A method for producing a soft magnetic material for an automotive fuel injection system

Abstract

The application discloses a preparation method of a soft magnetic material for a car fuel injection system, and optimizes and accurately controls alloy element proportioning, controls molybdenum content to improve corrosion resistance, optimizes smelting mode to improve sulfur content, improves cutting performance, optimizes rolling process, improves steel ingot-steel billet rolling ratio, improves sulfide distribution and shape, improves cutting performance and improves material original grain size, designs continuous furnace heat treatment process, simulates room furnace material different temperature section heating-heat preservation-cooling slow cooling process, improves production efficiency, and meets material technical indexes at the same time. The application has the beneficial effect that the preparation of a product with low coercive force, high magnetic permeability and high strength is realized, and the index requirements of the product with coercive force (Hcb) not more than 200 A / m, tensile strength (Rm) not less than 450 MPa, hardness (HRB) 80-90 and grain size not less than 4 levels under an applied magnetic field of 50000 A / m are met.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, and relates to a method for producing hot-rolled bars, and particularly to a method for preparing 00Cr17MoS soft magnetic material for automotive fuel injection systems. Technical Background

[0002] Hot-rolled bars used in automotive fuel injection systems are key automotive components. Their performance directly impacts the reliability and stability of the fuel injection system, determining its lifespan. Therefore, hot-rolled bars must possess excellent magnetic properties while maintaining good mechanical performance. 00Cr17MoS is a soft magnetic flaky stainless steel with low coercivity and high permeability. Its excellent magnetic properties improve the sensitivity of solenoid valves and precisely control fuel injection flow. Its good mechanical properties make it suitable for various pressure environments, and its excellent corrosion resistance allows it to be widely used in low-pressure and high-pressure fuel injection system components. In recent years, with the continuous expansion of the domestic automotive market and the rapid rise of domestic automotive companies, the localization and innovation of key core technologies and materials have accelerated. Traditionally, domestic material supply has primarily focused on raw materials, with limited in-depth research reports on the performance of materials used in high-precision components. In particular, the magnetic properties of materials used in automotive fuel injection systems are difficult to overcome due to foreign technological blockades. Therefore, the development of hot-rolled bar technology for 00Cr17MoS materials used in automotive fuel injection systems is of paramount importance. Summary of the Invention

[0003] This invention discloses a method for preparing soft magnetic materials for automotive fuel injection systems. The aim is to provide a method for producing hot-rolled bars that meet the strength requirements of automotive fuel injection systems, enabling them to possess excellent magnetic properties while satisfying strength requirements. This improves the sensitivity of the fuel injection system's fuel circuit and achieves precise fuel injection control. Specifically, in terms of magnetic properties, it meets the requirement of having a coercivity (Hcb) of no more than 200 A / m under an applied magnetic field of 50,000 A / m; in terms of mechanical properties, it meets the requirements of a tensile strength (Rm) of no less than 450 MPa and a hardness (HRB) of 80–90; and a grain size of no less than grade 4 after magnetic property treatment.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] The chemical composition of 00Cr17MoS stainless steel is designed based on the ASTM A838 standard, with specific requirements as follows: carbon not more than 0.025%, manganese not more than 0.50%, silicon: 0.5%–1.25%, sulfur: 0.20%–0.35%, phosphorus not more than 0.040%, chromium: 17.25%–18.00%, molybdenum:

[0006] 1.50%–2.00%, nitrogen not more than 0.030%, niobium: 0.15%–0.35%.

[0007] The optimized composition of 00Cr17MoS stainless steel is designed as follows: carbon not more than 0.020%, manganese: 0.30%~0.45%, silicon: 0.75%~0.95%, sulfur: 0.22%~0.33%, phosphorus not more than 0.025%, chromium: 17.40%~17.80%, molybdenum: 1.60%~1.80%, copper not more than 0.15%, aluminum not more than 0.04%, nitrogen not more than 0.020%, niobium: 0.20%~0.32%, with the balance being Fe.

