A kind of erosion-corrosion resistant steel for petrochemical bent pipe and its production method

Abstract

The present invention provides a erosion-corrosion resistant petrochemical pipe bending steel and a production method thereof. The chemical composition of the petrochemical pipe bending steel includes, by mass percentage, C: 0.08% to 0.12%, Si: 0.10% to 0.30%, Mn: 1.00% to 1.60%, P: ≤0.010%, S: ≤0.002%, Cr: 2.0% to 4.0%, W: 0.50% to 1.00%, Nb: 0.02% to 0.05%, V: 0. 02~0.08%, B: 0.002~0.005%, Ce: 0.02%~0.05%, N: 0.005%~0.010%, Alt: 0.015%~0.050%, the balance is Fe and inevitable impurities; the production method of petrochemical pipe bending steel includes molten steel smelting, casting, billet heating and rolling processes, and also includes a heat treatment process after rolling; the heat treatment process specifically includes high temperature quenching, quenching, tempering and stabilization treatment. The technical solution of the present invention solves the problems of existing steel for pipe bending, such as being unsuitable for simple high-frequency erosion and corrosive media, and expensive composition design.

Description

Technical Field

[0001] The invention relates to the technical field of production of steel for bent pipes, and in particular to an erosion-corrosion resistant steel for petrochemical bent pipes and a production method thereof. Background Art

[0002] There are crisscrossing and complex piping systems inside and between petrochemical plants. These piping systems are the main arteries of production and play a role in decomposition and cracking, process connection, and transportation of finished chemical products and semi-finished products in the entire production process, connecting the entire production line into a whole.

[0003] During operation, the pipeline system not only bears external conditions such as high temperature and loading pressure caused by the requirements of the refining process, but also has to resist the severe corrosion of cyclohexane acid on the equipment, especially at the bends, such as elbows, reducers, oil transfer lines, valves, etc., where corrosion and scouring work together. These complex factors seriously affect the long-term and safe production of the elbow parts. Under the long-term, high-frequency scouring corrosion and high-load impact of petroleum products, the pipe wall will be thinned to varying degrees; in addition, the plastic deformation of the material of the elbow is large and the deformation is uneven during the processing and forming process, which can easily cause stress concentration in the elbow. Under the influence of these two factors, the elbow has become the weakest link in the entire chemical pipeline system. There is a great risk of corrosion and perforation in long-term operation, which brings huge hidden dangers to production safety.

[0004] The existing steel for pipe bending is mostly used for long-distance oil and gas transportation or marine environment, and is not suitable for the simple high-frequency erosion and corrosive media in the pipeline system of oil refineries. It also has the problems of expensive component design, simple production method and lack of heat treatment stabilization process. Summary of the invention

[0005] Based on the above technical problems that the existing steel for bent pipes is not suitable for simple high-frequency erosion and corrosion media, the composition design is expensive, the production method is simple and lacks heat treatment stabilization process, and a new chemical composition design and a specific production method are provided. On the basis of low C and medium Mn, the harmful elements P and S are strictly controlled, and Cr, W, B, Alt alloy elements, Nb, V micro-alloy elements and Ce elements are added at the same time, and a specific smelting, rolling and heat treatment production method is used to obtain erosion and corrosion resistant petrochemical bent pipe steel, which meets the requirements of oil refineries for safe and long-term service of pipeline systems.

[0006] The technical means adopted by the present invention are as follows:

[0007] A kind of erosion-corrosion resistant petrochemical pipe bending steel, the chemical composition by mass percentage includes:

[0008] C: 0.08% ~ 0.12%, Si: 0.10% ~ 0.30%, Mn: 1.00% ~ 1.60%, P: ≤ 0.010%, S: ≤ 0.002%, Cr: 2.0% ~ 4.0%, W: 0.50% ~ 1.00%, Nb: 0.02% ~ 0.05%, V: 0.02 ~ 0.08%, B: 0.002 ~ 0.005%, Ce: 0.02% ~ 0.05%, N: 0.005% ~ 0.010%, Alt: 0.015% ~ 0.050, the balance is Fe and unavoidable impurities.

