JPH10195592A - Shape steel excellent in brittle fracture resistance under high speed deformation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shape steel for structural purpose excellent in brittle fracture resistance even under high speed deformation caused by active fault type big earthquakes, the collision of vessels or the like. SOLUTION: This shape steel is the one having a flange, a web or a flange and a fillet part as the joint part therebetween and having a compsn. contg., by weight, 0.05 to 0.2% C, 0.05 to 0.5% Si, 0.5 to 1.8% Mn, 0.001 to 0.06% Al, <=0.005% S, <=0.003% O, and the balance Fe with inevitable impurities. In a tension test using a test piece having a notch by which the stress concn. factor in the fillet part of the shape steel is >=5, it has >=30% value of reduction of area under static loading conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a section steel used for various types of buildings in the field of civil engineering and construction, ships, and energy, etc., and in particular, has excellent brittle resistance even under high-speed deformation caused by an earthquake, ship collision, or the like. The present invention relates to a structural section steel suitable for use in a building requiring fracture characteristics.

[0002]

2. Description of the Related Art In the event of an earthquake or a collision of a ship, a large deformation is applied to a steel material, which causes extremely large damage such as collapse of a building. In the seismic design method in the building field, designs are made to prevent the collapse of buildings by absorbing the energy of earthquakes by plastic deformation of steel materials, but steel materials applied to such buildings include Excellent plastic deformability is required, and is disclosed in JP-A-55-119152, JP-A-63-223123, and JP-A-1-115564.
No. 2, Japanese Unexamined Patent Publication No. 3-115524 and the like propose a steel material in which the uniform elongation property is improved by lowering the yield ratio. In addition, as stipulated in JIS G3136 that the yield ratio of rolled steel for building structures is set to be 80% or less, the response from the steel surface to the improvement of seismic resistance is to improve the plastic deformability by the low yield ratio. Is the center.

[0003]

However, in general, in the case of shaped steel, it is more difficult to refine the structure of the fillet, which is the joint thereof, than in the case of the flange and the web due to modeling problems, and the influence of segregation of impurities is less. Because of the remarkable appearance, deterioration of the material is likely to occur. In addition, a large stress concentration often occurs at the fillet portion in terms of shape, so that brittle fracture tends to easily occur under high-speed deformation such as an earthquake or ship collision.

[0004] Many steel structures were severely damaged by the Northridge Earthquake of January 1994 and the Great Hanshin-Awaji Earthquake of January 1995. Brittle fracture from a shape discontinuity such as a part or a scalloped part. In addition, the North Ridge earthquake and the Hanshin-Awaji Earthquake were considered to be very active, and the speed of shaking was very high because the epicenter was close, and the deformation rate reached a strain rate of 1 to 10 / sec. I have.

[0005] It is said that when a steel material undergoes high-speed deformation, the ductile-brittle transition temperature rises as compared with the normal static deformation speed. However, the failures observed in the Northridge earthquake and the Hanshin-Awaji great earthquake are column-like. It is considered that the high-speed deformation was applied to the stress-concentrated portion such as the beam joint and the scalloped portion, and the ductile-brittle transition temperature in that portion increased, and brittle fracture occurred before the steel material exhibited the plastic deformability. Therefore, the conventional concept of improving plastic deformability by a low yield ratio does not prevent buildings from collapsing due to brittle fracture when a high-speed earthquake such as the Northridge Earthquake or the Hanshin-Awaji Earthquake occurs. Suggests that you cannot.

[0006] Further, even in a collision accident of a ship, since steel materials are locally subjected to high-speed deformation, brittle fracture may occur, which is a problem. An object of the present invention is to provide a structural steel having excellent brittle fracture resistance even under high-speed deformation caused by an active fault type large earthquake or ship collision in order to solve the above problems. is there.

