TWI694160B - Stainless steel material excellent in supressing slag spots generation, welded structural member and manufacturing method thereof - Google Patents

Abstract

The present invention provides a stainless steel material capable of stably and remarkably suppressing generation of slag spots in arc welding using stainless steel as a base material.

The stainless steel of the present invention, in mass %, comprising: C: 0.005 to 0.100%, 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%, N: 0.005 to 0.200%, O: 0.0030 to 0.0150%, if necessary, it comprises Mo, Cu, Nb, V, Zr, W, Co, B, Ti, Al, Ca, Mg, REM (rare earth element excluding Y) and Y in a predetermined range, and it also includes balanced Fe and a chemical composition composed of inevitable impurities, the average CaO/(SiO₂ + MnO + CaO) mass ratio of the oxide-based inclusions observed in the metal structure is 0.40 or less, the average CaO/MnO mass ratio is 15.0 or less.

Description

Stainless steel material with excellent suppression ability of slag spot generation, welded structural member and manufacturing method thereof

The present invention relates to a stainless steel material, which is not easy to cause a kind of so-called "slag point" or "black spot" defect that can occur in arc welding molten beads. In addition, it relates to a welded structural member using the steel material and a method for manufacturing the same.

When stainless steel is used as a base material for arc welding, a defect called "slag point" in which oxide aggregates are scattered on the welding beads may sometimes occur. Figure 1 cites and exemplifies a photograph of the appearance of a welded bead with slag spots disclosed in Non-Patent Document 1. According to the description of Non-Patent Document 1, the slag spots are minute slags floating on the welding beads at island-shaped or spot-shaped intervals of several mm to several cm. It is believed that oxygen in the air that invades the molten pool during arc welding reacts with trace elements Al, Ca, Ti and other active elements in the steel to remain as slag spots, especially in high-speed TIG welding where it is difficult to fully gas shield the molten pool. The occurrence of slag spots becomes significant Propensity.

Figure 2 illustrates the appearance of slag spots seen on the weld beads of steel pipes made by TIG welding. The number of slag spots with a length of 1.0 mm or more seen in the steel pipe per m in the longitudinal direction of the bead (hereinafter, referred to as "slag spot generating rate") was 0.7 pieces/m.

When slag spots are frequently generated by welding beads, there are problems such as the following.

(i) Damage the beauty of the welded bead part. (ii) In order to remove it, it may be necessary to have troublesome finishing such as grinding of the surface of the molten beads. (iii) In the manufacture of welded steel pipes, there is also the use of carrying out internal grinding after pressing down the welding beads on the inner surface of the steel pipe to reduce the height of the beads. The slag spot may also occur on the back side of the molten bead. In this case, when the molten bead part of the inner surface of the steel pipe is pressed down, the slag spot is pressed in and a depression is formed on the metal surface of the molten bead, followed by the grinding step The unfinished part (unpolished part) is generated in the middle. (iv) Gap corrosion may sometimes occur between the foreign material constituting the slag point and the metal surface of the molten bead. (v) In the case of welded steel pipes, the slag spots generated on the inner surface of the molten beads fall off during the use of the steel pipes, which may cause foreign substances to be mixed into the fluid flowing inside. (vi) When foreign substances that cause slag spots are condensed in the molten pool during arc welding, the arc becomes unstable and the shape of the molten beads is easily disturbed.

Therefore, it is expected to develop a stainless steel material that can significantly suppress the occurrence of slag spots when used as a base material for arc welding.

Patent Documents 1 and 2 disclose a ferrite grain that reduces the generation of slag spots (black spots) by adjusting the content of oxidizable elements Al, Ti, Si, and Ca to an optimized steel composition. Department of stainless steel. However, based on According to the investigation by the inventors, only the steel composition is adjusted, and the suppression effect of the slag point is limited, and there is still room for further improvement.

