JPS599276B2 - Melting type flux for submerged arc slope welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a melting type flux for submerged arc welding that exhibits good welding workability, particularly in oblique welding of plates thinner than 20 mm.

In recent years, the submerged arc welding method has been widely applied to horizontal downward welding, horizontal fillet welding, horizontal horizontal welding, etc. from the viewpoint of high efficiency and welding work environment.

One field in which the submerged arc welding method is applied is inclined welding in which the weld line has an inclination angle with respect to the horizontal plane, such as in spiral steel pipe manufacturing. By the way, in such inclined welding, the weld metal flows along the weld line. This can now be explained schematically as follows. That is, FIG. 1a schematically represents the main part of the process of spiral pipe making and welding, in which hot rolled coil material 3 is continuously fed into a pipe making machine via straightening rolls 4, and first, The inner surface is welded using a steel pipe inner surface submerged arc welding machine 2, and after half a circumference, the outer surface is welded using a steel pipe outer surface submerged arc welding machine 1, thereby producing a spiral steel pipe 13. Of these, the internal submerged arc weld (inside circle A in FIG. 1a) is enlarged, and the cross section of the weld is schematically shown in FIG. 1b. In the case of the same figure, the state of downhill welding, which is a type of inclined submerged arc welding, is shown, and the phenomenon of the welded part can be qualitatively explained as follows.
The electrode 5 of the steel pipe inner surface submerged arc welding machine generates an arc between it and the base metal 14 within the flux layer 6, forming an arc cavity 9, molten metal 8, and welding slag layer 7, and welding progresses. The molten metal 8 tends to flow in the flow direction G shown in the figure due to gravity, but the molten metal is affected by the arc pressure in the arc 9, the resistance of the molten slag layer 7 whose kinematic viscosity is more than 100 times greater than that of the molten metal, Alternatively, the flow is suppressed by pressure caused by the flux layer 6 or the like. However, if the characteristics of the flux, welding conditions, etc. are inappropriate, the flow of the molten metal becomes excessive. Figure 2 is a schematic diagram of a bead cross section with typical defects in inclined submerged arc welding. Such defects occur.

That is, in downhill welding, the molten metal 8 moves in the welding direction G.
The bead flows into the arc cavity 9, and solidification is delayed.In other words, a concave portion is formed in the center of the bead, where it remains in a molten state for a long time, and solidification is completed and a concave is generated. Further, as the flow of molten metal 8 in direction G increases, the depth of concave 10 increases. Furthermore, as the flow of molten metal 8 becomes larger, in addition to flowing into the arc cavity 9,
The molten metal 8 begins to flow in the bead width direction, the bead rising angle α becomes large, and when the degree of the rising angle α increases further and the rising angle α becomes 900 or more, an overlap 11 occurs. On the other hand, although not shown, in the case of uphill welding, the molten metal 8 flows in the opposite direction to the welding direction G, making it impossible for the base metal 14 to completely fill the groove dug by the arc. A cut 12 occurs. In particular, when performing high-current welding to improve efficiency, the commonly used simple MnO-SiO2 type melting flux cannot suppress the flow of molten metal due to gravity (hereinafter referred to as molten metal flow). This will result in poor welding workability.

Therefore, there is no occurrence of welding defects as shown in Fig. 2.
There is a strong desire to develop welding materials that have welding workability that can withstand high-efficiency welding, that is, high-current welding. Therefore, the inventors of the present invention have conducted various studies to solve this problem from the perspective of flux, as a means to prevent such defects in inclined welding. As mentioned above, defects such as concave, overlap, and undercut in inclined welding are caused by the flow of molten metal.

