Normalized high-strength medium-carbon acid-resistant container steel and preparation method thereof

Abstract

The invention relates to normalized high-strength medium-carbon acid-resistant container steel and a preparation method, and belongs to the technical field of steel manufacturing. The acid-resistant container steel comprises the following chemical components in percentage by mass: less than or equal to 0.20% of C, less than or equal to 0.55% of Si, 1.20-1.70% of Mn, less than or equal to 0.025% of P, less than or equal to 0.010% of S, less than or equal to 0.050% of Nb, less than or equal to 0.050% of V, less than or equal to 0.030% of Ti, more than or equal to 0.020% of Al, less than or equal to 0.0060% of Ca and a matrix element Fe. A proper amount of Nb (niobium), V (vanadium) and Ti (titanium) alloy elements are added to replace a traditional Cu (copper) and Ni (nickel) alloy combination, and the alloy component cost is greatly reduced while high strength and acid resistance are guaranteed.

Description

Technical Field

[0001] The present application relates to the technical field of steel manufacturing, and in particular to a normalized high-strength medium-carbon acid-resistant container steel and a preparation method thereof. Background Art

[0002] In accordance with the requirements of green, environmentally friendly and clean energy, the petrochemical and coal chemical industries have developed rapidly. Sulfur-containing oil and gas have increasingly higher requirements for the hydrogen-induced cracking resistance of container steels used in wet H2S environments, and the corrosion and hydrogen-induced cracking accidents of pressure vessels and pipelines caused by wet H2S environments are increasing. Therefore, the demand for medium and thick plate pressure vessel steel with certain resistance to hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SSC) has increased significantly. How to simply and effectively improve the acid resistance of acid-resistant container steel is a technical problem that technicians in this field have always needed to solve.

[0003] At present, many steel mills are studying the production process of high-strength acid-resistant container steel, but the production and manufacturing method for high-strength normalized medium-carbon acid-resistant container steel plate has not been reported. The products in the published patent documents are even less used in actual engineering. CN201510014303-A normalized acid-resistant pressure vessel steel plate and its manufacturing method. The transverse tensile strength of this patent can only be guaranteed to be greater than 415MPa, and the transverse yield strength can only be guaranteed to be greater than 220MPa. And CN201810494189-A production method for extra-thick acid-resistant container steel plate, this patent adopts the design of adding Cu+Ni combination, and the blank used is die casting, the yield rate is low, and the production cost is high. CN114737027A-345MPa-grade container steel with excellent hydrogen-induced cracking resistance and its preparation method, this patent is for low-carbon steel grades. Summary of the invention

[0004] The present application provides a normalized high-strength medium-carbon acid-resistant container steel and a preparation method to solve the following technical problem: how to reduce production costs while ensuring the strength and acid resistance of the normalized medium-carbon acid-resistant container steel.

[0005] In the first aspect, an embodiment of the present application provides a normalized high-strength medium-carbon acid-resistant container steel. The chemical composition of the acid-resistant container steel, measured by mass fraction, includes: C≤0.20%, Si≤0.55%, Mn: 1.20%~1.70%, P≤0.025%, S≤0.010%, Nb≤0.050%, V≤0.050%, Ti≤0.030%, Al≥0.020%, Ca≤0.0060%, and matrix element Fe.

[0006] Optionally, by mass fraction, the chemical composition of the acid-resistant container steel includes: C: 0.15% - 0.19%, Si: 0.25% - 0.35%, Mn: 1.20% - 1.35%, P ≤ 0.010%, S ≤ 0.0020%, Nb: 0.025% - 0.035%, V: 0.030% - 0.040%, Ti: 0.010% - 0.030%, Al: 0.020% - 0.040%, Ca: 0.0025% - 0.0060%, H ≤ 0.00020%, O ≤ 0.0040%, and the matrix element Fe.

[0007] Optionally, the acid-resistant container steel satisfies at least one of the following properties:

[0008] Yield strength ≥ 325 MPa;

[0009] Tensile strength ≥ 500 Mpa;

[0010] Elongation ≥ 30%;

[0011] -30°C V-notch transverse impact energy ≥ 150 J;

[0012] The anti-HIC performance satisfies: CLR ≤ 5%, CSR ≤ 0.5%, CTR ≤ 1.5%;

[0013] The anti-SSCC test satisfies: there are no cracks and surface cracks after 10 times magnification in the tensile stress area of the sample loaded with 0.9 AYs.

[0014] Optionally, the thickness of the acid-resistant container steel is 15 mm - 60 mm.

