Fe-based alloy components

Abstract

To provide an Fe-based alloy for solid phase nitrogen absorption which can materialize high magnetic permeability, high electric resistance, high saturation magnetic flux density and high hardness, and a member using the Fe-based alloy for solid phase nitrogen absorption.SOLUTION: An Fe-based alloy for solid phase nitrogen absorption contains 0.020 mass% or less C, 0.030 mass% or less N, and 5.0 or more and 18.0 mass% or less Cr, and further contains one or two or more elements of 0.5 or more and 3.0 mass% or less Si, 0.1 or more and 3.0 mass% or less Al, and 0.05 or more and 3.0 mass% or less Ti, and the balance composed of Fe and inevitable impurities, and has an area ratio of a ferrite phase at 23°C of 95% or more. An Fe-based alloy member comprises: a base portion composed of the Fe-based alloy for solid phase nitrogen absorption; and a nitrogen absorption layer formed on the surface of the base portion, wherein hardness of the nitrogen absorption layer is 400 HV or more, and an area ratio of the ferrite phase of the base portion at 23°C is 95% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention , Fe-based alloy components More specifically, Fe-based alloys for solid-phase nitrogen absorption suitable for surface hardening treatment by solid-phase nitrogen absorption method Money This relates to the Fe-based alloy members used. [Background technology]

[0002] Components (e.g., injectors) that make up fuel injection systems for vehicles with internal combustion engines require not only corrosion resistance against fuel but also good magnetic properties to enable highly accurate fuel injection control. Because electromagnetic stainless steel has excellent corrosion resistance and soft magnetic properties, it is used in many of the components that make up fuel injection systems.

[0003] Various proposals have been made in the past regarding components that make up such fuel injection devices or materials suitable for them. For example, Patent Document 1 discloses an electromagnetic fuel injection valve that includes a fixed core, a coil wound around the outer periphery of the fixed core, a movable core positioned opposite the fixed core, and a valve housing that accommodates the movable core. The document also states that a hardened layer is formed on the surface of the annular guide portion (the portion along which the movable core slides as it reciprocates along the inner surface of the valve housing) provided on the inner peripheral surface of the valve housing by shot peening or chrome plating.

[0004] Patent Document 2 discloses a ferritic stainless steel material containing predetermined amounts of C, Si, Mn, P, S, Cr, N, Al, and Ti and having nitrides precipitated in the surface layer, although it is not intended to be applied to components that constitute a fuel injection device. The same document states: (A) When ferritic stainless steel is annealed (bright annealed) in a mixed gas atmosphere containing N2 and H2, nitrogen atoms penetrate to a depth of about 0.05 mm from the surface, and when the nitrogen diffuses beyond the solid solubility limit, fine nitrides are dispersed and precipitated in the surface layer. (B) Dispersion and precipitation of nitrides can improve the surface hardness of steel without reducing corrosion resistance, and (C) Bright annealing increases the hardness of only the surface layer, while the interior is a soft ferrite structure, making it easy to press. is stated.

[0005] Furthermore, Patent Document 3 discloses a composite material that is not intended for application to components that constitute a fuel injection device, but that comprises a ferromagnetic steel material containing predetermined amounts of C, Si, Mn, Cr, N, and Ni, with the balance being Fe and unavoidable impurities, and a non-magnetic portion formed on the surface layer of the ferromagnetic steel material. The same document states: (A) When nitrogen atoms are diffused into ferromagnetic steel (solid-phase nitrogen absorption method), a non-magnetic part enriched in solid solution of N can be formed in the surface layer, and (B) It is stated that such composite materials are suitable as magnetic circuit components used in electromagnetic actuators and the like.

[0006] In particular, injectors have traditionally been designed to save energy through precise fuel injection control. In recent years, there has been a trend toward increasing the drive pressure of injectors to further improve fuel efficiency. Therefore, the materials used for these parts are: (a) High magnetic permeability and high electrical resistivity for precise fuel control; (b) High saturation magnetic flux density for high voltage drive (≒ high load torque), and (c) High hardness to prevent material degradation due to collisions caused by sliding motion is required.

