JPS5946716B2 - Narrow gap submerged arc welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a narrow-gap latent arc welding method for thick plates, and is aimed at highly efficient and high-performance welding of thick plates.

Hitherto, the latent arc welding method has been widely used for welding thick plates because it has a high welding speed and fewer defects, but recently as structures have become larger, the plate thickness has become thicker. As the amount of plates used increases, there is a strong demand for improved welding efficiency.

That is, the deposition rate of the currently commonly used submerged arc welding method is relatively high. However, regarding the groove shape, it is necessary to have a groove angle of about 150 as shown by ΛBB'A' in the schematic diagram of Figure 1, and the groove angle increases in proportion to the square of the increase in plate thickness. Groove cross-sectional area increases.

Therefore, the groove cross-sectional area per unit plate thickness increases rapidly as the plate thickness increases, requiring a large amount of welding material and welding time, and inevitably increasing labor. Therefore, as a method to improve the efficiency of welding extremely thick plates, increasing the welding current or increasing the number of electrodes has been carried out. However, due to the constraints of welding within the groove, undercuts occur and slag spreads across both groove walls, resulting in deterioration of slag separation. Furthermore, deterioration of the toughness of the weld heat affected zone is inevitable. Therefore, the welding current is limited to about 800 A, and the number of electrodes is limited to about two, and it is practically difficult to increase the welding current beyond this. Therefore, we cannot expect much efficiency improvement. In addition, neutral or basic molten fine-grained flux is generally used for welding these extra-thick steels, and as a result, the bulk density is relatively large, so it is not affected by the flatus scattering height. Cheap.

This effect is particularly noticeable when the gap is narrow. by the way,
AUSTRALIAN WELDING JOURNA is a submerged arc welding method for I-shaped grooves with groove spacing of approximately 18m71L.
Although it is described in LMAY/JUNEL978, the present inventors have conducted experiments and found that since each layer is welded in two passes, slight deviations in the wire aiming position may cause problems such as insufficient penetration or slag entrainment. As a practical matter, the range of allowable welding conditions is very narrow because defects are likely to occur and the peeling properties of the slag deteriorate. In addition, it has been found that because it is necessary to perform welding with a small heat input of about 14 KJ/Cm, the welding speed is low, efficiency is low, and practicality is poor. In this way, simply reducing the groove angle greatly limits the range of welding conditions. On the other hand, when ultra-thick steel is subjected to latent arc welding, the welded part, especially the heat-affected zone, has low toughness, and there is a strong desire to improve this. However, it is considered difficult to make such an improvement using the conventional submerged arc welding method, and in order to solve this problem, it is being considered to employ MIG welding or the like. As a result of our research into narrowing the gap in latent arc welding, the present inventors found that defects are more likely to occur with conventional split welding, but on the contrary, defects occur when welding each layer in one pass. It has been found that welding becomes easier.

Furthermore, it has been found that the toughness of the heat-affected zone obtained by using such a method is very good. However, when such welding is performed using conventional flux, the slag seizes astride both walls within the groove, making it difficult to remove the slag.

However, in the sintered flux, which was previously thought to be unsuitable for welding within a groove or for welding with small currents (in narrow gap latent arc welding as described above), it was difficult to achieve a good bead shape and slag separation. We have discovered that there are some substances that have properties such as A as an acidic component (or active component).
! , 203 and one or more of SlO2, TiO2, ZrO2, MnO in a total of 15 to 80%, and At2O
35-38% SlO2≦23%, TiO2≦25%, Z
"02≦25%, MnO<-15%, a total of 10 or more of CaO, MgO, BaO as a basic component
~50%, and CaO≦25%, MgO≦35%, B
aO≦30%, and the total amount of metal fluoride converted to fluorine is 2
, 5 to 15%, alkali metal compound as oxide, 2 to 5% in total, and metal powder 0.2 to 3% as essential components (weight %). When used, it was found that the arc was stable and a smooth concave bead was obtained, and the slag was relatively thin and uniform and could be easily peeled off without burning into the weld.

The present invention has been completed based on these new findings, and provides a method that solves the problem of narrow gap welding and enables high-efficiency and high-performance latent arc welding of extra-thick steel. be.

