Structure modification strengthening process for carbon fiber induced high-damping nodular iron casting

Abstract

The invention relates to the technical field of black metal heat treatment, and discloses a structure modification strengthening process of a carbon fiber induced high-damping nodular iron casting, which comprises the following steps: austenitizing and preserving heat of the nodular iron casting with pre-buried directionally distributed carbon fiber bundles in a controlled carbon potential environment, so that a matrix forms a carbon concentration gradient field; quenching to be close to a martensite transformation starting point; intermittent spray cooling is executed through a cooling control unit in a martensite phase transformation interval; according to the method, martensite laths are induced to radially and directionally grow at an interface by utilizing a pulsating heat flow field generated by utilizing the axial high heat conduction characteristic of the carbon fibers, and a radial grain boundary structure with the carbon fibers as the axis is constructed, so that interface internal friction is generated by utilizing the radial grain boundary structure when a casting bears an excitation load, and vibration energy is dissipated; and the nodular iron casting generates damping response on the premise of maintaining the hardness of a matrix, and stress concentration at a heterogeneous interface is eliminated.

Description

Technical Field

[0001] This invention relates to a microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings, belonging to the field of ferrous metal heat treatment technology. Background Technology

[0002] Currently, high-performance machine tool guide rail components are made of ductile iron. The physical structure of the ferrous metal is changed through quenching to obtain a high-hardness martensitic structure to ensure the surface wear resistance. Under high-speed precision cutting conditions, the guide rail components are subjected to high-frequency alternating vibration. The martensitic structure obtained by existing heat treatment processes exhibits isotropic random distribution characteristics. There is a lack of effective dislocation sliding or interfacial friction sites between the laths. Mechanical vibration energy is repeatedly reflected at rigid grain boundaries, which restricts the improvement of machining accuracy and leads to micro-fatigue spalling on the guide rail surface.

[0003] Even with improvements in material composition or the introduction of reinforcing fibers, only the overall strength is typically enhanced; shortcomings remain in the control of phase transformation timing and spatial morphology. For example, Chinese invention patent CN113862812B discloses a polyacrylonitrile-based carbon fiber precursor for carbon paper and its preparation method. Although it improves fiber orientation and crystallinity by optimizing polymerization and drawing processes, it is limited to optimizing the performance of a single fiber component when processing large-size ferrous metal components. It ignores the thermal mismatch effect between the fiber and the metal matrix and fails to utilize the fiber as an endogenous heat sink to intervene in the latent heat conduction path of quenching. This results in the martensite nucleation and growth being somewhat uncontrolled and unable to be carried out in different phases. The ordered dissipative topology induced by the grain interface makes it difficult to solve the risk of brittle damage to high-hardness guide rails under complex stress fields. Martensitic phase transformation has nonlinear burst characteristics, releasing a large amount of latent heat of phase transformation during crystallization transients. Conventional heat treatment processes treat latent heat as thermal noise and lack means to adjust the latent heat conduction path. The disordered heat conduction mode leads to chaotic spatial orientation of phase transformation products, making it difficult to build an ordered energy dissipation architecture at the grain boundary level. Simply adding damping coatings or external vibration dampers will reduce the static stiffness of the system. Due to the difference in thermal expansion coefficients between different materials, geometric accuracy drift occurs during precision machining thermal cycles.

[0004] Therefore, how to utilize phase transformation physical fields to construct an ordered damping topology within a martensitic matrix, thereby improving damping performance while ensuring matrix hardness, is the technical problem this invention aims to solve. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings, comprising the following steps:

[0006] Step S1: The ductile iron casting with pre-embedded directional carbon fiber bundles is placed in a controlled carbon potential heating furnace for austenitization and heat preservation. The carbon potential in the furnace environment is controlled to be 0.8% to 1.2%, and a carbon concentration gradient field is formed at the carbon fiber interface of the ductile iron matrix.

[0007] Step S2: The austenitized ductile iron casting is quenched at a cooling rate of 20 to 50 °C / s to the martensitic transformation initiation temperature. nearby;

[0008] Step S3, at the martensitic transformation initiation temperature point Temperature at which martensitic transformation ends Between these times, the cooling control unit is adjusted to perform intermittent spray cooling, controlling the spray pressure to be between 0.3 and 0.6 MPa;

[0009] Step S4: Taking advantage of the thermal conductivity difference between the axial direction of the oriented carbon fiber bundles and the ductile iron matrix, the martensitic laths are guided to grow radially at the carbon fiber interface by the pulsed heat flow field generated by intermittent spray cooling.

[0010] Step S5 involves constructing a radial grain boundary distribution structure centered on carbon fibers within the ductile iron matrix through the self-organized arrangement of martensitic laths around the oriented carbon fiber bundles, thereby forming a damping modification layer on the ductile iron part under the condition that the matrix hardness is not less than 50 HRC.

