Gear super deep multi-section pulse carburizing and quenching process method for mining equipment

Abstract

The application discloses a kind of mining equipment gear ultra-deep layer multi-section pulse type carburizing quenching process method, comprising the following steps: one, to low-carbon alloy steel mining equipment gear blank is preheated;Two, using the multi-section pulse type carburizing treatment of strong penetration stage and diffusion stage alternate cycle, and accurately design carburizing parameter;Three, quenching treatment;Four, final quenching treatment;Five, tempering treatment.The application is by using short time strong penetration+isothermal diffusion high frequency cycle, designs strong penetration and diffusion stage parameter, inhibits Cr, W carbide grain boundary precipitation from source, utilizes pulse gap to make carbon atom migrate to depth, realizes periodic reconstruction carbon flux and carbon concentration gradient, accurately locks surface carbon concentration;Combined with quenching and tempering after carburizing obtains high hardness martensite, ensure that carbide is in small, spherical, dispersed form precipitation, obtains high hardness hardened layer and high toughness core gear, suitable for mining equipment field.

Description

Technical Field

[0001] This invention belongs to the field of alloy steel heat treatment technology, and in particular relates to a method for ultra-deep multi-stage pulse carburizing, tempering and quenching process for gears in mining equipment. Background Technology

[0002] Mining equipment (such as coal mining machines and tunneling machines) operates under high impact, heavy load, and harsh conditions for extended periods. Key transmission gears, such as geared wheels and drive wheels, require extremely high material properties. To meet the requirements for resistance to contact fatigue, bending fatigue, and wear, high-quality low-carbon alloy steel (such as 18Cr2Ni4WA) is typically used, undergoing carburizing, quenching, and low-temperature tempering to achieve a combination of a high-hardness hardened layer and a high-toughness core.

[0003] As mining equipment develops towards larger sizes and higher power densities, the load-bearing capacity requirements of gears are constantly increasing, placing higher demands on the effective hardened layer depth, often requiring ultra-deep carburizing exceeding 5.5 mm. However, traditional carburizing processes face the following technical challenges in achieving ultra-deep carburizing: (1) Low carburizing efficiency and long cycle: Traditional processes often use a two-stage process of strong carburizing + diffusion. In order to achieve ultra-deep layers, long-term high-temperature heat preservation is required, which can easily lead to problems such as coarse grains, excessively steep carbon concentration gradient, and coarse surface carbides. (2) Insufficient carbon potential control precision: Traditional single oxygen probe control method is greatly affected by changes in atmosphere composition. During ultra-long-term carburizing, carbon potential fluctuations are difficult to control precisely, which can easily result in excessively high or low surface carbon concentration, forming angular or blocky carbides or insufficient hardness. (3) Microstructure inheritance and grain coarsening: Steels containing Ni and W alloying elements, such as 18Cr2Ni4WA, are prone to microstructure inheritance after long-term carburizing, resulting in coarse grains and reduced toughness after final heat treatment. (4) Difficulty in achieving both core performance and hardened layer performance: In order to meet the requirements of ultra-deep layers, it is often necessary to increase the carburizing temperature or extend the heat preservation time, which further aggravates the coarsening of core grains and reduces the impact toughness of the core.

