9cr stainless steel quenched and tempered material for oil gas, and manufacturing method therefor and use thereof

Abstract

The present invention relates to the technical field of online heat treatments for 9Cr steel. Provided are a 9Cr stainless steel quenched and tempered material for oil gas, and a manufacturing method therefor and the use thereof. According to the 9Cr stainless steel quenched and tempered material for oil gas and the manufacturing method therefor, a quenched martensite is directly obtained from 9Cr steel mainly by controlling the finish rolling temperature and the rapid cooling method of the 9Cr steel; the quenching step in a traditional process is omitted, thereby shortening the period by 1-3 days; and a step of two instances of tempering consisting of a one-instance tempering treatment and a stress relief tempering treatment are used to replace annealing, straightening after annealing, scaling and chamfering in traditional steps, thereby greatly shortening the production period and reducing the production cost. Compared with a 9Cr stainless steel quenched and tempered material prepared by means of a traditional process, the 9Cr stainless steel quenched and tempered material prepared by means of the preparation method of the present invention has an equivalent grain size, hardness, tensile property and impact property.

Description

9Cr stainless steel quenched and tempered material for oil and gas, its manufacturing method and application Technical Field

[0001] The present invention relates to the technical field of 9Cr steel online heat treatment, and in particular to a 9Cr stainless steel quenched and tempered material for oil and gas, and a manufacturing method and application thereof. Background Art

[0002] As the global energy market continues to grow and develop, the oil and gas industry's demand for high-performance materials continues to increase. Stainless steel, with its excellent corrosion resistance and high-temperature performance, is widely used in the oil and gas industry. While there are numerous types of stainless steel used in oil and gas applications, 9Cr stainless steel, with its corrosion resistance, high-temperature resistance, and high-impact properties, has become a key steel material used in oil and gas production.

[0003] At present, the existing production process of 9Cr stainless steel tempered materials for oil and gas is: preparation of raw materials (molten iron, scrap steel, alloy, etc.), electric furnace smelting + refining outside the furnace + vacuum degassing (inclusion control, gas content control), continuous casting / mold casting (organization uniformity control), annealing / hot feeding, heating, rolling (material grain size and density control), annealing, straightening (flatness preparation before tempering), peeling, chamfering (quenching and crack prevention preparation before tempering), tempering (specifically including quenching → primary tempering → (straightening) → stress relief tempering), physical and chemical testing, surface polishing, flaw detection, surface inspection, inspection and judgment, packaging and warehousing.

[0004] The above-mentioned technology has a long production process and a delivery cycle of generally two to three months, which makes it difficult to meet user needs. In addition, the production cost is high, resulting in high selling prices and lack of market competitiveness. Therefore, there is an urgent need to improve the production process to reduce costs and increase efficiency.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The present invention aims to provide a 9Cr stainless steel quenched and tempered material suitable for the oil and gas field and a manufacturing method thereof. The manufacturing method of the 9Cr stainless steel quenched and tempered material breaks the traditional production process, shortens the production cycle and also reduces production costs. The performance and grain size of the 9Cr stainless steel quenched and tempered material produced by this manufacturing method are basically equivalent to those of the traditional process.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A first object of the present invention is to provide a method for manufacturing a 9Cr stainless steel quenched and tempered material for oil and gas, comprising the following steps:

[0009] S1. According to the chemical composition of the 9Cr stainless steel quenched and tempered material for oil and gas, the raw materials are subjected to primary refining, refining, vacuum degassing, continuous casting or die casting, annealing or hot rolling, heating and rolling to obtain 9Cr steel; wherein the final rolling temperature is ≥850℃;

[0010] S2. The 9Cr steel is rapidly cooled to transform its structure into quenched martensite, and then directly subjected to a tempering treatment;

[0011] S3. The steel after the primary tempering treatment is straightened and then subjected to stress relief tempering treatment to obtain 9Cr stainless steel quenched and tempered material for oil and gas.

[0012] Furthermore, based on the above technical solution of the present invention, in step S1, the final rolling temperature is ≥900°C.

[0013] Furthermore, based on the above technical solution of the present invention, in step S2, the cooling rate of the 9Cr steel during rapid cooling is ≥300°C / h;

[0014] And / or, in step S2, the 9Cr steel is rapidly cooled to below 150°C.