[0009] Furthermore, the petrochemical pipe bending steel has a martensitic tempered structure with a grain size of 9.0 to 10.0, including borides, tungsten intermetallic compounds, Cr 6 C and (Nb, V) (C, N) complex phase precipitates.

[0010] Furthermore, the steel for petrochemical bent pipe has a transverse elongation of 31.5-34.0%, a longitudinal elongation of 33.0-35.5%, a Brinell hardness of 180-190, and a yield strength ratio of 0.80-0.82.

[0011] The present invention also provides a production method for producing the erosion-corrosion resistant petrochemical pipe bending steel, comprising molten steel smelting, casting, billet heating and rolling processes, and also comprising a heat treatment process after rolling;

[0012] The heat treatment process specifically includes high temperature quenching, quenching, tempering and stabilization treatment;

[0013] High temperature quenching temperature is 930-980℃, holding time is 1.0-2.0min / mm, cooling rate is 20-30℃ / s;

[0014] The quenching temperature is 870-920°C, the holding time is 0.5-1.0 min / mm, and the cooling rate is 30-50°C / s;

[0015] The tempering temperature is 670-720°C and the holding time is 2.0-4.0 min / mm;

[0016] The stabilization treatment temperature is 500-600°C and the insulation time is 20-30h.

[0017] Furthermore, molten steel smelting includes converter smelting and refining:

[0018] During converter smelting, the proportion of molten iron is controlled at 75-85%, dephosphorization and decarburization are carried out separately in converter, the dephosphorization time is controlled at 8-10 minutes, and the decarburization time is controlled at 9-12 minutes, and the phosphorus content is finally controlled within 0.010%;

[0019] Deep desulfurization treatment is carried out in the LF refining furnace to control the sulfur content below 0.002%. Ce wire is fed into the steel in the later stage of refining. The wire feeding speed is 250-350m / min and the wire feeding depth is 1.5-2.5m below the slag layer. The thickness of the generated slag layer is 50-80mm. Degassing is completed in the RH furnace. The net circulation time is 10-15min and the calming time before pouring is 3-5min.

[0020] Furthermore, during the casting process: the superheat is 20-30°C, the stacking slow cooling time is 24-48h, and the stacking is performed below 300°C.

[0021] Furthermore, the billet heating temperature is controlled at 1220-1280° C., and the total heating time is 4.0-6.0 h.

[0022] Furthermore, in the rolling process: the starting rolling temperature in the rough rolling stage is 1050-1150°C, the cumulative reduction rate is ≥65%, and the intermediate billet thickness is 2.0-3.0 times the finished steel plate thickness; the starting rolling temperature in the finishing rolling stage is 910-950°C, the final rolling temperature is 850-900°C, and the cumulative deformation rate is ≥50%.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The erosion-corrosion resistant petrochemical pipe bending steel provided by the present invention strictly controls the content of harmful elements P and S on the basis of C, Si and Mn components, and obtains a martensitic tempered structure with a grain size of 9.0 to 10.0 by composite addition of Cr, W, Nb, V, B, Ce and N alloy elements combined with a specific production method, wherein the total amount of 15 to 100 nm boride, tungsten intermetallic compounds, M 6 C, (Nb, V) (C, N) complex phase precipitates and other stable and dense hard second phases ensure the comprehensive performance requirements of the bent pipe steel plate. The petrochemical bent pipe steel provided by the present invention has excellent erosion and corrosion resistance, and the steel plate forming process performance is excellent, which is suitable for the long-term erosion and corrosion environment in the petrochemical environment.

[0025] 2. The production method of erosion-corrosion resistant petrochemical pipe bending steel provided by the present invention has the following mechanical properties: transverse elongation after fracture of 31.5-34.0%, longitudinal elongation after fracture of 33.0-35.5%, Brinell hardness of 180-190, yield strength ratio of 0.80-0.82, and transverse and longitudinal cold bending results of D=2a, 180° show that the steel plate surface is intact and has no cracks.

