High-strength corrosion-resistant steel for gas pipeline and preparation method of high-strength corrosion-resistant steel

Abstract

The invention discloses high-strength corrosion-resistant steel for a gas pipeline and a preparation method of the high-strength corrosion-resistant steel. The method comprises: providing molten iron; the molten iron is smelted in a converter, steel ladle argon blowing is conducted after the molten iron is smelted in the converter, the terminal control temperature of an argon station is higher than 1535 DEG C, and molten steel in a first state is obtained; the molten steel in the first state is subjected to LF refining, specifically, the temperature of the molten steel in the first state entering an IF refining furnace is made to be higher than 1520 DEG C, the refining time is 40-45 minutes, alloy components are added in the refining process, the components of the molten steel are finely adjusted to the target content, and LF refined molten steel is obtained; the LF refined molten steel is subjected to continuous casting treatment in a soft reduction mode, and a continuous casting blank is obtained; the continuous casting blank is heated and rolled, and rolled steel is obtained; and the rolled steel is cooled, and the high-strength corrosion-resisting steel for the gas pipeline is obtained. The preparation method can be used for preparing the high-strength corrosion-resistant steel for the gas pipeline under a blast furnace gas working condition medium, and the problems of high operation cost and short service life of the gas pipeline are solved.

Description

Technical Field

[0001] The present application belongs to the field of metallurgical technology, and in particular relates to a high-strength corrosion-resistant steel for a gas pipeline and a preparation method thereof. Background Art

[0002] The biggest threat to gas pipelines during service is pipeline corrosion, which can lead to pipeline failure, frequent production accidents and great safety hazards. Gas pipeline corrosion is mainly caused by low-temperature dew-point acidic environment corrosion. The main components of gas are CO, CO 2 , H 2 S. SO 3 Acidic gases such as CaCl2, FeCl2, MgCl 2 These acidic gases and chlorine-containing inorganic salts dissolve into the gas condensate after the waste heat boiler cools down. The condensate containing a large amount of ions is transported to the rear-end pipeline along with the airflow over a long distance, causing the pipeline to be thinned or perforated due to corrosion, resulting in siltation or gas leakage, which is prone to accidents.

[0003] At present, the industry has adopted a variety of measures for protection, and there is still a lot of room for optimization in terms of cost-effectiveness and application effect. The main measures are: pH value control method, spraying alkaline solution in the gas pipeline, its advantage is that the pH value can be dynamically and accurately adjusted according to the actual production, and the pipeline corrosion can be well controlled. Its disadvantage is that the investment and operation and maintenance costs of the alkali system and the alkali solution delivery system are relatively large. Pipeline coating protection, its advantage is that it can effectively protect the pipeline from corrosion in the short term, but as the coating ages, there is still a risk of failure. Quality control is carried out on the raw material side, and low-sulfur and low-nitrogen iron ore powder and high-quality coal fuel are purchased. Its characteristics are that the concentration of sulfur and chlorine is reduced in the early stage of the production plan. With the continuous operation of production, the condensate containing sulfur and chlorine components is enriched in the local area of ​​the pipeline, and there is still the problem of pipeline corrosion. At the same time, the cost of raw materials entering the furnace is increased, and it is not conducive to the stability of the furnace condition. The margin compensation method increases the thickness of the steel used for the gas pipeline, and the safety thickness required during the service life is calculated according to the corrosion rate of the gas pipeline. Its disadvantage is that the investment cost of the steel pipe is relatively high.

[0004] The above measures can extend the life of gas pipelines to a certain extent, but none of them can solve the problem in the most economical and safest way. Therefore, there is an urgent need to provide a new solution that does not require increasing investment and operation and maintenance costs, while extending the service life and operation safety of gas pipelines. Summary of the invention

[0005] The embodiment of the present application provides a method for preparing high-strength corrosion-resistant steel for gas pipelines, which can be used to prepare high-strength corrosion-resistant steel for gas pipelines. The corrosion-resistant steel is suitable for blast furnace gas working conditions and solves the problems of high operating costs and short life of gas pipelines.

[0006] In a first aspect, the present application provides a method for preparing high-strength corrosion-resistant steel for gas pipelines, comprising: providing molten iron; subjecting the molten iron to converter smelting, blowing argon from a ladle after the molten iron is smelted in the converter, and controlling the temperature of the argon station terminal to be greater than 1535°C to obtain molten steel in a first state; subjecting the molten steel in the first state to LF refining, comprising subjecting the temperature of the molten steel in the first state entering the LF refining furnace to greater than 1520°C, and the refining time to 40 minutes to 45 minutes, adding alloy components during the refining process, and fine-tuning the composition of the molten steel to a target content to obtain LF refined molten steel at a temperature of 1585°C to 1620°C; subjecting the LF refined molten steel to continuous casting treatment in a light reduction mode to obtain a continuously cast ingot; heating and rolling the continuously cast ingot to obtain a rolled steel; cooling the rolled steel to control the structure of the rolled steel to obtain high-strength corrosion-resistant steel for gas pipelines.

