JP6146908B2 - Stainless steel with excellent surface properties and its manufacturing method - Google Patents

Stainless steel with excellent surface properties and its manufacturing method Download PDF

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JP6146908B2
JP6146908B2 JP2013211957A JP2013211957A JP6146908B2 JP 6146908 B2 JP6146908 B2 JP 6146908B2 JP 2013211957 A JP2013211957 A JP 2013211957A JP 2013211957 A JP2013211957 A JP 2013211957A JP 6146908 B2 JP6146908 B2 JP 6146908B2
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史明 桐原
史明 桐原
轟 秀和
秀和 轟
佳孝 山下
佳孝 山下
和貴 西嶋
和貴 西嶋
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Nippon Yakin Kogyo Co Ltd
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Description

本発明は、表面品質に優れたステンレス鋼に関するものである。さらに、ステンレス鋼の精錬方法に関し、スラグ塩基度および溶鋼中のMg、Al、Caといった微量成分を制御することにより、溶鋼中の有害な非金属介在物であるMgO・Alの生成を抑制して、ノズル内付着を防止しつつ、表面品質に優れたステンレス鋼を製造するものである。 The present invention relates to stainless steel having excellent surface quality. Furthermore, regarding the refining method of stainless steel, by controlling the slag basicity and trace components such as Mg, Al, Ca in molten steel, it is possible to generate MgO · Al 2 O 3 which is a harmful non-metallic inclusion in molten steel. It suppresses and produces stainless steel excellent in surface quality while preventing adhesion in the nozzle.

ステンレス鋼は、その優れた耐食性から表面に塗装やコーティングなどの処理をせず、使用される場合が多い。しかしながら、非金属介在物の形態によっては表面欠陥が発生するなどの問題がある。   Stainless steel is often used without its coating or coating treatment on the surface due to its excellent corrosion resistance. However, there is a problem that surface defects occur depending on the form of non-metallic inclusions.

ステンレス鋼の介在物の無害化を図る技術は幾つかの開示がある。例えば、特許文献1では、ステンレス鋼の精錬の際に、Al、CaおよびMg濃度の低いフェロシリコンを使用することにより、有害な非金属介在物であるMgO・Alを抑制している。この技術は、介在物形態をCaO−SiO−MgO−Al系に制御するためにスラグ塩基度を1.3〜2.7と比較的低めに制御する必要がある。そのため、場合によっては、十分な脱硫能が得られないことがあり、熱間加工性を低下させることがあった。 There are several disclosures of techniques for detoxifying stainless steel inclusions. For example, in Patent Document 1, MgO · Al 2 O 3 that is a harmful non-metallic inclusion is suppressed by using ferrosilicon having a low concentration of Al, Ca, and Mg when refining stainless steel. . In this technique, it is necessary to control the slag basicity to a relatively low value of 1.3 to 2.7 in order to control the inclusion form to the CaO—SiO 2 —MgO—Al 2 O 3 system. Therefore, in some cases, sufficient desulfurization ability may not be obtained, and hot workability may be reduced.

また、特許文献2では、溶鋼中Al濃度およびスラグ組成を制御することにより、溶鋼中非金属介在物をMgO系介在物に制御している。さらに、特許文献3では、溶鋼中Al濃度およびスラグ組成を制御することにより、溶鋼中非金属介在物をMgO系介在物あるいはCaO−Al系介在物に制御している。 Moreover, in patent document 2, the nonmetallic inclusion in molten steel is controlled by the MgO type inclusion by controlling Al concentration and slag composition in molten steel. Furthermore, in Patent Document 3, nonmetallic inclusions in molten steel are controlled to be MgO inclusions or CaO—Al 2 O 3 inclusions by controlling the Al concentration and slag composition in the molten steel.

上記2つの技術は、いずれもAl濃度を0.005%以上に調整する必要がある。Alは歩留まりが安定しないこともあり、本技術が完全に実施できるとは言い難かった。また、Alを積極的に添加するために、溶接を施す必要がある用途には、溶接後のビード部の品質に懸念があった。   Both of the above two techniques require the Al concentration to be adjusted to 0.005% or more. Since the yield of Al is not stable, it is difficult to say that the present technology can be completely implemented. In addition, there is a concern about the quality of the bead part after welding in applications that require welding in order to positively add Al.

特許文献4では、スラグ組成を制御して、非金属介在物組成をMgO・Al、CaO−Al系、MgO、CaO−SiO−MgO−Al−MnO系酸化物に制御する技術が開示されている。これによれば、耐食性、溶接性および表面性状に優れたステンレス鋼が得られると示されている。特許文献5では、非金属介在物組成をCaO−SiO−MgO−Al−MnO−Cr−FeO系酸化物に制御する技術が開示されている。これによれば、耐食性、溶接性および表面性状に優れたステンレス鋼が得られると示されている。 In Patent Document 4, the slag composition is controlled, and the non-metallic inclusion composition is changed to MgO · Al 2 O 3 , CaO—Al 2 O 3 system, MgO, CaO—SiO 2 —MgO—Al 2 O 3 —MnO system oxidation. Techniques for controlling objects are disclosed. According to this, it is shown that stainless steel excellent in corrosion resistance, weldability and surface properties can be obtained. Patent Document 5 discloses a technique for controlling a non-metallic inclusion composition to a CaO—SiO 2 —MgO—Al 2 O 3 —MnO—Cr 2 O 3 —FeO-based oxide. According to this, it is shown that stainless steel excellent in corrosion resistance, weldability and surface properties can be obtained.

上記2つの技術は、いずれも精錬方法が明確に示されていないために、制御が不安定である問題があった。   The above two techniques have a problem that the control is unstable because the refining method is not clearly shown.

また、特許文献6では、耐衝撃性および表面性状に優れたFe−Ni−Cr−Mo合金が示されている。本技術はFe基であり、Ni:30〜32%、Cr:26超〜28%、Mo:6〜7%を含有する合金に適用可能な技術であり、スラグの塩基度C/Sを5〜20と高く制御している。   Patent Document 6 discloses an Fe—Ni—Cr—Mo alloy excellent in impact resistance and surface properties. This technology is Fe-based, and is applicable to alloys containing Ni: 30 to 32%, Cr: more than 26 to 28%, Mo: 6 to 7%, and the basicity C / S of slag is 5 Control is as high as ~ 20.

特開2001−26811号公報JP 2001-26811 A 特開平9−256028号公報Japanese Patent Laid-Open No. 9-256028 特開2001−220619号公報Japanese Patent Laid-Open No. 2001-220619 特開2004−149833号公報JP 2004-149833 A 特開2007−277727号公報JP 2007-277727 A 特開2011−97224号公報JP 2011-97224 A

上記のように、従来の方法では、有害な介在物であるMgO・Al、AlあるいはCaOの生成を抑制しつつ、さらには熱間加工性も健全な状態にて、表面品質を確保することは困難であった。本発明の目的は表面性状に優れたステンレス鋼を提供するとともに、該ステンレス鋼を汎用の設備を用いて安価に製造する方法を提案することにある。 As described above, in the conventional method, while suppressing the generation of harmful inclusions MgO.Al 2 O 3 , Al 2 O 3 or CaO, the hot workability is also healthy, It was difficult to ensure quality. An object of the present invention is to provide a stainless steel having excellent surface properties and to propose a method for producing the stainless steel at low cost using general-purpose equipment.

発明者らは、上記課題を解決するために、鋭意研究を重ねた。まず、本発明者らは、実機にて発生した表面欠陥を研究した。すなわち、欠陥をSEM観察し、内部に含まれる異物組成を特定した。その結果、MgO・Al、CaOあるいはAlのいずれかであることが分かった。 Inventors repeated earnest research in order to solve the said subject. First, the present inventors studied surface defects generated in an actual machine. That is, the defect was observed by SEM, and the foreign material composition contained therein was specified. As a result, it was found to be either MgO.Al 2 O 3 , CaO or Al 2 O 3 .

