JP2003160836A - Drawable high-strength steel thin-sheet with burring property superior in shape freezability, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drawable high-strength steel thin-sheet with a burring property superior in shape freezability, and a manufacturing method therefor. <P>SOLUTION: The steel sheet comprises 0.01-0.1% C, 0.03% or less S, 0.005% or less N, 0.05-0.5% Ti in such a range as to satisfy Ti-48/12C-48/14N-48/32 S≥0%, and the balance Fe with unavoidable impurities, having 3 or more of an average random intensity ratio of X-rays for grains orientated in ä100}<011> to ä223}<110> on the sheet face in at least 1/2 thickness of the sheet, having 3.5 or less of an average random intensity ratio of X-rays for grains with three orientations of ä554}<225>, ä111}<112>, and ä111}<110>, having 1-3.5 of arithmetic average roughness Ra on at least one of both surfaces, and having the composition with a lubricating effect coated thereon. The manufacturing method therefor is also disclosed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a burring high-strength thin steel sheet which is excellent in shape fixability and is capable of being drawn, and is particularly suitable for a steel sheet having a texture which is disadvantageous for drawing. The drawability can be obtained.

[0002]

2. Description of the Related Art In recent years, application of light metals such as Al alloys and high-strength steel sheets to automobile members has been promoted for the purpose of weight reduction in order to improve fuel efficiency of automobiles. However, although light metals such as Al alloys have the advantage of high specific strength, they are significantly more expensive than steel, so their application is limited to special applications. Therefore, in order to promote the weight reduction of automobiles in a wider range, it is strongly required to apply inexpensive high strength steel sheets.

However, when bending deformation is applied to a high-strength steel sheet, the shape after processing tends to return to the shape before processing apart from the shape of the processing jig because of its high strength. The phenomenon of returning to the direction of the original shape after processing is called spring back. When this spring back occurs, it is not possible to obtain the desired shape of the processed part. Therefore, in the conventional car body, it has been mainly used only for the high strength steel plate of 440 MPa or less. For automobile bodies, although it is necessary to use high-strength steel sheets of 490 MPa or higher to reduce the weight of the vehicle body, the reality is that there are no high-strength steel sheets with few spring backs and good shape fixability. Is. Needless to say, it is needless to say that improving the shape fixability of a high-strength steel plate or mild steel plate of 440 MPa or less after processing is extremely important for improving the shape accuracy of products such as automobiles and home appliances. .

In Japanese Unexamined Patent Publication No. 10-72644, the amount of spring back (dimensions in the present invention is characterized in that the degree of accumulation of {200} texture in a plane parallel to the rolling surface is 1.5 or more. An austenitic stainless cold-rolled steel sheet with low accuracy is disclosed. However, it does not describe any technique for reducing the springback phenomenon and wall warpage phenomenon of ferritic steel sheets.

Further, as a technique for reducing the springback amount of ferritic stainless steel, Japanese Patent Laid-Open No. 2001-2001
Japanese Patent No. 325050 discloses an invention in which the reflected X-ray intensity ratio of the {100} plane parallel to the plate surface is 2 or more in the texture in the central part of the plate thickness. However, the present invention has no description about reduction of wall warpage, and {100} <011> ~
There is no regulation on {223} <110> direction group and {112} <110> which is an important direction for reducing wall warpage.

Further, in WO00 / 06791, a ferrite thin steel sheet having a ratio of {100} plane to {111} plane of 1 or more was disclosed for the purpose of improving shape fixability.
In the present invention, like the present invention, {100} <011> ~
{223} <110> direction group, and {554} <22
5>, {111} <112> and {111} <110
The value of the X-ray random intensity ratio of> is not described, and at the same time, the technique for improving the drawability is not disclosed.

Further, Japanese Patent Laid-Open No. 2001-64750 discloses a cold rolled steel sheet having a reflected X-ray intensity ratio of 3 or more on the {100} plane parallel to the sheet surface as a technique for reducing the amount of springback. , The present invention is the thickest surface {10
0} surface reflection X-ray intensity ratio is specified, and {100} at a plate thickness of 1 / 2t, which is the specification in the present invention.
The X-ray measurement position is different from the average X-ray intensity ratio of the <011> to {223} <110> orientation groups. Also, {554} <2
25>, {111} <112> and {111} <11
No mention is made of 0> direction, and at the same time, there is no disclosure of a technique for improving drawability.

Further, Japanese Unexamined Patent Publication No. 2000-297349 discloses a hot rolled steel sheet having an excellent in-plane anisotropy Δr of an r value of 0.2 or less as a steel sheet having a good shape fixability. . However, the present invention is characterized by improving the shape fixability by lowering the yield ratio, and regarding texture control for the purpose of improving the shape fixability based on the idea described in the present invention, ,Not listed.

[0009]

SUMMARY OF THE INVENTION Therefore, the present invention provides a burringable high strength thin steel sheet which is excellent in shape fixability so as to obtain good drawability even in a steel sheet having a texture which is disadvantageous for drawing and The manufacturing method is provided.
That is, an object of the present invention is to provide a burring high-strength thin steel sheet that can be drawn and a manufacturing method capable of stably manufacturing the steel sheet at low cost.

[0010]

The inventors of the present invention have taken into consideration the manufacturing process of the high-strength thin steel sheet that is produced on an industrial scale by the production equipment that is normally adopted at present, and the shape of the high-strength thin steel sheet. We have conducted intensive studies to achieve both freezing and squeezing properties. As a result, {100} <011> to {223} <110> of the plate surface at least ½ of the plate thickness
The average value of the X-ray random intensity ratio of the azimuth group is 3 or more, and
The average value of the X-ray random intensity ratio in the three directions of {554} <225>, {111} <112>, and {111} <110> is 3.5 or less, and the arithmetic mean roughness of at least one steel plate surface. A composition having a lubricating effect is applied to a steel plate having Ra of 1 to 3.5, and 0 to
It was newly found that at least one of the friction coefficients in the rolling direction at 200 ° C and in the direction perpendicular to the rolling direction is 0.05 to 0.2, which is very effective in achieving both shape fixability and drawability. It is an invention.

That is, the gist of the present invention is as follows. (1) In mass%, C = 0.01 to 0.1%, S ≦ 0.03%, N ≦ 0.005%, Ti = 0.05 to 0.5% are included, and Ti-48 is further included. / 12C-48 / 14N-48 / 32S ≧ 0% Ti is contained, and the balance is Fe and unavoidable impurities.
{100} <011> to {223} <of the plate surface in thickness
The average value of the X-ray random intensity ratios of the 110> orientation group is 3 or more and the average value of the X-ray random intensity ratios of the three orientations of {554} <225>, {111} <112> and {111} <110>. Is 3.5 or less, and a composition having a lubricating effect is applied to a steel sheet having an arithmetic average roughness Ra of 1 to 3.5 on at least one of the front and back surfaces of the shape freezing. High strength thin steel plate with excellent burring properties that can be drawn.

