Low-cost hot-rolled steel sheet for high-temperature enamel and its manufacturing method

Abstract

Disclosed is a low-cost hot-rolled steel sheet for high-temperature enamel. In addition to Fe and unavoidable impurities, the steel sheet further contains the following chemical composition in mass percent: C: 0.03-0.12%, Si: 0.1-0.5%, Mn: 0.3-1.5%, P: 0.03-0.10%, Al: 0.02-0.10%, Cr: 0.01-0.20%, Cu: 0.01-0.30%, N: 0.007-0.020%, and B: 0.0006-0.003%. The low-cost hot-rolled steel sheet for high-temperature enamel does not contain Ti, Nb, or V. Furthermore, the chemical composition satisfies the following condition: P×(N-14×B / 11)×10 3 >0.3, and P, N and B in the calculation are substituted with the numerical value before the percent sign in mass% of the corresponding chemical element.Further disclosed is a manufacturing method of low-cost hot-rolled steel sheet for high-temperature enamel, which includes the following steps:(1): smelting and casting;(2): heating;(3): hot rolling: controlling the rough rolling temperature to be over 850°C, controlling the finish rolling start temperature to be 900-1050°C, and controlling the finish rolling end temperature to be 840-900°C;(4): laminar cooling: controlling the cooling rate to be 10-35°C / s; and(5): coiling.

Description

[Technical field]

[0001] The present invention relates to a steel material and a manufacturing method thereof, and more particularly to a low-cost hot-rolled steel sheet for high-temperature enamel and a manufacturing method thereof. [Background technology]

[0002] In recent years, with the development of the enamel industry and the rapid progress of new energy technology, large-capacity enamel water heater tanks have become more and more popular in the market, and are mainly applied in commercial electric water heaters, air energy water heaters, pressurized solar water heaters, etc.

[0003] When manufacturing such large-capacity water heater tanks, special high-temperature glazes and high enameling temperature processes compatible with enameling temperatures, usually up to 870-950°C, are generally required. Therefore, the requirements for the steel sheets used are correspondingly higher, and the steel sheets are required to have high-temperature resistance while ensuring enameling properties, and to have sufficient yield strength even after firing at high temperatures to guarantee the performance of the final product.

[0004] In the prior art, some researchers have achieved research results regarding enameling steel materials for water heater tanks.

[0005] Patent Document 1, published on August 25, 2010, discloses a hot-rolled high-strength enameled steel sheet for deep drawing and a manufacturing method thereof. Such enameled steel sheet has a chemical composition including the following: 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 being Fe and unavoidable impurities.

[0006] Furthermore, Patent Document 2 published on January 29, 2014 discloses a hot-rolled enameled steel sheet having a chemical composition including the following: 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%, the balance being Fe and unavoidable impurities, and Ti / C=1.0-1.5.

[0007] Patent Document 3, published on September 14, 2011, discloses a steel plate used for enamel for water heater tanks and a thin slab continuous casting and rolling manufacturing method. The steel plate for enamel for water heater tanks has a chemical composition including the following: C: 0.03-0.10%, Mn: 0.15-0.40%, Si≦0.06%, S: 0.004-0.040%, P≦0.15%, Al: 0.03-0.05%, N: 0.002-0.008%, Ti: 0.02-0.10%, and the balance is Fe and unavoidable impurities.

[0008] It can be seen that the above prior arts show a common feature of adding Ti in the composition. Ti is an alloying element commonly used in enamel steels, and forms compounds such as TiC and TiN with C and N, which can act as hydrogen trapping sites to prevent fishscaling. In addition, the TiC phase also plays a role in precipitation strengthening.

[0009] However, it should be noted that the design of adding Ti element not only makes the manufacturing cost relatively high, but also causes the coarsening and growth of TiC precipitates during high-temperature enamel processing, significantly weakening the strengthening effect. The yield strength of the steel plate is significantly reduced after high-temperature enamel firing at 870 ° C or more, typically less than 300 MPa, which cannot meet the design requirements of large-capacity water heater tanks.

