JPH07276085A - Stainless steel flux cored wire for high temperature use - Google Patents

Abstract

PURPOSE:To improve the slag peelability and to reduce the amt. of spatters to be generated regulating the amounts of carbon and nitrogen in a sheath stainless steel and limiting the amt. of a slag forming agent in filling flux. CONSTITUTION:As the contents in the total weight of a stainless steel of the sheath, 50 to 1000ppm oxygen, <=0.015% Nb, <=0.10% V, <=0.015% C and <=0.025% N are regulated. By the weight ratio of the wire, 0.020 to 0.10% C and 0.008 to 0.08% N are incorporated into flux. A deoxidizer contg. Si is not incorporated into the flux, and as slag components, by the weight ratio of the wire, 5.50 to 15.50% Ti02, 0.20 to 1.50% Si02, 0.20 to 1.50% Al2O3, 0.25 to 1.35% metal fluorides and 0.02 to 1.00% of one or more kinds among the metal oxides of Fe, Mn and Mg are incorporated therein. Moreover, the amounts of Nb and V intruded inevitably are regulated to <=0.75% and <=0.10%. This wire has good high temp. properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel flux cored wire, and more particularly to a stainless steel flux cored wire developed for welding stainless steel for high temperature applications.

[0002]

2. Description of the Related Art Flux-cored wire for stainless steel is a welding material that has rapidly spread in the past few years, and it has excellent workability and good welding workability. It is a major factor in its popularity. However, with the spread of wires, in some industrial fields, the use of flux-cored wires causes unexpected problems.

That is, this is a field in which stainless steel is used as a heat-resistant steel, and a stainless steel welded product of a thick plate is subjected to solution treatment or hot bending. It is known that when a flux-cored wire for stainless steel is used for such a material in a high-temperature application field, a weld often cracks during high-temperature heating / cooling or hot bending. Also, in equipment that is operating for a long time at high temperature, cracks often occur in welds using flux-cored wire, and creep rupture life of welds is similar to that of conventional welding methods such as TIG welding and covered arc welding. In comparison, phenomena such as a marked decrease in ductility and a decrease in ductility at creep rupture have recently been confirmed (see FIG. 1).

In order to solve the above problems when using the current flux-cored wire, the present invention provides:
An object of the present invention is to provide a flux-cored wire for stainless steel, which has good properties as a welding material for high-temperature applications, has excellent welding workability, specifically, excellent slag removability and has a small amount of spatter.

[0005]

Means for Solving the Problems As a means for solving the above problems, the present invention provides a flux-cored wire for stainless steel in which an outer shell made of stainless steel is filled with flux. As the amount, the amount of oxygen: 50 to 1000 ppm, Nb: 0.015% or less, V: 0.10% or less, carbon: 0.015% or less, nitrogen: 0.025% or less, and the filling flux Inside, metal C as a carbon source and a nitrogen source
Carbon: 0.020 to 0.10% in wire weight ratio from at least one of r, metal Mn or various alloy raw materials or compounds with these elements, and / or carbon compound raw materials excluding graphite or carbonate. Nitrogen: 0.008 to 0.08% is included, the deoxidizing agent containing metal Si and / or Si alloy is not substantially included in the filling flux, and the wire is used as a slag component in the filling flux. at a weight _{ratio, TiO 2: 5.50~15.50%, SiO} 2: 0.20~1.50%, Al 2 O 3: 0.20~1.50%, metal fluoride: 0.25 ~ 1.35%, at least one metal oxide of Fe, Mn, Mg: 0.0.
02-1.00%, and Nb and V, which are mixed as unavoidable impurities from the filling flux, and these compounds, in Nb and V conversion amounts by wire weight ratio, Nb: 0.075 %, V: 0.10% or less, and the low melting point metals As, Sb, Pb, Bi and their oxides or compounds which are intentionally added or inevitably mixed in the filling flux. , Wire weight ratio, A
s, Sb, Pb, Bi conversion amount, As: 0.010% or less, S
b: 0.010% or less, Pb: 0.008% or less, Bi: 0.0.
The gist is a flux-cored wire for stainless steel, which is regulated to 008% or less.

The present invention also relates to S, As, S in the wire.
b, Pb, Bi in wire weight ratio S: 0.003 ~
0.035%, 5 × (Bi + Pb) + 2 × (As + Sb): 0.065% or less,
It is characterized by having been regulated.

