Steel for non-quenched and tempered seamless steel pipe for high-strength and high-toughness drilling resistant to erosion and its production method

Abstract

The present invention discloses a steel for non - quenched and tempered seamless steel pipes for erosion - resistant and high - strength and toughness drilling, and a production method thereof. On the basis of Mn - Mo - B, the present invention adds elements such as Ti, V, Nb, and Cu, and comprehensively controls the ratios of Si, Mo, Mn, Cu, B, and Ni to ensure the low - temperature toughness of the steel, and comprehensively controls the ratios of C, Mn, Si, Ti, Nb, V, Al, Cu, Cr, Mo, and Ni to ensure the erosion - resistant performance of the steel; and during production, through low - temperature tempering after pipe piercing, the low - temperature toughness and yield - strength ratio of the steel for non - quenched and tempered seamless steel pipes for erosion - resistant and high - strength and toughness drilling are further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel for seamless steel pipes, and in particular relates to a non-quenched and tempered seamless steel pipe for drilling with high strength and toughness and a production method thereof. Background Art

[0002] my country is both a major mineral resource producer and a major consumer. In recent years, with the acceleration of my country's engineering advancement and population growth, its reliance on mineral resources such as oil, coal, metals, and non-metals has gradually increased, leading to a significant increase in consumption and a shortage of mineral resources in my country. With the continuous exploitation and depletion of mineral resources, shallow-layer mineral reserves have gradually decreased, prompting geological exploration to move deeper into the earth. Drilling steel pipe is an essential material for geological surveys, mineral exploration, and other projects, used to transmit drilling power and transport sediment.

[0003] Drilling steel must possess not only high strength but also a certain reserve of toughness to withstand the adverse effects of strong tension, torsion, impact vibration, and various alternating loads caused by overload during drilling. Drill pipe consumes 2.5 to 3.0 kg of material for every meter of advance, and this material is primarily used for drilling at depths of 500 to 1500 meters. Beyond 1500 meters, geological exploration companies mostly use imported drill pipe. Currently, the highest grade of drill pipe commonly used in China has a tensile strength of 835 MPa, which is clearly insufficient for deep drilling. The development of higher-grade drill pipe is necessary.

[0004] Traditionally, mechanical structural steels have mostly been made from carbon steel and alloy steel that have undergone quenching and tempering (quenching and tempering). However, non-quenched and tempered steel can achieve the required strength simply by hot rolling or hot forging without quenching and tempering. This not only reduces component heat treatment costs, but also reduces process steps, shortening lead times and increasing productivity, significantly lowering costs and benefiting the environment. Therefore, non-quenched and tempered steel is now widely used for drilling applications. Conventional P+F drill pipes made from non-quenched and tempered steel only achieve a strength of 900 MPa. Further increases in strength would sharply reduce toughness, making them inadequate for drilling applications.

[0005] Erosion is a type of wear phenomenon that damages a material's surface when it is attacked by small, loose, flowing particles. It results from the combined mechanical action of solid particles and the corrosive effects of fluids. Drilling steel pipes are often exposed to erosion by small, loose, flowing particles during use, so they also need to possess a certain degree of erosion resistance. However, prior art has paid little attention to this aspect of drilling steel pipes.

