JPH07278730A - Electric resistance welded steel pipe having excellent ductility and toughness and a tensile strength of 1080 to 1450 MPa and a method for producing the same - Google Patents

Abstract

(57) [Abstract] [Object] The present invention is applied to various shafts such as propeller shafts, etc., which have high dimensional accuracy, are hard to soften the heat-affected zone during welding, and are required to have excellent ductility and toughness. The present invention relates to an economical high-precision and high-strength electric resistance welded steel pipe. [Composition] Component composition by weight C: 0.15 to 0.25
%, Si: 0.71 to 2.00%, Mn: 1.8 to 2.
5%, P: 0.005-0.020%, S: 0.000
5 to 0.006%, Al: 0.001 to 0.08%, T
i: 0.01 to 0.05%, B: 0.0010 to 0.0
030%, N: 0.002 to 0.005%, Mo: 0.
1-1.0%, Nb: 0.05% or less, balance F
An electric resistance welded steel pipe having a tensile strength of 1,080 to 1,450 MPa, which is excellent in ductility and toughness, and which is obtained by subjecting a hot rolled coil made of e and an unavoidable element to an electric resistance welded pipe and normalizing. [Effect] It is possible to obtain an economical electric resistance welded steel pipe having high strength, HAZ (heat affected zone) softening property during welding, and further excellent ductility and toughness as compared with the conventional technique.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a high dimensional accuracy, a heat-affected zone is less likely to be softened during welding, and an excellent strength-ductility balance and toughness are required, for example, various shafts such as propeller shafts and bicycles. High-precision and high-strength electric resistance welded steel pipes used for automobile frames, automobile door reinforcements, etc., and a method for manufacturing the same.

[0002]

2. Description of the Related Art Thorough weight reduction and functional enhancement of structural members such as automobiles, industrial machines, and bicycles have been studied, and thinning has been achieved by improving precision and strength. For example, regarding high-strength ERW steel pipes for automobile propeller shafts, Sumitomo Metals Vol. 43-3 (1991) P44
As shown in P60, a combination of material components, cold rolling, etc., with a tensile strength of 780 MPa class and an outer diameter accuracy of ± 0.
We have obtained a high-precision steel pipe with a thickness of 18 mm and a wall thickness accuracy of ± 0.10 mm. However, this method is one in which electric resistance welding is performed or annealing is subsequently performed, and a heat-affected structure during electric resistance welding still remains. Therefore, the toughness of the electric resistance welded portion is insufficient.

Further, the bicycle frame is mainly made of Cr-
The tensile strength of the Mo type is 800 MPa, and in order to further increase the strength, an example of using a resin containing structural fibers is disclosed, as in Japanese Patent Application No. 62-503103. Very expensive. Regarding the bicycle door reinforcing material, many patents including Japanese Patent Application Laid-Open No. 3-140441 are disclosed, but none of them is clear about the balance between strength and ductility.

[0004]

SUMMARY OF THE INVENTION The present invention has a strength of 1080 to 1450 for the purpose of weight reduction and high performance of parts.
Economical electric resistance welded steel pipe having high strength of MPa, HAZ (heat-affected zone) softening property during welding, higher precision and superior ductility and toughness than conventional technology, and a manufacturing method thereof. The purpose is to provide.

[0005]

The subject matter of the present invention is as follows. (1) Component composition is C: 0.15 to 0.25% by weight, S
i: 0.71 to 2.00%, Mn: 1.8 to 2.5%,
P: 0.005-0.020%, S: 0.00055-
0.006%, Al: 0.001 to 0.08%, Ti:
0.01-0.05%, B: 0.0010-0.003
0%, N: 0.002-0.005%, Mo: 0.1
Tensile strength with excellent ductility and toughness, characterized in that a hot-rolled coil containing 1.0% and Nb: 0.05% or less, and the balance of Fe and unavoidable elements is electric resistance welded and normalized. Of the electric resistance welded steel pipe of 1,080 to 1,450 Mpa.

