A method and system for suppressing c-type warpage of titanium alloy plate based on asynchronous hot rolling process

Abstract

The application discloses a method and system for inhibiting C-type warping of titanium alloy plate based on an asynchronous hot rolling process, and relates to the technical field of hot working of metal materials, wherein the method comprises the following steps: pretreating a titanium alloy surface blank; feeding the pretreated blank into an asynchronous rolling mill and setting asynchronous rolling parameters and tension control; dynamically adjusting the asynchronous rolling mill through temperature gradient compensation; monitoring the quality of the asynchronous rolling mill in real time, and performing closed-loop regulation and control to complete the inhibition of C-type warping. The application has a remarkable effect on inhibiting C-type warping, and the flatness is greatly improved. The warping amount is reduced from greater than or equal to 1.5 mm / m in the traditional process to less than or equal to 0.5 mm / m, with a reduction of more than 60%. The residual stress is also optimized, the stress difference between the surface and the core is reduced from plus or minus 150 MPa to plus or minus 30 MPa, and the risk of cracking in subsequent processing is effectively avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material hot working, in particular to a method and system for inhibiting C-type warping of titanium alloy plate based on asynchronous hot rolling process. BACKGROUND

[0002] Titanium alloy is widely used in aerospace, medical devices, ocean engineering and other high-end fields due to its excellent specific strength, corrosion resistance and biocompatibility. Especially in the field of aero-engine blades, human implants and deep-sea equipment, the size precision and mechanical properties of titanium alloy plate directly determine the reliability and service life of the product. Hot rolling, as a key process for forming titanium alloy plate, its core goal is to refine grains and homogenize the structure through plastic deformation at high temperature, while ensuring the flatness of the plate. However, in the traditional synchronous hot rolling process, the difference in residual stress caused by temperature gradient, uneven deformation and anisotropy of the structure leads to C-type warping (hereinafter referred to as "C warping"), which seriously restricts the product quality and production efficiency.

[0003] To deal with the C warping problem, the existing technology mainly adopts the following methods: reducing the single pass rolling reduction to reduce stress accumulation, but leading to an increase in rolling passes and a decrease in production efficiency; increasing the rolling temperature to the beta phase zone to enhance the plastic deformation ability of the material, but the grain coarsening leads to a decrease in mechanical properties; there are also repeated bending correction by multi-roll straightening machine, but the equipment investment is high; in addition, alternating the rolling direction to balance the stress distribution, but the multi-pass reversing leads to an increase in energy consumption of 30%, and the effect is limited for thick plates (>20mm).

[0004] Due to the difference in residual stress caused by temperature gradient, uneven deformation and anisotropy of the structure in the hot rolling process of titanium alloy, the probability of C warping of titanium alloy in the hot rolling process is very high, which has great challenge to the plate shape control, and has become a major process bottleneck for the industrialized production of high-precision titanium alloy thin plates in the field of aerospace. SUMMARY

[0005] To solve the problems in the above background art, the present application provides a method and system for inhibiting C-type warping of titanium alloy plate based on asynchronous hot rolling process, which systematically solves the C-type warping problem of titanium alloy plate caused by temperature gradient and residual stress difference in the traditional hot rolling process, improves the flatness of the plate, and optimizes the mechanical properties and microstructure.

[0006] To achieve the above purpose, the present application provides a method for inhibiting C-type warping of titanium alloy plate based on asynchronous hot rolling process, comprising the following steps:

[0007] Pretreating the titanium alloy surface blank; the pretreatment step includes cleaning the oxide layer and preheating the titanium alloy surface blank;

[0008] The pretreated blank is sent to an asynchronous rolling mill and asynchronous rolling parameter setting and tension control are performed; the set asynchronous rolling parameters include: asynchronous ratio, rolling speed, single pass reduction rate and total deformation amount; the tension control includes: applying front tension and rear tension during rolling;

[0009] Through temperature gradient compensation, dynamic process adjustment is performed on the asynchronous rolling mill, including real-time monitoring of rolling zone temperature by an infrared temperature measuring instrument and real-time control of the asynchronous ratio of the upper and lower rolls by a PLC controller;

[0010] Real-time quality monitoring is performed on the asynchronous rolling mill, and closed-loop regulation and control are performed to complete the inhibition of C-type warping.

[0011] Preferably, the surface blank of the titanium alloy is cleaned of the oxide layer by sandblasting or pickling process, and the surface roughness Ra is ≤3.2 μm; then, the titanium alloy blank surface is sprayed with a high-temperature glass protective agent; finally, the titanium alloy blank is preheated to the α+β phase region or β phase region temperature, and the holding time is 1h~4h.

[0012] Preferably, the calculation formula of the asynchronous ratio includes:

[0013] ,

[0014] wherein, is the linear speed of the fast roll, is the linear speed of the slow roll.

[0015] Preferably, the relationship between the asynchronous ratio and the reduction rate satisfies:

[0016] ,

[0017] wherein, ε is the reduction rate, and the expression is:

[0018] ,

[0019] wherein, is the initial thickness of the blank, is the thickness of the blank after rolling.