[0026] Based on the above reasons, the present invention can be widely promoted in the field of steel for pipe bending. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The present invention provides a erosion-corrosion resistant petrochemical elbow steel, the chemical composition of which includes, by mass percentage:

[0029] C: 0.08% ~ 0.12%, Si: 0.10% ~ 0.30%, Mn: 1.00% ~ 1.60%, P: ≤ 0.010%, S: ≤ 0.002%, Cr: 2.0% ~ 4.0%, W: 0.50% ~ 1.00%, Nb: 0.02% ~ 0.05%, V: 0.02 ~ 0.08%, B: 0.002 ~ 0.005%, Ce: 0.02% ~ 0.05%, N: 0.005% ~ 0.010%, Alt: 0.015% ~ 0.050, the balance is Fe and unavoidable impurities.

[0030] The components of the erosion-corrosion resistant petrochemical elbow provided by the present invention include:

[0031] C is an important and cheap strengthening element. The present invention adds a certain amount of C, firstly, utilizes its solid solution strengthening effect to improve the matrix strength of the elbow; secondly, utilizes the precipitation strengthening effect of C and elements such as Cr, W, Nb, and V to form stable high-hardness carbides to improve the erosion corrosion resistance of the elbow. However, too high a carbon content will lead to poor weldability and processing formability of the elbow, so the present invention sets the C content range to 0.08% to 0.12%;

[0032] Mn mainly plays a role in solid solution strengthening, increases the strength and hardness of the elbow steel matrix, is an element that strongly stabilizes austenite, can effectively reduce the decomposition rate of austenite, and improves the hardenability of steel. However, a high Mn content will enhance the temper brittleness of steel, so it is necessary to control the upper limit of Mn. Therefore, the present invention sets the Mn content range to 1.00% to 1.60%;

[0033] Si: In the present invention, a certain amount of Si is added to play the role of a deoxidizer during steelmaking. Silicon can also form a dense silicon dioxide protective film to improve the erosion corrosion resistance. However, when the Si element content is high, the hardness of the weld and the heat-affected zone is high. At the same time, the Si element is easy to segregate at the grain boundary, promote the formation of intergranular cracks, and increase the corrosion risk of the elbow. Therefore, the present invention sets the Si content range to 0.10% to 0.30%;

[0034] P and S are harmful elements in the present invention. P is easy to segregate at the austenite grain boundary, which weakens the interatomic bonding force at the grain boundary of the matrix material, resulting in high temper brittleness of the material. S forms MnS and FeS non-metallic inclusions distributed in bands in the steel, which affects the purity of the steel. Therefore, it must be strictly controlled. The present invention sets the P content range to ≤0.010% and the S content range to ≤0.002%.

[0035] Cr is a strong carbide-forming element. In the present invention, Cr is combined with Fe, Mn and W to form nano-scale alloy carbides, which form a stable organizational structure with the main phase of the present invention, ensure the matrix strength and improve the erosion corrosion resistance. Therefore, the present invention sets the Cr content range to 2.0% to 4.0%;

[0036] The addition of tungsten W partially melts into the matrix to play a role of solid solution strengthening. More importantly, it forms intermetallic compounds in the steel, thereby significantly improving the tempering stability, thermal strength and wear resistance of the steel. However, excessive addition is not conducive to the forming and manufacturing of pipe fittings. Therefore, the present invention sets the W content range to 0.50% to 1.00%;

[0037] Nb is a strong carbon and nitride forming element, and forms a dispersed precipitate phase at the grain boundary, which has a significant hindering effect on the slip and climb of dislocations. At the same time, its grain refinement effect can improve the erosion corrosion resistance and anisotropy, and improve the large plastic deformation performance of the elbow. Therefore, the present invention sets the Nb content range to 0.02% to 0.05%;

[0038] V can form high-temperature stable carbon and nitrides, which are dispersed in the crystal and at the grain boundary, and have a significant hindering effect on the slip and climb of dislocations, thereby enhancing the matrix strength and hardness of the steel and ensuring the erosion and corrosion resistance of the steel. However, if the content is too high, the yield strength ratio of the steel will be increased, which is not conducive to the forming and manufacturing of pipe fittings. Therefore, the present invention sets the V content range to 0.02-0.08%;

[0039] The addition of boron increases the hardenability of steel and utilizes the high-hardness boride formed by boron to improve the erosion corrosion resistance of the bent pipe steel. However, a boron content exceeding 0.007% will cause hot brittleness of the steel and affect the pipe forming processing performance. Therefore, the present invention controls the boron content range to 0.002-0.005%.

