Manufacturing method of soft magnetic steel sheet

Abstract

To provide a soft magnetic steel plate having good magnetic properties secured, even when made from raw materials containing impurities derived from iron scrap.SOLUTION: A soft magnetic steel plate produced from raw materials containing iron scrap comprises Fe as base material, 1.0 to 7.0 wt.% of Si, and 0.1 to 1.0 wt.% of Cu, which is a component derived from the iron scrap.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a soft magnetic steel sheet and a method for manufacturing the same. [Background technology]

[0002] In recent years, efforts to significantly reduce waste through waste prevention, reduction, reuse, and recycling have become more active. To achieve this, research and development into the recycling of steel scrap is being conducted.

[0003] Conventionally, there has been a technology for recycling iron scrap to produce electrical steel sheets for use in iron cores, etc. For example, a non-oriented electrical steel sheet is known that contains 0.0050% by mass or less of C, 1.5 to 5.0% by mass of Si, 0.2 to 3.0% by mass of Mn, 0.0030% by mass or less of sol. Al, 0.2% by mass or less of P, 0.0050% by mass or less of S, 0.0040% by mass or less of N, 0.0010 to 0.0080% by mass of T. Ca, 0.0100% by mass or less of TO, and 0.0001 to 0.0050% by mass of REM, with the balance being Fe and unavoidable impurities (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6989000 Summary of the Invention [Problem to be solved by the invention]

[0005] In the prior art described in Patent Document 1, when manufacturing an electrical steel sheet, a slab cast as the raw material is hot-rolled to form a hot-rolled steel sheet, and the hot-rolled steel sheet is further cold-rolled to form a cold-rolled steel sheet. When adopting such a manufacturing method that performs hot rolling, in order to avoid problems in manufacturing (e.g., the occurrence of cracks in the steel sheet during rolling) while ensuring the required magnetic properties, it is necessary to limit the unavoidable impurities contained in the electrical steel sheet to a predetermined allowable value (e.g., Cu is 0.01 mass% or less).

[0006] On the other hand, unlike iron ore, which is a raw material for steelmaking, iron scrap contains relatively high concentrations of elements that become impurities in electrical steel sheets. Some of these impurities (e.g., Cu, etc.) are difficult to remove even by refining using an electric furnace, etc., so it may be difficult to achieve the allowable values ​​for unavoidable impurities in electrical steel sheets described in Patent Document 1. Among the unavoidable impurities contained in iron scrap, Cu and Sn cause precipitation embrittlement in high-temperature, oxidizing atmospheres, adversely affecting hot workability, and it is known that this is further exacerbated when Cu and Sn are present simultaneously. Furthermore, Ni and Cr harden steel materials, adversely affecting cold workability. Furthermore, inclusions formed in the crystalline structure due to these impurity elements not only adversely affect cold workability but also significantly degrade magnetic properties by pinning domain wall motion and generating magnetic domains.

[0007] In order to solve the above-mentioned problems, the present invention aims to provide a soft magnetic steel sheet and a manufacturing method thereof that can ensure good magnetic properties even when impurities derived from iron scrap are contained in the raw materials, and ultimately contribute to a significant reduction in the generation of iron scrap as waste. [Means for solving the problem]

[0008] In order to solve the above problems, one embodiment of the present invention is a soft magnetic steel sheet manufactured from raw materials including iron scrap, and is configured to contain Fe as a base material, 1.0 to 7.0 wt% of Si, and 0.1 to 1.0 wt% of Cu, which is a component derived from the iron scrap.

[0009] According to this embodiment, even if Cu derived from iron scrap is contained as an impurity in the raw material, the soft magnetic steel sheet can have good magnetic properties.

[0010] In the above aspect, it is preferable that the components derived from the iron scrap further include 0.01 to 0.5 wt% of Cr, 0.01 to 0.5 wt% of Ni, and 0.01 to 0.3 wt% of Sn, and that the total of Cu, Cr, Ni, and Sn is 1.2 wt% or less.

