An acid corrosion resistant pipeline steel plate and a method for manufacturing the same

Abstract

The application discloses an acid corrosion resistant pipeline steel plate and a preparation method thereof. The steel plate is prepared by adding chromium and vanadium to a low-carbon silicon-manganese base, and improving anisotropy of the steel through magnesium treatment, so as to reduce central segregation and looseness, and improve crack arrest performance and acid corrosion resistance of the steel plate while the steel plate has excellent mechanical properties. The acid corrosion resistant pipeline steel plate with different strength grades is produced by adjusting a finish rolling temperature, a final cooling temperature and a cooling rate through flexible rolling technology, so as to obtain different phase change organizations. Different cold speeds and final cooling temperatures are adopted to realize good regulation and control of the organizations. Through the flexible rolling technology, the continuous casting billets cast by the same molten steel can produce steel plates with different grades under the same component system by controlling rolling and cold speed. The technology makes the rolling and cooling process of the steel plate be deeply developed and utilized, meets the needs of users with different strength grades, and fully shows precise control of the rolling and cooling process on the performance.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically relating to an acid corrosion resistant pipeline steel plate and its preparation method. Background Technology

[0002] While the amount of oil and gas resources developed has increased year by year, the quality of oil and gas has shown a downward trend, with the concentration of Cl in oil and gas decreasing. - SO4 2- The increased content of acidic substances, particularly sulfides, coupled with the use of ultra-large diameter pipes and high-pressure transportation technologies, exacerbates fluid erosion corrosion and corrosion fatigue in pipeline steel. On the one hand, this worsens the pipeline's service environment, leading to more frequent oil and gas leaks; on the other hand, oil and gas leaks cause serious casualties and environmental pollution, resulting in significant economic losses. Therefore, the extraction of shale gas and oil in acidic oil fields places higher demands on the acid resistance of pipeline steel used in gathering and transportation pipelines, necessitating the rapid development of more economical, safe, and environmentally friendly acid-resistant pipeline steel.

[0003] In existing technologies, acid-corrosion resistant pipeline steel plates typically use high levels of C, Si, and Mn. The resulting acid-corrosion resistant pipeline steel plates have poor acid corrosion resistance and crack arrest performance. Furthermore, the controlled rolling and cooling technology used in the production process cannot effectively refine the microstructure of the core of the continuously cast billet, and the center segregation cannot be effectively eliminated. As a result, cracks easily appear in the core of the steel plate during the HIC resistance test, leading to poor acid corrosion resistance.

[0004] Chinese patent CN1715435A describes a method for manufacturing X80 pipeline steel with HIC resistance and its hot-rolled plate. The alloy formula uses C: 0.025-0.055%, Si: 0.19-0.30%, Mn: 1.70-1.95%, V: 0.045-0.065%, Ti: 0.015-0.04%, Ni: 0.25-0.35%, Mo: 0.20-0.40%, Cu: 0.20-0.40%, and Nb: 0.02-0.10%. This alloy formula uses a low-carbon, high-manganese ratio and adds precious alloys such as molybdenum, nickel, niobium, vanadium, and copper. This alloy design is beneficial for microstructure transformation and performance improvement, but it suffers from severe central segregation, high alloy price, and high production cost.

[0005] Chinese patent CN113388785B describes "An acid-resistant pipeline steel plate and its preparation method". The composition design is C: 0.02-0.04%, Si: 0.15-0.20%, Mn: 0.3-0.5%, P≤0.012%, S≤0.002%, Nb: 0.072-0.10%, Cr: 0.6-0.9%. It adopts low carbon and low manganese, with the addition of a large amount of niobium, resulting in high alloy cost. The high silicon content causes center segregation that cannot be effectively removed, which is detrimental to the resistance to HIC and SSC.