[0008] The preparation method of the above-mentioned 00Cr17MoS soft magnetic material includes the following specific steps: smelting in an EAF furnace-LF furnace-VOD / VHD furnace → die casting → rolling → annealing → h9 finishing of bright silver bars. The specific technical solution is as follows:

[0009] 1. EAF furnace: The raw materials consist of scrap steel, pig iron, and recycled steel, etc. Residual and harmful elements are controlled, and the tapping temperature (T) is guaranteed to be no less than 1650℃.

[0010] 2. LF furnace: Chemical composition in the roughing furnace, controlled as follows: carbon: 0.50%~0.75%, sulfur: no more than 0.005%, silicon: no more than 0.30%, chromium: 17.90%~18.00%, molybdenum: 1.60%~1.80%, tapping temperature: 1680℃~1700℃.

[0011] 3. VOD / VHD Furnace: After oxygen blowing in the VOD furnace, aluminum granules and industrial silicon are added along with the slag (fluorite, quicklime, etc.). The controlled composition is: manganese: 0.40% (target value), chromium: 17.40%~18.00%, niobium: 0.30% (target value), molybdenum: 1.80% (target value). The vacuum degassing pressure (P) is not greater than 67 Pa, and the holding time is 10 min. The furnace is then lifted into the VHD furnace for heating to adjust the sulfur content. In order to improve the final machinability of the material, the sulfur content is controlled at 0.27% (target value). The pouring temperature is 1550℃~1570℃.

[0012] 4. Ingot casting: Ultra-low carbon protective slag is used, and argon gas is used for 1.7t steel ingot casting; argon gas flow rate is controlled at 2m. 3 / h~3m 3 / h, argon pressure 0.4MPa~0.8MPa, to ensure the cleanliness of the steel flow system and prevent inclusions.

[0013] 5. Rolling: The steel ingot is slowly heated to 1140℃~1160℃ and held for 3h~4h. Then, it is rolled into 120 square billets using an 850 rolling mill. The billets are then transported to the next process. The billets are heated to 1100℃~1120℃ and rolled into 38 square billets using a 430+320 rolling mill. Finally, the billets are rolled into Φ10mm~Φ15mm round bars using a 250 rolling mill. To improve the machinability of 00Cr17MoS, sulfur is added to the steel to 0.22%~0.33%. In the final rolling process, the heating temperature needs to be controlled at 1040℃~1060℃ to ensure that the grain size of the rolled structure is not too coarse, and to prevent splitting of the billet due to excessively low heating temperature.

[0014] 6. Annealing: Magnetic property annealing is carried out using a continuous heating furnace. Utilizing the characteristics of the continuous heating furnace, the material is heated from a low temperature to 850℃. By controlling the roll speed to 8m / h~8.5m / h, the material is held at this temperature for 3.5h~4h and then slowly cooled to 550℃~600℃ with the continuous furnace roll speed before being air-cooled. Table 1 shows the heat treatment process.

[0015] Table 1 Heat Treatment Process of 00Cr17MoS

[0016]

[0017] 7. Finishing: Control the straightness before heat treatment to ensure that the straightness meets the requirements of the finished product. At the same time, consider ensuring the magnetic properties of the finished material. In order to prevent the magnetic properties from being reduced and the coercivity from being increased due to the finishing process, the polishing allowance should be controlled within 0.2mm to 0.3mm. Reduce the straightening force and ensure that the finishing polishing is completed within 2 times to minimize the impact of processing on the material and achieve the best magnetic properties of the finished product.

[0018] The design concept of this invention is as follows:

[0019] By optimizing the composition design and precisely controlling the alloy element ratio, the appropriate molybdenum content control is beneficial to improve corrosion resistance and enhance the corrosion resistance of the material in the oil injection system. Optimizing the smelting method to increase the sulfur content allows sulfur to form fusible sulfides with elements such as manganese and chromium, making the steel chips easier to curl and break during the process of making machine parts, thereby improving the cutting performance.

[0020] By optimizing the rolling process, increasing the ingot-to-billet rolling ratio, improving the distribution and shape of sulfides, and enhancing machinability, the original grain size of the material is optimized, providing a foundation for magnetic annealing processes.

[0021] By designing a continuous furnace heat treatment process that meets the material specifications of automotive fuel injection systems, the advantages of a continuous heat treatment furnace are cleverly utilized to simulate the slow cooling process of heating, holding, and cooling materials at different temperature ranges in a chamber furnace. This improves production efficiency while ensuring that the material's coercivity (Hcb) is no greater than 200 A / m under an applied magnetic field of 50,000 A / m.

