A method for improving the bowl-shaped end face of drill collar steel straightening

Abstract

This invention relates to a method for improving the bowl-shaped end face of drill collar steel after straightening, belonging to the technical field of drill collar steel production processes in the metallurgical industry. The technical solution is as follows: a seven-roll straightening method is used, with the reduction of the No. 1 and No. 3 upper and lower rolls being 4-5 mm, and the reduction of the No. 2 upper and lower rolls being 1-2 mm; the reverse bending amount is 15-16 mm; the straightening roll angles are: No. 1 upper and lower roll angle 29.5-30°, No. 2 upper roll angle 30-31°, No. 3 upper roll angle 29.5-30°, and lower roll angle 32-32.5°; the end of the straightened round steel is chamfered, with a chamfer angle of 30-45° and a chamfer length of 1-2 mm. The beneficial effects of this invention are: it can reduce the internal structural stress of the drill collar steel, ensure the hardness of the drill collar, and ensure that the bowl-shaped end face depth of the straightened drill collar steel is within 2 mm, avoiding cracking at the end face face during processing.

Description

Technical Field

[0001] This invention relates to a method for improving the bowl-shaped end of the straightening head of drill collar steel, belonging to the technical field of drill collar steel production process in the metallurgical industry. Background Technology

[0002] In oil drilling, the drill collar is a crucial component of the drill string. Located at the bottom of the drill string and connected to the drill bit, the drill collar not only transmits torque but also generates drilling pressure to propel the drill bit forward. During use, environmental stress corrosion and alternating bending fatigue stress are the main factors causing drill collar failure. In recent years, there have been numerous incidents of oil drill collar fractures.

[0003] The raw materials for drill collars are delivered in a hot-rolled state. The manufacturer performs rough machining on the hot-rolled drill collars, followed by heat treatment, straightening to relieve stress, tempering to test mechanical properties, and then fine machining before delivery to the Ministry of Petroleum.

[0004] Due to its high alloy content, drill collar steel retains bainite structure in its microstructure even during the slow cooling process after rolling. This results in high hardness, typically between 280 and 300 HB. The steel exhibits significant stress, making it prone to cracking during straightening and drill collar machining, and also presenting significant sawing challenges. If the internal stress of the steel is not controlled during rolling, tensile stress will form between the processed and unprocessed layers during subsequent straightening, creating a "bowl-shaped" end face. This "bowl-shaped" end face is not a flat plane but a concave surface, as shown in the attached image. Figure 1 As shown, the "bowl" depth is more than 2mm. At the split point of its internal structure, a fracture source is easily formed. The internal stress of the steel plus the straightening stress makes it very easy for the drill collar processing user to crack at the end bowl during the rough machining process. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the bowl-shaped end face of drill collar steel, which can reduce the internal structural stress of the drill collar steel, ensure the hardness of the drill collar, and ensure that the depth of the bowl-shaped end face of the drill collar steel is within 2mm, thereby avoiding cracking from the bowl-shaped end face during processing and solving the problems existing in the background art.

[0006] The technical solution of this invention is:

[0007] A method for improving the bowl-shaped end of a straightened drill collar steel includes heating, high-pressure water descaling, billet rolling, continuous rolling, cooling, straightening, and end chamfering. In the heating process, the preheating zone temperature is 800-900℃, the heating rate is 57-160℃ / h, the soaking zone temperature is 1220-1250℃, and the heating time is 144-480min. The heating temperature and heating time are controlled at the upper limit to reduce the thermal stress during the heating of the continuously cast billet and to ensure the maximum release of structural stress, as well as to achieve uniform internal structure and compositional segregation.

[0008] The high-pressure water descaling process involves a water pressure of 28-29 MPa, and descaling is performed in all directions around the circumference of the round continuous casting billet for 3-4 seconds.

[0009] The roughing rolling process involves a roughing temperature of 1180–1190°C, followed by 7–11 passes of reciprocating rolling. Simultaneously, the roll cooling water and the ground roll cooling water are turned on to cool the intermediate billet. The roughing temperature of the billet mill is controlled because the steel collar has good hardenability, high alloy content, and rapid temperature drop.

