Open-close type circular heat treatment resistance furnace for cylindrical forgings, design method of open-close type circular heat treatment resistance furnace and method for improving heat treatment uniformity of cylindrical forgings

Abstract

The invention relates to an open-close type circular heat treatment resistance furnace for cylindrical forgings and a design method thereof, in particular to a method for improving the heat treatment uniformity of the cylindrical forgings, and belongs to the technical field of heat treatment of forgings. The problems that in the prior art, the heat treatment energy consumption is high and the homogeneity and toughness matching performance of products are poor due to the fact that the heat treatment deformation of the cylindrical forgings is large and the heating time is long are solved. Radial bearing beams are symmetrically arranged at the furnace bottom of the resistance furnace in the circumferential direction, and the distance between the radial bearing beams and the center of the furnace bottom is larger than or equal to 1500 mm; and a thermal field-structure field coupling model is adopted, and the furnace bottom structure is designed through the forge piece deformation calculated through parameter input simulation. Through the design, the area of the effective heating area of the center area of the furnace bottom is enlarged, the heating efficiency of the lower portion of the hearth is improved, temperature fields of the upper portion and the lower portion of the hearth are rapid and even in the heat treatment process, the overall temperature difference of forge pieces is reduced, the homogeneity and toughness matching performance of products are improved, and energy consumption is reduced; the number of fulcrums is designed according to the forging size, and product homogeneity is further improved.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for cylindrical forgings, and in particular to an openable circular heat treatment resistance furnace for cylindrical forgings and its design method, as well as a method for improving the uniformity of heat treatment of cylindrical forgings. Background Technology

[0002] Nuclear power reactor pressure vessels, steam generators, and petrochemical containers are assembled and welded from multiple forgings. The forgings that make up the containers mainly include cylindrical sections, heads, and tube sheets, which are basically circular rotating forgings. Nuclear power reactors operate under high temperature, high pressure, and radiation environments for a long time, while petrochemical containers operate under high temperature, high pressure, and corrosive environments for a long time. Therefore, nuclear power and petrochemical containers have extremely high requirements for safety and long-term service stability, and the forgings that make up the containers need to have good homogeneity and strength-toughness matching.

[0003] However, the forgings required for nuclear power and petrochemical containers are mostly thin-walled, large-diameter products. Uneven heating and cooling processes during heat treatment can easily lead to temperature differences throughout the forgings, causing asynchronous microstructural transformations. This ultimately results in significant dimensional deformation, poor homogeneity and strength-toughness matching, and even quality problems affecting subsequent processing and use. Currently, this problem is mainly compensated for by machining allowances. While increasing machining allowances can effectively reduce forging deformation, it reduces material utilization and increases energy consumption and manufacturing costs.

[0004] Therefore, there is an urgent need for a new method or equipment to effectively improve product homogeneity and reduce deformation during the heat treatment process of thin-walled, large-diameter forgings, thereby improving product performance and utilization while reducing energy consumption and costs. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide an openable circular heat treatment resistance furnace for cylindrical forgings and its design method, as well as a method for improving the heat treatment uniformity of cylindrical forgings, in order to solve at least one of the problems in the prior art, such as large deformation during heat treatment of cylindrical forgings, long heating time leading to high heat treatment energy consumption, and poor product homogeneity and strength-toughness matching.

[0006] In a first aspect, embodiments of the present invention provide a design method for an openable circular heat treatment resistance furnace for cylindrical forgings, the heat treatment resistance furnace comprising a circular furnace bottom and a furnace hood, wherein a heating resistance strip is disposed on the inner wall of the furnace hood, and the method comprises:

[0007] (1) A load-bearing beam is symmetrically arranged along the circumferential direction on the inner side wall of the furnace bottom. The load-bearing beam extends radially along the furnace bottom and does not intersect with each other. The rest of the furnace bottom is equipped with a heating resistance strip.

[0008] (2) Using thermal field-microstructure field coupling simulation software, input the parameters of the cylindrical forging and the number of support points, and simulate and calculate the deformation of the cylindrical forging after heat treatment;

[0009] (3) Determine whether the deformation amount of the cylindrical forging obtained in step (2) meets the requirements. If it does, determine the number of support points as the number of load-bearing beams. The deformation amount includes the elliptical deformation amount of the cylindrical forging in the diameter direction and the high-low undulation deformation amount in the height direction.

[0010] (4) If the deformation of the cylindrical forging obtained in step (2) does not meet the requirements, increase the number of support points in step (2) by 2, and repeat steps (2) and (3) until the deformation of the cylindrical forging meets the requirements.

[0011] Furthermore, in step (1), the distance between the load-bearing beam and the center of the furnace bottom is greater than or equal to 1500mm.

[0012] Furthermore, in step (2), the parameters of the cylindrical forging include the cylindrical forging dimensions, coefficient of thermal expansion, temperature and time of heat treatment, and heat treatment intensity.

[0013] Furthermore, the dimensions of the cylindrical forging include: an outer diameter of 3000-10000 mm, a thickness of 200-565 mm, and a height of 2000-5000 mm.

[0014] Furthermore, the coefficient of thermal expansion is 11-18×10⁻⁶. -6 / ℃.

[0015] Furthermore, the heat treatment temperature is 600-1100℃, and the time is 4-25h.

[0016] Furthermore, the heat treatment intensity is 30-380 MPa.

[0017] Furthermore, in step (2), the number of support points is 2+2n, where 1≤n≤7.