[0015] In a second aspect, the present application provides a method for preparing the acid-resistant container steel described in the first aspect, the method comprising:

[0016] Obtaining molten steel with the above chemical composition;

[0017] Continuous casting the molten steel to obtain a continuous casting billet;

[0018] Successively heating, rolling, cooling, and normalizing the continuous casting billet to obtain the finished acid-resistant container steel.

[0019] Optionally, the whole process of continuous casting adopts protective casting, and the casting temperature is 1525°C - 1538°C.

[0020] Optionally, the superheat of the molten steel for continuous casting is 15°C - 25°C, the drawing speed for continuous casting is 0.75 m / min - 1.20 m / min, and the liquid level fluctuation in the mold for continuous casting is within ±3 mm.

[0021] Optionally, the thickness of the continuous casting billet is 200 mm to 400 mm.

[0022] Optionally, the heating includes: a preheating section, a first heating section, a second heating section, and a soaking section; where:

[0023] The temperature of the preheating section is <850 °C;

[0024] The temperature of the first heating section is 950 °C to 1150 °C;

[0025] The temperature of the second heating section is 1180 °C to 1220 °C;

[0026] The temperature of the soaking section is 1180 °C to 1220 °C;

[0027] The total heating time is ≥3.5 h.

[0028] Optionally, the rolling includes: first-stage rolling and second-stage rolling; where:

[0029] The temperature of the first-stage rolling is 980 °C to 1130 °C, the reduction rate per pass of the first-stage rolling is 10% to 28%, and the cumulative reduction rate of the first-stage rolling is ≥50%;

[0030] The starting rolling temperature of the second-stage rolling is ≤950 °C, the finishing rolling temperature of the second-stage rolling is 810 °C to 860 °C, and the cumulative reduction rate of the second-stage rolling is >50%.

[0031] Optionally, the final cooling temperature of the cooling is 610 °C to 670 °C, and the recrystallization temperature of the cooling is 630 °C to 690 °C.

[0032] Optionally, the normalizing treatment includes:

[0033] Heating the cooled continuous casting billet to 890 °C to 910 °C;

[0034] If the thickness of the acid-resistant container steel is 15 mm to 40 mm, air-cool the heated continuous casting billet to room temperature;

[0035] If the thickness of the acid-resistant container steel is 40 mm to 60 mm, water-cool the heated continuous casting billet to 650 °C to 680 °C and then air-cool it to room temperature.

[0036] Optionally, the continuous casting of the molten steel to obtain a continuous casting billet includes:

[0037] Continuous casting the molten steel to obtain a continuous casting billet, and subjecting the continuous casting billet to heat preservation and slow cooling, and the time of the heat preservation and slow cooling is 48 h to 60 h.

[0038] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0039] The embodiments of the present application provide a normalized high-strength medium-carbon acid-resistant container steel. In terms of mass fraction, the chemical composition of the acid-resistant container steel includes: C≤0.20%, Si≤0.55%, Mn: 1.20% - 1.70%, P≤0.025%, S≤0.010%, Nb≤0.050%, V≤0.050%, Ti≤0.030%, Al≥0.020%, Ca≤0.0060%, and the matrix element Fe. By adding appropriate amounts of Nb (niobium), V (vanadium), and Ti (titanium) alloying elements to replace the traditional Cu (copper) + Ni (nickel) alloy combination, while ensuring high strength and acid resistance, the alloy composition cost is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings herein are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present application and, together with the specification, are used to explain the principles of the present application.

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0042] Figure 1 It is a schematic flow chart of a preparation method for a normalized high-strength medium-carbon acid-resistant container steel provided by the embodiments of the present application;

[0043] Figure 2 It is the normalized microstructure diagram provided by Embodiment 1 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present application belong to the scope of protection of the present application.

[0045] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and individual values within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0046] In this text, terms including "comprising" and the like mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, or B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "a plurality" means two or more; "at least one kind", "at least one of the following (items)" or similar expressions refer to any combination of these items, including any combination of single (item) or plural items; for example, "at least one of a, b, or c", or "at least one of a, b, and c" can both mean: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple respectively. The "parts representation method" such as parts by weight, parts by mass, etc. represents the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0047] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this text can be obtained through market purchase or can be prepared by existing methods.

[0048] In a first aspect, an embodiment of the present application provides a normalized high-strength medium-carbon acid-resistant container steel. In terms of mass fraction, the chemical composition of the acid-resistant container steel includes: C ≤ 0.20%, Si ≤ 0.55%, Mn: 1.20% - 1.70%, P ≤ 0.025%, S ≤ 0.010%, Nb ≤ 0.050%, V ≤ 0.050%, Ti ≤ 0.030%, Al ≥ 0.020%, Ca ≤ 0.0060%, and the matrix element Fe.

