A steel plate for a refinery pipe having high formability and resistance to a high temperature of 700 °c and a wet hydrogen sulfide environment, and a method for manufacturing the same

Abstract

The application discloses a kind of steel plate materials resistant to 700 DEG C, wet hydrogen sulfide environment, component includes by weight percentage: C:0.07-0.13%, Si:0.20-0.50%, Mn:0.30-0.60%, Cr:7.0-9.0%, Mo:1.00-1.20%, W:1.50-2.00%, Nb:0.06-0.10%, V:0.15-0.25%, N:0.040-0.100%.Its preparation method includes: smelting, casting, heating, rolling, heat treatment is normalized heat treatment after martensite is decomposed again, then stabilization treatment is carried out.The steel plate material prepared by the application has high-temperature tensile strength of 410-450 MPa at 700 DEG C, transverse elongation after fracture of 31.0-34.0%, and longitudinal elongation after fracture of 33.0-35.0%.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, specifically relating to a formable steel plate for refining pipe fittings that can withstand high temperatures of 700℃ and humid hydrogen sulfide environments, and its manufacturing method. Background Technology

[0002] Inside and between units in an oil refinery, there is a complex network of pipelines that form the main arteries of production. These pipelines play a vital role in the entire production process, including decomposition and cracking, process connection, and transfer of finished and semi-finished products, thus linking the entire production process together as a whole.

[0003] Pipeline systems actually consist of two main parts: pipes and fittings. During operation, they not only withstand external conditions such as high temperatures and pressures imposed by the refining process, but also come into contact with sulfides contained in crude oil and various additives used in the refining process, facing the risk of corrosion from high-temperature, wet hydrogen sulfide. These complex factors seriously affect the long-term, safe production of pipeline systems. In particular, fittings used for pipe bends exhibit significant and uneven plastic deformation during processing, easily leading to stress concentration in the bends. Prolonged operation in this high-temperature (700℃) environment with wet hydrogen sulfide greatly increases the risk of corrosion and perforation, causing significant losses to production safety.

[0004] The existing Chinese patent (publication number CN101760687A) discloses a high-temperature alloy pipe fitting and the production method of the steel and pipe fitting used therein. The material involved in this patent is a nickel-based alloy material, which does not belong to the category of steel. Moreover, the final product of the invention is a bent pipe and pipe fitting, and it does not solve the technical problem of high temperature resistance.

[0005] Chinese patent (publication number CN109161790A) discloses a high-grade, high-toughness pipe steel for use under acidic conditions and its production method. This patent mainly relates to pipe steel for long-distance transportation that is resistant to low-temperature corrosion environments, but it cannot meet the requirements of high-temperature corrosion environments.

[0006] Chinese patent (publication number CN108085593A) discloses a steel for bends and fittings used in oil and gas transportation in low-temperature environments and a manufacturing method thereof, which mainly solves the problems of strength and low-temperature toughness of bends and fittings used in low-temperature stations.

[0007] Chinese patent (publication number CN102912250A) discloses an economical low yield strength ratio pipe fitting steel for oil and gas transportation and its production method. The pipe fittings involved are mainly pipeline steel materials required for long-distance oil and gas transportation. The contact medium is crude oil and natural gas, and the external environment is high-altitude cold and earthquake zones. Therefore, the main issues to be addressed are the room temperature strength and low temperature toughness of the material.

[0008] Chinese patent (publication number CN112267068A) discloses a high-temperature corrosion-resistant pipe steel and its production process. It uses rare earth elements and external graphene spraying for corrosion protection. It is not only expensive and complex, but also does not show high temperature resistance and corrosion resistance among the beneficial effects.

