Steel pipe for drill pipe body and heat treatment method thereof

Abstract

The invention relates to a steel pipe for a drill pipe body, comprising the following components in mass percentage: C: 0.26% to 0.28%; Si: 0.25% to 0.28%; Mn: 0.85% to 0.90%; Ni: ≤0.04%; Cr: 1.00% to 1.05%; Mo: 0.24% to 0.27%; Cu: ≤0.02%; Al: 0.020% to 0.030%; V: 0.07% to 0.0 9%; P: ≤0.013%; S: ≤0.003%; H: ≤0.0002%; the rest are iron and unavoidable impurities; the present invention realizes high-precision dimensional tolerance through component design and seamless steel pipe preparation, and then undergoes a heat treatment system of water quenching + air quenching + oil quenching + tempering of the blank sample. The three-medium quenching can make the material enter the martensite phase region faster and last for a longer time, providing a wider quenching and tempering temperature control range and performance margin for the heat treatment of the whole pipe.

Description

Technical Field

[0001] The invention belongs to the technical field of steel pipes for oil production and preparation methods, and in particular relates to a steel pipe for a drill pipe body and a heat treatment method thereof. Background Art

[0002] Drill pipes are widely used in oil and gas mining, coal mining, geological exploration and other industries. During the drilling process, they have to withstand internal and external pressures, stratum impact and tension and compression fatigue, as well as the impact of low temperature environments. Therefore, the drill pipe body is required to have a good combination of strength and toughness, comprehensive mechanical properties, low temperature impact performance and high fatigue life.

[0003] Alloy structural seamless steel pipes for drill pipe bodies are generally delivered in a rolled state, and then subjected to heat treatment of the whole pipe after being roughened at the pipe end. The seamless steel pipe manufacturer needs to provide a heat treatment system for the blank sample at the time of delivery as a process guide for the subsequent heat treatment of the whole pipe. At present, double-liquid quenching is mostly used to improve the performance after heat treatment. However, due to the different heat treatment methods of the whole pipe and the blank sample, the performance deviation occurs under the same system. Therefore, in order to ensure the qualified heat treatment performance of the whole pipe, it is particularly important to design a wide range of heat treatment systems and provide sufficient performance margins.

[0004] Patent No. CN104975148B discloses "a method for double-liquid quenching of steel balls or steel forgings". This invention patent provides a double-liquid quenching method of primary water quenching + secondary water-soluble polymer water quenching to increase the martensitic transformation amount of steel parts and improve the quality of steel parts; but it does not give the applicable composition, and the CCT curve transformation laws of different compositions are different, so the applicability of this invention patent needs to be considered.

[0005] Patent No. CN105132637B discloses "double liquid quenching and tempering local strengthening heat treatment process for 5CrMnMo upper mold of hydraulic press". This invention patent provides a method for overall water cooling of the upper mold and local water cooling of the working part, and then transferring to an organic quenching liquid for overall cooling and local quenching cooling of the working part to improve the hardness and strength of the steel part; this method is suitable for mold steel with a carbon content of 0.5% to 0.6%.

[0006] Patent No. CN102851479B discloses "a heat treatment process for high-strength bolts". This invention patent provides a heat treatment process of normalizing + water quenching and oil cooling double liquid quenching + tempering, which obtains the specified non-proportional elongation strength of 970MPa, tensile strength of 1060MPa, elongation of 17%, hardness of 34.8HRC, and -40℃ impact absorption energy of 78J; however, its strength does not reach 150Ksi. Summary of the invention

[0007] The object of the present invention is to provide a steel pipe for a drill pipe body and a heat treatment method thereof, which adopts a quenching method combining three media of water quenching + air quenching + oil quenching to provide a complete quenched martensite structure, which serves as a basis for expanding the tempering temperature range and achieving a good strength-toughness ratio. At the same time, it also provides sufficient performance margin for the difference in heat treatment methods between the whole pipe and the blank sample.

