JPH07216498A - Production of oxide grain dispersed cast bloom and rolled shape steel with superior toughness, using this cast bloom as stock - Google Patents

Abstract

PURPOSE:To attain superior toughness by subjeating a cast bloom, in which Al-Mg-Ti compound oxides are dispersed, to heating/cooling type controlled rolling. CONSTITUTION:A molten steel, having a composition containing, by weight ratio, 0.04-0.20% C, 0.05-0.50% Si, 0.4-1.8% Mn, 0.05-0.20% V, 0.004-0.0150% N, and 0.005-0.025% Ti, is preliminarily deoxidized, by which the amount of remaining oxygen is regulated to 0.003-0.15%. Then, an Fe-Al-Mg alloy is added and the amounts of Al and Mg are regulated to 0.005-0.015% and 0.001-0.010%, respectively. The molten steel is cast and cooled down to 900 deg.C at a rate of (0.5 to 20) deg.C/s, by which Al-Mg-Ti oxides of a size of <=3mum are incorporated into the resulting cast bloom by >=20pieces/mm<2>. Subsequently, the cast bloom is heated to 1100-1200 deg.C and rolling is started, and then, water cooling is done until a cast bloom surface layer temp. of <=700 deg.C is reached and rolling is performed in the course of recuperation between passes. This process is repeated once or more. After the completion of rolling, cooling is done down to 650-400 deg.C at a rate of (1 to 20) deg.C/s, followed by air cooling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an oxide particle-dispersed slab for providing a material-controlled rolled steel having excellent toughness which is used as a structural member of a building, and an excellent toughness using the slab. The present invention relates to a method for manufacturing rolled shaped steel.

[0002]

2. Description of the Related Art Due to the construction of super-high-rise buildings and stricter safety standards, steel materials used for columns, such as H-section steel with a particularly large plate thickness (hereinafter referred to as extra-thick H-section steel) Are required to have higher strength, higher toughness, and lower yield ratio. In order to satisfy such required characteristics, conventionally, heat treatment such as normalizing treatment is performed after the rolling is completed. The addition of heat treatment causes a significant cost increase such as reduction of heat treatment cost and production efficiency, and there is a problem in economic efficiency. In order to solve this problem, it was necessary to develop a new alloy design slab and manufacturing method so that high-performance material properties could be obtained as-rolled.

Generally, shaped steel with a flange, such as H
When a shaped steel is manufactured by universal rolling, the web, flange, and
Differences occur in the rolling finish temperature, reduction rate, and cooling rate at each part of the fillet. As a result, variations in strength, ductility, and toughness occur between the parts, and for example, rolled steel for welded structures (JI
Some parts do not meet the criteria such as SG3106). In particular, when rolling an extremely thick H-section steel using a continuous casting slab as a raw material, there is a limit to the maximum thickness of the slab that can be produced by the continuous casting equipment, so that the lower pressure ratio is obtained. In addition, due to the dimensional accuracy restrictions on rolling modeling, the thick flange portion is hot rolled,
After the rolling is finished, the steel material is cooled gradually and the microstructure becomes coarse.

Although there is a grain refining method using TMCP, the shape rolling cannot be largely reduced at the time of hot rolling as in the method of manufacturing a steel sheet due to restrictions in shaping. Further, in the field of thick steel plates, there have been proposed techniques for producing high-strength and high-toughness steel by utilizing the precipitation effect of VN, for example, the techniques disclosed in JP-B-62-50548 and JP-B-62-54862. Since the molten steel is subjected to Al deoxidation treatment by the conventional method, fine Al that acts as an intragranular ferrite formation nucleus and has an effect on grain refinement
-Mg-Ti-based composite oxide was not formed, and the grain refinement of the structure was not sufficient. That is, in the conventional Al deoxidation, Al was added in the initial stage of the melting process to deoxidize the molten steel and the generated Al ₂
The purpose was to achieve high cleanliness by floating and separating O ₃ . That is,
The theme was how to reduce the oxygen concentration of molten steel and reduce the number of coarse primary deoxidized oxides in the steel.