[0007] According to an embodiment of the present application, the LF refined steel liquid is continuously cast in a light reduction mode, including: continuously casting the LF refined steel liquid at a continuous casting speed of 1.4m / min to 1.6m / min and a reduction of 5mm to 10mm to obtain a continuously cast slab; and stack cooling the continuously cast slab to a target temperature to obtain a continuously cast ingot.

[0008] According to an embodiment of the present application, the alloy components include silicon, manganese, titanium, niobium, chromium, nickel, copper, molybdenum, and antimony.

[0009] According to an embodiment of the present application, stack cooling the continuously cast slab to a target temperature includes: placing the continuously cast slab in a hot slab environment above 500°C for slow cooling treatment, until the temperature of the continuously cast slab drops below 300°C.

[0010] According to an embodiment of the present application, heating and rolling the continuous casting ingot includes: heating the continuous casting ingot to 1200℃~1250℃, requiring a heating time of 150min~250min, and a solution time of >30min, to obtain a continuous casting ingot in a first state; rolling the continuous casting ingot in the first state includes: performing rough rolling on the continuous casting ingot in the first state, with a rough rolling start temperature of 1150℃~1200℃ and a rough rolling finish temperature of 1050℃~950℃ to obtain rough rolled steel; performing finish rolling on the rough rolled steel, with a finish rolling start temperature of 1020℃~920℃ and a finish rolling finish temperature of 800℃~720℃ to obtain rolled steel.

[0011] According to the embodiments of the present application, the rolled steel is subjected to a cooling treatment to control the structure of the rolled steel, including: laminar cooling of the rolled steel at a cooling rate of 30°C / s to 40°C / s, so that the temperature of the finished rolled steel is finally cooled to 550°C to 580°C for coiling, thereby obtaining high-strength corrosion-resistant steel for gas pipelines.

[0012] According to the embodiments of the present application, the high-strength corrosion-resistant steel for gas pipelines includes, by mass percentage, carbon, 0.05% to 0.08%; silicon, 0.20% to 0.40%; manganese, 0.30% to 0.50%; sulfur, 0.02% to 0.035%; phosphorus ≤0.02%, titanium, 0.07% to 0.10%; niobium, 0.020%N0.025%; chromium, 0.50% to 0.90%; nickel, 0.20% to 0.30%, copper, 0.25% to 0.5%; molybdenum, 0.3% to 0.6%; acid-soluble aluminum, 0.02% to 0.05%; antimony, 0.10% to 0.20%; nitrogen ≤0.00060%; oxygen ≤0.0015%, hydrogen ≤0.00015%, and the rest are Fe and impurity elements remaining in the smelting process.

[0013] According to the embodiments of the present application, in the matrix structure of the high-strength corrosion-resistant steel for gas pipelines, the proportion of bainite structure is 80% to 90%, the proportion of ferrite is 10% to 20%, and the second phase particles are dispersed in the matrix structure.

[0014] According to an embodiment of the present application, among the second phase particles, taking the total volume of the second phase particles as 100%, the second phase particles with a particle size of 10nm to 100nm account for more than 60%, the second phase particles smaller than 10nm account for 10%, and the volume of the second phase particles larger than 100nm to 400nm accounts for ≤30%.

[0015] According to the embodiment of the present application, the yield strength of the high-strength corrosion-resistant steel for gas pipelines is 690MPa-750MPa, the tensile strength is 850MPa-950MPa, the yield strength ratio is ≤0.85, and the -40℃ KV 2 Type impact energy>27J, corrosion rate≤0.05mm / a.

[0016] The preparation method of high-strength corrosion-resistant steel for gas pipelines in the embodiment of the present application aims at the environment of complex mineral media such as acidic gas and chlorine-containing inorganic salts in the gas medium, and by adding four corrosion-resistant elements of chromium, nickel, copper and molybdenum as alloy components, the electrode potential of high-strength corrosion-resistant steel for gas pipelines is improved, thereby improving the corrosion resistance of steel; in particular, according to the actual situation that the condensate in the gas has dew point corrosion, antimony and sulfur elements are added to improve the corrosion resistance of the steel matrix in the sensitive temperature range. In order to improve the strength of the steel, the titanium content in the steel reaches 0.07% to 0.10%, ensuring that the bainite matrix of the steel has sufficient second phase precipitation to produce strengthening, ensuring that the yield strength of high-strength corrosion-resistant steel for gas pipelines reaches more than 690MPa, and the tensile strength reaches more than 800MPa. Under the same load, 30% of steel can be saved, the comprehensive investment can be reduced by more than 20%, and the service life of the gas pipeline can be extended from 8 years of Q355B material to 20 years, which can be the same age as blast furnace equipment, and has the characteristics of economic green and low carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solution of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0018] Figure 1 It is a schematic flow chart of a method for preparing high-strength corrosion-resistant steel for gas pipelines provided in an embodiment of the present application.

[0019] Figure 2 is the metallographic structure diagram of the high-strength corrosion-resistant steel for gas pipelines provided in Example 1 of the present application, Figure 2 In the example, the unit length is 20 μm.

