Gear pump base shell, spacer sleeve and base shell processing technology

Abstract

The application relates to a gear pump base shell, a spacer sleeve and a base shell processing technology, and relates to the alloy preparation technical field; the gear pump base shell is made of low-carbon high-purity steel, and the mass percentage of the low-carbon high-purity steel comprises the following components: 0.15-0.25wt% of carbon, 0.02-0.05wt% of niobium, 0.01-0.03wt% of titanium, 0.001-0.003wt% of boron, and the balance of iron; the processing technology steps comprise the following steps: blank preparation, temperature control forging, surface purification, tin hanging treatment, pouring, gradient cooling, tempering and forming processing steps; through the low-carbon high-purity steel metal phase composition and the processing technology, multiple grain refinement is realized, the grain growth is inhibited, and then the comprehensive mechanical properties of the base shell strength and toughness are improved, so that the service life is prolonged.

Description

Technical Field

[0001] This invention relates to the field of alloy preparation technology, and in particular to a gear pump base shell, spacer, and base shell processing technology. Background Technology

[0002] The gear pump housing is an important basic assembly component of the gear pump. After the gear pump spacer is combined with the inner wall of the housing, it undertakes the functions of limiting gear operation, wear resistance and sealing. The material properties, forming process and processing accuracy of the gear pump housing and gear pump spacer directly determine the working stability, service life and power loss level of the gear pump. They are key components in the structural design and manufacturing of gear pumps.

[0003] Currently, gear pump housings are mostly made of ordinary carbon steel or conventional alloy steel, and the matching gear components are mostly traditional homogeneous alloy structures. This results in insufficient wear resistance of the inner wall of the housing, and the gears are prone to severe friction with the housing and spacers during operation. This not only causes a large amount of power loss, but also generates significant vibration and noise. It also makes the gear surface more prone to wear, deformation and other faults, which further accelerates the wear rate of the housing and spacers, significantly reducing the overall reliability of the gear pump. This makes it difficult to meet the requirements of low loss, low noise and long service life of gear pumps in heavy-duty applications such as electric vehicles and ships.

[0004] Chinese invention patent application CN108167178A, published on June 15, 2018, discloses a gear pump for reducing power loss. The gear pump of this invention includes a housing and gears. The gears include a gear matrix and a wear-resistant layer coated on the gear matrix. The gear matrix comprises the following components: C, Si, Mn, Cr, Ni, Cu, Ag, Gd, silicate whiskers, porous calcium carbonate, with the balance being Fe. This solution achieves vibration and noise reduction by adding silicate whiskers and porous calcium carbonate. By coating the gear surface with a wear-resistant layer containing nano-Si3N4, the wear resistance and impact resistance of the gears are improved, reducing the frictional loss and operating noise of the gear pump.

[0005] However, the inventors discovered that the silicate whiskers and porous calcium carbonate added in the above technical solution are non-metallic phases. During the forming process of the steel matrix, these non-metallic phases will form interfacial gaps with the molten metal, resulting in a decrease in the local density of the matrix. The decrease in matrix density will reduce the resistance to atomic diffusion, making the austenite grain boundaries more likely to migrate and merge at high temperatures, indirectly accelerating the grain coarsening process, and ultimately deteriorating the mechanical properties of the gear pump. Summary of the Invention

[0006] To address the problem of coarse grains in the gear pump substrate, this invention provides a gear pump substrate, a spacer, and a substrate processing technology.

[0007] Firstly, the gear pump housing provided in this application adopts the following technical solution: A gear pump housing is made of low-carbon high-purity steel, wherein the low-carbon high-purity steel comprises, by mass percentage: 0.15-0.25 wt% carbon, 0.02-0.05 wt% niobium, 0.01-0.03 wt% titanium, 0.001-0.003 wt% boron, with the balance being iron.

[0008] By employing the above technical solution, niobium, titanium, and boron microalloying elements are used to form a triple fine grain structure. This suppresses grain growth from the material composition perspective. During the heating and phase transformation process of steel, niobium and titanium react with carbon to form nanoscale niobium carbide and titanium carbide carbides. These second-phase particles tightly pin the austenite grain boundaries, preventing grain boundary migration and merging at high temperatures and limiting the thermal growth of austenite grains. Boron is used as a grain boundary segregating element, enriched at the austenite grain boundaries, reducing grain boundary energy and atomic diffusion rate, further suppressing grain boundary migration, and simultaneously enhancing grain boundary bonding strength. A low carbon ratio ensures the plasticity and toughness of the matrix, avoiding grain boundary embrittlement caused by high carbon content. At the same time, the amount and morphology of carbonitride precipitation are controlled to ensure a fine and dispersed distribution, maximizing the grain boundary pinning effect.

[0009] By employing a pure metal alloy system, the interfacial gap between the non-metallic phase and the molten metal is eliminated, thereby improving the matrix density. This avoids the problems of reduced atomic diffusion resistance and accelerated grain coarsening caused by decreased density. Furthermore, the matrix structure is made uniform and dense through fine grain strengthening. When the gear pump vibrates during operation, the fine and uniform grains disperse the vibration energy through deformation and slippage at the grain boundaries, achieving vibration reduction and noise reduction effects. At the same time, it reduces energy loss during vibration propagation, further improving noise reduction performance.

[0010] Low-carbon, high-purity steel is used to prevent grain boundary embrittlement and improve the impact and fatigue resistance of the matrix. The addition of carbon, niobium, titanium, and boron achieves a balance between strength, hardness, and toughness, so that the base shell has sufficient load-bearing capacity to meet the mechanical requirements of the gear pump base shell as an assembly foundation, while providing a uniform and dense metal surface for metallurgical bonding with the spacer, improving the compatibility of the bonding interface.

[0011] Secondly, the present invention provides a gear pump spacer, which adopts the following technical solution: A gear pump spacer is metallurgically bonded to the inner wall of the gear pump base housing as described in the first aspect; the thickness of the gear pump spacer is 2.0 to 4.0 mm.