(2) Component composition by weight C: 0.15 to 0.15
0.25%, Si: 0.71 to 2.00%, Mn: 1.8
.About.2.5%, P: 0.005 to 0.020%, S: 0.
0005-0.006%, Al: 0.001-0.08
%, Ti: 0.01 to 0.05%, B: 0.0010
0.0030%, N: 0.002-0.005%, M
O: 0.1 to 1.0%, Nb: 0.05% or less, and further, one or more of Cr: 0.2 to 1.0% and V: 0.1% or less. However, the tensile strength excellent in ductility and toughness is characterized by the fact that a hot-rolled coil made up of the balance Fe and unavoidable elements is electric-sewn into a tube and normalized.
Manufacturing method of ERW steel pipe of 1450Mpa.

(3) In the electric resistance welded steel pipe of (1) or (2), the tensile strength excellent in ductility and toughness is 1080-1 in high dimensional accuracy characterized by continuous expansion.
Manufacturing method of 450MPa ERW steel pipe. (4) A method for producing an electric resistance welded steel pipe having high dimensional accuracy, excellent tensile ductility and toughness, and a tensile strength of 1080 to 1450 MPa in the electric resistance welded steel pipe of (3), which is followed by annealing or normalizing. (5) The tensile strength excellent in ductility and toughness is characterized by performing electric resistance welding of the hot-rolled coil of (1) or (2), expanding the tube after annealing, and then performing normalization.
Manufacturing method of MPa ERW steel pipe.

(6) Component composition by weight C: 0.15 to 0.15
0.25%, Si: 0.71 to 2.00%, Mn: 1.8
.About.2.5%, P: 0.005 to 0.020%, S: 0.
0005-0.006%, Al: 0.001-0.08
%, Ti: 0.01 to 0.05%, B: 0.0010
0.0030%, N: 0.002-0.005%, M
o: 0.1 to 1.0%, Nb: 0.05% or less, the balance Fe and unavoidable elements, and the microstructure has the same bainite main body in the electric resistance welded portion and the base metal portion. Tensile strength with excellent ductility and toughness is 108
ERW steel pipe of 0 to 1450Mpa.

(7) Component composition by weight C: 0.15 to 0.15
0.25%, Si: 0.71 to 2.00%, Mn: 1.8
.About.2.5%, P: 0.005 to 0.020%, S: 0.
0005-0.006%, Al: 0.001-0.08
%, Ti: 0.01 to 0.05%, B: 0.0010
0.0030%, N: 0.002-0.005%, M
O: 0.1 to 1.0%, Nb: 0.05% or less, and further, one or more of Cr: 0.2 to 1.0% and V: 0.1% or less. An electric resistance welded steel pipe having a tensile strength of 1080 to 1450 MPa, which is excellent in ductility and toughness, characterized in that the balance is Fe and inevitable elements, and the microstructure is mainly composed of the same bainite in the electric resistance welded part and the base metal part.

(8) Component composition by weight C: 0.15
0.25%, Si: 0.71 to 2.00%, Mn: 1.8
.About.2.5%, P: 0.005 to 0.020%, S: 0.
0005-0.006%, Al: 0.001-0.08
%, Ti: 0.01 to 0.05%, B: 0.0010
0.0030%, N: 0.002-0.005%, M
o: 0.1 to 1.0%, Nb: 0.05% or less, the balance Fe and unavoidable elements, and the microstructure has the same bainite main body in the electric resistance welded part and the base metal part, ERW steel pipe with excellent ductility and toughness and a tensile strength of 1080 to 1450 Mpa characterized by a diameter accuracy of ± 0.10 mm and a wall thickness accuracy of ± 0.05 mm.

