Method for improving coercive force of nozzle valve element of automobile high-pressure oil sprayer through soft magnetic material

Abstract

The invention discloses a method for improving the coercive force of a soft magnetic material for a nozzle valve element of an automobile high-pressure oil sprayer. The coercive force of the magnetic performance of an X2CrNi Mo12 material is stably controlled to be about 200 A / m to 230 A / m. The invention provides a heat treatment mode combining two steps of high-temperature treatment and magnetic property treatment, rolled grains are further grown by utilizing high-temperature heat treatment, and the grains after high-temperature treatment are better than the rolled grains; in order to ensure the lower coercive force attribute, the X2CrNiMo12 needs to ensure that the material is a ferritic structure, so that the material structure is transformed into ferrite again by adopting a furnace cooling mode with the optimal magnetic performance treatment temperature of 740-750 DEG C and the heat preservation time of 10 hours, the coercive force of the material is reduced to 200-230 A / m, and the magnetic performance of the material is improved. The X2CrNiMo12 soft magnetic stainless steel material has the beneficial effects that the magnetic performance of the X2CrNiMo12 soft magnetic stainless steel material for the nozzle valve element of the oil injector is further improved, and the coercive force is reduced to 200 A / m to 230 A / m.

Description

Technical Field

[0001] The invention belongs to the field of metal material processing, relates to a method for improving the coercive force of a soft magnetic material used in a valve core of a high-pressure fuel injector nozzle of an automobile, and particularly relates to a method for regulating the magnetic properties of a X2CrNiMo12 soft magnetic stainless steel hot-rolled bar. Technical Background

[0002] High-pressure fuel injectors (HDEV) are mainly used to be installed on fuel rails. They can quickly meter and atomize fuel under high-pressure conditions to form the best mixture directly in the combustion chamber. With increasingly stringent emission regulations and fuel consumption requirements, as well as the desire for low costs, the requirements for materials used in high-pressure fuel injector nozzle valve cores are increasing, especially in terms of magnetic coercivity. Further improving the coercivity (Hcb) can make the nozzle valve core more responsive, accurately control fuel consumption, and improve fuel efficiency. X2CrNiMo12 is an ultra-low carbon, low chromium ferritic stainless steel. Due to its good magnetic properties and welding performance, it is widely used in key components such as injector nozzle valve cores. With the continuous improvement of emission regulations and fuel consumption requirements, the material needs to be further improved in terms of magnetic coercivity. Compared with other Cr12 and Cr17 series soft magnetic ferrite materials, this material is affected by the composition design and has a microstructure phase change. The traditional magnetic annealing control method can only achieve a magnetic coercivity of around 300A / m~350A / m. In order to improve the responsiveness of nozzle valve core parts and more effectively realize the precise control of oil circuit injection, further improve the magnetic properties and reduce the coercivity, which has become a production control difficulty for X2CrNiMo12 materials. Summary of the invention

[0003] The invention discloses a method for improving the coercive force of a soft magnetic material used in a high-pressure fuel injector nozzle valve core of an automobile. The purpose of the invention is to provide a magnetic property heat treatment process for optimizing and improving the coercive force, so that the magnetic property coercive force of the X2CrNiMo12 material can be further reduced and stably controlled at about 200A / m to 230A / m.

[0004] The specific steps of the technical solution are as follows:

[0005] 1. X2CrN iMo12 stainless steel material is designed based on the standard of EN 10088-3:2014. Its composition (mass fraction / %) is as follows: carbon not more than 0.025%, manganese: 0.70%~1.54%, silicon: 0.5%~1.0%, sulfur: 0.01%~0.035%, phosphorus not more than 0.045%, chromium: 11.50%~12.65%, molybdenum: 0.30%~0.60%, nickel: 0.40%~0.60%, nitrogen not more than 0.025%, and the balance is Fe

[0006] The optimized design composition (mass fraction / %) of X2CrN iMo12 is: carbon not more than 0.020%, manganese: 1.00%~1.15%, silicon: 0.65%~0.75%, sulfur: 0.015%~0.025%, phosphorus not more than 0.030%, chromium: 12.00%~12.40%, molybdenum: 0.30%~0.40%, nickel: 0.40%~0.50%, nitrogen not more than 0.020%, and the balance is Fe.

[0007] 2. Smelting: Use electric furnace + LF + VOD / VHD to smelt electric furnace 1.7t steel ingots that meet standard requirements.

[0008] 3. Rolling: The steel ingot is heated to 1090℃~1110℃, and the steel ingot is opened by 850 rolling mill. The steel billet is heated to 1080℃~1100℃, and the steel billet is rolled into a product of Φ11mm~Φ15mm by 430+250 rolling mill. The finished product is cooled by air cooling after rolling.