In order to prevent such a flow, it is necessary to do the following. In order to prevent melt flow, the deformation resistance of the flux and slag layer covering the molten metal must be increased. Figure 3 shows the flow of two layers of slag and molten metal approximated by a one-dimensional flow, a numerical solution obtained using an electronic computer, and the behavior of the change in flow velocity at the slag-molten metal interface over time classified into slag viscosity and slag layer thickness. This is what was shown. As shown in FIG. 3, it can be seen that when the slag has a high viscosity or the slag layer is thin, the flow velocity at the slag-molten metal interface decreases and the flow of the molten metal is suppressed. The deformation resistance of the slag layer, that is, the magnitude of the force required for deformation, is proportional to the product of viscosity and flow velocity gradient. When the slag layer thickness is thin, the flow velocity gradient becomes large, and when the slag viscosity becomes large, the deformation resistance increases. The validity of the above theoretical estimation was confirmed by actual welding, and the present inventors previously proposed the following contents in Japanese Patent Application No. 52-96760 as a flux to realize this.

That is, in terms of weight ratio, SlO23O~65%, MrlOl
The flux has a bulk density of 1.259/C with O~50%, MgO5~30%, and CaF2l5% or less as the main components.
! This is a melting type flux for submerged arc inclined welding, which is characterized by a weight of 1 ton or more and a crystallization degree of 10% or more, and when welding with this flux, a thin slag layer with a high viscosity is formed. This flux is a material for spiral steel pipes, and the thickness of the hot-rolled coil is approximately 207mm! Submerged arc inclined welding (hereinafter referred to as thick welding), which is performed at temperatures above Tm and at relatively low welding speeds even with high efficiency welding, does not produce the various welding defects mentioned above and forms a good bead with a stable shape. It is something to do. However, as the inventors continued their studies, they found that submerged arc inclined welding (normally, the thinner the plate thickness is, the faster welding is performed) when the hot rolled coil plate thickness is thinner than approximately 2011 mm, or when the hot rolled coil plate thickness is thinner than approximately 2011 mm. When the welding speed is higher even when the plate thickness is around 201m or more (the welding speed is approximately 1
It has been found that in submerged arc inclined welding (hereinafter collectively referred to as thin welding) of 50CrI1/Mln or more), there are some difficulties in the alignment of the weld edges and the uniformity of height of the bead obtained by using the flux. In other words, when welding at high speeds such as when welding thin materials, arc fluctuations tend to affect the stability of the bead, but if the slag layer is thick, the slag layer becomes uneven, causing local deformation of the molten metal. Or, the base metal may be melted by secondary melting (the base metal is melted by conduction heat from the molten metal in addition to being directly melted by arc heat), and the bead uniformity may be reduced. is achieved. However, one of the characteristics of this flux is that it increases the crystallization rate and thins the slag layer formed by welding, and although such flux is suitable for welding thick materials, it has problems with arc fluctuations. When welding thin materials that are susceptible to the effects, the flux sintered part on the outer periphery of the slag layer acts as a wall, and the slag layer cannot act as a buffer to absorb the effects of arc fluctuations. Fluctuations and secondary melting of the base metal are limited and bead uniformity is inhibited. Therefore, if the condition of increasing the crystallization rate is met, the uniformity of the bead can be ensured, but at the same time the effect of suppressing the melt flow, which the flux has, will be sacrificed. Therefore, in order to vitrify the flux, some kind of measure is needed to overcome the effect of suppressing the melt flow. One possible solution to this problem is to increase the viscosity of the slag layer. Figure 4 shows the relationship between flux viscosity and temperature for each component. This viscosity is a value measured by the coaxial double cylinder rotation method, and flags A, B, and C are M, 1vr10, s102, caF2.
The main component is CaO,603,F, which is an unavoidable component.
The total amount of e0 etc. is 7.6%, 12.0%, 21 respectively.
．． The viscosity was changed to 5%. Further, FIG. 5 shows the relationship between flux viscosity, steel plate thickness, and weld bead. For each of the components of the waterfalls A, B, and C, we prototyped vitrified flux (with a degree of crystallinity of about 0%) and crystallized flux (with a degree of crystallinity of about 80%). Material 9, 12.7, 16, 20,
25m77! Thick steel plates were welded downhill at a 6° inclination. The heat input is 13.2, 13.4,
16.2, 21, 4, and 26.0 kJ. Further, the viscosity on the vertical axis in the same figure shows the viscosity at 1400° C. as a representative value. No melt flow is observed in the weld bead with crystallized flux, but when the plate thickness is less than 16 mm, the alignment and height of the heel of the bead become somewhat unstable, and the crystallized flux is 20 m7! It was insufficient for use in welding thinner than L. On the other hand, beads made from vitrified flux have good bead uniformity, but only 251! In the case of Lm, hot water flow was observed, and vitrification flux (medium 20m7
! It is insufficient for use in welding plate thicknesses greater than L. In addition, when the viscosity of the vitrified flux is low, molten metal flow occurs, and especially when the plate thickness is large, the concave caused by the molten metal flow is significant. In this way, when welding thin materials, it is essential that the vitrified flux has a viscosity above a certain level in order to suppress flow. In addition to viscosity, Mg
The effect of O was also observed. Figure 6 shows MgO-MnO-
The graph shows the relationship between the MgO content and the arc length during welding when the MgO content is varied in the SiO2-CaF2 flux. Arc length is 800A, 26V,
In flat plate submerged arc welding using an AC single electrode, X-rays were irradiated from a direction perpendicular to the direction of welding progress, and the distance between the steel plate surface and the electrode tip was measured. When the MgO content in the flux exceeds 10%, the arc length becomes short and the bead shape becomes convex. In other words, it is thought that the arc length becomes shorter and the arc force that pushes the molten metal backward increases, improving the effect of suppressing the flow of molten metal. Figure 7 shows SM4
L material 257nm steel plate (bevel depth 6 degrees, groove angle 60°)
MgOMnO-SiO2-CaF2 with a 2-electrode welder and a welding speed of 110Cr1L/Min (human heat amount 26kJ).
The relationship between the rising angle α of the concave depth h1 bead heel end and the flux bulk density is shown in Fig. As the bulk density increases, the concave depth h1 bead rise angle α decreases.

