Production method of hot-rolled pickled enamel steel capable of being subjected to deep drawing processing and suitable for double-sided enamel process

Abstract

The invention provides a production method of hot-rolled acid-pickled enamel steel capable of being subjected to deep drawing processing and suitable for a double-sided enamel process, and the hot-rolled acid-pickled enamel steel comprises the following chemical components in percentage by weight: 0.002-0.004% of C, 0.003-0.004% of P, 0.003-0.004% of S, 0.003-0.004% of P, less than or equal to 0.03% of Si; 0.10% to 0.20% of Mn; less than or equal to 0.020% of P; 0.01 to 0.02 percent of S; a1: 0.020% to 0.040%; 0.10% to 0.12% of Ti; n: 0.0060% to 0.0100%; 0.0015 to 0.0025 percent of B, and the balance of Fe and inevitable impurities; the production method of the hot-rolled pickled enamel steel capable of being subjected to deep drawing processing and suitable for the double-sided enamel process comprises the following process routes: molten iron desulfurization, converter smelting, RH vacuum refining, slab continuous casting, slab heating, descaling, rough rolling, finish rolling, coiling, pickling and coiling. The double-sided enamel is good in effect.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, and specifically to a method for producing hot-rolled pickled enamel steel that is capable of deep drawing and suitable for double-sided enamel enamel processing. Background Technology

[0002] Enameled steel refers to a composite material that combines the strength of metal with the excellent corrosion resistance, wear resistance, easy cleaning and aesthetic decoration properties of porcelain by fusing one or more layers of inorganic glassy enamel onto the surface of a low-carbon steel substrate at high temperature (usually 800-850℃).

[0003] Double-sided enamel coating technology refers to the process of applying enamel enamel to both surfaces of an enamel-coated steel sheet. This technology provides comprehensive protection for the base metal, significantly improving the overall corrosion resistance, service life, and hygiene level of the product. It has wide applications in household appliances (such as ovens and barbecue grills), building materials, and chemical containers.

[0004] However, double-sided enamel enamel processing places extremely stringent requirements on the substrate steel: ① Extremely high resistance to blistering: During the enamel firing process, hydrogen in the steel plate will precipitate and accumulate. If there are sufficient "hydrogen traps" inside the steel plate to fix the hydrogen, it can prevent the formation of high-pressure hydrogen bubbles at the interface, which would cause the enamel layer to crack, i.e., the "blistering" defect. For single-sided enamel enamel processing, gas in the steel can escape from the unenamel-covered parts, but in double-sided enamel enamel processing, since the entire steel plate is covered by the enamel layer, the requirements for the steel plate's resistance to blistering are even higher. ② Good formability, especially deep-drawing performance: For complex structural parts such as ovens and baking ovens, the steel plate needs to have excellent deep-drawing forming capabilities to process parts with complex shapes and large drawing ratios without cracking.

[0005] Currently, the oven manufacturing industry, both domestically and internationally, especially for mid-to-high-end products, is increasingly adopting double-sided enamel products to improve product quality. However, the industry faces challenges: to ensure deep-drawing formability and enamel quality, the oven industry currently mostly uses cold-rolled enamel steel sheets. While cold-rolled sheets offer good anti-scaling properties and formability, their high production costs (including cold rolling and subsequent annealing processes) result in high final component costs. Hot-rolled pickled sheets, due to their cost advantages, are gradually being used in the enamel product industry. However, ordinary hot-rolled pickled sheets have two major shortcomings: ① Unstable anti-scaling performance: The microstructure control of traditional hot-rolled sheets is not as precise as that of cold-rolled sheets, resulting in significant fluctuations in anti-scaling performance and a high risk of scaling when used for double-sided enamel. ② Insufficient formability: While their strength is high, their elongation and plastic strain ratio (r-value) are low, making it difficult to meet the deep-drawing requirements of oven parts. Cracking and wrinkling are common problems during complex forming processes. Therefore, the oven industry urgently needs a steel plate material that can meet the requirements of deep drawing, has stable double-sided enamel performance, and also has cost advantages.

