125ksi steel grade hydrogen sulfide stress corrosion resistant oil well pipe material suitable for environment containing 1MPa H2S at normal temperature and preparation method of 125ksi steel grade hydrogen sulfide stress corrosion resistant oil well pipe material

Abstract

The invention belongs to the technical field of preparation of hydrogen sulfide stress corrosion resistant oil well pipes, and relates to a 125ksi steel grade hydrogen sulfide stress corrosion resistant oil well pipe material suitable for a normal temperature environment containing 1MPa H2S and a preparation method of the 125ksi steel grade hydrogen sulfide stress corrosion resistant oil well pipe material. B, Ti, V and Nb elements are added, and the contents of Si, Mn and Ni elements, the Cr / Mo ratio and the sum of Nb, V and Ti in steel are controlled; the refined 100% sorbite structure, various compounds and microalloying are obtained through the processes of pure steel smelting, forging, controlled rolling and secondary heat treatment, so that high strength and high toughness in the 125 ksi range are obtained, and meanwhile the hydrogen sulfide corrosion resistance is high. The pipe product obtained by the process method disclosed by the invention has no corrosion cracking phenomenon after being subjected to a corrosion resistance test under the partial pressure of hydrogen sulfide of 1MPa.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of oil well pipes resistant to hydrogen sulfide stress corrosion, and relates to an oil well pipe material resistant to hydrogen sulfide stress corrosion of 125 ksi steel grade applicable to an environment containing 1 MPa H2S at normal temperature and a preparation method thereof. Background Art

[0002] In recent years, 60% of the newly added oil and gas reserves in the world come from deep formations, and the exploration potential is huge. Currently, deep and ultra-deep formations have become the main battlefields for major oil and gas discoveries. Mining in ultra-deep well environments faces higher pressures, higher temperatures, and more severe corrosive media, and some deep well oil and gas resources contain a certain amount of H2S gas. Conventional high-strength materials are prone to hydrogen sulfide stress corrosion (abbreviated as SSC) cracking in an H2S environment. Therefore, the exploitation of deep well oil and gas resources containing H2S must select special oil well pipe materials with SSC resistance performance.

[0003] There are many restrictions on the application conditions of existing 125 ksi steel grade SSC-resistant products of each manufacturer. For example, abroad: Sumitomo Metal's SM125S, Vallourec's VM125SS, and Tenaris' TN125SS require the use environment pH≥3.5, and the maximum applicable P H2S is only 0.003 MPa at most. Even Sumitomo Metal's SM125ES requires the use environment pH≥3.5, and the maximum applicable pH2S is only 0.010 MPa; domestically: Tianjin Pipe's TP125SS and Baosteel's BG125SS require the use environment pH≥3.5, and the maximum applicable P H2S is only 0.003 MPa at most or requires the use environment temperature≥60°C. The objective situation that the focus of oil and gas resource exploitation has shifted to deep wells, ultra-deep wells, and even 10,000-meter deep wells requires materials to have higher bearing strength. However, materials with higher performance also need to face naturally occurring or H2S acidic corrosive gas media generated during construction operations (such as acid fracturing or injecting media containing sulfate-reducing bacteria, etc.). This requires materials to have a certain SSC resistance while having higher strength. The essence of SSC is a hydrogen-induced cracking phenomenon. The higher the strength of the material, the higher the SSC sensitivity index level rises.

[0004] European Patent EP2403970 discloses a low-alloy steel with high strength and high sulfide stress cracking resistance, using a composition design of 0.3-0.5% C, 0.1-1.0% Mn, 0.3-1.5% Cr, 1.0-1.5% Mo, 0.03-0.06% V, 0.04-0.15% Nb, and obtaining a 125 ksi steel grade SSC-resistant material through two or three quenching and tempering treatments and high-temperature tempering. However, it can only meet the application under the environmental conditions of pH≥3.5, pH2S≤3 kPa, and the loading stress of 85% or 90% SMYS.

[0005] The sulfide stress corrosion resistance of 125 ksi steel grade in a weak sulfide environment (Corrosion, 2005, P05088) indicates that by using the original C110 steel type (1.0% Cr - 0.8% Mo) and reducing the tempering temperature to obtain materials with a strength range of 125 - 140 ksi, it is found that when the strength is 130 ksi, its applicable environment is pH ≥ 4.5, pH2S ≤ 100 kPa; when the strength is 140 ksi, its applicable environment is pH ≥ 5.5, pH2S ≤ 10 kPa or pH ≥ 6.5, pH2S ≤ 100 kPa.

