Acid-resistant steel, acid-resistant steel pipe, and method for manufacturing the same

Abstract

The application discloses an acid corrosion resistant steel, an acid corrosion resistant steel pipe and a preparation method thereof. The acid corrosion resistant steel comprises the following components in percentage by weight: C 0.15-0.32%, Si≤0.4%, Mn≤0.7%, Cr 0.4-0.8%, Mo 0.4-0.8%, V 0.05-0.08%, Nb 0.015-0.045%, Al 0.008-0.050%, S≤0.003%, P≤0.01%, Cu 0.3-0.6%, Cu+Mo: 0.80-1.35%, and Cu / Mo 0.4-0.82%, ΣAs+Sn+Pb+Sb+Bi≤0.035%, and the balance is iron and inevitable impurities. By balancing the chemical components of the acid corrosion resistant steel, the application solves the dual contradictory relationship between high strength and high toughness, high strength and SSC resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pipeline steel for oil and gas exploitation, in particular to an acid corrosion resistant steel, an acid corrosion resistant steel pipe and a preparation method thereof. BACKGROUND

[0002] In the field of oil and gas production, with the depletion of conventional shallow well oil and gas resources, the development of high pressure deep wells with high corrosion has been increasing. The deepening of oil and gas wells requires oil well steel pipes to have high strength and high toughness. On the other hand, most oil and gas wells contain hydrogen sulfide (H2S) which has corrosion, so the corrosion resistance of the steel pipe is also improved.

[0003] In the acid environment containing H2S, sulfide stress cracking (SSC) of steel is a difficult problem. The 110 ksi grade steel pipe, i.e. the steel pipe with a yield strength greater than 758 Mpa, has been mature, but most of them are low alloy steels with high content of alloy elements, including more Cr, Mo, V alloy elements for composite strengthening, the main disadvantage is that due to the high content of Mo, the cost of the material is high, and the requirements for smelting, rolling and heat treatment in the manufacturing process of the material are high.

[0004] The prior art has made a lot of research: for example, CN101082112A provides a 110Ks grade anti-CO2, H2S corrosion oil well pipe and manufacturing method, the steel grade component for the casing is C 0.20-0.35, Si 0.10-1.0, Mn 0.1-01.0, Cr 1.0-2.5, Mo 0.1-1.0, Ni 0.10-1.0, Nb 0.01-0.4, Cu 0.10-1.0, Al 0.01-0.10, the rest is Fe and inevitable impurities, and the final product is a tempered sorbite structure. The defect of the technology is that the strength provided by the sorbite structure is low, the oil casing steel grade cannot reach 110ksi, and the alloy content of the technology is high, the manufacturing cost is high. For example, CN100419111C (anti-hydrogen sulfide stress corrosion oil well pipe and its production method) provides a tempered martensite casing, the steel grade component for the casing is C 0.24-0.32, Si 0.17-0.40, Mn 0.40-0.70, Cr 0.80-1.20%, Mo 0.15-0.40%, S≤0.010%, P≤0.015%, Ni≤0.20%, Ti 0-0.06, the balance is Fe. A quenching and high temperature tempering heat treatment process is used to form a tempered martensite structure. The defects of the technology mainly have two points: one is that no grain refining element is added, and the high C content is easy to form coarse MC type carbide with Cr, which cannot guarantee good impact toughness and good SSC resistance; the second is that the total amount of alloying elements is low, and the final product cannot guarantee high content of tempered martensite structure, so that the casing steel grade cannot reach more than 110Ksi. The commonly disclosed 110Ksi anti-sulfur casing generally uses medium carbon, 0.2-0.7% Mn, Mo: 0.2-1.2%, Cr 0.5-1.2%, and a certain amount of V and Nb, and realizes the strength and toughness and anti-H2S corrosion by multi-alloy combination. These materials all have high cost, and there is a contradiction between tensile property and toughness, and the SSC resistance is unstable. SUMMARY

[0005] The present application aims to provide a kind of acid corrosion resistant steel, acid corrosion resistant steel pipe and preparation method thereof, to solve the problem that the steel for oil well pipe in prior art cannot meet high strength and high toughness, high strength and SSC resistance simultaneously.

