Title of invention : Hot-rolled steel sheet for non-oriented electrical steel sheet
Technical field
[0001]
The present invention relates to hot-rolled steel sheets for non-oriented electrical steel sheets with excellent magnetic properties, which are mainly used as iron core materials for electrical equipment.
This application claims priority based on Japanese Patent Application No. 2020-027497 filed in Japan on February 20, 2020, the content of which is hereby incorporated by reference.
Background technology
[0002]
In recent years, electrical equipment, especially in the fields of rotating machines, small and medium-sized transformers, electrical equipment, etc., where non-oriented electrical steel sheets are used as core materials, are represented by global power and energy savings, CO2 reduction, etc. In the global environment conservation movement, the demand for high efficiency and miniaturization is increasing more and more. Under such a social environment, it is of course an urgent task to improve the performance of non-oriented electrical steel sheets.
[0003]
Iron loss and magnetic flux density are required for non-oriented electrical steel sheets to improve the characteristics of motors. In the past, these problems have been improved by controlling the texture of the product sheet by recrystallizing 60% or more of the area by high-temperature coiling of hot rolling.
[0004]
Patent Document 1 discloses that by causing recrystallization and grain growth in the hot-rolled sheet stage, the crystal grains and texture in the product stage after annealing are affected, and the magnetic properties are improved. ing.
prior art documents
patent literature
[0005]
Patent Document 1: Japanese Patent Laid-Open No. 63-210237
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0006]
As the demand for non-oriented electrical steel sheets (hereinafter also simply referred to as "electromagnetic steel sheets") increases, there is also a demand for cost reduction. As one of the methods for reducing the manufacturing cost, it is conceivable to omit the annealing after hot rolling by increasing the hot rolling temperature in the hot rolling process. However, a hot-rolled steel sheet with an increased recrystallization rate has a lower toughness. This reduction in toughness causes cracks and breakage at the ends of the steel sheet in the pickling process after hot rolling accompanied by bending and unbending on a continuous line. If annealing after hot rolling is simply omitted, the toughness deteriorates and the risk of breaking the steel sheet increases.
[0007]
In view of the above circumstances, the present invention can suppress breakage due to bending and unbending in the subsequent pickling process even if annealing after hot rolling is omitted, and has excellent magnetic properties when used as an electrical steel sheet. An object of the present invention is to provide a hot-rolled steel sheet for non-oriented electrical steel sheet with improved toughness.
Means to solve problems
[0008]
The present inventors have found that hot-rolled steel sheets for non-oriented electrical steel sheets omit annealing in the hot-rolling process and have sufficient hot-rolled sheet toughness to suppress the occurrence of breakage at the steel sheet edges during pickling. , and conducted intensive research on methods for achieving both magnetic properties in electrical steel sheets.
[0009]
As a result, by controlling the soaking temperature, time, and cooling rate during self-annealing of the hot-rolled sheet by high-temperature coiling after hot rolling, the hardness at the center of the sheet thickness (1/2t part) can be reduced to Hv 220 or less. The inventors have found that the area of ​​processed tissue can be increased. As a result, even if the recrystallization rate is about 60% or more and about 80% or less, the toughness of the hot-rolled steel sheet is improved, breakage due to bending-unbending can be prevented, and excellent magnetic properties are obtained when made into a non-oriented electrical steel sheet. The inventors have found that
[0010]
The present invention was made based on the above findings, and the gist thereof is as follows.
[0011]
(1) In mass %, C: 0.0010 to 0.0050%, Si: 1.90% to 3.50%, Al: 0.10% to 3.00%, Mn: 0.05 to 2.0%. 00%, P: 0.100% or less, S: 0.005% or less, N: 0.0040% or less, B: 0.0060% or less, Sn: 0-0.50%, Sb: 0-0. 50%, Cu: 0-0.50%, REM: 0-0.0400%, Ca: 0-0.0400%, and Mg: 0-0.0400%, the balance being Fe and impurities A hot-rolled steel sheet for non-oriented electrical steel sheet, wherein the hardness HD of the processed structure at the sheet thickness center portion (1/2t position) is Hv220 at the end portion in the width direction of the hot-rolled steel sheet for non-oriented electrical steel sheet. A hot-rolled steel sheet for non-oriented electrical steel sheet characterized by the following.
[0012]
(2) The hardness between the hardness H D of the worked structure and the hardness H U of the recrystallized structure of the plate thickness surface layer portion (1/8t position) at the end portion in the width direction of the hot-rolled steel sheet for non-oriented electrical steel plate. The hot-rolled steel sheet for non-oriented electrical steel sheet according to (1), wherein the difference H S = H D - H U is within Hv20.