[0011] According to this embodiment, even if Cu, Cr, Ni, and Sn derived from iron scrap are contained as impurities in the raw material, the soft magnetic steel sheet can have good magnetic properties.

[0012] In addition, in order to solve the above problem, one aspect of the present invention is a method for manufacturing the soft magnetic steel sheet, which includes a strip-shaped thin plate formation process in which a strip-shaped thin plate is formed from the raw material by a single-roll liquid rapid solidification method, and a heat treatment process in which the strip-shaped thin plate is heat-treated in an inert atmosphere at 600 to 1200°C.

[0013] According to this embodiment, even when impurities derived from iron scrap are contained in the raw material, the strip-shaped thin plate is formed by the single-roll liquid rapid solidification method, so that it is possible to avoid the occurrence of cracks in the steel plate that occur when hot rolling a slab cast. Furthermore, by rapidly solidifying the molten metal, impurity elements are not segregated to specific locations in the crystalline structure, and inclusions that hinder domain wall movement are not formed, so that good magnetic properties of the soft magnetic steel plate can be ensured.

[0014] In the above aspect, the soft magnetic steel plate may have a thickness of 0.03 to 0.15 mm, a magnetic flux density B100 of 1.6 T or more, a magnetic orientation B10 / B100 of 0.78 or more, and an iron loss W10 / 400 of 10 W / kg or less.

[0015] According to this aspect, a high-quality soft magnetic steel sheet can be obtained.

[0016] In the above aspect, it is preferable that the strip thin plate is subjected to at least one of warm rolling and cold rolling before the heat treatment step.

[0017] According to this aspect, by performing at least one of warm rolling and cold rolling, the surface of the strip-shaped thin plate obtained by the strip-shaped thin plate forming process can be smoothed, and the thickness, width, and properties of the soft magnetic steel plate can be appropriately adjusted.

[0018] In the above-described embodiment, the method may further include a Si addition step of adding Si to the iron scrap as the raw material. The Si content is adjusted by adding Si in the form of metal Si or a Si-containing alloy during the refining process of the iron scrap in an electric furnace or during melting of the raw material by a single-roll liquid rapid solidification method.

[0019] According to this aspect, the magnetization characteristics of the soft magnetic steel plate can be appropriately improved. [Effects of the Invention]

[0020] According to the above-described embodiment, good magnetic properties can be ensured even when impurities derived from iron scrap are contained in the raw material. [Brief explanation of the drawings]

[0021] [Figure 1] An explanatory diagram showing an outline of a manufacturing apparatus for soft magnetic steel sheets to which the single-roll method is applied. [Figure 2] Graph showing the relationship between iron loss and B10 / B100 in soft magnetic steel sheets [Figure 3] A graph showing the relationship between the Cu and Sn content of soft magnetic steel sheets and whether they can be manufactured. [Figure 4] Graph showing the relationship between the Cu content of soft magnetic steel sheets and iron loss W10 / 400 [Figure 5] Graph showing the relationship between Cu content and B10 / B100 in soft magnetic steel sheets [Figure 6] A graph showing the relationship between the impurity content (total of Cu, Cr, Ni, and Sn) of soft magnetic steel sheet and iron loss W10 / 400 [Figure 7] A graph showing the relationship between the impurity content (total of Cu, Cr, Ni, and Sn) of soft magnetic steel sheet and B10 / B100 [Figure 8] Photograph of the crystal structure of soft magnetic steel sheet (Example 13) observed with an electron microscope [Figure 9] Photograph of the crystal structure of soft magnetic steel sheet (Example 14) observed with an electron microscope [Figure 10] Photograph of the crystal structure of soft magnetic steel sheet (Prior Art 2) observed with an electron microscope DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0023] As shown in Fig. 1, the soft magnetic steel sheet manufacturing apparatus 1 is an apparatus that applies the single roll method (single roll liquid rapid solidification method). The manufacturing apparatus 1 includes a rotatable cooling roll 2 and a nozzle 4 that sprays molten metal 3, which is the raw material for the soft magnetic steel sheet.

