Steel pipe quenching method

Abstract

The invention provides a steel pipe quenching method. The steel pipe quenching method comprises the following steps: heating a to-be-treated steel pipe to a first preset temperature; simultaneously carrying out inner spray cooling operation and outer spray cooling operation on the to-be-treated steel pipe; when the internal spraying cooling operation and the external spraying cooling operation are continued for a first preset time T1, the internal spraying cooling operation is stopped, and the external spraying cooling operation is continued; and when the external spraying cooling operation lasts for a second preset time T2, the external spraying cooling operation is stopped. According to the technical scheme, the steel pipe quenching method can solve the problem that in the steel pipe quenching process through an existing steel pipe quenching method, due to the fact that cooling inside and outside the steel pipe is not uniform, longitudinal quenching microcracks are prone to being generated on the steel pipe.

Description

Technical Field

[0001] This invention relates to the field of seamless steel pipe production technology, and more specifically, to a steel pipe quenching method. Background Technology

[0002] Among various quenching technologies for steel pipes, water, as the quenching medium, can reduce environmental pollution, lower steel pipe costs, and improve pipe performance. The practical technology of integral water quenching of seamless steel pipes has been widely applied in the quenching production of medium-carbon CrMo series steel pipes with strong hardenability. The main equipment includes horizontal steel pipe quenching machines and water circulation systems.

[0003] Currently, steel pipe quenching commonly employs a combination of external quenching, internal spraying, and rotary water quenching. Due to the slender structure of steel pipes, the cooling intensity of external quenching is often far lower than that of internal spraying, resulting in an unfavorable cooling pattern of "strong internal cooling and weak external cooling." This uneven cooling causes the inner wall of the steel pipe to bear enormous circumferential and radial tensile stresses in the critical temperature range of martensitic transformation, making the steel pipe highly susceptible to longitudinal microcracks. Summary of the Invention

[0004] The main objective of this invention is to provide a steel pipe quenching method that can solve the problem that longitudinal micro-cracks are easily generated in the steel pipe due to uneven cooling inside and outside the steel pipe during the quenching process using existing steel pipe quenching methods.

[0005] To achieve the above objectives, the present invention provides a steel pipe quenching method, comprising: heating the steel pipe to be treated to a first preset temperature; simultaneously performing internal spray cooling and external rinsing cooling operations on the steel pipe to be treated; stopping the internal spray cooling operation and continuing the external rinsing cooling operation when the internal spray cooling operation and the external rinsing cooling operation last for a first preset time T1; and stopping the external rinsing cooling operation when the external rinsing cooling operation lasts for a second preset time T2.

[0006] Furthermore, the first preset time T1 is the time required for the inner wall temperature of the steel pipe to be treated to reach the second preset temperature. The value range of the second preset temperature is Ms+30℃~Ms+50℃, where Ms is the martensitic transformation temperature.

[0007] Furthermore, the first preset time T1 and the second preset time T2 satisfy the following relationship: T2 = (2~4) × T1.

[0008] Furthermore, before the step of simultaneously performing internal spray cooling and external spray cooling on the steel pipe to be treated, the following steps are included: calculating the initial internal spray cooling operation time T0; obtaining the chemical composition data of the steel pipe to be treated; calculating the hardenability compensation factor K based on the chemical composition data of the steel pipe to be treated; and correcting the initial internal spray cooling operation time based on the hardenability compensation factor K to obtain a first preset time T1.

[0009] Furthermore, the initial internal spray cooling operation time T0 is calculated using the following formula: T0 = T3 × (t1 / t0) 2 Where T3 is the duration of the internal spray cooling operation of the reference steel pipe, t0 is the wall thickness of the reference steel pipe, and t1 is the wall thickness of the steel pipe to be treated.

[0010] Furthermore, the chemical composition data of the steel pipe to be treated includes the mass percentage of carbon (a1), manganese (b1), chromium (c1), molybdenum (d1), copper (e1), nickel (f1), and vanadium (g1) in the steel pipe to be treated.

