A hot-rolled enamel steel with excellent anti-scaling properties and its preparation method

Abstract

A hot-rolled enamel steel with excellent anti-scaling properties and its preparation method are disclosed. This paper belongs to the field of steel materials. The composition by weight percentage is: C 0.03~0.08%, Si≤0.03%, Mn 0.6~1.0%, P≤0.012%, S 0.02~0.04%, Ti 0.02~0.04%, Y 0.005~0.012%, N≤0.003%, O≤0.0008%, with the remainder being Fe and unavoidable impurities. The preparation method involves the following steps: (1) smelting; (2) continuous casting; (3) hot rolling; (4) laminar flow cooling; (5) coiling. The hot-rolled enamel steel has a yield strength ≥380MPa, tensile strength ≥510MPa, and anti-scaling sensitivity TH value ≥30min / mm. 2 The TH value after two firings is ≥25 min / mm 2 The microstructure consists of ferrite and a small amount of cementite.

Description

Technical Field

[0001] This invention belongs to the field of steel materials, specifically relating to a hot-rolled enamel steel with excellent anti-scaling properties and its preparation method. Background Technology

[0002] In today's civilian and industrial sectors, enamel steel is widely used in metallurgy, construction, home furnishings, and chemicals, among other industries. By applying a ceramic enamel coating to the surface of enamel steel, enamel products possess both the high strength and ease of forming of enamel steel itself, and the acid, alkali, high-temperature, wear-resistant, and easy-to-clean properties of the ceramic enamel coating. With the rapid development of the national economy and the steel industry, enamel steel sheets are increasingly favored by the general public. Hot-rolled enamel steel is a type of enamel steel, mainly used in large-scale water treatment equipment, environmental protection facilities, and large storage tanks. When producing enamel products using hot-rolled enamel steel, it is necessary to cold-bend and fire twice at 800-900℃. However, after these two firings, hot-rolled enamel steel is highly susceptible to scale bursting, leading to the scrapping of enamel products. Therefore, improving the anti-scale bursting performance of hot-rolled enamel steel is imperative.

[0003] Scale bursting in enamel steel is caused by the presence of a large amount of diffusible hydrogen in the steel. During the enameling process, a large amount of diffusible hydrogen penetrates into the interior of the hot-rolled enamel steel. After enameling, this diffusible hydrogen diffuses to the interface between the steel and the enamel layer and accumulates. When the pressure generated by the hydrogen accumulation exceeds the bonding strength between the steel and the enamel layer, scale bursting occurs. Introducing a large amount of hydrogen traps into the enamel steel is the main method to avoid scale bursting. Currently, to improve the anti-scale bursting performance of hot-rolled enamel steel, the common technique is to add microalloying elements to form nano-sized second-phase precipitates as hydrogen traps. For example, patent CN 115369329A, "A Wide-width, Thin-gauge, High-Surface-Quality Hot-rolled Deep-drawing Enameled Steel," discloses a hot-rolled enamel steel containing 0.03–0.06% Ti, with a scale bursting sensitivity (TH value) ≥12 min / mm. 2 Patent No. CN 115537664A, "A hot-rolled pickled enamel steel with a yield strength ≥300MPa after enameling and its production method," discloses that the hot-rolled enamel steel contains 0.030–0.060% Ti and 0.001–0.040% V. Patent No. CN103589953A, "Hot-rolled thin-plate enamel steel with a yield strength of 245MPa and its manufacturing method," discloses that the hot-rolled enamel steel contains 0.04–0.10% Ti. Patent No. CN 115418572A, "A hot-rolled pickled enamel steel and its preparation method," discloses that the hot-rolled enamel steel contains 0.01–0.05% Nb and 0.03–0.10% Ti.

