Hot-rolled steel sheets are suitable for electrostatic dry powder enamel coating and exhibit enhanced strength after enamel firing and this steel sheet production method.

Abstract

The invention relates to hot-rolled steel sheets suitable for electrostatic dry powder enamel coating and having a strengthening performance after enamel firing, and a method for producing such steel sheets. The chemical composition, expressed in mass percentage, of the hot-rolled steel sheets is: C: 0.030–0.080%, Si ≤ 0.030%, Mn: 0.30–0.80%, Al: 0.010–0.050%, Cr: 0.010–0.040%, Cu: 0.020–0.080%, N: 0.0040–0.0120%, B: 0.0010–0.0050%, and Mo: 0.005–0.050%, with the remainder being Fe and other unavoidable impurities; And hot-rolled steel plates need to satisfy the following additional condition: [B] / [N]×[Mo]×103>5.In this invention, the high-temperature stability of the precipitated phase is ensured by effectively using Mo to reinforce the BN and AlN precipitates; in addition, improving the air-cooled hardenability of steel plates by using B and Mo in solid solution achieves the goal of improving, rather than reducing, the yield strength of the steel plate after high-temperature enamel firing, on the premise that the steel plate meets the requirements for anti-scaling and adhesion performance as required by the electrostatic dry powder enameling process.

Description

A hot-rolled steel plate suitable for electrostatic dry powder enameling and having enameling strengthening properties and a manufacturing method thereof Technical Field

[0001] The invention belongs to the technical field of enameled steel plate processing, and in particular relates to a hot-rolled steel plate suitable for electrostatic dry powder enameling and having enameling strengthening properties, and a manufacturing method thereof. Background Art

[0002] Enameled steel is a composite material made by applying porcelain enamel to a steel substrate through high-temperature enameling. It is widely used in ovens, decorative panels, kitchen and bathroom appliances, enameled steel modular tanks, and electric water heater linings. Enameling processes primarily include wet enameling and electrostatic dry powder enameling. Dry powder enameling uses electrostatic adsorption to adhere the glaze to the steel surface, resulting in a more uniform enamel layer, higher surface quality, and increased production efficiency. In recent years, electrostatic dry powder enameling has been a trend in many enameled steel product production areas to replace wet enameling.

[0003] For specialized steel plates suitable for porcelain enamel, excellent anti-scale performance is a fundamental requirement. According to hydrogen theory, steel absorbs hydrogen generated during the enameling reaction at high temperatures. The solubility of hydrogen in steel increases at high temperatures, but decreases with cooling. During the firing process of enameled products, the steel reaches saturation with hydrogen. However, as the product cools in air until the enamel solidifies, hydrogen has no time to escape, resulting in a supersaturated state within the steel. This supersaturated hydrogen, trapped where it will later precipitate, generates a pressure dependent on the amount of hydrogen released from the steel at high temperatures and the degree of porosity within the porcelain layer. When this pressure builds to a level that can cause the porcelain layer to detach, the "fish scale" flaking defect forms. Because dry-powdered enamel powder has a finer particle size, the resulting enamel layer is denser than wet-process enamel, making it more difficult for hydrogen to escape. Consequently, higher requirements are placed on the steel plate for anti-scale performance.

[0004] Furthermore, because the enamel sintering process typically requires a period of time at temperatures exceeding 800°C, the ultimate strength of the enameled product depends on the strength of the enameled steel after high-temperature enameling. Typically, the strength of steel plate decreases significantly after such high-temperature heat treatment. This is because the microstructure of the steel plate undergoes a decrease in dislocation density, growth of ferrite grains, and coarsening of nano-precipitates during high-temperature heat treatment. These changes simultaneously weaken the effects of dislocation strengthening, grain refinement, and precipitation strengthening. Improving the strength of steel plate after high-temperature enameling has long been a key research topic in the development of enameled steel and holds significant practical value.

