JPH01317698A - Coating material for tip of coated electrode - Google Patents

Abstract

PURPOSE:To obtain a defectless weld metal in a start part by incorporating a specific ratio of a carbon material having a specific specific surface area and a specific ratio of iron oxide having a specific grain size into the coating material for the tip of a coated electrode. CONSTITUTION:The coated electrode is constituted by coating a core wire 1 with the coating material 2 and coating the tip coating material 3 to the tip. The tip coating material which contains 5-20wt.% coke or carbon black having >=10m<2>/g specific surface area and 30-50wt.% iron oxide having <=50mum grain size and the balance iron powder, viscosity adjusting agent and binder is used. The defectless weld metal in the start part is obtd. in this way.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is applicable to fillet welding rods for mild steel and high tensile strength steel that have excellent arc startability and no welding defects in the weld metal, and low hydrogen all-position welding rods. This relates to a tip coating agent used for.

<Conventional technology> In general, the evaluation items for the welding workability of coated arc welding rods include ■ arc stability and spray strength, ■ fluidity of slag and difficulty in peeling, ■ spatter generation state and amount. , ■ quality of arc start and segregation of components in the weld metal at the start part. - In terms of welding workability on a boat, it has been pointed out that the quality of the welding is good or bad, and many studies have been conducted on countermeasures and improvements are being made.

However, regarding arc starting in (■), there are many unresolved problems compared to (■ to ■).In other words, arc starting is an unsteady operation, the arc and generated gas are unstable, and the arc starting part is the most likely to be in the weld metal. This is a part where welding defects such as component segregation and blowholes are likely to occur.

A tip coating agent is used at the tip of the welding rod to facilitate arc starting, and the particle size of carbon and iron oxide added to this tip coating agent.

It is important to suppress the occurrence of component segregation, which occurs depending on the amount of addition, as this component segregation often develops into cracks in the weld metal.However, it is important to prevent this problem completely. has not been solved, and an effective countermeasure is desired. (Problems to be solved by the invention) In view of the above-mentioned current situation, the present invention has been developed to provide good arc starting performance and to ensure soundness, especially at the starting part. This invention was developed in order to provide a coating agent for coated arc welding rod tips that can yield a weld metal with a high quality.

<Means for Solving the Problems> The present invention provides coke or carbon black with a specific surface area of 10 nf/gr or more, which
This coated arc welding rod tip coating agent contains 30 to 50% by weight of iron oxide of 1 or less, with the remainder being iron powder, a viscosity modifier, and a fixing agent.

Function> The coated arc welding rod tip coating agent according to the present invention contains 5 to 20% by weight of coke or carbon black, which is an amorphous carbon raw material with a fine grain size and a specific surface area of 1 Onf/gr or more and which is easily ignited. (hereinafter abbreviated as %).

Therefore, since the particle size is appropriate and shows good ignitability, and the amount is appropriate, welding defects such as pitting and carbon segregation do not occur in the weld metal.

On the other hand, since the tip coating agent contains 30 to 50% iron oxide, which is a fine oxidizing agent with a particle size of 53 nm or less, no residual carbon, which is also a deoxidizing component, in the weld metal, that is, no segregation of carbon occurs.

Since the tip coating agent contains appropriate amounts of iron powder, viscosity modifier, and fixing agent, the coating agent can be applied in a good shape.

<Example> Welding tests were conducted using coated arc welding rods using various tip coating agents with different particle sizes and addition amounts of carbon and iron oxide, which are the main components of tip coating agents used for coated arc welding rods. We investigated arc startability, weld defects in weld metal, etc., and the results are shown in Table 1.

It is shown in Table 2.

That is, the welding test was conducted using a gravity welding machine using a corner coated arc welding rod for mild steel (rod length: 700 nua, rod diameter: 5
．． Omφ) to rod handling ratio: 1.2. Welding current = 220 static p
Set the welding rod to the steel plate 10 times each,
Determine the ignition condition and then inspect the pits inside and outside the weld.

The presence or absence of welding defects such as blowholes and the presence or absence of deoxidizing component (carbon) segregation were observed and the results are shown in the table. In this test, amorphous carbon black was used as carbon.

The test results are summarized below.

■When the specific surface area of carbon was less than 9%/gr, it did not ignite smoothly, and only when it was more than 10 rrf/gr did it show satisfactory ignitability.

5% even if the specific surface area is 10rrf/gr or more
If the amount added is less than 20%, it will not ignite, and if it exceeds 20%, it will show good ignitability, but pits or segregation of carbon, which is a deoxidizing component, were found on the surface of the weld metal, making it unsuitable for practical use. .

The reason why the specific surface area is used to express the particle size of the carbon raw material is to clarify the reaction with iron oxide.

(2) Next, when the particle size of iron oxide was 634 nm or more, segregation of deoxidizing components was observed in the weld metal, and when the grain size was 53 nm or less, no segregation of deoxidizing components was observed. This is probably because the oxidation reaction did not proceed to the center of the iron oxide when the particle size was large, and excess carbon remained.

Regarding the amount of iron oxide added, even with the appropriate combination until now, if it is less than 30%, pits will occur due to excessive deoxidation.
When it exceeded 50%, blowholes occurred frequently due to insufficient deoxidation.

Next, to select carbon raw materials, we tested crystalline graphite, amorphous coke, and carbon black.
The results are shown in Table 3. In this test, the carbon raw material, the specific surface area 2 grain size of iron oxide, and the amount added were within the range considered to be appropriate based on the results of the welding test described above. Graphite, which is crystalline carbon, has poor ignitability, and it has been discovered that carbon, which is a deoxidizing component, is segregated in weld metal. This is because the particle surface is not porous compared to other raw materials, so the contact area between carbon particles is small, and the crystalline nature slows down the reaction rate with iron oxide.

Although the fillet welding rod for mild steel was used in this welding test, similar results could be obtained with other coated welding rods such as low-hydrogen fillet welding rods and all-position welding rods. I can do it.

Regarding carbon raw materials, there is no description of the combination of amorphous raw materials, but as long as the carbon raw materials are amorphous and have a specific surface area that satisfies the above conditions, the same results can be obtained even if they are used alone or in combination. was gotten.

From the above results, arc starting performance can be improved by using a tip coating agent containing 5 to 20% of coke or carbon black with a specific surface area of Ion (/gr or more) and 30 to 50% of iron oxide with a particle size of 53 or less. It was found that the results were good and no welding defects occurred inside or outside the weld metal.

In addition, in the test, iron powder, a viscosity modifier, sodium silicate as a fixing agent, and a phenol resin were used as the remainder other than the main components.

<Effects of the Invention> When the coated arc welding rod tip coating agent according to the present invention is used,
As described above, good arc startability can be ensured, and a sound weld metal without welding defects can be obtained, especially at the starting part.

[Brief explanation of the drawing]

FIG. 1 is an explanatory cross-sectional view of the tip of a welding rod coated with a tip coating agent. l... Core wire, 2... Coating material, 3
...Tip coating agent, 4...Base material. Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Claims] Contains 5-20% by weight of coke or carbon black with a specific surface area of 10 m^2/gr or more, 30-50% by weight of iron oxide with a particle size of 53 μm or less, and the remainder is iron powder, viscosity modifier, and fixing agent. A coated arc welding rod tip coating agent characterized by: