JP3472017B2 - Refractory rolled steel and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolled shaped steel having a flange such as rolled H-shaped steel excellent in fire resistance and toughness, which is used as a structural member of a building, and a method for producing rolled shaped steel by controlled rolling. Is.

[0002]

2. Description of the Related Art The fire resistant design was reviewed by a Ministry of Construction comprehensive project due to the super-rise of buildings and the sophistication of building design technology, and the "New Fire Resistant Design Law" was enacted in March 1987. Under this regulation, the restriction that fire-resistant coating was set to keep the temperature of steel materials to 350 ° C or less at the time of fire under the old law was lifted, and the fire-resistant coating that complies with the high temperature strength of steel materials and the actual load of buildings You can now decide how. That is, when the designed high temperature strength at 600 ° C. can be secured, the fireproof coating can be reduced accordingly.

In response to such a trend, Japanese Patent Laid-Open No. 2-
Japanese Patent No. 77523 discloses a low yield ratio steel for construction having excellent fire resistance, a steel material, and a manufacturing method thereof. The gist of the invention of this prior application is to improve the high temperature strength by adding Mo and Nb so that the yield point at 600 ° C. becomes 2/3 or more of that at room temperature. The reason why the design high temperature strength of the steel material is set to 600 ° C. is based on the finding that it is the most economical in view of the balance between the increase of the steel material cost due to the alloying element and the construction cost of the conventional steel material for fireproof coating.

Further, in the past, Al deoxidation of steel was performed by adding Al in the initial stage of the melting process to deoxidize molten steel and form Al ₂ O.
_The purpose was to float and separate ₃ to make it highly clean. That is, the theme was how to reduce the oxygen concentration of the molten steel and reduce the number of coarse primary deoxidized oxides in the steel.

[0005]

The inventors of the present invention have made the steel materials manufactured by the above-mentioned prior art into various shaped steels, particularly, H-shaped steels having complicated restrictions from severe shaping. As a result of trying to apply it, there is a difference in rolling finish temperature, rolling reduction, cooling rate at each part of the web, flange and fillet. , Ductility,
The toughness varied, and some parts of the rolled steel for welded structures (JIS G3106) did not meet the criteria. Further, in the refinement of the structure due to the formation of intragranular ferrite, it is effective in the component having a relatively high proportion of the structure of ferrite, but there is a defect that the refinement of the structure becomes difficult when the proportion of bainite is high.

In order to solve the above problems, the γ grain size can be adjusted to ASTM N even at a heating temperature of 1200 to 1300 ° C. during rolling.
If the grain size is 6 or more at o., it is possible to refine the structure even if the bainite structure ratio is high. Therefore, the development of the γ-fine graining method at the time of heating at high temperature is an issue. In order to achieve this purpose, it is possible to disperse fine precipitates that do not decompose at high temperatures and disperse, pin the growing γ grain boundaries, and suppress γ grain growth to reduce the grain size. .
The present invention has found that Mg-based oxides and composite precipitates of Mg-based oxides and TiN are effective as the precipitates, and aimed to develop a steel in which these are finely crystallized and precipitated.

