

[0010] In order to solve the above technical problems, the present invention provides a high-strength steel for hot-rolled commercial vehicle tank body, wherein the chemical composition and mass percentage are: C: ≤0.100%, Si: ≤0.30%, Mn: ≤1.40, S: ≤0.005%, P: ≤0.008%, Al: ≥0.015%, Nb: 0.010-0.040%, Ti: 0.050-0.090%, N: ≤0.0040%, B≥0.0015%, and the rest are Fe and other inevitable impurities.

[0011] Furthermore, in the above technical scheme, a hot-rolled high-strength steel for commercial vehicle tank body has a width ≥2000mm, a thickness of 2.0mm~3.0mm, a tensile strength ≥570MPa level, a yield strength ≥520MPa, an elongation ≥25%, and a roughness ≤3mm / m, which is mainly used for the production of commercial vehicle tank body and special tank dump trucks, etc.

[0012] Furthermore, in the above technical solution, a method for preparing high-strength steel is provided, including a steelmaking process, a hot rolling process, and a bell annealing process;

[0013] Steelmaking process:

[0014] 1. Hot metal pretreatment

[0015] Pretreatment S≤0.0030% before entering the furnace. This steel grade requires that all molten iron entering the furnace must be pretreated and desulfurized. The desulfurization process is powder spraying desulfurization, and the ratio of magnesium powder to lime powder spraying is 1:3.

[0016] 2. Converter smelting

[0017] The converter smelting adopts constant oxygen pressure and variable gun position operation, and adopts single slag method for smelting and blowing. The oxygen supply time is controlled at 14min~18min. The process adopts auxiliary gun for fixed oxygen sampling to ensure the one-time hit rate of endpoint carbon and temperature.

[0018] Slag blocking in the early stage of steel tapping: Use slag blocking mud plug; select the appropriate slag blocking mud plug according to the size of the steel tapping port after the previous steel tapping. Slag blocking mark in the later stage of steel tapping to ensure that the slag thickness of the ladle is less than 120mm. The steel tapping time is guaranteed to be 4 to 7 minutes, and the shape of the steel tapping port is controlled to avoid steel tapping dispersion. Deoxidation and alloying begin when 1 / 5 of the steel is tapped, and the alloy must be added when 4 / 5 is tapped. Deoxidation is carried out by adding ferrosilicon and ferroaluminum. First add a certain amount of 650kg ferrosilicon, then add high manganese, and the ferroaluminum must be added after more than 1 minute.

[0019] The ladle should be purged with argon 1 minute before tapping to ensure the effect of argon blowing at the bottom of the ladle during the tapping process. The amount of argon should be controlled well. It is strictly forbidden to blow too much bottom gas, which will cause the steel liquid surface to be exposed to air inhalation and secondary oxidation. After tapping, soft argon should be blown for 3 to 5 minutes, and then the temperature should be measured and component samples should be taken.

[0020] 3. Refining process

[0021] The refining method adopted is the ladle refining furnace (LADLE FURNACE, referred to as LF furnace). The temperature requirement in front of the LF furnace is 1565-1575℃. According to the S content of the ladle, the amount of lime added is controlled at 200-500kg. If the sulfur exceeds the enterprise standard before treatment, the amount of lime added can be appropriately increased. Add a small amount of CaO and Al according to the arc buried situation and the color of the flue gas. Control the electrode arc buried during the power supply process and close the furnace cover opening. The first power supply is controlled at 6-10 minutes. After the power supply is completed, strong argon blowing and stirring are used for 2-3 minutes of desulfurization (if the ladle S meets the target requirements, strong argon blowing and stirring are not performed), and slag samples are taken to check the slag color. When the slag color is light green, it is considered to be good slag formation.

[0022] According to the oxygen value before argon, aluminum deoxidation and alloying are carried out, and aluminum wire is adjusted to aluminum by 0.04%. According to the analysis results of the composition sample before argon, alloy adjustment is carried out, with emphasis on carbon, silicon, manganese, and titanium adjustment. After alloying, the temperature is adjusted to 1560-1570°C or soft argon blowing (temperature increase is prohibited during soft argon blowing). The argon blowing at the bottom of the ladle is of medium intensity or less, and the argon blowing flow rate is 200-300L / min. It is strictly forbidden to use large amount of argon blowing, and it is strictly forbidden for molten steel to be exposed to air. Strengthen the furnace cover seal, control the furnace mouth micro-positive pressure, and the LF furnace control increase [N] is not greater than 7ppm.

