JP3068280B2 - 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 has a remarkable improvement in slag peeling property, good arc breaking resistance even when a no-load voltage of a welding machine is low, improvement in welding work efficiency, and good welding. The present invention relates to an all-position low-hydrogen-based coated arc welding rod (hereinafter, referred to as a low-hydrogen-based rod) that can ensure workability.

[0002]

2. Description of the Related Art Low hydrogen rods are generally made of CaCO ₃ , Ca
The main component is F ₂ , but CaCO ₃ in particular decomposes in the arc, generates CO ₂ gas and cuts the weld metal from nitrogen and oxygen from the atmosphere and reduces the partial pressure of hydrogen to prevent cracking. It is well known that it is applied to steel for important structures because of its good toughness and toughness.

However, low hydrogen rods tend to have a convex bead shape due to their dense slag and poor slag encapsulation, as compared to non-low hydrogen rods such as illuminite and lime titania. Due to these, there is a drawback that slag peelability is poor, resulting in a decrease in welding work efficiency.

When welding is performed when the no-load voltage of the welding machine is low, the arc may be broken during the welding. When this phenomenon occurs, generally the cladding is crushed and re-arcing is performed.However, since low-hydrogen rods are manufactured by drying at high temperature, the coating agent is fragile. The core will be exposed. If re-arcing is performed as it is, the tip of the welding rod may be short-circuited to the workpiece or blowholes or pits may occur in the weld metal at this point, reducing the welding work efficiency or obtaining a healthy weld metal. There was a problem.

[0005] By the way, some slag removability improvement of coated arc welding rods other than low hydrogen rods has been proposed and some of them have already been implemented. For example,
In JP-A 1-3597, while maintaining the viscosity of the slag by MgO in the coating agent, hydrogen gas generated from the water of crystallization is diffused into the slag to be porous, and the slag is easily peeled off. Suggest improvement.

Also, as already proposed in Japanese Patent Publication No. 60-40960, in a lime titania system of a coated arc welding rod for stainless steel, the surface activity of Group 6 of the Periodic Table, such as S and Se, is contained in the coating agent. It has been put into practical use by lowering the interfacial tension between a molten metal and a molten slag by adding a trace amount of a simple substance or a compound of an element.

[0007] The inventors of the present invention applied these techniques to low hydrogen rods and conducted experiments. As a result, hydrogen, oxygen or sulfur in the weld metal was increased, and the crack resistance and toughness of the weld metal and the heat affected zone were increased. Was deteriorated, and the characteristics as a low hydrogen rod were found to be impaired.

[0008] Further, as a means of improving the arc breaking resistance,
As disclosed in Japanese Patent Application Laid-Open No. Sho 52-117845, there is a technique for reducing arc breakage by reducing the amount of chlorine in sodium alginate used as a coating agent when manufacturing a welding rod. However, in the same publication, sodium alginate is adjusted for the amount of chlorine in sodium alginate by increasing the number of washings of sodium alginate more than usual, so that the cost of manufacturing sodium alginate is increased and the practicality is poor.

On the other hand, a non-low hydrogen welding rod has a characteristic that it is hard to break the arc because the arc state is better than that of the low hydrogen rod, but the following proposal has been made to eliminate the breaking of the arc. That is, JP-A-61-195796 discloses that the total Mn oxide content and the Mn
By limiting the content of O ₂ and limiting the content of the calcined manganese in the coating agent, it is intended to prevent arc breakage. When this method is applied to low hydrogen rods,
There has been a problem that the viscosity of the slag is reduced, the weld metal is easily drooped in the upright position, and furthermore, the increase in the amount of oxygen in the weld metal is liable to cause deterioration of the brohole resistance and toughness.

[0010] As described above, it is a fact that no improvement has been found that can improve the arc-breaking resistance while ensuring good slag removability in low-hydrogen rods. Improvement on the task was urgent.

[0011]

In view of the above situation,
The present invention seeks to provide an all-position low-hydrogen-based rod that improves the slag peelability of a low-hydrogen-based rod and has excellent arc-breaking resistance even when the no-load voltage of a welding machine is low, and improves the welding work efficiency. Is what you do.

[0012]

SUMMARY OF THE INVENTION In order to meet the above-mentioned demands, the present invention examines various coating components and secures good slag removability and arc breaking resistance. Where: CaCO ₃ ; 30-55% by weight
(Hereinafter referred to as%), CaF ₂ ; 5-35%, one or more of iron oxides is 0.40% or less in terms of FeO,
Si: 0.5 to 8.0%, Mn: 0.3 to 7.5%, T
iO _2; a low hydrogen type covered electrode, characterized in that it has applied around a steel core wire with a coating agent containing 0.4 to 8.4%.

