UNS S41427 stainless steel 95KSI-grade quenched and tempered bar for oil and gas and water quenching heat treatment method and application of UNS S41427 stainless steel 95KSI-grade quenched and tempered bar

Abstract

The invention belongs to the technical field of online heat treatment of stainless steel, and particularly relates to a UNS S41427 stainless steel 95KSI-grade quenched and tempered bar for oil gas and a water quenching heat treatment method and application of the UNS S41427 stainless steel 95KSI-grade quenched and tempered bar for the oil gas. Primary tempering and secondary tempering are carried out after the water outlet temperature is reached; wherein the temperature of the cooling water is lower than 38 DEG C. According to the method, the problems of many defects of air cooling or oil cooling are solved, and meanwhile, the UNS S41427 stainless steel subjected to water quenching reaches the 95KSI strength grade and meets the NACE MR0175 application.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel online heat treatment, and in particular relates to a UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas, and a water quenching heat treatment method and application thereof. Background Art

[0002] UNS S41427, primarily composed of chromium (Cr), nickel (Ni), nitrogen (N), manganese (Mn), and sulfur (S), is a high-strength, ultra-low-carbon martensitic stainless steel. Due to its high molybdenum and chromium content, UNS S41427 also exhibits excellent corrosion resistance. Its excellent physical and chemical properties have led to its widespread application in various fields. UNS S41427 is primarily used in the manufacture of critical equipment in the oil and gas industry under NACE MR0175 (ANSI / NACE MR0175 / ISO 15156-1:2015) and API 6A standards. Its 95 KSI strength grade is approved for use in NACE MR0175, making it a key material for completion tools. Its primary application is in environments containing carbon dioxide, chlorides, and low concentrations of hydrogen sulfide. Since these equipment must operate under extreme temperature and pressure conditions and is frequently exposed to corrosive environments, they require both excellent corrosion resistance and high strength. However, heat treatment is a key factor influencing material performance.

[0003] The international standard "ANSI / NACE MR0175 / ISO 15156-1:2015" clearly requires in Table A.21 that UNSS41427 can only be quenched using air cooling or oil cooling to meet the requirements of NACE MR0175. NACE MR0175 requires the following: The application of UNS S41427 material in completion tools must meet the corrosion conditions of a maximum hydrogen sulfide partial pressure of 10 kPa, a maximum chlorine concentration of 6100 mg / l, and UNS S41427 should be heat treated in the following three steps: a) austenitizing at 900°C to 980°C (1652°F to 1796°F), followed by air cooling or oil cooling to ambient temperature; b) tempering at 600°C to 700°C (1112°F to 1292°F), followed by air cooling to ambient temperature; c) tempering at 540°C to 620°C (1004°F to 1148°F), followed by air cooling to ambient temperature. However, air cooling has some disadvantages: (1) Poor heat transfer performance: Air cooling mainly relies on air heat conduction or convection heat transfer. Since the thermal conductivity of air is relatively low, the heat transfer performance is poor, resulting in low cooling efficiency. (2) Greatly affected by the environment: The performance of air cooling is greatly affected by natural conditions such as ambient temperature, wind speed, and wind direction. For example, in the high temperature of summer, the cooling effect of air cooling will drop significantly; and in the low temperature of winter, the actual temperature difference varies greatly with the changes in on-site logistics. At the same time, oil cooling also has some disadvantages: (1) Safety hazards: Although quenching oil has a high flash point and ignition point, there is still a certain fire risk during use if the oil temperature is not properly controlled or the operation is wrong. In addition, the oil cooling medium is flammable and special attention should be paid to fire safety. (2) Environmental pollution: Quenching oil will produce oil smoke and exhaust gas during long-term use. These pollutants will cause certain pollution to the environment. At the same time, oil leakage may also cause pollution to the soil and water bodies. (3) High cost: The price of quenching oil is relatively high and requires regular maintenance and replacement. This increases the cost of the heat treatment process. In addition, since quenching oil has a certain volatility, there will be a certain loss during use, which also increases the cost. (4) Impact on the health of operators: Quenching oil will produce oil smoke and harmful gases during the quenching process. These gases pose a threat to the health of operators. Long-term exposure to these gases may cause workers to suffer from health problems such as respiratory diseases and skin diseases.

