High-strength enameled steel and preparation method thereof

Abstract

The present invention discloses a high-strength enameled steel and a preparation method thereof, belonging to the technical field of enameled steel. The chemical composition of the high-strength enameled steel, measured by weight percentage, includes 0.08-0.10% C, ≤0.30% Si, 0.80-1.60% Mn, ≤0.005% P, ≤0.050% S, ≤0.0040% N, 0.020-0.040% Ti, 0.60-1.20% Cr, and 0.20-0.40% Cu, with the remainder being Fe and unavoidable impurities; the Cr:Cu ratio is 2.5:1 to 3.5:1. The enameled steel exhibits both excellent mechanical properties and anti-scale resistance. The preparation method comprises steelmaking, hot pressing, pickling, cold rolling, and annealing molten steel. The method is simple, easy to operate, and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of enameled steel, and in particular to a high-strength enameled steel and a preparation method thereof. Background Art

[0002] There are many types of enameled steel sheets. Based on the production process, they are classified into hot-rolled (i.e., pickled) sheets, cold-rolled sheets, and clad sheets. Based on yield strength, they are classified into different strength grades, such as 245MPa, 330MPa, and 360MPa. The performance requirements for enameled steel sheets primarily include strength, formability, weldability, and fishscale resistance. Strength, formability, and weldability are related to the alloying elements, matrix structure, and second-phase precipitates in the steel, while fishscale resistance is related to hydrogen traps (grain boundaries, dislocations, microscopic voids, and second-phase particles) in the steel.

[0003] The production process of cold-rolled enameled steel primarily includes steelmaking, hot rolling, pickling, cold rolling, and annealing. The chemical composition of the steel, along with the hot rolling, cold rolling, and annealing steps, plays a dominant role in determining the matrix structure, second-phase precipitation, and overall performance of cold-rolled enameled steel. As the application of enameled products continues to expand, higher requirements are being placed on the mechanical properties and fishscale resistance of cold-rolled enameled steel. In particular, the steel plate must maintain a sufficiently high yield strength after undergoing two high-temperature firings (base and top glaze) to meet the safety requirements for use in large structural components. Furthermore, it is crucial to maximize hydrogen traps within the material while maintaining sufficient strength to develop cold-rolled enameled steel products with excellent fishscale resistance.

[0004] The existing technologies for enameled steel currently have the following main problems: it is difficult for enameled steel to reach a high-strength level, and it is difficult to strike a balance between strength and scale resistance, resulting in unstable performance of the steel plate.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a high-strength enameled steel and a preparation method and application thereof, so as to solve or improve the above-mentioned technical problems.

[0007] The present invention can be implemented like this:

[0008] In a first aspect, the present invention provides a high-strength enameled steel, wherein the chemical composition of the high-strength enameled steel comprises, by weight percentage, 0.08% to 0.10% C, ≤0.30% Si, 0.80% to 1.60% Mn,

[0009] ≤0.005% P, ≤0.050% S, ≤0.0040% N, 0.020%-0.040% Ti, 0.60%-1.20% Cr and 0.20%-0.40% Cu, with the balance being Fe and unavoidable impurities; the mass ratio of Cr to Cu in the high-strength enameled steel is 2.5:1 to 3.5:1.

[0010] In an optional embodiment, the high-strength enameled steel contains 20 wt% to 40 wt% pearlite.

[0011] In an optional embodiment, the high-strength enameled steel further contains precipitates, and the precipitates include 1.5 wt % to 3.5 wt % of Cr-containing carbide particles.

[0012] In an alternative embodiment, the Cr-containing carbide particles include M 23 C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles.

[0013] In an optional embodiment, the particle size of the Cr-containing carbide particles is 0.2 μm to 1.0 μm.

[0014] In an optional embodiment, the high-strength enameled steel further has at least one of the following characteristics:

[0015] Feature 1: The yield strength of high-strength enameled steel is ≥700MPa;

[0016] Feature 2: The tensile strength of high-strength enameled steel is ≥750MPa;

[0017] Feature 3: The elongation after fracture of high-strength enameled steel is ≥10%;

[0018] Feature 4: The scale explosion sensitivity index TH value of high-strength enameled steel is ≥20min·mm -2 ;

[0019] Feature 5: The inclusion content in high-strength enameled steel is 25 per mm 2 ~45 pieces / mm 2 ;

[0020] Feature 6: The particle size of inclusions in high-strength enameled steel is 1.0μm to 6.0μm.

[0021] In a second aspect, the present invention provides a method for preparing high-strength enameled steel as described in any of the aforementioned embodiments, comprising the following steps: subjecting molten steel having the chemical composition of high-strength enameled steel to a steelmaking process, a hot rolling process, a pickling process, a cold rolling process, and an annealing process.