[0006] Chinese patent CN112226699B describes a method for producing acid-resistant pipeline steel. The chemical composition of the steel is C: 0.02-0.04%, Si: 0.15-0.35%, Mn: 1.10-1.25%, P≤0.010%, S≤0.0015%, Nb: 0.015-0.045%, Mo: 0.08-0.15%, Ni: 0.08-0.15%, Cu: 0.08-0.20%, Pcm=0.12-0.14%. It adopts an online quenching and tempering process to produce 8-26.4mm x 65MS pipeline steel. Due to the addition of an online heat treatment process, the production line is long, the production process is complex, and the production cost is high. Summary of the Invention

[0007] To address the shortcomings of existing technologies, namely the poor acid resistance and crack arrest performance of existing acid-resistant pipeline steel plates, and the inability to effectively refine the microstructure of the core of continuously cast slabs and effectively eliminate central segregation, this invention employs a low-carbon silicon-manganese alloy composition design with added chromium-vanadium alloy reinforcement, and a unique flexible rolling process. This significantly improves the crack arrest and acid corrosion resistance of the steel plate while maintaining excellent mechanical properties. It also solves the problems of existing steel plates easily developing cracks in the core of the steel plate and exhibiting poor acid corrosion resistance during HIC and SSCC tests.

[0008] To achieve the above-mentioned objective, the present invention provides an acid corrosion resistant pipeline steel plate comprising the following chemical composition by mass percentage: C: 0.01-0.03%, Si: 0.05-0.10%, Mn: 0.15-0.30%, P≤0.010%, S≤0.002%, Cr: 0.90-1.20%, V: 0.08-0.12%, Mg: 0.0010-0.0025%, H≤0.0002%, O≤0.0015%, with the balance being Fe and other unavoidable impurities.

[0009] [C] is the most effective element for improving strength, but high C content causes severe segregation, which is detrimental to welding performance. In addition, high C content easily produces banded structures, and harmful gases tend to accumulate at these banded structures, promoting the formation of HIC cracks and deteriorating H2S resistance. Therefore, the C content should be controlled between 0.01-0.03%.

[0010] Excessive Si content can easily form fir olivine on the surface of steel plates, which is difficult to remove during production and affects the surface quality of the steel plates. In addition, Si will reduce the low-temperature toughness of welded joints. Therefore, the Si content should be controlled between 0.05-0.10%.

[0011] Mn is the most common strengthening element. In steel, Mn easily combines with S to form MnS inclusions. H in H2S is very likely to agglomerate at MnS inclusions, forming cracks and causing the steel plate to crack. In addition, when the Mn content in steel exceeds 1.20%, it is easy to form central segregation in the continuously cast billet, leading to HIC cracking. Therefore, the Mn content is controlled at 0.15-0.30%.

[0012] [Cr] element can improve the hardenability of steel plates, promote phase transformation, reduce banded structure, and inhibit pearlite formation. In addition, in high-temperature H2S or H2S-H2 corrosive media, Cr-Mo steel is commonly used. In some severely corroded areas, Cr in the steel has the effect of inhibiting thiol adsorption and will generate stable spinel-type FeCr2S4 in the formed surface film, forming a passivation film in the steel, inhibiting the entry of harmful gases, and improving the acid corrosion resistance of the steel plate. Therefore, the Cr content is controlled at 0.90-1.20%.

[0013] [V]: Ferrite readily nucleates and grows using VN as a nucleus. Before the austenite-to-ferrite transformation, if there are many dispersed VN or V(C,N) particles of a certain size within the austenite grain boundaries or grains, the ferrite transformation is promoted. Solid-solution V also has a certain delaying effect on the pearlite transformation, effectively expanding the temperature range for proeutectoid ferrite transformation, thereby increasing the area fraction of ferrite transformation, promoting the precipitation of the passivation film, and improving acid corrosion resistance; therefore, the V content is controlled between 0.08% and 0.12%.

