Production method of high-strength acid pickling enamel steel for 300MPa-grade water heater inner container suitable for dry enamel process

Abstract

The invention provides a production method of high-strength acid-pickled enamel steel for a 300MPa-grade water heater inner container suitable for a dry enamel process, and the high-strength acid-pickled enamel steel for the 300MPa-grade water heater inner container suitable for the dry enamel process comprises the following chemical components in percentage by weight: 0.01-0.03% of C, 0.01-0.03% of P, 0.01-0.03% of S, 0.01-0.03% of Cr, 0.01-0.03% of Cr, 0.01-0.03% of Cr, 0.01-0.03% of Cr, 0.01-0.03% of Cr, 0.01-0.03% of Mo, 0.01- Less than or equal to 0.05% of Si; 0.10% to 0.25% of Mn; 0.015% to 0.022% of P; 0.01 to 0.02 percent of S; a1: 0.020% to 0.040%; 0.020% to 0.040% of Nb; 0.0040-0.0080% of N, and the balance of Fe and inevitable impurities. The process route of the production method comprises the following procedures of molten iron desulfurization, converter smelting, RH vacuum refining, LF refining, slab continuous casting, slab heating, descaling, rough rolling, finish rolling, laminar cooling, coiling, acid pickling, leveling and coiling.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal materials, in particular to a production method of a 300MPa-grade high-strength pickling enamel steel for water heater inner tank suitable for dry enamel process. BACKGROUND

[0002] Pickling enamel steel is a kind of steel specially prepared for enamel process, which is obtained by removing the surface iron oxide scale through pickling based on hot-rolled plate coil, thereby obtaining a clean and active surface. Compared with traditional cold-rolled enamel steel, the production cost is significantly reduced by eliminating the cold rolling and intermediate annealing process. Secondly, the high surface roughness of pickling steel can significantly improve the enamel adhesion performance.

[0003] The water heater inner tank is the core component of the storage type electric water heater, and its performance directly determines the service life and safety of the water heater. The inner tank is in a complex working condition of high temperature, high pressure and corrosive water medium (rich in chloride ions, calcium and magnesium ions, etc.) for a long time, and needs to have excellent corrosion resistance, creep resistance and pressure bearing capacity.

[0004] At present, the mainstream water heater inner tank manufacturing process is "steel plate punching / roll welding forming→inner surface enamel treatment". The enamel layer acts as a physical barrier to effectively isolate the water body from the steel base, which is the key to the corrosion resistance of the inner tank. However, the inner tank has high requirements for the formability, weldability and strength of the steel plate during the processing process, especially during the head punching and cylinder roll welding. If the strength of the steel plate is insufficient (such as the traditional 240MPa grade), the wall thickness of the inner tank must be increased to ensure the pressure bearing capacity, which not only increases the material cost and equipment weight, but also increases the difficulty of subsequent punching forming and welding. Therefore, the development of higher strength grade inner tank steel has become an important development direction of the industry to realize the lightweight of the inner tank under the premise of safety. The 300MPa strength is an ideal choice to balance the formability and lightweight requirements.

[0005] The enamel process is mainly divided into wet process (electrostatic spraying or dipping) and dry process (electrostatic powder spraying). Dry enamel process is an advanced technology that has developed rapidly in recent years, and its process flow is: dry enamel powder is directly adsorbed on the surface of the preheated inner tank by electrostatic spraying, and then is fired. Compared with the traditional wet process, the dry process has the following advantages: uniform coating, short firing period, and high production efficiency. However, the firing temperature of the dry process is usually higher and the time is shorter, the formed enamel layer is thinner, the hydrogen diffusion and penetration behavior is different from that of the wet process, and higher requirements are put forward for the number, distribution and efficiency of hydrogen traps in the steel. Therefore, at present, there is no steel plant that has developed a high-strength pickling enamel steel for water heater inner tank that can stably adapt to the dry enamel process.

[0006] According to the search, there are related patent literatures of high-strength acid-resistant enamel steel, such as Chinese patent publication No. CN115522129A “330MPa grade wide thin specification high-quality hot-rolled enamel steel and production method”, the mass percentage content of chemical elements is: C: 0.02-0.06%, Si: 0.05-0.1%, Mn: 0.5-0.9%, Ti: 0.03-0.08%, N: 0.003-0.008%, P≤0.015%, S≤0.008%, Mg: 0.001-0.004%, the balance is Fe and inevitable impurities; the application also discloses a manufacturing method of the steel plate. The 330MPa grade high-strength hot-rolled enamel steel described in the application has good enamel anti-phosphorus explosion performance and adhesion performance, but cannot be applied to dry enamel.