In addition, conventional high temperature steels guarantee high temperature strength at 600 ° C. However, in the present invention, higher temperature (700 ° C.) is applied for the purpose of expanding the range of application of non-refractory coatings for buildings. The challenge is to develop a refractory steel that can guarantee high-temperature strength at (° C). Unlike the conventional idea, the present invention controls the composition and size of oxides and the dispersion density by selecting the deoxidizing material in the steel making process, the addition order of the deoxidizing material, and the cooling control of the solidification process, and the produced oxide is heterophase precipitated. It is used as a preferential precipitation site for materials (TiN, etc.). The applicant of the present application has previously mentioned in Japanese Patent Application No. 6-11705 that the oxide is made to function as an intragranular ferrite transformation nucleus, the microstructure is made fine by the generation of intragranular ferrite, and the homogeneity of the material properties between the parts of the H-section steel. The invention has been proposed that achieves high strength and high toughness. In contrast to this, the present invention disperses fine Mg-based oxides (mainly MgO) having high high-temperature stability and composite precipitates of Mg-based oxides and TiN in high density, and these precipitates are heated at 1200 It functions as a pinning site for suppressing the grain growth of the γ phase at ˜1300 ° C., and the grain refinement of the γ phase achieves a finer structure. By miniaturizing this structure, homogenization of material properties between parts of H-section steel and high toughness are achieved, and in addition to improving hardenability by adding a trace amount of Nb and V, Cu precipitation strengthening by adding Cu The yield strength at 700 ° C is 220M, which is 2/3 of the lower limit of the yield point at room temperature according to JIS standard of SM490 steel, 325 MPa.
It is characterized by achieving high strength at a high temperature of Pa or higher. Furthermore, in order to improve the toughness in the bainite structure, the formation of high carbon island martensite (hereinafter abbreviated as M *), which causes the decrease in toughness, is suppressed by extremely low boron and low carbon by microalloying. It is also a characteristic of the present invention to be achieved by. In addition, T in the manufacturing method
The characteristic of MCP is different from the low temperature / large reduction rolling that is often performed on thick steel plates, and it is possible to efficiently refine the structure even in the hot rolling under light reduction in shaped steel so that the grain refinement of the structure can be performed efficiently. It is a method of taking a step of repeating water cooling, water cooling, rolling and water cooling.

[0008]

