Bimetallic corrosion-resistant sucker rod round steel and its production method

Abstract

The application discloses a double-metal corrosion-resistant sucker rod round steel and a production method thereof. The production method of the double-metal corrosion-resistant sucker rod round steel comprises the following steps: preparing an alloy structural steel and a stainless steel pipe, wherein the stainless steel pipe is 100 mm or more shorter than the alloy structural steel, inserting the alloy structural steel into the stainless steel pipe, wherein one end of the alloy structural steel is inserted into the stainless steel pipe by 5 mm to 10 mm, and the other end of the alloy structural steel is exposed from the stainless steel pipe by 100 mm or more; and forming a double-metal steel blank through a vacuum net interface assembly mode, and then heating and rolling the double-metal steel blank to obtain the double-metal corrosion-resistant sucker rod round steel. The double-metal steel blank formed through the vacuum net interface assembly mode is subjected to plastic deformation and metal diffusion under the action of high temperature and deformation stress in the rolling process, and metallurgical bonding is formed.

Description

Technical Field

[0001] This invention relates to the field of metal materials and oil extraction equipment technology, and more specifically, to bimetallic corrosion-resistant sucker rod round steel and its production method. Background Technology

[0002] Sucker rods are a key component of oilfield pumping systems, connecting the pumping unit and the pump and transmitting power; they are one of the "three pumping devices" in oilfields. Because oil well fluids contain not only crude oil but also highly mineralized water, salt, carbon dioxide, and hydrogen sulfide, corrosive media significantly reduce the service life of sucker rods, making corrosion fatigue fracture the primary cause of failure. Current methods to improve the corrosion resistance and lifespan of sucker rods include changing the material, applying surface coatings for reinforcement, modifying the well fluid medium to reduce its corrosiveness, and using sacrificial anodes and current cathodic protection to reduce corrosion. However, these methods still cannot meet the oilfield industry's requirements for long-life sucker rods.

[0003] The steel used for sucker rods is currently alloy structural steel. The corrosion resistance and fatigue performance of the steel are mainly improved by adjusting the alloy composition elements or proportions. However, this still cannot meet the requirements of the oil extraction industry for long service life of sucker rods. Although stainless steel coated sucker rod technology is publicly available, there is no manufacturing method for the steel used in stainless steel coated sucker rods. Moreover, different production methods result in significant differences in the quality or processing efficiency of the steel used for sucker rod processing.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing round steel for bimetallic corrosion-resistant sucker rods and the round steel for bimetallic corrosion-resistant sucker rods obtained by the method for producing round steel for bimetallic corrosion-resistant sucker rods.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a method for producing round steel for bimetallic corrosion-resistant sucker rods, comprising preparing alloy structural steel and stainless steel tube, wherein the stainless steel tube is more than 100 mm shorter than the alloy structural steel, extending the alloy structural steel into the stainless steel tube, wherein one end of the alloy structural steel extends into the stainless steel tube by 5 mm to 10 mm and the other end protrudes from the stainless steel tube by more than 100 mm; forming a bimetallic steel billet by vacuum clean interface assembly of the alloy structural steel and the stainless steel tube, and then heating and rolling the bimetallic steel billet to obtain round steel for bimetallic corrosion-resistant sucker rods.

[0008] In an optional embodiment, the alloy structural steel is a round steel or continuously cast round steel billet containing at least two elements selected from Mn, Cr, Ni, Mo and V; the stainless steel pipe is at least one of Cr-Ni austenitic stainless steel, Cr-Ni-Mo austenitic stainless steel and duplex stainless steel.

[0009] In an optional embodiment, the vacuum clean interface preform includes:

[0010] First, weld the gap between the bimetallic alloy structural steel extending into the stainless steel pipe end and then weld a disc-shaped steel plate with the same diameter as the outer diameter of the stainless steel pipe at that end to perform a secondary seal on the stainless steel pipe.

[0011] The end of the alloy structural steel exposed stainless steel pipe is divided into four equal parts along the circumference. First, two symmetrical gaps are welded. Then, the remaining gap space is evacuated to a vacuum degree of less than 10 Pa. The remaining gap is welded under this vacuum condition.

[0012] In an optional embodiment, the bimetallic billet has a diameter of 160mm to 170mm, and the billet is loaded into the heating furnace with the exposed end of the alloy structural steel as the rolling bite end. The heating step includes a preheating section, a heating section, and a soaking section.

[0013] The preheating section has a heating rate of no more than 12℃ / min and a temperature of no more than 650℃; the heating section has a temperature of 1120℃~1230℃; the soaking section has a temperature of 1120℃~1180℃; and the total heating time of the preheating section, heating section and soaking section is no less than 120min.

[0014] In an optional embodiment, the rolling mill equipment and arrangement in the rolling steps are as follows: 6 roughing mill stands → 6 intermediate mill stands → 4 pre-finishing mill stands → 4 finishing mill stands → 4 three-roll KOCKS mill stands. The roughing mill to the finishing mill stands are arranged alternately in horizontal and vertical configurations, and the KOCKS mill is arranged alternately in a forward Y and inverted Y configuration. The 6th roughing mill stand is 50m to 55m apart from the intermediate mill stand. The roughing mill group and the intermediate mill group do not form continuous rolling and adopt a split-rolling method.

[0015] In an optional implementation, the roughing rolling to KOCKS mill pass sequence is from pass 1 to pass 24. The roughing passes from pass 1 to pass 4 are all box-shaped passes, and the passes from pass 5 to pass 20 are arranged in an alternating elliptical-circular pattern.