[0011] Furthermore, the hardenability compensation factor K is calculated using the following formula: Where m is the sensitivity coefficient, and the value of m ranges from 1.0 to 2.5. As the benchmark hardenability equivalent, The hardenability equivalent of the steel pipe to be treated.

[0012] Furthermore, the hardenability equivalent of the steel pipe to be treated Calculate using the following formula: Baseline hardenability equivalent Calculate using the following formula: Where a2 is the mass percentage of carbon in the reference steel pipe, b2 is the mass percentage of manganese in the reference steel pipe, c2 is the mass percentage of chromium in the reference steel pipe, d2 is the mass percentage of molybdenum in the reference steel pipe, e2 is the mass percentage of copper in the reference steel pipe, f2 is the mass percentage of nickel in the reference steel pipe, and g1 is the mass percentage of vanadium in the reference steel pipe.

[0013] Furthermore, the external cooling operation includes spraying a first coolant onto the outer wall of the steel pipe to be treated, with the flow rate of the first coolant being Q1. The internal cooling operation includes spraying a second coolant onto the inner wall of the steel pipe to be treated, with the flow rate of the second coolant being Q2. Q1 can be calculated using the following formula: Q2 can be calculated using the following formula: A1 is a constant with a value range of 10~25, B1 is a constant with a value range of 5~15, C1 is a constant with a value range of 0.2~0.8, A2 is a constant with a value range of 2~6, B2 is a constant with a value range of 5~12, C2 is a constant with a value range of 0.3~1.0, D is the outer diameter of the steel pipe to be treated, and t1 is the wall thickness of the steel pipe to be treated.

[0014] Furthermore, the first preset temperature ranges from 840℃ to 940℃.

[0015] Applying the technical solution of this invention, the steel pipe to be treated is first heated to a first preset temperature to ensure complete austenitization and uniform microstructure, creating conditions for subsequent quenching. Then, the steel pipe to be treated is simultaneously subjected to internal spray cooling and external rinsing cooling. When the internal spray cooling and external rinsing cooling operations continue for a first preset time T1, the internal spray cooling operation is terminated. After the internal spray cooling operation stops, the external rinsing cooling operation continues until a second preset time T2. By extending the external rinsing time, sufficient cooling of the outer wall of the steel pipe to be treated can be achieved. At the same time, due to the interruption of the internal spray cooling operation, the cooling rate of the inner wall of the steel pipe to be treated decreases, which can reduce the temperature difference between the inner and outer walls of the steel pipe to be treated. This makes the cooling of the inner and outer walls of the steel pipe to be treated more synchronous in the martensitic transformation temperature range, thereby reducing the circumferential and radial tensile stress on the inner wall of the steel pipe to be treated in the martensitic transformation temperature range and effectively suppressing the generation of longitudinal microcracks.

[0016] The steel pipe quenching method of this application has the following advantages:

[0017] 1) Low cost, easy to implement, and significant results. By precisely controlling the timing and duration of internal spraying, rather than blindly improving cooling uniformity, it actively intervenes in and optimizes the stress evolution path during the quenching process.

[0018] 2) Precise targeting: Directly targets the structural stress in the martensitic transformation zone, the root cause of quenching cracks, rather than the entire cooling process;

[0019] 3) No need to modify expensive hardware facilities (such as nozzles and water pumps), it can be achieved simply by optimizing the control logic, solving the "soft problems" that "hard costs" cannot solve;

[0020] 4) Wide adaptability: This method is highly universal and can be adapted to existing equipment that commonly uses the external spraying + internal spraying method in steel pipe quenching, thus improving the equipment's adaptability to different steel types.

