A method for optimizing hot working parameters of large-scale aviation components made of ultra-high-strength steel

Abstract

A method for optimizing hot working parameters of large-scale aviation components of ultra-high-strength steel includes: performing friction and adiabatic temperature rise corrections on the stress-strain curve obtained by hot compression experiments, and calculating the power dissipation efficiency and instability factor based on the correction curve; statistically analyzing the grain size and grain size difference of the deformed specimens under different deformation parameters; calculating the corrected Zener-Hollomon parameter values ​​under different deformation parameters; coupling the power dissipation efficiency, instability factor, average grain size, average dynamic recrystallization grain size and corrected Zener-Hollomon parameters to obtain the optimized deformation temperature and strain rate ranges corresponding to different strains. In the forging process of large-scale aviation components of ultra-high-strength steel, the present invention adjusts the deformation temperature or strain rate or the two in coordination according to the actual strain in real time, ensuring that the hot working parameters are always in the optimized hot working parameter range, thereby ensuring that there is no plastic instability during the hot forging process of the component, and that the dynamic recrystallization is sufficient and the grain size is small and uniform.

Description

Technical Field

[0001] The present invention belongs to the field of metal thermoplastic forming, and more specifically, relates to a method for optimizing hot processing parameters of ultra-high-strength steel large-scale aviation components. Technical Background

[0002] Large-scale aviation components made of ultra-high-strength steel are key load-bearing components in aircraft, and their forming performance is directly related to the service life and safety of aircraft. However, the hot forging process of large-scale aviation components made of ultra-high-strength steel involves the coupled influence of deformation parameters such as deformation temperature, strain rate, and deformation amount, which makes their microstructure evolution complex and flow behavior difficult to control. In order to achieve shape-controlled and property-controlled forming of large-scale aviation components made of ultra-high-strength steel, its hot processing parameters must be reasonably optimized.

[0003] For the optimization of hot working parameters, the hot working map is an effective way. The hot working map consists of an instability factor and a power dissipation factor. The deformation parameter interval corresponding to the instability factor being greater than zero and the power dissipation efficiency being the peak power dissipation efficiency is generally considered to be a reasonable hot working parameter interval. At present, there are many reports on the use of hot working maps to optimize the hot working parameter interval. Chinese patent (201511025177.8) optimized the hot working process of GH984G18 using hot working maps. Chinese patent (201510897211.4) optimized the extrusion process parameters of nickel-based high-temperature alloys by combining constitutive models and hot working maps. Chinese patent (201810407510.9) introduced the deformed austenite grain size into the constitutive model, and then established a new hot working map. Chinese patent (201910101011.1) combined hot working maps with thermal activation energy to optimize the process parameters of bainitic steel.

[0004] For large-scale aviation components made of ultra-high-strength steel, grain size and grain size difference are important indicators for the quality inspection of forming of large-scale aviation components made of ultra-high-strength steel, which directly determine the forming quality and service performance of forgings. The degree of dynamic recrystallization is the core factor affecting grain size and grain size difference. However, there is no report on the current hot working parameter optimization process that considers the degree of dynamic recrystallization, nor is there any report on the influence of grain size and grain size difference on hot working performance. In addition, when optimizing the processing parameter interval of the hot working diagram, the deformation temperature and strain rate interval are only optimized under a fixed strain. In fact, the corresponding optimized deformation temperature and strain rate intervals under different strains are different. In the actual forming process, the deformation temperature and strain must be controlled in real time according to the change of strain to effectively ensure that the deformation process of large-scale aviation components made of ultra-high-strength steel is always in the optimized processing parameter interval. Therefore, in order to achieve the coordinated control of the shape and properties of the hot forging forming process of large-scale aviation components made of ultra-high-strength steel, it is urgent to develop new methods for optimizing hot working parameters. Summary of the invention

[0005] In response to the above defects or improvement needs of the existing hot working parameter optimization methods, the present invention provides a hot working parameter optimization method for large-scale aviation components made of ultra-high strength steel. Its purpose is to fully consider the influence of dynamic recrystallization progress, grain size and grain size difference when optimizing the hot working parameter range, so that the optimized hot working parameter range is more reasonable, ensuring the controlled shape and controlled forming manufacturing of large-scale aviation components made of ultra-high strength steel, thereby enhancing the competitiveness of my country's high-end equipment.