[0007]

The present invention will be described in more detail below.

[0008] In solving the above problems, the inventors of the present invention focused on the tensile properties of the flux-cored wire weld metal for stainless steel at high temperature, especially ductility, and as factors affecting this, We paid attention to both the shell component made of stainless steel, which is the raw material for forming the wire, and the composition of the raw material for the filled flux.

The inventors of the present invention consider that the above-mentioned problems occurring in the current stainless flux-cored wire are caused solely by the lack of high temperature ductility of the weld metal, and TIG which is the weld metal produced by the conventional construction method. The weld metal or the coated arc weld metal and the weld metal using the current commercially available flux-cored wire were subjected to a high temperature tensile test at 500 to 800 ° C. to compare ductility at break. An example of this test result is shown in FIG. As is clear from the above, it was found that the fracture ductility of the flux-cored wire-welded metal was obviously lowered at a high temperature of 600 ° C. or higher, although there was no great difference between the two up to about 600 ° C.

With respect to the reason for such a decrease in hot ductility at high temperatures, various causes have been considered in the past.
It is argued that it is effective to lower the FN value with gFN or the like so as to fall within the range of 2 to 6) or to reduce the oxygen content of the deposited metal. However, as a result of investigating the cause of the difference in ductility of these weld metals, the present inventors presume that the main cause is the presence of trace amounts of low melting point elements and their compounds contained in the weld metal. It was The low melting point elements referred to here are lead (Pb), bismuth (Bi), antimony.
(Sb), arsenic (As), etc., but among these elements, P
The melting points of b, Bi and the like, which are simple substances, are extremely low at 270 and 327 ° C., and it is considered that they are mostly present in the form of oxides and various compounds in the deposited metal. The melting point of Bi ₂ O ₃ is 820 ° C., the melting point of Pb ₃ O ₄ is 830 ° C., the melting point of Na ₃ Sb is 865 ° C., and the melting point of K ₃ Sb is 812 ° C.

Therefore, the present inventors have investigated the relationship between the content of these low melting point elements or their compounds in the weld metal and the behavior of the weld metal in reducing the high temperature ductility, and as a result, a clear relationship exists. I have found That is, in order to prevent the deterioration of the high temperature ductility of the deposited metal, the content of these low melting point elements in the total weight of the wire is As: 0.010% or less, Sb: 0.010% or less, Pb: 0.008% or less, B
i: It is restricted to 0.008% or less. Desirably, 5 × (Bi + Pb) + 2 × (As + Sb): 0.065% or less,
Is.

Furthermore, it is important that the high-temperature strength is large as a feature of the welding material for stainless steel which is required to have such high-temperature characteristics. Therefore, in order to ensure sufficient strength of the deposited metal, carbon (C) and nitrogen (N) added in the wire are added.
It is well known that the amount of is very important. However, the present inventors have found that from the viewpoint of welding workability, it is important to minimize the elements such as C and N contained in the outer coating stainless steel used for the flux-cored wire.

That is, the inventors of the present invention have investigated the relationship between the carbon content in the outer coating stainless steel and the welding workability, and as a result, the smaller the carbon content in the outer coating, the lower the spatter generation amount. It was found that even if the amount of carbon added to the filling flux increases, the amount of spatter generated is small when the carbon content in the outer coat is low.

Therefore, the smaller the amount of carbon in the outer shell is, the more preferable it is. However, in the present invention, the amount of carbon in the outer shell of stainless steel is 0 as a limit amount at which the effect of reducing spatter can be clearly recognized. It was set to 0.015% or less.

Regarding the nitrogen content in the outer coating stainless steel, the effect of reducing spatter by lowering the nitrogen content was confirmed as in the case of carbon. Therefore, the nitrogen content in the outer coating stainless steel was 0.025%. Below.

However, as described above, in order to secure the high temperature strength of the deposited metal as a stainless steel flux-cored wire for high temperature use, it is essential to add a certain amount of carbon source and / or nitrogen source to the wire. is there. In the present invention, in order to improve welding workability, C and N in the outer skin are
Since it is necessary to regulate the amount as described above, the inventors of the present invention pay attention to the fact that the welding workability is not impaired as much as possible, and the following as feed materials for C and N that can be added from the filling flux side. They were found, and the upper limit of addition of these raw materials was examined from the viewpoint of welding workability (spatter generation amount).

