Soft magnetic yoke and reverse magnetostrictive load sensor

Abstract

To provide a soft magnetic yoke with excellent soft magnetic properties and high strength, and an inverse magnetostrictive load sensor using this yoke as the pressure receiving part. [Solution] The soft magnetic yoke is made of precipitation-strengthened ferritic electromagnetic stainless steel. The precipitation-strengthened ferritic electromagnetic stainless steel contains 1.0≦Cr≦14.0mass%, 0.7≦Mo≦1.9mass%, 1.0≦Al≦5.0mass%, 1.1≦Ni≦5.0mass%, and Si≦0.4mass%, with the remainder being Fe and unavoidable impurities, having a ferrite phase area ratio of 90% or more at room temperature, containing precipitated particles made of NiAl with an average diameter of 1 nm to 10 nm, and having a Vickers hardness of 250 Hv or more. The reverse magnetostrictive load sensor uses such a soft magnetic yoke as the pressure receiving part.

Description

[Technical Field]

[0001] The present invention relates to a soft magnetic yoke and an inverse magnetostrictive load sensor, and more particularly to a soft magnetic yoke that exhibits minimal degradation of magnetic properties under repeated stress, and an inverse magnetostrictive load sensor using the same as a pressure-receiving part. [Background technology]

[0002] A "reverse magnetostrictive load sensor (or magnetostrictive load sensor)" refers to a sensor capable of detecting the magnitude of an external force acting on a pressure-receiving part made of a soft magnetic yoke as a change in the permeability of the soft magnetic yoke. Compared to other types of load sensors, reverse magnetostrictive load sensors are characterized by their low cost and high mechanical reliability. Various proposals have been made regarding such reverse magnetostrictive load sensors or their components.

[0003] For example, Patent Document 1 contains: A load-bearing part made of a ferromagnetic material exhibiting the inverse magnetostrictive effect, A coil wound around the load-bearing part, It comprises a load-receiving section and a housing section for housing coils, A magnetostrictive load sensor in which the load receiving section and the bottom and / or top sections of the housing are integrated. This has been disclosed.

[0004] The document states: (A) If the load-bearing portion and the housing portion are not integrated, when an external force is applied, the load-bearing portion may shift position, and bending stress may act on the load-bearing portion. (B) When bending stress is applied to the load-bearing part, the reproducibility of the output decreases, the output signal fluctuates due to plastic deformation of the load-bearing part, and the accuracy of the output signal deteriorates because the load-bearing part does not return to its original position when unloaded, and, (B) Integrating the load-receiving portion and the bottom and / or top portions of the housing portion reduces the likelihood of bending stress acting on the load-receiving portion when an external force is applied, thereby improving the accuracy and output reproducibility of the sensor. It is stated.

[0005] Patent Document 2 discloses a soft magnetic alloy that, although not a soft magnetic material for an inverse magnetostrictive load sensor, contains predetermined amounts of Ni, Al, Si, and V, with the remainder being Fe and unavoidable impurities. The document states that by optimizing the Ni content and the total content of Al, Si, and V, a soft magnetic alloy with a high saturation magnetic flux density of 1.7T or higher can be obtained.

[0006] Patent Document 3 discloses a precipitation-hardening soft magnetic ferritic stainless steel, which is not a soft magnetic material for inverse magnetostrictive load sensors, but contains predetermined amounts of C, Si, Mn, S, Cr, Ni, Al, Ti, Zr, and Bi, with the remainder being Fe and unavoidable impurities, whose structure is substantially that of a ferrite phase, and whose hardness is 300 Hv or higher. The document states that adding an appropriate amount of Bi to soft magnetic ferritic stainless steel improves machinability without degrading its soft magnetic properties, age hardness, or corrosion resistance.

[0007] The pressure-receiving section of an inverse magnetostrictive load sensor not only receives external forces but also functions as a soft magnetic yoke to concentrate magnetic flux, forming part of the magnetic circuit. Therefore, the pressure-receiving section requires high soft magnetic properties. Furthermore, since the pressure-receiving section is subjected to repeated stress during use, high strength is also required.

[0008] However, conventional inverse magnetostrictive load sensors used permalloy, pure iron, and silicon steel (electromagnetic steel sheets) for their pressure-receiving parts. While these materials exhibit high soft magnetic properties, they are mechanically soft. Therefore, when an external force is applied to the pressure-receiving part made of these materials, irreversible changes (plastic deformation, introduction of strain, etc.) occur inside the material, resulting in a deterioration of soft magnetic properties (for example, a decrease in maximum relative permeability). Furthermore, inverse magnetostrictive load sensors using soft materials for the pressure-receiving part have the problem that the upper limit of their range of motion is limited by the strength of the material in the pressure-receiving part. [Prior art documents]

Patent Document

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] The problem to be solved by the present invention is to provide a soft magnetic yoke having excellent soft magnetic properties and high strength. Another problem to be solved by the present invention is to provide an inverse magnetostrictive load sensor using such a soft magnetic yoke for a pressure receiving part.

Means for Solving the Problems

[0011] In order to solve the above problems, the soft magnetic yoke according to the present invention has the following configuration. (1) The soft magnetic yoke is made of precipitation-strengthened ferrite-based electromagnetic stainless steel. (2) The precipitation-strengthened ferrite-based electromagnetic stainless steel 1.0 ≦ Cr ≦ 14.0 mass%, 0.7 ≦ Mo ≦ 1.9 mass%, 1.0 ≦ Al ≦ 5.0 mass%, 1.1 ≦ Ni ≦ 5.0 mass%, and Si ≦ 0.4 mass% contains, with the balance being Fe and inevitable impurities, the area ratio of the ferrite phase at room temperature is 90% or more, contains precipitation particles composed of NiAl having an average diameter of 1 nm or more and 10 nm or less, and has a Vickers hardness of 250 Hv or more.

[0012] The inverse magnetostrictive load sensor according to the present invention consists of a soft magnetic yoke according to the present invention used in the pressure-receiving part. [Effects of the Invention]

[0013] In precipitation-strengthened ferritic electromagnetic stainless steel, optimizing the composition and precipitating fine NiAl particles in the matrix allows for increased strength without degrading soft magnetic properties. Using such a soft magnetic yoke made of precipitation-strengthened ferritic electromagnetic stainless steel as the pressure-receiving part of an inverse magnetostrictive load sensor enables the realization of a load sensor exhibiting high durability and excellent measurement sensitivity even when a large load is applied to the pressure-receiving part. [Brief explanation of the drawing]

[0014] [Figure 1] This is a front view of an inverse magnetostrictive load sensor according to the first embodiment of the present invention. [Figure 2] This is a front view of an inverse magnetostrictive load sensor according to a second embodiment of the present invention. [Figure 3] This is a front view of an inverse magnetostrictive load sensor according to a third embodiment of the present invention. [Figure 4] This is a front view of an inverse magnetostrictive load sensor according to a fourth embodiment of the present invention.

