A 160 ksi grade high strength and toughness non-standard oil casing and a production method thereof

Abstract

The present application relates to the technical field of ultra-high strength structural steel, and particularly relates to a 160ksi high strength and toughness non-standard oil casing and a production method thereof, characterized by the following chemical composition in percentage by weight: C 0.10-0.40%, Si 0.05-0.35%, Mn 0.55-2.50%, Cr 0.50-2.50%, Mo 0.50-2.50%, V 0.05-0.25%, Nb≤0.25%, Ni 0.25-0.95%, Cu 0.25-0.95%, Al≤0.05%, Ti≤0.05%, N≤0.005%, P≤0.015%, S≤0.005%, and the balance of Fe and inevitable impurities. The production method comprises billet smelting, continuous casting, pipe rolling and quenching and tempering. Compared with the prior art, the present application has the beneficial effects that: high-temperature rolling is matched with direct online quenching, so that secondary heating is not needed, energy is saved, and production efficiency is improved; offline quenching technology is adopted, the pipe is re-austenitized, and the matching effect of strength and toughness can be further improved. The yield strength Rt0.7 of the pipe is greater than or equal to 1100 MPa, the tensile strength Rm is greater than or equal to 1200 MPa, the elongation A is greater than or equal to 15%, and the 0℃ transverse and longitudinal Charpy impact Akv are greater than or equal to 110 J and 120 J respectively.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultra-high strength structural steel, and particularly relates to a 160 ksi grade high strength and toughness non-standard oil casing and a production method thereof. BACKGROUND

[0002] Petroleum and natural gas are the energy pillars of social development. China is in a period of rapid development, and the increasing demand for energy and rising prices have led to an increase in petroleum and natural gas exploration and exploitation activities. Oil well pipe is one of the necessary equipment in petroleum and natural gas development engineering and is a kind of special material. Generally speaking, 20%-30% of the cost of an oil and gas well is the cost of oil well pipe. In the total amount of steel used in the petroleum industry, oil well pipe accounts for 40%, and oil casing accounts for more than 90% of oil well pipe. Therefore, the amount of oil casing is huge, and the market prospect is broad.

[0003] At present, the easy-to-exploit shallow oil and gas resources are gradually depleted, which has prompted the depth of oil and gas wells to gradually increase and the increase rate of well depth to accelerate year by year. After the well depth increases, the pressure and temperature in the well increase continuously, the geological environment becomes more and more harsh, and the stress state of the oil casing is more complex and severe. In China, the focus of oil and gas development is gradually shifting to the west and the ocean. The highest grade Q125 steel grade of the existing API oil casing cannot meet the requirements, and the safe operation of deep and ultra-deep wells urgently needs high-toughness oil and gas development steel of 160 ksi or above.

[0004] With the increase of strength, the existing seamless pipe components or preparation processes with strength exceeding the Q125 steel grade have various problems. Although the yield strength of the product can reach 160 ksi, these technical solutions still have the disadvantages of high content of alloying elements, complex production process, and poor strength and toughness matching.

[0005] A 140 ksi steel grade seamless steel pipe and a production method thereof are disclosed in Chinese patent application No. CN201811165255.8. The yield strength of the steel pipe is 980-1120 MPa, and the full-size Charpy impact energy at 0℃ is not less than 120 J. In the component design, 0.0005%-0.0040% of B element and 1.00%-3.00% of Ni element are added. There is a significant difference between the present application and the application in that the present application does not add B and the content of Ni is not higher than 0.95%. In the production process, the pipe blank is produced into a hollow pipe blank by centrifugal casting, and after being rolled into a specified size by an MPM / PQF continuous rolling mill, the pipe blank is subjected to heat treatment. Since the piercing process is not needed, the formation of banded structure can be avoided, thereby obtaining excellent high strength and toughness matching. There is a significant difference between the present application and the application in that the present application uses a solid round blank and a piercing process for production.

