JPH1112681A - Steel member having excellent buckling resisting characteristic and fire resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a local buckling against a large compressive or bending load and moreover to obtain excellent fire resistance by using the steel specifying the content of Mo and specifying the strain quantity in the starting point of work hardening and the work hardening exponent in the nominal stress- nominal strain curve obtained with the tension test. SOLUTION: This steel member is composed of, by wt., 0.05-0.70% Mo, and further one kind or two kinds or more of 0.005-0.10% Nb, 0.005-0.10% V, 0.005-0.10% Ti. The strain quantity in the starting point of the work hardening in the nominal stress-nominal strain curve obtained with the tension test of this composition of steel is specified to be <=1.5% and moreover the work hardening exponent in the same is specified to be >=0.15. These characteristics are obtained by controlling the rolling condition at the time of hot rolling or applying the heat treatment after rolling, or acceleratedly cooling from the two-phase temperature zone of ferrite plus austenite of <=Ar3 transformation temperature to >=Ar1 transformation temperature or the like after hot rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel member used for various structures in the field of civil engineering and construction, and particularly to a steel member excellent in buckling resistance and fire resistance during an earthquake.

[0002]

2. Description of the Related Art Steel members having a box-shaped section or an H-shaped section are often used in columns, beams and piers of steel structures, and these members are formed by welding or cold forming a hot rolled steel sheet. Many are manufactured by. Steel materials used for these steel members are required to have excellent plastic deformability from the viewpoint of energy absorption at the time of earthquake, and are disclosed in JP-A-55-119152 and JP-A-63-2231.
No. 23, Japanese Patent Application Laid-Open No. 1-1156422, Japanese Patent Application Laid-Open No. 3-115524, and the like propose a steel member having improved uniform elongation characteristics by lowering the yield ratio. In addition, as stipulated in JIS G3136 for rolled steel for building structures that the yield ratio is set to 80% or less, the response from the steel surface to improve the seismic resistance is based on the plastic deformation ability due to the low yield ratio. Improvement is the main focus.

[0003] In a large-scale earthquake, a large tensile compression or bending load is repeatedly applied to these steel members to cause local buckling. In addition, cracks are generated from the buckled places, and tensile strength after buckling is generated. Deformation can lead to brittle fracture, causing significant damage such as building collapse. For such local buckling, the effect of lowering the yield ratio of steel is effective, as described in Toyoda, et al., "Effect of Steel Deformation Characteristics on Deformability of Steel Welded Structure," Journal of the Japan Welding Society, Vol. 8, N
o. 1, p122 (1990).

[0004] In recent years, as steel structures such as buildings and bridges have become larger, they are required to have sufficient seismic performance even in the case of large-scale earthquakes. It is becoming difficult to ensure high seismic performance. For this reason, steel members used for columns and beams, bridge piers, etc. of steel buildings use thicker steel plates and reduce the width-to-thickness ratio of their cross-sections, or reinforce them with stiffening plates, etc. This makes buckling less likely to occur and increases the holding strength.

However, the reduction in the width-to-thickness ratio and the use of the stiffening plate not only increase the cost, but also hinder the degree of freedom in design. Even when the width-to-thickness ratio is large, excellent buckling performance is obtained. Are desired.

[0006] On the other hand, with respect to fires in buildings, a review of fire-resistant design has made it possible to reduce the amount of fire-resistant coating using fire-resistant steel having excellent high-temperature strength. New design methods are becoming popular due to the advantages of reducing the number of buildings and expanding the effective area in buildings. Construction steel members having excellent fire resistance are disclosed in JP-A-4-83821, JP-A-4-56723, and JP-A-4-56823.
No. 56362 has been filed. However, these are all characterized by a low yield ratio,
As described above, it is difficult to say that it alone has sufficient seismic performance.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a large width-to-thickness ratio and a large stiffness against a large compression or bending load acting upon a large earthquake. It is an object of the present invention to provide a steel member which hardly causes local buckling even without a material, is suitable for use in columns and beams of steel structures, piers, and the like, and has excellent fire resistance.

[0008]

The inventors of the present invention have conducted intensive studies on the buckling characteristics of a steel member having a box-shaped cross section or an H-shaped cross section. There is a close relationship with the stress-strain curve obtained in the tensile test, and after the steel material yields, the strain that starts work hardening is reduced, and the work hardening index is increased to a certain value or more, so that the buckling resistance is improved. Was found to be greatly improved.