[0020] Preferably, the application modes of the front tension and the rear tension include: the front tension is provided by a coiler, and the tension value = 0.1σ y ; the rear tension is provided by an uncoiler, and the tension value = 0.15σ y ; wherein, σ y is the high-temperature yield strength of the material; the tension control precision is ≤±5%.

[0021] Preferably, the temperature gradient compensation rule comprises: when the temperature difference between the upper and lower surfaces of the rolling zone is greater than 30 DEG C, the asynchronous ratio Delta v is 1.3; when the temperature difference between the upper and lower surfaces of the rolling zone is between 10-30 DEG C, the asynchronous ratio is 1.2; and when the temperature difference between the upper and lower surfaces of the rolling zone is less than 10 DEG C, the asynchronous ratio is 1.1.

[0022] Preferably, the working principle of the PLC controller comprises: storing and tracing the fuzzy PID control data, and dynamically adjusting the asynchronous ratio and rolling speed; the data storage and tracing are used for recording the process parameters and quality data of each batch of plates, and generating a unique ID code.

[0023] Preferably, the step of real-time quality monitoring and closed-loop regulation of the asynchronous rolling mill comprises: on-line monitoring of the warping amount and residual stress distribution by using a laser displacement sensor and an X-ray stress meter, on-line monitoring of the flatness of the plate surface and residual stress, and dynamically adjusting the asynchronous ratio and the reduction rate so that the warping amount is less than or equal to 0.5 mm / m.

[0024] The application also provides a system for inhibiting C-type warping of a titanium alloy plate based on an asynchronous hot rolling process, which is used to realize the above method and comprises a pretreatment module, a setting module, an adjustment module and a monitoring module.

[0025] The pretreatment module is used for pretreating the titanium alloy surface blank.

[0026] The setting module is used for feeding the pretreated blank into the asynchronous rolling mill and setting the asynchronous rolling parameters and tension control.

[0027] The adjustment module is used for dynamically adjusting the asynchronous rolling mill through temperature gradient compensation.

[0028] The monitoring module is used for real-time quality monitoring of the asynchronous rolling mill and closed-loop regulation to complete the inhibition of C-type warping.

[0029] Preferably, the working process of the pretreatment module comprises: adopting sand blasting treatment or pickling process to clean the oxide layer of the titanium alloy surface blank, and the surface roughness Ra is less than or equal to 3.2 microns; then, spraying a high-temperature glass protective agent on the surface of the titanium alloy blank; and finally, preheating the titanium alloy blank to the alpha plus beta phase zone or beta phase zone temperature, and the holding time is 1h-4h.

[0030] Compared with the prior art, the application has the following beneficial effects:

[0031] (1) The C warping inhibition effect is remarkable, and the flatness is improved: the warping amount is reduced from greater than or equal to 1.5 mm / m in the traditional process to less than or equal to 0.5 mm / m, and the reduction is more than 60%; the residual stress is optimized: the stress difference between the surface and the core is reduced from ±150 MPa to ±30 MPa, and the risk of cracking in subsequent processing is avoided.

[0032] (2)Promote toughness: tensile strength is increased by 10-15% (such as Ti-6Al-4V 950-1050 MPa), elongation ≥12%, better than traditional process (800-900 MPa, elongation 8-10%). Dynamic recrystallization grain size is refined to 10-20 μm, fatigue life is increased by 30%.

[0033] (3) Process simplification: cancel offline straightening and pickling steps, production cost is reduced by 20-25%. Good rate is increased: real-time feedback system increases good rate from 85% to ≥98%, reduces rework loss.

[0034] (4) Response speed: online monitoring system realizes millisecond level parameter adjustment (traditional process delay ≥2 seconds), adapts to high speed rolling (5 m / s). Accurate prediction of process window, reduces trial and error cost by 50%.

[0035] (5) Green manufacturing: reduce acid pickling wastewater discharge, surface oxide layer thickness <5 μm (traditional process ≥10 μm). BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the present application, the following briefly introduces the drawings needed to be used in the embodiments, obviously, the drawings described in the following only some embodiments of the present application, for those skilled in the art, without paying the creative labor, can also obtain other drawings according to these drawings.

[0037] Figure 1 The method flowchart of the embodiment of the present application is shown in the figure.

[0038] Figure 2 The traditional synchronous rolling and asynchronous rolling stress distribution comparison schematic diagram of the embodiment of the present application is shown in the figure.

[0039] Figure 3 The asynchronous rolling mill structure and temperature field regulation module schematic diagram of the embodiment of the present application is shown in the figure.

[0040] Figure 4 The online monitoring and feedback system flowchart of the embodiment of the present application is shown in the figure.

[0041] Figure 5 The microstructure comparison diagram of different temperature asynchronous hot rolling of the embodiment of the present application is shown in the figure; wherein, (a) represents 950℃; (b) represents 900℃.

