JP5245647B2 - Hot-rolled steel sheet excellent in press formability and magnetic properties and method for producing the same - Google Patents

Description

  The present invention relates to a hot-rolled steel sheet excellent in press formability and magnetic properties suitable as a steel sheet for use in relays, high-efficiency motors and solenoids excellent in responsiveness applied to automobiles, mobile phones, digital cameras, and the like, and its manufacture It is about the method.

Electromagnetic soft iron (equivalent to SUYP) is used in automobiles, various communication relays and motor yokes, but recently, with the spread of mobile phones and digital cameras, the application to small high-performance motors is also increasing.
On the other hand, carbon steel suitable for required performance has often been applied to relatively large motors and relays. However, for such relatively large devices, there is a growing demand for higher efficiency from the viewpoint of global environmental problems, and from the viewpoint of cost, it is a pure alternative as a carbon steel alternative that has been used conventionally. Application of iron-based electromagnetic soft iron is being studied.

With respect to the application of pure iron-based electromagnetic soft iron, for example, Patent Document 1 and Patent Document 2 disclose an example of application as a steel plate for a CRT support frame.
Both of these improve grain growth by adjusting the ingredients and improve the magnetic properties by coarsening the grain size of the hot-rolled sheet by rolling in a two-phase region of Ar ₃ or less during hot rolling. It is a technique to try.
However, such a coarsening of the ferrite grains has a problem that although the magnetic properties are improved, the press formability is deteriorated and it cannot be processed into a desired shape.
JP-A-3-53023 JP-A-2-250942

  Moreover, although it is not a technique of a magnetic shielding material, in the field of a general steel plate for processing, there is a method of increasing the r value of a steel plate by performing cold rolling in order to improve press formability. However, increasing the r value is synonymous with increasing the degree of integration of the (111) plane orientation of the material. Since the (111) plane orientation is a disadvantageous aspect of the magnetic characteristics, the deterioration of the essential magnetic characteristics. Is inevitable. Conventionally, in the field of general steel sheets for processing, there is no example that achieves both high r value and high magnetic properties.

On the other hand, there are Patent Literature 3 and Patent Literature 4 as cold-rolled electromagnetic soft iron and steel plates, for example.
The technology disclosed in Patent Document 3 is limited to components for improving grain growth, coarsening in the final product and (100) plane orientation in the final product due to the coarse grain structure of the hot rolled sheet. This is a technique for improving the magnetic properties by integrating in However, the coarse grain structure accumulated in the (100) plane orientation has a problem in that press formability is difficult and its use is limited.
Moreover, the technique disclosed in Patent Document 4 is a technique for improving grain growth properties by limiting components and inclusions. However, in this case as well, as in Patent Document 3, in the final product, a coarse grain structure accumulated in the (100) plane orientation is obtained, and thus there remains a problem in press formability.
JP-A-5-78742 Japanese Patent Laid-Open No. 11-50207

  As described above, the conventional electromagnetic soft iron and steel sheet has been focused on the coarsening for improving the magnetic properties, so that only the steel sheet inferior in press formability is obtained at present.

Patent Document 5 is known as a device that has been studied to achieve both of these conflicting required characteristics. The technique of Patent Document 5 is to make a fine grain structure in the hot-rolled sheet stage in order to increase the accumulation on the (111) surface advantageous for press formability in the final product (cold-rolled steel sheet). As a material such as a motor yoke material and a solenoid cover, which are required to be large and have high efficiency, a hot-rolled steel plate having a larger thickness is required, so that it cannot be manufactured by applying this technology.
JP 2007-277699 A

  The present invention has been developed in view of the above-mentioned present situation, and an object thereof is to provide a hot-rolled steel sheet having excellent magnetic properties and excellent press formability together with an advantageous manufacturing method thereof.

