460mpa marine steel continuous casting thin plate explosive process and evaluation method

Abstract

The application provides a kind of suitable for 460MPa marine steel continuous casting medium thin plate pyrotechnic process, comprising the following steps: S1: component installation to specified position;S2: determine the shape of component heating zone, according to component steel plate thickness classification selection heating scheme, mark boundary line;S3: heating to heating zone;Using high frequency induction coil or neutral flame as heat source, according to heating scheme heating;S4: after heating, deformation treatment is carried out to meet the target shape requirement;If it can not meet, repeat step S3;S5: component inspection.The application introduces induction heating technology and classifies the pyrotechnic process according to the thickness of steel plate, and pyrotechnic is carried out on 3mm-16mm thickness 460MPa continuous casting steel plate, realizes that Ni-Cr-Mo series low alloy continuous casting steel has more stable mechanical properties and more accurate forming and straightening effect after pyrotechnic, and meets the requirements of ship structure construction.

Description

Technical Field

[0001] This invention relates to the field of shipbuilding technology, and in particular to a fire-working process and evaluation method for continuous casting of thin plates for 460MPa marine steel. Background Technology

[0002] Shipbuilding involves many complex curved structural components that need to be formed within enclosed spaces. Furthermore, significant deformation occurs after the processing and welding of large hull components, making large-scale mechanical forming difficult. Therefore, heat treatment is one of the fundamental forming and straightening processes for marine steel. In the shipbuilding industry, heat treatment is a technology used to handle thermal deformation. Specifically, it involves locally heating the steel. When the steel reaches a certain temperature, its local yield strength decreases. Under the influence of thermal expansion and contraction, the steel undergoes plastic deformation, and the high-temperature area experiences tensile stress. At this point, natural cooling or the application of cold water will cause the steel to form a new, permanent deformation. According to the processing purpose, heat treatment can be divided into heat processing and heat straightening, primarily to process steel into structures of desired shapes, or to restore deformed structures to straightness or correct them according to shape requirements. During these processes, in addition to deformation, the microstructure and mechanical properties of the heated steel also change.

[0003] As ships develop towards larger, greener, and ocean-going capabilities, in addition to general strength A-F grade hull structural steel below 355MPa, the application of high strength continuous casting hull structural steel of 400-600MPa grade is also gradually increasing. Due to the addition of a certain amount of Ni-Cr-Mo and other elements, it can ensure good low-temperature performance and high strength, and may be used in harsh sea conditions such as polar regions in the future.

[0004] Taking 460MPa marine steel as an example, considering its low-temperature toughness and welding requirements, this strength level of steel relies not only on the microstructure and solid solution strengthening brought by Ni-Cr-Mo, but also more on dislocation strengthening, grain refinement strengthening, and precipitation strengthening, thus having a lower carbon equivalent. The higher strength leads to a reduction in the steel plate specifications required for large ships, decreasing the use of thick plates, with medium-thin plates (3-16mm) accounting for the largest proportion. These are typically supplied in hot-rolled + high-temperature tempered or hot-rolled + normalized + high-temperature tempered states, with a microstructure of ferrite + pearlite or acicular ferrite, exhibiting a good strength-toughness balance. However, during the hot working process of the steel plate, due to the phase transformation kinetics characteristics of its composition and plate thickness range, as well as the moderate cooling rate, granular bainite is easily precipitated, leading to reduced or unstable low-temperature toughness. However, a search of relevant patents reveals that current domestic research on the heat treatment processes for high-strength ship hull structural steel of 400MPa grade and above has not yet been conducted. Shanghai Jiangnan Changxing Heavy Industry Co., Ltd. previously disclosed a patent (CN201410120402) for the pyrotechnic process and verification method of JFE-LT-FH32 low-temperature steel. Although the patent provides relatively clear specifications for the pyrotechnic process testing method, the material involved in this technology is general-strength hot-rolled F-grade ship hull steel. This type of material has a low tendency for granular bainite precipitation, and its mechanical properties are not very sensitive to pyrotechnic process parameters, environmental conditions, and plate thickness range. Therefore, the process evaluation method and process parameters provided by this patent may not be suitable for thin plates of 460MPa marine steel. Summary of the Invention

[0005] In view of this, the present invention aims to propose a heat treatment process for thin plates in continuous casting of 460MPa marine steel. By classifying the thickness of the steel plates, a more precise heat treatment process is determined to solve the problem of heat treatment process for thin plates in continuous casting of 460MPa with a thickness of 3-16mm.