[0015] [Figure 5] These are a plan view (left) and a front view (right) of an inverse magnetostrictive load sensor according to the fifth embodiment of the present invention. [Figure 6] These are a plan view (left) and a front view (right) of an inverse magnetostrictive load sensor according to the sixth embodiment of the present invention. [Figure 7] This is a front view of an inverse magnetostrictive load sensor according to the seventh embodiment of the present invention. [Figure 8] These are a plan view (left) and a front view (right) of an inverse magnetostrictive load sensor according to the eighth embodiment of the present invention. [Modes for carrying out the invention]

[0016] One embodiment of the present invention will be described in detail below. [1. Precipitation-strengthened ferritic electromagnetic stainless steel] [1,1. Constituent elements] The soft magnetic yoke according to the present invention is made of precipitation-strengthened ferritic electromagnetic stainless steel. The precipitation-strengthened ferritic electromagnetic stainless steel according to the present invention (hereinafter also simply referred to as "electromagnetic stainless steel") contains the following elements, with the remainder being Fe and unavoidable impurities. The types of added elements, their component ranges, and the reasons for their limitations are as follows.

[0017] (1) 1.0 ≤ Cr ≤ 14.0 mass%: In electromagnetic stainless steel, the higher the electrical resistivity, the better the soft magnetic properties in alternating current. This is because higher electrical resistivity leads to smaller eddy currents and thus lower losses. Cr is an element that contributes to improving electrical resistivity. Furthermore, Cr also contributes to improved corrosion resistance and stabilization of the ferrite phase.

[0018] If the amount of Cr is too low, the electrical resistivity may decrease excessively, or the corrosion resistance may decrease excessively. Therefore, the amount of Cr needs to be 1.0 mass% or more. Preferably, the amount of Cr is 8.0 mass% or more, or 10.0 mass% or more. On the other hand, if the amount of Cr is excessive, the saturation magnetization decreases, which can actually worsen the soft magnetic properties. Therefore, the amount of Cr needs to be 14.0 mass% or less. Preferably, the amount of Cr is 12.0 mass% or less. To obtain high corrosion resistance, the Cr content is preferably 10.0 mass% to 14.0 mass%.

[0019] (2) 0.7 ≤ Mo ≤ 1.9 mass%: Like Cr, Mo is an element that contributes to improving electrical resistivity, corrosion resistance, and stabilizing the ferrite phase. Mo is more effective than Cr in improving electrical resistivity and corrosion resistance. Therefore, using Mo and Cr together can reduce the total amount of Cr and Mo required to improve corrosion resistance and stabilize the ferrite phase. This also helps to suppress the decrease in soft magnetic properties (decrease in saturation magnetization and increase in coercivity).

[0020] If the amount of Mo becomes too low, the ferrite phase may become unstable. Therefore, the amount of Mo needs to be 0.7 mass% or more. Preferably, the amount of Mo is 1.0 mass% or more. On the other hand, if the amount of Mo is excessive, the saturation magnetization decreases, which can actually worsen the soft magnetic properties. Therefore, the amount of Mo needs to be 1.9 mass% or less. Preferably, the amount of Mo is 1.5 mass% or less.

[0021] (3) 1.0 ≤ Al ≤ 5.0 mass %: Al, together with Ni, forms the fine intermetallic compound NiAl, which contributes to improving strength. If the amount of Al is too low, the amount of NiAl particles formed will decrease, which may lead to a decrease in strength. Therefore, the amount of Al needs to be 1.0 mass% or more. Preferably, the amount of Al is 1.3 mass% or more, or 1.6 mass% or more. On the other hand, if the amount of Al is excessive, it may lead to a decrease in soft magnetic properties due to an increase in nonmetallic inclusions, and deterioration of processability due to embrittlement. Therefore, the amount of Al needs to be 5.0 mass% or less. Preferably, the amount of Al is 4.0 mass% or less, or 3.0 mass% or less.

[0022] (4) 1.1 ≤ Ni ≤ 5.0 mass%: Ni, together with Al, forms the fine intermetallic compound NiAl, which contributes to improving strength. If the amount of Ni is too low, the amount of NiAl particles formed will decrease, which may lead to a decrease in strength. Therefore, the amount of Ni needs to be 1.1 mass% or more. Preferably, the amount of Ni is 1.5 mass% or more. On the other hand, if the amount of Ni is excessive, the austenite phase is more likely to form, which may reduce the soft magnetic properties. Therefore, the amount of Ni needs to be 5.0 mass% or less. Preferably, the amount of Ni is 4.0 mass% or less, or 3.0 mass% or less.

[0023] (5) Si ≤ 0.4 mass %: Si is an element that can inevitably be present. Furthermore, Si is an element that contributes to the stabilization of the ferrite phase, improvement of soft magnetic properties, and improvement of electrical resistivity. Therefore, the electromagnetic stainless steel according to the present invention may contain Si. On the other hand, if the Si content is excessive, electromagnetic stainless steel may become brittle. Therefore, the Si content needs to be 0.4 mass% or less.

[0024] (6) Inevitable impurities: The electromagnetic stainless steel according to the present invention may contain unavoidable impurities. Here, "unavoidable impurities" refers to components that are mixed in during the industrial production of electromagnetic stainless steel due to various factors such as raw materials and manufacturing processes, and whose content is within a range that does not adversely affect the properties of the electromagnetic stainless steel according to the present invention.

[0025] In the electromagnetic stainless steel according to the present invention, if the following components are present in the amounts shown below, they shall be treated as unavoidable impurities. C < 0.04 mass%, P < 0.06 mass%, S < 0.06 mass%, O<1.0 mass%, N < 0.06 mass%.

[0026] [1.2. Ingredient Balance] (1)Ni / Al ratio (mass ratio): As mentioned above, Ni and Al are elements for forming the fine intermetallic compound NiAl. However, if Ni is in excess of Al, the ferrite phase may become unstable. Therefore, a Ni / Al ratio (mass ratio) of 1.0 or less is preferred. More preferably, the Ni / Al ratio is 0.95 or less, or 0.90 or less. On the other hand, if the Ni / Al ratio becomes too small, the amount of NiAl produced may decrease, potentially leading to a reduction in strength. Therefore, a Ni / Al ratio of 0.4 or higher is preferable. More preferably, the Ni / Al ratio is 0.5 or higher, or 0.6 or higher.

[0027] (2) Cr + 3.3Mo: As mentioned above, both Cr and Mo contribute to improving electrical resistivity, corrosion resistance, and stabilizing the ferrite phase, but the effect of Mo is approximately 3.3 times that of Cr. Therefore, in addition to keeping the amounts of Cr and Mo within the ranges mentioned above, optimizing the amount of Cr + 3.3Mo reduces the total amount of Cr and Mo required to improve electrical resistivity, corrosion resistance, or stabilize the ferrite phase. This also helps to suppress the decrease in soft magnetic properties (decrease in saturation magnetization and increase in coercivity).

[0028] If the amount of Cr+3.3Mo is too low, the electrical resistivity may decrease excessively, or the ferrite phase may become unstable. Therefore, the amount of Cr+3.3Mo is preferably 1.0 mass% or more. On the other hand, if the amount of Cr+3.3Mo is excessive, the saturation magnetization decreases, which can actually worsen the soft magnetic properties. Therefore, the amount of Cr+3.3Mo is preferably 14.0 mass% or less.

[0029] The optimal amount of Cr+Mo varies depending on the application. For example, to obtain electromagnetic stainless steel with excellent soft magnetic properties, the amount of Cr+3.3Mo is preferably 9.0 mass% or less. On the other hand, in order to obtain electromagnetic stainless steel with high electrical resistivity and excellent corrosion resistance, the amount of Cr+3.3Mo is preferably more than 9.0 mass%. More preferably, the amount of Cr+3.3Mo is 10.0 mass% or more, or 12.0 mass% or more.

