JP3739893B2 - Manufacturing method of 400N thick steel plate for construction with excellent fire resistance - Google Patents

Description

【００２３】
【表２】

【００２４】
本発明鋼 No.１〜 No.１５の例では、常温の強度は４００Ｎ／mm² 級鋼の強度レベルを満足し、降伏比（ＹＲ）も７２％以下である。また、７００℃のＹＳも規格強度の２／３（１５７Ｎ／mm² ）以上の良好な値である。
【００２５】
これに対し、比較鋼 No.１６では、Ｃ量やＤ_B の値が低すぎたため、常温の強度が４００Ｎ／mm² 級鋼の強度レベルを満足できず、７００℃の強度も不十分であった。
比較鋼 No.１７では、Ｃ量やＤ_B の値が高すぎたため、７００℃の強度は高い値が得られたが、常温の強度が４００Ｎ／mm² 級鋼の強度を超え、５９０Ｎ／mm² クラスの強度特性であった。
【００２６】
比較鋼 No.１８では、Ｎｂが添加されておらず、Ｄ_B の値も低いため、常温の強度、７００℃の強度とも不十分な値であった。
比較鋼 No.１９では、各々の成分は規制範囲となっているが、Ｄ_B の値が低いため、常温の強度、ＹＲは満足できるが、７００℃の強度が不十分であった。 比較鋼 No.２０では、Ｍｎ量やＤ_B の値が高すぎたため、７００℃の強度は高い値が得られたが、常温の強度が４００Ｎ／mm² 級鋼の強度を超える値であった。
【００２７】
【発明の効果】
本発明の化学成分および製造法で製造した鋼材は、常温の耐力（ＹＳ）が２３５Ｎ／mm² 以上でＹＲが８０％以下、７００℃のＹＳが常温規格値の２／３以上等の特性を備えており、建築用耐火鋼材として適用が可能である。また、従来にない全く新らしい鋼材である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing steel materials used for various buildings in the fields of architecture, civil engineering, and the like, and particularly relates to a method for manufacturing 400 N thick steel plates for buildings having high temperature strength at 700 ° C. and excellent fire resistance. is there.
[0002]
[Prior art]
As various construction steel materials in the fields of construction, civil engineering, etc., steel materials standardized by JIS etc. are widely used.
By the way, when using the above steel materials for buildings such as buildings, offices, residences, and multistory parking lots, it is obliged to provide sufficient fire-resistant coatings to ensure safety in fire. The law stipulates that the temperature of a steel material does not exceed 350 ° C during a fire.
[0003]
That is, the steel material has a proof stress of about 2/3 at room temperature at about 350 ° C., which is lower than the required strength. When steel is used for a building, it is used with a fireproof coating so that the temperature of the steel does not reach 350 ° C. during a fire. For this reason, it is inevitable that the cost of fireproof coating will be higher than the cost of steel materials, and the construction cost will rise significantly.
[0004]
Recently, for example, Japanese Patent Laid-Open No. 2-77523 has been disclosed in order to solve the above problems. However, Japanese Patent Application Laid-Open No. 2-77523 is a steel to which a considerable amount of Mo and Nb is added, and the proof stress at 600 ° C. ensures 70% or more of the normal temperature proof strength, but the proof strength at 700 ° C. is shown. Absent. That is, as in this example, steel having a high temperature strength of about 600 ° C. has already been used in the market, but it has been difficult to produce a practical steel capable of ensuring a high temperature strength at 700 ° C.
[0005]
[Problems to be solved by the invention]
As described above, when steel is used for a building, normal steel cannot be used with no coating or light coating because the high-temperature strength is low, and an expensive fireproof coating has to be applied. Further, even in newly developed steel, the limit of the fireproof temperature to 600 ° C. is the limit, and the development of a steel material that can withstand 700 ° C. has been desired.
The objective of this invention is providing the manufacturing method of the thick steel plate which was excellent in the high temperature strength in 700 degreeC .
[0006]
[Means for Solving the Problems]
The present invention overcomes the above-mentioned problems and achieves the object, and specific means thereof will be described below.
(1) By mass ratio,
C: 0.005-0.04%, Si: 0.3% or less,
Mn: 0.5 to 1.0%, P: 0.015% or less,
S: 0.015% or less, Mo: 1.0 to 1.3%,
Nb: 0.01 to 0.05%, Ti: 0.005 to 0.02%,
Al: 0.10% or less, N: 0.001 to 0.006%
Containing the balance consisting of Fe and unavoidable impurities, and, after reheating the steel value of the formula D _B by the product of the alloying elements consisting of 0.4 - 0.5 to 1100 ° C. to 1300 ° C., thermal The intermediate plastic working is finished at 850 to 1000 ° C., and then allowed to cool to room temperature, and the microstructure is bainite 50 to 80% , normal temperature YS is 235 N / mm ² or more, 700 A method for producing a 400 N thick steel sheet for construction having excellent fire resistance with YS at 2 ° C. being 2/3 or more of the normal temperature standard value.
