Finite element analogue simulation-based duplex stainless steel heat treatment process optimization method

Abstract

The invention discloses a finite element analogue simulation-based duplex stainless steel heat treatment process optimization method, which relates to the field of stainless steel heat treatment process optimization, and comprises the following steps: carrying out mechanical property experiments on a duplex stainless steel profile under different temperatures and different deformation conditions to obtain a stress-strain relation curve; constructing a deformation resistance model and a thermoplastic curve, and measuring related physical property parameters; the method comprises the following steps: establishing a three-dimensional geometric model comprising a heat treatment furnace, a cooling pool and a duplex stainless steel profile, setting radiation-convection composite boundary conditions, carrying out grid division, carrying out solid solution heating process simulation, heat preservation process simulation and cooling process simulation based on the three-dimensional geometric model, carrying out dynamic analysis on a temperature field and a stress field, and obtaining an analysis result; and optimizing and determining the solid solution temperature, the heat preservation time and the cooling rate according to an analysis result. Rapid matching of duplex stainless steel profiles of different specifications and the heat treatment process can be achieved, the heat treatment test cost can be reduced, and the heat treatment test period can be shortened.

Description

Technical Field

[0001] This invention relates to the field of stainless steel heat treatment process optimization technology, and in particular to a method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation. Background Technology

[0002] Duplex stainless steel has a two-phase structure of ferrite and austenite in the room temperature solution state. By properly controlling the chemical composition and heat treatment process, the excellent toughness and weldability of austenitic stainless steel can be combined with the high strength and chloride stress corrosion resistance of ferritic stainless steel, so that duplex stainless steel has the advantages of both ferritic and austenitic stainless steel.

[0003] In the actual production of duplex stainless steel profiles, improper heat treatment processes can lead to the finished stainless steel products failing to meet usage requirements in terms of microstructure, properties, and appearance. Specifically, insufficient or excessive soaking time during heat treatment can result in uneven microstructure; insufficient cooling rate can cause brittle phases to precipitate; and uneven distribution and changes in the temperature and microstructure fields during cooling after heat treatment can generate significant instantaneous and residual stresses, causing bending deformation and cracking of the profiles. Therefore, determining the appropriate heat treatment process for duplex stainless steel is crucial for its production.

[0004] Currently, when determining the heat treatment process for stainless steel, heat treatment experiments are generally conducted first, and the corresponding heat treatment process is determined based on the results of these experiments. Traditional heat treatment experiments mainly employ a trial-and-error approach, specifically: repeatedly adjusting heat treatment process parameters to conduct experiments until the relevant heat treatment process parameters capable of producing qualified products are determined. However, in practical use, this method has a long experimental cycle, results in significant material waste, and is costly. Summary of the Invention

[0005] To address some or all of the technical problems existing in the prior art, this invention provides an optimization method for the heat treatment process of duplex stainless steel based on finite element simulation.

[0006] The technical solution of the present invention is as follows:

[0007] A method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation is provided, including the following steps:

[0008] Material property basic modeling: Mechanical property experiments were conducted on duplex stainless steel profiles under different temperatures and deformation conditions to obtain stress-strain relationship curves of duplex stainless steel profiles, construct deformation resistance models and thermoplastic curves, and determine relevant physical property parameters of duplex stainless steel profiles in the range of 20 to 1200℃.

[0009] Full-process heat treatment simulation analysis: A three-dimensional geometric model including heat treatment furnace, cooling pool and duplex stainless steel profile is established, radiation-convection composite boundary conditions are set and mesh generation is performed. Based on the established three-dimensional geometric model, the solid solution heating process, heat preservation process and cooling process are simulated, and the temperature field and stress field dynamic analysis are performed to obtain the analysis results.

[0010] Process parameter optimization: Based on the simulation analysis results of the whole process heat treatment, the solution temperature, holding time and cooling rate are optimized and determined under the constraints of suppressing brittle phase precipitation and controlling residual stress deformation.

[0011] In some optional implementations, the relevant physical properties include: specific heat capacity, thermal conductivity, and coefficient of thermal expansion.