[0018] Furthermore, in step (2), the number of support points is preferably 4, 8, or 12.

[0019] Furthermore, in step (3), the ellipse deformation amount does not exceed 1 / 2 of the single-side allowance, and the height undulation deformation amount does not exceed 1 / 3 of the height allowance.

[0020] Furthermore, when the outer diameter R of the cylindrical forging is in the range of 3000mm≤R<5000mm and the thickness T is in the range of 200mm≤T<285mm, the number of load-bearing beams is at least 4.

[0021] Furthermore, when the outer diameter R of the cylindrical forging is in the range of 5000mm≤R≤7000mm and the thickness T is in the range of 285mm≤T<395mm, the number of load-bearing beams is at least 8.

[0022] Furthermore, when the outer diameter R of the cylindrical forging is in the range of 7000mm < R ≤ 10000mm and the thickness T is in the range of 395mm < T ≤ 565mm, the number of load-bearing beams is at least 12.

[0023] Secondly, embodiments of the present invention provide an openable circular heat treatment resistance furnace, which is designed by the aforementioned design method.

[0024] Thirdly, embodiments of the present invention also provide a method for improving the heat treatment uniformity of cylindrical forgings, wherein the method employs the openable circular heat treatment resistance furnace to heat treat the cylindrical forgings.

[0025] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0026] 1. Unlike existing openable heat treatment resistance furnaces with four intersecting load-bearing beams, the load-bearing beams of the openable heat treatment resistance furnace of this invention are shorter than the radius of the furnace platform and do not intersect each other. The central area of ​​the furnace platform is released as a heating zone. With the overall area of ​​the furnace platform unchanged, the heating area in the center of the furnace platform is increased compared to the previous one, which improves the heating efficiency of the lower part of the furnace chamber and realizes rapid heating of the inner surface of the cylinder. In a short time, the temperature field of the upper and lower parts of the furnace chamber is rapidly and uniformly uniform, and the heating of the upper and lower parts of the cylindrical forgings is uniform and uniform.

[0027] In addition, the present invention uses thermal field-microstructure field coupling simulation software to assist in designing the number of load-bearing beams of the openable heat treatment resistance furnace based on the relevant parameters of the cylindrical forging to be heat treated. This allows the designed openable heat treatment resistance furnace to not only improve heating efficiency during the heat treatment of large-diameter thin-walled cylindrical forgings, but also reduce the deformation tendency of the forgings during the heat treatment process, achieve the simultaneous transformation of the forging microstructure, and improve the product qualification rate.

[0028] 2. The heat treatment resistance furnace designed in this invention is mainly for large, heavy cylindrical forgings, the diameter of which is usually greater than 3000mm. Therefore, this invention designs the load-bearing beams symmetrically arranged along the circumference of the furnace bottom to be at least 1500mm away from the center of the furnace bottom, releasing the entire central area of ​​the furnace bottom with a diameter of at least 3000mm as a heating zone. This is different from the furnace bottom of existing openable heat treatment resistance furnaces (such as...). Figure 1Compared to (b), when the furnace diameter is 8000mm, the present invention increases the heating area of ​​Φ3000mm in the center of the furnace bottom by at least 1.63 times. The heat generated can accelerate the heating of the inner surface of the cylindrical forging, promote the rapid homogenization of the temperature field in the upper and lower parts of the furnace during the heat treatment process, reduce the overall temperature difference of the forging, improve the homogeneity and toughness matching of the product, and reduce energy consumption.

[0029] 3. Based on the dimensions (diameter, thickness, and height) and thermal expansion coefficient of the forging to be treated, the present invention designs an openable heat treatment resistance furnace with a dedicated load-bearing beam that matches the forging to be treated. After heat treatment at a certain temperature for a period of time, the cylindrical forging can not only improve heating efficiency and achieve the target strength and toughness through microstructure transformation, but also suppress the expansion or contraction of the cylindrical forging during the heat treatment process, reduce deformation, and effectively improve product homogeneity.

[0030] 4. This invention provides a heat treatment resistance furnace suitable for heat treating large-sized, thin-walled low-alloy steel cylindrical forgings. By heat treating the forgings, the deformation amount can be obtained within the range of subsequent machining allowances while shortening the heating time, thereby improving the homogeneity and strength-toughness matching performance of the product and reducing energy consumption and costs.

[0031] 5. In the design of the openable circular heat treatment resistance furnace for cylindrical forgings, the present invention considers the parameters of cylindrical forgings such as size, coefficient of thermal expansion, temperature and time of heat treatment, and heat treatment intensity when performing thermal field-microstructure field coupling simulation. The resulting openable circular heat treatment resistance furnace can meet the needs of various cylindrical forgings.

