JP6191393B2 - Submerged arc welding metal with excellent cryogenic toughness, and wire and flux for forming submerged arc welding - Google Patents

Description

  The present invention relates to a weld metal having a tensile strength of a seam weld of a UO steel pipe for line pipes manufactured by submerged arc welding of X60 to X80 grade steel plates and used in extremely cold regions, and the welding The present invention relates to a wire for submerged arc welding and a flux forming a metal.

  In recent years, energy sources have been developed in extremely cold regions, and UO steel pipes for line pipes are required to have low temperature toughness that can withstand even in extremely cold regions. Recently, materials that can maintain toughness at −60 ° C. have been developed. Accordingly, the seam welded portion of the UO steel pipe for line pipes is also required to have low temperature toughness that can withstand even in extremely cold regions.

  Seam welds are large and consist of a weld metal and a weld heat affected zone (HAZ), but one problem is to improve the low temperature toughness of the weld metal, and many improvements have been proposed so far.

  Patent Document 1 discloses a weld metal having high strength and high toughness and a method for forming the weld metal. In this method, the component composition and carbon equivalent of the weld metal are defined to ensure high strength of 700 N / mm or more and low temperature toughness at -40 ° C. or less. Since it is not taken into consideration, the improvement of low temperature toughness is insufficient.

  Patent Document 2 discloses an ultra high strength steel pipe excellent in low temperature toughness and a method for manufacturing the same. The target steel pipe is a high-strength UO steel pipe exceeding X100, but the oxygen content is not taken into account in the composition of the weld metal, so that the low-temperature toughness is still insufficiently improved.

  Patent Document 3 discloses a high-strength line pipe (X80 to X100 grade) excellent in low-temperature toughness. The yield strength YS of the weld metal is 550 MPa or more, but B is not added to the weld metal and the amount of Al is not taken into account, so that sufficient cryogenic toughness is not obtained.

  Patent Document 4 discloses a high-strength line pipe excellent in low-temperature toughness. In this high-strength line pipe, assuming that the strength is 690 MPa or more, since B is not added to the weld metal, the improvement in low-temperature toughness is insufficient.

  Patent Document 5 discloses a welded joint in which HAZ toughness is improved by using B in the weld metal. Although the component composition of the weld metal is defined, the amount of oxygen important for securing toughness is not taken into account, so that the improvement of low-temperature toughness is insufficient.

  Patent Document 6 discloses a low temperature high toughness UOE steel pipe. In an X80 grade weld metal, in addition to not considering solute B, the amount of Al necessary for improving toughness is not taken into account, so the improvement in low-temperature toughness is insufficient. In addition, although B is added to the weld metal from the welding wire, the addition of B to the welding wire is difficult in terms of yield and stability of component composition.

  Patent Document 7 discloses a method for producing a high-strength welded steel pipe. In the weld metal of this steel pipe, the amount of B is small, the relationship between the amount of oxygen and the amount of B is not considered, and solid solution B is not noted.

  Patent Document 8 discloses a low-temperature high-strength steel pipe. In this steel pipe, the HAZ toughness is improved, but in the weld metal, attention is not paid to the solid solution B, and the relationship between the oxygen amount and the B amount is not taken into consideration.

JP 09-049055 A JP 2000-256777 A JP 2000-355729 A JP 2004-043911 A JP-A-2005-002476 JP 2005-023429 A JP 2006-183127 A JP 2006-328523 A

  In view of the current state of the art, the present invention is manufactured by submerged arc welding of X60 to X80 grade steel plates, for example, “welding of seam welds of UO steel pipes for line pipes used in a cryogenic temperature range of −60 ° C. The object is to provide cryogenic toughness to "welded weld metal" (hereinafter referred to as "welded metal"), and provide a weld metal having cryogenic toughness, and a welding wire and welding flux forming the weld metal. The purpose is to do.

  The present inventors diligently studied a method for solving the above problems. In order to impart cryogenic toughness to the weld metal, it is necessary to stabilize the low temperature toughness of the weld metal to the cryogenic range. For that purpose, one means is to refine and optimize the structure of the weld metal.

  B is an element that suppresses the formation of intergranular ferrite that adversely affects toughness. However, as a result of the study by the present inventors, in order to ensure toughness at a very low temperature in a weld metal, simple addition of B is not sufficient. However, it was found that (x) the addition of B in consideration of the oxygen amount of the weld metal and (y) the resulting solid solution B amount were important.

  That is, in order to stabilize the low temperature toughness of the weld metal to the cryogenic temperature range, (z1) the amount of B added to the weld metal and (z2) the amount of solute B remaining in the weld metal are optimized. It was found that this optimization can stably maintain the low temperature toughness of the weld metal up to the cryogenic range.

  This invention was made | formed based on the said knowledge, and the summary is as follows.

(1) A weld metal having a tensile strength of a seam welded portion of a UO steel pipe manufactured by submerged arc welding of a steel plate of X60 to X80 class, of 500 to 850 MPa class,
(I) component composition is mass%,
C: 0.03% or more, 0.10% or less,
Si: 0.05% or more, 0.50% or less,
Mn: 0.80% or more, 2.20% or less,
P: 0.015% or less,
S: 0.010% or less,
Cu: 0.19% or more, 0.500% or less,
Nb: 0.050% or less,
V: 0.020% or less,
O: 0.020% or more, 0.035% or less,
N: 0.0045% or less,
Al: 0.003% or more, 0.018% or less,
Ti: 0.005% or more, 0.025% or less,
B: 0.0004% or more, 0.0040% or less,
Solid solution B: 0.0001% or more, 0.0020% or less, and the balance: Fe and inevitable impurities,
(Ii-1) the following formula (1) P _CM defined in 0.12 or more and 0.30 or less,
P _CM = [C] + [Si] / 30 + ([Mn] + [Cu] + [Cr]) / 20
+ [Ni] / 60 + [Mo] / 15 + [V] / 10 + 5 [B] (1)
[A] is the amount of element A (mass%)
(Ii-2) O amount [O] and B amount [B] satisfy the following formula (2),
0.10 × [O] −0.0015 ≦ [B] ≦ 0.20 × [O] −0.0015
... (2)
(Ii-3) O amount [O] and Al amount [Al] satisfy the following formula (3),
0.10 × [O] + 0.0013 ≦ [Al] ≦ 0.125 × [O] +0.0168
... (3)
(Ii-4) α ′ calculated by the following formula (4) based on the O amount [O], the N amount [N], the Al amount [Al], and the Ti amount [Ti], and the O amount [O] Satisfies the following formula (5) α ′ = (1.5 × ([O] −0.89 × [Al]) + 3.4 × [N]) − [Ti])
× 1000 (4)
592.0 × [O] −15.1 ≦ α ′ ≦ 642.0 × [O] +12.0 (5)
Submerged arc weld metal with excellent cryogenic toughness.

