JPS607582B2 - Shallow penetration submerged arc welding method for steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shallow-penetration submerged arc welding method for steel, particularly thick steel plates, and aims to efficiently obtain high-performance joints free of defects.

Recently, many steel plates used in pressure vessels, offshore structures, line pipes, etc. contain Nb and V.

However, when copper containing Nb and V is submerged arc welded, Nb and V migrate into the weld metal due to dilution, causing a problem in that the toughness of the weld metal deteriorates significantly. This is particularly noticeable when subjected to reheating and when subjected to stress relief dawn anchoring (hereinafter referred to as S.R.). This is unavoidable because conventional submerged arc welding involves welding on more than three sides and the dilution of the base metal is as high as 30 to 70%.Research is being conducted to address this issue from the perspective of welding materials. However, it is still not sufficient.

On the other hand, in butt submerged arc welding, there is a method to reduce the dilution of the base metal by adding an auxiliary welding agent, but the dilution rate is only about 30% at its smallest, and the adverse effect of the base metal components is Not enough to eliminate it.

Furthermore, variations in the amount of the auxiliary filler material added may cause problems such as insufficient penetration. There were hardly any other methods found that were particularly effective for butt heating. In addition, the submerged arc welding method is used to weld thick plates such as pressure vessels because of its high welding speed.

However, from the viewpoint of slag removability and high temperature cracking,
In the groove shown in the figure, the bottom radius R is at least 8
On the side, joints with a groove angle of about 15° are exclusively used. In addition, if a machine such as a saper for beveling is not available, the beveling angle is 50 to 70o as shown in Figure 1b.
The X-bevel is processed and used by gas cutting.
By the way, in joints having such a shape, the cross-sectional area of the groove becomes extremely large as the plate thickness increases, so two-electrode welding is used to improve efficiency.

However, there is a need to further improve efficiency and reduce the amount of material used after melting. A single-pass submerged arc welding method has been attempted, but it has been problematic because it tends to cause defects such as slag entrainment.
In other words, remove the initial layer using the junction shown in Figure 1, and use the wire B on the 4.0 to 4.8 side to distribute it under the granular flux F as shown in Figure 3b. When welding in layers with more than one pass, the tip of the wire E is welded close to the junction (base metal) A, A' wall when separating, so the penetration P into the base metal becomes large and the base metal is welded. Dilution increases.

In addition, defects such as slag entrainment may occur due to the fact that the wire target position is like a valley between the previous pass and the groove wall, or that the weld bead is deposited at an angle similar to horizontal welding. Easy to occur. In addition, the first
In the figure and Fig. 3b, A and A' are the steel plates to be welded (base), B and B' are weld metals,
F is the groove angle, R is the bottom radius of curvature, and W is the joint width.

The present invention is intended to solve the above-mentioned problems in welding thick plates and perform welding with high efficiency.
~14 Fence, the groove width WF on the plate thickness surface part is 2 mm or less, and WB Mi WF is set to 1 in welding within the joint excluding the final layer.
In one layer pass, the welding thickness of that one layer is 3 to 6 yen, using a wire with a diameter of 1.0 to 4.0, and 150 yen per electrode.
With a welding current of ~700A, 15 to 40 k/ for a single electrode
The present invention is a shallow welding deep arc welding method for steel, which is characterized by welding using a normal flux at a welding speed of 20 to 70 cm/min in the case of two electrodes.

The present invention will be described in detail below with reference to the drawings.

Figures 2 and 3a are diagrams showing the welding situation of the present invention, where A and A' are the materials to be welded (base metal), and the groove portion is approximately type 1; Groove spacing WB at the bottom is 6
~14 side, the groove bottom interval WF at the plate thickness surface part is 20
Make it WB/WF below the side.

F is a granular flux with a range of 1.0 to 4.
The facing wire E is placed as a consumable electrode approximately at the center of the width of the joint, and an arc is generated from it to perform latent arc welding.
As this welding condition, the welding current is 150 to 7
0 ships, the welding speed is 15 to 40 arc/mln for single electrode,
In the case of two electrodes, by welding in the range of 20 to 70 cm/min and under conditions where the weld thickness = weld cross-sectional area/joint width is 3 to 6 ribs, the penetration P into the mother village is approximately 1 skin or less. The water becomes shallower, and the dilution of the mother village becomes significantly smaller, about 20% or less.

Therefore, the amount of Nb and V in the base metal mixed into the weld metal B is extremely small, and good toughness can be obtained. Furthermore, defects such as slag entrainment are less likely to occur. Next, the reason why the joint shape and welding conditions were limited as described above will be described.