[0016] In an optional embodiment, the rolling mill cooling water is not turned on during the biting process of the first to sixth passes of rough rolling, and 20% to 30% of the normal water volume is turned on for cooling during the rolling process after biting.

[0017] In an optional embodiment, the first and second roughing passes are skipped without reduction; the reduction in the third pass is 5% to 7% of the bimetallic billet diameter; the reduction in the fourth pass is 10% to 13% of the width of the rolled piece after the third pass; the reduction in the fifth pass is 15% to 17% of the width of the rolled piece after the fourth pass; and the reduction in the sixth pass is 20% to 23% of the width of the rolled piece after the fifth pass, thus pressing together the bimetallic interface gap after roughing; and / or the reduction in the seventh, ninth, and eleventh intermediate rolling passes is 40% to 45% of the diameter of the rolled piece from the previous pass, and the reduction in the eighth, tenth, and twelfth passes is 38% to 43% of the width of the rolled piece from the previous pass.

[0018] In an optional implementation, flying shears are installed after the 6th, 12th, 16th, 20th and 24th passes, and the flying shears are numbered 1, 2, 3, 4 and 5 respectively.

[0019] The No. 1 flying shear does not cut the head, while the No. 2 flying shear removes the portion of the substrate without a sleeve from the head, with a total cutting length of 0.6m to 0.8m.

[0020] Secondly, the present invention provides a bimetallic corrosion-resistant sucker rod round steel obtained by the production method of any one of the foregoing embodiments, comprising, from the inside out, an alloy structural steel core, a bimetallic diffusion layer and a stainless steel layer, wherein the diameter of the alloy structural steel core is 16mm to 33mm, the thickness of the bimetallic diffusion layer is 40 to 70μm, and the thickness of the stainless steel layer is 0.7mm to 1.0mm.

[0021] The present invention has the following beneficial effects:

[0022] Bimetallic core substrate round steel billet and stainless steel tube are assembled into bimetallic steel billet through vacuum clean interface assembly technology. Under the action of high temperature and deformation stress during steel rolling, the bimetallic steel billet undergoes plastic deformation and metal diffusion, forming a metallurgical bond. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The microstructure of the finished bimetallic corrosion-resistant sucker rod obtained in Example 1 is shown in the image.

[0025] Figure 2 The microstructure of the finished bimetallic corrosion-resistant sucker rod round steel obtained in Example 1 is shown at 500x magnification.

[0026] Figure 3 The image shows the 100x magnification microstructure of the finished bimetallic corrosion-resistant sucker rod round steel obtained in Example 1. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0028] This embodiment provides a method for producing round steel for bimetallic corrosion-resistant sucker rods. Alloy structural steel and stainless steel tubing are prepared, wherein the stainless steel tubing is at least 100mm shorter than the alloy structural steel. The alloy structural steel is inserted into the stainless steel tubing, with one end of the alloy structural steel extending 5mm-10mm into the stainless steel tubing and the other end protruding at least 100mm. The alloy structural steel and stainless steel tubing are assembled into a bimetallic billet using a vacuum clean interface method. The bimetallic billet is then heated and rolled to obtain the round steel for bimetallic corrosion-resistant sucker rods.

[0029] The stainless steel tube is at least 100mm shorter than that of the alloy structural steel tube, and in some embodiments, it is preferably 100-200mm. The reason for the shorter length is that the surface of the stainless steel tube is smooth, and the rolled piece is prone to slippage and difficulty in biting during the rolling process. The round steel billet retains more than 100mm without the steel tube to facilitate biting during the rolling process. The portion of the substrate without the stainless steel tube is cleanly removed by flying shears during the rolling process.

[0030] In some embodiments of this application, the alloy structural steel is a round steel or continuously cast round steel billet containing at least two elements selected from Mn, Cr, Ni, Mo and V; the stainless steel pipe is at least one of Cr-Ni austenitic stainless steel, Cr-Ni-Mo austenitic stainless steel and duplex stainless steel.

[0031] The alloy structural steel constituting the bimetallic billet is used as the base material. It can be an alloy structural steel containing two or more alloying elements, such as Mn, Cr, Ni, Mo, and V. The steel grade depends on the grade of the sucker rod prepared by the end user. For example, K-grade sucker rods use 20Ni2MoA or 23Ni2MoVA, KD-grade sucker rods use 23NiCrMoVA or 25NiMnCrMoVA, and HL-type sucker rods use 25NiMnCrMoVA, 35CrMoA, or 42CrMoA. The base material can be rolled round steel or continuously cast round steel billets (collectively referred to as round steel billets). The round steel billet's shape and dimensions require: a curvature of less than 1.3 mm per meter and a total curvature of less than 0.13% to prevent jamming when the round steel is inserted into the stainless steel tube. Depending on the billet assembly process, the round steel billet is inserted into the stainless steel tube using an interference fit. The diameter of the round steel billet is 0.5 mm to 1.0 mm smaller than the inner diameter of the stainless steel tube.

[0032] The stainless steel tube forming the outer layer of the bimetallic billet is made of corrosion-resistant Cr-Ni or Cr-Ni-Mo austenitic stainless steel or duplex stainless steel, such as 022Cr19Ni10, 022Cr17Ni12Mo2, 022Cr23Ni5Mo3N, etc. The stainless steel tube's shape and dimensions are required to have a wall thickness of 6mm to 10mm. The actual wall thickness should be determined based on the finished round bar's stainless steel cladding thickness being ≥0.7mm and the total rolling deformation.

