110-KSI-grade quenched and tempered UNS s41427 stainless steel bar for oil and gas industry, and preparation method therefor and use thereof

Abstract

The present invention belongs to the technical field of the on-line heat treatment of stainless steel, and specifically relates to a 110-KSI-grade quenched and tempered UNS S41427 stainless steel bar for the oil and gas industry, and a preparation method therefor and the use thereof. The preparation method comprises: according to the chemical composition of a UNS S41427 stainless steel for the oil and gas industry, sequentially subjecting raw materials to primary smelting in an electric furnace, LF refining, vacuum degassing, ingot casting, annealing or hot charging, heating, rolling or forging, annealing and finishing, so as to obtain a stainless steel bar; and then sequentially subjecting the bar to an austenitizing treatment, water quenching, primary tempering, straightening and secondary tempering, so as to obtain a 110-KSI-grade quenched and tempered bar, wherein the content of N is controlled to be less than or equal to 0.03 wt% after vacuum degassing; and the water quenching comprises placing the bar in continuously flowing cooling water for immersion quenching, with the temperature of the cooling water being no more than 38°C, and the temperature at which the bar comes out of the cooling water being less than or equal to 100°C. The quenched and tempered bar prepared by the method of the present invention can pass the SSC test, and exhibits strong versatility.

Description

A UNS S41427 stainless steel 110KSI grade quenched and tempered bar for oil and gas applications, its preparation method, and its application. Technical Field

[0001] This invention belongs to the field of stainless steel online heat treatment technology, and in particular relates to a 110KSI grade quenched and tempered bar of UNS S41427 stainless steel for oil and gas use, its preparation method, and its application. Background Technology

[0002] UNS S41427 is a high-strength, ultra-low-carbon martensitic stainless steel material whose main components include chromium (Cr), nickel (Ni), nitrogen (N), manganese (Mn), and sulfur (S). Due to its high chromium content, UNS S41427 also exhibits excellent corrosion resistance and is widely used in various fields due to its superior physical and chemical properties. Under NACE MR 0175 (ANSI / NACE MR0175 / ISO 15156-1:2015) and API 6A standards, UNS S41427 is primarily used in the manufacture of critical equipment in the oil and gas industry, and its 95 KSI strength grade is approved for use in NACE MR0175, making it a key material for well completion tools. Its main applications are in environments containing carbon dioxide, chlorides, and low concentrations of hydrogen sulfide. Because these devices need to operate under extreme temperature and pressure conditions and are frequently exposed to corrosive environments, the material requires excellent corrosion resistance and high strength.

[0003] UNS S41427 110 KSI strength rating is also widely used, but only in carbon dioxide environments. It has certain drawbacks and limitations, such as:

[0004] 1. Balance between strength and toughness:

[0005] UNS S41427 110KSI has higher strength than 95KSI, but its toughness decreases. Under certain extreme conditions, its toughness may not meet the requirements of specific applications.

[0006] 2. Corrosion resistance limitations:

[0007] Although S41427 110KSI has good corrosion resistance, its corrosion resistance is very poor in H2S corrosive environments.

[0008] If 110KSI can be used in H2S environments, it can replace UNS S41427 95KSI, making it easier for users to select materials and increasing the versatility of materials. In view of this, the present invention is proposed. Summary of the Invention

[0009] The purpose of this invention is to provide a UNS S41427 stainless steel 110KSI grade quenched and tempered bar for oil and gas applications, its preparation method, and its application, in order to solve the problems that S41427 110KSI bars cannot meet the requirements of NACE MR0175, have poor corrosion resistance, are not included in the NACE MR0175 standard, and have a narrow range of applications.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] In a first aspect, a method for preparing 110KSI grade quenched and tempered bars of UNS S41427 stainless steel for oil and gas applications includes:

[0012] S1. According to the chemical composition of UNS S41427 stainless steel for oil and gas, the raw materials are subjected to electric furnace primary refining, LF refining, vacuum degassing, die casting, annealing or hot charging, heating, rolling or forging, annealing and finishing in sequence to obtain UNS S41427 stainless steel bars.

[0013] Wherein, the N content is controlled to be ≤0.03wt% after vacuum degassing;

[0014] S2. The UNS S41427 stainless steel bars are subjected to austenitization and quenching and tempering treatment in sequence. The quenching and tempering treatment includes water quenching, first tempering, straightening and second tempering in sequence to obtain UNS S41427 stainless steel 110KSI grade quenched and tempered bars.

[0015] During the water-cooled quenching process, the austenitized UNS S41427 stainless steel bar is immersed in continuously flowing cooling water for quenching. The temperature of the cooling water does not exceed 38°C, and the outlet temperature of the UNS S41427 stainless steel bar is ≤100°C.

