JPS5857279B2 - Melting type flux for submerged arc inclined welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a melt-type flux for submerged arc welding that exhibits good welding workability, particularly in inclined welding.

In recent years, the submerged arc welding method has been widely applied to horizontal downward welding, horizontal fillet welding, horizontal lateral welding, etc. from the viewpoint of high efficiency and welding work environment. There is oblique welding, such as in pipe manufacturing, where the weld line has an inclination angle with respect to the horizontal plane.

However, in such inclined welding, molten metal flows along the weld line.

Now, this can be explained schematically as follows.

That is, FIG. 1a schematically represents the main part of the process of spiral pipe manufacturing and welding, in which a hot rolled coil material 3 is continuously fed into a pipe manufacturing machine via a straightening roll 4, and first the inner surface of the steel pipe is The inner surface is welded with a submerged arc welding machine 2, and the outer surface is welded with a half-frequency steel pipe outer surface submerged arc welding machine 1, thereby producing a spiral steel pipe 13.

Of these, the internal latent arc weld (inside circle A in FIG. 1a) is enlarged, and the cross section of the weld is schematically shown in FIG.

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 molten slag layer 7, and welding progresses. .

The molten metal 8 tries to flow in the flow direction G shown in the figure due to gravity, but the molten metal flows into the molten slag layer 7, where the arc pressure and kinematic viscosity in the arc cavity 9 are about 100 times larger than those of the molten metal. Flow is suppressed by resistance, pressure by the flux layer 6, or the like.

However, if welding conditions such as flux characteristics 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 molten metal 8 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 the molten state for a long time, and solidification is completed and the cone cape 1 is formed.
0 occurs.

Further, as the flow of molten metal 8 in the welding direction G increases, the depth h of the cone cape 10 increases.

Furthermore, if the flow of the molten metal 8 is a dog, in addition to flowing into the arc cavity 9, the molten metal 8 will flow in the bead width direction, causing an overlap 11 in which the bead rising angle α is 90° or more, and the degree of overlap is large. Then, the bead rising angle α increases.

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 F, and the base metal 14 cannot completely fill the groove dug by the arc, resulting in an undercut 12. .

In particular, when performing high-current welding in order to improve efficiency, the simple Mn08IO2-based molten flux, which is commonly used, does not allow the flow of molten metal due to gravity (hereinafter referred to as immersion flow). It cannot be suppressed and welding workability deteriorates.

Therefore, there is no occurrence of welding defects as shown in Figure 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 aspect of flux as a means of preventing such defects in inclined welding.

First, as mentioned above, defects such as cone capes, overlaps, and undercuts in inclined welding are caused by the flow of molten metal.

Therefore, it has been found that the following steps are necessary to prevent such flow.

To prevent melt flow, it is necessary to increase the deformation resistance of the flux and slag layer covering the molten metal.

In other words, Fig. 3 approximates the two-layer flow of slag and molten metal as a one-dimensional flow, calculates a numerical solution using an electronic computer, and classifies the behavior of the change in flow velocity at the slag-molten metal interface over time 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 viscosity is high or when 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 is thin, the flow velocity gradient becomes large, and when the slag viscosity becomes large, the deformation resistance increases.

Furthermore, in FIG. 4, 5M41 material of 25 Nt is used, and the electrode material C: 0.
1%, Si: 0.02%, Mn: 1.09φ
, leading electrode diameter 4. OMφ, 1200A, 27V, trailing electrode diameter 4.8Mφ, 600A, 35V, welding speed 110c
m,/min welding conditions, Mn0-8i02 series, M
Figure 5 shows the relationship between slag layer thickness and slag melting point when 6° downward temporary welding is performed using various gO-Mn 0-8i 02-based fluxes, and Figure 5 shows the relationship between slag layer thickness and slag melting point in an electric furnace heated and maintained at 1400°C. 307 # in a carbon crucible with a diameter of 40 φ.
! MnO5I02 series, MgO with different degrees of quality depending on the height of
-Mn0-8 After adding various fluxes of the i02 series and holding for 5 minutes, the crucible was cut and the melting layer thickness was measured to determine the flux melting rate and the slag layer determined under the same conditions as in Figure 4. These are diagrams showing the relationship with thickness, respectively.
As is clear from these figures, when the slag melting point is high and when the flux melting rate is low, the slag layer thickness becomes thin.