[0007] One example of an existing material that combines high levels of magnetic properties and corrosion resistance is 13% chromium magnetic stainless steel. However, 13% chromium magnetic stainless steel has low hardness on its own, posing a challenge to its durability against valve collisions caused by high-pressure drive. To solve this problem, in injector applications, the surface of the material is typically chrome-plated to ensure surface hardness (see Patent Document 1). However, because chromium is non-magnetic, chrome plating inevitably results in a deterioration of the magnetic properties.

[0008] On the other hand, Patent Document 3 describes a method for forming a nonmagnetic portion in the surface layer of a ferromagnetic steel material using a solid-phase nitrogen absorption method. Here, the "solid-phase nitrogen absorption method" refers to a heat treatment method in which the steel material is held in high-temperature nitrogen, causing nitrogen atoms to diffuse from the material surface to the interior of the material, thereby increasing the nitrogen concentration near the material surface or throughout the material. The solid-phase nitrogen absorption method differs from nitriding methods in that it does not form nitrides. The solid-phase nitrogen absorption method can be used to dissolve nitrogen in the surface of a material, thereby strengthening the surface. However, if a non-magnetic layer is formed on the surface using the solid-phase nitrogen absorption method, the magnetic properties will inevitably deteriorate, just as with chrome plating. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-081356 [Patent Document 2] Japanese Patent Application Publication No. 11-350088 [Patent Document 3] Japanese Patent Application Publication No. 2013-028825 Summary of the Invention [Problem to be solved by the invention]

[0010] The problem to be solved by the present invention is to provide an Fe-based alloy for solid-phase nitrogen absorption that can achieve high magnetic permeability, high electrical resistance, high saturation magnetic flux density, and high hardness. Money?The object of the present invention is to provide a member comprising: [Means for solving the problem]

[0011] In order to solve the above problems, the present invention The Fe-based alloy member has the following configuration. (1) The Fe-based alloy member is a base made of an Fe-based alloy for solid-phase nitrogen absorption; a nitrogen absorption layer formed on the surface of the base; Equipped with The hardness of the nitrogen absorbing layer is 400 HV or more, The area ratio of the ferrite phase in the base at 23°C is 95% or more. (2) The solid phase nitrogen absorption Fe-based alloy is C≦0.020mass%, N≦0.030mass %、 5.0≦Cr≦18.0mass %、 Mn≦0.10mass%, P≦0.010mass%, S≦0.005mass%, Cu≦0.05mass%, Ni≦0.10 mass%, and O≦0.005mass% and further comprising 0.5≦Si≦3.0mass%, 0.1≦Al≦3.0 mass%, and 0.05≦Ti≦3.0mass% Contains one or more elements of the balance being Fe and unavoidable impurities, The area ratio of ferrite phase at 23°C is 95% or more. be. Here, the "solid phase nitrogen absorption" refers to a treatment in which the base is heated to a temperature of 900°C or higher and 1100°C or lower in a nitrogen atmosphere.

[0012] (delete) [Effects of the Invention]

[0013] In an Fe-based alloy containing a certain amount of Cr, the ferrite phase can be stabilized by minimizing the amounts of C and N, which have high austenite-forming properties, and adding a small amount of Ti, which has high ferrite-forming properties. Furthermore, the addition of appropriate amounts of Al and Si improves magnetic properties such as electrical resistance and magnetic anisotropy. As a result, an Fe-based alloy can be obtained in which the ferrite phase is stable not only at room temperature but also at high temperatures (temperature ranges where solid-phase nitrogen absorption treatment is performed), and which exhibits high magnetic permeability, high electrical resistance, and high saturation magnetic flux density at room temperature.

