CN116445817A - Soft magnetic steel for solenoid valve and manufacturing method thereof - Google Patents

Abstract

A soft magnetic steel for solenoid valves, the composition of which includes: 0.06%-0.08% C, no more than 0.05% Si, 1.05%-1.20% Mn, 0.065%-0.075% P and 0.29% by weight ‑0.32% S, and 0.003%‑0.01% Nb, 0.0018%‑0.01% Ti and 0.003%‑0.03% Mo. The soft magnetic steel has good mechanical properties and stable magnetic properties, can effectively improve the yield rate of gearbox solenoid valve manufacturing, and reduce manufacturing costs. The invention also provides a manufacturing method of the soft magnetic steel for the solenoid valve.

Description

Soft magnetic steel for solenoid valve and manufacturing method thereof

technical field

The invention belongs to the field of iron and steel, and in particular relates to a soft magnetic steel for electromagnetic valves and a manufacturing method thereof.

Background technique

The gearbox solenoid valve is the core component of the automobile automatic gearbox to realize the function. The gearbox controller realizes the movement of the clutch, brake, hydraulic torque converter and other components in the automatic gearbox by controlling the actuation of the solenoid valve, so as to realize automatic gear shifting Function. The gearbox solenoid valve is used to control the on-off and flow direction of the pressure fluid in the pipeline, adjust the pressure, and eliminate the hydraulic shock. It needs to respond quickly and accurately for a long time during the service cycle. Therefore, the requirements for the soft magnetic steel used in the manufacture of gearbox solenoid valves are very high, and they need to meet good mechanical strength, cutting performance and stable magnetic properties at the same time. Solenoid valve armatures and magnetic sleeves are currently made of imported 11SMn30 steel, but the cost of imported materials is high, and the magnetic properties, especially key indicators such as coercive force and magnetic induction intensity, fluctuate greatly, which cannot be accurately controlled, resulting in the scrap rate of parts in actual production. High, low production efficiency. At present, in the industry, the influence of processing and manufacturing parameters on the magnetic properties of soft magnetic steel is not sufficient. It is difficult for mass-produced soft magnetic steel to achieve ideal magnetic properties. The magnetic properties of different batches of products fluctuate significantly. How to specify can obtain The manufacturing parameters of soft magnetic steel materials with stable magnetic properties that meet the design requirements have always been a difficult problem in the industry. Therefore, providing a soft magnetic steel for solenoid valves with stable magnetic properties and its manufacturing method is of great significance for reducing production costs, improving product quality, and improving the localization rate of key parts in the automobile industry.

Contents of the invention

The object of the present invention is to provide a soft magnetic steel with stable magnetic properties, so as to reduce the rejection rate of electromagnetic valve products caused by fluctuations in magnetic properties. The invention further provides a method for manufacturing the steel for electromagnetic valves with stable magnetic properties.

According to an embodiment of one aspect of the present invention, there is provided a soft magnetic steel with stable magnetic properties, the composition of which includes: 0.06%-0.08% of C, no more than 0.05% of Si, 1.05%-1.20% of Mn, 0.065%-0.075% P and 0.29%-0.32% S, and 0.003%-0.01% Nb, 0.0018%-0.01% Ti and 0.003%-0.03% Mo.

C element affects the hardness of steel and has a significant impact on mechanical properties, but C is an austenite forming element that has a negative impact on magnetic properties, so the content of C element is further limited to 0.06%-0.08% on the basis of the composition of conventional 11SMn30 steel . S is beneficial to improve the machinability of steel, but excessive S will damage the mechanical properties of steel. Nb, Ti, and Mo belong to ferrite forming elements, which are beneficial to improve the magnetic properties of steel.

