JP2003293079A - Sour resistant steel for high energy density welding and steel structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide steel which has excellent HIC (hydrogen induced cracking) resistance and strength of 5L-X65 or higher in the API standards, and in which limit CTOD (crack tip opening displacement) at -10°C is ≥0.20 mm in both of WM (weld metal) and FL (fusion lines) in a weld zone with electron beam welding or laser welding applied, and to provide a steel structure. <P>SOLUTION: The sour resistant steel for high energy density welding having excellent toughness at the weld part has chemical components containing specified steel components, and the balance iron with inevitable impurities, and satisfying the following inequalities [1] to [3] calculated by using the mass% of the chemical components, and has a bainitic structure of ≥50% in an area ratio: Si+10Al+Mo≤0.8 [1], Cu+Ni+Cr≤1.0% [2], and C≤-0.175(Si+10Al+ Mo)+0.17 [3]. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sour resistant steel material for high energy density welding and a steel structure excellent in toughness of a welded portion when electron beam welding or laser welding is applied.

A welded steel structure for a sour environment using a steel sheet according to the present invention has good weld toughness even if electron beam welding or laser welding is applied in manufacturing.
For example, electron beam welding or laser welding can be applied when laying a sour resistant line pipe using the steel sheet according to the present invention. The invention is suitable when these high energy density welding processes are applied, even in non-sour environments.

[0003]

2. Description of the Related Art In recent years, there has been a strong need to apply high energy density welding methods such as electron beam welding and laser welding in the production of welded steel structures. As an example, when laying a line pipe, application of electron beam welding is being studied as a method for circumferentially welding pipes together at the site. In electron beam welding and laser welding, it is usual to melt and join the steel sheet itself, which is the base material, under reduced pressure or atmospheric pressure without using a special filler material.
At this time, a characteristic feature is that a narrow linear weld bead as shown in FIG. 1 is formed by one-pass welding.
As shown in FIG. 2, the weld metal 2
(WM) and fusion line 4 (FL) may be required to have toughness such as Charpy impact characteristics and CTOD characteristics in which notches (6, 7) are formed.

The following three methods are roughly known as means for increasing the toughness of the weld zone of steel to which electron beam welding or laser welding is applied. (1) Inserting a filler metal or a substance equivalent thereto into the groove and welding (2) heat treating the welded portion after welding (3) optimizing the chemical composition of the base steel sheet (1), for example, As described in JP-A-60-54287, a filler material containing Ni as a main component is inserted into the abutting surface, or as described in JP-A-03-180282, the abutting surface is made of a special composition. A technique is known in which electron beam welding is performed after temporary welding with an attachment bead to optimize the chemical composition and metal structure of the welded portion. With regard to (2), for example, as described in JP-A-57-104629, a technique for optimizing the metallographic structure of the welded portion by reheating the electron beam welded portion to Ac3 point or higher and then performing appropriate cooling. It has been known. Regarding (3), JP-A-6
No. 0-162758, the N content of the base material steel plate is lowered to add Ti, or as described in JP-A-61-246345, carbon steel is used as a base material steel plate in a predetermined ratio of T.
T of a base material steel sheet containing i, N, V or containing substantially no Al as described in JP-A-01-15321.
The contents of i, N, and O are specified, and JP-A-02-77
As described in 557, there is known a technique of optimizing the chemical composition and the metal structure of the electron beam welded portion by lowering the P and S contents of the base steel sheet. Above (1) ~
Among (3), the most simple and industrially preferable is (3). In other words, there is a demand for a steel sheet that can achieve good weld zone toughness in the as-welded state of the base steel sheet without requiring any special filler material or heat treatment after welding.

