METHOD FOR PRODUCING Fe-Co-BASED ALLOY STRIP MATERIAL, Fe-Co-BASED ALLOY STRIP MATERIAL, AND LAMINATED CORE MEMBER

Abstract

Provided is an Fe-Co-based alloy strip material having lower coercive force than the prior art.　Disclosed are: a method for producing an Fe-Co-based alloy strip material; an Fe-Co-based alloy strip material; and a laminated core member. The method for producing an Fe-Co-based alloy strip material comprises: a cold rolling step for cold rolling an Fe-Co-based alloy cold rolling material, which contains, in mass%, 40-60% of Co and 1.70-2.10% of V, with the remainder comprising Fe and inevitable impurities, at least once to obtain a cold rolled material; and an annealing step for softening annealing the cold rolled material to obtain an alloy strip material, wherein the softening annealing conditions in the annealing step are determined such that grain boundaries in the metal structure of the Fe-Co-based alloy strip material are mainly composed of bcc phases, the grain size number is 11.0 or less, and the coercive force is 110 A / m or less.

Description

Fe-Co alloy strip manufacturing method, Fe-Co alloy strip and laminated core member

[0001] The present invention relates to a method for producing an Fe—Co alloy strip, an Fe—Co alloy strip, and a laminated core member.

[0002] In recent years, growing awareness of environmental conservation has led to active efforts toward the electrification of automobiles and hybrid aircraft, and key technologies for these include increasing the output, miniaturization, and reducing loss of electric motors.The motor core used in these electric motors is a laminated core, which has a structure in which many thin sheets of soft magnetic alloy are stacked together, as this is advantageous for reducing iron loss.

[0003] One effective method for further increasing the output and miniaturizing this laminated core is to use a soft magnetic material with a high saturation magnetic flux density, and it is known that permendur (an Fe—Co alloy) with a high saturation magnetic flux density is suitable as a soft magnetic material for forming the laminated core. For example, Patent Document 1 discloses a laminated core in which single layers of permendur (an Fe—Co alloy) with a high saturation magnetic flux density are laminated.

[0004] Special Publication No. 2012-521649

[0005] The laminated cores of electric motors as described above are required to have higher efficiency and lower loss, and the permendur used as the material is also required to have lower coercive force. Therefore, an object of the present invention is to provide a method for producing an Fe—Co alloy strip and an Fe—Co alloy strip that can further reduce the coercive force.

[0006] The present invention has been made in view of the above-mentioned problems. That is, one aspect of the present invention is a method for producing an Fe—Co-based alloy strip, comprising: a cold rolling step of performing one or more cold rolling processes on a hot-rolled material of an Fe—Co-based alloy consisting, by mass%, of 40 to 60% Co, 1.70 to 2.10% V, the balance being Fe and unavoidable impurities, to obtain a cold-rolled material; and an annealing step of performing softening annealing on the cold-rolled material to obtain an alloy strip, wherein the softening annealing conditions in the annealing step are determined so that the grain boundaries in the metal structure of the Fe—Co-based alloy strip are mainly composed of bcc phases, the grain size number is 11.0 or less, and the coercive force is 110 A / m or less. Preferably, the alloy further contains one or more elements selected from the group consisting of Si, Mn, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, Cr, and Ta in a total amount of up to 2.5% by mass.

[0007] Another aspect of the present invention is an Fe—Co alloy strip comprising, by mass%, 40 to 60% Co, 1.70 to 2.10% V, the balance being Fe and unavoidable impurities, wherein the grain boundaries in the metallographic structure of the Fe—Co alloy strip are mainly bcc phases, the grain size number is 11.0 or less, and the coercive force is 110 A / m or less. Preferably, the strip further contains one or more elements selected from the group consisting of Si, Mn, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, Cr, and Ta in a total amount of up to 2.5% by mass. Another aspect of the present invention is a laminated core member in which the aforementioned Fe—Co alloy strips are laminated.

[0008] According to the present invention, it is possible to obtain an Fe--Co alloy strip material having a lower coercive force than conventional products.