[0024] In the manufacturing apparatus 1, molten metal 3 is discharged from an injection hole 4a of a nozzle 4 toward a chill roll 2 rotating at a predetermined speed (for example, 500 to 2000 rpm). The discharged molten metal 3 is quenched on the surface of the chill roll 2, thereby forming a strip-shaped thin plate 5 along the surface of the chill roll 2 (an example of a strip-shaped thin plate forming process). After peeling off from the surface of the chill roll 2, the strip-shaped thin plate 5 is continuously wound up by a winding device (not shown). In this way, a coil of the strip-shaped thin plate 5 is formed.

[0025] Chill roll 2 has a diameter of 200 mm and an outer circumferential surface made of a Cu-Cr alloy or carbon steel. A heater 7 is attached to the periphery of nozzle 4, which maintains the temperature of molten metal 3 inside nozzle 4 at an appropriate level. The molten metal 3 is ejected from injection hole 4a by the pressure of gas (e.g., nitrogen gas) supplied into nozzle 4.

[0026] The coil of strip 5 formed by the manufacturing apparatus 1 is heat treated (annealed) in an inert atmosphere in a heating furnace (not shown) (an example of a heat treatment process). This results in a soft magnetic steel sheet with predetermined magnetic properties. The inert atmosphere can be achieved by filling the furnace with an inert gas such as argon gas or helium gas. However, the furnace may also be filled with nitrogen gas or hydrogen gas.

[0027] The heat treatment temperature is preferably set in the range of 600 to 1200°C, for example, and more preferably in the range of 1050 to 1150°C. The heat treatment time is preferably set in the range of 10 seconds to 48 hours, for example, and more preferably in the range of 3 to 24 hours. This removes internal stress from the strip-shaped thin plate 5 and improves the structure, thereby improving the magnetic properties (for example, iron loss) of the soft magnetic steel sheet that is finally obtained.

[0028] Furthermore, in the production of soft magnetic steel sheets, after forming the strip sheet 5, at least one of warm rolling and cold rolling may be performed on the strip sheet 5 before heat treatment. Warm rolling is performed, for example, on the strip sheet 5 in a temperature range of 600 to 900°C using a known warm rolling mill. Cold rolling is performed on the strip sheet 5 at room temperature using a known cold rolling mill. By performing warm rolling or cold rolling, the surface of the strip sheet 5 can be smoothed, and the thickness, width, and properties of the finally obtained strip sheet 5 (i.e., soft magnetic steel sheet) can be appropriately adjusted.

[0029] The raw materials used in the production of soft magnetic steel sheets mainly include iron scrap. As the iron scrap, commercially available scrap that is generally available in the market can be used. For example, iron scrap discharged from automobile manufacturing plants or iron scrap recovered from scrapped automobiles may be used as the raw material.

[0030] The raw material, iron scrap, may contain not only Fe (iron), which is the base material of soft magnetic steel sheets, but also Cu (copper), Cr (chromium), Ni (nickel), Sn (tin), and the like, which are impurities (i.e., unnecessary components) for soft magnetic steel sheets. In other words, Cu, Cr, Ni, and Sn in soft magnetic steel sheets are components derived from iron scrap.

[0031] From the viewpoint of stably producing the soft magnetic steel sheet and ensuring good magnetic properties, the content of impurities (that is, Cu, Cr, Ni, and Sn) is preferably set within a predetermined range.

[0032] The Cu content in the soft magnetic steel sheet is preferably 0.1 to 1.0 wt%. The Cr content in the soft magnetic steel sheet is preferably 0.01 to 0.5 wt%. The Ni content in the soft magnetic steel sheet is preferably 0.01 to 0.5 wt%. The Sn content in the soft magnetic steel sheet is preferably 0.01 to 0.3 wt%. Furthermore, the total of Cu, Cr, Ni, and Sn in the soft magnetic steel sheet is preferably 1.2 wt% or less, and more preferably 1.0 wt% or less. Note that although the lower limit of the content of each impurity is shown here, these are not essential components for the soft magnetic steel sheet. Therefore, the content of some of these impurities may be zero.