  (2) In the above (1), the component composition includes one or more of Ni: 2.0% or less, Cr: 1.5% or less, and Mo: 1.0% or less. Submerged arc weld metal with excellent cryogenic toughness as described.

(3) A welding wire for forming a submerged arc weld metal having excellent cryogenic toughness according to (1) or (2),
Ingredient composition is mass%,
C: 0.005% or more, 0.400% or less,
Si: 0.005% or more, 1.00% or less,
Mn: 0.20% or more and 4.00% or less,
P: 0.015% or less,
S: 0.015% or less,
Cu: 0.250% or less,
Al: 0.0005% or more, 0.050% or less,
Ti: 0.002% or more, 0.500% or less,
Nb: 0.010% or less,
V: 0.050% or less,
N: 0.008% or less,
O: 0.005% or less, and
Remainder: A wire for submerged arc welding comprising Fe and inevitable impurities.

  (4) In the above (3), the component composition contains one or more of Ni: 6.0% or less, Cr: 3.0% or less, Mo: 4.0% or less Submerged arc welding wire as described.

(5) Using the submerged arc welding wire according to (3) or (4) above to form the submerged arc weld metal having excellent cryogenic toughness according to (1) or (2). Flux,
(I) component composition is mass%,
SiO ₂ : 6% or more, 23% or less,
CaO: 4% or more, 20% or less,
CaF ₂ : 10% or more, 60% or less,
MgO: 1% or more, 8% or less,
Al ₂ O ₃ : 6% or more, 45% or less,
B ₂ O _3: 0.05% or more, 0.6% or less and unavoidable impurities, and,
(Ii) A flux for submerged arc welding, wherein the basicity defined by the following formula (6) is 0.2 or more and 3.8 or less.
6.5 × {BaO} + 6.05 × {CaO} + 4 × {MgO} + 5.1 × {CaF ₂ } + 4.8 × {MnO} + 3.4 × {FeO} −0.2 × {Al ₂ O ₃ } −6.31 × {SiO ₂ } −2.2 × {TiO ₂ } −0.3 × {ZrO ₂ } (6)
Where {AB} is the mole percent of AB

(6) the component composition, by mass%, MnO: 1% or more, 10% or less, TiO _2: 1% or more, 25% or less, BaO: 1% or more, 15% or less, K ₂ O: 0.2 % Or more, 1.2% or less, Li ₂ O: 0.4% or more, 4.0% or less, FeO: 0.5% or more, 3.0% or less, and ZrO ₂ : 1% or more, 15% The flux for submerged arc welding according to (5) above, comprising one or more of the following.

  According to the present invention, as a weld metal of a seam welded portion of a UO steel pipe for a line pipe manufactured by submerged arc welding of X60 to X80 grade steel plates, a weld metal having stable toughness up to an extremely low temperature range of −60 ° C. is provided. can do. Moreover, according to this invention, the wire for submerged arc welding and the flux which form the weld metal whose toughness is stable to the very low temperature range of -60 degreeC can be provided.

It is a figure which shows the cross section of the seam welding part of the UO steel pipe for line pipes which manufactured the steel plate of X60-X80 grade by submerged arc welding. It is a figure which shows the result of having investigated experimentally the optimal amount of B added to a weld metal, and the optimal amount of the solid solution B which remains in a weld metal on the basis of -60 degreeC absorption energy> = 100J. (A) shows the relationship between the B amount (mass%) of the weld metal and the −60 ° C. absorbed energy (J), and (b) shows the solid solution B amount (mass%) of the weld metal and the −60 ° C. absorbed energy. The relationship of (J) is shown. It is a figure which shows the groove shape used in the Example. It is a figure which shows the position which extract | collects the test piece used in order to evaluate the mechanical characteristic of the weld metal created in the Example. (A) shows the sampling position of the weld metal impact test piece, and (b) and (c) show the sampling position of the weld metal tensile test piece.

  FIG. 1 shows a cross section of a seam welded portion of a UO steel pipe for a line pipe produced by submerged arc welding of X60 to X80 grade steel plates. Usually, UO steel pipes are formed by forming a steel sheet into a cylindrical shape, and then facing opposite ends from each of the inner and outer surfaces of the cylindrical molded product by submerged arc welding.

  Generally, tack welding is performed prior to submerged arc welding. Since this tack welding disappears by the subsequent submerged arc welding, it does not remain in the seam welded portion of the UO steel pipe.

  Welding is usually performed by tack welding from the outer surface, then from the inner surface, first by seam welding by submerged arc welding, and then by subsequent welding from the outer surface. However, the presence of tack welding and this submerged arc welding are performed. The order does not affect the effects of the present invention.

  The present invention stabilizes the low temperature toughness of a weld metal formed by one-layer submerged arc welding to a very low temperature range. In addition, if this invention can be welded by one-layer submerged arc welding, it is possible to apply other than a steel pipe.