[0009] The steel used in the pipe fittings disclosed in the aforementioned invention patents is mainly used for crude oil and natural gas transportation in the pre-refining process, primarily involving low-temperature environments. Even for pipe fittings applied in high-temperature corrosive environments, the corrosion resistance principle relies on the addition of expensive strategic rare earth resources or external coating with graphene. However, steel for easily formable pipe fittings truly suitable for 700℃ high-temperature humid hydrogen sulfide environments is still in the invention gap. Summary of the Invention

[0010] The purpose of this invention is to provide a formable steel plate for refining pipe fittings that can withstand 700℃ and humid H2S environments, and its manufacturing method, so as to solve the problem that existing pipe steel is difficult to withstand high temperature and corrosion.

[0011] To achieve the above objectives, the present invention provides a steel plate material resistant to 700℃ and a humid hydrogen sulfide environment, the composition of which by weight percentage includes: C: 0.07-0.13%, Si: 0.20-0.50%, Mn: 0.30-0.60%, Cr: 7.0-9.0%, Mo: 1.00-1.20%, W: 1.50-2.00%, Nb: 0.06-0.10%, V: 0.15-0.25%, N: 0.040-0.100%, with the balance being Fe.

[0012] This invention provides a method for preparing a steel plate material resistant to 700℃ and wet hydrogen sulfide environment, comprising the following steps:

[0013] S1. Smelting: The iron content is controlled at 50-70%, the temperature is controlled at 1600-1640℃, the silicon-calcium wire feeding speed is 2-4m / s, the wire feeding amount is 3-5m / t, and after desulfurization, impurity removal and vacuum degassing treatment, the steel is tapped.

[0014] S2. Casting: Control the superheat of the tundish to 15-25℃, and the billet pulling speed to 0.5-1.0m / min; after the billet is removed from the line, it is put into the stack for slow cooling, and the stacking slow cooling time is 36-48h;

[0015] S3. Heating: Control the heating temperature of the steel billet at 1200-1250℃ to allow the alloying elements to dissolve and inhibit the growth of the original austenite grains;

[0016] S4. Rolling: Control the roughing rolling termination temperature to 1000-1100℃, the total roughing rolling deformation rate to 60-65%, and the intermediate billet thickness to be 2.5-3.0 times the finished steel plate thickness; set the finishing rolling start temperature to 890-930℃ and the finishing rolling termination temperature to 850-900℃, so that the cumulative deformation rate is 60-70%.

[0017] S5. Heat treatment: Normalizing heat treatment yields fine martensite structure in lath bundles, followed by tempering heat treatment to decompose the martensite. After tempering, the structure is stabilized at 750-770℃ and held for 20-30 hours.

[0018] Preferably, the components, by weight percentage, include: C: 0.07-0.13%, Si: 0.20-0.50%, Mn: 0.30-0.60%, Cr: 7.0-9.0%, Mo: 1.00-1.20%, W: 1.50-2.00%, Nb: 0.06-0.10%, V: 0.15-0.25%, and N: 0.040-0.100%.

[0019] Preferably, the weight percentages are controlled as follows: P content ≤ 0.010% and S content ≤ 0.002%. Preferably, the desulfurization method includes blowing argon gas into the molten steel from the bottom of the ladle to agitate it for desulfurization.

[0020] Preferably, the vacuum degassing treatment method includes evacuating the vacuum in a VD furnace for 10-15 minutes, and then blowing in N2 after breaking the vacuum until it reaches 0.040-0.100%.

[0021] Preferably, the normalizing temperature is 1040-1080℃, the holding time is 1.0-3.0 min / mm, and the cooling rate is 2-5℃ / s.

[0022] Preferably, the tempering temperature is 770-810℃ and the holding time is 5.0-9.0 min / mm.

[0023] Preferably, the lath bundle size in the fine martensitic structure of the lath bundles is 200-300 nm.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The method of this invention is based on the chemical elements C, Mn and Si, strictly controls the harmful elements P and S, and adds high content of Cr and alloying elements Mo, W, Nb, V and N to achieve solid solution strengthening and precipitation strengthening, thereby obtaining a stable and dense tempered martensite structure, effectively preventing hydrogen penetration, and ensuring the comprehensive mechanical properties and high temperature corrosion resistance of steel for refining and bending pipes.

