JP2019171408A - Filler metal for welding ferritic stainless steel - Google Patents

Abstract

To provide a filler metal for welding a ferritic stainless steel which combines high oxidation resistance and excellent high temperature strength with excellent structural stability allowing for suppression of σ phase deposition and 475°C brittleness even in a reductive/carburization/sulfidation environment.SOLUTION: The filler metal for welding a ferritic stainless steel is provided that contains, by mass% based on the total mass of filler metal, Cr of 12.0 to 16.0%, C of 0.020% or less, Si of 0.60 to 2.50%, Mn of 0.30% or less, P of 0.020% or less, S of 0.0030% or less, Al of 1.00 to 2.50%, Nb of 0.001 to 1.00%, N of 0.030% or less, O of 0.010% or less, B of 0 to 0.0100%, Sn of 0 to 0.20%, Ga of 0 to 0.0200%, Mg of 0 to 0.0200%, Ca of 0 to 0.0100% and the balance Fe with impurities.SELECTED DRAWING: None

Description

  The present invention relates to a filler material for welding a ferritic stainless steel, and more particularly to a ferritic stainless steel filler material for TIG welding or plasma welding of Al-containing ferritic stainless steel used for a fuel cell high temperature member.

Recently, the spread of new systems replacing conventional power generation systems is accelerating due to problems such as depletion of fossil fuels such as petroleum and global warming due to CO ₂ emissions. As one of them, “fuel cell”, which has high practical value as a distributed power source and a power source for automobiles, is attracting attention. There are several types of fuel cells. Among them, polymer electrolyte fuel cells (PEFC) and solid oxide fuel cells (SOFC) have high energy efficiency, and are expected to expand in the future.

  A fuel cell is a device that generates electric power through a reaction process opposite to that of water electrolysis, and requires hydrogen as a fuel (fuel hydrogen). Fuel hydrogen is produced by reforming a hydrocarbon fuel such as city gas (LNG), methane, natural gas, propane, kerosene, gasoline, etc. in the presence of a catalyst. Above all, a fuel cell using city gas as a raw fuel has an advantage that hydrogen can be produced in an area where city gas piping is provided.

The fuel reformer is usually operated at a high temperature of 200 to 900 ° C. in order to ensure the amount of heat necessary for the hydrogen reforming reaction. In addition to the fuel reformer, the operating temperature of the combustor, the heat exchanger, the battery body, and the like that heat the reformer is very high.
Furthermore, in such a fuel cell under high temperature operation, in addition to a large amount of water vapor, carbon dioxide and carbon monoxide, an atmosphere containing a large amount of hydrogen and a small amount of hydrogen sulfide derived from hydrocarbon fuel (hereinafter referred to as carburizing / Reducing / sulfiding environment). When a steel material is exposed to such an atmosphere, for example, the surface of the material is corroded by carburization and sulfidation, and the operating environment is severe.

  Here, in high-temperature member applications in fuel cells, Al-containing ferrite systems that utilize the high oxidation resistance of Al-based oxide layers (Al-based oxide films) in order to exhibit good durability even under reformed gas environments Various stainless steels have been studied.

  On the other hand, ferritic stainless steel welding wires have been put into practical use. For example, in Patent Documents 1 to 4, welding excellent in heat resistance, corrosion resistance, oxidation resistance, durability in a high temperature environment, and the like. There is a disclosure of a ferritic stainless steel welding wire from which a metal is obtained.

However, the ferritic stainless steel welding wires described in Patent Literature 1 to Patent Literature 4 are MAG welding in an Ar—CO ₂ or Ar—O ₂ gas shield, and a large amount of spatter is generated. There was a problem that slag with poor peelability was generated on the surface. In addition, since the Al content is small, an oxide film mainly composed of Al ₂ O ₃ cannot be formed on the surface of the weld metal, so that the high-temperature oxidation resistance is insufficient.

On the other hand, a TIG welding wire (filler material) of ferritic stainless steel has also been put into practical use. For example, Patent Document 5 discloses a weld metal by containing appropriate amounts of Mg and Al in a welding wire and combining with O. There is a disclosure of a technique for improving the ductility and toughness of a welded portion by making the structure of the steel finer. However, in the technique described in Patent Document 5, since Mg is contained, slag with poor peelability is scattered on the surface of the weld bead. Further, since the Al content is as small as 0.5% by weight at the maximum, an oxide film mainly composed of Al ₂ O ₃ cannot be formed on the surface of the weld metal, so that the high-temperature oxidation resistance is insufficient.

Further, in Patent Document 6, by limiting the ratio of Ti and Al of the welding wire, the penetration depth is increased, and C and N of the weld metal are fixed as carbonitride with Nb and Ti, and the grain boundary is set. There is a disclosure of technology for preventing corrosion. However, since the welding wire described in Patent Document 6 has an Al content as small as 0.060% by mass at the maximum, an oxide film mainly composed of Al ₂ O ₃ cannot be formed on the weld metal surface. High temperature oxidation resistance was insufficient.