[0011] Preferably, in step S3, the cooling control unit controls the time ratio of the duration of a single spray to the stop time of a single spray to be 1:3 to 1:5; in the ductile iron casting, the volume percentage of the oriented carbon fiber bundles is 5% to 15%.

[0012] Preferably, in step S3, the ratio of the duration of a single spraying session to the time of stopping a single spraying session satisfies the following quantitative relationship: ,in, This refers to the pulse duty cycle. The duration of a single spray cycle set for the cooling control unit; The single spray stop time is set for the cooling control unit; by adjusting the pulse duty cycle. The latent heat conduction rate of phase change is 0.2 to 0.33, matching the axial latent heat conduction rate of the oriented carbon fiber bundles.

[0013] Preferably, in step S1, the heating temperature for austenitizing heat preservation is 850 to 950°C, and the heat preservation time is 2 to 4 hours, so that carbon atoms can be segregated at the interface between the carbon fiber and the matrix.

[0014] Preferably, the spraying medium used in step S3 is a polyvinyl alcohol aqueous solution with a mass fraction of 2% to 5%. The vapor film resistance generated by the spraying medium on the surface of the ductile iron part is used to regulate the heat exchange rate and coordinate the directional distribution of carbon fiber bundles to maintain the temperature gradient of the interface micro-region.

[0015] Preferably, the ductile iron part is a machine tool guide rail component, and the arrangement direction of the directional distributed carbon fiber bundles is perpendicular to the direction of the spindle excitation load of the machine tool guide rail component.

[0016] Preferably, after step S5, the method further includes step S6, which involves performing a low-temperature tempering treatment at 180 to 220°C on the ductile iron casting that has undergone structural strengthening, thereby precipitating dispersed nanoscale carbides in the matrix structure.

[0017] Preferably, the surface of the oriented carbon fiber bundles is pre-coated with a thickness of 1 to 3 mm. The nickel layer is m; in step S1, the nickel layer adjusts the undercooling of the carbon fiber periphery by local alloying, and in step S4, the interfacial bonding force between the radial grain boundary distribution structure and the directional carbon fiber bundle is increased.

[0018] Preferably, in step S3, the single cycle duration of intermittent spray cooling is 0.5 to 2.0 s, and the arrangement density of martensitic laths in the spatial hierarchy is controlled by adjusting the single cycle duration.

[0019] Preferably, by constructing a radial grain boundary distribution structure, the grain boundary density inside the ductile iron matrix is ​​increased, and the interfacial friction between martensitic laths is used to improve the dissipation rate of ductile iron parts for cyclic excitation energy.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. In the process of structural modification and strengthening, the endogenous heat sink effect formed by the high axial thermal conductivity of carbon fibers is utilized. Combined with intermittent cooling to regulate the latent heat conduction path of phase transformation inside the ductile iron matrix, the martensitic transformation initiation temperature in the interfacial micro-regions is directionally shifted, inducing nonlinear growth of martensite laths around the carbon fiber axis and establishing a spiral radial grain boundary topology. The establishment of the spiral grain boundary topology changes the energy transfer mode inside the matrix, enabling the component to generate cross-grain boundary cooperative shear dissipation when subjected to vibration load. This improves the material's ability to absorb high-frequency vibration energy and solves the technical defect of high-hardness guide rail components lacking energy dissipation dimension under high-speed cutting conditions.

[0022] 2. By controlling the environmental carbon potential during the austenitization stage to form an interfacial carbon concentration gradient field, and by utilizing the difference in local solute distribution to differentially adjust the phase transformation time, the phase transformation in the peripheral region of the carbon fiber is delayed compared to the overall phase transformation of the matrix. Then, by replacing transient impact with progressive extrusion at the phase transformation front, stress peaks at the heterogeneous interface are eliminated while maintaining the hardness of the matrix. This reduces the probability of internal cracks in high-hardness materials under cyclic loading, ensuring the structural integrity of precision components under extreme conditions and avoiding the risk of fatigue spalling in high-hardness castings.

[0023] 3. By combining the dislocation accumulation generated by cryogenic pre-tightening treatment with the segregation of solute atoms under subcritical energy level activation, a flexible residual austenite film with anchoring characteristics is constructed in the gaps between martensitic hierarchical laths. This stabilization mechanism based on the physical pinning effect blocks the path of spontaneous transformation of austenite to martensite, enabling the component to maintain a constant loss factor during long-term service, solving the problem of performance degradation of traditional damping materials with the length of use, and improving the dynamic accuracy and stability of machine tool guideway components. Attached Figure Description

[0024] Figure 1 This is a flowchart of the process steps for carbon fiber-induced microstructure modification and strengthening of high-damping ductile iron castings according to the present invention.

