A 135 ksi grade hydrogen sulfide corrosion resistant drill pipe steel and method of production, produced steel pipe, steel pipe heat treatment method and applications

Abstract

The application provides a 135ksi grade hydrogen sulfide corrosion resistant drilling steel and a production method, a produced steel pipe, a steel pipe heat treatment method and application thereof. The composition is as follows: Cr: 0.90-1.20%, Ni: 0.60-0.75%, Mo: 0.80-1.00%, Al: 0.020-0.050%, V: 0.15-0.25%, C: 0.22-0.27%, Si: 0.15-0.30%, Mn: 0.60-0.75%, P≤0.010%, S≤0.0015%, and the rest is Fe and other inevitable impurities. Compared with the prior art, the application is matched with a reasonable composition system, a pure steel refining control technology and a high uniformity heat treatment process, so that the material has good strength and toughness and excellent hydrogen sulfide corrosion resistance, and the produced steel pipe can be used in a 10,000m deep well.

Description

Technical Field

[0001] This invention belongs to the field of alloy steel, and particularly relates to a 135ksi grade steel resistant to hydrogen sulfide corrosion for drilling, its production method, the steel pipe produced, the heat treatment method of the steel pipe, and its application. Background Technology

[0002] Currently, many studies are attempting to develop 135ksi grade sulfur-resistant oil well tubing. However, while meeting the strength and toughness requirements, it is difficult to simultaneously ensure resistance to H2S corrosion, especially in passing the NACE TM0177 standard A solution test. Furthermore, some studies involve long process flows and low production efficiency. Therefore, it is essential to consider both chemical composition and process design to develop oil well tubing with excellent resistance to hydrogen sulfide corrosion and good strength and toughness, along with its manufacturing method, to ensure the safe and reliable use of oil well tubing in sulfur-containing deep wells.

[0003] Chinese patent CN107177797A, published on September 19, 2017, discloses a corrosion-resistant drill bit steel of 130KSI and 135KSI grades for oil and gas fields and its manufacturing method. The main principle of the disclosed technical solution is to add Mn, Cr, Mo and other main elements to improve the hardenability and toughness of the steel, and add trace amounts of V, Nb, Ni, Cu and other elements for strengthening. After one heat treatment, a tempered sorbite structure is obtained. However, its Charpy impact energy at -20℃ is only greater than 42J, which cannot meet the impact toughness requirements of drill bits at a depth of 10,000 meters.

[0004] Chinese patent CN115927960A, published on April 7, 2023, discloses a 125Ksi grade hydrogen sulfide corrosion resistant oil well pipe and its preparation method. The technical solution disclosed in this patent has the following composition: C: 0.10%–0.20%, Si: ≤0.50%, Mn: 0.3%–0.8%, V: 0.10%–0.20%, Mo: 0.20%–0.50%, Ni: 1.0%–1.5%, Cr: 1.5%–2.0%, Cu: 1.0%–2.0%, Als: ≤0.05%, P: ≤0.010%, S: ≤0.003%, with the balance being Fe and unavoidable impurities. The main principle is to obtain a tempered sorbite structure by adding a low-carbon Mn-Cr-Mo-V-Nb-Cu alloy. However, with tensile strength greater than 900MPa and yield strength greater than 863MPa, its strength cannot meet the requirements as drilling depth increases to over 10,000 meters. Summary of the Invention

[0005] The purpose of this invention is to provide a 135ksi grade steel resistant to hydrogen sulfide corrosion for drilling and its production method. Through optimization of composition and production process, it achieves good strength and toughness as well as excellent resistance to hydrogen sulfide corrosion.

