Seamless steel tube for high-toughness drill rod and manufacturing method of seamless steel tube

Abstract

The invention belongs to the technical field of seamless pipe preparation, and relates to a seamless steel pipe for a high-toughness drill pipe and a manufacturing method thereof, the seamless steel pipe comprises the following components by mass percent: 0.22%-0.25% of C, 0.25%-0.40% of Si, 0.25%-0.35% of Mn, less than or equal to 0.008% of P, less than or equal to 0.0010% of S, 0.20%-0.30% of Ni, 1.20%-1.30% of Cr, 1.15%-1.20% of Mo, 0.17%-0.20% of V, 0.02%-0.04% of Nb, 0.005%-0.020% of Al, 0.0005%-0.0040% of Ca, less than or equal to 0.0020% of O, less than or equal to 0.0050% of N, less than or equal to 0.00015% of H, less than or equal The rolling defect total percentage f is smaller than or equal to 1%, the yield strength ranges from 1094 MPa to 1176 MPa, the tensile strength ranges from 1189 MPa to 1238 MPa, the ductility ranges from 21% to 27%, the 250 DEG C high-temperature yield strength ranges from 930 MPa to 1023 MPa, the-20 DEG C longitudinal full-size impact energy ranges from 123 J to 138 J, and the grain size is larger than or equal to 9.5 level. The comprehensive advantages of high toughness and low defects are achieved through cooperation of calculation and optimization of alloy components, reasonable limiting, high-purity steel smelting, pipe blank segmented heating and secondary hardening, the brittle failure risk of the deep well drill rod is avoided, the principle that leakage is conducted before breaking is met, and use safety is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of seamless pipe preparation, and relates to a high-strength and tough seamless steel pipe for a drill rod and a manufacturing method thereof. Background Art

[0002] As oil and gas exploration advances to depths of 10,000 meters in the earth, the extremely harsh working conditions have placed more stringent demands on core drilling equipment and technologies. As an important component of drill pipe, the quality, strength, toughness and high temperature resistance of seamless steel pipes play a vital role in breaking through technical bottlenecks and ensuring drilling safety.

[0003] The complex geological conditions at a depth of 10,000 meters make the demand for high-strength and tough drill pipes more urgent. High-strength and tough drill pipes of 150 steel grade have reached large-scale production at home and abroad, and 165 steel grade has also been developed and trial-produced for application. Chinese patent CN103938095A discloses a 165ksi steel grade high-strength and high-toughness drill pipe, the drill pipe has a maximum longitudinal full-size impact energy of 126J at -20°C, and a grain size of 9. Although the mechanical properties of the drill pipe meet the strength requirements of 165KSI steel grade drill pipe, the effect of the proportion of rolling defects on the brittleness of the drill pipe is not fully considered. Under the action of alternating load stresses such as pulling, torsion, and bending during the actual downhole process, high-strength and tough drill pipes are at risk of brittle fracture. Therefore, when used in a well environment of 10,000 meters or deeper, whether the drill pipes made of existing seamless steel pipes can meet the principle of leaking first and then breaking, and ensure the safety of the drill pipe after failure, remains to be discussed. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a high-strength and toughness seamless steel pipe for drill pipe and its manufacturing method. By calculating and optimizing the alloy composition, reasonable limits + high-purity steel smelting + tube blank segmented heating + secondary hardening are carried out to synergistically achieve the comprehensive advantages of high strength and toughness and low defects (f≤1%), solve the risk of brittle fracture of deep well drill pipe, meet the principle of leakage before breaking, and improve the safety of use.

[0005] The technical solution adopted by the present invention to solve the technical problem is:

[0006] The first aspect of the present invention provides a high-strength and tough seamless steel pipe for drill pipe, the composition by mass percentage is: C: 0.22% to 0.25%, Si: 0.25% to 0.40%, Mn: 0.25% to 0.35%, P: ≤0.008%, S: ≤0.0010%, Ni: 0.20% to 0.30%, Cr: 1.20% to 1.30%, Mo: 1.15% to 1.20%, V: 0.17% to 0.20%, Nb: 0.02% to 0.04%, Al: 0.005% to 0.020%, Ca: 0.0005% to 0.0040%, O: ≤0.0 0.020%, N: ≤0.0050%, H: ≤0.00015%, Pb: ≤0.0150%, Sb: ≤0.0150%, As: ≤0.0150%, Bi: ≤0.0150%, Sn: ≤0.0150%, the rest are iron and unavoidable impurities, the total percentage of rolling defects f≤1%, yield strength 1094~1176MPa, tensile strength 1189~1238MPa, elongation 21%~27%, high temperature tensile yield strength at 250℃ 930~1023MPa, longitudinal full-size impact energy at -20℃ 123~138J, grain size ≥9.5.

