WO2009148193A1

WO2009148193A1 - Steel plate excellent in sour resistance and steel pipe for linepipes

Info

Publication number: WO2009148193A1
Application number: PCT/JP2009/060721
Authority: WO
Inventors: 澤村充; 村木太郎; 原卓也; 朝日均
Original assignee: 新日本製鐵株式会社
Priority date: 2008-06-06
Filing date: 2009-06-05
Publication date: 2009-12-10
Also published as: BRPI0915520B1; JPWO2009148193A1; CN102057070B; CN102057070A; JP4719313B2; BRPI0915520A2

Abstract

Provided are a steel plate excellent in sour resistance and a steel pipe for linepipes. The steel plate and the steel pipe are characterized by containing by mass C: 0.01 to 0.08%, Si: 0.10 to 0.50%, Mn: 1.00 to 1.50%, Ti: 0.005 to 0.030%, Nb: 0.01 to less than 0.04%, Ca: 0.0010 to 0.0040%, P: 0.015% or less, S: 0.0008% or less, O: 0.0020% or less, Al: 0.040% or less, with the balance being Fe and impurities, and are characterized in that the contents (in mass%) of Al and Si satisfy the relationships: Al < 0.005% and 0.25% < Si, or the relationships: Al > 0.005 and Al + 0.1Si > 0.03% and the contents (in mass%) of S, O, Si, and Ca satisfy the relationships: S/Ca < 0.33 and O/Si < 0.005.

Description

Description Title of Invention

Steel sheet and line pipe excellent in sour resistance

The present invention is a high-strength steel plate that is resistant to hydrogen-induced cracking in an environment containing hydrogen sulfide (H ₂ S), that is, excellent in sour resistance, and is used mainly for transportation of oil and natural gas. It relates to steel pipes for strength line pipes. Background art

Steel pipes used for sour oils containing hydrogen sulfide, line pipes for transporting sour gas, and steel pipes used in pipeline accessory equipment are required to have sour resistance. The sour resistance refers to hydrogen-induced crack resistance (HIC resistance) and stress crack resistance (SSCC resistance) in a corrosive environment containing hydrogen sulfide. In addition, steel sheets are being strengthened from the perspective of improving transportation efficiency and reducing costs by reducing the thickness, and steel sheets are required to have high toughness in consideration of use in cold regions. Has been.

For such problems, for example, Patent Documents 1 and 2 have proposed a method for producing a high-strength steel sheet with improved low-temperature toughness and sour resistance. By reducing the content of C and A 1 and adding Ti, embrittlement due to the hard phase is suppressed, and intragranular transformation is promoted to suppress toughness reduction. The addition of a controls the morphology of M n S and improves sour resistance.

Furthermore, MnS stretched in the rolling direction of the steel plate is the cause of the reduction in sour resistance. For this reason, for example, Patent Documents 3 and 4 propose steel sheets in which the elongation of M n S is suppressed by controlling the Ca content, the O content, and the S content. In addition to sulfide inclusions such as M n S, steel sheets and steel pipes that suppress the coarsening of N b _ T i _C— N inclusions that are the origin of HIC are, for example, patents Prior art document proposed in Document 5

Patent Literature

Patent Document 1 Japanese Patent Application Laid-Open No. 0 6-2 9 3 9 1 8

Patent Document 2 Japanese Patent Application Laid-Open No. 0 7 — 2 3 3 4 1 5

Patent Document 3 Japanese Patent Application Laid-Open No. 0-7 — 2 4 2 9 4 4

Patent Document 4 Japanese Patent Laid-Open No. 2 0 0 0-1 0 9 9 4 7

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Patent Document Japanese Patent Laid-Open No. 2 0 0 6 — 6 3 3 5 1 Patent Summary of the Invention

Problems to be solved by the invention

If the elongation of M n S is suppressed by reducing the amount of S and adding Ca, the thermal resistance of the steel sheet can be improved. However, even when the S content is lowered, for example, cracks due to HIC may occur in some thick steel plates and steel pipes. The present invention has been made in view of such a situation, and aims to propose a steel plate excellent in sour resistance and a steel pipe for a line pipe. Means

The present inventors conducted an investigation to clarify the cause of the occurrence of HIC in a steel sheet with reduced S content and addition of Ca. As a result, the amount of S is reduced to 8 ppm or less, and the steel sheet with added Ca Regardless, we found that the starting point of HIC is MnS stretched over 50 m. Therefore, the present inventors further examined this cause and concluded that deoxidation was inappropriate, so that Ca was an oxide and MnS was coarsened. It was.

