JP2009202213A - High heat input electroslag welding process - Google Patents

Abstract

[PROBLEMS] To secure stable toughness in the direction of a welded joint even in high heat input electroslag welding in which welding heat input exceeds 400 kJ / cm.
The welding wires are C: 0.02 to 0.25%, Si: 0.05 to 1.80%, Mn: 0.50 to 3.50%, Mo: 0.05 to 2.00. %, Al: 0.005 to 0.080%, Ti: 0.05 to 0.35%, B: 0.003 to 0.018%, Ni: 3.00% or less, Cr: 0.30% or less V: 0.030% or less, Nb: 0.030% or less, N: 0.012% or less. When the welding flux is FeO: 4.5% or less, B ₂ O ₃ : 1.5% or less, the basicity BL value is 0.5 to 1.5, and the B amount in the welding wire is (B) The variable (X) given by the following equation from the basicity BL and (B) is 9.8 to 20.8.
(X) = 1000 × (B) + 5.1 × BL
[Selection] Figure 3

Description

  The present invention relates to a high heat input electroslag welding method with a welding heat input of 400 kJ / cm or more, and in particular, in each part in the weld joint direction when welding a high-tensile steel plate of 490 to 740 MPa class (thickness of 40 mm or more). The present invention relates to a high heat input electroslag welding method capable of obtaining a good toughness value.

  The electroslag welding method is mainly used for the vertical welding of the inner diaphragm in a steel 4-sided BOX column, and the electroslag welding method is generally more efficient than the submerged arc welding, which can generally achieve high efficiency welding. Yes, it is a welding method capable of high-heat input one-pass welding.

  By the way, with regard to building members and frames to which electroslag welding is applied, in recent years, a high toughness value is also required for weld metal parts from the viewpoint of securing plastic deformation ability at the time of an earthquake and extending the life. However, electroslag welding has a large heat input of about 800 kJ / cm when it is thicker than other arc welding, so the cooling rate of the weld metal decreases and the structure becomes coarse. As a result, the toughness of the weld metal is reduced. There is a problem of lowering.

  In order to improve the toughness of such a weld metal, a method for refining the weld metal structure and improving the toughness by adding a small amount of Ti and B to the weld metal is known. However, in electroslag welding, the toughness value in the weld line direction varies greatly, and there remains a problem that a satisfactory toughness value cannot be obtained depending on the specimen collection location.

  Patent Documents 1 to 4 are disclosed as conventional techniques for ensuring toughness in electroslag welding.

In patent document 1 and patent document 2, while actively adding C, Si, Mn, Al, Ni, Mo, Ti or the like to the welding wire, and using a flux with low basicity, it is A technique is disclosed in which toughness is ensured by adding B, which finely disperses a TiO ₂ -based oxide serving as a nucleus for the formation of curaferrite, and further suppresses the growth of grain boundary ferrite.

  Further, in Patent Document 3, C, Si, Mn, Al, Ni, Mo, etc. are added to the welding wire, and an appropriate amount of B is added to suppress the grain boundary ferrite segregating from the prior austenite grain boundaries, Furthermore, toughness is ensured by containing an appropriate amount of Ti in order to form an oxide serving as a production nucleus of fine acicular ferrite. Patent Document 4 proposes an electroslag welding wire in which C, Si, Mn, Mo, Ni, B, etc. are added in appropriate ranges and the N amount is suppressed.

JP 2005-246399 A Japanese Patent Application Laid-Open No. 2004-114053 Japanese Patent Laid-Open No. 2003-340592 JP 2002-79396 A

  However, in Patent Documents 3 and 4, the flux component is not specified, and the oxygen content of the weld metal that greatly affects toughness is not considered.

  Moreover, in patent document 1 and patent document 2, although the basicity of a flux is prescribed | regulated, it is not disclosed at all about the oxygen amount of a weld metal, and since the appropriate B amount of a weld metal differs with oxygen amounts. In Patent Documents 1 and 2 in which only the basicity is defined, it cannot be said that the toughness of the weld metal is reliably improved. This makes it difficult to ensure stable toughness in the weld joint direction.

