JP3285731B2 - Rolled section steel for refractory 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 section steel having a flange such as an H-section steel excellent in fire resistance and toughness used as a structural member of a building and a method for producing a rolled section steel by controlled rolling. is there.

[0002]

2. Description of the Related Art Fireproof design has been reviewed by the Ministry of Construction's comprehensive project due to the increase in the height of buildings and the sophistication of building design techniques. In March 1987, the "New Fireproof Design Law" was enacted. According to this regulation, the restriction on fire-resistant coating to keep the temperature of steel at 350 ° C or less in the event of a fire according to the old law is lifted, and the fire-resistant coating method conforming to the balance between the high-temperature strength of steel and the actual load of the building is lifted. Can now be determined. That is, when the design high-temperature strength at 600 ° C. can be ensured, the refractory coating can be reduced accordingly.

In response to such a trend, Japanese Patent Laid-Open No.
No. 77523 discloses a low yield ratio steel and a steel material for building having excellent fire resistance and a method for producing the same. The gist of the invention of the prior application is that Mo and Nb are added to improve the high-temperature strength so that the yield point at 600 ° C. becomes 70% or more of that at normal temperature. The design high-temperature strength of the steel material was set to 600 ° C. based on the finding that it is the most economical in view of the balance between the increase in the cost of the steel material due to the alloying element and the cost of the refractory coating.

[0004] Conventionally, Al deoxidation of steel is carried out by adding Al in the initial stage of the smelting process, thereby deoxidizing the molten steel and forming Al ₂ O.
_The purpose was to float and separate ₃ for high purification. That is, the theme was how to reduce the oxygen concentration of the molten steel and the number of coarse primary deoxidized oxides in the steel.

[0005]

SUMMARY OF THE INVENTION The present inventors have applied the steel materials manufactured by the above-mentioned prior application to various shaped steels, particularly H-shaped steels having complicated shapes and severe rolling molding restrictions. As a result, the rolling finish temperature, rolling reduction, and cooling rate at each part of the web, flange, and fillet are different, so the structure, especially the bainite ratio, is significantly different depending on the part, and normal temperature / high temperature strength, ductility, There were parts where the toughness varied and did not meet the standards such as rolled steel materials for welded structures (JIS G3106). In the refinement of the structure by the formation of intragranular ferrite, a component having a relatively high ferrite structure ratio is effective. However, when the ratio of bainite is high, there is a disadvantage that the structure is difficult to be refined.

[0006] In order to solve the above-mentioned problems, it is necessary to reduce the γ particle size by ASTM even at a heating temperature of 1200 to 1300 ° C during rolling.
If the grain size can be reduced to No. 6 or more in No., the structure can be refined even in a structure having a high bainite ratio. In order to achieve this object, a method of dispersing and dispersing fine precipitates that are stably present without decomposition at high temperatures, thereby pinning the growing γ grain boundaries, suppressing γ grain growth, and reducing the grain size is considered. Can be The present invention has found that Mg-based oxides and TiN are effective as the precipitates, and has aimed to develop a steel in which these are finely crystallized and precipitated.

[0007] Unlike the conventional idea, the present invention controls the composition, size and dispersion density of an oxide by controlling the selection of a deoxidizing agent in the steelmaking process, the order of addition and the cooling in the solidification process. Is used as a preferential precipitation site for heterophase precipitation. The present application was filed in Japanese Patent Application No. Hei.
No. 5 provides a means for making the oxide function as an intragranular ferrite transformation nucleus, making the structure fine by generating intragranular ferrite, and achieving uniform material properties and high toughness between portions of the H-section steel. did. In the present invention, on the other hand, a fine Mg-based oxide (mainly MgO) and TiN having high temperature stability and high density are dispersed at a high density, and these precipitates are subjected to rolling and heating at 120 ° C.
It functions as a pinning site for suppressing the grain growth of γ grains at 0 to 1300 ° C., and by refining the structure by refining γ grains, homogenizing and improving the material properties between parts of the H-section steel. It is characterized by achieving toughness and high temperature and high strength.

[0008] The feature of TMCP in the manufacturing method is different from the low-temperature and large-reduction rolling that is often performed on thick steel plates.
In the hot rolling under light pressure in a section steel, there is a method in which water cooling is performed between rolling passes and water cooling, rolling, and water cooling are repeated so that the structure can be efficiently refined.