[0023] The aluminum component adjustment must be completed 15 minutes before the end of the treatment, and the soft argon blowing must be ≥10 minutes before the end of the treatment. The LF leaving station temperature of a normal furnace is controlled at 1563-1573℃.

[0024] 4. Continuous casting process

[0025] Protective pouring is performed throughout the entire process. Argon is used to purge the middle ladle before pouring. No molten steel is exposed during the pouring process. The shroud must be cleaned after each furnace is poured. The shroud must remain vertical during the pouring process. The immersion depth of the shroud of the large ladle is guaranteed to be 200-250mm. The slag detection is used to control the slag amount of the large ladle to avoid slag in the large ladle.

[0026] The secondary cooling section of this series of steel grades adopts weak cooling mode and light reduction mode. The drawing speed is controlled according to the cross-section and production rhythm to ensure constant speed steel casting.

[0027] 2. Hot rolling

[0028] 1. Heating

[0029] The continuous casting billet is hot-delivered and hot-charged, and the surface quality of the billet is strictly checked when loading into the furnace. Since the steel contains Ti, in order to effectively precipitate TiC in the steel and refine the grains, the heating temperature is ≥1200℃, the heating time is ≥150min, and the furnace temperature is 1200℃~1250℃.

[0030] 2. Rough rolling

[0031] The slab is heated to the required temperature and then taken out of the furnace after being kept warm. After being taken out of the furnace and before entering each rough rolling mill, high-pressure water dephosphorization is carried out. The rough rolling mill is equipped with width adjustment and control (AWC) and short stroke control (SSC) functions to ensure the width accuracy and surface quality requirements of the intermediate slab. The opening temperature of R1 (the first rough rolling mill) is greater than 1130℃, and the outlet temperature is 1050~1090℃; in order to remove the iron oxide scale on the surface of the steel grade, dephosphorization water is set between the rough rolling mill frames.

[0032] 3. Finish rolling

[0033] Finishing mills F1~F7 are equipped with automatic thickness control devices (AGC) to effectively control the thickness accuracy of the strip; F1~F7 use bending roll hydraulic system, F2~F4 use CVC rolls to effectively control the strip shape; cooling water between stands and rolling mill speed-up function can automatically control the final rolling temperature; two high-pressure water descaling points are set between the finishing mill stands to ensure the surface quality of the strip. In the actual production process, the temperature of the finishing rolling is ≥900℃, and the final rolling temperature of the finishing rolling is 850~880℃. AGC, X-monitoring, adaptive and other functions are all put into use.

[0034] 4. Coil

[0035] During laminar cooling, the edge is shielded to prevent moisture loss from the edge, making the cross section of the steel plate more uniform. Laminar cooling is automatically controlled by a computer, and the total length of the cooling section is 96 meters, which can achieve a maximum temperature drop of more than 360°C. It is calculated that the particles are the smallest when precipitation is precipitated at around 600°C, which can play the greatest precipitation strengthening role. The coiling temperature is set at around 600°C.

[0036] 3. Hood annealing

[0037] The hot-rolled finished coil is annealed in a hood to release the stress in the steel plate evenly, which can achieve a better effect on the steel plate shape. The annealing temperature is 600-700℃, the holding time is controlled within the range of 12-15h, and then slow cooling is performed; the recrystallized grains are partially grown appropriately, so that the grain size is 7-11μm, and fine grain strengthening is achieved; the tensile strength of the steel strip after annealing is not less than 570MPa, and the elongation is not less than 25%.

[0038] In the present invention

[0039] Carbon (C): C is the most economical strengthening element in low carbon steel, but too high a content can reduce the plasticity and impact toughness of the steel, and deteriorate the cold forming and welding properties. Therefore, while ensuring strength, the C content in the steel should be reduced as much as possible and controlled below 0.15%.

