JPH07106470B2 - Low-hydrogen coated arc welding rod - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-hydrogen coated arc welding rod for high-strength steel which is excellent in welding workability and mechanical performance.

[0002]

2. Description of the Related Art Conventionally, low hydrogen system coated arc welding rods have been
It is widely used for welded structures such as shipbuilding, vehicles, buildings, bridges, various pressure vessels, and offshore structures, where mechanical properties are particularly important. However, with the improvement in the technical level of the mechanical properties of steel materials, it has become difficult for the above welding rod to sufficiently fulfill its purpose.

As a measure for improving the toughness of weld metal, for example, in Japanese Patent Publication No. 2-42312, the toughness is improved by adding Ni and limiting the total amount of Mn and Ni. However, there is a problem in that even if high toughness is obtained, it is difficult to call it a sufficient method in terms of stabilization, that is, variation. On the other hand, JP-A-63-
In Japanese Patent No. 242491, Cr is added to a low-hydrogen coated arc welding rod for high-temperature steel for Cr-Mo system to reduce the amount of oxygen in the weld metal, and the structure is refined to provide crack resistance and ductility of the weld metal. Although a technique for improving the toughness is disclosed, it is insufficient for achieving high strength and high toughness.

With respect to cracking resistance of weld metal, high-strength steel of 60 kg or more has been commonly used, and cold cracking often occurs due to the amount of diffusible hydrogen in the weld metal, which often causes a problem. In order to prevent this phenomenon of cold cracking, preheating to a high temperature has to be performed, which is a problem in terms of on-site construction. Further, generally, the higher the strength, the lower the toughness of the weld metal. In order to improve these mechanical performances, a technique for reducing oxygen in the weld metal is known. In order to reduce the amount of oxygen in the weld metal, there is a method of adding metal Mg powder, which is a strong deoxidizer, as described above, but in order to improve crack resistance, the covered arc welding rod has a diffusible hydrogen content. It is necessary to reduce it. For this reason, it was found that the metal Mg powder was oxidized even though it was dried at a high temperature, and the original function of reducing oxygen was not exhibited.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a low hydrogen type covered arc welding rod which can improve crack resistance and obtain a weld metal having high strength and good toughness in welding of high strength steel. It is a thing.

[0006]

Under the circumstances as described above, the present inventors have made earnest studies on the soundness of the weld metal performance of the low-hydrogen coated arc welding rod in terms of the type of Mg compound. As a result, the Mg compound used was Mg ₂ Si
The present invention is made by limiting the above.

That is, the gist of the present invention is Mg ₂ Si:
0.1 to 10% by weight, metal carbonate: 25 to 60% by weight,
Metal fluoride: 5 to 30% by weight, and a coating material containing an arc stabilizer other than the above, a slag generator, a deoxidizing agent, an alloying agent, and a binder on the steel core wire. Mg
₂ A low-hydrogen coated arc welding rod, characterized in that the average particle size of ₂ Si is 40 to 180 μm.

The core wire used in the present invention is C: 0.15.
% By weight, Si: 0.5% by weight or less, Mn: 1.7% by weight or less, P: 0.01% by weight or less, S: 0.01% by weight or less, Cu: 0.1% by weight or less, balance May be Fe and inevitable impurities.

[0009]

The reason for limiting the component composition in the present invention will be described in detail below. Mg ₂ Si: 0.1 to 10 wt% Mg ₂ Si can reduce the amount of oxygen in the weld metal, improve the toughness of the weld metal, and stabilize it. Mg ₂
Si is more stable than metal Mg powder at high temperatures, does not decompose even when dried at high temperatures, and can sufficiently function as a strong deoxidizer during arc welding. Further, it also has the function of improving the stability of the arc.

If the added amount of Mg ₂ Si is less than 0.1% by weight, these effects do not work effectively. On the other hand, if the added amount exceeds 10% by weight, the covering rod of the welding rod is weakened and the fluidity of the slag deteriorates. And a good bead shape cannot be obtained. In addition, M to use
It has been confirmed that g ₂ Si having a Mg to Si ratio of about 2: 8 to 5: 5 can be used.

Metal carbonate: 25 to 60% by weight The metal carbonate used in the present invention means CaCO ₃ , BaC.
It refers to O ₃ , MgCO _3, etc., but these metal carbonates decompose in the arc, generate CO ₂ gas, shut off the molten metal from the atmosphere, and lower the hydrogen partial pressure in the arc atmosphere. And produces a basic slag.

If the addition amount of these is less than 25% by weight, the melting point of the slag is lowered and the encapsulation of the slag is deteriorated, so that good beads cannot be obtained. In addition, pits and blow holes are generated because the amount of gas that cuts off the atmosphere is insufficient. On the other hand, when it is added in excess of 60% by weight, the gas generation amount becomes excessive, the melting point of the slag rises, and the fluidity of the slag deteriorates. Become.

Metal Fluoride: 5 to 30% by Weight Metal fluoride in the present invention means CaF ₂ , BaF ₂ and M.
Although it refers to gF ₂ , LiF _2, etc., they all lower the melting point of the slag to produce slag with good fluidity. Further, the fluorine decomposed in the arc reacts with the hydrogen of the molten metal or the molten slag, lowers the hydrogen partial pressure of the weld metal, and produces weld metal with good crack resistance.

