JP2000117487A - Low hydrogen coated electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low hydrogen coated electrode which is capable of efficiently welding total layers from the penetration welding to the welding of a final layer, and obtaining the excellent arc stability and bead shape. SOLUTION: In a low hydrogen coated electrode, a coating flux is coated around a steel core rod, and the coating flux contains, by weight for the total weight of the coating flux, 3-15% rutile, 0.5-4% alumina, 5-15% silica sand, 4-12% fluorite, and 35-60% metallic carbonate. Potassium feldspar in the coating flux is regulated in weight to be <=20%.

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 suitable for use in circumferential welding of pipes by a sorting upward method, and more particularly, to an application from uranami welding to welding of a final layer. The present invention relates to a low-hydrogen-based coated arc welding rod that can obtain good arc stability and bead shape.

[0002]

2. Description of the Related Art Uranami welding, which is a first layer welding method for forming a uranami bead without using a backing material in pipe welding, determines the weldability of a pipe weld and the quality of a welded product obtained. Is an important factor. Therefore,
There has been proposed a welding rod exclusively used for Uranami welding in which the composition of the coating agent is appropriately adjusted (Japanese Patent Application Laid-Open Nos. 5-212586 and 56-148492).

[0003] In order to obtain a sufficient penetration and a good penetration bead, a welding rod for pipe penetration welding produces slag having good arc concentration and appropriate viscosity. The coating is coated. In addition, the welding rod for pipe reverse welding has a low arc breakage even when welded at a low current, and has good arc durability. By using a welding rod for Uranami welding,
Such welding rods have been applied to pipeline and plumbing backwashing because they make it easy to obtain good backwash beads and make a great contribution to the industry.

[0004]

However, the conventional welding rod for Uranami welding is used only for welding the first layer forming the Uranami bead, and is used for welding the second and subsequent layers. However, there is a problem that the viscosity of the slag becomes too high and the spread of the arc is insufficient for welding a wide groove. Therefore, when the conventional welding rod for Uranami welding is used for the welding of the second and subsequent layers, the bead shape becomes convex and the recess of the preceding layer does not melt in the welding of the second and subsequent layers. Poor fusion is likely to occur, and the soundness of the weld evaluated by an X-ray transmission test becomes poor.

[0005] Further, even when the welding rods disclosed in the above-mentioned JP-A-5-212586 and JP-A-56-148492 are used, excellent weldability can be obtained by uranami welding. If this welding rod is used after the first layer, welding becomes difficult, and poor fusion frequently occurs.

[0006] In order to use a welding rod for backside welding also in the welding of the second and subsequent layers, there is a method in which a bead is applied to each layer to smooth the beads, and then welding is performed. However, the use of this method significantly reduces the welding efficiency. There is also a method of applying a general all-position welding rod used for welding the second and subsequent layers to Uranami welding. However, in order to obtain a good Uranami bead using a general all-position welding rod, it is difficult even for a welding technician with high ability, and frequent rework is required. descend.

[0007] Therefore, conventionally, a welding rod for Uranami welding is used as a dedicated rod only at the time of welding of the first layer, and at the time of welding the second and subsequent layers, a general all-position welding rod is used. ing. Then, it is necessary to use two types of welding rods properly at the welding site, and the management becomes complicated.

Therefore, recently, there has been a demand for the development of a technique capable of performing the steps from the back side welding to the welding of the final layer with one type of welding rod. The present invention has been made in view of such a problem, and it is possible to efficiently weld all layers from the backside welding to the welding of the final layer, and to obtain good arc stability and bead shape. An object of the present invention is to provide a low hydrogen-based coated arc welding rod that can be used.

[0009]

According to the present invention, there is provided a low-hydrogen-based coated arc welding rod according to the present invention, wherein a coating agent is coated on a steel core wire. Per weight, 3 to 15% by weight of rutile, 0.5 to 4% by weight of alumina, 5 to 15% by weight of silica sand, 4 to 12% by weight of fluorite and 35 to 60% by weight of metal carbonate. And potassium feldspar is regulated to 2% by weight or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The inventor of the present invention has conducted intensive experiments and researches in consideration of the composition of a coating agent in order to develop a method capable of welding all layers with one welding rod. In particular, various studies have been conducted to develop coating agents that can satisfy any of the conditions regarding the differences in slag viscosity and arc spread required when welding Uranami and when welding the second and subsequent layers. went. As a result, it has been found that it is effective to appropriately adjust the contents of potassium feldspar, rutile and alumina in the coating agent.

