JPH116032A - Earthquake-proof welded steel tube excellent in local buckling resistance, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an earthquake-proof steel tube hardly causing local buckling at the time of big earthquake. SOLUTION: This steel tube is an earthquake-proof welded steel tube produced by using a hot rolled steel plate as a material and has a chemical composition which contains, by weight, 0.03-0.15% C, 1.0-2.0% Mn, and one or more kinds among 0.05-0.50% Cu, 0.05-0.50% Ni, 0.05-0.50% Cr, 0.05-0.50% Mo, 0.005-0.10% Nb, 0.005-0.10% V, and 0.005-0.080% Ti and in which the value of PCM, represented by equation PCM=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+ Mo/15+V/10+5×B (where the symbol of element stands for the weight percentage of each element), is regulated to 0.10-0.25. Further, the work hardening index at the tensile test in a tube-axis direction is >=0.10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an earthquake-resistant welded steel pipe which does not easily cause local buckling against bending stress and has excellent local buckling resistance, and a method for manufacturing the same.

[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.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and provides an earthquake-resistant welded steel pipe excellent in local buckling resistance which is less likely to cause local buckling against bending stress acting upon a large earthquake, and a method of manufacturing the same. The purpose is to provide.

[0018]

The first invention is an earthquake-resistant welded steel pipe made of a hot-rolled steel sheet, the chemical composition of which is C: 0.03-0. 15%, M
n: 1.0 to 2.0%, Cu: 0.05 to 0.
50%, Ni: 0.05 to 0.50%, Cr: 0.05
-0.50%, Mo: 0.05-0.50%, Nb:
0.005 to 0.10%, V: 0.005 to 0.10
%, Ti: one or more of 0.005 to 0.080%, and the PCM represented by the following formula is 0.10 to 0.25.
And a work hardening index in a tensile test in the pipe axis direction of 0.10 or more, which is an earthquake-resistant welded steel pipe excellent in local buckling resistance. PCM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10
+ 5 × B Here, the symbol of the element in the formula indicates the weight% of each 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 the region 1 between the bending jigs 11 of the test body 9 and local buckling occurs. After that, the area 2 other than the area 1 where the local buckling has occurred hardly deforms, and the deformation concentrates only on the area 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 in various ways such as the manufacturing method, it has been found that the bending angle θ can be increased with respect to a steel pipe using a steel having some chemical components. The buckling resistance was successfully demonstrated. In addition, when examining the relationship between these steel pipes and the results of the mechanical test, it was found that there was a close relationship with the behavior near the yield point in the tensile test.

Among them, it was found that the work hardening index when a tensile test specimen was taken from a steel pipe in a direction parallel to the axial direction and a tensile test was performed was a main factor of the occurrence of local buckling. That is, a steel pipe having a large work hardening index has a large bending angle θ at which local buckling occurs. In particular, when the work hardening index is 0.10 or more, the bending angle (one side) θ at which local buckling occurs has reached 3 ° or more, indicating that good buckling resistance is exhibited. As described above, in the present invention,
The work hardening index is set to 0.10 or more.

Next, the chemical composition of steel including other material properties was examined. As a result, while appropriately controlling the contents of C and Mn, Cu, Ni, Cr, Mo, N
It was found that it was necessary to contain at least one of b, V, and Ti. Further, a value PCM represented by the following equation (1)
It was also found that there was an appropriate range for. PCM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 × B (1) Here, the element symbols in the formulas are each component element % By weight.

The reasons for limiting the chemical components and the PCM
(Equation 1) will be described. C: In order to obtain sufficient strength as a structure, at least 0.03% is required. On the other hand, if the C content exceeds 0.15%, the possibility of welding cracks increases. Therefore, the amount of C is regulated to 0.03 to 0.15%.

Mn: In order to obtain sufficient strength and toughness as a structural steel, it is necessary to add 1.0% 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
%.

Cu, Ni, Cr, Mo: These are effective elements for increasing the strength, but no effect is obtained when each is less than 0.05%. However, if it exceeds 0.50%, the toughness of the base material and the welded portion is deteriorated. Therefore, Cu, N
When adding i, Cr, and Mo, the amount of addition is 0.05 to
0.50%.