[0006] To achieve the above object, according to one aspect of the present application, there is provided an acid corrosion resistant steel. The acid corrosion resistant steel comprises, in terms of weight percentage, C 0.15-0.32%, Si≤0.4%, Mn≤0.7%, Cr 0.4-0.8%, Mo 0.4-0.8%, V 0.05-0.08%, Nb 0.015-0.045%, Al 0.008-0.050%, S≤0.003%, P≤0.01%, Cu 0.3-0.6%, Cu+Mo: 0.80-1.35%, and Cu / Mo 0.4-0.82%, ΣAs+Sn+Pb+Sb+Bi≤0.035%, and the balance being iron and inevitable impurities.

[0007] Further, the acid corrosion resistant steel comprises, in terms of weight percentage, C 0.25-0.31%, Si≤0.4%, Mn 0.35-0.6%, Cr 0.5-0.8%, Mo 0.5-0.7%, V 0.05-0.08%, Nb 0.025-0.040%, Al 0.008-0.050%, S≤0.003%, P≤0.01%, Cu 0.35-0.5%, Cu+Mo: 0.85-1.25%, and Cu / Mo 0.45-0.8%, ΣAs+Sn+Pb+Sb+Bi≤0.025%, and the balance being iron and inevitable impurities.

[0008] Further, the acid corrosion resistant steel has a yield strength at room temperature of 758-828 MPa, a minimum tensile strength of 793 MPa, an average hardness value of not more than 29 HRC, a single point measurement maximum hardness value of 30 HRC, and a full-size minimum impact energy at 0°C of 80 J in the transverse direction and 100 J in the longitudinal direction.

[0009] Further, the acid corrosion resistant steel has a microstructure of more than 95% tempered martensite.

[0010] Further, the acid corrosion resistant steel has a resistance to hydrogen sulfide stress cracking in a sulfur jacket according to ANSI-NACETM0177, using Method A, a hydrogen sulfide stress corrosion test in A solution, a 6.35 mm standard test sample, and a stress of 644 MPa for at least 720 hours without breaking.

[0011] According to another aspect of the present application, there is provided an acid corrosion resistant steel pipe. The acid corrosion resistant steel pipe is made of any of the acid corrosion resistant steels described above.

[0012] According to another aspect of the present application, a method for preparing the acid corrosion resistant steel pipe is provided. The method comprises: S1, adding scrap steel, pig iron and ingredients into an electric furnace for primary refining, then carrying out secondary refining, calcium treatment, vacuum degassing treatment, arc continuous casting, pipe blank cooling and finishing to obtain a pipe blank; wherein the amount of scrap steel, pig iron and ingredients satisfies the components and the mass percentage of each component of the acid corrosion resistant steel in claim 1; S2, rolling the pipe blank obtained in S1 into a seamless steel pipe; and S3, carrying out quenching and tempering heat treatment on the seamless steel pipe obtained in S2.

[0013] Further, S2 comprises pipe blank inspection and grinding, saw cutting and blanking, ring furnace heating, conical roller piercing, pipe rolling, on-line normalizing, step furnace reheating, sizing and cold bed cooling to obtain the seamless steel pipe.

[0014] Further, the on-line normalizing is to refine the grains in the hot-rolled state, the grain size of the hot-rolled state is greater than or equal to 7, and the grains are uniform; preferably, in S2, the rolling ratio of rolling is greater than 3, more preferably the rolling ratio of rolling is 5-10; preferably, the temperature of primary rolling is controlled to be 1100-1150℃, and the temperature of finish rolling is controlled to be 830-950℃.