Means for Solving the Problems The present invention aims at refining the microstructure, performs appropriate deoxidation treatment in the steelmaking process, and highly cleans molten steel, adjusts the dissolved oxygen concentration, adds Ti, and finally The casting order in which Si-Mg alloy and Ni-Mg alloy are added and the amount of Mg added are limited, and a cast piece in which fine Mg-based oxide is finely dispersed in the cast piece, and this cast piece as a raw material Water cooling between the rolling passes creates a temperature difference between the surface and inside of the H-section steel flange, and
We have developed a water-cooling method during rolling that can enhance the reduction penetration into the higher temperature central part of the plate thickness, introduce work dislocations that become α-forming nuclei, and achieve the refinement of the structure in the central part of the plate thickness. In addition, by controlling the cooling of the γ / α transformation temperature range after rolling, the method of suppressing the grain growth of nucleated ferrite can make the microstructure fine, which is highly efficient and inexpensive to manufacture. The above problems have been solved based on the finding that it is possible to produce fire-resistant rolled steel, and the gist thereof is as follows. C: 0.02-0.06% by weight%, Si: 0.05-0.25%, Mn:
0.8-1.6%, Mo: 0.4-0.8%, Cu: 0.7-1.5%, N: 0.004-
0.010%, B: 0.0003% or less, Nb: 0.03% or less, V: 0.1% or less, Al: 0.005% or less, with the balance being 0.003 to 0.010% by weight of oxygen in molten steel consisting of Fe and unavoidable impurities. After adjusting to, Ti: 0.012 to 0.030% was added so that the ratio of Ti and N would be Ti / N: 3.0 to 3.5, and Mg: 0.0005 to 0.0050.
% Of Mg-based oxides and Mg-based oxides and TiN composite precipitates with a size of 3 μm or less in the cast steel with 50% added.
A fire-resistant rolled steel having a content of / mm ² or more. C: 0.02-0.06% by weight%, Si: 0.05-0.25%, Mn:
0.8-1.6%, Mo: 0.4-0.8%, Cu: 0.7-1.5%, N: 0.004-
0.010%, B: 0.0003% or less, Nb: 0.03% or less, V: 0.1% or less, Al: 0.005% or less, and Cr: 1.0% or less, Ni:
After adjusting the oxygen content of molten steel containing one or more of 2.0% or less and the balance being Fe and unavoidable impurities to 0.003 to 0.010% by weight, the ratio of Ti and N is Ti / N:
Ti: 0.012 to 0.030% was added so as to be 3.0 to 3.5, and Mg: 0.0005 to 0.0050% was further added to the cast steel slab to obtain Mg-based oxides and Mg-based oxides and Ti with a size of 3 μm or less.
A refractory rolled steel characterized by containing 50 or more composite precipitates of N / mm ² . C: 0.02-0.06% by weight%, Si: 0.05-0.25%, Mn:
0.8-1.6%, Mo: 0.4-0.8%, Cu: 0.7-1.5%, N: 0.004-
0.010%, B: 0.0003% or less, Nb: 0.03% or less, V: 0.1% or less, Al: 0.005% or less, with the balance being 0.003 to 0.010% by weight of oxygen in molten steel consisting of Fe and unavoidable impurities. After adjusting to, Ti: 0.012 to 0.030% was added so that the ratio of Ti and N would be Ti / N: 3.0 to 3.5, and Mg: 0.0005 to 0.0050.
% Of Mg-based oxide and Mg-based oxide and TiN
The composites were precipitate is contained 50 / mm ² or more slab 1200-13
Rolling is started after reheating to a temperature range of 00 ° C, the flange surface temperature of shaped steel is water-cooled to 700 ° C or less in the rolling process, and rolling is performed in the subsequent reheating process between rolling passes. A method for producing a fire-resistant rolled steel shape, which comprises repeatedly rolling more than once, cooling to 700 to 400 ° C at a cooling rate of 0.5 to 10 ° C / s, and then leaving to cool after the rolling is completed. C: 0.02-0.06% by weight%, Si: 0.05-0.25%, Mn:
0.8-1.6%, Mo: 0.4-0.8%, Cu: 0.7-1.5%, N: 0.004-
0.010%, B: 0.0003% or less, Nb: 0.03% or less, V: 0.1% or less, Al: 0.005% or less, and Cr: 1.0% or less, Ni:
After adjusting the oxygen content of molten steel containing one or more of 2.0% or less and the balance being Fe and unavoidable impurities to 0.003 to 0.010% by weight, the ratio of Ti and N is Ti / N:
Ti: 0.012 to 0.030% was added so as to be 3.0 to 3.5, and Mg: 0.0005 to 0.0050% was further added to cast a molten steel with the composition adjusted. A slab containing 50 or more composite precipitates of Mg-based oxide and TiN / mm ² is reheated to a temperature range of 1200 to 1300 ° C, then rolling is started, and the flange surface temperature of the shaped steel is controlled in the rolling process. 700
Water-cooling to below ℃ and rolling in the recuperation process between rolling passes thereafter are repeated one or more times, and after completion of rolling, cooling to 700-400 ℃ at a cooling rate of 0.5-10 ℃ / s. A method for producing a fire-resistant rolled steel shape, which comprises allowing to cool.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The high temperature strength of steel is almost equal to the melting point of iron.
At a temperature of 1/2 of 700 ° C or less, it is almost the same as the strengthening mechanism at room temperature, and it is controlled by the refinement of ferrite crystal grain size, solid solution strengthening by alloying elements, dispersion strengthening by the hardening phase, precipitation strengthening by fine precipitates, etc. To be done. Generally, the increase in high temperature strength is achieved by increasing precipitation resistance by adding Mo and Cr and increasing high temperature softening resistance by suppressing dislocation disappearance. However, the addition of Mo and Cr markedly increases the hardenability, and changes from the ferrite + pearlite structure without addition to the bainite structure in the hardened phase. Further, when a component steel that preferentially produces a bainite structure is applied to a rolled H-section steel, the web, flange,
Since there are differences in the rolling finish temperature, the rolling reduction, and the cooling rate at each part of the fillet, the proportion of the bainite structure generated between each part greatly changes. As a result, room temperature / high temperature strength, ductility, and toughness have different values depending on the site, resulting in variations between sites. In addition, depending on the part, some parts exhibit characteristics that do not meet the criteria. In addition, the addition of these elements significantly hardens the weld and reduces the toughness of the weld heat affected zone.

A feature of the present invention is that in the steelmaking process, a large number of fine Mg-based oxides and Mg-based oxides and TiN are contained in a cast piece by adjusting molten steel oxygen, selecting deoxidizing elements and optimizing the addition procedure. Dispersing the composite precipitate of (3) is to produce a slab having an effect of suppressing coarsening of the γ phase even under high-temperature heating conditions in the shape rolling. By using this slab as a raw material, it is possible to achieve a finer structure even by high-temperature heating / rolling, and it is possible to manufacture a shaped steel having excellent fire resistance and toughness.