[0006] Another objective of this invention is to provide a steel pipe and a heat treatment method for the steel pipe. The steel pipe produced using the aforementioned 135ksi grade hydrogen sulfide corrosion resistant steel, through a matched heat treatment process, yields a high-performance steel pipe with tensile strength ≥1030MPa, yield strength ≥931MPa, impact energy at -20℃ ≥100J, elongation ≥16%, low-angle grain boundary ratio ≥30%, austenite grain size ≥8.5 grade, and all ABCD grade non-metallic inclusions in the steel not exceeding grade 1.0, with a total not exceeding grade 2.5. This steel grade, under a loading strength of 75% SMYS, H2S partial pressure of 0.1MPa, and temperature of 25℃, passed a hydrogen sulfide corrosion resistance test using the American standard NACETM0177 Standard A method, and did not fracture after 720 hours of testing.

[0007] The final objective of this invention is to provide an application of a steel pipe produced using the above-mentioned heat treatment process for use in mining at depths of 10,000 meters.

[0008] The specific technical solution of this invention is as follows:

[0009] A type of 135ksi grade steel resistant to hydrogen sulfide corrosion for drills comprises the following components by weight percentage:

[0010] Cr: 0.90–1.20%, Ni: 0.60–0.75%, Mo: 0.80–1.00%, Al: 0.020–0.050%, V: 0.15–0.25%, C: 0.22–0.27%, Si: 0.15–0.30%, Mn: 0.60–0.75%, P≤0.010%, S≤0.0015%, with the remainder being Fe and other unavoidable impurities.

[0011] The steel used in the 135ksi grade hydrogen sulfide corrosion resistant drill bit also meets the following composition requirements:

[0012] T.O+[N]≤120ppm; the five harmful elements Sn, Sb, As, Pb, and Bi are controlled at ≤0.010%;

[0013] The 135ksi grade hydrogen sulfide corrosion resistant drill bit uses steel whose composition also satisfies: T = -2 × %Si + 1.0.

[0014] ×%Mn+1.3×%Mo+2.5×%Ni+1.8×%V≥3.10%, where each element represents its mass percentage content in the steel.

[0015] The 135ksi grade hydrogen sulfide corrosion resistant drill bit uses steel whose composition also meets the following requirement: R = -5 × (%Si + %Mn) + 12 × %Mo + 10 × %Cr + 18 × %V ≥ 19.00%. Each element represents its mass percentage content in the steel.

[0016] This invention provides a method for producing 135ksi grade hydrogen sulfide corrosion resistant drill steel, comprising the following process flow:

[0017] Hot metal pretreatment → converter smelting → LF furnace refining → RH vacuum degassing → continuous casting → rolling.

[0018] The molten iron pretreatment involves using Mg-based and CaO-based desulfurizing agents to reduce the sulfur content in the molten iron to 0.001%.

[0019] The converter smelting process involves deoxidation and alloying of the tapped steel, while strictly controlling the amount of slag added, with the final smelting endpoint P ≤ 0.008%.

[0020] The LF furnace refining process involves adjusting elements such as C, Si, Mn, Cr, Ni, Mo, and V to target values, maintaining white slag for ≥20 minutes, and completing a smelting cycle of ≤70 minutes.

[0021] The RH vacuum degassing process has the following parameters: pure degassing time ≥ 25 min, soft blowing time ≥ 20 min, and [H] ≤ 1.0 ppm after vacuum treatment.

[0022] RH vacuum degassing with calcium treatment is an effective method for modifying the morphology of sulfides in cast billets. Calcium treatment not only modifies the primary Al2O3 inclusions in the billet into liquid calcium aluminate inclusions, but also, during the cooling process, Ca preferentially combines with S to form CaS, lowering the precipitation temperature of MnS inclusions and reducing the amount of MnS inclusions precipitated. The Ca / S ratio ranges from 0.8 to 2.0. Here, the effective calcium-sulfur ratio Ca / S is defined by the following formula:

[0023] Ca / S=[T.Ca-(0.31+0.02×T.Ca)×(0.99×TO-5.44)] / 1.25×TS;

[0024] Where TS is the mass fraction of total sulfur in steel, 10 -6 This refers to the sulfur (S) content in the steel composition; T.Ca is the total calcium mass fraction in the steel, 10 -6 TO represents the total oxygen mass fraction in the steel, 10 -6 .