[0025] Figure 2 A synergistic causal analysis diagram of the key process parameter settings and multidimensional enhancement mechanism of this invention;

[0026] Figure 3 This is a schematic diagram of the pulse cooling closed-loop control principle based on phase change acoustic emission feedback of the present invention. Detailed Implementation

[0027] The present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the scope of protection of the present invention. Experimental methods in the following embodiments that do not specify specific conditions are generally carried out under conventional conditions or under the conditions recommended by the manufacturer.

[0028] This invention provides a microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings, comprising a stress pre-equilibrium solution treatment stage, a phase transformation pre-thermal stress reconstruction stage, a multi-level damping interface in-situ construction stage, and a physical dislocation locking stage. Utilizing the thermal mismatch effect of carbon fibers during the austenitic-to-martensite transformation of the ductile iron matrix, the cooling sequence is adjusted to guide the martensite laths to achieve controlled orientation, thereby constructing a radial grain boundary distribution structure centered on carbon fibers within ductile iron castings such as machine tool guideways. Addressing the issues of insufficient metallurgical bonding strength between the ductile iron matrix and carbon fiber interface and the susceptibility to quenching microcracks, during the stress pre-equilibrium solution treatment stage, the ductile iron casting with pre-embedded oriented carbon fiber bundles is placed in a controlled carbon potential heating furnace for austenitization and heat preservation. The heating temperature is set at... to The interval and the heat preservation time are set to to By controlling the carbon potential inside the furnace to be higher than the carbon content of the base metal... to To maintain the carbon potential of the environment at to During this process, carbon atoms are enriched towards the fiber periphery through physicochemical adsorption on the carbon fiber surface, resulting in a wide area at the interface between the carbon fiber and the ductile iron matrix. to A carbon concentration gradient field is used to determine the local martensitic transformation initiation temperature in the peripheral region of the carbon fiber. This results in a physical decrease, which delays the phase transformation in this region compared to the overall phase transformation of the matrix. This procedure, which regulates the phase transformation timing through chemical potential difference, allows the phase transformation front to be progressively extruded to adhere to the carbon fiber interface. This is used to cope with stress peaks at the heterogeneous interface and to generate the initial state for subsequent microstructure modification.

[0029] During the pre-phase transformation thermal stress reconstruction stage, the ductile iron castings that have undergone austenitization treatment will be... to The cooling rate of quenching to the martensitic transformation start temperature point Above to Within the specified range, isothermal residence is performed, with an isothermal residence time of [time value missing]. to By utilizing the physical difference in thermal expansion coefficients between carbon fiber and ductile iron matrix, the interfacial mismatch stress field in regions with different wall thicknesses is brought to physical saturation during isothermal conditions. The annular prestress field induced at the carbon fiber interface acts as the physical guiding field for subsequent martensite nucleation. By eliminating the thermal gradient differences caused by the geometric structure, it ensures the synchronicity of the phase transformation action across the entire cross-section. During the in-situ construction stage of the multi-level damped interface, at the martensite transformation initiation temperature... Temperature at which martensitic transformation ends Between these times, the cooling control unit is adjusted to perform intermittent spray cooling, and the spray medium uses a mass fraction of [missing information]. to The polyvinyl alcohol aqueous solution was sprayed at a pressure set to [value missing]. to This stage involves controlling the duration of a single spray. With single spray stop time The time ratio, i.e., the pulse duty cycle. The following quantitative relationship must be satisfied: ,in, The pulse duty cycle is set at [value]. to Between, the corresponding time ratio is to , The duration of a single spray cycle is set to [value]. to , The stop time for a single spray cycle is set to [time]. to Based on the characteristic dimensions of the casting With carbon fiber volume fraction Establishing a thermal balance calibration protocol is important for... The latent heat release rate of the core phase change in thick-walled components was determined by thermocouple embedding experiments. ,like Control unit locked for and take upper limit ,for Thin-walled components, based on surface heat transfer coefficient The gradient fitting results are taken as follows: lower limit ,extend to Inducing the matrix to produce no less than The martensitic lattice rotation, if the measured cooling rate deviates Target range, execute Dynamic gain correction eliminates uneven distribution of phase transformation stress caused by differences in cross-sectional heat capacity.