[0004] Since air cooling or oil cooling heat treatment has many disadvantages and there is no report on accurately controlling the heat treatment water quenching process of UNS S41427 material to achieve optimal performance, the present invention is proposed in view of this. Summary of the Invention

[0005] The present invention aims to provide a UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas use and a water quenching heat treatment method and application thereof, so as to solve the many shortcomings of air cooling or oil cooling, and at the same time make the UNS S41427 stainless steel after water quenching reach 95KSI strength grade and meet NACE MR0175 application.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, a water quenching heat treatment method for UNS S41427 stainless steel 95KSI grade quenched and tempered bars for oil and gas use comprises: placing the austenitized UNS S41427 stainless steel bars in continuously flowing cooling water for immersion quenching, and performing primary and secondary tempering after reaching the water outlet temperature; wherein the temperature of the cooling water is lower than 38°C.

[0008] Furthermore, the austenitizing temperature is 900-980° C., 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;

[0009] and / or, the water inlet temperature of the UNS S41427 stainless steel bar is ≥850°C;

[0010] And / or, the UNS S41427 stainless steel bar is filled with water within 2 minutes after being taken out of the austenitizing furnace;

[0011] and / or, the outlet water temperature of the UNS S41427 stainless steel bar is ≥ room temperature;

[0012] And / or, the cooling water flow rate is ≥250m 3 / h.

[0013] Furthermore, the UNS S41427 stainless steel bar is filled with water within 1 minute after being austenitized and taken out of the furnace;

[0014] And / or, the outlet water temperature of the UNS S41427 stainless steel bar is ≤150°C.

[0015] Furthermore, the cooling water is circulated as circulating water during water-cooling quenching.

[0016] Furthermore, the circulating water is used for water-cooling quenching after impurities are removed, and the impurity removal includes removing impurities such as oil, oxide scale, and suspended solids.

[0017] Furthermore, the holding temperature of the primary tempering is 600-650° C., and the holding time is (4 h / 100 mm*D)-(4 h / 100 mm*D+5 h), wherein h represents hours, and D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm; and / or, air cooling is performed after holding in the primary tempering to release quenching stress.

[0018] Furthermore, the holding temperature of the secondary tempering is 540-620° C., which is 30-50° C. lower than the holding temperature of the primary tempering, and the holding time is (4 h / 100 mm*D)-(4 h / 100 mm*D+5 h), wherein h represents hours and D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm; and / or, straightening is performed before the secondary tempering to remove bar deformation caused by water quenching, and air cooling is performed after holding in the secondary tempering to release straightening stress.

[0019] Furthermore, the UNS S41427 stainless steel bar is obtained by sequentially performing primary refining, refining, vacuum degassing, die casting, hot-melting, heating, rolling, annealing or hot-melting on the raw materials according to the chemical composition of UNS S41427 stainless steel for oil and gas;

[0020] And / or, the specification of the UNS S41427 stainless steel bar is round steel with a diameter of Φ12 to 310 mm.

[0021] In a second aspect, a UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas is produced using the water quenching heat treatment method described in the first aspect; the UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas 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%, and the remainder is Fe and unavoidable impurities.

[0022] In a third aspect, a completion tool is made of the UNSS41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas prepared by the water quenching heat treatment method described in the first aspect or the UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas described in the second aspect.

[0023] The present invention has at least the following beneficial effects:

[0024] The present invention provides a water quenching heat treatment method for UNS S41427 stainless steel 95KSI grade quenched and tempered bars for oil and gas use, which uses water quenching to replace air cooling or oil cooling heat treatment, avoiding many disadvantages of air cooling or oil cooling while allowing the UNS S41427 stainless steel to reach a 95KSI strength grade and meet NACE MR0175 applications. At the same time, when NACE0175 does not accept water-quenched products, Daye's water-quenched products are accepted. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The grain map (100x 5-grade grain size) of the UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas obtained in Example 1 of the present invention;

[0026] Figure 2 This is the grain map (100x 5-grade grain size) of the UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas obtained in Example 2 of the present invention;

[0027] Figure 3 This is a macroscopic image of a qualified SSC sample of UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas obtained in Example 1 of the present invention;

[0028] Figure 4 This is a macroscopic image of a qualified SSC sample of UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas obtained in Example 2 of the present invention;

[0029] Figure 5 This is a 10X viewing angle image of a qualified SSC sample of UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas obtained in Example 1 of the present invention;

[0030] Figure 6 This is a 10X field of view image of a qualified SSC sample of UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas obtained in Example 2 of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally based on conventional conditions.

