15cr1mo1v steel pipe and method for manufacturing the same

Abstract

This invention relates to the field of heat-resistant steel pipe manufacturing. Specifically, this invention provides a 15Cr1Mo1V steel pipe and its preparation method. The method for preparing the 15Cr1Mo1V steel pipe of this invention includes precise control of process parameters such as the composition of the 15Cr1Mo1V steel pipe, the heat treatment and cooling method of the billet, and the cooling rate, and preferably uses an ASSEL unit to manufacture the steel pipe. The method for preparing the 15Cr1Mo1V steel pipe of this invention employs a unique heat treatment process, which improves the comprehensive performance of the 15Cr1Mo1V steel pipe. The obtained 15Cr1Mo1V steel pipe has excellent strength and impact toughness, and uniform hardness.

Description

Technical Field

[0001] This invention relates to the field of heat-resistant steel pipe manufacturing. Specifically, this invention relates to a 15Cr1Mo1V steel pipe and its preparation method. Background Technology

[0002] 15Cr1Mo1V alloy steel is a heat-resistant steel with high thermal strength and high-temperature oxidation resistance. Russian standard TU 14-3P-55-2001 specifies that a bainite content between approximately 20% and approximately 100% is considered acceptable for 15Cr1Mo1V alloy steel, while tempered martensite and ferrite plus pearlite are considered unacceptable structures.

[0003] 15Cr1Mo1V alloy steel is mainly used to manufacture parts with operating temperatures below approximately 550℃, such as boilers, turbine blades, and high-pressure vessels. Furthermore, the 15Cr1Mo1V alloy steel exhibits good structural stability at high temperatures, ensuring not only the strength specifications stipulated in the standards but also excellent impact toughness.

[0004] However, the existing 15Cr1Mo1V alloy steel has the following defects and shortcomings: (1) 15Cr1Mo1V alloy steel is a high-strength heat-resistant steel. If the billet cooling method is not selected properly, stress cracking is likely to occur. (2) When the heat treatment process of 15Cr1Mo1V steel pipe is not properly selected, the impact absorption energy is unqualified, or the microstructure is unqualified, which is particularly obvious for steel pipes with a wall thickness of 20 mm or more; and (3) According to Russian standard TU 14-3P-55-2001, the tempering time during the heat treatment process of 15Cr1Mo1V steel pipe is required to be at least about 10 hours, which makes it difficult to organize large-scale production. Summary of the Invention

[0005] Purpose of the invention In view of the problems existing in the prior art described in the background section above, the object of the present invention is to provide a method for preparing 15Cr1Mo1V steel pipe and a 15Cr1Mo1V steel pipe prepared by the method.

[0006] Technical solution To achieve the above objectives, the present invention adopts the following technical solution: Option 1: A method for preparing 15Cr1Mo1V steel pipe, the method comprising the following steps: Step 1: The 15Cr1Mo1V steel round billet is subjected to a homogenization heat treatment at a temperature of about 1200 to about 1260°C, and the holding time of the homogenization heat treatment is at least about 90 minutes. Step 2: Roll the 15Cr1Mo1V steel round billet obtained from Step 1 after homogenization heat treatment into 15Cr1Mo1V steel pipe. Step 3: The 15Cr1Mo1V steel pipe obtained from Step 2 is normalized at a temperature of about 970 to about 1000°C. Step 4: Cool the normalized 15Cr1Mo1V steel pipe obtained from Step 3 to a temperature of about 100 to about 300°C at a cooling rate of about 80 to about 120°C / min, and then air cool it to a temperature of about 40°C or below. Step 5: The 15Cr1Mo1V steel pipe obtained from Step 4 and cooled to below about 40°C is tempered at a temperature of about 730 to about 760°C, and then air-cooled to a temperature of below about 40°C.

[0007] Option 2: According to the preparation method described in Option 1 above, the 15Cr1Mo1V steel pipe is composed of the following elements: Based on the total weight of the 15Cr1Mo1V steel pipe Approximately 0.11 to approximately 0.14% by weight of carbon; About 0.20 to about 0.30 wt% of Si element; Mn element, approximately 0.70 to approximately 0.90 wt%; Approximately 1.15 to approximately 1.30% by weight of Cr element; Mo element: about 0.90 to about 1.00 wt%; Approximately 0.20 to approximately 0.30% by weight of V; The balance consists of Fe and unavoidable impurity elements.

