A hot forging and residual heat quenching process for mining anchors

Abstract

This invention discloses a hot forging and residual heat quenching process for mining anchors, relating to the field of anchor manufacturing technology. The process includes: S1, billet pre-forming and segmented heating; S2, multiphase deformation hot forging; S3, forced uniform pre-cooling; S4, controlled residual heat quenching; and S5, heat conduction self-tempering and supplementary tempering. This invention achieves refined microstructure and improved performance of mining anchors through gradient heating, forging in the non-recrystallized zone, and staged cooling. Precise temperature control combined with large deformation accumulates lattice distortion energy. Gas-liquid pre-cooling and composite medium quenching optimize the cooling path, effectively breaking the vapor film and reducing thermal stress. Combined with residual heat self-tempering, residual stress is eliminated, enabling the product to maintain high hardness while possessing excellent impact toughness, thus solving the cracking problem.

Description

Technical Field

[0001] This invention relates to the field of anchor manufacturing technology, specifically to a hot forging and residual heat quenching process for mining anchors. Background Technology

[0002] Currently, the production of mining anchors mainly uses medium-carbon low-alloy steel as raw material. The required mechanical properties are obtained through heating, forging, and subsequent heat treatment processes. The conventional process usually involves heating the bar to a predetermined temperature and then forging it. The bar is then quenched and cooled using residual heat or reheating. Subsequently, it is tempered at high temperature to adjust the hardness and toughness. In industrial production, induction heating and continuous quenching tanks are often used for batch processing to improve efficiency and meet the needs of large-scale support.

[0003] However, in related technologies, due to the large diameter and abrupt shape of the anchor rod, traditional single heating methods cannot guarantee the uniformity of cross-sectional temperature, easily leading to uneven heat penetration or surface overheating. During the subsequent cooling process, conventional immersion quenching often hinders rapid heat dissipation due to the formation of a stable vapor film on the workpiece surface, resulting in a cooling rate insufficient to meet the requirements of martensitic transformation, thus causing soft spots or coarse microstructure. Furthermore, due to the lack of precise intervention in the cooling path, the temperature difference between the workpiece surface and core is too large, easily inducing high thermal and structural stresses during phase transformation, leading to the initiation of microcracks or even macroscopic cracking. This makes it difficult for the final product's impact toughness to consistently meet the safety support standards for deep mines. Summary of the Invention

[0004] The purpose of this invention is to provide a hot forging and residual heat quenching process for mining anchors, which solves the problems existing in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides a hot forging and residual heat quenching process for mining anchors, comprising the following steps:

[0006] S1. Billet prefabrication and segmented heating: After the medium carbon low alloy steel bar is cut, the surface is sandblasted to remove rust, and then it is sent into the induction heating furnace for segmented heating. First, it is heated to the preheating temperature at the first frequency, and then rapidly heated to the austenitizing temperature at the second frequency. It is held until the core is heated to obtain a hot billet.

[0007] S2. Multiphase deformation hot forging: The hot billet is transferred to a press for multi-pass forging, including primary forging and final forging; the primary forging breaks the original grains, the final forging temperature is controlled in the austenite non-recrystallization temperature range, and the single deformation amount of the final forging is controlled above the critical deformation amount. The distortion energy of the austenite grains is accumulated by the large deformation amount to obtain the forged semi-finished product.

[0008] S3, forced air-mist pre-cooling: The forging semi-finished product is immediately subjected to forced air-mist pre-cooling or isothermal residence treatment. By controlling the air volume and the flux of atomized droplets, the surface and core temperatures of the forging semi-finished product are reduced synchronously and converged to the quenching start temperature. The residence time is controlled within the preset time range to obtain the pre-cooled anchor.

[0009] S4. Controlled residual heat quenching: The pre-cooled anchor is quickly immersed in a self-made composite quenching medium for immersion cooling. During the cooling process, mechanical stirring or ultrasonic disturbance is applied to break the vapor film. When the surface temperature of the pre-cooled anchor drops to the outlet temperature range near the martensitic transformation termination temperature, the anchor is quickly removed from the composite quenching medium to obtain the quenched anchor.

[0010] S5. Heat conduction self-tempering and supplementary tempering: After the quenched anchor is removed from the liquid, it is placed in a heat preservation box and self-tempered by conducting the residual heat in the core to the surface. After the overall temperature is uniform, it is sent to a tempering furnace for supplementary tempering and stress relief treatment at a preset tempering temperature to obtain the finished mining anchor.

[0011] Preferably, in step S1, the temperature is 1100-1200℃, the holding time is 30-60s, the first frequency is 1-2.5kHz, and the second frequency is 4-8kHz; the temperature difference between the surface and the core is controlled to be ≤15℃ by gradient heating.

[0012] Preferably, in step S2, the final forging temperature is 850-950℃, and the single deformation amount is 30-45%; the final forging process is carried out in the non-recrystallized region of austenite to preserve lattice distortion energy.