[0015] Furthermore, based on the above technical solution of the present invention, in step S2, the 9Cr steel is rapidly cooled to below 150°C at a cooling rate of ≥300°C / h, and tempered within 48 hours;

[0016] And / or, in step S2, the rapid cooling method includes air cooling, wind cooling or water cooling.

[0017] Furthermore, based on the above technical solution of the present invention, in step S2, the tempering temperature of the primary tempering treatment is 550-750°C, and the primary tempering holding time is (4H / 100mm*D)-(4H / 100mm*D+6H), where H represents hours and D represents the diameter of the 9Cr steel, mm;

[0018] And / or, in step S2, the heating rate of the primary tempering treatment to the tempering temperature is ≤80°C / h;

[0019] And / or, in step S2, the cooling method of the primary tempering treatment is air cooling after leaving the furnace.

[0020] Furthermore, based on the above technical solution of the present invention, in step S2, for the 80KSI 9Cr stainless steel quenched and tempered material, the tempering temperature of the first tempering treatment is 650-750°C;

[0021] And / or, in step S2, for 100KSI 9Cr stainless steel quenched and tempered material, the tempering temperature of the first tempering treatment is 565-650°C;

[0022] And / or, in step S2, for the 9Cr stainless steel quenched and tempered material with a temperature of 110 KSI, the tempering temperature of the first tempering treatment is 565-620°C.

[0023] Furthermore, based on the above technical solution of the present invention, in step S3, the tempering temperature of the stress relief tempering treatment is 20-60°C lower than the tempering temperature of the primary tempering treatment, and the stress relief tempering holding time is (4H / 100mm*D) to (4H / 100mm*D+5H), where H represents hours and D represents the diameter of the steel, in mm;

[0024] And / or, in step S3, the heating rate of heating to the tempering temperature during the stress relief tempering treatment is ≤80°C / h;

[0025] And / or, in step S3, the stress relief tempering treatment is cooled in air after leaving the furnace.

[0026] A second object of the present invention is to provide a 9Cr stainless steel quenched and tempered material for oil and gas, which is produced by the above-mentioned method for producing a 9Cr stainless steel quenched and tempered material for oil and gas;

[0027] The 9Cr stainless steel quenched and tempered material for oil and gas includes the following chemical components in mass fraction: C: ≤0.15%, Si: ≤1.00%, Mn: 0.30-0.60%, P: ≤0.020%, S: ≤0.010%, Cr: 8.00-10.00%, Ni: ≤0.50%, Mo: 0.90-1.10%, and the rest is Fe and unavoidable impurities.

[0028] Furthermore, based on the above technical solution of the present invention, the 9Cr stainless steel quenched and tempered material for oil and gas includes the following chemical components by mass fraction: C: 0.09-0.15%, Si: ≤1.00%, Mn: 0.30-0.60%, P: ≤0.015%, S: ≤0.004%, Cr: 8.50-9.50%, Ni: ≤0.45%, Mo: 0.90-1.05%, and the rest is Fe and unavoidable impurities.

[0029] The third object of the present invention is to provide a pipe fitting for oil and gas wells, which is made of the 9Cr stainless steel quenched and tempered material for oil and gas produced by the above-mentioned manufacturing method or the above-mentioned 9Cr stainless steel quenched and tempered material for oil and gas.

[0030] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0031] (1) The manufacturing method of 9Cr stainless steel quenched and tempered material for oil and gas provided by the present invention breaks the traditional process. By adjusting or omitting some processes, the production cycle is shortened and the production cost (including annealing, quenching and other costs) is reduced. The grain size and tensile, impact and hardness properties of the 9Cr stainless steel quenched and tempered material manufactured by this manufacturing method do not change significantly compared with those of the traditional process, effectively ensuring product quality.

[0032] (2) The present invention provides a 9Cr stainless steel quenched and tempered material for oil and gas, which is produced by the above-mentioned manufacturing method of the 9Cr stainless steel quenched and tempered material for oil and gas. The 9Cr stainless steel quenched and tempered material has a grain size that is substantially the same as that of the 9Cr stainless steel quenched and tempered material produced by the conventional process, and has excellent tensile, impact and hardness properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0034] FIG1 is a metallographic image of a quenched and tempered 80KSI grade 9Cr stainless steel material prepared in Example 1;

[0035] FIG2 is a metallographic image of a 110KSI grade 9Cr stainless steel quenched and tempered material prepared in Example 2;

[0036] FIG3 is a metallographic image of a quenched and tempered 80KSI grade 9Cr stainless steel material prepared in Comparative Example 1;

[0037] FIG4 is a metallographic image of the 110KSI grade 9Cr stainless steel quenched and tempered material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0038] 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 in accordance with conventional conditions.