  In order to stabilize the low temperature toughness of the weld metal to the cryogenic temperature range, the present inventors have (z1) an optimum amount of B added to the weld metal, and (z2) an optimum amount of solute B remaining in the weld metal. Was experimentally investigated with reference to −60 ° C. absorbed energy ≧ 100 J. The results are shown in FIG.

  FIG. 2A shows the relationship between the total B amount (mass%) of the weld metal and −60 ° C. absorbed energy (J), and FIG. 2B shows the solid solution B amount (mass%) of the weld metal. The relationship of -60 degreeC absorption energy (J) is shown.

  There are two types of addition of B to the weld metal: (a) addition from the wire and (b) addition from the flux. However, the addition from the wire is an industrial issue such as the number of wire types actually increases. Therefore, in the above investigation, the addition from a flux that can easily adjust the components was adopted.

The amount of B in the weld metal was adjusted by changing the amount of B ₂ O ₃ (borax) in the flux, and the −60 ° C. absorbed energy (J) of the weld metal was evaluated. Flux A and flux B differ in the oxygen content of the weld metal.

  As shown in FIG. 2A, when the total B amount of the weld metal is arranged, the relationship with the −60 ° C. absorbed energy (J) is not clear due to the type of flux.

  On the other hand, as shown in FIG. 2B, when arranged by the amount of solute B, the absorption energy (J) at −60 ° C. is less than 100 J at about 20 ppm (0.0020 mass%) or more. That is, based on −60 ° C. absorbed energy ≧ 100 J, the low-temperature toughness of the weld metal rapidly decreases with solute B: more than 0.0020 mass%.

  This is a novel finding that the present inventors have found and forms the basis of the present invention.

  In addition, when the amount of solute B is excessive (for example, more than 20 ppm), it is estimated that hardenability will improve and a coarse bainite structure with low toughness will be formed.

  B exists in the form of solid solution B and B fixed mainly with oxygen in the weld metal. Since the amount of B fixed by oxygen varies depending on the amount of oxygen in the weld metal, as shown in FIG. 2A, when the amount of oxygen in the weld metal is different, toughness (−60 It is presumed that the correlation with the absorption energy (J) is not clear.

  Part of the B in the weld metal is fixed mainly with oxygen during welding, and the rest is present in the weld metal as solute B. In order to reduce the amount of dissolved B to 0.0020% or less, it is necessary to adjust the amount of elements that fix B in addition to oxygen and nitrogen.

  In particular, although the influence of oxygen is large, oxygen is first consumed by Al and Ti, and the remaining oxygen is consumed for fixing B. Therefore, when Al and Ti are excessive, oxygen for fixing B decreases and solid solution B increases.

  Moreover, excess Al and Ti act as a solid solution strengthening element and reduce the toughness of the weld metal structure. Therefore, it is necessary to adjust the amounts of Al and Ti to the optimum range. Further, if nitrogen is also present in an excessive amount, B is fixed, so an upper limit needs to be defined.

Based on the above, for B and solute B,
B: 0.0004% or more, 0.0040% or less,
Solid solution B: 0.0001% or more, 0.0020% or less,
And for O, N, Al, Ti,
O: 0.020% or more, 0.035% or less,
N: 0.0045% or less,
Al: 0.003% or more, 0.018% or less,
Ti: 0.005% or more, 0.025% or less,
Stipulated. The reason for limiting the component composition will be described later.

Therefore, the submerged arc weld metal excellent in the cryogenic toughness of the present invention (hereinafter sometimes referred to as “the present weld metal”) is a seam welded UO steel pipe manufactured by submerged arc welding of X60 to X80 grade steel plates. The tensile strength of the part is a weld metal of 500 to 850 MPa class, the component composition is mass%,
C: 0.03% or more, 0.10% or less,
Si: 0.05% or more, 0.50% or less,
Mn: 0.80% or more, 2.20% or less,
P: 0.015% or less,
S: 0.010% or less,
Cu: 0.19% or more, 0.500% or less,
Nb: 0.050% or less,
V: 0.020% or less,
O: 0.020% or more, 0.035% or less,
N: 0.0045% or less,
Al: 0.003% or more, 0.018% or less,
Ti: 0.005% or more, 0.025% or less,
B: 0.0004% or more, 0.0040% or less,
Solid solution B: 0.0001% or more, 0.0020% or less,
And, if necessary, it is characterized by comprising Ni: 2.0% or less, Cr: 1.5% or less, Mo: 1.0% or less, one or two or more and the balance: Fe and unavoidable impurities.

Furthermore, the weld metal of the present invention is
(Ii-1) the following formula (1) P _CM defined in 0.12 or more and 0.30 or less,
P _CM = [C] + [Si] / 30 + ([Mn] + [Cu] + [Cr]) / 20
+ [Ni] / 60 + [Mo] / 15 + [V] / 10 + 5 [B] (1)
[A] is the amount of element A (mass%)
(Ii-2) O amount [O] and B amount [B] satisfy the following formula (2),
0.10 × [O] −0.0015 ≦ [B] ≦ 0.20 × [O] −0.0015
... (2)
(Ii-3) O amount [O] and Al amount [Al] satisfy the following formula (3),
0.10 × [O] + 0.0013 ≦ [Al] ≦ 0.125 × [O] +0.0168
... (3)
(Ii-4) α ′ calculated by the following formula (4) based on the O amount [O], the N amount [N], the Al amount [Al], and the Ti amount [Ti], and the O amount [O] Satisfies the following formula (5) α ′ = (1.5 × ([O] −0.89 × [Al]) + 3.4 × [N]) − [Ti])
× 1000 (4)
592.0 × [O] −15.1 ≦ α ′ ≦ 642.0 × [O] +12.0 (5)
It is characterized by that.

  Here, the reason for limiting the component composition of the weld metal will be described. In addition, since the component composition of the weld metal naturally has dilution by the base material, the component composition of the weld metal of the present invention is defined in consideration of dilution by the base material. Hereinafter,% means mass%. The reasons for limiting the above formulas (1), (2), (3), (4), and (5) will be described later.