[0007] Chinese patent publication No. CN115537664A “A hot-rolled acid-resistant enamel steel with a post-burning yield strength of ≥300MPa and a production method thereof”, the mass percentage content of chemical elements is: C: 0.04%-0.07%; Si≤0.03%; Mn: 0.50%-0.65%; P≤0.020%; S: 0.010%-0.025%; Al: 0.010%-0.060%; Ti: 0.030%-0.060%; Cu: 0.001%-0.050%, Cr: 0.001%-0.050%, V: 0.001%-0.040%, Mo: 0.001%-0.030%, Ni: 0.001%-0.030%, the balance is Fe and inevitable impurities; the application also discloses a manufacturing method of the steel plate. The hot-rolled acid-resistant enamel steel with a post-burning yield strength of ≥300MPa described in the application has good enamel anti-phosphorus explosion performance and adhesion performance, and the post-burning yield strength is ≥300MPa, but the adaptability of the product to dry enamel process is not mentioned, and it cannot be applied to dry enamel.

[0008] In summary, the existing technology has the following problems: there is no 300MPa grade high-strength acid-resistant enamel steel for water heater inner tank suitable for dry enamel process. SUMMARY

[0009] The application provides a production method of 300MPa grade high-strength acid-resistant enamel steel for water heater inner tank suitable for dry enamel process, to provide a 300MPa grade high-strength acid-resistant enamel steel for water heater inner tank suitable for dry enamel process.

[0010] To this end, the present application provides a production method of a 300MPa high-strength pickling enamel steel for water heater inner tank suitable for dry enamel process, which comprises the following chemical components in percentage by weight: C: 0.01-0.03%; Si: ≤0.05%; Mn: 0.10%-0.25%; P: 0.015-0.022%; S: 0.01-0.02%; Al: 0.020%-0.040%; Nb: 0.020%-0.040%; N: 0.0040-0.0080%, and the rest is Fe and inevitable impurities.

[0011] The production method of the 300MPa high-strength pickling enamel steel for water heater inner tank suitable for dry enamel process comprises the following steps: desulfurized molten iron, converter smelting, RH vacuum refining, LF refining, slab continuous casting, slab heating, descaling, rough rolling, finish rolling, laminar cooling, coiling, pickling, flattening, coiling:

[0012] The slab heating ensures uniform and small austenite grains and alloy element solid solution, and a low-temperature heating process is adopted.

[0013] The finish rolling opening temperature is controlled at 940-990 DEG C, and the finish rolling temperature is controlled at 850-890 DEG C.

[0014] The present application also provides a 300MPa high-strength pickling enamel steel for water heater inner tank suitable for dry enamel process, which comprises the following chemical components in percentage by weight: C: 0.01-0.03%; Si: ≤0.05%; Mn: 0.10%-0.25%; P: 0.015-0.022%; S: 0.01-0.02%;

[0015] Al: 0.020%-0.040%; Nb: 0.020%-0.040%; N: 0.0040-0.0080%, and the rest is Fe and inevitable impurities.

[0016] Further, the 300MPa high-strength pickling enamel steel for water heater inner tank suitable for dry enamel process comprises the following chemical components in percentage by weight: C=0.0246%, Si=0.0251%, Mn=0.1632%, P=0.0191%, S=0.0143%, Nb=0.0346%, Ti=0.0019%, Al t=0.0237%, N=0.0074%, and the rest is Fe and inevitable impurities; and the finished product specification is 1.6mm.

[0017] Further, the chemical composition of the high-strength pickling enamel steel for 300MPa-grade water heater inner tank suitable for dry enamel process, by weight percentage, C=0.0194%, Si=0.0289%, Mn=0.1905%, P=0.0175%, S=0.0168%, Nb=0.0293%, Ti=0.0022%, Alt=0.0267%, N=0.0058%; the rest is Fe and inevitable impurities; the finished product specification is 1.8mm.

[0018] Further, the chemical composition of the high-strength pickling enamel steel for 300MPa-grade water heater inner tank suitable for dry enamel process, by weight percentage, C=0.0295%, Si=0.0272%, Mn=0.1858%, P=0.0188%, S=0.0162%, Nb=0.0324%, Ti=0.0016%, Alt=0.0257%, N=0.0067%, the rest is Fe and inevitable impurities; the finished product specification is 1.6mm.