[0049] In some embodiments, in terms of mass fraction, the chemical composition of the acid-resistant container steel includes: C: 0.15% - 0.19%, Si: 0.25% - 0.35%, Mn: 1.20% - 1.35%, P ≤ 0.010%, S ≤ 0.0020%, Nb: 0.025% - 0.035%, V: 0.030% - 0.040%, Ti: 0.010% - 0.030%, Al: 0.020% - 0.040%, Ca: 0.0025% - 0.0060%, H ≤ 0.00020%, O ≤ 0.0040%, and the matrix element Fe.

[0050] The positive effect of limiting the mass fraction of C to 0.15% - 0.19%: If the mass fraction of C is higher than 0.20%, segregation will occur at the center of the steel plate thickness, and the performance of resisting HIC and SSC will decline. Moreover, since this steel is medium-carbon acid-resistant steel and there is a lower limit for the mass fraction of C, the mass fraction of C is limited to the range of 0.15% - 0.19%.

[0051] The positive effect of limiting the mass fraction of Mn to 1.20% - 1.35%: Mn is a basic alloying element of high-strength low-alloy steel. Adding Mn to the steel can play a role in solid solution strengthening without reducing toughness and lower the brittle transition temperature of the steel. A high Mn / C ratio is beneficial to improving the yield strength and impact toughness. However, since Mn is as prone to form center segregation as C and P in the steel, resulting in different mechanical properties of the steel and a decline in the HIC resistance performance, the mass fraction of Mn should not be too high while ensuring strength, and it is limited to the range of 1.20% - 1.35%.

[0052] The positive effect of limiting P ≤ 0.010% and S ≤ 0.0020%: S is prone to combine with Mn to form MnS inclusions, and the existence of sulfide inclusions increases the sensitivity of HIC; P is an element prone to segregation in the steel, and the hardenability of the segregation zone is about twice that of carbon. The segregation of P promotes the formation of HIC, and the inclusions formed by P can cause red brittleness and a decrease in plasticity of the steel, increasing the hydrogen uptake effect of the metal, thereby reducing the stability of the steel in acidic media and H2S media. Therefore, the mass fractions of P and S in the steel should be minimized as much as possible. In the embodiment of the present application, P ≤ 0.010% and S ≤ 0.0020% are limited.

[0053] The positive effects of limiting the mass fraction of Nb to 0.025% - 0.035%, the mass fraction of V to 0.030% - 0.040%, and the mass fraction of Ti to 0.010% - 0.030%: The alloying elements Nb, V, and Ti can effectively prevent the growth of austenite grains, refine their grains, and inhibit the formation and growth of pearlite structures. This can not only increase the strength of the steel but also significantly improve the H2S corrosion resistance of the steel.

[0054] The higher the mass fraction of the gas element H, the greater the probability of HIC generation, the higher the corrosion rate, and the more significant the increase in the average crack length. If the mass fraction of the gas element O is too high, it will increase oxide inclusions and macroscopic inclusions, seriously affecting the cleanliness of the steel. Oxide inclusions in the steel are one of the sources of HIC and SSC in acid-resistant steel. Therefore, H ≤ 0.00020% and O ≤ 0.0040% are controlled.

[0055] Fe is the matrix element, and the specific content / content range of Fe can be obtained through the upper and lower limit formulas of the components, that is:

[0056] The sum of the percentage contents of each component in a composition should be equal to 100%. The content ranges of several components should meet the following conditions: the upper limit value of a certain component + the lower limit values of other components ≤ 100; the lower limit value of a certain component + the upper limit values of other components ≥ 100.

[0057] In some embodiments, the acid-resistant container steel satisfies at least one of the following properties:

[0058] Yield strength ≥ 325 MPa;

[0059] The yield strength is the maximum stress that the steel plate can withstand before plastic deformation. A higher yield strength means that the steel plate is more difficult to undergo plastic deformation when stressed, thus improving its load-bearing capacity and structural stability.

[0060] Tensile strength ≥ 500 Mpa;

[0061] The tensile strength is the maximum stress that the steel plate can withstand before fracture. A higher tensile strength indicates that the steel plate has stronger fracture resistance and can maintain integrity under greater external forces.

[0062] Elongation ≥ 30%;

[0063] Elongation is an important indicator to measure the plastic deformation ability of the steel plate. A higher elongation means that the steel plate can undergo greater plastic deformation without cracking when stressed, thus improving its toughness and formability.

[0064] -30 °C V-notch transverse impact energy ≥ 150 J;

[0065] This index measures the impact toughness of the steel plate under low-temperature conditions. A higher impact energy indicates that the steel plate can still maintain good toughness at low temperatures and is not prone to brittle fracture.

