JP6881616B2 - Manufacturing method of vertical narrow groove welded joint and vertical narrow groove welded joint - Google Patents

Description

The present invention relates to a method for manufacturing a welded joint used in various steel structures in fields such as ships, construction, and civil engineering, and in particular, a narrow groove gas that faces thick high-strength steel materials having a plate thickness of 40 mm or more. The present invention relates to a method for manufacturing an vertical narrow groove weld joint and a vertical narrow groove weld joint for improving the toughness of a welded portion in an vertical narrow groove weld joint joined by a shield arc welding method.

In recent years, steel structures such as ships, buildings, and civil engineering have become larger and larger, and the steel materials used have been actively promoted to have higher strength and thicker walls. These steel structures are usually finished in a desired shape by welding. Therefore, from the viewpoint of ensuring the safety of the steel structure (hereinafter, also referred to as welded steel structure) by this welding, the steel material used is excellent in strength and toughness of the base material, and is also welded. It is required to have excellent strength and toughness of the part.

In addition, as the size of the welded steel structure increases and the thickness of the steel material used increases, the amount of welding in the process of manufacturing the steel structure, especially in butt welding, increases, and the welding time becomes longer, resulting in longer construction costs. There is a problem that it is causing the increase of. To solve such a problem, for example, the application of narrow groove gas shield arc welding, in which a groove having a narrow gap with respect to the plate thickness is welded by an arc welding method, can be considered. This narrow groove gas shielded arc welding has a smaller welding amount than ordinary gas shielded arc welding, and can achieve high efficiency and energy saving in welding work, which is expected to reduce the construction cost.

Further, when manufacturing a welded steel structure, vertical welding may be required. Electroslag welding is usually applied as vertical welding. However, electroslag welding is basically one-pass large heat input welding. Therefore, when welding a steel material having a plate thickness of more than 40 mm, there is a concern that the toughness of the welded portion may decrease as a result of excessive welding heat input. For these reasons, it is desired to realize a high-quality and highly efficient welding method in which the above-mentioned narrow groove gas shielded arc welding is applied to vertical welding.

In response to such a request, for example, Patent Document 1 proposes a double-sided welding method. The double-sided welding method proposed in Patent Document 1 is a double-sided welding method in which a double-sided U-shaped groove joint is TIG welded, and is formed on or near the central portion of the plate thickness of the double-sided U-shaped groove joint on the front side. The bottom of the groove is wave-welded in the first layer to the height of the laminated bead, which is in the range of 1/5 or more and 2/5 or less of the groove depth before welding or the bisected plate thickness from the groove bottom including the first layer welded part. Front side laminated welding until it reaches, or reaches the remaining groove depth that is 4/5 or less and 3/5 or more of the pre-weld groove depth, or the upper limit of the groove shoulder width shrinkage amount approaches 2 mm. Then, the back side laminating welding is performed from the groove bottom portion of the U-shaped groove joint on the back side to the final layer of the groove upper portion, and then the front side laminating welding is performed from the remaining groove portion on the front side to the final layer of the groove upper portion. In this welding method, by using an inert gas, it is possible to suppress the generation of slag and spatter, prevent stacking defects, and obtain a high-quality double-sided laminated welded portion with low deformation.

Patent Document 2 proposes a narrow groove welding method. In the narrow groove welding method proposed in Patent Document 2, an arc is formed at the tip of the wire protruding from the tip inserted into the groove extending in the welding direction, and the tip of the wire is opposite to the welding progress direction. The narrow groove is gas-shield welded by controlling the stop time and speed at the time of reversal of the oscillating while oscillating by repeating so as to draw an arcuate locus on the side. At this time, the first forward step of oscillating in the welding progress direction to the vicinity of one open tip starting from the center position in the width direction of the narrow groove, and stopping the oscillating for a predetermined time near one open tip. The first step of progress, the first step of reverse movement in which the oscillating is performed in the direction opposite to the welding progress direction from the vicinity of one of the open ends to the center position in the width direction of the narrow groove, and the width direction of the narrow groove. A forward second step of oscillating in the welding progress direction from the center position to the vicinity of the other open tip, a progressive second step of stopping oscillating for a predetermined time near the other open tip, and the other open tip. A one-cycle welding process is formed by the second reverse step of oscillating in the direction opposite to the welding progress direction from the vicinity of the portion to the center position in the width direction of the narrow groove. As for the oscillating speed, the vertically downward oscillating speed is higher than the vertically upward oscillating speed. This makes it possible to prevent or suppress spatter and fusion defects.

Patent Document 3 proposes an vertical welding method. The vertical welding method proposed in Patent Document 3 is viewed from the welding direction of arc welding when performing arc welding while weaving a welding torch against a base metal in an vertical posture in which the groove wall is positioned to the left and right. The vertical direction in which the rod pattern is formed into a figure eight by the first pattern portion along the left and right groove walls and the second pattern portion connecting the root side and the opening side of these first pattern portions. It is a welding method. As a result, it is possible to prevent uneven thickness of the bead, poor penetration, undercut, poor appearance of the bead, and the like.

Patent Document 4 proposes an vertical electrogas welding apparatus. The vertical electrogas welding apparatus proposed in Patent Document 4 has a first electrode in which the tip penetrates into the groove, and the groove opening side in the groove in the thickness direction x of the steel plate from the tip of the first electrode. It is provided with a second electrode that penetrates into a position close to, a trolley that rises along the groove, and a vibrating means that is supported by the trolley and swings the first and second electrodes in the plate thickness direction x, and is substantially vertical. While supplying the flux-containing wire to the groove extending in the vertical direction z of the erected steel plate, welding is performed upward. As a result, welding work efficiency is improved, and one-pass welding of extremely thick materials is possible.