[0033] In some embodiments of this application, the vacuum clean interface preform includes:

[0034] First, weld the gap between the bimetallic alloy structural steel extending into the stainless steel pipe end and then weld a disc-shaped steel plate with the same diameter as the outer diameter of the stainless steel pipe at that end to perform a secondary seal on the stainless steel pipe.

[0035] The end of the alloy structural steel exposed stainless steel pipe is divided into four equal parts along the circumference. First, two symmetrical gaps are welded. Then, the remaining gap space is evacuated to a vacuum degree of less than 10 Pa. The remaining gap is welded under this vacuum condition.

[0036] To use vacuum clean interface assembly, several round, disc-shaped steel plates with a thickness of 5mm to 8mm and a diameter the same as the outer diameter of the stainless steel pipe need to be prepared.

[0037] Before assembling round steel billets, surface cleaning and washing are required: first, use peeling and grinding equipment to remove surface iron oxide scale and any existing defects such as cracks, scars, folds, and inclusions. The surface grinding depth is 0.5mm to 1.5mm. When the base material is rolled round steel, the surface grinding depth is 0.5mm to 1.0mm; when using continuously cast round steel billets, the surface grinding depth is 1.0mm to 1.5mm. After grinding, use acetone to clean the surface of oil stains, rust, and other adhering substances. Stainless steel pipes also have their inner surface cleaned with acetone to remove adhering substances.

[0038] After cleaning and washing, the round steel billet is inserted into the stainless steel tube using a pusher device. The alignment method between the two ends of the round steel billet and the stainless steel tube is as follows: one end of the round steel billet extends 5mm-10mm into the stainless steel tube, while the other end protrudes more than 100mm without the tube. After insertion, a plasma electron beam welding process is used to first weld the end of the round steel billet that extends into the stainless steel tube. Then, a disc-shaped steel plate is placed on the end for a second welding seal. The other end of the round steel billet is then welded, with the circumferential gap between the billet and the tube roughly divided into four equal parts. Two symmetrically shaped gaps are welded. After welding, the billet is moved to a vacuum device. After the vacuum device is sealed, a vacuum is drawn, and the remaining gap at the sealing joint is welded under a vacuum degree less than 10Pa.

[0039] For the assembled bimetallic billet, the exposed ends of the substrate are marked with paint to facilitate identification of both ends.

[0040] In some embodiments of this application, the bimetallic billet has a diameter of 160mm to 170mm, and the billet is loaded into the heating furnace with the exposed end of the alloy structural steel as the rolling bite end. The heating step includes a preheating section, a heating section and a soaking section.

[0041] The preheating section has a heating rate of no more than 12℃ / min and a temperature of no more than 650℃; the heating section has a temperature of 1120℃~1230℃; the soaking section has a temperature of 1120℃~1180℃; and the total heating time of the preheating section, heating section and soaking section is no less than 120min.

[0042] Billet heating method: The heating furnace is divided into three sections: preheating section, heating section, and soaking section. Due to the significant difference in chemical composition between the alloy steel substrate and the outer stainless steel tube, the thermal conductivity of the substrate is 1 to 2 times higher than that of the stainless steel tube. Furthermore, a gap exists between the substrate and the stainless steel tube. During the heating process, it is crucial not only to prevent rapid heating of the bimetallic billet from causing uneven local heating and widening of the gap between the substrate and stainless steel, but also to promote interfacial bonding between the substrate and stainless steel. The bimetallic billet heating method is as follows: the preheating section should have a slow heating rate, and the heating and soaking sections should be sufficiently long.

[0043] In some embodiments of this application, the rolling mill equipment and arrangement in the rolling steps are as follows: 6 roughing mill stands → 6 intermediate mill stands → 4 pre-finishing mill stands → 4 finishing mill stands → 4 three-roll KOCKS mill stands. The roughing mill to the finishing mill stands are arranged alternately in horizontal and vertical configurations, and the KOCKS mill is arranged alternately in a forward Y and inverted Y configuration. The 6th roughing mill stand is 50m to 55m apart from the intermediate mill stand. The roughing mill group and the intermediate mill group do not form continuous rolling and adopt a split-rolling method.

[0044] The KOCKS rolling mill is characterized by its small width, high deformation efficiency, and uniform deformation, which can significantly improve the accuracy of product dimensional control. The dimensional tolerance of round steel can be controlled within ±0.10mm.

[0045] In this embodiment, a high-pressure water descaling device for steel billets can be installed between the heating furnace and the first stand of the roughing mill. During rolling, the high-pressure water descaling is shut off to prevent rapid cooling of the high-temperature bimetallic steel billet from causing the gap between the base material and the stainless steel to widen.

[0046] In some embodiments of this application, the sequence of roughing to the KOCKS mill passes is from pass 1 to pass 24. The roughing passes from pass 1 to pass 4 are all box-shaped passes, and the passes from pass 5 to pass 20 are arranged in an alternating elliptical-circular pattern.

[0047] In some embodiments of this application, the rolling mill cooling water is not turned on during the biting process of the first to sixth passes of rough rolling to prevent the rolling mill head from bursting. After biting, the normal water volume is turned on for cooling during the rolling process to prevent the stainless steel layer from bubbling and delamination due to excessive cooling rate during rough rolling.

[0048] In some embodiments of this application, the first and second roughing passes are skipped without reduction; the reduction in the third pass is 5% to 7% of the bimetallic billet diameter; the reduction in the fourth pass is 10% to 13% of the width of the rolled piece after the third pass; the reduction in the fifth pass is 15% to 17% of the width of the rolled piece after the fourth pass; and the reduction in the sixth pass is 20% to 23% of the width of the rolled piece after the fifth pass, thus pressing together the bimetallic interface gap after roughing; and / or the reduction in the seventh, ninth, and eleventh intermediate rolling passes is 40% to 45% of the diameter of the rolled piece in the previous pass, and the reduction in the eighth, tenth, and twelfth passes is 38% to 43% of the width of the rolled piece in the previous pass.