For example, the following report is given as an example intended for (3). "Development of extra-thick steel plate with excellent electron beam weldability" described in Nippon Steel Technical Report 348 (1993), 32.
Then, the electron beam welded part is made acicular ferrite (A
F) It is effective to control toughness to improve the toughness, and as a steel intended for this purpose, the Ti content was reduced.
Oxide steel (low Al-Ti oxide steel) has been developed, and excellent Charpy impact properties of 100 J or more have been achieved in both WM and FL at -50 ° C. Also,
TWI Ref. 7221.02 / 95 / 886.3, “Effects of Al, Ti & V on microstructural
development in laser and electron beam steel weld
"metal" is a WM of a laser welded portion of a low O-based 0.1 wt% V-added steel having preferable Al / O and an AF structure of about 40%, and there is a possibility that good CTOD characteristics can be obtained at -70 ° C. It is shown. The above two reports show that it is effective to improve the toughness by optimizing the chemical composition of the base steel sheet and controlling the metal structure of WM and FL mainly to AF to refine the structure. There is. However,
Even by making full use of these AF generation techniques, C is generated in the FL of the welded portion to which electron beam welding or laser welding is applied.
There is no example of improving TOD characteristics. WM of these welds
In addition to FL, development of a steel sheet having excellent CTOD characteristics is desired.

The steel sheet having excellent CTOD characteristics at the welded portion to which the electron beam welding or laser welding described above is applied is promising for use as a raw material for line pipes. In this case, in addition to the toughness of the welded portion, it is necessary to have strength of API-X65 or more and hydrogen-induced crack resistance (HIC resistance). Therefore, it is strongly desired to provide a steel plate and a steel structure having the above-described composite characteristics in a high dimension.

[0007]

The present invention is excellent in hydrogen-induced cracking (HIC resistance) resistance, has strength of API standard 5L-X65 or more, and welds a welded portion to which electron beam welding or laser welding is applied. Metal (WM) and fusion line (FL)
In both cases, the limit CTOD at −10 ° C. is 0.20.
A steel plate and a steel structure having a size of not less than mm are provided.

[0008]

Means for Solving the Problems The gist of the present invention is, in mass%, C: 0.01 to 0.08% Si: 0.5% or less Mn: 1.0 to 1.6% P: 0.015 % Or less S: 0.001% or less Al: 0.001 to 0.05% Ti: 0.005 to 0.03% Ca: 0.0005 to 0.005% N: 0.001 to 0.008% O : 0.001 to 0.004%, and if necessary, in mass% Nb: 0.005 to 0.10% V: 0.005 to 0.10% REM: 0.0005 to 0.01% Zr: 0.0005-0.01% Cu: 0.05-1.0% Ni: 0.05-1.0% Cr: 0.05-1.0% Mo: 0.05-0.5% B: 0.0003 to 0.003% Mg: 0.0001 to 0.005% One or more kinds are contained, and the balance is iron and inevitable impurities. It has a chemical component composed of a substance, satisfies the following formulas [1] to [3] calculated using the mass% of the chemical component, and is composed of a bainite structure having an area ratio of 50% or more. It is a sour-resistant steel material for high energy density welding with excellent toughness in the welded part. The steel material is a concept including a steel plate and a steel pipe.

Si + 10Al + Mo ≦ 0.8 ... [1] Cu + Ni + Cr ≦ 1.0% ... [2] C ≦ −0.175 (Si + 10Al + Mo) +0.17 ... [3] Alternatively, the base material is Martensite-austenite mixed phase (MA: Martensite-Austeni) in the welded portion of steel components to which electron beam welding or laser welding is applied
te constituent) has an area ratio of 2% or less, and the inclusion particles of 0.5 to 10 μm in these welds have an average composition of 5% by mass or more of REM or /
A sour-resistant steel structure containing Zr and Zr and having a bainite structure with an area ratio of 50% or more and having excellent toughness in a welded portion to which electron beam welding or laser welding is applied. is there.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to increasing weld toughness without the need for special filler materials or post-weld heat treatments. The reasons why it is difficult to secure the CTOD characteristics in the welded part of the sour-resistant steel plate to which electron beam welding or laser welding is applied are as follows.・ It is difficult to design the WM component because it is almost determined by the chemical composition of the steel sheet. First, since the O content of WM is extremely small, the number of oxides, which are transformation nuclei of the AF structure, is reduced.
It is difficult to reduce the structure of WM by utilizing the F structure. In addition, MnS is less likely to precipitate in the steel sheet due to the extremely low S content and the addition of Ca, which are the characteristics of sour-resistant steel, and the formation of the AF structure is impeded in the weld heat affected zone (HAZ) near FL, and the fine metal structure Becomes difficult. As described above, it is difficult to make the structure finer depending on the AF structure in both WM and FL. -When making a notch in the FL, most of the notch coincides with the FL because the FL is linear. In such a case, the HAZ embrittlement region along the FL occupies most of the notch bottom, so that the toughness evaluation method is very strict. -Because it is one-pass welding, it is not possible to expect a reheating effect (structural refinement, tempering) by a post-pass like multi-pass welding.