[0006] Chinese Patent CN102994895A with a publication date of March 27, 2013 discloses a microalloyed high-strength and high-toughness steel for geological drilling and its production process. The chemical composition of this steel is as follows by weight percentage: C 0.36 - 0.42%, Si 0.40 - 0.60%, Mn 1.45 - 1.70%, Cr 0.20 - 0.30%, V 0.10 - 0.20%, Al 0.010 - 0.030%, Ti 0.015 - 0.035%, S ≤ 0.015%, P ≤ 0.020%, Cu ≤ 0.20%, and the balance is Fe. Its main principle is to strengthen by adding microalloying elements on the basis of C-Mn steel. Its tensile strength level only reaches up to 750 MPa at most, and the erosion resistance of the drilling pipe is not taken into account, so it can no longer meet the deep drilling requirements. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a non-quenched and tempered seamless steel pipe steel for erosion-resistant high-strength and high-toughness drilling and its production method. The present invention adds Ti, V, Nb, and Cu elements on the basis of Mn-Mo-B, and comprehensively controls the ratios of Si, Mo, Mn, Cu, B, and Ni to ensure the low-temperature toughness of the steel, and comprehensively controls the ratios of C, Mn, Si, Ti, Nb, V, Al, Cu, Cr, Mo, and Ni to ensure the erosion resistance of the steel; and through low-temperature tempering after pipe piercing during production, the low-temperature toughness and yield ratio of the non-quenched and tempered seamless steel pipe steel for erosion-resistant high-strength and high-toughness drilling are further improved.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A non-quenched and tempered seamless steel pipe steel for erosion-resistant high-strength and high-toughness drilling, including the following chemical components by weight percentage: C: 0.08 - 0.15%, Si: 0.30 - 0.80%, Mn: 2.00 - 3.00%, Cr: 0.20 - 1.00%, Ni: 0.10 - 0.30%, Mo: 0.20 - 1.00%, Al: 0.010 - 0.050%, Nb: 0.010 - 0.040%, V: 0.05 - 0.20%, Ti: 0.015 - 0.030%, Cu: 0.20 - 0.40%, B: 0.002 - 0.008%, P ≤ 0.012%, S ≤ 0.003%, O ≤ 0.0040%, N: 0.008% - 0.018%, and the rest is Fe and inevitable impurities; among them,

[0010] X = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 ≤ 1.14. Within this range, the non-quenched and tempered seamless steel pipe steel for erosion-resistant high-strength and high-toughness drilling has good welding performance;

[0011] Y = -2×Si - 0.8×B + 1.3×Mn + 1.5×Mo + 1.9×Ni + 0.8×Cu ≥ 3.0. Within this range, good low-temperature toughness of the steel can be ensured;

[0012] 0.9% ≤ Z = C + (Mn + Si) / 3 + (Ti + Nb + V) / 2 + (Ni + Cu + Al + Cr + Mo) / 7 ≤ 2.0. Within this range, good erosion resistance of the steel can be ensured;

[0013] In the above formulas, the values of each chemical component are the content in the steel × 100.

[0014] The metallographic structure of the steel for non-quenched and tempered seamless drill pipes with erosion resistance, high strength and toughness is granular bainite. This kind of non-quenched and tempered steel combines the high strength of low-temperature transformation structure and the high toughness of high-temperature transformation structure, and can better meet the requirements of drilling materials.

[0015] The steel for non-quenched and tempered seamless drill pipes with erosion resistance, high strength and toughness has a tensile strength ≥ 1050 MPa, a yield strength ≥ 960 MPa, a yield ratio ≥ 0.9, and a 0℃ KV2 ≥ 100 J; under the conditions of a sand content of 0.9 kg / m 3 , an erosion angle of 20°, and a rate of 50 m / s, the erosion rate ≤ 0.05 mg / g.

[0016] The present invention also provides a production method of the steel for non-quenched and tempered seamless drill pipes with erosion resistance, high strength and toughness, including the following steps: arc furnace or converter smelting → LF furnace refining → RH or VD vacuum degassing → round billet continuous casting → hot-rolled round steel → round steel heating → pipe piercing → sizing → cooling → low-temperature tempering → steel pipe grinding → flaw detection.

[0017] In the step of round billet continuous casting, the specification of the round billet is Φ380 mm to Φ700 mm.

[0018] In the step of hot-rolled round steel, the specification of the round steel is Φ90 mm to Φ250 mm.

[0019] In the step of round steel heating, the heating temperature is 1150 - 1210°C, and the holding time is 80 - 100 min. If the holding is carried out above 1210°C, the grains are liable to grow coarsely, which will deteriorate the performance of the round pipe billet.

[0020] In the step of pipe piercing, the temperature of pipe piercing rolling is controlled at 1050 - 1100°C. This temperature can effectively avoid the hot working failure zone of this steel grade.

[0021] In the step of cooling, due to the high hardenability of this steel grade, after sizing, it is first air-cooled for 1 - 1.5 h, and after the temperature drops below 400°C, it is then air-cooled.

[0022] In the low-temperature tempering step, the tempering temperature is 200 - 220°C, and the holding time is not less than 1 h; when the wall thickness ≥ 20 mm, the holding time is calculated as 3.0 - 4.0 min × wall thickness, with the unit of wall thickness being mm.