[0009] 4. Magnetic properties heat treatment: Use finite element software to calculate the X2CrNiMo12 material structure transformation phase diagram. When the heat treatment temperature is higher than 750℃, the structure changes. Figure 1 After rolling, high temperature treatment is given priority for structural adjustment. The material is heated to 1040℃~1060℃ in a chamber furnace and kept warm for 4 hours to further promote the initial grain growth after rolling. After the material is air-cooled to room temperature, it is annealed in a chamber furnace again. The heating temperature is 740℃~750℃ and the holding time is 10 hours. Then it is cooled to below 400℃ by furnace cooling.

[0010] 5. Finishing: After heat treatment, the material is cooled to room temperature and then finely polished.

[0011] Analysis of the invention points of the present invention:

[0012] The present invention proposes a heat treatment method combining "high temperature treatment + magnetic property treatment". High temperature heat treatment is used to further grow the rolled grains, ensuring that the grains after high temperature treatment are better than the rolled grains; X2CrNiMo12 needs to ensure that the material is ferrite in order to ensure a lower coercive force property. Combined with the phase diagram, it can be seen that since the material undergoes phase change above 750°C, the coercive force will deteriorate. In order to improve the magnetic property and reduce the coercive force index, the optimal temperature for magnetic property treatment is 740°C to 750°C, and the furnace cooling method with a holding time of 10h is used to transform the material structure into ferrite again, reduce the material coercive force to 200A / m to 230A / m, and improve the material magnetic property.

[0013] The beneficial effects of the present invention are: the magnetic properties of the X2CrNiMo12 soft magnetic stainless steel material used for the injector nozzle valve core are further improved, and the coercive force is reduced to 200A / m to 230A / m. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The simulated calculated phase diagram of X2CrN i Mo12 of the present invention, wherein the solid curve is the ferrite structure transformation phase diagram curve, and the dotted curve is the austenite structure transformation phase diagram curve;

[0015] Figure 2 This is a picture of the test results of the magnetic properties [coercive force (Hcb)] of the X2CrN i Mo12 stainless steel of the present invention. DETAILED DESCRIPTION

[0016] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0017] Examples 1 to 5 are all produced using the same process:

[0018] Smelting process: Electric furnace + LF + VOD / VHD is used to smelt an electric furnace 1.7t steel ingot that meets the standard requirements. The components (mass fraction / %) of Examples 1 to 4 are: carbon: 0.015%, manganese: 1.07%, silicon: 0.68%, sulfur: 0.022%, phosphorus: 0.022%, chromium: 12.10%, molybdenum: 0.35%, nickel: 0.45%, nitrogen: 0.011%, and the balance is Fe; the components (mass fraction / %) of Example 5 are: carbon: 0.015%, manganese: 1.06%, silicon: 0.71%, sulfur: 0.021%, phosphorus: 0.019%, chromium: 12.20%, molybdenum: 0.37%, nickel: 0.44%, nitrogen: 0.009%, and the balance is Fe;

[0019] Rolling process: The steel ingot is heated to 1100℃, and the 850 rolling mill is used to open the steel ingot. The steel billet is heated to 1090℃, and the 430+250 rolling mill is used to roll the steel into a product of Φ13mm. The finished product is cooled by air cooling after rolling.

[0020] Magnetic properties heat treatment: combined Figure 1 , using different temperatures for magnetic property treatment;

[0021] Finishing: After the material is cooled to room temperature, it is finely polished to Φ12.6mm.

[0022] Example 1 Magnetic property heat treatment: Magnetic property annealing is carried out in a chamber furnace with a heating temperature of 745°C and a holding time of 10 hours, followed by cooling to 385°C by furnace cooling.

[0023] Example 2 Magnetic property heat treatment: Magnetic property annealing is carried out in a chamber furnace with a heating temperature of 850°C and a holding time of 10 hours, followed by furnace cooling to 390°C before being taken out of the furnace.

[0024] Example 3 Magnetic property heat treatment: Magnetic property annealing was carried out in a chamber furnace with a heating temperature of 1050°C and a holding time of 10 hours, followed by furnace cooling to 390°C before being taken out of the furnace.

[0025] Example 4 adopts "high temperature treatment + magnetic property treatment": heating to 1050℃ in a chamber furnace, keeping the temperature for 4h, cooling to room temperature by air cooling, heating to 745℃ in a chamber furnace again, keeping the temperature for 10h, and then cooling to below 385℃ by furnace cooling. The magnetic properties can be seen. Figure 2 .