[0049] Due to the significant differences in deformation resistance and elongation coefficient between the base alloy steel and the sleeve stainless steel, and the presence of small gaps at the interface between the base and sleeve, the stainless steel layer is prone to bulging and folding during the rolling process. Based on the deformation resistance and elongation characteristics of alloy steel and stainless steel, a shape-and-property synergistic rolling method is adopted, which uses small deformation in the roughing pass to press together the gaps at the bimetallic interface, and large deformation in the intermediate rolling pass to promote the metallurgical bonding of the bimetallic interface.

[0050] Roughing involves small deformation rolling, with the deformation increasing gradually with each pass. Based on the mill configuration, the cross-sectional dimensions of the bimetallic billet, and the diameter of the finished product, the first and second roughing passes are set to pass without reduction. The reduction in the third pass is 5%–7% of the bimetallic billet diameter, the fourth pass is 10%–13% of the width of the workpiece after the third pass, the fifth pass is 15%–17% of the width of the workpiece after the fourth pass, and the sixth pass is 20%–23% of the width of the workpiece after the fifth pass. After roughing, the bimetallic interface gap is closed. Intermediate rolling uses large deformation rolling. The reduction in the 7th, 9th, and 11th passes is 40%–45% of the diameter of the workpiece from the previous pass, and the reduction in the 8th, 10th, and 12th passes is 38%–43% of the width of the workpiece from the previous pass.

[0051] In some embodiments of this application, flying shears are provided after the 6th, 12th, 16th, 20th and 24th passes, and the flying shears are numbered 1, 2, 3, 4 and 5 respectively.

[0052] The No. 1 flying shear does not cut the head to prevent the stainless steel clad round billet from bursting during the cutting process. The No. 2 flying shear removes the unsleeved part of the head substrate, and the total cutting length is 0.6m to 0.8m.

[0053] The bimetallic corrosion-resistant sucker rods are made of round steel with a diameter of 16mm to 33mm. The round steel is straightened one by one using a straightening machine. After straightening, the curvature per meter is ≤2mm and the total curvature is less than 0.13%.

[0054] Secondly, the present invention provides a bimetallic corrosion-resistant sucker rod round steel obtained by the production method of any one of the foregoing embodiments, comprising, from the inside out, an alloy structural steel core, a bimetallic diffusion layer and a stainless steel layer, wherein the diameter of the alloy structural steel core is 16mm to 33mm, the thickness of the bimetallic diffusion layer is 40 to 70μm, and the thickness of the stainless steel layer is 0.7mm to 1.0mm.

[0055] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0056] Example 1

[0057] Bimetallic steel billets are made from rolled round steel as the base material, and bimetallic corrosion-resistant sucker rods with a diameter of 22 mm and a fixed length of 9 m are rolled.

[0058] Base material: 42CrMoA, produced by continuous casting of 325mm×420mm cross-section billets in steelmaking, and rolled into round bars with a diameter of 158mm and a length of 9m by a bar mill. The curvature of the round bars is 0.5mm per meter, and the total curvature is 0.12%.

[0059] Stainless steel sleeve: made of 022Cr17Ni12Mo2 stainless steel seamless pipe, with a length of 8.75m, an outer diameter of 170mm, an inner diameter of 158mm, and a wall thickness of 6mm.

[0060] Prepare several round, disc-shaped steel plates with a thickness of 5mm and a diameter of 168mm.

[0061] First, use a peeling and grinding device to remove the iron oxide scale and any existing defects such as cracks, scars, folds, and inclusions from the surface of the round steel billet. The surface grinding depth is 0.6mm. After grinding, use acetone to clean the surface of oil stains, rust, and other adhering substances. Stainless steel pipes are also cleaned with acetone to remove adhering substances from the inner surface.

[0062] After cleaning and washing, the round steel billet is inserted into the stainless steel tube using a pusher device. The alignment method between the two ends of the round steel billet and the stainless steel tube is as follows: one end of the round steel billet extends 5mm into the stainless steel tube, and the other end of the round steel billet protrudes 245mm without the tube. After insertion, the gap between the round steel billet and the inner wall of the stainless steel tube is measured to be 0.6mm. Using plasma electron beam welding, the end of the round steel billet inserted into the stainless steel tube is first welded to seal it. Then, a disc-shaped steel plate is placed on the end for a second welding seal. The exposed end of the round steel billet is then welded. The circumferential gap between the round steel billet and the tube is roughly divided into four equal parts. Two symmetrical gaps are welded. After welding, the billet is moved to a vacuum device. After the vacuum device is sealed, a vacuum is drawn. The remaining gap of the sealing joint is welded under a vacuum degree of less than 10Pa, forming a bimetallic steel billet. The exposed end of the base material is marked with paint.

[0063] Bimetallic billets are transferred to the medium bar rolling mill. The rolling mill heating furnace is a walking beam type. The mill equipment and layout are as follows: 6 roughing mill stands → 6 intermediate mill stands → 4 pre-finishing mill stands → 4 finishing mill stands → 4 three-roll KOCKS mill stands. Based on the mill configuration and the diameter of the rolled round bars, the 1st, 2nd, 19th, and 20th mill stands are scheduled to run idle, and the 24th mill stand will produce the finished product.