[0012] In some optional implementations, the solid solution heating process simulation includes: using 1030–1080°C as the heating target, loading the temperature curve in a cold-loading manner, and completing the heating by simulating the heat transfer process of radiation and convection.

[0013] In some optional implementations, when simulating the heat preservation process, the heat preservation time is controlled to be h to 2h min or d to 2d min, where h represents the thickness of the duplex stainless steel profile and d represents the diameter of the duplex stainless steel profile.

[0014] In some alternative implementations, the cooling process employs water quenching.

[0015] In some alternative implementations, dynamic analysis of the temperature and stress fields is performed, including:

[0016] The temperature field changes, anisotropic thermal stress and equivalent stress distribution during the solution heating process are obtained, the equivalent stress of each part of the duplex stainless steel profile is calculated, and the maximum tensile stress zone and plastic deformation layer on the outer surface are identified.

[0017] The system acquires information on temperature field changes, anisotropic thermal stress and equivalent stress distribution during the cooling process, calculates the temperature gradient during the cooling process, quantifies the residence time of the core in the σ precipitation sensitive temperature range, and simultaneously outputs the triaxial tensile stress distribution on the surface.

[0018] In some optional implementations, the process parameter optimization step further includes:

[0019] Based on the determined solution treatment temperature, holding time, and cooling rate, duplex stainless steel profiles were heat-treated, and the microstructure and properties of the heat-treated duplex stainless steel profiles were verified.

[0020] In some alternative embodiments, the duplex stainless steel profile comprises the following chemical composition by weight percentage:

[0021] C≤0.030%, Si≤1.00%, Mn:0.50~2.00%, P≤0.035%, S≤0.003%, Cr:21.00~24.00%, Ni:4.50~6.00%, Mo:2.50~3.50%, N:0.08~0.20%, with the remainder being iron and unavoidable impurities.

[0022] The main advantages of the technical solution of this invention are as follows:

[0023] The present invention provides an optimization method for the heat treatment process of duplex stainless steel based on finite element simulation. Using finite element simulation software, a three-dimensional thermo-mechanical coupling numerical simulation is employed to perform a full-process simulation analysis of the heat treatment process of duplex stainless steel. This method acquires and analyzes data such as three-dimensional temperature evolution and stress-strain distribution, thereby optimizing and determining the heat treatment process parameters for duplex stainless steel profiles. This enables rapid matching of different specifications of duplex stainless steel profiles with the heat treatment process, ensuring the quality and performance of the heat-treated duplex stainless steel. Simultaneously, it reduces heat treatment test costs and shortens the heat treatment test cycle. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and constitute a part of this invention, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0025] Figure 1 The flowchart illustrates an optimization method for the heat treatment process of duplex stainless steel based on finite element simulation, as provided in this embodiment of the invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] The technical solutions provided by the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] refer to Figure 1 This invention provides a method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation, comprising the following steps:

[0029] Material property basic modeling: Mechanical property experiments were conducted on duplex stainless steel profiles under different temperatures and deformation conditions to obtain stress-strain relationship curves of duplex stainless steel profiles, construct deformation resistance models and thermoplastic curves, and determine relevant physical property parameters of duplex stainless steel profiles in the range of 20 to 1200℃.

[0030] Full-process heat treatment simulation analysis: A three-dimensional geometric model including heat treatment furnace, cooling pool and duplex stainless steel profile is established, radiation-convection composite boundary conditions are set and mesh generation is performed. Based on the established three-dimensional geometric model, the solid solution heating process, heat preservation process and cooling process are simulated, and the temperature field and stress field dynamic analysis are performed to obtain the analysis results.

[0031] Process parameter optimization: Based on the simulation analysis results of the whole process heat treatment, the solution temperature, holding time and cooling rate are optimized and determined under the constraints of suppressing brittle phase precipitation and controlling residual stress deformation.

[0032] It should be noted that, in this embodiment of the invention, the entire heat treatment simulation analysis process is implemented using finite element simulation analysis software.