[0015] Further, the heat treatment in S3 comprises: water quenching after heating the seamless steel pipe, the quenching temperature is 880-940℃, and the holding time is 30-90min; cooling the austenitized seamless steel pipe to room temperature to quench, preferably the cooling speed is 35℃ / s-80℃ / s; then high temperature tempering, the tempering temperature is 660-720℃, the tempering holding time is 40-100min; and finally hot straightening, the straightening end temperature is greater than or equal to 535℃.

[0016] By reducing the Mo content and increasing the Cu content on the basis of the existing steel grade, the technical scheme of the present application can change the metallographic structure of the acid corrosion resistant steel, thereby improving the SSC resistance of the acid corrosion resistant steel; and by increasing the precipitated phase of Cu, on one hand, the precipitated phase plays a role of precipitation strengthening, and on the other hand, the precipitated phase can also act as a “hydrogen trap” to increase the density of the “hydrogen trap”, thereby capturing the hydrogen entering the material and making the hydrogen uniformly and diffusely distributed in the material matrix, so as to inhibit the diffusion and aggregation of hydrogen, and further improve the SSC resistance of the acid corrosion resistant steel of the present application; at the same time, by adding Cu element in the chemical composition, a “film” barrier hindering the entry of hydrogen can be formed on the surface of the material, thereby improving the SSC resistance of the acid corrosion resistant steel of the present application. By forming carbide with the Nb element and C, the grains can be refined, and the strength and toughness of the acid corrosion resistant steel can be improved. By balancing the chemical components of the acid corrosion resistant steel of the present application, the dual contradictory relationship between high strength and high toughness, high strength and SSC resistance is solved. Another significant advantage is that the use of Cu to replace Mo can greatly reduce the cost of the material. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The drawings illustrate one illustrative embodiment of the application and, together with the description, serve to explain the application. In the drawings:

[0018] Figure 1 An OM image showing the tempered martensitic structure of Example 3 of the present application is shown; and

[0019] Figure 2 A TEM image showing the nanometer sized precipitates of Example 3 of the present application is shown. DETAILED DESCRIPTION

[0020] It should be noted that the embodiments herein and in the characteristics in the embodiments herein can be combined with each other in case there is no conflict. The application will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0021] As analyzed in the background of the present application, there are problems of high cost and unstable SSC resistance of the 110 ksi oil well pipe steel in the prior art.

[0022] The inventors have conducted in-depth research on various factors affecting the SSC resistance of 110 ksi grade low alloy steel high strength steel. The inventors have shown through research that the strength level, alloying elements, microstructure, etc. have important influence on the SSC resistance of the material. And there is a complex correlation between these factors, for example, the strength level is closely dependent on the residual strain, the influence of alloying elements on hardenability and tempering characteristics can change the uniformity or homogeneity of the microstructure. The superiority of quenching and tempering process to other manufacturing procedures is well known, and uniform tempered martensite with fine dispersed carbides is considered to be the best microstructure for inhibiting SSC. High temperature tempering to obtain the desired strength level is considered to be the dominant principle for improving the SSC resistance of high strength steel.

[0023] Therefore, based on the above findings, the inventors believe that there are three ways to improve the SSC resistance of the material: one is to hinder hydrogen from entering the material; two is to disperse the hydrogen that enters the material to avoid aggregation; and three is to design the structure of the material to make it less likely to have stress cracking. Based on this, the application provides an acid corrosion resistant steel, a preparation method thereof and an acid corrosion resistant pipe. According to a typical embodiment of the application, an acid corrosion resistant steel is provided. The chemical composition of the acid corrosion resistant steel includes, in terms of percentage by weight: C 0.15-0.32%, Si≤0.4%, Mn≤0.7%, Cr 0.4-0.8%, Mo 0.4-0.8%, V 0.05-0.08%, Nb 0.015-0.045%, Al 0.008-0.050%, S≤0.003%, P≤0.01%, Cu 0.3-0.6%, Cu+Mo: 0.80-1.35%, and Cu / Mo 0.40-0.82, ΣAs+Sn+Pb+Sb+Bi≤0.035%, and the balance being iron and unavoidable impurities.