Patent Document 3 describes that the Vostian iron-based Fe-Ni-Cr alloy for a covered tube reduces foreign matters on the surface of the welded part that will become the starting point of machining cracks. It also teaches that the foreign materials attached to the surface of the welded material are mainly composed of oxides and nitrides of Al, Ti, Si, Ca, Mg, etc., and the non-metallic inclusions in the base material are generally high melting points, so welding When it does not melt, it floats on the surface of the molten metal and aggregates. When solidified, it directly remains on the surface to form irregularities (paragraph 0035). In addition, the foreign matter adhering to the surface of the welded part originates from the non-metallic inclusions present in the base material (paragraph 0038). In the technique disclosed in Patent Document 3, by reducing the amount of Al, Ti, and Si as much as possible, and also reducing the Ca, Mg, N, and O of other inclusion constituent elements, the inclusions in the base material are reduced The number is used to reduce the foreign matter observed on the surface of the weld metal (paragraph 0039). However, according to the research of the inventors, simply reducing the amount of non-metallic inclusions present in stainless steel materials, it is difficult to stably obtain very few foreign materials required for welded steel pipes used in, for example, food processing production lines or semiconductor manufacturing equipment ( Arc welding welding beads. In addition, greatly reducing the amount of non-metallic inclusions present in the stainless steel material will increase the load on the steel-making step and incur a rise in steel cost. Therefore, it is expected to develop a new method for reducing the slag point without relying on the method for reducing the amount of inclusions.

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2010-202973

[Patent Document 2] Japanese Unexamined Patent Publication No. 2012-36444

[Patent Document 3] Japanese Patent Laid-Open No. 2014-84493

[Non-patent literature]

[Non-Patent Document 1] "Stainless Steel Toiletry 3rd Edition" edited by the Stainless Steel Association, Nikkan Kogyo Shimbun, 1995, p. 1030-1031

Welding methods that are effective in reducing the slag points of arc welding beads include, for example, a method of using a welding wire for an electrode and a method of adding a filler material. It is also effective to use solder wires containing flux. On the other hand, arc welding using non-expendable electrode type electrodes such as TIG welding is also widely performed, and many of them do not use fusion fillers.

The present invention is intended to provide a method that does not rely on the use of welding wires and fusion fillers. Even when the non-consumable electrode arc welding method is used, it can still be stable and significantly regardless of the variety of stainless steels in the Vostian iron system and the ferrite iron system. Technology to suppress the generation of slag spots.

As a result of detailed investigations by the inventors, it has been found that the above-mentioned problems can be achieved by using a method of controlling the composition of especially oxide-based inclusions in addition to reducing the amount of non-metallic inclusions present in the stainless steel base material. This specification discloses the following inventions.

[1] A stainless steel material having, by mass %, C: 0.005 to 0.100%, 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 0.500%, V: 0 to 0.500%, Zr: 0 to 0.500%, W : 0 to 0.500%, Co: 0 to 0.500%, 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 (rare earth elements other than Y): 0 to 0.050%, Y: 0 to 0.050%, O: 0.0030 to 0.0150%, chemical composition of residual Fe and inevitable impurities, and the presence of Mn Oxide-based inclusions, oxides observed in the metal structure in the composition of inclusions when the contents of Si, Mn, and Ca in the oxide-based inclusions are converted to the mass ratio of SiO ₂ , MnO, and CaO, respectively The average CaO/(SiO ₂ +MnO+CaO) mass ratio of the inclusions is 0.40 or less, and the average CaO/MnO mass ratio is 15.0 or less.

[2] A base material for arc welding comprising the stainless steel material described in [1] above.

[3] A steel plate base material for arc welding pipe forming, comprising the stainless steel material described in [1] above. .

[4] An arc welding structural member using the stainless steel material described in [1] above as a base material.

[5] An arc-welded steel pipe using the stainless steel material described in [1] above as a base material.

[6] A method of manufacturing a welded structural member, using the above [1] The above-mentioned stainless steel material is used in the base material, and non-consumable electrode type arc welding is performed without adding a filler material.

[7] A method of manufacturing a welded steel pipe, which uses the steel sheet of the stainless steel material described in [1] above as a base material, and forms a welded steel pipe by non-consumable electrode arc welding without adding a filler material.