(2) 0 to 0 on the surface of the steel sheet described in (1) above
A burring-type high-strength steel sheet capable of being drawn, which is excellent in shape fixability and has a coefficient of friction of 0.05 to 0.2 at 200 ° C.

(3) The steel according to (1) or (2) above further contains, in mass%, Nb = 0.01 to 0.5%, and further Ti + 48 / 93Nb-48 / 12C-48. / 14N-
A drawable burring high-strength thin steel sheet having excellent shape fixability, which is a steel containing Ti and Nb in a range satisfying 48 / 32S ≧ 0% and the balance being Fe and inevitable impurities.

(4) The steel according to any one of the above items (1) to (3) further contains Si = 0.0% by mass.
1 to 2%, Mn = 0.05 to 3%, P ≤ 0.1%, Al = 0.005 to 1%, excellent shape fixability, squeezable burring property, high strength and thinness steel sheet.

(5) The steel according to any one of (1) to (4) above is characterized by further containing B = 0.0002 to 0.002% in mass%. A burring, high-strength thin steel sheet with excellent shape-freezing properties that can be drawn.

(6) The steel according to any one of (1) to (5) above is characterized by further containing Cu = 0.2 to 1.2% in mass%. A burring, high-strength thin steel sheet with excellent shape-freezing properties that can be drawn.

(7) The steel according to any one of (1) to (6) above is characterized by further containing, in mass%, Ni = 0.1 to 0.6%. A burring, high-strength thin steel sheet with excellent shape-freezing properties that can be drawn.

(8) The steel according to any one of the above (1) to (7) further contains, in mass%, Ca = 0.005 to 0.002% and REM = 0.00.
A burring burring high-strength thin steel sheet having excellent shape-freezing properties, characterized by containing 05 to 0.02% of one or two kinds.

(9) The steel according to any one of the above (1) to (8), further in mass%, Mo = 0.05 to 1%, V = 0.02 to 0.2. %, Cr = 0.01 to 1%, Zr = 0.02 to 0.2%, and a burring high strength steel sheet having excellent shape fixability capable of being drawn.

(10) Excellent shape fixability, which is characterized in that the drawable burring high-strength steel sheet according to any one of (1) to (9) is galvanized. High strength thin steel plate with burring property that can be drawn.

(11) During hot rolling to obtain a thin steel sheet having the composition described in any one of (1) to (9), a steel piece having the composition is subjected to Ar3 transformation after rough rolling. Shape freezing, characterized in that finish rolling with a total reduction of steel plate thickness of 25% or more in a temperature range of point temperature + 100 ° C or less, then cooling and winding, and then applying a composition having a lubricating effect. A method for producing a burring high-strength thin steel sheet which is excellent in drawability and which can be drawn.

(12) In the hot rolling, lubrication rolling is performed in finish rolling after rough rolling, and the drawable burring high strength thin steel sheet excellent in shape fixability as described in (11) above. Production method.

(13) In the hot rolling as set forth in (11) or (12) above, descaling is performed after the rough rolling is finished, and descaling is performed. Manufacturing method.

[0024]

(14) In order to obtain a thin steel sheet having the composition described in any one of (1) to (9) above, a billet having the composition is hot-rolled, followed by pickling, and a steel plate thickness reduction rate. 80
After cold rolling of less than%, recovery temperature above Ac3 transformation point temperature +
Holding at a temperature range of 100 ° C. or lower for 5 to 150 seconds, and performing a heat treatment in a cooling step, and then applying a composition having a lubricating effect. Steel plate manufacturing method.

(15) In the manufacturing method according to any one of (11) to (13), after hot rolling, the steel sheet surface is galvanized by being immersed in a galvanizing bath,
A method for producing a burring high-strength steel sheet capable of being drawn, which is excellent in shape fixability, characterized by applying a composition having a lubricating effect.

(16) In the manufacturing method described in (14) above, after the heat treatment is finished, the surface of the steel sheet is galvanized by being immersed in a galvanizing bath, and then a composition having a lubricating effect is applied. A method for producing a burring high-strength thin steel sheet which is excellent in shape fixability and which can be drawn.

(17) In the production method according to (15) or (16), the composition having a lubricating effect is applied after dipping in a zinc plating bath for galvanizing and then alloying treatment. A method for producing a burring high strength steel sheet capable of being drawn, which is excellent in shape fixability.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION First, the details of the present invention relating to (1) or (2) above will be described. In order to obtain excellent shape fixability, {100} <01 of the plate surface at 1/2 thickness
The average value of the X-ray random intensity ratio of the 1> to {223} <110> orientation groups must be 3 or more. If this is less than 3, the shape fixability will be poor.

Here, {100} <011> to {22
3} The average value of the X-ray random intensity ratio of the <110> direction group is the main direction included in this direction group, {100} <01.
1>, {116} <110>, {114} <110>,
{113} <110>, {112} <110>, {33
5} <110> and {223} <110> X-ray diffraction intensities calculated by the vector method based on the {110} pole figure, or {110}, {100},
It was determined from a three-dimensional texture calculated by the series expansion method using a plurality of pole figures (preferably three or more) of the {211} and {310} pole figures.

For example, the X-ray random intensity ratio of each crystal orientation in the latter method is φ2 = 4 for a three-dimensional texture.
(001) [1-10], (116) at 5 ° cross section
[1-10], (114) [1-10], (113)
[1-10], (112) [1-10], (335)
The strengths of [1-10] and (223) [1-10] may be used as they are. However, {100} <011> to {22
3} The average value of the X-ray random intensity ratio of the <110> orientation group is the arithmetic average of the above orientations. If it is not possible to obtain the intensities in all of the above directions, {100} <01
1>, {116} <110>, {114} <110>,
You may substitute by the arithmetic mean of each direction of {112} <110> and {223} <110>.

Further, {554} <225>, {111}
The average value of the X-ray random intensity ratios in the three directions of <112> and {111} <110> must be 3.5 or less. If this exceeds 3.5, {100} <011> ~
Even if the average value of the X-ray random intensity ratio of the {223} <110> orientation group is appropriate, good shape fixability cannot be obtained. {554} <225>, {111} <112>
And the average value of the X-ray random intensity ratios in the three directions of {111} <110> may be obtained from the three-dimensional texture calculated in the same manner as the above method.

More preferably, the scope of the present invention is
The average value of the X-ray random intensity ratio of the {100} <011> to {223} <110> orientation groups is 4 or more, {554} <2.
25>, {111} <112> and {111} <11
The arithmetic mean value of the X-ray random intensity ratio of 0> is less than 2.5. The reason why the X-ray intensity of the crystal orientation described above is important for shape fixability during bending is not necessarily clear, but it is presumed that it is related to the slip behavior of the crystal during bending deformation. .