[0022] In an optional embodiment, the hot rolling process includes a heating stage, a rough rolling stage, a finishing rolling stage and a final rolling stage;

[0023] Among them, the temperature of the heating stage is 1180℃~1220℃, and the holding time is 108min~132min; the starting rolling temperature of the rough rolling stage is 1050℃~1150℃; the starting rolling temperature of the finishing rolling stage is 950℃~1050℃; and the temperature of the final rolling stage is 850℃~950℃.

[0024] In an optional embodiment, after the final rolling stage, a cooling stage and a coiling stage are also included; wherein the cooling stage includes a laminar cooling stage and an air cooling stage, the cooling rate of the laminar cooling is 15°C / s to 35°C / s, and the final temperature of the laminar cooling is 600°C to 700°C; the temperature of the coiling stage is 550°C to 650°C.

[0025] In an optional embodiment, the pickling process includes at least one of the following features:

[0026] Feature 7: The washing agent used for pickling is a dilute hydrochloric acid solution; preferably, the concentration of the dilute hydrochloric acid solution is 8% to 10%;

[0027] Feature 8: The pickling temperature is 60℃~70℃.

[0028] In an optional embodiment, the cold rolling reduction ratio of the cold rolling process is 60% to 70%.

[0029] In an optional embodiment, the annealing temperature of the annealing process is 550° C. to 650° C., and the holding time is 4 h to 6 h.

[0030] The beneficial effects of the present invention include:

[0031] The high-strength enameled steel with a specific chemical composition provided by the present invention combines excellent mechanical properties with fishscale resistance. By adding sufficient amounts of Cr and Cu and controlling the Cr:Cu mass ratio in the high-strength enameled steel to between 2.5:1 and 3.5:1, the steel is facilitated to form a large number of second-phase particles during the production process, enhancing the steel's solid solution strengthening and second-phase strengthening effects while significantly increasing the variety and number of solid hydrogen traps in the steel. This high-strength enameled steel boasts a simple production process and stable, controllable product performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1This is an optical microstructure diagram of the high-strength enameled steel prepared in Example 1;

[0034] Figure 2 This is an optical microstructure diagram of the high-strength enameled steel prepared in Example 2;

[0035] Figure 3 This is an optical microstructure diagram of the high-strength enameled steel prepared in Comparative Example 1;

[0036] Figure 4 This is the optical microstructure diagram of the high-strength enameled steel prepared in Comparative Example 2. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0038] The high-strength enameled steel and its preparation method provided by the present invention are described in detail below.

[0039] The present invention provides a high-strength enameled steel. The chemical composition of the high-strength enameled steel includes, by weight percentage, 0.08% to 0.10% C, ≤0.30% Si, 0.80% to 1.60% Mn, ≤0.005% P, ≤0.050% S, ≤0.0040% N, 0.020% to 0.040% Ti, 0.60% to 1.20% Cr, and 0.20% to 0.40% Cu, with the balance being Fe and unavoidable impurities.

[0040] Among them, C determines the strength, plasticity, and formability of the steel plate. The lower the C content, the lower the strength of the steel plate, but the better the formability; the higher the C content, the higher the strength but the disadvantage of weldability and formability. In order to obtain good isotropy while taking into account both weldability and formability, the C content is controlled to 0.08% to 0.10% in the present invention. For example, it can be 0.08%, 0.085%, 0.09%, 0.095% or 0.10%, etc., and can also be other values ​​within the range of 0.08% to 0.10%. The vast majority of the above-mentioned carbon precipitates in the form of carbides in the austenite stage. The precipitated carbide particles can significantly increase the strength of the steel plate.

[0041] Si exists in steel as a residual element. Too high a content thereof will impair the adhesion of the enamel. In the present invention, the Si content is controlled to be ≤0.30%, and illustratively can be 0.30%, 0.25%, 0.20%, 0.15%, 0.10% or 0.05%, etc., or other values ​​within the range of ≤0.30%.

[0042] Mn can act as a deoxidizer and desulfurizer in steel. Mn can react with S to form MnS precipitation, preventing the formation of FeS and cracks in the corners of the ingot. In addition, Mn acts as a solid solution strengthening element, increasing strength. However, excessive Mn content can reduce the plasticity of the steel. The present invention controls the Mn content to 0.80% to 1.60%, and illustratively, it can be 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, 1.05%, 1.10%, 1.15%, 1.20%, 1.25%, 1.30%, 1.35%, 1.40%, 1.45%, 1.50%, 1.55%, or 1.60%, or other values ​​within the range of 0.80% to 1.60%.

[0043] P is a harmful element in steel and easily segregates at grain boundaries, affecting the quality of enamel. The present invention controls the P content to ≤0.005%, which can be 0.005%, 0.0045%, 0.004%, 0.0035%, 0.003%, 0.0025%, 0.002%, 0.0015% or 0.001%, etc., and can also be other values ​​within the range of ≤0.005%.