[0012] By adopting the above technical solution, the metallurgical bond between the spacer and the base shell has a bonding strength far exceeding that of traditional mechanical and adhesive bonds, effectively preventing the spacer from detaching or cracking due to vibration and impact under heavy-load conditions. The tight metallurgical bond can effectively block the intrusion of external media into the interface and protect the grain boundaries of the fine grains of the base shell from corrosion. When the gear pump generates vibration and stress during operation, the fine grain structure of the base shell and the spacer layer disperses the stress through the joint deformation of the grain boundaries, avoiding stress concentration on local grains that could lead to grain coarsening or cracking. At the same time, during gear operation, the spacer absorbs vibration energy through slight deformation of the soft substrate, improving the vibration reduction and noise reduction effect of the gear pump and meeting the long-term use requirements of heavy-load conditions such as electric vehicles and ships.

[0013] Thirdly, this application provides a processing technology for the gear pump base housing, employing the following technical solution: A processing method for a gear pump base housing includes the following steps: Blank preparation: Low-carbon high-purity steel is used, and the temperature is maintained at 1150-1180℃ for 60-90 minutes; Temperature-controlled forging: Forging is performed at 20–40°C above the austenite transformation completion temperature, with a deformation amount of 35–55%. Further deformation is then carried out in the two-phase temperature range from the austenite initiation temperature to the austenite transformation completion temperature, with a deformation rate of 0.5–1.5 s⁻¹. -1 ; Surface cleaning includes the following steps: electric heating melting, alkaline washing, weak acid activation, and hot water rinsing. Tinning process: Perform a first tinning at 330-350℃ for 30-60 seconds, air cool for 2-3 minutes, and then perform a second tinning at 270-290℃ for 20-30 seconds. The thickness of the tin layer is 0.15-0.25 mm. Pouring: Pouring shall be carried out at 410~430℃ and a pouring speed of 0.8~1.2kg / s, with a total duration of ≤15s; Gradient cooling: First spray water to cool for 10-20 minutes, then let it cool naturally to room temperature; Tempering: Hold at 260-300℃ for 2-3 hours, then cool in the furnace to below 100℃ before unloading. Forming and processing: Dry cutting is used for processing.

[0014] By adopting the above technical solution, a temperature-controlled forging process involving high-temperature forging and two-phase deformation is used to achieve secondary grain refinement and microstructure homogenization. High-temperature forging with a deformation amount of 35% to 55% is performed at 20 to 40°C above the austenite transformation end temperature, breaking up the coarse grains in the cast state of the steel and forming fine austenite grains, while introducing a large number of dislocations. Then, deformation is performed in the two-phase region from the austenite initiation temperature to the end temperature. At this time, there are two phases of austenite and ferrite in the matrix. Deformation promotes dynamic recrystallization of austenite and induces ferrite to nucleate at austenite grain boundaries and dislocations, forming even finer ferrite grains.

[0015] A surface cleaning process is employed to remove impurities such as oxide scale, oil, and rust from the inner wall of the substrate, resulting in a clean and activated metal surface that enhances surface energy. A step-by-step tinning process is then used to form a tin layer on the clean surface. The first tinning process achieves initial metallurgical bonding between the tin and the substrate, while the second low-temperature tinning process refines the tin layer grains, fills micro-defects on the tin layer surface, and increases the density of the tin layer. As a transition layer, the tin layer reduces the internal stress at the bonding interface, enhances the metallurgical bonding strength, and prevents the spacer from falling off or cracking.

[0016] During the casting process, the raw material components of the spacer are fully filled into the inner wall of the base shell. During the gradient cooling process, water spray cooling is first used to quickly cool the combination of the base shell and the spacer to below the phase transformation temperature, which fixes the fine grains formed by dynamic recrystallization in time and avoids grain coarsening and rebound at high temperature. This not only strengthens the strength and toughness of the matrix, but also improves the fatigue resistance and impact resistance of the base shell.

[0017] The tempering and forming process reduces the residual internal stress generated inside the base shell, stabilizes the grain structure, and avoids grain growth and strength reduction caused by high-temperature tempering. The furnace cooling to below 100°C further reduces the thermal stress during the cooling process and ensures the stability of the matrix structure. The dry cutting process ensures the assembly dimensional accuracy of the base shell, meets the assembly requirements of the gear pump, and the slight work hardening generated during the dry cutting process further improves the surface hardness of the base shell and enhances its wear resistance.

[0018] Optionally, it also includes a dehydrogenation and carbonization treatment step, wherein the dehydrogenation and carbonization treatment step is set after the temperature-controlled forging step and before the surface cleaning step; The dehydrogenation and carbon treatment steps include: operating under a vacuum degree ≤ 5 × 10⁻⁶ -3 Under conditions of Pa and temperature of 600–650℃, keep warm for 90–120 minutes.

[0019] By adopting the above technical solution, the dehydrogenation and carbonization processes enable hydrogen atoms inside the substrate to diffuse and escape rapidly, eliminating hydrogen-induced micro-defects caused by the segregation of hydrogen atoms at grain boundaries and dislocations. This prevents grain boundaries from cracking or migrating due to hydrogen-induced stress, prevents abnormal grain growth along defects, and ensures the integrity of fine grains. The vacuum decarburization process promotes the diffusion of carbon from the surface decarburized layer into the substrate, restoring the uniformity of surface carbon content, eliminating the difference in microstructure between the surface and the substrate, avoiding uneven grain boundary migration rates caused by loose surface microstructure, and preventing local grain coarsening. The vacuum environment isolates oxygen and impurities, preventing oxidation and contamination of the grain boundaries of the high-temperature substrate after forging, ensuring the cleanliness and bonding strength of the grain boundaries, and further improving the overall mechanical property consistency of the substrate.

