JP7331802B2 - Non-oriented electrical steel sheet and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a non-oriented electrical steel sheet and its manufacturing method, and more particularly to a non-oriented electrical steel sheet used for the iron core of a motor and its manufacturing method.

Non-oriented electrical steel sheets are materials used as iron cores of motors and transformers, and low iron loss is required for non-oriented electrical steel sheets from the viewpoint of improving the efficiency of these electric devices. Increasing the specific resistance and reducing the thickness of the non-oriented electrical steel sheet are effective in reducing iron loss. However, increasing the resistivity of a non-oriented electrical steel sheet increases the cost of the alloy, and reducing the thickness increases the cost of rolling and annealing. .

As a method of reducing iron loss other than specific resistance and thinning, a method of improving hysteresis loss by applying tension to a non-oriented electrical steel sheet is known. As described in Patent Document 1, grain-oriented electrical steel sheets employ a method in which a film made of an oxide is formed on the surface of the steel sheet, and a glass coating is applied to the steel sheet to apply tension due to the difference in thermal expansion between the film and the steel sheet. there is

Further, in Patent Document 2, a method of applying tension to a steel sheet without impairing the adhesion between the coating and the steel sheet by forming a multi-layer structure coating mainly composed of oxides on the surface of the non-oriented electrical steel sheet. is disclosed.

JP-A-2008-31499 JP 2017-101292 A

However, in the methods disclosed in Patent Documents 1 and 2, since a hard oxide layer is formed on the surface of the steel sheet, the life of the die is shortened when the steel sheet is punched into a motor core, resulting in a decrease in productivity. , there is a problem that the cost increases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-oriented electrical steel sheet in which tension is applied to the steel sheet without forming an oxide layer on the surface of the steel sheet.
Another object of the present invention is to provide a method for manufacturing the non-oriented electrical steel sheet.

In order to solve the above problems, the present inventors focused attention on the effects of steel components dissolved in α-Fe and exerted on the lattice constant. As a result, the present inventors have found that by concentrating a specific solute element on the surface of the steel sheet, tensile stress is generated due to the difference in lattice constant between the surface layer of the steel sheet and the central layer of the thickness of the steel sheet, leading to the completion of the present invention.

That is, the gist and configuration of the present invention are as follows.
[1] % by mass,
C: 0.005% or less,
Si: 1.0% or more and 7.0% or less,
Mn: 0.02% or more and 4.0% or less,
Sol. Al: 0.001% or more and 4.0% or less,
P: 0.001% or more and 0.2% or less,
S: 0.005% or less,
N: having a component composition containing 0.005% or less, the balance being Fe and inevitable impurities,
A layer having a lattice constant larger than the lattice constant at the center of the plate thickness by 0.002 Å or more on both surfaces, and having a depth of 20 μm or less in the plate thickness direction from the surface of the A layer, non-oriented electromagnetic steel sheet.
[2] In addition to the above component composition, in mass%,
Sb: 0.002% or more and 0.5% or less,
Sn: 0.002% or more and 0.5% or less,
W: 0.002% or more and 0.5% or less,
Zn: The non-oriented electrical steel sheet according to [1], containing one or more selected from 0.002% or more and 0.5% or less.
[3] in % by mass,
C: 0.005% or less,
Si: 1.0% or more and 7.0% or less,
Mn: 0.02% or more and 4.0% or less,
Sol. Al: 0.001% or more and 4.0% or less,
P: 0.001% or more and 0.2% or less,
S: 0.005% or less,
A steel slab having a chemical composition containing N: 0.005% or less and the balance being Fe and unavoidable impurities is hot-rolled into a hot-rolled sheet, and the hot-rolled sheet is subjected to hot-rolled sheet annealing. Alternatively, a method for manufacturing a non-oriented electrical steel sheet in which cold rolling is performed once or twice or more with intermediate annealing without performing hot-rolled sheet annealing to obtain a cold-rolled sheet having a final thickness, and then finish annealing is performed. in
By applying any one of CVD, PVD, plating, and cladding,
A non-directional electromagnetic wave having on both surfaces a layer A having a lattice constant larger than the lattice constant at the center of the plate thickness by 0.002 Å or more, and having a depth of 20 μm or less in the plate thickness direction from the surface of the layer A. A method for manufacturing a non-oriented electrical steel sheet for manufacturing a steel sheet.
[4] In addition to the above component composition, in mass%,
Sb: 0.002% or more and 0.5% or less,
Sn: 0.002% or more and 0.5% or less,
W: 0.002% or more and 0.5% or less,
Zn: The method for producing a non-oriented electrical steel sheet according to [3], containing one or more selected from 0.002% or more and 0.5% or less.

