WO2019082427A1 - Stainless steel material having excellent slag spot occurrence prevention performance, welded structural member and method for producing same - Google Patents

Stainless steel material having excellent slag spot occurrence prevention performance, welded structural member and method for producing same

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Publication number
WO2019082427A1
WO2019082427A1 PCT/JP2018/018480 JP2018018480W WO2019082427A1 WO 2019082427 A1 WO2019082427 A1 WO 2019082427A1 JP 2018018480 W JP2018018480 W JP 2018018480W WO 2019082427 A1 WO2019082427 A1 WO 2019082427A1
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cao
mno
stainless steel
slag
steel
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PCT/JP2018/018480
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French (fr)
Japanese (ja)
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靖弘 江原
森田　一成
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日新製鋼株式会社
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Application filed by 日新製鋼株式会社 filed Critical 日新製鋼株式会社
Priority to KR1020207014455A priority Critical patent/KR102391566B1/en
Priority to CN201880068466.1A priority patent/CN112218965A/en
Publication of WO2019082427A1 publication Critical patent/WO2019082427A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
    • B23K31/02—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups relating to soldering or welding
    • B23K31/027—Making tubes with soldering or welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
    • B23K35/3053—Fe as the principal constituent
    • B23K35/308—Fe as the principal constituent with Cr as next major constituent
    • B23K35/3086—Fe as the principal constituent with Cr as next major constituent containing Ni or Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0006—Adding metallic additives
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a stainless steel material that is less likely to generate a defect called "slag spot” or "black spot”, which is a type of welding defect that occurs in arc welding beads.
  • the present invention also relates to a welded structural member using the steel material and a method of manufacturing the same.
  • slag spot When arc welding is performed using a stainless steel material as a base material, a defect called "slag spot" in which oxide aggregates are scattered on the weld bead may occur.
  • the appearance photograph of the weld bead which the slag spot which is published in the nonpatent literature 1 which arose in FIG. 1 is quoted and illustrated.
  • the slag spot is a minute slag which floats in the form of islands or spots at intervals of several mm to several cm on the weld bead.
  • FIG. 2 illustrates the appearance of a slag spot found on the weld bead of a steel pipe produced by TIG welding.
  • the number of slag spots per 1 m in the bead length direction (hereinafter referred to as “slag spot generation rate”) of slag spots having a major diameter of 1.0 mm or more found in this steel pipe was 0.7 piece / m.
  • Patent documents 1 and 2 are ferritic stainless steels in which the generation of slag spots (black spots) is reduced by adjusting the content of easily oxidizable elements Al, Ti, Si and Ca to an optimized steel composition. Is disclosed. However, according to the inventors' investigation, 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, foreign matter on the surface of a welded portion, which is a starting point of processing cracking, is reduced.
  • the foreign matter adhering to the surface of the weldment is mainly composed of oxides or nitrides such as Al, Ti, Si, Ca, and Mg, and nonmetallic inclusions present in the base material generally have a high melting point, It is taught that when welding, it does not melt, floats on the surface of the molten metal, condenses, and solidifies, it remains on the surface as it is to form irregularities (paragraph 0035).
  • the foreign matter attached to the surface of the welded portion is derived from nonmetallic inclusions present in the base material (paragraph 0038).
  • 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 material by reducing other inclusion constituent elements Ca, Mg, N, and O. Reduce the number of inclusions, thereby reducing foreign matter observed on the surface of the weld metal (paragraph 0039).
  • the method of using a welding wire for an electrode, and the method of adding a filler metal are mentioned. It is also effective to use fluxed welding wire.
  • arc welding using non-soldering electrodes, such as TIG welding is widely performed, and in many cases, no filler metal is used.
  • the present invention does not rely on the use of a welding wire or a filler metal, and even when non-electrode arc welding is employed, generation of slag spots is stable with various types of stainless steel regardless of whether austenitic or ferritic. To provide a technology that can be significantly suppressed.
  • the inventors in addition to reducing the amount of non-metallic inclusions present in the stainless steel base material, in particular by adopting a method of controlling the composition of oxide-based inclusions, We have found that the above tasks can be achieved.
  • the present invention discloses the following inventions.
  • a base material for arc welding made of the stainless steel material according to the above [1].
  • a steel plate base material for arc welded pipe making which is made of the stainless steel material according to the above [1].
  • a method for producing a welded steel pipe using a steel plate which is the stainless steel material described in the above-mentioned [1] as a base material and forming a welded steel pipe by non-smelting electrode type arc welding without adding a filler metal.
  • the content of each of the above-described steel components is the total content of the elements present in the steel. Therefore, the content of the metal element or oxygen partially present as an oxide includes the amount present as an oxide.
  • the average CaO / (SiO 2 + MnO + CaO) mass ratio of the oxide inclusions and the average CaO / MnO mass ratio can be determined as follows.
  • the arc welded structural member is a member having a weld formed by arc welding.
  • the arc welded steel pipe is a steel pipe having a weld formed by arc welding. These welds can be "welded parts without filler addition" (i.e. welds formed without the addition of filler).
  • the contents of Si, Mn, Ca, Al, Mg, Ti, Cr and Fe are respectively as oxide SiO 2 , MnO, CaO, Al 2 O 3 , MgO, TiO 2 , Cr 2 O 3 and FeO Converted to the mass proportion of SiO 2 , MnO and CaO in these eight oxides, respectively, the SiO 2 content (mass%), the MnO content (mass%) and the CaO content of the particles concerned (Mass%)
  • the average content (% by mass) of SiO 2 , MnO and CaO for all the measurement particles is calculated.
  • the average CaO / (SiO 2 + MnO + CaO) mass ratio is determined by substituting the value of the above-mentioned average content (mass%) of the oxide concerned in the part of the chemical formula of each of the following formula (1).
  • an average CaO / MnO mass ratio is determined by substituting the value of the above-mentioned average content (mass%) of the oxide concerned into a part of a chemical formula of each oxide of the following formula (2).
  • This technology can be applied to various stainless steel types, regardless of austenite type or ferrite type, and is particularly effective in TIG welding performed without adding a filler metal.
  • Component composition of steel In the present invention, various steel types are applicable regardless of austenite type or ferrite type. According to the inventors' investigation, the suppression effect of the slag spot by the below-mentioned inclusion composition control is acquired in the following composition ranges.
  • Ni, Mo, Cu, Nb, V, Zr, W, Co, B, Ti, Al, Ca, Mg, REM (a rare earth element other than Y), and Y are arbitrarily contained elements.
  • the following pattern can be considered as a generation factor of the slag spot which arises in the arc welding bead which used stainless steel materials as a base material.
  • the oxidizable element (Al, Ca, Ti, etc.) in the base material forms an oxide at a portion where the gas shield is insufficient and remains on the bead.
  • Patent 1 Non-metallic inclusions with high dissociation temperature present in the base material agglomerate and float along with the sweep of the arc, and when the agglomerated particles become large to some extent, they are left from the sweep of the arc and remain on the bead. According to the inventors' investigations, slag spots are generated even when the gas shielding is sufficiently performed.
  • the generation factor of the pattern 2 is used. It is necessary to overcome.
  • the generation factor of the pattern 1 can be eliminated by limiting the content of the oxidizable element and the like in the steel composition of the base material to the above-mentioned range.
  • the inclusion control in the base material is important.
  • the cause of slag spots is oxide inclusions having a high dissociation temperature.
  • SiO 2 , MnO, CaO, Al 2 O 3 , MgO and the like can be mentioned as typical components of the oxide inclusions present in the steel material.
  • CaO is not reduced even at the time of welding because it has a high dissociation temperature and remains as an oxide. As it agglomerates in the molten metal due to the heat of the arc, it appears as a slag spot after cooling.
  • MnO and SiO 2 have a relatively low dissociation temperature, Mn and Si constituting the oxide are reduced at the time of welding to form a metal and easily dissolve in the molten metal. Therefore, MnO and SiO 2 are less likely to be a cause of generation of slag spots.
  • SiO 2 -CaO type a general type oxide inclusion having a high content of SiO 2 and CaO
  • composition control of the inclusion decreases the Ca concentration and increases the Mn concentration.
  • oxide inclusions of the illustrated type are referred to as "SiO 2 -MnO-CaO type" for convenience.