[0006] To achieve the above objectives, this invention discloses a fire-casting process for 460MPa marine steel thin plates, comprising the following steps:

[0007] S1: Install the component to the designated position; hoist the component to the fire operation position, ensuring that the sleepers and auxiliary tools are in place;

[0008] S2: Determine the component heating scheme and mark the boundary lines; select the heating temperature according to the component steel plate thickness, and choose the heating scheme according to the component shape, deformation type and deformation amount, and mark the boundary lines;

[0009] S3: Heat the heating zone; According to the heating scheme, use a high-frequency induction coil or a neutral flame as the heat source. When using a high-frequency induction coil as the heat source, use the formula relating the angular deformation to the component steel plate thickness T, the heat preservation time t, and the air gap L to determine the heat preservation time t and the air gap L, and heat the component along the boundary line.

[0010] S4: After heating, deform the steel to meet the target shape requirements; if it cannot meet the requirements, repeat step S3. The 460MPa high-strength marine steel continuous casting plate with a thickness of 3-16mm can be repeatedly heated multiple times.

[0011] S5: Component inspection; Inspection shall be carried out in accordance with the testing items and methods required by the process.

[0012] Furthermore, in step S1, the component is made of 460MPa continuously cast steel with the following chemical composition: C≤0.12%, Mn≤1.5%, Si≤0.9%, 0.4%≤Cr≤1.2%, Mo≤0.5%, 0.4%≤Ni≤1.5%, V≤0.1%, Cu≤0.5%, and the steel plate thickness range is 3~16mm. The component is in the length direction of the steel plate rolling direction.

[0013] Furthermore, in step S2, linear heating or triangular heating is used for heating, with the flame width or heating zone being 25-30mm. During the heating process, a temperature measuring pen or infrared thermometer is used to detect and record the surface temperature of the measuring points on the component in real time, ensuring that the heating temperature range of the steel plate surface is between 707-900℃, while the heating range does not exceed the flame width. Air cooling or water cooling is used for cooling. When water cooling, air cooling is first used to lower the temperature to below 650℃ before water cooling, maintaining a water-fire distance of 100-150mm. After water cooling and flame tempering, direct hammering is not allowed.

[0014] Furthermore, in step S2, the steel plate thickness range is [3~7), unit: mm, and the heating temperature range is 707-800℃; the steel plate thickness range is [7~13), unit: mm, and the heating temperature range is 747-820℃; the steel plate thickness range is [13~16), unit: mm, and the heating temperature range is 792-859℃.

[0015] Furthermore, in step S3, when a high-frequency induction coil is used as the heat source, the relationship between the angular deformation and the thickness T of the component steel plate, the heat preservation time t, and the air gap L is as follows:

[0016] Angular deformation (air cooling): θ = -1.987lnT + 1.713lnt - 0.743lnL + 2.411

[0017] Angular deformation (water cooling): θ = -2.248lnT + 1.615lnt - 0.918lnL + 3.865

[0018] T should be 3–16 mm, t should be 12–24 s, and L should be 5–10 mm.

[0019] Furthermore, in step S4, the holding time t for repeated heating and the air gap L are determined according to the formula for angular deformation.

[0020] Furthermore, in steps S4 and S5, the deformation of the marine continuous casting steel plate shall not exceed ±4°.

