JP2618563B2 - High strength electric resistance welded steel pipe which is hardly softened in welding heat affected zone and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to components requiring high dimensional accuracy, a heat-affected zone that is hardly softened during welding, and excellent fatigue strength, for example, various shafts such as a propeller shaft,
The present invention relates to an economical high-precision, high-strength ERW steel pipe used for a bicycle frame or the like.

[0002]

2. Description of the Related Art Thorough weight reduction and high functionality are being studied for structural members of automobiles, industrial machines, bicycles and the like, and the thickness is reduced by increasing the precision and strength.

For example, a high-strength ERW steel pipe for a propeller shaft of an automobile is disclosed in Sumitomo Metal Vol. 43-3 (199
1) Tensile strength of 70 to 80 kgf / mm by combining the components of the material and cold rolling as shown in P44 to P60
Class ² , outer diameter accuracy ± 0.18mm, wall thickness accuracy ± 0.10
mm high precision steel pipe. The bicycle frame mainly has a Cr-Mo-based tensile strength of 80 to 90 kgf.
/ Mm ² class is used.
Although an example using a resin containing structural fibers such as 3103 is also disclosed, it is very expensive.

[0004]

SUMMARY OF THE INVENTION The present invention has a higher precision and a higher strength than the prior art, and has a resistance to HAZ (heat affected zone) softening during welding for the purpose of weight reduction and high performance of parts. It is an object of the present invention to provide an economical electric resistance welded steel pipe having:

[0005]

The gist of the present invention is as follows.

(1) The component composition is C: 0.10-0.1
0.20%, Si: 0.15 to 0.50%, Mn: 1.
3 to 2.5%, P: 0.005 to 0.020%, S:
0.0005-0.0060%, Al: 0.01-0.
08%, Ti: 0.02 to 0.2%, B: 0.0010
~ 0.0030%, N: 0.002-0.005%, C
Hot rolling at 950 ° C. or lower and Ar ₃ transformation point or higher of a material steel slab containing the balance of Fe and inevitable elements containing r: 0.3 to 0.7% and Mo: 0.3 to 1.0%. Then, a hot-rolled coil wound at 450 ° C. to 700 ° C. is subjected to ERW welding to produce a high-strength ERW steel pipe having a tensile strength of 100 to 130 kgf / mm ² , which hardly softens the heat-affected zone. Method.

(2) C: 0.10 to 0.10
0.20%, Si: 0.15 to 0.50%, Mn: 1.
3 to 2.5%, P: 0.005 to 0.020%, S:
0.0005-0.0060%, Al: 0.01-0.
08%, Ti: 0.02 to 0.2%, B: 0.0010
~ 0.0030%, N: 0.002-0.005%, C
r: 0.3 to 0.7%, Mo: 0.3 to 1.0%, N
b: Finish steel slab consisting of Fe and unavoidable elements containing 0.01 to 0.10% by balance, finishing temperature 950 ° C.
Hereinafter, hot rolling is performed at an Ar ₃ transformation point or higher, and the temperature is 450 ° C. to 700 ° C.
The hot rolled coil wound at ℃ is welded by electric resistance welding and has a tensile strength of 10
A method for producing a high-strength ERW steel pipe in which a heat-affected zone is hardly softened, which is characterized by being 0 to 130 kgf / mm ² .

(3) In the ERW steel pipe according to the above (1) or (2), after the pipe is formed, the steel is subjected to strain relief annealing to have a tensile strength of 1%.
A method for producing a high-precision, high-strength ERW steel pipe, characterized by obtaining a steel pipe of 100 to 130 kgf / mm ² .

(4) In the electric resistance welded steel pipe according to the above (1) or (2), normalizing is performed after the pipe is formed, and the tensile strength is 100 to 100%.
A method for producing a high-precision, high-strength ERW steel pipe, comprising obtaining a steel pipe of S130 kgf / mm ² .