Furthermore, in Patent Document 7, the corrosion resistance of the welded portion is reduced by reducing impurities adhering to the wire surface as well as the ratio of the sum of Nb and Ti of the welding wire to the sum of C and N and the limitations of the Mo and Cu components. There is a disclosure of a technique for obtaining an excellent weld metal. However, since the welding wire described in Patent Document 7 does not contain Al, an oxide film mainly composed of Al ₂ O ₃ cannot be formed on the surface of the weld metal, so that the high-temperature oxidation resistance is insufficient. There was a problem that there was.

JP 2003-320476 A JP 2006-231404 A JP 2012-11426 A JP 2014-46358 A Japanese Patent Laid-Open No. 9-225680 JP 2006-263811 A JP 2008-132515 A

The reformed gas of the fuel cell using the above-mentioned city gas as a raw fuel may contain a large amount of hydrogen and a sulfur component added as an impurity or odorant in addition to water vapor, carbon dioxide and carbon monoxide. is there. However, in the past, the effects of a large amount of hydrogen and sulfide components in the reformed gas on the properties of member steels and weld metal parts have not been evaluated and studied on the oxidation resistance. In other words, the oxidation characteristics of welds of ferritic stainless steel under harsh environments (carburizing / reducing / sulfiding environments) containing carbon dioxide, carbon monoxide, a large amount of hydrogen, and sulfide components are unknown. is there.
Further, in the case of the SOFC system and PEFC system, since the operating temperature of the fuel cell becomes high, further improvement in high temperature strength is required.
Furthermore, when a welded structure is employed as the fuel cell member, it is also required that the welded structure can avoid brittle fracture of the weld due to 475 ° C. brittleness or σ brittleness.
For these reasons, in recent years, when welding Al-containing ferritic stainless steel using a weld filler metal, the ferritic stainless steel weld metal has superior oxidation resistance, high-temperature strength, and brittleness resistance than before. There is a strong demand for a weld filler metal capable of obtaining the following.

  The present invention has been devised to solve the above-described problems, and is under an environment containing carbon dioxide, carbon monoxide, a large amount of hydrogen, and a sulfur component (a carburizing / reducing / sulfiding environment). However, the present invention provides a weld metal for ferritic stainless steel that combines the high oxidation resistance of weld metal, excellent high-temperature strength, and excellent brittleness characteristics.

The gist of the present invention is as follows.
[1]% by mass relative to the total mass of the filler metal,
Cr: 12.0 to 16.0%,
C: 0.020% or less,
Si: 0.60 to 2.50%,
Mn: 0.30% or less,
P: 0.020% or less,
S: 0.0030% or less,
Al: 1.00-2.50%,
Nb: 0.001 to 1.00%,
N: 0.030% or less,
O: 0.010% or less,
B: 0 to 0.0100%,
Sn: 0 to 0.20%,
Ga: 0 to 0.0200%,
Mg: 0 to 0.0200%,
Ca: 0 to 0.0100%,
Ni: 0 to 1.0%,
Cu: 0 to 1.0%
Mo: 0 to 1.0%,
Sb: 0 to 0.5%,
W: 0 to 1.0%
Co: 0 to 0.5%,
V: 0 to 0.5%
Ti: 0 to 0.5%,
Zr: 0 to 0.10%,
Y: 0 to 0.10%,
La: 0 to 0.10%,
Hf: 0 to 0.10%,
REM: 0 to 0.10%
A ferritic stainless steel welding filler material characterized by containing Fe and impurities.
[2] In mass% with respect to the total mass of the filler metal, B: 0.0002 to 0.0200%, Sn: 0.005 to 0.20%, Ga: 0.0002 to 0.0200% or less, Mg: The ferrite system according to the above [1], including one or more of 0.0005 to 0.0200% or less, Ca: 0.0005 to 0.0100% or less, and satisfying the following formula (1): Stainless steel welding material.
10 (B + Ga) + Sn + Mg + Ca> 0.020 (1)
In addition, each element symbol in Formula (1) shows content (mass%) of each element in a filler metal.
[3] In mass% with respect to the total mass of the filler metal, Ni: 0.10 to 1.0%, Cu: 0.10 to 1.0%, Mo: 0.10 to 1.0%, Sb : 0.01 to 0.5%, W: 0.10 to 1.0%, Co: 0.10 to 0.5%, V: 0.10 to 0.5%, Ti: 0.01 to 0 0.5%, Zr: 0.0001-0.10%, Y: 0.0001-0.10%, La: 0.0001-0.10%, Hf: 0.0001-0.10%, REM: The filler material for welding ferritic stainless steel according to the above [1] or [2], containing 0.001 to 0.10% of one or more.