[0064] The rolling process employs a shape-and-property synergistic rolling method, where the roughing passes involve small deformation to press together the bimetallic interface gap, while the intermediate rolling passes involve large deformation to promote metallurgical bonding at the bimetallic interface. In the roughing pass, the deformation increases progressively with each pass: the reduction in the third pass is 5%–7% of the bimetallic billet diameter; the reduction in the fourth pass is 10%–13% of the width of the workpiece after the third pass; the reduction in the fifth pass is 15%–17% of the width of the workpiece after the fourth pass; and the reduction in the sixth pass is 20%–23% of the width of the workpiece after the fifth pass. This process effectively presses together the bimetallic interface gap after roughing. In the intermediate rolling pass, large deformation is used: the reduction in the seventh, ninth, and eleventh passes is 40%–45% of the diameter of the workpiece from the previous passes; and the reduction in the eighth, tenth, and twelfth passes is 38%–43% of the width of the workpiece from the previous passes.

[0065] The billet is heated at 570℃~620℃ in the preheating section; 1120℃~1180℃ in the heating section; 1120℃~1150℃ in the soaking section, with a heating time of 65min~80min; the total heating time for the billet is 130min~150min. The billet's inlet temperature is 1030℃~1070℃ when entering the first stand of the roughing mill, 840℃~870℃ when entering the first stand of the intermediate mill, 850℃~890℃ when entering the first stand of the pre-finishing mill, 870℃~900℃ when entering the first stand of the finishing mill, 915℃~945℃ when entering the first stand of the KOCKS mill, and 920℃~940℃ when the finished product is placed on the cooling bed.

[0066] During rolling, the high-pressure water descaling is shut off to prevent the high-temperature bimetallic billet from being rapidly cooled, which would widen the gap between the base material and the stainless steel.

[0067] During the first to sixth passes of rough rolling, the roll cooling water is not turned on during the biting process to prevent the roll from bursting. After biting, the normal water volume is turned on for cooling during the rolling process to prevent the stainless steel layer from bubbling and delamination due to excessive cooling rate during rough rolling.

[0068] Flying shear #1 does not cut the head, while flying shear #2 has a total head length of 0.6m.

[0069] This embodiment uses a 22mm diameter bimetallic corrosion-resistant sucker rod made from a bimetallic billet composed of 42CrMoA rolled round steel. The surface is free of folds and internal delamination and other quality defects.

[0070] The microstructure of the finished bimetallic corrosion-resistant sucker rod round steel under a stereomicroscope is as follows. Figure 1 The substrate is circumferentially covered with a stainless steel layer. The thickness of the stainless steel coating at four symmetrically positioned points on the base circle are 0.7 mm, 0.83 mm, 0.75 mm, and 0.96 mm, respectively. The microstructure under a 500x microscope is as follows. Figure 2 The bonding surface is dense and without microscopic gaps. At the bonding interface, atoms diffuse into each other to form a bonding layer (transition layer), as follows: Figure 3 As shown, the bonding layer width is 41μm~65μm.

[0071] Example 2

[0072] Bimetallic steel billets are made from rolled round steel as the base material, and bimetallic corrosion-resistant sucker rods with a diameter of 22 mm and a fixed length of 9 m are rolled.

[0073] Base material: 35CrMoA, produced by continuous casting of 325mm×420mm cross-section billets in steelmaking, and rolled into round bars with a diameter of 158mm and a length of 9m by a bar mill. The curvature of the round bars is 0.6mm per meter, and the total curvature is 0.11%.

[0074] Stainless steel sleeve: 022Cr23Ni5Mo3N duplex stainless steel seamless pipe, with a length of 8.8m, an outer diameter of 170mm, an inner diameter of 158mm, and a wall thickness of 6mm.

[0075] Prepare several round, disc-shaped steel plates with a thickness of 5mm and a diameter of 168mm.

[0076] First, use a peeling and grinding device to remove the iron oxide scale and any defects such as cracks, scabs, folds, and inclusions from the surface of the round steel billet. The surface grinding depth is 0.8mm. After grinding, use acetone to clean the surface of oil stains, rust, and other adhering substances. Stainless steel pipes are also cleaned with acetone to remove adhering substances from the inner surface.

[0077] After cleaning and washing, the round steel billet is inserted into the stainless steel tube using a pusher device. The alignment method between the two ends of the round steel billet and the stainless steel tube is as follows: one end of the round steel billet extends 5mm into the stainless steel tube, and the other end of the round steel billet protrudes 195mm without the tube. After insertion, the gap between the round steel billet and the inner wall of the stainless steel tube is measured to be 0.8mm. Using plasma electron beam welding, the end of the round steel billet inserted into the stainless steel tube is first welded to seal it. Then, a disc-shaped steel plate is placed on the end for a second welding seal. The exposed end of the round steel billet is then welded. The circumferential gap between the round steel billet and the tube is roughly divided into four equal parts. Two symmetrical gaps are welded. After welding, the billet is moved to a vacuum device. After the vacuum device is sealed, a vacuum is drawn. The remaining gap of the sealed joint is welded under a vacuum degree of less than 10Pa, forming a bimetallic steel billet. The exposed end of the base material is marked with paint.

[0078] Bimetallic billets are transferred to the medium bar rolling mill. The rolling mill heating furnace is a walking beam type. The mill equipment and layout are as follows: 6 roughing mill stands → 6 intermediate mill stands → 4 pre-finishing mill stands → 4 finishing mill stands → 4 three-roll KOCKS mill stands. Based on the mill configuration and the diameter of the rolled round bars, the 1st, 2nd, 19th, and 20th mill stands are scheduled to run idle, and the 24th mill stand will produce the finished product.