[0006] In response to market demand, some steel mills both domestically and internationally have attempted to develop hot-rolled pickled enamel steel. However, existing technologies generally suffer from performance imbalances, making it difficult to simultaneously achieve both deep drawing and anti-scaling properties. Most steel mills develop pickled enamel steel primarily by adding sufficient amounts of strong carbonitride-forming elements such as titanium (Ti) and niobium (Nb), utilizing their precipitates as "hydrogen traps" to enhance anti-scaling performance. For example, Chinese Patent Publication No. CN107574375A, entitled "Hot-rolled pickled steel sheet for double-sided enamel with excellent coating performance and its manufacturing method," discloses the following chemical element mass percentage content: C: 0.010-0.020%, Mn: 0.5-1.0%, Si≤0.10%, P≤0.02%, S: 0.03-0.05%, Als≤0.01%, Cu: 0.20-0.40%, Nb: 0.03-0.06%, O: 0.0040-0.01%. This invention also discloses a method for manufacturing the steel sheet. The hot-rolled pickled steel sheet for double-sided enamel described in this invention has good anti-phosphorus explosion performance, but its finished product yield strength ≥300MPa, tensile strength ≥450MPa, and elongation ≤35%, lacking excellent deep-drawing forming performance.

[0007] Chinese Patent Publication No. CN 115478209 A, entitled "A Hot-Rolled Pickled Enamel Steel with Good Deep Drawing Performance and Its Production Method," discloses the following chemical element mass percentage content: C: 0.001-0.006%, N≤0.004%, S≤0.0080%, Als: 0.015-0.040%. When Mn is used for strengthening, Mn: 1.0-1.5%, Si: 0.001-0.03%, P≤0.015%; when Si is used for strengthening, Si: 0.4-0.6%, Mn: 0.15-0.3%, P≤0.015%; when P is used for strengthening, Si: 0.001-0.03%, Mn: 0.15-0.3%, P: 0.035-0.055%. The invention also discloses a method for manufacturing the steel plate. The hot-rolled pickled enamel steel with good deep-drawing performance described in this invention is mainly used in the water heater inner tank industry. Water heater inner tanks are all single-sided enamel process, and the adaptability of this product in double-sided enamel process is not mentioned. Moreover, its finished yield strength is ≥200MPa, tensile strength is ≥320MPa, and elongation is about 50%. The overall strength is too high and still does not meet the requirements for deep drawing.

[0008] In summary, the existing technology has the following problems: the deep drawing performance of hot-rolled pickled enamel steel suitable for double-sided enamel enamel process is poor. Summary of the Invention

[0009] This invention provides a hot-rolled pickled enamel steel that is suitable for deep drawing and double-sided enamel enamel processes, i.e., a hot-rolled pickled enamel steel with good deep drawing formability suitable for double-sided enamel enamel processes, in order to solve the problem of poor deep drawing formability of hot-rolled pickled enamel steel for double-sided enamel enamel processes.

[0010] Therefore, this invention proposes a production method for hot-rolled pickled enamel steel that is suitable for deep drawing and double-sided enamel enamel processing. The method uses the following chemical composition, by weight percentage: C: 0.002–0.004%; Si: ≤0.03%; Mn: 0.10%–0.20%; P ≤0.020%; S: 0.01–0.02%; Al: 0.020%–0.040%; Ti: 0.10%–0.12%; N: 0.0060–0.0100%; B: 0.0015–0.0025%, with the remainder being Fe and unavoidable impurities. The process route of the hot-rolled pickled enamel steel production method is as follows: desulfurized molten iron, converter smelting, RH vacuum refining, slab continuous casting, slab heating, descaling, rough rolling, finish rolling, coiling, pickling, and coiling.

[0011] This invention also proposes a hot-rolled pickled enamel steel that is suitable for deep drawing and double-sided enamel enamel processing, manufactured using the above-described production method. The chemical composition of this hot-rolled pickled enamel steel, by weight percentage, includes: C: 0.002–0.004%; Si: ≤0.03%; Mn: 0.10%–0.20%; P ≤0.020%; S: 0.01–0.02%; Al: 0.020%–0.040%; Ti: 0.10%–0.12%; N: 0.0060–0.0100%; B: 0.0015–0.0025%, with the remainder being Fe and unavoidable impurities.