[0006] The Chinese patent application CN200910069758.X discloses a 150 ksi grade high strength and toughness oil and gas well downhole service pipe and its production method. The yield strength of the pipe is 1034-1148 MPa, the 0℃ transverse half size Charpy impact energy is 46-53 J, and the longitudinal 3 / 4 size Charpy impact energy is not less than 87-101 J. In the component design, no Cu and Ni elements are added, which is significantly different from the present application which adds at least 0.25% of Cu and Ni elements. In the production process, Si-Ca wire is used to change the morphology of inclusions, which essentially improves the toughness and low temperature toughness of the steel. The present technical solution does not require special control of inclusions to obtain similar strength and toughness matching requirements.

[0007] The Chinese patent application CN201310409266.7 discloses a super deep well oil casing and its production process. The yield strength of the pipe is 1158-1167 MPa. In the component design, no Cu and Ni elements are added, and Ce and B elements are added, which is significantly different from the present technical solution which adds Cu and Ni elements and does not add Ce and B elements.

[0008] The Chinese patent application CN201410687981.1 discloses a preparation process of 150 ksi grade CO2 corrosion resistant oil well pipe produced by CPE unit. The yield strength of the pipe is 1050 MPa, and the 0℃ Charpy impact energy is 50 J. In the component design, 5%-6% of Cr element is added, which is significantly different from the present technical solution which has a Cr content of not more than 2.5%.

[0009] The Chinese patent application CN201510234477.0 discloses a 155 ksi grade perforating gun pipe and forming method. The yield strength of the pipe is 1070-1175 MPa, and the 0℃ Charpy V-notch longitudinal and transverse full size impact energy is 112-120 J and 76-83 J respectively. In the component design, 0.2%-0.4% of W element is added, which is significantly different from the present technical solution which does not add W element. In the production process, an electroslag remelting process of round pipe blank is added to improve the purity and composition uniformity of the initial blank, which significantly increases the cost.

[0010] The Chinese invention patent with the application number CN201510260763.4 discloses a 155 ksi grade high strength and toughness casing steel, casing and its preparation method. The yield strength of the steel pipe is 1069-1275 MPa, and the 0℃ Charpy V-notch longitudinal and transverse full-size impact energy is not less than 99-113J and 78.1-91.5J respectively. In the component design, Cu and Ni are not intentionally added and are regarded as residual elements, which is significantly different from the intentional addition of at least 0.25% of Cu and Ni in the technical solution. In the production process, the role of inclusion removal and modification is highlighted, while the technical solution does not have special requirements for this, and the process applicability is more optimal.

[0011] The Chinese invention patent with the application number CN202111540297.7 discloses a high-strength niobium-containing oil casing based on controlled cooling and its production method. The yield strength of the steel pipe is 1180-1300 MPa, and the 0℃ transverse impact energy is 80-150J. In the component design, Cu is not added and B is selectively added, which is significantly different from the present invention. In the production process, the "continuous cooling" and "sparse cooling" process methods are used to obtain a complex phase structure with a ferrite + pearlite content of not more than 10% by using an average cooling speed of 20-60℃ / s, and then a tempered sorbite structure is obtained after heat treatment to ensure the strength and toughness matching requirements. The technical solution adopts a simple water cooling process with a cooling speed of not less than 65℃ / s, which has the characteristics of obvious process simplicity difference.

[0012] The Chinese invention patent with the application number CN201710926992.4 discloses a low alloy steel for producing 170 ksi grade steel pipe. The yield strength of the steel pipe is 1175-1265 MPa, and the 0℃ Charpy U-notch transverse full-size impact energy is not less than 80J. In the component design, 0.01%-0.08% rare earth RE and 0.0005%-0.005% boron are added, which is significantly different from the present technical solution which does not add rare earth and B elements. In the production process, quenching and tempering heat treatment is used, with a quenching temperature of 880℃-920℃ and a tempering temperature of 500℃-530℃. This is significantly different from the quenching temperature of 830℃-870℃ and the tempering temperature of 540℃-640℃ used in the present technical solution.

[0013] In summary, the present invention overcomes the shortcomings of the prior art by appropriately increasing the Mn content and strictly controlling the Cu and Ni element content range, and using traditional solid round billet to produce 160 ksi grade seamless pipe products. SUMMARY

[0014] The purpose of the present application is to provide a 160ksi high strength and toughness non-standard oil casing and its production method, overcome the shortcomings of the prior art, through reasonable component design, preparation process optimization matching, using Mo instead of N element to promote the effective precipitation of V element, without special control rolling temperature and deformation during steel pipe rolling process, high temperature rolling and direct online quenching, improve production efficiency; or adopt offline quenching process, realize re-austenitizing, further improve the matching effect of strength and toughness.