[0030] [1.3. Organization] [1.3.1. Area ratio of the ferrite phase] "Ferrite phase area percentage (%)" refers to the ratio of the area of ​​the ferrite phase (S) to the field of view area (S0) when the microstructure of electromagnetic stainless steel is observed with an optical microscope at room temperature (= S × 100 / S0). In this invention, S0 is 25 mm 2 Let's assume

[0031] Generally, the larger the area ratio of the ferrite phase, the higher the soft magnetic properties obtained. To obtain this effect, the area ratio of the ferrite phase needs to be 90% or more. Preferably, the area ratio of the ferrite phase is 95% or more, or 99% or more.

[0032] [1.3.2. Precipitated particles] The electromagnetic stainless steel according to the present invention is obtained by solution treatment and aging treatment, as described later. Therefore, the electromagnetic stainless steel contains precipitated particles made of NiAl. The average diameter of the NiAl particles affects the soft magnetic properties of the electromagnetic stainless steel. Here, the "average diameter" of the precipitated particles made of NiAl refers to the value identified from the scattering peak of small-angle X-ray scattering.

[0033] If the average diameter of the precipitated particles becomes too small, a long heat treatment at a low temperature will be required for precipitation, which may worsen the heat treatment efficiency. Therefore, the average diameter of the precipitated particles must be 1.0 nm or larger. Preferably, the average diameter is 1.5 nm or larger, or 2.0 nm or larger. On the other hand, if the average diameter of the precipitated particles becomes too large, the soft magnetic properties may decrease, and further improvement in strength may not be achieved. Therefore, the average diameter of the precipitated particles must be 10.0 nm or less. Preferably, the average diameter is 8.0 nm or less, or 6.0 nm or less.

[0034] [1.4. Characteristics] [1.4.1. Vickers hardness] When the electromagnetic stainless steel according to the present invention is subjected to solution treatment and aging treatment under appropriate conditions, fine NiAl particles can be precipitated in the matrix. Generally, the greater the amount of fine NiAl particles precipitated, the higher the strength of the electromagnetic stainless steel.

[0035] Because NiAl particles are so fine, it is difficult to quantify their precipitate amount. However, the amount of NiAl particles precipitated is strongly correlated with Vickers hardness. High Vickers hardness indicates a large amount of NiAl particle precipitate. Furthermore, Vickers hardness is strongly correlated with the strength of electromagnetic stainless steel. To obtain high-strength electromagnetic stainless steel, the Vickers hardness must be 250 Hv or higher. Preferably, the Vickers hardness is 270 Hv or higher, or 300 Hv or higher.

[0036] [1.4.2. Coercive force Hc] To obtain high soft magnetic properties, a smaller coercivity Hc is desirable. In the electromagnetic stainless steel according to the present invention, by optimizing the composition and manufacturing conditions, the coercivity Hc becomes 1.0 [Oe] or less. By further optimizing the composition and manufacturing conditions, the coercivity Hc becomes 0.8 [Oe] or less, or 0.7 [Oe] or less.

[0037] [1.4.3. Magnetic fatigue degree F] "Magnetic fatigue degree F" refers to the value expressed by the following equation (1). F=μ m1 -μ m0 (1) however, μ m0is the initial maximum relative permeability of the precipitation-strengthened ferritic electromagnetic stainless steel, μ m1 is the maximum relative permeability of the precipitation-strengthened ferritic electromagnetic stainless steel after applying a stress of 400 MPa repeatedly for 10 6 times.

[0038] The electromagnetic stainless steel according to the present invention has higher strength than conventional soft magnetic materials (e.g., permalloy, pure iron, silicon steel, etc.). Therefore, even when repeated stress acts on a soft magnetic yoke made of such electromagnetic stainless steel, the decrease in the maximum relative permeability is small. In the electromagnetic stainless steel according to the present invention, when the components and manufacturing conditions are optimized, F becomes -500 or more.

[0039] [1.4.4. Change rate of maximum relative permeability Δμ m "The change rate of maximum relative permeability Δμ m " refers to the value represented by the following formula (2). Δμ m =(1 - μ m2 / μ m0 ) × 100 (%) (2) However, μ m0 is the initial maximum relative permeability of the precipitation-strengthened ferritic electromagnetic stainless steel, μ m2 is the maximum relative permeability of the precipitation-strengthened ferritic electromagnetic stainless steel when a stress of 330 MPa is applied.

[0040] The electromagnetic stainless steel according to the present invention has a large change rate of maximum relative permeability per unit stress. In other words, the electromagnetic stainless steel according to the present invention has high sensitivity to stress. In the electromagnetic stainless steel according to the present invention, when the components and manufacturing conditions are optimized, Δμ m becomes 60% or more. When the components and manufacturing conditions are further optimized, Δμ m becomes 70% or more.

[0041] [1.4.5. Magnetic fatigue strength σ wb ​​ "Magnetic fatigue strength σ wb " means, 10 for the aforementioned precipitation-strengthened ferritic electromagnetic stainless steel 6 In a test in which repeated stress is applied and the change in the maximum relative permeability before and after repeated stress application is measured, with the stress varied at 10 MPa intervals, This refers to the maximum stress at which the decrease in the maximum relative permeability before and after repeated stress application is 500 or less. "10 MPa intervals" means increasing the stress in increments of 10 MPa, starting from 0 MPa.

[0042] The electromagnetic stainless steel according to the present invention has a magnetic fatigue strength σ wb The reduction in maximum relative permeability (= absolute value of magnetic fatigue degree F) is small, even when used in environments where high stress is repeatedly applied. In the electromagnetic stainless steel according to the present invention, when the components and manufacturing conditions are optimized, σ wb This will be 400 MPa or more. Further optimization of the components and manufacturing conditions will result in σ wb This will be 500 MPa or more.

[0043] [2. Method for manufacturing precipitation-strengthened ferritic electromagnetic stainless steel (1)] A method for manufacturing precipitation-strengthened ferritic electromagnetic stainless steel according to the first embodiment of the present invention is: The first step involves melting and casting raw materials that have been formulated to have the specified components, The second step involves hot forging the resulting ingot, If necessary, a third step is to perform hot rolling on the hot forged body, A fourth step involves cold rolling of a hot-forged or hot-rolled body, The fifth step involves performing a solution treatment on the cold-rolled body, The sixth step involves performing finishing processing on the solution-treated body, The seventh step involves performing magnetic annealing on the finished workpiece, The eighth step involves performing an aging treatment on the magnetically annealed body. It is equipped with.

[0044] [2.1. 1st step] First, raw materials formulated to have the predetermined components are melted and cast (first step). In this invention, the method and conditions of melting and casting are not particularly limited, and the optimal method and conditions can be selected according to the purpose.

[0045] [2.2. 2nd process] Next, the obtained ingot is hot forged (second step). Hot forging is performed to break down the cast structure and to process the ingot into a shape suitable for the next step (slab, bloom, billet, etc.). In this invention, the method and conditions for hot forging are not particularly limited, and the optimal method and conditions can be selected according to the purpose.

[0046] [2.3. Third step] Next, if necessary, the hot-forged body is hot-rolled (third step). Hot rolling is primarily performed to reduce the thickness of the hot-forged body and to coarse the crystal grains, thereby improving the soft magnetic properties. Hot rolling is not always necessary, but if it is performed, production efficiency can be improved, and the soft magnetic properties of the electromagnetic stainless steel may also be improved. In this invention, the hot rolling method and conditions are not particularly limited, and the most suitable method and conditions can be selected according to the purpose.