[0079] The rolling process employs a shape-and-property synergistic rolling method, where the roughing passes involve small deformation to press together the bimetallic interface gap, while the intermediate rolling passes involve large deformation to promote metallurgical bonding at the bimetallic interface. In the roughing pass, the deformation increases progressively with each pass: the reduction in the third pass is 5%–7% of the bimetallic billet diameter; the reduction in the fourth pass is 10%–13% of the width of the workpiece after the third pass; the reduction in the fifth pass is 15%–17% of the width of the workpiece after the fourth pass; and the reduction in the sixth pass is 20%–23% of the width of the workpiece after the fifth pass. This process effectively presses together the bimetallic interface gap after roughing. In the intermediate rolling pass, large deformation is used: the reduction in the seventh, ninth, and eleventh passes is 40%–45% of the diameter of the workpiece from the previous passes; and the reduction in the eighth, tenth, and twelfth passes is 38%–43% of the width of the workpiece from the previous passes.

[0080] The billet is heated at 580℃~635℃ in the preheating section, 1125℃~1190℃ in the heating section, and 1120℃~1160℃ in the soaking section for 70min~85min. The total heating time for the billet is 130min~150min. The billet enters the first stand of the roughing mill at 1040℃~1080℃, the first stand of the intermediate mill at 850℃~880℃, the first stand of the pre-finishing mill at 860℃~900℃, the first stand of the finishing mill at 880℃~910℃, the first stand of the KOCKS mill at 925℃~955℃, and the finished product is placed on the cooling bed at 930℃~950℃.

[0081] During rolling, the high-pressure water descaling is shut off to prevent the high-temperature bimetallic billet from being rapidly cooled, which would widen the gap between the base material and the stainless steel.

[0082] During the first to sixth passes of rough rolling, the roll cooling water is not turned on during the biting process to prevent the roll from bursting. After biting, the normal water volume is turned on for cooling during the rolling process to prevent the stainless steel layer from bubbling and delamination due to excessive cooling rate during rough rolling.

[0083] Flying shear #1 does not cut the head, while flying shear #2 has a total head-cutting length of 0.7m.

[0084] This embodiment uses a bimetallic billet composed of 35CrMoA rolled round steel and 022Cr23Ni5Mo3N duplex stainless steel seamless tube to roll a 22mm diameter bimetallic corrosion-resistant sucker rod round steel. The surface is free of folds and internal delamination and other quality defects.

[0085] Example 3

[0086] Bimetallic steel billets are made from rolled round steel as the base material, and bimetallic corrosion-resistant sucker rods with a diameter of 25 mm and a fixed length of 9 m are rolled.

[0087] Base material: 35CrMoA, produced by continuous casting of 325mm×420mm cross-section billets in steelmaking, and rolled into round bars with a diameter of 158mm and a length of 9m by a bar mill. The curvature of the round bars is 0.6mm per meter, and the total curvature is 0.11%.

[0088] Stainless steel sleeve: 022Cr23Ni5Mo3N duplex stainless steel seamless pipe, with a length of 8.8m, an outer diameter of 170mm, an inner diameter of 158mm, and a wall thickness of 6mm.

[0089] Prepare several round, disc-shaped steel plates with a thickness of 5mm and a diameter of 168mm.

[0090] First, use a peeling and grinding device to remove the iron oxide scale and any existing defects such as cracks, scars, folds, and inclusions from the surface of the round steel billet. The surface grinding depth is 0.6mm. After grinding, use acetone to clean the surface of oil stains, rust, and other adhering substances. Stainless steel pipes are also cleaned with acetone to remove adhering substances from the inner surface.

[0091] After cleaning and washing, the round steel billet is inserted into the stainless steel tube using a pusher device. The alignment method between the two ends of the round steel billet and the stainless steel tube is as follows: one end of the round steel billet extends 8mm into the stainless steel tube, and the other end of the round steel billet protrudes 192mm without the tube. After insertion, the gap between the round steel billet and the inner wall of the stainless steel tube is measured to be 0.7mm. Using plasma electron beam welding, the end of the round steel billet inserted into the stainless steel tube is first welded to seal it. Then, a disc-shaped steel plate is placed on the end for a second welding seal. The exposed end of the round steel billet is then welded. The circumferential gap between the round steel billet and the tube is roughly divided into four equal parts. Two symmetrical gaps are welded. After welding, the billet is moved to a vacuum device. After the vacuum device is sealed, a vacuum is drawn. The remaining gap of the sealing joint is welded under a vacuum degree of less than 10Pa, forming a bimetallic steel billet. The exposed end of the base material is marked with paint.

[0092] Bimetallic billets are transferred to the medium bar rolling mill. The rolling mill heating furnace is a walking beam type. The mill equipment and layout are as follows: 6 roughing mill stands → 6 intermediate mill stands → 4 pre-finishing mill stands → 4 finishing mill stands → 4 three-roll KOCKS mill stands. Based on the mill configuration and the diameter of the rolled round bars, mill stands 1, 2, 19, 20, and 24 are scheduled to run idle, and mill stand 23 will produce the finished product.

