JP3655765B2 - Welded steel pipe with excellent weather resistance - Google Patents

Description

【００２９】
【表２】

【００３０】
【表３】

【００３１】
【表４】

【００３２】
実施例を表１〜表４に示す。本発明の溶接鋼管は母材および溶接部において優れた耐候性を有する。これに対して比較鋼は化学成分が適切でなく、いずれかの特性が劣る。
鋼１０は母材のＣ量が多すぎるため、母材の低温靱性が劣る。鋼１１は母材のＰ量が多すぎるため、母材の低温靱性が劣る。鋼１２は母材のＳ量が多すぎるため、母材の低温靱性が劣る。鋼１３は母材のＣｕ量が少ないため、母材の耐候性が劣る。鋼１４は母材のＮｉ量が少ないため、母材の耐候性が劣る。鋼１５は母材のＮｉ量が多すぎるため、母材にひび割れが発生する。鋼１６は母材のＣｒ量が多すぎるため、母材の耐候性が劣る。鋼１７は溶接金属のＣ量が多すぎるため、溶接金属において高温割れが発生する。鋼１８は溶接金属のＰ量が多すぎるため、溶接金属において高温割れが発生する。
【００３３】
鋼１９は溶接金属のＳ量が多すぎるため、溶接金属において高温割れが発生する。鋼２０は溶接金属のＮｉ量が少ないため、溶接金属の耐候性が劣る。鋼２１は溶接金属のＮｉ量が多すぎるため、溶接金属において高温割れが発生する。鋼２２は溶接金属のＣｒ量が多すぎるため、溶接金属の耐候性が劣る。鋼２３は溶接金属のＮｉ量が母材のＮｉ量よりも２．０％を超えて少なすぎるため、溶接金属の耐候性が劣る。鋼２４は溶接金属のＮｉ量が母材のＮｉ量よりも０．２％を超えて多すぎるため、溶接金属において高温割れが発生する。
【００３４】
【発明の効果】
本発明による海浜地区での優れた耐候性を有する溶接鋼管を橋梁などの鋼構造物の部材として採用することにより、鋼構造物の製造コストが低減されるとともに、保守管理の簡略化、管理費用の大幅な低減が可能となった。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a welded steel pipe having excellent weather resistance used for steel structures such as bridges and steel towers in an air environment where salt damage is a concern in a high-flying sea salt particle environment such as a beach area or a district where snow melting salt is dispersed. It is about.
[0002]
[Prior art]
Conventionally, as corrosion protection for steel structural members used in places where salt damage occurs such as coastal areas, use of ordinary steel coatings, plated steel sheets, surface coating such as spraying and mortar lining, high alloy high corrosion resistance materials such as stainless steel and titanium, etc. in use. Furthermore, as a technique for reducing the maintenance cost of the steel structure, there is a non-painting use of weathering steel (JISG 3141 weathering steel for welded structure).
In the case of painting, since it is necessary to repaint, the maintenance cost becomes high. In the case of plating, there is deformation due to thermal stress or peeling of the plating in the hot dipping of the structure. In the case of thermal spraying and mortar lining, there are problems such as peeling and deterioration of the anticorrosive film. Further, in the case of a high alloy corrosion resistant material, there is a problem that the material cost is high and it cannot be widely used as a main structural member.
[0003]
Weather-resistant steel is a steel material that, when used unpainted, forms a dense stable rust with excellent anticorrosion properties on the steel surface within a few years to 10 years after use, and this stable rust prevents the subsequent corrosion of the steel material. is there. For steel structures, weather-resistant welded structural steels that take weldability into account have been used so far, mainly in bridges and buildings. However, as shown in “Design and construction guidelines for unpainted weather-resistant bridges (draft): Ministry of Construction, Civil Engineering Research Institute, Steel Club, Japan Bridge Construction Association, March 1993” In areas where there are a lot of flying sea salt particles, such as the area where it is sprayed, the formation of stable rust with excellent protective properties is hindered by the salt attached to the steel surface, which makes it unsuitable for unpainted use.
