JPS6129835B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coated arc welding rod, and more particularly to a low-hydrogen coated arc welding rod for vertical downward welding, which has an improved function as a protective tube and has improved welding workability and joint performance. Various welding methods and welding materials have been proposed to improve welding efficiency and joint performance, and many technologies have also been developed for low-hydrogen coated arc welding rods that suppress hydrogen embrittlement. However, there are few methods that satisfy both the shortening of the total welding time including post-weld modifications (repair welding) and the joint performance.
Particularly in low-hydrogen coated arc welding rods for vertical downward welding, when high current welding is performed to shorten the welding time, the coating burns and becomes brittle, and may fall off during welding. As a result, the function of the coating as a protective tube deteriorates, resulting in insufficient shielding, atmospheric moisture, etc. enters the welding atmosphere, causing joint defects such as pits and blowholes, and hydrogen in the weld metal. As the amount increases, not only the characteristics as a low-hydrogen welding rod deteriorate significantly, but also welding workability deteriorates. The present inventor focused on the above-mentioned circumstances and developed a low-hydrogen welding rod that can provide excellent welding workability without impeding joint performance including hydrogen embrittlement, which is an inherent characteristic of low-hydrogen welding rods. In order to develop a coated arc welding rod for vertical downward welding, we have been conducting research on the composition of the coating material and the physical properties of the coating. The present invention was completed as a result of such research, and its composition is: _SiO2 : 3 to 8% (weight %: the same below), carbonate: 30 to 60 weight %, metal fluoride: 0.5 to 8%. 8
%, deoxidizing metal: In a low hydrogen coated arc welding rod for vertical downward welding, the bulk density of the coating material after firing is The gist lies in the creation of a low-hydrogen coated arc welding rod for vertical downward welding which has excellent resistance to shedding of the coating during welding, characterized by a weight of 1.9 to 3.0 g/cm ³ . In the present invention, by specifying the composition of the coating material and setting the bulk density of the coating within a specific range after firing, the coating is prevented from falling off during welding, and the original function as a protective tube is maintained. I was able to force it. As a result, good arc stability and shielding effect were ensured, and high quality welded joints were obtained with good workability. The basis for setting the numerical range in the present invention will be explained below. _SiO2 : 3 to 8% It acts as a slag viscosity modifier and also increases the arc force, and these effects are effectively exhibited when it is added in an amount of 3% or more. However, if it exceeds 8%, the arc separation property deteriorates significantly and workability decreases. The raw materials used are silica sand, talc, mica or other silicates, including SiO ₂ in water glass used as a binder. Carbonate: 30-60% An essential component as a gas generating agent, and the generated gas protects the weld metal from the atmosphere. 30
If it is less than 60%, there will be insufficient shielding, making joint defects such as blowholes more likely to occur, and hydrogen embrittlement resistance will decrease, while if it exceeds 60%, penetration will be too deep and undercuts will easily occur. _CaCO3 ,
MgCO ₃ , BaCO _{3 ,} etc. are used as equivalent substances, but the most common is CaCO ₃ . Metal fluoride: 0.5-8% This is an essential component as a pore preventer and a slag viscosity modifier.If it is less than 0.5%, these functions cannot be effectively exerted and pitting is likely to occur. On the other hand, if it exceeds 8%, the fluidity of the slag becomes too large and it tends to move forward. _CaF2 - _AlF3 -MgF2, _etc. all have these effects and can be used alone or in combination of two or more. Deoxidizing metal: 3 to 15% Mn, Si, Ti, Al, Mg, or an iron alloy thereof is used. If it is less than 3%, blowholes and undercuts are likely to occur due to insufficient deoxidation, while if it is 15% Exceeding this will cause the weld metal to become hard and its cracking resistance to decrease. In the present invention, the above-mentioned four components are essential components of the coating material, but the following components may be added as necessary. TiO ₂ : 7% or less Effective as a slag viscosity modifier, but 7%
If it exceeds this, the fluidity of the slag will become too large and problems caused by the leading slag will become significant. Iron powder: 40% or less It is extremely effective in increasing the amount of deposited metal and increasing welding efficiency, but if it exceeds 40%, the arc force becomes insufficient and downward welding becomes difficult. Although it is common to use iron powder alone, it can also be blended as an iron alloy such as Fe-Mn. Alloy powder: 5% or less In order to improve the mechanical properties and corrosion resistance of weld metal, it is extremely difficult to add alloying elements such as Cu, Mo, Ni, Cr, etc. or their iron alloys depending on the target performance. It is effective and is usually added in an amount of 5% or less. The composition of the coating material used in the present invention is as described above, but the performance of the welding rod of the present invention obtained by applying this coating material to the outer periphery of a mild steel core wire and firing it is closely related to the shedding resistance of the coating. have a relationship. That is, as explained above, the coating forms a protective tube during welding and has the effect of stabilizing the arc and enhancing the shielding effect, but if the coating falls off during welding, the above effect is lost. Therefore, we conducted an experiment to improve the shedding resistance of the coating, and found that the shedding resistance was closely related to the bulk density of the coating after firing, and the bulk density was 1.9.
It has been found that excellent shedding resistance can be ensured by setting the particle size of the coating material raw material, manufacturing conditions, etc. so that it is at least g/cm ³ . Incidentally, Figure 1 shows the relationship between the bulk density of the coating, the number of times it falls off during welding, and the yield during manufacturing (after drying) for a low-hydrogen coated arc welding rod for vertical downward welding that satisfies the above component composition. This is a graph. However, in the experiment to measure the number of falls, a test rod of 5.5 mmφ x 450 mml was used, and downward contact welding was performed at 360 A (AC) on a T-shaped fillet test piece. The bulk density of the coating was calculated using the following formula. In the formula, K: Bulk density (g/cm ³ ) G: Weight of the welding rod after cutting and removing both ends (g) l: Length of the welding rod after cutting and removing both ends (cm) d: Core wire diameter (cm) D: Covering diameter (cm) As is clear from Figure 1, the bulk density is 1.9g/
If the bulk density is less than 1.9 g/cm ³ , the coating will come off significantly, whereas if the bulk density is 1.9 g/cm ³ or more, the coating will not come off at all. The appropriate current when using a low-hydrogen coated arc welding rod for vertical downward welding with a diameter of about 5.5 mm is usually about 260 to 330 A, which is clear from the experimental data in Figure 1 (current: 360 A). It is thus understood that the welding rod of the present invention exhibits high drop-off resistance even under conditions of high welding current. However, if the bulk density exceeds 3.0 g/cm ³ , it is not preferable because the shedding resistance decreases, drying cracks are more likely to occur during manufacturing, and the yield decreases. It should be noted that the above preferred range of bulk density is applicable only when a coating material having the preferred component composition described above is used, and cannot be discussed in the same way for coating materials having different component compositions. The reason for this is that even if the bulk density is within a suitable range, if the component composition differs, the viscosity of the generated slag and the blowing strength of the arc will differ, making it difficult to achieve appropriate penetration. The method of adjusting the bulk density of the coating is not particularly limited, but the most common methods include adjusting the particle size composition of the coating material raw material, adjusting the pressure when applying it to the outer periphery of the mild steel core wire, the above-mentioned method,
Examples include methods that combine the following. The present invention is configured as described above, and by specifying the component composition of the coating material and adjusting the bulk density of the coating within a specific range, particularly after firing, it is possible to significantly improve the shedding resistance of the coating. It became a matter of fact. As a result, high-speed welding using high current becomes possible, and arc instability and insufficient shielding caused by shedding of the coating are eliminated, making it possible to achieve the two major requirements of welding efficiency and joint performance improvement all at once. Ta. In addition, if the requirements specified by the present invention are satisfied, drying cracks in the coating during production are extremely low, and the yield is improved. Next, experimental examples will be given to clarify the structure and effects of the present invention. Experimental example 1 A coating material having the composition shown in Table 1 (particle size composition is shown in Table 2) was applied to a mild steel core wire (5.5 mmφ x 450 mml).
The coating was applied to the outer periphery at a coating pressure of 55 kg/cm ² and a speed of 270 m/min, pre-dried at 50 to 100°C for 1 hour, and then fired at 400°C for 1 hour to form a low-hydrogen coating for vertical downward welding. Manufactured arc welding rods. Using each of the obtained welding rods, test pieces (material: SM-50, cross-sectional shape: 2nd
The vertical weld line shown in Figure) was welded downward at a current of 360A (AC). At this time, the number of times the coating fell off, welding workability, and physical properties of the obtained welded parts were investigated, and the results shown in Table 1 were obtained.

