JPH06306537A - Hot rolled high strength steel sheet excellent in formability and spot weldability and its production - Google Patents

Abstract

PURPOSE:To produce a hot rolled high strength steel sheet excellent in formability and spot weldability at a high yield by preparing a steel sheet in which the componental compsn., the microstructure, the space factor of retained austenite, the balance of strength-ductility and the range of the dispersion in strength are specified. CONSTITUTION:The hot roller high strength steel sheet having a compsn. contg., by weight, 0.05 to 0.3% C, 0.5 to 3.0% Si, 0.5 to 3.0% Mn, <=0.02% P, <=0.01% S, 0.005 to 0.10% Al and 0.0005 to 0.01% Ca or 0.005 to 0.05% rare earth metals, and the balance Fe with inevitable elements, in which the microstructure is constituted of three phases of ferrite, banite and retained austenite, the space factor of the retained austenite is regulated to <=5% over the whole length and whole width, and as characteristics, >=20000 (MPa.%) strength-ductility balance (tensile strengthXtotal elongation) is secured over the whole length and whole width and the range of the dispersion in strength is suppressed to <=50 (MPa.%) is prepd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has excellent moldability (strength-ductility balance, uniform elongation (protrudability), hole expandability (stretch flangeability)) intended for use in automobiles, industrial machines and the like. Bending property, secondary workability, toughness), high yield ratio (high yield strength), and excellent spot weldability, and a hot rolled high strength steel plate coil with little material variation over the entire length and width, and its The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art Demand for high-strength steel sheets is increasing mainly due to weight reduction of steel sheets for automobiles and ensuring safety at the time of collision. Even with high-strength steel sheets, demands for formability and weldability are high. A steel sheet that is strong and has both excellent formability and excellent spot weldability is desired. As a steel sheet having an excellent balance of strength and ductility, which is one of the factors of formability, a Dual Phas conventionally composed of ferrite and martensite has been used.
e steel (so-called DP steel) is known. This DP steel exhibits a strength-ductility balance superior to that of the solid solution strengthened high strength steel sheet and the precipitation strengthened high strength steel sheet, but the value is TS × T. E
L <20,000 MPa.% (TS: tensile strength, T.EL:
It is the total elongation), and it is the actual situation that the further demand for workability cannot be satisfied.

To overcome this situation, TS × T. EL ≧ 20
TRIP phenomenon of retained austenite (TRansformation Induced Plasti
city: transformation-induced plasticity). The inventors of the present invention utilize this TRIP phenomenon to make use of JP-A-63-4017.
JP-A-64-79345 and JP-A-3-10049 have proposed a high-strength hot-rolled steel sheet having an excellent strength-ductility balance and a method for producing the same. EL ≧ 20,000
Achieved MPa ·%.

However, when actually manufacturing this high-strength hot-rolled steel sheet coil, there is a problem in that there is a large variation in the material over the entire length and width of the coil. For example, the tensile strength at the end is 80 (MPa
%), And it was impossible to secure a strength-ductility balance (tensile strength x total elongation) ≧ 20000 (MPa ·%) over the entire length and width, and the product yield was remarkably reduced. .

[0005]

Therefore, according to the present invention,
The material variation of this high-strength hot-rolled steel sheet coil is reduced, and the variation range of tensile strength is 50 (MPa) over the entire length and width.
・ Providing a manufacturing method to improve the yield by maintaining the strength-ductility balance (tensile strength × total elongation) ≧ 20000 (MPa ・%) over the entire length and width, while keeping it within 100%. It is an issue.

[0006]

The gist of the present invention is as follows. (B) C = 0.05 to 0.3% by weight as a chemical component, S
i = 0.5 to 3.0% by weight, Mn = 0.5 to 3.0% by weight, P ≦ 0.02% by weight, S ≦ 0.01% by weight, Al =
0.005-0.10% by weight, Ca = 0.005-
0.01% by weight or REM = 0.005 to 0.05% by weight as a main component, and the microstructure is composed of three phases of ferrite, bainite, and retained austenite, and has a retained austenite space factor over the entire length and width. 5% or more. As a characteristic, the strength-ductility balance (tensile strength x total elongation) ≥ 20000 (MPa-%) is secured over the entire length and width, and the strength variation range is within 50 (MPa-%). A hot-rolled high-strength steel sheet with excellent formability and spot weldability characterized by being suppressed.

