A smelting process for inhibiting the reverse white mouth defect of passenger car brake support

Abstract

The application discloses a smelting process for inhibiting the inverse white mouth defect of a passenger car brake support, and belongs to the technical field of nodular cast iron smelting and casting. The application pre-establishes a graphitization health index GHI model, continuously collects characteristic parameters in the solidification process of the casting by means of ultrasonic waves, and calculates GHI(t) and the first derivative d(GHI) / dt in real time, sets a recession early warning threshold R_critical, triggers an early warning signal when d(GHI) / dt is less than R_critical, and immediately starts a fixed-point pulse inoculation program which does not depend on the solid phase fraction, temperature and solidification process, while synchronously executing local fixed-point heat compensation to ensure the diffusion and capture of inoculants, continues to monitor d(GHI) / dt after the intervention, and if it is not recovered, repeats the intervention and evaluates and iterates in real time until the solidification is completed. The application realizes real-time sensing and immediate closed-loop intervention on the inoculation recession trend, and actively inhibits the formation of the inverse white mouth defect from the mechanism.

Description

Technical Field

[0001] This invention belongs to the field of ductile iron smelting and casting technology, specifically relating to a smelting process for suppressing the white cast iron defect in passenger car brake brackets. Background Technology

[0002] Brake brackets for passenger vehicles are critical load-bearing components of the vehicle's braking system, and their safety and reliability directly affect driving safety. These castings are typically made of ductile iron, utilizing the characteristics of spheroidal graphite—low cutting force on the matrix and low stress concentration—to achieve an excellent balance of strength and toughness. However, significant differences in wall thickness and uneven distribution of thermal points in brake brackets make thicker sections highly susceptible to white iron defects in the as-cast state. White iron defects manifest as the precipitation of free cementite in the core of the casting, increasing local hardness and brittleness, severely deteriorating machinability, and increasing the risk of brittle fracture during service. Currently, conventional methods to suppress white iron defects mainly include the selection of high-purity furnace charge, enhanced inoculation treatment, and rational design of the gating system, aiming to suppress the segregation of anti-graphitizing elements and the tendency for carbide formation, and promote full graphitization during solidification.

[0003] The aforementioned existing technical solutions reduce the probability of white cast iron defects to some extent, but their control logic is based on a static model of pre-intervention before casting. Taking Chinese invention patent CN111621689A as an example, this patent prevents white cast iron defects by strictly controlling the selection of raw materials, tempering, molten iron pretreatment, spheroidizing inoculation treatment, and casting inoculation. However, the inoculation effect of ductile iron exhibits significant aging decay characteristics. The graphite nucleation cores provided by the inoculant gradually dissolve or deactivate during solidification, leading to a decrease in the number of effective cores, especially in hot spots, to below a critical level in the later stages of casting solidification. The aforementioned static control methods cannot detect or compensate for the asynchronous decay of the inoculation state in different parts during the solidification process, resulting in insufficient local graphitization and making it difficult to eradicate white cast iron defects. In addition, existing ultrasonic testing methods are only used to evaluate the spheroidization rate after the casting has solidified, and cannot detect the inoculation decline trend in real time during the solidification process and implement online intervention; the quality control mode that relies on post-production non-destructive testing or destructive testing can only identify defective products and lacks the ability to capture signs of decline in real time during the production process and actively control it.

[0004] Therefore, there is an urgent need in this field for a smelting process that can sense the incubation and decay trend during the solidification of ductile iron in real time and intervene immediately when decay occurs, so as to proactively intervene in the formation of white cast iron defects in brake brackets from the perspective of their occurrence mechanism. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a smelting process for suppressing the white-out defects in passenger vehicle brake brackets.