[0023] In the steel for non-quenched and tempered seamless steel pipes for erosion-resistant and high-strength and tough drilling provided by the present invention, the control and functions of each component are as follows:

[0024] C: C is the cheapest strengthening element. For every 0.1% increase in solid-solution C in the steel, the strength can be increased by 450 MPa, but at the same time, the plasticity and toughness of the steel will be reduced. C can significantly improve hardenability and help this steel grade obtain bainite structure under air-cooling conditions. In order to ensure the strength-toughness matching of the steel, the C content is controlled at 0.08 - 0.15%.

[0025] Si: As a non-carbide-forming element, Si can prevent the precipitation of carbides during the bainite phase transformation, making the retained austenite stable inside or between the bainite ferrite laths. For the steel with this kind of structure, after tempering at an appropriate temperature, the fracture toughness of the steel can be significantly improved. However, Si is prone to segregate at the austenite grain boundaries, reducing the grain boundary bonding force and causing brittleness. In addition, Si is easy to cause element segregation in the steel. Therefore, the Si content is controlled at 0.30% - 0.80%.

[0026] Mn: Mn is a common solid-solution strengthening element in steel. The solid-solution strengthening effect is weaker than that of Si, and Mn has beneficial effects such as expanding the austenite phase region, increasing hardenability, and refining grains. However, excessive Mn will reduce the plasticity of the steel. Therefore, the mass percentage of Mn is controlled at 2.00 - 3.00%.

[0027] Cr: Cr is a strong carbide-forming element. The precipitation strengthening of its carbides is an important strengthening mechanism in steel. Cr can improve both the hardenability and strength of the steel, but it is prone to cause temper brittleness. Cr can improve the oxidation resistance of the steel and increase the corrosion resistance. However, when the Cr content is too high, the reheat crack sensitivity will increase. The Cr content should be controlled at 0.20% - 1.00%.

[0028] Mo: In high-strength and high-toughness non-quenched and tempered geological drilling steel pipes, Mo is an important means to improve the strength of drilling pipes, improve toughness, and prevent pipe cracking. Mo can improve the hardenability of the steel, effectively reduce the segregation of impurity elements such as P, S, and As at the grain boundaries, and improve the toughness of the steel. Mo reduces the stability of M7C3. When the Mo content is relatively high, acicular Mo2C will be formed, resulting in a reduction in the Mo content of the matrix. Mo can improve the strength of the steel through the combined action of solid-solution strengthening and precipitation strengthening, and can also change the toughness of the steel by changing the precipitation of carbides. Therefore, Mo is controlled at 0.20 - 1.00%.

[0029] Ni: Ni can form a solid solution with infinite solubility with Fe. It is an austenite stabilizing element, which has the effect of expanding the phase region, increasing the stability of supercooled austenite, shifting the C curve to the right, and improving the hardenability of steel. Ni can refine the width of martensite laths and increase the strength. Ni significantly reduces the ductile-brittle transition temperature of steel and improves the low-temperature toughness. The Ni element is a precious metal element, and excessive addition leads to too high cost. Control the Ni content at 0.10 - 0.30%.

[0030] B: B can increase the hardenability of steel. Trace amounts of B dissolve in austenite and can significantly inhibit the nucleation of ferrite at the austenite grain boundaries, causing the ferrite transformation curve to shift significantly to the right. B segregates to the austenite grain boundaries, hindering the formation of the ferrite phase at the austenite grain boundaries, shifting the continuous cooling curve to the right, and prolonging the transformation incubation period, thus significantly improving the hardenability of steel. When the B content exceeds 0.008%, it will damage the toughness of the steel. Therefore, control the mass percentage of B at 0.002 - 0.008%.

[0031] Al: Al is the main deoxidizer in steelmaking. Al combines with N to form fine and dispersed AlN, and maintains a coherent relationship with the matrix, which can play a role in strengthening and refining the structure. However, when the mass percentage of Al exceeds 0.05%, it is not conducive to the casting process of steel. Therefore, control the mass percentage of Al at 0.01 - 0.05%.

[0032] Cu: Cu is an element that expands the austenite phase region and can play a role in solid-solution strengthening. Similar to Ni, it can replace part of Ni. In addition, Cu can improve the corrosion resistance and high-temperature oxidation resistance of steel. However, too high a Cu content will lead to cracking during hot working. Therefore, control the Cu content at 0.20 - 0.40%.