[0020] Optionally, in the surface cleaning step, the weak acid activation step includes: immersing in an activation solution at 25-35°C for 30-45 seconds; wherein the activation solution comprises, by mass percentage: sulfuric acid 2.0-3.0 wt%, alkyl sulfonate 0.1-0.3 wt%, and the balance being water.

[0021] By adopting the above technical solution, low-concentration sulfuric acid is used to gently corrode the residual oxide film on the surface, preventing the grain boundaries from being eroded by the acid and forming intergranular gaps, thus protecting the microstructure of the fine grains on the surface. The adsorption film formed by alkyl sulfonates on the surface effectively blocks excessive contact between the acid and the matrix grains, inhibits intergranular corrosion, and at the same time makes the corrosive effect of the acid evenly distributed on the surface, avoiding the local grains from falling off or coarsening due to excessive corrosion, further optimizing the metallurgical bonding performance between the base shell and the spacer, and improving the mechanical properties of the base shell surface.

[0022] Optionally, it also includes a plasma activation step, which is set after the surface cleaning treatment step and before the tinning treatment step; The plasma activation step includes: performing plasma micro-oxidation treatment for 30-90s under the conditions of argon to oxygen volume ratio of 95-98:2-5, power of 80-120W, and processing distance of 10-30mm to form an oxide layer of 10-30nm.

[0023] By employing the above technical solution, high-energy electrons and ions in plasma bombard the substrate surface, breaking the chemical bonds of the natural oxide film, removing trace impurities adsorbed on the surface, exposing fresh crystal faces and active sites of fine grains, restoring the high surface energy of the fine grain surface, and making the grain boundaries and crystal faces of the fine grains effective bonding sites for subsequent tinning; the micro-oxide layer formed under argon-oxygen mixed gas is uniformly attached to the surface of the fine grains without damaging the microstructure of the fine grains, and the micro-oxide layer forms a tight interface bond with the fine grains, utilizing the large number of grain boundaries of the fine grains to enhance the adhesion of the oxide layer and prevent the oxide layer from falling off; in addition, plasma treatment is a cold process without high-temperature thermal effects, which will not cause thermal growth of the surface fine grains, retaining the previously formed fine grain structure, and further improving the surface protection performance.

[0024] Optionally, it also includes a preheating step, which is set after the tinning step and before the casting step; The preheating step is as follows: preheat the mold to 260-300℃ and keep it at that temperature for 8-12 minutes.

[0025] By adopting the above technical solution, the mold is preheated, so that the base shell and the mold form a uniform medium-temperature environment, eliminating the sudden temperature difference during casting, avoiding the austenite grains from recrystallizing and growing due to sudden heating, and locking the fine-grained structure. At the same time, the fine-grained matrix in a uniform medium-temperature environment further improves the consistency of metallurgical bonding, enhances the interfacial bonding strength between the spacer and the base shell, and prevents the spacer from falling off or cracking due to insufficient bonding during use.

[0026] Optionally, it also includes a passivation step, which is performed after the tempering step and before the forming process step; The passivation process includes: a descaling step; The descaling step includes: immersing in pickling solution for 60-90 seconds, followed by rinsing in water for 10-20 seconds; wherein the pickling solution comprises, by mass percentage: 5-8 wt% nitric acid, 2-3 wt% citric acid, and the remainder being water.

[0027] By adopting the above technical solution, a pickling solution composed of nitric acid and citric acid is used to quickly dissolve the oxide scale formed by tempering. The complexing effect of citric acid can selectively remove coarse oxides in the oxide scale, preventing oxides from penetrating along the fine grain boundaries, protecting the integrity of the grain boundaries and the pinning effect of microalloyed carbides, so that the mechanical properties of the fine grain structure are reflected on the surface of the base shell. At the same time, the clean fine grain surface improves the subsequent processing accuracy.

[0028] Optionally, the passivation treatment step further includes a self-healing sealing step, wherein the self-healing sealing step is performed after the oxide scale removal step; The self-healing sealing step includes: immersing in a sealing solution at 55-65°C for 30-60 seconds, followed by drying with hot air at 70-80°C for 3-5 minutes; wherein the sealing solution comprises, by mass percentage: sodium molybdate 0.6-0.9 wt%, phosphoric acid 0.3-0.6 wt%, cerium nitrate 0.08-0.12 wt%, ammonium vanadate 0.05-0.08 wt%, with the balance being water.

[0029] By adopting the above technical solution, the phosphoric acid in the nitric acid sealing solution reacts with the fine grain surface of the substrate shell, and the generated phosphate conversion film fully fills the micropores and microcracks on the fine grain surface, eliminating the starting point of grain growth. At the same time, the conversion film adheres to the surface of the fine grains and the grain boundaries, forming a physical barrier to prevent external corrosive media from penetrating along the grain boundaries and protecting the cleanliness of the grain boundaries. The composite passivation film formed by sodium molybdate and cerium nitrate tightly coats the surface of the fine grains, and utilizes the large number of grain boundaries of the fine grains to form a denser passivation film structure, improving the adhesion and protective effect of the passivation film and preventing the fine grain surface from being oxidized or corroded.

[0030] In addition, cerium nitrate can quickly diffuse to the damaged area and form a new passivation film when the passivation film is slightly damaged, thus repairing the protective layer on the fine grain surface in time and preventing the grains at the damaged area from growing or corroding due to loss of protection. Ammonium vanadate forms microalloying compounds with elements such as iron and niobium on the surface of the substrate, further refining the grains. At the same time, it plays a bonding promoting role, enhancing the bonding force between the sealing liquid and the surface of the substrate, and further improving the wear resistance and corrosion resistance of the substrate.

[0031] Fourthly, the present invention provides an application of a gear pump base housing and a gear pump spacer, employing the following technical solution: A gear pump housing as described in the first aspect, or a gear pump spacer as described in the second aspect, or a gear pump housing manufactured by any of the processing methods described in the third aspect, is used in a gear pump component in a hydraulic control system for an electric vehicle, or in a heavy-duty gear pump component in a marine power system, a marine hydraulic steering gear system, or a marine ballast water system.