[0047] [2.4. 4th step] Next, the hot-forged or hot-rolled body is subjected to cold rolling (fourth step). Cold rolling is performed to produce a cold-rolled body having a predetermined shape (e.g., sheet metal, bar metal, wire metal, etc.). In this invention, the method and conditions of cold rolling are not particularly limited, and the optimal method and conditions can be selected according to the purpose.

[0048] [2.5. 5th step] Next, the cold-rolled body is subjected to solution treatment (step 5). By performing solution treatment on the cold-rolled body under appropriate conditions, Ni and Al can be completely dissolved in the matrix.

[0049] If the solution treatment temperature is too low, the solution treatment may be insufficient. Therefore, a solution treatment temperature of 800°C or higher is preferable. A solution treatment temperature of 850°C or higher is even more preferable. On the other hand, if the solution treatment temperature becomes too high, an austenite phase may form, or the soft magnetic properties may deteriorate due to the melting of nonmetallic inclusions. Therefore, the solution treatment temperature is preferably 1100°C or lower. More preferably, the solution treatment temperature is 1000°C or lower.

[0050] The solution treatment time should preferably be selected to be optimal according to the solution treatment temperature. Generally, the higher the solution treatment temperature, the shorter the time required to achieve the desired effect. The solution treatment time is usually around 1 to 8 hours. Solution treatment is preferably carried out under a non-oxidizing atmosphere in order to suppress oxidation of the cold-rolled material. A vacuum atmosphere is particularly preferred during the solution treatment. The cold-rolled material is held at a predetermined solution treatment temperature for a predetermined time, and then cooled. The cooling rate should be such that NiAl does not precipitate during the cooling process.

[0051] [2.6. 6th step] Next, the solution-treated body undergoes finishing processing (step 6). "Finishing process" refers to the processing required to shape a solution-treated body into its final product form.

[0052] The finishing method can be selected to best suit the shape of the hot-worked part and the final product shape. For example, finishing methods include: (a) Cold working processes such as cutting, bending, and forging, (b) Cutting, grinding, (c) Electrical discharge machining These are some examples.

[0053] [2.7. 7th step] Next, the finished workpiece is subjected to magnetic annealing (step 7). When magnetic annealing is performed on the finished workpiece under appropriate conditions, the strain introduced during the finishing process is removed, and the crystal grains become coarser. Generally, the larger the crystal grains, the smaller the coercivity Hc.

[0054] If the annealing temperature is too low, magnetic annealing may be insufficient. Therefore, an annealing temperature of 800°C or higher is preferable. More preferably, the annealing temperature is 850°C or higher. On the other hand, if the annealing temperature becomes too high, an austenite phase may form, or the soft magnetic properties may deteriorate due to the melting of nonmetallic inclusions. Therefore, an annealing temperature of 1100°C or lower is preferable. More preferably, the annealing temperature is 1000°C or lower.

[0055] The annealing time should preferably be selected to be optimal according to the annealing temperature. Generally, the higher the annealing temperature, the shorter the time required to achieve the desired effect. The annealing time is usually around 1 to 8 hours. Annealing is preferably carried out in a non-oxidizing atmosphere to suppress oxidation of the finished workpiece. A vacuum atmosphere is particularly preferred during annealing. The finished workpiece is held at a predetermined annealing temperature for a predetermined time, and then cooled. The cooling rate should be such that no NiAl precipitates during the cooling process.

[0056] [2.8. 8th step] Next, the magnetically annealed body is subjected to aging treatment (step 8). This causes fine NiAl particles to precipitate in the matrix, resulting in the electromagnetic stainless steel according to the present invention.

[0057] If the aging treatment temperature is too low, the amount of NiAl particles precipitated may be insufficient, and high strength may not be obtained. Therefore, the aging treatment temperature is preferably 500°C or higher. More preferably, the aging treatment temperature is 550°C or higher. On the other hand, if the aging treatment temperature becomes too high, the NiAl particles may coarseen, and the soft magnetic properties may deteriorate. Also, the NiAl may become thermodynamically unstable, and the NiAl particles may not precipitate. Therefore, the aging treatment temperature is preferably less than 650°C. More preferably, the aging treatment temperature is 600°C or lower.

[0058] The aging treatment time should preferably be selected to be optimal according to the aging treatment temperature. Generally, the higher the aging treatment temperature, the shorter the time required to achieve the desired effect. The aging treatment time is usually around 0.5 to 8 hours, but in the case of components that do not easily precipitate NiAl particles, the aging treatment may be extended to about 24 hours. The atmosphere during the statute of limitations process is not particularly limited; the most suitable atmosphere can be selected depending on the purpose.

[0059] [3. Method for manufacturing precipitation-strengthened ferritic electromagnetic stainless steel (2)] A method for producing precipitation-strengthened ferritic electromagnetic stainless steel according to a second embodiment of the present invention is: The first step involves melting and casting raw materials that have been formulated to have the specified components, The second step involves hot forging the resulting ingot, If necessary, a third step is to perform hot rolling on the hot forged body, A fourth step involves cold rolling of a hot-forged or hot-rolled body, Step 5' involves performing a solution treatment on the cold-rolled body, which also includes magnetic annealing. The sixth step involves performing finishing processing on the solution-treated body, Step 8' involves performing an aging treatment on the finished workpiece. It is equipped with.

[0060] The manufacturing method according to this embodiment involves performing a solution treatment on a cold-rolled body, which also includes magnetic annealing, and omitting magnetic annealing after finishing. This is a difference from the first embodiment. If the decrease in soft magnetic properties due to the strain introduced during finishing is within an acceptable range, magnetic annealing after finishing can be omitted. Other aspects are the same as in the first embodiment, so a description will be omitted. Here, "solution treatment combined with magnetic annealing" means: (a) Performing a single heat treatment under conditions suitable for both solution treatment and magnetic annealing, or (b) First, perform a heat treatment under conditions suitable for solution treatment, and then perform a heat treatment under conditions suitable for magnetic annealing. It refers to.

[0061] [4. Method for manufacturing precipitation-strengthened ferritic electromagnetic stainless steel (3)] A method for manufacturing precipitation-strengthened ferritic electromagnetic stainless steel according to a third embodiment of the present invention is: The first step involves melting and casting raw materials that have been formulated to have the specified components, The second step involves hot forging the resulting ingot, If necessary, a third step is to perform hot rolling on the hot forged body, A fourth step involves cold rolling of a hot-forged or hot-rolled body, The 6' process involves performing finishing work on the cold-rolled body, Step 7' involves performing a solution treatment on the finished workpiece, which also includes magnetic annealing. Step 8' involves performing an aging treatment on the solution-treated body. It is equipped with.

[0062] The manufacturing method according to this embodiment omits the solution treatment before finishing and performs a solution treatment on the finished product that also includes magnetic annealing. This is different from the first embodiment. If the cold-rolled product has a hardness suitable for finishing, the solution treatment before finishing can be omitted. Other points are the same as in the first and second embodiments, so a description will be omitted.

[0063] [5. Method for manufacturing precipitation-strengthened ferritic electromagnetic stainless steel (4)] A method for manufacturing precipitation-strengthened ferritic electromagnetic stainless steel according to a fourth embodiment of the present invention is: The first step involves melting and casting raw materials that have been formulated to have the specified components, The second step involves hot forging the resulting ingot, If necessary, a third step is to perform hot rolling on the hot forged body, A fourth step involves cold rolling of a hot-forged or hot-rolled body, Step 5' involves performing a solution treatment on the cold-rolled body, which also includes magnetic annealing. Step 8' involves performing an aging treatment on the solution-treated body. The ninth step involves performing finishing work on the aged body, It is equipped with.

