JPS6163396A - Submerged arc welding method - Google Patents

Abstract

PURPOSE:To improve low-temperature toughness and yield strength by using a flux containing MgO, Al2O3, metallic fluoride, metallic carbonate, etc. of specified wt%, and a wire containing Mn, Ni, Ti, etc. of prescribed %. CONSTITUTION:A titled welding method uses a flux which contains 10-15% MgO, <=30% Al2O3, 6-20% SiO2, 3-20% metal fluoride, 2.5-6.5% metal carbonate being a quantity corresponding to CO2, <=25% TiO2 and/or <=2.0% Ti, and also has limited Si content to <=1.5%. As for a wire, two kinds or more of 1.0-3.0% Mn, 0.3-1.5% Cr and 0.3-1.5% Mo, and 0.5-3.5% Ni, 0.01-0.30% Ti and <=0.28% Si are contained. According to this method, its low-temperature toughness and yield strength can be improved by welding whose welding heat input has been raised.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is directed to submerged arc welding of 70 to 80 kg of high-strength steel used in the construction of offshore structures for oil drilling or penstocks for hydroelectric power generation. The purpose is to obtain a bath weld metal that has excellent welding workability as well as stable low-temperature toughness and yield strength.

(Prior Art) Submerged arc bath welding has been widely used for welding high-strength steel because it allows high welding current and highly efficient welding.

On the other hand, when welding high-strength steel weighing 70 kg or more, cold cracking caused by hydrogen is particularly likely to occur, and to prevent this, it is necessary to reduce diffusible hydrogen in the weld metal as much as possible. From this point of view, sintered flux containing a large amount of metal carbonate has come to be used. That is, the metal carbonate in the sintered flux decomposes in the arc atmosphere, generates Cot or CO gas, and lowers the hydrogen partial pressure, which is extremely effective in reducing diffusible hydrogen.

For example, Japanese Patent Application Laid-Open No. 47-29237 describes a submerged arc welding method for high-strength steel, that is, a method consisting of CaC0t and/or MgCO5,5i (h, A403, CaO, MgO, corresponding to at least 7% COz). A sintered flux containing a metal carbonate with a basicity of 1,00 or more, Si, Mn, Cr, Mo, Ni, Cu,
Ti.

A submerged arc welding process is disclosed that combines wires with specified At, V and Nb contents. Furthermore, in Japanese Patent Publication No. 58-49356, TiO2,5i
ft, MgO1AttOa, CaCOx, BaC0
The content of a is specified, and the amount of CO2 is 5 to 1
A submerged arc welding flux is disclosed.

In these welding methods or fluxes, a large amount of metal carbonate is added in order to reduce diffusible hydrogen, and the weld metal components are adjusted as a means of improving toughness. In order to improve bath welding efficiency, stable addition of Ti or S from the yield point and the dynamic point to prevent the tendency of low-temperature toughness to decrease when high heat input welding is performed.
There is no effective countermeasure such as limiting the amount of i, and this point is a major problem.

Particularly in recent oil rigs, high-strength steel members have become thicker, while 80kg steel is required to have low-temperature toughness down to -80°C and a high yield point of 70Kqf/rLrIn2 stars. In other words, in order to cope with thicker walls,
Highly efficient welding with large heat input is necessary, but unless measures are taken to prevent the deterioration of weld metal properties, the high efficiency of submerged arc welding cannot be fully utilized, and low-efficiency dwarf thermal welding will have to be carried out. I don't get it.

Conventional submerged arc welding of high-strength steel (
The weld metal structure is expected to be refined by the reheating effect of subsequent passes, thereby exhibiting excellent low-temperature toughness and high yield strength. For this purpose, it is necessary to perform dwarf heat welding (35KJ/boiling or less) as much as possible, reduce the amount of welding in one pass (and increase the proportion of finer parts due to post-heating and ξ). However, this reduces welding efficiency and is unsatisfactory in terms of practicality.

That is, by using a large welding heat input of 40 to 60 KJ/G+), the amount of welding in one pass is increased, and the welding process is
It is most desirable to form a weld metal with excellent properties even if the portion of

(Problems to be Solved by the Invention) The purpose of the present invention is to achieve prevention of deterioration of weld metal properties, particularly low-temperature toughness and yield strength, in high heat input submerged arc welding of 70 to 80 kg high-strength steel. At the same time, the objective is to obtain excellent welding workability.