[0032] The main composition range of UNS S41427 steel for oil and gas use (wt%) is: 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%, Mo1.5-2.5%, Ti≤0.01%, V 0.01-0.50% (NACE MR0175 Table D.6).

[0033] The current production process for UNS S41427 oil and gas stainless steel tempered bar includes: raw material preparation—molten iron, scrap steel, alloys, etc. (control of the five harmful elements); 50t electric furnace smelting + LF + VD (control of inclusions and gas content); die casting (control of microstructure uniformity); annealing / hot-steaming; heating; forging / rolling (control of material grain size and density); annealing; straightening (preparation for straightness before tempering); tempering (quenching → primary tempering → (straightening) → stress relief tempering); physical and chemical testing; surface finishing; flaw detection; surface inspection; inspection and assessment; and packaging and warehousing. Tempering and quenching can only be performed using air or oil cooling. These methods have numerous drawbacks. Regarding the application of water-cooled materials, the prior art lacks any detailed reference for water-cooling process parameters, and there is no data demonstrating that water-cooled materials meet NACE MR0175 requirements.

[0034] In view of this, the present invention is proposed. However, during the research and development process, the inventors found that water cooling has the following control difficulties:

[0035] 1. Distortion and cracking:

[0036] Steel maintains a fast cooling rate in water, which may cause large internal stress in the bar during quenching, leading to deformation or cracking. Such deformation and cracking not only affect the appearance quality of the workpiece, but also may reduce its mechanical properties and service life.

[0037] 2. Steam film influence:

[0038] When a bar is immersed in water, a vapor film forms on its surface. This vapor film hinders heat transfer from the workpiece to the water, slowing cooling. If the vapor film phase is too long, it can lead to uneven hardness and stress distribution in the workpiece, causing cracks or soft spots.

[0039] 3. Impact on water quality:

[0040] Water's temperature, purity, and impurities all affect its cooling capacity. For example, rising water temperature leads to a sharp drop in cooling capacity; insoluble impurities, oils, and soaps can also significantly reduce cooling capacity. Furthermore, water quality strongly influences boiling heat transfer characteristics, an effect that carries significant uncertainty and is difficult to quantify.

[0041] 4. Cooling speed is difficult to control:

[0042] During the quenching water cooling process, the cooling rate is affected by many factors, such as water temperature, water flow rate, workpiece shape and size, etc. These factors make it difficult to accurately control the cooling rate, thus affecting the quenching effect.

[0043] Therefore, the following technical solutions were finally adopted:

[0044] In a first aspect, a water quenching heat treatment method for UNS S41427 stainless steel 95KSI grade quenched and tempered bars for oil and gas use comprises: placing the austenitized UNS S41427 stainless steel bars in continuously flowing cooling water for immersion quenching, and performing primary and secondary tempering after reaching the water outlet temperature; wherein the temperature of the cooling water is lower than 38°C.