[0010] In the continuous rolling process, the roller speed after the billet mill is 2.1–2.2 m / s, and 6–8 passes are performed. The roll cooling water is turned on. The inlet guide of the mill before the finished product is 0–1 mm wider than the workpiece. The temperature of the workpiece entering the continuous rolling mill is controlled at 1005–1100℃. Controlling the roller speed and continuous rolling temperature after startup is to ensure hot working within the austenitic temperature range, preventing the formation of structural stress during the precipitation of proeutectoid ferrite. Uneven volume shrinkage of ferrite and austenite leads to uneven deformation, resulting in microcrack initiation and phase transformation stress, causing increased internal stress and surface or internal cracks during subsequent processing. Controlling the inlet guide of the mill before the finished product to be 0–1 mm wider than the workpiece ensures better workpiece gripping and prevents the steel from tipping over. The dimensions of the finished round steel are controlled according to GB / T702-2017.

[0011] The cooling process involves sawing the continuously rolled round steel, which is then placed on a rapid collection platform at 750-800°C before entering a slow cooling pit. The exit temperature from the pit is ≤250°C. Controlling the pit temperature is to control the cooling rate, make the microstructure transformation more thorough, reduce internal stress, and control the hardness at 280-300 HB.

[0012] The straightening process employs a seven-roller straightening system to straighten the round steel bars after they exit the pit. The main machine speed is 350–395 r / min. The reduction of the No. 1 and No. 3 upper and lower rolls is 4–5 mm, and the reduction of the No. 2 upper and lower rolls is 1–2 mm. The straightening roll angles are: No. 1 upper and lower roll angle 29.5–30°, No. 2 upper roll angle 30–31°, No. 3 upper roll angle 29.5–30°, and No. 3 lower roll angle 32–32.5°. The reverse bending amount is 15–16 mm. The straightening roll angle refers to the angle between the center line of the straightening roll and the straightening center line. The reverse bending amount refers to the distance between the No. 2 lower roll surface and the line connecting the surfaces of the front and rear rolls (No. 1 and No. 3 lower rolls).

[0013] Increasing the pressing amount of the No. 1 and No. 3 upper and lower straightening rollers is to allow the No. 1 upper and lower straightening rollers to better pull the rolled piece in, and the No. 3 upper and lower straightening rollers to push the rolled piece out, giving the rolled piece a forward force; decreasing the pressing amount of the No. 2 upper and lower straightening rollers is to reduce the thickness of the surface processing layer, and increasing the angle and reverse bending amount of the No. 2 upper roller is to achieve higher straightness.

[0014] The end chamfering process involves chamfering the ends of the straightened rolled material using a chamfering machine. The chamfering angle is 30-45° and the chamfering length is 1-2mm. The end chamfering is to remove the bowl-shaped opening formed by the processed and unprocessed layers after straightening, thereby minimizing the bowl shape.

[0015] The aforementioned drill collar steel has the following chemical composition by weight percentage: C: 0.35–0.38%, Si: 0.15–0.35%, Mn: 0.85–1.00%, P≤0.015%, S≤0.003%, Als: 0.015–0.040%, Cr: 0.90–1.20%, Mo: 0.28–0.33%, Ni: 0.03–0.06%, Sn≤0.03%, Sb≤0.03%, As≤0.03%, Pb≤0.025%, Bi≤0.03%, with the remainder being Fe and unavoidable residual elements.

[0016] The diameter of the aforementioned drill collar steel is 100–150 mm.

[0017] This invention reduces thermal stress during continuous casting billet heating and ensures maximum release of structural stress by increasing heating temperature and extending heating time, resulting in uniform internal structure and compositional segregation. Controlling the rolling temperature is crucial because drill collar steel has good hardenability, high alloy content, and rapid temperature drop; this ensures a subsequent pit entry temperature of 750–800℃ and reduces internal stress in the rolled material. Controlling the width of the mill inlet guide before finished product is 0–1 mm larger than the workpiece width ensures better workpiece gripping and prevents steel collapse, ensuring the finished round steel dimensions are within the range required by GB / T702-2017. Controlling the pit entry temperature to 750–800℃ reduces the cooling rate, decreases bainite formation, and controls the hardness of the drill collar steel within the range of 280–300 HB.

[0018] The above-mentioned control of the heating and rolling processes is to reduce the structural stress and internal stress of the original rolled material, maintain the flatness and regularity of the billet during the rolling process, and prepare for the subsequent straightening process.

[0019] By controlling parameters such as the straightening roller angle, pressing amount, and reverse bending amount of the seven-roll straightener, the bowl-shaped opening of the straightened round steel end is within 2mm, and the straightness is within 2mm per meter.

[0020] Controlling the end chamfering is to minimize the end cup opening while ensuring the yield rate, so that the raw material will not crack from the end cup opening during rough machining with the drill collar.

[0021] The beneficial effects of this invention are:

[0022] (1) Reduce the internal structural stress of the drill collar steel to ensure that the hardness of the drill collar is 280-300 HB;

[0023] (2) It can ensure that the depth of the bowl at the end of the straightened drill collar steel is within 2mm, the end is neat and the appearance is beautiful, and it avoids cracking from the bowl at the end during processing. At the same time, it can achieve a flatness of within 2mm per meter, save annealing costs, reduce production costs and improve the operating rate. Attached Figure Description

[0024] Figure 1 Background technical image;

[0025] Figure 2 Images are from this invention;

[0026] Figure 3 Image of end chamfer;

[0027] Figure 4 A schematic diagram of the layout of a seven-roll straightener;

[0028] Figure 5 Schematic diagram of the straightening roller angle Implementation

[0029] The invention will be further described below with reference to the accompanying drawings and examples. Example 1

[0030] The drill collar steel in this embodiment has a specification of φ100mm, and its chemical composition and mass percentage are shown in Table 1.

[0031] The production method of drill collar steel in this embodiment includes heating, high-pressure water descaling, billet rolling, continuous rolling, cooling, seven-roll straightening, and end chamfering. The specific process steps are as follows:

[0032] (1) Heating process: φ300 round continuous casting billet cold billet is put into the furnace, the preheating zone temperature is 800℃, the temperature rise rate is 160℃ / h, the soaking zone temperature is 1222℃, and the heating time is 144min;

[0033] (2) High-pressure water descaling process: The water pressure is 28 MPa, and descaling is carried out in all directions in the circumference of the round continuous casting billet for 3 seconds;

[0034] (3) Billet rolling process: The distance between the front and rear guide beams of the billet mill and the bottom of the roll groove is 141mm. After the workpiece bites in, the opening of the front pusher bed is required to be 4mm larger than the width of the workpiece, the opening of the rear pusher bed is required to be 22mm larger than the width of the workpiece, the ground roll is 5mm higher than the front and rear guide beams, the roughing rolling temperature is 1182℃, and after 7 passes of reciprocating rolling, the roll cooling water and the ground roll cooling water are turned on at the same time to obtain the intermediate billet;

[0035] (4) Continuous rolling process: The speed of the roller table after the billet mill is 2.1m / s, and 6 passes of continuous rolling are carried out. The cooling water of the rolls is turned on. The opening degree of the inlet guide of the mill before the finished product is equal to the width of the rolled piece. The temperature of the rolled piece entering the continuous rolling is controlled to be 1008℃.

[0036] (5) Cooling process: The continuously rolled round steel is sawn, and after sawing, it enters the rapid collection table at 753°C and then enters the slow cooling pit. The temperature of the steel leaving the pit is 145°C.

[0037] (6) Straightening process: The round steel bars after exiting the pit are straightened. The main machine speed is 350 r / min. The reduction of rollers #1 and #3 is 4 mm, the reduction of roller #2 is 1 mm, the angle between the upper and lower rollers of #1 is 29.5°, the angle of the upper roller of #2 is 30°, the lower roller is the driven roller, the reverse bending amount is 15 mm, the angle of the upper roller of #3 is 29.5°, and the angle of the lower roller is 32°, as shown in the attached figure. Figure 4 , 5 As shown;

[0038] (7) Chamfering process: The ends of the straightened rolled material are chamfered using a chamfering machine. The chamfering angle is 35° and the chamfering length is 2mm. This results in rolled material with a hardness of 283HB, a flatness of ≤2mm / m, an end cup size of ≤2mm, and dimensions that meet the requirements of Group 2 in Table 1 of GB / T702-2017. Example 2

[0039] The drill collar steel in this embodiment has a specification of φ105mm, and its chemical composition and mass percentage are shown in Table 1.

[0040] The production method of drill collar steel in this embodiment includes heating, high-pressure water descaling, billet rolling, continuous rolling, cooling, seven-roll straightening, and end chamfering. The specific process steps are as follows:

[0041] Heating process: The φ300 round continuous casting billet is put into the furnace. The temperature of the preheating zone is 824℃, the temperature rise rate is 144℃ / h, the temperature of the soaking zone is 1228℃, and the heating time is 163.2min.

[0042] (2) High-pressure water descaling process: The water pressure is 28.4 MPa, and descaling is carried out in all directions of the circumference of the round continuous casting billet for 3 seconds;

[0043] (3) Billet rolling process: The distance between the front and rear guide beams of the billet mill and the bottom of the roll groove is 142mm. After the workpiece bites in, the opening of the front pusher bed is required to be 4mm larger than the width of the workpiece, the opening of the rear pusher bed is required to be 24mm larger than the width of the workpiece, the ground roll is 5mm higher than the front and rear guide beams, the roughing rolling temperature is 1183℃, and after 7 passes of reciprocating rolling, the roll cooling water and the ground roll cooling water are turned on at the same time to obtain the intermediate billet;

[0044] (4) Continuous rolling process: The speed of the roller table after the billet mill is 2.15m / s, and 6 passes of continuous rolling are carried out. The cooling water of the rolls is turned on. The opening degree of the inlet guide of the mill before the finished product is equal to the width of the rolled piece. The temperature of the rolled piece entering the continuous rolling is controlled to be 1010℃.

[0045] (5) Cooling process: The continuously rolled round steel is sawn, and after sawing, it enters the rapid collection platform at 759°C and then enters the slow cooling pit. The temperature of the steel leaving the pit is 122°C.

[0046] (6) Straightening process: The round steel bars after exiting the pit are straightened. The main machine speed is 350 r / min. The reduction of rollers #1 and #3 is 4.5 mm, the reduction of roller #2 is 1.5 mm, the angle between the upper and lower rollers of #1 is 29.5°, the angle of the upper roller of #2 is 30°, the lower roller is the driven roller, the reverse bending amount is 15.2 mm, the angle of the upper roller of #3 is 29.5°, and the angle of the lower roller is 32°. See attached. Figure 4 , 5 As shown;

[0047] (7) Chamfering process: The ends of the straightened rolled material are chamfered using a chamfering machine. The chamfering angle is 40° and the chamfering length is 1.5mm. This results in rolled material with a hardness of 281HB, a flatness of ≤2mm / m, an end cup size of ≤2mm, and dimensions that meet the requirements of Group 2 in Table 1 of GB / T702-2017. Example 3

[0048] The drill collar steel in this embodiment has a specification of φ110mm, and its chemical composition and mass percentage are shown in Table 1.

[0049] The production method of drill collar steel in this embodiment includes heating, high-pressure water descaling, billet rolling, continuous rolling, cooling, seven-roll straightening, and end chamfering. The specific process steps are as follows:

[0050] Heating process: The φ300 round continuous casting billet is put into the furnace. The temperature of the preheating zone is 855℃, the temperature rise rate is 125℃ / h, the temperature of the soaking zone is 1233℃, and the heating time is 182.4min.

[0051] (2) High-pressure water descaling process: The water pressure is 28.5 MPa, and descaling is carried out in all directions of the circumference of the round continuous casting billet for 3.5 seconds;

[0052] (3) Billet rolling process: The distance between the front and rear guide beams of the billet mill and the bottom of the roll groove is 143mm. After the workpiece bites in, the opening of the front pusher bed is required to be 4mm larger than the width of the workpiece, the opening of the rear pusher bed is required to be 25mm larger than the width of the workpiece, the ground roll is 5mm higher than the front and rear guide beams, the roughing rolling temperature is 1185℃, and after 7 passes of reciprocating rolling, the roll cooling water and the ground roll cooling water are turned on at the same time to obtain the intermediate billet;

[0053] (4) Continuous rolling process: The speed of the roller table after the billet mill is 2.15m / s, and 6 passes of continuous rolling are carried out. The cooling water of the rolls is turned on. The opening degree of the inlet guide of the mill before the finished product is equal to the width of the rolled piece. The temperature of the rolled piece entering the continuous rolling is controlled to be 1020℃.

[0054] (5) Cooling process: The continuously rolled round steel is sawn, and after sawing, it enters the rapid collection table at 755°C and then enters the slow cooling pit. The temperature of the steel leaving the pit is 120°C.