(5) C: 0.10-0.10
0.20%, Si: 0.15 to 0.50%, Mn: 1.
3 to 2.5%, P: 0.005 to 0.020%, S:
0.0005-0.0060%, Al: 0.01-0.
08%, Ti: 0.02 to 0.2%, B: 0.0010
~ 0.0030%, N: 0.002-0.005%, C
r: 0.3 to 0.7%, Mo: 0.3 to 1.0%, in an ERW steel pipe consisting of the balance Fe and unavoidable elements, after pipe forming, normalizing, annealing and cold drawing. Dimensional accuracy is ± 0.15mm or less in outer diameter and ±
0.05mm or less, tensile strength is 100-130k
A high-precision, high-strength ERW steel pipe characterized by gf / mm ² .

(6) C: 0.10-0.10
0.20%, Si: 0.15 to 0.50%, Mn: 1.
3 to 2.5%, P: 0.005 to 0.020%, S:
0.0005-0.0060%, Al: 0.01-0.
08%, Ti: 0.02 to 0.2%, B: 0.0010
~ 0.0030%, N: 0.002-0.005%, C
r: 0.3 to 0.7%, Mo: 0.3 to 1.0%, N
b: In an ERW steel pipe made of the balance of Fe and an unavoidable element containing 0.01 to 0.10%, dimensional accuracy is ± 0.15 mm in outer diameter by combining normalizing, annealing, and cold drawing after pipe forming. Below, thickness ± 0.05mm or less,
A high-precision, high-strength ERW steel pipe having a tensile strength of 100 to 130 kgf / mm ² .

(7) In the ERW steel pipe having the component composition of the above (5) or (6), normalization is performed after the pipe is formed, and then cold drawing is performed, so that the dimensional accuracy can be reduced to an outer diameter of ± 0. A method for producing a high-precision, high-strength electric resistance welded steel pipe, characterized by obtaining a steel pipe having a thickness of 15 mm or less, a thickness of ± 0.05 mm or less, and a tensile strength of 100 to 130 kgf / mm ² .

(8) In the ERW steel pipe having the component composition as described in the above (5) or (6), normalization is performed after the pipe is formed, and then cold drawing and annealing are performed, so that the dimensional accuracy is ± A method for producing a high-precision, high-strength ERW steel pipe, wherein a steel pipe having a thickness of 0.15 mm or less, a thickness of ± 0.05 mm or less, and a tensile strength of 100 to 130 kgf / mm ² is obtained.

(9) In the ERW steel pipe having the component composition as described in the above (5) or (6), annealing is performed after the pipe is formed, and subsequently, cold drawing, normalizing and annealing are combined to achieve dimensional accuracy. Outer diameter ± 0.15mm or less, wall thickness ± 0.
05mm or less, tensile strength of 100-130kgf
Precision high-strength electric resistance welded steel pipe production method, characterized in that to obtain a steel pipe is / mm ^2.

Hereinafter, the present invention will be described in detail. 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 since the required strength cannot be obtained, the lower limit is set to 0.10%. If it exceeds 0.20%, the heat-affected zone is hardened during welding such as TIG welding when used as a part, and there is a concern that the toughness may decrease. Therefore, the upper limit is set to 0.20%.

Si is effective as a deoxidizing material for killed steel, and its lower limit is set to 0.15% in order to secure strength.
On the other hand, if it exceeds 0.5%, the resistance to electric resistance welding and toughness deteriorate, so the upper limit was made 0.5%.

Mn has a good balance between strength and ductility, and must be at least 1.3% or more in order to increase strength and secure elongation. If it exceeds 2.5%, melting in the converter becomes extremely difficult, so the lower limit is 1.3% and the upper limit is 2.5%.
And

P is an element inevitably mixed during steel making, but it is difficult to make the content less than 0.005% in terms of steel making technology.
If the content exceeds 0.020%, particularly in the case of electric resistance welding of ultra-high tensile steel pipe, a welded portion is likely to be generated.
The upper limit was made 0.020%.

S is also an element inevitably mixed in steel making like P, and it is difficult to reduce the content to less than 0.0005% in steel making technology, and if it exceeds 0.0060%, a weld crack is likely to occur during electric resistance welding. Therefore, the lower limit is made 0.0005% and the upper limit is made 0.0060%. In order to further suppress cracking during electric resistance welding by S, Ca which is an element for controlling the form of MnS may be added.