[0013] Preferably, in step S3, the quenching starting temperature is 780-820℃ and the dwell time is 5-15s; the forced precooling uses a mixture of compressed air and atomized water, with atomized particles having a diameter of 20-50μm, which quickly removes the surface overheated heat through phase transformation heat absorption and inhibits austenite grain growth.

[0014] Preferably, in step S4, the outlet temperature is 180-240℃; the mechanical stirring speed is 200-400 r / min; and the liquid temperature of the composite quenching medium is controlled at 30-50℃.

[0015] Preferably, in step S5, the self-tempering time is 10-20 min, the supplementary tempering temperature is 450-550℃, and the supplementary tempering time is 60-90 min; the finished mining anchor has a grain size ≥ 8, a surface hardness of 45-50 HRC, and an impact energy Aku ≥ 50 J.

[0016] Preferably, the composite quenching medium in step S4 comprises, by weight, the following components: polyalkylene glycol stock solution: 8-12 parts; modified nano thermal conductive agent: 0.5-1.5 parts; film-forming aid: 1-2 parts; pH adjuster: 0.2-0.5 parts; bactericide and defoamer: 0.1-0.3 parts; deionized water: 80-90 parts.

[0017] Preferably, it includes the following steps:

[0018] A1. Preparation of modified nano-thermal conductive agent: Nano-silica was dispersed in anhydrous ethanol at a mass-to-volume ratio of 1 g:(10-20) mL. 3-glycidyl etheroxypropyltrimethoxysilane was added under ultrasonic dispersion conditions at a mass ratio of 1:(0.1-0.3). Grafting reaction was carried out at a temperature of 50-60℃ for 2-4 hours. After the reaction was completed, the mixture was centrifuged and the precipitate was dried under vacuum to obtain the modified nano-thermal conductive agent.

[0019] A2. Base solution preparation: Heat deionized water to 35-40℃, and slowly add polyalkylene glycol stock solution while mechanically stirring at a speed of 300-500r / min until a homogeneous and transparent solution is formed.

[0020] A3. Functional compounding: Add film-forming aid, pH adjuster and modified nano thermal conductive agent prepared in step A1 to the base liquid in sequence, increase the stirring speed to 800-1000 r / min for high shear emulsification and dispersion, and maintain for 20-30 min;

[0021] A4. Stabilization treatment: Cool to room temperature, add bactericidal and defoaming agent, and let stand for 12-24 hours to defoam, thus obtaining the composite quenching medium.

[0022] Preferably, the film-forming aid is a mixture of sodium polyacrylate and sodium benzoate in a mass ratio of 1:1; the pH adjuster is triethanolamine, which adjusts the pH of the medium to 9.0-10.5.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] By using gradient heating and deformation control in specific temperature zones, the problem of uneven internal and external temperatures in large cross-section workpieces was effectively solved. By utilizing the difference in penetration depth of currents at different frequencies, the core and surface temperatures were simultaneously increased, providing a uniform thermodynamic state for subsequent processing. Furthermore, large deformation forging was performed in regions where austenite had not recrystallized, forcing the accumulation of high-density distortion energy within the crystal lattice. These distortion sites became preferential nucleation points for new structures during phase transformation, thereby achieving grain refinement and matrix strength enhancement without reducing plasticity, and ensuring the compactness of the material's internal structure.

[0025] A cooling strategy combining gas-liquid two-phase flow precooling and composite medium immersion was adopted to optimize the heat exchange process of the workpiece. During the precooling stage, phase change endothermics acted as a thermal buffer, converging the temperature gradient between the workpiece surface and core to a reasonable range and reducing thermal shock upon immersion. During the immersion cooling stage, the micro- and nano-particles in the medium altered the interfacial heat transfer kinetics, rapidly disrupting the vapor film hindering heat dissipation in high-temperature regions. This allowed the cooling process to quickly enter the boiling heat exchange stage, ensuring a uniform cooling rate even on complex, irregularly shaped surfaces and effectively mitigating the risk of quenching cracks caused by poor localized heat dissipation.

[0026] A heat conduction self-tempering process is set up to make full use of the residual heat in the core of the workpiece to perform in-situ heat treatment on the surface. This can eliminate the peak stress generated by phase transformation immediately after quenching and prevent the generation of delayed cracks. The entire process chain organically combines hot working, temperature-controlled cooling and stress release, so that the final anchor can obtain high surface hardness while maintaining excellent impact energy reserve, achieving a good match between high strength and high toughness, and extending the service life of the product in complex geological environments. Detailed Implementation

[0027] Example 1

[0028] This embodiment provides a hot forging and residual heat quenching process for mining anchors, as a preferred embodiment of the present invention;

[0029] The process includes the following steps: S1, billet pre-fabrication and segmented heating: After the medium carbon low alloy steel bar is cut, the surface is sandblasted to remove rust, and then it is sent to an induction heating furnace for segmented heating. First, it is heated to the preheating temperature at a first frequency, and then rapidly heated to the austenitizing temperature at a second frequency. It is held at the temperature until the core is fully heated to obtain a hot billet. In this step, 40Cr steel is selected as the base material. In order to solve the problem of surface overheating or core underheating caused by traditional single-frequency heating, this invention introduces a cross-sectional temperature gradient control technology based on the skin effect. The first frequency is set to a lower frequency band, and the core temperature is preferentially increased by utilizing the deeper current penetration depth. The second frequency is set to a higher frequency band, and the surface temperature is rapidly increased to match the core heat, thereby achieving synchronous uniformity of internal and external temperatures. This dual-frequency coupled heating strategy eliminates the common phenomenon of hot skin and cold core in large cross-section workpieces.

