135ksi steel grade hydrogen sulfide corrosion resistant steel for drilling and production method thereof, produced steel pipe, heat treatment method of steel pipe and application of steel pipe

Abstract

The invention provides 135ksi steel-grade hydrogen sulfide corrosion resistant steel for drilling and production, a production method of the 135ksi steel-grade hydrogen sulfide corrosion resistant steel, a produced steel pipe, a heat treatment method of the steel pipe and application of the 135ksi steel-grade hydrogen sulfide corrosion resistant steel. The 135ksi steel-grade hydrogen sulfide corrosion resistant steel comprises the following components: 0.90-1.20% of Cr, 0.60-0.75% of Ni, 0.80-1.00% of Mo, 0.020-0.050% of Al, 0.15-0.25% of V, 0.22-0.27% of C, 0.15-0.30% of Si, 0.60-0.75% of Mn, less than or equal to 0.010% of P, less than or equal to 0.0015% of S and the balance of Fe and other inevitable impurities. Compared with the prior art, a reasonable component system, a pure steel refining control technology and a high-uniformity heat treatment process are matched, so that the material has good obdurability and excellent hydrogen sulfide corrosion resistance, and the produced steel pipe can be used in a deep well of ten thousand meters.

Description

Technical Field

[0001] The invention belongs to the field of alloy steel, and in particular relates to a 135ksi steel grade hydrogen sulfide corrosion resistant drill steel and a production method thereof, a produced steel pipe, a steel pipe heat treatment method and application. Background Art

[0002] At present, many studies are trying to develop 135ksi steel grade sulfur-resistant oil well pipes. However, the developed 135ksi steel grade sulfur-resistant oil well pipes are difficult to meet the index requirements while meeting the toughness requirements and are resistant to H2S corrosion, especially difficult to pass the assessment of NACE TM0177 standard A solution. In addition, the process flow of the oil well pipes in some studies is long and the production efficiency is low. Therefore, it is necessary to consider the chemical composition and process to develop oil well pipes with excellent hydrogen sulfide corrosion resistance and good toughness and their preparation methods to ensure the safe and reliable use of oil well pipes in sulfur-containing deep wells.

[0003] The Chinese patent with publication number CN107177797A published on September 19, 2017 discloses a 130KSI and 135KSI grade corrosion-resistant drill tool steel for oil and gas fields and a manufacturing method thereof. In the technical scheme disclosed therein, the main principle is to improve the hardenability and toughness of the steel by adding main elements such as Mn, Cr, Mo, and to strengthen it by adding trace amounts of V, Nb, Ni, Cu and other elements. After a single quenching and tempering treatment, a tempered bainite structure is obtained. However, its low-temperature Charpy impact energy at -20°C is only greater than 42J, which cannot meet the impact toughness requirements of the drill tool at a depth of 10,000 meters.

[0004] The Chinese patent with the publication date of April 7, 2023 and the publication number of CN115927960A discloses a 125Ksi steel grade oil well pipe resistant to hydrogen sulfide corrosion and its preparation method. In the technical scheme published in the patent, the composition is: C: 0.10% to 0.20%, Si: ≤0.50%, Mn: 0.3% to 0.8%, V: 0.10% to 0.20%, Mo: 0.20% to 0.50%, Ni: 1.0% to 1.5%, Cr: 1.5 to 2.0%, Cu: 1.0 to 2.0%, Als: ≤0.05%, P: ≤0.010%, S: ≤0.003%, and the balance is Fe and unavoidable impurities. The main principle is to add low carbon and supplemented by Mn-Cr-Mo-V-Nb-Cu alloy to obtain tempered bainite structure. However, the tensile strength is greater than 900MPa and the yield strength is greater than 863MPa. As the drilling depth increases to more than 10,000 meters, its strength cannot meet the demand. Summary of the invention

[0005] The object of the present invention is to provide a 135ksi steel grade hydrogen sulfide corrosion resistant drill steel and a production method thereof, which can obtain good strength and toughness and excellent hydrogen sulfide corrosion resistance through component and production process optimization.