[0006] The objective of this invention can be achieved through the following technical solutions: A smelting process for suppressing the white cast defect in passenger car brake brackets includes the following steps: (1) Batching and smelting: Low-sulfur scrap steel, recycled materials and stamping scrap are selected as metal furnace materials, and low-sulfur carbon raiser and silicon carbide are selected as carbon and silicon raising materials. The prepared furnace materials are added to the medium frequency induction furnace for smelting, the chemical composition of the original molten iron is controlled, and the smelting temperature is controlled at 1460~1520℃. (2) Establish a graphitization health index model in advance: Establish a quantitative correspondence between ultrasonic characteristic parameters and graphitization degree during the solidification process of ductile iron through standard tests, and define the graphitization health index GHI; (3) Continuous dynamic monitoring: After the casting is completed, the ultrasonic probe array is arranged at the predetermined monitoring position of the casting mold, the ultrasonic characteristic parameters of each monitoring point are continuously collected, the graphitization health index GHI(t) at each time is calculated in real time, where t represents time, and the first derivative of GHI(t) with respect to time d(GHI) / dt is calculated in real time as the trend of GHI(t). (4) Identification and early warning of gestational decline trend: Set a decline early warning threshold, which is defined as R_critical. When d(GHI) / dt reaches the early warning condition, a gestational decline early warning signal is triggered. (5) Rescue-type pulse incubation decision: After the warning signal is triggered, the fixed-point pulse incubation program is started immediately without conditions. The "unconditional" means that the decision does not depend on the current solid fraction, the temperature of the monitoring point, or the solidification process stage. (6) Synergistic execution of rescue pulse incubation and synchronous heat replenishment: Incubator is sprayed into the area where degradation is detected by the spraying device arranged on the mold; Simultaneously with the pulse incubation, the area is locally heated by the heating device arranged on the mold. (7) Evaluation and iteration of intervention effect: After the pulse incubation and heat replenishment are completed, continue to monitor the d(GHI) / dt of the region. If it does not recover, repeat steps (5) and (6). (8) After the casting has solidified, it is cooled, unpacked and post-processed.

[0007] As a preferred technical solution of the present invention, the chemical composition of the original molten iron in step (1) is as follows by mass percentage: C 3.6%~3.8%, Si 1.4%~1.7%, Mn 0.15%~0.25%, P≤0.04%, S≤0.015%; the content of anti-graphitizing elements controlled by mass percentage during batching is as follows: Cr≤0.05%, V≤0.03%, Sn≤0.01%, Sb≤0.005%, Te≤0.003%.

[0008] As a preferred embodiment of the present invention, the definition of GHI in step (2) is: ,in To measure the longitudinal wave velocity of ultrasound. The standard speed of sound in a fully graphitized state. To measure the ultrasonic attenuation coefficient, The standard attenuation coefficient is the one used in the fully graphitized state. To measure the ultrasonic nonlinear coefficient, The standard nonlinear coefficients are those in the fully graphitized state. , , The weighting coefficients and 1.

[0009] As a preferred technical solution of the present invention, the frequency of continuous acquisition in step (3) is 0.5~2 seconds / time.

[0010] As a preferred technical solution of the present invention, the decay warning threshold in step (4) is R_critical, and the value range of R_critical is -0.005~-0.015 / s. When d(GHI) / dt<R_critical, a warning signal is triggered.

[0011] As a preferred technical solution of the present invention, a multi-level early warning mechanism is established: when -0.015≤d(GHI) / dt<-0.010, a first-level early warning is triggered; when -0.025≤d(GHI) / dt<-0.015, a second-level early warning is triggered; and when d(GHI) / dt<-0.025, a third-level early warning is triggered.

[0012] As a preferred technical solution of the present invention, the injection device in step (6) is a high-pressure injection device with an injection pressure of 5~20MPa, an injection volume of 0.05%~0.15% of the mass of molten iron in the region, and an injection method of pulse; the inoculant is a nano-sized inoculant with a particle size ≤10μm.

[0013] As a preferred embodiment of the present invention, the pulsed spray parameters are: spray duration of 0.5 to 2 seconds, interval of 1 to 3 seconds, repeated 2 to 5 times.