[0026] (2) The steel plate for high temperature resistance and easy forming of pipe bending obtained by the present invention through special processes of smelting, rolling, ultra-high temperature normalizing and weak water cooling, high temperature tempering and low temperature long-term stabilization treatment has the following mechanical properties: high temperature tensile strength of 410-450MPa at 700℃, transverse elongation after fracture of 31.0-34.0%, longitudinal elongation after fracture of 33.0-35.0%, HBW of 170-180, yield strength ratio between 0.75-0.80, D=2a, and the results of transverse and longitudinal cold bending at 180° show that the surface of the steel plate is intact and without cracks. The above excellent comprehensive properties ensure the cold forming processability and long-term high temperature service performance of the steel plate in the pipe bending process.

[0027] (3) The present invention uses a unique smelting, rolling and heat treatment production process, so that the steel prepared can withstand hydrogen-induced cracking HIC test (A solution) at 700℃ and the CSR% is 0. The SSCC four-point bending test was continuously loaded for 720h without breaking.

[0028] In summary, the steel for refining and chemical pipe fittings that can be easily cold-formed in a high-temperature corrosive environment of 700℃ provides favorable support for the long-term safe development of large-scale and integrated refining and chemical equipment in my country. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0030] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0031] This invention provides a formable steel plate for refining pipe fittings that is resistant to 700℃ and humid H2S environment. Its chemical composition range is as follows by weight percentage: C 0.07-0.13%, Si 0.20-0.50%, Mn 0.30-0.60%, 0≤P≤0.010%, 0≤S≤0.002%, Cr 7.0-9.0%, Mo 1.00-1.20%, W 1.50-2.00%, Nb 0.06-0.10%, V 0.15-0.25%, N 0.040-0.100%, with the balance being Fe and unavoidable inclusions.

[0032] The reasons for limiting the amounts of alloying elements C, Si, Mn, P, S, Cr, Mo, W, Nb, V, and N in steel plates are detailed below:

[0033] Carbon (C) is the most important and inexpensive element for ensuring the strength of steel at both room and high temperatures. It enhances the strength of the matrix through solid solution and carbide forms. However, excessive carbon content can affect the weldability of steel, while insufficient content cannot guarantee the steel's performance in high-temperature environments. Therefore, this invention sets the C content range to 0.07-0.13%.

[0034] Silicon (Si) is a beneficial element in steel for resisting high-temperature corrosion. At high temperatures, it can form a protective and dense SiO2 film on the steel surface. A Si content of 0.20-0.50% in steel exhibits a significant antioxidant effect. However, a silicon content exceeding 1.0% leads to a deterioration in mechanical properties. Therefore, the silicon content in steel generally does not exceed 1.0%. Furthermore, the co-alloying of silicon and molybdenum has a significant effect on improving the oxidation resistance of steel, increasing it to 800℃. Therefore, this invention sets the Si content range to 0.20-0.50%.

[0035] Mn can increase the toughness, strength and hardness of steel. It is a strong austenite stabilizer and can effectively reduce the decomposition rate of austenite and improve the hardenability of steel. High Mn content will enhance temper brittleness. Therefore, the Mn content range is set to 0.30%-0.60% in this invention.

[0036] Both sulfur (S) and phosphorus (P) are harmful elements in steel, increasing its brittleness. Therefore, the content of phosphorus and sulfur in steel should be minimized, with a minimum of 0% for S and 0% for P.

[0037] Cr is a strong carbide-forming element. It forms alloy carbides with C in steel, which are not only stable but also dense. It not only has a strong effect of consuming carbon, preventing it from combining with H2 to form CH4, which would lead to hydrogen embrittlement or hydrogen-induced cracking, but also produces stable and dense carbides that can effectively prevent hydrogen penetration and C separation.

[0038] In this invention, the Cr content is set in the range of 7.0-9.0% to provide both high-temperature strengthening and high-temperature corrosion protection, ensuring the pipe fittings meet the requirements for long-term high-temperature use.