Furthermore, when A 1 is added to enhance deoxidation, a mixture of martensite and austenite (MA) is likely to occur, especially in the weld heat affected zone (HA Z). It has been found that toughness is reduced. When the toughness is required, the present inventors have succeeded in reducing A 1, adding an appropriate amount of S i to enhance deoxidation, and suppressing M n S stretching.

The present invention has been made based on such knowledge, and the gist thereof is as follows.

(1) By mass%

C: 0 • 0 1 0.0 0.08%,

S i: 0-1 0 0. 5 0,

M n: 1 00 to 1.5 50%,

T i: 0 • 0 0 “

O ~ 0.0 3 0%,

N b: 0 • 0 1% or more, 0 • 0 4 7 or less,

C a: 0 0 0 1 0 to 0 • 0 0 4 0%

Containing

P: 0 • 0 1 5% or less,

S: 0 • 0 0 0 8% or less,

○: 0 • 0 0 2 0% or less

A 1: 0 0 40 0% or less

The balance consists of Fe and impurities, and the content [mass%] of A 1 and S i is A 1 ≤ 0. 0 0 5% and 0.25% ≤ S 1,

Or

A 1> 0. 0 0 5% and one of A 1 + 0. 1 S i ≥ 0. 0 3% is satisfied, and the contents of S, O, S i, and C a [mass%] But

,

S / C a≤ 0. 3 3,

O / S i ≤ 0. 0 0 5

A steel plate with excellent sour resistance characterized by satisfying

(2) The steel sheet having excellent thermal resistance according to the above (1), wherein the amount of A 1 is limited to 0.020% or less in terms of mass%.

(3) The steel plate having excellent sour resistance as described in (1) or (2) above, wherein the amount of A 1 is limited to 0.0 0 0% or less by mass%.

(4) The steel sheet having excellent sour resistance as described in (3) above, wherein the Si amount is 0.225 to 0.40% by mass%.

(5) The Nb content is 0.01 to 0.02% by mass%, and the heat resistance according to any one of (1) to (4) above Excellent steel plate.

(6) The amount of Ca is from 0.020 to 0.040% in terms of mass%, according to any one of the above (1) to (5), Steel sheet with excellent heat resistance.

(7) By mass%

N: 0. 0 0 8% or less

The steel sheet having excellent sour resistance as described in any one of the above (1) and (6), characterized in that it is limited to

(8) Furthermore, in mass%,

B: 0. 0 0 2 0% or less The steel sheet having excellent sour resistance as set forth in any one of (1) to (7) above, characterized by comprising:

(9) Furthermore, in mass%,

V: 0.10% or less

The steel sheet having excellent sour resistance according to any one of the above (1) to (8), characterized by comprising:

(1 0) Furthermore, in mass%,

M g: 0.0 1% or less,

R E M: 0.0 5% or less

The steel plate excellent in sour resistance as described in any one of the above (1) to (9), wherein one or both of the above are contained.

(1 1) Furthermore, in mass%,

M o: 0.05 to 0.5%,

N i: 0.05 to 0.5%,

Cu: 0.05 to 0.5%

C r: 0.05-0.5%

The steel plate having excellent sour resistance according to any one of the above (1) to (10), characterized by containing one or more of the above.

(1 2) A steel pipe for a line pipe excellent in sour resistance, wherein the base material is made of the steel plate excellent in sour resistance described in any one of (1) to (11) above. The invention's effect

In the present invention, the amount of S is reduced, the amount of O (oxygen) is reduced by the addition of an appropriate deoxidizing agent, and the addition of an appropriate amount of Ca suppresses the stretching of M n S. According to the present invention, it is possible to reliably prevent the occurrence of cracks due to the HIC of steel plates and steel pipes. In addition, A 1 amount is low By reducing it, it becomes possible to improve the toughness of HAZ. Therefore, according to the present invention, it becomes possible to provide a steel plate and a steel pipe for line pipe excellent in sour resistance and further HA Z toughness, and the present invention has an extremely significant industrial contribution. . Brief Description of Drawings

FIG. 1 is a diagram showing an example of M n S stretched in the rolling direction.

