JPS6057433B2 - Flux for submerged welding of stainless steel - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a flux for submerged arc welding of stainless steel, and more particularly to a flux for suppressing the carbon content of weld metal to an ultra-low carbon level and improving corrosion resistance. It is something.

Stainless steel not only has excellent corrosion resistance, but also has many outstanding properties such as high-temperature strength and low-temperature toughness, so it is widely used in industry. The amount of stainless steel welding materials used is also on the rise.

In addition, recently, the environment in which they are used has become more severe, and the quality standards required of materials are also becoming stricter. Experimental research is continuing from various perspectives to address this issue.

Among stainless steels, for example, to prevent intergranular corrosion and stress corrosion cracking, low carbon and carbon stabilizing elements (T
It is widely known that addition of Nb (i, Nb, etc.) is effective.

In order to obtain even higher performance, various methods such as composite addition of carbon stabilizing elements such as Ta, Mo, W, and V have been investigated, but considering weldability and other mechanical properties, the most An effective means is to reduce the carbon content to an extremely low level, and recent steelmaking technology has reached the stage where steel with carbon content of 0.020% or less is fully practical. When welding these ultra-low carbon stainless steels, it is natural that the weld metal is required to maintain various properties such as corrosion resistance at the same level as the base metal. is defined as 0.020%C or less. In welding methods that use flux, such as shielded arc welding, non-gas shielded arc welding, and submerged arc welding, the causes of carbon being contained in the weld metal are: 1. Carbon migration from the base metal 2. Wire; Examples include migration of carbon contained in consumable electrode materials such as steel strips, migration of carbon contained in flux, etc.

Among these, the carbon content of 1 base material and 2 carbon content of electrode materials such as wire and steel strip depend on the steel manufacturing technology, and 0
．． It is kept at a very low level of 0.020%C or less, and welding materials such as wires are commercially available in particular with 0.010%C or less.

Therefore, the most effective way to keep the carbon content in the weld metal low is to keep the total carbon content in the flux low and to minimize the transfer of carbon in the flux into the weld metal during welding. be. However, in the conventional slag-covered welding method, which covers the heating surface with slag, welding workability, such as arc stability, slag peelability, heat shape, appearance, and related problems such as slag inclusions and blowholes, It has been difficult to create a flux composition that will reduce the degree of carbon transfer to the weld metal due to constraints to prevent welding defects such as.

In other words, ordinary bond flux for submerged arc welding contains 3 to 2 carbonates such as lime carbonate (CaCO3).
It contains approximately 5% of carbon dioxide, and its function is to decompose due to arc heat and generate CO2 gas, contributing to the stabilization of the arc, as well as blocking the arc from the atmosphere and reducing the partial pressure of nitrogen and hydrogen in the arc atmosphere. In addition to obtaining a sound weld, the decomposed oxides (eg, CaO) become a major component of slag and have the effect of improving the corrosion resistance and mechanical properties of the weld metal through desulfurization and other effects.

On the other hand, however, the generated CO2 gas dissociates into carbon and oxygen at the saw part due to the high temperature of the arc atmosphere, and the generated carbon migrates into the weld metal, causing an increase in the amount of carbon. In this case, if the base material to be welded is carbon steel, low alloy steel, or ordinary stainless steel with relatively loose regulations on carbon content, the amount of increase in carbon due to CO2 gas generated from the flux will be Since the amount of carbon is very small compared to the base material, it is a very effective means of carbonate addition without any problems. It is not preferable to add carbonates containing carbonate to the flux because various adverse effects arise due to an increase in carbon in the weld metal. Therefore, methods for improving conventional fluxes and reducing the carbon content of the weld metal depend on how to achieve sound welding without incorporating carbonates into the flux. For example, Japanese Patent Publication No. 52-19814 states that carbon dioxide generated from carbonates mixed in flux is decomposed into oxygen and carbon by a reduction reaction in the molten pool, and the carbon is mixed into the weld metal. In order to prevent the carbon content of the weld metal from increasing, austenite is produced by blending a slag agent, deoxidizing agent, alloying agent, etc. with the glassy powder obtained by melting and crushing it in advance, granulating it, and sintering it. There is an example of stainless steel flux, but in this case, it must be melted and then re-pulverized, blended as part of the raw material, granulated, sintered, and used, which reduces productivity. In addition to being low, the effect of low carbonization was also insufficient.

In this way, all conventional fluxes rely on the passive method of keeping the carbon source low by adding as little carbonate as possible, and all of them have the problems mentioned above, but they are not necessarily satisfactory. However, I could not say that.

