JPH09111397A - Production of cast bloom for 590n/mm2 class shape steel and high tensile strength rolled shape steel using same as stock - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a high tensile strength rolled shape steel by rolling a low carbon bainitic steel bloom, containing specific amounts of Mg, Nb, V, Mo, B, etc., under specific conditions. SOLUTION: A steel bloom for 590N/mm<2> class shape steel, which has a composition containing, by weight, 0.02-0.10% C, 0.05-0.50% Si, 0.4-1.6% Mn, 0.005-0.025% Ti, 0.0005-0.005% Mg, <0.04% Nb, <0.1% V, <0.4% Mo, <0.003% B, <0.004% N, and <0.1% Al or further containing <1% Cr and/or <2% Ni and also containing Nb, V, Mo, and B so that the value of MAEQ, represented by 10[Nb%]+5[V%]+[Mo%]+100[B%], becomes 0.4-1.0, is used. This steel bloom is reheated to 1200-1300 deg.C, hot-rolled, and subjected, one or more times, to a repetition of a water cooling and rolling process in which water cooling is performed between rolling passes to cool the flange surface temp. of a rolled shape steel down to <=700 deg.C one or more times during rolling and rolling is done in the course of recuperation between the following rolling passes. After rolling is finished, slow cooling is successively performed down to 700-400 deg.C at (0.5 to 10) deg.C/sec cooling rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slab for high-tensile rolled steel having excellent toughness which is used as a structural member of a building, and a method for producing a high-tensile rolled steel using the slab. is there.

[0002]

2. Description of the Related Art Due to the increase in height of buildings and stricter safety standards, steel materials used for pillars, for example, H-beams having a particularly large thickness (hereinafter referred to as extra-thick H-beams) have been developed. There is a demand for higher strength, higher toughness, and lower yield ratio. In order to satisfy such required characteristics, conventionally, a heat treatment such as a normalizing process has been performed after the completion of rolling. The addition of heat treatment causes a significant increase in cost, such as a decrease in heat treatment cost and production efficiency, and has a problem in economy. In order to solve this problem, it was necessary to develop a slab with a new alloy design and a manufacturing method so that high-performance material properties could be obtained as rolled.

Generally, a section steel having a flange, for example, H
When a section steel is manufactured by universal rolling, the web, flange,
Differences occur in the rolling finish temperature, rolling reduction, and cooling rate at each part of the fillet. As a result, variations in strength, ductility, and toughness occur between parts, for example, rolled steel for welded structures (JIS G3
106) Some parts do not meet the criteria such as. Especially, extremely thick H
When a shaped steel is rolled from a continuously cast slab, there is a limit to the maximum thickness of the slab that can be produced by a continuous casting facility, so the lower pressure ratio is used. Further, the flange portion having a large thickness is subjected to high-temperature rolling due to the restriction of dimensional accuracy in the rolling molding, and the steel material after the rolling is gradually cooled, and the microstructure is coarsened.

Although there is a grain refining method using TMCP (work heat treatment), the shape rolling cannot be greatly reduced during hot rolling as in the method for manufacturing a steel sheet because of restrictions in shaping. Further, in the field of thick steel plates, high strength and high toughness steel is manufactured by utilizing the precipitation effect of VN, for example, Japanese Patent Publication Nos. 62-50548 and 62.
Although the technology of Japanese Patent No. 54862 is proposed. However, this method includes a bainite structure in the case of a high strength material of 590 N / mm ² grade, and in this bainite structure, high carbon island martensite is generated by a high concentration of solute N, and the toughness is remarkably reduced. Therefore, it cannot be applied to high strength steel.

[0005]

In order to solve the above-mentioned problems, it is necessary to generate low carbon bainite as it is rolled to make the structure fine. For that purpose, it is essential to manufacture a slab whose composition is adjusted by controlling a small amount of addition of Mg and microalloy in the steelmaking process. In addition, the fillet part of the joint between the flange of H-section steel and the web coincides with the center segregation part of the CC slab, and MnS present in this part is remarkably stretched under the low temperature rolling condition, and the drawing value in the plate thickness direction is reduced. Lower,
May cause lamellae during welding. It is necessary to generate MgS by adding Mg, prevent harmful MnS from being generated, and prevent lamella formation. As described above, it is difficult for the conventional technique to manufacture the desired highly reliable rolled steel having high strength and high toughness online and to provide it at low cost.