In the case of killed steel, it is difficult to suppress the content of Al to less than 0.01% in terms of steelmaking technology, and if it exceeds 0.08%, cracks in slabs, internal defects due to formation of oxide-based giant inclusions, etc. Therefore, the lower limit was set to 0.01% and the upper limit was set to 0.08%.

B is an essential element for delaying ferrite transformation in the cooling process and obtaining a high-strength transformed structure. However, even in the composition of the steel of the present invention, if the content is less than 0.0010%, the strength becomes insufficient, and 0.0030% Beyond Bor
Since on-constituent is generated and ductility is significantly reduced, the lower limit is 0.001% and the upper limit is 0.00.
30%.

N is an element which is inevitably mixed during steel making. However, it is difficult in terms of steel making technology to keep the content below 0.002%, and if it exceeds 0.005%, the effect of increasing the strength of Ti and B is hindered. 0.002 lower limit to cause shortage
%, And the upper limit was made 0.005%.

Mo suppresses ferrite transformation, has an effect on grain refinement, and has a feature of strengthening precipitation. Mo is used after pipe forming to obtain a bainite structure partially containing martensite, thereby increasing the strength. Since it is effective, the content is 0.3% or more. However, even if added over 1.0%, the effect is little improved and ductility is deteriorated, so the lower limit was set to 0.3% and the upper limit was set to 1.0%.

Since Cr is a relatively economical component, it is effective in suppressing ferrite transformation, obtaining a bainite structure partially containing martensite by heat treatment after pipe formation, and increasing the strength. 3% or more is contained. In this case, if it is added in excess of 0.7%, welding defects due to oxides of Cr are likely to occur in the ERW pipe, and troublesome inert gas seal welding is required. Therefore, the upper limit is 0.7
%.

Ti, like Mo, has an effect on grain refinement in order to widen the unrecrystallized γ region in hot rolling, strengthens precipitation,
It is an element that increases the strength of the steel material and is effective for producing an ultra-high tensile strength electric resistance welded steel pipe. However, if it exceeds 0.20%, the toughness is impaired, so the lower limit was made 0.02% and the upper limit was made 0.20%.

Nb has the same effect as Ti, and has the effect of preventing the heat-affected zone from softening. Therefore, Nb is contained in an amount of 0.01% or more. However, even when 0.1% or more is added, there is almost no difference in solid solution strengthening, so the lower limit is 0.01% and the upper limit is 0.10%.
And

V enhances precipitation strengthening in the same manner as Mo and Ti, but the effect is small, and sufficient effects can be obtained with Mo and Ti.

Next, the manufacturing process will be described. The manufacturing process of the present invention is shown in FIGS. Claim 1 and Claim 2
1 is the process of FIG. 1, claim 3 is the process of FIG. 2, and claim 4 is the process of FIG. Claims 5 and 6 show FIG.
6 to FIG. In claim 7 4 steps,
In the process of claim 8 5, claim 9 is prepared in the step of FIG. In addition, although the previous process of the ERW pipe of FIGS. 4 to 6 was omitted, it is the same as that of FIGS. 1 to 3. Further, the drawing and annealing in FIGS. 5 and 6 may be repeated several times depending on the working ratio of the drawn tube. According to the present invention, it is desirable to heat the steel having the above components to 1150 ° C. or higher during hot thickness rolling, and to finish the finish rolling at 950 ° C. or lower and the Ar ₃ transformation point or higher. 1150 ° C
The heating is performed in order to sufficiently dissolve the Ti. 950 ° C or less Ar of steel of the above composition during hot strip rolling
It is desirable to finish the finish rolling at _three or more transformation points. This is necessary particularly when improvement in toughness is desired and when obtaining a low-strength steel plate to facilitate pipe making. 950
If the temperature exceeds ℃, the strength and ductility are deteriorated because there is no rolling in the non-recrystallized region. If the temperature is lower than the Ar ₃ transformation point, the strength is increased by the two-phase region rolling, but the ductility is significantly reduced. Therefore, by finishing the finish rolling at 950 ° C. or lower at the Ar ₃ transformation point or higher and hot-rolling the steel having the above-mentioned components at the Ar ₃ transformation point or lower at the time of hot plate rolling, the low-strength and ductile material which can be easily manufactured in the subsequent process is easily manufactured. Excellent material can be used.