C: 0.03% or more and 0.10% or less C is an element effective for ensuring the strength of the weld metal. In order to obtain a required strength, the content is made 0.03% or more. Even at extremely low C, hot cracking may occur during welding. Preferably it is 0.05% or more. On the other hand, if it exceeds 0.10%, the toughness decreases, so the content is made 0.10% or less. Preferably it is 0.08% or less.

Si: 0.05% or more and 0.50% or less Si is an element effective for deoxidation of weld metal and improvement of strength. To obtain the additive effect, the content is made 0.05% or more. Preferably it is 0.08% or more. On the other hand, if it exceeds 0.50%, the toughness decreases, so the content is made 0.50% or less. Preferably it is 0.40% or less.

Mn: 0.80% or more and 2.20% or less Mn, like Si, is an element effective for deoxidation of weld metal and improvement of strength. To obtain the effect of addition, the content is made 0.80% or more. Preferably it is 1.00% or more. On the other hand, if it exceeds 2.20%, the toughness decreases, so the content is made 2.20% or less. Preferably it is 2.00% or less.

P: 0.015% or less P is an element that inhibits the toughness of the weld metal. The smaller the content, the better. If it exceeds 0.015%, the weld metal becomes extremely brittle, so the content is made 0.015% or less. Preferably it is 0.010% or less. The lower limit includes 0%, but it is unavoidably mixed from the base material by about 0.002%.

S: 0.010% or less S, like P, is an element that inhibits the toughness of the weld metal. The smaller the content, the more preferable. If it exceeds 0.010%, the weld metal becomes extremely brittle, so the content is made 0.010% or less. Preferably it is 0.005% or less. The lower limit includes 0%, but it is unavoidably mixed from the base material by about 0.002%.

Cu: 0.500% or less Cu is an element effective for improving the hardenability of the weld metal and improving the strength and toughness. Therefore, even if contained, there is no problem in the properties, but if it exceeds 0.500%, Since toughness is inhibited, the content is made 0.500% or less. Moreover, when it contains excessively, the possibility that a hot crack will generate | occur | produce during welding will become high. Preferably it is 0.350% or less. On the other hand, it is preferably 0.19% or more from the viewpoint of enhancing hardenability and ensuring strength and toughness.

Nb: 0.050% or less If it exceeds 0.050%, the toughness is inhibited, so the content is made 0.050% or less. Preferably it is 0.035% or less. Although the lower limit is not particularly specified, about 0.001% is included as an impurity in the dilution from the base material and the production of the welding material.

V: 0.020% or less If over 0.020%, the toughness is inhibited, so 0.020% or less. Preferably it is 0.015% or less. Although the lower limit is not particularly specified, about 0.001% is included as an impurity in the dilution from the base material and the production of the welding material.

O: 0.020% or more and 0.035% or less O is an element that acts to control the structure of the weld metal that forms an oxide that becomes the nucleus of intragranular transformation. Also, unnecessary B is fixed.

  If it is less than 0.020%, in the weld metal having a strength of 500 to 850 MPa, the formation of an oxide serving as a nucleus of intragranular transformation necessary for making the structure mainly composed of acicular ferrite becomes insufficient. 0.020% or more.

  On the other hand, if it exceeds 0.035%, the oxide in the weld metal becomes coarse, the amount of solute B decreases, the upper shelf energy decreases, and the cryogenic toughness of the weld metal decreases. 0.035% or less.

N: 0.0045% or less N is an element that inevitably enters the weld metal and fixes B as a nitride. If it exceeds 0.0045%, the amount of B nitride increases, the necessary amount of dissolved B becomes insufficient, and the cryogenic toughness of the weld metal decreases, so the content is made 0.0045% or less. Preferably it is 0.0040% or less.

Al: 0.003% to 0.018% Al is an element that forms an oxide and controls the amount of O of the weld metal. If it is less than 0.003%, the amount of oxygen in the weld metal becomes excessive, and the generated oxide is coarsened to inhibit the cryogenic toughness of the weld metal, so the content is made 0.003% or more. Al is inevitably mixed from the flux and the base material.

  On the other hand, if it exceeds 0.018%, the amount of oxygen for fixing B is insufficient, the solid solution B increases, and the cryogenic toughness of the weld metal decreases, so the content is made 0.018% or less. Preferably it is 0.015% or less.

Ti: 0.005% or more and 0.025% or less Ti forms an oxide which becomes the nucleus of intragranular transformation, and ensures solid solution B in the weld metal and also controls the structure of the weld metal. Is an element.

  If it is less than 0.005%, in the weld metal of a steel pipe having a strength of X65 to X80 class, the formation of an oxide that is a nucleus of intragranular transformation necessary for making the structure mainly composed of acicular ferrite is insufficient. Therefore, it is made 0.005% or more. Preferably it is 0.008% or more.

  On the other hand, if it exceeds 0.025%, the amount of oxygen for fixing B is insufficient, so that the solid solution B increases and the cryogenic toughness of the weld metal decreases, so the content is made 0.025% or less.

B: 0.0004% or more and 0.0040% or less B is an element that enhances the hardenability of the weld metal and ensures the required amount of solid solution B to increase the cryogenic toughness. If it is less than 0.0004%, the effect of addition is not sufficiently exhibited, so the content is made 0.0004% or more. Preferably it is 0.0005% or more.

  On the other hand, when excessively added, the solid solution B increases, so the content is made 0.0040% or less. Preferably it is 0.0035% or less.

Solid solution B: 0.0001% or more and 0.0020% or less As shown in FIG. 2 (b), when the change in -60 ° C. absorption energy (J) is arranged by the amount of solid solution B, 100J is obtained at about 20 ppm or more. Below. That is, based on −60 ° C. absorbed energy ≧ 100 J, the low temperature toughness of the weld metal rapidly decreases with solute B: more than 0.0020%. Based on this, the solid solution B is made 0.0020% or less. Preferably it is 0.0015% or less. Since 0.0001% is the limit amount of the solid solution B, the solid solution B is made 0.0001% or more.