[0033] If the content of impurities is outside the above range (upper limit), it is possible to adjust it to be below the allowable value by, for example, selecting the type of iron scrap used as the raw material.

[0034] Furthermore, silicon (Si) is added to the raw material to reduce iron loss as it is an element that is insufficient in iron scrap. The Si content in the manufactured soft magnetic steel sheet is preferably 1.0 to 7.0 wt% (weight %).

[0035] The thickness of the soft magnetic steel sheet finally obtained is preferably 0.03 to 0.15 mm. Furthermore, the soft magnetic steel sheet preferably has magnetic properties such as a magnetic flux density B100 of 1.6 T or more, a magnetic orientation degree B10 / B100 of 0.78 or more, and an iron loss W10 / 400 of 10 W / kg or less. Here, "magnetic flux density B100" indicates the magnetic flux density at a magnetic field strength of 10,000 A / m. "B10 / B100" is the ratio of "B10" to "B100" and is a measure of the magnetic orientation degree. Furthermore, "iron loss W10 / 400" indicates the iron loss at a frequency of 400 Hz and a magnetic flux density of 1.0 T. [Example]

[0036] As Examples 1-19, soft magnetic steel sheets were manufactured using raw materials in which the content of Cu, Cr, Ni, and Sn as impurities was changed relative to Fe as the base material (i.e., the main component excluding other components such as impurities), and the feasibility of their manufacture and their magnetic properties were evaluated.

[0037] In the production of the soft magnetic steel sheets according to Examples 1 to 19, first, raw materials containing predetermined impurity contents were prepared. More specifically, pure iron and ferrosilicon were mixed and melted, and the raw materials were prepared so that the impurity contents, when the total content of Fe, Si, and impurities (here, Cu, Cr, Ni, and Sn) was taken as 100 wt%, were each predetermined chemical composition.

[0038] Thereafter, as described above, a strip-shaped thin plate 5 was formed using the manufacturing apparatus 1 (see FIG. 1) employing the single-roll method. More specifically, the molten metal 3 was discharged from the injection hole 4a of the nozzle 4 onto the outer peripheral surface of the chill roll 2, and then rapidly cooled and solidified to form a strip-shaped thin plate 5 having a predetermined thickness (see Table 1) and a width of 20 mm. The temperature of the molten metal 3 was adjusted to 1400 to 1700°C, the peripheral speed of the chill roll 2 to 5 to 20 m / s, the discharge pressure of the molten metal 3 to 10 kPa to 40 kPa, and the gap between the tip of the nozzle 4 and the chill roll 2 to 0.2 mm to 0.4 mm.

[0039] Furthermore, the obtained strip-shaped thin plate 5 was subjected to heat treatment in an inert atmosphere (here, Ar gas) in a heating furnace under predetermined conditions (see Table 1), as described above.

[0040] As Comparative Example 1-6, soft magnetic steel sheets were manufactured in the same manner as in Example 1-19 using raw materials that did not substantially contain Cu, Cr, Ni, and Sn as impurities, and their manufacturability and magnetic properties were evaluated.

[0041] The chemical compositions and heat treatment conditions (temperature, time) for Examples 1-19 and Comparative Examples 1-6 are shown in Table 1. In Table 1, the possibility of production is indicated by a circle (○) for those in which the strip-shaped thin plate 5 could be formed using the manufacturing apparatus 1, and by a cross (×) for those in which the strip-shaped thin plate 5 could not be formed (including those in which cracks occurred in the steel plate) (the same applies to Table 2 described later).

