JP2004115871A - Method for producing electroseamed steel pipe for high strength line pipe excellent in hydrogen-crack resistant characteristic and toughness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an electroseamed steel pipe for a line pipe excellent in hydrogen-crack resistant characteristic and toughness with which a problem of quality deterioration at the pipe-making time can easily be resolved while effectively using uniform and fine hot-rolled steel sheet structure before the pipe-making. <P>SOLUTION: A base stock of steel contains 0.01-0.10% C, 0.05 - 0.5% Si, 0.5-2.0% Mn, ≤ 0.03% P, ≤ 0.005% S, 0.005-0.50% Al, ≤ 0.0050% N, ≤ 0.0030% O and one or more elements among 0.005-0.1% Nb, 0.005-0.1% V, 0.005-0.1% Ti, 0.005-0.5% Mo, 0.0001-0.0030% B and 0.0005-0.0060% Ca. This steel base stock is heated to ≥ 1100°C and the hot-rolling at ≥ 50% rolling reduction ratio, is performed in non-recrystallized range of ≥ Ar<SB>3</SB>point temperature. After coiling at ≤ 660°C, the steel pipe is produced through an electroseamed steel pipe process, and this pipe is heated to 650-850°C at ≥ 3°C/s heating speed continuously with a high frequency induction heating so that the γ fraction becomes ≤ 20% at ≥ Ac<SB>1</SB>point, and after holding for ≤ 60s, the cooling is applied at 5-30°C/s cooling speed. <P>COPYRIGHT: (C)2004,JPO

