CN116136009B

CN116136009B - Hot-rolled enameling steel with enameling strengthening property and manufacturing method thereof

Info

Publication number: CN116136009B
Application number: CN202111351890.7A
Authority: CN
Inventors: 王双成; 孙全社; 陶孝勇
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2021-11-16
Filing date: 2021-11-16
Publication date: 2025-05-02
Anticipated expiration: 2041-11-16
Also published as: EP4435133A4; US20250003040A1; EP4435133A1; MX2024005957A; WO2023088294A1; CN116136009A

Abstract

The invention discloses a hot-rolled enamel steel with enamel firing strengthening property, which contains the following chemical elements ：C：0.03～0.07％,Si≤0.05％,Mn：1.5～2.5％,Al：0.01～0.05％,Cr：0.25～0.65％,Cu：0.02～0.20％,Ti：0.01～0.08％,V：0.01～0.10％,Mo：0.01～0.10％. in percentage by mass besides Fe and unavoidable impurities, and correspondingly, the invention also discloses a manufacturing method of the hot-rolled enamel steel, comprising the following steps: (1) smelting and casting; the method comprises the steps of (1) heating, (3) hot rolling, namely controlling the rough rolling temperature to be higher than 850 ℃, the finish rolling start temperature to be 900-1050 ℃, the finish rolling temperature to be 840-900 ℃, and (4) laminar cooling, namely controlling the cooling speed to be 10-35 ℃ per second, and (5) coiling. The steel for hot rolling enamel has lower strength and good forming property in a hot rolling state, and after being burnt at a high Wen Tang, the yield strength of the steel is not decreased but increased, so that the strength of a final enamel product can be effectively improved.

Description

Hot-rolled enamel steel with enamel firing strengthening property and manufacturing method thereof

Technical Field

The present invention relates to a steel material and a method for producing the same, and more particularly, to a hot rolled steel sheet for enameling and a method for producing the same.

Background

The hot-rolled enamel steel is a composite material formed by applying enamel on the surface of a pretreated hot-rolled steel plate and being matched with high-temperature sintering, and has the excellent characteristics of strength and toughness of the hot-rolled steel plate, corrosion resistance of the enamel, easy cleaning and the like.

Of course, not all steel sheets are suitable for enamel applications, and the steel sheet as a substrate directly affects the quality of the enamel steel product, and fish scale explosion is one of the most common and terrible defects of the enamel steel product.

The current mature theory holds that the scale explosion defect is mainly caused by hydrogen, the hydrogen mainly enters the steel plate in the processes of acid washing (the metal is dissolved in the acid to generate hydrogen) and enamel firing (the crystal water contained in an enamel mill additive or water vapor in the furnace atmosphere and the like react with the metal to generate hydrogen), the solubility of the hydrogen in the steel is reduced along with the reduction of the temperature and reaches a supersaturation state, so that the hydrogen is accumulated between the steel plate and an enamel layer in a gas form, a certain pressure is further formed, and the scale explosion defect is caused when the pressure is increased by a certain critical value.

Therefore, in addition to improving the enamel technology, the hydrogen storage performance of the steel plate needs to be improved, when the hydrogen storage capacity of the steel plate is strong, the diffusion of hydrogen in the steel plate is slow, less hydrogen enters the steel plate under the same enamel technology, and the capacity of the steel plate for containing hydrogen after the enamel is finished is also strong, so that the steel plate is beneficial to preventing the scale explosion of enamel products. Grain boundary, dislocation, cavity, inclusion and precipitation in steel are all good hydrogen storage traps, so for enamel steel, components and production processes of the steel are required to be adjusted according to different enamel applications, so that enough hydrogen storage traps are ensured in the steel, and good anti-scaling performance is realized.

In addition, since the enamel sintering process is usually performed at a high temperature of 820 ℃ or higher for a period of time, the final strength of the enamel product depends on the strength of the enamel steel after high temperature enameling. In general, the strength of a steel sheet is remarkably reduced after such high-temperature heat treatment because the microstructure of the steel sheet undergoes a reduction in dislocation density, a large growth of ferrite grains, coarsening of nano precipitated phases, etc. during the high-temperature heat treatment, and these changes result in dislocation strengthening, fine grain strengthening, precipitation strengthening, and the like, while weakening. How to improve the strength of the steel plate after high-temperature enameling is always an important research topic in the field of enamel steel development, and has important practical application value.

