JPS61154794A - Cored wire for non-shielded arc welding - Google Patents

Abstract

PURPOSE:To make possible the low-voltage welding with a DC reverse polarity by contg. separately from each other and tightly a low melting component and high melting component as a flux into the inside space of a hollow sheath. CONSTITUTION:The hollow sheath 1 consisting of a mild steel hoop of a cored wire is made into a special shape and the low melting component 3 and high melting component 2 of the flux are separately from each other and tightly contained into the inside space thereof to form the cored wire for non-shielded arc welding. The component 2 is made to the thickness which does not exceed 1/3 the outside diameter of the sheath 1 from the inside surface thereof. The component 3 is composed of 20-80wt% iron powder. 5-20% >=1 kinds among the fluorides of Na, K and Ba, 1-15% Fe-Si and 5-30% Fe-Mn. The component 2 is composed of 15-50% fluorite, 5-40% CaCO3, 5-25% wollastonite, 5-20% rutil, 5-20% magnesia clinker and 5-20% >=1 kinds among the silicofluorides of Na, K and Ba.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The results of research and development on a cored wire for unencapsulated gas welding that has excellent low-temperature toughness of the weld metal and is inexpensive are proposed below.

For so-called unencapsulated arc welding that does not use shielding gas or diffused flux, there are two methods: a solid wire method that uses a mild steel wire containing Aβ, T1, or Zr, and a cored wire method that uses a hollow sheath made of a mild steel hoop and fills the inner space with flux. method (or flux-cored wire method) is known.

Regarding the improvement of the latter of both types, the technical content described in this specification is mainly aimed at minimizing the absorption of N gas in the air, and especially at adapting to the welding conditions at low voltage. There is.

In the unencapsulated arc welding method using a cored wire, the inner space of the wire sheath is filled with flux, which is mixed with a gas generating component, and the shielding gas generated by the cored wire itself and the generated molten slag are used to remove the droplets at the tip of the wire. It is characterized by protection from the outside air.

Therefore, it has the advantage of being less affected by the welding environment, especially wind, and the cored wire weighs 10 to 20 kg.
Because it is wound into coils or spools in small units, continuous welding is possible, and unlike coated arc welding rods, there is no need to change the welding rod, and there is no loss of the gripping part. .

(Prior Art) Many proposals have been made for this type of unencapsulated arc welding, but most of them contain a large amount of A1, resulting in poor toughness of the weld metal. The result is that it is bad (for example,
(See Publication No. 771).

Therefore, cored wires are not often used in important structures, and are currently only slightly used for joint welding of foundation piles (steel pipe piles) for civil engineering.

In addition, this type of cored wire contains a low melting point component mainly made of metal powder as a flux in the inner space of the hollow sheath.
Due to the pre-mixed filling of high melting point components, mainly oxides and fluorides, a phenomenon often referred to as protrusion of unmelted flux during welding often causes non-compliance, especially under low voltage welding conditions. It was.

(Problems to be Solved by the Invention) It is an object of the present invention to provide a cored wire for non-encapsulated gas welding that is free from β addition, has no defects, and can obtain a weld metal with good toughness. When this type of unencapsulated gas welding is performed using DC reverse polarity, which is advantageous for preventing nitrogen absorption into the weld metal, which is the cause of the above defects, protrusion of unmelted flux often occurs. However, the present invention aims to overcome this problem and enable low voltage welding with DC reverse polarity.

(Means for Solving the Problem) This invention separates a low melting point component and a high melting point component having the following composition as flux into the inner space of a hollow sheath made of a mild steel hoop, and the high melting point component is Cored wire for unencapsulated arc welding, characterized in that it is tightly housed from the inner surface of the inner surface with a filling thickness not exceeding its outer diameter, and is used in direct current reverse polarity. Low melting point component iron powder: 20 ~ 3Qwt%, at least one of sodium, potassium and barium conjugates = 5-20
wt%, Fe-3i: 1-15 wt%, and Fe
-Mn: 5-3Qwt% High melting point component fluorite = 15-5Q wt%, calcium carbonate = 5-4Q
wt%, wollastonite: 5-25 wt%, rutile 5-2
0Ilit%.