[0039] The endpoints of the ranges and any values ​​disclosed herein 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0040] The existing production process for 9Cr quenched and tempered stainless steel for oil and gas applications involves sequentially refining, vacuum degassing, continuous casting or die casting, annealing or hot-rolling, heating, and rolling. The raw materials are then annealed, straightened, peeled, and chamfered. Tempering, which includes quenching, primary tempering, straightening, and stress-relief tempering, results in 9Cr quenched and tempered stainless steel. This production method results in a production cycle of two to three months for 9Cr quenched and tempered stainless steel for oil and gas applications, resulting in long production cycles, low production efficiency, and high production costs. Furthermore, this method cannot meet the needs of downstream customers who urgently need steel products in a short period of time. Therefore, the present invention was developed.

[0041] According to a first aspect of the present invention, there is provided a method for manufacturing a 9Cr stainless steel quenched and tempered material for oil and gas, comprising the following steps:

[0042] S1. According to the chemical composition of the 9Cr stainless steel quenched and tempered material for oil and gas, the raw materials are subjected to primary refining, refining, continuous casting or die casting, annealing or hot-rolling, heating and rolling in sequence to obtain 9Cr steel; wherein the final rolling temperature is ≥850℃;

[0043] S2. The 9Cr steel is rapidly cooled to transform its structure into quenched martensite and then directly subjected to a tempering treatment;

[0044] S3. The steel after the primary tempering treatment is straightened and then subjected to stress relief tempering treatment to obtain 9Cr stainless steel quenched and tempered material for oil and gas.

[0045] Specifically, the process of preparing 9Cr steel from raw materials in step S1 of the present invention is substantially the same as that of the existing production method, and the final rolling temperature in step S1 is mainly controlled to be ≥850°C.

[0046] Step S2 and step S3 of the present invention are different from the traditional process. They mainly control the final rolling temperature and rapid cooling method of the 9Cr steel so that the 9Cr steel directly obtains quenched martensite, thereby eliminating the quenching step in the original process (shortening the cycle by 1-3 days). In addition, two tempering steps (one tempering treatment and a stress relief tempering treatment) are used to replace the annealing (shortening the cycle by 4-7 days), (after annealing) straightening (shortening the cycle by 1-3 days), and peeling and chamfering (shortening the cycle by 1-3 days) in the traditional process, thereby greatly shortening the production cycle and reducing production costs.

[0047] It should be noted that if the final rolling temperature is lower than 850°C, the grain size and impact properties of the material will decrease. If the 9Cr steel cannot be cooled quickly, it will easily lead to incomplete structural transformation of the steel and the precipitation of brittle phases.

[0048] At the same time, the tensile strength, impact resistance and hardness of the 9Cr stainless steel quenched and tempered material for oil and gas prepared by the preparation method of the present invention are basically unaffected, and the performance is comparable to that of the 9Cr stainless steel quenched and tempered material for oil and gas produced by traditional processes.

[0049] As an optional embodiment of the present invention, in step S1, the types of raw materials can be conventional raw materials, such as molten iron, scrap steel, alloy, etc.

[0050] As an optional embodiment of the present invention, in step S1, primary refining is performed using an electric furnace, refining is performed using LF refining, and then vacuum degassing is performed. The inclusion content and gas content are controlled through primary refining, LF refining, and vacuum degassing.

[0051] As an optional embodiment of the present invention, in step S1, continuous casting or mold casting is used to achieve control of tissue uniformity.

[0052] Rolling can achieve control of the grain size and density of the material. As an optional embodiment of the present invention, in step S1, the final rolling temperature is ≥900°C, preferably 900-980°C, and typically but not limited to 900°C, 920°C, 940°C, 950°C, 960°C or 980°C.