In the prior art, the conventional patent technology for hot-rolled enamelled steel adopts a design of adding Ti element in the composition, and forms a precipitated phase such as TiC and Ti (C, N) with C, N to exert the functions of hydrogen storage trap, precipitation strengthening and the like.

For example, chinese patent literature with publication number CN101812630A and publication date of about 8/25/2010 entitled "hot rolled high strength enamelled steel sheet for deep drawing and method for producing same" discloses a hot rolled high strength enamelled steel sheet for deep drawing and method for producing same, wherein the steel sheet comprises C0.02-0.10%, si not more than 0.10%, mn 0.05-1.00%, P not more than 0.05%, S0.005-0.035%, al 0.01-0.10%, N not more than 0.015%, ti <0.10%, and the balance of iron and unavoidable impurities.

Also for example, chinese patent literature with publication number CN103540845A, publication date of 2014, 1 month and 29 days, named as hot rolled sheet enamel steel with yield strength of 330MPa and manufacturing method, also discloses hot rolled sheet enamel steel, which adopts the components of 0.02-0.07% of C, less than or equal to 0.05% of Si, 0.10-0.50% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.04-0.10% of Ti, 0.02-0.08% of Al, less than or equal to 0.008% of N, the balance of Fe and unavoidable impurities, and Ti/C=1.0-1.5.

For another example, the Chinese patent literature with publication number of CN102181805A and publication date of 2011, 9 months and 14 days, named as steel plate and method for producing water heater inner container enamel by using thin slab continuous casting and rolling line, discloses a steel plate and method for producing water heater inner container enamel by using thin slab continuous casting and rolling line, and the steel plate and method for producing water heater inner container enamel comprises the following components of 0.03-0.10 carbon, 0.15-0.40 manganese, less than or equal to 0.06 silicon, 0.004-0.040 sulfur, less than or equal to 0.15 phosphorus, 0.03-0.05 aluminum, 0.002-0.008 nitrogen, 0.02-0.10 titanium and the balance of iron and unavoidable impurities.

However, it should be noted that these solutions have a common disadvantage, and they disclose that the yield strength of the obtained enamelled steel after high temperature enamelling is lower than the yield strength in the hot rolled state.

In view of the above-described drawbacks of the prior art, the present invention has been made to provide a new hot-rolled enameling steel having a low strength and good formability in a hot rolled state, and having a yield strength which does not decrease but increases after being burned at a high Wen Tang, and which can effectively improve the strength of the final enamelled product.

Disclosure of Invention

The invention aims to provide hot-rolled enamel steel with enamel firing strengthening property, which has lower strength and good forming property in a hot rolling state, and after being fired at a temperature of Wen Tang ℃, the hot-rolled enamel steel can ensure that the yield strength of the hot-rolled enamel steel is not reduced and reversely increased through a phase change strengthening mechanism, thereby improving the strength of a final enamel product and prolonging the service life of the enamel product.

The hot rolled enamel steel can be used for preparing products with high enamel firing temperature, high yield strength performance requirement after enamel firing, such as large-volume water heater inner containers, water heater accessories, barbecue ovens and the like, and has very remarkable application value.

In order to achieve the above object, the present invention provides a hot-rolled enameling steel having enameling strengthening properties, which contains, in addition to Fe and unavoidable impurities, the following chemical elements in mass percent:

C：0.03～0.07％,Si≤0.05％,Mn：1.5～2.5％,Al：0.01～0.05％,Cr：0.25～0.65％,Cu：0.02～0.20％,Ti：0.01～0.08％,V：0.01～0.10％,Mo：0.01～0.10％.

further, in the steel for hot rolling enamel of the present invention, the mass percentages of the chemical elements are:

C：0.03～0.07％,Si≤0.05％,Mn：1.5～2.5％,Al：0.01～0.05％,Cr：0.25～0.65％,Cu：0.02～0.20％,Ti：0.01～0.08％,V：0.01～0.10％,Mo：0.01～0.10％, The balance being Fe and other unavoidable impurities.