[0032] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0033] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0034] Figure 1 (a) is a schematic diagram of a large-scale openable heat treatment furnace;

[0035] Figure 1 (b) is a schematic diagram of the furnace bottom structure of an existing large-scale openable heat treatment furnace;

[0036] Figure 2 A process flow diagram for designing the heat treatment furnace for this invention;

[0037] Figure 3 A schematic diagram of the furnace bottom structure with four load-bearing beams designed according to the present invention;

[0038] Figure 4 A schematic diagram of the furnace bottom structure of the heat treatment furnace with 8 load-bearing beams designed for this invention, (a) for processing small cylindrical forgings, (b) for processing large cylindrical forgings;

[0039] Figure 5 A schematic diagram of the furnace bottom structure of the heat treatment furnace with 16 load-bearing beams designed for this invention, (a) for processing small cylindrical forgings, (b) for processing large cylindrical forgings;

[0040] Figure label:

[0041] 1-Furnace bottom; 2-Bearing beam; 2-1-Primary bearing beam; 2-2-Secondary bearing beam; 2-3-Tertiary bearing beam; 3-Padded iron; 4-Cylindrical forging; 5-Furnace hood; 6-Furnace bottom heating zone. Detailed Implementation

[0042] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0043] Performance heat treatment is a crucial process for ensuring the various mechanical properties of forgings. The performance heat treatment process for forgings required for nuclear power and petrochemical containers demands uniform heating and cooling to guarantee the uniformity of properties across all parts of the forging. However, forgings for nuclear power and petrochemical containers are mostly thin-walled, large-diameter products. Uneven heating and cooling during the heat treatment process can easily lead to temperature differences throughout the forging, causing asynchronous microstructural transformations. This ultimately results in significant dimensional deformation, poor homogeneity and strength-toughness matching, and even quality problems affecting subsequent processing and use. Currently, this problem is mainly compensated for by machining allowances. While increasing machining allowances can effectively reduce forging deformation, it reduces material utilization and increases energy consumption and manufacturing costs.

[0044] In their research on the heat treatment of thin-walled, large-diameter cylindrical forgings, the inventors discovered that: Trolley-type heat treatment furnaces, with their rectangular box structure and primarily gas-fired heating, often fail to achieve a uniform temperature field around the circumference of circular forgings during heating, leading to increased deformation and reduced product homogeneity. Open-type heat treatment furnaces, also circular in structure and primarily electrically heated, have a furnace chamber structure similar to the shape of the forging. However, the furnace hood, made of lightweight refractory material, has low heat storage capacity, while the furnace bottom, composed of castable refractory bricks, has high heat storage capacity. This results in better circumferential heating uniformity but lower heating power at the furnace bottom. Furthermore, the significant temperature difference between the upper and lower parts of the furnace chamber during operation causes a noticeable temperature difference across the forging, similarly increasing deformation and reducing product homogeneity. Additionally, the longer heat treatment time increases energy consumption and cost.

[0045] Therefore, this invention provides a design method for an openable circular heat treatment resistance furnace for cylindrical forgings, and the relevant process flow diagram is as follows. Figure 2 As shown, the heat treatment resistance furnace includes a circular furnace bottom and a furnace hood, with heating resistance strips arranged on the inner wall of the furnace hood. The method includes:

[0046] (1) A load-bearing beam is symmetrically arranged along the circumferential direction on the inner side wall of the furnace bottom. The load-bearing beam extends radially along the furnace bottom and does not intersect with each other. The rest of the furnace bottom is equipped with a heating resistance strip.

[0047] (2) Using thermal field-microstructure field coupling simulation software, input the parameters of the cylindrical forging and the number of support points, and simulate and calculate the deformation of the cylindrical forging after heat treatment;

[0048] (3) Determine whether the deformation amount of the cylindrical forging obtained in step (2) meets the requirements. If it does, determine the number of support points as the number of load-bearing beams. The deformation amount includes the elliptical deformation amount of the cylindrical forging in the diameter direction and the high-low undulation deformation amount in the height direction.

[0049] (4) If the deformation of the cylindrical forging obtained in step (2) does not meet the requirements, increase the number of support points in step (2) by 2, and repeat steps (2) and (3) until the deformation of the cylindrical forging meets the requirements.

[0050] Unlike existing openable heat treatment resistance furnaces with four intersecting load-bearing beams, the load-bearing beams of this invention are shorter than the radius of the furnace platform and do not intersect each other. This releases the central area of ​​the furnace platform as a heating zone. With the overall area of ​​the furnace platform remaining unchanged, the heating area in the center of the furnace platform is increased compared to the previous design, improving the heating efficiency of the lower part of the furnace chamber and achieving rapid heating of the inner surface of the cylinder. This allows for rapid and uniform temperature field distribution in the upper and lower parts of the furnace chamber and uniform heating of the upper and lower parts of cylindrical forgings in a shorter time.

[0051] In addition, the present invention uses thermal field-microstructure field coupling simulation software to assist in designing the number of load-bearing beams of the openable heat treatment resistance furnace based on the relevant parameters of the cylindrical forging to be heat treated. This allows the designed openable heat treatment resistance furnace to not only improve heating efficiency during the heat treatment of large-diameter thin-walled cylindrical forgings, but also reduce the deformation tendency of the forgings during the heat treatment process, achieve the simultaneous transformation of the forging microstructure, and improve the product qualification rate.

[0052] Specifically, the thermal field-tissue field coupling simulation software is ABAQUS.

[0053] It should be noted that the heat treatment resistance furnace designed in this invention is mainly for large and heavy cylindrical forgings, the diameter of which is usually greater than 3000mm. Therefore, the distance between the load-bearing beam of the heat treatment resistance furnace and the center of the furnace bottom cannot be too small, so as not to affect the heat transfer rate.

[0054] Specifically, in step (1), the distance between the load-bearing beam and the center of the furnace bottom is greater than or equal to 1500mm. The specific distance is based on the ability to support the heat-treated cylindrical forging, so that it does not occupy or cover the furnace bottom heating zone corresponding to the inner diameter of the cylinder while supporting the heat-treated cylindrical forging.

