Medium-carbon low-alloy anti-SSC drilling steel and production method thereof, drilling steel pipe and heat treatment method and application

Abstract

The invention provides medium-carbon low-alloy anti-SSC steel for drilling and production, a production method of the medium-carbon low-alloy anti-SSC steel, a drilling and production steel pipe, a heat treatment method and application of the medium-carbon low-alloy anti-SSC steel. The medium-carbon low-alloy anti-SSC steel comprises the following components: 0.50-0.70% of Cr, 0.20-0.40% of Ni, 0.70-0.85% of Mo, 0.015-0.035% of Al, 0.05-0.10% of V, 0.070-0.150% of Ti, 0.27-0.33% of C, 0.15-0.30% of Si, 0.40-0.60% 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. Through component and heat treatment process design, a uniform and fine tempered sorbite structure is obtained and has relatively low dislocation density and high-angle grain boundary proportion, so that the material has good obdurability and excellent hydrogen sulfide corrosion resistance.

Description

Technical Field

[0001] The present invention belongs to the field of alloy steel, and in particular relates to a medium-carbon low-alloy SSC-resistant drilling steel and a production method, a drilling steel pipe, and a heat treatment method and application thereof. Background Art

[0002] Oil and natural gas are important energy sources that support the long-term stable and sustainable development of society and economy. With the increasing demand for oil and natural gas, mining work is carried out in deeper strata. For the service environment with high temperature, high pressure and hydrogen sulfide corrosion factors, it is of great significance to the oil and gas industry to develop drill steel with high strength, toughness and high resistance to SSC.

[0003] A variety of metallurgical factors, including the chemical composition of the material, metallurgical quality, thermal processing and microstructure, will have a significant impact on the anti-SSC performance. A large number of previous research results show that medium-carbon chromium-molybdenum steel prepared or produced by high homogenization treatment technology can form ferrite characteristics and fine carbides uniformly dispersed in the tempered martensite structure after quenching and high-temperature tempering heat treatment. This structure is expected to show the best anti-SSC performance.

[0004] The Chinese invention patent with publication number CN112813359A published on May 18, 2021, discloses a medium-carbon low-alloy high-strength hydrogen sulfide corrosion-resistant oil well pipe. The disclosed oil well pipe product is designed based on the Cr-Mo steel system, and micro-alloys V, Nb and rare earth elements RE are added to produce a 110ksi steel grade SSC-resistant oil well pipe. However, its strength is low and cannot meet the requirements for deep oil well exploitation.

[0005] The Chinese invention patent with publication number CN109913757A published on June 21, 2019 discloses a corrosion-resistant and highly collapse-resistant petroleum casing and a preparation method thereof. The main principle is to strengthen it by adding alloy elements such as Cr and Mo, but its strength is relatively low and cannot meet the requirements for deep oil well exploitation. Summary of the invention

[0006] The purpose of the present invention is to provide a medium-carbon low-alloy SSC-resistant drilling steel and a production method. Through component design optimization, the obtained steel has good strength and toughness and excellent resistance to hydrogen sulfide corrosion, and can be used for the manufacture of drilling steel pipes.

[0007] Another object of the present invention is to provide a drilling steel pipe and a heat treatment method, which is produced by utilizing the above-mentioned medium-carbon low-alloy SSC resistant drilling steel. Through a designed matching heat treatment method, a drilling steel pipe is obtained, which has a uniform and fine tempered bainite structure, a lower dislocation density and a higher recrystallization ratio, and the product has good strength and toughness and excellent resistance to hydrogen sulfide corrosion.

[0008] Another object of the present invention is to provide an application of a drilling steel pipe for use in deep well mining with a depth of ≥8000 meters.

[0009] The specific technical solutions of the present invention are as follows:

[0010] A medium carbon low alloy SSC resistant drill steel comprises the following components in percentage by weight:

[0011] Cr: 0.50~0.70%, Ni: 0.20~0.40%, Mo: 0.70~0.85%, Al: 0.015~0.035%, V: 0.05~0.10%, Ti: 0.070~0.150%, C: 0.27~0.33%, Si: 0.15~0.30%, Mn: 0.40~0.60%, P≤0.010%, S≤0.0015%, the balance is Fe and inevitable impurities.