The present invention is different from the conventional idea in that it has a high strength due to the refinement of the structure by the addition of Mg and the formation of a low carbon bainite structure by the minute control of the fine oxide and the microalloy produced by the addition of Mg. This is the point of achieving a rolled steel with high toughness. In addition, the feature of TMCP adopted is that between rolling passes, it is possible to efficiently refine the structure even in hot rolling under light reduction in shaped steel rolling instead of strong reduction rolling performed for thick steel plates. It is a method of repeating water cooling, rolling and water cooling.

[0007]

The present invention is of high strength and high strength.
For the formation of low carbon bainite for the purpose of obtaining toughness
Microstructure refinement by adding Mg and N in the steelmaking process
Alloying by adding trace amounts of b, V, Mo, B and high Cu
Steel plate by water cooling between the gauge and hot rolling pass
A temperature difference is applied between the surface layer and the inside of the
In addition, it enhances the pressure reduction penetration into the inside at higher temperature,
Intragranular bainite formation by introducing dislocations that become nuclei
Increase the nucleus. In addition, the γ / α transformation temperature range after rolling
Bainite nucleated by cooling control
According to the method of suppressing the grain growth of
Manufacture of controlled rolled steel that can be manufactured with high efficiency and low manufacturing cost
The above problems were solved based on the finding that
Therefore, the main points are as follows. % By weight, C: 0.02-0.10%, Si: 0.05-0.50%, Mn:
0.4-1.6%, Cu: 0.7-1.5%, Ti: 0.005-0.025%, Mg: 0.00
05 to 0.005%, Nb: 0.04% or less, V: 0.1% or less, Mo: 0.4%
B: 0.003% or less, N: 0.004% or less, Al: 0.1% or less
Including below, and MAEQ = 10 [Nb%] + 5 [V%] + [Mo%] + 100 [B%]
Contains the amount of Nb, V, Mo, B that makes the MAEQ in the formula 0.4 to 1.0%
However, the balance is Fe and inevitable impurities.
590N / mm ^TwoSlab for grade steel. % By weight, C: 0.02-0.10%, Si: 0.05-0.50%, Mn:
0.4-1.6%, Cu: 0.7-1.5%, Ti: 0.005-0.025%, Mg: 0.00
05 to 0.005%, Nb: 0.04% or less, V: 0.1% or less, Mo: 0.4%
B: 0.003% or less, N: 0.004% or less, Al: 0.1% or less
Including below, and MAEQ = 10 [Nb%] + 5 [V%] + [Mo%] + 100 [B%]
Contains the amount of Nb, V, Mo, B that makes the MAEQ in the formula 0.4 to 1.0%
In addition, Cr: 1.0% or less, Ni: 2.0% or less, either
Contains 1 or 2 or more with the balance being Fe and unavoidable impurities
590 N / mm characterized by being composed of ^TwoCasting for grade steel
Pieces. % By weight, C: 0.02-0.10%, Si: 0.05-0.50%, Mn:
0.4-1.6%, Cu: 0.7-1.5%, Ti: 0.005-0.025%, Mg: 0.00
05 to 0.005%, Nb: 0.04% or less, V: 0.1% or less, Mo: 0.4%
B: 0.003% or less, N: 0.004% or less, Al: 0.1% or less
Including below, and MAEQ = 10 [Nb%] + 5 [V%] + [Mo%] + 100 [B%]
Contains the amount of Nb, V, Mo, B that makes the MAEQ in the formula 0.4 to 1.0%
However, the slab with the balance Fe and unavoidable impurities is 1200-
After reheating to the temperature range of 1300 ℃, start rolling and
After cooling the flange surface temperature of the shaped steel to 700 ° C or less,
The water-cooling / rolling process that is performed in the recuperation process between the descending rolling passes
Repeat rolling one or more times, and after rolling finishes 0.5 ~ 10 ℃ / s
Characterized by cooling to 700 to 400 ° C at the cooling rate and allowing to cool
590N / mm^TwoOf high grade rolled steel of high grade. % By weight, C: 0.02-0.10%, Si: 0.05-0.50%, Mn:
0.4-1.6%, Cu: 0.7-1.5%, Ti: 0.005-0.025%, Mg: 0.00
05 to 0.005%, Nb: 0.04% or less, V: 0.1% or less, Mo: 0.4%
B: 0.003% or less, N: 0.004% or less, Al: 0.1% or less
Including below, and MAEQ = 10 [Nb%] + 5 [V%] + [Mo%] + 100 [B%]
Contains the amount of Nb, V, Mo, B that makes the MAEQ in the formula 0.4 to 1.0%
In addition, Cr: 1.0% or less, Ni: 2.0% or less, either
Contains 1 or 2 or more with the balance being Fe and unavoidable impurities
After reheating the slab made of material to the temperature range of 1200 to 1300 ℃
Rolling is started and the flange surface temperature of shaped steel is
Water-cool to 700 ℃ or less and pressurize during subsequent reheating between rolling passes.
Repeat the water-cooling / rolling process by rolling once or more
After completion, cool to 700-400 ℃ at a cooling rate of 0.5-10 ℃ / s.
590 N / mm, characterized by being left to cool^TwoHigh tension pressure
Method for manufacturing rolled steel.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. Higher strength of steel is achieved by solid solution strengthening by ferrite alloy refinement alloying elements, precipitation strengthening by dispersion strengthening fine precipitates by hardening phase, and the like. Higher toughness is the refinement of crystals. Reduction of solid solution N and C in the parent phase (ferrite). Origin of reduced fracture. High carbon martensite and coarse oxides in the hardened phase, reduction and refinement of precipitates, etc. Achieved by