[0066] The anti-HIC performance meets the requirements: CLR ≤ 5%, CSR ≤ 0.5%, CTR ≤ 1.5%;

[0067] Hydrogen-induced cracking (HIC) is a phenomenon in which cracks are formed inside metal materials due to the penetration and aggregation of hydrogen atoms in an environment containing corrosive media such as sulfides. The anti-HIC performance refers to the ability of the material to resist hydrogen-induced cracking in such an environment. CLR (Crack Length Ratio), CSR (Crack Sensitivity Ratio), and CTR (Crack Thickness Ratio) are key indicators for measuring the anti-hydrogen-induced cracking performance of steel plates. Lower CLR, CSR, and CTR values indicate that the steel plate has better anti-cracking ability in a hydrogen-containing environment.

[0068] The anti-SSCC test meets the requirements: there are no cracks and surface cracks after magnifying 10 times the tensile stress area of the sample loaded with 0.9AYs.

[0069] The anti-SSCC test, namely the anti-Sulfide Stress Corrosion Cracking test, is an important method for evaluating the ability of materials to resist stress corrosion cracking in an acidic environment containing hydrogen sulfide. This test is used to evaluate the ability of the steel plate to resist stress corrosion cracking in a sulfide environment. By applying a tensile stress close to the yield strength and observing the crack situation of the sample after magnification, the anti-SSCC performance of the steel plate can be judged. The absence of cracks and surface cracks indicates that the steel plate has good anti-SSCC ability.

[0070] In some embodiments, the thickness of the acid-resistant container steel is 15 mm to 60 mm.

[0071] The thickness range of the finished acid-resistant container steel determines its bearing capacity and processing performance in actual applications.

[0072] Figure 1 It is a schematic flow chart of a preparation method of a normalized high-strength medium-carbon acid-resistant container steel provided by an embodiment of the present application.

[0073] Please refer to Figure 1 , Second, the present application provides a preparation method of the acid-resistant container steel described in the first aspect, and the method includes:

[0074] S1. Obtain molten steel with the above chemical composition;

[0075] S2. Continuously cast the molten steel to obtain a continuous casting billet;

[0076] In some embodiments, the continuous casting process uses protective casting, and the casting temperature is 1525°C to 1538°C.

[0077] The protective casting technology is adopted throughout the continuous casting process to prevent the molten steel from reacting with oxygen, nitrogen, etc. in the air during the casting process, thereby avoiding defects such as pores and inclusions in the billet and improving the purity and quality of the billet. The selection of the casting temperature is crucial for the quality of the billet. If the casting temperature is higher than 1538°C, it may cause defects inside the billet, such as shrinkage cavities and porosity; while if the casting temperature is lower than 1525°C, it may increase the casting difficulty and the risk of slag adhesion. Exemplarily, the casting temperature can be 1525°C, 1527°C, 1529°C, 1531°C, 1533°C, 1535°C, 1537°C, 1538°C, etc.

[0078] In the embodiments of the present application, an ultra-low carbon covering flux is selected for the tundish, and a peritectic steel protective slag is selected for the mold. Using an ultra-low carbon covering flux can further reduce the carbon content in the molten steel, prevent the molten steel from being reoxidized, and maintain the cleanliness and temperature stability of the molten steel, which is particularly important for the production of high-quality, low-alloy steel. Selecting a peritectic steel protective slag helps to form a stable slag film in the mold, prevent the molten steel from directly contacting the mold wall, thereby reducing the risks of adhesion and breakout. At the same time, the protective slag can also play a role in lubrication and heat transfer, which is beneficial to the smooth withdrawal of the billet and the improvement of its quality.

[0079] In some embodiments, the superheat of the molten steel for continuous casting is 15°C to 25°C, the billet withdrawal rate for continuous casting is 0.75 m / min to 1.20 m / min, and the liquid level fluctuation in the mold for continuous casting is within ±3 mm.

[0080] The superheat of the molten steel refers to the degree to which the molten steel temperature is higher than its liquidus temperature. A superheat of 15°C to 25°C for the molten steel helps the uniform flow and filling of the molten steel, reducing defects during the casting process. However, if the superheat of the molten steel is higher than 25°C, it may cause the internal structure of the billet to be coarse, affecting its mechanical properties. Exemplarily, the superheat of the molten steel can be 15°C, 17°C, 19°C, 21°C, 23°C, 25°C, etc.