[0005] Chinese patent application CN101812630A discloses "hot-rolled high-strength enameled steel sheet for deep drawing and its manufacturing method". The chemical composition of the steel sheet is as follows by weight: C: 0.02-0.10%, Si≤0.10%, Mn: 0.05-1.00%, P≤0.05%, S: 0.005-0.035%, Al: 0.01-0.10%, N≤0.015%, Ti<0.10%, and the balance is iron and unavoidable impurities.

[0006] Chinese patent application CN103540845A discloses "hot-rolled thin-sheet enameled steel with a yield strength of 330 MPa and a manufacturing method thereof". The composition of the hot-rolled thin-sheet enameled steel is C: 0.02-0.07%, Si≤0.05%, Mn: 0.10-0.50%, P≤0.020%, S≤0.010%, Ti: 0.04-0.10%, Al: 0.02-0.08%, N≤0.008%, and the rest is Fe and unavoidable inclusions, and Ti / C = 1.0-1.5.

[0007] Chinese patent application CN102181805A discloses "a thin slab continuous casting and rolling line for producing steel plates for water heater liner enamel and a method thereof." The chemical composition of the steel plates is as follows: carbon 0.03-0.10%, manganese 0.15-0.40%, silicon ≤0.06%, sulfur 0.004-0.040%, phosphorus ≤0.15%, aluminum 0.03-0.05%, nitrogen 0.002-0.008%, titanium 0.02-0.10%, and the remainder is iron and unavoidable impurities.

[0008] The aforementioned hot-rolled enameled steels often incorporate Ti in their compositions, forming TiC and Ti(C,N) precipitates with C and N, acting as hydrogen traps and precipitation strengthening. However, it should be noted that these technical solutions are only applicable to wet enameling, and the yield strength of the enameled steels obtained from these methods after high-temperature enameling is lower than that of the hot-rolled steel.

[0009] Summary of the Invention

[0010] The object of the present invention is to provide a hot-rolled steel plate suitable for electrostatic dry powder enameling and having enameling strengthening properties, and a manufacturing method thereof. After high-temperature enameling, the yield strength of the steel plate does not decrease but increases, which can effectively improve the strength of the final enameled product. At the same time, the obtained steel plate meets the anti-scale and adhesion performance requirements required by the electrostatic dry powder enameling process and can be widely used in fields such as water heater inner tanks.

[0011] To achieve the above object, the technical solution of the present invention is:

[0012] A hot-rolled steel plate suitable for electrostatic dry powder enameling and having enameling strengthening properties, wherein the chemical composition by weight is as follows: C: 0.030-0.080%, Si≤0.030%, Mn: 0.30-0.80%, Al: 0.010-0.050%, Cr: 0.010-0.040%, Cu: 0.020-0.080%, N: 0.0040-0.0120%, B: 0.0010-0.0050%, Mo: 0.005-0.050%, the balance including Fe and other unavoidable impurities; and the following chemical composition must also be satisfied: [B] / [N]×[Mo]×10 3 >5.0.

[0013] In some embodiments, the hot rolled steel sheet of the present invention does not contain Ti.

[0014] Furthermore, the balance is Fe and other inevitable impurities.

[0015] In some embodiments, the hot rolled steel sheet satisfies: [B] / [N]×[Mo]×10 3 ≥5.5. In some embodiments, the hot rolled steel sheet satisfies: [B] / [N]×[Mo]×10 3 In the range of 5.5 to 26.0.

[0016] The microstructure of the steel plate of the present invention comprises equiaxed ferrite + pearlite. The ferrite grain size is grade 7-9, and BN and AlN precipitates are dispersed within the ferrite matrix. The precipitate size (maximum length for non-spherical forms and diameter for spherical forms) ranges from 10 to 800 nm. The proportion of pearlite per unit area in the microstructure of the steel plate of the present invention is less than 10%.

