JP7042057B2 - Stainless steel materials and welded structural members with excellent slag spot generation suppression ability and their manufacturing methods - Google Patents

Description

The present invention relates to a stainless steel material that does not easily generate defects called "slag spots" or "black spots", which are a type of welding defects that occur in arc weld beads. Further, the present invention relates to a welded structural member using the steel material and a manufacturing method thereof.

When arc welding is performed using a stainless steel material as a base material, defects called "slag spots" in which oxide aggregates are scattered on the weld bead may occur. FIG. 1 exemplifies by quoting an external photograph of a weld bead in which a slag spot is generated, which is published in Non-Patent Document 1. According to the description in the non-patent document, the slag spot is a minute slag that remains and floats on the weld bead in the form of islands or dots at intervals of several mm to several cm. It is considered that oxygen in the air that has entered the molten pool during arc welding reacts with active elements such as Al, Ca, and Ti, which are trace components in the steel material, and remains as slag spots. It is said that slag spots tend to be noticeable in high-speed TIG welding, which is difficult to shield.

FIG. 2 illustrates the appearance of the slag spot seen on the weld bead of the steel pipe formed by TIG welding. The number of slag spots having a major axis of 1.0 mm or more per 1 m in the bead length direction (hereinafter referred to as “number density in the bead length direction”) seen in this photograph is 0.7 pieces / m.

If slag spots frequently occur on the weld bead, there are the following problems, for example.
(I) The appearance of the weld bead is spoiled. (Ii) Cumbersome maintenance such as bead surface polishing may be required for removal. (Iii) In the manufacture of welded steel pipes, there is also an application in which the weld bead on the inner surface of the steel pipe is pressed to lower the height of the beat and then the inner surface is polished. Slag spots may also occur on the back bead side, in which case the slag spots are pushed in when the bead portion on the inner surface of the steel pipe is pressed down to form a dent on the metal surface of the bead, which is polished in a later polishing process. Remaining (unpolished part) is generated. (Iv) Gap corrosion may occur between the foreign matter constituting the slag spot and the metal surface of the bead. (V) In the case of a welded steel pipe, the slag spots generated on the inner bead may fall off during use of the steel pipe, causing foreign matter to enter the fluid flowing through the pipe. (Vi) If foreign matter that causes slag spots aggregates in the molten pool during arc welding, the arc becomes unstable and the bead shape tends to be disturbed.
Therefore, the development of a stainless steel material that can remarkably suppress the generation of slag spots when used as a base material for arc welding is awaited.

Patent Documents 1 and 2 describe ferritic stainless steels in which the formation of slag spots (black spots) is reduced by adjusting the contents of the easily oxidizing elements Al, Ti, Si, and Ca to an optimized steel composition. Is disclosed. However, according to the investigation by the inventors, the effect of suppressing the slag spot is limited only by adjusting the steel composition, and there is room for further improvement.

Patent Document 3 describes that in an austenitic Fe—Ni—Cr alloy for a cladding tube, it is possible to reduce foreign matter on the surface of a welded portion which is a starting point of processing cracks. The foreign matter adhering to the surface of the weld is mainly composed of oxides and nitrides such as Al, Ti, Si, Ca and Mg, and the non-metal inclusions present in the base metal generally have a high melting point. It is taught that it does not melt during welding but floats on the surface of the molten metal and aggregates, and when it solidifies, it remains on the surface as it is to form irregularities (paragraph 0035). Further, it is said that the foreign matter adhering to the surface of the weld is derived from the non-metal inclusions present in the base metal (paragraph 0038). In the technique disclosed in Patent Document 3, in addition to reducing the amounts of Al, Ti, and Si as much as possible, they are present in the base metal by reducing Ca, Mg, N, and O, which are other inclusion constituent elements. The number of inclusions is reduced, thereby reducing the amount of foreign matter observed on the surface of the weld metal (paragraph 0039). However, according to the studies of the inventors, simply reducing the number of non-metal inclusions present in the stainless steel material is extremely foreign matter, for example, as required for welded steel pipes used in food processing lines and semiconductor manufacturing equipment. It is difficult to stably obtain an arc welded bead with few (slag spots). Further, significantly reducing the amount of non-metal inclusions present in the stainless steel material increases the load in the steelmaking process and leads to an increase in the steel material cost. Therefore, it is desired to develop a new method capable of reducing slag spots without relying on the method of reducing the abundance of inclusions.