In order to solve the above-mentioned problems, the inventors have studied in detail the factors controlling the CTOD suppression of electron beam welds using API5L-X65 to X80 grade sour line pipe steel. As a result, as shown in FIG.
We found that there is a correlation between MA area ratio and critical CTOD in M and FL. When the MA area ratio is 2% or less in WM and 4% or less in FL, both in WM and FL-
It has been found that a marginal CTOD of greater than 0.20 mm is obtained at 10 ° C. FIG. 3 is a graph showing the minimum limit CTOD value obtained by performing three CTOD tests each having a notch in the WM and the FL with respect to 10 welded portions that were electron beam welded under the same conditions. WM and F with the same weld code
The CTOD value for L indicates that it was taken from the same weld. From this weld code, the WM MA area ratio is 2
It can be read that the MA area ratio of FL is 4% or less if the percentage is less than%. Thus, the CTOD characteristics of the weld and M
Although the A area ratio has already been tried in the conventional welding method, it has not been systematically examined in the electron beam welding or the laser welding, which has a thermal history greatly different from that of the conventional welding method. MA is a locally harder phase than the matrix, and since many MAs are associated with its surroundings, it is considered that the MA acts as a starting point of brittle fracture during a CTOD test and adversely affects it. From the above examination, in order to achieve the target CTOD characteristics in both WM and FL in the welded part of sour-resistant steel to which electron beam welding or laser welding is applied, the MA area ratio of WM should be 2% or less. That is the basic guideline.

Next, the influence of the chemical composition of the steel sheet on the formation of MA in the electron beam weld was examined. As a result, MA
It was clarified that the following three component factors (unit is mass%) influence the production amount.・ C ・ Si + 10Al + Mo ・ Cu + Ni + Cr Since MA increases as these component factors increase, M
It is necessary to clarify the limit component range in which the A area ratio exceeds 2%. FIG. 4 shows that the WM of the electron beam welded portion of the steel for API 5L-X65 to X80 grade sour resistant line pipe has a MA area ratio of 2 using C and Si + 10Al + Mo.
It shows a border line exceeding%. Boundary line a is Si + 10
The upper limit of C is shown regardless of Al + Mo. The following formula must be satisfied in order to reduce the MA area ratio to 2% or less. The unit is% by mass. C ≦ 0.08 In the boundary line b, both C and Si + 10Al + Mo are linearly involved, and it is necessary to satisfy the following expression [3] in order to reduce the MA area ratio to 2% or less. The unit is% by mass. C ≦ −0.175 (Si + 10Al + Mo) +0.17 ... [3] The boundary line c represents the upper limit of Si + 10Al + Mo regardless of C. The following expression [1] needs to be satisfied in order to reduce the MA area ratio to 2% or less. The unit is% by mass. Si + 10Al + Mo ≦ 0.8 ... [1] Further, even if the MA area ratio is 2% or less in FIG. 4, the remaining component factor Cu + Ni + Cr is 1.0%.
If it exceeds, there is a risk that the MA area ratio will exceed 2%. Therefore, in order to stably suppress the MA area ratio to 2% or less, it is necessary to satisfy the following expression [2] in addition to satisfying the appropriate range of FIG. The unit is% by mass. Cu + Ni + Cr ≦ 1.0 ... [2]

Next, as a result of studying the structure refinement of a welded portion to which electron beam welding or laser welding is applied, the present inventors have found that by adding Mg to the chemical composition of the steel sheet, the austenite crystal grains of HAZ near FL are added. Found that the particles became finer. This is because a large number of ultrafine Mg-based oxides are generated, the growth of crystal grains is strongly pinned even in the vicinity of FL, and coarsening of crystal grains is suppressed. As a result, it was discovered that even in sour-resistant steel that cannot use the AF structure, it is possible to more stably improve the CTOD characteristics in FL.