In contrast to the conventional idea, the present invention was produced by controlling the composition and size of oxides and the dispersion density by selecting the deoxidizer in the steelmaking process, the order of addition, and the cooling control in the solidification process. The point is to utilize the oxide as a preferential precipitation site for heterophasic precipitation. That is, it is possible to disperse and crystallize a fine composite oxide that functions as an intragranular ferrite transformation nucleus, and to make the structure fine without applying a load to the rolling process by this oxide. In addition, the feature of TMCP adopted is that the structure can be efficiently refined even in the hot rolling under light reduction in the shape rolling instead of the strong reduction rolling performed for thick steel plates. It is a method of repeating water cooling, rolling and water cooling.

[0006]

In order to solve the above-mentioned problems, Al-Mg-Ti-based composites which function as preferential precipitation nuclei for intragranular ferrite and heterophase precipitation by adjusting the composition of the steelmaking process and devising the addition procedure. It is necessary to produce a slab in which oxide is crystallized and dispersed. In addition, the fillet part of the joint between the flange of the H-section steel and the web coincides with the center segregation part of the CC slab, and MnS present in this part remarkably stretches under the low temperature rolling condition, and the drawing value in the plate thickness direction is reduced. And may cause lamellae during welding. 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.

[0007]

DISCLOSURE OF THE INVENTION The present invention is intended to make a structure finer, and to perform a proper deoxidizing treatment in a steelmaking process to highly clean molten steel, regulate dissolved oxygen concentration, and Fe.
-Al (5 to 20%)-Mg (5 to 20%) alloy is added last and the addition order and Al and Mg addition amounts are specified.
By dispersing and crystallizing a large number of fine composite oxides that function as intragranular ferrite formation nuclei in the slab and water-cooling between hot rolling passes, a temperature difference is given between the surface layer and the inside of the steel sheet, and Even under the conditions, the infiltration into the inside at a higher temperature is enhanced, the work dislocation that becomes the intragranular ferrite forming nuclei is introduced, and the intragranular ferrite forming nuclei are increased. in addition,
By cooling the γ / α transformation temperature range after rolling,
According to the knowledge that the method of suppressing the grain growth of the nucleated ferrite can refine the microstructure, it is possible to manufacture a controlled rolled steel with high efficiency and low manufacturing cost. The main point of the solution is C: 0.04 to 0.20% and Si: 0.05% by weight.
~ 0.50%, Mn: 0.4-1.8%, V: 0.05
.About.0.20%, N: 0.004 to 0.015%, Ti:
A molten steel containing 0.005 to 0.025% and the balance being Fe and unavoidable impurities was adjusted to 0.003 to 0.015% by weight of dissolved oxygen by preliminary deoxidation treatment. -Mg alloy was added and Al in weight percent:
0.005-0.015%, Mg: 0.001-0.0
Molten steel with the composition adjusted to 10% is cast, cooled to 900 ° C at a cooling rate of 0.5 to 20 ° C / s, and the size is 3μ in the slab.
m The following Al-Mg-Ti-based composite oxide 20 / mm ²
Oxide particle-dispersed slab for rolled steel having excellent toughness, characterized by containing the above, C: 0.04 to 0.20% by weight, Si: 0.05
~ 0.50%, Mn: 0.4-1.8%, V: 0.05
.About.0.20%, N: 0.004 to 0.015%, Ti:
Including 0.005-0.025%, in addition Mo: 0.3
% Or less, Cr: 1.0% or less, Cu: 1.0% or less, N
i: 2.0% or less, Nb: 0.05% or less, B: 0.0
A molten steel containing one or two or more of any of 03% or less and the balance consisting of Fe and unavoidable impurities is subjected to a preliminary deoxidation treatment to obtain a dissolved oxygen content of 0.003 to 0.
After adjusting to 015%, a Fe-Al-Mg alloy is further added, and Al: 0.005 to 0.015% by weight% and Mg:
Molten steel with a composition adjusted to 0.001 to 0.010% is cast, cooled to 900 ° C at a cooling rate of 0.5 to 20 ° C / s, and Al-Mg-Ti-based composite oxide having a size of 3 µm or less is cast in a slab. Oxide particles dispersed slab for rolled shape steel having excellent toughness, characterized by containing at least 20 pieces / mm ² , C: 0.04 to 0.20% by weight, Si: 0.05
~ 0.50%, Mn: 0.4-1.8%, V: 0.05
.About.0.20%, N: 0.004 to 0.015%, Ti:
A molten steel containing 0.005 to 0.025% and the balance being Fe and unavoidable impurities was adjusted to 0.003 to 0.015% by weight of dissolved oxygen by preliminary deoxidation treatment. -Mg alloy was added and Al in weight percent:
0.005-0.015%, Mg: 0.001-0.0
Molten steel with the composition adjusted to 10% is cast, cooled to 900 ° C at a cooling rate of 0.5 to 20 ° C / s, and the size is 3μ in the slab.
m The following Al-Mg-Ti-based composite oxide 20 / mm ²
A step of starting rolling after reheating the contained slab to a temperature range of 1100 to 1300 ° C., water cooling the temperature of the surface layer of the billet to 700 ° C. or less in the rolling step, and rolling in a reheat process between passes Repeatedly rolled once or more, and after rolling is 1 to 20 ° C.
Method for producing rolled steel having excellent toughness, which comprises cooling to 650 to 400 ° C at a cooling rate of / s and allowing to cool, and C: 0.04 to 0.20% by weight% and Si: 0. .05
~ 0.50%, Mn: 0.4-1.8%, V: 0.05
.About.0.20%, N: 0.004 to 0.015%, Ti:
Including 0.005-0.025%, in addition Mo: 0.3
% Or less, Cr: 1.0% or less, Cu: 1.0% or less, N
i: 2.0% or less, Nb: 0.05% or less, B: 0.0
A molten steel containing one or more of any of the following 03 or less and the balance consisting of Fe and unavoidable impurities is subjected to a preliminary deoxidation treatment to dissolve oxygen in an amount of 0.003 to 0.0% by weight.
After adjusting to 15%, a Fe-Al-Mg alloy was further added, and Al: 0.005 to 0.015% and Mg: 0.
Cast molten steel with composition adjusted to 001 to 0.010%,
To 00 ° C. and cooled at a cooling rate of 0.5 to 20 ° C. / s, the cast slab containing a large inside slab of 3μm following Al-Mg-Ti-based composite oxide 20 / mm ² or more 1100-1300
Rolling is started after reheating to the temperature range of ℃, the temperature of the surface layer of the slab is water-cooled to 700 ℃ or less in the rolling process, and the process of rolling in the heat recovery process between passes is repeated once or more, and rolling is completed. The method for producing a rolled shaped steel having excellent toughness is characterized by cooling to 650 to 400 ° C. at a cooling rate of 1 to 20 ° C./s and then allowing to cool.

[0008]

The present invention will be described in detail below. Higher strength of steel is achieved by solid solution strengthening by ferrite grain refinement alloying elements, precipitation strengthening by dispersion strengthening fine precipitates by hardening phase, and the like. In addition, toughness is the grain 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. Etc.

Generally, as the strength of steel is increased, the toughness is lowered, and it is necessary to take contradictory measures against the increase in strength and the increase in toughness.
The only metallurgical factor that satisfies both is grain refinement. The feature of the present invention is to control deoxidation in the steelmaking process,
To regulate the cooling rate after solidification, to obtain a slab obtained by dispersing and crystallizing a large number of fine composite oxides that function as intragranular ferrite formation nuclei in the slab, in a hot rolling process using it as a material, By repeating water cooling between hot rolling passes and rolling at the time of recuperation, the number of intragranular ferrite formation nuclei is increased.In addition, accelerated cooling is performed after rolling to suppress the growth of the ferrite and reduce the microstructure. The in-line rolling process for graining achieves high strength and high toughness of the base material.