[0021] Furthermore, in step S5, the mechanical properties of the component after pyrotechnic treatment are as follows: Rel or Rp0.2 ≥ 460 MPa, Rm 570~720 MPa, A ≥ 16%, and when the ambient temperature is -40℃, KV2: ≥ 34 J (10 mm impact), KV2: ≥ 28 J (7.5 mm impact), KV2: ≥ 23 J (5 mm impact).

[0022] Another objective of this invention discloses an evaluation method for the heat treatment process of thin plates in continuous casting of 460MPa marine steel. Based on any of the above heat treatment processes for thin plates in continuous casting of 460MPa marine steel, the specific steps are as follows:

[0023] S1: Cut plates for pyrotechnic testing from 460MPa Ni-Cr-Mo series low alloy marine continuous casting steel plates; classify them according to thickness [3~7), [7~13), [13~16) mm, and cut the plates with length and width dimensions of 1000×600 mm, and mark the flame channel boundary lines along the rolling direction of the steel plate;

[0024] S2: High-frequency induction coils or neutral flames are used as heat sources for pyrotechnic process tests. Temperature pens or infrared thermometers are used to detect and record the surface temperature of each test plate in real time. Processing parameters are selected according to the formula relating angular deformation to the thickness T of the component steel plate, the holding time t, and the air gap L. Each temperature measuring point is operated according to the selected holding time t and air gap L. The cooling method is carried out according to the process requirements.

[0025] S3: Detect the angular deformation of each group of test plates, and conduct flame channel tensile, joint tensile, transverse tensile flame core and flame side low temperature impact tests on the test plates tested in S2 according to national standards, and record the test data of each group;

[0026] S4: Determine whether the various indicators of the test board meet the usage requirements according to the process requirements.

[0027] Furthermore, in step S2, the uncertainty of the temperature measuring pen or infrared thermometer is <1%.

[0028] Compared with existing technologies, the fire-working process and evaluation method for continuous casting of thin plates for marine steel described in this invention have the following advantages:

[0029] 1. This invention is mainly aimed at medium and thin plates of 3-16mm. These types of steel plates are used in the largest quantities in large ocean-going and polar vessels. The provided pyrotechnic process parameters completely avoid the influence of granular bainite precipitation on material properties, which is of great significance for ensuring the quality of ship construction.

[0030] 2. Considering the significant impact of water cooling on the performance of medium-thin plates of 3-16mm, the mechanical properties of the flame-worked zone were restored by flame channel tempering, thereby improving the adaptability of the flame-worked process in shipbuilding.

[0031] 3. This invention provides a basis for selecting process parameters for high-frequency induction heating. Compared with traditional flame heating, its application on thin plates of 3-16mm can achieve a larger temperature gradient, save more time, and have less impact on material properties.

[0032] 4. The developed pyrotechnic process takes into account the influence of environmental conditions, plate thickness range, and heating method. The analysis of material microstructure and properties ensures the rationality of the process and its safety. Key parameters such as maximum temperature and maximum number of repetitions are clearly defined and explained, and the process is easy to use in actual shipyard construction.

[0033] 5. The linear heating and triangular heating methods of the present invention are particularly suitable for medium and thin plate components with large deformation. Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0035] Figure 1 This is a table showing the chemical composition and specification range of the steel used in this invention;

[0036] Figure 2 The table shows the mechanical properties of the steel plate used in this invention.

[0037] Figure 3 These are the pyrotechnic process parameters in this invention;

[0038] Figure 4 The steel plate thickness classification fire process parameters in this invention;

[0039] Figure 5 These are the process parameters and deformations of the induction heating air cooling process in this invention;

[0040] Figure 6 These are the process parameters and deformations of the induction heating water cooling process in this invention. Detailed Implementation

[0041] To make the technical means and objectives and effects of the present invention easier to understand, the embodiments of the present invention will be described in detail below with reference to specific illustrations.