That is, the present invention has been made based on the above-mentioned findings, and the gist thereof is as follows: (1) Mo: 0.005 to 0.70% by weight, and obtained by a tensile wiping test. In the nominal stress-nominal strain curve, a steel having a work hardening start point strain of 1.5% or less and a work hardening index of 0.15 or more was used, Steel members with excellent fire resistance. (2) In addition to containing Mo: 0.05 to 0.70% by weight, Nb: 0.005 to 0.10
%, V: 0.005 to 0.10%, Ti: 0.005 to
It contains 0.10% or more, and in a nominal stress-nominal strain curve obtained by a tensile test, a strain amount at a work hardening start point is 1.5% or less and a work hardening index is 0.1%. It is a steel member excellent in buckling resistance and fire resistance, characterized by using steel of 15 or more.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the constituent elements in the present invention will be described below. First, in the present invention, a nominal stress-nominal strain curve is obtained in a tensile test. Although the test method is not particularly limited, a test is performed based on a metal material tensile test method specified in JIS-Z2241, and the direction of collection of the test piece at that time is determined by the compression or tensile stress acting on the member used. It is desirable to sample from a direction that is equal to the direction.

Next, the nominal stress obtained in the above tensile test is
In the nominal strain curve, the work-hardening start strain is set to 1.5% or less. This is because when the work-hardening start strain exceeds 1.5%, the deformation of the steel material becomes uneven because the yield shelf region becomes long. This is because deformation is localized and local buckling is likely to occur. The reason why the work hardening index is 0.15 or more is that if the work hardening index is less than 0.15, deformation is localized and local buckling is likely to occur.

Note that the strain at the start of work hardening is the nominal stress minus the strain in FIG.
This is a strain corresponding to ε0 in the schematic diagram of the nominal strain curve, and the work hardening index (n) is n from the nominal εu at which the nominal stress is maximum.
= In (1 + εu).

Next, the reasons for limiting the chemical components of the steel of the present invention will be described. Mo: 0.05 to 0.70% Mo is an element effective for increasing the strength of steel by improving hardenability, precipitation strengthening, and the like, and is extremely effective especially for medium and high temperature strength. However, if it is less than 0.05%, it is difficult to obtain the effect, and even if it is added at 0.70% or more, not only the effect corresponding to the addition cost is not seen, but also the weldability is deteriorated. Content is 0.05
To 0.70%.

Nb: 0.005% to 0.10% V: 0.005% to 0.10% Ti: 0.005% to 0.10% Nb, V and Ti improve toughness and strength at room temperature and high temperature by adding a small amount. Is an effective element, but its content is 0.00
If it is less than 5%, the effect cannot be exhibited effectively,
If it exceeds 0.10%, the toughness of the weld is deteriorated.
The content is made 0.005 to 0.10%.

The steel of the present invention is not particularly limited with respect to chemical components and production methods other than those described above. As the chemical components, C: 0.03 to 0.25%, Mn:
0.5-2.0%, and if necessary, S
i: 0.01 to 1.0%, Cu: 0.05 to 0.50
%, Ni: 0.05-0.5%, Cr: 0.05-0.
It is desirable to contain 5% of one or more of them.
The reason why steel having such a composition range is desirable is as follows.

C: 0.03 to 0.25% C is an element necessary to secure the strength of steel.
If it is less than 0.03%, the strength is insufficient, and if it exceeds 0.25%, the weldability is impaired.
~ 0.25% is preferred.

Mn: 0.5 to 2.0% Mn is added to increase the strength of steel.
If it is less than 10%, the strength is insufficient, and if it exceeds 2.0%, the toughness and weldability of the base metal and the welded part are deteriorated, so that the content is preferably 0.5 to 2.0%.

Si: 0.01 to 1.0% Si is necessary as a deoxidizing agent in the steel making process while increasing the strength of the steel. If it is less than 0.01%, its effect is insufficient. %, The toughness of the weld is degraded, so the content is preferably 0.01 to 1.0%.

Cu: 0.05-0.5% Ni: 0.05-0.5% Cr: 0.05-0.5% Cu, Ni, and Cr are effective in increasing the strength, but each is 0%. If less than 0.05%, the effect is not exhibited, and 0.5%
If the content exceeds 0.1%, the weldability will be degraded.
It is preferably from 0.5 to 0.5%.