[0055] Specifically, when the distance between the load-bearing beam and the center of the furnace bottom is greater than or equal to 1500mm, the entire central area of ​​the furnace bottom with a diameter of at least 3000mm can be released as a heating zone, similar to the furnace bottom of existing openable heat treatment resistance furnaces (such as...). Figure 1 Compared to (b), when the furnace diameter is 8000mm, the present invention increases the heating area of ​​Φ3000mm in the center of the furnace bottom by at least 1.63 times. The heat generated can accelerate the heating of the inner surface of the cylindrical forging, promote the rapid homogenization of the temperature field in the upper and lower parts of the furnace during the heat treatment process, reduce the overall temperature difference of the forging, improve the homogeneity and toughness matching of the product, and reduce energy consumption.

[0056] It should be noted that, in order to ensure that the deformation of the cylindrical forging after heat treatment, as simulated and calculated using the thermal field-microstructure field coupling simulation software, can truly reflect the actual deformation of the cylindrical forging after heat treatment, this invention needs to limit the input parameters during the thermal field-microstructure field coupling simulation.

[0057] Specifically, in step (2), during the process of using the thermal field-organic field coupling simulation software, the parameters of the cylindrical forging include the cylindrical forging size, thermal expansion coefficient, heat treatment temperature and time, and heat treatment intensity. Except for the number of support points provided by the heat treatment resistance furnace, these parameters will affect the degree of expansion or contraction of the cylindrical forging after heat treatment, and directly affect the degree of deformation of the forging.

[0058] More specifically, the dimensions of the cylindrical forging are: outer diameter greater than 3000mm, thickness greater than 200mm, and height less than 5000mm. Preferably, according to actual application needs, the outer diameter of the cylindrical forging is 3000-10000mm, the thickness is 200-565mm, and the height is 2000-5000mm.

[0059] More specifically, the cylindrical forgings described in this invention are made of low alloy steel, such as 16Mn, 18MnNiMo, 20MnNiMo, 20MnMoNb, 12Cr2Mo1, 12Cr2Mo1V, etc.

[0060] More specifically, the coefficient of thermal expansion of the cylindrical forging is 11-18×10⁻⁶. -6 / ℃, can be 11×10 -6 / ℃, 12.5×10 -6 / ℃, 13×10 -6 / ℃, 14×10 -6 / ℃, 15.5×10 -6 / ℃, 16×10 -6 / ℃, 18×10 -6 / ℃, if the coefficient of thermal expansion is too large, it will cause premature instability and deformation during heating. The smaller the coefficient of thermal expansion, the better the dimensional stability at the same temperature.

[0061] More specifically, the heat treatment temperature is 600-1100℃, which can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, or 1100℃. The higher the heating temperature, the lower the strength of the material, and the greater the tendency to deform under its own weight, requiring more support points to ensure dimensional stability. The lower the heating temperature, the smaller the tendency to deform. If the heat treatment temperature is too high, it will lead to increased deformation tendency, coarse grains, and severe oxidation and decarburization. If it exceeds the optimal heat treatment temperature range, performance deterioration will occur, and the performance indicators will not be met after heat treatment. If the heat treatment temperature is too low, although better dimensional stability can be obtained, the performance of the forging after heat treatment will not meet the standards.

[0062] Specifically, the heat treatment time is 4-25 hours, which can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours. If the heating time is too short, the heat treatment effect will be insufficient and the mechanical performance index requirements after heat treatment will not be met. If the heating time is too long, it will lead to performance degradation, severe oxidation and decarburization, and increased energy consumption.

[0063] It should be noted that, in order to improve the accuracy of the thermal field-microstructure field coupling simulation, this invention requires inputting the strength of the forging at the heat treatment temperature and the heat treatment strength when using software to simulate and calculate the deformation of the heat-treated cylindrical forging. The heat treatment strength can be determined based on the target strength of the cylindrical forging after heat treatment (at room temperature).

[0064] More specifically, the target strength of the cylindrical forging after heat treatment is 400-750MPa, preferably 550-700MPa, and can be 550MPa, 560MPa, 580MPa, 600MPa, 610MPa, 630MPa, 650MPa, 670MPa, or 700MPa. If the strength is too low, the forging will not meet the performance requirements. If the strength is too high, the toughness will be poor and there will be a mismatch between strength and toughness.

[0065] More specifically, the heat treatment strength of the cylindrical forging is 30-380MPa, which can be 30MPa, 60MPa, 80MPa, 100MPa, 130MPa, 150MPa, 180MPa, 200MPa, 220MPa, 245MPa, 270MPa, 300MPa, 330MPa, 350MPa, or 380MPa. The heat treatment strength cannot be too low, so as to avoid severe deformation of the forging during the heat treatment process, which would lead to the scrapping of the forging.

[0066] It should be noted that when the deformation of the cylindrical forging is simulated using thermal field-microstructure field coupling simulation software, the number of support points is determined to be the number of load-bearing beams.

[0067] It should be noted that, in order to meet the requirements of subsequent processing of heat-treated forgings, ensure the normal use of forgings, and reduce waste, this invention needs to limit the type and size of deformation of the cylindrical forgings after heat treatment.

[0068] Specifically, in step (2), the deformation includes the elliptical deformation of the cylindrical forging in the diameter direction and the undulating deformation in the height direction. Only when the deformation of the forging after heat treatment meets the requirements in both the diameter and height directions can a qualified product be obtained. The smaller the deformation of the forging after heat treatment, the better. The larger the deformation, the greater the difficulty in ensuring the final finishing. Constraints can be uniformly made according to a ratio. The allowable deformation varies for cylinders of different diameters. This invention limits the deformation during the heat treatment process based on the forging allowance.

