JPH116027A - Earthquake-resistant steel pipe with excellent local buckling resistance - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide an earthquake-resistant steel pipe excellent in local buckling resistance, which is less likely to cause local buckling against bending stress acting upon a large earthquake. SOLUTION: In an earthquake-resistant steel pipe made of a welded steel pipe made of a hot-rolled steel sheet, the chemical composition of the material is C: 0.03 to 0.15%, Mn: 0.5 to 100% by weight.
2.0% and one or more of Nb, V, and Ti in a range satisfying the following inequality, and the balance is Fe, an additional element required for production, and an unavoidable impurity. Earthquake-resistant steel pipe with excellent local buckling. C- (12/9
3) Nb- (12/51) V- (12/48) Ti ≦ 0.10 Here, the symbol of the element in the formula represents the weight% of each component element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an earthquake-resistant steel pipe which is less likely to cause local buckling against bending stress and has excellent local buckling resistance.

[0002]

2. Description of the Related Art Carbon steel pipes such as UOE steel pipes, spiral steel pipes, seamless steel pipes, electric resistance welded steel pipes, press-bend steel pipes, and low alloy steel pipes can be manufactured in large quantities and in a stable manner. Due to its welding workability, it is widely used as a steel pipe for transporting fluids such as gas pipelines and water pipes, or as a pillar for construction and civil engineering.

As for steel pipes for construction, several steel pipes have been proposed in consideration of seismic performance. For example, Japanese Unexamined Patent Publication
The -173719 discloses, reheating after quenching the steel sheet from after rolling Ar ₃ point or more temperature or Ac of _three or more temperature,
After that, it is bent at a processing rate of 3% or more to form a steel pipe,
Thereafter, a technique of performing a tempering treatment at a temperature lower than the Ac ₁ transformation point has been proposed. As a result, a yield ratio of 80% or less is obtained, and a yield ratio of 72 to 79% is described as an example.

[0004] JP-A-5-65535 and JP-A-5-65535
In Japanese Patent Application Laid-Open No. 117746 and Japanese Patent Application Laid-Open No. 5-117747, t / D (t: plate thickness, D: steel pipe outer diameter, the same applies hereinafter) is 1.
A method for producing a relatively low-yield steel pipe having a low yield ratio of 0% or less for buildings has been proposed. In this method, a steel tube of Ti-added steel is cold-formed to produce a steel pipe, and then annealed at 500 to 650 ° C. Looking at the examples described, t / D is 3-10% and the yield ratio is less than 80%.

[0005] JP-A-5-156357 discloses N
There has been proposed a method for producing a steel pipe having a low yield ratio by using low carbon steel to which b, Ti, and the like are not added. This technology has reduced the use of low-carbon steel to 9
It is hot-rolled and air-cooled so that the rolling reduction at 50 ° C. or less is 50% or more. According to the described examples, the yield ratio is 76 to 78%.

JP-A-6-49540 and JP-A-6-49540
Japanese Patent Publication No. 49541 and Japanese Patent Application Laid-Open No. 6-128641 propose a method for producing a relatively thick building low yield ratio steel pipe having a t / D of 10% or less. In this method, Nb-
A steel pipe is manufactured by cold-forming a steel sheet of Ti-added steel, and then normalizing is performed at 700 to 850 ° C. Looking at the examples described, t / D is 4-10% and the yield ratio is less than 80%.

JP-A-6-264143, JP-A-6-264143
-264144 also discloses that t / D is 10% or less.
Proposed a method for producing relatively low-yield ratio steel pipes for construction.
ing. In this method, a steel sheet of Ti-added steel is cold-formed.
To make a steel pipe and then Ac ₁Tempering below transformation point
It is carried out. Looking at the described example, t / D is 4
-10%, and the yield ratio is 70-78%.

[0008] JP-A-7-233416 discloses Ni
There has been proposed a method for producing a low yield ratio steel pipe for building using Cr-Mo-Ti added steel. In this method, a steel pipe is cold-formed to produce a steel pipe, and then normalizing is performed at 650 to 750 ° C. Looking at the described example, t / D is 4 to
9%, and the yield ratio is 72-77%.