[0025] The above is the Ca treatment formula designed for this type of steel. Since the precipitated elongated sulfides will deteriorate the overall performance of the material, the formula was obtained by thermodynamic calculation fitting of inclusions in the cooling process of the steel billet using relevant thermodynamic calculation software.

[0026] The continuous casting process involves round billets, with the tundish superheat controlled at 20–50°C above the liquidus. The billet diameter D and casting speed v should conform to the formula: D = 1029 - 1980 × v - 1470 × v 2 The unit for the diameter D of the continuously cast billet is mm, and the unit for the casting speed v is m / min. When calculating, simply substitute the values ​​before the units into the formula.

[0027] The rolling process involves rolling the billet into finished products. The billet is fed into a walking beam furnace, with a heating temperature ≥1230℃ for round steel. The diameter D of the continuously cast billet and the heating time t should conform to the formula: D = 180 + 0.42t. The initial rolling temperature is ≥1180℃, and the final rolling temperature is 700~950℃. After rolling, the billet is cooled using an insulation cover or a slow cooling pit. The unit for the diameter D of the continuously cast billet is mm, and the unit for the heating time t is min. For calculation, simply substitute the values ​​before the units into the formula.

[0028] This invention rolls continuously cast round billets of Φ380mm~Φ700mm into round steel bars of Φ95mm~Φ320mm.

[0029] The present invention provides a steel pipe, which is a steel pipe made from the above-mentioned 135ksi grade steel resistant to hydrogen sulfide corrosion.

[0030] The steel pipe has a low-angle grain boundary ratio of ≥30%, an austenite grain size of ≥8.5 grade, and the A, B, C, and D type non-metallic inclusions in the steel are all no greater than grade 1.0, and the total of A, B, C, and D type non-metallic inclusions is no greater than grade 2.5.

[0031] The grain size at half the wall thickness of the end cross section of the steel pipe is ≤20μm, and the microstructure is tempered sorbite.

[0032] The steel pipe was subjected to a hydrogen sulfide corrosion test at a load strength of 75% SMYS, an H2S partial pressure of 0.1 MPa, and a temperature of 25°C, using the American standard NACE TM0177 Standard A method. No fracture occurred during the 720-hour test.

[0033] The steel pipe has a tensile strength ≥1030MPa, a yield strength ≥931MPa, an impact energy ≥100J at -20℃, and an elongation ≥16%.

[0034] The present invention provides a heat treatment method for steel pipes, which involves heat treating steel pipes produced using the aforementioned 135ksi grade steel resistant to hydrogen sulfide corrosion.

[0035] The heat treatment methods include normalizing, quenching, and tempering.

[0036] The normalizing process involves heating to a temperature of 900–930°C, with the holding time t1 determined by the steel pipe wall thickness S, where t1 = 3.5 × S. After holding, the pipe is air-cooled. The unit for holding time t1 is minutes, and the unit for steel pipe wall thickness S is millimeters.

[0037] The quenching process involves heating at a temperature of 900–930℃, with the holding time t2 determined by the steel pipe wall thickness S, where t2 = 3.2 × S. Water cooling follows the holding time. The unit for holding time t2 is minutes, and the unit for steel pipe wall thickness S is millimeters.

[0038] The tempering process involves a tempering temperature of 670–710℃ and a holding time t3 determined by the steel pipe wall thickness S, where t3 = 6 × S. After holding, the pipe is air-cooled. The unit for holding time t3 is minutes, and the unit for steel pipe wall thickness S is mm.

[0039] Normalizing, as a pretreatment, refines the original coarse grains, thereby improving the strength and toughness of the steel and laying a good foundation for subsequent quenching and tempering. Quenching and tempering heat treatment (quenching and tempering) aims to obtain fine tempered sorbite. The heat treatment temperature is set according to the material's AC3 temperature to ensure complete austenitization (controlled at 900–930℃ in this invention). The holding time is determined based on the material's wall thickness; a reasonable annealing time is designed to ensure complete austenitization.