[0033] Nb: The Nb element is the main precipitation strengthening element. The strengthening effect of the Nb element is mainly achieved through the solute drag effect during the rolling process and the grain boundary pinning of precipitates. Controlling the austenite grain size and refining the structure can improve the strength and toughness of steel. Solute drag can prevent the growth of austenite grains. At the same time, Nb in the solute state can make austenite more stable, thus improving the hardenability of steel. Moreover, Nb combines more easily with C and, together with Mo and B, can promote bainite transformation. However, too high a Nb content will form coarse carbides, which is not conducive to the strength and toughness of steel. Therefore, it is necessary to control the mass percentage of Nb at 0.010 - 0.040%.

[0034] V: The V element is an important precipitation strengthening element in steel. V has a very strong affinity with carbon, nitrogen, oxygen, etc. in steel, forming stable carbides, nitrides, and carbonitrides. The formed VC precipitation strengthens ferrite and can prevent grain growth, effectively improving the strength of steel. If the V content is too high, it will affect the strength and toughness of steel. Therefore, control the V content at 0.05 - 0.20%.

[0035] Ti: The addition of Ti element is used to fix the residual nitrogen in steelmaking, thereby forming TiN and increasing the effective precipitation of NbC in steel. At the same time, the precipitated particles of Ti(C, N) play an important role in suppressing the growth of austenite grains during the rolling process of drill pipes. Since the content of residual nitrogen in steelmaking is generally between 0.0050% and 0.0080%, the addition amount of Ti can be determined as 0.015% - 0.030% according to the atomic ratio.

[0036] O and N: T.O forms oxide inclusions in steel, and control T.O ≤ 0.0040%; N in steel can form fine precipitation phases with nitride-forming elements to refine the microstructure, and can also precipitate Fe4N. The diffusion rate is slow, resulting in the aging of steel and reducing the processing performance. Therefore, N is controlled at 0.008% - 0.018%.

[0037] In order to ensure that the steel has good low-temperature toughness, the ratios of Si, Mo, Mn, Cu, B, and Ni need to be limited. Since Si is prone to segregate at the austenite grain boundaries, reducing the crystallization binding force, deteriorating the low-temperature toughness, and increasing the temper brittleness, the coefficient of Si is -2. B can increase the hardenability of steel, but when B is added to steel, it is easy to form brittle phases such as Fe 23 (B,C)6, BN, etc., thus deteriorating the low-temperature toughness of steel, so the coefficient of B is -0.8; Mn can significantly affect the variant selection during the phase transformation process, increasing the number of variants in the phase transformation, thereby improving the low-temperature toughness, so the coefficient of Mn is 1.3; Mo can improve the hardenability of steel, effectively reduce the segregation of impurity elements such as P, S, and As at the grain boundaries, and effectively improve the low-temperature toughness of steel, so the coefficient of Mo is 1.5; Ni can significantly reduce the ductile-brittle transition temperature of steel and improve the low-temperature toughness, so the coefficient of Ni is 1.9; Cu can form fine ε-Cu to refine the microstructure and improve the temper stability of steel, thereby improving the low-temperature toughness, so the coefficient of Cu is 0.8: that is, Y = -2×Si - 0.8×B + 1.3×Mn + 1.5×Mo + 1.9×Ni + 0.8×Cu ≥ 3.0.

[0038] Erosion resistance is mainly related to the strength and corrosion resistance of materials. In order to endow the steel for drill pipes with good erosion resistance, the proportions of C, Mn, Si, Ti, Nb, V, Al, Cu, Cr, Mo, and Ni need to be specified. C is the cheapest strengthening element in steel. For every 0.1% increase in solid solution C, the strength can be increased by approximately 450 MPa. C forms precipitation phases with alloying elements in the steel, playing a role in precipitation strengthening. Mn and Si can form substitutional solid solutions in the steel to strengthen it. Elements such as Ti, Nb, and V can form carbides, nitrides, or carbonitrides, which precipitate during rolling or cooling to play a role in secondary phase precipitation strengthening. Alloying elements such as Cr, Al, Cu, and Ni can increase the corrosion potential of the steel in static seawater, and the addition of Mo can also inhibit the development of pitting corrosion. Therefore, the main alloying elements should satisfy the erosion resistance formula: 0.9% ≤ Z = C + (Mn + Si) / 3 + (Ti + Nb + V) / 2 + (Ni + Cu + Al + Cr + Mo) / 7 ≤ 2.0.