[0042] Figure 6 The different plate warping amount comparison photo of the embodiment of the present application is shown in the figure; wherein, (a) represents synchronous hot rolling; (b) represents asynchronous hot rolling. DETAILED DESCRIPTION

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Before proceeding with the explanation, let's first introduce the technical terms used in this embodiment.

[0046] Pure titanium undergoes a crystal structure transformation at 882℃. This embodiment involves the following two allotropes.

[0047] α-Ti (low-temperature phase): Hexagonal close-packed structure (HCP), existing below 882℃. Characterized by few slip systems and weak plastic deformation capacity.

[0048] β-Ti (high-temperature phase): Body-centered cubic (BCC) structure, existing above 882℃. It is characterized by numerous slip systems, good plasticity, and ease of deformation.

[0049] When titanium alloys are below the α-phase transformation point, the α and β phases coexist, forming an "α+β dual-phase region". This is because β-stabilizing elements (such as 4% V in Ti-6Al-4V) inhibit the complete transformation from β to α, allowing the β phase to be partially retained at low temperatures.

[0050] For example, in Ti-6Al-4V, the β transition point T~β~ ≈ 980℃ (882℃ for pure titanium). Its temperature range is:

[0051] T~β~< 980℃: α + β biphase region (e.g., 750–980℃);

[0052] T~β~≥ 980℃: Single-phase β region.

[0053] Example 1

[0054] like Figure 1 The diagram shown is a schematic representation of the method flow in this embodiment, and the steps include:

[0055] S1. Pre-treat the surface of the titanium alloy blank.

[0056] The surface of the titanium alloy blank is cleaned of the oxide layer, sandblasting treatment or pickling process is adopted, and the surface roughness Ra is less than or equal to 3.2 microns; then, the surface of the titanium alloy blank is sprayed with a high-temperature glass protective agent (a protective agent of a silicon-based glass system, the main components of which are SiO2+Al2O3+CaO, etc.); before spraying, the oil stains, dust and any contaminants on the surface of the titanium alloy are completely removed by using acetone, and then the surface is sandblasted for roughening treatment, and then the remaining sand particles and dust are cleaned again using a cleaning agent to ensure that the workpiece is completely dry before spraying; the glass protective agent is diluted to prepare a spraying suspension of tens of microns, and the titanium alloy surface is sprayed in multiple times to a thickness of one hundred microns by using a low-pressure spray gun, and drying is required between each layer to prevent sagging; the workpiece after spraying is fully dried in a room temperature or low temperature oven (60-80 DEG C); finally, the titanium alloy blank is preheated to the alpha + beta phase region or beta phase region temperature, and the holding time is 1h~4h.

[0057] S2. The pretreated blank is sent to an asynchronous rolling mill and asynchronous rolling parameter setting and tension control are performed.

[0058] The rotational speed ratio of the upper and lower rollers is set to 1.05-1.5 (asynchronous ratio Δv), the rolling speed is 0.5-5 m / s, the single pass reduction rate is 7-15%, and the total deformation amount is 60-95%; during the rolling process, front tension and rear tension are applied, and the tension value is 10-30% of the material yield strength. The calculation formula of the asynchronous ratio Δv is:

[0059] ,

[0060] wherein, is the linear speed of the fast roller, is the linear speed of the slow roller; when the plate thickness is less than or equal to 10 mm, the asynchronous ratio is 1.2-1.5; when the thickness is greater than 10 mm, the asynchronous ratio is 1.05-1.2.

[0061] According to the volume invariance condition of plastic processing, the metal volume flowing into the deformation zone per unit time is equal to the volume flowing out:

[0062] ,

[0063] wherein, is the speed at the inlet of the plate, is the speed at the outlet of the plate, is the initial thickness of the blank, is the thickness of the blank after rolling, is the width of the plate. The on both sides of the equation can be neglected, and the following is obtained:

[0064] .

[0065] Because the sheet metal is often rolled close to the high-speed rolls during the rolling process, the sheet metal exit speed... Approximately equal to The speed of the sheet at the rolling inlet Approximately equal to :

[0066] .

[0067] And the reduction ratio ε is equal to:

[0068] .

[0069] Therefore, the relationship between the asynchronous ratio and the reduction rate satisfies:

[0070] ,

[0071] The conversion yields:

[0072] ,

[0073] This relationship is achieved by adjusting the speeds of the uncoiler and coiler to ensure that the flow rate per second is equal and the tension is stable during the rolling process.

[0074] The front and back tensions are applied as follows: the front tension is provided by the winding machine, and the tension value is 0.1σ. y (σ) y (This refers to the material's high-temperature yield strength); the post-tension is provided by the uncoiler, with a tension value of 0.15σ. y Tension control accuracy ≤ ±5%. Figure 2 This is a schematic diagram comparing the stress distribution in traditional synchronous rolling and asynchronous rolling.

[0075] S3. Dynamic process adjustment of asynchronous rolling mill through temperature gradient compensation.