(B) As a chemical component, C = 0.05 to 0.
3% by weight, Si = 0.5 to 3.0% by weight, Mn = 0.5
.About.3.0 wt%, P ≦ 0.02 wt%, S ≦ 0.01 wt%, Al = 0.005 to 0.10 wt%, Ca = 0.
0005-0.01% by weight or REM = 0.005
Using a billet obtained by casting steel with 0.05% by weight as the main component, finish rolling is performed with a total reduction rate of ≧ 80%, and the finish rolling end temperature at the center portion of the steel sheet width direction is Ar ₃ ± 50 ° C. Cooling is performed on the hot run table so that the cooling rate at the central portion in the width direction of the steel plate is 30 ° C./sec or more. At this time, both ends of the steel plate are partially or at several points on the hot run table. Since the coil is masked so that water does not splash on the part within 200 to 50 mm, the coiling temperature is 350 to 450 ° C. over the entire length and width of the coil. A hot rolled high-strength steel sheet with excellent ductility balance (tensile strength x total elongation) ≥ 20000 (MPa ·%) and strength variation range within 50 (MPa ·%) and excellent spot weldability. Production method.

(C) As a chemical component, C = 0.05 to 0.
3% by weight, Si = 0.5 to 3.0% by weight, Mn = 0.5
.About.3.0 wt%, P ≦ 0.02 wt%, S ≦ 0.01 wt%, Al = 0.005 to 0.10 wt%, Ca = 0.
0005-0.01% by weight or REM = 0.005
Using a billet obtained by casting a steel containing 0.05 wt% as a main component, finish rolling is performed with a total reduction rate of ≧ 80% and a finish rolling end temperature at the center of the steel sheet width direction ≧ Ar ₃ −50. Cooling at a hot run table is performed at a cooling rate in the central portion in the width direction of the steel sheet of ₃ or less up to a temperature T1 of Ar _{1 or} more and more than Ar _1.
It is performed at a temperature of less than 0 ° C / sec and a temperature of 30 ° C / sec or more after T1, and at this time, a mask is applied so that water is not splashed on a part of the hot run table or several parts within 200 to 50 mm from both ends of the steel plate. By doing so, the coiling temperature over the entire length and width of the steel sheet is set to 350 to 450 ° C. The strength-ductility balance (tensile strength × total elongation) ≧ 20,000 (MPa) over the entire length and width.・ The manufacturing method of hot rolled high strength steel sheet with excellent formability and spot weldability, with the strength variation range kept within 50 (MPa ・%).

(D) As a chemical component, C = 0.05 to 0.
3% by weight, Si = 0.5 to 3.0% by weight, Mn = 0.5
.About.3.0 wt%, P ≦ 0.02 wt%, S ≦ 0.01 wt%, Al = 0.005 to 0.10 wt%, Ca = 0.
0005-0.01% by weight or REM = 0.005
Using a billet obtained by casting a steel containing 0.05 wt% as a main component, finish rolling is performed with a total reduction rate of ≧ 80% and a finish rolling end temperature at the center of the steel sheet width direction ≧ Ar ₃ −50. Cooling at a hot run table at a central portion in the width direction of the steel plate at a temperature of 30 ° C. up to a temperature T1 of Ar ₃ or higher and higher than Ar _1.
Water cooling at a temperature of at _{least 1} second / second, at 30 ° C./second or less after T1, and at 30 ° C. or more after the temperature of T1 or lower and Ar ₁ or higher.
Water cooling at a speed of at least 1 second per second, and at the time of water cooling, 200 to 5 from both ends of the steel plate at a part or several places on the hot run table.
By masking the part within 0 mm so that water is not splashed, the coiling temperature over the entire length and width of the steel plate is 3
Strength-ductility balance (tensile strength x total elongation) ≥ 200 over the entire length and width, which is characterized in that the temperature is 50 to 450 ° C.
00 (MPa ・%) and the strength variation range is 50 (M
A method for manufacturing hot rolled high strength steel sheet with excellent formability and spot weldability that are kept within Pa.%).

(E) As a chemical component, C = 0.05 to 0.
3% by weight, Si = 0.5 to 3.0% by weight, Mn = 0.5
.About.3.0 wt%, P ≦ 0.02 wt%, S ≦ 0.01 wt%, Al = 0.005 to 0.10 wt%, Ca = 0.
0005-0.01% by weight or REM = 0.005
Using a billet obtained by casting a steel containing 0.05% by weight as a main component, after heating both ends of the steel sheet before finish rolling, the total rolling reduction of finish rolling ≧ 80%, the width of the steel sheet The finish rolling at the center of the direction is within the range of Ar ₃ ± 50 ° C, and the finish rolling is performed so that the variation range of the finishing rolling finish temperature over the entire length and width of the steel sheet is within 50 ° C. Cooling is performed so that the cooling rate at the central portion in the width direction of the steel sheet is 30 ° C./sec or more. At this time, at a portion on the hot run table or at several locations, within 200 to 50 mm from both ends of the steel sheet. By masking so that water does not splash, the winding temperature over the entire length and width of the steel sheet is set to 350 to 450 ° C. Strength-ductility balance (tensile strength x total width) over the entire length and width. Elongation) ≧ 2 000 method for producing (MPa ·%) to ensure moldability and spot weldability excellent hot rolled high strength steel sheet with reduced variation range of intensity within 30 (MPa ·%).