[0064] The manufacturing method according to this embodiment involves finishing after solution treatment and aging treatment. This differs from the first embodiment. Finishing can be performed after aging treatment if the material has sufficient hardness to allow for finishing, and the reduction in soft magnetic properties due to strain introduced during finishing is within an acceptable range. Other aspects are the same as in the first and second embodiments, so their explanation will be omitted.

[0065] [6. Soft Magnetic Yoke] The soft magnetic yoke according to the present invention is made of precipitation-strengthened ferritic electromagnetic stainless steel according to the present invention.

[0066] [6.1. Precipitation-strengthened ferritic electromagnetic stainless steel] Details regarding precipitation-strengthened ferritic electromagnetic stainless steel are as described above, so we will omit further explanation.

[0067] [6.2. Shape] The shape of a soft magnetic yoke is not particularly limited, and the optimal shape can be selected according to the purpose. Examples of soft magnetic yoke shapes include plate shape, rod shape, rectangular tube shape, ring shape, C-tube shape, and C-ring shape.

[0068] A "plate-shaped" soft magnetic yoke is a soft magnetic yoke that has a plate-like shape and is used to apply a load in the direction of the long or short side of the plate, thereby causing magnetic flux to flow in the direction of the applied load. See Figures 1 and 2. A "rod-shaped" soft magnetic yoke is a soft magnetic yoke that has a rectangular or round rod shape and is used to apply a load perpendicular to the axis of the rectangular or round rod, thereby allowing magnetic flux to flow in the axial direction of the rectangular or round rod. See Figure 5.

[0069] A "rectangular tube" soft magnetic yoke is a soft magnetic yoke that has a rectangular tube shape and is used to apply a load perpendicular to the opposing outer walls of the tube, thereby causing magnetic flux to flow in the circumferential direction of the tube. See Figures 3 and 4. A "ring-shaped" soft magnetic yoke is a soft magnetic yoke that exhibits a ring-like or annular shape and is used to apply a load in the axial direction of the ring or annular ring, thereby allowing magnetic flux to flow in the circumferential direction of the ring or annular ring. See Figure 6.

[0070] A "C-shaped" soft magnetic yoke is a soft magnetic yoke that has a shape in which an air gap is formed on one outer wall surface of a rectangular tube (hereinafter also referred to as a "C tube"), and is used to apply a load perpendicular to the opposing outer wall surfaces of the C tube (preferably the outer wall surface without an air gap) and to cause magnetic flux to flow in the circumferential direction of the C tube. See Figure 7. A "C-ring type" refers to a soft magnetic yoke exhibiting a shape in which an air gap is formed on the outer wall surface of a ring or square ring (hereinafter also referred to as a "C-ring"), and which is used to apply a load in the axial direction of the C-ring and to allow magnetic flux to flow in the circumferential direction of the C-ring. See Figure 8.

[0071] [6.3. Usage] The soft magnetic yoke according to the present invention can be used for various applications. It is particularly preferable to use the soft magnetic yoke according to the present invention as the pressure-receiving part of an inverse magnetostrictive load sensor. Details of the inverse magnetostrictive load sensor will be described later.

[0072] [7. Inverse magnetostrictive load sensor] The inverse magnetostrictive load sensor according to the present invention consists of a soft magnetic yoke according to the present invention used as the pressure-receiving part. The shape of the pressure-receiving part, the method for detecting changes in magnetic permeability, etc., are not particularly limited and can be selected to be optimal according to the purpose.

[0073] [7.1. Specific Example 1] Figure 1 shows a front view of an inverse magnetostrictive load sensor according to a first embodiment of the present invention. In Figure 1, the inverse magnetostrictive load sensor 10a is an inductance type sensor and comprises a pressure receiving section 12a, a magnetic flux detection yoke 14a, a coil 16, and an AC power supply 20. The pressure-receiving portion 12a is made of precipitation-strengthened ferritic electromagnetic stainless steel according to the present invention. In this embodiment, the pressure-receiving portion 12a is plate-shaped and is arranged so that a load is applied in the direction of the long side or the short side of the plate. The height, width, and depth of the pressure-receiving portion 12a are not particularly limited, and optimal dimensions can be selected according to the purpose.

[0074] The magnetic flux detection yoke 14a forms a magnetic circuit together with the pressure receiving section 12a. In this embodiment, the magnetic flux detection yoke 14a is U-shaped, and both ends of the U-shape are positioned close to the pressure receiving section 12a. Furthermore, the magnetic flux detection yoke 14a is positioned so that the magnetic flux flows in the direction in which the load is applied to the pressure receiving section 12a. The material of the magnetic flux detection yoke 14a is not particularly limited, as long as it is a soft magnetic material. Examples of materials for the magnetic flux detection yoke 14a include electromagnetic stainless steel, permalloy, pure iron, and silicon steel according to the present invention.

[0075] The coil 16 is wound around the magnetic flux detection yoke 14a. An AC power supply 20 is also connected to the coil 16. When an alternating current is applied to the coil 16 and a load is applied to the pressure-receiving part 12a, the permeability of the pressure-receiving part 12a changes. As a result, the inductance of the coil 16 changes. By detecting the amount of this change in inductance, the magnitude of the load can be determined.

[0076] [7.2. Specific Example 2] Figure 2 shows a front view of an inverse magnetostrictive load sensor according to a second embodiment of the present invention. In Figure 2, the inverse magnetostrictive load sensor 10b is a Hall element type sensor and comprises a pressure receiving section 12a, a magnetic flux detection yoke 14b, a permanent magnet 22, and a Hall element 24. The details of the pressure-receiving section 12a are the same as in the first embodiment, so a description will be omitted.

[0077] The magnetic flux detection yoke 14b forms a magnetic circuit together with the pressure receiving section 12a. In this embodiment, the magnetic flux detection yoke 14b is U-shaped, and both ends of the U are positioned close to the pressure receiving section 12a. Furthermore, the magnetic flux detection yoke 14b is positioned so that the magnetic flux flows in the direction in which the load is applied to the pressure receiving section 12a. In addition, a permanent magnet 22 and a Hall element 24 are inserted into the central part of the magnetic flux detection yoke 14b. The permanent magnet 22 is for generating magnetic flux. The Hall element 24 is for detecting the magnetic flux density within the magnetic circuit (permanent magnet 22, pressure receiving section 12a, and magnetic flux detection yoke 14b) by utilizing the Hall effect.

[0078] In this embodiment, the material of the magnetic flux detection yoke 14b is not particularly limited, as long as it is a soft magnetic material. Examples of materials for the magnetic flux detection yoke 14a include electromagnetic stainless steel, permalloy, pure iron, and silicon steel according to the present invention. In this embodiment, the material of the permanent magnet 22 is not particularly limited, as long as it is a hard magnetic material. Examples of permanent magnets 22 include neodymium magnets, ferrite magnets, alnico magnets, and SmCo magnets. The permanent magnet 22 may be a sintered magnet or a bonded magnet. Furthermore, in this embodiment, the structure of the Hall element 24 is not particularly limited, and the most suitable structure can be selected depending on the purpose.