  According to the present invention, even in an environment containing carbon dioxide, carbon monoxide, a large amount of hydrogen, and a sulfur component (carburizing / reducing / sulfiding environment), the weld metal has high oxidation resistance and excellent performance. It is possible to provide a ferritic stainless steel welding filler material having both high-temperature strength and excellent brittleness characteristics.

FIG. 1 is a diagram showing a groove shape of a welding test in an example of the present invention.

The present inventors welded using various types of ferritic stainless steel welding filler materials, and investigated the oxidation resistance, high-temperature strength, and embrittlement resistance properties of the obtained weld metal in the reformed gas. The effect of the constituent elements of the weld filler metal on the weld was investigated. As a result, by controlling the component composition of the filler metal within a predetermined range, in an environment containing carbon dioxide, carbon monoxide, a large amount of hydrogen, and a sulfur component (carburizing / reducing / sulfiding environment). Even in such a case, it has been found that excellent oxidation resistance and embrittlement resistance can be exhibited, and furthermore, excellent 0.2% proof stress can be exhibited even in a high temperature region around 750 to 800 ° C. The “high temperature strength” in the present embodiment is a characteristic that can exhibit excellent 0.2% proof stress even in a high temperature region around 750 to 800 ° C., and “oxidation resistance” means carbon dioxide, monoxide It means oxidation characteristics in a reformed gas environment (carburizing / reducing / sulfiding environment) containing carbon, a large amount of hydrogen, and sulfur components. Further, the “brittleness characteristic” indicates the stability of a structure in which σ brittleness and 475 ° C. brittleness can be suppressed.
The knowledge obtained by the present invention will be described below.

"About embrittlement characteristics"
(A) Usually, since the weld metal part of Al-containing ferritic stainless steel is constituted by the growth of columnar crystals, it tends to be coarser than ferritic stainless steel not containing Al. When the crystal grains of the weld metal part become coarse, there is a risk of causing breakage due to 475 ° C. brittleness and σ brittleness. However, it has been found that the formation of equiaxed crystals is promoted by the formation of carbonitrides composed of Nb (C, N) by controlling the chemical composition in the weld metal, and the weld structure can be refined. .

(B) In order to obtain the effect of promoting the formation of equiaxed crystals by carbonitride Nb (C, N), it is preferable that 10 (B + Ga) + Sn + Mg + Ca be more than 0.020 in the chemical component of the weld metal part. I understood. In the case of a weld metal, Mg, Ca, and Ga can generate oxides and sulfides, and can increase the cleanliness of crystal grain boundaries. In addition, since Mg, Ca, and Ga effectively act as Nb (C, N) nucleation sites, formation of equiaxed crystals of the weld metal can be promoted.

(C) Further, in the component composition of the filler metal, adjusting the content of Cr, Si, Nb, Al can improve the embrittlement resistance characteristics of the obtained weld metal part, particularly the precipitation of intermetallic compound σ phase (σ It has been found effective in suppressing brittleness) and 475 ° C brittleness itself. σ brittleness and 475 ° C. brittleness are derived from the formation of intermetallic compounds mainly containing Cr and containing Si and Al, and the production sites are often grain boundaries. That is, in order to suppress the σ brittleness and the 475 ° C. brittleness, it can be said that it is effective to suppress the generation of the intermetallic compound itself and to reduce the generation site. As a result of further investigation by the present inventors, the formation of intermetallic compounds is suppressed by limiting the amount of Cr, and the structure is stabilized by suppressing generation sites by segregation to the crystal grain boundaries of Nb. As a result, it was found that σ brittleness and 475 ° C brittleness can be suppressed. Furthermore, since the formation of intermetallic compounds containing Si and Al can be suppressed by limiting the amount of Cr and adding Nb, the amount of Si and Al contributing to the oxidation resistance described later can be secured, so that the oxidation resistance and the tissue stability can be secured. It is also possible to balance sex.

"High temperature strength"
(D) Usually, in order to suppress deformation which becomes a problem in a structure operating in a high temperature range near 750 to 800 ° C., the high temperature strength of the ferritic stainless steel as a material and the welded portion, particularly 0 at around 750 ° C. It is effective to increase the 2% proof stress and suppress the decrease of the 0.2% proof stress in the vicinity of 800 ° C.

(E) It has been found that the improvement of 0.2% proof stress and the suppression of the decrease in the above-described high temperature range are remarkably improved by adding a small amount of B, Nb, Sn, Mg, Ca, Ga and adjusting the addition amount. . That is, in the welded metal part of ferritic stainless steel, the characteristics of increasing the 0.2% proof stress near 750 ° C. and suppressing the decrease of the 0.2% proof strength near 800 ° C. New knowledge was obtained that this can be achieved by adding elements. Although there are still many unclear points regarding the action of improving the high-temperature strength, the action mechanism described below is inferred based on experimental facts.