[0081] A billet withdrawal rate of 0.75 m / min to 1.20 m / min can ensure the smooth withdrawal of the billet and the stability of its quality. Exemplarily, the billet withdrawal rate for continuous casting can be 0.75 m / min, 0.85 m / min, 0.95 m / min, 1.05 m / min, 1.15 m / min, 1.20 m / min, etc.

[0082] The stable control of the liquid level in the mold can ensure the uniform cooling and solidification of the billet, thereby improving its quality. Excessive liquid level fluctuation may cause defects inside the billet, such as slag inclusions and cracks.

[0083] In some embodiments, the thickness of the continuous casting billet is 200 mm to 400 mm.

[0084] This thickness range is suitable for the production of steel of various specifications. In addition, billets with a thickness of 200 mm to 400 mm can provide better mechanical properties and processing stability in subsequent processing. Exemplarily, the thickness of the continuous casting billet can be 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, etc.

[0085] S3. Heat, roll, cool, and normalize the continuous casting billet in sequence to obtain the finished acid-resistant container steel.

[0086] In some embodiments, the heating includes: a preheating section, a first heating section, a second heating section, and a soaking section; where:

[0087] The temperature of the preheating section is <850 °C;

[0088] The temperature of the first heating section is 950 °C to 1150 °C;

[0089] The temperature of the second heating section is 1180 °C to 1220 °C;

[0090] The temperature of the soaking section is 1180 °C to 1220 °C;

[0091] The total heating time ≥ 3.5 h.

[0092] Heating is directly related to the heating uniformity of the steel billet, the change of internal structure, and the subsequent processing performance. In the embodiments of the present application, the heating process is divided into a preheating section, a first heating section, a second heating section, and a soaking section, and each stage has a different temperature. This heating system helps to homogenize the internal structure of the steel billet and stably control the temperature.

[0093] The main purpose of the preheating section is to initially heat the billet, gradually raise its temperature, and reduce the thermal stress during the subsequent heating process. The preheating temperature should be lower than 850 °C to avoid premature oxidation and decarburization of the billet surface. Exemplarily, the temperature of the preheating section can be 815 °C, 820 °C, 825 °C, 830 °C, 835 °C, 840 °C, etc. The main purpose of the first heating section is to continue raising the temperature of the billet and initiate changes in its internal structure. In this stage, the carbides in the billet start to dissolve, preparing for subsequent soaking and rolling. Exemplarily, the temperature of the first heating section can be 950 °C, 990 °C, 1030 °C, 1070 °C, 1110 °C, 1150 °C, etc. The second heating section is a further heating based on the first heating section to raise the billet to a higher temperature. In this stage, the carbides in the billet are almost completely dissolved to form austenite structure. Meanwhile, a temperature of 1180 °C - 1220 °C in the second heating section also helps release the internal stress of the billet and homogenize the structure. Exemplarily, the temperature of the second heating section can be 1180 °C, 1190 °C, 1200 °C, 1210 °C, 1220 °C, etc. The soaking section is the heat preservation process after heating in the second heating section, aiming to make the temperature and structure inside the billet uniform. A soaking temperature of 1180 °C - 1220 °C can ensure that the billet has an appropriate structure and temperature state before rolling. Exemplarily, the temperature of the soaking section can be 1180 °C, 1190 °C, 1200 °C, 1210 °C, 1220 °C, etc. The total heating time refers to the total time required from when the billet enters the heating furnace until it reaches the soaking temperature and the heat preservation ends. A total heating time ≥ 3.5 h can ensure the full homogenization of the internal structure of the billet and stable control of the temperature, thereby improving the quality of the steel. Exemplarily, the total heating time can be 3.5 h, 4 h, 4.5 h, 5 h, etc.

[0094] In some embodiments, the rolling includes: first-stage rolling and second-stage rolling; wherein:

[0095] The temperature of the first-stage rolling is 980 °C - 1130 °C, the reduction ratio per pass of the first-stage rolling is 10% - 28%, and the cumulative reduction ratio of the first-stage rolling ≥ 50%;

[0096] The starting rolling temperature of the second-stage rolling ≤ 950 °C, the finishing rolling temperature of the second-stage rolling is 810 °C - 860 °C, and the cumulative reduction ratio of the second-stage rolling > 50%.