[0007] The total rolling defect percentage f is calculated by the following steps:

[0008] (1) Define the mapping relationship between alloy elements and defects: f = A n +B n +C n +D n +E n +F n +G n , A is eddy current flaw detection defect, B is inner fold defect, C is inner scar defect, D is outer fold defect, E is outer scar defect, F is inner edge defect, G is pitting defect, defect unit is percentage, n is the serial number of different steel grades; alloy composition is related by the following formula: a n C+b n ·Si+d n Mn+e n ·Ni+g n ·Cr+h n ·Mo+i n ·V+j n Nb+k n ·Al+l n Ca→A n +B n +C n +D n +E n +F n +G n

[0009] Where a, b, d, e, g, h, i, j, k, and l are the mass percentages of the alloying elements C, Si, Mn, Ni, Cr, Mo, V, Nb, Al, and Ca, respectively;

[0010] (2) BP neural network was used to optimize the components, the Levenberg-Marquardt feedforward propagation method was called, the double hidden layer node setting was 10-10-8-7, and the number of training times was 500 times; in the order of steel grades, a, b, d, e, g, h, i, j, k, l were imported into the neural network input, and A, B, C, D, E, F, G were imported into the neural network output for calculation and fitting;

[0011] (3) Call the simulation function sim to predict rolling defects and ensure that f≤1%.

[0012] Furthermore, the addition ratio of alloying elements is adjusted. When Nb≥0.025% or V≥0.20%, B n Increase the weight coefficient by 1.2 before; when Mo / 10+V+Nb≥0.33, D n and E n The weight coefficient should be increased by 1.25 before adding; after weighting, round it up according to scientific notation.

[0013] A second aspect of the present invention provides a method for preparing a high-strength and tough seamless steel pipe for a drill pipe, comprising the following steps:

[0014] (1) Steelmaking:

[0015] Electric arc furnace smelting → refining outside the furnace → vacuum treatment.

[0016] The electric arc furnace smelting uses all scrap steel as the raw material, without adding molten iron or pig iron. Oxygen is blown from the bottom of the furnace to remove slag. Bottom lime and dephosphorization agent are added into the furnace. Then, two pours of refining are carried out outside the furnace. The weak stirring time is 6 to 20 minutes. Vacuum bottom blowing of argon is used for stirring. The tapping temperature is controlled at 1620 to 1680℃.

[0017] (2) Continuous casting:

[0018] When pouring begins, throw out 1% of the tapping volume (used for other varieties to ensure sufficient purity), control the molten steel flow rate at 0.3-0.6 m / min, and the continuous casting billet drawing speed at 0.3-2.0 m / min. When the molten steel volume is ≤20t, the drawing speed is controlled at 1.2-1.6 m / min, and when the molten steel volume is ≤10t, the drawing speed is controlled at 0.3-0.6 m / min, and the continuous casting billet yield is controlled at 94%-96%;

[0019] (3) Rolling: Ring furnace heating → piercing → rolling → sizing

[0020] The heating of the tube billet in the annular furnace is divided into three stages. The first stage is 700±20℃ and kept warm for 0.5h. Then it is slowly heated at 60-80℃ / h to 800±20℃ in the second stage and kept warm for 2.5-3h. Then it is rapidly heated at 150-200℃ / h to 1260±20℃ in the third stage and kept warm for 2.5-3h. The furnace discharge temperature is controlled at 1260±10℃.

