A steel plate for a refinery pipe fitting which is easily formed and resistant to a high temperature of 500 °c and a wet hydrogen sulfide environment, and a method for manufacturing the same

Abstract

The application discloses a steel plate material resistant to 500 DEG C and hydrogen sulfide environment, which comprises the following components in percentage by weight: C: 0.06%-0.10%, Si: 0.20%-0.50%, Mn: 0.30%-0.60%, Cr: 4.0%-6.0%, Mo: 0.40%-0.80%, V: 0.05%-0.10%, and N: 0.010%-0.030%. The preparation method comprises the following steps: smelting, casting, heating, rolling, and decomposing bainite through tempering after normalizing, and then stabilizing treatment. The steel plate material prepared by the application has the tensile strength of 380-410 MPa at 500 DEG C, the transverse elongation of 34.0-36.5%, the longitudinal elongation of 36.5-38.5%, the Brinell hardness of 160-170, the yield strength ratio of 0.73-0.75, and the SSCC four-point bending test continuous loading of 720h without fracture.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal materials, and particularly relates to a steel plate for easy-to-form refining pipe fittings resistant to 500 DEG C high temperature and wet hydrogen sulfide environment and a manufacturing method thereof. BACKGROUND

[0002] Inside the device, between the devices and the devices, there are crisscrossed and complex structured pipe systems, which are the arteries of production and play a role in cracking, process connection, product and semi-product transfer, etc. in the whole production, and connect the whole production to form a whole.

[0003] The pipe system actually includes two parts of a pipeline and a pipe fitting. In work, they not only bear the external conditions such as high temperature and loading pressure brought by the requirements of refining process, but also contact sulfides in crude oil and various additives added in the refining process, and face the risk of high-temperature wet hydrogen sulfide corrosion. These complex factors seriously affect the long-period and safe production of the pipe system. Especially the pipe fitting part for pipe turning, the plastic deformation of the material is large and the deformation is uneven in the process of forming, which is easy to cause stress concentration of the elbow pipe. This part is easy to cause corrosion perforation under the long-term operation in the high temperature of about 500 DEG C and the wet hydrogen sulfide environment, which brings great loss to the production safety.

[0004] The prior art Chinese patent (publication number CN101760687A) discloses a high-temperature alloy pipe fitting and a steel material and a production method of the pipe fitting. The material involved in the patent is a nickel-based alloy material, which does not belong to the steel category, and the final product of the invention is an elbow pipe and a pipe fitting, and the technical problem of high-temperature resistance is not solved.

[0005] The Chinese patent (publication number CN109161790A) discloses a high-grade high-toughness pipe fitting steel used under acidic conditions and a production method thereof. The patent mainly relates to a pipe fitting steel for long-distance transportation in a low-temperature corrosion environment, but cannot meet the requirements of a high-temperature corrosion environment.

[0006] The Chinese patent (publication number CN108085593A) discloses a steel for an elbow pipe and a pipe fitting suitable for oil and gas transportation in a low-temperature environment and a manufacturing method thereof. The main problem solved by the patent is the strength and low-temperature toughness of the elbow pipe and the pipe fitting used in a low-temperature station.

[0007] The Chinese patent (publication number CN102912250A) discloses an economic low-yield ratio pipe fitting steel for oil and gas transportation and a production method thereof. The pipe fitting involved in the patent is mainly a pipe line steel material required for long-distance oil and gas transportation, the contact medium is crude oil and natural gas, and the external environment is a high-cold and earthquake zone. Therefore, the main problem solved by the patent is the normal temperature strength and low-temperature toughness of the material.

[0008] Chinese patent (publication number CN112267068A) discloses a high-temperature corrosion-resistant pipeline steel and its production process, which is corrosion-resistant by adding rare earth elements and externally spraying graphene. The process is not only expensive but also complex, and the beneficial effects do not reflect the high-temperature and corrosion-resistant effects.

[0009] Therefore, the existing pipe steel is mainly used for crude oil and natural gas transportation in the pre-refining sequence, and the environment is usually low-temperature environment. The easily-formed pipe steel suitable for 500 DEG C high-temperature and wet hydrogen sulfide environment is still in the state of invention blank. SUMMARY

[0010] The purpose of the present application is to provide a 500 DEG C high-temperature and wet hydrogen sulfide environment-resistant easily-formed refining pipe steel plate and its manufacturing method, to solve the problem that the existing pipeline steel material is difficult to withstand high temperature and corrosion.