[0008] Option 3: The preparation method according to Option 2 above, wherein the unavoidable impurity element is: The Ni content is controlled to be below approximately 0.20% by weight; The content of Cu element is controlled to be below approximately 0.20% by weight; The content of Al is controlled to be below approximately 0.020% by weight; The content of phosphorus (P) is controlled to be below approximately 0.015% by weight; The sulfur content is controlled to be below approximately 0.010% by weight; The content of As element is controlled to be below approximately 0.015% by weight; The content of Sb element is controlled to be below approximately 0.010% by weight; The content of Bi element is controlled to be below approximately 0.010% by weight; The Sn content is controlled to be below approximately 0.015% by weight; and / or The Pb content is controlled to be below approximately 0.015% by weight.

[0009] Option 4: According to the preparation method described in Option 3 above, the total content of the unavoidable impurity elements As, Sb, Bi, Sn and Pb is controlled to be below about 0.035% by weight.

[0010] Option 5: According to the preparation method described in Option 1 above, the 15Cr1Mo1V steel round billet in step 1 is obtained by the following method: 15Cr1Mo1V steel ingots cast from molten steel are forged to obtain 15Cr1Mo1V steel round billets. Before forging, the temperature of the 15Cr1Mo1V steel ingots is adjusted to a range of approximately 1140°C to approximately 1260°C. During forging, the initial forging temperature is controlled above approximately 1000°C, the final forging temperature above approximately 780°C, and the forging ratio is not less than approximately 3. The 15Cr1Mo1V steel round billets obtained by forging are then annealed at a temperature not less than approximately 600°C, with a holding time of at least approximately 10 hours. Finally, the annealed 15Cr1Mo1V steel round billets are cooled to a temperature below approximately 40°C at a cooling rate not exceeding approximately 40°C / hour, thereby obtaining 15Cr1Mo1V steel round billets to be subjected to homogenization treatment.

[0011] Option 6: According to the preparation method described in Option 1 above, the 15Cr1Mo1V steel round billet in step 1 is obtained by the following method: The billet temperature of the 15Cr1Mo1V steel round billet, which is directly cast from molten steel, is controlled in the range of about 500 to about 700°C. Then, it is slowly cooled to a temperature of about 40°C or below at a cooling rate of no more than about 10°C / hour, thereby obtaining the 15Cr1Mo1V steel round billet to be subjected to homogenization treatment.

[0012] Scheme 7: The preparation method according to any one of Schemes 1 to 6 above, wherein the rolling in step 2 includes rolling using an ASSEL rolling mill.

[0013] Option 8: According to the preparation method described in Option 1 above, the wall thickness of the 15Cr1Mo1V steel pipe does not exceed about 100 mm, preferably in the range of about 20 to about 100 mm.

[0014] Option 9: The preparation method according to any one of Options 1 to 8 above, wherein the holding time for the normalizing treatment in step 3 is not less than about 1.5 minutes per millimeter of the wall thickness of the 15Cr1Mo1V steel pipe.

[0015] Scheme 10: The preparation method according to any one of Schemes 1 to 7 above, wherein the holding time for the tempering treatment in step 5 is not less than about 3 minutes per millimeter of the wall thickness of the 15Cr1Mo1V steel pipe.

[0016] Option 11: A 15Cr1Mo1V steel pipe prepared according to any one of Options 1 to 10 above, wherein the 15Cr1Mo1V steel pipe preferably has one or more of the following properties: The microstructure is tempered bainite or bainite plus ferrite, without tempered martensite, wherein the bainite content is more than about 20%, preferably more than about 50%, and more preferably more than about 60%. The yield strength Rp0.2 reaches approximately 314 MPa or higher; The tensile strength Rm is in the range of about 490 to about 686 MPa; The elongation after fracture reaches approximately 18.0% or more; The hardness deviation is within approximately 20 HBW; The grain size reaches approximately 5.0 or higher; The impact absorption energy at 20℃ reaches approximately 100 J or more; and The shock absorption energy at -20℃ reaches approximately 100 J or more.

[0017] Technical effect The method for preparing 15Cr1Mo1V steel pipe provided by this invention includes precise control of process parameters such as the composition of the 15Cr1Mo1V steel pipe, the heat treatment and cooling method of the billet, and the cooling rate, and preferably uses an ASSEL unit to manufacture the steel pipe. The method for preparing 15Cr1Mo1V steel pipe of this invention employs a unique heat treatment process, which improves the comprehensive performance of the 15Cr1Mo1V steel pipe, resulting in 15Cr1Mo1V steel pipe with excellent strength and impact toughness, and uniform hardness.