[0022] The beneficial effects of the above-mentioned preparation method of the present invention are as follows: it realizes the preparation of products with low coercivity and high permeability, and meets the requirements of having a coercivity (Hcb) of not more than 200 A / m, tensile strength (Rm) of not less than 450 MPa, hardness (HRB) of 80-90 and grain size of not less than level 4 under an external magnetic field of 50000 A / m. Attached Figure Description

[0023] Figure 1 Image of the grain size of 00Cr17MoS stainless steel (50x magnification) of this invention;

[0024] Figure 2 Image of the grain size of 00Cr17MoS stainless steel (100x magnification) of this invention;

[0025] Figure 3 The image shows the test results of the magnetic properties [coercivity (Hcb)] of 00Cr17MoS stainless steel according to the present invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] Examples 1-3 were all produced using the same process: EAF furnace-LF furnace-VOD / VHD furnace smelting → die casting → rolling → annealing → h9 finishing; finished product specifications for Examples 1-3: Example 1: Φ16mm, Example 2: Φ15mm, Example 3: Φ14mm.

[0028] Example 1

[0029] 1. EAF furnace: The raw materials consist of scrap steel, pig iron, and recycled steel, etc. Residual and harmful elements are controlled, and the tapping temperature is 1655℃.

[0030] 2. LF furnace: The chemical composition of the roughing furnace is adjusted to control the carbon, sulfur, silicon, chromium and molybdenum elements. The specific measured results are: carbon: 0.58%, sulfur: 0.005%, silicon: 0.06%, chromium: 17.98%, molybdenum: 1.80%, and the tapping temperature is 1690℃.

[0031] 3. VOD / VHD Furnace: After oxygen blowing in the VOD furnace, aluminum granules and industrial silicon are added along with the slag (fluorite, quicklime, etc.) to control the composition of manganese, chromium, niobium, and molybdenum. The specific measured results are: manganese: 0.35%, target value of chromium: 17.50%, niobium: 0.26%, molybdenum: 1.80%, vacuum degassing pressure (P) 67 Pa, holding time 10 min, then hoisted into the VHD furnace for heating to adjust the sulfur content, sulfur: 0.29%, casting temperature: 1560℃; the chemical composition of the steel is shown in Table 2.

[0032] 4. Ingot Casting: Ultra-low carbon protective slag is used, and argon gas is used for 1.7t steel ingot casting; argon gas flow rate is controlled at 2.5m. 3 / h, argon pressure 0.58MPa.

[0033] 5. Rolling: The steel ingot is slowly heated to 1150℃ and held for 3.5 hours. Then, it is rolled into a 120 square billet using an 850 rolling mill. The billet is then transported to the next process. The billet is heated to 1105℃ and rolled into a 38 square billet using a 430+320 rolling mill. Finally, the billet is rolled into Φ16mm round steel using a 250 rolling mill. The final rolling heating temperature is 1050℃.

[0034] 6. Annealing: Magnetic property annealing is carried out using a continuous heating furnace. The specific heating temperatures are shown in Table 3.

[0035] 7. Finishing: Control the polishing allowance within 0.25mm to ensure that finishing polishing is completed in 2 times, and the finished product has the best magnetic properties.

[0036] 8. Performance: Test results are shown in Table 4; grain size (50x) is shown in Table 4. Figure 1 See grain size (100x) Figure 2 Magnetic property [coercivity (Hcb)] test see Figure 3 .

[0037] Example 2

[0038] 1. EAF furnace: The raw materials consist of scrap steel, pig iron, and recycled steel, etc. Residual and harmful elements are controlled, and the tapping temperature is 1655℃.

[0039] 2. LF furnace: The chemical composition of the roughing furnace is adjusted to control the carbon, sulfur, silicon, chromium and molybdenum elements. The specific measured results are: carbon: 0.62%, sulfur: 0.005%, silicon: 0.08%, chromium: 17.95%, molybdenum: 1.75%, and the tapping temperature: 1695℃.