[0008] The present invention solves the technical problem by adopting the following technical solutions:

[0009] The steel pipe for drill pipe body includes the following components in mass percentage:

[0010] C: 0.26% ~ 0.28%; Si: 0.25% ~ 0.28%; Mn: 0.85% ~ 0.90%; Ni: ≤0.04%; Cr: 1.00% ~ 1.05%; Mo: 0.24% ~ 0.27%; Cu: ≤0.02%; Al: 0.020% ~ 0.030%; V: 0.07% ~ 0.09%; P: ≤0.013%; S: ≤0.003%; H: ≤0.0002%; the rest are iron and unavoidable impurities.

[0011] Furthermore, the dimensional tolerances of the steel pipe after rolling are: outer diameter deviation -0.3%D~+0.7%D, pipe body wall thickness deviation 0~+20%t, pipe end wall thickness deviation 0~+25%t, wall thickness unevenness ≤1.5mm, full length straightness deviation ≤0.15%, and pipe end 1.5m straightness deviation ≤2.25mm.

[0012] Furthermore, the heat treatment mechanical properties of the steel pipe are as follows: total elongation strength Rt0.7 ranges from 1050 to 1200 MPa, tensile strength ranges from 1100 to 1290 MPa, elongation ≥19%, cross-sectional shrinkage ≥45%; longitudinal full-size impact energy at -20°C ≥110J, longitudinal full-size impact energy at -40°C ≥110J, longitudinal full-size impact energy at -60°C ≥100J; hardness HRC ranges from 37 to 39.5; original austenite grain size ≥8 levels.

[0013] Furthermore, the inclusions of the steel pipe are A coarse ≤0.5 grade, A fine ≤0.5 grade, B coarse ≤0.5 grade, B fine ≤1.0 grade, C coarse ≤0 grade, C fine ≤0.5 grade, D coarse ≤0.5 grade, D fine ≤0.5 grade, and the total is ≤2.0 grade.

[0014] Furthermore, the tensile and compressive vibration fatigue limit life of the steel pipe is 55%×the specified total elongation strength Rt0.7≥stress cycle number 10 7 .

[0015] The above-mentioned heat treatment method of the steel pipe for the drill pipe body comprises the following steps:

[0016] 1) Billet cutting: Cut the billet into 6 pieces evenly along the rolling direction.

[0017] 2) Quenching: Open the high-temperature furnace, heat quickly to 600℃, heat to 850℃ at 10-15℃ / min, and then heat to 920℃ at 5-10℃ / min; open the furnace door after the temperature stabilizes, lay the blank sample flat into the furnace, and adjust the temperature to the austenitizing temperature at ≤5℃ / min; keep warm for 30-40min after the temperature stabilizes; take the blank sample out of the furnace for water quenching in turn, the transfer time is ≤3s, and continue to move in the water, the immersion time is 5-6s, wherein the water inlet and outlet of the water tank are opened at the same time, and the water temperature is maintained at 15-25℃ to ensure that the blank sample is quickly cooled to the upper part of the martensitic phase region; take out the sample and keep it in the air for 8-12s, so that it slowly descends to the middle part of the martensitic phase region at a slower cooling rate; then immerse it in oil for ≥10s, so that it passes through the lower part of the martensitic phase region at a slightly faster cooling rate to generate a full martensitic structure;

[0018] 3) Tempering: Open the low-temperature furnace, heat quickly to 500℃, and heat to T+10℃ at 5-10℃ / min; open the furnace door after the temperature stabilizes, put in a quenched blank sample, and adjust the temperature to temperature T at ≤5℃ / min; when the temperature T stabilizes to T±2℃, keep it warm for 60-70min; after the insulation is completed, take out the blank sample and air cool it at room temperature, and the room temperature is kept at 5-25℃. Among them: T is 580℃, 585℃, 590℃, 595℃, 600℃, and 610℃ respectively.

[0019] Furthermore, before heat treatment, the steel pipe needs to be subjected to continuous transformation measurement of supercooled austenite at cooling rates of 1°C / s, 3°C / s, 5°C / s, 8°C / s, 20°C / s, 40°C / s, and 60°C / s, respectively, and a CCT curve of the steel grade is drawn; the austenitizing temperature is determined according to the CCT curve; the material is rapidly cooled to the martensite phase region at a cooling rate that avoids the bainite phase region, and stays in the martensite phase region for a sufficiently long time to generate more martensite.