Further, the performance of the soft magnetic steel satisfies: tensile strength ≥ 300MPa, yield strength ≥ 210MPa, hardness HBW 110-150, coercive force 150A/m-200A/m; magnetic induction intensity 1.20T ≤ B ₁₀₀₀ ≤1.42T, 1.46T≤B ₂₀₀₀ ≤1.58T, 1.65T≤B ₅₀₀₀ ≤1.70T,

1.77T ≤ B ₁₀₀₀₀ ≤ 1.82T, 1.92T ≤ B ₂₀₀₀₀ ≤ 1.96T, 2.01T ≤ B ₃₀₀₀₀ ≤ 2.05T. At the same time, stable mechanical properties and magnetic properties can be better applied to the manufacture of solenoid valves and reduce product scrap rates. Generally, 11SMn30 steel for solenoid valves requires coercive force Hc≤250A/m. The inventors have found in practice that further limiting the value range of coercive force to 150A/m-200A/m can make the solenoid valves made of this steel obtain More stable response speed and precision, less prone to out-of-tolerance, and improved product qualification rate.

Further, the grain size grade in the structure of the soft magnetic steel is 3-5. Fine-grained structure is conducive to improving the mechanical properties of steel, and larger grains can maintain stable magnetic properties.

According to an embodiment of another aspect of the present invention, there is provided a method for manufacturing soft magnetic steel, the method comprising the following steps: hot rolling the billet, the initial rolling temperature is 870°C-920°C, the final rolling temperature is 910°C-940°C, and Processed into bars; the hot-rolled bars are cold-drawn, and the cold-drawing area reduction rate is 7%-18%; the cold-drawn bars are kept at 780°C-860°C for more than 8-20h Complete magnetic heat treatment.

After the above heat treatment process, a suitable and uniform grain structure can be formed in the steel for solenoid valves, and the precipitates are evenly distributed, so that the steel has stable magnetic properties and coercive properties while having good mechanical properties and cutting properties. Force, remanence, magnetic saturation and magnetic induction can all be controlled within the scope of the design requirements without exceeding the tolerance.

Further, the rod components used in the manufacturing method include: 0.06%-0.08% of C, no more than 0.05% of Si, 1.05%-1.20% of Mn, 0.065%-0.075% of P and 0.29%- 0.32% S, and 0.003%-0.01% Nb, 0.0018%-0.01% Ti and 0.01%-0.03% Mo. Steel produced within the commercial 11SMn30 steel composition range cannot achieve stable magnetic properties, and is prone to out-of-tolerance indicators such as coercive force and magnetic induction. Therefore, on the basis of the general 11SMn30 steel composition, it is necessary to further limit the content of C element components that are unfavorable to magnetic properties, and increase Nb, Ti, Mo and other elements that help improve magnetic properties.

Preferably, the area reduction rate of the cold drawing process is 10.25%-13.22%, the heating temperature for the magnetic heat treatment is 820±20° C., and the time for the magnetic heat treatment is 12 hours.

Further, the manufacturing method also includes the step of smelting rods, in the step of smelting rods, the residual O content is controlled at 40ppm-100ppm when tapping, and the sulfides in the rods comply with SEP1572 standard 2.2 or 2.3, The inclusion rating is less than 2. In order to achieve good mechanical properties, machinability and magnetic properties, it is necessary to strictly control the structure of the bar. The residual O content is controlled to reduce oxide inclusions; the sulfide distribution affects the machinability of steel.

Further, before hot-rolling the bar, the bar is firstly heated to 1170° C.-1190° C. for 2h-4h. Preheating and heat preservation ensures uniform temperature distribution inside and outside the bar before hot rolling, reducing structural defects in the bar.

Further, in the magnetic heat treatment process, firstly, the rod is preheated to 650±20°C for 2 hours, and then heated to 820±20°C for 3.5 hours; after the heat preservation is completed, it is first cooled to 650±20°C for 7 hours , and then cooled to 200±20°C with the furnace. During the magnetic heat treatment, the heating and cooling process is controlled to ensure the uniform structure of the semi-finished steel product.

Further, the manufacturing method also includes a grinding step, grinding the semi-finished steel material that has undergone magnetic heat treatment to a required size. After magnetic heat treatment, the semi-finished steel product has a uniform structure after recrystallization, and can no longer introduce deformation and residual stress through mechanical deformation such as drawing or thickening, otherwise the magnetic properties will be unstable.