[0014] When a solid-phase nitrogen absorption treatment is performed on a member made of such an Fe-based alloy, the nitrogen concentration in the surface layer increases, and eventually only the surface layer becomes austenite phase. Rapid cooling from this state causes the austenite phase in the surface layer to transform into martensite. As a result, a member can be obtained in which the core is made of a ferrite phase with high magnetic properties and the surface layer is made of a martensite phase with high hardness. The martensite phase in the surface layer has inferior magnetic properties compared to the ferrite phase in the core, but exhibits soft magnetic properties. Therefore, the Fe-based alloy member of the present invention exhibits higher magnetic properties than conventional members in which a nonmagnetic layer is formed in the surface layer. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described in detail below. [1. Fe-based alloys for solid-phase nitrogen absorption] [1.1. Main constituent elements] The Fe-based alloy for solid-phase nitrogen absorption according to the present invention (hereinafter simply referred to as "Fe-based alloy") contains the following elements, with the balance consisting of Fe and unavoidable impurities. The types of added elements, their component ranges, and the reasons for their limitations are as follows:

[0016] (1) C≦0.020 mass%: Carbon deteriorates the magnetic properties of Fe-based alloys and promotes austenitization of the parent phase. Therefore, the smaller the carbon content, the better. To prevent deterioration of the magnetic properties and austenitization of the parent phase, the carbon content must be 0.020 mass% or less. The carbon content is preferably 0.010 mass% or less, and more preferably 0.00510 mass% or less.

[0017] (2) N≦0.030 mass%: N promotes austenitization of the matrix. Therefore, the smaller the N content before solid-phase nitrogen absorption treatment, the better. To suppress austenitization of the matrix, the N content must be 0.030 mass% or less. The N content is preferably 0.010 mass% or less, and more preferably 0.00510 mass% or less.

[0018] (3) 5.0≦Cr≦18.0mass% Cr has the effect of improving the corrosion resistance of Fe-based alloys and the effect of improving the equilibrium nitrogen concentration during solid-phase nitrogen absorption. To achieve these effects, the Cr content must be 5.0 mass% or more. The Cr content is preferably 6.0 mass% or more, and more preferably 11.0 mass% or more. On the other hand, if the Cr content is excessive, the maximum magnetic flux density decreases. Therefore, the Cr content must be 18.0 mass% or less. The Cr content is preferably 15.0 mass% or less, and more preferably 13.0 mass% or less.

[0019] (4) 0.5≦Si≦3.0mass%: Si has the effect of promoting ferrite formation in the matrix and the effect of increasing the hardness and electrical resistance of the matrix. To obtain these effects, the Si content must be 0.5 mass% or more. On the other hand, if the Si content is excessive, the maximum magnetic flux density and workability decrease. Therefore, the Si content must be 3.0 mass% or less. The Si content is preferably 2.30 mass% or less, and more preferably 1.55 mass% or less.

[0020] (5) 0.1≦Al≦3.0mass% Al has the effect of promoting ferritization of the matrix and the effect of increasing the electrical resistance of the matrix. To obtain these effects, the Al content must be 0.1 mass% or more. The Al content is preferably 0.3 mass% or more. On the other hand, if the Al content is excessive, the surface layer will not transform into martensite during quenching after solid-phase nitrogen absorption, and the hardness of the surface layer will decrease. Therefore, the Al content must be 3.0 mass% or less. The Al content is preferably 2.5 mass% or less, and more preferably 1.1 mass% or less.

[0021] (6) 0.05≦Ti≦3.0mass% Ti has the effect of promoting ferrite formation in the matrix even when added in small amounts. To obtain this effect, the Ti content must be 0.05 mass% or more. The Ti content is preferably 0.10 mass% or more. On the other hand, if the Ti content is excessive, the surface layer will not transform into martensite during quenching after solid-phase nitrogen absorption, and the hardness of the surface layer will decrease. Therefore, the Ti content must be 3.0 mass% or less. The Ti content is preferably 2.5 mass% or less, and more preferably 0.5 mass% or less.

