JP3107696B2 - Method for producing shaped steel having flange excellent in strength, toughness and fire resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a shaped steel used as a structural member of a building.

[0002]

2. Description of the Related Art Due to stricter safety standards for buildings, etc., H-section steel, which is a typical section steel having flanges used for beams and columns, is required to have higher functions. I have. As an example, the fire resistance design was reviewed by the Comprehensive Ministry of Construction Project, and as of March 1987, the "New Fire Resistance Design Law" was enacted to reduce the temperature of steel materials to 350 ° C or less in the event of a fire under the old laws. The restriction on fire-resistant coating was lifted, and it became possible to determine the appropriate fire-resistant coating method according to the balance between the high-temperature strength of steel and the actual load of the building. 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 proposes a low yield point ratio steel and a steel material for building having excellent fire resistance and a method for producing the same. The gist of this invention is that the yield point at 600 ° C. is 70% of that at normal temperature.
As described above, Mo and Nb are added to improve the high-temperature strength. 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 increase in the cost of the steel material due to the alloy element and the cost of the construction of the fireproof coating.

[0004] On the other hand, H-shaped steels used for columns and beams are required to have higher strength and higher toughness due to the increase in height of buildings and stricter safety standards. In the H-section steel having the above-mentioned fire resistance performance, and having a thick flange in which high strength and high toughness are ensured, first, one of the measures is to add a large amount of alloying elements in order to secure the strength. However, in this case, at the same time, the toughness is reduced. On the other hand, in order to secure the toughness, a low alloy component is a necessary condition. As a method of satisfying strength with low alloy components,
The accelerated cooling method (TMCP method) of steel after rolling is well known, but in the case of an H-section steel having a thick flange, the required strength is obtained by cooling from a γ region where the temperature of the steel immediately after finish rolling is at least ₃ points of Ar. If the accelerated cooling is performed until the temperature is secured, the structure fraction of the bainite phase or the martensite phase increases, and the toughness is significantly impaired. In the field of thick steel plates, high strength and high toughness steels are produced by utilizing the precipitation effect of VN.
Japanese Patent Publication No. -50548 and Japanese Patent Publication No. Sho 62-54862 have been proposed. However, in this conventional method, the production cost is increased due to the addition of V, and it is difficult to control the N component.
On the other hand, in order to secure the strength and the toughness at the same time, conventionally, a heat treatment such as a normalizing process has been performed after the completion of the rolling and cooling. However, the addition of heat treatment causes a significant increase in cost, such as a decrease in heat treatment cost and production efficiency, and there is a problem in economy.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a novel manufacturing method which comprehensively covers the steps from steel making, rolling and cooling to strength, toughness and fire resistance. An object of the present invention is to provide a shaped steel having an excellent flange at low cost.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the feature of the present invention is to perform appropriate deoxidation treatment in the steel making process, to clean the molten steel, and to solve the dissolved oxygen concentration. Controlling the amount of Al by adjusting the order of addition of Al among the alloying elements, etc., and dispersing a large number of fine composite oxides in the steel to generate intragranular ferrite, and then accelerated cooling To prevent an increase in the structure fraction of the bainite phase or the martensite phase, form a fine-grained ferrite structure, and secure strength and toughness. Further, if necessary, the temperature of the surface layer portion of the steel material between the passes of the intermediate rolling step is Ar ₃ −20 ° C. or less, water-cooled to Ar ₃ −100 ° C. or more, and rolled at least once in the recuperation process,