In view of the actual situation, the applicant has already filed a patent application in 1972-
129138 in combination with ultra-low carbon austenitic stainless steel wire with a carbon content of 0.02% or less, Ae2O3lO~40%, ZrO23~25%
We have proposed a flux that can produce ultra-low carbon weld metal by blending a large amount of fluoride with a flux that has 100% carbonate as an essential component and the rest consisting of ordinary welding metal components, and does not substantially contain carbonates. .

With this flux, sound welding can be achieved and ultra-low carbon weld metal with a carbon content of 0.02% or less can be obtained, but the flux cannot be expected to have a positive decarburization effect, and the When the carbon content of the weld metal and the base metal are both at the upper limit of the specification, it cannot be said that there is no possibility that the carbon content of the weld metal will deviate from the specification, and there was some room for improvement in this respect. Therefore, the present inventors conducted various experiments in order to further improve the above-mentioned flux and develop a flux that can actively reduce the carbon content in weld metal by imparting decarburization ability to the flux itself. The present invention was made based on the discovery that there is a certain relationship between the SiO2 and ZrO2 contents in the flux and the carbon in the weld metal. That is, the present inventors added SiO2 to a flux consisting of 62% fluorite, 28% alumina, 5% aluminum fluoride, and 5% metallic chromium as the basic components of the flux.
Wollastonite, silica sand as source, zirconium oxide as ZrO2 source, zircon sand as SiO2 and ZrO2 source were added varying from 0 to 70%, and 0.008% ClO. l
3% Slll. 93%Mnl9.6%Nill9.37
%CrlO. 4. Diameter containing 45% Nb. Welding conditions in combination with the wire 500A134V140cff1/
Min, SM4lB (plate thickness 2
0m), 6 layers were built up in 7 baths for each layer, and the chemical components of the final layer, which are not affected by the base material components, were analyzed, and the Si in the flux was
The relationship between O2 and ZrO2 and carbon in weld metal was investigated.

The results are shown in FIG.

As is clear from the figure, as the amount of [SiO2 + νRO2] in the flux increases, the amount of carbon in the weld metal tends to decrease, and when the amount of [SiO2 + νRO2] exceeds 20%, the amount of carbon in the weld metal increases. is less than the amount of carbon in the wire. In other words, it is found that it has a decarburizing effect and is suitable for ultra-low carbon stainless steel. In addition, in order to use such a flux in combination with a wire containing 0.02% C or less, and to satisfy the standard that the carbon content of the weld metal is 0.02% or less, the carbon increase in the weld metal must be 0.01%. It is necessary to make the [SiO2+
It can be seen that the amount of closed ZrO2 must be 5% or more. However, if it exceeds 45%, practical problems such as the arc tends to become unstable during welding and the bead shape tends to be disordered occur, so a restriction is necessary from this point of view. The present invention has been made based on this knowledge. That is, the gist of the present invention is that 20 to 60% of one or more of calcium fluoride, aluminum fluoride, magnesium fluoride, barium fluoride, sodium fluoride, and lithium fluoride, wollastonite, silica sand, and feldspar. 1 or more 2-40%, alumina 5-30
%, one or more of zirconium oxide, zircon sand, 3~
25% and was determined from the SiO2 equivalent values of wollastonite, silica sand, feldspar, and zircon sand and the ZrO2 equivalent values of zirconium oxide and zircon sand (SiO2 + νZrO
2) A flux for submerged arc welding of stainless steel characterized by a carbon content of 5 to 45% and used in combination with an ultra-low carbon austenitic stainless steel wire having a carbon content of 0.02% or less.

In addition, in the present invention, Mn, Si, Ae, Ni, Cr, MO, V, Nb, Ti may be added to the above composition as necessary.
It is also possible to add appropriate amounts of deoxidizing and alloying elements such as.

The present invention will be explained in detail below.

The flux of the present invention does not contain any carbonate, which is a carbon source, which is normally contained in Shibuya's bond flux, maintains good welding workability, and further actively promotes SiO2
By adding . Calcium fluoride,
aluminum fluoride, magnesium fluoride, barium fluoride,
It is necessary to contain at least 20% of at least one of sodium fluoride and lithium fluoride.