Figure 2 is a diagram showing the relationship between the maximum length of M n S in steel sheets and 3 x 3 and ○ 3 1.

FIG. 3 is a view showing ranges of the Si amount and the A 1 amount of the steel sheet of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The origin of HIC generated in the steel sheet with 0.005% Ca added and the amount of S being 0.000% is M n S extending in the rolling direction existing in the center segregation part. Note that% means mass%, and the same applies hereinafter.

As illustrated in Fig. 1, the length of the stretched M n S exceeds 50 m. This steel plate has 0.039% C, 0.24% Si, 1.20% Mn, and 0.00 as the main components other than S and Ca. 2 Contains 1% of ○ (oxygen), and further contains 0.01% or less of A1 and about 0.01% of Nb and Ti.

In this way, the amount of S and the amount of O are reduced, and even if a sufficient amount of Ca is added, if the amount of oxygen exceeds 0.020%, M n S is generated in the center segregation part. To do was unpredictable.

In other words, this result means that the fixation of S by Ca becomes insufficient when the oxygen amount exceeds 0.0 0 20%. Therefore, prolapse It is considered that the acid should be strengthened. Addition of A 1 is effective for strengthening deoxidation. On the other hand, when A 1 is added, there is a concern that the low-temperature toughness will decrease due to the increase in inclusions and the suppression of intragranular transformation. With the increase in the amount of A 1, MA is generated especially in HAZ, and it is thought that the low temperature toughness decreases due to this.

Therefore, the present inventors tried to enhance deoxidation by increasing the amount of Si added in order to achieve both sour resistance and low temperature toughness. On the other hand, since S 1 is an element that reduces toughness, the upper limit of the amount of Si added was also examined.

Specifically, C: 0.0 1 to 0.0 8%, M n: l. 0 0 to: 1.5 0%, T 1: 0. 0 0 5 to 0.0 3 0%, N b: 0. 0 1 to 0. 0 2%, P: 0. 0 1 5% or less, A 1: 0. 0 0 5 0% or less,! And steel plates with varying amounts of addition of ^, S and O were produced by hot rolling, and the length of M n S was measured.

A sample was taken from the location corresponding to the center segregation part of the steel sheet (12 parts in the thickness direction), and M n S was observed with a scanning electron microscope (S E M). The lengths of longitudinally extending M n S and spherical M n S present in the field of view in the range of 50 mm square were measured. The measurement was performed at 15 locations on each steel plate, and the maximum measured M n S length was taken as the maximum M n S length of the steel plate.

As a result, as shown in Fig. 2, it was found that there was a correlation between the maximum length of M n S in the steel sheet and S no C a and 〇 S i. FIG. 2 shows that when S / C a> 0.33, the elongation of M n S cannot be suppressed even if OZ S i is decreased. On the other hand, in the case of S / C a ≤ 0.33, 〇 S i decreases and the elongation of M n S is remarkably suppressed, and when OS i becomes less than 0.005, M n It can be seen that the maximum length is suppressed to 20; m or less. In addition, the resistance to corrosion is correlated with the maximum length of M n,

S / C a≤ 0. 3 3,

O / S i ≤ 0. 0 0 5

When satisfying the above, it was found that the maximum length of M n S of the steel sheet was extremely suppressed, and the crack-induced area ratio (C A R) of hydrogen-induced cracking was 0%. In addition, the relationship between S i amount and A 1 amount and sour resistance and H A Z toughness was examined in detail. C: 0.0 1 to 0.0

