JP2002194436A - Method for producing steel pipe having excellent buckling resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a steel pipe in which local buckling is hardly caused by compression and bending stress acted in the axial direction in case of a big earthquake and in the laying of a submarine pipe, and which is suitable for gas pipelines, water piping, the columns of civil engineering and construction or the like. SOLUTION: A steel sheet obtained by hot rolling steel having a composition containing, by mass%, 0.03 to 0.15% C, 0.05 to 0.5% Si and 1 to 2% Mn, and the balance substantially Fe, and in which PCM shown by the following formula (1) satisfies 0.10 to 0.20 is made into a steel pipe by cold or hot forming. After that, the steel pipe is reheated at 800 deg.C to 1,100 deg.C. Successively, the steel pipe is cooled at a cooling rate of >=5 deg.C/sec. In this way, the steel pipe in which the stress ratio (σr) as a ratio between the yield strength in the axial direction of the pipe and the stress in the case the nominal strain is 1.5% (σ1.5) is >=1.05, or the stress ratio (σr) as a ratio between the yield strength in the circumferential direction of the steel pipe and in the axial direction of the pipe and stress in the case the nominal strain is 1.5% (σ1.5) is >=1.05, and having excellent buckling resistance is produced: PCM=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5xB (1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel pipe suitable as a gas pipeline, a water supply pipe, a pillar for construction and civil engineering, and the like.

[0002]

2. Description of the Related Art Carbon steel pipes such as UOE steel pipes, electric resistance welded steel pipes, spiral steel pipes, and press-bend steel pipes and low alloy steel pipes can be manufactured in large quantities and in a stable manner. It is widely used as a pipe for transporting fluids such as gas pipelines and water pipes.

However, when a large earthquake occurs or when laying a submarine pipe, a large force such as tension, compression, or bending is applied in the longitudinal direction of the steel pipe to cause local buckling and, in some cases, cracks in the circumferential direction. May result in formation or breakage.

To cope with such measures against local buckling, Japanese Patent Application Laid-Open Nos. 3-173719, 5-65535, 5-117746, and 5-11
7747, JP-A-5-156357, JP-A-6-49540, JP-A-6-49541, JP-A-6-128641, JP-A-6-264
No. 143 and JP-A-6-264144 disclose a method of manufacturing a steel pipe in which the yield ratio, which is the ratio of yield stress to tensile strength, is reduced to improve buckling resistance.

Further, Japanese Patent Application Laid-Open Nos. 9-196243, 9-196244 and 9-316599.
In the publication, the slope of the stress-strain curve, the work hardening index (n value), and the yield ratio (Y) obtained by dividing the yield strength by the tensile strength.
A method for improving the buckling performance at the time of compression or bending deformation of a line pipe by controlling such as R) is disclosed.

[0006]

However, JP-A-3-173719, JP-A-5-65535, JP-A-5-117746, and JP-A-5-117.
747, JP-A-5-156357, JP-A-6-49540, JP-A-6-49541,
JP-A-6-128541, JP-A-6-26414
No. 3 and Japanese Patent Application Laid-Open No. 6-264144 each relate to the ability of a column to absorb plastic deformation against bending stress, and studies are being conducted to prevent the occurrence of local buckling due to the axial force of compression. Not done.

Further, Japanese Patent Application Laid-Open Nos. 9-196243, 9-196244 and 9-316599.
In any of the techniques disclosed in Japanese Patent Application Laid-Open Publication No. H11-107, the strain range in the stress-strain curve is not clear.

As described above, the prior art does not show a method of controlling the stress-strain relationship by focusing on a low strain region where the line pipe buckles. Furthermore, there is no disclosure of a technique for controlling characteristics in the circumferential direction and the longitudinal direction of the steel pipe to improve buckling resistance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is not liable to cause local buckling against a compressive or bending stress acting in an axial direction at the time of a large earthquake or laying a submarine pipe. An object of the present invention is to provide a method of manufacturing a steel pipe having excellent buckling resistance suitable for a water supply pipe, a pillar for construction and civil engineering, and the like.