With the aim of further improving the CTOD characteristics in a stable manner, the embrittlement factors of the test pieces having a CTOD value below the target of 0.20 mm were investigated in detail. As a result, it was confirmed that the inclusion particles of 0.5 to 10 μm mainly composed of oxide acted as a starting point of occurrence of brittle fracture. Therefore, an attempt was made to render the inclusion particles of such a size that adversely affect the CTOD characteristics harmless.
When inclusion particles of 0.5 to 10 μm in the welded portion contain 5% by mass or more of REM or Zr in the average composition, the fracture characteristics of the particles themselves are improved and the adverse effect on brittle fracture is reduced, and the CTOD characteristics are improved. I found that it improved.

The above is a new technique for improving the toughness of a welded portion to which electron beam welding or laser welding is applied.

Next, the reasons for limiting the chemical components will be explained. Unless otherwise specified, the welded portion described below is a welded portion to which electron beam welding or laser welding is applied.

C is required to be 0.01% or more in order to secure the strength and toughness of the base material and the welded portion. However, 0.08%
MA area ratio of the welded portion exceeds 2% and CTOD
The characteristics deteriorate. In addition, the HIC resistance of the base material deteriorates. Therefore, 0.08% is the upper limit. C is 0.08%
Even below, it is necessary to control to a low C satisfying the formula [3] depending on the amounts of Si, Al, and Mo that promote the formation of MA.

Si can be added mainly for deoxidation, but it is not essential in the present invention because it can be deoxidized by Ca, Al, Ti and the like. As shown in FIG. 4 and the equation [1], S
i is an unfavorable element because it promotes the formation of MA in the welded portion. If the Si content exceeds 0.5%, the MA of the welded portion will increase drastically and the CTOD characteristics will become unstable, so this is the upper limit.

Mn is required to be 1.0% or more in order to secure the strength and toughness of the base material and the welded portion. However, when Mn is 1.
If it exceeds 6%, center segregation during continuous casting is promoted, and toughness and HIC resistance of the base material are deteriorated at the center portion of the plate thickness of the steel sheet. Therefore, this is the upper limit.

P is an impurity element in the present invention, and is 0.015% in order to secure good base metal and weld material.
It needs to be reduced to: Particularly, from the viewpoint of sour resistance of the base material, it is preferable to reduce P that promotes center segregation as much as possible.

S is an impurity element in the present invention, and is 0.001% in order to secure good base metal and weld material.
It needs to be reduced to: Especially, HIC resistance of the base material
From the viewpoint of properties, it is necessary to strictly limit S so as not to form MnS. MnS is stretched by hot rolling and is harmful as a starting point of HIC. S is 0.00
It is preferable to reduce it to 05% or less.

Al functions as a deoxidizing element, and when Mg is added, it forms an ultrafine oxide together with Mg, and H
Contributes to the refinement of the AZ structure and enhances the FL toughness. Therefore, 0.001% or more of Al is required. On the other hand, as shown in FIG. 4 and the formula [1], Al promotes MA generation in the welded portion. If the Al content exceeds 0.05%, the MA of the welded portion will increase sharply and the toughness will become unstable like Si, so this is the upper limit.

Ti forms TiN, suppresses the coarsening of the structure during slab heating, contributes to the refinement of the structure of the steel sheet after hot rolling, and enhances the strength and toughness of the base material. Similarly, the HAZ of the weld contributes to the refinement of the structure and prevents the deterioration of the toughness of the FL.
In particular, when Mg is added, TiN is deposited on the Mg-based ultrafine oxide, forming fine particles of a composite form and M
Efficiently enhance the effect of g (pinning effect). Also, C
When a, Al and Si are small, Ti also contributes to deoxidation. In order to fulfill these roles, 0.005% or more of Ti is required. However, if the content of Ti exceeds 0.03%, excessive TiC is precipitated in the base metal or HAZ, or TiN
A part of the particles is coarsened to several μm, so that the base material and HAZ become brittle. For this reason, the upper limit of Ti is 0.03%.

Ca is added for the purpose of suppressing the formation of MnS. Since CaS is difficult to be stretched, HIC is improved as compared with MnS. Therefore, 0.0005% or more of C
a is required. Some of the added Ca may also contribute to deoxidation. However, when Ca exceeds 0.005%, Ca-based oxides increase, and these remain in the steel in a huge state where they are aggregated and united, which may cause embrittlement of the base material and HAZ. Therefore, 0.005% Ca is the upper limit.

