JPH0953145A - ERW welded steel pipe excellent in carbon dioxide gas corrosion resistance and its manufacturing method - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide an electric resistance welded steel pipe that does not cause selective corrosion of a welded portion in a carbon dioxide corrosive environment and a method for manufacturing the same. SOLUTION: As a main component (% by weight), C: 0.2%
Hereinafter, Si: 0.5% or less, Mn: 2% or less, Al:
0.07% or less, Cr: 0.2% to 3% and N: 0.0
An electric resistance welded steel pipe containing 1% or less, the balance being substantially Fe, and having a melt-solidified structure in the electric resistance welded portion. Further, a step of preparing a steel sheet made of the above components, a step of forming the steel sheet into an open pipe, and a step of heating both opposing edge portions of the open pipe to a melting temperature of steel or lower,
This is a method for producing electric resistance welded steel pipe that includes laser irradiation on both edges of the open pipe and melting and also upsetting. Both the base metal and electric resistance welded portion have excellent wet carbon dioxide corrosion and corrosion resistance. It is an electric resistance welded pipe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric resistance welded steel pipe having excellent corrosion resistance in a humid environment containing carbon dioxide gas, such as a steel pipe for pipelines for transporting petroleum or natural gas containing carbon dioxide gas, and a method for producing the same. .

[0002]

2. Description of the Related Art It is known that steel pipes used in pipelines for transporting petroleum and natural gas containing carbon dioxide are exposed to a moist environment containing carbon dioxide, so that the inner surface of the steel pipe is corroded. In order to improve the corrosion resistance under this corrosive environment, Japanese Patent Laid-Open No. 4-341540 discloses 0.5% Cr-added steel, which is a seamless steel pipe having excellent corrosion resistance or arc welding. The UOE steel pipe to be manufactured is obtained.

From the standpoint of manufacturing steel pipes, the seamless steel pipe and the manufacturing method thereof are suitable for the case where the wall thickness is thicker than the outer diameter of the steel pipe, and the UOE steel pipe is for manufacturing steel pipe having a large outer diameter. It is a suitable method. A method of manufacturing a steel pipe having a smaller diameter than a UOE steel pipe and a smaller wall thickness / outer diameter ratio than a seamless steel pipe is to continuously form a steel strip into an open pipe, and heat the opposite edges to weld them. There is a method to make a pipe.

This method is called an electric resistance welding method. Since this method has an advantage of high efficiency as compared with other manufacturing methods of welded steel pipes, it can be used for machine structural steel pipes and the like. It is used for many purposes. In addition, high-frequency heating or resistance heating is used as a method of heating the welded portion.

However, the electric resistance welding method is essentially a welding method in which minute welding defects are liable to occur, and it has been unsuitable for applications in which corrosion resistance is strictly required. The main reason for the poor corrosion resistance of ERW welded pipes is that the weld is in the middle of normal fusion welding and pressure welding, and there is no clear molten pool formed in the weld, and therefore oxidation at the time of welding. It is because the inclusions formed by are difficult to be discharged from the inside of the steel and remain continuously.

Therefore, it has been attempted to upset the open pipe at the time of welding so as to discharge the above inclusions and the like to the outside as much as possible. As a result, a metal flow in the vicinity of the welded portion rises, so to speak. As a result, a section of steel during rolling (inferior in corrosion resistance to the surface during rolling) appears on the inner and outer surfaces of the pipe, and a phenomenon in which corrosion progresses occurs at that portion. Fig. 1 (a) shows the metallographic structure of the welded portion of the conventional electric resistance welded steel pipe. As described above, no clear molten pool was formed in the welded portion, and the texture was exposed and exposed on the bead surface. There is.

Further, it is impossible to completely discharge the oxide, and a considerable amount of the oxide remains, which naturally appears on the surface of the steel pipe when the bead is ground and deteriorates the corrosion resistance. It goes without saying that the rising of the metal flow and the presence of inclusions are extremely harmful even in the carbon dioxide corrosive environment which is the purpose of using the steel pipe of the present invention.