[0020] Figure 3 is the metallographic structure diagram of the high-strength corrosion-resistant steel for gas pipelines provided in Example 2 of the present application, Figure 3 The unit length is 20 μm.

[0021] Figure 4 is a particle size and volume distribution histogram of the second phase particles precipitated from the high-strength corrosion-resistant steel for gas pipelines provided in Example 1 of the present application, Figure 4 In the figure, the abscissa D (nm) represents the particle size of the second phase particles, and the ordinate represents the volume percentage of the second phase particles in the corresponding particle size range. DETAILED DESCRIPTION

[0022] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0023] It should be noted that, in this article, relational terms such as first and second, etc. 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. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0024] As mentioned in the background technology section, common steel used for oil and gas pipelines cannot meet the requirements for coal gas pipelines. Therefore, it is of great significance to develop an economical steel material suitable for coal gas medium service conditions.

[0025] In order to solve the problems of the prior art, the present application provides a method for preparing high-strength corrosion-resistant steel for gas pipelines, which can produce steel suitable for gas medium service conditions and has good economic efficiency. The following first introduces the method for preparing high-strength corrosion-resistant steel for gas pipelines provided in the present application.

[0026] Figure 1 The figure shows a schematic flow chart of a method for preparing high-strength corrosion-resistant steel for gas pipelines provided in one embodiment of the present application. Figure 1 As shown, the preparation method of high-strength corrosion-resistant steel for gas pipelines comprises:

[0027] S1, provide molten iron;

[0028] S2, smelting the molten iron in a converter, blowing argon into a ladle after the molten iron is smelted in a converter, and the terminal temperature of the argon station is controlled to be greater than 1535° C., thereby obtaining molten steel in a first state;

[0029] S3, performing LF refining on the molten steel in the first state, including making the temperature of the molten steel in the first state entering the LF refining furnace greater than 1520° C., the refining time being 40 minutes to 45 minutes, adding alloy components during the refining process, fine-tuning the composition of the molten steel to a target content, and obtaining LF refined molten steel at a temperature of 1585° C. to 1620° C.;

[0030] S4, performing continuous casting treatment on the LF refined molten steel in a light pressure reduction mode to obtain a continuous casting ingot;

[0031] S5, heating and rolling the continuous casting ingot to obtain a rolled steel product;

[0032] S6. Cooling the rolled steel to control its structure and obtain high-strength corrosion-resistant steel for gas pipelines.

[0033] The preparation method of high-strength corrosion-resistant steel for gas pipelines of the present application aims at the environment of complex mineral media such as acidic gas and chlorine-containing inorganic salts in the gas medium, adds four corrosion-resistant elements of chromium, nickel, copper and molybdenum, improves the electrode potential of high-strength corrosion-resistant steel for gas pipelines, thereby improving the corrosion resistance of steel; in particular, according to the actual situation of dew point corrosion in the condensate in the gas, adds antimony and sulfur elements to improve the corrosion resistance of the steel matrix in the sensitive temperature range. In order to improve the strength of the steel, the titanium content in the steel reaches 0.07% to 0.10%, ensuring that the bainite matrix of the steel has sufficient second phase precipitation to produce strengthening, ensuring that the yield strength of high-strength corrosion-resistant steel for gas pipelines reaches more than 690MPa, and the tensile strength reaches more than 800MPa. Under the same load, 30% of steel can be saved, the comprehensive investment can be reduced by more than 20%, and the service life of the gas pipeline can be extended from 8 years of Q355B material to 20 years, which can be the same age as blast furnace equipment, and has the characteristics of economic green and low carbon.

[0034] In the embodiments of the present application, fine-tuning the composition of the molten steel to the target content refers to adjusting the content of the component elements in the molten steel to within the content range specified for high-strength corrosion-resistant steel for gas pipelines.

[0035] According to the embodiments of the present application, the light reduction mode refers to the continuous casting of steel billets. In the second cooling section of the continuous casting machine, pressure is applied in the thickness direction by pinch rollers to reduce the thickness of the billet by 5 mm to 10 mm to reduce defects in the core of the billet.

[0036] According to an embodiment of the present application, the continuous casting process of LF refined molten steel in a soft reduction mode includes:

[0037] S401, continuously casting LF refined steel liquid at a continuous casting speed of 1.4 m / min to 1.6 m / min and a reduction of 5 mm to 10 mm to obtain a continuously cast slab;

[0038] S402, stack cooling the continuous casting slab to a target temperature to obtain a continuous casting slab.

[0039] Illustratively, continuous casting can be carried out at a continuous casting speed of 1.4, 1.45, 1.5, 1.55, 1.58, or 1.6 m / min and a reduction of 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 10 mm.

[0040] In the embodiments of the present application, the alloy components include silicon, manganese, titanium, niobium, chromium, nickel, copper, molybdenum, and antimony. It should be noted that the target content refers to the content of the corresponding elements in the high-strength corrosion-resistant steel for gas pipelines.

[0041] According to an embodiment of the present application, stack cooling the continuous casting slab to the target temperature includes: placing the continuous casting slab in a hot slab environment above 500° C. for slow cooling until the temperature of the continuous casting slab drops below 300° C. The target temperature refers to a temperature below 300° C.

