Fe-Co alloy rods

Abstract

As the performance of products increases, raw materials are also required to be combined with the purpose of the product, taking into account both high strength and good magnetic properties. Therefore, a Fe-Co alloy rod that can take into account both high strength and good magnetic properties is provided. A Fe-Co alloy rod has 30% to 80% of the grains with a grain orientation spread (GOS) value of more than 0.5° in terms of area ratio, and the average grain size number exceeds 8.5 and is less than 12.0. In order to cope with various high-strength applications, the Fe-Co alloy rod of the present invention also has a high 0.2% yield strength after magnetic annealing.

Description

Technical Field

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

[0002] The rods of Fe-Co alloys represented by Permendur, which is known as an alloy having excellent magnetic properties, are used in various products such as sensors or cylindrical magnetic shields, solenoid valves, magnetic cores, etc. As a method for manufacturing the Fe-Co alloy rods, for example, Patent Document 1 describes the following: after heating the ingot to 1000°C to 1100°C, hot working it into a billet of about φ90 mm, removing scratches on the surface using a lathe, and hot rolling it to about φ6 mm to φ9 mm after heating it to 1000°C to 1100°C, thereby manufacturing the raw material (rod).

[0003] Prior art literature

[0004] Patent Literature

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

[0006] Problems to be solved by the invention

[0007] As the performance of the products increases, miniaturization is becoming more common in products such as solenoid valves, which requires both high strength and good magnetic properties. In the previous manufacturing method described in Patent Document 1, the above-mentioned strength and magnetic properties have not been studied, leaving room for further research.

[0008] Therefore, an object of the present invention is to provide a Fe—Co alloy rod material that can achieve both high strength and good magnetic properties.

[0009] Technical means of solving problems

[0010] The present invention is a Fe-Co alloy rod having 30% to 80% of grains showing a grain orientation spread (GOS) value of 0.5° or more in terms of area ratio, and an average grain size number exceeding 8.5 and being below 12.0.

[0011] Effects of the Invention

[0012] According to the present invention, it is possible to obtain a Fe-Co alloy rod material suitable for applications requiring both high strength and good magnetic properties. DETAILED DESCRIPTION

[0013] The following is an explanation of the embodiments of the present invention. The Fe-Co alloy rod of the present invention is a straight rod having a cross-sectional shape including a circular (including an elliptical) and a square shape. When the Fe-Co alloy rod is a round rod, the diameter is set to 5 mm to 20 mm. In addition, for rods other than round rods, the circle equivalent diameter of the cross section can also be set to 5 mm to 20 mm. The rod of this embodiment is a round rod having a circular cross-sectional shape unless otherwise specified.

[0014] First, in this 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 containing 95% or more of Fe+Co by mass and 25% to 60% of Co. This can achieve a high magnetic flux density.

[0015] Next, the elements that may be contained in the Fe-Co alloy of the present invention are described. In order to improve the processability or magnetic properties, the Fe-Co alloy of the present invention may contain one or more elements of V, Si, Mn, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, and Cr in a total of up to 5.0% by mass%. In addition, as impurity elements that are inevitably contained, for example, C, S, P, and O can be listed, and it is preferred that the upper limit of each of the elements is set to 0.1%, for example.

[0016] The Fe-Co alloy rod of the present invention has 30% to 80% of the grains with a grain orientation spread (GOS) value of 0.5° or more in terms of 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 crystal orientation difference obtained according to the GOS value is an index representing the strain given to the alloy by processing. In the case of grains with a GOS value of 0.5° or more of 30% or more in terms of area ratio, the driving force for grain growth is introduced into the rod, which has the advantage of obtaining good magnetic properties. Moreover, setting the upper limit of the grains with a GOS value of 0.5° or more to 80% in terms of area ratio is also one of the characteristics of the present invention. According to the above characteristics, it is possible to suppress the excessive coarsening of the grains without deteriorating the magnetic properties, thereby improving the strength of the rod. When the area ratio of grains with a GOS value of 0.5° or more is less than 30%, it is impossible to obtain good magnetic properties because the driving force for grain growth is insufficient. The lower limit of the preferred area ratio is 35%, and more preferably 40%. In addition, when the area ratio of grains with a GOS value of 0.5° or more exceeds 80%, there is a tendency that the magnetic properties are improved but the strength is reduced. The upper limit of the preferred area ratio is 78%, and more preferably 75%. In addition, the grains with a GOS value of 0.5° or more can be observed in the cross section of the bar in the direction perpendicular to the axis. In addition, the cross section for observing the area ratio also has a cross section in the direction perpendicular to the axis and an axial cross section, but in both cases of observing in the cross section in the direction perpendicular to the axis of the bar and observing in the axial cross section, it is preferred that the area ratio is 30% to 80%. This is because the influence of the strain caused by the rolling mark generated in the parent material is easily observed in the axial cross section of the bar during the hot rolling process, and the area ratio observed in the axial cross section may be smaller than the area ratio observed in the cross section in the direction perpendicular to the axis. Therefore, even in an axial cross section where the area ratio tends to be small, the effect of the present invention can be more reliably achieved as long as the numerical value of the area ratio is satisfied.