Further, the processing capacity of the grinding step is 0.02mm-0.03mm per side. If the amount of grinding process is too high, it will increase the consumption of man-hours, and if the amount of grinding process is too low, the surface quality of the product will be unqualified.

Description of drawings

Figure 1a is a schematic diagram of a partial structure of a solenoid valve in an embodiment;

Fig. 1b is a structural schematic diagram of a magnetic sleeve and an armature in an embodiment;

Fig. 1c is a schematic diagram of a cross-sectional structure of a magnetic sleeve in an embodiment;

Fig. 1d is a schematic cross-sectional structure diagram of an armature in an embodiment;

Fig. 2 is a range curve of magnetic induction B in steel under different magnetic field strengths in an embodiment.

The purpose of the above drawings is to describe the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, but not intended to limit the present invention. For the sake of brevity, the above drawings only schematically show the structure related to the technical features of the present invention, and do not strictly follow the actual scale to draw the complete structure and all the details.

Detailed ways

The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment herein. The appearances of this phrase in various places in the specification are not necessarily referring to the same embodiment, nor are mutually exclusive independent or alternative embodiments defined. Those skilled in the art should be able to understand that the embodiments herein can be combined with other embodiments on the premise that there is no principle conflict.

Various solenoid valves are installed in the automatic transmission of automobiles to control the hydraulic system in the transmission to realize complex actions such as gear shifting and torque conversion. With the increasingly complex structure and function of automatic transmission, the requirements for the response speed and motion precision of the solenoid valve are also getting higher and higher. In one embodiment, in the solenoid valve shown in FIG. 1a, the materials of the solenoid valve armature 2 and the magnetic sleeve 1 are crucial to the overall performance of the solenoid valve. 1b-1d, the magnetic sleeve 1 and the solenoid valve housing 3 are relatively fixedly connected, and the armature 2 is nested in the cavity 11 inside the magnetic sleeve 1. When the solenoid valve is energized, the magnetic sleeve 1 and the armature 2 produce a sense of the same direction A magnetic field is generated, the lower armature 2 is attracted by the magnetic sleeve 1, and moves leftward along the axial direction. The installation hole 21 of the valve stem 4 is arranged in the armature 2, and one end of the valve stem 4 passes through the through hole 12 at the end of the magnetic sleeve 1 and is fixed. Connected to the mounting hole 21, the armature 2 drives the solenoid valve stem 4 to move when it moves. The valve stem 4 is provided with a radially penetrating through hole (not shown). When the valve stem 4 moves to different positions, the through hole can be connected to or staggered with different oil passages 6a or 6b respectively, so as to realize the oil passage adjustment. The other end of the valve stem 4 is connected to the reset device 5 , once the magnetic force between the magnetic sleeve 1 and the armature 2 weakens under the action of the reset device 5 , the valve stem 4 will be pushed to move to the right. Thus, the magnitude of the magnetic force between the magnetic sleeve 1 and the armature 2 is controlled by the strength of the current passing through the solenoid valve, thereby realizing precise control of the liquid circuit. Due to the high structural accuracy requirements of the armature 2 and the magnetic sleeve 1, the magnetic material of the solenoid valve needs to have good cutting performance to ensure the dimensional accuracy of machining; it also needs to meet the strength requirements to achieve long-term high-frequency high-strength service conditions. Design life requirements; at the same time, it also needs to have stable magnetic properties to ensure the response speed and accuracy of the solenoid valve actuation. At present, solenoid valves are usually made of easy-to-cut 11SMn30 steel. Usually, domestic 11SMn30 steel is only produced as a raw material for machining. It lacks control over magnetic properties and cannot meet the needs of solenoid valve manufacturing. The out-of-poor performance of critical properties such as recalcitrance leads to an increase in product scrap rate. At present, there are few studies on 11SMn30 steel in this field, and there is a lack of knowledge and technology accumulation on how to accurately control the composition and processing technology of steel to obtain products with stable magnetic properties. Since 11SMn30 steel has a long process from raw material smelting to finished product processing, each of which will have an impact on the final magnetic properties, iron and steel production enterprises, machining enterprises or solenoid valve production enterprises research and optimize process parameters within the scope of their respective processes It is difficult to effectively correlate the factors that affect the quality of the final product, so it is always difficult to provide a finished steel product that meets the quality requirements.