[0024] The acid corrosion resistant steel of the application has a low carbon content, which gives the acid corrosion resistant steel a high SSC resistance. By increasing the types of precipitated phases (carbides-carbides of Cr, carbides of V and Mo, nitrides-nitrides of V and Cu-rich phases), the precipitated phases play a role in precipitation strengthening, and also have a good SSC resistance. At the same time, by adding Cu elements in the steel, a "film" barrier that hinders hydrogen from entering can be formed on the surface of the material, thereby further improving the SSC resistance of the acid corrosion resistant steel of the application. By balancing the chemical composition of the acid corrosion resistant steel of the application, the dual contradictory relationship between high strength and high toughness, high strength and SSC resistance is solved.

[0025] Specifically, the roles of the elements are as follows:

[0026] (1) Role of C

[0027] C is the most effective element for enhancing the hardenability of the acid corrosion resistant steel of the application. A high C content is easy to obtain a martensite structure, and C also plays a role in solid solution strengthening. The content of C should not be less than 0.05%. Therefore, the content of C in the steel should not exceed 0.35%. The content of C in the steel of the application is 0.15-0.32%.

[0028] (2) Role of Cr

[0029] Cr: can strongly improve the hardenability element, strong carbide forming element, precipitates carbide to improve the strength of the steel during tempering, but when the content is too high, coarse M 23C6 carbide, lose its beneficial effect, preferably the content of 0.40-0.8%.

[0030] (3) the role of Mo

[0031] Mo has two aspects in the acid corrosion resistant steel of the application: one is to form Mo carbide to improve tempering resistance, and fine and uniform tempering martensite structure can be obtained; two is that Mo can improve the temper brittleness, thereby improving the toughness of the acid corrosion resistant steel of the application. In order to achieve the dual effect of Mo, the content of Mo is controlled in 0.4-0.95%, in addition, Mo can also reduce the segregation of P at grain boundary by reducing the diffusion coefficient of P, but when Mo is too high, coarse carbide will be formed, which is not conducive to the H2S stress corrosion resistance, therefore, Mo is controlled in 0.4-0.8%.

[0032] (4) the role of V

[0033] V is a component added according to the need in the acid corrosion resistant steel of the application. Vanadium carbide and nitride are fine and dispersed in ferrite, which can further achieve the effect of precipitation strengthening in the tempering process. On the other hand, it improves the SSC resistance: the carbide of V acts as "hydrogen trap" to capture hydrogen entering the material, so that hydrogen is uniformly dispersed in the material matrix, avoiding local hydrogen enrichment causing hydrogen embrittlement fracture. Preferably, the content of V is 0.05-0.08% by weight. But the carbide of V is easy to precipitate when the tempering temperature is higher than 500℃.

[0034] (5) the role of Nb

[0035] Nb can combine with N and C to form carbonitride, which can refine the grain and improve the strength and toughness of the steel on the one hand, and improve the SSC resistance on the other hand: the carbide of Nb acts as "hydrogen trap" to capture hydrogen entering the material, so that hydrogen is uniformly dispersed in the material matrix, avoiding local hydrogen enrichment causing hydrogen embrittlement fracture. If the content of Nb is too low, the effect cannot be achieved. On the other hand, when the content of Nb becomes excessive, carbonitride inclusions are excessively generated, which makes the SSC resistance of the steel unstable. Therefore, the content of Nb is 0.015-0.45%, and the preferred upper limit of the content of Nb is 0.040%.

[0036] (6) the role of Al

[0037] Al: traditional deoxidizing and nitrogen-fixing element, forming AlN can refine the austenite grain, which is beneficial to the improvement of SSC resistance, and the content of Al is preferably 0.008-0.050% by weight.