[0026] Example 5 adopts "high temperature treatment + magnetic property treatment": heating to 1050℃ in a chamber furnace, keeping the temperature for 4h, cooling to room temperature by air cooling, heating to 745℃ in a chamber furnace again, keeping the temperature for 10h, and then cooling to below 395℃ by furnace cooling. The magnetic properties can be seen. Figure 2 .

[0027] Magnetic property test: The magnetic property test results of Examples 1 to 5 are shown in Table 1.

[0028] Table 1

[0029]

[0030]

Claims

1. A method for improving the coercive force of a soft magnetic material used in a high-pressure fuel injector nozzle valve core of an automobile, characterized in that: The soft magnetic material and the method for improving coercivity: ⑴ The optimized design composition (mass fraction / %) of the soft magnetic material X2CrNiMo12 is: carbon not more than 0.020%, manganese: 1.00% ~ 1.15%, silicon: 0.65% ~ 0.75%, sulfur: 0.015% ~ 0.025%, phosphorus not more than 0.030%, chromium: 12.00% ~ 12.40%, molybdenum: 0.30% ~ 0.40%, nickel: 0.40% ~ 0.50%, nitrogen not more than 0.020%, and the balance is Fe; ⑵Methods to improve coercivity: ⑴ Smelting: Use electric furnace + LF + VOD / VHD to smelt electric furnace 1.7t steel ingots that meet standard requirements; (2) Rolling: The steel ingot is heated to 1090℃~1110℃, and the steel ingot is opened by 850 rolling mill. The steel billet is heated to 1080℃~1100℃, and the steel billet is rolled into a product of Φ11mm~Φ15mm by 430+250 rolling mill. The finished product is cooled by air cooling after rolling; ⑶ Magnetic property heat treatment: The X2CrNiMo12 material undergoes a microstructure change when the heat treatment temperature is 750℃. After rolling into products, high temperature treatment is given priority for microstructure adjustment. The material is heated to 1040℃~1060℃ in a chamber furnace and kept warm for 4h to further promote the initial grain growth after rolling. After the material is air-cooled to room temperature, it is again subjected to magnetic property annealing in a chamber furnace at a heating temperature of 740℃~750℃ and a holding time of 10h. It is then cooled to below 400℃ by furnace cooling and then taken out of the furnace; ⑷Finishing: After heat treatment, the material is cooled to room temperature and then finely polished.

2. The method for improving the coercive force of a soft magnetic material used in a high-pressure fuel injector nozzle valve core of an automobile according to claim 1, characterized in that: The soft magnetic material composition (mass fraction / %) is: carbon: 0.015%, manganese: 1.07%, silicon: 0.68%, sulfur: 0.022%, phosphorus: 0.022%, chromium: 12.10%, molybdenum: 0.35%, nickel: 0.45%, nitrogen: 0.011%, and the balance is Fe; Rolling: The steel ingot is heated to 1100℃, and the 850 rolling mill is used to open the steel ingot. The steel billet is heated to 1090℃, and the 430+250 rolling mill is used to roll the steel into a product with a diameter of Φ13mm. The finished product is cooled by air cooling after rolling. Adopt "high temperature treatment + magnetic property treatment": use a chamber furnace to heat to 1050℃, keep it at this temperature for 4 hours, cool it to room temperature by air cooling, and then use a chamber furnace to heat to 745℃ again, keep it at this temperature for 10 hours, and then use the furnace cooling method to cool it to below 385℃ before taking it out of the furnace; After the magnetic heat treatment, the material is cooled to room temperature and finely polished to Φ12.6mm; Magnetic properties Hcb (A / m) test results: 208, 215.

3. The method for improving the coercive force of a soft magnetic material used in a high-pressure fuel injector nozzle valve core of an automobile according to claim 1, characterized in that: The soft magnetic material composition (mass fraction / %) is: carbon: 0.015%, manganese: 1.06%, silicon: 0.71%, sulfur: 0.021%, phosphorus: 0.019%, chromium: 12.20%, molybdenum: 0.37%, nickel: 0.44%, nitrogen: 0.009%, and the balance is Fe; Rolling: The steel ingot is heated to 1105℃, and the 850 rolling mill is used to open the steel ingot. The steel billet is heated to 1090℃, and the 430+250 rolling mill is used to roll the steel into a product of Φ13mm. The finished product is cooled by air cooling. Adopt "high temperature treatment + magnetic property treatment": use a chamber furnace to heat to 1050℃, keep it at this temperature for 4 hours, cool it to room temperature by air cooling, and then use a chamber furnace to heat to 745℃ again, keep it at this temperature for 10 hours, and then use the furnace cooling method to cool it to below 395℃ before taking it out of the furnace; After the magnetic heat treatment, the material is cooled to room temperature and then finely polished to Φ12.6mm; Magnetic properties Hcb (A / m) test results: 210, 216.

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