[0004] Therefore, there is an urgent need to develop an ultra-deep carburizing process suitable for gears in mining equipment, so as to simultaneously meet the comprehensive performance requirements of ultra-deep hardened layer, excellent microstructure and high core toughness. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for ultra-deep multi-stage pulsed carburizing, tempering, and quenching of gears for mining equipment. This method employs a high-frequency alternating cycle of "short-time strong carburizing + isothermal diffusion," and by designing parameters for the strong carburizing and diffusion stages, it inhibits the precipitation of Cr and W carbides along the grain boundaries from the source. Utilizing the pulse gap (diffusion stage), carbon atoms migrate deeper, achieving periodic reconstruction of carbon flux and carbon concentration gradient, and precisely locking the surface carbon concentration. Combined with tempering and quenching after carburizing, high-hardness martensite is obtained, ensuring that carbides precipitate in a fine, spherical, and dispersed form. This constructs a synergistic strengthening mechanism of grain boundary pinning to block inheritance, homogenization of the microstructure, and grain refinement across the entire cross-section, solving the problem of simultaneously achieving high toughness in the core and high hardness in the hardened layer of low-carbon alloy steel after ultra-deep carburizing.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for ultra-deep multi-segment pulse carburizing, tempering and quenching process for gears in mining equipment, characterized in that the method includes the following steps: Step 1: Preheat the low-carbon alloy steel gear blank for mining equipment; Step 2: The preheated low-carbon alloy steel mining equipment gear blank from Step 1 is subjected to multi-stage pulse carburizing treatment to obtain a carburized blank. The multi-stage pulse carburizing treatment is carried out in alternating cycles of a strong carburizing stage and a diffusion stage. The parameters for the strong carburizing stage are: carburizing temperature 920℃~940℃, carbon potential 1.15%~1.25%, and holding time 12h~20h. The parameters for the diffusion stage are: carburizing temperature 920℃~940℃, carbon potential 0.80%~0.90%, and holding time 8h~15h. Step 3: The carburized billet obtained in Step 2 is subjected to quenching and tempering treatment to obtain a quenched and tempered billet; the quenching and tempering treatment is performed by quenching and first tempering in sequence. Step 4: Perform final quenching treatment on the tempered billet obtained in Step 3 to obtain a quenched billet. Step 5: Perform a second tempering treatment on the quenched billet obtained in Step 4 to obtain gears for ultra-deep carburized mining equipment.

[0007] This invention abandons the traditional continuous carbon supply mode and adopts a high-frequency alternating cycle of "short-time intense infiltration + isothermal diffusion". During the intense infiltration stage, the time and carbon potential are designed and controlled to ensure that the surface carbon concentration is just below the critical supersaturation level for the network or blocky nucleation of Cr and W carbides, thus inhibiting their precipitation along the crystallization path from the source. During the diffusion stage, the carbon potential is reduced to 0.80%~0.90% and maintained isothermally. The high-flow-rate enriched gas input for intense infiltration is stopped, and only a trace amount of enriched gas is added to maintain the set low carbon potential. Driven by the concentration gradient, carbon atoms migrate deeper, providing a basis for achieving an effective hardened layer depth greater than 5.5 mm. This process enables periodic re-infiltration. Carbon flux and carbon concentration gradient: In each pulse cycle, the surface carbon concentration is "shaving off peaks and filling valleys", and the overall envelope shows a gentle, linear decreasing trend, completely eliminating the steep gradient; after subsequent tempering and final heat treatment, the carbides are further spheroidized and dispersed, and the matrix carbon concentration is precisely locked in the target window of 0.80%~0.90% (this window has been experimentally verified to be in the safe zone of Cr and W carbide precipitation curves), which not only ensures the acquisition of high-hardness martensite after quenching, but also ensures that the carbides precipitate in a fine, spherical, and dispersed form, fundamentally preventing the formation of network and blocky carbides, while obtaining an ideal gentle carbon concentration gradient; Subsequently, a quenching and tempering process is introduced. Through the synergistic effect of quenching and tempering, supersaturated carbides precipitate from the non-equilibrium bainite structure and undergo spheroidization transformation to form dispersed granular carbides. At the same time, the lath structure of bainite is eliminated, and the structure changes from a non-equilibrium state to a uniform, equiaxed tempered sorbite. This achieves a leap from "crystallographic preferred orientation" to "low-energy equiaxed structure", providing a preparatory structure with uniform composition, low stress, high thermal stability, and no hereditary tendency for the subsequent final quenching, thus avoiding local overheating or abnormal grain growth. During the quenching and tempering process, the dispersed granular carbides precipitated in situ at the grain boundaries can be distributed along the original austenite grain boundaries and bainite lath boundaries. During the final quenching heating, they physically inhibit the migration and merging of austenite grain boundaries, forcing new austenite to nucleate independently among a large number of dispersed carbide particles. The growth direction is random, which completely cuts off the crystallographic inheritance path of the original structure and simultaneously eliminates the structural inheritance phenomenon commonly seen after traditional ultra-long carburizing. It achieves dual grain refinement of the hardened layer and the core structure (the surface layer has a grain size ≥8 after final quenching due to the carbide pinning effect; the core has a grain size ≥8.5 after final quenching due to the elimination of coarse structure by the quenching and tempering pretreatment). This significantly increases the impact energy of the core to over 100J, with a typical value of up to 120J, which is more than 20% higher than the traditional process. This forms an ideal performance match of "high hardness hardened layer + high toughness core", making ultra-deep carburized gears suitable for heavy-load and impact conditions.

