JPH07216496A - Production of oxide grain dispersed cast bloom for refractory use and rolled shape steel for refractory use, using this cast bloom as stock - Google Patents

Abstract

PURPOSE:To attain superior refractoriness and toughness by subjecting 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, 0.4-1.0% Mo, 0.05-0.20% V, 0.004-0.015% N, and 0.005-0.025% Ti, is preliminarily deoxidized, by which the amount of dissolved oxygen is regulated to 0.003-O.015%. 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 resulating cast bloom by >=20pieces/mm<2>. Subsequently, the cast bloom is heated to 1100-1200'C and rolling is started, and then, water cooling is done until a 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 1. Field of the Invention The present invention relates to a slab for rolled steel having excellent fire resistance and toughness which is used as a structural member of a building, and a method for producing rolled steel by controlled rolling using the slab. 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 of fireproof coating to keep the temperature of steel materials to 350 ° C or less at the time of fire under the old law was lifted, and due to the balance between high-temperature strength of steel materials and actual load of buildings, a fireproof coating method suitable for it You can now decide. 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. is 70% 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 fire protection coating construction cost due to it.

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, how to lower the oxygen concentration of the molten steel and reduce the number of coarse primary deoxidized oxides in the steel. 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 to be used as the preferential precipitation site of. That is, a fine composite oxide that functions as an intragranular ferrite transformation nucleus is included in a slab to enable the refinement of the structure without imposing a load on the rolling process. Additionally adopted TM
The characteristic of CP is that water cooling between rolling passes is repeated and rolling and water cooling are repeated in order to enable efficient grain refinement even in hot rolling under light reduction in shaped steel instead of heavy reduction rolling on thick steel plates. On the way.

[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 attempting to apply it, the structure, especially the bainite ratio is remarkably different depending on the parts due to the difference in rolling finish temperature, reduction ratio and cooling rate at each part of web, flange and fillet, and room temperature / high temperature strength, ductility, toughness Variation,
Some parts such as rolled steel for welded structure (JIS G3106) did not meet the criteria.

In order to solve the above problems, the present invention functions as a preferential precipitation nucleus for intragranular ferrite and heterophase precipitation by adjusting the composition of the steelmaking process and devising the addition procedure.
It is necessary to manufacture a slab in which the Ti-based composite oxide is crystallized and dispersed. In addition, the fillet part of the joint between the flange of H-section steel and the web matches the center segregation part of the CC slab,
MnS present in this portion may be significantly stretched under the low temperature rolling condition, which may reduce the drawing value in the plate thickness direction and cause lamella tear during welding. As described above, it is difficult for the conventional technique to manufacture the desired highly reliable and high toughness fire-resistant rolled shaped steel by the on-line rolling process and provide it at a 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.
A slab in which a large number of fine composite oxides that function as intragranular ferrite-forming nuclei are dispersed in a slab and rolled using this as a material, and water-cooled between hot rolling passes Giving a temperature difference, even under conditions of light pressure,
It enhances the infiltration into the interior at higher temperature, introduces work dislocations that become intragranular ferrite formation nuclei, and further increases the intragranular ferrite formation nuclei. In addition, by controlling the cooling of the γ / α transformation temperature range after rolling, the method of suppressing the grain growth of the nucleated ferrite can make the microstructure finer, resulting in high efficiency and high manufacturing cost. The above problems have been solved based on the finding that it is possible to manufacture an inexpensive fire-resistant rolled steel, and the gist thereof is: C: 0.04 to 0.20% by weight%, Si: 0 .05
~ 0.50%, Mn: 0.4-1.8%, Mo: 0.4
~ 1.0%, V: 0.05-0.20%, N: 0.00
Molten steel containing 4 to 0.015%, Ti: 0.005 to 0.025%, and the balance Fe and unavoidable impurities,
Pre-deoxidation treatment allows dissolved oxygen to be 0.003% by weight.
Fe-Al-Mg alloy is further added after adjusting to 0.015%, 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. Refractory oxide-dispersed cast slab characterized by containing 20 or more complex oxides / mm ² , C: 0.04 to 0.20% by weight, Si: 0.05
~ 0.50%, Mn: 0.4-1.8%, Mo: 0.4
~ 1.0%, V: 0.05-0.20%, N: 0.00
4 to 0.015%, Ti: 0.005 to 0.025%, and Cr: 1.0% or less, Cu: 1.0% or less, Ni: 2% or less, Nb: 0.05% Hereinafter, B: 0.
A molten steel containing one or two or more of the following, and the balance consisting of Fe and unavoidable impurities, is subjected to 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. 20% / mm ² or more of refractory oxide dispersed cast slab, C: 0.04 to 0.20% by weight, Si: 0.05
~ 0.50%, Mn: 0.4-1.8%, Mo: 0.4
~ 1.0%, V: 0.05-0.20%, N: 0.00
Molten steel containing 4 to 0.015%, Ti: 0.005 to 0.025%, and the balance Fe and unavoidable impurities,
Pre-deoxidation treatment allows dissolved oxygen to be 0.003% by weight.
Fe-Al-Mg alloy is further added after adjusting to 0.015%, 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 billet surface layer part 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 manufacturing a fire-resistant rolled shaped steel characterized by cooling to 0 ° C. and allowing to cool, C: 0.04 to 0.20% by weight, Si: 0.05
~ 0.50%, Mn: 0.4-1.8%, Mo: 0.4
~ 1.0%, V: 0.05-0.20%, N: 0.00
4 to 0.015%, Ti: 0.005 to 0.025%, and 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 to 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 billet surface layer part 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
It is a method for producing a fire-resistant rolled shaped steel characterized by cooling to 0 ° C. and allowing to cool.