[0012] The composition of the steel used in the medium carbon low alloy anti-SSC drill also meets the following requirements: T.O+[N]≤120ppm; the five harmful elements Sn, Sb, As, Pb, and Bi are controlled at ≤0.010%;

[0013] The composition of the steel used in the medium carbon low alloy SSC resistant drill also satisfies: T = -2×%Si+1.0×%Mn+1.3×%Mo+2.5×%Ni+2.0×(%V+%Ti)≥2.00%. Each element represents its mass percentage content in the steel.

[0014] The composition of the steel used in the medium carbon low alloy SSC resistant drill also satisfies: R = -5 × (% Si + % Mn) + 12

[0015] ×%Mo+10×%Cr+20×%Ti+18×%V≥15.00%. Each element represents its mass percentage content in steel.

[0016] The present invention provides a method for producing medium-carbon low-alloy SSC-resistant drill steel, comprising the following process flow:

[0017] Electric arc furnace smelting → LF furnace refining → RH vacuum degassing → continuous casting → rolling.

[0018] In the electric arc furnace smelting, the steel is deoxidized and alloyed, and the amount of slag is strictly controlled. The smelting end point S is less than or equal to 0.030%, and P is less than or equal to 0.120%.

[0019] In the LF furnace refining, elements such as C, Si, Mn, Cr, Ni, Mo, V, and Ti are adjusted to target values, the white slag retention time is ≥20 minutes, and the smelting cycle is ≤70 minutes.

[0020] The RH vacuum degassing, pure degassing time ≥ 25min, soft blowing time ≥ 20min, after vacuum treatment

[0021] [H]≤1.0ppm.

[0022] Calcium treatment during the RH vacuum degassing stage 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 continuous casting is for round billets, the overheating degree 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 , where the unit of continuous casting billet diameter D is mm, and the unit of casting speed v is m / min. Match according to the above formula to improve the quality of the billet. When calculating, just substitute the value before the unit into the formula. Continuous casting obtains round billets with a diameter of 380mm to 700mm, and the general specifications are: 380mm, 450mm, 500mm, 600mm, 700mm.

[0026] The rolling process rolls the Φ380mm~Φ700mm continuous casting round billets into Φ90mm~Φ250mm round steels, and then finishes them into finished products. Specifically, the billet is sent into a step-type heating furnace, the heating temperature of the round steel is ≥1230°C, the diameter D of the continuous casting billet and the heating time t should meet the requirement of D=180+0.42t, where the unit of the diameter D of the continuous casting billet is mm, and the unit of the heating time t is min. According to the above process matching, the quality of rolled steel is improved. When calculating, just substitute the value before the unit into the formula. The starting rolling temperature is ≥1180°C, the final rolling temperature is 700~950°C, and after rolling, a heat preservation cover is used or the billet enters a slow cooling pit for slow cooling.

[0027] The present invention provides a drilling steel pipe, which is produced by adopting the above-mentioned medium-carbon low-alloy SSC-resistant drilling steel.

[0028] The dislocation density of the drilling steel pipe is 3.0×10 14 / m 2 ~8.0×10 14 / m 2 , recrystallization ratio ≥15%, high-angle grain boundary ratio ≤70%.

[0029] The area of ​​tempered bainite in the drilling and production steel pipe accounts for more than 98%; the austenite grain size is ≥8.5, and the grain size is ≤20μm.

[0030] The yield strength of the drilling steel pipe is ≥830MPa, the tensile strength is ≥940MPa, the impact energy at -20°C is ≥110J, and the elongation is ≥16%.

[0031] The drilling steel pipe passed the hydrogen sulfide corrosion resistance test using the American standard NACE TM0177 standard A method at a loading strength of 80% 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.

[0032] The invention provides a heat treatment method for a drilling steel pipe, which includes quenching and two temperings, specifically: first quenching, then one tempering, and then two temperings.

[0033] The quenching: heating temperature W = AC3 + 30 ~ 50 ° C, holding time t1 is determined by the steel pipe wall thickness S, t1 = 3.2 × S, water cooling. When calculating, directly substitute the value before the unit into the formula for calculation.