[0013]
(3) In mass%, Sn: 0.01% or more and 0.50% or less, Sb: 0.01% or more and 0.50% or less, Cu: 0.01% or more and 0.50% or less, REM: 0.0005 % or more and 0.0400% or less, Ca: 0.0005% or more and 0.0400% or less, Mg: 0.0005% or more and 0.0400% or less. The hot-rolled steel sheet for non-oriented electrical steel sheet according to (1) or (2).
Effect of the invention
[0014]
According to the present invention, even when annealing is omitted in the hot rolling process, the hot-rolled sheet has sufficient toughness, and when it is made into a non-oriented electrical steel sheet, it achieves both low core loss and high magnetic flux density. A hot-rolled steel sheet for non-oriented electrical steel sheet can be provided.
MODE FOR CARRYING OUT THE INVENTION
[0015]
A hot-rolled steel sheet for non-oriented electrical steel sheets according to one aspect of the present invention will be described in detail below.
The hot-rolled steel sheet for non-oriented electrical steel sheet is a material for non-oriented electrical steel sheet, and is hereinafter sometimes simply referred to as "hot-rolled steel sheet". A non-oriented electrical steel sheet can be obtained by subjecting the hot-rolled steel sheet to cold rolling and finish annealing. The mechanical properties and metallographic structure of the non-oriented electrical steel sheet subjected to the above processes are completely different from those of the hot-rolled steel sheet. Non-oriented electrical steel sheets are generally softer than hot-rolled steel sheets. This is because the recrystallized structure is softer than the worked structure, and the amount of the recrystallized structure is increased by the finish annealing in the non-oriented electrical steel sheet.
The processed structure of the hot-rolled steel sheet according to the present embodiment means a structure elongated by hot rolling. Further, the recrystallized structure of the hot-rolled steel sheet according to the present embodiment means a structure recrystallized by self-annealing after being stretched once by hot rolling. A person skilled in the art can easily distinguish between a processed structure and a recrystallized structure. For example, "Structural control of steel" (Masashi Maki, 2015, Rokaku Uchida), page 30, Fig. 2.22 "Changes in structure and properties due to annealing (annealing) of cold-worked material (recovery → re- Crystal → Grain Growth)” schematically explains the visual difference between the worked structure and the recrystallized structure. Although the hot-rolled steel sheet according to the present embodiment is not a cold-rolled material, the worked structure and recrystallized structure in the hot-rolled steel sheet according to the present embodiment have aspects similar to the worked structure and recrystallized structure described in the above literature. present.
In addition, one of the problems of the hot-rolled steel sheet according to the present embodiment is to exhibit excellent magnetic properties when it becomes an electrical steel sheet through the above-described steps. No need to consider. Hereinafter, in the description of the hot-rolled steel sheet according to the present embodiment, the magnetic properties are not the magnetic properties of the hot-rolled steel sheet itself, but the magnetic properties of the non-oriented electrical steel sheet obtained by subjecting the hot-rolled steel sheet to the above-described process. means.
[0016]
[Chemical composition of hot-rolled steel sheets for non-oriented electrical steel sheets]
First, the reason for limiting the composition of the hot-rolled steel sheet for non-oriented electrical steel sheet according to the present embodiment will be described. Hereinafter, "%" for the components of the hot-rolled steel sheet means "% by mass".
[0017]
C: 0.0010-0.0050%
C segregates at grain boundaries to strengthen toughness, so it is preferable to contain 0.0010% or more. On the other hand, C is a harmful component that deteriorates iron loss and causes magnetic aging, so the C content is made 0.0050% or less. The C content is more preferably 0.0015% or more, 0.0020% or more, or 0.0025% or more. The C content is preferably 0.0040% or less, 0.0035% or less, or 0.0030% or less.
[0018]
　Si: 1.90% to 3.50%
Si is a component that has the effect of reducing iron loss by increasing electrical resistance and reducing eddy current loss, and by increasing the yield ratio, it has the effect of improving the punching workability of the iron core. also have In order to exhibit these effects, it is necessary to contain 1.90% or more of Si. On the other hand, when the Si content increases, the magnetic flux density decreases, and in the manufacturing process itself of the non-oriented electrical steel sheet, workability such as cold rolling decreases and the cost increases. .50% or less. The Si content is preferably 2.00% or more, 2.20% or more, or 2.50% or more. The Si content is preferably 3.20% or less, 3.00% or less, or 2.80% or less.