[0014] As a preferred technical solution of the present invention, the local fixed-point heating in step (6) raises the local temperature of the spray area by 20~80°C, and the heating duration is synchronized with the pulse incubation, which is 2~10 seconds; the heating device is an induction heating device or a resistance heating device, and the heating power is 5~20kW.

[0015] As a preferred technical solution of the present invention, in step (7), if d(GHI) / dt rises to ≥R_critical, normal monitoring is resumed; if d(GHI) / dt is still lower than R_critical, steps (5) and (6) are repeated within 10 to 30 seconds, and repeated 1 to 3 times.

[0016] The beneficial effects of this invention are as follows: By pre-establishing a graphitization health index model, ultrasonic characteristic parameters are continuously collected throughout the solidification process of the casting, and GHI(t) and its first derivative d(GHI) / dt are calculated in real time. d(GHI) / dt is used to identify and provide multi-level warnings for inoculation decline, overcoming the technical limitation of traditional static inoculation treatment which cannot detect graphitization decline in the later stages of solidification. When d(GHI) / dt reaches the warning condition, a fixed-point pulse inoculation program is immediately initiated without conditions. High-pressure pulse injection of nano-level inoculators rapidly replenishes the nucleation cores, and simultaneously, induction heating or resistance heating is used to locally and precisely heat the declining area to improve the local temperature field. The synergistic effect of these two methods effectively inhibits the formation of anti-white cast iron cementite and restores the graphitization capacity of local tissues that have shown signs of decline. After intervention, d(GHI) / dt is continuously monitored. If it does not recover, the intervention is repeated and iterative compensation is performed until the graphitization state returns to normal. This invention effectively suppresses the white cast iron defect in the thick part of the brake bracket, significantly improves the uniformity and toughness of the casting structure, reduces the risk of brittle fracture caused by white cast iron and the scrap rate of subsequent processing, and has a high degree of automation, rapid response and strong adaptability. Attached Figure Description

[0017] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0018] Figure 1 This is a general flow chart of the overall smelting process of the present invention; Figure 2 This is the closed-loop control logic diagram of the present invention; Figure 3 This is a flowchart of the multi-level early warning and intervention process of the present invention. Detailed Implementation

[0019] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided.

[0020] Please see Figures 1 to 3 This invention provides a smelting process for suppressing the white-line defect in passenger vehicle brake brackets. The specific steps are as follows.

[0021] (1) Batching and smelting: Low-sulfur scrap steel, recycled materials, and stamping offcuts are selected as the metal charge, while low-sulfur recarburizing agents and silicon carbide are used as carbon and silicon increasing materials. The proportionally proportioned charge is added to a medium-frequency induction furnace for melting, with the melting temperature controlled between 1460℃ and 1520℃. Within this temperature range, the charge can fully melt and form homogeneous molten iron. During the melting process, the chemical composition of the original molten iron must be controlled to meet the requirements of subsequent spheroidizing and inoculation treatments.

[0022] As a preferred option, the chemical composition of the molten iron is controlled by mass percentage as follows: C 3.6%~3.8%, Si 1.4%~1.7%, Mn 0.15%~0.25%, P≤0.04%, S≤0.015%; the content of anti-graphitizing elements during batching is controlled by mass percentage as follows: Cr≤0.05%, V≤0.03%, Sn≤0.01%, Sb≤0.005%, Te≤0.003%. By controlling the composition as described above, the segregation tendency of anti-graphitizing elements can be reduced from the source, creating favorable conditions for subsequent graphitization.

[0023] (2) Establish a graphitization health index model in advance: Before actual casting production, it is necessary to establish a quantitative correspondence between ultrasonic characteristic parameters and graphitization degree during the solidification process of ductile iron through standard tests, and define the graphitization health index GHI accordingly.