[0010]

Means for Solving the Problems In order to achieve the above object, the present inventors have intensively studied the buckling performance. As a result, prevention of local buckling due to compression is the most important for improvement of buckling resistance. Yield strength and nominal distortion in the tube axis direction are: 1. It is effective to control the stress ratio (σ _r ), which is the ratio with the stress at 5% (σ _1.5 ), to an appropriate value;
Further, such a steel pipe having an appropriately controlled stress ratio (σ _r ) can be stably manufactured by subjecting a steel pipe obtained by forming a steel sheet having a specific component composition to an appropriate heat treatment. Was found.

The present invention has been made based on such findings, and has the following configuration.

[1] In mass%, C: 0.03 to 0.1
5%, Si: 0.05 to 0.5%, Mn: 1 to 2%, the balance being substantially Fe, and the following formula (1)
After in indicated by P _CM is the molded into the steel pipe between the steel to hot rolling and cold and the resulting steel sheet or heat to satisfy the 0.10-0.20, temperature steel tube: 800 ° C. ~ Yield strength and nominal strain in the axial direction of the tube characterized by reheating at 1100 ° C. and subsequently cooling at a cooling rate of 5 ° C./sec or more:
Stress ratio (σ _r ), which is the ratio to the stress at 1.5% (σ _1.5 )
The method for producing a steel pipe having excellent buckling resistance, which is 1.05 or more. P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 × B (1) [2] At mass%, C: 0.03-0 .15%, Si:
0.05 to 0.5%, Mn: 1 to 2%, the balance substantially consisting of Fe, and P represented by the following formula (1)
_After a steel sheet obtained by hot rolling a steel satisfying _CM of 0.10 to 0.20 is cold or hot formed into a steel pipe, the steel pipe is re-heated at a temperature of 800 ° C to 1100 ° C. The ratio of the yield strength in the circumferential direction and the axial direction of the steel pipe to the stress (σ _1.5 ) at a nominal strain of 1.5%, characterized by heating and then cooling at a cooling rate of 5 ° C./sec or more. A method for producing a steel pipe excellent in buckling resistance having a stress ratio (σ _r ) of 1.05 or more. P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 × B (1) [3] In the above [1] or [2], , Mass%
, Cu: 0.05-0.5%, Ni: 0.05-0.
5%, Cr: 0.05 to 0.5%, and Mo: 0.05
A method for producing a steel pipe excellent in buckling resistance, characterized by using steel containing one or more selected from the group of 0.5% to 0.5%.

[4] In the above items [1] to [3], further, by mass%, Nb: 0.005 to 0.1%, V:
0.005 to 0.1%, and Ti: 0.005 to 0.0
A method for producing a steel pipe having excellent buckling resistance, characterized by using a steel containing one or more selected from the group of 8%.

[5] In the above items [1] to [4], further, Ca: 0.0005 to 0.003 in mass%.
%, Mg: 0.0005 to 0.003%. A method for producing a steel pipe having excellent buckling resistance, characterized by using steel containing one or two kinds selected from the group of 0.0005 to 0.003%.

[0015] In these means, "substantially Fe" means, unless the effects of the present invention are lost.
It means that those containing other trace elements including unavoidable impurities can be included in the scope of the present invention.

Further, in this specification, all percentages indicating the components of steel are mass%.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention and the reasons for limiting the same will be described below.

First, the reason for limiting the stress ratio (σ _r ) will be described.

The steel pipe obtained by the production method of the present invention is a steel pipe whose stress ratio (σ _r ) is appropriately controlled in order to obtain excellent buckling resistance. Here, the stress ratio (σ _r ) is a ratio between the yield strength and the stress (σ _1.5 ) at a nominal strain of 1.5%, and if the stress ratio (σ _r ) is 1.05 or more, Since the buckling resistance during compression or bending strain imparting is improved, the stress ratio (σ _r ) needs to be 1.05 or more, and obtaining this is the most important requirement in the present invention. . The stress ratio (σ _r ) is the case where only the stress ratio (σ _r ) in the tube axis direction is 1.05 or more, and the stress ratio (σ _r ) in the steel pipe circumferential direction and the tube axis direction is 1.05 or more. It is specified in two cases.

By setting the stress ratio (σ _r ) in the pipe axis direction to 1.05 or more, local buckling due to compression or bending can be prevented, and the stress ratio (σ _r ) in the steel pipe circumferential direction can be reduced to 1.05. By doing so, it is possible to prevent local buckling when external pressure is applied in addition to bending and compression deformation when laying a submarine line pipe or the like. Therefore, for example, when used for land-based seismic line pipes and the like, when the steel pipe of the present invention that defines only the stress ratio (σ _r ) in the pipe axis direction is used for submarine pipes that are subjected to bending and external pressure during laying, the steel pipe periphery is used. Using the steel pipe of the present invention that defines the stress ratio (σ _r ) in the direction and the pipe axis direction, etc.
It is preferable to use them properly according to the situation at the time of use.