さらに、操業との関連を調査したところ、これらの酸化物は、溶鋼中に含まれる非金属介在物であり、連続鋳造機におけるタンディッシュからモールドに溶鋼を供給するノズルに付着堆積し、その一部が脱落することで、大型の欠陥を引き起こすことが明らかとなった。その防止には、スラグの塩基度を制御すると共に、溶鋼中のAlを極力低減せねばならないということも分かった。したがって、これらの非金属介在物を防止せねばならないという指針が得られた。   Furthermore, when investigating the relationship with the operation, these oxides are non-metallic inclusions contained in the molten steel, and are deposited and deposited on the nozzle that supplies the molten steel from the tundish to the mold in the continuous casting machine. It became clear that a large-scale defect was caused by dropping off the part. In order to prevent this, it was found that the basicity of the slag must be controlled and Al in the molten steel must be reduced as much as possible. Therefore, guidance has been obtained that these non-metallic inclusions must be prevented.

同時に、介在物組成が、MgOまたはCaO−SiO−Al−MgO系であれば、ノズルに付着がなく、表面欠陥も生じないことが分かった。なお、MgO・Alは個数比率にして50%以下であれば、表面欠陥を生じないことも分かった。さらに、化学成分を詳細に調べたところ、微量に含まれるMg、CaおよびOといった微量成分を制御せねばならないということも分かった。 At the same time, it was found that when the inclusion composition was MgO or CaO—SiO 2 —Al 2 O 3 —MgO, there was no adhesion to the nozzle and no surface defects. It was also found that MgO.Al 2 O 3 does not cause surface defects when the number ratio is 50% or less. Furthermore, when the chemical components were examined in detail, it was found that trace components such as Mg, Ca and O contained in trace amounts had to be controlled.

そこで発明者らは、操業条件が微量成分および介在物組成におよぼす影響について、次のように実験室検討を行った。まず、実験室にてマグネシアるつぼを用いて、幾つかの合金成分を縦型抵抗炉で溶解した。合金成分は、Fe−18%Cr−8%Ni合金、Fe−18%Cr−12%Ni−2.5Mo合金、Fe−15%Cr−5%Ni−3%Cu−0.25%Nb合金、Fe−20%Cr−10%Ni−0.7%Nb合金を用いて実験した。この溶鋼中にSi、Mn、Al、Caのうちいずれか1種または2種以上添加して脱酸を行った後、CaO−SiO−Al−MgO−F系スラグを添加した後、所定時間で溶鋼を採取し、試料を得た。この試料の化学成分および試料中の介在物組成を測定し、実験条件による微量成分および介在物組成におよぼす影響について調査した。 Therefore, the inventors conducted a laboratory study on the influence of the operating conditions on the trace components and the inclusion composition as follows. First, some alloy components were melted in a vertical resistance furnace using a magnesia crucible in a laboratory. Alloy components are Fe-18% Cr-8% Ni alloy, Fe-18% Cr-12% Ni-2.5Mo alloy, Fe-15% Cr-5% Ni-3% Cu-0.25% Nb alloy , Fe-20% Cr-10% Ni-0.7% Nb alloy was used for the experiment. Si in molten steel, Mn, Al, after the addition to deoxidation any one or more of Ca, after the addition of CaO-SiO 2 -Al 2 O 3 -MgO-F slag The molten steel was collected at a predetermined time to obtain a sample. The chemical composition of this sample and the inclusion composition in the sample were measured, and the influence of the experimental conditions on the trace component and inclusion composition was investigated.

試料中の化学成分は、化学分析により測定し、試料中の介在物組成は採取した試料をSEM/EDSにて観察し、任意に5μm以上の介在物を20個選んで測定した。その結果、まず、Siにて脱酸を行い、なおかつ、Alを0.005%未満に制御することが肝要でことが分かった。併せて、Si濃度を0.2〜1%に制御しつつ、Mgを0.0001〜0.01%、Caを0.0001〜0.01%、Oを0.0005〜0.01%に調節することで、基本的に介在物組成をMgOまたはCaO−SiO−Al−MgO系に制御することが可能である指針を得た。さらには、MgO・Alは個数比率にして50%以下に抑制できることも明らかとなった。その際のスラグ組成は、スラグ塩基度を2〜5未満に制御することが必要である指針も得られた。 The chemical component in the sample was measured by chemical analysis, and the inclusion composition in the sample was measured by observing the collected sample with SEM / EDS, and arbitrarily selecting 20 inclusions of 5 μm or more. As a result, it was found that it is important to first perform deoxidation with Si and to control Al to less than 0.005%. At the same time, while controlling the Si concentration to 0.2 to 1%, Mg is 0.0001 to 0.01%, Ca is 0.0001 to 0.01%, and O is 0.0005 to 0.01%. By adjusting, a guideline was obtained that can basically control the inclusion composition to MgO or CaO—SiO 2 —Al 2 O 3 —MgO system. Furthermore, it became clear that MgO.Al 2 O 3 can be suppressed to 50% or less in terms of the number ratio. The slag composition in that case also gave a guideline that it was necessary to control the slag basicity to less than 2-5.

本発明は上記知見に基づいて成されたものであり、すなわち、C:0.1%以下、Si:0.2〜1%、Mn:0.2〜2%、S:0.005%以下、Ni:3〜15%、Cr:13〜20%、Al:0.005%未満、Mg:0.0001〜0.01%、Ca:0.0001〜0.01%、O:0.0005〜0.01%、残部がFeおよび不可避的不純物からなるステンレス鋼において該ステンレス鋼中に含まれる非金属介在物が、MgO、MgO・Al、CaO−SiO−MgO−Al系酸化物の1種または2種以上を含み、非金属介在物のうち長さ5μm以上の物が任意の1cmあたり100個以下であり、非金属介在物のうちMgO・Alが個数比率で50%以下であることを特徴とするステンレス鋼である。 The present invention has been made based on the above findings, that is, C: 0.1% or less, Si: 0.2-1%, Mn: 0.2-2%, S: 0.005% or less Ni: 3-15%, Cr: 13-20%, Al: less than 0.005%, Mg: 0.0001-0.01%, Ca: 0.0001-0.01%, O: 0.0005 0.01%, nonmetallic inclusions balance contained in the stainless steel in a stainless steel consisting of Fe and unavoidable impurities, MgO, MgO · Al 2 O 3, CaO-SiO 2 -MgO-Al 2 O comprises one or more 3-based oxides, more than a length 5μm of non-metallic inclusions is not more than 100 per 2 any 1 cm, MgO · Al 2 O 3 among non-metallic inclusions The stainless steel is characterized in that the number ratio is 50% or less. It is steel.

本発明においては、非金属介在物のうちMgO・Alが個数比率で20%以下であることが好ましく、さらに、個数比率で0%であることがさらに好ましい。 In the present invention, among the non-metallic inclusions, MgO.Al 2 O 3 is preferably 20% or less in number ratio, and more preferably 0% in number ratio.

また、上記の非金属介在物は、MgO・AlはMgO:10〜40%、Al:60〜90%であり、CaO−SiO−Al−MgO系酸化物は、CaO:20〜60%、SiO:10〜40%、Al:30%以下、MgO:5〜50%であるとより好ましい。 Also, the non-metallic inclusions, MgO · Al 2 O 3 is MgO: 10~40%, Al 2 O 3: a 60~90%, CaO-SiO 2 -Al 2 O 3 -MgO based oxide it is, CaO: 20~60%, SiO 2 : 10~40%, Al 2 O 3: 30% or less, MgO: more preferably between 5 to 50%.