[0042] It should be noted that all directional and positional terms used in this invention, such as "up," "down," "left," "right," "front," "back," "vertical," "horizontal," "inner," "outer," "top," "lower," "lateral," "longitudinal," and "center," are only used to explain the relative positional relationships and connections between components in a specific state (as shown in the accompanying drawings). They are merely for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0043] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0044] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0045] This invention discloses a fire-casting process for 460MPa marine steel thin plates, comprising the following steps:

[0046] S1: Install the component to the designated position; hoist the component to the fire operation position, ensuring that the sleepers and auxiliary tools are in place;

[0047] S2: Determine the component heating scheme and mark the boundary lines; select the heating temperature according to the component steel plate thickness, and choose the heating scheme according to the component shape, deformation type and deformation amount, and mark the boundary lines;

[0048] S3: Heat the heating zone; According to the heating scheme, use a high-frequency induction coil or a neutral flame as the heat source. When using a high-frequency induction coil as the heat source, use the formula relating the angular deformation to the component steel plate thickness T, the heat preservation time t, and the air gap L to determine the heat preservation time t and the air gap L, and heat the component along the boundary line.

[0049] S4: After heating, deform the steel to meet the target shape requirements; if not, repeat step S3. The 3-16mm thick 460MPa high-strength marine steel continuous casting plate can be repeated multiple times.

[0050] S5: Component inspection; Inspection shall be carried out in accordance with the testing items and methods required by the process.

[0051] This process uses 460MPa high-strength marine continuous casting steel as the processing target. Its mechanical properties are more sensitive to the heat treatment process. Through analysis and experiments, a new heating temperature range and other process parameters were determined to avoid the problem of granular bainite precipitating from ferrite + pearlite or acicular ferrite after heating, which would lead to a decrease or instability in low-temperature toughness. This ensures that the mechanical properties of the components meet the requirements after heat treatment. The introduction of high-frequency induction heating technology, when applied to medium and thin plates, can achieve a larger temperature gradient than traditional flame heating methods, which saves more time and has less impact on material properties.

[0052] Preferably, the number of heating cycles for thin plates in continuous casting of 460MPa high-strength marine steel does not exceed three.

[0053] Specifically, in step S1, the component is made of 460MPa continuously cast steel with the following chemical composition: C≤0.12%, Mn≤1.5%, Si≤0.9%, 0.4%≤Cr≤1.2%, Mo≤0.5%, 0.4%≤Ni≤1.5%, V≤0.1%, Cu≤0.5%. The steel plate thickness ranges from 3 to 16 mm, and the component's length is determined by the rolling direction of the steel plate. This steel contains a certain amount of Ni-Cr-Mo elements, which ensures good low-temperature performance and high strength, making it suitable for harsh sea conditions such as polar regions. Besides relying on the microstructure and solid solution strengthening provided by Ni-Cr-Mo, this type of steel relies more on dislocation strengthening, grain refinement strengthening, and precipitation strengthening, resulting in a lower carbon equivalent. The higher strength allows for a reduction in the steel plate specifications required for large ships, reducing the amount of thick plates used.

[0054] Specifically, in step S2, linear or triangular heating methods are used. The width of the flame channel or the heating zone is 25-30mm. During the heating process, a temperature measuring pen or infrared thermometer is used to monitor and record the surface temperature of the measuring points on the component in real time, ensuring that the surface heating temperature of the steel plate is between 707 and 900℃, while the heating range does not exceed the width of the flame channel. Air cooling or water cooling is used for cooling. When water cooling, air cooling is performed first to lower the temperature to below 650℃ before water cooling, maintaining a water-fire distance of 100-150mm. After water cooling and flame channel tempering, direct hammering is not allowed. Since hull components often have large plate thicknesses, high rigidity, or large deformation, linear or triangular heating can better achieve the correction effect and ensure the mechanical properties of the components. Real-time monitoring of the heating process and recording the measured temperature allows for better control of the heating process, preventing overheating that could alter the mechanical properties of the components, facilitating subsequent inspection. Furthermore, the analysis of the heating data is beneficial for optimizing subsequent process measures and achieving more precise process design.