[0044] Sulfur is an impurity element in steel, primarily present as MnS. In enameled steel, sulfides exhibit beneficial effects within a certain range. By adding Ti, complex inclusions such as TiS and Ti4C2S2 can be formed. These inclusions are often spherical, which can reduce damage to plasticity and act as hydrogen traps, improving anti-scale performance. Furthermore, increasing sulfur content can also improve fatigue performance. In the present invention, the S content is controlled to ≤0.050%, and illustratively can be 0.050%, 0.045%, 0.040%, 0.035%, 0.030%, 0.025%, 0.020%, 0.015%, or 0.010%, or other values ​​within the range of ≤0.050%.

[0045] The effect of N is similar to that of C. Generally, it will increase the yield strength and hardness of steel and reduce the r value. At the same time, the precipitated nitrides can serve as effective hydrogen storage sites, improving the steel's anti-scale explosion performance. When the N content is too high, it will damage the stamping performance of the steel plate. At the same time, it can also reduce the amount of alloying elements added and lower the recrystallization temperature. In Ti-containing enameled steel, N will precipitate in the form of TiN and Ti (C, N), thereby improving the steel's anti-scale explosion performance. In the present invention, the N content is controlled to be ≤0.0040%, and can be illustratively 0.004%, 0.0035%, 0.003%, 0.0025%, 0.002%, 0.0015% or 0.001%, etc., or other values ​​within the range of ≤0.004%.

[0046] Ti plays a role in fixing nitrogen in steel, hindering recrystallization, and achieving fine grains. Ti generally forms second-phase precipitates with carbon and nitrogen, such as TiC, TiN, TiS, Ti(C, N), and Ti4C2S2. These precipitates have relatively high binding energies with hydrogen atoms and can act as irreversible hydrogen traps, effectively securing hydrogen atoms near the precipitate particles and reducing scale. They also inhibit the precipitation of large-scale MnS and improve the fatigue and formability of the steel sheet. The present invention controls the Ti content to 0.020% to 0.040%, illustratively, 0.020%, 0.025%, 0.030%, 0.035%, or 0.040%, or other values ​​within the range of 0.020% to 0.040%.

[0047] Cr can significantly change the morphological distribution of ferrite and refine the grains, and can change the dynamic strain aging behavior of low carbon steel. Cr can also dissolve in ferrite, produce solid solution strengthening, and improve the strength of the ferrite matrix. The Cr-containing second phase in the microstructure has a smaller tendency to grow during the annealing process, ensuring the stability of the performance after annealing. At the same time, Cr can also improve the surface condition of the steel plate after rolling and improve the adhesion of the enamel. The present invention controls the Cr content to 0.60% to 1.20%, and illustratively can be 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, 1.05%, 1.10%, 1.15% or 1.20%, etc., and can also be other values ​​within the range of 0.60% to 1.20%.

[0048] Cu precipitates before austenite transformation, which can refine austenite grains, increase material strength, improve steel formability, and reduce the hardening index. An appropriate amount of Cu can also improve the adhesion of enameled steel sheets. The present invention controls the Cu content to 0.20% to 0.40%, illustratively, 0.20%, 0.25%, 0.30%, 0.35%, or 0.40%, or other values ​​within the range of 0.20% to 0.40%.

[0049] In the high-strength enameled steel provided by the present invention, the mass ratio of Cr to Cu is 2.5:1 to 3.5:1, such as 2.5:1, 3:1, or 3.5:1. In some preferred embodiments, the mass ratio of Cr to Cu is 3:1. With this element ratio, the Cr and Cu elements can maximize their functionality.

[0050] The high-strength enameled steel of the present invention comprises ferrite and pearlite, with the pearlite accounting for approximately 20 to 40% by weight and the ferrite accounting for approximately 55 to 75% by weight. The steel also contains a large amount of deformed structure and dislocations, and a high content and variety of second-phase particles.

[0051] The above-mentioned precipitates include 1.5wt% to 3.5wt% (such as 1.5wt%, 2wt%, 2.5wt%, 3wt% or 3.5wt%) of Cr-containing carbide particles. The Cr-containing carbide particles include M 23 C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles. Preferably, the particle size of the Cr-containing carbide particles is 0.2 μm to 1.0 μm.

[0052] As mentioned above, the present invention adds three key alloying elements, Ti, Cr, and Cu, to the steel. Most of the alloying elements in the steel are uniformly dispersed and precipitated in the form of carbides, which significantly improves the dislocation strengthening, second phase strengthening, and solid solution strengthening effects of the steel, thereby significantly optimizing the mechanical properties of the steel, such as yield strength ≥700MPa, tensile strength ≥750MPa, and elongation after fracture ≥10%. In addition, the Cr and Cu in the steel satisfy Cr=(2.5~3.5)Cu. Due to the addition of sufficient Cr and Cu, the alloying elements in the matrix solid solution increase, and the precipitated M 23 The number of particles such as C6 and M7C3 containing Cr carbides increases, and the effects of solid solution strengthening and second phase strengthening of the steel are significantly improved, so that the steel still maintains excellent mechanical properties after annealing.

