JP2647313B2 - Oxide-containing rolled steel with controlled yield point and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide-containing controlled rolled steel section having excellent seismic performance and guaranteeing a yield point range of a section steel used as a structural member of a building, and a method for producing the same.

[0002]

2. Description of the Related Art Due to stricter safety standards such as super-high rise and large span of buildings and accompanying seismic resistance, thin H-shaped steel used for beams has been further enhanced in strength and strength. Higher toughness and lower yield ratio are required. Recently, in addition to the above, in order to reduce the difference between the design strength and the actual strength of the structural member and to further enhance the reliability, a narrow-width YP steel having an upper limit of the yield point is required. In order to satisfy such required characteristics, in the field of steel plates,
As shown in MP-ISIJ Vol. 4 (1991) 758p, heat treatment such as normalizing and tempering was performed after the rolling was completed. In the case of shaped steel, it is possible to satisfy the material properties by performing such treatment. However, the addition of heat treatment lowers the heat treatment cost and production efficiency, or, like H-shaped steel,
In a member having a shape in which the thickness ratio between the flange and the web is 2 to 3 times, deformation of the web is caused by generation of stress due to a difference in thermal expansion between the web and the flange during a post heat treatment.
There is a problem in economy and deterioration in shape performance.

Generally, a section steel having a flange, for example, H
When a section steel is manufactured by universal rolling, the web, flange,
Differences occur in the rolling finish temperature, rolling reduction, and cooling rate at each part of the fillet. As a result, variations in strength, ductility, and toughness occur between the parts, for example, a rolled steel material for a welding structure (JISG3
106) Some parts do not meet the criteria. Also recently,
An externally formed constant H-section steel having a thin web and reduced weight, and having a high cross-sectional performance, in which the web thickness is reduced to about 1/3 of the flange thickness, has been developed. Of these, the flange is forcibly cooled in order to prevent a web wave due to a stress caused by a difference in thermal expansion between the web and the flange particularly in the production of a thin size having a web thickness of 12 mm or less. Under such manufacturing conditions, low-temperature finishing is inevitably performed, the structure becomes finer and a high yield point is obtained, and there is a problem that the required value cannot exceed the minimum value of YP defined by JIS + 100 N / mm ² . .

In order to solve these problems, it is necessary to develop a steel material by a combination of a new alloy design and a manufacturing method so that high-performance material characteristics can be obtained as-rolled.

[0005]

In order to solve the above-mentioned problems, low-temperature rolling is inevitable due to the conditions for manufacturing thin materials, ferrite is refined, and the yield point is increased. In this case, it is necessary to develop a method in which ferrite is not refined. In the present invention, Al and Ti are contained in steel by controlling the amount of dissolved oxygen in the molten steel and adding a small amount of Al immediately before tapping in the steelmaking process.
, Mn, and Si are dispersed, and active cooling oxides functioning as preferential precipitation sites for precipitates are sparsely precipitated during solidification and by slow cooling after solidification, and MnS, TiN And the like are deposited and coarsened during cooling, and the effect of fine graining due to the pinning action of the grain boundary from these dispersions is eliminated. Using this method, even under the rolling conditions specific to thin steel bars as described above, austenite is coarsened, ferrite after transformation is coarsened, the yield point is reduced, and the desired yield point control is achieved. Shaped steel can be manufactured online and provided at low cost.

[0006]