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

[Method for obtaining the average CaO/(SiO ₂ +MnO+CaO) mass ratio and average CaO/MnO mass ratio]

SEM observation was performed on the cross section of the steel material, and more than 30 particles were randomly selected from the particles of the oxide-based inclusions present in the cross section and analyzed by EDX (energy dispersive X-ray analysis). For each particle, the contents of Si, Mn, Ca, Al, Mg, Ti, Cr, and Fe are converted into oxides SiO ₂ , MnO, CaO, Al ₂ O ₃ , MgO, TiO ₂ , Cr ₂ O ₃ and The mass ratio of FeO, the mass ratio of SiO ₂ , MnO and CaO in these 8 kinds of oxides is set as the SiO ₂ content (mass %), MnO content (mass %) and CaO content (mass %) of the particles ). The average content (mass %) of SiO ₂ , MnO, and CaO for all the measured particles is calculated by adding and averaging the SiO ₂ content, MnO content, and CaO content of each particle, respectively. The value of the aforementioned average content (mass %) of the oxide is substituted for the chemical formula of each oxide of the following formula (1), thereby determining the average CaO/(SiO ₂ +MnO+CaO) mass ratio. Similarly, the value of the aforementioned average content (mass %) of the oxide is substituted into the chemical formula of each oxide of the following formula (2), thereby determining the average CaO/MnO mass ratio.

CaO/(SiO ₂ +MnO+CaO)...(1)

CaO/MnO...(2)

According to the present invention, the generation of slag spots can be stably and significantly suppressed in the arc welding of stainless steel materials. This technology is applicable to various stainless steel types regardless of the Vostian iron system and the ferrite iron system, and it is particularly effective in TIG welding without adding filler material.

Figure 1 is a photograph of the appearance of a welded bead that has generated slag spots as disclosed in Non-Patent Document 1.

Figure 2 is a photograph of the appearance of the slag point seen on the welding beads of a steel pipe made by TIG welding.

Figure 3 is a graph showing the relationship between the average CaO/(SiO ₂ +MnO+CaO) mass ratio of oxide-based inclusions and the slag point generation rate.

Figure 4 shows the average CaO/MnO mass of oxide-based inclusions A graph showing the relationship between the ratio and the slag point generation rate.

Fig. 5 is an enlarged view of the area where the average CaO/MnO mass ratio in Fig. 4 is low.

Figure 6 is a graph showing the relationship between the total oxygen content in steel and the average CaO/MnO mass ratio of oxide-based inclusions.

FIG. 7 is an enlarged view of the area where the average CaO/MnO mass ratio in FIG. 6 is low.

Figure 8 is a graph showing the relationship between the total oxygen content in steel and the slag point generation rate.

Figure 9 is a graph showing the relationship between the slag basicity during refining and the slag point generation rate.

[The composition of steel]

In the present invention, regardless of the Vostian iron system and the ferrite grain iron system, various steel types are applied. According to the studies of the inventors, the effect of suppressing the slag point due to the inclusion composition described below is controlled within the following composition range.

In terms of mass %, C: 0.005 to 0.100%, 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 0.500%, V: 0 to 0.500%, Zr: 0 to 0.500%, W: 0 to 0.500%, Co: 0 to 0.500%, 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 (except Rare earth elements other than Y): 0 to 0.050%, Y: 0 to 0.050%, O: 0.0030 to 0.0150%, residual Fe and inevitable impurities.

The content of P and S in steel is generally lower, but excessive dephosphorization and desulfurization will increase the load of steel making and become uneconomical, so the steel with P and S content in the above range is targeted here . Ni, Mo, Cu, Nb, V, Zr, W, Co, B, Ti, Al, Ca, Mg, REM (rare earth elements other than Y), Y is an arbitrary element. These are general elements that are appropriately added to stainless steel in order to improve the hot workability and various characteristics of the steel. If the content is within the above range, as long as the average CaO/MnO mass ratio of the oxide-based inclusions is controlled to be described later The range does not hinder the slag point suppression effect of arc welding beads. Regarding Ti and Al, when the content is excessive, it may cause adverse effects on the composition of inclusions, and may be the cause of the slag point. Therefore, Ti is limited to 0.050% or less, and Al is limited to 0.100% or less. It is better to adjust the composition so that Ti becomes less than 0.010% and Al becomes 0.007% or less. To sufficiently reduce the Al content, Si deoxidation during refining is preferred.

[Composition of oxide-based inclusions]

The main reason for the occurrence of the slag point generated by the arc welding bead of the stainless steel material for the base material is considered to be the following mode.

(Mode 1) The easily oxidizable elements (Al, Ca, Ti, etc.) in the base material form oxides where gas shielding is insufficient, and remain on the beads.