  • Metal oxides generally dissociate into metal and oxygen as the temperature increases. For example, when assuming the partial pressure of oxygen at 10 ⁇ 12 atm in Elingham diagram, the dissociation temperature is estimated: SiO 2 : about 1530 ° C., MnO: about 1380 ° C., CaO: about 2100 ° C., Al 2 O 3 : about 2020 It will be ° C.
  • the inclusion of SiO 2 -CaO type advantageously as possible by changing the SiO 2 -MnO-CaO type, i.e. be a composition of inclusions relatively SiO 2 -MnO-CaO type dominance, suppression of slag spot It becomes.
  • Al 2 O 3 has a high dissociation temperature, steel materials adjusted to the above-described steel composition are less likely to cause slag spots because the amount of Al 2 O 3 is small.
  • the present invention employs an "average CaO / MnO mass ratio". As this value is smaller, it can be evaluated that the inclusion composition is relatively dominated by the SiO 2 -MnO-CaO type, which is advantageous to suppression of the occurrence of the slag spot.
  • the average CaO / MnO mass ratio can be determined by the method described above.
  • the average CaO / MnO mass ratio is more preferably 10.0 or less, and may be controlled to 6.0 or less.
  • an inclusion composition having 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.
  • the above-mentioned stainless steel material in which the average CaO / (SiO 2 + MnO + CaO) mass ratio of oxide inclusions and the average CaO / MnO mass ratio are optimized, is manufactured using a general stainless steel melting facility be able to. Typically, VOD process and AOD process can be mentioned. In any case, first, decarburization in which oxygen is blown into the Cr-containing molten iron is applied, and a molten steel having a Cr oxide-containing slag on the hot water surface (C content is, for example, 0.20% or less) is manufactured by a conventional method.
  • the molten steel at this stage is a de-carburized steel into which oxygen is blown, the 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.
  • a part of Cr contained in a large amount in the molten steel is also oxidized to form a slag on the surface of the molten steel as Cr oxide.
  • the molten steel contains a large amount of dissolved oxygen blown for decarburization. Therefore, it is necessary to deoxidize before casting. Final composition adjustments are made using FeSi alloys rather than Al as the deoxidizer.
  • (1) Refinement is performed so that the oxygen content in the steel (total oxygen content including oxygen present as an oxide) is 0.0030% (30 ppm) or more.
  • the oxygen content is less than 0.0030%, it becomes difficult to refine the average CaO / MnO mass ratio stably to 15.0 or less.
  • it is more preferable to adjust the oxygen content to be 0.0040% (40 ppm) or more.
  • the oxygen content is too high, a large amount of inclusions having a high Cr oxide content is generated, which is a factor causing deterioration of the product quality.
  • the oxygen content is limited to 0.0150% (150 ppm) or less, and more preferably 0.0100% (100 ppm) or less. It may be controlled to 0.0060% (60 ppm) or less.
  • Si deoxidation is performed using a high purity FeSi alloy having a Ca content of, for example, 0.20% or less.
  • Slag basicity CaO / SiO 2 is adjusted to a range of 1.20 to 1.60.
  • the stainless steel shown in Table 1 was melted using a VOD process to obtain a continuously cast slab.
  • inclusion control was attempted by changing the total oxygen content in the steel, the type of FeSi alloy as a deoxidizer, and the condition of slag basicity (CaO / SiO 2 ).
  • Table 2 shows each condition.
  • the oxygen content in Table 2 is the value shown in Table 1 again.
  • As the FeSi alloy which is a deoxidizer high-purity products having a small amount of impurities and normal products were used.
  • the high purity product is one in which the Ca content is reduced to 0.20 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 collected from the slag.
  • a cold-rolled and annealed steel sheet with a thickness of 0.5 to 1.5 mm was obtained in a process including hot rolling and cold rolling.
  • SEM scanning electron microscope
  • observation is performed on a cross section (L cross section) parallel to the rolling direction and thickness direction of this cold rolled annealed steel sheet, and an oxide system is obtained by EDX (energy dispersive X-ray analysis) attached to the SEM Composition analysis of inclusions was performed.
  • Welded steel pipes were manufactured under normal conditions by TIG welding using each cold rolled annealed steel sheet as a raw material.
  • the outer diameter of the tube is in the range 25-51 mm. No filler metal was added during welding.
  • Samples were randomly drawn from the obtained steel pipe products, and the occurrence of slag spots was investigated for continuous weld beads of 50 m or more in length.
  • the number of slag spots having a major axis (diameter of the longest portion of the particles) of 1.0 mm or more was counted, and the number of generated slag spots per 1 m was regarded as the slag spot generation rate (piece / m).
  • the slag spot generation rate of the said size is 0.30 piece / m or less, it can be evaluated that generation
  • the steel composition of the present invention example in which the steel composition satisfies the specified range of the present invention and the average CaO / (SiO 2 + MnO + CaO) mass ratio of the oxide inclusions and the average CaO / MnO mass ratio is controlled within the specified range of the present invention is There is very little occurrence of slag spots.
  • FIG. 3 shows the relationship between the average CaO / (SiO 2 + MnO + CaO) mass ratio of the oxide inclusions and the slag spot generation rate for each example.
  • the black circle plot is an example using “high purity product” as the deoxidizer FeSi alloy, and the white circle plot is an example using “normal product” (same in FIGS. 4 to 9 below).
  • inclusion and a slag spot generation rate is shown in FIG. 4, FIG. 5 about each case.
  • FIG. 5 is an enlarged view of the region where the average CaO / MnO mass ratio in FIG. 4 is low.
  • FIG. 6 The relationship between the total oxygen content in steel materials and the average CaO / MnO mass ratio of oxide inclusions is shown in FIG. 6 and FIG. 7 for each example.
  • FIG. 7 is an enlarged view of the region 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 inclusions to a low level.
  • FIG. 8 shows the relationship between the total oxygen content in the steel material and the slag spot generation rate for each example. It turns out that it is effective in generation
  • 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” as the deoxidizer FeSi alloy and adjusting the slag basicity to a range of 1.20 to 1.60 is effective in suppressing the generation of slag spots.

Abstract

This stainless steel material can stably and markedly suppress the occurrence of slag spots during arc welding, the stainless steel material having a chemical composition that contains, in terms of mass%, 0.005-0.100% of C, 0.10-3.00% of Si, 0.10-6.50% of Mn, 0.001-0.050% of P, 0.0001-0.0200% of S, 0-20.00% of Ni, 10.50-26.00% of Cr, 0.005-0.200% of N, 0.0030-0.0150% of O and, if necessary, prescribed quantities of Mo, Cu, Nb, V, Zr, W, Co, B, Ti, Al, Ca, Mg, REM (rare earth elements excluding Y) and Y, with the remainder comprising Fe and unavoidable impurities, with the average CaO/(SiO2+MnO+CaO) mass ratio being 0.40 or less and the average CaO/MnO mass ratio being 15.0 in oxide-based inclusions observed in the steel structure.

Description

スラグスポット発生抑止能に優れるステンレス鋼材並びに溶接構造部材およびその製造法Stainless steel material and welded structural member excellent in ability to suppress generation of slag spot and method for manufacturing the same
　本発明は、アーク溶接ビードに生じる溶接欠陥の一種である「スラグスポット」あるいは「ブラックスポット」と呼ばれる欠陥を発生させにくいステンレス鋼材に関する。また、その鋼材を用いた溶接構造部材、およびその製造法に関する。 The present invention relates to a stainless steel material that is less likely to generate a defect called "slag spot" or "black spot", which is a type of welding defect that occurs in arc welding beads. The present invention also relates to a welded structural member using the steel material and a method of manufacturing the same.
　ステンレス鋼材を母材に用いてアーク溶接を行うと、溶接ビード上に酸化物の凝集体が点在した「スラグスポット」と呼ばれる欠陥が生じることがある。図１に、非特許文献１に掲載されているスラグスポットが生じた溶接ビードの外観写真を引用して例示する。非特許文献１の記載によれば、スラグスポットは、溶接ビード上に数ｍｍから数ｃｍ間隔で島状あるいは点状に残留浮上する微小なスラグであるとされる。アーク溶接時に溶融池に侵入した空気中の酸素が、鋼材中の微量成分であるＡｌ、Ｃａ、Ｔｉ等の活性元素と反応してスラグスポットとして残留すると考えられ、特に、溶融池の十分なガスシールドが難しい高速度ＴＩＧ溶接でスラグスポットの発生が顕著になる傾向があるという。 When arc welding is performed using a stainless steel material as a base material, a defect called "slag spot" in which oxide aggregates are scattered on the weld bead may occur. The appearance photograph of the weld bead which the slag spot which is published in the nonpatent literature 1 which arose in FIG. 1 is quoted and illustrated. According to the description of Non-Patent Document 1, it is considered that the slag spot is a minute slag which floats in the form of islands or spots at intervals of several mm to several cm on the weld bead. It is believed 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 minor components in steel materials, and remains as slag spots, and in particular, sufficient gas in the molten pool It is said that the occurrence of slag spots tends to be remarkable in high-speed TIG welding where shielding is difficult.