[0008] The above-mentioned deep multi-stage pulse carburizing, tempering and quenching process for mining equipment gears is characterized in that the low-carbon alloy steel mining equipment gear blank in step one is made of 18Cr2Ni4WA steel.

[0009] The above-mentioned deep multi-stage pulse carburizing, tempering and quenching process for gears in mining equipment is characterized in that the preheating in step one includes normalizing and high-temperature tempering, wherein the normalizing temperature is 930℃~950℃ and the high-temperature tempering temperature is 650℃~680℃.

[0010] The above-mentioned deep multi-stage pulse carburizing, tempering and quenching process for gears of mining equipment is characterized in that the total duration of the multi-stage pulse carburizing treatment in step two is not less than 150 hours, the time ratio of the strong carburizing stage to the diffusion stage is (1.5~1):1, and the effective hardened layer depth of the carburized billet is greater than 5.5 mm.

[0011] This invention controls the time ratio of the strong infiltration stage to the diffusion stage to be (1.5~1):1, and combines this with controlling the duration of the strong infiltration stage and the carbon potential to ensure that the surface carbon concentration is sufficiently increased to just below the critical supersaturation of Cr and W carbide network or block nucleation. This ensures a sufficient increase in surface carbon concentration, establishes a larger carbon concentration gradient and a stronger diffusion driving force, while avoiding the obstruction of diffusion by carbide precipitation. This allows carbon atoms to migrate more efficiently into the workpiece, achieving an effective hardened layer depth greater than 5.5 mm. This ratio design avoids the situation where the strong infiltration time is too short and the diffusion time is too long, resulting in insufficient carbon concentration gradient and weak diffusion driving force. It also avoids the situation where the strong infiltration time is too long and the diffusion time is too short, causing carbon atoms to be forced to stop diffusing as soon as they leave the surface, resulting in most of the carbon accumulating in an extremely thin layer on the surface, making it difficult to penetrate into deeper layers.

[0012] The above-mentioned deep multi-stage pulse carburizing, tempering and quenching process for gears in mining equipment is characterized in that, in the multi-stage pulse carburizing process in step two, a dual-factor variable control of an online CO analyzer and an oxygen probe is adopted. The oxygen potential measured by the oxygen probe is used as the main control parameter, and the flow rate of enriched gas and air is dynamically adjusted in conjunction with the real-time CO content measured in the furnace by the online CO analyzer to regulate the carbon potential in the furnace in real time; the enriched gas is propane.

[0013] This invention achieves ultra-deep carburizing with an effective hardened layer depth >5.5mm by introducing a dual-factor variable control of an online CO analyzer and an oxygen probe, combined with a multi-segment pulsed carburizing process. The surface carbon concentration gradient is gentle, with no angular or blocky carbides. After quenching and low-temperature tempering, the residual austenite content is controlled to within 15%, and the surface oxidation depth is <45μm. By using the oxygen potential measured by the oxygen probe as the main control parameter, and simultaneously utilizing an online CO analyzer to measure the dynamic changes in CO content within the furnace during each pulse stage, a closed-loop carbon potential control system based on dynamic compensation of atmosphere components was constructed by on-site correction of the oxygen probe-dominated carbon potential calculation model based on the measured CO values. Specifically, the carbon potential calculation model is as follows: ,in, C represents carbon potential, expressed as a mass fraction (% C); T represents furnace temperature, expressed as a K. The oxygen partial pressure in the furnace is expressed in atm and is calculated from the millivolt value of the oxygen probe. CO is the volume percentage of CO gas in the furnace expressed as a decimal. In the specific calculation, the actual CO content in the furnace is measured by extracting gas from the furnace through an online CO analyzer and substituted into the carbon potential calculation model for real-time correction.

[0014] The above-mentioned deep multi-segment pulsed carburizing, tempering and quenching process for gears in mining equipment is characterized in that the carbon potential control accuracy is ±0.02%.

[0015] The above-mentioned deep multi-stage pulse carburizing, tempering and quenching process for gears in mining equipment is characterized in that the quenching process in step three is as follows: heating to 840℃~860℃ and holding for 3h~4.5h followed by oil cooling; and the first tempering process is as follows: heating to 600℃~660℃ and holding for 5h~6h followed by air cooling.