Description

【００３１】
【表２】

【００３２】
【表３】

【００３３】
【表４】

【００３４】
本発明要件を満たす製造方法で製造された鋼管（発明例）はいずれも、ＡＰＩＸ６０〜Ｘ８０の要求強度特性を満たしながら、優れた耐水素割れ特性および靭性を示した。
【００３５】
【発明の効果】
本発明によれば、造管前の均一微細な熱延鋼板組織を有効に活用しつつ、造管時の材質劣化の問題を容易に解決しうる耐水素割れ特性および靭性に優れる高強度ラインパイプ用電縫鋼管が得られるという優れた効果を奏する。
【図面の簡単な説明】
【図１】電縫溶接後の熱処理条件と強度、靭性の関係の例を示すグラフである。
【図２】熱処理条件の例を示す温度パターン図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a high-strength ERW steel pipe for line pipes having excellent hydrogen cracking resistance and toughness, and more particularly, to an ERW steel pipe for high-strength line pipes having a thickness of 25 mm or less and an API X60 class or higher. The present invention relates to a method for producing an electric resistance welded steel pipe for a high-strength line pipe having excellent hydrogen cracking resistance and toughness capable of efficiently imparting hydrogen cracking resistance and low-temperature toughness.
[0002]
[Prior art]
In general, ERW steel pipe is inferior in hydrogen cracking resistance and low-temperature toughness even if the same material is used due to the difference in pipe making method compared to UO steel pipe. In this case, it is necessary to use a material having better properties, which is disadvantageous.
[0003]
As a technique to solve this disadvantage by subjecting the ERW pipe to heat treatment, in order to simultaneously provide the ERW pipe with sour resistance, low temperature toughness, and a low yield ratio, the entire ERW pipe is heated at 800 ° C or higher. A method of heating and then quenching a steel pipe has been proposed (see Patent Document 1). In this method, the component composition is C ≦ 0.12%, Mn: 0.5 to 1.4%, Si: 0.10 to 0.25%, P ≦ 0.015%, S ≦ 0.0020%, Ca: the electric resistance welded steel pipe of low carbon steel in the 0.0010 to 0.0060% in the range, and the austenitic state of the above _{a 3} transformation point or higher 800 ° C., to remove the cold distortion, it then quenching , An acicular ferrite or a low carbon bainite structure, and no tempering is performed.
[0004]
[Patent Document 1]
Japanese Patent Publication No. 6-63040
[Problems to be solved by the invention]
However, the method of Patent Document 1 Shosai, since the entire electric resistance welded steel pipe austenitic state more than ₃ transformation point or higher 800 ° C. A, controlled rolling - the pipe-making before steel tissue much trouble miniaturized by controlled cooling There is a problem that it cannot be used at all. In general, atmosphere furnace heating (so-called batch heating) is used to heat the entire tube. However, in batch heating, the temperature in the furnace varies depending on the location, and the entire tube is heated to a uniform temperature. Therefore, there is a problem that it is difficult to control the structure uniformly and finely.
[0006]
The present invention has been made in view of the above-mentioned problems of the prior art, and effectively utilizes a uniform fine hot-rolled steel sheet structure before pipe forming, and can easily solve the problem of material deterioration during pipe forming. An object of the present invention is to provide a method of manufacturing an electric resistance welded steel pipe for a high-strength line pipe having excellent cracking characteristics and toughness.
[0007]
[Means for Solving the Problems]
The present inventors can achieve the above object by rapidly heating, short-time holding, and rapidly cooling an as-formed ERW steel pipe having the same steel component composition as the UO steel pipe to a temperature range around Ac ₁ point. I wondered if there were any, and conducted the following experiment.
C: 0.05%, Si: 0.25%, Mn: 1.2%, P: 0.009%, S: 0.002%, Al: 0.033%, Nb: 0.045%, Ti : A slab having a steel composition of 0.009%, N: 0.036%, O: 0.0018%, and Ca: 0.0022% was heated to 1200 ° C, and then 70% It was rolled in the recrystallization zone and wound at 570 ° C. to form a hot-rolled coil. Using this hot-rolled coil as a material, an ERW steel pipe having an outer diameter of 24 inch (× 25.4 mm / inch) × 12.7 mm in thickness is formed, and subjected to three types of heat treatment shown in FIG. , Low temperature toughness). Short-time heating was performed by high-frequency induction heating from the outer surface, and the temperature of the outer surface of the steel pipe was measured to be the heating temperature.
[0008]
FIG. 1 shows the mechanical properties of the steel pipe after the heat treatment. As is clear from FIG. 1, the characteristics of the short-time heating were clearly different from those of the relatively long-time heating by the batch heat treatment using the atmosphere furnace. That is, the short-time heating-water cooling (: A) does not significantly change the strength even when heated to a temperature range in which the strength is normally reduced (C: batch heat treatment), and the low-temperature toughness due to pipe-forming strain. It has been found that a considerable improvement in toughness can be obtained to compensate for the deterioration. On the other hand, if cooling is performed by air cooling even after heating for a short period of time (: B), not only does the strength decrease occur in the heating temperature range on the relatively low temperature side, but yield elongation occurs due to aging considered to be strain aging. As a result, YR (yield ratio) deteriorates.
[0009]
It is not clear why these properties differed, but because of the short heating time, the difference in time between tube forming strain, relaxation of dislocations and structural change, and diffusion of interstitial solid solution elements and substitutional solid solution elements. It seems that such changes in characteristics were complicatedly related. In addition, as a result of investigating the hydrogen cracking resistance of these heat-treated materials, it was found that pipe-forming strains were improved as compared with the as-tube-formed materials due to relaxation of pipe-forming distortion.
[0010]