[0010] Based on the above-mentioned drawbacks of the conventional technology, the present invention aims to provide a low-cost hot-rolled steel sheet for high-temperature enamel, which has low manufacturing costs and does not require the addition of expensive alloy elements such as Ti, Nb, or V, while still achieving good enameling adaptability. Furthermore, this low-cost hot-rolled steel sheet for high-temperature enamel has excellent mechanical properties even after high-temperature enameling, and meets various requirements for high-temperature enamel steel sheets for large-capacity water heater tanks. The present invention has great practical significance. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] China Patent Application Publication No. 101812630 [Patent Document 2] China Patent Application Publication No. 103540845 [Patent Document 3] China Patent Application Publication No. 102181805 Summary of the Invention

[0012] One of the objects of the present invention is to provide a low-cost hot-rolled steel sheet for high-temperature enameling, which has low manufacturing costs and does not require the addition of expensive alloy elements such as Ti, Nb, or V, while still achieving good enameling adaptability. Furthermore, this low-cost hot-rolled steel sheet for high-temperature enameling has excellent mechanical properties even after high-temperature enameling, meets various requirements for high-temperature enameling steel sheets for large-capacity water heater tanks, and is of great practical significance.

[0013] In order to achieve the above object, the present invention provides a low-cost hot-rolled steel sheet for high-temperature enameling, which in addition to Fe and unavoidable impurities further comprises the following chemical composition in mass%: C:0.03~0.12%, Si:0.1~0.5%, Mn:0.3~1.5%, P:0.03~0.10%, Al:0.02~0.10 %, Cr:0.01~0.20%, Cu:0.01~0.30%, N:0.007~0.020%, and B:0.0006~0.003%; Low-cost hot-rolled steel plate for high-temperature enamel does not contain Ti, Nb, and V; and The chemical composition further satisfies the following condition: P×(N-14×B / 11)×10 3 >0.3; In the calculation, P, N, and B are substituted with the numerical value before the percent sign in the mass percent of the corresponding chemical element. For example, if the mass percent of P is 0.10%, the numerical value substituted in the formula is 0.10.

[0014] Preferably, the low-cost hot-rolled steel sheet for high-temperature enameling in the present invention comprises the following chemical composition in mass%: C: 0.03-0.12%, Si: 0.1-0.5%, Mn. 0.3-1.5%, P: 0.03-0.10%, Al: 0.02-0.10%, Cr: 0.01-0.20%, Cu: 0.01-0.30%, N: 0.007-0.020%, B: 0.0006-0.003%, and the balance is Fe and other unavoidable impurities; Here, the chemical composition further satisfies the following condition: P × (N-14 × B / 11) × 10 3 >0.3; In the calculation, P, N, and B are substituted with the numerical value before the percent sign in the mass percent of the corresponding chemical element. For example, if the mass percent of P is 0.10%, the numerical value substituted in the formula is 0.10.

[0015] In the present invention, a composition system with higher contents of P, N and B compared to conventional enamel steel for water heaters is creatively adopted, and the addition of expensive alloy elements such as Ti, Nb and V is avoided, thereby making it possible to effectively reduce manufacturing costs.

[0016] In the low-cost hot-rolled steel plate for high-temperature enameling in the present invention, the design principles of each chemical element are as follows: C: Carbon is an important strengthening element of steel, and can strengthen the matrix and improve the yield strength of the steel sheet by dissolving in ferrite under certain conditions or forming pearlite. However, since carbide-forming elements such as Ti, Nb, and V are not added in the present invention, it should be noted that if the carbon content is high, pearlite will be excessively formed during enamel processing, and a large amount of gas such as CO will be generated. This will cause defects such as bubbles and pinholes in the enamel layer, which will have a significant impact on the enamel quality. Therefore, in the low-cost hot-rolled steel sheet for high-temperature enamel in the present invention, the mass% of C element is limited to 0.03 to 0.12%.