[0011] To achieve the above-mentioned purpose, the present application provides a steel plate material resistant to 500 DEG C and hydrogen sulfide environment, the composition includes, by weight percentage: C: 0.06-0.10%, Si: 0.20-0.50%, Mn: 0.30-0.60%, Cr: 4.0-6.0%, Mo: 0.40-0.80%, V: 0.05-0.10%, N: 0.010-0.030%, and the balance is Fe.

[0012] The present application provides a preparation method of a steel plate material resistant to 500 DEG C and hydrogen sulfide environment, comprising the following steps:

[0013] 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 wire feeding amount is 3-5 m / t, after desulfurization, impurity removal treatment and vacuum degassing treatment, the molten steel is tapped;

[0014] S2, casting: the superheat degree of the tundish is controlled at 20-30 DEG C, and the blank drawing speed is 1.0-1.5 m / min; the cast blank is stacked and slowly cooled, and the stacking and slow cooling time is 36-48 h;

[0015] S3, heating: the heating temperature of the billet is controlled at 1200-1250 DEG C, so that the alloy elements are solid-solved and the original austenite grain growth is inhibited;

[0016] S4, rolling: the final temperature of rough rolling is controlled at 1000-1100 DEG C, the total deformation rate is 60-70%, and the intermediate billet thickness is 2.5-3.0 times the thickness of the finished steel plate; the starting temperature of finish rolling is set at 860-900 DEG C, and the final temperature of finish rolling is set at 820-850 DEG C, so that the cumulative deformation rate is 60-70%;

[0017] S5, heat treatment: first normalizing heat treatment to obtain bainite structure with small packet, then decompose bainite through tempering heat treatment, and after tempering, carry out stabilization treatment at 710-740℃ for 20-30h.

[0018] Preferably, each component includes by weight percentage: C: 0.06-0.10%, Si: 0.20-0.50%, Mn: 0.30-0.60%, Cr: 4.0-6.0%, Mo: 0.40-0.80%, V: 0.05-0.10%, N: 0.010-0.030%.

[0019] Preferably, control the weight percentage: P content ≤0.010%, S content ≤0.002%. Preferably, the desulfurization method includes blowing argon from the bottom of the ladle to stir the molten steel for desulfurization.

[0020] Preferably, the method of vacuum degassing treatment includes vacuumizing in the VD furnace for 10-15min, and after breaking the vacuum, blowing N2 until 0.010-0.030% is reached.

[0021] Preferably, the normalizing temperature is 920-950℃, the holding time is 1.0-3.0min / mm, and the cooling speed is 2-5℃ / s.

[0022] Preferably, the tempering temperature is 740-770℃, and the holding time is 3.0-7.0min / mm.

[0023] Preferably, the bainite structure with small packet has packet size of 300-400nm.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] (1) The present application is based on C, Mn and Si chemical elements, strictly controls harmful elements P and S, adds high content of Cr, Mo, V and N alloy elements to play solid solution strengthening and precipitation strengthening, obtains stable and dense tempered bainite structure, effectively prevents hydrogen from penetrating, and ensures the comprehensive mechanical properties and high temperature corrosion resistance of the steel for refining and bending pipe.

[0026] (2) The high temperature resistant and easy forming bending pipe steel plate obtained by the special process of smelting, rolling, high temperature normalizing, high temperature tempering and high temperature long time stabilization treatment has the following mechanical properties: tensile strength at 500℃ high temperature is 380-410MPa, transverse elongation after fracture is 34.0-36.5%, longitudinal elongation after fracture is 36.5-38.5%, Brinell hardness is 160-170, yield strength ratio is 0.73-0.75, D=2a, 180° transverse and longitudinal cold bending results show that the surface of the steel plate is intact without cracks.

[0027] (3) The steel prepared by the present application has a CSR% of 0 and does not break in a SSCC four-point bending test for 720 hours under continuous loading.

[0028] In summary, the steel prepared by the present application is resistant to 500℃ high temperature and corrosion environment and is easy to cold form, which is beneficial to support the long-term safe development of the large-scale and integration of China's refining equipment. DETAILED DESCRIPTION

[0029] The present application is further described below in conjunction with specific examples, but in no way limits the present application.