　図２には、ＴＩＧ溶接により造管した鋼管の溶接ビード上に見られたスラグスポットの外観を例示する。この鋼管に見られる長径１.０ｍｍ以上の大きさのスラグスポットのビード長さ方向１ｍ当たりの個数（以下、「スラグスポット発生率」という。）は０.７個／ｍであった。 FIG. 2 illustrates the appearance of a slag spot found on the weld bead of a steel pipe produced by TIG welding. The number of slag spots per 1 m in the bead length direction (hereinafter referred to as “slag spot generation rate”) of slag spots having a major diameter of 1.0 mm or more found in this steel pipe was 0.7 piece / m.
　溶接ビードにスラグスポットが多発すると、例えば以下のような問題がある。
　（i）溶接ビード部の美観を損ねる。（ii）除去のためにビード表面研磨などの煩雑な手入れが必要となる場合がある。（iii）溶接鋼管の製造では、鋼管内面の溶接ビードを圧下してビートの高さを低くしてから内面研磨を施す用途もある。スラグスポットは裏ビード側にも生じることがあり、その場合には、鋼管内面のビード部を圧下した際にスラグスポットが押し込まれてビードの金属面に凹みが形成され、後の研磨工程で研磨残り（未研磨部）が生じる。（iv）スラグスポットを構成する異物とビードの金属表面の間で隙間腐食が生じる場合がある。（v）溶接鋼管の場合、内面ビード上に生成したスラグスポットが鋼管使用中に脱落し、中を流れる流体への異物混入の原因となり得る。（vi）アーク溶接時にスラグスポットの原因となる異物が溶融池内に凝集してくると、アークが不安定となり、ビード形状が乱れやすい。
　したがって、アーク溶接の母材として使用したときにスラグスポットの発生が顕著に抑制できるステンレス鋼材の開発が待たれている。 When slag spots occur frequently in the weld bead, for example, there are the following problems.
(I) The appearance of the weld bead is impaired. (Ii) It may require complicated care such as bead surface grinding for removal. (Iii) In the manufacture of welded steel pipe, there is also an application of applying internal grinding after depressing the weld bead on the inner surface of the steel pipe to reduce the height of the beat. Slag spots may also occur on the back bead side. In this case, when the bead portion on the inner surface of the steel pipe is pressed down, the slag spot is pushed in and a recess is formed on the metal surface of the bead, and it is polished in a later polishing process. The remainder (unpolished part) occurs. (Iv) There may be crevice corrosion between foreign matter constituting the slag spot and the metal surface of the bead. (V) In the case of a welded steel pipe, a slag spot formed on the inner surface bead may fall off during use of the steel pipe, which may cause contamination of the fluid flowing therethrough. (Vi) When foreign matter causing the slag spot condenses in the molten pool during arc welding, the arc becomes unstable and the bead shape is easily disturbed.
Therefore, development of a stainless steel material that can significantly suppress the occurrence of slag spots when used as a base material for arc welding is awaited.
　特許文献１、２には、易酸化性元素であるＡｌ、Ｔｉ、Ｓｉ、Ｃａの含有量を最適化した鋼組成に調整することによってスラグスポット（ブラックスポット）の生成を低減したフェライト系ステンレス鋼が開示されている。しかし、発明者らの調査によれば、鋼組成の調整のみではスラグスポットの抑制効果は限定的であり、さらなる改善の余地が残されている。 Patent documents 1 and 2 are ferritic stainless steels in which the generation of slag spots (black spots) is reduced by adjusting the content of easily oxidizable elements Al, Ti, Si and Ca to an optimized steel composition. Is disclosed. However, according to the inventors' investigation, the effect of suppressing the slag spot is limited only by adjusting the steel composition, and there is room for further improvement.
　特許文献３には、被覆管用オーステナイト系Ｆｅ－Ｎｉ－Ｃｒ合金において、加工割れの起点となる溶接部表面の異物を低減することが記載されている。溶接物表面に付着する異物はＡｌ、Ｔｉ、Ｓｉ、Ｃａ、Ｍｇ等の酸化物や窒化物を主体とするものであり、母材中に存在する非金属介在物は一般に高融点であるため、溶接時に溶融せず溶融金属の表面に浮上して凝集し、凝固する際、そのまま表面に残存して凹凸を形成すると教示されている（段落００３５）。また、溶接部表面に付着した異物は、母材中に存在する非金属介在物に由来するものであるという（段落００３８）。特許文献３に開示の技術では、Ａｌ、Ｔｉ、Ｓｉの量を極力低減することに加えて、他の介在物構成元素であるＣａ、Ｍｇ、ＮおよびＯを低減することによって母材中に存在する介在物の個数を低減し、それによって溶接金属表面に観察される異物の低減を図っている（段落００３９）。しかしながら、発明者らの検討によれば、ステンレス鋼材中に存在する非金属介在物の数を単に低減するだけでは、例えば食品加工ラインや半導体製造設備で使用される溶接鋼管に要求されような、極めて異物（スラグスポット）の少ないアーク溶接ビードを安定して得ることは難しい。また、ステンレス鋼材中に存在する非金属介在物の量を大幅に低減することは、製鋼工程での負荷を増大させ、鋼材コストの上昇を招く。したがって、介在物の存在量を低減するという手法に頼らずにスラグスポットの低減を図ることができる、新たな手法の開発が望まれる。 Patent Document 3 describes that, in an austenitic Fe-Ni-Cr alloy for a cladding tube, foreign matter on the surface of a welded portion, which is a starting point of processing cracking, is reduced. The foreign matter adhering to the surface of the weldment is mainly composed of oxides or nitrides such as Al, Ti, Si, Ca, and Mg, and nonmetallic inclusions present in the base material generally have a high melting point, It is taught that when welding, it does not melt, floats on the surface of the molten metal, condenses, and solidifies, it remains on the surface as it is to form irregularities (paragraph 0035). Further, it is said that the foreign matter attached to the surface of the welded portion is derived from nonmetallic inclusions present in the base material (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 material by reducing other inclusion constituent elements Ca, Mg, N, and O. Reduce the number of inclusions, thereby reducing foreign matter observed on the surface of the weld metal (paragraph 0039). However, according to the study of the inventors, it is extremely foreign matter which is required for a welded steel pipe used in, for example, a food processing line or a semiconductor manufacturing facility, by merely reducing the number of nonmetallic inclusions present in stainless steel. It is difficult to stably obtain an arc weld bead with less (slag spots). In addition, significantly reducing the amount of nonmetallic inclusions present in the stainless steel material increases the load in the steel making process, resulting in an increase in the cost of the steel material. Therefore, development of a new method capable of reducing the slag spot without relying on the method of reducing the amount of inclusions is desired.
特開２０１０－２０２９７３号公報JP, 2010-202973, A 特開２０１２－３６４４４号公報JP 2012-36444 A 特開２０１４－８４４９３号公報JP, 2014-84493, A
　アーク溶接ビードのスラグスポットを低減する上で有効な溶接法として、溶接ワイヤを電極に使用する方法や、溶加材を添加する方法が挙げられる。フラックス入りの溶接ワイヤを使用することも有効である。一方で、ＴＩＧ溶接など、非溶極式の電極を用いるアーク溶接も広く行われており、溶加材を使用しないことも多い。
　本発明は、溶接ワイヤや溶加材の使用に頼ることなく、非溶極式のアーク溶接法を採用した場合でも、オーステナイト系、フェライト系を問わず種々のステンレス鋼種でスラグスポットの発生が安定して顕著に抑制できる技術を提供しようというものである。 As a welding method effective in reducing the slag spot of an arc welding bead, the method of using a welding wire for an electrode, and the method of adding a filler metal are mentioned. It is also effective to use fluxed welding wire. On the other hand, arc welding using non-soldering electrodes, such as TIG welding, is widely performed, and in many cases, no filler metal is used.
