JPS5811312B2 - Submerged mark welding method for extra-thick steel plates - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing welding defects, particularly slag entrainment defects, when submerged arc welding ultra-thick steel plates with a thickness of 50 to 300 mm, such as Cr-Mo steel, using a tandem method. It is.

Recently, a tandem method (two-electrode method) has been increasingly adopted as a submerged arc welding method for extremely thick steel plates in order to improve welding efficiency.

In the case of such extra-thick steel, repair is very time-consuming and the occurrence of welding defects such as slag entrainment is a major problem.

In the tandem method, the arc tends to become unstable due to mutual interference between the arc between the two poles and the molten pool, and there are also more variable factors than in the case of single welding (one pole), so it is difficult to prevent the occurrence of slag entrainment defects. It is important to select construction conditions for this purpose.

Although welding conditions have been determined empirically and welding has been carried out, defects may occur due to sudden changes in conditions such as the characteristics of the welding machine and fluctuations in power supply voltage, and these are treated as accidental defects. Apparently, sufficient measures were not taken.

In particular, when circumferentially welding extremely thick steel plates (large-diameter pressure vessels, etc.), the length of the single bead at 1 welding point is 10.
It was thought that it would be difficult to ensure no defects even in this case.

Generally, when welding low-alloy, extra-thick steel plates such as Cr-Mo steel, high performance (strength, toughness, ductility, etc.) is required for the weld metal, so flux with a high basicity composition is often used. As a general feature of this highly basic flux, the so-called welding workability (beat forming ability, weld defect resistance performance) tends to be inferior to that of neutral fluxes, making it more disadvantageous for the above problems. There is.

The present inventors have conducted many experiments on the construction conditions for tandem welding using highly basic flux, and as a result, the results are vastly different from the knowledge generally known as the appropriate construction conditions for tandem welding. Discovered new knowledge.

That is, conventional knowledge (Reference: Ito, Bessho; Research on beat formation in submargin arc tandem method, Journal of the Welding Society, Vol. 39 (1970) No. 10).

1099-1106), ``If the trailing arc voltage is made extremely low compared to the leading arc voltage, the bead appearance will become very thin, and as the voltage increases, the bead width will become wider and the appearance will become better.

However, if it is set too high, the beat will meander and the appearance will not be good.

As a result, it is determined that the voltage of the trailing arc is equal to or higher than the voltage of the leading arc, and the difference therebetween is 6 volts at most.

'' (Page 1100 of the above-mentioned document, 4th line from the bottom of the left column to 3rd line from the top of the right column) However, as a result of detailed experimental studies on multi-layer welding of extra-thick steel plates, the present inventors found that It is essential to minimize the distance between the two electrodes in terms of the bead shape and the occurrence of slag entrainment defects.Furthermore, when this distance between the two electrodes is made small; the beat width is not affected by the arc voltage of the trailing electrode. rather, it becomes dominated by the arc voltage of the leading electrode (Figure 2),
It has been found that in view of the beat shape and the occurrence of slag entrainment, it is necessary that the arc voltage of the trailing electrode be lower than that of the leading electrode, and that the voltage value be as low as possible.

It has also been found that these tendencies are more pronounced when the arc is generated at a slightly inclined surface, such as in circumferential welding.

In other words, Fig. 2 shows the results of horizontal welding and oblique welding with a bead-over plate as shown in Fig. 1, with one of the voltages of the leading electrode and the trailing electrode held constant while the other voltages were varied. The figure shows the resultant change in bead width.As can be seen in the figure, the bead width hardly changes depending on the voltage of the trailing electrode, but rather changes greatly depending on the voltage of the leading electrode. The larger the bead width, the larger the bead width, and this tendency is remarkable in the case of inclined welding.

And in relation to the occurrence of slag entrainment defects. Looking at the effects of these voltages, the results of this bead-on-plate test showed that defects occurred only when the trailing electrode was raised to 36V.

Furthermore, after that, we conducted experiments using extra-thick steel and varying the voltage in multilayer welding within an actual groove, but the frequency of defect occurrence increased as the voltage of the trailing electrode increased. In addition, we have found that it is necessary to set the trailing electrode voltage lower than the leading electrode voltage, considering both welding workability such as bead shape and the frequency of occurrence of defects.

It should be noted that during fluctuations in the trailing electrode voltage, the voltage increases as the voltage increases; for example, even if it is set to about 36V, the highest voltage recorded value may be close to 50V. It was also found that there is a high probability of defect occurrence in some cases.

The present invention has been made based on the above findings, and is a method that makes it possible to drastically reduce the occurrence of slag entrainment defects in tandem submerged arc welding of extremely thick steel plates.

In other words, the leading electrode wire (L pole) is perpendicular to the steel plate surface ±5
°, and the trailing electrode wire (electrode) is 5~20° with respect to the L pole.
° In the AC-AC tandem submerged arc welding method for extremely thick steel plates, which is performed by tilting backwards, the distance between the centers of the tips of the L-electrode wires should be 15 mm or less, and the arc voltage at both poles should be welded under the following conditions. This is a submerged arc welding method for extremely thick steel plates.

Here (1) VL (L pole) ≧ VT (electrode) (volt) (2) V
T (electrode)≦A150+α (volt) However, by adopting the method of the present invention, the influence of material properties,
Even taking into account the effects of the welding machine and sudden changes in conditions such as power supply voltage fluctuations, it is possible to significantly reduce the occurrence of slag entrainment defects and improve the appearance of the bead in circumferential welding. It became possible to obtain a good weld.