[0032] By adopting the above technical solutions, the grain refinement and density of the base shell, along with the metallurgical bonding of the base shell and the spacer, ensure the working stability and reliability of the gear pump. The corrosion resistance and self-healing properties of the base shell extend the service life of the gear pump in complex working environments. At the same time, the vibration reduction and noise reduction performance of the base shell and the spacer reduces the vibration and noise of ship equipment, improving the navigation comfort of the ship.

[0033] In summary, this application includes at least one of the following beneficial technical effects: 1. By adopting a low-carbon, high-purity steel metallic phase composition of carbon, niobium, titanium, boron, and the balance iron, multiple grain refinement is achieved, grain growth is suppressed, and the comprehensive mechanical properties of the base shell strength and plasticity are improved. At the same time, the pure metal alloy system eliminates interfacial gaps and improves the matrix density. The fine-grained structure and dense structure achieve vibration reduction and noise reduction by dispersing vibration energy through grain boundaries.

[0034] 2. By employing dehydrogenation and carbon treatment steps, abnormal grain growth along defects is prevented, ensuring the integrity of fine grains; a weak acid activation step is used to protect the microstructure of the surface fine grains, while preventing grains from falling off or coarsening due to excessive corrosion; a plasma activation step is used to remove trace impurities adsorbed on the surface and restore the high surface energy of the fine grain surface; overall, the mechanical and protective properties of the substrate surface are further improved.

[0035] 3. By employing passivation treatment, the integrity of grain boundaries and the pinning effect of microalloyed carbides are protected, allowing the mechanical properties of the fine-grained structure to be reflected on the surface of the substrate. Phosphoric acid in the sealing liquid reacts with the fine-grained surface of the substrate to eliminate the starting point of grain growth. Cerium nitrate can promptly repair the protective layer on the fine-grained surface, preventing grains at damaged locations from growing or corroding due to loss of protection, further improving the wear resistance and corrosion resistance of the substrate. Attached Figure Description

[0036] Figure 1 This is a process flow diagram of the processing of a gear pump base shell provided in Embodiment 1 of this application. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the embodiments.

[0038] Unless otherwise specified, the experimental methods used in the embodiments of this application are conventional methods, and the materials used are commercially available unless otherwise specified.

[0039] Example 1: This example discloses a gear pump base shell, spacer, and base shell processing technology.

[0040] 1. A gear pump housing made of low-carbon high-purity steel, wherein the low-carbon high-purity steel comprises, by mass percentage: 0.15wt% carbon, 0.05wt% niobium, 0.01wt% titanium, 0.003wt% boron, with the balance being iron.

[0041] The inner wall of the gear pump base is connected to a gear pump spacer by a metallurgical bonding method. The thickness of the spacer is 3.0 mm. The gear pump spacer is cast from tin-based Babbitt alloy. The mass percentage composition of the tin-based Babbitt alloy includes: antimony 11.0 wt%, copper 6.0 wt%, cadmium 1.0 wt%, nickel 0.20 wt%, and the balance is tin.

[0042] 2. A processing technology for the base shell of a gear pump, as shown in the attached figure. Figure 1 The processing flow shown includes the following steps: (1) Blank preparation: Low carbon high purity steel with the above composition is placed in a heating furnace and kept at 1165℃ for 75 min; (2) Temperature-controlled forging: Forging is carried out at 30°C above the austenite transformation completion temperature, which is 850°C in this case, with a deformation amount of 45%, to complete the initial forming; then deformation is carried out in the two-phase temperature region from the austenite initiation temperature of 780°C to the austenite transformation completion temperature of 820°C, with a deformation rate of 1.0 s. -1 This achieves the goal of further refining the grain size; (3) Surface cleaning: The following steps are performed in sequence: ① Electrothermal melting: Electrothermal melting is performed for 10 minutes using 200℃ electrothermal melting solution, wherein the mass percentage of the electrothermal melting solution formula is: 10wt% sodium hydroxide, 5wt% sodium carbonate, 4wt% trisodium phosphate, 1wt% sodium silicate, and the remainder is water; ② Alkaline washing: The blank after melting is immersed in 10wt% sodium hydroxide solution at 50℃ for 15 minutes; ③ Weak acid activation: Immerse in 5wt% dilute hydrochloric acid solution at 30℃ for 2 minutes; ④ Hot water rinsing: The blank is rinsed three times countercurrently with hot water at 80℃, each rinse lasting 2 minutes. (4) Tinning treatment: tinning is performed once at 340℃ for 45s, and then air-cooled for 2.5min. Then the temperature is lowered to 280℃ for a second tinning for 25s, forming a tin layer with a thickness of 0.20mm. (5) Casting: The molding material for the gear pump spacer was cast at 420℃ and a casting speed of 1.0 kg / s for a total time of 12s. (6) Gradient cooling: First spray water to cool for 15 minutes, then let it cool naturally to room temperature; (7) Tempering: Hold at 280℃ for 2.5h, then cool in the furnace to 80℃ before unloading; (8) Forming process: Dry cutting, turning, milling and drilling are carried out. After processing, the burrs are removed and the surface iron filings are cleaned to complete the preparation of the gear pump base shell.