Further, the microstructure is refined, and particularly in an H-section steel, the toughness of a fillet portion at a high temperature rolling and a low cooling rate is improved. That is, the present invention is to provide a method for producing a high-quality steel material which is economical, efficiently and excellent in toughness without requiring special equipment. The gist of the present invention is the following (1) to
It is as described in (4). (1) In mass%, C: 0.05 to 0.15%, Si:
0.05-0.50%, Mn: 0.8-2.0%,
N: 0.003 to 0.015%, Ti: 0.005 to
The molten steel containing 0.025%, Mo: 0.30 to 0.70%, and the balance being Fe and unavoidable impurities is dissolved in pre-deoxidation treatment to dissolve oxygen in a mass% of 0.003 to 0.01.
After being adjusted to 5%, the mixture was further deoxidized by adding metallic aluminum or ferroaluminum, and the Al content was 0.00% by mass.
5 to 0.015%, and based on the dissolved oxygen [O%] of the molten steel, -0.004 ≦ [Al%] − 1.1 [O%] ≦ 0.
006 is cast by continuous casting, the slab is reheated to a temperature range of 1100 to 1300 ° C., and after rolling is started, any one of the following manufacturing steps (a) and (b) A method for producing a shaped steel having a flange excellent in strength, toughness, and weldability, characterized by passing through. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. (2) In mass%, C: 0.05 to 0.15%, Si:
0.05-0.50%, Mn: 0.8-2.0%,
N: 0.003 to 0.015%, Ti: 0.005 to
The molten steel containing 0.025%, Mo: 0.30 to 0.70%, and the balance being Fe and unavoidable impurities is dissolved in pre-deoxidation treatment to dissolve oxygen in a mass% of 0.003 to 0.01.
After being adjusted to 5%, the mixture was further deoxidized by adding metallic aluminum or ferroaluminum, and the Al content was 0.00% by mass.
5 to 0.015%, and based on the dissolved oxygen [O%] of the molten steel, -0.004 ≦ [Al%] − 1.1 [O%] ≦ 0.
006 is cast by continuous casting, the slab is reheated to a temperature range of 1100 to 1300 ° C., and rolling is started, and the temperature of the surface layer of the steel material is set to Ar between passes of the intermediate rolling process.
₃ -20 ° C. or less, and water-cooled over Ar ₃ -100 ° C., was rolled at least once in its recuperation process the following (a), and characterized in that go through any of the manufacturing process of (b) For producing a shaped steel having a flange with excellent strength, toughness and fire resistance. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. (3) In mass%, C: 0.05 to 0.15%, Si:
0.05-0.50%, Mn: 0.8-2.0%,
N: 0.003 to 0.015%, Ti: 0.005 to
0.025%, Mo: 0.30 to 0.70%, plus V ≦ 0.20%, Cr ≦ 0.7%, Nb ≦ 0.0
5%, Ni ≦ 1.0%, Cu ≦ 1.0%, Mo ≦ 0.3
% Of molten steel containing one or two or more kinds and the balance of Fe and unavoidable impurities is adjusted to 0.003 to 0.015% by mass of dissolved oxygen by preliminary deoxidation treatment. Deoxidized by addition of aluminum, the Al content is 0.005 to 0.015% by mass
And -0.004 with respect to the dissolved oxygen [O%] of the molten steel.
≤ [Al%]-1.1 [O%] ≤ 0.006.
A shape having a flange excellent in strength, toughness and fire resistance characterized in that after rolling is started after reheating to a temperature range of 00 ° C., one of the following manufacturing steps (a) and (b) is performed. Steel production method. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. (4) In mass%, C: 0.05 to 0.15%, Si:
0.05-0.50%, Mn: 0.8-2.0%,
N: 0.003 to 0.015%, Ti: 0.005 to
0.025%, Mo: 0.30 to 0.70%, plus V ≦ 0.20%, Cr ≦ 0.7%, Nb ≦ 0.0
5%, Ni ≦ 1.0%, Cu ≦ 1.0%, Mo ≦ 0.3
% Of molten steel containing one or two or more kinds and the balance of Fe and unavoidable impurities is adjusted to 0.003 to 0.015% by mass of dissolved oxygen by preliminary deoxidation treatment. Deoxidized by addition of aluminum, the Al content is 0.005 to 0.015% by mass
And -0.004 with respect to the dissolved oxygen [O%] of the molten steel.
≤ [Al%]-1.1 [O%] ≤ 0.006.
Rolling was started after reheating to a temperature range of 00 ° C., and the temperature of the surface layer of the steel material was reduced to Ar ₃ −20 ° C. or less between passes of the intermediate rolling step,
Ar ₃ −100 ° C. or more, and after being rolled at least once in the recuperation process, pass through any one of the following manufacturing steps (a) and (b), and strength, toughness, and fire resistance For producing shaped steel having a flange with excellent heat resistance. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s.