[0017] In addition, the Fe-Co alloy rod of the present invention is preferably an average crystal grain size numbering more than 8.5 and less than 12.0. Thus, there is a tendency to stably obtain high-strength alloy rods while exerting good magnetic properties after magnetic annealing. The lower limit of the more preferred average crystal grain size numbering is more than 9.0, and the upper limit of the more preferred average crystal grain size numbering is less than 11.5. And then the upper limit of the preferred average crystal grain size numbering is less than 11.0. In addition, the average crystal grain size numbering can be measured based on Japanese Industrial Standards (JIS) G 0551. And, it can be measured in the cross section or axial section perpendicular to the axis of the rod.

[0018] The strength of the Fe-Co alloy rod of the present invention can be evaluated by the 0.2% yield strength measured in the room temperature tensile test. In order to cope with various high-strength applications, the rod of the present invention preferably has a 0.2% yield strength of 200 MPa or more after magnetic annealing. A more preferred 0.2% yield strength is 210 MPa or more. The 0.2% yield strength can be measured based on the metal material tensile test method of JIS Z2241.

[0019] 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 of the Fe-Co alloy bar, a billet obtained from a Fe-Co alloy steel block having the above composition is hot rolled to obtain a hot rolled material. Since an oxide layer is formed on the intermediate raw material by hot rolling, a grinding process for removing the oxide layer mechanically or chemically may also be introduced. The hot rolled material has, for example, a shape of a "hot rolled bar" equivalent to the Fe-Co alloy bar. Moreover, considering the processability in the subsequent process, the diameter may also be set to 5 mm to 20 mm. In addition, for bars other than round bars, the equivalent circle diameter of the cross section may also be set to 5 mm to 20 mm. Here, in order to satisfy the area ratio of the grains having a GOS value of 0.5° or more of the present invention, it is preferred that the hot rolled bar is not subjected to a solid solution treatment. Solid solution treatment refers to a process in which the hot rolled bar is heated at, for example, 800°C to 1050°C and then rapidly cooled. Moreover, it is preferred that the solid solution treatment is not performed, and the heating straightening process described later is performed.

[0020] <Heating and straightening process>

[0021] In this embodiment, for the hot-rolled material, a heating straightening process of imparting 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 impart the tensile stress. Through the process, a bar having very good magnetic properties and straightness can be obtained while imparting residual strain to the hot-rolled material. The heating temperature at this time is set to 500°C to 900°C. When it is lower than 500°C, the workability is reduced, and the bar may break when imparting tensile stress. On the other hand, when the heating temperature exceeds 900°C, the hot-rolled material cannot be given a preferred residual strain. The lower limit of the preferred heating temperature in the heating straightening process is 600°C, and more preferably 700°C. In addition, the upper limit of the preferred heating temperature is 850°C, more preferably 830°C, and more preferably 800°C. In addition, when the solution treatment process is omitted, the lower limit of the preferred heating temperature is 700°C, more preferably 730°C, and more preferably 740°C.

[0022] In the heating straightening process, a heating method such as electric heating or induction heating can be used, which allows current to flow directly to the conductive heated object and uses the Joule heat generated by the internal resistance of the heated object for heating. In terms of the effect of easily aligning the easy magnetization axis of the grains in the hot-rolled material in a certain direction, or the advantage of being able to quickly (for example, within 1 minute) and uniformly heat the material to the target temperature, it is preferred to apply electric heating. In addition, in order to more reliably obtain the required residual strain, the tension during the heating straightening process is preferably adjusted to 1MPa to 4MPa. In addition, it is preferably adjusted to an elongation of 3% to 10% relative to the total length before the heating straightening process.

[0023] In this embodiment, the bar material that has completed the heat straightening process can also be subjected to centerless grinding using a centerless grinder, for example. This can remove the black skin on the surface of the bar material, and further improve the roundness or tolerance accuracy of the shape. In the present invention, since the straightness of the bar material is improved by the heat straightening process, a long bar material with a length of more than 1000 mm can also be subjected to centerless grinding without cutting.

[0024] Example

[0025] (Example 1)

[0026] An Fe-Co alloy steel ingot having the composition shown in Table 1 was divided into blocks and then hot-rolled to prepare hot-rolled bars having a diameter of 11.5 mm.

[0027] <Sample No. 1, Sample No. 2>

[0028] The hot rolled bars were subjected to a heating straightening step of stretching the hot rolled bars in their longitudinal direction under a tension of 2.7 MPa while being heated to a bar temperature of 750° C., thereby producing Fe—Co alloy bars of Sample No. 1 and Sample No. 2 as examples of the present invention.