[0076] like Figure 3 As shown, the temperature of the rolling zone is monitored in real time using an infrared thermometer, and the asynchronous speed ratio of the upper and lower rolls is controlled in real time using a PLC controller. Specifically, the asynchronous ratio Δv = 1.1-1.3 is dynamically adjusted based on the infrared temperature measurement data. When the temperature difference between the upper and lower surfaces of the rolling zone is greater than 30℃, the asynchronous ratio Δv is set to 1.3; when the temperature difference between the upper and lower surfaces is between 10-30℃, the asynchronous ratio is selected as 1.2; and when the temperature difference between the upper and lower surfaces is less than 10℃, the asynchronous ratio is selected as 1.1.

[0077] Specifically, the asynchronous rolling introduces gradient shear strain in the plate by the speed difference of the upper and lower rollers (asynchronous ratio 1.05-1.5). This strain distribution can offset the uneven distribution of thermal stress caused by temperature gradient. Specifically, asynchronous rolling makes the deformation rate of the upper and lower surfaces of the plate different, thereby forming a gradient stress field inside the plate. During rolling, the temperature difference between the upper and lower surfaces of the plate will cause uneven thermal expansion and contraction, thereby generating residual stress. By monitoring the temperature gradient in real time (such as an infrared thermometer) and dynamically adjusting the asynchronous ratio, the distribution of gradient shear strain can be optimized to better compensate for the thermal stress caused by temperature gradient.

[0078] The synergistic effect of asynchronous ratio and temperature is reflected in dynamic adjustment. When the temperature gradient is large (such as the temperature difference between the upper and lower surfaces > 30℃), the asynchronous ratio takes a larger value (such as 1.3) to introduce stronger gradient shear strain to offset the thermal stress; when the temperature gradient is small (such as the temperature difference < 10℃), the asynchronous ratio takes a smaller value (such as 1.1) to avoid excessive introduction of shear strain.

[0079] The algorithm of the above PLC controller includes: using fuzzy PID control data storage and traceability, while controlling the dynamic adjustment of asynchronous ratio and rolling speed; data storage and traceability are used to record the process parameters and quality data of each batch of plates, and to generate a unique ID code.

[0080] S4. Real-time quality monitoring of asynchronous rolling mill and closed-loop control to complete the suppression of C-type warping.

[0081] Using laser displacement sensor and X-ray stress meter to monitor warping amount and residual stress distribution online, monitoring plate surface flatness and residual stress online, dynamically adjusting asynchronous ratio and reduction rate to make warping amount ≤0.5mm / m. The process of current detection and feedback is as shown in Figure 4 .

[0082] In terms of optimization and control of residual stress, asynchronous rolling changes the stress distribution inside the plate by gradient shear strain, reducing residual stress caused by uneven deformation. Since temperature gradient will cause thermal stress inside the plate, by controlling the rolling temperature (such as preheating to α+β phase zone or β phase zone temperature) and monitoring the temperature distribution in real time, the generation of thermal stress can be reduced.

[0083] The synergistic effect of asynchronous ratio and temperature is realized through online monitoring and feedback adjustment (such as laser displacement sensor and X-ray stress meter). According to the real-time monitoring of residual stress distribution and temperature data, the asynchronous ratio and reduction rate are dynamically adjusted to ensure that the surface compressive stress of the plate is ≤-50 MPa and the core tensile stress is ≤+30 MPa, thereby optimizing the stress state of the plate.

[0084] In terms of optimizing the microstructure and properties of the plate, asynchronous rolling promotes dynamic recrystallization and grain refinement within the plate by introducing gradient shear strain, thereby improving the strength and toughness of the plate. Rolling temperature control (e.g., 750-1000°C) ensures that the plate is in the α+β phase region or the β phase region, which is conducive to uniform deformation and recrystallization of the grains. The synergistic effect of the asynchronous ratio and temperature is achieved by optimizing the deformation kinetics. At the appropriate temperature, the gradient shear strain of asynchronous rolling can promote uniform deformation and refinement of the grains, thereby improving the tensile strength (≥ 950 MPa) and elongation (≥ 13%) of the plate.

[0085] In terms of improving the flatness of the plate, asynchronous rolling counteracts the plate warping caused by uneven deformation and temperature gradient by introducing gradient shear strain. Temperature control ensures uniform deformation of the plate during rolling, reducing warping caused by thermal stress. The synergistic effect of the asynchronous ratio and temperature is achieved by real-time monitoring and dynamic adjustment. According to the online monitoring of the warping amount (laser displacement sensor) and temperature data, the asynchronous ratio and reduction are dynamically adjusted to ensure the flatness of the plate (warping amount ≤ 0.5 mm / m).

[0086] In summary, the synergistic effect of the asynchronous ratio and temperature is achieved by introducing gradient shear strain, optimizing residual stress, improving microstructure and properties, and controlling plate flatness, which comprehensively improves the performance of titanium alloy plates. The synergistic effect of the two is mainly reflected in:

[0087] Dynamic adjustment, real-time adjustment of asynchronous ratio according to temperature gradient, optimization of stress distribution.

[0088] Online monitoring and feedback, real-time monitoring of warping amount and residual stress by laser displacement sensor and X-ray stress analyzer, dynamic adjustment of process parameters.