Next, the reasons for limiting the composition range and control conditions of the shaped steel of the present invention will be described. First, C is added as an effective component for improving the strength of steel, and if it is less than 0.04%, the strength required for structural steel cannot be obtained. Also, 0.
Excessive addition of more than 20% significantly lowers the base metal toughness, weld crack resistance, weld heat affected zone toughness, etc., so the lower limit was made 0.04% and the upper limit was made 0.20%.

Next, Si is necessary for securing the strength of the base metal and pre-deoxidizing molten steel, but if it exceeds 0.50%, HAZ
It forms a high carbon martensite of hardened structure in the structure and significantly reduces the toughness of the welded joint. Further, if less than 0.05%, the necessary preliminary deoxidation of molten steel cannot be performed, so the Si content is limited to the range of 0.05 to 0.50%. Although Mn needs to be added in an amount of 0.4% or more to secure the strength and toughness of the base metal, the upper limit was set to 1.8% within the allowable range of the toughness and cracking property of the welded portion.

V is VN, which is an extremely important element that contributes to grain refinement by nucleation of intragranular ferrite and strengthening by precipitation strengthening. If it is less than 0.05%, the precipitation of VN is insufficient and those The effect is not obtained, and if it exceeds 0.20%, the precipitation amount becomes excessive and the base material toughness decreases, so 0.20.
% Or less. N is an extremely important element for the precipitation of TiN and VN. If it is less than 0.004%, TiN, VN
Therefore, the precipitation amount was insufficient, and the precipitation strengthening and the sufficient amount of the intragranular ferrite structure were not obtained, so the content was made 0.004% or more.
On the other hand, if the content exceeds 0.015%, the toughness of the base material is deteriorated and the surface crack of the slab is caused during continuous casting, so the content is limited to 0.020% or less.

[0013] Ti forms an Al-Mg-Ti-based composite oxide in the cast slab, and TiN is added to the outer shell of the particles during rolling.
To promote the formation of intragranular ferrite and to precipitate fine TiN to improve the toughness of the base material and the welded portion due to the austenite grain refining effect. Therefore, 0.0
If it is less than 05%, the Ti content in the composite oxide becomes insufficient, and the action as intragranular ferrite-forming nuclei decreases, so the lower limit of the Ti content was made 0.005% or more. But 0.025
%, Excess Ti forms TiC, which causes precipitation hardening and significantly reduces the toughness of the weld heat affected zone.

The molten steel having the adjusted components is subjected to a preliminary deoxidation treatment to control the dissolved oxygen to 0.003 to 0.015% by weight in order to highly clean the molten steel and at the same time to form a fine composite oxide in the slab. Is to generate. After pre-deoxidation

If the [0] concentration is less than 0.003%, the amount of the complex oxide of the intragranular ferrite forming nuclei that promotes the intragranular ferrite transformation is reduced, and the grain size cannot be reduced to improve the toughness. On the other hand, 0.01
If it exceeds 5%, even if other conditions are satisfied, the oxide coarsens to a size of 3 μm or more and becomes a starting point of brittle fracture, and toughness is reduced.

The [0] concentration was limited to 0.003 to 0.015% by weight.

The preliminary deoxidizing treatment is performed by vacuum degassing, Al, Si,
It was performed by Mg deoxidation. The reason is that the vacuum degassing process directly removes oxygen in molten steel as gas and CO gas,
This is because oxide-based inclusions such as l, Si, and Mg produced by strong deoxidation are easy to float and remove, and are effective for cleaning molten steel. Next, the Fe-Al-Mg alloy was added to the above-mentioned molten steel, and Al: 0.005 to 0.015% by weight% and Mg:
Casting the molten steel whose composition is adjusted to 0.001 to 0.010% and cooling it to 900 ° C. at a cooling rate of 0.5 to 20 ° C./s is due to Al-Mg-Ti having a size of 3 μm or less in the cast piece.
And performs the purpose of incorporating the system composite oxide into 20 / mm ² or more cast piece, sequentially described in detail the necessary reasons below below.