[0018] The method for preparing 15Cr1Mo1V steel pipe of the present invention is particularly applicable to preparing 15Cr1Mo1V steel pipe with a thickness in the range of about 20 mm to about 100 mm. It can still be used when the wall thickness is less than about 20 mm or greater than about 100 mm.

[0019] The method for preparing 15Cr1Mo1V steel pipe of the present invention, under existing furnace conditions, by selecting a suitable heat treatment process, and with a tempering temperature and tempering time of less than about 10 hours, can meet the various performance requirements specified in the standard. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 An optical microscope photograph with a magnification of 200x of the 15Cr1Mo1V steel pipe prepared for Example 1 of the present invention.

[0022] Figure 2 This is a photograph of the 15Cr1Mo1V steel tube blank prepared in Comparative Example 1 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions 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 for the purpose of aiding understanding of this invention and should not be considered as specific limitations on this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Process parameters in the following embodiments that are not specifically specified are generally performed under conventional conditions.

[0024] 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. The term "about" as used in this invention means that the number it modifies may fluctuate within ±20%, ±15%, ±10%, ±5%, or ±2% of that number. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and the individual point values ​​contained within them, and the 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.

[0025] According to a first aspect of the present invention, the present invention provides a method for preparing 15Cr1Mo1V steel pipe.

[0026] In a first aspect of the invention, the wall thickness of the 15Cr1Mo1V steel pipe is preferably no more than about 100 mm, and particularly preferably in the range of about 20 to about 100 mm, for example, about 40 mm, about 60 mm, or about 80 mm, simply because there is currently little market demand for specifications with wall thicknesses exceeding about 100 mm. In fact, the method of the invention is still applicable to steel pipes with wall thicknesses below about 20 mm and above about 100 mm.

[0027] The 15Cr1Mo1V steel pipe prepared by the preparation method according to the first aspect of the present invention is composed of the following elements: Based on the total weight of the 15Cr1Mo1V steel pipe From about 0.11 to about 0.14% by weight, for example about 0.12% or about 0.13% by weight of element C; About 0.20 to about 0.30% by weight, for example about 0.25% by weight of Si element; From about 0.70 to about 0.90% by weight, for example about 0.80% by weight of Mn element; From about 1.15 to about 1.30% by weight, for example about 1.20% by weight or about 1.25% by weight of Cr element; From about 0.90 to about 1.00% by weight, for example about 0.95% by weight of Mo; From about 0.20 to about 0.30% by weight, for example about 0.25% by weight of element V; The balance consists of Fe and unavoidable impurity elements.

[0028] In the 15Cr1Mo1V steel pipe prepared by the preparation method according to the first aspect of the present invention, the design of the range of element contents included in the Russian standard TU 14-3P-55-2001 is mainly based on the following concept: Excessive carbon content will reduce the weldability of steel pipes, therefore the carbon content should be controlled within the lower limit range. Cr can improve the corrosion resistance of steel at high temperatures and is beneficial to high-temperature creep strength, thus raising the lower limit requirement; Mo can improve the hardenability and hot strength of steel, but Mo alloys are expensive. Considering economic factors, the Mo content should be controlled at the lower end of the range. V reduces the durable plasticity of materials, so it should be kept in the lower-middle range.

[0029] In some further preferred embodiments, based on the total weight of the 15Cr1Mo1V steel pipe, the unavoidable impurity elements can be: The Ni content is controlled to be below approximately 0.20% by weight; The content of Cu element is controlled to be below approximately 0.20% by weight; The content of Al is controlled to be below approximately 0.020% by weight; The content of phosphorus (P) is controlled to be below approximately 0.015% by weight; The sulfur content is controlled to be below approximately 0.010% by weight; The content of As element is controlled to be below approximately 0.015% by weight; The content of Sb element is controlled to be below approximately 0.010% by weight; The content of Bi element is controlled to be below approximately 0.010% by weight; The Sn content is controlled to be below approximately 0.015% by weight; and / or The Pb content is controlled to be below approximately 0.015% by weight.