[0089] Microstructure and property optimization, at the appropriate temperature, asynchronous rolling promotes grain refinement and uniform deformation, improving strength and toughness.

[0090] This synergistic effect ultimately enables titanium alloy plates to achieve excellent comprehensive performance: tensile strength of 970±5 MPa, elongation of 14.2±0.3%, warping amount of 0.2±0.04 mm / m, and residual stress gradient of 23±0.7 MPa / mm.

[0091] The laser displacement sensor in the above-mentioned online monitoring and feedback module is a line array CCD with a resolution of 0.01 mm; the X-ray stress analyzer is equipped with a two-dimensional detector with a scanning speed of ≥ 10 points / second; the PLC controller processes real-time data and the response time of the adjustment command is ≤ 1 second.

[0092] Example Two

[0093] The advantages of the present application will be illustrated in specific cases in combination with the present embodiment. In the present embodiment, the rolling speed ratio (asynchronous ratio 1.05-1.5) is regulated to introduce gradient shear strain in the rolling process, so as to offset the residual stress difference of titanium alloy caused by temperature gradient and uneven deformation; the laser displacement sensor and X-ray stress meter are used to monitor the warping amount and residual stress distribution on line, and the asynchronous ratio, reduction rate (20-50%) and rolling speed (0.5-5 m / s) are adjusted in real time to ensure the flatness of the plate (warping amount ≤0.5 mm / m).

[0094] Specifically, a Ti-6Al-4V titanium alloy with a thickness of 35 mm, a length of 100 mm and a width of 50 mm is taken, the surface of the blank is cleaned of the oxidation layer, sand blasting treatment or pickling process is adopted, and the surface roughness Ra is ≤3.2 μm.

[0095] The surface of the Ti-6Al-4V titanium alloy blank is sprayed with silicate-graphite-based protective agent; the β transition point of the Ti-6Al-4V titanium alloy is 980℃, the Ti-6Al-4V titanium alloy blank is preheated to the α+β phase region 950℃, the holding time is 1 h, and the infrared thermal imager is used to monitor and ensure that the temperature difference in the thickness direction is <5℃.

[0096] The Ti-6Al-4V titanium alloy blank is sent to the asynchronous rolling mill, the upper roller speed is set to 10 rpm, the lower roller speed is set to 8 rpm, the asynchronous ratio is 1.25, the single pass reduction rate is 10%, and the thickness is reduced to 18 mm; then the upper roller speed is set to 13 rpm, the lower roller speed is set to 10 rpm, the asynchronous ratio is 1.3, the 18 mm thick Ti-6Al-4V titanium alloy plate is hot rolled again, the single pass reduction rate is 12%, and the thickness is reduced to 10 mm; finally, the upper roller speed is set to 15 rpm, the lower roller speed is set to 11 rpm, the asynchronous ratio is 1.36, the 10 mm thick Ti-6Al-4V titanium alloy plate is hot rolled again, the single pass reduction rate is 10%, and the thickness is reduced to 3 mm.

[0097] The front tension value is 7 MPa and the rear tension value is 10 MPa during rolling; the asynchronous ratio Δv=1.1-1.5 is dynamically adjusted according to the infrared temperature data during rolling; when the temperature difference between the upper and lower surfaces is greater than 30℃, the asynchronous ratio Δv is 1.4; when the temperature difference between the upper and lower surfaces is between 10-30℃, the asynchronous ratio is 1.2; when the temperature difference between the upper and lower surfaces is less than 10℃, the asynchronous ratio is 1.1.

[0098] The plate surface flatness and residual stress are monitored on line, the asynchronous ratio and reduction rate are dynamically adjusted, and the warping amount is ≤0.5 mm / m. The metallographic graph of the Ti-6Al-4V titanium alloy plate prepared in the present embodiment is shown in Figure 5It can be seen that a large number of dynamic recrystallization grains appear in the microstructure of the Ti-6Al-4V titanium alloy plate asynchronously hot-rolled at 950°C, and the strength of the material reaches 900 MPa, the tensile strength reaches 980 MPa, and the elongation reaches 12%. The plate shape of the plate after asynchronous hot rolling is as shown in Figure 6 .

[0099] Example Three

[0100] In this example, the preheating temperature is reduced from 950°C to 900°C (lower limit of the α+β phase region), and other parameters are the same as in Example Two.

[0101] Performance results: tensile strength: 940 MPa (4.1% lower than Example Two), elongation: 10.5% (12.5% lower than Example Two), warpage: 0.6 mm / m, residual stress gradient: 35 MPa / mm (surface compressive stress -60 MPa, core tensile stress +45 MPa), microstructure as shown in Figure 5 (b), the proportion of dynamic recrystallization grains is reduced to 60% (85% in Example Two), the grain size distribution is uneven (5-15 μm), and there are elongated grains that have not been recrystallized.

[0102] Reason analysis:

[0103] Effect of temperature on phase change: 900°C is close to the lower limit of the α+β phase region, and the volume fraction of β phase is reduced (about 30% vs 45% at 950°C), resulting in reduced plastic deformation ability and insufficient driving force for dynamic recrystallization.