The Fe-Al-Mg alloy is Al: 1-20.
%, Mg: 1 to 20% The balance is Fe.
When Al or Mg metal alone is added, both are strong oxide-forming elements and produce stable Al ₂ O ₃ and MgO, which are active complex oxides of interest (cation vacancy of spinel crystal structure). Pore type, [Mg, Ti] O.Al ₂ O ₃ ) cannot be generated. In addition, these metals have a low melting point and a low density, and the addition yield to molten steel is low, so that they cannot be added uniformly. In order to improve this, an Fe-Al-Mg alloy was used to increase the melting point and density, and at the same time, lower the concentrations of Al and Mg, suppressing the reaction during oxide formation and enabling stable addition.

Al is limited to 0.005 to 0.015% because Al is a strong deoxidizing element, and the content of more than 0.015% forms a complex oxide which promotes intragranular ferrite transformation. However, in order to reduce the toughness, and excessive solid solution Al combines with N to form AlN, which is limited to 0.015% or less in order to reduce the amount of VN precipitation. Also, 0.
If it is less than 005%, the target composite oxide containing Al cannot be formed, so the content was made 0.005% or more.

The Mg content is limited to 0.001 to 0.010% because Mg is also a strong deoxidizing element, and the content of more than 0.010% produces a complex oxide that promotes intragranular ferrite transformation. However, in order to form coarse MgO and reduce toughness and ductility, it was limited to 0.010% or less. Also, 0.00
If it is less than 1%, the desired composite oxide containing Mg cannot be formed, so the content was made 0.001% or more.

The amounts of P and S contained as unavoidable impurities are not particularly limited, but welding cracks due to solidification segregation,
Since the toughness is reduced, it should be reduced as much as possible, and the P and S contents are preferably less than 0.02%, respectively. In addition to the above components, one of Mo, Cr, Cu, Ni, Nb, and B is used for the purpose of increasing the strength of the base metal and improving the toughness of the base metal.
It may contain one species or two or more species.

Mo is an element effective in securing the strength of the base material, but is expensive, so it is limited to 0.3% or less. Cr is effective in strengthening the base metal due to improvement in hardenability. However, excessive addition exceeding 1.0% is harmful from the viewpoint of toughness and curability, so the upper limit was made 1.0%.

Cu is an element effective for strengthening and weathering of the base material, but in order to promote temper embrittlement due to stress relief annealing, weld crackability, and hot work cracking, the upper limit was made 1.0%. Ni is an extremely effective element that enhances the toughness of the base material, but addition of more than 2.0% increases alloy cost and is not economical, so the upper limit was made 2.0%. Nb and B can be made into a low alloy and the welding characteristics can be improved because the rolling structure can be refined by adding a small amount. However, since excessive addition of these elements brings about hardening of the welded portion and increase of the yield point of the base metal, the upper limit of the content of each is Nb: 0.05%,
B: 0.003%.

The molten steel whose composition has been adjusted is 90
Cooling to 0 ° C at a cooling rate of 0.5 to 20 ° C / s is
This is done for the purpose of increasing the number of oxide particles and controlling their size. That is, the number of nucleated complex oxides crystallized by supercooling is increased, grain growth during cooling is suppressed at the same time, and the oxide having a size of 3 μm or less is cast on a slab.
This is done in order to contain more than 1 piece / mm ² . In slow cooling with a cooling rate of less than 0.5 ° C / s between these temperatures, the complex oxide aggregates and coarsens to less than 20 pieces / mm ² and reduces the toughness and ductility, so the cooling rate is 0.5 ° C / s or more. And The upper limit is set to 20 ° C./s because it is the limit of the cooling rate in the current casting technology. Next, the reason why the slab needs to contain 20 or more complex oxides / mm ² will be described. The material properties of the product are controlled by steelmaking, solidification structure of cast slab which is an innate factor governed by the casting process, component segregation, fine composite oxide of the present invention, precipitation and rolling, TMCP, heat treatment process, etc. It is determined by the microstructure of specific factors. Naturally, the property of the slab, which is an innate factor, is inherited in the subsequent process. The feature of the present invention resides in controlling one of the innate factors of the slab, and the composition of Al which functions as a preferential precipitation site for intragranular ferrite and heterophase precipitation in the slab.
-Mg-Ti-based composite oxide is generated and included. If the number of dispersed particles is less than 20 particles / mm ² , the number of precipitation sites of TiN, AlN and VN that precipitate on the composite oxide particles and express the intragranular ferrite nucleation function is insufficient, and the amount of intragranular ferrite formed is insufficient. This is because it cannot be made finer. The number of complex oxides is determined by measuring with an X-ray microanalyzer (EPMA).