[0021] 5) Quality leap: It can further reduce the quenching crack rate from a low level (such as 0.5%) to zero, and achieve high-quality and stable production of steel grades with quenching crack risk;

[0022] 6) Intelligent interface: It can be combined with big data on materials to achieve dynamic adaptive control. Attached Figure Description

[0023] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1 A flowchart of a steel pipe quenching method according to an embodiment of the present invention is shown. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] Currently, steel pipe quenching commonly employs an external spray + internal spray + rotary water quenching method. Due to the slender structure of steel pipes, the cooling intensity of external spray is often much lower than that of internal spray, resulting in an unfavorable cooling pattern of "strong internal and weak external." This uneven cooling causes the inner wall of the steel pipe to experience enormous circumferential and radial tensile stresses in the martensitic transformation zone, making it highly susceptible to longitudinal microcracks. Traditional solutions focus on optimizing nozzle layout, increasing external spray flow rate, or changing the medium, but these are costly, complex to modify, and fail to fundamentally solve the problem of excessive instantaneous stress. Quenching cracks are defined as unacceptable defects in many standards and cannot be repaired by grinding. For high-performance medium carbon steel pipes, even a quenching crack rate as low as 0.5% signifies significant quality risks and economic losses.

[0027] To solve the above problems, such as Figure 1 As shown, the present invention provides a steel pipe quenching method, which includes: heating the steel pipe to be treated to a first preset temperature; simultaneously performing internal spray cooling and external rinsing cooling operations on the steel pipe to be treated; when the internal spray cooling and external rinsing cooling operations last for a first preset time T1, stopping the internal spray cooling operation and continuing the external rinsing cooling operation; when the external rinsing cooling operation lasts for a second preset time T2, stopping the external rinsing cooling operation.

[0028] In this embodiment, the steel pipe to be treated is first heated to a first preset temperature, which is the temperature at which the steel pipe to be treated transforms from a ferrite and pearlite state to an austenite state, ensuring that the steel pipe to be treated is austenitized and has a uniform microstructure, creating conditions for subsequent quenching. Then, the steel pipe to be treated is simultaneously subjected to internal spray cooling and external rinsing cooling operations. When the internal spray cooling and external rinsing cooling operations continue for a first preset time T1, the internal spray cooling operation is terminated. After the internal spray cooling operation stops, the external rinsing cooling operation continues until a second preset time T2. By extending the external rinsing time, sufficient cooling of the outer wall of the steel pipe to be treated can be achieved. At the same time, due to the interruption of the internal spray cooling operation, the cooling rate of the inner wall of the steel pipe to be treated decreases, which can reduce the temperature difference between the inner and outer walls of the steel pipe to be treated, making the cooling of the inner and outer walls of the steel pipe to be treated more synchronous in the martensitic transformation temperature range. This reduces the circumferential and radial tensile stress on the inner wall of the steel pipe to be treated in the martensitic transformation temperature range, effectively suppressing the generation of longitudinal microcracks.

[0029] It should be noted that the steel pipe to be treated rotates around its own central axis during the internal spray cooling operation and the external water cooling operation. The external water cooling operation can ensure that the cross section of the steel pipe to be treated is fully cooled to room temperature and complete the microstructure transformation. The internal spray cooling operation and the external water cooling operation can be carried out using existing equipment that realizes "external watering + internal spraying + rotary water quenching" of steel pipe. The specific structure will not be described here.

[0030] The steel pipe quenching method described in this application is applicable to medium carbon alloy steel / low alloy steel pipes (such as 42CrMo, 35CrMo, 30CrMo, 29Mn5, 4140, 4130), but is not limited to the above-mentioned types.

[0031] In one embodiment, the first preset time T1 ranges from 5s to 20s. The specific value of the first preset time T1 needs to be determined according to the actual production situation, such as the outer diameter of the steel pipe, the wall thickness, and the cooling water volume.

[0032] In one embodiment of the present invention, the first preset time T1 is the time required for the inner wall temperature of the steel pipe to be treated to reach the second preset temperature, and the value range of the second preset temperature is Ms+30℃~Ms+50℃, wherein Ms is the martensitic transformation temperature.

[0033] In this embodiment, the first preset time T1 is the time required for the inner wall temperature of the steel pipe to be treated to reach the second preset temperature. When the temperature of the inner wall of the steel pipe to be treated drops to Ms+30℃~Ms+50℃, and then drops below Ms, the steel pipe to be treated begins to undergo martensitic transformation. This process is accompanied by volume expansion. If the inner wall of the steel pipe to be treated cools too quickly, the resulting volume expansion and structural stress relative to the outer wall will cause the inner wall of the steel pipe to be treated to be subjected to higher tensile stress, thereby initiating longitudinal cracks.