If the addition amount of these is less than 5% by weight, proper fluidity of the slag cannot be obtained, the bead shape is bad, and pits are generated. On the other hand, if it is added in an amount of more than 30% by weight, the viscosity of the slag is insufficient, the bead shape is deteriorated, the covering cylinder is weak, and the welding workability is deteriorated. The coated arc welding rod of the present invention uses, in addition to the above-mentioned components, an arc stabilizer, a slag forming agent such as TiO ₂ and Al ₂ O ₃ , and a deoxidizing agent and an alloying agent such as Si, Ni, Mo, Cr and Mn. , Ti
And the like, and as the binder, sodium silicate, potassium silicate, etc. are used.

The invention of claim 1 has the above-mentioned constitution, but in addition to this, by further limiting the grain size of Mg ₂ Si,
The amount of oxygen in the weld metal can be reduced, and a weld metal with good toughness can be obtained in welding of higher strength steel. The effect is exhibited when the average particle diameter of Mg ₂ Si is 40 to 180 μm, and problems such as flux fluidity and coating cracking may occur outside the range.

The average particle size was calculated using the following equation after determining the weight ratio between the particle sizes according to JIS Z8801. Average particle diameter D (μm) = (w1 × 210 + w2 × 194 +
w3 x 163 + w4 x 137 + w5 x 115 + w6 x 9
7 + w7 × 76 + w8 × 54 + w9 × 22) / 100 However, each number represents the average particle size between the measuring sieves, and w1 to
w9 has the following meaning.

W1: wt% of 210 μm or more, w
6: 105-88 μm wt% w2: 210-177 μm wt%, w7: 88-63
μm wt% w3: 177-149 μm wt%, w8: 63-44
μm wt% w4: 149 to 125 μm wt%, w9: less than 44 μm wt% w5: 125 to 105 μm wt%, The coated arc welding rod of the present invention is coated and coated by a normal welding rod coating machine, 300-55 to remove water
It is manufactured by firing at 0 ° C.

[0018]

EXAMPLES The effects of the present invention will be more specifically described below with reference to examples. As shown in Table 1, the strength of the weld metal is 740 due to the combination of Mg ₂ Si and other raw materials for the coating agent.
N / mm ² A welding rod designed as described above was manufactured. A welding experiment was conducted based on JISZ3212 using each of the obtained welding rods. The welding rod was 4.0 mm in core diameter, welding current was 170 A, welding heat input was 17 kJ / cm, and the welding was carried out in a downward position. went. Furthermore, JIS
A crack resistance test was performed at room temperature based on Z3157 with a plate thickness of 30 mm.

The evaluation standard is that the average value among the three absorbed energies in the -60 ° C. impact test is 98 J or more and the difference between the maximum value and the minimum value is within 29 J is good.
If the difference between the maximum value and the minimum value exceeds 29 J even if it is J or more, it is defined as a defective X mark. About the amount of oxygen, 250pp
Those with m or less were evaluated as good ◯, and those exceeding 250 ppm were evaluated as bad x.

Regarding the workability of welding, those which are comparable to the conventional rods were marked with a good ◯, and those which were inferior were marked with a bad X. Regarding the U-shaped weld cracking test, those having a root cracking ratio of less than 20% were evaluated as good ◯, and those of 20% or more were evaluated as bad x. Table 1
As is clear from the above, the welding rod N satisfying all the requirements of the present invention
o. 1-No. No. 7 has a low oxygen content in the weld metal, a good impact value, and a healthy weld metal was obtained.
Good crack resistance.

On the other hand, the comparative rod No. 8 is Mg ₂ Si
However, the impact value is bad because the amount of oxygen in the weld metal is large because it is oxidized by high temperature drying. No. In No. 9, since the amount of Mg ₂ Si is small, the amount of oxygen in the weld metal is large and the impact value is poor. No. 10 is Mg ₂
Since the amount of Si is too large, the fluidity of the slag is deteriorated and the welding workability is poor. No. In No. 11, since the amount of metal carbonate was too small, the amount of gas generated was insufficient, the amount of oxygen in the weld metal was large, and the performance was poor. No. In No. 12, the coating cylinder is weak because the metal fluoride is too much, and the welding workability is poor.

[0022]

[Table 1]

[0023]

As described above, according to the welding rod of the present invention, a weld metal having high strength and good toughness can be obtained, which is a great industrial contribution.

Claims (2)

[Claims] 1. Mg ₂ Si: 0.1 to 10% by weight, metal carbonate: 25 to 60% by weight, metal fluoride: 5 to 30% by weight, an arc stabilizer other than the above, a slag forming agent,
A low-hydrogen coated arc welding rod, characterized in that a steel core wire is coated with a coating material containing a deoxidizer, an alloying agent, and a binder. _2. The average particle size of Mg ₂ Si is 40 to 180 μm.
The low hydrogen-based coated arc welding rod according to claim 1, which is m.