  The present invention has been made in view of such problems, and can ensure stable toughness in the weld joint direction even in high heat input electroslag welding in which the heat input of welding exceeds 400 kJ / cm. It is an object of the present invention to provide a high heat input electroslag welding method capable of obtaining a good toughness value in the weld joint direction when welding a 490 to 740 MPa class thick plate (thickness of 40 mm or more). .

The high heat input electroslag welding method according to the present invention is a high heat input electroslag welding method using a welding wire and a welding flux.
The welding wire has C: 0.02 to 0.25% by mass, Si: 0.05 to 1.80% by mass, Mn: 0.50 to 3.50% by mass, Ni: 3. 00 mass% or less, Mo: 0.05 to 2.00 mass%, Al: 0.005 to 0.080 mass%, Ti: 0.05 to 0.35 mass%, B: 0.003 to 0.018 Contains: mass%, Cr: 0.30 mass% or less, V: 0.030 mass% or less, Nb: 0.030 mass% or less, N: 0.012 mass% or less, and the balance from Fe and inevitable impurities Become
The welding flux contains FeO: 4.5% by mass or less, B ₂ O ₃ : 1.5% by mass or less per total mass of the flux,
The SiO ₂ content (% by mass) of the flux is [SiO ₂ ], the CaO content (% by mass) is [CaO], the Al ₂ O ₃ content (% by mass) is [Al ₂ O ₃ ], and CaF _{2 is} contained. The amount (mass%) is [CaF ₂ ], the MgO content (mass%) is [MgO], the MnO content (mass%) is [MnO], the TiO ₂ content (mass%) is [TiO ₂ ], FeO When the content (mass%) is [FeO], the basicity BL value given by the following mathematical formula (1) is set to 0.5 to 1.5,
When the B content in the welding wire is (B), the variable (X) given by the following formula (2) from the basicity BL and the B amount (B) in the welding wire is 9.8 to 20.8. It is characterized by satisfying.

  In this high heat input electroslag welding method, the Ni content of the welding wire is preferably Ni: 0.50 to 3.00 mass% with respect to the total mass of the wire. Particularly preferably, the Ni content of the welding wire is Ni: 0.50 to 2.00% by mass.

  According to the present invention, in the high heat input electroslag welding in which the welding heat input exceeds 400 kJ / cm, such as welding of a high-tensile steel plate of 490 to 740 MPa class (thickness of 40 mm or more), in the weld joint direction. Stable toughness can be ensured.

  In order to ensure stable toughness in the weld joint direction even in large heat input electroslag welding where the heat input exceeds 400 kJ / cm, the present inventors mainly set the amount of weld metal B and the amount of weld metal oxygen appropriately. The present invention has been completed by obtaining the knowledge that it is necessary to define it.

  Hereinafter, the present invention will be described in more detail. First, the composition of the welding wire used in the present invention and the reasons for limiting its components will be described.

“C: 0.02 to 0.25 mass%”
C is an effective element for ensuring the strength and toughness of the weld metal, but if the C content is less than 0.02% by mass, the effect cannot be obtained. On the other hand, if the C content exceeds 0.25% by mass, the toughness of the weld metal is lowered and there is a concern of hot cracking. Therefore, the C content is 0.02 to 0.25% by mass.

“Si: 0.05 to 1.80 mass%”
Si is an element necessary for ensuring the deoxidation action and hardenability of the weld metal and stabilizing the molten metal flow of the weld metal. However, when the Si content is less than 0.05% by mass, this effect cannot be obtained. On the other hand, if the Si content exceeds 1.80% by mass, the occurrence of hot cracking is a concern, and the toughness deteriorates due to the hardening of the weld metal part. Therefore, the Si content is 0.05 to 1.80 mass%.

“Mn: 0.50 to 3.50 mass%”
Mn acts as a deoxidizer and is an element that improves the hardenability of the weld metal, and is an element necessary for stabilizing the toughness of the weld metal. However, when the Mn content is less than 0.50% by mass, sufficient hardenability and toughness cannot be obtained. On the other hand, when Mn exceeds 3.50 mass%, hardenability will become high too much, strength will go up, hot cracking resistance will deteriorate, and toughness will deteriorate. Therefore, the Mn content is 0.50 to 3.50 mass%.