[0029] <Sample No.3>

[0030] The hot rolled bar was subjected to a solution treatment of heating at 850°C and then quenching, and then subjected to a heating and straightening step to produce a Fe-Co alloy bar of sample No. 3 as a comparative example. The conditions of the heating and straightening step were the same as those of samples No. 1 and No. 2.

[0031] <Sample No. 4>

[0032] A Fe-Co alloy rod of sample No. 4 was also prepared as a comparative example. In the comparative example, the hot-rolled rod was subjected to solution treatment under the same conditions as sample No. 3, without the heating straightening step, and the other steps were the same as those of the present invention example.

[0033] [Table 1]

[0034] (quality%)

[0035] Sample No. C Si Mn Co V Remaining part 1 0.01 0.04 0.13 49.07 1.97 Fe and inevitable impurities 2 0.01 0.04 0.13 49.25 1.99 Fe and inevitable impurities 3 0.01 0.04 0.13 49.01 1.97 Fe and inevitable impurities 4 0.01 0.03 0.13 49.01 1.98 Fe and inevitable impurities

[0036] Then, the average grain size, GOS value and DC magnetic properties of the samples of the present invention and the comparative example were confirmed. Regarding the average grain size, in the cross section (cross section in the direction perpendicular to the axis), an optical microscope manufactured by Olympus was used to observe ten 500μm×350μm fields of view, and the grain size number was determined using the grain size standard plate I according to JIS G 0551. Regarding the GOS value, a field emission scanning electron microscope manufactured by Zeiss (ZEISS) and an EBSD measurement and analysis system orientation imaging micrograph (Orientation-Imaging-Micrograph, OIM) manufactured by TSL were used. Regarding sample No. 4, the cross section (cross section in the direction perpendicular to the axis) was observed, and regarding sample No. 1, sample No. 2, and sample No. 3, in addition to observing the cross section of the sample, the longitudinal section (axial section through the central axis) was also observed. The measurement field of view is 100μm×100μm, and the step distance between adjacent pixels is set to 0.2μm. In addition, the observation is carried out under the condition that the boundary with an azimuth difference of 5° or more between adjacent pixels is judged as a grain boundary, and the area ratio of grains with a GOS value of 0.5° or more relative to the entire observation field of view is calculated based on the mapping of the obtained GOS value. Regarding DC magnetic properties, after collecting samples from the obtained rods, magnetic annealing at 850℃×3 hours is implemented, and the maximum magnetic permeability and coercive force are measured using a DC magnetization specific test device. Table 2

[0037] The observation results are shown in .

[0038] [Table 2]

[0039]

[0040] According to Table 2, it can be confirmed that the average grain size number of sample No. 1 and sample No. 2 as examples of the present invention is larger than that of the comparative example (the grain size is smaller than that of the comparative example), and the area ratio of grains with a GOS value of 0.5° or more in the present invention example is a smaller value than that of the comparative example. Regarding magnetic properties, sample No. 1 to sample No. 3 have higher magnetic permeability and lower coercive force than the previous example. Therefore, it can be confirmed that sample No. 1, sample No. 2 of the present invention example and sample No. 3 of the comparative example have better magnetic properties than the previous example.

[0041] (Example 2)

[0042] The 0.2% yield strength at room temperature was measured for the bars No. 1 to No. 3 subjected to magnetic annealing at 850°C for 3 hours. The test piece used in the measurement was a test piece of 1 / 2 scale of the JIS No. 4 test piece specified in JIS Z 2241, and the measurement of the 0.2% yield strength was carried out based on the metal material tensile test method of JIS Z 2241. The results are shown in Table 3. According to the results in Table 3, it can be confirmed that the examples of the present invention in which the area ratio of grains with a GOS value of 0.5° or more is 30% to 80% have a better 0.2% yield strength than the comparative example in which the area ratio of grains with a GOS value of 0.5° or more exceeds 80%. Therefore, the Fe-Co alloy bar of the present invention has both good magnetic properties and high mechanical strength, and is suitable for various product applications such as sensors or cylindrical magnetic shields, solenoid valves, and magnetic cores.

[0043] [Table 3]

[0044] Sample No. 0.2% yield strength [MPa] 1 211 2 213 3 191

Claims

1. A Fe-Co alloy bar containing 25% to 60% Co by mass, Contains one or more elements selected from the group consisting of V, Si, Mn, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, and Cr in an amount of up to 5.0% by mass, The total content of Fe+Co is 95% or more by mass. The crystal grains having a crystal grain orientation extension value of 30% to 80% in terms of area ratio showing 0.5° or more have an average grain size number exceeding 8.5 and being 12.0 or less.

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