In addition, in the present invention, in the hot rolling step, the flange surface is water-cooled between hot rolling passes, and rolling is repeated at the time of recuperation of the hot rolling, thereby repeating the rolling to impart a reduction infiltration effect to the central portion of the flange thickness. However, even in this part, T
The effect of microstructure refinement by MCP is enhanced, and the microstructure refinement improves the mechanical properties of the base material in each portion 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, in bainite structure steel
Excessive addition exceeding 0.06% produces M *, toughness of base material, weld crack resistance, and weld heat affected zone (abbreviated as HAZ below).
The lower limit was set to 0.02% and the upper limit was set to 0.06% because it significantly reduces toughness.

Next, Si is necessary for securing the strength of the base metal and deoxidizing molten steel, but if it exceeds 0.25%, high carbon island martensite with a hardened structure is formed in the HAZ, and the toughness of the welded joint is increased. Is significantly reduced. 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 0.25.
Limited to the range of%. Mn needs to be added in an amount of 0.8% or more in order to secure the strength and toughness of the base metal, but it is set to 1.6% from the upper limit of the allowable concentration for the toughness and crackability of the welded portion.

Mo is an element effective in securing the strength of the base material and the high temperature strength. If it is less than 0.4%, the precipitation of Mo carbide (Mo2C) is insufficient and the strengthening effect cannot be exhibited, so that sufficient high temperature strength cannot be secured, and if it exceeds 0.8%, the base metal and HAZ are excessively hardened due to the increase in hardenability. , Toughness deteriorates 0.4 ~
Limited to 0.8%. Cu retains in the α temperature range and is slowly cooled to precipitate a Cu phase on the dislocations in the α phase, and the precipitation hardening increases the room temperature strength of the base material. Further, it suppresses the decrease in strength during heating at a guaranteed temperature of 700 ° C as refractory steel. However, if the precipitation of the Cu phase in α is less than 0.7%, it is within the solid solubility limit of Cu in α, and since precipitation does not occur, C
No strengthening due to u precipitation is obtained. Further, when the content exceeds 1.5%, the precipitation strengthening is saturated, so the Cu content is limited to 0.7 to 1.5%.

N dissolves in α to increase its strength,
In the upper bainite structure, M * is generated and the toughness is deteriorated, so it is necessary to reduce the solute N as much as possible. However, N in the present invention is compounded with Ti to finely precipitate TiN in the steel to reduce solid solution N, and then added in order to suppress grain growth of crystals due to TiN and achieve microstructure refinement. ing. Therefore, in order to achieve this effect, if the N content is less than 0.004%, the precipitation amount of TiN is insufficient, and if it exceeds 0.010%, the precipitation amount is sufficient, but coarse TiN is precipitated and the toughness is impaired. Limited to ~ 0.010%.

Although a small amount of B increases the hardenability and contributes to the increase in strength, it was found that when more than 0.0003% B is contained, M * is formed in the upper bainite structure and the toughness is remarkably reduced. Limited to less than%. Nb has strengthening due to precipitation of Nb carbonitride and strengthening due to increase in hardenability, and is added for the purpose of increasing room temperature / high temperature strength. However, if Nb is added in excess of 0.03%, coarse NbTi carbonitrides are generated, and the toughness of the base metal and weld zone is reduced to 0.0%.
Limited to 3% or less.

The addition of a small amount of V makes it possible to make the rolling structure finer and strengthens it by the precipitation of vanadium carbonitride, so that it can be made into a low alloy and the 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%. In addition, "Ti
The ratio of N and Ti is Ti / N: 3.0 to 3.5 is included. The reason is that almost all the added Ti and N are stoichiometrically precipitated as TiN, which causes the toughness to decrease. Solid solution T
The content ratio of Ti and N is limited in order to reduce i and N as much as possible.