When a part of these fluorides is exposed to the arc during welding, it decomposes and vaporizes, exhibiting a strong arc stabilizing effect.This stabilizing effect minimizes disturbance of the arc atmosphere and prevents melt from the wire tip into the molten pool. Since droplet transfer occurs smoothly, it is possible to suppress the occurrence of welding defects such as slag entrainment blowholes. Furthermore, these fluorides all have a low melting point of about 1000-1350°C and form slag with low viscosity, so during welding, the slag quickly covers the weld metal surface and protects it from the atmosphere, resulting in a healthy weld metal. can be obtained. In this case, the content of one or more of these fluorides was limited to 20 to 60% because if it was less than 20%, the above-mentioned effects would not be sufficient.
This is because if the content exceeds 0%, the arc becomes unstable and it becomes difficult to perform sound welding. As mentioned above, wollastonite, silica sand, and feldspar serve as SiO2 sources, and it goes without saying that they have a significant effect in reducing the carbon content in the weld metal through a synergistic effect with ZrO2. It also plays a major role in obtaining weld metal.

In other words, by blending a large amount of fluoride in the flux of the present invention, it has the effect of enveloping the arc atmosphere and enables sound welding, but as a result, the fluoride in the slag increases and the slag The viscosity of the bead becomes too low, making it difficult to obtain stable beads. At that time S
By adding wollastonite, silica sand, and feldspar, which are lO2 sources, it is possible to increase the viscosity of the slag and obtain a good bead shape. In order to expect these effects, the content must be 2% or more, but if it is added in excess, it will cause slag seizure and the amount of silicon in the weld metal will become excessively large, so the content should be 40% or less. When alumina is added in an amount of 5% or more, the fluidity of the slag is improved, the slag shape is stabilized, the base metal and the weld metal become compatible, and it is effective in preventing undercuts, but if it is added in excess, the melting point of the slag It is necessary to keep the content at 30% or less, since this will increase the fluidity and cause the arc to become unstable. As mentioned above, zirconium oxide and zircon sand are ZrO2 source or Zr
In addition to the effect of reducing the carbon content in the weld metal due to the synergistic effect with SjO2 as a source of O2 and slO2, the addition of 3% or more improves slag removability and gives gloss to the bead, but too much will cause slag. Since this causes the blow-up phenomenon and the slag shape becomes disordered, resulting in poor bead shape, it is limited to 25% or less. In addition, in normal stainless steel welding, deoxidizing agents and alloying agents are added to electrode wires, flux, etc. for the purpose of preventing weld defects such as blowhole cracks and improving the mechanical properties and corrosion resistance of the welded part.
In carrying out the present invention, metals such as Si, Mn, Ni, Cr, MO, Nb, Ti, and A, which are usually added to ordinary submerged arc welding flux, are used.
E, etc. can be added in appropriate amounts in the form of metal powder, alloy powder, iron alloy powder, etc.

The flux of the present invention is obtained by mixing the above-mentioned various raw materials with a binder such as water glass, granulating the mixture, and then firing the mixture at a temperature of usually 300 to 500°C. The effects of the present invention will be shown below in more detail through Examples.

A stainless steel plate shown in Table 1 was used as the base material.

The groove is deep, 30T1r! N8R3OOU bevel. Table 2 shows the wires used. Table 3 shows all the fluxes used. For comparison, we also investigated fluxes outside the scope of the present invention. The welding results are shown in Table 4.Fluxes J and K shown as comparative examples have almost the same good welding workability as the examples of the present invention, but the (SiO2+NRO2) value of the fluxes is less than 5%. Therefore, the carbon content of the weld metal is 0.023% and 0.02%, respectively.
It is as high as 2% and cannot be put to practical use. Furthermore, fluxes L and M have drawbacks in welding workability such as arc stability, slag peelability, and bead shape, and although the desired weld metal can be obtained, it is difficult to say that they are practical. Compared to these, in the examples using the flux of the present invention, the welding workability was good and the chemical composition of the weld metal was also the target.

As explained in detail above, according to the present invention, welding workability is good and the carbon content of the weld metal is 0.02%.
It is an excellent flux for submerged arc welding that can be used in the following manner.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the amount of (SiO2+nRO2) in the flux and the amount of carbon in the molten metal.

Claims (1)

[Claims] 1 20-60% of one or more of calcium fluoride, aluminum fluoride, magnesium fluoride, barium fluoride, sodium fluoride, lithium fluoride, 2-40% of one or more of wollastonite, silica sand, feldspar, alumina 5 ~30%, zirconium oxide,
Contains 3 to 25% of one or more types of zircon sand, and (SiO_2 + 1/2 ZrO_2)% determined from the SiO_2 equivalent value of wollastonite, silica sand, feldspar, and zircon sand and the ZrO_2 equivalent value of zirconium oxide and zircon sand. A flux for submerged arc welding of stainless steel, characterized in that the flux is ~45%.