JPH05263191A - Hot rolled steel sheet high in young's modulus in width direction and its manufacture - Google Patents

Abstract

PURPOSE:To provide a hot rolled steel sheet high in a Young's modulus in the width direction and to provide its manufacturing method. CONSTITUTION:(1) This hot rolled steel sheet high in a Young's modulus contains, by weight, <=0.8% C, <=3% Si, 0.1 to 3.0% Mn and 0.01 to 3% sol.Al, and the balance Fe with inevitable impurities, and in which the reflection strength on the {311} plane parallel to the sheet face shows >= five times as much by random ratio. (2) This is a method for manufacturing the steel sheet high in a Young's modulus (1) characterized by heating steel stock having the said chemical compsn. in the range of 920 to 1250 deg.C, thereafter executing hot rolling in such a manner that the total draft in the alpha+gamma two phase region is regulated to >=50% and the finishing temp. of the hot rolling is regulated to the Ar1 to (the Ar1 -70 deg.C) and coiling it at the Ar1 to (the Ar1 -250 deg.C) or executing annealing at the Ar1 to (the Ar1 -250 deg.C) after the coiling at the Ar1 point or below. This steel in the (1) and steel stock in the (2) may be incorporated with <=2.5% Ni and/or one or more kinds among <=0.1% Nb, <=0.2% V and <=0.1% Ti.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolled steel sheet having a high Young's modulus in the width direction and a method for producing the hot rolled steel sheet.

[0002]

2. Description of the Related Art As means for ensuring the rigidity of a structure mainly composed of a steel plate such as automobiles and home electric appliances, the rigidity of the steel plate itself which is a constituent material is increased or the shape of the structure is used. However, until now, there has been nothing to be seen in the results of research on improving the rigidity of the steel sheet itself, that is, increasing the Young's modulus.

The Young's modulus of steel is extremely higher than that of other structural materials, and the value of steel has been designed to be a constant value of about 21000 kgf / mm ² . However, α
Looking at the Fe single crystal, the Young's modulus has anisotropy, <111
>Young's modulus in the axial direction is the highest at 29000kgf / mm ² , <1
The 00> axial direction has a minimum value of 13150 kgf / mm ^2, and the former is more than twice as large as the latter. Under these circumstances, the Young's modulus of steel materials greatly depends on the texture,
By controlling it, Young's modulus in a specific direction can be increased. For example, in the case of a steel sheet, in order to increase the Young's modulus in a specific one direction within the plane, it is sufficient to strongly integrate the orientation close to the <111> axis in that direction. However, in the texture of the steel sheet recrystallized after cold rolling, the main orientation is {111} <UVW>, and there is no <111> axis or orientation close to it in the plane. On the other hand, the texture of hot-rolled steel sheet is almost random.

In recent years, attempts have been made to increase the Young's modulus in a specific direction by controlling the texture by changing the components contained in the steel sheet and the manufacturing conditions. For example, in Japanese Unexamined Patent Publication (Kokai) No. 56-23223, during hot working, α + γ two-phase region rolling is performed as part of the rolling, and the working reduction rate at the Ar ₃ temperature or less is set to 5% or more.
A method characterized by controlling the cooling rate after rolling finish and then tempering is proposed, but it is not specifically shown which texture is developed, and the Young's modulus in the strip width direction is also not shown. Only about 10% has improved.

On the other hand, the invention disclosed in Japanese Patent Laid-Open No. 59-83721 has a hot rolling stability orientation in the ferrite region {11.
2} <110> is used as it is, but a high pressure reduction ratio is required to integrate this orientation in ordinary rolling, and the reduction ratio described in the embodiment is 24000 kgf / m at most.
Only Young's modulus of m ² can be obtained.

The invention disclosed in Japanese Patent Laid-Open No. 64-11926 is {110} <00 after hot rolling in the ferrite region and recrystallization.
It is an attempt to increase the Young's modulus in the plate width direction by accumulating 1>. However, as shown in the examples, only Young's modulus of about 24000 kgf / mm ² is obtained.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a steel sheet having a very high Young's modulus in a specific in-plane direction, and a practical method for producing the steel sheet.