[0006] The metallurgical design of C125 steel grade in a medium - acidic service environment (Corrosion 2006, P06125) indicates that on the basis of the original C110 composition, V and Nb are added, and materials with a steel grade of 125 - 140 ksi are obtained through quenching and tempering treatment. Through the combined action of V / Nb, dispersed spherical precipitates are formed to improve the SSC resistance of high - strength materials, and the materials can pass the test with pH ≥ 3.5 - pH2S ≤ 5 kPa.

[0007] The development of C125 high - strength low - alloy steel for SSC survey of OCTG in a slightly acidic environment (Corrosion, 2008, P08115) indicates that on the basis of the original C110 composition, V is added, Cr is reduced, and the Mo content is increased. Materials with a steel grade of 125 ksi are obtained through quenching and tempering treatment. The type, distribution, and scale of precipitates in the materials are improved, and the dislocation density of the materials is adjusted to obtain high - grade SSC - resistant materials that can pass the test with pH ≥ 3.5 - pH2S ≤ 3 kPa.

[0008] Existing 125 ksi steel grade SSC - resistant products have limited applications and limited resistance to H2S pressure. Developing 125 ksi steel grade SSC - resistant materials with an applicable environment of room temperature, pH ≥ 3.5, and pH2S of 1 MPa is particularly important for promoting the safe exploitation of deep - well oil and gas resources. Summary of the Invention

[0009] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a kind of oil - well pipe material for resisting hydrogen sulfide stress corrosion of 125 ksi steel grade applicable to normal temperature and containing 1 MPa H2S environment and its preparation method. Through the combined effect of C, Cr, Mo, Ni, V, Ti, Nb, B within a reasonable range and secondary quenching and tempering, an oil - well pipe material with high strength and toughness and corrosion resistance to high - pressure hydrogen sulfide is obtained, achieving the purpose of corrosion resistance under high strength (125 ksi) and high hydrogen sulfide partial pressure (1 MPa).

[0010] The technical solution adopted by the present invention to solve the technical problems is:

[0011] On the one hand, the present invention provides an oil well pipe material suitable for resisting hydrogen sulfide stress corrosion of 125 ksi steel grade in a normal temperature environment containing 1 MPa H2S. The mass percentages of its components are as follows: C: 0.25 - 0.30%, Si: 0.17 - 0.35%, Mn: 0.4 - 0.5%, P: ≤0.015%, S: ≤0.003%, Ni: 0.10 - 0.25%, Cr: 0.4 - 1.1%, Mo: 0.6 - 0.8%, Cu: 0.03 - 0.20%, Al: 0.005 - 0.050%, V: 0.06 - 0.18%, Nb: 0.03 - 0.06%, B: 0.0015 - 0.0030%, Ti: 0.005 - 0.040%. The Cr / Mo ratio is controlled between 1 and 1.7, and the total amount of Nb + V + Ti is controlled within the range of 0.09 - 0.145%. The rest is iron and inevitable impurities. The tensile strength of the oil well pipe material is 862 - 931 MPa, the yield strength is 920 - 1000 MPa, and the elongation is ≥25%.

[0012] Furthermore, the metallographic structure of the oil well pipe material is 100% sorbite structure, and the precipitated phases are TiCN, NbCN, VC, VB, and Mo3C. The class A inclusions in the oil well pipe material are ≤0.5 grade, the class B inclusions are ≤1.0 grade, the class C inclusions are ≤0.5 grade, the class D inclusions are ≤1.0 grade, and the grain size is ≥10.

[0013] On the other hand, the present invention provides a preparation method of the above-mentioned oil well pipe material. The main process is: steelmaking (electric furnace - refining - vacuum treatment) - ingot casting, forging - rolling (billet heating - piercing - hot rolling - stretch reducing - straightening) - quenching and tempering.

[0014] The preparation method specifically includes:

[0015] (1) Steelmaking, ingot casting, forging: Weigh the raw materials according to the mass percentage content of the above elements. After passing through the EAF electric furnace, LF refining furnace, and VD vacuum, it is ingot cast into a round billet and forged. The size after forging meets the requirement of a rolling ratio of 6 - 25. When it exceeds 25, the proportion of external and internal fold defects increases significantly, and the residual stress increases, which is not conducive to the corrosion resistance. When it is less than 6, the rolling deformation is insufficient, resulting in coarse grains and low mechanical properties. Therefore, the total rolling ratio must be controlled between 6 and 25;

[0016] (2) Rolling: The steel billet is heated to 1200 - 1250 °C and held for 2 - 2.5 hours. After high-pressure descaling, it is pierced, followed by stretch reducing sizing and straightening, and then through continuous rolling. The rolling temperature is 1100 - 1150 °C to obtain a rolled tube;

[0017] (3) Heat treatment: The as-rolled pipe is quenched at a quenching temperature of 880 - 940 °C and tempered at 680 - 740 °C. After secondary quenching and tempering, the oil well pipe material is obtained.

