Patent Application
20240309481
The present invention relates to a steel material and its manufacturing method, particularly to a low-cost hot-rolled steel plate for high temperature enameling, and its manufacturing method.
In recent years, with the development of enamel industry and the rapid progress of new energy technology, large-capacity enameled water heater tanks have become increasingly popular in the market and can be mainly applied in commercial electric water heaters, air energy water heaters, and pressurized solar water heaters.
When such large-capacity water heater tanks are produced, special high temperature glazes and matching high enameling temperature processes with the enameling temperature being usually up to 870-950° C. are typically required. Therefore, the requirements for steel plates used are correspondingly increased, and the steel plate is required to have high temperature resistance while ensuring enameling property, and to still have sufficient yield strength after being fired at high temperatures to guarantee the performance of the final products.
In the prior art, some researchers have achieved some research results regarding steel for enameling for water heater tanks.
The Chinese patent document with the Publication No. CN101812630A, published on Aug. 25, 2010, discloses a hot-rolled high-strength enameled steel plate for deep drawing and a manufacturing method therefor. Such an enameled steel plate adopts a chemical composition comprising: 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 inevitable impurities.
The Chinese patent document with the Publication No. CN103540845A, published on Jan. 29, 2014, also discloses a hot-rolled sheet enameled steel, which adopts a chemical composition comprising: 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%, with the balance being Fe and inevitable impurities, and Ti/C=1.0-1.5.
The Chinese patent document with the Publication No. CN102181805A, published on Sep. 14, 2011, discloses a steel plate used for enameling for a water heater tank and a thin slab continuous casting and rolling production method. The steel plate for enameling for a water heater tank adopts a chemical composition comprising: 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 being Fe and inevitable impurities.
It can be seen that the above-mentioned prior art exhibits a common characteristic: Ti is added in the composition. Ti is a commonly used alloying element in steel for enameling and can form compounds such as TiC and TiN with C and N, acting as hydrogen trapping sites to resist fish scaling. Moreover, TiC phases also play a role of precipitation strengthening.
However, it should be noted that the design of adding the Ti element not only leads to relatively high in production cost, but also causes coarsening and growth of TiC precipitates during high temperature enameling, significantly weakening the strengthening effect. The yield strength of the steel plate will be greatly lowered after high temperature enamel firing at above 870° C., typically below 300 MPa, which cannot satisfy design requirements of the large-capacity water heater tanks.
Based on the above shortcomings in the prior art, the present invention aims to provide a low-cost hot-rolled steel plate for high temperature enameling, which has lower production costs and does not require the addition of expensive alloying elements such as Ti, Nb, or V, while still achieving good enameling adaptability. The low-cost hot-rolled steel plate for high temperature enameling still has excellent mechanical properties after high temperature enameling, meeting various demands of steel for high temperature enameling for large-capacity water heater tanks. The present invention holds significant practical significance.
One of the objectives of the present invention is to provide a low-cost hot-rolled steel plate for high temperature enameling, which has lower production costs and does not require the addition of expensive alloying elements such as Ti, Nb, or V, while still achieving good enameling adaptability. The low-cost hot-rolled steel plate for high temperature enameling still has excellent mechanical properties after high temperature enameling, meeting various demands of steel for high temperature enameling for large-capacity water heater tanks. It holds significant practical significance.
To achieve the above-mentioned objective, the present invention provides a low-cost hot-rolled steel plate for high temperature enameling, wherein in addition to Fe and inevitable impurities, the hot-rolled steel plate further comprises a chemical composition in mass percentage as follows:
Preferably, the low-cost hot-rolled steel plate for high temperature enameling in the present invention comprises the chemical composition in mass percentage as follows:
In the present invention, compared to previous enameled steel for water heaters, the present invention creatively adopts a composition system with high content of P, N and B and avoids the addition of expensive alloying elements such as Ti, Nb, and V, so that the production costs can be effectively reduced.