[0004]
For improving the weather resistance of steel materials in the beach area of weathering steel, for example, Japanese Patent Publication No. 56-9356 discloses a corrosive environment containing 0.03 to 0.20% P, excellent weldability and sea water. Steel materials having excellent weather resistance in general atmospheric environments are disclosed. JP-A-2-125839 describes that the addition of a complex oxide of Ca and Al is effective for the complex addition of low Si—P—Cu—Ni. Japanese Patent Application Laid-Open No. 5-51668 discloses that it is effective to finely disperse oxides in a steel material to suppress a decrease in pH of the steel material surface. As described above, steel materials having excellent weather resistance in the beach area, which is a drawback of conventional weather resistant steel, have been developed.
[0005]
In recent years, it has been proposed to use steel pipes for bridge girders in order to omit welding of members that occupy a large specific gravity in bridge construction costs. A steel pipe used as a bridge girder is a large-diameter welded steel pipe manufactured mainly by UOE or BR (bending roll). Although these steel pipes are manufactured by submerged arc welding (SAW), the amount of welding heat input becomes large. Therefore, when a large amount of Ni is contained, hot cracking (solidification cracking) occurs during welding. For this reason, a welded steel pipe excellent in weather resistance in the beach area is strongly desired.
[0006]
[Problems to be solved by the invention]
The present invention provides a welded steel pipe having excellent weather resistance in a beach area.
[0007]
[Means for Solving the Problems]
The gist of the present invention is, by weight%, C: 0.03 to 0.15%, Si: 0.6% or less,
Mn: 0.3 to 2.0%, P: 0.03% or less,
S: 0.005% or less, Cu: 0.3-1.0%,
Ni: 1.0 to 5.5%, Cr: 0.1% or less,
Ti: 0.005 to 0.03%, Al: 0.09% or less,
N: 0.001 to 0.006%, O: 0.006% or less, Mo: 0.1 to 1.0%, Nb: 0.005 to 0.1%, V: 0.01 to 0 0.1%, B: 0.0003 to 0.002%, Ca: 0.001 to 0.005%, or one or two or more kinds, and the balance is made of iron and inevitable impurities,
C: 0.03 to 0.09%, Si: 0.6% or less,
Mn: 0.3 to 2.0%, P: 0.03% or less,
S: 0.005% or less, Cu: 0.1-1.0%, Ni: 1.0-3.5%, Cr: 0.1% or less,
Ti: 0.005 to 0.03%, Al: 0.09% or less,
N: 0.001-0.006%, O: 0.02-0.06%
Furthermore, Mo: 0.1 to 1.0%, Nb: 0.005 to 0.1%, V: 0.01 to 0.1%, B: 0.0003 to 0.002%, Ca: 0 .001-0.005% of one or two or more types, the balance is made of iron and inevitable impurities, and the amount of Ni is less than 2.0% of the base material to 0.16% less Having a weld metal part in range.
[0008]
Below, the welded steel pipe excellent in the weather resistance in the beach area of this invention is demonstrated in detail.
Conventionally, it is known that Cr is effective for improving weather resistance in an inland area where there are few flying sea salt particles. However, it has been found that Cr has an adverse effect on the weather resistance in a high-flying salt particle environment such as a beach area or a snow spray salt application area. Further, as a result of studies for improving the weather resistance of various alloy elements, it has been clarified that the combined addition of Ni of Cu-1% or more is effective for generating stable rust in the beach area. Furthermore, it has been found that the application limit of Cu—Ni system (the upper limit of the annual average amount of sea salt particles that can be sufficiently formed by stable rust) can be roughly arranged by adding Ni.