"Ni: 3.00 mass% or less"
In 1st invention of this application, Ni content is 3.00 mass% or less. Ni is generally added to the welding wire to strengthen the matrix and improve the toughness. In the first invention of the present application, the toughness improving effect is supplemented by the addition of Mo. However, if the Ni content exceeds 3.00% by mass, the solid-liquid coexistence region is increased due to the decrease in the A3 transformation point, and as a result, the hot cracking resistance deteriorates. Therefore, the Ni content is 3.00% or less.

“Ni: 0.50 to 3.00 mass%”
Moreover, in this-application 2nd invention, Ni content is 0.50 to 3.00 mass%. In order to further improve toughness, Ni may be positively added to 0.50% by mass or more. In order to obtain the effect of improving toughness, it is necessary to add 0.50% by mass or more of Ni. Therefore, the Ni content when Ni is actively added is 0.50 to 3.00 mass%. When the Ni content in the welding wire exceeds 2.00% by mass, the effect of improving the toughness of the weld metal is saturated while the manufacturing cost of the welding wire is increased. 50 to 2.00% by mass.

“Mo: 0.05 to 2.00% by mass”
Mo enhances the hardenability of the weld metal and has a great effect on improving the strength and toughness of the weld metal. However, if the Mo content is less than 0.05% by mass, the above effect cannot be expected. On the other hand, if the Mo content exceeds 2.00% by mass, hot cracking of the weld metal may occur, and the toughness of the weld metal deteriorates due to excessive curing. Therefore, the Mo content is 0.05 to 2.00% by mass.

“Al: 0.005 to 0.080 mass%”
Al is an element contained for the deoxidation effect of the weld metal. However, when the Al content is less than 0.005% by mass, the effect is not exhibited and the hardenability of the weld metal is lowered and the toughness is deteriorated. On the other hand, when the Al content exceeds 0.080% by mass, a large amount of Al oxide is formed, and the production of Ti oxide that becomes the core of the generation of acicular ferrite is inhibited, so that the toughness is deteriorated. Therefore, the Al content is set to 0.005 to 0.080 mass%.

“Ti: 0.05 to 0.35 mass%”
Since Ti serves as a nucleus for generating acicular ferrite as a Ti oxide, it is an element necessary for preventing the formation of coarse grain boundary ferrite. However, when the Ti content is less than 0.05% by mass, the generation of oxides is insufficient and the toughness of the weld metal cannot be improved. On the other hand, when Ti exceeds 0.35 mass%, the amount of Ti precipitates in the weld metal increases so that the toughness decreases. Therefore, the Ti content is 0.05 to 0.35 mass%.

“B: 0.003 to 0.018 mass%”
B is an element that improves the hardenability of the weld metal and improves toughness by suppressing the growth of pro-eutectoid ferrite. However, when the B content is less than 0.003% by mass, the above effect cannot be expected. On the other hand, if the B content exceeds 0.018% by mass, the hardenability of the weld metal becomes excessive, and hot cracking is likely to occur, and the toughness of the weld metal deteriorates due to the formation of the martensite phase. Therefore, the B content is set to 0.003 to 0.018 mass%.

“Cr: 0.30 mass% or less”
In general, Cr is an element that improves strength and toughness. However, in the first and second inventions of the present application, the improvement in strength and toughness is obtained mainly by the addition of Mo, while the content of Cr If it exceeds 0.30 mass%, hot cracking occurs or the toughness deteriorates due to hardening of the weld metal. Therefore, Cr content shall be 0.30 mass% or less.

“V: 0.030 mass% or less”
V generally improves the strength of the weld metal, but as described above, in the present invention, the strength is ensured by addition of other elements such as Mo, while the V content is 0.030 mass. If it exceeds 50%, the weld metal hardens and the toughness deteriorates. Therefore, V content shall be 0.030 mass% or less.

“Nb: 0.030 mass% or less”
Nb generally improves the strength of the weld metal in the same way as V, but in the present invention, the strength is ensured by adding other elements such as Mo, while the Nb content is 0.030 mass. If it exceeds 50%, the weld metal hardens and the toughness deteriorates. Therefore, Nb content shall be 0.030 mass% or less.