ADVANTAGE OF THE INVENTION According to this invention, the non-oriented electrical steel sheet which applied tension|tensile_strength to a steel plate can be provided, without forming an oxide layer on the steel plate surface.

The non-oriented electrical steel sheet according to the present invention achieves both productivity in punching and excellent iron loss properties. The non-oriented electrical steel sheet of the present invention is suitable for motor cores.

It is an example of a graph showing the relationship between the depth from the steel plate surface and the Al concentration in the plate thickness direction. It is an example of the graph which shows the relationship between the depth from the steel plate surface and the lattice constant difference with the plate|board thickness center.

First, the chemical composition of the non-oriented electrical steel sheet of the present invention will be described. Note that "%" indicating the content of each element means % by mass unless otherwise specified. For elements whose concentration changes in the plate thickness direction, the average value in the plate thickness direction is taken as the content of the element.

C: 0.005% or less C is a harmful element that causes magnetic aging and deteriorates the magnetic properties of the product sheet. Therefore, in the present invention, the C content is limited to 0.005% or less. C is an element to be reduced as much as possible, and the C content is preferably 0.003% or less.

Si: 1.0% or more and 7.0% or less Si is an element effective in increasing the specific resistance of the steel sheet and reducing iron loss, so in the present invention, the Si content is made 1.0% or more. . On the other hand, the addition of Si exceeding 7.0% makes the steel extremely embrittled, so the Si content is limited to 7.0% or less. The Si content is preferably 1.5% or more, more preferably 1.8% or more. Also, the Si content is preferably 6.5% or less, more preferably 4.8% or less.

Mn: 0.02% or more and 4.0% or less Mn must be added in an amount of 0.02% or more in order to prevent red hot brittleness during hot rolling. However, when it exceeds 4.0%, the magnetic flux density decreases and embrittlement becomes remarkable. Therefore, the Mn content is in the range of 0.02% or more and 4.0% or less. The Mn content is preferably in the range of 0.02% or more and 2.0% or less. Mn is an element that increases the lattice constant by forming a solid solution in α-Fe, so it is preferable to make a large amount of Mn form a solid solution in the A layer on the surface layer side of the steel sheet.

Sol. Al: 0.001% or more and 4.0% or less Al is an element effective in increasing the specific resistance of the steel sheet and reducing iron loss, so in the present invention, 0.001% or more is added. However, adding more than 4.0% causes embrittlement. Therefore, the Al content is the Sol. The range of Al is 0.001% or more and 4.0% or less. Since Al is an element that increases the lattice constant by dissolving in α-Fe, it is preferable to make a large amount of Al dissolve in the A layer on the surface layer side of the steel sheet.

P: 0.001% or more and 0.2% or less In the present invention, the P content is set to 0.2% or less because embrittlement is severe when added in excess of 0.2%, and productivity is significantly reduced. do. In addition, if the P content is less than 0.001%, the cost will increase significantly, so the lower limit of the P content is made 0.001%.

S: 0.005% or less S is a harmful element that forms sulfides such as MnS and increases iron loss, so the upper limit of the S content is made 0.005%. The S content is preferably 0.003% or less.

N: 0.005% or less N is a harmful element that forms nitrides and increases iron loss, so the upper limit of the N content is made 0.005%. The N content is preferably 0.003% or less.

The non-oriented electrical steel sheet of the present invention preferably has a chemical composition containing the above components with the balance being Fe and unavoidable impurities.