Japanese Unexamined Patent Publication No. 2010-202973 Japanese Unexamined Patent Publication No. 2012-36444 Japanese Unexamined Patent Publication No. 2014-84493

"Stainless Steel Handbook 3rd Edition" edited by Stainless Steel Association, Nikkan Kogyo Shimbun, 1995, p.1030-1031

As an effective welding method for reducing the slag spot of the arc welding bead, there are a method of using a welding wire for an electrode and a method of adding a filler material. It is also effective to use a welded wire containing flux. On the other hand, arc welding using non-melting type electrodes such as TIG welding is also widely performed, and filler metal is often not used.
The present invention stabilizes the generation of slag spots in various stainless steel grades regardless of austenitic or ferritic stainless steel, even when a non-welded arc welding method is adopted without relying on the use of welding wires or filler metal. The aim is to provide a technology that can be significantly suppressed.

As a result of detailed research, the inventors have adopted a method of controlling the composition of oxide-based inclusions in addition to reducing the amount of non-metal inclusions present in the stainless steel base material. It was found that the above problems can be achieved. The following inventions are disclosed herein.

[1] In terms of mass%, C: 0.005 to 0.10%, Si: 0.10 to 3.00%, Mn: 0.10 to 6.50%, P: 0.001 to 0.050%. , S: 0.0001 to 0.0200%, Ni: 0 to 20.00%, Cr: 10.50 to 26.00, Mo: 0 to 2.50%, Cu: 0 to 3.50%, Nb : 0 to 0.50%, V: 0 to 0.50%, Zr: 0 to 0.50%, W: 0 to 0.50%, Co: 0 to 0.50, B: 0 to 0.020 , N: 0.005 to 0.200%, Ti: 0 to 0.050%, Al: 0 to 0.10%, Ca: 0 to 0.0010%, Mg: 0 to 0.0010%, REM ( Rare earth elements excluding Y): 0 to 0.050%, Y: 0 to 0.050%, O: 0.0030 to 0.0150%, having a chemical composition consisting of the balance Fe and unavoidable impurities, and Mn. Oxide-based inclusions are present, and in the composition of inclusions when the contents of Si, Mn, and Ca in the oxide-based inclusions are converted into the mass ratios of SiO ₂ , MnO, and CaO, respectively, in the metal structure. A stainless steel material having an average CaO / (SiO ₂ + MnO + CaO) mass ratio of 0.40 or less and an average CaO / MnO mass ratio of 15.0 or less observed in.
[2] A base material for arc welding made of the stainless steel material according to the above [1].
[3] A steel plate base material for arc welding pipe making made of the stainless steel material according to the above [1].
[4] An arc welded structural member using the steel material according to the above [1] as a base material.
[5] An arc welded steel pipe using the steel material according to the above [1] as a base material.
[6] A method for manufacturing a welded structural member in which the stainless steel material according to the above [1] is used as a base material and non-melting type arc welding is performed without adding a fillering material.
[7] A method for manufacturing a welded steel pipe, in which a steel plate which is a stainless steel material according to the above [1] is used as a base material, and a welded steel pipe is formed by non-melting electrode type arc welding without adding a filler metal.