[0039] In the production method of the steel for non-quenched and tempered seamless drill pipes with erosion resistance, high strength and toughness provided by the present invention, non-quenched and tempered seamless steel pipes with high yield ratio, erosion resistance, high strength and toughness, and excellent low-temperature toughness are produced through the control of various process parameters during the production process.

[0040] Compared with the prior art, the steel for non-quenched and tempered seamless drill pipes with erosion resistance, high strength and toughness provided by the present invention has excellent strength and toughness and erosion resistance, and excellent low-temperature toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is the metallographic structure diagram of the steel for non-quenched and tempered seamless drill pipes in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0042] The steel for non-quenched and tempered seamless drill pipes with erosion resistance, high strength and toughness provided by the present invention includes the following chemical components in weight percentages: C: 0.08 - 0.15%, Si: 0.30 - 0.80%, Mn: 2.00 - 3.00%, Cr: 0.20 - 1.00%, Ni: 0.10 - 0.30%, Mo: 0.20 - 1.00%, Al: 0.010 - 0.050%, Nb: 0.010 - 0.040%, V: 0.05 - 0.20%, Ti: 0.015 - 0.030%, Cu: 0.20 - 0.40%, B: 0.002 - 0.008%, P ≤ 0.012%, S ≤ 0.003%, O ≤ 0.0040%, N: 0.008% - 0.018%, and the balance is Fe and unavoidable impurities; among them,

[0043] X = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 ≤ 1.14;

[0044] Y = -2×Si - 0.8×B + 1.3×Mn + 1.5×Mo + 1.9×Ni + 0.8×Cu ≥ 3.0;

[0045] 0.9% ≤ Z = C + (Mn + Si) / 3 + (Ti + Nb + V) / 2 + (Ni + Cu + Al + Cr + Mo) / 7 ≤ 2.0;

[0046] In the above formulas, the values of each chemical component are the content in the steel × 100. The production method of the steel for non - quenched and tempered seamless steel pipes for erosion - resistant high - strength and tough drilling includes the following steps: electric arc furnace or converter smelting → LF furnace refining → RH or VD vacuum degassing → continuous casting of round billets with a diameter of Φ380mm - Φ700mm → hot - rolled round steel with a diameter of Φ90mm - Φ250mm → heating of round steel → pipe piercing → sizing → cooling → low - temperature tempering → grinding of steel pipes → flaw detection.

[0047] In the step of heating the round steel, the heating temperature is 1150 - 1210°C and the holding time is 80 - 100 min.

[0048] In the step of pipe piercing, the temperature of pipe - piercing rolling is controlled at 1050 - 1100°C.

[0049] In the step of cooling, after sizing, air cooling is first carried out for 1 - 1.5 h. After the temperature drops below 400°C, air cooling is carried out again.

[0050] In the step of low - temperature tempering, the tempering temperature is 200 - 220°C and the holding time is not less than 1 h; when the wall thickness ≥ 20 mm, the holding time is calculated according to 3.0 - 4.0 min × wall thickness, and the unit of wall thickness is mm.

[0051] The present invention will be described in detail below with reference to the embodiments.

[0052] The chemical components and weight percentages of the steel for non - quenched and tempered seamless steel pipes in each embodiment and comparative example are shown in Table 1.

[0053] Table 1

[0054] Steel grade C Si Mn Cr Mo Ni Cu Al Nb V Ti B P S N O X value Y value Z value Example 1 0.09 0.34 2.87 0.26 0.32 0.27 0.23 0.020 0.013 0.07 0.017 0.003 0.003 0.002 0.009 0.0035 0.73 4.23 1.37 Example 2 0.10 0.37 2.13 0.31 0.27 0.37 0.34 0.025 0.012 0.09 0.018 0.004 0.004 0.003 0.012 0.0032 0.64 3.41 1.18 Example 3 0.14 0.76 2.91 0.91 0.83 0.24 0.25 0.031 0.037 0.18 0.024 0.007 0.005 0.003 0.016 0.0028 1.04 4.16 1.81 Example 4 0.14 0.71 2.20 0.88 0.89 0.32 0.37 0.028 0.035 0.17 0.027 0.007 0.003 0.001 0.011 0.0021 0.94 3.67 1.58 Comparative example 1 0.14 0.74 2.13 0.83 0.87 0.29 0.38 0.025 0.035 0.18 0.028 0.006 0.004 0.002 0.015 0.0023 0.92 3.44 1.56 Comparative example 2 0.15 0.44 2.56 0.80 0.53 \ \ 0.028 0.021 \ \ 0.002 0.006 0.003 0.014 0.0020 0.84 3.24 1.35

