JP7040435B2 - Multi-layered arc welding method for thick steel plates - Google Patents

Description

The present invention relates to a multi-layered arc welding method in which arc welding is performed in two or more passes in order to join thick steel plates.

As for structures using steel materials such as thick steel plates (for example, high-rise buildings, etc.), large-scale structures have been constructed with the recent improvement in manufacturing technology for thick steel plates. In other words, as a result of the development of technology that not only increases the thickness of thick steel plates but also increases their strength, it has become possible to construct large-scale structures.

Thick steel plates with a thickness of about 50 mm are widely used, but thick steel plates with a thickness of 50 mm or more (so-called extra-thick steel plates) are used for large-scale structures, and the steel frames that support the structures are used. Thick steel plates with a thickness of 50 mm or more are also used for (so-called box columns). In order to build a high-rise building or the like using such a thick steel plate, a technique for welding the thick steel plate is indispensable. Submerged arc welding has been widely used for welding thick steel sheets, but various welding techniques are being studied in order to further improve the efficiency of welding work.

For example, Patent Document 1 discloses a technique for welding a thick steel plate having a plate thickness of 50 mm or more in one pass using two electrodes. This technology welds thick steel plates by submerged arc welding with high heat input, but welding thick steel plates by high heat input and one-pass welding leaves many technical and equipment restrictions. Therefore, welding with two or more passes (so-called multi-layer welding) is widespread at construction sites.

Patent Document 2 discloses a technique for welding a thick steel sheet by submerged arc welding of two or more passes.
Further, a technique of multi-layer welding that combines submerged arc welding and carbon dioxide arc welding is also being studied, but the problem of low-temperature cracking is solved as in the case of multi-layer welding by submerged arc welding only disclosed in Patent Document 2. It has not been.

In the following, multi-layer welding using only submerged arc welding and multi-layer welding that combines submerged arc welding and carbon dioxide arc welding are collectively referred to as multi-layer arc welding.

Japanese Patent No. 2947731 Japanese Patent No. 3624727

It is an object of the present invention to provide a multi-layered arc welding method for a thick steel plate capable of solving the problems of the prior art and preventing low temperature cracking of the weld metal.

The present inventor performed multi-layered arc welding of thick steel sheets under various conditions, and investigated the relationship between the state of occurrence of low-temperature cracks in the weld metal and the welding conditions. As a result, when performing multi-layered arc welding only by submerged arc welding,
(1) Perform the first pass by submerged arc welding with heat input of 300 kJ / cm or more.
(2) Perform the second to final passes by submerged arc welding with heat input of 300 kJ / cm or more as needed.
(3) It was found that low temperature cracking can be prevented by adjusting the components of the welding material (for example, wire, flux, etc.) used in the first pass to the final pass to control the components of the weld metal.

In addition, when performing multi-layered arc welding that combines submerged arc welding and carbon dioxide gas arc welding,
(1) Perform the first pass by submerged arc welding with heat input of 300 kJ / cm or more.
(2) Perform the second to final passes by carbon dioxide arc welding with heat input of less than 70 kJ / cm.
(3) It was found that low temperature cracking can be prevented by adjusting the components of the welding material (for example, wire, flux, etc.) used in the first pass to control the components of the weld metal.

The present invention has been made based on such findings.
That is, the present invention is a multi-layered arc welding method for performing multi-layered arc welding on a thick steel plate, in which submerged arc welding is performed at least in the first pass with a large heat input of 300 kJ / cm or more, and further, 300 kJ / cm or more until the final pass. Submerge arc welding is sequentially performed by combining heat input and heat input of less than 300 kJ / cm as necessary to form a weld metal, and the Mo, Cr, V, B, N content (mass%) of the weld metal is determined. As [% Mo], [% Cr], [% V], [% B], and [% N], the components of the weld metal are as follows (1) in all passes from the first pass to the final pass. This is a multi-layered arc welding method for thick steel plates in which multi-layered welding is performed using welding materials that satisfy Eqs.) And (2).

Further, according to the present invention, in a multi-layered arc welding method for performing multi-layered arc welding on a thick steel plate, the first pass has a large heat input of 300 kJ / cm or more, and the weld metal Mo, Cr, V, B, N The content (% by mass) is [% Mo], [% Cr], [% V], [% B], and [% N], respectively, and the components of the weld metal obtained in the first pass are as follows (1). Submerged arc welding is performed using welding materials that satisfy Eqs. Eq. And Eq. (2), and carbon dioxide arc welding is sequentially performed with heat input of less than 70 kJ / cm from the second pass to the final pass to perform multi-layered arc welding. This is a multi-layered arc welding method for thick steel plates.