[0020] The advantages and positive effects of the present invention are:

[0021] The invention realizes high-precision dimensional tolerance through component design and seamless steel pipe preparation, and then undergoes a heat treatment system of water quenching + air quenching + oil quenching + tempering of the blank sample. The three-medium quenching can enable the material to enter the martensitic phase region faster and last for a longer time, thereby generating a full martensitic structure, achieving good strength-toughness ratio and low-temperature toughness, high fatigue limit strength, high quenching stability, and good tempering resistance of the blank sample, providing a wider quenching and tempering temperature control range and performance margin for the heat treatment of the whole pipe, thereby preventing the performance failure caused by differences in the heat treatment system and large temperature fluctuations. The comprehensive mechanical properties are higher than those of similar products, and the fatigue limit is nearly 5% to 10% higher than that of the drill pipe body of the same strength grade. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but it should be understood that these drawings are designed only for explanation purposes and are not intended to limit the scope of the present invention. In addition, unless otherwise specified, these drawings are intended only to conceptually illustrate the structural configurations described herein and are not necessarily drawn to scale.

[0023] Figure 1 The CCT curve of the steel provided in Example 2 of the present invention;

[0024] Figure 2 This is the fully martensitic metallographic structure of sample 1# in Example 2 of the present invention after quenching 500 times. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0026] Example 1

[0027] The steel pipe for the drill pipe body provided in this embodiment includes the following components in percentage by mass:

[0028] C: 0.26% ~ 0.28%; Si: 0.25% ~ 0.28%; Mn: 0.85% ~ 0.90%; Ni: ≤0.04%; Cr: 1.00% ~ 1.05%; Mo: 0.24% ~ 0.27%; Cu: ≤0.02%; Al: 0.020% ~ 0.030%; V: 0.07% ~ 0.09%; P: ≤0.013%; S: ≤0.003%; H: ≤0.0002%; the rest are iron and unavoidable impurities.

[0029] The dimensional tolerances of the steel pipe after rolling are: outer diameter deviation -0.3%D~+0.7%D, pipe body wall thickness deviation 0~+20%t, pipe end wall thickness deviation 0~+25%t, wall thickness unevenness ≤1.5mm, full length straightness deviation ≤0.15%, pipe end 1.5m straightness deviation ≤2.25mm; the heat treatment mechanical properties of the steel pipe are: total elongation strength Rt0.7 range 1050~1200MPa, tensile strength range 1100~1290MPa, elongation ≥19%, section shrinkage ≥45%; -20℃ longitudinal full-size impact Work ≥ 110J, -40℃ longitudinal full-size impact work ≥ 110J, -60℃ longitudinal full-size impact work ≥ 100J; hardness HRC range 37~39.5; original austenite grain size ≥ 8 levels; inclusions of the steel pipe A coarse ≤ 0.5 level, A fine ≤ 0.5 level, B coarse ≤ 0.5 level, B fine ≤ 1.0 level, C coarse ≤ 0 level, C fine ≤ 0.5 level, D coarse ≤ 0.5 level, D fine ≤ 0.5 level, the total ≤ 2.0 level; the tensile and compressive vibration fatigue limit life of the steel pipe is 55% × the specified total elongation strength Rt0.7 ≥ the number of stress cycles 10 7 .

[0030] The above-mentioned heat treatment method of the steel pipe for the drill pipe body comprises the following steps:

[0031] 1) Billet cutting: Cut the billet into 6 pieces evenly along the rolling direction.

[0032] 2) Quenching: Open the high-temperature furnace, heat quickly to 600℃, heat to 850℃ at 10-15℃ / min, and then heat to 920℃ at 5-10℃ / min; open the furnace door after the temperature stabilizes, lay the blank sample flat into the furnace, and adjust the temperature to the austenitizing temperature at ≤5℃ / min; keep warm for 30-40min after the temperature stabilizes; take the blank sample out of the furnace for water quenching in turn, the transfer time is ≤3s, and continue to move in the water, the immersion time is 5-6s, wherein the water inlet and outlet of the water tank are opened at the same time, and the water temperature is maintained at 15-25℃ to ensure that the blank sample is quickly cooled to the upper part of the martensitic phase region; take out the sample and keep it in the air for 8-12s, so that it slowly descends to the middle part of the martensitic phase region at a slower cooling rate; then immerse it in oil for ≥10s, so that it passes through the lower part of the martensitic phase region at a slightly faster cooling rate to generate a full martensitic structure;