(F) As a chemical component, C = 0.05-0.
3% by weight, Si = 0.5 to 3.0% by weight, Mn = 0.5
.About.3.0 wt%, P ≦ 0.02 wt%, S ≦ 0.01 wt%, Al = 0.005 to 0.10 wt%, Ca = 0.
0005-0.01% by weight or REM = 0.005
Using a billet obtained by casting a steel containing 0.05% by weight as a main component, after heating both ends of the steel sheet before finish rolling, the total rolling reduction of finish rolling ≧ 80%, the width of the steel sheet The finishing rolling finish temperature at the center of the direction becomes higher than Ar ₃ -50 ° C, and the finishing rolling is performed so that the variation range of the finishing rolling finish temperature over the entire length and width of the steel sheet is within 50 ° C. Cooling at the table is 3 until the cooling rate at the central portion in the width direction of the steel sheet is Ar ₃ or less and is higher than Ar ₁ up to the temperature T1.
Perform at a temperature of less than 0 ° C / sec and a temperature of 30 ° C / sec or more after T1, and at this time, use a mask to prevent water from splashing on a part of the hot run table or several parts within 200 to 50 mm from both ends of the steel plate. By doing so, the winding temperature over the entire length and width of the steel sheet is set to 350 to 450 ° C. The strength-ductility balance (tensile strength × total elongation) ≧ 22000 (MPa) over the entire length and width.・ The manufacturing method of hot rolled high strength steel sheet which is excellent in formability and spot weldability with the strength variation range kept within 30 (MPa ・%).

(G) As a chemical component, C = 0.05 to 0.
3% by weight, Si = 0.5 to 3.0% by weight, Mn = 0.5
.About.3.0 wt%, P ≦ 0.02 wt%, S ≦ 0.01 wt%, Al = 0.005 to 0.10 wt%, Ca = 0.
0005-0.01% by weight or REM = 0.005
Using a billet obtained by casting a steel containing 0.05% by weight as a main component, the finish rolling end temperature at the widthwise center of the steel sheet is A
r ₃ −50 ° C., finish rolling is performed so that the variation range of finish rolling end temperature over the entire length and width of the steel plate is within 50 ° C., and cooling on the hot run table is performed in the steel plate width direction. In the central portion, water is cooled at a temperature of 30 ° C./sec or more up to a temperature T1 of Ar ₃ or higher and higher than Ar ₁ , and T
1 or later, 30 ℃ / sec or less, and T1 or less A
Water cooling at 30 ° C / sec or more after temperature T2 above r _{1, and} when cooling with water, mask a part of the hot run table or several places within 200 to 50 mm from both ends of the steel plate so that water is not masked. Therefore, the winding temperature over the entire length and width of the steel sheet is 350 to 450 ° C., and the strength-ductility balance (tensile strength × total elongation) ≧ 22000 (MPa ·%) over the entire length and width. ), The range of strength variation is kept within 30 (MPa ·%), and a method for manufacturing hot-rolled high-strength steel sheet with excellent formability and spot weldability.

[0013]

In the following, the basic conditions for obtaining a hot rolled high strength steel sheet excellent in formability and spot weldability will be described. Explain the regulation value of the main component and the reason for the limitation.
C is added in an amount of 0.05 wt% or more in order to secure residual austenite (hereinafter referred to as residual γ), but in order to prevent embrittlement of the welded portion and obtain the best spot weldability,
The upper limit of addition is less than 0.3% by weight.

Si and Mn are strengthening elements. Further, Si has an action of securing the residual γ by promoting the production of ferrite (hereinafter referred to as α) and suppressing the production of carbides, and Mn stabilizes γ and secures the residual γ. There is. When the content of C is as low as less than 0.15% by weight, that is, when it is difficult to obtain the residual γ, it is necessary to sufficiently exert the action of Si and Mn. Therefore, the effects of Si and Mn can be sufficiently exerted only by controlling the lower limit of addition of each of them. That is, Si,
The lower limit of addition of each Mn must be 0.5% by weight or more. However, even if Si and Mn are excessively added, the above effect is saturated, and conversely, weldability deteriorates and slab cracking occurs. Therefore, the upper limit of addition of each of Si and Mn is 2.
It should be 5% by weight or less. When particularly excellent surface properties are required, Si = 1.0 wt% to 2.0 wt% is desirable.