(Means and effects for solving the problems) The gist of the present invention is that MgO1O~50wt%, A4030wt% or less, 5ift 6~20wt%, metal fluoride 3~20wt%.
t%, metal carbonate as COZ equivalent amount 2.5 to 6.5
wt%, Ti1t 25wt% or less and/or Ti2
．． 0wt% or less, and the Si content is 1.5wt.
% or less, and Mn 1.0~
3.0wt%, Cr 0. :3-1.5 wt%, Mo
Two or more types from 0.3 to 1.5 wt% and Ni 0
．． 5-3.5 wt%, Ti0.01-0.30 wt%
The submerged arc welding method uses a wire containing 0.28 wt% or less of Si.

The present invention will be explained in detail below.

First, the flux used in the present invention has a composition of Mg
Although it is necessary to contain 10 to 50 wt% of O,
This is because it imparts appropriate fire resistance to welding slag and is effective in improving bead shape on the high heat input side. Also, Mg
O is a highly basic component and also has the effect of improving low-temperature toughness by reducing the amount of oxygen in the m-joint metal. The effect of MgO is difficult to obtain when it is less than 10 wt% of the total weight of the flux, and when it exceeds 50 wt%, the fire resistance of the flux becomes excessive, the bead shape becomes irregular with medium height, and the slag removability is also poor. This is not desirable because it deteriorates.

The raw material to which MgO is added is magnesia clinker.
Or spinel containing MgO (-NigO・A
t20g), Olivine Sand (MgO-8iOz)
Composite oxides such as magnesium carbonate (MgCO
3), Dolomy) (CaMg (C03) 2:1
It may also be added from carbonates such as.

In addition, the flux in the present invention is At203 at 30w.
Although the content is less than t%, At203 has a high melting point like MgO, improves the fire resistance of the flux, and improves the bead shape under large heat input. Furthermore, the addition of A7-zo3 improves the conformability of the bead end portion, and from this point of view as well, it is a preferable component. However, if added in a large amount, the bead surface will lose its smoothness and the bead shape will also become unstable, so it is necessary to add less than 30 wt%. A40
For the addition of 3, a complex oxide such as mullite or chamotte containing alumina or Al103 is used.

By the way, the Sich component is a useful component for increasing the viscosity of the slag and adjusting the bead shape, and is 6 to 20 wt%.
It is necessary to add However, adding more than 20 wt% is not preferable because it increases Si and oxygen in the weld metal and deteriorates low-temperature toughness.

In addition, the flux in the method of the present invention is CaFz, MgF
x, NaF, BaFz, AtFa, Na
It is necessary to contain a total of 3 to 20 wt % of one or more metal fluorides, which are compounds of a metal element such as aAtFa and fluorine, based on the total flux. Metal fluoride has a low melting point and is useful for adjusting the melting point of flux and improving the bead shape.It also has a low boiling point and is easily gasified in an arc atmosphere, making the slag porous. Since the slag becomes easily friable, the peelability of the slag is significantly improved.The total amount of metal fluoride is 3wt.
If it is less than 20 wt %, the above effect cannot be obtained, and if it exceeds 20 wt %, the fluidity of the slag becomes excessive, the coagulation waves of the bead become rough, and the bead shape becomes unstable.

Furthermore, the flux of the present invention includes CaC03, lVfg
It contains 2.5 to 6.5 wt% of metal carbonates such as cOa, BaCO3, SrCO3, NaC0a, etc. as a Co equivalent amount, but this is because the metal carbonates decompose due to welding heat and Co Alternatively, CO gas is generated, which lowers the hydrogen partial pressure in the arc atmosphere, and is extremely effective in reducing diffusible hydrogen in the weld metal.

In welding where the purpose is to obtain a weld metal with a tensile strength of 70 kg or more, as in the present invention, if the content of diffusible hydrogen is high, there is a marked tendency for cracks to occur in the welded part, and measures must be taken to prevent this. A metal carbonate that reduces diffusible hydrogen is essential, and at least 2.5 wt% as CO2 equivalent is required. However, if it exceeds 6.5 wt%, the gas pressure in the arc atmosphere becomes excessive, the arc cavity blows up significantly, and the bead shape deteriorates, which is not preferable.

However, in the present invention, the amount of Si added to the flux as a deoxidizing agent is limited to 1.5 wt% or less, and the Si content in the wire is limited to 0.28 wt% or less. To improve the low temperature toughness of weld metal,
This is because it is effective to reduce Si in the weld metal as much as possible.

That is, a weld metal containing a considerable amount of Mn, Cr, Mo, etc. has poor hardenability and therefore exhibits an upper bainite structure. On the other hand, from the standpoint of toughness, such a structure is undesirable, and generally satisfactory toughness cannot be obtained.

