JP2892575B2 - Non-consumable nozzle type electroslag welding wire and welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-consumable nozzle type having a small diameter and capable of stably obtaining a high toughness weld metal when performing electroslag welding of a thick plate at a high efficiency with a high welding speed. The present invention relates to a wire for electroslag welding and a welding method using the same.

[0002]

2. Description of the Related Art As a method of increasing the welding speed and performing non-consumable nozzle type electroslag welding of a thick plate with high efficiency, there are the following methods.
For example, there is JP-A-57-156884. In this publication, a non-consumable nozzle that automatically rises with a wire diameter of 2.0 mm or less and a wire protrusion length (hereinafter, referred to as dry extension) between a molten slag bath surface and a welding tip of 30 mm or more for the purpose of highly efficient electroslag welding is disclosed. The electroslag welding method used is disclosed. According to this method, since the wire has a small diameter, the dry extension portion generates heat at a high temperature during welding, thereby increasing the melting speed of the wire and performing welding with high efficiency. However, the toughness of the weld metal sometimes becomes low due to large heat input welding, and improvement is desired in terms of improving the safety of the welded structure.

In Japanese Patent Application Laid-Open No. Sho 50-7737, in consumable electroslag welding, gas is blown out through a consumable nozzle onto a molten slag surface to adjust a gas component in a weld metal to improve mechanical properties. It has been proposed to do so. However, the method of constantly discharging Ar gas or CO ₂ gas into a groove for a long time during welding requires additional cost related to gas and various functions of discharging gas, and also complicates welding work. There is a problem.

[0004] Conventional techniques for the components are as follows. That is, C is added in an amount of about 0.1% in order to adjust the strength of the weld metal. However, in electroslag welding, since the base material is greatly diluted, the C may be cracked when the base material has a large C content. In addition, Si is generally added as a deoxidizing agent in an amount of 0.4% or more, but the effect as a deoxidizing agent is not required in electroslag welding, but rather lowers toughness. Mn is effective in deoxidizing the weld metal and improving the hardenability, and is effective in ensuring strength and low-temperature toughness. Generally, Mn is added at about 1.5%. However, the effect is not so obtained at this level. Mo is added in order to enhance the hardenability of the weld metal and to increase the strength and toughness. However, if it exceeds 1%, Mo carbides are formed and the weld metal is hardened, and the toughness is significantly impaired. Ti prevents oxidation of the weld metal and
Oxide formation refines the microstructure of the weld metal,
Effective for improving toughness. However, if the amount is small, the effect of improving the toughness by microstructural refinement cannot be obtained, and if the amount is large, carbides are formed and the toughness is significantly impaired.

[0005]

SUMMARY OF THE INVENTION According to the present invention, from the viewpoint of improving the safety of a welded structure, even if a non-consumable nozzle type electroslag welding is performed with high efficiency while actively generating heat in a wire at a dry extension part, An object of the present invention is to provide a wire and a welding method capable of stably obtaining a high toughness weld metal.

[0006]

In order to solve the above-mentioned problems, the present invention utilizes the effect of improving the hardenability of the weld metal and making the microstructure fine by the formation of Ti oxide by using a high Mn-Ti component. , Characterized in that the weld metal is toughened. That is, the gist of the present invention is
C: 0.07% or less, Si: 0.15% or less, M
n: 1.80 to 3.50%, P: 0.020% or less,
S: 0.020% or less, Ti: 0.005 to 0.100
%, Mn ≧ 3 (C + Si + MofTi), the balance being iron and unavoidable impurities, and a wire diameter of 1.2 to 2.0 mm. is there. Here, Mo is 0.1 when Mn is 1.80 to 2.50%.
It is also characterized by adding 5 to 0.55%. Also, there is provided a non-consumable nozzle type electro slag welding method, characterized in that the above-mentioned wire is used for welding while maintaining a wire projection length between a molten slag bath surface and a welding tip at 20 mm or more and 50 mm or less.

[0007]

FIG. 1 is a view showing the state of non-consumable nozzle type electroslag welding, in which 6 is a groove, 7 is a non-consumable nozzle which automatically rises as welding progresses, 4 is a solid wire, 2 is a molten slag bath. Reference numeral 3 denotes a weld metal. The present inventors have observed in detail the dry extension portion during welding in the non-consumable nozzle type electroslag welding method using a wire having a diameter of 1.6 mm, and found that the dry extension 1 was long as shown in FIG. Near the wire tip 5
The part turned into a brilliant color, sparks were occasionally emitted, and the phenomenon of being sent to the molten slag bath 2 at a high temperature was confirmed.

Considering this phenomenon, in FIG. 1, since the upper part of the molten slag bath 2 is the atmosphere, the vicinity 5 of the tip of the wire is nitrided due to the high temperature state and is fed into the molten slag bath. The weld metal 3 is also nitrided. During welding, the degree of bright coloration near the wire tip 5 becomes more remarkable as the dry extension 1 is longer, but if the welding current is constant, the longer the dry extension 1, the higher the welding speed and the higher the efficiency. The degree to which the vicinity 5 of the wire tip becomes brilliant becomes more remarkable when the wire diameter is reduced to 1.2 mm and welding is performed, and it is confirmed that the smaller the diameter of the wire, the more heat is generated in the dry extension portion and the easier the wire is to melt. did. When the wire diameter exceeded 2.0 mm, no bright coloring phenomenon was observed, but the welding speed was slow and the efficiency was not good despite the increase in welding heat input.