In addition to the above chemical composition, the non-oriented electrical steel sheet of the present invention has Sb: 0.002% or more and 0.5% or less, Sn: 0.002% or more and 0.5% or less, W: 0.002 % or more and 0.5% or less, and Zn: 0.002% or more and 0.5% or less. Since these elements are elements that increase the lattice constant by dissolving in α-Fe, it is preferable to dissolve many of them in the A layer on the surface layer side of the steel sheet.

Next, the component gradient of the non-oriented electrical steel sheet of the present invention and the stress state in the steel sheet will be described.

In the non-oriented electrical steel sheet of the present invention, the steel sheet surface layer region and the plate thickness center region have different lattice constants. Specifically, the non-oriented electrical steel sheet of the present invention has layers A on both surfaces, which are regions in which the lattice constant is 0.002 Å or more larger than the lattice constant at the thickness center (thickness center plane). Between the A layers, there is a B layer, which is a region having a lattice constant different from the lattice constant at the center of the plate thickness by less than 0.002 Å.

Since the non-oriented electrical steel sheet of the present invention has the layer A on the surface layer, tension can be applied to the steel sheet. Therefore, the non-oriented electrical steel sheet of the present invention can apply tension to the steel sheet without forming an oxide layer for applying tension to the steel sheet.

The depth (thickness) of the A layer described above is 20 μm or less from the surface (the thickness of the A layer is 20 μm or less). Compressive stress is applied to the A layer from the B layer, so if the depth of the A layer exceeds 20 μm, the core loss of the non-oriented electrical steel sheet deteriorates. The depth of the A layer is preferably 15 μm or less.

In order to obtain a sufficient iron loss improvement effect, the tensile stress exerted by the layer A on the layer B is preferably 0.1 MPa or more.

In order to obtain a sufficient iron loss improvement effect, the gradient of the lattice constant with respect to the thickness direction depth at the boundary between the A layer and the B layer is preferably 0.0001 Å/μm or more.

The A layer can be formed, for example, by concentrating an element, such as Al, Mn, Sb, Sn, W, and Zn, which increases the lattice constant by forming a solid solution with α-Fe in the surface layer of the steel sheet. That is, it can be formed by increasing (concentrating) the Al, Mn, Sb, Sn, W, and Zn concentrations of the steel sheet surface layer (A layer) above the center of the sheet thickness. In addition, such component inclination can be performed by CVD, PVD, plating, and clad, which will be described later. Further, when one or more selected from the above-mentioned Sb, Sn, W, and Zn are contained in the steel sheet by CVD, PVD, plating, or clad, these elements are contained only in the steel sheet surface layer (A layer). may be included.

Next, the method for manufacturing the non-oriented electrical steel sheet of the present invention will be described.
A method for producing a non-oriented electrical steel sheet according to the present invention includes hot-rolling a steel slab into a hot-rolled sheet, and performing hot-rolled sheet annealing on or without hot-rolled sheet annealing. A method for manufacturing a non-oriented electrical steel sheet, which is subjected to cold rolling twice or more with double or intermediate annealing to obtain a cold-rolled sheet having a final thickness, and then to final annealing, further comprising CVD (Chemical Vapor Deposition), It includes a step of increasing the lattice constant of the region of the surface layer of the steel sheet by performing any one of PVD (Physical Vapor Deposition), plating, and cladding.

Each step will be described in detail. First, a steel slab is produced from molten steel adjusted to have the above-described preferred chemical composition. A steel slab may be produced by a normal ingot casting-blooming method or a continuous casting method, or may be produced by a direct casting method from a thin slab having a thickness of 100 mm or less.

The steel slab is then heated in the usual manner and subjected to hot rolling, although it may be subjected to hot rolling immediately after casting without heating. Here, the thickness of the steel sheet (hot-rolled sheet) after hot rolling is preferably in the range of 1.0 to 5.0 mm. If the thickness is less than 1.0 mm, rolling troubles in hot rolling tend to increase.