In the multi-layered arc welding method of the present invention, a welding material in which the area ratio α (%) of the grain boundary ferrite generated in the microstructure of the weld metal satisfies the following equation (3) is used from the first pass to the final pass. It is preferable to perform multi-layer welding. It is preferable that the thickness of at least one of the thick steel plates to be used for multi-layered arc welding is in the range of 60 to 100 mm. The B content of the weld metal is preferably in the range of 0.0008 to 0.0025% by mass. The amount of diffusible hydrogen in the weld metal is preferably 10 cc / 100 g or less.
0.40 ≤ [% Mo] + [% Cr] + [% V] + 75 [% B] ≤ 0.80 ・ ・ ・ (1)
[% B] / [% N] ≤ 1.0 ・ ・ ・ (2)
α ≦ 20.0－1.3 [HD] ・ ・ ・ (3)
[HD]: Diffusible hydrogen content of weld metal measured according to JIS standard Z3118 (cc / 100g)

According to the present invention, it is possible to prevent low-temperature cracking of the weld metal in multi-layered arc welding of thick steel sheets, which is extremely effective in industry.

It is sectional drawing which shows typically the example of the groove shape to which this invention is applied. It is sectional drawing which shows the other example of the groove shape which applies this invention schematically.

When observing the cut surface parallel to the welding progress direction of the weld metal with low temperature cracks, cracks inclined in the diagonal 45 ° direction (so-called chevron cracks) occur, and the cracks occur along the coarse grain boundary ferrite. do. Although the detailed mechanism is unknown, the residual stress in the welding progress direction increases due to the thermal shrinkage of the weld metal after welding is completed, and movable dislocations are introduced into the grain boundary ferrite that is soft and whose longitudinal direction coincides with the maximum shear stress direction. As a result, it is presumed that the diffusible hydrogen that has moved to the grain boundaries and accumulated has caused low-temperature cracking.

That is, it is considered that low-temperature cracking of the weld metal can be prevented by appropriately controlling the components of the weld metal obtained by multi-layered arc welding of the thick steel sheet and suppressing the formation of grain boundary ferrite.

Therefore, in the present invention, the content of Mo, Cr, V, B, N in the weld metal is controlled by adjusting the components of the welding material (that is, wire, flux) used in submerged arc welding, and the solid melt B is formed. The formation of grain boundary ferrite is suppressed by the effect of segregating into the old austenite grain boundary and the effect of Mo, Cr, and V lowering the ferrite transformation temperature. By suppressing the formation of grain boundary ferrite in this way, the amount of accumulated diffusible hydrogen can be reduced, and by extension, low-temperature cracking can be prevented.

In the following, the contents of Mo, Cr, V, B, and N in the weld metal are described as [% Mo], [% Cr], [% V], [% B], and [% N], respectively.

Mo, Cr, V, and B added to the weld metal from wires and flux in submerged arc welding have the effect of improving the hardenability of the weld metal, suppressing the formation of grain boundary ferrite, and improving toughness. Although it is an element, if [% Mo] + [% Cr] + [% V] + 75 [% B] is less than 0.40, the formation of grain boundary ferrite cannot be suppressed and the occurrence of low temperature cracking cannot be prevented.

On the other hand, when [% Mo] + [% Cr] + [% V] + 75 [% B] exceeds 0.80, the formation of grain boundary ferrite is suppressed, but it is restored to the range of 600 to 900 ° C by the subsequent pass. Carbonitrides are likely to be generated at the old austenite grain boundaries of the heated heat-affected zone, and probably because these carbonitrides reduce the grain boundary strength, the possibility of low-temperature cracking increases. Moreover, the precipitates formed in the weld metal cause a decrease in the toughness of the weld metal. Therefore, the contents of Mo, Cr, V, and B must satisfy the following equation (1).
0.40 ≤ [% Mo] + [% Cr] + [% V] + 75 [% B] ≤ 0.80 ・ ・ ・ (1)
In particular, B in the weld metal is an element sensitive to the formation of nitrides, and its interaction with N in the weld metal has a great influence on the formation of nitrides. That is, when [% B] / [% N] exceeds 1.0, the solid solution B increases, so that B is precipitated as carbonitride due to the influence of the welding heat of the trailing pass, and low temperature cracking is likely to occur. .. Therefore, the contents of B and N must satisfy the following equation (2).
[% B] / [% N] ≤ 1.0 ・ ・ ・ (2)
In the present invention, the low temperature of the weld metal is controlled by controlling the content of Mo, Cr, V, B, N in the weld metal obtained by submerged arc welding so as to satisfy the equations (1) and (2). Can prevent cracking. In particular, when the B content is in the range of 0.0008 to 0.0025% by mass, the effect of preventing low-temperature cracking of the weld metal is remarkably exhibited.