[0034] This application precisely controls the internal spray cooling operation to stop at a time T1, allowing the inner wall temperature of the steel pipe to cool to the range of Ms+30℃ to Ms+50℃. This effectively reduces the cooling rate of the inner surface, decreases phase transformation stress, and prevents the inner wall of the steel pipe from experiencing excessive tensile stress during the martensitic transformation. This synchronizes the cooling rate and microstructure transformation process of the inner and outer walls of the steel pipe, thereby reducing the probability of longitudinal cracks. Furthermore, by stopping the internal spray cooling operation at an appropriate time, the cooling rate of the inner wall of the steel pipe is slowed down, becoming closer to the cooling rate of the outer wall. This optimizes the overall cooling uniformity, ensuring consistency in the hardness and mechanical properties of the steel pipe and improving product quality.

[0035] It should be noted that the martensitic transformation temperature Ms is different for different types of steel, that is, the martensitic transformation temperature Ms is different for steel pipes of different types of steel.

[0036] For medium carbon manganese steel and low alloy steel, the martensitic transformation temperature Ms (°C) ranges from 250°C to 450°C.

[0037] In one embodiment of the present invention, the first preset time T1 and the second preset time T2 satisfy the following relationship: T2 = (2~4) × T1.

[0038] In this embodiment, since the external spray cooling operation time is much longer than the internal spray cooling operation time, the outer wall of the steel pipe to be treated can be cooled more fully. After the internal spray cooling operation is stopped, the cooling rate of the inner wall of the steel pipe to be treated decreases. At this time, the difference in cooling rate between the inner and outer walls of the steel pipe to be treated becomes smaller, so that the inner and outer walls of the steel pipe to be treated can be cooled synchronously in the martensitic transformation temperature range, thereby reducing the generation of longitudinal cracks caused by uneven cooling of the inner and outer walls of the steel pipe to be treated.

[0039] In one embodiment of the present invention, before the step of simultaneously performing internal spray cooling and external spray cooling on the steel pipe to be treated, the following steps are included: calculating the initial internal spray cooling operation time T0; obtaining the chemical composition data of the steel pipe to be treated; calculating the hardenability compensation factor K based on the chemical composition data of the steel pipe to be treated; and correcting the initial internal spray cooling operation time based on the hardenability compensation factor K to obtain a first preset time T1.

[0040] In this embodiment, by acquiring the chemical composition data of the steel pipe to be treated, the corresponding hardenability compensation factor K is calculated. The hardenability compensation factor K reflects the difference in hardenability of the steel pipe material to be treated. The initial internal spray cooling operation time is corrected according to the hardenability compensation factor K to obtain the first preset time T1. By optimizing T1, the cooling of the inner and outer walls of the steel pipe to be treated in the martensitic transformation temperature range can be made more synchronous, thereby reducing the circumferential and radial tensile stress on the inner wall of the steel pipe to be treated in the martensitic transformation temperature range and effectively suppressing the generation of longitudinal microcracks.

[0041] It should be noted that for high-transparency steels (such as 30CrMo, 35CrMo, 42CrMo, and 4140), the value of K ranges from 80 to 120; for medium-transparency steels (such as 30Mn2 and 25Cr), the value of K ranges from 120 to 180; and for low-transparency steels (such as 29Mn5 steel), the value of K ranges from 180 to 250.

[0042] In one embodiment of the present invention, the initial internal spray cooling operation time T0 is calculated by the following formula: T0 = T3 × (t1 / t0) 2 Where T3 is the duration of the internal spray cooling operation of the reference steel pipe, t0 is the wall thickness of the reference steel pipe, and t1 is the wall thickness of the steel pipe to be treated.