[0019]
Al: 0.10% to 3.00%
Al is also a component that has the effect of reducing iron loss by increasing electrical resistance and reducing eddy current loss like Si. However, compared with Si, the amount of increase in hardness due to Al is small. Therefore, it is necessary to contain 0.10% or more of Al. On the other hand, when the Al content increases, the saturation magnetic flux density decreases, causing a decrease in the magnetic flux density, and further, a decrease in the yield ratio, which deteriorates the punching accuracy, so the Al content is 3.00. % or less. It is preferably 2.50% or less.
[0020]
　Mn: 0.05 to 2.00%
Mn has the effect of increasing the electrical resistance and reducing the eddy current loss, as well as improving the primary recrystallization texture and developing the {110}<001> crystal orientation desirable for improving rolling direction magnetic properties. Furthermore, Mn has the effect of lowering the solubility of MnS contained in the slab. As a result, the amount of MnS that dissolves during slab heating is reduced, and the amount of fine MnS that reappears during cooling of the slab is reduced. That is, the addition of Mn suppresses precipitation of fine sulfides such as MnS that are harmful to grain growth.
For these purposes, it is necessary to contain 0.05% or more of Mn. However, if the Mn content increases, the crystal grain growth itself during annealing deteriorates and the core loss increases, so the Mn content is made 2.00% or less. The Mn content is preferably 0.20% or more, 0.40% or more, or 0.80% or more. The Mn content is preferably 1.50% or less, 1.20% or less, or 1.00% or less.
[0021]
P: 0.100% or less
P has the effect of increasing the punching accuracy, and may be contained in the hot-rolled steel sheet. However, when the P content increases, steel sheets containing 2% or more of Si become very brittle. Therefore, the P content is 0.100% or less, preferably 0.10% or less, 0.080% or less, 0.05% or less, 0.050% or less, or 0.030% or less. The P content may be 0%, but may be, for example, 0.001% or more, 0.002% or more, or 0.003% or more in order to avoid an increase in refining cost.
[0022]
S: 0.005% or less
S inhibits recrystallization and grain growth during final annealing due to fine precipitation of sulfides such as MnS. Therefore, the S content is 0.005% or less, preferably 0.004% or less, 0.003% or less, or 0.002% or less. The S content may be 0%, but may be, for example, 0.0001% or more, 0.0002% or more, or 0.0003% or more in order to avoid an increase in refining costs.
[0023]
N: 0.0040% or less
N reduces the coverage of the internal oxide layer on the surface of the hot-rolled sheet by fine precipitation of nitrides such as AlN generated during hot-rolled sheet annealing and finish annealing, and further reduces recrystallization and grain growth during finish annealing. impede. Therefore, the N content is 0.0040% or less, preferably 0.0030% or less, 0.0020% or less, or 0.0010% or less. The N content may be 0%, but may be, for example, 0.0001% or more, 0.0002% or more, or 0.0003% or more in order to avoid an increase in refining costs.
[0024]
B: 0.0060% or less
B inhibits recrystallization and grain growth during final annealing due to fine precipitation of nitrides such as BN. Therefore, the B content is 0.0060% or less, preferably 0.0040% or less, and 0.00 30% or less, or 0.0020% or less. The B content may be 0%, but may be, for example, 0.0001% or more, 0.0002% or more, or 0.0003% or more in order to avoid an increase in refining costs.
[0025]
Sn: 0-0.50%
Sb: 0-0.50%
Sn and Sb are not essential elements, but improve the primary recrystallization texture of the steel sheet, develop it into a {110}<001> texture desirable for improving the rolling direction magnetic properties, and improve the magnetic properties. It has the effect of suppressing undesirable {111}<112> texture. Therefore, Sn and Sb may be contained in the hot-rolled steel sheet as necessary. For these purposes, one or both of Sn and Sb are preferably contained in an amount of 0.01% or more. On the other hand, even if the contents of Sn and Sb are increased, the action is saturated, and rather the toughness of the hot-rolled sheet may be lowered. Therefore, even when Sn and Sb are contained, the contents of Sn and Sb are each set to 0.50% or less. The lower limit of the Sn content and the lower limit of the Sb content may be 0.02%, 0.03%, or 0.05%, respectively. The upper limit of the Sn content and the upper limit of the Sb content may be 0.45%, 0.40%, or 0.20%, respectively.
[0026]
Cu: 0-0.50%
Although Cu is not an essential element, it precipitates in steel and exhibits the effect of improving strength, so it may be contained in the hot-rolled steel sheet as necessary. In order to obtain this action, it is preferable to contain 0.01% or more of Cu. On the other hand, if the Cu content exceeds 0.50%, cracks and flaws may occur during rolling. Therefore, the Cu content is preferably 0.50% or less. The Cu content may be 0.02% or more, 0.03% or more, or 0.05% or more. The Cu content may be 0.40% or less, 0.30% or less, or 0.20% or less.