That is, the present invention uses At2O3, SiO2, and TlO as acidic components (or active components) constituting the slag forming agent.
2. A total of 15 or more of one or more of ZrO2 and MnO
80%, and At2O35-38%, SlO2≦23
%, TlO2≦25%, ZrO2≦25? , MnOku1
5%, one or more of CaO, MgO, and BaO as basic components, totaling 10 to 50? And CaO〈25
%, MgO≦35%, BaO≦30%, metal fluoride converted to fluorine 2.5-15%, alkali metal compound converted to oxide total 2-5%, metal powder 0.2 ~3%
Using a fired or sintered flux containing as an essential component (wt%), the groove shape is approximately I-shaped, the groove depth is H, the groove bottom interval WB is 6 to 14 mm, and the groove is The surface spacing WF is 12 mu or more, and WB is less than HWF≦
2 (-+7), and the groove spacing is at least -25
One pass per layer up to 18 mm or less, the weld thickness - weld cross-sectional area/groove width is 3 to 6 mm, and the welding speed is 15 to 400 f with a single electrode! l/Milt, 20 to 70 for 2 electrodes? This is a narrow-gap latent arc welding method that is characterized by welding at a depth of /m.

The present invention will be explained in detail below.

First, the reason for the limitations on the flux used in the present invention will be described.

First, the type of flux used was limited to the firing type and the sintering type for the following reason. That is, in the narrow gap welding of the present invention, stable welding is required more than ever. Therefore, if a molten type flux is used in this case, the addition of an alkali metal compound as an arc stabilizer will result in a bead with a rough waveform and a convex central portion, resulting in poor slag removability. On the other hand, fired or sintered fluxes use water glass as a fixing agent. However, the above-mentioned phenomenon does not occur, probably because the slag forming agent has high refractory properties, and smooth, concave beads are obtained. In addition, in order to improve gas release during welding and to reduce the influence of the flux scattering height, it is necessary that the bulk density of the flux be small or that the flux particle size be relatively coarse. Pumice-like molten flux with low bulk density contains a lot of diffusible hydrogen and is not suitable for welding extremely thick steel.

Furthermore, if the flux particle size is made coarser in the molten type flux, a bead with a rough wave shape will be formed in the middle and high heights, and the slag peeling properties will be deteriorated. On the other hand, a calcined or sintered flux has relatively coarse grains, a low bulk density, and a low amount of diffusible hydrogen, which can be easily produced. Furthermore, by using a fired type or sintered type flux, the penetration depth becomes shallower, and the reheating action of the next bead is effectively utilized to refine the structure. Next, the flux composition is limited for the following reasons.

First, as the acid component (or active component), At2O
3 is less than 5% or At2O3 and SlO2, TlO2
, ZrO2, MnO total is 15? If it is less than 1, the viscosity of the slag is too small, and the bead waveform becomes rough, medium to high bead, the slag removability deteriorates, and the arc becomes unstable.

On the other hand, when At2O3 exceeds 38%, the bead width is small and it is difficult for the bead to bridge the groove sidewall in one-layer, one-pass welding. Furthermore, solidification cracking is likely to occur. At2O3 and Sl
If the total content of one or more of O2, TiO2, ZrO2, and MnO exceeds 80%, slag removability deteriorates, and the amount of oxygen in the weld metal increases, resulting in a decrease in toughness. Matata, SlO2
, TiO2, ZrO2, and MnO are added to partially replace At2O3, or to improve welding workability and adjust the weld metal components, but the reason for this limitation is as follows. SiO2 is mainly added to improve welding workability, but if SiO2 exceeds 23%, the slag will vitrify.
Slag removability deteriorates.

In addition, the amount of oxygen in the weld metal increases and the toughness decreases. Ti
O2 is added to alloy a small amount of Ti and to adjust welding work conditions, but if it exceeds 25%, the amount of Ti in the weld metal becomes too large and the bead waveform becomes rough.

ZrO2 is added to adjust the basicity and improve welding workability, but if it exceeds 25%, the bead waveform becomes rough and hook marks are likely to occur. MnO is added to adjust the Mn yield of the weld metal and improve the pottery mark and blowhole resistance, but if it exceeds 15%, the amount of oxygen in the weld metal increases and the slag removability and toughness deteriorate.

