JP4954123B2 - Electroslag welding method with excellent weld metal toughness - Google Patents

Description

  The present invention relates to a high heat input electroslag welding method having a welding heat input of 400 kJ / cm or more, and in particular, a toughness value of a high-strength steel plate (thickness of 40 mm or more) of 490 to 740 MPa class at each part in the weld joint direction. The present invention relates to a high heat input electroslag welding method in which the toughness of a weld metal part that can be obtained and welded is excellent.

  Electroslag welding is mainly used for upright welding of the inner diaphragm in a steel 4-sided BOX column. And generally compared with the submerged arc welding in which high-efficiency welding is realized, electroslag welding has a higher efficiency and is known as a welding method capable of large-heat-input one-pass welding.

  By the way, with regard to building members and frames to which electroslag welding is applied, in recent years, high toughness values are also required for welded metal parts from the viewpoint of securing plastic deformation capability at the time of an earthquake and extending the life.

  However, electroslag welding has a large heat input of about 800 kJ / cm when compared to other arc welding, so the cooling rate of the weld metal decreases and the structure becomes coarse, resulting in the toughness of the weld metal. There is a problem that it decreases. In order to prevent such a decrease in toughness of the weld metal, there is a method for improving the toughness by refining the weld metal structure by adding a small amount of Ti and B to the weld metal.

  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 location where the specimen is collected.

  Thus, techniques for ensuring toughness in electroslag welding are disclosed in Patent Documents 1 to 3.

Patent Document 1 includes a predetermined amount of Si, Mo, Cr, Nb, and V, which are elements that stabilize the δ ferrite phase and improve the hardenability in the welding wire, and are coarse proeutectoids at austenite grain boundaries. It is characterized by containing a predetermined amount of B that has the effect of suppressing the formation of ferrite, and further contained in this welding wire in order to suppress the formation of cementite (Fe ₃ C) that impairs the toughness in the crystal grains. By suppressing the C content and increasing the Si content, the toughness of the weld metal during high heat input electroslag welding is improved.

  In Patent Document 2, a large amount of Ti is added from a welding wire and a low basicity welding flux is used, so that a sufficient amount of oxide containing Ti that becomes a nucleus of acicular ferrite formation is added to the molten metal. It is possible to disperse and to obtain a high toughness weld metal mainly composed of an acicular ferrite structure. In addition, in high heat input electroslag welding, the cooling rate of the weld metal is extremely slow and the toughness of the weld metal deteriorates, so the hardenability of the weld metal is adjusted or segregated at the prior austenite grain boundaries, B to suppress ferrite is added.

In Patent Document 3, by adding a large amount of Ti from a welding wire and using a welding flux with a low basicity, a sufficient amount of oxide containing Ti that becomes a nucleus of acicular ferrite formation is added to the molten metal. It is possible to disperse and to obtain a high toughness weld metal mainly composed of an acicular ferrite structure. In high heat input electroslag welding, it is necessary to appropriately add B that segregates at austenite grain boundaries and suppresses the formation of intergranular ferrite. Thus, in order to obtain a yield in the weld metal, a welding wire containing a predetermined amount of B and a flux previously added with a predetermined amount of B ₂ O ₃ are used for electroslag welding.

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

  However, in the technique described in Patent Document 1, no consideration is given to the flux component that greatly affects the oxygen content of the weld metal, and it cannot be said that a stable toughness value in the weld line direction can be obtained.

Moreover, in the technique described in Patent Document 2, it cannot be said that a high toughness value is obtained in both the examples and the comparative examples. Moreover, although the flux component is specified, the amount of B ₂ O ₃ is not specified, a stable yield of B amount in the weld line direction cannot be obtained, and a stable toughness value in the weld line direction is obtained. I can't say that.

Further, in Patent Document 3, although the amount of B ₂ O ₃ in the flux is specified, most amount of B ₂ O ₃ as described in the Examples and Comparative Examples are more than 1.5 wt% It is excessive, the yield of B on the welding start side is excessive, the toughness on the starting side is lowered, and cracking may occur in some cases.

  This invention is made | formed in view of this problem, Comprising: It aims at providing the electroslag welding method which can obtain the weld metal which has a stable high toughness value.