[0104] Limited microstructure refinement: the unrecrystallized area becomes a stress concentration point, reducing the elongation.

[0105] Insufficient compensation of residual stress: the yield strength of the material increases at low temperature, and the shear strain of asynchronous rolling is difficult to completely offset the thermal stress, resulting in an increase in the residual stress gradient.

[0106] Example Four

[0107] Other parameters are the same as in Example Two, the roller speed is reduced (first rolling: upper roller 7.2 rpm / lower roller 6 rpm, asynchronous ratio 1.2→ final asynchronous ratio 1.33), and the total rolling passes are reduced (3 passes→ 3 passes, but the distribution of reduction is different).

[0108] Performance results: tensile strength: 960 MPa, elongation: 11%, warpage: 0.7 mm / m, residual stress gradient: 40 MPa / mm, microstructure: grain size 8-12 μm (coarsened compared to Example Two), shear band density reduced, and local deformation texture present.

[0109] Reason analysis:

[0110] Rolling speed and strain rate matching: Low-speed rolling (30% reduction of roll speed) leads to less accumulation of deformation heat, incomplete dynamic recrystallization.

[0111] Insufficient asynchronous ratio gradient: Small improvement in asynchronous ratio (1.2→1.33 vs. 1.25→1.36 in Example Two), insufficient gradient shear strain distribution, and decreased residual stress neutralization effect.

[0112] Process window limitation: When rolling thick plates (25→15→10 mm), the core has slow heat dissipation, and a higher asynchronous ratio is needed for compensation (not actually adjusted), resulting in a higher tensile stress in the core.

[0113] Example Five

[0114] Other parameters are the same as in Example Two, with the front tension reduced from 7 MPa to 5 MPa, and the back tension maintained at 10 MPa.

[0115] Performance results: Tensile strength: 970 MPa, elongation: 11.8%, warpage: 0.9 mm / m (close to the upper threshold), residual stress gradient: 45 MPa / mm, edge flatness: local wavy deformation (amplitude ≤0.3 mm).

[0116] Cause analysis:

[0117] Tension distribution imbalance: Reduction of front tension (5 MPa vs. 7 MPa) leads to increased material flow resistance at the entrance of the rolling zone, resulting in uneven transverse deformation.

[0118] Stress field interference: Imbalance in front / back tension ratio (0.5:1 vs. 0.7:1 in Example Two) induces additional shear stress, which, when superimposed with the asynchronous rolling stress field, produces micro-area stress concentration.

[0119] Plate shape control failure: Insufficient tension adjustment leads to insufficient local stress release, with warpage close to the allowed upper limit.

[0120] Example Six

[0121] Synchronous rolling of upper and lower rollers (asynchronous ratio 1.0), with other parameters the same as in Example Two.

[0122] Performance results: Tensile strength: 880 MPa; elongation: 9%; warpage: 2.0 mm / m (significant C-type warpage); residual stress gradient: >80 MPa / mm (surface compressive stress -120 MPa, core tensile stress +100 MPa).

[0123] Microstructure: Coarse alpha phase grains (20~30 μm) and beta phase network distribution; deformation bands penetrate grains, with no signs of dynamic recrystallization.

[0124] Cause analysis:

[0125] Thermal stress without compensation: synchronous rolling cannot introduce gradient shear strain, and the temperature difference between the upper and lower surfaces (about 40°C) leads to the accumulation of thermal stress.

[0126] Tissue degradation: lack of dynamic recrystallization driven by shear strain, grain coarsening and existence of brittle beta phase, significant deterioration of mechanical properties.

[0127] Stress concentration: high residual stress gradient causes spontaneous warping of the plate, forming obvious C-type defects.

[0128] Example seven

[0129] Other parameters are the same as in example two, only the first rolling uses asynchronous ratio 1.25, and the subsequent passes are synchronous rolling.

[0130] Performance results: tensile strength: 910 MPa; elongation: 9.5%; warping amount: 1.5 mm / m; residual stress distribution: first rolling area: surface compressive stress -70 MPa; subsequent synchronous rolling area: core tensile stress +80 MPa.

[0131] Microstructure: grain refinement to 10 μm in the first rolling zone; grain coarsening to 25 μm in the subsequent rolling zone.

[0132] Cause analysis:

[0133] Process inconsistency: subsequent synchronous rolling offsets the shear strain advantage of initial asynchronous rolling, resulting in stress distribution fault.

[0134] Uneven tissue: the deformation mechanism of different rolling stages conflicts, causing grain size jump and reducing material homogeneity.

[0135] Residual stress superposition: the stress direction of asynchronous and synchronous areas is contradictory, which aggravates the overall warping.

[0136] Example eight

[0137] Cancel the front and rear tension, other parameters are the same as in example two.

[0138] Performance results: tensile strength: 950 MPa; elongation: 10%; warping amount: 1.8 mm / m; residual stress gradient: 60 MPa / mm; edge defect: "fish tail" shaped edge wrinkle (depth 0.5 mm) appears.