[0004] The aforementioned patents for hot-rolled enamel steel all utilize fine microalloyed second-phase precipitates as hydrogen traps to improve the anti-scaling performance of hot-rolled enamel steel. The smaller the size of the second-phase precipitates, the better the anti-scaling performance of the enamel steel. A problem with hot-rolled enamel steel containing microalloying elements is that the second-phase precipitates grow significantly during the two enameling processes, leading to a sharp decrease in the anti-scaling performance of the hot-rolled enamel steel after two enameling processes. This makes it prone to scaling after enameling, resulting in the scrapping of enamel products. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a hot-rolled enamel steel that exhibits excellent anti-scaling properties both before and after enameling. The microstructure of this hot-rolled enamel steel consists of ferrite and a small amount of cementite. Within the ferrite matrix, numerous spherical Mn-SOY inclusions, as well as YS, Y2O3, and Y2O2S inclusions, are distributed. Simultaneously, a large number of TiC precipitates with a size smaller than 10 nm are present. These inclusions and precipitates can act as hydrogen traps, significantly improving the anti-scaling properties of the hot-rolled enamel steel.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A hot-rolled enamel steel with excellent anti-scaling properties has the following chemical composition by weight percentage: C: 0.03-0.08%, Si≤0.03%, Mn: 0.6-1.0%, P≤0.012%, S: 0.020-0.040%, Ti: 0.02-0.04%, Y: 0.005%-0.012%, N≤0.0030%, O≤0.0008%, with the remainder being Fe and unavoidable impurities. The microstructure of this hot-rolled enamel steel consists of ferrite and a small amount of cementite. A large number of spherical Mn-SOY inclusions, as well as YS, Y2O3, and Y2O2S inclusions are distributed in the ferrite matrix. At the same time, a large number of TiC precipitates with a size of less than 10 nm are also present.

[0008] A method for preparing hot-rolled enamel steel with excellent anti-scaling properties includes the following steps:

[0009] (1) Smelting;

[0010] (2) Continuous casting;

[0011] (3) Hot rolling;

[0012] (4) Laminar flow cooling;

[0013] (5) Roll up.

[0014] in:

[0015] In step (1), the hot metal pretreatment, converter smelting, LF furnace refining and VD furnace refining are carried out in sequence.

[0016] In step (1), after the molten iron is pretreated, the S content is between 0.010 and 0.030%.

[0017] In step (1), the top and bottom blowing process is used during converter smelting, and the tapping temperature is greater than or equal to 1620℃.

[0018] In step (1), aluminum particles are used for precipitation deoxidation in the early stage of LF process refining, and aluminum particles and calcium carbide are used for diffusion deoxidation in the refining process. The alkalinity of refining slag is controlled between 6.0 and 6.4.

[0019] In step (1), the pure degassing time of the VD process should be greater than or equal to 8 minutes, followed by argon soft blowing, alloying, and the addition of rare earth Y with a purity of 99.9%.

[0020] In step (1), after the VD process is completed, the chemical composition of the molten steel meets the above-mentioned requirements for the chemical composition of hot-rolled enamel steel.

[0021] In step (2), the billet pulling speed during continuous casting is 1.2 to 1.5 m / min.

[0022] In step (3), the heating temperature during hot rolling is controlled at 1200-1250℃, the initial rolling temperature is 1130-1180℃, and the final rolling temperature is 870-890℃.

[0023] In step (3), the final thickness of the hot-rolled steel plate is 3 to 12 mm.

[0024] In step (4), during laminar flow cooling, the cooling medium is water, and the cooling rate is controlled at 5 to 20°C / s.

[0025] In step (5), the winding temperature is 660-680℃.

[0026] The role of each chemical element in this invention is mainly based on the following principles:

[0027] Carbon (C) is the most important strengthening element in steel, existing in hot-rolled enamel steel as interstitial solid solution, cementite, and TiC. Interstitial solid solution C, cementite, and TiC are beneficial for improving the strength of hot-rolled enamel steel, while nano-sized TiC is beneficial for improving resistance to spalling. Excessive C content is detrimental to the surface quality of hot-rolled enamel steel during enameling, while excessively low C content is detrimental to its strength. In this invention, the C content is controlled between 0.03% and 0.08%.

[0028] Si: Si has an adverse effect on the surface quality of hot-rolled enamel steel after enameling, so the Si content is controlled to be less than or equal to 0.03%.

[0029] Mn: Mn is a commonly used strengthening element in steel. In order to ensure that hot-rolled enamel steel has a certain strength, the Mn content is controlled between 0.6% and 1.0%.

[0030] P: P can segregate at grain boundaries, which can reduce the formability and toughness of hot-rolled enamel steel. In order to ensure the formability and toughness of hot-rolled enamel steel, the P content is controlled to be less than or equal to 0.012% in this invention.