[0007]

In order to solve the above problems and achieve the object, the present invention uses the following means. (1) The shaped steel of the present invention is expressed in terms of% by weight, C: 0.05 to 0.1%.
2%, Si: 0.05 to 0.5%, Mn: 0.5 to
1.8%, Al: 0.001 to 0.06%, and S ≦
A shape steel having a flange, a web or a flange, and a fillet portion that is a joint portion thereof, the shape steel comprising 0.005%, O ≦ 0.003%, and the balance being Fe and unavoidable impurities. Stress concentration factor of steel fillet is 5
In a tensile test using a specimen having a notch as described above, a structural section steel excellent in brittle fracture resistance under high-speed deformation characterized by having a drawing value of 30% or more under static loading conditions. is there.

(2) The shaped steel according to the present invention further includes Ti ≦ 0.1%, Nb ≦ 0.04%, V ≦ 0.1% by weight.
%, Cu ≦ 0.5%, Ni ≦ 0.5%, Cr ≦ 1%, M
o ≦ 0.6%, Ca ≦ 0.005%, and REM ≦ 0.
The structural steel according to the above (1), which has excellent brittle fracture resistance under high-speed deformation, containing one or more selected from the group of 03%.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The inventor of the present invention has proposed a method for producing structural steel having excellent brittle fracture resistance even under high-speed deformation caused by an active fault type large earthquake or ship collision. As a result of intensive studies on the fracture characteristics of shaped steel in
The following findings have been obtained.

When a steel material undergoes plastic deformation, the energy required for the plastic deformation is converted to heat energy. However, under high-speed deformation, the time required for heat to be dissipated by heat conduction is short, and the temperature of the steel material rises. Then, the greater the amount of plastic deformation, the greater the amount of heat generated thereby. In general, the higher the temperature, the higher the Charpy absorbed energy of the steel material and the lower the brittle fracture surface ratio.However, if the stress-concentrated portion is sufficiently plastically deformed even under high-speed deformation, the temperature of the stress-concentrated portion rises, resulting in high-speed deformation. This can suppress an increase in the ductile-brittle transition temperature, that is, an increase in the brittle fracture surface ratio, thereby making it possible to prevent a brittle fracture as seen in the Great Hanshin-Awaji Earthquake and the like.

[0011] However, the plastic deformability of steel materials is based on JIS Z
In general, it is evaluated by the reduction value and elongation obtained from a tensile test piece having a parallel portion specified in 2201.
Since a stress concentrated portion such as a scallop portion of a section steel is in a high triaxial stress state, the plastic deformability at such a stress concentrated portion cannot be correctly evaluated by a conventional tensile test piece having a parallel portion. . Therefore, as a result of repeated studies on a method of evaluating plastic deformability under a high triaxial stress state, H
If a tensile test is performed using a notched round bar specimen having a stress concentration coefficient equivalent to the stress concentration state seen in the scallop part of a shaped steel, etc., the plastic deformation ability at the stress concentration part will be determined by the drawing value at that time. It turns out that we can evaluate correctly.

A notched round bar test piece (FIG. 1) taken from a fillet portion 3 of an H-shaped steel having a flange 1, a web 2, and a fillet portion 3 as a joining portion shown in FIG.
FIG. 2 shows the relationship between the brittle fracture surface ratio and the temperature when a tensile test was performed using (b), stress concentration coefficient α = 6.7).
The average strain rate between grades is 0.001 / sec (static deformation) and 1
0 / sec (corresponding to high-speed deformation at the time of earthquake), but the brittle fracture rate of high-speed deformation is higher than that of static deformation.
It is clear that the transition temperature of the ductile brittle fracture surface has risen, and that the fracture behavior under high-speed deformation, as seen in the Northridge earthquake and the Hanshin-Awaji great earthquake, is reproduced.

