JP2012006073A - High strength welded metal excellent in ctod characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength welded metal obtained by submerged arc welding, excellent in a CTOD (crack tip opening displacement) characteristic.SOLUTION: This high strength welded metal is obtained by the submerged arc welding, contains, in terms of mass%, 0.02-0.12% of C, 0.1-0.70% of Si, 1.0-2.0% of Mn, 0.1-2.5% of Cu and/or 0.5-3.5% of Ni, 1.0% or less (excluding 0%) of Cr and/or 0.5-1.5% of Mo, 0.005% or less (including 0%) of Ca, 0.0050% or less (including 0%) of Ti, 0.005-0.050% of Al, and 0.010-0.050% of O, satisfies formula (1) and has an area ratio of an Al-containing oxide within a range of 0.5 or more to 2.0% or less. Formula (1): 0.45≤[C]+[Mn]/6+([Cu]+[Ni])/15+([Cr] +[Mo]/5)≤0.75.

Description

  The present invention relates to a high-strength weld metal, and more particularly to a high-strength weld metal excellent in CTOD (Crack Tip Opening Displacement) characteristics among the toughness evaluation criteria.

  In recent years, marine structures are becoming larger and colder, and steel sheets and welds used in marine structures are required to have higher strength and toughness. The toughness required for offshore structures is a characteristic called CTOD characteristics, and a weld metal having a tensile strength of 780 MPa or more and excellent CTOD characteristics is required. CTOD characteristics are an index for evaluating the fracture toughness of structures with defects, and are calculated by measuring the crack tip opening displacement (CTOD value) immediately before the crack progresses rapidly using a CTOD test. Is done. Even if a small test such as a conventional V-notch Charpy impact test shows a good result, a CTOD test of a welded joint of a large structure does not necessarily show a good fracture toughness value. On the other hand, as a welding method for a large structure as described above, submerged arc welding is often used from the viewpoint that high-efficiency construction is possible and the quality of the weld metal is stable.

  When defects such as cracks exist, it is known that fractures progress by connecting voids generated during loading. Conventionally, inclusions (mainly oxides) that are the source of voids are finely divided. Attempts have been made to improve the CTOD characteristics by refining crystal grains after being dispersed.

  For example, in Patent Document 1, the amount of O (oxygen) in the welded joint and the amount of Ti are adjusted, the amount of O is set to 20 ppm or more, and a predetermined amount of fine Ti oxide is secured, and the amount of O is about 70 ppm at most. The CTOD characteristics of the electron beam welded joint are improved by suppressing the amount of coarse oxide (particle size of 2.0 μm or more). In Patent Document 1, oxygen contained in the welded joint is about 70 ppm at most in order to suppress coarse oxides, but submerged arc welding is a method in which the oxygen content contained in the weld metal is relatively high. It is difficult to apply the technique of Patent Document 1 to submerged arc welding. Patent Document 2 discloses a technique for improving the fracture toughness value by making the amount of Ni in the welded joint more than 4% and making the hardness of the weld metal part equal to or greater than the hardness of the base metal part. Yes. However, the addition of a large amount of Ni causes an increase in cost.

JP 2008-88504 A JP 2008-87034 A

  The present invention has been made in view of the above-described problems, and an object of the present invention is to obtain a high-strength weld metal that is a weld metal obtained by submerged arc welding and excellent in CTOD characteristics.

The present invention that has achieved the above object is a weld metal obtained by submerged arc welding, and C: 0.02 to 0.12% (meaning mass%; hereinafter the same for chemical composition), Si: 0.00. 1 to 0.70%, Mn: 1.0 to 2.0%, Cu: 0.1 to 2.5% and / or Ni: 0.5 to 3.5%, Cr: 1.0% or less ( And / or Mo: 0.5 to 1.5%, Ca: 0.005% or less (including 0%), Ti: 0.0050% or less (including 0%), Al: 0.005 to 0.050%, O: 0.010 to 0.050% and satisfy the following formula (1), the balance is iron and inevitable impurities, the area ratio of the Al-containing oxide is It is a high strength weld metal characterized by being 0.5% or more and 2.0% or less.
0.45 ≦ [C] + [Mn] / 6 + ([Cu] + [Ni]) / 15 + ([Cr] + [Mo]) / 5 ≦ 0.75 (1)
(However, [] means the content (mass%) of each element.)