Next, the reasons for limiting the component composition range will be described.

C: If C is added in less than 0.03% or more than 0.15%, a stress ratio (σ _r ) of 1.05 or more cannot be obtained stably, and the weldability also deteriorates. I do. Therefore, in the present invention, the C content is 0.03% to 0.1%.
15%.

Si: In order to obtain sufficient strength and toughness as structural steel, 0.05% or more must be added. On the other hand, if added over 0.5%, the weldability will be degraded. Therefore, in the present invention, the amount of Si is 0.05% to
0.5%.

Mn: In order to obtain sufficient strength and toughness as structural steel, Mn must be added in an amount of 1% or more. Meanwhile, 2
%, The weldability is degraded. Therefore, in the present invention, the amount of Mn is set to 1 to 2%.

Cu, Ni, Cr, Mo: elements effective for increasing the strength, and one or more selected from the group consisting of Cu, Ni, Cr, and Mo can be added. However, in order to increase the strength, each of the elements has a content of 0.1.
Addition of not less than 0.5% is required, while addition of more than 0.5% deteriorates the toughness and weldability of the base material and the welded portion of the steel pipe. Therefore, in the present invention, Cu, Ni, C
When one or two or more selected from the group of r and Mo are added, it is preferable to add each component at 0.05 to 0.5%.

Nb, V, Ti: an element effective for improving the toughness and strength of a steel sheet or preventing slab damage during casting, and adding one or more members selected from the group consisting of Nb, V, and Ti Can be done. However, in order to improve the toughness and strength of the steel sheet, Nb: 0.005% or more,
V: 0.005% or more must be added. To improve the toughness of the steel sheet and to prevent slab damage during casting, Ti: 0.0
More than 05% is required. On the other hand, Nb: exceeds 0.1%,
Addition of V: more than 0.1% and Ti: more than 0.08% deteriorates weldability and toughness of a welded portion. Therefore, in the present invention, when one or more kinds selected from the group of Nb, V, and Ti are added, each component is Nb: 0.005 to 0.005.
0.1%, V: 0.005 to 0.1%, Ti: 0.00
It is preferable to add 5 to 0.08%.

Ca, Mg: Indispensable elements for controlling the morphology of sulfide-based inclusions, one or two selected from the group consisting of Ca and Mg can be added. However, each element is 0.0005 in order to control the morphology of sulfide inclusions.
%, On the other hand, if it exceeds 0.003%, the effect is saturated, and conversely, the cleanliness is reduced and the buckling resistance is deteriorated. Therefore, in the present invention, when one or two kinds selected from the group of Ca and Mg are added, it is preferable to add each component at 0.0005 to 0.003%.

[0028] P _CM: In the present invention, the P _CM C + Si
/ 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20
+ Mo / 15 + V / 10 + 5 × B, which is an index having a good correlation with the strength and toughness of steel. In order to obtain sufficient strength as a structure and to obtain good buckling resistance, it is necessary to use 0.1%.
10 or more are required. On the other hand, when it exceeds 0.20, buckling resistance and weldability are deteriorated. Therefore, in the present invention, P
_CM is set to 0.10 to 0.20.

Next, the reasons for limiting the steel pipe manufacturing process will be described.

[0030] The steel pipe of the present invention is obtained by heating a steel having the above-mentioned components and then hot-rolling it into a steel sheet.
Cold working by bending roll, press bend, etc., forming into a steel pipe or hot working to make a seamless steel pipe.

Next, the reasons for limiting the heat treatment conditions for steel pipes will be described.

In the present invention, a heat treatment is performed after the steel pipe is formed in the above-described steel pipe manufacturing process. At this time, in order to stably obtain a stress ratio (σ _r ) of 1.05 or more and obtain good buckling resistance, the reheating temperature is set to 800 ° C. to 1100 ° C., and the cooling rate after the heat treatment is set to 5 ° C. C / sec or more. If the reheating temperature is less than 800 degrees, sufficient strength and toughness cannot be obtained,
On the other hand, if the reheating temperature exceeds 1100 ° C., the toughness deteriorates, which is not preferable. On the other hand, if the cooling rate is less than 5 ° C./sec, it is not preferable because sufficient strength cannot be obtained.