[0053] As an optional embodiment of the present invention, in step S2, the cooling rate of the 9Cr steel during rapid cooling is ≥300°C / h, preferably ≥400°C / h; typical but non-limiting cooling rates are 300°C / h, 400°C / h, 500°C / h, 600°C / h, 800°C / h, 1000°C / h, 1200°C / h, 1400°C / h, 1500°C / h, 1600°C / h, 1700°C / h or 1800°C / h, etc.

[0054] As an optional embodiment of the present invention, rapid cooling is performed to below 150°C, such as 145°C, 140°C, 130°C, 120°C, 110°C, 100°C, 90°C or 80°C.

[0055] As an optional embodiment of the present invention, in step S2, the 9Cr steel is rapidly cooled to below 150°C at a cooling rate of ≥300°C / h, and is tempered within 48 hours.

[0056] By limiting the specific process parameters of the rapid cooling process and the interval between rapid cooling and the first tempering treatment, it can be ensured that the structure is fully transformed into quenched martensite.

[0057] As an optional embodiment of the present invention, the rapid cooling method includes any one of air cooling, wind cooling or water cooling.

[0058] As an optional embodiment of the present invention, in step S2, the tempering temperature of the primary tempering treatment is 550-750°C, for example, 550°C, 565°C, 580°C, 600°C, 620°C, 640°C, 650°C, 660°C, 680°C, 700°C, 720°C, 740°C or 750°C.

[0059] Different grades of steel use different tempering temperatures. As an optional embodiment of the present invention, in step S2, for 80KSI 9Cr stainless steel quenched and tempered material, the tempering temperature of the first tempering treatment is 650-750℃;

[0060] For 100KSI 9Cr stainless steel quenched and tempered material, the tempering temperature of the first tempering treatment is 565-650℃;

[0061] For 110KSI 9Cr stainless steel quenched and tempered material, the tempering temperature of the first tempering treatment is 565-620℃.

[0062] As an optional embodiment of the present invention, in step S2, the heating rate of heating to the tempering temperature during the first tempering treatment is ≤80°C / h.

[0063] Since the temperature rises from the surface to the core of steel primarily through heat conduction, if the temperature rises too quickly, the surface will reach warm temperature, but the core will take a long time to reach warm temperature. This phenomenon is more pronounced with larger steel sizes. Therefore, based on production experience, the heating rate is limited to no more than 80°C / h. However, the heating rate cannot be infinitely low, otherwise it will affect production time and cost. Generally speaking, the heating rate is 50-80°C / h.

[0064] As an optional embodiment of the present invention, the tempering holding time for a single tempering treatment is (4H / 100mm*D) to (4H / 100mm*D+6H), where H represents hours and D represents the diameter (outer diameter) of the 9Cr steel, in mm. For example, when the diameter of the 9Cr steel is 100mm, according to the above formula, the tempering holding time is 4 to 10 hours. When the diameter of the 9Cr steel is 200mm, the tempering holding time is 8 to 14 hours, and so on.

[0065] As an optional embodiment of the present invention, in step S2, the cooling method of the primary tempering treatment is air cooling after leaving the furnace.

[0066] Too high a tempering temperature for stress relief tempering may change the properties of the material, while too low a tempering temperature for stress relief tempering may not achieve the stress relief effect. As an optional embodiment of the present invention, in step S3, the tempering temperature for stress relief tempering is 20-60°C lower than the tempering temperature for the primary tempering treatment.

[0067] As an optional embodiment of the present invention, in step S3, the heating rate of heating to the tempering temperature during the stress relief tempering treatment is ≤80°C / h.

[0068] As an optional embodiment of the present invention, in step S3, the stress relief tempering holding time is (4H / 100mm*D) to (4H / 100mm*D+5H), where H represents hours and D represents the diameter (outer diameter) of the steel, in mm. For example, when the diameter of the 9Cr steel is 100mm, according to the above formula, the tempering holding time is 4 to 9 hours. When the diameter of the 9Cr steel is 200mm, the tempering holding time is 8 to 13 hours, and so on.

[0069] As an optional embodiment of the present invention, in step S3, the cooling method for the stress relief tempering treatment is air cooling after leaving the furnace.