Although P is effective in securing the residual γ, in the present invention, the upper limit is set to 0.02% by weight in order to maintain the secondary workability, toughness and weldability at the best. If these characteristics are not strictly required, it may be added up to 0.2% to help increase the residual γ. In order to prevent the hole expandability from deteriorating due to oxide inclusions, the upper limit of S is 0.01% by weight.
And Al is α that has undergone deoxidation and grain refinement of γ by AlN
0.005% by weight or more is added for the purpose of increasing the space factor, refining α, increasing residual γ, and refining, but the upper limit of addition is 0.10% by weight because of the saturation of the effect. In addition, in order to help increase the residual γ, Al may be added up to 3%.

Ca is 0.000 in order to improve the hole expandability by controlling the shape (spherical shape) of sulfide inclusions.
Although 5% by weight or more is added, the upper limit is made 0.01% by weight from the viewpoint of saturation of the effect and adverse effect due to increase of inclusions (deterioration of hole expandability). For the same reason, the addition amount of REM is 0.005 to 0.05% by weight.

The above is the reason for adding the main components of the present invention. However, Nb, Ti, Cr, Cu, Ni, V, B and Mo are added to the range of 1 within the range that does not deteriorate the characteristics for the purpose of ensuring strength and fine graining.
You may add 1 type (s) or 2 or more types. Heating regulation, rolling regulation,
Values such as the cooling regulation and the winding regulation and the reasons for the limitation will be described. The lower limit of the finish rolling finish temperature is set to Ar ₃ −50 ° C. to prevent deterioration of workability (deterioration of elongation) due to the appearance of a worked structure (worked ferrite). In addition, the upper limit of the finish rolling finish temperature is one-stage cooling (Fig. 3), in order to secure the α space factor increasing effect, α grain refining effect, and fine grain residual γ increasing effect in the rolling process. Ar ₃ + 50 ° C. Two-stage cooling,
In the case of three-stage cooling (Fig. 3), α
Since the effect of increasing the space factor, the effect of refining α, and the effect of increasing the residual γ of fine particles can be expected, it is not particularly necessary to set the upper limit of the finishing temperature of finish rolling, but it is preferable to further enhance the effect. The upper limit is Ar ₃ + 50 ° C.

The total rolling reduction of finish rolling is 80% or more in order to secure the effect of increasing the α space factor, the effect of refining α, and the effect of increasing the residual γ of fine particles. It is desirable that the reduction ratio of each of the preceding four passes is 40% or more. The lower limit of the cooling rate of the first-stage cooling shown in FIG. 3 is 30 ° C./second in order to prevent the formation of pearlite. In the two-stage cooling shown in FIG. 3, in order to obtain the effect of increasing the α space factor and the effect of increasing the residual γ of fine particles, the cooling in the first stage requires Ar ₃ at a cooling rate of less than 30 ° C./sec.
Although the temperature is lowered to the following, in order to avoid the formation of pearlite, the cooling of the second stage from above Ar ₁ is started at a cooling rate of 30 ° C./sec or more. It should be noted that even if the temperature is maintained equal to or lower than Ar _{3 and} higher than Ar ₁ , it does not matter. However, in order to maintain the TRIP phenomenon over a wide strain range and obtain excellent characteristics, it is desirable that the cooling rate in the first stage is 5 to 20 ° C./sec.

In the three-stage cooling shown in FIG. 3, the first stage cooling is performed at 30 ° C./sec or more to Ar ₃ or less because α is made finer. The second stage cooling is less than 30 ° C / sec in order to obtain the effect of increasing α space factor and the effect of increasing fine grain residual γ, but in order to avoid the formation of pearlite, the cooling from the third stage above Ar _{1 is performed.} Is started at a cooling rate of 30 ° C./sec or more. It should be noted that even if the temperature is maintained equal to or lower than Ar _{3 and} higher than Ar ₁ , it does not matter. However, in order to maintain the TRIP phenomenon over a wide strain range and obtain excellent characteristics, it is desirable that the cooling rate in the second stage is 5 to 20 ° C./sec.