Japanese Patent Application Laid-Open No. Hei 7-150247 discloses N
A steel pipe to which one or more of b, V, and Ti are added is cold-formed to produce a steel pipe, and then reheated to a two-phase temperature range. Looking at the examples described, the yield ratio is 55-70%.
It has become.

JP-A-7-188748 discloses that a steel pipe is manufactured by cold-forming a steel sheet in which a parameter indicating the tendency of island-like martensite formation at the time of two-phase temperature heating is within a predetermined range. Reheating to two-phase temperature range. Looking at the examples described, the yield ratio is 49-66%.

In these technologies, a yield ratio, which is a ratio between yield stress and tensile strength, is taken as the seismic performance, and a method of manufacturing a steel pipe for reducing this ratio is emphasized. These are all related to the plastic absorption capacity against the bending stress of the column. By reducing the yield ratio, the energy absorption capacity up to the plastic collapse is increased, and the collapse of the building is prevented.

[0012]

However, any of the techniques (hereinafter referred to as prior art) relates to the ability to absorb the plastic deformation against the bending stress of the column, and the emphasis is on reducing the yield ratio. The material test values described are yp or YS, TS, YR (= YS / TS) or vEo, which are normal tensile test values (yield stress, tensile strength) and Charpy impact. It is considered a test value (absorbed energy at 0 ° C.).

In the prior art, a yield ratio of the order of 70% (or less in some technologies) is used as an index. In order to obtain such a low yield ratio, heat treatment is performed after forming a steel pipe in almost all technologies. ing. Therefore, the manufacturing cost increases and it becomes difficult to supply a relatively inexpensive earthquake-resistant steel pipe. Since the volume occupied by the hollow portion of the steel pipe is large, the equipment required for the heat treatment becomes larger than the heat treatment of the steel plate or the like.

[0014] Other material test values are not described in any prior art, and no bending test or the like of the steel pipe itself is performed. This is because the purpose of the prior art is to increase the plastic deformation absorbing ability at the time of bending a column as a steel pipe for building. This can be solved by increasing the plastic deformation absorbing ability of the steel sheet by setting the yield ratio to be low.

However, as will be described later, it has been found that simply setting a low yield ratio does not improve the earthquake resistance of the steel pipe. This is due to local buckling occurring before or during absorption of bending strain due to plastic deformation of a large portion of the steel pipe. In the prior art, little consideration has been given to preventing local buckling due to such lateral stress of the column and prevention of brittle cracks due to deformation after local buckling occurs.

In line pipes for transporting fluids such as gas, when stress is applied in the circumferential direction such as ductile fracture or brittle fracture, that is, resistance to internal pressure has been studied. Was hardly considered except for the bending deformation at the time of laying.

The present invention solves the above problems and provides an earthquake-resistant steel pipe excellent in local buckling resistance which is less likely to cause local buckling against bending stress acting upon a large earthquake. Aim.

[0018]

According to the present invention, there is provided an earthquake-resistant steel pipe comprising a welded steel pipe made of a hot-rolled steel sheet, wherein the chemical composition of the material is C: 0.03 to 0.3% by weight.
0.15%, Mn: 0.5 to 2.0%, and Nb;
Characterized in that at least one of V and Ti is contained in a range of 0.1% or less and the following inequality is satisfied, and the balance is made up of Fe, additional elements required for production, and unavoidable impurities. It is an earthquake-resistant steel pipe with excellent resistance. C- (12/93) Nb- (12/51) V- (12/48) Ti ≦ 0.10 Here, the symbol of the element in the formula represents the weight% of each component element.

The present invention has been made as a result of earnestly studying the deformation behavior of a steel pipe with respect to a bending stress acting upon a large earthquake. During the course of the study, it was discovered that the deformation of the steel pipes resulted in local buckling after the overall bending had progressed and before buckling over a wide area.

When local buckling occurs in the steel pipe as described above,
Since the bending stress concentrates on that portion, it is rapidly deformed and a brittle crack is generated, leading to destruction. In order to improve seismic resistance, it is necessary to use a steel pipe that does not easily cause local buckling. However, it was found that such a local buckling could not be solved by simply setting a low yield ratio as in the prior art, and further studies were continued.