[0079] When a load is applied to the pressure-receiving section 12a while the magnetic flux from the permanent magnet 22 is passing through the pressure-receiving section 12a, the density of the magnetic flux passing through the pressure-receiving section 12a changes. By detecting this change in magnetic flux density with the Hall element 24, the magnitude of the load can be determined.

[0080] [7.3. Specific Example 3] Figure 3 shows a front view of an inverse magnetostrictive load sensor according to a third embodiment of the present invention. In Figure 3, the inverse magnetostrictive load sensor 10c is an inductance type sensor and comprises a pressure receiving unit 12b, a coil 16, and an AC power supply 20. The pressure-receiving section 12b is made of precipitation-strengthened ferritic electromagnetic stainless steel according to the present invention. In this embodiment, the pressure-receiving section 12b has a rectangular tube shape and is arranged so that a load is applied perpendicularly to the opposing outer wall surfaces of the rectangular tube (the upper and lower outer wall surfaces in the example shown in Figure 2). The height, width, and depth of the pressure-receiving section 12b, as well as the height and width of the hollow section, are not particularly limited, and optimal dimensions can be selected according to the purpose.

[0081] In this embodiment, the pressure-receiving section 12b forms a magnetic circuit itself. A coil 16 is wound around one of the column portions of the pressure-receiving section 12b. Here, "column portion" refers to the outer wall on the inside of the outer wall of the rectangular tube, to which a load is applied in the in-plane direction of the outer wall surface. Furthermore, an AC power supply 20 is connected to the coil 16. Therefore, in this embodiment, the magnetic flux flows in the circumferential direction of the rectangular tube-shaped pressure-receiving section 12b. When an alternating current is applied to the coil 16 and a load is applied to the pressure-receiving part 12b, the permeability of the pressure-receiving part 12b changes. As a result, the inductance of the coil 16 changes. By detecting the amount of this change in inductance, the magnitude of the load can be determined.

[0082] [7.4. Specific Example 4] Figure 4 shows a front view of an inverse magnetostrictive load sensor according to a fourth embodiment of the present invention. In Figure 4, the inverse magnetostrictive load sensor 10d is a Hall element type sensor and comprises a pressure receiving section 12c, a permanent magnet 22, and a Hall sensor 24. The pressure-receiving section 12c is made of precipitation-strengthened ferritic electromagnetic stainless steel according to the present invention. In this embodiment, the pressure-receiving section 12c has a rectangular tube shape and is arranged so that a load is applied perpendicularly to the opposing outer wall surfaces of the rectangular tube. The height, width, and depth of the pressure-receiving section 12c, as well as the height and width of the hollow section, are not particularly limited, and optimal dimensions can be selected according to the purpose.

[0083] In this embodiment, a permanent magnet 22 and a Hall element 24 are inserted into one of the columnar portions of the pressure-receiving section 12c. The permanent magnet 22 and the Hall element 24 are joined to the pressure-receiving section 12c and both constitute part of a rectangular tube. Furthermore, the pressure-receiving section 12c and the permanent magnet 22 form a magnetic circuit. Therefore, in this embodiment, the magnetic flux flows in the circumferential direction of the rectangular tube-shaped pressure-receiving section 12c. The permanent magnet 22 is for generating magnetic flux. The Hall element 24 is for detecting the magnetic flux density in the magnetic circuit using the Hall effect. Other aspects of the permanent magnet 22 and the Hall element 24 are the same as in the second embodiment, so their explanation will be omitted.

[0084] When a load is applied to the pressure-receiving section 12c while the magnetic flux from the permanent magnet 22 is passing through the pressure-receiving section 12c, the density of the magnetic flux passing through the pressure-receiving section 12c changes. By detecting this change in magnetic flux density with the Hall element 24, the magnitude of the load can be determined.

[0085] [7.5. Specific Example 5] Figure 5 shows a plan view (left) and a front view (right) of an inverse magnetostrictive load sensor according to a fifth embodiment of the present invention. In Figure 5, the inverse magnetostrictive load sensor 10e is an inductance type sensor and comprises a pressure receiving section 12e, a magnetic flux detection yoke 14e, a coil 16, and an AC power supply 20. The pressure-receiving section 12e is made of precipitation-strengthened ferritic electromagnetic stainless steel according to the present invention. In this embodiment, the pressure-receiving section 12e is rod-shaped and is positioned so that the load is applied perpendicular to the axial direction of the rectangular bar. The height, width, and depth of the pressure-receiving section 12e are not particularly limited, and optimal dimensions can be selected according to the purpose.

[0086] In this embodiment, the magnetic flux detection yoke 14e forms a magnetic circuit together with the pressure receiving section 12e. The magnetic flux detection yoke 14e is U-shaped, and both ends of the U are positioned close to the pressure receiving section 12e. Furthermore, the magnetic flux detection yoke 14e is positioned so that the magnetic flux flows perpendicular to the direction in which the load is applied to the pressure receiving section 12e. This point differs from the first embodiment. Other points are the same as in the first embodiment, so their explanation will be omitted.

[0087] When an alternating current is applied to the coil 16 and a load is applied to the pressure-receiving part 12e, the permeability of the pressure-receiving part 12e changes. As a result, the inductance of the coil 16 changes. By detecting the amount of change in this inductance, the magnitude of the load can be determined. Furthermore, in Figure 5, if a permanent magnet and a Hall element are inserted in the central part of the magnetic flux detection yoke, as shown in Figure 2, instead of the coil 16 and AC power supply 20, a Hall element type sensor can be created.

[0088] [7.6. Specific Example 6] Figure 6 shows a plan view (left) and a front view (right) of an inverse magnetostrictive load sensor according to the sixth embodiment of the present invention. In Figure 6, the inverse magnetostrictive load sensor 10f is an inductance type sensor and comprises a pressure receiving section 12f, a magnetic flux detection yoke 14f, a coil 16, and an AC power supply 20. The pressure-receiving portion 12f is made of precipitation-strengthened ferritic electromagnetic stainless steel according to the present invention. In this embodiment, the pressure-receiving portion 12f has an annular shape and is positioned so that the load is applied in the axial direction of the annule. The thickness, outer diameter, and inner diameter of the pressure-receiving portion 12f are not particularly limited, and the optimal dimensions can be selected according to the purpose. In Figure 6, the pressure-receiving portion 12f is an annular shape, but it may also be an angular annular shape.

[0089] In this embodiment, the pressure-receiving section 12f forms a magnetic circuit itself. The magnetic flux detection yoke 14f is U-shaped, and both ends of the U are positioned close to the pressure-receiving section 12f. Furthermore, the tip of the magnetic flux detection yoke 14f is curved to conform to the surface of the annular pressure-receiving section 12f. In addition, the magnetic flux detection yoke 14f is positioned so that the magnetic flux flows in the circumferential direction of the pressure-receiving section 12f. Other points are the same as in the first embodiment, so their explanation will be omitted.

[0090] When an alternating current is applied to the coil 16 and a load is applied to the pressure-receiving part 12f, the permeability of the pressure-receiving part 12f changes. As a result, the inductance of the coil 16 changes. By detecting the amount of change in this inductance, the magnitude of the load can be determined. Furthermore, in Figure 6, if a permanent magnet and a Hall element are inserted in the central part of the magnetic flux detection yoke, as shown in Figure 2, instead of the coil 16 and AC power supply 20, a Hall element type sensor can be created.