[0055] Comparative example 3 0.10 0.41 2.50 0.56 0.65 \ \ 0.022 0.034 \ \ 0.003 0.004 0.002 0.011 0.0041 0.76 3.40 1.26 Comparative example 4 0.13 0.75 2.1 0.47 0.23 0.12 0.23 0.034 0.024 0.12 0.023 0.003 0.005 0.003 0.013 0.0024 0.67 1.98 1.32

[0056] The production processes of the steel for non - quenched and tempered seamless steel pipes in each embodiment and comparative examples 2 - 3 are as follows:

[0057] Electric furnace smelting: determining oxygen before tapping, and adopting the operation of leaving steel during tapping to avoid slagging;

[0058] LF furnace: adjusting elements such as C, Si, Mn, Cr, Ni, Mo, Ti, Nb, V, B, Cu to the target values;

[0059] Vacuum degassing: The pure degassing time shall be ≥15 minutes to ensure that the [H] content after vacuum treatment is ≤1.5 ppm, avoiding the appearance of white spots in the steel and causing hydrogen embrittlement;

[0060] Continuous casting: The target temperature of the molten steel in the tundish is controlled at 10 - 40°C above the liquidus temperature, and continuous casting of round billets with a diameter of Φ380mm - Φ700mm is carried out.

[0061] Rolling: The continuously cast round billets with a diameter of Φ380mm - Φ700mm are rolled into round steel with a diameter of Φ90mm - Φ250mm.

[0062] Pipe manufacturing route: Hot-rolled round steel → Heating → Pipe piercing → Sizing → Cooling (air cooling + air cooling).

[0063] Steel pipe processing route: Low-temperature tempering → Steel pipe grinding → Steel pipe flaw detection → Precision machining → Flaw detection → Packaging and warehousing.

[0064] The specific process parameter control is shown in Table 2.

[0065] Table 2

[0066]

[0067]

[0068] The steel for non-quenched and tempered seamless steel pipes produced in the above-mentioned examples and comparative examples is subjected to performance testing, and the performance testing method is as follows:

[0069] Microstructure: Samples are taken from the cross-section at 1 / 2 wall thickness of the pipe end for metallographic and grain size analysis.

[0070] Performance: The yield strength is obtained by processing the manufactured steel pipe into an API arc-shaped specimen and taking the average value after inspection according to the API standard. The full-size Charpy V-notch impact absorption work data is obtained by taking a semi-size V-notch impact specimen with a cross-sectional area of 5×10×55mm from the manufactured steel pipe and taking the average value after inspection according to the GB / T 229 standard. The erosion specimen is a sample block with a cross-sectional area of 24×12×6mm taken from the manufactured steel pipe. After the steel pipe is subjected to low-temperature tempering, the tensile strength, yield strength, yield ratio, and erosion rate are shown in Table 3 and Table 4.

[0071] Table 3 Mechanical property test results of examples and comparative examples

[0072]

[0073] Table 4 List of erosion property test results of examples and comparative examples

[0074]

[0075]

[0076] The chemical compositions and production methods of the steels in Examples 1 to 4 are properly controlled, and their chemical compositions ensure that X ≤ 1.14%, Y ≥ 3.0%, 0.9% ≤ Z ≤ 2.0%. The strength, plasticity, toughness and erosion resistance of the steels are all good.

[0077] Comparative Example 1 was not subjected to low-temperature tempering treatment, and the yield ratio and toughness were low. In Comparative Examples 2 and 3, Ni, Cu, V, and Ti alloying were not carried out. The unreasonable control of the elements for improving the strength and plasticity of the material resulted in insufficient strength, and the low-temperature toughness index was too low, resulting in insufficient toughness, thus leading to poor erosion resistance. In Comparative Example 4, although the contents of each element were controlled within the range defined by the present invention, due to the improper control of the value of Y, the impact performance of the steel pipe was worse than that of the examples.