That is, since potassium feldspar is a component having the effect of increasing the viscosity of slag and improving the concentration of the arc, it forms a good back wave bead at the time of back wave welding and facilitates welding. It is an effective raw material for maintaining arc stability during low current welding. However, when the content of potassium feldspar in the coating material increases, the viscosity of the slag becomes too high during the welding of the second and subsequent layers, and the spread of the arc is reduced, so that the bead shape becomes convex. Therefore, at the time of welding of the second and subsequent layers, defective fusion, which is a phenomenon in which the recesses of the previous layer do not melt, occurs.

Therefore, in the present invention, the content of potassium feldspar in the coating material coated on the welding rod is restricted to 2% by weight or less so as not to affect the welding of the second and subsequent layers. It is assumed that all layers from the first layer to the final layer can be welded by Uranami welding. In addition, in the present invention, instead of potassium feldspar, by including an appropriate amount of rutile and alumina in the coating agent, it is possible to form a good Uranami bead and facilitate Uranami welding, Arc stability during low current welding can be maintained.

Hereinafter, the components contained in the coating agent for the low hydrogen-based coated arc welding rod according to the present invention and the reasons for limiting the composition will be described.

Potassium feldspar: 2% by weight or less As described above, when the content of potassium feldspar in the coating agent is increased, the fluidity of the slag is reduced, and a slag having an appropriate viscosity can be obtained during uranami welding. As well as the arc concentration is improved, good backside welding can be performed. However, the content of potassium feldspar in the coating agent is 2% by weight.
When welding exceeds the second layer, the viscosity of the slag becomes too high during welding of the second and subsequent layers, and in particular, the flow of the slag decreases during welding in the vertical position and the upward position, and the concentration of the arc increases to increase the arc concentration. Since the spread is reduced, the bead shape becomes convex. Therefore, in order to prevent any adverse effect during welding of the second and subsequent layers, the content of potassium feldspar in the coating material is restricted to 2% by weight or less based on the total weight of the coating material.

Rutile: 3 to 15% by weight When the content of potassium feldspar in the coating agent is regulated to 2% by weight or less, the fluidity of slag during uranami welding increases.
Uranami beads are not formed properly. Rutile is a component that can prevent the formation of a backwash bead due to excessive fluidity of slag during backwash welding. If the content of rutile in the coating agent is less than 3% by weight, the viscosity of the slag cannot be sufficiently increased, and it is difficult to obtain a good backside bead. On the other hand, when the content of rutile in the coating agent exceeds 15% by weight, the viscosity of the slag becomes too high at the time of welding the second and subsequent layers, and the flow of the slag particularly during welding in the vertical position and the upward position. Since it is lowered, the bead shape becomes convex. Therefore, the amount of rutile in the coating is 3 to 15% by weight based on the total weight of the coating.

Alumina: 0.5 to 4% by weight Alumina, like rutile, is one of the slag forming agents that adjusts the fluidity of the slag, and is an important component that affects the arc concentration. Therefore, by adjusting the content of alumina in the coating agent, it is possible to prevent a decrease in arc concentration caused by regulating the content of potassium feldspar. When the content of alumina in the coating agent is less than 0.5% by weight, the arc concentration and the slag viscosity cannot be sufficiently increased, and it is difficult to obtain a good backside bead. On the other hand, when the content of alumina in the coating agent exceeds 4% by weight, the arc concentration becomes too high, and the arc spread becomes insufficient. In addition, when welding the second and subsequent layers, the viscosity of the slag becomes too high.
Since the flow of the slag is reduced during welding in the vertical position and the upward position, the bead shape becomes convex. Therefore, the amount of alumina in the coating is 0.5 to 4% by weight based on the total weight of the coating.