Al is set to 0.005% or less because Al is a strong deoxidizing element. If the content of Al exceeds 0.005%, the production of MgO is hindered and fine dispersion cannot be achieved, so the content is limited to 0.005% or less. Next, the oxygen content of the molten steel with adjusted composition is expressed in weight percent.
The adjustment to 0.003 to 0.010% is carried out in order to highly clean the molten steel and crystallize fine Mg-based oxide in the cast slab. If the [O] concentration of this molten steel is less than 0.003%, fine oxides are reduced, and γ-fine graining cannot be performed during rolling reheating.
On the other hand, if it exceeds 0.010%, even if the other conditions are satisfied, the oxides agglomerate and coarsen to a size of 3 μm or more, and become the starting point of brittle fracture, leading to deterioration of toughness.
[O] concentration was limited to 0.003-0.010% by weight.

The oxygen content of this molten steel is adjusted by adjusting the oxygen content to 0.010%.
When it exceeds 0.003%, it is reduced to 0.010% or less by vacuum degassing and addition of Al, Si, and Mg, and when it is less than 0.003%, iron oxide is added to increase it. Next, T
The reason why i and Mg are sequentially added is that Mg is a strong deoxidizing element and reacts with the Ti oxide previously formed and Mg to deprive oxygen to form fine MgO.

Furthermore, the addition of the Mg alloy makes Mg:
Molten steel adjusted to 0.001 to 0.005% is cast at a constant casting cooling rate described later. Ti precipitates TiN and suppresses the formation of M * by reducing the solid solution N. The finely precipitated TiN also contributes to the grain refinement of the γ phase. These Ti
By the action of, the structure is refined and the strength and toughness are improved.
Therefore, if it is less than 0.012%, the precipitation amount of TiN will be insufficient and these effects will not be exhibited, so the lower limit of the Ti amount was made 0.012%. However, if it exceeds 0.030%, excessive Ti precipitates TiC, and the precipitation hardening deteriorates the toughness of the base material and the weld heat affected zone, so the content was limited to 0.030% or less.

The Mg alloy used for adding Mg is Si-Mg-Al and
It is Ni-Mg. The reason for using Mg alloy is M
This is because the g-containing concentration is reduced, the deoxidation reaction during addition to molten steel is suppressed, the safety during addition is ensured, and the Mg yield is improved. Limiting Mg to 0.0005 to 0.0050% is M
g is also a strong deoxidizing element, and the crystallized Mg oxide is easily floated and separated in the molten steel, so even if it is added in excess of 0.005%, the yield does not rise any further, so the upper limit was made 0.0050%. . 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%. Note that the Mg-based oxide here is mainly described as MgO, but according to electron microscope analysis and the like, this oxide is a composite oxide with Ti, a trace amount of Al, and Ca contained as impurities. Is forming a thing.

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, and the amounts of P and S each are less than 0.02%. It is desirable to limit to. 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.

Cr is effective in strengthening the base material by improving the hardenability. However, 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 cooling rate when pouring molten steel after the composition adjustment is controlled is 0.5 to 20 ℃ / s from the start of casting to 900 ℃ in order to suppress the increase in the number of Mg-based oxide particles and the particle growth. Cooling is desirable.
That is, to suppress the grain growth during the same time increasing the number of nuclei generating the composite oxide crystallized cooled by supercooling, for inclusion 50 / mm ² or more oxides below size 3μm cast slab Is what you do. This is because in slow cooling at a cooling rate of less than 0.5 ° C./s between these temperatures, the composite oxide aggregates and coarsens to less than 50 pieces / mm ² , which reduces toughness and ductility. On the other hand, the upper limit of the cooling rate is 20 ° C./s or less, which is the limit of the cooling rate in the current casting technology.