[0038] (7) P, S and five harmful elements

[0039] P, S and the five harmful elements are all related to the purity and grain boundary segregation of the steel, and if the content is high, it will have a greater impact on the SSC resistance of the steel, and should be strictly controlled. The patent controls it to be S≤0.003%, P≤0.010%, ΣAs+Sn+Pb+Sb+Bi≤0.025%,

[0040] (8) The role of Cu

[0041] Cu is a key alloying element, which has multiple roles in the steel of the present application: first, to improve the SSC resistance of the steel, which is manifested as: (1) Cu and H2S form a Cu sulfide "membrane barrier" attached to the material surface, which can effectively hinder hydrogen from entering the material interior; (2) after tempering, nanoscale Cu-rich phases are formed in the microstructure, which act as beneficial "hydrogen traps" to capture hydrogen entering the material, allowing hydrogen to be uniformly dispersed in the material matrix, avoiding local hydrogen enrichment causing hydrogen embrittlement fracture. Second, to improve the strength, which is manifested as: after tempering, nanoscale Cu-rich phases are precipitated, which play a role in precipitation strengthening. Cu should not be too high, as too high Cu can easily cause cracks in the material during continuous casting and rolling, and generally the Cu content is controlled at Cu 0.3-0.6%.

[0042] (9) The role of Si

[0043] Si can be used as a strengthening element, but too high a content will reduce plasticity, and generally the Si content is controlled at ≤0.4%.

[0044] (10) The role of Mn

[0045] Mn is a strengthening element that can also improve material toughness, but too high a content can reduce the formation of banded structures and affect the SSC resistance, and generally the Mn content is controlled at ≤0.7%.

[0046] According to the chemical composition of the above-mentioned acid corrosion-resistant steel (steel for H2S corrosion-resistant oil casing), the microstructure is controlled through the quenching and tempering process implemented during heat treatment, thereby reducing dislocation density and improving the toughness and H2S corrosion resistance of the material.

[0047] According to a typical embodiment of the present application, the method for preparing the above-mentioned acid corrosion-resistant steel comprises: adding scrap steel, pig iron and ingredients into an electric furnace for primary refining, followed by secondary refining, calcium treatment, vacuum degassing treatment, arc continuous casting, pipe blank cooling and finishing to obtain a pipe blank.

[0048] The steel for H2S corrosion-resistant oil casing prepared by the method of the present application meets the strength and toughness and H2S corrosion resistance of the material by adding Cu elements and assisting the reasonable combination of Cr, Mo, Nb and other carbonitrides, while also making the steel have a relatively low cost.

[0049] The smelting method of the material is not particularly limited, and the smelting method commonly used in the art can be used in the present application. Preferably, the smelting method is one of vacuum induction smelting, electric arc furnace smelting, converter smelting + secondary refining + vacuum degassing.

[0050] The heating temperature and holding time commonly used in the art can be used in the present application.

[0051] The rolling process of the present application can refer to the rolling process commonly used in the art. In step S2, in order to make the metallographic structure of the material of the present application uniform and dense, the rolling ratio of rolling is greater than 3, and preferably the rolling ratio of rolling is 5-10; in order to obtain good mechanical properties of the H2S corrosion resistant oil casing, the temperature of the rough rolling is controlled to be 1100-1150℃, and the temperature of the finish rolling is controlled to be 830-950℃.

[0052] Due to the different chemical compositions of the raw materials, the amount of carbonitride precipitation phase generated in the tempering process of heat treatment is affected by different temperature conditions. In order to meet the requirements of strength, toughness and H2S corrosion resistance, high temperature tempering is required. In some embodiments, the tempering temperature is controlled to be 660-720℃, the holding time of the tempering treatment is 40-100min, and preferably 60-90min. In order to make the carbonitride precipitated in the tempering process uniform and dispersed, the tempering temperature should be as high as possible. Due to the moderate carbon content and the presence of a large amount of alloy, the preferred tempering temperature is determined to be 660-720℃, which can make the carbon fully react with Mo, C, V, Nb, Cu and other elements to form a variety of carbides, thereby playing a full precipitation strengthening role. Through high temperature tempering, the dislocation density of the final tempering martensite is reduced, and the martensite plate structure after tempering is recovered, widened and polygonized, so that the high-angle grain boundaries (≥15 degrees) increase, become hydrogen traps, and improve the H2S corrosion resistance of the oil.