[0042] In addition, soft magnetic steel sheets were manufactured using a conventional hot rolling technique (hereinafter referred to as "Prior Art 1-3"), and their manufacturing feasibility and magnetic properties were evaluated. In Prior Art 1-3, an ingot with its chemical composition adjusted using a vacuum melting furnace was hot rolled to a thickness of 2 mm at a temperature of 1100°C, and then cold rolled to form a steel sheet with a thickness of 0.1 mm. However, in Prior Art 3, cracks occurred during cold rolling and it was impossible to form the steel sheet. The obtained steel sheet was subjected to heat treatment in the same manner as in Example 1-19.

[0043] [Table 1]

[0044] Table 2 shows the thickness and magnetic properties of each of the soft magnetic steel sheets obtained for Examples 1-19 and Comparative Examples 1-6. In Table 2, "W10 / 400" indicates the iron loss at a frequency of 400 Hz and a magnetic flux density of 1.0 T. Also, "B10," "B50," and "B100" indicate the magnetic flux densities at magnetic field strengths of 1000 A / m, 5000 A / m, and 10000 A / m, respectively. Also, "B10 / B100" is the ratio of "B10" to "B100," and is a measure of the degree of magnetic orientation.

[0045] [Table 2]

[0046] Next, with reference to FIGS. 2 to 7 based on the data shown in Tables 1 and 2, the evaluation results of the magnetic properties of the soft magnetic steel sheets of Examples 1 to 19 and Comparative Examples 1 to 6 will be described.

[0047] Figure 2 shows the relationship between iron loss and B10 / B100. The iron loss W10 / 400 of soft magnetic steel sheets should be 10 W / kg or less to reduce energy consumption. In addition, the B10 / B100 ratio of soft magnetic steel sheets should be 0.78 or more from the perspective of magnetic orientation.

[0048] In Examples 14-17, in which the Cu content exceeded 1.0 wt%, the iron loss W10 / 400 exceeded 10 W / kg, and the B10 / B100 was less than 0.78. In other words, the Cu content of the soft magnetic steel sheet is preferably set to 1.0 wt% or less in order to ensure good magnetic properties.

[0049] For Comparative Examples 1-6, which did not contain impurities, the iron loss W10 / 400 of the soft magnetic steel sheets was 10 W / kg or less, and the B10 / B100 of the soft magnetic steel sheets was 0.78 or more. For Conventional Technique 2, the iron loss W10 / 400 exceeded 10 W / kg, and for Conventional Technique 3, which contained impurities, it was difficult to manufacture the soft magnetic steel sheets.

[0050] Fig. 3 shows the relationship between the Cu and Sn contents of soft magnetic steel sheets and whether they can be manufactured. For Examples 1-17 and 19 (i.e., Cu contents in the range of 0.10 to 3.60 and Sn contents in the range of 0.1 to 0.70), soft magnetic steel sheets could be manufactured. On the other hand, for Example 18, in which the Cu content was 5.0 wt% and the Sn content was 1.0 wt%, it was difficult to manufacture the soft magnetic steel sheet. In other words, from the viewpoint of stable manufacturing of soft magnetic steel sheets, it is preferable to set the Cu content of soft magnetic steel sheets to 3.6 wt% or less. Similarly, it is preferable to set the Sn content of soft magnetic steel sheets to 0.7 wt% or less.

[0051] FIG. 4 shows the relationship between the Cu content of a soft magnetic steel sheet and the iron loss W10 / 400. Example 12 (see the colored circles in FIG. 4) contains only Cu as an impurity. That is, regardless of whether the soft magnetic steel sheet contains only Cu as an impurity or contains other impurities in addition to Cu, the Cu content of the soft magnetic steel sheet is preferably set to 1.0 wt% or less, as described above, from the viewpoint of reducing the iron loss W10 / 400 to 10 W / kg or less. In this case, the Cr content is preferably 0.3 wt% or less. The Ni content is preferably 0.3 wt% or less. The Sn content is preferably 0.25 wt% or less.