As the bulk density increases, the pressure within the flux layer increases,
The frictional force against deformation increases, and the deformation resistance of the flux layer increases. In other words, it can be seen that as the bulk density increases, the flow of the molten metal is suppressed. Based on this knowledge, the flux of the present invention satisfies the above-mentioned factors of preventing melt flow, prevents defects such as concave, overlap, and undercut in inclined welding of plates thinner than 20 mTL, and improves bead uniformity. It was developed to ensure that

That is, in the present invention, SiO2 is 35 to 65% by weight, M
nOlO~40%, MgOlO~40%, CaF2O.
A fusion type flatus for submerged arc inclined welding, characterized in that the main component is 5 to 15%, the unavoidable component is 15% or less, the flux bulk density is 1.259/d or more, and the crystallinity is less than 10e. be. In addition, the bulk density here is JIS
Flux crystallinity is defined by the following formula and indicates the degree of crystallization of flux.

In addition, unavoidable components are CaO, FeO, Fe2O3, A
! 03, Na20, K201, and one or more impurities that are present in trace amounts and are unavoidably contained in the flux raw material. Crystallinity degree 1 [(weight of crystalline particles in flux)
:(Total flatus weight)]×100 The present invention will be explained in detail below.

First, SlO2 is added to increase the slag viscosity, but if the SlO2 amount is less than 35%, the slag viscosity becomes too small and flow occurs, and if it is more than 65%, the bead surface r
Wrinkles occur and the appearance of the bead is damaged.

