JPS6033878A - Submerged arc welding method of high-carbon steel - Google Patents

Abstract

PURPOSE:To prevent high-temp. cracking and to improve welding efficiency in submerged arc welding of a high-carbon steel by limiting the sum of and difference between preceding electrode current and succeeding electrode current as well as an inter-electrode distance and subjecting at least one side to single-layer build-up welding with two electrodes. CONSTITUTION:Welding of a high-carbon steel contg. 0.20-0.33W% C is accomplished by regulating the sum of preceding electrode current and succeeding electrode current to >=1,200A, the difference between the succeeding electrode current and preceding electrode current to 0-200A and an inter-electrode distance to 25-50mm., respectively. If the sum of both electrodes is <1,200, there is substantially no effect in terms of efficiency. High-temp. cracking arises when the preceding electrode current is higher than the succeeding electrode current. An undercut and consequent defective appearance arise when the succeeding electrode current has over 200A difference from the preceding electrode current. High-temp. cracking arises at <25mm. inter-electrode distance. The unstable arc and consequent defective bead appearance arise if said distance exceeds 50mm..

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a two-electrome submerged arc welding method for high carbon steel, and provides a submerged arc welding method that can reliably prevent high-temperature cracking of weld metal. It is something to do.

5B42.5B46.5B49 specified by JIS G3103 or ASTMA515. A315Gr6
0. For steel materials such as A315Gr65゜A315Gr70, C is added as a component of the steel by 0.20 to 0.33w.
Contains t%. In this way, submerged arc welding is widely used for plate joining or pipe making of steel materials containing a relatively large amount of C, as it has a high welding speed, enables high-speed welding, and can perform highly efficient welding.

However, in such submerged arc welding in which both sides of high-strength carbon steel are welded in one layer or at least one side with one stitch, there is a problem in that high-temperature cracks are likely to occur in the weld metal.

Generally, in initial layer welding or fillet welding in a groove of mild steel or 50 gyro high tensile strength steel, a high temperature crack 3 is generated in the center of the weld metal 2 as shown in FIG. This occurs when the weld metal solidifies, and C and S in the weld metal increase the solidus temperature range between the liquid phase and the solidus line, and FeS and Fe5-F
It is well known that low-melting-point substances such as E are more likely to segregate at grain boundaries in the final stage of solidification.

However, the high-temperature cracks that occur during 1rrJ welding of high carbon steel are high-temperature cracks 4 that are formed in the weld metal 2 in the form of a V or 7' shape, as shown in FIG. 5
This is different from the high-temperature cracks that occur during initial layer welding or fillet welding in a groove with 0 kg high tensile strength steel, and is more likely to occur during single-layer welding. It was previously thought that C2S in the weld metal was the main cause of this high temperature cracking. Methods for preventing this are described in the following publications.

Moatzu, JP-A-57-6449 and JP-A-5'8
The invention described in Publication No. 77778 is a method for preventing this high-temperature cracking by lowering C2P and S in the weld metal by lowering c, p, and s of the wire and flux.
Furthermore, by lowering the basicity of the flux and increasing the oxygen content in the weld metal, nonmetallic inclusions are increased and low melting point sulfides are prevented from precipitating. Furthermore, large current MIG
+2 There are ways to prevent high temperature cracks by dividing the heat input using the SAW method.

[7 However, these methods sacrifice the impact value to some extent because the welding materials are limited and the oxygen content in the weld metal increases. In addition, the high current MHG+2SAW method has problems such as the equipment itself being complicated and the working environment being poor due to visible arcs and fumes.

JP-A No. 58-377 discloses a method of inserting a low-carbon block into the root of the groove and welding by a deep penetration method that creates a leaking arc to lower C in the weld metal and prevent high-temperature cracking. It is shown. This method has problems in terms of efficiency due to the addition of the work of inserting a steel slab block into the groove root before welding, which increases the number of work steps.

(Problems to be Solved by the Invention) The present inventors have conducted detailed studies on welding conditions that can provide the above-mentioned welded portion without high-temperature cracking and that are highly efficient in single-layer welding of high carbon steel.

As a result, it became clear that the cross-sectional shape of the bead rather than the C and S leaves in the weld metal contributed significantly to the occurrence of high temperature cracking.

That is, as shown in Fig. 3 (A) Ic, if it suddenly spreads from b of 4 to 5w+ below the steel plate surface a toward the steel plate surface a (referred to as an inverted hat type), high-temperature cracks are likely to occur.
As shown in FIG. 3) and FIG. 3(C), it has become clear that V-shaped or U-shaped materials are less likely to break.