[0006] The present invention is achieved through the following technical solutions.

[0007] The method for optimizing hot working parameters of ultra-high strength steel large aviation components of the present invention comprises the following steps:

[0008] Step 1: Process the ultra-high strength steel material into cylindrical specimens and conduct hot compression tests at different deformation temperatures, strain rates and strains on a Gleeble thermal simulation test machine. The deformation temperature range is 1173K to 1473K, and the strain rate range is 0.01 to 10s -1 , the deformation is 10% to 70%. When the deformation reaches the set value, the equipment automatically quenches the deformed sample to retain the high temperature structure of the material.

[0009] Step 2: The stress-strain curves obtained under different deformation parameters are corrected for adiabatic temperature rise and friction effect to eliminate the influence of temperature rise and friction on flow stress. According to the corrected stress-strain curves, the instability factor and power dissipation efficiency under different deformation parameters are calculated respectively, and a three-dimensional instability diagram and power dissipation efficiency diagram are drawn to analyze the influence of deformation temperature, strain rate and strain on the instability factor and power dissipation efficiency.

[0010] Step 3: Perform metallographic etching on the samples under different deformation parameters, and calculate the average grain size and average dynamic recrystallization grain size of the samples under different deformation parameters to obtain the grain size and grain size difference of the deformed samples. The average grain size and average dynamic recrystallization grain size are plotted as a three-dimensional contour map to analyze the effects of deformation temperature, strain rate, and strain on grain size and grain size difference.

[0011] Step 4: Calculate the modified Zener–Hollomon parameter values ​​under different deformation parameters, and determine the critical modified Zener–Hollomon parameter value for complete dynamic recrystallization by combining the statistical average grain size and the average dynamically recrystallized grain size.

[0012] Furthermore, the Zener–Hollomon parameter is often used to determine whether dynamic recrystallization is complete under different deformation parameters, but the parameter calculation method does not consider the influence of strain. The present invention proposes a modified Zener–Hollomon parameter, and the calculation method is as shown in formula (1):

[0013]

[0014] Where μ is the material constant, R is the gas constant, Q is the deformation activation energy, ε and T are strain rate, strain and deformation temperature, respectively.

[0015] When the average grain size and the average dynamically recrystallized grain size are equal, it means that the dynamic recrystallization is complete; otherwise, the dynamic recrystallization is incomplete.

[0016] After obtaining the modified Zener–Hollomon parameters under different deformation parameters, a three-dimensional contour map of the modified Zener–Hollomon parameters was drawn to analyze the influence of different deformation temperatures, strain rates and strains on the progress of dynamic recrystallization.

[0017] Step 5: Couple the instability factor, power dissipation efficiency, average dynamic recrystallization grain size, average grain size and modified Zener–Hollomon parameter under different deformation parameters to draw an integrated hot working parameter optimization diagram. The integrated hot working parameter optimization diagram is used to comprehensively evaluate and optimize the hot working parameters of large-scale aviation components made of ultra-high-strength steel.

[0018] Specifically, according to the integrated hot working parameter optimization diagram, the deformation temperature and strain rate range corresponding to the peak power dissipation efficiency under different strains are first determined. For ultra-high strength steel, the power dissipation efficiency greater than 32% is considered to be the peak power dissipation efficiency. Then, it is determined whether there is an unstable interval in the peak power dissipation efficiency interval. If so, the deformation temperature and strain rate interval corresponding to the instability factor should be eliminated, and the interval with an instability factor less than 0 is considered to be an unstable interval. Then, according to the modified Zener–Hollomon parameter, it is determined whether the interval corresponding to the power dissipation efficiency is completely dynamically recrystallized. If the dynamic recrystallization is incomplete, the deformation temperature and strain rate interval with incomplete dynamic recrystallization should be eliminated. Finally, the grain size and grain size difference in the interval corresponding to the peak power dissipation efficiency are determined. The grain size should be between 6 and 8, and the grain size difference should be within 2 levels. The deformation temperature and strain rate whose grain size and grain size difference are not in this range are eliminated. Through the above steps, the optimized deformation temperature and strain rate range under different strains can be obtained, so that within the optimized processing parameter range, no plastic instability occurs, dynamic recrystallization is sufficient, and the grain size is small and uniform.