[0043] In this embodiment, by mathematically quantifying the relationship between the duration T3 of the internal spray cooling operation of the reference steel pipe and the wall thickness t1 and t0 of the steel pipe to be treated, a precise match between the cooling time and the steel pipe wall thickness is achieved. For steel pipes with larger wall thicknesses, the internal spraying time T0 calculated by the formula is longer, ensuring that the inner wall of the steel pipe to be treated can be sufficiently cooled; while for steel pipes with thinner walls, the calculated time will be correspondingly shorter, avoiding changes in material properties caused by over-cooling. By accurately calculating the initial internal spray cooling operation time T0 using the above formula, and then combining the hardenability compensation factor K to correct the initial internal spray cooling operation time T0, an internal spray cooling operation time adapted to the wall thickness of the steel pipe to be treated can be obtained. This allows for more accurate control of the cooling rate of the inner wall of the steel pipe to be treated, reducing the temperature difference between the inner and outer walls of the steel pipe to be treated, and ensuring uniform cooling of the inner and outer walls of the steel pipe to be treated.

[0044] It should be noted that the reference steel pipe refers to a steel pipe with known and stable performance parameters, used as a reference standard to evaluate and adjust the heat treatment process of the steel pipe to be treated. The duration and wall thickness of the internal spray cooling operation of the reference steel pipe are known, and the duration of the internal spray cooling operation of the reference steel pipe is obtained through a limited number of tests conducted in actual production.

[0045] When determining and selecting the reference steel pipe, the following conditions must be met: the reference steel pipe should have a similar chemical composition to the steel pipe to be treated, especially the content of carbon, manganese, chromium, molybdenum, etc.

[0046] For example, if the wall thickness t0 of the reference steel pipe is 5.51 mm and the duration of the internal spray cooling operation of the reference steel pipe is T3, and the wall thickness t1 of the steel pipe to be treated is 8 mm, the initial internal spray cooling operation time T0 = T3 × (t1 / t0). 2 =5s×(5.51 / 8)2≈5s×(1.45)2≈5s×2.1≈10.5s.

[0047] In one embodiment of the present invention, the chemical composition data of the steel pipe to be treated includes the percentage content of carbon a1, manganese b1, chromium c1, molybdenum d1, copper e1, nickel f1, and vanadium g1 in the steel pipe to be treated.

[0048] In this embodiment, the percentage content of chemical components such as carbon, manganese, chromium, molybdenum, copper, nickel, and vanadium in the steel pipe to be treated is obtained, and a hardenability compensation factor is calculated based on the percentage content of the above chemical components. Then, the initial internal spray cooling operation time T0 is corrected by the hardenability compensation factor to obtain a first preset time T1, which matches the material characteristics of the steel pipe to be treated. For example, high-carbon steel or steel pipes containing more alloying elements require a shorter cooling time to prevent overcooling, while low-carbon steel or steel pipes with lower alloying element content require a longer cooling time to promote the completion of microstructure transformation. This allows the duration of the internal spray cooling operation to be adjusted according to the actual hardenability requirements of the steel pipe to be treated, ensuring synchronous cooling of the inner and outer walls within the martensitic transformation temperature range, thereby effectively preventing crack formation.

[0049] It should be noted that the percentage content of chemical components such as carbon, manganese, chromium, molybdenum, copper, nickel, and vanadium in the steel pipe to be treated will be recorded in detail when the material leaves the factory or is inspected upon arrival, and there is no need to measure it again.

[0050] In one embodiment of the present invention, the hardenability compensation factor K is calculated by the following formula: Where m is the sensitivity coefficient, and the value of m ranges from 1.0 to 2.5. As the benchmark hardenability equivalent, The hardenability equivalent of the steel pipe to be treated.

[0051] In this embodiment, m is a sensitivity coefficient, representing the time adjustment ratio caused by each unit change in CE value. By comparing the hardenability equivalent of the steel pipe to be treated with the benchmark hardenability equivalent and multiplying by the sensitivity coefficient, a hardenability compensation factor can be obtained. The hardenability compensation factor is used to correct the initial internal spray cooling operation time T0, ensuring that the cooling rate of the inner and outer walls of the steel pipe to be treated matches the microstructure transformation process. For steel pipes with high hardenability, the hardenability compensation factor is smaller; for steel pipes with low hardenability, the hardenability compensation factor is larger.