  According to the present invention, among the chemical components of the weld metal, in particular, the content of Al, Ti, and O (oxygen) is appropriately controlled, and the area ratio of the Al-containing oxide is controlled within a predetermined range. As a result of suppressing the progress of cracks, the CTOD characteristics can be improved. Further, since the contents of C, Mn, Cu, Ni, Cr, and Mo are controlled with each other as well as the individual contents of chemical components of the weld metal, high strength can be achieved.

FIG. 1 is a graph showing the magnitude of work of adhesion between oxides of various elements of Ti, Mg, Ca and Al and a matrix (welded metal). FIG. 2A is a diagram showing a groove shape of the base steel plate used in the examples, and FIG. 2B is a diagram showing a welding lamination procedure. FIG. 3A is a diagram showing a sampling position of a tensile test piece in the example, and FIG. 3B is a diagram showing a sampling position of a Charpy impact test piece in the example.

  In order to improve the CTOD characteristics of the weld metal, the present inventors have examined in detail the mechanism of crack propagation in the CTOD test. In the CTOD test, a crack grows, and when it reaches a certain limit, it progresses at a stretch and leads to fracture. However, during the crack growth process, a high strain is generated at the crack tip. The lower the strain at the crack tip, the less likely the crack will grow and the higher the CTOD characteristic. Conventionally, it is considered that destruction progresses by connecting voids resulting from inclusions, and the presence of inclusions is thought to deteriorate the CTOD characteristics. As disclosed in Patent Document 1 described above, coarseness is considered. In other words, the inclusion of particles (with a particle size of 2.0 μm or more) is suppressed, and a fine oxide is secured at a predetermined level or more to refine the structure, thereby improving the CTOD characteristics. However, as a result of investigations by the present inventors, it is possible to improve the CTOD characteristics by appropriately dispersing inclusions of a certain size and actively forming voids. The inventors discovered that an oxide effective for improvement is an oxide containing Al, and completed the present invention.

  That is, when inclusions are present in the weld metal, peeling occurs at the interface between the inclusions and the matrix (welded metal) (hereinafter sometimes simply referred to as “inclusion interface”) due to the load, resulting in voids. However, when a void is generated in the vicinity of the crack tip, the void is also distorted. The strain generated in the void near the crack tip is a dispersion of the strain generated in the crack tip, and the present inventors appropriately adjust the size and amount (area ratio) of the void to determine the crack tip. It was thought that the strain could be dispersed efficiently and the strain at the crack tip could be reduced.

As described above, in order to reduce the strain at the crack tip by dispersing the strain generated near the crack tip into the void, it is necessary to form the void at the initial stage of the load in the CTOD test by peeling the inclusion interface. is there. Therefore, the present inventors examined the generation of voids at the inclusion interface, particularly from the viewpoint of work of adhesion at the inclusion interface. Here, the work of adhesion is the energy required to adhere the matrix and inclusions in the state where solid phase inclusions are present in the liquid phase matrix (welded metal). It was considered that the smaller the work, the less the adhesive force at the inclusion interface after the matrix was hardened and the easier it was to peel off. The inventors paid attention to oxides among inclusions, and examined the work of adhesion of these oxides for elements such as Ti, Mg, Ca, and Al, which have high oxide forming ability. In FIG. 1, the magnitude | size of the adhesion work of the oxide of various elements of Ti, Mg, Ca, and Al and a matrix (welding metal) is shown. FIG. 1 is a graph showing the relationship between θ: wettability (contact angle) and adhesion work based on the equation of adhesion work γ _LV = (1 + cos θ). The γ _LV indicates the interfacial tension between the liquid phase and the gas phase, and “BJ Keene, Reviews of data”.
for the surface tension of pure metals,
International Materials Reviews, vol. 38,
No. 4 (1993), pp. The value shown in “157-192” was used. Further, the contact angle θ between the oxides of various elements and the matrix used was a value shown in “Supervision by Samsonov, latest oxide manual, physicochemical properties, Nisso News Agency (1978)”. According to FIG. 1, it can be understood that the adhesion work of Al oxide is the smallest among the elements of Ti, Mg, Ca and Al.