The present invention has been made based on the above findings, and the gist of the present invention is as follows: C: 0.01 to 0.10%; Si: 0.05 to 0.5%; Mn: 0.5 to 2.0%, P: 0.03% or less, S: 0.005% or less, Al: 0.005 to 0.050%, N: 0.0050% or less, O: 0. 0030% or less, and Nb: 0.005 to 0.1%, V: 0.005 to 0.1%, Ti: 0.005 to 0.1%, Mo: 0.05 to 0.5% , B: 0.0001% to 0.0030%, Ca: 0.0005% to 0.0060%, a steel material containing at least one of Fe and inevitable impurities is heated to 1100 ° C. or more. performs hot rolling reduction rate at the pre-recrystallization region at least the Ar ₃ point is 50% or more, coiled at 600 ° C. or less After the coil I, a steel pipe by electric resistance welded steel pipe process, followed by the steel pipe at a high frequency heating continuously 3 ° C. / s or more in the heating rate of 650 ° C. or higher 850 ° C. or less and Ac ₁ point or more A high-strength line pipe excellent in hydrogen cracking resistance and toughness characterized by heating to a temperature at which the γ fraction becomes 20% or less, holding the same for 60 s or less, and then cooling at a cooling rate of 5 to 30 ° C./s. Manufacturing method of electric resistance welded steel pipe.
[0011]
In the present invention, the steel material may further include one or more of Ni: 0.05 to 1.0%, Cu: 0.05 to 1.0%, and Cr: 0.05 to 1.0% by mass%. It may contain two or more types.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the reasons for limiting the steel composition in the present invention will be described below.
C: 0.01 to 0.10%
C must be contained in an amount of 0.01% or more to secure the strength. On the other hand, if it exceeds 0.10%, both the hydrogen cracking resistance and the toughness are reduced, so the content of C is 0.10% or less. In order to achieve a high balance of API X60 or higher and a good balance of hydrogen cracking resistance and toughness, the content is particularly preferably 0.025 to 0.07%.
[0013]
Si: 0.05-0.5%
Si requires at least 0.05% as a deoxidizing agent and a strength securing element. However, excessive addition lowers the HAZ (welding heat affected zone) toughness and is not preferable for welding, so the upper limit is set to 0.5%. .
Mn: 0.5 to 2.0%
Mn is an element necessary for increasing the strength, and 0.5% or more is added. On the other hand, if it exceeds 2.0%, not only the base material toughness is deteriorated, but also a hard segregated phase is formed to prevent hydrogen cracking. Since the characteristics are significantly deteriorated, the content is limited to the range of 0.5 to 2.0%. In order to obtain particularly excellent hydrogen cracking resistance, the content is preferably 1.2% or less.
[0014]
P: 0.03% or less P is an element that segregates at the grain boundary and lowers the grain boundary strength, and lowers the toughness of the base metal and the welded portion. And In particular, when high toughness is required, the content is preferably 0.015% or less.
S: 0.005% or less S is an element that exists in steel as a sulfide such as MnS and significantly deteriorates hydrogen cracking resistance and toughness. To suppress the effect, 0.005% or less, preferably Must be 0.003% or less.
[0015]
Al: 0.005 to 0.050%
Al is necessary for deoxidation and N fixation, and it is necessary to add 0.005% or more. On the other hand, if the content exceeds 0.050%, alumina-based inclusions increase and the hydrogen cracking resistance and toughness are impaired, so 0.050% was made the upper limit.
N: 0.0050% or less If N exceeds 0.0050%, coarse nitrides are formed to deteriorate the hydrogen cracking resistance and toughness.
[0016]
O: 0.0030% or less O is present as an inclusion, and when it is coagulated and coarsened, it acts as a starting point for hydrogen cracking, so that it is preferably as small as possible. .0030% or less. When particularly excellent hydrogen cracking resistance is required, the content is preferably 0.0020% or less.
[0017]
Further, in the present invention, one or more of the following components are added for the purpose of improving hydrogen cracking resistance, improving toughness, and increasing strength.
Nb: 0.005 to 0.1%
Nb forms fine carbonitrides and increases strength, and also works favorably in strain accumulation in hot controlled rolling to improve toughness by making the structure finer. However, if the content is less than 0.005%, there is no effect, and if it exceeds 0.1%, the toughness of the weld is unfavorably affected, so that the content is limited to 0.005 to 0.1%.
[0018]
V: 0.005 to 0.1%
V is an element having almost the same effect as Nb, but has a slightly lower precipitation hardening ability than Nb. If it is less than 0.005%, the hardening ability is poor, and if it exceeds 0.1%, the toughness of the weld is deteriorated, so the content is made 0.005 to 0.1%.
Ti: 0.005 to 0.1%
Ti is a strong nitride-forming element, and suppresses N aging by the addition of N equivalent (N% × (48/14)). Further, further addition forms fine carbides to increase the strength, and B is precipitated and fixed as BN by N in the steel, but is added so that its effect is not suppressed. If it is less than 0.005%, there is no effect, and it is particularly preferable to add (N% × (48/14)) or more. On the other hand, if added in excess of 0.1%, coarse nitrides are likely to be formed and the toughness is deteriorated.
[0019]
Mo: 0.05-0.5%
Mo has the effect of increasing the strength without causing significant toughness degradation by forming a solid solution or forming carbides. However, if it exceeds 1.0%, the effect is not only saturated but also becomes expensive. You may add in the range of 0% or less. In order to exhibit the strength increasing effect, it is preferable to add 0.05% or more.
[0020]
B: 0.0001 to 0.0030%
B, like Nb, is important for controlling the structure of the rolled material, and its effect requires the addition of 0.0001% or more. In particular, when added in combination with Nb, a synergistic effect is exhibited. Further, as a grain boundary strengthening element, it suppresses grain boundary cracking and contributes to improvement in toughness. On the other hand, even if it is added excessively, the effect is not only saturated, but also the toughness of the weld is deteriorated, so the upper limit is 0.0030%.
[0021]
Ca: 0.0005 to 0.0060%
Ca is added for the purpose of controlling the shape of the inclusions that are the starting points of hydrogen cracking into a sphere, but 0.0005% or more is required to exhibit its effect. Is not only saturated, but also forms coarse inclusions, so the content is made 0.0005 to 0.0060%.
[0022]