(F) The addition of a small amount of B contributes to the increase in yield strength and tensile strength at 750 to 800 ° C., and has the effect of significantly improving the 0.2% yield strength. The addition of a small amount of B suppresses the formation of cavities (nano-sized gaps) generated from the grain boundaries as a result of B segregating at the grain boundaries, delaying the grain boundary sliding, and dislocation density within the crystal grains. This has the effect of increasing the internal stress associated with the rise of. Moreover, the novel effect which the effect of these B becomes remarkable with Nb addition steel was discovered.

(G) The effect of B that becomes remarkable in the above-described Nb-added steel is superimposed by the combined addition of Mg, Ca, and Ga. Mg and Ca generate non-metallic inclusions and sulfides, enhance the cleanliness of the crystal grain boundaries and promote the grain boundary segregation of B, and more efficiently express the above-described effects of B. Moreover, since Ga also improves the cleanliness of steel, the above-described effects of B can be efficiently expressed by the combined addition with B.

(H) Furthermore, in order to exert the effect of increasing the internal stress accompanying the increase in the dislocation density in the grains described in (f) above, the combined addition with Sn is effective. Although Sn is a grain boundary segregation element, the combined action with B increases the effect as a solid solution strengthening element in the crystal grains, and is effective in increasing the high-temperature strength accompanying an increase in internal stress.

"Oxidation resistance"
(I) Moreover, in order to improve the oxidation resistance of the weld metal part under the reformed gas environment containing the hydrogen and sulfide components described above, the contents of Si, Al, Nb, and Mn in the filler metal are set within a predetermined range. By adjusting the inside, it is effective to promote the formation of an Al-based oxide film and to enhance the protection of the film. Furthermore, the addition of B, Nb, Sn, Mg, Ca, and Ga in the ferritic stainless steel filler material does not impair the oxidation resistance in the reformed gas environment, but rather a small amount of Mg and Sn is added in the Al content. The protective property of the system oxide film is further increased and the effect of oxidation resistance is also exhibited. Si, like Al, is also an element that promotes columnar crystallization of the weld structure. Therefore, if the Si content is increased from the viewpoint of promoting the formation of an Al-based oxide film, there is a concern about the coarsening of the weld metal part. The However, since the columnar crystallization of the welded structure can be sufficiently suppressed by adding a small amount of Nb, Sn, Mg, Ca, and Ga, even when the Si amount is relatively high as in this embodiment, the Al-based oxide film It becomes possible to achieve both formation promotion and suppression of the coarsening of the weld metal part. Here, in this embodiment, the surface film before being exposed to a high temperature reformed gas environment is a “passive film”, and the passive film exposed to a high temperature reformed gas environment is composed by various reactions. This is described by distinguishing it from “Al-based oxide film”.

(J) The above-described reformed gas environment (carburizing / reducing / sulfiding environment) tends to generate defects in the Al-based oxide film as compared with a steam oxidation environment that does not contain air or hydrogen. The reason why the reformed gas environment facilitates the generation of defects in the oxide film is not clear, but it is speculated that sulfides generated under the reformed gas containing sulfide components have some adverse effects on the oxide film. . If a defect occurs in the Al-based oxide film in a modified gas environment, oxidation of Cr and Fe may proceed on the exposed steel surface. For such oxidation promotion in the reformed gas, Mg is dissolved in the Al-based oxide film, and Sn is segregated on the surface of the base material to delay the outward diffusion of Cr and Fe, so that the Al-based The protective property of the oxide film can be further increased. As a result, the oxidation resistance of the ferritic stainless steel can be improved.

  Hereinafter, the components of the ferritic stainless steel welding filler material (hereinafter also simply referred to as a filler material) to which the present invention is applied, the content of the components, and the reasons for the limitation of each component will be described. The content of each component is expressed by mass% with respect to the total mass of the ferritic stainless steel welding filler metal, and when expressing the mass%, it is simply expressed as%.

<Cr: 12.0 to 16.0%>
Cr improves the corrosion resistance required for stainless steel weld metal. In addition, Cr has an effect of improving the oxidation resistance by improving the adhesion of the Al-based oxide film on the surface of the weld metal, and is also an element contributing to the improvement of the high temperature strength. In order to obtain these effects, a Cr amount of 12.0% or more is required. Preferably it is 13.0% or more. On the other hand, when Cr is excessively contained, in addition to remarkable material hardening due to brittleness at 475 ° C., the formation of a σ phase which is an embrittlement phase when exposed to a high temperature atmosphere is promoted. Moreover, since an increase in alloy cost and Cr evaporation may be promoted, the upper limit is made 16.0% or less. Preferably, it is 15.0% or less.

<C: 0.020% or less>
C is inevitably contained in the filler metal, and inhibits oxidation resistance by forming a solid solution or Cr carbide in the ferrite phase in the weld metal. On the other hand, when the amount of C is excessive, hot cracking is likely to occur in the weld metal, and the ductility of the weld metal is lowered, resulting in poor workability. For this reason, the smaller the amount of C, the better, and the upper limit is made 0.020% or less. Preferably it is 0.015% or less. However, since excessive reduction leads to an increase in refining costs, the lower limit of the C amount is preferably set to 0.001% or more. More preferably, it is 0.002% or more.