[0009]
On the other hand, in a welded steel pipe, as a result of intensive studies on a weld metal component having excellent weather resistance in the beach area and excellent weld quality, the Ni content of the weld metal is at least 2.0% less than that of the base metal. If it exists, it discovered that favorable weather resistance was acquired. Furthermore, a large amount of Ni is contained by limiting the amount of Ni in the weld metal to 0.2% or less and 3.5% or less of the base metal, and limiting the amount of C, P, and S in the weld metal. In this case, it was found that hot cracking does not occur, and the present invention has been achieved.
That is, the feature of the present invention is that a Ni-Cu-based component is applied as a steel pipe base material, and a C amount, a P amount, an S amount and a Ni amount are used as a weld metal from the viewpoint of weather resistance and prevention of hot cracking in a beach area. By limiting the range to an appropriate range, a welded steel pipe having excellent weather resistance in the beach area is provided.
[0010]
First, the reasons for limiting the components of the steel pipe base material will be described.
C is an element necessary for ensuring the strength of the base metal and the welded portion, and its lower limit is 0.03%. However, if the amount of C is too large, the low temperature toughness and weldability deteriorate, so the upper limit value was made 0.15%.
Si is an element added for deoxidation and strength improvement, but if added in a large amount, the weld heat-affected zone (HAZ) toughness deteriorates, so the upper limit was made 0.6%. For the deoxidation of steel, only Al or Ti is sufficient, and Si does not necessarily have to be added.
[0011]
Mn is an indispensable element for securing strength and low temperature toughness, and its lower limit is 0.3%. However, too much Mn not only increases the hardenability of the steel and deteriorates the weldability, but also promotes center segregation of the continuously cast steel slab and deteriorates the low temperature toughness, so the upper limit was made 2.0%.
P is an element that improves weather resistance, but if it exceeds 0.03%, the low temperature toughness and weldability deteriorate, so the upper limit value was made 0.03%. In particular, 0.015% or less is preferable in order to prevent hot cracking of the weld.
[0012]
Since S is an unavoidable impurity that deteriorates the toughness and weather resistance of the steel pipe, the smaller the amount, the better. In particular, if it exceeds 0.01%, the low temperature toughness deteriorates, so 0.005% or less is preferable.
Cu is an element that improves the weather resistance in an environment with a lot of incoming sea salt particles to suppress crystallization and coarsening of the rust particles during the formation of the rust layer and maintain the fineness of the rust. Therefore, addition of 0.3% or more is necessary. However, if it exceeds 1.0%, precipitation hardening causes toughness deterioration of the base material and HAZ and Cu-cracks are generated during hot rolling, so the upper limit value was made 1.0%.
[0013]
Ni suppresses the penetration of Cl ions adhering to the surface of the rust layer as flying sea salt particles into the rust layer / ground metal interface, and suppresses crystallization and coarse growth of the rust particles with a low Cl environment inside the rust layer. This has the effect of maintaining the denseness of the rust layer. In order to exert this effect, addition of 1.0% or more is necessary. However, addition of 5.5% or more causes cracks on the steel sheet surface, so the upper limit value was set to 5.5%. Since Cr is a base metal rather than iron, the addition of a few percent inhibits the weather resistance and weldability in an environment with many sea salt particles. In particular, if it exceeds 0.1%, the weather resistance deteriorates, so the upper limit value was made 0.1%.
[0014]
Ti forms fine TiN, suppresses coarsening of γ grains of HAZ during reheating of the slab, refines the microstructure, improves the low temperature toughness of the base material and HAZ, and is an essential element in the present invention It is. In order to exert this effect, 0.005% or more must be added. On the other hand, if the amount is too large, TiN coarsening and precipitation hardening due to TiC occur and the low-temperature toughness is deteriorated. Therefore, the upper limit value is limited to 0.03%.
Al usually has an effect as a deoxidizing element. However, if the Al content exceeds 0.09%, Al-based non-metallic inclusions increase and the cleanliness of the steel is deteriorated, so the upper limit was made 0.09%. For the deoxidation of steel, only Ti is sufficient, and Al is not necessarily added.