[0021] The piercing bite angle is 11-12°, the rolling speed limit V is 0.8-1.2 m / s, the starting rolling temperature Ta is 1030±15°C, the finishing rolling temperature Tb is 950±10°C, and (Ta-Tb) is satisfied. 1 / 2 × V = 6 to 10, and the rolled tube is obtained;

[0022] (4) Heat treatment of blank sample:

[0023] When the seamless steel pipe is 165 steel grade, it is quenched at 900±5℃ and kept warm for 25±5min, water quenched, tempered at 550±5℃ and kept warm for 60~70min, air cooled, quenched again, kept warm at 900±5℃ for 25±5min, water quenched, secondary hardening at 570±10℃ and kept warm for 60min, air cooled, tempered at 660±5℃ and kept warm for 90~100min, air cooled;

[0024] When the seamless steel pipe is 150 steel grade, it is quenched and kept at 860-865℃ for 25±5min, water quenched, kept at 640±5℃ for 110-120min, and air cooled.

[0025] Furthermore, in step (1), the bottom oxygen blowing for slag removal is specifically as follows: the KT oxygen gun and the carbon gun adopt a fixed blowing curve and manual intermittent blowing, wherein the oxygen flow rate of the oxygen gun is 2000-2200m 3 / h, natural gas flow rate 400~450m 3 / h, the carbon gun blowing flow rate is 50-55kg / min.

[0026] Furthermore, in step (1), the bottom lime and the dephosphorization agent account for 1.5-2 wt% and 0.1-0.2 wt% of the scrap steel material, respectively.

[0027] Furthermore, the temperature is controlled at 1630-1650°C at the end of the first out-of-furnace refining and continuous pouring, and is controlled at 1570-1600°C at the end of the vacuum treatment. The temperature is controlled at 1610-1630°C at the end of the second out-of-furnace refining and continuous pouring, and is controlled at 1550-1570°C at the end of the vacuum treatment.

[0028] Furthermore, when the amount of molten steel is 10t≤≤20t, the pulling speed is controlled to be 1.2-1.6m / min; when the amount of molten steel is ≤10t, the pulling speed is controlled to be 0.3-0.6m / min.

[0029] The advantages and positive effects of the present invention are:

[0030] The present invention obtains a high-strength, high-toughness, high-purity, high-temperature resistant seamless steel pipe for drill pipe body by adding alloy elements that are prone to rolling defects in limited amounts, and combining high-purity steel smelting technology + limited billet drawing, segmented heating and insulation of tube billets and speed-controlled heating technology, two-time tempering + secondary hardening and other technical means. The proportion of rolling defects is significantly improved, the risk of brittle fracture of deep well drill pipe is solved, the principle of leaking first and then breaking is met, and the safety of use is improved. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0032] A high-strength and tough seamless steel pipe for drill pipe, the composition by mass percentage is: C: 0.22% to 0.25%, Si: 0.25% to 0.40%, Mn: 0.25% to 0.35%, P: ≤0.008%, S: ≤0.0010%, Ni: 0.20% to 0.30%, Cr: 1.20% to 1.30%, Mo: 1.15% to 1.20%, V: 0.17% to 0.20%, Nb: 0.02% to 0.04%, Al: 0.005% to 0.020%, Ca: 0.0005% to 0.0040%, O: ≤0.0020% , N: ≤0.0050%, H: ≤0.00015%, Pb: ≤0.0150%, Sb: ≤0.0150%, As: ≤0.0150%, Bi: ≤0.0150%, Sn: ≤0.0150%, the rest are iron and unavoidable impurities, the total percentage of rolling defects f≤1%, yield strength 1094~1176MPa, tensile strength 1189~1238MPa, elongation 21%~27%, high temperature yield strength at 250℃ 930~1023MPa, longitudinal full-size impact energy at -20℃ 123~138J, grain size ≥9.5.