[0013] The cause of deterioration of the slag removability is that the difference in the shrinkage rate with respect to the expansion rate in the process of solidifying the molten slag is small, and the density of the formed slag is high and the contact area of the slag with the bead surface area is large. It is said. It is known that the slag tends to adhere to the bead toe when the bead has a convex shape as a further major cause.

Accordingly, the present inventors have conducted intensive studies and as a result, the amount of iron oxide in terms of FeO has been reduced as much as possible, irrespective of one or a combination of two or more types of iron oxide added to the coating agent. It was found that the difference between the thermal expansion and the contraction could be increased, and the solidification of the slag was accelerated, so that the gas was easily confined in the slag and a porous slag could be formed, which was effective in improving the slag removability. Furthermore, it has been found that the viscosity of the slag is increased, so that the slag can be encapsulated well and the bead shape is smooth, which can also contribute to the improvement of the slag peelability.

On the other hand, it has been found that, since iron oxide has an effect of increasing the arc voltage, if it is added in an excessive amount, the re-ignition voltage becomes higher than the no-load voltage and the arc breaks easily during welding. Accordingly, it was also found that it is important to add as little iron oxide in the coating material as possible in low-hydrogen rods in order to improve the resistance to arc breaking even when the no-load voltage of the welding machine is low. . Here, iron oxide means FeO, Fe ₂ O ₃ , and Fe ₃ O ₄ . As described above, suppressing the amount of iron oxide in terms of FeO is effective for slag peeling property and arc breaking resistance, but finding an upper limit value thereof was also an important point in completing the present invention.

[0016]

The operation of the present invention will be described below in detail.
First, one or more iron oxides are added to the coating agent, and how the FeO equivalent affects the slag removability and the number of arc breaks, and grasps the appropriate content In order to do this, the following experiment was performed. That is,
The coating composition of the low-hydrogen rod for all postures shown in Table 1 was changed so that the FeO equivalent of iron oxide was 0 to 1.52%, and this was changed to JIS G3 having a diameter of 4.0 mm and a length of 450 mm.
523, SWY11 mild steel core wire was coated and dried to prepare a welding rod, and the slag peeling property and the number of arc breaks at a no-load voltage of 70 V of an AC welding machine were examined.

[0017]

[Table 1]

In the investigation of the slag peeling property, vertical and downward butt welding was performed using mild steel plate having a thickness of 20 mm and a groove shape of 50 ° V. In the vertical butt welding, a welding current of 15 mm was used.
A welding current of 180 A and a welding speed of 15 cm / min were used for downward butt welding at 0 A and a welding speed of 6 cm / min.

Judgment is a comprehensive judgment of vertical butt welding and downward butt welding. The criteria are as follows: ○ is good (slag is removed by tapping with a chipping hammer), and Δ is slightly poor (slightly hit with a chipping hammer). To remove slag), defective X mark (slag removal by hitting with chipping hammer)
And

In the investigation of the number of arc breaks, the sheet thickness was 12.7 m.
m, width 100mm, length 500mm mild steel plate assembled into T type,
Using a current of 180 A in a horizontal fillet welding position, the number of arc cuts during the length of the molten bar of 400 mm was investigated. The value is an average value of 5 test welding rods, and it was determined that less than 1.0 times was good, and that it was slightly inferior from 1.0 times to less than 3.5 times, and poor in 3.5 times or more.

FIG. 1 shows the results obtained from the above test. The FeO equivalent for the combination of iron oxide types is 0.7
At 0% or more, the slag peeling property was deteriorated due to the densification of the slag and the appearance of a convex bead due to the deterioration of the slag encapsulation property. The content of FeO is 0.40%
When the temperature exceeds 1, the arc force increases, the arc voltage increases, and the restrike voltage also increases. Therefore, the arc is easily broken during welding, and the average exceeds 1.0 times.

As described above, the slag removability is good if the content in terms of FeO is less than 0.70%, and the arc breaking resistance is good if it is 0.40% or less. The purpose is to improve the arc breaking resistance while satisfying the slag peeling property.
It was found that the O equivalent should be 0.40% or less.

The function of each component in the present invention and the reason for limiting the component range will be described below. (CaCO ₃ ; 30 to 55%) Since CaCO ₃ is decomposed in the arc and generates CO ₂ gas, the weld metal and the molten slag are shielded from the atmosphere, preventing the invasion of nitrogen and oxygen and reducing the hydrogen partial pressure. It is also possible to prevent hydrogen cracking of the weld metal. Further, it is added to secure the arc force and adjust the fluidity and viscosity of the slag. If it is less than 30%, the melting point of the slag decreases, and the fluidity of the slag becomes excessive, so that good beads cannot be formed. In addition, since the amount of generated gas is insufficient, the atmosphere is affected and pits and blowholes are generated. On the other hand, if it exceeds 55%, the amount of generated gas becomes excessive, so that many blowholes are generated, and the fluidity of the slag deteriorates, resulting in poor bead appearance.