Of course, measures for solving this problem are also being studied. For example, Japanese Patent Application Laid-Open No. 63-24116 proposes a method of shielding the electric-welded portion with non-oxidizing gas and performing electric-welding welding to reduce defects in the electric-welded portion. However, in reality, no shield device has been developed that has excellent shielding properties and can withstand continuous operation. Under the circumstances as described above, it has been conventionally considered that an electric resistance welded pipe having sufficient corrosion resistance in a carbon dioxide environment cannot be manufactured.

[0009]

As described above, the conventional technique does not always meet the purpose of obtaining an electric resistance welded pipe having sufficient corrosion resistance in a carbon dioxide corrosive environment. An object of the present invention is to provide an electric resistance welded pipe which has excellent general corrosion resistance in a carbon dioxide corrosive environment and does not cause selective corrosion of a welded portion, and a method for producing the same.

[0010]

[Means for Solving the Problems] The present inventors clarified these factors by 1) the composition of steel, 2) the structure of steel, and 3) the cleanliness of steel, as factors that affect the corrosion resistance to carbon dioxide corrosion. The present invention has been completed through repeated research.

That is, in the first invention, (a) as a main component (component composition is% by weight), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, Al: 0. An electric resistance welded steel pipe containing 0.07% or less, Cr: 0.2% to 3%, N: 0.01% or less, and the balance being substantially Fe, (b) the electric resistance welding It is an electric resistance welded steel pipe excellent in carbon dioxide gas corrosion resistance, which is characterized in that the electric resistance welded portion of the steel pipe has a melt-solidified structure.

In the second aspect of the invention, the main component (a) (component composition is% by weight) is C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, Al: 0. 07% or less, Cr: 0.2% to 3%, N: 0.01% or less, further containing: Ni: 1% or less, Co: 1% or less, Mo: 1% or less, W: 1% or less Cu: 1% or less, Nb: 0.2% or less, V: 0.2% or less, Ti: 0.1% or less, Zr: 0.1% or less, REM: 0.1% or less, Y: 0. 1% or less, Ca: 0.01% or less, Mg: 0.01% or less, As: 0.01% or less, Pb: 0.1% or less, Sn: 0.1% or less, Sb: 0.1 % Or less, an electric resistance welded steel pipe containing one or more of the following, and the balance being substantially Fe, and (b) a melt solidification structure in the electric resistance welded portion of the electric resistance welded steel pipe. It is an electric resistance welded steel pipe excellent in carbon dioxide gas corrosion resistance having the features described above.

The third invention has the characteristics of the first and second inventions, respectively, and the corrosion resistance to carbon dioxide gas is such that the rising angle of the metal flow in the vicinity of the electric resistance welded portion is 45 ° or less. Excellent electric resistance welded steel pipe.

A fourth invention is a method for producing an electric resistance welded steel pipe having excellent carbon dioxide gas corrosion resistance, which is characterized by comprising the following steps. (A) As a main component (component composition is% by weight), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, Al: 0.07% or less, Cr: 0.2% ˜3%, N: 0.01% or less, a step of preparing a steel sheet containing the balance substantially Fe, (b) a step of forming the steel sheet into an open pipe, and (c) the open A step of heating both opposite edge portions of the pipe to a melting temperature of steel or lower; (d) irradiating both opposite edge portions of the open pipe with a laser beam to melt, and controlling an upset amount with a squeeze roll. , Pressure welding process.

Further, a fifth invention is a method for producing an electric resistance welded steel pipe having excellent carbon dioxide gas corrosion resistance, which is characterized by comprising the following steps. (A) As a main component (component composition is% by weight), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, Al: 0.07% or less, Cr: 0.2% 3%, N: 0.01% or less, further Ni: 1% or less, Co: 1% or less, Mo: 1% or less, W: 1% or less, Cu: 1% or less, Nb: 0 0.2% or less, V: 0.2% or less, Ti: 0.1% or less, Zr: 0.1% or less, REM: 0.1% or less, Y: 0.1% or less, Ca: 0.01 % Or less, Mg: 0.01% or less, As: 0.01% or less, Pb: 0.1% or less, Sn: 0.1% or less, Sb: 0.1% or less, or one or more types thereof. Of steel, the balance of which is substantially Fe, and (b) the step of forming the steel sheet into an open pipe; Heating both edge portions below the melting temperature of the steel, and (d) irradiating the opposite edge portions with a laser beam to melt them, and controlling the amount of upset by a squeeze roll and pressing them.