Magnesia clinker: 5 to 20111 t%; and at least one of sodium, potassium, and barium silicate: 5 to 2 Qwt%.

The flux filling rate here is 5% to 20% of the total amount of low melting point components based on the total weight of the cored wire.
The total amount of high melting point components is also preferably 5% to 20%.

Now, the mild steel hoop used for forming hollow sheaths usually has a thickness of 0.1~0.8m+n and a width of 10~30ff11.
Tl, which is formed into hollow sheaths with various cross-sections while entraining flux into the internal space, is then subjected to a drawing process to form hollow sheaths as shown in Figure 1 (a), (b) or (C). Cored wires with various cross-sectional shapes are used.

In the figure, 1 is a hollow sheath, 2.3 is a high melting point component and a low melting point component as flux, and in particular, the high melting point component 2 is at the maximum filling thickness F that does not exceed the outer diameter from the inner surface of the hollow sheath 1. , along with the low melting point component, the hollow sheath 1
tightly housed within the internal space of the

In contrast, conventional cored wires are
They had a cross-sectional shape as shown in e), and most of them were filled with a mixture of a low melting point component and a high melting point component in advance. Therefore, during welding, Fig. 3 (a) ~
Because of the drawback that protrusions 4 of unmelted flux as shown in FIG. 2(d) tend to occur, wires having a smaller diameter or having a complicated cross-section as shown in FIG. 2(e) have been used. However, even if we try to reduce the diameter of the wire, in non-encapsulated arc welding, it is necessary to maintain a certain amount of slag, so the proportion of the cross section occupied by the encapsulated flux becomes large and unmelted. The occurrence of flux protrusion 4 is unavoidable. Similarly, for objects with a complex cross section as shown in Figure 1(e), as long as high melting point components and low melting point components are mixed, the proportion of the cross section occupied by the included flux will inevitably increase, resulting in unresolved problems during welding. Not only is it impossible to prevent the molten flux from protruding, but the cross-sectional shape is extremely asymmetrical, which causes the wire to be twisted and has problems in feeding performance.

(Function) Therefore, the hollow sheath 1 is made into a cross section as shown in FIG. By setting the filling thickness F of the high melting point component 2 not exceeding the outer diameter of the hollow sheath 1, protrusion of unmelted flux during welding can be effectively prevented.

Note that the hollow sheath itself having a cross-sectional shape as shown in FIG. 2(a) is shown in Japanese Patent Publication No. 44-2336,
In this case, the objective is simply to divide the included flux into two to lead to uniform melting of the electrode.

Next, FIGS. 2(b) and 2(C) show a structure in which the low-melting point component 3 and the high-melting point component 2 can be separately accommodated, and the maximum filling thickness F of the latter can be made within one diameter of the outer diameter of the hollow sheath 1. An example was given.

Another feature of this invention is that in order to perform unencapsulated arc welding without the need to contain a strong nitrogen-fixing element such as A1 in the weld metal, it is necessary to suppress the absorption of N gas in the air. , here, the power supply characteristics must be the opposite polarity of the DC constant voltage characteristics.

That is, when comparing positive polarity and reverse polarity, as shown in FIG. 4, the amount of N in the weld metal is much lower in reverse polarity. However, with reverse polarity, as mentioned in Figure 3, protrusion of unmelted flux is likely to occur, making it impossible to weld under low voltage conditions; therefore, with positive polarity, a large amount of N is required. Therefore, defects are more likely to occur.

According to this invention, the high melting point component 2 that causes the protrusion 4 is
However, by housing the low melting point component 3 separately, the protrusion 4 can be significantly reduced, so that even when the polarity is reversed, welding at a low voltage as shown in FIG. 6 is not hindered. In this invention, composition ranges for both flux components are also essential.