The present invention does not rely on the use of a welding wire or a filler metal, and even when non-electrode arc welding is employed, generation of slag spots is stable with various types of stainless steel regardless of whether austenitic or ferritic. To provide a technology that can be significantly suppressed.
　発明者らは詳細な研究の結果、ステンレス鋼母材中に存在する非金属介在物の量を低減することに加え、特に酸化物系介在物の組成を制御するという手法を採用することにより、上記課題が達成できることを知見した。本明細書では、以下の発明を開示する。 As a result of detailed researches, the inventors, in addition to reducing the amount of non-metallic inclusions present in the stainless steel base material, in particular by adopting a method of controlling the composition of oxide-based inclusions, We have found that the above tasks can be achieved. The present invention discloses the following inventions.
　［１］質量％で、Ｃ：０.００５～０.１００％、Ｓｉ：０.１０～３.００％、Ｍｎ：０.１０～６.５０％、Ｐ：０.００１～０.０５０％、Ｓ：０.０００１～０.０２００％、Ｎｉ：０～２０.００％、Ｃｒ：１０.５０～２６.００、Ｍｏ：０～２.５０％、Ｃｕ：０～３.５０％、Ｎｂ：０～０.５００％、Ｖ：０～０.５００％、Ｚｒ：０～０.５００％、Ｗ：０～０.５００％、Ｃｏ：０～０.５００、Ｂ：０～０.０２０、Ｎ：０.００５～０.２００％、Ｔｉ：０～０.０５０％、Ａｌ：０～０.１００％、Ｃａ：０～０.００１０％、Ｍｇ：０～０.００１０％、ＲＥＭ（Ｙを除く希土類元素）：０～０.０５０％、Ｙ：０～０.０５０％、Ｏ：０.００３０～０.０１５０％、残部Ｆｅおよび不可避的不純物からなる化学組成を有し、Ｍｎを含有する酸化物系介在物が存在し、酸化物系介在物中のＳｉ、ＭｎおよびＣａの含有量をそれぞれＳｉＯ２、ＭｎＯおよびＣａＯの質量割合に換算した場合の介在物組成において、金属組織中に観察される酸化物系介在物の平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比が０.４０以下、平均ＣａＯ／ＭｎＯ質量比が１５.０以下であるステンレス鋼材。
　［２］上記［１］に記載のステンレス鋼材からなるアーク溶接用母材。
　［３］上記［１］に記載のステンレス鋼材からなるアーク溶接造管用鋼板母材。
　［４］上記［１］に記載の鋼材を母材に用いたアーク溶接構造部材。
　［５］上記［１］に記載の鋼材を母材に用いたアーク溶接鋼管。
　［６］上記［１］に記載のステンレス鋼材を母材に用いて、溶加材を添加せずに非溶極式のアーク溶接を行う溶接構造部材の製造法。
　［７］上記［１］に記載のステンレス鋼材である鋼板を母材に用いて、溶加材を添加せずに非溶極式のアーク溶接にて溶接鋼管とする、溶接鋼管の製造法。 [1] 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 excluding Y): 0 to 0.050%, Y: 0 to 0.050%, O: 0.0030 to 0.0150%, the balance being Fe and unavoidable impurities, Mn Containing oxide system In the inclusion composition in the presence of the presence, when the contents of Si, Mn and Ca in the oxide inclusion are converted to the mass proportions of SiO 2 , MnO and CaO, respectively, the oxidation observed in the metal structure A stainless steel material having an average CaO / (SiO 2 + MnO + CaO) mass ratio of substance inclusions of 0.40 or less and an average CaO / MnO mass ratio of 15.0 or less.
[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 welded pipe making, which is 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 described in the above [1] as a base material.
[6] A method for producing a welded structural member, using the stainless steel material described in the above [1] as a base material, and performing non-electrode-type arc welding without adding a filler metal.
[7] A method for producing a welded steel pipe, using a steel plate which is the stainless steel material described in the above-mentioned [1] as a base material and forming a welded steel pipe by non-smelting electrode type arc welding without adding a filler metal.
　ここで、上記の各鋼成分の含有量は、鋼中に存在する当該元素のトータル含有量である。したがって、一部が酸化物として存在する金属元素や酸素の含有量は、酸化物として存在する量を含んでいる。酸化物系介在物の平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比、平均ＣａＯ／ＭｎＯ質量比は、以下のようにして求めることができる。アーク溶接構造部材は、アーク溶接により形成された溶接部を有する部材である。同様に、アーク溶接鋼管は、アーク溶接により形成された溶接部を有する鋼管である。これらの溶接部は、「溶加材無添加の溶接部」（すなわち、溶加材を添加せずに形成された溶接部）とすることができる。 Here, the content of each of the above-described steel components is the total content of the elements present in the steel. Therefore, the content of the metal element or oxygen partially present as an oxide includes the amount present as an oxide. The average CaO / (SiO 2 + MnO + CaO) mass ratio of the oxide inclusions and the average CaO / MnO mass ratio can be determined as follows. The arc welded structural member is a member having a weld formed by arc welding. Similarly, the arc welded steel pipe is a steel pipe having a weld formed by arc welding. These welds can be "welded parts without filler addition" (i.e. welds formed without the addition of filler).
〔平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比、平均ＣａＯ／ＭｎＯ質量比の求め方〕
　鋼材の断面についてＳＥＭ観察を行い、断面内に存在する酸化物系介在物の粒子から無作為に３０個以上の粒子を選択してＥＤＸ（エネルギー分散型Ｘ線分析）により組成分析を行う。個々の粒子について、Ｓｉ、Ｍｎ、Ｃａ、Ａｌ、Ｍｇ、Ｔｉ、ＣｒおよびＦｅの含有率をそれぞれ酸化物ＳｉＯ２、ＭｎＯ、ＣａＯ、Ａｌ２Ｏ３、ＭｇＯ、ＴｉＯ２、Ｃｒ２Ｏ３およびＦｅＯの質量割合に換算し、これら８種類の酸化物に占めるＳｉＯ２、ＭｎＯおよびＣａＯの質量割合を、それぞれ当該粒子のＳｉＯ２含有量（質量％）、ＭｎＯ含有量（質量％）およびＣａＯ含有量（質量％）とする。個々の粒子のＳｉＯ２含有量、ＭｎＯ含有量およびＣａＯ含有量をそれぞれ相加平均することにより、全測定粒子についてのＳｉＯ２、ＭｎＯおよびＣａＯの平均含有量（質量％）を算出する。下記（１）式の各酸化物の化学式の箇所に、当該酸化物の前記平均含有量（質量％）の値を代入することにより、平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比が定まる。同様に、下記（２）式の各酸化物の化学式の箇所に、当該酸化物の前記平均含有量（質量％）の値を代入することにより、平均ＣａＯ／ＭｎＯ質量比が定まる。
　ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）　…（１）
　ＣａＯ／ＭｎＯ　…（２） [Mean ratio of average CaO / (SiO 2 + MnO + CaO) mass ratio, 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 particles of oxide inclusions present in the cross section, and composition analysis is performed by EDX (energy dispersive X-ray analysis). For individual particles, the contents of Si, Mn, Ca, Al, Mg, Ti, Cr and Fe are respectively as oxide SiO 2 , MnO, CaO, Al 2 O 3 , MgO, TiO 2 , Cr 2 O 3 and FeO Converted to the mass proportion of SiO 2 , MnO and CaO in these eight oxides, respectively, the SiO 2 content (mass%), the MnO content (mass%) and the CaO content of the particles concerned (Mass%) By averaging the SiO 2 content, the MnO content and the CaO content of the individual particles respectively, the average content (% by mass) of SiO 2 , MnO and CaO for all the measurement particles is calculated. The average CaO / (SiO 2 + MnO + CaO) mass ratio is determined by substituting the value of the above-mentioned average content (mass%) of the oxide concerned in the part of the chemical formula of each of the following formula (1). Similarly, an average CaO / MnO mass ratio is determined by substituting the value of the above-mentioned average content (mass%) of the oxide concerned into a part of a chemical formula of each oxide of the following formula (2).