【table】

[Table] From Table 1, the following conclusions can be drawn. (1) Comparison bars B-1 and B-2 have SiO ₂ content outside the specified range, and in the case of insufficient SiO 2 (B-1), penetration is insufficient due to poor slag viscosity and weak arc force. , resulting in poor fusion. On the other hand, in the case of excess (B-2), the slag becomes vitrified and peeling becomes extremely difficult. (2) Comparison bars B-3 and 4 have carbonate content outside the specified range; in the case of insufficient carbonate (B-3), blowholes occur due to insufficient shielding, and in the case of excess (B-4). ) penetrates deeper and many undercuts occur in the final finishing layer. (3) Comparison bars B-5 and B-6 have metal fluoride content outside the specified range; in the case of insufficient metal fluoride (B-5), the porosity prevention effect is insufficient and blowholes occur.
In the case of excess (B-6), the fluidity of the slag becomes too large and precedes the weld metal, causing the slag to become entangled in the weld metal. (4) Comparison bars B-7, 8, 9, and 10 have deoxidizing metal content outside the specified range, so if there is a shortage (B-
In case 10), blowholes and pits occur due to insufficient deoxidation, and in case of excessive deoxidation (B-7, 8 and 9), the weld metal becomes hard and crack resistance deteriorates. (5) Comparative bars B-8, 11, and 12 have coating bulk densities outside of the specified range, and in all cases, the coating fell off during welding. Moreover, when the bulk density was too high (B-12), vertical cracks were observed in the coating before welding. (6) In contrast, the welding rods (A-1 to A-14) that satisfy the requirements of the present invention have no shedding of the coating during welding, no problems with welding workability, and no problems such as slag entrainment or blowholes. A sound weld is obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the bulk density of the coating and the number of times it falls off, and FIG. 2 is an explanatory diagram showing the shape of the welded part employed in the experimental example.

Claims (1)

[Claims] 1 A coating agent containing SiO ₂ : 3 to 8% by weight, carbonate: 30 to 60% by weight, metal fluoride: 0.5 to 8% by weight, and deoxidizing metal: 3 to 15% by weight is applied to the outer periphery of the mild steel core wire. A low-hydrogen coated arc welding rod for vertical downward welding, which has been fired, has a bulk density of 1.9 to 3.0 g/cm ³ after firing. Excellent low-hydrogen coated arc welding rod for vertical downward welding.