  Next, the reasons for limiting the above formulas (1) to (5) will be described.

The formula (1): 0.12 or more, the P _CM as defined 0.30 above formula (1) is less than 0.12, because to obtain a weld metal strength 500~850MPa difficult 0 .12 or more. On the other hand, if it exceeds 0.30, the strength becomes excessive and the toughness may be lowered.

Expression (2): Relationship between O amount [O] and B amount [B] As described above, B in the weld metal is partially oxygen, nitrogen, and other elements that fix B during welding. The remainder is present in the weld metal as solute B. In particular, since the influence of oxygen is large, in order to maintain the solid solution B amount at 0.0015% or less, it is necessary to define the B amount in anticipation of the B amount consumed by oxygen. Therefore, the present inventors investigated the optimum relationship between the oxygen amount [O] and the B amount [B].

  As a result, when the B amount [B] is less than (0.10 × [O] −0.0015), it is difficult to secure a solid solution B amount of 0.0001% or more, and (0.20 × When [O] -0.0015) is exceeded, it was found that the amount of dissolved B increases and the cryogenic toughness of the weld metal decreases. Therefore, the B amount [B] satisfies the above formula (2).

Expression (3): Relationship between O amount [O] and Al amount [Al] Oxygen is mainly consumed by Al, and the remaining oxygen is consumed for fixing B. Therefore, when Al is excessive, the amount of O fixing B is reduced and the solid solution B is increased. Moreover, excess Al reduces the toughness of a weld metal as a solid solution strengthening element. Therefore, it is necessary to optimize the relationship between the O amount [O] and the Al amount [Al] of the weld metal, and the present inventors investigated this relationship.

  As a result, when the Al amount [Al] is less than (0.10 × [O] +0.0013), the Al amount is small, the O amount fixing B is increased, and the solid solution B is decreased. It is difficult to obtain the required cryogenic toughness. On the other hand, if it exceeds (0.125 × [O] +0.0168), the amount of solute Al increases and the toughness of the weld metal decreases. Therefore, the Al amount [Al] satisfies the above formula (3).

The relationship between the above formula (4): α ′ and the amount of element O [O] The structure of the weld metal having a tensile strength of 500 to 850 MPa class is mainly composed of acicular ferrite, and these are refined with oxides as the formation nuclei. Ensure toughness.

  As a guideline of the effect of O, N, Al, and Ti on the above effect, there is α ′ obtained by the above formula (4). As a result of further detailed investigation, this optimum value varies depending on the amount of O, and the above formula It was found to be represented by (5).

  When α ′ is less than the lower limit represented by the formula (5), the amount of O is insufficient, and generation nuclei necessary for the refinement of the structure are not sufficiently generated. On the other hand, when it exceeds the upper limit shown by the said Formula (5), oxygen will become excess and toughness will fall.

  The weld metal of the present invention is Ni: 2.0% or less, Cr: 1.5% or less, Mo: 1 within a range not impairing the weldability and cryogenic toughness of the weld metal of the present invention in order to improve the strength of the weld metal. You may contain 1 type or 2 types or less of 0.0% or less.

Ni: 2.0% or less Ni is an element that enhances the hardenability of the weld metal and contributes to improving the strength. If it exceeds 2.0%, the possibility of solidification cracking increases, so the content is made 2.0% or less. Preferably it is 1.5% or less.

Cr: 1.5% or less Cr is an element that enhances the hardenability of the weld metal and contributes to strength improvement. If it exceeds 1.5%, the toughness is hindered. Preferably it is 1.0% or less.

Mo: 1.0% or less Mo is an element that enhances the hardenability of the weld metal and contributes to improvement in strength. If it exceeds 1.0%, the toughness is inhibited, so the content is made 1.0% or less. Preferably it is 0.5% or less.

  The wire for submerged welding used to form the weld metal of the present invention (hereinafter sometimes referred to as “the wire of the present invention”) is preferably a wire having the following component composition as a wire.

Component composition is mass%, C: 0.005% or more, 0.400% or less, Si: 0.005% or more, 1.00% or less, Mn: 0.20% or more, 4.00% or less, P: 0.015% or less, S: 0.015% or less, Cu: 0.250% or less, Al: 0.0005 % or more, 0.050% or less, Ti: 0.002% or more, 0.500% Hereinafter, a wire composed of Nb: 0.010% or less, V: 0.050 % or less, N: 0.008% or less, O: 0.005% or less, and the balance: Fe and inevitable impurities.

  The reason for limiting the component composition of the wire of the present invention will be described.

C: 0.005% or more and 0.400% or less C is 0.005% or more and 0.400% or less in order to secure the C amount (0.03% or more and 0.10% or less) of the weld metal. And Preferably they are 0.008% or more and 0.300% or less.

Si: 0.005 % or more and 1.00% or less Si is 0.005 % or more and 1.00% or less in order to secure the Si amount (0.05% or more and 0.50% or less) of the weld metal. And Preferably they are 0.05% or more and 0.50% or less.

Mn: 0.20% or more and 4.00% or less Mn is 0.20% or more and 4.00% or less in order to secure the amount of Mn (0.80% or more, 2.20% or less) of the weld metal. And Preferably they are 0.50% or more and 3.00% or less.

P: 0.015% or less P is an impurity element and is preferably less than 0.015% because it is preferably less. Preferably it is 0.010% or less. The lower limit includes 0%, but about 0.001% is inevitably mixed from the raw material in the manufacturing process.

S: 0.015% or less S is an impurity element, and since the smaller one is preferable, the content is 0.015% or less. Preferably it is 0.010% or less. The lower limit includes 0%, but about 0.001% is inevitably mixed from the raw material in the manufacturing process.