[0039] Mo is a strong carbide-forming element. It forms stable alloy carbides with carbon in steel and has excellent resistance to temper brittleness. It plays an important role in the high-temperature resistance of bent pipes. However, excessive content will affect the processing performance of steel. Therefore, this invention sets the Mo content range to 1.00-1.20%.

[0040] W can increase the tempering stability, hot hardness, and hot strength of steel, and improve its creep resistance at high temperatures. In addition, W can effectively prevent the coarsening behavior of alloy carbides during high-temperature heat treatment; therefore, the W content in this invention is set in the range of 1.50%-2.00%.

[0041] Nitrogen (Nb) is a strong carbon and nitride-forming element. It forms a dispersed precipitate phase at grain boundaries, which significantly hinders dislocation slip and climb, thus providing excellent high-temperature strengthening. At the same time, its grain-refining effect can reduce the overheating sensitivity and temper brittleness of steel. Under certain conditions, it can improve toughness and resistance to creep. Therefore, the present invention sets the Nb content range to 0.06-0.10%.

[0042] Vanadium (V) is a refractory metal with a high melting point of 1910℃. Vanadium is an alloying element that shrinks the γ-Fe phase and expands the α-Fe phase. The carbon and nitrides it forms are dispersed within the grains and at grain boundaries, significantly hindering dislocation slip and climb, thus contributing to high-temperature thermal strength. However, excessive V content increases the yield strength ratio of steel, which is detrimental to the forming and manufacturing of pipe fittings. Therefore, this invention sets the V content range to 0.15-0.25%.

[0043] Like carbon, nitrogen (N) can dissolve in iron to form interstitial solid solutions. It can also form stable nitrides with elements such as Cr, V, and Nb, which can strengthen the steel. At the same time, it can improve the strength and impact toughness of high-chromium steel without reducing its plasticity, thus improving the high-temperature creep strength of the steel. Therefore, the present invention sets the N content range to 0.050-0.100%.

[0044] A method for manufacturing an easily formable steel for refining pipe fittings that can withstand a 700℃ humid H2S environment is as follows:

[0045] 1. Electric arc furnace—LF furnace—VD furnace—slab continuous casting—slab finishing—heating—rolling—straightening—heat treatment—performance evaluation.

[0046] 2. Smelting Process: The composition designed in this invention contains 7.0-9.0% Cr element and refractory tungsten and molybdenum elements. Therefore, smelting needs to be carried out in an electric arc furnace with high temperature and thermal efficiency. To ensure steel purity, high-quality scrap steel and molten iron are used as raw materials, with the iron content controlled at 50-70%. Since the carbon content in this invention is 0.07-0.13%, chromium is added in the form of low-carbon ferrochrome and metallic chromium. To prevent chromium oxidation, it is added at the initial stage of reduction. Ferromolybdenum and ferrotungsten are also added at the initial stage of reduction. The tapping temperature is controlled at 1600-1640℃. An LF furnace is used for composition fine-tuning, i.e., adding alloying elements to achieve the target chemical composition values; then ferroniobium and ferrovanadium are added, with a silicon-calcium wire feed speed of 2-4 m / s and a feed rate of 3-5 m / t. Argon gas is blown into the bottom of the ladle to agitate the molten steel for further desulfurization treatment, controlling inclusions in the steel to an extremely low level to ensure steel purity and guarantee high-temperature performance. Vacuum degassing is carried out in a VD furnace for 10-15 minutes. After the vacuum is broken, N2 is blown until the N2 content reaches 0.040-0.100%, then the steel is ready to be tapped.

[0047] 3. Casting process: The tundish is superheated to 15-25℃, and the billet pulling speed is 0.5-1.0m / min. The billet is then placed in a stack for slow cooling for 36-48 hours.

[0048] 4. Heating process: By controlling the heating process of the steel billet, the alloying elements are fully dissolved and the growth of the original austenite grains is effectively suppressed. The heating temperature of the slab is controlled at 1200-1250℃, and the total heating time is 6-8 hours.