In general, toughness is reduced by increasing the strength of steel, and it is necessary to contradict high strength and toughness.
The only metallurgical factor that satisfies both at the same time is crystal refinement. The feature of the present invention is to achieve high strength and high toughness by fine grain structure refinement by dispersion of fine Mg oxide by addition of Mg and low carbon bainite microstructure based on microalloying alloy design in the steelmaking process.

Further, in the present invention, in the hot rolling step,
By repeatedly cooling the surface of the flange between the hot rolling passes with water and rolling at the time of recuperation, a reduction infiltration effect is imparted to the central portion of the flange thickness, and TMC is also applied to this portion.
The effect of refinement of the structure by P is enhanced, and the refinement of the structure improves the mechanical properties of the base material in each part of the H-section steel and reduces variations to achieve homogenization.

The reasons for limiting the composition range and control conditions of the shaped steel of the present invention will be described below. First, C is added to strengthen the steel. If it is less than 0.02%, the strength required for structural steel cannot be obtained. In addition, if added in excess of 0.10%, the base metal toughness, weld crack resistance, and weld heat affected zone (hereinafter HA
(It is abbreviated as Z) It significantly reduces the toughness, etc., so the lower limit is 0.
02% and the upper limit was 0.10%.

Next, Si is necessary for securing the strength of the base metal and pre-deoxidizing molten steel, but if it exceeds 0.50%, high carbon island martensite with a hardened structure is formed in the HAZ and the welded joint part is formed. Remarkably reduces toughness. On the other hand, if it is less than 0.05%, the pre-deoxidation of molten steel cannot be sufficiently performed, so that the Si content is 0.05 to
It was limited to the range of 0.50%. Mn must be added in an amount of 0.4% or more to secure the strength and toughness of the base metal, but
It was set to 1.6% from the upper limit of the allowable concentration for cracking.