[0069] More specifically, in step (2), the ellipse deformation amount does not exceed 1 / 2 of the single-side allowance, and the height undulation deformation amount does not exceed 1 / 3 of the height allowance.

[0070] Within the size range of the cylindrical forgings to be processed, in order to effectively distribute the weight of the materials and heating elements in the furnace, reduce local stress concentration, enhance the load-bearing capacity and stability of the furnace body, and ensure that the heat deformation of the forgings meets the requirements, this invention needs to limit the number of load-bearing beams of the heat treatment resistance furnace.

[0071] Specifically, in step (2), the number of support points is 2+2n, where 1≤n≤7, and can be 4, 6, 8, 10, 12, 14, or 16. If the number of load-bearing beams in the heat treatment resistance furnace is too small, it will reduce the load-bearing capacity and stability of the furnace body. If the number of load-bearing beams in the heat treatment resistance furnace is too large, it will have limited effect on reducing the deformation of the forgings during heat treatment, and will also increase the complexity and cost of furnace construction.

[0072] Specifically, in step (2), the number of support points is preferably 4, 8, and 16, which are common multiples of the minimum number of load-bearing beams, which is beneficial to the actual construction of the heat treatment resistance furnace.

[0073] It should be noted that, in order to achieve a uniform temperature distribution inside the furnace, reduce the temperature gradient, improve heating efficiency, and ensure that the heat-treated forgings have good homogeneity, the load-bearing beams of this invention are arranged at equal intervals along the circumference of the furnace bottom, and the beams are of equal length.

[0074] It should be noted that, in order to improve the heating efficiency of the inner wall of the furnace hood, the distance L between the inner wall of the furnace hood and the cylindrical forging is adjusted to 300-2500mm, which can be 300mm, 400mm, 500mm, 600mm, 700mm, 800mm, 900mm, 1000mm, 1100mm, 1200mm, 1300mm, 1400mm, 1500mm, 1600mm, 1700mm, 1800mm, 1900mm, 2000mm, 2100mm, 2200mm, 2300mm, 2400mm, or 2500mm. If the cylindrical forging is too close or too far from the inner wall of the furnace hood, it will hinder the forging's utilization of heat from the inner wall.

[0075] Specifically, the length of the load-bearing beam is greater than or equal to the sum of the distance L and the thickness of the cylindrical forging, and the width of the load-bearing beam is equal to the width of the shim.

[0076] It should be noted that, in order to improve the heating efficiency of the furnace bottom heating resistance band, the present invention needs to limit the size of the shim.

[0077] Specifically, the height of the shim is 800-1200mm, the width is 266.7-500mm, and the ratio of the height to the width of the shim should be ≤3; the length of the shim is ≥ the thickness of the cylindrical forging.

[0078] According to some preferred embodiments of the present invention, when the outer diameter R of the cylindrical forging is in the range of 3000mm≤R<5000mm and the thickness T is in the range of 200mm≤T<285mm, the number of the load-bearing beams is at least 4.

[0079] According to some preferred embodiments of the present invention, when the outer diameter R of the cylindrical forging is in the range of 5000mm≤R≤7000mm and the thickness T is in the range of 285mm≤T<395mm, the number of the load-bearing beams is at least 8;

[0080] According to some preferred embodiments of the present invention, when the outer diameter R of the cylindrical forging is in the range of 7000mm < R ≤ 10000mm and the thickness T is in the range of 395mm < T ≤ 565mm, the number of load-bearing beams is at least 12.

[0081] Secondly, embodiments of the present invention provide an openable circular heat treatment resistance furnace, wherein the resistance furnace is designed by the aforementioned design method, and the number of load-bearing beams at the bottom of the resistance furnace is 2+2n, where 1≤n≤7.

[0082] In the design of the openable circular heat treatment resistance furnace for cylindrical forgings, this invention considers parameters of the cylindrical forgings, such as the size of the cylindrical forgings, the coefficient of thermal expansion, the temperature and time of heat treatment, and the intensity of heat treatment, when performing thermal field-microstructure field coupling simulation. The resulting openable circular heat treatment resistance furnace can meet the needs of various cylindrical forgings.

[0083] It should be noted that, in order to achieve multiple uses of one furnace, reduce the manufacturing cost of the heating furnace, reduce the footprint, and improve the thermal energy utilization rate, the load-bearing beam of the heat treatment resistance furnace of the present invention includes multi-level load-bearing beams with different distances from the center of the furnace platform, wherein the length of each level of load-bearing beam is equal, so as to adapt to the requirements of heat treatment processes for forgings with different diameters, wall thicknesses, and shapes.

[0084] Specifically, the multi-stage load-bearing beams include a primary load-bearing beam and a secondary load-bearing beam, with the distance between the end of the primary load-bearing beam closest to the center of the furnace platform and the center of the furnace platform increasing sequentially, and the number of each secondary load-bearing beam is 4. The distance between the end of the primary load-bearing beam closest to the center of the furnace platform and the center of the furnace platform is greater than 1500mm. The primary and secondary load-bearing beams abut against the furnace platform wall, as shown below. Figure 4 (a) Figure 4 As shown in (b).

[0085] More specifically, when the diameter of the heat-treated forging is small, only four primary weighing beams are needed for support to successfully complete the heat treatment of the forging, such as... Figure 4As shown in (a); when the diameter of the heat-treated forging is large, the heat treatment of the forging can be successfully completed by using a total of 8 primary and secondary load-bearing beams for support. Figure 4 As shown in (b).