[0055] Preferably, the component is plate-shaped with length and width dimensions of 1000 (rolling direction) × 600 mm.

[0056] Specifically, in step S2, the steel plate thickness range is [3~7), unit: mm, and the heating temperature range is 707-800℃; the steel plate thickness range is [7~13), unit: mm, and the heating temperature range is 747-820℃; the steel plate thickness range is [13~16), unit: mm, and the heating temperature range is 792-859℃. This setting takes into account the influence of environmental conditions, plate thickness range, and heating method, and provides specific process parameters for steel plates of different specifications with thicknesses of 3~16mm. This avoids drastic changes in the mechanical properties of the steel plate due to temperature sensitivity, and is conducive to the steel plate having better mechanical properties after heat treatment, meeting the needs of hull structure processing.

[0057] Specifically, in step S3, when using a high-frequency induction coil as the heat source, the holding time t and air gap L are determined before heating; when using a neutral flame as the heat source, the neutral flame combination, heating nozzle size, welding torch tilt angle, and flame core distance are determined before heating. High-frequency induction heating has the characteristics of skin effect and penetrating heat transfer. Compared with flame heating, induction heating of steel plate thickness section has a larger temperature gradient, resulting in better forming and straightening effects. It is conducive to realizing automated control of the heating process, reducing damage to the paint film on the hull surface and fuel consumption, and improving operational safety and environmental friendliness. Neutral flame heating equipment is more common, and operators are skilled, making it easier to arrange production. This setting can increase the adaptability of the process scheme, making it convenient to formulate pyrotechnic processes according to production and specific production environment, and achieving better application results.

[0058] Preferably, in step S3, when a high-frequency induction coil is used as the heat source, the heat preservation time ranges from 12 to 24 seconds, and the heating distance is from 5 to 10 mm.

[0059] Specifically, when using a high-frequency induction coil as a heat source, the surface temperature of the steel plate can be controlled by adjusting the heating current and heating rate. This feature enriches the control methods for using high-frequency induction coils as heat sources, helps to better control various variables and parameters during the process, achieves precise control of the heating process, improves the accuracy of process parameters, and ensures the quality of the heating process.

[0060] Specifically, a neutral oxy-acetylene flame is used as the heat source. The heating nozzle diameter of the welding torch is 1.0–3.0 mm, the torch tilt angle is not less than 60°, and the flame core distance is ≤3 mm. This setup allows the heating device to better meet the requirements of the heating scheme, ensuring the heating effect of continuously cast steel with a thickness of 3–16 mm, meeting the mechanical performance requirements of the hull structure, and facilitating large-scale division of labor and assembly line operations for hull structure construction, thereby improving production efficiency and ensuring quality.

[0061] Specifically, in step S3, when a high-frequency induction coil is used as the heat source, the relationship between the angular deformation and the thickness T of the steel plate of the component, the heat preservation time t, and the air gap L is as follows:

[0062] Angular deformation (air cooling): θ = -1.987lnT + 1.713lnt - 0.743lnL + 2.411

[0063] Angular deformation (water cooling): θ = -2.248lnT + 1.615lnt - 0.918lnL + 3.865

[0064] The thickness T should be between 3 and 16 mm, the heating rate V between 12 and 24 s, and the length L between 5 and 10 mm. This formula, which establishes a logarithmic linear relationship between the component thickness T, heating rate V, and angular deformation, can guide the optimization of process measures, achieve more precise process parameter settings, quantitatively control forming and straightening effects, reduce the number of subsequent corrections, and save overall costs.

[0065] Specifically, in step S4, the holding time t and air gap L for the second heating are determined based on the formula for angular deformation. By utilizing the formula relating the holding time t and air gap L to angular deformation, the heating parameters can be calculated more accurately, resulting in better forming or straightening effects, reducing the number of subsequent corrections, and saving overall costs.