[0017] The steel sheet of the present invention has a yield strength of 285-345 MPa. After high-temperature annealing at 840°C, the yield strength of the steel sheet is 340-395 MPa. In some embodiments, the yield strength of the steel sheet of the present invention increases by at least 10.0%, such as 10.0-20.0%, after annealing at 840°C. The increase is the difference between the yield strength after annealing and the yield strength before annealing, divided by the yield strength before annealing.

[0018] In some embodiments, according to the drop weight test method described in European standard BS EN 10209-1996, the adhesion performance of the hot-rolled steel sheet of the present invention subjected to the enamel adhesion test is grade I or II.

[0019] In some embodiments, the hot-rolled steel plate has a thickness of 1.5 to 3.0 mm, such as 1.7 to 3.0 mm.

[0020] Herein, "hot-rolled steel sheet" refers to a steel sheet obtained after hot rolling, coiling and pickling.

[0021] In the chemical composition design of the hot-rolled steel plate with electrostatic dry powder enameling and enameling strengthening properties of the present invention:

[0022] Carbon: Carbon in steel primarily forms pearlite, strengthening the structure. However, excessive carbon content can impair the formability of the steel sheet. Furthermore, excessively high carbon content can lead to excessive pearlite formation, which can cause large amounts of gases like CO to be generated during the enamel firing process. This can lead to poor pore structure in the enamel layer and defects like pinholes, seriously affecting the quality of the enamel. Therefore, the carbon content in the present invention is controlled between 0.030% and 0.080%.

[0023] Silicon: Silicon element will deteriorate the plasticity of steel and also affect the adhesion between the steel plate and the enamel. It is controlled as a residual element. Therefore, the present invention controls the Si content to ≤0.030%.

[0024] Manganese: While manganese can improve steel plate strength, excessive strength can cause springback after the water heater inner tank is rolled, compromising welding performance and weld quality. Furthermore, manganese expands the austenite phase and lowers the Ac3 point, which negatively impacts the steel plate's enameling properties. Because austenite dissolves hydrogen more strongly than ferrite, cooling makes scale more likely, so excessive addition is advised. Therefore, the manganese content in this invention is controlled within a range of 0.30% to 0.80%.

[0025] Copper and Chromium: Adding appropriate amounts of copper and chromium facilitates surface deposition, thereby improving adhesion to the enamel and anti-scale performance. The chromium in the steel partially replaces iron to form the alloy cementite (Fe, Cr)3C, enhancing its stability. A portion dissolves into ferrite, resulting in solid solution strengthening and increasing the ferrite's strength and hardness. However, excessive copper and chromium content not only increases costs but also enhances the steel's corrosion resistance, negatively impacting its adhesion during the enameling process. Therefore, in the present invention, the copper content is controlled between 0.02% and 0.08%, and the chromium content is controlled between 0.010% and 0.040%.

[0026] Aluminum: Aluminum is a strong deoxidizing element. To keep the oxygen content in the steel as low as possible, aluminum is often used for deoxidation in medium- and low-carbon steels. Dissolved aluminum in the steel also combines with free nitrogen to precipitate AlN, a high precipitation temperature that refines the austenite grains. This fine grain structure not only promotes fine-grain strengthening but also improves the hydrogen storage capacity of the steel plate. Therefore, the aluminum content in the present invention is controlled to 0.010-0.050%.

[0027] Boron: Boron (B) has very low solubility in steel and primarily precipitates as BN by combining with free nitrogen in the steel. In the present invention, the BN precipitate acts as a primary hydrogen trap, contributing to the enamel's anti-scale properties. However, dissolved boron in steel increases the strength of the steel sheet while reducing formability. Therefore, the B content should not be too high. In the present invention, the boron content is controlled within a range of 0.0010% to 0.0050%.

[0028] Nitrogen: Under normal circumstances, the nitrogen content in steel should be as low as possible. In the present invention, an appropriate amount of nitrogen is added mainly to form a BN composite precipitate phase. Excess nitrogen can also form an AlN precipitate phase with Al. In the present invention, the nitrogen content is controlled at 0.0040-0.0120%.