Further, in the present invention, one or more of the following elements can be added for the purpose of increasing strength.
Ni: 0.05 to 1.0%
Ni is an element effective for improving strength and toughness. When Cu is added, it is effective in preventing Cu cracking during rolling, but it is expensive, and even if it is added excessively, its effect is saturated, so that it is in the range of 0.05 to 1.0%. Limited to. Particularly, from the viewpoint of Cu cracking, it is preferable to add (Cu% × 0.3) or more.
[0023]
Cu: 0.05-1.0%
Cu is added to improve the strength and the resistance to hydrogen cracking, but it is necessary to add 0.05% or more in order to exert its effects. On the other hand, if it exceeds 1.0%, hot embrittlement is likely to occur. Also, the toughness is reduced, so that the content is in the range of 0.05 to 1.0%.
Cr: 0.05-1.0%
Cr is effective in increasing the strength, but if added excessively, it reduces the toughness, so Cr may be added in a range of 1.0% or less. However, if the content is less than 0.05%, the effect is not exhibited, so it is preferable to add 0.05% or more.
[0024]
Next, the reasons for limiting the process conditions will be described below.
First, the steelmaking method may be performed according to a conventional method, and the conditions thereof are not particularly limited. However, it is preferable to take measures to reduce inclusions such as levitation treatment and aggregation suppression. The center segregation may be reduced by a forging pressure during casting or a soaking furnace.
Regarding rolling, in order to improve the hydrogen cracking resistance and toughness, which are the features of the present invention, heating at 1100 ° C. or more is required before solidifying the carbide before rolling. According to the method, non-recrystallization zone rolling at a rolling reduction temperature of 50% or more with a rolling finish temperature of ₃ points or more is required as controlled rolling. At this time, even if the cast slab is continuously rolled without cooling to less than 1100 ° C., or is heated to 1100 ° C. or more while cooling from 1100 ° C. to room temperature, and then rolled after soaking, it is a feature of the present invention. Does not impair.
[0025]
Further, in order to effectively exert the effect of controlled rolling, it is necessary to form a coil at a winding temperature of 600 ° C. or less after rolling. At this time, the cooling method and the cooling rate from the end of rolling to the start of winding are not particularly limited, but it is preferable to secure a cooling rate of 10 ° C./s or more for improving toughness. An improvement in cracking characteristics can also be expected.
The obtained hot-rolled coil is made into a steel pipe in accordance with the conventional electric-resistance-welded steel pipe process. At this time, the pipe-forming strain inevitably occurs. . In order to suppress this, a pipe forming method (for example, a CBR method) that reduces pipe forming strain may be used.
[0026]
The formed steel pipe is subjected to a short-time heating-cooling process which is a feature of the present invention, continuously or after appropriate in the line. The heating rate requires a heating rate of 3 ° C./s or more in order to effectively utilize a time difference such as a structural change due to strain relaxation and diffusion of interstitial solid solution elements and substitutional solid solution elements. In order to perform high-speed heating, high-frequency heating is inevitably required. At this average heating rate, heating is performed at 650 ° C. or more and 850 ° C. or less for 60 seconds or less for the purpose of improving the characteristics. If the temperature is lower than 650 ° C., not only the improvement of toughness cannot be obtained, but also the deterioration of YR occurs and the API standard cannot be satisfied. On the other hand, if the temperature exceeds 850 ° C., the strength is reduced, so the upper limit is set to 850 ° C. However, when 850 ° C. is _one point or more of Ac, the upper limit is the temperature at which the γ (austenite) fraction during heating becomes 20% or less by volume. When the γ fraction exceeds 20%, the toughness is significantly deteriorated by rapid quenching, so that the temperature at which the γ fraction is 20% or less is set as the upper limit. The method of heating by high frequency is not particularly limited, but unidirectional heating from the outer surface may be used from the viewpoint of productivity. In this case, a temperature difference is inevitably generated between the inner and outer surfaces of the steel pipe at the time of heating due to the high-speed heating.
[0027]
The steel pipe after heating needs to be cooled at a cooling rate of 5 to 30 ° C./s. If the cooling rate is less than 5 ° C./s, not only does the strength decrease and the YR increase, but also the improvement in toughness is small. Cooling at a cooling rate of more than 30 ° C./s requires enormous costs in terms of equipment, and uniform cooling is difficult, so the upper limit was set at 30 ° C./s.
Further, the line pipe obtained by the present invention may be subjected to a surface modification or the like which is usually performed, such as a plating process for construction, since its characteristics are not impaired.
[0028]
【Example】
A steel slab having the composition shown in Table 1 was hot-rolled under the heating-rolling-cooling-winding conditions shown in Table 2, and a steel pipe was formed by an electric resistance steel pipe process using the obtained hot-rolled coil as a material. For the as-cast steel pipe and the steel pipe that was heat-treated under the conditions shown in Table 3 after the pipe formation, YS (yield strength), TS (tensile strength), YR (yield ratio = YS / TS), DWTT 85% FATT (DWTT 85% ductile fracture transition temperature) and CLR (crack length ratio which is an index of hydrogen crack resistance characteristics) were measured.
[0029]
YS, TS, YR: Measured by the test method using API 5L DWTT 85% FATT: Measured by the test method using API RP 5L3 CLR: Performed according to NACE TM-02-84 Test solution: Solution A (0.5% acetic acid + 5% NaCl) Aqueous solution, pH 2.7 ± 0.1)
Gas: 100% H ₂ S
Test temperature: 25 ° C ± 3 ° C
Test time: 96 hours The results are shown in Table 3.
[0030]
[Table 1]