Therefore, in order to improve this point and obtain excellent low-temperature toughness, it is necessary to upgrade the quality of the metal IJ socks. To achieve this, on the one hand, it is necessary to reduce the amount of oxygen in the weld metal as much as possible and to introduce a large amount of Ni into solid solution, but on the other hand, it is effective to reduce the amount of Si in the weld metal.
be. That is, the Si content in the weld metal is 0.30 wt%.
It is preferable to keep the amount of Si in the flux below 1.5 wt% and the amount of Si in the wire to 0.
．． It is necessary to limit the amount to 28 wt% or less. however,
As a deoxidizing agent, Si is useful for reducing the amount of oxygen in the weld metal, and is also effective in improving bead shape and preventing pock marks. Therefore, it is necessary to add flux and/or wire within the above range.

Next, in the present invention, the low temperature toughness of weld metal is improved,
In addition, for the purpose of obtaining a high yield point, an appropriate amount of Ti is contained in the weld metal.

That is, Ti becomes a ferrite nucleation site in the form of Ti oxide in the weld metal, producing a fine ashular ferrite structure.

Therefore, mixing the ashcular ferrite structure into the weld metal structure of the present invention, which exhibits an upper bainite structure which is originally preferable from the viewpoint of toughness and yield point, has a remarkable effect on improving the structure. , such an effect occurs when the amount of Ti in the weld metal is 0.005 to 0.00.
A range of 0.05 wt% is effective, and if it exceeds this range, the toughness tends to deteriorate.

This is considered to be due to the precipitation of Ti carbides.

By the way, in order to stably add such Ti to the weld metal, it is necessary to use both a flux containing Ti12 and/or Ti and a wire containing Ti. In other words, the addition of Ti to the weld metal is
This can be achieved by including Ti as a metal or TiO□ as an oxide in the flux, or by including Ti in the wire.

In the case of oxide Tie, it is reduced during the welding process,
It migrates into the weld metal as Ti. In this case, the entire amount of added Ti does not migrate into the weld metal;
The amount of Ti that is reduced from O2 is extremely small.
Also, Ti in the flux or Ti in the wire is consumed in large quantities in the arc atmosphere (oxidation is consumed, and only a limited amount becomes effective Ti. In other words, the transfer rate (yield rate) into the weld metal is Ti0z in the flux is Mo: 1 wt%, Ti in the 7 lux is 1 wt%, and Ti in the wire is about 15 wt%.

Therefore, in order to strictly control the amount of Ti in the weld metal, it is important to minimize the influence of welding conditions on the transfer of Ti to the weld metal. The factor that has the greatest influence on arc voltage is the arc voltage.

In other words, when the arc voltage increases and the arc length increases,
The degree of oxidation consumption of Ti in the wire is high, and the weld metal Ti
is in short supply. On the other hand, TiO□ and Ti in the flux
In this case, the arc voltage increases, the arc atmosphere becomes larger, the amount of flux melted increases, and the amount of Ti transferred into the weld metal tends to increase. Therefore,
If Ti is added to the wire and flux in an appropriate proportion, even if there are voltage fluctuations, the Ti from the wire and flux will compensate for each other's increase and decrease, resulting in stable Ti in the weld metal.

Note that the amount of Tie added to the flux must be 25 wt% or less. This is because if more than 25 wt% of TiO2 is added to the flux, the fluidity of the slag becomes excessive and the bead shape tends to become disordered. Further, it is necessary that the amount of Ti added to the flux is 2% wt% or less, and the amount of Ti added is 0.01 to 0.30 wt%. That is, the amount of Tl in the flux is 2wt%
This is because if the value exceeds 1, the amount of Ti in the weld metal will fluctuate greatly depending on the arc voltage, making it unstable. Ti is 2w
In the range of t% or less, the amount may be determined by taking into consideration the amount of Ti0z in the flux and the amount of Ti in the wire.

If the amount of Ti in the wire is less than 0.01 wt%, the effect of adding Ti to the weld metal and its stabilization will not be obtained, and if it exceeds 0.30 wt%, the amount of T in the weld metal will not be obtained.
If the amount of i becomes excessive, the wire will harden and the forgeability at the time of manufacture will deteriorate, which is not preferable.

By the way, Ti0z is added to the flux using Ti oxide such as rutile or titanium slag. Further, titanium slag is a low-order oxide of Ti such as Ti3O5, but the amount added in such a case is treated as equivalent to Tie based on Ti. Further, when adding Ti, metal Ti or a Ti alloy such as Fe-Ti is used. Generally, Ti or Ti alloy has a high N content (which tends to deteriorate low temperature toughness), so it is preferable to limit the amount of N in Ti or Ti alloy to 300 ppm or less.

