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CN-121972611-A - Low-stress ferroalloy casting molding process for high-strength driving unit shell

CN121972611ACN 121972611 ACN121972611 ACN 121972611ACN-121972611-A

Abstract

The invention discloses a low-stress ferroalloy casting forming process of a high-strength driving unit shell, which relates to the technical field of mechanical manufacturing and aims to solve the technical problem that the current driving unit shell cannot balance high strength and low stress states after casting. According to the invention, through uniformly stirring molten iron added with the composite alloy additive in the step three, the alloy elements are ensured to be uniformly distributed in the molten iron, so that local stress concentration caused by coarse grains can be effectively relieved, meanwhile, the 'cracking effect' of the matrix can be reduced due to the spheroidized graphite form after casting, the stress concentration generated by graphite tips is avoided, and the internal stress of castings is further reduced.

Inventors

  • ZHANG JIAFU
  • CAI ZHENGGUANG

Assignees

  • 六安市龙兴汽车零部件有限公司

Dates

Publication Date
20260505
Application Date
20251015

Claims (10)

  1. 1. A casting process of a low stress ferroalloy for a high strength drive unit housing, the casting process comprising the steps of: Selecting high-grade iron ore with iron content more than or equal to 95% and scrap steel with impurity content less than or equal to 0.5% as main raw materials, preparing a composite alloy additive, carrying out jaw crushing pretreatment on the raw materials, outputting non-metallic inclusion content less than or equal to 0.15% in the raw materials, and ensuring that the granularity uniformity is more than or equal to 90%; Adding the output raw materials into a furnace return material, outputting the furnace return material to an electric furnace for smelting, heating to 1350-1380 ℃ for smelting, adding the composite alloy additive twice, mechanically skimming slag when the temperature is raised to 1420-1430 ℃, stopping heating after the temperature is raised to 1530-1550 ℃, and standing for 5-10min for high-temperature purification; Stirring the purified molten iron at the stirring speed of 300-500r/min for 5-8min, detecting the state of alloy elements in the molten iron, and adding a stream inoculant and an instantaneous inoculant according to the state of the alloy elements; Preheating a casting die, wherein the casting die comprises a casting base, a partition plate positioned above the casting base and a cover plate positioned above the partition plate, so that the casting die is preheated to 300-400 ℃, the water content is kept to be less than or equal to 0.05%, molten iron is cast in a layered casting mode, namely a bottom casting area is arranged between the casting base and the partition plate, the molten iron is cast to the bottom casting area and then cooled, a middle casting area is arranged between the partition plate and the cover plate, and the molten iron is cast to the bottom casting area and then cooled; and fifthly, demolding after cooling, removing two parts of castings positioned in the middle casting area and the bottom casting area in a demolding mode from top to bottom, performing ultrasonic detection and metallographic analysis to ensure that the equivalent of internal defects is less than or equal to phi 2mm, the pearlite content is more than or equal to 90%, the graphite spheroidization rate is more than or equal to 95%, and ensuring that the tensile strength of the castings is more than or equal to 320MPa and the elongation is more than or equal to 2%, wherein the casting is finished.
  2. 2. The casting molding process of the low-stress ferroalloy of the high-strength driving unit shell according to claim 1, wherein the composite alloy additive in the first step consists of at least two or more of ferromanganese, ferrosilicon, copper-chromium alloy and copper-tin alloy, the granularity after crushing in the first step is 20-50mm, and multi-layer screening and high-intensity magnetic separation are further needed before the raw materials are output, wherein the screening pore diameters of the multi-layer screening are 60 mm/30 mm/20 mm respectively, and the magnetic field intensity of the high-intensity magnetic separation is 12000-15000Gs.