[0040] Silicon (Si): Si has a strong affinity with oxygen and is a strong deoxidizing element. It promotes ferrite transformation, purifies ferrite, and inhibits the formation of pearlite. It is a solid solution strengthening element of ferrite, which improves the strength, fatigue limit, corrosion resistance and wear resistance of steel. It can also improve the hardenability of steel and improve the processing performance of steel. However, high silicon content is harmful to the surface quality of the plate.

[0041] Manganese (Mn): Mn exists in the steel in a solid solution state and is a solid solution strengthening element that can improve the strength of ferrite. Mn in low carbon steel has a significant effect on improving strength. Therefore, Mn is used as another main element besides titanium for low-cost steel to reach a predetermined strength level. However, Mn and S are prone to form MnS plastic inclusions, which are elongated along the rolling direction during hot rolling, deteriorating the formability of the steel. As the Mn content increases, the average length of the sulfide increases significantly and the impact toughness decreases. In addition, too high a Mn content will significantly deteriorate the welding performance, so when considering the composition of low-cost steel, the Mn content is controlled within a fixed range, and the strength level of the steel cannot be blindly increased by increasing the Mn content.

[0042] Phosphorus (P): P is an impurity element in steel. The lower the content, the better. During the continuous casting process, phosphorus will aggravate the composition segregation of the slab and lead to uneven structure.

[0043] Sulfur (S): S is an impurity element in steel, which easily forms MnS in steel. The amount and shape of sulfides in steel directly affect the hole expansion rate of the steel plate, especially strip-shaped sulfides included in deformation, which easily lead to cracks.

[0044] Aluminum (Al): Al has a high solubility in steel, has the greatest affinity with oxygen, and can refine grains, making it a good deoxidizer. However, Al's deoxidation product, Al2O3, has a high melting point. It is solid at steelmaking temperature, and the precipitation shape is mostly irregular or angular. Oxygen in steel exists in two forms: oxygen dissolved in steel and oxygen present in oxide inclusions. According to the data, [Al]s in aluminum-deoxidized steel is 0.01% to 0.05% at 1600°C, and [O]s in thermodynamic equilibrium is very low, about 4 to 8ppm. It can be seen that under the premise of fully considering the final deoxidation of molten steel, [Al]s should be controlled between 0.015% and 0.04%. From the perspective of affecting performance, in the finished steel plate, Al mainly controls the organization of the steel plate and the position of interstitial atoms through the second phase AlN, improves the stamping performance of the steel plate, reduces aging, and prevents the generation of slip lines during the stamping process. A small amount of it will have no effect, but a large amount of it will make the grains of the finished steel plate finer, increase the strength, and cause greater springback after forming.

[0045] Niobium (Nb): Nb has a strong binding force with carbon, nitrogen and oxygen, and forms corresponding extremely stable compounds, which can refine the grains, reduce the overheat sensitivity and temper brittleness of steel, affect the mobility of grain boundaries, and also affect the phase transformation behavior and the formation of carbides. Niobium has a significant effect on grain refinement. The addition of trace amounts of niobium has a significant effect on grain refinement, phase transformation behavior, carbon enrichment in austenite and martensite nucleation, and can make process control easier, and can further increase the strength of steel without significantly reducing toughness. Niobium will increase the carbon content in the retained austenite, hinder the formation of bainite, promote martensite nucleation, and increase the content of acicular ferrite, thereby increasing the content of retained austenite in the organization. Niobium can improve the welding performance of steel.

[0046] Titanium (Ti): Ti is a strong deoxidizer for steel. The main role of Ti in steel is fine grain strengthening and precipitation strengthening. At high temperature, Ti can dissolve into austenite and block the (γ→α) phase transformation. TiN and TiC precipitated in steel can prevent grain growth in austenite and hinder the recrystallization of deformed austenite, thereby refining the grains. In addition, the precipitation of finely distributed TiN and TiC in steel can hinder or pin dislocation movement, improve the deformation resistance of the steel matrix, and play a precipitation strengthening role. The rational use of Ti element can make the internal structure of steel dense, refine the grains, reduce aging sensitivity and cold brittleness, and improve welding performance. Nitrogen (N): N can cause quenching aging and deformation aging of carbon steel, thereby significantly affecting the performance of carbon steel. Due to the aging effect of nitrogen, the hardness and strength of steel are improved, but the plasticity and toughness are reduced, especially in the case of deformation aging, the reduction of plasticity and toughness is more significant. Nitrogen can improve weldability and increase aging sensitivity.