[0040] An application of a steel pipe: the steel pipe produced using the above-mentioned heat treatment process is used for mining in a 10,000-meter deep well.

[0041] The design concept of this invention is as follows:

[0042] C: Ensures the strength of steel and improves hardenability, thereby increasing the percentage of martensite transformation; in addition, increasing the C content can increase the amount of carbides precipitated during tempering, which are good H traps; however, excessively high C content will not only cause segregation itself, but also greatly increase the segregation of Mn and P, thereby reducing the resistance to SSC, so the C content is controlled at 0.22-0.27%.

[0043] Mn: Improves the strength and hardenability of steel, but Mn is an element that is prone to segregation. Excessive Mn content is prone to segregation with S and P at grain boundaries, which is detrimental to the resistance to SSC. The Cr and Mo content designed in this invention is relatively high, which is sufficient to ensure the hardenability and strength of the steel. Therefore, the Mn content is controlled at 0.60 to 0.75%.

[0044] Cr: Improves strength and hardenability, and enhances corrosion resistance; however, excessive Cr content can cause large Cr deposits to precipitate at grain boundaries during tempering. 23 C6 carbides are not conducive to resistance to H2S stress corrosion, so the Cr content is controlled between 0.90% and 1.20%.

[0045] Mo (Mo) is an important solid solution strengthening and temper precipitation strengthening element, and it also improves the hardenability of steel. Mo carbides precipitate during high-temperature tempering, increasing tempering resistance; therefore, sufficient Mo must be added to ensure high strength and high tempering temperature. Additionally, Mo can reduce P segregation at grain boundaries by decreasing the diffusion coefficient of P. However, excessive Mo content can lead to the formation of coarse carbides, which is detrimental to resistance to H₂S stress corrosion. Therefore, the Mo content is controlled between 0.80% and 1.00%.

[0046] Ni: Ni is an austenite stabilizing element, which expands the phase region, increases the stability of supercooled austenite, and improves the hardenability of steel. Simultaneously, Ni improves the toughness of materials through solid solution treatment, particularly by significantly lowering the ductile-brittle transition temperature. Furthermore, Ni can refine the width of martensite laths, increasing strength; however, excessive addition reduces the steel's resistance to solid-state corrosion cracking (SSC). Therefore, the Ni content is controlled between 0.60% and 0.75%.

[0047] In quenched and tempered steel, volatile organic compounds (V) play a role in inhibiting temper softening and increasing the tempering temperature. During high-temperature tempering, the precipitation of V carbides provides precipitation strengthening, thus ensuring that the dislocation density is reduced and the resistance to precipitated solids (SSC) is improved during high-temperature tempering, while also maintaining the high strength requirement of 135 ksi. However, if the V content in the steel exceeds a certain upper limit, the resistance to SSC will no longer improve; therefore, the V content is controlled between 0.15% and 0.25%.

[0048] P, S, and the five harmful elements: P, S, and the five harmful elements Sn, Sb, As, Pb, and Bi, as impurity elements in steel, significantly reduce the material's resistance to stress cracking (SSC), and their content in steel should be minimized. P readily forms segregation in steel, while the stress zones at the tips of MnS inclusions are prone to becoming the initiation sites for sulfide stress cracking. Therefore, P, S, and the five harmful elements should be controlled at ≤0.010%, ≤0.0015%, and ≤0.010%, respectively.

[0049] TO and [N]: Oxygen in steel easily forms oxide inclusions, especially type B inclusions along the rolling direction. The presence of free nitrogen increases the brittleness of the material and impairs its toughness. The total amount of T.O+[N] should be ≤120ppm.

[0050] Ca / S: Calcium treatment is an effective means of modifying the morphology of sulfides in cast billets. It can also modify Al2O3 inclusions and magnesium-aluminum spinel in steel, improving the castability of molten steel during continuous casting. To achieve good calcium treatment results, based on practical production experience, the Ca / S ratio should be controlled between 0.8 and 2.0.