The electroslag welding method with excellent toughness of the weld metal part according to the present invention is an electroslag welding method for electroslag welding of a steel plate, in which 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% by mass or less, Mo: 0.05 to 2.00% by mass, Al: 0.005 to 0.080% by mass, Ti : 0.05 to 0.35 mass%, B: 0.003 to 0.018 mass%, Cr: 0.30 mass% or less, V: 0.030 mass% or less, Nb: 0.030 mass% or less, N: a welding wire containing 0.012% by mass or less, with the balance being Fe and inevitable impurities;
SiO ₂ : 25 to 50% by mass, CaO: 5 to 25% by mass, Al ₂ O ₃ : 15% by mass or less, CaF ₂ : 20% by mass or less, MgO: 16% by mass or less, MnO: 25% by mass or less, TiO ₂ : welding flux containing 10% by mass or less, FeO: 4.5% by mass or less, B ₂ O ₃ : 1.5% by mass or less,
Welding using
When the B content in the welding wire is [mass% of B in the wire] and the B ₂ O ₃ content in the welding flux is [mass% of B ₂ O _{3 in} the flux], the following formula ( The value X of 1) is 0.122 to 1.022;
The welding flux has a SiO ₂ content (mass%) of [SiO ₂ ], a CaO content (mass%) of [CaO], an Al ₂ O ₃ content (mass%) of [Al ₂ O ₃ ], and CaF _2. Content (mass%) is [CaF ₂ ], MgO content (mass%) is [MgO], MnO content (mass%) is [MnO], TiO ₂ content (mass%) is [TiO ₂ ], When the FeO content (% by mass) is [FeO] and the B ₂ O ₃ content (% by mass) is [B ₂ O ₃ ], the basicity BL represented by the following formula (2) is 0.5 to 0.5. 1.5
A value Y of the following mathematical formula (3) obtained from the B content in the welding wire and the basicity BL of the welding flux is 9.8 to 20.8.

  In the electroslag welding method in which the toughness of the weld metal part is excellent, the content of Ni in the welding wire is preferably Ni: 0.50 to 3.00 mass%. Particularly preferably, the content of Ni in the welding wire is Ni: 0.50 to 2.00% by mass.

  According to the present invention, stable toughness can be secured in the weld joint direction even in high heat input electroslag welding in which heat input exceeds 400 kJ / cm.

In order to ensure stable toughness in the weld joint direction even in high heat input electroslag welding where the heat input exceeds 400 kJ / cm, the present inventors mainly used B amount of electroslag welding wire and electroslag welding flux. Thus, the present inventors have found that it is essential that the amount of B ₂ O ₃ greatly affects and the amount of B is uniformly distributed in the weld line direction.

  Hereinafter, the present invention will be described in detail. First, in the composition of the welding wire, the reason for adding the component and the reason for limiting the composition 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 that hot cracking will occur. 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 has the effect of improving the hardenability, 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, if it exceeds 3.50% by mass, the hardenability becomes too high, the strength increases, the hot cracking resistance deteriorates, and the toughness deteriorates. Therefore, the Mn content is 0.50 to 3.50 mass%.

"Ni: 3.00 mass% or less"
Ni generally has the effect of strengthening the matrix and improving toughness by addition, but in the present invention, the improvement in toughness is supplemented by the addition of Mo. On the other hand, if the Ni content exceeds 3.00 mass%, the solid-liquid coexistence region is increased due to a decrease in the A3 transformation point, and as a result, the hot crack resistance is deteriorated. Therefore, the Ni content is 3.00% by mass or less. In addition, in order to acquire the effect of a toughness improvement, it is necessary to add Ni 0.50 mass% or more. Therefore, when Ni is positively added, the Ni content is 0.50 to 3.00 mass%. Note that even if Ni is added in excess of 2.00 mass%, the toughness cannot be improved anymore and the cost increases. Therefore, the Ni content is more preferably 0.50 to 2.00 mass%.

“Mo: 0.05 to 2.00% by mass”
Mo has a great effect on enhancing the hardenability and improving the strength and toughness of the weld metal, but the above effect cannot be expected if the Mo content is less than 0.05% by mass. 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 and toughness of the weld metal are deteriorated. On the other hand, when the Al content exceeds 0.080% by mass, a large amount of Al oxide is formed, and the toughness deteriorates because it inhibits the formation of Ti oxide, which is the nucleus of acicular ferrite formation. Therefore, the Al content is set to 0.005 to 0.080 mass%.