[0006] Another object of the present invention is to provide a steel pipe and a heat treatment method for the steel pipe, wherein the steel pipe produced by the above-mentioned 135ksi steel grade hydrogen sulfide corrosion resistant drill steel is treated by a matching heat treatment process to obtain a steel pipe with excellent performance, tensile strength ≥1030MPa, yield strength ≥931MPa, -20℃ impact energy ≥100J, elongation ≥16%, low angle grain boundary ratio ≥30%, austenite grain size ≥8.5, ABCD grade non-metallic inclusions in the steel are all not greater than 1.0 grade, and the total is not greater than 2.5 grade. The steel grade passes the hydrogen sulfide corrosion resistance test using the American standard NACETM0177 standard A method at a loading strength of 75% SMYS, a H2S partial pressure of 0.1MPa, and a temperature of 25℃, and no fracture occurs during the test for 720 hours.

[0007] The last object of the present invention is to provide an application of a steel pipe, wherein the steel pipe produced by the above-mentioned heat treatment process is used for mining in a 10,000-meter deep well.

[0008] The specific technical solutions of the present invention are as follows:

[0009] A 135 ksi steel grade hydrogen sulfide corrosion resistant drill steel comprises the following components in mass 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%, and the rest are Fe and other inevitable impurities.

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

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

[0013] The composition of the steel used in the 135ksi steel grade hydrogen sulfide corrosion resistant drill also satisfies: T = -2×% Si + 1.0

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

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

[0016] The present invention provides a method for producing 135ksi steel 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: using Mg-based and CaO-based desulfurizers to remove sulfur from the molten iron to 0.001%.

[0019] The converter smelting: deoxidation and alloying are carried out after steel is tapped, and the amount of slag is strictly controlled, and the smelting end point P is ≤ 0.008%.

[0020] The LF furnace refining: elements such as C, Si, Mn, Cr, Ni, Mo, and V are adjusted to target values, the white slag retention time is ≥20 minutes, and the smelting cycle is ≤70 minutes.

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

[0022] Calcium treatment in RH vacuum degassing is an effective means to modify the sulfide morphology in the ingot. Calcium treatment not only modifies the original Al2O3 inclusions in the ingot into liquid calcium aluminate inclusions, but also combines with S to form CaS during the cooling process, which reduces the precipitation temperature of MnS inclusions and reduces the precipitation amount of MnS inclusions. The Ca / S range is 0.8 to 2.0, and the effective calcium-sulfur ratio Ca / S formula is defined as:

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

[0024] Where TS is the total sulfur content in steel, 10 -6 , that is, the S content in the steel composition; T.Ca is the total calcium mass fraction in the steel, 10 -6 ; TO is the total oxygen mass fraction in steel, 10 -6 .

[0025] The above is the Ca treatment formula designed for this type of steel. Since the precipitated long strips of sulfides will deteriorate the comprehensive performance of the material, the formula is obtained by thermodynamic calculation fitting of the inclusions in the cooling process of the steel ingot through relevant thermodynamic calculation software.

[0026] The continuous casting is performed for round billet continuous casting, the tundish superheat is controlled to be 20-50°C above the liquidus line, and the continuous casting billet diameter D and the drawing speed v should meet D=1029-1980×v-1470×v 2 The unit of continuous casting billet diameter D is mm, and the unit of casting speed v is m / min. When calculating, just substitute the value before the unit into the formula.

[0027] The rolling process: rolling and finishing, sending the ingot into a step-beam heating furnace, the round steel heating temperature ≥1230℃, the continuous casting ingot diameter D and the heating time t should meet D=180+0.42t. The starting rolling temperature is ≥1180℃, the final rolling temperature is 700~950℃, and after rolling, a heat preservation cover is used or the ingot is placed in a slow cooling pit for slow cooling. Among them, the unit of the continuous casting ingot diameter D is mm, and the unit of the heating time t is min. When calculating, the value before the unit can be directly substituted into the formula for calculation.

[0028] The invention rolls Φ380mm-Φ700mm continuous casting round billets into Φ95mm-Φ320mm round steels.

[0029] The present invention provides a steel pipe produced by using the above-mentioned 135ksi steel grade hydrogen sulfide corrosion resistant drill steel.

[0030] The steel pipe has a low-angle grain boundary ratio of ≥30%, an austenite grain size of ≥8.5, non-metallic inclusions of types A, B, C, and D in the steel are all not greater than level 1.0, and the sum of non-metallic inclusions of types A, B, C, and D is not greater than level 2.5.

[0031] The grain size at 1 / 2 wall thickness of the end cross section of the steel pipe is ≤20 μm, and the structure is a tempered bainite structure.

[0032] The steel pipe passed the hydrogen sulfide corrosion resistance test using the American standard NACE TM0177 standard A method under a loading strength of 75% SMYS, a H2S partial pressure of 0.1 MPa, and a temperature of 25°C, and no fracture occurred during the test for 720 hours.

