Fe-Co alloy bar

Abstract

Provided is an Fe—Co based alloy bar capable of stably obtaining excellent magnetic properties. An Fe—Co based alloy bar has, in terms of area ratio, more than 80% of grains with a Grain Orientation Spread (GOS) value of 0.5° or more, and the difference between the area ratio of grains with a GOS value of 0.5° or more observed in the cross-section perpendicular to the axis of the bar and the area ratio of grains with a GOS value of 0.5° or more observed in the axial cross-section of the bar is within 10%. Preferably, the average crystal grain size number is 6.0 or more and 8.5 or less.

Description

Technical Field

[0001] The present invention relates to an Fe-Co alloy bar. Background Art

[0002] Bars of Fe-Co alloys typified by permendur, which are known as alloys having excellent magnetic properties, are used in various products such as sensors, cylindrical magnetic shields, solenoid valves, and magnetic cores. As a method for manufacturing the Fe-Co alloy bar, for example, Patent Document 1 describes the following main idea: After heating an ingot to 1000°C to 1100°C, it is hot-worked into a blank of about φ90 mm, the surface scratches are removed by a lathe, and then it is heated to 1000°C to 1100°C and hot-rolled to about φ6 mm to φ9 mm to produce a raw material (bar).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Laid-Open No. 7-166239 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] With the high performance of the products, further improvement in magnetic properties is required for the raw materials.

[0008] Therefore, an object of the present invention is to provide an Fe-Co alloy bar capable of stably obtaining excellent magnetic properties.

[0009] Technical Means for Solving the Problems

[0010] The present invention has been made in view of the above problems. That is, the present invention is an Fe-Co alloy bar having, in terms of area ratio, more than 80% of grains with a Grain Orientation Spread (GOS) value of 0.5° or more, and the difference between the area ratio of grains with a GOS value of 0.5° or more observed in a cross-section perpendicular to the axis of the bar and the area ratio of grains with a GOS value of 0.5° or more observed in an axial cross-section of the bar is within 10%.

[0011] Preferably, the average crystal grain size number is 6.0 or more and 8.5 or less.

[0012] Effects of the Invention

[0013] According to the present invention, an Fe-Co alloy bar having excellent magnetic properties can be stably obtained. Detailed Description of the Invention

[0014] The embodiments of the present invention will be described below. The Fe-Co alloy bar of the present invention is a straight bar having a cross-sectional shape including a circular shape (including an elliptical shape) and a square shape. When the Fe-Co alloy bar is a round bar, the diameter is set to 5 mm to 20 mm. In addition, for bars other than round bars, the equivalent circular diameter of the cross-section may also be set to 5 mm to 20 mm. Unless otherwise specified, the bar in the present embodiment is a round bar having a circular cross-sectional shape.

[0015] <Hot-rolled material composition>

[0016] First, in the present embodiment, a hot-rolled material of an Fe-Co alloy is prepared. The Fe-Co alloy in the present invention refers to an alloy material in which Fe + Co is 95% or more by mass and contains 25% to 60% of Co. Thereby, a high magnetic flux density can be exhibited.

[0017] Next, the elements that can be contained in the Fe-Co alloy of the present invention will be described. In order to improve workability or magnetic properties, the Fe-Co alloy of the present invention may contain, by mass%, one or more of V, Si, Mn, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, and Cr in a total amount of at most 5.0%. In addition, as impurity elements inevitably contained, for example, C, S, P, and O can be cited, and preferably, the upper limit of each of the elements is set to 0.1%, for example.

[0018] The Fe-Co alloy bar of the present invention has grains with a Grain Orientation Spread (GOS) value of 0.5° or more accounting for more than 80% by area ratio. The GOS value can be measured by the previously known "scanning electron microscope - electron backscatter diffraction (SEM-EBSD) method (electron beam backscatter diffraction method)", and can be derived by calculating the azimuth difference of the points (pixels) constituting the grains. The crystallographic azimuth difference obtained from the GOS value is an index indicating the strain imparted to the alloy by processing. In the case where grains with a GOS value of 0.5° or more account for more than 80% by area ratio, the driving force for grain growth is introduced into the bar, which has the advantage of stably obtaining good magnetic properties. When the area ratio of grains with a GOS value of 0.5° or more is 80% or less, since the bar has insufficient driving force for grain growth, good magnetic properties cannot be stably obtained. Among the grains with a GOS value of 0.5° or more, it is preferably 82% or more, more preferably 84% or more by area ratio. There is no particular limitation on the upper limit of the area ratio of grains with a GOS value of 0.5° or more, and it can be set to 99%, for example. In addition, the grains with a GOS value of 0.5° or more can be observed in the cross-section perpendicular to the axis of the bar. In addition, the cross-sections for observing the area ratio include the cross-section perpendicular to the axis and the axial cross-section, but in both cases of observing in the cross-section perpendicular to the axis of the bar and observing in the axial cross-section, it is preferably more than 80% by area ratio (more preferably 82% or more, and further preferably 84% or more). This is because in the hot rolling process, the influence of the strain caused by the rolling marks generated in the base material is easily observed in the axial cross-section of the bar, and the area ratio observed in the axial cross-section may be smaller than the area ratio observed in the cross-section perpendicular to the axis. Therefore, even in the axial cross-section where the area ratio tends to be small, as long as the numerical value of the area ratio is satisfied, the effects of the present invention can be more reliably achieved.