[0012] Furthermore, the chemical composition of the hot-rolled pickled enamel steel, which is suitable for deep drawing and double-sided enamel processing, includes, by weight percentage: C 0.0027, Si 0.0162, Mn 0.191, P 0.0142, S 0.016, Ti 0.1066, Alt 0.0354, N 0.0093, B 0.0018, with the remainder being Fe and unavoidable impurities.

[0013] Furthermore, the chemical composition of the hot-rolled pickled enamel steel, which is suitable for deep drawing and double-sided enamel processing, includes, by weight percentage: C 0.0029, Si 0.0102, Mn 0.162, P 0.0091, S 0.019, Ti 0.1167, Alt 0.0367, N 0.0078, B 0.0023, with the remainder being Fe and unavoidable impurities.

[0014] Furthermore, the chemical composition of the hot-rolled pickled enamel steel, which is suitable for deep drawing and double-sided enamel processing, includes, by weight percentage: C 0.0035, Si 0.0132, Mn 0.159, P 0.0155, S 0.015, Ti 0.1033, Alt 0.0351, N 0.0083, B 0.0019, with the remainder being Fe and unavoidable impurities.

[0015] Furthermore, the chemical composition of the hot-rolled pickled enamel steel, which is suitable for deep drawing and double-sided enamel processing, includes, by weight percentage: C 0.0026, Si 0.0084, Mn 0.187, P 0.0099, S 0.015, Ti 0.1050, Alt 0.0211, N 0.0072, B 0.0021, with the remainder being Fe and unavoidable impurities.

[0016] Furthermore, the finished product specifications of the hot-rolled pickled enamel steel, which is suitable for deep drawing and double-sided enamel processing, are 3-4 mm. For example, the finished product specifications are 3.5 mm and 4 mm.

[0017] The hot-rolled pickled enamel steel obtained by this invention is suitable for deep drawing and double-sided enamel enameling. Its microstructure is entirely F, with a grain size of 7.0. The yield strength ReL is 177–192 MPa, the tensile strength Rm is 297–305 MPa, and the elongation after fracture A... 50 The saturation rate is 55-57%, the double-sided enamel flake test is qualified, the adhesion test level is 1-2, and the anti-flake sensitivity TH value is ≥18min / mm. 2 The enamel finish is excellent. However, double-sided enamel enamel prevents gas from escaping from the steel (unlike single-sided enamel enamel, where gas can escape from the non-enamel side), thus requiring higher resistance to gas explosion. Attached Figure Description

[0018] Figure 1 This is a metallographic image of Example 1 of the present invention;

[0019] Figure 2 A metallographic photograph of Comparative Example 1;

[0020] Figure 3 This is a photograph of a double-sided enamel test in Embodiment 1 of the present invention;

[0021] Figure 4 This is a photograph of the double-sided enamel test in Comparative Example 1. Detailed Implementation

[0022] To provide a clearer understanding of the technical features, objectives, and effects of this invention, the invention is now described.

[0023] I. Design Scheme: An ultra-low carbon composition system is adopted to minimize residual elements in the steel. This is achieved by adding Ti microalloying and appropriately increasing the S and N content, combined with a suitable rolling process, to produce steel with a yield strength range of 170–200 MPa, a tensile strength range of 290–310 MPa, and an elongation A… 50 With a strength greater than 50%, it meets the requirements for phosphorus explosion resistance in double-sided enamel applications and possesses excellent deep-drawing forming performance.