[0022] The Fe-based alloy according to the present invention comprises at least (a) Cr and (b) One or more elements of 0.5≦Si≦3.0mass%, 0.1≦Al≦3.0mass%, and 0.05≦Ti≦3.0mass% It is sufficient that it contains the above. Here, "containing one or more elements of 0.5≦Si≦3.0 mass%, 0.1≦Al≦3.0 mass%, and 0.05≦Ti≦3.0 mass%" means that when the content of at least one of Si, Al, and Ti is equal to or greater than the above-mentioned lower limit, the content of the remaining elements may be less than the above-mentioned lower limit or equal to or greater than the above-mentioned lower limit.

[0023] 1.2. Inevitable impurities "Inevitable impurities" refer to trace components that are mixed in from raw materials or refractories when producing an Fe-based alloy. Examples of inevitable impurities include: (a) 0.10 mass% or less of Mn; (b) 0.010 mass% or less of P; (c) 0.005 mass% or less of S; (d) 0.05 mass% or less of Cu; (e) 0.10 mass% or less of Ni, (f) 0.005 mass% or less of O, etc.

[0024] In particular, both Ni and Mn have the effect of promoting austenitization of the matrix. Therefore, the less Ni and Mn they contain, the better. To suppress austenitization of the matrix, the Ni content and Mn content are each preferably 0.01 mass% or less.

[0025] [1.3. Metal structure] The Fe-based alloy according to the present invention has optimized components, and therefore has a ferrite phase area ratio of 95% or more at 23°C before solid-phase nitrogen absorption treatment. The "ferrite phase area ratio" will be described later. In the Fe-based alloy according to the present invention, the matrix of the metal structure (region excluding inclusions) is usually a single ferrite phase not only at room temperature but also at high temperatures (temperature ranges where solid-phase nitrogen absorption treatment is performed). However, depending on the composition, a small amount of austenite may be generated at high temperatures.

[0026] [1.4. Ferrite stabilization index] The Fe-based alloy according to the present invention preferably satisfies the following formula (1). ([Cr]+2.6[Si]+7[Al]+7[Ti]) / (5[C]+5[N]+0.35)≧33 …(1) Here, [X] represents the mass percentage (mass%) of the element X contained in the solid-phase nitrogen-absorbing Fe-based alloy.

[0027] The variable on the left side of equation (1) represents the "ferrite stabilization index." If the ferrite stabilization index becomes too small, the core matrix may not become a single ferrite phase in the temperature range (900 to 1100°C) where solid-phase nitrogen absorption treatment is performed, and an austenite phase may form. If rapid cooling is performed from this state, a martensite phase will also form in the core, reducing the magnetic flux density.

[0028] On the other hand, the larger the ferrite stabilization index, the easier it is for ferrite to be stabilized at high temperatures. In order to make the core matrix approach a single ferrite phase in the temperature range where solid-phase nitrogen absorption treatment is performed, the ferrite stabilization index is preferably 33 or more. On the other hand, if the ferrite stabilization index is too large, the nitrogen absorption layer may not become austenite at high temperatures, and surface hardness may not be obtained by quenching. Therefore, the ferrite stabilization index is preferably 80 or less.

[0029] [2. Fe-based alloy components] The Fe-based alloy member according to the present invention has a base portion made of the solid phase nitrogen absorption Fe-based alloy according to the present invention; a nitrogen absorption layer formed on the surface of the base; It is equipped with:

[0030] [2.1. Base] [2.1.1. Materials] The base is made of an Fe-based alloy for solid-phase nitrogen absorption. Details of the Fe-based alloy are as described above, so further explanation will be omitted.

[0031] [2.1.2. Area ratio of ferrite phase] "Area ratio (%) of ferrite phase" refers to the ratio of the area of ​​the ferrite phase to the area of ​​the cross section of the Fe-based alloy at 23°C. In other words, the "area ratio (%) of the ferrite phase" is (a) cutting the Fe-based alloy member after the solid-phase nitrogen absorption treatment in a direction perpendicular to the surface, and polishing and etching the cross section; (b) The area near the center of the cross section (the area not including the nitrogen absorption layer) was observed with an optical microscope at room temperature, and the area of ​​the field of view (S0) and the area of ​​the ferrite phase included in the field of view (S) were calculated. (c) The value obtained by dividing S by S0 (=S×100 / S0) This refers to... In the present invention, S0 is set to 1 mm x 4 mm.