また、上記の成分に加えて、Mo:5%以下、Cu:1〜5%、Nb:0.05〜1%、N:0.01〜0.05%、B:0.01%以下の1種または2種以上を含んでもよい。   In addition to the above components, Mo: 5% or less, Cu: 1-5%, Nb: 0.05-1%, N: 0.01-0.05%, B: 0.01% or less You may include 1 type, or 2 or more types.

さらに本発明においては、上記ステンレス鋼の製造方法も提供する。すなわち、原料を溶解し、Ni:3〜15%、Cr:13〜20%を含有するステンレス溶鋼を溶製し、次いで、AODおよび/またはVODにおいて脱炭した後に、石灰、蛍石、フェロシリコン合金を投入しCaO/SiO比:2〜5未満、MgO:3〜15%、Al:5%未満からなるCaO−SiO−MgO−Al−F系スラグを用い、C:0.1%以下、Si:0.2〜1%、Mn:0.2〜2%、S:0.005%以下、Ni:3〜15%、Cr:13〜20%、Al:0.005%未満、Mg:0.0001〜0.01%、Ca:0.0001〜0.01%、O:0.0005〜0.01%、残部がFeおよび不可避的不純物からなるステンレス溶鋼に調整することを特徴とするステンレス鋼の製造方法である。 Furthermore, the present invention also provides a method for producing the above stainless steel. That is, after melting the raw material, melting a molten stainless steel containing Ni: 3-15% and Cr: 13-20% and then decarburizing in AOD and / or VOD, lime, fluorite, ferrosilicon alloy was poured CaO / SiO 2 ratio: less than 2~5, MgO: 3~15%, Al 2 O 3: CaO-SiO 2 using -MgO-Al 2 O 3 -F-based slag consisting of less than 5%, C: 0.1% or less, Si: 0.2-1%, Mn: 0.2-2%, S: 0.005% or less, Ni: 3-15%, Cr: 13-20%, Al: Stainless steel molten steel comprising less than 0.005%, Mg: 0.0001 to 0.01%, Ca: 0.0001 to 0.01%, O: 0.0005 to 0.01%, the balance being Fe and inevitable impurities For producing stainless steel, characterized by A.

本発明によれば、合金成分の比率および介在物の絶対数および比率を特定の範囲内に制御することにより、熱間加工性を健全な状態に維持し、さらに、表面性状に優れたステンレス鋼を提供することができる。   According to the present invention, by controlling the ratio of alloy components and the absolute number and ratio of inclusions within a specific range, the hot workability is maintained in a healthy state, and the stainless steel has excellent surface properties. Can be provided.

まず本発明に用いる鋼の化学成分の限定理由について説明する。なお、以下の説明において「%」は「質量%」を意味する。   First, the reasons for limiting the chemical components of the steel used in the present invention will be described. In the following description, “%” means “mass%”.

C:0.1%以下
Cはオーステナイト安定化元素であるが、多量に存在すると、CrおよびMo等と結合して炭化物を形成し、母材に含まれる固溶CrおよびMo量を低下させ、耐食性を劣化させる。そのため、C含有量は0.1%以下とした。なお、好ましくは0.08%以下であり、より好ましくは0.07%である。
C: 0.1% or less C is an austenite stabilizing element, but when present in a large amount, it combines with Cr and Mo to form carbides, and reduces the amount of solid solution Cr and Mo contained in the base material, Deteriorates corrosion resistance. Therefore, the C content is set to 0.1% or less. In addition, Preferably it is 0.08% or less, More preferably, it is 0.07%.

Si:0.2%〜1%
Siは本発明で、とても重要な元素である。Siは脱酸に有効な元素であり、酸素濃度を0.01%以下に制御するためには、0.2%は必要である。さらに、CaO−SiO−MgO−Al−F系スラグ中のCaOやMgOを還元し、溶鋼中にCaやMgをそれぞれ0.0001%以上供給する役割もある。その観点からも0.2%は必要である。一方、1%を超えて含有すると、スラグ中のCaOやMgOを還元しすぎてしまい、Ca、Mgを0.01%超供給してしまう。その結果Caは、CaO単体の介在物を形成させてしまい、製品に表面欠陥を発生させてしまう。また、Mgはスラブ中にMg気泡を形成して表面欠陥をもたらす危険がある。そのため、Si含有量は、0.2%〜1%と規定した。好ましくは0.4〜0.8%である。
Si: 0.2% to 1%
Si is a very important element in the present invention. Si is an element effective for deoxidation, and 0.2% is necessary to control the oxygen concentration to 0.01% or less. Furthermore, there is also a role of reducing CaO and MgO in the CaO—SiO 2 —MgO—Al 2 O 3 —F-based slag and supplying 0.0001% or more of Ca and Mg to the molten steel, respectively. From that point of view, 0.2% is necessary. On the other hand, when it contains exceeding 1%, CaO and MgO in slag will be reduced too much and Ca and Mg will be supplied over 0.01%. As a result, Ca forms inclusions of CaO alone and causes surface defects in the product. Further, Mg has a risk of causing surface defects by forming Mg bubbles in the slab. Therefore, the Si content is defined as 0.2% to 1%. Preferably it is 0.4 to 0.8%.

Mn:0.2%〜2%
Mnは脱酸に有効な元素である。Mn含有量が、0.2%未満では、その効果が十分に得られず、逆に、2%を超えて存在すると、シグマ相の生成を促進し、脆化を招く。そのため、Mn含有量は0.2%〜2%と規定した。
Mn: 0.2% to 2%
Mn is an element effective for deoxidation. If the Mn content is less than 0.2%, the effect cannot be sufficiently obtained. Conversely, if the Mn content exceeds 2%, the formation of the sigma phase is promoted and embrittlement occurs. Therefore, the Mn content is defined as 0.2% to 2%.

S:0.005%以下
Sは熱間加工性を阻害する元素であるため、極力低下させるべきであり、S含有量は0.005%以下とした。好ましくは0.003%以下である。さらに好ましくは0.002%以下である。そのためには、AODおよび/またはVODにてスラグを用いて脱硫する必要がある。スラグの塩基度C/Sを2〜5未満として、溶鋼中にSiを0.2%〜1%含有させることで脱硫することが可能であり、本範囲を満たすことが出来る。
S: 0.005% or less Since S is an element that inhibits hot workability, it should be reduced as much as possible, and the S content is set to 0.005% or less. Preferably it is 0.003% or less. More preferably, it is 0.002% or less. For this purpose, it is necessary to desulfurize using slag at AOD and / or VOD. By setting the basicity C / S of slag to less than 2 to 5 and containing 0.2% to 1% of Si in the molten steel, it is possible to desulfurize and satisfy this range.

Ni:3%〜15%
Niは塩化物を含む溶液環境における耐孔食性、耐隙間腐食性ならびに耐応力腐食割れ性を改善する効果を有する。しかしながら、その効果を得る為には、3%以上の必要である。しかしながら、その効果は、15%以下の添加で十分であり、それ以上ではコスト上昇を招くため好ましくない。そこで、Ni含有量は、3%〜15%と規定した。
Ni: 3% to 15%
Ni has an effect of improving pitting corrosion resistance, crevice corrosion resistance and stress corrosion cracking resistance in a solution environment containing chloride. However, in order to obtain the effect, 3% or more is necessary. However, for the effect, addition of 15% or less is sufficient, and beyond that, the cost increases, which is not preferable. Therefore, the Ni content is defined as 3% to 15%.