Next, described why Mg-based oxides and Mg-based oxides and complex precipitates of TiN in the slab has to contain 50 / mm ² or more. The material properties of the product are 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, rolling with precipitate, etc., TMC
P, determined by the microstructure of the acquired factors governed by the heat treatment process, etc. 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 this slab, and in the slab, fine Mg particles exhibiting a function of suppressing γ grain growth at high temperature.
The purpose is to crystallize dispersed oxides. If the number of dispersed particles is less than 50 particles / mm ² , 1200 to 1300 ° C
Since it is not possible to obtain fine particles having a γ particle size of more than ASTM No. 6 in heating, the lower limit is set to 50 particles / mm ² .

The number of Mg-based oxides is determined by measuring with an X-ray microanalyzer (EPMA).
The cast piece that has been subjected to the above treatment is then 1200 to 1300 ° C.
Reheat to the temperature range. The reason for limiting the reheating temperature to this temperature range is that in the production of shaped steel by hot working, heating at 1200 ° C. or higher is required to facilitate plastic deformation, and elements such as V, Nb and Mo are added. The lower limit of the reheating temperature was set to 1200 ° C because it was necessary to form a sufficient solid solution. The upper limit was set to 1300 ° C. in view of the performance and economical efficiency of the heating furnace.

One water-cooling / rolling step is carried out 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 is performed in the recuperating process in order to suppress quench hardening of the surface due to accelerated cooling after finish rolling and to make the hardness distribution uniform in the thickness direction. It is something to do. The reason is that if the flange surface temperature is cooled to 700 ° C or less, the γ / α transformation temperature is temporarily cut in the surface layer portion, and the surface layer portion is reheated by the next rolling, and the γ / α two-phase coexistence occurs. Processing is performed in the temperature range, and a mixed structure of γ-fine graining and processed fine α is formed. This is because the hardenability of the surface layer portion can be remarkably reduced, and quench hardening of the surface layer caused by accelerated cooling can be suppressed.

After the rolling is finished, 0.5-10
The reason for cooling to 700 to 400 ° C at a cooling rate of ° C / s and allowing to cool is to suppress grain growth of ferrite and refine the bainite structure by accelerated cooling to obtain high strength and high toughness. Then, the accelerated cooling is stopped at 700 to 400 ° C. When it is stopped at a temperature higher than 700 ° C, a part of the surface layer portion becomes Ar1 point or more and the γ phase remains, and ferrite grows with this as a nucleus. The accelerating cooling stop temperature was set to 700 ° C. or lower in order to coarsen the grains. Further, in the case of cooling below 400 ° C., M * generated between laths of the bainite phase during subsequent cooling cannot be decomposed by being tempered during precipitation and precipitating cementite, so that it exists as a hardening phase. Become.
This M * acts as a starting point of brittle fracture, leading to a decrease in toughness. For these reasons, the stop temperature of accelerated cooling is set to 700
Limited to ~ 400 ° C.

[0029]

[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 rate of the slab was controlled to about 5 ° C./s by selecting the amount of water in the secondary cooling zone below the mold and the withdrawal rate of the slab. The slab was heated and rolled into H-section steel by the universal rolling apparatus train shown in FIG. 1, although the rough rolling step is not shown. 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 and reverse rolling on the outer surface of the flange. The outer side surface of the flange was spray-cooled by the cooling device 5b installed in.

The mechanical characteristics are shown in FIG. 2, which is 1 / 4,1 / of the total flange width (B) at the center (1 / 2t2) of the plate thickness t2 of the flange 2.
2 From the width (1 / 4B, 1 / 2B), it was determined using the collected test pieces.
The characteristics of these points were determined because the flange 1 / 4F shows the average mechanical characteristics of H-section steel and the flange 1 / 2F has the lowest deterioration of these characteristics. This is because it was judged that the mechanical test characteristics of H-section steel can be represented by.