[0007]

Hereinafter, the operation of the present invention will be described in detail based on embodiments. The strength and toughness of a steel material depend on the alloy component and the crystal grain size. That is, the toughness improves as the amount of the component that dissolves in the structure is smaller or the ferrite grains in the structure are finer. When a steel section having a flange, for example, an H-section steel is manufactured by universal hot rolling using a continuously cast slab as a raw material, central segregation of the raw material is accumulated in a fillet portion, and the segregated component is significantly concentrated. At the same time, since the fillet portion has a higher rolling temperature than other portions, even when hot rolling is performed, ferrite grains are coarsened more than, for example, a flange portion or a web portion. It is also known to use the following strengthening mechanism when manufacturing a high-strength section steel.

[0008] Refinement of ferrite crystal grain size Solid solution strengthening by alloy element Precipitation strengthening by fine precipitate Among these, solid solution strengthening by alloy element is most common. For example, Mn which is a typical solid solution strengthening element is used.
Addition significantly increases the hardenability of the steel material and changes the ferrite + pearlite structure to a bainite structure. When a component steel that easily forms a bainite structure is applied to a rolled H-section steel, Mn is segregated, particularly in a fillet portion processed so that the center segregation portion of a continuous cast slab as a material is integrated in a rolling process. It is concentrated as a component, and the bainite and island martensite structure fractions are significantly increased. As a result, the toughness is particularly reduced. In addition, precipitation strengthening by fine precipitates also reduces toughness. Therefore, only the refinement of the ferrite crystal grain size can increase the strength while securing the toughness.

Regarding the fire resistance, the high temperature strength of the steel material is almost the same as the strengthening mechanism at room temperature below 700 ° C., which is about half the melting point of iron, and is generally precipitation strengthened by the addition of Mo and Cr. This is achieved by increasing the softening resistance at high temperatures by reducing the dislocation loss. However, the addition of Mo and Cr significantly increases the 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 Mo, Cr, particularly in a fillet portion processed so that the center segregation portion of a continuous cast slab as a material is integrated in a rolling process. Is concentrated, and the bainite and island martensite structure fractions are significantly increased. As a result, the toughness is particularly reduced.

A feature of the present invention is that, during the production of an H-section steel having a thick flange by hot rolling, air is cooled before or after finish rolling to allow a part of ferrite to appear, and then accelerated cooling is performed to accelerate the bainite phase or The purpose is to prevent an increase in the structure fraction of the ferrite phase, to provide a fine-grained ferrite structure, and to satisfy all of the strength, toughness, and fire resistance. Next, the reasons for limiting the range of the basic components targeted by the present invention will be described. First, C is added as an effective component for improving the strength of steel. If it is less than 0.05%, the strength required for structural steel cannot be obtained. Since the material toughness, weld cracking resistance, and toughness of the heat affected zone are significantly reduced, the lower limit is 0.05% and the upper limit is 0.
15%.

[0011] Si is necessary for securing the strength of the base material, preliminary deoxidation of the molten steel, etc. If it exceeds 0.50%, high carbon martensite having a hardened structure is formed in the heat affected zone of the weld, and the toughness of the weld joint is reduced. Is significantly reduced. If the content is 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%. Mn needs to be added in an amount of 0.8% or more to ensure the strength and toughness of the base material, but the upper limit is set to 2.0% within an acceptable range of the toughness, cracking, and the like of the welded portion.