[0016] The above-mentioned deep multi-stage pulse carburizing, tempering and quenching process for gears in mining equipment is characterized in that the specific process of the final quenching treatment in step four is: heating to 800℃~820℃ followed by oil cooling.

[0017] The above-mentioned deep multi-stage pulse carburizing, tempering and quenching process for gears in mining equipment is characterized in that the specific process of the second tempering treatment in step five is: heating to 160℃~200℃ and holding for 3h~5h followed by air cooling.

[0018] The above-mentioned ultra-deep multi-stage pulse carburizing, tempering and quenching process for mining equipment gears is characterized in that, in step five, the surface hardness of the ultra-deep carburized mining equipment gear is 58HRC~64HRC, the effective hardened layer depth is 5.5mm~7.0mm, the surface oxidation depth is <45μm, the residual austenite content in the carburized layer is ≤15%, and there are no angular or blocky carbides; the core hardness of the ultra-deep carburized mining equipment gear is 38HRC~45HRC, and the core impact energy is ≥100J.

[0019] Compared with the prior art, the present invention has the following advantages: 1. This invention employs a high-frequency alternating cycle of "short-time strong carburizing + isothermal diffusion," and by designing the parameters of the strong carburizing and diffusion stages, it inhibits the precipitation of Cr and W carbides along the grain from the source. Utilizing the pulse gap, it enables carbon atoms to migrate deeper, and periodically reconstructs the carbon flux and carbon concentration gradient, ultimately locking the surface carbon concentration precisely at 0.80%~0.90%. This ensures both the acquisition of high-hardness martensite after quenching and the precipitation of carbides in a fine, spherical, and dispersed form, fundamentally preventing the formation of network and blocky carbides, while achieving an ideal, gentle carbon concentration gradient. Combined with the tempering treatment after carburizing and the synergistic effect of quenching, a synergistic strengthening mechanism is constructed, which includes grain boundary pinning to block inheritance, homogenization of the microstructure, and refinement of grains across the entire cross-section, increasing the depth of the effective hardened layer to greater than 5.5 mm.

[0020] 2. This invention introduces an online CO analyzer and an oxygen probe to collaboratively control carbon potential during multi-segment pulsed carburizing. The oxygen potential measured by the oxygen probe is used as the main control parameter. At the same time, the online CO analyzer is used to measure the dynamic changes of CO content in the furnace in real time during each pulse stage. Based on the measured CO values, the carbon potential calculation model dominated by the oxygen probe is corrected on-site, and a closed-loop carbon potential control system based on dynamic compensation of atmosphere composition is constructed. The carbon potential control accuracy can reach ±0.02%. This solves the problem of carbon potential instability caused by atmosphere drift of a single oxygen probe in ultra-long carburizing cycles, and achieves high stability and high consistency control of surface carbon concentration.

[0021] 3. The method of this invention is applicable to heavy-duty gears of mining equipment made of low-carbon alloy steel. Its process design has a clear theoretical basis (Fick's second law, Harris's formula) and good parameter adjustability. It can be extended to other heavy-duty transmission components that require ultra-deep carburizing. It has broad process applicability, excellent engineering stability and significant industrialization promotion value.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a graph showing the carbon concentration gradient of the carburized layer in the gear of the ultra-deep carburizing mining equipment in Embodiment 1 of the present invention.

[0024] Figure 2 This is a metallographic diagram of the carburized layer of the gear in the ultra-deep carburized mining equipment of Embodiment 1 of the present invention.

[0025] Figure 3 This is a metallographic diagram of the core of the gear in the ultra-deep carburizing mining equipment of Embodiment 1 of the present invention. Detailed Implementation