“Ti: 0.05 to 0.35 mass%”
Ti serves as a nucleus for generating acicular ferrite as a Ti oxide, and 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, if it exceeds 0.35% by mass, the amount of Ti precipitates in the weld metal becomes excessive and 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 0.0030% by mass, the above effect cannot be expected. On the other hand, if the B content exceeds 0.0180% by mass, the hardenability of the weld metal becomes excessive, and hot cracking is likely to occur, or the toughness of the weld metal deteriorates due to the formation of a 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 a component that improves strength and toughness, but in the present invention, the above performance is supplemented by other components such as Mo, and hot cracking occurs when the Cr content exceeds 0.30% by mass. Or toughness deteriorates due to the 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 in the present invention, the strength is secured by other components such as Mo, and when the V content exceeds 0.030 mass%, the weld metal is cured. And 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 manner as V, but in the present invention, the strength is secured by other components such as Mo, and if the Nb content exceeds 0.030 mass%, the weld metal Hardens and 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 as low 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 reason for adding the component and the reason for limiting the composition in the welding flux composition in the present invention will be described.

“SiO ₂ : 25 to 50% by mass”
SiO ₂ is an acidic component and an essential component for slag formation. When the SiO ₂ content is less than 25% by mass, the slag viscosity is insufficient and welding is likely to stop. On the other hand, if the SiO ₂ content exceeds 50% by mass, the amount of oxygen in the weld metal becomes excessive, and sufficient toughness cannot be ensured. Therefore, the SiO ₂ content is 25 to 50% by mass.

“CaO: 5 to 25% by mass”
CaO is a basic component, has an effect of lowering the solidification temperature of molten slag and an effect of lowering viscosity, and is added in an appropriate amount. When the CaO content is less than 5% by mass, the weld metal oxygen amount becomes excessive and the toughness deteriorates. On the other hand, if the CaO content exceeds 25% by mass, the viscosity of the slag becomes low and welding stops easily. Therefore, the CaO content is 5 to 25% by mass.

“Al ₂ O ₃ : 15% by mass or less”
Al ₂ O ₃ acts as a slag forming agent and has the effect of lowering the viscosity of the molten slag, but this effect is sufficiently supplemented by the addition of CaO. On the other hand, when the Al ₂ O ₃ content exceeds 15% by mass, the fluidity of the molten slag is deteriorated, and welding is likely to stop. Therefore, the Al ₂ O ₃ content is regulated to 15% by mass or less.

“CaF ₂ : 20% by mass or less”
CaF ₂ is a very effective component for reducing the oxygen content of the weld metal, but since this effect can be compensated by adjusting other components, the addition of CaF ₂ is not an essential component. On the other hand, when CaF ₂ exceeds 20% by mass, the viscosity of the slag increases and welding is likely to stop. Therefore, the CaF ₂ content is regulated to 20% by mass or less.

“MgO: 16% by mass or less”
MgO is a basic component and is added to reduce the oxygen content of the weld metal and adjust the viscosity. However, since this effect is expected by the addition of CaO, it cannot be said to be an essential component. On the other hand, if MgO exceeds 16% by mass, the viscosity becomes excessive and welding is likely to stop. Therefore, the MgO content is restricted to 16% by mass or less.

“MnO: 25% by mass or less”
MnO is effective in adjusting the viscosity of the slag. However, since this effect can be ensured by the addition of SiO _2, the addition of MnO is not essential. On the other hand, when the content of MnO exceeds 25% by mass, the viscosity of the slag increases and welding is likely to stop. Therefore, the MnO content is regulated to 25% by mass or less.

“TiO ₂ : 10% by mass or less”
TiO ₂ generally improves the yield of Ti to the weld metal, but in the present invention, the addition of TiO ₂ is not particularly required. On the other hand, when TiO ₂ exceeds 10% by mass, the viscosity of the slag increases and welding is likely to stop. Therefore, the TiO ₂ content is restricted to 10% by mass or less.

