JPH0647191B2 - Flux-cored wire for gas shield arc welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to welding defects such as pits, gas grooves and blow holes in the welding of primer-coated steel sheets, which are widely used in the fields of shipbuilding, bridges, steel frames and the like. The present invention relates to a flux-cored wire for gas shielded arc welding, which is capable of obtaining few high-quality welded parts with high efficiency.

(Prior Art) In recent years, the use of flux-cored wires has increased remarkably in terms of high welding efficiency and good welding workability when flux-cored wires are used. The flux-cored wire has a welding efficiency that is more than twice that of the coated arc welding rod, and has less spatter during welding than the solid wire. Further, due to the effect of the contained flux, an excellent weld bead appearance can be obtained. For this reason, flux-cored wires have been widely used for butt welding and strain-wall welding of steel materials.

However, many steel materials are coated with a shop primer (anticorrosion paint) before processing such as cutting or welding to prevent rusting, and when the steel materials are welded, various defects such as welding defects are likely to occur. . Particularly, in fillet welding of primer-coated steel sheets, primer decomposition gas such as hydrogen and carbon monoxide generated by welding arc heat penetrates into the molten metal, and pits, gas grooves and blowholes are easily generated. There is a problem in that the original purpose of the flux-cored wire, namely, the high efficiency of welding, has not been achieved due to the reduction and increase in man-hours due to rework.

As a measure for solving such a problem, Japanese Patent Laid-Open No. 52-68040
Japanese Laid-Open Patent Publication No. 52-144341 and Japanese Laid-Open Patent Publication No. 52-144341 have proposed flux-cored wires. In all of these, a predetermined amount of hydrogen is supplied from the shield gas or filling flux to accelerate the gas release rate in the molten metal and release the gas before the molten metal solidifies, thereby welding pits, blowholes, etc. It is intended to prevent defects. However, in these methods, the hydrogen content in the weld metal is large, so the steel type and plate thickness are limited in terms of cracking resistance, and the arc stability is poor, so high-speed welding cannot be performed, etc. There's a problem.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-described problems, and defects such as pits, gas grooves and blow holes are generated even in fillet welding of shop primer-coated steel sheets. It is an object of the present invention to provide a low hydrogen type flux-cored wire for gas shielded arc welding, which has excellent bead appearance and shape while being excellent in high speed weldability.

(Means for Solving the Problem) The gist of the flux-cored wire for gas shielded arc welding according to the present invention is that the potential hydrogen content of the wire is 90.
It is below ppm, and the following components are essential for the total weight of the wire.

The total amount of slag forming agent (A); (in F converted value) 0.3 to 1.0% metal _{fluorides;; 2.5~5.5% TiO 2; 1.5~3.5} % TiO 2 / A; 0.45~0.77 ZrO 2 0.01~0.23% Si 0.3-1.0% Mn; 0.8-2.8% The total (B) of one or more of Al, Mg and Ti must satisfy the following formula: 0.7 ≦ (A / 10) + B ≦ 1.2 The reason why the wire concerned has the above configuration will be described in detail.

(Operation) The inventors of the present invention conducted various experiments on pits, gas grooves (gas indentations), and blowhole generation mechanisms in horizontal fillet welding of primer-coated steel sheets, and as a result, obtained the following findings. Is completed.

(1) Minimize the amount of gas, especially hydrogen, in the weld metal that causes pits and blowholes.

(2) The amount of generated slag is reduced as much as possible to facilitate the release of gas from the molten metal and molten slag.

(3) It is necessary to adjust the strong deoxidizer according to the amount of slag in order to prevent slag encapsulation deterioration (bead shape deterioration) due to the reduction of slag amount.

The present invention has been completed based on the above findings, and the reasons why the present invention is configured will be described in detail below.

First, the reason for limiting the potential hydrogen amount of the wire to 90 ppm or less is as follows. That is, the hydrogen in the wire is contained in the filling flux, the steel shell, and the wire surface deposits.This hydrogen, together with hydrogen in the pyrolysis gas of the primer, increases the hydrogen partial pressure in the arc atmosphere during welding and Intrudes into and causes pits and blowholes.
In order to suppress the pits and blow holes caused by hydrogen, it is necessary to keep the amount of potential hydrogen in the wire as low as possible, and the result of the experiment is 90 ppm or less. The upper limit of the amount was 90 ppm. The amount of potential hydrogen in the wire is the total amount of hydrogen extracted by heating to 2000 ° C. or higher in an inert gas atmosphere, and is the sum of the amounts of hydrogen contained in the filling flux, the outer coat and the surface deposit.