[0009] The Fe—Co alloy of the present invention contains 40 to 60% Co by mass. This allows the alloy to exhibit high magnetic flux density and high magnetic permeability. The preferred lower limit of the Co content is 44%, and the preferred upper limit is 55%. Furthermore, since too little V causes embrittlement problems during cold rolling, and too much V leads to a decrease in magnetic flux density, the present invention specifies a content of 1.70 to 2.10%. The preferred upper limit of V is 2.00%. The remainder consists of Fe and unavoidable impurities. The Fe—Co alloy strip of the present invention includes at least a strip wound into a coil shape, and also includes rectangular (sheet) and part-shaped thin plates.

[0010] Next, elements that may be contained in the Fe—Co-based alloy of the present invention will be described. In addition to the elements described above, the Fe—Co-based alloy of the present invention may contain one or more of the following elements in a total amount of up to 2.5% by mass in order to improve magnetic properties and cold workability. Examples of other impurity elements that may be inevitably contained include C, S, P, and O, and it is preferable to set the upper limit of each of these elements to 0.1%. A preferred Fe—Co-based alloy contains 0.1% or less C, 1.70 to 2.10% V, 0.01 to 1.0% Si, 0.01 to 0.40% Mn, 40 to 60% Co, and the balance being Fe and unavoidable impurities.

[0011] Next, the manufacturing method of the present invention will be described. In the present invention, first, a cold-rolling material (hereinafter also referred to as an intermediate material) having the above-described Fe—Co alloy composition and disordered by rapid cooling from an ordering temperature of approximately 710°C or higher is subjected to cold rolling. This intermediate material can be produced using a hot-rolled material or a strip-shaped material obtained by pre-cold rolling the hot-rolled material. Next, in the manufacturing method of the present invention, the intermediate material is cold-rolled to obtain a cold-rolled material with a desired thickness. The cold-rolling conditions can be adjusted according to the desired shape and properties. The thickness of the cold-rolled material is not particularly limited, but since eddy current loss increases in proportion to the square of the thickness, it is preferably 0.5 mm or less. More preferably, it is 0.35 mm or less, even more preferably 0.2 mm or less, and 0.1 mm or less. The lower limit of the thickness can be 0.02 mm, preferably 0.04 mm.

[0012] Next, in the present invention, an annealing process is performed in which the obtained cold-rolled material is softened. Then, in the present invention, the alloy strip (also referred to as an Fe-Co alloy strip) after the above-mentioned annealing process is annealed so that the grain boundaries in the metal structure are predominantly bcc phase, the grain size number is 11.0 or less, and the coercive force is 110 A / m or less. This allows for low loss in laminated motor cores. Here, "grain boundaries predominantly bcc phase" means that no traces of fcc phase precipitation are observed at the grain boundaries, or that the traces of fcc phase precipitation account for less than 50% of the grain boundaries. V segregates at the traces of fcc phase precipitation, preventing domain wall motion and deteriorating soft magnetic properties, leading to increased iron loss. In addition, suppressing grain growth during heat treatment tends to reduce the grain size, resulting in a deterioration in soft magnetic properties. The lower limit of the grain size number is not particularly limited, but it may be set to 3.0 because it can be obtained with short softening annealing times. The preferred lower limit of the grain size number is 3.5. The preferred upper limit of the grain size number is 10.5. The Fe—Co-based alloy strip of the present invention may have a duplex structure. When the strip has a duplex structure, it is desirable that 40% or more of the grains have a grain size number of 6.0 or less. The grain size number may be measured in accordance with the comparative method of JIS G 0551. The grain size number of the present invention may be measured after corroding the surface of the alloy strip with a mixed acid solution or the like. The preferred upper limit of the coercive force is 100 A / m. Since the softening annealing of the present invention improves the coercive force as described above, it can also be referred to as magnetic annealing. The fcc phase at the grain boundaries in this embodiment can be identified by measuring the black areas, which appear as wide black areas at the grain boundaries or triple points in a microstructure photograph taken with an optical microscope after corroding the surface of the alloy strip with a mixed acid solution or the like. Alternatively, the observation can be made by taking an elemental map using an electron probe microanalyzer (EPMA) or SEM-EDX.