“FeO: 4.5% by mass or less”
When FeO exceeds 4.5 mass%, welding stability deteriorates, and in some cases, welding stop occurs, and oxygen in the weld metal increases. At the same time, in the present invention, B ₂ O ₃ is added to stabilize the B amount in the weld line direction, and the amount of weld metal oxygen increases due to the reduction reaction from B ₂ O ₃ to B. For this reason, when FeO exceeds 4.5 mass%, the amount of oxygen in the weld metal further increases, the balance between the amount of weld metal B and the amount of oxygen is lost, and good toughness cannot be obtained. Restricted to 5 mass% or less.

“B ₂ O ₃ : 1.5% by mass or less”
In the present invention, B ₂ O ₃ is an auxiliary component necessary for stably supplying B into the weld metal, and the amount of B in the electroslag welding wire is as low as 0.004% by mass or less. Sometimes, B ₂ O ₃ addition from the flux becomes unnecessary. On the other hand, if the amount of B ₂ O ₃ exceeds 1.5% by mass, the amount of B in 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 ₂ O ₃ content is regulated to 1.5% by mass or less.

“Basicity BL: 0.5 to 1.5”
Next, the regulation 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 the slag, and is composed of oxide and fluoride. In the present invention, basicity BL is used as an index for determining the amount of oxygen in the weld metal. This basicity BL is a value calculated by Equation 2. When the basicity BL is less than 0.5, the amount of weld metal oxygen becomes excessive, and the toughness cannot be improved. On the other hand, if the basicity BL exceeds 1.5, the melting point of the slag becomes too high, and welding stops easily. Therefore, the basicity BL needs to be 0.5 to 1.5.

“Relationship between the basicity BL of the welding flux and the B amount of the welding wire: the value Y in Equation 3”
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 defines 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 solid solution B. In order to form such a solid solution B, it is necessary to add B that is not fixed as an oxide or nitride. When it is difficult to obtain stable toughness as in electroslag welding, it is possible to generate solid solution B by controlling the B amount of the weld metal and the oxygen amount of the weld metal to obtain a stable toughness in the weld line direction. Is possible. For this purpose, it is necessary that the numerical formula 3 represented by the B content in the wire and the basicity BL satisfies 9.8 to 20.8.

  That is, when Y = 1000 × [mass% of B in the wire] + 5.1 × BL is less than 9.8, the amount of B of the welding wire is too low with respect to the basicity BL of the welding flux. Molten B is not generated and stable toughness cannot be obtained. On the other hand, if Y = 1000 × [mass% of B in the wire] + 5.1 × BL exceeds 20.8, the amount of B of the welding wire is too high with respect to the basicity BL of the welding flux. The amount becomes excessive, the weld metal is hardened, the toughness is deteriorated, and hot cracking may occur. Therefore, the value of Y = 1000 × [mass% of B in the wire] + 5.1 × BL is 9.8 to 20.8.

“Relationship between the amount of B in the wire and the amount of B ₂ O ₃ in the flux: the value X in Equation 1”
Next, the relationship between the amount of B in the wire and the amount of B ₂ O ₃ in the flux will be described. As described above, in order to ensure the toughness of the welded portion, it is essential to add the B amount in balance with the oxygen amount of the weld metal. However, if the amount of weld metal B is not constant in the weld line direction, the balance with the amount of weld metal oxygen is lost, and the toughness deteriorates. Addition of B ₂ O ₃ in the flux is effective for uniform addition of the amount of weld metal B. However, if the flux B ₂ O ₃ is excessive, that is, the value X = 128 × [in the wire If the mass% of B]-[mass% of B ₂ O _{3 in} the flux] is less than 0.122, the amount of weld metal B becomes excessive, the amount of solid solution B becomes excessive, the weld metal hardens, and the toughness is increased. to degrade. On the other hand, when the flux B ₂ O ₃ is insufficient, that is, when the value X of Equation 1 = 128 × [mass% of B in the wire] − [mass% of B ₂ O _{3 in} the flux] exceeds 1.022. The solid solution B is not generated, and stable toughness cannot be obtained. Therefore, the value X = 128 × [mass% of B in the wire] − [mass% of B ₂ O _{3 in} the flux] in Equation 1 is set to 0.122 to 1.022.