In order to solve the above-mentioned problems, the inventor has gone through a lot of research and experiments, tracked and analyzed the complete process of solenoid valve production and processing from the raw material link, comprehensively analyzed and verified smelting, heat treatment, and mechanical processing, and proposed a stable magnetic valve. A steel for solenoid valves and a manufacturing method thereof.

According to an embodiment of one aspect of the present invention, a steel for a solenoid valve with stable magnetic properties is provided. Conventional commercial 11SMn30 steel is used as raw material for machining, and its composition is 0.04%-0.1% C, not more than 0.09% Si, 0.09%-1.26% Mn, not more than 0.15% P and 0.25%- 0.35% S. The steel for solenoid valves with stable magnetic properties provided by the embodiments of the present invention further requires that the C content is 0.06%-0.08%, the Si content is not more than 0.05%, the Mn content is 1.05%-1.20%, and the P content is 0.065%- 0.075%, the S content is 0.29%-0.32%, and further adding 0.003%-0.01% of Nb, 0.0018%-0.01% of Ti and 0.01%-0.03% of Mo. Among them, C and Mn belong to austenite forming elements, which are beneficial to improve the strength and toughness, but are not conducive to the magnetic properties of finished steel; Si, Nb, Ti, and Mo belong to ferrite forming elements, which are beneficial to the magnetic properties of finished steel. Both Nb and Ti are used to adjust and improve the mechanical properties of finished steel. The grain size of the finished steel for the solenoid valve is 3-5, and has good mechanical properties, cutting properties and stable magnetic properties. The tensile strength of the finished steel product for the solenoid valve is ≥300MPa, and the yield strength

≥210MPa, hardness HBW is 110-150. In terms of magnetic properties, the coercive force Hc is 150A/m-200A/m; the numerical range of the magnetic induction intensity B of the steel for solenoid valves under different external magnetic field strengths H satisfies the BH curve shown in Figure 2, and at 1000A/m The magnetic induction intensity B ₁₀₀₀ at 2000A/m, the magnetic induction intensity B ₂₀₀₀ at 2000A/m, the magnetic induction intensity B ₅₀₀₀ at 5000A/m,

The magnetic induction intensity B ₁₀₀₀₀ at 10000A/m, the magnetic induction intensity B ₂₀₀₀₀ at 20000A/m and the magnetic induction intensity B ₃₀₀₀₀ at 30000A/m respectively satisfy 1.20T≤B ₁₀₀₀ ≤1.42T,

1.46T≤B ₂₀₀₀ ≤1.58T, 1.65T≤B ₅₀₀₀ ≤1.70T, 1.77T≤B ₁₀₀₀₀ ≤1.82T,

_{1.92T≤B20000≤1.96T} , _{2.01T≤B30000≤2.05T} . The above performance indicators ensure that the steel for solenoid valves can meet the requirements of fast response and precise actuation of solenoid valves on the basis of good mechanical properties.

According to an embodiment of another aspect of the present invention, a method for manufacturing steel for a solenoid valve is provided, the method comprising the following steps:

Firstly, the steel billet is hot-rolled, the initial rolling temperature is controlled at 870°C-920°C, and the final rolling temperature is controlled at 910°C-940°C. The hot rolling process breaks the columnar crystals formed during the solidification of the billet, transforms the structure into relatively uniform and fine equiaxed crystals, promotes the redistribution of precipitates in the billet structure, and forms a dispersed, uniform and fine strengthening phase. Processing billets into bars.

Next, the bar is cold-drawn with appropriate parameters, and finally magnetically heat-treated to obtain stable magnetic properties and qualified mechanical properties. Usually, cold drawing processing is carried out in the range of 7%-18% for the bars obtained through hot rolling, and the heat preservation of the cold drawn bars at 780°C-860°C for 8-20h Magnetic heat treatment is carried out within a long time range to obtain soft magnetic steel with stable magnetic properties.