[0055] (6) Straightening process: The round steel bars after exiting the pit are straightened. The main machine speed is 350 r / min. The reduction of rollers #1 and #3 is 4.5 mm, the reduction of roller #2 is 1.3 mm, the angle between the upper and lower rollers of #1 is 29.6°, the angle of the upper roller of #2 is 30.3°, the lower roller is the driven roller, the reverse bending amount is 15.2 mm, the angle of the upper roller of #3 is 29.5°, and the angle of the lower roller is 32°. See attached. Figure 4 , 5 As shown;

[0056] (7) Chamfering process: The ends of the straightened rolled material are chamfered using a chamfering machine. The chamfering angle is 40° and the chamfering length is 1.8mm. This results in rolled material with a hardness of 285HB, a flatness of ≤2mm / m, an end cup size of ≤2mm, and dimensions that meet the requirements of Group 2 in Table 1 of GB / T702-2017. Example 4

[0057] The drill collar steel in this embodiment has a specification of φ115mm, and its chemical composition and mass percentage are shown in Table 1.

[0058] The production method of drill collar steel in this embodiment includes heating, high-pressure water descaling, billet rolling, continuous rolling, cooling, seven-roll straightening, and end chamfering. The specific process steps are as follows:

[0059] Heating process: The φ300 round continuous casting billet is put into the furnace. The temperature of the preheating zone is 831℃, the temperature rise rate is 107℃ / h, the temperature of the soaking zone is 1235℃, and the heating time is 192min.

[0060] (2) High-pressure water descaling process: The water pressure is 29 MPa, and descaling is carried out in all directions in the circumferential direction of the round continuous casting billet for 4 seconds;

[0061] (3) Billet rolling process: The distance between the front and rear guide beams of the billet mill and the bottom of the roll groove is 145mm. After the workpiece bites in, the opening of the front pusher bed is required to be 4mm larger than the width of the workpiece, the opening of the rear pusher bed is required to be 26mm larger than the width of the workpiece, the ground roll is 5mm higher than the front and rear guide beams, the roughing rolling temperature is 1188℃, and after 7 passes of reciprocating rolling, the roll cooling water and the ground roll cooling water are turned on at the same time to obtain the intermediate billet;

[0062] (4) Continuous rolling process: The speed of the roller table after the billet mill is 2.1m / s, and 6 passes of continuous rolling are carried out. The cooling water of the rolls is turned on. The opening degree of the inlet guide of the mill before the finished product is equal to the width of the rolled piece. The temperature of the rolled piece entering the continuous rolling is controlled to be 1025℃.

[0063] (5) Cooling process: The continuously rolled round steel is sawn, and after sawing, it enters the rapid collection platform at 751°C and then enters the slow cooling pit. The temperature of the steel leaving the pit is 110°C.

[0064] (6) Straightening process: The round steel bars after exiting the pit are straightened. The main machine speed is 355 r / min. The reduction of rollers #1 and #3 is 4.6 mm, the reduction of roller #2 is 1.4 mm, the angle between the upper and lower rollers of #1 is 29.8°, the angle of the upper roller of #2 is 30.5°, the lower roller is a driven roller, the reverse bending amount is 15.3 mm, the angle of the upper roller of #3 is 29.6°, and the angle of the lower roller is 32.2°. See attached. Figure 4 , 5 As shown;

[0065] (7) Chamfering process: The ends of the straightened rolled material are chamfered using a chamfering machine. The chamfering angle is 43° and the chamfering length is 1.6mm. This results in rolled material with a hardness of 282HB, a flatness of ≤2mm / m, an end cup of 1~2mm, and dimensions that meet or exceed the second group in Table 1 of GB / T702-2017. Example 5

[0066] The drill collar steel in this embodiment has a specification of φ120mm, and its chemical composition and mass percentage are shown in Table 1.

[0067] The production method of drill collar steel in this embodiment includes heating, high-pressure water descaling, billet rolling, continuous rolling, cooling, seven-roll straightening, and end chamfering. The specific process steps are as follows:

[0068] Heating process: The φ380 round continuous casting billet is put into the furnace. The temperature of the preheating zone is 821℃, the temperature rise rate is 93℃ / h, the temperature of the soaking zone is 1238℃, and the heating time is 240min.