Patent Document 5 proposes a vertical narrow groove gas shielded arc welding method. The vertical narrow groove gas shield arc welding method proposed in Patent Document 5 has a groove angle of 20 ° or less, a groove gap of 20 mm or less, and weaving of two thick steel materials having a plate thickness of 40 mm or more. This is an vertical narrow groove gas shielded arc welding method for joining by single-layer welding or multi-layer welding. At that time, as the welding wire, a welding wire containing 0.015 to 0.100% by mass of REM and 0.005 to 0.100% by mass of one or two selected from Se and Te in total is used, and at the time of initial layer welding. , The angle of the welding torch is 10 ° or more and 75 ° or less with respect to the horizontal direction, the welding heat input is 500 kJ / cm or less, the weaving depth in the plate thickness direction is 15 mm or more and 50 mm or less, and welding in the first layer welding. When the bead width is W, the welding torch is weaved with the maximum weaving width in the plate thickness direction and the direction perpendicular to the welding line set to (W-6) mm or more and W mm or less. As a result, a high-quality, high-toughness welded joint can be obtained while stabilizing the weld bead shape and preventing the occurrence of welding defects, and less spatter is generated as compared with ordinary gas shielded arc welding. It is said that there are few welding defects and high efficiency of welding can be achieved, and welding construction cost can be significantly reduced.

Japanese Unexamined Patent Publication No. 2009-61483 Japanese Unexamined Patent Publication No. 2010-115700 Japanese Unexamined Patent Publication No. 2001-205436 Japanese Unexamined Patent Publication No. 10-118771 Japanese Patent No. 6119948

The TIG welding used in the welding method proposed in Patent Document 1 is a non-consumable electrode method, and the efficiency of the welding method itself is significantly inferior to that of _{MAG welding or CO 2 welding using a steel wire which is a consumable electrode.} Therefore, the double-sided welding method proposed in Patent Document 1 using TIG welding cannot be expected to significantly increase the welding efficiency.

In the welding method proposed in Patent Document 2, since the weaving direction of the welding torch is not the groove depth direction but the steel plate surface direction, it is necessary to weave the welding torch before the molten metal drips, and the welding current. It is necessary to set the current to a low current of about 150 A and suppress the welding amount (≈ heat input amount) per pass. Therefore, when this welding method is applied to the welding of thick-walled steel materials, there is a problem that a small amount and a large number of passes are laminated, the number of lamination defects such as poor penetration increases, and the welding efficiency is greatly reduced.

In the vertical welding method proposed in Patent Document 3, the surface angle (groove angle) is as wide as 26.3 to 52 °, but the weaving of the welding torch here is also performed in the groove depth direction. Therefore, it is possible to take a relatively large amount of welding per pass. However, since the weaving amount in the groove depth direction is small and the welding metal and welding wire composition are not taken into consideration, it is necessary to suppress the welding amount per pass (≈ heat input amount), and the welding depth per pass. The width is as shallow as about 10 mm. Therefore, when this method is applied to the welding of thick-walled steel materials, there is a problem that the welding efficiency is lowered as well as the laminating defects such as poor penetration are increased due to the laminating welding of a small amount and many passes.

By using the electrogas arc welding apparatus proposed in Patent Document 4, although it is possible to join thick steel materials up to a plate thickness of about 70 mm, the amount of heat input is significantly increased to about 360 kJ / cm. Therefore, the heat effect on the material to be welded (thick steel plate) becomes large, and the welded joint characteristics such as strength and toughness are significantly deteriorated. Further, in this two-electrode electrogas arc welding apparatus, it is indispensable to provide a ceramic backing on the back surface side and a water-cooled copper metal pressing mechanism on the front surface (welding machine side) at the groove. Although there is no concern about dripping of molten metal, the welding equipment becomes complicated. Further, in this two-electrode electrogas arc welding apparatus, one-pass welding is basic, and it is difficult to reduce heat input as multi-pass laminated welding.

Since the vertical narrow groove gas shielded arc welding method proposed in Patent Document 5 is welding accompanied by weaving, in a welded joint made of a thick-walled high-strength steel material containing a large amount of alloying elements, a portion repeatedly affected by heat is formed. In some cases, the toughness was significantly reduced.

An object of the present invention is to solve the problems of the prior art and to provide a method for manufacturing an vertical narrow groove welded joint having excellent weld toughness and an vertical narrow groove welded joint having excellent weld toughness. And.

The term "thick" as used herein means a case where the plate thickness (thickness) is 40 mm or more, and the "high strength" means a case where the yield strength is 440 MPa or more. In addition, "steel material" shall include steel plates, shaped steels, strips, steel bars, etc. Further, the "narrow groove" means a case where the groove angle is 20 ° or less. Further, in this narrow groove, the minimum groove width (hereinafter, also referred to as groove gap) between the steel materials to be welded is 50% or less of the steel plate thickness (wall thickness) and 20 mm or less. The case is suitable.

In order to achieve the above-mentioned object, the present inventors first suitable a thick-walled high-strength steel material having a plate thickness (wall thickness) of 40 mm or more and a yield strength of 440 MPa or more for the above-mentioned welded steel structure. The composition of steel required to ensure mechanical properties was examined. As a result, in order to stably produce the above-mentioned thick-walled high-strength steel material by a conventional manufacturing method that combines hot rolling and cooling, it is indispensable to add a certain amount of alloying elements. The composition of the ingredients is C: 0.03% by mass or more, and then
C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15
(Here, C, Mn, Cr, Mo, V, Cu, Ni: the content (mass%) of each element, and the content of the element not contained is 0.)
The hardenability index defined in is the following equation (1)
0.40 ≤ C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 ≤ 0.50 ... (1)
It was found that it is necessary to adjust the components to the extent that the above is satisfied.