The content of Mo, Cr, V, B, and N in such a weld metal is controlled by adjusting the components of the weld material (that is, wire, flux) used. That is, before performing multi-layered arc welding of a thick steel sheet, a welding test is performed in advance, and the composition of the welding material that can satisfy the above equations (1) and (2) is designed.

The lower the diffusible hydrogen amount (cc / 100g) of the weld metal, the better from the viewpoint of suppressing low temperature cracking, but it is inevitably introduced at the time of welding in arc welding. Especially in submerged arc welding, the water adsorbed on the flux decomposes during welding and infiltrates into the weld metal as hydrogen. Low-temperature cracking has a strong correlation between the area ratio α of the grain boundary ferrite and the amount of diffused hydrogen [HD], and the relationship between α and [HD] satisfies Eq. (3), so that low-temperature cracking can be suppressed. [HD] is the amount of diffusible hydrogen (cc / 100 g) of the weld metal measured according to JIS standard Z3118.
α ≦ 20.0－1.3 [HD] ・ ・ ・ (3)
In performing multi-layered arc welding of thick steel sheets by appropriately selecting such welding materials, the number of passes from the first pass to the final pass is set according to the thickness of the thick steel sheet and the difficulty of welding. However, it is particularly preferable to apply the present invention to a thick steel plate having a plate thickness of 60 to 100 mm, which is said to be difficult to prevent low-temperature cracking by conventional techniques, because low-temperature cracking can be prevented without preheating.

In the first pass of multi-layered arc welding, submerged arc welding is performed with a large heat input of 300 kJ / cm or more in order to improve the efficiency of welding work. However, in submerged arc welding with large heat input, welding defects are likely to occur and slag is difficult to peel off. Therefore, in order to prevent welding defects, it is possible to secure a sufficient amount of weld metal by using a wire with a diameter of 4.8 mm or more in the first pass and using a bond flux with iron powder added. preferable. In the first pass, a welding material from which a welding metal having a component satisfying the equations (1) and (2) can be obtained is used. Further, it is preferable that the groove angle is 38 ° or more in the V shape from the viewpoint of preventing high temperature cracking and ensuring slag peeling. More preferably, it is 45 ° or more, or the angle of the second step is set to 45 ° or more as the groove of the second step, and the weld metal of the first pass is welded so as to include the angle change point of the second step.

When submerged arc welding is continued for the second and subsequent passes, the second to final passes may be performed with welding heat input of less than 300 kJ / cm, or may be performed with welding heat input of 300 kJ / cm or more as appropriate. .. In the second and subsequent passes where the welding heat input is 300 kJ / cm or more, it is preferable to use a wire having a diameter of 4.8 mm or more and a bond flux to which iron powder is added, as in the first pass. Also in the second pass to the final pass, a welding material from which a welding metal having a component satisfying the equations (1) and (2) can be obtained is used.

In order to reduce the effect of welding heat on the weld metal of the preceding pass in either multi-layer welding in which the second and subsequent passes are performed by submerged arc welding or multi-layer welding in which the second and subsequent passes are performed by carbon dioxide arc welding. It is preferable to reduce the welding heat input after the second pass. However, if the welding heat input is too low, the number of passes must be increased, resulting in a decrease in the efficiency of welding work. Therefore, the welding heat input from the second pass to the final pass is preferably in the range of 80 kJ / cm or more and less than 300 kJ / cm in the case of submerged arc welding.

When the second and subsequent passes are performed by carbon dioxide arc welding, the second to final passes are performed with welding heat input of less than 70 kJ / cm. If it exceeds 70 kJ / cm, the carbon dioxide arc weld metal absorbs the atmosphere and the quality deteriorates.

Further, the number of electrodes and the number of passes of the first pass to the final pass are not particularly limited. However, the number of electrodes is preferably two or one from the viewpoint of simplifying the operation management in the welding work and the simplification of the welding equipment.

A thick steel plate A (plate thickness 70 mm) having the components shown in Table 1 was grooved to form a Y groove having the shape shown in FIG. Further, the thick steel plate B (thickness 70 mm) shown in Table 1 was grooved to form a Y groove having the shape shown in FIG. In the following, the groove having the shape shown in FIG. 1 will be referred to as groove G, and the groove having the shape shown in FIG. 2 will be referred to as groove H.

Then, multi-layered arc welding of the groove G and the groove H was performed. The components of the wire used are as shown in Table 2. The flux used is a bond flux to which iron powder is added. Specifically, it contains 20% by mass of SiO ₂ , 20% by mass of MgO, 10% by mass of CaCO ₃ , and 25% by mass of iron powder, and a small amount of iron molybdenum alloy. It is a flux to which powder, iron-chromium alloy powder, iron vanadium alloy powder, and B ₂ O ₃ are added.