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

[0034] The present invention provides a steel pipe heat treatment method, which uses the above-mentioned 135ksi steel grade hydrogen sulfide corrosion resistant drill to produce steel to perform heat treatment on the steel pipe.

[0035] The heat treatment method includes normalizing, quenching and tempering.

[0036] The normalizing is carried out at a heating temperature of 900-930°C, and the holding time t1 is determined by the steel pipe wall thickness S, t1=3.5×S, and air cooling is performed after the holding time. The unit of the holding time t1 is min, and the unit of the steel pipe wall thickness S is mm.

[0037] The quenching is carried out at a heating temperature of 900-930°C, and the holding time t2 is determined by the steel pipe wall thickness S, t2=3.2×S, and water cooling is performed after the holding time t2, wherein the unit of the holding time t2 is min, and the unit of the steel pipe wall thickness S is mm.

[0038] Tempering: Tempering temperature is 670-710°C, holding time t3 is determined by the steel pipe wall thickness S, t3=6×S, and air cooling is performed after holding. The unit of holding time t3 is min, and the unit of steel pipe wall thickness S is mm.

[0039] Normalizing as a pretreatment can refine the original coarse grains, which can improve the strength and toughness of the steel and lay a good foundation for the subsequent quenching and tempering treatment. The quenching and tempering heat treatment (quenching and tempering) is to obtain fine tempered troostite. The heat treatment temperature is set according to the AC3 temperature of the material to ensure that the material can be completely austenitized (the present invention controls it to 900-930°C). The insulation time is determined according to the wall thickness of the material. A reasonable annealing time is designed to ensure that it can be completely austenitized.

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

[0041] The design ideas of the present invention are as follows:

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

[0043] Mn: improves the strength and permeability of steel, but Mn is an easily segregated element. Excessive Mn content is easily segregated with S and P at the grain boundaries, so it is not good for the anti-SSC performance. The Cr and Mo contents designed in the present invention are relatively high, which are sufficient to ensure the hardenability and strength of the steel, so the Mn content is controlled at 0.60-0.75%.

[0044] Cr: Improves strength and hardenability, improves corrosion resistance, but excessive Cr content will precipitate large Cr at the grain boundary during tempering 23 C6 carbide is not conducive to the resistance to H2S stress corrosion, so the Cr content is controlled at 0.90-1.20%.

[0045] Mo: It is an important solid solution strengthening and tempering precipitation strengthening element, and it improves the hardenability of steel. Mo carbides precipitate during high temperature tempering to improve tempering resistance, so sufficient Mo must be added to ensure high strength and high tempering temperature. In addition, Mo can also reduce the segregation of P at the grain boundary by reducing the diffusion coefficient of P, but when Mo is too high, coarse carbides will also be formed, which is not conducive to the resistance to H2S stress corrosion, so the Mo content is controlled at 0.80-1.00%.

[0046] Ni: Ni is an austenite stabilizing element, which has the function of expanding the phase region, increasing the stability of supercooled austenite, and improving the hardenability of steel. At the same time, Ni improves the toughness of the material by solid solution, especially significantly reducing the tough-brittle transition temperature. Ni can also refine the width of martensite laths and improve strength, but excessive addition reduces the SSC resistance of steel. Therefore, the Ni content is controlled at 0.60% to 0.75%.

[0047] V: Its role in quenched and tempered steel is to inhibit tempering softening and increase tempering temperature. During high temperature tempering, VC carbides are precipitated to play a precipitation strengthening role, thus ensuring that the dislocation density of the steel is reduced during high temperature tempering, improving the SSC resistance, and ensuring the high strength requirement of 135ksi; however, when the V content in the steel exceeds a certain upper limit, the SSC resistance will no longer be improved, so the V content is controlled at 0.15-0.25%.

[0048] P, S and five harmful elements: P, S and five harmful elements Sn, Sb, As, Pb, Bi are impurity elements in steel, which significantly reduce the material's SSC resistance. Their content in steel should be reduced as much as possible. P is easy to form segregation in steel, and the stress zone at the tip of MnS inclusions is easy to become the starting point of sulfide stress cracking. Therefore, P, S and 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 to modify the morphology of sulfides in the ingot. It can also modify Al2O3 inclusions and magnesia-alumina spinel in the steel and improve the castability of the molten steel during the continuous casting process. In order to obtain a good calcium treatment effect, according to actual production experience, the Ca / S ratio should be controlled at 0.8-2.0.