[0091] [7.7. Specific Example 7] Figure 7 shows a front view of an inverse magnetostrictive load sensor according to the seventh embodiment of the present invention. In Figure 7, the inverse magnetostrictive load sensor 10g is a Hall element type sensor and comprises a pressure receiving section 12g, a permanent magnet 22, and a Hall sensor 24. The pressure-receiving portion 12g is made of precipitation-strengthened ferritic electromagnetic stainless steel according to the present invention. In this embodiment, the pressure-receiving portion 12g has a C-shaped cylindrical form and is arranged so that a load is applied perpendicularly to the opposing outer wall surfaces of the C-shaped cylinder.

[0092] In this embodiment, an air gap is formed in one of the columnar portions of the pressure-receiving portion 12g. Furthermore, a permanent magnet 22 and a Hall element 24 are inserted within the air gap at intervals. This point differs from the fourth embodiment. As shown in Figure 4, if the permanent magnet 22 and the Hall element 24 are integrated with the pressure receiving section 12c, the permanent magnet 22 and / or Hall element 24 may break when a large load is applied to the pressure receiving section 12c. In contrast, as shown in Figure 7, if the permanent magnet 22 and Hall element 24 are inserted into the air gap of the pressure receiving section 12g, it becomes easier to maintain a non-contact state between the pressure receiving section 12g and the permanent magnet 22 and Hall element 24 even when a large load is applied. As a result, the permanent magnet 22 and / or Hall element 24 are less likely to break even when a large load is applied. Other points are the same as in the fourth embodiment, so the explanation will be omitted.

[0093] When a load is applied to the pressure-receiving part 12g while the magnetic flux from the permanent magnet 22 is passing through the pressure-receiving part 12g, the density of the magnetic flux passing through the pressure-receiving part 12g changes. By detecting this change in magnetic flux density with the Hall element 24, the magnitude of the load can be determined.

[0094] [7.8. Specific Example 8] Figure 8 shows a plan view (left) and a front view (right) of an inverse magnetostrictive load sensor according to the eighth embodiment of the present invention. In Figure 8, the inverse magnetostrictive load sensor 10h is a Hall element type sensor and comprises a pressure receiving section 12h, a permanent magnet 22, and a Hall sensor 24. The pressure-receiving portion 12h is made of precipitation-strengthened ferritic electromagnetic stainless steel according to the present invention. In this embodiment, the pressure-receiving portion 12h has a C-ring shape and is arranged so that the load is applied in the axial direction of the C-ring. In Figure 8, the pressure-receiving portion 12h is an annular shape, but it may also be an angular annular shape.

[0095] In this embodiment, an air gap is formed in the pressure-receiving section 12h. A permanent magnet 22 and a Hall element 24 are inserted within the air gap at intervals. The pressure-receiving section 12h and the permanent magnet 22 constitute a magnetic circuit. Therefore, in this embodiment, the magnetic flux flows in the circumferential direction of the C-ring. Other aspects are the same as in the seventh embodiment, so their explanation is omitted.

[0096] When a load is applied to the pressure-receiving section 12h while the magnetic flux from the permanent magnet 22 is passing through the pressure-receiving section 12h, the density of the magnetic flux passing through the pressure-receiving section 12h changes. By detecting this change in magnetic flux density with the Hall element 24, the magnitude of the load can be determined.

[0097] [8. Effect] Inverse magnetostrictive load sensors, a type of load sensor, can directly measure stress and, compared to strain gauge load sensors, do not suffer from problems such as sensor delamination or deterioration due to deformation of strain gauges, thus offering superior durability. However, due to its structure, inverse magnetostrictive load sensors have the problem that the output fluctuates due to plastic deformation or fatigue of the magnetic material, as the magnetic material itself deforms under stress. In addition, the magnetic hysteresis of the magnetic material causes hysteresis in the sensor, so the magnetic material used must have low coercivity and high strength.

[0098] In contrast, by optimizing the composition of precipitation-strengthened ferritic electromagnetic stainless steel and precipitating fine NiAl particles in the matrix, it is possible to increase strength without degrading soft magnetic properties. When a soft magnetic yoke made of such precipitation-strengthened ferritic electromagnetic stainless steel is used as the pressure-receiving part of an inverse magnetostrictive load sensor, it is possible to realize a load sensor that exhibits high durability and excellent measurement sensitivity even when a large load is applied to the pressure-receiving part. [Examples]

[0099] (Examples 1-10, Comparative Examples 1-4) [1. Sample Preparation] In a vacuum induction furnace, 50 kg of alloy with the composition shown in Table 1 was melted and cast. The resulting ingot was then subjected to hot forging, hot rolling, and cold rolling to process it into a 3.3 mm thick plate. Next, the cold-rolled sheets were processed into toroidal cores. Then, the cores were subjected to vacuum heat treatment at 850°C for 2 hours (solution treatment combined with magnetic annealing). Furthermore, with the exception of Comparative Example 1, the sheets after vacuum heat treatment were subjected to aging treatment at 500-650°C for 0.5-24 hours.

[0100] [2. Test Method] [2.1. DC Magnetic Measurement] A toroidal core with an outer diameter of 28 mm, an inner diameter of 20 mm, and a thickness of 3 mm was fabricated. The DC magnetic properties of the obtained core were measured. The number of turns in the coil was 200 turns for the primary coil and 100 turns for the secondary coil. The measurement was performed using the two-coil method. A DC BH analyzer (BHS-40, manufactured by RIKEN Electron Co., Ltd.) was used as the measuring instrument. The maximum applied magnetic field was 63 [Oe] (approximately 5000 A / m). The coercivity was estimated based on the obtained hysteresis loop.

[0101] [2.2. X-ray small-angle scattering measurement] For the X-ray source, we used the large synchrotron radiation facility (SPring-8), specifically the industrial beamline: BL19B2. Thin sections with a thickness of 30-50 μm were prepared from toroidal cores subjected to DC magnetic measurement. These thin sections were then analyzed. Camera length: 3 m, exposure time: 30 sec, wavelength range: 0.01 <q<3.2(nm -1 The small-angle X-ray scattering of ) was measured. Peak fitting was performed on the scattering peaks originating from NiAl in the obtained scattering profiles using a particle size distribution assumed to be log-normal, and the average diameter of NiAl was determined.

[0102] [2.3. Hardness] A toroidal core that had undergone DC magnetic measurement was cut to a length of approximately 5 mm. This was embedded in resin, and the surface of the test piece was polished. The Vickers hardness (Hv) of this test piece was measured using a Vickers hardness tester.

[0103] [2.4. Magnetic fatigue degree F] A toroidal core with an outer diameter of 19 mm, an inner diameter of 15 mm, and a thickness of 2.5 mm was fabricated. The obtained core was subjected to a pressure of 400 MPa in the thickness direction, and 10 6 Repeated stress was applied several times. DC magnetic field measurements were performed before and after the application of repeated stress. The number of turns of the coils was 100 turns for the primary coil and 100 turns for the secondary coil. The measurement was performed using the two-coil method. A DC BH analyzer (BHS-40, manufactured by RIKEN Electron Co., Ltd.) was used as the measurement device. The maximum applied magnetic field was 63 [Oe] (approximately 5000 A / m). Based on the obtained hysteresis loop, the maximum relative permeability was estimated, and the change in maximum relative permeability (magnetic fatigue degree F) before and after the application of repeated stress was calculated.