Cu retains in the α temperature range and is slowly cooled to precipitate a Cu phase on dislocations in the α phase, and the precipitation hardening increases the room temperature strength of the base material. However, C in this α
If the precipitation of u phase is less than 0.7%, it is within the solid solubility limit of Cu in α, and since precipitation does not occur, strengthening by Cu precipitation cannot be obtained. At 1.5% or more, the precipitation strengthening is saturated, so Cu:
Limited to 0.7-1.5%.

Ti precipitates TiN and reduces solid solution N. As a result, it is added to suppress the precipitation of BN, increase the amount of solid solution B, and enhance the hardenability increasing effect of B. The finely precipitated TiN also contributes to the refinement of the γ phase. The action of these Ti increases the strength. Therefore, if less than 0.005%, the precipitation amount of TiN is insufficient, and these effects are not exhibited, so the lower limit of the Ti amount is O.
It was set to 005%. However, if it exceeds 0.025%, excess Ti becomes Ti
C was precipitated, and its precipitation hardening deteriorates the toughness of the base material and the weld heat affected zone, so the content was limited to 0.025% or less.

The Mg alloy used for adding Mg is Si-Mg-Al and
Ni-Mg. The reason for using Mg alloy is that M
This is because the content of g is reduced, the deoxidation reaction at the time of addition to molten steel is suppressed, the safety at the time of addition and the yield of Mg are improved. Mg is limited to 0.0005-0.005% because Mg
Is also a strong deoxidizing element, and the Mg oxide crystallized is easily floated and separated in molten steel. Therefore, even if it is added in excess of 0.005%, the yield does not exceed this value, so the upper limit was made 0.005%.
If it is less than 0.0005%, the dispersion density of the target Mg-based oxide is insufficient, so the lower limit was made 0.0005%. Although the Mg-based oxide here is mainly described as MgO, according to electron microscopic analysis and the like, this oxide is Ti, a trace amount of Al.
And a complex oxide with Ca and the like contained as impurities.

Nb is added for the purpose of significantly increasing hardenability and increasing strength by coexistence of solid solution Nb and B.
If it exceeds 0.04%, the precipitation amount of Nb carbonitride increases and the effect as solid solution Nb is saturated, so it was limited to 0.04% or less. The addition of a small amount of V can make the rolling structure finer and strengthening it by precipitation of vanadium carbonitride, so that a lower alloy can be obtained and welding characteristics can be improved. However, excessive addition of V causes hardening of the weld and higher yield point of the base metal, so the upper limit of the content was made V: 0.1%.

Mo is an element effective for securing the strength of the base material and the high temperature strength. If it exceeds 0.4%, Mo carbide (Mo2 C) will precipitate and the effect of improving the hardenability as solid solution Mo will be saturated.
Limited to 0.4% or less. B increases hardenability by adding a small amount and contributes to an increase in strength. Further, when B exceeds 0.003%, an iron boron compound is formed and hardenability is reduced, so the content is limited to 0.003% or less.

N forms nitrides and suppresses precipitation strengthening and grain growth, while solute N strengthens ferrite and promotes formation of high carbon island martensite at lath boundaries of bainite phase to improve toughness. The N content was limited to 0.004% or less for deterioration. Al is set to 0.1% or less because Al is a strong deoxidizing element, and if the content exceeds 0.1%, the formation of coarse inclusions and the nozzle clogging at the time of casting cause 0.1%.
Limited to:

Next, among the micro alloys, Nb, V, M
Regarding the content of o and B, MAEQ = 10 [Nb%] + 5 [V%] + [Mo%] + 1
The MAEQ expressed by the formula of 00 [B%] was specified to be 0.4 to 1.0%. As described above, in the present invention, in order to improve the hardenability and to obtain the bainite structure, solid solution Nb, V, M
By adding o and B, it was found that there was a certain relationship between the mutual contents of these elements and the contribution to the above-mentioned hardenability, and this was found to be the microalloy equivalent (Micro alloy Equiva
lent: Defined as MAEQ. ). If the MAEQ in this formula is less than 0.4%, the target bainite structure ratio cannot be obtained, and if it exceeds 1.0%, bainite can be obtained, but excess elements precipitate as carbonitrides and lead to a decrease in toughness, so the range of 0.4-1.0%. Limited to.