Furthermore, in manufacturing welded joints by joining thick-walled high-strength steel materials by vertical narrow groove gas shield arc welding, we decided to apply vertical welding with weaving, and the thermal effect of welding with weaving. We investigated the decrease in toughness of the welded part due to the above. As a result, when a welded joint is manufactured by applying welding with weaving to a thick-walled high-strength steel material to which a large amount of alloying elements are added as described above, a region affected by repeated welding heat, particularly once at 1100 ° C. It was found that the region (region) exposed to the above high temperature becomes a remarkably embrittled structure in the region where it is reheated to the temperature region (two-phase region) from _{the Ac 1} transformation point to _{the Ac 3 transformation point.} did. It is considered that this is due to the formation of a hard layer at the coarsened crystal grains and their grain boundaries.

Therefore, in the above welding, it is avoided that the portion (region) once exposed to a high temperature of 1100 ° C. or higher is reheated to the temperature region (two-phase region) from _{the Ac 1} transformation point to _{the Ac 3 transformation point.} We enthusiastically examined the measures to be taken. As a result, I came up with the idea of adjusting the welding conditions with weaving to an appropriate range. That is, the vertical upward welding speed v (mm / min) and the reciprocal f (s ^-1 ) of the time required for one weaving cycle are calculated by the following equation (2).
2v / 60 / f ≦ 9.0 …… (2)
It was found that if the welding conditions accompanied by weaving were adjusted so as to satisfy the above, no significant decrease in weld toughness was observed. If vertical welding with weaving is applied so as to satisfy the above equation (2), the region once exposed to a high temperature of 1100 ° C. or higher becomes the Ac ₁ transformation point again after one cycle of weaving. It is not reheated to the temperature region (two-phase region) of the Ac _{3 transformation point.} Therefore, it is possible to prevent a significant decrease in the toughness of the welded joint. The above equation (2) holds regardless of the amount of heat input to welding.

The present invention has been completed with further studies based on the above findings. That is, the gist of the present invention is as follows.
(1) A method for manufacturing an vertical narrow groove welded joint in which two steel materials are butted through a narrow groove having a groove angle of 20 ° or less and joined by vertical gas shielded arc welding using weaving. ,
The steel material by mass%
C: 0.03 to 0.15%,
Si: 0.01-0.10%,
Mn: 1.0-2.5%,
A steel material containing P: 0.02% or less and S: 0.01% or less, satisfying the following formula (1), having a component composition in which the balance is Fe and unavoidable impurities, and having a yield strength of 440 MPa or more. ,
^{In the vertical gas shielded arc welding, the reciprocal f (s -1} ) of the upward speed v (mm / min) of the vertical welding and the time (s) required for one cycle of the weaving is calculated by the following equation (2). A method of manufacturing an vertical narrow groove welded joint that is adjusted to a satisfactory range.
Record
0.40 ≤ C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 ≤ 0.50 …… (1)
Here, C, Mn, Cr, Mo, V, Cu and Ni are the contents (mass%) of each element, and the content of the elements not contained is 0.
2v / 60 / f ≤ 9.0 …… (2)

(2) In the above (1), the weaving is a method for manufacturing an vertical narrow groove welded joint in which the weaving pattern of the welding torch viewed from the direction of the welding line is U-shaped.

(3) In the above (1) or (2), the component composition is further increased by mass%.
Al: 0.005 to 0.100%,
Cu: 0.01-1.00%,
Ni: 0.01-1.00%,
Nb: 0.003 to 0.030%,
Ti: 0.003 to 0.030%,
N: 0.0020-0.0100% and
Ca: 0.0003 to 0.0030%
A method for manufacturing an vertical narrow groove welded joint containing one or more selected from the above.

(4) In the above (1), (2) or (3), the component composition is further increased by mass%.
Cr: 0.01-0.50%,
Mo: 0.01-0.50%,
V: 0.001 to 0.100%,
B: 0.0003 to 0.0030%,
Mg: 0.005 to 0.0100%,
Zr: 0.0010-0.0200% and
REM: 0.0005 to 0.0100%
A method for manufacturing an vertical narrow groove welded joint containing one or more selected from the above.

(5) An vertical narrow groove welded joint manufactured by the method for manufacturing an vertical narrow groove welded joint according to any one of (1) to (4) above.

(6) An vertical narrow groove welded joint in which two steel materials are joined via a narrow groove having a groove angle of 20 ° or less.
The steel material is by mass%
C: 0.03 to 0.15%,
Si: 0.01-0.10%,
Mn: 1.0-2.5%,
It contains P: 0.02% or less and S: 0.01% or less, satisfies the following formula (1), has a component composition in which the balance is Fe and unavoidable impurities, and has a yield strength of 440 MPa or more.
Test temperature of Charpy impact test: Vertical narrow groove welded joint having a welded bond portion with _{absorbed energy E-20 (J) at -20 ° C of 80 J or more.}
Record
0.40 ≤ C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 ≤ 0.50 …… (1)
Here, C, Mn, Cr, Mo, V, Cu and Ni are the contents (mass%) of each element, and the content of the elements not contained is 0.

(7) In the above (6), the component composition is further increased by mass%.
Al: 0.005 to 0.100%,
Cu: 0.01-1.00%,
Ni: 0.01-1.00%,
Nb: 0.003 to 0.030%,
Ti: 0.003 to 0.030%,
N: 0.0020-0.0100% and
Ca: 0.0003 to 0.0030%
An vertical narrow groove welded joint containing one or more selected from the above.