[0104] [2.5. Rate of change of maximum relative permeability Δμ m ] A toroidal core with an outer diameter of 19 mm, an inner diameter of 15 mm, and a thickness of 2.5 mm was fabricated. A stress of 330 MPa was applied to the obtained core in the thickness direction. DC magnetic measurements were performed before and after the stress was applied. The number of turns in the coils was 100 turns for the primary coil and 100 turns for the secondary coil. The measurement was performed using the two-coil method. A DC BH analyzer (BHS-40, manufactured by RIKEN Electron Co., Ltd.) was used as the measuring device. The maximum applied magnetic field was 63 [Oe] (approximately 5000 A / m). Based on the obtained hysteresis loop, the maximum relative permeability was estimated, and the rate of change of the maximum relative permeability before and after stress application was calculated as Δμ. m I calculated it.

[0105] [2.6. Magnetic fatigue strength σ wb ] A toroidal core with an outer diameter of 19 mm, an inner diameter of 15 mm, and a thickness of 2.5 mm was fabricated. The obtained core was subjected to stress changes in the thickness direction at 10 MPa intervals. 6 Repeated stress was applied several times. DC magnetic field measurements were performed before and after the application of repeated stress. The number of turns of the coils was 100 turns for the primary coil and 100 turns for the secondary coil. The measurement was performed using the two-coil method. A DC BH analyzer (BHS-40, manufactured by RIKEN Electron Co., Ltd.) was used as the measuring device. The maximum applied magnetic field was 63 [Oe] (approximately 5000 A / m). Based on the obtained hysteresis loop, the maximum relative permeability was estimated, and the change in maximum relative permeability before and after the application of repeated stress was calculated. Furthermore, the maximum repeated stress at which the decrease in maximum relative permeability was 500 or less was calculated.

[0106] [2.7. Area ratio of the ferrite phase] A toroidal core that had undergone DC magnetic measurement was cut into pieces approximately 5 mm long. These pieces were embedded in resin, and the surface of the test specimen was polished. The polished surface was etched to reveal the microstructure, and the area ratio of the ferrite phase was measured.

[0107] [3. Results] Table 1 shows the results. Table 1 also shows the material composition and heat treatment conditions. Table 2 shows the magnetic fatigue strength σ of the sample obtained in Example 1. wb An example of the measurement results is shown below. From Tables 1 and 2, the following can be seen.

[0108] (1) Comparative Example 1 had a low Vickers hardness, F was well below -500, and σ wbThe pressure was significantly below 400 MPa. This is likely because the material has not undergone aging treatment and does not contain fine NiAl particles. (2) Comparative Example 2 had a low Vickers hardness, F was well below -500, and σ wb The pressure was significantly lower than 400 MPa. This is thought to be because, due to the low amount of Ni, fine NiAl particles did not precipitate even after aging treatment.

[0109] (3) Comparative Example 3 has a coercivity exceeding 1.0 [Oe] and Δμ m The percentage fell below 60%. This is thought to be due to excessive amounts of Cr and Mo. (4) Comparative Example 4 had a low Vickers hardness, F was well below -500, and σ wb The pressure was significantly below 400 MPa. This is thought to be because, due to the low amount of Al, fine NiAl particles did not precipitate even after aging treatment.

[0110] (5) All of Examples 1 to 10 had a Vickers hardness of 250 Hv or higher and an F of -500 or higher. Also, all of Examples 1 to 10 had a Δμ m is 60% or more, and σ wb The coercivity was 400 MPa or higher. This is thought to be due to the deposition of an appropriate amount of fine NiAl particles in the matrix. Furthermore, the coercivity of all Examples 1 to 10 was 1.0 [Oe] or less. This is thought to be because the content of elements that increase coercivity (especially Cr and Mo) was optimized.

[0111] (6) In Examples 2, 8, and 9, NiAl was less likely to precipitate compared to the other examples, so long-term aging treatment at low temperatures was required to precipitate NiAl. Furthermore, even after long-term aging treatment at low temperatures, the Vickers hardness of Examples 2, 8, and 9 was lower than that of the other examples. This is thought to be due to the small amount of NiAl precipitated.

[0112] [Table 1]

[0113] [Table 2]

[0114] Although embodiments of the present invention have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Industrial applicability]

[0115] The soft magnetic yoke according to the present invention can be used in the pressure-receiving part of an inverse magnetostrictive load sensor. [Explanation of symbols]

[0116] 10a~10h Reverse magnetostrictive load sensor 12a~12h Pressure receiving part 14a~14e Magnetic flux detection yoke 16 coils 20 AC power supply 22 Permanent Magnets 24 Hall elements

Claims

1. A soft magnetic yoke with the following configuration. (1) The soft magnetic yoke is made of precipitation-strengthened ferritic electromagnetic stainless steel. (2) The precipitation-strengthened ferritic electromagnetic stainless steel is 1.0≦Cr≦14.0mass%, 0.7≦Mo≦1.9mass%, 1.0≦Al≦5.0mass%, 1.1 ≤ Ni ≤ 5.0 mass%, and, Si≦0.4mass% It contains, with the remainder consisting of Fe and unavoidable impurities. The area fraction of the ferrite phase at room temperature is 90% or more. It contains precipitated particles made of NiAl with an average diameter of 1 nm to 10 nm. The Vickers hardness is 250 Hv or higher.

2. A soft magnetic yoke according to claim 1, used as a pressure-receiving part of an inverse magnetostrictive load sensor.

3. The soft magnetic yoke according to claim 1, wherein the precipitation-strengthened ferritic electromagnetic stainless steel has a coercivity Hc of 1.0 [Oe] or less.

4. The soft magnetic yoke according to claim 1, wherein the precipitation-strengthened ferritic electromagnetic stainless steel has a magnetic fatigue degree F represented by the following formula (1) of -500 or more. F=μ m1 -m m0 (1) however, μ m0 The initial maximum relative permeability of the aforementioned precipitation-strengthened ferritic electromagnetic stainless steel is μ m1 The stress of 400 MPa is 10 6 The maximum relative permeability of the precipitation-strengthened ferritic electromagnetic stainless steel after repeated application.

5. The aforementioned precipitation-strengthened ferritic electromagnetic stainless steel has a rate of change of maximum relative permeability Δμ, which is expressed by the following formula (2). m The soft magnetic yoke according to claim 1, wherein the content is 60% or more. Dm m =(1-μ m2 / m m0 )×100(%)(2) however, μ m0 The initial maximum relative permeability of the aforementioned precipitation-strengthened ferritic electromagnetic stainless steel is μ m2 This is the maximum relative permeability of the precipitation-strengthened ferritic electromagnetic stainless steel when a stress of 330 MPa is applied.

6. The aforementioned precipitation-strengthened ferritic electromagnetic stainless steel has a magnetic fatigue strength σ wb The soft magnetic yoke according to claim 1, wherein the pressure is 400 MPa or more. However, the above-mentioned "magnetic fatigue strength σ wb " means, 10 for the aforementioned precipitation-strengthened ferritic electromagnetic stainless steel 6 In a test in which repeated stress is applied and the change in the maximum relative permeability before and after repeated stress application is measured, with the stress varied at 10 MPa intervals, This refers to the maximum stress at which the decrease in the maximum relative permeability before and after repeated stress application is 500 or less.

7. A soft magnetic yoke according to claim 1, having a plate shape, rod shape, rectangular tube shape, ring shape, C-tube shape, or C-ring shape.

8. An inverse magnetostrictive load sensor using the soft magnetic yoke described in claim 1 as the pressure receiving part.

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