Smelting and processing method for high-toughness non-magnetic steel pipe of petroleum drilling tool

Abstract

The invention discloses a smelting and machining method for a high-toughness non-magnetic steel pipe in the field of petroleum drilling tools, and solves the problems existing in non-magnetic steel pipe manufacturing in the prior art. (1) high alloy components are adjusted again, the alloy element ratio is strictly controlled, the manganese element is highly controlled, and it is ensured that the steel is non-magnetic; the low-control chromium element ensures the corrosion resistance of the steel, and meanwhile, high chromium is prevented from forming ferrite to influence the magnetism; the nitrogen element is accurately controlled, and high nitrogen is prevented from generating cracks and low nitrogen is prevented from influencing magnetism; (2) a bar drilling process is replaced by an extrusion and cold rolling process in the processing process, so that the yield is improved, and time and processing cost are saved; carrying out gradient heating on the round billet through a secondary heating furnace; a two-pass rolling process is adopted, the wall thickness is increased and decreased in the first pass, and then the product performance is controlled through second-pass rolling. The technology has the technical advantages that the blank is subjected to hot extrusion forming and two-pass cold rolling, the pipe meeting the requirement is obtained, and the product obtained through the technology has the characteristic of high toughness on the non-magnetic basis.

Description

Technical Field

[0001] This invention relates to the field of stainless steel, and more specifically to a smelting and processing method for high-strength and tough non-magnetic steel pipes used in oil drilling tools. Background Technology

[0002] Non-magnetic steel pipes are widely used in the petrochemical industry due to their dual advantages of being unaffected by magnetic fields and possessing excellent mechanical properties. They are primarily used to manufacture oil well pipes, oil pipelines, and heat exchanger pipes for chemical equipment, ensuring that precision downhole measuring instruments operate in a non-magnetic environment. Simultaneously, thanks to their austenitic stainless steel material, they effectively resist the erosion of high temperatures, high pressures, and corrosive media, guaranteeing production safety and long-term stable equipment operation. The core technology of non-magnetic steel lies in adding a high proportion of alloying elements such as manganese, nickel, chromium, and nitrogen, allowing the steel to form a stable austenitic structure at room temperature, thereby achieving extremely low magnetic permeability and excellent mechanical properties. Currently, the preparation of non-magnetic steel pipes in the domestic petroleum industry mainly adopts electric furnace smelting + AOD / VOD refining combined with temperature-controlled forging technology to obtain steel billets, which are then shaped into target steel pipes through machining. While machining non-magnetic steel pipes has the advantage of lower processing costs, it also has significant drawbacks, including low yield, poor corrosion resistance, and long processing cycles. Another manufacturing process combines hot extrusion and cold rolling for the production of this type of steel pipe. However, this process is extremely demanding to control. On the one hand, high alloy content can easily cause surface defects and internal cracks in the forged billet, and slight deviations in the alloy element ratio or heat treatment process can lead to excessive magnetism or decreased material toughness. On the other hand, non-magnetic steel exhibits high deformation resistance during cold rolling; if the cold rolling deformation is not properly controlled, work hardening can easily occur, leading to the accumulation of residual stress. While the hot extrusion + cold rolling process offers a higher yield and better performance, its difficulty in control has prevented its current application in the production of this type of steel pipe. Summary of the Invention

[0003] This invention discloses a smelting and processing method for high-strength and tough non-magnetic steel pipes used in the field of oil drilling tools, which solves the problems existing in the manufacturing of non-magnetic steel pipes in the prior art.

[0004] The specific technical solution is as follows: 1. Chemical composition (mass fraction / %) of steel 1Cr18Mn18N: carbon not more than 0.05, silicon not more than 0.6, manganese: 20-22, chromium: 15.5-16.5, molybdenum: 0.5-0.6, nickel: 1-1.3, copper: 0.1-0.2, nitrogen: 0.5-0.6, the remainder being the base element iron.

[0005] 2. Electric furnace smelting, ladle refining: Raw materials such as this steel grade, Cr13 type and other similar return steels are smelted using electric furnace / non-vacuum induction furnace + LF + VOD / VHD or electric furnace + AOD + LF methods.