[0016] Furthermore, after the initial smelting in the electric furnace and before the ingot casting, the ladle is protected with argon gas instead of nitrogen gas throughout the entire process;

[0017] And / or, the annealing temperature before finishing is 610~640℃, and the holding time is (4h / 100mm*D)~(4h / 100mm*D+5h), where h represents hours and D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm;

[0018] And / or, the austenitizing temperature is 900~980℃, and the austenitizing holding time is (2h / 100mm*D)~(2h / 100mm*D+5h), where h represents hours and D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm.

[0019] Furthermore, during the water-cooling quenching process, the inlet water temperature of the UNS S41427 stainless steel bar is ≥850℃.

[0020] And / or, the cooling water is used as circulating water during water-cooled quenching.

[0021] Furthermore, the UNS S41427 stainless steel bar is water-filled within 2 minutes after austenitization; even further, the UNS S41427 stainless steel bar is water-filled within 1 minute after austenitization.

[0022] Furthermore, the circulating water is used for water-cooled quenching after impurities are removed. Moreover, the removal of impurities includes removing oil stains, oxide scale, and suspended solids.

[0023] Furthermore, the flow rate of the cooling water is 250–1000 m³ / h. 3 / h.

[0024] Furthermore, the holding temperature for the first tempering is 560–620°C, and the holding time is (4h / 100mm*D)–(4h / 100mm*D+5h), where h represents hours, D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm; and / or, the quenching stress is released by air cooling after the holding temperature during the first tempering.

[0025] Furthermore, the holding temperature of the secondary tempering is 540-600℃, preferably 30-50℃ lower than the holding temperature of the primary tempering, and the holding time is (4h / 100mm*D) to (4h / 100mm*D+5h), where h represents hours and D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm; and / or, before the secondary tempering, straightening is performed to remove the deformation of the bar caused by water quenching, and after holding in the secondary tempering, air cooling is performed to release the straightening stress.

[0026] Secondly, an oil and gas-use UNS S41427 stainless steel 110KSI grade quenched and tempered bar stock is prepared by the preparation method described in the first aspect.

[0027] The UNS S41427 stainless steel 110KSI grade quenched and tempered bar for oil and gas applications comprises the following chemical composition by mass fraction: C≤0.03%, Si≤0.50%, Mn≤1.0%, P≤0.02%, S≤0.005%, Ni 4.5-6.0%, Cr 11.5-13.5%, Mo 1.5-2.5%, Ti≤0.01%, V 0.01-0.50%, N≤0.03%, with the remainder being Fe and unavoidable impurities.

[0028] Thirdly, a well completion tool is made of quenched and tempered oil and gas grade UNS S41427 stainless steel 110KSI grade steel bar stock prepared by the preparation method described in the first aspect or the quenched and tempered oil and gas grade UNS S41427 stainless steel 110KSI grade steel bar stock described in the second aspect.

[0029] The present invention has at least the following beneficial effects:

[0030] This invention provides a method for preparing UNS S41427 stainless steel 110KSI grade quenched and tempered bars for oil and gas applications. The prepared UNS S41427 110KSI grade quenched and tempered bars can pass SSC testing and can replace UNS S41427 95KSI bars, exhibiting strong versatility. Attached Figure Description

[0031] Figure 1 shows the grain size (100 x 5 grain size) of the 110KSI grade quenched and tempered UNS S41427 stainless steel bar for oil and gas obtained in Example 1 of the present invention.

[0032] Figure 2 shows the grain size (500 x 5 grain size) of the 110KSI grade quenched and tempered UNS S41427 stainless steel bar for oil and gas obtained in Example 1 of the present invention.

[0033] Figure 3 shows the grain size (100 x 5 grain size) of the 110KSI grade quenched and tempered UNS S41427 stainless steel bar for oil and gas obtained in Example 2 of the present invention.

[0034] Figure 4 shows the grain size (500 x 5 grain size) of the 110KSI grade quenched and tempered UNS S41427 stainless steel bar for oil and gas obtained in Example 2 of the present invention.

[0035] Figure 5 is a macroscopic surface view of the UNS S41427 stainless steel 110KSI grade quenched and tempered bar for oil and gas obtained in Example 1 of the present invention.

[0036] Figure 6 is a 10X field-view surface view of the 110KSI grade quenched and tempered UNS S41427 stainless steel bar for oil and gas obtained in Example 1 of the present invention.

[0037] Figure 7 is a macroscopic surface view of the UNS S41427 stainless steel 110KSI grade quenched and tempered bar for oil and gas obtained in Example 2 of the present invention.

[0038] Figure 8 is a 10X field-view surface view of the 110KSI grade quenched and tempered UNS S41427 stainless steel bar for oil and gas obtained in Example 2 of the present invention.

[0039] Figure 9 is a macroscopic surface view of the UNS S41427 stainless steel 110KSI grade quenched and tempered bar for oil and gas obtained in Comparative Example 1 of the present invention.