[0040] Ce has a strong affinity with harmful elements such as oxygen, sulfur, phosphorus, hydrogen, and nitrogen in molten steel. After forming a stable rare earth compound, its own density is less than that of the molten steel, and it floats up to form slag, which plays a role in purifying the molten steel. In addition, by controlling the morphology of inclusions, the long strip-shaped manganese sulfide inclusions are changed into spherical sulfides or oxides, so that the sulfide morphology is completely controlled and the anisotropy of the steel is improved; in addition, the segregation of Ce at the grain boundary can inhibit the segregation of sulfur, phosphorus and other low-melting point inclusions at the grain boundary, and form high-melting point compounds with these inclusions, reducing the harmful effects of low-melting point inclusions, reducing the tendency of intergranular cracks to form and expand, improving the purity of steel, and ensuring the comprehensive performance of steel; but Ce is a rare earth strategic resource and should not be added too much, so the present invention sets the Ce content range to 0.02% to 0.05%;

[0041] N: The present invention mainly utilizes N to form stable nitrides with elements such as V and Nb to play a precipitation strengthening role, and can also improve the strength and toughness of steel without reducing plasticity. Therefore, the present invention sets the N content range to 0.005% to 0.010%;

[0042] Alt aluminum in steel mainly plays the role of deoxidation and grain refinement; excessive aluminum will promote the graphitization tendency of steel when used at medium and high temperatures for a long time, so the present invention sets the Alt content range to 0.015% to 0.050%.

[0043] Furthermore, the petrochemical pipe bending steel has a martensitic tempered structure with a grain size of 9.0 to 10, including 2 to 5% of total amount and a size of 15 to 100 nm of boride, tungsten intermetallic compounds, Cr 6 Stable, dense and hard second phases such as C and (Nb, V) (C, N) multiphase precipitates.

[0044] Furthermore, the transverse elongation of the petrochemical bent pipe steel is 31.5-34.0%, the longitudinal elongation is 33.0-35.5%, the Brinell hardness is 180-190, the yield strength ratio is 0.80-0.82, and the transverse and longitudinal cold bending results of D=2a and 180° show that the steel plate surface is intact and has no cracks.

[0045] In order to obtain the comprehensive mechanical properties and corrosion resistance of the erosion-corrosion resistant petrochemical pipe bending steel of the present invention, it is necessary not only to add necessary alloy elements, but also to obtain a stable organizational structure through an organic combination of heat treatment processes. The present invention also provides a production method for producing the erosion-corrosion resistant petrochemical pipe bending steel, including molten steel smelting, casting, billet heating and rolling processes;

[0046] It also includes a heat treatment process after rolling; the heat treatment process specifically includes high temperature quenching, quenching, tempering and stabilization treatment;

[0047] High temperature quenching temperature is 930-980℃, holding time is 1.0-2.0min / mm, cooling rate is 20-30℃ / s;

[0048] The quenching temperature is 870-920°C, the holding time is 0.5-1.0 min / mm, and the cooling rate is 30-50°C / s;

[0049] The tempering temperature is 670-720°C and the holding time is 2.0-4.0 min / mm;

[0050] The stabilization treatment temperature is 500-600°C and the insulation time is 20-30h.