[0066] Specifically, in steps S4 and S5, the deformation of the marine continuous casting steel plate shall not exceed ±4°. This setting can meet and unify the technical requirements in the hull processing process, facilitate subsequent processing, and improve work efficiency.

[0067] Specifically, in step S5, the mechanical properties of the components after pyrotechnic treatment are as follows: Rel or Rp0.2 ≥ 460 MPa, Rm 570~720 MPa, A ≥ 16%, and at an ambient temperature of -40℃, KV2: ≥ 34 J (10mm impact), KV2: ≥ 28 J (7.5mm impact), and KV2: ≥ 23 J (5mm impact). This setting can meet and unify the technical requirements in the hull processing process, facilitate subsequent processing, and improve work efficiency.

[0068] Another objective of this invention discloses a method for evaluating the heat treatment process of thin plates in continuous casting of 460MPa marine steel. Based on any of the above heat treatment processes for thin plates in continuous casting of 460MPa marine steel, the specific steps are as follows:

[0069] S1: Cut plates for pyrotechnic testing from 460MPa Ni-Cr-Mo series low alloy marine continuous casting steel plates; classify them according to thickness [3~7), [7~13), [13~16) mm, and cut the plates with length and width dimensions of 1000×600 mm, and mark the flame channel boundary lines along the rolling direction of the steel plate;

[0070] S2: High-frequency induction coils or neutral flames are used as heat sources for pyrotechnic process tests. Temperature pens or infrared thermometers are used to detect and record the surface temperature of each test plate in real time. Processing parameters are selected according to the formula relating angular deformation to the thickness T of the component steel plate, the holding time t, and the air gap L. Each temperature measuring point is operated according to the selected holding time t and air gap L. The cooling method is carried out according to the process requirements.

[0071] S3: Detect the angular deformation of each group of test plates, and conduct flame channel tensile, joint tensile, transverse tensile flame core and flame side low temperature impact tests on the test plates tested in S2 according to national standards, and record the test data of each group;

[0072] S4: Determine whether the various indicators of the test plate meet the usage requirements according to the process requirements. This setting is used to evaluate the pyrotechnic process using high-frequency induction coils or neutral flames as heat sources. Tests are conducted using selected processing parameters, and various tests are performed according to national standards to determine whether the process requirements are met. The entire judgment method is comprehensive in its testing items, with complete and detailed data collection and recording, traceable parameters, standardized operation methods, and easy to promote and apply.

[0073] Specifically, each test plate and temperature measuring point is marked with a number for tracking and recording the heating process.

[0074] Specifically, the uncertainty of the temperature measuring pen or infrared thermometer is <1%. This setting can reduce stable detection errors, achieve stable and precise control, better leverage the controllable advantages of the induction heating process, and thus achieve the purpose of precise forming and straightening effects.

[0075] Example 1

[0076] Pyrotechnic straightening (flame heating and induction heating, air cooling)

[0077] Fire-induced straightening was performed on the 8mm thick 460MPa continuous cast marine steel bulkhead structure with initial properties as shown in Table 7.

[0078] Table 7 Original Properties of Fire-Standardized Steel Plate Matrix

[0079]

[0080] By adjusting the oxygen, acetylene, and flame height, the maximum heating temperature of the steel plate surface was ensured to be 750–800℃. Flame channels were arranged from both ends to the middle for flame straightening, with a channel width of approximately 25mm. This process was repeated once and three times to ensure the straightness met the requirements. The mechanical properties were analyzed from the model, and the results are shown in Table 8.

[0081] Table 8 Mechanical properties of the pyrotechnic zone after pyrotechnic straightening

[0082]

[0083] To compare the mechanical properties of the pyrotechnic zone using induction correction, heating was performed along the back side of the center of the wall weld, with an air gap of 10 mm and a heating time of 16 s. This was repeated once, and the mechanical properties of the pyrotechnic zone were measured as shown in Table 9.