[0032] The Fe-based alloy according to the present invention has an optimized composition, so that the area ratio of the ferrite phase in the base is 95% or more. When the composition of the Fe-based alloy is optimized, the area ratio of the ferrite phase is 98% or more.

[0033] [2.1.3. Grain size] "Grain size" refers to the value obtained by measuring the grain size from an optical microscope photograph using the cutting method using a straight test line as specified in JIS G0551, and converting the grain size using Table A.1 in Annex A of JIS G0551.

[0034] The crystal grain size of the base affects the magnetic properties of the Fe-based alloy member. Generally, the larger the crystal grain size of the base, the higher the magnetic properties of the Fe-based alloy member. The Fe-based alloy member according to the present invention is subjected to solid-phase nitrogen absorption treatment, which causes grain growth during the treatment. When the manufacturing conditions are optimized, the crystal grain size of the base becomes 150 μm or more. When the manufacturing conditions are further optimized, the crystal grain size of the base becomes 300 μm or more. On the other hand, if the crystal grain size of the base portion is made larger than necessary, the mechanical properties of the Fe-based alloy member may deteriorate, so the crystal grain size of the base portion is preferably 1000 μm or less.

[0035] [2.2. Nitrogen absorption layer] The term "nitrogen absorption layer" refers to a layer formed by subjecting a substrate to solid-phase nitrogen absorption treatment, thereby dissolving nitrogen in the surface layer of the substrate.

[0036] 2.2.1. Solid-phase nitrogen absorption treatment and quenching The solid-phase nitrogen absorption treatment is carried out by heating the substrate to a predetermined temperature in a predetermined nitrogen atmosphere.

[0037] The heating temperature affects the nitrogen concentration on the substrate surface. Therefore, it is preferable to select an optimal heating temperature depending on the composition of the substrate. In general, the lower the heating temperature, the higher the equilibrium nitrogen concentration on the substrate surface. However, if the heating temperature is too low, CrN may precipitate, which may deteriorate the magnetic properties. Therefore, the heating temperature is preferably 900°C or higher. On the other hand, if the heating temperature is too high, the equilibrium nitrogen concentration on the substrate surface may decrease, resulting in a decrease in hardness. Therefore, the heating temperature is preferably 1100°C or less.

[0038] The nitrogen partial pressure affects the nitrogen concentration on the substrate surface. Therefore, it is preferable to select an optimum value for the nitrogen partial pressure depending on the composition of the substrate. Generally, the higher the nitrogen partial pressure, the higher the equilibrium nitrogen concentration on the substrate surface. To achieve this effect, the nitrogen partial pressure is preferably 0.035 MPa or higher. In particular, when the matrix of the surface layer has a composition that is difficult to form a martensite single phase (for example, a composition with a low Cr content), it is preferable to increase the nitrogen partial pressure to dissolve more nitrogen and convert the surface layer to austenite. On the other hand, if the nitrogen partial pressure is too high, the nitrogen concentration increases excessively, lowering the martensitic transformation start temperature. As a result, the austenite phase tends to remain after quenching, which may reduce hardness. Therefore, the nitrogen partial pressure is preferably 0.7 MPa or less.

[0039] The nitrogen concentration on the substrate surface is determined by the heating temperature and nitrogen partial pressure. On the other hand, the treatment time affects the thickness of the nitrogen absorbing layer. Therefore, it is preferable to select an optimum treatment time depending on the required thickness of the nitrogen absorbing layer. The treatment time is usually about 1 to 300 minutes.

[0040] After diffusing a predetermined amount of nitrogen into the surface layer portion, the member is quenched, whereby the austenite phase in the surface layer portion is transformed into martensite. The quenching conditions are not particularly limited as long as the conditions are such that the surface layer portion can be transformed into martensite. For example, quenching may be performed by rapidly cooling the substrate from the treatment temperature during solid-phase nitrogen absorption treatment. Alternatively, quenching may be performed by heating the substrate to the quenching temperature after solid-phase nitrogen absorption treatment and then rapidly cooling. Rapid cooling may be performed using gas cooling, water cooling, ice water cooling, oil cooling, or the like.