Furthermore, FIG. 6 shows the relationship between the flux crystallization degree and the flux melting rate, and it can be seen that the greater the flux crystallization degree, the lower the flux melting rate.

Here, the flux quality degree is defined by the following equation, and indicates the degree of crystallization of the flux.

Degree of quality - [(weight of crystal particles in flux): (total flux weight) Although it quickly becomes almost 100% amorphous, by increasing the degree of quality, it is possible to suppress the flow of the molten metal.

From the above, it can be seen that the flow of molten metal is suppressed by increasing the viscosity, melting point, and quality of the slag.

Figure 7 shows the cone cape depth h obtained from the bead cross section (see Figure 2) when welding under the same conditions as in Figure 4.
1 The relationship between the rising angle d of the bead toe and the flux bulk density is shown. As the flux bulk density increases, the cone cape depth h1 bead rising 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 in the present invention is
It was developed to satisfy the above-mentioned factors of preventing metal flow and to prevent defects such as cone capes, overlaps, and undercuts in inclined welding.

That is, in the present invention, SiO□30-65φ2M in weight ratio
n010~50φ2MgO5~30φ, CaF215%
The following is the main component of flux, and the Franks bulk density measured in a roughly packed state using the bulk density measurement method specified in JIS K6721 is 1.25 g//7 or more, and the degree of quality defined by the following formula is 10% or more. This is a melt-type flux for submerged arc inclined welding.

Degree of quality - [(weight of quality particles in flux): (total flux weight)') X], OO The present invention will be described in detail below.

First, SiO2 is added to increase the slag viscosity, but if the amount of 5i02 is less than 30 mm, the slag viscosity becomes too small and flow occurs, and if it is in excess of 65 mm, wrinkles will occur on the bead surface and the bead appearance will be 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 is impossible to form a uniform slag layer, and it is desired that the beads have uniformity.

In addition, the bulk density of the flux decreases and flow occurs.

On the other hand, if it exceeds 50 yen, the viscosity and melting point of the slag will decrease, and molten metal will flow.

MgO is added to increase the slag melting point and quality, but if the amount of MgO is less than 5%, the slag melting point,
The degree of quality decreases, the slag layer becomes thicker, and melt flow occurs.

If it is in excess of 30%, 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 promote flux quality and adjust the viscosity and slag melting point.
If the amount exceeds 1.5%, the viscosity and melting point will decrease, causing melt flow.

In addition, as shown in Figure 7 earlier, the flux bulk density is 1
．． If it is less than 25 g/Crt1, cone cape will occur and melt flow will occur.

If the bulk density is 1.25 glcrflJa or above, the bead shape will be good, so there is no particular upper limit, but a value up to 2.0 g/crfl is practical.

Furthermore, as shown in FIGS. 5 and 6 above, if the degree of quality of the flux is less than 10, the melting rate of the flux increases, the slag layer thickness becomes excessive, and melt flow occurs.

As for the upper limit, as is clear from the figure, <, 100
It goes without saying that the one with the highest quality is the most desirable.

The following methods are available for adjusting the bulk density and degree of quality.

Normally, in the molten type flux production method, carbon is added and mixed, the raw materials are resistance-melted, and then the slag is discharged to a rotary cooler that is externally cooled underwater or on a steel plate, or to a water-cooled roll. It can be adjusted depending on the amount and cooling method.

For example, if a large amount of carbon is discharged into a large amount of water, the bulk density and degree of quality will decrease.

On the other hand, if the amount of carbon is reduced so that it flows out onto the iron plate and the cooling rate is slowed, the bulk density and degree of quality will increase.

Furthermore, by using a roller cooler, water-cooled roll, etc., it is possible to control the cooling rate and produce a flux having an arbitrary bulk density quality.

In fact, in order to ensure a degree of quality of 10φ or more, it is necessary to avoid the conventional methods of immersing the material in water without adding carbon or rapidly cooling it with water jet.

Pouring the molten flux onto an iron plate and slowly cooling it is a surefire way to improve quality.