[0009]

DISCLOSURE OF THE INVENTION The present invention aims at refining the structure, performing appropriate deoxidation treatment in the steel making process, purifying the molten steel, regulating the dissolved oxygen concentration, adding Ti, and finally The order of addition of the Si-Mg alloy and the Ni-Mg alloy and the amount of Mg are limited, and a slab in which fine Mg-based oxides are finely dispersed in a slab is rolled into an H-section steel; By water cooling between the hot rolling passes using the slab as a raw material, a temperature difference is given between the surface and the inside of the flange of the H-section steel, and even under light rolling conditions, the penetration into the higher temperature inside is increased, We have developed a water cooling method during rolling that introduces working dislocations, which are α-generating nuclei, and can achieve a finer structure at the center of the sheet thickness. In addition, by controlling the cooling of the γ / α transformation temperature range after rolling, the microstructure can be refined according to the method of suppressing the grain growth of the nucleated ferrite, resulting in high efficiency and low production cost. The above-mentioned problem has been solved based on the finding that inexpensive refractory rolled steel can be produced, and the gist thereof is as follows. (1) In mass%, C: 0.04 to 0.20%, Si:
0.05-0.50%, Mn: 0.4-1.8%, M
o: 0.4 to 1.0%, N: 0.004 to 0.015
%, Al: 0.004% or less, Ti: 0.005 to 0.5%.
025%, Mg: 0.001 to 0.005%, a slab consisting of the balance of Fe and unavoidable impurities and containing at least 50 Mg-based oxides having a size of 3 μm or less / 50 / mm ² or more. A rolled refractory section steel manufactured by hot rolling. (2) In mass%, Cr: 1.0% or less, Cu:
1.0% or less, Ni: 2.0% or less, Nb: 0.01%
The refractory rolled section steel according to the above (1), comprising one or more of the following. (3) The method for producing a refractory rolled steel section according to the above (1), wherein the slab containing the component composition is 1200 to 130.
Rolling is started after reheating to a temperature range of 0 ° C., and a water cooling / rolling step of rolling the flange surface temperature of the section steel to 700 ° C. or less in this rolling step, and rolling in a recuperation process between rolling passes thereafter. Rolled repeatedly one or more times, 0.5 ~ after rolling
Cooling to 700-400 ° C. at a cooling rate of 10 ° C./s,
The method for producing a refractory rolled steel according to claim 1, wherein the steel is allowed to cool. (4) The method for producing a refractory rolled steel section according to the above (2), wherein the slab containing the component composition is 1200 to 130.
Rolling is started after reheating to a temperature range of 0 ° C., and a water cooling / rolling step of rolling the flange surface temperature of the section steel to 700 ° C. or less in this rolling step, and rolling in a recuperation process between rolling passes thereafter. Rolled repeatedly one or more times, 0.5 ~ after rolling
Cooling to 700-400 ° C. at a cooling rate of 10 ° C./s,
3. The method according to claim 2, wherein the steel is cooled.

[0010]

Hereinafter, the present invention will be described in detail. The high-temperature strength of steel material is almost the same as the strengthening mechanism at room temperature at 700 ° C or less, which is almost half the melting point of iron. It is governed by precipitation strengthening by fine precipitates and the like. In general, the increase in high-temperature strength is achieved by increasing precipitation resistance by adding Mo and Cr and increasing softening resistance at high temperatures by suppressing the disappearance of dislocations. But M
The addition of o and Cr markedly enhances hardenability and changes the ferrite + pearlite structure of the base material to a bainite structure. When a component steel that easily forms a bainite structure is applied to a rolled H-section steel, the rolling finish temperature, rolling reduction,
Since there is a difference in cooling rate, the ratio of bainite structure changes greatly depending on each part. As a result, there are variations in room-temperature / high-temperature strength, ductility, and toughness, and parts that do not meet the standards. In addition, the addition of these elements significantly hardens the weld and reduces toughness.

The feature of the present invention is that, in the steel making process, the control of deoxidation, the cooling rate after casting is regulated, and the cast slab in which a large number of fine Mg-based oxides are crystallized and dispersed in the cast slab, Rolling from a state where the γ grain size at the time of rolling heating is reduced
The purpose is to obtain an H-section steel having excellent toughness. In addition, in the present invention, in the hot rolling step, the flange surface is water-cooled between hot rolling passes, and the rolling process is repeated at the time of reheating to impart a rolling reduction effect to the center of the flange thickness. The microstructure refinement effect of TMCP is also enhanced in the parts, and the refinement of the microstructure improves the mechanical properties of the base material in each part of the H-section steel and achieves uniformity.

