Large-lifting-capacity offshore lifting hook manufacturing method and offshore lifting hook thereof

Abstract

The invention discloses a large-lifting-capacity offshore lifting hook manufacturing method and an offshore lifting hook thereof, and belongs to the technical field of lifting hooks. The large-lifting-capacity offshore lifting hook manufacturing method comprises the steps that S100, 20CrMnMo steel is selected to forge a hook body; s200, the hook body is subjected to double normalizing and double tempering heat treatment to obtain a hook body subjected to heat treatment, and the hook body subjected to heat treatment is subjected to pre-cooling, water cooling, oil cooling and tempering to obtain a quenched and tempered hook body; s300, the quenched and tempered hook body is subjected to finish machining to obtain a machined hook body, the machined hook body and the hook tip are welded to form the lifting hook body, and assembly of the welded hook body and the hook tip meets the design requirement; and S400, the surface of the lifting hook body is coated to obtain the lifting hook. According to the invention, the large-lifting-capacity offshore lifting hook can be manufactured.

Description

Technical Field

[0001] The present invention application relates to the technical field of lifting hooks, and more specifically, to a manufacturing method for a large lifting capacity offshore hook and the offshore hook thereof. Background Art

[0002] As a core component in lifting machinery, offshore hooks are widely used in ports, offshore and other fields, and their performance is directly related to the safety and reliability of lifting equipment. With the development of industrial technology, the requirements for the bearing capacity, fatigue life and manufacturing accuracy of offshore hooks are increasing day by day. Especially in the scenario of large lifting capacity (for example, above 3500 tons), offshore hooks need to bear extremely high tensile stress and cyclic loads under complex working conditions. However, there are some deficiencies in the traditional manufacturing methods of offshore hooks. For example, the material properties are not fully utilized, it is difficult to ensure the tissue uniformity in the forging process, defects are easily generated in the welded joints, and it is difficult to control the deformation after heat treatment. As a result, the strength, durability and dimensional accuracy of offshore hooks are difficult to meet the modern heavy load requirements.

[0003] In the prior art, hooks are often manufactured by forging or casting with ordinary carbon steel or low alloy steel, and then simple heat treatment and processing are carried out. For example, Patent CN101704468A discloses a safety hook and its manufacturing method, which does not involve the manufacturing method for a large lifting capacity offshore hook; the applicant's previous patent CN109434390A proposed a processing technology method for a large forging hook, which discloses: material selection and blanking, forging, normalizing plus high temperature tempering, shell making, quenching and tempering treatment, load test, and comprehensive inspection and flaw detection after the load test. The forged hook produced can meet the overall load capacity of the hook and its internal quality, but it does not solve the technical problems of strength improvement, tissue uniformity or deformation improvement in the heat treatment process of large-sized hooks. In addition, the traditional method lacks further systematic optimization in the finishing and surface treatment links, resulting in insufficient corrosion resistance on the hook surface and restricting its application in extreme environments.

[0004] In view of the above technical problems, there is an urgent need for an improved manufacturing method for a large lifting capacity offshore hook and the offshore hook thereof. By optimizing the material selection, forging process, heat treatment plan, as well as the finishing and surface treatment processes, the comprehensive performance of the hook is improved to meet the requirements of the offshore operation environment with high load, long life and high precision. Summary of the Invention

[0005] Based on this, the present invention application provides a manufacturing method for a large lifting capacity offshore hook and the offshore hook thereof, aiming to partially or fully solve the above technical problems. The present invention application provides a manufacturing method for a large lifting capacity offshore hook, optimizing the manufacturing method for large-sized offshore hooks, and improving the strength and quality of the hook in the heat treatment process, etc. The present invention application is realized through the following technical solutions:

[0006] In a first aspect, a manufacturing method for a large-lifting-capacity offshore hook includes:

[0007] Step S100: Select 20CrMnMo steel to forge the hook body;

[0008] Step S200: Perform double normalizing and double tempering heat treatment on the hook body to obtain the heat-treated hook body, and pre-cool, water-cool, oil-cool, and temper the heat-treated hook body to obtain the quenched and tempered hook body;

[0009] Step S300: Perform finish machining on the quenched and tempered hook body to obtain the machined hook body, and weld the machined hook body and the hook tip to form the hook body, so that the assembled hook body and hook tip after welding meet the design requirements;

[0010] Step S400: Coat the surface of the hook body to obtain the hook.