Here, the content of each of the above steel components is the total content of the element present in the steel. Therefore, the content of the metal element or oxygen that is partially present as an oxide includes the amount that is present as an oxide. The average CaO / (SiO ₂ + MnO + CaO) mass ratio and the average CaO / MnO mass ratio of the oxide-based inclusions can be obtained as follows. The arc welded structural member is a member having a welded portion formed by arc welding. Similarly, an arc welded steel pipe is a steel pipe having a welded portion formed by arc welding. These welds can be "welded portions without the filler material added" (that is, weld portions formed without the filler metal added).

[How to obtain the average CaO / (SiO ₂ + MnO + CaO) mass ratio and the average CaO / MnO mass ratio]
SEM observation is performed on the cross section of the steel material, and 30 or more particles are randomly selected from the particles of the oxide-based inclusions existing in the cross section, and the composition is analyzed by EDX (energy dispersive X-ray analysis). For each particle, the content of Si, Mn, Ca, Al, Mg, Ti, Cr and Fe is the oxide SiO ₂ , MnO, CaO, Al ₂ O ₃ , MgO, TiO ₂ , Cr ₂ O ₃ and FeO, respectively. The mass ratios of SiO ₂ , MnO and CaO in these eight types of oxides are the SiO ₂ content (mass%), MnO content (mass%) and CaO content of the particles, respectively. (% by mass). By arithmetically averaging the SiO ₂ content, MnO content, and CaO content of the individual particles, the average content (mass%) of SiO ₂ , MnO, and CaO for all the measured particles is calculated. By substituting the value of the average content (mass%) of the oxide into the chemical formula of each oxide of the following formula (1), the average CaO / (SiO ₂ + MnO + CaO) mass ratio is determined. Similarly, the average CaO / MnO mass ratio is determined by substituting the value of the average content (mass%) of the oxide into the chemical formula of each oxide of the following formula (2).
CaO / (SiO ₂ + MnO + CaO)… (1)
CaO / MnO ... (2)

According to the present invention, it has become possible to stably and remarkably suppress the generation of slag spots in arc welding of stainless steel materials. This technique can be applied to various stainless steel grades regardless of whether it is austenitic or ferritic, and is particularly effective in TIG welding performed without adding a filler material.

A quotation of an external photograph of a weld bead with a slag spot, which is published in Non-Patent Document 1. External photograph of the slag spot seen on the weld bead of the steel pipe made by TIG welding. The graph which showed the relationship between the average CaO / (SiO ₂ + MnO + CaO) mass ratio of oxide-based inclusions, and the slag spot generation rate. The graph which showed the relationship between the average CaO / MnO mass ratio of oxide-based inclusions, and the slag spot generation rate. The graph which magnified and displayed the region where the average CaO / MnO mass ratio of FIG. 4 is low. The graph which showed the relationship between the total oxygen content in a steel material and the average CaO / MnO mass ratio of oxide-based inclusions. The graph which magnified and displayed the region where the average CaO / MnO mass ratio of FIG. 6 is low. The graph which showed the relationship between the total oxygen content in a steel material and the slag spot generation rate. A graph showing the relationship between slag basicity and slag spot occurrence rate during refining.

[Steel composition]
In the present invention, various steel types are applicable regardless of whether they are austenitic or ferritic. According to the studies by the inventors, the effect of suppressing slag spots by controlling the composition of inclusions described later can be obtained in the following composition range.
By mass%, C: 0.005 to 0.10%, Si: 0.10 to 3.00%, Mn: 0.10 to 6.50%, P: 0.001 to 0.050%, S: 0.0001 to 0.0200%, Ni: 0 to 20.00%, Cr: 10.50 to 26.00, Mo: 0 to 2.50%, Cu: 0 to 3.50%, Nb: 0 to 0.50%, V: 0 to 0.50%, Zr: 0 to 0.50%, W: 0 to 0.50%, Co: 0 to 0.50, B: 0 to 0.020, N: 0.005 to 0.200%, Ti: 0 to 0.050%, Al: 0 to 0.10%, Ca: 0 to 0.0010%, Mg: 0 to 0.0010%, REM (excluding Y) Rare earth elements): 0 to 0.050%, Y: 0 to 0.050%, O: 0.0030 to 0.0150%, balance Fe and unavoidable impurities.