In the steel for hot rolling enamel according to the present invention, the design principle of each chemical element is as follows:

In the hot-rolled enamelled steel, the element C is an important strengthening element in the steel, and can be dissolved in ferrite or form a pearlite structure under certain conditions, so that the function of strengthening a matrix structure is achieved, and the yield strength of the steel plate is improved. Meanwhile, the element C can be combined with strong carbide forming elements such as Ti, V and the like to form a certain size and number of precipitated phases, and the precipitated phases can improve the hydrogen storage performance of the steel plate, so that the effect of resisting scale explosion of enamel is exerted. However, the C element in the steel is not too high, and when the content of the C element in the steel is too high and the proportion of solid solution carbon or pearlite structure in the steel is too high, a large amount of CO and other gases can be generated during enamel firing, so that the bad bubble structure of an enamel layer is caused, further defects such as pinholes and bubbles are generated, and the quality of the enamel surface is affected. Therefore, in the steel for hot-rolled enameling according to the present invention, the content of the element C is limited to 0.03 to 0.07% by mass.

Si is present in the steel as a residual element in the hot rolled enamelled steel, and when the Si content in the steel is too high, the plasticity of the steel is deteriorated, and in addition, particularly when a enamelling-enamelling process is adopted, the higher Si content also affects the adhesion performance between the steel plate and the enamel. Therefore, in the steel for hot rolling enameling according to the present invention, the mass percentage of Si element is controlled to satisfy Si.ltoreq.0.05% in view of the adverse effect of Si element on the steel properties.

Mn and Cr in the steel for hot-rolled enameling according to the present invention, mn and Cr elements are important elements for ensuring high strength properties of the steel after being burned at a high Wen Tang. The combination of the two elements can lead the steel plate to generate bainite transformation under lower cooling speed, thereby improving the strength of the matrix structure. Therefore, in the hot-rolled enamelled steel according to the present invention, the mass percentage of Mn element is limited to 1.5 to 2.5%, and the mass percentage of Cr element is limited to 0.25 to 0.65%.

Mo in the hot rolled enamel steel, mo element can be dissolved in ferrite, austenite and carbide to play the role of solid solution strengthening, and meanwhile, the stability of the carbide can be improved, and the coarsening phenomenon of carbide precipitated phases caused by high-temperature enameling is reduced, so that the high-temperature stability of the steel is improved. In addition, the addition of a proper amount of Mo element in the steel has a promoting effect on the phase change of the steel plate under the air cooling condition after high-temperature enamelling. Therefore, in the steel for hot-rolled enameling according to the present invention, the content of Mo element is limited to 0.01 to 0.10% by mass.

In the hot-rolled enamelled steel of the invention, the addition of Mn, mo and Cr elements can remarkably improve the stability of supercooled austenite, and when the steel plate is burnt at a high Wen Tang and air-cooled to room temperature, the combination of the three elements can lead the steel plate to generate bainite transformation at a lower cooling speed, thereby obtaining high strength performance.

Al in the hot rolled enamelled steel according to the invention, al is a strongly deoxidizing element, which is often used in medium and low carbon steels to ensure that the O content in the steel is kept at a low value. Therefore, in the steel for hot-rolled enameling according to the present invention, the content of Al element is limited to 0.01 to 0.05% by mass.

Cu is added into the steel for hot rolling enamel, so that the surface deposition is facilitated, the adhesion performance between the steel and the enamel is improved, and the anti-scaling performance of the steel is further improved. Therefore, in the steel for hot-rolled enameling according to the present invention, the content of Cu element is limited to 0.02 to 0.20% by mass.

Ti and V are main elements for obtaining good hydrogen storage performance of the steel, and can form fine and dispersed TiC and VC precipitated phases under proper control and cooling process, and the precipitated phases can be used as irreversible hydrogen storage traps to effectively improve the hydrogen storage performance of the steel plate, thereby playing the role of enamel anti-scaling. Therefore, the mechanical property and cost factors of the steel are comprehensively considered, the mass percentage of Ti element is limited to 0.01-0.08%, and the mass percentage of V element is limited to 0.01-0.10%.