Table 3 shows the combinations of the wires and the setting conditions used in the multi-layered arc welding of the groove G and the groove H. Of the two electrodes, the first electrode in Table 3 is an electrode arranged in front of the welding progress direction, and the second electrode is an electrode arranged in the rear. In the second to thirteenth passes of the condition 4, the second electrode was not used, and only the first electrode was used.

In this way, multi-layered arc welding was performed, and the components of the weld metal were investigated for each pass. The results are shown in Table 4. However, the data from the second pass to the thirteenth pass of the joint 15 show the average value of the weld metal components of each pass.

Table 5 shows the results of calculating [% Mo] + [% Cr] + [% V] + 75 [% B] and [% B] / [% N] using the data shown in Table 4. Further, the results of measuring the area ratio α of the grain boundary ferrite of the weld metal for each pass are shown in Table 5. The amount of diffusible hydrogen [HD] of the weld metal is as shown in Table 5, and the results of calculating 20.0-1.3 [HD] are as shown in Table 5.

After the multi-layered arc welding from the first pass to the final pass was completed for the joints 11 to 15, ultrasonic flaw detection of the weld metal was performed to investigate the presence or absence of low temperature cracking. The results are shown in Table 5. In Table 5, 〇 is an example in which low temperature cracking did not occur, and × is an example in which low temperature cracking occurred.
As is clear from Table 5, low-temperature cracking did not occur in the invention examples (that is, the joints 11, 14, 15) that satisfied both the equations (1) and (2).
In the joint 12 as a comparative example, the fourth pass does not satisfy the equation (1), and in the joint 13, the fourth pass does not satisfy the equation (1), and the first to fourth passes satisfy the equation (2). Since this is an unsatisfactory example, low temperature cracking occurred.

Claims (6)

In the multi-layered arc welding method in which multi-layered arc welding is performed on a thick steel plate, submerged arc welding is performed on at least the first pass with a large heat input of 300 kJ / cm or more to form a weld metal, and the weld metal Mo, Cr, The contents (% by mass) of V, B, and N are set to [% Mo], [% Cr], [% V], [% B], and [% N], respectively, from the first pass to the final pass. In all the passes, the components of the weld metal satisfy the following equations (1) and (2), and the area ratio α (%) of the grain boundary ferrite generated in the microstructure of the weld metal is as follows ( 3) A method for multi-layered arc welding of thick steel plates, which comprises performing the multi-layered arc welding using a welding material satisfying the formula 3).
Record
0.40 ≤ [% Mo] + [% Cr] + [% V] + 75 [% B] ≤ 0.80 ・ ・ ・ (1)
[% B] / [% N] ≤ 1.0 ・ ・ ・ (2)
α ≦ 20.0－1.3 [HD] ・ ・ ・ (3)
[HD]: Diffusible hydrogen content of weld metal measured according to JIS standard Z3118 (cc / 100g) In the multi-layered arc welding method in which multi-layered arc welding is applied to a thick steel plate, the first pass is 300k.
With a large heat input of J / cm or more, the content (% by mass) of Mo, Cr, V, B, and N of the weld metal is [% Mo], [% Cr], [% V], [%, respectively. As B] and [% N], submerged arc welding is performed using a welding material in which the components of the weld metal obtained in the first pass satisfy the following equations (1) and (2). A method for multi-layered arc welding of thick steel plates, which comprises sequentially performing carbon dioxide arc welding with heat input of less than 70 kJ / cm from 2 passes to the final pass to perform the multi-layered arc welding.
Record
0.40 ≤ [% Mo] + [% Cr] + [% V] + 75 [% B] ≤ 0.80 ・ ・ ・ (1)
[% B] / [% N] ≤ 1.0 ・ ・ ・ (2) The welding material in which the area ratio α (%) of the grain boundary ferrite generated in the microstructure of the weld metal satisfies the following equation (3) is used from the first pass to the final pass to perform the multi-layer welding. The multi-layered arc welding method for a thick steel plate according to claim 2, wherein the method is performed.
Note α ≤ 20.0-1.3 [HD] ・ ・ ・ (3)
[HD]: Diffusible hydrogen content of weld metal measured according to JIS standard Z3118 (cc / 100g) The method for multi-layered arc welding of a thick steel sheet according to any one of claims 1 to 3, wherein at least one of the thick steel sheets to be subjected to the multi-layered arc welding has a thickness of 60 to 100 mm. The multi-layered arc welding method for a thick steel sheet according to any one of claims 1 to 4, wherein the B content of the weld metal is in the range of 0.0008 to 0.0025% by mass. The multi-layered arc welding method for a thick steel sheet according to claim 1 or 3, wherein the diffusible hydrogen amount [HD] of the weld metal is 10 cc / 100 g or less.

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