JP3208556B2 - Flux-cored wire for arc welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux-cored wire for arc welding which is intended for high-strength steel of 490 N / mm ² or higher class and which improves the low-temperature crack resistance of a steel weld.

[0002]

2. Description of the Related Art With the increase in size of ships and buildings, the use of high-tensile steel materials has been increasing in order to reduce the weight of steel materials. Since high-tensile steel contains a small amount of alloying elements in order to increase the yield point and tensile strength, it is known that low-temperature cracking often occurs when high-tensile steel is subjected to arc welding.

[0003] The causes of low-temperature cracking include hardening of welds,
There are factors such as the amount of diffusible hydrogen and the degree of constraint on the welded members,
In particular, it is known that the influence of the amount of diffusible hydrogen is great.
Thus, low-temperature cracking that occurs when the weld metal is high in hydrogen is determined by the structure of the weld metal and the amount of hydrogen. A hardenable element is contained in the steel to improve the strength and toughness, and cracks tend to occur in the weld zone from the base metal heat affected zone.

[0004] Several methods have been found as means for preventing or reducing weld cracks, and among these methods, among them, the most commonly used method and the most effective method for weld cracks have been used. This is a method of preheating or post-heating the base material. This method has the effect of slowing down the cooling rate of the weld, reducing the formation of martensite in the structure of the weld, and prolonging the release time of diffusible hydrogen in the weld to suppress hydrogen embrittlement. This has the effect of reducing the generation of residual stress. The preheating temperature for achieving these effects varies depending on the components of the base material, the thickness of the base material, the strength, the composition of the welding material, and the like, but generally about 100 ° C. for welding 590 N / mm ² class high strength steel. It is as high as 200 ° C. Such a high preheating temperature makes the welding operation extremely difficult, and also causes a sudden increase in welding work cost. It does not require preheating, or a flux-containing flux with excellent crack resistance that can reduce the preheating temperature. There is a need for wire development.

[0005] As a method of preventing welding cracks without preheating an extremely thick steel plate, there is a method of reducing the amount of diffusible hydrogen in the welding material itself. However, even if the amount of diffusible hydrogen in the welding material is reduced, when the water vapor in the air is hot and humid, the water in the air is involved during welding and causes an increase in hydrogen. As a flux-cored wire containing V, for example,
No. 146295 discloses a specific weight% of C, Si and M.
Proposal of a metal powder type flux-cored wire that contains n and at least one of Nb, Ta, B, V, and Cr and identifies the potential hydrogen amount of the wire to reduce the occurrence of welding defects such as pits and blowholes. However, the resistance to low temperature cracking has not been improved. Also, JP-A-61-67
593 and JP-A-61-135499,
A steel wire has been proposed in which the yield ratio is increased and the toughness is improved by adding a specific amount of V, but the improvement in low-temperature cracking resistance has not been achieved.

On the other hand, in Japanese Patent Application Laid-Open Nos. 62-101394 and 62-14795, steel wires for welding Cr-Mo based low alloy heat-resistant steel have been proposed. The purpose is to improve the creep properties, but also not to improve the low temperature cracking resistance.
Therefore, these techniques cannot be expected to perform construction without preheating or to reduce the preheating temperature.

[0007]

[0008] The present invention was made to solve the problems of the prior art, even when predominantly 490 N / mm ² or higher grade of welding a high strength steel, require preheating An object of the present invention is to provide a flux-cored wire for arc welding which is extremely excellent in crack resistance and can reduce the preheating temperature.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors have developed a flux-cored wire that can prevent low-temperature cracking even if the preheating temperature is reduced by a method other than a method of reducing the amount of diffusible hydrogen. As a result of repeated research, conventional Cr-
Focusing on V, which is mainly used for improving the high-temperature strength properties in the welding material for Mo steel, hydrogen is absorbed in the weld metal by including a specific amount in the weld metal,
Further, it has been found that by forming fine carbides and fixing the carbon in the weld metal, the susceptibility to cracking by carbon can be reduced, thereby improving the crack resistance and securing the strength. .