[0019] Further, the chemical composition of the high-strength pickling enamel steel for 300MPa-grade water heater inner tank suitable for dry enamel process, by weight percentage, C=0.0173%, Si=0.0234%, Mn=0.2079%, P=0.0203%, S=0.0181%, Nb=0.0289%, Ti=0.0021%, Alt=0.0281%, N=0.0061%, the rest is Fe and inevitable impurities; the finished product specification is 1.8mm.

[0020] The high-strength pickling enamel steel for 300MPa-grade water heater inner tank suitable for dry enamel process and the production method thereof provided by the application adopt a low-carbon composition system, Nb micro-alloy strengthening, appropriate increase of the content of Mn, S and N elements in the steel, and reasonable rolling process, and the metallographic structure is F+ a small amount of P, F grain size is 12.0 grade, the yield strength range is 300-350MPa, the tensile strength range is 380-420MPa, the elongation A 80 > 30%, which can adapt to the dry enamel process and has the enamel phosphorus explosion resistance and adhesion performance meeting the use requirements. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is the metallographic structure photo of example 1 of the application;

[0022] Figure 2 It is the metallographic structure photo of comparative example 1;

[0023] Figure 3 It is the enamel effect schematic diagram of example 1 of the application;

[0024] Figure 4 A schematic view of the enamel effect of Comparative Example 1. DETAILED DESCRIPTION

[0025] In order to have a clearer understanding of the technical features, objects and effects of the present application, the present application will now be described.

[0026] The present application provides a 300MPa-grade high-strength enamel steel for water heater inner tank and a production method thereof, which is suitable for dry enamel process. 80 The steel has a yield strength range of 300-350MPa, a tensile strength range of 380-420MPa, an elongation A 2 30%, and a TH value of anti-scaling explosion sensitivity of ≥25min / mm, which can be adapted to dry enamel process and has enamel anti-phosphorus explosion performance and adhesion performance meeting use requirements.

[0027] The technical scheme adopted is as follows:

[0028] 1. The 300MPa-grade high-strength enamel steel for water heater inner tank and the production method thereof, which are suitable for dry enamel process, have the following chemical components in terms of percentage by weight: C: 0.01-0.03%; Si: ≤0.05%; Mn: 0.10%-0.25%; P: 0.015-0.022%; S: 0.01-0.02%; Al: 0.020%-0.040%; Nb: 0.020%-0.040%; N: 0.0040-0.0080%, and the rest is Fe and inevitable impurities.

[0029] C: C is a solid solution strengthening element, and adding a certain amount of C in the steel can improve the strength, and C can form precipitated phase with Nb to form a "hydrogen trap", which can effectively improve the anti-phosphorus explosion performance; however, too high C content will affect the forming performance of the material, and gas is easy to be generated in the enameling process, which affects the enamel quality. The enamel layer formed by dry enamel is usually thin, and if gas is generated in the steel in the enameling process, it is very easy to break through the enamel layer to form scaling explosion, therefore, low carbon composition design is adopted, and the C content is controlled to be 0.01-0.03% in the present application.

[0030] Si: Too high Si content is easy to generate iron silicate in the hot rolling process, which makes it difficult to remove the iron oxide scale, easily causes residual iron oxide scale, and affects the local enamel quality, therefore, the Si content is controlled to be less than 0.05%.

[0031] Mn: Mn is a solid solution strengthening element, adding a certain amount of Mn in steel can improve the strength, at the same time, Mn can form MnS with S to avoid the hot brittleness caused by high S content, and can also form "hydrogen trap" to improve the anti-phosphorus explosion performance. However, too high Mn content will cause oxidation of the steel in high temperature environment and form surface oxide film, which has a great impact on the quality of dry enamel. The straight seam welding of the inner barrel of the water heater is usually carried out by laser welding, and the heat affected zone of the welding will form an oxide film due to the high temperature, which will cause the enamel leakage defect in the dry enamel process. Therefore, the Mn content in the present application is controlled at 0.10% to 0.25%.

[0032] P: P is usually a harmful element in steel, and high P content will damage the forming performance of the material. However, P is also a solid solution strengthening element, and adding an appropriate amount of P can have a certain strengthening effect to improve the strength of the steel. In order to reduce the influence of C on the quality of enamel, the C content is designed to be low, and a small amount of P is added for strengthening. The P content is controlled in the range of 0.015% to 0.022%.