Silica sand: 5 to 15% by weight silica sand is a component having an effect of appropriately maintaining the viscosity of the slag and increasing the arc spraying force to improve the stability of the arc. By appropriately adjusting the content, an effect of improving overall welding workability can be obtained. When the content of silica sand in the coating agent is less than 5% by weight, the spraying power of the arc is weakened, and the arc becomes unstable particularly at the time of welding at a low current, such as uranami welding. On the other hand, when the content of the silica sand in the coating agent exceeds 15% by weight, the spraying of the arc becomes strong, but the viscosity of the slag becomes too high during the welding of the second and subsequent layers, and the bead shape becomes convex. Therefore, the amount of silica sand in the coating agent is 5 to 15% by weight based on the total weight of the coating agent.

Fluorite: 4 to 12% by weight, metal carbonate: 3
5 to 60% by weight of fluorite and metal carbonate are components necessary for improving the porosity resistance of the low-hydrogen welding rod and maintaining good overall welding workability. When the content of the fluorite in the coating agent is less than 4% by weight, the viscosity of the slag becomes too high, and the overall welding workability deteriorates. On the other hand, when the content of the fluorite in the coating agent exceeds 12% by weight, the viscosity of the slag becomes too low, and the overall welding workability deteriorates. When the content of the metal carbonate in the coating agent is less than 35% by weight, the shielding effect is insufficient, and blowholes are easily generated. On the other hand, when the content of the metal carbonate in the coating agent exceeds 60% by weight, the spraying of the arc becomes weak,
Arc becomes unstable. Therefore, the fluorite in the coating is 4 to 12% by weight based on the total weight of the coating, and the metal carbonate in the coating is 35 to 60% by weight based on the total weight of the coating.

In the present invention, in addition to the above components, an arc stabilizer, an alloying agent, a deoxidizing agent, a slag forming agent, water glass and the like can be contained in the coating material. In the present invention, the coverage calculated by the formula ((weight of coating agent / total weight of welding rod) × 100) is 20 to 3
Preferably it is 5% by weight.

[0020]

EXAMPLES Hereinafter, examples of the low hydrogen-based coated arc welding rod according to the present invention will be specifically described in comparison with comparative examples. First, coating agents having various compositions shown in the following Tables 1 and 2 were applied to the outer peripheral surface of a carbon steel core wire specified in JIS G3523 at a coating rate of 25% by weight, and thereafter, 11%
By performing predrying at 0 ° C. for 1 hour and baking at 450 ° C. for 1 hour, a low hydrogen coated arc welding rod was produced. In this embodiment, the diameter of the cord is set to 3.
The length was 2 mm and the length was 350 mm.

Next, a horizontal fixed pipe having an outer diameter of 254 mm and a thickness of 12.7 mm was circumferentially welded using the obtained covered arc welding rod. At this time, a welding current of 80 A was used for welding the back layer of the first layer, and a welding current of 110 to 120 A was used for welding of the second and subsequent layers. FIG.
FIG. 4 is a sectional view showing a groove shape of a horizontal pipe fixed as a welding base material in the present embodiment. As shown in FIG. 1, the pipe tubes 1 and 2 are provided with notches from the outer peripheral surfaces 1a and 2a toward the end surfaces 1b and 2b, and are fixed horizontally with the end surfaces 1b and 2b facing each other. Thus, a V groove is formed between the pipe 1 and the pipe 2. In this example, the width of the root surface was 0.5 mm, the root interval was 3.2 mm, and the bevel angle was 35 °.

The welding workability is evaluated by observing the stability of the arc during the Uranami welding and the uniformity of the Uranami bead after the Uranami welding, and the soundness of the welded part is determined by an X-ray transmission test. Was evaluated. FIG. 2 is a cross-sectional view showing a method for evaluating the uniformity of a Uranami bead. As shown in FIG. 2, with respect to the weld metal 3 formed between the pipe pipe 1 and the pipe pipe 2, the height A of the protruding portion 3a protruding from the inner peripheral surfaces 1c and 2c of the pipe pipes 1 and 2 is welded. It is measured over the entire length of the wire, and when the height A is 0 to 2 mm,
(Good) and others (poor).

The stability of the arc during backside wave welding was evaluated by observing the presence or absence of an arc during welding and the state of the arc.
A sample which was not more than once per book and in which the state of the arc was stable was evaluated as ○ (good), and the others were evaluated as × (defective). In order to form a good Uranami bead, welding at a relatively low current is required.
The evaluation was performed in a low current region of A.