[0084] Table 9 Mechanical properties of the pyrotechnic zone after pyrotechnic straightening

[0085]

[0086] Example 2

[0087] Pyrotechnic straightening (air-cooled)

[0088] Fire-induced straightening was performed on 6mm thick 460MPa continuous cast marine steel bulkheads with initial properties as shown in Table 10.

[0089] Table 10 Original Properties of the Matrix of Fire-Standardized Steel Plates

[0090]

[0091] By adjusting the oxygen, acetylene, and flame height, the maximum heating temperature of the steel plate surface was ensured to be 750–800℃. Flame channels were arranged from both ends to the middle for flame straightening, with a channel width of approximately 25mm. This process was repeated once and three times to ensure the straightness met the requirements. The mechanical properties were analyzed from the model, and the results are shown in Table 11.

[0092] Table 11 Mechanical properties of the pyrotechnic zone after pyrotechnic straightening

[0093]

[0094] Example 3

[0095] Fire-forming (water-cooled)

[0096] Fire forming was performed on the 10mm thick 460MPa continuous cast marine steel bulkhead structure with initial properties as shown in Table 12.

[0097] Table 12 Original Properties of the Matrix of Fire-Formed Steel Plates

[0098]

[0099] By adjusting the oxygen, acetylene, and flame height, the maximum heating temperature of the steel plate surface was ensured to be 750–800℃ and 800–850℃ respectively. Flame channels were arranged from both ends to the middle for flame forming, with a channel width of approximately 25mm. This process was repeated once and three times to ensure the straightness met the requirements. The mechanical properties were analyzed from the model, and the results are shown in Table 13.

[0100] Table 13 Mechanical properties of the pyrotechnic zone after pyrotechnic forming

[0101]

[0102] Example 4

[0103] Fire-forming (water-cooled)

[0104] The 16mm thick 460MPa continuous cast marine steel keel structure with initial properties as shown in Table 14 was subjected to fire forming.

[0105] Table 14 Original Properties of the Matrix of Fire-Formed Steel Plates

[0106]

[0107] By adjusting the oxygen, acetylene, and flame height, the maximum heating temperature of the steel plate surface was ensured to be 800–850℃. Flame channels were arranged from both ends to the middle for flame forming, with a channel width of approximately 25mm. This process was repeated three times to ensure the straightness met requirements, and the tempering results of the flame channels were compared. The mechanical properties were analyzed from the model, and the results are shown in Table 15.

[0108] Table 15 Mechanical properties of the pyrotechnic zone after pyrotechnic forming

[0109]

[0110] To compare the mechanical properties of the pyrotechnic zone using induction correction, heating was performed along the back side of the center of the wall weld with an air gap of 5 mm and a heating time of 24 s. This was repeated twice, and the mechanical properties of the pyrotechnic zone were measured as shown in Table 16.

[0111] Table 16 Mechanical properties of the pyrotechnic zone after pyrotechnic straightening

[0112]