[0042] According to an embodiment of the present application, heating and rolling the continuous casting ingot includes:

[0043] S501, heating the continuous casting billet to 1200° C. to 1250° C., with a heating time of 150 min to 250 min and a solution time of more than 30 min, to obtain a continuous casting billet in a first state;

[0044] S502, rolling the continuous casting billet in the first state, including:

[0045] S5021, performing rough rolling on the continuous casting billet in the first state, wherein the rough rolling start temperature is 1150° C. to 1200° C., and the rough rolling finish temperature is 1050° C. to 950° C., to obtain a rough rolled steel product;

[0046] S5022, the rough-rolled steel is subjected to finish rolling, the start temperature of the finish rolling is 1020°C to 920°C, the final temperature of the finish rolling is 800°C to 720°C, and rolled steel is obtained.

[0047] According to the embodiments of the present application, the rolled steel is subjected to a cooling treatment to control the structure of the rolled steel, including: laminar cooling of the rolled steel at a cooling rate of 30°C / s to 40°C / s, so that the temperature of the rolled steel is finally cooled to 550°C to 580°C for coiling, thereby obtaining high-strength corrosion-resistant steel for gas pipelines.

[0048] In the embodiment of the present application, at a cooling rate of 30°C / s to 40°C / s, the temperature at which the high-temperature austenite matrix structure of the rolled steel begins to transform into bainite is 590°C, and the termination temperature of the transformation into bainite is 540°C. The transformation into the low-temperature bainite structure after finish rolling is achieved through a reasonable cooling rate, providing a basic structure for high-strength mechanical properties.

[0049] In the preparation method of high-strength corrosion-resistant steel for gas pipelines in the embodiment of the present application, hot rolling is based on metal deformation, phase change and other processes, and solid solution strengthening, precipitation strengthening, dislocation strengthening and other hardening measures are completed under the specified deformation and temperature conditions to obtain mechanical properties and good corrosion resistance, reduce manufacturing costs, and make full use of the rolling and cooling capacity of the continuous rolling mill. High-strength corrosion-resistant steel for gas pipelines is produced by controlled rolling and accelerated cooling, that is, the best mechanical effect is obtained through deformation recrystallization in the high-temperature austenite zone, deformation in the low-temperature austenite non-recrystallization zone, and accelerated cooling coupling effect after rolling. In the high-temperature austenite zone, Cr, Ni, Cu, Mo, and Sb corrosion-resistant elements are dissolved into the steel matrix, and the controlled rolling and controlled cooling technology is used to ensure that the alloy elements are in a solid solution state, thereby ensuring that the passivation film has sufficient alloy elements to participate in the film formation, so that the steel of high-strength corrosion-resistant steel for gas pipelines has good corrosion resistance.

[0050] In an embodiment of the present application, after the high-strength corrosion-resistant steel for gas pipelines is coiled, it can be placed in a cooling bin to allow the steel coils to undergo natural cooling, cross-cutting, flattening, inspection and storage, so as to obtain high-strength corrosion-resistant steel for gas pipelines that meets the use requirements and specifications.

[0051] In a second aspect, an embodiment of the present application provides a high-strength corrosion-resistant steel for a gas pipeline, which is prepared according to the above-mentioned method for preparing the high-strength corrosion-resistant steel for a gas pipeline. The high-strength corrosion-resistant steel for a gas pipeline comprises, by mass percentage: carbon, 0.05% to 0.08%; silicon, 0.20% to 0.40%; manganese, 0.30% to 0.50%; sulfur, 0.02% to 0.035%; phosphorus ≤ 0.02%, titanium, 0.07% to 0.1 0%; niobium, 0.020%~0.025%; chromium, 0.50%~0.90%; nickel, 0.20%~0.30%, copper, 0.25%~0.5%; molybdenum, 0.3%~0.6%; acid-soluble aluminum, 0.02%~0.05%; antimony, 0.10%~0.20%; nitrogen ≤0.00060%; oxygen ≤0.0015%, hydrogen ≤0.00015%, and the rest are Fe and impurity elements remaining in the smelting process.

[0052] In the embodiments of the present application, the applicant considers the following factors in the composition design of high-strength corrosion-resistant steel for gas pipelines:

[0053] Carbon: Carbon is the most easily available and economical alloying element in steel. The low carbon content design can ensure that the steel has good welding performance. At the same time, it cooperates with titanium and niobium in the steel to form second phase particles that play a strengthening role, ensuring the strength performance of the steel plate. With the corresponding cooling rate, a full bainite structure can be obtained to ensure that the matrix structure has good strength while also having good toughness and good corrosion resistance. The carbon content is controlled at 0.05% to 0.08%.

[0054] Silicon: Silicon can be deoxidized during the smelting process, but too high a content will affect weldability and toughness. Its content is controlled at 0.20% to 0.40%.

[0055] Manganese: Manganese is beneficial to improving the high-temperature brittleness of steel, but it is easy to form MnS inclusions in the steel. MnS inclusions are harmful to impact toughness and welding performance. Its content is controlled at 0.30% to 0.50%.