Specifically, for the steel used in this embodiment, hot-rolled bars are prepared first, and then the area reduction rate of cold drawing is selected to be 10.25%-13.22%, and the optimal area reduction rate q=12.8%. The cold drawing process introduces plastic deformation in the bar as the driving force for the solid-state phase transformation during the subsequent heat treatment.

Finally, the semi-finished steel after cold drawing is heated to above the Curie temperature for degaussing. After iterative testing, the locking process is to perform magnetic heat treatment at 780°C-860°C for 12 hours, preferably at 820±20°C, so that the deformed grains occur Fully recrystallized to form a uniform and fine grain structure, so that the grain size can meet the requirements of mechanical properties and magnetic properties. It should be understood that the magnetic heat treatment temperature can be adaptively adjusted within the temperature range according to the different degrees of deformation during the cold drawing process.

Among them, the chemical composition of the rod is controlled to be 0.06%-0.08% C, no more than 0.05% Si, 1.05%-1.20% Mn, 0.065%-0.075% P and 0.29%-0.32% S, and, 0.003%-0.01% Nb, 0.0018%-0.01% Ti and 0.003%-0.03% Mo. Among them, C element is beneficial to enhance the mechanical properties of steel, but will have a negative impact on magnetic properties; Mn can enhance the toughness of steel, but will promote the formation of austenite and damage the magnetic properties of finished products; excessive P and S will lead to mechanical properties , but when it is controlled within a certain range, it can significantly improve the cutting performance of steel; Si element has a significant impact on the magnetic properties of steel, and it is necessary to accurately control its composition content; after long-term research, the inventors found that in order to achieve The balance of the mechanical properties and magnetic properties of the steel for solenoid valves also requires the addition of Nb, Ti and Mo. These elements not only improve the magnetic properties of the steel, but also help to improve the mechanical properties of the finished steel. During the bar smelting process, the residual O content is controlled at 40ppm-100ppm when the steel is tapped, the sulfide in the bar complies with SEP1572 standard 2.2 or 2.3, and the inclusion level is less than 2 to ensure that the structure of the finished steel is stable and can be obtained through subsequent processing Finished steel with qualified mechanical properties and stable magnetic properties.

Before the bar is hot-rolled, the bar is heated first, and the bar is heated to 1170°C-1190°C for 2h-4h. During the heating process, it is preferable to carry out at least one preheating treatment when the temperature does not exceed 950°C, so that the internal and external temperatures of the bar are consistent, and then further heating and heating. The temperature, segmentation and holding time of the preheating treatment should be adapted according to the actual heating capacity of the heat treatment furnace. sexual selection. During the heating process, the cooling rate is controlled by adjusting the cooling water and cooling air flow of the hot rolling equipment, so that the initial rolling temperature is always maintained at 870°C-920°C, and the final rolling temperature is maintained at 910°C-940°C. Too low a temperature will result in insufficient hot rolling, while too high a temperature will result in excessively large grain sizes, impairing the mechanical properties of the finished steel.

In the magnetic heat treatment stage, first preheat the bar to 650±20°C for 2 hours, then heat it to 820±20°C for 12 hours of magnetic heat treatment, then cool it down to 650±20°C for 7 hours, and then cool it to 200±20°C with the furnace. 20 ℃ out of the furnace to complete the heat treatment process. Those skilled in the art should understand that for a general heat treatment furnace, on the basis of given initial temperature, target temperature and heating/cooling time, the heat treatment furnace can realize feedback adjustment of temperature based on its own PLC control system, and then complete heating/cooling The temperature control of the cooling process, the heating/cooling process is realized at an approximately uniform speed, limited by the heating and heat dissipation capabilities of different heat treatment furnaces and the accuracy of the controller, the temperature may have reasonable small fluctuations within the normal heat treatment parameter range.