  In addition, the separation at the inclusion interface is considered to be affected by the difference in strength between the inclusion and the matrix, and the greater the strength difference, the greater the stress concentration at the inclusion interface. Is likely to occur. The Al-containing oxide usually has a longitudinal elastic modulus about twice that of steel, and the difference in strength from the matrix is extremely large. From this viewpoint, it is an inclusion that is likely to generate voids from the interface. I can say that.

  Furthermore, as described above, in order to efficiently disperse the distortion at the crack tip, it is necessary to form a void having an appropriate size. This is because if the void size is too small, the crack tip strain cannot be dispersed efficiently, whereas if the void size is too large, the total amount of strain generated near the crack tip becomes large and the crack tip strain increases. This is because it becomes larger. According to the study by the present inventors, it was found that the Al-containing oxide is useful for forming a void having an appropriate size, and that the Al-containing oxide is also effective from the viewpoint of the size of the void.

  In the present invention, the Al-containing oxide means an element in which peaks of Al and O (oxygen) are detected when elemental analysis is performed by EPMA (electron beam microanalyzer), and includes elements other than Al. It may be a complex oxide. However, as described later, since the elements (Ti, Ca, etc.) forming the oxide are suppressed to a small amount in the present invention, the Al-containing oxide of the present invention is a single oxide of Al or other than Al. It is a complex oxide containing a small amount of other elements, and such an Al-containing oxide of the present invention has a particle size of about 0.5 to 2 μm. The void formed at the interface between the Al-containing oxide of this size and the matrix becomes larger than the size of the Al-containing oxide due to the macro deformation of the surroundings, and the size is approximately four times the area of the Al-containing oxide. It is clear from the study by the present inventors that this value is effective, and voids of such a size are effective in dispersing and reducing the distortion at the crack tip.

  In order to effectively exhibit the effect of reducing the distortion at the crack tip by the void, the area ratio of the Al-containing oxide is set to 0.5% or more and 2.0% or less. This is because if the area ratio of the Al-containing oxide is too small, the effect of dispersing the strain is not sufficient, while if the area ratio is too large, the total amount of strain near the crack tip increases. The range of the area ratio of the Al-containing oxide was found to be that if the void area ratio is 2% or more and 8.0% or less, the effect of reducing distortion at the crack tip due to the void can be effectively obtained. It is obtained in terms of the oxide area ratio (1/4 of the void area ratio). The area ratio of the Al-containing oxide is preferably 1.0% or more and 1.5% or less.

  Next, chemical components of the weld metal of the present invention will be described below. In the present invention, a predetermined amount of the above-mentioned Al-containing oxide is formed and a weld metal having a tensile strength of 780 MPa or more is obtained. In particular, the content of strong deoxidizing elements (Ti, Al) and oxygen in the weld metal , And the contents of elements having a large influence on strength (C, Mn, Cu, Ni, Cr, Mo) are mutually adjusted.

C: 0.02-0.12%
C is an element indispensable for ensuring the strength of the weld metal. Therefore, the C amount is set to 0.02% or more. The amount of C is preferably 0.03% or more. On the other hand, if the amount of C is excessive, the toughness deteriorates due to the formation of a hard structure. Therefore, the C amount is set to 0.12% or less. The amount of C is preferably 0.10% or less.

Si: 0.1 to 0.70%
Si is a deoxidizing element, has an action of cleaning the weld metal, and has an action of strengthening the weld metal by solid solution strengthening when it remains in the weld metal. Therefore, the Si amount is determined to be 0.1% or more. The amount of Si is preferably 0.2% or more, and more preferably 0.3% or more. On the other hand, when the amount of Si is excessive, Si is contained in the oxide, the Young's modulus of the Al-containing oxide is lowered, and the interface between the oxide and the weld metal is difficult to peel off. As a result, voids are less likely to occur and the CTOD characteristics are degraded. In addition, the toughness is likely to be lowered by excessively increasing the strength of the weld metal or generating a hard structure. Therefore, the Si amount is determined to be 0.70% or less. The amount of Si is preferably 0.6% or less, and more preferably 0.55% or less.

Mn: 1.0-2.0%
Mn has the effect of ensuring the strength and toughness of the weld metal by refining the structure. Therefore, the amount of Mn is set to 1.0% or more. The amount of Mn is preferably 1.2% or more, more preferably 1.3% or more. On the other hand, when the amount of Mn becomes excessive, the toughness deteriorates due to the excessive increase in hardenability. Therefore, the amount of Mn is set to 2.0% or less. The amount of Mn is preferably 1.9% or less, more preferably 1.8% or less.