[0015]
N forms TiN and suppresses coarsening of γ grains of HAZ during reheating of the slab and improves the low temperature toughness of the base material and HAZ. The minimum amount required for this is 0.001%. However, if the amount of N is too large, it will cause deterioration of the HAZ toughness due to slab surface flaws and solid solution N, so the upper limit value must be limited to 0.006%.
Since O is an unavoidable impurity that deteriorates the toughness of the steel pipe, the smaller the amount, the better. In particular, if it exceeds 0.006%, a large amount of coarse oxides are produced in the steel and the toughness deteriorates, so the upper limit value was made 0.006%.
[0016]
Next, the reason for adding Mo, Nb, V, Ca, and B will be described. The main purpose of adding these elements to the basic components is to improve the properties such as strength and low temperature toughness without impairing the characteristics of the steel of the present invention. Therefore, the amount added is of a nature that should be restricted by itself.
Mo is an element that increases the strength of the base metal and the welded portion. However, if it exceeds 1.0%, the toughness and weldability of the base material and HAZ are deteriorated. In addition, the effect is small when 0.1% or less is added.
[0017]
Nb not only suppresses the recrystallization of γ during controlled rolling and refines the crystal grains, but also contributes to precipitation hardening and an increase in hardenability, and has the effect of strengthening the steel. To obtain this effect, 0.005% Nb is required. However, if the amount of Nb is too large, the HAZ toughness deteriorates, so the upper limit value was limited to 0.1%.
V has almost the same effect as Nb, but the effect is much weaker than Nb. In order to exhibit the effect, addition of 0.01% or more is necessary. Further, the upper limit is acceptable up to 0.1% from the viewpoint of on-site weldability and HAZ toughness.
[0018]
B is a very small amount and dramatically improves the hardenability of the steel, and good strength and toughness can be obtained. In order to exert this effect, 0.0003% or more must be added. Moreover, since HAZ toughness will deteriorate when there is too much, the upper limit was limited to 0.002%. Ca controls the form of sulfide (MnS) and improves low-temperature toughness (such as an increase in absorbed energy in the Charpy test). Less than 0.001%, the effect is small, and if added over 0.005%, CaO-CaS is produced in large quantities, resulting in clusters and large inclusions, not only detracting from the cleanliness of the steel, but also in the field weldability. Also adversely affects. For this reason, the amount of Ca added is limited to 0.001 to 0.005%.
[0019]
Next, the reason for limiting the components of the weld metal will be described.
When a steel having a good weather resistance and containing a large amount of Ni is welded with a large heat input, hot cracking occurs. Therefore, in order to prevent hot cracking of the weld metal and ensure good weather resistance, C: 0.03 to 0.09%, P: 0.01% or less, S: 0.005% or less, Ni: 1. It is necessary to limit the range of 0 to 3.5% and the range where Ni amount is 2.0% less than the base material to 0.2% more. By limiting the amounts of C, P, S and Ni, hot cracking can be prevented. For this reason, the upper limit of the amount of C, P, and S was limited to 0.09%, 0.01%, and 0.005%, respectively.
[0020]
Furthermore, hot cracking can be prevented if the amount of Ni in the weld metal is not more than 0.16% less than the base metal and not more than 3.5%. In addition, if the amount of Ni in the weld metal is at least 2.0% less than the base material, good weather resistance can be obtained, so the lower limit value is 1.0% and at least 2.0% less than the base material. The amount. Further, C is an element necessary for ensuring the strength of the welded portion, and the lower limit value is limited to 0.03% in order to exert the effect.
[0021]
Si is an element added for deoxidation and strength improvement, but if added in a large amount, the low temperature toughness deteriorates, so the upper limit was made 0.6%.
Mn is an indispensable element for securing strength and low temperature toughness, and its lower limit is 0.3%. However, if there is too much Mn, the hardenability of the steel increases and the low temperature toughness deteriorates, so the upper limit was made 2.0%.