[0056] Sulfur: Sulfur can form a CuS passivation film during the contact between steel and acid medium, which can effectively isolate the contact between the acid and the steel matrix medium, so its content is controlled in the range of 0.02% to 0.035%.

[0057] Phosphorus: Excessive phosphorus will cause grain boundary segregation and increase the brittleness of steel. The phosphorus content should be controlled within 0.02%.

[0058] Titanium: During the continuous casting solidification process, titanium combines with nitrogen to form TiN, reducing the impact of boron nitride. The presence of fine TiN can inhibit the coarsening of grains in the welding heat affected zone. When the concentration of Ti in the steel is greater than 0.035%, a large number of dispersed TiC particles can be formed, which have a strong second-phase particle strengthening effect and contribute significantly to the strength of the steel.

[0059] Niobium: Adding more than 0.015% Nb to steel can significantly refine the grains, increase strength, and improve low-temperature toughness. Therefore, it is more appropriate to control niobium to 0.020% to 0.025%.

[0060] Aluminum: Too much aluminum will damage the toughness of steel and the isotropy of mechanical properties. Its content is controlled at 0.025% to 0.035%.

[0061] Chromium: Chromium content greater than 0.2% can improve the corrosion resistance of steel, while enhancing the liquid permeability of steel, which is conducive to the formation of bainite. Chromium content controlled at 0.50% to 0.9% can promote the rust layer structure from porous β-Fe 2 O 3 Transformed into dense α-Fe 2 o 3 , which can effectively isolate the contact between the corrosive liquid medium and the substrate, so that the steel is effectively protected.

[0062] Copper: Adding 0.25% to 0.5% copper can increase the electrode potential of the steel matrix. After adding antimony to copper-containing corrosion-resistant steel, the Cu-Sb elements work together to form Cu 2 Sb precipitates and later forms a denser Sb after contacting with a sulfuric acid medium. 2 O 5film, forming a dense passivation film, inhibiting the Sb element from segregating at the grain boundary and improving the grain boundary brittleness.

[0063] Nickel: A small amount of Ni is added to the steel. Ni and Cr work synergistically to enhance the corrosion resistance of the steel matrix. At the same time, the addition of Ni forms multiple mutual solutions and clusters with Cu and Fe, thereby avoiding copper embrittlement of the slab at a temperature of around 1080°C and avoiding cracks on the edge and surface of the steel plate. Therefore, considering the needs of economy and performance, the amount of Ni added is controlled at 0.20% to 0.30%.

[0064] Molybdenum: Mo is conducive to the refinement of bainite structure and improves the yield strength of steel, but it can also improve the yield strength ratio of steel and increase the ability of rust layer or passivation film to resist chloride ion corrosion. Therefore, the content of Mo is controlled at about 0.3% to 0.6%.

[0065] Antimony is the most significant chemical element that improves the corrosion resistance of steel in sulfuric acid environment. Sb significantly improves the corrosion resistance of steel. However, Sb is an element that has an adverse effect on the strength, toughness, plasticity and weldability of steel. Sb added to the metal surface can form Sb in the corrosive medium. 2 O 5 The stability is higher than that of the steel matrix, which is beneficial to prevent the metal matrix from being further corroded by the corrosive medium. In the present invention, the content of antimony is controlled at 0.10% to 0.20%, which is coupled with Cu and Mo, has good corrosion resistance, and does not damage the toughness.

[0066] Gaseous elements such as nitrogen, oxygen, and hydrogen are extremely detrimental to the performance stability of steel and should be strictly controlled: nitrogen <0.00060%, oxygen ≤0.00015%, and hydrogen ≤0.00 15%.

[0067] In the matrix structure of the high-strength corrosion-resistant steel for gas pipelines in the embodiment of the present application, the bainite structure accounts for 80% to 90%, the ferrite structure accounts for 10% to 20%, and the second phase particles are dispersed in the matrix structure.

[0068] The proportion of bainite structure and ferrite can be measured by metallographic ratio method.

[0069] In the embodiments of the present application, the proportions of bainite and ferrite in the matrix structure of the high-strength corrosion-resistant steel for gas pipelines meet the above-mentioned limitations, and the second phase particles are dispersed, so that the high-strength corrosion-resistant steel for gas pipelines has good corrosion resistance and mechanical properties.

[0070] In the second phase particles in the matrix structure of the high-strength corrosion-resistant steel for gas pipelines in the embodiment of the present application, the second phase particles with a particle size of 10nm to 100nm account for more than 60%, calculated based on the total volume of the second phase particles as 100%.

[0071] In an embodiment of the present application, among the second phase particles in the matrix structure of high-strength corrosion-resistant steel for gas pipelines, taking the total volume of the second phase particles as 100%, the second phase particles smaller than 10 nm account for 10%, and the volume of the second phase particles larger than 100 nm to 400 nm accounts for ≤30%.