[0030] Among the aforementioned unavoidable impurity elements, Ni is an unavoidable impurity element, and the lower its content, the better. However, excessive control will limit the choice of alloy materials and increase manufacturing costs. As an unavoidable impurity element, the lower the content of Cu, the better. However, excessive control will limit the choice of alloy materials and increase manufacturing costs. As an unavoidable impurity element, the lower the content of Al, the better. However, since Al is used for deoxidation in the smelting process, the content should not be too low, and it is advisable to limit the upper limit. As an unavoidable impurity element, phosphorus (P) increases temper brittleness and affects weldability. The lower its content, the better. However, excessively low P content will limit the choice of alloy materials, leading to a significant increase in cost. As an unavoidable impurity element, sulfur content should be kept as low as possible, but excessive desulfurization leads to a significant increase in costs. As an unavoidable impurity element, the lower the content of arsenic, the better. However, excessive control will significantly increase costs. Considering economic efficiency, it is advisable to limit the upper limit. As an unavoidable impurity element, the lower the content of Sb, the better. However, excessive control will significantly increase costs. Considering economic factors, it is advisable to limit the upper limit. Bi is an unavoidable impurity element, and the lower its content, the better. However, excessive control will significantly increase costs. Considering economic efficiency, it is advisable to limit the upper limit. Sn is an unavoidable impurity element, and its lower content is better. However, excessive control will significantly increase costs. Considering economic efficiency, it is advisable to limit the upper limit. As an unavoidable impurity element, Pb should be kept to a lower content. However, excessive control will significantly increase costs. Considering economic efficiency, it is advisable to limit the upper limit.

[0031] In some further preferred embodiments, the total content of the unavoidable impurity elements As, Sb, Bi, Sn and Pb is preferably controlled to below about 0.035% by weight, otherwise it may lead to a significant decrease in the strength, toughness, weldability and high-temperature performance of the material.

[0032] The method for preparing 15Cr1Mo1V steel pipe according to the first aspect of the present invention includes steps 1 to 5 as described in the following detailed description.

[0033] Step 1: Soaking Heat Treatment Step 1 includes subjecting a 15Cr1Mo1V steel round billet to a homogenization heat treatment at a temperature of about 1200 to about 1260°C, wherein the holding time of the homogenization heat treatment is at least about 90 minutes.

[0034] In step 1, the homogenization heat treatment temperature of the 15Cr1Mo1V steel billet should be in the range of about 1200 to about 1260°C, for example, about 1215°C, about 1230°C, or about 1245°C. Here, the homogenization heat treatment temperature should not be too high, for example, not higher than about 1260°C, otherwise it may lead to overheating or burning of the billet; in addition, the homogenization heat treatment temperature should not be too low, for example, not lower than about 1200°C, otherwise it may lead to increased piercing resistance during the rolling process into a steel pipe, greatly increasing the risk of internal folding defects.

[0035] Furthermore, in step 1, the homogenization heat treatment time for the 15Cr1Mo1V steel round billet should be at least about 90 minutes, for example, about 100 minutes or about 120 minutes. Here, the homogenization heat treatment time should not be less than about 90 minutes; otherwise, it may lead to greater fluctuations during piercing, resulting in internal folding defects, poor surface quality, and significantly reduced product quality.

[0036] In some preferred embodiments of step 1, the 15Cr1Mo1V steel billet used in step 1 can be obtained by conventional means in the art, for example, by the following means: Method 1: Forging 15Cr1Mo1V steel ingots cast from molten steel to obtain 15Cr1Mo1V steel round billets, wherein before forging, the temperature of the 15Cr1Mo1V steel ingots is adjusted to the range of about 1140°C to about 1260°C, for example, controlled at about 1150°C, about 1200°C, or about 1250°C, and during forging, the initial forging temperature is controlled above about 1000°C, the final forging temperature is controlled above about 780°C, and the forging ratio is not less than about 3; then, the 15Cr1Mo1V steel round billets obtained by forging are annealed at a temperature not less than about 600°C, and the holding time of the annealing treatment is at least about 10 hours; and finally, the annealed 15Cr1Mo1V steel round billets are cooled to a temperature below about 40°C at a cooling rate not exceeding about 40°C / hour, for example, cooled to room temperature (e.g., about 20 to about 30°C), thereby obtaining 15Cr1Mo1V steel round billets for the production of steel pipes. or Method 2: The billet temperature of the 15Cr1Mo1V steel round billet, which is directly cast from molten steel, is controlled in the range of about 500 to about 700°C, for example, about 600°C. Then, it is slowly cooled to a temperature below 40°C, for example, to room temperature, at a cooling rate of no more than 10°C / hour, thereby obtaining the 15Cr1Mo1V steel round billet for the production of steel pipes.

[0037] Step 2: Rolling Step Step 2 includes rolling the heat-treated 15Cr1Mo1V steel billet obtained from Step 1 into a 15Cr1Mo1V steel pipe.

[0038] In the rolling process of step 2, it is preferred to use the ASSEL rolling mill, which is commonly used in the art, for the rolling process.

[0039] Step 3: Normalizing process Step 3 includes normalizing the 15Cr1Mo1V steel pipe obtained from Step 2 above at a temperature of about 970°C to about 1000°C.