[0018] Utilize the pinning effect of the precipitates of Ti and Nb during the rolling process to obtain the initially refined as-rolled structure; subsequently, reheat the pipe to the temperature range of 880 - 940 °C for quenching. Ensure the formation of a complete sorbite structure after quenching by adding elements such as C, Mn, Cr, Mo, and B. Obtain fine grains and structure through the pinning effect of the precipitates of V, Nb, and Ti; then heat the pipe to 680 - 740 °C for tempering. Increase the tempering temperature of the material by adding Cr, Mo, V, and Nb, reduce the diffusion channels of hydrogen, and form a fine-grained high-temperature tempered sorbite structure with fine and dispersed precipitates.

[0019] Furthermore, in step (3), clear water quenching liquid is used for quenching, with external spraying and internal spraying. A cooling rate of more than 15 °C / s can quench the pipe through.

[0020] Furthermore, in step (2), the heating temperature of the steel billet is 1220 - 1250 °C.

[0021] Furthermore, in step (2), the rolling temperature is 1120 - 1150 °C.

[0022] Furthermore, in step (3), the quenching temperature is 890 - 910 °C.

[0023] In the formula of the present invention, by adding elements Cr and Mo, solid solution strengthening is achieved in the steel, and by controlling the range of the Cr / Mo ratio between 1 and 1.7, the anti-hydrogen sulfide corrosion performance is greatly improved.

[0024] By controlling the content of element Si at 0.17 - 0.35%, the purity of the steel is improved. Silicon is solid dissolved in the steel. When the steel transforms from martensite to sorbite, it strongly inhibits the precipitation of carbides along the grain boundaries, increases the grain boundary bonding force, and improves the toughness.

[0025] By adding and controlling the content of element Ni at 0.10 - 0.25%, the hardenability of the steel is improved, the fracture mechanism of the material is changed, and the strength and toughness and the corrosion resistance of the steel are improved. The strength and toughness matching degree of the steel type of the present invention is increased, and at the same time, it has processing performance and does not affect the requirements for subsequent processing of different connection buckle types.

[0026] By adding V and controlling the content of V at 0.06 - 0.18%, fine, uniform, and dispersed carbides are formed, reducing the diffusion rate of atoms. Prevent local depletion of Mo and Cr and improve the tissue stability.

[0027] By adding Nb and controlling the Nb content to be 0.03 - 0.06%, the hardenability of the steel is improved by solid solution in austenite. The pinning of niobium carbide (NbC) refines the grains and improves a certain strength and toughness.

[0028] And the total content of Nb + V + Ti is limited to 0.09 - 0.145, giving full play to the microalloying effects of Nb, V, and Ti, so that TiC particles with extremely high stability above 1000 °C inhibit grain growth at grain boundaries, pin dislocations, and reduce the corrosion risk.

[0029] By adding a trace amount of B element, the martensite content after quenching is increased, effectively reducing the addition amounts of C and Mn in the steel and ensuring the tissue uniformity of thick-walled products; B reduces the diffusion and aggregation of hydrogen by reducing the vacancy concentration at grain boundaries, improving the SSC resistance. Composite compounds more stable than carbides and similar to Si and V carbides are formed, acting together with TiC particles to make the grains finer, damping the movement of dislocations, and making the rolling deformation more uniform.

[0030] By controlling the Cu content, the tensile strength and yield strength of the steel are improved, while maintaining good plasticity and toughness of the steel, and reducing the tendency of intergranular corrosion and stress corrosion cracking.

[0031] In the steel grade of the oil well pipe material prepared by the present invention, the M martensite phase region on the C curve shifts to the right, so that when the cooling rate is only 15 °C / S, complete martensite can be obtained.

[0032] The following is a specific description through chemical elements and their limitations:

[0033] C: The carbon element is an inexpensive element to improve the strength of the material and is also an element that significantly improves the hardenability of the material. With the increase of the C element content, it can promote the material to obtain as much sorbite tissue as possible after quenching, ensure that the material meets the requirements of as uniform tempered tissue as possible, and reduce the appearance of tissues that are not conducive to SSC resistance; at the same time, C can form different types of precipitation phases such as MC and M3C with other alloy elements, refine the grains, improve the strength and toughness of the material, and play the role of a dispersed hydrogen trap, effectively improving the SSC resistance of the material. However, when the C content exceeds 0.32%, it is easy to cause quenching cracks during the quenching process of the material, resulting in a batch of irreparable products. Therefore, the carbon content of the steel designed in the present invention is controlled within the range of 0.25 - 0.30%.