[0024] The specific operating procedure for the standard test is as follows: A standard ductile iron sample of the same material as the target casting is prepared. During the sample solidification process, ultrasonic characteristic parameters such as longitudinal wave velocity, ultrasonic attenuation coefficient, and ultrasonic nonlinear coefficient are continuously collected at fixed time intervals, and temperature field data of the sample is collected simultaneously. After the sample solidifies, metallographic analysis is used to obtain the number, diameter, and nodularity of graphite spheres at each time point. A quantitative relationship model between ultrasonic characteristic parameters and the degree of graphitization is established through regression analysis.

[0025] As a preferred option, the Graphitized Health Index (GHI) is defined as follows: ,in To measure the longitudinal wave velocity of ultrasound. The standard speed of sound in a fully graphitized state. To measure the ultrasonic attenuation coefficient, The standard attenuation coefficient is the one used in the fully graphitized state. To measure the ultrasonic nonlinear coefficient, The standard nonlinear coefficients are those in the fully graphitized state. , , The weighting coefficients and 1. As a further optimization, the weighting coefficient Take 0.5, Take 0.3, Take 0.2, the standard speed of sound The value ranges from 5680 to 5820 m / s.

[0026] The graphitization health index (GHI) ranges from 0 to 1, with a GHI value closer to 1 indicating a better degree of graphitization. During solidification, the GHI value gradually increases as graphite precipitates and grows; when incubation decline occurs, the graphitization process is hindered, and the rate of increase in the GHI value slows down or even decreases.

[0027] (3) Continuous dynamic monitoring: After the casting is completed, an ultrasonic probe array is placed at the predetermined monitoring position of the casting mold. Preferably, the ultrasonic probe array is arranged with at least 3 monitoring points in the thick and hot section of the brake bracket crossbeam, which are labeled as monitoring point 1, monitoring point 2, and monitoring point 3, in order to achieve key monitoring of critical areas.

[0028] The ultrasonic probe array begins to continuously acquire ultrasonic characteristic parameters at each monitoring point. The acquired parameters include ultrasonic longitudinal wave velocity, ultrasonic attenuation coefficient, and ultrasonic nonlinear coefficient. The acquired data is transmitted to the signal processing module in real time for calculation and processing. The signal processing module first calculates the graphitization health index GHI(t) at each time point using the ultrasonic characteristic parameters acquired at each monitoring point based on the graphitization health index model established in step (2), where t represents time; then, it calculates the first derivative of GHI(t) with respect to time, d(GHI) / dt, in real time as the trend of GHI(t). Preferably, the frequency of continuous acquisition is 0.5 to 2 seconds / time.

[0029] The physical meaning of d(GHI) / dt is the rate of change of the graphitization health index. When d(GHI) / dt is positive and has a large absolute value, it indicates that the graphitization process is proceeding normally and the number of graphite spheres is continuously increasing; when d(GHI) / dt decreases to close to zero or becomes negative, it indicates that the graphitization process is hindered and a decline is occurring.

[0030] (4) Identification and early warning of declining trends in fertility: According to the process requirements, a decay warning threshold is preset, and the d(GHI) / dt calculated in real time in step (3) is compared with the decay warning threshold. When d(GHI) / dt reaches the warning condition, it is determined that the gestation decay is occurring, and the system automatically triggers the gestation decay warning signal.

[0031] Preferably, the degradation warning threshold is defined as R_critical, with a value ranging from -0.005 to -0.015 per second. A warning signal is triggered when d(GHI) / dt is less than R_critical. R_critical is negative, and its absolute value reflects the warning sensitivity: when R_critical is -0.005 per second, a warning is triggered when d(GHI) / dt is less than -0.005 per second, indicating high sensitivity; when R_critical is -0.015 per second, a warning is triggered only when d(GHI) / dt is less than -0.015 per second, indicating low sensitivity. Users can select an appropriate threshold within this range based on the specific quality requirements of the product and the metallurgical state of the molten iron.