[0072] In the embodiments of the present application, the second phase particle distribution of the matrix structure of the high-strength corrosion-resistant steel for gas pipelines meets the above-mentioned definition, which can further improve the corrosion resistance and mechanical properties of the corrosion-resistant steel for gas pipelines. The percentage of the second phase particles is obtained by means of electrolytic phase analysis, and the particle size of the second phase particles is obtained by transmission electron microscopy analysis.

[0073] The high-strength corrosion-resistant steel for gas pipelines in the embodiment of the present application has a yield strength of >690MPa, a tensile strength of >800MPa, an impact energy of >27J at -40°C, and a corrosion rate of ≤0.05mm / a. The structure of the high-strength corrosion-resistant steel for gas pipelines is bainite.

[0074] The high-strength corrosion-resistant steel for gas pipelines prepared by the preparation method of high-strength corrosion-resistant steel for gas pipelines in the embodiment of the present application is suitable for blast furnace gas working conditions, can solve the problems of high operating costs and short life, and extend the life cycle of the gas pipeline from 8 years of the existing Q335B material to 20 years, thereby reducing the comprehensive cost of high-strength corrosion-resistant steel for gas pipelines by more than 20%.

[0075] Test Section

[0076] Example 1

[0077] A method for preparing high-strength corrosion-resistant steel for a gas pipeline, comprising:

[0078] S1, desulfurizing molten iron by KR desulfurization process to obtain desulfurized molten iron;

[0079] S2, smelting the desulfurized molten iron in a 210-ton converter, blowing argon from a ladle after smelting the desulfurized molten iron in a converter, and controlling the terminal temperature of the argon station at 1545° C. to 1550° C. to obtain molten steel in a first state;

[0080] S3, LF refining the molten steel in the first state, including making the temperature of the molten steel in the first state entering the LF refining furnace 1525°C to 1530°C, the refining time is 42±2 minutes, adding alloy components silicon, manganese, titanium, niobium, chromium, nickel, copper, molybdenum, and antimony during the refining process, and fine-tuning the composition of the molten steel to the target content in Table 1, so as to obtain LF refined molten steel with a temperature of 1585°C to 1590°C;

[0081] S4. LF refined steel liquid is continuously cast in a light pressure reduction mode, including:

[0082] S401, continuously casting LF refined steel liquid at a continuous casting speed of 1.5 m / min and a reduction of 7.25±2.5 mm to obtain a continuously cast slab;

[0083] S402, stack cooling the continuous casting slab to below 300° C., including: placing the continuous casting slab in a hot slab environment at 500° C. for slow cooling, until the temperature of the continuous casting slab drops to 300° C., to obtain a continuous casting slab;

[0084] S5, heating and rolling the continuous casting ingot, including:

[0085] S501, heating the continuous casting billet to the furnace discharge temperature, i.e., 1240° C., with a required heating time of 200 min and a solution time of 35 min, to obtain a continuous casting billet in a first state;

[0086] S502, rolling the continuous casting billet in the first state, including:

[0087] S5021, performing rough rolling on the continuous casting billet in the first state, wherein the rough rolling start temperature is 1240° C., i.e., the heating temperature of the continuous casting billet, and the rough rolling finish temperature is 1185° C., to obtain a rough rolled steel product;

[0088] S5022, performing finish rolling on the rough rolled steel, wherein the start rolling temperature of the finish rolling is 1010° C. and the final rolling temperature of the finish rolling is 780° C., to obtain a rolled steel;

[0089] S6. Cooling the rolled steel, including: laminar cooling the rolled steel at a cooling rate of 35°C / s to control the structure of the rolled steel, finally cooling the rolled steel to 560°C for coiling, and obtaining high-strength corrosion-resistant steel for gas pipelines.

[0090] Embodiment 2-4

[0091] Examples 2-4 and Example 1 both adopt the preparation method of high-strength corrosion-resistant steel for gas pipelines of the present application to prepare high-strength corrosion-resistant steel for gas pipelines. Compared with Example 1, the corrosion-resistant steel for gas pipelines of Examples 2-4 differs in the composition content of LF refined steel liquid, heating and rolling treatment of continuous casting ingots, and process parameters for cold short treatment of rolled steel during the preparation process. The composition difference of LF refined steel liquid is shown in Table 1, and the difference in process parameters for heating and rolling treatment of continuous casting ingots and cold short treatment of rolled steel is shown in Table 2.

[0092] The high-strength corrosion-resistant steel for gas pipelines prepared in Examples 1-4 was respectively made into samples with thicknesses of 6 mm, 12 mm, 18 mm, and 24 mm. The samples for mechanical property testing are generally prepared perpendicular to the rolling direction. The examples and comparative examples of this application are all prepared perpendicular to the rolling direction of the steel.

[0093] Comparative Example 1

[0094] Comparative Example 1: Q335B steel was used to make the comparison steel sample, and the sample thickness was 18 mm.

[0095] Table 1 Thickness and component content of steel samples of Examples 1-4 and Comparative Example 1

[0096]

[0097] Note: In Table 1, “-” indicates that the Q335B steel of Comparative Example 1 does not include this component.