[0053] In some embodiments, the fishscale sensitivity index TH value of the high-strength enameled steel provided by the present invention is ≥20min·mm -2 .

[0054] In some embodiments, the content of inclusions in the high-strength enameled steel provided by the present invention is 25 / mm 2 ~45 pieces / mm 2 , such as 25 / mm 2 , 30 pieces / mm 2 , 35 pieces / mm 2 , 40 pieces / mm 2 or 45 pieces / mm 2 wait.

[0055] In some embodiments, the particle size of inclusions in the high-strength enameled steel provided by the present invention is 1.0 μm to 6.0 μm, such as 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm.

[0056] As mentioned above, the high-strength enameled steel provided by the present invention can have both excellent mechanical properties and anti-scale burst performance.

[0057] Accordingly, the present invention also provides a method for preparing the above-mentioned high-strength enameled steel, comprising the following steps: subjecting molten steel having the chemical composition meeting the requirements of high-strength enameled steel to steelmaking, hot rolling, pickling, cold rolling and annealing.

[0058] Among them, the steelmaking process refers to smelting molten steel that meets the chemical composition of high-strength enameled steel, alloying it, and casting it into slabs.

[0059] The hot rolling process includes a heating stage, a rough rolling stage, a finishing rolling stage, and a final rolling stage. The temperature in the heating stage may be 1180°C to 1220°C (e.g., 1180°C, 1185°C, 1190°C, 1195°C, 1200°C, 1205°C, 1210°C, 1215°C, or 1220°C), and the holding time may be 108 min to 132 min (e.g., 108 min, 120 min, or 132 min). The starting rolling temperature in the rough rolling stage may be 1050°C to 1150°C (e.g., 1050°C, 1100°C, or 1150°C). The starting rolling temperature in the finishing rolling stage may be 950°C to 1050°C (e.g., 950°C, 1000°C, or 1050°C). The temperature in the final rolling stage may be 850°C to 950°C (e.g., 850°C, 900°C, or 950°C). A higher finishing temperature is used to ensure the precipitation of the second phase.

[0060] Furthermore, after the final rolling stage, a cooling stage and a coiling stage are also included. Among them, the cooling stage includes a laminar cooling stage and an air cooling stage. Specifically, laminar cooling is performed after final rolling, and then air cooling is performed to the coiling temperature. For reference, the cooling rate of laminar cooling can be 15℃ / s~35℃ / s (such as 15℃ / s, 20℃ / s, 25℃ / s, 30℃ / s or 35℃ / s, etc.), and the final temperature of laminar cooling can be 600℃~700℃ (such as 600℃, 650℃ or 700℃, etc.). The temperature of the coiling stage can be 550℃~650℃ (such as 550℃, 600℃ or 650℃, etc.). The hot-rolled structure is ferrite and a small amount of cementite.

[0061] The pickling process involves pickling the hot-rolled plate. The pickling agent used can be a dilute hydrochloric acid solution, such as a dilute hydrochloric acid solution with a concentration of 8% to 10% (e.g., 8%, 8.5%, 9%, 9.5%, or 10%). The pickling temperature can be 60°C to 70°C (e.g., 60°C, 65°C, or 70°C). The pickling time should not be too long to ensure that the iron oxide scale is completely removed.

[0062] The cold rolling reduction ratio of the cold rolling process may be 60% to 70% (eg, 60%, 65%, or 70%, etc.).

[0063] The annealing temperature of the annealing process can be 550° C. to 650° C. (e.g., 550° C., 600° C., or 650° C.), and the holding time can be 4 h to 6 h (e.g., 4 h, 4.5 h, 5 h, 5.5 h, or 6 h.) A lower annealing temperature can ensure the number of solid hydrogen traps.

[0064] As mentioned above, the preparation method of the high-strength enameled steel provided by the present invention is simple and easy to operate, can provide the stability of the steel plate, and is suitable for industrial production.

[0065] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0066] Example 1

[0067] This embodiment provides a high-strength enameled steel. The chemical composition and content (mass percentage) of the high-strength enameled steel are shown in Table 1, with the remainder being Fe and unavoidable impurities.

[0068] Table 1 Chemical composition and composition (%)

[0069] element C Si Mn P S Ti Cr Cu N content(%) 0.090 0.14 0.93 ＜0.0050 0.044 0.031 0.72 0.24 0.0030

[0070] The preparation of the high-strength enameled steel includes:

[0071] 1) Steelmaking process: Smelting is carried out according to the chemical composition designed above, and alloying treatment is performed, and then it is cast into slabs.

[0072] 2) Hot Rolling: The ingot undergoes heating, rough rolling, finishing rolling, final rolling, laminar cooling, air cooling, and coiling to produce hot-rolled plates. The heating temperature is 1200°C with a holding time of 2 hours; the start temperature of rough rolling is controlled at 1100°C; the start temperature of finishing rolling is 1000°C; and the final rolling temperature is controlled at 890°C. After final rolling, the ingot is laminar cooled to 700°C at a cooling rate of 25°C / s, followed by air cooling to the coiling temperature, which is set at 650°C.