Cu is an element that improves the weather resistance in an environment with a lot of incoming sea salt particles in order to suppress the rust particles from being crystallized and coarsened during the formation of the rust layer and maintain the fineness of the rust. In order to exhibit the effect, addition of 0.1% or more is necessary. However, if it exceeds 1.0%, the toughness deteriorates due to precipitation hardening, so the upper limit value was made 1.0%.
[0022]
Since Cr is a base metal rather than iron, addition of a few percent inhibits the weather resistance in an environment with a large amount of sea salt particles. In particular, if it exceeds 0.1%, the weather resistance deteriorates, so the upper limit value was made 0.1%.
Ti forms fine TiN and TiO, refines the microstructure, and improves the low temperature toughness of the weld metal. In order to exert this effect, 0.005% or more must be added. Moreover, since precipitation hardening by TiC will arise if there is too much and low temperature toughness will deteriorate, the upper limit value was limited to 0.03%.
[0023]
Al usually has an effect as a deoxidizing element. However, if the Al content exceeds 0.09%, Al-based non-metallic inclusions increase and the cleanliness of the steel is deteriorated, so the upper limit was made 0.09%. For the deoxidation of steel, only Ti is sufficient, and Al is not necessarily added.
N forms TiN, refines the microstructure, and improves low temperature toughness. The minimum amount required for this is 0.001%. However, if the amount of N is too large, it causes toughness due to solute N, so the upper limit value must be suppressed to 0.006%. O forms an oxide in the weld metal, acts as a nucleus of intragranular transformed ferrite, and is effective in refining the structure. However, if the amount is too large, the low temperature toughness of the weld metal deteriorates and welding defects such as slag entrainment occur. For this reason, the lower limit of the amount of O is set to 0.02%, and the upper limit is set to 0.06%.
[0024]
Next, the reason for adding Mo, Nb, V, B, and Ca will be described.
In addition to the basic components, the main purpose of adding these elements as necessary is to improve properties such as strength and low temperature toughness of the weld metal without impairing the excellent characteristics of the steel of the present invention. Therefore, the amount of addition is a property that should be restricted by itself.
Mo is an element that increases the strength of the welded portion, but if it exceeds 1.0%, the low temperature toughness is deteriorated. In addition, the effect is small when 0.1% or less is added.
[0025]
Nb not only refines crystal grains, but also contributes to precipitation hardening and hardenability, and has the effect of strengthening steel. To obtain this effect, a minimum of 0.005% Nb is required. However, if the amount of Nb is too large, the HAZ toughness deteriorates, so the upper limit value was limited to 0.1%.
V has almost the same effect as Nb, but the effect is much weaker than Nb. In order to exhibit the effect, addition of 0.01% or more is necessary. The upper limit is acceptable up to 0.1% from the viewpoint of low temperature toughness.
[0026]
B is a very small amount and dramatically improves the hardenability of the steel, and good strength and toughness can be obtained. In order to exert this effect, 0.0003% or more must be added. Moreover, since the low temperature toughness deteriorates if it is too much, the upper limit value is limited to 0.002%.
Ca controls the form of sulfide (MnS) and improves low-temperature toughness (such as an increase in absorbed energy in the Charpy test). If the amount is less than 0.001%, the effect is small, and if added over 0.005%, a large amount of CaO-CaS is formed to form clusters and large inclusions, which impairs the cleanliness of the steel. For this reason, the amount of Ca added is limited to 0.001 to 0.005%.
[0027]
【Example】
Examples of the present invention will be described. Steel pipes of various steel components were used to manufacture steel pipes and various properties were investigated. The quality (presence or absence of welding defects) of the welded portion of the steel pipe was evaluated using an ultrasonic flaw detector after performing SAW (submerged arc welding) of one layer on the inner and outer surfaces. The test steel pipes were subjected to exposure tests at points where the separation distance (average amount of sea salt particles) was 5 m (1.3 mdd), 50 m (0.8 mdd), 200 m (0.5 mdd), and 800 m (0.2 mdd), respectively. Provided. The weather resistance in the high sea salt particle environment was evaluated from the average reduction in plate thickness obtained from the ion permeation resistance and corrosion amount of rust. In the rust ion permeation resistance measurement, the rust ion permeation resistance value was measured by the AC impedance method, and a value of 3 kΩ or more was judged as the formation of dense stable rust. The average reduction in thickness is obtained from the corrosion-time curve at four locations, and the estimated reduction in thickness after 50 years is calculated. The standard for the use of unpainted bridges is 0.4mm / 50 years. It was.