[0015] To achieve the above purpose, the present application realizes the following technical scheme:

[0016] One of the technical schemes: a 160ksi high strength and toughness non-standard oil casing, characterized in that the chemical composition is composed of C 0.10-0.40%, Si 0.05-0.35%, Mn 0.55-2.50%, Cr 0.50-2.50%, Mo 0.50-2.50%, V 0.05-0.25%, Nb≤0.25%, Ni 0.25-0.95%, Cu 0.25-0.95%, Al≤0.05%, Ti≤0.05%, N≤0.005%, P≤0.015%, S≤0.005%, the balance being Fe and inevitable impurities.

[0017] The second technical scheme: a production method of a 160ksi high strength and toughness non-standard oil casing, characterized in that it comprises billet smelting and continuous casting, pipe rolling and quenching and tempering treatment, and the specific production steps are as follows:

[0018] 1) Billet smelting and continuous casting: the molten iron is first smelted by an electric furnace, sent to an LF furnace for refining, and fed with Al wire, and then continuously cast into a round pipe blank after VD furnace vacuum treatment;

[0019] 2) Pipe rolling: the round pipe blank is heated to 1205-1255℃ (T1), rolled after 2-4h of total furnace time, the temperature before piercing is 1160-1220℃ (T2), the temperature before skew rolling is 950-1130℃ (T3), and the temperature before tension reducing is 850-920℃ (T4);

[0020] 3) Quenching and tempering treatment: after the tension reducing of the pipe is completed, quenching is carried out, the quenching temperature is 830-870℃ (T5), the quenching medium is water or oil, the tempering temperature is 540-640℃ (T6), the tempering holding time is 0.5-2h (t), and the pipe is air cooled after tempering.

[0021] The main alloying element effects and ranges in the present application are as follows:

[0022] Carbon C: C is the second major element in steel after Fe, which directly affects the strength, plasticity, toughness and other properties of steel. C has a significant effect on improving the strength of steel through solid solution strengthening and precipitation strengthening, but increasing the C content has a negative impact on the plasticity and toughness of steel. Therefore, the C content range is set to 0.10-0.40% in the present application.

[0023] Silicon Si: Si is an important reducing agent and deoxidizer in the steelmaking process, which can dissolve in ferrite and austenite to improve the hardness and strength of steel. Increasing the content of Si can reduce the precipitation tendency of Fe3C. Too high Si content will significantly reduce the plasticity and toughness of steel. Therefore, the Si content range is set to 0.05-0.35% in the present application.

[0024] Manganese Mn: Mn can improve the hardenability of steel, which is beneficial to the strength of steel; it can eliminate the influence of S (sulfur) and improve the hot working performance of steel. Since Mn is relatively cheap and can be infinitely solid-solved with Fe, it can improve the strength of steel while having relatively small impact on plasticity. Therefore, Mn is widely used as a strengthening element in steel. Too high Mn content will exacerbate the segregation of continuous casting billet, increase the grade of banded structure of steel pipe, and deteriorate the uniformity of the structure, which is not conducive to the plasticity and low temperature toughness of the steel pipe. Therefore, the Mn content range is set to 0.55-2.50% in the present application.

[0025] Chromium Cr: Cr can increase the hardenability of steel and has the effect of secondary hardening, which can improve the strength, hardness and wear resistance of steel without making the steel brittle, but it will reduce the elongation and reduction of area. The main role of Cr in the quenched and tempered structure is to improve the hardenability, so that the steel has good comprehensive mechanical properties after quenching and tempering. If Cr is added too much, Cr-containing carbides will precipitate and grow on the original austenite grain boundaries during the tempering process, which will seriously damage the low temperature toughness of the steel pipe. The Cr content range selected in the present application is 0.50-2.50%.

[0026] Molybdenum Mo: Mo has similar effects as Cr, but its price is high, so the addition amount should not be too high. Compared with Cr element, Mo element tends to form M2C carbide, and the size of the carbide is smaller and has higher thermal stability. In addition, adding Mo element can effectively promote the precipitation of V element and improve the precipitation strengthening effect of V. The Mo content range selected in the present application is 0.50-2.50%.