[0093] The rolling process employs a shape-and-property synergistic rolling method, where the roughing passes involve small deformation to press together the bimetallic interface gap, while the intermediate rolling passes involve large deformation to promote metallurgical bonding at the bimetallic interface. In the roughing pass, the deformation increases progressively with each pass: the reduction in the third pass is 5%–7% of the bimetallic billet diameter; the reduction in the fourth pass is 10%–13% of the width of the workpiece after the third pass; the reduction in the fifth pass is 15%–17% of the width of the workpiece after the fourth pass; and the reduction in the sixth pass is 20%–23% of the width of the workpiece after the fifth pass. This process effectively presses together the bimetallic interface gap after roughing. In the intermediate rolling pass, large deformation is used: the reduction in the seventh, ninth, and eleventh passes is 40%–45% of the diameter of the workpiece from the previous passes; and the reduction in the eighth, tenth, and twelfth passes is 38%–43% of the width of the workpiece from the previous passes.

[0094] The billet is heated at 600℃~640℃ in the preheating section, 1125℃~1180℃ in the heating section, and 1125℃~1150℃ in the soaking section for 70min~85min. The total heating time for the billet is 130min~150min. The billet enters the first stand of the roughing mill at 1045℃~1075℃, the first stand of the intermediate mill at 840~870℃, the first stand of the pre-finishing mill at 870~900℃, the first stand of the finishing mill at 890℃~930℃, the first stand of the KOCKS mill at 930℃~950℃, and the finished product is placed on the cooling bed at 930℃~960℃.

[0095] During rolling, the high-pressure water descaling is shut off to prevent the high-temperature bimetallic billet from being rapidly cooled, which would widen the gap between the base material and the stainless steel.

[0096] During the first to sixth passes of rough rolling, the roll cooling water is not turned on during the biting process to prevent the roll from bursting. After biting, the normal water volume is turned on for cooling during the rolling process to prevent the stainless steel layer from bubbling and delamination due to excessive cooling rate during rough rolling.

[0097] Flying shear #1 does not cut the head, while flying shear #2 has a total head length of 0.65m.

[0098] This embodiment uses a bimetallic billet composed of 35CrMoA rolled round steel and 022Cr23Ni5Mo3N duplex stainless steel seamless tube to roll a 25mm diameter bimetallic corrosion-resistant sucker rod round steel. The surface is free of folds and internal delamination and other quality defects.

[0099] Comparative Example 1

[0100] The only difference from Example 1 is that: in the first to sixth passes of rough rolling, after the billet head bites in, the normal water cooling is turned on during the rolling process. As a result, the stainless steel layer of the rolled piece bubbling occurs in the fifth pass, and the stainless steel layer is severely folded after the sixth pass. The rolling is terminated after rough rolling, and the rolled piece is scrapped.

[0101] Comparative Example 2

[0102] The only difference from Example 1 is that the length of the stainless steel tube is the same as the length of the round steel billet. After the round steel billet is sleeved, both ends of the round steel billet and the stainless steel tube are flush. Both ends are sealed by a second welding using a disc-shaped steel plate. After rough rolling, the bimetallic billet is rolled in the intermediate rolling mill. In the first pass, the billet slips and cannot be bitten. It is necessary to manually use a flame cutter to blow the upper surface of the bimetallic billet head to create a slanted plane before it can be bitten and continue rolling.

[0103] Comparative Example 3

[0104] The only difference from Example 1 is that the billet was heated to 700-750°C in the preheating section, 1130-1180°C in the heating section, and 1120-1170°C in the soaking section. The heating time in the preheating section was 55 minutes, and the total heating time for the billet was 110 minutes. The billet's inlet temperature at the first stand of the roughing mill was 1035-1080°C, and its inlet temperature at the first stand of the intermediate mill was 845-880°C. As a result, due to the high preheating temperature and short heating time of the billet in the preheating section, and the short total heating time in the preheating, heating, and soaking sections, the stainless steel layer of the rolled round steel did not achieve metallurgical bonding with the base material, and "ears" appeared on the surface of the round steel.

[0105] Comparative Example 4:

[0106] The difference from Example 1 lies only in the following: increasing the deformation amount in the roughing passes and decreasing the deformation amount in the intermediate rolling passes. Specifically, the reduction in the third roughing pass is 10%–12% of the bimetallic billet diameter; the reduction in the fourth pass is 15%–18% of the width of the rolled piece after the third pass; the reduction in the fifth pass is 25%–27% of the width of the rolled piece after the fourth pass; and the reduction in the sixth pass is 30%–33% of the width of the rolled piece after the fifth pass. In the intermediate rolling passes, the reduction in the seventh, ninth, and eleventh passes is 25%–35% of the diameter of the rolled piece from the previous pass; and the reduction in the eighth, tenth, and twelfth passes is 28%–33% of the width of the rolled piece from the previous pass. As a result, the stainless steel layer of the finished round steel did not achieve metallurgical bonding with the substrate, and "ears" appeared on the surface of the round steel.

[0107] Test case

[0108] Four samples were taken from each of the bimetallic corrosion-resistant sucker rods produced in Examples 1 to 3. The samples were heat-treated according to the method in Table 1. After heat treatment, the tensile and drop hammer impact properties were tested.

[0109] Table 1. Heat treatment regime of the samples

[0110]

[0111] The performance test results of the above heat-treated samples are shown in Table 2 below.

[0112] Table 1 Mechanical properties of round steel for bimetallic corrosion-resistant sucker rods

[0113]

[0114] 1. A bimetallic core substrate round steel billet and a stainless steel tube are assembled into a bimetallic steel billet through vacuum clean interface assembly technology. The bimetallic steel billet adopts shape-property synergistic rolling technology, which causes plastic deformation and metal diffusion under the action of high temperature and deformation stress of steel rolling, forming a metallurgical bond.