[0045] The water quenching heat treatment method of the UNS S41427 stainless steel bar of the present invention uses water as a medium for immersion quenching. When the cooling water continuously flows through the surface of the bar to continuously exchange heat and remove heat, the cooling water temperature in the quenching tank is controlled to be lower than 38° C., thereby ensuring that the bar has the same performance as the material obtained by air cooling or oil cooling. While overcoming many disadvantages of air cooling or oil cooling, it also overcomes the four difficulties of water cooling mentioned above, ensuring that the material obtained by water quenching does not suffer from stress cracking or grain boundary cracking of the structure, reaches a strength grade of 95 KSI, passes the SSC evaluation, and meets the application requirements of NACE MR0175. Specifically, under normal circumstances, the bar temperature is high, and the cooling water in contact with the bar will inevitably boil, forming a steam film on the bar surface. However, if the cooling water continues to flow, it can quickly exchange heat with the bar and / or boiling water, quickly transfer heat, and reduce the water temperature after heat exchange. After extensive research, the inventors found that by controlling the water temperature in the quenching tank to no more than 38°C, that is, by controlling the cooling water flow rate based on the size of the quenching tank and the size of the bar, etc., the water boiling can be avoided, and the bar can be cooled stably and evenly from the outside to the inside, ensuring stable material transformation, without residual austenite, stress cracking, or grain boundary cracking. In addition, immersion quenching can process large quantities of steel bars, avoiding spray quenching, which can only process single bars or small quantities of bars. During spray quenching, the steel bars must be rotated to ensure uniform contact with the water, and the presence of air contact with the steel bars may affect cooling. Therefore, as an optional embodiment of the present invention, the temperature of the cooling water can typically but not limitatively be selected as 37°C, 35°C, 30°C, 25°C, 20°C, 15°C, 10°C, 5°C, etc.

[0046] In the present 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 recycled water. Inexpensive industrial water is preferred for low production costs. Cooling water can generally be used directly at room temperature to begin water-cooled quenching, without the need for specialized cooling or heating treatment. As long as the water is continuously flowing throughout the quenching process and the water temperature is maintained below 38°C after contact and heat exchange with the bar, stable material transformation and the absence of retained austenite are ensured.

[0047] As an optional embodiment of the water quenching heat treatment method of the present invention, the cooling water is circulated as circulating water during water-cooled quenching; further, the circulating water is used for water-cooled quenching after impurities are removed, and further, the impurity removal includes removing impurities such as oil, oxide scale, and suspended solids.

[0048] In the above technical solution, cooling water is recycled as circulating water during water-cooled quenching, which not only ensures that the cooling water is in a continuous flow state during water-cooled quenching, but also saves water. However, the circulating water should be clean water. Before using the circulating water for water-cooled quenching, it is important to filter and clean it to remove impurities such as oil, scale, suspended solids, etc., because the presence of these impurities can seriously affect the cooling effect of the circulating water and may even cause equipment blockage and damage. Therefore, filtering and cleaning the circulating water and removing impurities can ensure clean water quality, extend the service life of equipment, and improve production efficiency.

[0049] As an optional embodiment of the water quenching heat treatment method of the present invention, the austenitizing temperature is 900-980°C (such as 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 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, mm.

[0050] In the present invention, UNS S41427 stainless steel bars are austenitized at a temperature of 900-980°C and held for a predetermined time before water-quenching. The austenitized bars can be directly water-quenched, i.e., placed in water at a furnace temperature of 900-980°C for water cooling. However, in actual operation, the bars need to undergo a certain period of time and space transfer after being removed from the furnace, so the surface of the bars is affected by the environment and the temperature drops. Furthermore, the surface of the bars actually has an oxide scale. Therefore, the water inlet temperature of the bars can be controlled based on the oxide scale temperature or the time from the time of removal from the furnace to the time of complete water inlet. The latter is preferred and is more convenient for on-site operation in actual production. Optionally, the water inlet temperature of the UNS S41427 stainless steel bar is ≥ 850°C. Furthermore, the water inlet is completed within 2 minutes after the UNS S41427 stainless steel bar emerges from the austenitizing furnace. Furthermore, the water inlet is completed within 1 minute after the UNS S41427 stainless steel bar emerges from the austenitizing furnace to ensure stable material properties. Preferably, the water inlet temperature is controlled by controlling the water inlet time to facilitate on-site operation in actual production. During on-site operation, workers only need to be instructed to complete water inlet within one or two minutes. Therefore, in the present invention, the water inlet temperature of the UNS S41427 stainless steel bar can be typically but not limited to 850° C., 870° C., 890° C., 910° C., 930° C., 950° C., 970° C., etc., and / or the UNS S41427 stainless steel bar is filled with water within 110s, 100s, 90s, 80s, 70s, 60s, 50s, 40s, 30s, 25s, 20s, 15s, 10s, 0s, etc. after being taken out of the austenitizing furnace.