The reasons for limiting the range of components and the control conditions of the shaped steel according to the present invention will be described below. First, C is added to strengthen the steel. If it is less than 0.04%, the strength required for structural steel cannot be obtained. Excessive addition of more than 0.20% results in base metal toughness, weld cracking resistance, heat affected zone (hereinafter referred to as HA).
Z) The lower limit is set to 0.
04%, with an upper limit of 0.20%.

[0013] Next, Si is necessary for securing the strength of the base material, preliminary deoxidation of molten steel, and the like. If it exceeds 0.50%, high-carbon island-like martensite having a hardened structure is formed in the HAZ structure. Significantly lowers toughness. If the content is less than 0.05%, the necessary molten steel cannot be preliminarily deoxidized, so the Si content is reduced to 0.
Limited to the range of 05 to 0.50%. Mn must be added in an amount of 0.4% or more to ensure the strength and toughness of the base material, but the upper limit is set to 1.8% in an acceptable range of the toughness and cracking properties of the welded portion.

Mo is an element effective for securing the base material strength and the high-temperature strength. If less than 0.4%, Mo carbide (Mo ₂ C)
Sufficient precipitation at a high temperature could not be ensured due to insufficient precipitation and no sufficient strengthening effect. If it exceeds 1.0%, the hardenability is too high, and the toughness of the base metal and HAZ is deteriorated. N is an extremely important element for the precipitation of TiN.
If it is less than 004%, the precipitation amount of TiN is insufficient, and
Since the growth of γ grains at the time of reheating at 00 ° C. cannot be suppressed and the γ grains cannot be refined, the content is set to 0.004% or more. 0.015% content
If it exceeds, the toughness and ductility decrease due to hardening of the ferrite and strain aging, etc., so it was limited to 0.015% or less.

The reason why the content of Al is set to 0.004% or less is that Al is a strong deoxidizing element. If the content exceeds 0.004%, an Al-Mg-based composite oxide having a large Al content and a large particle diameter is formed. Since no Mg-based oxide having a thickness of 3 μm or less was formed and γ-graining could not be performed at the time of high-temperature reheating, Al was set to 0.004% or less. Ti makes γ fine by precipitation of fine TiN and improves the toughness of the base metal and the welded portion. Therefore, 0.005%
In the following, the lower limit of the amount of Ti was set to 0.005% because the amount of precipitated TiN was insufficient and γ refinement was not possible. However, if it exceeds 0.025%, excessive Ti precipitates TiC, and the precipitation hardening deteriorates the toughness of the base metal and the weld heat affected zone.
Limited to 5% or less.

[0016] Preliminary deoxidation treatment of the molten steel whose components have been adjusted to adjust the dissolved oxygen to 0.003 to 0.015% by weight means that the fine Mg oxide is crystallized in the slab at the same time that the molten steel is highly purified. It is done to make it. If the [O] concentration after the pre-deoxidation is less than 0.003%, the amount of fine oxides decreases, and the fineness cannot be reduced, so that the toughness cannot be improved. On the other hand, if the content exceeds 0.015%, the oxide coarsens to a size of 3 μm or more and becomes the starting point of brittle fracture even if other conditions are satisfied, and the [O] concentration after preliminary deoxidation to reduce toughness Was limited to 0.003 to 0.015% by weight.

Preliminary deoxidation treatment includes vacuum degassing, Al, Si,
Performed by Mg deoxidation. The reason is that vacuum degassing directly removes oxygen in molten steel as gas and CO gas,
This is because oxide-based inclusions generated by strong deoxidation such as l, Si, and Mg are easy to float and remove, and are effective for cleaning molten steel. Next, an Mg alloy was added to the above molten steel, and Mg: 0.0
The molten steel whose composition is adjusted to 01 to 0.005% is cast at a constant casting cooling rate described later.