CaO / (SiO 2 + MnO + CaO) (1)
CaO / MnO (2)
　本発明によれば、ステンレス鋼材のアーク溶接においてスラグスポットの発生を安定して顕著に抑制することが可能になった。この技術はオーステナイト系、フェライト系を問わず種々のステンレス鋼種に適用でき、特に溶加材を添加せずに行うＴＩＧ溶接で効果が大きい。 According to the present invention, it has become possible to stably and remarkably suppress the generation of a slag spot in arc welding of a stainless steel material. This technology can be applied to various stainless steel types, regardless of austenite type or ferrite type, and is particularly effective in TIG welding performed without adding a filler metal.
非特許文献１に掲載されているスラグスポットが生じた溶接ビードの外観写真の引用。Reference of the photograph of the appearance of the weld bead which the slag spot which is published in nonpatent literature 1 arose. ＴＩＧ溶接により造管した鋼管の溶接ビード上に見られたスラグスポットの外観写真。The photograph of the appearance of the slag spot seen on the weld bead of the steel pipe produced by TIG welding. 酸化物系介在物の平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比とスラグスポット発生率の関係を示したグラフ。The graph which showed the relationship between the average CaO / (SiO 2 + MnO + CaO) mass ratio of an oxide system inclusion, and a slag spot generating rate. 酸化物系介在物の平均ＣａＯ／ＭｎＯ質量比とスラグスポット発生率の関係を示したグラフ。The graph which showed the relationship of the average CaO / MnO mass ratio of an oxide type inclusion, and a slag spot generation rate. 図４の平均ＣａＯ／ＭｎＯ質量比が低い領域を拡大表示したグラフ。The graph which expanded and displayed the area | region where average CaO / MnO mass ratio is low of FIG. 鋼材中のトータル酸素含有量と酸化物系介在物の平均ＣａＯ／ＭｎＯ質量比の関係を示したグラフ。The graph which showed the relationship between the total oxygen content in steel materials, and the average CaO / MnO mass ratio of oxide type inclusions. 図６の平均ＣａＯ／ＭｎＯ質量比が低い領域を拡大表示したグラフ。The graph which expanded and displayed the area | region where average CaO / MnO mass ratio is low of FIG. 鋼材中のトータル酸素含有量とスラグスポット発生率の関係を示したグラフ。The graph which showed the relationship between the total oxygen content in steel materials, and the slag spot generation rate. 精錬時のスラグ塩基度とスラグスポット発生率の関係を示したグラフ。The graph which showed the relationship between the slag basic degree at the time of refinement, and the slag spot generation rate.
〔鋼の成分組成〕
　本発明では、オーステナイト系やフェライト系を問わず、種々の鋼種が適用対象となる。発明者らの検討によれば、以下の組成範囲において後述の介在物組成制御によるスラグスポットの抑止効果が得られる。
　質量％で、Ｃ：０.００５～０.１００％、Ｓｉ：０.１０～３.００％、Ｍｎ：０.１０～６.５０％、Ｐ：０.００１～０.０５０％、Ｓ：０.０００１～０.０２００％、Ｎｉ：０～２０.００％、Ｃｒ：１０.５０～２６.００、Ｍｏ：０～２.５０％、Ｃｕ：０～３.５０％、Ｎｂ：０～０.５００％、Ｖ：０～０.５００％、Ｚｒ：０～０.５００％、Ｗ：０～０.５００％、Ｃｏ：０～０.５００、Ｂ：０～０.０２０、Ｎ：０.００５～０.２００％、Ｔｉ：０～０.０５０％、Ａｌ：０～０.１００％、Ｃａ：０～０.００１０％、Ｍｇ：０～０.００１０％、ＲＥＭ（Ｙを除く希土類元素）：０～０.０５０％、Ｙ：０～０.０５０％、Ｏ：０.００３０～０.０１５０％、残部Ｆｅおよび不可避的不純物。 [Component composition of steel]
In the present invention, various steel types are applicable regardless of austenite type or ferrite type. According to the inventors' investigation, the suppression effect of the slag spot by the below-mentioned inclusion composition control is acquired in the following composition ranges.
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: in mass% 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 (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.
　鋼材中のＰ、Ｓの含有量は一般に低い方が好ましいが、過剰な脱燐、脱硫は製鋼の負荷を高め不経済となるので、ここではＰ、Ｓ含有量が上記範囲の鋼を対象とする。Ｎｉ、Ｍｏ、Ｃｕ、Ｎｂ、Ｖ、Ｚｒ、Ｗ、Ｃｏ、Ｂ、Ｔｉ、Ａｌ、Ｃａ、Ｍｇ、ＲＥＭ（Ｙを除く希土類元素）、Ｙは任意含有元素である。これらは、鋼材の熱間加工性や各種特性を改善するためにステンレス鋼に適宜添加される一般的な元素であり、上記範囲内の含有量であれば、酸化物系介在物の平均ＣａＯ／ＭｎＯ質量比が後述の所定範囲に制御されている限り、アーク溶接ビードのスラグスポット抑止効果を阻害するものではない。Ｔｉ、Ａｌ、については、含有量が過剰であると介在物組成に悪影響を及ぼすことがあり、スラグスポットの発生原因となり得るので、Ｔｉは０.０５０％以下、Ａｌは０.１００％以下にそれぞれ制限される。Ｔｉは０.０１０％未満、Ａｌは０.００７％以下の含有量範囲となるように成分調整することがより好ましい。Ａｌ含有量を十分に低減するには、精錬においてＳｉ脱酸を行うことが望ましい。 Generally, lower contents of P and S in steel materials are preferable, but excessive dephosphorization and desulfurization increase the load of steel making and become uneconomical, so here, for steels with P and S contents in the above range Do. Ni, Mo, Cu, Nb, V, Zr, W, Co, B, Ti, Al, Ca, Mg, REM (a rare earth element other than Y), and Y are arbitrarily contained elements. These are general elements suitably 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 inclusions As long as the MnO mass ratio is controlled within a predetermined range described later, the slag spot suppressing effect of the arc weld bead is not inhibited. With regard to Ti and Al, excessive content may adversely affect inclusion composition, which may cause the generation of slag spots, so Ti is less than 0.050% and Al is less than 0.100%. Each is restricted. It is more preferable to adjust the component so that the content range of Ti is less than 0.010% and Al is 0.007% or less. In order to sufficiently reduce the Al content, it is desirable to carry out Si deoxidation in the refining.
〔酸化物系介在物の組成〕
　ステンレス鋼材を母材に用いたアーク溶接ビードに生じるスラグスポットの発生要因としては、以下のパターンが考えられる。
　（パターン１）母材中の易酸化性元素（Ａｌ、Ｃａ、Ｔｉ等）がガスシールドの不十分であった箇所で酸化物を形成してビード上に残留する。
　（パターン２）母材中に存在する解離温度の高い非金属介在物がアークの掃引に随伴して凝集浮上し、ある程度凝集粒子が大きくなるとアークの掃引から取り残されてビード上に残留する。
　発明者らの検討によると、ガスシールドを十分に行った場合であってもスラグスポットは発生することから、スラグスポットの発生を安定して顕著に抑制するためには上記パターン２の発生要因を克服することが必要である。上記パターン１の発生要因については母材の鋼組成において易酸化性元素等の含有量を上述の範囲に制限することによって解消できる。 [Composition of oxide inclusions]
The following pattern can be considered as a generation factor of the slag spot which arises in the arc welding bead which used stainless steel materials as a base material.
(Pattern 1) The oxidizable element (Al, Ca, Ti, etc.) in the base material forms an oxide at a portion where the gas shield is insufficient and remains on the bead.
(Pattern 2) Non-metallic inclusions with high dissociation temperature present in the base material agglomerate and float along with the sweep of the arc, and when the agglomerated particles become large to some extent, they are left from the sweep of the arc and remain on the bead.
According to the inventors' investigations, slag spots are generated even when the gas shielding is sufficiently performed. Therefore, in order to stably and remarkably suppress the generation of the slag spots, the generation factor of the pattern 2 is used. It is necessary to overcome. The generation factor of the pattern 1 can be eliminated by limiting the content of the oxidizable element and the like in the steel composition of the base material to the above-mentioned range.