(8) In the above (6) or (7), the component composition is further increased by mass%.
Cr: 0.01-0.50%,
Mo: 0.01-0.50%,
V: 0.001 to 0.100%,
B: 0.0003 to 0.0030%,
Mg: 0.005 to 0.0100%,
Zr: 0.0010-0.0200% and
REM: 0.0005 to 0.0100%
An vertical narrow groove welded joint containing one or more selected from the above.

According to the present invention, even a thick-walled high-strength steel material having a plate thickness of 40 mm or more and a yield strength of 440 MPa or more has excellent toughness of the weld heat-affected zone and a high-quality vertical narrow groove gas shield. It is possible to manufacture arc welded joints with high efficiency, and the welding construction cost of welded steel structures can be significantly reduced, which is extremely effective in industry.

It is explanatory drawing which shows an example of the groove shape. It is explanatory drawing which shows typically the procedure of the welding joint of the vertical narrow groove gas shield arc welded joint. It is explanatory drawing which shows the weaving pattern.

In the method for manufacturing an vertical narrow groove gas shielded arc welded joint of the present invention, for example, a thick-walled high-strength steel material having a plate thickness of 40 mm or more and a yield strength of 440 MPa or more is used as the material to be welded. In general rolled steel, the maximum thickness of the steel is 100 mm. Therefore, the plate thickness of the steel material is preferably 100 mm or less.

First, the component composition (steel material composition) of the thick-walled high-strength steel material to be used will be described. Hereinafter, the mass% in the composition of the steel material is simply expressed as%.
C: 0.03 to 0.15%
C is an element having an action of increasing the strength of steel, and in the present invention, 0.03% or more is contained in order to secure a desired high strength. On the other hand, if the content exceeds 0.15%, island-shaped martensite is likely to be formed in the vicinity of the welded portion, which causes a decrease in toughness of the welded portion. Therefore, C was limited to the range of 0.03 to 0.15%. It is preferably 0.05 to 0.10%.

Si: 0.01-0.10%
Si is an element that acts as a deoxidizer when melting steel, and a content of 0.01% or more is required to obtain such an effect. On the other hand, if the content exceeds 0.10%, island-shaped martensite is formed in the vicinity of the welded portion, which causes a decrease in toughness of the welded portion. Therefore, Si was limited to the range of 0.01 to 0.10%. It is preferably 0.02 to 0.08%.

Mn: 1.0-2.5%
Mn is an element having an action of increasing the strength of steel, and in the present invention, it is contained in an amount of 1.0% or more in order to secure a desired base material strength. On the other hand, if it is contained in excess of 2.5%, the toughness in the vicinity of the weld is significantly reduced. Therefore, Mn was limited to the range of 1.0 to 2.5%. It should be noted that it is preferably 1.2 to 2.2%.

P: 0.02% or less P promotes the formation of island-shaped martensite in the vicinity of the weld, and excessive content greatly reduces the toughness of the weld. Therefore, it is preferable to reduce it as much as possible, but 0.02% or less is acceptable. Therefore, in the present invention, P is limited to 0.02% or less. It should be noted that it is preferably 0.016% or less.

S: 0.01% or less S is mainly present in steel as a sulfide-based inclusion, and if it is excessively contained, the toughness of the steel material is lowered. Therefore, it is preferable to reduce S as much as possible, but 0.01% or less is acceptable. It is preferably 0.005% or less.

In the present invention, the above-mentioned components are adjusted to the above-mentioned contents and the hardenability index (= C + Mn / 6 + (Cr + Mo + V) / 5+ (Cu + Ni) / 15) is adjusted to a range satisfying the following formula (1). The composition.
0.40 ≤ C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 ≤ 0.50 …… (1)
(However, C, Mn, Cr, Mo, V, Cu and Ni are the contents (mass%) of each element)
If the element described in the above formula (1) is not contained, the content of the element is set to zero and the formula (1) is calculated.

In the present invention, molten steel having a predetermined composition is melted and made into a steel material (slab) by a continuous casting method, and the slab is reheated, hot-rolled, and cooled to have a thick wall and high strength of a predetermined dimension. Use steel material. From the viewpoint of reducing the manufacturing cost, in the present invention, a thick-walled high-strength steel material is manufactured without performing heat treatment or the like as much as possible. Therefore, it was decided to adjust the hardenability index Ceq (= C + Mn / 6 + (Cr + Mo + V) / 5+ (Cu + Ni) / 15) within a predetermined range to the composition of the steel material.

In the present invention, the content of each component of the thick-walled high-strength steel material is adjusted so that the hardenability index Ceq is in the range of 0.40 to 0.50. That is, if the hardenability index is less than 0.40, the hardenability is insufficient and the desired strength of the steel material cannot be secured. On the other hand, when the hardenability index exceeds 0.50, the hardenability is excessively increased, the toughness of the welded portion is lowered, and the desired toughness of the welded portion cannot be secured. Therefore, in the present invention, the component composition is adjusted so as to satisfy the above formula (1). The hardenability index Ceq is preferably 0.42 to 0.48.

The above-mentioned component composition is basic, but in the present invention, in addition to the above-mentioned basic component composition, Al: 0.005 to 0.100%, Cu: 0.01 to 1.00%, Ni: 0.01 to 1.00%, Nb: 0.003 to It can contain one or more selected from 0.030%, Ti: 0.003 to 0.030%, N: 0.0020 to 0.0100% and Ca: 0.0003 to 0.0030%. The preferred amount of each element added and the reason for the addition are as follows.