[0014] To precisely control the type and size of inclusions and ensure that the inclusion size is below 10 μm during the solidification of molten steel, magnesium treatment can be used. The principle is that easily deformable MnS inclusions are transformed into high-melting-point, difficult-to-deform spherical MgS inclusions or Al2O3-MgO-MnS composite inclusions, and clustered Al2O3 inclusions are transformed into small-particle Al2O3-MgO composite inclusions. This is beneficial to hydrogen-induced cracking (HIC) and stress corrosion cracking (SSCC) of submarine acid-resistant pipelines. Therefore, the Mg content in steel is controlled at 0.0010% to 0.0025%.

[0015] [P], [S]: When the sulfur content in steel is greater than 0.005%, the susceptibility to HIC (high brittle fracture) increases significantly with increasing sulfur content. When the sulfur content in steel is less than 0.002%, HIC decreases significantly. Since sulfur readily combines with manganese to form MnS inclusions, the presence of sulfide inclusions in steel increases the susceptibility to HIC. Phosphorus is an element that easily segregates in steel, and the hardenability of the segregated zone is approximately twice that of carbon. P segregation promotes HIC formation, and P inclusions can cause a decrease in the red brittleness and plasticity of steel, increase the hydrogen-enriching effect of the metal, and thus reduce the stability of steel in acidic and H2S media. Reducing the P content can significantly improve the steel's resistance to HIC; S ≤ 0.002% and P ≤ 0.010% should be controlled.

[0016] [H] and [O]: Hydrogen is the main cause of white spots and cracking. The higher the mass fraction of hydrogen, the greater the probability of HIC formation, the higher the corrosion rate, and the more significant the increase in average crack length. In addition, it is necessary to avoid moisture absorption of slag-forming agents, modifiers, alloying agents, protective slags, and covering agents added in subsequent processes. Excessive oxygen content in steel, along with increased oxide inclusions and macroscopic inclusions, is one of the root causes of HIC and SSCC in pipeline steel, harming various properties of the steel. To prevent oxide inclusions larger than 10 micrometers in diameter and reduce their number, the oxygen content in the steel is generally controlled to be less than 0.0015%. A common method for controlling oxygen is to add strong deoxidizers. Therefore, [O] should be controlled to ≤0.0015%, and [H] to ≤0.0002%.

[0017] The design employs a low-carbon silicon-manganese alloy with added chromium-vanadium alloy reinforcement. On one hand, the low-carbon composition inhibits the formation of pearlite banded structures, which creates a significant potential difference between pearlite and ferrite, making them prone to hydrogen-induced cracking. On the other hand, the low-manganese composition reduces the formation of MnS inclusions in the steel plate, weakens the control of harmful element S, reduces steelmaking difficulty, and improves the acid corrosion resistance and production efficiency of the steel plate. After magnesium treatment, easily deformable MnS inclusions are transformed into high-melting-point, difficult-to-deform MgS spherical inclusions or Al2O3-MgO-MnS composite inclusions, and clustered Al2O3 inclusions are transformed into small-particle Al2O3-MgO inclusions. Furthermore, the magnesium treatment process improves the anisotropy of the steel, reducing center segregation and porosity. The low-silicon composition improves the surface quality of the steel plate, reduces center segregation and porosity, and is beneficial for improving resistance to HIC and SSCC.

[0018] However, the reduction in carbon, silicon, and manganese content is detrimental to the mechanical strength of steel plates. The approach of strengthening with chromium-vanadium alloys addresses this by using precipitation, solid solution, and desorption of Cr and V to compensate for the strength reduction caused by the absence of C, Si, and Mn. Furthermore, V, as a strong carbide-forming element, readily forms VC precipitates. Acicular ferrite readily nucleates in the carbon-depleted regions of austenite, and the precipitation of VC in austenite inevitably leads to carbon depletion. Therefore, the addition of V promotes the formation of acicular ferrite. In addition, Cr increases hardenability in steel while forming a passivation film, inhibiting the entry of harmful gases and effectively suppressing H2S corrosion, thus improving the steel plate's resistance to HIC and SSCC corrosion. Cr and V elements can improve the hardenability of steel plates, enabling rapid phase transformation, reducing the formation of banded structures, central segregation, and porosity, and inhibiting pearlite transformation, thereby improving resistance to HIC and SSCC.