[0051] As an optional embodiment of the water quenching heat treatment method of the present invention, the water flow rate of the cooling water is ≥250m 3 / h(such as 300m 3 / h、400m 3 / h、500m 3 / h、600m 3 / h、700m 3 / h、800m 3 / h、900m 3 / h, etc.).

[0052] In the above technical solution, by controlling the cooling water flow rate ≥ 250m 3 / h, which can not only ensure that the cooling water temperature does not exceed 38°C and avoid water boiling, but also ensure that the cooling process of the rod from the inside to the outside is uniform, and realize the precise control of the cooling rate of the rod during the water cooling process, and avoid stress cracking or grain boundary cracking of the structure; but also can take away the steam film in time to reduce the impact of the steam film. In the present invention, there is no special upper limit requirement for the water flow rate of the cooling water, and it can be selected according to the flow rate upper limit of the existing equipment to avoid the water pressure from acting on the rod. For example, the water flow rate of the cooling water can be 250 to 1000m 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 does not exceed 38°C.

[0053] As an optional embodiment of the water quenching heat treatment method of the present invention, the outlet water temperature of the UNS S41427 stainless steel bar is ≥ room temperature; further, the outlet water temperature of the UNS S41427 stainless steel bar is ≤150°C (such as 150°C, 140°C, 130°C, 120°C, 110°C, 100°C, 90°C, 80°C, 70°C, 60°C, 50°C, 40°C, 30°C, 20°C, etc.).

[0054] In the above technical solution, the outlet water temperature is further controlled to ensure that the material is fully quenched while meeting performance requirements and preventing cracking. The outlet water temperature in this invention refers to the outlet water temperature of the steel bar, reflecting the surface temperature of the steel bar. The temperature at the core of the steel bar is higher than the surface temperature because it is only affected by heat conduction.

[0055] As an optional embodiment of the water quenching heat treatment method of the present invention, the primary tempering holding temperature is 600-650°C (such as 610°C, 620°C, 630°C, 640°C, etc.), 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, air cooling is performed after the primary tempering to release quenching stress.

[0056] As an optional embodiment of the water quenching heat treatment method of the present invention, the secondary tempering holding temperature is 540-620°C (such as 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, etc.), preferably 30-50°C (such as 35°C, 40°C, 45°C, etc.) 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, straightening is performed before the secondary tempering to remove bar deformation caused by water quenching, and air cooling is performed after holding in the secondary tempering to release straightening stress.

[0057] As an optional embodiment of the water quenching heat treatment method of the present invention, the UNS S41427 stainless steel bar is obtained by sequentially performing primary refining, refining, vacuum degassing, die casting, hot-rolling, heating, rolling, annealing or hot-rolling on the raw materials according to the chemical composition of UNS S41427 stainless steel for oil and gas.

[0058] As an optional embodiment of the water quenching heat treatment method of the present invention, the specification of the UNS S41427 stainless steel bar is round steel with a diameter of Φ12-310 mm (such as 15 mm, 50 mm, 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, etc.).

[0059] In a second aspect, a UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas use is produced by the water quenching heat treatment method described in the first aspect;

[0060] The UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas comprises the following chemical components 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%, and the remainder is Fe and unavoidable impurities; further, the UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas comprises the following chemical components 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<0.005%, V 0.01-0.50%, the rest is Fe and inevitable impurities.

[0061] In a third aspect, a completion tool is made of the UNSS41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas prepared by the water quenching heat treatment method described in the first aspect or the UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas described in the second aspect.

[0062] The specific embodiments of the present invention will be further explained below in conjunction with Examples and Comparative Examples:

[0063] Example 1

[0064] This embodiment provides a UNS S41427 steel suitable for the oil and gas field, with a production specification of 95KSI steel grade and Φ120mm round steel. The main chemical components of the steel and their contents (wt%) are: C: 0.01%, Si: 0.24%, Mn: 0.40%, P: 0.018%, S: 0.001%, Cr: 12.00%, Ni: 5.4%, Mo: 1.9%, V: 0.13%, Ti: <0.005%, and the rest is Fe and unavoidable impurities.