Next, to explain the basic components, first of all, CaO is 25%
Exceeding this will cause slag seizure in the case of Cr-MO steel and the like.

When MgO exceeds 35%, the slag becomes a strong crystalline slag, making it difficult to remove the slag. If the BaO content exceeds 30%, the arc length becomes long, the density of the flux increases, the bead width becomes small and the bead becomes medium to high, the slag removability deteriorates, and fusion failure is likely to occur.

The total of one or more of CaO, MgO, BaO is 1
If it is less than 0%, the slag peeling condition deteriorates, and the amount of oxygen in the weld metal increases, resulting in a decrease in toughness.

On the other hand, if the total content of any one or more of CaO, MgO, and BaO exceeds 50%, the melting point becomes too high, the bead waveform becomes rough and becomes a medium-height bead, and the slag removal properties deteriorate. Next, metal fluorides are CaF2, MgF2, BaF2, MnF2
, AtF3, etc. When converted to fluorine, if the amount of fluorine is less than 2.5%, the flowability of the slag is poor and hook marks occur.

Furthermore, the bead spread is small and fusion failure is likely to occur. Furthermore, the toughness of the weld metal is low. On the other hand, if the amount of fluorine exceeds 15%, the viscosity of the slag becomes too small and the arc becomes unstable, resulting in medium-high beads with rough waveforms and deterioration in slag removability. Furthermore, slag entrainment defects are likely to occur. A gamma alkali metal compound is an oxide such as water glass as a fixing agent, or an oxide such as Na2cO3, K2CO3, Li2C.
It refers to one or more types of carbonates of O3 and fluorides such as Na2SiF6 and K2ZrF6, and if the total amount of these in terms of oxides is less than 2%, the arc stability deteriorates and the waveform becomes rough.

5 on the contrary? If it exceeds , the amount of slag will increase and the removability of slag will deteriorate. Furthermore, it becomes a medium-high bead. Also, usually
Metal powders such as ferrosilicon, ferromanganese, metal manganese, and metal aluminum are added to firing and sintering type fluxes for the purpose of deoxidation or alloying, but the amount of added calories is 3? If it exceeds this, these metal powders are likely to separate from flux particles and segregate during use.

Due to the lack of power, many countermeasures and strict management will be required to deal with changes in flux conditions. Figure 2 shows that the metal powder in the flux is 1
The results of investigating the segregation during use of 0% and 3%
The relationship between the number of times the flux passes through the collector and the metal powder segregation storage, that is, the metal powder content in the flux of 100 mesh or less, before and after use is shown.

As is clear from these results, the flux containing 10% metal powder segregates about 1.5 times when it is collected 3 or 4 times, and nearly twice when it is collected 5 or 6 times. On the other hand, it was found that when the metal powder content was 3%, there was no segregation at all. Therefore, by using a material with a metal powder content of 3% or less, there is no fear of cracking or performance deterioration due to metal powder segregation. On the other hand, if the amount of metal powder added is less than 0.2%, the slag at the rear of the molten pool will blow up during welding, the slag and beads will become uneven, and the slag removability will deteriorate.
The flux raw material oxide used in the method of the present invention is M
Similar effects can be obtained with peroxides and suboxides such as n3O4 and Tl3O5, and in the present invention, these are expressed in terms of the above-mentioned stable oxides. Next, the reason for limiting the groove shape and welding conditions will be explained. All of these conditions were set with the intention of fully demonstrating the effect of narrowing the groove, preventing deterioration and defects in welding work due to narrowing the groove, and improving the toughness of the weld heat affected zone. Fig. 1 is a front sectional view schematically showing the groove shape in narrow gap latent arc welding of thick plates, and the groove shape indicated by ABB2A' in the figure is the groove shape of the conventional method. It shows.