[0040] Figure 10 is a 10X field-view surface view of the 110KSI grade quenched and tempered UNS S41427 stainless steel bar for oil and gas obtained in Comparative Example 1 of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0042] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0043] The main component range (wt%) of UNS S41427 steel for oil and gas applications is as follows: C≤0.03%, Si≤0.50%, Mn≤1.0%, P≤0.02%, S≤0.005%, Ni 4.5-6.0%, Cr 11.5-13.5%, Mo 1.5-2.5%, Ti≤0.01%, V 0.01-0.50% (NACE MR0175 Table D.6).

[0044] The current production process for UNS S41427 oil and gas stainless steel tempered material includes: raw material preparation (molten iron, scrap steel, alloys, etc., control of five harmful elements), electric furnace smelting + VOD + LF + VD (inclusion control, gas content control), die casting (structure uniformity control), annealing / hot casting, heating, forging / rolling (material grain size, density control), annealing, straightening (straightness preparation before tempering), tempering [air quenching or oil quenching → first tempering → (straightening) → stress relief tempering], physical and chemical testing, surface finishing, flaw detection, surface inspection, inspection judgment, packaging and warehousing. This production process yields 95KSI and 110KSI grade steel according to UNS S41427. While the 95KSI grade steel can pass the SSC evaluation, the 110KSI grade cannot. This is because the tensile strength of 110KSI is higher than that of 95KSI. Normally, 110KSI grade steel can only be used in CO2 environments and is not suitable for environments containing H2S. However, after extensive research, the inventors discovered that only by making the material's tensile strength and hardness close to those of 95KSI, while simultaneously meeting the yield strength requirements of 110KSI, can the yield strength ratio be adjusted. This ensures that the material's strength and hardness are not excessively high, allowing it to achieve both the 110KSI grade and pass the SSC test (suitable for H2S environments). Specifically, the yield strength ratio can be adjusted by controlling the content of the solid solution strengthening element N and by water-cooling quenching (water quenching) treatment. Therefore, the following technical solution is ultimately adopted:

[0045] In a first aspect, a method for preparing 110KSI grade quenched and tempered bars of UNS S41427 stainless steel for oil and gas applications includes:

[0046] S1. According to the chemical composition of UNS S41427 stainless steel for oil and gas, the raw materials are subjected to electric furnace primary refining, LF refining, vacuum degassing, die casting, annealing or hot charging, heating, rolling or forging, annealing and finishing in sequence to obtain UNS S41427 stainless steel bars.

[0047] Wherein, the N content is controlled to be ≤0.03wt% after vacuum degassing;

[0048] S2. The UNS S41427 stainless steel bars are subjected to austenitization and quenching and tempering treatment in sequence. The quenching and tempering treatment includes water quenching, first tempering, straightening and second tempering in sequence to obtain UNS S41427 stainless steel 110KSI grade quenched and tempered bars.

[0049] During the water-cooled quenching process, the austenitized UNS S41427 stainless steel bar is immersed in continuously flowing cooling water for quenching. The temperature of the cooling water does not exceed 38°C, and the outlet temperature of the UNS S41427 stainless steel bar is ≤100°C.

[0050] This invention discloses a method for preparing UNS S41427 stainless steel 110KSI grade quenched and tempered bars for oil and gas applications. By controlling the content of nitrogen (N) as a solid solution strengthening element during steelmaking, and by finishing the bars before quenching and tempering and then using water as a medium for immersion quenching, the steel is kept submerged in water as much as possible while ensuring no cracking occurs. This improves the yield strength ratio of the material, enabling the UNS S41427 stainless steel quenched and tempered bars to achieve 110KSI grade strength, thus becoming UNS S41427 stainless steel 110KSI grade quenched and tempered bars. It also exhibits relatively low hardness, high toughness, and resistance to H2S corrosion, meeting the requirements of NACE MR0175. This method replaces UNS S41427 95KSI, facilitating material selection for users and increasing the versatility of the material.

[0051] If the nitrogen (N) content is not controlled in the preparation method of this invention, the yield of the bars will be unstable, and may not meet the requirements of NACE MR0175. This is because the chromium (Cr) content in the steel grade is too high, and Cr has the effect of fixing nitrogen. Since nitrogen is a solid solution strengthening element, it will lead to higher material strength and hardness, affecting the SSC corrosion results. Therefore, the N content should be controlled to ≤0.03wt%, and further not exceeding 0.02wt%. Typical but non-limiting options include 0.03wt%, 0.027wt%, 0.025wt%, 0.023wt%, 0.02wt%, 0.017wt%, 0.015wt%, 0.013wt%, 0.01wt%, 0.007wt%, 0.005wt%, 0.001wt%, 0.0005wt%, and 0.0001wt%. However, if water is not used as the medium for immersion quenching, air cooling quenching will lead to uneven and fluctuating material properties, making it difficult to obtain the desired results. Spray quenching requires the steel bar to be rotated to ensure uniform contact with water, and there is a possibility that air contact with the steel bar may affect cooling. Moreover, it can only process single or small quantities of bars, while immersion quenching can process large quantities of steel bars. Therefore, this invention adopts immersion quenching with water as the medium, controlling the cooling water to be continuously flowing and maintaining the water temperature not exceeding 38°C. Finally, by controlling the water exit temperature of the bar and pre-finishing to avoid the source of crack induction, the water-quenched material is guaranteed to be free from stress cracking or grain boundary fine cracks, achieving a strength grade of 110KSI and passing SSC evaluation, meeting the NACE MR0175 application requirements.