[0011] Optionally, step S200 includes:

[0012] Step S201: Heat the hook body to 950 - 1000 °C for the first normalizing, hold for 2 - 5 hours, and then air-cool; after an interval of the first set time T1, then heat the hook body to 850 - 900 °C for the second normalizing, hold for 3 - 8 hours, and then air-cool;

[0013] Step S202: Heat the air-cooled hook body to 850 - 900 °C, hold for 1 - 2 hours, and then quickly oil-quench to room temperature;

[0014] Step S203: Heat the room-temperature hook body to 550 - 600 °C for the first tempering, hold for 5 - 10 hours, and then air-cool; after an interval of the second set time T2, heat the hook body to 650 - 700 °C again for the second tempering, hold for 8 - 15 hours, and then furnace-cool, with the furnace-out temperature less than 250 °C, to obtain the heat-treated hook body.

[0015] Optionally, after step S203, it further includes:

[0016] Step S204: Air-cool from 860 °C to 700 °C before quenching for about 30 minutes;

[0017] Step S205: Water-cool the hook body for 10 - 20 minutes and oil-cool for 180 - 210 minutes to obtain the quenched hook body;

[0018] Step S206: Heat the quenched hook body to the tempering temperature of 150 - 250 °C, control the tempering holding time within 12 - 30 hours, and after holding, furnace-cool or air-cool to obtain the quenched and tempered hook body.

[0019] Optionally, S1 ≤ |T1 - T2| ≤ S2, where S1 is the first preset time and S2 is the second preset time.

[0020] Optionally, the first preset time S1 and the second preset time S2 are as follows:

[0021]

[0022] Wherein, r is the preset radius of the hook body, a is the thermal diffusivity of the hook body material, α is the first process adjustment coefficient, β is the second process adjustment coefficient, 0 ≤ α ≤ 1, 1 ≤ β ≤ 2.

[0023] Optionally, in step S100, the mass fractions of each element of 20CrMnMo steel are: C: 0.17% - 0.23%, Si: 0.17% - 0.37%, Mn: 0.90% - 1.20%, Cr: 1.10% - 1.40%, Mo: 0.20% - 0.30%, Nb: ≤ 0.030%, Al: ≥ 0.015%, Cu: ≤ 0.25%, P: ≤ 0.025%, S: ≤ 0.015%, and the balance is Fe.

[0024] Optionally, in step S400, a fluorocarbon topcoat is applied to the surface of the hook body.

[0025] In a second aspect, a large lifting capacity offshore hook is manufactured by using the manufacturing method of a large lifting capacity offshore hook described in the first aspect, and includes: a hook body and a plurality of hook tips, and the hook body and the plurality of hook tips are welded.

[0026] Optionally, the material of the hook body is 20CrMnMo steel, and the mass fractions of each element of 20CrMnMo steel are: C: 0.17% - 0.23%, Si: 0.17% - 0.37%, Mn: 0.90% - 1.20%, Cr: 1.10% - 1.40%, Mo: 0.20% - 0.30%, Nb: ≤ 0.030%, Al: ≥ 0.015%, Cu: ≤ 0.25%, P: ≤ 0.025%, S: ≤ 0.015%, and the balance is Fe.

[0027] Optionally, a fluorocarbon topcoat coating is formed on the outer periphery of the hook, and the thickness of the fluorocarbon topcoat coating is controlled between 15 - 30 microns.

[0028] Optionally, the plurality of hook tips include a first hook tip, a second hook tip, a third hook tip, and a fourth hook tip. The centers of the first hook tip, the second hook tip, the third hook tip, and the fourth hook tip are connected to form a rectangle, and the large lifting capacity is 3500t and above.

[0029] The beneficial technical effects of the present invention application:

[0030] (1) In the present invention application, the first normalizing high-temperature heating promotes the coarsening of austenite grains, laying a foundation for the subsequent refinement process; during the air cooling process, austenite transforms into pearlite or other structures, and the grains are initially refined; the structure after high-temperature normalizing provides a uniform basis for the second normalizing; the lower heating temperature enables the recrystallization of austenite grains on a finer basis, and finer grains are obtained after air cooling; by controlling the temperature and cooling rate, the tissue inhomogeneity is reduced, the overall performance is improved, and an ideal microstructure basis is provided for the subsequent tempering treatment;

[0031] (2) In the present invention application, first, the first tempering uses air cooling to quickly cool to room temperature to stabilize the structure, and the second tempering uses furnace cooling to slowly cool to an out-of-furnace temperature less than 250 °C to reduce thermal stress. The stepped heating and differential cooling methods during the tempering process ensure that the hardness is gradually adjusted to the target value while improving toughness and machining performance; in addition, the first tempering effectively releases the residual stress generated during the normalizing process, reduces the risk of workpiece deformation, can adjust the hardness to a moderate level, prepares for subsequent machining and the second tempering, promotes the decomposition of retained austenite in the structure, and enhances the tissue stability; the second tempering makes the carbides in the structure evenly distributed, improves toughness and plasticity, reduces the tool wear during subsequent rough machining by reducing the hardness to an appropriate ideal range through long-time high-temperature holding. The structure is uniform and the hardness is moderate, ensuring that the workpiece is easy to cut during subsequent machining, reducing the depth of cut, and achieving the comprehensive effects of grain refinement and tissue uniformity.

