JPH0436795B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a low-hydrogen coated arc welding rod, and more specifically, a low-hydrogen coated electrode that is produced by controlling the roughness of the coated surface and has no coating cracks and has excellent moisture absorption resistance. This relates to arc welding rods. [Prior Art] Generally, coated arc welding rods (hereinafter simply referred to as welding rods) are coated with a coating agent around the outer periphery of a core wire of mild steel or alloy steel, and then dried. It is divided into several systems depending on the purpose. Among these, low-hydrogen welding rods are mainly used for welding thick plates of mild steel and high-strength steel of 50 kg or more.
In addition to the mechanical performance of the weld metal, the resistance of the weld is particularly important. One of the factors that has a very serious effect on this resistance is the diffusible hydrogen in the weld metal. Diffusible hydrogen sources are mainly moisture in the atmosphere and the welding rods and steel materials used. There is moisture attached. The flux raw materials used for this purpose must not only be selected from those with a low hydrogen source, but also treated to make moisture-absorbing materials difficult to absorb moisture, or, as disclosed in Japanese Patent Publication No. 1982-827, Efforts have been made to use an alkaline silicate aqueous solution containing lithium, which has low adhesive properties, as a fixing agent. However, all of these methods focus on the material used for the coating material of welding rods, and their main purpose is to reduce the hydrogen source in the coating material or prevent the hygroscopic reaction between some coating materials and water. It cannot be expected to be effective in reducing moisture that physically adheres to the surface. Therefore, with conventional techniques, there is a limit to the improvement of moisture absorption resistance. [Problems to be Solved by the Invention] The present invention has been made to solve the above-mentioned problems, and aims to improve the moisture absorption resistance required for low hydrogen welding rods while reducing the occurrence of coating cracking. This made it possible while preventing it. [Means for Solving the Problems] The gist of the present invention is low hydrogen-based coated arc welding having a coated surface whose centerline average roughness (Ra) specified in JIS _B0601-1982 is 3.0 to 6.5 μm. It's on the stick. [Function] In order to further improve the moisture absorption resistance of low-hydrogen welding rods, in addition to improving the covering material as in the prior art, the present inventors have developed a method to make them even more resistant to moisture absorption. We conducted various studies based on the idea that it would be effective to reduce the amount of water that physically adheres to the coated surface and permeates through it. As a result, the amount of moisture absorbed is related to the roughness of the coating surface, and by expressing this roughness as center line average roughness (Ra) specified in JIS _B0601-1982 , the correlation shown in Figure 1 can be established. was gotten. The center line average roughness (Ra) is calculated by extracting a portion of measurement length l from the roughness curve in the direction of its center line, taking the center line of this sampled portion as the X axis, and the vertical magnification direction as the Y axis. When the curve is expressed as y=f(x), the value obtained by the following equation is expressed in micrometers (μm). Ra=1/l∫ ^l _p ｜f(x)｜dx Roughness curve: When the surface to be measured is cut with a plane perpendicular to the surface to be measured, the contour that appears at the cut end is called the cross-sectional curve. A curve that cuts out surface waviness components that are longer than the wavelength of . Center line of roughness curve: A straight line or curve that follows the geometrical shape of the surface to be measured, and the line set so that the sum of squares of deviations from that line to the roughness curve is minimum is called the average line. , when a straight line is drawn parallel to the average line, the area surrounded by the straight line and the roughness curve is equal on both sides of the straight line. That is, when the roughness Ra of the coating surface of the welding rod was varied and the coating material was left in a high humidity atmosphere to investigate the amount of moisture absorbed by the coating material, it was found that there was a curved relationship as shown in Figure 1. Then, the coated surface
If Ra is too large or too small, the amount of moisture absorbed increases, but it has been found that there is an appropriate range of Ra for the coated surface that is relatively difficult to absorb moisture. The moisture absorption amount of the coating material of low-hydrogen welding rods is about 0.5%, which is the limit value for welding defects and welding workability. The force increases and welding workability deteriorates. From this, the coated surface