[0052] Specifically, under normal circumstances, the temperature of the bar stock is relatively high, and the cooling water in contact with the bar stock will inevitably boil, forming a vapor film on the bar stock surface. However, with continuous flow of cooling water, it can rapidly exchange heat with the bar stock and / or the boiling water, quickly transferring heat and lowering the water temperature after heat exchange. Through extensive research, the inventors discovered that by controlling the water temperature in the quenching tank to not exceed 38°C—that is, by controlling the flow rate of cooling water according to the size of the quenching tank and the size of the bar stock—boiling of the water can be avoided, the cooling rate of the bar stock can be controlled, and the bar stock can be cooled stably and uniformly from the outside in, ensuring stable material transformation without residual austenite, stress cracking, or grain boundary fine cracks in the microstructure. Therefore, the temperature of the cooling water can typically, but not exclusively, be selected as 37°C, 35°C, 30°C, 25°C, 20°C, 15°C, 10°C, 5°C, etc. In addition, the outlet water temperature of the UNS S41427 stainless steel bar can typically, but not exclusively, be selected as 100℃, 90℃, 80℃, 70℃, 60℃, 50℃, 40℃, 30℃, 20℃, etc. By controlling the outlet water temperature of the bar, it is ensured that the material is fully quenched while meeting the performance requirements and preventing the material from cracking.

[0053] In this invention, the cooling water can be ordinary fresh water, including hard or soft water such as purified water, tap water, deionized water, distilled water, etc., or recycled treated wastewater or circulating water; preferably, inexpensive industrial water is preferred due to its low production cost. The cooling water can usually be used directly at room temperature for water-cooled quenching without special cooling or heating treatment. As long as the water remains continuously flowing throughout the quenching process, and the water temperature stabilizes below 38°C after contact with the bar stock for heat exchange, a stable material transformation without residual austenite is ensured.

[0054] In this invention, the outlet water temperature is the outlet water temperature of the steel rod, which reflects the temperature of the steel rod surface. The temperature of the core of the steel rod is higher than the surface temperature because it is only affected by heat conduction.

[0055] As an optional embodiment of the preparation method of the present invention, the cooling water is used as circulating water during water quenching; further, the circulating water is used for water quenching after impurities are removed; and even further, the removal of impurities includes removing oil stains, oxide scale, and suspended solids.

[0056] In the above technical solution, cooling water is used as circulating water during water-cooled quenching. This ensures a continuous flow of cooling water during the process and conserves water. However, the circulating water must be clean. Before using the circulating water for water-cooled quenching, it is essential to filter and clean it to remove impurities such as oil, scale, and suspended solids. These impurities can severely affect the cooling effect of the circulating water and may even cause equipment blockage and damage. Therefore, filtering and cleaning the circulating water to remove impurities ensures water quality, extends equipment lifespan, and improves production efficiency.

[0057] As an optional embodiment of the preparation method of the present invention, after the electric furnace primary refining and before the ingot casting, the ladle is protected by argon gas instead of nitrogen gas throughout the process, thereby ensuring the N content in the steel.

[0058] As an optional embodiment of the preparation method of the present invention, the annealing temperature before finishing is 610~640℃ (such as 615℃, 620℃, 625℃, 630℃, 635℃, etc.), and the holding time is (4h / 100mm*D)~(4h / 100mm*D+5h), where h represents hours and D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm.

[0059] In the above technical solutions, phase transformation is likely to occur if the annealing temperature exceeds the range, especially above 650℃, while there is no effect if the temperature is below the range, especially below 600℃. The annealing time should also not be too long or too short; if the time is too short, the stress relief requirement will not be met, and if the time is too long, production capacity will be wasted.

[0060] As an optional embodiment of the preparation method of the present invention, the austenitizing temperature is 900-980℃ (e.g., 910℃, 920℃, 930℃, 940℃, 950℃, 960℃, 970℃, etc.), and the austenitizing holding time is (2h / 100mm*D) to (2h / 100mm*D+5h), where h represents hours and D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm.