[0024] 1. Chemical composition by weight percentage includes: C: 0.002–0.004%; Si: ≤0.03%; Mn: 0.10%–0.20%; P ≤0.020%; S: 0.01–0.02%; Al: 0.020%–0.040%; Ti: 0.10%–0.12%; N: 0.0060–0.0100%; B: 0.0015–0.0025%, with the remainder being Fe and unavoidable impurities. The roles of each alloying element are as follows:

[0025] C: C is a solid solution strengthening element. Excessive C content can affect the material's formability. To ensure deep drawing performance, an ultra-low carbon design is required. However, the C content cannot be too low; a small amount of C still needs to be retained in enamel steel to form precipitates with Ti, creating "hydrogen traps" that effectively improve resistance to phosphorus explosion. Therefore, considering all factors, the C content in this invention is controlled between 0.002% and 0.004%.

[0026] Si: If the Si content is too high, iron silicate is easily generated during the hot rolling process, making it difficult to remove iron oxide scale and causing iron oxide scale residue, which affects the quality of local enamel. Therefore, the Si content should be controlled within 0.03%.

[0027] Mn: Mn is a solid solution strengthening element. Adding Mn to steel increases its strength. To improve the deep-drawing performance of the material, the Mn content in the steel needs to be controlled at a low level, but it cannot be too low either. This is because Mn can form MnS with S, which avoids hot brittleness caused by high S content, and can also form "hydrogen traps" to improve resistance to phosphorus explosion. Therefore, in this invention, the Mn content is controlled at 0.10% to 0.20%.

[0028] P: P is generally considered a harmful element in steel, and a high P content can impair the material's formability. In this invention, the P content is controlled within the range of ≤0.020%.

[0029] S: S can react with Mn and Ti in steel to form MnS and TiC2S2, creating a "hydrogen trap," which is beneficial to the steel plate's resistance to phosphorus explosion. However, excessive S content will affect weldability and formability. Based on the amount of Mn and Ti added in this invention, the S content is controlled at 0.01–0.02%.

[0030] Al: Al acts as a deoxidizer in the steelmaking process. Sufficient Al content is required in the steel to ensure effective deoxidation. Simultaneously, Al combines with N to form AlN two-phase particles, improving the steel plate's resistance to phosphorus explosion. However, excessive Al content can negatively impact the adhesion of enamel. In this invention, the Al content is controlled between 0.020% and 0.040%.

[0031] Ti: Ti is an important component element in the design of enamel steel products. Ti can form TiC₂S₂, TiC, and TiN two-phase particles with C, N, and S in steel, improving the steel plate's resistance to phosphorus explosion. In this invention, adding Ti also plays another role: eliminating interstitial atoms between C and N in the steel, greatly improving deep-drawing performance. However, excessive Ti content will deteriorate the enamel adhesion performance. Therefore, considering all factors, the Ti content in this invention is controlled at 0.10% to 0.12%.

[0032] Nitrogen (N): Nitrogen increases the aging sensitivity of steel, affecting its formability and weldability. In this invention, the N content in the steel needs to be appropriately increased to ensure that enough N can form two-phase particles with Ti, Al, and B, thereby improving resistance to phosphorus explosion. Based on the amount of Ti and B added, the N content in this invention is controlled between 0.0060% and 0.0100%.

[0033] Boolean (B): Boolean (B) can combine with nitrogen (N) to form BN two-phase particles. Adding trace amounts of B to steel can improve its resistance to phosphorus explosion. However, if the B content is too high, a large amount of BN will precipitate at the grain boundaries during hot rolling, causing rolling defects such as peeling and black lines. In this invention, the B content is controlled between 0.0015% and 0.0025%.

[0034] 2. Process route: Desulfurized molten iron → converter smelting → RH vacuum refining → slab continuous casting → slab heating → descaling → rough rolling → finish rolling → coiling → pickling → coiling.

[0035] 3. Converter steelmaking: To ensure the stability of S content control, desulphurization of molten iron is required to ensure that the S content of the molten iron entering the furnace is ≤0.005%. The smelting process adopts bottom blowing nitrogen throughout, and the nitrogen flow rate is increased in the later stage of blowing to strengthen the stirring of the molten pool. The final target of the converter is: C: ≤0.06%, P ≤0.018%.

[0036] 4. Alloy addition sequence: Ferrosulfur is added during the converter tapping process, while ferrosilicon nitride and ferrotitanium are added during the RH process.