[0034] Si: Si is added to steel as a deoxidizer in steelmaking. It can combine with FeO in molten steel to form low-density silicates that float up and improve the cleanliness of steel. Silicon element is dissolved in steel and plays a role in solid solution strengthening. During the transformation of steel from martensite to troostite, carbides are strongly inhibited from precipitating along grain boundaries, increasing the bonding force of grain boundaries and improving toughness. When the silicon content is too high, it will be dissolved in the material, promoting the hardening of the material, reducing the material's SSC resistance, and causing defects such as surface folding. Therefore, the silicon content of the steel designed by the present invention is controlled within the range of 0.17-0.35%.

[0035] Mn: Mn is a strong austenitizing element, which helps to increase the hardenability of the material and is a significant strengthening element. The addition of a small amount of Mn during the steel smelting process helps to form MnS inclusions with S and float up and remove them, which improves the purity of the steel and reduces the cracking tendency of the steel during the rolling process. However, Mn is an element that is very easy to segregate, and the segregation band formed leads to uneven microhardness of the structure, reducing the stability of the material's anti-SSC performance. Therefore, the manganese content of the steel designed by the present invention is controlled within the range of 0.40-0.50%.

[0036] P: P is a residual impurity element that is easy to form segregation in steel and form low-melting eutectic inclusions to reduce the plasticity of the material. At the same time, P inhibits the recombination process of hydrogen atoms (Had+Had→H2), which further increases the content of hydrogen in the metal. The increase of P will reduce the material's resistance to sulfide stress cracking. Therefore, the designed phosphorus content of the steel of the present invention should be as low as possible under the premise of ≤0.015%.

[0037] S: S is a residual impurity element. When the sulfur content in steel is high, it is easy to form sulfide inclusions (especially long strips of MnS), which aggravates stress concentration and promotes the aggregation of H, significantly reducing mechanical properties and SSC resistance. At the same time, sulfur can increase the hydrogen content in the material. Therefore, the sulfur content of the steel designed in the present invention should be as low as possible under the premise of ≤0.003%.

[0038] Ni: Ni is an element that expands the austenite phase region. The increase of Ni reduces the phase transition temperature of Ac1 and Ac3 of the material, so that the SSC-resistant material forms part of austenite during the tempering process at the highest possible temperature, and forms bainite or martensite during the subsequent cooling process, which changes the structure and hardness of the material and reduces the material's resistance to sulfide stress cracking. Ni is insoluble in carbides but completely dissolved in austenite, which fully improves the hardenability of steel. But at the same time, the addition of excessive Ni changes the fracture mechanism of the material. And when the nickel content exceeds 0.25%, the processability of the steel decreases, affecting the processing yield of the pipe. Therefore, the nickel content of the steel designed for the present invention should be between 0.10 and 0.25%.

[0039] Cr: Cr is a strong carbide-forming element and also a solid-solution strengthening element. The addition of Cr element can further increase the tempering temperature of the material while ensuring the same strength, enhance the anti-tempering softening ability of the material, reduce the dislocation density in the material, and decrease the diffusion path of hydrogen atoms. It forms fine carbides with C element, serves as a beneficial hydrogen trap to improve the distribution of hydrogen atoms in the material, reduces the concentration of hydrogen atoms, and improves the anti-SSC performance of the material. However, excessive Cr element is prone to form coarse M7C3 and M23C6-type precipitates distributed along the grain boundaries, which causes excessive aggregation of hydrogen atoms at these grain boundary precipitates, initiates cracks, and reduces the SSC resistance. Therefore, the chromium content of the steel in the present invention is designed to be controlled within the range of 0.40 - 1.1%.