[0017] Si: The element Si can play a role in solid solution strengthening of steel. In addition, Si can improve the high-temperature deformation resistance and softening resistance of the steel sheet during high-temperature enameling. However, it should be noted that excessive content of Si in steel not only reduces its plasticity but also can affect the adhesion between the steel sheet and the enamel layer. Therefore, in the low-cost hot-rolled steel sheet for high-temperature enameling in the present invention, the mass% of the element Si is limited to 0.1-0.5%.

[0018] Mn: Mn element is one of the most cost-effective alloying elements that can improve the strength of steel, and is a key element for achieving high strength of steel in the present invention. However, it should be noted that Mn element can further expand the austenite phase region, lower the Ac3 temperature, and adversely affect the enameling properties of the steel sheet. This is because the austenite phase has higher hydrogen solubility than the ferrite phase, which makes it more likely to cause fish scaling after cooling. Therefore, excessive addition of Mn to steel should be avoided. For this reason, in the low-cost hot-rolled steel sheet for high-temperature enameling in the present invention, the mass% of Mn element is limited to 0.3-1.5%.

[0019] P: P is an important strengthening element. Its solid solution strengthening effect can be fully utilized even after high-temperature enameling, and is crucial in ensuring that the steel of the present invention has a high yield strength even after high-temperature enameling. However, it should be noted that excessive addition of P to the steel should be avoided. If the content of P element is too high, the plasticity, toughness and welding properties of the steel will be reduced. Therefore, in the low-cost hot-rolled steel sheet for high-temperature enameling in the present invention, the mass% of P element is limited to 0.03-0.10%.

[0020] Al: Al is a strong deoxidizing element. In order to maintain a low O content in steel, Al is usually adopted for deoxidizing low carbon steel and medium carbon steel. Furthermore, Al element dissolved in steel can combine with free N to precipitate AlN. The precipitation temperature of AlN is high, and it can refine austenite grains. In the present invention, it is necessary to increase the yield strength of the steel sheet even under air-cooling conditions after high-temperature enameling. Due to the high-temperature grain refinement effect of AlN, the steel sheet after high-temperature enameling can have a fine grain structure, and the mechanism of fine grain strengthening is fully utilized. Therefore, in the low-cost hot-rolled steel sheet for high-temperature enameling in the present invention, the mass% of Al element is limited to 0.02 to 0.10%.

[0021] Cr and Cu: Adding an appropriate amount of Cr and Cu elements to steel is beneficial for surface precipitation. The adhesion between the steel and the enamel layer is improved, and the resistance of the steel to fishscaling is improved. A part of Cr in the steel can be substituted with Fe to form alloy carbide (Fe,Cr)3C, thereby improving stability. Another part of Cr can dissolve in ferrite to bring about solid solution strengthening, effectively improving the strength and hardness of ferrite. However, it should be noted that excessive addition of Cr and Cu elements in steel should be avoided. High contents of Cr and Cu elements not only increase the alloy cost, but also increase the corrosion resistance of the steel and adversely affect the enamel adhesion during the enamel processing of the steel sheet. Therefore, in the low-cost hot-rolled steel sheet for high-temperature enamel in the present invention, the mass% of Cr element is limited to 0.01-0.20%, and the mass% of Cu element is limited to 0.01-0.30%.

[0022] N: Under normal conditions, the content of N element in steel should be kept as low as possible. However, in the present invention, a moderate amount of free N is an important prerequisite for the formation of BN precipitates and AlN precipitates. Therefore, in the low-cost hot-rolled steel sheet for high-temperature enamel in the present invention, the mass% of N element is limited to 0.007 to 0.020%.