[0027]
　REM: 0 to 0.0400% or less
　Ca: 0 to 0.0400% or less
　Mg: 0 to 0.0400% or less
Although REM, Ca, and Mg are not essential elements, they are elements that promote grain growth and may be contained in the hot-rolled steel sheet as necessary. In order to obtain this effect, the content of one or more elements selected from the group consisting of REM, Ca, and Mg is preferably 0.0005% or more, more preferably 0.0010% or more, More preferably, it is 0.0050% or more or 0.0100% or more. On the other hand, if the content of each of REM, Ca, and Mg exceeds 0.0400%, the magnetic properties deteriorate, so the content should be 0.0040% or less. Preferably, the content of any element is 0.0300% or less, more preferably 0.0200% or less or 0.0150% or less.
The term "REM" refers to a total of 17 elements consisting of Sc, Y and lanthanoids, and the above "REM content" means the total content of these 17 elements. When lanthanides are used as REMs, REMs are industrially added in the form of misch metals.
[0028]
The rest of the components of the hot-rolled steel sheet of the present embodiment other than the above components are Fe and impurity elements. Impurities are raw materials such as ores or scraps, or components that are mixed in due to various factors in the manufacturing process when steel materials are industrially manufactured, for example, and adversely affect the hot-rolled steel sheet of the present embodiment. It means what is permissible within the scope of
[0029]
By making the hot-rolled steel sheet have the above-described components, it is possible to obtain a non-oriented electrical steel sheet having excellent magnetic properties when the hot-rolled steel sheet is made into an electrical steel sheet.
[0030]

Next, the hot-rolled steel sheet of this embodiment is characterized in that the hardness HD of the processed structure at the thickness center (1/2t position) is Hv220 or less. Here, "t" means plate thickness.
[0031]
If the hardness HD of the worked structure at the center of the plate thickness (1/2t position) of the hot-rolled steel sheet exceeds Hv220, the magnetic properties appearing from the cold-rolled structure and then the annealing deteriorate {111 } The recrystallization driving force of grains is increased. Therefore, the magnetic properties of the non-oriented electrical steel sheet deteriorate. If the hardness HD of the processed structure is Hv 220 or less, the recrystallization driving force of the {111} grains is almost the same as that of the {110} grains that improve the magnetic properties, so the magnetic properties do not deteriorate. Therefore, it is desirable that the hardness HD of the worked structure at the thickness center (1/2t position) of the hot-rolled steel sheet is Hv220 or less. The hardness HD of the worked structure at the thickness center (1/2t position) of the hot-rolled steel sheet is more preferably Hv215 or less, Hv210 or less, or Hv200 or less.
[0032]
In general, the processed structure is harder than the recrystallized structure. When the hot-rolled sheet has a large proportion of processed structure, the hardness of the hot-rolled sheet increases. Cold rolling of such a hot-rolled sheet with high hardness increases the degree of {211}<011> accumulation in the cold-rolled sheet. Then, the annealing increases the degree of {111} orientation appearing from the portion where the degree of {211}<011> is high, thereby degrading the magnetic properties. Conventionally, in order to suppress the deterioration of magnetic properties, the hot-rolled sheet is annealed so as to reduce the processed structure of the hot-rolled sheet as much as possible, and the recrystallized region of the hot-rolled sheet is increased to about 80% or more. and annealed. However, although the recrystallized structure is softer than the worked structure, it has fewer dislocations that affect toughness. Therefore, increasing the recrystallized region above about 80% reduces the toughness of the hot-rolled steel sheet and increases the likelihood that the steel sheet will fracture during the subsequent pickling and bend-unbend in the cold-rolling line. Therefore, in order to improve the toughness of the hot-rolled steel sheet and improve the magnetic properties of the non-oriented electrical steel sheet obtained from the hot-rolled steel sheet, recrystallization of the hot-rolled steel sheet must be suppressed as much as possible (for example, hot-rolled By setting the recrystallization rate of the steel sheet to about 60% or more and about 80% or less), the worked structure is left in the hot rolled steel sheet, and the hardness HD of the worked structure at the center of the plate thickness (1/2t position) is Hv220. It is desirable to: That is, in the hot-rolled steel sheet according to the present embodiment, the hardness of the hot-rolled steel sheet is lowered by softening the worked structure while setting the amount of the worked structure to a predetermined value or more.