Nb: An element effective for improving the toughness and strength of a steel pipe, but no effect is observed when the content is less than 0.005%. On the other hand, if it exceeds 0.10%, the weldability and the toughness of the welded portion are deteriorated. Therefore, when adding Nb, the addition amount is set to 0.005 to 0.10%.

V: Like Nb, it is an element effective in improving the toughness and strength of a steel pipe, but no effect is seen below 0.005%. On the other hand, if it exceeds 0.10%, the weldability and the toughness of the welded portion are deteriorated. Therefore, when V is added,
The added amount is 0.005 to 0.10%.

Ti: an element effective for improving the toughness of the steel pipe and for preventing the slab from being damaged during casting.
%, No effect is seen. On the other hand, when the content exceeds 0.08%, the weldability and the toughness of the welded portion are deteriorated. Therefore, Ti
Is added, the amount is 0.005 to 0.08%.

PCM: This value must be a predetermined value in order to obtain sufficient strength as a structure and to obtain good local buckling resistance, and 0.10 is the minimum required value. . On the other hand, if it exceeds 0.25, the weldability deteriorates, and
Local buckling resistance also decreases. Therefore, the value of PCM is set to 0.1
0 to 25.

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 contained as necessary 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.

According to a second aspect of the present invention, the steel having the chemical composition according to the first aspect of the present invention is hot-rolled, and after the completion of the rolling, the temperature is reduced to 600 ° C. or less by 5 ° C./sec.
The steel sheet is manufactured by cooling at a cooling rate of c or more, and the steel sheet is cold-formed to produce a steel pipe, whereby the work hardening index in the tensile test in the pipe axis direction is set to 0.10 or more. This is a method for producing an earthquake-resistant welded steel pipe having excellent local buckling resistance.

The present invention specifies the cooling conditions after rolling. If the cooling rate is less than 5 ° C./sec, 0.10
The above work hardening index cannot be obtained, and good local buckling resistance cannot be obtained. When the cooling stop temperature exceeds 600 ° C., a work hardening index of 0.10 or more and good local buckling resistance cannot be obtained. Therefore, the cooling condition after rolling is set to 5 ° C./sec or more up to 600 ° C. or less.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the method of producing a steel pipe is not particularly limited as long as it is a chemical component of the present invention. Further, deoxidizing elements such as Si and Al may be included as necessary. 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. In other cases, B may be contained in a range not exceeding 0.001%.

The production conditions such as the rolling conditions of the steel sheet may be conditions suitable for the production method and equipment. As the heating temperature,
For example, the temperature may be 1050 to 1250 ° C. The method of cooling after the completion of rolling is not particularly limited as long as a work hardening index of 0.10 or more can be obtained, but it is necessary to perform accelerated cooling. The cooling condition is preferably 5 ° C./sec or more up to 600 ° C. or less.

In the pipe making step of manufacturing a steel pipe, a steel sheet obtained by hot rolling is processed into a shape of a steel pipe by a cold forming method such as UOE, bending roll, press bending and the like.
In addition, the method of forming the steel pipe is not limited as long as it is a cold work. Thereafter, the butted portions are welded to produce a steel pipe. As for welding, if it is a material within the component range of the present invention, it can be welded by ordinary welding methods and conditions without any particular problem.

[0040]

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 P of the equation (1).
The results of CM, actual pipe test and tensile test are shown. Regarding chemical components, steel types A (A1, A2) to K are within the scope of the invention, and steel types L to Q are outside the scope of the invention. Steel pipes A1, B1, CK (represented by the same symbols as steel types in the table) made of these steels are steel pipes of the invention, and steel pipes A2, B2, L to Q are steel pipes for comparison.

Regarding the test results, the local buckling resistance (buckling resistance in the table) is such that the bending angle (one side) θ at the time when local buckling occurs in an actual pipe bending test is 3% or more. The case where the condition is satisfied is indicated by a circle, and the case where the condition is not reached is indicated by an X mark.