8%, M n: 1. 0 0 to 1. o “0% T 1: 0.0 0 5 to 0.0 3

0%, N b: 0.0 1% or more, but less than 0.0 4%, C a: 0.0 0 1 0

~ 0. 0 0 40 0%, P: 0. 0 15% or less, S: 0. 0 0

0 8% or less, 〇: Limit to 0. 0 0 2 0% or less,

S / C a≤ 0. 3 3,

O / S i ≤ 0. 0 0 5

Was satisfied, and the evaluation was made using a steel sheet in which the Si and A 1 contents were changed. The steel plates were manufactured by hot rolling, and samples were taken from the obtained steel plates to evaluate the sour resistance and HAZ toughness. For the sour resistance, we investigated the material properties of each sample in the TM 0 1 7 7 – 90 Method A environment specified by NA C E and measured the crack occurrence area ratio (C A R). In addition, HA Z toughness was evaluated by taking a sample from a steel plate, performing a heat treatment (reproducible thermal cycle test) to simulate the thermal history of HA Z, and conducting a Charpy impact test. The reproducible thermal cycle test was conducted under the condition that induction heating was performed at 1400 and the cooling time from 800 to 50:00 was 3 8 s. The Charpy impact test was performed in accordance with JI S Z 2 2 4 2.

Qualitatively explain the relationship between the S i and A 1 contents and the HA Z toughness and sour resistance. First, in the range where the S i amount is 0.25 to 0 _: 40% and the A1 amount is 0.05 50% or less (region 1 in Fig. 3), the H AZ toughness and sour resistance were found to be very good. Next, the sour resistance is very good in the range of 0.11 to 0.50% and the amount of A1 exceeding 0.020.0% (area 4 in Fig. 3). However, it was found that the HAZ toughness slightly decreased.

Next, A 1 amount is not more than 0.0 0 5%, S i amount is more than 0.4 0%, 0.5 0% or less, and A 1 amount is more than 0.0 0 5%, 0.0 In the range of 20% or less and Si content of 0.25 to 0.50% (region 2 in Fig. 3), the sour resistance is very good, but HA Z toughness is slightly reduced. I understood it. In addition, in order to improve the HAZ toughness, it was found that the upper limit of the Si amount is preferably 0.40% or less. In addition, the HA Z toughness of region 2 in Fig. 3 was found to be superior to that of region 4, which is inferior to region 1.

Furthermore, the amount of Si is 0.1% or more and less than 0 25%, and the amount of A 1 is 0.0 0.

More than 50%, 0.02% or less, and,

A 1 + 0. 1 S i ≥ 0. 0 3%

It was found that extremely good thermal resistance can be obtained within the range that satisfies the above (region 3 in FIG. 3). However, when the Si amount is 0.1% or more and less than 0.25%, the A1 amount is more than 0.050% and less than 0.02%, the amount of A1 per mass% This means that the deoxidation capacity is about 10 times that of S i.

It was also found that the HAZ toughness of region 3 was slightly better than regions 2 and 4, although it was slightly inferior to region 1. It was found that the resistance to saliency was higher in region 1, region 2 and region 4 than in region 3.

On the other hand, the amount of A 1 is less than 0.0 0 50%, the amount of Si is less than 0.25%, and the amount of A 1 is more than 0.0 0 50% and less than 0.0 2 0 0% , S i amount is 0.1 0% or more and less than 0.2 5%, A 1 + 0. IS i <0. 0 3%

In the range of, it was found that the sour resistance deteriorates compared to the areas 1 to 4.

Hereinafter, the present invention will be described in detail.

S i is the most important element in the present invention, and is used as a deoxidizing agent. On the other hand, if added excessively, H A Z toughness may be impaired. In order to secure sour resistance, it is necessary to add 1 to 0.1% or more. Furthermore, in order to reduce the amount of O and improve the sour resistance, it is preferable to add 0.25% or more. On the other hand, excessive addition of S i impairs the toughness, so the upper limit is made 0.5% or less. In order to improve HA Z toughness, the upper limit of the Si content is preferably set to 0.40% or less.

A 1 is a deoxidizing element, and is an effective element for suppressing the formation of Ca oxide and fixing S as C a S. If A 1 is added excessively, the low temperature toughness, particularly the HA Z toughness, is impaired by the formation of inclusions, so the content is limited to 0.040% or less. Since HA Z toughness is improved by reducing the amount of A 1, the upper limit is preferably made 0.020% or less. Furthermore, in order to suppress the formation of MA, and in particular to increase the low temperature toughness of HA Z, it is preferable to limit the amount to less than 0.005%.