In order to obtain a sample to be subjected to X-ray diffraction, a test piece cut to 30 mmφ from a position of 1/4 W or 3/4 W of the plate width is ground with three peaks, and then strain is removed by chemical polishing or electrolytic polishing. To produce. In addition,
The crystal orientation represented by {hkl} <uvw> means that the normal direction of the plate surface is parallel to <hkl> and the rolling direction is <uvw>.
It is shown to be parallel to. The crystal orientation measurement by X-ray can be performed, for example, by the new edition of the Kariti X-ray diffraction theory (published in 1986, translated by Gentaro Matsumura, Agne Co., Ltd.) 274-296
Follow the method described on page.

Next, the state of the steel sheet surface, which is important for ensuring the drawability in the present invention, will be described. In the present invention, the arithmetic mean roughness Ra of at least one of the front and back surfaces of the steel sheet before being coated with the composition having a lubricating effect
Is 1 or more and 3.5 or less. This arithmetic average roughness Ra is 1
If the amount is less than the range, it becomes difficult to retain the composition having a lubricating effect applied later on the surface of the steel sheet. On the other hand, if the arithmetic average roughness Ra exceeds 3.5, a sufficient lubricating effect cannot be obtained even if a composition having a lubricating effect is applied. Therefore, at least one of the front and back surfaces of the steel sheet has an arithmetic average roughness Ra of 1 to 3.5. It is preferably 1 to 3. here,
The arithmetic average roughness Ra is the arithmetic average roughness Ra described in JIS B0601-1994.

Furthermore, at least one of the coefficient of friction in the rolling direction at 0 to 200 ° C. and the direction perpendicular thereto of the steel sheet after the composition having the lubricating effect is applied is 0.0.
It is set to 5 or more and 0.2 or less. If the coefficient of friction is less than 0.05, the crease holding force (BHF: Blank Holding Fo) is increased in order to improve shape fixability during press molding.
(rce) is increased, the steel sheet cannot be held and flows in, deteriorating the shape fixability.

On the other hand, when the coefficient of friction exceeds 0.2, the wrinkle holding force (BHF: Blank Holding Force) is increased.
Even if e) is reduced within a practical range, the flowability of the steel sheet is reduced, and therefore drawability may be reduced. Therefore, at least one of the friction coefficients is 0.05 to 0.2.

In the temperature range in which the coefficient of friction is limited, frost or the like adheres at temperatures below 0 ° C., making proper evaluation impossible. If it exceeds 200 ° C, the composition having a lubricating effect applied to the surface of the steel sheet may become unstable. Therefore, the temperature range limiting the friction coefficient is set to 0 to 200 ° C.

Here, the friction coefficient means that after a composition having a lubricating effect is applied to the surface of a steel sheet to be evaluated, it is sandwiched between two flat plates having a Vickers hardness of Hv600 or more, and the surface pressure is A vertical force (F) is applied to the surface of the steel sheet so as to be 1.5 to ² kgf / mm ^2, and then the steel sheet is pulled out. At that time, the ratio of the pulling force f to F (f
/ F) is defined as the friction coefficient.

Next, the drawability index of the steel sheet is obtained by dividing the maximum diameter (D) that can be drawn out by the cylindrical punch diameter (d) when the steel sheet is processed into a circular shape and then drawn using a cylindrical punch. Defined value (D / d). In this measurement, the circular processing size of the steel sheet is various diameters of 300 to 400φ, the diameter of the cylindrical punch is 175φ, the bottom shoulder portion is 10R, and the die surface shoulder portion is 15R.

Next, the microstructure of the steel sheet according to the present invention will be described. The microstructure of the steel sheet is preferably a ferrite single phase in order to ensure excellent burring workability (hole expandability). However, some bainite may be included if necessary. In order to ensure good burring workability, the volume fraction of bainite is 10%.
The following is desirable. However, inevitable martensite,
It is allowed to contain residual austenite and perlite. Further, in the case where the crystal structure such as retained austenite is not bcc, the X-ray random intensity ratio converted by the volume fraction of the other structures may be within the range of the present invention, and the effect of the present invention can be obtained. can get.
The term "ferrite" used herein includes bainitic ferrite and ashular ferrite structures. Further, in order to secure good fatigue characteristics, it is desirable that the volume fraction of pearlite containing coarse carbides be 5% or less. Further, in order to secure good burring property (hole expandability), it is desirable that the volume fraction of residual austenite and martensite is less than 5%.

Here, the volume fraction of ferrite, bainite, retained austenite, pearlite, and martensite means that a sample cut out from a position of 1/4 W or 3/4 W of the width of a steel plate is ground to a section in the rolling direction, and a Nital reagent is used. It is defined as the area fraction of the microstructure at 1/4 t of the plate thickness, which was etched and used under an optical microscope at a magnification of 200 to 500 times.

Next, the reasons for limiting the chemical components of the present invention will be explained. If the content of C exceeds 0.1%, the workability and weldability deteriorate, so the content is made 0.1% or less. If it is less than 0.01%, the strength will decrease, so 0.01
% Or more.

If S is too large, it causes cracking during hot rolling, so it should be reduced as much as possible, but if it is 0.03% or less, it is within the allowable range.

N forms a precipitate with Ti and Nb at a temperature higher than that of C and is effective for fixing C.
b is reduced. Therefore, it should be reduced as much as possible,
If it is 0.005% or less, it is in an allowable range.

Ti is one of the most important elements in the present invention. That is, Ti contributes to the strength increase of the steel sheet by precipitation strengthening. However, if it is less than 0.05%, this effect is insufficient, and if it exceeds 0.5%, not only the effect is saturated but also the alloy cost is increased. Therefore, T
The content of i is 0.05% or more and 0.5% or less. Further, in order to contribute to the improvement of the burring workability by precipitating and fixing C, which causes carbides such as cementite, which deteriorates the burring workability, and contributing to the improvement of the burring workability, Ti-48 / 12C-48 /
It is necessary to satisfy the condition of 14N-48 / 32S ≧ 0%. Here, since S and N form precipitates with Ti in a relatively high temperature range than C, in order to secure Ti ≧ 48 / 12C, Ti-48 / 12C-48 / 14 is inevitable.
It is necessary to satisfy the condition of N-48 / 32S ≧ 0%.

Nb, like Ti, contributes to the strength increase of the steel sheet by precipitation strengthening. It also has the effect of improving the burring workability by refining the crystal grains. However, 0.01
If it is less than 0.5%, this effect is insufficient, and if it exceeds 0.5%, not only the effect is saturated but also the alloy cost rises. Therefore, the content of Nb is 0.01% or more, 0.5
% Or less. Furthermore, C, which causes carbides such as cementite, which deteriorates burring workability, is precipitated and fixed,
To contribute to the improvement of burring workability, Ti + 48
/ 93Nb-48 / 12C-48 / 14N-48 / 32
It is necessary to satisfy the condition of S ≧ 0%. Where N
Since b forms carbides at a relatively lower temperature than Ti, Ti
In order to secure + 48 / 93Nb ≧ 48 / 12C, Ti + 48 / 93Nb-48 / 12C-48 / 1 is inevitable.
It is necessary to satisfy the condition of 4N-48 / 32S ≧ 0%.