N forms TiN and contributes to the toughness by refining the microstructure of the base material and HAZ. It is also effective to enhance the effect of Mg. Therefore, 0.001% or more of N
is necessary. However, if N exceeds 0.008%, the amount of solid solution N increases, the base material and HAZ become brittle, and the surface properties of the slab deteriorate, so this is the upper limit.

O forms an ultra-fine oxide when Mg is added to pin the crystal grain growth in the HAZ, and FL
In order to contribute to toughness, 0.001% or more is necessary. However, when O exceeds 0.004%, many oxides of several μm are generated, which may cause brittle fracture in the base material and the welded portion, so this is made the upper limit.

Next, the reasons for limiting the selection elements will be described. N
b and V can be used to increase the strength of the base material and the weld. Nb is also effective in increasing the toughness by refining the structure of the base material. To obtain these effects, Nb,
V is required to be 0.005% or more. On the other hand, Nb and V
Is more than 0.10%, the welded portion becomes brittle and the HIC resistance and weldability of the base material may deteriorate, so this is the upper limit.

REM and Zr contribute to deoxidation and desulfurization, and are effective in improving the materials of the base material and the welded portion. Inclusions of 0.5 to 10 μm in the welded portion are often composed mainly of oxide and compounded with sulfide and nitride. R in these inclusions
When EM and Zr are contained in an amount of 5% or more, the CTOD characteristics of the welded portion are improved. To do so, REM and / or Z
r is required to be 0.0005% or more in total. However, if the content of these elements exceeds 0.01%, the effect is saturated, so this is the upper limit. REM here means La, C
It is also possible to point to a lanthanoid-based element such as e and add a misch metal in which these elements are mixed.

Cu, Ni, and Cr are strengths of the base material and the welded portion,
It can be used to improve the toughness, corrosion resistance and weldability of the base material. For that purpose, 0.05% or more of each element is required.
However, it is preferable that the amount of these elements is small from the viewpoint of the CTOD characteristics of the welded portion. In order to suppress the generation of MA in the welded portion, it is necessary to adjust the sum of these elements to 1.0% or less as shown in the formula [2], with each element having an upper limit of 1.0%.

Mo is the strength of the base metal and welded portion, the toughness of the base metal,
Can be used to improve. For that purpose, 0.05% or more is necessary. On the other hand, as shown in FIG. 4 and the equation [1], Mo
Promotes MA generation in the weld as much as Si. M
If o exceeds 0.5%, the MA of the welded portion is drastically increased and the toughness becomes unstable like Si, so this is the upper limit.

B can be used to improve the strength and toughness of the base material and the welded portion. For that purpose, 0.0003% or more is necessary. However, when B exceeds 0.003%, MA of the welded part
Since the generation is remarkably promoted and the toughness is greatly deteriorated, this is the upper limit.

Mg forms a large number of ultrafine oxides with Al, and most of them form HAZ with complex precipitation of TiN.
Plays a pinning effect and contributes to FL toughness. For that purpose, 0.0001% or more is necessary. If it exceeds 0.005%, the effect of Mg saturates and brings an economical disadvantage, so this is the upper limit.

When the above selection elements are contained below the lower limit, they can be regarded as unavoidable impurities.

In order to stably achieve the sour resistance of the present invention, the chemical composition was limited to the above and the optimization of the metal structure of the steel sheet was examined. As a result, it was found that the HIC resistance is stabilized when the metal structure of the steel sheet is composed of a bainite structure having an area ratio of 50% or more. Furthermore, when the base metal has a fine structure mainly composed of bainite, it has been discovered that the HAZ structure of the welded portion to which electron beam welding or laser welding is applied has a tendency to inherit the refinement.
It was found that the CTOD characteristics of C. If the area ratio of the bainite structure of the base material is less than 50%, the above effect is small. From the above, it is effective to control the metallographic structure of the steel sheet mainly to bainite by optimizing the hardenability in the chemical composition, applying accelerated cooling after hot rolling, or performing various heat treatments. .