Further, the soundness of the welded portion was evaluated by conducting an X-ray transmission test after the welding of all the layers was completed, and observing the occurrence of defective fusion and blowholes. In the classification of the flaws specified in JIS Z3104, those of the first or second kind were evaluated as ○ (good), and the others were evaluated as x (bad). The evaluation results are shown in Tables 3 and 4 below. In the comprehensive evaluation columns shown in Tables 3 and 4 below, in each of the evaluation tests, the evaluation result was （(good), and the evaluation result was ○, and at least one type of evaluation result was × (poor). Was evaluated as x.

[0025]

[Table 1]

[0026]

[Table 2]

In the coating compositions shown in Tables 1 and 2, other components include a fixing agent, other slag forming agents, alloying agents, and inevitable impurities.

[0028]

[Table 3]

[0029]

[Table 4]

As shown in Tables 1 to 4 above, Example N
o. In Nos. 1 to 16, the composition of the coating agent was appropriately adjusted, so that welding workability was good and a sound weld was obtained.

On the other hand, in Comparative Example No. In Nos. 17 to 20, since the content of potassium feldspar in the coating agent exceeded the upper limit of the range of the present invention, the viscosity of the slag became too high at the time of welding the second and subsequent layers. The slag flow was reduced during welding. In addition, since the spread of the arc was reduced, the bead shape became convex, and poor fusion sporadically occurred. Therefore, the soundness of the welded part in the X-ray transmission test was poor. In particular, in Comparative Example No. In Nos. 19 and 20, since the content of rutile or alumina in the coating material exceeded the upper limit of the range of the present invention, the soundness of the weld was further deteriorated.

Comparative Example No. In No. 21, since the content of rutile in the coating agent was less than the lower limit of the range of the present invention, the viscosity of the slag became small, and a good backside bead could not be formed. Comparative Example No. In No. 22, since the content of rutile in the coating agent exceeds the upper limit of the range of the present invention, the viscosity of the slag becomes too high at the time of welding of the second and subsequent layers, and as a result, the bead shape becomes convex and becomes fused. Bad sporadic, X
The integrity of the weld was poor in the line transmission test.

Comparative Example No. 23, since the content of alumina in the coating agent is less than the lower limit of the range of the present invention, the arc concentration is reduced, and the viscosity of the slag is reduced,
A good Uranami bead could not be formed. Comparative Example No. In No. 24, the viscosity of the slag became too high during welding of the second and subsequent layers because the alumina content in the coating agent exceeded the upper limit of the range of the present invention, and as a result, the bead shape became convex and fused. Defectiveness sporadically occurred, and the soundness of the welded portion in the X-ray transmission test became poor.

Comparative Example No. 25, since the content of silica sand in the coating agent is less than the lower limit of the range of the present invention, the spraying power of the arc is weakened, and arc breaks are sporadic during Uranami welding,
Arc stability decreased. Comparative Example No. In No. 26, since the content of silica sand in the coating agent exceeded the upper limit of the range of the present invention, the spraying power of the arc became strong, but the viscosity of the slag became too high, and the soundness of the welded part by the X-ray transmission test was confirmed. The property became poor. Comparative Example No. In Nos. 27, 28 and 29, since the content of the fluorite or the metal carbonate in the coating agent was out of the range of the present invention, the porosity and welding workability of the low hydrogen welding rod were all reduced.

[0035]

As described in detail above, according to the present invention,
Since the composition of the coating agent of the low hydrogen-based coated arc welding rod is properly adjusted, all layers from the backwash to the final layer can be efficiently welded, and good arc stability and bead shape can be achieved. Obtainable.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a groove shape of a horizontal fixed pipe used as a welding base material in the present embodiment.

FIG. 2 is a cross-sectional view showing a method for evaluating the uniformity of a Uranami bead.

[Explanation of symbols]

 1, 2; pipe tube 1a, 2a; outer peripheral surface 1b, 2b; end surface 1c, 2c; inner peripheral surface 3: weld metal 3a;

Claims (1)

[Claims] 1. A low-hydrogen coated arc welding rod in which a steel core wire is coated with a coating agent, wherein the coating agent is 3 to 15% by weight of rutile, alumina:
0.5 to 4% by weight, silica sand: 5 to 15% by weight, fluorite:
4 to 12% by weight and metal carbonate: 35 to 60% by weight
And a K-feldspar is regulated to 2% by weight or less.