Further, in any of the one-stage cooling, two-stage cooling and three-stage cooling methods, the α space factor increasing effect, α grain refining effect, fine grain residual γ increasing effect, and further cooling table length May be quenched immediately after rolling for the purpose of reducing The lower limit of the coiling temperature is higher than 350 ° C in order to prevent the formation of martensite and secure the residual γ. The upper limit is less than 500 ° C. in order to prevent excessive bainite transformation and secure residual γ while preventing the formation of pearlite.

The above are the reasons for restricting the production method of the present invention. The effect of increasing the α space factor, the effect of refining α, and the residual γ of fine particles
In order to increase the effect of increasing
Alternatively, the starting temperature of finish rolling may be equal to or lower than the finish rolling end temperature + 100 ° C., or may be used alone or in combination. Further, the upper limit may be set to 1170 ° C. in order to secure the best surface properties.

Further, cooling after winding may be performed by cooling or by forced cooling. In order to suppress the excessive bainite transformation and enhance the effect of securing the residual γ, the temperature may be cooled to less than 200 ° C at 30 ° C / hour or more. You may combine with the said heating temperature regulation and finish rolling start temperature regulation. The steel pieces used for rolling are so-called cold piece reheating, H
It may be either CR or HDR. Further, a steel piece produced by so-called thin wall continuous casting may be used.
Further, the hot-rolled steel sheet according to the present invention may be used as the original plating plate.

The above are the basic conditions for obtaining a hot rolled high strength steel sheet coil having excellent formability and spot weldability.
However, in actual manufacturing, it is difficult to satisfy all of the above conditions for the entire length and width of the coil, and as a result, as described above, the tensile strength at the end is greater than at the widthwise center. It was as high as about 60 to 100 (MPa ·%), and it was impossible to secure a strength-ductility balance (tensile strength × total elongation) ≧ 20000 (MPa ·%) over the entire length and width.

Then, as a result of repeated experiments and experiments, the present inventors have found that in order to solve the problems of this prior art, ROT (runout table between finish rolling and winding) is cooled with water. It has been found that it is most important to reduce the difference in cooling rate between the center and the end in the width direction and make the winding temperature as uniform as possible.

In normal water cooling performed over the width direction of the steel sheet, the cooling rate at the end portion is considerably higher than at the center portion in the width direction. Therefore, the winding temperature at the center in the width direction is set to 35
Even if the temperature is 0 ° C. or higher, the end portion becomes 350 ° C. or lower, and martensite appears instead of bainite and hardens. Therefore, TS is higher in the end portion than in the central portion. Therefore,
Masking to prevent water from splashing on the edges reduces the cooling rate at the edges and reduces the gap with the cooling rate at the center to prevent the formation of martensite and prevent hardening of the edges. It becomes possible.

As for how much the length from the end should be masked, it was found from various experiments that the length should be adjusted in the range of 50 mm to 200 mm. When the winding temperature of the central portion is high, the mask length is made short, and when the winding temperature of the central portion is low, the mask length is made long.

As shown in FIGS. 1 and 2, when the ROT is water-cooled, the end portion is masked so that the coiling temperature is 350 to 450 ° C. over the entire length and width of the coil, so that the coil is wound over the entire length and width. It was experimentally confirmed that it is possible to secure the strength-ductility balance (tensile strength x total elongation) ≥ 20000 (MPa ·%) and suppress the strength variation range within 50 (MPa ·%). Further, in addition to the above-mentioned treatment, it was discovered that by heating the end portion before finish rolling to reduce the difference in finish temperature between the center portion in the width direction and the end portion, it is possible to further reduce material variation.

In normal rolling, the temperature tends to lower at the end portion than at the widthwise central portion, so that the finish rolling temperature becomes lower at the end portion than at the central portion. Therefore, the ferrite grain size in the end portion is likely to be smaller than that in the center portion.
This also causes an increase in material variation.
Therefore, it is possible to further reduce the material variation by heating the end portion before finish rolling to reduce the difference in finish rolling temperature between the center portion in the width direction and the end portion.

The inventors of the present invention have conducted various experiments to heat the ends in the width direction before finish rolling so that the variation range of the finish rolling finish temperature over the entire length and width of the coil is within 50 ° C. After carrying out finish rolling,
By performing the mask treatment during ROT water cooling as described above, the strength-ductility balance (tensile strength x total elongation) ≥ 22000 (MPa%) is secured over the entire length and width, and the strength variation range is 30 ( It was confirmed that it would be possible to reduce the pressure to within (MPa%). An example is shown in FIGS. 1 and 2.