[0051] To ensure good low-temperature toughness in steel, the proportions of Si, Mo, Mn, Ni, and V need to be carefully controlled. Since Si tends to segregate at austenite grain boundaries, reducing crystal bonding strength, worsening low-temperature toughness, and increasing temper brittleness, the coefficient for Si is -2.0. Mn significantly affects the selection of variants during phase transformation, increasing the variety of variants and thus improving low-temperature toughness; therefore, the coefficient for Mn is 1.0. Mo improves the hardenability of steel and effectively reduces the segregation of impurities such as P, S, and As at grain boundaries, effectively improving low-temperature toughness; therefore, the coefficient for Mo is 1.3. Ni significantly lowers the ductile-brittle transition temperature of steel and improves low-temperature toughness; therefore, the coefficient for Ni is 2.5. V precipitates fine VC particles, refining the microstructure and improving the tempering stability of steel, thus improving low-temperature toughness; therefore, the coefficient for V is 1.8.

[0052] That is, T=-2×%Si+1.0×%Mn+1.3×%Mo+2.5×%Ni+1.8×%V≥3.10%.

[0053] To ensure good resistance to hydrogen sulfide corrosion (SSC) corrosion in steel, the proportions of Si, Mn, Cr, Mo, and V must be carefully controlled. Since Si and Mn tend to segregate at austenite grain boundaries, reducing the crystallization bonding force and causing microstructure inhomogeneity, leading to decreased corrosion resistance, their coefficient is -5. Mo improves the hardenability of steel, effectively reducing the segregation of impurities such as P and S at grain boundaries. Furthermore, during tempering, it precipitates carbides (Mo₂C), which act as traps for H atoms, effectively improving the steel's resistance to sulfur dioxide (SSC), hence the coefficient for Mo is 12. The precipitated VC from V effectively inhibits grain growth and, as an irreversible H trap, greatly enhances SSC resistance. In addition, vanadium improves the steel's resistance to tempering softening, reduces dislocation density, and enhances SSC resistance, hence the coefficient for V is 18. The irreversible H hydrogen traps provided by Cr effectively capture H atoms, slowing down their diffusion rate and improving SSC resistance, hence the coefficient for Cr is 10.

[0054] That is, R=-5×(%Si+%Mn)+12×%Mo+10×%Cr+18×%V≥19.00%.

[0055] The alloying elements added in this invention, through normalizing and tempering processes, cause the material to precipitate more fine alloy carbides. On the one hand, this refines the grains and improves the strength and toughness of the material; on the other hand, it can also act as an irreversible hydrogen trap to improve the material's resistance to SSC.

[0056] Compared with existing technologies, this invention employs a rational composition system, refining control technology, and a highly uniform heat treatment process. This allows for the production of a tempered sorbite matrix with a dispersed and refined second phase at room temperature, resulting in a lower dislocation density and a higher proportion of low-angle grain boundaries. Consequently, the material exhibits excellent strength, toughness, and resistance to hydrogen sulfide corrosion. This invention enables the production of 135ksi grade high-strength, SSC-resistant drill-safe steel in a converter, suitable for use in wells reaching depths of tens of thousands of meters. Attached Figure Description

[0057] Figure 1 For Comparative Example 3, see the tissue diagram;

[0058] Figure 2 This is an organizational diagram of Example 1. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] Examples 1-3

[0061] A 135ksi grade steel resistant to hydrogen sulfide corrosion is used in a drill bit, comprising the following composition by mass percentage as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurities.

[0062] Comparative Examples 1-4

[0063] A 135ksi grade steel resistant to hydrogen sulfide corrosion is used in a drill bit, comprising the following composition by mass percentage as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurities.