N is an element mixed into steel as an unavoidable impurity, and is an element that reduces toughness when it is dissolved excessively. Therefore, it is desirable to reduce N as much as possible.
If it is less than 03%, the cost for denitrification will be high and the production cost will be high, so the lower limit was made 0.003%. On the other hand, if the content exceeds 0.015%, the base material toughness deteriorates, and a surface crack occurs in the slab during continuous casting, so the upper limit was made 0.015%.

[0013] Ti forms a Ti-based oxide, promotes the formation of intragranular ferrite during rolling, or produces fine TiN.
Has the effect of promoting the refinement of austenite and the formation of intragranular ferrite and improving the toughness of the base metal and the welded portion. However, if it is less than 0.005%, the Ti content in the oxide is insufficient. When the content exceeds 0.025%, excessive Ti forms TiC, causes precipitation hardening, and significantly reduces toughness, so that the content is limited to 0.005 to 0.025%. did.

Mo is an element effective for refractory performance, that is, for strengthening the base material at high temperatures. However, if it is less than 0.30%, it is not suitable because it cannot exhibit sufficient high-temperature strength. If this is the case, it is unsuitable because welding cracks, hot working cracks, and the like may be a concern, and alloy costs may be increased and uneconomical. Therefore, a suitable component range is set to 0.1.
30% to 0.70%.

Although the amounts of P and S contained as unavoidable impurities are not particularly limited, they should be reduced as much as possible because macrosegregation at the time of solidification causes welding cracks and a decrease in toughness. The amount of S that can be reduced to the target amount is less than 0.02% each. The above are the basic components of the steel that is the subject of the present invention. For the purpose of increasing the base metal strength and improving the toughness, V, Cr, Ni, Nb,
One or more of Cu, may be contained.

First, V is extremely important as VN for the formation of an intragranular ferrite structure, its grain refinement, and the securing of high-temperature strength. However, if it exceeds 0.20%, precipitates become excessive and the base material toughness increases. And weld heat affected zone toughness deteriorate, so the upper limit is 0.2
Limited to 0%. Ni is a very effective element for increasing the toughness of the base material, but the addition of more than 1.0% increases the alloy cost and is not economical, so the upper limit was made 1.0%.

Cr improves the hardenability, strengthens the base material,
Effective for high temperature strengthening. However, an excessive addition exceeding 0.7% is harmful from the viewpoint of toughness and curability, so the upper limit is set to 0.7%. Nb is effective for toughening the base material, but an excessive addition exceeding 0.05% is harmful from the viewpoint of toughness and hardenability, so the upper limit was made 0.05%.

Although Cu is an element effective for strengthening the base material and weathering resistance, the upper limit is set to 1.0% in consideration of temper brittleness due to stress relief annealing, welding cracks, hot working cracks, and the like. Preliminary deoxidation of the molten iron is performed, and the dissolved oxygen is reduced to 0.00% by weight.
The reason for controlling the content to 3 to 0.015% is because it is extremely important to highly purify the molten iron and to disperse fine oxides in the slab. [O] concentration after preliminary deoxidation is 0.0
If the content is less than 03%, the amount of the composite oxide of the intragranular ferrite nucleus that promotes intragranular ferrite transformation decreases, and the grain cannot be refined, so that the toughness cannot be improved. On the other hand, if it exceeds 0.015%, the oxide coarsens even if other conditions are satisfied,
It becomes a starting point of brittle fracture and lowers toughness. For the above reasons, the [O] concentration after the preliminary deoxidation is 0.003 to
It was limited to 0.015%.

The preliminary deoxidation is performed by vacuum degassing and Al,
The deoxidation was performed by one or more of Si, Zr, Ca, and 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 i, Zr, Ca, and Mg easily float and are easily removed, and are extremely effective in cleaning molten steel.