Cu: 0.1-2.5% and / or Ni: 0.5-3.5%
Cu and Ni are both effective elements for ensuring strength and toughness. Therefore, the Cu amount is set to 0.1% or more, and the Ni amount is set to 0.5% or more. The amount of Cu is preferably 0.3% or more, and more preferably 0.5% or more. The amount of Ni is preferably 1.0% or more, and more preferably 1.3% or more. On the other hand, if both Cu and Ni are excessive, the toughness deteriorates due to the excessive increase in hardenability. Therefore, the Cu content is set to 2.5% or less, and the Ni content is set to 3.5% or less. The amount of Cu is preferably 2.2% or less, more preferably 2.0% or less. The amount of Ni is preferably 2.5% or less, more preferably 2.2% or less. Cu and Ni may be contained singly or both may be contained at the same time.

Cr: 1.0% or less (not including 0%) and / or Mo: 0.5 to 1.5%
Cr and Mo are both effective elements for ensuring strength. In order to effectively exhibit such an action, the Cr content is preferably 0.15% or more, and more preferably 0.2% or more. The amount of Mo is 0.5% or more, preferably 0.6% or more. On the other hand, if both Cr and Mo are excessive, the toughness deteriorates due to the excessive increase in hardenability. Therefore, the Cr content is 1.0% or less, and the Mo content is 1.5% or less. The amount of Cr is preferably 0.8% or less, and more preferably 0.6% or less. The Mo amount is preferably 1.3% or less, more preferably 1.0% or less. Cr and Mo may be contained singly or both may be contained at the same time.

Ca: 0.005% or less (including 0%)
Ca is a strong deoxidizing element and has a function of cleaning the weld metal by a deoxidizing action. In order to effectively exhibit such an action, the content is preferably 0.002% or more, more preferably 0.003% or more. Further, Ca forms an oxide with a small work of adhesion at the interface with the weld metal. However, if the amount of Ca becomes excessive and the amount of Ca-based oxide increases, the above-described Al-containing oxide cannot be secured. Therefore, the Ca content is determined to be 0.005% or less. The amount of Ca is more preferably 0.004% or less.

Ti: 0.0050% or less (including 0%)
Ti has the effect of cleaning the weld metal by deoxidation. In order to effectively exhibit such an action, the Ti content is preferably 0.0005% or more, more preferably 0.0010% or more. On the other hand, since Ti oxide has a large adhesion work with the matrix and is difficult to peel off at the interface, there is little effect of reducing the distortion at the crack tip as described above, and a desired Al-containing oxide is secured when the amount of Ti increases. Can not do it. Therefore, the Ti amount is determined to be 0.0050% or less. The amount of Ti is preferably 0.0040% or less, and more preferably 0.0030% or less.

Al: 0.005 to 0.050%
Al is a strong deoxidizing element and has a function of cleaning the weld metal by a deoxidizing action. In addition, as described above, excellent oxide inclusions that easily peel off at the interface are generated, so that voids are likely to occur during the CTOD test, and distortion at the crack tip can be dispersed in the voids, improving CTOD characteristics. be able to. Therefore, the Al content is determined to be 0.005% or more. The amount of Al is preferably 0.010% or more, more preferably 0.020% or more. On the other hand, when the amount of Al becomes excessive, the area ratio of the Al-containing oxide increases so much that the CTOD characteristics deteriorate. Therefore, the Al content is determined to be 0.050% or less. The amount of Al is preferably 0.040% or less, and more preferably 0.030% or less.

O: 0.010 to 0.050%
O is an element necessary for forming an appropriate amount of an Al-containing oxide. Therefore, the O amount is determined to be 0.010% or more. The amount of O is preferably 0.015% or more, and more preferably 0.020% or more. On the other hand, when the amount of O becomes excessive, the amount of oxide becomes excessive and the CTOD characteristics deteriorate. Therefore, the amount of O is set to 0.050% or less. The amount of O is preferably 0.045% or less, and more preferably 0.040% or less.

  The chemical components of the weld metal of the present invention are as described above, and the balance is substantially iron. However, it is naturally allowed that inevitable impurities brought into the weld metal are brought into the weld metal depending on the situation of the raw materials, materials, manufacturing equipment, and the like.