Due to the high-order changes in the magnetic properties of the finished material as the deformation increases during the cold drawing process, the stability of the magnetic properties of the finished product is very sensitive to the area reduction rate during the cold drawing process; at the same time, after the magnetic heat treatment is completed, the The plastic deformation of the material will affect the magnetic properties, and the cutting process will introduce a residual stress layer on the surface, which will also significantly interfere with the magnetic properties of the steel. Therefore, the steel for the solenoid valve needs to control the size of the parts during the hot rolling stage. After the cold drawing process is completed, the bar size should be similar to the finished product size, and only the machining allowance is reserved. After the magnetic heat treatment is completed, the grinding process is adopted. The bar is processed into a finished steel product. In a preferred embodiment, the single-side processing amount of the grinding process is controlled at 0.02mm-0.03mm. If the amount of grinding processing is too low, the surface roughness of the steel will not meet the standard, while if the amount of grinding processing is too high, the processing loss will be too large and the production efficiency will be reduced.

Through the above method, soft magnetic steel bars with stable magnetic properties can be obtained in mass production, which are used in the manufacture of solenoid valves. The overall pass rate is significantly higher than that of imported 11SMn30 steel, which effectively improves production efficiency and reduces parts manufacturing costs.

In the long-term practice, the inventor tried to lock the heat treatment parameters first and then adjust the cold drawing deformation rate. Grain boundary slip will occur, and the magnetic properties of the sample will change nonlinearly, making it difficult to grasp the changing law of magnetic properties. Finally, the inventors determined the above process development method.

In one embodiment of the present invention, the following method is used to manufacture soft magnetic steel for gearbox solenoid valves.

First, steel is smelted, and the composition of the steel is regulated, and the composition is controlled by weight ratio: C content 0.06%-0.08, Si content ≤ 0.05%, Mn content 1.05%-1.20%, P content 0.065%-0.075%, S content 0.29 %-0.32%, Cr content≤0.15%, Ni content≤0.10%, Mn content 0.01%-0.03%, Nb content 0.003%-0.01%, Ti content 0.018%-0.01%, Mo content 0.01%-0.03%. The principle of controlling the composition is to adjust the ratio of element composition that is beneficial to the magnetic performance as much as possible on the basis of ensuring that the mechanical properties are qualified. The molten iron is smelted in a blast furnace, transferred to a converter for steelmaking, and then transferred to a refining furnace for refining, and finally cast to obtain billets. The sulfide index in the steel is inspected according to the SEP1572 standard, and its typical field of view should conform to Figure 2.2 or 2.3 to ensure the cutting performance of the finished steel. When tapping out of the smelting furnace, control the residual O content to 40-100ppm; standardize the slag removal process to prevent foreign inclusions from mixing into the steel, and the distribution of endogenous inclusions should be fine, uniform, and dispersed, and the inclusion grade should be less than 2.

Next the billets are hot rolled. Before starting hot rolling, the steel billet is first heated, and the steel billet is gradually heated to 1170°C-1190°C and kept for 2h-4h by means of segmental heating. The heating can first be preheated below 950°C to make the temperature inside and outside the billet uniform. In other embodiments, two or more stages of preheating may be adopted according to the heating and heat preservation capabilities of the heat treatment furnace. By adjusting the flow rate of water cooling and air cooling of the hot rolling equipment, the initial rolling temperature of the steel billet is controlled at 870°C-920°C, and the final rolling temperature is controlled at 910°C-940°C to complete the rolling of the steel billet. During the rolling process, the columnar crystals formed during the solidification of the slab are broken, the solidification defects in the structure are eliminated, the precipitates are redistributed, and the structure is improved. Since the subsequent cold drawing process has strict restrictions on the plastic deformation introduced by the billet, the size of the billet should be controlled during the hot rolling process, so that the size of the billet after cold drawing can be similar to the size of the finished product, and only the machining allowance is reserved. In this embodiment, according to the size of the finished product, the billet after hot rolling is processed into a round bar with a diameter of 19 ± 0.1 mm, calculated according to the area reduction rate while retaining a machining allowance of 0.02 mm on one side.