[0033] 3) Tempering: Open the low-temperature furnace, heat quickly to 500℃, and heat to T+10℃ at 5-10℃ / min; open the furnace door after the temperature stabilizes, put in a quenched blank sample, and adjust the temperature to temperature T at ≤5℃ / min; when the temperature T stabilizes to T±2℃, keep it warm for 60-70min; after the insulation is completed, take out the blank sample and air cool it at room temperature, and the room temperature is kept at 5-25℃. Among them: T is 580℃, 585℃, 590℃, 595℃, 600℃, and 610℃ respectively.

[0034] Specifically, the method for preparing the steel pipe comprises the following steps:

[0035] S1. Steelmaking:

[0036] 1) Electric arc furnace smelting: charging weight ≤ 80% of the basket capacity, furnace door with molten iron, KT injection, lime 45-55 kg / t, final temperature ≥ 1550°C, argon gas during steel tapping, deoxidizer and alloy material added when 20-40 tons of steel are tapped, tapping time ≤ 2 min;

[0037] 2) Refining outside the furnace: LF furnace is blown with argon for stirring throughout the whole process, the molten steel is uniform, the temperature is controlled, strong stirring is performed when adding alloy materials, and aluminum wire is fed for sufficient stirring; VD furnace bottom is blown with argon for deoxidation and denitrification, the argon flow rate is controlled at 70-90L / min, and the vacuum time is ≥10min;

[0038] 3) Continuous casting: Control the billet drawing speed, the billet starting speed is 0.5-1.0m / min, the normal billet drawing speed is 2.0-2.5m / min, and the acceleration time is ≥3min. The billet straightening temperature is 1000±50℃;

[0039] S2. Rolling:

[0040] 1) Ring furnace: control the heating temperature to 1250±20℃ and the holding time to 4.5±1h;

[0041] 2) Piercing: Control the rolling temperature at 1200±50℃, the rough tube temperature at 1150±100℃;

[0042] 3) PQF continuous rolling: control the rolling temperature ≥ 930 ° C, the inlet speed ≤ 1.8 m / s, and the outlet speed 5.5 m / s;

[0043] 4) Sizing: Control the inlet temperature at 900±30℃ and the outlet temperature drop at ≤80℃;

[0044] 5) Straightening: The steel pipe is cold straightened after being fully cooled on the cooling bed;

[0045] 6) Flaw detection: ultrasonic flaw detection;

[0046] 7) Sampling and testing: The chemical finished product composition is 40×20mm, 7 CCT curve round bar samples with a diameter of 3mm and a length of 10mm are cut longitudinally, the length of the blank heat-treated blank is 300-350mm, and the original austenite grain size is 10×10mm;

[0047] 8) Dimension tolerance inspection.

[0048] S3. Continuous transformation measurement of supercooled austenite at cooling rates of 1℃ / s, 3℃ / s, 5℃ / s, 8℃ / s, 20℃ / s, 40℃ / s and 60℃ / s is carried out respectively, and the CCT curve of the steel grade is drawn; the austenitizing temperature is determined according to the CCT curve; the material is rapidly cooled to the martensite phase region at a cooling rate avoiding the bainite phase region, and stays in the martensite phase region for a long enough time to generate more martensite.

[0049] The dimensional tolerances of seamless steel pipes after rolling meet the following requirements: outer diameter deviation -0.3%D~+0.7%D, pipe body wall thickness deviation 0~+20%t, pipe end wall thickness deviation 0~+25%t, wall thickness unevenness ≤1.5mm, full length straightness deviation ≤0.15%, pipe end 1.5m straightness deviation ≤2.25mm.

[0050] Example 2

[0051] The steel pipe specification of this embodiment is Φ149.2×10.54mm, and its chemical composition is as follows:

[0052] C: 0.26%; Si: 0.28%; Mn: 0.85%; Ni: 0.03%; Cr: 1.00%; Mo: 0.27%; Cu: 0.02%; Al: 0.030%; V: 0.09%; P: 0.011%; S: 0.003%; H: 0.00013%; the rest is iron and unavoidable impurities.