[0043] 3. The following indicators were tested on the prepared gear pump base shell: average grain size, density, impact toughness, bonding strength between the spacer and the base shell, and interface porosity. (1) Average grain size (grade): reflects the grain refinement effect. The higher the grain size grade, the finer the grains, the higher the material strength and toughness, and the better the resistance to deformation and impact. The test standard is GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals". The test method is as follows: the base shell sample is inlaid, ground and polished, etched with nitric acid alcohol solution, the field of view is selected under an optical microscope, and the intercept point method is used to determine and calculate the average grain size. (2) Density (%): Reflects the internal pores and interfacial gaps of the matrix. The higher the density, the greater the resistance to atomic diffusion, which can inhibit high-temperature grain boundary migration and grain coarsening, while improving the strength and wear resistance of the matrix. The test standard is GB / T38507-2020 "Method for Determination of Density of Dense Metallic Materials". The test method is as follows: the volume and mass of the sample are measured by Archimedes' water displacement method, and the measured density is calculated. The relative density / relative density is calculated based on the theoretical density. (3) Impact toughness (J): The fracture resistance of the base material under dynamic load, avoiding the increase of brittleness due to coarse grains, and ensuring that the gear pump does not crack or break under heavy load and impact conditions; The test standard is GB / T229-2020 "Charpy impact test method for metallic materials". The test method is as follows: cut a standard V-notch specimen with a specimen size of 10mm×10mm×55mm and a notch depth of 2mm; use a pendulum impact tester to conduct an impact test on the specimen at room temperature, record the impact energy absorbed by the specimen when it breaks, and calculate the impact toughness value; (4) Bond strength between spacer and base shell (MPa): reflects the reliability of the metallurgical bond between the spacer and the base shell, prevents the spacer from peeling off and debonding during use, and ensures the stability of sealing, limiting and wear resistance functions; test standard: GB / T 13222-2021 "Metallic Bond Strength Test Method"; test method: process tensile specimens so that the stress interface is perpendicular to the loading direction, perform tensile test on universal testing machine, record the maximum load when the interface cracks, and calculate the bond strength; (5) Interface porosity (%): reflects the tightness of the interface between the base shell and the spacer. The lower the porosity, the better the interface sealing performance, and at the same time, it reduces frictional heat generation and local wear. Test standard: GB / T 15711-2018 "Method for determination of microporosity of metallic materials"; Test method: cut the interface cross-section sample, grind and polish it, and take pictures of the interface morphology under a metallographic microscope. The ratio of pore area to total interface area is calculated by image analysis to obtain the interface porosity.

[0044] 4. The resulting gear pump housing and spacer are used as gear pump components in electric vehicle hydraulic control systems, or as heavy-duty gear pump components in marine power systems, marine hydraulic steering systems, or marine ballast water systems.

[0045] Example 2: This example discloses a gear pump base shell, spacer, and base shell processing technology.

[0046] A gear pump housing is made of low-carbon high-purity steel, wherein the low-carbon high-purity steel comprises, by mass percentage: 0.25 wt% carbon, 0.02 wt% niobium, 0.03 wt% titanium, 0.001 wt% boron, with the balance being iron.

[0047] Everything else is exactly the same as in Example 1.

[0048] Example 3: This example discloses a gear pump base shell, spacer, and base shell processing technology.

[0049] A gear pump housing is made of low-carbon high-purity steel, wherein the low-carbon high-purity steel comprises, by mass percentage: 0.20 wt% carbon, 0.035 wt% niobium, 0.02 wt% titanium, 0.002 wt% boron, with the balance being iron.

[0050] Everything else is exactly the same as in Example 1.

[0051] The gear pump housings prepared in Examples 1-3 were tested respectively, and the test results are shown in Table 1: Table 1: detection indicators Example 1 Example 2 Example 3 Average grain size (grade) 9.2 8.8 9.0 Density (%) 99.1 99.3 99.2 Impact toughness (J) 68 70 69 Bond strength between spacer and base shell (MPa) 185 182 184 Interfacial porosity (%) 0.85 0.82 0.80 Comparing the data from Examples 1-3, it can be seen that Example 1 has the best average grain size, presumably because it has the highest niobium content. As a strong carbide-forming element, niobium can effectively hinder grain growth and has a more significant grain refinement effect. Example 2 has the highest carbon content and the lowest niobium content, resulting in a slightly lower grain size, but slightly higher impact toughness. This may be because a moderate increase in carbon content promotes a balance between matrix strength and toughness. The performance of Example 3 is at the middle level among the three examples, and the data shows that niobium has a more prominent effect on grain refinement. Overall, all three examples can achieve the effects of grain refinement, improved matrix density, and improved interfacial bonding reliability.

[0052] Example 4: This example discloses a gear pump base shell, spacer, and base shell processing technology.

[0053] In this embodiment, the processing technology for a gear pump base shell is based on the process of Example 3, with the addition of dehydrogenation and carbon treatment steps, as follows: The dehydrogenation and carbon treatment steps are set after the temperature-controlled forging step and before the surface cleaning step. The dehydrogenation and carbon treatment steps are as follows: under a vacuum of 3×10 -3 The process was carried out at 625°C for 105 minutes; the remaining processing steps and parameters were exactly the same as in Example 3.

[0054] Example 5: This example discloses a gear pump base shell, spacer, and base shell processing technology.

[0055] In this embodiment, in the processing technology of a gear pump base shell, the weak acid activation step in the surface activation step is: immersion in an activation solution at 30°C for 35 seconds; wherein, the activation solution has the following composition by mass percentage: sulfuric acid 2.5wt%, alkyl sulfonate 0.2wt%, and the balance is water; The remaining processing steps and parameters are exactly the same as in Example 4.

[0056] Example 6: This example discloses a gear pump base shell, spacer, and base shell processing technology.

[0057] In this embodiment, a plasma activation step is added to the processing technology of a gear pump base shell, as follows: The plasma activation step is set after the surface cleaning treatment step and before the tin plating treatment step; the plasma activation step is as follows: under the conditions of argon to oxygen volume ratio of 96:4, equipment power of 100W, and treatment distance of 20mm, plasma micro-oxidation treatment is performed for 60s to form an oxide layer of 20nm. The remaining processing steps and parameters are exactly the same as in Example 5.