The gist of the present invention is as follows: C: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn:
0.4-2.0%, Ti: 0.005-0.025%, N ≦ 0.004%, S ≦ 0.
01%, Al: 0.005 to 0.015%, the balance being Fe and unavoidable impurities, and Ti / Al-based double oxide and M
Oxide-containing, yield-controlled rolling section steel having a composite precipitate with nS and TiN dispersed at 20 particles / mm ² or less, C: 0.04 to 0.20% by weight, Si: 0.05 to 0.50%, Mn:
0.4-2.0%, Ti: 0.005-0.025%, N ≦ 0.004%, S ≦ 0.
01%, Al: 0.005 to 0.015%, plus V ≦ 0.20%,
Cr ≦ 0.7%, Nb ≦ 0.05%, Mo ≦ 0.3%, Ni ≦ 0.1%, Cu ≦ 1.0
%, Ca ≤ 0.003%, REM ≤ 0.010%, the balance consisting of Fe and unavoidable impurities and T
Oxide-containing controlled yield point rolled steel with 20 / mm ² or less of composite precipitates of i-Al-based composite oxide and MnS and TiN, C: 0.04 to 0.20% by weight, Si: 0.05 to 0.50%, Mn:
0.4-2.0%, Ti: 0.005-0.025%, N ≦ 0.004%, S ≦ 0.
0.1% by weight of molten steel containing Fe and unavoidable impurities by the pre-deoxidation treatment.
After being adjusted to 03 to 0.015%, it is further deoxidized by adding metallic aluminum or ferroaluminum, and the Al content is expressed in weight%.
0.005 to 0.015% and relative to the dissolved oxygen [O%] of the molten steel
After casting into a slab that satisfies the relationship of 0.004 ≦ [Al%]-1.1 [O%] ≦ 0.006, the slab was cooled from the solidification temperature to 900 ° C by 0.05.
Cooling was performed at a cooling rate of ~ 0.5 ° C / sec to obtain a composite precipitate of Ti · Al-based double oxide, MnS, and TiN in the steel at a rate of 20 / mm.
Rolling is started after re-heating the slab dispersed below ² to a temperature range of 1100 to 1300 ° C, and 20% at 900 ° C or less.
Method for producing oxide-containing yield point controlled rolled steel bars produced by controlled rolling with reduction as described above. C: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn:
0.4-2.0%, Ti: 0.005-0.025%, N ≦ 0.004%, S ≦ 0.
01%, plus V ≦ 0.20%, Cr ≦ 0.7%, Nb ≦ 0.05
%, Mo ≦ 0.3%, Ni ≦ 0.1%, Cu ≦ 1.0%, Ca ≦ 0.003%, REM
≦ 0.010%, the balance of molten steel containing Fe and unavoidable impurities is adjusted to 0.003 to 0.015% by weight of dissolved oxygen by pre-deoxidation treatment. The Al content is 0.005 to 0.015% by weight, and -0.004≤ [Al%]-1.1 [O
%] ≦ 0.006, and the slab is cooled from the solidification temperature to 900 ° C. at a cooling rate of 0.05 to 0.5 ° C./sec, and Ti / Al-based double oxide and MnS , TiN
Rolling is started after re-heating the slab, in which the composite precipitates are dispersed to 20 pieces / mm ² or less, in a temperature range of 1100 to 1300 ° C., and is manufactured by controlled rolling in which the reduction is reduced by 20% or more at 900 ° C. or less. The present invention relates to a method for producing an oxide-containing yield-controlled rolled steel section.

[0007]

Hereinafter, the present invention will be described in detail. The yield strength of steel is generally expressed by the following equation (1). σ _y = σ _i + κ · d ^-1/2式 (1) where σ _y : yield stress σ _i : Peierls + solid solution + precipitation + dislocation interaction stress d: ferrite grain size κ: constant The σ _i term is largely determined by the alloy-designed component depending on the strength level of the steel material, and therefore has a small degree of freedom. Therefore, the control of the yield strength by the process focuses on the control of the ferrite grain size.

The ferrite (α) grain size is determined by the number of α nucleation sites of the γ / α transformation and the growth rate,
It is governed by the austenite (γ) grain size just before transformation, the amount of work strain and cooling rate by working heat treatment represented by controlled rolling cooling (TMCP), and the dispersion of precipitates. The present invention is determined from the manufacturing conditions, although the effect of the present invention is large,
In particular, it is difficult to change the rolling temperature and the cooling condition in order to prevent web wave in thin materials, and the possibility of coarsening α due to this was examined. It was found that the dispersed particles of MnS, AlN, TiN, etc., which had not received much attention in the past, acted as γ fine-graining and α nucleation sites, contributing to α fine-graining. Therefore, the reduction of the total number was studied by introducing a new concept by controlling the steelmaking process.