Molten fluxes having the compositions of Examples AI and &5 described below were poured onto a steel plate, and the layer thickness was varied (8 m, 16 M, 55 m).
Figure 8 shows the degree of quality when cooled.

The cooling rate in the figure shows that the melt flux is 1670°C to 1
．． The average cooling rate during cooling to OO0°C is shown.

A: A flux having a composition of 5 can ensure a degree of quality of 10% or more at any (common sense) layer thickness.

With a flux having a composition of 1, the degree of quality decreases by well over 10 when the layer thickness reaches 8wl1.

The degree of quality changes as described above depending on the flux composition, but in general, the quality level 1 is achieved by making the layer thickness 20M or more.
This is a sure way to ensure that the ratio is below 0%.

It is also possible to mix two or more types of fluxes with different degrees of quality and bulk density to adjust the degree of quality and bulk density.

The effects of the present invention will be explained in more detail with reference to Examples below.

Table 1 shows the chemical composition of the sample flux.

In the table, fluxes 1 to 6 are inventive fluxes, and fluxes 7 to 12 are comparative fluxes.

Welding was carried out using 8M41 material with a thickness of 25M and a groove angle of 600 and a groove depth of 6M, with a 6° downward tatami slope, and by two-electrode welding.

The conditions are shown in Table 2. Among the examples of the present invention, Ai: 1. ,
A 2 and Yo 5 were slag poured onto an iron plate and air-cooled.

Arashi 3 and A4 are slag that appeared in the water.

Fu 6 is the slag discharged from the water-cooled roll.

All of the examples of the present invention gave beautiful beads with no melt flow or defects.

Comparative Example Moderate 7 had an excessive amount of MnO and an excessive amount of MgO, resulting in low viscosity and low melting point, resulting in cone cape and overlap.

In A:8, the amount of SiO2 is too small, and cone cape and overlap occur.

A9 has an excessive amount of MgO, and although there is no cone cape or overlap, the bead width and height become unstable.
The bead shape deteriorates.

Jf'i:10 and 11 have too low bulk density, and cone cape and overlap occur.

In A12, the degree of quality is too low, and overlap and cone cape occur.

Note that A, 1, 11, and Al 2 have the same flux components, but the flux manufacturing conditions were changed, resulting in a difference in the degree of bulk density quality.

Slag No. 11 is obtained by cooling with water after pouring the slag onto a water-cooled roll.

A12 is the sludge discharged into the dissolved and drained water without adding carbon.

As described above, the flux of the present invention prevents melt flow in inclined welding and provides good welding workability, making it an extremely significant contribution to industry.

[Brief explanation of the drawing]

Figures 1a and b are diagrams schematically showing spiral pipe welding as an example of inclined welding, Figure 2 is a schematic diagram of defects in inclined welding, and Figure 3 is a diagram showing changes over time in the flow velocity at the interface between slag and molten steel. , Fig. 4 shows the relationship between the slag melting point and the slag layer thickness, Fig. 5 shows the relationship between the flux melting rate and the slag layer thickness, and Fig. 6 shows the relationship between the quality of flux and the flux melting rate. FIG. 7 is a diagram showing the relationship between flux bulk density, cone cape depth, and bead rising angle. FIG. 8 is a diagram showing the relationship between flux quality degree and layer thickness. 1: Steel pipe external submerged arc welding machine, 2: Steel pipe internal submerged arc welding machine, 3
: Hot rolled coil material, 4: Straightening roll, 5: Steel pipe inner surface submerged arc welding machine electrode, 6: Flux layer, 7: Molten slag layer, 8:
Molten metal, 9: Arc cavity, G: Molten metal flow direction, 1
0: corn cape, 11 nitrogen burlap, 12: undercut, 13: spiral steel pipe, 14: base metal, h:
Cone cape depth, α: bead rise angle.

Claims (1)

[Claims] 1 5i02 30-65% by weight, Mn0 10-
50%, Mg05~30%, CaF215% or less, as the main components of the flux, and the bulk density of Fusix is 1.25
A melting type flux for submerged arc inclined welding, characterized in that it has a g7crtt or higher and a crystallization degree of 10% or higher.