When the appropriate range of Ra was determined, it was 3.0 to 6.5 μm. The effect of Ra on the coating surface on the amount of moisture absorbed by the coating is that as Ra increases, the surface area of the coating increases and the proportion of contact with the atmosphere increases, so the amount of moisture absorbed by the coating also increases. Until now, this increasing trend was gradual, but when Ra reached 6.5 μ
If it exceeds m, the amount of moisture absorbed increases significantly. Also,
When Ra is less than 3.0 μm, the surface of the coating material is dense, so cracks in the coating are likely to occur during the welding rod manufacturing process, and when cracking occurs, the surface area of the coating material also becomes large. This resulted in an increase in the amount of moisture absorbed. No coating cracking occurred when Ra was 3.0 μm or more. Therefore, if Ra of the coated surface is less than 3.0 μm and more than 6.5 μm, the object of the present invention cannot be achieved. Next, as means for adjusting the roughness of the coating surface, (1) the type and particle size distribution of the coating flux, (2) the amount of water in the adhesive, (3) the kneading conditions, (4) the coating pressure, (5) )Drying (firing) conditions, etc., and welding rods with different coating surface roughness can be produced depending on each combination. In order to reduce the roughness of the coating surface to 6.5 μm or less, the coating flux should generally have a rounded particle surface with few irregularities, and should be closely packed with raw materials that have good water wettability. The particle size structure is as follows, the amount of water added in the water glass as a fixing agent is reduced as much as possible, the concentration is high and the molar ratio is high, and the conditions are such that a relatively long period of time is required so that the fixing agent is thinly and uniformly coated on the particle surface. It is effective to increase the drying speed by kneading the powder and applying a coating pressure of about 4000 N/mm ² . In order not to reduce the roughness of the coating surface to less than 3.0 μm, the particle size of the coating flux must be adjusted;
For example, CaCO ₃ , TiO ₂ with an average particle size of 50 μm or more,
Using fluxes such as MgCO ₃ and CaF ₂ ,
Alternatively, it is necessary to coat the welding rod with a coating pressure of 5000N/mm ² or less. [Example] In the present invention, welding rods having various coated surface roughnesses were produced by varying the above-mentioned factors, and their performance was investigated. This will be explained using a specific example. The two types of coating flux and adhesive shown in Table 1 were combined to form a coating agent, which was coated onto a 4.0 mmφ x 450 mml mild steel core wire, dried and fired to produce a welding rod. This welding rod is coated with a coating surface roughness,
Moisture absorption and welding defects (pits, blowholes)
The survey was conducted in the following manner. The results are shown in Table 2. Covering cracks: The presence or absence of cracks was visually inspected. Coating surface roughness: Center line average roughness (Ra) was measured using a stylus type surface roughness measuring device. Adsorption amount: The weight increase rate was measured after standing for 5 hours in an atmosphere of 30°C and 80% RH. Welding defects: The presence or absence of pits and blowholes was investigated at a welding current of 170A and in a downward welding position using a welding rod that had absorbed moisture under the above conditions. Comprehensive evaluation: The case where neither coating nor welding defects were observed was judged as good (○ mark), and the other cases were judged as poor (x mark).

【table】

[Table] Nos. 1 to 3, No. 6, and No. 7 have coating surface roughness.
Because Ra is too small, coating will occur, especially in No.
Welding defects (pits) were observed in No. 1, No. 2, and No. 6. Samples No. 4, No. 5, and Nos. 8 to 10 absorbed a large amount of moisture due to their rough coating surfaces, causing pits, and blowholes were also observed in Samples No. 5 and No. 10. In contrast, the examples of the present invention were coated, and showed sufficiently satisfactory results in terms of moisture absorption and welding defects. [Effects of the Invention] As described above, the present invention makes it possible to make a low-hydrogen welding rod difficult to absorb moisture without causing problems such as coating, and has a wide range of applicability and has no industrial value. It is extremely large.

[Brief explanation of drawings]

Figure 1 is a chart showing the influence of the center line average roughness (Ra) of the coating surface of a low hydrogen welding rod on the amount of moisture absorbed by the coating material (a plot of the data in Table 2).

Claims (1)

[Claims] 1. A low-hydrogen coated arc welding rod having a coated surface with a centerline average roughness (Ra) of 3.0 to 6.5 μm as specified in JIS _B0601-1982 .