[0070] According to a second aspect of the present invention, there is also provided a 9Cr stainless steel quenched and tempered material for oil and gas, which is produced by the above-mentioned method for producing the 9Cr stainless steel quenched and tempered material for oil and gas;

[0071] The 9Cr stainless steel quenched and tempered material for oil and gas includes the following chemical components in mass fraction: C: ≤0.15%, Si: ≤1.00%, Mn: 0.30-0.60%, P: ≤0.020%, S: ≤0.010%, Cr: 8.00-10.00%, Ni: ≤0.50%, Mo: 0.90-1.10%, and the rest is Fe and unavoidable impurities.

[0072] As an optional embodiment of the present invention, the 9Cr stainless steel quenched and tempered material for oil and gas includes the following chemical components in mass fraction: C: 0.09-0.15%, Si: ≤1.00%, Mn: 0.30-0.60%, P: ≤0.015%, S: ≤0.004%, Cr: 8.50-9.50%, Ni: ≤0.45%, Mo: 0.90-1.05%, and the rest is Fe and unavoidable impurities.

[0073] According to a third aspect of the present invention, there is also provided a pipe fitting for oil and gas wells, which is made of the 9Cr stainless steel quenched and tempered material for oil and gas made by the manufacturing method of the 9Cr stainless steel quenched and tempered material for oil and gas or the 9Cr stainless steel quenched and tempered material for oil and gas.

[0074] In view of the advantages of the above-mentioned 9Cr stainless steel quenched and tempered material for oil and gas, the produced oil and gas well pipe fittings also have the same advantages.

[0075] The present invention will be described in detail below with reference to the accompanying drawings and embodiments of the present invention. Each example is provided by way of explanation of the present invention and does not limit the present invention. In fact, it will be clear to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit of the present invention. For example, a feature shown or described as part of one embodiment can be used in another embodiment to produce yet another embodiment. Therefore, it is intended that the present invention encompasses such modifications and variations within the scope of the appended claims and their equivalents.

[0076] Example 1

[0077] This embodiment provides a 9Cr stainless steel quenched and tempered material for oil and gas use, with a production specification of 80KSI steel grade and φ210mm round steel. The main chemical components of the steel and their contents (wt%) are: C: 0.10%, Si: 0.31%, Mn: 0.47%, P: 0.018%, S: 0.003%, Cr: 8.61%, Ni: 0.11%, Mo: 0.92%, and the remainder is Fe and unavoidable impurities.

[0078] Specifically, the method for manufacturing the 9Cr stainless steel quenched and tempered material in this embodiment includes the following steps:

[0079] S1. Steel Preparation: The raw materials are sequentially subjected to electric furnace smelting, LF refining, vacuum degassing, continuous casting, hot-rolling, heating, and rolling to produce 9Cr round steel; wherein the final rolling temperature is 926°C;

[0080] S2 rapid cooling: The 9Cr round steel obtained in step S1 was rapidly cooled by a water tank, taking 30min to cool to 50 ° C, 9Cr round steel water reheated to 72 ° C, placed 26h, into the tempering furnace for a tempering treatment;

[0081] Primary tempering treatment: 9Cr round steel is heated to the tempering temperature of 720℃ at a heating rate of 75℃ / h and then kept at this temperature for 13h. After the heat preservation is completed, it is taken out of the furnace and air-cooled to complete the primary tempering treatment;

[0082] S3 straightening: straightening the steel billet after the primary tempering treatment;

[0083] Stress relief tempering treatment: the straightened 9Cr round steel is heated to the stress relief tempering temperature of 690℃ at a heating rate of 75℃ / h and then kept warm for 13h. After the insulation is completed, it is taken out of the furnace and air-cooled to obtain 9Cr stainless steel quenched and tempered material.

[0084] Example 2

[0085] This embodiment provides a 9Cr stainless steel quenched and tempered material for oil and gas use, with a production specification of 110KSI steel grade and φ90mm round steel. The main chemical components of the steel and their contents (wt%) are: C: 0.09%, Si: 0.32%, Mn: 0.51%, P: 0.017%, S: 0.002%, Cr: 9.10%, Ni: 0.09%, Mo: 0.97%, and the rest are Fe and unavoidable impurities.