[0113] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fire-casting process for 460MPa marine steel thin plates, characterized in that, Includes the following steps: S1: Install the component to the designated position; hoist the component to the pyrotechnic operation position, ensuring that the sleepers and auxiliary tools are in place; the component is made of 460MPa continuously cast steel, with the following chemical composition: C≤0.12%, Mn≤1.5%, Si≤0.9%, 0.4%≤Cr≤1.2%, Mo≤0.5%, 0.4%≤Ni≤1.5%, V≤0.1%, Cu≤0.5%; steel plate thickness range: 3~16mm; the component is in the length direction of the steel plate rolling direction. S2: Determine the component heating scheme and mark the boundary lines; select the heating temperature according to the component steel plate thickness, and select the heating scheme according to the component shape, deformation type and deformation amount, and mark the boundary lines; steel plate thickness range: [3~7), unit: mm, heating temperature range: 707-800℃; steel plate thickness range: [7~13), unit: mm, heating temperature range: 747-820℃; steel plate thickness range: [13~16), unit: mm, heating temperature range: 792-859℃; S3: Heating the heating zone; according to the heating scheme, a high-frequency induction coil is used as the heat source. The holding time t and air gap L are determined using the formula relating angular deformation to the component steel plate thickness T, holding time t, and air gap L. The component is heated along the boundary line. When using a high-frequency induction coil as the heat source, the relationship between angular deformation and the component steel plate thickness T, holding time t, and air gap L is as follows: When air cooling is used, the angular deformation is: θ = -1.987lnT + 1.713lnt - 0.743lnL + 2.411 When water cooling is used, the angular deformation is: θ = -2.248lnT + 1.615lnt - 0.918lnL + 3.865 T should be 3~16mm, t should be 12~24s, and L should be 5~10mm; S4: After heating, deform the steel to meet the target shape requirements; if not, repeat step S3. The 460MPa high-strength marine steel continuous casting plate with a thickness of 3~16mm can be repeatedly heated multiple times. S5: Component inspection; Tests shall be conducted in accordance with the testing items and methods required by the process.

2. The fire-working process for continuous casting of thin plates of 460MPa marine steel according to claim 1, characterized in that, In step S2, the heating zone is 25~30mm. During the heating process, a temperature measuring pen or infrared thermometer is used to detect and record the surface temperature of the measuring point on the component in real time. Air cooling or water cooling is used for cooling. When water cooling, air cooling is used first to lower the temperature to below 650℃ before water cooling. After water cooling and flame channel tempering, direct hammering is not allowed.

3. The fire-working process for continuous casting of thin plates of 460MPa marine steel according to claim 1, characterized in that, In step S4, the holding time t and air gap L for repeated heating are determined according to the formula for angular deformation.

4. The fire-working process for continuous casting of thin plates of 460MPa marine steel according to claim 1, characterized in that, In steps S4 and S5, the deformation of the marine continuous casting steel plate shall not exceed ±4°.

5. The fire-working process for continuous casting of thin plates of 460MPa marine steel according to claim 1, characterized in that, In step S5, the mechanical properties of the component after pyrotechnic treatment are: Rel or Rp0.2 ≥ 460 MPa, Rm 570~720 MPa, A ≥ 16%, and when the ambient temperature is -40℃, KV2: ≥ 34 J (10 mm impact), KV2: ≥ 28 J (7.5 mm impact), KV2: ≥ 23 J (5 mm impact).

6. A method for evaluating the fire-working process of continuous casting thin plates for 460MPa marine steel, characterized in that, Based on any one of the heat treatment processes for continuous casting of thin plates of 460MPa marine steel according to claims 1 to 5, the specific steps are as follows: S1: Cut plates for pyrotechnic testing from 460MPa Ni-Cr-Mo series low alloy marine continuous casting steel plates; classify them according to thickness [3~7), [7~13), [13~16) mm, and cut plates with length and width dimensions of 1000×600 mm, and mark the flame channel boundary lines along the rolling direction of the steel plate; S2: High-frequency induction coils are used as heat sources for pyrotechnic process tests. Temperature pens or infrared thermometers are used to detect and record the surface temperature of each test plate in real time. Processing parameters are selected according to the formula relating angular deformation to the thickness T of the component steel plate, heat preservation time t, and air gap L. Each temperature measurement point is operated according to the selected heat preservation time t and air gap L. Cooling is carried out according to process requirements. S3: Detect the angular deformation of each group of test plates, and conduct flame channel tensile, joint tensile, transverse tensile flame core and flame side low temperature impact tests on the test plates tested in S2 according to national standards, and record the test data of each group; S4: Determine whether the various indicators of the test board meet the usage requirements according to the process requirements.

7. The evaluation method for the fire-working process of thin plates in continuous casting of 460MPa marine steel according to claim 6, characterized in that, In step S2, the uncertainty of the temperature measuring pen or infrared thermometer is <1%.

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