[0033] The total rolling defect percentage f is calculated by the following steps:

[0034] (1) Define the mapping relationship between alloy elements and defects: f = A n +B n +C n +D n +E n +F n +G n, A is eddy current flaw detection defect, B is inner fold defect, C is inner scar defect, D is outer fold defect, E is outer scar defect, F is inner edge defect, G is pitting defect, defect unit is percentage, n is the sequence number of different steel grades; alloy composition is related by the following formula: Steel grade 1: a1·C+b1·Si+d1·Mn+e1·Ni+g1·Cr+h1·Mo+i1·V+j1·Nb+k1·Al+l1·Ca→A1+B1+C1+D1+E1+F1+G1,

[0035] Steel type 2: a2·C+b2·Si+d2·Mn+e2·Ni+g2·Cr+h2·Mo+i2·V+j2·Nb+k2·Al+l2·Ca→A2+B2+C2+D2+E2+F2+G2,

[0036] Steel type 3: a3·C+b3·Si+d3·Mn+e3·Ni+g3·Cr+h3·Mo+i3·V+j3·Nb+k3·Al+l3·Ca→A3+B3+C3+D3+E3+F3+G3,

[0037] Steel type n: a n C+b n ·Si+d n Mn+e n ·Ni+g n ·Cr+h n ·Mo+i n ·V+j n Nb+k n ·Al+l n Ca→A n +B n +C n +D n +E n +F n +G n ,

[0038] Where a, b, d, e, g, h, i, j, k, and l are the mass percentages of the alloying elements C, Si, Mn, Ni, Cr, Mo, V, Nb, Al, and Ca, respectively;

[0039] (2) BP neural network was used to optimize the components, the Levenberg-Marquardt feedforward propagation method was called, the double hidden layer node setting was 10-10-8-7, and the number of training times was 500 times; in the order of steel grades, a, b, d, e, g, h, i, j, k, l were imported into the neural network input, and A, B, C, D, E, F, G were imported into the neural network output for calculation and fitting;

[0040] (3) Call the simulation function sim, set α = [abdeghijkl]; f = sim(net, α'); disp(f), perform rolling defect prediction, and ensure that f ≤ 1%.

[0041] Preferably, the proportion of alloying elements is adjusted, when Nb≥0.025% or V≥0.20%, B n Increase the weight coefficient by 1.2 before; when Mo / 10+V+Nb≥0.33, D n and E n The weight coefficient should be increased by 1.25 before adding; after weighting, round it up according to scientific notation.

[0042] The present invention provides a method for preparing a high-strength and tough seamless steel pipe for a drill pipe, comprising the following steps:

[0043] (1) Steelmaking:

[0044] Electric arc furnace smelting → refining outside the furnace → vacuum treatment.

[0045] The electric arc furnace smelting uses all scrap steel as the raw material, without adding molten iron or pig iron. Bottom lime and dephosphorization agent are added to the furnace, followed by two pours of refining outside the furnace. The weak stirring time is 6 to 20 minutes, and vacuum bottom argon blowing is used for stirring. The tapping temperature is controlled at 1620 to 1680℃.

[0046] (2) Continuous casting:

[0047] When pouring begins, throw out 1% of the tapping volume (used for other varieties to ensure sufficient purity), control the molten steel flow rate at 0.3-0.6 m / min, and the continuous casting billet drawing speed at 0.3-2.0 m / min. When the molten steel volume is ≤20t, the drawing speed is controlled at 1.2-1.6 m / min, and when the molten steel volume is ≤10t, the drawing speed is controlled at 0.3-0.6 m / min, and the continuous casting billet yield is controlled at 94%-96%;

[0048] (3) Rolling: Ring furnace heating → piercing → rolling → sizing

[0049] The heating of the tube billet in the annular furnace is divided into three stages. The first stage is 700±20℃ and kept warm for 0.5h. Then it is slowly heated at 60-80℃ / h to 800±20℃ in the second stage and kept warm for 2.5-3h. Then it is rapidly heated at 150-200℃ / h to 1260±20℃ in the third stage and kept warm for 2.5-3h. The furnace discharge temperature is controlled at 1260±10℃.

[0050] The piercing bite angle is 11-12°, the rolling speed limit V is 0.8-1.2 m / s, the starting rolling temperature Ta is 1030±15°C, the finishing rolling temperature Tb is 950±10°C, and (Ta-Tb) is satisfied. 1 / 2 × V = 6 to 10, and the rolled tube is obtained;

[0051] (4) Heat treatment of blank sample:

[0052] When the seamless steel pipe is grade 165, the rolled pipe is quenched at 900±5℃ and kept warm for 25±5min, water quenched, tempered at 550±5℃ and kept warm for 60-70min, air-cooled, and then quenched again, kept warm at 900±5℃ for 25±5min, water quenched, secondary hardening at 570±10℃ and kept warm for 60min, air-cooled, tempered at 660±5℃ and kept warm for 90-100min, and air-cooled to obtain the seamless steel pipe;

[0053] When the seamless steel pipe is of grade 150, it is quenched and kept at 860-865°C for 25±5min, water quenched, kept at 640±5°C for 110-120min, and air-cooled to obtain a seamless steel pipe.