[0026] Example 1 The method in this embodiment includes the following steps: Step 1: The 18Cr2Ni4WA steel mining equipment gear blank is subjected to normalizing at 930℃~950℃ and high-temperature tempering at 650℃~680℃ in sequence, and the dimensions of the 18Cr2Ni4WA steel mining equipment gear blank are processed according to the design requirements. Step 2: The 18Cr2Ni4WA steel mining equipment gear blank processed in Step 1 is subjected to multi-stage pulse carburizing treatment, with a total carburizing time of 150 hours. During the multi-stage pulse carburizing process, a dual-factor variable control using an online CO analyzer and an oxygen probe is employed. The oxygen potential measured by the oxygen probe is used as the main control parameter, and the flow rates of propane and air are dynamically adjusted in conjunction with the real-time CO content measured by the online CO analyzer to control the carbon potential in the furnace in real time, with an adjustment accuracy of ±0.02%, resulting in a carburized blank with an effective hardened layer depth of 6.1 mm. The multi-stage pulse carburizing treatment is carried out in alternating cycles of a strong carburizing stage and a diffusion stage. The parameters for the strong carburizing stage are: carburizing temperature 930℃, carbon potential 1.20%, and holding time 15 hours. The parameters for the diffusion stage are: carburizing temperature 930℃, carbon potential 0.85%, and holding time 15 hours. Step 3: Heat the carburized billet obtained in Step 2 to 850℃ and hold for 3 hours, then quench it in oil, then heat it to 660℃ and hold for 5 hours, then air cool it to obtain a tempered billet. Step 4: Heat the tempered billet obtained in Step 3 to 820℃ and hold for 3 hours, then oil cool to obtain the quenched billet. Step 5: Heat the quenched billet obtained in Step 4 to 180℃ and hold for 3 hours, then air cool to obtain the gear for ultra-deep carburized mining equipment.

[0027] The carbon concentration of the carburized layer was measured on the gear of the ultra-deep carburized mining equipment prepared in this embodiment, and the results are as follows: Figure 1 As shown, the curve decreases gently, with a peak carbon concentration of approximately 0.89%, and an effective hardened layer depth of 6.1 mm. The carbon concentration gradient is gentle. Metallographic analysis was performed on the carburized layer and core of the gear, as shown in the figure. Figure 2 and Figure 3 As shown, the carburized layer consists of fine tempered martensite and dispersed spherical carbides, without angular or blocky carbides; the core structure consists of uniform equiaxed low-carbon tempered martensite and a small amount of bainite, with fine grains. Upon inspection, the gear has a surface hardness of 64.0 HRC, an effective hardened layer depth of 6.1 mm, an internal oxidation depth of 32 μm, a residual austenite content of 12% in the carburized layer, and a carburized layer grain size of grade 9; the core hardness is 42.3 HRC, the core impact energy (KU2) is 128 J, and the core grain size is grade 9.

[0028] Comparative Example 1 This comparative example uses a traditional two-stage carburizing + direct quenching process, specifically including the following steps: Step 1: The 18Cr2Ni4WA steel mining equipment gear blank is subjected to normalizing and high-temperature tempering in sequence, and the dimensions of the 18Cr2Ni4WA steel mining equipment gear blank are processed according to the design requirements. Step 2: The 18Cr2Ni4WA steel mining equipment gear blank processed in Step 1 is subjected to a strong carburizing stage at 930℃ and carbon potential of 1.20% for 75 hours, and a diffusion stage at 930℃ and carbon potential of 0.85% for 75 hours, for a total carburizing time of 150 hours. A single oxygen probe is used to control the carbon potential to obtain the carburized blank. Step 3: After furnace cooling the carburized billet obtained in Step 2 to 850℃ and holding it at that temperature for 3 hours, oil quench it. Step four, low-temperature tempering treatment: heat to 180℃ and hold for 3 hours, then air cool to obtain the mining equipment gear.

[0029] Testing revealed that the gear prepared in this comparative example had a surface hardness of 59.8 HRC, an effective hardened layer depth of 5.8 mm, an internal oxidation depth of 68 μm, a small amount of angular carbides in the carburized layer, a residual austenite content of approximately 25%, and a carburized layer grain size of grade 7. The core hardness was 41.5 HRC, the core impact energy was 86 J, and the core grain size was grade 7.5. Compared with Example 1, this comparative example, under the same total carburizing time, had a shallower effective hardened layer depth, a more fluctuating carbon concentration gradient, a significantly reduced core impact toughness, and more severe internal oxidation. This indicates that the multi-stage pulse carburizing process combined with tempering and quenching treatment can significantly improve the overall performance of 18Cr2Ni4WA steel gears.