<Si: 0.60 to 2.50%>
Si is an important element for improving the compatibility between the weld metal and the base material and ensuring oxidation resistance. Si slightly dissolves in the Al-based oxide film and also concentrates directly under the oxide film / steel interface to improve the oxidation resistance under the reformed gas environment. In order to obtain these effects, the lower limit is made 0.60% or more. Preferably it is 0.70% or more. On the other hand, when Si is excessively contained, the 475 ° C. brittleness resistance may be reduced, or a slag having poor peelability may be produced when contacting. Moreover, since the toughness of steel, workability fall, and formation of Al type oxide film may be inhibited, the upper limit of Si amount is made into 2.50% or less. A preferable upper limit is 2.00% or less.

<Mn: 0.30% or less>
Mn can be dissolved in or directly under the Al-based oxide film together with Si in the reformed gas environment to increase the protection and contribute to the improvement of the oxidation resistance. Moreover, there exists an effect which makes the hot cracking resistance of a weld metal favorable. In order to obtain these effects, the lower limit is preferably 0.05%. On the other hand, excessive inclusion inhibits the corrosion resistance of steel and the formation of an Al-based oxide film, and generates slag with poor peelability during welding, so the upper limit is made 0.30% or less. Preferably it is 0.2% or less.

<Al: 1.00-2.50%>
Al is an element that contributes to the improvement of oxidation resistance by forming an Al-based oxide film on the surface of the weld metal in a reformed gas atmosphere. In the present embodiment, these effects cannot be obtained if the Al content is less than 1.00%, so the lower limit is made 1.00% or more. Preferably it is 1.20% or more. However, if Al is contained excessively, the ductility of the weld metal is lowered, the workability becomes poor, and further brittle fracture in the welded portion is promoted, so the upper limit is made 2.50% or less. Preferably it is 2.30% or less.

<Nb: 0.001 to 1.00%>
Nb is a stabilizing element that fixes C and N in the weld metal, and contributes to suppressing the formation of Cr carbide during welding and improving the adhesion of the Al-based oxide film. Further, intermetallic compounds that cause σ brittleness and 475 ° C. brittleness mainly precipitate with the grain boundary as a production site, but this production site is reduced by the segregation of Nb to the crystal grain boundary. The stability of the structure is increased, and as a result, the σ brittleness and 475 ° C. brittleness of the weld metal can be suppressed. In order to obtain these effects, the lower limit of Nb is 0.001% or more, preferably 0.15% or more. On the other hand, when Nb is excessively contained, in addition to an increase in the alloy cost, the ductility of the weld metal is lowered, the workability becomes poor, and brittle fracture is promoted. Therefore, the upper limit of Nb is 1.00% or less. To do. Preferably it is 0.6% or less.

<P: 0.020% or less>
P is an element that impedes manufacturability and weldability and lowers the grain boundary strength at the weld. The lower the content, the better, so the upper limit is made 0.020% or less. However, excessive reduction leads to an increase in refining costs, so the lower limit is preferably 0.003% or more. From the viewpoint of manufacturability and weldability, the preferred range is 0.005 to 0.015%.

<S: 0.0030% or less>
S is an impurity element inevitably contained in the steel, and lowers the protective properties of the Al-based oxide film. In particular, the presence of Mn-based inclusions and solute S also acts as a fracture starting point for Al-based oxide films when used at high temperatures for long periods of time. It is also an element that lowers the grain boundary strength in the weld zone. Therefore, the lower the amount of S, the better. Therefore, the upper limit is made 0.0030% or less. However, excessive reduction leads to an increase in raw materials and refining costs, so the lower limit is preferably 0.0001% or more. From the viewpoint of manufacturability, oxidation resistance, and 475 ° C. brittleness, the preferred range is 0.0001 to 0.0010%.

<O: 0.010% or less>
O is an impurity that is inevitably mixed, but if the O content exceeds 0.010%, Si, Mn, and Al are oxidized during welding to generate slag with poor peelability. Therefore, O is set to 0.010% or less.

<N: 0.030% or less>
N, like C, is an element that inhibits oxidation resistance. Moreover, it is an element which reduces the ductility of a weld metal and causes deterioration of workability. For these reasons, the smaller the amount of N, the better, and the upper limit is made 0.030% or less. However, excessive reduction leads to an increase in refining costs, so the lower limit is preferably 0.001% or more. From the viewpoint of oxidation resistance and manufacturability, the preferred range is 0.002 to 0.020%.