[0016]

DETAILED DESCRIPTION OF THE INVENTION The basis of the present invention is to weld a steel sheet by irradiation with a high energy beam such as a laser beam. Conventionally, electric resistance welded steel pipes have been manufactured by laser beam irradiation using stainless steel pipes, but there is no case where the purpose is to improve the corrosion resistance of carbon steel or low alloy steel as in the present invention.

The main reason for using laser beam irradiation is that it is possible to locally melt steel in a short time. Further, the energy possessed by the laser beam irradiation is capable of melting the steel, finely crushing the oxides generated in the welded portion, finely dispersing them, and discharging them. As the laser, there are a carbon dioxide gas laser, a YAG laser, an excimer laser and the like, and any of them can be applied, but the carbon dioxide gas laser is economical.

The term "melt-solidified structure" as used in the present invention means a structure in which steel is melted and re-solidified by laser beam irradiation. The solidification structure of the welded portion of the electric resistance welded steel pipe according to FIG. 1 (b) is shown. A dense solidification structure is observed, which is distinct from the conventional metal structure of the welded part. Since this coagulated tissue is generated while the upset is being applied, a tissue that is slightly deformed may naturally occur.

By crushing the inclusions into fine particles by laser beam irradiation and making them spherical, it is possible to prevent the corrosion from propagating through the inclusions. Further, since the molten pool is generated by the laser beam irradiation, in the production of the conventional electric resistance welded steel pipe, the strength upset required for ensuring the soundness of the welded portion is no longer necessary.

As a result, the rising angle of the metal flow can be minimized, and it is possible to eliminate the demerit of the metal flow crossing the surface of the pipe at a high angle, which deteriorates the corrosion resistance in a carbon dioxide corrosive environment. It was As a steel strip from which a steel pipe is manufactured, a steel strip having sufficient corrosion resistance under a carbon dioxide corrosive environment is used. The basic elements that improve the corrosion resistance of steel in a carbon dioxide corrosive environment are C, Si, Mn, Al, Cr and N.

First, the reasons why the composition of the steel (% by weight) is limited as described above in the present invention will be described below. C increases the strength of steel, but if added in excess of 0.2%, the weldability and toughness deteriorate. Therefore, the upper limit is 0.2%. In order to secure the strength, addition of 0.01% or more is preferable. Si is a deoxidizing element of steel,
If added in excess of 0.5%, adverse effects such as deterioration of toughness will occur, so 0.5% is made the upper limit. Mn also increases the strength of steel, but if added in excess of 2%, weldability and toughness deteriorate. Therefore, the upper limit is 2%. Al is also a deoxidizing element of steel, but if it is added in an amount exceeding 0.07%, adverse effects such as deterioration of toughness will occur, so that it is less than 0.1%.
The upper limit is 07%.

Next, Cr, which is a basic additive element in the present invention,
And N will be described. By adding 0.2% or more of Cr, the desired corrosion resistance can be obtained in both the base metal portion and the welded portion. On the other hand, Cr is an element harmful to weldability. In particular, if the addition amount is 3% or more, the adverse effect becomes remarkable, so the addition range is 0.2 to 3%. N is also an element that is usually absorbed by the steel from the atmosphere during melting, but if its content exceeds 0.01%, it adversely affects the toughness. Therefore, the upper limit of addition is 0.01%.