[0033] The finite element simulation-based method for optimizing the heat treatment process of duplex stainless steel provided in this invention uses finite element simulation analysis software and three-dimensional thermo-mechanical coupling numerical simulation to perform full-process simulation analysis of the heat treatment process of duplex stainless steel. It acquires and analyzes data such as three-dimensional temperature evolution and stress-strain distribution, thereby optimizing and determining the heat treatment process parameters of duplex stainless steel profiles. This method can achieve rapid matching of different specifications of duplex stainless steel profiles with heat treatment processes, ensuring the quality and performance of the heat-treated duplex stainless steel, while reducing the cost of heat treatment tests and shortening the heat treatment test cycle.

[0034] Furthermore, in this embodiment of the invention, the relevant physical properties include: specific heat capacity, thermal conductivity, and coefficient of thermal expansion.

[0035] In this embodiment of the invention, mechanical property experiments were conducted on duplex stainless steel profiles under different temperatures and deformation conditions to obtain stress-strain curves, construct deformation resistance models and thermoplasticity curves, and determine relevant physical property parameters of duplex stainless steel profiles in the range of 20–1200℃, including specific heat capacity, thermal conductivity, and coefficient of thermal expansion. The stress-strain curves can be used to analyze the high-temperature rheological behavior of duplex stainless steel profiles and predict the deformation resistance and plastic instability risk during heat treatment. The deformation resistance model can be used to quantify the change of stress with temperature / strain rate and accurately calculate the thermal stress distribution. The thermoplasticity curves can be used to locate the temperature window of the brittle region and avoid the risk of cracking during heat treatment. The relevant physical property parameters can characterize the essential laws of heat transfer and deformation, and construct the basis for coupled temperature field-stress field calculations.

[0036] Furthermore, in this embodiment of the invention, the solid solution heating process simulation includes: using 1030 to 1080°C as the heating target, loading the temperature curve in a cold-loading furnace manner, and completing the heating process by simulating radiation and convection heat transfer.

[0037] In this embodiment of the invention, by simulating the solution heating process in the above manner, the real heating kinetics can be reproduced, and the accurate simulation of the solution heating process of the heat treatment of duplex stainless steel profiles can be achieved.

[0038] Furthermore, in this embodiment of the invention, when simulating the heat preservation process, the heat preservation time is determined based on the thickness or diameter of the duplex stainless steel profile.

[0039] Specifically, the heat preservation time is controlled to be h~2h min or d~2d min. Where h represents the thickness of the duplex stainless steel profile and d represents the diameter of the duplex stainless steel profile.

[0040] In this embodiment of the invention, by adaptively adjusting the heat preservation time according to the size of the duplex stainless steel profile, it is possible to avoid setting the heat preservation time too short or too long.

[0041] Furthermore, in this embodiment of the invention, the cooling process employs a water quenching cooling method.

[0042] Specifically, the cooling process was simulated based on the water quenching cooling method.

[0043] Furthermore, in this embodiment of the invention, dynamic analysis of the temperature field and stress field is performed, including:

[0044] The temperature field changes, anisotropic thermal stress and equivalent stress distribution during the solution heating process are obtained, the equivalent stress of each part of the duplex stainless steel profile is calculated, and the maximum tensile stress zone and plastic deformation layer on the outer surface are identified.

[0045] The system acquires information on temperature field changes, anisotropic thermal stress and equivalent stress distribution during the cooling process, calculates the temperature gradient during the cooling process, quantifies the residence time of the core in the σ precipitation sensitive temperature range, and simultaneously outputs the triaxial tensile stress distribution on the surface.

[0046] In this embodiment of the invention, dynamic analysis of temperature and stress fields based on simulation results reveals that all parts of the duplex stainless steel profile are in an equivalent tensile stress state during the heating process. The larger the size, the greater the equivalent stress. The outer surface bears the greatest tensile stress. If there are internal defects during the heating process, cracking will begin from the weakest point. The near-surface layer exceeding the yield strength will produce small plastic deformations.