All of these conditions were set with the intention of making the penetration into the base metal as shallow as possible and not causing poor fusion, etc. First, if the groove width WB at the bottom of the groove is less than 6 sides, If the welding heat input is not extremely small, the weld thickness will be large and hot cracking or fusion failure will likely occur.

In addition, when the heat input is small, the molten pool is small and solidification is rapid, resulting in slight wire feeding failures, flux spreading too deep or too shallow, and welding becomes unstable, resulting in defects such as poor penetration and slag entrainment. Easy to do. As a result, the range of appropriate conditions is narrow and there are practical problems. If the joint width WB at the joint bottom exceeds 14 ribs, or if the groove width WF at the plate thickness surface exceeds 2 ribs, the joint cross-sectional area will increase, efficiency will deteriorate, and the amount of welding material used will increase. I don't like it.

Furthermore, in the latter case, unless the welding current is increased, the tip (base metal) surfaces at both ends cannot be sufficiently melted, which tends to cause fusion failure.

Furthermore, when WB>WF, the groove shape becomes trapezoidal, making it difficult to remove the slag. In addition, the welding within the joint, excluding the final layer, was limited to one pass per layer in order to obtain the above-mentioned effects. Defects such as slag entrainment are more likely to occur due to deeper penetration, a valley between the junction wall and the weld metal, and a nearly horizontal position. In addition, 2.4
When using a wire with a height below the center of the amplitude),
Align with the center of the groove, shake 6 yanagi or less, cycle 1~1$noS
Even if lateral vibration is added to the wheel, the effects of the method of the present invention do not change, and even more stable beams can be obtained. The deposited thickness, that is, the welded cross-sectional area/groove width, is substantially determined by the welding conditions at a predetermined joint width, and is determined by the combination of welding current and welding speed.

Therefore, if the welding current is small and the welding thickness is less than three legs, the lacquering of the base material will be insufficient, resulting in poor fusion. When the welding speed is high and the weld thickness is small, poor fusion similarly occurs, and defects such as undercuts and slag entrainment are likely to occur. Conversely, if the weld thickness exceeds 6 skins,
If the metal runs ahead of the metal, it may cause poor fusion or high-temperature cracking. The wire diameter is 1. If it is less than 0, both the absolute value and the range of the appropriate current are small, so the range that can be welded per layer in one pass is narrowed, and the practicality is poor. The wire diameter is 4. If the current is exceeded, the absolute value of the appropriate current is large, so the port becomes too deep and adder cuts are likely to occur. Next, when the welding current per electrode is 15 mm, the range that can be welded in one pass per layer is narrow, as is the case when the wire diameter is small, and the welding speed is low, the efficiency is poor, and the welding is impractical.

On the other hand, when the welding current exceeds 700 A, the welding current is too large, the arc force becomes strong, and a solid surface gouged by the arc is likely to occur in the molten pool, causing slag entrainment and undercut. In addition, if the penetration becomes too deep, the toughness deteriorates and hot cracking is likely to occur. When the welding speed is less than 15 arcs/min for a single electrode and less than 20 arcs/min for two electrodes, the molten metal protrudes from the molten pool and runs ahead of the molten pool, which tends to cause insufficient cross-over and slag entrainment. .

If the welding speed exceeds 40 k/min in the case of a single electrode, or exceeds 7 k/min in the case of two electrodes, hot cracking is likely to occur.

Furthermore, poor fusion and undercuts occur, making it difficult to weld one pass per layer. The following reasons are believed to be why, in the method of the present invention, the twilling into the base material is very shallow and defects such as slag entrainment are less likely to occur.

In arc welding, penetration is generally formed by the direct action of the arc and the heat conduction action of the arc heat through convection of the molten metal.

By the way, in the method of the present invention, the gap between the grooves is narrowed, the wire with a relatively large diameter is positioned at the center of the groove, and the welding is performed in a completely downward position at a low speed. A molten metal is interposed between the metal and the base metal, and arc heat is transmitted through the molten metal to melt the base material. Therefore, the arc does not act directly on the base material as in the conventional method, which makes it easier for slag to adhere and become trapped, and the base material (
solid) surface does not occur. Therefore, it is thought that extremely shallow penetration can be obtained uniformly, and defects such as slag entrainment are unlikely to occur.

Since the present invention is as described above, it can exhibit many excellent effects such as the following.

'1' The dilution of the base material is very small, and the base material components (especially N
The influence of b, V, and C) is small, good plowability is obtained, and hot cracking is less likely to occur.