[0049] 5. Rolling Process: Roughing end temperature 1000-1100℃, total roughing deformation rate 60-70%, intermediate billet thickness 2.5-3.0 times the finished steel plate thickness; Finishing start temperature 890-930℃, finishing end temperature 850-900℃, cumulative finishing deformation rate 60-70%. The above parameters are designed based on the steel's composition and performance requirements. Since the material is used in high-temperature environments, the optimized controlled rolling process maximizes the refinement of the rolled microstructure through topographic deformation, ensuring excellent high-temperature strength of the steel plate after final heat treatment. Rolling thickness is 10-40mm.

[0050] 6. Heat Treatment Process: A relatively refined original rolled microstructure was obtained through controlled rolling. However, due to the large amount of alloying elements such as Cr, Mo, W, V, Nb, and N in the steel, ultra-high temperature normalizing is required to fully dissolve and homogenize these alloying elements to maximize their synergistic strengthening effect. After normalizing, accelerated cooling with water medium is used to obtain a fine martensitic microstructure of 200-300 nm lath bundles. The normalizing temperature is 1040-1080℃, the holding time is 1.0-3.0 min / mm, and the cooling rate is 2-5℃ / s. Although martensite has excellent high-temperature strength, its poor plasticity and high hardness are extremely unfavorable for forming bent pipes. This invention promotes martensite decomposition through high-temperature tempering to obtain a (Fe, Mn, Cr, Mo, W) microstructure with excellent precipitation strengthening effect. 23 The tempered martensitic microstructure of C6 and (Nb, V)CN second phases is obtained by tempering at 770-810℃ for 5.0-9.0 min / mm. To further eliminate residual austenite and stress in the steel and prevent stress cracking during cold forming, this invention adds a long-term stabilization treatment process after high-temperature tempering, namely, holding at 750-770℃ for 20-30 hours. The microstructure obtained under this process has the following three characteristics: First, internal stress is completely eliminated. Second, unstable residual austenite is completely transformed into tempered martensite. Finally, more stable second-phase particles are formed in the steel, and during this process, they undergo aggregation, growth, and stabilization until they no longer change. There are no free C atoms in the steel that interact with H2 generated in the medium, causing hydrogen-induced cracking. The final microstructure obtained under this heat treatment process is fine, uniform, and dense, exhibiting excellent high-temperature resistance, corrosion resistance, and cold forming properties.

[0051] Table 1 shows the chemical composition of the steel plates prepared in Examples 1-10 of the present invention; Table 2 shows the process parameters for preparing the steel plates in Examples 1-10 of the present invention; Table 3 shows the mechanical properties of the steel plates prepared in Examples 1-10; Table 4 shows the HIC test results (solution A) of the steel plates in Examples 1-10 at 700℃; and Table 5 shows the SSCC four-point bending test results of the steel plates prepared in Examples 1-10 of the present invention at 700℃.

[0052] Table 1. Chemical composition (wt, %) of steel plates prepared in Examples 1-10

[0053]

[0054] Table 2. Production process parameters for preparing steel plates in Examples 1-10 of the present invention

[0055]

[0056]

[0057] Table 3. Mechanical property tests of steel plates prepared in Examples 1-10 of the present invention

[0058]

[0059] Table 4. Results of the HIC test (solution A) on the resistance of the steel plates prepared in Examples 1-10 of the present invention to hydrogen-induced cracking at 700℃.

[0060]

[0061]

[0062] Table 5. Results of the SSCC four-point bending test of the steel plates prepared in Examples 1-10 of the present invention at 700℃.