[0019] The Fe-Co alloy bar of the present invention is further characterized in that the difference between the area ratio of grains with a GOS value of 0.5° or more observed in a cross-section perpendicular to the axis of the bar and the area ratio of grains with a GOS value of 0.5° or more observed in an axial cross-section of the bar is within 10%. This is because if the difference (anisotropy) between the area ratio observed in the cross-section perpendicular to the axis and the area ratio observed in the axial cross-section becomes large, it implies that the deviation of the strain distribution becomes large, and the crystal grain size of the specimen subjected to annealing for imparting magnetic properties deviates, thereby greatly inhibiting the growth of grains and becoming a factor leading to a decrease in magnetic properties. The preferred difference in area ratio is within 7%, more preferably within 5%, and even more preferably within 3%.

[0020] In addition, the Fe-Co alloy bar of the present invention preferably has an average crystal grain size number of 6.0 or more and 8.5 or less. Thereby, it has a tendency to easily exhibit high magnetic properties after magnetic annealing and further improve workability. The lower limit of the more preferred average crystal grain size number is 6.5 or more, and the upper limit of the more preferred average crystal grain size number is 8.0 or less. In addition, the average crystal grain size number can be measured based on Japanese Industrial Standards (JIS) G 0551. Moreover, the measurement can be performed in a cross-section perpendicular to the axis or an axial cross-section of the bar.

[0021] Next, an example of a manufacturing method for obtaining the Fe-Co alloy bar of the present invention is shown. In the present embodiment, as an intermediate raw material for the Fe-Co alloy bar, hot rolling is performed on a billet obtained from an Fe-Co alloy steel block having the above composition, whereby a hot-rolled material can be obtained. Since an oxide layer is formed on the intermediate raw material by hot rolling, a grinding process for removing the oxide layer, for example, mechanically or chemically, can also be introduced.

[0022] The hot-rolled material has, for example, the shape of a "hot-rolled bar" corresponding to the Fe-Co alloy bar. Moreover, considering the workability in subsequent processes, the diameter can also be set to 5 mm to 20 mm. In addition, for bars other than round bars, the equivalent circular diameter of the cross-section can also be set to 5 mm to 20 mm.

[0023] <Solid solution treatment process>

[0024] In this embodiment, at least one solution treatment is performed on the hot-rolled material before the subsequent heating straightening process. By performing the solution treatment, it is also possible to expect the effect of removing the compositional segregation of the hot-rolled material and improving the magnetic properties, thereby improving the workability. If the heating temperature during the solution treatment is too low, the workability tends to deteriorate, and if it is too high, the magnetic properties deteriorate. Therefore, it is preferably carried out at a temperature of 800°C to 1050°C. The lower limit of the more preferable temperature is 850°C. The upper limit of the more preferable temperature is 950°C, and the upper limit of the further preferable temperature is 900°C. In addition, the heating time can also be set to 10 minutes to 60 minutes. In addition, in the solution treatment process, in order not to precipitate harmful precipitates, dissolve, suppress ordering, and improve workability, a quenching treatment is performed after heating.

[0025] <Heating Straightening Process>

[0026] In this embodiment, for the hot-rolled material, a heating straightening process of applying a tensile stress while heating is performed. At this time, if the hot-rolled material is in the shape of a "bar", it is stretched along the length direction of the hot-rolled bar to apply the tensile stress. Through this process, while imparting residual strain to the hot-rolled material, a bar having very good magnetic properties and straightness can be obtained. The heating temperature at this time is set to 500°C to 900°C. When it is lower than 500°C, the workability decreases, and the bar may break when applying the tensile stress. On the other hand, when the heating temperature exceeds 900°C, it is impossible to impart a preferable residual strain to the hot-rolled material. The lower limit of the preferable heating temperature in the heating straightening process is 600°C, and more preferably 700°C. In addition, the upper limit of the preferable heating temperature is 850°C, more preferably 830°C, and further preferably 800°C. In addition, when the solution treatment process is omitted, the lower limit of the preferable heating temperature is 700°C, more preferably 730°C, and further preferably 740°C.