[0052] The steel pipes to be treated may come from different batches, with slight differences in chemical composition and hardenability. By calculating the hardenability compensation factor to correct the initial internal spray cooling operation time T0, the first preset time can be adjusted in a personalized manner according to the hardenability difference of the steel pipes to be treated, ensuring that the inner and outer walls are cooled synchronously in the martensitic transformation temperature range.

[0053] In one embodiment of the present invention, the hardenability equivalent of the steel pipe to be treated Calculate using the following formula: Baseline hardenability equivalent Calculate using the following formula: Where a2 is the percentage of carbon in the reference steel pipe, b2 is the percentage of manganese in the reference steel pipe, c2 is the percentage of chromium in the reference steel pipe, d2 is the percentage of molybdenum in the reference steel pipe, e2 is the percentage of copper in the reference steel pipe, f2 is the percentage of nickel in the reference steel pipe, and g1 is the percentage of vanadium in the reference steel pipe.

[0054] In this embodiment, the hardenability equivalent of the steel pipe to be treated and the benchmark hardenability equivalent are used to calculate the hardenability compensation factor. The initial internal spray cooling operation time is corrected by the hardenability compensation factor to match the hardenability requirements of the steel pipe to be treated, which can significantly reduce the probability of crack formation, improve the product qualification rate, reduce scrap, and reduce production costs.

[0055] It should be noted that the percentage content of chemical components such as carbon, manganese, chromium, molybdenum, copper, nickel, and vanadium in the reference steel pipe will be recorded in detail when the material leaves the factory or is inspected upon arrival, and there is no need to measure it yourself. Furthermore, the above-mentioned formulas for calculating the reference hardenability equivalent and the hardenability equivalent of the steel pipe to be treated are applicable to steel pipes with a carbon content greater than 0.12%.

[0056] In one embodiment of the present invention, the external cooling operation includes spraying a first coolant onto the outer wall of the steel pipe to be treated, wherein the flow rate of the first coolant is Q1. The internal cooling operation includes spraying a second coolant onto the inner wall of the steel pipe to be treated, wherein the flow rate of the second coolant is Q2. Q1 can be calculated using the following formula: Q2 can be calculated using the following formula: A1 is a constant with a value range of 10~25, B1 is a constant with a value range of 5~15, C1 is a constant with a value range of 0.2~0.8, A2 is a constant with a value range of 2~6, B2 is a constant with a value range of 5~12, C2 is a constant with a value range of 0.3~1.0, D is the outer diameter of the steel pipe to be treated, and t1 is the wall thickness of the steel pipe to be treated.

[0057] In this embodiment, the above formula can calculate the flow rate of the first coolant used for external cooling and the flow rate of the second coolant used for internal spray cooling based on the outer diameter and wall thickness of the steel pipe to be treated. This ensures that the coolant coverage area and flow velocity match the physical properties of the steel pipe, thereby improving cooling efficiency, avoiding uneven cooling or resource waste caused by insufficient or excessive flow, and ensuring the uniformity of the steel pipe along its entire length. By establishing a quantitative relationship between the coolant flow rate and the dimensions (outer diameter and wall thickness) of the steel pipe to be treated, it is easy to integrate coolant flow control into the automatic control system, improving the automation level and operational efficiency of the heat treatment process.

[0058] In one embodiment of the present invention, the first preset temperature ranges from 840°C to 940°C.

[0059] In this embodiment, heating the steel pipe to be treated to a temperature range of 840℃~940℃ ensures that the steel pipe transforms from structures such as pearlite and ferrite into austenite. This is a necessary step before quenching and creates conditions for subsequent rapid cooling, resulting in the formation of martensite structure inside the material, thereby giving the steel pipe to be treated good strength and toughness.

[0060] In one embodiment of the present invention, before the step of calculating the initial internal spray cooling operation time T0, the following steps are included: establishing a database, which stores the reference quenching process parameters of steel pipes of different specifications, the process parameters including at least a first preset time T1 and a second preset time T2; and obtaining the wall thickness t1 of the steel pipe to be processed.