[0019] A method for preparing the above-mentioned acid corrosion resistant pipeline steel plate includes the following steps:

[0020] ① Weigh each component raw material according to the formula ratio, and then smelt it to obtain molten steel. The molten steel includes the following chemical composition by mass percentage: C: 0.01-0.03%, Si: 0.05-0.10%, Mn: 0.15-0.30%, P≤0.010%, S≤0.002%, Cr: 0.90-1.20%, V: 0.08-0.12%, Mg: 0.0010~0.0025%, H≤0.0002%, O≤0.0015%, with the balance being Fe and other unavoidable impurities.

[0021] ②The smelting process includes desulfurization of molten iron, converter smelting, ladle refining, RH vacuum refining, and magnesium treatment steps to obtain molten steel; the magnesium treatment step is to add magnesium cored wire at the end of the refining process.

[0022] ③ The molten steel is continuously cast into a continuous casting billet, and then a flexible rolling process is used to heat, rough roll, finish roll, laminar flow cooling and slow cooling treatment of the continuous casting billet to obtain acid-resistant pipeline steel plates of X65MS and X70MS grades.

[0023] In the above technical solution, the molten steel is further subjected to continuous casting to obtain a continuously cast billet, which is then heated in a heating furnace at a temperature of 1160-1170℃ for 120 minutes. The thickness of the continuously cast billet is 250mm. Before entering the roughing mill, high-pressure water descaling is performed. The continuously cast billet enters the roughing mill and adopts a "0+7" rolling method. The initial roughing temperature is 1130-1140℃, and the final roughing pass temperature is 960-970℃. To fully refine the austenitic structure of the steel plate and accumulate phase transformation, the reduction rate of the final roughing pass is 28-30%, and the total reduction rate of the roughing stages is 72-76%. The initial finishing temperature is 960-960℃, and the final finishing temperature is 830-840℃. The cooling rate in the cooling step is 14-16℃ / s, and the coiling temperature is 500-520℃. The coiled steel coils are subjected to a slow cooling process in the warehouse and can only be moved after 48 hours. By using a lower rolling temperature in the austenite recrystallization zone and a larger roughing deformation, the austenite microstructure of the steel plate is sufficiently refined, improving the crack arrest performance of the steel plate; in addition, the higher reduction rate in the last roughing pass further refines the core microstructure and reduces center segregation.

[0024] Furthermore, by controlling the target temperatures for the initial and final rolling stages, the cooling rate, and the coiling temperature, the pearlite transformation zone was avoided using a relatively high cooling rate and a low final rolling temperature, thus suppressing the formation of pearlite microstructure. Simultaneously, the higher cooling rate increased the phase transformation rate of the steel plate, inhibiting element diffusion and segregation, reducing banded microstructure, lowering hydrogen-induced cracking, and improving acid resistance. The resulting steel plate exhibited a quasi-polygonal ferrite microstructure, with a yield strength of 510–530 MPa, tensile strength of 590–610 MPa, elongation after fracture of 44–46%, and a yield strength ratio ≤0.87. At -20°C, the drop weight dip rate (DWTT) reached 100%, meeting the requirements for HIC and SSCC resistance without any cracking or fissures. This method significantly improved the acid resistance of the steel plate. X65MS acid-resistant pipeline steel was obtained using this method.