The other elements take into account those which aid the effect of Cr, other properties of the steel, namely strength, workability, toughness, weldability, and corrosion resistance to any corrosion which may occur simultaneously with carbon dioxide corrosion. May be added. In particular, in natural gas pipelines, hydrogen sulfide often coexists in addition to carbon dioxide, and HIC (hydrogen-induced cracking) and SSCC (sulfide stress corrosion cracking) due to hydrogen sulfide must be constantly considered in this application as well. There is.

Therefore, one or two of the various elements described below are used.
It is advisable to add more than one seed. First, Ni improves the HIC resistance of steel. It also has the effect of reducing the adverse effect of Cu on the hot workability. However, these elements are expensive elements, and the heat treatment characteristics change when added in an extremely large amount, so the upper limit is made 1%. The same is true for Co.

Mo is an element that improves the corrosion resistance of steel.
It also improves the HIC resistance. However, it is an expensive element, and if added in a significantly large amount, the heat treatment characteristics change, so the upper limit is made 1%. The same applies to the case of W.
If any of Ni, Co, Mo, and W is added in excess of 1%, the SSCC resistance deteriorates. Therefore, when SSCC resistance is required, the upper limit of addition is 0.5%.

Ca is associated with S to granulate inclusions and improve corrosion resistance under various corrosive environments through morphology control. HIC resistance is improved by adding 0.001% or more. On the other hand, if added in excess of 0.01%, the toughness of the steel deteriorates, so the upper limit of addition is made 0.01%.

Mg also binds to S to granulate inclusions and improve corrosion resistance under various corrosive environments through morphology control. From the viewpoint of HIC resistance, addition of 0.001% or more is preferable. Similar to Ca, the upper limit is 0.01%, which is a range in which the toughness of steel does not deteriorate. REM and Y also combine with S to granulate inclusions and improve corrosion resistance under various corrosive environments through morphology control. 0.001 from HIC resistance
% Or more is preferable. The upper limit is set to 0.1% within the range in which the toughness of steel does not deteriorate.

Ti is a deoxidizing element and a strengthening element, but if added in excess of 0.1%, adverse effects such as deterioration of toughness occur, so 0.1% is made the upper limit. Z
Similar to Ti, r is a deoxidizing element and a strengthening element. However, if added in an amount of more than 0.1%, adverse effects such as deterioration of toughness occur, so 0.1% is made the upper limit. . N
b and V increase the strength of steel, but if both are added in excess of 0.2%, the toughness deteriorates, so the upper limit is 0.2.
%.

As is effective for the carbon dioxide corrosion environment corrosion resistance of steel. The effect becomes more significant than about 0.005%.
The upper limit value is 0.1% due to weldability. Sn is also effective for carbon dioxide corrosion environment corrosion resistance of steel. The effect is 0.005
It becomes more remarkable than about%. The upper limit value is 0.1% due to weldability. Sb is also effective for carbon dioxide corrosion environment corrosion resistance of steel. The effect becomes more significant than about 0.005%. The upper limit value is 0.1% due to weldability. Pb is also effective for carbon dioxide corrosion environment corrosion resistance of steel. The effect becomes more significant than about 0.005%. The upper limit value is 0.1% due to weldability. Note that S is usually 0.03 contained in steel.
% May be contained.

The welding at the time of manufacturing the electric resistance welded steel pipe according to the conventional method is a welding having a small heat input as compared with the arc welding, so that the cooling rate of the joint portion is high. For this reason, part of MnS once solid-dissolved during heating precipitates as FeS or MnS, but it cannot be completely re-precipitated, and most of it remains in a supersaturated solid solution. As a result, the electric resistance welded portion has a higher concentration of solid solution S than the base material portion, and therefore the immersion potential becomes baser than the base material portion. This is the main reason why the corrosion resistance of the electric resistance welded part is poor.

On the other hand, corrosion of another type, mainly due to S, progresses to the rising portion of the metal near the electric resistance welded portion. The corrosion of this part is often an A-based inclusion such as MnS or FeS, and the corrosion proceeds along the inclusion in the initial stage. In the base material portion, these inclusions extend in parallel (L direction) along the rolling direction and are not exposed on the surface of the plate. However, in the production of the electric resistance welded pipe, it is necessary to perform upsetting, a metal flow rises, and a surface corresponding to the C cross section of the plate appears on the inner and outer surfaces of the steel pipe, and corrosion progresses from here. From this viewpoint, the lower the S content, the more preferable.