Furthermore, if the amount of A 1 is decreased, Ca oxide may be generated and Ca S may not be generated sufficiently. In order to suppress the formation of Ca oxide, when the amount of A 1 is 0.05% or less, it is necessary to add 1 to 0.25% or more. If the amount of A 1 is more than 0.0 0 5%,

A 1 + 0. I S i ≥ 0. 0 3%

It is necessary to satisfy This improves sour resistance Can.

From the above, the content [% by mass] of A l and S i is

A 1 ≤ 0. 0 0 5%, and 0.25% ≤ S i,

Or

A 1> 0. 0 0 5% and A 1 + 0. 1 S i ≥ 0. 0 3%

It is necessary to satisfy one of these.

C a is an extremely important element that suppresses the formation of M n S and improves sour resistance. Even if the amount of S is reduced, in order to suppress the formation of M n S, addition of 0.0% or more is required. From the viewpoint of H A Z toughness, when the amount of A 1 is reduced, it is preferable to add Ca in an amount of 0.000% or more. On the other hand, if Ca is added excessively, inclusions become coarse and the toughness decreases, so the upper limit is made 0.0%.

S is an impurity that promotes the generation of M n S as a starting point of H IC as the content increases. In the present invention, the upper limit of the allowable content is set to 0.0 0 8%. In order to suppress the formation of M n S, it is preferable to reduce the content to 0.05% or less.

O is an impurity forming a Ca oxide added for controlling the form of sulfide. In the present invention, the upper limit of the allowable content is set to 0.0 0 20%. In order to effectively exhibit the effect of Ca addition and suppress the formation of M n S, the content is preferably reduced to 0.001% or less.

Furthermore, in the present invention, in order to suppress the formation of stretched M n S,

S / C a≤ 0. 3 3 and OZ S i ≤ 0. 0 0 5

It is necessary to satisfy

As described above, the present inventors have found that, when Si is added to enhance deoxidation, MnS stretching can be suppressed, and as a result, generation of HIC can be suppressed. Based on this knowledge, the maximum suppression effect of HIC In order to secure the limit, it is necessary to adjust the amount of Ca and S i to be added (mass%, the same shall apply hereinafter) in relation to the amount of S and O. Therefore, the present inventors adopted S ZC a and OZ S i as indices.

As described above, C a is fixed as C a S and suppresses the generation of M n S. Therefore, it is 0.0 0 1 0% or more, and when the amount of A 1 is reduced, 0.0 0 Add 20% or more, but set the appropriate amount of Ca to be added for S fixation by S ZC a. In the present invention, if force S / C a> 0.3 3 is defined as S ZC a ≤ 0.3 3, the amount of Ca is insufficient, and fixing S as C a S is insufficient. Become.

As described above, S i is added at least 0.1% or more, preferably 0.25% or more in order to sufficiently reduce the amount of O so that no Ca oxide is formed. Set the amount with OZ S i. In the present invention, OZ S i ≤ 0. 0 0 5 is specified. However, if ZS i> 0. 0 0 5, deoxidation by S i is insufficient, and the added Ca is an oxide. Does not contribute to the fixation of S. Note that OZ Si is more preferably less than 0.05.

Therefore, it is necessary to satisfy both S / C a ≤ 0.33 and OZ S i ≤ 0.0 0 5 in order to ensure the maximum suppression effect of H IC generation.

C is an element that contributes to increasing the strength of the steel, and it is necessary to contain 0.0 1% or more. On the other hand, if C exceeds 0.08%, coarse carbides are formed especially in the central portion, and sour resistance is lowered. Therefore, the upper limit is set to 0.08%. In order to improve toughness, 0.07% or less is preferable.

M n is an element that improves hardenability, and is added at 1.0% or more. To improve strength and toughness, 1. 10% or more is preferred Yes. On the other hand, if M n exceeds 1.5%, center segregation becomes prominent and the sour resistance is impaired. Therefore, the upper limit is set to 1.5%. In order to suppress the formation of M n S and hard phase in the central segregation part and improve the sour resistance and toughness, it is preferable to set M n to 1.40% or less.