Al is a strong deoxidizing element.
If the content exceeds 5%, a composite oxide that promotes intragranular ferrite transformation is not formed, and the toughness is reduced.
If the content is less than 005%, the target composite oxide cannot be produced, so the content was limited to 0.005 to 0.015%. Further, the Al content [Al%] of the molten steel is -0.004 ≦ [Al%]-1.1 [O%] ≦ 0.0 with respect to the dissolved oxygen [O%] of the molten steel.
The reason for limiting the relationship to satisfy the relation of 06% is that, in this relation, when Al is excessive in weight% with respect to the [O] concentration, the number of composite oxides produced is reduced, and it is ineffective as intragranular ferrite formation nuclei. When a large amount of Al ₂ O ₃ is formed, the structure cannot be refined and the toughness is reduced, and when the Al content is too small relative to the [O] concentration in weight%, the composite oxide which becomes the intragranular ferrite nucleus is remarkably formed. This is because the structure cannot be refined due to the decrease and the toughness decreases. The reason why the order of addition of Al is the last is that when added at the initial stage of steelmaking, Al has a strong deoxidizing power, generates Al ₂ O ₃ which is invalid as intragranular ferrite generation nuclei, and is easy to float. This is because it is difficult to form a low melting point composite oxide.

After the molten steel produced by the above-described production method is produced into a slab by a continuous casting machine, it is reheated to a temperature range of 1100 to 1300 ° C. The reason for limiting the reheating temperature to this temperature range is that the production of shaped steel by hot working requires heating at 1100 ° C. or higher to facilitate plastic deformation, and also from the performance and economy of the heating furnace. The upper limit was 1300 ° C. The heated steel material is roll-formed in each of the steps of rough rolling, intermediate rolling and finish rolling. Rolling end temperature 750-1050
The reason why the temperature was set to 0 ° C is that the lower the temperature, the better the toughness is, but the processing at less than 750 ° C is difficult due to the shaping of the shaped steel.
This is because processing at a temperature exceeding 0 ° C. generates a coarse-grained structure and lowers toughness.

Further, the temperature of the steel surface layer portion between rolling passes in the intermediate rolling step Ar ₃ -20 ° C. or less, Ar ₃ -1
Water cooling to at least 00 ° C., rolling at least once in the recuperation process, and terminating the rolling at a temperature in the range of 750 to 1050 ° C. are performed by low-temperature rolling so that the surface layer has an ultrafine-grained structure. Thereby, the ferrite is transformed again to austenite to remove working strain. Due to the combination of the water cooling, the rolling pass, and the recuperation, the surface layer of the steel material has an ultrafine grained ferrite + pearlite structure without distortion, and the toughness is improved.

After the completion of the intermediate rolling and before or after the finish rolling, the surface temperature is allowed to cool to Ar ₃ -20 ° C. or lower and Ar ₁ or higher because the ferrite transformation proceeds to a thickness of about 20 mm from the surface. This is because the formation of a ferrite suppresses the formation of a bainite phase or a martensite phase. When the cooling is stopped in a temperature range higher than this temperature range and accelerated cooling is performed, the structure fraction of the bainite phase or the martensite phase is significantly increased, and the toughness is reduced.
Further, if the temperature is allowed to cool to a temperature lower than this temperature range, the effect of ferrite fine graining by accelerated cooling is not seen, and the strength is reduced. The cooling to the above-mentioned optimum temperature range may be performed before or after finish rolling. The reason is that the amount of reduction in the finish rolling is small, and the material variation due to the presence or absence of the finish rolling can be ignored.

The steel material which has been cooled before the finish rolling is finished after the finish rolling.
The steel that has been cooled after finish rolling is immediately subjected to accelerated cooling.
The average cooling rate from 700 ° C to 400 ° C is 0.5 ° C /
The reason why the cooling is performed within the range of s to 3.0 ° C./s is that when accelerated cooling is performed at a higher cooling rate than this cooling rate range, the structural fraction of the bainite phase or the martensite phase increases, and the toughness increases. Decrease. In addition, even if accelerated cooling is performed at a cooling rate lower than this cooling rate range, the effect of ferrite grain refinement by accelerated cooling is not observed, and strength is reduced. Therefore, the above-described range of the cooling rate is set as the optimum cooling rate range.