[0030]

[Examples] Table 1 shows the chemical composition of the sample steel other than Fe.
Actual rolling was performed using these steels, and the materials of the steel sheets were investigated. Table 2 shows the manufacturing conditions and the material of the steel sheet at that time.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

In Table 2, No. Nos. 1 to 12 are inventive examples, and No. In Nos. 1 to 6, the strength-ductility balance (tensile strength x total elongation) ≥ 20000 (MPa ·%) was secured over the entire length and width and the variation range of strength was suppressed to within 50 (MPa ·%). In Nos. 7 to 12, the strength-ductility balance (tensile strength × total elongation) ≧ 22000 (MPa ·%) was secured over the entire length and width, and the strength variation range was suppressed to within 30 (MPa ·%). Also, all of them have good spot weldability.

On the other hand, No. 13 to 22 are comparative examples. No. No. 13 has an excessive Si content and is No. No. 14 has an excessive amount of C and is no.
In No. 17, P is excessive and the spot weldability is deteriorated. No. In No. 15, S was excessive and hole expandability was deteriorated. N
o. No. 16 has a low Mn and No. In No. 18, the amount of residual γ was insufficient because the amount of C was small, and the strength-ductility balance could not be secured.

No. In 19, the finish rolling finish temperature is Ar ₃
It became lower than -50 ° C, and No. In No. 20, the total rolling reduction did not reach 80%, so the amount of residual γ was insufficient and the strength-
Ductility balance is not secured. No. In No. 21, since the cooling rate in the first stage cooling did not reach 30 ° C./sec, pearlite was generated and residual γ could not be secured at all. No. 22
However, since the amount of mask at the edge portion is too small, the range of tensile strength variation over the entire length and width cannot be set within 50 MPa.

[0037]

According to the present invention, the high strength hot-rolled steel sheet excellent in formability and weldability is kept within 50 (MPa.%) In the range of tensile strength variation over the entire length and width, and the entire length and width are reduced. Strength-ductility balance (tensile strength x total elongation) ≧
20,000 (MPa ·%) can be secured and the product can be manufactured with high yield, and the industrial and economic effects are very large.

[Brief description of drawings]

FIG. 1 is a chart showing a cooling pattern required for the present invention.

FIG. 2 is a table showing the effects of the end mask before the finish rolling and the end mask at the time of cooling on the tensile strength variation range over the entire length and width.

FIG. 3 is a table showing the effect of the end mask before the finish rolling and the end mask during cooling on the minimum value of tensile strength × total elongation over the entire length and width.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication C22C 38/58

Claims (13)