[0058] The gear pump housings prepared in Examples 4-6 were tested respectively, and the test results are shown in Table 2: Table 2: detection indicators Example 4 Example 5 Example 6 Average grain size (grade) 9.4 9.4 9.5 Density (%) 99.5 99.5 99.5 Impact toughness (J) 72 72 72 Bond strength between spacer and base shell (MPa) 186 190 198 Interfacial porosity (%) 0.75 0.68 0.55 By comparing Example 4 with Example 3, it can be seen that Example 4, after temperature-controlled forging and before surface cleaning, added vacuum dehydrogenation and carbon treatment. The average grain size, density, impact toughness, and bonding strength of Example 4 were all improved, and the interfacial porosity was reduced. This is because vacuum dehydrogenation and carbon treatment can effectively remove hydrogen elements and excess carbon layers generated during forging, reduce internal defects in the matrix, optimize grain morphology, promote further grain refinement, thereby improving the density and toughness of the matrix, improving the interfacial bonding environment between the base shell and the spacer, reducing interfacial porosity, and improving bonding strength.

[0059] By comparing Example 5 with Example 4, it can be seen that Example 5 optimized the weak acid activation step in surface purification. The average grain size, density, and impact toughness remained unchanged. However, the bonding strength between the spacer and the base shell in Example 5 was higher than that in Example 4, and the interfacial porosity was lower than that in Example 4. The sulfuric acid in the activation solution could gently and uniformly remove the oxide layer on the surface of the base shell, avoiding excessive corrosion by dilute hydrochloric acid that would lead to uneven surface roughness. The addition of alkyl sulfonate improved the wettability of the activation solution, ensuring uniform activation of the base shell surface, thereby improving the metallurgical bonding effect between the spacer and the base shell, reducing the interfacial porosity, and increasing the bonding strength.

[0060] By comparing Example 6 with Example 5, it can be seen that Example 6 adds a plasma activation step after surface cleaning and before tinning. The average grain size is slightly better than that of Example 5, while the density and impact toughness remain unchanged. The bonding strength between the spacer and the base shell is improved, and the interfacial porosity is reduced. The oxide layer formed on the surface of the base shell by plasma micro-oxidation treatment can enhance the activity of the base shell surface. At the same time, the oxide layer, as a transition layer, promotes atomic diffusion between the base shell and the spacer molding material, strengthens the metallurgical bonding, reduces interfacial gaps and pores, thereby improving the bonding strength and reducing the interfacial porosity.

[0061] Example 7: This example discloses a gear pump base shell, spacer, and base shell processing technology.

[0062] In this embodiment, a preheating step is added to the processing technology of a gear pump base housing, as follows: The preheating step is set after the tinning step and before the pouring step; the preheating step is: preheating the mold used for pouring the spacer to 280°C and holding it at that temperature for 10 minutes; The remaining processing steps and parameters are exactly the same as in Example 6.

[0063] Example 8: This example discloses a gear pump base shell, spacer, and base shell processing technology.

[0064] In this embodiment, a passivation treatment step is added to the processing technology of a gear pump base housing, as follows: The passivation treatment step is set after the tempering step and before the forming process step; it includes a descaling step, which is: immersing in pickling solution for 75 seconds, followed by rinsing in water at 20°C for 15 seconds; wherein, the pickling solution comprises, by mass percentage: 6.5 wt% nitric acid, 2.5 wt% citric acid, and the remainder is water; The remaining processing steps and parameters are exactly the same as in Example 7.

[0065] Example 9: This example discloses a gear pump base shell, spacer, and base shell processing technology.

[0066] In this embodiment, the passivation process of a gear pump base housing further includes a self-healing sealing step, as detailed below: The self-healing sealing step is set after the oxide scale removal step, specifically: immersing in a sealing solution at 60°C for 45 seconds, followed by drying with hot air at 75°C for 4 minutes; wherein, the sealing solution comprises, by mass percentage: sodium molybdate 0.75wt%, phosphoric acid 0.45wt%, cerium nitrate 0.10wt%, ammonium vanadate 0.065wt%, with the remainder being water; The remaining processing steps and parameters are exactly the same as in Example 8.

[0067] The gear pump housings prepared in Examples 7-9 were tested respectively, and the test results are shown in Table 3: Table 3: detection indicators Example 7 Example 8 Example 9 Average grain size (grade) 9.4 9.5 9.5 Density (%) 99.6 99.6 99.8 Impact toughness (J) 74 75 77 Bond strength between spacer and base shell (MPa) 202 203 206 Interfacial porosity (%) 0.48 0.48 0.42 Comparing Example 7 with Example 6, it can be seen that Example 7 adds a mold preheating step. The average grain size of Example 7 is slightly lower than that of Example 6. The density, impact toughness, and bonding strength between the spacer and the base shell are all improved, and the interfacial porosity is reduced. Mold preheating reduces the temperature difference between the base shell and the mold, avoiding shrinkage stress caused by sudden cooling of the tin-based Babbitt alloy during casting, reducing the generation of interfacial cracks and porosity. At the same time, the preheated mold allows the casting material to solidify slowly, promoting the full diffusion of atoms between the base shell and the spacer, further strengthening the metallurgical bond, improving the bonding strength and density, and improving the toughness of the matrix while reducing the interfacial porosity.

[0068] By comparing Example 8 with Example 7, it can be seen that Example 8 adds a descaling step in the passivation process, resulting in a slightly better average grain size than Example 7. The density and interfacial porosity remain consistent, and the impact toughness and the bonding strength between the spacer and the base shell are slightly improved. The descaling step removes the oxide scale generated on the surface of the base shell during tempering, avoiding the oxide scale from affecting the accuracy of subsequent molding processes. At the same time, it reduces the damage of oxide scale to the properties of the substrate, refines the grains, and improves the impact toughness of the substrate and the bonding strength between the spacer and the base shell.

[0069] By comparing Example 9 with Example 8, it can be seen that Example 9 adds a self-healing sealing step after the oxide scale removal step in the passivation treatment. Except for maintaining the same average grain size, all other performance test indicators are improved. The reason is that in the self-healing sealing step, the sealing liquid forms a dense passivation film on the surface of the substrate, filling the micropores on the surface and interface of the substrate, improving the density and corrosion resistance of the substrate. At the same time, the passivation film can further strengthen the interface bonding between the substrate and the spacer, reduce interface defects, thereby improving impact toughness and bonding strength, reducing interface porosity, and achieving further performance optimization.