[0032] (4) In the present invention application, the heat treatment method adopts multi-stage heat treatments such as double normalizing, oil quenching, double quenching, and tempering. The manufacturing parameter range is relatively wide, the heat treatment method is reasonably designed, and the advantages of the multi-stage heat treatment process are fully utilized to comprehensively improve the strength, toughness, and dimensional stability of the large-lifting-capacity hook, and it can also be optimized and adjusted according to specific production conditions and product requirements to achieve process customization. Description of the Drawings

[0033] Figure 1 is a schematic flow chart of a manufacturing method for a large-lifting-capacity offshore hook according to the present invention application;

[0034] Figure 2 is a schematic flow chart of step S201, step S202, and step S203 according to the present invention application;

[0035] Figure 3 is a schematic structure diagram of a large-lifting-capacity offshore hook according to the present invention application Figure 1 ;

[0036] Figure 4 is a schematic structure diagram of a large-lifting-capacity offshore hook according to the present invention application Figure 2 . Detailed implementation manners

[0037] In order to make the objectives, technical solutions and advantages of the embodiments of the present disclosure clearer, the following further describes the embodiments of the present disclosure in detail with reference to the accompanying drawings and embodiments; it should be understood that the specific embodiments described herein are only used to explain the embodiments of the present disclosure, and are not used to limit the embodiments of the present disclosure;

[0038] The structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in this technology to understand and read, and are not used to limit the limiting conditions for the implementation of this invention application. Therefore, they do not have technical essence. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effects that this invention application can produce and the objectives that can be achieved, should still fall within the scope that the technical content disclosed in this invention application can cover; at the same time, terms such as "and" and "or" cited in this specification are only for the convenience of clear narration and are not used to limit the scope of implementation. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope that this invention application can implement; in addition, the various embodiments of this invention application are not independent of each other, but can be combined;

[0039] The terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features; thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features; in the description of this invention application, unless otherwise stated, the meaning of "a plurality" is two or more, and steps S100, S200, S300 and S400 may not represent a specific order of steps.

[0040] In a first aspect, as Figures 1 to 4 shown, this invention application provides a manufacturing method for a large-lifting-capacity offshore hook, including:

[0041] Step S100: Select 20CrMnMo steel to forge the hook body;

[0042] In some embodiments, the heavy lifting capacity is 3500t or more. The tonnage of the lifting hook is relatively large and has exceeded the range of the maximum 500t tonnage in the national standard GB / T 10051-2010 Lifting Hooks. High-strength forging materials need to be selected. Considering the working conditions of the lifting hook, the design safety factor, performance requirements, product cost, etc., 20CrMnMo steel is selected as the manufacturing material for the lifting hook product. 20CrMnMo steel is a kind of structural steel for forging. 20CrMnMo steel is an alloy structural steel optimized by alloying elements such as carbon C, chromium Cr, manganese Mn, and molybdenum Mo. The mass fractions of each element are: C: 0.17% - 0.23%, Si: 0.17% - 0.37%, Mn: 0.90% - 1.20%, Cr: 1.10% - 1.40%, Mo: 0.20% - 0.30%, Nb: ≤0.030%, Al: ≥0.015%, Cu: ≤0.25%, P: ≤0.025%, S: ≤0.015%, and the rest is Fe.

[0043] In some embodiments, first, Nb combines with carbon (C) and nitrogen (N) in the steel to form fine carbonitrides (such as NbC, NbN). These precipitates can effectively inhibit the growth of austenite grains at high temperatures, thereby refining the grain structure of the steel. The fine grains improve the strength and toughness of the lifting hook, making it less likely to undergo brittle fracture under high loads. In addition, Nb improves the performance of the welding area, especially in the heat-affected zone of welding, which can reduce the phenomenon of grain coarsening and lower the risk of welding cracks. This is particularly important for the welding of the hook body and the hook tip during the manufacture of the lifting hook to ensure the strength and reliability of the welded joint. In addition, the microalloying effect of Nb enhances the atmospheric corrosion resistance of the steel. Especially in marine environments such as humid and salt spray, it can effectively slow down the corrosion rate of the lifting hook and extend its service life.

[0044] In some embodiments, Al is a strong deoxidizer. It combines with oxygen in the steel to form Al2O3, significantly reducing the oxygen content in the steel and enhancing the purity of the steel. The pure steel has better toughness and ductility, reducing internal defects caused by inclusions. Al combines with nitrogen (N) to form fine AlN particles. These nitrides further refine the grains, enhance the strength and toughness of the lifting hook, improve the anti-fatigue performance of the lifting hook, and extend its service life under high-frequency loads.