[0023] B: In the technical solution of the present invention, B has very low solubility in steel. It mainly combines with free N in steel and precipitates in the form of BN. BN precipitates preferentially at high temperatures, and its precipitation temperature is higher than that of AlN. In the present invention, BN precipitates can be used as the main hydrogen trapping site, which contributes to fishscaling resistance during enameling. However, it should be noted that since free N in steel is consumed in the precipitation process of BN, the precipitation temperature of AlN decreases and the precipitation amount of AlN decreases, which affects the refinement of austenite grains caused by AlN and increases the grain size. Therefore, the content of B element in steel should not be too high. In the low-cost hot-rolled steel sheet for high-temperature enameling in the present invention, the mass% of B element is limited to 0.0006-0.003%.

[0024] In the present invention, the elements P, N and B in the low-cost hot-rolled steel sheet for high-temperature enamel must be controlled to satisfy the following formula while controlling the mass percentage of each chemical element: P×(N−14×B / 11)×10 3>0.3. The inventors have found through experimental research that if the contents of P, N and B in steel satisfy the above relationship, the decrease in the yield strength of the steel sheet after high-temperature enameling can be kept within 10% and the yield strength can be guaranteed to reach a level of 342 MPa or more. When such a formula is satisfied, a sufficient amount of BN precipitates can be formed in the steel matrix as hydrogen trapping sites, and then a sufficient amount of AlN precipitates can be formed, so that the grain refinement effect of AlN precipitates can be fully utilized. In particular, even after high-temperature enameling of the steel sheet, a very fine grain structure can be realized, which exerts the strengthening effect of fine grains. In combination with the solid solution strengthening effect of P, a significant decrease in the yield strength of the steel sheet can be prevented, which is one of the important innovative aspects of the composition design of the present invention.

[0025] Preferably, the microstructure of the low-cost hot-rolled steel sheet for high-temperature enameling in the present invention is ferrite and pearlite.

[0026] Preferably, in the low-cost hot-rolled steel sheet for high-temperature enamel of the present invention, the average grain size of ferrite is grade 10 to 12. The fine grains ensure a sufficient effect of grain refinement strengthening.

[0027] Preferably, the low-cost hot-rolled steel sheet for high-temperature enameling in the present invention has a thickness of 1.5 to 3.5 mm.

[0028] Preferably, in the low-cost hot-rolled steel sheet for high-temperature enameling of the present invention, the yield strength of the hot-rolled steel sheet in the hot-rolled state is 364 to 410 MPa, the reduction in yield strength after high-temperature enameling in a temperature range of 870 to 950°C is within 10%, and the yield strength value is 342 MPa or more.

[0029] Correspondingly, another object of the present invention is to provide a method for manufacturing a low-cost hot-rolled steel sheet for high-temperature enamel. This manufacturing method has a simple manufacturing process. By using this manufacturing method, a low-cost hot-rolled steel sheet for high-temperature enamel with good enamel adaptability can be obtained.

[0030] In order to achieve the above object, the present invention provides a method for producing a low-cost hot-rolled steel sheet for high-temperature enameling, comprising the following steps: (1) Smelting and foundry; (2) heating; (3) Hot rolling: the rough rolling temperature is controlled to be over 850°C, the finish rolling start temperature is controlled to be 900-1050°C, and the finish rolling end temperature is controlled to be 840-900°C; (4) Laminar cooling: The cooling rate is controlled to 10 to 35°C / s; and (5) Coiling.

[0031] In the present invention, the casting in step (1) can be carried out by continuous casting or die casting, which can ensure uniform composition and good surface quality of the cast slab. In some other embodiments, die casting can also be used. The die casting steel ingot needs to be rolled into a steel slab by a blooming mill.

[0032] Correspondingly, during the hot rolling step of step (3) above, the heated cast slab can be subjected to rough rolling to first form an intermediate slab, and then finish rolling to obtain the desired slab.

[0033] In the step (4) of the present invention, the slab is water-cooled at a cooling rate of 10 to 35°C / s to the coiling temperature of the step (5), and then air-cooled to room temperature. By adopting such controlled rolling and cooling steps in the present invention, a fine ferrite grain structure can be obtained, sufficient effect of grain refinement strengthening can be ensured, and the yield strength of the steel plate can be improved, so that the performance of the steel plate can be further improved, and it is possible to realize the production of a low-cost hot-rolled steel plate for high-temperature enamel suitable for a large-capacity water heater tank.