The cast pieces that have been subjected to the above treatment are then 1100-1.
Reheat to a temperature range of 300 ° C. The reason for limiting the reheating temperature to this temperature range is that in the production of shaped steel by hot working, heating at 1100 ° C. or higher is required to facilitate plastic deformation, and 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 was set to 1100 ° C. The upper limit was set to 1300 ° C. in view of the performance and economical efficiency of the heating furnace.

The reason is that water cooling is performed between hot rolling passes, the temperature of the surface layer of the slab is cooled to 700 ° C. or less during rolling once, and hot rolling is performed in the recuperating process. By water cooling between rolling passes, a temperature difference is created between the surface layer and the inside of the slab, and in order to infiltrate the processing inside even under light reduction conditions,
This is because low-temperature rolling is performed efficiently in a short time. Cooling the temperature of the surface layer of the cast slab to 700 ° C. or lower is accelerated cooling following rolling, so that cooling from the normal γ temperature range causes the surface layer to be hardened to form a hardened phase and improve workability. Spoil. If cooled within such a limited temperature range, γ
/ Α transformation temperature or less, the surface layer temperature rises to the recuperative temperature until the next rolling, and processing is performed in the two-phase coexisting temperature range, hardenability can be significantly reduced, and hardening of the surface layer due to accelerated cooling can be prevented. .

After the rolling is completed, the temperature is continuously 1 to 20 ° C. /
When it is cooled down to 650 to 400 ° C. at the cooling rate of S and finished
The reason is that accelerated cooling suppresses ferrite grain growth.
Increased pearlite and bainite microstructure ratios with low alloy
To obtain the target strength, accelerate at 650-400 ℃
Cooling is stopped by accelerated cooling above 650 ° C. ₁
Above the point, some γ phase remains, and ferrite grain growth
Of pearlite and increase of pearlite and bainite structure ratio
Therefore, the temperature was set to 600 ° C. or lower. Also, 4
If cooled below 00 ° C, ferrite will be released by subsequent cooling.
The supersaturated solid solution of C and N is used as a carbide and a nitride.
Cannot be precipitated by reducing the ductility of the ferrite phase
Therefore, the temperature range is limited to this.

[0026]

[Example] A prototype shaped steel was melted in a converter, added with an alloy, and then pre-deoxidized to adjust the oxygen concentration of the molten steel, and then Fe-Al.
-Mg alloy added, continuous casting 250-300mm
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 drawing speed of 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 performed by providing water cooling devices 5a before and after the intermediate universal rolling mill 4 and repeating spray cooling of the inner and outer surfaces of the flange and reverse rolling. The flange and the web were spray-cooled by the cooling device 5b installed in.

The mechanical characteristics shown in FIG. 2 are 1/4 and 1/2 width (1 / 4B, 1/1) of the total flange width (B) at the central portion (1 / 2t ₂ ) of the plate thickness t ₂ of the flange 2. From 2B), a test piece was sampled and determined. The characteristics at these points were determined because the flange 1 / 4F section shows the average mechanical characteristics of the H-section steel, and the flange 1 / 2F section has the most deteriorated characteristics. This is because it was judged that it can represent the mechanical test characteristics of shaped steel.

Tables 1 and 2 show the chemical composition values of the trial steels,
The cooling rate after casting and the number of Al-Mg-Ti-based complex oxides in the slab are shown.

[0029]

[Table 1]

[0030]

[Table 2]

Tables 3 and 4 show rolling and accelerated cooling conditions and mechanical test properties of the product.