[0045] In some embodiments, the combination of Nb and Al significantly enhances the strength, toughness, wear resistance, and corrosion resistance of the hook. Nb plays a role by refining the grain size and improving weldability, while Al provides support by enhancing the purity and oxidation resistance of the steel. The synergistic effect of the two ensures the reliability of the hook under high loads and harsh environments. At the same time, the addition of Nb and Al improves the hardenability and tempering stability of the steel, enabling the hook to obtain better microstructure and properties after heat treatment (such as quenching and tempering). This reduces performance fluctuations, improves the quality of the hook, and endows the hook with forgeability, high strength, toughness, and fatigue resistance.

[0046] In some embodiments, the raw materials used for manufacturing the hook assembly of 3500t and above are 20CrMnMo steel, and a special procurement technical specification is formulated for special customization from the steel mill. The raw material procurement technical specification includes requirements for material chemical composition, requirements for non-metallic inclusions, etc., to control the quality of raw materials and ensure the quality of the final product. 20CrMnMo steel is selected to forge the hook body and make the hook tip. The welding of the hook body and the hook tip meets the CCS welding procedure specification WPS-JY19WA08, realizing the welding conditions of the hook tip, greatly reducing the overall forging and processing costs of the hook, and being more economical.

[0047] In some embodiments, the mechanical properties of the offshore hook made of 20CrMnMo steel are as follows: tensile strength ≥500 MPa, yield strength ≥390 MPa, elongation after fracture ≥18%, and Akv2(-10°C) ≥42 J.

[0048] Step S200: Perform double normalizing and double tempering heat treatments on the hook body to obtain the heat-treated hook body, and then perform pre-cooling, water cooling, oil cooling, and tempering on the heat-treated hook body to obtain the quenched and tempered hook body;

[0049] In some embodiments, step S200 can at least perform double normalizing and double tempering heat treatments on the hook body to obtain the heat-treated hook body, and then perform pre-cooling, water cooling, oil cooling, and tempering on the heat-treated hook body to obtain the quenched and tempered hook body. Specifically, step S200 includes:

[0050] Step S201: Heat the hook body to 950 - 1000°C for the first normalizing, hold for 2 - 5 hours, and then air cool; after an interval of the first set time T1, then heat the hook body to 850 - 900°C for the second normalizing, hold for 3 - 8 hours, and then air cool;

[0051] In some embodiments, after a first normalizing and after an interval of a first set time T1, the hook body is air-cooled to room temperature. The first set time T1 can ensure that the hook body is completely cooled as much as possible, reducing residual thermal stress, which is particularly important for large-sized hook bodies, and avoiding deformation or cracking caused by temperature gradients during the second normalizing heating. The first set time T1 allows any residual thermal stress after the first normalizing to relax at room temperature, which can improve the dimensional stability of the hook body and reduce the risk of deformation during subsequent processing or use; in addition, the first set time T1 ensures that the hook body reaches a uniform room temperature state before the second normalizing, reducing the impact of temperature non-uniformity on the second normalizing, which is particularly crucial for thick-walled components, and can improve the distribution consistency of hardness and toughness. For large-sized hook bodies, uniform cooling helps to avoid performance differences between the center and the surface, indirectly enhancing the fatigue resistance performance, which is particularly suitable for the scenario where the hook body of an offshore crane bears high loads; furthermore, the first set time T1 can be used for production scheduling, allowing quality inspection, dimensional measurement or surface treatment to be carried out during the interval between the two normalizings, enhancing quality control. For example, it can be checked whether the hardness after the first normalizing reaches the expectation, and the parameters of the second normalizing can be adjusted.

[0052] In the present invention application, the first normalizing temperature of 950 - 1000 °C is higher than the second normalizing temperature of 850 - 900 °C, and the difference is controlled within 100 - 150 °C. The holding time of the second normalizing of 3 - 8 hours is designed to be 1.5 - 2 times that of the first normalizing of 2 - 5 hours. The larger temperature difference helps to coarsen the grains first and then refine the grains through a lower temperature, forming a more excellent microstructure. The longer holding time ensures that austenite is fully recrystallized at a lower temperature, further refining the grains.

[0053] In the present invention application, the high-temperature heating during the first normalizing promotes the coarsening of austenite grains, laying a foundation for the subsequent refinement process; during the air-cooling process, austenite transforms into pearlite or other structures, and the grains are initially refined; the structure after high-temperature normalizing provides a uniform basis for the second normalizing; the lower heating temperature enables austenite grains to recrystallize on a finer basis, and finer grains are obtained after air-cooling; by controlling the temperature and cooling rate, the tissue non-uniformity is reduced, the overall performance is improved, and an ideal microstructure basis is provided for the subsequent tempering treatment.