[0034] Preferably, in the above step (2), the heating temperature is controlled to 1150 to 1260°C.

[0035] Preferably, in the above step (5), the coiling temperature is controlled to 550 to 680°C.

[0036] In the above technical solution, the coiling temperature is controlled to 550-680°C. Coiling within this temperature range is not only advantageous for refining ferrite grains, but also for uniform precipitation of the BN phase. As a result, a low-cost hot-rolled steel sheet for high-temperature enamel can be obtained that has good mechanical properties and good resistance to fishscaling.

[0037] Compared with the prior art, the low-cost hot-rolled steel sheet for high-temperature enameling and its manufacturing method of the present invention have the following advantages and beneficial effects: In the present invention, a composition system having high contents of P, N, and B is creatively adopted, and the addition of expensive alloy elements such as Ti, Nb, and V is avoided. In addition, in the present invention, a low-cost hot-rolled steel sheet for high-temperature enamel suitable for large-capacity water heater tanks is manufactured by rationally designing the chemical composition and optimizing the controlled rolling and cooling processes after rolling. This makes it possible to manufacture a low-cost hot-rolled steel sheet for high-temperature enamel with good enamel adaptability while reducing the manufacturing cost.

[0038] After high-temperature enameling in the temperature range of 870-950℃, the yield strength of the low-cost hot-rolled steel sheet for high-temperature enameling is reduced by only 10%, and the yield strength still reaches 342MPa or more. Therefore, this hot-rolled steel sheet retains excellent mechanical properties and meets various requirements for high-temperature enameling steel for large-capacity water heater tanks. This has important practical significance. [Brief description of the drawings]

[0039] [Figure 1]FIG. 1 is a diagram showing the relationship between the defined chemical element synergistic effect M* in the present invention and the yield strength of a low-cost hot-rolled steel sheet for high-temperature enameling after enameling. [Diagram 2] FIG. 2 is a photograph of the microstructure of the low-cost hot-rolled steel sheet for high-temperature enamel in Example 1 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] The low-cost hot-rolled steel sheet for high-temperature enamel and its manufacturing method in the present invention will be further explained and described in the following with the accompanying drawings and specific embodiments, however, the explanation and description are not intended to unduly constitute the technical solution of the present invention. EXAMPLES

[0041] Examples 1 to 6 and Comparative Examples 1 to 3 The low-cost hot-rolled steel sheets for high-temperature enameling of Examples 1 to 6 and the comparative steel sheets of Comparative Examples 1 to 3 are produced according to the following steps: (1) Smelting and casting: Smelting and casting are carried out according to the chemical composition shown in Table 1 below. The steel after smelting and casting is then vacuum degassed and continuously cast to obtain a continuous cast slab; (2) Heating: The obtained continuous casting slab is heated and the heating temperature is controlled to 1150-1260°C; (3) Hot rolling: the rough rolling temperature is controlled to be over 850°C, the finish rolling start temperature is controlled to be 900-1050°C, and the finish rolling end temperature is controlled to be 840-900°C; (4) Laminar cooling: Laminar water cooling is performed, and the cooling rate is controlled to 10 to 35 ° C / s; and (5) Coiling: The coiling temperature is controlled at 550 to 680°C.

[0042] Table 1 shows the mass percentages of various chemical elements in the low-cost hot-rolled steel sheets for high-temperature enameling of Examples 1-6 and the comparative steel sheets of Comparative Examples 1-3.

[0043] [Table 1]

[0044] Table 2 shows specific process parameters in the above-mentioned manufacturing process for the low-cost hot-rolled steel sheets for high-temperature enamel of Examples 1-6 and the comparative steel sheets of Comparative Examples 1-3.