“N: 0.012 mass% or less”
Since N is an element that lowers the toughness of the weld metal, its content is preferably reduced as much as possible. When the N content exceeds 0.012% by mass, the toughness is significantly deteriorated. Therefore, N content shall be 0.012 mass% or less.

Next, the reasons for limiting the components of FeO and B ₂ O ₃ which are the compositions of the welding flux in the present invention will be described.

“FeO: 4.5% by mass or less”
If FeO exceeds 4.5 mass%, welding stability deteriorates, and in some cases, welding stops, oxygen in the weld metal increases, and the balance between the B content and the oxygen content in the weld metal is lost. Therefore, since good toughness cannot be obtained, FeO is regulated to 4.5% by mass or less.

“B ₂ O ₃ : 1.5% by mass or less”
In the present invention, since B is supplied into the weld metal by a wire, basically, it is not necessary to add B ₂ O ₃ . On the other hand, when the amount of B ₂ O ₃ exceeds 1.5% by mass, the amount of B in the weld metal becomes excessive, and the toughness of the weld metal is deteriorated due to the formation of the martensite phase, and high temperature cracking is likely to occur. Therefore, the B ₂ O ₃ content is regulated to 1.5% by mass or less.

  Next, the reason for limiting the numerical value of the basicity BL of the welding flux in the present invention will be described. The composition of the welding flux is determined in consideration of characteristics such as melting point, fluidity and viscosity of slag, and is composed of oxide and fluoride. In the present invention, the basicity BL is used as an index for determining the oxygen content in the weld metal, and the oxygen content in the weld metal is adjusted to an appropriate range by making the range of the basicity BL appropriate. The basicity BL is a value calculated by the formula 1.

“Basicity BL: 0.5 to 1.5”
When the basicity BL is less than 0.5, the amount of oxygen in the weld metal becomes excessive, and improvement in toughness cannot be expected. On the other hand, if the basicity BL exceeds 1.5, the melting point of the slag becomes too high and a stop occurs during welding. The welding stop is a phenomenon in which the melting point of the slag bath is high and the viscosity becomes excessively high, the conduction between the wire and the slag is deteriorated, the conduction is stopped during welding, and the welding is stopped. Therefore, the basicity BL is set to 0.5 to 1.5.

“Variable (X): 9.8 to 20.8”
Next, the relationship between the basicity BL of the welding flux and the B amount of the welding wire will be described. As described above, the basicity BL of the welding flux is a value that correlates with the amount of oxygen in the weld metal. On the other hand, the amount of B in the welding wire is extremely effective for toughness because it suppresses the growth of the pro-eutectoid ferrite phase by the generation of proper solute B. In order to form such a solid solution B, it is necessary to add B that is not fixed as an oxide and nitride of B. When it is difficult to obtain stable toughness as in electroslag welding, it is possible to generate solid solution B by controlling the amount of B in the weld metal and the amount of oxygen in the weld metal to obtain stable toughness in the weld line direction. It is. At that time, the B content (B) in the welding wire and the value of Equation 2 (variable (X)) obtained from the basicity BL are set to 9.8 to 20.8. When (X) is less than 9.8, since the B amount of the welding wire is too low with respect to the basicity BL of the welding flux, solid solution B is not generated, and stable toughness cannot be obtained. On the other hand, if (X) exceeds 20.8, the amount of B of the welding wire is too high with respect to the basicity BL of the welding flux, so the amount of dissolved B becomes excessive, the weld metal hardens, and the toughness deteriorates. , Hot cracking may occur. Therefore, the range of (X) is 9.8 to 20.8.

In addition, the component composition of a welding flux is as follows, for example.
SiO ₂ : 25 to 50% by mass
CaO: 5 to 25% by mass
Al ₂ O ₃ : 15 mass% or less CaF ₂ : 20 mass% or less MgO: 16 mass% or less MnO: 25 mass% or less TiO ₂ : 10 mass% or less

  Next, the effects of the present invention will be described in comparison with comparative examples that are out of the scope of the present invention. FIG. 1 shows a welded joint used in a welding test, in which a flat bar defined in JIS standard SN490 is used as a side plate c. The numerical value in a figure is a dimension of each member, and welding length is 800 mm. Skin plate a and diaphragm b are thick plates having a thickness of 60 mm.