The steel sheet of the present invention is manufactured by adjusting the chemical composition in the steelmaking process of the steel industry and reheating the continuously cast slab to variously control each process of rolling, cooling and heat treatment. Although the present invention does not require any special regulation in the method for producing a steel sheet, from the viewpoint of sour resistance, it is preferable to take measures to reduce center segregation, such as a light reduction treatment in continuous casting and an increase in heating temperature. Further, in order to obtain a base material structure mainly composed of bainite, it is effective to apply accelerated cooling from a temperature of Ar 3 point or higher after rolling. It is also possible to perform hot charge rolling without temporarily cooling the slab.

The MA area ratio specified in the present invention is quantitatively measured by the following method, for example. The vicinity of the center of the welded area to which electron beam welding or laser welding is applied is mirror-polished and then etched using a repeller liquid to expose island-shaped MA in white, and the area ratio of the white area is analyzed by image analysis. Measured by the device. The welding conditions at this time are not particularly specified.

The average composition of inclusions of 0.5 to 10 μm specified in the present invention is quantitatively measured by the following method, for example. HAZ near the center of the welded part where electron beam welding or laser welding is applied, or near FL
Mirror-polished, and then X-ray micro analyzer (EP
(MA) is used to randomly analyze the composition of 10 or more inclusions of 0.5 to 10 μm. The detected Fe is regarded as base iron, and Fe is subtracted to calculate the weight ratio of the elements forming the inclusions. An average composition is obtained from the composition of 10 or more inclusions thus obtained.

[0038]

【Example】

[0039]

[Table 1]

[0040]

[Table 2]

Steel 1 to Steel 23 having the chemical composition shown in Table 1
The steel slab of No. 2 was heated and rolled, and then accelerated cooling was applied to promote generation of a bainite structure, and steel plates of Steel 1 to Steel 23 were produced. Table 2 shows the base material of the steel plate and the material of the welded part.

Steels 1 to 13 are steels of the present invention, and the chemical composition, base metal structure, weld structure and weld inclusions are properly controlled according to the present invention. As a result, API5L-
The strength of X65 or more, good HIC resistance, and good weld toughness are all satisfied at the same time. Steel 8 and Steel 9 are RE
Since M and Zr are added, the inclusion particles in the welded portion contain these elements in an amount of 5 mass% or more. as a result,
The welds of Steel 8 and Steel 9 have good CTOD properties. Steel 8 has a high limit CTOD despite a large MA area ratio of 1.9% in the welded portion due to high C, because inclusion particles contain 10% REM. Steel 14
-Steel 23 is a comparative steel and is inferior in HIC resistance and weld toughness because the chemical composition is not appropriate. Steel 14 has A too high C, Steel 15 has too high Si, Steel 19 has A
Since 1 and the formula [1] are too high and the formula [3] is too low relative to C, the steel 21 has the formula [1] too high, and the steel 22 has the formula [2] too high. Since the expression [3] is too low for C, the MA area ratio of the welded portion exceeds 2%,
The CTOD characteristics and Charpy characteristics of WM and FL are significantly deteriorated. Further, steel 14 has too high C, steel 16 has too high Mn, steel 17 has too high P, steel 18 has too high S, and steel 20 has too low Ca. In addition, the HIC resistance is not sufficient. Steel 1
In No. 7, since P is high, not only the HIC resistance but also the toughness of the welded portion is low.

[0043]

According to the present invention, even if a welded steel structure for sour environment is manufactured by applying electron beam welding or laser welding, the safety of the welded portion is secured. For example, when laying a sour resistant line pipe having a strength of API 5L-X65 or more using the steel sheet according to the present invention, while applying high-efficiency electron beam welding, a good weld part CTOD characteristic at −10 ° C. is obtained. To be

[Brief description of drawings]

FIG. 1 schematically shows the appearance of a welded portion to which electron beam welding or laser welding is applied.

FIG. 2 schematically shows the cutout positions of the weld metal (WM) and the fusion line (FL) of the welded portion.

FIG. 3 shows the effect of M on the WM and FL CTOD characteristics of the welded part.
A shows the influence of the area ratio.

FIG. 4 shows C and Si + that affect the WM MA area ratio of the welded portion.
The effect of 10Al + Mo is shown.