[0025]

EXAMPLE A prototype steel was melted from a converter, the components were adjusted, and then cast into a slab of 240 to 300 mm thick by continuous casting.
After being heated in the heating furnace 1 having the layout shown in FIG. 1 and rough-rolled by the rough rolling mill 2, subsequently, the first intermediate rolling mill 3 and the second intermediate rolling mill 4 form the steel until it becomes an H-shaped steel having a predetermined size. Do.
In this case, among the rolling passes of the second intermediate rolling mill 4 as required, the temperature of the steel surface layer portion Ar ₃ -20 ° C. or less, Ar ₃
Water cooling to -100 ° C or higher, and at least 1
Rolling more than once and finishing the intermediate rolling in a temperature range of 750 to 1050 ° C. After that, before the finish rolling by the finish rolling mill 5, the predetermined temperature range, that is, the steel material surface is Ar ₃ -20 at an arbitrary position between the second intermediate rolling mill 4 and the finish rolling mill 5.
℃ below, it is allowed to cool to Ar ₁ or more temperature region. afterwards,
After the finish rolling, a predetermined cooling rate, that is, a cooling rate from 700 ° C. to 400 ° C. by 0.5 is accelerated by a water-cooled accelerated cooling device 6 for steel material installed downstream of the finishing mill 5.
Accelerated cooling is performed so that the temperature can be maintained in the range of ° C / s to 3.0 ° C / s. After cooling, it is allowed to cool on the cooling floor 7 until it is corrected in the next step.

The mechanical properties of the H-shaped steel 8 shown in FIG.
Thickness t of J9_TwoCenter (1 / 2t _Two) At full flange width
Take a test piece from 1/4 width (1 / 4B) of length (B)
I asked. The characteristics of this location were determined by the flange
Since the 1 / 4B section shows the average mechanical properties of the base material,
Because it was possible to represent the mechanical test characteristics of H-section steel
is there.

Tables 1 and 2 show the chemical component values of the prototype steel, and Table 3 shows the mechanical test characteristics with respect to the rolling and cooling conditions. It is well known that the heating temperature is adjusted to 1280 ° C., in general, it is well known that the reduction of the heating temperature improves the mechanical properties, and it is estimated that the high-temperature heating condition shows the lowest value of the mechanical properties. Was determined to be able to represent the characteristics at a lower heating temperature.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

Further, in the component ranges in Tables 1 and 3,
Ar_ThreeThe point is between 860 ° C and 800 ° C, Ar₁The point is
Because the temperature is between 700 ° C and 650 ° C,
Ar ₁Ar points_ThreeTo reduce the temperature to -20 ° C or less,
It is necessary to be at least 700 ° C or more and 780 ° C or less. table
As shown in FIG. 3, steels 1 to 6 according to the present invention represent a base material.
Target base metal strength at the flange 1 / 4B part
(JIS G3106, SM490) and a
Target value of rupee impact absorption energy (JISG31
06, SM490C) of 45 (J) or more.
Add.