Al: 0.005 to 0.100%
Al is an element that acts as a deoxidizer for steel, and in order to obtain such an effect, it is preferably contained in an amount of 0.005% or more. On the other hand, if it is contained in excess of 0.100%, not only the toughness of the base metal but also the toughness of the weld metal is lowered. Therefore, it is preferable to add Al in the range of 0.005 to 0.100%. It should be noted that it is more preferably 0.010 to 0.080%.

Cu: 0.01-1.00%
Cu is an element that improves hardenability and effectively contributes to ensuring the desired high strength (base metal strength). In order to obtain such an effect, the content is preferably 0.01% or more. On the other hand, if it is contained in excess of 1.00%, the above-mentioned effect is saturated. Therefore, it is preferable to add Cu in the range of 0.01 to 1.00%. It should be noted that it is more preferably 0.020 to 0.080%.

Ni: 0.01-1.00%
Ni is an element that has the effect of increasing the strength of steel (base metal strength) and improving toughness. In order to obtain such an effect, the content is preferably 0.01% or more. On the other hand, even if it is contained in excess of 1.00%, the effect is saturated. Therefore, it is preferable to add Ni in the range of 0.01 to 1.00%. More preferably, it is more than 0.01% and 1.00% or less. More preferably, it is 0.20 to 0.80%.

Nb: 0.003 to 0.030%
Nb is a useful element that contributes to the improvement of steel material strength, and in order to secure the desired steel material strength (base material strength), it is preferably contained in an amount of 0.003% or more. On the other hand, if it is contained in excess of 0.030%, the toughness of the welded portion decreases. Therefore, it is preferable to add Nb in the range of 0.003 to 0.030%. It should be noted that it is more preferably 0.008 to 0.025%.

Ti: 0.003 to 0.030%
Ti is an element that effectively contributes to the improvement of steel material strength, precipitates as nitride (TiN) during solidification, suppresses coarsening of austenite grains, and contributes to improvement of steel material toughness. In order to obtain such an effect, the content is preferably 0.003% or more. On the other hand, if it is contained in excess of 0.030%, the precipitated TiN may become coarse and the above-mentioned effect may not be obtained. Therefore, Ti is preferably added in the range of 0.003 to 0.030%. It is more preferably 0.008 to 0.0025%.

N: 0.0020-0.0100%
N suppresses the grain growth of austenite through the formation of TiN and contributes to the improvement of toughness. In order to obtain such an effect, the content is preferably 0.0020% or more. On the other hand, if the content exceeds 0.0100%, TiN may be melted by the heat during welding, the amount of solid solution N may increase, and the toughness may decrease. Therefore, it is preferable to add N in the range of 0.0020 to 0.0100%. It is more preferably 0.0030 to 0.0090%, and even more preferably 0.0035 to 0.0085%.

Ca: 0.0003-0.0030%,
Ca is an element that contributes to morphological control of sulfide-based inclusions, and is an element that contributes to the improvement of toughness of steel materials through such effects. In order to obtain such an effect, the content is preferably 0.0003% or more. On the other hand, if the content exceeds 0.0030%, the cleanliness may be lowered and the toughness may be deteriorated. Therefore, it is preferable to add Ca in the range of 0.0003 to 0.0030%. It is more preferably 0.0005 to 0.0025%.

Furthermore, if necessary, Cr: 0.01 to 0.50%, Mo: 0.01 to 0.50%, V: 0.001 to 0.100%, B: 0.0003 to 0.0030%, Mg: 0.005 to 0.0100%, Zr: 0.0010 to 0.0200% and REM. : One or more selected from 0.0005 to 0.0100% may be contained.

Cr: 0.01 to 0.50%, Mo: 0.01 to 0.50%, V: 0.001 to 0.100% and B: 0.0003 to 0.0030%
Cr, Mo, V and B are all elements that contribute to increasing the strength of the steel material, and can be selected and contained in one or more types as necessary.
In order to obtain such an effect, it is preferable that Cr is 0.01% or more, Mo is 0.01% or more, V is 0.001% or more, and B is 0.0003% or more. On the other hand, if Cr is contained in a large amount exceeding 0.50%, Mo is 0.50%, V is 0.001%, and B is 0.0030%, the toughness may be adversely affected. Therefore, when it is contained, it is preferably in the range of Cr: 0.01 to 0.50%, Mo: 0.01 to 0.50%, V: 0.001 to 0.100%, and B: 0.0003 to 0.0030%.

Mg: 0.005 to 0.0100%, Zr: 0.0010 to 0.0200% and REM: 0.0005 to 0.0100%
Mg, Zr and REM are elements that are dispersed as oxides and have the effect of improving the toughness of the base metal and welds. In addition, Mg, Zr and REM are useful elements that contribute to the improvement of toughness through morphological control of sulfide-based inclusions, and can be contained as needed. In order to exhibit such an effect, it is preferable that Mg is contained in an amount of 0.005% or more, Zr is contained in an amount of 0.0010% or more, and REM is contained in an amount of 0.0005% or more. On the other hand, even if Mg and REM are contained in an amount of more than 0.0100% and Zr is contained in an amount of more than 0.0200%, the effect is only saturated. Therefore, it is preferable that the range is 0.0100% or less when Mg and REM are contained, and 0.0200% or less when Zr is contained.

The rest of the components other than those mentioned above consist of Fe and unavoidable impurities. As an unavoidable impurity, O (oxygen): 0.0080% or less is acceptable.