The inventors have conducted intensive research to solve the above-mentioned problems. In particular, as a result of radically reviewing the alloy design of the steel sheet, the degree of integration on the (111) surface, which is advantageous for press formability in a hot-rolled steel sheet, is increased. In order to obtain coarse grains advantageous for magnetic properties, it has been found that it is effective to terminate the hot rolling at a ferrite region temperature and then to obtain a structure annealed at an appropriate temperature.
That is, the strain that promotes the development of (111) is accumulated in the hot rolling final rolling process, and in the next annealing process, the (111) orientation plane can be developed simultaneously with the recrystallization starting from the strain as a nucleus, and the annealing temperature can be changed. It was found that by controlling the size of the crystal grains, a hot-rolled steel sheet having excellent magnetic shielding properties and press formability can be obtained.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. % By mass
C: 0.005% or less,
Si: 0.1% or less,
Mn: 0.1-0.5%
P: 0.1% or less,
S: 0.01% or less,
sol.Al: 0.004% or less,
N: 0.005% or less and O: 0.02% or less, with the balance being the composition of Fe and inevitable impurities, an average crystal grain size of 40 μm or more, and an average Rankford value (average r value): 1.0 or more, A hot-rolled steel sheet with excellent press formability and magnetic properties, characterized by a coercive force of 79.6 A / m or less.

2. 1. A hot rolled steel sheet having excellent press formability and magnetic properties, wherein the in-plane anisotropy (Δr value) of the r value is 0.3 or less.

3. % By mass
C: 0.005% or less,
Si: 0.1% or less,
Mn: 0.1-0.5%
P: 0.1% or less,
S: 0.01% or less,
sol.Al: 0.004% or less,
Steel containing N: 0.005% or less and O: 0.02% or less, with the balance being Fe and inevitable impurities, heated to 1000-1180 ° C, and then hot-rolled at a finishing temperature of 600-750 ° C A method for producing a hot-rolled steel sheet excellent in press formability and magnetic properties, characterized by annealing in a temperature range of 750 to 850 ° C. after completion.

4). 3. A method for producing a hot-rolled steel sheet excellent in press formability and magnetic properties, characterized in that the annealing temperature after hot rolling is 750 ° C. or higher and lower than 800 ° C. in 3 above.

  According to the present invention, a hot rolled steel sheet having an average crystal grain size of 40 μm or more, an average Rankford value (average r value) of 1.0 or more, and a coercive force of 79.6 A / m or less is obtained. Is excellent in both magnetic properties and press formability, and is extremely useful in industry.

The first point of the hot-rolled steel sheet of the present invention is to reduce the amount of solute Al in the steel and suppress the formation of fine AlN that significantly impairs the grain growth property in order to improve the grain growth property.
The second point is to improve the press formability by collecting the coarse crystal grains on the (111) plane by performing the hot rolling temperature at the ferrite region temperature and then annealing at 750 to 850 ° C. .

Hereinafter, the present invention will be specifically described.
First, the reason why the component composition of the steel slab is limited to the above range in the present invention will be described. Unless otherwise specified, “%” in relation to ingredients means mass%.
C: 0.005% or less Since C is an element that forms carbides and deteriorates magnetic properties, its content is preferably small. Therefore, the upper limit of C is 0.005%. More preferably, it is 0.004% or less.

Si: 0.1% or less
Si is an element useful not only as a deoxidizer but also as a solid solution strengthening element. However, excessive addition degrades the surface properties, so the upper limit is made 0.1%. Moreover, when using for the use for which chemical conversion treatment property is required in order to improve corrosion resistance, it is preferable to make the upper limit into 0.03% from a viewpoint of the adhesiveness of a chemical conversion treatment film.

Mn: 0.1-0.5%
Since Mn is an element that forms sulfides and improves hot brittleness, it needs to be added in an amount of 0.1% or more. On the other hand, the upper limit is 0.5% from the viewpoint of cost increase.

P: 0.1% or less Since P is effective as a solid solution strengthening element, it is preferable to contain 0.005% or more. However, if it exceeds 0.1%, it segregates at the grain boundary and inhibits the grain growth, so the upper limit. Is 0.1%.

S: 0.01% or less Since S is an element that forms sulfides and degrades magnetic properties, the upper limit is made 0.01%.

sol.Al: 0.004% or less
sol.Al inhibits grain growth by forming fine nitrides and significantly deteriorates magnetic properties. Therefore, it is desirable to reduce the content of sol.Al as much as possible, and the upper limit is made 0.004%. More preferably, it is 0.002% or less.

N: 0.005% or less N is desirably as small as possible, and if contained in excess of 0.005%, precipitates are formed to inhibit grain growth and deteriorate magnetic properties, so the upper limit is made 0.005%. More preferably, it is 0.003% or less.