[0065] Specifically, the method for manufacturing UNS S41427 steel produced in this embodiment includes the following steps:

[0066] S1. Preparation of steel billets: The raw materials are sequentially subjected to electric furnace smelting, LF refining + VD vacuum degassing, die casting, hot rolling, heating, and rolling to obtain UNS S41427 rolled round steel; wherein the final rolling temperature is 935°C;

[0067] S2, Annealing: After the material cools to room temperature, it is put into the furnace for annealing. The annealing temperature is set at 640℃. After keeping the temperature for 11 hours, it is taken out of the furnace and air-cooled to eliminate rolling stress.

[0068] S3, finishing: In order to prevent water quenching cracking, the material is finished and flaw detection is carried out, and the defects and cracks in the rolling process are repaired and ground away. After the flaw detection is qualified, it is transferred to the heat treatment line;

[0069] S4, the material is austenitized, the austenite temperature is set to 960 ° C, kept at this temperature for 3 hours, and then taken out of the furnace for quenching;

[0070] S5, water-cooled quenching: open the circulating water, use industrial water to circulate continuously in the quenching tank to water-cool the steel bars. Before using the circulating water, ensure that it is filtered and cleaned to remove impurities such as oil, oxide scale, and suspended solids. The time from the steel bar leaving the furnace to the water inlet is 35s, and the circulating water flow rate is 300m 3 / h; circulating water temperature before entering the water is 21℃, circulating water temperature after leaving the water is 25℃, and the surface temperature of the steel outlet is 120℃;

[0071] S6, primary tempering: the tempering holding temperature is set to 620℃, the holding time is 6h, and after holding, the furnace is taken out of the furnace and air-cooled to complete the primary tempering;

[0072] S7, straightening;

[0073] S8. Secondary tempering: The tempering holding temperature is set at 590°C for 6 hours. After holding, the steel is taken out of the furnace and air-cooled to complete the tempering. UNS S4142795KSI steel is obtained.

[0074] Example 2

[0075] This embodiment provides a UNS S41427 steel suitable for the oil and gas field, with a production specification of 95KSI steel grade and Φ270mm round steel. The main chemical components of the steel and their contents (wt%) are: C: 0.01%, Si: 0.26%, Mn: 0.39%, P: 0.017%, S: 0.001%, Cr: 12.10%, Ni: 5.6%, Mo: 2.1%, V: 0.12%, Ti: <0.005%, and the rest is Fe and unavoidable impurities.

[0076] Specifically, the method for manufacturing UNS S41427 steel produced in this embodiment includes the following steps:

[0077] S1. Preparation of steel billets: The raw materials are sequentially subjected to electric furnace smelting, LF refining outside the furnace + VD vacuum degassing, die casting, hot-melting, heating, and forging to obtain UNS S41427 forged round steel; wherein the final forging temperature is 902°C;

[0078] S2, Annealing: After the material cools to room temperature, it is put into the furnace for annealing. The annealing temperature is set at 630℃. After keeping the temperature for 23 hours, it is taken out of the furnace and air-cooled to eliminate rolling stress.

[0079] S3, finishing: In order to prevent water quenching cracking, the material is finished and flaw detection is carried out, and the defects and cracks in the forging process are ground away. After the flaw detection is qualified, it is transferred to the heat treatment line;

[0080] S4, the material is austenitized, the austenite temperature is set to 970 ° C, after keeping it at this temperature for 6 hours, it is taken out of the furnace for quenching;

[0081] S5, water-cooled quenching: open the circulating water, use industrial water to circulate continuously in the quenching tank to water-cool the steel bars. Before using the circulating water, ensure that it is filtered and cleaned to remove impurities such as oil, oxide scale, and suspended solids. The time from the steel bar leaving the furnace to the water inlet is 35s, and the circulating water flow rate is 300m 3 / h; circulating water temperature before entering the water is 15℃, circulating water temperature after leaving the water is 22℃, and the surface temperature of the steel outlet is 96℃;

[0082] S6. Primary tempering: The tempering holding temperature is set to 610℃ and the holding time is 12h. After holding, the furnace is taken out of the furnace and air-cooled to complete the primary tempering.