[0031] S: S is generally an undesirable element in steel, and its content should be as low as possible. In most steels, the S content is controlled to be less than or equal to 0.010%. However, in this invention, S plays a role in the formation of a large number of Mn-SOY inclusions, as well as YS and Y2O2S inclusions. These inclusions can act as hydrogen traps, improving the anti-scaling performance of hot-rolled enamel steel. To form a large number of S-containing inclusions, the S content should be ≥0.020%. However, when the S content exceeds 0.040%, it can lead to inclusion agglomeration and a decrease in anti-scaling performance. Therefore, the S content is controlled between 0.020% and 0.040%.

[0032] Ti: The role of Ti is to combine with C to form TiC. TiC is an irreversible hydrogen trap in steel, which can improve the anti-scaling properties of hot-rolled enamel steel. Due to the high price of Ti, the Ti content is controlled at 0.02-0.04% to reduce production costs.

[0033] Y: The main function of Y is to modify inclusions, forming spherical Mn-SOY inclusions as well as YS, Y2O3, and Y2O2S inclusions. These inclusions can act as hydrogen traps, improving the anti-scaling properties of hot-rolled enamel steel. When the Y content is less than 0.005%, it does not modify inclusions and is detrimental to the formability of hot-rolled enamel steel. When the Y content is greater than 0.012%, inclusions will aggregate, resulting in larger sizes. Therefore, the Y content is controlled between 0.005% and 0.012%.

[0034] Nitrogen (N): Nitrogen is a harmful element in steel. It also reacts with Ti to form TiN, thereby reducing the amount of TiC in the steel. To obtain a higher TiC content, the N content should be controlled to be less than or equal to 0.0030%.

[0035] O: The main role of O in the hot-rolled enamel steel of this invention is to participate in the formation of O-containing inclusions. However, when the O content is high, the size of the inclusions is large, which is not conducive to improving the anti-scaling performance. In order to obtain small-sized O-containing inclusions, this invention controls the O content to less than or equal to 0.0008%.

[0036] It should be noted that obtaining excellent anti-scaling properties in hot-rolled enamel steel is related not only to composition design but also to its production process. Only through reasonable composition control combined with optimized production processes can the desired microstructure be obtained, thereby improving the anti-scaling properties of hot-rolled enamel steel.

[0037] The selection of the hot-rolled enamel steel production process described in this invention is explained as follows:

[0038] 1. Limiting the S content after hot iron pretreatment, limiting the tapping temperature during converter smelting, limiting the basicity of refining slag during LF refining, and limiting the pure degassing time in the VD process can ensure that the N and O content of hot-rolled enamel steel is controlled at the expected level, which is beneficial to improving the anti-scaling performance of hot-rolled enamel steel.

[0039] 2. Limiting the billet pulling rate during continuous casting can ensure that the surface of the continuously cast billet is free of defects.

[0040] 3. Controlling the heating temperature during hot rolling ensures that all titanium precipitates are completely dissolved, which is beneficial for increasing the TiC content in hot-rolled enamel steel.

[0041] 4. By setting the initial rolling temperature, final rolling temperature, and coiling temperature, TiC is made to exist in the form of interphase precipitation. The interphase precipitation of TiC can ensure that the TiC size is less than 10nm, which is beneficial to improving the anti-scaling performance of hot-rolled enamel steel.

[0042] 5. To ensure the continuity of hot rolling production, the cooling rate during laminar flow cooling should be greater than or equal to 5℃ / s. However, when the laminar flow cooling rate is greater than 20℃ / s, bainite will appear in the hot-rolled enamel steel of this invention, which will seriously impair the formability of the hot-rolled enamel steel. Therefore, the cooling rate during laminar flow cooling is controlled between 5 and 20℃ / s.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] Through reasonable composition design and optimized process control, a large number of spherical Mn-SOY inclusions, as well as YS, Y2O3, and Y2O2S inclusions, and a large number of TiC precipitates with a size of less than 10 nm can be obtained in the hot-rolled enamel steel matrix. These inclusions and TiC precipitates can act as effective hydrogen traps, capturing a large amount of diffusible hydrogen, thereby improving the anti-scaling performance of hot-rolled enamel steel. In addition, since the Mn-SOY inclusions and YS, Y2O3, and Y2O2S inclusions do not grow significantly during the enamel firing process (firing temperature of 800-900℃), that is, their hydrogen capture capacity does not decrease significantly, the hot-rolled enamel steel still has good anti-scaling performance even after two firings. Attached Figure Description

[0045] Figure 1Microstructure of the hot-rolled enamel steel prepared in Example 1 of this invention. Detailed Implementation

[0046] The chemical composition of Examples 1-8 is shown in Table 1.