[0086] Specifically, the multi-level load-bearing beams include a primary load-bearing beam, a secondary load-bearing beam, and a tertiary load-bearing beam, with the distance between the end near the center of the furnace platform and the center increasing sequentially, in quantities of 4, 4, and 8 respectively. The distance between the end of the primary load-bearing beam near the center of the furnace platform and the center of the furnace platform is greater than 0. Furthermore, considering both enhancing the load-bearing capacity of the load-bearing beams, the limited space of the furnace platform, and the heating efficiency of the lower part of the furnace chamber, the primary load-bearing beams are designed not to abut against the furnace platform wall, while the secondary and tertiary load-bearing beams abut against the furnace platform wall. The end of the primary load-bearing beam furthest from the center of the furnace platform and the end of the tertiary load-bearing beam closest to the center of the furnace platform are located on the same circumference centered on the center of the furnace platform. Figure 5 As shown in (a) and 5(b).

[0087] More specifically, when the diameter of the heat-treated forging is small, only four primary load-bearing beams are needed for support to successfully complete the heat treatment; when the diameter of the heat-treated forging is large, a total of eight primary and secondary load-bearing beams are used for support to successfully complete the heat treatment. Figure 5 As shown in (a); when the diameter of the heat-treated forging is larger, the heat treatment of the forging can be successfully completed by simultaneously using a total of 12 secondary and tertiary load-bearing beams for support, as shown in (a). Figure 5 As shown in (b).

[0088] To improve the overall service life of the heating furnace, effectively distribute the weight of materials and heating elements within the furnace, reduce localized stress concentration, and enhance the furnace's load-bearing capacity and stability; and to help achieve uniform temperature distribution within the furnace, reduce temperature gradients, and improve heating efficiency, the load-bearing beams at each level are arranged sequentially at equal intervals, and the length of each level of load-bearing beam is equal. In a preferred embodiment of the invention, the primary load-bearing beams and secondary load-bearing beams are arranged sequentially at equal intervals, and the lengths of the primary load-bearing beams and secondary load-bearing beams are all equal. Figure 4 As shown in (a) and (b), primary, secondary, and tertiary load-bearing beams are arranged at equal intervals, with all primary, secondary, and tertiary load-bearing beams having the same length. Figure 5 As shown in (a) and (b).

[0089] Thirdly, embodiments of the present invention also provide a method for improving the heat treatment uniformity of cylindrical forgings, wherein the method employs the openable circular heat treatment resistance furnace to heat treat the cylindrical forgings.

[0090] According to some preferred embodiments of the present invention, during the heat treatment process, the central axis of the cylindrical forging coincides with the central axis of the resistance furnace to ensure that the forging is heated uniformly during the heat treatment process and to improve the homogeneity of the treated product.

[0091] The technical solution of the present invention will be further explained below with reference to specific embodiments.

[0092] The heat treatment resistance furnace includes a circular furnace bottom and a furnace cover, wherein a heating resistance strip is provided on the inner wall of the furnace cover.

[0093] Example 1

[0094] For a low-alloy steel cylindrical forging 1, an openable circular resistance furnace for heat treatment is designed. The forging material is 18MnNiMo, and before heat treatment, its outer diameter is 4832mm, inner diameter is 4280mm, thickness is 276mm, height is 4296mm, and the single-sided allowance in the inner diameter direction is 30mm, and the height allowance is 30mm. The specific steps include:

[0095] (1) The inner diameter of the circular furnace hood is 8000mm and the height is 8000mm. Load-bearing beams are symmetrically arranged along the circumference on the inner side wall of the furnace bottom. The load-bearing beams extend radially along the furnace bottom and do not intersect each other. The length of the load-bearing beam is 2500mm and the width is 350mm. The distance between the load-bearing beam and the center of the furnace bottom is 1500mm. The number of load-bearing beams is determined by the following steps; In addition to the load-bearing beams, heating resistance strips are installed in the remaining part of the furnace bottom.

[0096] (2) Using the ABAQUS thermal-microstructure field coupling simulation software, the input items include: cylindrical forging dimensions: outer diameter 4832mm, thickness 276mm, height 4296mm, and average thermal expansion coefficient of 12.5×10. -6 The heat treatment temperature was 890℃ and the time was 6h. The target strength was 580MPa. The number of support points was 4. The deformation of the cylindrical forging after heat treatment was calculated by simulation: the average elliptical deformation obtained after measuring 8 different cross sections was 11mm, and the high and low undulation deformation was 6mm.

[0097] (3) It was determined that the deformation of the cylindrical forging was within the specified deformation range, i.e., the elliptical deformation was less than 1 / 2 of the single-sided allowance; the undulating deformation did not exceed 1 / 3 of the height allowance. Therefore, the number of support points 4 in step (2) was determined to be the number of load-bearing beams. Figure 3 As shown.

[0098] Example 2

[0099] For a low-alloy steel cylindrical forging 2, an openable circular resistance furnace for heat treatment is designed. The forging is made of 12Cr2Mo1, with an outer diameter of 5520mm, an inner diameter of 4990mm, a thickness of 265mm, a height of 2150mm, a single-sided allowance of 30mm in the inner diameter direction, and a height allowance of 30mm. The specific steps include:

[0100] (1) The inner diameter of the circular furnace hood is 8000mm and the inner cavity height is 8000mm. Load-bearing beams are symmetrically arranged along the circumference on the inner side wall of the furnace bottom. The load-bearing beams extend radially along the furnace bottom and do not intersect each other. The length of the load-bearing beam is 2500mm and the width is 350mm. The distance between the load-bearing beam and the center of the furnace bottom is 1500mm. The number of load-bearing beams is determined by the following steps; In addition to the load-bearing beams, heating resistance strips are installed in the rest of the furnace bottom.