[0061] In this invention, before water quenching, UNS S41427 stainless steel bars undergo austenitizing treatment at a temperature of 900–980°C for a certain holding time. The austenitized bars can then be directly water quenched, meaning they are placed directly into water at a furnace exit temperature of 900–980°C. However, in practice, the bars undergo a certain period of time and space transfer after exiting the furnace, causing the surface temperature to drop due to environmental influences. Furthermore, the surface of the bars actually has an oxide scale. Therefore, the water entry temperature can be controlled based on either the oxide scale temperature or the time from furnace exit to complete immersion in water. The latter is preferred as it is more convenient for on-site production operations. Optionally, the inlet water temperature of the UNS S41427 stainless steel bar is ≥850℃; further, the UNS S41427 stainless steel bar is inlet water within 2 minutes after austenitization; even further, the UNS S41427 stainless steel bar is inlet water within 1 minute after austenitization to ensure stable material properties. Therefore, in this invention, the inlet water temperature of the UNS S41427 stainless steel bar is typically, but not limited to, 850℃, 870℃, 890℃, 910℃, 930℃, 950℃, 970℃, etc., and / or, the UNS S41427 stainless steel bar is inlet water within a time frame such as 110s, 100s, 90s, 80s, 70s, 60s, 50s, 40s, 30s, 25s, 20s, 15s, 10s, 0s, etc., after austenitization.

[0062] As an optional embodiment of the preparation method of the present invention, the flow rate of the cooling water is 250-1000 m³ / h. 3 / h (e.g., 300m) 3 / h, 400m 3 / h, 500m 3 / h, 600m 3 / h, 700m 3 / h、800m 3 / h、900m 3 / h etc).

[0063] In the above technical solution, the cooling water flow rate is controlled to be ≥250m³ / h. 3 The flow rate of the cooling water is [ / h], which not only ensures that the cooling water temperature does not exceed 38°C and avoids boiling, but also ensures uniform cooling of the bar from the inside out, achieving precise control of the cooling rate during water cooling and preventing stress cracking or grain boundary cracks in the microstructure; it also effectively removes the vapor film, reducing its impact. In this invention, the flow rate can be selected based on the upper limit of existing equipment, as long as water pressure does not act on the bar, such as a cooling water flow rate of 250–1000 m³ / h. 3 / h, when the quenching tank is large and / or the bar is large, a larger water flow rate is used to ensure that the cooling water in the quenching tank submerges the bar and the cooling water temperature does not exceed 38℃.

[0064] As an optional embodiment of the preparation method of the present invention, the holding temperature of the first tempering is 560-620℃ (e.g., 570℃, 580℃, 590℃, 610℃, etc.), and the holding time is (4h / 100mm*D) to (4h / 100mm*D+5h), where h represents hours, D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm; and / or, the first tempering is followed by air cooling to release quenching stress.

[0065] In the above technical solution, the tempering temperature is controlled between 560 and 620°C to avoid the steel's tensile strength and yield strength becoming lower as the temperature increases.

[0066] As an optional embodiment of the preparation method of the present invention, the holding temperature of the secondary tempering is 540-600℃ (e.g., 550℃, 560℃, 570℃, 580℃, 590℃, etc.), preferably 30-50℃ lower than the holding temperature of the primary tempering (e.g., 35℃, 40℃, 45℃, etc.), and the holding time is (4h / 100mm*D) to (4h / 100mm*D+5h), where h represents hours, D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm; and / or, before the secondary tempering, straightening is performed to remove the deformation of the bar caused by water quenching, and after holding in the secondary tempering, air cooling is performed to release the straightening stress.

[0067] In the above technical solution, it is preferable that the secondary tempering temperature is 30-50°C lower than the holding temperature of the primary tempering, which can avoid some possible abnormal situations.

[0068] As an optional embodiment of the preparation method of the present invention, the specifications of the UNS S41427 stainless steel bar are round bars with a diameter of Φ12~310mm (such as 15mm, 50mm, 100mm, 150mm, 200mm, 250mm, 300mm, etc.).

[0069] Secondly, an oil and gas-use UNS S41427 stainless steel 110KSI grade quenched and tempered bar stock is prepared by the preparation method described in the first aspect.

[0070] The UNS S41427 stainless steel 110KSI grade quenched and tempered bar stock for oil and gas applications comprises the following chemical composition by mass fraction: C≤0.03%, Si≤0.50%, Mn≤1.0%, P≤0.02%, S≤0.005%, Ni 4.5-6.0%, Cr 11.5-13.5%, Mo 1.5-2.5%, Ti≤0.01%, V 0.01-0.50%, N≤0.03%, with the remainder being Fe and unavoidable impurities; furthermore, the UNS S41427 stainless steel 110KSI grade quenched and tempered bar stock for oil and gas applications comprises the following chemical composition by mass fraction: C≤0.03%, Si≤0.25%, Mn≤0.5%, P≤0.02%, S≤0.005%, Ni 5.0-6.0%, Cr 11.5-13.5%, Mo 1.5-2.2%, Ti<0.005%, V 0.01-0.20%, N≤0.02%, the remainder being Fe and unavoidable impurities.