The present invention has been made on the basis of the above findings, and the gist of the present invention is that a steel sheath has a TiO ₂ content of 2.5 to 6.5% based on the total weight of the wire, and other than TiO _2. Arc stabilizers and slag generators: 0.5-4.5
%, Deoxidizing agent: In a mag-welding flux cored wire filled with a titania-based flux containing 1.0 to 4.0%, one or both of the steel sheath and the filled flux has a V with respect to the total weight of the wire. : A flux-cored wire for arc welding, which contains 0.05 to 0.25% to improve low-temperature crack resistance of steel welds.

Here, V to be added to the filling flux refers to alloys and compounds such as metal vanadium and ferrovanadium, as well as mixtures and mixed powders thereof.

[0011]

The present invention will be described below in detail. Filling a 590 N / mm ² class titania-based wire using a mild steel sheath V in the flux to 0.002-0.5 with respect to the total weight of the wire.
U-shaped welding crack test (JIS Z 3157) for investigating the cracking resistance of the weld metal was performed using ten kinds of prototype wires finished to 1.2 mmφ added in the range of%. The steel material used is JIS SM570 plate thickness of 50 mm, shielding gas: CO ₂ , wire protrusion length: 20 mm, welding current: 270 A, arc voltage: 30 V, welding heat input: 16
The test was performed under the conditions of kJ / cm, temperature: 30 ° C., and relative humidity: 80%, and the preheating temperature required for stopping cracking was determined.

As apparent from FIG. 1, the preheating temperature required for stopping the breaking of a wire having a V content of less than 0.05% by weight is 100.
１２５125 ° C. On the other hand, the preheating temperature required for stopping the cracking of a wire having a V content of 0.05 to 0.25% by weight is such that the hydrogen storage function of the weld metal and the formation of fine carbides fix the carbon in the weld metal. To 50 ° C. or lower due to the synergistic effect of the above, especially when the V content in the wire is 0.07 to 0.20 wt%
In the vicinity of the wire, remarkably excellent crack resistance was obtained. However, a wire having a V content exceeding 0.25% by weight cannot be expected to produce fine carbides, and on the contrary, the strength becomes too high.
The preheating temperature required for stopping cracking is 100 to 150 ° C.

When adding from one or both of the steel sheath and the filling flux, V can be selected at an arbitrary ratio as long as it is within the range of 0.05 to 0.25% with respect to the total weight of the wire. In the present invention, based on the above characteristics, the content of each component is determined as follows. TiO _2: 2.5~6.5% TiO ₂ increases the stability and the slag encapsulated arc,
It is an indispensable component for improving the weldability in all positions.
If it is less than 2.5%, the effect cannot be obtained. However, 6.
If it exceeds 5%, the slag viscosity becomes too high and the bead shape deteriorates, and further, excessive reduced Ti is produced in the weld metal, and the mechanical properties (particularly the toughness) deteriorate. Therefore, T
iO ₂ is in the range of 2.5 to 6.5%.

Arc stabilizers and slag forming agents other than TiO ₂ : 0.5 to 4.5% In the wire of the present invention mainly composed of TiO ₂ , these are used in order to stabilize the arc and reduce the amount of spatter generated. Addition is required. Examples of the arc stabilizer include alkali metals such as Li, Na, and K and compounds thereof. The slag forming agent needs to be added in a range that does not decrease the welding speed in order to improve the bead shape. If the arc stabilizer and the slag forming agent other than TiO ₂ are less than 0.5%, the effect of improving the bead shape is not recognized, and if it exceeds 4.5%, the slag amount increases and defects such as slag entrainment occur. Or the welding efficiency is reduced. Therefore, arc stabilizers and slag generators are 0.5
To 4.5%. In addition, as a slag generating agent, Si
Oxides such as O ₂ , ZrO ₂ , Al ₂ O ₃ , MnO, and MgO; fluorides such as CaF ₂ , BaF ₂ , and LiF;
Carbonates such as CO ₃ and BaCO ₃ can be used.