Next, regarding the wire used in the present invention, the purpose of the present invention is to
When welding high-strength steel of 70 kg or more, it is necessary to add two or more of Mo and Cr and Ni to ensure the strength of the weld metal.

Ni is an essential component not only for the strength of the weld metal but also for improving the toughness of the matrix.
It is necessary to add ~3.5 wt%.
If added in excess of wt%, the cracking resistance of the weld metal will deteriorate and must be avoided.

On the other hand, Mo, Cr are extremely effective in improving the strength of weld metal, Mn 1.0-3.0 wt%, C
r0.3-1.5wt%, Mo 0.3-1.5wt%
It is necessary to add at least two of them.

Below the lower limit of the above component range, 70 Kq f /1m
If the strength of the weld metal of 2 or more cannot be obtained, and if the upper limit is exceeded, the strength will become excessive, the hydrogen cracking resistance will rapidly deteriorate, and the low-temperature toughness will also decrease, so it must be avoided.

(Example) Eleven types of sintered fluxes shown in Table 1 F-1 to F-11 were created. As for the manufacturing method, a predetermined raw material powder was granulated with water glass and fired at 530° C. for 2 hours.

The final particle size range was 12X100 mesh. Among the fluxes shown in Table 1, F-1 to F-5 are examples of the present invention, and F-6 to F-11 are comparative examples for making the effects of the present invention more clear.

Next, as shown in Table 2, 15 types of wires W-1 to W-15 were created. W-1 to W-8 are the main development side, W
-9 to W-15 are comparative examples.

By appropriately combining the above fluxes and wires,
Welding of 21 tsubo weight class as shown in Table 5, Genus 1 to &21 was carried out.

The test steel plates, welding conditions, groove shapes and lamination procedures in this case are shown in Table 3, Table 4, FIG. 1 and FIG. 2. That is, using C-1 (HT-70 steel) and C-2 (HT-80 steel) as test steel plates, the fourth
Welding was performed under the conditions shown in Tables W-1 (single welding) and W-2 (tandem welding).

In addition, (a) of FIG. 2 shows the lamination procedure regarding W-1, and (b) shows the lamination procedure regarding W-2, both of which were subjected to .

After welding as described above, the bead appearance, crack investigation, weld metal tensile test, and impact test were investigated and tested. Investigation of cracks is 1. First, an ultrasonic flaw detection test was conducted to investigate the presence or absence of internal defects in the welded part, and where a defect signal was observed, a macroscopic cross section was taken from that area to investigate the presence or absence of cracks.

The tensile test was performed using JIS Z3111 A11 from the weld metal part.
No. 1 test was taken, and the impact test was also taken from the welded metal part.
The test was conducted by taking a JIS Z3112 No. 4 test piece.

The above results are shown in the right column of Table 5.
Although fully satisfactory results were obtained due to the effects of the present invention, results for Y9 to A21 were unsatisfactory, and the reasons and details thereof are as shown in the remarks column of Table 5.

Note that the above embodiments describe examples of application to 70 and 80 kg steel, but the method of the present invention can of course be applied to 90 kg (100 kg) high tensile strength steel, etc. .

(Effect of the invention) As described above, the effect of the present invention is that in submerged arc welding of high-strength steel of 70 kg or more, the welding heat input can be increased to about 40 to 60 KJ/m in order to improve welding efficiency. The present invention provides submerged arc bath welding in which excellent low-temperature toughness and high yield point can be obtained, and other weldability is sufficiently satisfactory.

[Brief explanation of the drawing]

Fig. 1 is a front view showing the groove shape used in the embodiment of the present invention, and Figs. Figure 1 Figure 2 (b) Procedural amendment voluntarily) October 9, 1982

Claims (1)

[Claims] MgO 10-15wt%, Al_2O_330wt% or less, SiO_26-20wt%, metal fluoride 3-20w
t%, metal carbonate as CO_2 equivalent amount: 2.5 to 6.
5wt%, TiO_225wt% or less and/or Ti2
．． 0wt% or less, and the Si content is 1.5wt.
% or less and Mn1.0-3
．． 0wt%, Cr0.3~1.5wt%, Mo0.3~
2 or more of 1.5wt% and Ni0.5~3.5w
t%, Ti0.01-0.30wt%, and S
A submerged arc welding method characterized by using a wire whose i content is limited to 0.28 wt% or less.