[0101] (2) Using the ABAQUS thermal-microstructure coupling simulation software, the input items include: dimensions of the cylindrical forging: outer diameter 5520mm, thickness 265mm, height 2150mm, and coefficient of thermal expansion of 14×10⁻⁶ mm. -6 The heat treatment temperature is 950℃ and the time is 6h. The target strength is 560MPa. The number of support points is 4. The deformation of the cylindrical forging after heat treatment is calculated to be: elliptical deformation is 40mm and undulating deformation is 12mm.

[0102] (3) It was determined that the deformation of the cylindrical forging was not within the specified deformation range, that is, the elliptical deformation was greater than 1 / 2 of the single-sided allowance, and the undulating deformation was greater than 1 / 3 of the height allowance.

[0103] (4) Repeat the thermal field-organic field coupling simulation in step (2), keep other input items unchanged, increase the number of support points to 6, and simulate and calculate the deformation of the cylindrical forging after heat treatment as follows: elliptical deformation is 14mm, and undulating deformation is 8mm.

[0104] Based on the assessment, the deformation of the cylindrical forging is within the specified deformation range, i.e., the elliptical deformation is less than 1 / 2 of the single-sided allowance, and the undulating deformation does not exceed 1 / 3 of the height allowance. Therefore, the number of support points, 6, is determined to be the number of load-bearing beams.

[0105] Example 3

[0106] Using the same method as in Example 2, a hinged circular heat treatment resistance furnace was designed for the low-alloy steel cylindrical forging 3. The forging is made of 20MnNiMo, with an outer diameter of 5760mm, an inner diameter of 4975mm, a thickness of 392.5mm, a height of 2490mm, a single-sided allowance of 25mm in the inner diameter direction, and a height allowance of 30mm. The difference is:

[0107] Step (1) The inner diameter of the circular furnace hood is 8000mm and the inner cavity height is 8000mm. First-level and second-level load-bearing beams are symmetrically arranged along the circumference on the inner side wall of the furnace bottom. The load-bearing beams extend radially along the furnace bottom and do not intersect each other. The lengths of the first-level and second-level load-bearing beams are 2000mm and 2500mm respectively, and the width is 350mm. The distances between the load-bearing beams and the center of the furnace bottom are 2000mm and 1500mm respectively. The number of load-bearing beams is determined by the following steps; In addition to the load-bearing beams, heating resistance strips are installed in the remaining part of the furnace bottom.

[0108] Step (2): Using thermal field-microstructure field coupling simulation software, the input items include: cylindrical forging dimensions: outer diameter 5760mm, thickness 392.5mm, height 2490mm, and thermal expansion coefficient of 13×10. -6 The heat treatment temperature was 940℃ and the time was 6h. The target strength was 610MPa. The number of support points was 4. The deformation of the cylindrical forging after heat treatment was calculated by simulation. The average elliptical deformation obtained after measuring 8 different cross sections was 40mm, and the high and low undulation deformation was 11mm.

[0109] As determined in step (3), the deformation of the cylindrical forging is not within the specified deformation range, that is, the elliptical deformation is greater than 1 / 2 of the single-sided allowance, and the undulating deformation exceeds 1 / 3 of the height allowance.

[0110] In step (4), the number of support points is increased. After repeating steps (2) and (3) twice, the deformation of the cylindrical forging after heat treatment is simulated and calculated to be within the specified deformation range: the average elliptical deformation is 10mm, and the undulating deformation is 6mm. Finally, the number of support points is determined to be 8, which is the number of load-bearing beams. Figure 4 As shown in (b).

[0111] Example 4

[0112] Using the same method as in Example 2, a hinged circular heat treatment resistance furnace was designed for the low-alloy steel cylindrical forging 4. The forging is made of 20MnMoNb, with an outer diameter of 9048mm, an inner diameter of 8230mm, a thickness of 409mm, a height of 2130mm, a single-sided allowance of 45mm in the inner diameter direction, and a height allowance of 30mm. The difference is:

[0113] Step (1) The inner diameter of the circular furnace hood is 11000mm and the inner cavity height is 8000mm. First-level, second-level and third-level load-bearing beams are symmetrically arranged along the circumference on the inner side wall of the furnace bottom. The load-bearing beams extend radially along the furnace bottom and do not intersect each other. The lengths of the first-level, second-level and third-level load-bearing beams are 2000mm, 3500mm and 2000mm respectively, and the width is 350mm. The distances between the load-bearing beams and the center of the furnace bottom are 1500mm, 2000mm and 3500mm respectively. The number of load-bearing beams is determined by the following steps; In addition to the load-bearing beams, heating resistance strips are installed in the remaining part of the furnace bottom.

[0114] Step (2): Using thermal field-microstructure field coupling simulation software, the input items include: cylindrical forging dimensions: outer diameter 9048mm, thickness 409mm, height 2130mm, and thermal expansion coefficient of 12.5×10. -6 The heat treatment temperature was 900℃ and the time was 8.5h. The target strength was 630MPa. The number of support points was 4. The deformation of the cylindrical forging after heat treatment was calculated by simulation. The average elliptical deformation obtained after measuring 8 different cross sections was 91mm, and the high and low undulation deformation was 15mm.