In the process, in order to evaluate the buckling resistance of the steel pipe against bending stress acting from the lateral direction (perpendicular to the axis), an actual pipe bending test is performed together with various material tests, and a method of manufacturing the steel pipe and The correlation between material properties and local buckling behavior was investigated. FIG. 1 is a diagram schematically showing the arrangement of a test body and a test apparatus in an actual pipe bending test. This exam is
The test piece 9 is formed by the four bending jigs 11 and 12 of the test apparatus.
This is an actual pipe bending test of a four-point bending method in which bending stress is applied to (steel pipe).

In the initial stage of the bending test, the portion between the bending jigs 12 of the test body 9 (steel pipe) is bent as a whole. However, when further bending deformation is applied, the deformation locally progresses in a portion of the test body 9 between the bending jigs 11 and 11, and local buckling occurs. After that, the portion 2 other than the portion 1 where the local buckling has occurred hardly deforms, and the deformation concentrates only on this portion 1.

Therefore, the bending test was evaluated at the bending angle (one side) θ at the time when local buckling occurred. If the angle of the bending deformation is less than the bending angle θ, no buckling occurs and no breakage occurs. Therefore, the resistance to the lateral external force at the time of the earthquake can be evaluated by the bending angle (one side) θ.

In examining the factors affecting the bending angle θ, various studies have been made on the manufacturing method and the like, and it has been found that the bending angle θ can be increased with respect to steel having some chemical components. Succeeded in showing.
Examination of the relationship between these steels and the results of mechanical tests revealed that they had a close relationship with the behavior near the yield point in tensile tests.

In particular, when a tensile test specimen parallel to the axial direction of the steel pipe is taken and subjected to a tensile test, the gradient of the stress-strain curve (horizontal axis: nominal strain, vertical axis: nominal stress) is as follows. It was found to be the main factor of local buckling. That is, a steel pipe in which the gradient of the stress-strain curve is positive near the yield point has a bending angle θ at which local buckling occurs of 3% or more, and shows good buckling resistance.

Next, the chemical composition of steel for obtaining such a stress-strain curve was examined. As a result, C, N
It has been found that it is necessary to appropriately control the contents or addition amounts of b, V, and Ti. The results of the study are shown in FIG. 2 with the value Ceff expressed by the following equation (1) on the horizontal axis and the ratio D / t of the outer diameter D of the steel pipe to the pipe thickness t on the vertical axis. Ceff = C- (12/93) Nb- (12/51) V- (12/48) Ti (1) Here, the element symbols in the formula represent weight% of each component element.

A circle in the figure indicates a steel pipe in which the gradient of the stress-strain curve near the yield point is positive for any strain.
The symbol ● indicates a steel pipe whose slope is partially 0 or negative. Here, the range taken near the yield point may be any point before the point at which the maximum stress is applied from the yield point, but here, 5% from the yield point (in a state where a load is applied).
The range up to was used.

From this figure, it can be seen that when Ceff is 0.1% or less, the gradient of the stress-strain curve near the yield point becomes positive. Expressing this as an inequality, C eff ≦ 0.1 When rewritten using equation (1), C− (12/93) Nb− (12/51) V− (12/48) Ti ≦ 0.10 (2) Become. Here, the symbol of the element in the formula is the weight% of each component element.
Represents

Hereinafter, the reasons for limiting the chemical components will be described. C: In order to obtain sufficient strength as a structure, at least 0.03% is required. On the other hand, when the C content exceeds 0.15%, it becomes difficult to obtain a positive gradient in the stress-strain curve near the yield point, and when steel having such a C content is welded, the possibility of weld cracking increases. Therefore, the amount of C is set to 0.03
It is regulated to ~ 0.15%.

Mn: In order to obtain sufficient strength and toughness as structural steel, it is necessary to add 0.5% or more.
However, when the amount of Mn exceeds 2.0%, the toughness of the base material and the welded part is deteriorated. Therefore, the amount of Mn is 0.5 to 2.0
%.