[0053] In this embodiment, the heat treatment method of the blank sample is as shown in Table 1

[0054] Table 1: Heat treatment method of blank samples

[0055]

[0056] The mechanical properties of the blank after heat treatment are shown in Table 2:

[0057] Table 2: Mechanical properties of heat-treated steel tube blanks

[0058]

[0059]

[0060] The original austenite grain size heat treatment system is quenching at 900℃×30min water quenching + tempering at 300℃×15min air cooling, and the grade is 8.5.

[0061] The inclusion grades of the blank sample after heat treatment are: A coarse 0 grade, A fine 0 grade, B coarse 0 grade, B fine 0.5 grade, C coarse 0 grade, C fine 0 grade, D coarse 0 grade, D fine 0.5 grade, the total is 1.0 grade.

[0062] The fatigue limit of the blank after heat treatment is shown in Table 3

[0063] Table 3: Fatigue limit properties of steel pipes

[0064]

[0065] Example 3

[0066] The steel pipe specification is Φ127×10.92mm, and its chemical composition is as follows:

[0067] C: 0.27% ~ 0.28%; Si: 0.25% ~ 0.26%; Mn: 0.88% ~ 0.90%; Ni: 0.02%; Cr: 1.03% ~ 1.05%; Mo: 0.24% ~ 0.25%; Cu: 0.018%; Al: 0.020%; V: 0.07% ~ 0.08%; P: 0.010%; S: 0.002%; H: 0.00011%; the rest is iron and unavoidable impurities.

[0068] S1. Steelmaking:

[0069] 1) Electric arc furnace smelting: charging weight ≤ 80% of the basket capacity, furnace door with molten iron, KT injection, lime 45-55 kg / t, final temperature ≥ 1550°C, argon gas during steel tapping, deoxidizer and alloy material added when 20-40 tons of steel are tapped, tapping time ≤ 2 min;

[0070] 2) Refining outside the furnace: LF furnace is blown with argon for stirring throughout the whole process, the molten steel is uniform, the temperature is controlled, strong stirring is performed when adding alloy materials, and aluminum wire is fed for sufficient stirring; VD furnace bottom is blown with argon for deoxidation and denitrification, the argon flow rate is controlled at 70-90L / min, and the vacuum time is ≥10min;

[0071] 3) Continuous casting: Control the billet drawing speed, the billet starting speed is 0.5-1.0m / min, the normal billet drawing speed is 2.0-2.5m / min, and the acceleration time is ≥3min; the billet straightening temperature is 1000±50℃;

[0072] S2. Rolling:

[0073] 1) Ring furnace: control the heating temperature to 1250±20℃ and the holding time to 4.5±1h;

[0074] 2) Piercing: Control the rolling temperature at 1200±50℃, the rough tube temperature at 1150±100℃;

[0075] 3) PQF continuous rolling: control the rolling temperature ≥ 930 ° C, the inlet speed ≤ 1.8 m / s, and the outlet speed 5.5 m / s;

[0076] 4) Sizing: Control the inlet temperature at 900±30℃ and the outlet temperature drop at ≤80℃;

[0077] 5) Straightening: The steel pipe is cold straightened after being fully cooled on the cooling bed;

[0078] 6) Flaw detection: ultrasonic flaw detection;

[0079] 7) Sampling and testing: The chemical finished product composition is 40×20mm, 7 CCT curve round bar samples with a diameter of 3mm and a length of 10mm are cut longitudinally, the length of the blank heat-treated blank is 300-350mm, and the original austenite grain size is 10×10mm;

[0080] 8) Dimension tolerance inspection;

[0081] S3. Continuous transformation of supercooled austenite is measured at cooling rates of 1°C / s, 3°C / s, 5°C / s, 8°C / s, 20°C / s, 40°C / s, and 60°C / s, and the CCT curve of the steel grade is drawn; according to the CCT curve, the austenitizing temperature is 900°C; during quenching, the material is rapidly cooled to the martensite phase region at a cooling rate of ≥40°C / s, and stays in the martensite phase region for a long enough time to generate more martensite.

[0082] S4. Heat treatment of blank sample:

[0083] 1) Billet cutting: Cut the billet into 6 pieces evenly along the rolling direction.