Further, the steel for hot-rolled enameling according to the present invention further contains 0.0006 to 0.003% of B.

In the above-described embodiment of the present invention, in order to obtain a more preferable effect, it is preferable to add an appropriate amount of B element to the steel for hot-rolled enameling.

In the steel for hot rolling enamel, the solubility of the B in the steel is very low, and the B can be mainly combined with residual nitrogen in the steel and separated out in a BN form, can be used as a hydrogen storage trap and plays a role in resisting scale explosion of enamel. Therefore, in order to exert the beneficial effect of the B element, the mass percentage of the B element in the steel for hot rolling enamel is controlled to be 0.0006-0.003%.

Further, in the steel for hot-rolled enameling according to the present invention, each chemical element satisfies (C-Ti/4-V/4.25) × (Mn+Cr) >0.05, wherein C, ti, V, cr and Mn each represent a value of mass percent of the corresponding element.

The hot-rolled enamelled steel can preferably control C, ti, V, cr and Mn elements to meet the formula (C-Ti/4-V/4.25) x (Mn+Cr) >0.05 while controlling the mass percentage of single chemical elements.

The inventor finds through experimental study that when the C, ti, V, cr and Mn element contents in the steel are controlled to meet the above relation, the steel plate can obtain the enamel firing strengthening performance, namely the strength of the steel plate after being fired at a high Wen Tang is not only reduced, but also increased.

This is because, when these elements in the steel satisfy this relational expression, C element remaining after formation of the precipitated phases of Ti and V and Mn and Cr elements in the steel act together, so that the microstructure is transformed from pearlite to bainite or martensite after the steel sheet is subjected to high Wen Tang firing and air cooling, and further, by this transformation strengthening effect, the steel sheet is given higher strength performance than in the hot rolled state, which is one of the key innovations in the composition design of the present invention.

Further, in the steel for hot-rolled enameling according to the present invention, the microstructure is ferrite+pearlite.

Further, in the steel for hot-rolled enameling according to the present invention, the ferrite grain size is 8 to 10 grades.

Further, in the steel for hot-rolled enameling according to the present invention, the thickness is 1.5 to 3.5mm.

Further, in the steel for hot-rolled enamel, the yield strength in a hot-rolled state is 345-389 MPa, and after high-temperature enameling in a temperature range of 870-950 ℃, the yield strength is 402-439 MPa.

Accordingly, it is still another object of the present invention to provide a method for manufacturing the hot-rolled enamel steel as described above, which is simple in production process, and the hot-rolled enamel steel manufactured by the method has low strength and good formability in a hot rolled state, and which can prevent its yield strength from being lowered and raised by a phase change strengthening mechanism after being burned by a high Wen Tang.

In order to achieve the above object, the present invention provides a method for manufacturing the hot rolled enamelled steel, comprising the steps of:

(1) Smelting and casting;

(2) Heating;

(3) Hot rolling, namely controlling the rough rolling temperature to be higher than 850 ℃, the finish rolling start temperature to be 900-1050 ℃ and the finish rolling temperature to be 840-900 ℃;

(4) Laminar cooling, namely controlling the cooling speed to be 10-35 ℃ per second;

(5) And (5) coiling.

In the technical scheme of the invention, in order to obtain a proper hot rolling state structure and enable the hot rolled steel to have lower strength and higher forming performance, the hot rolling process parameters of the step (3) and the laminar cooling parameters of the step (4) are strictly controlled, and the performance of the hot rolled enamel steel can be ensured by controlling rolling and cooling.

In the hot rolling process of the step (3), the heated casting blank is firstly rough rolled into an intermediate blank, then the obtained intermediate blank is subjected to finish rolling, and finally the intermediate blank is subjected to finish rolling to form a required plate blank. Wherein the rough rolling temperature is controlled to be higher than 850 ℃, the finish rolling start temperature is controlled to be 900-1050 ℃, and the finish rolling temperature is controlled to be 840-900 ℃.