[0054] Preferably, in step (1), the bottom oxygen blowing for slag removal is specifically as follows: the KT oxygen lance and the carbon lance adopt a fixed blowing curve and manual intermittent blowing, wherein the oxygen flow rate of the oxygen lance is 2000-2200m 3 / h, natural gas flow rate 400~450m 3 / h, the carbon gun blowing flow rate is 50-55kg / min.

[0055] Preferably, the temperature is controlled at 1630-1650°C at the end of the first refining and continuous pouring outside the furnace, and is controlled at 1570-1600°C at the end of the vacuum treatment. The temperature is controlled at 1610-1630°C at the end of the second refining and continuous pouring outside the furnace, and is controlled at 1550-1570°C at the end of the vacuum treatment.

[0056] Preferably, when the amount of molten steel is 10t≤≤20t, the pulling speed is controlled to be 1.2-1.6m / min; when the amount of molten steel is ≤10t, the pulling speed is controlled to be 0.3-0.6m / min.

[0057] Example 1

[0058] A high-strength and tough seamless steel pipe for drill pipe, the composition mass percentages of which are shown in Table 1, and the preparation method comprises the following steps:

[0059] (1) Steelmaking:

[0060] The electric arc furnace smelting adopts all scrap steel as the raw material, without adding molten iron and pig iron. The KT oxygen gun and carbon gun adopt fixed injection curve and manual intermittent injection. The oxygen flow rate of the oxygen gun is 2000~2200m 3 / h, natural gas flow rate 400~450m 3 / h, the carbon gun blowing flow rate is 50-55kg / min. Oxygen is blown from the bottom of the furnace to remove slag, and bottom lime accounting for 1.5-2wt% of the scrap steel batch and dephosphorization agent accounting for 0.1-0.2wt% of the scrap steel batch are added into the furnace. Then, two rounds of off-furnace refining are carried out. At the end of the first off-furnace refining continuous pour, the temperature is controlled at 1645-1650℃, and at the end of the vacuum treatment, it is controlled at 1590-1600℃. At the end of the second off-furnace refining continuous pour, the temperature is controlled at 1625-1630℃, and at the end of the vacuum treatment, it is controlled at 1565-1570℃. The weak stirring time is 15 minutes, and argon is blown from the bottom of the vacuum furnace for stirring, and the tapping temperature is controlled at 1670-1680℃.

[0061] (2) Continuous casting:

[0062] When pouring begins, 1% of the tapping volume is thrown out (used for other varieties to ensure sufficient purity), the molten steel flow rate is controlled at 0.3-0.6 m / min, and the continuous casting billet drawing speed is 1.5-2.0 m / min. When the molten steel volume is 10t≤≤20t, the drawing speed is controlled at 1.2-1.6 m / min. When the molten steel volume is ≤10t, the drawing speed is controlled at 0.3-0.6 m / min. The continuous casting billet yield is controlled at 94%-96%;

[0063] (3) Rolling: Ring furnace heating → piercing → rolling → sizing

[0064] The heating of the tube billet in the annular furnace is divided into three stages. The first stage is 700±5℃ and kept warm for 0.5h. Then it is slowly heated at 80℃ / h to 800±5℃ in the second stage and kept warm for 2.5h. Then it is rapidly heated at 200℃ / h to 1260±5℃ in the third stage and kept warm for 3h. The furnace discharge temperature is controlled at 1260±2℃.