[0033]
The Vickers hardness is measured at a cross section parallel to the rolling direction and perpendicular to the sheet surface at a position 10 mm from the width direction end face of the hot rolled steel sheet to the width direction center (hereinafter referred to as the width direction end). do. The hardness HD of the processed structure at the center of the plate thickness (1/2t position) of this cross section and the hardness HU of the recrystallized structure at the plate thickness surface portion (1/8t position) are measured in the direction parallel to the rolling direction, Ten points are measured at intervals of 10 μm. Vickers hardness is measured according to JIS Z 2244 (2009). Specific measurement conditions are
Indenter = Vickers quadrangular pyramid diamond indenter with facing angle of 136°,
　Indentation load = 10 gf,
Pressing time = 20 sec
is.
[0034]
In addition, the hardness HD of the processed structure at the plate thickness center (1/2t position) at the end in the plate width direction of the hot-rolled steel sheet for non-oriented electrical steel plate and the recrystallization of the plate thickness surface layer (1/8t position) The magnetic properties can be further improved by setting the hardness difference H S =H D -H U from the hardness H U of the tissue within Hv20. This is because the higher the Hv of the hot-rolled sheet, the easier it is to recrystallize in the post-cold-rolling annealing. This is because the recrystallized structure favorable to the magnetic properties appearing in the surface layer of the steel sheet after rolling and annealing is less likely to be affected by the recrystallized structure unfavorable to the magnetic properties appearing in the center of the steel sheet. The hardness HU of the recrystallized structure at the plate thickness surface portion (1/8t position) can also be measured by the same method as the hardness HD of the worked structure at the plate thickness central portion (1/2t position).
In hot-rolled steel sheets, the surface layer is usually harder than the central part. This is because, in the hot-rolled steel sheet, the amount of recrystallized structure in the surface layer is larger than that in the central portion. Considering the above circumstances, in the hot-rolled steel sheet according to the present embodiment, the hardness of the central portion, which is expected to be the hardest, is controlled to a predetermined value or less. On the other hand, in a non-oriented electrical steel sheet obtained by cold-rolling and finish-annealing a hot-rolled steel sheet, the difference in hardness between the surface layer and the central portion is usually small or almost non-existent.
[0035]
[Production method]
Next, a method for manufacturing the hot-rolled steel sheet for non-oriented electrical steel sheet according to this embodiment will be described. The method for producing a hot-rolled steel sheet for non-oriented electrical steel sheet according to the present embodiment includes:
A process of continuously casting molten steel having the above components to obtain a slab,
a step of heating the slab to a temperature range of 1080-1200°C;
a step of hot-rolling a slab within the temperature range of 1080-1200°C at a finishing temperature of 850-1000°C to obtain a hot-rolled sheet;
A step of winding the hot-rolled sheet at a winding temperature of 700-850°C;
A step of self-annealing the hot-rolled sheet at a heat retention temperature of 670°C or higher and a holding time of 1 minute or more and 2 hours or less;
Self-annealing with an average cooling rate CR1 from the coiling temperature after hot rolling to 400 ° C. and / or an average cooling rate CR2 in the temperature range of 600 to 400 ° C. after self-annealing of 30 to 120 ° C./hr. A step of cooling the hot-rolled sheet that has produced
have
[0036]
The hot-rolled steel sheet for non-oriented electrical steel sheet of the present embodiment is obtained by continuously casting molten steel having the above-described components into a slab, hot-rolling it into a hot-rolled sheet, and heating it with the heat of a coil wound after hot-rolling. Manufactured by self-annealing. A conventional method may be used to manufacture the slab.
[0037]

The slab is then preferably heated to 1080-1200°C and subjected to hot rolling. The reason why the heating temperature is preferably set to 1080° C. or higher is that the finishing temperature is set to 850° C. or higher to omit annealing by reheating after winding, as will be described later. The reason why the heating temperature is preferably 1200° C. or less is to prevent solid solution and fine precipitation of impurities such as sulfides and to prevent an increase in iron loss.
[0038]
The finishing temperature in hot rolling is preferably 850-1000°C. This is because, as will be described later, self-annealing is performed with coil heat at a coiling temperature of 700 to 850° C., thereby increasing the recrystallization rate and omitting annealing by reheating. Also, if the finishing temperature is low, the hot workability may deteriorate, and the uniformity of the thickness along the width direction of the steel sheet, that is, the accuracy of the thickness may deteriorate. On the other hand, the finishing temperature is preferably 1000° C. or less in order to prevent deterioration of toughness due to coarsening of the ferrite grain size.
[0039]

Next, the hot-rolled steel sheet after finish rolling is wound up at 700-850°C. By winding at 700 to 850° C., self-annealing can be performed by heat accumulated in the wound coil. According to this self-annealing, it is possible to increase the recrystallization rate in the hot-rolled steel sheet, and to suppress the growth of {111}-oriented crystal grains, which adversely affect the magnetic properties, even if annealing by reheating is omitted. becomes. In order to improve the magnetic properties, especially the magnetic flux density, it is preferable to increase the recrystallized region of the structure of the hot-rolled steel sheet before cold rolling. and the effect of improving the toughness cannot be obtained. Therefore, the winding temperature is preferably 850° C. or lower.