(9) Component composition by weight C: 0.15
0.25%, Si: 0.71 to 2.00%, Mn: 1.8
.About.2.5%, P: 0.005 to 0.020%, S: 0.
0005-0.006%, Al: 0.001-0.08
%, Ti: 0.01 to 0.05%, B: 0.0010
0.0030%, N: 0.002-0.005%, M
O: 0.1 to 1.0%, Nb: 0.05% or less, and further, one or more of Cr: 0.2 to 1.0% and V: 0.1% or less. However, the balance consists of Fe and unavoidable elements, the microstructure is mainly bainite in the electric resistance welded part and the base metal part, and the outer diameter accuracy is ± 0.10 mm and the wall thickness accuracy is ± 0.05 mm. ERW steel pipe with excellent ductility and toughness and a tensile strength of 1080 to 1450 Mpa.

The present invention will be described in detail below. First, the reasons for limiting the components of the steel sheet used in the present invention will be described. If the C content is small, the ductility is good and the workability is excellent, but the required strength is not obtained, so the lower limit is set to 0.
It was set to 15%. On the other hand, if it exceeds 0.25%, the heat-affected zone is hardened during welding such as TIG welding when used as a component, and there is a concern that the toughness may decrease, so the upper limit is 0.25.
%. Si is effective as a deoxidizer for killed steel,
Particularly in the present invention, it is necessary to secure ductility, and the lower limit was made 0.71%. If it exceeds 2.00%, the electric resistance weldability and toughness deteriorate, so 2.00%
Was set as the upper limit.

[0013] Mn has a good balance between strength and ductility, and at least 1.8% or more is required to increase strength and secure elongation. If it exceeds 2.5%, melting in a converter becomes extremely difficult, so the lower limit was made 1.8% and the upper limit was made 2.5%. P is an element that is inevitably mixed during steelmaking,
It is difficult to make it less than 0.005% because of steelmaking technology, and
If it exceeds 020%, weld cracking tends to occur particularly during electric resistance welding of ultra-high strength steel pipes, so the lower limit was made 0.005% and the upper limit was made 0.020%. S, like P, is an element that is unavoidably mixed during steelmaking, and it is difficult to make it less than 0.0005% in terms of steelmaking technology, and if it exceeds 0.0060%, weld cracking tends to occur during electric resistance welding. Was 0.0005% and the upper limit was 0.0060%. In order to further suppress the cracking during electric resistance welding with S, C, which is an element that controls the morphology of MnS.
You may add a.

In the case of killed steel, it is difficult to control Al to less than 0.001% in terms of steelmaking technology, and if it exceeds 0.08%, slab cracks, internal defects due to formation of oxide-based giant inclusions, etc. Therefore, the lower limit was made 0.001% and the upper limit was made 0.08%. N is an element that is inevitably mixed in during steelmaking, but it is difficult to control it to less than 0.002% in terms of steelmaking technology, and if it exceeds 0.005%, the strength increasing effect of Ti and B is obstructed and the strength becomes insufficient. Therefore, the lower limit was made 0.002% and the upper limit was made 0.005%. Mo suppresses ferrite transformation, has an effect of grain refining, and has a characteristic of precipitation strengthening, and is effective in increasing the strength and toughness by obtaining a bainite structure containing a part of martensite by heat treatment after pipe forming. Therefore, 0.1% or more is contained. However, even if added over 1.0%, the improvement of the effect is small and the ductility is deteriorated, so the lower limit was made 0.1% and the upper limit was made 1.0%.

Like Mo, Ti has the effect of refining because it expands the unrecrystallized γ region in hot rolling, and strengthens precipitation.
It is an element that increases the strength of the steel material and is effective in the production of ultra-high-strength electric resistance welded steel pipe, so 0.01% or more is contained. However, if it exceeds 0.05%, the ductility is impaired, so the lower limit was made 0.01% and the upper limit was made 0.05%. B is an essential element for delaying the ferrite transformation in the cooling process to obtain a high-strength transformation structure, but even in the composition of the steel of the present invention, if it is less than 0.001%, the strength becomes insufficient, and
If the content exceeds 003%, the ductility is remarkably reduced, so the lower limit was made 0.001% and the upper limit was made 0.003%.