[0008]

The present invention will be described in detail below. The high-temperature strength of steel materials is almost the same as the strengthening mechanism at room temperature at 700 ° C or lower, which is about half the melting point of iron, and the grain size of ferrite is refined, solid solution strengthening by alloying elements, dispersion strengthening by hardening phase , And precipitation strengthening by fine precipitates. Generally, Mo and C are used to increase high temperature strength.
This is achieved by increasing the softening resistance at high temperatures by strengthening the precipitation by adding r and suppressing the dislocation disappearance. However, the addition of Mo and Cr markedly enhances the hardenability and changes the ferrite + pearlite structure of the base material into a bainite structure. When a component steel that easily forms a bainite structure is applied to a rolled steel, the rolling finish temperature, the reduction ratio, the web, the flange, and the fillet at each site due to its unique shape.
Because of the difference in cooling rate, the bainite structure ratio changes greatly depending on each part. As a result, the room temperature / high temperature strength, ductility, and toughness vary, and some parts do not meet the standard. In addition, the addition of these elements significantly hardens the weld and reduces toughness.

A feature of the present invention is that in the steelmaking process, the deoxidation is controlled, the cooling rate after casting is regulated, and a cast product in which a large number of fine composite oxides functioning as intragranular ferrite formation nuclei are dispersed By increasing the number of intragranular ferrite formation nuclei by repeatedly obtaining pieces and water-cooling between them in the hot rolling process using the material as a raw material, and rolling during this recuperation, austenite grains during rolling Intragranular ferrite transformation from the inside is promoted, changes in the proportion of bainite and ferrite in each part of the H-section steel are reduced, and the improvement and homogenization of the mechanical properties of the base material are achieved. The high temperature strength is increased by the precipitation strength of. In addition, accelerated cooling is performed after rolling to suppress the growth of the ferrite and to refine the microstructure to achieve 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% remarkably lowers the base material 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 produces high carbon martensite with a 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 is set to 1.8% within the allowable range of the toughness and crackability of the welded portion.

Mo is an element effective for securing the strength of the base material and the high temperature strength. If it is less than 0.4%, sufficient high-temperature strength cannot be ensured even by the combined action of precipitation strengthening of VN.
If it exceeds 0%, the hardenability is excessively increased, and the toughness of the base material and HAZ toughness are deteriorated, so the content is limited to 0.4 to 1.0%. V is V
As N, it is extremely important for the formation of an intragranular ferrite structure, its refinement, and securing of high temperature strength. If it is less than 0.05%, the precipitation amount of VN is insufficient, and if it exceeds 0.2%, the precipitation amount is large. Becomes excessive and the toughness of the base metal and the toughness of the welded part deteriorate, so the content was limited to 0.05 to 0.2%.