Cr:13%〜20%
Crは、耐食性を確保するために必要不可欠な不動態皮膜を、鋼鈑表面に形成させる元素であり、耐酸性、耐孔食性、耐隙間腐食性ならびに耐応力腐食割れ性を改善するための母材の構成成分として、最も重量な元素である、しかしながら、Cr含有量が13%未満では、十分な耐食性が得られない。逆に、含有量が20%を超えると、シグマ相を生成し脆化を招く。以上の理由から、Cr含有量は13%〜20%と規定した。
Cr: 13% to 20%
Cr is an element that forms a passive film, which is indispensable for ensuring corrosion resistance, on the surface of the steel sheet, and is a matrix for improving acid resistance, pitting corrosion resistance, crevice corrosion resistance and stress corrosion cracking resistance. As a constituent component of the material, it is the heaviest element. However, if the Cr content is less than 13%, sufficient corrosion resistance cannot be obtained. On the other hand, if the content exceeds 20%, a sigma phase is generated and embrittlement occurs. For the above reason, the Cr content is defined as 13% to 20%.

Al:0.005%未満
Alは、クラスター起因の表面欠陥をもたらすMgO・Alを50個数%以上形成させるとともに、アルミナ介在物を形成する元素であるため、極力低減せねばならない元素である。さらには、溶接ビード部の品質を劣化させる元素でもある。そのため、Al含有量は0.005%未満と規定した。好ましくは0.004%以下である。この範囲に制御するには、もちろんAlを脱酸剤として用いないことが最重要である。
Al: Less than 0.005% Al is an element that forms 50% or more of MgO.Al 2 O 3 that causes surface defects due to clusters and also forms alumina inclusions. Therefore, Al is an element that must be reduced as much as possible. is there. Furthermore, it is an element that deteriorates the quality of the weld bead portion. Therefore, the Al content is specified to be less than 0.005%. Preferably it is 0.004% or less. Of course, in order to control within this range, it is of utmost importance not to use Al as a deoxidizer.

Mg:0.0001%〜0.01%
Mgは鋼中の非金属介在物の組成を、クラスターを形成せず、表面品質に悪影響の無い酸化物系MgOあるいはCaO−SiO−Al−MgO系酸化物に制御するために有効な元素である。その効果は、含有量が0.0001%未満では得られず、逆に、0.01%を超えて含有させると、スラブ中にMg気泡を形成するため、最終製品に表面欠陥をもたらす。そのため、Mg含有量は、0.0001%〜0.01%と規定した。好ましくは、0.0002〜0.005%である。より好ましくは、0.0003〜0.003%である。
Mg: 0.0001% to 0.01%
Mg is the composition of nonmetallic inclusions in the steel, without the formation of clusters, effective to control the oxide MgO or CaO-SiO 2 -Al 2 O 3 -MgO based oxide no adverse effect on surface quality Element. The effect cannot be obtained when the content is less than 0.0001%. Conversely, when the content exceeds 0.01%, Mg bubbles are formed in the slab, resulting in surface defects in the final product. Therefore, the Mg content is defined as 0.0001% to 0.01%. Preferably, it is 0.0002 to 0.005%. More preferably, it is 0.0003 to 0.003%.

溶鋼中に効果的にMgを添加させるには、下記の反応を利用することが好ましい。
2(MgO)+Si=(SiO)+2Mg …(1)
括弧内はスラグ中成分を示し、下線は溶鋼中成分を示す。
上記の範囲にMgを制御するには、スラグ塩基度を2〜5未満に制御するとともに、スラグ中MgO濃度を3〜15%に調整すればよい。
In order to effectively add Mg into the molten steel, it is preferable to use the following reaction.
2 (MgO) + Si = (SiO 2 ) +2 Mg (1)
The parentheses indicate the components in the slag, and the underline indicates the components in the molten steel.
In order to control Mg within the above range, the slag basicity may be controlled to be less than 2 to 5 and the MgO concentration in the slag may be adjusted to 3 to 15%.

Ca:0.0001%〜0.01%
Caは鋼中の非金属介在物の組成を、クラスターを形成せず、表面品質に悪影響の無いCaO−SiO−Al−MgO系酸化物に制御するために有効な元素である。その効果は、含有量が0.0001%未満では得られず、逆に、0.01%を超えて含有させると、CaO単体の介在物が形成し、最終製品に表面欠陥をもたらす。そのためCa含有量は、0.0001%〜0.01%と規定した。好ましくは、0.0002〜0.005%である。より好ましくは、0.0003〜0.003%である。
溶鋼中に効果的にCaを添加させるには、下記の反応を利用することが好ましい。
2(CaO)+Si=(SiO)+2Ca …(2)
上記の範囲にCaを制御するには、スラグ塩基度を2〜5未満に制御すればよい。
Ca: 0.0001% to 0.01%
Ca is an effective element for controlling the composition of non-metallic inclusions in steel to a CaO—SiO 2 —Al 2 O 3 —MgO-based oxide that does not form clusters and does not adversely affect the surface quality. The effect cannot be obtained when the content is less than 0.0001%. Conversely, when the content exceeds 0.01%, inclusions of simple CaO are formed, resulting in surface defects in the final product. Therefore, the Ca content is defined as 0.0001% to 0.01%. Preferably, it is 0.0002 to 0.005%. More preferably, it is 0.0003 to 0.003%.
In order to effectively add Ca to the molten steel, it is preferable to use the following reaction.
2 (CaO) + Si = (SiO 2 ) +2 Ca (2)
What is necessary is just to control slag basicity to less than 2-5 in order to control Ca to said range.

O:0.0005%〜0.01%
Oは、鋼中に0.01%を超えて存在すると、脱硫を阻害し、溶鋼中S濃度が0.005%を超えてしまう。逆に0.0005%未満と低くなると、Siがスラグ中のMgOやCaOを還元する能力を高めすぎてしまう。つまり、上記の(1)および(2)式の反応が進行しすぎてしまうことにより、溶鋼中のMgやCaがそれぞれ、0.01%を超えて高くなってしまう。そのため、O含有量は、0.0005%〜0.01%と規定した。この範囲に制御するためには、Si濃度を0.2%〜1%に調整することと、スラグの塩基度を2〜5未満に調整することが必要である。好ましくは、0.0006〜0.005%未満であり、さらに好ましくは、0.001〜0.004%である。
O: 0.0005% to 0.01%
If O is present in the steel in an amount exceeding 0.01%, desulfurization is inhibited, and the S concentration in the molten steel exceeds 0.005%. On the other hand, if the content is less than 0.0005%, Si excessively enhances the ability to reduce MgO and CaO in the slag. That is, when the reactions of the above formulas (1) and (2) proceed too much, Mg and Ca in the molten steel become higher than 0.01%, respectively. Therefore, the O content is defined as 0.0005% to 0.01%. In order to control within this range, it is necessary to adjust the Si concentration to 0.2% to 1% and to adjust the basicity of the slag to less than 2 to 5. Preferably, it is 0.0006 to less than 0.005%, More preferably, it is 0.001 to 0.004%.