[0040] 3. VOD / VHD Furnace: After oxygen blowing in the VOD furnace, aluminum granules and industrial silicon are added along with the slag (fluorite, quicklime, etc.) to control the composition of manganese, chromium, niobium, and molybdenum. The specific measured results are: manganese: 0.38%, chromium: 17.60%, niobium: 0.26%, molybdenum: 1.80%, vacuum degassing pressure (P) 67 Pa, holding time 10 min, then hoisted into the VHD furnace for heating to adjust the sulfur content to 0.27%, casting temperature: 1560℃; the chemical composition of the steel is shown in Table 2.

[0041] 4. Ingot casting: Ultra-low carbon protective slag is used, and argon gas is used for 1.7t steel ingot casting; argon gas flow rate is controlled at 2.6m. 3 / h, argon pressure 0.61MPa.

[0042] 5. Rolling: The steel ingot is slowly heated to 1155℃ and held for 3.5 hours. Then, it is rolled into a 120 square billet using an 850 rolling mill. The billet is then transported to the next process. The billet is heated to 1110℃ and rolled into a 38 square billet using a 430+320 rolling mill. Finally, the billet is rolled into Φ15mm round steel using a 250 rolling mill. The final rolling heating temperature is 1050℃.

[0043] 6. Annealing: Magnetic property annealing is carried out using a continuous heating furnace. The specific heating temperatures are shown in Table 3.

[0044] 7. Finishing: Control the polishing allowance within 0.25mm to ensure that finishing polishing is completed in 2 times, and the finished product has the best magnetic properties.

[0045] 8. Performance: The test results are shown in Table 4.

[0046] Example 3

[0047] 1. EAF furnace: The raw materials consist of scrap steel, pig iron, and recycled steel, etc. Residual and harmful elements are controlled, and the tapping temperature is 1655℃.

[0048] 2. LF furnace: The chemical composition of the roughing furnace is adjusted to control the carbon, sulfur, silicon, chromium and molybdenum elements. The specific measured results are: carbon: 0.64%, sulfur: 0.005%, silicon: 0.10%, chromium: 17.90%, molybdenum: 1.65%, and the tapping temperature is 1680℃.

[0049] 3. VOD / VHD Furnace: After oxygen blowing in the VOD furnace, aluminum granules and industrial silicon are added along with the slag (fluorite, quicklime, etc.) to control the composition of manganese, chromium, niobium, and molybdenum. The specific measured results are: manganese: 0.41%, chromium: 17.80%, niobium: 0.30%, molybdenum: 1.78%, vacuum degassing pressure (P) 67 Pa, holding time 10 min, then hoisted into the VHD furnace for heating to adjust the sulfur content to 0.30%, casting temperature: 1560℃; the chemical composition of the steel is shown in Table 2.

[0050] 4. Ingot Casting: Ultra-low carbon protective slag is used, and argon gas is used for 1.7t steel ingot casting; argon gas flow rate is controlled at 2.5m. 3 / h, argon pressure 0.59MPa.

[0051] 5. Rolling: The steel ingot is slowly heated to 1150℃ and held for 3.5 hours. Then, it is rolled into a 120 square billet using an 850 rolling mill. The billet is then transported to the next process. The billet is heated to 1120℃ and rolled into a 38 square billet using a 430+320 rolling mill. Finally, the billet is rolled into Φ14mm round steel using a 250 rolling mill. The final rolling heating temperature is 1050℃.

[0052] 6. Annealing: Magnetic property annealing is carried out using a continuous heating furnace. The specific heating temperatures are shown in Table 3.

[0053] 7. Finishing: Control the polishing allowance within 0.25mm to ensure that finishing polishing is completed in 2 times, and the finished product has the best magnetic properties.

[0054] 8. Performance: The test results are shown in Table 4.

[0055] Table 2 shows the chemical composition of Examples 1-3.

[0056]

[0057] Table 3 shows the actual heat treatment curves for Examples 1-3.