FIG. 3 shows cutaway round bar specimens (FIG. 1 (b)) taken from fillets of various H-beams.
The relationship between the aperture value when performing a static tensile test at room temperature and the change in the fracture surface transition temperature due to high-speed deformation is shown. When a tensile test was performed under static conditions using a notched round bar specimen, the aperture value was
If it is 30% or more, no increase in the fracture surface transition temperature due to high-speed deformation is observed. This is considered to be due to the fact that, when plastic deformation is sufficient even under high-speed deformation, the temperature of the stress concentrated portion was increased, and the rate of brittle fracture was reduced.

Conventionally, the resistance of steel to brittle fracture has been conventionally evaluated by a Charpy impact test or the like defined in JIS Z2242. However, the Charpy impact test cannot compare the difference in fracture behavior with the deformation rate, and the resistance to an increase in the brittle fracture rate due to high-speed deformation as seen in an earthquake, that is, brittle fracture under high-speed deformation It is impossible to evaluate properties. In order to improve the brittle fracture resistance under high-speed deformation, it is important to increase the plastic deformability under high triaxial stress conditions.
Even if the fracture surface transition temperature (vTr
Even if the steel has a low s), that is, a high toughness, it is difficult to suppress an increase in the brittle fracture rate during high-speed deformation if the drawing value of the notched specimen is low.

It has been known for some time that sulfide and oxide inclusions have an adverse effect on the plastic deformability, ie, ductility, of steel. Generally, S and O are reduced to such an extent that the material does not deteriorate. Have been. However, under a high triaxial stress state such as a scalloped portion of an H-section steel, even if the amount of S or O is such that the elongation and the drawing value do not decrease as evaluated in a normal tensile test, the sulfide-based In addition, the oxide-based inclusions serve as starting points of microvoids, and ductile cracks are easily propagated, so that sufficient plastic deformability may not be obtained. Therefore, in order to increase the plastic deformability at the stress concentration portion, it is necessary to severely limit the amount of S or O.

Based on the above findings, the present inventor has proposed that S
The amount of O or O is severely restricted, and the drawing value in a tensile test under a static loading condition using a notched test specimen with a specified stress concentration coefficient at the fillet portion of a shaped steel is controlled to a certain value or more, so that high speed The present inventors have found a shaped steel of the present invention having excellent brittle fracture resistance under deformation, and have completed the present invention.

That is, the present invention limits the tensile properties (aperture value) under static loading conditions of the steel composition and the notched test specimen to the following ranges, so that a high-speed active fault-type earthquake or ship collision occurs. A section steel having excellent brittle fracture resistance under deformation can be provided. The reasons for adding the components of the present invention below,
The reason for limiting the components and the reason for limiting the plastic deformation characteristics in the stress concentration portion will be described.

(1) Component composition range C: 0.05 to 0.2% C is an element necessary for securing the strength of the steel material.
If it is less than 0.05%, the strength is insufficient, and if it exceeds 0.2%, the properties of the segregated portion and the weldability are impaired, so the content is 0.05 to 0.2%. Si: 0.05 to 0.5% Si is necessary not only to increase the strength of the steel material but also as a deoxidizing agent in the steel making process, but if it is less than 0.05%, its effect is insufficient, and it exceeds 0.5%. If added in such a manner, the properties of the segregated portion and the toughness of the welded portion are deteriorated, so the content is 0.05 to 0.5%.

Mn: 0.5 to 1.8% Mn is added to increase the strength of the steel material.
If the content is less than 1.8%, the strength is insufficient, and if the content exceeds 1.8%, segregation becomes remarkable and toughness is deteriorated, so that the content is 0.5 to 1.8%. Al: 0.001 to 0.06% Al is required as a deoxidizing agent, but if it is less than 0.001%, deoxidation is insufficient, and if it exceeds 0.06%, surface defects of the slab , Causing its content to be 0.1.
001 to 0.06%. S ≦ 0.005% S is an element that forms sulfide inclusions, but in a high triaxial stress state such as a stress-concentrated portion such as a column-beam joint or a scallop, sulfide inclusions are not formed. It becomes the starting point of microvoid generation and promotes the development of ductile cracks, so that the plastic deformability at the stress concentrated portion is significantly reduced. However, 0.005
% Or less, the upper limit of the content is 0.00%.
5%.