[0030] During the spray pulse duration, the surface layer of the ductile iron matrix rapidly cools down. The carbon fibers, utilizing their higher thermal conductivity (higher in the axial direction than the matrix metal), conduct the latent heat of phase transformation released from the internal martensitic nucleation to the cooling medium, generating localized heat at the periphery of the carbon fibers. The point rise phenomenon causes martensitic laths to grow from the carbon fiber interface. During the intervals between spraying stops, the phase transformation driving force generates thermal relaxation, causing the growing martensitic laths to undergo lattice rotation under the combined action of phase transformation strain energy and thermal mismatch stress field. The intermittent cyclic action causes the martensitic laths to form a spiral radial arrangement around the carbon fiber, retaining a thickness of [missing information] in situ between the laths. to The residual austenitic flexible film is used to construct a damping topology based on interface-coordinated shear dissipation within the matrix; to control the distribution density of the damping interface, acoustic emission feedback control logic is adopted when the casting is cooled to a certain temperature. After reaching the specified temperature, a vibration sensing unit positioned along the quenching path monitors the acoustic emission signal generated by the phase transformation shear. The vibration sensing unit extracts the signal through spectral analysis. to Energy value within the frequency band When the monitored energy value Exceeding the preset energy threshold At that time, it was determined to be a martensitic nucleation burst window and a high-pressure spray pulse was triggered in real time to establish the martensitic lath thickness. Integral with acoustic emission energy Topological mapping function Perform closed-loop spray regulation and set the energy increment within the sliding time window. As the basis for triggering the judgment, if The decision-making center issued a spraying command, forcing The transient cooling intensity within a given time period meets the critical undercooling required for radial martensite growth. To address fluctuations in the carbon content of raw materials, a correction factor is introduced. According to the spectral analysis Dynamic reset If the implementing agency's response is delayed By adjusting the pulse phase through a lead-compensation algorithm, the temperature gradient pulsation is synchronized with the peak of the martensitic nucleation dynamics, thus controlling the dispersion of the damping loss factor within a certain range. Within, of which, The energy threshold is determined experimentally based on the carbon content of the matrix material and the flow rate of the quenching medium. This procedure enables the temperature pulse and the martensitic nucleation sequence to be physically coupled, which is used to adjust the damping interface distribution density at different parts of the precision guide rail.

[0031] During the physical dislocation locking stage, the casting that has undergone microstructural modification is cooled to - Maintain in liquid nitrogen environment to This causes geometrically necessary dislocations to accumulate at the interface, raising the temperature back to [a certain level]. Near the temperature point, and in conjunction with to The low-temperature tempering treatment utilizes thermal activation energy to drive alloying elements to segregate towards the austenite-martensite phase boundary. The pinning effect of the alloying elements at the phase boundary locks the lattice rotation path of the residual austenite film, maintaining its structural stability under mechanical cyclic loading, thereby ensuring the dynamic accuracy of machine tool guide rail components. In scenarios involving directional reinforcement of the guide rail under stress, to ensure the controlled directional arrangement of carbon fiber bundles within the matrix, a mechanical tensioning and positioning procedure is executed during the ductile iron molten casting and subsequent stress pre-equilibrium solution treatment stages. This is achieved by applying high-temperature resistant clamps to the carbon fiber bundles at both ends of the casting mold. to The pretension ensures that the axial direction of the carbon fiber bundle is parallel to the main working surface of the guide rail, and the parallelism error is checked by a laser collimator and is not higher than [the specified value]. This ensures that the latent heat energy released during the subsequent martensitic phase transformation is axially conducted along a preset geometric path, thus solving the problem of damping vector deviation caused by the uncertainty of the phase space orientation.

[0032] Example 1: In the manufacturing scenario of guide rails for ultra-high-speed machining centers of large aerospace thin-walled parts, the guide rail components maintain a surface hardness of not less than... At the same time, it is necessary to suppress the influence of High-frequency cutting vibration caused by spindle speed, due to the isotropic arrangement of martensite within the ductile iron matrix produced by traditional quenching processes, leads to repeated reflections and accumulation of mechanical vibration energy at rigid grain boundaries. This, in turn, induces fatigue spalling on the guide rail surface, restricting the long-term stability of machining accuracy. To address surface damage caused by alternating vibration, ductile iron parts pre-embedded with directionally distributed carbon fiber bundles are placed... Austenitizing and heat preservation are carried out in a controlled carbon potential heating furnace, and the carbon potential in the furnace environment is adjusted to be higher than the carbon content of the base metal. Establish a width of [missing information] at the carbon fiber interface The carbon concentration gradient field.