Si is effective as a solid solution strengthening element for increasing strength. To obtain the desired strength, it is necessary to contain 0.01% or more. However, if the content exceeds 2%, the workability deteriorates. Therefore, the Si content is 0.01% or more,
2% or less.

Mn is effective as a solid solution strengthening element for increasing strength. In order to obtain the desired strength, 0.05% or more is necessary. When elements other than Mn, such as Ti, which suppress the occurrence of hot cracking due to S, are not sufficiently added, it is desirable to add the amount of Mn such that Mn / S ≧ 20 in mass%. On the other hand, if added in excess of 3%, slab cracking will occur, so the content should be 3% or less.

P is an impurity and is preferably as low as possible.
If the content exceeds 0.1%, the workability and weldability are adversely affected and the fatigue properties are deteriorated, so the content is made 0.1% or less.

Although Al needs to be added in an amount of 0.005% or more for deoxidation of molten steel, it causes an increase in cost, so the upper limit is made 1%. Also, if you add too much,
Since non-metallic inclusions increase and elongation deteriorates, it is preferably 0.5% or less.

B has the effect of increasing the fatigue limit by suppressing the grain boundary embrittlement due to P, which is considered to be caused by the decrease in the amount of solid solution C, so it is added as necessary. However,
If it is less than 0.0002%, it is insufficient to obtain the effect, and if it exceeds 0.002%, slab cracking occurs.
Therefore, the addition of B is 0.0002% or more and 0.002%.
% Or less.

Cu has an effect of improving fatigue characteristics in a solid solution state, so Cu is added if necessary. However, if it is less than 0.2%, its effect is small, and if it exceeds 1.2%, it may be precipitated during winding and remarkably deteriorate the workability. Therefore, the Cu content is set in the range of 0.2 to 1.2%.

Ni is added as necessary to prevent hot embrittlement due to the inclusion of Cu. However, if less than 0.1%, the effect is small, and even if added over 0.6%, the effect is saturated, so 0.1 to 0.6% is set.

[0056] Ca and REM are elements that change the form of non-metallic inclusions that become the starting point of fracture or deteriorate workability and render them harmless. However, even if added less than 0.0005%, it has no effect. If Ca, 0.002%
If it is more than REM, the effect will be saturated even if more than 0.02% is added, so Ca = 0.0005 to 0.002%, REM
= 0.0005 to 0.02% is desirable.

Further, in order to impart strength, Mo,
One or more of V, Cr and Zr precipitation strengthening or solid solution strengthening elements may be added. However,
If less than 0.05%, 0.02%, 0.01%, 0.02%, the effect cannot be obtained. Also, respectively
Even if added over 1%, 0.2%, 1%, 0.2%, the effect is saturated.

In addition, Sn, C
The total content of o, Zn, W, and Mg may be 1% or less. However, Sn may be flawed during hot rolling, so 0.05% or less is preferable.

Next, the reasons for limiting the manufacturing method of the present invention will be described in detail below. The present invention, after casting, after hot rolling after cooling or after hot rolling, after hot rolling after cooling, pickling and cold rolling, heat treatment, or heat treatment of hot rolled steel sheet or cold rolled steel sheet in a hot dip line It can be obtained as it is, or by subjecting these steel plates to a separate surface treatment.

The production method prior to hot rolling in the present invention is not particularly limited. That is, after the smelting in a blast furnace, an electric furnace, etc., the components are adjusted in various secondary smelting so that the target component content is obtained, and then, in addition to ordinary continuous casting, ingot casting, thin slab casting, etc. It may be cast by the method. Scrap may be used as a raw material. In the case of a slab obtained by continuous casting, it may be directly sent to a hot rolling mill as it is as a high temperature slab, or may be reheated in a heating furnace after being cooled to room temperature and then hot rolled.

The reheating temperature is not particularly limited,
If it is 1400 ° C or higher, the scale-off amount increases and the yield decreases, so the reheating temperature is preferably lower than 1400 ° C. In addition, since heating below 1000 ° C. significantly impairs operating efficiency on schedule, the reheating temperature is 100
0 ° C or higher is desirable. Further, heating below 1100 ° C. not only causes precipitates containing Ti and / or Nb to coarsen without redissolving in the slab and loses precipitation strengthening ability, but also has Ti and / or Ti and / or a size and distribution desirable for burring workability. Since the precipitate containing Nb does not precipitate, the reheating temperature is preferably 1100 ° C or higher.

In the hot rolling step, finish rolling is carried out after the rough rolling is completed. When descaling is carried out after the rough rolling is completed, the collision pressure P (MPa) of the high-pressure water on the surface of the steel sheet x the flow rate L (liter). / Cm ² ) ≧ 0.0025 is preferable.

The collision pressure P of high-pressure water on the surface of the steel sheet is described as follows ("Iron and Steel" 1991 vol.77).
No. 9 p1450). P (MPa) = 5.64 × P ₀ × V / H ² where P ₀ (MPa): Liquid pressure V (liter / min): Nozzle flow rate H (cm): Distance between steel plate surface and nozzle

The flow rate L is described as follows. L (liter / cm ² ) = V / (W × v) However, V (liter / min): Nozzle flow amount W (cm): Width v (cm / min) where the jet liquid hits the steel plate surface per nozzle: Plate passing speed

The upper limit of the collision pressure P.times.the flow rate L does not have to be specified in order to obtain the effect of the present invention. However, if the flow rate of the nozzle liquid is increased, the wear of the nozzle becomes severe, and the like. It is desirable to set it to 0.02 or less.

Further, the maximum height R of the steel sheet after finish rolling
y is 15 μm (15 μm Ry, l2.5 mm, ln1
2.5 mm) or less is desirable. This is clear, for example, from the fact that the fatigue strength of a hot rolled or pickled steel sheet correlates with the maximum height Ry of the steel sheet surface as described in Metal Material Fatigue Design Handbook, edited by Japan Society of Materials, page 84. is there. In addition, the finish rolling after that is performed in order to prevent the scale from being generated again after the descaling.
It is desirable to do it within seconds.

Further, in order to obtain the effect of reducing the friction coefficient by applying a composition having a lubricating effect, the arithmetic mean roughness Ra of the steel sheet after finish rolling is preferably 3.5 or less. However, this does not apply when skin pass rolling or cold rolling is performed after hot rolling or pickling.

Further, after the rough rolling or the subsequent descaling, the sheet bars may be joined and continuously subjected to finish rolling. At that time, wind the coarse bar once in a coil,
If necessary, the sheets may be stored in a cover having a heat retaining function, rewound, and then joined.

In the final rolling, when the final product is a hot-rolled steel sheet, it is necessary to perform rolling with a total reduction of 25% or more in the temperature range of Ar3 transformation point temperature + 100 ° C. or lower in the latter half of the finish rolling. Here, the Ar3 transformation point temperature is simply shown in relation to the steel composition, for example, by the following calculation formula. That is, Ar3 = 910-310 ×% C + 25 ×% Si-80
×% Mn

If the total rolling reduction in the temperature range of Ar3 transformation point temperature + 100 ° C. or less is less than 25%, the texture of the rolled austenite does not sufficiently develop. Therefore, no matter what kind of cooling is performed thereafter, However, the effect of the present invention cannot be obtained. Ar3 for a sharper texture
It is desirable that the total rolling reduction in the temperature range of the transformation point temperature + 100 ° C. or less is 35% or more.