[0061] In this embodiment, the baseline quenching process parameters for steel pipes of different specifications in the database are derived from the quenching results of multiple batches of steel pipes, including a first preset time T1 and a second preset time T2 for quenching steel pipes of different specifications. The establishment of the database achieves the standardization of heat treatment process parameters. For steel pipes of the same specifications, the process parameters in the database can be quickly retrieved without redesigning or adjusting each time, which greatly improves the efficiency of heat treatment and reduces the impact of human factors on the heat treatment effect.

[0062] In one embodiment of the present invention, the steel pipe quenching method further includes: establishing a database related to the hardenability of batches of steel pipe materials to be processed, and adjusting a first preset time T1 based on the chemical composition or hardenability data of the incoming batches. For example, for batches with high carbon content or high hardenability, the first preset time T1 is shortened.

[0063] In this embodiment, the hardenability-related data in the database provides a basis for adjusting the heat treatment parameters. T1 can be adjusted according to the chemical composition or hardenability data of the incoming steel pipe to ensure synchronous cooling of the inner and outer walls within the martensitic transformation temperature range.

[0064] In one embodiment, the steel pipe to be treated is a 30CrMo steel pipe with an outer diameter of 73mm and a wall thickness of 5.51mm. Both the first and second coolants are water. The flow rate of the first coolant in the internal spray cooling operation is 200m³ / h to 400m³ / h, and the flow rate of the second coolant in the external spray cooling operation is 1700m³ / h. Under the condition that the rotation speed of the steel pipe to be treated is 50RPM, the first preset time T1 is 3s to 8s, preferably 4s to 6s, and the second preset time T2 is 10s to 15s.

[0065] Example 1:

[0066] The steel pipe to be treated is a 30CrMo steel pipe with an outer diameter of 73mm and a wall thickness of 5.51mm. The quenching temperature is 860℃, and it is water quenched. The quenching method of this application is adopted, and the internal spray cooling operation and the external spray cooling operation are carried out simultaneously. The internal spray cooling operation is stopped after 5 seconds, and the external spray cooling operation continues until 12 seconds. The quenching crack rate is reduced to below 0.05%, and the hardness of the steel pipe fully meets the technical requirements.

[0067] Comparative example:

[0068] The steel pipe is a 30CrMo steel pipe with an outer diameter of 73mm, a wall thickness of 5.51mm, a quenching temperature of 860℃, water quenching, external rinsing and internal spraying for 10 seconds, and a quenching crack rate of about 0.5%.

[0069] Example 2:

[0070] The steel pipes to be processed were from a certain batch of 30CrMo steel pipes. Spectroscopic analysis revealed that their carbon content was at the upper limit of the standard (0.33%). Information about this batch was retrieved from the material database, classifying it as a "high-risk batch." The first preset time T1 was automatically reduced from 5 seconds to 4 seconds before quenching. This successfully avoided the potential peak quenching crack rate for this batch, ensuring quality stability.

[0071] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: The steel pipe to be treated is first heated to a first preset temperature to ensure that the austenite structure of the steel pipe to be treated is uniform, creating conditions for subsequent quenching. Then, the steel pipe to be treated is simultaneously subjected to internal spray cooling and external rinsing cooling. When the internal spray cooling and external rinsing cooling operations continue for a first preset time T1, the internal spray cooling operation of the steel pipe to be treated is terminated. After the internal spray cooling operation stops, the external rinsing cooling operation continues until a second preset time T2. By extending the external rinsing time, the outer wall of the steel pipe to be treated can be fully cooled. At the same time, due to the interruption of the internal spray cooling operation, the cooling rate of the inner wall of the steel pipe to be treated decreases, which can reduce the temperature difference between the inner and outer walls of the steel pipe to be treated, making the cooling of the inner and outer walls of the steel pipe to be treated more synchronous in the martensitic transformation temperature range. This reduces the circumferential and radial tensile stress borne by the inner wall of the steel pipe to be treated in the martensitic transformation temperature range, effectively suppressing the generation of longitudinal microcracks.