[0054] Step S202: Heat the hook body after air-cooling to 850 - 900 °C, hold for 1 - 2 hours, and then quickly oil-quench to room temperature;

[0055] In the present invention application, oil quenching forms a high-hardness martensite structure, significantly improving the yield strength and tensile strength, meeting the requirements of large-lifting-capacity offshore hooks. By controlling the quenching cooling rate (oil quenching is milder than water quenching), the thermal stress and phase transformation stress are reduced, and the deformation risk is decreased; the uniform martensite structure after hardening is conducive to further releasing stress during subsequent double tempering, improving toughness, and balancing strength and ductility.

[0056] Step S203: Heat the hook body at room temperature to 550 - 600 °C for the first tempering, hold for 5 - 10 hours, and then air cool; after an interval of the second set time T2, heat the hook body to 650 - 700 °C again for the second tempering, hold for 8 - 15 hours, and then cool with the furnace, with the furnace outlet temperature less than 250 °C to obtain the heat-treated hook body;

[0057] In some embodiments, first, after an interval of the second set time T2, it is possible to ensure that the hook body is completely cooled as much as possible, reducing residual thermal stress, which is particularly important for large-sized hook bodies, avoiding deformation or cracking caused by temperature gradients during the second tempering heating, enabling the hook body to reach a uniform room temperature state before the second tempering, and reducing the impact of temperature non-uniformity on the second tempering; in addition, after the first tempering, tempering at 550 - 600 °C may trigger primary carbide precipitation, and the second set time T2 allows these precipitations to stabilize at room temperature, providing a more consistent initial microstructure for the second tempering at 650 - 700 °C, which can improve the fatigue resistance performance, especially suitable for the scenario where the hook body of an offshore crane bears high loads; furthermore, the interval of the second set time T2 can also be used for production scheduling needs, allowing quality inspection, dimensional measurement, or surface treatment during the interval between the two temperings, enhancing quality control. For example, it can be checked whether the hardness after the first tempering reaches the expected value, and the parameters of the second tempering can be adjusted.

[0058] In the present invention application, air cooling is used for the first tempering, quickly cooling to room temperature to stabilize the structure, and furnace cooling is used for the second tempering, slowly cooling to a furnace outlet temperature less than 250 °C to reduce thermal stress. The stepped temperature rise and differential cooling methods during the tempering process ensure that the hardness is gradually adjusted to the target value while improving toughness and machining performance.

[0059] In the present invention application, the first tempering effectively releases the residual stress generated during the normalizing process, reduces the risk of workpiece deformation, can adjust the hardness to a moderate level, prepares for subsequent processing and the second tempering, promotes the decomposition of retained austenite in the structure, and enhances the structure stability; the second tempering evenly distributes the carbides in the structure, improves toughness and plasticity, reduces the hardness to the ideal range through long-time high-temperature holding, reduces the tool wear during subsequent rough machining, and has a uniform structure and moderate hardness, ensuring that the workpiece is easy to cut during subsequent processing, further reducing the depth of cut, and achieving the comprehensive effects of grain refinement and uniform structure.

[0060] In some embodiments, S1 ≤ |T1 - T2| ≤ S2, where S1 is the first preset time and S2 is the second preset time.

[0061] In the application of the present invention, first, by controlling the difference between the first set time T1 and the second set time T2, the cooling time of the hook body during the normalizing and tempering stages is ensured to be balanced, thereby reducing the uneven distribution of thermal stress. The first set time T1 affects the cooling stability after two normalizings, and the second set time T2 affects the stress release after two tempers. If |T1 - T2| is too large, it may lead to inconsistent stress releases in different heat treatment stages and affect the performance of the hook body. In addition, controlling |T1 - T2| within a certain range helps the hook body maintain similar microstructures and mechanical properties among different production batches. By limiting the difference range, fluctuations in hardness and toughness can be reduced, ensuring stable product quality. Setting S1 ≤ |T1 - T2| ≤ S2 allows the first set time T1 and the second set time T2 to be adjusted within a certain range, facilitating production scheduling and quality control. During production, the time can be flexibly adjusted according to the production rhythm or equipment conditions while ensuring that the performance meets the standards, taking into account both quality and efficiency.

[0062] In some embodiments, the first preset time S1 and the second preset time S2 are:

[0063]

[0064] where r is the preset radius of the hook body, a is the thermal diffusivity of the hook body material. For 20CrMnMo steel, a ≈ 10 -5 m 2 / s, α is the first process adjustment coefficient, β is the second process adjustment coefficient, 0 ≤ α ≤ 1, 1 ≤ β ≤ 2.