[0028]
[Table 1]

[0029]
[Table 2]

[0030]
[Table 3]

[0031]
[Table 4]

[0032]
Examples are shown in Tables 1 to 4. The welded steel pipe of the present invention has excellent weather resistance in the base material and the welded portion. On the other hand, the chemical composition of the comparative steel is not appropriate, and any of the characteristics is inferior.
Steel 10 because the C content of the base material is too large, the low temperature toughness of the base material is poor. Since the steel 11 has too much P content of the base material, the low temperature toughness of the base material is inferior. Since steel 12 has too much S content in the base material, the low temperature toughness of the base material is inferior. Since steel 13 has a small amount of Cu in the base material, the weather resistance of the base material is inferior. Since the steel 14 has a small amount of Ni in the base material, the weather resistance of the base material is inferior. Since the amount of Ni in the base material of the steel 15 is too large, the base material is cracked. Since steel 16 has too much Cr in the base material, the weather resistance of the base material is inferior. Since the steel 17 has too much C in the weld metal, hot cracking occurs in the weld metal. Since the steel 18 has too much P amount of the weld metal, hot cracking occurs in the weld metal.
[0033]
Since the steel 19 has too much S in the weld metal, hot cracking occurs in the weld metal. Since the steel 20 has a small amount of Ni in the weld metal, the weather resistance of the weld metal is inferior. Since the steel 21 has too much Ni in the weld metal, hot cracking occurs in the weld metal. Since the steel 22 has too much Cr in the weld metal, the weather resistance of the weld metal is inferior. Steel 23 is inferior in the weather resistance of the weld metal because the Ni content of the weld metal exceeds 2.0% and is less than the Ni content of the base metal. Since the amount of Ni in the weld metal of the steel 24 is more than 0.2% than the amount of Ni in the base metal, hot cracking occurs in the weld metal.
[0034]
【The invention's effect】
By adopting a welded steel pipe having excellent weather resistance in the beach area according to the present invention as a member of a steel structure such as a bridge, the manufacturing cost of the steel structure is reduced and the maintenance management is simplified and the management cost is increased. Can be significantly reduced.

Claims (4)

% By weight
C: 0.03 to 0.15%, Si: 0.6% or less,
Mn: 0.3 to 2.0%,
P: 0.03% or less,
S: 0.005% or less, Cu: 0.3-1.0%,
Ni: 1.0 to 5.5%,
Cr: 0.1% or less,
Ti: 0.005 to 0.03%,
Al: 0.09% or less,
N: 0.001 to 0.006%,
O: a base material consisting of iron and inevitable impurities with 0.006% or less remaining,
C: 0.03-0.09%,
Si: 0.6% or less,
Mn: 0.3 to 2.0%,
P: 0.01% or less,
S: 0.005% or less,
Cu: 0.1 to 1.0%
Ni: 1.0 to 3.5%
Cr: 0.1% or less,
Ti: 0.005 to 0.03%,
Al: 0.09% or less,