Nb has the same effect as Ti and has the effect of preventing softening of the heat-affected zone during joint welding, so it is included. However, even if the content of 0.05% or more is contained, the effect is saturated and the toughness is rather deteriorated.
%. If necessary, one or more of Cr and V may be contained. The reasons for limiting the individual components are shown below. When Cr is contained, welding defects due to oxides of Cr easily occur in ERW pipe making, and cumbersome inert gas seal welding is required.
Therefore, it is desirable not to contain it. However, when the inert gas sealing technology has been established, Cr is a relatively economical component, suppresses the formation of ferrite, and obtains a bainite structure partially containing martensite by normalizing after pipe forming. 0.2% because it is effective in increasing strength
The above is included. However, if 1.0% or more is contained, the toughness of the welded portion deteriorates, so the lower limit is 0.2% and the upper limit is 1.
It was set to 0%. V improves the strength of the electric resistance welded steel pipe through the formation of precipitates, has the effect of preventing the softening of the joint weld, and is included. However, if the content exceeds 0.10%, the toughness of the electric resistance welded portion deteriorates, so the upper limit was made 0.10%.

Next, the manufacturing process will be described. The manufacturing process of the present invention is shown in FIGS. Claims 1, 2, 6 and 7 are the steps of FIG. 1, claim 3 is the step of FIG.
Is the step of FIG. 3, claim 5 is the step of FIG.
9 is manufactured by the process of FIGS. 2 to 4 may be repeated several times depending on the working ratio of the drawn tube. According to the present invention, the steel having the above components is heated to 1150 ° C. or higher during hot plate thickness rolling (hereinafter referred to as hot rolling) to 950 ° C.
It is desirable to finish the finish rolling below the Ar ₃ transformation point. The heating at 1150 ° C. or higher is for sufficiently performing solid solution of Ti.

At the time of hot rolling, the steel having the above components is heated to 950 ° C. or less Ar
It is desirable to finish rolling at _three or more transformation points. This is necessary especially when an improvement in toughness is desired and when a low strength steel plate is obtained to facilitate pipe making. 950
If the temperature exceeds ℃, there is no rolling in the non-recrystallized region, so the strength and ductility deteriorate. If it is less than the Ar ₃ transformation point, the two-phase rolling causes the strength to increase, but the ductility significantly decreases. Therefore, by finishing rolling the steel having the above-mentioned components at 950 ° C. or lower and at the Ar ₃ transformation point or higher during hot rolling, and subsequently winding it under the conditions of the present invention, it is possible to easily manufacture the steel in the post-process and to obtain low strength and excellent ductility. It can be a material.

If the coiling temperature is 400 ° C. or higher, it is not quenched and the ductility necessary for pipe making can be secured, but it is preferably 450 ° C. or higher in consideration of the temperature variation in manufacturing. Also Mo,
The precipitation strengthening of Ti becomes maximum at about 600 ° C, and if the coiling temperature is 600 ° C or higher, the cooling rate in the coil is close to the furnace cooling, so precipitation of Mo etc. is overaged and ferrite precipitates. It is possible to manufacture a steel sheet having relatively low strength and ductility. However, the upper limit is preferably 700 ° C. because the strength changes greatly in the two-phase region. The steel sheet manufactured in this manner has sufficient ductility for forming an electric resistance welded pipe. It should be noted that although FIGS. 1 to 4 do not include a pickling step after hot rolling, they may be carried out depending on the application because they are effective for improving the skin of the product.

In the present invention, normalization is performed at least once. The reason for normalizing is as follows. The electric resistance welded part is rapidly cooled to have a martensite structure, and Mn, P, S, etc. are solid-dissolved while segregated in the austenite grain boundaries, so that the toughness is poor. Further, if this is cold-rolled, there is a problem that the ductility and the toughness are significantly reduced due to the influence of processing strain. In order to improve this, normalization to once convert to austenite is necessary. The normalization is that the structure of the welded part and the base metal part, which have the martensitic structure, is composed mainly of a uniform bainite structure, a low yield ratio of about 70% is obtained, and the ductility is large and the work hardening is large and the high strength is high. It is also done to obtain a steel pipe.