D _B = 0.258√C (1 + 0.3Si) (1 + 1.5Mn) (1 + 3.8Mo) (1 + 12Nb)
(The amount of each element is mass%)
[0007]
(2) By mass ratio,
C: 0.005 to 0.04%, Si: 0.3% or less,
Mn: 0.5 to 1.0%, P: 0.015% or less,
S: 0.015% or less, Mo: 1.0 to 1.3%,
Nb: 0.01 to 0.05%, Ti: 0.005 to 0.02%,
Al: 0.10% or less, N: 0.001 to 0.006%
Further Cu: 0.05-0.3%, V: 0.01-0.05%,
Ca: 0.0005-0.003%, REM: 0.001-0.005%
Containing one or two or more of, the balance being Fe and unavoidable impurities, and, 1100 ° C. The steel value of the formula D _B by the product of the alloying elements consisting of 0.4 - 0.5 1300 After reheating to ℃, hot plastic working is finished at 850 to 1000 ℃, and then it is allowed to cool to room temperature, and the microstructure is bainite 50 to 80%. / in mm ² or more, a manufacturing method excellent building 400N thick steel YS is 2/3 or more refractory at room temperature standard value at 700 ° C..
D _B = 0.258√C (1 + 0.3Si) (1 + 1.5Mn) (1 + 3.8Mo) (1 + 0.37Cu) (1 + 12Nb) (1 + 0.8V)
(The amount of each element is mass%)
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors have already found a steel having excellent high-temperature strength at 600 ° C. and are mainly used in the construction field, but there is a very strong demand for steel that can withstand higher temperatures (700 ° C.) in the market.
Even in this case, it is necessary to provide weldability, low YR, and other properties as architectural steel as in the conventional case, so obtaining a steel having excellent high-temperature strength at 700 ° C. was an extremely difficult task.
[0009]
In order to solve this problem, the present inventors have intensively studied, and that a steel having a strength of 400 N / mm ² class has a microstructure mainly composed of bainite and a method of adding a considerable amount of Mo is an effective means. I found it.
The present inventors have conducted intensive studies, the steel components and low C based, as a range of 0.4 to 0.5 the alloy components with a value of D _B, and high-temperature heating / hot rolling, bainite mainly (50 microstructure ˜80%), it has been found that a steel having excellent characteristics of high temperature strength at 700 ° C. with a low yield ratio (yield strength / tensile strength) can be obtained.
[0010]
First, to the microstructure and bainite principal, it is necessary to regulate the steel component in a specific range, it is necessary to 0.4-0.5 with D _B parameter.
Here, D _B is the parameter of the present inventor has obtained extensive studies, and made to correspond with the change of the microstructure, it revealed that the role of Mo and Nb is increased, the same effect also V It can be calculated by the following calculation formula.
D _B = 0.258√C (1 + 0.3Si) (1 + 1.5Mn) (1 + 3.8Mo) (1 + 0.37Cu) (1 + 12Nb)
(1 + 0.8V)
[0011]
However, if D _B parameter value exceeds 0.5, microstructure becomes a bainite single-phase, since the TS is over the standard strength, is required to be 0.5 or less. If it is less than 0.4, the strength of 400N steel cannot be satisfied, so 0.4 to 0.5 is an appropriate range.
[0012]
C is a characteristic element in the steel of the present invention, but it must be controlled within a narrow range, and 0.005 to 0.04% is an appropriate range. If the C content is less than this, the strength is insufficient, and if it exceeds this, the YS ratio (YS at 700 ° C./normal temperature YS) decreases, and it becomes impossible to satisfy the normal strength and the yield strength at 700 ° C. at the same time.
[0013]
Further, Nb is an important element in the steel of the present invention, but an appropriate amount of Nb is 0.01 to 0.05%. If it is less than this, the effect is small, and if it exceeds this, the microstructure tends to be a bainite one-phase, and the toughness of the welded part is also impaired.
[0014]
In addition, in order to ensure a high temperature strength of 700 ° C. with a microstructure mainly of bainite, it is essential to add an appropriate amount of Mo together with the addition of Nb.