[0040] In step 3, the normalizing temperature is required to be in the range of approximately 970°C to approximately 1000°C, for example, approximately 980°C, approximately 985°C, or approximately 990°C. Here, the normalizing temperature should not be too high, for example, not higher than approximately 1000°C, otherwise it may cause grain growth and a larger grain size range in the obtained 15Cr1Mo1V steel pipe; in addition, the normalizing temperature should not be too low, for example, not lower than approximately 970°C, otherwise it may cause a decrease in the strength and plasticity of the obtained 15Cr1Mo1V steel pipe, and a larger fluctuation in the impact absorption energy at -20°C, making it difficult to meet the standard requirements.

[0041] In some preferred embodiments of step 3, the holding time for the normalizing treatment is no less than about 1.5 minutes per millimeter of the 15Cr1Mo1V steel pipe wall thickness, for example, about 2 minutes or about 2.5 minutes. Here, the holding time per millimeter of the 15Cr1Mo1V steel pipe wall thickness should not be less than about 1.5 minutes; otherwise, it may lead to a decrease in material strength, a deterioration in plasticity, a significant decrease in impact absorption energy at 20°C, and a significant deficiency in impact absorption energy at -20°C.

[0042] Step 4: Cooling Step Step 4 includes rapidly cooling the normalized 15Cr1Mo1V steel pipe obtained from Step 3 to a temperature of about 100 to about 300°C at a cooling rate of about 80 to about 120°C / min, and then air cooling it to a temperature of about 40°C or below, preferably to room temperature.

[0043] In step 4, the rapid cooling method is preferably water mist cooling.

[0044] Furthermore, the rapid cooling rate in step 4 should be in the range of approximately 80 to approximately 120°C / min, for example, approximately 90°C / min, approximately 100°C / min, or approximately 110°C / min. Here, the cooling rate should not be too high, for example, not exceeding approximately 120°C / min, otherwise martensite may form in the microstructure, and the strength may approach or exceed the upper limit; conversely, the cooling rate should not be too low, for example, not below approximately 80°C / min, otherwise tensile strength may decrease, and the bainite content may be insufficient.

[0045] Furthermore, in step 4, the temperature reached by rapid cooling should be in the range of approximately 100 to approximately 300°C, for example, cooling to 150°C, 200°C, or approximately 250°C. Here, the temperature reached by rapid cooling should not be too high, for example, it should not exceed approximately 300°C, otherwise it may lead to incomplete bainitic transformation and insufficient tensile strength; conversely, the temperature reached by rapid cooling should not be too low, for example, it should not be below approximately 100°C, otherwise it may lead to stress cracking of the steel pipe.

[0046] In addition, in step 4, after rapidly cooling to the required temperature, the 15Cr1Mo1V steel pipe can be cooled to a temperature below about 40°C by air cooling, preferably to room temperature.

[0047] Step 5: Tempering process Step 5 includes tempering the 15Cr1Mo1V steel pipe obtained from step 4 above, which has been cooled to below about 40°C, at a temperature of about 730 to about 760°C, and then air-cooling it to a temperature below 40°C, preferably to room temperature.

[0048] In step 5, the tempering temperature should be in the range of approximately 730 to approximately 760°C, for example, approximately 740°C, approximately 745°C, or approximately 750°C. Here, the tempering temperature should not be too high, for example, it should not exceed approximately 760°C, otherwise it may lead to a decrease in the strength of the 15Cr1Mo1V steel pipe, an increase in plasticity, and grain growth. Furthermore, the tempering temperature should not be too low, for example, it should not be lower than approximately 730°C, otherwise it may lead to an excessive increase in the strength of the 15Cr1Mo1V steel pipe, exceeding the standard requirements, and a significant decrease in plasticity, a marked decrease in elongation at break, and failure to meet the standard requirements for impact absorption energy at -20°C.

[0049] In some preferred embodiments of step 5, the holding time for the tempering treatment is no less than about 3 minutes per millimeter of the 15Cr1Mo1V steel pipe wall thickness, for example, about 4 minutes or about 5 minutes. Here, the holding time per millimeter of the 15Cr1Mo1V steel pipe wall thickness should not be less than about 3 minutes; otherwise, it may lead to a significant reduction in the plasticity of the 15Cr1Mo1V steel pipe, with the elongation after fracture falling below the standard lower limit, and a particularly significant reduction in impact absorption energy at -20℃.

[0050] In addition, in some specific embodiments of the present invention, the holding time of the tempering treatment does not need to exceed about 10 hours to meet the various performance requirements specified in the standard.