[0008]

SUMMARY OF THE INVENTION The gist of the present invention is the following hot rolled steel sheets (1) to (4) and their manufacturing methods (5) and (6).

(1) C: 0.8% or less, Si: 3% by weight
Below, Mn: 0.1 to 3.0%, sol.Al: 0.01 to 3%, the balance consisting of Fe and unavoidable impurities, the {311} plane reflection intensity parallel to the plate surface is 5 times or more at random ratio. A hot rolled steel sheet with a high Young's modulus in the width direction.

(2) C: 0.8% or less, Si: 3% by weight
Below, Mn: 0.1-3.0%, sol.Al: 0.01-3%, Ni: 2.
A hot-rolled steel sheet having a high Young's modulus in the sheet width direction, containing 5% or less, the balance being Fe and inevitable impurities, and having a {311} plane reflection intensity parallel to the sheet surface of 5 times or more in a random ratio.

(3) W: C: 0.8% or less, Si: 3%
Below, Mn: 0.1 to 3.0%, sol.Al: 0.01 to 3%, and Nb: 0.1% or less, V: 0.2% or less and Ti: 0.1% or less, and the balance contains Fe and A hot-rolled steel sheet having a high Young's modulus in the sheet width direction, which is composed of inevitable impurities and has a reflection intensity of {311} plane parallel to the sheet surface of 5 times or more at a random ratio.

(4) C: 0.8% or less, Si: 3% by weight
Below, Mn: 0.1-3.0%, sol.Al: 0.01-3%, Ni: 2.
5% or less, Nb: 0.1% or less, V: 0.2% or less and Ti: 0.1% or less, and the balance is Fe.
And unavoidable impurities, parallel to the plate surface {31
A hot-rolled steel sheet having a high Young's modulus in the sheet width direction and having a 1} plane reflection intensity of 5 times or more in random ratio.

(5) After heating the steel material having the composition according to any one of (1) to (4) in the range of 920 to 1250 ° C.,
alpha + gamma total reduction amount in the two-phase region is 50% or more, and hot rolled to hot rolled finishing temperature is _{Ar 1 ~ (Ar 1 + 70} ℃), Ar 1 ~
Wherein the winding in _{(Ar 1 -250 ℃) (1} ) ~ (4)
The method for manufacturing a hot rolled steel sheet according to any one of 1.

(6) After heating the steel material having the composition according to any one of (1) to (4) in the range of 920 to 1250 ° C.,
Hot rolling is performed so that the total reduction amount in the α + γ two-phase region is 50% or more and the hot rolling finish temperature is Ar ₁ to (Ar ₁ + 70 ° C), and after winding at Ar ₁ or less, Ar ₁ to (Ar _The method for producing a hot-rolled steel sheet according to any one of (1) to (4), characterized in that annealing is performed at _{1 to} 250 ° C.

[0015]

The Young's modulus in the sheet width direction can be improved by limiting the components of the steel sheet and selecting the production conditions, for example, hot rolling conditions.

The present inventor investigated how the texture of the steel sheet changes when the manufacturing conditions are changed, and what kind of mode the Young's modulus changes with it.

First, in order to suppress the recrystallization of the γ phase, a low carbon steel containing a small amount of Nb, V, and Ti was used to perform strong working in the γ phase unrecrystallized region and to cool at various cooling rates. The steel plate was investigated. By performing strong working in the γ-phase unrecrystallized region, the surface area of the γ grain boundary, which is the α-nucleus generation site, and the annealing twin boundary increases, so it is possible to obtain a fine ferrite-pearlite structure after transformation. The texture formed at this time is formed by rolling in the γ region or α + γ two-phase region, and finally remains as the texture of α, and recovery, recrystallization or carbonitride in the process occurs. It is affected by the precipitation of and the transformation behavior from γ to α.
The orientation component characteristic of this texture is {311} <0
11> and {332} <113>. And these azimuth components were almost the same.

The TD direction of the {311} <011> orientation component is <332>, which is very close to the orientation axis <111> showing the maximum Young's modulus in the αFe single crystal as described above. In order to improve the Young's modulus, a means for increasing the <011> direction component should be taken.