O ≦ 0.003% O is present in the steel as oxide-based inclusions, but, like sulfide-based inclusions, becomes a starting point of microvoids and promotes the development of ductile cracks. The plastic deformability at the concentrated part is significantly reduced. However, since there is no problem if the content is 0.003% or less, the upper limit of the content is 0.003%.

In the present invention, in addition to the above alloying elements, Ti, Nb, V, Cu, N
One or more of i, Cr, Mo, Ca, and REM may be contained, and the reasons for limiting the components are described below.

Ti ≦ 0.1% Ti forms TiN, suppresses the structure coarsening of the welded portion, and
It is an element that contributes to the improvement of AZ toughness, and a large effect can be obtained with a small amount of addition. However, if added in excess of 0.1%, the weldability is reduced, so the content is 0.1% or less. It is. Nb ≦ 0.04% Nb is an element that precipitates finely as Nb (C, N) and contributes to an increase in strength. However, if added over 0.04%, the weldability or the toughness of the welded portion is reduced. , Its content is not more than 0.04%. V ≦ 0.1% V precipitates as VC and contributes to the improvement of strength.
If the content is less than 5%, the effect cannot be obtained, and if the content exceeds 0.1%, the effect is saturated.
Between 0.5 and 0.1%. Cu ≦ 0.5% Cu is an element effective for improving strength and toughness.
%, The hot workability is lowered and the surface flaws are liable to be generated.
5% or less. Ni ≦ 0.5% Ni is an extremely effective element for improving toughness, but is an extremely expensive element, so if added over 0.5%, it is disadvantageous in terms of cost. Is 0.5%
It is as follows. Cr ≦ 1% Cr is an element effective for improving the strength, but if added in excess of 1%, the weldability is reduced, so the content is 1% or less. Mo ≦ 0.6% Mo is an element effective for improving the strength similarly to Cr,
If added in excess of 0.6%, not only will the weldability be reduced, but it will also be disadvantageous in terms of cost.
% Or less. Ca ≦ 0.005% Ca is an element that improves toughness by controlling the shape of sulfide-based inclusions. However, if added over 0.005%, the cleanliness of steel is adversely affected. The amount of addition is 0.005% or less. REM ≦ 0.03% REM (rare earth element) is also an element that improves toughness by controlling the shape of sulfide-based inclusions, similar to Ca, but when added in excess of 0.03%, the steel becomes rare. Since the material has an adverse effect, the amount of addition is 0.03% or less. P is allowed to be mixed in a range that does not impair the effects of the present invention.

By adjusting to the above-mentioned composition range, high plastic deformability can be obtained in the stress-concentrated portion, so that it is possible to obtain a shaped steel having a large calorific value at high-speed deformation and excellent brittle fracture resistance. Becomes

The section steel having such properties has tensile properties under static loading conditions by the following notched test pieces. (2) Tensile Properties of Notched Specimen under Static Loading Conditions A section steel (H-section steel) having a flange 1 and a web 2 of the present invention shown in FIG. ) Indicates that the stress concentration coefficient obtained from the fillet portion 3 is 5
In the tensile test using the test piece having the notch as described above, it has an aperture value of 30% or more under the static loading condition.

The reason why the fillet portion 3 in the section steel was selected as the notch test piece is that, in general, in the section steel, compared with the flange 1 and the web 2, the microstructure of the fillet section 3, which is the joint portion, is smaller than that of the flange 1 and the web 2 due to modeling problems. Difficult to
The material is apt to deteriorate, and the fillet 3
In this case, large stress concentration often occurs, so that brittle fracture tends to occur under high-speed deformation such as an earthquake or ship collision.