The gas grooves that are characteristic of horizontal fillet welding of primer-coated steel sheets due to the flux-cored wire are generated due to the slag on the bead surface hindering the release of gas.The larger the amount of slag, the stronger the tendency. To be Therefore, as a result of an experiment on the relationship between the slag amount, that is, the total amount of the slag forming agent in the wire and the frequency of occurrence of surface defects such as pits and gas grooves, if the total amount of the slag forming agent is 5.5% or less, these defects can be significantly reduced. I understood. On the other hand, if the amount of slag is extremely small, the surface of the horizontal fillet beads will not be uniformly covered with the slag, and the bead shape and appearance will be deteriorated and the high-speed weldability will be sacrificed. In order to satisfy both the slag encapsulation property and the high speed weldability, 2.5% or more of the slag forming agent is necessary even if the slag composition described below is adjusted. Therefore, the total amount of slag forming agent in the wire is 2.5-5.5%. The slag forming agent includes oxides such as TiO ₂ , metal fluorides and metal carbonates.

TiO ₂ is the main component of the flux in the present invention,
It is an essential component as a slag former and as an arc stabilizer. That is, TiO ₂ has the function of improving the fluidity of the slag, uniformly encapsulating the entire bead, and adjusting the shape of the fillet bead. It also acts as an arc stabilizer,
It has the effect of maintaining a stable arc. TiO ₂ content is 1.5
If it is less than%, the above effect is not exhibited and the slag does not cover the entire surface of the bead, so that a good appearance and shape cannot be obtained. Spatter also increases. On the other hand, if it exceeds 3.5%, slag encapsulation,
Although the beaded shape is improved, the slag viscosity is increased and gas emission is hindered, resulting in frequent pits and gas grooves.
Therefore, the range of addition of TiO ₂ is 1.5 to 3.5% of the total weight of the wire.
And

The reason for limiting the amount of TiO ₂ in the total amount (A) of the slag forming agent is as follows. That is, when TiO ₂ / A exceeds 0.77, the arc stability and the bead shape are good, but the viscosity of the slag is high and the generation of pits and gas grooves cannot be suppressed. On the other hand, when TiO ₂ / A is less than 0.45, the amount of TiO ₂ is relatively decreased, so that the arc stability is deteriorated and the bead shape and appearance are deteriorated. Therefore, TiO ₂ / A is 0.45 to 0.77.

ZrO ₂ has the effect of adjusting the viscosity of the slag, improving the slag encapsulation in the present invention in which the amount of slag is kept low,
In order to obtain a good bead shape, it is an essential component together with TiO ₂ . If ZrO ₂ is less than 0.3%, the slag encapsulation effect cannot be expected and the bead shape deteriorates. On the other hand, if it exceeds 1.0%, the slag becomes viscous and becomes dense, so that the generated slag inhibits the release of gas and the formation of pits and gas grooves becomes remarkable. Therefore, the amount of ZrO ₂ added is in the range of 0.3 to 1.0%.

The metal fluoride adjusts the viscosity of the slag to make the fillet bead shape smoother and to improve the compatibility with the base material.
The stirring action of the molten metal facilitates the release of gas and is effective in reducing pits and blow holes. Metal fluoride is F
If the converted value is less than 001%, the above effect is not observed and the pit,
If blowholes occur and the amount exceeds 0.23%, the fluidity of the slag becomes excessive, the slag encapsulation and bead shape deteriorate, and the arc becomes unstable. 0.01 to 0.23%. As the metal fluoride, a fluoride such as Li, Na, K, Mg, Ca, Al or an alkali metal silicofluoride compound such as K ₂ SiF ₆ is used.

Si mainly functions as a deoxidizer, improves the mechanical properties of the deposited metal, and improves the familiarity of beads. However, if it is less than 0.3%, pores will frequently occur due to insufficient deoxidation and the bead will not fit well. On the other hand, if the amount of Si added exceeds 1.0%, the mechanical properties of the deposited metal, especially the impact value, will deteriorate, so the amount of Si added should be 0.3-1.0%.