  Furthermore, among the chemical components described above, it is important that C, Mn, Cu, Ni, Cr, and Mo satisfy the following formula (1).

0.45 ≦ [C] + [Mn] / 6 + ([Cu] + [Ni]) / 15 + ([Cr] + [Mo] / 5) ≦ 0.75 (1)
The above equation (1) is an equation calculated experimentally from the relationship between the content and strength of each element. Each element contained in the formula (1) is an element that affects the strength of the weld metal, and [C] + [Mn] / 6 + ([Cu] + [Ni]) / 15 + ([Cr] + [ The strength of the weld metal can be improved (780 MPa or more) by setting the value of Mo]) / 5 (hereinafter referred to as the X value) to 0.45 or more. The X value is preferably 0.50 or more, and more preferably 0.52 or more. On the other hand, if the X value exceeds 0.75, the strength of the weld metal becomes too high and the toughness deteriorates. The X value is preferably 0.70 or less, and more preferably 0.68 or less. When calculating the above equation (1), if there is an element that is not contained, the content may be set to 0.

  The weld metal of the present invention is obtained by submerged arc welding. This is because, in the technique of actively using oxides for improving CTOD characteristics as in the present invention, it is necessary to supply oxygen to the weld metal to some extent. The wire and flux used for submerged arc welding for obtaining the weld metal of the present invention, and the base steel plate are not particularly limited. For example, the following can be used.

As the wire, C: 0.02 to 0.12% (preferably 0.05 to 0.12%), Si: 0.05 to 0.5% (preferably 0.1 to 0.4%), Mn: 1.0 to 2.5% (preferably 1.5 to 2.2%), Cu: 0.10 to 2.5% (preferably 0.10 to 2.0%) and / or Ni: 0.5 to 3.5% (preferably 1.5 to 3.0%), Cr: 1.0% or less (excluding 0%) (preferably 0.8% or less) and / or Mo: 0 0.5 to 1.5% (preferably 0.6 to 1.0%), Ca: 0.005% or less (including 0%) (preferably 0.003% or less), Ti: 0.01% or less (Including 0%) (preferably 0.008% or less), Al: 0.01% or less (not including 0%) (preferably 0.008% or less), with the balance being iron and A variable avoid impurities, is preferably a wire which satisfies the following equation (2).
0.45 ≦ [C] + [Mn] / 6 + ([Cu] + [Ni]) / 15 + ([Cr] + [Mo]) / 5 ≦ 0.75 (2)
As for the amount of oxygen, the amount of oxygen in the weld metal is greatly affected by the flux at the time of submerged arc welding and the oxygen from the atmosphere. The amount of oxygen in the wire is not particularly problematic as long as it is a normal inevitable impurity level.

As the flux, it is preferable to use a flux having a basicity of 2.0 to 4.0 and a mass ratio of Al ₂ O ₃ to 10 to 16% with respect to the total mass of the flux. Here, the basicity is {CaO + MgO + CaF ₂ + BaO + SrO + Na ₂ O + K ₂ O + Li ₂ O + 0.5 (MnO + FeO)} / {SiO ₂ +0.5 (Al ₂ O ₃ + TiO ₂ + ZrO ₂ )}. If the basicity is less than 2.0, the amount of oxygen in the weld metal becomes excessive. On the other hand, if the basicity exceeds 4.0, the amount of oxygen in the weld metal becomes too low. The Al-containing oxide cannot be properly secured. Further, Al ₂ O ₃ in the flux greatly affects the amount of Al in the weld metal and also affects the area ratio of the Al-containing oxide. In order to appropriately secure the Al-containing oxide, the mass ratio of Al ₂ O _{3 in} the flux is preferably 10 to 16%.

  As the base material steel plate, for example, ASTM standard A517 steel plate can be used.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Welding was performed under the following welding conditions using the wires and fluxes shown in Tables 1 and 2 and the grooved base steel plate shown in FIG. 2A (unit: mm). Welding was performed according to the lamination procedure shown in FIG. In the base steel plate, C: 0.12%, Si: 0.24%, Mn: 0.79%, P: 0.005%, S: 0.003%, Cu: 0.21%, Ni: 0.79%, C
A steel plate containing r: 0.49%, Mo: 0.45%, V: 0.040%, B: 0.0007%, the balance being iron and inevitable impurities was used.