[0073] 3) Pickling process: The hot-rolled plate is placed in a 10% dilute hydrochloric acid solution for pickling, and the pickling temperature is controlled at 70°C.

[0074] 4) Cold rolling process: The pickled steel plate is cold rolled, and the cold rolling reduction rate is controlled at 60%.

[0075] 5) Annealing process: annealing the cold-rolled thin strip steel at a temperature of 550° C. for 5 h.

[0076] The precipitates in the high-strength enameled steel include 2.8 wt% of Cr-containing carbide particles (M 23 C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles), the particle size of the Cr-containing carbide particles is 0.2μm to 0.5μm.

[0077] The optical microstructure of the high-strength enameled steel is shown in Figure 2. Figure 1 As shown in the figure, it can be seen that the structure of the high-strength enameled steel includes ferrite and pearlite, and contains a large amount of deformed structure and dislocation.

[0078] The mechanical properties of the enameled steel produced in Example 1 were tested in accordance with GB / T 228.1-2021 Metallic Materials - Tensile Tests - Part 1: Room Temperature Test Methods. The anti-scale performance was also tested in accordance with GB / T 29515-2013 Cold-Rolled Steel Sheet for Enameling - Scale-Degree Sensitivity - Hydrogen Permeation Test Method. Furthermore, the number and size of inclusions in the enameled steel were statistically analyzed, as shown in Table 2.

[0079] Table 2 Test results

[0080]

[0081] Example 2

[0082] This embodiment provides a high-strength enameled steel, the chemical composition and content (mass percentage) of the high-strength enameled steel are the same as those in Example 1.

[0083] The preparation of the high-strength enameled steel includes:

[0084] 1) Steelmaking process: smelting according to the chemical composition designed above, alloying, and then casting into slabs;

[0085] 2) Hot Rolling: The ingot undergoes heating, rough rolling, finishing rolling, final rolling, laminar cooling, air cooling, and coiling to produce hot-rolled plates. The hot rolling process is held at 1200°C for 2 hours, the start temperature for rough rolling is controlled at 1100°C, the start temperature for finishing rolling is 1000°C, and the final rolling temperature is controlled at 890°C. After final rolling, the ingot is laminar cooled to 650°C at a cooling rate of 25°C / s, followed by air cooling to the coiling temperature, which is set at 650°C.

[0086] 3) Pickling process: The hot-rolled plate is placed in a 10% dilute hydrochloric acid solution for pickling, and the pickling temperature is controlled at 70°C.

[0087] 4) Cold rolling process: The pickled steel plate is cold rolled, and the cold rolling reduction rate is controlled at 60%.

[0088] 5) Annealing process: anneal the cold-rolled thin strip steel at a temperature of 600° C. for a holding time of 5 h.

[0089] The precipitates in the high-strength enameled steel include 2.6 wt% of Cr-containing carbide particles (M 23 C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles), the particle size of the Cr-containing carbide particles is 0.4μm to 0.9μm.

[0090] The optical microstructure of the high-strength enameled steel is shown in Figure 2. Figure 2As shown in the figure, it can be seen that the structure of the high-strength enameled steel includes ferrite and pearlite, and contains a large amount of deformed structure and dislocation.

[0091] The mechanical properties, fishscale resistance, and the number and size of inclusions of the enameled steel produced in Example 2 were statistically analyzed in the same manner as in Example 1. The results are shown in Table 3.

[0092] Table 3 Test results

[0093]

[0094]

[0095] Example 3

[0096] This embodiment provides a high-strength enameled steel. The chemical composition and content (mass percentage) of the high-strength enameled steel are shown in Table 4, with the remainder being Fe and unavoidable impurities.

[0097] Table 4 Chemical composition and composition (%)

[0098] element C Si Mn P S Ti Cr Cu N content(%) 0.091 0.15 0.89 ＜0.0050 0.044 0.031 0.77 0.26 0.0030

[0099] The preparation of the high-strength enameled steel includes:

[0100] 1) Steelmaking process: Smelting is carried out according to the chemical composition designed above, and alloying treatment is performed, and then it is cast into slabs.

[0101] 2) Hot Rolling: The ingot undergoes heating, rough rolling, finishing rolling, final rolling, laminar cooling, air cooling, and coiling to produce hot-rolled plates. The heating temperature is 1180°C with a holding time of 132 minutes. The start temperature of rough rolling is controlled at 1050°C; the start temperature of finishing rolling is 950°C; and the final rolling temperature is controlled at 850°C. After final rolling, the ingot is laminar cooled to 600°C at a cooling rate of 15°C / s, followed by air cooling to the coiling temperature, which is set at 550°C.

[0102] 3) Pickling process: The hot-rolled plate is placed in 8% dilute hydrochloric acid solution for pickling, and the pickling temperature is controlled at 60°C.