Next, a preferable manufacturing method of the thick-walled high-strength steel material used in the present invention will be described.
The steel material used in the present invention is, for example, molten steel melted in a regular melting furnace such as a converter or an electric furnace, and preferably further secondary smelted in a regular secondary smelting furnace such as RH degassing. The molten steel adjusted to an appropriate composition range is used as a steel material such as a slab through a continuous casting process or an ingot-breaking process. Then, the steel material is reheated and hot-rolled to obtain a steel material having a desired size and shape, and then allowed to cool, a step of performing accelerated cooling treatment after hot rolling, and a step of direct quenching and then firing. After undergoing a backing process, a reheating quenching process and then a tempering process, a reheating quenching process and then a tempering process, etc., the plate thickness is 40 mm or more and the yield strength. It is preferable to use a thick-walled high-strength steel material having a thickness of 440 MPa or more. In particular, it is more preferable to change the conditions of the accelerated cooling treatment and the conditions of the tempering treatment so that the plate thickness is 40 mm or more and the yield strength is 440 MPa or more.

Next, using the above-mentioned two thick-walled high-strength steel materials as the materials to be welded, two thick-walled high-strength steel materials are used, and a narrow groove having a groove angle θ of 20 ° or less and a groove gap G of 20 mm or less is used. Butt through. Then, these thick-walled high-strength steel materials are joined by an vertical gas shielded arc welding method using weaving to manufacture a single-layer or multi-layered vertical narrow groove gas shielded arc welded joint.

Here, the groove shape can be either a V-shaped groove (including an I-shaped groove and a Les-shaped groove) or a Y-shaped groove. Further, the Y-shaped groove can be a multi-stage Y-shaped groove. A typical groove shape is shown in FIG. In FIG. 1, reference numeral 1 is a steel material and reference numeral 2 is a groove surface, FIG. 1A is an example of a V-shaped groove, and FIG. 1B is an example of a Y-shaped groove.

Hereinafter, the present invention will be described by taking a V-shaped groove as an example. The same applies when a Y-shaped groove is used.
Groove angle θ: 20 ° or less The smaller the groove angle θ of the steel material, the more likely it is that defects such as fusion defects will occur, but high-efficiency welding will be possible. Therefore, in the present invention, high-efficiency welding is aimed at, and the groove angle is limited to 20 ° or less. The V-shaped groove has a groove angle of 0 °, and the I-shaped groove enables the most efficient welding, but from the viewpoint of construction stability, it is preferably 2 to 10 °.

Groove gap G: 50% or less and 20 mm or less of the steel plate thickness If the groove gap G exceeds 50% or 20 mm or more of the steel plate thickness, the molten metal tends to drip and welding becomes difficult. .. Therefore, it is necessary to take measures such as keeping the welding current low, but if the welding current is kept low, welding defects such as slag entanglement are likely to occur. Therefore, the groove gap is preferably 50% or less and 20 mm or less of the steel plate thickness. From the viewpoint of construction efficiency, it is more preferably 0 mm or more and 15 mm or less.

In the present invention, the steel materials 1 and 1 to be welded are joined by one-layer or multi-layer welding by an upright (upward) gas shielded arc welding method using weaving. FIG. 2 schematically shows a procedure for welding and joining by a gas shielded arc welding method using a V-shaped groove. Here, in FIG. 2, reference numeral 3 is a backing material, reference numeral 4 is a welding torch, and reference numeral 5 is a welding wire (consumable electrode wire). In the gas shielded arc welding method to be applied, an arc is generated between the consumable electrode wire and the material to be welded (steel material) while shielding with shield gas, and the electrode wire and the material to be welded (steel material) are melted. Any of the gas shielded arc welding methods of is applicable. The electrode wire used in the gas shielded arc welding method has a tensile strength of 60 kg class (HT-60 class) corresponding to the strength of the steel material to be welded, for example, as specified in the JIS standard. ) It is preferable to use a solid wire for steel materials.

In the vertical (upward) gas shielded arc welding used in the present invention, the welding conditions need not be particularly limited. However, if the average welding current is too low, poor fusion and slag entrainment are likely to occur. On the other hand, if the average welding current is excessively high, dripping of molten metal, fume, spatter, and the like become remarkable. Therefore, the average welding current is preferably 250 A or more and 400 A or less. The welding voltage increases with the welding current, but the welding voltage may be 25 V or more and 40 V or less, and the welding speed (upward) may be 1 to 15 cm / min. Further, as the shield gas to be used, any of ordinary shield gases such as carbon dioxide gas or a mixed gas of carbon dioxide gas and argon gas can be applied, and there is no particular need to limit the shield gas.

Further, in the vertical (upward) gas shielded arc welding method used in the present invention, vertical welding using weaving is performed. The weaving pattern of the welding torch is not particularly limited, but from the viewpoint of suppressing the dripping of molten metal and the occurrence of welding defects, weaving of the welding torch as seen from the direction of the welding line, for example, as shown in FIG. 3A. The pattern is preferably U-shaped. With the U-shaped weaving pattern, the welding torch 4 can be moved in parallel along the groove surface 2, and the molten metal can be prevented from dripping and the occurrence of welding defects can be suppressed. The weaving pattern other than the U-shape may be, for example, a V-shape, a trapezoid, or a triangle as shown in FIGS. 3 (b) to 3 (d). The deepest groove point during weaving (for example, points B and C in FIG. 3A) is usually about 0 to 10 mm at a distance from the back surface 1a of the steel material.

In the vertical narrow groove welding used in the present invention, it is necessary to limit the weaving depth L in the plate thickness direction and the weaving width W in the plate thickness direction and the direction perpendicular to the welding line as shown in FIG. However, it is preferable to perform welding corresponding to the desired bonding depth, such as appropriately adjusting the weaving depth L and the weaving width W according to the desired bonding depth.