The normalization is carried out by heating to the Ac ₃ point or more and austenitizing, and then cooling in the same manner as air cooling to obtain a bainite-based structure containing a part of ferrite and martensite. The work hardening margin is increased to increase the strength. The normalizing temperature is preferably Ac ₃ + 20 ° C. or higher in consideration of temperature variation, and the upper limit is preferably Ac ₃ + 70 ° C. or lower in order to maintain fine grain and balance strength ductility. Also, the air cooling here has a cooling rate up to 200 ° C of 1
It is in the range of 0 to 150 ° C./minute. According to claims 1 and 2 and claims 7 and 8, normalization is performed after the electric resistance welded pipe in order to improve the toughness of the electric resistance welded portion.

Claims 3 to 5 and Claims 8 and 9
Performs drawing to obtain a special high-precision steel pipe. When the pipe is drawn, the ductility and toughness are further deteriorated when the normalization is not performed, and therefore the normalization process is essential. The third aspect of the present invention is a manufacturing process in which the processing rate of the drawn tube is small and the required ductility and toughness can be secured without the tube being drawn. As shown in FIG. The heat treatment of the raw pipe after ERW pipe is to remove the processing strain caused by cold working during pipe making, soften the quench-hardened part of the ERW welded part, and improve the ductility and toughness for elongation. However, in the heat treatment of the blank tube in the case of FIG. 2, since there is no heat treatment after the tube is drawn, normalization is performed.

Claim 4 is a case where the processing rate of the drawn pipe is large and it is difficult to secure the required ductility and toughness with the drawn pipe.
As shown in (3), after the tube is stretched, annealing or normalization is performed as a final heat treatment to recover ductility and toughness. Normalizing is performed for the heat treatment of the tube. In the method of annealing the final heat treatment, the ductility and toughness are recovered and Mo and Ti are precipitated,
Since a high-strength steel pipe having a yield ratio of 90% or more can be obtained, there is an advantage that the strength of the final product can be adjusted by the annealing temperature.

According to a fifth aspect of the present invention, as shown in FIG. 4, annealing is performed after pipe forming, and normalization is performed after expanding. When annealing is carried out after pipe forming, if the annealing temperature is 500 ° C. or higher, sufficient recovery of ductility and toughness for elongation can be obtained.
Up to an Ac ₁ point of about 730 ° C., the strength is largely reduced and the ductility is increased, so that the processing becomes easy, which is desirable. Since the material of the present invention can be softer than normal in the case of annealing, this method is suitable because it has a high pipe drawing rate and can be drawn many times. The tube is drawn by cold drawing using a die and plug. Normalize after tube drawing.

[0025]

EXAMPLES Table 1 shows conditions and results for producing electric resistance welded steel pipes of size φ42.7 × t3.0 mm by the conventional method and the method of the present invention.

[0026]

[Table 1]

[0027]

[Table 2]

The cold-expanded tube here was drawn into a circular cross-section by using a die and a plug. The cold pipe drawing ratio indicates the decreasing ratio of the pipe cross-sectional area before and after the pipe drawing. The strength and elongation are tensile test results, and the ductile fracture surface ratio of the electric resistance welded portion is -40.
It is a Charpy test result in ° C. The presence or absence of the HAZ (heat affected zone) structure in the welded part was judged by the microstructure of the final product.