[0032] As a further optimization, a multi-level early warning mechanism can be established, setting different early warning levels according to different ranges of d(GHI) / dt. Specifically, a Level 1 early warning is triggered when -0.015 sec ≤ d(GHI) / dt < -0.010 sec, indicating a slight tendency for molten iron to decline; a Level 2 early warning is triggered when -0.025 sec ≤ d(GHI) / dt < -0.015 sec, indicating a moderate tendency for molten iron to decline; and a Level 3 early warning is triggered when d(GHI) / dt < -0.025 sec, indicating a severe tendency for molten iron to decline. The higher the early warning level, the more severe the decline, requiring stronger intervention measures.

[0033] (5) Rescue-type pulse pregnancy decision: When step (4) triggers the incubation decline warning signal, the control system immediately and unconditionally starts the fixed-point pulse incubation program. The term "unconditional" means that the decision does not depend on the current solid fraction, the temperature at the monitoring point, or the stage of the solidification process.

[0034] Traditional thinking holds that inoculation must be completed in the early stages of solidification; once the molten iron enters the semi-solid stage, inoculation treatment can no longer be effectively carried out. This invention breaks this technical bias. Upon detecting signs of fading, intervention is immediately initiated regardless of the current solid fraction range, the temperature level at the monitoring point, or the stage of solidification. The time interval from warning triggering to actuator activation is controlled within 1 second, ensuring immediate intervention. The actuator includes a high-pressure injection device and a heating device arranged on the mold, wherein the high-pressure injection device sprays towards the casting area corresponding to the specific monitoring point where fading is detected.

[0035] (6) Synergistic execution of rescue-type pulse incubation and synchronous reheating: Upon triggering of the warning, a nano-sized inoculant is sprayed onto the monitored fading area using a high-pressure spraying device mounted on the mold. Preferably, the spraying pressure is controlled between 5 and 20 MPa, the spray volume is controlled at 0.05% to 0.15% of the molten iron mass in that area, and the spraying method is pulsed. The pulsed spraying parameters are: spraying duration 0.5 to 2 seconds, interval 1 to 3 seconds, repeated 2 to 5 times. The inoculant is a nano-sized inoculant, preferably a zirconium-containing potent anti-fading inoculant or a rare earth-containing potent anti-fading inoculant, with a particle size not exceeding 10 μm.

[0036] Simultaneously with the pulse inoculation, a heating device arranged on the mold provides localized, targeted heating to the area. Preferably, this localized, targeted heating raises the local temperature of the spraying area by 20 to 80°C, with the heating duration synchronized with the pulse inoculation, ranging from 2 to 10 seconds. The heating device is either an induction heating device or a resistance heating device, with a heating power of 5 to 20 kW.

[0037] The synergistic execution of heat replenishment and pulsed inoculation constitutes one of the core innovations of this invention: the purpose of heat replenishment is to locally improve the fluidity of the melt, ensuring that the high-pressure injected nanoscale inoculant can effectively diffuse and be captured by the growing solid tissue. Heat replenishment itself does not directly solve the white cast problem, but rather creates conditions for successful rescue inoculation, enabling the inoculant to effectively supplement the nucleation core even under semi-solid conditions. This causal synergistic effect differs from the simple superposition of detection, heating, and inoculation functions in existing technologies.

[0038] (7) Evaluation and iteration of intervention effects: After the pulse incubation and reheating are completed, the d(GHI) / dt ratio in the affected area is monitored to assess the intervention effect. If d(GHI) / dt rises to a level greater than or equal to R_critical, the intervention is considered successful, the graphitization state has returned to normal, and the system returns to normal monitoring mode. If d(GHI) / dt remains below R_critical, the intervention effect is considered insufficient, and steps (5) and (6) are repeated within 10 to 30 seconds. The number of repetitions is 1 to 3. After each repetition, it is reassessed whether d(GHI) / dt rises to a level greater than or equal to R_critical. If it does, the repetition is stopped and normal monitoring is resumed. If d(GHI) / dt remains below R_critical after 3 repetitions, the system issues an alarm signal, prompting manual intervention. Through the above closed-loop feedback mechanism, continuous tracking and precise intervention of incubation decline are achieved until the graphitization state is fully restored.