Cu: 0.250% or less Cu is made 0.250% or less in order to secure the Cu amount (0.50% or less) of the weld metal. Preferably it is 0.200% or less. Depending on the type of wire, Cu is plated on the surface of the wire material in order to ensure feedability and electrical conductivity. In this case, this Cu is also added to the weld metal during welding to become Cu in the weld metal.

Al: 0.0005% or more, 0.050% or less Al is a deoxidizing element, and in order to secure the Al amount (0.003% or more, 0.018% or less) of the weld metal, 0.0005% or more. , 0.050% or less.

Ti: 0.002% or more, 0.500% or less Ti is an element necessary for the structure control of the weld metal, and in order to ensure the Ti amount (0.005% or more, 0.025% or less) of the weld metal, 0.002% or more and 0.500% or less. Preferably they are 0.010% or more and 0.300% or less.

Nb: 0.010% or less Nb is made 0.010% or less in order to secure the Nb amount (0.050% or less) of the weld metal. Preferably it is 0.007% or less. Actually, about 0.001% is unavoidably included in production.

V: 0.050% or less V is made 0.050% or less in order to secure the V amount (0.020% or less) of the weld metal. Preferably it is 0.040% or less. Actually, about 0.001% is unavoidably included in production.

N: 0.008% or less N is set to 0.008% or less in order to secure the N amount (0.0045% or less) of the weld metal. Preferably it is 0.005% or less.

O: 0.005% or less,
O is 0.005% or less in order to secure the O content (0.020% or more and 0.035% or less) of the weld metal. Preferably it is 0.003% or less.

  In addition to the above elements, the wire of the present invention may contain one or more of Ni: 6.0% or less, Cr: 3.0% or less, and Mo: 4.0% or less.

  When the present weld metal contains one or more of Ni: 2.0% or less, Cr: 1.5% or less, Mo: 1.0% or less, Ni: 6.0% or less, Cr : The wire of the present invention containing one or more of 3.0% or less and Mo: 4.0% or less is used.

The following flux is preferable as the flux used when forming the weld metal of the present invention using the wire of the present invention (hereinafter sometimes referred to as “the flux of the present invention”).
(I) component composition is mass%,
SiO ₂ : 6% or more, 23% or less,
CaO: 4% or more, 20% or less,
CaF ₂ : 10% or more, 60% or less,
MgO: 1% or more, 8% or less,
Al ₂ O ₃ : 6% or more, 45% or less,
B ₂ O ₃ : 0.05% or more and 0.6% or less and unavoidable impurities, and
(Ii) A flux for submerged arc welding, wherein the basicity defined by the following formula (6) is 0.2 or more and 3.8 or less.
6.5 × {BaO} + 6.05 × {CaO} + 4 × {MgO} + 5.1 × {CaF ₂ } + 4.8 × {MnO} + 3.4 × {FeO} −0.2 × {Al ₂ O ₃ } −6.31 × {SiO ₂ } −2.2 × {TiO ₂ } −0.3 × {ZrO ₂ } (6)
Where {AB} is the mole percent of AB

The component composition of the flux of the present invention basically follows the component composition of the conventional flux, but in order to ensure the required amount of solid solution B by supplying the required amount of B to the weld metal of the present invention, B ₂ O ₃ is contained 0.05% or more and 0.6% or less. Further, the oxygen content of the weld metal is generally determined by the basicity defined by the formula (6), and in order to make the oxygen content in the weld metal 0.020% or more and 0.035% or less, the above formula ( The basicity defined in 6) is 0.2 or more and 3.8 or less.

The present invention flux, by mass%, MnO: 1% or more, 10% or less, TiO _2: 1% or more, 25% or less, BaO: 1% or more, 15% or less, K ₂ O: 0.2% or more, 1.2% or less, Li ₂ O: 0.4% or more, 4.0% or less, FeO: 0.5% or more, 3.0% or less, and ZrO ₂ : 1% or more, 15% or less Or you may contain 2 or more types.

  The base material of the UO steel pipe for line pipe, which uses the wire of the present invention and the flux of the present invention to form the weld metal of the present invention by submerged arc welding, may be an X60 to X80 grade steel plate, and in particular, a specific component composition. It is not limited to the steel plate.

  Usually, the penetration of the base metal affects the component composition of the weld metal. However, in the component composition of the present weld metal and the above formulas (1) to (5), as described above, dilution with the base metal is performed. Therefore, the base material of the UO steel pipe for line pipes is not particularly limited to a steel sheet having a specific component composition, as long as it is an X60 to X80 grade steel sheet.

  In addition, the preferable component composition of a base material (steel plate) is as follows.

C: 0.03% or more, 0.10% or less,
Si: 0.05% or more, 0.40% or less,
Mn: 0.8% or more, 2.5% or less,
P: 0.015% or less,
S: 0.005% or less,
Nb : 0 . 05% or less V: 0.05% or less Al: 0.001% or more, 0.040% or less,
Ti: 0.005% or more, 0.030% or less,
N: 0.006% or less,
O: 0.005% or less, and
Remainder: Fe and unavoidable impurities As required, Ni: 1.0% or less, Cr: 1.5% or less, Mo: 1.2% or less, Cu: 0.8% or less The reason for limiting the preferred component composition will be described.

C: 0.03% to 0.10% C is an element effective for securing the strength of the base material (steel plate). Therefore, if it is less than 0.03%, the effect of addition is not sufficiently exhibited, and if it exceeds 0.10%, the hardness of the seam welded portion is increased and cold cracking is likely to occur.

Si: 0.05% or more and 0.40% or less Si is an element effective for increasing the strength of the base metal and HAZ by solid solution strengthening. If it is less than 0.05%, the effect of addition is not sufficiently exhibited, and if it exceeds 0.40%, the toughness is remarkably lowered.