The hot-rolled bar is cold-drawn by a combined drawing machine, and the area reduction rate q of the cold-drawing process is controlled to be 11.24%. The bar is drawn to a diameter of 17.9mm and then straightened, cut, polished and flaw detected. Compared with the final product, the cold-drawn bar has a machining allowance of 0.02mm-0.03mm on one side.

Magnetic heat treatment is performed on the cold-drawn rods, and the heat treatment is carried out in a gas-fired bell furnace. First, preheat the bar to 648°C for 2 hours, then heat it to 825°C for 3.5 hours and hold it for 12 hours. After the heat preservation is completed, cool it down to 650°C for 7 hours, then cool it to 200°C with the furnace, and then take it out of the furnace. The above process is automatically completed by the heat treatment furnace by inputting the target temperature and time into the heat treatment furnace. After magnetic heat treatment, the plastic deformation introduced in the cold drawing process drives the recrystallization of the grains. The holding temperature, time and cooling rate of the subsequent cooling process have a key influence on the final structure. The grain size after the magnetic heat treatment is 3 -Class 5, to meet the requirements of mechanical properties and magnetic properties of materials at the same time.

Finally, the magnetic heat-treated steel is ground to the required size, and the grinding volume is 0.02mm-0.03mm per side. After the magnetic heat treatment is completed, the steel should not be plastically deformed or cut to change the grain structure or introduce high residual stress, so as to ensure the stability of the magnetic properties of the finished product.

The mass-produced solenoid valve steel obtained through the above processing process has the following mechanical properties: the tensile strength reaches 357MPa, the yield strength is 265MPa, and the hardness HBW is 128; the magnetic properties meet: the coercive force is 188A/m; under different external magnetic fields The magnetic induction intensity meets: B ₁₀₀₀ = 1.433T, B ₂₀₀₀ = 1.568T, B ₅₀₀₀ = 1.693T, B ₁₀₀₀₀ = 1.807T, B ₂₀₀₀₀ = 1.953T,

B ₃₀₀₀₀ = 2.048T. The mechanical properties and magnetic properties all meet the design requirements. At the same time, the steel has good cutting performance. Using this steel to process and manufacture gearbox solenoid valves has fast response speed, precise actuation, and good durability. It can serve in automatic gearboxes for a long time, effectively improving the pass rate of solenoid valve production lines, reducing the risk of scrapping, and realizing Effective optimization of manufacturing costs.

In the first comparative example, the composition of the steel is controlled to have a C content of 0.04%-0.06%, and a Si content of

≤0.09%, Mn content 0.99%-1.26%, P content ≤0.15%, S content 0.25%-0.35%, after the same hot rolling, cold drawing processing and magnetic heat treatment as in the example, the test result tensile strength is 290MPa , The mechanical properties are unqualified.

In the second comparative example, the composition of the steel is controlled to have a C content of 0.06%-0.08%, and a Si content of

≤0.09%, Mn content 0.99%-1.26%, P content ≤0.15%, S content 0.25%-0.35%, after the same hot rolling, cold drawing processing and magnetic heat treatment as in the embodiment, the mechanical properties of the sample meet the requirements of The design is standard, but the magnetic properties are out of tolerance, and the coercive force reaches 270A/m, which exceeds the upper limit. If the coercive force is too high, the response time of the magnetic sleeve and the armature will be prolonged when the current of the solenoid valve changes, which will slow down the action of the solenoid valve and affect the control accuracy.

In the third comparative example, the steel composition and hot rolling processing parameter control are the same as the first embodiment. During the cold drawing process, the bar is cold drawn from a diameter of 19mm to 18.5mm, and after the same magnetic heat treatment as the first embodiment , further lightly pulled to a diameter of 17.5mm. The obtained sample was tested, and due to the plastic deformation introduced by light pulling, the grain structure of the rod was distorted, and the measured coercive force Hc=350A/m exceeded the limit.