[0065] In some embodiments, the preset radius r of the hook body can be selected between the minimum radius and the maximum radius of the hook body; the first process adjustment coefficient α and the second process adjustment coefficient β can be used to adjust the magnitude of the first preset time S1 or the second preset time S2 to ensure process flexibility.

[0066] Step S204: Air cool from 860°C to 700°C before quenching, for about 30 minutes;

[0067] In some embodiments, air cooling from 860°C to 700°C for about 30 minutes before quenching can appropriately reduce the temperature range of the initial temperature difference, reduce the cooling rate difference between the surface and the core of the hook body, and reduce thermal stress.

[0068] Step S205: Water cool the hook body for 10 - 20 minutes and oil cool for 180 - 210 minutes to obtain the quenched hook body;

[0069] In some embodiments, slow cooling of the hook body can avoid cracking.

[0070] Step S206: Heat the quenched hook body to a tempering temperature of 150 - 250°C, control the tempering holding time within 12 - 30 hours, and after holding, cool it in the furnace or in air to obtain the tempered hook body.

[0071] In some embodiments, the temperature uniformity of the heat treatment furnace can be tested to ensure that the temperature of the workpiece inside the furnace is not restricted by space; determine that the loading position is more than 200 mm away from the four walls of the furnace in all directions (left, right, front, and back), and there is a special tooling support at the bottom; at the same time, determine the temperature holding time according to the cross-sectional size to ensure uniform heating of the hook body during the heat treatment process, so that the hook body has good mechanical properties.

[0072] In the present invention application, the cooling method of first water cooling and then oil cooling can be comprehensively considered in combination with the performance and the actual shape and size of the forging, in order to reduce the risk of cracking of the hook body while ensuring the performance of the hook body; at the same time, the mechanical properties of the hook body, as well as the internal and external quality of the hook body, are ensured through the quenching and tempering treatment process to meet technical requirements such as flaw detection.

[0073] In some embodiments, the Deform software can be used to simulate the stress and temperature changes in each part of the hook body during the quenching process to determine the optimal quenching time. Exemplarily, the optimal quenching and cooling method is: water cooling for 15 min and then oil cooling for 190 min. At this time, both the strength of the hook body and the impact energy at - 30°C can meet the design requirements.

[0074] Step S300: Perform finish machining on the tempered hook body to obtain the machined hook body, and weld the machined hook body and the hook tip to form the hook body of the lifting hook, so that the assembly of the welded hook body and hook tip meets the design requirements;

[0075] In some embodiments, the finish machining process is usually used to machine the tempered hook body to make the assembly of the hook body and the hook tip meet the design requirements. For example, the left - right symmetry and the center deviation of the hook body are both less than or equal to 4 mm. Three - dimensional software such as UG can be used for programming, and the difficult points and error - prone points of the product are verified by simulation machining. During the actual machining, intuitive technical disclosure is carried out for the operators in combination with technical documents such as drawings and processes, and numerical control finish machining is performed on it to ensure the dimensional accuracy requirements of the hook body.

[0076] Step S400: Coat the surface of the hook body to obtain the lifting hook.

[0077] In some embodiments, the lifting hook is used for a marine crane. In order to prevent corrosion by seawater, it is necessary to coat the hook body with fluorocarbon topcoat, and the coating thickness is controlled between 15 - 30 microns to ensure good corrosion resistance and weather resistance.

[0078] In the application of the present invention, first of all, due to its fluorocarbon resin component, the fluorocarbon topcoat can form a dense protective layer, effectively blocking the erosion of corrosion media such as seawater and salt spray on the hook, greatly extending the service life. The excellent anti-ultraviolet and anti-aging characteristics of the fluorocarbon topcoat enable the hook to resist the damage of natural factors such as sunlight and sand in the marine environment and maintain the long-term use of the coating. In addition, the coating thickness is controlled within 15 - 30 microns (including 15 microns and 30 microns), which not only provides sufficient protection but also does not affect the dimensional accuracy and service performance of the hook, meeting the high-standard requirements. The fluorocarbon topcoat mostly adopts a water-based formula, with little impact on the environment and human body during the construction process, meeting the environmental protection requirements. The mature construction process makes it easy to spray or brush, with fast drying, shortening the production cycle and improving the efficiency. Coating with a high-performance fluorocarbon topcoat provides reliable protection for the hook of the offshore crane, taking into account environmental protection, economy and efficiency, and ensuring the long-term stable operation of the hook in the harsh marine environment.