[0103] 4) Cold rolling process: The pickled steel plate is cold rolled, and the cold rolling reduction rate is controlled at 65%.

[0104] 5) Annealing process: annealing the cold-rolled thin strip steel at a temperature of 600° C. for a holding time of 6 h.

[0105] The precipitates in the high-strength enameled steel include 2.5 wt% of Cr-containing carbide particles (M 23C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles), the particle size of the Cr-containing carbide particles is 0.4μm to 1.0μm.

[0106] The mechanical properties of the enameled steel produced in Example 3 were tested in accordance with GB / T 228.1-2021 Metallic Materials - Tensile Tests - Part 1: Room Temperature Test Methods. The fishscale resistance of the steel was tested in accordance with GB / T 29515-2013 Cold-rolled Steel Sheet for Enameling - Scale-Degree Sensitivity - Hydrogen Permeation Method. Furthermore, the number and size of inclusions in the enameled steel were statistically analyzed, and the results are shown in Table 5.

[0107] Table 5 Test results

[0108]

[0109] Example 4

[0110] This embodiment provides a high-strength enameled steel. The chemical composition and content (mass percentage) of the high-strength enameled steel are shown in Table 6, with the remainder being Fe and unavoidable impurities.

[0111] Table 6 Chemical composition and composition (%)

[0112] element C Si Mn P S Ti Cr Cu N content(%) 0.095 0.15 0.95 ＜0.0050 0.040 0.035 0.70 0.30 0.0030

[0113] The preparation of the high-strength enameled steel includes:

[0114] 1) Steelmaking process: Smelting is carried out according to the chemical composition designed above, and alloying treatment is performed, and then it is cast into slabs.

[0115] 2) Hot Rolling: The ingot undergoes heating, rough rolling, finishing rolling, final rolling, laminar cooling, air cooling, and coiling to produce hot-rolled plates. The heating temperature is 1220°C with a holding time of 108 minutes. The start temperature of rough rolling is controlled at 1150°C; the start temperature of finishing rolling is 1050°C; and the final rolling temperature is controlled at 950°C. After final rolling, the ingot is laminar cooled to 675°C at a cooling rate of 35°C / s, followed by air cooling to the coiling temperature, which is set at 600°C.

[0116] 3) Pickling process: The hot-rolled plate is placed in a 9% dilute hydrochloric acid solution for pickling, and the pickling temperature is controlled at 65°C.

[0117] 4) Cold rolling process: The pickled steel plate is cold rolled, and the cold rolling reduction rate is controlled at 70%.

[0118] 5) Annealing process: annealing the cold-rolled thin strip steel at a temperature of 650° C. for 4 h.

[0119] The precipitates in the high-strength enameled steel include 2.8 wt% of Cr-containing carbide particles (M 23 C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles), the particle size of the Cr-containing carbide particles is 0.2μm to 0.5μm.

[0120] The mechanical properties of the enameled steel produced in Example 4 were tested in accordance with GB / T 228.1-2021 Metallic Materials - Tensile Tests - Part 1: Room Temperature Test Methods. The fishscale resistance of the steel was tested in accordance with GB / T 29515-2013 Cold-rolled Steel Sheet for Enameling - Scale-Desirability Test - Hydrogen Permeation Method. Furthermore, the number and size of inclusions in the enameled steel were statistically analyzed. The results are shown in Table 7.

[0121] Table 7 Test results

[0122]

[0123] Comparative Example 1

[0124] This comparative example provides a high-strength enameled steel, the chemical composition and content (mass percentage) of the high-strength enameled steel are the same as those in Example 1.

[0125] The preparation of the high-strength enameled steel includes:

[0126] 1) Steelmaking process: smelting according to the chemical composition designed above, alloying, and then casting into slabs;

[0127] 2) Hot Rolling: The ingot undergoes heating, rough rolling, finishing rolling, final rolling, laminar cooling, air cooling, and coiling to produce hot-rolled plates. The heating temperature is 1200°C with a 2-hour holding time. The start temperature for rough rolling is controlled at 1100°C, and the start temperature for finishing rolling is 1000°C. The final rolling temperature is controlled at 890°C. After final rolling, the ingot is laminar cooled to 700°C at a cooling rate of 25°C / s, followed by air cooling to the coiling temperature, which is set at 650°C.

[0128] 3) Pickling process: The hot-rolled plate is placed in a 10% dilute hydrochloric acid solution for pickling, and the pickling temperature is controlled at 70°C.

[0129] 4) Cold rolling process: The pickled steel plate is cold rolled, and the cold rolling reduction rate is controlled at 60%.

[0130] 5) Annealing process: anneal the cold-rolled thin strip steel at a temperature of 700° C. for a holding time of 5 h.

[0131] The precipitates in the high-strength enameled steel include 2.7 wt% of Cr-containing carbide particles (M 23C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles), the particle size of the Cr-containing carbide particles is 0.5μm to 1.0μm.