When the hot-rolled sheet is annealed after hot rolling, the soaking temperature is preferably in the range of 900 to 1200°C. When the soaking temperature is 900° C. or higher, the effect of hot-rolled sheet annealing can be more enjoyed, and the magnetic properties can be more easily improved. Further, when the soaking temperature is 1200° C. or less, it is advantageous in terms of cost, and it becomes easy to suppress the occurrence of surface flaws caused by scale.

In place of hot-rolled sheet annealing, self-annealing of a coil wound after hot rolling may be utilized, and in this case, the coil winding temperature is preferably 600° C. or higher.

A hot-rolled sheet after hot rolling or a hot-rolled annealed sheet after hot-rolled sheet annealing is cold-rolled once or twice or more with intermediate annealing to obtain a cold-rolled sheet. In particular, for the final cold rolling, if there is no cost problem due to equipment or production restrictions, warm rolling, in which the sheet temperature is raised to about 200°C for the purpose of improving the magnetic flux density, is adopted. preferably.

The thickness (final thickness) of the cold-rolled sheet is preferably in the range of 0.1 to 1.0 mm. When the thickness of the cold-rolled sheet is 0.1 mm or more, it becomes easier to suppress the decrease in productivity caused by reducing the sheet thickness. When the thickness of the cold-rolled sheet is 1.0 mm or less, it becomes easier to enhance the effect of reducing iron loss.

In the method of manufacturing the non-oriented electrical steel sheet of the present invention, any one of CVD, PVD, plating, and clad treatment is further performed.

(treatment by clad)
During the above hot rolling or cold rolling, the mother steel sheet (base material) is subjected to a clad treatment in which thin sheets (laminated sheets) having a lattice constant larger than that of the mother steel sheet are stacked vertically in the thickness direction and crimped. , the lattice constant of the region of the surface layer of the steel sheet can be increased. At this time, the thickness of the thin plate (laminated plate) to be crimped is preferably 5% or less of the thickness of the mother steel plate.

Specifically, when the steel slab is hot-rolled to form a hot-rolled sheet, the cladding process uses the steel slab as a base material, and coats both surfaces of the steel slab with a thin sheet having a lattice constant larger than that of the base material. plates) can be overlapped and crimped. The cladding treatment may be a process in which a hot-rolled sheet or a cold-rolled sheet is used as a base material, and thin sheets (laminated sheets) having a lattice constant larger than that of the base material are superimposed on both surfaces of the base material and crimped. The thin plate is not particularly limited as long as it has a lattice constant larger than that of the base material, but it preferably has the above-mentioned suitable component composition as well as the base material, and further includes Sb, Sn, W, and Zn. It is preferred to have a component composition.

(Processing by CVD, PVD, plating)
In addition, the cold-rolled sheet after the cold rolling is subjected to any one of CVD, PVD, and plating so that it dissolves in α-Fe such as Al, Mn, Sb, Sn, W, and Zn. A concentrated layer of an element that increases the lattice constant may be formed on the surface of the steel sheet to increase the lattice constant of the region of the surface layer of the steel sheet. In that case, the thickness of the thickened layer is preferably 20 μm or less on one side of the steel sheet, more preferably 10 μm or less, and even more preferably 3 μm or less.

Thereafter, the cold-rolled sheet having the final thickness is subjected to finish annealing. For the final annealing, it is preferable to employ continuous annealing in which the steel is soaked at a temperature of 700 to 1100° C. for 1 to 3000 seconds. When the soaking temperature is 700° C. or higher, recrystallization can be sufficiently advanced, and in addition to being likely to obtain good magnetic properties, it is easy to obtain a sufficient shape correction effect in continuous annealing. In addition, when the soaking temperature is 1100° C. or lower, excessive coarsening of crystal grains can be easily suppressed, and reduction in strength and toughness can be easily suppressed. The soaking temperature is more preferably 800-1100°C. The soaking time is more preferably 1 to 100 seconds.