[0032]

[Table 3]

[0033]

[Table 4]

It is well known that the rolling heating temperature is set to 1280 ° C. Generally, it is well known that the reduction of heating temperature improves the mechanical properties, and the high temperature heating condition is presumed to show the minimum value of the mechanical properties. This is because it was judged that this value can represent the characteristics at heating temperatures lower than that. As shown in Table 5 and Table 6, the steels 1 to 7 and the steels A1 to A6 according to the present invention are
Target yield point range is JIS standard lower limit +80 N / mm ²
In SM490, YP = 325-405N / mm ² , S
For M520, YP = 335-415N / mm ² , SM57
At 0, YP was controlled to 430 to 510 N / mm ² , and the yield ratio (YP / TS) also satisfied the low YR value of 0.8 or less, and the tensile strength (said JISG3106) and the Charpy impact value at -10 ° C 47. (J) The above is sufficiently satisfied.

[0035]

[Table 5]

[0036]

[Table 6]

On the other hand, the comparative steels, Steel 8 and Steel B2, have the same composition and Fe.
-Al-Mg alloy addition and rolling conditions are also satisfied, but the cooling rate after casting is not more than the lower limit of the claims, and Al-
The number of Mg-Ti-based composite oxides is insufficient, and the generation of intragranular ferrite is insufficient. Therefore, the temperature of 1 / 2F is -10 ° C.
The target value of the Charpy test in vE _-10 ≧ 47J cannot be cleared. Nos. 9 to 11 were subjected to the usual Al kill treatment, the amount of Al exceeded the limit of the present invention, and Mg was not added. Therefore, since Al-Mg-Ti-based composite oxides were not produced, 1/2 F part The impact value cannot reach the target.

In addition, since steel 10 and steel B2 were not water-cooled during rolling and the cooling conditions after rolling were out of the claimed range, the ferrite phase could not be refined and the yield point was It falls and falls below the lower limit of the standard value. That is, when all the requirements of the present invention are satisfied, the steels 1 to 1 shown in Tables 5 and 6 are
7. Like steels A1 to A6, highly reliable high toughness shaped steels having a narrow yield point and high toughness of rolled shaped steels can be manufactured as rolled. The rolled shaped steel to which the present invention is applied is not limited to the H-shaped steel of the above-described embodiment, but is also applicable to shaped steel having a flange such as I-shaped steel, chevron steel, grooved steel, and unequal-thickness chevron steel. Of course you can.

Although the present invention is premised on the production in a converter, an electric furnace in which preliminary deoxidizing treatment is more easily performed, or a combination process of those and other auxiliary melting treatment furnaces is adopted. It may be adjusted to dissolved oxygen. Further, as the complex oxide of the present invention, an oxide containing Al, Mg, Ti as a base and other elements such as Si and Mn is referred to as an Al-Mg-Ti-based oxide. Of course. In addition to the Fe-Al-Mg alloy, an alloy of one or two of Fe, Al and Mg may be used for addition of Al and Mg of the present invention. The reheating process between the passes is performed between the passes from the start to the end of the reverse rolling or the continuous rolling, but this recuperation may be performed by a means for forcibly and rapidly heating.

[0040]

EFFECT OF THE INVENTION The slab according to the present invention and the rolled shape steel to which the controlled rolling method is applied have sufficient strength even in the flange plate thickness 1/2 and width 1/2 part where mechanical test characteristics are the most difficult to guarantee.
Production of shaped steel with excellent toughness is possible without rolling,
Industrial effects such as improvement of reliability, ensuring safety, and economic efficiency of large steel structures are extremely remarkable.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an example of device arrangement for carrying out the method of the present invention.