The amounts of P and S contained as unavoidable impurities are not particularly limited, but since weld cracking due to solidification segregation and deterioration of toughness occur, they should be reduced as much as possible, preferably the amounts of P and S respectively. It is desirable to limit it to less than 0.02%. In addition to the above elements, one or more of Cr and Ni can be contained for the purpose of increasing the strength of the base material and improving the toughness of the base material.

[0021] Cr is effective in strengthening the base material by improving the hardenability. However, an excessive addition exceeding 1.0% is harmful from the viewpoint of toughness and curability, so the upper limit was made 1.0%. Ni is an extremely effective element that enhances the toughness of the base metal, but the addition of more than 2.0% increases the alloy cost and is not economical, so the upper limit was made 2.0%. The slab that has undergone the above treatment is then reheated to a temperature range of 1200 to 1300 ° C. The reason why the reheating temperature is limited to this temperature range is that the manufacturing of shaped steel by hot working requires heating of 1200 ° C. or higher to facilitate plastic deformation, and that elements such as V and Nb are sufficiently added. Since it is necessary to form a solid solution, the lower limit of the reheating temperature is 1200 ° C.
And The upper limit is 1300 from the performance and economical efficiency of the heating furnace.
° C.

One water-cooling / rolling step is performed in which water is cooled between hot rolling passes, the flange surface temperature is cooled to 700 ° C. or less during rolling once, and rolling is performed in the reheat process between the next rolling passes. The reason for repeating the above is to impart a temperature difference between the surface layer portion and the inside of the flange by water cooling between rolling passes, and to permeate the processing strain into the inside even under a light reduction condition, and in a short time by water cooling. This is because low-temperature rolling is realized and TMCP is efficiently performed.

After the flange surface temperature is cooled to 700 ° C. or lower, rolling in the recuperating process is carried out in order to suppress quench hardening and soften the surface due to accelerated cooling after finish rolling. The reason is that the flange surface temperature is 700 ° C
Once cooled, the γ / α transformation temperature is temporarily cut off, and the surface layer is reheated and heated by the next rolling. Rolling is performed in the γ / α two-phase coexisting temperature range. A mixed structure with the fine α thus formed is formed. Thereby, the hardenability of the surface layer can be significantly reduced, and the hardening of the surface layer caused by accelerated cooling can be prevented.

After the rolling is completed, 0.5 to 10 ° C./s continues.
The reason for cooling to 700 to 400 ° C. at the cooling rate and allowing to cool is to suppress the grain growth of ferrite and refine the bainite structure by accelerated cooling to obtain high strength and high toughness. Next, the accelerated cooling is stopped at 700 to 400 ° C. When the cooling is stopped at a temperature higher than 700 ° C., a part of the surface layer becomes an Ar1 point or more and a γ phase remains.
The stop temperature of the accelerated cooling was set to 700 ° C. or lower because ferrite transformation was performed with the coexisting ferrite as a nucleus. Also, with cooling below 400 ° C.,
The high carbon martensite generated between the laths of the bainite phase during the subsequent cooling can not be decomposed due to the precipitation of cementite during the cooling, and exists as a hardened phase. This high carbon martensite acts as a starting point of brittle fracture, resulting in a decrease in toughness. For these reasons, the stop temperature of the accelerated cooling was limited to 700 to 400 ° C.

[0025]

[Examples] Prototype shaped steel was melted in a converter, added with an alloy, and then pre-deoxidized to adjust the oxygen concentration in the molten steel.
Next, add Mg alloy and 250-300mm by continuous casting
It was cast into a thick slab. The cooling of the slab was controlled by selecting the amount of water in the secondary cooling zone below the mold and the speed of drawing the slab. Although the slab is heated and the rough rolling step is not shown,
It was rolled into an H-section steel by the universal rolling apparatus train shown in FIG. Water cooling between rolling passes is provided with a water cooling device 5a before and after the intermediate universal rolling mill 4, and spray cooling and reverse rolling are repeated on the outer surface of the flange. Accelerated cooling after rolling is performed after finishing rolling by the finishing universal rolling mill 6. The outer surface of the flange was spray-cooled by the cooling device 5b installed in the above.