On the other hand, in Comparative Steel No. 7, other than Al and O
Component, cooling stop temperature, cooling from 700 ° C to 400 ° C
The speed is compatible with the conditions in the present invention, but Al and O
Concentration balance of [Al%]-1.1 [O] is 0.0
073, which is the condition in the present invention, -0.004 or more,
The strength is better than the target value because it deviates from the range of 0.006 or less.
The value is low. In steel 8, the cooling stop temperature, 4
The cooling rate up to 00 ° C is within the range of the manufacturing conditions in the present invention.
, The concentration of Mn is 2.03%,
Does not meet the target value of Charpy impact absorption energy.
In steel 9, the components, the cooling rate from 700 ° C to 400 ° C,
Although both satisfy the production conditions of the present invention,
The temperature is 640 ° C. and Ar₁The temperature is lower than the point
Therefore, the intensity is lower than the target value. In steel 10, the composition is 7 after cooling
The cooling rate from 00 ° C to 400 ° C is the same as that of the present invention.
Although the cooling conditions are satisfied, the cooling stop temperature is
r _ThreePoint -20 ° C or higher, Charpy impact absorption at 0 ° C
The energy harvest is extremely low and below the target value. With steel 11
Are the components and the cooling stop temperature are the production conditions in the present invention.
Cooling rate from 700 ° C to 400 ° C
Is 0.4 ° C./s, the lower limit of the cooling rate in the present invention.
Since the value is lower than 0.5 ° C / s, the intensity is lower than the target value.
Value. Steel 12 has both components and cooling stop temperature.
Although it satisfies the manufacturing conditions of the invention, it is
The cooling rate to 3.1 ° C. is 3.1 ° C./s.
The cooling rate exceeds the upper limit of 3.0 ° C./s.
Low Charpy impact absorption energy at ℃
Not satisfied.

Regarding the fire resistance, the Mo concentration is set at 0.1.
If it is 30 or more, excellent weldability can be secured, and it can be determined that steels 1 to 6 have good weldability because they satisfy the conditions. That is, when all of the requirements of the present invention are satisfied, as in steels 1 to 6 shown in Table 3, production of a thick flange H-section steel excellent in base material strength, toughness, and fire resistance by hot rolling is performed. Will be possible. The rolled section steel to which the present invention is applied is applicable not only to the above-mentioned H-section steel, but also to section steels having flanges such as I-section steel, angle steel, channel steel, and unequal thickness angle steel. Of course, you can.

The steel making method in the above embodiment is premised on the production in a converter, but employs an electric furnace in which preliminary deoxidation is more easily performed, or a step of combining them with an auxiliary melting furnace. Then, the dissolved oxygen of the present invention may be adjusted. In addition, the recuperation process between the rolling passes is performed during the pass from the start to the end of the reverse rolling or the continuous rolling, but the recuperation may be forcibly performed by the rapid heating means.

[0035]

According to the present invention, it is possible to produce a thick flange H-section steel having excellent base metal strength, toughness and fire resistance by hot rolling, thereby improving the reliability of a large building and ensuring safety.
Industrial effects such as improvement of economic efficiency are extremely remarkable.

[Brief description of the drawings]

FIG. 1 is an explanatory schematic view of an example of a device arrangement row for implementing the method of the present invention.

FIG. 2 is a view showing a cross-sectional shape of an H-section steel, showing names of respective parts and a sampling position of a mechanical test piece.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Heating furnace 2 ... Rough rolling mill 3 ... 1st intermediate rolling mill 4 ... 2nd intermediate rolling mill 5 ... Finishing rolling mill 6 ... Steel cooling device 7 ... Cooling floor 8 ... H-shaped steel 9 ... Flange 10 ... Web 11 ... Fillet part

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kazuhiko Eda 1 at Chikko Yawatacho, Sakai City, Osaka Prefecture Nippon Steel Corporation Sakai Works (72) Inventor Noriaki Onodera 1 at Chikko Yawatacho Sakai City, Osaka New Nippon Steel Corporation Sakai Works (56) References JP-A-5-105947 (JP, A) JP-A-2-163341 (JP, A) JP-A-7-238318 (JP, A) JP 6-100923 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 8/00-8/10

Claims (4)