In the fourth comparative example, the composition control of the steel is the same as that of the first embodiment. During the hot rolling process, the initial rolling temperature is controlled at 870°C-910°C. Due to improper cooling rate control, the final rolling temperature is 800°C. After the same cold drawing process and magnetic heat treatment as in the example, the mechanical and magnetic properties of the sample were tested to be out of tolerance. The tensile strength was only 280MPa, and the coercive force exceeded the upper limit by 290A/m, which did not meet the design requirements.

The purpose of the above embodiments is to further describe the present invention in detail in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the claims of the present invention, optimization or equivalent replacement of the components, methods and steps involved, as well as the combination of the implementation methods in different embodiments on the premise of no conflict of principles, all fall within the scope of the present invention. scope of protection.

Claims (11)

1. A soft magnetic steel for solenoid valve, characterized in that its composition by weight ratio comprises: 0.06%-0.08% C, no more than 0.05% Si, 1.05%-1.20% Mn, 0.065%-0.075% P and 0.29%-0.32% S, And, 0.003%-0.01% of Nb, 0.0018%-0.01% of Ti and 0.003%-0.03% of Mo. 2. The soft magnetic steel according to claim 1, characterized in that the tensile strength of the soft magnetic steel is ≥300MPa, the yield strength is ≥210MPa, and the hardness HBW is 110-150; The coercive force is 150A/m-200A/m; The magnetic induction intensity meets: 1.20T≤B ₁₀₀₀ ≤1.42T, 1.46T≤B ₂₀₀₀ ≤1.58T, 1.65T≤B ₅₀₀₀ ≤1.70T, 1.77T≤B ₁₀₀₀₀ ≤1.82T, 1.92T≤B ₂₀₀₀₀ ≤1.96T, 2.01T ≤ B ₃₀₀₀₀ ≤ 2.05T. 3. The soft magnetic steel according to claim 1 or 2, characterized in that the grain size grade in the steel structure is 3-5. 4. A manufacturing method of soft magnetic steel for electromagnetic valve, is characterized in that, comprises the following steps: Hot rolling the steel billet, the initial rolling temperature is 870°C-920°C, the final rolling temperature is 910°C-940°C, and processed into bars; Carrying out cold drawing processing on the bar, the area reduction rate of the bar after cold drawing is 7%-18%; The cold-drawn bar is kept at 780° C.-860° C. for 8-20 hours to complete the magnetic heat treatment. 5. the manufacture method of soft magnetic steel according to claim 4, is characterized in that, described rod composition comprises: 0.06%-0.08% C, no more than 0.05% Si, 1.05%-1.20% Mn, 0.065%-0.075% P and 0.29%-0.32% S, And, 0.003%-0.01% of Nb, 0.0018%-0.01% of Ti and 0.01%-0.03% of Mo. 6. The manufacturing method of soft magnetic steel according to claim 4 or 5, characterized in that, the area reduction rate of the cold drawing process is 10.25%-13.22%, and the heating temperature for magnetic heat treatment is 820±20°C, the magnetic The heat treatment time is 12h. 7. The manufacturing method of soft magnetic steel according to claim 4 or 5, characterized in that, it also includes the step of smelting bars, in the step of smelting bars, the residual O content is controlled at 40ppm-100ppm when tapping , the sulfide in the bar meets SEP1572 standard 2.2 or 2.3, and the inclusion level is less than 2. 8. The manufacturing method of soft magnetic steel according to claim 4 or 5, characterized in that, before hot rolling the bar, first heat the bar to 1170°C-1190°C and keep it warm for 2h-4h . 9. The manufacturing method of soft magnetic steel according to claim 4 or 5, characterized in that, in the magnetic heat treatment process, firstly, the cold-drawn rod is preheated to 650±20° C. for 2 hours, After 3.5 hours, it is heated to the magnetic heat treatment temperature; after the heat preservation is completed, it is first cooled to 650±20°C after 7 hours, and then cooled to 200±20°C with the furnace. 10. The method for manufacturing soft magnetic steel according to claim 4 or 5, further comprising a grinding step of grinding the magnetically heat-treated bar to a required size to obtain a finished steel product. 11. The manufacturing method of soft magnetic steel according to claim 10, characterized in that the processing amount in the grinding step is 0.02mm-0.03mm per side.