[0098] The process parameters for heating and rolling the continuous casting ingots in Examples 1-4 and Comparative Example 1 are shown in Table 2 below:

[0099] Table 2 Heating and rolling process parameters of Examples 1-4 and Comparative Example 1

[0100]

[0101] Microstructure

[0102] like Figure 2 As shown, it is the metallographic structure of the high-strength corrosion-resistant steel for gas pipelines of Example 1. In the metallographic structure of the steel sample of Example 1, the needle-shaped structure is a bainite structure, the bainite structure accounts for 90%, and the ferrite accounts for 10%. Figure 2 The black particles dispersed in the solution are second phase precipitates, i.e. second phase particles. Figure 4 As shown, among the second phase particles, taking the total volume of the second phase particles as 100%, the second phase particles of 10nm to 100nm account for more than 60%, the second phase particles of less than 10nm account for 10%, and the volume of the second phase particles greater than 100nm to 400nm accounts for 30%.

[0103] like Figure 3 As shown, it is the metallographic structure of the high-strength corrosion-resistant steel for gas pipelines in Example 2. In the metallographic structure of the steel sample in Example 2, the needle-shaped structure is bainite structure, the bainite structure accounts for 85%, the ferrite accounts for 15%, and the black particles are second-phase precipitates, i.e., second-phase particles. The bainite structure and the second-phase particles are dispersed and strengthened in the matrix structure, so that the steel has high strength and good plasticity and toughness.

[0104] Mechanical properties test

[0105] According to GB / T228.1-2021 standard, the steel samples of Examples 1-4 and Comparative Example 1 were subjected to mechanical property tests including yield strength, tensile strength, yield strength ratio, elongation at break, and -40°C impact energy (longitudinal). The test results are shown in Table 3 below:

[0106] , Table 3

[0107]

[0108] It can be concluded from Table 3 that the yield strength (Rel) of the high-strength corrosion-resistant steel samples for gas pipelines prepared in Examples 1-4 is 708MPa-742MPa, the tensile strength (Rm) is 916MPa-945MPa, the yield strength ratio is 0.772-0.788, the elongation of the steel is 15%-17%, and the longitudinal impact energy at -40°C is 55J-69J; the yield strength (Rel) of the Q335B steel sample of Comparative Example 1 is 380MPa, the tensile strength (Rm) is 550MPa, the yield strength ratio is 0.69, the elongation of the steel is 22.5%, and the longitudinal impact energy at -40°C is 98J-120J. From the above comparison data, it can be concluded that the yield strength and tensile strength of the high-strength corrosion-resistant steel samples for gas pipelines prepared in Examples 1-4 of the present application are higher than the yield strength and tensile strength of the Q335B steel samples in Comparative Example 1, thereby making the yield strength ratio of the high-strength corrosion-resistant steel for gas pipelines higher than the yield strength ratio of the steel samples in Comparative Example 1, and can effectively resist deformation and damage when subjected to external forces, thereby improving the overall performance and safety of the structure. The elongation and longitudinal impact energy of the high-strength corrosion-resistant steel samples for gas pipelines in Examples 1-4 of the present application are lower than those of the Q335B steel samples in Comparative Example 1, but the elongation of the high-strength corrosion-resistant steel samples for gas pipelines in Examples 1-4 is still ≥15%, which can meet the requirements of high-strength corrosion-resistant steel for gas pipelines. The longitudinal impact energy of the high-strength corrosion-resistant steel samples for gas pipelines in Examples 1-4 at -40°C is all >27J, which can meet the requirements of high-strength corrosion-resistant steel for gas pipelines.

[0109] Corrosion resistance test

[0110] The high-strength corrosion-resistant steel for gas pipelines prepared in Examples 1-4 and the steel of Comparative Example 1 (Q335B) were subjected to corrosion resistance tests in accordance with the GB / T1929.1-2018 standard hanger in the actual working conditions of Lianyuan Steel's 7# blast furnace (ambient temperature 60-70°C, humidity RH less than 60-70%, pH value 4-6), and the test results are recorded in the following Table 4:

[0111] Table 4

[0112] serial number Actual corrosion thickness in 1 year, mm Actual corrosion thickness in 2 years, mm Example 1 0.038 0.062 Example 2 0.036 0.053 Example 3 0.033 0.061 Example 4 0.042 0.055 Comparative Example 1 Corrosion scrap Corrosion scrap

[0113] By comparing the actual corrosion thickness of the steel samples of Examples 1-4 and Comparative Example 1 in Table 4 after 1 year and 2 years, it is found that the actual corrosion thickness of the high-strength corrosion-resistant steel for gas pipelines prepared in Examples 1-4 is 0.033mm to 0.042mm in 1 year, and the actual corrosion thickness is 0.053mm to 0.062mm in 2 years. The Q335B steel sample of Comparative Example 1 was completely corroded and scrapped. It can be concluded from the above comparative data that the high-strength corrosion-resistant steel for gas pipelines in the embodiments of the present application has excellent corrosion resistance.

[0114] Combining the comparison contents of Tables 1 to 4, it can be concluded that the method for preparing high-strength corrosion-resistant steel for gas pipelines in the embodiment of the present application can prepare steel for gas pipelines with high strength and excellent corrosion resistance.