[0139] Cause analysis:

[0140] Material flow out of control: no tension leads to increased lateral flow, and the accumulation of edge material forms wrinkles.

[0141] Stress distribution disorder: asynchronous rolling shear strain competes with free deformation, and the residual stress gradient increases.

[0142] Dynamic recrystallization inhibition: local high strain rate area (edge) grain refinement is hindered, and elongation decreases.

[0143] Example Nine

[0144] Fixed asynchronous ratio rolling (no dynamic adjustment).

[0145] Process parameters: same as example two, but the asynchronous ratio is fixed at 1.25 (not adjusted with temperature gradient).

[0146] Performance results: warpage: 1.2 mm / m (significantly higher than ≤0.5 mm / m in example two); tensile strength: 920 MPa, elongation: 10%; residual stress gradient: 50 MPa / mm (surface compressive stress -80 MPa, core tensile stress +60 MPa).

[0147] Reason analysis:

[0148] Fixed asynchronous ratio cannot dynamically compensate thermal stress according to temperature gradient. When the temperature difference between the upper and lower surfaces is >30℃, the asynchronous ratio is not adjusted (should be 1.4), resulting in thermal stress that cannot be offset by shear strain, increased residual stress gradient, and excessive warpage. In addition, under the fixed asynchronous ratio, the microstructure is not refined enough, and dynamic recrystallization is not sufficient, resulting in decreased strength and elongation.

[0149] Example Ten

[0150] No temperature gradient control (no preheating uniformity).

[0151] Process parameters: same as example two, but no infrared thermal imager is used to monitor temperature, and the temperature difference in the thickness direction of the blank reaches 20℃.

[0152] Performance results: warpage: 0.8 mm / m; tensile strength: 940 MPa, elongation: 11%; microstructure: uneven grain size (5-20 μm), with local non-recrystallized areas.

[0153] Reason analysis:

[0154] Uneven temperature distribution results in low matching degree of thermal stress and asynchronous rolling shear strain, poor residual stress neutralization effect. At the same time, the local low temperature area has insufficient plasticity, incomplete dynamic recrystallization, and uneven grain refinement, resulting in fluctuations in mechanical properties.

[0155] Example Eleven

[0156] Other parameters are the same as example two, but only single pass rolling is performed (reduction 30%, total deformation 35mm→3mm).

[0157] Performance results: warpage amount: 2.5 mm / m (severe C-type warpage); tensile strength: 850 MPa, elongation: 8%; edge cracking: multiple micro cracks appeared.

[0158] Cause analysis:

[0159] Single pass high reduction rate leads to deformation heat concentration, exacerbating temperature gradient (temperature difference > 50℃), and asynchronous ratio cannot compensate thermal stress in time. In addition, high strain rate inhibits dynamic recrystallization, grain coarsening (average size 15 μm), and stress concentration causes edge cracking.

[0160] The index results of each embodiment are shown in Table 1:

[0161] Table 1

[0162] .

[0163] Example twelve

[0164] The embodiment also provides a system for inhibiting C-type warpage of titanium alloy plate based on asynchronous hot rolling process, comprising a pretreatment module, a setting module, an adjustment module and a monitoring module.

[0165] The pretreatment module is used for pretreating the titanium alloy surface blank; the pretreatment step includes oxide layer cleaning and preheating the titanium alloy surface blank. The setting module is used for sending the pretreated blank into the asynchronous rolling mill and setting the asynchronous rolling parameters and tension control; the set asynchronous rolling parameters include: asynchronous ratio, rolling speed, single pass reduction rate and total deformation amount; the tension control includes: applying front tension and rear tension during rolling. The adjustment module is used for dynamically adjusting the asynchronous rolling mill through temperature gradient compensation, the steps including real-time monitoring the rolling zone temperature by an infrared temperature detector, and using a PLC controller to real-time control the asynchronous ratio of the upper and lower rollers. The monitoring module is used for real-time quality monitoring of the asynchronous rolling mill, and closed-loop control to complete the inhibition of C-type warpage.

[0166] The workflow of the pretreatment module includes: using sand blasting or pickling process to clean the oxide layer of the titanium alloy surface blank, and the surface roughness Ra is less than or equal to 3.2 microns; then, the titanium alloy blank surface is sprayed with a high-temperature glass protective agent (a protective agent of a silicon-based glass system, mainly composed of SiO2+Al2O3+CaO, etc.); before spraying, the oil stains, dust and any contaminants on the surface of the titanium alloy are completely removed by using acetone, then the surface is sandblasted and roughened, then the remaining sand particles and dust are cleaned again using a cleaning agent, and the workpiece is ensured to be completely dry before spraying; the glass protective agent is diluted to prepare a spraying suspension of several tens of microns, the titanium alloy surface layer thickness is sprayed several times to several tens of microns to more than one hundred microns by using a low-pressure spray gun, and the layers need to be dried to prevent sagging; the workpiece after spraying is fully dried in a room temperature or low temperature oven (60-80 DEG C); finally, the titanium alloy blank is preheated to the alpha + beta phase region or beta phase region temperature, and the holding time is 1h~4h.