[0025] Furthermore, the molten steel is continuously cast to obtain a continuously cast billet, which is then heated in a furnace at a temperature of 1150-1160℃ for 110 minutes. The thickness of the billet is 250mm. Optionally, high-pressure water descaling is performed before entering the roughing mill. The continuously cast billet enters the roughing mill and is rolled using a "0+7" rolling method. The initial rolling temperature is 1120-1130℃, the target temperature for the final roughing pass is 950-960℃, the reduction rate for the final roughing pass is 26-28%, and the total reduction rate for all roughing passes is 70-74%. The initial rolling temperature for the finishing mill is 940-950℃, the final rolling temperature is 810-820℃, the cooling rate during the cooling process is 20-22℃ / s, the coiling temperature is 400-420℃, and the coiled steel coils are subjected to a slow cooling process in the warehouse and can only be moved after 72 hours. By using a lower rolling temperature in the austenite recrystallization zone and a larger roughing deformation, the austenite microstructure of the steel plate is sufficiently refined, improving the crack arrest performance of the steel plate; the higher reduction rate in the last roughing pass further refines the core microstructure, reducing center segregation. Furthermore, by controlling the initial rolling temperature, final rolling temperature, cooling rate, and final cooling temperature of the finishing mill, the pearlite phase transformation zone was avoided using a relatively high cooling rate and a low final rolling temperature, thus suppressing the formation of pearlite microstructure. Simultaneously, the higher cooling rate increased the phase transformation rate of the steel plate, inhibiting element diffusion and segregation, reducing banded microstructure, lowering hydrogen-induced cracking, and improving acid corrosion resistance. The resulting steel plate exhibited a acicular ferrite microstructure, a yield strength of 550-570 MPa, a tensile strength of 640-660 MPa, an elongation after fracture of 40-42%, and a yield strength ratio ≤0.88. At -20℃, with a drop weight DWTT of 100%, it met the requirements for HIC and SSCC resistance without any cracking or fissures, achieving a good balance between toughness, yield strength ratio, strength, crack arrest, and acid resistance. This method was used to obtain X70MS acid corrosion resistant pipeline steel.

[0026] The aforementioned method for preparing acid-corrosion-resistant pipeline steel plates utilizes flexible rolling technology. By adjusting the finishing rolling temperature, final cooling temperature, and cooling rate, different phase transformation structures are obtained, resulting in the production of acid-corrosion-resistant pipeline steel plates with varying strengths. Lower finishing rolling temperatures lead to higher dislocation densities in the austenitic deformation structure, making it easier for acicular ferrite to nucleate at dislocations. Therefore, lower final rolling temperatures are favorable for the formation of acicular ferrite. Thus, when producing higher-strength steel plates, the final rolling temperature is controlled at 810-820℃; when producing lower-strength steel plates, to improve production efficiency, the final rolling temperature is controlled at 830-840℃. Based on the phase transformation characteristics, different cooling rates and final rolling temperatures are set to achieve effective control over the phase transformation structure.

[0027] Meanwhile, the above-mentioned method for preparing acid corrosion resistant pipeline steel plates adopts flexible rolling production technology. Under the same composition system, steel plates with different properties can be produced through different rolling and cooling processes. The steelmaking composition is simple, and steel plates with different strength grades can be produced from the continuous casting billets obtained from the same furnace of molten steel. In addition, this technology has enabled in-depth development and utilization of the rolling and cooling processes of steel plates, fully demonstrating the precise control of performance by the rolling and cooling process.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention provides an acid-corrosion-resistant pipeline steel plate and its preparation method. The plate employs a low-carbon silicon-manganese alloy composition design with added chromium-vanadium alloy reinforcement, resulting in excellent mechanical properties while significantly improving its crack arrest and acid corrosion resistance. The simplified composition design and flexible rolling process enable a single composition design to produce acid-corrosion-resistant pipeline steel of varying strength grades. Attached Figure Description

[0030] Figure 1 The image shows the microstructure of the X65MS acid corrosion resistant pipeline steel in Example 1 (F+ with a small amount of acicular F+ carbon-rich phase);

[0031] Figure 2 The inclusion morphology (B0.5 D0.5) of the X65MS acid corrosion resistant pipeline steel in Example 1;

[0032] Figure 3 The image shows the microstructure of the X70MS acid corrosion resistant pipeline steel in Example 2 (F+ with a small amount of acicular F+ carbon-rich phase);

[0033] Figure 4 The inclusion morphology (B0.5 D0.5) of the X70MS acid corrosion resistant pipeline steel in Example 2;

[0034] Figure 5 Micrographs of the acid-resistant pipeline steel in Comparative Example 1 (F+B+M);

[0035] Figure 6 The inclusion morphology in the acid-resistant pipeline steel of Comparative Example 1 is shown (A1.0 D0.5).