[0115] The above is only a specific implementation method of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working process described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here. It should be understood that the protection scope of the present application is not limited to this. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application.

Claims

1. A method for preparing high-strength corrosion-resistant steel for gas pipelines, characterized in that: include: Provide molten iron; The molten iron is subjected to converter smelting, and after the converter smelting, argon is blown into a ladle, and the terminal temperature of the argon station is controlled to be greater than 1535° C., so as to obtain molten steel in a first state; The molten steel in the first state is subjected to LF refining, including making the temperature of the molten steel in the first state entering the LF refining furnace greater than 1520° C., the refining time being 40 minutes to 45 minutes, adding alloy components during the refining process, fine-tuning the components of the molten steel to a target content, and obtaining LF refined molten steel at a temperature of 1585° C. to 1620° C.; The LF refined steel liquid is continuously cast in a soft reduction mode to obtain a continuous casting ingot; The continuous casting billet is heated and rolled to obtain rolled steel; The rolled steel is subjected to cooling treatment to control the structure of the rolled steel and obtain high-strength corrosion-resistant steel for gas pipelines.

2. The preparation method according to claim 1, characterized in that: The alloy components include silicon, manganese, titanium, niobium, chromium, nickel, copper, molybdenum and antimony.

3. The preparation method according to claim 2, characterized in that: The continuous casting process of the LF refined molten steel in a light pressure reduction mode comprises: Continuously casting LF refined steel liquid at a continuous casting speed of 1.4 m / min to 1.6 m / min and a reduction of 5 mm to 10 mm to obtain a continuously cast slab; The continuous casting slab is stack-cooled to a target temperature to obtain a continuous casting slab.

4. The preparation method according to claim 3, characterized in that: The stack cooling of the continuous casting slab to a target temperature comprises: The continuously cast slab is placed in a hot slab environment at a temperature above 500°C for slow cooling until the temperature of the continuously cast slab drops to below 300°C.

5. The preparation method according to claim 1, characterized in that: The heating and rolling treatment of the continuous casting billet comprises: The continuous casting billet is heated to 1200° C. to 1250° C., the heating time is required to be 150 min to 250 min, and the solution time is greater than 30 min, to obtain a continuous casting billet in a first state; The continuous casting billet in the first state is subjected to a rolling process, comprising: The continuous casting billet in the first state is subjected to rough rolling, wherein the rough rolling start temperature is 1150° C. to 1200° C., and the rough rolling finish temperature is 1050° C. to 950° C., to obtain a rough rolled steel product; The rough rolled steel is subjected to a finish rolling treatment, wherein the start rolling temperature of the finish rolling is 1020° C. to 920° C., and the final rolling temperature of the finish rolling is 800° C. to 720° C., to obtain a rolled steel.

6. The preparation method according to claim 5, characterized in that: The step of cooling the rolled steel to control the structure of the rolled steel includes: The rolled steel is subjected to laminar cooling at a cooling rate of 30°C / s to 40°C / s, and the temperature of the finished rolled steel is finally cooled to 550°C to 580°C for coiling to obtain high-strength corrosion-resistant steel for gas pipelines.

7. A high-strength corrosion-resistant steel for gas pipelines, characterized in that: The high-strength corrosion-resistant steel for gas pipelines according to any one of claims 1 to 6 is prepared, and comprises, by mass percentage: carbon, 0.05% to 0.08%; silicon, 0.20% to 0.40%; manganese, 0.30% to 0.50%; sulfur, 0.02% to 0.035%; phosphorus ≤ 0.02%; titanium, 0.07% to 0.10%; niobium, 0.020% to 0.0 25%; chromium, 0.50%~0.90%; nickel, 0.20%~0.30%, copper, 0.25%~0.5%; molybdenum, 0.3%~0.6%; acid-soluble aluminum, 0.02%~0.05%; antimony, 0.10%~0.20%; nitrogen ≤0.00060%; oxygen ≤0.0015%, hydrogen ≤0.00015%, and the rest are Fe and impurity elements remaining in the smelting process.

8. The high-strength corrosion-resistant steel for gas pipeline according to claim 7, characterized in that: In the matrix structure of the high-strength corrosion-resistant steel for gas pipelines, bainite accounts for 80% to 90%, ferrite accounts for 10% to 20%, and second phase particles are dispersed in the matrix structure.

9. The high-strength corrosion-resistant steel for gas pipeline according to claim 8, characterized in that: Among the second phase particles, taking the total volume of the second phase particles as 100%, the second phase particles with a particle size of 10nm to 100nm account for more than 60%, the second phase particles smaller than 10nm account for 10%, and the volume of the second phase particles larger than 100nm to 400nm accounts for ≤30%.

10. The high-strength corrosion-resistant steel for gas pipeline according to any one of claims 7 to 9, characterized in that: The high-strength corrosion-resistant steel for the gas pipeline has a yield strength of 690MPa-750MPa, a tensile strength of 850MPa-950MPa, a yield strength ratio of ≤0.85, a -40°C KV2 type impact energy of >27J, and a corrosion rate of ≤0.05mm / a.

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