[0006] (1) If the electric furnace / non-vacuum induction furnace + LF + VOD / VHD smelting route is adopted, the electric furnace shall adopt the non-oxidizing method for smelting, and the furnace charge shall consist of the steel grade, Cr13 type and other similar return steels. The tapping temperature shall not be lower than 1630℃, and the carbon content in the tapping steel shall not exceed 0.8%. After the LF arrives, SiC powder shall be used for deoxidation at a dosage of 2kg / t to 3kg / t, and the slag charging time shall be greater than 10min. Among them, the VOD shall be sampled in the ladle, the primary smelting slag shall be removed, and the temperature after blowing shall not be lower than 1650℃. At ℃, the total amount of deoxidizer aluminum powder added with the slag should not exceed 4 kg / t, Ca-Si blocks or Fe-Si: 5 kg / t~10 kg / t, pressure not exceeding 67 Pa, and holding time not less than 10 min; after degassing, samples are taken for analysis, the carbon content is not greater than 0.7%, and red-hot medium manganese steel (manganese: 8%~12%) and electrolytic manganese are added in batches, nitrogen is blown from the bottom of the ladle, and nitrogen is sampled for analysis; while for the VHD process, slag replacement is carried out before entering the tank according to the slag condition and sulfur content, heating is performed, and considering the nitrogen in the furnace, pre-baked chromium nitride is added in batches according to the target value. After the composition is appropriate, it is poured at 1420℃~1440℃, the casting electrode is protected by argon gas, and it is air-cooled without annealing.

[0007] (2) If the electric furnace + AOD + LF smelting route is adopted, the electric furnace smelting steps are the same as above. In the AOD process, high chromium is added according to the composition control specifications, and nitrogen, argon and oxygen are used for blowing. Ferrosilicon is added during reduction. After adding reduced ferrosilicon, stirring and slag removal are carried out to ensure that the low-basicity slag in the furnace is removed and new slag is formed (basicity range 2-4) so ​​that the slag sample taken from the AOD tapping can be quickly pulverized. 0.50 kg / t to 0.55 kg / t of calcium silicate blocks are added with the steel flow to ensure deoxidation and desulfurization effects (sulfur is controlled to be no more than 0.005% during refining). In the LF process, temperature measurement and power supply are carried out, and slag material is adjusted. Diffusion deoxidation is carried out using calcium silicate powder, silicon carbide and aluminum particles. After sampling, slag is removed directly to control the amount of slag in the furnace to be no more than 1.5 t, with the final standard being the fluidity of the steel slag. After taking chemical composition analysis samples, metallic manganese and electrolytic manganese are added in batches, and the tapping temperature is 1420℃ to 1440℃.

[0008] Forging and billet preparation: Rapid forging is a multi-fire forging process, involving 2 to 4 fires. The first fire involves minor deformation, followed by a second fire at 1180℃ to 1230℃ for 2 to 3 hours, with a final forging temperature not lower than 950℃. For precision forging, the billet is heated to 1170℃ ± 10℃ and held for 2 to 3 hours. After forging, the billet is peeled to a good surface and then an initial hole is drilled in the center of the billet through machining.

[0009] Hot extrusion molding: The round billet is subjected to gradient heating in a secondary heating furnace at an external temperature of 1180℃~1200℃ and an internal temperature of 1150℃~1170℃. The mandrel diameter is 77±1mm and the extrusion die diameter is 110.5±1mm, resulting in a final outer diameter of 107.2mm~107.9mm, averaging 107.5mm, and a head wall thickness of 15.20mm~16.36mm, averaging 15.75mm. After piercing, the main plunger advances, pushing the metal through the annular gap formed by the extrusion die and the mandrel. Subsequently, reaming is performed with a reaming force of 3.6±0.1MN. The extrusion force is 31MN (650±1mm billet). The billet thickness is 28±1MN (470±1mm); the extrusion resistance is 290MPa~310MPa; the extrusion process adopts "reversing extrusion", when the billet is extruded to about half, it is taken out, rotated 180 degrees and then extruded a second time; the thickness of the extruded rough tube is measured ultrasonically, and then it is solution treated at a temperature of 1060℃~1065℃ and a roller speed of 0.20m / min~0.25m / min. The hardness (HBW) of the product after solution treatment is 235~245, softening the steel tube for subsequent rolling.

[0010] Cold rolling: A two-pass rolling process is adopted. The first pass adjusts the wall thickness by at least 2mm to 3mm, followed by a second pass to control the product performance and obtain the finished steel pipe. The steel pipe is then pickled to remove oil and ground to remove oxide scale. Finally, the product is tested for hardness, yield strength, tensile strength and impact mechanical properties.

[0011] Explanation of the invention points: 1. The high-alloy composition was readjusted, and the ratio of alloying elements was strictly controlled. By controlling the manganese element to a high level, the non-magnetic nature of the steel was ensured; by controlling the chromium element to a low level, the corrosion resistance of the steel was ensured, while avoiding the formation of ferrite by high chromium, which would affect the magnetism; the nitrogen element was precisely controlled to avoid cracking caused by high nitrogen and to avoid affecting the magnetism by low nitrogen.