Abb'a' indicates an example of the groove shape used in the method of the present invention. In the groove Abb'a', the groove shape formed by the materials to be welded 1 and 2 is approximately I-shaped, the groove depth is H, and the distance WB of the groove interval Bb' at the groove bottom is 6. ~14m77! Then, the distance WF of the groove interval Aa' on the groove surface part is 12 mm or more, and HWB<WF≦2(-+7), and the wire E is set at least until the groove interval, that is, the distance Ce is 18 mm or more. Place it approximately in the center of the groove width, and in one pass per layer, the welding thickness = weld cross-sectional area / groove width is 3 to 6 mm, and the welding speed is 15 to 40 CTIL/MUl for single electrode, 20 for two electrodes. ~70CIrL/Mill, by welding using the above-mentioned flux F, the bead shape Cd
e becomes a smooth concave, and the penetration P of the base material becomes smaller.
Welding with a groove spacing of 18 mm or less, which was conventionally considered difficult, can be easily performed, and a high-performance welded joint can be obtained.

To explain in more detail below, the groove bottom interval WB is 6m7
When it is less than 1 L and the groove surface spacing is less than 127 nm,
Unless the welding heat input is extremely small, the weld thickness will be large and solidification cracks will likely occur.

In addition, undercuts occur on the side walls of the groove, making it difficult to remove the slag. If the heat input is further reduced, the molten pool is small and solidification is rapid, resulting in slight wire feeding defects and inappropriate flux distribution height, making welding unstable, resulting in defects such as poor penetration and slag entrainment. Easy to do. In the end, the range of appropriate conditions becomes narrower, and there is a problem with practical soil. Bevel width WB at the bottom of the groove
is 14m77! or when the groove width WF of the H groove surface exceeds 2(-+7) Mu, the groove cross-sectional area increases, resulting in a decrease in efficiency and an increase in the amount of welding material used. Undesirable.

Furthermore, when WB>WF, the groove shape becomes trapezoidal, making it difficult to remove the slag. Furthermore, the groove spacing is 18mTI.
The reason why welding below L is limited to one pass per layer is to achieve the above-mentioned effects. Swing welding causes deep penetration into the base metal and the possibility that the groove wall and weld metal This creates valleys and becomes nearly horizontal, making it more likely that defects such as slag entrainment will occur.

In addition, in split welding, the amount of welding in one pass is greatly limited. Furthermore, the reheating effect due to welding heat f becomes smaller. The weld thickness, that is, the weld cross-sectional area/groove width, is substantially determined by the welding conditions at a predetermined groove width, and is determined by the combination of welding current and welding speed.

Therefore, if the welding electrode is small and the welding thickness is less than 3 mm, penetration into the base material will be insufficient, resulting in poor penetration. When the welding speed is high and the weld thickness is small, poor penetration similarly occurs, and defects such as undercuts and slag entrainment are likely to occur. On the other hand, if the weld thickness exceeds 6 mm, poor penetration or hot cracking is likely to occur due to metal running ahead. If welding speed is single electrode, 15c
When it is less than m/Mm, or less than 20 cm/m- in the case of two electrodes, the molten metal protrudes from the molten pool, tends to lead to the front of the molten pool, causing insufficient penetration and slag inclusion. Furthermore, the effect of refining the structure of the weld heat-affected zone due to the reheating action of the next bead, which is a major effect of the method of the present invention, cannot be sufficiently obtained, resulting in a decrease in toughness. When the welding speed is single electrode, it is more than 40 cm/min, 2
In the case of electrodes, if it exceeds 70 CfL/Mm, solidification cracking is likely to occur.

Furthermore, poor fusion and undercuts occur, making it difficult to weld one pass per layer. Although the method of the present invention is based on welding each layer in one pass, it is still possible to weld parts with groove spacing of 20 mm or more using the conventional method, such as when steel plates are 100 mm or more thick. The effect of narrowing the gap in the invention method can be fully demonstrated.

As described above, the present invention is based on reducing the groove spacing and welding each layer in one pass, and provides the following excellent effects.

(1) Since the cross-sectional area of the groove and the cumulative bead surface area are greatly reduced, it is highly efficient and the amount of welding material used is greatly reduced.

12) Since it is not split welding, there is no change in the target position of the wire during circumferential continuous welding, and gaps such as slag entrainment and insufficient penetration are unlikely to occur.

Further, addition of auxiliary filler materials is also easy. (3) The dilution of the base material is very small, and the influence of the base material components, particularly C, Nb, and V, is small and solidification cracking is less likely to occur, resulting in good toughness.