[0051] In order to ensure good low-temperature toughness of steel, the ratio of Si, Mo, Mn, Ni and V needs to be limited. Since Si is easy to segregate at the austenite grain boundary, it reduces the crystal bonding force, deteriorates the low-temperature toughness and increases the temper brittleness, so the coefficient of Si is -2.0. Mn can significantly affect the variant selection during the phase transformation process, increase the types of variants in the phase transformation, and thus improve the low-temperature toughness, so the coefficient of Mn is 1.0; Mo can improve the hardenability of steel, effectively reduce the segregation of impurity elements such as P, S, and As at the grain boundary, and effectively improve the low-temperature toughness of steel, so the coefficient of Mo is 1.3; Ni can significantly reduce the tough-brittle transition temperature of steel and improve the low-temperature toughness, so the coefficient of Ni is 2.5; V can precipitate fine VC, refine the microstructure and improve the tempering stability of steel, thereby improving the low-temperature toughness, so the coefficient of 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] In order to ensure the steel has good resistance to hydrogen sulfide corrosion, the ratio of Si, Mn, Cr, Mo and V needs to be limited. Since Si and Mn are easy to segregate at the austenite grain boundary, the crystal bonding force is reduced, resulting in uneven microstructure and reduced corrosion resistance, so the coefficient is -5. Mo can improve the hardenability of steel, effectively reduce the segregation of impurity elements such as P and S at the grain boundary, and precipitate carbide Mo2C during tempering, which can become a trap for capturing H, effectively improving the sulfur resistance of steel, so the coefficient of Mo is 12; VC precipitated by V can effectively inhibit grain growth, and as an irreversible H trap, greatly improve the SSC resistance. In addition, vanadium can improve the steel's resistance to tempering softening, reduce the material's dislocation density, and improve the SSC resistance, so the coefficient of V is 18; the irreversible H hydrogen trap provided by Cr can effectively capture H atoms, slow down the diffusion rate of H atoms, and improve the SSC resistance, so the coefficient of Cr is 10:

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

[0055] The alloy elements added in the present invention are processed by normalizing + quenching and tempering process, so that the material precipitates more fine alloy carbides, which not only refines the grains and improves the toughness of the material, but also acts as an irreversible hydrogen trap to improve the SSC resistance of the material.

[0056] Compared with the prior art, the present invention adopts a reasonable component system, refining control technology and high uniformity heat treatment process, and can obtain a dispersed and refined second phase distributed on the tempered troostite matrix at room temperature, a lower dislocation density and an increased low-angle grain boundary ratio, so that the material has good toughness and excellent resistance to hydrogen sulfide corrosion. The present invention can produce 135ksi steel grade high-strength SSC-resistant drill steel through a converter, which can be used in 10,000-meter deep wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is the organizational diagram of Comparative Example 3;

[0058] Figure 2 This is the organizational diagram of Example 1. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] Example 1-Example 3

[0061] A 135 ksi steel grade hydrogen sulfide corrosion resistant drill adopts steel, which includes the following mass percentage components: as shown in Table 1, and the balance not shown in Table 1 is Fe and inevitable impurities.

[0062] Comparative Example 1-Comparative Example 4

[0063] A 135 ksi steel grade hydrogen sulfide corrosion resistant drill adopts steel, which includes the following mass percentage components: as shown in Table 1, and the balance not shown in Table 1 is Fe and inevitable impurities.

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

[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 measured by the equipment. In addition, the five harmful elements Sn, Sb, As, Pb, and Bi are controlled at ≤0.010%.

[0068] The production method of the 135ksi steel grade hydrogen sulfide corrosion resistant drill steel of the above embodiment and comparative example 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: using Mg-based and CaO-based desulfurizers to remove sulfur from the molten iron to 0.001%.

[0071] The converter smelting: deoxidation and alloying are carried out after steel is tapped, and the amount of slag is strictly controlled, and the smelting end point P is ≤ 0.008%.

[0072] The LF furnace refining: elements such as C, Si, Mn, Cr, Ni, Mo, and V are adjusted to target values, the white slag retention time is ≥20 minutes, and the smelting cycle is ≤70 minutes.