さらに本発明鋼は、下記の元素を1種または2種以上含有してもよい。
Cu:1〜5%
Cuは、加工効果しにくくして成形性を高めたるため、有用な元素である。さらに、抗菌性や硫酸に対する耐食性を向上する元素でもある。しかしながら、多量に添加すると熱間加工性が低下すると共に靱性も低下する。そのため、1〜5%が望ましい。より望ましくは2〜4%である。なお、精錬に及ぼす作用として、Cuは溶鋼中Mgの溶解度を高め、MgO介在物を形成しやすくする作用を持つ。同時に逆の側面では、Cuは溶鋼中のAlの作用を強くするため、Mgと反応して、MgO・Alスピネル介在物を形成し易くする作用もある。そのため、Cu含有鋼に対しては、本発明の適用は極めて効果的である。
Further, the steel of the present invention may contain one or more of the following elements.
Cu: 1 to 5%
Cu is a useful element because it is less prone to processing effects and improves formability. It is also an element that improves antibacterial properties and corrosion resistance to sulfuric acid. However, when added in a large amount, hot workability is lowered and toughness is also lowered. Therefore, 1 to 5% is desirable. More desirably, it is 2 to 4%. As an effect on refining, Cu has an effect of increasing the solubility of Mg in molten steel and facilitating the formation of MgO inclusions. At the same time, on the opposite side, since Cu strengthens the action of Al in the molten steel, it also has an action of reacting with Mg to easily form MgO.Al 2 O 3 spinel inclusions. Therefore, the application of the present invention is extremely effective for Cu-containing steel.

Mo:5%以下
Moは耐食性を向上する元素である。5%を超えると、σ相の形成傾向が強まり、脆化する傾向がある。そのため、5%以下に留めるのが望ましい。好ましくは3%以下である。
Mo: 5% or less Mo is an element that improves corrosion resistance. If it exceeds 5%, the tendency to form a σ phase becomes strong and tends to become brittle. Therefore, it is desirable to keep it at 5% or less. Preferably it is 3% or less.

Nb:0.05〜1%
Nbは析出硬化型ステンレス鋼に必要な元素であり、硬化に対して寄与するとともに、Cを固着して耐食性を高める。このような効果を得るためには、0.05%以上必要である。一方、これらの元素の含有量が過剰になると、固溶化熱処理温度においてフェライトが多く形成されてしまい、時効硬化後の硬さが低下してしまう。したがって、これらの元素の総含有量は、1%以下とすべきである。よって、0.05〜1%が望ましい範囲である。好ましくは0.1〜0.7%である。
Nb: 0.05 to 1%
Nb is an element necessary for precipitation hardening stainless steel, contributes to hardening, and fixes C to enhance corrosion resistance. In order to obtain such an effect, 0.05% or more is necessary. On the other hand, if the content of these elements is excessive, a large amount of ferrite is formed at the solution heat treatment temperature, and the hardness after age hardening decreases. Therefore, the total content of these elements should be 1% or less. Therefore, 0.05 to 1% is a desirable range. Preferably it is 0.1 to 0.7%.

N:0.01%〜0.05%
Nは、侵入型元素であり、鋼の硬さ及び耐食性を向上させるので、0.01%以上の添加が好ましい。しかしながら、N含有量が過剰になると、Nb、Crと共に窒化物を形成し、加工性に悪影響を及ぼす。したがって、N含有量は、0.05%以下である必要がある。よって、0.01%〜0.05%が望ましい。好ましくは、0.015〜0.04%である。
N: 0.01% to 0.05%
N is an interstitial element and improves the hardness and corrosion resistance of steel, so addition of 0.01% or more is preferable. However, when the N content is excessive, a nitride is formed together with Nb and Cr, which adversely affects workability. Therefore, the N content needs to be 0.05% or less. Therefore, 0.01% to 0.05% is desirable. Preferably, it is 0.015 to 0.04%.

B:0.01%以下
Bは900℃程度の比較的低温側での熱間加工性を改善する元素である。しかしながら、0.01%を超えての添加は、1200℃程度の比較的高温側での熱間加工性を阻害する。そのため、添加は0.01%以下に留めるのが良い。好ましくは0.005%以下である。
B: 0.01% or less B is an element that improves hot workability on the relatively low temperature side of about 900 ° C. However, addition exceeding 0.01% inhibits hot workability on the relatively high temperature side of about 1200 ° C. For this reason, the addition should be limited to 0.01% or less. Preferably it is 0.005% or less.

非金属介在物
本発明では、非金属介在物組成は、MgO、MgO・Al、CaO−SiO−MgO−Al系酸化物の1種または2種以上を含み、MgO・Alを個数比率で50%以下であることを好ましい態様としている。以下、非金属介在物の個数比率限定の根拠を示す。
Non-metallic inclusions In the present invention, the non-metallic inclusion composition includes one or more of MgO, MgO.Al 2 O 3 , CaO—SiO 2 —MgO—Al 2 O 3 -based oxide, A preferred embodiment is that Al 2 O 3 is 50% or less in terms of the number ratio. Hereinafter, the grounds for limiting the number ratio of non-metallic inclusions will be shown.

非金属介在物組成は、MgO、MgO・Al 、CaO−SiO −MgO−Al 系酸化物の1種または2種以上を含み、MgO・Al を個数比率で50%以下
本発明に係るステンレス鋼は、鋼のSi、Al、Mg、Caの含有量に従い、MgO、MgO・Al、CaO−SiO−MgO−Al系酸化物のうち1種または2種以上含む。これらの介在物を含有させる理由は、まず、MgOは融点が2800℃と高いために、連続鋳造機の浸漬ノズル内で焼結しないため付着堆積しない。そのため、表面欠陥を引き起こさない。CaO−SiO−MgO−Al系酸化物は、融点が1300℃程度と低いため、これも焼結しない。そのため、表面欠陥を引き起こさない。
MgO・Alは表面欠陥を引き起こす介在物であるので、極力少ない方が好ましい。ただし、その含有量が個数割合で50%以下であれば、MgO・Alはノズル内に付着しないことから、個数比率で50%以下と定めた。
The non-metallic inclusion composition includes one or more of MgO, MgO.Al 2 O 3 , CaO—SiO 2 —MgO—Al 2 O 3 based oxide, and MgO · Al 2 O 3 in a number ratio. 50% or less The stainless steel according to the present invention is made of MgO, MgO.Al 2 O 3 , CaO—SiO 2 —MgO—Al 2 O 3 -based oxides according to the contents of Si, Al, Mg and Ca in the steel. Contains one or more. The reason for including these inclusions is that MgO has a high melting point of 2800 ° C., and therefore does not sinter in the immersion nozzle of the continuous casting machine, and therefore does not adhere and deposit. Therefore, no surface defects are caused. Since the CaO—SiO 2 —MgO—Al 2 O 3 -based oxide has a low melting point of about 1300 ° C., it is not sintered either. Therefore, no surface defects are caused.
Since MgO.Al 2 O 3 is an inclusion that causes surface defects, it is preferable that it be as small as possible. However, if the content is 50% or less in terms of the number ratio, MgO.Al 2 O 3 does not adhere in the nozzle, so the number ratio was determined to be 50% or less.

MgO・Alの構成成分を規定した理由を説明する。
MgO:10〜40%、Al :60〜90%
MgO・Alは比較的広い固溶体を持つ化合物である。上記の範囲で固溶体となるので、このように定めた。
The reason why the constituent components of MgO.Al 2 O 3 are specified will be described.
MgO: 10~40%, Al 2 O 3: 60~90%
MgO.Al 2 O 3 is a compound having a relatively wide solid solution. Since it became a solid solution in the above range, it was determined in this way.