[0033] By physically lowering the martensitic transformation initiation temperature around the carbon fiber periphery. Combined with pulse duty cycle for Intermittent spray cooling guides the martensitic laths to grow directionally along the axial heat flow path of the carbon fiber, utilizing the high thermal conductivity of the carbon fiber along its axial direction and the short duration of each spray cycle. The thermal stress relaxation within the carbon fiber generates physical synergy, driving lattice rotation in the growing martensite laths and forming a layer of thickness [missing information] around the carbon fiber periphery. The spiral radial topology encapsulated by a flexible film of retained austenite, through a microstructure modification and strengthening process, resolves the technical conflict between material hardness requirements and vibration energy dissipation capacity by constructing a radial grain boundary structure centered on carbon fibers in situ within the ferrous metal matrix. The martensitic laths provide the load support required for the guide rail, while the retained austenite film, under the elastic mismatch torque between the carbon fibers and the ferrous metal matrix, converts cutting excitation energy into interfacial shear friction heat. Combined with physical dislocation locking treatment in a liquid nitrogen environment, this guide rail continuously... During the working condition test, the surface hardness remained at Furthermore, its damping loss factor is stable at that of conventional quenched guide rails. This doubles the effect, eliminating fatigue spalling on the guide rail surface.

[0034] Example 2: In the test scenario used to verify the dynamic characteristics of the column support guide rail of a high-precision machining center, a sample containing a mass fraction of... to The test platform for ductile iron parts with directionally distributed carbon fiber bundles included a pulse hardening machine with an integrated nozzle pressure regulation system and a vibration characteristic testing platform equipped with acoustic emission sensors. The original vibration excitation data used in the test were generated by converting the spindle resonance spectrum acquired by the physical experimental platform. The sampling frequency of the measuring instruments was [missing information]. Its measurement resolution is In the parameter setting logic, the pulse duty cycle The value of [value] directly affects the balance between the conduction gradient of the latent heat of martensitic phase transformation and the depth of thermal stress relaxation, among which, the pulse duty cycle The setting needs to balance the phase transition-induced driving force and the interface dislocation density. If the pulse duty cycle tending towards the lower limit of the value range The thermal relaxation depth per unit time increases, which is used to induce a larger lattice rotation angle in martensite laths. If the pulse duty cycle... trending toward the upper limit This increases the cooling intensity, and is used to refine the thickness of the residual austenitic flexible film in the gaps between the slats. To simulate the interference of the real industrial electromagnetic environment on the acoustic emission feedback control logic, a signal-to-noise ratio of [value missing] is actively superimposed in the sensor signal source during the experiment. Gaussian noise was used to verify the control stability of the acoustic emission feedback-induced mechanism under non-ideal conditions.

[0035] During the in-situ construction of the multi-level damping interface, the experimental group adopted the tissue modification and strengthening process provided by this invention to adjust the pulse duty cycle. Set as Duration of a single spray for Single spray stop time for The vibration sensing unit extracts data by performing spectrum analysis. to Energy value within the frequency band And in energy value Exceeding the preset energy threshold The spray pulse is triggered at specific times. Table 1 compares the damping performance and microstructure parameters under different process paths. Among them, control group 1 uses a conventional quenching process without carbon fiber, control group 2 uses a continuous spray quenching process with pre-embedded carbon fiber, and control group 3 uses a pulse duty cycle of [missing information]. Set as The data in Table 1 shows that, exceeding the upper limit of the scope defined in this invention, after intermittent spray cooling, the martensitic laths formed a spiral radial topology around the carbon fiber with an average rotation angle of 35.5°, and its damping loss factor reached [value missing]. The levels were higher than those in control groups 1 and 2.

[0036] Table 1: Comparison of Damping Performance and Microstructure Parameters

[0037]

[0038] Analysis of the data from control group 3 in Table 1 shows that when the pulse duty cycle... After exceeding the upper limit of the specified range, due to the interval between spray stops... Shortening of the matrix and insufficient thermal stress relaxation within the ductile iron matrix prevent sufficient lattice rotation in the martensitic laths, hindering the development of the helical radial topology and reducing the damping loss factor. This demonstrates that the defined parameter range is the optimal working window that balances the driving force of phase transformation dynamics and the stress relaxation effect. Experimental data confirms that the concentration gradient field formed by carbon atoms in the solid solution stage and the temperature pulse in the quenching stage generate an energy dissipation mechanism based on interfacial shear friction in situ within the martensitic matrix through physical coupling, thus solving the problem of insufficient damping of high-performance machine tool guide rail components under high hardness conditions.

[0039] Example 3: This example combines Figures 1 to 3 The process for microstructure modification and strengthening of a carbon fiber-induced high-damping ductile iron casting is described, such as... Figure 1As shown, starting from the pretreatment stage of ductile iron castings, directional carbon fiber bundles are pre-embedded in the castings, and the castings are sent into the controlled carbon potential austenitization holding stage. During this process, a carbon concentration gradient field is formed in the matrix. Quenching treatment is performed to cool the castings to near the martensitic transformation start point. Then, the cooling control unit performs intermittent spray cooling in the martensitic phase transformation range. By utilizing the pulsating heat flow field generated by the high axial thermal conductivity of carbon fibers, radial grain boundary structures are constructed and martensitic laths grow radially and directionally at the interface. Finally, a high-damping modified casting that can dissipate vibration energy while maintaining the hardness of the matrix is ​​obtained.