[0030] Example 2 The method in this embodiment includes the following steps: Step 1: The 18Cr2Ni4WA steel mining equipment gear blank is subjected to normalizing at 930℃~950℃ and high-temperature tempering at 650℃~680℃ in sequence, and the dimensions of the 18Cr2Ni4WA steel mining equipment gear blank are processed according to the design requirements. Step 2: The 18Cr2Ni4WA steel mining equipment gear blank processed in Step 1 is subjected to multi-stage pulse carburizing treatment, with a total carburizing time of 175 hours. During the multi-stage pulse carburizing process, a dual-factor variable control using an online CO analyzer and an oxygen probe is employed. The oxygen potential measured by the oxygen probe is used as the main control parameter, and the flow rates of propane and air are dynamically adjusted in conjunction with the real-time CO content measured by the online CO analyzer to control the carbon potential in the furnace in real time, with an adjustment accuracy of ±0.02%, resulting in a carburized blank with an effective hardened layer depth of 6.5 mm. The multi-stage pulse carburizing treatment is carried out in alternating cycles of a strong carburizing stage and a diffusion stage. The parameters for the strong carburizing stage are: carburizing temperature 920℃, carbon potential 1.18%, and holding time 20 hours. The parameters for the diffusion stage are: carburizing temperature 920℃, carbon potential 0.82%, and holding time 15 hours. Step 3: Heat the carburized billet obtained in Step 2 to 840℃ and hold for 4 hours, then quench it in oil, then heat it to 600℃ and hold for 5 hours, then air cool it to obtain a tempered billet. Step 4: Heat the tempered billet obtained in Step 3 to 820℃ and hold for 4 hours, then oil cool to obtain the quenched billet. Step 5: Heat the quenched billet obtained in Step 4 to 160℃ and hold for 4 hours, then air cool to obtain the gear for ultra-deep carburized mining equipment.

[0031] Testing revealed that the surface hardness of the ultra-deep carburized mining equipment gear prepared in this embodiment was 59.2 HRC, the effective hardened layer depth was 6.5 mm, the surface oxidation depth was 38 μm, the residual austenitic content of the carburized layer was 14%, there were no angular or blocky carbides, and the grain size of the carburized layer was grade 9; the core hardness was 44.5 HRC, the core impact energy was 115 J, and the core grain size was grade 8.5.

[0032] Example 3 The method in this embodiment includes the following steps: Step 1: The 18Cr2Ni4WA steel mining equipment gear blank is subjected to normalizing at 930℃~950℃ and high-temperature tempering at 650℃~680℃ in sequence, and the dimensions of the 18Cr2Ni4WA steel mining equipment gear blank are processed according to the design requirements. Step 2: The 18Cr2Ni4WA steel mining equipment gear blank processed in Step 1 is subjected to multi-stage pulse carburizing treatment, with a total carburizing time of 180 hours. During the multi-stage pulse carburizing process, a dual-factor variable control using an online CO analyzer and an oxygen probe is employed. The oxygen potential measured by the oxygen probe is used as the main control parameter, and the flow rates of propane and air are dynamically adjusted in conjunction with the real-time CO content measured by the online CO analyzer to control the carbon potential in the furnace in real time, with an adjustment accuracy of ±0.02%, resulting in a carburized blank with an effective hardened layer depth of 6.7 mm. The multi-stage pulse carburizing treatment is carried out in alternating cycles of a strong carburizing stage and a diffusion stage. The parameters for the strong carburizing stage are: carburizing temperature 940℃, carbon potential 1.22%, and holding time 12 hours. The parameters for the diffusion stage are: carburizing temperature 940℃, carbon potential 0.88%, and holding time 8 hours. Step 3: Heat the carburized billet obtained in Step 2 to 860℃ and hold for 4.5 hours, then quench it in oil, then heat it to 660℃ and hold for 6 hours, then air cool it to obtain a tempered billet. Step 4: Heat the tempered billet obtained in Step 3 to 800℃ and hold for 3 hours, then oil cool to obtain the quenched billet. Step 5: Heat the quenched billet obtained in Step 4 to 200℃ and hold for 5 hours, then air cool to obtain the gear for ultra-deep carburized mining equipment.