　上記パターン２の発生要因対策としては母材中の介在物制御が重要となる。非金属介在物のうち、スラグスポットの原因となるのは解離温度が高い酸化物系介在物である。上述の鋼組成を有するステンレス鋼の場合、鋼材中に存在する酸化物系介在物の代表的な構成成分としてＳｉＯ２、ＭｎＯ、ＣａＯ、Ａｌ２Ｏ３、ＭｇＯなどが挙げられる。これらのうち、ＣａＯは解離温度が高いため溶接時にも還元されず酸化物のまま存在する。これがアークの熱で溶融した金属の中で凝集合体すると、冷却後にスラグスポットとして現れる。一方、ＭｎＯやＳｉＯ２は解離温度が比較的低いため、酸化物を構成するＭｎやＳｉは溶接時に還元されてメタルとなり、溶融金属中に溶解しやすい。そのためＭｎＯやＳｉＯ２はスラグスポットの発生要因にはなりにくい。 As measures against the causes of the occurrence of the pattern 2, the inclusion control in the base material is important. Among nonmetallic inclusions, the cause of slag spots is oxide inclusions having a high dissociation temperature. In the case of the stainless steel having the above-described steel composition, SiO 2 , MnO, CaO, Al 2 O 3 , MgO and the like can be mentioned as typical components of the oxide inclusions present in the steel material. Among these, CaO is not reduced even at the time of welding because it has a high dissociation temperature and remains as an oxide. As it agglomerates in the molten metal due to 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 at the time of welding to form a metal and easily dissolve in the molten metal. Therefore, MnO and SiO 2 are less likely to be a cause of generation of slag spots.
　発明者らは上述の鋼組成範囲にある種々のステンレス鋼種について、鋼材中に含まれている酸化物系介在物の組成を詳細に調べた。その結果、一般的なステンレス鋼材中に存在する酸化物系介在物の多くは、ＳｉＯ２およびＣａＯの含有量が多いタイプのものであることがわかった。また、精錬条件を変えることによって、介在物のＣａＯ含有量を減少させ、代わりにＭｎＯ含有量を増加させるという介在物の組成制御が可能であることも確かめられた。さらに、介在物組成においてＳｉＯ２、ＣａＯと共存するＭｎＯの含有量を増加させていくと、ＣａＯが存在しているにもかかわらず、スラグスポットの発生が顕著に抑制されることが明らかとなった。以下において、ＳｉＯ２およびＣａＯの含有量が多い一般的なタイプの酸化物系介在物を便宜上「ＳｉＯ２－ＣａＯタイプ」と呼び、介在物の組成制御によりＣａ濃度の減少およびＭｎ濃度の増加を図ったタイプの酸化物系介在物を便宜上「ＳｉＯ２－ＭｎＯ－ＣａＯタイプ」と呼ぶ。 The inventors investigated in detail the composition of oxide inclusions contained in the steel for various stainless steel types in the above-described steel composition range. As a result, it was found that most of the oxide inclusions present in general stainless steel materials are of the type having a high content of SiO 2 and CaO. In addition, it was also confirmed that the composition control of inclusions is possible by reducing the CaO content of inclusions and instead increasing the MnO content by changing the refining conditions. Furthermore, it has become clear that, if the content of MnO coexisting with SiO 2 and CaO in the inclusion composition is increased, the generation of slag spots is remarkably suppressed despite the presence of CaO. The In the following, for the sake of convenience, a general type oxide inclusion having a high content of SiO 2 and CaO is referred to as “SiO 2 -CaO type”, and the composition control of the inclusion decreases the Ca concentration and increases the Mn concentration. The oxide inclusions of the illustrated type are referred to as "SiO 2 -MnO-CaO type" for convenience.
　金属酸化物は温度が上昇すると一般に金属と酸素に解離する。例えばエリンガムダイヤグラムにおいて酸素分圧を１０－１２ａｔｍと仮定した場合の解離温度を見積もると、ＳｉＯ２：約１５３０℃、ＭｎＯ：約１３８０℃、ＣａＯ：約２１００℃、Ａｌ２Ｏ３：約２０２０℃となる。ＳｉＯ２－ＣａＯタイプの介在物を、できるだけＳｉＯ２－ＭｎＯ－ＣａＯタイプに変えること、すなわち介在物の組成を相対的にＳｉＯ２－ＭｎＯ－ＣａＯタイプ優位とすることが、スラグスポットの抑制に有利となる。なお、Ａｌ２Ｏ３は解離温度が高いが、上述の鋼組成に調整されている鋼材ではＡｌ２Ｏ３の存在量が少ないため、スラグスポットの発生要因にはなりにくい。 Metal oxides generally dissociate into metal and oxygen as the temperature increases. For example, when assuming the partial pressure of oxygen at 10 −12 atm in Elingham diagram, the dissociation temperature is estimated: SiO 2 : about 1530 ° C., MnO: about 1380 ° C., CaO: about 2100 ° C., Al 2 O 3 : about 2020 It will be ° C. The inclusion of SiO 2 -CaO type, advantageously as possible by changing the SiO 2 -MnO-CaO type, i.e. be a composition of inclusions relatively SiO 2 -MnO-CaO type dominance, suppression of slag spot It becomes. Although Al 2 O 3 has a high dissociation temperature, steel materials adjusted to the above-described steel composition are less likely to cause slag spots because the amount of Al 2 O 3 is small.
　介在物組成におけるＳｉＯ２－ＣａＯタイプとＳｉＯ２－ＭｎＯ－ＣａＯタイプの相対的な優位性を定量的に表す指標として、本発明では「平均ＣａＯ／ＭｎＯ質量比」を採用する。この値が小さいほど、相対的にＳｉＯ２－ＭｎＯ－ＣａＯタイプ優位の介在物組成であると評価でき、スラグスポットの発生抑制に有利となる。平均ＣａＯ／ＭｎＯ質量比は上述した方法で求めることができる。詳細な検討の結果、鋼組成が上述の範囲に調整されているステンレス鋼において、平均ＣａＯ／ＭｎＯ質量比が１５.０以下であるとき、従来のステンレス鋼材と比べスラグスポットの顕著な低減効果が認められる。平均ＣａＯ／ＭｎＯ質量比が１０.０以下であることがより好ましく、６.０以下に管理してもよい。 As an index quantitatively indicating the relative superiority of SiO 2 -CaO type and SiO 2 -MnO-CaO type of composition of inclusions, the present invention employs an "average CaO / MnO mass ratio". As this value is smaller, it can be evaluated that the inclusion composition is relatively dominated by the SiO 2 -MnO-CaO type, which is advantageous to suppression of the occurrence of the slag spot. 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-mentioned range, when the average CaO / MnO mass ratio is 15.0 or less, the remarkable reduction effect of the slag spot compared with the conventional stainless steel is Is recognized. The average CaO / MnO mass ratio is more preferably 10.0 or less, and may be controlled to 6.0 or less.
　一方、酸化物系介在物中のＭｎＯ含有量が高い場合でも、ＣａＯ含有量が過度に高いと、スラグスポットの発生抑制効果が十分に得られない。検討の結果、平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比が０.４０以下である介在物組成とすることが望ましい。平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比は上述した方法で求めることができる。 On the other hand, even when the content of MnO in the oxide inclusions is high, if the content of CaO is excessively high, the effect of suppressing the generation of slag spots can not be sufficiently obtained. As a result of examination, it is desirable to set an inclusion composition having 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.
〔介在物の組成制御〕
　酸化物系介在物の平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比、および平均ＣａＯ／ＭｎＯ質量比が適正化された上述のステンレス鋼材は、一般的なステンレス鋼の溶製設備を利用して製造することができる。代表的にはＶＯＤプロセスおよびＡＯＤプロセスが挙げられる。いずれにおいても、まず、含Ｃｒ溶鉄に酸素を吹き込む脱炭を施し、Ｃｒ酸化物含有スラグを湯面上に有する溶鋼（Ｃ含有量は例えば０.２０％以下）を常法にて製造する。この段階の溶鋼は酸素を吹き込む脱炭を終えた溶鋼であるから、易酸化性元素Ｓｉ、Ｔｉ、Ａｌ、Ｃａ、Ｍｇなどは、溶鋼中から酸化除去されている。すなわち、溶鋼中にはＳｉ、Ｔｉ、Ａｌ、Ｃａ、Ｍｇはほとんど存在していない。また、溶鋼中に多量に含まれるＣｒもその一部が酸化され、Ｃｒ酸化物として溶鋼の湯面上にスラグを形成している。一方、溶鋼中には脱炭のために吹き込んだ酸素が多量に溶存している。そのため、鋳造前には脱酸を行う必要がある。脱酸剤としてＡｌではなくＦｅＳｉ合金を使用して、最終的な成分調整を行う。 [Composition control of inclusions]
The above-mentioned stainless steel material, in which the average CaO / (SiO 2 + MnO + CaO) mass ratio of oxide inclusions and the average CaO / MnO mass ratio are optimized, is manufactured using a general stainless steel melting facility be able to. Typically, VOD process and AOD process can be mentioned. In any case, first, decarburization in which oxygen is blown into the Cr-containing molten iron is applied, and a molten steel having a Cr oxide-containing slag on the hot water surface (C content is, for example, 0.20% or less) is manufactured by a conventional method. Since the molten steel at this stage is a de-carburized steel into which oxygen is blown, the 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. In addition, a part of Cr contained in a large amount in the molten steel is also oxidized to form a slag on the surface of the molten steel as Cr oxide. On the other hand, the molten steel contains a large amount of dissolved oxygen blown for decarburization. Therefore, it is necessary to deoxidize before casting. Final composition adjustments are made using FeSi alloys rather than Al as the deoxidizer.