[0052] Fig. 5 shows the relationship between the Cu content of soft magnetic steel sheets and B10 / B100. Here, Example 12 (see the colored circles in Fig. 4) contains only Cu as an impurity. In other words, as described above, the Cu content of the soft magnetic steel sheets is preferably set to 1.0 wt% or less in order to achieve a B10 / B100 ratio of 0.78 or more, regardless of whether the soft magnetic steel sheets contain only Cu as an impurity or other impurities in addition to Cu.

[0053] 6 shows the relationship between the impurity content (total of Cu, Cr, Ni, and Sn) of soft magnetic steel sheets and iron loss W10 / 400. From the viewpoint of reducing iron loss W10 / 400 to 10 W / kg or less, the impurity content of soft magnetic steel sheets is preferably set to 1.2 wt% or less as the total of Cu, Cr, Ni, and Sn.

[0054] 7 shows the relationship between the impurity content (total of Cu, Cr, Ni, and Sn) of soft magnetic steel sheets and B10 / B100. From the viewpoint of achieving a B10 / B100 ratio of 0.78 or more, the impurity content of soft magnetic steel sheets is preferably set to 1.2 wt% or less as the total of Cu, Cr, Ni, and Sn.

[0055] 8 to 10 show photographs of the crystalline structure of soft magnetic steel sheets observed with a scanning electron microscope (SEM). FIG. 8 shows the crystalline structure of Example 13, and no inclusions due to impurity elements are visible. On the other hand, in the microstructure photograph of Example 14 (i.e., Cu content of 1.2 wt%) shown in FIG. 9, inclusions are present at the grain boundaries. Furthermore, in the microstructure photograph of Prior Art 2 shown in FIG. 10, inclusions due to impurity elements are also present, and these inclusions deteriorate the magnetic properties.

[0056] From the above results, from the viewpoint of stably producing soft magnetic steel sheets from raw materials including iron scrap and ensuring good magnetic properties (i.e., realizing magnetic properties equivalent to those of soft magnetic steel sheets with a low impurity content), the Cu content in the soft magnetic steel sheets is preferably 1.0 wt% or less. The Cr content is preferably 0.3 wt% or less. The Ni content is preferably 0.3 wt% or less. The Sn content is preferably 0.25 wt% or less. Furthermore, it is preferable that the impurity content of the soft magnetic steel sheets be set to 1.2 wt% or less as the sum of Cu, Cr, Ni, and Sn.

[0057] Although the description of the specific embodiment has been completed above, the present invention is not limited to the above embodiment and its modifications, and can be modified in a wide range of ways. [Explanation of symbols]

[0058] 1: Manufacturing equipment 2: Cooling roll 3: Molten metal 4: Nozzle 4a: Injection hole 5: Thin strip 7: Heater

Claims

1. A method for manufacturing a soft magnetic steel plate manufactured from raw materials including iron scrap, The raw material is Fe as a main component of the soft magnetic steel plate; 1.0 to 7.0 wt% Si; 0.1 to 1.0 wt% of Cu, which is a component derived from the iron scrap; 0.01 to 0.5 wt% Cr; 0.01 to 0.5 wt% Ni; 0.01 to 0.3 wt% Sn, a raw material melting step of melting the raw material; a strip-shaped thin plate forming step of forming a strip-shaped thin plate from the raw material by a single-roll liquid quenching solidification method; a heat treatment step of heat treating the strip-shaped thin plate in an inert atmosphere at 1050 to 1150°C for 3 to 24 hours; A method for manufacturing a soft magnetic steel sheet, comprising:

2. 2. The method for producing a soft magnetic steel sheet according to claim 1, wherein the total content of Cu, Cr, Ni, and Sn in the soft magnetic steel sheet is 1.2 wt % or less.

3. 3. The method for producing a soft magnetic steel sheet according to claim 1, wherein at least one of warm rolling and cold rolling of the strip-shaped thin plate is carried out before the heat treatment step.

4. The method for producing a soft magnetic steel sheet according to claim 1 or 2, further comprising a Si addition step of adding Si to the iron scrap as the raw material.

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