The filler material according to the present embodiment is composed of Fe and impurities other than the above-described elements (remainder), but can also contain arbitrary elements described later. Therefore, the lower limit of the content of B, Sn, Ga, Mg, Ca, Ni, Cu, Mo, Sb, W, Co, V, Ti, Zr, Y, La, Hf, Ta, and REM is 0% or more. .
The “impurities” in the present embodiment are components that are mixed due to various factors in the manufacturing process including raw materials such as ores and scraps when industrially manufacturing steel, and are inevitably mixed. Including ingredients.

  The chemical composition of the weld metal part of the joint according to this embodiment is as follows: B: 0.0002 to 0.0200%, Sn: 0.005 to 0.20%, Ga: 0.0002 to 0.00. One or more of 0200% or less, Mg: 0.0005 to 0.0200% or less, Ca: 0.0005 to 0.0100% or less, and may be contained so as to satisfy the following formula (1).

<B, Sn, Ga, Mg, Ca>
B, Sn, Ga, Mg, and Ca are elements that can express the effect of increasing the high-temperature strength more as described above. Furthermore, these elements are elements that contribute to the improvement of oxidation resistance by promoting the formation of an Al-based oxide film. Sn, Ga, Mg, and Ca have an action of concentrating near the surface and promoting selective oxidation of Al. Therefore, it is preferable to contain one or more of B, Sn, Ga, Mg, and Ca in addition to the above component composition.
B segregates at the grain boundary due to segregation at the grain boundary, and can increase the internal stress accompanying the increase in the dislocation density in the crystal grains and improve the 0.2% yield strength. Mg and Ca are effective elements for enhancing the cleanliness and hot workability of steel. In addition, by forming inclusions made of MgO, CaO or the like during welding, formation of equiaxed crystals is promoted, and it is also an element contributing to refinement of the weld structure. In order to obtain these effects, it is preferable that Sn is contained by 0.005% or more, and B, Ga, Mg, and Ca are each contained by 0.0002% or more. On the other hand, excessive inclusion of these elements leads to an increase in the refining cost of the steel and also a decrease in manufacturability, so that Sn is 0.20% or less, B, Ga, and Mg are 0.0200% or less, Ca is preferably 0.0100% or less.

When one or more of B, Sn, Ga, Mg, and Ca are contained, the following formula (1) is satisfied.
10 (B + Ga) + Sn + Mg + Ca> 0.020% Formula (1)
In addition, each element symbol in Formula (1) shows content (mass%) of each element in a filler metal.

  From the viewpoint of improving the high temperature strength and oxidation resistance, the formula (1) is preferably 0.025% or more, more preferably 0.035% or more. In addition, although the upper limit of Formula (1) is not specifically prescribed | regulated by the upper limit of B, Sn, Ga, Mg, Ca, it is preferable to set it as 0.2% from a viewpoint of high temperature strength and manufacturability.

  The chemical composition of the filler metal according to this embodiment is as follows: Ni: 0.10 to 1.0%, Cu: 0.10 to 1.0%, Mo: 0.10 to 1.0% , Sb: 0.01 to 0.5%, W: 0.10 to 1.0%, Co: 0.10 to 0.5%, V: 0.10 to 0.5%, Ti: 0.01 -0.5%, Zr: 0.0001-0.10%, Y: 0.0001-0.10%, La: 0.0001-0.10%, Hf: 0.0001-0.10%, REM: 0.001-0.10% of 1 type or 2 types or more may be contained.

  Ni, Cu, Mo, Sb, W, Co, V, and Ti are effective elements for increasing the high-temperature strength and corrosion resistance of the welded portion, and may be contained as necessary. However, if excessively contained, it will lead to an increase in alloy costs and obstruct manufacturability, so the upper limit of Ni, Cu, W is 1.0% or less. Since Mo is an element effective for suppressing high-temperature deformation due to a decrease in the thermal expansion coefficient, it is preferable to contain Mo after setting the upper limit to 1.0% or less. Since Sb is an element that concentrates in the vicinity of the steel surface to promote selective oxidation of Al and has an effect of improving corrosion resistance, the upper limit is preferably set to 0.5% or less. The upper limit of Co, Ti, and V is 0.5% or less. The lower limit of the preferable content of any element of Ni, Cu, Mo, W, Co, and V is 0.10% or more. The minimum of preferable content of Sb and Ti shall be 0.01% or more.

  Zr, La, Y, Hf, and REM are elements that have been conventionally effective for improving hot workability and steel cleanliness and improving oxidation resistance, and may be contained as necessary. However, from the technical idea of the present invention and the reduction of alloy costs, it does not depend on the effect of addition of these elements. When Zr, La, Y, Hf, and REM are contained, the upper limit of Zr, La, Y, Hf, and REM is 0.1%. A preferable lower limit of Zr, La, Y, Hf, and REM is 0.001%. Here, REM is an element belonging to atomic numbers 58 to 71 excluding La and Y and Sc (scandium), and is, for example, Ce, Pr, Nd, or the like. Moreover, REM as used in this embodiment is comprised by 1 or more types selected from the element which belongs to atomic number 58-71, and Sc, and REM amount is these total amounts.