[0047] Boron (B): Boron can improve the hardenability of steel and improve the performance consistency of the steel cross section.

[0048] Beneficial effects of the present invention

[0049] (1) In terms of composition design, a low-cost composition design of composite microalloying with low C, low Nb and high Ti is adopted to give full play to the fine grain strengthening effect of Nb and the precipitation strengthening effect of Ti, so as to control the cost and achieve the designed mechanical properties requirements.

[0050] (2) Make full use of reasonable rolling temperature design, reasonable distribution of rolling force, reasonable edge shielding design, reasonable hood annealing and other processes to ensure that the steel has good plate shape control while the width reaches 2000 mm and the thickness reaches 2.0 mm. The final measured plate shape unevenness is ≤3 mm / m, and the steel plate shape achieves better results.

[0051] (3) The thin and wide steel for commercial vehicle tank bodies produced by this process has various mechanical properties that meet the requirements and has good cost control.

[0052] (4) The high-strength steel for thin and wide specification tank body of the present invention has a width of 2000mm and a thickness of 2.0mm, and at the same time has a tensile strength of ≥570MPa, a yield strength of ≥520MPa, an elongation of ≥25%, and a roughness of ≤3mm / m. It has a good plate shape and meets the production requirements of commercial vehicle tank bodies. The advantage of the wide specification is that it can reduce the number of welding passes, reduce production costs, and increase the utilization rate of steel, thereby reducing the weight of commercial vehicle bodies and achieving the purpose of lightweighting the body. Compared with conventional specifications of high-strength steel for tank bodies, it is more competitive in the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Process flow chart for high-strength steel for vehicle tank bodies.

[0054] Figure 2 This is the metallographic structure diagram of the high-strength steel for the tank body prepared in Example 1 of the present invention.

[0055] Specific implementation content

[0056] In order to further understand the present invention, three groups of embodiments of the composition and preparation method of the high-strength steel for thin and wide can bodies of the present invention are provided for illustration.

[0057] This embodiment uses the hot rolling production line of our company to produce a product with a specification of 2.0mm*2000mm and a tensile strength of 570MPa-grade high-strength steel for tank body as an example to further illustrate the present invention. The high-strength steel for tank body in the embodiment is formulated according to the weight percentage of Table 1: the balance is Fe and unavoidable impurities.

[0058] The actual production steps of high-strength steel for tank body with a product specification of 2.0mm*2000mm and a tensile strength of 570MPa manufactured by the technical solution of the present invention are as follows: the production route includes molten iron pretreatment, converter re-blowing, LF refining, slab continuous casting, hot rolling production line rolling, intermittent cooling, and hood annealing.

[0059] The steelmaking process of high-strength hot-rolled coil for hot-rolled commercial vehicle tank body in the following embodiments includes:

[0060] 1. Hot metal pretreatment

[0061] Pretreatment S≤0.0030% before entering the furnace. This steel grade requires that all molten iron entering the furnace must be pretreated and desulfurized. The desulfurization process is powder spraying desulfurization, and the ratio of magnesium powder to lime powder spraying is 1:3.

[0062] 2. Converter smelting

[0063] The converter smelting adopts constant oxygen pressure and variable gun position operation, and adopts single slag method for smelting and blowing. The oxygen supply time is controlled at 14min~18min. The process adopts auxiliary gun for fixed oxygen sampling to ensure the one-time hit rate of endpoint carbon and temperature.

[0064] Slag blocking in the early stage of steel tapping: Use slag blocking mud plug; select the appropriate slag blocking mud plug according to the size of the steel tapping port after the previous steel tapping. Slag blocking mark in the later stage of steel tapping to ensure that the slag thickness of the ladle is less than 120mm. The steel tapping time is guaranteed to be 4 to 7 minutes, and the shape of the steel tapping port is controlled to avoid steel tapping dispersion. Deoxidation and alloying begin when 1 / 5 of the steel is tapped, and the alloy must be added when 4 / 5 is tapped. Deoxidation is carried out by adding ferrosilicon and ferroaluminum. First add a certain amount of 650kg ferrosilicon, then add high manganese, and the ferroaluminum must be added after more than 1 minute.