[0071] Thirdly, a well completion tool is made of quenched and tempered oil and gas grade UNS S41427 stainless steel 110KSI grade steel bar stock prepared by the preparation method described in the first aspect or the quenched and tempered oil and gas grade UNS S41427 stainless steel 110KSI grade steel bar stock described in the second aspect.

[0072] The specific embodiments of the present invention will be further explained below with reference to examples and comparative examples:

[0073] Example 1

[0074] This embodiment provides a UNS S41427 steel suitable for the oil and gas field, produced as a 110KSI grade, Φ130mm round bar. The main chemical composition and content (wt%) of the steel are: C: 0.02%, Si: 0.24%, Mn: 0.38%, P: 0.015%, S: 0.002%, Cr: 12.15%, Ni: 5.39%, Mo: 1.95%, V: 0.12%, Ti: <0.005%, N: 0.012%, with the remainder being Fe and unavoidable impurities.

[0075] Specifically, the manufacturing method of UNS S41427 steel produced in this embodiment includes the following steps:

[0076] S1. Preparation of steel billets: The raw materials are successively smelted in an electric furnace, refined in an LF ladle and degassed in a VD vacuum (after vacuum degassed, the N content is analyzed and the N content should be ≤0.03%; the ladle is protected by argon gas instead of nitrogen gas throughout the process), ingot casting, hot feeding, heating and rolling to obtain UNS S41427 rolled round steel; the final rolling temperature is 927℃.

[0077] S2, Annealing: After the material cools to room temperature, it is loaded into the furnace for annealing. The annealing temperature is set at 630℃. After holding at this temperature for 7 hours, the material is taken out of the furnace and air-cooled to eliminate rolling stress.

[0078] S3 Finishing: To prevent water quenching cracking, the material is finished and inspected for defects and cracks from the rolling process. After passing the inspection, the material is transferred to the heat treatment line.

[0079] S4. The material is austenitized at an austenitizing temperature of 950℃. After holding at this temperature for 4 hours, it is then removed from the furnace and quenched.

[0080] S5. Water-cooled quenching: Turn on the circulating water. Before use, ensure the circulating water is filtered and cleaned to remove impurities such as oil, scale, and suspended solids. The time from the bar stock exiting the furnace to entering the water is 45 seconds, and the circulating water flow rate is 260 m³ / h. 3 / h; Circulating water temperature before inlet: 18℃. Circulating water temperature after outlet: 26℃. Steel surface temperature at outlet: 76℃;

[0081] S6. First tempering: The tempering holding temperature is set to 590℃ and the holding time is 7h. After holding, the furnace is removed and air-cooled to complete the first tempering.

[0082] S7, Straightening;

[0083] S8. Secondary tempering: The tempering holding temperature is set at 550℃ and the holding time is 7h. After holding, the steel is removed from the furnace and air-cooled to complete the tempering; UNS S41427 110KSI steel is obtained.

[0084] Example 2

[0085] This embodiment provides a UNS S41427 steel suitable for the oil and gas field, produced as a 110KSI grade, Φ250mm round bar. The main chemical composition and content (wt%) of the steel are: C: 0.01%, Si: 0.23%, Mn: 0.41%, P: 0.014%, S: 0.001%, Cr: 12.21%, Ni: 5.55%, Mo: 2.17%, V: 0.13%, Ti: <0.005%, N: 0.011%, with the remainder being Fe and unavoidable impurities.

[0086] Specifically, the manufacturing method of UNS S41427 steel produced in this embodiment includes the following steps:

[0087] S1. Preparation of steel billets: The raw materials are successively smelted in an electric furnace, refined in an LF ladle and vacuum degassed in a VD vacuum (after vacuum degassed, the N content is analyzed and the N content should be ≤0.03% and the ladle is protected by argon gas instead of nitrogen gas throughout the process), ingot casting, hot feeding, heating and forging to obtain UNS S41427 forged round steel; the final forging temperature is 907℃.

[0088] S2, Annealing: After the material cools to room temperature, it is loaded into the furnace for annealing. The annealing temperature is set at 620℃. After holding at the temperature for 13 hours, the material is taken out of the furnace and air-cooled to eliminate rolling stress.

[0089] S3 Finishing: To prevent water quenching cracks, the material is finished and inspected for defects and cracks from the forging process. After passing the inspection, the material is transferred to the heat treatment line.

[0090] S4. The material is austenitized at an austenitizing temperature of 970℃. After holding at this temperature for 6 hours, it is then removed from the furnace and quenched.