MnO is added to increase the bulk density of the flux and to form a uniform slag layer, but if the amount of MnO is less than 10%, it will be impossible to form a uniform slag layer, resulting in poor bead uniformity. In addition, the bulk density of the flux decreases and flow occurs. On the other hand, if it exceeds 40%, the viscosity decreases,
A flow of hot water occurs. MgO is added to shorten the atta length and adjust the viscosity, but when the amount of MgO is 1
If it is less than 0%, the arc length becomes longer as shown in Figure 6,
A flow of hot water occurs. If the amount is more than 40%, the slag melting point will become too high and a uniform slag layer will not be formed, resulting in unstable bead width and bead height.

CaF2 is added to adjust the viscosity and melting point of the slag, but if the amount exceeds 15%, the viscosity and melting point will decrease and flow will occur. Also, if it is less than 0.5%, Ca
There is no effect of F2 addition. In other words, the bead shape becomes unstable and avatars tend to occur. Incidentally, the degree of crystallization of the flux and the thickness of the welding slag layer are closely related as described above. As mentioned above, the flux of the present invention has a low degree of crystallization to ensure bead uniformity when welding thin materials, and since the welding slag layer thickness increases, the thin slag layer suppresses metal flow. The effect of this has been diminished. Therefore, it is necessary to ensure sufficient viscosity in order to improve the effect of suppressing the flow of hot metal. Generally, the more multi-component the system is, the lower the melting point and viscosity will be. Therefore, MgO, MnO, SiO2, CaF that determine the skeleton of the flux component of the present invention
It is desirable to keep the amount of components other than 2 as small as possible. As shown in FIG. 4, the amount of unavoidable components has a large effect on the viscosity of the flux, so in view of the welding results shown in FIG. 5, this amount must be reliably limited to 15% or less. Such components are Mn in MnO-based flux.
Since O is contained in quite large amounts in raw materials, it is necessary to carefully examine and select its components. Further, as shown in FIG. 7, when the flux bulk density is less than 1.259/d, melt flow occurs, the rise angle increases, and concave occurs.

If the bulk density is 1.259/d, the bead shape will be good, so there is no upper limit set, but in practice it is 2.0 f1.
/Cd is possible. As mentioned above, increasing the degree of crystallization reduces the thickness of the slag layer and prevents flow of the molten metal, but there is a slight difficulty in bead uniformity when welding thin materials.

Therefore, when welding thin materials, it is necessary to vitrify the flux and stabilize the bead shape in order to minimize the latent heat taken away when the crystals in the flux melt and to ensure a certain slag layer thickness. For this purpose, the flux is poured into water after being dissolved and rapidly cooled. However, the method of introducing the molten flux into the water depends on whether the molten flux is introduced in small amounts at a time, in large quantities all at once, or in such a way that the molten flux is scattered by pressurized water. Therefore, the degree of crystallization of the flux fluctuates, albeit to a small extent. In the flux component of the present invention, when the degree of crystallization exceeds 10%, the width and height of the bead become somewhat unstable. Of course, a degree of crystallinity of 0% is desirable, but 1
If it is less than 0%, sufficient bead uniformity is ensured.
For this reason, when producing flux, it is desirable to pour it into water in small amounts after melting, and to disperse it with pressurized water, so that the whole is uniformly quenched. However, in this case, if the amount of carbon added to the raw material of the flux as a conductive agent or for other purposes is too large, bubbles will form in the flux after water cooling and the bulk density of the flux will decrease, so the amount must be limited to an appropriate amount. Must be. Incidentally, since the grain size of the flux does not have a large effect on the present invention, it is sufficient to make the grain size finer than the common sense grain size, that is, 8 meshes. The effects of the present invention will be specifically explained below using Examples.

Table 1 shows the chemical composition of the sample flux and various properties of the flux.

Claims (1)

[Claims] 1 SiO_235-65%, MnO10-4 by weight ratio
0%, MgO10-40%, CaF_20.2-15%
is the main component, and the unavoidable components are 15% or less, the bulk density of the flux is 1.25 g/cm^3 or more, and the degree of crystallinity is 1.
A melting type flux for submerged arc slope welding, characterized in that the flux is less than 0%.