[0041] Furthermore, prior to quenching, a nitrogen diffusion treatment may be performed to diffuse nitrogen into the component. Specifically, following solid-phase nitrogen absorption treatment, the component is held at a high temperature of approximately 900 to 1100°C in an inert atmosphere such as argon gas, thereby diffusing nitrogen into the component. The nitrogen diffusion treatment thickens the nitrogen absorption layer, allowing for consistent surface hardness after quenching. However, if the nitrogen absorption layer becomes too thick, the magnetic properties (magnetic flux density) will decrease. Therefore, the holding temperature and holding time of the nitrogen diffusion treatment should be set taking into account the magnetic properties (magnetic flux density) required of the component. In addition, after hardening, sub-zero treatment may be performed in which the material is kept at or below 0°C.

[0042] 2.2.2. Hardness of the nitrogen absorption layer "Hardness of nitrogen absorption layer" means (a) cutting the Fe-based alloy member after the solid-phase nitrogen absorption treatment perpendicular to the surface and polishing the cross section; (b) Measure the Vickers hardness at any five points located at a depth of 20 μm ± 5 μm from the surface of the component. (c) Calculate the average Vickers hardness of the five points. This refers to the value obtained by

[0043] In the Fe-based alloy member according to the present invention, when the composition of the substrate and the conditions for solid-phase nitriding and quenching are optimized, the hardness of the nitrogen absorption layer becomes 400 HV or more. When the composition of the substrate and manufacturing conditions are optimized, the hardness of the nitrogen absorption layer becomes 500 HV or more.

[0044] 2.2.3. Nitrogen absorption layer thickness The interface between the ferrite phase in the core and the nitrogen absorption layer in the surface layer is usually not flat, but has a shape with significant irregularities. (a) cutting the Fe-based alloy member after the solid-phase nitrogen absorption treatment perpendicular to the surface and polishing the cross section; (b) Observe the surface vicinity of the cross section at three arbitrary points at a magnification that allows observation of an area with a width (distance parallel to the surface of the substrate) of approximately 500 μm. (c) Calculating the shortest distance from the surface of the component to the ferrite phase in each field of view; (d) Calculate the average of the three shortest distances. This refers to the value obtained by

[0045] In the present invention, the thickness of the nitrogen absorption layer is not particularly limited. Generally, the thicker the nitrogen absorption layer, the better the wear resistance. On the other hand, if the nitrogen absorption layer is too thick, the magnetic properties of the member may be deteriorated. Therefore, it is preferable to select an optimal thickness for the nitrogen absorption layer taking these points into consideration. As mentioned above, the thickness of the nitrogen absorbing layer mainly depends on the processing time of the solid-phase nitrogen absorption process. When the manufacturing conditions are optimized, the thickness of the nitrogen absorbing layer becomes about 20 to 200 μm.

[0046] [2.3. Usage] The Fe-based alloy member according to the present invention can be used in a variety of applications. (a) a moving core of an electromagnetic fuel injection device; (b) Rotor core for electric vehicle motor etc.

[0047] [3. Effect] In an Fe-based alloy containing a certain amount of Cr, the ferrite phase can be stabilized by minimizing the amounts of C and N, which have high austenite-forming properties, and adding a small amount of Ti, which has high ferrite-forming properties. Furthermore, the addition of appropriate amounts of Al and Si improves magnetic properties such as electrical resistance and magnetic anisotropy. As a result, an Fe-based alloy can be obtained in which the ferrite phase is stable not only at room temperature but also at high temperatures (temperature ranges where solid-phase nitrogen absorption treatment is performed), and which exhibits high magnetic permeability, high electrical resistance, and high saturation magnetic flux density at room temperature.