[0086] Specifically, the manufacturing method of the 9Cr stainless steel quenched and tempered material in this embodiment includes the following steps:

[0087] S1. Steel Preparation: The raw materials are sequentially subjected to electric furnace primary refining, LF furnace refining, vacuum degassing, continuous casting, hot-rolling, heating, and rolling to produce 9Cr round steel; wherein the final rolling temperature is 934°C;

[0088] S2 rapid cooling: The 9Cr round steel obtained in step S1 was rapidly cooled to 80°C by air cooling at 400°C / h and then directly into the tempering furnace for a tempering treatment;

[0089] Primary tempering treatment: 9Cr round steel is heated to the tempering temperature of 595℃ at a heating rate of 80℃ / h and then kept at this temperature for 6 hours. After the end of the heat preservation, it is taken out of the furnace and air-cooled to complete the primary tempering treatment;

[0090] S3 straightening: straighten the 9Cr steel after a tempering treatment;

[0091] Stress relief tempering treatment: the straightened 9Cr round steel is heated to the stress relief tempering temperature of 560℃ at a heating rate of 80℃ / h and then kept warm for 6h. After the insulation is completed, it is taken out of the furnace and air-cooled to obtain 9Cr stainless steel quenched and tempered material.

[0092] Comparative Example 1

[0093] This comparative example provides a 9Cr stainless steel quenched and tempered material for oil and gas use, whose production specifications, dimensions and chemical composition are the same as those of Example 1.

[0094] The manufacturing method of the 9Cr stainless steel quenched and tempered material of this comparative example (old process) comprises the following steps:

[0095] S1. Steel Preparation: The raw materials are sequentially subjected to electric furnace smelting, primary refining, LF refining, vacuum degassing, continuous casting, hot-rolling, heating, and rolling to produce 9Cr round steel; wherein the final rolling temperature is 917°C;

[0096] S2 annealing: The 9Cr round steel obtained in step S1 was annealed in an annealing furnace, the annealing furnace was heated to the annealing holding temperature at a heating rate of 80 ℃ / h, the annealing holding temperature was 700 ℃, and the holding time was 13h; after which the furnace was air-cooled to room temperature;

[0097] S3. Straightening;

[0098] S4. Peeling and chamfering;

[0099] S5. The 9Cr round steel is transferred to the tempering line for tempering, the quenching temperature is 926 ° C, the holding time is 5h, and the water quenching is carried out after the furnace, and the surface temperature of the water-quenched billet is below 100 ° C;

[0100] S6. Primary tempering: The water-quenched steel is placed in a tempering furnace and heated at a rate of 75°C / h to a tempering temperature of 720°C. The temperature is then held for 13 hours. After the temperature is reached, the steel is removed from the furnace and air-cooled to complete the primary tempering process.

[0101] S7. Straightening: Straighten the steel after the primary tempering treatment;

[0102] Stress relief tempering treatment: the straightened 9Cr round steel is heated to the stress relief tempering temperature of 690℃ at a heating rate of 75℃ / h and then kept warm for 13h. After the insulation is completed, it is taken out of the furnace and air-cooled to obtain 9Cr stainless steel quenched and tempered material.

[0103] Comparative Example 2

[0104] This comparative example provides a 9Cr stainless steel quenched and tempered material for oil and gas use, whose production specifications, dimensions and chemical composition are the same as those of Example 2.

[0105] The manufacturing method of the 9Cr stainless steel quenched and tempered material of this comparative example (old process) comprises the following steps:

[0106] S1. Steel Preparation: The raw materials are sequentially subjected to electric furnace smelting, primary refining, LF refining, vacuum degassing, continuous casting, hot-rolling, heating, and rolling to produce 9Cr round steel billets; wherein the final rolling temperature is 921°C;

[0107] S2 Annealing: The 9Cr round steel obtained in step S1 was annealed in an annealing furnace, the annealing furnace was heated to the annealing holding temperature at a heating rate of 80 ° C / h, the annealing holding temperature was 710 ° C, and the holding time was 6h; then the furnace was air-cooled to room temperature;

[0108] S3. Straightening;

[0109] S4. Peeling and chamfering;

[0110] S5. The 9Cr round steel billet is transferred to the quenching and tempering line for quenching and tempering at a quenching temperature of 934°C for a holding time of 5h. After being discharged from the furnace, the surface temperature of the water-quenched billet is lower than 100°C.

[0111] S6. Primary tempering treatment: The water-quenched billet is placed in a tempering furnace after being discharged from the water. The temperature is raised to a tempering temperature of 595°C at a heating rate of 80°C / h and then held for 6 hours. After the end of the holding period, the billet is discharged from the furnace and air-cooled to complete a tempering treatment.