When the elements such as Al, Mn, Sb, Sn, W, and Zn are concentrated on the surface of the steel sheet by CVD, PVD, or plating, it is necessary to diffuse the elements into the steel by final annealing. . At this time, if the diffusion distance increases, the volume to which the tensile stress is applied decreases, and a sufficient iron loss reduction effect cannot be obtained. Temperature should be controlled.

Here, if the atmosphere during the soaking of the continuous annealing is oxidizing, oxides that grow rapidly on the surface inhibit grain growth and deteriorate iron loss, so the oxygen potential P _H2O /P _H2 is 0. A non-oxidizing atmosphere of 0.001 or less is preferable. The oxygen potential is more preferably 0.0005 or less.

After the finish annealing, if necessary, an insulating coating is applied to obtain a product sheet. Known insulating coatings can be used, and inorganic coatings, organic coatings, inorganic-organic mixed coatings, etc. may be used depending on the purpose.

In addition, the non-oriented electrical steel sheet of the present invention has the above-described A layer on the surface layer, so that tension is applied to the steel sheet without forming a film (such as an oxide layer) for applying tension to the steel sheet. can be granted.

Next, a method for evaluating the non-oriented electrical steel sheet of the present invention will be described.

From the plate after finish annealing (non-oriented electrical steel sheet, hereinafter also referred to as finish annealing plate) manufactured by the above-described manufacturing method, the angles φ made with respect to the rolling direction are φ = 0 ° and 90 °. A test piece of 300 mm × 100 mm long in the direction was taken, and the iron loss W _15/50 when excited by a sine wave of 1.5 T and 50 Hz was measured in a single plate magnetic measurement test, and φ = 0 ° and 90 °. The average iron loss of the test pieces was obtained.

A 10 mm square test piece was taken from the finish annealed plate, embedded in a C mold, and then the surface was polished to prepare a test piece for observing the steel plate cross section. distribution was evaluated.

A 30 mm square X-ray diffraction test piece is taken from the finish annealed sheet, and X-ray diffraction is performed while gradually scraping the steel sheet by chemical polishing. The change in lattice constant up to the plane) was evaluated. In addition, a region having a lattice constant larger than the lattice constant at the thickness center by 0.002 Å or more is defined as layer A, and a region having a lattice constant difference of less than 0.002 Å with respect to the lattice constant at the thickness center is defined as layer B. , the depth (thickness) from the surface of the A layer was evaluated.

A test piece for stress measurement of 300 mm × 30 mm is taken from the finish annealed sheet, a region of 50 μm is removed from one side of the test piece by chemical polishing, and then the amount of warpage of the steel sheet is measured. (tensile stress) was evaluated.

(Example 1)
C: 0.0020, Si: 2.5%, Mn: 0.5%, Sol. A steel having a chemical composition of Al: 0.7%, P: 0.05%, S: 0.0020%, and N: 0.0023% was melted in a laboratory and hot-rolled to obtain a plate thickness of 2.5%. A 0 mm hot-rolled sheet was obtained. The hot-rolled sheet was hot-rolled and annealed at 1000° C. for 10 seconds, pickled, and then cold-rolled to a finished thickness of 0.30 mm to obtain a cold-rolled sheet. The cold-rolled sheet was subjected to CVD treatment using aluminum organic metal gas or heat treatment in _N2 atmosphere at 950°C for 100 seconds, and the cold-rolled sheet under each condition was further subjected to 950°C in _N2 atmosphere. Finish annealing was performed by changing the soaking time between 30 and 15000 seconds to produce a finish annealed sheet (non-oriented electrical steel sheet). A test piece for magnetic measurement, a test piece for cross-sectional observation, and a test piece for X-ray diffraction were prepared from the obtained finish-annealed sheet, and the magnetic properties and element distribution in the sheet thickness direction were measured.

FIG. 1 shows the distribution of elements in the plate thickness direction under some conditions (Conditions 2, 3, and 7 in Table 1 below). The Al concentration was high on the surface of the steel sheet of the CVD-treated test piece, decreased as it approached the center of the plate thickness, and became almost constant near the center of the plate thickness. Moreover, as shown in FIG. 2, the lattice constant decreased as the Al concentration decreased, and became almost constant near the center of the plate thickness.