[0132] The optical microstructure of the high-strength enameled steel is shown in Figure 2. Figure 3 As shown in the figure, it can be seen that the structure of the high-strength enameled steel includes equiaxed ferrite and a small amount of pearlite, the amount of deformed structure is significantly reduced, and the grains are coarsened.

[0133] The mechanical properties, fishscale resistance, and the number and size of inclusions of the enameled steel produced in Comparative Example 1 were statistically analyzed in the same manner as in Example 1. The results are shown in Table 8.

[0134] Table 8 Test results

[0135]

[0136] Comparative Example 2

[0137] This comparative example provides a high-strength enameled steel. The chemical composition and content (mass percentage) of the high-strength enameled steel are shown in Table 9, with the remainder being Fe and unavoidable impurities.

[0138] Table 9 Chemical composition and composition (%)

[0139] element C Si Mn P S Ti Cr Cu N content(%) 0.10 0.11 1.19 ＜0.0050 0.031 0.033 1.00 0.07 0.0030

[0140] The preparation of the high-strength enameled steel includes:

[0141] 1) Steelmaking process: Smelting is carried out according to the chemical composition designed above, and alloying treatment is performed, and then it is cast into slabs.

[0142] 2) Hot Rolling: The ingot undergoes heating, rough rolling, finishing rolling, final rolling, laminar cooling, air cooling, and coiling to produce hot-rolled plates. The heating temperature is 1200°C with a 2-hour holding time. The start temperature for rough rolling is controlled at 1100°C, and the start temperature for finishing rolling is 1000°C. The final rolling temperature is controlled at 890°C. After final rolling, the ingot is laminar cooled to 700°C at a cooling rate of 25°C / s, followed by air cooling to the coiling temperature, which is set at 650°C.

[0143] 3) Pickling process: The hot-rolled plate is placed in a 10% dilute hydrochloric acid solution for pickling, and the pickling temperature is controlled at 70°C.

[0144] 4) Cold rolling process: The pickled steel plate is cold rolled, and the cold rolling reduction rate is controlled at 60%.

[0145] 5) Annealing process: anneal the cold-rolled thin strip steel at a temperature of 600° C. for a holding time of 5 h.

[0146] The precipitates in the high-strength enameled steel include 2.0 wt% of Cr-containing carbide particles (M 23 C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles), the particle size of the Cr-containing carbide particles is 1.0μm to 1.5μm.

[0147] The optical microstructure of the high-strength enameled steel is shown in Figure 2. Figure 4 As shown in the figure, it can be seen that the structure of the high-strength enameled steel includes ferrite and a small amount of pearlite, and contains a small amount of deformed structure and dislocation.

[0148] The mechanical properties, fishscale resistance, and the number and size of inclusions of the enameled steel produced in Comparative Example 2 were statistically analyzed in the same manner as in Example 1. The results are shown in Table 10.

[0149] Table 10 Test results

[0150]

[0151] Comparative Example 3

[0152] The difference between this comparative example and Example 1 is that the chemical composition of the high-strength enameled steel includes 1.2% Cr and 0.2% Cu, that is, the mass ratio of Cr to Cu in the high-strength enameled steel is 6:1.

[0153] The precipitates in the high-strength enameled steel include 5.0 wt% of Cr-containing carbide particles (M 23 C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles), the particle size of the Cr-containing carbide particles is 2.0μm to 3.5μm.

[0154] The mechanical properties, fishscale resistance, and the number and size of inclusions of the enameled steel produced in Comparative Example 3 were statistically analyzed in the same manner as in Example 1. The results are shown in Table 11.

[0155] Table 11 Test results

[0156]

[0157]

[0158] Comparative Example 4

[0159] The difference between this comparative example and Example 1 is that the chemical composition of the high-strength enameled steel includes 0.6% Cr and 0.4% Cu, that is, the mass ratio of Cr to Cu in the high-strength enameled steel is 1.5:1.

[0160] The precipitates in the high-strength enameled steel include 2.0 wt% of Cr-containing carbide particles (M 23C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles), the particle size of the Cr-containing carbide particles is 0.4μm to 2.0μm.

[0161] The mechanical properties, fishscale resistance, and the number and size of inclusions of the enameled steel produced in Comparative Example 4 were statistically analyzed in the same manner as in Example 1. The results are shown in Table 12.

[0162] Table 12 Test results

[0163]

[0164] In Examples 1, 2, 3, and 4 above, the composition system and corresponding processing technology adopted form a large number of dislocations or second-phase particles in the steel, so that the cold-rolled enameled steel takes into account both strength and fishscale resistance, with stable performance and controllable cost. In Comparative Example 1, due to the high annealing temperature (700°C), at the same holding time, although the second-phase particle density is large, the degree of recovery and recrystallization increases, the dislocation density is significantly reduced, the strengthening effect and the density of solid hydrogen traps decrease, resulting in a significant decrease in strength and fishscale resistance. It can be seen from Example 1 and Comparative Examples 2, 3, and 4 that if the mass ratio of Cr to Cu in the high-strength enameled steel is not in the range of 2.5:1 to 3.5:1, the number of second-phase particles in the steel will be significantly reduced or the size will increase, and the product will also fail to achieve both strength and fishscale resistance.