[0030] In this embodiment, in step S1, the temperature is 1100-1200℃, and the holding time is 30-60s; the first frequency is 1-2.5kHz, and the second frequency is 4-8kHz; the temperature difference between the surface and the core is controlled to be ≤15℃ through gradient heating. Specifically, in this embodiment, the heating temperature is set to 1100℃, the holding time is 60s, the first frequency is precisely set to 1kHz, and the second frequency is 4kHz. This gradient heating strategy not only strictly controls the temperature difference within 15℃, effectively avoiding the initiation of microcracks caused by thermal stress, but also ensures that the austenitizing temperature of 1100℃ fully dissolves the carbides, laying a material basis for obtaining a uniform martensitic structure in the future.

[0031] S2. Multiphase deformation hot forging: The hot billet is transferred to a press for multi-pass forging, including primary forging and final forging. The primary forging breaks down the original grains, and the final forging temperature is controlled within the austenite non-recrystallization temperature range. The single deformation amount of the final forging is controlled above the critical deformation amount. The distortion energy of the austenite grains is accumulated by using the large deformation amount to obtain the forged semi-finished product. This step is the core of achieving deformation strengthening. After the hot billet is transferred to the press, the primary forging quickly breaks down the original coarse dendrites. The key is the final forging stage, which is strictly limited to the austenite non-recrystallization region. The hardening-recovery competition mechanism of the lattice is used to suppress the occurrence of recrystallization.

[0032] For the 40Cr material selected in this embodiment, the critical deformation threshold is set to 15% in the temperature range of 850-950℃. In actual operation, the single deformation amount is controlled to 30% to ensure that the critical value is completely exceeded to stimulate dynamic recovery and dislocation multiplication in the lattice.

[0033] In this embodiment, in step S2, the final forging temperature is 850-950℃, and the single deformation amount is 30-45%. The final forging process is carried out in the non-recrystallized region of austenite to retain lattice distortion energy. Specifically, the final forging temperature is controlled at 850℃, and the single deformation amount is controlled at 30%. Under these low-temperature and large-deformation conditions, the austenite grains are significantly elongated, the grain boundary surface area is greatly increased, and high-density dislocation entanglements and subgrain boundaries are introduced into the grains. These high-energy defect sites become preferential nucleation sites for martensite in the subsequent phase transformation process, thereby significantly reducing the grain size of the final product through the deformation-induced refinement mechanism.

[0034] S3. Forced Pre-cooling with Mist: Forced pre-cooling with mist or isothermal residence treatment is immediately applied to the forging semi-finished product. By controlling the air volume and the flux of atomized droplets, the surface and core temperatures of the forging semi-finished product are reduced synchronously and converged to the quenching initiation temperature. The residence time is controlled within a preset time range to obtain the pre-cooled anchor. This step is designed as a heat buffer stage. Traditional direct quenching is prone to local overheating due to the forging heat effect. This step utilizes the latent heat of phase change of the gas-liquid two-phase flow to perform peak-shaving cooling on the surface of the workpiece.

[0035] In this embodiment, in step S3, the quenching start temperature is 780-820℃, and the dwell time is 5-15s; the forced pre-cooling uses a mixture of compressed air and atomized water, with atomized particles of 20-50μm in diameter. Through phase change heat absorption, it quickly removes the surface overheating heat and inhibits austenite grain growth. Specifically, the quenching start temperature is controlled to converge to 780℃, and the dwell time is precisely controlled at 15s; a mixture of atomized particles with a diameter of 20μm is used. These micron-sized droplets vaporize instantly upon contact with the high-temperature surface, removing a large amount of heat, allowing the heat generated by plastic deformation to dissipate rapidly. This not only inhibits the secondary growth of austenite grains at high temperatures, but more importantly, it reduces the temperature gradient of the cross-section through temperature control delay, thus preparing the thermodynamics for reducing the thermal stress of subsequent quenching.

[0036] Specifically, the forced pre-cooling device adopts a ring-shaped spray structure, with compressed air pressure set at 0.4-0.6 MPa, atomized water pressure set at 0.2-0.4 MPa, and air-to-water volume ratio controlled at (200-300):1. The high-pressure gas imparts extremely high kinetic energy to the atomized droplets, enabling them to penetrate the thermal boundary layer of the workpiece surface and achieve efficient heat absorption through the instantaneous latent heat of vaporization of the droplets.