[0012] 2. The main innovation of the processing technology lies in replacing the bar blanking process with extrusion + cold rolling, which improves the yield and saves time and processing costs.

[0013] Gradient heating of round billets in a secondary heating furnace can lead to increased resistance if the temperature is too low, or coarse grains or overheating of the surface if the temperature is too high. During billet processing, extruded tubes may have problems such as orange peel texture in the inner hole at the tail and uneven wall thickness at the head. Since cold rolling has a certain effect on uniform wall thickness, a two-pass rolling process is adopted. The first pass is used to adjust the wall thickness, and then the second pass is used to control the product performance.

[0014] Technical advantages of the present invention: Steel ingots are obtained through electric furnace smelting, ladle refining, and electroslag remelting. Then, the ingots are forged and billeted. The billets are then hot extruded and cold rolled in two passes. The purpose of the first pass is to uniformly thicken the wall, and the purpose of the second pass is to improve the performance of the steel pipe and obtain pipes that meet the requirements. The products obtained by this process have high strength and toughness characteristics while being non-magnetic. Attached Figure Description

[0015] Figure 1 This is a flowchart of the smelting and processing method of the present invention. Detailed Implementation

[0016] refer to Figure 1 The present invention will be described in detail with reference to the embodiments.

[0017] Examples 1-3 use steel grade 1Cr18Mn18N. Raw materials such as this steel grade, Cr13 type, and other similar recycled steels are smelted using an electric furnace / non-vacuum induction furnace + LF + VOD / VHD or an electric furnace + AOD + LF method. The resulting ingots are cast to obtain qualified steel ingots. Subsequently, the steel billets are forged using fast forging and precision forging, and finally hot extrusion is performed to obtain rough tubes. Cold rolling is then used to control the dimensions and properties of the steel tubes. The target performance of the products is shown in Table 1.

[0018] Table 1 Target Performance of Target Steel Pipes Example 1

[0019] Step 1: Smelting is carried out using this steel grade, Cr13 type and other similar return steel as the main raw materials. While controlling costs, the introduction of impurities is reduced. The electric furnace adopts the non-oxidation method to reduce element burn-off and gas absorption. The tapping temperature is 1635℃ and the carbon content at tapping is 0.6%.

[0020] The molten steel was then transported to the LF refining furnace using a ladle. SiC powder was added for diffusion deoxidation, and white slag was generated by electric current for more than 10 minutes. After the slag was adjusted to a white slag with good fluidity, samples were taken for analysis. The composition of the molten steel was adjusted according to the analysis results. The tapping temperature of the steel was 1650 ℃, and the carbon content, silicon content, and sulfur content at tapping were 0.4%, 0.2%, and 0.01%, respectively. After the LF refining was completed, vacuum oxygen blowing decarburization (VOD) was performed. After entering the ladle, the primary slag was removed, and then oxygen blowing decarburization was performed. Overblowing was strictly prohibited to prevent the large-scale oxidation of chromium in the steel. Deoxidizer was added with the slag, and deep degassing was performed under high vacuum for 15 minutes. After the vacuum was broken, pre-baked red-hot metallic manganese was added for alloying, and nitrogen was added by bottom blowing. The composition of the steel ingot after VOD was shown in Table 2.

[0021] Table 2 Composition of steel ingots obtained from VOD Step 2: Rapid forging is multi-fire forging, 4 fires. The first fire is for small deformation: reheat temperature 1200℃, reheat time is 2.5h; final forging temperature 1000℃; precision forging: billet heating temperature 1170℃, holding temperature for 2.5h; after forging, air cooling, after grinding the billet to a good surface, a 50mm initial hole is drilled in the center of the billet by machining.

[0022] Step 3: Select a shorter billet (470mm) for extrusion (extrusion pressure 28MN). The round billet is gradient heated in a secondary heating furnace, with a surface temperature of 1190℃ and an internal temperature of 1160℃. Too low a temperature will lead to increased resistance, while too high a temperature may result in coarse grains or surface overheating. The extrusion die has a diameter of 110.5mm, a mandrel diameter of 77mm, and a theoretical wall thickness of 16.75mm. The die is preheated to 400℃. Then, the hole is expanded with an expansion force of 3.59 MN. After piercing, the main plunger advances, pushing the metal through the annular gap formed by the extrusion die and the mandrel. The measured extrusion pressure reaches 31MN, and the material's deformation resistance is 300MPa.

[0023] The extrusion process employs a "reverse extrusion" strategy. When the billet is extruded to about half its original size, it is removed, rotated 180 degrees, and then extruded a second time. This is intended to utilize the metal flow in different directions to compensate for and improve the uniformity of the wall thickness of the rough tube.