[0029] Molybdenum: In the technical solution described in the present invention, on the one hand, molybdenum can be dissolved in ferrite, austenite, and carbides, exerting a solid solution strengthening effect. At the same time, it can also interact with solid-solution boron to jointly improve the hardenability of the steel plate, thereby increasing the strength of the steel plate under air cooling conditions. On the other hand, molybdenum can also improve the stability of BN and AlN precipitates, reduce the aggregation and coarsening of precipitates caused by high-temperature enameling (usually enameling temperatures of 830-850°C), thereby improving the high-temperature stability of the steel and avoiding the decrease in yield strength caused by the weakening of precipitation strengthening after enameling. However, excessive addition of Mo significantly increases manufacturing costs. Therefore, in the ultra-low carbon cold-rolled high-strength steel described in the present invention, the mass percentage of Mo is limited to 0.005-0.050%.

[0030] The above-mentioned B, N, and Mo elements must also satisfy the following relationship: [B] / [N]×[Mo]×10 3 >5. Meeting this relationship can make the steel plate have enameling strengthening properties. After high-temperature enameling at 840℃, the yield strength can be increased by more than 10.0%. This is because: on the one hand, a sufficient amount of BN precipitation phase can be obtained, while ensuring sufficient Mo element to ensure the high-temperature stability of the precipitation phase; on the other hand, a certain amount of B and Mo elements can be ensured to exist in solid solution, which can improve the air-cooling hardenability of the steel plate, so that the strength of the steel plate can be improved under air-cooling conditions after high-temperature enameling.

[0031] The addition of boron, nitrogen, molybdenum, and aluminum to the steel creates secondary phases of BN and AlN that act as hydrogen traps, enhancing the enamel's anti-scale properties. Mo enhances the stability of BN and AlN precipitates, reducing their aggregation and coarsening caused by high-temperature enameling, thereby improving the steel's high-temperature stability. Furthermore, the interaction between dissolved boron and molybdenum enhances the steel's air-cooling hardenability, allowing high-temperature enameling to produce increased strength even under air-cooling conditions. This achieves enameling strengthening, ensuring that the steel's yield strength increases after high-temperature enameling, rather than decreasing.

[0032] In some embodiments, the present invention provides an enameled steel sheet comprising a substrate and an enamel layer on either or both surfaces of the substrate. The substrate is a hot-rolled steel sheet suitable for electrostatic dry powder enameling and having enameling-enhancing properties as described in any embodiment of this application. In some embodiments, the enamel layer is formed on the surface using a dry powder enameling method. In some embodiments, the enamel layer has a thickness of 120 to 150 μm.

[0033] The present invention also provides a method for manufacturing a hot-rolled steel plate suitable for electrostatic dry powder enameling and having enameling strengthening properties, comprising the following steps:

[0034] 1) Smelting, refining, and continuous casting

[0035] Smelting, RH or LF refining and continuous casting into billets according to the above composition;

[0036] 2) Hot rolling

[0037] Heating temperature: 1150-1250℃, rough rolling and finishing rolling are carried out in sequence, the rough rolling temperature is ≥850℃, the finishing rolling start temperature is 900-1050℃, and the finishing rolling final temperature is 860-900℃;

[0038] 3) Coiling

[0039] The steel plate after hot rolling is laminar cooled at a cooling rate of 10-35°C / s, and then coiled to obtain hot rolled coil at a coiling temperature of 650-700°C.

[0040] 4) Pickling

[0041] The hot-rolled coil is pickled, dephosphorized and straightened to obtain a hot-rolled pickled steel plate.

[0042] In the method for manufacturing the steel plate of the present invention:

[0043] Smelting and refining ensure that the basic composition of the molten steel meets the design requirements of the present invention. Casting can be carried out by continuous casting or die casting to ensure that the internal composition of the ingot is uniform and the surface quality is good. If die casting is adopted, the cast ingot needs to be rolled into a billet by a primary rolling mill.