  3. 3. The casting molding process of the low-stress ferroalloy of the high-strength driving unit shell according to claim 1, wherein in the second step, an intermediate frequency induction furnace of 200-500Hz is adopted as an electric furnace, the temperature is raised to 1350-1380 ℃ based on the speed of 5-8 ℃ per min, the interval between the two adding steps of the composite alloy additive is 10-15min, the carburant and the ferrosilicon are added after the adding of the second composite alloy additive, the slag-removing rate is more than or equal to 98% during slag-removing in the second step, and the carbon, silicon, manganese content and carbon equivalent in molten iron are 3.6-3.8% based on the detection of a direct-reading spectrometer.
  4. 4. The casting and forming process of the low-stress ferroalloy of the high-strength driving unit shell according to claim 3, wherein argon is introduced into molten iron for air washing during high-temperature purification in the second step, wherein the flow rate of the argon is 5-10L/min, the carburant in the second step is specifically graphitization carburant, the fixed carbon content of the carburant is more than or equal to 98%, and the sulfur content of the carburant is less than or equal to 0.05%.
  5. 5. The casting molding process of the low-stress ferroalloy for the high-strength driving unit housing according to claim 1, wherein the alloy element detection in the third step is based on the operation of a metal element detector, the detection content and the data required value are respectively 0.6% -0.8% of copper, 0.04% -0.06% of tin and 0.25% -0.30% of chromium, and when the alloy element content is not in the range, the element or the reactant is added according to the data difference.
  6. 6. The casting molding process of the low-stress ferroalloy of the high-strength driving unit shell according to claim 5, wherein the stream inoculant in the third step is 0.3% -0.6% of molten iron content and is continuously added in a runner, the instant inoculant in the third step is 0.1% -0.15% of molten iron content and is added in batches in a pouring cup, the stream inoculant in the third step is silicon particles with the purity of more than or equal to 99.5%, and the instant inoculant in the third step is silicon particles with the particle size of 0.5-1 mm.
  7. 7. The casting and forming process of the low-stress ferroalloy for the high-strength driving unit shell according to claim 6, wherein the casting mode of the bottom casting area and the middle casting area in the fourth step is based on a gradient temperature control mode, wherein the initial temperature is 1380-1400 ℃, the middle temperature is 1350-1380 ℃, the casting speed is 1300-1350 ℃ at the end, the casting speed is adjusted according to the initial temperature of 5-8L/min, the middle temperature of 10-15L/min and the end temperature of 5-8L/min, and the sectional slow cooling mode is adopted during cooling, namely, the cooling rate is more than 200 ℃ and less than or equal to 5 ℃ per hour, and natural cooling is carried out below 200 ℃.
  8. 8. The casting molding process of the low-stress ferroalloy for the high-strength driving unit shell according to claim 7, wherein the casting is cooled to 650-700 ℃ for 4-6 hours after the casting is completed in the fourth step, the casting stress is detected based on a stress detector, the casting stress is cooled to 200 ℃ or below with a furnace at a temperature of 5 ℃ or below per hour when the casting stress is less than or equal to 30MPa, and the casting stress is continuously kept at 650-700 ℃ and continuously detected when the casting stress is more than or equal to 30 MPa.
  9. 9. The casting molding process of the low-stress ferroalloy of the high-strength driving unit shell according to claim 1, wherein the low-temperature aging treatment is carried out before cooling and demolding in the fifth step, specifically, the heat preservation is carried out for 8-12h at 180-220 ℃, the ultrasonic detection in the fifth step is specifically based on the detection of internal defects between ultrasonic detectors at the frequency of 2.5-5MHz, the metallographic analysis in the fifth step is specifically to analyze graphite states by adopting an image analyzer, the graphite length is ensured to be less than or equal to 200 mu m, and dendrite-free graphite is adopted.
  10. 10. The casting process of low-stress ferroalloy for high-strength driving unit shells according to claim 1, wherein positioning holes for positioning are formed between the bottom casting area and the partition plate in the fourth step and between the partition plate and the cover plate, and a casting pipe penetrating through the cover plate is arranged on the cover plate.