[0024] The extruded rough tube (total length 3300 mm) was cut into sections, and the wall thickness was measured by an ultrasonic thickness gauge; the outer diameter was 107.2 mm to 107.9 mm (average 107.5 mm), and the head wall thickness was 15.2 mm to 16.36 mm (average 15.75 mm), with a certain amount of wall thickness deviation.

[0025] The extruded product was subjected to solution treatment at 1065℃ / roll speed 0.25 / min, and the hardness (HBW) of the product after solution treatment was 240.

[0026] Step 4: The extruded billet (Φ107.5mm×15.75mm) is rolled into a finished steel pipe of Φ90mm×15mm through two cold rolling processes. The main purpose of the first pass is to achieve "uniform wall thickness." Based on the wall thickness deviation of the extruded billet, the wall thickness of the rough pipe is adjusted, and most of the wall reduction is completed. The second pass rolls the product to the final size, and the performance of the finished product is ensured to meet the standards by controlling the amount of cold rolling deformation. After rolling, the finished product is pickled to remove oil, ground to remove oxide scale, and finally straightened by a method of first roll straightening and then pressure straightening. Finally, the hardness, yield strength, tensile strength, and impact mechanical properties of the finished product are tested, and the test results are shown in Table 3.

[0027] Table 3. Results of Finished Product Performance Tests Example 2

[0028] High-strength, high-toughness, non-magnetic steel pipes were smelted and processed according to the method in Example 1, with the difference being that the cold rolling process was as follows: Φ108mm×16 mm was rolled into Φ90mm×15mm with a deformation of 22%, and Φ90mm×15 mm was rolled into Φ76mm×14 mm with a deformation of 22.8%. The finished product specification was Φ76mm×14 mm. The test performance results of the finished product are shown in Table 4.

[0029] Table 4 Results of Finished Product Performance Tests Example 3

[0030] High-strength and high-toughness non-magnetic steel pipes were smelted and processed according to the method in Example 1, except that the finished product specifications were Φ89mm×15.5mm and the deformation was 21.16%. The test performance results of the finished product are shown in Table 5.

[0031] Table 5. Results of Finished Product Performance Tests

[0032] Comparative Example 1 High-strength and high-toughness non-magnetic steel pipes were smelted and processed according to the method in Example 1, except that the finished product specifications were Φ80mm×15.75mm and the cold rolling deformation was 30%. Due to the excessive deformation, the rolled parts were bent, warped and other "not straightened", and the elongation after fracture and impact energy were not up to standard. The test performance results of the finished products are shown in Table 6.

[0033] Table 6 Results of Finished Product Performance Tests

[0034] Comparative Example 2 High-strength and high-toughness non-magnetic steel pipes were smelted and processed according to the method of Example 1, except that the finished product specifications were Φ97.25mm×16mm and the cold rolling deformation was 10%. Compared with Example 1, the yield and tensile strengths were significantly reduced. The test performance results of the finished product are shown in Table 7.

[0035] Table 7 Results of Finished Product Performance Tests

[0036] Comparative Example 3 High-strength and high-toughness non-magnetic steel pipes were smelted and processed according to the method of Example 1. The difference was that after forging Φ100mm bars, the finished steel pipes with diameters of Φ90mm×15mm were obtained by machining. The test performance results of the finished products are shown in Table 8.

[0037] Table 8. Results of Finished Product Performance Tests

[0038] Although the performance of the finished product obtained by this method is similar to that of Example 1, it has problems such as low yield (machining yield is 56%, while the yield of Example 1 is 70%), poor corrosion resistance, and long processing cycle.