[0040]

In order to coarsen the crystal grain size of the hot-rolled steel sheet before cold rolling, the coil after winding is covered with a heat insulating cover to retain heat. From the viewpoint of lowering the hardness of the processed structure of the hot-rolled sheet, the heat retention temperature is set to 670° C. or higher and the holding time is set to 1 minute or longer. On the other hand, if the recrystallization rate is too high, breakage tends to occur in the pickling process and the cold rolling process, so the holding time is preferably 2 hours or less. The holding time is the time during which the heat insulating cover is placed over the coil.
Note that the heat retaining process may be performed without using the heat retaining cover. In this case, the heat retention step means the process from the time the hot-rolled steel sheet is wound into a coil to the time the temperature of the coil starts to drop. The time point at which the coil is formed is the time point at which one turn of the coil is finished from the hot-rolled steel sheet in one zone. In addition, the point in time when the temperature of the coil starts to decrease is the point in time when the cooling rate of the coil changes.is an inflection point on the cooling rate curve. Depending on the heat retention temperature, the temperature change in the coil may be extremely small for a predetermined period of time after winding the coil, and after the predetermined period of time, the temperature of the coil begins to drop rapidly.
[0041]

In this embodiment, it is important to control the cooling rate in order to reduce the hardness of the processed structure. Specifically, the average cooling rate CR1 from the coiling temperature after hot rolling to 400 ° C. and / or the average cooling rate CR2 in the temperature range of 600 to 400 ° C. after holding in the heat retention process is 30 to 120. C./hr is preferred.
Here, the “average cooling rate CR1 from the coiling temperature after hot rolling to 400°C” refers to the period from coiling to the start of heat retention, and the time from the end of heat retention to the coil temperature reaching 400°C. It is the average value of the cooling rate for the period. In other words, "the average cooling rate CR1 from the coiling temperature after hot rolling to 400°C" is a value calculated by the following formula.
　CR1 = (winding temperature - 400°C) / (time from winding temperature to 400°C - time covered with heat insulating cover)
Also, the "average cooling rate CR2 in the temperature range of 600 to 400°C after holding in the heat retention step" is the average value of the cooling rate during the period from 600°C to 400°C. In other words, the “average cooling rate CR2 in the temperature range of 600 to 400° C. after holding in the heat holding step” is a value calculated by the following formula.
　CR2 = (600°C-400°C)/(time from 600°C to 400°C)
It should be noted that the cooling after holding in the heat holding step is preferably started immediately after removing the cover described above. Alternatively, the cooling process preferably begins by the time the coil temperature begins to drop.
[0042]
The average cooling rate applied in the production of the hot-rolled steel sheet according to this embodiment is much slower than usual. Normally, the coil after winding is water-cooled, and the average cooling rate is far above 120° C./hr. Water cooling of the coil is believed to result in an average cooling rate of at least 150°C/hr. The reason for water-cooling the coil is to shorten the time required to manufacture the non-oriented electrical steel sheet. In order to cold-roll the hot-rolled steel sheet, the temperature of the hot-rolled steel sheet must be kept at room temperature. If the hot-rolled steel sheet is not quenched using a cooling means such as water cooling, the waiting time before starting cold rolling becomes longer, and the time required for manufacturing the non-oriented electrical steel sheet becomes longer. It is generally considered preferable to water-cool the coils unless there is a specific reason not to do so. In addition, there is no knowledge in the prior art that the hardness of the worked structure should be reduced in hot-rolled steel sheets for non-oriented electrical steel sheets.
However, the inventors have found that the coil after heat retention must be slowly cooled in order to reduce the hardness of the worked structure of the hot-rolled steel sheet. If the average cooling rates CR1 and/or CR2 are too high, the hardness of the processed structure cannot be lowered sufficiently. On the other hand, if the average cooling rate is too low, the self-annealing time is lengthened, the worked structure is lost, and the toughness is deteriorated. Therefore, the average cooling rates CR1 and/or CR2 are preferably 30° C./hr or more and 120° C./hr or less.
[0043]
It should be noted that cooling after heat retention is performed in a state in which the steel sheet is wound into a coil. The above cooling rates are at the outer periphery of the coil. Further, as described above, the ends of the steel plate are cracked and lead to breakage of the steel plate, so the above cooling rate is for the ends of the steel plate (that is, both ends in the winding core direction of the coil).