[0064] Table 1. Components (wt%) of each embodiment and comparative example

[0065]

[0066]

[0067] Note: The components of Example 3 and Comparative Example 3 are the same. In Table 1, T.Ca is the actual data obtained by the equipment. In addition, the five harmful elements Sn, Sb, As, Pb, and Bi are controlled to be ≤0.010%.

[0068] The steel production method for the 135ksi grade hydrogen sulfide corrosion resistant drills used in the above embodiments and comparative examples includes the following process flow:

[0069] Hot metal pretreatment → converter smelting → LF furnace refining → RH vacuum degassing → continuous casting → rolling (finishing) into finished products.

[0070] The molten iron pretreatment involves using Mg-based and CaO-based desulfurizing agents to reduce the sulfur content in the molten iron to 0.001%.

[0071] The converter smelting process involves deoxidation and alloying of the tapped steel, while strictly controlling the amount of slag added, with the final smelting endpoint P ≤ 0.008%.

[0072] The LF furnace refining process involves adjusting elements such as C, Si, Mn, Cr, Ni, Mo, and V to target values, maintaining white slag for ≥20 minutes, and completing a smelting cycle of ≤70 minutes.

[0073] The RH vacuum degassing process has the following parameters: pure degassing time ≥ 25 min, soft blowing time ≥ 20 min, and [H] ≤ 1.0 ppm after vacuum treatment.

[0074] RH vacuum degassing with calcium treatment is an effective means of modifying the morphology of sulfides in cast billets. This invention controls the Ca / S ratio within the range of 0.8–2.0. The effective calcium-sulfur ratio Ca / S is defined here using the following formula:

[0075] Ca / S=[T.Ca-(0.31+0.02×T.Ca)×(0.99×TO-5.44)] / 1.25×TS;

[0076] Where TS is the mass fraction of total sulfur in steel, 10 -6 T.Ca is the total calcium mass fraction in steel, 10 -6 TO represents the total oxygen mass fraction in the steel, 10 -6 The controlled effective calcium-to-sulfur ratio (Ca / S) for each embodiment and comparative example is shown in Table 1.

[0077] The continuous casting process involves round billets, with the tundish superheat controlled at 20–50°C above the liquidus. The billet diameter D and casting speed v should conform to the formula: D = 1029 - 1980 × v - 1470 × v 2 The unit for the diameter D of the continuously cast billet is mm, and the unit for the casting speed v is m / min. Specifically, for a continuously cast round billet with a diameter D = 500 mm, a superheat of 45℃, and a casting speed v = 0.23 m / min, the production process is as follows:

[0078] The rolling process involves rolling a Φ500mm continuously cast round billet into a Φ150mm hot-rolled round bar. The billet is then fed into a walking beam furnace, heated to a temperature ≥1230℃, and held for 762 minutes, conforming to the formula D=180+0.42t. The initial rolling temperature is ≥1180℃, and the final rolling temperature is 700~950℃. After rolling, the billet is either placed under a heat preservation cover or placed in a slow cooling pit for slow cooling.

[0079] In the actual production of the steel described in the above embodiments and comparative examples, production can be achieved by controlling the process within the above range.

[0080] The steel pipes produced using 135ksi grade hydrogen sulfide corrosion resistant drill steel in the various embodiments and comparative examples follow the following manufacturing process: Φ95mm~Φ320mm hot-rolled round steel → heating → pipe threading → sizing → heat treatment → steel pipe grinding → steel pipe flaw detection → finishing → flaw detection → packaging and warehousing. Specific heat treatment methods include normalizing + quenching and tempering. This invention uses Φ150mm hot-rolled round steel for production.

[0081] The normalizing process involves heating at a temperature of 900–930°C, with the holding time t1 determined by the steel pipe wall thickness S, where t1 = 3.5 × S, followed by air cooling. The unit for holding time t1 is minutes, and the unit for steel pipe wall thickness S is mm.

[0082] The quenching process involves heating at a temperature of 900–930℃, with the holding time t2 determined by the steel pipe wall thickness S, where t2 = 3.2 × S, and water cooling is used. The unit of holding time t2 is min, and the unit of steel pipe wall thickness S is mm.