[0039] (8) After the casting has solidified, it is cooled, unpacked, and post-processed: After solidification, the casting is allowed to cool naturally in the sand mold until its temperature does not exceed 300℃ before being unpacked. Upon unpacking, hydraulic clamps are used to separate the casting from the gating system on the production line. A special anti-impact transfer bucket is used to catch the casting, ensuring the bucket's height does not exceed the bucket's lug height. The transfer bucket containing the casting is then transported to the shot blasting process, where a suspended shot blasting machine is used. After shot blasting, the casting surface has a uniform silver-gray color, and the lettering on the surface is complete and clear. After shot blasting, a special trimming die is used to remove the gate and excess flash. Castings that pass inspection are then packed and stored.

[0040] Example 1 This embodiment provides a specific implementation method for producing QT550-6 material passenger vehicle brake brackets using the above-described smelting process.

[0041] (1) Batching and Smelting: Low-sulfur scrap steel, recycled materials, and stamping scrap are selected as metal furnace materials. The sulfur content of low-sulfur scrap steel is no more than 0.015%, and the chromium content is no more than 0.05%. The batching mass percentage is: scrap steel 45%, recycled materials 35%, stamping scrap 17.2%, low-nitrogen carbon raiser 2.0%, and silicon carbide 0.8%. The nitrogen content of the low-nitrogen carbon raiser is no more than 0.02%, the carbon content is no less than 98%, the sulfur content is no more than 0.03%, and the particle size is 1 to 5 mm. The silicon carbide content is 90%, and the particle size is 1 to 5 mm. The target composition of the raw molten iron is controlled as follows: carbon content 3.7%, silicon content 1.6%, manganese content 0.20%, phosphorus content 0.025%, and sulfur content 0.012%. The content of anti-graphitizing elements is controlled as follows: chromium 0.04%, vanadium 0.02%, tin 0.008%, antimony 0.003%, and tellurium 0.001%. The prepared charge is added to a medium-frequency induction furnace for melting at a melting temperature of 1480℃.

[0042] (2) Establishing a pre-defined graphitization health index model: Standard samples were prepared using the same QT550-6 material as the target casting. During the solidification process of the samples, the longitudinal wave velocity, attenuation coefficient, and nonlinear coefficient of ultrasonic waves were continuously collected at 1-second intervals. Temperature field data of the samples were collected simultaneously, and the number of graphite spheres and the spheroidization rate at each time point were obtained through metallographic analysis after solidification. A GHI model was established through regression analysis to determine... =5750 m / s, take =0.5、 =0.3、 =0.2.

[0043] (3) Continuous dynamic monitoring: Four ultrasonic probe arrays are arranged at the thick and hot section of the crossbeam of the brake bracket mold. Monitoring is started immediately after the casting is completed, with a sampling frequency of 1 time / second. GHI(t) and d(GHI) / dt at each monitoring point are calculated in real time.

[0044] (4) Identification and early warning of recession trend: Set the recession warning threshold R_critical = -0.010 per second. 45 seconds after pouring, the calculated value of d(GHI) / dt at monitoring point 2 is -0.013 per second, which is lower than the threshold, triggering the early warning signal.

[0045] (5) Rescue pulse incubation decision: Within 0.8 seconds after the warning is triggered, the control system starts the fixed-point pulse incubation program.

[0046] (6) Synergistic execution of rescue-type pulse inoculation and synchronous heat replenishment: A zirconium-containing potent inoculant is injected into the area corresponding to monitoring point 2 through a high-pressure injection device. The particle size of the inoculant is no greater than 8μm, the injection pressure is 12MPa, and the injection amount is 0.10% of the mass of molten iron in the area. The pulse injection parameters are: injection duration of 1 second, interval of 2 seconds, repeated 3 times. The induction heating device is started simultaneously to raise the local temperature of the injection area by about 50°C for 6 seconds, with a heat replenishment power of 10kW.