[0036] Figure 7 Micrographs of the acid-resistant pipeline steel in Comparative Example 2 (acicular B+F);

[0037] Figure 8 The inclusion morphology of acid-resistant pipeline steel in Comparative Example 2 is shown in B1.0 and D1.0. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, but this does not limit the invention in any way. To avoid redundancy, unless otherwise specified, the raw materials used in the following embodiments are all commercially available products, and the methods used are all conventional methods unless otherwise specified. The mechanical properties, crack arrest properties, and acid resistance properties of the acid-resistant pipeline steel plates prepared in the embodiments and comparative examples were tested. Specifically, yield strength, tensile strength, elongation (elongation after fracture), and yield strength ratio were tested according to ASTM A370 test method; DWTT (drop hammer tear test) was tested according to APIPR 5L36 test method; and HIC test was tested according to NACETM0284 test method.

[0039] Example 1

[0040] This embodiment provides an acid corrosion resistant pipeline steel plate and its preparation method, including the following steps:

[0041] ① Weigh each component raw material according to the formula ratio, and then carry out smelting. The smelting steps include desulfurization of molten iron, converter smelting, ladle refining, RH vacuum refining, and magnesium treatment to obtain molten steel. The chemical composition of the molten steel, in mass percentage, is as follows: C: 0.01%, Si: 0.05%, Mn: 0.16%, P: 0.007%, S: 0.001%, Cr: 0.94%, V: 0.085%, Mg: 0.0012%, H: 0.00015%, O: 0.0009%, with the remainder being Fe and other unavoidable impurities.

[0042] ② Molten steel is continuously cast into 250mm thick continuous casting billets. The billets are then heated, rough rolled, finish rolled, cooled, and slowly cooled to room temperature to obtain X65MS acid corrosion resistant pipeline steel plates. The heating temperature is 1170℃, the heating time is 120min, and the "0+7" rolling method is adopted. The rough rolling start temperature is 1140℃, the rough rolling last pass temperature is 970℃, the rough rolling last pass reduction is 28%, and the total rough rolling reduction is 72%. The finish rolling start temperature is 960℃, and the finish rolling temperature is 830℃. Water cooling is used in the cooling step, the cooling rate is 15℃ / s, the coiling temperature is 500℃, and the coiled steel coils are slowly cooled in the warehouse for 48 hours before they can be moved.

[0043] The performance test results of the steel plate obtained through this step are shown in Tables 1 and 2: It meets the following requirements: yield strength 510–530 MPa, tensile strength 590–610 MPa, elongation after fracture 44–46%, yield strength ratio ≤0.87, drop weight DWTT = 100% at -20℃, and meets the requirements for HIC and SSC resistance without any cracks or fissures. This improves the acid corrosion resistance of the steel plate. X65MS acid corrosion resistant pipeline steel plate was obtained using this method.

[0044] Example 2

[0045] This embodiment provides an acid-resistant pipeline steel plate and its preparation method, including the following steps:

[0046] ① Weigh each component raw material according to the formula ratio, and then carry out smelting. The smelting steps include desulfurization of molten iron, converter smelting, ladle refining, RH vacuum refining, and Mg treatment to obtain molten steel. The molten steel has the following mass percentage composition: C: 0.03%, Si: 0.09%, Mn: 0.28%, P: 0.009%, S: 0.002%, Cr: 1.19%, V: 0.12%, Mg: 0.0023%, H: 0.0001%, O: 0.0012%, with the remainder being Fe and other unavoidable impurities.