[0045] [Table 2]

[0046] The obtained low-cost hot-rolled steel sheets for high-temperature enamel of Examples 1 to 6 and the comparative steel sheets of Comparative Examples 1 to 3 are sampled. The properties of the steel sheets of the Examples and Comparative Examples are tested to obtain the test results shown in Table 3. The methods and procedures of the relevant performance tests are described below. Tensile test: GB / T 228.1-2010 Metallic materials - Tensile test - Part 1 "Test method at room temperature" is based on the SCL233 room temperature tensile tester. The test was performed using a JIS5 tensile test piece at a tensile speed of 3mm / min;

[0047] Hole expansion test: for the test according to GB / T 24524-2009 Metallic materials-Sheets and strips-"Hole expansion test", use SCL250 cupping tester. The test speed is 6mm / min; Drop weight test: for the adhesion test of enamel based on the drop weight test method described in the European standard BS EN 10209-1996, adopt the corresponding drop weight test device; and Average grain size of ferrite: The average grain size is determined according to GB / T 6394-2017 "Methods for estimating the average grain size of metals" by using a metallographic microscope to compare with the standard grade table.

[0048] Table 3 shows the results of performance tests of the low-cost hot-rolled steel sheets for high-temperature enamel of Examples 1 to 6 and the comparative steel sheets of Comparative Examples 1 to 3, as well as the microstructures and grain sizes of ferrite.

[0049] [Table 3]

[0050] In order to further demonstrate the performance after enameling of the low-cost hot-rolled steel sheets for high-temperature enameling of Examples 1-6 and the comparative steel sheets of Comparative Examples 1-3, it is necessary to subject the steel sheets of the Examples and Comparative Examples to enameling: Specifically, Ferro EMP6515 high-temperature glaze was used to perform one-sided wet enameling on the steel sheets of the examples and comparative examples. The enameling was controlled to a temperature of 870-950°C and a holding time of 10 minutes, and then air-cooled to obtain the enameled steel sheets of Examples 1-6 and Comparative Examples 1-3.

[0051] After the above operations were completed, the enameled hot-rolled steel sheets of Examples 1 to 6 and the enameled comparative steel sheets of Comparative Examples 1 to 3 were observed and tested. After enameling, the steel sheets were left for 48 hours, and no fish scaling phenomenon was observed on the steel sheet surface. In addition, the adhesion between the steel sheet and the enamel was confirmed by a drop weight test, and the adhesion was found to be good. A tensile test was conducted to measure the yield strength of the enameled steel sheets of each Example and Comparative Example. The test results are shown in Table 4.

[0052] Table 4 shows the results of performance tests of the low-cost hot-rolled steel sheets for high-temperature enameling of Examples 1 to 6 and the comparative steel sheets of Comparative Examples 1 to 3 after enameling.

[0053] [Table 4]

[0054] With reference to Table 4 and Tables 1 to 3 together, it can be seen that the low-cost hot-rolled steel sheets for high-temperature enamel of Examples 1 to 6 have a thickness in the range of 1.5 to 3.5 mm, a yield strength of 364 to 410 MPa, a tensile strength of 456 to 512 MPa, an elongation of 27 to 31%, and a hole expansion ratio of 80 to 92% in the hot-rolled state. After high-temperature enameling in the temperature range of 870 to 950°C, the yield strength of the steel sheets of Examples 1 to 6 is reduced by 10% or less, and the yield strength is still 342 MPa or more. This indicates that the steel sheets have excellent high-temperature enamel resistance. After leaving the finally obtained enameled steel sheets of Examples 1 to 6 for 48 hours, no fish scaling phenomenon was observed on the enamel surface. A drop weight test confirmed that the adhesion between the steel sheet and the enamel layer was good, which fully met the requirements of users.

[0055] In contrast, the performance of the comparative steel sheets of Comparative Examples 1 to 3 is significantly inferior to the performance of the low-cost hot-rolled steel sheets for high-temperature enamel of Examples 1 to 6. In Comparative Examples 1 to 3, the contents of P, N and B in the steel are P×(N-14×B / 11)×10 3 >0.3. After high-temperature enameling in the temperature range of 870-950°C, the yield strength decreases by 18% or more, and the yield strength is in the range of 220-290 MPa.