[0037] S4. Controlled residual heat quenching: The pre-cooled anchor is rapidly immersed in a self-made composite quenching medium for immersion cooling. During the cooling process, mechanical stirring or ultrasonic disturbance is applied to break the vapor film. When the surface temperature of the pre-cooled anchor drops to the outlet temperature range near the martensitic transformation termination temperature, the anchor is quickly removed from the composite quenching medium to obtain the quenched anchor. This step uses a specific medium and flow field control to solve the problem of uneven cooling caused by the complex shape of mining anchors. The turbulence introduced by mechanical stirring forcibly breaks the Leiden Frost vapor film on the surface of the workpiece, so that the cooling process quickly enters the boiling heat transfer stage.

[0038] In this embodiment, in step S4, the outlet temperature is 180-240℃; the mechanical stirring speed is 200-400 r / min; the liquid temperature of the composite quenching medium is controlled at 30-50℃, and the specific parameters are set as follows: medium liquid temperature 30℃, mechanical stirring speed 200 r / min; the liquid is rapidly discharged when the surface temperature drops to 180℃.

[0039] The composite quenching medium in step S4, by weight, includes the following components: polyalkylene glycol stock solution: 8-12 parts; modified nano-thermal conductive agent: 0.5-1.5 parts; film-forming aid: 1-2 parts; pH adjuster: 0.2-0.5 parts; bactericide and defoamer: 0.1-0.3 parts; deionized water: 80-90 parts. The specific formulation in this embodiment is as follows: 8 parts of polyalkylene glycol stock solution, selected from ethylene oxide-propylene oxide random copolymer with a weight-average molecular weight of 15,000-20,000 and a cloud point temperature of 60-65℃; 0.5 parts of modified nano-thermal conductive agent; 1 part of film-forming aid; 0.2 parts of pH adjuster; 0.1 parts of bactericide and defoamer; and 90 parts of deionized water. The sodium polyacrylate in the film-forming aid is selected from industrial-grade products with a weight-average molecular weight of 3 million-5 million to ensure the formation of a sufficiently strong heat-insulating film at high temperatures.

[0040] In the specific preparation, fumed silica nanoparticles with an average particle size of 20-30 nm were selected. The ratio of nano-silica to anhydrous ethanol was 1 g:10 mL, and the ratio of silane coupling agent was 1:0.1. The reaction was carried out at 50 °C for 4 hours. After the reaction, the mixture was centrifuged at 4000 r / min for 15 min. The resulting precipitate was dried at 60 °C and -0.08 MPa vacuum for 12 hours. After air jet milling and sieving, the modified nano-thermal conductive agent was obtained. The water temperature was 35 °C when preparing the base solution. The shear rate was 1000 r / min when functionalizing the compound.

[0041] The film-forming aid is a mixture of sodium polyacrylate and sodium benzoate in a mass ratio of 1:1; the pH adjuster is triethanolamine, which adjusts the pH of the medium to 9.0-10.5. In this embodiment, the pH is adjusted to 9.0. This composite medium utilizes the micro-disturbance effect of nanoparticles to break the gas film in the high-temperature zone, while in the low-temperature martensitic transformation zone, the polyalkylene glycol polymer is reverse-soluble and precipitates on the workpiece surface to form a heat-insulating film, which significantly reduces the cooling rate. This ideal cooling characteristic of rapid cooling at high temperatures and slow cooling at low temperatures effectively avoids quenching cracks.

[0042] In step S4, to ensure a uniform flow field, a guide tube and a propeller are installed inside the composite quenching tank, causing the medium to circulate from bottom to top with a flow velocity controlled at 0.5-1.0 m / s, ensuring that the relative flow velocity between the anchor surface and the medium is consistent throughout. Simultaneously, if ultrasonic disturbance is used, ultrasonic transducers are evenly distributed on the sidewalls of the tank, with a power density of 0.5-1.0 W / cm² and a frequency of 20-28 kHz, utilizing the micro-jets generated by cavitation to peel away the vapor film adhering to the workpiece surface.

[0043] The modified nano-thermal conductive agent added in this invention exerts a dual mechanism of microscopic thermal disturbance and enhanced interfacial heat transfer during the quenching process:

[0044] Disruption of the vapor film: Nano-silica particles undergo intense Brownian motion in high-temperature media. Due to the grafting of silane coupling agents, they have good dispersion stability. These high-speed solid particles continuously collide with the gas-liquid interface, puncturing the vapor film wrapped around the workpiece surface. This causes the cooling process to change from film boiling to nucleation boiling in advance, significantly improving the cooling rate of the high-temperature zone.

[0045] Enhanced dynamic thermal conductivity: The thermal conductivity of nanofluids is significantly higher than that of ordinary base fluids. The micro-convection formed by particles further enhances the heat transfer efficiency inside the medium. Combined with the reverse solubility film-forming properties of polyalkylene glycol polymers in the low-temperature region, an ideal quenching curve is achieved: high-temperature rapid cooling to avoid pearlite transformation nose tip, and low-temperature slow cooling to prevent martensitic phase transformation cracking.