[0047] ② Molten steel is continuously cast into 250mm thick continuous casting billets. The billets are then heated, rough rolled, finish rolled, cooled, and slowly cooled to room temperature to obtain X70MS acid corrosion resistant pipeline steel plates. The heating temperature is 1155℃, the heating time is 110min, and the "0+7" rolling method is adopted. The rough rolling start temperature is 1128℃, the rough rolling last pass temperature is 955℃, the rough rolling last pass reduction is 27%, and the total rough rolling reduction is 73%. The finish rolling start temperature is 950℃, and the finish rolling temperature is 819℃. Water cooling is used in the cooling step, the cooling rate is 22℃ / s, the coiling temperature is 415℃, and the coiled steel coils are slowly cooled in the warehouse for 72 hours before they can be moved.

[0048] The performance test results of the steel plate obtained through this step are shown in Tables 1 and 2: The prepared steel plate has a acicular ferrite structure, a yield strength of 550-570 MPa, a tensile strength of 640-660 MPa, an elongation after fracture of 40-42%, a yield strength ratio ≤0.88, and at -20℃, a drop weight DWTT of 100%, meeting the requirements for HIC and SSCC resistance without any cracks or fissures. This method achieves a good balance of toughness, yield strength ratio, strength, crack arrest, and acid corrosion resistance. X70MS acid corrosion resistant pipeline steel plate was obtained using this method.

[0049] Comparative Example 1

[0050] Comparative Example 1 provides an acid-corrosion-resistant pipeline steel plate and its preparation method. The only difference between Comparative Example 1 and Example 1 is that the chemical composition of the molten steel in step ①, by mass percentage, is: C: 0.05%, Si: 0.25%, Mn: 1.0%, P: 0.012%, S: 0.015%, Nb: 0.045%, Cr: 0.20%, Ti: 0.025%, Mo: 0.30%, Al: 0.03%, with the remainder being Fe and other unavoidable impurities. The performance test results of the steel plate obtained in Comparative Example 1 are shown in Tables 1 and 2.

[0051] Comparative Example 2

[0052] Comparative Example 2 provides an acid-corrosion-resistant pipeline steel plate and its preparation method. The only difference between Comparative Example 2 and Example 2 is that the chemical composition of the molten steel in step ①, by mass percentage, is: C: 0.08%, Si: 0.22%, Mn: 1.50%, P: 0.010%, S: 0.012%, Nb: 0.075%, Cr: 0.50%, Ti: 0.035%, Mo: 0.45%, Al: 0.03%, with the remainder being Fe and other unavoidable impurities. The performance test results of the steel plate obtained in Comparative Example 2 are shown in Tables 1 and 2.

[0053] Table 1. Test Results of Acid Corrosion Resistant Pipeline Steel Plates

[0054]

[0055] Table 2 Results of HIC Crack Measurement and Analysis of Acid Corrosion Resistant Pipeline Steel Plates

[0056]

[0057]

[0058] Analysis of the data in Tables 1 and 2 shows that the acid-corrosion resistant pipeline steel plates of different strength grades, X65MS and X70MS, produced by the technical composition and flexible rolling process design of this invention not only possess good plasticity but also a low yield strength ratio, as well as good crack arrest and acid corrosion resistance. In the comparative examples, the different composition design resulted in poorer acid corrosion resistance of the steel plates.