[0115] As determined in step (3), the deformation of the cylindrical forging is not within the specified deformation range, that is, the elliptical deformation is greater than 1 / 2 of the single-sided allowance, and the undulating deformation exceeds 1 / 3 of the height allowance.

[0116] In step (4), the number of support points is increased. After repeating steps (2) and (3) four times, the deformation of the cylindrical forging after heat treatment is simulated and calculated to be within the specified deformation range: the average elliptical deformation is 18mm, and the undulating deformation is 8mm. Finally, the number of support points is determined to be 12, which is the number of load-bearing beams. Figure 5 As shown in (b).

[0117] Application examples

[0118] The openable circular heat treatment resistance furnace designed in Examples 1-4 and the existing openable circular heat treatment resistance furnace (with furnace bottom structure as shown) are respectively used. Figure 1 (b) As shown, the cylindrical forgings 1-4 in Examples 1-4 were subjected to heat treatment respectively. The actual treatment process and the performance of the obtained products are shown in Table 1. Among them, the strength fluctuation value is the maximum difference obtained by comparing the strength test results after testing the strength at different positions (50 locations) of the forgings after heat treatment.

[0119] Table 1. Process conditions and product performance of simulated or / and actual heat treatment of cylindrical forgings in Examples 1-4 and Comparative Examples 1-4.

[0120]

[0121] As can be seen from Table 1, compared with the comparative example, the heat treatment resistance furnace designed with the assistance of thermal field-microstructure field coupling simulation software based on the size of the cylindrical forging to be treated, the coefficient of thermal expansion, the temperature and time of heat treatment, and the target strength, can not only improve the heating efficiency, shorten the heat treatment time of the cylindrical forging, and reduce energy consumption in the actual heat treatment process of the cylindrical forging, but also significantly reduce the deformation of the forging during the heat treatment process, reduce the strength fluctuation (less than or equal to 13MPa), and at the same time ensure the subsequent processing and normal use of the forging, thereby improving the product qualification rate.

[0122] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A design method for an openable circular heat treatment resistance furnace for cylindrical forgings, the heat treatment resistance furnace comprising a circular furnace bottom and a furnace hood, wherein a heating resistance strip is provided on the inner wall of the furnace hood, characterized in that, The method includes: (1) A load-bearing beam is symmetrically arranged along the circumferential direction on the inner side wall of the furnace bottom. The load-bearing beam extends radially along the furnace bottom and does not intersect with each other. The rest of the furnace bottom is equipped with a heating resistance strip. (2) Using thermal field-structure field coupling simulation software, input the parameters of the cylindrical forging and the number of support points, and simulate and calculate the deformation of the cylindrical forging after heat treatment. The deformation includes the elliptical deformation of the cylindrical forging in the diameter direction and the undulating deformation in the height direction. (3) Determine whether the deformation of the cylindrical forging obtained in step (2) meets the requirements. If it does, determine the number of support points as the number of load-bearing beams. (4) If the deformation of the cylindrical forging obtained in step (2) does not meet the requirements, increase the number of support points in step (2) by 2, and repeat steps (2) and (3) until the deformation of the cylindrical forging meets the requirements.

2. The design method according to claim 1, characterized in that, In step (1), the distance between the load-bearing beam and the center of the furnace bottom is greater than or equal to 1500mm.

3. The design method according to claim 1, characterized in that, In step (2), the parameters of the cylindrical forging include the cylindrical forging dimensions, coefficient of thermal expansion, temperature and time of heat treatment, and heat treatment intensity.

4. The design method according to claim 3, characterized in that, The dimensions of the cylindrical forging include: an outer diameter of 3000-10000 mm, a thickness of 200-565 mm, and a height of 2000-5000 mm; And / or, the coefficient of thermal expansion is 11-18×10⁻⁶. -6 / ℃; And / or, the heat treatment temperature is 600-1100℃ and the time is 4-25h; And / or, the heat treatment intensity is 30-380 MPa.

5. The design method according to claim 1, characterized in that, In step (2), the number of support points is 2+2n, where 1≤n≤7.

6. The design method according to claim 5, characterized in that, In step (2), the number of support points is preferably 4, 8, or 12.

7. The design method according to claim 1, characterized in that, In step (3), the ellipse deformation amount does not exceed 1 / 2 of the single-side allowance, and the height undulation deformation amount does not exceed 1 / 3 of the height allowance.

8. The design method according to claim 7, characterized in that, When the outer diameter R of the cylindrical forging is in the range of 3000mm≤R<5000mm and the thickness T is in the range of 200mm≤T<285mm, the number of load-bearing beams is at least 4. When the outer diameter R of the cylindrical forging is in the range of 5000mm≤R≤7000mm and the thickness T is in the range of 285mm≤T<395mm, the number of load-bearing beams is at least 8. When the outer diameter R of the cylindrical forging is in the range of 7000mm < R ≤ 10000mm and the thickness T is in the range of 395mm < T ≤ 565mm, the number of load-bearing beams is at least 12.

9. A hinged circular heat treatment resistance furnace, characterized in that, The resistance furnace is designed using the design method described in any one of claims 1-8.

10. A method for improving the heat treatment uniformity of cylindrical forgings, characterized in that, The method uses the openable circular heat treatment resistance furnace as described in claim 9 to perform heat treatment on the cylindrical forging.

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