In addition, P and S contained as impurity elements, and Al added as a deoxidizing agent may be contained. Further, by controlling the rolling conditions during hot rolling or adding a post-rolling heat treatment to steel having such a composition, the performance specified in the present invention can be imparted. After rolling, below the Ar3 transformation temperature,
There are methods such as accelerated cooling from a ferrite + austenite two-phase temperature range equal to or higher than the Ar1 transformation temperature, and reheating after rolling to rapidly cool from the two-phase temperature range.

[0021]

Embodiments of the present invention will be described below.
Steels having the components shown in Table 1 were hot-rolled into steel plates having a thickness of 12 mm. Here, steel types A to E are steels satisfying the component range of the present invention, and steel type F is steel whose Mo is out of the component range of the present invention. Then, tensile test pieces were sampled from a direction parallel to the rolling direction of these steel sheets, a nominal stress-nominal strain curve was measured by a tensile test, and the work-hardening initiation strain and the number of work-hardening were determined. Table 2 shows the production conditions of the steel sheet, the results of the tensile test at room temperature, and the results of the tensile test at 600 ° C.
A-1, A-2, B-1, B-2, C-
1, 1, C-2, D-1, and E-1 all have a work hardening initiation strain of 1.5% or less and a work hardening index of 0.15 or more, and Comparative Examples A-3, B-3, and C-3. , D-2 and E-2, one or both of the work hardening initiation strain and the work hardening index are out of the range of the present invention. Moreover, since the Mo of Comparative Example F-1 is less than 0.05%, the yield strength at 600 ° C. is less than ／ of the yield strength at room temperature, and has sufficient performance as fire-resistant steel. Absent.

Next, short column compression specimens (FIG. 2) of various sizes of H-shaped cross section and square cross section were manufactured by welding.
Here, a short column compression test specimen having an H-shaped cross section and a square cross section (FIG. 2) was manufactured. Here, in the H-shaped cross section, the flange thickness (the portion of the thickness t in FIG.
Web (part of thickness w in FIG. 2 (a))
Used 9 mm thick steel plates having the same strength and the same components.
Further, the longitudinal direction of the short column compression test specimen was made to coincide with the rolling direction of the steel sheet. Then, a compression test was performed by the method shown in FIG. 3, and the strain at which load reduction started due to the occurrence of buckling was evaluated as buckling strain. Table 3 shows the results of the compression test.

Examples H-1 to H-8 and H-14 of the present invention
To H-21, C-1 to C-8, and C-14 to C-21 all have a work-hardening initiation strain of 1.5% or less and a work-hardening index of 0.1%.
Since it is 15 or more, the steel member using the steel material has high buckling strain and has excellent buckling resistance. On the contrary,
H-9 to H-13, H-22 to H-26, which are comparative examples,
In C-9 to C-13 and C-22 to C-26, one or both of the work hardening initiation strain and the work hardening index are out of the range of the present invention, so that the steel member using the steel material is buckled. Low distortion and poor buckling resistance.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

As described above, according to the present invention, a steel member having excellent buckling resistance and excellent fire resistance against a large compression or bending load received during a large earthquake is provided. It can be said that it is suitable for use in steel structures such as steel buildings and bridges that require earthquake resistance.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a nominal stress-nominal strain curve.

FIG. 2 is a view showing a shape of a short column compression test piece used for a compression test.

FIG. 3 is a diagram showing a setting state of a test machine and a test body in a compression test.

Claims (2)

[Claims] 1. Mo: 0.05 to 0.70% by weight
In a nominal stress-nominal strain curve obtained by a tensile test, the strain amount at the work hardening start point is 1.5% or less,
A steel member having excellent buckling resistance and fire resistance, characterized by using steel having a work hardening index of 0.15 or more. 2. Mo: 0.05 to 0.70% by weight.
And Nb: 0.005 to
0.10%, V: 0.005 to 0.10% ", Ti:
A nominal stress-nominal strain curve obtained by a tensile test having a strain amount at a work hardening start point of 1.5% or less and a workability of 0.005 to 0.10%. A steel member having excellent buckling resistance and fire resistance, characterized by using a steel having a hardening index of 0.15 or more.