[0059] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A steel plate for acid corrosion resistant pipelines, characterized in that, The acid corrosion resistant pipeline steel plate is composed of the following chemical composition by mass percentage: C: 0.01%–0.03%, Si: 0.05%–0.09%, Mn: 0.16%–0.28%, P≤0.010%, S≤0.002%, Cr: 0.94%–1.19%, V: 0.085%–0.12%, Mg: 0.0010%–0.0025%, H≤0.00015%, O≤0.0015%, with the balance being Fe and other unavoidable impurities; The method for preparing the acid corrosion resistant pipeline steel plate includes the following steps: ① Weigh each component raw material according to the formula ratio, and then smelt it. The smelting process includes desulfurization of molten iron, converter smelting, ladle refining, RH vacuum refining and magnesium treatment steps to obtain molten steel. The molten steel is composed of the following chemical composition by mass percentage: C: 0.01%~0.03%, Si: 0.05%~0.09%, Mn: 0.16%~0.28%, P≤0.010%, S≤0.002%, Cr: 0.94%~1.19%, V: 0.085%~0.12%, Mg: 0.0010%~0.0025%, H≤0.00015%, O≤0.0015%, with the balance being Fe and other unavoidable impurities. ②The molten steel is continuously cast into a continuous casting billet, and the billet is then subjected to heating, rough rolling, fine rolling, laminar flow cooling and slow cooling treatment in sequence using a flexible rolling process to obtain an acid corrosion resistant pipeline steel plate of X65MS grade. The continuous casting billet is heated at 1160℃~1170℃ for 120 minutes, and its thickness is 250mm. The roughing rolling start temperature is 1130℃~1140℃, and the final roughing rolling temperature is 960℃~970℃. The final roughing rolling reduction rate is 28%~30%, and the total reduction rate of the roughing rolling stages is 72%~76%. The finishing rolling start temperature is 950℃~960℃, and the finishing rolling temperature is 830℃~840℃. The cooling rate is 14-16℃ / s, the coiling temperature is 500℃-520℃, and the coiled steel is kept away from the furnace door after coiling and slowly cooled for 48 hours. The resulting steel plate has a quasi-polygonal ferritic structure, a yield strength of 510-530MPa, a tensile strength of 590-610MPa, an elongation after fracture of 44%-46%, and a yield strength ratio ≤0.

87. At -20℃, the drop weight DWTT = 100% yields X65MS acid corrosion resistant pipeline steel.

2. A type of acid-corrosion resistant pipeline steel plate, characterized in that, The acid corrosion resistant pipeline steel plate is composed of the following chemical composition by mass percentage: C: 0.01%–0.03%, Si: 0.05%–0.09%, Mn: 0.16%–0.28%, P≤0.010%, S≤0.002%, Cr: 0.94%–1.19%, V: 0.085%–0.12%, Mg: 0.0010%–0.0025%, H≤0.00015%, O≤0.0015%, with the balance being Fe and other unavoidable impurities; The method for preparing the acid corrosion resistant pipeline steel plate includes the following steps: ① Weigh each component raw material according to the formula ratio, and then smelt it. The smelting process includes desulfurization of molten iron, converter smelting, ladle refining, RH vacuum refining and magnesium treatment steps to obtain molten steel. The molten steel is composed of the following chemical composition by mass percentage: C: 0.01%~0.03%, Si: 0.05%~0.09%, Mn: 0.16%~0.28%, P≤0.010%, S≤0.002%, Cr: 0.94%~1.19%, V: 0.085%~0.12%, Mg: 0.0010%~0.0025%, H≤0.00015%, O≤0.0015%, with the balance being Fe and other unavoidable impurities. ②The molten steel is continuously cast into a continuous casting billet, and the billet is then subjected to heating, rough rolling, fine rolling, laminar flow cooling and slow cooling treatment in sequence using a flexible rolling process to obtain X70MS grade acid corrosion resistant pipeline steel plate. The continuous casting billet is heated at 1150℃~1160℃ for 110 minutes, and the billet thickness is 250mm; the roughing rolling start temperature is 1120℃~1130℃, the final roughing rolling temperature is 950℃~960℃, the final roughing rolling reduction rate is 26%~28%, and the total reduction rate of the roughing rolling stages is 70%~74%; the finishing rolling start temperature is 940℃~950℃, and the finishing rolling temperature is 810℃~820℃. The cooling rate is 20-22℃ / s, the coiling temperature is 400℃-420℃, and the coiled steel is kept away from the furnace door and slowly cooled for 72 hours. The resulting steel plate has a acicular ferrite structure, a yield strength of 550-570MPa, a tensile strength of 640-660MPa, an elongation after fracture of 40%-42%, and a yield ratio ≤0.

88. At -20℃, the drop weight DWTT = 100% is used to obtain X70MS acid corrosion resistant pipeline steel.

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