Correspondingly, in the step (4), water is cooled to a coiling temperature through a cooling speed of 10-35 ℃ per second, and then air cooling is carried out to room temperature. The invention adopts the controlled rolling and cooling process, which is favorable for obtaining fine ferrite and pearlite grain structure and ensures that the steel plate has good processing and forming performance.

The hot rolled enamel steel manufactured by the manufacturing method can be further used for single-sided enamel or double-sided enamel to manufacture enamel products.

In the step (1) of the present invention, the casting may be performed by continuous casting or die casting, which ensures uniformity of the internal components of the cast slab and good surface quality. In some other embodiments, the die casting mode can be adopted, and the die cast steel ingot is rolled into a steel billet through a blooming mill.

Further, in the manufacturing method of the present invention, in the step (2), the heating temperature is 1150 to 1260 ℃.

Further, in the manufacturing method of the present invention, in the step (5), the winding temperature is controlled to 550 to 680 ℃.

In the technical scheme, the coiling temperature can be preferably controlled to be 550-680 ℃, and when the coiling is performed in the temperature range, the method is favorable for refining ferrite grains and homogenizing TiC and VC precipitated phases in steel so as to obtain the hot-rolled enamel steel with excellent mechanical properties and anti-scaling properties.

Compared with the prior art, the manufacturing method of the hot-rolled enamelled steel has the following advantages:

The invention reasonably designs chemical components and combines and optimizes a controlled rolling and cooling process for rapid cooling after rolling, thereby effectively preparing the hot-rolled enamel steel with excellent performance in a hot rolling state, the production process is simple, the prepared hot-rolled enamel steel has lower strength and good forming performance in the hot rolling state, after being burnt by a high Wen Tang, the hot-rolled enamel steel can ensure that the self yield strength is not reduced and raised by a phase change strengthening mechanism, and the invention not only can improve the strength of enamel products, but also can prolong the service life of the enamel products.

The yield strength of the steel for hot rolling enamel is 345-389 MPa in a hot rolling state, after high-temperature enamelling in a temperature range of 870-950 ℃, the yield strength can be raised to 402-439 MPa, and the steel can be used for preparing products with high enameling temperature, such as large-volume water heater inner containers, water heater accessories, barbecue ovens and the like, and has very remarkable application value on products with high yield strength performance requirements after enameling.

Drawings

FIG. 1 shows the effect of different enamelling temperatures on the yield strength properties of the steels of example 1 and comparative example 1 of the present invention after enamelling.

FIG. 2 is a photograph showing the metallographic structure of the steel for hot-rolled enameling of example 1 in a hot-rolled state.

FIG. 3 is a photograph showing a metallographic structure of the hot rolled enamel steel of example 1 which was subjected to high temperature enameling at 870℃and air cooling after 10 minutes of heat preservation.

Detailed Description

The hot rolled enamelled steel and the method for manufacturing the same according to the invention will be further explained and illustrated in the accompanying drawings and specific examples, which, however, do not constitute an undue limitation on the solution according to the invention.

Examples 1 to 7 and comparative examples 1 to 2

The manufacturing method of the hot rolled enamelled steels of examples 1 to 7 and the comparative steels of comparative examples 1 to 2 were prepared by the following steps:

(1) Smelting and casting are carried out according to the chemical compositions shown in the following table 1, namely, molten steel after smelting is subjected to vacuum degassing treatment and then continuous casting is carried out, and a continuous casting blank is obtained.

(2) Heating, namely heating the obtained continuous casting blank, and controlling the heating temperature to 1150-1260 ℃.

(3) And hot rolling, namely controlling the rough rolling temperature to be higher than 850 ℃, controlling the finish rolling start temperature to be 900-1050 ℃ and controlling the finish rolling temperature to be 840-900 ℃.

(4) Laminar cooling, namely performing laminar water cooling, and controlling the cooling speed to be 10-35 ℃ per second.

(5) Coiling, namely controlling the coiling temperature to be 550-680 ℃.

The hot rolled enamelled steel of examples 1-7 according to the invention is prepared by the above steps, and the chemical composition and the relevant process parameters thereof meet the control requirements of the design specification of the invention.