[0083] S7, straightening;

[0084] S8. Secondary tempering: The tempering holding temperature is set at 575°C for 12 hours. After holding, the steel is taken out of the furnace and air-cooled to complete the tempering. UNS S4142795KSI steel is obtained.

[0085] Comparative Example 1

[0086] This embodiment provides a UNS S41427 steel suitable for the oil and gas field, with a production specification of 95KSI steel grade and Φ270mm round steel. The main chemical components of the steel and their contents (wt%) are: C: 0.01%, Si: 0.26%, Mn: 0.39%, P: 0.017%, S: 0.001%, Cr: 12.10%, Ni: 5.6%, Mo: 2.1%, V: 0.12%, Ti: <0.005%, and the rest is Fe and unavoidable impurities.

[0087] Specifically, the method for manufacturing UNS S41427 steel produced in this embodiment includes the following steps:

[0088] S1. Preparation of steel billets: The raw materials are sequentially subjected to electric furnace smelting, LF refining outside the furnace + VD vacuum degassing, die casting, hot-melting, heating, and forging to obtain UNS S41427 forged round steel; wherein the final forging temperature is 902°C;

[0089] S2, Annealing: After the material cools to room temperature, it is put into the furnace for annealing. The annealing temperature is set at 630℃. After keeping the temperature for 23 hours, it is taken out of the furnace and air-cooled to eliminate rolling stress.

[0090] S3, finishing: In order to prevent water quenching cracking, the material is finished and flaw detection is carried out, and the defects and cracks in the forging process are ground away. After the flaw detection is qualified, it is transferred to the heat treatment line;

[0091] S4, the material is austenitized, the austenite temperature is set to 970 ° C, after keeping it at this temperature for 6 hours, it is taken out of the furnace for quenching;

[0092] S5. Water-cooled quenching: Without circulating water, the steel bars are directly quenched using industrial water from the quenching tank. The industrial water in the quenching tank must be filtered and cleaned to remove impurities such as oil, scale, and suspended solids before use. The time from the steel bar leaving the furnace to entering the water is 115 seconds. The water temperature before entering the water is 25°C, the water temperature after leaving the water is 57°C, and the surface temperature of the steel bar exiting the water is 146°C.

[0093] S6. Primary tempering: The tempering holding temperature is set to 610℃ and the holding time is 12h. After holding, the furnace is taken out of the furnace and air-cooled to complete the primary tempering.

[0094] S7, straightening;

[0095] S8. Secondary tempering: The tempering holding temperature is set at 575°C for 12 hours. After holding, the steel is taken out of the furnace and air-cooled to complete the tempering. UNS S4142795KSI steel is obtained.

[0096] Performance Testing

[0097] 1. With reference to API 6A standard, mechanical properties of samples taken at 1 / 2R of UNS S4142795KSI steel obtained in Example 1 and Example 2 were tested. The results are shown in the following table:

[0098]

[0099] As can be seen from the table above, the UNS S41427 steel obtained by water quenching heat treatment of the present invention can reach a strength level of 95KSI. The grain size of the UNS S4142795KSI steel obtained in Example 1 is as follows: Figure 1 As shown in the figure, it can be seen that the grain size level is 5, the grains are uniform, and no defects are seen. The grain size of the UNS S4142795KSI steel obtained in Example 2 is as follows Figure 2 As shown in the figure, it can be seen that the grain size level is 5, the grains are uniform, and no defects are seen.

[0100] 2. According to the requirements of NACE0175, the UNS S4142795KSI steel obtained in Examples 1 and 2 was subjected to SSC test (test temperature 22°C to 24°C, H2S partial pressure 0.01 bar, total pressure 1 bar, CO2 balance gas, Cl - :140000 mg / L, Buffer for balancing pH value: 0.82 g / LCH3COONa+CH3COOH, pH 4.50, loading according to 90% of the actual yield strength), the test results show that after 720h, the macroscopic surface of the sample of Example 1 (such as Figure 3 As shown) and the sample 10X field of view surface (as shown Figure 5 No cracks were generated on the specimens, and the specimens were qualified. The macroscopic surface of the specimens in Example 2 (as shown) Figure 4 As shown) and the sample 10X field of view surface (as shown Figure 6 As shown in the figure, no cracks were generated and the samples were qualified. It can be seen that the UNS S41427 controlled by water quenching according to the present invention passed the inspection requirements.