[0065] The ladle should be purged with argon 1 minute before tapping to ensure the effect of argon blowing at the bottom of the ladle during the tapping process. The amount of argon should be controlled well. It is strictly forbidden to blow too much bottom gas, which will cause the steel liquid surface to be exposed to air inhalation and secondary oxidation. After tapping, soft argon should be blown for 3 to 5 minutes, and then the temperature should be measured and component samples should be taken.

[0066] 3. Refining process

[0067] The refining method adopted is the ladle refining furnace (LADLE FURNACE, referred to as LF furnace). The temperature requirement in front of the LF furnace is 1565-1575℃. According to the S content of the ladle, the amount of lime added is controlled at 200-500kg. If the sulfur exceeds the enterprise standard before treatment, the amount of lime added can be appropriately increased. Add a small amount of CaO and Al according to the arc buried situation and the color of the flue gas. Control the electrode arc buried during the power supply process and close the furnace cover opening. The first power supply is controlled at 6-10 minutes. After the power supply is completed, strong argon blowing and stirring are used for 2-3 minutes of desulfurization (if the ladle S meets the target requirements, strong argon blowing and stirring are not performed), and slag samples are taken to check the slag color. When the slag color is light green, it is considered to be good slag formation.

[0068] According to the oxygen value before argon, aluminum deoxidation and alloying are carried out, and aluminum wire is adjusted to aluminum by 0.04%. According to the analysis results of the composition sample before argon, alloy adjustment is carried out, with emphasis on carbon, silicon, manganese, and titanium adjustment. After alloying, the temperature is adjusted to 1560-1570°C or soft argon blowing (temperature increase is prohibited during soft argon blowing). The argon blowing at the bottom of the ladle is of medium intensity or less, and the argon blowing flow rate is 200-300L / min. It is strictly forbidden to use large amount of argon blowing, and it is strictly forbidden for molten steel to be exposed to air. Strengthen the furnace cover seal, control the furnace mouth micro-positive pressure, and the LF furnace control increase [N] is not greater than 7ppm.

[0069] The aluminum component adjustment must be completed 15 minutes before the end of the treatment, and the soft argon blowing must be ≥10 minutes before the end of the treatment. The LF leaving station temperature of a normal furnace is controlled at 1563-1573℃.

[0070] 4. Continuous casting process

[0071] Protective pouring is performed throughout the entire process. Argon is used to purge the middle ladle before pouring. No molten steel is exposed during the pouring process. The shroud must be cleaned after each furnace is poured. The shroud must remain vertical during the pouring process. The immersion depth of the shroud of the large ladle is guaranteed to be 200-250mm. The slag detection is used to control the slag amount of the large ladle to avoid slag in the large ladle.

[0072] The secondary cooling section of this series of steel grades adopts weak cooling mode and light reduction mode. The drawing speed is controlled according to the cross-section and production rhythm to ensure constant speed steel casting.

[0073] 3. Hot rolling

[0074] 1. Heating

[0075] The continuous casting billet is hot-delivered and hot-charged, and the surface quality of the billet is strictly checked when loading into the furnace. Since the steel contains Ti, in order to effectively precipitate TiC in the steel and refine the grains, the heating temperature is ≥1200℃, the heating time is 210min, and the furnace temperature is 1245℃.

[0076] 2. Rough rolling

[0077] The slab is heated to the required temperature and then taken out of the furnace after being kept warm. After being taken out of the furnace and before entering each rough rolling mill, high-pressure water dephosphorization is carried out. The rough rolling mill is equipped with width adjustment and control (AWC) and short stroke control (SSC) functions to ensure the width accuracy and surface quality requirements of the intermediate slab. The opening temperature of R1 (the first rough rolling mill) is greater than 1130℃, and the outlet temperature is 1075℃; 3 passes of rolling are carried out, and dephosphorization is carried out every time; in order to remove the iron oxide scale on the surface of the steel grade, appropriate dephosphorization water is added between the stands.