[0053] According to a typical embodiment of the present application, the heat treatment in S3 includes: heating the seamless steel pipe and then water quenching, the quenching temperature is 880-940℃, and the holding time is 30-90min; the austenitized seamless steel pipe is cooled to room temperature for quenching (preferably, the austenitized steel pipe is rapidly cooled to room temperature by the inner spray and outer spray method), then high temperature tempering, the tempering temperature is 660-720℃, and the tempering holding time is 40-100min; finally, hot straightening, the straightening termination temperature is ≥535℃ (preferably 530-650℃). Preferably, the present application controls the metallographic structure of the oil casing by controlling the cooling process in the heat treatment process. In order to obtain more than 95% of martensite, the preferred cooling medium in step S3 is water, and the cooling speed is higher than the critical speed of martensite transformation, and preferably the cooling speed is 35℃ / s-80℃ / s.

[0054] According to a typical embodiment of the present application, the acid corrosion resistant steel of the present application has a yield strength of 758-828 MPa at room temperature, a minimum tensile strength of 793 MPa, an average hardness value of not more than 29 HRC, a maximum hardness value of 30 HRC measured at a single point, and a minimum full-size impact energy at 0°C of 80 J in the transverse direction and 100 J in the longitudinal direction. The hydrogen sulfide stress cracking test of the acid corrosion resistant steel is performed according to ANSI-NACETM0177, using Method A, in A solution, using a 6.35 mm standard sample, and maintaining a stress of 644 MPa for at least 720 hours without cracking.

[0055] The beneficial effects of the present application will be further illustrated below with reference to examples.

[0056] Example 1

[0057] The components of the present application are compared with those of the prior art in Table 1.

[0058] CN105177434B and CN107002201B provide a material with a high Mo content, but the low component content is too wide, and a qualified product cannot be guaranteed at a low content. Moreover, the alloy content is high, the manufacturing difficulty is great, and the cost is high.

[0059] CN101082112A provides a 110Ks grade CO2 and H2S corrosion resistant oil well pipe and a manufacturing method. The steel grade used in the pipe has the following components in mass percent: C 0.20-0.35%, Si 0.10-1.0%, Mn 0.1-1.0%, Cr 1.0-2.5%, Mo 0.1-1.0%, Ni 0.10-1.0%, Nb 0.01-0.1%, Cu 0.10-1.0%, Al 0.01-0.10%, and the balance of Fe and unavoidable impurities. The final product has a tempered sorbite structure. The defect of this technology is that the sorbite structure provides low strength, and cannot guarantee that the oil casing steel grade reaches 110 ksi or above.

[0060] CN100419111C provides tempered martensite casing, patent name: anti hydrogen sulfide stress corrosion oil well pipe and its production method, the steel grade composition of the casing is: C 0.24-0.32%, Si 0.17-0.40%, Mn 0.40-0.70%, Cr 0.80-1.20%, Mo 0.15-0.40%, S≤0.010%, P≤0.015%, Ni≤0.20%, Ti 0-0.06%, the balance is Fe. The heat treatment process of quenching and high temperature tempering is used to form the tempered martensite structure. The defects of this technology are two points: one is that there is no grain refining element, and the high C content is easy to form coarse MC type carbide with Cr, which cannot guarantee good impact toughness and good SSC resistance; The total amount of alloying elements is low, and the final product cannot guarantee high content of tempered martensite structure, so the steel grade of the oil casing cannot reach 110Ksi level.

[0061] The patent CN 101440460A has too high Mn content, and the material is easy to form banded structure, which cannot guarantee the SSC resistance of the oil casing steel grade to reach 110Ksi level.

[0062] Table 1 Composition comparison of the present patent and prior art (%)

[0063]

[0064] Example 2

[0065] According to the composition formula in Table 2, 11 implementation formulas A1-A11 are prepared, and the smelting, continuous casting and rolling processes of different examples are basically the same, and the difference lies in the change of C, Mo and Cu content.

