JPH05111791A - Low hydrogen coated arc welding electrode - Google Patents

Abstract

PURPOSE:To provide the low hydrogen coated are welding electrode for all positions which is greatly improved in slag removability, has good arc break resistance even if no-load voltage of a welder is low and assures good welding workability. CONSTITUTION:This coated electrode is constituted by restricting the amts. of the essential components of the low hydrogen type coating material to be added and restricting the content of iron oxide in terms of FeO to the lowest possible ratio. The welding operation efficiency of field operations is greatly improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention significantly improves slag removability, has good arc breaking resistance even when the no-load voltage of the welding machine is low, and improves welding work efficiency, and also provides good welding. The present invention relates to a low-hydrogen coated arc welding rod for all postures (hereinafter referred to as a low-hydrogen rod) which can ensure workability.

[0002]

2. Description of the Related Art Low-hydrogen rods are generally made of CaCO ₃ , Ca.
Although F ₂ as a main component, in particular CaCO ₃ decomposes in the arc, crack resistance in order to lower the partial pressure of hydrogen with to generate CO ₂ gas weld metal to block the nitrogen and oxygen from the atmosphere It is well known that it is applied to steel materials for important structures because of its good toughness.

However, the low hydrogen type rod is more likely to have a convex bead shape because the slag is denser than the non-low hydrogen type welding rods such as illuminite type and lime titania type and the slag has a poor encapsulation property. Due to these, there is a drawback that the peelability of the slag is poor, leading to a decrease in welding work efficiency.

If welding is performed when the no-load voltage of the welding machine is low, the arc may break during welding. When this phenomenon occurs, the coated cylinder is generally crushed and re-arced, but since the low hydrogen rod is manufactured by drying at high temperature, the coating agent is fragile, and if a shock is applied to the coated steel, the steel will be damaged. The core wire will be exposed. If you try to re-arc as it is, the tip of the welding rod may be short-circuited to the work piece, or blowholes or pits may occur in the weld metal at this part, reducing the welding work efficiency and failing to obtain a sound weld metal. There was a problem.

By the way, regarding the improvement of the slag releasability of coated arc welding rods other than low hydrogen type rods, there are some proposals and some have already been implemented. For example, Japanese Patent Publication 6
In JP-A-3597, while maintaining the viscosity of slag by MgO in the coating material, hydrogen gas generated from water of crystallization is diffused into the slag to make it porous, and the slag is easily slag-removable. Propose improvement.

Further, as already proposed in Japanese Patent Publication No. 60-40960, in the lime titania system of the coated arc welding rod for stainless steel, the surface activity of Group 6 of the Periodic Table such as S and Se in the coating agent. It has been put to practical use by reducing the interfacial tension between the molten metal and the molten slag by adding a trace amount of elemental elements or compounds.

Therefore, the inventors of the present invention applied these techniques to a low hydrogen system rod and conducted an experiment, which resulted in an increase of hydrogen, oxygen or sulfur in the weld metal, and the crack resistance and toughness of the weld metal and the heat affected zone. Was deteriorated and the characteristics as a low hydrogen system rod were hindered.

Further, as a means for improving arc breaking resistance,
As disclosed in JP-A-52-117845, there is a technique for reducing arc breakage by reducing the amount of chlorine in sodium alginate used as a coating agent for manufacturing a welding rod in a low hydrogen type rod. However, in the publication, in adjusting the chlorine content of sodium alginate, the sodium alginate is produced by increasing the number of times of washing more than usual, which increases the production cost of sodium alginate, which is not practical.

On the other hand, the non-low hydrogen type welding rod has a characteristic that it is less likely to be broken because it has a better arc state than the low hydrogen type rod, but the following proposals have been made to eliminate the arc breaking. That is, in JP-A-61-195796, the total Mn oxide content and Mn in burned manganese are
By limiting the content of O ₂ and limiting the content of the calcined manganese in the coating material, it is intended to prevent arc breakage. Applying this method to low hydrogen rods,
There is a problem that the viscosity of the slag is reduced, the weld metal is likely to sag in a vertical position, and the increase in the amount of oxygen in the weld metal tends to cause deterioration of brohole resistance and toughness.