[0115] 2. Shape-and-property synergistic rolling method: The roughing pass has a small deformation amount process to press together the gap of the bimetallic interface, and the intermediate rolling pass has a large deformation amount process to promote the metallurgical bonding of the bimetallic interface. The deformation amount of the roughing pass is controlled in the range of 5% to 23%, and increases in each pass from small to large. The deformation amount of the intermediate rolling pass is controlled in the range of 38% to 45%, of which the deformation amount of the elliptical pass is 40% to 45% and the deformation amount of the round pass is 38% to 40%.

[0116] 3. The first pass of the intermediate bar mill adopts de-heading rolling. The base material round steel billet at one end of the combined bimetallic steel billet should be retained for more than 100mm. Preferably, a 100mm to 200mm long unsleeved steel pipe can effectively solve the problem of the rolled piece slipping and not being able to bite in the first pass of the intermediate mill.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing round steel for bimetallic corrosion-resistant sucker rods, characterized in that, Prepare alloy structural steel and stainless steel pipe, wherein the stainless steel pipe is more than 100mm shorter than the alloy structural steel. Insert the alloy structural steel into the stainless steel pipe, with one end of the alloy structural steel extending into the stainless steel pipe by 5mm to 10mm and the other end protruding from the stainless steel pipe by more than 100mm. The alloy structural steel and stainless steel pipe are assembled into a bimetallic steel billet through a vacuum clean interface method. Then, the bimetallic steel billet is heated and rolled to obtain round steel for bimetallic corrosion-resistant sucker rods. The vacuum clean interface preform assembly includes: first, welding and sealing the gap between the alloy structural steel extending into the stainless steel pipe end and the bimetallic part; then welding a disc-shaped steel plate with the same diameter as the outer diameter of the stainless steel pipe at this end to perform a secondary seal on the stainless steel pipe; dividing the end of the alloy structural steel exposed from the stainless steel pipe into four equal parts along the circumference; first welding two symmetrically divided gaps; then evacuating the remaining gap space to a vacuum degree of less than 10 Pa; and welding the remaining gap under this vacuum condition. In the rolling process, the mill equipment and layout are as follows: 6 roughing mill stands → 6 intermediate mill stands → 4 pre-finishing mill stands → 4 finishing mill stands → 4 three-roll KOCKS mill stands. The roughing mill to the finishing mill stands are arranged alternately in horizontal and vertical configurations, and the KOCKS mill is arranged alternately in a forward Y and inverted Y configuration. The 6th roughing mill stand is 50m to 55m away from the intermediate mill stand. The roughing mill group and the intermediate mill group do not form continuous rolling and adopt a split-rolling method. During the biting process of the workpiece in the first to sixth passes of the roughing mill, the roll cooling water is not turned on. After biting, the normal water volume is turned on for cooling during the rolling process. In the roughing mill, the first and second passes are passed without reduction. The reduction in the third pass is 5% to 7% of the bimetallic billet diameter. The reduction in the fourth pass is 10% to 13% of the width of the rolled piece after the third pass. The reduction in the fifth pass is 15% to 17% of the width of the rolled piece after the fourth pass. The reduction in the sixth pass is 20% to 23% of the width of the rolled piece after the fifth pass. After roughing, the gap at the bimetallic interface is pressed together. And / or in the intermediate mill, the reduction in the seventh, ninth, and eleventh passes is 40% to 45% of the diameter of the rolled piece in the previous pass. The reduction in the eighth, tenth, and twelfth passes is 38% to 43% of the width of the rolled piece in the previous pass.

2. The method for producing bimetallic corrosion-resistant round steel for sucker rods according to claim 1, characterized in that, The alloy structural steel is a round steel or continuously cast round steel billet containing at least two of the elements Mn, Cr, Ni, Mo and V; the stainless steel pipe is at least one of Cr-Ni austenitic stainless steel, Cr-Ni-Mo austenitic stainless steel and duplex stainless steel.

3. The method for producing bimetallic corrosion-resistant round steel for sucker rods according to claim 1, characterized in that, The bimetallic billet has a diameter of 160mm to 170mm. The bimetallic billet is loaded into the heating furnace with the exposed end of the alloy structural steel as the rolling bite end. The heating step includes a preheating section, a heating section and a soaking section. The preheating section has a heating rate of no more than 12℃ / min and a temperature of no more than 650℃; the heating section has a temperature of 1120℃~1230℃; the soaking section has a temperature of 1120℃~1180℃; and the total heating time of the preheating section, heating section and soaking section is no less than 120min.

4. The method for producing round steel for bimetallic corrosion-resistant sucker rods according to claim 1, characterized in that, The sequence of passes from roughing to the KOCKS mill is from pass 1 to pass 24. The roughing passes from pass 1 to pass 4 are all box-shaped passes, and the passes from pass 5 to pass 20 are arranged with alternating elliptical and circular patterns. The bimetallic billet enters the first stand of the roughing mill at a temperature of 1030℃~1080℃, the first stand of the intermediate mill at a temperature of 840℃~880℃, the first stand of the pre-finishing mill at a temperature of 850℃~900℃, the first stand of the finishing mill at a temperature of 870℃~930℃, the first stand of the KOCKS mill at a temperature of 915℃~955℃, and the finished product enters the cooling bed at a temperature of 920℃~960℃.

5. The method for producing round steel for bimetallic corrosion-resistant sucker rods according to claim 1, characterized in that, Flying shears are installed after the 6th, 12th, 16th, 20th and 24th lanes, and the flying shears are numbered 1, 2, 3, 4 and 5 respectively. The No. 1 flying shear does not cut the head, while the No. 2 flying shear removes the portion of the substrate without a sleeve from the head, with a total cutting length of 0.6m to 0.8m.

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