As a result, in the wire of the present invention, metal Cr, as a carbon source and a nitrogen source, are contained in the filling flux.
Carbon: 0.020 to 0.10% by weight of wire from at least one of metal Mn or various alloy raw materials or compounds with these elements and / or carbon compound raw materials excluding graphite or carbonate. Nitrogen: It contains 0.008 to 0.08%. The lower limit of each addition is the minimum amount necessary to secure strength. Here, as the carbon source and the nitrogen source, the metal Cr, the metal Mn, and the alloy raw material or compound with these elements are mentioned. The reason is that the ratio of the amount of C that participates in the oxidation reaction during welding is made as small as possible, and it occurs as a result of oxidation. This is because the aim was to suppress the generation of CO ₂ gas as much as possible. This is because the generation of spatter increases as the amount of CO ₂ gas generated increases. For this reason, in the present invention, the amount of various carbonates mixed in as impurities is less than 0.1% based on the total weight of the wire in terms of CO _2. Is desirable. In addition,
The reason why metal Cr, metal Mn, etc. are mentioned as the carbon source is that they contain carbon and nitrogen as impurities. Examples of the carbon compound raw material excluding carbonates include CF (fluorinated carbon).

Further, the present inventors have examined the influence of Si, Ti, Al, Zr and their iron-based alloys or composite alloys, which are usually added as deoxidizers in the welding material, on the welding workability. As a result, metal Si, Ca-Si, Fe-Si, Fe-Si
It has been clarified that the use of a Si alloy-based deoxidizing agent such as -Mn or Fe-Si-Mg reduces the slag releasability during welding. Therefore, in the present invention, the metals Si and Si are
It has been decided that the alloy-based deoxidizer is not substantially contained. The level of substantially no inclusion in the present invention may be 0.2% or less (filling flux weight%) as the amount of metal Si in the filling flux in consideration of mixing as impurities. .

The slag forming agent in the flux filled in the wire of the present invention is TiO ₂ , SiO ₂ , Al ₂ O ₃ ,
Although it is mainly composed of metal fluorides, metal oxides, etc., it is necessary to limit the content of these raw materials (total wire weight ratio) as follows.

TiO ₂ : TiO ₂ is the main raw material of the slag forming agent of the wire of the present invention, and is added in the range of 5.5 to 15.50% in the total weight ratio of the wire. If it is less than 5.5%, the covering property of the welding bead deteriorates and the stability of the arc becomes insufficient. Further, if it exceeds 15.50%, the viscosity of the slag becomes too high, and welding defects such as slag winding and fusion failure are likely to occur.

SiO ₂ : SiO ₂ forms a slag-forming agent together with TiO ₂ , and has the effect of adjusting the bead shape during welding and improving the compatibility with the base material. However, if the content of SiO ₂ is less than 0.20%, such an effect cannot be expected. On the contrary, if the content is too large, the viscosity of the molten slag is lowered and the bead shape is rather deteriorated. At the same time, SiO ₂
The slag releasability at the time of welding also decreases with the increase of Therefore, the amount of SiO ₂ is 0.20 to 1.50% in the total weight ratio of the wire.
And

Al ₂ O ₃ : Al ₂ O ₃ also forms a slag-forming agent together with TiO ₂ and SiO ₂ , and has the effect of adjusting the bead shape during welding and improving the compatibility with the base material as in the case of SiO _2. There is. Particularly, it is a raw material effective for appropriately adjusting the high temperature viscosity of the slag, and if it is less than 0.20%, the viscosity of the slag is too low and the beads are liable to drop during vertical welding. However, on the contrary, if the amount is too large, the viscosity of the slag becomes too high, and welding defects such as slag winding are likely to occur and the slag releasability is also deteriorated. Therefore, Al ₂ O
The addition range of ₃ is 0.20 to 1.50% by weight of the wire.

Metal Fluoride: Various metal fluoride raw materials such as CaF ₂ , sodium fluoride, potassium fluorite, and cryolite are generally well known for adjusting the high temperature viscosity and basicity of slag during welding. Has been. However, the present inventors have found that in the wire of the present invention, the addition of these metal fluorides improves the slag removability. The effect of improving the slag releasability is not clear when the wire weight ratio is less than 0.25%, and the slag releasability improves with an increase in metal fluoride, and the slag releasability is improved up to about 5.0%. It was confirmed to maintain. However, since the generation of sputter becomes remarkable as the amount of metal fluoride increases, the upper limit of addition of metal fluoride is set to 1.35% in the present invention.