[0051] Since the rolled steel plate has defects such as coarse, uneven, segregated and carbide chain distribution, it is extremely unfavorable for the petrochemical pipe bending steel to obtain fine grains, high dispersion of nano-scale second phase particles, excellent forming and erosion corrosion resistance. Therefore, it is necessary to adjust the structure through heat treatment to obtain the erosion corrosion resistant petrochemical pipe bending steel of the present invention. For this reason, the steel of the present invention adds a heat treatment process of high temperature quenching + quenching + tempering + stabilization treatment after rolling:

[0052] The present invention designs the high temperature quenching temperature to be 930-980°C, the heat preservation is 1.0-2.0min / mm, and the cooling rate is 20-30°C / S. This is because the addition of easily segregated elements and the existence of selective crystallization will cause uneven composition of the steel billet. In the hot rolling process, the alloy compound cannot be fully dissolved and homogenized, resulting in coarse and uneven structure of the steel plate and carbides after rolling. It is necessary to fully dissolve the alloy elements at the austenitizing temperature, rearrange the crystal structure, and obtain a refined lath martensite structure.

[0053] The purpose of secondary quenching is to dissolve the residual austenite in the first quenching again and completely transform it. The quenching temperature is designed to be 870-920℃, the holding time is 0.5-1.0min / mm, the cooling rate is 30-50℃ / S, and it is quickly cooled to room temperature. Since the first quenching is carried out on the basis of the grain after quenching and refinement of the steel, the original quenching structure is relatively small. After low temperature and short-time holding, the grains have not grown yet. After rapid cooling, a small and uniform single bainite structure is obtained, and the density of the structure is significantly improved;

[0054] However, since the martensite after quenching has the characteristics of high hardness, poor plasticity and low stability, it is not conducive to forming and making pipes. Therefore, it is necessary to further control the organization through tempering heat treatment. The present invention designs a tempering temperature of 670-720°C and a holding time of 2.0-4.0 min / mm. Under this process, the martensite organization obtained by quenching is fully restored and softened, and the boride, tungsten intermetallic compounds, Cr 6C, (Nb, V) (C, N) complex phase precipitates and other second phases in steel are fully precipitated at this stage, but boride, tungsten intermetallic compounds and Cr 6 The stability of hard second phases such as C is relatively poor, which is not conducive to long-term erosion and corrosion performance. Therefore, further stabilization treatment is required, that is, keeping the temperature within the range of 500-600℃ for 20-30h;

[0055] By adopting the post-rolling heat treatment process provided by the present invention, a martensitic tempered structure with fine grains can be obtained, wherein the structure contains dispersed and precipitated stable hard second phase boride, tungsten intermetallic compounds, Cr 6 C and (Nb, V)(C, N) complex phase precipitates which play a precipitation strengthening role, thereby ensuring that the steel plate has excellent strength, elongation after fracture, cold bending performance, appropriate hardness and erosion corrosion resistance.

[0056] Furthermore, the specific process of the production method of the erosion-corrosion resistant petrochemical elbow steel is: molten iron pretreatment - converter dephosphorization - converter decarburization - refining outside the furnace (LF+RH) - slab continuous casting - stacking slow cooling - ingot cleaning - billet heating - finished product rolling - hot straightening - slow cooling - high temperature quenching - quenching - tempering - stabilization treatment - comprehensive performance evaluation.

[0057] Furthermore, molten steel smelting includes converter smelting and refining:

[0058] During the converter smelting process, molten iron and high-quality scrap steel are used as smelting raw materials, with the proportion of molten iron controlled at 75-85%. At the same time, in order to effectively reduce the content of harmful elements P, dephosphorization and decarburization are carried out separately in the converter. The dephosphorization time is controlled at 8-10 minutes, and the decarburization time is controlled at 9-12 minutes. Finally, the phosphorus content is controlled within 0.010%;

[0059] Deep desulfurization treatment is carried out in the LF refining furnace to control the sulfur content below 0.002%. Ce wire is fed into the steel in the later stage of refining. The wire feeding speed is 250-350m / min and the wire feeding depth is 1.5-2.5m below the slag layer. This treatment changes the morphology of non-metallic inclusions, forming fine Ce sulfide and oxide non-metallic inclusion points, increasing the equiaxed ratio of the steel billet while purifying the steel quality, improving the purity and the hydrogen resistance of the steel. The thickness of the generated slag layer is 50-80mm; degassing is completed in the RH furnace, the net cycle time is 10-15min, and the calming time before pouring is 3-5min.