A test piece having a notch with a stress concentration coefficient of 5 or more is used for a test piece having a notch with a stress concentration coefficient of less than 5 or a test piece without a notch under high-speed deformation (1/3 at a strain rate). This is because it is impossible to evaluate the brittle fracture resistance in (seconds or more). In addition, the reason why the aperture value at the time of performing the tensile test under the static loading condition is limited to 30% or more is that, as shown in FIG. This is because the deformability is not sufficient, and the temperature rise in the stress concentrated portion is small under high-speed deformation, and the brittle transition temperature rises, that is, the brittle fracture rate is increased, so that brittle fracture is likely to occur. In addition, any notch test piece can be used as long as the stress concentration coefficient is 5 or more. Further, the section steel of the present invention includes a section steel (unequal angle angle steel) having a flange 1, a web 2, and a fillet portion 3 as a joint portion thereof as shown in FIG. Shaped steel (equilateral angle steel) having the flange 1 shown in 3), the flange 1 and the fillet portion 3 which is a joint thereof is also included.

By adjusting the above composition range and tensile properties (aperture value) under static loading conditions using notched test pieces, even under high-speed deformation caused by an active fault type large earthquake or ship collision, etc. It is possible to obtain a structural steel having excellent brittle fracture resistance.

The manufacturing method is not particularly limited in the present invention. In other words, the method of smelting steel, the method of rolling at the time of producing the structural steel, and the method of heat treatment may be conditions that are usually adopted. Further, as for the steel material used for the section steel, for example, it is also possible to adopt the production conditions of the low yield ratio steel material such as controlled rolling, accelerated cooling, and slow cooling after rolling. Hereinafter, examples of the present invention will be described to demonstrate the effects of the present invention.

[0029]

【Example】

(Example 1) Steel having the components shown in Table 1 (Steel No. 1 of the present invention)
-9, Comparative steel No. 10-13) are melted, and 600 × 3
It was rolled into an H-beam having a size of 00 × 12 × 25 mm.

From a fillet portion of each H-section steel, a round bar tensile test piece, a Charpy impact test piece and a test piece having a notch with a stress concentration coefficient of 6.5 as shown in FIG. 1B were collected. The round bar test piece was subjected to a JIS Z2241 tensile test to measure the yield stress (YS) and the tensile strength (TS). The Charpy impact test piece was JIS Z224.
The Charpy impact test of No. 2 was performed to measure the fracture surface transition temperature.

With respect to the test piece having a notch, a static tensile test at an average strain rate of 0.001 / sec between the scores and an average strain rate of 10 /
A high-speed tensile test was performed for a second to measure the aperture value (RA) and the brittle fracture ratio. In addition, the brittle fracture resistance was evaluated based on the amount of change in the brittle fracture rate due to high-speed deformation. The test temperature was performed at room temperature for the tensile test, and -80 ° C for the Charpy impact test.
The test was performed at a temperature ranging from to room temperature.

The results are shown in Table 1. The steel No. of the present invention which satisfies all the component ranges of the present invention conditions. 1
No. 9 to No. 9 each have a reduction value of 30% or more in a static tensile test and a low brittle fracture rate in a high-speed tensile test. It is clear that the properties are excellent. On the other hand, Comparative Steel No. which does not satisfy the conditions of the present invention. In Nos. 10 to 13, the drawing value in the static tensile test is smaller than the range of the present invention, so that the brittle fracture rate is greatly increased in the high-speed tensile test. In addition, even if the fracture surface transition temperature in the Charpy impact test specimen is low, the brittle fracture surface ratio is found to increase if the range of the present invention is not satisfied.

[0033]

[Table 1]

(Example 2) Steels having the components shown in Table 2 (steel Nos. 14 to 18, 22 to 24 of the present invention, comparative steel No. 19)
To 21). 14-21 is 350 × 10
Non-equilateral angle iron with a size of 0 × 12 × 17 mm, steel no. Each of Nos. 22 to 24 was rolled into an extremely thick H-section steel having a size of 400 × 400 × 60 × 80 mm. Some unequal angle irons were subjected to accelerated cooling after rolling.