[0046] S5. Heat conduction self-tempering and supplementary tempering: After the quenched anchor is removed from the liquid, it is placed in a heat preservation box and the residual heat in the core is conducted to the surface for self-tempering. After the overall temperature is uniform, it is sent to a tempering furnace for supplementary tempering and stress relief treatment at a preset tempering temperature to obtain the finished mining anchor. This step makes full use of the heat that has not been completely dissipated in the core of the workpiece.

[0047] In this embodiment, in step S5, the self-tempering time is 10-20 min, the supplementary tempering temperature is 450-550℃, and the supplementary tempering time is 60-90 min; the finished mining anchor after treatment has a grain size ≥ 8, a surface hardness of 45-50 HRC, and an impact energy Aku ≥ 50 J. Specifically, the self-tempering is performed for 10 min, the supplementary tempering temperature is 450℃, and the time is 90 min; the final finished product has a grain size of 8, a surface hardness of 45 HRC, and an impact energy of 52 J; self-tempering The process utilizes the residual heat in the core to perform in-situ tempering of the surface martensite. Immediately after the martensitic transformation is completed, it promotes the diffusion of carbon atoms and the dispersion precipitation of carbides, effectively eliminating the peak structural stress generated by the phase transformation and preventing the generation of delayed cracks. The inner liner of the insulated box uses aluminum silicate fiber cotton as the insulation layer, with a thermal conductivity ≤0.035W / (m·K). The box structure is semi-enclosed, using the heat released by the workpiece itself to maintain a slightly positive pressure environment, reducing convective heat dissipation and ensuring the temperature uniformity of the self-tempering process.

[0048] Example 2

[0049] This embodiment provides a hot forging and residual heat quenching process for mining anchors, which strictly follows the technical solution, but the process parameters are biased towards the upper limit to adapt to the production needs of large-size anchors.

[0050] In step S1, the heating temperature is 1100-1200℃, the holding time is 30-60s, and it is set to 1200℃ for 30s; the first frequency is 1-2.5kHz, the second frequency is 4-8kHz, and it is set to 2.5kHz and 8kHz; high-frequency rapid heating is beneficial to reduce the formation of oxide scale on the surface of large-diameter billets.

[0051] In step S2, the final forging temperature is 850-950℃, and the single deformation amount is 30-45%. The final forging temperature is set at 950℃ and the deformation amount is 45%. Although the larger deformation amount at the higher final forging temperature accelerates the dynamic recovery, it is still in the non-recrystallization zone, which effectively promotes the dispersed precipitation of carbides.

[0052] In step S3, the quenching starting temperature is 780-820℃, the dwell time is 5-15s, and it is set to 820℃ for 5s; the atomized particle diameter is 20-50μm, and it is set to 50μm; the shorter dwell time and higher starting temperature are to meet the hardenability requirements of large cross-section workpieces.

[0053] In step S4, the outlet temperature is 180-240℃, set to 240℃; the composition of the composite quenching medium is as follows: 12 parts polyalkylene glycol, 1.5 parts modified nano thermal conductive agent, 2 parts film-forming aid, pH adjusted to 10.5, and 80 parts deionized water; the higher outlet temperature aims to reduce the structural stress during martensitic transformation and prevent cracking of large workpieces.

[0054] In step S5, the self-tempering time is 10-20 min, the supplementary tempering temperature is 450-550℃, and the self-tempering time is set to 20 min, followed by supplementary tempering at 550℃ for 60 min. This embodiment shows that for large-sized workpieces, by increasing the heating and final forging temperatures and using a high-concentration quenching medium, a balance between high hardness and acceptable toughness can be achieved while ensuring hardenability.

[0055] Example 3

[0056] This embodiment provides a hot forging and residual heat quenching process for mining anchors, with parameter values ​​located in the middle of the range, aiming to obtain products with the best overall performance;

[0057] In step S1, the heating temperature is 1100-1200℃, set to 1150℃, and held for 45 seconds; the first frequency is 1-2.5kHz, the second frequency is 4-8kHz, set to 1.8kHz and 6kHz, to ensure the temperature difference is ≤12℃.

[0058] In step S2, the final forging temperature is 850-950℃, and the single deformation amount is 30-45%. At 900℃, the deformation amount is 38%. This combination of parameters ensures plasticity and fluidity while maximizing the accumulation of distortion energy, and strengthens the matrix through deformation-induced precipitation.

[0059] In step S3, the quenching starting temperature is 780-820℃, set to 800℃, held for 10 seconds, and the atomized particles are 35μm. Through precise forced temperature uniformity, local hot spots generated during forging are eliminated.

[0060] In step S4, the composite quenching medium is formulated with 10 parts polyalkylene glycol, 1.0 part modified nano thermal conductive agent, 1.5 parts film-forming aid, pH 9.8, and 85 parts deionized water; the medium temperature is 40℃, the stirring speed is 300 r / min, and the outlet temperature is 210℃; the appropriate amount of modified nano thermal conductive agent is added to make the cooling curve closest to the ideal state.