[0047] Simulations were conducted on duplex stainless steel profiles of different specifications, and the equivalent Von Mises tensile stress on the outer surface of the tube blank during the heating process was obtained as shown in the table below:

[0048]

[0049] During the cooling process, the temperature changes in different parts are different. The surface comes into contact with the cooling medium and cools down rapidly. The corners and edges cool down the fastest because their surface volume is larger than other parts. The core temperature drops the slowest due to factors such as profile size, cooling time, and material properties.

[0050] The simulations conducted on duplex stainless steel profiles of different specifications yielded the following table showing the time required to cool to 200℃:

[0051]

[0052] During the cooling process, the stress state of different parts of the tube blank changes with the quenching time. The triaxial equivalent stress is in a tensile stress state, and the stress value is the largest at the surface and corners.

[0053] Simulations were conducted on duplex stainless steel profiles of different specifications, and the equivalent Von Mises tensile stress on the outer surface of the tube blank during the quenching and cooling process was obtained as shown in the table below:

[0054]

[0055]

[0056] Furthermore, in this embodiment of the invention, the process parameter optimization step further includes:

[0057] Based on the determined solution treatment temperature, holding time, and cooling rate, duplex stainless steel profiles were heat-treated, and the microstructure and properties of the heat-treated duplex stainless steel profiles were verified.

[0058] In this embodiment of the invention, by verifying the microstructure and properties of duplex stainless steel profiles based on the determined solution temperature, holding time, and cooling rate, the accuracy and feasibility of the obtained solution temperature, holding time, and cooling rate in actual production can be ensured.

[0059] Specifically, if the microstructure and performance verification results meet the usage requirements, the determined solution temperature, holding time, and cooling rate will be used as the optimal heat treatment process parameters; if the microstructure and performance verification results do not meet the usage requirements, the heat treatment process will be optimized again to determine the solution temperature, holding time, and cooling rate.

[0060] Furthermore, in this embodiment of the invention, the duplex stainless steel profile to which this method is applied comprises the following chemical composition by weight percentage:

[0061] C≤0.030%, Si≤1.00%, Mn:0.50~2.00%, P≤0.035%, S≤0.003%, Cr:21.00~24.00%, Ni:4.50~6.00%, Mo:2.50~3.50%, N:0.08~0.20%, with the remainder being iron and unavoidable impurities.

[0062] To make the above technical solutions of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0063] Example 1

[0064] In this embodiment 1, a heat treatment simulation was performed on a duplex stainless steel round bar with a diameter of 200 mm and a length of 6000 mm.

[0065] The chemical composition of duplex stainless steel round bars is as follows:

[0066] C: 0.019%, Si: 0.52%, Mn: 0.54%, P: 0.017%, S: 0.001%, Cr: 22.80%, Ni: 5.10%, Mo: 3.00%, N: 0.15%, with the remainder being iron and unavoidable impurities.

[0067] Specifically, based on the above-defined optimization method for the heat treatment process of duplex stainless steel using finite element simulation, the heating, holding, and cooling processes of duplex stainless steel round bars were simulated. The temperature field changes and stress-strain changes in each process were simulated and analyzed, and the heat treatment process parameters were obtained as follows: solution temperature 1050℃, holding time 120min, and water quenching cooling method.

[0068] Furthermore, duplex stainless steel round bars were subjected to actual heat treatment based on the heat treatment process parameters obtained above. The resulting duplex stainless steel round bars had a ferrite phase ratio of 51.8% and a longitudinal impact energy of 315Akv at low temperature (-40℃). Compared with conventional heat treatment processes, the low-temperature impact performance was improved by 18 times.

[0069] Example 2

[0070] In this embodiment 2, a heat treatment simulation was performed on a duplex stainless steel round bar with a diameter of 300 mm and a length of 8000 mm.

[0071] The chemical composition of duplex stainless steel round bars is as follows:

[0072] C: 0.023%, Si: 0.60%, Mn: 0.62%, P: 0.020%, S: 0.001%, Cr: 23.40%, Ni: 4.96%, Mo: 3.10%, N: 0.14%, with the remainder being iron and unavoidable impurities.