N is an extremely important factor for precipitation of TiN and VN. If it is less than 0.004%, the precipitation amount of VN is insufficient, and a sufficient ferrite structure generation amount cannot be obtained.
Since the high temperature strength at 00 ° C cannot be ensured, the content is set to 0.004% or more. If the content exceeds 0.015%, the toughness of the base material is lowered and the surface cracks of the slab are caused during continuous casting, so the content is limited to 0.015% or less.

Ti forms an Al-Mg-Ti type composite oxide in the cast slab, and TiN is added to the outer shell of the particles during rolling.
To promote the generation 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 remarkably lowers 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 so that the molten steel can be highly cleaned and at the same time fine composite oxides in the slab can be obtained. Is to generate. After pre-deoxidation
If the [O] concentration is less than 0.003%, the amount of the composite oxide of intragranular ferrite-forming nuclei that promotes intragranular ferrite transformation is reduced, and the grain size cannot be reduced to improve toughness. On the other hand, 0.01
If it exceeds 5%, even if the other conditions are satisfied, the oxide coarsens to a size of 3 μm or more and becomes a starting point of brittle fracture, and to reduce toughness, the [O] concentration after pre-deoxidation is weighted. % To 0.003 to 0.015%.

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, an 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.
Detailing the system composite oxide below 20 and performs the purpose to be contained in / mm ² or more slab successively the necessary reasons.

The Fe-Al-Mg alloy is Al: 1-20.
%, Mg: 1-20% The balance is an alloy consisting of Ni.
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 empty space of spinel crystal structure). Pore type, [Mg, Ti] O.Al ₂ O ₃ ) cannot be generated. In addition, they 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, a 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 precipitation amount of VN. 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% forms a complex oxide that promotes intragranular ferrite transformation. However, in order to generate coarse MgO and reduce toughness and ductility, the content 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 inevitable impurities are not particularly limited, but weld 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 or more of Cr, Cu, Ni, Nb, and B may be contained for the purpose of increasing the strength of the base material and improving the toughness of the base material.

[0021] Cr is effective in strengthening the base material by improving the hardenability. However, 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 the base material and weathering resistance, but since it promotes temper embrittlement due to stress relief annealing, weld crackability, and hot work cracking, its upper limit is 1.0%.
And

Ni is an extremely effective element that enhances 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,
B can be made into a low alloy because the rolling structure can be refined by adding a trace amount, and welding characteristics can be improved. However, excessive addition of these elements leads to hardening of the welded portion and increase of the yield point of the base metal, so the upper limit of the content of each element is Nb: 0.
05% and B: 0.003%.

The molten steel whose composition has been adjusted is cast 90 times after casting.
Cooling to 0 ° C at a cooling rate of 0.5 to 20 ° C / s is
This is done to increase the number of oxide particles and control their size. That is, the number of nucleated complex oxides crystallized by supercooling is increased and at the same time grain growth during cooling is suppressed, and the oxides having a size of 3 μm or less are added to the slab.
This is carried out in order to contain 0 / mm ² or more. 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 toughness,
In order to reduce the ductility, the cooling rate was set to 0.5 ° C / s or more. 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 undergone 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 the water cooling is performed between the passes of the hot rolling, the temperature of the surface layer of the billet is cooled to 700 ° C. or less once during the rolling, and the hot rolling is performed in the reheating process. This is because a temperature difference is caused between the surface layer portion and the inside of the steel slab by water cooling between the passes so as to infiltrate the internal processing even under a light reduction condition, and to perform low-temperature rolling efficiently in a short time. Cooling the temperature of the steel slab surface layer to 700 ° C. or lower is accelerated cooling subsequent to rolling. Therefore, in the cooling from the normal γ temperature range, the surface layer part is hardened, a hardened phase is generated, and workability is improved. Spoil.
If cooled within such a limited temperature range, once γ / α
When the temperature falls below the transformation temperature, the surface layer part is reheated by the time of the next rolling, and the work is carried out in the two-phase coexisting temperature range, the hardenability can be significantly reduced, and the 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. /
The reason why the cooling is completed at the cooling rate of S to 650 to 400 ° C. is to accelerate the grain growth of ferrite and the bainite structure by accelerated cooling to obtain high strength and high toughness.
650 ° C to stop accelerated cooling at 650 to 400 ° C
When the accelerated cooling was stopped at the above temperature, a part of Ar became ₁ point or higher, a part of the γ phase remained, and ferrite was grain-grown, so that the temperature was set to 600 ° C. or lower. Further, if the temperature is lower than 400 ° C., the high carbon martensite formed in the bainite phase cannot be decomposed during the subsequent cooling and the toughness is lowered, so the temperature range is limited to this range.