The lower limit of the temperature range for rolling at a total reduction of 25% or more is not particularly limited, but if it is lower than the Ar3 transformation point temperature, the ferrite precipitated during rolling retains the work structure and the ductility decreases. Processability deteriorates,
The lower limit of the temperature range for rolling at a total reduction of 25% or more is Ar.
3 A transformation temperature or higher is desirable.

In the present invention, Ar3 transformation point temperature + 100 ° C.
The upper limit of the total rolling reduction in the following temperature range is not particularly limited, but if the total rolling reduction exceeds 97.5%, the rolling load increases and the rigidity of the rolling mill needs to be excessively increased, which is economically disadvantageous. 97.5% is desirable in order to cause disadvantages
Below.

Here, when the friction between the hot rolling roll and the steel sheet during hot rolling in the temperature range of Ar3 transformation point temperature + 100 ° C. or less is large, the {110} plane is formed on the sheet surface in the vicinity of the steel sheet surface. Since the main crystal orientation develops and the shape fixability deteriorates, lubrication is applied as necessary to reduce the friction between the hot rolling roll and the steel sheet.

In the present invention, the upper limit of the friction coefficient between the hot rolling roll and the steel sheet is not particularly limited, but if it exceeds 0.2, {1
Since the crystal orientation mainly in the 10} plane becomes remarkable and the shape fixability deteriorates, at least one pass during hot rolling in the temperature range of Ar3 transformation point temperature + 100 ° C or less, the hot rolling roll and the steel sheet It is desirable that the coefficient of friction with is 0.2 or less. More preferably, the coefficient of friction between the hot rolling roll and the steel sheet is 0.15 or less for all passes during hot rolling in the temperature range of Ar3 transformation point temperature + 100 ° C. or less. Here, the friction coefficient between the hot rolling roll and the steel sheet is a value obtained by calculation based on the theory of rolling from the values of the advance rate, rolling load, rolling torque and the like.

The final pass temperature (FT) of finish rolling is not particularly limited, but the final pass temperature (F) of finish rolling is
It is desirable that T) ends at the Ar3 transformation temperature or higher. This is because if the rolling temperature is lower than the Ar3 transformation point temperature during hot rolling, the work structure remains in the ferrite precipitated before or during rolling, and the ductility decreases and the workability deteriorates.

On the other hand, there is no particular upper limit on the finishing temperature, but if the Ar3 transformation point temperature exceeds 100 ° C.
Since it is practically impossible to carry out rolling with a total reduction of 25% or more in a temperature range of r3 transformation point temperature + 100 ° C. or less, the upper limit of finishing temperature is preferably Ar3 transformation point temperature + 100 ° C. or less.

In the present invention, the steps from the completion of finish rolling to the winding at a predetermined winding temperature (CT) are not particularly specified, but when aiming at compatibility with ductility without deteriorating the burring property so much. From the Ar3 transformation point to Ar1
It may be allowed to stay for 1 to 20 seconds in the temperature range up to the transformation point (two-phase range of ferrite and austenite). The residence here is performed in order to accelerate the ferrite transformation in the two-phase region, but if it is less than 1 second, sufficient ductility cannot be obtained because the ferrite transformation in the two-phase region is insufficient, and if it exceeds 20 seconds, T
The size of the precipitate containing i and / or Nb may become coarse and may not contribute to the strength increase due to precipitation strengthening.
In addition, the temperature range in which the steel is retained for 1 to 20 seconds is 8 or higher than the Ar1 transformation point in order to facilitate the ferrite transformation easily.
60 ° C or lower is desirable. Further, the residence time of 1 to 20 seconds is preferably 1 to 10 seconds in order not to extremely reduce the productivity.

In order to satisfy these conditions, it is necessary to quickly reach the temperature range at a cooling rate of 20 ° C./s or more after finishing rolling. Although the upper limit of the cooling rate is not specified, 300 ° C./s or less is a reasonable cooling rate in view of the capacity of the cooling equipment. Furthermore, if this cooling rate is too fast, the cooling end temperature cannot be controlled, and there is a possibility of overshooting and overcooling to below the Ar1 transformation point, and the effect of improving ductility will be lost. Is preferably 150 ° C./s or less.

Next, a predetermined winding temperature (C
Although it is cooled to T), the cooling rate is not particularly required to obtain the effects of the present invention. However, if the cooling rate is too slow, the size of precipitates containing Ti and / or Nb may become coarse and may not contribute to the increase in strength due to precipitation strengthening. Therefore, the lower limit of the cooling rate is preferably 20 ° C./s or more. Further, although the upper limit of the cooling rate up to the winding temperature can obtain the effect of the present invention without particularly defining,
Since there is concern about plate warpage due to thermal strain, 300 ° C
It is desirable to be below / s.

In the present invention, the coiling temperature (CT) is not particularly specified, but the upper limit is the Ar3 transformation point temperature + 1.
In order to inherit the texture of austenite obtained by rolling at a total rolling reduction of 25% or more in a temperature range of 00 ° C. or less, it is desirable to wind at a winding temperature T ₀ or less shown below. This T ₀ is a temperature that is thermodynamically defined as a temperature at which austenite and ferrite having the same component as austenite have the same free energy, and in consideration of the effects of components other than C, the following formula is used. Can be calculated. T ₀ = −650.4 ×% C + B where B is determined as follows. B = −50.6 × Mneq + 894.3 Further, here, Mneq is determined by the mass% of the contained elements shown below. Mneq =% Mn + 0.24 ×% Ni + 0.13 ×% S
i + 0.38 ×% Mo + 0.55 ×% Cr + 0.16 ×
% Cu-0.50x% Al-0.45x% Co + 0.9
0 ×% V Note that the influence of the mass% of the components other than the above specified in the present invention on T ₀ is not so large and can be ignored here.

On the other hand, the lower limit of the winding temperature (CT) is 350.
Precipitates containing sufficient Ti and / or Nb will not be generated at a temperature of not higher than 0 ° C, and solid solution C may remain in the steel to lower the workability. Further, although the cooling rate after winding is not particularly limited, when Cu is added in an amount of 1% or more, if the winding temperature (CT) is higher than 450 ° C., Cu precipitates after winding and workability deteriorates. However, since Cu in a solid solution state that is effective in improving fatigue characteristics may be lost, when the coiling temperature (CT) is higher than 450 ° C, the cooling rate after coiling is 30 ° C / s up to 200 ° C. It is desirable to set the above.

After completion of the hot rolling process, pickling is carried out if necessary, and then in-line or off-line reduction of 10%.
The following skin pass or cold rolling up to a rolling reduction of about 40% may be performed. However, in this case, in order to apply a composition having a lubricating effect and obtain the effect of reducing the friction coefficient, at least one of the surfaces of the front and back surfaces of the steel sheet after the skin pass has an arithmetic average roughness Ra of 1 to 3. The skin pass reduction is controlled to be 5.