Regarding the weldability, the presence or absence of weld cracks was examined for the vertical seam weld after forming the steel pipe. The strength is J
The test was performed according to the tensile test specified in ISZ2241.
These test results show that there is no weld crack and the tensile strength is 50 k.
In the case of g / mm ² or more, ○ is shown, and in the case of g / mm ² or less, X is shown in the column of weldability / strength in Table 1. The work hardening index (n value in the table) was determined from the stress-strain curve by an ordinary method.

[0044]

[Table 1]

With respect to the invention steel pipes A1, B1 and CK,
The work hardening index is 0.10 or more, indicating good local buckling resistance.

As for the comparative steel pipes, the chemical compositions of the steel pipes A2 and B2 are within the scope of the present invention, but the work hardening index (n value) is less than 0.10. As a result, the local buckling resistance (buckling resistance) is poor. C, Cu, and PCM of the comparative steel pipe L exceeded the upper limit, and the local buckling resistance was poor. Comparative steel pipe M is Mn
And V exceed the upper limit, and the weldability is poor.

The comparative steel pipe N has a C less than the lower limit, and has poor local buckling resistance and strength. The comparative steel pipe O has a PCM exceeding the upper limit, and has poor local buckling resistance and poor weldability. The comparative steel pipe P has a PCM of less than the lower limit, and has poor local buckling resistance and strength. In the comparative steel pipe Q, Ti exceeds the upper limit, and the weldability is poor.

Here, in the comparative steel pipes L, O, and P, the work hardening index is 0.10 or more of the invention range, but the local buckling resistance is poor because the chemical components are not within the scope of the invention. And the strength or weldability is also poor. Also,
In the comparative steel pipes M and Q, the work hardening index is 0.1 in the range of the invention.
It is 0 or more and the local buckling resistance is good, but the weldability is poor because the chemical component is not within the range of the invention.

Next, after hot rolling, similar tests were performed on steel pipes manufactured from steel sheets manufactured under various cooling conditions. Table 2 shows the results. Steel pipes A-3, A-4,
B-1 to J-1 are invention steel pipes, and others are comparative steel pipes.

[0050]

[Table 2]

The steel pipes A-3 to J-1 of the invention have a work hardening index of 0.10 or more, indicating good local buckling resistance.

The comparative steel pipe A-1 had a cooling stop temperature of 600 ° C.
Since the cooling rate of the comparative steel pipe A-2 is lower than 5 ° C./s, the work hardening index is lower than the invention range (0.10 or more), and the local buckling resistance is poor.

Comparative steel pipes L-1, L-2, M-1, O-
1, P-1 and Q-1 are not in the range of the chemical components of the invention, and therefore have poor local buckling resistance or local buckling resistance regardless of the application of accelerated cooling after hot rolling. Is good but poor in weldability (Comparative Steel Pipe M-1).

[0054]

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.

[Explanation of symbols]

 1 area where local buckling occurred 2 area where local buckling did not occur 9 specimen (steel pipe) 11 bending jig (inside) 12 bending jig (outside)

Claims (2)

[Claims] 1. An earthquake-resistant welded steel pipe made of a hot-rolled steel sheet, the chemical composition of which is represented by:
0.03-0.15%, Mn: 1.0-2.0%, Cu: 0.05-0.50%, Ni: 0.05-
0.50%, Cr: 0.05 to 0.50%, Mo: 0.
05 to 0.50%, Nb: 0.005 to 0.10%,
V: 0.005 to 0.10%, Ti: 0.005 to 0.
080%, and contains at least one kind of P represented by the following formula.
An earthquake-resistant welded steel pipe having excellent local buckling resistance, wherein CM has a value of 0.10 to 0.25 and a work hardening index in a tensile test in a pipe axis direction of 0.10 or more. PCM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10
+ 5 × B Here, the symbol of the element in the formula indicates the weight% of each element. 2. The steel having the chemical composition according to claim 1 is hot-rolled, and after the rolling is completed, the steel is cooled to 600 ° C. or less at a cooling rate of 5 ° C./sec or more to produce a steel sheet, and the steel sheet is cold-formed. A method for producing an earthquake-resistant welded steel pipe having excellent local buckling resistance, wherein a work hardening index in a tensile test in the pipe axis direction is set to 0.10 or more by producing a steel pipe.