[0051] According to a second aspect of the present invention, the present invention provides a 15Cr1Mo1V steel pipe prepared by the method for preparing 15Cr1Mo1V steel pipe described in the first aspect of the present invention.

[0052] The 15Cr1Mo1V steel pipe according to the second aspect of the present invention particularly possesses one or more of the following properties: The microstructure is tempered bainite or bainite plus ferrite, without tempered martensite, wherein the bainite content is more than about 20%, preferably more than about 50%, and more preferably more than about 60%. The yield strength Rp0.2 reaches approximately 314 MPa or higher, preferably approximately 485 MPa or higher; The tensile strength Rm is in the range of about 490 to about 686 MPa, preferably in the range of about 645 to about 655 MPa; The elongation after fracture reaches approximately 18.0% or more, preferably approximately 25.0% or more; The hardness deviation is within approximately 20 HBW, preferably within approximately 3 HBW; wherein the hardness deviation is the hardness difference across the entire cross-section of the steel pipe wall thickness; The grain size level reaches approximately 5.0 or higher, preferably approximately 7.0 or higher; The impact absorption energy at 20℃ reaches approximately 100 J or more, preferably approximately 340 J or more; and The low-temperature impact absorption energy at -20℃ reaches approximately 100 J or more, preferably approximately 200 J or more.

[0053] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0054] Example 1: Preparation of 15Cr1Mo1V steel pipe A forged 15Cr1Mo1V steel round billet with a diameter of approximately 460 mm is provided for the preparation of the 15Cr1Mo1V steel pipe. The 15Cr1Mo1V steel round billet is composed of the following elements: Based on the total weight of the 15Cr1Mo1V steel round billet Approximately 0.13% by weight of carbon; Approximately 0.24% by weight of Si element; Approximately 0.77% by weight of Mn element; Approximately 1.20% by weight of Cr element; Approximately 0.94% by weight of Mo; Approximately 0.22% by weight of V; Approximately 0.05% by weight of Ni element; Approximately 0.03% by weight of Cu element; Approximately 0.018% by weight of Al element; Approximately 0.012% by weight of P element; Approximately 0.003% by weight of sulfur; Approximately 0.0064% by weight of As element; Approximately 0.0010 wt% of Sb element; Approximately 0.0005% by weight of Bi element; Approximately 0.0034% by weight of Sn element; Approximately 0.0005% by weight of Pb element; The balance consists of Fe and other unavoidable impurity elements.

[0055] The preparation process includes the following steps: Step 0: Anneal the forged 15Cr1Mo1V steel round billet at a temperature not lower than about 600°C for at least about 10 hours, and then slowly cool it to room temperature at a cooling rate not exceeding about 40°C / hour. Step 1: The annealed 15Cr1Mo1V steel round billet obtained from Step 1 and cooled to room temperature is subjected to homogenization heat treatment at a temperature of about 1230°C for at least about 90 minutes. Step 2: The 15Cr1Mo1V steel round billet obtained from Step 1 after heat treatment is rolled into 15Cr1Mo1V steel pipe using an ASSEL rolling mill. The outer diameter of the steel pipe is about 426 mm and the wall thickness is about 56 mm. Step 3: The 15Cr1Mo1V steel pipe obtained from Step 2 is subjected to normalizing treatment at a temperature of approximately 985°C, and the holding time for the normalizing treatment is at least approximately 90 minutes. Step 4: Cool the normalized 15Cr1Mo1V steel pipe obtained from Step 3 to a temperature of about 250°C using water mist cooling at a cooling rate of about 100°C / min, and then air cool it to room temperature. Step 5: The 15Cr1Mo1V steel pipe obtained from Step 4 and cooled to room temperature is tempered at a temperature of about 745°C for about 220 minutes, and then air-cooled to room temperature.

[0056] The cross-section of the 15Cr1Mo1V steel pipe prepared in Example 1 above was observed under an optical microscope. (See attached instruction manual.) Figure 1 An optical microscope photograph with a magnification of 200x is shown, from the attached image. Figure 1 The photograph shows that the microstructure of the 15Cr1Mo1V steel pipe prepared in Example 1 is B+F, with a bainite content of more than 60% and a grain size of 7.0.

[0057] Example 2: Preparation of 15Cr1Mo1V steel pipe The 15Cr1Mo1V steel pipe was prepared using a process similar to that in Example 1, except that a continuously cast round billet was used. Step 0 included controlling the exit temperature of the 15Cr1Mo1V continuously cast round billet, which was directly cast from molten steel, to about 650°C, and then slowly cooling it to room temperature at a cooling rate not exceeding about 10°C / hour to obtain a 15Cr1Mo1V steel round billet with a diameter of about 460 mm for the production of steel pipes.

