JPS5938877B2 - High cellulose coated arc welding rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coated arc welding rod, and more particularly to a high cellulose-based coated arc welding rod that exhibits excellent welding workability in butt downward welding of fixed pipes and the like.

High cellulose-based coated arc welding rods have a strong arc force and produce a small amount of slag, so they are suitable for downward welding, and their arc properties also allow for easy welding.

In addition, extremely high welding speeds can be obtained during the first layer welding of downward welding of fixed pipes, so it has long been used in Europe and America for on-site welding of pipelines. However, since the coating material contains a large amount of cellulose-based organic matter, the Joule heat during welding easily causes the organic matter in the unused parts of the coating material to decompose and burn, causing so-called stick burn. The disadvantage of using a section is that the arc becomes unstable during welding. Therefore, when using this type of welding rod, it is necessary to keep the welding current low compared to other coated arc welding rods such as low hydrogen type or illuminite type. However, in downward welding of pipelines, especially in first-layer urana welding, it is necessary to use high-voltage sulfur in order to ensure sufficient penetration and form an appropriate urana bead, and in addition, the electric arc of the welding rod must be Since the end is strongly pressed against the inner root of the groove while being used continuously, it is easy to cause stick burns. If this happens, the arc becomes unstable, causing poor penetration and the uranami bead is disturbed, making it impossible to obtain a sound joint. Moreover, the effective length of the rod in the high current range (the length of the rod actually used until it becomes unusable due to burnout) is shortened, making it extremely uneconomical. Under these circumstances, various studies have been conducted in an effort to prevent stick burns, but no effective improvement measures have been announced so far.

The present inventors focused on the circumstances described in -H, and developed coating material raw materials and materials in order to prevent stick burn when using high current without impairing the features of the high cellulose coated arc welding rod as described above. Research focused on the component composition of binders.

The present invention was completed as a result of such research, and consists of a high-cellulose coating material made by kneading coating material raw materials containing a large amount of cellulose with a binder and coating the outer periphery of the steel core wire. In the coated arc welding rod, water glass with a SlO2/Na2O molar ratio of 2.8 to 3.8 is used as a binder in a solid content of 10 to 21% based on the total weight of the coating material.
% (weight 0!): hereinafter the same), and also contains in the coating mass, the weight ratio of the coating to the total weight of the welding rod is 0.1 to 0.18, and furthermore, The content of C as an inorganic substance is 0.07 to 0.5%.
The gist is there.

The effects of each component used in the present invention and the basis for setting the content will be explained below.

1 Cellulose: 17-40% It plays the role of a gas generating agent and is an essential component to provide the original characteristics of high cellulose.
If it is less than Ft), deep penetration and a powerful arc cannot be obtained, making it impossible to obtain suitability for downward welding.

Moreover, if it exceeds 40 f), burnout cannot be prevented even if other components are adjusted, and the arc becomes unstable. 2 metal Mn
and/or Fe-Mn: 3 to 10% in terms of Mn It is an essential component as a deoxidizing agent, and if it is less than 3%, deoxidation is insufficient and clean weld metal cannot be obtained; on the other hand, 10(f) If it exceeds this, the deoxidation becomes excessive and pits are likely to form on the bead surface.

0Ti02: 8-25f) In order to stabilize the arc, it is necessary to contain 8(f) or more, but if it exceeds 25%, the arc force becomes weak and downward welding becomes difficult.

0Si02: 15-30% SiO2 is a component mixed in as water glass and silicate mineral, and is an essential component to obtain the appropriate amount and viscosity of slag.

If it is less than 15%, the amount of slag produced will be insufficient and the elongation of the bead will be poor, making it impossible to obtain a healthy Uranami bead.

On the other hand, if it exceeds 30%, the amount of slag becomes too large and downward welding becomes difficult. 9Mg0: 2 to 12% Must be contained in an amount of 2% or more as it has the effect of increasing the peelability of slag.

However, if it exceeds 12%, the fluidity of the slag becomes excessive and downward welding becomes difficult. Hydrous minerals containing water of crystallization released at temperatures above 050'C: 0.3 to 3% in terms of water of crystallization released at temperatures above 500'C.Hydrous minerals such as talc are used and contribute to arc spraying. do.