[2] Since the groove cross-sectional area and cumulative bead surface area are significantly reduced, efficiency is high and the amount of welding material used is significantly reduced.

Since it is not glue distribution welding, there is no change in the target position of the wire during circumferential continuous welding, and it is easy to add auxiliary welding material, so defects such as slag entrainment and insufficient penetration are unlikely to occur.

However, compared to the conventional method, the present invention provides even better performance not only with steel whose base metal contains components undesirable for welding, but also with steel that does not contain such components.
Moreover, it will dramatically improve efficiency and save money. The effects of the present invention will be described in more detail below based on Examples.

Examples Table 1 shows the combinations of steel plates, wires and fluxes, welding conditions, S/R conditions, and welding results according to the method of the present invention.

Similarly, the conventional method and comparative examples are shown in Table 2. Numbers 1, 2, 3, 4, 5 and 6 in the same table are the methods of the present invention, and number 7
, 8 and 9 show conventional methods. Also numbers 10 and 11
is a comparative example. Note that the groove shapes and dimensions of the steel plates used for these weldings are shown in FIGS. 4 to 11. In FIG. 5, CW is a granular metal (cut wire), Cu is a copper backing plate, and SB is a backing steel plate in FIGS. 7 and 9. Further, steel plates, wires, and fluxes are shown in Tables 2, 3, 4, and 5, respectively.

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〉Cicada N-Chicken [Ant 82 paper It is not contained in the flux, and only migrates from the base metal (steel plate) into the weld metal, and the rate at which it oxidizes and migrates into the slag is very small.

Therefore, it can be used as an index indicating dilution (penetration) of the base material. Comparing the method of the present invention and the conventional method in terms of Nb content, in the case of the method of the present invention, the Nb content is much lower;
It can be seen that the penetration is shallow.

Further, no abnormal decrease in the impact value of the meeting area due to Nb is observed in the method of the present invention. Therefore, it can be seen that the method of the present invention is suitable for welding steel whose base metal components include components undesirable for the weld metal.

Furthermore, when comparing the economical efficiency, the difference is slight when the plate thickness is 25 ribs, but the groove cross-sectional area is small in the method of the present invention.

In addition, the number of welding passes is less than two passes, and it is much more efficient when considering the back chiseling work. This effect becomes greater as the plate thickness increases. In addition, side bending test,
It can be seen that a reliable welded joint can be obtained without any defects in the UST inspection.

It should be noted that there was no problem with regard to slag removability, which is a problem in multilayer welding, because the generated slag can be removed relatively easily by selecting a neutral or basic flux.

As detailed above, the method of the present invention can easily weld steel, for which application of submerged arc welding was problematic due to the base metal composition. Furthermore, a highly reliable welded joint that can manufacture thick plates extremely efficiently, requires less welding material, and has fewer defects can be obtained very economically, and is of great industrial value.

[Brief explanation of the drawing]

Figure 1 is a front sectional view showing the tip shape of the conventional method and the layered method.
Figure 2 is a front sectional view showing the joint shape and layered method of the present invention, Figure 3a is a front sectional view showing the welding situation of the invention method, and Figure 3b is the welding situation of the conventional method. Front sectional view, Figure 4~
FIG. 8 is a front sectional view showing the shape of the connection point in the method of the present invention, FIGS. 9 and 10 are front sectional views showing the shape of the connection point in the secondary method, and
FIG. 1 is a front sectional view showing the groove shape of a comparative example. A, A': Material to be welded (base metal), B, B': Weld metal, E
: welding wire, F: welding flux, P: penetration depth,
8, 88, 8F: Groove angle, R: Bottom curvature radius, W, W
F, WB: groove width, CW: granular metal (cut wire),
Cu: steel backing plate, SB: backing steel plate. Many? Figures of multiple figures ' Figures of multiple figures 2 Figures of 3 Figures of 4 Figures of hair Ta Figures of Figures of Figures of Figures of 7 Figures of Figures of Figures of multiple figures

Claims (1)

[Claims] 1 The groove width W_B at the groove bottom of the welded material is 6 to 1.
4mm, the groove width W_F at the plate thickness surface is 20mm or less, and W_B≦W_F, and the welding thickness of one layer is 3 to 6mm in one pass per layer in welding inside the groove excluding the final layer, and the diameter is Using a wire of 1.0 to 4.0 mm and a welding current of 150 to 700 A per electrode, 15 to 15 mm for a single electrode.
40cm/min, 20-70cm/min for 2 electrodes
A shallow penetration submerged arc welding method for steel, characterized by welding using a normal flux at a welding speed of n.