[0058] Comparative Example 1 15Cr1Mo1V steel pipes were prepared using a process similar to that in Example 1, except that the annealing treatment in step 0 was not performed, and the pipes were directly air-cooled to room temperature.

[0059] Comparative Example 2 15Cr1Mo1V steel pipes were prepared using a process similar to that in Example 2, except that the slow cooling process in step 0 was omitted, and the pipes were directly air-cooled to room temperature.

[0060] In Comparative Examples 1 and 2 above, stress cracks occurred due to the excessively rapid cooling rate of the billets, making it impossible to manufacture steel pipes. Furthermore, stress cracks were clearly visible on the surface of the 15Cr1Mo1V steel round pipe billet in Comparative Example 1 (see appendix to the specification). Figure 2 ).

[0061] Comparative Examples 3 to 11: Preparation of 15Cr1Mo1V Steel Pipes 15Cr1Mo1V steel pipes were prepared using a process similar to that in Example 1, except that the process parameters listed in Table 1 were used.

[0062] Table 1 Table 2 *: The structure "B+F" indicates "bainite + ferrite", with bainite accounting for more than 50%; The "F+B" structure indicates "ferrite + bainite", with ferrite comprising more than 50%. The performance parameters of the 15Cr1Mo1V steel pipes obtained from Examples 1 and 2 and Comparative Examples 3 to 11 were determined. The room temperature tensile properties were tested according to EN ISO 6892-1; the impact absorption energy was tested according to EN ISO 148-1; the hardness was tested according to Chinese National Standard GB / T 231.1-2018 "Metallic materials - Brinell hardness test - Part 1: Test method"; the microstructure was tested according to Chinese National Standard GB / T 13298-2015 "Metallic materials - Microstructure test method"; and the grain size was tested according to Chinese National Standard GB / T 6394-2017 "Metallic materials - Average grain size determination method".

[0063] The performance test results are shown in Table 2.

[0064] As can be seen from the performance parameter data in Table 2 above: Comparative Example 3: After reducing the normalizing cooling rate in step 3, both the material strength and plasticity indicators decreased, and the energy absorbed by the 20°C and -20°C impacts decreased significantly, failing to achieve the intended target. Comparative Example 4: After accelerating the normalizing cooling rate in step 3, the material strength increased, the hardness deviation increased, and tempered martensite appeared in the microstructure transformation, which did not meet the standard requirements. Comparative Example 5: After reducing the heat treatment holding time of the round tube blank in step 1, the performance after heat treatment is qualified and not much different from the example. However, due to insufficient heating time of the tube blank, internal folding defects occur during piercing, the surface quality deteriorates, and the product quality is greatly reduced. Comparative Example 6: After reducing the normalizing temperature in step 3, the strength and plasticity of the material both decreased, and the impact absorption energy at -20℃ could not meet the expected requirements. Comparative Example 7: After increasing the normalizing temperature in step 3, the strength and plasticity of the material meet the standard requirements, but the grain size difference becomes larger. Comparative Example 8: After reducing the normalizing holding time in step 3, the strength of the material decreased, the plasticity deteriorated, the impact absorption energy at 20℃ decreased significantly, and the impact absorption energy at -20℃ was less than 100 J. Comparative Example 9: After reducing the tempering and heat preservation temperature in step 5, the strength of the material is significantly improved, exceeding the standard requirements, while the plasticity is greatly reduced, the elongation at break is significantly reduced, and the impact absorption energy at -20℃ is less than 100 J. Comparative Example 10: After increasing the tempering and heat preservation temperature in step 5, the strength of the material decreased slightly, the plasticity increased, the grains grew, and the impact absorption energy at -20℃ decreased significantly. Comparative Example 11: After reducing the tempering temperature and time in step 5, the strength of the material decreased slightly, the plasticity decreased significantly, the elongation at break was lower than the standard lower limit, and the impact absorption energy at -20℃ decreased significantly, less than 100 J.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions claimed by the present invention.