In order to effectively exhibit this effect, it is necessary to add 0.3 (:fl) or more. However, if it exceeds 3%, the arc force decreases and the arc becomes unstable. The reason for specifying crystallization water as water released at temperatures above 500°C is that when water is released at temperatures below 500°C, such as so-called adsorbed water, water is released before the welding rod wears out due to the high temperature during welding. This is because it will be released into the atmosphere from the coated surface and will have no effect on the arc. Binder: SlO2/
The SiO2/Na2O molar ratio (hereinafter simply referred to as molar ratio) and the amount of water glass mixed are the most important requirements in the present invention. , is closely related to the stick burn resistance of welding rods.

That is, as will be described later, when the stick burn resistance of welding rods obtained by varying the molar ratio and blending amount of water glass was investigated, it was found that the performance was significantly improved in the above range. The reason for this is that, as is clear from the experimental data described below, the coating obtained by combining the above preferred ranges has extremely good firmness after drying, and the combustion reaction of cellulose in the coating material is delayed. Conceivable. Incidentally, Fig. 1 shows that a coating material having the same composition as code 2 in the experimental example (Table 1) described later was used, and a coating material prepared by changing the molar ratio and blending amount of water glass was applied to a steel core wire (4 This shows the results of measuring the coating diameter after drying by passing it through a die with an inner diameter of 5.6 mm ψ along with .0 x 350 mm 1). As is clear from this result, when a coating material containing 10 to 21% solid content of water glass with a molar ratio of 2.8 to 3.8 is used, the coating diameter becomes considerably small and the coating becomes tight. It is confirmed that it is in a state of ivy. The reason for this tendency can be inferred from the results of microscopic observation of the cross section of the coating as follows. That is, in the combination of the above-mentioned preferred molar ratio and blending amount, water glass is difficult to penetrate into the cellulose contained in a large amount in the coating material, is evenly distributed between the particles of the coating material raw material, and forms a film, and forms a film between the raw material particles. It is thought that this is because the sliding between the glass becomes better and the coating material is more likely to be densely packed, and the water in the water glass evaporates as it dries, causing a hardening phenomenon. However, low molar ratio water glass (molar ratio less than 2.8), which is most commonly used as a binder for coatings, easily penetrates into cellulose, causing cellulose to swell and tightening the coating. becomes worse. Furthermore, if the water glass has a molar ratio exceeding 3.8, the water in the water glass will easily escape when kneaded with the coating material raw material, and the coating will tend to fade during coating, resulting in poor coating firmness. On the other hand, if the amount of water glass is less than 10%, a film will not be formed evenly between the raw material particles,
The slippage between the raw material particles becomes poor, creating spaces due to scratches, and the tightness of the coating deteriorates. If it exceeds 21%, it will easily penetrate into the cellulose, similar to when low molar ratio water glass is used, causing swelling of the cellulose and deteriorating its firmness. Figure 2 is a graph showing the results of investigating the effective usable rod length (stick burn resistance) when performing downward welding using each of the welding rods obtained above. The effective usable rod length of a welding rod using 10 to 21% water glass of .8 is:
This is an improvement of over 50% compared to the conventional rod.

The test method for effective rod length was as follows. Welding method:
As shown in Fig. 3a, steel pipes of 11.1 mmt x 356 mmφ are butted together and welded downward in the direction of arrows A and B in Fig. 3b.

The groove shape is as shown in Figure 4, and the arc end of the welding rod is Press firmly against the root of the groove to create a strip. As shown in Figure 5, form a code.

Welding conditions: Current...DC-RP. 17 OA, welding speed...30-40 CTrL/min 8 Weight ratio of coating material to total weight of welding rod (coverage rate): 0.1-0.18 Basic conditions for facilitating downward welding of fixed pipes If it is less than 0.1, the function of the coating as a protective tube becomes insufficient and the arc becomes unstable, while if it exceeds 0.18, the concentration of the arc decreases and it becomes difficult to form a uranami bead. In either case, good downward weldability cannot be achieved.

90. Content of C as an inorganic substance in ττIX type: C content calculated from [C% in steel core wire] × [1-coverage rate] + [C% as inorganic substance in coating material] × coverage rate. , which contributes to improving the workability of first-layer underwave downward welding of fixed pipes by converting the arc into a spray.