Table 1 shows the evaluation results of tensile stress and iron loss. When the finish annealing was performed for 30 seconds, a tensile stress of about 50 MPa was applied to the steel sheet (Condition 2), but when the finish annealing was performed for 15000 seconds, no change in stress was observed (Condition 7). This is probably because Al diffused over a long distance by lengthening the diffusion time, and the lattice constant difference between the thickness center and the surface layer almost disappeared. Iron loss W _15/50 was lower in the tensile stressed test piece.

From the above results, it was found that the iron loss was reduced by dissolving and diffusing Al on the steel sheet surface, forming a region with a large lattice constant on the steel sheet surface layer, and applying tensile stress to the steel sheet.

(Example 2)
Steel having the chemical composition shown in Table 2 was melted in a laboratory, and steel ingots were cut to a thickness of 1 mm or 140 mm. Steel ingots (laminated material) of 1 mm were laminated on the upper and lower sides of the plate, and electron beam welding was performed in a vacuum atmosphere. The welded steel ingot was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.8 mm. The hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000° C. for 10 seconds, pickled, and cold-rolled to a finished thickness of 0.30 mm to obtain a cold-rolled sheet. The cold-rolled steel sheet was subjected to finish annealing for 10 seconds in a _N2 atmosphere at 1000°C, and iron loss and stress from the steel sheet surface were evaluated. Table 3 shows the evaluation results. From this result, it can be seen that iron loss is improved by forming a steel sheet surface layer with a large lattice constant and applying tensile stress to the inside of the steel sheet.

Claims (4)

in % by mass,
C: 0.005% or less,
Si: 1.8 % or more and 7.0% or less,
Mn: 0.02% or more and 4.0% or less,
Sol. Al: 0.001% or more and 4.0% or less,
P: 0.001% or more and 0.2% or less,
S: 0.005% or less,
N: having a component composition containing 0.005% or less, the balance being Fe and inevitable impurities,
A layer having a lattice constant larger than the lattice constant at the center of the plate thickness by 0.002 Å or more on both surfaces, and having a depth of 20 μm or less in the plate thickness direction from the surface of the A layer, non-oriented electromagnetic steel sheet. In addition to the component composition, in mass %,
Sb: 0.002% or more and 0.5% or less,
Sn: 0.002% or more and 0.5% or less,
W: 0.002% or more and 0.5% or less,
2. The non-oriented electrical steel sheet according to claim 1, containing one or more selected from Zn: 0.002% or more and 0.5% or less. in % by mass,
C: 0.005% or less,
Si: 1.8 % or more and 7.0% or less,
Mn: 0.02% or more and 4.0% or less,
Sol. Al: 0.001% or more and 4.0% or less,
P: 0.001% or more and 0.2% or less,
S: 0.005% or less,
A steel slab having a chemical composition containing N: 0.005% or less and the balance being Fe and unavoidable impurities is hot-rolled into a hot-rolled sheet, and the hot-rolled sheet is subjected to hot-rolled sheet annealing. Alternatively, a method for manufacturing a non-oriented electrical steel sheet in which cold rolling is performed once or twice or more with intermediate annealing without performing hot-rolled sheet annealing to obtain a cold-rolled sheet having a final thickness, and then finish annealing is performed. in
By applying any one of CVD, PVD, plating, and cladding,
A non-directional electromagnetic wave having on both surfaces a layer A having a lattice constant larger than the lattice constant at the center of the plate thickness by 0.002 Å or more, and having a depth of 20 μm or less in the plate thickness direction from the surface of the layer A. A method for manufacturing a non-oriented electrical steel sheet for manufacturing a steel sheet. In addition to the component composition, in mass %,
Sb: 0.002% or more and 0.5% or less,
Sn: 0.002% or more and 0.5% or less,
W: 0.002% or more and 0.5% or less,
4. The method for producing a non-oriented electrical steel sheet according to claim 3, containing one or more selected from Zn: 0.002% or more and 0.5% or less.

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