The relationship between the crystal grain size and the degree of dispersion of the precipitate particles is represented by the following equation (2). R = 3/4 · r / F──────────── (2) where R: grain size r: particle radius F: volume fraction of particles volume fraction of precipitate particles Is constant, the crystal grain size is proportional to the precipitate particle radius. Therefore, in order to reduce the volume fraction (F) of the particles, it is necessary to reduce MnS, AlN, and TiN as much as possible in order to reduce the volume fraction (F) of the particles, which is the target of the present invention, and to aggregate and combine the particles. Coarsening (r) to reduce the total number of precipitates.

The realization of these principles is a feature of the present invention. In the steelmaking process, Ti.Al-based double oxides having a preferential function as precipitation sites for precipitates are formed in steel, and these are formed during solidification. , Then slowly cool down
Simultaneously with the reduction of the number, MnS, TiN and the like were adhered during the cooling and were coarsened, thereby reducing the total number of precipitates. As a result, austenite coarsening and ferrite nucleation are reduced, and α is coarsened even under the conditions of low-temperature rolling and accelerated cooling unique to thin steel bars, and the yield point can be controlled online. Things.

Next, the reasons for limiting the range of the basic components of the steel of the present invention will be described. C is added as an effective component to improve the strength of the steel. If it is less than 0.04%, the strength required for structural steel cannot be obtained. Since the cracking property and HAZ toughness are significantly reduced, the upper limit is set to 0.20%.

Si is necessary for securing the strength of the base material and performing preliminary deoxidation, but if it exceeds 0.5%, high carbon martensite having a hardened structure is generated in the heat-treated structure, and the toughness is significantly reduced. On the other hand, if it is less than 0.05%, the deoxidation becomes insufficient and the Si content is limited to this range. Mn needs to be added in an amount of 0.4% or more to ensure the strength and toughness of the base metal.
The upper limit was set to 2.0% within an acceptable range such as cracking.

Ti is an element necessary for producing an Al.Ti-based composite oxide as a deoxidizing agent. If the content is less than 0.005%, the composite oxide is remarkably reduced and has no effect. Was set to 0.005% or more. However, if it exceeds 0.025%, excessive Ti forms TiN and TiC, causing grain refinement and precipitation hardening, increasing the yield point, and at the same time, significantly reducing the toughness of the heat affected zone. did.

Since N precipitates TiN and AlN and increases the yield strength by refining γ and dissolving in ferrite, the content of N is 0.00
Limited to 4% or less. S precipitates MnS and acts as a grain refinement of γ and acts as an intragranular ferrite nucleus. Therefore, it is desirable to reduce S as much as possible. However, if it is 0.01% or less, it can adhere to Ti oxide to be coagulated and exceed 0.01%. And MnS alone
Was precipitated, and the number of deposited particles rapidly increased, so that the content was limited to 0.01% or less.

[0015] The dissolved oxygen of the molten steel having the above components is controlled by a preliminary deoxidation treatment. Control of dissolved oxygen not only purifies molten steel but also activates Al in the slab in the next deoxidation step.
-To form Ti-based double oxides. The reason for adjusting the dissolved oxygen to the range of 0.003 to 0.015% by weight is that if the [O] concentration after preliminary deoxidation is less than 0.003%, an Al.Ti-based double oxide cannot be formed, and if it exceeds 0.015%. Even if other conditions are satisfied, the double oxide becomes coarse and becomes a starting point of brittle fracture, and the [O] concentration after preliminary deoxidation is limited to 0.003 to 0.015% by weight in order to reduce toughness.