If the C content is less than 0.07%, the above effects will not be effectively exhibited, and if it exceeds 0.5%, the cracking resistance of the weld metal will decrease. Note that C is added to the coating material in the form of high carbon Fe-Mn, graphite, or the like. The coated arc welding rod of the present invention satisfies the requirements 1 to 9 above, but in addition, Ni, Cr,
In order to improve welding efficiency and workability, it is possible to incorporate appropriate amounts of alloying elements such as MO, or to improve welding efficiency and workability.
5% or less) can also be blended.

Furthermore, when obtaining a welding rod for an AC power source, the performance can be further improved by adding a small amount of K2O as an arc stabilizer. The present invention is configured as described above,
In particular, by setting the molar ratio and blending amount of water glass used as a binder within a specific range, the stick burn resistance, which was the biggest drawback of high cellulose-based arc welding rods, has been improved, and downward welding In addition to improving the workability and joint performance of the welding rod, the wasteful consumption of welding rods can be greatly reduced by shortening the remaining rod length.

Next, examples will be shown.

Example A coating material having the composition shown in Table 1 was applied to a steel core wire (4.0m7
! A coated arc welding rod was manufactured by coating the outer periphery of 1φ×350 mm 1) to a predetermined coverage rate.

Using each of the obtained welding rods, downward welding of a fixed tube was performed in the same manner as described above, and the welding conditions and effective usable rod length were examined. If welding becomes impossible due to stick burn during welding,
At that point, the welding rod was replaced with a new welding rod, welding was performed all around, and the average value of the effective length of the used welding rod was determined. The results are summarized in Table 1.

From Table 1, the following can be considered.

(1) Code 1 is a typical example of a conventional high cellulose coated arc welding rod that uses low molar ratio water glass as a binder.
The effective usable rod length is extremely short, and 40% of the welding rods are wasted unused.

(2) Reference numeral 13 is a comparative example in which the molar ratio of water glass is less than 2.8, and the stick burn resistance is poor and the effective usable rod length is only about the same as that of the conventional rod.

(3) Reference numeral 14 is a comparative example in which the amount of water glass blended is too large, and the effect of improving stick burn resistance is insufficient.

(4) Reference numeral 15 is a comparative example in which the coverage is too small, and the protection tube is weak and the arc is unstable, making welding impossible. (5)
Reference numeral 16 is a comparative example in which the coverage is too large, and a healthy underwave bead is not formed due to weak arc force and insufficient penetration.

(6) Reference number 17 is a comparative example in which the inorganic C content in the welding rod is too low, and the arc is particularly unstable during initial layer welding, resulting in poor penetration.
A healthy Uranami bead is not formed.

On the other hand, reference numeral 18 is a comparative example in which the amount of inorganic C is too high, and although a good Uranami bead is formed, bead cracking occurs. (7) On the other hand, codes 2 to 12 are examples that satisfy all the requirements stipulated by the present invention, and the effective rod lengths used are all 300m77! It has extremely good stick burn resistance, and can form a sound Uranami bead without poor penetration.

[Brief explanation of the drawing]

Figures 1 and 2 are graphs showing the relationship between the molar ratio of water glass, the coating diameter after drying, and the effective usable rod length, and Figures 3 to 5 are explanatory diagrams showing the downward welding method employed in the experiment.

Claims (1)

[Scope of Claims] 1. A high-cellulose-based coated arc welding rod in which the outer periphery of a steel core wire is coated with a coating material obtained by kneading a coating material raw material containing a large amount of cellulose with a binder, in which SiO_ is used as a binder.
Water glass with a molar ratio of 2/Na_2O of 2.8 to 3.8 is used in a solid content of 10 to 21% by weight based on the total weight of the coating material.
In addition to containing cellulose in the coating material: 17 to 40
Weight% metal Mn and/or Fe-Mn: 3-10% by weight in terms of Mn TiO_2: 8-25% by weight SiO_2: 15-30% by weight MgO: 2-12% by weight Crystals released at 500°C or higher Hydrous minerals containing water: 50
In addition to containing 0.3 to 3% by weight in terms of crystallization water released at temperatures above 0°C, the weight ratio of the coating material to the weight of the welding rod is 0.1 to 0.18, and the proportion of coating material in the entire welding rod is A high cellulose-based coated arc welding rod, characterized in that the content of C as an inorganic substance is 0.07 to 0.5% by weight.