Tables 1 and 3 show the chemical composition values of the invention steels and comparative steels, and Tables 2 and 4 show the Ti content of these steels.
The oxygen concentration before addition and the distribution density of the Mg-based oxide in the slab and the composite thereof with TiN are shown. Tables 5 and 6 show the γ grain size during rolling heating, rolling and accelerated cooling conditions, and Tables 7 and 8 show the mechanical test characteristic values of these H-section steels. The reason why the rolling heating temperature is set to 1300 ° C is that
It is well known that γ-grains become finer and generally improve mechanical test properties due to a decrease in heating temperature, and it is estimated that the minimum value of mechanical properties is exhibited under high temperature heating conditions. This is because it was determined that the mechanical test characteristics in

As shown in Tables 7 and 8, in the H-section steels 1 to 5 and A1 to A3 according to the present invention, the lower limit value of the JIS standard yield strength of SM490 grade steel is within 120 N / mm ² (YP = 325 to 445N / m
m ² ), the yield ratio (YP / TS) also satisfies the low YR value of 0.8 or less, and the tensile strength (JISG3106 described above) and the yield strength at 700 ° C. satisfy 220 N / mm ² or more. Charpy impact absorption energy value is also -10
It is 47 (J) or more at ℃, and it sufficiently satisfies the JIS standard value.

On the other hand, the Mo content in the H-section steel 6 of the comparative steel and the Cu content in the H-section steel 7 are below the lower limit value,
The target value of the high temperature strength at 700 ° C is not satisfied. in addition,
In H-section steel 7, since Si exceeds the upper limit value, the toughness value becomes equal to or less than the target value. In H-section steel 8, in addition to lack of N content,
Since the Ti / N value exceeds 3.5, the γ grain size becomes coarse and the toughness becomes less than the target value.

In the H-section steel 9, since N and Ti are excessive and the value of Ti / N is too small, the toughness is lowered by the formation of M * and coarse TiN by the solute N. The toughness value cannot be cleared in the H-section steel 10 because B is in excess and in the H-section steel 11 is excessive in Al. Further, in the H-section steel, the amount of Mg is insufficient, the number of generated Mg oxides is insufficient, the γ grain size becomes coarse grain, and the refinement of the structure cannot be achieved, and the toughness value cannot be cleared.

In the H-section steel A4 of the comparative steel, the oxygen concentration of the molten steel before the addition of Ti is below the lower limit value of the present invention, and therefore the number of Mg-based oxides is insufficient.
In the shaped steel A5, a coarse oxide having a size of 3 μm or more is formed because the oxygen concentration exceeds the upper limit value.
Can't achieve more than 47J. In H-section steel A6, water cooling is not performed during rolling, sufficient microstructure refinement cannot be achieved, and target values of yield strength at 700 ° C and Charpy impact value at -10 ° C cannot be achieved.

That is, when all the requirements of the manufacturing method of the present invention are satisfied, H-section steels 1 to 5 and A1 to A shown in Tables 7 and 8 are obtained.
As shown in Fig. 3, the mechanical test characteristics of rolled steel, which are the most difficult to guarantee, have sufficient room temperature / high temperature strength and low temperature toughness even at a flange plate thickness of 1/2 and width of 1/2, and have excellent fire resistance and toughness. Allows production of rolled steel. 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.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

[Table 5]

[0042]

[Table 6]

[0043]

[Table 7]

[0044]

[Table 8]

[0045]

EFFECTS OF THE INVENTION The rolled steel according to the present invention has sufficient strength and toughness even in the flange plate thickness 1/2 and width 1/2 part where the mechanical test characteristics are the most difficult to guarantee, and has excellent high temperature characteristics and is a refractory material. Shaped steel with excellent fire resistance and toughness that can largely omit the coating can be manufactured as it is rolled, reducing the construction cost and the cost by shortening the construction period, and improving the reliability of large buildings The industrial effects such as ensuring safety and economic efficiency 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]

1 ... H section steel 2 ... Flange 3 ... Web 4 ... Intermediate rolling mill 5a ... Water cooling device on front and rear surfaces of intermediate rolling mill 5b ... Cooling device for rear surface of finishing rolling mill 6 ... Finishing rolling mill

Claims (4)