[0048] When a solid-phase nitrogen absorption treatment is performed on a member made of such an Fe-based alloy, the nitrogen concentration in the surface layer increases, and eventually only the surface layer becomes austenite phase. Rapid cooling from this state causes the austenite phase in the surface layer to transform into martensite. As a result, a member can be obtained in which the core is made of a ferrite phase with high magnetic properties and the surface layer is made of a martensite phase with high hardness. The martensite phase in the surface layer has inferior magnetic properties compared to the ferrite phase in the core, but exhibits soft magnetic properties. Therefore, the Fe-based alloy member of the present invention exhibits higher magnetic properties than conventional members in which a nonmagnetic layer is formed in the surface layer.

[0049] The martensite phase in the surface layer of the component has magnetic properties similar to the ferrite phase, so the deterioration of magnetic properties is less than with non-magnetic plating. Furthermore, the Fe-based alloy according to the present invention has optimized components, so it can achieve high hardness and magnetic properties equal to or better than those of conventional materials. [Example]

[0050] (Examples 1 to 21, Comparative Examples 1 to 8) 1. Sample Preparation 50 kg of steel having the composition shown in Table 1 was melted in a vacuum induction furnace and cast into an ingot. Then, a φ35 mm round bar was forged at a starting temperature of 1100°C and a final temperature of 900°C, followed by air cooling. Furthermore, a ring test piece with an outer diameter of 28 mm, an inner diameter of 20 mm, and a thickness of 3 mm, and a square bar test piece with dimensions of 3 mm x 3 mm x 50 mm were cut out from the obtained round bar.

[0051] [Table 1]

[0052] Next, each test piece was subjected to solid-phase nitrogen absorption treatment and quenching. That is, first, the test piece was placed in a treatment chamber, and then the treatment chamber was evacuated by a pressure reducing means. Next, nitrogen gas was introduced into the treatment chamber, and the pressure in the treatment chamber was maintained at a predetermined value. The pressure in the treatment chamber was (a) 0.1 MPa (Examples 1-2, Examples 4-19, Comparative Examples 3-5), or (b) 0.7 MPa (Example 3, Example 20, Comparative Examples 1 and 2) It was decided. In this state, the test pieces were heated at temperatures between 900 and 1100°C for a predetermined time. The heating time was adjusted so that the thickness of the nitrogen absorption layer after quenching was 10 μm or more. Furthermore, after the solid-phase nitrogen absorption treatment was completed, the test pieces were quenched. Quenching was performed by gas cooling, followed by sub-zero treatment at -70°C for 2 hours.

[0053] 2. Test Method [2.1. Nitrogen absorption layer thickness] After the solid-phase nitrogen absorption treatment, the test piece was cut and the thickness of the nitrogen-absorbed layer was measured. [2.2. Surface nitrogen concentration (nitrogen concentration in the nitrogen absorption layer)] The nitrogen concentration in the surface layer of the test piece was measured using an electron probe microanalyzer (EPMA).

[0054] [2.3. Surface hardness (hardness of nitrogen absorption layer)] The test piece after the solid-phase nitrogen treatment was cut, and the Vickers hardness was measured at a position 20 μm±5 μm deep from the surface. [2.4. Magnetic flux density B 30000 ] The above-mentioned hardened ring test piece was placed in a resin case, and a 500-turn magnetic field application coil and a 100-turn detection coil were wound around the case. Using a DC magnetization characteristic analyzer, the magnetic flux density B 30000 was measured.

[0055] 2.5. Electrical Resistivity The electrical resistance of the square bar test piece after quenching was measured by the four-terminal method. [2.6. Area ratio of ferrite phase in the core] The test piece after the solid phase nitrogen absorption treatment was cut, and the area ratio of the ferrite phase in the core was calculated.

[0056] [3. Results] The results are shown in Table 2. From Table 2, the following can be seen. (1) Comparative Example 1 had low surface hardness, which is thought to be because the surface layer did not transform into martensite due to the excessive Al content. (2) Comparative Example 2 had low surface hardness, which is thought to be because the surface layer did not transform into martensite due to the excessive Si content. (3) Comparative Example 3 is B 30000 This is thought to be because the excessive C content caused austenite to form in the core at high temperatures, preventing the core matrix from becoming a single ferrite phase at room temperature. (4) Comparative Example 4 is B 30000 This is thought to be due to the excessive amount of Cr.