Mn: 0.8% or more and 2.5% or less Mn is an element that enhances the hardenability and contributes to the strength improvement of the base material and the HAZ. If the content is less than 0.8%, the effect of addition is not sufficiently exhibited.

P: 0.015% or less P is an impurity element and is preferably as low as possible, so is 0.015% or less. The lower limit includes 0%, but a reduction to less than 0.0001% leads to an increase in manufacturing cost. Therefore, in practical steel, 0.0001% is the lower limit.

S: 0.005% or less S is an impurity element, and the smaller the better, the more the content is 0.005% or less. The lower limit includes 0%, but a reduction to less than 0.0001% leads to an increase in manufacturing cost. Therefore, in practical steel, 0.0001% is the lower limit.

Nb: 0.05% or less Nb is an element that forms carbides and contributes to the improvement of the temper softening resistance of the HAZ of the base material, and may be added to the base material. If it exceeds, the amount of Nb in the weld metal becomes excessive.

V: 0.05% or less V is an element that forms carbides and contributes to the improvement of temper softening resistance of HAZ, and may be added to obtain this effect. The amount of V in the metal becomes excessive.

Al: 0.001% to 0.040% Al is an element effective for deoxidation. If it is less than 0.001%, the effect of addition does not appear, and if it exceeds 0.040%, the amount of oxide increases, the cleanliness of the steel decreases, and the toughness decreases.

Ti: 0.005% or more and 0.030% or less Ti forms nitrides and reduces the amount of solute N in the steel, and also suppresses austenite grain coarsening due to the pinning effect of nitrides. It is an element that contributes to improving the toughness of materials and HAZ. If it is less than 0.005%, the effect of addition does not appear, and if it exceeds 0.030%, the toughness deteriorates.

N: 0.006% or less N is an element that forms TiN and suppresses the coarsening of austenite. Therefore, N may be added to the base material. N content of the steel increases and the toughness of the weld metal decreases.

O: 0.005% or less,
If it exceeds 0.005%, the oxide becomes coarse and the toughness decreases, so O is made 0.005% or less.

Ni: 1.0% or less, Cr: 1.5% or less, Mo: 1.2% or less, Cu: 0.8% or less 1 type or 2 types or more Ni: 1.0% or less Ni is hardenability Although it is an improving element, since it is an expensive element, if it exceeds 1.0%, the manufacturing cost increases.

Cr: 1.5% or less, Mo: 1.2% or less, Cu: 0.8% or less All of Cr, Mo, and Cu are hardenability improving elements and contribute to improving the strength of the base material and HAZ. However, if Cr exceeds 1.5%, Mo exceeds 1.2%, or Cu exceeds 0.8%, the effect of addition is saturated.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

(Example)
Welded parts simulating seam welded parts of UO steel pipes for line pipes by submerged arc welding using X60, X70 and X80 grade steel sheets A, B, C, and D as the base materials shown in Table 1 It was created.

  Welding was performed from the back surface of the steel plate by pre-welding simulating the inner surface welding of the steel pipe, and then the subsequent welding simulating the outer surface welding on the surface of the steel plate. Evaluation was performed with respect to the subsequent welding part.

  Usually, welding for temporary fixing is performed prior to preceding welding, but this temporary fixing welding disappears by subsequent preceding welding or subsequent subsequent welding, and thus does not affect the effect of the present invention. Therefore, tack welding was not performed in the examples.

  Table 2 shows the component composition of the welding wire used, and Table 3 shows the component composition of the welding flux used. FIG. 3 shows the shape of the groove used. Table 4 shows the groove dimensions for each thickness of the steel sheet. Table 5 shows welding conditions according to the plate thickness of the steel plate.

  The characteristics of the weld metal were evaluated by conducting a tensile test and an impact test of the weld metal in accordance with JIS Z3111. FIG. 4 shows the sampling position of the test piece. FIG. 4A shows the sampling position of the weld metal impact test piece. The impact test piece 1 was collected so that the direction of the notch was the weld line direction. 4 (b) and 4 (c) show the sampling positions of the weld metal tensile test pieces. As the tensile test piece 2, a JIS A2 tensile test piece was sampled along the weld line direction.

  Table 6 shows the component composition of the weld metal of the subsequent welding formed using the welding wire having the component composition in Table 2, and the welding flux having the component composition in Table 3, and Table 7 (continuation of Table 6) The characteristic value of this weld metal is shown. Table 8 shows the results of evaluating the characteristics of the formed subsequent weld metal.

  In the inventive examples, the component composition of the weld metal and the amount of solute B satisfy the scope of the present invention. As a result, the -60 ° C. absorbed energy exceeds 100 J for both the average value and the minimum value. It can be seen that the cryogenic toughness is excellent.

  On the other hand, in Comparative Examples 1 and 2, the toughness is low due to excessive Ti or Mn. In Comparative Examples 3 and 4, since the solid solution B is insufficient, quenching is insufficient and the toughness of the weld metal is low. In Comparative Example 3, since the arc is disturbed during welding, N of the weld metal becomes excessive and the toughness is low.

  In Comparative Example 5, since the oxygen is excessive and the solid solution B is small, the toughness of the weld metal is low. In Comparative Examples 6 and 7, the toughness is low because Ti or Si is excessive. Moreover, since Ni is excessive, hot cracking also occurs. In Comparative Example 7, since P and S are excessive, hot cracking occurs during welding. In Comparative Example 8, since B is excessive, solid solution B is also excessive, the structure becomes coarse and toughness is low.

  In Comparative Examples 9 and 10, oxygen becomes excessive, resulting in low toughness. This is because fluxes p and q having low basicity are used. In Comparative Example 11, Cu and Mn are excessive, and hot cracks are generated during welding. Moreover, since the solid solution B is also insufficient, the toughness is low. In Comparative Example 12, the toughness is relatively good, but because of excessive C, hot cracking occurs during welding.