[0165] In summary, compared with the existing technology, the composition system and production method of the cold-rolled enameled steel designed in this invention have a simple process flow, stable and controllable product performance, and take into account both strength and fishscale resistance. The mechanical properties of the steel plate after annealing are yield strength ≥700MPa, tensile strength ≥750MPa, elongation after fracture ≥10%, and anti-enamel fishscale sensitivity index TH value ≥20min·mm -2 ; Since sufficient amounts of Cr and Cu elements are added to the enameled steel composition of the present invention, and the mass ratio of Cr to Cu is 2.5:1 to 3.5:1, a large number of second-phase particles are formed, which increases the solid solution strengthening and second-phase strengthening effects of the steel, and at the same time significantly increases the types and number of solid hydrogen traps in the steel, so that the enameled steel of the present invention has both excellent mechanical properties and anti-scale explosion properties.

[0166] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A high-strength enameled steel, characterized in that: The chemical composition of the high-strength enameled steel is, by weight percentage, 0.08% to 0.10% C, ≤0.30% Si, 0.80% to 1.60% Mn, ≤0.005% P, ≤0.050% S, ≤0.0040% N, 0.020% to 0.040% Ti, 0.60% to 1.20% Cr, and 0.20% to 0.40% Cu, with the balance being Fe and unavoidable impurities; the mass ratio of Cr to Cu in the high-strength enameled steel is 2.5:1 to 3.5:1; The high-strength enameled steel contains 20wt% to 40wt% pearlite; the high-strength enameled steel also contains precipitates, the precipitates include 1.5wt% to 3.5wt% of Cr-containing carbide particles; the Cr-containing carbide particles include M 23 C6 type Cr-containing carbide particles and M7C3 type Cr-containing carbide particles; the fishscale sensitivity index TH value of the high-strength enamel steel is ≥20min·mm -2 ; The preparation of the high-strength enameled steel comprises the following steps: subjecting molten steel having the chemical composition of the high-strength enameled steel to a steelmaking process, a hot rolling process, a pickling process, a cold rolling process and an annealing process; The annealing temperature of the annealing process is 550°C to 650°C, and the holding time is 4h to 6h.

2. The high-strength enameled steel according to claim 1, characterized in that The particle size of the Cr-containing carbide particles is 0.2 μm to 1.0 μm.

3. The high-strength enameled steel according to claim 1 or 2, characterized in that: The high-strength enameled steel also has at least one of the following characteristics: Feature 1: The yield strength of the high-strength enameled steel is ≥700 MPa; Feature 2: The tensile strength of the high-strength enameled steel is ≥750MPa; Feature 3: The elongation after fracture of the high-strength enameled steel is ≥10%; Feature 4: The inclusion content in the high-strength enameled steel is 25 inclusions / mm 2 ~45 pieces / mm 2 ; Feature 5: The particle size of the inclusions in the high-strength enameled steel is 1.0 μm to 6.0 μm.

4. A method for preparing high-strength enameled steel according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: subjecting molten steel having the chemical composition of the high-strength enameled steel to a steelmaking process, a hot rolling process, a pickling process, a cold rolling process and an annealing process; The annealing temperature of the annealing process is 550°C to 650°C, and the holding time is 4h to 6h.

5. The preparation method according to claim 4, characterized in that The hot rolling process includes heating stage, rough rolling stage, finishing rolling stage and final rolling stage; Among them, the temperature in the heating stage is 1180℃~1220℃, and the holding time is 108min~132min; the starting rolling temperature in the rough rolling stage is 1050℃~1150℃; the starting rolling temperature in the finishing rolling stage is 950℃~1050℃; and the temperature in the final rolling stage is 850℃~950℃.

6. The preparation method according to claim 5, characterized in that After the final rolling stage, it also includes a cooling stage and a coiling stage; among them, the cooling stage includes a laminar cooling stage and an air cooling stage, the cooling rate of the laminar cooling is 15℃ / s~35℃ / s, and the final temperature of the laminar cooling is 600℃~700℃; the temperature of the coiling stage is 550℃~650℃.

7. The preparation method according to claim 4, characterized in that The pickling process includes at least one of the following features: Feature 6: The cleaning agent used for pickling is dilute hydrochloric acid solution; Feature 7: The pickling temperature is 60℃~70℃.

8. The preparation method according to claim 7, characterized in that The concentration of the dilute hydrochloric acid solution is 8% to 10%.

9. The preparation method according to claim 4, characterized in that The cold rolling reduction rate of the cold rolling process is 60%~70%.

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