When corrosion progresses to the rising portion of this metal flow, it becomes selective corrosion. The selective corrosion of the electric resistance welded portion was evaluated by the index α value shown by the following equation. Note that α = 1.
0 indicates that the selective corrosion of the electric resistance welded portion has not occurred at all, but practically, if α ≦ 1.2, the trouble of the selective corrosion of the electric resistance welded portion hardly occurs.

Α = d1 / d2 where: d1: Corrosion depth of the electric resistance portion (mm) d2: Corrosion depth of the base material portion (mm) In the present invention, since laser beam irradiation is performed, a normal A large amount of heat input is applied to the electric resistance welded portion compared to the electric resistance welded steel pipe. Therefore, the cooling rate is slower than that of a normal electric resistance welded steel pipe, and S is likely to precipitate during cooling, so that it is less base than the base metal portion.

Next, it is possible to reduce the rise of the metal flow. The probability that the inclusions, which are the starting points of this selective corrosion, appear on the inner and outer surfaces of the steel pipe changes depending on the rising angle of the metal flow, but is relatively low when the rising angle of the metal flow is 45 ° or less, and is substantially M.
The appearance of nS and FeS on the inner and outer surfaces of the steel pipe can be ignored. On the other hand, if the rising angle of the metal flow exceeds 45 °, the probability of MnS and the like appearing on the surface increases, so the rising angle of the metal flow is set to 45 °.
Limited to the following.

For these reasons, excellent carbon dioxide gas corrosion resistance can be obtained, but it goes without saying that a lower S content is desirable. For example, when the S content is 0.015% or less, more excellent performance can be obtained. On the other hand, the effect of P on the corrosion resistance is negligible,
The upper limit is about 0.3%. In addition, in order to have both HIC resistance and SSCC resistance, it is desirable that the upper limit of the amount of S be 0.01%. The above is the reason for limiting the composition.

In the present invention, a laser irradiation beam is used for welding. Therefore, it is not necessary to discharge the inclusions in the electric resistance welded portion, and it is not necessary to set a large upset amount. Even when the same upset amount as the conventional method is used,
Due to the presence of the fusion zone, the rising angle of the metal flow is naturally small. Here, the upset amount is defined as follows. Upset amount (mm) = coil width before pipe making (mm) -pipe circumference length
(mm) Next, specific examples of the invention will be described.

[0037]

EXAMPLES Steels having the chemical compositions shown in Table 1 were melted. The steels A to N in the table were vacuum melted in a laboratory and cast into a 50 kg ingot. Both are steels having a composition within the scope of the present invention. (O-Q steel will be described later)

Further, Table 2 shows the composition of the steel of the comparative example having a composition outside the range of the present invention. Each of the steels except the R and S steels in the table is vacuum melted in the laboratory in the same manner as the A to N steels, and is 50 kg.
It was cast into an ingot. 120 of these steels
It was heated to 0 ° C., rolled to a plate thickness of 50 mm, and then air-cooled.
A 50 × 150 × 400 mm plate was cut out from the air-cooled steel plate and rolled to a plate thickness of 12 mm at a heating temperature of 1200 ° C. and a rolling end temperature of 820 ° C.

Immediately after the completion of rolling, after cooling to 550 ° C. with a mist spray at a cooling rate of about 10 ° C./sec, 5
After inserting into an electric furnace that had been heated to 50 ° C., the furnace was cooled. These steps simulate the manufacturing conditions of a steel strip by hot rolling.

[0040]

[Table 1-1]

[0041]

[2 in Table 1]

[0042]

[1 of Table 2]

[0043]

[Table 2-2]

6 × 35 × 1 from steel sheet cooled to room temperature
A 00 mm test piece 1 was cut out and welded using an electric resistance welding simulator. As shown in FIG. 2, this apparatus feeds two test pieces (steel plates) 1 from a guide roll, resistance-heats an edge portion of the opposing steel plate with a high frequency current supplied from a contact tip 2, and then press-contacts it with a squeeze roll 3. In addition, it has a function of irradiating the edge joining portion with the carbon dioxide laser beam 4.