[0066] The preparation method specifically includes:

[0067] S1: using scrap steel, pig iron and ingredients to initially smelt in an electric furnace, then carrying out secondary refining outside the furnace, then carrying out calcium treatment, then carrying out vacuum degassing treatment, then carrying out arc continuous casting, then carrying out pipe blank cooling and finishing to obtain a pipe blank;

[0068] S2: rolling the pipe blank obtained in S1 into a seamless steel pipe; blank inspection and grinding → saw cutting and cutting → ring furnace heating → conical roller piercing → pipe rolling → online normalizing → step furnace reheating → sizing → cold bed cooling; wherein, the online normalizing is to refine the grains in the hot rolled state, and the key is to ensure that the grain size of the hot rolling is≥7.5 level, and the grains are uniform;

[0069] S3: the seamless steel pipe obtained in S2 is quenched and tempered, the heat treatment process is: hot rolling and then water quenching, quenching temperature: 880-940℃, holding time: 30-90min; the austenitized steel pipe is cooled to room temperature by means of inner spraying and outer spraying; then high-temperature tempering, tempering temperature: 680-720℃, tempering holding time: 40-100min; hot straightening, and then the hot straightening temperature is 550-600℃. Finally, the H2S corrosion resistant oil casing is obtained.

[0070] Different examples are carried out from 11 different components according to the heat treatment process provided in the application, and the properties of the obtained H2S resistant oil casing are shown in Table 3.

[0071] Table 2 also lists 5 comparative examples B1-B5, in which the main components C, Mo and Cu are not within the required range of the application, and the performance results of the comparative examples are shown in Table 3. It can be seen from the table that the properties of some of the comparative examples cannot meet the requirements of strength and impact. At the same time, the SSC performance of the comparative examples cannot meet the requirements.

[0072] Table 2

[0073]

[0074] Table 2 (continued)

[0075]

[0076]

[0077] Table 3: Performance of different examples and comparative examples

[0078]

[0079]

[0080] Metallographic observation is carried out on the oil casing material of Example 3, and the results show that the microstructure of the steel obtained in the application is tempered martensite + 3% carbide, as shown in Figure 1 It can also be seen from Table 3 that the oil casing provided in the application can provide better SSC performance and meet the requirements of API 5CT.

[0081] The steel of the application solves the multiple contradictory relationships between high strength and high toughness, high strength and SSC performance. This is mainly due to the low dislocation density of the tempered martensite microstructure ( Figure 1 ) and the high density of nanoscale precipitates ( Figure 2 ) which play a role as a favorable hydrogen trap and the formation of Cu sulfide on the surface of the material to hinder the entry of hydrogen.

[0082] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects: based on the characteristics of reducing Mo and adding Cu in the component design, the acid-resistant steel is endowed with better SSC resistance; and by increasing the types of precipitated phases (carbides - carbides of Cr, carbides of V and Mo, nitrides - nitrides of V and Cu-rich phases), on the one hand, the precipitated phases play a role in precipitation strengthening; at the same time, by adding Cu element in the chemical composition, a "film" barrier that hinders the entry of hydrogen can be formed on the surface of the material, thereby further improving the SSC resistance of the acid-resistant steel of the present application. By forming carbides with Nb element and C, the grain can be refined, and the strength and toughness of the acid-resistant steel can be improved. By balancing the chemical components of the acid-resistant steel of the present application, the dual contradictory relationship between high strength and high toughness, high strength and SSC resistance is solved, and the material cost is reduced.