[0069] (2) High-pressure water descaling process: The water pressure is 28.5 MPa, and descaling is carried out in all directions of the circumference of the round continuous casting billet for 3.3 seconds;

[0070] (3) Billet rolling process: The distance between the front and rear guide beams of the billet mill and the bottom of the roll groove is 146mm. After the workpiece bites in, the opening of the front pusher bed is required to be 4.5mm larger than the width of the workpiece, the opening of the rear pusher bed is 24mm larger than the width of the workpiece, the ground roll is 5mm higher than the front and rear guide beams, the roughing rolling temperature is 1189℃, and after 9 passes of reciprocating rolling, the roll cooling water and the ground roll cooling water are turned on at the same time to obtain the intermediate billet;

[0071] (4) Continuous rolling process: The speed of the roller table after the billet mill is 2.1m / s, and 6 passes of continuous rolling are carried out. The cooling water of the rolls is turned on. The opening degree of the inlet guide of the mill before the finished product is equal to the width of the rolled piece. The temperature of the rolled piece entering the continuous rolling is controlled to be 1028℃.

[0072] (5) Cooling process: The continuously rolled round steel is sawn, and after sawing, it enters the rapid collection platform at 771°C and then enters the slow cooling pit. The temperature of the steel leaving the pit is 104°C.

[0073] (6) Straightening process: The round steel bars after exiting the pit are straightened. The main machine speed is 358 r / min. The reduction of rollers #1 and #3 is 4.7 mm, the reduction of roller #2 is 1.5 mm, the angle between the upper and lower rollers of #1 is 29.8°, the angle of the upper roller of #2 is 30.6°, the lower roller is a driven roller, the reverse bending amount is 15.4 mm, the angle of the upper roller of #3 is 29.7°, and the angle of the lower roller is 32.3°. (See attached...) Figure 4 , 5 As shown;

[0074] (7) Chamfering process: The ends of the straightened rolled material are chamfered using a chamfering machine. The chamfering angle is 44° and the chamfering length is 1.7mm. This results in rolled material with a hardness of 284HB, a flatness of ≤2mm / m, an end cup of 1~2mm, and dimensions that meet or exceed the second group in Table 1 of GB / T702-2017. Example 6

[0075] The drill collar steel in this embodiment has a specification of φ130mm, and its chemical composition and mass percentage are shown in Table 1.

[0076] The production method of drill collar steel in this embodiment includes heating, high-pressure water descaling, billet rolling, continuous rolling, cooling, seven-roll straightening, and end chamfering. The specific process steps are as follows:

[0077] Heating process: The φ380 round continuous casting billet is put into the furnace. The temperature of the preheating zone is 846℃, the temperature rise rate is 81℃ / h, the temperature of the soaking zone is 1239℃, and the heating time is 259.2min.

[0078] (2) High-pressure water descaling process: The water pressure is 28.6 MPa, and descaling is carried out in all directions of the circumference of the round continuous casting billet for 3.4 seconds;

[0079] (3) Billet rolling process: The distance between the front and rear guide beams of the billet mill and the bottom of the roll groove is 147mm. After the workpiece bites in, the opening of the front pusher bed is required to be 4.6mm larger than the width of the workpiece, the opening of the rear pusher bed is required to be 27mm larger than the width of the workpiece, the ground roll is 5.3mm higher than the front and rear guide beams, the roughing rolling temperature is 1190℃, and after 9 passes of reciprocating rolling, the roll cooling water and the ground roll cooling water are turned on at the same time to obtain the intermediate billet;

[0080] (4) Continuous rolling process: The speed of the roller table after the billet mill is 2.16m / s, and 6 passes of continuous rolling are carried out. The cooling water of the rolls is turned on. The opening degree of the inlet guide of the mill before the finished product is equal to the width of the rolled piece. The temperature of the rolled piece entering the continuous rolling is controlled to be 1032℃.

[0081] (5) Cooling process: The continuously rolled round steel is sawn, and after sawing, it enters the rapid collection platform at 764°C and then enters the slow cooling pit. The temperature of the steel leaving the pit is 107°C.