[0040] Mo: Mo element is a solid-solution strengthening element that forms a solid solution with Fe. An appropriate amount of Mo plays a role in solid-solution strengthening, improves the stability of carbides, enhances the strength and toughness of the steel, and at the same time can improve the anti-tempering softening ability of the material. Mo element can hinder the diffusion of various atoms during tempering, delay the decomposition of martensite and the aggregation and growth of carbides, improve the tempering stability, enable the steel to be tempered at a higher temperature, effectively reduce the residual stress, improve the plasticity of the steel, and reduce the risk of hydrogen sulfide stress cracking caused by residual stress; when the Mo content is low, Mo has a strong carbide-forming ability and forms MC and M3C-type carbides, and the carbides gradually become finer and more uniform with the increase of Mo content, which is beneficial to improving the distribution of hydrogen, inhibiting the aggregation of hydrogen atoms, preventing hydrogen embrittlement in an acidic environment, and improving the anti-SSC performance of the material. Mo element delays the cold brittleness transition, increases the toughness of the steel, improves the strength of the steel, and can prevent the grain coarsening during austenitization, shifts the C curve to the right, reduces the supercooling degree, and greatly improves the hardenability. At the same time, the synergistic effect of Cr-Mo can further improve the anti-sulfide stress cracking performance of the material. However, when the Mo content exceeds a certain limit, it is prone to form M2C and M6C-type carbides, which will also lead to an increase in the content of retained austenite and is not conducive to the anti-sulfide stress cracking fracture of the material; at the same time, the addition of Mo element can reduce the segregation of elements such as P / As / Tb at the grain boundaries. Therefore, the molybdenum content of the steel in the present invention is designed to be controlled within the range of 0.60 - 0.80%, and the Cr / Mo ratio is controlled between 1 and 1.7, so that both Mo element and Cr element can play their respective advantages in the steel of the present invention.

[0041] Cu: Copper can enhance the strength and hardness of steel, improve tempering stability, promote grain boundary retardation and dispersed precipitation phase formation, and has a significant effect on improving the tensile strength and yield strength of steel, while maintaining the good plasticity and toughness of steel. Copper can form copper compounds (Cu2S, Cu5FeS4) in steel, which are resistant to sulfide and oxide corrosion. In addition, Cu can also reduce the tendency of intergranular corrosion and stress corrosion cracking. However, Cu is also easily oxidized at high temperatures, which reduces the surface tension of molten steel and reduces the fluidity of molten steel. Therefore, the content of Cu is controlled at 0.03-0.20% so that Cu can play a beneficial role in the present invention.

[0042] V: The V element is a strong carbide-forming element. The MC-type nano-scale precipitation phase formed during the quenching process can effectively inhibit the growth of austenite grains and refine the grain and substructure size. During the tempering process, precipitation strengthening can significantly increase the tempering temperature, reduce the dislocation density of the material, and reduce the diffusion path of hydrogen atoms. At the same time, the fine and dispersed precipitation phase can act as a benign hydrogen trap to improve the distribution of hydrogen atoms in the material. It plays multiple roles in low-alloy tempered SSC-resistant materials and is a microalloying element that can significantly improve the material's SSC resistance. However, excessive V elements can lead to the production of coarse liquid inclusions during the smelting process, and excessive V elements will not continue to improve the material's SSC resistance. Therefore, the vanadium content of the steel designed for the present invention is controlled within the range of 0.06-0.18%.

[0043] Nb: Nb is a strong carbide-forming element, and its role in improving the material's SSC resistance is almost the same as that of V. At the same time, the MC-type precipitation phase formed by the combination of Nb and C has extremely high high-temperature stability, and can still play a role in pinning and refining the structure at 1200°C, making the structure more refined before quenching and tempering after rolling, and further improving the material's SSC resistance. However, excessive Nb will cause liquid precipitation during the electric furnace smelting process, and will increase the difficulty of material rolling. Therefore, the steel design vanadium content of the present invention is controlled within the range of 0.03-0.06%.

[0044] B: B is an element that can significantly improve the hardenability of materials. The addition of trace amounts of B can significantly improve hardenability, increase the content of troostite after quenching, effectively reduce the amount of C and Mn added to the steel, and ensure the uniformity of the structure of thick-walled products; on the other hand, B reduces the vacancy concentration at the grain boundary and reduces the diffusion and aggregation of hydrogen. It promotes the chemical reaction of steel and forms a composite compound with Si and V carbides in steel. It is more stable than carbides and can work together with nano-carbides to make them smaller, reduce the precipitates produced by supersaturation, and damp the movement of dislocations. However, too much B may also form coarse M 23(C,B)6, Fe2B, Fe3(C,B) and Mo2B, thus impairing the SSC resistance of the steel. Therefore, the designed boron content of the steel in the present invention is controlled within the range of 0.0015 - 0.0030%.

[0045] Ti: Ti is a strong carbide-forming element. Ti forms carbonitrides with C and N. This compound is extremely stable and can precipitate either in combination with the Nb element or alone, inhibiting grain growth during rolling and quenching and tempering heat treatment, and refining the sizes of various organizational structures; the affinity of Ti with the N element is greater than that of the B element. The addition of the Ti element can ensure that B plays its role in improving the hardenability of the steel in a solid-solution form. Therefore, the designed Ti content of the steel in the present invention is controlled within the range of 0.005 - 0.040%.