  In Comparative Example 13, since the oxygen is excessive, the solid solution B is insufficient, and further, the toughness is low because Ti is excessive. On the contrary, in Comparative Examples 14 and 15, due to the insufficient amount of O, an oxide necessary for refining the structure is not formed and the toughness is low. In Comparative Example 16, the toughness is low because V is excessive. Furthermore, hot cracking has occurred due to insufficient C content.

Also in Comparative Example 17, toughness is low because V is excessive. Furthermore, in Comparative Example 18, because C is excessive, the strength is excessive and the toughness is low, and hot cracking also occurs. In Comparative Example 19, V and Ti is excessive, and high P _CM, is low toughness becomes excessive strength.

  As described above, according to the present invention, as a weld metal of a seam welded portion of a UO steel pipe for a line pipe manufactured by submerged arc welding of X60 to X80 grade steel plates, it is tough to -60 ° C. Can provide a stable weld metal. Moreover, according to this invention, the wire for submerged arc welding and the flux which form the weld metal whose toughness is stable to the very low temperature range of -60 degreeC can be provided.

  Since the UO steel pipe for line pipes provided with the above weld metal can be used with high reliability in extremely cold regions, the present invention has high applicability in the line pipe manufacturing industry and the line pipe construction industry.

1 Impact test piece 2 Tensile test piece

Claims (6)

A weld metal having a tensile strength of a seam weld of a UO steel pipe manufactured by submerged arc welding of X60 to X80 grade steel plates,
(I) component composition is mass%,
C: 0.03% or more, 0.10% or less,
Si: 0.05% or more, 0.50% or less,
Mn: 0.80% or more, 2.20% or less,
P: 0.015% or less,
S: 0.010% or less,
Cu: 0.19% or more, 0.500% or less,
Nb: 0.050% or less,
V: 0.020% or less,
O: 0.020% or more, 0.035% or less,
N: 0.0045% or less,
Al: 0.003% or more, 0.018% or less,
Ti: 0.005% or more, 0.025% or less,
B: 0.0004% or more, 0.0040% or less,
Solid solution B: 0.0001% or more, 0.0020% or less, and the balance: Fe and inevitable impurities,
(Ii-1) the following formula (1) P _CM defined in 0.12 or more and 0.30 or less,
P _CM = [C] + [Si] / 30 + ([Mn] + [Cu] + [Cr]) / 20
+ [Ni] / 60 + [Mo] / 15 + [V] / 10 + 5 [B] (1)
[A] is the amount of element A (mass%)
(Ii-2) O amount [O] and B amount [B] satisfy the following formula (2),
0.10 × [O] −0.0015 ≦ [B] ≦ 0.20 × [O] −0.0015
... (2)
(Ii-3) O amount [O] and Al amount [Al] satisfy the following formula (3),
0.10 × [O] + 0.0013 ≦ [Al] ≦ 0.125 × [O] +0.0168
... (3)
(Ii-4) α ′ calculated by the following formula (4) based on the O amount [O], the N amount [N], the Al amount [Al], and the Ti amount [Ti], and the O amount [O] Satisfies the following formula (5) α ′ = (1.5 × ([O] −0.89 × [Al]) + 3.4 × [N]) − [Ti])
× 1000 (4)
592.0 × [O] −15.1 ≦ α ′ ≦ 642.0 × [O] +12.0 (5)
Submerged arc weld metal with excellent cryogenic toughness.   2. The cryogenic temperature according to claim 1, wherein the component composition includes one or more of Ni: 2.0% or less, Cr: 1.5% or less, and Mo: 1.0% or less. Submerged arc weld metal with excellent toughness. A welding wire for forming a submerged arc weld metal excellent in cryogenic toughness according to claim 1 or 2,
Ingredient composition is mass%,
C: 0.005% or more, 0.400% or less,
Si: 0.005% or more, 1.00% or less,
Mn: 0.20% or more and 4.00% or less,
P: 0.015% or less,
S: 0.015% or less,
Cu: 0.250% or less,
Al: 0.0005% or more, 0.050% or less,
Ti: 0.002% or more, 0.500% or less,
Nb: 0.010% or less,
V: 0.050% or less,
N: 0.008% or less,
O: 0.005% or less, and
Remainder: A wire for submerged arc welding comprising Fe and inevitable impurities.   4. The submerged arc according to claim 3, wherein the component composition includes one or more of Ni: 6.0% or less, Cr: 3.0% or less, and Mo: 4.0% or less. Welding wire. Using the wire for submerged arc welding according to claim 3 or 4, a flux used when forming a submerged arc weld metal having excellent cryogenic toughness according to claim 1 or 2,
(I) component composition is mass%,
SiO ₂ : 6% or more, 23% or less,
CaO: 4% or more, 20% or less,
CaF ₂ : 10% or more, 60% or less,
MgO: 1% or more, 8% or less,
Al ₂ O ₃ : 6% or more, 45% or less,
B ₂ O _3: 0.05% or more, 0.6% or less and unavoidable impurities, and,
(Ii) A flux for submerged arc welding, wherein the basicity defined by the following formula (6) is 0.2 or more and 3.8 or less.
6.5 × {BaO} + 6.05 × {CaO} + 4 × {MgO} + 5.1 × {CaF ₂ } + 4.8 × {MnO} + 3.4 × {FeO} −0.2 × {Al ₂ O ₃ } −6.31 × {SiO ₂ } −2.2 × {TiO ₂ } −0.3 × {ZrO ₂ } (6)
Where {AB} is the mole percent of AB The component composition is, by mass, MnO: 1% or more, 10% or less, TiO ₂ : 1% or more, 25% or less, BaO: 1% or more, 15% or less, K ₂ O: 0.2% or more, 1.2% or less, Li ₂ O: 0.4% or more, 4.0% or less, FeO: 0.5% or more, 3.0% or less, and ZrO ₂ : 1% or more, 15% or less Or the flux for submerged arc welding of Claim 5 containing 2 or more types.