[0033] S: S can form MnS with Mn in steel to form "hydrogen trap", which is beneficial to the anti-phosphorus explosion performance of the steel plate, but too high S content will affect the welding performance and forming performance. Combined with the addition amount of Mn element in the present application, the S content is controlled at 0.01% to 0.02%.

[0034] Al: Al is used as a deoxidizer in the steelmaking process, and Al forms AlN two-phase particles with N in steel. Through reasonable rolling process design, AlN is precipitated after hot rolling and slow cooling to improve the anti-phosphorus explosion performance of the steel plate. However, too high Al content will affect the enamel adhesion performance. In the present application, the Al content is controlled at 0.020% to 0.040%.

[0035] Nb: Nb and Ti are important component elements in the design of enamel steel products. Adding these two alloy elements in enamel steel can form a large number of two-phase particles to improve the anti-phosphorus explosion performance of the steel plate, and can also refine the grain size and improve the strength. However, the TiN precipitation temperature is relatively high, and its hydrogen fixation capacity decreases significantly after fully growing. The two-phase particles of Nb are mainly precipitated during hot rolling, and the precipitation size is relatively fine, so the hydrogen fixation effect is good. In addition, the grain refining effect of Nb is stronger than that of Ti, and finer grain size can obtain more grain boundaries and dislocations, further improving the anti-phosphorus explosion performance. Considering the above factors, the Nb content in the present application is controlled at 0.02% to 0.04%.

[0036] N: N element can increase the aging sensitivity of steel and affect the welding performance. In the present application, the N content in the steel is appropriately increased to ensure that enough N can form two-phase particles with Nb and Al to improve the anti-phosphorus explosion performance. The N content in the present application is controlled at 0.0040% to 0.0080%.

[0037] 2. Process route: desulfurized molten iron → converter smelting → RH vacuum refining → LF refining → slab continuous casting → slab heating → descaling → rough rolling → finish rolling → coiling → pickling → skin pass → coiling.

[0038] 3. Converter molten steel smelting: In order to ensure the stability of S content control, molten iron desulfurization is needed to ensure that the molten iron entering the converter is S≤0.010%, and argon is used for bottom blowing during the whole smelting process; the target of converter end point: C: ≤0.07%, P≤0.018%.

[0039] 4. Material addition sequence: first add lime and pre-melted slag (or refining slag), then add alloy, complete addition 3 minutes before tapping, and complete addition of refining slag before and after tapping. Add deoxidizer at the end of tapping.

[0040] 5. RH molten steel vacuum refining treatment: the maximum vacuum holding time is ≥10 min; the net circulation time is ≥3 min.

[0041] 6. LF molten steel refining treatment: first add lime and pre-melted slag (or refining slag), then add alloy, complete addition 3 minutes before tapping, and complete addition of refining slag before and after tapping, and add deoxidizer at the end of tapping. The setting time is 18-35 min.

[0042] 7. Continuous casting: weak cooling parameters are used for mold cooling and secondary cooling; the drawing speed is stably controlled at 0.9 m / min-1.40 m / min.

[0043] 8. Slab heating: low-temperature heating process is used to ensure uniform and small austenite grain size and alloy element solid solution. The heating temperature is 1230℃-1270℃, and the heating time is ≥100 min. The billet thickness is 220 mm, and the intermediate billet design thickness is 38 mm.

[0044] 9. Finish rolling temperature: the design of finish rolling temperature mainly considers rolling in the austenite zone at low temperature to avoid rolling in the two-phase zone, which will cause difficult shape control; however, due to the addition of high Nb content in the steel, Nb will precipitate a lot during finish rolling, inhibiting the dynamic recrystallization process between stands during rolling. When using straight rolling, due to the large temperature difference between the head and tail of the strip, if high finish rolling temperature is to be ensured, high rolling speed is needed, which will lead to insufficient dynamic recrystallization between stands, resulting in uneven performance of the strip head and tail. Therefore, considering comprehensively, the finish rolling start rolling temperature is controlled at 940℃-990℃, and the finish rolling temperature is controlled at 850℃-890℃. The finish rolling reduction is 95%.