[Claims] 1. C = 0.05-0.3% by weight and Si = 0.5-3.0 as chemical components.
% By weight, Mn = 0.5 to 3.0% by weight, P ≦ 0.02% by weight, S ≦ 0.01% by weight, Al = 0.005%
0.10 wt%, Ca = 0.005-0.01 wt% or REM = 0.
005 to 0.05% by weight The balance consists of Fe and unavoidable elements, and is composed of three phases of ferrite, bainite, and retained austenite as a microstructure, and the retained austenite space factor is 5% or more over the entire length and width. As a characteristic, the strength-ductility balance (tensile strength x total elongation) ≧ 2000 over the entire length and width.
0 (MPa ・%) is secured and the variation range of strength is 50 (MPa ・%
・ Hot rolled high strength steel sheet with excellent formability and spot weldability, characterized by being kept within%). 2. C = 0.05-0.3% by weight and Si = 0.5-3.0 as chemical components.
% By weight, Mn = 0.5 to 3.0% by weight, P ≦ 0.02% by weight, S ≦ 0.01% by weight, Al = 0.005%
0.10 wt%, Ca = 0.005-0.01 wt% or REM = 0.
005-0.05 wt%, and Nb, Ti, Cr, Ni, V, B, Mo
1 or 2 or more of, and the balance consists of Fe and unavoidable elements, is composed of three phases of ferrite, bainite, and retained austenite as a microstructure, and has a retained austenite space factor of 5 over the entire length and width. % Or more,
As a characteristic, the strength-ductility balance (tensile strength x total elongation) ≧ 20000 (MPa ·%) is secured over the entire length and width, and the strength variation range is suppressed within 50 (MPa ·%). Hot rolled high strength steel sheet with excellent formability and spot weldability. 3. C = 0.05 to 0.3% by weight and Si = 0.5 to 3.0 as chemical components.
% By weight, Mn = 0.5 to 3.0% by weight, P ≦ 0.02% by weight, S ≦ 0.01% by weight, Al = 0.005%
0.10 wt%, Ca = 0.005-0.01 wt% or REM = 0.
005-0.05 wt% The balance is finish rolling using a billet obtained by casting steel consisting of Fe and unavoidable elements. Total rolling reduction ≧ 80%, finish rolling at the central portion in the width direction of the steel sheet Temperature is Ar ₃ ± 50 ° C
Cooling is performed on the hot run table so that the cooling rate at the central portion in the width direction of the steel plate is 30 ° C./sec or more. At this time, both ends of the steel plate are partially or at several points on the hot run table. By masking the part within 200 to 50 mm from water, the coiling temperature over the entire length and width of the coil is 350 to 450.
The strength-ductility balance (tensile strength x total elongation) ≥ 20000 (MPa.
%) And the strength variation range is kept within 50 (MPa ·%), and a method for manufacturing hot rolled high strength steel sheet with excellent formability and spot weldability. 4. In addition to C, Si, Mn, P, S, Al, Ca or REM, Nb, Ti, Cr, Ni, V, B, M
The method for producing a hot-rolled high-strength steel sheet having excellent formability and spot weldability according to claim 3, characterized in that it contains one or more of o. 5. C = 0.05 to 0.3% by weight and Si = 0.5 to 3.0 as chemical components.
% By weight, Mn = 0.5 to 3.0% by weight, P ≦ 0.02% by weight, S ≦ 0.01% by weight, Al = 0.005%
0.10 wt%, Ca = 0.005-0.01 wt% or REM = 0.
005-0.05 wt% The balance is finish rolling using a billet obtained by casting steel consisting of Fe and unavoidable elements. Total rolling reduction ≧ 80%, finish rolling at the central portion in the width direction of the steel sheet Temperature ≧ Ar ₃ −50 ° C.
The cooling rate in the hot run table is such that the cooling rate at the central portion in the width direction of the steel sheet is less than 30 ° C./sec until the temperature T1 above Ar _{3 and above} Ar ₁ and 30 ° C./sec or more after T1. At this time, at some or several places on the hot run table, masking was performed so that water was not applied to the portions within 200 to 50 mm from both ends of the steel plate, so that the coiling temperature over the entire length and width of the coil was 350. ~ 4
The strength-ductility balance (tensile strength x total elongation) ≥ 20,000 (MPa
・%) Is secured and the variation range of strength is 50 (MPa ・%)
A method for producing a hot-rolled high-strength steel sheet excellent in formability and spot weldability, which are suppressed within the range. 6. In addition to C, Si, Mn, P, S, Al, Ca or REM, Nb, Ti, Cr, Ni, V, B, M
The method for producing a hot-rolled high-strength steel sheet having excellent formability and spot weldability according to claim 5, characterized in that it contains one or more of o. 7. C = 0.05-0.3% by weight and Si = 0.5-3.0 as chemical components.
% By weight, Mn = 0.5 to 3.0% by weight, P ≦ 0.02% by weight, S ≦ 0.01% by weight, Al = 0.005%
0.10 wt%, Ca = 0.005-0.01 wt% or REM = 0.
005-0.05 wt% The balance is finish rolling using a billet obtained by casting a steel consisting of Fe and unavoidable elements. Total rolling reduction ≧ 80%, finish rolling at the center in the width direction of the steel sheet Temperature ≧ Ar ₃ −50 ° C.
In the central part of the steel sheet width direction, cooling with a hot run table is performed at 30 ° C./sec or more up to a temperature T1 of Ar ₃ or more and above Ar ₁ , and at 30 ° C./sec or less after T1, Furthermore, after the temperature T2 below T1 and above Ar _1, it is water-cooled at 30 ° C./sec or more, and at the time of water-cooling, at some or several places on the hot run table, 20 from both ends of the steel plate is used.
By masking the part within 0 to 50 mm so that water does not splash, the coiling temperature is 350 to 450 ° C. over the entire length and width of the coil.