  The ferritic stainless steel filler metal according to the present embodiment is composed of Fe and impurities (including unavoidable impurities) other than the elements described above. In addition to the elements described above, the effect of the present invention is also achieved. It can contain in the range which does not impair. It is preferable to reduce as much as possible Bi, Se, etc. as well as the aforementioned P and S, which are general impurity elements. On the other hand, the content ratio of these elements is controlled to the extent that the problems of the present invention are solved, and may contain one or more of Bi ≦ 100 ppm and Se ≦ 100 ppm as necessary.

  Here, the metal structure of the ferritic stainless steel filler material of the present embodiment is a ferrite single phase structure. This means that an austenite phase and a martensite structure are not included. When an austenite phase or a martensite structure is included, in addition to an increase in raw material cost, a yield reduction such as an ear crack is likely to occur at the time of manufacture, so the metal structure is a ferrite single phase structure. Although precipitates such as carbonitrides are present in the steel, they do not take account of the effects of the present invention, so these are not considered, and the above describes the structure of the main phase.

In addition, the filler material which concerns on this embodiment can be used as welding wires for welding methods, such as TIG welding and plasma welding. These are applicable not only to the welding of ferritic stainless steel, but also to the repair of those structures and the welding of different materials between ferritic stainless steel and ordinary steel / low alloy steel.
Further, when the Al-containing ferritic stainless steel is welded using the filler material according to the present embodiment, a weld metal having both high oxidation resistance, excellent high-temperature strength, and excellent brittleness characteristics can be obtained. Therefore, the filler material of this embodiment is a fuel reformer, a heat exchanger, etc. used when reforming hydrocarbon-based fuels such as city gas, methane, natural gas, propane, kerosene, and gasoline into hydrogen. Can be suitably used for welding when manufacturing a fuel cell member of the present invention, and in particular, manufacturing of a high temperature member of a solid oxide fuel cell (SOFC) or a polymer electrolyte fuel cell (PEFC) that has a high operating temperature (welding) ). Further, it can be suitably used in the manufacture of all members that are in contact with the reformed gas and used in a high-temperature environment, such as fuel cell peripheral members such as a burner and a combustor that stores the burner.

Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used to confirm the feasibility and effects of the present invention, and the present invention was used in the following examples. It is not limited to the conditions. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
In addition, the underline in the table | surface shown below shows what has remove | deviated from the scope of the present invention.

  The filler materials W1 to W16 having various components shown in Table 1 were prototyped and drawn to a diameter of 1.5 mm to form a 15 kg spool.

  As shown in FIG. 1, the welding test was performed using a test body in which an I groove 3 without a gap was formed between steel plates 1 having a plate thickness t of 1.5 mm, and a copper alloy 2 was applied to the back surface. Each component which comprises the steel plate 1 was as shown in Table 2, and TIG welding was carried out on the welding conditions shown in Table 3 using the filler materials W1-W16. The appearance of the bead after welding, the state of slag formation, and the presence or absence of hot cracking were investigated by appearance observation. As a result, the bead appearance after TIG welding was all good, but as shown in Table 4, the slag was produced in Nos. 11, 16 where the contents of Mn and O were outside the scope of the present invention. In Nos. 12, 15 where the contents of S and P are outside the scope of the present invention, hot cracking occurred.

  Next, the following characteristics were investigated in the joint after TIG welding.

[Oxidation resistance]
In the oxidation test, first, an oxidation test piece having a width of 20 mm and a length of 25 mm was cut out from the weld. At this time, it cut out so that a welding line may be arrange | positioned in the width center of an oxidation test piece, ie, a test piece longitudinal direction and a bead direction may become parallel. In addition, the bead of the welded part was not polished and removed, and was subjected to the next oxidation test as it was (with surplus). Next, assuming a reformed gas using city gas as fuel, 28 volume% H ₂ O—10% volume% CO—8 volume% CO ₂ —0.01% H ₂ S-bal. In an atmosphere of H ₂ , the oxidation test piece was heated to 650 ° C., held for 1000 hours, then cooled to room temperature, and an oxidation increase ΔW (mg / cm ² ) was measured.
The evaluation of oxidation resistance was as follows.
A: Weight increase ΔW is less than 0.2 mg / cm ² .
A: Weight increase ΔW is 0.2 to 0.3 mg / cm ² .
X: Weight increase ΔW exceeds 0.3 mg / cm ² .
In addition, as for oxidation resistance, the case of "(double-circle)" and "(circle)" was set as the pass.