[0045] 10. Cascade cooling temperature: in order to ensure the precipitation of two-phase particles in the steel and improve the anti-scaling performance, the cascade cooling adopts backward cooling mode, and high temperature coiling process is used, and the coiling temperature is controlled at 700-740℃.

[0046] 11. Pickling process: 1# acid tank ≥ 40g / l, 2# acid tank ≥ 60g / l, 3# acid tank ≥ 110g / l, the temperature of acid solution is controlled at 70-85℃, pickling speed is 100-150m / min, to ensure that the strip surface obtains good pickling effect, and to avoid under-pickling or over-pickling.

[0047] Effects

[0048] The high-strength pickling porcelain enamel steel for 300MPa-grade inner tank of water heater suitable for dry-process porcelain enamel process and the production method thereof have yield strength ReL of 301-322MPa, tensile strength Rm of 393-408MPa, elongation A 80 after fracture of 34-38%, dry-process porcelain enamel explosion test is qualified, adhesion test level is all 1st grade, the porcelain enamel effect is good, and the point-shaped porcelain enamel defect commonly seen in the dry-process porcelain enamel process does not appear in the straight seam welding position and heat-affected zone of the middle cylinder.

[0049] Examples and comparative examples

[0050] The high-strength pickling porcelain enamel steel for 300MPa-grade inner tank of water heater suitable for dry-process porcelain enamel process of the present application adopts the following component proportion and specific process. Table 1 is the components (in terms of weight percentage) of the steel of each example and comparative example. Table 2 is the process parameters corresponding to the steel of the cases described in Table 1. Table 3 is the performance index corresponding to the component steel of each case. Figure 1 is the metallographic structure corresponding to the example, the structure of Example 1 is: F+ a small amount of P, F grain size is 12.0 grade, and cementite rating is 1st grade; Figure 2 is the metallographic structure corresponding to Comparative Example 1, the structure of Comparative Example 1 is: F+ a small amount of P, F grain size is 10.0 grade, and cementite rating is 2nd grade. Table 4 and Figure 3 and Figure 4 are the porcelain enamel test results of each case, Figure 3 is the porcelain enamel effect of Example 1, and no porcelain enamel explosion occurs, Figure 4 is the porcelain enamel effect of Comparative Example 1, and porcelain enamel explosion occurs.

[0051] Table 1: Product chemical composition (wt%)

[0052] Example C Si Mn P S Nb Ti Alt N Example 1 0.0246 0.0251 0.1632 0.0191 0.0143 0.0346 0.0019 0.0237 0.0074 Example 2 0.0295 0.0272 0.1858 0.0188 0.0162 0.0324 0.0016 0.0257 0.0067 Example 3 0.0194 0.0289 0.1905 0.0175 0.0168 0.0293 0.0022 0.0267 0.0058 Example 4 0.0173 0.0234 0.2079 0.0203 0.0181 0.0289 0.0021 0.0281 0.0061 Comparative Example 1 0.0514 0.0274 0.1618 0.0147 0.0121 0.0004 0.0341 0.0286 0.0066 Comparative Example 2 0.0601 0.0248 0.1895 0.0132 0.0098 0.0006 0.0387 0.0243 0.0061

[0053] Table 2: Specific process parameters of each case

[0054]

[0055] Table 3: Performance index of each case (A refers to elongation A 80 )

[0056]

[0057] The metallographic structure of the four examples of the present application is: F + a small amount of P, F grain size 12.0 grade, cementite rating 1, the metallographic structure of Comparative Examples 1 and 2 is: F + a small amount of P, F grain size 10.0 grade, cementite rating 2. In addition: the carbide in the example of the present application is precipitated and dispersed, the cementite rating is 1, the P phase in the comparative example is relatively thick, the cementite rating is 2, the dispersed precipitated carbide of the present application can effectively improve the anti-scaling performance.

[0058] Table 4: Enamel test results of each example

[0059]

[0060] The comparison of the above examples and comparative examples shows that different component designs form performance differences, in addition, suitable rolling process parameter designs are also proposed.

[0061] The above description is merely illustrative of the present application and is not intended to limit the scope of the present application. The various components of the present application can be combined with each other under the condition of no conflict, any equivalent changes and modifications made by any person skilled in the art without departing from the concept and principle of the present application shall fall within the scope of protection of the present application.