CaO−SiO−Al−MgO系酸化物の各成分を規定した理由を説明する。
CaO:20〜60%、SiO :10〜40%、Al :30%以下、MgO:5〜50%
基本的には、CaO−SiO−Al−MgO系酸化物の融点を1300℃程度以下に保つために、上記範囲に設定した。なお、CaOが20%未満では融点が高くなり、CaOが60%を超えるとCaO介在物が共存する。SiOが10%未満ならびに40%超では、融点が高くなってしまう。Alが30%超では純粋なAl介在物が共存する。MgOが5%未満ならびに40%超では、融点が高くなってしまう。以上から、CaO:20〜60%、SiO:10〜40%、Al:30%以下、MgO:5〜50%とした。
The reason for defining each component of the CaO—SiO 2 —Al 2 O 3 —MgO-based oxide will be described.
CaO: 20~60%, SiO 2: 10~40%, Al 2 O 3: 30% or less, MgO: 5 to 50%
Basically, in order to keep the melting point of the CaO—SiO 2 —Al 2 O 3 —MgO-based oxide at about 1300 ° C. or less, the above range was set. In addition, when CaO is less than 20%, the melting point becomes high, and when CaO exceeds 60%, CaO inclusions coexist. If SiO 2 is less than 10% or more than 40%, the melting point becomes high. If Al 2 O 3 exceeds 30%, pure Al 2 O 3 inclusions coexist. If MgO is less than 5% or more than 40%, the melting point becomes high. From the above, CaO: 20 to 60%, SiO 2 : 10 to 40%, Al 2 O 3 : 30% or less, and MgO: 5 to 50%.

製造方法
本発明では、ステンレス鋼の製造方法も提案する。まず、原料を溶解し、Ni:3〜15%、Cr:13〜20%を含有するステンレス溶鋼を溶製し、次いで、AODおよび/またはVODにおいて脱炭した後に、石灰、蛍石、フェロシリコン合金を投入しCaO/SiO比:2〜5未満、MgO:3〜15%、Al:5%未満からなるCaO−SiO−MgO−Al−F系スラグを用いて溶鋼を精錬する方法である。これによれば、本発明のステンレス溶鋼中S濃度を効果的に0.005%以下まで低下させることが可能である。さらに、非金属介在物もMgO、MgO・Al、CaO−SiO−MgO−Al系酸化物の1種または2種以上を含み、MgO・Alを個数比率で50%以下に制御して、最終製品での表面欠陥を防止して良好な表面性状を確保することが可能となる。
Manufacturing Method The present invention also proposes a method for manufacturing stainless steel. First, raw materials are melted, molten stainless steel containing Ni: 3 to 15% and Cr: 13 to 20%, and then decarburized in AOD and / or VOD, and then lime, fluorite, ferrosilicon alloy was poured CaO / SiO 2 ratio: less than 2~5, MgO: 3~15%, Al 2 O 3: using a CaO-SiO 2 -MgO-Al 2 O 3 -F -based slag consisting of less than 5% This is a method for refining molten steel. According to this, it is possible to effectively reduce the S concentration in the molten stainless steel of the present invention to 0.005% or less. Further, the non-metallic inclusions also include one or more of MgO, MgO.Al 2 O 3 , CaO—SiO 2 —MgO—Al 2 O 3 based oxide, and MgO · Al 2 O 3 in a number ratio. By controlling to 50% or less, it becomes possible to prevent surface defects in the final product and ensure good surface properties.

本発明に係るステンレス合金の製造方法では、上述のようにスラグの組成に特徴を有している。以下、本発明で規定するスラグ組成の根拠を説明する。
CaO/SiO 比:2〜5未満
合金溶湯を効率よく脱酸、脱硫し、かつ非金属介在物組成を本発明の範囲に制御するためには、スラグのCaO/SiO比を制御する必要がある。この比の値が5を超えると、スラグ中CaOの活量が高くなり、(2)式の反応が進行しすぎる。そのため、溶鋼中に還元されるCa濃度が0.01%を超えて高くなり、CaO単体の非金属介在物が生成し、ノズル内に付着して、最終製品に表面欠陥をもたらす。そのため、上限を5(未満)とした。一方、CaO/SiO比が2未満になると、脱酸、脱硫が進まずに、本発明におけるS濃度、O濃度の範囲に制御することができなくなる。そのため、下限を2とした。このようなCaO/SiO2比に制御するため、CaO成分として、石灰または蛍石を添加することで調整可能である。一方、SiO2成分は脱酸剤であるSiの酸化により得ることが出来る。すなわち、Cr還元期にFeSi合金を投入して、Cr酸化物を還元すると、スラグ中にはSiOシリカが形成される。限定はしないが、不足があれば、SiO成分として珪砂を適宜添加しても構わない。したがって、塩基度は2〜5未満と定めた。好ましくは、2.7超〜4.9である。
The method for producing a stainless alloy according to the present invention is characterized by the composition of the slag as described above. Hereinafter, the basis of the slag composition defined in the present invention will be described.
CaO / SiO 2 ratio: It is necessary to control the CaO / SiO 2 ratio of slag in order to efficiently deoxidize and desulfurize molten alloy of less than 2 to 5 and to control the composition of non-metallic inclusions within the scope of the present invention. There is. When the value of this ratio exceeds 5, the activity of CaO in the slag becomes high, and the reaction of the formula (2) proceeds too much. Therefore, the Ca concentration reduced in molten steel exceeds 0.01%, non-metallic inclusions of CaO alone are generated, adhere to the nozzle, and cause surface defects in the final product. Therefore, the upper limit was set to 5 (less than). On the other hand, when the CaO / SiO 2 ratio is less than 2, deoxidation and desulfurization do not proceed, and the S concentration and O concentration ranges in the present invention cannot be controlled. Therefore, the lower limit is set to 2. In order to control to such a CaO / SiO2 ratio, it can be adjusted by adding lime or fluorite as a CaO component. On the other hand, the SiO2 component can be obtained by oxidation of Si as a deoxidizer. That is, when an FeSi alloy is introduced during the Cr reduction period and the Cr oxide is reduced, SiO 2 silica is formed in the slag. Although there is no limitation, if there is a shortage, silica sand may be appropriately added as the SiO 2 component. Therefore, the basicity was determined to be less than 2-5. Preferably, it is more than 2.7 to 4.9.

MgO:3〜15%
スラグ中のMgOは、溶鋼中に含まれるMg濃度を請求項に記載される濃度範囲に制御するために、重要な元素であるとともに、非金属介在物を本発明に好ましい組成に制御するためにも重要な元素である。そこで、下限を3%とした。一方、MgO濃度が15%を超えると、(2)式の反応が進行しすぎてしまい、溶鋼中のMg濃度が高くなり、スラブ中にMg気泡を形成するため、最終製品に表面欠陥をもたらす。そこで、MgO濃度の上限を15%とした。スラグ中のMgOは、AOD精錬、あるいはVOD精錬する際に使用されるドロマイトレンガ、またはマグクロレンガがスラグ中に溶け出すことで、所定の範囲となる。あるいは、所定の範囲に制御するため、ドロマイトレンガ、またはマグクロレンガの廃レンガを添加してもよい。
MgO: 3-15%
MgO in the slag is an important element in order to control the Mg concentration contained in the molten steel to the concentration range described in the claims, and to control the nonmetallic inclusions to a composition preferable for the present invention. Is also an important element. Therefore, the lower limit was made 3%. On the other hand, if the MgO concentration exceeds 15%, the reaction of the formula (2) proceeds too much, the Mg concentration in the molten steel becomes high, and Mg bubbles are formed in the slab, resulting in surface defects in the final product. . Therefore, the upper limit of the MgO concentration is set to 15%. MgO in the slag is in a predetermined range by dissolving dolomite bricks or magcro bricks used in AOD refining or VOD refining into the slag. Or in order to control to a predetermined range, you may add the waste brick of a dolomite brick or a magchrom brick.