Next, a small amount of Al is added, casting is performed, and the steel making process is completed. However, Al is a strong deoxidizing element, and
When the content exceeds 015%, a double oxide which becomes a preferential precipitation site of MnS, TiN, etc. is not generated, and excessive solid solution Al combines with N to form AlN, and α is refined to 0.015% Limited to the following. If the content is less than 0.005%, the desired double oxide containing Al cannot be produced, so the content was made 0.005% or more. And the amount of Al is -0.004 by weight% with respect to the dissolved oxygen [O%] of the molten steel.
≤ [Al%]-1.1 [O%] ≤ 0.006 is limited to satisfy the relation: in this relational expression, when Al is excessive with respect to the [O] concentration by weight%, MnS, TiN, etc. This is because the number of double oxides that form precipitation sites decreases, and instead, a large number of Al ₂ O _3, which are ineffective as precipitation nuclei, are generated, and α cannot be coarsened. If the Al content is too small relative to the [O] concentration in weight%, the double oxide effective for precipitation is remarkably reduced. The reason why Al is added at the latter stage of the steelmaking process is that Al forms a strong Al ₂ O ₃ with a strong deoxidizing power, and it is difficult to form the desired low melting point double oxide.

Although the amount of P contained as an unavoidable impurity is not particularly limited, it is necessary to reduce the amount of P as much as possible, because the solidification segregation causes a decrease in welding cracks and toughness, etc., and the P content is desirably less than 0.02%. The above are the basic components of the steel of the present invention. For the purpose of increasing the strength of the base material and improving the toughness of the base material, V, Cr, Mo, Nb, Ni, Cu, Ca, and
One or more REMs can be contained.

V, Cr, Mo, Nb, Ni, and Cu are added as strengthening elements for ensuring the strength of the base material. V ≦ 0.20%, Cr ≦ 0.7%, Nb ≦ 0.05%, Mo ≦ 0.3%,
The respective upper limits of Ni ≦ 0.1% and Cu ≦ 1.0% are shown in the above because of the balance between strengthening ability and economy. Ca and R
EM is added for the purpose of preventing UST defects and reduction in toughness caused by stretching of MnS during hot rolling. The reason is that instead of MnS, Ca-OS with small hot deformability or
The purpose is to generate the spherical sulfide oxide of REM-OS and control the properties and shape of the inclusions so that they do not stretch like MnS even by rolling. However, Ca is 0.003% by weight%.
Is added over 0.01% by REM, each Ca-OS,
REM-OS becomes a large amount and coarse inclusions, which deteriorates the toughness of the base metal and the welded part.
Rem was limited to 003% or less and REM to 0.01% or less.

The reason why the molten steel of these components is cooled at a cooling rate of 0.05 to 0.5 ° C./sec from 900 ° C. to the solidification temperature of the slab is that the number of Al.Ti-based double oxides in the steel is To 20 pieces / mm ² or less, and the previously generated Al
This is because MnS and TiN are adhered and aggregated by cooling the Ti-based double oxide at a cooling rate in this range. That is, if the cooling rate is less than 0.5 ° C / sec, the composite
Although it is a sufficient condition to disperse the particles into pieces / mm ² or less, it was limited to 0.5 ° C./sec or more due to operational difficulties such as the risk of slab breakout during continuous casting. Also, 0.5 ℃ / s
When the cooling rate exceeds ec, Al.Ti-based double oxides are finely precipitated, and the number exceeds 20 / mm ^2. Therefore, the cooling rate is limited to 0.5 ° C./sec or less.

It should be noted that the Al.Ti-based double oxide in steel and Mn
The reason for dispersing the composite precipitate of S and TiN to 20 grains / mm ² or less is that if it exceeds 20 grains / mm ² , intragranular ferrite is generated and γ is refined, and the desired yield point is obtained. This is because it cannot be changed. The slab that has undergone the above treatment is then 1100
Reheat to a temperature range of ~ 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 the upper limit is the performance and economy of the heating furnace. From 1300
° C.

[0021] The heated steel material is roll-formed by each of rough rolling, intermediate rolling and finish rolling, and is reverse-rolled in an intermediate rolling mill, and at the same time, the flange portion is water-cooled before and after rolling to reduce the temperature difference with the web. Therefore, in order to improve toughness by controlled rolling, the total reduction amount is 20 ° C. or less at 900 ° C. or less.
% Of rolling is required, and such a restriction is imposed on the rolling conditions. After the rolling, the flange water cooling may be performed as necessary.