[0040] like Figure 2 As shown, the carbon fiber-induced microstructure modification and strengthening of high-damping ductile iron castings is achieved through the synergistic effect of four dimensions. The austenitization pretreatment dimension includes controlled carbon potential of 0.8% to 1.2%, forming a carbon concentration gradient field, and holding at 850 to 950°C. The cooling control strategy dimension involves intermittent spray cooling, pulse duty cycle control of 0.2 to 0.33, and the use of a 2% to 5% PVA aqueous solution. The microstructure construction dimension relies on the effect of pulsating heat flow field to guide the directional growth of martensite laths and form a radial grain boundary structure. The material and post-treatment dimension includes a directional carbon fiber bundle content of 5% to 15%, low-temperature tempering at 180 to 220°C, and promotion of carbide precipitation and dispersion. Figure 3 As shown, the control system uses a ductile iron casting containing directional carbon fiber bundles as the controlled object. The phase change acoustic emission signal generated during the phase change process is transmitted to the phase change sensing end, which consists of an acoustic emission sensor and a spectrum analysis module. After processing, the sensing end outputs an energy threshold signal to the decision control center, which includes a martensitic phase change identification algorithm and a pulse timing logic controller. Based on this, the decision control center issues a pulse trigger command to the pulse cooling execution end, which consists of a high-frequency solenoid valve group and an intermittent spray matrix. The execution end uses the spray action of PVA aqueous solution as the medium to generate an intermittent heat flow field and feeds it back to the ductile iron casting, thereby forming a closed-loop control loop.

[0041] Example 4: In the scenario of mass quenching process of high-precision machine tool bed guideways, the carbon content of the base material is... to To address the phase transition timing drift challenge caused by fluctuations within the specified range, the following parameter calibration and feedback control procedures were implemented to determine the energy threshold used to trigger intermittent spraying. In an offline state, a ferrous metal sample of the same material as the guide rail to be processed was selected, with an initial hardness of [missing information]. to Using a quenching platform equipped with a thermal simulation detection unit, a single continuous quenching process was performed without activating spray cooling. The original acoustic emission signals of the entire phase transition process were collected by a vibration sensing unit. The sampling frequency of the original acoustic emission signals was [missing information]. Sampling depth is The following algorithmic logic steps are performed on the collected acoustic emission signals to achieve the desired effect. The signal is divided into sliding segments within a time window, and a Fast Fourier Transform is performed on each segment of the time-domain signal to obtain... to The power spectral density distribution within the frequency band is used to calculate the energy integral value within that frequency band. Energy threshold The calculation formula is as follows: ,in, The preset energy threshold is expressed in units of... , The temperature at which the ferrous metal matrix begins its martensitic transformation. forward The arithmetic mean of the internal background noise energy values, in units of , The standard deviation of the background noise energy value, in units of This formula introduces a three-times-standard-deviation component of the background noise to eliminate the physical interference of industrial field vibrations on the identification of martensitic nucleation signals.

[0042] To verify the moderating effect of the carbon concentration gradient field on the local phase transition time, during the stress pre-equilibrium solution treatment stage, electron probe microanalysis was used to measure the solute distribution at the carbon fiber interface. The heating temperature was set to... The heat preservation time is The carbon potential in the furnace environment is controlled at At that time, the measured carbon fiber surface towards the matrix interior The carbon content within the depth is determined by It decays exponentially to the matrix mean. According to thermodynamic equilibrium calculations, this concentration gradient distribution causes the local martensitic transformation to begin at the interface immediately adjacent to the carbon fiber. The central region of the matrix was reduced This localized undercooling difference, derived from the chemical potential energy of solute atoms, induces a two-stage phase transformation front within the matrix during subsequent cooling. The first stage involves explosive martensite nucleation in the matrix region far from the carbon fiber, generating acoustic emission signals and triggering spray pulses. The second stage involves rapid conduction of latent heat along the carbon fiber axis, providing additional undercooling to the austenite region at the periphery of the carbon fiber, thereby guiding the in-situ germination of martensite laths at the fiber interface in a radial orientation. During the elastic mismatch locking stage, to ensure consistency in the microstructure of different batches of guide rails, the system implements the following adaptive compensation method: if the arithmetic mean of the background noise energy monitored online... More than The control unit will adjust the new energy threshold based on the trend of deviation. By automatically correcting the trigger timing of the pulse spray and implementing the aforementioned calibration and control procedures, the coverage of the spiral radial topology formed by the martensitic laths around the carbon fiber in the guide rail remained stable in five different batches of production verification. The thickness dispersion of the retained austenitic flexible film is less than that of the above. This study demonstrates that determining the control threshold by the statistical characteristics of acoustic emission signals, combined with thermodynamic adjustment of the carbon concentration gradient, can solve the problem of unstable tissue modification and strengthening effects caused by fluctuations in raw material composition.