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:
It should be noted that, in the low-cost hot-rolled steel plate for high temperature enameling in the present invention, the P, N and B elements need to be controlled to satisfy a formula: P×(N−14×B/11)×103>0.3 while the mass percentage of individual chemical elements are controlled. Through experimental research, the inventors found that when the content of the P, N, and B elements in the steel satisfy the above-mentioned relational expression, it can ensure that the reduction in the yield strength of the steel plate after high temperature enameling is within 10%, and the yield strength can still reach the level of 342 MPa or higher. This is because when such an expression is satisfied, a sufficient amount of BN precipitates can be formed as hydrogen trapping sites in the steel matrix, followed by the formation of a sufficient amount of AlN precipitates, thus fully utilizing the grain-refining effect of AlN precipitates. Particularly, after the steel plate is subjected to high temperature enameling, it can still achieve a very fine grain structure, thereby exerting the strengthening effect of fine grains. In combination with the solid solution strengthening effect the P element, it can prevent a significant decrease in yield strength of the steel plate, which is one of key innovative aspects of composition design in the present invention.
Preferably, the microstructure of the low-cost hot-rolled steel plate for high temperature enameling in the present invention is ferrite and pearlite.
Preferably, in the low-cost hot-rolled steel plate for high temperature enameling in the present invention, the average grain size of the ferrite is at grade 10-12. The fine grains ensure the full effect of grain refinement strengthening.
Preferably, the thickness of the low-cost hot-rolled steel plate for high temperature enameling in the present invention is 1.5-3.5 mm.
Preferably, in the low-cost hot-rolled steel plate for high temperature enameling in the present invention, the yield strength of the hot-rolled steel plate in its hot-rolled state is 364-410 MPa, after high temperature enameling within a temperature range of 870-950° C., a decrease in yield strength is within 10%, and a value of the yield strength is greater than or equal to 342 MPa.
Correspondingly, another objective of the present invention is to provide a manufacturing method for a low-cost hot-rolled steel plate for high temperature enameling. The manufacturing method is simple in a production process. By using this manufacturing method, the low-cost hot-rolled steel plate for high temperature enameling with good enameling adaptability can be obtained.
To achieve the above-mentioned objective, the present invention provides the above-mentioned manufacturing method for the low-cost hot-rolled steel plate for high temperature enameling, including the following steps:
In the present invention, the casting in above-mentioned 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 implementations, die casting can also be used, a die-cast steel ingot needs to be rolled into a steel slab by a blooming mill.
Correspondingly, during the hot rolling process of above-mentioned step (3), the heated cast slab can be subjected to rough rolling to form an intermediate slab firstly, and then subjected to finish rolling to obtain the desired slab.
In step (4) of the present invention, the slab is water cooled to the coiling temperature in step (5) at a cooling rate of 10-35° C./s, and then air cooled to room temperature. By adopting such a controlled rolling and cooling process in the present invention, a fine ferrite grain structure can be obtained, ensuring the full effect of grain refinement strengthening, and improving the yield strength of the steel sheet, thereby further enhancing the performance of the steel plate, and realizing the production of the low-cost hot-rolled steel plate for high temperature enameling, which is suitable for a large-capacity water heater tank.
Preferably, in the above-mentioned step (2), the heating temperature is controlled at 1150-1260° C.
Preferably, in the above-mentioned step (5), the coiling temperature is controlled at 550-680° C.
In the above-mentioned technical solutions, the coiling temperature is controlled at 550-680° C., because the coiling within such a temperature range is not only beneficial to the refinement of ferrite grains, but also beneficial to the uniform precipitation of BN phase. This results in the low-cost hot-rolled steel plate for high temperature enameling with excellent mechanical properties and resistance to fish scaling.
Compared to the prior art, the low-cost hot-rolled steel plate for high temperature enameling, and the manufacturing method therefor in the present invention have the following advantages and beneficial effects:
The present invention creatively adopts a composition system with high content of P, N, and B and avoids the addition of expensive alloying elements such as Ti, Nb, and V. In addition, in the present invention, by rational design of the chemical composition and optimization of the controlled rolling and cooling process after rolling, the present invention achieves the production of low-cost hot-rolled steel plate for high temperature enameling suitable for large-capacity water heater tanks. This allows for the production of low-cost hot-rolled steel plate for high temperature enameling with good enameling adaptability while reducing the production costs.