[0034] Among them, the unit of heating temperature W is ℃, the unit of holding time t1 is min, and the unit of steel pipe wall thickness S is mm;

[0035] Primary tempering: The primary tempering temperature W1 is 650-720℃, and the holding time t2 is determined by the steel pipe wall thickness S, t2=6×S, air-cooled to room temperature, and then secondary tempering. When calculating, directly substitute the value before the unit into the formula.

[0036] Among them, the unit of the primary tempering temperature W1 is ℃, the unit of the holding time t2 is min, and the unit of the steel pipe wall thickness S is mm;

[0037] Secondary tempering: Secondary tempering temperature W2 = W1-10℃, holding time t3 is determined by the steel pipe wall thickness S, t3 = 4×S, air cooling. When calculating, just substitute the value before the unit into the formula.

[0038] Among them, the unit of secondary tempering temperature W2 is ℃, the unit of holding time t3 is min, and the unit of steel pipe wall thickness S is mm.

[0039] When calculating the above formula, simply substitute the value before the unit into the formula.

[0040] The invention uses two short-term tempering treatments, and the size of the precipitates and the dislocation density are significantly reduced. DCB tests show that the SSC resistance is improved in the case of double tempering. The proportion of Σ3 boundaries, high-angle grain boundaries and high Taylor factor values ​​in the double tempered samples is lower, and the sensitivity to crack initiation and propagation is reduced.

[0041] Preferably, the specific production process of the drilling steel pipe of the present invention using the above-mentioned heat treatment method is: hot-rolled round steel→heating→pipe threading→sizing→heat treatment→steel pipe grinding→steel pipe flaw detection→finishing→flaw detection→packaging and warehousing.

[0042] The invention provides an application of a drilling steel pipe for use in deep well mining with a depth of ≥8000 meters.

[0043] The design ideas of the present invention are as follows:

[0044] 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 0.27-0.33%.

[0045] 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 0.40-0.60%.

[0046] 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 0.50-0.70%.

[0047] 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 0.70-0.85%.

[0048] 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 0.20% to 0.40%.

[0049] 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 0.05-0.10%.

[0050] Ti: A strong irreversible hydrogen trap is generated by producing a large amount of TiC precipitation in the matrix, and the proportion of low-angle grain boundaries is increased to increase the density of reversible hydrogen traps. This results in a more uniform distribution of hydrogen atoms, hindering the aggregation of hydrogen at the crack initiation point and crack tip, and effectively improving the material's SSC resistance. However, too high Ti may lead to the appearance of oversized chain and block TiN inclusions during the steelmaking process, reducing material properties, so the Ti content is controlled at 0.070% to 0.150%.

[0051] 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.

[0052] 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.

[0053] Ca / S: During the refining process, Ca wire is added to treat the molten steel with calcium. On the one hand, the solid Al2O3 inclusions in the steel are modified into liquid calcium aluminates, which improves the castability of the molten steel during the continuous casting process. On the other hand, Ca has a stronger binding ability with S than Mn, and point-like CaS inclusions are preferentially generated during the solidification of molten steel, which can reduce the total amount and aggregation of MnS precipitation in the steel. For low-sulfur steel, when Ca / S is in the range of 0.8 to 2.0, small-sized spherical CaS and MnS inclusions can be formed, which is beneficial to reduce the formation of long strip-shaped MnS inclusions in the steel, so the Ca / S ratio is controlled at 0.8 to 2.0.

[0054] In order to ensure good low-temperature toughness of steel, the ratio of Si, Mo, Mn, Ni, V and Ti 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; Ti and V can precipitate fine MC carbides, refine the structure and improve the tempering stability of steel, thereby improving the low-temperature toughness, so the coefficients of Ti and V are 2.0:

[0055] That is, T=-2×%Si+1.0×%Mn+1.3×%Mo+2.5×%Ni+2.0×(%V+%Ti)≥2.00%.