Metal oxides of Fe, Mn and Mg: When the influence of various metal oxide raw materials on the welding workability was investigated in developing the wire of the present invention, TiO ₂ , FeO (Fe ₂ O ₃
), MnO, MgO, etc. improve the slag releasability,
It was found that SiO ₂ , CrO (Cr ₂ O ₃ ), NbO, V ₂ O _{3 and the} like lower the amount, and Al ₂ O ₃ has an optimum addition range. Therefore, in the present invention, as described above, regarding TiO ₂ , SiO ₂ , and Al ₂ O ₃ , the optimum range thereof is determined in consideration of the overall welding workability, and FeO, MnO, MgO, etc. are positively set. At least one or more of Fe, Mn, and Mg metal oxides are added. The lower limit of the amount of addition is 0.02% at which the improvement effect by the addition can be seen. However, since spattering becomes remarkable when any of these oxides is excessively added, the upper limit of addition is set to 1.00%.

Nb, V: As described above, the presence of Nb oxide and V oxide in the wire has been found to deteriorate the peelability of the weld slag even if the amount thereof is very small. Although these oxides were conventionally considered as unavoidable impurities, they have succeeded in improving the slag removability by positively eliminating them in the present invention.

However, such an element is often mixed in the outer stainless steel as the same component as an impurity, which is oxidized during welding and mixed in the slag, resulting in deterioration of slag removability. It was also confirmed. Therefore, in the present wire, the Nb content as impurities in the outer stainless steel is set to 0.015% or less, the V content is set to 0.10% or less, and further, these elements mixed from the filling flux are included. And its compounds such as oxides
b, V conversion value, wire weight ratio, Nb: 0.075%
Hereinafter, V: 0.10% or less.

S: S in an ordinary flux-cored wire for stainless steel is mixed as an unavoidable impurity from both the shell / filling flux, and the presence of S together with P increases the hot cracking susceptibility of the deposited metal. In the prior art, efforts have been made to reduce this as much as possible.
However, the present inventors succeeded in lowering the viscosity of the molten metal by positively adding an appropriate amount of S to the wire, and thereby the detachment of the molten metal at the tip of the wire during welding /
It has been discovered that the transition state can be greatly stabilized and spatter generation can be drastically reduced. From this knowledge, in the present invention, S can be positively added if necessary. When S is added, the lower limit of S, at which such an effect is recognized, is 0.003% in the total weight ratio of the wire, and the upper limit of the addition is 0. It is set to 035%.

O: Oxygen contained in the skin is usually mostly present in the form of inclusions as oxides. It is clear that such an oxide acts as the starting point of the arc in the unmelted part of the wire during welding, and serves as a stable arc generation point at the wire tip, which in turn is effective in reducing the amount of spatter generation. It was The effect of increasing the arc stability is that the amount of oxygen in the skin is 50 ppm.
The above is clear. However, if the amount of oxygen in the skin is too large, the oxide (inclusions) in the skin will cause wire breakage during wire drawing, so the upper limit of the oxygen content is 300 pp.
It has become clear that it is desirable to keep m. However, since the oxide as such an arc stabilizer only needs to be present on the surface as the welding wire, it does not need to be present as an oxide contained in the outer coat of the wire, and the surface after the wire drawing is performed. The purpose will be achieved even by forcedly oxidizing. Considering the case of carrying out such a treatment, the total oxygen amount in the wire sheath is preferably 50 ppm to 1000 ppm.
Here, the upper limit is set to 1000 ppm because, when a treatment such as surface oxidation is performed, the wire feeding property is deteriorated due to the oxidation of the wire surface as an adverse effect of the excessive oxidation treatment.

It is needless to say that the component composition of the stainless steel skin can be the element and content contained in so-called stainless steel as long as the content of each of the above components is regulated. As an example of stainless steel, JIS G 4304 “Hot rolled stainless steel sheet”, JIS G 4305 “Cold rolled stainless steel sheet”, JIS G 4307 “Cold rolled stainless steel strip”
The austenitic stainless steels described in (1) and (2) are also possible, and those having a composition similar to these are also possible. Of course, the stainless steel to which the present invention is applied may have these component systems and compositions as long as it is used at high temperatures. Further, the cross-sectional shape of the flux-cored wire, the wire diameter, etc. are also appropriately determined.