Claims

1. A method for smelting and processing high-strength, high-toughness, non-magnetic steel pipes for oil drilling tools, characterized in that, The smelting method is as follows: smelting is carried out using an electric furnace / non-vacuum induction furnace + LF + VOD / VHD or an electric furnace + AOD + LF method; The processing method: (1) Forging and billet preparation: Rapid forging involves multiple forging processes, with 2 to 4 forgings. The first forging involves minor deformation, followed by a second forging at 1180℃ to 1230℃ for 2 to 3 hours, with a final forging temperature not lower than 950℃. For precision forging, the billet is heated to 1170℃ ± 10℃ and held for 2 to 3 hours. After forging, the billet is peeled to a good surface and then an initial hole is drilled in the center of the billet through machining. (2) Hot extrusion forming: The round billet is subjected to gradient heating in a secondary heating furnace at an external temperature of 1180℃~1200℃ and an internal temperature of 1150℃~1170℃. The mandrel diameter is 77±1mm and the extrusion die diameter is 110.5±1mm, resulting in a final outer diameter of 107.2mm~107.9mm, averaging 107.5mm, and a head wall thickness of 15.20mm~16.36mm, averaging 15.75mm. After piercing, the main plunger advances, pushing the metal through the annular gap formed by the extrusion die and the mandrel. Subsequently, reaming is performed with a reaming force of 3.6±0.1MN; the extrusion force is 31MN, and the billet pressure is 650±1... mm, 28±1MN, billet 470±1mm; extrusion resistance 290MPa~310MPa; the extrusion process adopts "turning extrusion", when the billet is extruded to about half, it is taken out, rotated 180 degrees and then extruded a second time; the extruded rough tube is ultrasonically measured for thickness, and then solution treated at a temperature of 1060℃~1065℃ and a roller speed of 0.20m / min~0.25m / min. After solution treatment, the product hardness is 235~245 HBW, softening the steel pipe for subsequent rolling; (3) Cold rolling: A two-pass rolling process is adopted. The first pass adjusts the wall thickness by at least 2mm to 3mm, and then the second pass is used to control the product performance to obtain the finished steel pipe. (4) Surface cleaning: The steel pipes are then pickled to remove oil and ground to remove oxide scale. (5) Performance testing: Finally, the product was tested for its hardness, yield strength, tensile strength, and impact energy mechanical properties.

2. The smelting and processing method for high-strength and tough non-magnetic steel pipes for oil drilling tools according to claim 1, characterized in that, The smelting method described above: The steel ingots were smelted using an electric furnace / non-vacuum induction furnace + LF + VOD / VHD method, with the electric furnace employing a non-oxidizing process; the composition of the steel ingots obtained by VOD is shown in Table 1. Table 1. Composition results of steel ingots obtained by VOD The processing method: (1) Forging billet opening: Fast forging is multi-fire forging, 4 fires, the first fire is small deformation: the reheating temperature is 1200℃, the reheating time is 2.5h; the final forging temperature is 1000℃; for precision forging, the billet heating temperature is 1170℃, the holding time is 2.5h; after forging, air cooling is performed, the billet is ground to a good surface and then a 50mm initial hole is drilled in the center of the billet by machining; (2) Hot extrusion forming: Select a shorter billet of 470mm for extrusion, with an extrusion pressure of 28MN. The round billet is subjected to gradient heating in a secondary heating furnace, with a surface temperature of 1190℃ and an internal temperature of 1160℃. Too low a temperature will increase resistance, while too high a temperature may lead to coarse grains or surface overheating. The extrusion die has a bore diameter of 110.5mm, a mandrel diameter of 77mm, and a theoretical wall thickness of 16.75mm. The die is preheated to 400℃. Subsequently, the bore is expanded with an expansion force of 3.59 MN. After piercing, the main plunger advances, pushing the metal through the annular gap formed by the extrusion die and mandrel. The measured extrusion pressure reaches 31 MN, and the material's deformation resistance is 300 MPa. The extrusion process adopts a "reverse extrusion" strategy. When the billet is extruded to about half its length, it is taken out, rotated 180 degrees, and then extruded a second time. This is intended to use the metal flow in different directions to compensate for and improve the uniformity of the wall thickness of the rough tube. The extruded rough tube, with a total length of 3300 mm, was cut into sections, and the wall thickness was measured using an ultrasonic thickness gauge. The outer diameter ranged from 107.2 mm to 107.9 mm, with an average of 107.5 mm. The head wall thickness ranged from 15.2 mm to 16.36 mm, with an average of 15.75 mm, indicating a certain degree of wall thickness deviation. The extruded product was subjected to solution treatment at 1065℃ and a roller speed of 0.25m / min, resulting in a product hardness of 240HBW. (3) Cold rolling: The extruded billet (Φ107.5mm×15.75mm) is rolled into a finished steel pipe (Φ90mm×15mm) through two cold rolling processes. The main purpose of the first pass is to achieve "uniform wall thickness". The wall thickness of the rough pipe is adjusted according to the wall deviation of the extruded billet, and most of the wall reduction is completed. The second pass rolls the product to the final size. By controlling the amount of cold rolling deformation, the performance of the finished product is ensured to meet the standards. (4) Surface cleaning: After rolling, the finished product is pickled to remove oil, and the oxide scale is removed by grinding; finally, the cold-rolled tube is straightened by first roll straightening and then pressure straightening. (5) Performance testing: Finally, the hardness, yield strength, tensile strength and impact mechanical properties of the finished product were tested. The test results are shown in Table 2. Table 2. Results of Finished Product Performance Tests

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