Description

Low-stress ferroalloy casting molding process for high-strength driving unit shell Technical Field The invention relates to the technical field of mechanical manufacturing, in particular to a low-stress ferroalloy casting molding process of a high-strength driving unit shell. Background The driving unit shell is a shell structure for accommodating and protecting the internal components of the driving unit, and is required to have the characteristics of bearing larger stress and good mechanical property aiming at high-strength use scenes, and the driving unit shell made of iron alloy is commonly used on heavy vehicles or high-load gearboxes due to the characteristics of high strength and low cost, aiming at the high-strength driving unit shell applied to the gearbox, the high strength of the driving unit shell needs to be ensured, and the load condition caused by stress needs to be reduced, so that the raw material proportion and the process of the driving unit shell need to be controlled when the driving unit shell is cast in a self-loving way, and the driving unit shell can reach the optimal state after casting. The common problem of the existing gearbox adopting an integral casting molding process is that air in the gearbox after casting cannot be timely discharged based on a physical mode, so that casting flow is required to be controlled to ensure that gas can be rapidly discharged during single casting, and in order to achieve the purpose of low stress, the integration during casting is required to be achieved, the effective average of internal stress of external strength during casting cannot be ensured, and therefore the problem that larger deviation occurs between the strength and stress data of the gearbox shell after casting and an ideal value occurs. In view of this, we propose a low stress ferroalloy cast molding process for high strength drive unit housings. Disclosure of Invention The invention aims to overcome the defects of the prior art, adapt to the actual needs, and provide a low-stress ferroalloy casting molding process of a high-strength driving unit shell so as to solve the technical problem that the existing driving unit shell cannot balance high strength and low stress after casting. In order to solve the technical problems, the invention provides the following technical scheme that the casting and forming process of the low-stress ferroalloy of the high-strength driving unit shell comprises the following steps: Selecting high-grade iron ore with iron content more than or equal to 95% and scrap steel with impurity content less than or equal to 0.5% as main raw materials, preparing a composite alloy additive, carrying out jaw crushing pretreatment on the raw materials, outputting non-metallic inclusion content less than or equal to 0.15% in the raw materials, and ensuring that the granularity uniformity is more than or equal to 90%; Adding the output raw materials into a furnace return material, outputting the furnace return material to an electric furnace for smelting, heating to 1350-1380 ℃ for smelting, adding the composite alloy additive twice, mechanically skimming slag when the temperature is raised to 1420-1430 ℃, stopping heating after the temperature is raised to 1530-1550 ℃, and standing for 5-10min for high-temperature purification; Stirring the purified molten iron at the stirring speed of 300-500r/min for 5-8min, detecting the state of alloy elements in the molten iron, and adding a stream inoculant and an instantaneous inoculant according to the state of the alloy elements; Preheating a casting die, wherein the casting die comprises a casting base, a partition plate positioned above the casting base and a cover plate positioned above the partition plate, so that the casting die is preheated to 300-400 ℃, the water content is kept to be less than or equal to 0.05%, molten iron is cast in a layered casting mode, namely a bottom casting area is arranged between the casting base and the partition plate, the molten iron is cast to the bottom casting area and then cooled, a middle casting area is arranged between the partition plate and the cover plate, and the molten iron is cast to the bottom casting area and then cooled; and fifthly, demolding after cooling, removing two parts of castings positioned in the middle casting area and the bottom casting area in a demolding mode from top to bottom, performing ultrasonic detection and metallographic analysis to ensure that the equivalent of internal defects is less than or equal to phi 2mm, the pearlite content is more than or equal to 90%, the graphite spheroidization rate is more than or equal to 95%, and ensuring that the tensile strength of the castings is more than or equal to 320MPa and the elongation is more than or equal to 2%, wherein the casting is finished. Preferably, the composite alloy additive in the first step consists of at least two or more than two of ferromanganese, ferrosilicon, copper-chromium alloy and coppe