T i is an element that forms carbonitrides and contributes to refinement of the microstructure of steel, and also forms oxides that form the nuclei of intragranular transformation. Add 0.005% or more . On the other hand, if Ding 1 exceeds 0.030%, coarse carbonitrides are produced in the center and the sour resistance is lowered, so the upper limit is set to 0.030%. Preferably, it is 0.0 0.09 to 0.0 2 1%

Nb is an element that enhances hardenability and contributes to refinement of the steel structure by forming carbonitrides, and is added in an amount of 0.01% or more. On the other hand, when 0.04% or more of Nb is added, the HA Z toughness decreases, so the upper limit is made less than 0.04%. Further, if Nb exceeds 0.02%, coarse carbonitrides are produced in the center portion and sour resistance may be lowered, so the upper limit is preferably made 0.02%. A more preferable range of the Nb amount is 0.01 2 to 0.015%.

P is an impurity, and segregates in the central part to reduce toughness. Therefore, the upper limit is set to 0.0 15%. Preferably, it is not more than 0.0 0 1%.

Furthermore, to improve sour resistance and HA Z toughness, it is preferable to limit the amount of N. N is an impurity, and when it is contained in excess, a nitride is formed in the central part and lowers the heat resistance. Therefore, the upper limit is preferably made 0.08% or less. In order to suppress the formation of nitrides and improve the HA Z toughness, the upper limit of the N content is preferably set to 0.05% or less.

V is a source of carbonitride that contributes to refinement of the steel structure. It is prime. In particular, in order to improve the strength and HA Z toughness, it is preferable to add 0.01% or more of V. However, if excessively added, coarse nitrides may be formed and HAZ toughness may be impaired, so the upper limit is preferably made 0.10% or less.

B is an element effective for improving hardenability. In particular, when excellent strength is required, it is preferable to add 0.003% or more. However, if contained excessively, sour resistance is lowered, so the upper limit is preferably made 0.0% or less.

Furthermore, you may add 1 type (s) or 2 or more types of Mo, Cr, Ni, and Cu which contribute to an improvement in intensity | strength and toughness. In order to improve the strength and toughness of the steel, it is preferable to add 0.05% or more of Mo, Cr, Ni and Cu, respectively. Ni is also effective for improving toughness, so 0.15% or more is preferably added. On the other hand, if Mo, Cr, Ni, and Cu are added in excess of 0.5%, the weldability may be impaired. Therefore, the upper limit is set to 0.5%. . Preferably, both are 0.1 to 0.4%.

Mo, Cr, Ni, and Cu are elements that contribute to the improvement of corrosion resistance and are effective in improving sour resistance. However, since they are expensive elements, the upper limit is 0.3. It is preferable to be less than%. Further, with respect to Cr, the upper limit is preferably set to less than 0.3% from the viewpoint of the toughness of the weld heat affected zone and the field weldability.

Furthermore, one or both of Mg and REM, which are effective for refinement of inclusions and control of the form of sulfide, may be added. In particular, Mg is an element that forms fine oxides, suppresses the coarsening of the crystal grains in the heat affected zone, and improves toughness. However, if Mg and REM are contained excessively, coarse inclusions may be formed and the toughness may be impaired. Therefore, the upper limit of the Mg content is preferably 0.01% or less, and the content of REM is The upper limit of the amount is preferably 0.05% or less. Since Mg and REM exhibit an effect even in a trace amount, a preferable lower limit of the content is 0.001% or more.

Next, the preferable manufacturing method of the steel plate of this invention is demonstrated.

It is preferable that the steel is melted and forged by a conventional method, the obtained steel slab is heated, hot-rolled, and then accelerated cooled. Forging is preferably continuous forging from the viewpoint of productivity.

The heating temperature of the steel slab is preferably 1 100 or more so that MnS produced during forging is dissolved. On the other hand, if the heating temperature exceeds 1300, the crystal grain size may become coarse, so the heating temperature is preferably 1300 ° C or lower.

When the finish rolling temperature of hot rolling is less than the Ar ₃ transformation point, processed ferrite may be generated and toughness may be reduced. Since the Ar ₃ transformation point varies depending on the chemical composition and air cooling rate, use a sample taken from a steel slab or a sample that has almost the same component, and use a laboratory to simulate hot rolling and air cooling. It is preferable to obtain a _three- point Ar by performing heat treatment and measuring transformation expansion.