Next, there is a case where a cold rolled steel sheet is used as a final product, but hot finish rolling conditions are not particularly limited.
However, in order to obtain better shape fixability, Ar3
The total rolling reduction in the temperature range below the transformation point temperature + 100 ° C is 2
It is preferably 5% or more. Also, the final pass temperature (FT) of finish rolling may be completed below the Ar3 transformation point temperature, but in that case, since a strong work structure remains in ferrite precipitated before or during rolling,
It is desirable to recover and recrystallize by the subsequent winding treatment or heat treatment.

The total reduction ratio of the cold rolling after the subsequent pickling was 80.
Less than%. This is because the total reduction ratio of cold rolling is 80%.
As described above, the X-axis of the {111} plane or the {554} plane of the crystal plane parallel to the plate surface which is a general cold rolling-recrystallization texture
This is because the line diffraction integrated surface intensity ratio becomes high. Further, it is preferably 70% or less. The effect of the present invention can be obtained without particularly defining the lower limit of the cold rolling rate, but it is preferably 3% or more in order to control the strength of the crystal orientation within an appropriate range.

The heat treatment of the cold rolled steel sheet is premised on the continuous annealing step. First, the recovery temperature or higher Ac
3 Perform for 5 to 150 seconds in the temperature range of the transformation point temperature + 100 ° C. or less. Here, the Ac3 transformation point temperature is shown in relation to the steel composition by a calculation formula described on page 273, for example, Leslie Steel Science (issued in 1985, translated by Hiroshi Kumai, translated by Tatsuhiko Noda, Maruzen Co., Ltd.). When the heat treatment temperature (ST) is lower than the recovery temperature, the worked structure remains and ductility is significantly deteriorated. Therefore, the heat treatment temperature (ST) is set to the recovery temperature or higher. In order to obtain even better ductility, the recrystallization temperature or higher is desirable. Further, when the heat treatment temperature (ST) exceeds the Ac3 transformation point temperature + 100 ° C, the ferrite produced by recrystallization transforms to austenite, the texture by austenite grain growth is randomized, and the finally obtained texture is also obtained. Since it is randomized, the heat treatment temperature (ST) is set to Ac3 transformation point temperature + 100 ° C. or less.

On the other hand, the holding time (Tim in this temperature range
With respect to e), if it is less than 5 seconds, carbonitrides of Ti and Nb are insufficient for complete solid solution again. On the other hand, even if the heat treatment is performed for more than 150 seconds, the effect is not only saturated but also produced. Retention time (Time) of 5 to 15
0 seconds.

The cooling conditions thereafter are not particularly limited, but the T ₀ above 350 ° C. at a cooling rate of 20 ° C./s or more is used.
It is desirable to cool to a temperature range below the temperature. This is because if the cooling rate is less than 20 ° C./s, the size of the precipitate containing Ti and / or Nb may become coarse and may not contribute to the strength increase due to precipitation strengthening. If the cooling end temperature is 350 ° C. or lower, sufficient precipitates containing Ti and / or Nb will not be generated, and solid solution C may remain in the steel to reduce workability.
More than 50 ° C is desirable. Also, the end temperature of the cooling process is 2
If the temperature exceeds 00 ° C, aging may deteriorate, so 200 ° C
The following is desirable. In addition, the lower limit is preferably 50 ° C. or higher because when the coil is water-cooled or when it is cooled with a mist, if the coil is wet with water for a long period of time, there is a fear of appearance failure due to rust.

After that, if necessary, skin pass rolling is carried out. However, in this case, in order to apply a composition having a lubricating effect and obtain the effect of reducing the friction coefficient, at least one of the surfaces of the front and back surfaces of the steel sheet after the skin pass has an arithmetic average roughness Ra of 1 to 3. The skin pass reduction is controlled to be 5.

In order to galvanize the hot-rolled steel sheet after pickling or the cold-rolled steel sheet after completion of the above recrystallization heat treatment,
It may be immersed in a galvanizing bath and may be alloyed if necessary.

Finally, in order to secure the drawability, a composition having a lubricating effect is applied after the above manufacturing process. The coating method is not particularly limited as long as a desired coating thickness can be obtained, but an electrostatic coating method or a roll coater method is generally used.

[0090]

EXAMPLES The present invention will be further described below with reference to examples. Steels A to L having the chemical components shown in Table 1 were melted in a converter, continuously cast, then reheated at the heating temperature shown in Table 2, and 1.2 to 12 in rough rolling followed by finish rolling. It was rolled up after the plate had a thickness of 5.5 mm. However, the chemical composition shown in the table is% by mass. In addition, some lubrication rolling was performed as shown in Table 2. Further, the steel L was subjected to descaling under conditions of a collision pressure of 2.7 MPa and a flow rate of 0.001 liter / cm ² after rough rolling. Furthermore, as shown in Table 2, after a hot rolling process,
Pickling, cold rolling, and heat treatment were performed. Board thickness is 0.7 to 2.3 m
m. On the other hand, among the above steel sheets, Steel G and Steel A-8 were galvanized.

Details of the manufacturing conditions are shown in Table 2. here,
"SRT" is the slab heating temperature, "FT" is the final pass finish rolling temperature, and "rolling rate" is the Ar3 transformation point temperature +10.
The total reduction rate in the temperature range of 0 ° C or lower is shown. However, when rolling is performed later in the cold rolling process, such limitation is not applied, and thus "-" is set. Further, "lubrication" indicates the presence or absence of lubrication in the temperature range of Ar3 transformation point temperature + 100 ° C or lower. Furthermore, "CT" indicates the winding temperature. However, in the case of a cold-rolled steel sheet, it is not necessary to specifically limit the manufacturing conditions, so "-" is set. Next, "cold rolling rate" is the total cold rolling rate, "ST" is the heat treatment temperature, "Time".
Is the heat treatment time.

After passing through the above manufacturing process, a composition having a lubricating effect was applied by an electrostatic coating device or a roll coater.

The tensile test of the hot-rolled sheet thus obtained was carried out by first processing the test material into a No. 5 test piece described in JIS Z2201 and performing the test method described in JIS Z2241. Table 2 shows the yield strength (σ _Y ), the tensile strength (σ _B ), and the breaking elongation (El). On the other hand, regarding burring workability (hole expandability), the Japan Iron and Steel Federation Standard JF
Evaluation was performed according to the hole expansion test method described in ST 1001-1996. Table 2 shows the hole expansion ratio (λ).

Here, the volume fraction of ferrite, bainite, retained austenite, pearlite, and martensite means that a sample cut from a position of 1/4 W or 3/4 W of the steel plate width is polished and etched in a cross section in the rolling direction, It is defined as the area fraction of the microstructure at 1/4 t of the plate thickness observed under a microscope at a magnification of 200 to 500 times.