[0013] As described above, specific annealing conditions may be adjusted so that the grain size number is 11.0 or less, the coercive force is 110 A / m or less, and the grain boundaries are mainly composed of bcc phase. For example, continuous annealing may be performed by passing the cold-rolled strip through a continuous annealing furnace, or batch annealing may be performed by winding the cold-rolled strip into a coil and then annealing it in a batch furnace. For example, when annealing a cold-rolled Fe—Co alloy material having a thickness of 0.5 mm or less (preferably 0.04 mm to 0.35 mm, and more preferably 0.1 to 0.2 mm), it is preferable to perform the annealing under conditions of a set heating temperature of 820 to 920°C. In this case, when performing the above-mentioned batch annealing, it is preferable to perform the dwell time in the heating furnace for 1 hour or more in order to heat the entire coil. Furthermore, from the viewpoint of productivity, continuous annealing is preferable. Here, when performing continuous annealing, rapid heating can be achieved, so it can be performed even under conditions of a dwell time in the heating furnace of 30 minutes or less. The residence time in the heating furnace is within 20 minutes, and preferably within 10 minutes. Furthermore, when performing continuous annealing, the residence time in the heating furnace is preferably 3 minutes or more to ensure the strain removal effect. Even more preferable conditions for continuous annealing are a residence time of 7 to 30 minutes when the set heating temperature is 830 to 870°C, and a residence time of 3 to 30 minutes when the set heating temperature is 880 to 920°C. The Fe—Co alloy strip obtained by the manufacturing method of the present invention described above has excellent magnetic properties. Furthermore, the laminated core member formed by stacking multiple sheets of the aforementioned Fe—Co alloy strip contributes to the high performance of motor cores and the like due to its excellent magnetic properties. To obtain this laminated core member, a known manufacturing process may be applied. For example, an insulating layer may be formed on one or both sides of the Fe-Co alloy strip, or the Fe-Co alloy strip may be formed into a desired shape by punching, cutting, or the like, and magnetic annealing may be further performed before or after the shaping process such as the punching or cutting described above.

[0014] Cold-rolled Fe—Co alloy materials with a thickness of 0.1 mm were prepared as shown in Table 1. Subsequently, ring test pieces with an outer diameter of 45 mm and an inner diameter of 33 mm for measuring magnetic properties were obtained by pressing. Each test piece was then placed in a heat treatment furnace in an argon atmosphere at 750°C to 1050°C, held there for 8 minutes, and then removed, yielding Samples No. 1 to 7. The pressed ring test pieces for measuring magnetic properties were then heated to 850°C in a hydrogen atmosphere in a heat treatment furnace over 2 hours, held at 850°C for 3 hours, and then naturally cooled (furnace-cooled) in the furnace to obtain Sample No. 8. The pressed ring test pieces for measuring magnetic properties were then placed in a heat treatment furnace in an argon atmosphere at 850°C to 900°C, held there for 4 to 16 minutes, and then removed, yielding Samples No. 31 to 35.

[0015] Cold-rolled Fe—Co alloy materials with a thickness of 0.2 mm were prepared as shown in Table 2. Subsequently, ring test pieces for measuring magnetic properties with an outer diameter of 45 mm and an inner diameter of 33 mm were obtained by pressing. Each test piece was then placed in a heat treatment furnace in an argon atmosphere at 750°C to 1050°C, held there for 8 minutes, and then removed, yielding Samples No. 11 to 17. The pressed ring test pieces for measuring magnetic properties were then heated to 850°C in a hydrogen atmosphere in a heat treatment furnace over 2 hours, held at 850°C for 3 hours, and then naturally cooled (furnace-cooled) in the furnace to obtain Sample No. 18. The pressed ring test pieces for measuring magnetic properties were then placed in a heat treatment furnace in an argon atmosphere at 850°C to 900°C, held there for 4 to 16 minutes, and then removed, yielding Samples No. 41 to 45.