If the coiling temperature is 400 ° C. or higher, quenching is not performed, and the ductility required for pipe making can be ensured. Also, M
The precipitation strengthening of o and Ti is maximized at about 600 ° C. If the coiling temperature is 600 ° C or higher, the cooling rate in the coil is close to the furnace cooling. Precipitation can produce a relatively low-strength and ductile steel sheet. However, in the two-phase region, the fluctuation in strength becomes large, so the upper limit was set to 700 ° C. The steel plate manufactured in this manner has sufficient ductility to form an ERW pipe. Although FIGS. 1 to 3 include a pickling step, they are not necessarily required depending on the use of the product.

The as-tube-formed product shown in the manufacturing process of FIG. 1 is economical, and a high-strength steel pipe can be obtained by work hardening at the time of forming and forming. The heat treatment after pipe forming is for removing working strain due to cold working at the time of pipe forming, softening the quenched and hardened part of the electric resistance welded part, and improving ductility and toughness, and performing annealing or normalizing. The component system of the present invention comprises, as shown in FIG.
When annealing is performed after pipe forming, ductility and toughness are recovered, and Mo and Ti are precipitated, and a high-strength steel pipe having a yield ratio of 90% or more is obtained. If the annealing temperature is 500 ° C. or higher, sufficient recovery of ductility and toughness can be obtained, and strength does not decrease much up to 650 ° C. In addition, in order to obtain a high-strength steel pipe with a low yield ratio of about 70%, a large ductility, and a large work hardening, it is necessary to continue heat treatment of the pipe after ERW pipe to make the structure of the welded part and the base metal part uniform. The normalization of FIG. 3 is performed. This is Ac3
After heating to austenite by heating above the point, the formation of ferrite is suppressed by air-cooled cooling, and a bainite-based structure partially containing martensite is formed. To increase the strength. The normalizing temperature is set to Ac3 + 20 in consideration of temperature variation.
C. or more, and the upper limit is desirably Ac3 + 70 or less in order to maintain fine grains and maintain a balance between strength and ductility. The air cooling here is performed at a cooling rate up to 300 ° C.
Range of minutes. The present invention is directed to FIG.
6 through FIG. The heat treatment of the raw pipe immediately after the ERW pipe is for removing the work strain due to the cold working during pipe making, softening the hardened and hardened portion of the ERW weld, and improving the cold workability at 500 ° C. The above softening annealing or normalizing is performed. However, when the component system of the present invention is annealed, Mo and Ti precipitate, and work hardening can hardly be expected. Therefore, claim 7
In claim 8, normalizing is subsequently performed as heat treatment of the shell after the electric resistance welded pipe. This is to cool to austenite by heating to more than the Ac3 point and then suppress the formation of ferrite by air-cooling-like cooling to form a bainite-based structure partially containing martensite. Increase work hardening allowance and increase strength. The normalizing temperature is set to Ac3 + 20 ° C. or more in consideration of temperature variation, and the upper limit is Ac3 + 70 ° C. in order to keep fine grains and secure the balance of strength ductility.
The following is desirable. The air cooling here has a cooling rate up to 300 ° C. in a range of 10 to 150 ° C./min. If the heat treatment is less than the Ac3 point, the above effects cannot be obtained, and the predetermined strength cannot be obtained.

A seventh aspect of the present invention relates to a manufacturing process in which the required elongation and toughness can be ensured with a low elongation rate of the elongate pipe, as shown in FIG. Claim 8 is a case where it is difficult to secure necessary ductility and toughness because the working ratio of the drawn tube is large, and annealing is performed after the drawn tube to recover ductility and toughness. According to a ninth aspect, annealing is performed after pipe forming, and normalizing is performed in the middle of drawing to improve strength by work hardening. Since the material of the present invention can be made softer than in normalizing in the case of annealing, this method is suitable when the drawing ratio is large and the drawing is repeated many times because the drawing is easy. Normalization is performed before the last drawing, and the strength and ductility are adjusted by the working ratio and annealing temperature of the last drawing. It should be noted that the material of the present invention can secure the strength and produce a good product even if repeated drawing and annealing are repeated several times if an appropriate annealing temperature is selected. Therefore, there is no problem even if the annealing and drawing in FIGS. 5 and 6 are repeated several times. The drawing is performed by cold drawing using a die and a plug.