(4) The bond and heat-affected zone, which tend to deteriorate in toughness, are almost completely reheated by the next bead welding and become fine grained, resulting in good toughness.

(5) The number of welded layers is greatly reduced, and the accumulation of strain, residual stress, and hydrogen is reduced, so intermediate SR can be reduced or omitted.

(6) Since welding is performed using firing flux at low speed in one pass per layer, molten metal is interposed between the arc and unmolten metal, and the arc heat is transmitted through this molten metal, causing the base metal to melt. be done.

Therefore, since there are almost no solid surfaces in the molten pool to which slag is likely to adhere and be restrained, slag entrainment defects are less likely to occur. The effects of the present invention will be described in more detail below based on examples.

Examples Tables 1 and 2 show the combinations of steel plates, wires and flats, welding conditions and S.I. The R conditions and welding results are shown.

Similarly, the conventional method and comparative examples are shown in Tables 1 and 2. Numbers 1, 2, 3, 4, 5, 6, 7, 8, 16 in the same table
, 17, and 18 are the methods of the present invention, and numbers 9, 10, 1
1, 12, 13 and 14 are comparative examples. Numbers 15 and 19 are conventional methods. Note that the groove shapes and dimensions of the steel plates used for these weldings are shown in FIGS. 3 to 8.

Further, steel plates/wires and fluxes are shown in Tables 3, 4, and 5, respectively. In the case of the method of the present invention, welding stability was excellent in all cases, slag removability and bead appearance were both good, and there were no defects as a result of the side bending test.

Further, in the method of the present invention, the penetration into the base metal is very small, and even in the case of Nb-containing steel, the abnormal decrease in toughness unlike the conventional method did not occur, and good values were obtained.

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, as shown in Table 2, the toughness of the heat-affected zone welded by the method of the present invention is very good.

In addition, the cross-sectional area of the groove is dramatically reduced compared to the conventional method, and the welding speed is comparable to that of the conventional submerged arc welding method, so welding performance is greatly improved.

As described above in detail, the method of the present invention enables easy and highly efficient welding of steels to which latent arc welding cannot be applied due to problems with base metal composition or HAZ toughness. The amount of welding material used is small, and defects are less likely to occur. Therefore, highly reliable welded joints can be obtained very economically and are of great industrial value.

[Brief explanation of drawings]

Figure 1 is a front sectional view schematically showing the groove shape in narrow gap latent arc welding of thick plates, and Figure 2 shows the relationship between the number of times flux passes through a flux recovery machine and the segregation and extraction of metal powder in the flux. The diagrams shown in FIGS. 3 to 8 are front sectional views showing the groove shapes used in the examples. 1 and 2... Welding material (base metal), 3...
...Welding metal, E...Welding wire, H...
... Groove depth, F... Flux, WB, WF
...... Groove width, P... Penetration depth, B.
P...Batting pass, F. P...Finishing pass.

Claims (1)

[Claims] 1 Al_2O as an acidic component constituting the slag forming agent
_3 and one or more of SiO_2, TiO_2, ZrO_2, MnO in a total of 15 to 80%, and Al_2
O_35-38%, SiO_2≦23%, TiO_2≦
25%, ZrO_2≦25%, MnO≦15%, a total of 10 to 50% of any one or more of CaO, MgO, and BaO as basic components, and CaO≦25%, MgO≦
35%, BaO≦30%, metal fluoride converted to fluorine, total 2.5-15%, alkali metal compound converted to oxide, total 2-5%, metal powder 0.2-3% Using a fired type or sintered type flux containing as an essential component (wt%), the groove shape is approximately I type, the groove depth is H, the groove bottom interval W_B is 6 to 14 mm, and the groove is The surface interval W_F is 12 mm or more, and W_B<W_F≦2
(H/25+7), and the groove spacing is at least 18mm.
The following steps are performed in one pass per layer, with the welding thickness = weld cross-sectional area / groove width being 3 to 6 mm, and the welding speed being 15 to 40 cm/min for single electrode, 20 to 70 cm for two electrodes.
A narrow gap latent arc welding method characterized by welding at m/min.