[0082] (6) Straightening process: The round steel bars after exiting the pit are straightened. The main machine speed is 359 r / min. The reduction of rollers #1 and #3 is 4.8 mm, the reduction of roller #2 is 1.6 mm, the angle between the upper and lower rollers of #1 is 29.9°, the angle of the upper roller of #2 is 30.7°, the lower roller is a driven roller, the reverse bending amount is 15.5 mm, the angle of the upper roller of #3 is 29.8°, and the angle of the lower roller is 32.4°. (See attached...) Figure 4 , 5 As shown;

[0083] (7) Chamfering process: The ends of the straightened rolled material are chamfered using a chamfering machine. The chamfering angle is 45° and the chamfering length is 1.8mm. This results in rolled material with a hardness of 286HB, a flatness of ≤2mm / m, an end cup of 1~2mm, and dimensions that meet or exceed the second group in Table 1 of GB / T702-2017. Example 7

[0084] The drill collar steel in this embodiment has a specification of φ140mm, and its chemical composition and mass percentage are shown in Table 1.

[0085] The production method of drill collar steel in this embodiment includes heating, high-pressure water descaling, billet rolling, continuous rolling, cooling, seven-roll straightening, and end chamfering. The specific process steps are as follows:

[0086] Heating process: The φ450 round continuous casting billet is put into the furnace. The temperature of the preheating zone is 850℃, the temperature rise rate is 67℃ / h, the temperature of the soaking zone is 1240℃, and the heating time is 432min.

[0087] (2) High-pressure water descaling process: The water pressure is 28.7 MPa, and descaling is carried out in all directions of the circumference of the round continuous casting billet for 3.5 seconds;

[0088] (3) Billet rolling process: The distance between the front and rear guide beams of the billet mill and the bottom of the roll groove is 148mm. After the workpiece bites in, the opening of the front pusher bed is required to be 4.7mm larger than the width of the workpiece, the opening of the rear pusher bed is required to be 28mm larger than the width of the workpiece, the ground roll is 5.5mm higher than the front and rear guide beams, the roughing rolling temperature is 1189℃, and after 11 passes of reciprocating rolling, the roll cooling water and the ground roll cooling water are turned on at the same time to obtain the intermediate billet;

[0089] (4) Continuous rolling process: The speed of the roller table after the billet mill is 2.18m / s, and 8 passes of continuous rolling are carried out. The cooling water of the rolls is turned on. The opening degree of the inlet guide of the mill before the finished product is 0.5mm larger than the width of the rolled piece. The temperature of the rolled piece entering the continuous rolling is controlled to be 1035℃.

[0090] (5) Cooling process: The continuously rolled round steel is sawn, and after sawing, it enters the rapid collection platform at 765°C and then enters the slow cooling pit. The temperature of the steel leaving the pit is 95°C.

[0091] (6) Straightening process: The round steel bars after exiting the pit are straightened. The main machine speed is 360 r / min. The reduction of rollers #1 and #3 is 4.9 mm, the reduction of roller #2 is 1.7 mm, the angle between the upper and lower rollers of #1 is 30°, the angle of the upper roller of #2 is 30.8°, the lower roller is a driven roller, the reverse bending amount is 15.6 mm, the angle of the upper roller of #3 is 29.9°, and the angle of the lower roller is 32.5°. (See attached...) Figure 4 , 5 As shown;

[0092] (7) Chamfering process: The ends of the straightened rolled material are chamfered using a chamfering machine. The chamfering angle is 45° and the chamfering length is 1.9mm. This results in rolled material with a hardness of 290HB, a flatness of ≤2mm / m, an end cupping of 1~2mm, and dimensions that meet or exceed the second group in Table 1 of GB / T702-2017. Example 8

[0093] The drill collar steel in this embodiment has a specification of φ150mm, and its chemical composition and mass percentage are shown in Table 1.

[0094] The production method of drill collar steel in this embodiment includes heating, high-pressure water descaling, billet rolling, continuous rolling, cooling, seven-roll straightening, and end chamfering. The specific process steps are as follows:

[0095] Heating process: The φ450 round continuous casting billet is put into the furnace. The temperature of the preheating zone is 900℃, the temperature rise rate is 57℃ / h, the temperature of the soaking zone is 1250℃, and the heating time is 480min.