[0063]

[0064] Based on the above results, it can be concluded that the easily formable bending steel plate for resistant to 700℃ high-temperature humid hydrogen sulfide working environment provided by the present invention has excellent properties such as transverse elongation after fracture of 31.0-34.0%, longitudinal elongation after fracture of 33.0-35.0%, Brinell hardness of 170-180, yield strength ratio of 0.75-0.80, and tensile strength at 700℃ of 410-450MPa. The transverse and longitudinal cold bending results at D=2a and 180° show that the steel plate surface is intact without cracks. The HIC test (A solution) results at 700℃ show that the CSR% is 0. The SSCC four-point bending test shows that the plate did not break after continuous loading for 720h.

[0065] 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 sheet material resistant to a 700°C, wet hydrogen sulfide environment, characterized by, The ingredients include, by weight percentage: C: 0.07-0.13%, Si: 0.20-0.50%, Mn: 0.30-0.60%, Cr: 7.0-9.0%, Mo: 1.00-1.20%, W: 1.50-2.00%, Nb: 0.06-0.10%, V: 0.15-0.25%, N: 0.040-0.100%, and the balance being Fe; The preparation method of the steel plate material resistant to 700 DEG C, wet hydrogen sulfide environment comprises the following steps: S1, smelting: the content of molten iron is controlled at 50-70%, the temperature is controlled at 1600-1640 DEG C, the feeding speed of silicon-calcium wire is 2-4 m / s, the feeding amount is 3-5 m / t, after desulfurization, impurity removal treatment and vacuum degassing treatment, the molten steel is tapped; S2, casting: the superheat degree of the tundish is controlled at 15-25 DEG C, and the blank drawing speed is 0.5-1.0 m / min; the cast blank is stacked and slowly cooled, and the stacking and slow cooling time is 36-48 h; S3, heating: the heating temperature of the steel blank is controlled at 1200-1250 DEG C, so that the alloy elements are dissolved and the original austenite grain growth is inhibited; S4, rolling: the final temperature of rough rolling is controlled at 1000-1100 DEG C, the total deformation rate of rough rolling is 60-65%, the thickness of the intermediate blank is 2.5-3.0 times the thickness of the finished steel plate; the starting temperature of finish rolling is set at 890-930 DEG C, and the final temperature of finish rolling is 850-900 DEG C, so that the cumulative deformation rate is 60-70%; S5, heat treatment: the normalizing heat treatment obtains the lath bundle fine martensite structure, and then the martensite is decomposed through tempering heat treatment; after tempering, the stabilization treatment is carried out at 750-770 DEG C for 20-30 h; The ingredients added during smelting include, by weight percentage: C: 0.07-0.13%, Si: 0.20-0.50%, Mn: 0.30-0.60%, Cr: 7.0-9.0%, Mo: 1.00-1.20%, W: 1.50-2.00%, Nb: 0.06-0.10%, V: 0.15-0.25%, N: 0.040-0.100%. The weight percentage of P is controlled to be ≤0.010%, and the weight percentage of S is controlled to be ≤0.002%.

2. The steel sheet material resistant to a 700 °C, wet hydrogen sulfide environment according to claim 1, characterized by, The desulfurization method comprises stirring the molten steel by blowing argon from the bottom of the ladle to carry out desulfurization.

3. The steel sheet material resistant to a 700 °C, wet hydrogen sulfide environment according to claim 1, characterized by, The vacuum degassing treatment method comprises the following steps: vacuumizing in the VD furnace for 10-15 min, and then blowing N2 after breaking the vacuum until the content of N reaches 0.040-0.100%.

4. The steel sheet material resistant to a 700 °C, wet hydrogen sulfide environment according to claim 1, characterized by, The normalizing temperature is 1040-1080 DEG C, the holding time is 1.0-3.0 min / mm, and the cooling speed is 2-5 DEG C / s.

5. The steel sheet material resistant to a 700 °C, wet hydrogen sulfide environment according to claim 1, characterized by, The tempering temperature is 770-810 DEG C, and the holding time is 5.0-9.0 min / mm.

6. The steel sheet material resistant to a 700 °C, wet hydrogen sulfide environment according to claim 1, characterized by, The size of the lath bundle in the lath bundle fine martensite structure is 200-300 nm.

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