[0079] In the application of the present invention, in the heat treatment method of the manufacturing method of the large-lifting-capacity offshore hook, multi-stage heat treatments such as double normalizing, double quenching and tempering are adopted. The parameter range is relatively wide, and the heat treatment method is reasonably designed, making full use of the advantages of the multi-stage heat treatment process to achieve an overall improvement in the strength, toughness and dimensional stability of the large-lifting-capacity hook. Moreover, it can be optimized and adjusted according to specific production conditions and product requirements to achieve process customization.

[0080] As Figure 3 、 Figure 4 shown, secondly, a large-lifting-capacity offshore hook, manufactured by using the manufacturing method of a large-lifting-capacity offshore hook in the first aspect, includes: a hook body and a plurality of hook tips, and the hook body and the plurality of hook tips are welded.

[0081] It should be noted that a large-lifting-capacity offshore hook of the present invention application is manufactured by using any one of the manufacturing methods of a large-lifting-capacity offshore hook in the first aspect. Correspondingly, it also includes: all the technical problems, technical solutions and technical effects recorded in any one of the manufacturing methods of a large-lifting-capacity offshore hook in the first aspect. The present invention application will not elaborate here.

[0082] Optionally, the hook body is made of 20CrMnMo steel, and the mass fractions of the elements in the 20CrMnMo steel are as follows: C: 0.17% to 0.23%, Si: 0.17% to 0.37%, Mn: 0.90% to 1.20%, Cr: 1.10% to 1.40%, Mo: 0.20% to 0.30%, Nb: ≤0.030%, Al: ≥0.015%, Cu: ≤0.25%, P: ≤0.025%, S : ≤0.015%, the rest is Fe, Nb can form fine carbonitrides, refine the grains, thereby improving the strength and toughness of the steel. Trace Nb can also help improve the performance of the welding area and reduce welding defects. Al is a strong deoxidizer, which can reduce the oxygen content in the steel and improve the purity and toughness of the steel. Aluminum combines with nitrogen to form AlN, which further refines the grains, enhances the strength of the steel, and improves the quality of the hook, making the hook forgeable and having high strength, toughness and fatigue resistance.

[0083] Optionally, a fluorocarbon topcoat coating is formed on the outer periphery of the hook, and the thickness of the fluorocarbon topcoat coating is controlled between 15-30 microns.

[0084] In the present invention application, the coating thickness is controlled at 15-30 microns (including 15 microns and 30 microns). The fluorocarbon topcoat can form a dense protective layer due to its fluorocarbon resin component, effectively blocking the erosion of the hook by corrosive media such as seawater and salt spray, greatly extending the service life. The excellent anti-UV and anti-aging properties of the fluorocarbon topcoat enable the hook to resist damage from natural factors such as sunlight, wind and sand in the marine environment, and maintain the long-term use of the coating. The application of high-performance fluorocarbon topcoat provides reliable protection for the hook of offshore cranes, while taking into account environmental protection, economy and efficiency, to ensure the long-term and stable operation of the hook in harsh marine environments.

[0085] Optionally, the multiple hook tips include a first hook tip, a second hook tip, a third hook tip and a fourth hook tip, and the center of the first hook tip, the center of the second hook tip, the center of the third hook tip and the center of the fourth hook tip are connected to form a rectangle, and the maximum lifting weight is 3500t or more.

[0086] In the present application, the maximum lifting capacity is 3500t or more, such as 3500t, 4000t, 4500t, 6000t, etc. The hook body includes a first hook body, a second hook body, a third hook body, and a fourth hook body. The first hook body is welded to the first hook tip, the second hook body is welded to the second hook tip, the third hook body is welded to the third hook tip, and the fourth hook body is welded to the fourth hook tip. The centers of the four hook tips are located at the four vertices of the rectangle, which can evenly disperse the weight of the hoisted object and reduce the risk of tilting or imbalance caused by uneven force. The symmetrical rectangular structure helps to maintain the stability of the hoisted object and reduce shaking during the hoisting process, thereby improving the overall safety and the lifting capacity of the hoisting.

[0087] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification;

[0088] Those skilled in the art of this technology can understand that the steps, measures, and solutions in the various operations, methods, and processes discussed in this invention application can be alternated, changed, combined, or deleted; further, other steps, measures, and solutions in the various operations, methods, and processes discussed in this invention application can also be alternated, changed, rearranged, decomposed, combined, or deleted; further, the steps, measures, and solutions in the prior art that are the same as those disclosed in the various operations, methods, and processes in this invention application can also be alternated, changed, rearranged, decomposed, combined, or deleted.

[0089] The above-described embodiments merely represent several implementation manners of the embodiments of the present disclosure. The description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the embodiments of the present disclosure; it should be noted that for those of ordinary skill in the art, without departing from the concept of the embodiments of the present disclosure, several modifications and improvements can still be made, and these all belong to the protection scope of the embodiments of the present disclosure; therefore, the protection scope of the embodiments of the present disclosure should be subject to the appended claims.