(CaF ₂ ; 5 to 35%) CaF ₂ is contained to lower the melting point of the slag and to produce a slag having good fluidity. If it is less than 5%, appropriate fluidity cannot be obtained. If the bead appearance is poor, and if it exceeds 35%, the encapsulating property of the slag will be poor, so that the bead appearance will deteriorate and the arc stability will deteriorate.

(One or more of iron oxides may be FeO
It is the most important part in the present invention that the amount of FeO conversion by the combination of iron oxides is reduced as much as possible. The slag is made porous and the bead is smoothed to improve the slag removability. In addition, since the re-ignition voltage is reduced, even when the no-load voltage is low, the effect of making the arc hard to break during welding is exhibited. One or two or more iron oxides are reduced to 0.40 in terms of FeO. The reason is set as follows. That is, the slag peeling property is 0.70.
%, The slag becomes more porous and smooth bead, but the arc breaking resistance is 0.40%.
In the following cases, an appropriate reduction in the arc voltage is extremely good, and therefore, to satisfy both, the content needs to be 0.40% or less. However, the FeO equivalent of Fe ₂ O ₃ and Fe ₃ O ₄ was calculated based on the molecular weight ratio with FeO.

(Si; 0.5-8.0%) Si is mainly composed of F
When added as e-Si, the effect on the welding work and impact toughness, such as the arc state, slag state, and bead appearance, is extremely large, and is indispensable for maintaining good overall welding performance. If it is less than 0.5%, the arc force is weak, and the adaptability of the weld metal to the steel sheet in the upright posture is deteriorated, and the bead appearance is deteriorated. If it exceeds 8.0%, the arc force becomes excessive, resulting in undercut or deterioration of bead appearance,
Further, the toughness of the weld metal also deteriorated.

(Mn; 0.3-7.5%) In the present invention, Mn is Mn mixed with metal Mn or Fe-Mn.
It refers to the sum of the quantities, and has the functions of both welding workability and alloying agents. If it is less than 0.3%, the fluidity of the slag deteriorates, the waveform of the bead is disturbed, and the appearance of the bead deteriorates, so that it does not act as an alloying agent. When the viscosity of the slag exceeding 7.5% is reduced, the weld metal drips in a vertical or upward welding to form a convex bead.

(TiO ₂ ; 0.4 to 8.4%) TiO ₂
Acts as a slag forming agent and viscosity control, increases the slag encapsulation, and is also effective as an arc stabilizer. If it is less than 0.4%, the stability of the arc is deteriorated, the scattering of spatter is increased, and the encapsulation of the slag is deteriorated, so that the bead appearance is also deteriorated. On the other hand, if it exceeds 8.4%, the arc force is weakened, and when welding is performed using a high current, the welding rod glows red, the coating agent deteriorates, and the viscosity of the slag increases. The bead takes on a convex shape. The fixing agent of the present invention includes Si
Those containing O ₂ , K ₂ O and Na ₂ O as main components were used.

[0029]

EXAMPLES Next, the effects of the present invention will be described more specifically with reference to examples. A coating having the composition and composition shown in Table 2 was applied to a JIS G3523, SWY having a diameter of 4.0 mm and a length of 450 mm.
After coating and coating the -11 mild steel core wire, it was dried to prepare 28 types of test welding rods, and using an AC welding machine with a no-load voltage of 70 V, under the following conditions, slag peeling resistance, The arc breaking properties and the welding work were investigated.

In the investigation of the slag peeling property, vertical and downward butt welding was performed using mild steel plate having a thickness of 20 mm and a groove shape of 50 ° V. In the vertical butt welding, a welding current of 15 mm was used.
A welding current of 180 A and a welding speed of 15 cm / min were used for downward butt welding at 0 A and a welding speed of 6 cm / min.

The judgment is a comprehensive judgment of the vertical butt welding and the downward butt welding. The criteria are as follows: ○ is good (slag is removed by tapping with a chipping hammer), and Δ is slightly poor (slightly hit by chipping hammer). To remove slag), defective X mark (slag removal by hitting with chipping hammer)
And

In the investigation of the number of times of arc breakage, the sheet thickness was 12.7.
mm, width 100mm, length 500mm mild steel plate assembled into T type,
Using a current of 180 A in a horizontal fillet welding position, the number of arc cuts during the length of the molten bar of 400 mm was investigated. The value is an average value of 5 test welding rods, and it was determined that less than 1.0 times was good, and that it was slightly inferior from 1.0 times to less than 3.5 times, and poor in 3.5 times or more.