First, regarding the low melting point component, it is necessary that iron powder accounts for 20 wt% or more and 3Q wt% or less of the entire low melting point component. If the iron powder content is less than 20%, the melting point of the inner low-melting point component becomes high, making it easy for unmelted flux to protrude, and furthermore, the amount of welding decreases.

On the other hand, if the iron powder content exceeds 80%, the timing of melting of the flux becomes uneven, and the required amount of other deoxidizing agents and the like cannot be obtained.

Next, sodium buttride, potassium buttride, and barium buttide alone or in a mixture are used as the buttride.
It is necessary that the content be at least 2Qwt% and not more than 2Qwt%. If the amount of debris is less than 5%, the weld metal tends to become porous due to the wire drawing lubricant remaining on the wire surface and hydrogen generated from moisture contained in the flux raw material, and the shielding effect is also reduced. As the weld metal deteriorates, the amount of N in the weld metal increases, making it easier for the performance of the weld metal to deteriorate and for blowholes to occur. On the other hand, if the content of flammable substances exceeds 20%, the potential gradient of the arc column increases due to the neutralization of the arc atmosphere by F gas, making the arc extremely unstable and causing significant spatter. Moreover, since the melting point of the slag is too low, workability, especially in vertical welding, deteriorates.

Next, Fe-5i (40% Si) needs to be 1% or more and 15wt% or less. Fe-3i
If it is less than 1wt%, the weld metal will be insufficiently deoxidized,
Blowholes are likely to occur and the performance of the weld metal will deteriorate. Also, slag tends to adhere to the bead surface,
The removability of the slag also deteriorates. On the other hand, if it exceeds 15 wt%, Si in the weld metal becomes excessive and the performance of the weld metal deteriorates.

Fe-Mn (3Q%Mn) is 5wt% or more and 3Q%Mn
Q wt% or less is required. Fe-M
When n is less than 5 wt%, the amount of Mn in the weld metal becomes too small, resulting in insufficient deoxidation of the weld metal, and blowholes are likely to occur. Moreover, when it exceeds 3Qwt%, the amount of Mn in the weld metal becomes excessive, and cracks in the weld metal tend to occur.

Next, regarding the high melting point components, fluorite accounts for 1% of the total high melting point components.
It is necessary that the content be 5 wt% or more and 5Q wt% or less. If the amount of fluorite is less than 15 wt%, the melting point of the slag will rise, the bead shape will be poor, and the shielding of droplets at the tip of the wire from the air will be incomplete, resulting in an increase in the amount of N in the weld metal. On the other hand, if the fluorite content exceeds 5Q wt%, the melting point of the slag will drop too much, resulting in poor vertical welding workability and an increase in spatter.

Next, calcium carbonate is 5wt% or more and 4Qwt%
It is necessary that the following is true. Calcium carbonate is 5wt
If it is less than %, the melting point of the slag will drop too much, making it difficult to weld in an upright position, and shielding of droplets at the tip of the wire will be incomplete, resulting in N and H in the weld metal.
The amount increases. On the other hand, when calcium carbonate exceeds 4Q wt%, the scattering (spatter) of droplets at the tip of the wire increases due to decomposition due to arc heat.

The content of wollastonite must be 5% or more and 25% or less by weight. Wollastonite improves welding workability, but if it is less than 5 wt%, the effect cannot be expected;
If it exceeds wt%, Si02 content becomes excessive and the performance of the weld metal deteriorates.

Rutile needs to be 5 wt% or more and 20 wt% or less. Rutile improves welding workability without lowering the basicity too much, but if it is less than 5 wt%, no such effect can be expected, and if it exceeds 20 wt%, the basicity will drop too much and the performance of the weld will deteriorate. Magnesia clinker has the effect of raising the melting point of slag, but 5w
If it is less than t%, no effect can be expected, and if it exceeds 20wt%, the melting point of the slag will rise too much, resulting in poor bead shape.