[0097] Rolling obtains steel plates with the desired shape and size by plastically deforming the heated billets. This application adopts the controlled rolling process, and by precisely controlling parameters such as temperature and reduction ratio during rolling, good microstructure and properties of the steel plates can be obtained. In the first-stage rolling, the billets are plastically deformed at high temperatures. The rolling temperature of 980°C to 1130°C and the pass reduction ratio of 10% to 28% contribute to the homogenization and refinement of the internal structure of the billets, while reducing the energy consumption during rolling and the defects inside the steel plates. Exemplarily, the temperature of the first-stage rolling can be 980°C, 1010°C, 1040°C, 1070°C, 1100°C, 1130°C, etc.; the pass reduction ratio of the first-stage rolling can be 10%, 13%, 16%, 19%, 22%, 25%, 28%, etc. The cumulative reduction ratio ≥ 50% can ensure that the steel plates obtain good shape and size during subsequent rolling. Exemplarily, the cumulative reduction ratio of the first-stage rolling can be 50%, 51%, 52%, 53%, 54%, 55%, etc. In the second-stage rolling, the temperature of the steel plates gradually decreases, but sufficient plasticity still needs to be maintained for plastic deformation. By controlling the starting rolling temperature ≤ 950°C and the finishing rolling temperature of 810°C to 860°C, the internal structure of the steel plates can be further refined, and the strength and toughness of the steel plates can be improved. Exemplarily, the starting rolling temperature of the second-stage rolling can be 875°C, 885°C, 895°C, 905°C, 915°C, 925°C, 935°C, 945°C, 950°C, etc.; the finishing rolling temperature of the second-stage rolling can be 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, etc. At the same time, the cumulative reduction ratio > 50% to ensure that the steel plates obtain the desired shape and size after rolling. Exemplarily, the cumulative reduction ratio of the second-stage rolling can be 52%, 54%, 56%, 58%, 60%, etc.

[0098] In some embodiments, the final cooling temperature of the cooling is 610°C to 670°C, and the recrystallization temperature of the cooling is 630°C to 690°C.

[0099] In the embodiments of the present application, ACC control cooling is adopted. ACC control cooling, that is, Accelerated Cooling Control. The final cooling temperature refers to the final temperature reached by the steel plate during the ACC control cooling process. A final cooling temperature of 610°C to 670°C helps to obtain ideal steel plate microstructure and properties. A final cooling temperature higher than 670°C may result in coarse grains, affecting the strength and toughness of the steel plate; while a final cooling temperature lower than 610°C may increase the brittleness of the steel plate. Exemplarily, the final cooling temperature of the cooling can be 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, etc. The recrystallization temperature refers to the temperature rise phenomenon generated by the steel plate during the cooling process due to internal heat conduction and phase change reactions. A recrystallization temperature of 630°C to 690°C helps to ensure that the steel plate has uniform microstructure and good properties after cooling. Exemplarily, the recrystallization temperature of the cooling can be 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, etc.

[0100] In some embodiments, the normalizing treatment includes:

[0101] Heating the cooled continuous casting billet to 890°C to 910°C;

[0102] If the thickness of the acid-resistant container steel is 15 mm to 40 mm, air-cool the heated continuous casting billet to room temperature;

[0103] If the thickness of the acid-resistant container steel is 40 mm to 60 mm, water-cool the heated continuous casting billet to 650°C to 680°C and then air-cool it to room temperature.

[0104] In the embodiments of the present application, the temperature of the normalizing treatment is in the range of 890°C to 910°C to ensure the consistency and stability of the heat treatment effect. The cooling method is an important factor affecting the microstructure and properties of the steel plate. For thinner steel plates (15 mm to 40 mm), due to their smaller heat capacity, air-cooling can be used to slowly cool them to room temperature, thereby obtaining a relatively uniform microstructure. For thicker steel plates (40 mm to 60 mm), due to their larger heat capacity, weak water-cooling is required to quickly reduce their temperature to the final cooling temperature range to avoid overheating and coarsening of the internal microstructure. Subsequently, air-cooling is used to cool them to room temperature to ensure the stability and uniformity of the internal microstructure of the steel plate.

[0105] In some embodiments, the step of continuously casting the molten steel to obtain a continuous casting billet includes:

[0106] Continuously cast the molten steel to obtain a continuous casting billet, and perform heat preservation and slow cooling on the continuous casting billet. The time for heat preservation and slow cooling is 48 h to 60 h.

[0107] The purpose of heat preservation and slow cooling is to control the cooling rate of the continuous casting billet, reduce internal stress and tissue defects, obtain a more uniform and stable structure, and improve the performance of subsequent processing and the finished product quality. In the embodiments of the present application, the continuous casting billet can be sent to a heat preservation pit for heat preservation and slow cooling. The heat preservation pit is a facility with heat preservation function, and the internal temperature is relatively stable, which can provide a suitable slow cooling environment for the continuous casting billet. The heat preservation and slow cooling time is the time that the continuous casting billet stays in the heat preservation pit, and it is also one of the key factors affecting the structure and performance of the billet. In the embodiments of the present application, the slow cooling time is strictly controlled within the range of 48h to 60h, which helps to homogenize the internal structure of the billet and release the stress. Exemplarily, the heat preservation and slow cooling time can be 48h, 50h, 52h, 54h, 56h, 58h, 60h, etc.