[0083] The tempering process involves a tempering temperature of 670–710℃ and a holding time t3 determined by the steel pipe wall thickness S, where t = 6 × S. Air cooling is also used. The unit for holding time t3 is minutes, and the unit for steel pipe wall thickness S is mm.

[0084] The main heat treatment parameters for each embodiment and comparative example are shown in Table 2.

[0085] Table 2 lists the heat treatment processes of the embodiments and comparative examples of the present invention.

[0086]

[0087] The performance testing methods for the steel pipes in each embodiment and comparative example are as follows:

[0088] Organization: Samples were taken from half the wall thickness of the end cross section of the steel pipe for metallographic and grain size analysis.

[0089] Performance: Tensile, impact, and SSC resistance specimens were taken from half the radius of the steel pipe. Mechanical property tests were conducted according to GB / T228 and GB / T229. SSC resistance tests were conducted according to NACE TM0177 Standard A method (load strength of 75% SMYS, H2S partial pressure of 0.1MPa, temperature of 25℃). Average grain size was observed according to GB / T 6394. Low-angle grain boundaries (2°≤θ≤15°) were observed and analyzed using EBSD. The results are shown in Table 3.

[0090] Non-metallic inclusions: Samples were taken from 1 / 2 radius of the hot-rolled round steel and tested according to Method A of ASTM E45. The properties are shown in Table 4.

[0091] Table 3. Performance testing results of embodiments and comparative examples of the present invention.

[0092]

[0093]

[0094] Table 4 Requirements for Non-metallic Inclusion Levels (Unit: Level)

[0095]

[0096] Figure 1 The microstructure diagram for Comparative Example 3 shows that the material was not fully quenched due to the quenching temperature not being within the range of 900–930℃, resulting in the formation of bainite microstructure during the cooling process.

[0097] Figure 2 The diagram shows the microstructure of Example 1. Due to proper composition and heat treatment process, the microstructure is fine tempered sorbite.

[0098] The chemical composition and production methods of the steels in Examples 1-3 were appropriately controlled, and their chemical compositions met the requirements. The steels exhibited good strength, toughness, and SSC resistance. In Comparative Example 1, the C content was not controlled according to the present invention, resulting in a low T value. Even when produced according to the steel production method and heat treatment process of the present invention, the produced steel pipe had low low-temperature toughness and could not meet the requirements of the present invention. Although the composition of Comparative Example 2 met the requirements of the present invention, its low R value led to a significant decrease in SSC resistance. Comparative Example 3 had its chemical composition properly controlled, and the steel was produced according to the present invention; however, the improper heat treatment process resulted in unsatisfactory overall performance. Although the composition of Comparative Example 4 met the requirements of the present invention, both its R and T values ​​were low. Even when the heat treatment process met the requirements of the present invention, the proportion of low-angle grain boundaries in the product was significantly reduced, resulting in extremely poor SSC resistance.

[0099] The data underlined above do not meet the requirements of this invention.

[0100] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A type of 135ksi grade steel resistant to hydrogen sulfide corrosion for drilling, characterized in that, The 135ksi grade hydrogen sulfide corrosion resistant drill steel used in this drill comprises the following components by weight percentage: Cr: 0.90-1.20%, Ni: 0.60-0.75%, Mo: 0.80-1.00%, Al: 0.020-0.050%, V: 0.15-0.25%, C: 0.22-0.27%, Si: 0.15-0.30%, Mn: 0.60-0.75%, P≤0.010%, S≤0.0015%, with the remainder being Fe and other unavoidable impurities; The steel used in the 135ksi grade hydrogen sulfide corrosion resistant drill bit also meets the following composition requirements: T=-2×%Si+1.0×%Mn+1.3×%Mo+2.5×%Ni+1.8×%V≥3.10%; R=-5×(%Si+%Mn)+12×%Mo+10×%Cr+18×%V≥19.00%; The 135ksi grade hydrogen sulfide corrosion resistant drill bit is used to produce steel pipes. The steel pipes have a low-angle grain boundary ratio of ≥30%, an austenite grain size of ≥8.5 grade, and the A, B, C, and D type non-metallic inclusions in the steel are all no greater than grade 1.0, and the total of A, B, C, and D type non-metallic inclusions is no greater than grade 2.