[0112] S7. Straightening: Straighten the steel billet after the primary tempering treatment;

[0113] Stress relief tempering treatment: the straightened 9Cr round steel billet is heated to the stress relief tempering temperature of 560℃ at a heating rate of 80℃ / h and then kept warm for 6h. After the insulation is completed, it is taken out of the furnace and air-cooled to obtain 9Cr stainless steel quenched and tempered material.

[0114] Comparative Example 3

[0115] This comparative example provides a 9Cr stainless steel quenched and tempered material for oil and gas and a preparation method thereof. Except that the final rolling temperature in step S1 is adjusted to 825° C., the remaining steps are the same as those in Example 1.

[0116] Comparative Example 4

[0117] This comparative example provides a 9Cr stainless steel quenched and tempered material for oil and gas and a preparation method thereof. Except that the rapid cooling rate in step S2 is adjusted to 30°C / h during furnace cooling, the remaining steps are the same as those in Example 1.

[0118] In order to compare the technical effects of the above embodiments and comparative examples, the following experimental examples are specially set up.

[0119] Experimental Example 1

[0120] The metallographic structures of the 9Cr quenched and tempered stainless steel materials for oil and gas use provided in each of the Examples and Comparative Examples were analyzed, as shown in Figures 1-4. Figures 1 and 3 show that the 9Cr quenched and tempered stainless steel materials for oil and gas use in Example 1 and Comparative Example 1 have essentially the same grain size. Figures 2 and 4 also show that the grain sizes of the 9Cr quenched and tempered stainless steel materials for oil and gas use in Example 2 and Comparative Example 2 are also essentially equivalent.

[0121] Experimental Example 2

[0122] Samples were taken at 1 / 2R of the 9Cr steel (80KSI) prepared in Example 1 and Comparative Examples 1, 3 and 4, and room temperature tensile properties and low temperature impact properties were tested. The testing methods were based on ASTM A370 and ASTM E23. The actual data comparison is shown in Table 1:

[0123] Table 1

[0124] At the same time, samples were taken at 1 / 2R of the 9Cr steel (110KSI) prepared in Example 2 and Comparative Example 2, and room temperature tensile properties and low temperature impact properties were tested. The testing method was based on ASTM A370 and ASTM E23. The actual data comparison is shown in Table 2:

[0125] Table 2

[0126] It can be seen from the data in Table 1 that the 9Cr stainless steel quenched and tempered materials for oil and gas prepared by Example 1 of the present invention and Comparative Example 1 both have excellent tensile and impact properties. However, the production cycle of Example 1 of the present invention is shortened by approximately 4 days, which significantly improves production efficiency and has obvious cost advantages.

[0127] Comparing Comparative Examples 3 and 4 with Example 1 reveals that when the final rolling temperature is too low (below 850°C), the impact properties of 9Cr quenched and tempered stainless steel significantly degrade. This is primarily due to a decrease in grain size. When 9Cr steel cannot be rapidly cooled (the cooling rate is too low), the impact properties and hardness also significantly decrease due to incomplete microstructural transformation and the precipitation of brittle phases.

[0128] The data in Table 2 demonstrates that the 9Cr stainless steel quenched and tempered materials for oil and gas applications produced using Example 2 of the present invention and Comparative Example 2 exhibit comparable tensile properties and hardness. While the impact performance of Example 2 is slightly lower than that of Comparative Example 2, it remains well above standard requirements. Furthermore, due to the adjustment or omission of multiple process steps, the production cycle of Example 2 of the present invention is significantly shortened compared to Comparative Example 2, significantly reducing production costs and achieving the goal of cost reduction and efficiency improvement.

[0129] The foregoing description is merely a preferred embodiment of the present invention and is 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 manufacturing method of quenched and tempered 9Cr stainless steel for oil and gas, characterized in that, It includes the following steps: S1. According to the chemical composition of the quenched and tempered material of 9Cr stainless steel for oil and gas, the raw materials are successively subjected to primary melting, refining, vacuum degassing, continuous casting or ingot casting, annealing or hot charging, heating and rolling to obtain 9Cr steel; wherein, the final rolling temperature of rolling is ≥850°C; S2. The 9Cr steel is rapidly cooled to transform its structure into quenched martensite, and then directly subjected to a single tempering treatment; S3. The steel after the single tempering treatment is straightened, and then stress relief tempering treatment is carried out to obtain the quenched and tempered material of 9Cr stainless steel for oil and gas.