Here, the weaving depth L in the plate thickness direction is preferably 15 to 50 mm. This is because if the weaving depth in the plate thickness direction is less than 15 mm, it may be difficult to obtain a desired bonding depth. On the other hand, if the weaving depth in the plate thickness direction exceeds 50 mm, not only is it difficult to obtain the desired joint depth, but also the amount of heat input to the weld becomes excessive, which is a desired machine in the heat-affected zone of weld metal or steel. There is a risk that it will be difficult to secure the target characteristics. The weaving depth L is more preferably 20 to 40 mm in the case of single-layer welding and 25 to 40 mm in the case of multi-layer welding. The stop time during weaving (stop time at each point A, B, etc. in the weaving pattern) is preferably about 0 to 0.5 seconds. Further, it is preferable that the weaving width W is appropriately adjusted according to the distance between the grooves at the plate thickness position where welding is performed so as to prevent the occurrence of melting defects.

In the present invention, in vertical gas shielded arc welding with weaving, the ascending speed v (mm / min) of vertical welding and the reciprocal f (s ^-1 ) of the time (s) required for one cycle of weaving are used. , The following equation (2)
2v / 60 / f ≦ 9.0 …… (2)
The vertical gas shielded arc welded joint is manufactured by adjusting the above to a satisfactory range.

Here, one cycle of weaving is 1/2 of the time required for the minimum unit of the reciprocating motion performed by the welding torch in the cross section of the groove. Specifically, it is 1/2 of the time required for "A-> B-> C-> D-> C-> B-> A" in FIG. 3 (a), and similarly, "A-> B->" in FIG. 3 (b). 1/2 of the time required for "C-> B-> A", 1/2 of the time required for "A-> B-> C-> D-> A" in FIG. 3 (c), "A-> B->" in FIG. 3 (d) It is 1/2 of the time required for "C → A".

Usually, in welding with weaving, the same place is often exposed to multiple reheatings, and in particular, the temperature once heated to 1100 ° C. or higher is the temperature above the Ac ₁ transformation point and below the Ac _{3 transformation point.} When reheated to the region (two-phase temperature region), it causes a significant decrease in toughness of the weld heat affected zone. This is because when the region where the austenite crystal grains are coarsened by heating to 1100 ° C or higher is reheated to the two-phase temperature region, reverse transformation austenite is generated at the grain boundaries, and C (carbon) is concentrated there. It is believed that this is due to the formation of a hard phase, which is a factor in reducing toughness.

In the present invention, the ascending speed v of vertical upward welding accompanied by weaving and the reciprocal f of the time required per cycle of weaving are adjusted so as to satisfy the above equation (2). As a result, it is possible to prevent the region once heated to 1100 ° C. or higher from being reheated to _{the temperature region (two-phase temperature region) of the Ac 1} transformation point or more and the Ac ₃ transformation point or less, and the vertical narrow groove gas. It is possible to prevent significant deterioration in toughness of the weld heat affected zone, particularly the weld bond portion, in the shielded arc welded joint.
The lower limit of 2v / 60 / f is not particularly limited, but it is desirable that the value is large from the viewpoint of welding construction efficiency.

The vertical narrow groove welded joint obtained according to the above manufacturing method has a welded bond portion and welded portion toughness having an _{absorbed energy E-20 (J) of 80 J or more at a test temperature of Charpy impact test: -20 ° C.} It becomes an excellent joint. Here, the "welded bond portion" refers to a position where the ratio of the weld metal to the heat-affected zone in the notch bottom of the Charpy impact test in the welded portion of the joint is 1: 1. Since this welded bond portion has the lowest toughness in the welded portion, if the absorbed energy E- ₂₀ (J) of the welded bond portion at -20 ° C is 80 J or more, the toughness of the bonded portion having the lowest toughness. Is ensured, and therefore the toughness of other welds in the weld bond is also guaranteed.

Hereinafter, the present invention will be further described based on Examples.
The molten steel having the composition shown in Table 1 was melted using a high-frequency melting furnace and cast into a mold to obtain a steel ingot (150 kg). Each of the obtained ingots was heated and hot-rolled to obtain steel pieces (thickness: 200 mm or less). The obtained steel pieces are placed in a heating furnace, held at a heating temperature of 1150 ° C. for 2 hours, and then hot-rolled to a finish rolling temperature of 700 to 900 ° C. 100 mm). Then, accelerated cooling at a cooling rate of 3 ° C./s or higher at the plate thickness 1/2 position is applied to a temperature of 350 ° C at the plate thickness 1/2 position (cooling stop temperature), and then allowed to cool. The product board (base material) was used.

Regarding the obtained product plate (base material), JIS No. 4 test pieces were collected from the plate thickness 1/4 position so that the longitudinal direction of the test piece was perpendicular to the rolling direction, and conformed to the provisions of JIS Z 2241. The tensile test was carried out to measure the tensile properties (yield strength YS, tensile strength TS) of the steel material. In addition, a V-notch test piece is collected from the plate thickness 1/4 position so that the longitudinal direction of the test piece is parallel to the rolling direction, and the test temperature is -40 ° C in accordance with JIS Z 2242-2005. A Charpy impact test was carried out to determine the absorbed energy vE _-40 (J) of the base metal. The results obtained are shown in Table 2.