[0056] In order to ensure the steel has good hydrogen sulfide corrosion resistance, the ratio of Si, Mn, Cr, Mo, Ti, 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; Ti and V precipitate MC-type carbides can effectively inhibit grain growth, and as irreversible H traps, greatly improve the SSC resistance. In addition, it can improve the steel's resistance to temper softening, reduce the material's dislocation density, and improve the SSC resistance. According to relevant research, TiC has a greater ability to capture hydrogen than VC, so the coefficient of V is 18 and the coefficient of Ti is 20; the irreversible hydrogen trap provided by Cr can effectively capture H atoms, slow down the diffusion rate of H atoms, and improve the anti-SSC performance, so the coefficient of Cr is 10:

[0057] That is, R=-5×(%Si+%Mn)+12×%Mo+10×%Cr+20×%Ti+18×%V≥15.00%.

[0058] Compared with the prior art, the present invention adopts reasonable medium carbon system composition, pure steel smelting technology and two-time quenching and tempering heat treatment process to obtain uniform and fine tempered troostite structure with lower dislocation density and higher recrystallization ratio, so that the material has good strength and toughness and excellent resistance to hydrogen sulfide corrosion. The products produced can meet the use of deep well mining with a depth of ≥8000 meters. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 EBSD recrystallization diagram of Example 1 (blue represents recrystallized grains);

[0060] Figure 2 This is the EBSD recrystallization diagram of comparative example 2. DETAILED DESCRIPTION

[0061] 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.

[0062] Example 1-Example 3

[0063] A medium carbon low alloy SSC resistant drill steel comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0064] Comparative Example 1-Comparative Example 3

[0065] A medium carbon low alloy SSC resistant drill steel comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0066] Table 1 shows the steel composition (wt%) of each embodiment and comparative example

[0067]

[0068] In Table 1, T.Ca is the actual data measured by the equipment; the five harmful elements Sn, Sb, As, Pb, and Bi are controlled at ≤0.010%.

[0069] The production method of the carbon low alloy SSC resistant drill steel in the above embodiments and comparative examples includes the following process flow:

[0070] Electric arc furnace smelting → LF furnace refining → RH vacuum degassing → continuous casting → rolling.

[0071] In the electric arc furnace smelting, the steel is deoxidized and alloyed, and the amount of slag is strictly controlled. The smelting end point S is less than or equal to 0.030%, and P is less than or equal to 0.120%.

[0072] In the LF furnace refining, elements such as C, Si, Mn, Cr, Ni, Mo, V, and Ti 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 ≥ 25min, soft blowing time ≥ 20min, after vacuum treatment

[0074] [H]≤1.0ppm, calcium treatment is carried out, and the effective calcium-sulfur ratio Ca / S formula is:

[0075] Ca / S = [T.Ca-(0.31+0.02×T.Ca)×(0.99×TO-5.44)] / 1.25×TS; 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 The effective calcium-sulfur ratio Ca / S of each embodiment and comparative example is shown in Table 1.

[0076] The continuous casting is a round billet with a diameter of 500 mm, a superheat of 45°C, and a pulling speed of 0.23 m / min. The diameter D of the continuous casting billet and the pulling speed v should meet the requirement of D = 1029-1980×v-1470×v 2 , where the unit of continuous casting billet diameter D is mm, and the unit of casting speed v is m / min.

[0077] The rolling process is to roll a Φ500mm continuous casting round billet into a Φ150mm hot-rolled round steel, and send the billet into a walking beam heating furnace, with a heating temperature of ≥1230°C, a holding time of 762min, and a continuous casting billet diameter D and a heating time t that meet the condition of D=180+0.42t, wherein the unit of the continuous casting billet diameter D is mm, and the unit of the heating time t is min. The starting rolling temperature is ≥1180°C, the final rolling temperature is 700-950°C, and after rolling, a heat preservation cover is used or the billet enters a slow cooling pit for slow cooling.

[0078] 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.

[0079] The above-mentioned medium-carbon low-alloy SSC resistant drill steel is used to produce drilling steel pipes, and the specific process is: hot-rolled round steel → heating → pipe threading → sizing → heat treatment → steel pipe grinding → steel pipe flaw detection → fine processing → flaw detection → packaging and warehousing.

[0080] The heat treatment is specifically: quenching first, then tempering once, and then tempering twice.