[0030] The instruments, reagents, materials, etc. involved in the following examples, if not specifically stated, are conventional instruments, reagents, materials, etc. already existing in the prior art, which can be obtained through regular commercial channels. The experimental methods, detection methods, etc. involved in the following examples, if not specifically stated, are conventional experimental methods, detection methods, etc. already existing in the prior art.

[0031] The present application provides a steel plate for refining pipe fittings which is easy to form and resistant to 500℃ and wet H2S environment, and the chemical composition range is: C 0.06-0.10%, Si 0.20-0.50%, Mn 0.30-0.60%, P≤0.010%, S≤0.002%, Cr 4.0-6.0%, Mo 0.40-0.80%, V 0.05-0.10%, N 0.010-0.030%, and the balance is Fe and unavoidable inclusions.

[0032] The reasons for limiting the amounts of alloying elements C, Si, Mn, P, S, Cr, Mo, V, and N in the steel plate are described in detail as follows:

[0033] C is the most important and inexpensive element for ensuring the strength of steel at room temperature and high temperature, and it improves the strength of the matrix in the form of solid solution and carbide, but too high carbon content will affect the welding performance of the steel, and too low carbon content cannot guarantee the use requirements of the steel in high temperature environment, therefore, the C content range is set to 0.06-0.10% in the present application.

[0034] Si is a beneficial element for resisting high temperature corrosion in steel, and at high temperature, it can form a dense SiO2 film on the surface of the steel with good protection. When the Si content in the steel is 0.20-0.50%, there is a more obvious oxidation resistance effect. However, when the silicon content exceeds 1.0%, it will cause the mechanical properties to deteriorate. Therefore, the silicon content in the steel is generally not more than 1.0%. Moreover, the co-alloying of silicon and molybdenum has a significant effect on improving the oxidation resistance of the steel, which can increase the oxidation resistance to 800℃, therefore, the Si content range is set to 0.20-0.50% in the present application.

[0035] Mn can increase the toughness, strength and hardness of steel, is a strong stable austenite element, can effectively reduce the decomposition rate of austenite, improve the hardenability of steel, high Mn content will enhance the temper brittleness, therefore the Mn content range of the application is set to 0.30-0.60%.

[0036] S and P are harmful elements in steel, increase the brittleness of steel, therefore the content of phosphorus and sulfur in steel should be reduced as much as possible, S≤0.002%, P≤0.010%.

[0037] Cr is a strong carbide forming element, it generates alloy carbide with C in steel, not only stable and dense, not only has a strong carbon element effect, prevent its combination with H2, generate CH4, lead to hydrogen embrittlement or hydrogen induced cracking, and the produced carbide is stable and dense, can effectively prevent the penetration of hydrogen and the separation of C.

[0038] In the application, Cr plays a role in high temperature strengthening while having high temperature corrosion resistance, ensuring the long time high temperature use requirement of pipe fittings, therefore the Cr content range of the application is set to 4.0-6.0%.

[0039] Mo is a strong carbide forming element, it forms stable alloy carbide with carbon element in steel, at the same time has excellent anti temper brittleness effect, plays an important role in high temperature resistance of bent pipe, too high content will affect the processing performance of steel, therefore the Mo content range of the application is set to 0.40-0.80%.

[0040] V is a refractory metal, the melting point is high 1910℃. Vanadium is an alloying element that narrows the γ-Fe zone and expands the α-Fe phase zone, the carbon and nitride formed in the crystal and grain boundary are dispersedly distributed, which obviously hinders the slip and climb of dislocation, thereby playing a role in high temperature thermal strength, too high content will increase the yield ratio of steel, which is not conducive to the forming and manufacturing of pipe fittings, therefore the V content range of the application is set to 0.05-0.10%.

[0041] N and carbon can be dissolved in iron to form interstitial solid solution, form stable nitride with Cr, V and other elements, play a role in strengthening, at the same time can improve the strength and impact toughness of high chromium steel, and the plasticity does not decrease, improve the high temperature enduring strength of steel, therefore the N content range of the application is set to 0.010-0.030%.

[0042] A kind of easy-to-form pipe fitting steel plate for refining used in 500℃ and wet H2S environment is manufactured as follows:

[0043] 1, electric arc furnace-LF furnace-VD furnace-continuous casting of slab-slab finishing-heating-rolling-straightening-heat treatment-performance evaluation.