Generally, it is preferable that the content of P and S in the steel material is low, but excessive dephosphorization and desulfurization increase the load of steelmaking and become uneconomical. do. Ni, Mo, Cu, Nb, V, Zr, W, Co, B, Ti, Al, Ca, Mg, REM (rare earth elements excluding Y), and Y are optional contained elements. These are general elements that are appropriately added to stainless steel in order to improve the hot workability and various properties of steel materials, and if the content is within the above range, the average CaO / of oxide-based inclusions As long as the MnO mass ratio is controlled within a predetermined range described later, it does not hinder the slag spot suppressing effect of the arc weld bead. Regarding Ti and Al, if the content is excessive, it may adversely affect the composition of inclusions and may cause the generation of slag spots. Therefore, Ti is 0.050% or less and Al is 0.100% or less. Each is restricted. It is more preferable to adjust the components so that the content of Ti is less than 0.010% and that of Al is 0.007% or less. In order to sufficiently reduce the Al content, it is desirable to perform Si deoxidation in refining.

[Composition of oxide-based inclusions]
The following patterns can be considered as factors that generate slag spots in arc weld beads using stainless steel as the base material.
(Pattern 1) Easy-oxidizing elements (Al, Ca, Ti, etc.) in the base metal form an oxide at a portion where the gas shield is insufficient and remain on the bead.
(Pattern 2) Non-metal inclusions having a high dissociation temperature present in the base metal aggregate and float with the sweep of the arc, and when the aggregated particles become large to some extent, they are left behind from the sweep of the arc and remain on the bead.
According to the study by the inventors, slag spots are generated even when the gas shield is sufficiently performed. Therefore, in order to stably and remarkably suppress the generation of slag spots, the cause of the above pattern 2 is considered. It is necessary to overcome it. The cause of the pattern 1 can be eliminated by limiting the content of easily oxidizing elements and the like in the steel composition of the base metal to the above range.

Control of inclusions in the base metal is important as a countermeasure against the cause of the above pattern 2. Among the non-metal inclusions, the ones that cause slag spots are oxide-based inclusions having a high dissociation temperature. In the case of stainless steel having the above-mentioned steel composition, SiO ₂ , MnO, CaO, Al ₂ O ₃ , MgO and the like can be mentioned as typical constituents of oxide-based inclusions present in the steel material. Of these, CaO has a high dissociation temperature, so it is not reduced even during welding and remains as an oxide. When this aggregates and coalesces in the metal melted by the heat of the arc, it appears as a slag spot after cooling. On the other hand, since MnO and SiO ₂ have a relatively low dissociation temperature, Mn and Si constituting the oxide are reduced during welding to become a metal, which is easily dissolved in the molten metal. Therefore, MnO and SiO ₂ are unlikely to cause slag spots.

The inventors have investigated in detail the composition of oxide-based inclusions contained in the steel material for various stainless steel grades in the above-mentioned steel composition range. As a result, it was found that most of the oxide-based inclusions present in general stainless steel materials are of the type having a high content of SiO ₂ and CaO. It was also confirmed that by changing the refining conditions, it is possible to control the composition of the inclusions by reducing the CaO content of the inclusions and increasing the MnO content instead. Furthermore, it was clarified that when the content of MnO coexisting with SiO ₂ and CaO was increased in the inclusion composition, the generation of slag spots was remarkably suppressed despite the presence of CaO. rice field. In the following, a general type of oxide-based inclusions having a high content of SiO ₂ and CaO will be referred to as “SiO ₂ -CaO type” for convenience, and the Ca concentration will decrease and the Mn concentration will increase by controlling the composition of the inclusions. The oxide-based inclusions of the planned type are referred to as "SiO ₂ -MnO-CaO type" for convenience.