[0019] Step 6: According to the optimized deformation temperature and strain rate ranges, in the actual forming process of large-scale ultra-high-strength steel aviation components, the deformation temperature or strain rate or the coordinated control of the two is carried out in real time according to the strain distribution, so as to ensure that the deformation parameter range is always within the optimized processing parameter range, thereby ensuring the good forming quality and excellent service performance of large-scale ultra-high-strength steel aviation components.

[0020] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0021] (1) The present invention integrates the concepts of modified Zener–Hollomon parameters, grain size, and grain size difference into the traditional hot working diagram, so that within the optimized processing parameter range, dynamic recrystallization is sufficient, no plastic instability occurs, and the grain size is small and uniform, thereby achieving precise control of the microstructure and properties of large-scale aviation components of ultra-high-strength steel.

[0022] (2) The present invention proposes to use a new processing parameter optimization method to optimize the deformation temperature and strain rate range under different strains, and to adjust the deformation temperature and strain rate in real time according to the different strains during the actual forging process of large-scale aviation components made of ultra-high-strength steel, so that the forming process parameters are always in the optimized processing range, thereby ensuring the high-quality forming of large-scale aviation components. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Friction-corrected stress-strain curves.

[0024] Figure 2 Adiabatic temperature rise corrected stress-strain curve.

[0025] Figure 3 Power dissipation efficiency plot for a strain of 0.3.

[0026] Figure 4 Power dissipation efficiency plot for a strain of 1.2.

[0027] Figure 5 Plot of the instability factor when the strain is 0.3.

[0028] Figure 6 Plot of the instability factor at a strain of 1.2.

[0029] Figure 7 Average grain size at strain 1.2.

[0030] Figure 8 Average dynamically recrystallized grain size at a strain of 1.2.

[0031] Fig. 9 lnZ at strain 1.2 m Value distribution.

[0032] Fig.10 Integrated hot working parameters optimization diagram. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] This embodiment takes 300 ultra-high strength steel hot forging as an example, and the specific steps are as follows:

[0035] Step 1: Use wire cutting to process the hot compression specimens with a diameter of 8 mm and a height of 12 mm. The processed hot compression specimens are subjected to hot compression experiments in the Gleeble3500 thermal simulation equipment, with deformation temperatures of 1173 K, 1273 K, 1373 K and 1473 K, and a strain rate of 0.01 s -1 , 0.1s -1 , 1s -1 and 10s -1 , the strain is 1.2. When the strain reaches 1.2, the equipment automatically quenches the deformed sample to retain the high temperature structure of the material.

[0036] Step 2: Perform adiabatic temperature rise correction and friction effect correction on the stress-strain curves under different deformation parameters obtained in the experiment to eliminate the influence of temperature rise and friction on flow stress. The friction factor calculation method is as follows:

[0037]

[0038] in,

[0039]

[0040]

[0041] △r=r m -r t (5)

[0042]

[0043] In the formula, parameter b determines the amount of bowing of the deformed specimen, r0 is the radius of the initial specimen, r is the average radius of the deformed specimen, and r t and r m are the minimum and maximum radii of the deformed specimen, respectively, and Δh is the difference between the initial specimen height h0 and the height h of the deformed specimen.m and h are measured, the friction factor μ can be calculated. According to the friction factor calculated above, the flow stress obtained in the experiment can be corrected using formula (7):

[0044]

[0045] In the formula, σ cf To eliminate the flow stress affected by friction, ε and σ0 are the flow strain and flow stress obtained from the experiment, respectively. The adiabatic temperature rise effect can be corrected according to formula (8):

[0046]

[0047] in,

[0048]

[0049]

[0050] In the formula, σ ct is the flow stress after adiabatic temperature rise correction, ΔT is the adiabatic temperature rise value, ρ is the material density, C p is the specific heat and κ is the adiabatic temperature rise correction factor.