Mn also has a function as a deoxidizing agent similar to Si, and improves the mechanical properties of the deposited metal, but if it is less than 0.8%, pores are generated due to insufficient deoxidation, while if it exceeds 2.8%, Mn of the deposited metal Since the strength becomes too high and the impact value deteriorates and cracks occur, the amount of Mn added is 0.8 to 2.8%.

If the above requirements are satisfied, pits and blowholes are unlikely to occur, and a horizontal fillet bead with a good bead shape and appearance can be obtained, but if welding is accelerated, the slag will recede and the encapsulation property will partly deteriorate. There is a case. Therefore, we further examined the conditions under which stable slag encapsulation was obtained even in high-speed welding. As a result, they have found that it is effective to add an appropriate amount of one or more of Al, Mg and Ti according to the amount of slag.
That is, only the amount of the slag forming agent is changed stepwise while keeping the addition ratio of each slag forming agent constant, and at the same time, the flux with various addition amounts of Al, Mg, and Ti is filled into the steel shell,
A wire having a diameter of 1.2 mm and having a cross-sectional shape shown in FIG. In this case, the amount of the slag forming agent was changed in the range of 2.0 to 6.5%, and the total amount of Al, Mg and Ti was changed in the range of 0 to 1.2%. FIG. 2 is a graph of experimental results showing the slag encapsulation property and the primer resistance in horizontal fillet welding of these trial wires. However, the welding conditions under which this experiment was performed are as follows.

<Welding conditions> ・ Test steel plate; SM-50B, 12.7t (Inorganic zinc primer is applied to a thickness of 20 to 25 μm) ・ Test plate shape: T-shaped fillet welding test plate ・ Welding position ； Horizontal fillet welding ・ Welding current; 300A-Welding voltage: 33V-Welding speed: 80cm / min-Wire protrusion length: 25mm-Torch angle; 45 ° from lower plate (advancing angle 5 °) -CO ₂ flow rate: 20 / min From Fig. 2, slag agent When the total amount (A) is in the range of 2.5 to 5.5%, the relationship between Al + Mg + Ti amount (B) and A is (A / 10)
When + B is less than 0.7, at the welding speed of 80 cpm, the slag does not completely cover the bead surface, and the beads are uneven. On the other hand, when (A / 10) + B exceeds 1.2, the slag encapsulation and the bead appearance are improved, but many pits and gas grooves are generated. (A / 10) + B
In the range of 0.7 to 1.2, slag encapsulation, bead appearance and primer resistance were all good. Therefore, the relationship between the total amount (A) of the slag agent and the total amount (B) of one kind or two or more kinds of Al, Mg, and Ti is 0.7 ≦ (A / 10) + B ≦ 1.2. Thus, depending on the amount of slag agent, A which is a strong deoxidizer
It was found that by adjusting the addition amounts of l, Mg, and Ti, welding defects such as pits and gas grooves can be prevented while maintaining good slag encapsulation and bead shape even in high-speed welding. The reason for this is presumed as follows. That is, by adding the strong deoxidizers Al, Mg, and Ti, the consumption of Si and Mn having a weaker deoxidizing power, especially Mn, is suppressed, and MnO in the slag is reduced. Since this MnO has the effect of lowering the melting point and viscosity of the slag, especially when the amount of slag is small, molten slag tends to flow to the lower leg side of the bead in horizontal fillet welding, and the slag encapsulation of the upper leg part tends to deteriorate. Show. By controlling the addition amounts of Al, Mg, and Ti within the range of the present invention, excessive MnO production is suppressed, and deoxidation products of higher melting point Al ₂ O ₃ , MgO, and TiO ₂ are provided to the slag. It is considered that the slag composition has an appropriate viscosity and melting point, and the slag encapsulation property and the primer resistance are improved. If the amount of Al, Mg, and Ti added is small relative to the amount of slag, the above effect cannot be expected. Conversely, if the amount of these strong deoxidizers is too large, the viscosity of the slag increases and gas release is impaired, and The primer property deteriorates.

The above is the main configuration of the present invention, in order to stabilize the arc and improve the bead shape by adjusting the slag physical properties, the above
Other than TiO ₂ and ZrO ₂ , for example Na ₂ O, K ₂ O, Li ₂ O, SiO ₂ , MnO,
Al ₂ O ₃ , MgO, FeO, oxides such as Fe ₂ O ₃ , CaCO ₃ , MgCO ₃ , K
Carbonates such as ₂ CO ₃ and Li ₂ CO ₃ can be added within a total amount of 5.5% or less.