Metal oxides generally dissociate into metal and oxygen as the temperature rises. For example, when estimating the dissociation temperature when the oxygen partial pressure is assumed to be 10 ^-12 atm in the Ellingham diagram, SiO ₂ : about 1530 ° C., MnO: about 1380 ° C., CaO: about 2100 ° C., Al ₂ O ₃ : about 2020. It becomes ℃. Changing the SiO ₂ -CaO type inclusions to the SiO ₂ -MnO-CaO type as much as possible, that is, making the composition of the inclusions relatively dominant in the SiO ₂ -MnO-CaO type is advantageous for suppressing slag spots. It becomes. Although Al ₂ O ₃ has a high dissociation temperature, it is unlikely to cause slag spots because the abundance of Al ₂ O ₃ is small in the steel material adjusted to the above-mentioned steel composition.

In the present invention, the "average CaO / MnO mass ratio" is adopted as an index for quantitatively expressing the relative superiority of the SiO _{2-CaO type and the SiO 2 -} MnO-CaO type in the inclusion composition. The smaller this value is, the more it can be evaluated that the inclusion composition is relatively dominant in the SiO ₂ -MnO-CaO type, which is advantageous in suppressing the generation of slag spots. The average CaO / MnO mass ratio can be determined by the method described above. As a result of detailed examination, in the stainless steel whose steel composition is adjusted to the above range, when the average CaO / MnO mass ratio is 15.0 or less, the effect of significantly reducing the slag spot is remarkable as compared with the conventional stainless steel material. Is recognized. The average CaO / MnO mass ratio is more preferably 10.0 or less, and may be controlled to 6.0 or less.

On the other hand, even when the MnO content in the oxide-based inclusions is high, if the CaO content is excessively high, the effect of suppressing the generation of slag spots cannot be sufficiently obtained. As a result of the examination, it is desirable that the inclusion composition has an average CaO / (SiO ₂ + MnO + CaO) mass ratio of 0.40 or less. The average CaO / (SiO ₂ + MnO + CaO) mass ratio can be determined by the method described above.

[Control of composition of inclusions]
The above-mentioned stainless steel material in which the average CaO / (SiO ₂ + MnO + CaO) mass ratio of the oxide-based inclusions and the average CaO / MnO mass ratio are optimized is manufactured by utilizing a general stainless steel melting facility. be able to. Typical examples include a VOD process and an AOD process. In either case, first, the Cr-containing molten iron is decarburized by blowing oxygen, and molten steel having Cr oxide-containing slag on the molten metal surface (C content is, for example, 0.20% or less) is produced by a conventional method. Since the molten steel at this stage is a molten steel that has been decarburized by blowing oxygen, the easily oxidizable elements Si, Ti, Al, Ca, Mg and the like are oxidized and removed from the molten steel. That is, Si, Ti, Al, Ca, and Mg are hardly present in the molten steel. Further, a part of Cr contained in the molten steel is also oxidized to form slag on the molten steel surface as Cr oxide. On the other hand, a large amount of oxygen blown in for decarburization is dissolved in the molten steel. Therefore, it is necessary to deoxidize before casting. The final component adjustment is performed using a FeSi alloy instead of Al as the deoxidizing agent.

In order to sufficiently reduce the average CaO / MnO mass ratio while maintaining the average CaO / (SiO ₂ + MnO + CaO) mass ratio of the oxide-based inclusions at 0.40 or less, deoxidation and final component adjustment are performed. At that time, it was found that it is extremely effective to perform refining so as to satisfy the following three points, for example.