[0047] Table 1. Chemical composition (mass fraction, %) of Examples 1-8

[0048]

[0049]

[0050] The microstructure of the hot-rolled enamel steel prepared according to the chemical composition of Example 1 in Table 1 and the production process of Example 1 in Table 2 is shown in the figure below. Figure 1 As shown.

[0051] The main production process parameters for Examples 1 to 8 are shown in Table 2. In addition, the S content after hot metal pretreatment in all examples was 0.020%, the tapping temperature was 1630℃, the basicity of the refining slag was 6.2, the billet pulling speed during continuous casting was 1.2 m / min, and the final thickness of the hot-rolled steel plate was 5 mm.

[0052] Table 2 Main production process parameters of Examples 1-8

[0053]

[0054] The mechanical properties and anti-explosion properties of Examples 1 to 8 are shown in Table 3.

[0055] Table 3 Mechanical properties and anti-explosion properties of Examples 1-8

[0056]

[0057] As shown in Table 3, the yield strength of Examples 1 to 8 is ≥380MPa, the tensile strength is ≥510MPa, and the TH value for anti-scaling sensitivity before enameling is ≥30.0min / mm. 2 The TH value after two firings is ≥25.0 min / mm. 2 It is evident that the hot-rolled enamel steel prepared by this invention exhibits excellent anti-scaling properties both before and after enameling, making it suitable for producing products with high anti-scaling performance requirements.

Claims

1. A hot-rolled enamel steel having excellent resistance to spangle, characterized in that, The chemical composition of the enamel steel is as follows in percentage by weight: C: 0.03-0.08%, Si≤0.03%, Mn: 0.6-1.0%, P≤0.012%, S: 0.020-0.040%, Ti: 0.02-0.04%, Y: 0.005%-0.012%, N≤0.0030%, O≤0.0008%, and the rest is Fe and inevitable impurities; The microstructure of the hot-rolled enamel steel is ferrite and a small amount of cementite, a large number of spherical Mn-S-O-Y inclusions, and YS, Y2O3, Y2O2S inclusions are distributed in the ferrite matrix, and a large number of TiC precipitates with a size less than or equal to 10 nm also exist.

2. A method of manufacturing the hot-rolled enamel steel having excellent spangle resistance according to claim 1, characterized in that, The method comprises the following steps: (1) smelting: sequentially carrying out hot metal pretreatment, converter smelting, LF furnace refining, and VD furnace refining; wherein during the converter smelting, a top and bottom combined blowing process is adopted, and the tapping temperature is greater than or equal to 1620℃; (2) continuous casting; (3) hot rolling: the heating temperature is controlled at 1200-1250℃ during hot rolling, the opening rolling temperature is 1130-1180℃, and the final rolling temperature is 870-890℃; (4) laminar cooling: the cooling medium is water, and the cooling rate is controlled at 5-20℃ / s; (5) coiling, to obtain the hot-rolled enamel steel with excellent anti-scaling performance.

3. A method of producing a hot-rolled enamel steel having excellent spangle resistance according to claim 2, characterized in that, In the step (1), after the hot metal pretreatment, the S content is between 0.010-0.030%; In the LF refining process, aluminum particles and calcium carbide are used for diffusion deoxidation, and the basicity of the refining slag is controlled at 6.0-6.4; The pure degassing time of the VD process should be greater than or equal to 8 min, and then argon soft blowing, alloying and the addition of rare earth Y with a purity of 99.9% are carried out; After the VD process, the chemical composition of the molten steel meets the chemical composition requirements of the hot-rolled enamel steel.

4. A method of producing a hot-rolled enamel steel having excellent scale spalling resistance according to claim 2, characterized in that, In the step (2), the casting speed during continuous casting is 1.2-1.5 m / min.

5. The method for preparing a hot-rolled enamel steel with excellent anti-scaling properties according to claim 2, characterized in that, In the step (3), the final thickness of the hot-rolled steel plate is 3-12 mm.

6. A method of producing a hot-rolled enamel steel having excellent spangle resistance according to claim 2, characterized in that, In the step (5), the coiling temperature is 660-680℃.

7. A method of producing a hot-rolled enamel steel having excellent spangle resistance according to claim 2, characterized in that, The hot-rolled enamel steel has yield strength ≥380MPa, tensile strength ≥510MPa, and anti-scaling sensitivity before enameling TH ≥30.0min / mm 2 , after twice enameling TH ≥25.0min / mm 2 .

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