The welding conditions were a welding speed of 15 m / min, an input power of 200 kW from the contact tip 2, and the upset amount was changed in the range of 0 to 4 mm. The laser output was 5 kW, the beam diameter at the focal position was 0.5 mm, and irradiation was performed by focusing on the edge joining point from vertically above the steel sheet.

The manufacturing conditions are shown in Table 3. In Table 2, T-W steel and Y-e steel are all C, Si, and M.
n, Cr, Mo, W, Nb, V, Ti, Zr, REM,
The amount of one or more of Y, Al, N, Ca, Mg, As, Sb, Sn, and Pb added exceeded the range of the present invention, and cracking occurred during welding, and a test piece could not be collected. Further, in the X steel, the amount of Cu added exceeded the range of the present invention, cracking occurred during hot rolling, and welding could not be performed.

[0047]

[Table 3-1]

[0048]

[Table 3-2]

[0049]

[3 in Table 3]

3.5 × from the weld produced by the above method
After cutting out a sample 5 of 30 × 60 mm and polishing the surface,
A carbon dioxide corrosion test was conducted using the apparatus shown in FIG. The test solution was artificial seawater saturated with carbon dioxide and the temperature of the solution was 80.
C., the liquid flow rate is 3 m / sec, and the test time is 300 hr. The weight of Sample 5 before and after the corrosion test was measured to determine the C value (mg / cm ² ) as the corrosion weight loss per unit area.
For use in a wet carbon dioxide environment, C ≦ 80 mg /
It must be cm ² .

After the test, the cross section of Sample 5 was examined under a microscope to examine the degree of selective corrosion of the electric seam. For the evaluation of the selective corrosion of the electric resistance welded portion, the α value which is the index shown above was used. The test results are shown in Table 3. In all the examples of the present invention, the C value was 80.
mg / cm ² and an α value of 1.2 or less, indicating excellent performance.

On the other hand, although the composition is within the range of the present invention, the C value of the comparative example not subjected to laser beam irradiation satisfies 80 mg / cm ² or less, but the α value is larger than 1.2. It shows that selective corrosion is occurring at a large size. The O to Q steels in Table 1 and the R and S steels in Table 2 are melted at the factory to form a hot rolled steel strip having a thickness of 7.5 mm with a hot strip mill, and the steel strip is used to make 76.3φ. (Diameter) ×
A 7.5 t (thickness) mm electric resistance welded steel pipe was manufactured, and a test was performed with and without laser beam irradiation. The upset amount is almost constant.

After the steel pipe was manufactured, the electric resistance welded portion was cut out, and further, a sample 5 of 3.5 × 30 × 60 mm was processed, and the same test as that for the laboratory melting material was conducted. The results are shown in Table 4,
It can be seen that when the composition range is within the range of the present invention and the laser irradiation is performed, excellent corrosion resistance is exhibited.
On the other hand, the steel with insufficient Cr content has a C value of 80 mg /
Since it exceeds cm ² , it can be seen that it cannot be used in a carbon dioxide corrosive environment. Although slightly, P with a high S content,
The α value of Q steel is high.

In Table 3, Tests 1 to 32 to 37, 40
Nos. 43 to 43 are the results obtained by collecting and welding test pieces of steel strip from hot-rolled steel strips of O-Q steel, R and S steel having a thickness of 7.5 mm, and the same tendency was observed. To be

[0055]

[Table 4]

[0056]

According to the present invention, an electric resistance welded pipe having excellent corrosion resistance can be obtained in a wet carbon dioxide corrosive environment for both the base material and the electric resistance welded portion. Further, the electric resistance welded steel pipe produced by the method of the present invention has a small amount of corrosion loss in both the electric resistance welding and the base metal portion, and selective corrosion in the vicinity of the electric resistance welding portion is not recognized.