[0058] A section Second section Three sections Four sections Five-stage Six Dan Seven Dan Eight Dan 9th Dan Ten dan Roller speed Example 1 550℃ 700℃ 846℃ 848℃ 852℃ 849℃ 752℃ 630℃ 604℃ 575℃ 8.5m / h Example 2 554℃ 705℃ 848℃ 852℃ 850℃ 848℃ 745℃ 640℃ 600℃ 565℃ 8.5m / h Example 3 552℃ 708℃ 845℃ 853℃ 852℃ 850℃ 745℃ 630℃ 595℃ 556℃ 8.5m / h

[0059] Table 4 shows the test results for Examples 1-3.

[0060] Inspection items Hcb(A / m) Rm HRB Grain size Example 1 155、164 519、525 83、85 4 Example 2 148、152 512、509 82、83 4-5 Example 3 145、149 507、520 84、85 5

Claims

1. A method for preparing a soft magnetic material for an automotive fuel injection system, characterized in that, The controlled composition by mass percentage of the soft magnetic material is as follows: carbon not more than 0.020%, manganese: 0.30%–0.45%, silicon: 0.75%–0.95%, sulfur: 0.22%–0.33%, phosphorus not more than 0.025%, chromium: 17.40%–17.80%, molybdenum: 1.60%–1.80%, copper not more than 0.15%, aluminum not more than 0.04%, nitrogen not more than 0.020%, niobium: 0.20%–0.32%, with the balance being Fe; The preparation method specifically involves the following steps: smelting in an EAF furnace-LF furnace-VOD / VHD furnace → die casting → rolling → annealing → h9 finishing of bright silver bars. The specific technical solution is as follows: (1) EAF furnace: The raw materials consist of scrap steel, pig iron, and recycled steel. Residual and harmful elements are controlled, and the tapping temperature T is guaranteed to be no less than 1650℃. (2) LF furnace: The chemical composition of the roughing furnace is controlled as follows: carbon: 0.50%~0.75%, sulfur: no more than 0.005%, silicon: no more than 0.30%, chromium: 17.90%~18.00%, molybdenum: 1.60%~1.80%, and the tapping temperature is 1680℃~1700℃; (3) VOD / VHD furnace: After oxygen blowing in the VOD furnace, aluminum granules and industrial silicon are added along with the slag fluorite and quicklime. The mass percentage of the composition is controlled as follows: manganese: target value 0.40%, chromium: 17.40%~18.00%, niobium: target value 0.30%, molybdenum: target value 1.80%. The vacuum degassing pressure P is not greater than 67Pa and the holding time is 10min. The furnace is then hoisted into the VHD furnace for heating to adjust the sulfur content. The sulfur content is controlled at the target value of 0.27%. The casting temperature is 1550℃~1570℃. (4) Ingot casting: Ultra-low carbon protective slag is used, and argon gas is used for 1.7t steel ingot casting; argon gas flow rate is controlled at 2m³ / h~3m³ / h, and argon gas pressure is 0.4MPa~0.8MPa; (5) Rolling: The steel ingot is slowly heated to 1140℃~1160℃ and held for 3h~4h. Then, it is rolled into 120 square billets using an 850 rolling mill. The billets are then transported to the next process. The billets are heated to 1100℃~1120℃ and rolled into 38 square billets using a 430+320 rolling mill. Finally, the billets are rolled into Φ10mm~Φ15mm round bars using a 250 rolling mill. To improve the machinability of 00Cr17MoS, sulfur is added to the steel to 0.22%~0.33%. The heating temperature needs to be controlled at 1040℃~1060℃ in the final rolling process. (6) Annealing: Magnetic property annealing is carried out using a continuous heating furnace. Utilizing the characteristics of the continuous heating furnace, the material is heated from a low temperature to 850℃. By controlling the roll speed to 8m / h~8.5m / h, the material is held at this temperature for 3.5h~4h, then slowly cooled to 550℃~600℃ with the continuous furnace roll speed before being air-cooled. The heat treatment process is as follows: Section 1: not higher than 650℃; Section 2: not higher than 750℃; Section 3: not higher than 850℃; Section 4: 850℃±10℃; Section 5: 850℃±10℃; Section 6: 850℃±10℃; Section 7: not lower than 730℃; Section 8: not lower than 600℃; Section 9: furnace cooling; Section 10: furnace cooling; Roller speed 8m / h~8.5m / h. (7) Finishing: Before heat treatment, control the straightness. The polishing allowance should be controlled within 0.2mm to 0.3mm. Reduce the straightening force and complete the finishing polishing within 2 times.