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

[0074] Calcium treatment in RH vacuum degassing is an effective means to modify the morphology of sulfides in the ingot. The present invention controls the Ca / S range to be 0.8 to 2.0. The effective calcium-sulfur ratio Ca / S formula is defined as follows:

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

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

[0077] The continuous casting is performed for round billet continuous casting, the superheat of the tundish is controlled to be 20-50°C above the liquidus line, and the diameter D of the continuous casting billet and the drawing speed v should meet D=1029-1980×v-1470×v 2 The unit of continuous casting billet diameter D is mm, and the unit of pulling speed v is m / min. The specific production diameter D = 500mm continuous casting round billet, superheat 45℃, pulling speed v = 0.23m / min.

[0078] The rolling process: Φ500mm continuous casting round billet is rolled into Φ150mm hot-rolled round steel, and the billet is sent into a walking beam heating furnace, the heating temperature is ≥1230℃, the holding time is 762min, and it meets D=180+0.42t. The starting rolling temperature is ≥1180℃, the final rolling temperature is 700~950℃, and after rolling, a heat preservation cover is used or the billet is put into a slow cooling pit for slow cooling.

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

[0080] The steel pipes are produced by using the steel grade 135ksi hydrogen sulfide corrosion resistant drill steel of each embodiment and comparative example. The pipe making route is: Φ95mm~Φ320mm hot-rolled round steel → heating → pipe threading → sizing → heat treatment → steel pipe grinding → steel pipe flaw detection → fine processing → flaw detection → packaging and storage. The specific heat treatment method includes normalizing + quenching and tempering. The present invention uses Φ150mm hot-rolled round steel for production.

[0081] The normalizing process has a heating temperature of 900-930°C, a holding time t1 determined by the steel pipe wall thickness S, t1=3.5×S, and air cooling, wherein the holding time t1 is expressed in min, and the steel pipe wall thickness S is expressed in mm.

[0082] The quenching is carried out at a heating temperature of 900-930°C, and the holding time t2 is determined by the steel pipe wall thickness S, t2=3.2×S, and water cooling is used. The unit of the holding time t2 is min, and the unit of the steel pipe wall thickness S is mm.

[0083] Tempering: Tempering temperature is 670-710°C, holding time t3 is determined by the steel pipe wall thickness S, t=6×S, air cooling. The unit of holding time t3 is min, and the unit of steel pipe wall thickness S is mm.

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

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

[0086]

[0087] The performance testing methods of the steel pipes in the embodiments and comparative examples are as follows:

[0088] Organization: Take samples from 1 / 2 wall thickness of the cross section at the end of the steel pipe for metallographic and grain size analysis.

[0089] Performance: tensile, impact and SSC resistance specimens were taken on the 1 / 2 radius of the steel pipe, and mechanical properties tests were carried out according to GB / T228 and GB / T229. The SSC resistance test was carried out according to NACE TM0177 standard A method (loading strength was 75% SMYS, H2S partial pressure was 0.1 MPa, and temperature was 25°C). The average grain size was observed according to GB / T 6394, and 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 are taken from the 1 / 2 radius of the hot-rolled round steel and tested according to Method A in ASTM E45. The properties are shown in Table 4.

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

[0092]

[0093]

[0094] Table 4 Non-metallic inclusion level requirements (unit: level)

[0095]

[0096] Figure 1 This is the organization diagram of comparative example 3. Since the quenching temperature is not within the range of 900-930°C, the material is not completely quenched and bainite structure appears during the cooling process.

[0097] Figure 2 This is the organizational diagram of Example 1. Due to proper composition and heat treatment process, the organization is a fine tempered troostite organization.

[0098] The chemical composition and production method of the steel of Examples 1 to 3 are properly controlled, and their chemical composition meets the requirements, and the strength, toughness and SSC resistance of the steel are good. The C content of Comparative Example 1 is not controlled according to the present invention, and the T value is small. Even if it is produced according to the production method and heat treatment process of the steel of the present invention, the low-temperature toughness of the produced steel pipe is low and cannot meet the requirements of the present invention. Although the composition of Comparative Example 2 meets the requirements of the present invention, the R value is low, resulting in a significant decrease in the SSC resistance. The chemical composition of Comparative Example 3 is properly controlled, and the steel is also produced according to the present invention; it is just that the heat treatment process is improper, resulting in unsatisfactory overall performance. Although the composition of Comparative Example 4 meets the requirements of the present invention, the R value and T value are both low. Even if the heat treatment process meets the requirements of the present invention, the proportion of low-angle grain boundaries of the product is significantly reduced, and the SSC resistance is extremely poor.

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

[0100] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 present invention should be within the protection scope of the present invention.

Claims

1. A 135ksi steel grade hydrogen sulfide corrosion resistant drill steel, characterized in that: The 135ksi steel grade hydrogen sulfide corrosion resistant drill steel comprises the following mass percentage components: 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 are Fe and other inevitable impurities.