[0060] Furthermore, after breaking the vacuum, a continuous casting machine is used for casting. During the casting process: the superheat is 20-30°C, the ingots are stacked for slow cooling after coming off the production line, the stacking slow cooling time is 24-48h, and the ingots are unstackered below 300°C to prevent cracks inside the ingots due to rapid cooling.

[0061] Furthermore, by controlling the parameters of the billet heating process to ensure sufficient solid solution of alloy elements and dissolution of large-sized eutectic carbides, while effectively inhibiting the growth of original austenite grains, the billet heating temperature is controlled at 1220-1280°C, and the total heating time is 4.0-6.0h.

[0062] Furthermore, in the rolling process: the starting rolling temperature in the rough rolling stage is 1050-1150°C, the cumulative reduction rate is ≥65%, and the intermediate billet thickness is 2.0-3.0 times the finished steel plate thickness; the starting rolling temperature in the finishing rolling stage is 910-950°C, the final rolling temperature is 850-900°C, and the cumulative deformation rate is ≥50%; the rolled structure is refined through two-stage rolling to obtain a 20-50 mm thick bent pipe steel plate.

[0063] The erosion-corrosion resistant petrochemical pipe bending steel and its production method provided by the present invention will be specifically described below in conjunction with Examples 1 to 10. The specific composition of the petrochemical pipe bending steel and the specific control parameters of the production method corresponding to each embodiment are shown in Tables 1-3. Tables 4-5 show the mechanical property test results, internal organizational structure and grain size grade of the petrochemical pipe bending steel corresponding to each embodiment.

[0064] Table 1 Chemical composition of steel for petrochemical elbow corresponding to Examples 1 to 10

[0065]

[0066] Table 2 Production process parameters of steel for petrochemical elbow corresponding to Examples 1 to 10

[0067]

[0068] Table 3 Heat treatment process parameters of petrochemical elbow steel corresponding to Examples 1 to 10

[0069]

[0070] Table 4 Mechanical properties test results of petrochemical elbow steel corresponding to Examples 1 to 10 (1. Surface Brinell hardness; 2. a is the sample thickness, D is the bending head diameter)

[0071]

[0072] Table 5 Organization structure and grain size grade of steel for petrochemical elbow corresponding to Examples 1 to 10

[0073]

[0074] According to Tables 4-5, it can be concluded that the erosion-corrosion resistant petrochemical pipe bending steel provided by the present invention has a transverse elongation of 31.5-34.0%, a longitudinal elongation of 33.0-35.5%, a Brinell hardness of 180-188, a yield strength ratio of 0.80-0.82, and the transverse and longitudinal cold bending results of D=2a and 180° show that the steel plate surface is intact without cracks; and the erosion-corrosion resistant petrochemical pipe bending steel provided by the present invention, on the basis of C, Si, and Mn components, strictly controls the content of harmful elements P and S, and obtains a martensitic tempered structure with a grain size of 9.0-10.0 by compositely adding Cr, W, Nb, V, B, Ce and N alloy elements combined with a specific production method, wherein the total amount of 15-100nm boride, tungsten intermetallic compounds, M 6 C, (Nb, V) (C, N) complex phase precipitates. It has excellent erosion corrosion resistance and excellent steel plate forming process performance, and is suitable for long-term erosion corrosion environment in petrochemical environment.