[0047] (7) Intervention effect evaluation and iteration: After the intervention, continue to monitor d(GHI) / dt in this area. Before the intervention, d(GHI) / dt was -0.013 per second. Within 10 seconds after the intervention, d(GHI) / dt rose to -0.006 per second. This value is greater than R_critical, so the rescue was deemed successful and normal monitoring was resumed.

[0048] (8) After the casting has solidified, it is cooled, unpacked and post-processed: The casting is naturally cooled in the sand mold to no more than 300°C and then unpacked. The casting is separated from the gating system using hydraulic pliers, the casting is picked up using an anti-impact transfer bucket, and transported to the shot blasting process. The casting is shot blasted using a suspended shot blasting machine, and the gate and flash are removed using a special trimming mold.

[0049] The QT550-6 passenger car brake bracket produced using the process described in this embodiment has the following characteristics after testing: spheroidization level is 2, spheroidization rate is 88%, graphite size is 6, pearlite content is 65%, cementite content is not greater than 2%, Brinell hardness is 210HBW, tensile strength is 585MPa, elongation is 8.5%, and no reverse white caster defects were detected.

[0050] Example 2 The difference between this embodiment and Embodiment 1 is that at monitoring point 3, d(GHI) / dt reached -0.022 seconds after pouring, triggering a level 3 warning. Enhanced intervention was implemented: the injection pressure was increased to 18 MPa, the injection volume was increased to 0.14% of the molten iron mass in that area, and the pulse injection parameters were: injection duration 1.5 seconds, interval 1.5 seconds, repeated 4 times; the synchronous reheating temperature was increased by approximately 70°C for 8 seconds, and the reheating power was 15 kW. After the first intervention, d(GHI) / dt recovered to -0.008 seconds, returning to normal. Testing showed a spheroidization rate of 86%, a cementite content of no more than 3%, and no white cast iron defects detected.

[0051] Comparative Example The same model QT550-6 passenger car brake bracket was produced using a traditional smelting process. This process does not include ultrasonic dynamic monitoring or rescue pulse inoculation; it only uses conventional pre-furnace inoculation treatment. Testing revealed obvious white cast iron defects in the core of the bracket crossbeam, with a cementite content of 8% to 12%, a spheroidization rate of only 72%, a tensile strength of 520 MPa, and an elongation of 4.5%, failing to meet product acceptance standards. The comparison between Example 1 and the comparative example shows that this invention, by real-time sensing of the inoculation decline trend and implementing immediate closed-loop intervention, can effectively suppress the formation of white cast iron defects and significantly improve the spheroidization rate, mechanical properties, and yield of the casting.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A smelting process for suppressing the white cast defect in passenger vehicle brake brackets, characterized in that, Includes the following steps: (1) Batching and smelting: Low-sulfur scrap steel, recycled materials and stamping scrap are selected as metal furnace materials, and low-sulfur carbon raiser and silicon carbide are selected as carbon and silicon raising materials. The prepared furnace materials are added to the medium frequency induction furnace for smelting, the chemical composition of the original molten iron is controlled, and the smelting temperature is controlled at 1460~1520℃. (2) Establish a graphitization health index model in advance: Establish a quantitative correspondence between ultrasonic characteristic parameters and graphitization degree during the solidification process of ductile iron through standard tests, and define the graphitization health index GHI; (3) Continuous dynamic monitoring: After the casting is completed, the ultrasonic probe array is arranged at the predetermined monitoring position of the casting mold, the ultrasonic characteristic parameters of each monitoring point are continuously collected, the graphitization health index GHI(t) at each time is calculated in real time, where t represents time, and the first derivative of GHI(t) with respect to time d(GHI) / dt is calculated in real time as the trend of GHI(t). (4) Identification and early warning of gestational decline trend: Set a decline early warning threshold, which is defined as R_critical. When d(GHI) / dt reaches the early warning condition, a gestational decline early warning signal is triggered. (5) Rescue-type pulse incubation decision: After the warning signal is triggered, the fixed-point pulse incubation program is started immediately without conditions. The "unconditional" means that the decision does not depend on the current solid fraction, the temperature of the monitoring point, or the solidification process stage. (6) Synergistic execution of rescue pulse incubation and synchronous heat replenishment: Incubator is sprayed into the area where degradation is detected by the spraying device arranged on the mold; Simultaneously with the pulse incubation, the area is locally heated by the heating device arranged on the mold. (7) Evaluation and iteration of intervention effect: After the pulse incubation and heat replenishment are completed, continue to monitor the d(GHI) / dt of the region. If it does not recover, repeat steps (5) and (6). (8) After the casting has solidified, it is cooled, unpacked and post-processed.