[0065] The piercing bite angle is 11-12°, the rolling speed limit V is 1.2m / s, the starting rolling temperature Ta is 1015℃, the finishing rolling temperature Tb is 960℃, and (Ta-Tb) is satisfied. 1 / 2 × V = 6 to 10, and the rolled tube is obtained;

[0066] (4) Heat treatment of blank sample:

[0067] When the seamless steel pipe is grade 165, the rolled pipe is subjected to water quenching at 900°C for 25 minutes + tempering at 550°C for 60 minutes (air cooling) + water quenching at 905°C for 28 minutes + secondary hardening at 560°C for 60 minutes (air cooling) + air cooling at 660°C for 100 minutes to obtain a seamless pipe.

[0068] Examples 2 to 8

[0069] The seamless steel pipes of Examples 2 to 8 were prepared using the method of Example 1, with the only difference being the element content and the heat treatment system.

[0070] The mass percentages of the components of Examples 1 to 8 are shown in Table 1, the heat treatment schedules are shown in Table 2, the mechanical properties of the prepared seamless steel pipes are shown in Table 3, and the inclusions in the seamless steel pipes are shown in Table 4. The statistics of the qualified rate of rolled pipe quality are shown in Table 5.

[0071] Comparative Example 1

[0072] The only difference from Example 1 is that the addition of alloy elements is not controlled according to the percentage f of the total amount of rolling defects, and more Mo, V, and Nb are added.

[0073] Comparative Example 2

[0074] The only difference from Example 1 is that the clean steel smelting technology is not used in step (1) steelmaking and the limited motion casting technology is not used in step (2) continuous casting.

[0075] Step (1) is: the electric arc furnace smelting adopts steel and molten iron as the raw material, the KT oxygen gun and the carbon gun adopt a fixed blowing curve, wherein the oxygen flow rate of the oxygen gun is 2000~2200m 3 / h, natural gas flow rate 400~450m 3 / h, the carbon gun injection flow rate is 50-55kg / min. After that, the furnace refining is carried out. When the furnace refining continuous pouring is finished, the temperature is controlled at 1625-1650℃, and the tapping temperature is controlled at 1670-1680℃;

[0076] Step (2) is: controlling the molten steel flow rate to 0.3-0.6 m / min and the continuous casting billet drawing speed to 1.5-2.0 m / min;

[0077] Comparative Example 3

[0078] The only difference from Example 1 is that the tube billet speed regulation and temperature raising technology is not used before rolling in step (3), and the rolling process does not satisfy the formula (Ta-Tb) 1 / 2 ×V=6~10.

[0079] Step (3) is specifically as follows: the heating of the tube billet in the annular furnace is divided into three sections, the first section is kept at 700±5°C for 0.5h, the second section is kept at 800±5°C for 2.5h, the third section is kept at 1260±5°C for 3h, and the furnace temperature is controlled at 1260±2°C;

[0080] The piercing bite angle is 11-12°, the rolling limit speed V is 0.8 m / s, the starting rolling temperature Ta is 1010°C, and the final rolling temperature Tb is 960°C to obtain the rolled tube;

[0081] Comparative Example 4

[0082] The only difference from Example 1 is that the blank sample heat treatment in step (4) is not subjected to secondary hardening.

[0083] Step (4) is specifically: water quenching at 900°C for 25 minutes + tempering at 550°C for 60 minutes (air cooling) + water quenching at 905°C for 28 minutes + air cooling at 660°C for 100 minutes to obtain a seamless pipe.

[0084] The mass percentages of the components of Comparative Examples 1 to 4 are shown in Table 1, the heat treatment schedules are shown in Table 2, the mechanical properties of the prepared seamless steel pipes are shown in Table 3, and the inclusions in the seamless steel pipes are shown in Table 4. The statistics of the pipe rolling quality pass rate are shown in Table 5.

[0085] Table 1 Chemical composition of the embodiments and comparative examples (mass fraction / %)

[0086]

[0087]

[0088] Note: Among them, the measured gas O: ≤0.0020%; N: ≤0.0050%; H: ≤0.00015%; Five harmful substances: Pb: ≤0.0150%; Sb: ≤0.0150%; As: ≤0.0150%; Bi: ≤0.0150%; Sn: ≤0.0150%;

[0089] Table 2 Heat treatment system of seamless steel tube samples of embodiment and comparative example

[0090]

[0091]

[0092] Table 3 Mechanical properties of seamless steel pipes of embodiments and comparative examples

[0093]

[0094] Table 4 Inclusions in seamless steel pipes of Examples and Comparative Examples

[0095]

[0096] Table 5 Statistics of quality pass rate of pipe rolled in Examples and Comparative Examples (unit / piece)

[0097]

[0098]

[0099] According to the data in Tables 1 to 4, it can be seen that Examples 1 to 4 all meet the 165Ksi requirement, and Examples 5 to 8 all meet the 150Ksi requirement, and the mechanical properties, inclusion content, and pipe rolling quality pass rate are excellent.