[0096] (2) High-pressure water descaling process: The water pressure is 29 MPa, and descaling is carried out in all directions in the circumferential direction of the round continuous casting billet for 4 seconds;

[0097] (3) Billet rolling process: The distance between the front and rear guide beams of the billet mill and the bottom of the roll groove is 150mm. After the workpiece bites in, the opening of the front pusher bed is required to be 6mm larger than the width of the workpiece, the opening of the rear pusher bed is required to be 30mm larger than the width of the workpiece, the ground roll is 6mm higher than the front and rear guide beams, the roughing rolling temperature is 1190℃, and after 11 passes of reciprocating rolling, the roll cooling water and the ground roll cooling water are turned on at the same time to obtain the intermediate billet;

[0098] (4) Continuous rolling process: The speed of the roller table after the billet mill is 2.2m / s, and 8 passes of continuous rolling are carried out. The cooling water of the rolls is turned on. The opening of the inlet guide of the mill before the finished product is 1mm larger than the width of the rolled piece. The temperature of the rolled piece entering the continuous rolling is controlled to be 1100℃.

[0099] (5) Cooling process: The continuously rolled round steel is sawn, and after sawing, it enters the rapid collection table at 780°C and then enters the slow cooling pit. The temperature of the steel leaving the pit is 84°C.

[0100] (6) Straightening process: The round steel bars after exiting the pit are straightened. The main machine speed is 395 r / min. The reduction of rollers #1 and #3 is 5 mm, the reduction of roller #2 is 2 mm, the angle between the upper and lower rollers of #1 is 30°, the angle of the upper roller of #2 is 31°, the lower roller is a driven roller, the reverse bending amount is 16 mm, the angle of the upper roller of #3 is 30°, and the angle of the lower roller is 32.5°. (See attached...) Figure 4 , 5 As shown;

[0101] (7) Chamfering process: The ends of the straightened rolled material are chamfered using a chamfering machine. The chamfering angle is 45° and the chamfering length is 2mm. This results in rolled material with a hardness of 294HB, a straightness of ≤2mm / m, an end cup of 1~2mm, and dimensions that meet or exceed the 2nd group in Table 1 of GB / T702-2017.

[0102] Table 1. Chemical composition and mass percentage (%) of drill collar steel in each embodiment

[0103]

[0104] In Table 1, the balance is Fe and unavoidable impurities.

Claims

1. A method for improving the bowl-shaped end face of a drill collar steel straightening device, characterized in that: The chemical composition (weight percentage) of drill collar steel is as follows: C: 0.35–0.38%, Si: 0.15–0.35%, Mn: 0.85–1.00%, P≤0.015%, S≤0.003%, Als: 0.015–0.040%, Cr: 0.90–1.20%, Mo: 0.28–0.33%, Ni: 0.03–0.06%, Sn≤0.03%, Sb≤0.03%, As≤0.03%, Pb≤0.025%, Bi≤0.03%, with the remainder being Fe and unavoidable residual elements. The method for improving the straightening of the drill collar steel's end face includes a heating process, a billet rolling process, a continuous rolling process, a cooling process, a straightening process, and an end chamfering process, wherein: Heating process: The preheating zone temperature is 800-900℃, the heating rate is 57-160℃ / h, the soaking zone temperature is 1220-1250℃, and the heating time is 144-480min; The initial rolling process: the initial rolling temperature is 1180~1190℃; Continuous rolling process: The initial rolling temperature is 1005~1100℃; Cooling process: The rolled round steel is naturally cooled to 750-800℃, and then put into a slow cooling pit. The temperature when it comes out of the pit is ≤250℃. Straightening process: Seven-roller straightening is adopted. The pressing amount of the No. 1 upper and lower rollers and the No. 3 upper and lower rollers is 4-5mm, and the pressing amount of the No. 2 upper and lower rollers is 1-2mm; the reverse bending amount is 15-16mm; the straightening roller angles are: No. 1 upper and lower roller angle 29.5-30°, No. 2 upper roller angle 30-31°, No. 3 upper roller angle 29.5-30°, and lower roller angle 32-32.5°. End chamfering process: Chamfer the ends of the straightened round steel. The chamfering angle is 30-45° and the chamfering length is 1-2mm.

2. The method for improving the bowl-shaped end face of a drill collar steel straightening device according to claim 1, characterized in that: The diameter of the round steel is 100-150 mm.

3. The method for improving the bowl-shaped end face of a drill collar steel straightening device according to claim 1, characterized in that: The hardness of the round steel is controlled to be 280-300 HB.

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