　酸化物系介在物の平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比を０.４０以下に維持しながら平均ＣａＯ／ＭｎＯ質量比を十分に低減するためには、脱酸および最終的な成分調整を行う際に、例えば以下の３点を満たすように精錬を行うことが極めて有効であることがわかった。 In order to sufficiently reduce the average CaO / MnO mass ratio while maintaining the average CaO / (SiO 2 + MnO + CaO) mass ratio of oxide inclusions to 0.40 or less, deacidification and final component adjustment are performed. At that time, for example, it was found that it is extremely effective to carry out refining so as to satisfy the following three points.
　（１）鋼中の酸素含有量（酸化物として存在する酸素も含めたトータル酸素含有量）が０.００３０％（３０ｐｐｍ）以上となるように精錬を行う。酸素含有量が０.００３０％を下回ると平均ＣａＯ／ＭｎＯ質量比を安定して１５.０以下とするような精錬が難しくなる。平均ＣａＯ／ＭｎＯ質量比を１０.０以下、あるいは６.０以下にまで大きく低減させたい場合には酸素含有量を０.００４０％（４０ｐｐｍ）以上となるように調整することがより好ましい。ただし、酸素含有量が多くなりすぎるとＣｒ酸化物含有量の多い介在物が多量に生成し、製品品質の低下を招く要因となる。酸素含有量は０.０１５０％（１５０ｐｐｍ）以下に制限され、０.０１００％（１００ｐｐｍ）以下とすることがより好ましい。０.００６０％（６０ｐｐｍ）以下に管理してもよい
　（２）Ｃａ含有量が例えば０.２０％以下の高純度ＦｅＳｉ合金を用いてＳｉ脱酸を行う。
　（３）スラグ塩基度ＣａＯ／ＳｉＯ２を１.２０～１.６０の範囲に調整する。 (1) Refinement is performed so that the oxygen content in the steel (total oxygen content including oxygen present 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 stably to 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 be 0.0040% (40 ppm) or more. However, when the oxygen content is too high, a large amount of inclusions having a high Cr oxide content is generated, which is a factor causing deterioration of the product quality. The oxygen content is limited to 0.0150% (150 ppm) or less, and more preferably 0.0100% (100 ppm) or less. It may be controlled to 0.0060% (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) Slag basicity CaO / SiO 2 is adjusted to a range of 1.20 to 1.60.
　ＶＯＤプロセスを利用して、表１に示すステンレス鋼を溶製し、連続鋳造スラブを得た。最終的な精錬過程で、鋼中のトータル酸素含有量、脱酸剤のＦｅＳｉ合金の種類、およびスラグ塩基度（ＣａＯ／ＳｉＯ２）の条件を変えて、介在物制御を試みた。表２中にそれぞれの条件を示してある。表２中の酸素含有量は、表１の値を再掲したものである。脱酸剤であるＦｅＳｉ合金としては、不純物量が少ない高純度品と、通常品を使用した。高純度品はＣａ含有量が０.２０質量％以下に低減されたものである。通常品のＣａ含有量は約０.５～１.５質量％である。スラグ塩基度は、スラグから採取したサンプルを分析して求めた。 The stainless steel shown in Table 1 was melted using a VOD process to obtain a continuously cast slab. In the final refining process, inclusion control was attempted by changing the total oxygen content in the steel, the type of FeSi alloy as a deoxidizer, and the condition of slag basicity (CaO / SiO 2 ). Table 2 shows each condition. The oxygen content in Table 2 is the value shown in Table 1 again. As the FeSi alloy which is a deoxidizer, high-purity products having a small amount of impurities and normal products were used. The high purity product is one in which the Ca content is reduced to 0.20 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 collected from the slag.
　得られた連続鋳造スラブを用いて、熱間圧延、冷間圧延を含む工程で板厚０.５～１.５ｍｍの冷延焼鈍鋼板を得た。この冷延焼鈍鋼板の圧延方向および板厚方向に平行な断面（Ｌ断面）についてＳＥＭ（走査型電子顕微鏡）観察を行い、ＳＥＭに付属のＥＤＸ（エネルギー分散型Ｘ線分析）にて酸化物系介在物の組成分析を行った。無作為に選択した３０個の酸化物系介在物の測定値に基づいて、前掲の「平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比、平均ＣａＯ／ＭｎＯ質量比の求め方」に従い、平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比および平均ＣａＯ／ＭｎＯ質量比を求めた。結果を表２中に示してある。 Using the obtained continuous cast slab, a cold-rolled and annealed steel sheet with a thickness of 0.5 to 1.5 mm was obtained in a process including hot rolling and cold rolling. SEM (scanning electron microscope) observation is performed on a cross section (L cross section) parallel to the rolling direction and thickness direction of this cold rolled annealed steel sheet, and an oxide system is obtained by EDX (energy dispersive X-ray analysis) attached to the SEM Composition analysis of inclusions was performed. Based on the measurement values of the 30 randomly selected inclusions based on the oxides, the average CaO / (average of CaO / (SiO 2 + MnO + CaO) mass ratio, average CaO / MnO mass ratio) described above, average CaO / ( The SiO 2 + MnO + CaO) mass ratio and the average CaO / MnO mass ratio were determined. The results are shown in Table 2.
　各冷延焼鈍鋼板を素材に用いて、ＴＩＧ溶接にて通常の条件で溶接鋼管を製造した。管の外径は２５～５１ｍｍの範囲にある。溶接に際し溶加材は添加していない。得られた鋼管製品から無作為にサンプルを抜き出し、連続する長さ５０ｍ以上の溶接ビードについてスラグスポットの発生を調査した。長径（粒子の最も長い部分の直径）が１.０ｍｍ以上であるスラグスポットの数をカウントし、１ｍあたりの上記スラグスポットの発生個数をスラグスポット発生率（個／ｍ）とした。上記サイズのスラグスポット発生率が０.３０個／ｍ以下であれば、従来より大幅にスラグスポットの発生が抑制されていると評価することができる。したがって、スラグスポット発生率が０.３０個／ｍ以下のものを合格と判定した。
　これらの結果を表２に示す。 Welded steel pipes were manufactured under normal conditions by TIG welding using each cold rolled annealed steel sheet as a raw material. The outer diameter of the tube is in the range 25-51 mm. No filler metal was added during welding. Samples were randomly drawn from the obtained steel pipe products, and the occurrence of slag spots was investigated for continuous weld beads of 50 m or more in length. The number of slag spots having a major axis (diameter of the longest portion of the particles) of 1.0 mm or more was counted, and the number of generated slag spots per 1 m was regarded as the slag spot generation rate (piece / m). If the slag spot generation rate of the said size is 0.30 piece / m or less, it can be evaluated that generation | occurrence | production of a slag spot is suppressed significantly rather than before. Therefore, the thing of 0.30 piece / m or less of slag spot generation rates was determined to be pass.
The results are shown in Table 2.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　鋼組成が本発明規定範囲を満たし、かつ酸化物系介在物の平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比および平均ＣａＯ／ＭｎＯ質量比が本発明規定範囲に制御された本発明例のものは、スラグスポットの発生が非常に少ない。 The steel composition of the present invention example in which the steel composition satisfies the specified range of the present invention and the average CaO / (SiO 2 + MnO + CaO) mass ratio of the oxide inclusions and the average CaO / MnO mass ratio is controlled within the specified range of the present invention is There is very little occurrence of slag spots.