[0046] The microalloying of Nb, V, and Ti will produce dispersed carbides, pinning the grain boundaries, inhibiting austenite grain growth during heating, and obtaining fine structures during cooling. However, the total amount of Nb + V + Ti should be controlled at 0.09 - 0.145% to ensure that in addition to the roles of Nb and V in the steel, the stable carbides formed by trace amounts of Ti are evenly distributed in the steel, inhibiting grain growth.

[0047] In summary, by adding elements B, Ti, V, and Nb, controlling the contents of elements Si, Mn, Ni in the steel, the Cr / Mo ratio, and the total sum of Nb + V + Ti, under the process method of the present invention, through the process of pure steel smelting + forging + controlled rolling + secondary heat treatment, a refined 100% tempered sorbite structure + various compounds + microalloying is obtained. While achieving high strength and high toughness, the anti-hydrogen sulfide corrosion performance of the steel under a hydrogen sulfide partial pressure of 1 MPa is enhanced. The secondary quenching and tempering refine the grains, improve the distribution of the precipitated phases, obtain a uniform and fine tempered sorbite structure, and the carbides are dispersed at the grain boundaries, with a lower dislocation density. The electrochemically measured hydrogen diffusion coefficient is larger, and the reduction of diffusible hydrogen makes it more difficult to initiate cracks, thus obtaining better SSC resistance.

[0048] The advantages and positive effects of the present invention are:

[0049] The present invention adopts the addition of elements B, Ti, V, and Nb, controls the contents of elements Si, Mn, Ni in the steel, the Cr / Mo ratio, and the total sum of Nb + V + Ti, and combines the process of pure steel smelting + forging + controlled rolling + secondary heat treatment to obtain a refined 100% tempered sorbite structure + various compounds + microalloying, thereby obtaining a high-strength and high-toughness oil well pipe material that meets the 125 ksi range and has high anti-hydrogen sulfide corrosion performance. The pipe products obtained under the process method of the present invention have passed the anti-corrosion test under a hydrogen sulfide partial pressure of 1 MPa without corrosion cracking. Brief Description of the Drawings

[0050] Figure 1C curve of the steel grade of the oil well pipe material prepared in Example 1;

[0051] Figure 2 Microscopic structure diagrams of the oil well pipe materials prepared in Comparative Example 1 and Example 1; among them, Figure a corresponds to Comparative Example 1, and Figure b corresponds to Example 1.

[0052] Figure 3 Metallographic structure diagrams of the oil well pipe materials prepared in Comparative Example 1 and Example 1, where Figure a) corresponds to Comparative Example 1 and Figure b) corresponds to Example 1. Detailed implementation manners

[0053] The present invention will be further described in detail below through specific examples. The following examples are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0054] An oil well pipe material suitable for resisting hydrogen sulfide stress corrosion of 125 ksi steel grade in a normal temperature environment containing 1 MPa H2S, the mass percentages of its components are: C: 0.25 - 0.30%, Si: 0.17 - 0.35%, Mn: 0.4 - 0.5%, P: ≤0.015%, S: ≤0.003%, Ni: 0.10 - 0.25%, Cr: 0.4 - 1.1%, Mo: 0.6 - 0.8%, Cu: 0.03 - 0.20%, Al: 0.005 - 0.050%, V: 0.06 - 0.18%, Nb: 0.03 - 0.06%, B: 0.0015 - 0.0030%, Ti: 0.005 - 0.040%, the Cr / Mo ratio is controlled between 1 and 1.7, and the total amount of Nb + V + Ti is controlled within the range of 0.09 - 0.145%, and the rest is iron and inevitable impurities.

[0055] Preferably, the class A inclusions in the oil well pipe material are ≤0.5 grade, the class B inclusions are ≤1.0 grade, the class C inclusions are ≤0.5 grade, the class D inclusions are ≤1.0 grade, and the grain size is ≥10.