The present inventors diligently studied and found that the appropriate value of Mo is 1.0 to 1.3%. If it is less than 1.0%, the strength at 700 ° C. cannot be satisfied, and if it exceeds 1.3%, the microstructure becomes a bainite one-phase and the strength at 700 ° C. is sufficient, but the strength at normal temperature exceeds the standard range. .
[0015]
Next, other component elements related to the present invention and the addition amount thereof will be described.
Si is effective as a deoxidizing element and is effective in improving the strength of steel. However, excessive addition causes deterioration of toughness, so 0.3% or less is an appropriate range.
Mn is an effective element for improving the strength of steel. However, excessive addition causes the microstructure to be bainite-phased and the strength becomes excessive, and if it is too small, the strength cannot be secured. 0% is an appropriate range.
[0016]
P and S are impurity elements and are preferably as small as possible. However, if they are 0.015% or less, there is no fear of impairing the characteristics of the steel of the present invention.
Ti is necessary for improving the toughness of the welded portion, but excessive addition forms TiC and greatly deteriorates the toughness, so 0.005 to 0.02% is an appropriate range.
[0017]
Al is used as a deoxidizing element, but excessive addition impairs the cleanliness of the steel, so addition of 0.1% or less is an appropriate range.
N has a function of increasing the high-temperature strength, but excessive addition causes surface cracks during slab casting, so 0.001 to 0.006% is an appropriate range.
[0018]
As described above, the properties of the steel of the present invention can be exhibited with these basic components, but a greater effect can be expected by selectively adding the following elements.
Cu is effective in improving the strength at normal temperature and high temperature, and is also effective in weather resistance (corrosion resistance), but excessive addition tends to cause high temperature cracking during solidification of steel, so 0.05 to 0.3% Is the appropriate range.
V, like Nb, is effective for bainite of the microstructure, but adding a large amount impairs the toughness of the weld zone, so 0.01 to 0.05% is an appropriate range.
Ca and REM combine with S, which is an impurity, to have an effect of improving toughness and preventing cracking due to diffusion hydrogen in the welded portion. 0.001 to 0.005% is an appropriate range.
[0019]
The conditions concerning the reheating, rolling and cooling of the steel together with the steel components are important.
In order to increase the strength at 700 ° C. by the combined addition of Mo, Cu, and Nb, it is necessary to sufficiently dissolve these elements during reheating. For this reason, the lower limit of the reheating temperature is 1100 ° C. To do.
Further, if the reheating temperature is too high, the austenite grains become coarse and the low temperature toughness deteriorates, so the upper limit must be 1300 ° C.
[0020]
Furthermore, the reason why the rolling end temperature is set to a high temperature of 850 ° C. or higher is to prevent precipitation of Mo carbides and Nb carbonitrides during rolling. Is significantly reduced. Further, at the end of rolling in a temperature range exceeding 1000 ° C., the toughness is extremely lowered, so 1000 ° C. is the upper limit of the rolling end temperature.
Note that after producing the steel according to the present invention, even when reheated to purposes Ac ₁ transformation point temperature, such as dehydrogenation, no intact features of the present invention.
[0021]
【Example】
Various steels were manufactured in the converter, continuous casting, and thick plate processes, and room temperature strength and high temperature strength were investigated. In Table 1, No. 1 to No. 15 show the steel of the present invention, and No. 16 to No. 20 show the chemical composition of the comparative steel. Table 2 shows the mechanical properties of the steel of the present invention and the comparative steel according to heating and rolling cooling conditions.
[0022]
[Table 1]