　これに対し、比較例であるＮｏ.２１～２３は精錬時のスラグ塩基度が高かったので酸化物系介在物の平均ＣａＯ／ＭｎＯ質量比が高くなり、スラグスポットの発生が多かった。Ｎｏ.２４～２６は鋼中のトータル酸素含有量が低すぎ、かつ精錬時のスラグ塩基度が高かったので酸化物系介在物の平均ＣａＯ／ＭｎＯ質量比が他の例より著しく高くなり、スラグスポットの抑制効果は得られなかった。Ｎｏ.２７～３０は脱酸剤であるＦｅＳｉ合金に「通常品」を使用したので所望の介在物制御ができず、酸化物系介在物の平均ＣａＯ／ＭｎＯ質量比が高くなってスラグスポットの発生が多かった。 On the other hand, in the comparative examples No. 21 to 23, since the slag basicity at the time of refining was high, the average CaO / MnO mass ratio of oxide inclusions became high, and the occurrence of slag spots was large. Nos. 24 to 26 had too low total oxygen content in the steel and high slag basicity at the time of refining, so the average CaO / MnO mass ratio of oxide inclusions becomes significantly higher than other examples, and slag The spot suppression effect was not obtained. Since No. 27 to 30 used the “normal product” for the FeSi alloy which is a deoxidizer, desired inclusion control can not be performed, and the average CaO / MnO mass ratio of oxide inclusions becomes high, and the slag spots There were many outbreaks.
　図３に、各例について酸化物系介在物の平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比とスラグスポット発生率の関係を示す。黒丸プロットは脱酸剤のＦｅＳｉ合金として「高純度品」を使用した例、白丸プロットは「通常品」を使用した例である（以下の図４～図９において同様）。また、図４、図５に、各例について酸化物系介在物の平均ＣａＯ／ＭｎＯ質量比とスラグスポット発生率の関係を示す。図５は、図４の平均ＣａＯ／ＭｎＯ質量比が低い領域を拡大表示したものである。酸化物系介在物の平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比を０.４０以下、かつ平均ＣａＯ／ＭｎＯ質量比を１５.０以下に制御することにより、スラグスポット発生抑制効果が顕著に向上することがわかる。 FIG. 3 shows the relationship between the average CaO / (SiO 2 + MnO + CaO) mass ratio of the oxide inclusions and the slag spot generation rate for each example. The black circle plot is an example using “high purity product” as the deoxidizer FeSi alloy, and the white circle plot is an example using “normal product” (same in FIGS. 4 to 9 below). Moreover, the relationship of the average CaO / MnO mass ratio of an oxide type interference | inclusion and a slag spot generation rate is shown in FIG. 4, FIG. 5 about each case. FIG. 5 is an enlarged view of the region where the average CaO / MnO mass ratio in FIG. 4 is low. By controlling the average CaO / (SiO 2 + MnO + CaO) mass ratio of oxide inclusions to 0.40 or less and the average CaO / MnO mass ratio to 15.0 or less, the slag spot generation suppressing effect is remarkably improved. I understand that.
　図６、図７に、各例について鋼材中のトータル酸素含有量と酸化物系介在物の平均ＣａＯ／ＭｎＯ質量比の関係を示す。図７は、図６の平均ＣａＯ／ＭｎＯ質量比が低い領域を拡大表示したものである。酸素含有量を０.００３０％以上にすることが酸化物系介在物の平均ＣａＯ／ＭｎＯ質量比を低く制御する上で極めて有効であることがわかる。 The relationship between the total oxygen content in steel materials and the average CaO / MnO mass ratio of oxide inclusions is shown in FIG. 6 and FIG. 7 for each example. FIG. 7 is an enlarged view of the region 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 inclusions to a low level.
　図８に、各例について鋼材中のトータル酸素含有量とスラグスポット発生率の関係を示す。脱酸剤のＦｅＳｉ合金に「高純度品」を使用し、酸素含有量を０.００３０％以上にすることが、スラグスポットの発生抑制に効果的であることがわかる。 FIG. 8 shows the relationship between the total oxygen content in the steel material and the slag spot generation rate for each example. It turns out that it is effective in generation | occurrence | production suppression of a slag spot that it is effective to use "high-purity goods" for the FeSi alloy of a deoxidizer, and to make oxygen content 0.0030% or more.
　図９に、精錬時のスラグ塩基度とスラグスポット発生率の関係を示す。脱酸剤のＦｅＳｉ合金に「高純度品」を使用し、スラグ塩基度を１.２０～１.６０の範囲に調整することが、スラグスポットの発生抑制に効果的であることがわかる。 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” as the deoxidizer FeSi alloy and adjusting the slag basicity to a range of 1.20 to 1.60 is effective in suppressing the generation of slag spots.

Claims (7)

  1. 　質量％で、Ｃ：０.００５～０.１００％、Ｓｉ：０.１０～３.００％、Ｍｎ：０.１０～６.５０％、Ｐ：０.００１～０.０５０％、Ｓ：０.０００１～０.０２００％、Ｎｉ：０～２０.００％、Ｃｒ：１０.５０～２６.００、Ｍｏ：０～２.５０％、Ｃｕ：０～３.５０％、Ｎｂ：０～０.５００％、Ｖ：０～０.５００％、Ｚｒ：０～０.５００％、Ｗ：０～０.５００％、Ｃｏ：０～０.５００、Ｂ：０～０.０２０、Ｎ：０.００５～０.２００％、Ｔｉ：０～０.０５０％、Ａｌ：０～０.１００％、Ｃａ：０～０.００１０％、Ｍｇ：０～０.００１０％、ＲＥＭ（Ｙを除く希土類元素）：０～０.０５０％、Ｙ：０～０.０５０％、Ｏ：０.００３０～０.０１５０％、残部Ｆｅおよび不可避的不純物からなる化学組成を有し、Ｍｎを含有する酸化物系介在物が存在し、酸化物系介在物中のＳｉ、ＭｎおよびＣａの含有量をそれぞれＳｉＯ２、ＭｎＯおよびＣａＯの質量割合に換算した場合の介在物組成において、金属組織中に観察される酸化物系介在物の平均ＣａＯ／（ＳｉＯ２＋ＭｎＯ＋ＣａＯ）質量比が０.４０以下、平均ＣａＯ／ＭｎＯ質量比が１５.０以下であるステンレス鋼材。 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: in mass% 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 (excluding Y Rare earth elements): 0 to 0.050%, Y: 0 to 0.050%, O: 0.0030 to 0.0150%, the balance containing Fe and incidental impurities, oxidation containing Mn Object inclusions In the inclusion composition when the contents of Si, Mn and Ca in the oxide inclusions are converted to the mass proportions of SiO 2 , MnO and CaO respectively, the oxide inclusions observed in the metal structure Stainless steel having an average CaO / (SiO 2 + MnO + CaO) mass ratio of at most 0.40 and an average CaO / MnO mass ratio of at most 15.0.
  2. 　請求項１に記載のステンレス鋼材からなるアーク溶接用母材。 An arc welding base material comprising the stainless steel material according to claim 1.
  3. 　請求項１に記載のステンレス鋼材からなるアーク溶接造管用鋼板母材。 A steel plate base material for arc welded tube-making, which comprises the stainless steel material according to claim 1.
  4. 　請求項１に記載の鋼材を母材に用いたアーク溶接構造部材。 An arc welded structural member using the steel material according to claim 1 as a base material.
  5. 　請求項１に記載の鋼材を母材に用いたアーク溶接鋼管。 An arc welded steel pipe using the steel material according to claim 1 as a base material.
  6. 　請求項１に記載のステンレス鋼材を母材に用いて、溶加材を添加せずに非溶極式のアーク溶接を行う溶接構造部材の製造法。 A method of manufacturing a welded structural member, using the stainless steel material according to claim 1 as a base material, and performing non-electrode-type arc welding without adding a filler metal.
  7. 　請求項１に記載のステンレス鋼材である鋼板を母材に用いて、溶加材を添加せずに非溶極式のアーク溶接にて溶接鋼管とする、溶接鋼管の製造法。 A method for producing a welded steel pipe, wherein a steel plate which is the stainless steel material according to claim 1 is used as a base material, and a welding steel pipe is formed by non-smelting electrode arc welding without adding a filler metal.
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