[0044]
Furthermore, among CR1 and CR2 described above, the average cooling rate CR1 from the winding temperature to 400°C can be controlled more preferably. By setting CR1 to 50 to 80 ° C./hr, the hardness of the processed structure HD and the hardness of the recrystallized structure in the plate thickness surface layer portion (1/8t position) at the end of the hot-rolled steel sheet for non-oriented electrical steel plate. The hardness difference H S = H D - H U can be within Hv20. This can further improve the toughness of the hot-rolled steel sheet.
[0045]

When Sn and Sb are added to the steel sheet, these elements contribute to low iron loss and high magnetic flux density, so the heat retention temperature can be lowered, and as a result, toughness can be improved. can be done. At this time, by setting the heat retention temperature to 850° C. or lower, preferably 800° C. or lower, and more preferably 750° C. or lower, it is possible to highly achieve both appropriate toughness, low iron loss, and high magnetic flux density. can.
[0046]
The mechanism by which the addition of Sn and Sb contributes to low core loss and high magnetic flux density is thought to be that these elements suppress the growth of {111} oriented grains that adversely affect magnetic properties.
[0047]
The hot-rolled steel sheet for non-oriented electrical steel sheet of the present embodiment obtained as described above is subjected to pickling, cold rolling, and finish annealing by a conventional method to obtain a non-oriented electromagnetic steel sheet having excellent magnetic properties. You can get steel plates. At this time, as described above, the hot-rolled steel sheet for non-oriented electrical steel sheet of the present embodiment is excellent in toughness, so even if it is pickled by a normal method, cracks do not occur due to bending and unbending.
Example
[0048]
Next, examples of the present invention will be described. The conditions in the examples are one example of conditions adopted for confirming the feasibility and effect of the present invention, and the present invention is based on this one example of conditions. It is not limited. Various conditions can be adopted in the present invention as long as the objects of the present invention are achieved without departing from the gist of the present invention.
[0049]

Steel was cast with the ingredients shown in Table 1 and hot rolled to produce a hot rolled sheet with a thickness of 2.0 mm. Then, under the conditions shown in Table 2, it was wound into a coil, heat-retained, and then cooled. In addition, production code B0 is a reference example in which hot-rolled sheet annealing was performed in a nitrogen atmosphere of 100% after coiling and cooling. Table 3 shows the measurement results of the fracture surface transition temperature in the Charpy test conducted to evaluate the hardness and toughness of the processed hot-rolled sheet structure at the edge of the hot-rolled sheet.
[0050]
The hardness of the edge of the steel sheet is measured at the position 10 mm from the edge in the width direction of the steel sheet to the center in the width direction (edge ​​in the width direction) and in the cross section parallel to the rolling direction, at the center of the thickness (1/2t position ) and the hardness HU of the recrystallized structure of the sheet thickness surface layer portion (1/8t position) were measured at 10 points at intervals of 10 μm in the direction parallel to the rolling direction. The Vickers hardness was measured at HV10 according to JIS Z 2244 (2009). Specific measurement conditions are as follows: indenter = Vickers quadrangular pyramid diamond indenter with facing angle of 136°, indentation load = 10 gf, indentation time = 20 sec.
[0051]
The fracture surface transition temperature was measured by performing a Charpy test in accordance with JIS Z 2242. In this example, when the fracture surface transition temperature was less than 0°C, it was determined that the toughness was good.
[0052]
In addition, the magnetic properties of the obtained non-oriented electrical steel sheets were measured according to JIS C 2556.
[0053]
For iron loss, a 55 mm square sample was taken from the non-oriented electrical steel sheet, and W15/50 (iron loss when the steel sheet was magnetized at 50 Hz to a magnetic flux density of 1.5 T) was measured using a Single Sheet Tester (SST). evaluated. The magnetic flux density was evaluated using B50, which is the magnetic flux density at a magnetic field strength of 5000 A/m. The measurement results are also shown in Table 3. Samples with a B50 of 1.60 or more and a W15/50 of 2.6 W/kg or less were judged to pass the electromagnetic properties.
[0054]
[table 1]

[0055]
[Table 2]

[0056]
[Table 3]

[0057]
By using the hot-rolled steel sheet for non-oriented electrical steel sheet of the present invention, the steel sheet does not break in pickling, and the non-oriented hot-rolled steel sheet for non-oriented electrical steel sheet subjected to conventional hot-rolled sheet annealing is used. It was confirmed that a non-oriented electrical steel sheet having excellent properties similar to the grain-oriented electrical steel sheet can be obtained.
[0058]

Using the steel shown in Table 1 and the manufacturing method shown in Table 2, hot-rolled steel sheets for non-oriented electrical steel sheets were similarly produced, and then non-oriented electrical steel sheets were obtained.