[0072] Obviously, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0073] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for quenching steel pipes, characterized in that, include: Heat the steel pipe to be processed to the first preset temperature; The steel pipe to be treated is simultaneously subjected to internal spray cooling and external spray cooling operations; When the internal spray cooling operation and the external spray cooling operation continue for a first preset time T1, the internal spray cooling operation is stopped and the external spray cooling operation continues. When the external cooling operation continues for a second preset time T2, the external cooling operation is stopped.

2. The steel pipe quenching method according to claim 1, characterized in that, The first preset time T1 is the time required for the inner wall temperature of the steel pipe to be treated to reach the second preset temperature. The value range of the second preset temperature is Ms+30℃~Ms+50℃, where Ms is the martensitic transformation temperature.

3. The steel pipe quenching method according to claim 1, characterized in that, The first preset time T1 and the second preset time T2 satisfy the following relationship: T2 = (2~4) × T1.

4. The steel pipe quenching method according to any one of claims 1 to 3, characterized in that, Before performing both internal spray cooling and external spray cooling operations on the steel pipe to be treated, the following steps are included: Calculate the initial internal spray cooling operation time T0; Obtain the chemical composition data of the steel pipe to be processed; The hardenability compensation factor K is calculated based on the chemical composition data of the steel pipe to be treated; The initial internal spray cooling operation time is corrected according to the hardenability compensation factor K to obtain the first preset time T1.

5. The steel pipe quenching method according to claim 4, characterized in that, The initial internal spray cooling operation time T0 is calculated using the following formula: T0 = T3 × (t1 / t0) 2 Where T3 is the duration of the internal spray cooling operation of the reference steel pipe, t0 is the wall thickness of the reference steel pipe, and t1 is the wall thickness of the steel pipe to be treated.

6. The steel pipe quenching method according to claim 5, characterized in that, The chemical composition data of the steel pipe to be treated includes the mass percentage of carbon (a1), manganese (b1), chromium (c1), molybdenum (d1), copper (e1), nickel (f1), and vanadium (g1) in the steel pipe to be treated.

7. The steel pipe quenching method according to claim 5, characterized in that, The hardenability compensation factor K is calculated using the following formula: Where m is the sensitivity coefficient, and the value of m ranges from 1.0 to 2.

5. As the benchmark hardenability equivalent, The hardenability equivalent of the steel pipe to be treated.

8. The steel pipe quenching method according to claim 7, characterized in that, The hardenability equivalent of the steel pipe to be treated Calculate using the following formula: The reference hardenability equivalent Calculate using the following formula: Wherein, a2 is the mass percentage of carbon in the reference steel pipe, b2 is the mass percentage of manganese in the reference steel pipe, c2 is the mass percentage of chromium in the reference steel pipe, d2 is the mass percentage of molybdenum in the reference steel pipe, e2 is the mass percentage of copper in the reference steel pipe, f2 is the mass percentage of nickel in the reference steel pipe, and g1 is the mass percentage of vanadium in the reference steel pipe.

9. The steel pipe quenching method according to any one of claims 1 to 3, characterized in that, The external cooling operation includes spraying a first coolant onto the outer wall of the steel pipe to be treated. When spraying the first coolant onto the outer wall of the steel pipe to be treated, the flow rate of the first coolant is Q1. The internal cooling operation includes spraying a second coolant onto the inner wall of the steel pipe to be treated. When spraying the second coolant onto the inner wall of the steel pipe to be treated, the flow rate of the second coolant is Q2. Q1 can be calculated using the following formula: Q2 can be calculated using the following formula: A1 is a constant with a value range of 10 to 25, B1 is a constant with a value range of 5 to 15, C1 is a constant with a value range of 0.2 to 0.8, A2 is a constant with a value range of 2 to 6, B2 is a constant with a value range of 5 to 12, C2 is a constant with a value range of 0.3 to 1.0, D is the outer diameter of the steel pipe to be processed, and t1 is the wall thickness of the steel pipe to be processed.

10. The steel pipe quenching method according to any one of claims 1 to 3, characterized in that, The first preset temperature ranges from 840℃ to 940℃.

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