In other words, it can be said that, in the case of pursuing high-efficiency weldability in such a welding method, the amount of N dissolved in the weld metal increases, which may be a factor of toughness degradation. Therefore, as long as high weldability is pursued, it is necessary to prevent N in the weld metal from increasing, or to take measures to prevent harm to the toughness even if it increases. As a countermeasure that does not harm the toughness even if the N in the weld metal increases, T which has a strong affinity with N
If i is added to the wire, even if the nitrided wire melts and becomes a N-rich weld metal, N becomes a high melting point material such as TiN and is dispersed in the matrix, so that the amount of solid solution should be reduced. is there. Therefore, if the wire composition is high Mn-Ti
As a result of considering and considering that it is effective to use a system, the present invention has been obtained as exemplified in Examples described later.

By the way, TiO ₂ becomes not become only by the TiN was added alone in the wire of Ti when there is N in the weld metal in the electro-slag welding according to the JP-A-48-4346, Ti and Al Only when Al coexists does Al become Al due to the difference in affinity between both elements with oxygen.
_It is pointed out that Ti becomes TiN in the form of ₂ O _3, and it is stated that adding Ti alone as in the present invention makes the crystal of the weld metal acicular and lowers the impact value. However, this is the case where a wire having a large diameter of 3.2 mm is used. When the wire diameter is large, the tip of the wire is immersed and melted in a molten slag bath, whereas the wire diameter is 2.0 mm. In the case of the present invention described below, since the melting speed of the wire is high and the tip of the wire is melted on the surface of the molten slag, it is considered that the welding phenomenon is different from that of JP-A-48-4346, which is a feature of the present invention.

Hereinafter, the reasons for limiting the configuration of the present invention will be described. First, the reasons for limiting the components of the wire will be described.

C is added in an appropriate amount to adjust the strength of the weld metal in other welding methods for ferritic steels.
In this welding method, the base metal dilution ratio is large,
Is transferred to the weld metal, so C is not intentionally added to the wire. If it exceeds 0.07%, the content becomes excessive, resulting in problems of high strength and cracking.

[0013] Si is generally used as a main and essential deoxidizing agent in gas shielded arc welding and the like.
Add 0% or more. However, in the electroslag welding, the temperature of the atmosphere at the wire tip where the wire melts is lower than in the case of arc welding, so that the oxidation reaction becomes slower, and therefore, unlike in the case of arc welding, the addition is not essential. Also, S
When i exceeds 0.15%, Mn silicate is generated in the molten slag bath during electroslag welding, and this combines with oxides such as Ti to form large-scale composite inclusions, which is effective for refining the microstructure of the weld metal. The number of nucleation sites is reduced to form a coarse microstructure, or the solid solution is dissolved in the matrix and hardened, resulting in a decrease in toughness. Therefore, Si
Has an upper limit of 0.15%.

Mn is effective for deoxidizing the weld metal and improving the hardenability and ensuring the strength and low-temperature toughness. However, the amount of Mn that exerts this effect is 1.80% or more. However, if it is added in excess of 3.50%, a special treatment is required to melt the steel, which is the material of the wire, and it becomes expensive.

Mo is added in consideration of the amount of Mn. When Mn is 2.50% or less, the strength of the weld metal is reduced. Therefore, 0.15 to 0.55% is added as a countermeasure. Precipitation of ferrite was also suppressed. If the Mo content is less than 0.15%, the above effect is insufficient, and if the Mo content is more than 0.55%, a problem arises in that Mo carbide is precipitated, the weld metal is hardened, and the toughness is reduced.

As described above, Ti is used to dissolve a wire whose dry extension is long and nitrided. However, in order to prevent the solid solution N from being fixed in the weld metal and to prevent the toughness of the weld metal from deteriorating, 0.005% is used. Add above. On the other hand, even if Ti is added in excess of 0.100%, the effect is not so great, but if excessively added, a large precipitate is formed and the toughness is impaired.

P and S are preferably as small as possible, since a low-melting point compound is formed at the grain boundary during solidification of the weld metal and the crack sensitivity of the weld metal is increased as in the case of Si described above.
Both P and S in the wire are set to 0.020% or less.

As the alloy composition of the entire wire, it is effective to increase the ratio between the austenite forming element and the other elements in order to secure the toughness of the large heat input weld metal having a low cooling rate. That is, by increasing the austenite forming element,
It is effective to reduce C, Si, Mo, and Ti to such an extent that the strength is not impaired. Therefore, the configuration is made so as to satisfy Mn ≧ 3 (C + Si + Mo + Ti) as a result of various studies. If this is not satisfied, the alloy balance will be poor and the toughness of the weld metal will decrease.