  Table 1 below shows the composition (mass%) of skin plate a and diaphragm b. However, the balance in Table 1 is Fe and inevitable impurities. Then, electroslag welding was performed under the welding conditions shown in Table 2 below. The amount of welding flux input was 120 g. The composition of the welding wire is shown in the following Table 3-1, Table 3-2, Table 3-3, and Table 3-4. Moreover, the basicity BL of welding flux, the value of variable (X), and a composition are shown according to the said Tables 3-1 to 3-4. In Tables 3-1 to 3-4, the compositions of the types of flux F1 to F6 are as shown in Table 4 below.

  After the welding was completed, the presence or absence of hot cracking was confirmed by an ultrasonic exploration test, and a tensile test piece d and a Charpy impact test piece e were collected from the sampling position shown in FIG. 2, and the mechanical properties of the weld metal were investigated. Tensile test pieces were collected only at a location of 300 mm and subjected to a tensile test. The impact test piece was sampled at 200 mm, 400 mm, and 600 mm in the weld line direction, and the test temperature was 0 ° C. (n = 3, average value). The test results are shown in Tables 5-1 and 5-2 below.

  As shown in Tables 5-1 and 5-2, Example No. 1 to 19, the chemical composition of the welding wire, the basicity BL of the welding flux, and the value (X) of Equation 2 satisfy the scope of the present invention, so that good tensile performance and good impact in the weld line direction are obtained. Performance was obtained.

On the other hand, Comparative Example No. About 20, since the C content was lower than the specified range, the tensile strength was low and the toughness was low. Comparative Example No. For No. 21, since the amount of C was higher than the specified range, hot cracking occurred and the test was stopped. Comparative Example No. Regarding No. 22, since the Si amount was lower than the specified range, the hardenability of the weld metal was insufficient, and the tensile strength and toughness were low. Comparative Example No. For No. 23, the amount of Si was higher than the specified range, so hot cracking occurred and the test was stopped. Comparative Example No. About 24, since the amount of Mn was lower than the regulation range, hardenability was inadequate and tensile strength and toughness were low values. Comparative Example No. For No. 25, since the amount of Mn was higher than the specified range, the hardenability was excessive and cracking occurred, and the test was stopped. Comparative Example No. For No. 26, the amount of Ni was higher than the specified range, so hot cracking occurred and the test was stopped. Comparative Example No. For No. 27, the Mo content was lower than the specified range, so the hardenability was insufficient and the tensile strength and toughness were low. Comparative Example No. For 28, the amount of Mo was higher than the specified range, so hot cracking occurred, and the test was stopped. Comparative Example No. Regarding No. 29, since the Al content was lower than the specified range, the deoxidation effect was not sufficient and the toughness value was low. Comparative Example No. For No. 30, since the Al content was higher than the specified range, the toughness deteriorated due to the large amount of Al oxide. Comparative Example No. Regarding No. 31, since the Ti amount was lower than the specified range, the generation of the acicular ferrite phase was not sufficient, and the toughness value was low. Comparative Example NO. Regarding No. 32, since the Ti amount was higher than the specified range, the Ti precipitates of the weld metal became excessive and the toughness deteriorated. Comparative Example No. As for No. 33, since the amount of B is lower than the specified range, the effect of suppressing the growth of pro-eutectoid ferrite is not sufficient, and since the value (X) of Formula 2 is lower than the specified range, solid solution B is not generated. As a result, the effect of suppressing initial ferrite was insufficient, and the toughness value was low. Comparative Example No. For No. 34, the amount of B is higher than the specified range, and since the value (X) of Formula 2 is higher than the specified range, the solid solution B is excessive, and hot cracking occurs due to hardening of the weld metal, and the test is stopped. did. Comparative Example No. For 35, the amount of Cr was higher than the specified range, so hot cracking occurred and the test was stopped. Comparative Example No. As for 36, the toughness deteriorated because the V amount was higher than the specified range. Comparative Example No. For No. 37, the toughness deteriorated because the Nb amount was higher than the specified range. Comparative Example No. For No. 38, the toughness deteriorated because the N content was higher than the specified range. Comparative Example No. For No. 39, since the basicity BL of the welding flux was lower than the specified range, the oxygen content of the weld metal was excessive and the toughness value was low. Comparative Example No. About 40, since BL was higher than a regulation range, since melting | fusing point of slag was high and welding stopped, it stopped. Comparative Example No. For 41 and 42, since the value (X) of Formula 2 was lower than the specified range, solid solution B was not generated, and accordingly, the effect of suppressing the initial ferrite became insufficient and the toughness deteriorated. Comparative Example No. For 43, 44, and 45, the value (X) in Equation 2 was higher than the specified range, so the amount of dissolved B was excessive, and the toughness deteriorated due to the hardening of the weld metal. Comparative Example No. For 46, the amount of FeO was higher than the specified range, so welding was not stable and the welding test was stopped. Comparative Example No. For 47, since the amount of B ₂ O ₃ was higher than the specified range, hot cracking occurred and the test was stopped.