In the present invention, a strength of 1,080 to 1,450 MPa can be achieved, and strength × elongation showing a strength-elongation balance is greatly improved as compared with the conventional material. Therefore, if the strength is the same, the ductility is superior to that of the conventional material. This is mainly due to the effects of Si and Mn. Further, according to the present invention, the microstructure of the base material portion and the electric resistance welded portion is uniform (without HAZ) and is mainly composed of bainite structure by applying a normalizing heat treatment after the pipe making. Therefore, in particular, as can be seen from the ductile fracture surface ratio of the welded portion, it is possible to obtain an ultra-high-strength electric resistance welded steel pipe having excellent toughness at the electric resistance welded portion.

FIG. 5 shows the conventional method No. 3 and the method of the present invention No. 5 shows the difference in the microstructure on the outer surface side of the electric resistance welded portion of FIG. The conventional method is
Although there is a heat affected zone (HAZ) structure at the time of electric resistance welding, the heat affected zone is not recognized in the method of the present invention and is uniform.
When the final product of the present invention is arc-welded, the welding is good, and the strength reduction of the softest part of the heat-affected zone is about 20 MPa or less, which is higher than that of the conventional material. By adding cold pipe drawing after heat treatment, the dimensional accuracy can be achieved with an outer diameter of ± 0.15 mm and a wall thickness of ± 0.05 mm. Also, since various sizes can be easily manufactured by cold drawing, small lots can be handled and it is economical.

[0031]

According to the present invention, 1080-1450MP
A strength of a can be achieved, and strength x elongation value is 16000.
Can be significantly improved to MPa *%. Since the normalization is performed, the base material portion and the electric resistance welded portion have a uniform microstructure mainly composed of bainite, and in particular, it is possible to obtain an ultrahigh strength electric resistance welded steel pipe having excellent toughness of the electric resistance welded portion. Further, when arc welding is performed, the welding is good, and the degree of softening of the heat affected zone is equal to or higher than that of the conventional material.

By adding cold pipe drawing,
Outer diameter ± 0.15mm and wall thickness ± 0.05mm can be achieved, and various sizes can be easily manufactured, so small lots can be handled and it is economical. Further, if necessary, by appropriately controlling the finish rolling temperature and the coiling temperature in the hot plate thickness rolling, it is possible to manufacture a raw material steel plate having low strength and excellent ductility and facilitate pipe forming. .

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a method according to claims 1 and 2 and claim 6 and 7 of the present invention.

FIG. 2 is a manufacturing process drawing of the method according to claim 3 and claims 8 and 9;

FIG. 3 is a manufacturing process diagram of the method according to claim 4 and claims 8 and 9;

FIG. 4 is a view showing a manufacturing process of the method according to claim 5 and claims 8 and 9;

FIG. 5 (a) shows the conventional method No. No. 3, (b) is the method No. of the present invention.
5 is a micrograph showing the difference in the microstructure on the outer surface side of the electric resistance welded portion of FIG.

Claims (9)