[Explanation of symbols]

1 base material 2 Weld metal (WM) 3 Heat affected zone (HAZ) 4 Weld line (FL) 5 Plate thickness 6 WM cutout 7 FL cutout

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tetsuji Kadoya             1 Kimitsu, Kimitsu-shi Mr. Nippon Steel Corporation             Tsu Steel Works (72) Inventor Masahiko Murata             1 Kimitsu, Kimitsu-shi Mr. Nippon Steel Corporation             Tsu Steel Works

Claims (13)

[Claims] 1. C .: 0.01 to 0.08% Si: 0.5% or less Mn: 1.0 to 1.6% P: 0.015% or less S: 0.001% or less Al in mass% : 0.001 to 0.05% Ti: 0.005 to 0.03% Ca: 0.0005 to 0.005% N: 0.001 to 0.008% O: 0.001 to 0.004% A welded portion containing, the balance having a chemical component consisting of iron and inevitable impurities, and further satisfying the following formulas [1] to [3] calculated using the mass% of the chemical component. Sour resistant steel for high energy density welding with excellent toughness. Si + 10Al + Mo ≦ 0.8 ... [1] Cu + Ni + Cr ≦ 1.0% ... [2] C ≦ −0.175 (Si + 10Al + Mo) +0.17 ... [3] 2. The welded part according to claim 1, further comprising one or more of Nb: 0.005 to 0.10% V: 0.005 to 0.10% in mass%. Sour resistant steel for high energy density welding with excellent toughness. 3. The composition according to claim 1, further comprising at least one of REM: 0.0005 to 0.01% and Zr: 0.0005 to 0.01% in mass%. Sour-resistant steel for high energy density welding with excellent toughness at the weld. 4. Further, in mass%, Cu: 0.05 to 1.0%, Ni: 0.05 to 1.0%, Cr: 0.05 to 1.0%, Mo: 0.05 to 0.5%. B: 0.0003 to 0.003% of one or more kinds are contained, The sour resistance steel material for high energy density welding excellent in toughness of the welded part according to any one of claims 1 to 3. 5. A high energy density excellent in toughness of a welded portion according to claim 1, further containing Mg: 0.0001 to 0.005% by mass%. Sour resistant steel for welding. 6. A sour-resistant steel material for high energy density welding having excellent toughness of a welded portion according to claim 1, characterized in that it is composed of a bainite structure having an area ratio of 50% or more. . 7. Mass% C: 0.01 to 0.08% Si: 0.5% or less Mn: 1.0 to 1.6% P: 0.015% or less S: 0.001% or less Al : 0.001 to 0.05% Ti: 0.005 to 0.03% Ca: 0.0005 to 0.005% N: 0.001 to 0.008% O: 0.001 to 0.004% Area ratio of martensite-austenite mixed phase (MA: Martensite-Austenite constituent) in a welded part that contains a chemical component consisting of iron and unavoidable impurities and the balance is high energy density welding. Is 2% or less, a sour resistant steel structure excellent in toughness of a welded portion. 8. The chemical composition of the base material is characterized by further containing, in mass%, one or more of Nb: 0.005 to 0.10% V: 0.005 to 0.10%. Item 7. A sour-resistant steel structure excellent in toughness of the welded part. 9. The chemical composition of the base material further contains one or more kinds of REM: 0.0005 to 0.01% and Zr: 0.0005 to 0.01% in mass%. Item 7. A sour-resistant steel structure excellent in toughness of a welded part according to item 7 or 8. 10. The chemical composition of the base material further comprises, in mass%, Cu: 0.05 to 1.0% Ni: 0.05 to 1.0% Cr: 0.05 to 1.0% Mo: 0. 05-0.5% B: 0.0003-0.003% of one or more kinds are contained, The sour resistance steel excellent in toughness of the welded part according to any one of claims 7 to 9. Structure. 11. The toughness of the welded portion according to claim 7, wherein the chemical composition of the base material further contains Mg: 0.0001 to 0.005% by mass%. Excellent sour resistance steel structure. 12. The welded portion according to claim 7, wherein the average composition of inclusions of 0.5 to 10 μm contains 5% by mass or more of REM and / or Zr. Sour-resistant steel structure with excellent toughness at the weld. 13. A sour-resistant steel structure excellent in toughness of a welded portion according to claim 7, wherein the base material is composed of a bainite structure having an area ratio of 50% or more. .