[0108] The product prepared by the preparation method of the normalized high-strength medium-carbon acid-resistant container steel is the above-mentioned normalized high-strength medium-carbon acid-resistant container steel. Since the preparation method of the normalized high-strength medium-carbon acid-resistant container steel adopts some or all of the technical solutions of the embodiments of the normalized high-strength medium-carbon acid-resistant container steel, it has at least all the beneficial effects brought by the technical solutions of the embodiments of the normalized high-strength medium-carbon acid-resistant container steel, which will not be elaborated one by one here.

[0109] The following further elaborates the present application in combination with specific embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually measured according to national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out according to general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0110] Example 1

[0111] The whole process of continuous casting adopts protective casting, with a superheat of 15 - 25°C. After the continuous casting billet is taken offline, it is stacked and slowly cooled, and the stacking and cooling time is 50 hours. The continuous casting billet is heated to 1200°C, with a total heating time of 280 min. The first-stage rolling start temperature is 1120°C; the second-stage rolling start temperature is 895°C, and the final rolling temperature is 820°C. After rolling, it is water-cooled, and the recrystallization temperature is 670°C. The thickness of the steel plate is 25 mm; a normalizing heat treatment method is adopted. The steel plate is loaded into a heating furnace, kept at 900°C for 30 min, and then air-cooled.

[0112] Example 2

[0113] The whole process of continuous casting adopts protective casting, with a superheat of 15 - 25°C. After the continuous casting billet is taken offline, it is stacked and slowly cooled, and the stacking and cooling time is 48 hours. The continuous casting billet is heated to 1220°C, with a total heating time of 335 min. The first-stage rolling start temperature is 1124°C; the second-stage rolling start temperature is 900°C, and the final rolling temperature is 810°C. After rolling, it is water-cooled, and the recrystallization temperature is 650°C. The thickness of the steel plate is 25 mm; a normalizing heat treatment method is adopted. The steel plate is loaded into a heating furnace, kept at 900°C for 40 min, and then air-cooled.

[0114] Example 3

[0115] During the whole continuous casting process, protective casting is adopted, with a superheat of 15 - 25°C. After the continuous casting billet is taken off the production line, it is stacked and slowly cooled for 52 hours. The continuous casting billet is heated to 1220°C with a total heating time of 300 min. The starting rolling temperature in the first stage is 1128°C; the starting rolling temperature in the second stage is 875°C, and the final rolling temperature is 815°C. After rolling, it is water-cooled, and the return red temperature is 630°C. The thickness of the steel plate is 50 mm. The normalizing heat treatment method is adopted. The steel plate is loaded into the heating furnace, held at 900°C for 80 min, and then sprayed with weak water cooling.

[0116] The preparation method of Comparative Example 1 is the same as that of Example 1, the preparation method of Comparative Example 2 is the same as that of Example 2, and the preparation method of the comparative example is the same as that of Example 3.

[0117] The chemical compositions of the molten steel in Examples 1 - 3 and Comparative Examples 1 - 3 are shown in Table 1.

[0118] Table 1 Chemical compositions of the molten steel in examples and comparative examples (wt%)

[0119]

[0120] The acid-resistant container steel obtained from the examples and comparative examples was subjected to performance tests, and the results are shown in Table 2.

[0121] Table 2 Performance list of examples and comparative examples

[0122]

[0123] As can be seen from Tables 1 - 2, the normalized medium-carbon acid-resistant container steel provided by this application has a yield strength ≥ 325 MPa, a tensile strength ≥ 500 Mpa, an elongation ≥ 30%, a - 30°C V-notch transverse impact energy ≥ 150 J, and the anti-HIC performance meets: CLR ≤ 5%, CSR ≤ 0.5%, CTR ≤ 1.5%; in the anti-sulfide stress corrosion cracking test, there are no cracks and no surface cracks after 10 - fold magnification of the tensile stress area of the sample loaded with 0.9 AYs. When the chemical composition of the comparative example is not within the range provided by this application, the anti-hydrogen-induced cracking performance deteriorates.

[0124] Appendix Figure 2 Detailed description:

[0125] Figure 2 This is the microstructure diagram of the normalized state provided by Example 1 of this application, as Figure 2 shown, with uniform structure and fine grains.