As described above, it is the actual situation that there is no improvement measure that can improve the arc breakage resistance while ensuring good slag removability in the low hydrogen type rod. There was an urgent need to improve the issues.

[0011]

In view of the above situation,
The present invention intends to provide an all-position low-hydrogen rod that improves the slag releasability of the low-hydrogen rod and has excellent arc breaking resistance even when the no-load voltage of the welding machine is low, thereby improving welding work efficiency. To do.

[0012]

SUMMARY OF THE INVENTION In order to meet the above-mentioned demands, the present invention has investigated various coating agent components and ensured good slag peeling resistance and arc breaking resistance. Where is done, CaCO ₃ ; 30-55 wt%
(Hereinafter referred to as%), CaF ₂ ; 5 to 35%, 0.40% or less of one or more iron oxides in terms of FeO,
Si; 0.5 to 8.0%, Mn; 0.3 to 7.5%, T
A low-hydrogen coated arc welding rod characterized by being coated around a steel core wire by using a coating material of iO ₂ ; 0.4 to 8.4%.

The cause of the deterioration of the slag removability is that the difference in the contraction rate with respect to the expansion rate in the course of solidification of the molten slag is small, and the density of the formed slag is high and the contact area of the slag with respect to the bead surface area is large. It is said that. It is known that the slag tends to adhere to the toe of the bead when the bead has a convex shape, which is a major cause.

Therefore, as a result of intensive studies by the present inventors, the FeO equivalent of iron oxide was suppressed as much as possible regardless of the combination of one kind or two or more kinds of iron oxide added to the coating agent, so that the slag content was improved. It was found that the difference between thermal expansion and contraction can be increased, and the solidification of the slag becomes faster, so that the gas is easily trapped in the slag and a porous slag can be formed, which is effective in improving the slag removability. Furthermore, since the viscosity of the slag is increased, the slag has a good encapsulation property and the bead shape is smooth, which is also found to contribute to the improvement of the slag removability.

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

[0016]

The function of the present invention will be described in detail below.
First, iron oxide is added to the coating agent in one kind or in a combination of two or more kinds, and it is investigated how the FeO equivalent affects the slag removability and the number of arc breaks, and the proper content is grasped. In order to do so, the following experiment was conducted. That is,
The FeO conversion of iron oxide was changed to 0 to 1.52% with respect to the coating material for all-position low-hydrogen rods shown in Table 1, which was JIS G3 with a diameter of 4.0 mm and a length of 450 mm.
523, SWY11 was coated and coated on a mild steel core wire and dried to prepare a welding rod, and the slag peeling property and the number of arc breaks at an unloaded voltage of 70 V of an AC welding machine were investigated.

[0017]

[Table 1]

In the investigation of the slag releasability, vertical and downward butt welding was carried out using a mild steel plate having a plate thickness of 20 mm and a groove shape of 50 ° V, and in the vertical butt welding, a welding current of 15 was used.
A welding current of 180 A and a welding speed of 15 cm / min were used for downward butt welding using 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, and the criteria are as follows: ○ is good (slag is removed by tapping with a chipping hammer), △ is slightly bad (slightly with a chipping hammer). Remove slag), x mark is bad (slag is removed by smashing with a chipping hammer)
And

According to the survey of the number of arc breaks, the plate thickness is 12.7
Assemble a mild steel plate of m, width 100 mm, length 500 mm into T type,
A current of 180 A was used in a horizontal fillet welding position, and the number of arc breaks was investigated during a melting rod length of 400 mm. The value is an average value of five test welding rods, less than 1.0 times is good, 1.0 times or more and less than 3.5 times is slightly inferior, and 3.5 times or more is inferior.

The results obtained from the above tests are shown in FIG. The FeO conversion amount by the combination of iron oxide types is 0.7
At 0% or more, the slag removability deteriorated due to densification of the slag and appearance of convex beads due to deterioration of the slag encapsulation property. FeO content is 0.40%
When it exceeds, the arc force becomes stronger, the arc voltage becomes higher, and the re-ignition voltage also increases, so that the arc easily breaks during welding, and the average exceeds 1.0 times.