[0043] Example 5: When the system faces fluctuations in carbon content due to the replacement of raw material batches for ductile iron castings, in order to determine the heating temperature and environmental carbon potential during the stress pre-equilibrium solution treatment stage, a pre-calibration procedure is initiated on-site, and the original carbon content of the matrix of this batch of castings is determined by a spectrometer. According to the formula Determine the environmental carbon potential, among which, Environmental carbon potential, in units of , This represents the original carbon content, in units of... , The preset carbon potential enhancement coefficient has a range of values. to This is used to adjust the adsorption flow rate of carbon atoms onto the carbon fiber surface. After setting the heating temperature, three identical furnace-fed samples were selected for a duration of [duration missing]. , and The gradient insulation treatment, through analysis of cross-sectional carbon concentration distribution data, determined the width to be... to The required holding time for the carbon concentration gradient field The calibration parameters generated by this process are stored in the initial parameter library of the quenching control system to guide subsequent heat treatment processes.

[0044] In the scenario of adjusting the acoustic emission feedback-induced mechanism for environmental background noise, to eliminate the interference of vibration waves generated by workshop equipment operation on the identification of martensitic nucleation signals, the system executes offline calibration and data filling procedures. Before the ductile iron casting enters intermittent spray cooling, the vibration sensing unit is activated for a duration of [duration missing]. The unloaded sampling is extracted by performing a fast Fourier transform. to Calculate the energy fluctuation dispersion of the time-domain envelope signal within the frequency band over the sampling period. When the measured dispersion When the system's built-in stability threshold is exceeded, the preset energy threshold is re-determined based on the energy distribution of the current frequency band. This allows the trigger point of the spray pulse to be anchored to the acoustic signal characteristic parameters generated by the martensitic nucleation. The control system, after this adaptive calibration, controls the response delay of each actuator to within a certain range. Within this range, closed-loop management of process parameters throughout the entire process can be achieved in heterogeneous environments.

[0045] Example 6: In scenarios where process adaptation is performed for guide rails with different geometric cross-sections, to address the challenge of asymmetric local thermal mismatch stress field caused by the directional displacement of carbon fiber bundles within the ductile iron matrix, a pre-geometric parameter calibration procedure is implemented, and ultrasonic array detection technology is used to determine the actual deflection angle of the carbon fiber bundles within the ductile iron part. Actual deflection angle The angle between the carbon fiber axis and the main force direction of the guide rail is used. The measured deflection angle data is input into the quenching control unit, and the result is calculated according to the formula. Real-time compensation is performed on the pulse duty cycle, whereby, This is the corrected pulse duty cycle. The preset pulse duty cycle is set to a value according to the specific implementation method. to between, The deflection angle is expressed in units of 1 / 200°. By adjusting the heat flux density distribution, it is ensured that the conduction path of the latent heat of interfacial phase transformation can still guide the martensitic laths to produce radial deflection even when the carbon fiber orientation is off, thus controlling the damping consistency error at different positions along the guide rail axially within a certain range. Within this range, regarding the thickness of flexible films containing residual austenite... In the modeling scenario for prediction, for the condition where fluctuations in the concentration of polyvinyl alcohol in the cooling medium cause instability in tissue evolution, the system executes an offline data filling procedure, configuring mass fractions as follows: , and Aqueous solutions of polyvinyl alcohol, at the same pulse duty cycle Comparative quenching tests were conducted under specific conditions, and the thickness of the residual austenite film in each sample group was measured using a transmission electron microscope. A film thickness response feature matrix is ​​established, which is used to record the concentration of the cooling medium. Spray pressure With film thickness The mapping relationship between them, where, This refers to the concentration of the cooling medium, in units of... , The spray pressure is expressed in units of... , The thickness of the thin film is expressed in units of 1000 mm. When the system detects the spray pressure When fluctuations occur, the control unit automatically adjusts the duration of a single spray based on the gradient vector in the feature matrix. This ensures that the effective cooling rate of the ductile iron matrix within the martensitic transformation range is maintained at the process calibration point.