(57) [Claims] 1. C: 0.02 to 0.06%, Si: 0.05 to 0.25%, Mn: 0.8 to 1.6%, Mo: 0.4 to 0.8%, Cu: 0.7 to 1.5%, N: 0.004 to 0.010% by weight. B: 0.0003% or less, Nb: 0.03% or less, V: 0.1% or less, Al: 0.005% or less, and the balance of molten steel consisting of Fe and unavoidable impurities, after adjusting the oxygen content to 0.003 to 0.010% by weight. , Ti: N ratio of Ti / N: 3.0-3.5, Ti: 0.012-0.030% was added, and further Mg: 0.0005-0.0050% was added. A fire-resistant rolled steel comprising a Mg-based oxide and a composite precipitate of Mg-based oxide and TiN of 50 or more / mm ² . 2. C: 0.02 to 0.06%, Si: 0.05 to 0.25%, Mn: 0.8 to 1.6%, Mo: 0.4 to 0.8%, Cu: 0.7 to 1.5%, N: 0.004 to 0.010% by weight%. B: 0.0003% or less, Nb: 0.03% or less, V: 0.1% or less, Al: 0.005% or less, and one or more of Cr: 1.0% or less and Ni: 2.0% or less. After adjusting the oxygen content of the molten steel containing the balance Fe and unavoidable impurities to 0.003 to 0.010% by weight, the ratio of Ti and N should be Ti / N: 3.0 to 3.5.
Ti: 0.012 to 0.030% was added, and further, Mg: 0.0005 to 0.0050% was added, and 50 or less composite precipitates of Mg-based oxide and Mg-based oxide and TiN with a size of 3 μm or less were cast in the cast steel slab. mm ²
A refractory rolled steel characterized by containing the above. 3. C: 0.02 to 0.06%, Si: 0.05 to 0.25%, Mn: 0.8 to 1.6%, Mo: 0.4 to 0.8%, Cu: 0.7 to 1.5%, N: 0.004 to 0.010% by weight%. B: 0.0003% or less, Nb: 0.03% or less, V: 0.1% or less, Al: 0.005% or less, and the balance of oxygen of molten steel consisting of Fe and unavoidable impurities after adjusting to 0.003 to 0.010% by weight , Ti: N ratio of Ti / N: 3.0-3.5 was added, Ti: 0.012-0.030% was added, and further Mg: 0.0005-0.0050% was added to cast the molten steel in which the composition was adjusted. 50 μm / m of composite precipitate of Mg-based oxide and Mg-based oxide and TiN with a size of 3 μm or less.
After reheating the slab containing m ² or more to a temperature range of 1200 to 1300 ° C, rolling is started, the flange surface temperature of the shaped steel is water-cooled to 700 ° C or less in the rolling process, and the temperature between the subsequent rolling passes is restored. The water-cooling / rolling process of rolling in the heat process is repeated one or more times, and after completion of rolling, 700-400 at a cooling rate of 0.5-10 ° C / s.
A method for producing a fire-resistant rolled steel shape, which comprises cooling to ℃ and allowing to cool. 4. C .: 0.02 to 0.06%, Si: 0.05 to 0.25%, Mn: 0.8 to 1.6%, Mo: 0.4 to 0.8%, Cu: 0.7 to 1.5%, N: 0.004 to 0.010% by weight%. B: 0.0003% or less, Nb: 0.03% or less, V: 0.1% or less, Al: 0.005% or less, and one or more of Cr: 1.0% or less and Ni: 2.0% or less. After adjusting the oxygen content of the molten steel containing the balance Fe and unavoidable impurities to 0.003 to 0.010% by weight, the ratio of Ti and N should be Ti / N: 3.0 to 3.5.
Ti: 0.012 to 0.030% added, and Mg: 0.0005 to 0.0050%
The molten steel with the composition adjusted by adding is cast, and the cast piece containing the Mg-based oxide and the composite precipitate of Mg-based oxide and TiN of 3 μm or less in size of 50 pieces / mm ² or more is cast in the cast piece. ~ 1300
Rolling is started after reheating to the temperature range of ℃, water temperature of flange surface of shaped steel is cooled to 700 ℃ or less in the rolling process, and rolling is performed once in the reheat process between rolling passes. A method for producing a fire-resistant rolled shape steel, which comprises repeatedly rolling the above and cooling to 700 to 400 ° C at a cooling rate of 0.5 to 10 ° C / s and then leaving to cool.