  The relationship between the amount of weld metal B-basicity and absorbed energy is shown in FIG. In FIG. 3, the values in Tables 5-1 and 5-2 are arranged by the amount of B (B) in the wire and the value of basicity BL. In FIG. 3, ○ indicates that the toughness value is good (when it exceeds 100 J at all three sampling positions), and × indicates that the toughness value is low (if one of the three sampling positions does not satisfy 100J). Show. As shown in FIG. 3, the basicity BL is 0.5 to 1.5, and the value (X) in Equation 2 is related to the B amount (B) in the wire and the basicity BL. When it is in the range indicated by the solid line, the toughness value is high, and when it is out of this range, the toughness value is low.

It is a schematic diagram which shows the welded joint used for the welding test. It is a schematic diagram which shows the collection position of a test piece. It is a graph which shows the range whose toughness value is high, taking the amount of B in the welding wire on the horizontal axis and taking the basicity BL on the vertical axis.

Explanation of symbols

a: Skin plate b: Diaphragm c: Side plate d: Tensile test piece e: Charpy impact test piece

Claims (3)

In a high heat input electroslag welding method using a welding wire and welding flux,
The welding wire has C: 0.02 to 0.25% by mass, Si: 0.05 to 1.80% by mass, Mn: 0.50 to 3.50% by mass, Ni: 3. 00 mass% or less, Mo: 0.05 to 2.00 mass%, Al: 0.005 to 0.080 mass%, Ti: 0.05 to 0.35 mass%, B: 0.003 to 0.018 Contains: mass%, Cr: 0.30 mass% or less, V: 0.030 mass% or less, Nb: 0.030 mass% or less, N: 0.012 mass% or less, and the balance from Fe and inevitable impurities Become
The welding flux contains FeO: 4.5% by mass or less, B ₂ O ₃ : 1.5% by mass or less per total mass of the flux,
The SiO ₂ content (% by mass) of the flux is [SiO ₂ ], the CaO content (% by mass) is [CaO], the Al ₂ O ₃ content (% by mass) is [Al ₂ O ₃ ], and CaF _{2 is} contained. The amount (mass%) is [CaF ₂ ], the MgO content (mass%) is [MgO], the MnO content (mass%) is [MnO], the TiO ₂ content (mass%) is [TiO ₂ ], FeO When the content (mass%) is [FeO], the basicity BL value given by the following mathematical formula (1) is set to 0.5 to 1.5,
When the B content in the welding wire is (B), the variable (X) given by the following formula (2) from the basicity BL and the B amount (B) in the welding wire is 9.8 to 20.8. A high heat input electroslag welding method characterized by satisfying

... (1)
(X) = 1000 × (B) + 5.1 × BL (2) The high heat input electroslag welding method according to claim 1, wherein the Ni content of the welding wire is Ni: 0.50 to 3.00 mass% per total mass of the wire. The high heat input electroslag welding method according to claim 2, wherein the Ni content of the welding wire is Ni: 0.50 to 2.00 mass% per total mass of the wire.

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