[0022]

EXAMPLES A prototype steel was melted in a converter, added with an alloy, preliminarily deoxidized, the oxygen concentration of the molten steel was measured, and an Al amount corresponding to the amount was added.
After casting into a thick slab, the rough rolling step was not illustrated, but was rolled into an H-beam by a universal rolling mill row shown in FIG. The cooling rate after casting was controlled by selecting the amount of water in the cooling zone of the slab and the speed of drawing the slab.

For water cooling on the outer surface of the flange, water cooling devices 5a are provided before and after the intermediate rolling mill 4, and after repeating the spray cooling and the reverse rolling between the rolling passes and finishing the rolling by the finishing universal rolling mill 6, the finishing universal rolling mill 6 Spray cooling was performed by a cooling device 5b provided on the rear surface. Mechanical properties 1/4 flange width total length (B) at the center of the plate thickness t ₂ of the flange 2 shown in FIG. ₂ (1 / 2t 2), 1/2 width (1 / 4B, 1 / 2B ), At the center of the thickness of the web 3, test pieces were collected from 1 / 2H of the web height. The characteristics of these locations were determined by measuring the average mechanical properties of the flange 1 / 4F section and the web 1 / 2W section for each of the flange section and the web section. This is because the mechanical test characteristics of the H-section steel can be represented by these three locations because the strength decreases.

Tables 1 and 2 show the chemical component values of the test steel, the dissolved oxygen concentration during deoxidation, and the residual Al with respect to the dissolved oxygen.
The relationship with the amount and the cooling rate during solidification are shown.

[0025]

[Table 1]

[0026]

[Table 2]

Tables 3 and 4 show mechanical test characteristics of each part of the H-section steel with respect to rolling conditions and production conditions such as the presence or absence of flange water cooling. It is well known that the rolling 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 3]

[0029]

[Table 4]

As shown in Table 3, steels 1 to 8 according to the present invention
Is YP = 245 to 345N / mm ^{2 for} the target SM400, YP for the SM490
= 324 ~ 424N / mm ² , SM570 YP = 461 ~ 561N / mm ² JIS
It is controlled within the lower limit of the standard +100 N / mm ² , and the yield ratio (YP / TS) also satisfies the low YR value of 0.8 or less, and the tensile strength (JIS 3106) and the Charpy value at -5 ° C are 4
7 (J) or more is fully satisfied. On the other hand, as shown in Table 4, comparative steels 9, 11, and 13 were subjected to ordinary Al deoxidation,
Control of oxygen concentration in molten steel and trace A in the steelmaking process of the present invention
l Deoxidation has not been carried out, and no Al / Ti-based oxide has been produced, and since it is manufactured under normal continuous casting conditions and not cooled slowly, precipitates such as MnS are finely dispersed, lead to grain refining of ferrite, beyond the range of the lower limit value + 100 N / mm ² goal YP of JIS standard, yield ratio (YP / TS) also
0.8 or less is not satisfied. In addition, comparative steels 10, 12,
In the steelmaking process of the present invention, although the control of the oxygen concentration of the molten steel and the deoxidation of a small amount of Al were performed in the steelmaking process of the present invention, the cooling rate at the time of solidification exceeded 0.5 ° C / sec. 20 / mm ² or more, exceeding the target YP lower limit of JIS standard + 100 N / mm ² , and the yield ratio does not satisfy 0.8 or less.

That is, when all the requirements of the present invention are satisfied, as shown in Tables 3 to 8, high yield points due to low-temperature rolling of thin-sized rolled steel sections are suppressed, and It is possible to manufacture as-rolled shaped steel that satisfies the mechanical properties required for structural members for use. Note that the rolled section steels to which the present invention is applied are not limited to the H-section steels of the above-described embodiment, but include I-section steels, angle irons,
It is needless to say that the present invention can also be applied to a section steel having a flange such as a channel section steel, an unequal side unequal thickness angle section steel or the like.