[0057] (5) Comparative Example 5 has low surface hardness and B 30000 The low surface hardness is thought to be due to the low Cr content, the low concentration of dissolved nitrogen, and the absence of alloying elements such as Si that improve hardness. 30000 The reason why the value is low is thought to be that since the core matrix is ​​almost completely transformed into martensite during quenching due to the absence of Al, Si, and Ti, the core matrix does not become a ferrite single phase at room temperature. (6) Comparative Example 6 has low surface hardness, B 30000 The low surface hardness is thought to be due to the fact that the surface layer did not transform into martensite due to the excessive amount of Ti. 30000 The reason why the value is low is thought to be that the excessive Ti content causes the formation of a Laves phase, preventing the core matrix from becoming a ferrite single phase at room temperature. (7) Comparative Example 7 is B 30000 This is thought to be because the amount of Si is small, so austenite is formed in the core at high temperatures, and the matrix in the core does not become a single ferrite phase at room temperature. (8) Comparative Example 8 has poor magnetic properties. This is thought to be because the excessive amount of N caused austenite to form in the core, preventing the core from becoming a single phase of ferrite.

[0058] (9) In all of Examples 1 to 21, the surface hardness was 400 HV or more, and the area ratio of the ferrite phase in the core was 95% or more at room temperature. (10) Examples 3 and 20 have higher surface hardness than other materials with roughly the same composition. This is thought to be because a larger amount of nitrogen was dissolved in the surface layer by setting the nitrogen partial pressure to 0.7 MPa. On the other hand, in Comparative Examples 1 and 2, the surface hardness was less than 400 HV even when the nitrogen partial pressure was set to 0.7 MPa. This is thought to be because the surface layer did not transform into martensite due to the excessive Al or Si content. (11) The lower the amount of Al and / or Si, the lower the amount of B. 30000 On the other hand, the electrical resistance increased as the amount of Al and / or Si increased.

[0059] [Table 2]

[0060] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the present invention. [Industrial Applicability]

[0061] The Fe-based alloy according to the present invention can be used for the moving core of an electromagnetic fuel injection device, the rotor core of a motor for an electric vehicle, and the like.

Claims

1. An Fe-based alloy component having the following configuration: (1) The Fe-based alloy member is a base portion made of an Fe-based alloy for solid-phase nitrogen absorption; a nitrogen absorption layer formed on the surface of the base; Equipped with The hardness of the nitrogen absorbing layer is 400 HV or more, The area ratio of the ferrite phase in the base at 23°C is 95% or more. (2) The solid phase nitrogen absorption Fe-based alloy is C≦0.020mass%, N≦0.030mass%, 5.0≦Cr≦18.0mass%, Mn≦0.10mass%, P≦0.010mass%, S≦0.005mass%, Cu≦0.05mass%, Ni≦0.10 mass%, and O≦0.005mass% and further comprising 0.5≦Si≦3.0mass%, 0.1≦Al≦3.0 mass%, and 0.05≦Ti≦3.0mass% Contains one or more elements of the balance being Fe and unavoidable impurities; The area ratio of the ferrite phase at 23°C is 95% or more. Here, the "solid phase nitrogen absorption" refers to a treatment in which the base is heated to a temperature of 900° C. or more and 1100° C. or less in a nitrogen atmosphere.

2. The Fe-based alloy for solid-phase nitrogen absorption is an Fe-based alloy component according to claim 1, which satisfies the following formula (1): ([Cr]+2.6[Si]+7[Al]+7[Ti]) / (5[C]+5[N]+0.35)≧33...(1) Here, [X] represents the mass percentage (mass %) of the element X contained in the solid-phase nitrogen-absorbing Fe-based alloy.

3. 3. The Fe-based alloy member according to claim 1, wherein the grain size of the base portion is 150 μm or more.

4. 4. The iron-based alloy member according to claim 1, which is a movable core of an electromagnetic fuel injection device.

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