It should be noted that, unlike the hot-rolled enamelled steels of examples 1 to 7, the comparative steels of comparative examples 1 to 2 also use the step flow paths of the steps (1) to (5), but all of the chemical element components have parameters which do not satisfy the design requirements of the present invention.

Table 1 shows the mass percentages of the respective chemical elements in the hot-rolled enamelled steels of examples 1 to 7 and the comparative steels of comparative examples 1 to 2.

TABLE 1 (balance Fe and other unavoidable impurities)

Note that M = (C-Ti/4-V/4.25) × (mn+cr) >0.05, wherein C, ti, V, cr and Mn represent the values of the mass percentages of the respective elements, respectively.

Table 2 shows the specific process parameters for the above-described manufacture of the hot-rolled enamelled steels of examples 1-7 and the comparative steels of comparative examples 1-2.

Table 2.

The hot rolled enamelled steels of examples 1 to 7 and the comparative steels of comparative examples 1 to 2 in a hot rolled state were sampled respectively, and the properties of the hot rolled state steels of each example and comparative example were tested, and the test results obtained are shown in Table 3, and the relevant property test methods and means are as follows:

Tensile test according to GB/T228.1-2010 "method for room temperature tensile test of metallic Material", a test was conducted by means of a SCL233 room temperature tensile tester at a tensile speed of 3mm/min and a tensile test specimen of JIS5 to obtain yield strength, tensile strength and elongation A ₅₀ of hot rolled steels corresponding to examples 1-7 and comparative examples 1-2.

Table 3.

As shown in FIG. 3, in the present invention, the hot rolled enamelled steels of examples 1 to 7 all had lower yield strengths and good formability in the hot rolled state, the yield strengths were 345 to 389MPa, the tensile strengths were 558 to 625MPa, and the elongation A ₅₀ was 28 to 32%.

The lower yield strength is beneficial to stamping and cold bending forming processing of the steel plate in the use process of a user, for example, rebound after cold bending and rolling can be avoided in the process of processing the water heater inner container barrel body, so that the welding processing is facilitated. The higher yield strength of the comparative steels of comparative examples 1-2 compared to examples 1-7 is detrimental to the user in terms of handling.

To further demonstrate the enamelled properties of the hot rolled enamelled steels of examples 1-7 and the comparative steels of comparative examples 1-2 according to the present invention, enamelled steel sheets of each example and comparative example were required to be enamelled:

The steel plates of each example and the comparative example are subjected to double-sided wet enamel treatment by adopting high-temperature enamel with Fulu EMP6515, and the enamel firing process is controlled to be 870-950 ℃ and is kept for 10 minutes, and then the steel plates of examples 1-7 and comparative examples 1-2 after enamel are obtained through air cooling.

In this embodiment, examples 1 to 7 and comparative examples 1 to 2 were each controlled to be high-temperature baked at 870 to 950 ℃ and kept for 10 minutes, and specific high Wen Tang baking temperatures of each example and comparative example are shown in the following table 4.

Table 4.

After the completion of the above high temperature enameling, the hot rolled enameling steels of examples 1 to 7 and the comparative steels of comparative examples 1 to 2, which had been subjected to the high temperature enameling treatment, were subjected to further observation analysis and test verification:

The steel sheets of examples 1 to 7 and comparative examples 1 to 2 were allowed to stand for 48 hours and then observed for the occurrence of the scaling phenomenon on the surfaces, the adhesion property between the steel sheets and enamel was verified by a drop weight test, and the yield strength, tensile strength and elongation A ₅₀ of each of the steel sheets of examples and comparative examples after enamel were determined by a tensile test, and the results of the test are shown in Table 5.

Table 5 shows the mechanical properties and enamel properties of the hot-rolled enamelled steels of examples 1 to 7 and the comparative steels of comparative examples 1 to 2 after enameling.

Table 5.