Next, examples of the present invention will be described in comparison with comparative examples that are out of the scope of the present invention. As shown in FIG. 1, in the welding test, a flat bar defined in JIS standard SN490 is erected as a pair of side plates c on a skin plate a having a thickness of 60 mm, and a plate material having a thickness of 60 mm is provided between the side plates c. A welded joint sandwiching the diaphragm b was produced (weld length 800 mm). The welding location in this weld joint is a space surrounded by the diaphragm b, the side plate c, and the skin plate a. The dimensions of each member are as shown in FIG. Table 1 shows the chemical composition (mass%) of the skin plate a and the diaphragm b. And electroslag welding was implemented on the welding conditions shown in Table 2. The flux input was 120 g. The compositions of the welding wire and the welding flux are shown in the following Table 3-1, Table 3-2, Table 3-3, Table 3-4 and Table 4. However, in the flux column of Table 3, the flux composition is as shown in Table 4. Among them, only FeO and B ₂ O ₃ were extracted and listed in the flux column of Table 3.

  After welding was completed, high temperature cracking was confirmed by UT (ultrasonic exploration), and a tensile test piece d and a Charpy impact test piece e were collected at the sampling position shown in FIG. 2 to investigate the mechanical properties of the weld metal. 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.

  In Examples 1 to 20 of the present invention, the composition of the welding wire, the composition of the welding flux, and the basicity BL of the welding flux satisfy the specified range of the present invention. Good impact performance was obtained.

  On the other hand, in Comparative Example 21, since the C content was lower than the specified range, the tensile strength was low and a sufficient toughness value could not be obtained. About Comparative Example 22, since the amount of C was higher than the specified range, hot cracking occurred and the test was stopped. In Comparative Example 23, 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 not sufficiently satisfied. About Comparative Example 24, since the amount of Si was higher than the specified range, hot cracking occurred and the test was stopped. About Comparative Example 25, since the amount of Mn was lower than the specified range, the hardenability was insufficient, and the tensile strength and toughness values were low. About Comparative Example 26, since the amount of Mn was higher than the specified range, the hardenability was excessive and cracking occurred, and the test was stopped. About Comparative Example 27, since the amount of Ni was higher than the specified range, hot cracking occurred and the test was stopped.

  About Comparative Example 28, since the Mo amount was lower than the specified range, the hardenability was insufficient, and the tensile strength and toughness were low. For Comparative Example 29, the amount of Mo was higher than the specified range, so hot cracking occurred and the test was stopped. In Comparative Example 30, since the Al amount was lower than the specified range, the deoxidation effect was not sufficient and the toughness value was low. About Comparative Example 31, since the Al amount was higher than the specified range, the toughness was low due to the large amount of Al oxide generated. In Comparative Example 32, 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. In Comparative Example 33, since the Ti amount was higher than the specified range, the Ti precipitate of the weld metal was excessive and the toughness was deteriorated. For Comparative Example 34, the amount of Cr was higher than the specified range, so hot cracking occurred and the test was stopped. In Comparative Example 35, the toughness deteriorated because the V amount was higher than the specified range. In Comparative Example 36, the toughness deteriorated because the Nb amount was higher than the specified range. About Comparative Example 37, 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 Y of Formula 3 is lower than the specified range, solid solution B is not generated, and toughness The value was low.

For Comparative Example 38, the amount of B was higher than the specified range, and because the value Y in Formula 3 was higher than the specified range, hot cracking occurred due to hardening of the weld metal, and the test was stopped. In Comparative Example 39, the toughness deteriorated because the N amount was higher than the specified range. About the comparative example 40, since basicity BL was higher than the regulation range, since melting | fusing point of slag was high and welding stopped, it stopped. In Comparative Example 41, since the basicity BL of the welding flux was lower than the specified range, the oxygen amount of the weld metal was excessive and the toughness value was low. About Comparative Example 42, since the amount of FeO in the flux was higher than the specified range, welding stability deteriorated and welding was stopped. Comparative Example 43, since the amount of B ₂ O ₃ in the flux is higher than the specified range, hot cracking occurred, the test was stopped. In Comparative Examples 44 and 46, since the value Y in Formula 3 was higher than the specified range, the amount of solute B was excessive, and the toughness deteriorated due to the hardening of the weld metal. In Comparative Examples 45 and 47, since the value Y in Formula 3 was lower than the specified range, solid solution B was not generated, and accordingly, the effect of suppressing pro-eutectoid ferrite became insufficient and the toughness deteriorated. In Comparative Examples 48 and 50, since the value X in Formula 1 was higher than the specified range, the solid solution B was not generated, and accordingly, the effect of suppressing pro-eutectoid ferrite became insufficient and the toughness deteriorated. In Comparative Examples 49 and 51, since the value X in Formula 1 was lower than the specified range, the weld metal was hardened and the toughness deteriorated.