[0070] Comparative Example 1: This comparative example discloses a gear pump base housing, a spacer, and a base housing processing technology.

[0071] This comparative example is made of conventional low-carbon high-purity steel. The mass percentage of the low-carbon high-purity steel composition is: carbon content of 0.20 wt%, with the balance being iron. The remaining processing steps and parameters are exactly the same as in Example 3.

[0072] Comparative Example 2: This comparative example discloses a gear pump base housing, a spacer, and a base housing processing technology.

[0073] In this comparative example, the low-carbon high-purity steel composition retains only 0.035 wt% niobium and removes titanium and boron; the composition is as follows: 0.20 wt% carbon, 0.035 wt% niobium, and the balance is iron. The remaining processing steps and parameters are exactly the same as in Example 3.

[0074] Comparative Example 3: This comparative example discloses a gear pump base housing, a spacer, and a base housing processing technology.

[0075] In this comparative example, the low-carbon high-purity steel composition retains only 0.02 wt% titanium and removes niobium and boron; that is, the composition is as follows: carbon 0.20 wt%, titanium 0.02 wt%, and the balance is iron. The remaining processing steps and parameters are exactly the same as in Example 3.

[0076] The gear pump housings prepared in Comparative Examples 1-3 were tested respectively, and the test results are shown in Table 4: Table 4: detection indicators Comparative Example 1 Comparative Example 2 Comparative Example 3 Average grain size (grade) 6.5 7.8 7.6 Density (%) 98.0 98.7 98.8 Impact toughness (J) 45 58 60 Bond strength between spacer and base shell (MPa) 152 170 165 Interfacial porosity (%) 2.10 1.55 1.48 By comparing Comparative Example 1 with Example 3, it can be seen that Comparative Example 1 did not add niobium, titanium, and boron, so its performance was significantly worse than that of Example 3. This is because niobium, titanium, and boron can all play a role in grain refinement. Niobium and titanium can form carbides to hinder grain growth, while boron can strengthen grain boundaries and promote grain refinement. The synergistic effect of the three elements significantly improves the density and toughness of the matrix and improves the interfacial bonding effect. In Comparative Example 1, the grains could not be effectively refined, the internal defects of the matrix increased, and the interfacial bonding was not tight, resulting in a significant decline in various performances.

[0077] By comparing Comparative Example 2 and Example 3, it can be seen that the low-carbon high-purity steel of Comparative Example 2 retains only niobium and removes titanium and boron. Its performance is inferior to that of Example 3. Titanium and boron can work synergistically with niobium. Titanium helps niobium form more stable carbides, further refining the grains and increasing density. However, after Comparative Example 2 is missing titanium and boron, the effect of niobium alone is insufficient to achieve the optimal grain refinement and interface bonding effect, resulting in a decline in performance.

[0078] By comparing Comparative Example 3 with Example 3, it can be seen that the low-carbon high-purity steel of Comparative Example 3 only retains titanium and removes niobium and boron. Although titanium can form carbides to refine grains, its refining effect is far less than that of niobium, titanium and boron when used alone. Moreover, the stability of carbides decreases and the grain growth trend is enhanced after the absence of niobium. After the absence of boron, the grain boundary strength is insufficient and the interfacial bonding performance is affected. Therefore, all properties are lower than those of Example 3.

[0079] Comparative Example 4: This comparative example discloses a gear pump base housing, a spacer, and a base housing processing technology.

[0080] In this comparative example, the low-carbon high-purity steel composition retains only 0.002 wt% boron and removes niobium and titanium; that is, the composition is as follows: carbon 0.20 wt%, boron 0.002 wt%, and the balance is iron. The remaining processing steps and parameters are exactly the same as in Example 3.

[0081] Comparative Example 5: This comparative example discloses a gear pump base housing, a spacer, and a base housing processing technology.

[0082] In the temperature-controlled forging process, the deformation rate of the low-temperature deformation in the two-phase temperature zone is 0.3 s. -1 ; The remaining processing steps and parameters are exactly the same as in Example 3.

[0083] Comparative Example 6: This comparative example discloses a gear pump base housing, a spacer, and a base housing processing technology.

[0084] In the tempering step, the tempering temperature is 330℃ and the holding time is 4h; The remaining processing steps and parameters are exactly the same as in Example 3.

[0085] The gear pump housings prepared in Comparative Examples 4-6 were tested respectively, and the test results are shown in Table 5: Table 5: detection indicators Comparative Example 4 Comparative Example 5 Comparative Example 6 Average grain size (grade) 7.2 8.2 8.7 Density (%) 98.5 99.0 99.1 Impact toughness (J) 55 63 60 Bond strength between spacer and base shell (MPa) 165 178 180 Interfacial porosity (%) 1.62 1.10 0.95 By comparing Comparative Example 4 with Example 3, it can be seen that the low-carbon high-purity steel of Comparative Example 4 retains only boron and removes niobium and titanium. Its performance is inferior to that of Example 3, and its overall performance is between that of Comparative Example 1 and Comparative Examples 2 and 3. The analysis is that although boron can strengthen grain boundaries and assist in grain refinement, it cannot form stable carbides to effectively hinder grain growth like niobium and titanium. When boron is added alone, the grain refinement effect is limited, there are more defects in the matrix, and the density and toughness are not improved enough. At the same time, the interfacial bonding performance is affected by the lack of synergistic effect of niobium and titanium.

[0086] By comparing Comparative Example 5 with Example 3, it can be seen that in the temperature-controlled forging step of Comparative Example 5, the deformation rate of low-temperature deformation in the two-phase temperature zone was changed to 0.3 s. -1 The average grain size will be lower than 9.0 grade, and the density, impact toughness, and bonding strength will all decrease, while the interfacial porosity will increase. This is because the deformation rate in the two-phase temperature zone during temperature-controlled forging is the key factor affecting grain refinement; Example 3 uses 1.0s. -1The deformation rate of the sample can be improved by dynamic recrystallization to refine the grains. However, the deformation rate of Comparative Example 5 is too low, and the grains cannot be fully broken during the deformation process. The dynamic recrystallization effect is poor, resulting in coarse grains, reduced matrix density and toughness. At the same time, coarse grains will affect the interfacial bonding stability between the shell and the spacer, increase interfacial porosity, and reduce bonding strength.