From the above, it is possible to obtain a steel pipe which is less likely to cause local buckling and has excellent buckling resistance. The occurrence of local buckling due to the stress acting in the axial direction of the steel pipe and the brittle cracks and Breakage can be prevented, bending strain can be applied, and local buckling at the time of external pressure can be prevented.

[0034]

(Example 1) Steel having the components shown in Table 1 was heated and hot-rolled to form a steel sheet. The obtained steel sheet was subjected to cold working or hot rolling to form a steel pipe, and then subjected to the conditions shown in Table 2. Heat treatment was performed to obtain a steel pipe having an outer diameter of 600 mm. At this time,
The ratio of outer diameter to tube thickness (D / t) was varied from 35 to 60.

[0035]

[Table 1] The obtained steel pipe, stress ratio in the tube axis direction (sigma _r), determine the strain buckling of the steel pipe. In obtaining the stress ratio (σ _r ) in the tube axis direction, a tensile test in the tube axis direction was performed using a full-thickness test piece having a parallel portion width of 38 mm and a gauge length of 50 mm. The buckling strain of the steel pipe was a value obtained by dividing a buckling strain obtained by a compression test of an actual steel pipe by a value obtained by an equation: εb (buckling strain) = 35 · t / D. Table 2 shows the performance evaluation results together with the manufacturing conditions. Here, the evaluation of the buckling strain was 1.2 or better. In addition, the weldability was checked by checking for the presence of weld cracks in the circumferential weld of the steel pipe.

[0036]

[Table 2] As shown in Table 2, the stress ratio (σ _r ) in the pipe axis direction was 1.05 or more and the buckling strain was 1 in the steel pipes A1, F1, G1, and H1 in which the chemical composition and the heat treatment conditions of the steel pipe were within the range of the present invention. It can be seen that a steel pipe which is twice or more excellent in weldability and excellent in buckling resistance is obtained.

On the other hand, although the chemical composition is within the scope of the present invention, the heat treatment conditions for the steel pipe are less than the scope of the present invention.
In C1, the stress ratio (σ _r ) in the tube axis direction is 1.05
It can be seen that the buckling strain was low and the buckling resistance was poor. Further, in the steel pipes D1 and E1 whose chemical compositions are out of the range of the present invention, the stress ratio (σ _r ) in the pipe axis direction is less than 1.05 regardless of whether the heat treatment conditions of the steel pipe are in the range of the present invention or not. It can be seen that the buckling strain is low, the weldability is poor, and the buckling resistance is poor.

(Example 2) Steel having the components shown in Table 3 was heated,
A steel plate was formed by hot rolling, and the obtained steel plate was subjected to cold working or hot rolling to form a steel pipe, and then subjected to a heat treatment under the conditions shown in Table 4 to obtain a steel pipe having a pipe outer diameter of 600 mm. At this time, the ratio (D / t) between the outer diameter and the tube thickness was changed from 35 to 60.

[0039]

[Table 3] The obtained steel pipe, stress ratio in the steel pipe circumferential direction and axial direction of the tube _{(σ r C, σ r L} ), was calculated distortion buckling of the steel pipe. Stress ratio (σ _r)
C, σ _r L) is determined by using a round bar test piece with a parallel part diameter of 6 mmφ and a gauge length of 25 mm taken from the circumferential direction of an uncorrected steel pipe. The tensile test in the axial direction was performed using a full-thickness test piece having a parallel portion width of 38 mm and a distance between gauge points of 50 mm. The buckling strain of a steel pipe is obtained by calculating the buckling strain obtained by a compression test (with external pressure) of an actual steel pipe using the following equation: εb (buckling strain) = 35 ·
The value was divided by the value obtained by t / D. Table 4 shows the performance evaluation results together with the manufacturing conditions. Here, the evaluation of the buckling strain was 1.2 or more as good. In addition, the weldability was checked by checking for the presence of weld cracks in the circumferential weld of the steel pipe.