[0032]

According to the rolled steel according to the present invention, the yield point can be controlled in the range of the lower limit of JIS standard +100 N / mm ² even under low-temperature rolling conditions, and a narrow width yield point and a low yield ratio can be achieved.
Efficient production of building section steel is possible in-line,
Industrial effects such as improvement in reliability of large structures and economic efficiency are extremely remarkable.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of an apparatus arrangement for performing the method of the present invention.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... H-shaped steel 2 ... Flange 3 ... Web 4 ... Intermediate rolling mill 5a ... Water cooling device of the front and rear surface of an intermediate rolling mill 5b ... Finishing rolling machine rear surface cooling device 6 ... Finishing rolling mill

Claims (4)

(57) [Claims] C. 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, Ti: 0.005 to 0.025%, N ≦ 0.004%, S ≦ 0.01%, Al: 0.005% by weight% Oxide-containing yield point characterized by containing 0.015%, the balance being Fe and unavoidable impurities, and dispersing a composite precipitate of Ti.Al-based double oxide, MnS and TiN to 20 / mm ² or less. Controlled rolled section steel. 2. In weight%, C: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, Ti: 0.005 to 0.025%, N ≦ 0.004%, S ≦ 0.01%, Al: 0.005 to 0.015%, V ≦ 0.20%, Cr ≦ 0.7%, Nb ≦ 0.05%, Mo
≦ 0.3%, Ni ≦ 0.1%, Cu ≦ 1.0%, Ca ≦ 0.003%, REM ≦ 0.01
0% of one or more kinds, the balance being Fe and unavoidable impurities, and a Ti · Al-based double oxide and Mn
An oxide-containing yield-point controlled rolled steel having a composite precipitate of S and TiN dispersed at 20 particles / mm ² or less. 3. In% by weight, C: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, Ti: 0.005 to 0.025%, N ≦ 0.004%, S ≦ 0.01%, and the balance is The molten oxygen consisting of Fe and unavoidable impurities was reduced to 0.003% by weight of dissolved oxygen by preliminary deoxidation.
After adjusting the content to 0.015%, the mixture was further deoxidized by adding metallic aluminum or ferroaluminum.
05 to 0.015%, and -0.0 to the dissolved oxygen [O%] of the molten steel
After casting into a slab that satisfies the relationship of 04 ≦ [Al%] − 1.1 [O%] ≦ 0.006, the slab is cast from a solidification temperature to 900 ° C. in a range of 0.05 to 0.2%.
The slab was cooled at a cooling rate of 5 ° C./sec, and the precipitate obtained by dispersing a composite precipitate of a Ti · Al-based double oxide, MnS, and TiN in a steel at a rate of 20 / mm ² or less at 1100-1300 ° C. A method for producing an oxide-containing yield-point-controlled rolled steel section, wherein rolling is started after reheating to a temperature range and reduced by 20% or more at 900 ° C or lower. 4. In% by weight, C: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, Ti: 0.005 to 0.025%, N ≦ 0.004%, S ≦ 0.01%. V ≦ 0.20%, Cr ≦ 0.7%, Nb ≦ 0.05%, Mo
≦ 0.3%, Ni ≦ 0.1%, Cu ≦ 1.0%, Ca ≦ 0.003%, REM ≦ 0.01
The molten steel containing 0% or 1 or more kinds and the balance consisting of Fe and unavoidable impurities is adjusted to 0.003 to 0.015% by weight of dissolved oxygen by preliminary deoxidation treatment. Deoxidation by addition, the Al
The content is 0.005 to 0.015% by weight, and -0.004 ≦ [Al%]-1.1 [O%] ≦ 0.00 with respect to the dissolved oxygen [O%] of the molten steel.
After casting into a slab that satisfies the relationship of 6, the slab is cooled from the solidification temperature to 900 ° C. at a cooling rate of 0.05 to 0.5 ° C./sec, and Ti / Al-based double oxide, MnS, TiN The slab in which the composite precipitates were dispersed to 20 particles / mm ² or less was 1100
Rolling was started after reheating to a temperature range of
A method for producing an oxide-containing yield-controlled rolled steel section comprising reducing the temperature by 20% or more at 0 ° C or lower.