N: 0.001 to 0.006%,
O: 0.02 to 0.06%
In addition, the weather resistance is characterized in that the balance is made of iron and unavoidable impurities, and further has a weld metal part in which the amount of Ni is in the range of 2.0% less than the base metal to 0.16% less. Excellent welded steel pipe. % By weight
C: 0.03-0.15%,
Si: 0.6% or less,
Mn: 0.3 to 2.0%,
P: 0.03% or less,
S: 0.005% or less,
Cu: 0.3 to 1.0%,
Ni: 1.0 to 5.5%,
Cr: 0.1% or less,
Ti: 0.005 to 0.03%,
Al: 0.09% or less,
N: 0.001 to 0.006%,
O: 0.006% or less, Mo: 0.1-1.0%, Nb: 0.005-0.1%, V: 0.01-0.1%, B: 0.0003-0 0.002%, Ca: one or two or more of 0.001 to 0.005%, with the balance being composed of iron and inevitable impurities,
C: 0.03-0.09%,
Si: 0.6% or less,
Mn: 0.3 to 2.0%,
P: 0.01% or less,
S: 0.005% or less,
Cu: 0.1 to 1.0%
Ni: 1.0 to 3.5%
Cr: 0.1% or less,
Ti: 0.005 to 0.03%,
Al: 0.09% or less,
N: 0.001 to 0.006%,
O: 0.02 to 0.06%
And the balance is made of iron and inevitable impurities, and further has a weld metal part in which the Ni amount is in the range of 2.0% less than the base metal to 0.16% less. Welded steel pipe. % By weight
C: 0.03-0.15%,
Si: 0.6% or less,
Mn: 0.3 to 2.0%,
P: 0.03% or less,
S: 0.005% or less,
Cu: 0.3 to 1.0%,
Ni: 1.0 to 5.5%,
Cr: 0.1% or less,
Ti: 0.005 to 0.03%,
Al: 0.09% or less,
N: 0.001 to 0.006%,
O: a base material consisting of iron and inevitable impurities with 0.006% or less remaining,
C: 0.03-0.09%,
Si: 0.6% or less,
Mn: 0.3 to 2.0%,
P: 0.01% or less,
S: 0.005% or less,
Cu: 0.1 to 1.0%
Ni: 1.0 to 3.5%
Cr: 0.1% or less,
Ti: 0.005 to 0.03%,
Al: 0.09% or less,
N: 0.001 to 0.006%,
O: 0.02 to 0.06%
Furthermore, Mo: 0.1 to 1.0%, Nb: 0.005 to 0.1%, V: 0.01 to 0.1%, B: 0.0003 to 0.002%, Ca: 0 .001-0.005% of one or two or more types, the balance is made of iron and inevitable impurities, and the amount of Ni is less than 2.0% of the base material to 0.16% less A welded steel pipe excellent in weather resistance, characterized by having a weld metal part in a range. % By weight
C: 0.03-0.15%,
Si: 0.6% or less,
Mn: 0.3 to 2.0%,
P: 0.03% or less,
S: 0.005% or less,
Cu: 0.3 to 1.0%,
Ni: 1.0 to 5.5%,
Cr: 0.1% or less,
Ti: 0.005 to 0.03%,
Al: 0.09% or less,
N: 0.001 to 0.006%,
O: 0.006% or less, Mo: 0.1-1.0%, Nb: 0.005-0.1%, V: 0.01-0.1%, B: 0.0003-0 0.002%, Ca: one or two or more of 0.001 to 0.005%, with the balance being composed of iron and inevitable impurities,
C: 0.03-0.09%,
Si: 0.6% or less,
Mn: 0.3 to 2.0%,
P: 0.01% or less,
S: 0.005% or less,
Cu: 0.1 to 1.0%
Ni: 1.0 to 3.5%
Cr: 0.1% or less,
Ti: 0.005 to 0.03%,
Al: 0.09% or less,
N: 0.001 to 0.006%,
O: 0.02 to 0.06%,
Furthermore, Mo: 0.1 to 1.0%, Nb: 0.005 to 0.1%, V: 0.01 to 0.1%, B: 0.0003 to 0.002%, Ca: 0 .001-0.005% of one or two or more types, the balance is made of iron and inevitable impurities, and the amount of Ni is less than 2.0% of the base material to 0.16% less A welded steel pipe excellent in weather resistance, characterized by having a weld metal part in a range.