As can be seen from Table 4, in combination with tables 1 to 3, the thickness of the hot rolled enamelled steel of examples 1 to 7 can be in the range of 1.5 to 3.5mm, the strength of the steel plates of examples 1 to 7 is not reduced and increased after high temperature enamelling treatment in the temperature range of 870 to 950 ℃, the yield strength is increased to 402 to 439MPa, the tensile strength is increased to 610 to 660MPa, and the elongation A ₅₀ is 18 to 22%.

The finally obtained enamelled steel sheets of examples 1-7 have no scale explosion phenomenon after observing the enamel surface for 48 hours, and have excellent adhesion performance between the steel sheet and the porcelain layer through drop hammer experiment tests, thereby completely meeting the use requirements of users.

Accordingly, the comparative steel sheets of comparative examples 1 to 2 were significantly inferior in performance to the hot-rolled enamelled steels of examples 1 to 7. In comparative examples 1-2, the yield strength of the steel products of comparative examples 1-2 was extremely lowered after the high temperature enameling treatment, and the steel plates were deformed by buckling due to the lowered yield strength before and after enameling, which was not advantageous for the processing and use by users. Meanwhile, the comparative example 2 has the defect of scale explosion after the double-sided enamel, and cannot meet the requirement of the double-sided enamel on the scale explosion resistance.

As can be seen from FIG. 1, the yield strength of the steel of example 1 was in an increasing trend, and the yield strength was as high as 425MPa when the enameling temperature was 930 ℃, while the yield strength of the steel of comparative example 1 was in a decreasing trend when the enameling temperature was 930 ℃, and the yield strength of the steel of comparative example 1 was as low as 289MPa.

As shown in fig. 2 and 3, in the present invention, the microstructure of the steel for hot-rolled enameling of example 1 is ferrite+pearlite in the hot rolled state, and is transformed into a bainitic structure after high-temperature enameling.

It should be noted that the combination of the technical features in the present invention is not limited to the combination described in the claims or the combination described in the specific embodiments, and all the technical features described in the present invention may be freely combined or combined in any manner unless contradiction occurs between them.

It should also be noted that the above-recited embodiments are merely specific examples of the present invention. It is apparent that the present invention is not limited to the above embodiments, and similar changes or modifications will be apparent to those skilled in the art from the present disclosure, and it is intended to be within the scope of the present invention.

Claims

1. A hot-rolled steel for enameling with enameling strengthening properties, characterized in that the mass percentage of each chemical element is:

C: 0.03-0.07%, Si≤0.05%, Mn: 1.5-2.5%, Al: 0.01-0.05%, Cr: 0.25-0.65%, Cu: 0.02-0.20%, Ti: 0.01-0.08%, V: 0.01-0.10%, Mo: 0.01-0.10%; the balance is Fe and other inevitable impurities;

Each chemical element also satisfies: (C-Ti/4-V/4.25)×(Mn+Cr)＞0.05; wherein C, Ti, V, Cr and Mn represent the numerical values of the mass percentage of the corresponding elements respectively;

Its hot-rolled yield strength is 345-389 MPa, and after high-temperature calcination in the temperature range of 870-950°C, the yield strength is 402-439 MPa.

2. The hot-rolled steel for enameling according to claim 1, characterized in that it further contains B: 0.0006-0.003%.

3. The hot-rolled steel for enameling as claimed in claim 1, characterized in that its microstructure is ferrite + pearlite.

4. The hot-rolled enameled steel as claimed in claim 3, characterized in that the grain size of ferrite is 8 to 10.

5. The hot-rolled steel for enameling as claimed in claim 1, characterized in that its thickness is 1.5-3.5 mm.

6. The method for producing hot-rolled steel for enameling according to any one of claims 1 to 5, characterized in that it comprises the steps of:

(1) Smelting and casting;

(2) Heating;

(3) Hot rolling: control the rough rolling temperature to be greater than 850°C, the finishing rolling start temperature to be 900-1050°C, and the finishing rolling final temperature to be 840-900°C;

(4) Laminar cooling: control the cooling rate to 10-35°C/s;

(5) Coiling.

7. The manufacturing method according to claim 6, characterized in that in step (2), the heating temperature is 1150-1260°C.

8. The manufacturing method according to claim 6, characterized in that in the step (5), the coiling temperature is controlled to be 550-680°C.