[0081] The quenching: heating temperature W = AC3 + 30 ~ 50 ° C, holding time t1 is determined by the steel pipe wall thickness S, t1 = 3.2 × S, water cooling. AC3 is tested using a Gleeble-2000D thermal simulation tester. W1 in each embodiment and comparative example satisfies W1 = AC3 + 30 ~ 50 ° C, generally 910-930 ° C.

[0082] Among them, the unit of heating temperature W is ℃, the unit of holding time t1 is min, and the unit of steel pipe wall thickness S is mm;

[0083] First tempering: The first tempering temperature W1 is 650-720℃, the holding time t2 is determined by the steel pipe wall thickness S, t2=6×S, and air-cooled to room temperature;

[0084] Among them, the unit of the primary tempering temperature W1 is ℃, the unit of the holding time t2 is min, and the unit of the steel pipe wall thickness S is mm;

[0085] Second tempering: Second tempering temperature W2 = W1-10 ° C, holding time t3 depends on the steel pipe wall thickness S, t3 = 4 × S, air cooling.

[0086] Among them, the unit of the second tempering temperature W2 is ℃, the unit of the holding time t3 is min, and the unit of the steel pipe wall thickness S is mm.

[0087] The heat treatment parameters of each embodiment and comparative example are shown in Table 2.

[0088] Table 2 List of heat treatment processes for the embodiments of the present invention and comparative examples

[0089]

[0090] The performance testing methods of the drilling steel pipes produced in each embodiment and comparative example are as follows:

[0091] 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.

[0092] 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, and SSC resistance tests were carried out according to NACE TM0177 standard A method (at a loading strength of 80% SMYS, a H2S partial pressure of 0.1 MPa, and a temperature of 25°C), and average grain size observation was carried out according to GB / T 6394. The results are shown in Table 3.

[0093] Non-metallic inclusions: Samples were taken from the 1 / 2 radius of the hot-rolled round steel and tested according to Method A in GB / T 10561. The results are shown in Table 4.

[0094] Table 3 Performance test results of the embodiments of the present invention and the comparative examples

[0095]

[0096]

[0097] The higher the recrystallization ratio, the better the material's resistance to hydrogen sulfide corrosion is generally. The recrystallization process refines the material's grains and makes them uniform, reducing defects such as large-angle grain boundaries, thereby reducing the segregation and diffusion channels of hydrogen sulfide at the grain boundaries, making it difficult for corrosion to proceed along the grain boundaries, and improving the material's corrosion resistance. During the recrystallization process, the diffusion and migration of atoms help to make the distribution of alloying elements and impurity elements in the material more uniform, reducing the corrosion microcells formed in local areas due to impurity segregation, reducing the corrosion rate, and thus improving the material's resistance to hydrogen sulfide corrosion. Figure 1 EBSD recrystallization diagram of Example 1 (blue represents recrystallized grains); Figure 2 This is the EBSD recrystallization of Comparative Example 2. It can be clearly seen that the recrystallization ratio of Example 1 is higher than that of Comparative Example 2.

[0098] Table 4 Non-metallic inclusion level requirements (unit: level)

[0099]

[0100] The chemical composition and production method of the steel of Examples 1-3 are properly controlled, and their chemical composition meets the requirements, and the strength, toughness and SSC resistance of the steel are good. Comparative Example 1 has an inappropriate chemical composition, a small T value, and the heat treatment is not carried out according to the present invention, resulting in low strength and low-temperature toughness. Comparative Example 2 has an inappropriate chemical composition, a small R value, and the heat treatment is not carried out according to the present invention, resulting in a decrease in SSC resistance. The chemical composition of Comparative Example 3 meets the requirements of the present invention, but the heat treatment process is improperly handled, resulting in unsatisfactory overall performance.

[0101] The underlined data above do not meet the requirements of the present invention.

[0102] 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 medium carbon low alloy SSC resistant drill steel, characterized in that: The medium carbon low alloy SSC resistant drill steel comprises the following components in mass percentage: Cr: 0.50~0.70%, Ni: 0.20~0.40%, Mo: 0.70~0.85%, Al: 0.015~0.035%, V: 0.05~0.10%, Ti: 0.070~0.150%, C: 0.27~0.33%, Si: 0.15~0.30%, Mn: 0.40~0.60%, P≤0.010%, S≤0.0015%, the balance is Fe and inevitable impurities.