(57) [Claims] 1. C: 0.05 to 0.15 by mass%
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.015%, Ti: 0.005 to 0.025%, Mo: 0. The molten steel consisting of 30 to 0.70%, the balance being Fe and unavoidable impurities was dissolved in a pre-deoxidation treatment to reduce dissolved oxygen to 0.000% by mass.
After being adjusted to 3 to 0.015%, it is further deoxidized by adding metallic aluminum or ferroaluminum. The Al content is 0.005 to 0.015% by mass%, and the dissolved oxygen [O%] of the molten steel. -0.004 ≦ [Al%]-1.1
[O%] ≦ 0.006 is cast by continuous casting to a slab, and after re-heating the slab to a temperature range of 1100 to 1300 ° C., rolling is started, and then the following (a) and (b) A method for producing a shaped steel having a flange excellent in strength, toughness and weldability, which is characterized by passing through any one of the production steps of (1). (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. 2. C: 0.05 to 0.15 by mass%
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.015%, Ti: 0.005 to 0.025%, Mo: 0. The molten steel consisting of 30 to 0.70%, the balance being Fe and unavoidable impurities was dissolved in a pre-deoxidation treatment to reduce dissolved oxygen to 0.000% by mass.
After being adjusted to 3 to 0.015%, it is further deoxidized by adding metallic aluminum or ferroaluminum. The Al content is 0.005 to 0.015% by mass%, and the dissolved oxygen [O%] of the molten steel. -0.004 ≦ [Al%]-1.1
[O%] ≤ 0.006 is cast by continuous casting to a slab, and the slab is reheated to a temperature range of 1100 to 1300 ° C and rolling is started. The temperature of the part is water-cooled to Ar ₃ -20 ° C. or lower and Ar ₃ -100 ° C. or higher, and after at least one rolling in the recuperation process, any one of the following manufacturing steps (a) and (b) is performed. A method for producing a shaped steel having a flange excellent in strength, toughness and fire resistance characterized by passing through. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. 3. C: 0.05 to 0.15 by mass%
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.015%, Ti: 0.005 to 0.025%, Mo: 0. And V ≦ 0.20%, Cr ≦ 0.7%, N
b ≦ 0.05%, Ni ≦ 1.0%, Cu ≦ 1.0%, M
After the molten steel containing one or more kinds of o ≦ 0.3%, the balance being Fe and inevitable impurities, the dissolved oxygen is adjusted to 0.003 to 0.015% by mass% by preliminary deoxidation treatment, Furthermore, deoxidation is performed by adding metallic aluminum or ferroaluminum, and the Al content is 0.005 to 0.5% by mass.
015% and relative to the dissolved oxygen [O%] of the molten steel,
0.004 ≦ [Al%] − 1.1 [O%] ≦ 0.006
Is cast by continuous casting to a slab satisfying the relationship of
After starting rolling after reheating to a temperature range of 00 to 1300 ° C., a flange excellent in strength, toughness and fire resistance characterized by passing through any of the following manufacturing steps (a) and (b): A method for producing a shaped steel having (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. 4. C: 0.05 to 0.15 by mass%
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.015%, Ti: 0.005 to 0.025%, Mo: 0. And V ≦ 0.20%, Cr ≦ 0.7%, N
b ≦ 0.05%, Ni ≦ 1.0%, Cu ≦ 1.0%, M
After the molten steel containing one or more kinds of o ≦ 0.3%, the balance being Fe and inevitable impurities, the dissolved oxygen is adjusted to 0.003 to 0.015% by mass% by preliminary deoxidation treatment, Furthermore, deoxidation is performed by adding metallic aluminum or ferroaluminum, and the Al content is 0.005 to 0.5% by mass.
015% and relative to the dissolved oxygen [O%] of the molten steel,
0.004 ≦ [Al%] − 1.1 [O%] ≦ 0.006
Is cast by continuous casting to a slab satisfying the relationship of
Rolling starts after reheating to a temperature range of 00 to 1300 ° C,
The temperature of the surface layer of the steel material is set to Ar ₃ -2 between passes of the intermediate rolling process.
After water cooling to 0 ° C. or lower and Ar ₃ −100 ° C. or higher and rolling at least once in the recuperation process, the following (a)
A method for producing a section steel having a flange excellent in strength, toughness, and fire resistance, which is performed through any one of the production steps (b). (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s.