[Claims] 1. By weight, C: 0.15-0.25%, Si: 0.71-2.00%, Mn: 1.8-2.5%, P: 0.005-0.020%. , S: 0.0005 to 0.006%, Al: 0.001 to 0.08%, Ti: 0.01 to 0.05%, B: 0.0010 to 0.0030%, N: 0.002 .About.0.005%, Mo: 0.1 to 1.0%, Nb: 0.05% or less, characterized in that a hot-rolled coil consisting of the balance Fe and unavoidable elements is electrosewn and normalized. A method for producing an electric resistance welded steel pipe having excellent ductility and toughness and a tensile strength of 1080 to 1450 Mpa. 2. By weight, C: 0.15-0.25%, Si: 0.71-2.00%, Mn: 1.8-2.5%, P: 0.005-0.020%. , S: 0.0005 to 0.006%, Al: 0.001 to 0.08%, Ti: 0.01 to 0.05%, B: 0.0010 to 0.0030%, N: 0.002 To 0.005%, Mo: 0.1 to 1.0%, Nb: 0.05% or less, and further Cr: 0.2 to 1.0%, V: 0.1% or less Containing one or more of
A method for producing an electric resistance welded steel pipe having a tensile strength of 1,080 to 1,450 Mpa, which is excellent in ductility and toughness, and which comprises hot-rolling a hot-rolled coil made of e and an unavoidable element and normalizing it. 3. The method for producing an electric resistance welded steel pipe according to claim 1 or 2, wherein the pipe is expanded to obtain high dimensional accuracy, and the tensile strength excellent in ductility and toughness is 1080 to 1450 MPa. Manufacturing method of ERW steel pipe. 4. The method for manufacturing an electric resistance welded steel pipe according to claim 3, wherein annealing or normalizing is continuously performed to obtain high dimensional accuracy, and the tensile strength excellent in ductility and toughness is 1
A method for producing an electric resistance welded steel pipe of 080 to 1450 MPa. 5. The tensile strength excellent in ductility and toughness is characterized in that the hot-rolled coil according to claim 1 or 2 is electrically sewn into a pipe, and after annealing, the pipe is stretched and then normalized.
Manufacturing method of ERW steel pipe of 0 to 1450MPa. 6. By weight, C: 0.15-0.25%, Si: 0.71-2.00%, Mn: 1.8-2.5%, P: 0.005-0.020%. , S: 0.0005 to 0.006%, Al: 0.001 to 0.08%, Ti: 0.01 to 0.05%, B: 0.0010 to 0.0030%, N: 0.002 -0.005%, Mo: 0.1-1.0%, Nb: 0.05% or less The balance consists of Fe and unavoidable elements, and the microstructure is mainly the same bainite in the electric resistance welded part and the base metal part. Tensile strength excellent in ductility and toughness, which is characterized by
ERW steel pipe of 1450Mpa. 7. By weight, C: 0.15-0.25%, Si: 0.71-2.00%, Mn: 1.8-2.5%, P: 0.005-0.020%. , S: 0.0005 to 0.006%, Al: 0.001 to 0.08%, Ti: 0.01 to 0.05%, B: 0.0010 to 0.0030%, N: 0.002 To 0.005%, Mo: 0.1 to 1.0%, Nb: 0.05% or less, and further Cr: 0.2 to 1.0%, V: 0.1% or less Containing one or more of
e and unavoidable elements, and the microstructure is mainly composed of the same bainite in the electric resistance welded portion and the base metal portion, and the tensile strength excellent in ductility and toughness is 1080 to 145.
0Mpa ERW steel pipe. 8. By weight, C: 0.15-0.25%, Si: 0.71-2.00%, Mn: 1.8-2.5%, P: 0.005-0.020%. , S: 0.0005 to 0.006%, Al: 0.001 to 0.08%, Ti: 0.01 to 0.05%, B: 0.0010 to 0.0030%, N: 0.002 -0.005%, Mo: 0.1-1.0%, Nb: 0.05% or less The balance consists of Fe and unavoidable elements, and the microstructure is mainly the same bainite in the electric resistance welded part and the base metal part. The outer diameter accuracy is ± 0.10 mm and the wall thickness accuracy is ± 0.05 mm, and the tensile strength with excellent ductility and toughness is 1
ERW steel pipe of 080 to 1450Mpa. 9. By weight, C: 0.15-0.25%, Si: 0.71-2.00%, Mn: 1.8-2.5%, P: 0.005-0.020%. , S: 0.0005 to 0.006%, Al: 0.001 to 0.08%, Ti: 0.01 to 0.05%, B: 0.0010 to 0.0030%, N: 0.002 To 0.005%, Mo: 0.1 to 1.0%, Nb: 0.05% or less, and further Cr: 0.2 to 1.0%, V: 0.1% or less Containing one or more of
e and unavoidable elements, the microstructure is mainly the same bainite in the electric resistance welded part and the base metal part, and the outer diameter accuracy is ±
Tensile strength with excellent ductility and toughness characterized by satisfying thickness accuracy of ± 0.05 mm at 0.10 mm is 1080
ERW steel pipe of ~ 1450Mpa.