[0061] In step S5, the tempering temperature is supplemented at 450-550℃, set to 500℃ for 75 minutes; the resulting product has a grain size of grade 9, a surface hardness of 48HRC, and an impact energy of 55J; this embodiment demonstrates the superiority of the center value of the process window and obtains a microstructure with the best match between strength and toughness.

[0062] Example 4

[0063] This embodiment focuses on examining the impact of adjusting the composite quenching medium preparation parameters in step S4 on process stability.

[0064] Steps S1 to S3 use the same process parameters as in Example 3; the key point is the preparation method of the composite quenching medium in step S4. When preparing the modified nano-thermal conductive agent, the ratio of nano-silica to anhydrous ethanol is 1:15, the ratio of silane coupling agent is 1:0.2, the reaction temperature is 55℃, and the reaction time is 3 hours. After the reaction, the centrifugation speed is set to 4500 r / min, the vacuum drying temperature is 65℃, and the drying time is 10 hours to ensure the grafting rate and prevent hard agglomeration. The water temperature is 38℃ when preparing the base liquid. The high-shear emulsification dispersion speed in the functional compounding stage is 900 r / min, which is maintained for 25 min. This optimized preparation process ensures the high dispersion of nanoparticles in the medium and the steric hindrance effect, preventing agglomeration and sedimentation.

[0065] In step S5, the supplementary tempering temperature is 450-550℃, set to 480℃ for 80 minutes; the finished product has a grain size of 8.5 grade, a surface hardness of 47HRC, and an impact energy of 53J; this embodiment verifies that the fine control of the medium preparation process plays a decisive role in ensuring the consistency of heat treatment quality, and the prepared medium has excellent stability over time.

[0066] Example 5

[0067] This embodiment aims to verify the process effect under conditions of lower heating temperature and larger deformation, thereby exploring the potential for energy saving and consumption reduction;

[0068] In step S1, the heating temperature is controlled at 1120℃ from 1100-1200℃ and held for 50 seconds; the lower heating temperature directly reduces energy consumption.

[0069] In step S2, the final forging temperature is 850-950℃, and the single deformation amount is 30-45%. The final forging temperature is controlled at 880℃, and the single deformation amount is 42%. Large deformation is carried out at a lower temperature, which significantly improves the work hardening degree of austenite and drives the dynamic recrystallization to evolve towards ultrafine grains.

[0070] In step S3, the quenching starting temperature is 780-820℃, set to 790℃, and the holding time is 12s.

[0071] In step S4, the composite quenching medium contains 11 parts polyalkylene glycol, 0.8 parts modified nano thermal conductive agent, 1.2 parts film-forming aid, 0.3 parts pH adjuster to adjust pH to 10.0, 0.2 parts bactericide and defoamer, and 86 parts deionized water; the outlet temperature is 190℃.

[0072] In step S5, the tempering temperature was supplemented at 450-550℃, set at 520℃ for 70 minutes; the final product achieved a grain size of 9.5, a surface hardness of 46HRC, and an impact energy of 58J; the results show that low-temperature large deformation combined with precise pre-cooling can obtain the finest grain structure, significantly improve toughness, and reduce energy consumption.

[0073] Comparative Example 1

[0074] This comparative example uses a traditional quenching and tempering process, namely: the raw material is heated and forged, then air-cooled to room temperature, then reheated to 860°C for quenching (water quenching), and finally tempered at 500°C; it does not include the forced uniform temperature pre-cooling of S3, the special composite medium and liquid discharge control in S4, or the self-tempering step in S5 of this invention; this comparative example represents the existing conventional production benchmark.

[0075] Comparative Example 2

[0076] This comparative example uses a common residual heat quenching process, namely: after forging (final forging temperature of about 900℃), without the forced uniform temperature pre-cooling of S3 air mist, it is directly immersed in a common polyalkylene glycol quenching liquid (without the addition of modified nano thermal conductive agent) to cool to room temperature, and then tempered at 500℃; this comparative example is used to verify the necessity of the pre-cooling step and the special medium.

[0077] Comparative Example 3

[0078] This comparative example uses the process flow of the present invention, but the quenching medium used in step S4 does not contain modified nano-thermal conductive agents and film-forming aids, but is only a common polyalkylene glycol aqueous solution. The remaining parameters are consistent with those in Example 3. This comparative example aims to reveal the key role of modified nano-thermal conductive agents in disrupting the gas film and controlling the cooling rate.

[0079] To verify the technical effect of the hot forging and residual heat quenching process of the mining anchor of the present invention, a verification experiment was set up to evaluate the comprehensive performance of the mining anchors prepared in Examples 1-5 and Comparative Examples 1-3.