O: 0.02% or less O is more preferably contained in a smaller amount because O generates inclusions and deteriorates magnetic properties and workability. Therefore, the upper limit of O is 0.02%. However, excessive reduction leads to an increase in solute Al and solute Si, so the lower limit is preferably 0.003%.

The component composition range of the present invention has been described above. In the present invention, the crystal grain size of the steel sheet and the Rankford value (r value) indicating the degree of integration on the (111) plane are also important.
Average crystal grain size: 40 μm or more The crystal grain size is preferably coarse in order to obtain magnetic properties necessary for the magnetic shield material, particularly low coercive force. That is, when the average crystal grain size is less than 40 μm, the coercive force becomes higher than 79.6 A / m, which is the target of the present invention.

Average rank ford value (average r value) ≧ 1.0
The r value is improved by controlling the crystal orientation of the steel sheet and increasing the accumulation on the (111) plane. In the present invention, the average value (average r value) of the Rankford value (r value) is limited to 1.0 or more to ensure good press formability.
Here, the average r value is obtained by the following equation (1).
Average r value = (r _L + 2 × r _D + r _C ) / 4— (1)
However, r _L is a direction parallel to the rolling direction, r _D is a 45 ° direction with respect to the rolling direction, and r _C is a r value in the 90 ° direction with respect to the rolling direction.

In order to increase the accumulation on the (111) surface in a hot-rolled steel sheet, finish rolling in the ferrite region and subsequent annealing are necessary conditions. The finish rolling temperature only needs to be the ferrite region temperature of the steel, and the lower the value, the higher the Lankford value is expected. On the other hand, the rolling load is increased, and therefore the finishing rolling temperature is set in consideration of the capability of the rolling mill.
The higher the annealing temperature, the larger the grain size of the hot-rolled steel sheet, which is the final product, which is advantageous for the magnetic properties, but the in-plane anisotropy of Δr, that is, the r value increases, and the flange end after drawing Since the shape becomes uneven, an upper limit is set and it is necessary to set the temperature to 850 ° C. or lower. Especially preferably, it is less than 800 degreeC.

Here, Δr is obtained by the following equation (2).
Δr value = (r _L −2 × r _D + r _C ) / 2 (2)
However, r _L is a direction parallel to the rolling direction, r _D is a 45 ° direction with respect to the rolling direction, and r _C is a r value in the 90 ° direction with respect to the rolling direction.
In the present invention, it is preferable to satisfy Δr ≦ 0.3 in order to prevent anisotropy problems at the time of drawing, such as unevenness of the flange end shape after the drawing. Particularly preferably, Δr ≦ 0.2.

  Note that the hot-rolled steel sheet of the present invention can provide a material at a lower cost because the number of processes is less than that of a cold-rolled steel sheet. However, since it is difficult to manufacture a thin product, the thickness is preferably 1.2 mm or more. It is.

Next, the manufacturing conditions of the present invention will be described.
The steel slab adjusted to the above preferred component composition is heated to 1000-1180 ° C. and then hot-rolled at a finishing temperature of 600-750 ° C. If the heating temperature is less than 1000 ° C, the size of the initial austenite grains cannot be obtained sufficiently, so it is difficult to obtain a coarse grain size after finish rolling. On the other hand, if it exceeds 1180 ° C, MnS and the like are dissolved. The heating temperature was limited to the range of 1000 to 1180 ° C. because it was finely deposited on the hot-rolled sheet and the grain growth property during the subsequent annealing was hindered.
Further, the finish rolling temperature needs to be a ferrite single phase region. Therefore, in the present invention, the finish rolling temperature is limited to a range of 600 to 750 ° C.

Next, after winding, annealing is performed to coarsen the crystal grains.
In winding, if the winding temperature is too low, the shape of the steel sheet may be deteriorated. On the other hand, if the winding temperature is too high, loss due to an increase in the amount of surface scale generation (loss of steel material) increases and costs increase. It is preferable that the temperature be about 650 ° C.
In the subsequent annealing, if the annealing temperature is less than 750 ° C, sufficient crystal grain coarsening is not achieved. On the other hand, if it exceeds 850 ° C, Δr, that is, in-plane anisotropy increases, and the flange end shape after drawing Therefore, the annealing temperature was limited to the range of 750 to 850 ° C. In particular, from the viewpoint of reducing Δr, the temperature is preferably less than 800 ° C.