(1) Refining is performed so that the oxygen content in the steel (total oxygen content including oxygen existing as an oxide) is 0.0030% (30 ppm) or more. When the oxygen content is less than 0.0030%, it becomes difficult to refine the average CaO / MnO mass ratio so as to be stable at 15.0 or less. When it is desired to greatly reduce the average CaO / MnO mass ratio to 10.0 or less or 6.0 or less, it is more preferable to adjust the oxygen content to 0.0040% (40 ppm) or more. However, if the oxygen content is too high, a large amount of inclusions having a high Cr oxide content are generated, which causes deterioration of product quality. The oxygen content is limited to 0.0150% (150 ppm) or less, more preferably 0.0100% (100 ppm) or less. It may be controlled to 0.0036% (60 ppm) or less. (2) Si deoxidation is performed using a high-purity FeSi alloy having a Ca content of, for example, 0.20% or less.
(3) Adjust the slag basicity CaO / SiO ₂ to the range of 1.20 to 1.60.

Using the VOD process, the stainless steels shown in Table 1 were melted to obtain continuously cast slabs. In the final refining process, inclusion control was attempted by changing the conditions of total oxygen content in steel, type of FeSi alloy of deoxidizer, and slag basicity (CaO / SiO ₂ ). Each condition is shown in Table 2. The oxygen content in Table 2 is a reprint of the values in Table 1. As the FeSi alloy as the deoxidizing agent, a high-purity product having a small amount of impurities and a normal product were used. The high-purity product has a Ca content reduced to 0.20% by mass or less. The Ca content of the normal product is about 0.5 to 1.5% by mass. The slag basicity was determined by analyzing a sample taken from the slag.

Using the obtained continuously cast slab, a cold-rolled annealed steel sheet having a plate thickness of 0.5 to 1.5 mm was obtained in a process including hot rolling and cold rolling. SEM (scanning electron microscope) observation was performed on the cross section (L cross section) parallel to the rolling direction and the plate thickness direction of this cold-rolled annealed steel sheet, and the oxide system was observed by the EDX (energy dispersive X-ray analysis) attached to the SEM. The composition of inclusions was analyzed. Based on the measured values of 30 oxide-based inclusions selected at random, the average CaO / (mean CaO / (SiO ₂ + MnO + CaO) mass ratio, how to obtain the average CaO / MnO mass ratio" described above. SiO ₂ + MnO + CaO) mass ratio and average CaO / MnO mass ratio were determined. The results are shown in Table 2.

Welded steel pipes were manufactured under normal conditions by TIG welding using each cold-rolled annealed steel sheet as a material. The outer diameter of the tube is in the range of 25-51 mm. No filler metal was added during welding. Samples were randomly sampled from the obtained steel pipe products, and the occurrence of slag spots was investigated for continuous weld beads having a length of 50 m or more. The number of slag spots having a major axis (diameter of the longest part of the particles) of 1.0 mm or more was counted, and the number of slag spots generated per 1 m was defined as the slag spot generation rate (pieces / m). If the slag spot generation rate of the above size is 0.30 pieces / m or less, it can be evaluated that the generation of slag spots is significantly suppressed as compared with the conventional case. Therefore, those having a slag spot generation rate of 0.30 pieces / m or less were judged to be acceptable.
These results are shown in Table 2.

Examples of the present invention in which the steel composition satisfies the specified range of the present invention and the average CaO / (SiO ₂ + MnO + CaO) mass ratio and the average CaO / MnO mass ratio of the oxide-based inclusions are controlled within the specified range of the present invention are Very few slag spots occur.

On the other hand, in Comparative Examples Nos. 21 to 23, the slag basicity at the time of refining was high, so that the average CaO / MnO mass ratio of the oxide-based inclusions was high, and slag spots were frequently generated. In Nos. 24 to 26, the total oxygen content in the steel was too low and the slag basicity at the time of refining was high, so that the average CaO / MnO mass ratio of the oxide-based inclusions was significantly higher than in the other examples, and the slag. No spot-suppressing effect was obtained. In Nos. 27 to 30, since the "normal product" was used for the FeSi alloy as the deoxidizing agent, the desired inclusions could not be controlled, and the average CaO / MnO mass ratio of the oxide-based inclusions became high, so that the slag spots had a high mass ratio. There were many outbreaks.