Deoxidizing agent: 1.0 to 4.0% The deoxidizing agent is necessary for accelerating deoxidation, preventing internal defects in the weld metal, and securing the target weld metal strength. is there. If the addition amount is less than 1.0%, it is difficult to secure necessary strength, and an internal defect occurs in the weld metal due to insufficient deoxidation. On the other hand, if added in excess of 4.0%, the weld metal is hardened and the toughness is reduced. Therefore, the addition amount of the deoxidizing agent is set in the range of 1.0 to 4.0%. As the deoxidizing agent, metals, alloys and compounds such as Si, Mn, Al, Ti and Mg can be used.

The above are the essential components of the wire of the present invention.
Iron powder may be added to improve welding efficiency, Ni, Cr, and Mo may be added to improve strength, and B may be added to improve low-temperature toughness. Further, the flux filling rate of the wire according to the present invention is desirably 8 to 20%. The reason for this is that if the filling ratio exceeds 20%, disconnection troubles occur frequently during wire drawing and the productivity deteriorates, and if it is less than 8%, the stability of the arc is impaired.

There is no restriction on the cross-sectional shape of the wire, and a relatively simple cylindrical shape is generally used for a small diameter of 2 mm or less. In the case of a seamless wire, it is also effective to apply a plating treatment of Cu or the like to the surface.

[0018]

EXAMPLE Table 1 shows the steel sheath used for the wire of this example. Tables 2 and 3 (continuation of Table 2-1) and Table 4 (Table 2)
Table 2 (continued in Table 2-3), Table 6 (continued in Table 22-4), and Table 7 (continued in Table 2-5) show the flux composition of the Example wire. Each wire diameter is 1.2 mm.

U-shaped welding crack test (JIS Z 3157) for investigating the cracking resistance of the weld metal with these wires.
Was done. Depending on the strength of the wire, the steel material has a thickness of 590 N / mm ² class and 780 N / mm ² class 5
0 mm was selected. The welding conditions were: welding current: 270 A,
Voltage: 30 V, wire protrusion length: 20 mm, shielding gas: CO ₂ , welding heat input: 16 kJ / cm, temperature: 30
C., relative humidity: 80%, and the preheating temperature required for stopping cracking was determined.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

[Table 5]

[0025]

[Table 6]

[0026]

[Table 7]

The welding crack stop preheating temperature of the wire of the present invention is 590 N / mm since an appropriate V amount is contained.
Class ² wire and 780 N / mm Class ² wire are both 50
° C or less, and especially the V amount of the whole wire is 0.07 to 0.
In the case of the wire no. 1, 3, 4, 6 and No.
Nos. 7, 10, and 11 have welding crack stop temperatures as low as 30 ° C., and have very good low-temperature cracking resistance.

The comparative wire No. Nos. 12 and 16 are ordinary wires containing no V in the wires, and the welding crack stop preheating temperature was 125 ° C. or higher. No. 14, 15,
In Nos. 17 and 19, the preheating temperature for stopping welding cracks was 100 ° C. or more because of too much vanadium. No. Nos. 13 and 18 contain V from the steel shell and the filling flux, but the preheating temperature for stopping welding cracks is 100 because the added amount is too small.
° C or higher.

[0029]

As described above, according to the flux-cored wire of the present invention, the low-temperature cracking resistance is remarkably improved as compared with the conventional flux-cored wire for high-strength steel. Flux-cored wires for tensile steel cannot be achieved at all, and contribute significantly to the development of various industries.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of V in a filling flux and a crack stop preheating temperature.

──────────────────────────────────────────────────の Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 35/30 B23K 35/368

Claims (1)

(57) [Claims] 1. The steel sheath is made of TiO with respect to the total weight of the wire.
₂ : 2.5 to 6.5%, arc stabilizer and slag forming agent other than TiO ₂ : 0.5 to 4.5%, deoxidizer: 1.0
In a flux-cored mag-weld wire filled with a titania-based flux containing フ ラ 4.0%, one or both of the steel sheath and the filling flux have a V of 0.05 to 0.25% based on the total weight of the wire. A flux-cored wire for arc welding which improves the low-temperature crack resistance of a steel weld, characterized by containing.