In particular, the preferable range of the finish rolling temperature is 770 to 950. If the finish rolling temperature is 770 or more, the formation of C and Mn enriched layers in the center segregation part and the formation of a hardened phase of the metal structure are suppressed, and the resistance to hydrogen-induced cracking is improved. In order to refine the crystal grain size and improve the strength and toughness, the finish rolling temperature is preferably 950 or less.

It is preferable to perform accelerated cooling after hot rolling. If the start temperature of accelerated cooling is less than (A r ₃ transformation point 1 1 0 0), a continuous pearlite hardening phase is generated at the center segregation part, which promotes the propagation of hydrogen-induced cracking. There is. The accelerated cooling may be water cooling. Furthermore, the steel plate is formed into a tubular shape, and the seam is arc welded to form a steel pipe.

It is preferable to form the steel sheet in the UOE process. Further, from the viewpoint of productivity, submerged arc welding is preferable for arc welding of the seam portion. Example

Example 1

Steels with the composition shown in Table 1 were melted and turned into billets by a continuous forging method. Table 1 also shows the composition ratio of S ZC a and OZ S i. The obtained steel slab was hot-rolled under the rolling conditions shown in Table 2 and subjected to accelerated cooling to produce a steel plate.

table 1

Airborne means no intentional addition.

Table 2

Take a specimen from the center of the thickness of the steel sheet and measure the length of M n S in the longitudinal direction existing in the field of view of a range of 5 O mm square at 30 points for each steel sheet using SEM. did. In the hydrogen induced cracking property survey, the material property survey of each sample was conducted in the TM 0 1 7 7 — 90 Method A environment specified by NA CE, and the crack initiation area ratio (CAR ) Passed 0%. The results are shown in Table 3. Table 3

As shown in Table 3, Steel Nos. 1 to 7, which are chemical components that satisfy all the scope of the present invention, have a CAR of less than 1%, and all show that excellent HIC resistance can be obtained. On the other hand, the steel number deviating from the scope of the present invention 1 0 1 to: Of the comparative examples of 1 0 5, steel number 1 0 1 has high OZ S i, and steel number 1 0 2 does not decrease due to insufficient S i amount, and OZ S i is also high This is an example. Steel No. 1 0 3 has a high SC a, Steel No. 1 0 4 has a small amount of Ca, and Steel No. 1 0 5 has an excessive amount of S. In these steels of Comparative Examples 101 to 10: I 0 5, stretched M n S and hydrogen-induced cracks starting from the stretched M n S were observed.

These steel plates were piped in the UOE process, and the seam was submerged arc welded to produce steel pipes. A sample was taken from the steel pipe in the same manner as the steel plate, and the CAR was measured. As a result, almost the same as in Table 3, steel numbers 1 to 7 have a CAR of less than 1%, and steel numbers 1001 to 105 have hydrogen-induced cracking starting from stretched MnS. It was. '

Example 2

Steels having the composition shown in Table 4 were melted and made into billets by the continuous forging method. Table 4 also shows the composition ratio of 3 3 and 0 3 i. The obtained steel slab was hot-rolled under the rolling conditions shown in Table 2 and subjected to accelerated cooling to produce a steel plate.

A1: More than 0.0005¾, less than 0.0200, Si: Only steel with 0.10 or more and less than 0.25¾ showed the calculated value of Al + 0.ISi.

The length measurement of M n S and the investigation of hydrogen-induced cracking characteristics were performed in the same manner as in Example 1. HA Z toughness was evaluated by taking a specimen after a reproducible thermal cycle test and conducting a Charpy impact test in accordance with J I S Z 2 2 4 2. The longitudinal direction of the test piece was the width direction of the steel sheet. In addition, the regenerative heat cycle test was conducted under the condition of cooling from 8 0 00 to 5 0 00 in 38 seconds after induction heating to 1400. The Charpy impact test was conducted while changing the test temperature, and the 50% fracture surface transition temperature was obtained. The results are shown in Table 5. Table 5

As shown in Table 5, Steel Nos. 11 to 26 have a CAR of less than 1%, HA Z 50% fracture surface transition temperature is 0 and below, and sour resistance and HAZ toughness are good. is there. On the other hand, Steel No. 20:! To 2 10 is a comparative example, and sour resistance or HA Z toughness is lowered. Steel No. 2 0 1 has high OZ S i, Steel No. 2 0 2 has high S ZC a, Steel No. 2 0 3 has a large amount of S, and HA Z toughness is good, but M n S is stretched The sour resistance is reduced.