[Brief description of drawings]

FIG. 1 is a drawing-substituting photograph showing a metal structure of a welded portion (a) of a conventional electric resistance welded steel pipe and a welded portion (b) of the electric resistance welded steel pipe according to the present invention.

FIG. 2 is a schematic view of an electric resistance welded pipe welding simulator used in an embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing a carbon dioxide corrosion test apparatus used in an example of the present invention.

[Explanation of symbols]

 1 Test piece 2 Contact tip 3 Squeeze roll 4 Laser beam 5 Sample

Front Page Continuation (72) Inventor Akio Sato 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Steel Pipe Co., Ltd. (72) Inventor Kenichi Iwasaki 1-1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Steel Pipe Co., Ltd.

Claims (5)

[Claims] 1. An electric resistance welded steel pipe excellent in carbon dioxide gas corrosion resistance having the following features. (A) As a main component (component composition is% by weight), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, Al: 0.07% or less, Cr: 0.2% 3%, N: 0.01% or less, and the balance is substantially Fe, which is an electric resistance welded steel pipe, and (b) a molten solidification structure is formed in the electric resistance welded portion of the electric resistance welded steel pipe. Have. 2. An electric resistance welded steel pipe excellent in carbon dioxide corrosion resistance having the following characteristics. (A) As a main component (component composition is% by weight), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, Al: 0.07% or less, Cr: 0.2% 3%, N: 0.01% or less, further Ni: 1% or less, Co: 1% or less, Mo: 1% or less, W: 1% or less, Cu: 1% or less, Nb: 0 0.2% or less, V: 0.2% or less, Ti: 0.1% or less, Zr: 0.1% or less, REM: 0.1% or less, Y: 0.1% or less, Ca: 0.01 % Or less, Mg: 0.01% or less, As: 0.01% or less, Pb: 0.1% or less, Sn: 0.1% or less, Sb: 0.1% or less, or one or more types thereof. Is contained in the electric resistance welded steel pipe, and (b) the electric resistance welded portion of the electric resistance welded steel pipe has a melt-solidified structure. 3. The electric resistance welded steel pipe excellent in carbon dioxide corrosion resistance according to claim 1 or 2, wherein the rising angle of the metal flow in the vicinity of the electric resistance welded portion is 45 ° or less. 4. A method for producing an electric resistance welded steel pipe having excellent carbon dioxide gas corrosion resistance, which comprises the following steps. (A) As a main component (component composition is% by weight), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, Al: 0.07% or less, Cr: 0.2% ˜3%, N: 0.01% or less, a step of preparing a steel sheet containing the balance substantially Fe, (b) a step of forming the steel sheet into an open pipe, and (c) the open A step of heating both opposite edge portions of the pipe to a melting temperature of steel or lower; (d) irradiating both opposite edge portions of the open pipe with a laser beam to melt and controlling an upset amount with a squeeze roll. , Pressure welding process. 5. A method for producing an electric resistance welded steel pipe having excellent carbon dioxide gas corrosion resistance, characterized by comprising the following steps. (A) As a main component (component composition is% by weight), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, Al: 0.07% or less, Cr: 0.2% 3%, N: 0.01% or less, further Ni: 1% or less, Co: 1% or less, Mo: 1% or less, W: 1% or less, Cu: 1% or less, Nb: 0 0.2% or less, V: 0.2% or less, Ti: 0.1% or less, Zr: 0.1% or less, REM: 0.1% or less, Y: 0.1% or less, Ca: 0.01 % Or less, Mg: 0.01% or less, As: 0.01% or less, Pb: 0.1% or less, Sn: 0.1% or less, Sb: 0.1% or less, or one or more types thereof. Of steel, the balance of which is substantially Fe, and (b) the step of forming the steel sheet into an open pipe; Heating both edge portions below the melting temperature of the steel, and (d) irradiating the opposite edge portions with a laser beam to melt them, and controlling the amount of upset by a squeeze roll and pressing them.