2. The manufacturing method of the quenched and tempered 9Cr stainless steel material for oil and gas according to claim 1, characterized in that, In step S1, the final rolling temperature of rolling is ≥900°C.

3. The manufacturing method of 9Cr stainless steel for oil and gas according to claim 1, characterized in that In step S2, the cooling rate during the rapid cooling of the 9Cr steel is ≥300°C / h; And / or, in step S2, the 9Cr steel is rapidly cooled to below 150°C.

4. The manufacturing method of the quenched and tempered 9Cr stainless steel material for oil and gas according to claim 3, characterized in that, In step S2, the 9Cr steel is rapidly cooled to below 150°C at a cooling rate of ≥300°C / h, and a single tempering treatment is carried out within 48 hours; And / or, in step S2, the rapid cooling method includes air cooling, air blast cooling or water cooling.

5. The manufacturing method of the quenched and tempered 9Cr stainless steel material for oil and gas according to claim 1, characterized in that In step S2, the tempering temperature of the single tempering treatment is 550 - 750°C, and the single tempering holding time is (4H / 100mm*D) - (4H / 100mm*D + 6H), where H represents hours and D represents the diameter of the 9Cr steel, in mm; And / or, in step S2, the heating rate to the tempering temperature during the single tempering treatment is ≤80°C / h; And / or, in step S2, the cooling method of the single tempering treatment is air cooling after furnace discharging.

6. The manufacturing method of the quenched and tempered 9Cr stainless steel material for oil and gas according to claim 5, characterized in that, In step S2, for the quenched and tempered material of 9Cr stainless steel with 80KSI, the tempering temperature of the single tempering treatment is 650 - 750°C; And / or, in step S2, for the quenched and tempered material of 9Cr stainless steel with 100KSI, the tempering temperature of the single tempering treatment is 565 - 650°C; And / or, in step S2, for the quenched and tempered material of 9Cr stainless steel with 110KSI, the tempering temperature of the single tempering treatment is 565 - 620°C.

7. The manufacturing method of the quenched and tempered 9Cr stainless steel material for oil and gas according to claim 5 or 6, characterized in that In step S3, the tempering temperature of the stress relief tempering treatment is 20 - 60°C lower than the tempering temperature of the single tempering treatment, and the stress relief tempering holding time is (4H / 100mm*D) - (4H / 100mm*D + 5H), where H represents hours and D represents the diameter of the steel, in mm; And / or, in step S3, the heating rate to the tempering temperature during the stress relief tempering treatment is ≤80°C / h; And / or, in step S3, the cooling method of the stress relief tempering treatment is air cooling after furnace discharging.

8. A quenched and tempered material of 9Cr stainless steel for oil and gas, characterized in that, It is obtained by using the manufacturing method of the quenched and tempered material of 9Cr stainless steel for oil and gas according to any one of claims 1 - 7; The quenched and tempered material of 9Cr stainless steel for oil and gas includes the following chemical components by mass fraction: C: ≤0.15%, Si: ≤1.00%, Mn: 0.30 - 0.60%, P: ≤0.020%, S: ≤0.010%, Cr: 8.00 - 10.00%, Ni: ≤0.50%, Mo: 0.90 - 1.10%, and the rest is Fe and inevitable impurities.

9. The quenched and tempered material of 9Cr stainless steel for oil and gas according to claim 8, characterized in that, The quenched and tempered 9Cr stainless steel material for oil and gas contains the following chemical components by mass fraction: C: 0.09 - 0.15%, Si: ≤1.00%, Mn: 0.30 - 0.60%, P: ≤0.015%, S: ≤0.004%, Cr: 8.50 - 9.50%, Ni: ≤0.45%, Mo: 0.90 - 1.05%, and the balance is Fe and inevitable impurities.

10. A pipe fitting for oil and gas wells, characterized in that, It is made of the quenched and tempered 9Cr stainless steel material for oil and gas prepared by the manufacturing method according to any one of claims 1 - 7 or the quenched and tempered 9Cr stainless steel material for oil and gas according to claim 8 or 9.

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