[0084] 2) Quenching: Open the high-temperature furnace, heat quickly to 600℃, heat to 850℃ at 10-15℃ / min, and then heat to 920℃ at 5-10℃ / min; open the furnace door after the temperature stabilizes, lay the blank sample into the furnace, and adjust the temperature to 900℃ at ≤5℃ / min; keep the temperature for 30-40min after the temperature stabilizes to 900±10℃; take the blank samples out of the furnace for water quenching in turn, the transfer time is ≤3s, and continue to move in the water, the immersion time is 5-6s, wherein the water inlet and outlet of the water tank are opened at the same time, the water temperature is maintained at 15-25℃, and the blank sample is ensured to be cooled to 350-400℃ at a rate of ≥40-60℃ / s; take out the sample and keep it in the air for 8-12s; then immerse it in oil for ≥10s to generate a full martensitic structure.

[0085] 3) Tempering: Open the low-temperature furnace, heat quickly to 500℃, and heat to T+10℃ at 5-10℃ / min; open the furnace door after the temperature stabilizes, put in a quenched blank sample, and adjust the temperature to temperature T at ≤5℃ / min; when the temperature T stabilizes to T±2℃, keep it warm for 60-70min; after the insulation is completed, take out the blank sample and air cool it at room temperature, and the room temperature is kept at 5-25℃. Among them: T is 580℃, 585℃, 590℃, 595℃, 600℃, and 610℃ respectively.

[0086] 4) Test: After the blank sample is completely cooled, sample preparation and mechanical property tests are carried out.

[0087] S5, original austenite grain size:

[0088] Quenching at 900±10℃×30min water quenching + tempering at 300±10℃×15min air cooling.

[0089] The dimensional tolerances of seamless steel pipes after rolling meet the following requirements: outer diameter deviation -0.3%D~+0.7%D, pipe body wall thickness deviation 0~+20%t, pipe end wall thickness deviation 0~+25%t, wall thickness unevenness ≤1.5mm, full length straightness deviation ≤0.15%, pipe end 1.5m straightness deviation ≤2.25mm.

[0090] The heat treatment method of the blank sample in this embodiment is shown in Table 4:

[0091] Table 4: Heat treatment method of blank samples

[0092]

[0093] The mechanical properties of the blank sample after heat treatment in this embodiment are shown in Table 5:

[0094] Table 5: Mechanical properties of heat-treated steel tube blanks

[0095]

[0096] The original austenite grain size heat treatment system is quenching at 900℃×30min water quenching + tempering at 300℃×15min air cooling, and the grade is 8.5.

[0097] The inclusion grades of the blank sample after heat treatment are: A coarse 0 grade, A fine 0 grade, B coarse 0 grade, B fine 0 grade, C coarse 0 grade, C fine 0 grade, D coarse 0 grade, D fine 0.5 grade, the total is 0.5 grade.

[0098] The fatigue limit of the blank sample after heat treatment is shown in Table 6:

[0099] Table 6: Fatigue limit properties of steel pipes

[0100]

[0101] The tensile and compressive vibration fatigue limit of the drill pipe body of the same strength grade is generally (45% to 50%) × the specified total elongation strength Rt0.7. The fatigue limit stress of Examples 2 and 3 is set to 55% × the specified total elongation strength Rt0.7, which is nearly 5% to 10% higher.

[0102] Through the examples, when the blank sample is heat treated at a quenching temperature of 890-910°C, a quenching time of 30-40 min, a tempering temperature of 580-610°C, and a tempering time of 60-70 min, the mechanical properties do not fluctuate significantly, and maintain good low-temperature impact toughness and fatigue properties, all of which meet the technical requirements, providing sufficient temperature fluctuation range and performance margin for the heat treatment of the whole tube.