[0033] Testing revealed that the surface hardness of the ultra-deep carburized mining equipment gear prepared in this embodiment was 61.3 HRC, the effective hardened layer depth was 6.7 mm, the surface oxidation depth was 35 μm, the residual austenite content in the carburized layer was 11%, there were no angular or blocky carbides, and the grain size of the carburized layer was grade 9; the core hardness was 40.1 HRC, the core impact energy was 122 J, and the core grain size was grade 9.5.

[0034] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for ultra-deep multi-stage pulse carburizing, tempering, and quenching process for gears in mining equipment, characterized in that, The method includes the following steps: Step 1: Preheat the low-carbon alloy steel mining equipment gear blank; the low-carbon alloy steel mining equipment gear blank is made of 18Cr2Ni4WA steel. Step 2: The preheated low-carbon alloy steel mining equipment gear blank from Step 1 is subjected to multi-stage pulse carburizing treatment to obtain a carburized blank. The multi-stage pulse carburizing treatment is carried out in alternating cycles of a strong carburizing stage and a diffusion stage. The parameters for the strong carburizing stage are: carburizing temperature 920℃~940℃, carbon potential 1.15%~1.25%, and holding time 12h~20h. The parameters for the diffusion stage are: carburizing temperature 920℃~940℃, carbon potential 0.80%~0.90%, and holding time 8h~15h. The total duration of the multi-stage pulse carburizing treatment is not less than 150 hours, and the effective hardened layer depth of the carburized billet is greater than 5.5 mm. Step 3: The carburized billet obtained in Step 2 is subjected to quenching and tempering treatment to obtain a quenched and tempered billet. The quenching and tempering treatment consists of quenching and a first tempering. The purpose of the quenching and tempering treatment is to eliminate the heritability of the microstructure caused by the ultra-long carburizing process and to provide a pre-structure without heritability for the final quenching. The specific quenching process is as follows: heating to 840℃~860℃ and holding for 3h~4.5h followed by oil cooling. The specific tempering process is as follows: heating to 600℃~660℃ and holding for 5h~6h followed by air cooling. Step 4: Perform final quenching treatment on the tempered billet obtained in Step 3 to obtain a quenched billet. Step 5: Perform a second tempering treatment on the quenched billet obtained in Step 4 to obtain an ultra-deep carburized mining equipment gear; the surface hardness of the ultra-deep carburized mining equipment gear is 58HRC~64HRC, the effective hardened layer depth is 5.5mm~7.0mm, the surface oxidation depth is <45μm, the residual austenite content in the carburized layer is ≤15%, and there are no angular or blocky carbides; the core hardness of the ultra-deep carburized mining equipment gear is 38HRC~45HRC, and the core impact energy is ≥100J.

2. The ultra-deep multi-segment pulse carburizing, tempering, and quenching process for gears in mining equipment according to claim 1, characterized in that, The preheating mentioned in step one includes normalizing and high-temperature tempering. The normalizing temperature is 930℃~950℃, and the high-temperature tempering temperature is 650℃~680℃.

3. The ultra-deep multi-segment pulse carburizing, tempering, and quenching process for gears in mining equipment according to claim 1, characterized in that, The time ratio of the strong infiltration stage to the diffusion stage in step two is (1.5~1):

1.

4. The ultra-deep multi-segment pulse carburizing, tempering and quenching process for gears in mining equipment according to claim 1, characterized in that, In step two, the multi-stage pulse carburizing process employs a dual-factor variable control system using an online CO analyzer and an oxygen probe. The oxygen potential measured by the oxygen probe is used as the main control parameter, and the flow rates of enriched gas and air are dynamically adjusted in conjunction with the real-time CO content measured by the online CO analyzer to regulate the carbon potential in the furnace in real time. The enriched gas is propane.

5. The ultra-deep multi-segment pulse carburizing, tempering and quenching process for gears in mining equipment according to claim 4, characterized in that, The carbon potential is controlled with an accuracy of ±0.02%.

6. The ultra-deep multi-segment pulse carburizing, tempering and quenching process for gears in mining equipment according to claim 1, characterized in that, The specific process of the final quenching treatment described in step four is as follows: heat to 800℃~820℃ and then oil cool.

7. The ultra-deep multi-segment pulse carburizing, tempering and quenching process for gears in mining equipment according to claim 1, characterized in that, The specific process of the second tempering treatment in step five is as follows: heat to 160℃~200℃, hold for 3h~5h, and then air cool.

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