Al :5%未満
スラグ中のAlは、高いと溶鋼中のAl濃度も0.005%以上と高くなり、MgO・Alが50個数%を超えて生成させる。また、アルミナ介在物も形成してしまうため、スラグ中のAl濃度は極力下げる必要がある。そのため、上限を5%(未満)とした。なお、上限を満足させるためには、Alを脱酸剤として用いないことが重要である。
Al 2 O 3: Al 2 O 3 of less than 5% in the slag is higher the Al concentration in the molten steel is also increased to 0.005% or more, MgO · Al 2 O 3 is to produce more than 50% by number. Moreover, since alumina inclusions are also formed, it is necessary to reduce the Al 2 O 3 concentration in the slag as much as possible. Therefore, the upper limit was made 5% (less than). In order to satisfy the upper limit, it is important not to use Al as a deoxidizer.

次に実施例を提示して、本発明の構成および作用効果をより、明らかにするが、本発明は以下の実施例にのみ限定されるものではない。
容量60トンの電気炉により、フェロニッケル、純ニッケル、フェロクロム、鉄屑、ステンレス屑、Fe−Ni合金屑などを原料として、溶解した。一部の鋼種ではFeMo、FeNbあるいはCuも原料として添加した。その後、AODまたはVODにおいてCを除去するための酸素吹精(酸化精錬)を行い、石灰石および蛍石を投入し、CaO−SiO−Al−MgO−F系スラグを生成させ、さらに、FeSi合金を投入し、Cr還元を行い、次いで脱酸した。その後、さらにAr撹拌して脱硫を進めた。AOD、VODではマグクロレンガをライニングした。その後、取鍋に出鋼して、温度調整ならびに成分調整を行い、連続鋳造機によりスラブを製造した。
Next, although an Example is shown and the structure and effect of this invention are clarified more, this invention is not limited only to a following example.
Using an electric furnace with a capacity of 60 tons, ferronickel, pure nickel, ferrochrome, iron scrap, stainless steel scrap, Fe-Ni alloy scrap, and the like were melted as raw materials. In some steel types, FeMo, FeNb or Cu was also added as a raw material. Thereafter, oxygen blowing (oxidative refining) for removing C in AOD or VOD is performed, limestone and fluorite are added, and CaO—SiO 2 —Al 2 O 3 —MgO—F-based slag is generated. The FeSi alloy was added, Cr reduction was performed, and then deoxidation was performed. Thereafter, desulfurization was further carried out by stirring with Ar. In AOD and VOD, magcro bricks were lined. Thereafter, the steel was taken out in a ladle, temperature adjustment and component adjustment were performed, and a slab was produced by a continuous casting machine.

製造したスラブは、表面を研削し、1200℃で加熱して熱間圧延を実施し、厚み6mmの熱帯を製造した。その後、焼鈍、酸洗を行い、表面のスケールを除去した。最終的に冷間圧延を施し、板厚1mm×幅1m×長さ1000mの薄板コイルを製造した。   The manufactured slab was ground and heated at 1200 ° C. to perform hot rolling, thereby manufacturing a tropics having a thickness of 6 mm. Thereafter, annealing and pickling were performed to remove the scale on the surface. Finally, cold rolling was performed to manufacture a thin coil having a thickness of 1 mm, a width of 1 m, and a length of 1000 m.

表1および2に、得られたステンレス鋼の化学成分、AODもしくはVOD精錬終了時のスラグ組成、非金属介在物組成および介在物の形態および品質評価を示す。なお、表1中の―は、無添加のため、分析限界以下であったことを示す。   Tables 1 and 2 show the chemical composition of the obtained stainless steel, the slag composition at the end of AOD or VOD refining, the nonmetallic inclusion composition, and the form and quality evaluation of the inclusion. In Table 1, “-” indicates that it was below the analysis limit because it was not added.

なお、表1および2に記載の諸項目は、下記のようにして求めた。
1)合金の化学成分およびスラグ組成:蛍光X線分析装置を用いて定量分析を行い、合金の酸素濃度は不活性ガスインパルス融解赤外線吸収法で定量分析を行った。
2)非金属介在物組成:鋳込み開始直後、タンディッシュにて採取したサンプルを鏡面研磨し、SEM−EDSを用いて、サイズ5μm以上の介在物を20点ランダムに測定した。
3)スピネル介在物の個数比率:上記2)の測定の結果から個数比率を評価した。
4)品質評価:圧延により製造した上記薄板表面を目視で観察し、非金属介在物起因の表面欠陥(板幅中央近傍に線状の疵が発生、線状欠陥)ならびに熱間加工性低下起因の表面欠陥(板のエッジ部にめくれ状に疵が発生、耳割れ)の発生有無を判定した。コイル全長を観察して、その欠陥数をそれぞれ示した。
In addition, various items described in Tables 1 and 2 were obtained as follows.
1) Chemical composition and slag composition of alloy: Quantitative analysis was performed using a fluorescent X-ray analyzer, and oxygen concentration of the alloy was quantitatively analyzed by an inert gas impulse melting infrared absorption method.
2) Nonmetallic inclusion composition: Immediately after the start of casting, a sample collected by tundish was mirror-polished, and inclusions having a size of 5 μm or more were randomly measured using SEM-EDS at 20 points.
3) Number ratio of spinel inclusions: The number ratio was evaluated from the measurement result of 2) above.
4) Quality evaluation: The surface of the thin plate produced by rolling is visually observed, and surface defects caused by non-metallic inclusions (linear flaws are generated near the center of the plate width, linear defects) and hot workability are reduced. The presence or absence of surface defects (turned wrinkles on the edge of the plate, ear cracks) was determined. The total length of the coil was observed to indicate the number of defects.

発明例の1〜9は、本発明の範囲を満足していたために、最終製品での表面に介在物起因の欠陥は無いか極めて少なく(11箇所以下)、良好な品質を得ることが出来た。   Since Examples 1 to 9 of the invention satisfied the scope of the present invention, the surface of the final product had no or very few defects due to inclusions (11 or less), and good quality could be obtained. .

一方、比較例は本発明の範囲を逸脱したため、表面欠陥が発生した。以下に、各例について説明する。比較例10は塩基度が5.45と5よりも高かったため、酸素濃度も低くなりすぎ、Ca濃度が0.0117%と0.01%よりも高くなってしまった。また、スラグ中MgO濃度も1.7%と3.0%よりも低く、Mg濃度が分析限界以下となってしまった。その結果、CaO単体の非金属介在物を生成し、最終製品で介在物起因の欠陥が生じた。   On the other hand, since the comparative example deviated from the scope of the present invention, surface defects occurred. Each example will be described below. In Comparative Example 10, the basicity was higher than 5.45 and 5, so the oxygen concentration was too low, and the Ca concentration was 0.0117% and higher than 0.01%. Further, the MgO concentration in the slag was 1.7%, which was lower than 3.0%, and the Mg concentration was below the analysis limit. As a result, non-metallic inclusions of simple CaO were generated, and defects due to the inclusions occurred in the final product.

比較例11は塩基度が1.73と2未満であったため、脱酸および脱硫が進まなかった。そのため、介在物個数が156個/cmと100個/cmを超えて多くなってしまった。さらに、Caが分析限界以下と低く、介在物中のMnOが47.5%と高くなったと同時に、S濃度が0.0058%と0.005%よりも高くなってしまった。その結果、熱間加工性が低下し、表面欠陥を生じた。 Since Comparative Example 11 had a basicity of 1.73 and less than 2, deoxidation and desulfurization did not proceed. Therefore, inclusions number has become much greater than the 156 / cm 2 and 100 / cm 2. Furthermore, Ca was low below the analysis limit, MnO in the inclusions was as high as 47.5%, and at the same time, the S concentration was 0.0058%, which was higher than 0.005%. As a result, hot workability decreased and surface defects occurred.