The Mg alloy used for adding Mg is Si-Mg and Ni.
-Mg. The reason for using Mg alloy is that
This is to reduce the concentration of Mg, suppress the reaction at the time of generating Mg oxide, ensure safety at the time of addition, and increase the yield of Mg. Mg
Is limited to 0.001 to 0.005%, Mg is also a strong deoxidizing element, and the crystallized Mg oxide is easily floated and separated in molten steel, so the addition over 0.005% has a low yield. Therefore, the upper limit was made 0.005%. If the content is less than 0.001%, the target M
Since the dispersion density of the g-based oxide is insufficient, the lower limit is set to 0.001%. Note that the Mg-based oxide here mainly represents MgO, but this oxide is often complexed with a small amount of Al and an oxide such as Ca contained as an impurity. Expression was used.

The amounts of P and S contained as inevitable impurities are not particularly limited, but welding cracks due to solidification segregation,
Since toughness is reduced, the content should be reduced as much as possible. Desirably, the P and S contents are each less than 0.02%. In addition to the above components, one or more of Cr, Cu, Ni, and Nb can be contained for the purpose of increasing the strength of the base material and improving the toughness of the base material.

[0020] Cr is effective for 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 is 1.0%
And Cu is an element effective for strengthening the base material and weathering resistance. However, the upper limit is set to 1.0% in order to promote temper brittleness by stress relief annealing, weld cracking, and hot work cracking.

Ni is a very effective element for increasing the toughness of the base material, but the addition of more than 2.0% increases the alloy cost and is not economical, so the upper limit was made 2.0%. Nb can refine the rolled structure by adding a small amount of it, and since it is strengthened by the precipitation of carbonitrides, it is possible to reduce the alloy and improve the welding characteristics. However, excessive addition of these elements causes hardening of the welded portion and a high yield point of the base metal, so the upper limit of each content was set to 0.01% Nb. Here, the Nb content is set to 0.
The reason why the content is set to 01% or less is that Nb is combined with Ti and coarse Nb · T
Since i-carbonitride is formed, which inhibits the fine precipitation of TiN, the upper limit is limited to 0.01% to prevent this formation.

In order to control the increase in the number and the size of the Mg-based oxide particles, the cooling rate at the time of casting the molten steel whose component adjustment has been completed is set at a cooling rate from the start of casting to 900 ° C.
It is desirable to cool at 0.5 to 20 ° C / s. That is, in order to increase the number of nuclei generated in the composite oxide crystallized by supercooling and at the same time to suppress the growth of particles during cooling, the slab contains at least 50 oxides / mm ² having a size of 3 μm or less. What to do. The cooling rate between these temperatures is 0.5 ° C /
At a slow cooling of less than s, the composite oxide becomes coarse and coarse and becomes less than 50 particles / mm ² , which lowers the toughness and ductility. On the other hand, the upper limit of the cooling rate is 20 ° C./cm 2 which is the limit of the cooling rate in the current casting technology. s.

Next, the composite slab contains 50 composite oxides / mm ²
The reason why it is necessary to include the above is described. The material properties of the product are congenital factors governed by the steelmaking and casting processes, such as the solidification structure of the cast slab, component segregation, the fine composite oxides and precipitates of the present invention, and the acquired properties governed by rolling, TMCP, heat treatment processes, etc. Is determined by the microstructure of the objective factor. Naturally, the property of the slab, which is this innate factor, is inherited by the subsequent steps. A feature of the present invention is to control one of the innate factors of the slab, and disperse and crystallize a fine Mg-based oxide exhibiting a function of suppressing γ grain growth at a high temperature in the slab. It is in.
When the number of dispersed particles is less than 50 particles / mm ² ,
The particle size of γ when heated at 0 to 1300 ° C. is ASTM No.
Since fine grains of No. 6 or more cannot be obtained, the lower limit was set to 50 grains / mm ² .

The number of Mg-based oxides was determined by measuring with an X-ray microanalyzer (EPMA).
The slab that has undergone the above treatment is then reheated to a temperature range of 1200 to 1300 ° C. The reason for limiting the reheating temperature to this temperature range is that the production of a shaped steel by hot working requires heating at 1200 ° C. or higher in order to facilitate plastic deformation.
The lower limit of the reheating temperature was set to 1200 ° C. because elements such as Nb need to be sufficiently dissolved. The upper limit was set to 1300 ° C. in view of the performance and economy of the heating furnace.

A water-cooling / rolling step of cooling by water between passes of hot rolling, cooling the flange surface temperature to 700 ° C. or less at least once during rolling, and rolling in the reheating process between the subsequent rolling passes is performed in one step. The reason for performing the repetition more than once is to provide a temperature difference between the surface layer and the inside of the flange by water cooling between rolling passes, and to infiltrate the processing into the inside even under light rolling conditions, and to perform low-temperature rolling in a short time This is for efficient operation.