(Mode 2) Non-metallic inclusions with a high dissociation temperature existing in the base material agglomerate and float with the scanning of the arc, and the aggregated particles become large to some extent, The scan from the arc is left behind and remains on the molten beads.

According to the research of the inventors, even if the gas shielding is sufficiently performed, slag spots will still be generated. Therefore, in order to stabilize and significantly suppress the generation of slag spots, the main cause of the above mode 2 must be overcome. The main cause of the above mode 1 can be solved by limiting the content of easily oxidizable elements and the like to the above range in the steel composition of the base material.

Regarding the countermeasures for the main cause of the above mode 2, the control of inclusions in the base material is important. Among non-metallic inclusions, oxide-based inclusions having a high dissociation temperature are responsible for the slag point. In the case of stainless steel having the above-mentioned steel composition, representative constituent components of oxide-based inclusions present in the steel material include, for example, SiO ₂ , MnO, CaO, Al ₂ O ₃ , and MgO. Among these, CaO has a high dissociation temperature, so it is not reduced during welding and continues to exist as an oxide. If it aggregates among the metal melted by the heat of the arc, it will appear as slag spots after cooling. On the other hand, since the dissociation temperature of MnO and SiO ₂ is relatively low, the Mn and Si constituting the oxide are reduced during welding to become a metal, and are easily dissolved in the molten metal. Therefore, it is difficult for MnO and SiO ₂ to be the main causes of slag spots.

The inventors have studied in detail the composition of oxide-based inclusions contained in steel materials for various types of stainless steel in the above-mentioned steel composition range. As a result, it can be seen that most of the oxide-based inclusions present in general stainless steel materials are types with a large content of SiO ₂ and CaO. In addition, it can also be confirmed that by changing the refining conditions, the composition control of the inclusions that can reduce the CaO content of the inclusions and instead increase the MnO content can be performed. Furthermore, it was found that when the content of MnO coexisting with SiO ₂ and CaO is increased in the inclusion composition, although CaO is present, the generation of slag spots can be significantly suppressed. In the following, the general type of oxide-based inclusions with a large content of SiO ₂ and CaO is called “SiO ₂ -CaO type” for convenience, and the Ca concentration will be reduced by controlling the composition of the inclusions and The oxide-type inclusions of the type with increased Mn concentration are called "SiO ₂ -MnO-CaO type" for convenience.

Metal oxides generally dissociate into metals and oxygen when the temperature rises. For example, if the dissociation temperature at an oxygen partial pressure of 10 ^-12 atm is estimated in the Ellingham diagram, then SiO ₂ : about 1530°C, MnO: about 1380°C, CaO: about 2100°C, Al ₂ O ₃ : about 2020°C. The SiO ₂ -CaO type of inclusions as far as possible changes to the SiO ₂ -MnO-CaO type, i.e. the composition of inclusions is set to SiO ₂ -MnO-CaO type opposite to advantage, it is advantageous in suppressing the slag point. In addition, the dissociation temperature of Al ₂ O ₃ is high, but in the steel material adjusted to the above-mentioned steel composition, since the amount of Al ₂ O ₃ is small, it is difficult to be the main cause of slag spots.

It can be expressed quantitatively in the composition of inclusions and the SiO ₂ -CaO type indication of the relative advantage of the SiO ₂ -MnO-CaO type of, in the present invention, a system using "average CaO / MnO mass ratio." The smaller the value, the more favorable the inclusion composition of the SiO ₂ -MnO-CaO type, which is beneficial to suppress the generation of slag spots. The average CaO/MnO mass ratio can be obtained by the method described above. As a result of detailed studies, in stainless steels with the steel composition adjusted to the above range, when the average CaO/MnO mass ratio is 15.0 or less, a significant reduction effect of slag points can be seen compared to conventional stainless steel materials . The average CaO/MnO mass ratio of 10.0 or less is better, and it can also be controlled to 6.0 or less.