2. The medium carbon low alloy SSC resistant drill steel according to claim 1 is characterized in that: The composition of the steel used in the medium-carbon low-alloy SSC-resistant drill also satisfies: T=-2×%Si+1.0×%Mn+1.3×%Mo+2.5×%Ni+2.0×(%V+%Ti)≥2.00%.

3. The medium carbon low alloy SSC resistant drill steel according to claim 1 or 2, characterized in that: The composition of the steel used in the medium-carbon low-alloy SSC-resistant drill also satisfies: R=-5×(%Si+%Mn)+12×%Mo+10×%Cr+20×%Ti+18×%V≥15.00%.

4. A method for producing medium carbon low alloy SSC resistant drill steel according to any one of claims 1 to 3, characterized in that: The production method comprises the following process flow: Electric arc furnace smelting → LF furnace refining → RH vacuum degassing → continuous casting → rolling.

5. The production method according to claim 4, characterized in that: The RH is vacuum degassed and calcium treated, and the effective calcium-sulfur ratio Ca / S formula is: Ca / S=[T.Ca-(0.31+0.02×T.Ca)×(0.99×TO-5.44)] / 1.25×TS; the Ca / S range is 0.8-2.0; 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 .

6. The production method according to claim 4, characterized in that: The continuous casting is a round billet, and the diameter D of the continuous casting billet and the drawing speed v meet D=1029-1980×v-1470×v 2 , where 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: For the rolling, the billet is fed into a walking beam heating furnace, and the billet diameter D and the heating time t should satisfy D=180+0.42t; wherein the unit of the billet diameter D is mm, and the unit of the heating time t is min.

8. A drilling steel pipe, characterized in that: The medium-carbon low-alloy SSC-resistant drill is produced by using steel as described in any one of claims 1 to 3.

9. The drilling steel pipe according to claim 8, characterized in that: The dislocation density of the drilling steel pipe is 3.0×10 14 / m 2 ~8.0×10 14 / m 2 , recrystallization ratio ≥15%.

10. The drilling steel pipe according to claim 8, characterized in that: The yield strength of the drilling and production steel pipe is ≥830MPa, the tensile strength is ≥940MPa, and the impact energy at -20℃ is ≥110J; the drilling and production steel pipe passes the hydrogen sulfide corrosion test using the American standard NACE TM0177 standard A method under a loading strength of 80% SMYS, an H2S partial pressure of 0.1MPa, and a temperature of 25℃, and no fracture occurs during the test for 720 hours.

11. A heat treatment method for a drilling steel pipe according to any one of claims 8 to 10, characterized in that: The heat treatment method is: quenching first, then tempering once, and then tempering twice.

12. The heat treatment method according to claim 11, characterized in that: The quenching: heating temperature W = AC3 + 30 ~ 50 ° C, the holding time t1 is determined by the steel pipe wall thickness S, t1 = 3.2 × S, water cooling; Among them, the unit of heating temperature W is ℃, the unit of holding time t1 is min, and the unit of steel pipe wall thickness S is mm.

13. The heat treatment method according to claim 11 or 12, characterized in that: Primary tempering: The primary tempering temperature W1 is 650-720°C, the holding time t2 is determined by the steel pipe wall thickness S, t2 = 6 × S, air cooling; Among them, the unit of the primary tempering temperature W1 is ℃, the unit of the holding time t2 is min, and the unit of the steel pipe wall thickness S is mm.

14. The heat treatment method according to claim 11 or 13, characterized in that: Secondary tempering: secondary tempering temperature W2 = W1-10 ° C, holding time t3 is determined by the steel pipe wall thickness S, t3 = 4 × S, air cooling; Among them, the unit of secondary tempering temperature W2 is ℃, the unit of holding time t3 is min, and the unit of steel pipe wall thickness S is mm.

15. Use of the drilling steel pipe according to any one of claims 8 to 10, characterized in that: Used for deep well mining with a depth of ≥8000 meters.

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