Rolling in the reheating process after the flange surface temperature is cooled to 700 ° C. or lower is performed to suppress quenching and hardening of the surface due to accelerated cooling after finish rolling and to soften the surface. 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 end of the rolling, the rolling is continued for 0.5 to 10
The reason for cooling to 700 to 400 ° C. at a cooling rate of ° C./S and allowing to cool is to suppress the grain growth of ferrite and to refine the bainite structure by accelerated cooling to obtain high strength and high toughness. The reason why the subsequent accelerated cooling is stopped at 700 to 400 ° C. is that when the accelerated cooling is stopped at a temperature exceeding 700 ° C., a part becomes _one or more Ar and a γ phase remains. The temperature for stopping the accelerated cooling was set to 700 ° C. or less in order to transform the ferrite into a ferrite and further grow the ferrite and coarsen the ferrite. Further, in cooling at a temperature lower than 400 ° C., high-carbon martensite generated between laths of the bainite phase during the subsequent cooling is not decomposed by precipitation of cementite during cooling, and exists as a hardened phase. . Since this acts as a starting point of brittle fracture and causes a decrease in toughness, the temperature is limited to this range.

[0028]

[Example] A prototype steel was melted from a converter, added with an alloy, preliminarily deoxidized, and adjusted for oxygen concentration in the molten steel.
Mg alloy was added and cast into a 250-300 mm thick slab by continuous casting. 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. The slab was heated and rolled into an H-beam by a universal rolling mill row shown in FIG. 1, although illustration of the rough rolling step was omitted. 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, and 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 properties are shown in FIG. 2 at the center (1 / 2t ₂ ) of the thickness t ₂ of the flange 2 at 1 / 4,1 / of the overall flange width (B).
2 Test pieces were collected from the widths (1 / 4B, 1 / 2B). In addition,
The characteristics of these locations were determined because the flange 1 / 4F section shows the average mechanical properties of the H-section steel, and the flange 1 / 2F section has the lowest properties. This is because it has been determined that the mechanical test characteristics can be represented.

Tables 1 and 3 show the chemical composition values of the steels of the present invention and comparative steels, and Tables 2 and 4 show the cooling rates after casting of these steels and the Mg-based oxides in the slabs. Shows the dispersion density.
Tables 5, 6, and 7 show the γ grain size at the time of rolling heating, rolling / accelerated cooling conditions, and mechanical test characteristic values of the product. It is well known that the rolling heating temperature is adjusted to 1300 ° C. because it is generally known that a decrease in the heating temperature reduces the γ grains to improve mechanical test characteristics. This is because it was determined that this value could represent the mechanical test characteristics at a lower heating temperature.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

[Table 4]

[0035]

[Table 5]

[0036]

[Table 6]

[0037]

[Table 7]

As shown in Tables 5, 6 and 7, the H-shaped steels 1 to 5 and A1 to A3 according to the present invention have YP values of SM490 whose target yield point range at room temperature is within the lower limit of JIS standard +120 N / mm ^2.
= 325~445N / mm ^2, SM520 in YP = 355~475N / mm ^2, it is controlled to, moreover, the yield ratio (YP / TS) also satisfy the 0.8 or lower YR value, tensile strength (the JISG3106) and 600 ° C.
The ratio between the yield strength at room temperature and the yield strength at room temperature is 2/3 or more, and sufficiently satisfies the Charpy impact value at -10 ° C. of 47 (J) or more. On the other hand, in the comparative steel H-section steel 6, the component N was 0.003 wt%, which is below the lower limit of the present invention, and Al was 0.00%.
7 wt%, which exceeds the upper limit of the present invention.
Insufficient amount of precipitation and the number of dispersed Mg-based oxides is 50 / mm
² , and the γ particle size is ASTM No. Coarse-grained to No. 6 or less and a fine structure cannot be obtained. Therefore, the Charpy impact value cannot reach 47 J or more at the development target of -10 ° C. In the comparative steel H-section steel 7, the oxygen concentration of the molten steel before the addition of Mg was lower than the lower limit of the present invention, so that the number of Mg-based oxides was insufficient. In this case, since a coarse oxide having a size of 3 μm or more is formed because the oxygen concentration exceeds the upper limit value, the Charpy impact value cannot achieve 47 J or more at the development target of −10 ° C. In the comparative steel H-section steel 9, the Ti content is less than the lower limit of the present invention, so that the precipitation amount of TiN is insufficient, and the γ grain size is ASTM No. The grain size is reduced to 6 or less, and the Charpy impact value cannot be cleared. In the comparative steel H-section steel 10, Mg was not added. Next, in the comparative steel H-section steel 11, since the cooling rate after casting is lower than the lower limit, the number of Mg-based oxides is insufficient and the Charpy impact value cannot be cleared. In the comparative steel H-section steel 12, although the composition and steelmaking conditions are satisfied, the outer surface of the flange during rolling is 7 mm.
Since the water-cooling process is not performed below 00 ° C, the water-cooling stop temperature exceeds the upper limit of the water-cooling stop temperature of 725 ° C, and the cooling rate after rolling is equal to or lower than the lower limit of the limited cooling rate in the 1 / 2F section. Insufficient strength at room temperature and at 600 ° C.