In addition, two materials to be welded are collected from the obtained product plate (base material), butted so as to have a narrow groove shape shown in Table 3, and weaving is performed under the welding conditions shown in Table 3. Vertical (upward) gas shield welding was performed to produce an vertical narrow groove welded joint. In the vertical gas shield welding, a 1.2 mmφ solid wire (KC-500) for steel materials with a tensile strength of 60 kg was used as the welding wire. The shield gas was carbon dioxide. In addition, the groove processing of the material to be welded was performed using gas cutting, and the groove surface processing such as grinding was not performed.

A V-notch test piece was taken from a position 2 mm below the surface of the produced welded joint so that the notch position was the weld bond portion. The term "welded bond portion" as used herein refers to a position where the ratio of the weld metal to the heat-affected zone in the notch bottom of the test piece is 1: 1. Then, a Charpy impact test was carried out at a test temperature of −20 ° C., and the absorbed energy vE _-20 (J) was determined. In addition, three tests were carried out, and the average of the obtained absorbed energy values was defined as the absorbed energy value (J) of the welded bond portion of the welded joint, and the toughness of the welded bond portion was compared.
The results obtained are shown in Table 4.

In each of the examples of the present invention, the yield strength of the base metal is 440 MPa or more, and the absorbed energy vE _-20 (J) of the welded bond portion at the test temperature: −20 ° C. shows a high absorbed energy value exceeding 80 J. Welded bond part This is an vertical narrow groove gas shield welded joint with excellent toughness. On the other hand, in a comparative example outside the scope of the present invention, the absorbed energy vE _-20 (J) of the weld bond portion at a test temperature of −20 ° C. is less than 80 J, and the toughness of the weld portion is reduced, or the yield strength of the base metal The temperature is less than 440 MPa and the strength as a structure is insufficient.

1 Steel material (welded material)
2 Groove surface 3 Backing material 4 Welding torch 5 Welding wire

Claims (8)

This is a manufacturing method for vertical narrow groove welded joints in which two steel materials with a thickness of 40 mm or more are butted through a narrow groove with a groove angle of 20 ° or less and joined by vertical gas shield arc welding using weaving. hand,
The steel material by mass%
C: 0.03 to 0.15%,
Si: 0.01-0.10%,
Mn: 1.0-2.5%,
A steel material containing P: 0.02% or less and S: 0.01% or less, satisfying the following formula (1), having a component composition in which the balance is Fe and unavoidable impurities, and having a yield strength of 440 MPa or more. ,
^{In the vertical gas shielded arc welding, the reciprocal f (s -1} ) of the upward speed v (mm / min) of the vertical welding and the time (s) required for one cycle of the weaving is calculated by the following equation (2). A method of forming an vertical narrow groove welded joint that is adjusted to a satisfactory range.
Record
0.40 ≤ (C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15) ≤ 0.50 …… (1)
Here, C, Mn, Cr, Mo, V, Cu and Ni are the contents (mass%) of each element, and the content of the elements not contained is 0.
2v / 60 / f ≤ 9.0 …… (2) In claim 1, the weaving is a method for manufacturing an vertical narrow groove welded joint in which the weaving pattern of the welding torch viewed from the direction of the welding line is U-shaped. In claim 1 or 2, the component composition is further in mass%.
Al: 0.005 to 0.100%,
Cu: 0.01-1.00%,
Ni: 0.01-1.00%,
Nb: 0.003 to 0.030%,
Ti: 0.003 to 0.030%,
N: 0.0020-0.0100% and
Ca: 0.0003 to 0.0030%
A method for manufacturing an vertical narrow groove welded joint containing one or more selected from the above. In claims 1, 2 or 3, the component composition is further in mass%.
Cr: 0.01-0.50%,
Mo: 0.01-0.50%,
V: 0.001 to 0.100%,
B: 0.0003 to 0.0030%,
Mg: 0.005 to 0.0100%,
Zr: 0.0010-0.0200% and
REM: 0.0005 to 0.0100%
A method for manufacturing an vertical narrow groove welded joint containing one or more selected from the above. An vertical narrow groove welded joint manufactured by the method for manufacturing an vertical narrow groove welded joint according to any one of claims 1 to 4. An vertical narrow groove welded joint in which two steel materials with a thickness of 40 mm or more are joined via a narrow groove with a groove angle of 20 ° or less.
The steel material is by mass%
C: 0.03 to 0.15%,
Si: 0.01-0.10%,
Mn: 1.0-2.5%,
It contains P: 0.02% or less and S: 0.01% or less, satisfies the following formula (1), has a component composition in which the balance is Fe and unavoidable impurities, and has a yield strength of 440 MPa or more.
Test temperature of Charpy impact test: Vertical narrow groove welded joint having a welded bond portion with _{absorbed energy E-20 (J) at -20 ° C of 80 J or more.}
Record
0.40 ≤ (C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15) ≤ 0.50 …… (1)
Here, C, Mn, Cr, Mo, V, Cu and Ni are the contents (mass%) of each element, and the content of the elements not contained is 0. In claim 6, the component composition is further increased by mass%.
Al: 0.005 to 0.100%,
Cu: 0.01-1.00%,
Ni: 0.01-1.00%,
Nb: 0.003 to 0.030%,
Ti: 0.003 to 0.030%,
N: 0.0020-0.0100% and
Ca: 0.0003 to 0.0030%
An vertical narrow groove welded joint containing one or more selected from the above. In claim 6 or 7, the component composition is further in mass%.
Cr: 0.01-0.50%,
Mo: 0.01-0.50%,
V: 0.001 to 0.100%,
B: 0.0003 to 0.0030%,
Mg: 0.005 to 0.0100%,
Zr: 0.0010-0.0200% and
REM: 0.0005 to 0.0100%
An vertical narrow groove welded joint containing one or more selected from the above.

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