The mechanical characteristics are shown in FIG. 2, which is 1/4 of the overall flange width (B) at the center (1 / 2t2) of the plate thickness t2 of the flange 2.
From the 1/2 width (1 / 4B, 1 / 2B), it was determined using the collected test piece. The characteristics of these points were calculated as
Flange 1 / 4F shows the average mechanical properties of H-section steel,
This is because the properties of the flange 1 / 2F part are most deteriorated, and it was judged that these two points can represent the mechanical test properties of the H-section steel.

Tables 1 and 2 show the chemical composition values of the steels of the present invention and comparative steels, Tables 3 and 4 show the rolling and accelerated cooling conditions of those steels, and Tables 5 and 6 show them. The mechanical test characteristic values, the number of Al-Mg-based oxides, and the MAEQ values of these H-section steels are shown. It is well known that the rolling heating temperature is set to 1300 ° C. It is generally known that the γ grains become finer and the mechanical test characteristics are improved by lowering the heating temperature. This is because it is estimated that the value shows a value, and it is judged that this value can represent the mechanical test characteristics at a heating temperature lower than that.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

[Table 5]

[0033]

[Table 6]

As shown in Tables 5 and 6, in the H-section steels 1 to 5 and A1 to A2 according to the present invention, both the yield strength and the tensile strength are 59.
Meets JIS standard values for 0 N / mm ² grade steel. That is, the yield strength exceeds its lower limit of 445 N / mm ² , and the tensile strength is 590 N.
/ mm ² and their yield ratio (YS / TS) is 0.
A low YR value of 8 or less is satisfied. The Charpy impact value also exceeds 47 (J) at -10 ° C, which sufficiently meets the JIS standard value.

On the other hand, the H content steel 6 of the comparative steel has a Mo content, the H content steel 6 has a Cu content, and the H shape steel 7 has a Ti content less than the lower limit value. Does not meet the value. In the H-section steel 8, since Mg is not added and the refinement of the structure is not achieved, the strength is sufficient, but the toughness does not satisfy the standard value. Since the H-section steel 9 has an excessive amount of N, the solid solution B becomes ineffective as BN, so that the hardenability decreases and the strength becomes insufficient. Further, in the H-section steel 10 and the H-section steel A3, the MAEQ value is less than the lower limit value of the present invention, so that insufficient strength occurs. On the other hand, in H-section steel 11 and H-section steel A4, since the MAEQ value exceeds the upper limit value of 1.0, precipitation strengthening occurs, the toughness value is lowered, and the standard value cannot be satisfied.

That is, when all the requirements of the manufacturing method of the present invention are satisfied, H-section steels 1 to 5 and A1 shown in Tables 5 and 6 are obtained.
It is possible to produce a high-strength rolled steel having sufficient strength and low temperature toughness even at a flange plate thickness of 1/2 and width of 1/2, which is the most difficult to guarantee the mechanical test characteristics of rolled steel, as shown by A2. become. The rolled section steel to which the present invention is applied is not limited to the H section steel of the above embodiment, but is also applicable to section steels having flanges such as I section steel, angle steel, channel steel, and unequal thickness angle steel. Of course, you can.

[0037]

According to the present invention, the alloy-designed cast slab and the rolled section steel to which the controlled rolling method is applied have sufficient strength even in a flange plate thickness 1/2 and a width 1/2 part where mechanical test characteristics are hardly guaranteed. The production of shaped steel with excellent toughness becomes possible as it is rolled, and the industrial effects such as improvement of reliability, safety and economical efficiency of large steel structures are extremely remarkable. .

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of an apparatus arrangement for performing the method of the present invention.