FIG. 2 is a view showing a cross-sectional shape of 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 for front and rear surfaces of intermediate rolling mill 5b ... Finishing mill Rear surface cooling device 6 ... Finishing rolling mill

Claims (4)

[Claims] 1. By weight%, C: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 1.8%, V: 0.05 to 0.20. %, N: 0.004 to 0.0150%, Ti: 0.005 to 0.025%, and the balance of Fe and unavoidable impurities in a molten steel by pre-deoxidation treatment to obtain a dissolved oxygen content of 0% by weight. After adjusting to 0.003 to 0.015%, Fe-Al-Mg alloy is further added, and A is added in% by weight.
1: 0.005-0.015%, Mg: 0.001-
Molten steel with the composition adjusted to 0.010% is cast, cooled to 900 ° C at a cooling rate of 0.5 to 20 ° C / s, and 20 pieces of Al-Mg-Ti-based complex oxide having a size of 3 µm or less are included in the cast slab. / Mm ² or more, an oxide particle-dispersed cast slab for rolled steel with excellent toughness, characterized by being contained. 2. C: 0.04 to 0.20% by weight%, Si: 0.05 to 0.50%, Mn: 0.4 to 1.8%, V: 0.05 to 0.20 %, N: 0.004 to 0.015%, Ti: 0.005 to 0.025%, and Mo:
0.3% or less, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 2.0% or less, Nb: 0.05% or less, B:
0.003 or less, a molten steel containing one or more of any one of the following and the balance consisting of Fe and unavoidable impurities, and a dissolved oxygen content of 0.003% by weight by preliminary deoxidation treatment.
After adjusting to 0.015%, Fe-Al-Mg alloy is further added, and Al: 0.005-0.015% by weight%, M
g: Molten steel having a composition adjusted to 0.001 to 0.010% is cast, cooled to 900 ° C. at a cooling rate of 0.5 to 20 ° C./s, and an Al-Mg-Ti system having a size of 3 μm or less in a cast piece. An oxide particle-dispersed cast slab for rolled shaped steel having excellent toughness, characterized by containing 20 or more complex oxides / mm ² . 3. C: 0.04 to 0.20% by weight, Si: 0.05 to 0.50%, Mn: 0.4 to 1.8%, V: 0.05 to 0.20. %, N: 0.004 to 0.015%, Ti: 0.005 to 0.025%, with the balance being Fe and unavoidable impurities, a dissolved steel having a residual oxygen content of 0. After adjusting to 003 to 0.015%, Fe-Al-Mg alloy is further added, and A
1: 0.005-0.015%, Mg: 0.001-
Molten steel with the composition adjusted to 0.010% is cast, cooled to 900 ° C at a cooling rate of 0.5 to 20 ° C / s, and 20 pieces of Al-Mg-Ti-based complex oxide having a size of 3 µm or less are included in the cast slab. / Mm ² or more contained slabs are reheated to a temperature range of 1100 to 1300 ° C, then rolling is started, water temperature of the surface layer of the slabs is cooled to 700 ° C or less in the rolling process, and rolling is performed in a reheat process between passes. Repeat the above process one or more times,
A method for producing a rolled shaped steel having excellent toughness, which comprises cooling to 650 to 400 ° C at a cooling rate of 20 ° C / s and allowing to cool. 4. C: 0.04 to 0.20% by weight%, Si: 0.05 to 0.50%, Mn: 0.4 to 1.8%, V: 0.05 to 0.20 %, N: 0.004 to 0.015%, Ti: 0.005 to 0.025%, and Mo:
0.3% or less, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 2.0% or less, Nb: 0.05% or less, B:
A molten steel containing one or more of 0.003 or less and the balance consisting of Fe and unavoidable impurities is subjected to a preliminary deoxidation treatment so as to have a dissolved oxygen content of 0.003 to 0.003% by weight.
After adjusting to 0.015%, Fe-Al-Mg alloy is further added, and Al: 0.005-0.015% by weight%, M
g: Molten steel having a composition adjusted to 0.001 to 0.010% is cast, cooled to 900 ° C. at a cooling rate of 0.5 to 20 ° C./s, and an Al-Mg-Ti system having a size of 3 μm or less in a cast piece. 1100 to slabs containing 20 or more complex oxides / mm ²
Rolling is started after reheating to a temperature range of 1300 ° C., the temperature of the surface layer of the cast slab is water-cooled to 700 ° C. or less in the rolling step, and the step of rolling in the reheat process between passes is repeated once or more,
650-40 at a cooling rate of 1-20 ° C / s after rolling
A method for producing rolled steel having excellent toughness, which comprises cooling to 0 ° C. and cooling.