Next, examples of the present invention will be described.

[0031]

[Examples] Various flux-cored wires (wire diameter 1.2φ) having the composition shown in Table 1, Table 2, Table 3 and Table 4 were prototyped and subjected to a welding test to examine high temperature characteristics, welding workability, etc. It was 304L stainless steel (main component is
Cr: 19%, Ni: 10% included) was used.

The high temperature characteristics are as follows: high temperature 304 type stainless steel (commonly referred to as 304H) as a base material, current 200A, voltage 30
Carbon dioxide arc welding was performed under welding conditions according to JIS Z3323 of V, tensile test pieces were sampled from the welded portion, and a high temperature tensile test was performed. The cases where the high temperature tensile ductility and the high temperature rupture strength at 750 ° C. were 27% and 210 N / mm ² or more, respectively, were regarded as acceptable within the design range of the present invention.

The welding workability was evaluated at the time of welding in the above-mentioned high temperature characteristic test, and was also evaluated by performing horizontal fillet welding using SUS304 steel having a plate thickness of 6 mmt. Also,
As other characteristics, the hot cracking susceptibility was evaluated by the crater cracking occurrence state by the FISCO cracking test. The wire drawability was evaluated under the wire drawing conditions used in the actual production line.

As the test results are shown in Tables 5 and 6, in the examples of the present invention, excellent high temperature characteristics were obtained, and the slag removability was excellent and the amount of spatter generated was small. Is also good.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

[0040]

[Table 6]

[0041]

As described in detail above, according to the present invention,
We can provide flux-cored wire for stainless steel that has good high-temperature properties as a welding material for high-temperature applications, excellent welding workability, and particularly excellent slag removability and low spatter generation. The effect of contributing to further diffusion is remarkable.

[Brief description of drawings]

FIG. 1 is a diagram showing high temperature characteristics of a TIG weld metal and a conventional flux-cored wire weld metal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shogo Natsume 100-1 Urakawachi Urakawachi, Fujisawa City, Kanagawa Stock Company, Kobe Steel Fujisawa Works

Claims (2)

[Claims] 1. A flux-cored wire for stainless steel, comprising a stainless steel sheath filled with flux in a weight percentage (hereinafter the same), wherein the content of oxygen in the total weight of the stainless steel sheath is 50 to 1000 ppm. , Nb: 0.015% or less, V: 0.10% or less, carbon: 0.015% or less, nitrogen: 0.025% or less, and as a carbon source and a nitrogen source in the filling flux. , Metal C
Carbon: 0.020 to 0.10% in wire weight ratio from at least one of r, metal Mn or various alloy raw materials or compounds with these elements, and / or carbon compound raw materials excluding graphite or carbonate. Nitrogen: 0.008 to 0.08% is included, the deoxidizing agent containing metal Si and / or Si alloy is not substantially included in the filling flux, and the wire is used as a slag component in the filling flux. at a weight _{ratio, TiO 2: 5.50~15.50%, SiO} 2: 0.20~1.50%, Al 2 O 3: 0.20~1.50%, metal fluoride: 0.25 ~ 1.35%, at least one metal oxide of Fe, Mn, Mg: 0.0.
02-1.00%, and Nb and V, which are mixed as unavoidable impurities from the filling flux, and these compounds, in Nb and V conversion amounts by wire weight ratio, Nb: 0.075 %, V: 0.10% or less, and the low melting point metals As, Sb, Pb, Bi and their oxides or compounds that are intentionally added to the filling flux or are unavoidably mixed. , Wire weight ratio, As,
In terms of Sb, Pb, Bi conversion, As: 0.010% or less, Sb: 0.010% or less, Pb: 0.008% or less, Bi: 0.008% or less, stainless steel characterized by Flux-cored wire for steel. 2. S, As, Sb, Pb, Bi in the wire,
In the wire weight ratio, S: 0.003 to 0.035%, 5 × (Bi + Pb) + 2 × (As + Sb): 0.065% or less,
The flux-cored wire for stainless steel according to claim 1, which is regulated as follows.