In the case of the inverted cap type shown in Figure 3 (A), high-temperature cracks occur from the part that suddenly spreads from 4 to 5 ran b below the steel plate surface a, and this is because stress is concentrated in this part. It is. The V-shape and U-shape shown in Fig. 3 ω) and Fig. 3 C) are difficult to break because stress is dispersed. As a result of examining the welding conditions that affect the cross-sectional shape of the bead, it was found that the difference between the leading and trailing electrode currents and the distance between the electrodes have an effect. In other words, if the leading electrode current is higher than the trailing electrode current, it will be an inverted cap shape, and conversely, if the leading electrode current is the same or lower than the trailing electrode current, and the distance between the electrodes is 25
-50m, V-type or (Structure of the Invention) The gist of the present invention, which was made based on the knowledge of the beam, is that C is 0.20-0.33wt9
In submerged arc welding of steel containing 6, the sum of the leading electrode current and the trailing electrode current is 1200 At, the difference between the trailing electrode current and the leading electrode current is 0 to 200 A%, and the distance between the electrodes is 25 A submerged arc welding method for high carbon steel, which is characterized by performing one-layer welding on at least one side with two electrodes.

What is the difference between trailing electrode current and leading electrode current (trailing electrode current)?
- (preceding 1a, polar current).

The present invention will be described in detail below.

The sum of the leading electrode current and the trailing electrode current must be 1,200 or more. If it is less than 1200A, the efficiency advantage of using two-electrode welding will be almost negligible.

Next, the difference between the trailing electrode current and the leading electrode current must be between 0 and 200A. When the leading electrode current is higher than the trailing electrode current, high-temperature cracking occurs with an inverted cap-shaped bead cross-sectional shape. Also, the trailing electrode current is 20OA lower than the leading electrode current.
If the difference is too large, the cross-sectional shape of the bead becomes U-shaped, and although high temperature cracks do not occur, undercuts occur and the appearance of the bead becomes poor.

Furthermore, the distance between the thunderbolts must be 25 to 50 degrees. 2
If it is less than 5fi, the cross-sectional shape of the bead becomes an inverted cap shape and high temperature cracking occurs. Moreover, if it exceeds 50 degrees, the arc becomes unstable and the bead appearance becomes poor. The inter-electrode distance herein refers to the distance between the centers of the tips of the leading electrode, trailing type, and pole wire on the welding line of the object to be welded.

Also, as a matter of course, welding efficiency is very high if one thread welding is performed on both sides with two electrodes. However, when welding small-diameter pipes, there are times when it is not possible to weld the inner surface with two electrodes due to equipment limitations, or when welding extra-thick steel plates, it may not be possible to perform single-thread welding on both sides. Even in these cases, welding efficiency can be improved by welding one thread on one side with two electrodes.

Although welding voltage and welding speed also affect the cross-sectional shape of the bead, their influence is not so large within the range of the welding current difference and interelectrode distance, and the welding voltage is within the commonly used range of 28 to 42V. If the welding current is low, use a lower voltage (for example, 31V ± 4V for about 600A), if the welding current is high, use a higher voltage (for example, 3gv ± 3V for about 120OA), and the trailing electrode voltage is The bead appearance is better when the voltage is 0 to 7 V higher than the electrode voltage. However, if this level becomes too high, it will affect the cross-sectional shape of the bead and affect high-temperature brittleness, which is undesirable.

If the power source is DC, the appropriate voltage is 3 to 4 volts lower than the AC voltage. Also, the appropriate cylinder and pressure range for these voltages may vary depending on the type of flux.

The welding speed varies depending on the groove shape and welding flow, but from the viewpoint of efficiency and welding workability, it is 35 to 1501M/
Min level is good.

In addition, the wire components include C0.12% or less, SIo,
551 or less, Mn 1.25-2.80 tlI%P
O, 020% or less, So, 015% or less, especially C,
It is preferable that S be as low as possible. However, if C is too low, F! , St or Mn because the impact value decreases.
The higher the value, the better.

Any type of flux, such as molten type or fired type, may be used as long as it has good workability in high current and high speed welding.

(Example) Embodiments of the present invention will be described below.