In the welding workability, a vertical butt and a T-shaped horizontal fillet were welded, and an arc state, a slag state, a bead appearance and the like were examined using the above-described test pieces and welding conditions, respectively. The judgment was made by comprehensively judging each welding posture, and the mark “○” was good, the mark “Δ” was slightly inferior, and the mark “x” was inferior.

Further, the slag peeling property, arc breaking resistance and welding workability were comprehensively evaluated, and the mark “○” was good, the mark “Δ” was slightly inferior, and the mark “X” was inferior. The results shown in Table 2 were obtained by performing each judgment and comprehensive judgment under these welding conditions.

[0035]

[Table 2]

[0036]

[Table 3]

No. 1 to No. No. 14 is an example of the present invention;
15-No. 28 shows a comparative example. The low hydrogen type rod of the present invention has the following characteristics. 1 to No. In No. 14, the individual components satisfy the requirements of the present invention, and the content of iron oxide in terms of FeO is 0.40% or less. It has a small number of times and at the same time has excellent welding workability.

Comparative Example No. No. 15 has a small amount of iron oxide in terms of FeO, so the slag is porous and the bead is smooth, so that the slag peeling property is good, and the arc voltage is also appropriately reduced, so that the arc breaking resistance is good. CaCO
_Because of the large amount of _{3 and the} small amount of CaF ₂ , the fluidity of the slag became poor, and the welding workability became slightly poor.

No. In No. 16, the arc was easily broken because FeO was slightly large. In addition, since the amount of Si was small, the arc force was weak, the adaptability of the weld metal to the steel sheet was deteriorated, and the welding workability was slightly deteriorated. No. In No. 17, since the TiO ₂ content was too small, the stability of the arc deteriorated and the scattering of spatter increased, and the bead appearance deteriorated as the slag encapsulation property deteriorated, resulting in extremely poor welding workability.

No. 18, No. 20 and no. 26
Is easy to break the arc because of the large amount of FeO conversion,
No. 20 and no. In No. 26, the removability of the slag was deteriorated because the FeO content was excessively added. No. In No. 19, the FeO equivalent of iron oxide was slightly large, so the arc breaking resistance was poor, the CaCO ₃ content was small, and the Mn content was large, so that the viscosity of the slag was reduced. It began to take shape.

No. In No. 21, since the amount of TiO ₂ was large, the arc force was weak, the fluidity of the slag was poor, the bead appearance was deteriorated, and the welding workability was deteriorated. No. 22 is Ca
Since CO ₃ was excessively added and Mn was small, the arc force was strong, the fluidity of the slag was poor, and the bead appearance was poor. No. 23 has a low CaCO ₃ content, CaF ₂ and Mn
The melting point of the slag was lowered due to the large amount of slag, and the encapsulation of the slag was deteriorated. In addition, the arc was extremely weak due to too much TiO ₂ .

No. 24 and no. In No. 25, since the amount of Si was large, the arc force was increased, and the bead appearance was deteriorated. No.
In No. 25, the amount of iron oxide in terms of FeO was excessively added, so that the slag was dense and the slag was likely to remain at the bead toe. No. 27, bead appearance with the encapsulated degradation of the slag is deteriorated because CaF ₂ is large, TiO ₂
, The arc stability was poor and spatter increased. In addition, since the amount of Si is small, the familiarity of the weld metal deteriorates, the bead appearance deteriorates, and the welding workability deteriorates considerably.
No. In No. 28, since the Mn was too large, the viscosity of the slag was reduced, and in particular, the bead became convex in the vertical or horizontal shin posture, and welding workability was deteriorated.

[0043]

As described above, the low-hydrogen rod of the present invention has good slag peeling properties in all positions of welding, and has very little arc breakage even when the no-load voltage is low. This ensures good welding workability. The low-hydrogen rod according to the present invention having such an effect is used for shipbuilding, bridges, construction, and the like, and can significantly improve the efficiency of welding work on site.

[Brief description of the drawings]

FIG. 1 is a chart showing the number of arc breaks and the slag removability when the amount of FeO equivalent of iron oxide is changed.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-207496 (JP, A) JP-A-3-275294 (JP, A) JP-A-56-80391 (JP, A) JP-A-58-1983 38695 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 35/365

Claims (1)

(57) [Claims] 1. CaCO ₃ ; 30 to 55% by weight CaF ₂ ; 5 to 35% by weight One or more of iron oxides is 0.40% in terms of FeO.
0.5% to 8.0% by weight Mn; 0.3% to 7.5% by weight TiO ₂ ; around the steel core wire using a coating agent containing 0.4% to 8.4% by weight. A low hydrogen coated arc welding rod characterized by being applied.