[0073] Specifically, based on the above-defined optimization method for the heat treatment process of duplex stainless steel using finite element simulation, the heating, holding, and cooling processes of duplex stainless steel round bars were simulated. The temperature field changes and stress-strain changes in each process were simulated and analyzed, and the heat treatment process parameters were obtained as follows: solution temperature 1060℃, holding time 170min, and water quenching cooling method.

[0074] Furthermore, duplex stainless steel round bars were subjected to actual heat treatment based on the heat treatment process parameters obtained above. The ferrite phase ratio in the duplex stainless steel round bars was 53.2%, and the longitudinal impact energy at low temperature (-40℃) was 267Akv. Compared with conventional heat treatment processes, the low temperature impact performance was improved by 10 times.

[0075] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Additionally, the terms "front," "back," "left," "right," "upper," and "lower" in this document refer to the placement shown in the accompanying drawings.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation, characterized in that, Includes the following steps: Material property basic modeling: Mechanical property experiments were conducted on duplex stainless steel profiles under different temperatures and deformation conditions to obtain stress-strain relationship curves of duplex stainless steel profiles, construct deformation resistance models and thermoplastic curves, and determine relevant physical property parameters of duplex stainless steel profiles in the range of 20 to 1200℃. Full-process heat treatment simulation analysis: A three-dimensional geometric model including heat treatment furnace, cooling pool and duplex stainless steel profile is established, radiation-convection composite boundary conditions are set and mesh generation is performed. Based on the established three-dimensional geometric model, the solid solution heating process, heat preservation process and cooling process are simulated, and the temperature field and stress field dynamic analysis are performed to obtain the analysis results. Process parameter optimization: Based on the simulation analysis results of the whole process heat treatment, the solution temperature, holding time and cooling rate are optimized and determined under the constraints of suppressing brittle phase precipitation and controlling residual stress deformation.

2. The method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation according to claim 1, characterized in that, The relevant physical properties include: specific heat capacity, thermal conductivity, and coefficient of thermal expansion.

3. The method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation according to claim 1, characterized in that, The simulation of the solution heating process includes: using 1030 to 1080°C as the heating target, loading the temperature curve in a cold-loading furnace manner, and completing the heating process by simulating radiation and convection heat transfer.

4. The method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation according to claim 1, characterized in that, When simulating the heat preservation process, the heat preservation time is controlled to be h~2h min or d~2d min, where h represents the thickness of the duplex stainless steel profile and d represents the diameter of the duplex stainless steel profile.

5. The method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation according to claim 1, characterized in that, The cooling process employs water quenching.

6. The method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation according to claim 1, characterized in that, Dynamic analysis of the temperature and stress fields is performed, including: The temperature field changes, anisotropic thermal stress and equivalent stress distribution during the solution heating process are obtained, the equivalent stress of each part of the duplex stainless steel profile is calculated, and the maximum tensile stress zone and plastic deformation layer on the outer surface are identified. The system acquires information on temperature field changes, anisotropic thermal stress and equivalent stress distribution during the cooling process, calculates the temperature gradient during the cooling process, quantifies the residence time of the core in the σ precipitation sensitive temperature range, and simultaneously outputs the triaxial tensile stress distribution on the surface.

7. The method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation according to claim 1, characterized in that, The process parameter optimization steps also include: Based on the determined solution treatment temperature, holding time, and cooling rate, duplex stainless steel profiles were heat-treated, and the microstructure and properties of the heat-treated duplex stainless steel profiles were verified.

8. The method for optimizing the heat treatment process of duplex stainless steel based on finite element simulation according to claim 1, characterized in that, The duplex stainless steel profile comprises the following chemical composition by weight percentage: C≤0.030%, Si≤1.00%, Mn:0.50~2.00%, P≤0.035%, S≤0.003%, Cr:21.00~24.00%, Ni:4.50~6.00%, Mo:2.50~3.50%, N:0.08~0.20%, with the remainder being iron and unavoidable impurities.

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