Claims

1. A method for producing high-strength acid-washed enamel steel for 300MPa grade water heater inner tanks suitable for dry enamel processing, characterized in that, The high-strength pickled enamel steel for 300MPa-grade water heater inner tanks, suitable for dry enamel processing, has the following chemical composition by weight percentage: C: 0.01–0.03%; Si: ≤0.05%; Mn: 0.10%–0.25%; P: 0.015–0.022%; S: 0.01–0.02%; Al: 0.020%–0.040%; Nb: 0.020%–0.040%; N: 0.0040–0.0080%, with the remainder being Fe and unavoidable impurities. The production method of high-strength pickled enamel steel for 300MPa grade water heater inner tanks, applicable to dry enamel processing, includes the following steps: desulfurized molten iron, converter smelting, RH vacuum refining, LF refining, slab continuous casting, slab heating, descaling, rough rolling, finish rolling, laminar flow cooling, coiling, pickling, leveling, and coiling. Among them, slab heating: to ensure uniform and fine austenite grains and solid solution of alloying elements, a low-temperature heating process is adopted; The initial rolling temperature of the finishing mill is controlled at 940℃~990℃, and the final rolling temperature is controlled at 850℃~890℃.

2. The production method of high-strength acid-washed enamel steel for 300MPa grade water heater inner tanks as described in claim 1, characterized in that, In the slab heating process, the low-temperature heating process is as follows: heating temperature 1230℃~1270℃, heating time ≥100min.

3. The production method of high-strength acid-washed enamel steel for 300MPa grade water heater inner tanks as described in claim 1, characterized in that, The laminar flow cooling adopts a backward cooling mode and a high-temperature winding process, with the winding temperature controlled at 700-740℃.

4. The production method of high-strength acid-washed enamel steel for 300MPa grade water heater inner tanks as described in claim 1, characterized in that, Pickling process: 1# acid tank ≥40g / l, 2# acid tank ≥60g / l, 3# acid tank ≥110g / l, acid temperature controlled at 70~85℃, pickling speed 100~150m / min.

5. The production method of high-strength acid-washed enamel steel for 300MPa grade water heater inner tanks as described in claim 1, characterized in that, Converter steelmaking: To ensure the stability of sulfur content control, desulfurization of molten iron is required to ensure that the sulfur content of the molten iron entering the furnace is ≤0.010%. The smelting process uses bottom blowing argon gas throughout. Converter final target: C: ≤0.07%, P ≤0.018%.

6. The production method of high-strength acid-washed enamel steel for 300MPa grade water heater inner tanks as described in claim 1, characterized in that, Vacuum refining treatment of RH steel: ultimate vacuum holding time ≥ 10 min; net circulation time ≥ 3 min.

7. The production method of high-strength acid-washed enamel steel for 300MPa grade water heater inner tanks as described in claim 1, characterized in that, LF steel refining process: First add lime and pre-melted slag (or refining slag), then add alloys, completing the addition 3 minutes before tapping. The refining slag is added both before and after tapping. Deoxidizer is added at the end of tapping. The settling time is 18-35 minutes.

8. The production method of high-strength acid-washed enamel steel for 300MPa grade water heater inner tanks as described in claim 1, characterized in that, Continuous casting: The crystallizer casting speed is controlled between 0.9 m / min and 1.40 m / min.

9. The production method of high-strength acid-washed enamel steel for 300MPa grade water heater inner tanks as described in claim 1, characterized in that, The high-strength acid-washed enamel steel for the 300MPa grade water heater inner tank, suitable for dry enamel processing, has the following chemical composition by weight percentage: C = 0.0246%, Si = 0.0251%, Mn = 0.1632%, P = 0.0191%, S = 0.0143%, Nb = 0.0346%, Ti = 0.0019%, Alt = 0.0237%, N = 0.0074%, with the remainder being Fe and unavoidable impurities. The finished product has a thickness of 1.6mm, a dry enamel finish, and no crackling or spalling.

10. The production method of high-strength acid-washed enamel steel for 300MPa grade water heater inner tanks as described in claim 1, characterized in that, The high-strength acid-washed enamel steel for the 300MPa grade water heater inner tank, suitable for dry enamel processing, has the following chemical composition by weight percentage: C = 0.0194%, Si = 0.0289%, Mn = 0.1905%, P = 0.0175%, S = 0.0168%, Nb = 0.0293%, Ti = 0.0022%, Alt = 0.0267%, N = 0.0058%. The finished product has a thickness of 1.8mm, a dry enamel finish, and no crackling or spalling.

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