[0037] 5. Vacuum refining treatment of RH steel: ultimate vacuum holding time ≥ 10 min; net circulation time ≥ 5 min. Determination time 20–35 min.

[0038] 6. Continuous casting: The cooling of the crystallizer and the secondary cooling adopt strong cooling parameters; the casting speed is stably controlled between 0.9m / min and 1.60m / min.

[0039] 7. Slab heating: To ensure uniform and fine austenite grains and solid solution of alloying elements, a low-temperature heating process is adopted. Heating temperature: 1180℃~1230℃, heating time: ≥100min.

[0040] 8. Finishing rolling temperature: Rolling is mainly carried out in the austenitic region of the low-temperature range, avoiding rolling in the two-phase region. The main purpose is to control the grain size of the steel plate and avoid coarse grains and mixed grain phenomena. According to calculations, the Ac3 temperature of this composition system is about 860-890℃; the precipitation temperature of BN two-phase particles is about 800℃. If the temperature of the strip edge is low during the finishing rolling process, the precipitation of BN particles is prone to causing edge peeling defects. Therefore, taking all factors into consideration, the initial finishing rolling temperature is controlled at 950℃-1030℃, and the final rolling temperature is controlled at 890℃-930℃.

[0041] 9. Laminar Cooling Temperature: To eliminate the negative impact of C and N interstitial atoms on the deep-drawing performance of the material, allowing them to combine with Ti, Al, and B in the steel to form two-phase particles that precipitate and grow fully during the hot rolling process, thus improving resistance to flaking. Laminar cooling adopts a forward rapid cooling mode, with the coiling temperature controlled at 700–740℃. Higher coiling temperatures promote ferrite grain growth, which can better enhance the material's plastic deformation capacity.

[0042] 10. Pickling process: 1# pickling tank ≥40g / l, 2# pickling tank ≥60g / l, 3# pickling tank ≥110g / l, acid temperature controlled at 70~85℃, pickling speed 100~150m / min, to ensure that the strip steel surface obtains a good pickling effect and avoid under-pickling or over-pickling.

[0043] The hot-rolled pickled enamel steel of this invention, which is suitable for deep drawing and double-sided enamel processing, adopts the following composition ratio and specific process. Table 1 shows the composition (by weight percentage) of the steels in each embodiment and comparative example. Table 2 shows the process parameters corresponding to Table 1. Table 3 shows the mechanical properties of the steels with the compositions described in each case. Table 4 shows the enamel test results for each case. Figures 1-2 The metallographic structures corresponding to the embodiments and comparative examples are shown below. The metallographic structure of Embodiment 1 of the present invention is F with a grain size of 7.0 grade; the metallographic structure of Comparative Example 1 is F+P with a grain size of 8.5 grade. Figures 3-4These are photographs of enamel tests corresponding to the examples and comparative examples, wherein... Figure 3 Example 1: The double-sided enamel is of good quality and no crackling is observed; Figure 4 Comparative Example 1: Scale cracking occurred after double-sided enamel coating.

[0044] Table 1: Chemical Composition of the Product (wt%)

[0045] Example C Si Mn P S Ti Alt N B Example 1 0.0027 0.0162 0.191 0.0142 0.016 0.1066 0.0354 0.0093 0.0018 Example 2 0.0029 0.0102 0.162 0.0091 0.019 0.1167 0.0367 0.0078 0.0023 Example 3 0.0035 0.0132 0.159 0.0155 0.015 0.1033 0.0351 0.0083 0.0019 Example 4 0.0026 0.0084 0.187 0.0099 0.015 0.1050 0.0211 0.0072 0.0021 Comparative Example 1 0.0651 0.0183 0.2805 0.0159 0.0151 0.0012 0.0294 0.0064 0.0002 Comparative Example 2 0.0558 0.0121 0.2707 0.012 0.0148 0.0011 0.0257 0.007 0.0002 Comparative Example 3 0.0013 0.0163 0.0473 0.0097 0.0194 0.0828 0.0291 0.0098 0.0001 Comparative Example 4 0.0027 0.0191 0.0803 0.012 0.0161 0.0794 0.0315 0.0084 0.0002