[0027] In the heating straightening process, heating methods such as electric heating, which directly passes an electric current through a conductive object to be heated and generates Joule heat using the internal resistance of the object to be heated, or induction heating can be used. In terms of obtaining the effect of easily aligning the easy magnetization axes of the grains in the hot-rolled material in a certain direction, or the advantage of quickly (for example, within 1 minute) and uniformly heating the material to the target temperature, electric heating is preferably applied. In addition, in order to more reliably obtain the required residual strain, the tension during the heating straightening process is preferably adjusted to 1 MPa to 4 MPa. In addition, it is preferably adjusted to an elongation rate of 3% to 10% with respect to the total length before the heating straightening process.

[0028] In this embodiment, for the bar that has completed the straightening process by heating, centerless grinding using a centerless grinder can also be performed, for example. Thereby, the black skin on the surface layer of the bar can be removed, and the roundness or tolerance accuracy of the shape can be further improved. In the present invention, since the straightness of the bar is improved by the straightening process by heating, centerless grinding can also be performed on a long bar with a length of 1000 mm or more without cutting.

[0029] Example

[0030] (Example 1)

[0031] The Fe-Co series alloy steel block having the composition shown in Table 1 was divided into pieces and then hot-rolled to prepare a hot-rolled bar with a diameter of φ11.5 mm.

[0032] <Specimen No.1>

[0033] After solution treatment of heating the hot-rolled bar at 850 °C and then quenching, a straightening process by heating was performed in which the hot-rolled bar was stretched in the longitudinal direction under a tension of 2.7 MPa while heating so that the temperature of the bar reached 750 °C, thereby producing an Fe-Co series alloy bar as Specimen No.1 of the present invention example.

[0034] <Specimen No.2>

[0035] For the hot-rolled bar, a straightening process by heating was performed without solution treatment, thereby producing an Fe-Co series alloy bar as Specimen No.2 of the comparative example. The conditions of the straightening process by heating were set to be the same as those of Specimen No.1.

[0036] [Table 1]

[0037] (mass %)

[0038] Specimen No. C Si Mn Co V Remainder 1 0.01 0.04 0.13 49.01 1.97 Fe and inevitable impurities 2 0.01 0.04 0.13 49.07 1.97 Fe and inevitable impurities

[0039] Subsequently, the average crystal grain size, GOS value, and DC magnetic properties of the specimens of the present invention example and the comparative example were confirmed. Regarding the average crystal grain size, in the cross-section (the direction cross-section perpendicular to the axis), using an optical microscope manufactured by Olympus, ten fields of view of 500 μm × 350 μm were observed, and according to JIS G 0551, the grain size number was determined using the crystal grain size standard chart I. Regarding the GOS value, it was measured using a field emission scanning electron microscope manufactured by ZEISS and an orientation imaging micrograph (OIM) analysis system manufactured by TSL Corporation. The cross-section (the direction cross-section perpendicular to the axis) and the longitudinal section (the axial cross-section passing through the central axis) of the specimen were observed. The measurement field of view was 100 μm × 100 μm, and the step distance between adjacent pixels was set to 0.2 μm. In addition, observation was carried out under the condition that the boundary with an azimuth difference of 5° or more between adjacent pixels was determined as the grain boundary, and based on the obtained GOS value mapping, the area ratio of the grains with a GOS value of 0.5° or more to the entire observation field of view was calculated. Regarding the DC magnetic properties, after collecting specimens from the obtained bar materials, magnetic annealing at 850 °C for 3 hours was carried out, and the maximum magnetic permeability and coercive force were measured using a DC magnetization specific test device. The observation results are shown in Table 2.

[0040] [Table 2]

[0041]

[0042] According to Table 2, as a result, the average crystal grain size number of Specimen No. 1 of the present invention example is smaller than that of Specimen No. 2 of the comparative example (the crystal grain diameter is larger than that of the comparative example). Regarding the area ratio of the grains with a GOS value of 0.5° or more, it was confirmed that the present invention example has a very large value compared to the comparative example, and the difference between the cross-section and the longitudinal section is small. Regarding the magnetic properties, Specimen No. 1 of the present invention example has a higher magnetic permeability and a lower coercive force than Specimen No. 2 of the comparative example. Thus, it was confirmed that the present invention example has more excellent magnetic properties than the comparative example.

Claims

1. An Fe-Co alloy bar contains 25% to 60% of Co by mass, contains one or more elements of V, Si, Mn, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, Cr with a total of at most 5.0% by mass, the total content of Fe + Co is 95% or more by mass, has a grain orientation spread value of more than 80% showing grains with a grain orientation spread value of 0.5° or more. The difference between the area ratio of grains with a grain orientation spread value of 0.5° or more observed in the cross-section perpendicular to the axis of the bar and the area ratio of grains with a grain orientation spread value of 0.5° or more observed in the axial cross-section of the bar is within 10%.

2. The Fe-Co alloy bar according to claim 1, wherein the average crystal grain size number is 6.0 or more and 8.5 or less.

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