Furthermore, 1/4 W or 3/4 W of the plate width
The specimen cut to 30 mmφ from the position was ground to 3 mm on the specimen cut to 30 mmφ, and then the strain was removed by chemical polishing or electrolytic polishing to prepare a new edition of the Kariti X-ray diffraction theory (issued in 1986, The X-ray diffraction intensity was measured according to the method described in Gentaro Matsumura, Agne Co., Ltd. pp. 274-296.

Here, {100} <011> to {22
3} The average value of the X-ray random intensity ratio of the <110> direction group is the main direction included in this direction group, {100} <01.
1>, {116} <110>, {114} <110>,
{113} <110>, {112} <110>, {33
5} <110> and {223} <110> X-ray diffraction intensities calculated by the vector method based on the {110} pole figure, or {110}, {100},
It was determined from a three-dimensional texture calculated by the series expansion method using a plurality of pole figures (preferably three or more) of the {211} and {310} pole figures.

For example, the X-ray random intensity ratio of each crystal orientation in the latter method is φ2 = 4 of the three-dimensional texture.
(001) [1-10], (116) at 5 ° cross section
[1-10], (114) [1-10], (113)
[1-10], (112) [1-10], (335)
The strengths of [1-10] and (223) [1-10] may be used as they are. However, {100} <011> to {22
3} The average value of the X-ray random intensity ratio of the <110> orientation group is the arithmetic average of the above orientations. If it is not possible to obtain the intensities in all of the above directions, {100} <01
1>, {116} <110>, {114} <110>,
You may substitute by the arithmetic mean of each direction of {112} <110> and {223} <110>.

Next, {554} <225> and {111} <
The average value of the X-ray random intensity ratios in the three directions of 112> and {111} <110> may be obtained from the three-dimensional texture calculated in the same manner as the above method.

In Table 2, "intensity ratio 1" of the X-ray random intensity ratio means {100} <011> to {223}.
The average value of the X-ray random intensity ratio of the <110> orientation group, “intensity ratio 2” is {554} <225>, {111} <11.
2 is an average value of X-ray random intensity ratios in 3 directions of 2> and {111} <110>.

Next, in order to investigate the shape fixability of the steel sheet, a test piece having a width of 50 mm and a length of 270 mm was prepared from the position of 1/4 W or 3/4 W of the sheet width so that the rolling direction was the long side. , A punch width of 78 mm, a punch shoulder R5 and a die shoulder R5 were used to perform a hat bending test. For the test piece that underwent the bending test, the shape of the center of the plate width was measured with a three-dimensional shape measuring device, and as shown in Fig. 1, the value obtained by subtracting the punch width from the length between the left and right points was used for dimensional accuracy. , Spring-back amount is the average value on the left and right of the value obtained by subtracting 90 # from the intersection angle between the tangents of the points and the tangent of the points, and the reciprocal of the curvature between the points is averaged on the left and right. The shape freezing property was evaluated using the amount of wall warpage.

By the way, the amount of springback and the amount of wall warp also change depending on BHF (wrinkle holding force). The tendency of the effect of the present invention does not change regardless of which BHF is evaluated, but since BHF that is too high cannot be applied when pressing actual parts at the production site, this time BHF29
A hat bending test of each steel type was performed at kN. The shape fixability can be finally judged by the dimensional accuracy (Δd) based on the dimensional accuracy and the wall warp amount obtained by the bending test. It is well known that the dimensional accuracy deteriorates as the strength of the steel sheet increases.
d / σ _B was used as an index.

Regarding the arithmetic mean roughness Ra, JIS B060 is used by using a non-contact type measuring device using a laser.
It was determined by the method described in 1-1994.

Further, as shown in FIG. 2, the coefficient of friction is sandwiched between two flat plates having a Vickers hardness of Hv600 or more on the surface of the steel plate so that the surface pressure becomes 1.5 to ² kgf / mm ^2. After applying a vertical force (F) to
Pull out the steel plate. It was determined as a ratio (f / F) of the pulling force f to F at that time.

Finally, the drawability index of the steel plate is obtained by dividing the maximum diameter (D) that can be drawn out by the cylindrical punch diameter (d) when the steel plate is processed into a circular shape and then drawn by a cylindrical punch. Value (D / d). In this measurement, the circular processing size of the steel plate is various diameters of 300 to 400φ,
Cylindrical punch diameter is 175φ, bottom shoulder is 10R, die surface shoulder is 15R, wrinkle holding force is 10kN for steel B,
Steel J is 100 kN, Steel A, Steel C, Steel E, Steel F, Steel G,
Steel H, steel I, and steel K were 120 kN.

Steel sheets having a coefficient of friction within the range of the present invention have a higher reduction index value (D / d) than steel sheets having a coefficient of friction higher than the range of the present invention, and are both 1.91 or more. Recognize.

According to the present invention, steels A-1, A-3,
A-4, A-8, A-10, C, E, G, H, I, J,
L steel 12 containing a predetermined amount of steel component, and {100} <011 of the plate surface at least at ½ of the plate thickness.
> To {223} <110> the average value of the X-ray random intensity ratio of the orientation group is 3 or more, and {554} <225>, {11
The average value of the X-ray random intensity ratios in the three directions of 1} <112> and {111} <110> is 3.5 or less, and the arithmetic average roughness Ra of at least one of the front and back surfaces is 1 or more 3 A steel sheet having a hardness of 0.5 or less is coated with a composition having a lubricating effect, and at least one of friction coefficients in a rolling direction and a direction perpendicular to the rolling direction at 0 to 200 ° C. is 0.05 or more and 0. A drawable burring high-strength steel sheet excellent in shape fixability, which is characterized by being 2 or less, is obtained, and therefore exceeds the shape fixability index of the conventional steel evaluated by the method according to the present invention. There is.

Steels other than the above are out of the scope of the present invention for the following reasons. That is, since the steel A-2 has a total reduction ratio in the temperature range of the finish rolling end temperature (FT) and the Ar3 transformation point temperature + 100 ° C or less, it is outside the scope of claim 11 of the present invention. And the shape fixability (Δd / σ _B ) is not sufficiently obtained. Steel A-5 was not coated with a composition having a lubricating effect, so that the target friction coefficient of claim 2 was not obtained and sufficient drawability (D / d) was not obtained. Steel A
In No. 6, since the arithmetic average roughness Ra is outside the scope of claim 1 of the present invention, the desired friction coefficient of claim 2 is not obtained and sufficient drawability (D / d) is not obtained. . Steel A-7
Since the heat treatment temperature (ST) is outside the scope of claim 14 of the present invention, the target texture of claim 1 is not obtained and sufficient shape fixability (Δd / σ _B ) is not obtained. . Steel A-9 has a cold rolling ratio outside the scope of claim 14 of the present invention, and therefore the desired texture of claim 1 is not obtained and sufficient shape fixability (Δd / σ _B ) is obtained. Not not.