2. The method for preparing a soft magnetic material for an automotive fuel injection system according to claim 1, characterized in that, The soft magnetic material comprises the following components by mass percentage: carbon: 0.017%, manganese: 0.39%, silicon: 0.85%, sulfur: 0.27%, phosphorus: 0.017%, chromium: 17.62%, molybdenum: 1.74%, copper: 0.08%, aluminum: 0.01%, niobium: 0.26%, balance Fe; The preparation method specifically involves the following steps: smelting in an EAF furnace-LF furnace-VOD / VHD furnace → die casting → rolling → annealing → h9 finishing of bright silver bars. The specific technical solution is as follows: (1) EAF furnace: The raw materials consist of scrap steel, pig iron, and recycled steel. Residual and harmful elements are controlled, and the tapping temperature T is not lower than 1655℃. (2) LF furnace: The chemical composition of the roughing furnace is as follows (mass percentage): Carbon: 0.58%, Sulfur: 0.005%, Silicon: 0.06%, Chromium: 17.98%, Molybdenum: 1.80%, and the tapping temperature is 1690℃. (3) VOD / VHD furnace: After oxygen blowing in the VOD furnace, aluminum granules and industrial silicon are added along with the slag fluorite and quicklime. The actual mass percentage of the components is as follows: Manganese: 0.35%, chromium target value: 17.50%, niobium: 0.26%, molybdenum: 1.80%, vacuum degassing pressure 67Pa, holding time 10min, hoisted into VHD furnace for heating to adjust sulfur content, sulfur: 0.29%, casting temperature: 1560℃; (4) Ingot casting: Ultra-low carbon protective slag is used, and argon gas is used for 1.7t steel ingot casting; argon gas flow rate is 2.5m³ / h, and argon gas pressure is 0.58MPa; (5) Rolling: The steel ingot is slowly heated to 1150℃ and held for 3.5 hours. Then, it is rolled into a 120mm square billet using an 850mm rolling mill. The billet is then transported to the next process. The billet is heated to 1105℃ and rolled into a 38mm square billet using a 430mm + 320mm rolling mill. Finally, the billet is rolled into Φ16mm round steel using a 250mm rolling mill. The final rolling heating temperature is 1050℃. (6) Annealing: Magnetic property annealing is carried out in a continuous heating furnace. The actual heat treatment process is as follows: Section 1: 550℃, Section 2: 700℃, Section 3: 846℃, Section 4: 848℃, Section 5: 852℃, Section 6: 849℃, Section 7: 752℃, Section 8: 630℃, Section 9: 604℃, Section 10: 575℃, Roller speed 8.5m / h; (7) Finishing: Control the polishing allowance within 0.25mm, and complete the finishing polishing in 2 passes.