The effects of the present invention will be further illustrated by the following examples.

[0028]

[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.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

[Table 4]

Tables 3 and 4 show rolling and heating / cooling conditions and mechanical test characteristics of the products. The rolling heating temperature is 12
It is well known that reducing the heating temperature improves the mechanical properties, and it is estimated that the high temperature heating condition shows the minimum value of the mechanical properties, and this value is set to 80 ° C. This is because it was determined that the characteristics in (1) can be represented.

[0036]

[Table 5]

[0037]

[Table 6]

As shown in Tables 5 and 6, according to the present invention,
Shaped steels 1 to 7 and A1 to A6 are target yield point ranges at room temperature
Is the lower limit of JIS standard +100 N / mm²SM49 within
0 for YP = 325-425N / mm², In SM520
YP = 335-435N / mm ², SM570 has YP =
430-530N / mm²Controlled, and the yield ratio
(YP / TS) also satisfies the low YR value of 0.8 or less,
Force (said JISG3106) and yield strength at 600 ° C
And the yield strength at room temperature is 2/3 or more, at -10 ° C
Charpy impact value of 47 (J) or more
It On the other hand, the comparative steel, shaped steel 8, has a composition and Fe-Al-Mg combination.
Cooling speed after casting is satisfied, even though gold addition and rolling conditions are satisfied.
The degree is less than or equal to the lower limit, and Al-Mg-Ti-based complex oxides
Insufficient number of particles results in insufficient formation of intragranular ferrite. That
For the purpose of the Charpy test at -10 ℃ of 1 / 2F part
Target value, vE_-TenI cannot clear ≧ 47J. Shaped steel B
In addition to 2, water cooling is not applied during rolling, water cooling stop temperature
Is 650 ° C or higher, and the cooling rate after rolling is the lower limit.
Since it is less than the value, the Charpy value of the 1 / 2F part is the target
VE_-TenI cannot clear ≧ 47J.

Since the shaped steels 9, B1 and B3 are subjected to the usual Al kill treatment, the amount of Al exceeds the limit of the present invention, and Mg is not added, an Al-Mg-Ti type composite oxide is produced. Therefore, the impact value of the 1 / 2F part cannot reach the target. In addition, since the shaped steel B1 lacks the Mo addition amount, the target yield strength at 600 ° C. cannot be guaranteed.

Since the shaped steel B2 was not water-cooled during rolling and the accelerated cooling conditions after rolling were not satisfied, the ferrite phase could not be fine-grained and the yield point was lowered, which was below the lower limit of the standard value. Become. That is, when all the requirements of the manufacturing method of the present invention are satisfied, the shaped steels 1 to 7 and A shown in Tables 5 and 6 are obtained.
1 to A6, the flange plate thickness 1/2, which is the most difficult to guarantee the mechanical test characteristics of rolled steel, has sufficient strength and toughness even in the width 1/2 part, and the flange plate thickness 1/2 and the width 1/4
It is possible to manufacture rolled steel having excellent fire resistance and toughness, which has sufficient room temperature and high temperature strength even in the part. 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 deoxidation treatment is more easily performed, or a combination process of them and other auxiliary melting treatment furnaces is adopted. It may be adjusted to dissolved oxygen. 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.

[0042]