[0046] Table 2: Specific process parameters for each case

[0047]

[0048]

[0049] Table 3: Mechanical properties obtained from each case (A in the table represents elongation after fracture). 50 )

[0050] Example Specifications / mm ReL / MPa Rm / MPa A / ％ Example 1 3.5 177 298 56 Example 2 3.5 188 300 55 Example 3 4.0 192 305 56 Example 4 4.0 184 297 57 Comparative Example 1 3.5 267 358 41 Comparative Example 2 4.0 281 355 43 Comparative Example 3 3.5 190 302 53 Comparative Example 4 4.0 184 301 56

[0051] Table 4: Enamel Test Results for Each Example (Related to Which Performance(s)). Double-sided enamel has higher requirements for anti-scaling performance. The table shows the anti-scaling sensitivity TH value; a higher value indicates better anti-scaling performance.

[0052]

[0053]

[0054] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. The various components of the present invention can be combined with each other without conflict. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for producing hot-rolled pickled enamel steel that is suitable for deep drawing and double-sided enamel processing, characterized in that, The chemical composition is as follows, by weight percentage: C: 0.002-0.004%; Si: ≤0.03%; Mn: 0.10%-0.20%; P ≤0.020%; S: 0.01-0.02%; Al: 0.020%-0.040%; Ti: 0.10%-0.12%; N: 0.0060-0.0100%; B: 0.0015-0.0025%, with the remainder being Fe and unavoidable impurities. The process route for producing hot-rolled pickled enamel steel suitable for deep drawing and double-sided enamel processing is as follows: desulfurized molten iron, converter smelting, RH vacuum refining, slab continuous casting, slab heating, descaling, rough rolling, finish rolling, coiling, pickling, and coiling.

2. The production method of hot-rolled pickled enamel steel as described in claim 1, which is capable of deep drawing and is suitable for double-sided enamel processing, is characterized in that... In RH vacuum refining, the ultimate vacuum holding time is ≥10 min; the net circulation time is ≥5 min; and the quenching time is 20–35 min.

3. The production method of hot-rolled pickled enamel steel as described in claim 1, which is capable of deep drawing and suitable for double-sided enamel processing, is characterized in that... The initial rolling temperature of the finishing mill is controlled at 950℃~1030℃, and the final rolling temperature is controlled at 890℃~930℃.

4. The production method of hot-rolled pickled enamel steel as described in claim 1, which is capable of deep drawing and suitable for double-sided enamel processing, is characterized in that... Laminar flow cooling adopts a forward rapid cooling mode, and the winding temperature is controlled at 700-740℃.

5. The method for producing hot-rolled pickled enamel steel as described in claim 1, which is suitable for deep drawing and double-sided enamel processing, is characterized in that... In slab continuous casting, the casting speed is stably controlled between 0.9 m / min and 1.60 m / min.

6. The method for producing hot-rolled pickled enamel steel as described in claim 1, which is capable of deep drawing and is suitable for double-sided enamel processing, is characterized in that... Slab heating: To ensure uniform and fine austenite grains and solid solution of alloying elements, a low-temperature heating process is adopted, with a heating temperature of 1180℃~1230℃ and a heating time of ≥100min.

7. The method for producing hot-rolled pickled enamel steel as described in claim 1, which is capable of deep drawing and suitable for double-sided enamel processing, is 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.

8. The method for producing hot-rolled pickled enamel steel as described in claim 1, which is capable of deep drawing and suitable for double-sided enamel processing, is characterized in that... C:0.0026～0.0035％。 9. The method for producing hot-rolled pickled enamel steel as described in claim 1, which is capable of deep drawing and suitable for double-sided enamel processing, is characterized in that... Mn: 0.159%~0.191%.

10. The method for producing hot-rolled pickled enamel steel as described in claim 1, which is capable of deep drawing and is suitable for double-sided enamel processing, is characterized in that... B:0.0018～0.0023％。

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