On the other hand, even if the content of MnO in the oxide-based inclusions is high, if the content of CaO is too high, the effect of suppressing the generation of slag spots cannot be sufficiently obtained. As a result of the investigation, the composition of inclusions with an average CaO/(SiO ₂ +MnO+CaO) mass ratio of 0.40 or less is preferred. The average CaO/(SiO ₂ +MnO+CaO) mass ratio can be obtained 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 and the average CaO/MnO mass ratio of the oxide-based inclusions are optimized can be manufactured using general stainless steel melting equipment. Representative examples include the VOD process and the AOD process. In either case, first, decarburization by blowing oxygen into molten iron containing Cr is carried out, and a molten steel having a molten slag containing Cr oxide on the surface of the hot melt is manufactured by a common method (C content is, for example, 0.20% or less) . The molten steel at this stage is a decarburized molten steel that has been blown with oxygen, so the easily oxidizable elements Si, Ti, Al, Ca, Mg, etc. are oxidized and removed from the molten steel. That is, Si, Ti, Al, Ca, and Mg hardly exist in molten steel. In addition, a part of Cr contained in a large amount in molten steel is also oxidized, and slag is formed on the hot melt surface of the molten steel in the form of Cr oxide. On the other hand, the oxygen blown in molten steel for decarburization will be dissolved in a large amount. Therefore, deoxidation must be performed before casting. Instead of using Al, FeSi alloy is used as a deoxidizer to adjust the final composition.

In order to sufficiently reduce the average CaO/MnO mass ratio while maintaining the average CaO/(SiO ₂ +MnO+CaO) mass ratio of oxide-based inclusions below 0.40, it is known that when deoxidation and final component adjustment are performed, For example, the following three points are very effective for refining.

(1) Refining is performed so that the oxygen content in steel (including all oxygen content in the form of oxides) is 0.0030% (30 ppm) or more. When the oxygen content is less than 0.0030%, it becomes difficult to stabilize the average CaO/MnO mass ratio and set it to 15.0 or less. When the average CaO/MnO mass ratio is to be significantly reduced to 10.0 or less or 6.0 or less, it is preferable to adjust the oxygen content to 0.0040% (40 ppm) or more. However, when the oxygen content is too large, inclusions with a large amount of Cr oxide will be generated in large quantities, which will be the main cause of the degradation of product quality. The oxygen content is limited to 0.0150% (150 ppm) or less, preferably 0.0100% (100 ppm) or less. It can also be controlled below 0.0060% (60ppm).

(2) Deoxidation of Si is performed using a high-purity FeSi alloy with a Ca content of, for example, 0.20% or less.

(3) The slag basicity CaO/SiO _{2 is} adjusted to the range of 1.20 to 1.60.

[Example]

Using the VOD process, the stainless steel shown in Table 1 was melted to obtain a continuous casting slab. In the final refining process, change the total oxygen content in the steel, the type of FeSi alloy of the deoxidizer, and the conditions of the slag basicity (CaO/SiO ₂ ) to try to control the inclusions. Table 2 shows the individual conditions. The oxygen content in Table 2 reveals the values in Table 1 again. The FeSi alloy of the deoxidizer uses high-purity products and ordinary products with few impurities. The Ca content of the high-purity strain is reduced to less than 0.20% by mass. The Ca content of ordinary products is about 0.5 to 1.5% by mass. The slag basicity is obtained by analyzing the sample taken from the slag.

Using the obtained continuous cast thick plate, a cold-rolled annealed steel plate with a plate thickness of 0.5 to 1.5 mm is obtained in steps including hot rolling and cold rolling. The cross section (L cross section) parallel to the rolling direction and the thickness direction of the cold rolled annealed steel sheet was observed by SEM (scanning electron microscope), and the oxide system was performed by EDX (energy dispersive X-ray analysis) attached to the SEM Analysis of the composition of inclusions. According to the measured values of 30 oxide-based inclusions randomly selected, the average CaO/( is calculated according to the aforementioned "method of obtaining the average CaO/(SiO ₂ +MnO+CaO) mass ratio and average CaO/MnO mass ratio" SiO ₂ +MnO+CaO) mass ratio and average CaO/MnO mass ratio. The results are shown in Table 2.