[0044] The cast slab is heated at 1150-1250°C to transform the slab into an austenitic structure and achieve full homogenization during the heating process; the slab is then rough rolled into an intermediate slab at a rough rolling temperature of 850°C or higher. In some embodiments, the rough rolling temperature is 850-1080°C. In some embodiments, the rough rolling temperature is 880-1080°C.

[0045] The present invention designs a finishing rolling start temperature of 900-1050°C and a finishing rolling temperature of 860-900°C. Laminar cooling is used, with water cooling at a cooling rate of 10-35°C / s to a coiling temperature of 650-700°C, followed by air cooling to room temperature. The present invention optimizes the C, B, Al, and N components, combined with a controlled rolling and cooling process that utilizes high-temperature finishing rolling, high-temperature coiling, and rapid cooling. This facilitates the full recovery and recrystallization of ferrite grains during hot rolling, thereby obtaining a uniform, equiaxed ferrite grain structure. This results in the final steel plate having excellent comprehensive mechanical properties.

[0046] In addition, the finishing rolling temperature is controlled at 860-900°C, which is beneficial for strengthening the bonding between the element Mo and the BN and AlN precipitates, thereby utilizing the Mo element to improve the high-temperature stability of the BN and AlN precipitates. In addition, the finishing rolling temperature is higher than the enameling temperature during the enameling process (830-850°C), which can reduce the impact of the enameling temperature on the steel sheet structure and properties, and improve the quality of the final enameled product.

[0047] The coiling temperature is controlled at 650-700°C. Coiling in this temperature range is beneficial to the refinement of ferrite grains and the homogenization of BN and AlN precipitation phases, so as to obtain excellent mechanical properties and anti-scale performance.

[0048] In some embodiments, the present invention provides a method for preparing enameled steel, comprising the following steps:

[0049] (1) providing a hot-rolled steel sheet as described in any embodiment of the present invention; and

[0050] (2) A dry powder enamel method is used to form an enamel layer on either or both surfaces of the hot-rolled steel sheet.

[0051] In some embodiments, the enameling process includes: an enameling temperature of 830-850° C. and a holding time of 3-8 minutes.

[0052] In some embodiments, the enamel layer has a thickness of 120 to 150 μm.

[0053] The enameling can be performed using materials known in the art that are suitable for forming an enamel layer using a dry powder enamel process. An exemplary enamel material is Ferro TR1042 electrostatic powder.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The present invention utilizes a composition system high in nitrogen, boron, and aluminum, forming BN and AlN secondary phases in the steel that act as hydrogen traps, providing excellent anti-scale protection and meeting the requirements for electrostatic dry powder enamel. Mo also enhances the stability of the BN and AlN precipitates, reducing the aggregation and coarsening of the precipitates caused by high-temperature enameling, thereby improving the steel's high-temperature stability. Furthermore, the interaction between the solid-solution boron and molybdenum elements enhances the air-cooling hardenability of the steel sheet, increasing its strength under the cooling rate conditions of air cooling after high-temperature enameling. This results in an increase in the yield strength of the steel sheet after high-temperature enameling, rather than a decrease, achieving enameling strengthening. The yield strength of the steel sheet after enameling can be increased by over 10.0%.

[0056] Based on the composition design, the present invention combines the controlled rolling and controlled cooling process to obtain a fine equiaxed ferrite + pearlite grain structure, and the ferrite grain size level is 7 to 9, which is conducive to the steel plate obtaining higher yield strength and good comprehensive performance.