[0027] Vanadium V: V has strong affinity with C, N and O, and forms corresponding stable compounds. V mainly exists in the form of carbide in steel, which has the effects of refining the structure and grain, improving the strength and toughness, and reducing the overheating sensitivity. Vanadium can increase the tempering stability of quenched steel and produce secondary hardening effect; in quenched and tempered steel, it mainly improves the strength of steel. The V content range selected in the present application is 0.05-0.25%.

[0028] Titanium Ti, nitrogen N: Ti and C, N, O have strong affinity, and form corresponding stable compounds, which is one of the main solid N elements. The Ti-containing precipitated phase has strong binding force, is stable and not easy to decompose, and can prevent the grain growth tendency of steel at high temperature and improve the welding performance of steel. Using Ti to fix N and S is beneficial to improve the strength and plasticity of steel. Increasing the content of Ti, the Ti-containing precipitated phase will coarsen and adversely affect the performance. The core role of Ti in the present application is to fix N and avoid the combination of N and V affecting the synergistic precipitation of V and Mo. The present application selects Ti content not higher than 0.05%, N content not higher than 0.05%, and N element addition amount not higher than one half of Ti element.

[0029] Niobium Nb: Nb is one of the main micro-alloying elements, part of which is dissolved into solid solution to play a solid solution strengthening role; when it exists in the form of carbide, nitride and oxide particles, it can increase the tempering stability of steel and has a secondary hardening effect. A small amount of Nb can improve the strength of steel without affecting the plasticity or toughness of the steel. Due to the effect of grain refinement, it can improve the impact toughness of the steel and reduce the brittle transition temperature. During rolling, solid solution Nb significantly improves the recrystallization temperature of the steel, which can complete the rolling process of the steel at a higher temperature range, thereby reducing the internal stress of the steel pipe. The present application selects Nb content not higher than 0.25%.

[0030] Copper Cu, nickel Ni: Cu can improve the strength of steel, but when the content is high, it is not conducive to hot deformation processing, which leads to copper brittleness phenomenon during hot deformation processing, and adding a certain amount of Ni can avoid the occurrence of this phenomenon. Ni also has the effects of stabilizing austenite and improving hardenability. Adding a certain amount of Ni to steel can improve strength, toughness, corrosion resistance, and reduce the ductile-brittle transition temperature. Ni-containing steel is generally not easy to overheat, so it can prevent grain growth at high temperature and still maintain fine grain structure. However, considering the cost factor, the present application selects the Ni, Cu content range of 0.25-0.95%.

[0031] Aluminum Al: Al is added to steel as a deoxidizer or alloying element, and its deoxidizing ability is much stronger than that of silicon and manganese. The main role of aluminum in steel is to refine the grain and fix the nitrogen in the steel, thereby significantly improving the impact toughness of the steel and reducing the cold brittleness tendency and aging tendency; aluminum can also improve the corrosion resistance of steel, especially when used in combination with elements such as molybdenum, copper, silicon, and chromium, the effect is better; the disadvantage of aluminum is that it affects the hot working performance, welding performance and cutting performance of steel. The present application selects Al content range not higher than 0.05%.

[0032] Phosphorus P: P is brought into steel from ore, and S is one of the harmful elements. P can increase the strength and hardness of steel, but it can significantly reduce the plasticity and impact toughness. Especially at low temperature, it can make the steel brittle, and the higher the P content, the greater the cold brittleness. Removing P to a lower level can significantly increase the cost of steelmaking. The P content range selected by the present application is not higher than 0.015%.

[0033] Sulfur S: S is derived from the ore and fuel coke of steelmaking, and is one of the most common harmful elements in steel, which is not conducive to the ductility, toughness, weldability and corrosion resistance of steel. If S exists in the form of FeS in steel, it can also produce "hot brittleness" during hot working. The S content range selected by the present application is not higher than 0.005%.