[0023]
[Table 2]

[0024]
In the examples of the inventive steels No. 1 to No. 15, the strength at normal temperature satisfies the strength level of 400 N / mm ² grade steel, and the yield ratio (YR) is 72% or less. 700 ° C. YS is also a good value of 2/3 (157 N / mm ² ) or more of the standard strength.
[0025]
In contrast, in Comparative Steel No.16, because the value of the C amount and D _B was too low, normal temperature strength can not be satisfied the intensity level of 400 N / mm ² class steel, also insufficient strength of 700 ° C. It was.
In Comparative steel No.17, because the value of the C amount and D _B is too high, although the strength is high value of 700 ° C. obtained, room temperature strength greater than the strength of 400 N / mm ² class steel, 590N / mm ^{There were two} classes of strength characteristics.
[0026]
In Comparative steel No.18, Nb has not been added, since lower values of D _B, room temperature strength was insufficient values with the strength of 700 ° C..
In Comparative steel No.19, although each of the components has a restricted range, the value of D _B is low, the room temperature strength, but YR is satisfactory, the strength of 700 ° C. was insufficient. In Comparative steel No.20, because the value of the Mn content and D _B is too high, although the strength is high value of 700 ° C. obtained, normal temperature strength is a value that exceeds the strength of 400 N / mm ² class steel .
[0027]
【The invention's effect】
Steel materials manufactured by the chemical composition and manufacturing method of the present invention have properties such as normal temperature proof stress (YS) of 235 N / mm ² or more, YR of 80% or less, and 700 ° C. YS of 2/3 or more of the normal temperature standard value. It can be applied as a fireproof steel for construction. Moreover, it is a completely new steel material that has never existed before.

Claims (2)

By mass ratio,
C: 0.005-0.04%,
Si: 0.3% or less,
Mn: 0.5 to 1.0%
P: 0.015% or less,
S: 0.015% or less,
Mo: 1.0 to 1.3%,
Nb: 0.01-0.05%
Ti: 0.005 to 0.02%,
Al: 0.10% or less,
N: 0.001 to 0.006%
Containing the balance consisting of Fe and unavoidable impurities, and, after reheating the steel value of the formula D _B by the product of the alloying elements consisting of 0.4 - 0.5 to 1100 ° C. to 1300 ° C., thermal The intermediate plastic working is finished at 850 to 1000 ° C., and then allowed to cool to room temperature, and the microstructure is bainite 50 to 80% , normal temperature YS is 235 N / mm ² or more, 700 A method for producing a 400 N thick steel sheet for building having excellent fire resistance with YS at 2 ° C. being 2/3 or more of the normal temperature standard value.
D _B = 0.258√C (1 + 0.3Si) (1 + 1.5Mn) (1 + 3.8Mo) (1 + 12Nb)
(The amount of each element is mass%) By mass ratio,
C: 0.005-0.04%,
Si: 0.3% or less,
Mn: 0.5 to 1.0%
P: 0.015% or less,
S: 0.015% or less,
Mo: 1.0 to 1.3%,
Nb: 0.01-0.05%
Ti: 0.005 to 0.02%,
Al: 0.10% or less,
N: 0.001 to 0.006%
Further Cu: 0.05 to 0.3%,
V: 0.01 to 0.05%,
Ca: 0.0005 to 0.003%,
REM: 0.001 to 0.005%
Containing one or two or more of, the balance being Fe and unavoidable impurities, and, 1100 ° C. The steel value of the formula D _B by the product of the alloying elements consisting of 0.4 - 0.5 1300 After reheating to ℃, hot plastic working is finished at 850 to 1000 ℃, and then it is allowed to cool to room temperature, and the microstructure is bainite 50 to 80%. / in mm ² or more, a manufacturing method excellent building 400N thick steel YS is 2/3 or more refractory at room temperature standard value at 700 ° C..
D _B = 0.258√C (1 + 0.3Si) (1 + 1.5Mn) (1 + 3.8Mo) (1 + 0.37Cu) (1 + 12Nb) (1 + 0.8V)
(The amount of each element is mass%)