[0078] The above detailed description of a non-quenched and tempered seamless steel pipe for high-strength and high-toughness erosion-resistant drilling and its production method with reference to the examples is illustrative rather than restrictive. Several examples can be listed according to the defined range. Therefore, changes and modifications without departing from the general concept of the present invention should fall within the protection scope of the present invention.

Claims

1. A steel for non-quenched and tempered seamless steel pipe for high-strength and tough drilling resistant to erosion, characterized in that, It includes chemical components in the following weight percentages: C: 0.08 - 0.15%, Si: 0.30 - 0.80%, Mn: 2.00 - 3.00%, Cr: 0.20 - 1.00%, Ni: 0.10 - 0.30%, Mo: 0.20 - 1.00%, Al: 0.010 - 0.050%, Nb: 0.010 - 0.040%, V: 0.05 - 0.20%, Ti: 0.015 - 0.030%, Cu: 0.20 - 0.40%, B: 0.002 - 0.008%, P ≤ 0.012%, S ≤ 0.003%, O ≤ 0.0040%, N 0.008% - 0.0180%, and the balance is Fe and inevitable impurities; among them, X = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 ≤ 1.14; Y = -2×Si - 0.8×B + 1.3×Mn + 1.5×Mo + 1.9×Ni + 0.8×Cu ≥ 3.0; 0.9% ≤ Z = C + (Mn + Si) / 3 + (Ti + Nb + V) / 2 + (Ni + Cu + Al + Cr + Mo) / 7 ≤ 2.0; In the above formulas, the value of each chemical component is its content in the steel × 100.

2. The steel for non-quenched and tempered seamless steel pipes for erosion-resistant high-strength and tough drilling, as described in claim 1, is characterized in that, The metallographic structure of the steel for the non - quenched and tempered seamless steel pipe for erosion - resistant high - strength and high - toughness drilling is granular bainite.

3. The steel for non-quenched and tempered seamless steel pipes for erosion-resistant and high-strength and tough drilling, according to claim 1, is characterized in that, The steel for non-quenched and tempered seamless steel pipes for high-strength and high-toughness drilling resistant to erosion has a tensile strength ≥ 1050 MPa, a yield strength ≥ 960 MPa, a yield ratio ≥ 0.9, and a KV2 at 0 °C ≥ 100 J; under the conditions of a sand content of 0.9 kg / m 3 , an erosion angle of 20°, and a rate of 50 m / s, the erosion rate ≤ 0.05 mg / g.

4. The production method of the steel for non-quenched and tempered seamless steel pipes for high-strength and tough drilling resistant to erosion according to any one of claims 1-3, characterized in that, It includes the following steps: Electric arc furnace or converter smelting → LF furnace refining → RH or VD vacuum degassing → Continuous casting of round billets → Hot - rolled round steel → Heating of round steel → Pipe piercing → Sizing → Cooling → Low - temperature tempering → Grinding of steel pipe → Flaw detection.

5. The production method according to claim 4, characterized in that, In the step of heating the round steel, the heating temperature is 1150 - 1210 °C and the holding time is 80 - 100 min.

6. The production method according to claim 4, characterized in that, In the step of pipe piercing, the temperature of pipe - piercing rolling is controlled at 1050 - 1100 °C.

7. The production method according to claim 4, characterized in that, In the step of cooling, first perform air cooling for 1 - 1.5 h. When the temperature drops below 400 °C, then perform air cooling.

8. The production method according to claim 4, characterized in that, In the step of low - temperature tempering, the tempering temperature is 200 - 220 °C and the holding time is not less than 1 h; when the wall thickness ≥ 20 mm, the holding time is calculated according to 3.0 - 4.0 min × wall thickness, and the unit of wall thickness is mm.

9. The production method according to claim 4, characterized in that, In the step of continuous casting of round billets, the specifications of the round billets are Φ380 mm - Φ700 mm.

10. The production method according to claim 4, characterized in that, In the step of hot - rolled round steel, the specifications of the round steel are Φ90 mm - Φ250 mm.

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