[0044] 2、Smelting process: the component designed in the application contains 4.0%-6.0% Cr element and refractory molybdenum element, so the smelting needs to be carried out in an electric arc furnace with high temperature and high thermal efficiency, and high-quality scrap steel and molten iron are used as raw materials to ensure the purity of the steel, and the molten iron content is controlled at 50-70%. Since the carbon content in the application is 0.06-0.10%, chromium is added in the form of low-carbon chromium iron and metallic chromium, and the addition period is selected at the initial stage of reduction to prevent oxidation of chromium, and molybdenum iron is also added at the initial stage of reduction. The tapping temperature is controlled at 1600-1640℃, and the LF furnace is used for component fine adjustment, that is, adding alloying elements to meet the target value requirements of chemical composition, then adding vanadium iron, and feeding silicon-calcium wire at a speed of 2-4m / s and a feeding amount of 3-5m / t. The molten steel is further desulfurized by blowing argon from the bottom of the ladle to stir the molten steel, the inclusions in the steel are controlled at a very low level to ensure the purity of the steel and the high-temperature performance of the steel. Vacuum degassing treatment is carried out in VD, the vacuum time is 10-15min, and N2 blowing treatment is carried out after breaking the vacuum until the content reaches 0.010-0.030%, and then the steel is tapped.

[0045] 3、Casting process: the superheat of the tundish is 20-30℃, and the blank drawing speed is 1.0-1.5m / min. The cast blank is cooled in the stack, and the stack cooling time is 36-48h.

[0046] 4、Heating process: by controlling the heating process of the steel billet, the alloying elements are fully solid-solved, and the growth of the original austenite grains is effectively inhibited, and the slab heating temperature is controlled at 1200-1250℃, and the total heating time is 6-8 hours.

[0047] 5、Rolling process parameters: the final temperature of rough rolling is 1000-1100℃, the total deformation rate is 60-70%, and the intermediate billet thickness is 2.5-3.0 times the thickness of the finished steel plate; the starting temperature of finish rolling is 860-900℃, the final temperature of finish rolling is 820-850℃, and the cumulative deformation rate is 60-70%. The above parameters are designed based on the composition and performance requirements of the steel grade, and since the material is used in high-temperature environment, the rolling process is optimized to maximize the deformation and refine the rolling structure, so that the steel plate has excellent high-temperature strength after final heat treatment. The rolling thickness is 10-40mm.

[0048] 6. Heat treatment process: the original rolling structure is relatively refined by controlled rolling, but since the steel contains a large amount of alloying elements such as Cr, Mo, V, N, etc., in order to fully exert their synergistic strengthening effect, high temperature normalizing treatment is needed to completely solid-solution and homogenize the alloying elements, and after normalizing, a fine bainite structure with a packet size of 300-400 nm is obtained, wherein the normalizing temperature is 920-950℃, the holding time is 1.0-3.0 min / mm, and the cooling speed is 2-5℃ / s. Although bainite has excellent high-temperature strength, its poor plasticity and high hardness characteristics are extremely unfavorable for forming a bent pipe, and the present application promotes the decomposition of bainite by high-temperature tempering to obtain a(Fe, Mn, Cr, Mo) 23 C6 and VCN second phase bainite tempered structure, tempering temperature 740-770℃, holding time 3.0-7.0 min / mm. In order to further eliminate residual austenite and stress in the steel and prevent stress cracking during cold forming, the present application adds a long-time holding stabilization treatment process after high-temperature tempering treatment, i.e. holding at 710-740℃ for 20-30h, and the structure obtained under this process has the following three characteristics: first, the internal stress is completely eliminated. Second, the unstable residual austenite is completely converted into tempered bainite. Finally, more stable second phase particles are formed in the steel, and during this process, they undergo aggregation and growth to a stabilized state and no longer change, and there are no free C atoms in the steel to react with H2 generated in the medium to cause hydrogen-induced cracking hazards. The final structure obtained under this heat treatment process is fine, single and dense, and has excellent high-temperature resistance, corrosion resistance and cold forming characteristics.

[0049] Table 1 is the chemical composition of the steel plates prepared in Examples 1-10 of the present application, Table 2 is the process parameters of the steel plates prepared in Examples 1-10 of the present application, Table 3 is the mechanical properties of the steel plates prepared in Examples 1-10 of the present application, Table 4 is the hydrogen-induced cracking HIC test results at 500℃ of the steel plates prepared in Examples 1-10 of the present application (A solution), and Table 5 is the SSCC four-point bending test results at 500℃ of the steel plates prepared in Examples 1-10 of the present application.