The wire of the present invention can be manufactured by rolling and drawing a steel ingot in the same manner as a normal wire, and applying copper plating if necessary.

In the present invention, the wire component is limited as described above, and the wire diameter is set to 1.2 to 2.0 mm. This is because if the wire diameter exceeds 2.0 mm, a large amount of heat is not generated in the dry extension portion during welding, so that the melting speed of the wire becomes slow and the welding speed becomes slow, resulting in inefficiency. On the other hand, if it is less than 1.2 mm, the melting speed of the wire becomes extremely high, the wire separates from the slag bath and an arc is generated, and stable welding cannot be performed.

Further, in the present invention, welding is performed while keeping the dry extension at 20 mm to 50 mm. If the dry extension is less than 20 mm, some abnormality occurs during welding, and the molten slag bath is bumped and slag is spun. The thickness is set to 20 mm or more because this may adhere to the chip and cause welding interruption. On the other hand, if it exceeds 50 mm, the straightness of the wire is deteriorated, so that one-sided melting occurs and stable penetration cannot be obtained.

As the various conditions in the present invention, the main composition of the flux for forming the molten slag bath is SiO.
₂ : 20 to 40%, MnO: 5 to 15%, MgO: 10
~20%, CaO: 5~15%, TiO 2: 2~6%,
Al ₂ O ₃ : 5 to 13%, and if the addition amount of the flux is 25 to 240 g depending on the plate thickness, the depth of the molten slag bath becomes approximately 30 to 40 mm. The wire feed speed was 7 to 9 m / min, and the welding current was 340 to 4 m / min.
50A, welding voltage 40-53V, welding speed 5-50
mm / min, the heat input is 160-2700 kJ / cm.

[0023]

EXAMPLES C: 0.17%, Si: 0.36%, Mn:
1.44%, P: 0.013%, S: 0.004% A SM490B steel plate having a thickness of 30 mm made of iron and having a balance of iron is assembled as shown in FIG. The enclosed groove 6 was subjected to non-consumable nozzle electroslag welding with a wire having a diameter of 1.6 mm. The dimensions of the groove are as shown in FIG.

The flux for forming the molten slag bath was of a molten type having a main composition of SiO ₂ -MnO-MgO. 54 g was added at the start of welding so that the molten slag bath depth was about 30 mm. The wire feed speed during welding was 8.5 m / min, the welding current was 380 A, and the welding voltage was 46.
V, welding speed 22.5 mm / min, dry extension 38 mm, and heat input 466 kJ / cm.

After welding is completed, J
An IS Al round bar tensile test piece and a JIS No. 4 2 mm V notch Charpy impact test piece were sampled and subjected to a tensile test and an impact test. Tables 1 and 2 show the wire components and test results. In the case of welding with the wires of the present invention of Nos. 1 to 8, good results were obtained. On the other hand, in Comparative Example No. 8, Si was higher than the appropriate value and Mn was lower, and Mn / (C +
Si + Mo + Ti) is also less than 3. In the case of No. 9, C is high, and Mn / (C + Si + Mo + Ti) is also low.
Therefore, the impact value is low in each case.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Effect of the Invention] Tensile as a mechanical performance of SM490B strength 490 N / mm ² or more, a yield point 315N / mm ² or more, whereas the Charpy impact test value is required or 27J at 0 ° C., the present invention wire and According to the welding method, as shown in Tables 1 and 2, it can be seen that the weld metal satisfies these conditions.

[Brief description of the drawings]

FIG. 1 is a view showing a state of non-consumable nozzle type electroslag welding.

FIG. 2 is a schematic diagram showing a test plate shape and a welding state in an embodiment.

FIG. 3 is a view showing dimensions of a groove portion in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Dry extension 2 Molten slag bath 3 Weld metal 4 Solid wire 5 Near wire tip 6 Groove 7 Non-consumable nozzle 8 Steel equivalent 10, 11 Steel plate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-138885 (JP, A) JP-A-53-73444 (JP, A) JP-B-49-24778 (JP, B1) JP-B-42 17419 (JP, B1) (58) Field surveyed (Int. Cl. ⁶ , DB name) B23K 35/30 320 B23K 25/00

Claims (3)

(57) [Claims] 1. In weight%, C: 0.07% or less Si: 0.15% or less Mn: 1.80 to 3.50% P: 0.020% or less S: 0.020% or less Ti: 0 0.005 to 0.100%, satisfying Mn ≧ 3 (C + Si + Mo + Ti),
The balance consists of iron and unavoidable impurities, and the wire diameter is 1.
A non-consumable nozzle type electroslag welding wire having a thickness of 2 to 2.0 mm. 2. When Mn is 1.80 to 2.50%, M
The non-consumable nozzle type electroslag welding wire according to claim 1, wherein 0.15 to 0.55% of o is added. 3. The wire according to claim 1 or 2, wherein the wire protrusion length between the molten slag bath surface and the welding tip is 2
A non-consumable nozzle-type electroslag welding method, characterized in that welding is performed while the welding is performed while being held at 0 mm or more and 50 mm or less.