[0051] Typical flow stress-strain curves after correction of friction and adiabatic temperature rise effects are shown in Figure 2. Figure 1 and Figure 2 According to the modified stress-strain curve, the power dissipation efficiency and instability factor under different deformation parameters are calculated respectively. The power dissipation efficiency diagram when the strain is 0.3 is shown in Figure 3 It can be seen that the deformation temperature range corresponding to the peak power dissipation efficiency is 1348~1473K, and the strain rate range is 0.01~0.04s -1 When the strain is 1.2, the power dissipation efficiency diagram is as follows: Figure 4 The deformation temperature range corresponding to the peak power dissipation efficiency is 1250~1473K, and the strain rate range is 0.01~0.08s -1 The peak power dissipation efficiency is obviously different under different strains, which further proves that it is necessary to study the power dissipation efficiency under different strains in depth, and then to control the processing range of the actual forging process in real time. Figure 5 and Figure 6 These are the instability factor diagrams when the strain is 0.3 and 1.2 respectively. As the strain increases, the instability range will gradually increase.

[0052] Step 3: Perform metallographic etching on the samples under different deformation parameters, and calculate the average grain size and average dynamic recrystallization grain size of the samples under different deformation parameters. The average grain size and average dynamic recrystallization grain size under continuous deformation conditions can be obtained by interpolation processing. Figure 7 and Figure 8 It can be seen that with the increase of deformation temperature and the decrease of strain rate, the average grain size first decreases and then increases, while the average dynamic recrystallization grain size gradually increases, which is mainly due to the dynamic recrystallization mechanism. Therefore, it is necessary to accurately judge the progress of dynamic recrystallization.

[0053] Step 4: Calculate the modified Zener-Hollomon parameter values ​​under different deformation parameters, and combine the statistical average grain size and the average dynamic recrystallization grain size to determine the critical modified Zener-Hollomon parameter value when dynamic recrystallization is complete. Among them, the critical modified Zener-Hollomon parameter value is lnZ m =32.85. This means that when lnZ m When it is less than 32.85, dynamic recrystallization is complete, otherwise, dynamic recrystallization is incomplete. Fig. 9 lnZ m From the distribution of values, we can see that with the increase of deformation temperature and the decrease of strain rate, lnZ m It gradually decreases, which means that the degree of dynamic recrystallization increases.

[0054] Step 5: Couple the instability factor, power dissipation efficiency, average dynamic recrystallization grain size, average grain size and modified Zener-Hollomon parameter under different deformation parameters to draw an integrated hot working parameter optimization diagram as shown in Fig.10 As shown. The integrated hot working parameter optimization diagram is used to comprehensively evaluate and optimize the hot working parameters of ultra-high strength steel large aviation components. Among them, the shaded area is the area corresponding to the instability factor, the gray dotted line is the power dissipation efficiency, the black dotted line is the average grain size, the gray solid line is the average dynamically recrystallized grain size, and the black solid line is lnZ m value.

[0055] First, determine the deformation temperature and strain rate range corresponding to the peak power dissipation efficiency; then, combine the instability factor to determine whether plastic instability will occur in this range. If instability exists, the instability range should be removed; then determine the progress of dynamic recrystallization to ensure that complete dynamic recrystallization occurs in the range corresponding to the peak power dissipation efficiency; finally, combine the average dynamic recrystallization and average grain size distribution to further optimize the hot working range, so that the grain size is between 6 and 8 in the optimized processing range, meeting the die forging requirements of large components. For ultra-high strength steel, its peak power dissipation efficiency is often small. In this case, the area with a power dissipation efficiency greater than 32% is regarded as the area corresponding to the peak power dissipation efficiency, then Fig.10 It can be seen that the deformation range corresponding to the peak power dissipation efficiency is 1223~1473K, 0.01~0.14s -1 Further judging the instability interval, it can be seen that the instability interval has no intersection with the interval corresponding to the peak power dissipation efficiency. m It can be seen from the value that there is lnZ in the interval corresponding to the peak power dissipation efficiency m When the value is greater than 32.85, it indicates that there is incomplete dynamic recrystallization in the interval corresponding to the peak power dissipation efficiency, and this deformation interval needs to be eliminated. Since the material will grow grains as the deformation continues after complete dynamic recrystallization. Therefore, it is necessary to further judge the grain size and grain size difference. The grain size should be between 4 and 6 levels and the grain size difference should be within 2 levels. The deformation temperature and strain rate ranges of the final optimized processing interval are 1263~1363K and 0.01~0.075s -1 In the optimized hot working range, dynamic recrystallization is complete, and the average dynamic recrystallization grain size is between 20.85 and 40.66 μm, which meets the requirements of grain size and grain size difference of large aviation components of ultra-high strength steel.