[0100] Compared with Example 1, Comparative Example 1: Mo / V / Nb exceeded the standard (Mo 1.21%, V 0.25%, Nb 0.05%), and the defect rate increased to 1.39%.

[0101] Comparative Example 2: Pure steel smelting technology was not adopted, the number of inclusions increased (Class B fine series 1.0), and the impact energy was only 114J.

[0102] Comparative Example 3: The tube billet speed regulation and heating technology was not used, and the rolling process did not meet the formula (Ta-Tb) 1 / 2 ×V=6-10, the defect rate is 1.29%, and the high temperature strength (955 MPa) is lower than that of Examples 1-4 (≥994 MPa).

[0103] The defect rate f of the embodiments is ≤0.85%, which is mainly caused by external scarring / internal bending residual stress, while the defect rate f of comparative examples 1 to 3 exceeds 1.30% due to substandard ingredients / processes.

[0104] Comparative Example 4 did not undergo secondary hardening during heat treatment, which affected the strength indicators: yield strength was 1121 MPa, tensile strength was 1190 MPa, longitudinal full-size impact energy at -20°C was 121 J, and the strength-toughness ratio did not meet the 165 Ksi requirement.

[0105] Therefore, the present invention optimizes the alloy composition through calculation, performs reasonable limit + high-purity steel smelting + tube blank segmented heating + secondary hardening, and synergistically achieves the comprehensive advantages of high strength and toughness and low defects (f≤1%), solves the risk of brittle fracture of deep well drill pipe, satisfies the principle of leakage before breaking, and improves safety of use.

[0106] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the present invention.

Claims

1. A high-strength and tough seamless steel pipe for drill pipe, characterized in that: The composition by mass percentage is: C: 0.22% to 0.25%, Si: 0.25% to 0.40%, Mn: 0.25% to 0.35%, P: ≤0.008%, S: ≤0.0010%, Ni: 0.20% to 0.30%, Cr: 1.20% to 1.30%, Mo: 1.15% to 1.20%, V: 0.17% to 0.20%, Nb: 0.02% to 0.04%, Al: 0.005% to 0.020%, Ca: 0.0005% to 0.0040%, O: ≤0.0020%, N: ≤0. 0.050%, H: ≤0.00015%, Pb: ≤0.0150%, Sb: ≤0.0150%, As: ≤0.0150%, Bi: ≤0.0150%, Sn: ≤0.0150%, the rest are iron and unavoidable impurities, the total percentage of rolling defects f ≤ 1%, yield strength 1094 ~ 1176MPa, tensile strength 1189 ~ 1238MPa, elongation 21% ~ 27%, 250 ℃ high temperature yield strength 930 ~ 1023MPa, -20 ℃ longitudinal full-size impact energy 123 ~ 138J, grain size ≥ 9.5; The total rolling defect percentage f is calculated by the following steps: (1) Define the mapping relationship between alloy elements and the total percentage of rolling defects f: f = A n +B n +C n +D n +E n +F n +G n , where A is the eddy current flaw detection defect, B is the inner fold defect, C is the inner scar defect, D is the outer fold defect, E is the outer scar defect, F is the inner edge defect, G is the pitting defect, the defect unit is the percentage of quantity, and n is the serial number of the steel grade; the alloy composition is related by the following formula: a n ·C+b n ·Si+d n ·Mn+e n ·Ni+g n ·Cr+h n ·Mo+i n ·V+j n ·Nb+k n ·Al+l n ·Ca→A n +B n +C n +D n +E n +F n +G n Where a, b, d, e, g, h, i, j, k, and l are the mass percentages of the alloying elements C, Si, Mn, Ni, Cr, Mo, V, Nb, Al, and Ca, respectively; (2) BP neural network optimization components were used, Levenberg-Marquardt feedforward propagation method was called, double hidden layer node setting was 10-10-8-7, and the number of training times was 500 times; according to the steel grade sequence number n, a, b, d, e, g, h, i, j, k, l were imported into the neural network input, and A, B, C, D, E, F, G were imported into the neural network output for calculation fitting; (3) Call the simulation function sim to predict rolling defects and ensure that f≤1%.