3. The method for preparing a soft magnetic material for an automotive fuel injection system according to claim 1, characterized in that, The soft magnetic material is composed of the following components by mass percentage: carbon: 0.016%, manganese: 0.39%, silicon: 0.79%, sulfur: 0.29%, phosphorus: 0.019%, chromium: 17.65%, molybdenum: 1.72%, copper: 0.06%, aluminum: 0.02%, niobium: 0.27%, with the balance being Fe; The preparation method specifically involves the following steps: smelting in an EAF furnace-LF furnace-VOD / VHD furnace → die casting → rolling → annealing → h9 finishing of bright silver bars. The specific technical solution is as follows: (1) EAF furnace: The raw materials consist of scrap steel, pig iron, and recycled steel. Residual and harmful elements are controlled, and the tapping temperature T is not lower than 1655℃. (2) LF furnace: The mass percentage of chemical composition in the coarse adjustment furnace, the actual measured result is carbon: 0.62%, Sulfur: 0.005%, Silicon: 0.08% chromium, 17.95% molybdenum, 1.75% steel, tapping temperature: 1695℃; (3) VOD / VHD furnace: After oxygen blowing in the VOD furnace, aluminum granules and industrial silicon are added along with the slag fluorite and quicklime. The actual mass percentage of the components is as follows: Manganese: 0.38%, Chromium: 17.60%, Niobium: 0.26%, Molybdenum: 1.80%, Vacuum degassing pressure 67 Pa, holding time 10 min, hoisted into VHD furnace for heating to adjust sulfur content, sulfur: 0.27%, casting temperature: 1560℃; (4) Ingot casting: Ultra-low carbon protective slag is used, and argon gas is used for 1.7t steel ingot casting; argon gas flow rate is 2.6m³ / h, and argon gas pressure is 0.61MPa; (5) Rolling: The steel ingot is slowly heated to 1155℃ and held for 3.5 hours. Then, it is rolled into a 120mm square billet using an 850mm rolling mill. The billet is then transported to the next process. The billet is heated to 1110℃ and rolled into a 38mm square billet using a 430mm + 320mm rolling mill. Finally, the billet is rolled into Φ15mm round steel using a 250mm rolling mill. The final rolling heating temperature is 1050℃. (6) Annealing: Magnetic property annealing is carried out in a continuous heating furnace. The actual heat treatment process is as follows: Section 1: 554℃, Section 2: 705℃, Section 3: 848℃, Section 4: 852℃, Section 5: 850℃, Section 6: 848℃, Section 7: 745℃, Section 8: 640℃, Section 9: 600℃, Section 10: 565℃, Roller speed 8.5m / h; (7) Finishing: Control the polishing allowance within 0.25mm, and complete the finishing polishing in 2 passes.

4. The method for preparing a soft magnetic material for an automotive fuel injection system according to claim 1, characterized in that, The soft magnetic material comprises the following components by mass percentage: carbon: 0.018%, manganese: 0.37%, silicon: 0.84%, sulfur: 0.27%, phosphorus: 0.014%, chromium: 17.54%, molybdenum: 1.75%, copper: 0.08%, aluminum: 0.01%, niobium: 0.28%, balance Fe; The preparation method specifically involves the following steps: smelting in an EAF furnace-LF furnace-VOD / VHD furnace → die casting → rolling → annealing → h9 finishing of bright silver bars. The specific technical solution is as follows: (1) EAF furnace: The raw materials consist of scrap steel, pig iron, and recycled steel. Residual and harmful elements are controlled, and the tapping temperature T is not lower than 1655℃. (2) LF furnace: The mass percentage of chemical composition in the coarse adjustment furnace, the actual measured result is carbon: 0.64%, Sulfur: 0.005%, Silicon: 0.10%, Chromium: 17.90%, Molybdenum: 1.65%, Tack temperature: 1680℃; (3) VOD / VHD furnace: After oxygen blowing in the VOD furnace, aluminum granules and industrial silicon are added along with the slag fluorite and quicklime. The actual mass percentage of the components is as follows: Manganese: 0.41%, Chromium: 17.80%, Niobium: 0.30%, Molybdenum: 1.78%, Vacuum degassing pressure (P) 67 Pa, holding time 10 min, hoisted into VHD furnace for heating to adjust sulfur content, sulfur: 0.30%, casting temperature: 1560℃; (4) Ingot casting: Ultra-low carbon protective slag is used, and argon gas is used for 1.7t steel ingot casting; argon gas flow rate is 2.5m³ / h, and argon gas pressure is 0.59MPa; (5) Rolling: The steel ingot is slowly heated to 1150℃ and held for 3.5 hours. Then, it is rolled into a 120mm square billet using an 850mm rolling mill. The billet is then transported to the next process. The billet is heated to 1120℃ and rolled into a 38mm square billet using a combination of a 430mm and a 320mm rolling mill. Finally, the billet is rolled into Φ14mm round steel using a 250mm rolling mill. The final rolling heating temperature is 1050℃. (6) Annealing: Magnetic property annealing is carried out in a continuous heating furnace. The actual heat treatment process is as follows: Section 1: 552℃, Section 2: 708℃, Section 3: 845℃, Section 4: 853℃, Section 5: 852℃, Section 6: 850℃, Section 7: 745℃, Section 8: 630℃, Section 9: 595℃, Section 10: 556℃, Roller speed 8.5m / h; (7) Finishing: Control the polishing allowance within 0.25mm, and complete the finishing polishing in 2 passes.

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