[0031]
[Table 2]

[0032]
[Table 3]

[0033]
[Table 4]

[0034]
Each of the steel pipes (inventive examples) manufactured by the manufacturing method satisfying the requirements of the present invention exhibited excellent hydrogen cracking resistance and toughness while satisfying the required strength characteristics of APIX60 to X80.
[0035]
【The invention's effect】
Advantageous Effects of Invention According to the present invention, a high-strength line pipe excellent in hydrogen cracking resistance and toughness capable of easily solving the problem of material deterioration during pipe forming while effectively utilizing the uniform fine hot-rolled steel sheet structure before pipe forming. It has an excellent effect that an electric resistance welded steel pipe can be obtained.
[Brief description of the drawings]
FIG. 1 is a graph showing an example of a relationship between heat treatment conditions after electric resistance welding, strength, and toughness.
FIG. 2 is a temperature pattern diagram showing an example of a heat treatment condition.

Claims (2)

Mass%
C: 0.01 to 0.10%, Si: 0.05 to 0.5%, Mn: 0.5 to 2.0%, P: 0.03% or less, S: 0.005% or less, Al : 0.005 to 0.050%, N: 0.0050% or less, O: 0.0030% or less, Nb: 0.005 to 0.1%, V: 0.005 to 0.1% , Ti: 0.005 to 0.1%, Mo: 0.05 to 0.5%, B: 0.0001 to 0.0030%, Ca: 0.0005 to 0.0060%
A steel material containing one or more of the following, with the balance being Fe and unavoidable impurities, is heated to 1100 ° C. or more, and the reduction ratio in the unrecrystallized region of Ar ₃ points or more becomes 50% or more. After rolling and winding at 600 ° C. or less to form a coil, a steel pipe is formed by an electric resistance welded steel pipe process. Subsequently, the steel pipe is continuously heated by high frequency heating at a heating rate of 3 ° C./s or more to 650 ° C. to 850 ° C. C. or less and at _one or more Ac, heating to a temperature at which the γ fraction is 20% or less, holding at 60 s or less, and then cooling at a cooling rate of 5 to 30 ° C./s. A method for manufacturing an electric resistance welded steel pipe for a high-strength line pipe having excellent properties and toughness. The steel material further comprises
Ni: 0.05 to 1.0%, Cu: 0.05 to 1.0%, Cr: 0.05 to 1.0%
The method for producing an electric resistance welded steel pipe for a high-strength line pipe according to claim 1, which comprises one or more of the following, and is excellent in hydrogen cracking resistance and toughness.

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