From the fillet portion of each section steel, a round bar tensile test piece, a Charpy impact test piece and a test piece having a notch with a stress concentration coefficient of 6.5 as shown in FIG. 1 were collected. For round bar tensile test specimens, a JIS Z2241 tensile test was performed to measure the yield stress (YS) and tensile strength (TS). For Charpy impact test specimens, JIS Z224
The Charpy impact test of No. 2 was performed to measure the fracture surface transition temperature.

For the test piece having a notch, a static tensile test at an average strain rate of 0.001 / sec between the scores and an average strain rate of 10 /
A high-speed tensile test for a second was performed to measure the aperture value and the brittle fracture ratio. Also, from the change in brittle fracture rate due to high-speed deformation,
The brittle fracture resistance was evaluated. In addition, as for the test temperature, the tensile test was performed at room temperature, and the Charpy impact test was performed at a temperature in the range of -80 ° C to room temperature.

The results are shown in Table 2. The steel No. of the present invention which satisfies all the component ranges of the present invention conditions. 1
Nos. 4 to 18 and 22 to 24 each have a reduction value of 30% or more in the static tensile test, and the brittle fracture rate does not change or decreases in the high-speed tensile test. It is clear that steel has excellent brittle fracture resistance under high speed deformation. On the other hand, Comparative Steel No. which does not satisfy the conditions of the present invention. In Nos. 19 to 21, since the drawing value in the static tensile test is smaller than the range of the present invention, the brittle fracture rate is greatly increased in the high-speed tensile test. In addition, even if the fracture surface transition temperature in the Charpy impact test specimen is low, the brittle fracture surface ratio is found to increase if the range of the present invention is not satisfied.

[0038]

[Table 2]

[0039]

As described above, according to the present invention, by specifying the steel composition and the tensile characteristics (drawing value) under the static loading condition by the notched test piece, the stress concentration portion can be obtained even under high-speed deformation. It does not cause the phenomenon that the brittle fracture rate increases, and it can provide shaped steel with excellent brittle fracture resistance, and is suitable for use in buildings that are subject to high-speed deformation due to earthquakes, ship collisions, etc. It can be said that.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a section steel according to an example of the present invention and a diagram showing the shape of a tensile test piece. (A-1) is a schematic diagram of an H-section steel. (A
-2) is a schematic view of an unequal angle iron. (A-3) is a schematic diagram of an equilateral angle iron. (B) is a diagram showing the shape of a tensile test piece.

FIG. 2 is a diagram showing a relationship between temperature and brittle fracture rate in a tensile test according to the embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a drawing value in a static tensile test and an increase in brittle transition temperature due to high-speed deformation according to the embodiment of the present invention.

[Explanation of symbols]

 1. Flange 2. Web 3. Fillet

Claims (2)

[Claims] (1) C: 0.05 to 0.2% by weight.
Si: 0.05 to 0.5% and Mn: 0.5 to 1.8%
And Al: 0.001 to 0.06%, and S ≦ 0.005
%, O ≦ 0.003%, and the balance consisting of Fe and inevitable impurities, having a flange, a web or a flange, and a fillet portion that is a joint portion thereof, wherein the fillet of the shaped steel is provided. In a tensile test using a notch with a notch where the stress concentration coefficient of the part is 5 or more, the brittle fracture resistance under high-speed deformation is characterized by having a drawing value of 30% or more under static loading conditions. Excellent structural steel. 2. In% by weight, Ti ≦ 0.1%, N
b ≦ 0.04%, V ≦ 0.1%, Cu ≦ 0.5%, Ni
≦ 0.5%, Cr ≦ 1%, Mo ≦ 0.6%, Ca ≦ 0.
The structural section steel having excellent brittle fracture resistance under high-speed deformation according to claim 1, comprising one or more members selected from the group of 005% and REM ≤ 0.03%.