[0057] The yield strength of the steel plate of the present invention is 285-345 MPa. After high-temperature enameling at 840°C, the yield strength of the steel plate is 340-395 MPa, achieving a good match between the mechanical properties and enameling properties of the steel plate and meeting the anti-scale explosion performance requirements of electrostatic dry powder enamel. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] FIG1 is a microstructure photograph of the steel plate according to Example 1 of the present invention. DETAILED DESCRIPTION

[0059] The present invention is further illustrated below by way of examples and drawings, but this is not intended to limit the present invention. Those skilled in the art may make modifications or improvements based on the basic idea of ​​the invention, but as long as they do not depart from the basic idea of ​​the invention, they are all within the scope of the present invention.

[0060] The compositions of the embodiments of the present invention and the comparative examples are shown in Table 1, wherein the balance of the compositions comprises Fe and other unavoidable impurities. The process parameters of the embodiments of the present invention and the comparative examples are shown in Table 2.

[0061] The performance tests were performed on the samples obtained in Examples 1-9 of the present invention, and the test results are listed in Table 3.

[0062] Tensile test: According to GB / T 228.1-2010 “Room temperature tensile test method for metallic materials”, the test was carried out using an SCL233 room temperature tensile testing machine with a tensile speed of 3 mm / min and a JIS5 tensile specimen.

[0063] Drop hammer test: According to the drop hammer test method described in European standard BS EN 10209-1996, the enamel adhesion performance test is carried out using the corresponding drop hammer test device.

[0064] Ferrite grain: According to GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals", the average grain size is evaluated by comparison with the standard series rating chart using a metallographic microscope and the comparison method.

[0065] Enameling Performance: Ferro TR1042 electrostatic powder was used for single-side enameling. The enameling process was 840°C for 5 minutes, and the enamel layer thickness was 120-150μm. After enameling, the steel plate was left to stand for 48 hours and observed to show no scale cracking. A drop hammer test was used to verify the excellent adhesion between the steel plate and the enamel.

[0066] As shown in FIG1 , a microstructure photograph of the steel plate obtained in Example 1 of the present invention shows that the microstructure is composed of ferrite and pearlite. The grain size of the ferrite is level 8, and the proportion of pearlite per unit area is less than 10%.

[0067] As shown in Table 3, the yield strength of the hot-rolled steel sheets obtained by the present invention ranges from 285 to 345 MPa. After sintering at 840°C, the yield strength reaches 340 to 395 MPa. Observation of the surface of the resulting enameled steel sheets after 48 hours reveals no scale cracking. Drop hammer testing demonstrates excellent adhesion between the steel sheet and the enameled layer, fully meeting user requirements.

[0068] In Comparative Examples 1 to 3, [B] / [N]×[Mo]×10 3 <5.0, scale defects appear on the steel plate after electrostatic dry powder enameling, and the yield strength after enameling is significantly reduced.

[0069] Table 1 (Unit: weight percentage)

[0070] Table 2

[0071] Table 3 Note: ○ represents no scale-blasting defect, × represents scale-blasting defect.

[0072] It should be noted that the embodiments listed above are only specific embodiments of the present invention. Within the scope of protection of the present invention, similar changes or modifications made can be directly derived or easily associated with by those skilled in the art from the contents disclosed in the present invention, and should all fall within the scope of protection of the present invention.

Claims

1. A hot-rolled steel plate suitable for electrostatic dry powder enameling and having enameling strengthening properties, wherein the chemical composition by weight percentage is: C: 0.030-0.080%, Si≤0.030%, Mn: 0.30-0.80%, Al: 0.010-0.050%, Cr: 0.010-0.040%, Cu: 0.020-0.080%, N: 0.0040-0.0120%, B: 0.0010-0.0050%, Mo: 0.005-0.050%, and the balance includes Fe and other unavoidable impurities; and it is also necessary to simultaneously meet the following requirements: [B] / [N]×[Mo]×103>5.

0.

2. The hot-rolled steel sheet suitable for electrostatic dry powder enameling and having enameling strengthening properties according to claim 1, characterized in that: The balance is Fe and other inevitable impurities.