2. The seamless steel pipe according to claim 1, characterized in that When Nb≥0.025% or V≥0.20%, B n Increase the weight coefficient by 1.2 before; when Mo / 10+V+Nb≥0.33, D n and E n The weight coefficient should be increased by 1.25 before adding the weights, and the weighted values ​​should be rounded according to scientific notation.

3. The method for manufacturing a seamless steel pipe according to claim 1 or 2, wherein: The steps include: (1) Steelmaking: Electric arc furnace smelting uses all scrap steel as feed, oxygen blowing from the bottom of the furnace to remove slag, bottom lime and dephosphorization agent are added into the furnace, followed by two pours of refining outside the furnace, weak stirring time of 6 to 20 minutes, vacuum bottom blowing argon stirring, and the tapping temperature is controlled at 1620 to 1680 °C; (2) Continuous casting: When pouring, throw out 1% of the steel output, the molten steel flow rate is 0.3-0.6 m / min, the continuous casting billet drawing speed is 0.3-2.0 m / min, and the continuous casting billet yield is controlled at 94%-96%; (3) Rolling: The annular furnace billet is heated in three stages, the perforation bite angle is 11-12°, the rolling speed limit V is 0.8-1.2 m / s, the starting rolling temperature Ta is 1030±15°C, the final rolling temperature Tb is 950±10°C, and (Ta-Tb) is satisfied. 1 / 2 × V = 6 to 10, and the rolled tube is obtained; (4) Heat treatment of the blank: When the seamless steel pipe is 165 steel grade, it is quenched at 900±5℃ and kept warm for 25±5min, water quenched, tempered at 550±5℃ and kept warm for 60~70min, air cooled, quenched again, kept warm at 900±5℃ for 25±5min, water quenched, secondary hardening at 570±10℃ and kept warm for 60min, air cooled, tempered at 660±5℃ and kept warm for 90~100min, air cooled; When the seamless steel pipe is 150 steel grade, it is quenched and kept at 860-865℃ for 25±5min, water quenched, kept at 640±5℃ for 110-120min, and air cooled.

4. The manufacturing method according to claim 3, characterized in that In step (1), the bottom oxygen blowing for slag removal is as follows: KT oxygen gun and carbon gun adopt fixed blowing curve and manual intermittent blowing, wherein the oxygen flow rate of oxygen gun is 2000~2200m 3 / h, natural gas flow rate 400~450m 3 / h, the carbon gun blowing flow rate is 50-55kg / min.

5. The manufacturing method according to claim 3, characterized in that In step (1), the bottom lime and the dephosphorization agent account for 1.5-2.0 wt% and 0.1-0.2 wt% of the scrap steel material, respectively.

6. The manufacturing method according to claim 3, characterized in that When the first out-of-furnace refining and continuous pouring is finished, the temperature is controlled at 1630-1650°C, and when the vacuum treatment is finished, the temperature is controlled at 1570-1600°C. When the second out-of-furnace refining and continuous pouring is finished, the temperature is controlled at 1610-1630°C, and when the vacuum treatment is finished, the temperature is controlled at 1550-1570°C.

7. The manufacturing method according to claim 3, characterized in that When the amount of molten steel is 10t≤≤20t, the pulling speed is controlled at 1.2~1.6m / min; when the amount of molten steel is ≤10t, the pulling speed is controlled at 0.3~0.6m / min.

8. The manufacturing method according to claim 3, characterized in that The three-stage heating in step (3) is as follows: the first stage is kept at 700±20℃ for 0.5h, then slowly heated at 60~80℃ / h to 800±20℃ in the second stage, kept warm for 2.5~3h, then rapidly heated at 150~200℃ / h to 1260±20℃ in the third stage, kept warm for 2.5~3h, and the furnace temperature is controlled at 1260±10℃.

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