FIG. 2 is a diagram illustrating a cross-sectional shape of an H-section steel and a sampling position of a mechanical test piece.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... H-shaped steel 2 ... Flange 3 ... Web 4 ... Intermediate rolling mill 5a ... Water cooling device of the front and rear surface of an intermediate rolling mill 5b ... Finishing rolling machine rear surface cooling device 6 ... Finishing rolling mill

Claims (4)

[Claims] 1. By weight%, C: 0.02 to 0.10%, Si: 0.05 to 0.50%, Mn: 0.4 to 1.6%, Cu: 0.7 to 1.5%, Ti: 0.005 to 0.025%, Mg: 0.0005 to 0.005%, Nb: 0.04% or less, V: 0.1% or less, Mo: 0.4% or less, B: 0.003% or less, N: 0.004% or less, Al: 0.1% or less, and MAEQ = 10 [Nb%] + 5 [V%] + [Mo
%] + 100 [B%] MAEQ is 0.4-1.0% Nb, V, M
A slab for 590 N / mm ² grade steel, containing o and B contents and the balance being Fe and inevitable impurities. 2. C: 0.02 to 0.10% by weight%, Si: 0.05 to 0.50%, Mn: 0.4 to 1.6%, Cu: 0.7 to 1.5%, Ti: 0.005 to 0.025%, Mg: 0.0005 to 0.005%, Nb: 0.04% or less, V: 0.1% or less, Mo: 0.4% or less, B: 0.003% or less, N: 0.004% or less, Al: 0.1% or less, and MAEQ = 10 [Nb%] + 5 MAEQ shown by the formula of [V%] + [Mo%] + 100 [B%] is 0.
It contains 4 to 1.0% of Nb, V, Mo and B, and Cr: 1.0
%, Ni: 2.0% or less, a 590 N / mm ² grade steel slab containing any one or more of Ni and 2.0 or more, and the balance being Fe and inevitable impurities. 3. C: 0.02 to 0.10%, Si: 0.05 to 0.50%, Mn: 0.4 to 1.6%, Cu: 0.7 to 1.5%, Ti: 0.005 to 0.025%, Mg: 0.0005 to 0.005%, in weight%. Nb: 0.04% or less, V: 0.1% or less, Mo: 0.4% or less, B: 0.003% or less, N: 0.004% or less, Al: 0.1% or less, and MAEQ = 10 [Nb%] + 5 [V%] + [Mo
%] + 100 [B%] MAEQ is 0.4-1.0% Nb, V, M
The slab containing O and B and the balance of Fe and unavoidable impurities is reheated to a temperature range of 1200 to 1300 ° C, and then rolling is started to reduce the flange surface temperature of the shaped steel to 700 ° C or less during the rolling process. Water cooling, rolling in the recuperation process between the subsequent rolling passes, the water cooling / rolling process is repeatedly rolled once or more, and after the rolling is completed, 0.
A method for producing a 590 N / mm ² class high-strength rolled shaped steel, which comprises cooling to 700 to 400 ° C at a cooling rate of 5 to 10 ° C / s and allowing to cool. 4. C: 0.02 to 0.10%, Si: 0.05 to 0.50%, Mn: 0.4 to 1.6%, Cu: 0.7 to 1.5%, Ti: 0.005 to 0.025%, Mg: 0.0005 to 0.005% by weight%. Nb: 0.04% or less, V: 0.1% or less, Mo: 0.4% or less, B: 0.003% or less, N: 0.004% or less, Al: 0.1% or less, and MAEQ = 10 [Nb%] + 5 [V%] + [Mo
%] + 100 [B%] MAEQ is 0.4-1.0% Nb, V, M
A slab containing 1 or 2 or more of Cr: 1.0% or less and Ni: 2.0% or less and the balance consisting of Fe and unavoidable impurities at 1200 to 1300 ° C. Rolling is started after reheating to the temperature range, the flange surface temperature of shaped steel is water-cooled to 700 ° C or less in the rolling process, and the water-cooling / rolling process is repeated at least once in the reheating process between rolling passes. After rolling, after finishing rolling 700 ~ 40 at 0.5-10 ℃ / s cooling rate
590N / mm ² characterized by cooling to 0 ℃ and allowing to cool
Of high grade rolled steel of high grade.