[0101] In summary, it can be seen that the UNS S4142795KSI steel obtained by the water quenching process of the present invention meets the requirements of international standards, and its performance and microstructure meet the requirements for use of completion tools.

[0102] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A water quenching heat treatment method for UNS S41427 stainless steel 95KSI grade quenched and tempered bars for oil and gas, characterized in that: include: The austenitized UNS S41427 stainless steel bar is placed in continuously flowing cooling water for immersion quenching, and is subjected to primary and secondary tempering after reaching the water outlet temperature; wherein the temperature of the cooling water is lower than 38°C.

2. The water quenching heat treatment method according to claim 1, characterized in that: The austenitizing temperature is 900-980° C., and the austenitizing holding time is: (2h / 100mm*D)-(2h / 100mm*D+5h), where h represents hours, and D represents the diameter of the UNSS41427 stainless steel bar in the black skin state, in mm; and / or, the water inlet temperature of the UNS S41427 stainless steel bar is ≥850°C; And / or, the UNS S41427 stainless steel bar is filled with water within 2 minutes after being taken out of the austenitizing furnace; and / or, the outlet water temperature of the UNS S41427 stainless steel bar is ≥ room temperature; And / or, the cooling water flow rate is ≥250m 3 / h.

3. The water quenching heat treatment method according to claim 2, characterized in that: The UNS S41427 stainless steel bar is filled with water within 1 minute after being taken out of the austenitizing furnace; And / or, the outlet water temperature of the UNS S41427 stainless steel bar is ≤150°C.

4. The water quenching heat treatment method according to claim 1, characterized in that: The cooling water is used as circulating water during water-cooling quenching.

5. The water quenching heat treatment method according to claim 4, characterized in that: The circulating water is used for water-cooling quenching after impurities are removed, and the impurity removal includes removing oil stains, oxide scales, and suspended solid impurities.

6. The water quenching heat treatment method according to claim 1, characterized in that: The holding temperature of the primary tempering is 600-650° C., and the holding time is (4h / 100mm*D)-(4h / 100mm*D+5h), wherein h represents hours, and D represents the diameter of the UNS S41427 stainless steel bar in the black skin state, in mm; and / or, air cooling is performed after the holding in the primary tempering to release quenching stress.

7. The water quenching heat treatment method according to claim 1, characterized in that: The holding temperature of the secondary tempering is 540-620° C., which is 30-50° C. lower than the holding temperature of the primary tempering, and the holding time is (4 h / 100 mm*D)-(4 h / 100 mm*D+5 h), 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, straightening is performed before the secondary tempering to remove bar deformation caused by water quenching, and air cooling is performed after holding in the secondary tempering to release straightening stress.

8. The water quenching heat treatment method according to claim 1, characterized in that: The UNS S41427 stainless steel bar is obtained by sequentially performing primary refining, refining, vacuum degassing, die casting, hot-melting, heating, rolling, annealing or hot-melting on the raw materials according to the chemical composition of UNS S41427 stainless steel for oil and gas; And / or, the specification of the UNS S41427 stainless steel bar is round steel with a diameter of Φ12 to 310 mm.

9. A UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas, characterized by: Prepared by the water quenching heat treatment method according to any one of claims 1 to 8; The UNS S41427 stainless steel 95KSI grade quenched and tempered bar for oil and gas includes the following chemical components 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%, and the remainder is Fe and unavoidable impurities.

10. A completion tool, characterized in that: The oil and gas UNS S41427 stainless steel 95KSI grade quenched and tempered bar is made by the water quenching heat treatment method according to any one of claims 1 to 8, or the oil and gas UNS S41427 stainless steel 95KSI grade quenched and tempered bar according to claim 9.

Images