[0016]

[0017]

[0018] Subsequently, multiple ring test specimens were placed in a plastic ring case to a total thickness of 1 mm (with interlayer paper inserted between the rings), and 120 primary and 50 secondary windings were applied. The coercive force was measured as a DC magnetic property. The coercive force was measured under an applied magnetic field of 800 A / m. The microstructure and average grain size of the specimens were also confirmed. The microstructure was defined as "predominantly bcc phase" if no traces of fcc phase precipitation were observed at the grain boundaries in optical microscope images, or if traces of fcc phase precipitation accounted for less than 50% of the grain boundaries. The average grain size was determined using an Olympus optical microscope and the grain size number according to the comparison method of JIS G 0551. The microstructure measurements were performed after the sample surfaces were etched with a mixed acid solution or the like. The results of the DC magnetic measurements, microscopic observations, and grain size number measurements are shown in Table 3.

[0019]

[0020] As shown in Table 3, Invention Examples Nos. 3, 4, 8, 13, 14, 18, 33-35, and 43-45, whose metallurgical grain boundaries are primarily bcc phase and have a grain size number of 10.0 or less, exhibited lower coercive forces (100 A / m or less) than the Comparative Examples, confirming their excellent soft magnetic properties. By using the materials of the present invention, improved motor core performance can be expected. Comparative Examples Nos. 1, 2, 11, and 12, whose grain size numbers are 11.0 or greater, exhibit coercive forces greater than 110 A / m, indicating poor soft magnetic properties. Comparative Examples Nos. 5 and 15 exceeded the bcc / fcc transformation temperature, which is above 900°C and below 950°C. This suggests that slight fcc phase precipitation occurred at the grain boundaries, leaving traces. V segregated in these traces, hindering domain wall motion, resulting in extremely poor soft magnetic properties. Comparative Example Nos. In Nos. 6, 7, 16, and 17, the metal structure became mainly fcc because the heat treatment temperature was much higher than the bcc / fcc transformation temperature, and then, during cooling, the fcc phase transformed back into the bcc phase, causing distortion due to structural changes, which is thought to be why the bcc phase was the main phase but the soft magnetic properties deteriorated.In the comparative examples, Nos. 31, 32, 41, and 42, the heat treatment time was insufficient, so distortion recovery did not progress sufficiently and the soft magnetic properties deteriorated.

Claims

1. A method for producing an Fe-Co alloy strip, comprising: a cold rolling step of cold rolling an Fe-Co alloy material for cold rolling at least once, the material consisting of, by mass, 40-60% Co, 1.70-2.10% V, the balance being Fe and unavoidable impurities, to obtain a cold-rolled material; and an annealing step of softening and annealing the cold-rolled material to obtain an alloy strip, wherein the softening and annealing conditions in the annealing step are determined so that the grain boundaries in the metal structure of the Fe-Co alloy strip are mainly bcc phases, the grain size number is 11.0 or less, and the coercive force is 110 A / m or less.

2. The method for producing an Fe-Co alloy strip according to claim 1, wherein the Fe-Co alloy cold rolling material further contains one or more elements selected from the group consisting of Si, Mn, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, Cr, and Ta in a total amount of up to 2.5% by mass.

3. An Fe-Co alloy strip consisting of, by mass%, 40-60% Co, 1.70-2.10% V, the remainder being Fe and unavoidable impurities, wherein the grain boundaries in the metal structure of the Fe-Co alloy strip are mainly bcc phases, the grain size number is 11.0 or less, and the coercive force is 110 A / m or less.

4. The Fe-Co alloy strip according to claim 3, further containing one or more elements of Si, Mn, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, Cr, and Ta in a total amount of up to 2.5% by mass.

5. A laminated core member in which the Fe-Co alloy strip material according to claim 3 or 4 is laminated.

Images