[0056] The above calculation process is for the case where the strain is 1.2. The same method can be used to obtain the optimized hot working parameter range under different strains. In the actual forging process, according to the strain change, the deformation temperature or strain rate or the two can be properly adjusted to keep it within the optimized hot working range under different strains.

Claims

1. A method for optimizing hot working parameters of ultra-high strength steel large aviation components, characterized in that The following steps are involved: Step 1: Process the ultra-high strength steel material into cylindrical specimens and conduct hot compression tests at different deformation temperatures, strain rates and strains on a Gleeble thermal simulation test machine; the deformation temperature range is 1173K~1473K, and the strain rate range is 0.01~10s -1 , the deformation is 10% to 70%; when the deformation reaches the set value, the equipment automatically quenches the deformed sample to retain the high-temperature structure of the material; Step 2: The stress-strain curves under different deformation parameters obtained in the experiment are corrected for adiabatic temperature rise and friction effect, thereby eliminating the influence of temperature rise and friction on flow stress; according to the corrected stress-strain curves, the instability factor and power dissipation efficiency under different deformation parameters are calculated respectively, and a three-dimensional instability diagram and power dissipation efficiency diagram are drawn to analyze the influence of deformation temperature, strain rate and strain on the instability factor and power dissipation efficiency; Step 3: metallographically etch the samples under different deformation parameters, and calculate the average grain size and average dynamic recrystallization grain size of the samples under different deformation parameters to obtain the grain size and grain size difference of the deformed samples; plot the average grain size and average dynamic recrystallization grain size into a three-dimensional contour map to analyze the effects of deformation temperature, strain rate and strain on grain size and grain size difference; Step 4: Calculate the modified Zener–Hollomon parameter values ​​under different deformation parameters, and determine the critical modified Zener–Hollomon parameter value for complete dynamic recrystallization by combining the statistical average grain size and the average dynamic recrystallization grain size; The modified Zener–Hollomon parameter is calculated as shown in formula (1): Where μ is the material constant, R is the gas constant, Q is the deformation activation energy, ε and T are strain rate, strain and deformation temperature, respectively; After obtaining the modified Zener–Hollomon parameters under different deformation parameters, a three-dimensional contour map of the modified Zener–Hollomon parameters was drawn to analyze the influence of different deformation temperatures, strain rates and strains on the progress of dynamic recrystallization. Step 5: Couple the instability factor, power dissipation efficiency, average dynamic recrystallization grain size, average grain size and modified Zener–Hollomon parameter under different deformation parameters to draw an integrated hot working parameter optimization diagram; use the integrated hot working parameter optimization diagram to comprehensively evaluate and optimize the hot working parameters of large-scale aviation components made of ultra-high-strength steel; Step 6: According to the optimized deformation temperature and strain rate ranges, in the actual forming process of large-scale ultra-high-strength steel aviation components, the deformation temperature or strain rate or the coordinated control of the two is carried out in real time according to the strain distribution, so as to ensure that the deformation parameter range is always within the optimized processing parameter range, thereby ensuring the good forming quality and excellent service performance of large-scale ultra-high-strength steel aviation components.

2. The method for optimizing hot working parameters of ultra-high strength steel large aviation components according to claim 1 is characterized in that The step 5 comprises the following steps: firstly, judging the deformation temperature and strain rate intervals corresponding to the peak power dissipation efficiency under different strains according to the integrated hot working parameter optimization diagram, and the power dissipation efficiency greater than 32% is considered to be the peak power dissipation efficiency; then judging whether there is an unstable interval in the peak power dissipation efficiency interval, if so, the deformation temperature and strain rate intervals corresponding to the instability factor should be eliminated, and the interval with the instability factor less than 0 is considered to be the unstable interval; then judging whether the interval corresponding to the power dissipation efficiency is completely dynamically recrystallized according to the modified Zener-Hollomon parameter, if the dynamic recrystallization is incomplete, the deformation temperature and strain rate intervals with incomplete dynamic recrystallization should be eliminated; finally, judging the grain size and grain size difference in the interval corresponding to the peak power dissipation efficiency, the grain size should be between 6 and 8, and the grain size difference should be within 2, and the deformation temperature and strain rate whose grain size and grain size difference are not in this range are eliminated to obtain the optimized deformation temperature and strain rate intervals under different strains.

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