After high temperature enameling within the temperature range of 870-950° C., a decrease in yield strength of the low-cost hot-rolled steel plate for high temperature enameling is only within 10%, and the yield strength can still reach 342 MPa or higher. Therefore, the hot-rolled steel plate retains excellent mechanical properties, meeting various requirements of steel for high temperature enameling for large-capacity water heater tanks. This has significant practical implications.
The low-cost hot-rolled steel plate for high temperature enameling, and the manufacturing method therefor in the present invention will be further explained and described below in conjunction with the accompanying drawings and specific embodiments. However, the explanation and description do not constitute improper limitations on the technical solutions of the present invention.
The low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and comparative steel plates in Comparative Examples 1-3 are prepared according to the following steps:
Table 1 presents the mass percentages of various chemical elements in the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3.
Table 2 presents the specific process parameters of the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3 in the above-mentioned manufacturing steps.
The obtained low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3 are respectively sampled, properties of the steel plates in the Examples and comparative examples are tested to obtain test results which are listed in Table 3, and the relevant performance testing methods and procedures are described as follows:
Table 3 presents the performance test results, microstructures and grain sizes of ferrite of the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3.
To further demonstrate the performance of the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3 after enameling, it is necessary to enamel the steel plates in the Examples and the comparative examples:
Specifically, a Ferro EMP6515 high-temperature glaze is adopted to perform single-sided wet-process enameling on the steel plates in the Examples and the Comparative Examples. The enameling process was controlled at an enameling temperature of 870-950° C. with a holding time of 10 minutes, followed by air cooling to obtain the enameled steel plates in Examples 1-6 and Comparative Examples 1-3.
After the above-mentioned operations are completed, the enameled hot-rolled steel plates in Examples 1-6 and the enameled comparative steel plates in Comparative Examples 1-3 were observed and tested. After enameling, the steel plates were enabled to stand for 48 hours, no fish scaling phenomenon was observed on surfaces of the steel plates. The adhesion performance between the steel plates and enamel was verified by the drop-weight test, and the adhesion was excellent. Tensile tests were conducted to determine the yield strength of the enameled steel plates of each example and comparative sample. The test results are listed in Table 4.
Table 4 presents the performance test results of the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3 after enameling.
It can be seen from Table 4 in conjunction with Tables 1-3 that the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 have the thickness within a range of 1.5-3.5 mm, the yield strength in the hot-rolled state of 364-410 MPa, the tensile strength of 456-512 MPa, the elongation of 27-31%, and the hole expanding rate of 80-92%. After high temperature enameling within a temperature range of 870-950° C., the decrease in the yield strength of the steel plates in Examples 1-6 is within 10%, and the yield strength is still greater than or equal to 342 MPa. This indicates the steel plates have excellent high temperature enameling resistance. After the enameled steel plates finally obtained in Examples 1-6 were enabled to stand for 48 h, no fish scaling phenomenon was observed on the enamel surfaces. The drop-weight test confirmed the excellent adhesion between the steel plates and an enamel layer, fully meeting user requirements.
In contrast, the performance of the comparative steel plates in Comparative Examples 1-3 are significantly inferior to those of the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6. In Comparative Examples 1-3, the content of the P, N, and B elements in the steel does not satisfy the condition P×(N−14×B/11)×103>0.3. After high temperature enameling within the temperature range of 870-950° C., the decrease in the yield strength reaches 18% or above, and the value of the yield strength is within 220-290 MPa.
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It should be noted that combination manners of technical features in this case are not limited to combination manners recorded in the claims of this case or combination manners recorded in the specific embodiments, and all the technical features recorded in this case can be freely combined or incorporated in any manners unless there are conflicts between them.
It should be further noted that the embodiments listed above are merely the specific embodiments of the present invention. The present invention is not limited to the above-mentioned embodiments, similar changes or variants made therewith can be directly obtained or readily envisioned from the content disclosed by the present invention by those skilled in the art so as to fall within the protection scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202110175137.0 | Feb 2021 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2022/075614 | 2/9/2022 | WO |