[0080] Grain size determination: Grain size was determined by comparison according to GB / T6394-2017 "Method for determination of average grain size of metals"; Surface hardness determination: Rockwell hardness of anchor surface was measured according to GB / T230.1-2018 "Metallic materials Rockwell hardness test"; Impact energy determination: V-notch specimens were prepared and impact absorbed energy was determined according to GB / T229-2020 "Metallic materials Charpy pendulum impact test"; Crack detection rate: Crack situation of 100 samples in each group was statistically analyzed according to JB / T4730.4-2005 "Non-destructive testing of pressure equipment Part 4: Magnetic particle testing".

[0081] To ensure the comparability of test results, Examples 1-5 and Comparative Examples 1-3 all used mining-grade left-hand threaded steel anchor bolts without longitudinal ribs as test objects, with specifications of MG500-22 and a diameter of... ,length The material is 40Cr; supplementary notes on crack detection: the sensitivity of magnetic particle testing is based on the clear display of the A-type 15 / 50 test piece, the magnetization current is AC, and 100% full coverage flaw detection is performed on the entire length of the anchor rod and the threaded section at the tail.

[0082] Specific testing process

[0083] 100 finished anchors were randomly selected from each set of examples and comparative examples. First, non-destructive magnetic particle testing was performed, and the number of cracks detected was recorded. Then, 5 samples were randomly selected from the crack-free samples, and metallographic and impact specimens were prepared by cutting. After etching the metallographic specimens with 4% nitric acid alcohol, the microstructure was observed and the grain size was evaluated under an optical microscope. The impact test was carried out at room temperature, and the average value of the 5 specimens was taken as the final result. The hardness test was performed at 3 points along the axial direction on the surface of the anchor rod, and the average value was taken.

[0084] Data table

[0085] Group Grain size Surface hardness (HRC) Impact energy (J) Crack detection rate % Example 1 8.0 45.2 52.4 0 Example 2 8.5 50.1 50.3 0 Example 3 9.0 48.5 55.1 0 Example 4 8.5 47.3 53.2 0 Example 5 9.5 46.1 58.4 0 Comparative Example 1 6.5 42.0 35.5 0 Comparative Example 2 5.0 52.3 15.2 25 Comparative Example 3 8.0 46.4 40.1 8

[0086] Results Analysis

[0087] As shown in Table 1, Examples 1-5 of the present invention are significantly better than the comparative examples in all performance indicators, verifying the superiority of the thermo-mechanical-time coupling control process.

[0088] Regarding the balance between grain refinement and strength / toughness: Example 5 achieved a grain size of 9.5 and an impact energy of 58.4 J, far exceeding Comparative Example 1's 6.5 and 35.5 J. This is attributed to the large deformation forging in the non-recrystallized austenite region during step S2, where high-density dislocation entanglement provided numerous nucleation sites for phase transformation. Simultaneously, the pre-cooling by air and mist in step S3 effectively suppressed secondary grain growth caused by residual heat after forging through temperature control delay effect. In contrast, Comparative Example 1 underwent a reheating process, resulting in a tendency for austenite grains to grow, leading to insufficient toughness.

[0089] Regarding crack control and cooling uniformity: the crack detection rate of the example group was 0%, while that of Comparative Example 2 was as high as 25%, and that of Comparative Example 3 was 8%. This significant difference reveals the key role of the S3 precooling and S4 composite medium in this invention. Due to the lack of precooling and temperature equalization, Comparative Example 2 had a large temperature difference between the inside and outside of the workpiece. Direct immersion in the liquid caused thermal stress and structural stress to be superimposed, making it very easy to crack. Although Comparative Example 3 used polyalkylene glycol, it lacked modified nano-thermal conductive agents and could not effectively destroy the stable vapor film at high temperature, resulting in slow local cooling speed and easy to generate soft spots or microcracks caused by uneven cooling. In contrast, the composite medium of this invention utilizes the Brownian motion and thermal conductivity of nanoparticles to break the gas film in the high temperature zone to achieve rapid cooling. Combined with the slow cooling of the polyalkylene glycol film in the low temperature zone, it perfectly realizes the cooling path of crack suppression and toughening.

[0090] In summary, this invention successfully solves the problems of coarse grains and easy cracking in the residual heat treatment of mining anchors by means of the synergistic effect of segmented heating, non-recrystallization forging, air-fog pre-cooling and residual heat quenching of nanocomposite media, and obtains excellent comprehensive mechanical properties.