EFFECT OF THE INVENTION The rolled steel according to the present invention has sufficient strength and toughness even at a flange plate thickness of 1/2 and width of 1/2 where it is most difficult to guarantee mechanical test properties, has excellent high temperature properties, and is a refractory material. With the coating thickness of 20 to 50% of the conventional one, it is possible to manufacture shaped steel with excellent fire resistance and toughness, which can achieve the purpose of fire resistance, as it is rolled, and it is possible to reduce construction cost and construction time significantly The industrial effects such as reliability improvement, safety assurance, and economic efficiency of large-scale buildings 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. C: 0.04 to 0.20% by weight%, S
i: 0.05 to 0.50%, Mn: 0.4 to 1.8%,
Mo: 0.4 to 1.0%, V: 0.05 to 0.20%,
N: 0.004 to 0.015%, Ti: 0.005 to
A molten steel containing 0.025 and the balance of Fe and unavoidable impurities was subjected to a preliminary deoxidation treatment to dissolve oxygen by weight%.
After adjusting to 0.003 to 0.015% with Fe-A
Addition of 1-Mg alloy, Al: 0.005 to 0.
015%, Mg: 0.001 to 0.010% of the molten steel whose composition is adjusted, and the cooling rate is 0.5 to 20 up to 900 ° C.
Al-M with a size of 3 μm or less
refractory oxide for dispersion cast piece, characterized in that the g-Ti-based composite oxide containing 20 / mm ² or more. 2. C: 0.04 to 0.20% by weight%, S
i: 0.05 to 0.50%, Mn: 0.4 to 1.8%,
Mo: 0.4 to 1.0%, V: 0.05 to 0.20%,
N: 0.004 to 0.015%, Ti: 0.005 to
0.025 in addition to Cr: 1.0% or less, Cu:
1.0% or less, Ni: 2.0% or less, Nb: 0.05%
Hereinafter, one or two of B: 0.003 or less
After adjusting the dissolved oxygen to 0.003 to 0.015% by weight by a preliminary deoxidation treatment, the molten steel containing at least one species and the balance consisting of Fe and unavoidable impurities is further mixed with Fe-Al.
-Mg alloy is added, and Al is 0.005-0.0% by weight.
15%, Mg: 0.001 to 0.010% of molten steel with the composition adjusted to cast, and cooling rate up to 900 ° C 0.5 to 20 ° C
Al / Mg with a size of 3 μm or less
Refractory oxide for dispersion cast piece, characterized in that it contains a -Ti-based composite oxide 20 / mm ² or more. 3. C: 0.04 to 0.20% by weight, S
i: 0.05 to 0.50%, Mn: 0.4 to 1.8%,
Mo: 0.4 to 1.0%, V: 0.05 to 0.20%,
N: 0.004 to 0.015%, Ti: 0.005 to
A molten steel containing 0.025 and the balance of Fe and unavoidable impurities was subjected to a preliminary deoxidation treatment to dissolve oxygen by weight%.
After adjusting to 0.003 to 0.015% with Fe-A
Addition of 1-Mg alloy, Al: 0.005 to 0.
015%, Mg: 0.001 to 0.010% of the molten steel whose composition is adjusted, and the cooling rate is 0.5 to 20 up to 900 ° C.
Al-M with a size of 3 μm or less
A slab containing 20 or more g-Ti-based complex oxides / mm ² is reheated to a temperature range of 1100 to 1300 ° C and then rolling is started, and the temperature of the surface layer of the slab is water-cooled to 700 ° C or less in the rolling process. Then, the step of rolling in the recuperative process between passes is repeatedly rolled once or more, and after the rolling is finished, it is cooled to 650 to 400 ° C at a cooling rate of 1 to 20 ° C / s and left to cool. Rolled shaped steel manufacturing method. 4. C: 0.04 to 0.20% by weight%, S
i: 0.05 to 0.50%, Mn: 0.4 to 1.8%,
Mo: 0.4 to 1.0%, V: 0.05 to 0.20%,
N: 0.004 to 0.015%, Ti: 0.005 to
0.025 in addition to Cr: 1.0% or less, Cu:
1.0% or less, Ni: 2.0% or less, Nb: 0.05%
Hereinafter, one or two of B: 0.003 or less
After adjusting the dissolved oxygen to 0.003 to 0.015% by weight by a preliminary deoxidation treatment, the molten steel containing at least one species and the balance consisting of Fe and unavoidable impurities is further mixed with Fe-Al.
-Mg alloy is added, and Al is 0.005-0.0% by weight.
15%, Mg: 0.001 to 0.010% of the component adjusted cast, cooled to 900 ° C at a cooling rate of 0.5 to 20 ° C / s, and Al-Mg-Ti having a size of 3 µm or less in a cast piece.
110 cast slab containing system composite oxide 20 / mm ² or more
Rolling is started after reheating to a temperature range of 0 to 1300 ° C, the temperature of the surface layer of the slab is water-cooled to 700 ° C or less in the rolling process, and the process of rolling in the reheat process between passes is repeated one or more times. 650 at a cooling rate of 1 to 20 ° C./s after completion of rolling
A method for producing a fire-resistant rolled shaped steel, which comprises cooling to 400 ° C. and cooling.