Next, the steel sheets having the same composition are hot-rolled in the α + γ two-phase region, not in the γ-phase non-recrystallization region,
The rolling end temperature was set just above the Ar ₁ point and then slowly transformed. As a result, the orientation component of the transformation texture {311}
It was confirmed that <011> accumulates much more strongly than {332} <113> and Young's modulus is greatly improved.

Hereinafter, various conditions in the hot rolled steel sheet and the method for producing the same of the present invention will be described in detail.

(A) Hot-rolled steel sheet (a) Chemical composition (hereinafter, all "%" of the content of alloy components are "% by weight.") Of the alloy elements in the hot-rolled steel sheet of the present invention, C, Si, M
n, sol.Al and Ni are selected so that the α + γ two-phase region appears in an appropriate width in order to control the texture after the α + γ → α transformation.

C (carbon): 0.8% or less C is an element which is preferably contained in order to form a fine carbide that suppresses recrystallization in the α + γ two-phase region and to control the texture by the α + γ → α transformation. Is. However, when C is too large, the α + γ two-phase region disappears, so the upper limit is 0.8%, which is the eutectoid concentration. However, if the α + γ two-phase region has an appropriate width, the invention of the above (5) and (6) It is preferably 0.2% or less because the method is easy to carry out.

Si: 3% or less Si is an α-stabilizing element and expands the α + γ two-phase region for controlling the texture by α + γ → α transformation. It is also an element that acts as a deoxidizer. However, if the Si content is too high, the solutionability of the steel decreases due to solid solution hardening, and the formation of low-melting-point oxide firelite (Fe ₂ SiO ₄ ) is promoted. It becomes difficult to wash, and the weldability deteriorates, leading to breakage of the welded joint in the pickling line. In order to avoid these adverse effects, the upper limit of Si content is 3%. However, even if this element does not exist, the α + γ two-phase region does not disappear, so it is not always necessary to include it.

Mn (manganese): 0.1% or more and 3.0% or less Mn is a γ-stabilizing element, and is an element added for the purpose of controlling the α + γ two-phase region for controlling the texture by α + γ → α transformation. is there. It is also an element that fixes S (sulfur), which causes brittle fracture during hot rolling, as MnS, so it is desirable to contain 0.1% or more, preferably about 1.5%. However, if the Mn content is too high, solution hardening is impaired by solid solution hardening, so the upper limit is made 3.0%.

Sol.Al (aluminum): 0.01% or more, 3
% Or less Al is an α-stabilizing element and is added for the purpose of expanding the α + γ two-phase region for controlling the texture by α + γ → α transformation. Al also serves as a deoxidizer for steel. To obtain these effects, at least 0.01 as sol.Al.
% Content is required.

When the amount of Al is small, the precipitated AlN becomes fine, which hinders the growth of crystal grains. Therefore, it is desirable to set the sol.Al content to about 0.2% or more so that the AlN becomes coarse enough not to hinder the crystal grain growth. On the other hand, if too much Al is added, the solution property is significantly impaired due to solid solution hardening, so the upper limit of the sol.Al content is 3%.

In addition to the above components, the balance consists of Fe and inevitable impurities, but Ni may be contained if necessary.

Ni (nickel): 2.5% or less Ni is a γ-stabilizing element and is preferably added for the purpose of expanding the α + γ two-phase region for controlling the texture by α + γ → α transformation. However, since Ni is an expensive element, its upper limit is set to 2.5% in consideration of economic efficiency.

In addition to the above components, it is desirable to contain one or more elements selected from the element group consisting of Nb, V and Ti.

Nb (niobium): 0.1% or less Nb is preferably contained in an amount of 0.01% or more in order to form a fine precipitate that suppresses recrystallization in the α + γ two-phase region.
It is more preferable to contain 0.03% or more.
However, if the Nb content is too large, the precipitates become coarse and the effect of suppressing recrystallization is lost. Therefore, the upper limit of the Nb content is 0.1%.

V (vanadium): 0.2% or less V, like Nb, also produces fine precipitates that suppress recrystallization in the α + γ two-phase region. In order to obtain this effect, it is desirable to contain 0.01% or more. A more desirable content is 0.03% or more. However, the upper limit of V content is 0.2% for the same reason as Nb.