Strength-ductility balance (tensile strength x total elongation) over the entire width
A method for manufacturing hot-rolled high-strength steel sheet with excellent formability and spot weldability, with ≧ 20,000 (MPa ·%) secured and variation range of strength kept within 50 (MPa ·%). 8. In addition to C, Si, Mn, P, S, Al, Ca or REM, Nb, Ti, Cr, Ni, V, B, M
The method for producing a hot-rolled high-strength steel sheet having excellent formability and spot weldability according to claim 7, characterized in that it contains one or more of o. 9. C = 0.05-0.3% by weight and Si = 0.5-3.0 as chemical components.
% By weight, Mn = 0.5 to 3.0% by weight, P ≦ 0.02% by weight, S ≦ 0.01% by weight, Al = 0.005%
0.10 wt%, Ca = 0.005-0.01 wt% or REM = 0.
005-0.05% by weight The balance is Fe and the steel sheet obtained by casting a steel consisting of unavoidable elements is used to heat both ends of the steel sheet before finish rolling, and then the total reduction ratio of finish rolling ≧ 80%, the finish rolling finish temperature in the widthwise center of the coil is within the range of Ar ₃ ± 50 ° C, and the finish rolling is performed so that the variation range of the finish rolling finish temperature over the entire length and width of the coil is within 50 ° C. Cooling is performed on the hot run table so that the cooling rate at the central portion in the width direction of the steel sheet is 30 ° C./sec or more. At this time, 200 or more from both ends of the steel sheet at a part or several places on the hot run table. By masking the part within ~ 50mm from water, the coiling temperature is 350-450 ° C over the entire length and width of the coil. Strength over the entire length and width- Of a hot rolled high strength steel sheet with excellent formability and spot weldability by ensuring the property balance (tensile strength x total elongation) ≥ 22000 (MPa ·%) and suppressing the strength variation range within 30 (MPa ·%). Production method. 10. C, Si, Mn, P, S, Al, Ca
Or in addition to REM, Nb, Ti, Cr, Ni, V, B,
The method for producing a hot-rolled high-strength steel sheet having excellent formability and spot weldability according to claim 9, comprising one or more types of Mo. 11. C = 0.05 to 0.3% by weight and Si = 0.5 to 3.0 as chemical components.
% By weight, Mn = 0.5 to 3.0% by weight, P ≦ 0.02% by weight, S ≦ 0.01% by weight, Al = 0.005%
0.10 wt%, Ca = 0.005-0.01 wt% or REM = 0.
005-0.05% by weight The balance is Fe and the steel sheet obtained by casting a steel consisting of unavoidable elements is used to heat both ends of the steel sheet before finish rolling, and then the total reduction ratio of finish rolling ≧ 80%, the finish rolling end temperature of the widthwise center portion of the coil is higher than Ar ₃ -50 ° C., worked up as variations range finish rolling end temperature of the entire length and width of the coil is within 50 ° C. After rolling, the hot run table is cooled at a temperature T at which the cooling rate at the central portion in the width direction of the steel sheet is Ar ₃ or less and more than Ar _1.
It is carried out so that it is less than 30 ° C / sec up to 1 and 30 ° C / sec or more after T1, and at this time, water is not splashed on a part or several places on the hot run table within 200 to 50 mm from both ends of the steel plate. By masking in this way, the coiling temperature over the entire length and width of the coil is 35
Strength-ductility balance (tensile strength x total elongation) ≥ 2200 over the entire length and width characterized by 0 to 450 ° C
0 (MPa ・%) is secured and the strength variation range is 30 (MPa
・ Method for producing hot-rolled high-strength steel sheet excellent in formability and spot weldability, which is suppressed within%). 12. C, Si, Mn, P, S, Al, Ca
Or in addition to REM, Nb, Ti, Cr, Ni, V, B,
The method for producing a hot-rolled high-strength steel sheet having excellent formability and spot weldability according to claim 11, comprising one or more types of Mo. 13. C = 0.05 to 0.3% by weight and Si = 0.5 to 3.0 as chemical components.
% By weight, Mn = 0.5 to 3.0% by weight, P ≦ 0.02% by weight, S ≦ 0.01% by weight, Al = 0.005%
0.10 wt%, Ca = 0.005-0.01 wt% or REM = 0.
005-0.05% by weight The balance is the steel strip obtained by casting the steel consisting of Fe and unavoidable elements, and the finish rolling end temperature of the widthwise central part of the coil is higher than Ar ₃ -50 ° C. , Finish rolling is performed so that the variation range of finish rolling end temperature over the entire length and width of the coil is within 50 ° C., and cooling is performed on the hot run table at the central portion in the width direction of the steel sheet.
Water cooling is performed at a temperature of 30 ° C./sec or more up to a temperature T1 of Ar ₃ or higher and above Ar ₁ , water cooling is performed at a temperature of 30 ° C./sec or lower after T1, and water cooling is performed at a temperature of 30 ° C./sec or higher after T2 of T1 or higher and higher than Ar _1. However, at the time of water cooling, by masking part of the hot run table or several parts within 200 to 50 mm from both ends of the steel plate so that water is not sprayed, the winding temperature over the entire length and width of the coil can be increased. 350-4
The strength-ductility balance (tensile strength x total elongation) ≥ 22000 (MPa over the entire length and width characterized by being set at 50 ° C
・%) And the strength variation range is 30 (MPa ・%)
A method for producing a hot-rolled high-strength steel sheet excellent in formability and spot weldability, which are suppressed within the range.