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

The action of each component and the reason for limiting the component range in the present invention will be described below. (CaCO ₃ ; 30-55%) Since CaCO ₃ decomposes in the arc and generates CO ₂ gas, it shields the weld metal and molten slag from the atmosphere, prevents nitrogen and oxygen from entering, and lowers the hydrogen partial pressure. It is also possible to prevent hydrogen cracking of the weld metal. Also, 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 is lowered and the fluidity of the slag becomes excessive, so that a good bead cannot be formed. Further, since the amount of gas generated is insufficient, it is affected by the atmosphere, and pits and blowholes are generated, which is not suitable. On the other hand, if it exceeds 55%, the gas generation amount becomes excessive, a large number of blowholes are generated, the fluidity of the slag is deteriorated, and the bead appearance is deteriorated.

(CaF ₂ ; 5 to 35%) CaF ₂ is contained in order to lower the melting point of the slag and to make a slag having good fluidity. If it is less than 5%, suitable fluidity cannot be obtained. The bead appearance is poor, and if it exceeds 35%, the encapsulation of the slag is poor, so the bead appearance is degraded and the arc stability is poor.

(One or more iron oxides are used as FeO
It is the most important part of the present invention that the FeO equivalent amount by the combination of iron oxides is reduced as much as possible. The slag is made porous and the beads are smoothed to improve the slag releasability. In addition, since the re-ignition voltage is lowered, it has the effect of making it difficult for the arc to break during welding even when the no-load voltage is low. The reason for setting the percentage below is as follows. That is, the slag removability is 0.70
%, The slag is made porous and the smooth beads are good, but the arc breaking resistance is 0.40%.
In the following cases, an appropriate reduction in arc voltage results in a very good result, so to satisfy both, it is necessary to set it to 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 F
It is added as e-Si and has a great influence on welding work such as arc state, slag state, and bead appearance and impact toughness, and is essential to maintain good overall welding performance. If it is less than 0.5%, the arc force is weak, and the familiarity of the weld metal to the steel sheet in the vertical posture deteriorates, and the bead appearance deteriorates. If it exceeds 8.0%, the arc force becomes excessive and undercut occurs or the bead appearance deteriorates,
Furthermore, the toughness of the weld metal also deteriorated.

(Mn; 0.3 to 7.5%) In the present invention, Mn is Mn mixed with metallic Mn or Fe-Mn.
It indicates the total amount, and also has the function of welding workability and alloying agent. When it is less than 0.3%, the fluidity of the slag is deteriorated, the waveform of the bead is disturbed, the bead appearance is deteriorated, and it does not act as an alloying agent. When the viscosity of the slag exceeds 7.5%, the weld metal drops in vertical or upward welding to form a convex bead.

(TiO ₂ ; 0.4 to 8.4%) TiO ₂
Acts as a slag generator and viscosity adjuster, enhances 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 slag encapsulation property is deteriorated, so that the bead appearance is also deteriorated. On the other hand, when it exceeds 8.4%, the arc force becomes weak, and when welding is performed using a high current, the welding rod becomes red hot and the coating material deteriorates, and the viscosity of the slag becomes high and the fluidity of the slag is poor in the vertical position. The bead has a convex shape. The adhesive of the present invention contains 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 by way of examples. A coating material having the composition and composition shown in Table 2 was applied to JIS G3523, SWY having a diameter of 4.0 mm and a length of 450 mm.
After coating the -11 mild steel core wire with coating and drying, 28 types of test welding rods were prepared, and using an AC welding machine with a no-load voltage of 70 V, the slag peeling resistance and resistance were measured under the following conditions. The arc cutting property and the welding work were investigated.