After the above annealing, pickling and temper rolling as necessary to obtain a product plate. Thus, a hot rolled steel sheet having excellent magnetic properties and press formability can be obtained.
In addition, the hot-rolled steel sheet of the present invention may be subjected to a plating treatment for improving the corrosion resistance such as zinc, chromium and nickel, or a treatment for improving the corrosion resistance such as chemical conversion treatment.

Example 1
The steel slab having the composition shown in Table 1 was heated at 1100 ° C. for 1 hour, and then hot-rolled under the conditions shown in Table 2 to obtain a hot-rolled sheet having a thickness of 2.4 mm. Then, after pickling, annealing was performed at the temperature shown in Table 2 to obtain a product plate.

Each of the hot-rolled steel sheets thus obtained is defined in JIS Z 2201 from the L direction (rolling direction), D direction (a direction that forms 45 ° with the rolling direction), and C direction (a direction that forms 90 ° with the rolling direction). No. test piece was cut out and each r value (r _L , r _D , r _C ) was calculated according to JIS Z 2254, and average r value and in-plane anisotropy (Δr value) were calculated according to the following formula did. The applied plastic strain was 15% within the range of uniform elongation as specified.
Average r value = (r _L + 2 × r _D + r _C ) / 4
Δr value = (r _L −2 × r _D + r _C ) / 2
A ring-shaped test piece having an inner diameter of 33 mm and an outer diameter of 45 mm was sampled, and magnetic measurement was performed with a maximum excitation magnetic field of 796 (A / m).
Furthermore, the average crystal grain size of the steel sheet was measured according to the cutting method of JIS G 0552 (1998).
The obtained results are also shown in Table 2.

  As shown in Table 2, an improvement in the average r value was observed on the side where the finish rolling temperature was low. This is probably because the (111) plane orientation increased in proportion to the amount of strain accumulated by rolling in the ferrite region. On the other hand, improvement of the average r value was recognized also on the higher annealing temperature side. This reason is considered to be due to the fact that the crystal grain size is increased. In this case, since the crystal grains are particularly large, the coercive force is kept at a low level.

Example 2
In the same manner as in Example 1, steel pieces having the composition shown in Table 3 were processed under the conditions shown in Table 4 to obtain product plates.
The average grain size, average r value, Δr value, and coercivity of the hot rolled steel sheet thus obtained are shown in Table 4.

  In the inventive example obtained according to the present invention, a low Δr value and a low coercive force were obtained together with a high average r value, but in the comparative example in which the component composition deviated from the appropriate range, the desired characteristics were not obtained, and in particular the retention It was inferior in terms of magnetic force.

Claims (4)

% By mass
C: 0.005% or less,
Si: 0.1% or less,
Mn: 0.1-0.5%
P: 0.1% or less,
S: 0.01% or less,
sol.Al: 0.004% or less,
N: 0.005% or less and O: 0.02% or less, with the balance being the composition of Fe and inevitable impurities, an average crystal grain size of 40 μm or more, and an average Rankford value (average r value): 1.0 or more, A hot-rolled steel sheet with excellent press formability and magnetic properties, characterized by a coercive force of 79.6 A / m or less.   The hot-rolled steel sheet having excellent press formability and magnetic properties according to claim 1, wherein the in-plane anisotropy (Δr value) of the r value is 0.3 or less. % By mass
C: 0.005% or less,
Si: 0.1% or less,
Mn: 0.1-0.5%
P: 0.1% or less,
S: 0.01% or less,
sol.Al: 0.004% or less,
Steel containing N: 0.005% or less and O: 0.02% or less, with the balance being Fe and inevitable impurities, heated to 1000-1180 ° C, and then hot-rolled at a finishing temperature of 600-750 ° C A method for producing a hot-rolled steel sheet excellent in press formability and magnetic properties, characterized by annealing in a temperature range of 750 to 850 ° C. after completion.   The method for producing a hot-rolled steel sheet excellent in press formability and magnetic properties according to claim 3, wherein the annealing temperature after hot rolling is set to 750 ° C or higher and lower than 800 ° C.