In order to improve the mechanical properties of the weld metal, Ni, Mo,
Alloying elements such as B can be added, and iron powder can be added for the purpose of increasing the deposition rate.

Further, in the present invention, the flux filling rate can be selected within the range of 7 to 20% as long as the above conditions are satisfied, and the wire diameter is not particularly limited, but a small diameter of 1.0 to 2.0 mm is desirable in terms of the welding speed. The cross-sectional shape of the wire can be any of those shown in Fig. 1, but considering automation and robotization, the seamless wire shown in Fig. 1 (d), which has good wire straightness and feedability, is most suitable. . Ar-CO ₂ in addition to CO ₂ as the shielding gas composition when welding further using the present invention wire, Ar-O ₂
Etc. are also applicable.

Even if horizontal fillet welding of a shop primer-coated steel plate is performed at high speed using the flux-cored wire configured as described above, a good horizontal fillet bead shape with few pits, gas grooves, and blow holes can be obtained.

Next, the wire of the present invention will be described more specifically based on Examples.

(Example) Table 1 shows the flux compositions of the wire of the present invention and the comparative wire (numerical values of the flux components in the table are percentages with respect to the total weight of the wire). Both are mild steel skins (C; 0.04
7%, Si: 0.01%, Mn: 028%), with the first cross-sectional shape
The flux-cored wire of 1.2 mmφ in Fig. (D) was prepared. Table 2 shows the test results of horizontal fillet welding of inorganic zinc primer-coated steel sheets using these wires.

In Tables 1 and 2, No. 1 and No. 9 are examples of the present invention, N
o.10 to No. 21 are comparative examples. All of No. 1 to No. 9 satisfying the constitutional requirements of the present invention have good primer resistance and high-speed welding workability.

On the other hand, No. 10 has poor primer resistance due to the large amount of potential hydrogen in the wire, and No. 11 has poor slag encapsulation and primer resistance due to the small amount of slag agent and the large amount of strong deoxidizer. No. 12 had too much slag agent and many pits and gas grooves, and No. 13 and No. 14 had TiO ₂ and ZrO.
_The bead appearance and shape are poor because there are few ₂ . No. 1
5, No. 16 and No. 17 are the amount and ratio of TiO ₂ , or Z
Since rO ₂ does not satisfy the requirements of the present invention, the primer resistance and the bead shape are deteriorated. In No. 18 and No. 19, metal fluoride and Si and Mn were out of the scope of the present invention, so that pits were generated over the entire bead line. Furthermore, No. 20, No. 21
Has a large amount of Si and Mn, the performance of the deposited metal deteriorates.
O.21 cracked.

(Effects of the Invention) As described above, the flux-cored wire for gas shield arc welding of the present invention is excellent in welding workability such as good bead appearance / shape and little spatter in fillet welding of primer-coated steel sheet, and This wire has very few pits, blow holes, and gas grooves on the bead surface. Therefore, it is possible to reduce the reworking of the welding bead, which greatly contributes to the improvement of the reliability of the welded portion and the improvement of the welding efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing the cross-sectional shape of a flux-cored wire, and FIG. 2 is a diagram showing the relationship between the total amount of slag forming agent and the addition amounts of Al, Mg, Ti and fillet welding performance. is there. 1: Outer skin, 2: Flux

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Harutoshi Kubota 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa Inside the Second Research Laboratory, Nippon Steel & Co., Ltd. (56) Reference Japanese Patent Laid-Open No. 61-283493 A) Japanese Patent Publication Sho 63-32560 (JP, B2)

Claims (1)

[Claims] 1. A flux-cored wire for gas shielded arc welding, comprising a steel shell filled with flux, wherein the potential hydrogen content of the wire is 90 ppm or less, and the following components are essential with respect to the total weight of the wire. A flux-cored wire for gas shielded arc welding characterized by: The total amount of slag forming agent (A); (in F converted value) 0.3 to 1.0% metal _{fluorides;; 2.5~5.5% TiO 2; 1.5~3.5} % TiO 2 / A; 0.45~0.77 ZrO 2 0.01~0.23% Si 0.3-1.0% Mn; 0.8-2.8% The total (B) of 1 or 2 or more types of Al, Mg and Ti must satisfy the following formula 0.7 ≦ (A / 10) + B ≦ 1.2