5. The grain size at half the wall thickness of the end cross section of the steel pipe is ≤20μm, and the microstructure is tempered sorbite. The steel pipe has a tensile strength ≥1030MPa, a yield strength ≥931MPa, an impact energy ≥100J at -20℃, and an elongation ≥16%.

2. A method for producing the 135ksi grade hydrogen sulfide corrosion resistant drill steel as described in claim 1, characterized in that, The production method includes the following process flow: Hot metal pretreatment → converter smelting → LF furnace refining → RH vacuum degassing → continuous casting → rolling.

3. The production method according to claim 2, characterized in that, The effective calcium-to-sulfur ratio (Ca / S) formula for the calcium treatment in the RH vacuum degassing process is: Ca / S = [T.Ca - (0.31 + 0.02 × T.Ca) × (0.99 × TO - 5.44)] / 1.25 × TS; Ca / S ranges from 0.8 to 2.0, where TS is the total sulfur mass fraction in the steel. -6 ; T.Ca is the total calcium mass fraction in steel, 10 -6 ; TO is the mass fraction of total oxygen in steel, 10 -6 .

4. The production method according to claim 2, characterized in that, In the continuous casting process, the billet diameter D and casting speed v should conform to the formula: D = 1029 - 1980 × v - 1470 × v 2 The unit for the diameter D of the continuously cast billet is mm, and the unit for the casting speed v is m / min.

5. The production method according to claim 2, characterized in that, The rolling process involves feeding the billet into a walking beam furnace. The diameter D of the continuously cast billet and the heating time t should conform to the formula D = 180 + 0.42t. The initial rolling temperature is ≥ 1180℃. The unit of the diameter D of the continuously cast billet is mm, and the unit of the heating time t is min.

6. A heat treatment method for steel pipes, characterized in that, The steel pipe produced using the 135ksi grade hydrogen sulfide corrosion resistant drill steel described in claim 1 is subjected to heat treatment, the heat treatment method including normalizing, quenching and tempering.

7. The heat treatment method according to claim 6, characterized in that, The normalizing process involves heating to a temperature of 900-930℃, with the holding time t1 determined by the steel pipe wall thickness S, where t1 = 3.5 × S. After holding, the pipe is air-cooled. The unit of holding time t1 is min, and the unit of steel pipe wall thickness S is mm.

8. The heat treatment method according to claim 6, characterized in that, The quenching process involves heating at a temperature of 900-930℃, with the holding time t2 determined by the steel pipe wall thickness S, where t2 = 3.2 × S. After holding, the pipe is water-cooled. The unit of holding time t2 is min, and the unit of steel pipe wall thickness S is mm.

9. The heat treatment method according to claim 6, characterized in that, The quenching and tempering are as follows: the tempering temperature is 670-710℃, the holding time t3 is determined by the steel pipe wall thickness S, t3=6×S, and the steel pipe wall thickness S is air-cooled after holding. The unit of holding time t3 is min, and the unit of steel pipe wall thickness S is mm.

10. A steel pipe, characterized in that, It is produced by the heat treatment method described in any one of claims 6-9.

11. The steel pipe according to claim 10, characterized in that, Under a load strength of 75% SMYS, an H2S partial pressure of 0.1 MPa, and a temperature of 25°C, the hydrogen sulfide corrosion resistance test was conducted using the American standard NACE TM0177 Standard A method. No fracture occurred after 720 hours of testing.

12. An application of the steel pipe according to claim 10 or 11, characterized in that, Used for mining in wells 10,000 meters deep.

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