In the case of the H-section steel A4, which is a comparative steel classified into a 520 MPa class steel with a specified strength, the Mo content is below the lower limit of the present invention, so that the strength is insufficient at 600 ° C., and Mg is added. Therefore, the structure cannot be refined, and the Charpy impact value cannot reach 47 J or more at the development target of −10 ° C. Further, in the comparative steel H-section steel A5, the number of Mg-based oxides is insufficient because the cooling rate after casting is lower than the lower limit of the limit, and the Charpy impact value cannot be cleared.

That is, when all the requirements of the production method of the present invention are satisfied, H-section steels 1 to 5 shown in Tables 5, 6 and 7
As in A1 to A3, it has sufficient room temperature / high temperature strength and low temperature toughness even in the flange thickness 1/2 and width 1/2 parts where the mechanical test characteristics of the rolled steel are the least guaranteed. Excellent rolled steel production is possible. 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.

[0041]

The rolled section steel according to the present invention has sufficient strength and toughness even at a flange plate thickness of 1/2 and a width of 1/2 part where mechanical test characteristics are most difficult to be guaranteed, has excellent high-temperature characteristics, and is a refractory material. Can achieve the purpose of fire resistance with a coating thickness of 20 to 50% of the conventional one,
Shaped steel with excellent fire resistance and toughness can be manufactured as it is rolled, reducing construction costs and shortening the construction period to achieve significant cost reductions, improving the reliability of large buildings, ensuring safety, and economical efficiency Industrial effects such as these 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 back surface of an intermediate rolling mill 5b ... Finishing rolling machine rear cooling device 6 ... Finishing rolling mill

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 C21C ⁷ /00-7/06 C21D 8/00

Claims (4)

(57) [Claims] C: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 1.8%, Mo: 0.4 to 1. 0%, N: 0.004 to 0.015%, Al: 0.004% or less, Ti: 0.005 to 0.025%, Mg: 0.001 to 0.005%, the balance being Fe And a hot rolled cast slab composed of unavoidable impurities and containing at least 50 Mg-based oxides having a size of 3 μm or less per 50 mm ² / mm ² . 2. In% by mass, Cr: 1.0% or less,
Cu: 1.0% or less, Ni: 2.0% or less, Nb: 0.
The refractory rolled section steel according to claim 1, comprising one or more kinds of not more than 01%. 3. The method for producing a rolled refractory steel section according to claim 1, wherein the slab containing the component composition is 1200-200.
After reheating to a temperature range of 1300 ° C., rolling is started. In this rolling process, the flange surface temperature of the section steel is water-cooled to 700 ° C. or less, and water-cooling is performed in a reheating process between subsequent rolling passes.
The rolling process is repeated one or more times, and after the rolling is completed, the rolling process is performed.
The method according to claim 1, wherein the steel is cooled to 700 to 400C at a cooling rate of 5 to 10C / s, and then cooled. 4. The method for producing a refractory rolled section steel according to claim 2, wherein the slab containing the component composition is 1200-200.
After reheating to a temperature range of 1300 ° C., rolling is started. In this rolling process, the flange surface temperature of the section steel is water-cooled to 700 ° C. or less, and water-cooling is performed in a reheating process between subsequent rolling passes.
The rolling process is repeated one or more times, and after the rolling is completed, the rolling process is performed.
The method according to claim 2, wherein the steel is cooled to 700 to 400C at a cooling rate of 5 to 10C / s, and then cooled.