[0091] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A hot forging and residual heat quenching process for mining anchors, characterized in that, Includes the following steps: S1. Billet prefabrication and segmented heating: After the medium carbon low alloy steel bar is cut, the surface is sandblasted to remove rust, and then it is sent into the induction heating furnace for segmented heating. First, it is heated to the preheating temperature at the first frequency, and then rapidly heated to the austenitizing temperature at the second frequency. It is held until the core is heated to obtain a hot billet. S2. Multiphase deformation hot forging: The hot billet is transferred to a press for multi-pass forging, including primary forging and final forging; the primary forging breaks the original grains, the final forging temperature is controlled in the austenite non-recrystallization temperature range, and the single deformation amount of the final forging is controlled above the critical deformation amount. The distortion energy of the austenite grains is accumulated by the large deformation amount to obtain the forged semi-finished product. S3, forced air-mist pre-cooling: The forging semi-finished product is immediately subjected to forced air-mist pre-cooling or isothermal residence treatment. By controlling the air volume and the flux of atomized droplets, the surface and core temperatures of the forging semi-finished product are reduced synchronously and converged to the quenching start temperature. The residence time is controlled within the preset time range to obtain the pre-cooled anchor. S4. Controlled residual heat quenching: The pre-cooled anchor is quickly immersed in a self-made composite quenching medium for immersion cooling. During the cooling process, mechanical stirring or ultrasonic disturbance is applied to break the vapor film. When the surface temperature of the pre-cooled anchor drops to the outlet temperature range near the martensitic transformation termination temperature, the anchor is quickly removed from the composite quenching medium to obtain the quenched anchor. S5. Heat conduction self-tempering and supplementary tempering: After the quenched anchor is removed from the liquid, it is placed in a heat preservation box and self-tempered by conducting the residual heat in the core to the surface. After the overall temperature is uniform, it is sent to a tempering furnace for supplementary tempering and stress relief treatment at a preset tempering temperature to obtain the finished mining anchor.

2. The hot forging and residual heat quenching process for a mining anchor as described in claim 1, characterized in that, In step S1, the temperature is 1100-1200℃, the holding time is 30-60s, the first frequency is 1-2.5kHz, and the second frequency is 4-8kHz; the temperature difference between the surface and the core is controlled to be ≤15℃ by gradient heating.

3. The hot forging and residual heat quenching process for a mining anchor as described in claim 1, characterized in that, In step S2, the final forging temperature is 850-950℃, and the deformation amount per step is 30-45%. The final forging process is carried out in the non-recrystallized region of austenite to preserve lattice distortion energy.

4. The hot forging and residual heat quenching process for a mining anchor as described in claim 1, characterized in that, In step S3, the quenching starting temperature is 780-820℃ and the dwell time is 5-15s; forced precooling with air mist uses a mixture of compressed air and atomized water, with atomized particles having a diameter of 20-50μm. Through phase transformation heat absorption, the surface overheating heat is quickly removed, inhibiting austenite grain growth.

5. The hot forging and residual heat quenching process for a mining anchor as described in claim 1, characterized in that, In step S4, the outlet temperature is 180-240℃; the mechanical stirring speed is 200-400 r / min; and the liquid temperature of the composite quenching medium is controlled at 30-50℃.

6. The hot forging and residual heat quenching process for a mining anchor as described in claim 1, characterized in that, In step S5, the self-tempering time is 10-20 min, the supplementary tempering temperature is 450-550℃, and the supplementary tempering time is 60-90 min; the finished mining anchor has a grain size ≥ 8, a surface hardness of 45-50 HRC, and an impact energy Aku ≥ 50 J.

7. The hot forging and residual heat quenching process for a mining anchor as described in claim 1, characterized in that, The composite quenching medium in step S4, by weight, includes the following components: polyalkylene glycol stock solution: 8-12 parts; Modified nano thermal conductive agent: 0.5-1.5 parts; film-forming aid: 1-2 parts; pH adjuster: 0.2-0.5 parts; bactericide and defoamer: 0.1-0.3 parts; deionized water: 80-90 parts.

8. The hot forging and residual heat quenching process for a mining anchor as described in claim 7, characterized in that, Includes the following steps: A1. Preparation of modified nano-thermal conductive agent: Nano-silica was dispersed in anhydrous ethanol at a mass-to-volume ratio of 1 g:(10-20) mL. 3-glycidyl etheroxypropyltrimethoxysilane was added under ultrasonic dispersion conditions at a mass ratio of 1:(0.1-0.3). Grafting reaction was carried out at a temperature of 50-60℃ for 2-4 hours. After the reaction was completed, the mixture was centrifuged and the precipitate was dried under vacuum to obtain the modified nano-thermal conductive agent. A2. Base solution preparation: Heat deionized water to 35-40℃, and slowly add polyalkylene glycol stock solution while mechanically stirring at a speed of 300-500r / min until a homogeneous and transparent solution is formed. A3. Functional compounding: Add film-forming aid, pH adjuster and modified nano thermal conductive agent prepared in step A1 to the base liquid in sequence, increase the stirring speed to 800-1000 r / min for high shear emulsification and dispersion, and maintain for 20-30 min; A4. Stabilization treatment: Cool to room temperature, add bactericidal and defoaming agent, and let stand for 12-24 hours to defoam, thus obtaining the composite quenching medium.

9. The hot forging and residual heat quenching process for a mining anchor as described in claim 8, characterized in that, The film-forming aid is a mixture of sodium polyacrylate and sodium benzoate in a mass ratio of 1:1; the pH adjuster is triethanolamine, which adjusts the pH of the medium to 9.0-10.5.