[0040]

[Table 4] From Table 4, it is the chemical composition and heat treatment conditions the stress ratio of a steel pipe A2 in steel pipe circumferential direction and a longitudinal direction that are within the scope the present invention of the steel tube _{(σ r C, σ r L} ) is 1.05 or more, strain bending seat It can be seen that a steel pipe having a ratio of 1.2 times or more, excellent weldability, and excellent buckling resistance was obtained.

On the other hand, although the chemical composition is within the scope of the present invention, the heat treatment conditions for the steel pipe are less than the scope of the present invention.
In C2, the stress ratio in the circumferential direction and the longitudinal direction of the steel pipe (σ
_r C, σ _r L) is less than 1.05, the buckling strain is low, and the buckling resistance is poor. Further, in the steel pipe D2 whose chemical composition is out of the range of the present invention, the stress ratio (σ _r C, σ _r L) in the circumferential direction and the longitudinal direction of the steel pipe is 1. regardless of whether the heat treatment condition of the steel pipe is within the range of the present invention. It is understood that the buckling strain was low, the weldability was poor, and the buckling resistance was poor.

[0042]

As described above, according to the present invention, a steel pipe excellent in buckling resistance can be obtained. Since the steel pipe obtained by the present invention has excellent buckling resistance, it is most suitable as a steel pipe used for gas pipelines, water pipes, columns for construction and civil engineering, and the like.

Further, the steel pipe of the present invention is resistant to compression and bending stress acting in the axial direction when a large earthquake or submarine pipe is laid.
Since local buckling is unlikely to occur, it is possible to prevent disasters such as damage to gas pipelines and water pipes and the outflow of internal fluid when a large earthquake occurs, or collapse due to breakage of pier pillars on a highway.

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Nobuhisa Suzuki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Takeshi Kondo 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun F-term in Honko Co., Ltd. (reference) 4K042 AA06 AA24 BA01 BA02 CA01 CA03 CA05 CA06 CA08 CA09 CA10 CA12 CA13 DA04 DC02 DE05

Claims (5)

[Claims] 1. Mass%, C: 0.03 to 0.15
% Si: 0.05 to 0.5% Mn: it contains 1-2%, the balance being substantially Fe, and the P _CM represented by the following formula (1) from 0.10 to 0. After a steel sheet obtained by hot rolling a steel satisfying No. 20 is cold or hot formed into a steel pipe, the steel pipe is reheated at a temperature of 800 ° C. to 1100 ° C., and then a cooling rate of 5 Yield strength and nominal strain in the tube axis direction characterized by cooling at a rate of at least ° C / sec.
A method for producing a steel pipe excellent in buckling resistance, wherein a stress ratio (σ _r ) which is a ratio to a stress (σ _1.5 ) at 5% is 1.05 or more. P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 × B (1) 2. Mass%, C: 0.03 to 0.15
% Si: 0.05 to 0.5% Mn: it contains 1-2%, the balance being substantially Fe, and the P _CM represented by the following formula (1) from 0.10 to 0. After a steel sheet obtained by hot rolling a steel satisfying No. 20 is cold or hot formed into a steel pipe, the steel pipe is reheated at a temperature of 800 ° C. to 1100 ° C., and then a cooling rate of 5 A cooling ratio at a rate of not less than 1 ° C./second is a stress ratio (σ _r ) which is a ratio of a yield strength in a circumferential direction of the steel pipe and a pipe axis direction to a stress at 1.5% (σ _1.5 ) at 1.5%. A method for producing a steel pipe having excellent buckling resistance of not less than 0.05. P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 × B (1) 3. The method according to claim 1, further comprising:
0.5%, Ni: 0.05 to 0.5%, Cr: 0.0
The steel according to claim 1 or 2, wherein a steel containing one or more selected from the group of 5 to 0.5% and Mo: 0.05 to 0.5% is used. A method for manufacturing steel pipes with excellent buckling properties. 4. Further, in mass%, Nb: 0.00
5 to 0.1%, V: 0.005 to 0.1%, and Ti:
One or two selected from the group of 0.005 to 0.08%
The steel containing at least one kind is used.
4. The method for producing a steel pipe having excellent buckling resistance according to any one of items 3 to 3. 5. Further, in mass%, Ca: 0.00
0.05 to 0.003%, Mg: 0.0005 to 0.003
5. The method for producing a steel pipe having excellent buckling resistance according to claim 1, wherein steel containing one or two selected from the group of% is used.