[0034] The main manufacturing process parameter control range of the present application is as follows: the present application adopts the composite precipitation strengthening of Cu, Cr, Mo, V, Nb and other elements, the continuous casting round billet heating temperature is between 1205-1255℃, and the total furnace time is between 2-4h, which ensures that the precipitated phase of alloy elements is fully dissolved into austenite, and fully plays the beneficial effects of inhibiting recrystallization, solid solution strengthening, precipitation strengthening and grain refinement in the subsequent process, so as to prepare the composition and temperature for obtaining the final microstructure. If the selected temperature and time range is lower, the solid solution will be insufficient, which will affect the final strength of the steel pipe; if the selected time and temperature range is higher, the original austenite grain of the continuous casting billet is easy to be too coarse, which is not conducive to the control of the toughness of the steel pipe.

[0035] After rolling, the steel pipe can be directly quenched on-line or reheated off-line and then quenched. By properly controlling the production process, the temperature of the reduced pipe can meet the quenching requirements, direct on-line quenching can be easily realized, energy can be saved, production composition can be reduced, reheating process can be reduced, production efficiency can be improved, and economic benefits can be significantly improved.

[0036] After the accelerated cooling of the steel pipe is completed, the steel pipe is subjected to tempering heat treatment, the tempering holding temperature is higher than 640℃, the strength of the steel pipe is significantly reduced, which is not conducive to the final strength and toughness matching of the steel pipe; and if the tempering holding temperature is lower than 540℃, the quenching organization is insufficient, and the low temperature toughness is low. If the tempering holding time is too long, the strength will be poor; and if the tempering holding time is too short, the toughness will be insufficient. By controlling the appropriate tempering temperature, tempering holding time and the content of key alloy elements Mo, V and Ti, the beneficial precipitated phase can be fully precipitated and small in size. Thus, under a relatively wide quenching and tempering process window, the strength and toughness matching is good and the performance stability characteristics are good.

[0037] Compared with the prior art, the beneficial effects of the present application are:

[0038] 1) Steel pipe rolling process does not need special control rolling temperature and deformation, only need to ensure that the tension before reducing the diameter to meet the quenching temperature, high temperature rolling and direct online quenching, can be without secondary heating, saving energy, improve the production efficiency; using offline quenching process, the steel pipe has experienced reaustenitizing, can further improve the matching effect of strength and toughness.

[0039] 2) Using Mo instead of N element to promote the effective precipitation of V element, compared with V(C,N), (Mo,V)C has higher thermal stability and more spherical morphology, which can realize more stable strength and toughness matching effect in a wider range of heat treatment process parameters; using Cu precipitation strengthening, the influence on low temperature toughness is small, which is beneficial to improve the matching degree of strength and toughness.

[0040] 3) The yield strength Rt0.7 of the prepared steel pipe is greater than or equal to 1100MPa, the tensile strength Rm is greater than or equal to 1200MPa, the elongation A is greater than or equal to 15%, and the 0℃ transverse and longitudinal charpy impact Akv is not less than 110J and 120J respectively. DETAILED DESCRIPTION

[0041] The technical solutions of the present application will be described below in conjunction with specific embodiments. Obviously, the described embodiments are some of the embodiments of the present application, not all the embodiments.

[0042] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the specific embodiments needed to be used in the description of the specific embodiments or the prior art will be briefly introduced. Obviously, the specific embodiments described below are some embodiments of the present application, and those skilled in the art can obtain other specific embodiments without creative labor on the basis of these specific embodiments.

[0043] The components of the embodiments of the present application described and shown in the specific embodiments herein can be arranged and designed in countless different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the specific embodiments is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application.

[0044] The application discloses a 160ksi high-strength and high-toughness non-standard oil casing and a production method thereof. The chemical composition of the oil casing is as follows in terms of percentage by weight: C 0.10-0.40%, Si 0.05-0.35%, Mn 0.55-2.50%, Cr 0.50-2.50%, Mo 0.50-2.50%, V 0.05-0.25%, Nb≤0.25%, Ni 0.25-0.95%, Cu 0.25-0.95%, Al≤0.05%, Ti≤0.05%, N≤0.005%, P≤0.015%, S≤0.005%, and the balance of Fe and inevitable impurities. The production method comprises billet smelting and continuous casting, pipe rolling and quenching and tempering treatment, and the specific production steps are as follows:

[0045] 1) billet smelting and continuous casting: the molten iron is first smelted by an electric furnace, is sent into an LF furnace for refining, is fed with an Al wire, is subjected to VD furnace vacuum treatment, and is continuously cast into a round pipe blank;

[0046] 2) pipe rolling: the round pipe blank is heated to 1205-1255 DEG C (T1), is rolled after a total furnace time of 2-4 h, has a temperature of 1160-1220 DEG C (T2) before piercing, has a temperature of 950-1130 DEG C (T3) before cross rolling, and has a temperature of 850-920 DEG C (T4) before tension reducing;

[0047] 3) quenching and tempering treatment: the pipe is quenched after tension reducing is completed, the quenching temperature is 830-870 DEG C (T5), the quenching medium is water or oil, the tempering temperature is 540-640 DEG C (T6), the tempering holding time is 0.5-2 h (t), and the pipe is air-cooled after tempering.

[0048] Table 1 is the chemical composition of the steel in the application examples 1-9; Table 2 is the rolling and heat treatment process parameters of the steel in the application examples 1-9; and Table 3 is the mechanical properties of the steel in the application examples 1-9.

[0049] Table 1 Chemical composition of the steel pipe in the application examples

[0050]

[0051] Note: * represents content calculated in terms of ppm.

[0052] Table 2 Rolling and heat treatment process parameters of the steel in the application examples

[0053]

[0054] Table 3 Mechanical properties of the steel in the application examples

[0055]

[0056] As can be seen from the data in Table 1, Table 2 and Table 3, the prepared steel pipe has yield strength ≥1110MPa, tensile strength ≥1200MPa, elongation ≥15%, and Charpy impact energy at -0℃ in transverse and longitudinal directions of not less than 110J and 120J respectively, and has excellent strength and toughness matching.

[0057] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely divergences of the principles and spirit of the application and that numerous modifications, changes, substitutions, and alterations can be made thereto without departing from the spirit and scope of the application as defined by the appended claims and their equivalents.

Claims

1. A method for producing a 160ksi grade high-strength and high-toughness non-standard oil casing, characterized in that, Its chemical composition by weight percentage is as follows: C 0.10–0.40%, Si 0.05–0.35%, Mn 0.55–2.50%, Cr 0.50–2.50%, Mo 0.50–2.50%, V 0.05–0.25%, Nb 0.06–0.25%, Ni 0.70–0.95%, Cu 0.27–0.95%, Al≤0.05%, Ti≤0.05%, N≤0.005%, P 0.01–0.015%, S 0.003–0.005%, with the balance being Fe and unavoidable impurities; Its production methods include billet smelting and continuous casting, steel pipe rolling and quenching and tempering, and the specific production steps are as follows: 1) Steel billet smelting and continuous casting: Molten iron is first smelted in an electric furnace, then sent to an LF furnace for refining, and fed with Al wire. After vacuum treatment in a VD furnace, it is continuously cast into round tube billets. 2) Steel pipe rolling: The round billet is heated to 1205~1235℃ and rolled after a total furnace time of 2~4h. The temperature before piercing is 1160~1220℃, the temperature before skew rolling is 950~1045℃, and the temperature before tension reduction is 850~920℃. 3) Quenching and tempering treatment: After the steel pipe is tensioned and reduced in diameter, it is quenched at a temperature of 830-870℃, using water or oil as the quenching medium. The tempering temperature is 540-580℃, and the tempering holding time is 0.5-2 hours. After tempering, it is air-cooled.

2. The method for producing a 160ksi grade high-strength and tough non-standard oil casing according to claim 1, characterized in that, The quenching operation can be either direct online quenching or offline reheating followed by quenching.

3. The method for producing a 160ksi grade high-strength and tough non-standard oil casing according to claim 1, characterized in that, The quenching process uses other cooling media with an average cooling rate of over 65°C / s.

4. The method for producing a 160ksi grade high-strength and tough non-standard oil casing according to claim 1, characterized in that, The yield strength R of the manufactured steel pipe t0.7 ≥1100MPa, tensile strength R m ≥1200MPa, elongation A≥15%, and Charpy impact Akv at 0℃ is not less than 110J and 120J respectively in the transverse and longitudinal directions.

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