In the case of steel plates with the composition shown in Table 1 and thicknesses of 18mm and 25+mm, with the X groove shown in Figure 4, and steel plate symbol A, H: 18n.
Roff army, θ: 70°, hl:6van+h2
Two six tan.

h3: 6-, H: 25 for steel plate symbols B and C
mm *θ near 0°, h+: 11mm+ h2
: fimm+h3:Rm+n, and the wire diameter between 4.8 and the composition shown in Table 2 and the type 7 shown in Table 3.
In the case of steel plate symbol A, BP side, '
Under the same conditions with two electrodes on the FP side, steel plate symbols B and C
In this case, the welding conditions on the BP side are 1 electrode welding and a welding current of 900
A, Welding voltage 36V, Welding speed 40cm/min Ichichukyu〃L〒Hakubo 1'T' P Cloth i? The sum and difference of the trailing electrode currents and the distance between the electrodes were varied to examine the appearance of the bead after welding, the cross-sectional shape of the bead, and the presence or absence of high-temperature fluctuations.

The results are summarized in Table 4.

In addition, for the inspection of high temperature cracks, a side bending test was performed on 10 sheets of each sheet.

Test example in which welding was performed under welding conditions that satisfy the present invention].

2.3.4,5. In Fi and Test Example 7, the bead appearance was good, the bead cross-sectional shape was V-shaped or U-shaped, and no high temperature cracks were observed in the side bend test pieces.

Furthermore, no differences were observed depending on the steel sheet composition, wire composition, or flux type.

Among the comparative examples, in Test Example 8, the leading electrode current was higher than the trailing electrode current.
Because of the high temperature, the cross-sectional shape of the bead had an inverted cap shape, and high-temperature cracking occurred in the side bend test piece.

In Test Example 9, the trailing electrode current was too high, so undercutting occurred and the bead appearance was poor.

In Test Example 10, the current difference and the distance between the electrodes satisfied the present invention.
- Is it wholesale outside the bead? , Bee? Although the cross-sectional shape of the pile was V-shaped and there was no high temperature in the side-bending test piece, the welding speed was slow due to the low sum of the leading electrode current and the trailing electrode current, resulting in very poor welding efficiency.

In Test Example 11, the distance between the electrodes was short, so the cross-sectional shape of the bead had an inverted cap shape, and high-temperature cracking occurred in the side bend test piece.

In Test Example 12, the distance between the electrodes was long, so the arc was unstable and the appearance of the sheave was poor.

In Test Example 13, because the leading electrode current was higher than the trailing electrode current and the distance between the electrodes was short, the cross-sectional shape of the bead became an inverted cap shape, and high-temperature cracking occurred in the side bend test piece.

In Test Example 14, because the leading electrode current was higher than the trailing electrode current and the distance between the electrodes was long, the arc became unstable, the bead appearance was poor, the cross-sectional shape of the bead became an inverted cap shape, and the side bending test piece was exposed to high temperatures. Occurred.

In Test Example 15, because the trailing electrode current was too high and the distance between the electrodes was too long, the arc became unstable, undercutting occurred, and the bead appearance was poor.

Regarding Test Examples 3, 4, 5.6 and Test Example 7, which satisfy the present invention, J
An IS No. 4 Charpy test piece was taken and tested at a test temperature of 0° C. As a result, an impact value of 6 to 12 and 9 I-m was obtained.

Table 2 Chemical composition of wire (wt%) (Effect of the invention) As shown in the example above, the method of the present invention is highly efficient and effective in single thread submerged arc welding of high carbon steel. A sound welded joint without high-temperature cracking can be obtained, and the industrial value of the present invention is extremely high.

[Brief explanation of drawings]

Figure 1 shows the form of high-temperature cracks that occur at the first layer weld in a groove of mild steel and 50kg high-strength steel, and Figure 2 shows the form of high-temperature cracks that occur during single-thread welding of high-carbon steel. Figure 3 is a diagram showing the bead cross-sectional shape when changing the difference between the leading current and trailing current and the distance between poles, and Figure 4 is the groove shape of the steel plate in an example of the present invention. FIG. Explanation of symbols]: Base metal, 2: Weld metal, 3: High temperature welding, 4: High temperature welding, IL = steel plate surface, position 4 to 5 below baa, H: plate thickness, h@*h*: open Tip depth, h2: root face,
θ: Groove angle.

Claims (1)

[Claims] In submerged arc welding of steel containing 0.20 to 0.33 wt C, the sum of the leading electrode current and the trailing electrode' current is 1200 A or more, the difference between the trailing electrode current and the leading electrode current is 0 to 20 OA, A submerged arc welding method for high carbon steel, characterized in that the distance between the electrodes is 25 to 50 degrees, and at least one side is welded with two electrodes in one thread.