[High temperature strength]
In the high-temperature tensile test, first, after removing the welded portion, a plate-like high-temperature tensile test piece (plate thickness: 1.5 mm, parallel part width: 10.5 mm, parallel part length: 35 mm) is removed from the joint. Cut out. At this time, it cut out so that a weld metal part may be arrange | positioned in the longitudinal direction center (parallel part center) of a tensile test piece. Next, at each of 750 ° C. and 800 ° C., the strain rate was 0.3% / min up to 0.2% proof stress, and thereafter 3 mm / min. 750 ° C. proof strength, 800 ° C. proof strength) were measured (according to JIS G 0567).
Evaluation of high-temperature strength is evaluated as a pass (“◯”) when the 750 ° C. yield strength is over 120 MPa and the 800 ° C. yield strength is over 40 MPa, and is rejected (“×”) when neither is satisfied. evaluated. When the 750 ° C. yield strength exceeded 150 MPa and the 800 ° C. yield strength exceeded 60 MPa, it was evaluated that the high-temperature strength was particularly excellent (indicated by “」 ”in the table).

[Structure stability (σ brittleness / 475 ° C brittleness)]
Two samples were taken from the weld metal so that the center on the cross section perpendicular to the plate surface (plate thickness center: around t / 2) could be observed, one of which was heat-treated at 500 ° C. × 1000 hours (500 ° C. Heat treatment), and the other was heat treated at 650 ° C. for 1000 hours (heat treatment at 600 ° C.). The atmosphere for these heat treatments was in the air. Next, after each heat-treated sample was buried in a resin and polished, the Vickers hardness Hv after 500 ° C. heat treatment was _{500 ° C.} , and the Vickers hardness after heat treatment at _{650 ° C.} was Hv _{650 ° C. according} to JIS Z 2244. Measured at .8N, the amount of increase in hardness ΔHv _{500 ° C.} and ΔHv _{650 ° C.} from pre-heat-treatment Vickers hardness measured in advance before heat treatment was calculated.
The evaluation of the structural stability (σ brittleness / 475 ° C brittleness) was evaluated as a pass (“◯”) when both ΔHv _{500 ° C} and ΔHv _{650 ° C} were less than 20, and when either was 20 or more It was rejected ("x") because the hardness increase after heat treatment was large and the structure was unstable.

  Table 4 shows the test results. No. In Nos. 1 to 9, the filler material component satisfies the components specified in the present invention, and all the evaluations of the properties are “◯” or “◎”.

  On the other hand, no. In Nos. 10 to 16, the filler material component deviates from the components specified in the present invention, and the respective characteristics targeted by the present invention could not be satisfied, and either evaluation was “x”.

DESCRIPTION OF SYMBOLS 1 ... Steel plate, 2 ... Copper alloy, 3 ... I groove

Claims (3)

% By mass relative to the total mass of the filler metal
Cr: 12.0 to 16.0%,
C: 0.020% or less,
Si: 0.60 to 2.50%,
Mn: 0.30% or less,
P: 0.020% or less,
S: 0.0030% or less,
Al: 1.00-2.50%,
Nb: 0.001 to 1.00%,
N: 0.030% or less,
O: 0.010% or less,
B: 0 to 0.0100%,
Sn: 0 to 0.20%,
Ga: 0 to 0.0200%,
Mg: 0 to 0.0200%,
Ca: 0 to 0.0100%,
Ni: 0 to 1.0%,
Cu: 0 to 1.0%
Mo: 0 to 1.0%,
Sb: 0 to 0.5%,
W: 0 to 1.0%
Co: 0 to 0.5%,
V: 0 to 0.5%
Ti: 0 to 0.5%,
Zr: 0 to 0.10%,
Y: 0 to 0.10%,
La: 0 to 0.10%,
Hf: 0 to 0.10%,
REM: 0 to 0.10%
A ferritic stainless steel welding filler material characterized by containing Fe and impurities. In mass% with respect to the total mass of the filler metal, B: 0.0002 to 0.0200%, Sn: 0.005 to 0.20%, Ga: 0.0002 to 0.0200% or less, Mg: 0.0005 The ferritic stainless steel welding according to claim 1, wherein the ferritic stainless steel welding includes at least one of ≦ 0.0200% and Ca: 0.0005 to 0.0100% and satisfies the following formula (1): Filler material.
10 (B + Ga) + Sn + Mg + Ca> 0.020 (1)
In addition, each element symbol in Formula (1) shows content (mass%) of each element in a filler metal.   Further, Ni: 0.10 to 1.0%, Cu: 0.10 to 1.0%, Mo: 0.10 to 1.0%, Sb: 0.0% by mass% with respect to the total mass of the filler metal. 01 to 0.5%, W: 0.10 to 1.0%, Co: 0.10 to 0.5%, V: 0.10 to 0.5%, Ti: 0.01 to 0.5% , Zr: 0.0001-0.10%, Y: 0.0001-0.10%, La: 0.0001-0.10%, Hf: 0.0001-0.10%, REM: 0.001 The filler material for ferritic stainless steel welding according to claim 1 or 2, characterized by containing 0.10% or one or more of 0.10%.

Images