Using each cold-rolled annealed steel sheet as a raw material, TIG welding is used to manufacture welded steel pipes under normal conditions. The outer diameter of the tube is in the range of 25 to 51 mm. When welding, no filler material is added. Samples were randomly taken from the obtained steel pipe products, and the occurrence of slag points was investigated for continuous welding beads with a length of more than 50m. Calculate the number of slag spots whose long diameter (the diameter of the longest part of the particles) is 1.0 mm or more, and take the number of slag spots generated per 1 m as the rate of slag spot generation (pieces/m). If the generation rate of the slag spots of the above size is 0.30 pieces/m or less, it can be evaluated that the generation of slag spots is more greatly suppressed than in the past. Therefore, those with a slag point generation rate of 0.30 pieces/m or less were judged as passing. The results are shown in Table 2.

The steel composition satisfies the prescribed 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 prescribed range of the present invention. Very little.

In contrast, Nos. 21 to 23 belonging to the comparative examples have high slag basicity during refining, so the average CaO/MnO mass ratio of oxide-based inclusions becomes high, and slag spots are generated more frequently. The total oxygen content in No.24 to 26 series steel is too low, and the slag basicity during refining is high, so the average CaO/MnO quality ratio of oxide-based inclusions is significantly higher than other examples, and the slag point cannot be obtained The inhibitory effect. Nos. 27 to 30 use "ordinary products" as FeSi alloys that are deoxidizers, so the desired inclusion control cannot be achieved, and the average CaO/MnO mass ratio of oxide-based inclusions becomes high, and the slag point Produce more.

Fig. 3 shows the relationship between the average CaO/(SiO ₂ +MnO+CaO) mass ratio of the oxide-based inclusions of each example and the slag point generation rate. The black dots use the "high purity product" as an example of the FeSi alloy that belongs to the deoxidizer, and the white dot use the "normal product" (the same applies to the following Figures 4 to 9). In addition, FIG. 4 and FIG. 5 show the relationship between the average CaO/MnO mass ratio of the oxide-based inclusions of each example and the slag point generation rate. FIG. 5 is an enlarged view showing the area where the average CaO/MnO mass ratio in FIG. 4 is low. It can be seen that by controlling the average CaO/(SiO ₂ +MnO+CaO) mass ratio of 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 remarkable Promote.

Figures 6 and 7 show the relationship between the total oxygen content in the steel materials of each example and the average CaO/MnO mass ratio of oxide-based inclusions. FIG. 7 is an enlarged view showing the area where the average CaO/MnO mass ratio in 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 oxide-based inclusions to be low.

Figure 8 shows the relationship between the total oxygen content in the steel materials of each example and the slag point generation rate. It can be seen that the FeSi alloy using the "high purity product" as the deoxidizer has an oxygen content of 0.0030% or more, which is effective in suppressing the generation of slag spots.

Figure 9 shows the relationship between the slag basicity during refining and the slag point generation rate. It can be seen that FeSi alloys using "high-purity products" as deoxidizers are effective in suppressing the occurrence of slag spots by adjusting the slag basicity to a range of 1.20 to 1.60.

Claims (7)

A stainless steel material, in mass %, having C: 0.005 to 0.100%, 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 0.500%, V: 0 to 0.500%, Zr: 0 to 0.500%, W: 0 to 0.500%, Co: 0 to 0.500%, 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 (rare earth elements other than Y): 0 to 0.050%, Y: 0 to 0.050%, O: 0.0030 to 0.0150%, chemical composition of residual Fe and inevitable impurities, and there are oxide systems containing Mn Inclusions, oxide inclusions observed in the metal structure in the composition of inclusions when the contents of Si, Mn, and Ca in oxide-based inclusions are converted to the mass ratio of SiO ₂ , MnO, and CaO, respectively The average CaO/(SiO ₂ +MnO+CaO) mass ratio is 0.40 or less, and the average CaO/MnO mass ratio is 15.0 or less. A base material for arc welding, including the stainless steel material described in item 1 of the patent application. A steel plate base material for arc welding pipe manufacturing, which includes the stainless steel material described in item 1 of the patent application scope. An arc welding structural member, which uses the stainless steel material described in item 1 of the patent scope as a base material. An arc-welded steel pipe, which will not be described in item 1 of the patent application Rust steel is used in the base material. A method for manufacturing a welded structural member, which uses the stainless steel material described in item 1 of the patent scope as a base material, and performs non-consumable electrode arc welding without adding a filler material. A method of manufacturing a welded steel pipe, which uses a stainless steel sheet according to item 1 of the patent scope as a base material and forms a welded steel pipe by non-consumable electrode arc welding without adding a filler material.

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