[0033]

EXAMPLES Table 1 shows the size φ42.7 × t3.0 mm.
The conditions and results of the ERW steel pipe manufactured by the conventional method and the method of the present invention are shown. Here, the cold drawing was performed to have a round cross-sectional shape using a die and a plug. When the cold drawing ratio was 60% or more, annealing and drawing were repeated twice or more. Although the strength of 100 kgf / mm ² or more has not been achieved in the conventional method, it can be achieved in the present invention. When the final product of the present invention is arc welded, the welding is good,
The strength of the softest part of the heat-affected zone is superior to that of the conventional material. Further, according to the present invention, it is possible to obtain an ultra-high tensile strength electric resistance welded steel pipe having a uniform base material portion and a welded portion and an excellent balance of strength and ductility by applying normalizing heat treatment after pipe forming. By adding a cold drawing process after heat treatment, the dimensional accuracy has achieved outer diameter ± 0.15mm and wall thickness ± 0.05mm. And economical. In the present invention, since the end of the manufacturing process is annealing or drawing, the yield ratio is high and the fatigue strength is advantageous.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

According to the present invention, 100 kgf / mm ²
The above strength can be achieved, the welding is good in the case of arc welding, and the degree of softening of the heat-affected zone is superior to the conventional material. Further, according to the present invention, a high-strength ERW pipe having a uniform base material portion and a welded portion and an excellent balance of strength and ductility can be obtained by performing normalizing heat treatment after pipe forming.
By adding cold drawing after the heat treatment, the dimensional accuracy can achieve outer diameter ± 0.15mm and wall thickness ± 0.05mm, and various dimensions can be easily manufactured. Is economical. Further, in the present invention, since the end of the manufacturing process is annealing or drawing, the yield ratio is high, which is advantageous in terms of fatigue strength. Further, since it can be processed into an arbitrary cross section, a square tube or the like having excellent bending workability can be manufactured. In addition, if necessary, by appropriately controlling the finish rolling temperature and the winding temperature in the hot thickness rolling, it is possible to produce a low-strength, excellent ductility material steel sheet and facilitate pipe making. .

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of the method according to claim 1 of the present invention.

FIG. 2 is a manufacturing process diagram of the method according to claim 2.

FIG. 3 is a manufacturing process diagram of the method according to claim 3.

FIG. 4 is a manufacturing process diagram of the method according to claim 4, 5, or 6.

FIG. 5 is a manufacturing process diagram of the method according to claim 4, 5 or 7.

FIG. 6 is a manufacturing process diagram of the method according to claim 4, 5 or 8.

Claims (9)