FIG. 3 shows the relationship between the average CaO / (SiO ₂ + MnO + CaO) mass ratio of oxide-based inclusions and the slag spot generation rate for each example. The black circle plot is an example in which a "high-purity product" is used as the FeSi alloy of the deoxidizer, and the white circle plot is an example in which a "normal product" is used (the same applies to FIGS. 4 to 9 below). Further, FIGS. 4 and 5 show the relationship between the average CaO / MnO mass ratio of oxide-based inclusions and the slag spot generation rate for each example. FIG. 5 is an enlarged view of the region where the average CaO / MnO mass ratio of FIG. 4 is low. By controlling the average CaO / (SiO ₂ + MnO + CaO) mass ratio of the oxide-based inclusions to 0.40 or less and the average CaO / MnO mass ratio to 15.0 or less, the effect of suppressing the generation of slag spots is remarkably improved. You can see that.

6 and 7 show the relationship between the total oxygen content in the steel material and the average CaO / MnO mass ratio of the oxide-based inclusions for each example. FIG. 7 is an enlarged view of the region where the average CaO / MnO mass ratio of FIG. 6 is low. It can be seen that setting the oxygen content to 0.0030% or more is extremely effective in controlling the average CaO / MnO mass ratio of the oxide-based inclusions to be low.

FIG. 8 shows the relationship between the total oxygen content in the steel material and the slag spot generation rate for each example. It can be seen that using a "high-purity product" for the FeSi alloy of the deoxidizer and increasing the oxygen content to 0.0030% or more is effective in suppressing the generation of slag spots.

FIG. 9 shows the relationship between the slag basicity and the slag spot generation rate during refining. It can be seen that using a "high-purity product" for the FeSi alloy of the deoxidizer and adjusting the slag basicity in the range of 1.20 to 1.60 is effective in suppressing the generation of slag spots.

Claims (7)

By mass%, C: 0.005 to 0.10%, Si: 0.10 to 3.00%, Mn: 0.10 to 6.50%, P: 0.001 to 0.050%, S: 0.0001 to 0.0200%, Ni: 0 to 20.00%, Cr: 10.50 to 26.00, Mo: 0 to 2.50%, Cu: 0 to 3.50%, Nb: 0 to 0.50%, V: 0 to 0.50%, Zr: 0 to 0.50%, W: 0 to 0.50%, Co: 0 to 0.50, B: 0 to 0.020, N: 0.005 to 0.200%, Ti: 0 to 0.050%, Al: 0 to 0.100%, Ca: 0 to 0.0010%, Mg: 0 to 0.0010%, REM (excluding Y) Rare earth element): 0 to 0.050%, Y: 0 to 0.050%, O: 0.0030 to 0.0150%, balance Fe and unavoidable impurities. Oxide containing Mn. Material-based inclusions are present and are observed in the metallographic structure in the inclusion composition when the Si, Mn and Ca contents in the oxide-based inclusions are converted to the mass ratios of SiO ₂ , MnO and CaO, respectively. A stainless steel material having an average CaO / (SiO ₂ + MnO + CaO) mass ratio of 0.40 or less and an average CaO / MnO mass ratio of 15.0 or less. A base material for arc welding made of the stainless steel material according to claim 1. A steel plate base material for arc welding pipe making made of the stainless steel material according to claim 1. An arc welded structural member using the steel material according to claim 1 as a base material. An arc welded steel pipe using the steel material according to claim 1 as a base material. A method for manufacturing a welded structural member using the stainless steel material according to claim 1 as a base material and performing non-melting arc welding without adding a fillering material. A method for manufacturing a welded steel pipe, wherein a steel plate which is a stainless steel material according to claim 1 is used as a base material, and a welded steel pipe is formed by non-melting arc welding without adding a filler metal.

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