[0075] The present invention provides a method for producing erosion-corrosion resistant petrochemical pipe bending steel. The obtained erosion-corrosion resistant petrochemical pipe bending steel has the following mechanical properties: transverse elongation after fracture of 31.5-34.0%, longitudinal elongation after fracture of 33.0-35.5%, Brinell hardness of 180-190, yield strength ratio of 0.80-0.82, and transverse and longitudinal cold bending results of D=2a and 180° show that the steel plate surface is intact and has no cracks.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A erosion-corrosion resistant petrochemical pipe elbow steel, characterized in that: The chemical composition by mass percentage includes: C: 0.08% ~ 0.12%, Si: 0.10% ~ 0.30%, Mn: 1.00% ~ 1.60%, P: ≤ 0.010%, S: ≤ 0.002%, Cr: 2.0% ~ 4.0%, W: 0.50% ~ 1.00%, Nb: 0.02% ~ 0.05%, V: 0.02 ~ 0.08%, B: 0.002 ~ 0.005%, Ce: 0.02% ~ 0.05%, N: 0.005% ~ 0.010%, Alt: 0.015% ~ 0.050, the balance is Fe and unavoidable impurities; The petrochemical pipe bending steel has a tempered martensitic structure with a grain size of 9.0 to 10.0, including borides, tungsten intermetallic compounds, Cr6C and (Nb, V)(C, N) complex phase precipitates with a total amount of 2 to 5% and a size of 15 to 100 nm; The production method of the erosion-corrosion resistant petrochemical elbow steel includes a heat treatment process after rolling; the heat treatment process specifically includes high-temperature quenching, quenching, tempering and stabilization treatment; High temperature quenching temperature is 930-980℃, holding time is 1.0-2.0min / mm, cooling rate is 20-30℃ / s; The quenching temperature is 870-920°C, the holding time is 0.5-1.0 min / mm, and the cooling rate is 30-50°C / s; The tempering temperature is 670-720°C and the holding time is 2.0-4.0 min / mm; The stabilization treatment temperature is 500-600°C and the insulation time is 20-30h.

2. The erosion-corrosion resistant petrochemical pipe elbow steel according to claim 1, characterized in that: The steel for petrochemical bent pipe has a transverse elongation of 31.5-34.0%, a longitudinal elongation of 33.0-35.5%, a Brinell hardness of 180-190, and a yield strength ratio of 0.80-0.

82.

3. A method for producing the erosion-corrosion resistant petrochemical pipe bending steel as claimed in any one of claims 1 to 2, comprising the steps of molten steel smelting, casting, billet heating and rolling, characterized in that: It also includes a heat treatment process after rolling; The heat treatment process specifically includes high temperature quenching, quenching, tempering and stabilization treatment; High temperature quenching temperature is 930-980℃, holding time is 1.0-2.0min / mm, cooling rate is 20-30℃ / s; The quenching temperature is 870-920°C, the holding time is 0.5-1.0 min / mm, and the cooling rate is 30-50°C / s; The tempering temperature is 670-720°C and the holding time is 2.0-4.0 min / mm; The stabilization treatment temperature is 500-600°C and the insulation time is 20-30h.

4. The method for producing erosion-corrosion resistant petrochemical pipe bend steel according to claim 3, characterized in that: Molten steel smelting includes converter smelting and refining: During converter smelting, the proportion of molten iron is controlled at 75-85%, dephosphorization and decarburization are carried out separately in converter, the dephosphorization time is controlled at 8-10 minutes, and the decarburization time is controlled at 9-12 minutes, and the phosphorus content is finally controlled within 0.010%; Deep desulfurization treatment is carried out in the LF refining furnace to control the sulfur content below 0.002%. Ce wire is fed into the steel in the later stage of refining. The wire feeding speed is 250-350m / min and the wire feeding depth is 1.5-2.5m below the slag layer. The thickness of the generated slag layer is 50-80mm. Degassing is completed in the RH furnace. The net circulation time is 10-15min and the calming time before pouring is 3-5min.

5. The method for producing erosion-corrosion resistant petrochemical pipe bend steel according to claim 3, characterized in that: During the casting process, the superheat is 20-30℃, the stacking slow cooling time is 24-48h, and the stacking is unstacking below 300℃.

6. The method for producing erosion-corrosion resistant petrochemical pipe bend steel according to claim 3, characterized in that: The billet heating temperature is controlled at 1220-1280°C, and the total heating time is 4.0-6.0h.

7. The method for producing erosion-corrosion resistant petrochemical pipe bend steel according to claim 3, characterized in that: In the rolling process: the starting rolling temperature in the rough rolling stage is 1050-1150°C, the cumulative reduction rate is ≥65%, the intermediate billet thickness = 2.0-3.0 times the finished steel plate thickness; the starting rolling temperature in the finishing rolling stage is 910-950°C, the final rolling temperature is 850-900°C, and the cumulative deformation rate is ≥50%.

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