Claims

1. A method for preparing 15Cr1Mo1V steel pipe, characterized in that, The method includes the following steps: Step 1: The 15Cr1Mo1V steel round billet is subjected to homogenization heat treatment at a temperature of 1200 to 1260°C, and the holding time of the homogenization heat treatment is at least 90 minutes; Step 2: Roll the 15Cr1Mo1V steel round billet obtained from Step 1 after homogenization heat treatment into 15Cr1Mo1V steel pipe. Step 3: The 15Cr1Mo1V steel pipe obtained from Step 2 is normalized at a temperature of 970 to 1000℃. Step 4: Cool the normalized 15Cr1Mo1V steel pipe obtained from Step 3 to a temperature of 100 to 300°C at a cooling rate of 80 to 120°C / min, and then air cool it to a temperature below 40°C. Step 5: The 15Cr1Mo1V steel pipe obtained from Step 4 and cooled to below 40°C is tempered at a temperature of 730 to 760°C, and then air-cooled to below 40°C.

2. The preparation method according to claim 1, characterized in that, The 15Cr1Mo1V steel pipe is composed of the following elements: Based on the total weight of the 15Cr1Mo1V steel pipe 0.11 to 0.14 wt% of C; 0.20 to 0.30 wt% of Si element; 0.70 to 0.90 wt% of Mn element; 1.15 to 1.30 wt% of Cr element; 0.90 to 1.00 wt% of Mo; 0.20 to 0.30 wt% of V; The balance consists of Fe and unavoidable impurity elements.

3. The preparation method according to claim 2, characterized in that, The unavoidable impurity elements: The Ni content is controlled below 0.20% by weight; The content of Cu element is controlled below 0.20% by weight; The content of Al element is controlled below 0.020% by weight; The content of phosphorus (P) should be controlled below 0.015% by weight. The sulfur content is controlled below 0.010% by weight; The content of As element is controlled below 0.015% by weight; The content of Sb element is controlled below 0.010% by weight; The content of Bi element is controlled below 0.010% by weight; The Sn content is controlled below 0.015% by weight; and / or The Pb content is controlled to be below 0.015% by weight.

4. The preparation method according to claim 3, characterized in that, The total content of the unavoidable impurity elements As, Sb, Bi, Sn and Pb is controlled to be below 0.035% by weight.

5. The preparation method according to claim 1, characterized in that, The 15Cr1Mo1V steel round billet in step 1 is obtained through the following method: 15Cr1Mo1V steel ingots cast from molten steel are forged to obtain 15Cr1Mo1V steel round billets. Before forging, the temperature of the 15Cr1Mo1V steel ingots is adjusted to a range of 1140°C to 1260°C. During forging, the initial forging temperature is controlled above 1000°C, the final forging temperature above 780°C, and the forging ratio is not less than 3. Then, the 15Cr1Mo1V steel round billets obtained through forging are annealed at a temperature not lower than 600°C, with a holding time of at least 10 hours. Finally, the annealed 15Cr1Mo1V steel round billets are cooled to a temperature below 40°C at a cooling rate not exceeding 40°C / hour, thereby obtaining 15Cr1Mo1V steel round billets to be subjected to homogenization treatment. or The billet temperature of the 15Cr1Mo1V steel round billet, which is directly cast from molten steel, is controlled within the range of 500 to 700℃. Then, it is slowly cooled to a temperature below 40℃ at a cooling rate of no more than 10℃ / hour, thereby obtaining the 15Cr1Mo1V steel round billet to be subjected to homogenization treatment.

6. The preparation method according to claim 1, characterized in that, The rolling in step 2 includes rolling using an ASSEL rolling mill.

7. The preparation method according to claim 1, characterized in that, The wall thickness of the 15Cr1Mo1V steel pipe shall not exceed 100 mm, preferably in the range of 20 to 100 mm.

8. The preparation method according to any one of claims 1 to 7, characterized in that, The holding time for the normalizing treatment in step 3 is no less than 1.5 minutes per millimeter of the 15Cr1Mo1V steel pipe wall thickness.

9. The preparation method according to any one of claims 1 to 7, characterized in that, The holding time for the tempering treatment in step 5 is no less than 3 minutes per millimeter of the 15Cr1Mo1V steel pipe wall thickness.

10. A 15Cr1Mo1V steel pipe prepared by the preparation method according to any one of claims 1 to 9, characterized in that, The 15Cr1Mo1V steel pipe has one or more of the following properties: The microstructure is bainite plus ferrite, without tempered martensite, wherein the bainite content is above 20%, preferably above 50%; The yield strength Rp0.2 reaches over 314 MPa; The tensile strength Rm is in the range of 490 to 686 MPa; The elongation after fracture reaches 18.0% or more; Hardness deviation is within 20 HBW; The grain size level reaches 5.0 or higher; The impact absorption energy at 20℃ reaches over 100 J; and The low-temperature impact absorption energy at -20℃ reaches over 100 J.

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