Nb, V, Ti: It is necessary to include at least one kind of Nb, V, Ti in order to keep the slope of the stress-strain curve near the yield point positive. In addition, it is necessary to include an amount satisfying the above-described equation (2). If the amount of addition is too small, there is no effect, so it is preferably 0.005% or more. on the other hand,
If each exceeds 0.1%, the toughness and weldability of the base metal weld are deteriorated. Therefore, at least one of Nb, V, and Ti is contained, and the amount of each of them is 0.00
Preferably, it is 5% to 0.1%.

Other elements may be contained as long as the object of the invention is not impaired. It goes without saying that elements other than those described above may be included as needed in production, such as deoxidizing elements in ordinary steelmaking operations. In addition, elements brought in from raw materials such as scrap are also inevitable impurities within the range of ordinary steel.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Regarding the material of a steel pipe, the production method is not particularly limited as long as it is a chemical component of the invention. Also, S
i and deoxidizing elements such as Al and the like may be contained as required for production. In addition, it is better that impurities such as P, S, N, and O are small. In addition, Ca for controlling inclusions
Elements such as and REM may be included because they do not particularly impair the purpose of the present invention.

The production conditions such as the rolling conditions of the steel sheet may be conditions suitable for the production method and equipment. There is no limitation on the method of forming the steel pipe as long as the method is cold working. For welding,
If the material is within the composition range of the present invention, it can be welded by ordinary methods and conditions without any particular problems.

[0035]

EXAMPLE A steel plate was manufactured by hot rolling from steels having various chemical components, and the tube thickness was 10 to 30 mm by cold forming.
A welded steel pipe having a pipe outer diameter of 600 mm was manufactured. These steel pipes were subjected to the above-described actual pipe test and tensile test.

Table 1 shows the chemical composition of the steel pipe and the value C of the formula (2).
eff (Effective C), and the gradient and toughness of the stress-strain curve near the yield point in the tensile test. The toughness is such that the shock absorption energy vEo by the Charpy impact test is 50.
J and above (below) are indicated by Ｘ and others are indicated by X.
Here, steel pipes BG are steel pipes of the invention, and steel pipes A and HL are steel pipes for comparison.

[0037]

[Table 1]

With respect to the invention steel pipes, the slope of the stress-strain curve in the vicinity of the yield point is positive, indicating excellent toughness. Regarding the comparative steel pipe, the steel pipe A is inferior in toughness when the amounts of C and Mn are less than the lower limits of the invention, the steel pipe H is the C content, and the steel pipe I is the M
Since each of the n amounts exceeds the upper limit, the toughness is poor. For the steel pipe J (and the steel pipe H), Ceff (Equation 1) exceeds the upper limit and does not satisfy the inequality of Equation (2).
The slope of the stress-strain curve near the yield point is negative. In the steel pipe K, the amount of Nb added, and in the steel pipe L, the V amount and the Ti amount exceed the upper limits, respectively, and both are inferior in toughness.

[0039]

By using the steel pipe of the present invention, it is possible to prevent the occurrence of local buckling due to an external force acting on the steel pipe from the lateral direction and the occurrence of brittle cracks or breakage due to the local buckling.
As a result, when a large earthquake occurs, it is possible to prevent disasters such as breakage of gas pipelines and water pipes and outflow of internal fluid, or collapse due to breakage of bridge piers on expressways.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an arrangement of a test body and a test apparatus in an actual pipe bending test.

FIG. 2 shows the effect of Ceff on the slope of the stress-strain curve.

[Explanation of symbols]

 1 Part where local buckling occurred 2 Part where local buckling did not occur 9 Specimen (steel pipe) 11 Bending jig (inside) 12 Bending jig (outside)

Claims (1)

[Claims] 1. An earthquake-resistant steel pipe made of a welded steel pipe made of a hot-rolled steel sheet, wherein the chemical composition of the material is C: 0.03-0.15%, Mn: 0.5% by weight. ~
2.0% and one or more of Nb, V, and Ti at 0.1%.
An earthquake-resistant steel pipe excellent in local buckling resistance, containing 1% or less and a range satisfying the following inequality, with the balance being Fe, additional elements required for production, and unavoidable impurities. C- (12/93) Nb- (12/51) V- (12/48) Ti ≦ 0.10 Here, the symbol of the element in the formula represents the weight% of each component element.