Ti (titanium): 0.1% or less The effect of Ti is the same as that of Nb and V described above. Desirably, the content is 0.01% or more, and more desirably 0.03% or more. The upper limit is 0.1% for the same reason as Nb and V.

(B) Texture The hot-rolled steel sheet of the present invention has the above-mentioned chemical composition, and is characterized in that the {311} plane reflection intensity parallel to the sheet surface is 5 times or more at a random ratio.

As described above, the Young's modulus of αFe single crystal is
Maximum value <111> direction is 29,000 kgf / mm ² , minimum value is <1
The 00> direction is 13150 kgf / mm ² . Therefore, the degree of integration effective for improving the Young's modulus by controlling the texture is such that the {311} plane reflection intensity by X-ray diffraction is 5 times or more, preferably 10 times or more in random ratio. When it is about 2 to 3 times, it is almost the same as the random orientation, and it is not effective for improving the Young's modulus.

(B) Manufacturing Method The steel sheet of the present invention having the above-mentioned texture has the above-mentioned (5)
And it can be manufactured by the method of (6).

In the method of the present invention, hot rolling is an essential condition in a region containing two phases of α + γ. Furthermore, the growth of crystal grains is suppressed as much as possible, and α grains after transformation are nucleated γ
In order to keep the grain boundary area as large as possible,
The heating temperature of the steel material (for example, slab) should be as low as possible. However, if the temperature is too low, the rolling load becomes excessive. For these reasons, the appropriate heating temperature range for hot rolling is 920 ° C to 1250 ° C.

In order to suppress the generation of the {332} <113> orientation component and increase the proportion of the {311} <011> orientation component in the texture of the steel sheet, the cumulative reduction amount in the α + γ region should be 50% or more. There must be. Particularly, when the rolling reduction in the two-phase region is 80% or more, the increase of {311} <011> orientation component is remarkable.

The rolling reduction in the α + γ range can be inevitably increased if the difference between the Ar ₃ point and the Ar ₁ point is large. However, even if this difference is small, reheating or heat retention during rolling can be performed. The rolling reduction can be increased by carrying out rolling while maintaining the temperature in the α + γ range.

Further, in order to increase the ratio of the unrecrystallized γ phase as much as possible, the rolling is finished in the temperature range of Ar ₁ point to (Ar ₁ point + 70 ° C.). Further, in order to allow the transformation to proceed slowly and to develop the transformation texture sufficiently, it is preferable to reduce the cooling rate after the completion of rolling.

When winding this hot-rolled steel sheet after rolling,
The temperature (winding temperature) is Ar ₁ point ~ (Ar ₁ point-250 ° C)
It is desirable to set it in the range of. If the coil is wound at a temperature above the Ar ₁ point, the γ phase recrystallizes and the transformation texture is hard to develop.
On the contrary, if this temperature is lower than (Ar ₁ point −250 ° C.), the effect of developing {311} <011> texture due to α grain growth becomes poor, which is not preferable. This {311} <01
The texture of 1> orientation is more likely to develop at a temperature as high as Ar ₁ point or less, so that it is more preferable to wind it at Ar ₁ point to (Ar ₁ point −150 ° C.).

When the hot rolled steel sheet is annealed, Ar ₁
It is recommended to perform in the temperature range from ₁ point to (Ar ₁ point-250 ° C). Ar does not develop the texture and performed at _one point the temperature exceeding, to randomize, the temperature (Ar ₁ point - 250 ° C.) in the opposite {311} by low and α grain growth than <011> set It is not preferable because the tissue is hard to develop. This temperature is also {311} <
In order to further develop the texture of 011> orientation, Ar ₁ point to (Ar ₁ point−150 ° C.) is more preferable. Even when the coiling temperature is lower than (Ar ₁ point −250 ° C.), the steel material of the present invention can be manufactured by performing this annealing treatment.

[0042]

Example 1 A steel ingot having a chemical composition shown in Table 1 was hot-forged into a steel piece having a thickness of 50 mm. Various kinds of steels having different transformation temperatures and α + γ two-phase temperature range (between Ar ₃ point and Ar ₁ point) were adjusted. Table 1 shows the measured values from Ar ₃ points to Ar ₁ points.