(57) [Claims] 1. Composition: C: 0.10 to 0.20% Si: 0.15 to 0.50% Mn: 1.3 to 2.5% P: 0.005 to 0.020% by weight S: 0.0005 to 0.0060% Al: 0.01 to 0.08% Ti: 0.02 to 0.2% B: 0.0010 to 0.0030% N: 0.002 to 0.005% A material steel slab containing Cr: 0.3 to 0.7% Mo: 0.3 to 1.0% and the balance being Fe and unavoidable elements is hot-rolled at a finishing temperature of 950 ° C or lower and an Ar ₃ transformation point or higher. Hot-rolled coil wound at 450 ° C. to 700 ° C. is welded by electric resistance welding, and has a tensile strength of 100 to 130 kgf / mm ² , characterized in that the heat-affected zone is not easily softened. . 2. The composition of the component is: C: 0.10 to 0.20% Si: 0.15 to 0.50% Mn: 1.3 to 2.5% P: 0.005 to 0.020% by weight S: 0.0005 to 0.0060% Al: 0.01 to 0.08% Ti: 0.02 to 0.2% B: 0.0010 to 0.0030% N: 0.002 to 0.005% Cr: 0.3% to 0.7% Mo: 0.3% to 1.0% Nb: 0.01% to 0.10%, and finish steel slab consisting of Fe and unavoidable elements at a finishing temperature of 950 ° C or lower. Softening of the heat-affected zone characterized in that the hot-rolled coil hot-rolled at the Ar ₃ transformation point or higher and wound at 450 ° C. to 700 ° C. is subjected to electric resistance welding and has a tensile strength of 100 to 130 kgf / mm ^2. Manufacturing method of high strength ERW steel pipe that is difficult to perform. 3. The electric resistance welded steel pipe according to claim 1 or 2, wherein after pipe forming, strain relief annealing is performed, and the tensile strength is 100 to 1%.
A method for producing a high-precision, high-strength ERW steel pipe, comprising obtaining a steel pipe of 30 kgf / mm ² . 4. The electric resistance welded steel pipe according to claim 1, wherein normalization is performed after pipe forming, and the tensile strength is 100 to S130.
A method for producing a high-precision, high-strength ERW steel pipe, characterized by obtaining a steel pipe of kgf / mm ² . 5. The composition of the component is: C: 0.10 to 0.20% Si: 0.15 to 0.50% Mn: 1.3 to 2.5% P: 0.005 to 0.020% by weight S: 0.0005 to 0.0060% Al: 0.01 to 0.08% Ti: 0.02 to 0.2% B: 0.0010 to 0.0030% N: 0.002 to 0.005% In an ERW steel pipe containing Cr: 0.3 to 0.7% Mo: 0.3 to 1.0% and the balance being Fe and unavoidable elements, after pipe forming, normalizing, annealing, and cold drawing are performed. Dimensional accuracy is ± 0.1
A high-precision, high-strength ERW steel pipe having a thickness of 5 mm or less, a thickness of 0.05 mm or less, and a tensile strength of 100 to 130 kgf / mm ² . 6. The component composition is C: 0.10 to 0.20% Si: 0.15 to 0.50% Mn: 1.3 to 2.5% P: 0.005 to 0.020% by weight S: 0.0005 to 0.0060% Al: 0.01 to 0.08% Ti: 0.02 to 0.2% B: 0.0010 to 0.0030% N: 0.002 to 0.005% Cr: 0.3 to 0.7% Mo: 0.3 to 1.0% Nb: 0.01 to 0.10% In an electric resistance welded steel pipe composed of the balance Fe and inevitable elements, Combination of pre-annealing and cold-drawing with dimensional accuracy of outer diameter ± 0.15
A high-precision, high-strength ERW steel pipe having a thickness of at most 0.05 mm, a thickness of at most ± 0.05 mm, and a tensile strength of 100 to 130 kgf / mm ² . 7. An electric resistance welded steel pipe comprising the component composition according to claim 5 or 6, wherein normalization is performed after pipe forming, and then cold drawing is performed, so that the dimensional accuracy has an outer diameter of ± 0.
A method for producing a high-precision, high-strength ERW steel pipe, wherein a steel pipe having a thickness of 15 mm or less, a thickness of ± 0.05 mm or less, and a tensile strength of 100 to 130 kgf / mm ² is obtained. 8. An electric resistance welded steel pipe comprising the component composition according to claim 5 or 6 is subjected to normalization after pipe forming, and subsequently to cold drawing and annealing, so that the dimensional accuracy is reduced to ±
A method for producing a high-precision, high-strength ERW steel pipe, wherein a steel pipe having a thickness of 0.15 mm or less, a thickness of ± 0.05 mm or less, and a tensile strength of 100 to 130 kgf / mm ² is obtained. 9. An electric resistance welded steel pipe having the composition of claim 5 or 6 is annealed after being formed, and is continuously subjected to cold drawing, normalizing, and annealing, so that dimensional accuracy is reduced to ± 0.15mm or less, wall thickness ± 0.05mm
And a tensile strength of 100 to 130 kgf / mm ²
A method for producing a high-precision, high-strength electric resistance welded steel pipe, characterized by obtaining a steel pipe as described above.