In addition, the high melting point component is 5wt% or more of sodium silicofluoride, potassium silicofluoride, barium silicofluoride, or a mixture of silicofluoride, and 2Qwt.
% or less.

If the content of silicofluorides is less than 5 wt%, the weld metal tends to become porous due to the hydrogen generated by the wire drawing lubricant remaining on the wire surface and the moisture in the flux, and the shielding properties deteriorate. As the amount of N increases, performance deterioration of the weld metal and blowholes are more likely to occur. On the other hand, if the content of silicofluorides exceeds 20%, the potential gradient of the arc column increases due to the neutralization of the arc atmosphere by F gas, making the arc extremely unstable and causing significant spatter. Moreover, since the melting point of the slag is too low, workability, especially in vertical welding, deteriorates. Next, regarding the filling rate of the flux, it is desirable that the amount of the low melting point component is 5 to 2 Qwt% and the amount of the high melting point component is 5 to 20 IIlt%, based on the total weight of the flux-cored wire. In other words, if the amount of the low melting point component is less than 5 wt%, the alloy component in the weld metal will be low and the performance of the weld will deteriorate. Also,
If it exceeds 2 Qwt%, the alloy components in the weld metal will become too high, causing problems such as performance deterioration of the weld and cracking.

On the other hand, if the amount of high melting point components is less than 5wt%, shielding of the droplets at the tip of the wire will be incomplete, leading to an increase in the amount of N in the weld metal, and in the worst case, defects such as blowholes will occur. . Moreover, if it exceeds 20 wt%, the amount of slag becomes excessive and the bead shape deteriorates.

(Example) Table 1 shows blending examples of flux components for compatible examples according to the present invention and comparative examples.

After wrapping these fluxes with respect to the total weight of the wire at a predetermined filling rate listed in Table 1, a cored wire with a diameter of IQ mm was manufactured through a wire drawing process. This wire was wound into a coil and unencapsulated arc welding was performed under the following welding conditions to examine welding workability and mechanical performance of the welded part.

(1) Welding conditions: welding current 25 OA, arc voltage 2
0V welding speed IQ cm 7m in.

Polarity RP (rod positive) Power supply characteristics: DC constant voltage extension: 2011MIl (2) Material to be welded: Steel plate SM-5OA (plate thickness 20m
m) Mechanical performance of welded parts is shown in Table 2, comparing conforming examples with comparative examples for all weld metals.

According to the present invention, it is possible to perform non-encapsulated arc welding that allows obtaining a high-toughness weld metal without using special raw materials such as Al-Mg.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a cored wire according to the present invention, Fig. 2 is a sectional view of a conventional cored wire, and Fig. 3 is a schematic % formula for the occurrence of protrusion of unmelted flux. Figure 5 is a graph showing the influence of the filling thickness of the high melting point component on the appropriate minimum voltage. 1...Hollow sheath 2...High melting point component 3...
・Low melting point component 4... Protrusion Figure 3 Figure 4 /6 /7 f8 /q2D2f22 237-
ritffi ('bit) Figure 5

Claims (1)

[Claims] 1. A low melting point component and a high melting point component having the following composition are separated from each other as a flux in the inner space of a hollow sheath made of a mild steel hoop, and the high melting point component is distributed from the inner surface of the hollow sheath to the outside. A cored wire for non-encapsulated arc welding, which is characterized by being closely packed in a filling thickness not exceeding 1/3 of the diameter and used in direct current reverse polarity.Low melting point component iron powder: 20 to 80 wt% , at least one of sodium, potassium, and barium fluorides: 5 to 20 wt%, Fe-Si: 1 to 15 wt%, and Fe-Mn: 5 to 30 wt%, high melting point component fluorite: 15 to 50 wt%, carbonic acid Calcium: 5-40 wt%, wollastonite: 5-25 wt%, rutile 5-20 wt%, magnesia clinker: 5-20 wt%, and at least one of sodium, potassium, and barium silicofluorides: 5-20 wt%