Since the transformation temperature varies depending on the steel type as shown in Table 1, the hot rolling finish temperature and the coiling temperature are individually selected as shown in Table 2 and hot rolling is performed to obtain the final strip thickness of 3
mm. From the center of these hot-rolled steel sheets, 0.5 mm thickness x 25
An X-ray diffraction sample having a width of 25 mm and a length of 25 mm and a Young's modulus measuring sample having a thickness of 10 mm, a width of 20 mm and a length of 20 mm having a longitudinal axis in the plate width direction were cut out.

Table 3 shows {110}, {22 by X-ray diffraction.
0}, {211}, {222}, {322}, {62
The measurement results of the reflection strength (relative to the random ratio), Young's modulus and tensile strength of the 2} plane are shown. Since the reflection intensity of the {311} plane cannot be measured directly, the reflection intensity of the {622} plane was measured as an alternative. This measured value substantially means the reflection intensity of the {311} plane.

The {622} plane reflection strengths of the steel types A to K are extremely high, being 5 times or more, and the Young's modulus in the plate width direction is all high.
It was 24000 kgf / mm ² or more. However, steel grade L ~
At T, the {622} plane reflection intensity is weak and the Young's modulus is 18500.
It is as low as ~ 21000kgf / mm ² . Since the steel types Q, R, S, and T were rolled only in the α region, {200}, which is the main component of the rolling texture, that is, {100} <011>, is extremely high.
Young's modulus is 21,000 kgf / mm ² or less.

Since the steel types L and M have a low cumulative rolling reduction in the α + γ two-phase region, the Young's modulus is lower than that of the steel types A to K.
It stays around 21000kgf / mm ² .

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

[0050]

Example 2 As shown in Table 4, steel pieces of steel type A in Table 1 are
Hot rolling was performed under different conditions of heating temperature, hot rolling end temperature, and winding temperature, and a sample was cut out in the same manner as in Example 1 and {110}, {220}, {211}, {2 by X-ray diffraction.
22}, {322}, and {622} plane reflection intensity and Young's modulus in the plate width direction were compared. The results are shown in Table 5.

As described above, one of the conditions for increasing the ratio of the orientation component {311} <011> effective for improving the Young's modulus in the texture of the steel sheet is the cumulative rolling reduction amount in the α + γ region. In order to increase the amount and the ratio of the unrecrystallized γ phase as much as possible, the rolling should be performed with Ar ₁ point or more (Ar ₁ point +70
It is preferable to finish at a temperature of (° C.) or less. Considering this condition for steel A, the hot rolling finish temperature is 793 ℃ (Ar
₍₁ point) and 793 ℃ + 70 ℃ are desirable, and in order to maximize the cumulative reduction, the lower limit of 7
Temperatures close to 93 ° C would be desirable. When the hot rolling end temperature is lower than 793 ° C, the rolling reduction in the α region increases and the rolling reduction in the α + γ region decreases, which is not preferable.

As shown in Table 4, in the case of A3 steel and A4 steel, Ar ₃ −
Since the hot rolling end temperature is close to 200 ° C, the rolling reductions in the α + γ range can be 77% and 88%, which is considerably higher than the 33-46% of other A1, A2, A5, A6 steels. As shown in Table 5, the X-ray diffraction-induced {622} plane reflection intensities are 8.0 and 6.1 times higher for A3 and A4, respectively, compared to 1.8 to 2.9 times higher for others. And the Young's modulus in the width direction is
A3 and A4 are 24500kgf / mm ² and 25600kgf / mm ² , other
The value is remarkably higher than that of 15800 to 19500 kgf / mm ² .

[0053]

[Table 4]

[0054]

[Table 5]

[0055]

Example 3 As shown in Table 6, a steel piece of steel type I (50 mm thick) in Table 1 was hot-rolled to a thickness of 3 mm under different heating temperature, hot rolling end temperature, and coiling temperature. A sample was cut out in the same manner as in Example 1, and the {622} plane reflection intensity by X-ray diffraction and the Young's modulus in the plate width direction were measured. The results are also shown in Table 6.