[0083] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An acid corrosion resistant steel, characterized in that, The chemical composition of the acid corrosion resistant steel includes, by weight percentage, C 0.15-0.32%, Si≤0.4%, Mn≤0.7%, Cr 0.4-0.8%, Mo 0.4-0.8%, V 0.05-0.08%, Nb 0.015-0.045%, Al 0.008-0.050%, S≤0.003%, P≤0.01%, Cu 0.3-0.6%, Cu+Mo: 0.80-1.35%, and Cu / Mo 0.4-0.82%, ΣAs+Sn+Pb+Sb+Bi≤0.035%, and the balance being iron and inevitable impurities; the yield strength of the acid corrosion resistant steel at room temperature is 758-828 MPa, the minimum tensile strength is 793 MPa, the average hardness value is not greater than 29 HRC, the single-point measurement maximum hardness value is 30 HRC, and the full-size minimum impact energy at 0 ℃ is 80 J in the transverse direction and 100 J in the longitudinal direction.

2. The acid corrosion resistant steel according to claim 1, characterized in that, The chemical composition of the acid corrosion resistant steel includes, by weight percentage, C 0.25-0.31%, Si≤0.4%, Mn 0.35-0.6%, Cr 0.5-0.8%, Mo 0.5-0.7%, V 0.05-0.08%, Nb 0.025-0.040%, Al 0.008-0.050%, S≤0.003%, P≤0.01%, Cu 0.35-0.5%, Cu+Mo: 0.85-1.25%, and Cu / Mo 0.45-0.8%, ΣAs+Sn+Pb+Sb+Bi≤0.025%, and the balance being iron and inevitable impurities.

3. The acid corrosion resistant steel according to claim 1 or 2, characterized in that, The microstructure of the acid corrosion resistant steel is more than 95% tempered martensite.

4. The acid corrosion resistant steel according to claim 1 or 2, characterized in that, The acid corrosion resistant steel is subjected to a hydrogen sulfide stress cracking test according to ANSI-NACE TM0177, method A, in A solution, using a 6.35 mm standard sample, and is not cracked for at least 720 hours under a stress of 644 MPa.

5. An acid corrosion resistant steel pipe characterized by, The acid corrosion resistant steel is made of any one of claims 1 to 4.

6. A method of producing the acid corrosion resistant steel pipe according to claim 5, characterized by, The acid corrosion resistant steel is made of any one of claims 1 to 4. S1, scrap steel, pig iron and ingredients are added to an electric furnace for primary refining, followed by secondary refining, calcium treatment, vacuum degassing treatment, arc continuous casting, tube blank cooling and finishing to obtain a tube blank; wherein the amount of scrap steel, pig iron and ingredients meets the components and mass percentages of the components of the acid corrosion resistant steel in claim 1; S2, the tube blank obtained in S1 is rolled into a seamless steel pipe; S3, the seamless steel pipe obtained in S2 is subjected to quenching and tempering heat treatment.

7. The production method according to claim 6, characterized by, The S2 includes tube blank inspection and grinding, saw cutting and blanking, ring furnace heating, conical roller piercing, pipe rolling, online normalizing, step furnace reheating, sizing and cold bed cooling to obtain the seamless steel pipe.

8. The method of claim 7, wherein, The online normalizing refines the grains of the hot-rolled state, the grain size of the hot-rolled state is greater than or equal to 7 levels, and the grains are uniform.

9. The production method according to claim 8, characterized by, In the S2, the rolling ratio of rolling is greater than 3.

10. The method of claim 9, wherein, The rolling ratio of rolling is 5-10.

11. The preparation method according to claim 8, characterized in that, In the S2, the temperature of the initial rolling is 1100-1150℃, and the temperature of the final rolling is 830-950℃.

12. The method of claim 6, wherein, The heat treatment in the S3 comprises: water quenching after heating the seamless steel pipe, quenching temperature: 880-940℃, holding time: 30-90min; cooling the austenitized seamless steel pipe to room temperature for quenching; then high temperature tempering, tempering temperature: 660-720℃, tempering holding time: 40-100min; and finally hot straightening, straightening end temperature≥535℃.

13. The method of claim 12, wherein, The cooling speed of the austenitized seamless steel pipe cooling to room temperature for quenching is 35℃ / s-80℃ / s.

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