[0056] Preparation method of the oil well pipe material, specifically including:

[0057] (1) Steelmaking, ingot casting, forging: Weigh the raw materials according to the mass percentage content of the elements, pass through the EAF electric furnace, LF refining furnace, VD vacuum, cast into round billets, and forge. The size after forging meets the requirements of the controlled rolling ratio of 6 - 25; when it exceeds 25, the proportion of external and internal fold defects increases significantly, the residual stress increases, which is not conducive to the corrosion resistance performance. When it is less than 6, the rolling deformation is insufficient, resulting in coarse grains and low mechanical properties. Therefore, the total rolling ratio must be controlled within the range of 6 - 25;

[0058] (2) Rolling: The steel billet is heated to 1200 - 1250 °C and held for 2 - 2.5 hours. After descaling under high pressure, piercing is carried out, controlling the deformation amount < 0.3. Subsequently, stretch reducing and sizing, and straightening are carried out, followed by continuous rolling of the tube. The rolling temperature is 1100 - 1150 °C to obtain the as-rolled tube; the rolling deformation rate is 15% - 30%. For quenching, clean water quenching liquid is used, spraying externally and internally, and the cooling rate of more than 15 °C / s can quench the tube through.

[0059] (3) Heat treatment: The as-rolled tube is quenched at a quenching temperature of 880 - 940 °C, and high-temperature tempering is carried out at 680 - 740 °C. After secondary quenching and tempering, the oil well pipe material is obtained. The initial refined as-rolled structure is obtained by the pinning effect of the precipitated phases of Ti and Nb during the rolling process; subsequently, the tube is reheated to the temperature range of 880 - 940 °C for quenching. By adding elements such as C, Mn, Cr, Mo, and B, a complete martensite structure is ensured after quenching. Fine grains and structures are obtained by the pinning effect of the precipitated phases of V, Nb, and Ti; then the tube is heated to 680 - 740 °C for tempering. By adding Cr, Mo, V, and Nb, the tempering temperature of the material is increased, the diffusion channel of hydrogen is reduced, and a fine-grained high-temperature tempered sorbite structure with fine and dispersed precipitated phases is formed.

[0060] The mass percentage contents of chemical elements in the oil well pipe materials in Examples 1 - 3 are specifically shown in Table 1, the rolling process parameters are shown in Table 2, and the heat treatment process parameters are shown in Table 3.

[0061] Table 1 Mass percentage contents of chemical elements in the oil well pipe materials in Examples 1 - 3

[0062]

[0063] Table 2 Rolling process parameters of the oil well pipe materials in Examples 1 - 3

[0064] Example Slab heating temperature / °C Rolling temperature / °C Rolling ratio Example 1 1220 1120 6.68 Example 2 1230 1145 8.14 Example 3 1222 1131 10.99

[0065] Table 3 Heat treatment process parameters of the oil well pipe materials in Examples 1 - 3

[0066]

[0067]

[0068] The oil well pipe materials prepared in Examples 1 - 3 are analyzed, and the performance parameters are shown in Table 5, and the anti-hydrogen sulfide stress corrosion test is shown in Table 6. Figure 1 The C curve of the steel grade of the oil well pipe material prepared in Example 1 is shown. It can be seen that the martensite phase region shifts to the right, so that when the cooling rate is only 15 °C / S, a complete martensite can be obtained. Figure 2 In which b is the microstructure of the oil well pipe material. Figure 3In Figure b), it is a metallographic structure photograph of the oil well pipe material prepared in Example 1. It can be seen that the oil well pipe material prepared by the present invention has a uniform and fine tempered sorbite structure, and carbides are dispersed at the grain boundaries, with a lower dislocation density.

[0069] Table 5 Microstructure parameters of the oil well pipe materials prepared in Examples 1 to 3

[0070]

[0071] For the evaluation of the sulfide stress corrosion resistance of the oil well pipe materials prepared in Examples 1 to 3, the uniaxial tensile test method in the NACE TMO177 standard was used, and the corrosion test was carried out on a high-pressure stress ring test device. The corrosion conditions were: loading 85% of the nominal yield strength, temperature 24 °C, P H2S were 0.8 MPa and 1 MPa respectively, PH = 3.5, and the results are shown in Table 6.

[0072] Table 6 Evaluation of the sulfide stress corrosion resistance of the oil well pipe materials prepared in Examples 1 to 3

[0073]

[0074]

[0075] Comparative Example 1

[0076] The difference from Example 1 is that the Cr / Mo ratio is 1.8, Cr is 1.37% and Mo is 0.76%.

[0077] Comparative Example 2

[0078] The difference from Example 1 is that the Cr / Mo ratio is 0.9, Cr is 0.693% and Mo is 0.77%.

[0079] Comparative Example 3

[0080] The difference from Example 1 is that the total amount of Nb + V + Ti is 0.075%, Nb is 0.03%, V is 0.04%, and Ti is 0.005%.

[0081] Comparative Example 4

[0082] The difference from Example 1 is that the total amount of Nb + V + Ti is 0.17%, Nb is 0.07%, V is 0.07%, and Ti is 0.03%.