3. The hot-rolled steel sheet suitable for electrostatic dry powder enameling and having enameling strengthening properties according to claim 1 or 2, characterized in that: The hot-rolled steel sheet satisfies: [B] / [N]×[Mo]×10 3 ≥5.

5.

4. The hot-rolled steel sheet suitable for electrostatic dry powder enameling and having enameling strengthening properties according to claim 1, characterized in that: The hot-rolled steel sheet satisfies: [B] / [N]×[Mo]×10 3 In the range of 5.5 to 26.

0.

5. The microstructure of the steel plate as described in any one of claims 1 to 4 is equiaxed ferrite + pearlite; the ferrite grain size grade is 7 to 9, BN and AlN precipitates are dispersed in the ferrite matrix, and the precipitate size is 10 to 800 nm; preferably, the proportion of pearlite per unit area is within 10%.

6. The hot-rolled steel sheet suitable for electrostatic dry powder enameling and having enameling strengthening properties according to any one of claims 1 to 5, characterized in that: The yield strength of the steel plate is 285-345 MPa. After being sintered at 840° C., the yield strength of the steel plate is 340-395 MPa.

7. The hot-rolled steel sheet suitable for electrostatic dry powder enameling and having enameling strengthening properties according to any one of claims 1 to 6, characterized in that: The yield strength of the hot-rolled steel plate after sintering at 840° C. increases by at least 10.0%, such as 10.0-20.0%.

8. The hot-rolled steel sheet suitable for electrostatic dry powder enameling and having enameling strengthening properties according to any one of claims 1 to 7, characterized in that: According to the drop weight test method described in European standard BS EN 10209-1996, the adhesion performance of the hot rolled steel sheet obtained by the enamel adhesion performance test is level I or II.

9. The method for producing a hot-rolled steel sheet suitable for electrostatic dry powder enameling and having enameling strengthening properties according to any one of claims 1 to 8, characterized in that: The steps include: 1) Smelting, refining and continuous casting Smelting, RH or LF refining, and continuous casting into billets according to any one of claims 1 to 4; 2) Hot rolling Heating temperature: 1150-1250℃, rough rolling and finish rolling are carried out in sequence, the rough rolling temperature is ≥850℃, the finish rolling start temperature is 900-1050℃, and the finish rolling final temperature is 860-900℃; 3) Coiling The steel plate after hot rolling is laminar cooled, and the cooling rate is controlled at 10-35°C / s. After cooling, the hot rolled coil is coiled, and the coiling temperature is 650-700°C. 4) Pickling The hot-rolled coil is pickled, dephosphorized and straightened to obtain a hot-rolled pickled steel plate.

10. The manufacturing method according to claim 9, characterized in that: The obtained steel plate has a thickness of 1.7 to 3.0 mm.

11. The manufacturing method according to claim 9, characterized in that: The rough rolling temperature is 850-1080°C, preferably 880-1080°C.

12. An enameled steel sheet comprising the hot-rolled steel sheet suitable for electrostatic dry powder enameling and having enameling strengthening properties as claimed in any one of claims 1 to 8 as a substrate, and an enamel layer on either or both surfaces of the substrate.

13. The enameled steel sheet according to claim 12, characterized in that: The enamel layer is an enamel layer formed on the surface by a dry powder enamel method; preferably, the thickness of the enamel layer is 120-150 μm.

14. The method for producing an enameled steel sheet according to claim 12 or 13, characterized in that: The method comprises: (1) providing a hot-rolled steel sheet according to any one of claims 1 to 8; and (2) A dry powder enameling method is used to form an enamel layer on either or both surfaces of the hot-rolled steel sheet.

15. The manufacturing method according to claim 14, characterized in that: The method further comprises: manufacturing the hot-rolled steel plate by the method according to any one of claims 9 to 11; and / or The dry powder enamel process includes: the enamel temperature is 830-850° C., and the heat preservation time is 3-8 minutes.

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