[0078] 3. Finish rolling

[0079] Finishing mills F1~F7 are equipped with automatic thickness control devices (AGC) to effectively control the thickness accuracy of the strip; F1~F7 use bending roll hydraulic system, F2~F4 use CVC rolls to effectively control the strip shape; cooling water between stands and rolling mill speed increase function can automatically control the final rolling temperature; two high-pressure water descaling points are set between the finishing mill stands to ensure the surface quality of the strip. The inlet temperature of finishing rolling F1 is 1055℃, and the final rolling temperature of finishing rolling is 880℃. AGC, X-monitoring, adaptive and other functions are all put into use. Finishing rolling to a thickness of 2mm.

[0080] 4. Coil

[0081] Laminar cooling adopts the back-stage intermittent cooling mode with a temperature of 600℃. Edge shielding is used during laminar cooling to prevent moisture loss from the edges and make the cross section of the steel plate more uniform. Laminar cooling is automatically controlled by a computer, and the total length of the cooling section is 96 meters. It is calculated that the particles are the smallest when precipitation is precipitated at around 600℃, which can play the greatest precipitation strengthening role. The coiling temperature is set to around 600℃.

[0082] 3. Hood annealing

[0083] The hot-rolled finished coil is annealed in a hood to release the stress in the steel plate evenly, which can achieve a better effect on the steel plate shape. The annealing temperature is 600-700℃, the holding time is controlled within the range of 12-15h, and then slow cooling is performed; the recrystallized grains grow moderately.

[0084] The steel strip produced according to the steps of this embodiment has the steel composition shown in Table 1, its performance indicators are shown in Table 2, and its metallographic structure is shown in Table 2. Figure 2 .

[0085] The present invention is further described below in conjunction with Examples 1 to 3. Table 1 shows the chemical composition (by weight percentage) of the steel of the present invention, with the remainder being Fe and unavoidable impurities.

[0086] Table 1 Chemical composition of the examples / wt%

[0087]

[0088] Table 2 Performance test results of the embodiment

[0089]

[0090] According to the chemical composition in Table 1 and the performance test results of the three groups of embodiments obtained in Table 2, the high-strength steel for hot-rolled commercial vehicle tank body and the preparation method disclosed in the present invention achieve the high-strength steel for the tank body produced by reasonable rolling temperature design, reasonable distribution of rolling force, reasonable edge shielding design, reasonable hood annealing and other processes, which meet the mechanical properties requirements such as strength, plasticity, and toughness, and have a width of 2000mm and a thickness of 2.0mm. At the same time, the tensile strength is ≥570MPa, the yield strength is ≥520MPa, the elongation is ≥25%, and the unevenness is ≤3mm / m, wherein the metallographic structure is mainly ferrite and pearlite, and the metallographic structure is as follows Figure 2 As shown, the structure is uniform and fine, and the grain size is 13.

Claims

1. A high-strength hot-rolled coil for hot-rolled commercial vehicle tank body, characterized in that: The following ingredients are included by weight percentage: C: ≤0.100%, Si: ≤0.30%, Mn: ≤1.40%, S: ≤0.005%, P: ≤0.008%, Al: ≥0.015%, Nb: 0.010~0.040%, Ti: 0.050~0.090%, N: ≤0.0040%, B≥0.0015%, the rest are Fe and other inevitable impurities; The rolled plate has a grain size of 7 to 11 μm, a width of ≥2000 mm, a thickness of 2.0 to 3.0 mm, a tensile strength of ≥570 MPa, a yield strength of ≥520 MPa, an elongation of ≥25%, and an unevenness of ≤3 mm / m; The metallographic structure is ferrite and pearlite; The method for preparing the high-strength hot-rolled coil comprises a steelmaking process, a hot rolling process, and a hood annealing process; The steelmaking process includes molten iron pretreatment, converter smelting, refining process and continuous casting process; The hot rolling process comprises the following steps: (1) Heating: The continuous casting billet is heated and loaded, the heating temperature is ≥1200℃, and the furnace discharge temperature is 1200℃~1250℃; (2) Rough rolling: The rough rolling mill is equipped with width adjustment and short stroke control functions; (3) Finishing rolling: Finishing mills F1 to F7 are equipped with automatic thickness control devices. F1 to F7 use a bending roll hydraulic system, and F2 to F4 use CVC rolls. Two high-pressure water descaling stations are set between the finishing mill stands. (4) Coiling: The laminar cooling adopts the intermittent cooling mode in the rear section; the edge shielding is used during cooling to prevent moisture loss at the edge and make the cross section of the steel plate more uniform; the coiling temperature is 600℃±15℃ to obtain the hot-rolled finished product; The hood annealing is to hood anneal the hot-rolled finished coil; the annealing temperature is 600-700°C, the holding time is 12-15h, and then slow cooling; recrystallization; In the hot rolling process, the heating time in step (1) is ≥ 150 min; In the hot rolling process, in the step (2) of rough rolling, the slab after being discharged from the furnace is first subjected to high-pressure water dephosphorization before entering each rough rolling mill; the first rough rolling mill has a starting rolling temperature of ≥1130°C and an outlet temperature of 1050-1090°C; dephosphorization water is provided between the rough rolling mill racks; In the hot rolling process, in the step (3) finishing rolling, the finishing rolling F1 inlet temperature is ≥ 900°C, and the finishing rolling final rolling temperature is 850-880°C; In the hot rolling process, during the coiling in step (4), the total length of the cooling section is 96 m.