[0091] S5. Water-cooled quenching: Turn on the circulating water. Before use, ensure the circulating water is filtered and cleaned to remove impurities such as oil, scale, and suspended solids. The time from the bar stock exiting the furnace to entering the water is 35 seconds, and the circulating water flow rate is 270 m³ / h. 3 / h; Circulating water temperature before inlet: 15℃. Circulating water temperature after outlet: 26℃. Surface temperature of steel at outlet: 75℃;

[0092] S6. First tempering: The tempering holding temperature is set at 590℃ and the holding time is 13h. After holding, the furnace is removed and air-cooled to complete the first tempering.

[0093] S7, Straightening;

[0094] S8. Secondary tempering: The tempering holding temperature is set at 550℃ and the holding time is 13h. After holding, the steel is removed from the furnace and air-cooled to complete the tempering; UNS S41427 110KSI steel is obtained.

[0095] Comparative Example 1

[0096] This comparative example provides a UNS S41427 steel suitable for the oil and gas industry, produced as a 110KSI grade, Φ250mm round bar. The main chemical composition and content (wt%) of the steel are: C: 0.01%, Si: 0.26%, Mn: 0.43%, P: 0.012%, S: 0.001%, Cr: 12.30%, Ni: 5.62%, Mo: 2.13%, V: 0.11%, Ti: <0.005%, N: 0.043%, with the remainder being Fe and unavoidable impurities.

[0097] Specifically, the manufacturing method of UNS S41427 steel produced in this comparative example includes the following steps:

[0098] S1. Preparation of steel billet: The raw materials are successively smelted in an electric furnace, refined in an LF ladle and degassed in a VD vacuum (without specific control for nitrogen), cast in a die, hot-pressed, heated and forged to obtain UNS S41427 forged round steel; the final forging temperature is 907℃.

[0099] S2, Annealing: After the material cools to room temperature, it is loaded into the furnace for annealing. The annealing temperature is set at 620℃. After holding at the temperature for 13 hours, the material is taken out of the furnace and air-cooled to eliminate rolling stress.

[0100] S3 Finishing: To prevent water quenching cracks, the material is finished and inspected for defects and cracks from the forging process. After passing the inspection, the material is transferred to the heat treatment line.

[0101] S4. The material is austenitized at an austenitizing temperature of 970℃. After holding at this temperature for 6 hours, it is then removed from the furnace and quenched.

[0102] S5. Water-cooled quenching: Circulating water is not turned on. Before using the cooling water, ensure it is filtered and cleaned to remove impurities such as oil, scale, and suspended solids. The time from the bar exiting the furnace to entering the water is 59 seconds; the water temperature before entering the water is 25℃; the water temperature after exiting the water is 51℃; and the surface temperature of the steel exiting the water is 165℃.

[0103] S6. First tempering: The tempering holding temperature is set at 590℃ and the holding time is 13h. After holding, the furnace is removed and air-cooled to complete the first tempering.

[0104] S7, Straightening;

[0105] S8. Secondary tempering: The tempering holding temperature is set at 550℃ and the holding time is 13h. After holding, the steel is removed from the furnace and air-cooled to complete the tempering; UNS S41427 110KSI steel is obtained.

[0106] Performance testing

[0107] 1. Mechanical properties were tested at 1 / 2R of the UNS S41427110KSI steel obtained in Examples 1, 2, and Comparative Example 1, according to API 6A standard. The results are shown in the table below:

[0108] As can be seen from the table above:

[0109] The mechanical properties of Examples 1, 2, and Comparative Example 1 all meet the requirements of conventional UNS S41427110KSI. However, the tensile strength and hardness of Examples 1 and 2 are lower than those of Comparative Example 1. If the tensile strength and hardness of Comparative Example 1 are further reduced, the yield strength will fail to meet the requirements, thus failing to meet the basic requirements for material use.

[0110] Furthermore, the grain size of the UNS S41427 stainless steel 110KSI grade quenched and tempered bar stock for oil and gas obtained in Example 1 is shown in Figures 1 and 2. It can be seen from the figures that the grain size is grade 5, the grains are uniform, and no defects are observed. The grain size of the UNS S41427 stainless steel 110KSI grade quenched and tempered bar stock for oil and gas obtained in Example 2 is shown in Figures 3 and 4. It can be seen from the figures that the grain size is grade 5, the grains are uniform, and no defects are observed.

[0111] 2. SSC testing was performed on the UNS S41427 110KSI steels obtained in Examples 1, 2, and Comparative Example 1 according to the NACE0175 requirements for 95KSI (test temperature 22℃~24℃, H2S partial pressure 0.01 bar, total pressure 1 bar, CO2 equilibrium gas, Cl...). - 140,000 mg / L, Buffer for pH balancing: 0.82 g / L CH3COONa + CH3COOH, pH 4.50, loaded at 90% of actual yield strength.