[0103] The above embodiments describe the present invention in detail, but the contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A heat treatment method for a steel pipe for a drill pipe body, characterized in that: The steel pipe for the drill pipe body comprises the following components in percentage by mass: C: 0.26% ~ 0.28%; Si: 0.25% ~ 0.28%; Mn: 0.85% ~ 0.90%; Ni: ≤ 0.04%; Cr: 1.00% ~ 1.05%; Mo: 0.24% ~ 0.27%; Cu: ≤ 0.02%; Al: 0.020% ~ 0.030%; V: 0.07%~0.09%; P: ≤0.013%; S: ≤0.003%; H: ≤0.0002%; the rest is iron and unavoidable impurities; The heat treatment method comprises the following steps: 1) Billet cutting: the billet is evenly cut into 6 pieces along the rolling direction; 2) Quenching: Open the high-temperature furnace, quickly heat to 600°C, increase the temperature to 850°C at 10-15°C / min, and then increase the temperature to 920°C at 5-10°C / min; After the temperature is stable, open the furnace door, lay the blank sample flat and add it into the furnace, adjust the temperature to the austenitizing temperature at ≤5℃ / min; keep the temperature for 30-40min after the temperature is stable; take the blank sample out of the furnace for water quenching in turn, the transfer time is ≤3s, and continue to move in the water, the immersion time is 5-6s, wherein the water inlet and outlet of the water tank are opened at the same time, and the water temperature is maintained at 15-25℃ to ensure that the blank sample is quickly cooled to the upper part of the martensite phase area; take out the sample and keep it in the air for 8-12s, so that it descends slowly to the middle part of the martensite phase area at a slower cooling rate; then immerse it in oil for ≥10s, so that it passes through the lower part of the martensite phase area at a slightly faster cooling rate to generate a full martensite structure; 3) Tempering: Open the low temperature furnace, quickly heat to 500℃, and increase the temperature to T+10℃ at 5-10℃ / min; After the temperature stabilizes, open the furnace door and put a quenched billet sample in, and adjust the temperature to temperature T at a rate of ≤5℃ / min; when the temperature T stabilizes to T±2℃, keep it warm for 60-70min; after the insulation is over, take out the billet sample and air-cool it at room temperature, and the room temperature is maintained at 5-25℃, where T is 580℃, 585℃, 590℃, 595℃, 600℃, and 610℃ respectively.

2. The heat treatment method for a steel pipe for a drill pipe body according to claim 1, characterized in that: Before heat treatment, the steel pipe needs to be subjected to continuous transformation measurement of supercooled austenite at cooling rates of 1°C / s, 3°C / s, 5°C / s, 8°C / s, 20°C / s, 40°C / s, and 60°C / s, respectively, and a CCT curve of the steel grade needs to be drawn; the austenitizing temperature needs to be determined based on the CCT curve; the material needs to be rapidly cooled to the martensite phase region at a cooling rate that avoids the bainite phase region, and stays in the martensite phase region for a sufficiently long time to generate more martensite.

3. The heat treatment method for a steel pipe for a drill pipe body according to claim 1, characterized in that: The dimensional tolerances of the steel pipe after rolling are: outer diameter deviation -0.3%D~+0.7%D, pipe body wall thickness deviation 0~+20%t, pipe end wall thickness deviation 0~+25%t, wall thickness unevenness ≤1.5mm, full length straightness deviation ≤0.15%, and pipe end 1.5m straightness deviation ≤2.25mm.

4. The heat treatment method for a steel pipe for a drill pipe body according to claim 1, characterized in that: The heat-treated mechanical properties of the steel pipe are as follows: total elongation strength Rt0.7 ranges from 1050 to 1200 MPa, tensile strength ranges from 1100 to 1290 MPa, elongation ≥19%, and cross-sectional shrinkage ≥45%; longitudinal full-size impact energy at -20°C ≥110J, longitudinal full-size impact energy at -40°C ≥110J, and longitudinal full-size impact energy at -60°C ≥100J; hardness HRC ranges from 37 to 39.5; and original austenite grain size ≥8 levels.

5. The heat treatment method for a steel pipe for a drill pipe body according to claim 1, characterized in that: The steel pipe has inclusions of A coarse ≤0.5 grade, A fine ≤0.5 grade, B coarse ≤0.5 grade, B fine ≤1.0 grade, C coarse ≤0 grade, C fine ≤0.5 grade, D coarse ≤0.5 grade, D fine ≤0.5 grade, and the total is ≤2.0 grade.

6. The heat treatment method for a steel pipe for a drill pipe body according to claim 1, characterized in that: The tensile and compressive vibration fatigue limit life of the steel pipe is 55%×the specified total elongation strength Rt0.7≥stress cycle number 10 7 .

Images