2. The 135ksi steel grade hydrogen sulfide corrosion resistant drill steel according to claim 1 is characterized in that: The composition of the steel used in the 135ksi steel grade hydrogen sulfide corrosion resistant drill also satisfies: T = -2×% Si + 1.0 ×%Mn+1.3×%Mo+2.5×%Ni+1.8×%V≥3.10%.

3. The 135ksi steel grade hydrogen sulfide corrosion resistant drill steel according to claim 1 or 2, characterized in that: The composition of the steel used in the 135ksi steel grade hydrogen sulfide corrosion resistant drill also satisfies: R=-5×(%Si+%Mn)+12×%Mo+10×%Cr+18×%V≥19.00%.

4. A method for producing 135ksi steel grade hydrogen sulfide corrosion resistant drill steel according to any one of claims 1 to 3, characterized in that: The production method comprises the following process flow: Hot metal pretreatment → converter smelting → LF furnace refining → RH vacuum degassing → continuous casting → rolling.

5. The production method according to claim 4, characterized in that: The formula for the effective calcium-sulfur ratio Ca / S in the calcium treatment of the RH vacuum degassing is: Ca / S = [T.Ca-(0.31+0.02×T.Ca)×(0.99×TO-5.44)] / 1.25×TS; Ca / S range is 0.8~2.0, where TS is the total sulfur mass fraction in steel, 10 -6 ; T.Ca is the total calcium mass fraction in steel, 10 -6 ; TO is the total oxygen mass fraction in steel, 10 -6 .

6. The production method according to claim 4, characterized in that: The continuous casting, continuous casting billet diameter D and drawing speed v should meet D = 1029-1980×v-1470×v 2 ; The unit of continuous casting billet diameter D is mm, and the unit of casting speed v is m / min.

7. The production method according to claim 4, characterized in that: The rolling process: the billet is fed into a step-beam heating furnace, the billet diameter D and the heating time t should meet D = 180 + 0.42t, and the rolling temperature ≥ 1180℃, where the unit of continuous casting billet diameter D is mm, and the unit of heating time t is min.

8. A steel pipe heat treatment method, characterized in that: The steel pipe produced by using the 135ksi steel grade hydrogen sulfide corrosion resistant drill steel as described in any one of claims 1 to 3 is subjected to heat treatment, and the heat treatment method includes normalizing, quenching and tempering.

9. The heat treatment method according to claim 8, characterized in that: The normalizing is performed at a heating temperature of 900-930°C, and the holding time t1 is determined by the steel pipe wall thickness S, t1=3.5×S, and air cooling is performed after holding. Among them, the unit of the holding time t1 is min, and the unit of the steel pipe wall thickness S is mm.

10. The heat treatment method according to claim 8, characterized in that: For the quenching, the heating temperature is 900-930°C, the holding time t2 is determined by the steel pipe wall thickness S, t2=3.2×S, and water cooling is performed after holding; wherein, the unit of the holding time t2 is min, and the unit of the steel pipe wall thickness S is mm.

11. The heat treatment method according to claim 8, characterized in that: The quenching and tempering: the tempering temperature is 670-710°C, the holding time t3 is determined by the steel pipe wall thickness S, t3=6×S, and air cooling is performed after holding; wherein, the unit of the holding time t3 is min, and the unit of the steel pipe wall thickness S is mm.

12. A steel pipe, characterized in that: The steel pipe is produced by the heat treatment method according to any one of claims 8 to 11, characterized in that the proportion of low-angle grain boundaries of the steel pipe is ≥30%, the ABCD-level non-metallic inclusions in the steel are all not greater than level 1.0, the sum of the ABCD-level non-metallic inclusions is not greater than level 2.5, and the grain size at 1 / 2 of the wall thickness of the end cross section of the steel pipe is ≤20μm.

13. The steel pipe according to claim 12, characterized in that Under the conditions of loading strength of 75% SMYS, H2S partial pressure of 0.1MPa and temperature of 25°C, the steel pipe passed the hydrogen sulfide corrosion test using the American standard NACE TM0177 standard A method, and no fracture occurred during the test for 720 hours; the tensile strength of the steel pipe is ≥1030MPa, the yield strength is ≥931MPa, and the impact energy at -20°C is ≥100J.

14. Use of the steel pipe according to claim 12 or 13, characterized in that: Used for mining in 10,000-meter deep wells.

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