[0056] FIG. 1 shows the defined chemical element synergistic effect M * 1 is a graph showing the relationship between the yield strength of low-cost hot-rolled steel sheet for high-temperature enamel processing and the yield strength of low-cost hot-rolled steel sheet for high-temperature enamel processing after enameling; * =P×(N-14×B / 11)×10 3 It is.

[0057] As can be seen from FIG. 1, in the present invention, the yield strength and M of the steel plate after enameling are * There is a clear correlation between the values ​​of M * If the value is 0.3 or more, the yield strength can be made 342 MPa or more, which satisfies the design target requirements of the product.

[0058] FIG. 2 is a photograph of the microstructure of the low-cost hot-rolled steel sheet for high-temperature enameling in Example 1.

[0059] As shown in FIG. 2, the microstructure of the low-cost hot-rolled steel sheet for high-temperature enamel in Example 1 is ferrite and pearlite, and the average grain size of ferrite is 10 grades.

[0060] It should be noted that the combination aspects of the technical features in this case are not limited to the combination aspects described in the claims of this case or the combination aspects described in the specific embodiments, and all the technical features described in this case can be freely combined or incorporated in any manner as long as there is no contradiction between them.

[0061] It should be further noted that the above listed embodiments are merely specific embodiments of the present invention. The present invention is not limited to the above embodiments. Those skilled in the art can directly obtain or easily think of similar modifications or variations from the contents disclosed by the present invention, so as to fall within the protection scope of the present invention.

Claims

1. A low-cost hot-rolled steel sheet for high-temperature enamel, The hot rolled steel sheet has the following chemical composition in mass percent: C: 0.03 to 0.12%, Si: 0.1 to 0.5%, Mn: 0.3 to 1.5%, P: 0.03 to 0.10%, Al: 0.02 to 0.10%, Cr: 0.01 to 0.20%, Cu: 0.01 to 0.30%, N: 0.007 to 0.020%, and B: 0.0006 to 0.003%, and the balance is Fe and other inevitable impurities; The low-cost hot-rolled steel sheet for high-temperature enamel does not contain Ti, Nb, and V; and The chemical composition further satisfies the following condition: P x (N-14 x B / 11) x 10 ３ >0.3; In the calculation, P, N, and B are substituted with the numerical values ​​before the percent signs in the mass % of the corresponding chemical elements. Low-cost hot-rolled steel sheet for high-temperature enamel.

2. The low-cost hot-rolled steel sheet for high-temperature enamel according to claim 1, wherein the microstructure of the hot-rolled steel sheet is ferrite and pearlite.

3. The low-cost hot-rolled steel sheet for high-temperature enamel according to claim 2, wherein the average grain size of ferrite is 10 to 12 grades.

4. The low-cost hot-rolled steel sheet for high-temperature enamel according to claim 1, wherein the thickness of the hot-rolled steel sheet is 1.5 to 3.5 mm.

5. The hot-rolled steel sheet has a yield strength of 364 to 410 MPa in a hot-rolled state, and the reduction in yield strength after high-temperature enameling in a temperature range of 870 to 950 ° C. is within 10%, and the yield strength value is 342 MPa or more.

6. A method for producing a low-cost hot-rolled steel sheet for high-temperature enamel according to claim 1, comprising the following steps: Step (1): Smelting and casting; Step (2): heating; Step (3): Hot rolling: the rough rolling temperature is controlled to be more than 850°C, the finish rolling start temperature is controlled to be 900-1050°C, and the finish rolling end temperature is controlled to be 840-900°C; Step (4): Laminar cooling: controlling the cooling rate to 10 to 35 ° C. / s; and Step (5): Coiling.

7. The method according to claim 6, wherein in the step (2), the heating temperature is controlled to 1150 to 1260°C.

8. The method according to claim 6, wherein in the step (5), the coiling temperature is controlled to 550 to 680°C.

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