[0046] In scenarios involving optimization of martensitic rotational dynamics parameters, to determine the time ratio of intermittent spray cooling, the system executes a thermal balance calibration procedure at the martensitic transformation initiation temperature. The following describes how to adjust the duration of a single spray. Instantaneous subcooling is generated when the time ratio, i.e., the pulse duty cycle, is reached. In to When the range is defined, the transient thermal mismatch stress field at the carbon fiber interface Above the critical shear force required to induce martensitic lattice rotation, where, Thermal mismatch stress, unit: If the time ratio is less than If the average cooling intensity per unit time is insufficient to sustain the phase change, and the time ratio is greater than 1, then the phase change will continue. Due to the weakening effect of thermal stress relaxation during the interval between spraying stops, the martensitic laths undergo isotropic explosive growth and cannot form a controlled radial orientation. The proportion determined by this process is used to guide the cooling control logic of castings with different heat capacities.

[0047] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings, characterized in that, Includes the following steps: Step S1: The ductile iron casting with pre-embedded directional carbon fiber bundles is placed in a controlled carbon potential heating furnace for austenitization and heat preservation. The carbon potential in the furnace environment is controlled to be 0.8% to 1.2%, and a carbon concentration gradient field is formed at the carbon fiber interface of the ductile iron matrix. Step S2: The austenitized ductile iron casting is quenched at a cooling rate of 20 to 50 °C / s to the martensitic transformation initiation temperature. nearby; Step S3, at the martensitic transformation initiation temperature point Temperature at which martensitic transformation ends Between these times, the cooling control unit is adjusted to perform intermittent spray cooling, controlling the spray pressure to be between 0.3 and 0.6 MPa; Step S4: Taking advantage of the thermal conductivity difference between the axial direction of the oriented carbon fiber bundles and the ductile iron matrix, the martensitic laths are guided to grow radially at the carbon fiber interface by the pulsed heat flow field generated by intermittent spray cooling. Step S5 involves constructing a radial grain boundary distribution structure centered on carbon fibers within the ductile iron matrix through the self-organized arrangement of martensitic laths around the oriented carbon fiber bundles, thereby forming a damping modification layer on the ductile iron part under the condition that the matrix hardness is not less than 50 HRC.

2. The microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings according to claim 1, characterized in that, In step S3, the cooling control unit controls the time ratio of the duration of a single spray to the stop time of a single spray to be 1:3 to 1:5; in the ductile iron casting, the volume percentage of the oriented carbon fiber bundles is 5% to 15%.

3. The microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings according to claim 2, characterized in that, In step S3, the ratio of the duration of a single spraying session to the stop time of a single spraying session satisfies the following quantitative relationship: ,in, This refers to the pulse duty cycle. The duration of a single spray cycle set for the cooling control unit; The single spray stop time is set for the cooling control unit; by adjusting the pulse duty cycle. The latent heat conduction rate of phase change is 0.2 to 0.33, matching the axial latent heat conduction rate of the oriented carbon fiber bundles.

4. The microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings according to claim 1, characterized in that, In step S1, the heating temperature for austenitizing heat preservation is 850 to 950°C, and the heat preservation time is 2 to 4 hours, so that carbon atoms can be segregated at the interface between carbon fiber and matrix.

5. The microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings according to claim 1, characterized in that, The spraying medium used in step S3 is a polyvinyl alcohol aqueous solution with a mass fraction of 2% to 5%. The heat exchange rate is adjusted by the vapor film resistance generated on the surface of the ductile iron casting by the spraying medium, and the temperature gradient of the interface micro-region is maintained by the directional distribution of carbon fiber bundles.

6. The microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings according to claim 1, characterized in that, The ductile iron part is a machine tool guide rail component, and the direction of the directional distribution of carbon fiber bundles is perpendicular to the direction of the spindle excitation load of the machine tool guide rail component.

7. The microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings according to claim 1, characterized in that, Step S5 is followed by step S6, in which the ductile iron casting with the completed microstructure is subjected to a low-temperature tempering treatment at 180 to 220°C, and nanoscale carbides are precipitated in the matrix microstructure.

8. The microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings according to claim 1, characterized in that, The surface of the oriented carbon fiber bundles is pre-coated with a thickness of 1 to 3 The nickel layer is m; in step S1, the nickel layer adjusts the undercooling of the carbon fiber periphery by local alloying, and in step S4, the interfacial bonding force between the radial grain boundary distribution structure and the directional carbon fiber bundle is increased.

9. The microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings according to claim 1, characterized in that, In step S3, the single cycle duration of intermittent spray cooling is 0.5 to 2.0 s, and the arrangement density of martensite laths in the spatial hierarchy is controlled by adjusting the single cycle duration.

10. The microstructure modification and strengthening process for carbon fiber-induced high-damping ductile iron castings according to claim 1, characterized in that, By constructing a radial grain boundary distribution structure, the grain boundary density inside the ductile iron matrix is ​​increased, and the interfacial friction between martensitic laths is utilized to improve the dissipation rate of ductile iron parts for cyclic excitation energy.

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