[0059]
For the obtained hot-rolled steel sheet, in addition to the measurement results of Example 1, the hardness H of the worked structure at the center of the thickness (1/2t position) at the end in the width direction of the hot-rolled steel sheet for non-oriented electrical steel sheet. A hardness difference H S = H D - H U between D and the hardness H U of the recrystallized structure at the sheet thickness surface layer portion (1/8t position) was measured. Magnetic properties of the non-oriented electrical steel sheets were measured in the same manner as in Example 1. Table 4 shows the results.
[0060]
[Table 4]

[0061]
By setting the hardness difference HS between the hardness H D of the processed structure at the central portion of the plate thickness (1/2t position) and the hardness HU of the recrystallized structure at the surface layer portion of the plate thickness (1/8t position) within HV20. , it was confirmed that even better toughness can be obtained.
[0062]

Inventive Example C1 and Comparative Example c16 disclosed in Table 3 were subjected to cold rolling and finish annealing under the cold rolling conditions of 75% rolling reduction and the soaking conditions in the finish annealing conditions of 1000°C for 30 seconds, A non-oriented electrical steel sheet was used. The hardness of these non-oriented electrical steel sheets was measured at the plate thickness center portion (1/2t position) at the end portion in the plate width direction.
　The hardness of the edges of the non-oriented electrical steel sheets was measured according to the following procedure. A cross section parallel to the rolling direction at a position 10 mm from the width direction end face of the steel plate to the width direction center (width direction end) was used as the measurement surface. On this measurement surface, the hardness at the thickness center (1/2t position) was measured at 10 points at 10 μm intervals in the direction parallel to the rolling direction. The Vickers hardness was measured at HV10 according to JIS Z 2244 (2009). Specific measurement conditions are as follows: indenter = Vickers quadrangular pyramid diamond indenter with facing angle of 136°, indentation load = 10 gf, indentation time = 20 sec. Table 5 shows the measurement results.
[0063]
[Table 5]

[0064]
C1 and c16 have the same chemical composition, and the hardness at the stage of non-oriented electrical steel sheet is almost the same level, but the worked structure hardness at the stage of hot-rolled steel sheet is greatly different. In other words, it is difficult to estimate the hardness at the stage of the hot-rolled steel sheet from the hardness measured at the stage of the non-oriented electrical steel sheet.
Industrial applicability
[0065]
According to the present invention, even when annealing is omitted in the hot rolling process, the hot-rolled sheet has sufficient toughness, and when it is made into a non-oriented electrical steel sheet, it achieves both low core loss and high magnetic flux density. A hot-rolled steel sheet for non-oriented electrical steel sheet can be provided. As a result, non-oriented electrical steel sheets with low iron loss and high magnetic flux density can be produced stably without breakage. It can fully respond to production, and its industrial value is extremely high.
The scope of the claims
[Claim 1]
in % by mass,
　　C: 0.0010 to 0.0050%,
　　Si: 1.90% to 3.50%,
Al: 0.10% to 3.00%,
　Mn: 0.05 to 2.00%,
　　P: 0.100% or less,
　　S: 0.005% or less,
　　N: 0.0040% or less,
B: 0.0060% or less,
Sn: 0-0.50%,
Sb: 0 to 0.50%,
　　Cu: 0 to 0.50%,
REM: 0 to 0.0400%,
　　Ca: 0 to 0.0400%, and
　Mg: 0 to 0.0400%
A hot-rolled steel sheet for a non-oriented electrical steel sheet containing the balance Fe and impurities,
A non-oriented electrical steel sheet, wherein the hardness HD of the processed structure at the sheet thickness center (1/2t position) is Hv 220 or less at the end in the width direction of the hot-rolled steel sheet for non-oriented electrical steel sheet. Hot-rolled steel sheet for
[Claim 2]
Hardness difference H S between the hardness H D of the worked structure and the hardness H U of the recrystallized structure of the plate thickness surface layer portion (1/8t position) at the end in the plate width direction of the hot-rolled steel sheet for non-oriented electrical steel plate The hot-rolled steel sheet for non-oriented electrical steel sheet according to claim 1, characterized in that =H D-H U is within Hv20.
[Claim 3]
% by mass, Sn: 0.01% or more and 0.50% or less, Sb: 0.01% or more and 0.50% or less, Cu: 0.01% or more and 0.50% or less, REM: 0.0005% or more, 0.040 0% or less, Ca: 0.0005% or more and 0.0400% or less, Mg: 0.0005% or more and 0.0400% or less 1 or 2 or more 2. The hot-rolled steel sheet for non-oriented electrical steel sheet according to 2.