FIG. 3 is a graph showing the range in which the toughness value is good with ◯, with the B content in the wire on the horizontal axis and the basicity on the vertical axis. FIG. 4 is a graph showing the range in which the toughness value is good with ◯, where the horizontal axis represents the B content in the wire and the vertical axis represents the B ₂ O ₃ content in the flux. In Table 5, ○ indicates that the toughness value is good. In Table 5, the case where the toughness value is 100 J or more is extracted and plotted at all three sampling positions, and x indicates that the toughness value is low. In Table 5, the case where the toughness value does not satisfy 100J among the three sampling positions is extracted and plotted. As shown in FIG. 3, a high toughness value is obtained when the basicity BL and the value Y of Formula 3 satisfy claim 1. Moreover, as shown in FIG. 4, when the value X of Formula 1 satisfies Claim 1, a high toughness value is obtained.

It is a figure which shows the joint shape in a welding test. It is a figure which shows the sampling position of a test piece. It is a graph which shows the relationship between B content in a wire, basicity, and absorbed energy. Is a graph showing the relationship between the B content in the wire and B ₂ O ₃ content in the flux and the absorbed energy.

Explanation of symbols

a: skin plate, b: diaphragm, c: side plate, d: tensile test piece, e: Charpy impact test piece

Claims (3)

In the electroslag welding method of electroslag welding a steel plate, C: 0.02 to 0.25% by mass, Si: 0.05 to 1.80% by mass, Mn: 0.50 to 3.50 per total mass of the wire. 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 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, the balance A welding wire consisting of Fe and inevitable impurities;
Per total mass of flux, SiO ₂ : 25 to 50% by mass, CaO: 5 to 25% by mass, Al ₂ O ₃ : 15% by mass or less, CaF ₂ : 20% by mass or less, MgO: 16% by mass or less, MnO: 25 A welding flux containing: mass% or less, TiO ₂ : 10 mass% or less, FeO: 4.5 mass% or less, B ₂ O ₃ : 1.5 mass% or less,
Welding using
When the B content in the welding wire is [mass% of B in the wire] and the B ₂ O ₃ content in the welding flux is [mass% of B ₂ O _{3 in} the flux], the following formula ( The value X of 1) is 0.122 to 1.022;
The welding flux has a SiO ₂ content (mass%) of [SiO ₂ ], a CaO content (mass%) of [CaO], an Al ₂ O ₃ content (mass%) of [Al ₂ O ₃ ], and CaF _2. Content (mass%) is [CaF ₂ ], MgO content (mass%) is [MgO], MnO content (mass%) is [MnO], TiO ₂ content (mass%) is [TiO ₂ ], When the FeO content (% by mass) is [FeO] and the B ₂ O ₃ content (% by mass) is [B ₂ O ₃ ], the basicity BL represented by the following formula (2) is 0.5 to 0.5. 1.5
The toughness of the weld metal part is excellent in that the value Y of the following mathematical formula (3) obtained by the B content in the welding wire and the basicity BL of the welding flux is 9.8 to 20.8. Electroslag welding method.
X = 128 × [mass% of B in wire] − [mass% of B ₂ O _{3 in} flux]
... (1)

... (2)
Y = 1000 × [mass% of B in the wire] + 5.1 × BL (3) 2. The electroslag welding with excellent toughness of the weld metal part according to claim 1, wherein the Ni content of the welding wire is Ni: 0.50 to 3.00 mass% per the total mass of the wire. Method. The electroslag welding with excellent toughness of the weld metal part according to claim 2, wherein the Ni content of the welding wire is Ni: 0.50 to 2.00% by mass with respect to the total mass of the wire. Method.

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