[0087] By comparing Comparative Example 6 with Example 3, it can be seen that in the tempering step of Comparative Example 6, the tempering temperature is 330℃ and the holding time is 4h. The average grain size does not change significantly, but the impact toughness, density, bonding strength and interfacial porosity will also deteriorate. Tempering is mainly to eliminate the internal stress generated during forging and cooling, optimize the grain morphology and improve the toughness of the matrix. Example 3 avoids grain growth and carbide precipitation while eliminating internal stress. However, the tempering temperature and holding time of Comparative Example 6 are too high, which will cause slight coarsening of the matrix grains, increase the amount of carbide precipitation, and decrease the grain boundary strength, thereby reducing the impact toughness and density of the matrix. At the same time, excessive elimination of internal stress will affect the interfacial bonding stability between the shell and the spacer, resulting in a decrease in bonding strength and an increase in interfacial porosity.

[0088] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A gear pump base housing, characterized in that, It is made of low-carbon high-purity steel, wherein the low-carbon high-purity steel comprises the following components by mass percentage: carbon 0.15-0.25 wt%, niobium 0.02-0.05 wt%, titanium 0.01-0.03 wt%, boron 0.001-0.003 wt%, and the balance being iron.

2. A gear pump spacer, characterized in that, The spacer is metallurgically bonded to the inner wall of the gear pump base housing as described in claim 1; the thickness of the gear pump spacer is 2.0 to 4.0 mm.

3. A processing method for the gear pump base housing according to claim 1 or 2, characterized in that, Includes the following steps: Blank preparation: Low-carbon high-purity steel is used, and the temperature is maintained at 1150-1180℃ for 60-90 minutes; Temperature-controlled forging: Forging is performed at 20–40°C above the austenite transformation completion temperature, with a deformation amount of 35–55%. Further deformation is then carried out in the two-phase temperature range from the austenite initiation temperature to the austenite transformation completion temperature, with a deformation rate of 0.5–1.5 s⁻¹. -1 ; Surface cleaning includes the following steps: electric heating melting, alkaline washing, weak acid activation, and hot water rinsing. Tinning process: Perform a first tinning at 330-350℃ for 30-60 seconds, air cool for 2-3 minutes, and then perform a second tinning at 270-290℃ for 20-30 seconds. The thickness of the tin layer is 0.15-0.25 mm. Pouring: Pouring shall be carried out at 410~430℃ and a pouring speed of 0.8~1.2kg / s, with a total duration of ≤15s; Gradient cooling: First spray water to cool for 10-20 minutes, then let it cool naturally to room temperature; Tempering: Hold at 260-300℃ for 2-3 hours, then cool in the furnace to below 100℃ before unloading. Forming and processing: Dry cutting is used for processing.

4. The processing technology for the gear pump base housing according to claim 3, characterized in that, It also includes dehydrogenation and carbon treatment steps, which are set after the temperature-controlled forging step and before the surface cleaning step; The dehydrogenation and carbon treatment steps include: operating under a vacuum degree ≤ 5 × 10⁻⁶ -3 Under conditions of Pa and temperature of 600–650℃, keep warm for 90–120 minutes.

5. The processing technology for the gear pump base housing according to claim 4, characterized in that, In the surface purification step, the weak acid activation step includes: immersing in an activation solution at 25-35°C for 30-45 seconds; wherein the activation solution comprises, by mass percentage: sulfuric acid 2.0-3.0 wt%, alkyl sulfonate 0.1-0.3 wt%, and the balance being water.

6. The processing technology for the gear pump base housing according to claim 5, characterized in that, It also includes a plasma activation step, which is set after the surface cleaning treatment step and before the tinning treatment step; The plasma activation step includes: performing plasma micro-oxidation treatment for 30-90s under the conditions of argon to oxygen volume ratio of 95-98:2-5, power of 80-120W, and processing distance of 10-30mm to form an oxide layer of 10-30nm.

7. The processing technology for the gear pump base housing according to claim 6, characterized in that, It also includes a preheating step, which is set after the tinning process and before the casting process; The preheating step is as follows: preheat the mold to 260-300℃ and keep it at that temperature for 8-12 minutes.

8. The processing technology for the gear pump base housing according to claim 7, characterized in that, It also includes a passivation treatment step, which is performed after the tempering step and before the forming process step; The passivation process includes: a descaling step; The descaling step includes: immersing in pickling solution for 60-90 seconds, followed by rinsing in water for 10-20 seconds; wherein the pickling solution comprises, by mass percentage: 5-8 wt% nitric acid, 2-3 wt% citric acid, and the remainder being water.

9. The processing technology for the gear pump base housing according to claim 8, characterized in that, The passivation treatment step further includes a self-healing sealing step, which is set after the oxide scale removal step. The self-healing sealing step includes: immersing in a sealing solution at 55-65°C for 30-60 seconds, followed by drying with hot air at 70-80°C for 3-5 minutes; wherein the sealing solution comprises, by mass percentage: sodium molybdate 0.6-0.9 wt%, phosphoric acid 0.3-0.6 wt%, cerium nitrate 0.08-0.12 wt%, ammonium vanadate 0.05-0.08 wt%, with the balance being water.

10. The application of a gear pump base shell prepared by the processing technology of the gear pump base shell according to claim 1, or the gear pump spacer according to claim 2, or the gear pump base shell according to any one of claims 3-9, characterized in that, Gear pump components used in the hydraulic control system of electric vehicles, or heavy-duty gear pump components used in the power system, hydraulic steering gear system or ballast water system of ships.

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