[0083] Comparative Example 5

[0084] The difference from Example 1 is that the amount of B is 0.0010%, the amount of C is 0.31%, and the amount of Mn is 0.6%.

[0085] Comparative Example 6

[0086] The difference from Example 1 is that the amount of B is 0.0035%, the amount of C is 0.24%, and the amount of Mn is 0.4%.

[0087] The tissue parameters of the oil well pipe materials prepared in Comparative Examples 1-6 are shown in Table 7. The micrograph of the oil well pipe material prepared in Comparative Example 1 is as Figure 2 shown in a) below. Figure 3 a) in the following is the metallographic structure photograph of the oil well pipe material prepared in Comparative Example 1.

[0088] Table 7 Microstructure parameters of the oil well pipe materials prepared in Comparative Examples 1-6

[0089]

[0090] The evaluation of the oil well pipe materials prepared in Comparative Examples 1-6 for hydrogen sulfide stress corrosion resistance test was carried out by the same method as in the examples, and the results are shown in Table 8.

[0091] Table 8 Evaluation of the oil well pipe materials prepared in Comparative Examples 1-6 for hydrogen sulfide stress corrosion resistance test

[0092]

[0093] The mechanical tests were carried out on the oil well pipe materials prepared in the examples and comparative examples, and the performance parameters are shown in Table 9.

[0094] Table 9 Performance parameters of the oil well pipe materials prepared in the examples and comparative examples

[0095]

[0096]

[0097] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A kind of oil well pipe material suitable for 125 ksi steel grade resisting hydrogen sulfide stress corrosion in an environment containing 1 MPa H2S at normal temperature, characterized in that, The mass percentage contents of chemical elements in the oil well pipe material are as follows: C: 0.25 - 0.30%, Si: 0.17 - 0.35%, Mn: 0.4 - 0.5%, P: ≤0.015%, S: ≤0.003%, Ni: 0.10 - 0.25%, Cr: 0.4 - 1.1%, Mo: 0.6 - 0.8%, Cu: 0.03 - 0.20%, Al: 0.005 - 0.050%, V: 0.06 - 0.18%, Nb: 0.03 - 0.06%, B: 0.0015 - 0.0030%, Ti: 0.005 - 0.040%. The Cr / Mo ratio is controlled between 1 and 1.7, and the total amount of Nb + V + Ti is controlled within the range of 0.09 - 0.145%. The rest is iron and inevitable impurities. The yield strength of the oil well pipe material is 862 - 931 MPa, the tensile strength is 920 - 1000 MPa, and the elongation is ≥25%.

2. The oil well pipe material according to claim 1, characterized in that, The metallographic structure of the described oil well pipe material is 100% sorbite structure, and the precipitated phases are TiCN, NbCN, VC, VB, and Mo3C. The class A inclusions are ≤0.5 grade, the class B inclusions are ≤1.0 grade, the class C inclusions are ≤0.5 grade, the class D inclusions are ≤1.0 grade, and the grain size is ≥10.

3. The preparation method of the oil well pipe material according to claim 1 or 2, characterized in that, Including: (1) Steelmaking, ingot casting, and forging: Weigh the raw materials according to the mass percentage contents of the elements, and through the EAF electric furnace, LF refining furnace, and VD vacuum, then conduct ingot casting and forging into round billets; (2) Rolling: Heat the steel billet to 1200 - 1250 °C, keep it warm for 2 - 2.5 hours, conduct piercing after high-pressure descaling, then carry out stretch reducing and sizing, straightening, and then continuous rolling. The rolling temperature is 1100 - 1150 °C to obtain the as-rolled pipe; (3) Heat treatment: Quench the as-rolled pipe, with the quenching temperature of 880 - 940 °C, and conduct high-temperature tempering at 680 - 740 °C. After secondary quenching and tempering, the oil well pipe material is obtained.

4. The preparation method according to claim 3, characterized in that, In step (2), the rolling ratio is 6 - 25.

5. The preparation method according to claim 3, characterized in that, In step (3), clean water quenching liquid is used for quenching, with external spraying and internal spraying, and the cooling rate is 15 - 60 °C / s.

6. The preparation method according to claim 3, characterized in that, In step (2), the heating temperature of the steel billet is 1220 - 1250 °C.

7. The preparation method according to claim 3, characterized in that, In step (2), the rolling temperature is 1120 - 1150 °C.

8. The preparation method according to claim 3, characterized in that, In step (3), the quenching temperature is 890 - 910 °C.

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