Claims

1. A manufacturing method for a large-lifting-capacity offshore hook, characterized in that, Including: Step S100: Select 20CrMnMo steel to forge the hook body; Step S200: Perform double normalizing and double tempering heat treatments on the hook body to obtain the heat-treated hook body, and perform pre-cooling, water cooling, oil cooling, and tempering on the heat-treated hook body to obtain the quenched and tempered hook body; Step S300: Perform finish machining on the quenched and tempered hook body to obtain the machined hook body, and weld the machined hook body and the hook tip to form the hook body, so that the assembled hook body and hook tip after welding meet the design requirements; Step S400: Coat the surface of the hook body to obtain the hook.

2. The manufacturing method of a large lifting capacity offshore hook according to claim 1, characterized in that, Step S200 includes: Step S201: Heat the hook body to 950 - 1000 °C for the first normalizing, hold for 2 - 5 hours, and then air cool; after an interval of the first set time T1, then heat the hook body to 850 - 900 °C for the second normalizing, hold for 3 - 8 hours, and then air cool; Step S202: Heat the air-cooled hook body to 850 - 900 °C, hold for 1 - 2 hours, and then quickly oil quench to room temperature; Step S203: Heat the hook body at room temperature to 550 - 600 °C for the first tempering, hold for 5 - 10 hours, and then air cool; after an interval of the second set time T2, heat the hook body to 650 - 700 °C again for the second tempering, hold for 8 - 15 hours, and then furnace cool, and the furnace outlet temperature is less than 250 °C to obtain the heat-treated hook body.

3. A manufacturing method of a large-lifting-capacity offshore hook according to claim 2, characterized in that, After step S203, it further includes: Step S204: Air cool from 860 °C to 700 °C before quenching for about 30 minutes; Step S205: Water cool the hook body for 10 - 20 minutes and oil cool for 180 - 210 minutes to obtain the quenched hook body; Step S206: Heat the quenched hook body to the tempering temperature of 150 - 250 °C, control the tempering holding time within 12 - 30 hours, and after holding, furnace cool or air cool to obtain the quenched and tempered hook body.

4. A manufacturing method of a large lifting capacity offshore hook according to claim 3, characterized in that, S1 ≤ |T1 - T2| ≤ S2, where S1 is the first preset time and S2 is the second preset time.

5. A manufacturing method of a large-lifting-capacity offshore hook according to claim 4, characterized in that, The first preset time S1 and the second preset time S2 are: Where r is the preset radius of the hook body, a is the thermal diffusivity of the hook body material, α is the first process adjustment coefficient, β is the second process adjustment coefficient, 0 ≤ α ≤ 1, 1 ≤ β ≤ 2.

6. A manufacturing method of a large-lifting-capacity offshore hook according to claim 5, characterized in that, In step S100, the mass fractions of each element in 20CrMnMo steel are: C: 0.17% - 0.23%, Si: 0.17% - 0.37%, Mn: 0.90% - 1.20%, Cr: 1.10% - 1.40%, Mo: 0.20% - 0.30%, Nb: ≤0.030%, Al: ≥0.015%, Cu: ≤0.25%, P: ≤0.025%, S: ≤0.015%, and the rest is Fe.

7. A manufacturing method of a large lifting capacity offshore hook according to claim 6, characterized in that, In step S400, fluorocarbon topcoat is applied to the surface of the hook body.

8. A large-lifting-capacity offshore hook, manufactured by using the manufacturing method of a large-lifting-capacity offshore hook according to any one of claims 1-7, comprising: The hook body and multiple hook tips are welded.

9. The large lifting capacity offshore hook according to claim 8, wherein, The material of the hook body is 20CrMnMo steel, and the mass fractions of the various elements of 20CrMnMo steel are as follows: C: 0.17% - 0.23%, Si: 0.17% - 0.37%, Mn: 0.90% - 1.20%, Cr: 1.10% - 1.40%, Mo: 0.20% - 0.30%, Nb: ≤0.030%, Al: ≥0.015%, Cu: ≤0.25%, P: ≤0.025%, S: ≤ 0.015%, and the balance is Fe.

10. The large-lifting-capacity offshore hook according to claim 9, wherein, A fluorocarbon topcoat coating is formed on the outer periphery of the hook, and the thickness of the fluorocarbon topcoat coating is controlled between 15 - 30 microns; and / or, the multiple hook tips include a first hook tip, a second hook tip, a third hook tip, and a fourth hook tip. The centers of the first hook tip, the second hook tip, the third hook tip, and the fourth hook tip are connected to form a rectangle, and the maximum lifting capacity is 3500t and above.

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