[0167] The above-described embodiments are only descriptions of the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for suppressing C-shaped warpage of titanium alloy sheets based on asynchronous hot rolling process, characterized in that the steps include... include: Pretreatment of the titanium alloy surface blank; The pretreatment steps include oxide layer removal and preheating of the titanium alloy surface blank; The pretreated billet is fed into an asynchronous rolling mill, and asynchronous rolling parameters and tension control are set. The set asynchronous rolling parameters include: asynchronous ratio, rolling speed, single-pass reduction rate, and total deformation; tension control includes: applying pre-tension and post-tension during the rolling process; Dynamic process adjustment of asynchronous rolling mill is achieved through temperature gradient compensation. The steps include real-time monitoring of rolling zone temperature using an infrared thermometer and real-time control of the speed ratio of upper and lower rolls using a PLC controller. Real-time quality monitoring and closed-loop control of the asynchronous rolling mill are implemented to suppress C-shaped warpage.

2. The method for suppressing C-shaped warpage of titanium alloy sheets based on asynchronous hot rolling process according to claim 1, characterized in that, The oxide layer on the titanium alloy blank is removed by sandblasting or pickling, and the surface roughness Ra≤3.2μm. Then, a high-temperature glass protective agent is sprayed onto the surface of the titanium alloy blank. Finally, the titanium alloy blank is preheated to the temperature of the α+β phase region or the β phase region and held for 1h~4h.

3. The method for suppressing C-shaped warpage of titanium alloy sheets based on asynchronous hot rolling process according to claim 1, characterized in that, The formula for calculating the asynchronous ratio includes: ， in, The linear velocity of the fast roller, This represents the linear speed of the slow roller.

4. The method for suppressing C-shaped warpage of titanium alloy sheets based on asynchronous hot rolling process according to claim 3, characterized in that, The relationship between the asynchronous ratio and the reduction rate satisfies: ， Where ε is the reduction ratio, expressed as: ， in, The initial thickness of the billet. This refers to the thickness of the billet after rolling.

5. The method for suppressing C-shaped warpage of titanium alloy sheets based on asynchronous hot rolling process according to claim 1, characterized in that, The application methods for front and back tension include: front tension is provided by the winding machine, with a tension value of 0.1σ. y The back tension is provided by the uncoiler, with a tension value of 0.15σ. y ; where σ y The high-temperature yield strength of the material; tension control accuracy ≤ ±5%.

6. The method for suppressing C-shaped warpage of titanium alloy sheets based on asynchronous hot rolling process according to claim 1, characterized in that, The rules for temperature gradient compensation include: when the temperature difference between the upper and lower surfaces of the rolling zone is greater than 30℃, the asynchronous ratio Δv is 1.3; when the temperature difference between the upper and lower surfaces of the rolling zone is between 10-30℃, the asynchronous ratio is 1.2; and when the temperature difference between the upper and lower surfaces of the rolling zone is less than 10℃, the asynchronous ratio is 1.

1.

7. The method for suppressing C-shaped warpage of titanium alloy sheets based on asynchronous hot rolling process according to claim 1, characterized in that, The working principle of the PLC controller includes: using fuzzy PID control data storage and tracing, while controlling the dynamic adjustment of asynchronous ratio and rolling speed; data storage and tracing are used to record the process parameters and quality data of each batch of plates, generating a unique ID code.

8. The method for suppressing C-shaped warpage of titanium alloy sheets based on asynchronous hot rolling process according to claim 1, characterized in that, The steps for real-time quality monitoring and closed-loop control of asynchronous rolling mills include: using laser displacement sensors and X-ray stress meters to monitor warpage and residual stress distribution online, monitoring the surface flatness and residual stress of the plate online, and dynamically adjusting the asynchronous ratio and reduction rate to ensure that warpage is ≤0.5mm / m.

9. A system for suppressing C-shaped warpage of titanium alloy sheets based on asynchronous hot rolling process, said system being used to implement the method according to any one of claims 1-8, characterized in that, include: Preprocessing module, setting module, adjustment module, and monitoring module; The pretreatment module is used to pretreat the titanium alloy surface blank; The setting module is used to feed the pre-treated billet into the asynchronous rolling mill and set the asynchronous rolling parameters and control the tension. The adjustment module is used to dynamically adjust the asynchronous rolling mill through temperature gradient compensation; The monitoring module is used to perform real-time quality monitoring of the asynchronous rolling mill and to implement closed-loop control to suppress C-shaped warpage.

10. The system for suppressing C-shaped warpage of titanium alloy sheets based on asynchronous hot rolling process according to claim 9, characterized in that, The workflow of the pretreatment module includes: cleaning the oxide layer of the titanium alloy blank by sandblasting or pickling, with a surface roughness Ra≤3.2μm; then, spraying a high-temperature glass protective agent onto the surface of the titanium alloy blank; and finally, preheating the titanium alloy blank to the temperature of the α+β phase region or the β phase region for 1h~4h.

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