The reasons for limiting the numerical values of the present invention will be explained in detail below.

First, in the present invention, a leading electrode (L pole) and a trailing electrode (
The distance between the centers of the wire tips of the electrodes was set to 15 mm or less, which is a necessary condition in terms of bead width, bead shape, and slag entrainment defects.

In particular, the U-groove is commonly used for extra-thick steel.
The wire is layered in two or three passes, and in this case the wire target position (distance to the groove wall) is important.

For example, in the case of circumferential welding, beads are layered one after another, but in this case it is necessary to change the wire aim position during welding.

In this case, the wider the bead width, the more space there is between the bead and the groove wall, making the welding process easier.

When the distance between the centers of the wire tips exceeds 15 mm, the bead width is greatly affected by the trailing electrode voltage, as stated in the above cited document, and it becomes necessary to increase the arc voltage to increase the bead width, which causes slag. This is not preferable because it increases the frequency of occurrence of curling defects.

Next, as mentioned above, the relationship between the arc voltages of the leading and trailing electrodes was determined to be VL (L pole) ≧ VT (T pole), which was determined experimentally from the relationship between the bead external shape and the occurrence of defects. However, VL mainly affects the bead shape (bead width), and is related to the relative relationship of VL≧■T or arc stability, etc.
This affects the occurrence of slag entrainment.

It goes without saying that this relationship was obtained under the condition that the distance between the centers of the wire tips of the L pole and the T pole was 15 degrees or less.

For example, if the distance between the centers of the wire tips is about 30 mm,
If welding is performed with such a relationship between the arc voltages of the L pole and the T pole, the result will be very poor in terms of bead shape welding defects.

Furthermore, the arc voltage of the T pole is determined by the wire diameter and the current used: VT≦A150+α (volts).
×D+29 A is the operating current of the T pole (ampere) D is the wire diameter (mm) The relationship was determined experimentally by varying the wire diameter and current value.

That is, as a general tendency, as the wire diameter becomes larger, the current density becomes smaller when compared at the same current value, and the arc force becomes weaker. Therefore, by lowering the voltage, slag entrainment defects are reduced.

Also, when the current (ampere) used with the same diameter wire becomes smaller, the current density becomes smaller and the arc force becomes weaker as before, so it becomes necessary to lower the voltage accordingly.

This is illustrated using an actual numerical example as follows.

That is, when experiments were conducted under various conditions, D, α
In the above combination of and A, the arc voltage of the T pole ■T
As mentioned above, it has been experimentally confirmed that when the settings of 1 and 2 exceed these values, the frequency of occurrence of slag entrainment defects increases with the increasing tendency during voltage fluctuation.

Therefore, the relationship between D, α, A, and V (T pole) is determined as described above.

The present invention will be explained in more detail below using Examples.

Example: A with a thickness of 100 mm, a length of 1000 mm, and a width of 200 mm.
STMA387G22 material (21/4Cr-1MO steel) was beveled and butted as shown in Figure 3, and basic flux (molten type) with the component particle size shown in Table 2 and 21
/4 Multi-layer welding using Cr-1M0 wire 3
The test was carried out at a slope of °.

As shown in Table 1 and FIG. 4, the construction conditions were 4 conditions of the present invention and 6 other conditions.

The welding speed is 70cm/1, which is fast for this type of welding.
We use min.

The appearance of the bead during welding was observed, and after welding was completed, an X-ray test was conducted to count the number of defects.

The results are shown in Table 1.

In terms of the bead appearance, the shape of the bead was almost good in all cases except that the bead became slightly thinner in conditions No. 7 because the distance between the centers of the tips of the electrode wires was large and the arc voltage of the trailing electrode was low.

The X-ray results showed that there were no defects under the conditions of the present invention.

On the other hand, defects occur in all of the other six conditions,
Among them, a large number of defects were observed when the distance between the centers of the tips of both electrode wires was large and the trailing electrode voltage was high (No. 5).

However, even if the inter-electrode distance is small and appropriate, if the arc voltage is higher at the trailing electrode than at the leading electrode, which is outside the scope of the present invention (No. 8, 9, 10), There are still quite a few flaws.

As described above, according to the method of the present invention, in an efficient tandem welding method for extra-thick steel plates that requires labor to repair when an internal defect occurs, the occurrence of slag entrainment defects is almost completely eliminated. is significant.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the electrode arrangement and other situations in horizontal welding a and inclined welding in tandem welding. FIG. 2 is a diagram showing the influence of the arc voltage of the trailing and leading electrodes on the bead width, where a shows the influence of the trailing voltage and b shows the influence of the leading voltage. FIG. 3 is a schematic diagram showing the groove shape and the state of the layered method in the example. FIG. 4 is an explanatory diagram showing the situation of electrode positions in the example.

Claims (1)

[Scope of Claims] 1. An extremely thick steel plate in which the leading electrode wire (L pole) is set at an angle of ±5° perpendicular to the surface of the steel plate, and the trailing electrode wire (T pole) is tilted backward at 5 to 20° with respect to the L pole. In the AC-AC tandem submerged arc welding method, the distance between the centers of the tips of the L-T pole wires is 15 mm or less, and the arc voltage of both poles is welded under the following conditions. Submerged arc welding method. (1) VL (L pole) ≧ T (T pole) (volt) (2) V
T (T pole) ≦A150+α (volt) However