In the investigation of the slag releasability, vertical and downward butt welding was carried out using a mild steel plate having a plate thickness of 20 mm and a groove shape of 50 ° V, and in the vertical butt welding, the welding current was 15
A welding current of 180 A and a welding speed of 15 cm / min were used for downward butt welding using 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, and the criteria are as follows: ○ is good (slag is removed by tapping with a chipping hammer), △ is slightly bad (slightly with a chipping hammer). Remove slag), x mark is bad (slag is removed by smashing with a chipping hammer)
And

According to the investigation of the number of arc breakage resistance, the plate thickness is 12.7.
mm, width 100 mm, length 500 mm mild steel plate assembled into a T-shape,
A current of 180 A was used in a horizontal fillet welding position, and the number of arc breaks was investigated during a melting rod length of 400 mm. The value is an average value of five test welding rods, less than 1.0 times is good, 1.0 times or more and less than 3.5 times is slightly inferior, and 3.5 times or more is inferior.

For the welding workability, vertical butt welding and T-type horizontal fillet welding were performed, and the arc state, slag state, bead appearance, etc. were investigated using the above-mentioned test pieces and welding conditions. 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, the arc breaking resistance and the welding workability were comprehensively judged, and the good marks were good, the good marks were slightly bad, and the bad marks were bad. When each judgment and comprehensive judgment under these welding conditions were performed, the results shown in Table 2 were obtained.

[0035]

[Table 2]

[0036]

[Table 3]

No. 1-No. No. 14 is an example of the present invention.
15-No. 28 shows a comparative example. The low hydrogen type rod No. of the present invention. 1-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, so that the slag removability is good and the arc is cut even when the no-load voltage is low. The number of times is small and at the same time it has excellent welding workability.

Comparative Example No. In No. 15, since the FeO equivalent of iron oxide is small, the slag is porous and the beads are smooth, so that the slag removability is good, and the arc voltage is also appropriately reduced, so the arc cutting resistance is good, CaCO
_Since there is a large amount of _{3 and a} small amount of CaF ₂ , the fluidity of the slag is poor and the welding workability is somewhat poor.

No. In No. 16, since the FeO content was a little large, the arc was easily broken. Further, since the amount of Si is small, the arc force is weak, the conformability of the weld metal to the steel plate is deteriorated, and the welding workability is slightly deteriorated. No. In No. 17, since the amount of TiO ₂ was too small, the stability of the arc deteriorated, the scattering of spatter increased, the bead appearance deteriorated as the slag encapsulation property deteriorated, and the welding workability deteriorated extremely.

No. 18, No. 20 and No. 20. 26
Has a large amount of FeO equivalent, which makes arcing easy,
No. 20 and No. In No. 26, the FeO content was added excessively, so the slag removability deteriorated. No. In No. 19, since the amount of iron oxide converted to FeO is slightly large, the arc cutting resistance is poor, the amount of CaCO ₃ is small, and the amount of Mn is large, the viscosity of the slag is reduced, and the weld metal easily drips in the vertical posture, and the convex bead is present. It began to take on a shape.

No. No. 21 had a large amount of TiO ₂ , so the arc force was weakened, the fluidity of the slag was deteriorated, 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 less CaCO ₃ and CaF ₂ and Mn
Since the melting point of the slag is low, the encapsulation property of the slag is deteriorated. Further, the arc became extremely weak because the amount of TiO ₂ was too much.

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

[0043]

As described above, the low hydrogen type rod of the present invention has good slag releasability in all postures of welding, and extremely low arc breakage even when the no-load voltage is low, and is good. Welding workability is secured. The low hydrogen type rod of the present invention which brings about such an effect is used for shipbuilding, bridges, construction, etc., and can significantly improve the welding work efficiency of field work.

[Brief description of drawings]

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

Claims (1)

[Claims] 1. CaCO ₃ ; 30 to 55% by weight CaF ₂ ; 5 to 35% by weight 0.40 in terms of FeO of one or more iron oxides.
Applied around a steel core wire with a consist from 0.4 to 8.4 wt% coating; wt% or less Si: 0.5 to 8.0 wt% Mn; from .3 to 7.5 wt% TiO ₂ A low-hydrogen coated arc welding rod characterized in that