Steel No. 2 0 4 has a large amount of O and good HA Z toughness, but has low sour resistance. Steel No. 2 0 6 has low A 1 + 0. 1 Si, and Steel No. 2 0 7 has low A 1 and S i contents, so HA Z toughness is good, but sour resistance is reduced. ing.

Steel No. 20 07 has a large amount of Si, and steel No. 20 08 has a large amount of A 1, so the sour resistance is good, but the HAZ toughness is reduced. Steel No. 20 9 is an example where the Nb content is high and the HAZ toughness is reduced. Steel No. 2 1 0 has a small amount of Ca and has low sour resistance.

These steel plates were piped in the UOE process, and the seam was submerged arc welded to produce steel pipes. A sample was taken from the steel pipe in the same manner as the steel plate, and the CAR was measured. As a result, as in Table 5, steel numbers 11 to 26 had good sour resistance and good toughness in the HA Z part. On the other hand, steel numbers 2 0 1 to 2 1 0 were confirmed to have reduced sour resistance or HA Z toughness.

Claims

Claim scope Claim 1

%so,

C: 0 0 1 to 0. 0 8%,

S i: 0.10 to 0.50%,

M n: 1.0 0. to 1.550%,

T i: 0.0 0 5 to 0.0 30%,

Nb: 0.01% or more, less than 0.04%,

C a: 0. 0 0 1 0 to 0.0. 0 0 4 0%

Containing

P: 0 0 1 o “

%Less than,

S: 0 0 0 0 8% or less,

O: 0 0 0 2 0% or less,

A 1: 0.0 40% or less

The remainder consists of Fe and impurities, and

The quantity [quality]

A 1 ≤ 0. 0 0 5%, and 0.25% ≤ S i,

Or

A 1> 0. 0 0 5% and one of A 1 + 0. 1 S 1 ≥ 0. 0 3% is satisfied, and the contents of S, 0, S i, and Ca [mass%] But

S / C a≤ 0. 3 3,

O / S i ≤ 0. 0 0 5

A steel plate with excellent sour resistance characterized by satisfying

Claim 2

A 1 content is limited to 0.0 2 0 0% or less by mass% The steel plate excellent in sour resistance according to claim 1.

Claim 3

The steel sheet with excellent sour resistance according to claim 1 or 2, wherein the amount of A 1 is limited to not more than 0.050% by mass%.

Claim 4

The steel sheet having excellent sour resistance according to claim 3, wherein the amount of Si is 0.25 to 0.40% by mass%.

Claim 5

The steel sheet having excellent sour resistance according to any one of claims 1 to 4, wherein the Nb content is 0.01 to 0.02% by mass. Claim 6

The steel sheet having excellent sour resistance according to any one of claims 1 to 5, wherein the amount of Ca is from 0.0% to 20% in mass%. .

Claim 7

% By mass

N: 0. 0 0 8% or less

The steel plate having excellent sour resistance according to any one of claims 1 to 6, wherein the steel plate is excellent in sour resistance.

Claim 8

Furthermore, in mass%,

B: 0. 0 0 2 0% or less

The steel plate excellent in sour resistance according to any one of claims 1 to 7, characterized by comprising:

Claim 9

Furthermore, in mass%,

V: 0.10% or less The steel sheet having excellent sour resistance according to any one of claims 1 to 8, wherein the steel sheet contains.

Claim 1 0

Furthermore, in mass%,

M g: 0. 0 1% or less,

R E M: 0.0 5% or less

One or both of these are contained, The steel plate excellent in sour resistance of any one of Claims 1-9 characterized by the above-mentioned.

Claim 1 1

Furthermore, in the stomach%

M o: 0.0 “

O ~ 0.

o

N i: 0.0 “

o to 0.50,

C u: 0.0 5 "

~ 0.o / o,

C r: 0.0 0 to 0.5 0

1 or 2 types or more of these are contained, The steel plate excellent in sour resistance of any one of Claims 1-10 characterized by the above-mentioned.

Claim 1 2

A steel pipe for a line pipe excellent in sour resistance, wherein the base material is made of the steel plate excellent in sour resistance described in any one of claims 1 to 11.