[0112] The test results show that after 720 hours, the sample of Example 1 did not break, and no cracks were generated on the macroscopic surface (as shown in Figure 5) and the 10X field of view surface (as shown in Figure 6), indicating that the sample was qualified. The sample of Example 2 did not break after 720 hours, and no cracks were generated on the macroscopic surface (as shown in Figure 7) and the 10X field of view surface (as shown in Figure 8), indicating that the sample was qualified. The sample of Comparative Example 1 did not break after 720 hours, and no cracks were generated on the macroscopic surface (as shown in Figure 9) and the 10X field of view surface (as shown in Figure 10), but severe pitting corrosion occurred, indicating that the sample was unqualified. Therefore, the UNS S41427 produced according to the method of this invention passed the SSC test, met the NACE requirements, and its performance and microstructure met the usage requirements.

[0113] The above are merely preferred embodiments of the present invention and are 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 of manufacturing a quenched and tempered bar of UNS S41427 stainless steel 110 KSI grade for oil and gas applications, characterized in that, include: S1. According to the chemical composition of UNS S41427 stainless steel for oil and gas, the raw materials are subjected to electric furnace primary refining, LF refining, vacuum degassing, die casting, annealing or hot charging, heating, rolling or forging, annealing and finishing in sequence to obtain UNS S41427 stainless steel bars. Wherein, the N content is controlled to be ≤0.03wt% after vacuum degassing; S2. The UNS S41427 stainless steel bars are subjected to austenitization and quenching and tempering treatment in sequence. The quenching and tempering treatment includes water quenching, first tempering, straightening and second tempering in sequence to obtain UNS S41427 stainless steel 110KSI grade quenched and tempered bars. During the water-cooled quenching process, the austenitized UNS S41427 stainless steel bar is immersed in continuously flowing cooling water for quenching. The temperature of the cooling water does not exceed 38°C, and the outlet temperature of the UNS S41427 stainless steel bar is ≤100°C.

2. The method of claim 1, wherein, After the initial smelting in the electric furnace and before the ingot casting, the ladle is protected by argon gas instead of nitrogen gas throughout the entire process. And / or, the annealing temperature before finishing is 610~640℃, and the holding time is (4h / 100mm*D)~(4h / 100mm*D+5h), where h represents hours and D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm; And / or, the austenitizing temperature is 900~980℃, and the austenitizing holding time is (2h / 100mm*D)~(2h / 100mm*D+5h), where h represents hours and D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm.

3. The preparation method according to claim 1, characterized in that, During the water-cooling quenching process, the inlet water temperature of the UNS S41427 stainless steel bar is ≥850℃. And / or, the cooling water is used as circulating water during water-cooled quenching.

4. The preparation method according to claim 3, characterized in that, The UNS S41427 stainless steel bars are immersed in water within 2 minutes after austenitization; and / or the circulating water is used for water quenching after impurities are removed.

5. The preparation method according to claim 4, characterized in that, The UNS S41427 stainless steel bar is water-filled within 1 minute after austenitization; and / or, the removal of impurities includes the removal of oil, scale, and suspended solids.

6. The preparation method according to claim 1, characterized in that, The water flow rate of the cooling water is 250 to 1000 m 3 / h.

7. The preparation method according to claim 1, characterized in that, The holding temperature for the first tempering is 560–620°C, and the holding time is (4h / 100mm*D)–(4h / 100mm*D+5h), where h represents hours, D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm; and / or, the quenching stress is released by air cooling after the holding temperature during the first tempering.

8. The preparation method according to claim 1, characterized in that, The holding temperature for the secondary tempering is 540–600℃, which is 30–50℃ lower than the holding temperature for the primary tempering. The holding time is (4h / 100mm*D) to (4h / 100mm*D+5h), where h represents hours and D represents the diameter of the UNS S41427 stainless steel bar in its black skin state (mm). Alternatively, before the secondary tempering, straightening is performed to remove deformation caused by water quenching, and after holding during the secondary tempering, air cooling is performed to release the straightening stress.

9. A quenched and tempered bar of UNS S41427 stainless steel 110KSI grade for oil and gas applications, characterized in that, Prepared by the preparation method according to any one of claims 1-8; The UNS S41427 stainless steel 110KSI grade quenched and tempered bar for oil and gas applications comprises the following chemical composition by mass fraction: C≤0.03%, Si≤0.50%, Mn≤1.0%, P≤0.02%, S≤0.005%, Ni 4.5-6.0%, Cr 11.5-13.5%, Mo 1.5-2.5%, Ti≤0.01%, V 0.01-0.50%, N≤0.03%, with the remainder being Fe and unavoidable impurities.

10. A well completion tool, characterized in that, The oil and gas grade UNS S41427 stainless steel 110KSI grade quenched and tempered bar stock is prepared by the preparation method described in any one of claims 1-8 or the oil and gas grade UNS S41427 stainless steel 110KSI grade quenched and tempered bar stock described in claim 9.

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