[0126] One or more technical solutions in the embodiments of the present invention at least further have the following technical effects or advantages:

[0127] While ensuring high strength and acid resistance, the embodiments of the present invention greatly reduce the alloy composition cost, and also reduce the quality control of the continuous casting billet and the rolling difficulty. The normalizing heat treatment mode is used to replace other heat treatment processes, with simple process, low production cost, and batch production can be realized.

[0128] The products of the embodiments of the present invention have the characteristics of high purity, uniform composition, excellent mechanical properties, high strength, excellent acid resistance, and low production cost.

[0129] The above are only specific embodiments of the present application, which enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A normalized high-strength medium-carbon acid-resistant container steel, wherein the chemical composition of the acid-resistant container steel comprises, by mass fraction: C≤0.20%, Si≤0.55%, Mn: 1.20%~1.70%, P≤0.025%, S≤0.010%, Nb≤0.050%, V≤0.050%, Ti≤0.030%, Al≥0.020%, Ca≤0.0060%, and matrix element Fe.

2. The acid-resistant container steel according to claim 1, characterized in that: Measured in mass fraction, the chemical composition of the acid-resistant container steel includes: C: 0.15%~0.19%, Si: 0.25%~0.35%, Mn: 1.20%~1.35%, P≤0.010%, S≤0.0020%, Nb: 0.025%~0.035%, V: 0.030%~0.040%, Ti: 0.010%~0.030%, Al: 0.020%~0.040%, Ca: 0.0025%~0.0060%, H≤0.00020%, O≤0.0040%, and matrix element Fe.

3. The acid-resistant container steel according to claim 1, characterized in that: The acid-resistant container steel meets at least one of the following properties: Yield strength ≥325MPa; Tensile strength ≥500Mpa; Elongation ≥30%; -30℃ V-type transverse impact energy ≥150J; Anti-HIC performance meets: CLR ≤ 5%, CSR ≤ 0.5%, CTR ≤ 1.5%; The anti-SSCC test meets the following requirements: the tensile stress area of ​​the sample loaded with 0.9AYs has no cracks or surface cracks after being magnified 10 times.

4. The acid-resistant container steel according to claim 1, characterized in that: The thickness of the acid-resistant container steel is 15 mm to 60 mm.

5. A method for preparing the acid-resistant container steel according to any one of claims 1 to 4, the method comprising: Obtaining molten steel having the chemical composition; Continuously casting the molten steel to obtain a continuously cast billet; The continuous casting billet is sequentially heated, rolled, cooled and normalized to obtain a finished acid-resistant container steel.

6. The method according to claim 5, characterized in that The continuous casting adopts protective casting throughout the whole process, and the casting temperature is 1525° C. to 1538° C.; and / or, The superheat of the molten steel during continuous casting is 15°C to 25°C, the casting rate during continuous casting is 0.75m / min to 1.20m / min, and the liquid level fluctuation of the continuous casting mold is within ±3mm; and / or, The thickness of the continuous casting billet is 200 mm to 400 mm.

7. The method according to claim 5, characterized in that The heating includes: a preheating section, a first heating section, a second heating section and a soaking section; wherein: The temperature of the preheating section is less than 850°C; and / or, The temperature of the first heating stage is 950°C to 1150°C; and / or, The temperature of the second heating stage is 1180°C to 1220°C; and / or, The temperature of the soaking section is 1180°C to 1220°C; and / or, The total heating time is ≥3.5h.

8. The method according to claim 5, characterized in that The rolling process includes: first-stage rolling and second-stage rolling; wherein: The temperature of the first stage rolling is 980°C to 1130°C, the pass reduction rate of the first stage rolling is 10% to 28%, and the cumulative reduction rate of the first stage rolling is ≥50%; and / or, The starting rolling temperature of the second stage rolling is ≤950°C, the finishing rolling temperature of the second stage rolling is 810°C to 860°C, and the cumulative reduction ratio of the second stage rolling is >50%.

9. The method according to claim 5, characterized in that The final cooling temperature of the cooling is 610°C to 670°C, and the red-returning temperature of the cooling is 630°C to 690°C; and / or, The normalizing treatment comprises: The cooled continuous casting billet is heated to 890° C. to 910° C.; If the thickness of the acid-resistant container steel is 15 mm to 40 mm, air-cooling the heated continuous casting billet to room temperature; If the thickness of the acid-resistant container steel is 40 mm to 60 mm, the heated continuous casting billet is water-cooled to 650° C. to 680° C. and then air-cooled to room temperature.

10. The method according to claim 5, characterized in that The method of continuously casting the molten steel to obtain a continuously cast billet comprises: The molten steel is continuously cast to obtain a continuously cast billet, and the continuously cast billet is kept warm and slowly cooled, wherein the time for the kept warm and slowly cooled is 48 hours to 60 hours.

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