Welding condition current: 500-550A
Voltage: 26-32V
Speed: 30cm / min
Heat input: 26-36 kJ / cm
Preheating temperature and interpass temperature: 140-160 ° C
Number of passes: 15

  The obtained weld metal was evaluated in the following manner.

(1) Measurement of tensile strength, Charpy absorbed energy, and CTOD value From the position shown in FIG. 3A, a No. A1 test piece of JIS Z2201 was sampled, and a tensile test of the weld metal was performed according to JIS Z2241. Further, Charpy impact test pieces were collected from the position shown in FIG. 3B in accordance with JIS Z2242, and Charpy absorbed energy (vE- ₆₀ ) at -60 ° C. was measured. Further, CTOD specimens were collected from the position shown in FIG. 3B in accordance with WES1108 (Japan Welding Association standard), and the CTOD value was measured at −40 ° C. In the present invention, the tensile strength (TS), the Charpy absorbed energy (vE- ₆₀ ), and the CTOD value were determined to be 780 MPa or more, 47 J or more, and 0.30 mm or more, respectively.

(2) Measurement of Al-containing oxide SEM photograph obtained by observing a region of 100 μm × 100 μm at the same site as the sampling position of the tensile test piece using a scanning electron microscope (SEM) at a magnification of 1000 times. The area ratio of the Al-containing oxide was measured by image analysis. At this time, whether the oxide is an Al-containing oxide or not is confirmed by EPMA analysis of the inclusions observed in the region, and it is confirmed that it has aluminum and oxygen peaks (that is, contains aluminum and oxygen). Were determined to be Al-containing oxides. In addition, in the SEM observation, inclusions having a major axis of less than 0.1 μm were excluded from the measurement target because it was difficult to analyze with EPMA.

  The results are shown in Table 3.

  Test No. In Nos. 1 to 7, since the chemical ratio of the weld metal and the area ratio of the Al-containing oxide satisfied the requirements of the present invention, the results were excellent in tensile strength, Charpy absorbed energy, and CTOD value.

  On the other hand, test no. In Nos. 8 to 19, since at least one of the chemical components and the area ratio of the Al-containing oxide deviated from the requirements of the present invention, at least one of tensile strength, Charpy absorbed energy, and CTOD value was inferior.

  Test No. In No. 8, since the Al amount was large, the area ratio of the Al-containing oxide was increased and the CTOD value was deteriorated. Test No. In No. 9, since the amount of Ti was large, the area ratio of the Al-containing oxide could not be ensured, and the CTOD value deteriorated. Test No. Since 10, 11 and 12 had a large amount of Mo, Cr and Ni, respectively, and the value of the formula (1) was large, the strength was excessively improved and the toughness (Charpy absorbed energy) was deteriorated. Test No. No. 13 could not secure the tensile strength of the weld metal because the value of the formula (1) was small. Test No. In Nos. 14 and 15, since the amount of Mn and the amount of C were small and the value of formula (1) was small, the tensile strength of the weld metal could not be ensured. Test No. Since 16 and 17 had little amounts of Al and O, respectively, the area ratio of the Al-containing oxide could not be secured, and the CTOD value was deteriorated. Test No. Since No. 18 had a large amount of Al and O, the area ratio of the Al-containing oxide increased and the CTOD value deteriorated. Test No. 19 had a large amount of Si, so the CTOD value deteriorated.

Claims (1)

A weld metal obtained by submerged arc welding,
C: 0.02 to 0.12% (meaning mass%, hereinafter the same for chemical composition),
Si: 0.1 to 0.70%,
Mn: 1.0-2.0%,
Cu: 0.1-2.5% and / or Ni: 0.5-3.5%,
Cr: 1.0% or less (excluding 0%) and / or Mo: 0.5-1.5%
Ca: 0.005% or less (including 0%),
Ti: 0.0050% or less (including 0%),
Al: 0.005 to 0.050%,
O: It contains 0.010 to 0.050%, satisfies the following formula (1), the balance is iron and inevitable impurities,
A high-strength weld metal, wherein the area ratio of the Al-containing oxide is 0.5% or more and 2.0% or less.
0.45 ≦ [C] + [Mn] / 6 + ([Cu] + [Ni]) / 15 + ([Cr] + [Mo]) / 5 ≦ 0.75 (1)
(However, [] means the content (mass%) of each element.)