2. The smelting process for suppressing the white cast defect in passenger vehicle brake brackets according to claim 1, characterized in that, The chemical composition of the raw molten iron in step (1) is as follows by mass percentage: C 3.6%~3.8%, Si 1.4%~1.7%, Mn 0.15%~0.25%, P≤0.04%, S≤0.015%; the content of anti-graphitizing elements controlled during batching is as follows by mass percentage: Cr≤0.05%, V≤0.03%, Sn≤0.01%, Sb≤0.005%, Te≤0.003%.

3. The smelting process for suppressing the white cast defect in passenger vehicle brake brackets according to claim 1, characterized in that, The definition of GHI mentioned in step (2) is: ,in To measure the longitudinal wave velocity of ultrasound. The standard speed of sound in a fully graphitized state. To measure the ultrasonic attenuation coefficient, The standard attenuation coefficient is the one used in the fully graphitized state. To measure the ultrasonic nonlinear coefficient, The standard nonlinear coefficients are those in the fully graphitized state. , , The weighting coefficients and 1.

4. The smelting process for suppressing the white cast defect in passenger vehicle brake brackets according to claim 1, characterized in that, The frequency of continuous acquisition in step (3) is 0.5~2 seconds / time.

5. The smelting process for suppressing the white cast defect in passenger vehicle brake brackets according to claim 1, characterized in that, The decay warning threshold mentioned in step (4) is R_critical, and the value range of R_critical is -0.005 to -0.015 / s. When d(GHI) / dt < R_critical, the warning signal is triggered.

6. The smelting process for suppressing the white cast defect in passenger vehicle brake brackets according to claim 5, characterized in that, Establish a multi-level early warning mechanism: trigger a level 1 early warning when -0.015≤d(GHI) / dt<-0.010, trigger a level 2 early warning when -0.025≤d(GHI) / dt<-0.015, and trigger a level 3 early warning when d(GHI) / dt<-0.

025.

7. The smelting process for suppressing the white cast defect in passenger vehicle brake brackets according to claim 1, characterized in that, The spraying device mentioned in step (6) is a high-pressure spraying device with a spraying pressure of 5~20MPa, a spraying amount of 0.05%~0.15% of the mass of molten iron in the area, and a pulse spraying method; the inoculant is a nano-sized inoculant with a particle size ≤10μm.

8. The smelting process for suppressing the white cast defect in passenger vehicle brake brackets according to claim 7, characterized in that, The pulsed spray parameters are as follows: spray duration 0.5~2 seconds, interval 1~3 seconds, repeated 2~5 times.

9. The smelting process for suppressing the white cast defect in passenger vehicle brake brackets according to claim 1, characterized in that, The localized point heating in step (6) raises the local temperature of the spray area by 20~80℃, and the heating duration is synchronized with the pulse incubation, which is 2~10 seconds; the heating device is an induction heating device or a resistance heating device, and the heating power is 5~20kW.

10. The smelting process for suppressing the white cast defect in passenger vehicle brake brackets according to claim 1, characterized in that, If d(GHI) / dt rises to ≥R_critical in step (7), normal monitoring is resumed. If d(GHI) / dt is still below R_critical, steps (5) and (6) are repeated within 10 to 30 seconds, and repeated 1 to 3 times.

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