Heating temperature of slab before rolling is too high 3-1
Or, in the case of 3-5 where the hot rolling finishing temperature is ₁ point or less of Ar, {62
Both the 2} plane reflection intensity and the Young's modulus in the plate width direction are low.

[0057]

[Table 6]

[0058]

Example 4 As shown in Table 7, steel pieces of steel type C in Table 1 (thickness: 50 mm) were hot-rolled to a thickness of 3 mm under different heating temperature, hot-rolling end temperature, and coiling temperature. A sample was cut out in the same manner as in Example 1, and the {622} plane reflection intensity by X-ray diffraction and the Young's modulus in the plate width direction were measured. The results are also shown in Table 7.

[0059] coiling temperature was lower than (Ar ₁ -250 ℃)
In 4-5, both the {622} plane reflection intensity and the Young's modulus in the plate width direction were low.

This sample 4-5 was annealed at 680 ° C. for 10 hours and is shown in Table 7 as 4-6. A test piece of the same size was cut out from the center part of the plate thickness and analyzed by X-ray diffraction {622}
When the surface reflection strength and the Young's modulus in the plate width direction were measured, the {622} surface reflection strength was 12.7 and the Young's modulus was 24802 kgf.
It was / mm ² .

[0061]

[Table 7]

[0062]

The hot-rolled steel sheet of the present invention has a very high Young's modulus in the sheet width direction and is suitable for use as an outer panel of an automobile. The hot rolled steel sheet can be manufactured relatively easily and inexpensively by the above-described method of the present invention.

[0063]

Claims (6)

[Claims] 1. C .: 0.8% or less, Si: 3% or less, Mn: 0.1 to 3.0%, sol.Al: 0.01 to 3% by weight.
The balance consists of Fe and unavoidable impurities, and the {311} plane reflection intensity parallel to the plate surface is 5 times or more at a random ratio. 2. By weight%, C: 0.8% or less, Si: 3% or less, Mn: 0.1 to 3.0%, sol.Al: 0.01 to 3%, Ni: 2.5.
% Or less, the balance consisting of Fe and unavoidable impurities, and the {311} plane reflection intensity parallel to the plate surface is 5 times or more at a random ratio, with a high Young's modulus in the plate width direction. 3. In% by weight, C: 0.8% or less, Si: 3% or less, Mn: 0.1 to 3.0%, sol.Al: 0.01 to 3%, and
Contains at least one of Nb: 0.1% or less, V: 0.2% or less, and Ti: 0.1% or less, the balance being Fe and inevitable impurities, and the {311} plane reflection intensity parallel to the plate surface is random. A hot-rolled steel sheet having a high Young's modulus in the sheet width direction that is 5 times or more the ratio. 4. By weight%, C: 0.8% or less, Si: 3% or less, Mn: 0.1 to 3.0%, sol.Al: 0.01 to 3%, Ni: 2.5.
% Or less and Nb: 0.1% or less, V: 0.2% or less and
Ti: Contains at least one of 0.1% or less, the balance being Fe and inevitable impurities, and parallel to the plate surface {311}
A hot-rolled steel sheet having a high Young's modulus in the sheet width direction having a surface reflection strength of 5 times or more in a random ratio. 5. A steel material having the composition according to any one of claims 1 to 4 is heated in the range of 920 to 1250 ° C., and then α
The total rolling reduction in the + γ two-phase region is 50% or more, and the hot rolling finishing temperature is
Hot-roll to Ar ₁ ~ (Ar ₁ + 70 ° C), then Ar ₁ ~ (A
The method for producing a hot-rolled steel sheet according to claim 1, wherein the hot-rolled steel sheet is wound at r ₁ -250 ° C.). 6. A steel material having the composition according to any one of claims 1 to 4 is heated in the range of 920 to 1250 ° C., and then α
The total rolling reduction in the + γ two-phase region is 50% or more, and the hot rolling finishing temperature is
5. Hot rolling to obtain Ar ₁ to (Ar ₁ + 70 ° C.), winding at Ar ₁ or less, and annealing at Ar ₁ to (Ar ₁ −250 ° C.). The method for manufacturing a hot-rolled steel sheet according to any one of claims.