Steel B does not have sufficient strength (σ _B ) because the content of C is outside the scope of claim 1 of the present invention.
Steel D has a Ti content outside the scope of claim 1 of the present invention, and therefore has sufficient strength (σ _B ) and shape fixability (Δd / σ _B).
) Has not been obtained. Steel F has a C content outside the scope of claim 1 of the present invention, so a sufficient hole expansion ratio (λ) is not obtained. In Steel I, since the content of S is outside the scope of claim 1 of the present invention, a sufficient hole expansion ratio (λ) and elongation (E) are obtained.
l) has not been obtained. Steel K does not have a sufficient hole expansion ratio (λ) and elongation (El) because the N content is outside the scope of claim 1 of the present invention.

[0109]

[Table 1]

[0110]

[Table 2]

[0111]

As described in detail above, the present invention relates to a drawable burring high strength steel sheet which is excellent in shape fixability and a manufacturing method thereof. By using these high strength steel sheets, Since it is possible to obtain good drawability even in a steel sheet having a texture that is disadvantageous to draw forming, compatibility of shape fixability and drawability can be expected, so the present invention can be said to be an invention of high industrial value. .

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a cross-sectional shape of a sample that has been subjected to a bending test.

FIG. 2 is a diagram illustrating a friction coefficient measuring instrument.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22C 38/58 C22C 38/58 (72) Inventor Natsuko Sugiura 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Co., Ltd. (72) Inventor Takaaki Nakamura 1st Nishinosu, Oita-shi, Oita Prefecture Nippon Steel Co., Ltd. Oita Steel Co., Ltd. (72) Inventor Takehiro Nakamoto 1st Nishinosu, Oita-shi, Oita Nippon Steel Co., Ltd. Company Oita Steel Works F-term (reference) 4E002 AD04 AD05 BC05 BC08 BD07 BD10 CB01 4K037 EA01 EA02 EA05 EA09 EA11 EA13 EA15 EA16 EA17 EA18 EA19 EA20 EA23 EA25 EA03 FB03 GA08 EA03 FB08 EA03 FB03 EA35 FB03 EA03 FB03 EA35 FB03 EA35 FB03 EA35 FB08 EA03 FB08 EA03 FB03 EA35 FB03 EA03 FB08 EA03 FB03 FB05 EA36 FB08 EA35 FB03 FB03 FB07 FB07 FB08

Claims (17)

[Claims] 1. In mass%, C: 0.01 to 0.1%, S ≤ 0.03%, N ≤ 0.005%, Ti: 0.05 to 0.5% are included, and Ti is further included. -48 / 12C-48 / 14N-48 / 32S ≧ 0
% Ti in a range of satisfying at least 1.0%, and the balance being Fe and unavoidable impurities, and having {100} <011> to {223} <1 of the plate surface at least at 1/2 the plate thickness.
10> The average value of the X-ray random intensity ratios of the orientation groups of 3 or more and the average value of the X-ray random intensity ratios of the three orientations of {554} <225>, {111} <112> and {111} <110>. Is 3.5 or less, and a composition having a lubricating effect is applied to a steel plate having an arithmetic average roughness Ra of at least one steel plate surface of 1 to 3.5. Excellent squeezable burring high strength steel sheet. 2. The surface of the steel sheet according to claim 1, which is 0 to 200.
A burring-type high-strength thin steel sheet which is excellent in shape fixability and has a coefficient of friction of 0.05 to 0.2 at ℃. 3. The steel according to claim 1 or 2, further comprising, in mass%, Nb = 0.01 to 0.5%, and further Ti + 48 / 93Nb-48 / 12C-48 / 14N-.
A drawable burring high-strength thin steel sheet having excellent shape fixability, which is a steel containing Ti and Nb in a range satisfying 48 / 32S ≧ 0% and the balance being Fe and inevitable impurities. 4. The steel according to claim 1, further comprising, in mass%, Si: 0.01 to 2%, Mn: 0.05 to 3%, and P ≤ 0. 1%, Al: 0.005 to 1% is contained, and a burringable high-strength thin steel sheet having excellent shape fixability and capable of being drawn. 5. The shape fixability according to claim 1, wherein the steel according to claim 1 further contains B: 0.0002 to 0.002% in mass%. Excellent squeezable burring high strength steel sheet. 6. The shape fixability according to claim 1, wherein the steel according to claim 1 further contains Cu: 0.2 to 1.2% in mass%. Excellent squeezable burring high strength steel sheet. 7. The shape fixability according to claim 1, wherein the steel according to any one of claims 1 to 6 further contains, in mass%, Ni: 0.1 to 0.6%. Excellent squeezable burring high strength steel sheet. 8. The steel according to claim 1, further comprising, in mass%, Ca: 0.0005 to 0.002% and REM: 0.0005 to 0.02%. A burring high-strength thin steel sheet with excellent shape fixability, which contains one or two kinds. 9. The steel according to claim 1, further comprising, in mass%, Mo: 0.05 to 1%, V: 0.02 to 0.2%, Cr: 0.01 to 1%, Zr: 0.02 to 0.2%, and one or more of them are contained. 10. A drawable burring property excellent in shape fixability, characterized in that the drawable burring high strength steel sheet according to claim 1 is galvanized. High strength thin steel sheet. 11. When hot rolling to obtain a thin steel sheet having a component according to any one of claims 1 to 9, Ar3 transformation point temperature + 100 ° C. after rough rolling of a steel slab having the component. Finishing rolling with a total reduction of 25% or more of steel plate thickness in the following temperature range, then cooling and winding, and then applying a composition having a lubricating effect. For producing a high strength thin steel sheet with excellent burring property. 12. The lubrication rolling is performed in the finishing rolling after the rough rolling during the hot rolling.
1. A method for producing a burring high-strength thin steel sheet capable of being drawn, which is excellent in shape fixability. 13. A method for producing a drawable burring high strength steel sheet having excellent shape fixability, which comprises descaling after rough rolling in the hot rolling according to claim 11 or 12. 14. In order to obtain a thin steel sheet having a component according to any one of claims 1 to 9, hot rolling of a slab having the component, subsequent pickling, and a steel plate thickness reduction of less than 80%. After cold rolling, recovery temperature is above Ac3 transformation point temperature + 100 ° C
A burring high-strength thin steel sheet having excellent shape fixability, which is characterized by applying a composition having a lubricating effect after performing heat treatment in a step of cooling for 5 to 150 seconds in the following temperature range. Production method. 15. The method according to any one of claims 11 to 13, wherein after hot rolling, the surface of a steel sheet is galvanized by being immersed in a galvanizing bath, and then a composition having a lubricating effect is obtained. A method for producing a burring high-strength steel sheet capable of being drawn, which is excellent in shape fixability and is characterized by being applied. 16. In the manufacturing method according to claim 14,
After finishing the heat treatment, the steel sheet surface is dipped in a galvanizing bath to be galvanized, and then a composition having a lubricating effect is applied. Production method. 17. The manufacturing method according to claim 15 or 16, wherein the composition having a lubricating effect is applied after dipping in a galvanizing bath for galvanizing and then alloying treatment. A method for producing a burring high-strength steel sheet capable of being drawn, which is excellent in shape fixability.