2. The high-strength hot-rolled coil for hot-rolled commercial vehicle tank body according to claim 1, characterized in that: In the molten iron pretreatment, S entering the furnace after pretreatment is ≤0.0030wt%; the desulfurization method is powder spray desulfurization, and the spraying ratio of magnesium powder to lime powder is 1:

3.

3. The high-strength hot-rolled coil for hot-rolled commercial vehicle tank body according to claim 1, characterized in that: In the converter smelting, constant oxygen pressure and variable gun position operation are adopted, single slag method smelting and blowing are adopted, the oxygen supply time is 14min-18min, and the auxiliary gun is used for fixed oxygen sampling in the process to ensure the one-time hit rate of the terminal carbon and temperature; slag blocking is adopted in the early stage of steel tapping; the slag thickness of the ladle is less than 120mm, and the steel tapping time is 4-7min; deoxidation and alloying are started when 1 / 5 of the steel is tapped, and the alloy must be added when 4 / 5 is tapped, and deoxidation is carried out by ferrosilicon and ferroaluminum, and a quantitative amount of 650kg ferrosilicon is added first, and then high manganese is added, and the ferroaluminum must be added more than 1min later; the ladle is purged with argon 1min before steel tapping, and argon is soft-blown for 3-5min after steel tapping.

4. The high-strength hot-rolled coil for hot-rolled commercial vehicle tank body according to claim 1, characterized in that: In the refining process, LF furnace treatment is adopted, and the temperature in front of LF furnace is 1565-1575°C; in the refining process, according to the S content of ladle, the amount of lime added is 200-500kg; CaO and Al are added according to the arc burial situation and the color of flue gas, and the electrode arc burial is controlled during the power supply process, and the furnace cover opening is closed; the first power supply is 6-10min, and after the power supply is finished, strong argon blowing is used for stirring for 2-3min for desulfurization.

5. The high-strength hot-rolled coil for hot-rolled commercial vehicle tank body according to claim 1, characterized in that: In the refining process, aluminum deoxidation and alloying are carried out according to the oxygen value before argon, and the aluminum wire is adjusted by 0.04%; the temperature after alloying is adjusted to 1560-1570°C or soft argon is blown, the argon blowing flow rate at the bottom of the ladle is 200-300L / min, and the LF furnace is controlled to increase [N] ≤ 7ppm; the aluminum component adjustment must be completed 15 minutes before the end of the treatment, the soft argon blowing before the end of the treatment is ≥ 10 minutes, and the LF furnace leaving the station temperature is 1563-1573°C.

6. The high-strength hot-rolled coil for hot-rolled commercial vehicle tank body according to claim 1, characterized in that: In the continuous casting process, protective pouring is performed throughout the continuous casting process; the tundish is purged with argon before pouring, and no molten steel is exposed during the pouring process. The long shroud must be cleaned after each furnace of pouring is completed; the long shroud is required to remain in a vertical state during the pouring process.

7. The high-strength hot-rolled coil for hot-rolled commercial vehicle tank body according to claim 1, characterized in that: In the continuous casting process, the immersion depth of the long shroud of the large ladle is 200-250mm, and the large ladle adopts slag detection to control the slag amount to avoid slag in the large ladle; during the continuous casting process, the secondary cooling section adopts weak cooling mode and light pressure mode to cast steel at a constant speed.

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