[0050] Table 1, chemical composition of Examples 1-10 of the present application (wt, %)

[0051]

[0052] Table 2, production process parameters of Examples 1-10 of the present application

[0053]

[0054] Table 3, mechanical property test of Examples 1-10 of the present application

[0055]

[0056] Table 4, SSCC four-point bending test results of the steel plates of Examples 1-10 of the present application at 500°C

[0057]

[0058] Table 5, SSCC four-point bending test results of the steel plates of Examples 1-10 of the present application at 500°C

[0059]

[0060] According to the above results, it can be concluded that the steel plate for easy forming elbow pipe provided by the present application, which is resistant to 500°C high temperature and wet hydrogen sulfide working environment, has excellent properties such as transverse elongation of 34.0-36.5%, longitudinal elongation of 36.5-38.5%, Brinell hardness of 60-170, yield ratio of 0.73-0.75, and tensile strength at 500°C of 380-410 MPa, etc. The results of transverse and longitudinal cold bending of D=2a, 180° show that the surface of the steel plate is intact without cracks, the results of hydrogen-induced cracking HIC test (A solution) at 500°C show that the CSR / % is 0, and the results of SSCC four-point bending test show that the steel plate does not break after continuous loading for 720h, etc.

[0061] For any person skilled in the art, many possible changes and modifications, or modifications to equivalent embodiments, can be made to the technical solutions of the present application using the technical content disclosed above without departing from the scope of the technical solutions of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, as long as it does not depart from the content of the technical solutions of the present application, should still be within the scope of protection of the technical solutions of the present application.

Claims

1. A method for preparing a steel plate material resistant to 500℃ and hydrogen sulfide environment, characterized in that, Includes the following steps: 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. S2. Casting: Control the superheat of the tundish to 20-30℃, and the billet pulling speed to 1.0-1.5m / 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; 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; S4. Rolling: Control the rough rolling termination temperature to 1000-1100℃, the total deformation rate to 60-70%, and the thickness of the intermediate billet to be 2.5-3.0 times the thickness of the finished steel plate; set the finishing rolling start temperature to 860-900℃ and the finishing rolling termination temperature to 820-850℃, so that the cumulative deformation rate is 60-70%. S5. Heat treatment: First, normalizing heat treatment is performed to obtain a fine bainite structure of lath bundles. Then, tempering heat treatment is performed to decompose the bainite. After tempering, stabilization treatment is performed at 710-740℃ and held for 20-30 hours. The normalizing temperature is 920-950℃, the holding time is 1.0-3.0 min / mm, and the cooling rate is 2-5℃ / s; Tempering temperature 740-770℃, holding time 3.0-7.0 min / mm; The steel plate material resistant to 500℃ and hydrogen sulfide environment comprises, by weight percentage: C: 0.06-0.10%, Si: 0.20-0.50%, Mn: 0.30-0.60%, Cr: 4.0-6.0%, Mo: 0.40-0.80%, V: 0.05-0.10%, N: 0.010-0.030%, balance Fe.

2. The method for preparing the steel plate material resistant to 500℃ and hydrogen sulfide environment according to claim 1, characterized in that, The components added during smelting, by weight percentage, include: C: 0.06-0.10%, Si: 0.20-0.50%, Mn: 0.30-0.60%, Cr: 4.0-6.0%, Mo: 0.40-0.80%, V: 0.05-0.10%, and N: 0.010-0.030%.

3. The method for preparing the steel plate material resistant to 500℃ and hydrogen sulfide environment according to claim 1, characterized in that, Control weight percentage: P content ≤ 0.010%, S content ≤ 0.002%.

4. The method for preparing the steel plate material resistant to 500℃ and hydrogen sulfide environment according to claim 1, characterized in that, The desulfurization method includes blowing argon gas into the bottom of the ladle to agitate the molten steel for desulfurization.

5. The method for preparing the steel plate material resistant to 500℃ and hydrogen sulfide environment according to claim 1, characterized in that, The vacuum degassing process includes evacuating the vacuum in a VD furnace for 10-15 minutes, then blowing in N2 after breaking the vacuum until the concentration reaches 0.010-0.030%.

6. The method for preparing the steel plate material resistant to 500℃ and hydrogen sulfide environment according to claim 1, characterized in that, The lath bundles in the fine bainitic structure have a lath bundle size of 300-400 nm.

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