比較例12は、Siが1.23%と1.0%を超えて高かったこと、および、Al濃度が0.006%と0.005%よりも高かったために、溶鋼中Mgと相まってMgO・Al介在物が多く形成してしまった。その結果スピネル比率が95%と50%を超えてしまい、表面欠陥が発生した。 In Comparative Example 12, since Si was higher than 1.23% and 1.0%, and Al concentration was higher than 0.006% and 0.005%, MgO. A lot of Al 2 O 3 inclusions were formed. As a result, the spinel ratio exceeded 95% and 50%, and surface defects occurred.

比較例13はSiが0.11%と0.2%未満であったため、脱酸が進まず、介在物個数が127個/cmと100個/cmを超えて多くなってしまった。MgとCa濃度が分析限界以下となってしまい、介在物中のMnO濃度も36.3%と高くなった。さらに、脱酸や脱硫が進まず、S濃度が0.0068%と0.005%よりも高くなってしまった。その結果、熱間加工性が低下し、表面欠陥を生じた。 In Comparative Example 13, since Si was 0.11% and less than 0.2%, deoxidation did not proceed, and the number of inclusions increased to 127 / cm 2 and exceeded 100 / cm 2 . The Mg and Ca concentrations were below the analytical limit, and the MnO concentration in the inclusions was as high as 36.3%. Furthermore, deoxidation and desulfurization did not proceed, and the S concentration was 0.0068%, which was higher than 0.005%. As a result, hot workability decreased and surface defects occurred.

比較例14はスラグ中アルミナ濃度が8.5%と5%を超えて高かったため、溶鋼中Al濃度が0.025%と0.005%を超えて高くなり、アルミナ単体の非金属介在物が生成し、表面欠陥が生じた。   In Comparative Example 14, the alumina concentration in the slag was as high as 8.5%, exceeding 5%. Therefore, the Al concentration in the molten steel was increased beyond 0.025% and 0.005%, and the non-metallic inclusions of the alumina alone were found. Produced surface defects.

比較例15はスラグ中アルミナ濃度が7.5%と5%を超えて高く、溶鋼中のAl濃度が0.007%と0.005%よりも高くなり、MgO・Al比率が60%と50%を超えてしまい、表面欠陥が発生した。 In Comparative Example 15, the alumina concentration in the slag is higher than 7.5% and 5%, the Al concentration in the molten steel is higher than 0.007% and 0.005%, and the MgO · Al 2 O 3 ratio is 60 % And over 50%, and surface defects occurred.

比較例16はスラグ中MgO濃度が17.5%と15%を超えて高く、溶鋼中のMg濃度が0.0112%と0.01%よりも高くなり、スラブ中にMg気泡を形成し、最終製品に表面欠陥をもたらした。   In Comparative Example 16, the MgO concentration in the slag is higher than 17.5% and 15%, the Mg concentration in the molten steel is higher than 0.0112% and 0.01%, and Mg bubbles are formed in the slab. It resulted in surface defects in the final product.

比較例17は、Siが1.02%と1.0%を超えて高かった。さらに、スラグ中のアルミナ濃度が5.5%と5%を超えて高かったために、溶鋼中のAl濃度が0.008%と0.005%よりも高くなった。その結果、MgO・Al介在物のみが形成してしまい表面欠陥が発生した。

In Comparative Example 17, Si was higher than 1.02% and 1.0%. Furthermore, since the alumina concentration in the slag was 5.5%, which is higher than 5%, the Al concentration in the molten steel was higher than 0.008% and 0.005%. As a result, only MgO.Al 2 O 3 inclusions were formed and surface defects were generated.

Claims (6)

C:0.1%以下、Si:0.2〜1%、Mn:0.2〜2%、S:0.005%以下、Ni:3〜15%、Cr:13〜20%、Al:0.005%未満、Mg:0.0001〜0.01%、Ca:0.0001〜0.01%、O:0.0005〜0.01%、残部がFeおよび不可避的不純物からなるステンレス鋼において、
該ステンレス鋼中に含まれる非金属介在物が、MgO、MgO・Al、CaO−SiO−MgO−Al系酸化物の1種または2種以上を含み、
前記非金属介在物のうち長さ5μm以上の物が任意の1cmあたり100個以下であり、
前記非金属介在物のうちMgO・Alが個数比率で50%以下であることを特徴とするステンレス鋼。
C: 0.1% or less, Si: 0.2-1%, Mn: 0.2-2%, S: 0.005% or less, Ni: 3-15%, Cr: 13-20%, Al: Stainless steel with less than 0.005%, Mg: 0.0001 to 0.01%, Ca: 0.0001 to 0.01%, O: 0.0005 to 0.01%, the balance being Fe and inevitable impurities In
Nonmetallic inclusions contained in the stainless steel include one or more of MgO, MgO.Al 2 O 3 , CaO—SiO 2 —MgO—Al 2 O 3 oxide,
Among the non-metallic inclusions, those having a length of 5 μm or more are 100 or less per 1 cm 2 ,
Stainless steel characterized in that MgO.Al 2 O 3 is 50% or less in number ratio among the non-metallic inclusions.
前記非金属介在物のうちMgO・Alが個数比率で20%以下であることを特徴とする請求項1に記載のステンレス鋼。 2. The stainless steel according to claim 1, wherein MgO · Al 2 O 3 is 20% or less in number ratio among the non-metallic inclusions. 前記非金属介在物のうちMgO・Alが個数比率で0%であることを特徴とする請求項1に記載のステンレス鋼。 2. The stainless steel according to claim 1, wherein among the non-metallic inclusions, MgO · Al 2 O 3 is 0% in number ratio. 前記非金属介在物のうち、MgO・AlはMgO:10〜40%、Al:60〜90%であり、CaO−SiO−Al−MgO系酸化物は、CaO:20〜60%、SiO:10〜40%、Al:30%以下、MgO:5〜50%であることを特徴とする請求項1または2に記載のステンレス鋼。 Among the non-metallic inclusions, MgO · Al 2 O 3 is MgO: 10 to 40%, Al 2 O 3 : 60 to 90%, and CaO—SiO 2 —Al 2 O 3 —MgO-based oxide is CaO: 20~60%, SiO 2: 10~40%, Al 2 O 3: 30% or less, MgO: stainless steel according to claim 1 or 2, characterized in that 5 to 50%. さらに、Mo:5%以下、Cu:1〜5%、Nb:0.05〜1%、N:0.01〜0.05%、B:0.01%以下の1種または2種以上を含むことを特徴とする請求項1〜4のいずれか1項に記載のステンレス鋼。   Furthermore, Mo: 5% or less, Cu: 1-5%, Nb: 0.05-1%, N: 0.01-0.05%, B: 0.01% or less The stainless steel according to any one of claims 1 to 4, wherein the stainless steel is included. 請求項1〜5のいずれか1項に記載のステンレス鋼の製造方法であって、原料を溶解し、Ni:3〜15%、Cr:13〜20%を含有するステンレス溶鋼を溶製し、次いで、AODおよび/またはVODにおいて脱炭した後に、石灰、蛍石、フェロシリコン合金を投入しCaO/SiO比:2〜5未満、MgO:3〜15%、Al:5%未満からなるCaO−SiO−MgO−Al−F系スラグを用い、C:0.1%以下、Si:0.2〜1%、Mn:0.2〜2%、S:0.005%以下、Ni:3〜15%、Cr:13〜20%、Al:0.005%未満、Mg:0.0001〜0.01%、Ca:0.0001〜0.01%、O:0.0005〜0.01%、残部がFeおよび不可避的不純物からなるステンレス溶鋼に調整することを特徴とするステンレス鋼の製造方法。
It is a manufacturing method of stainless steel given in any 1 paragraph of Claims 1-5, Comprising: A raw material is melted, Melting stainless steel containing Ni: 3-15% and Cr: 13-20%, Next, after decarburizing in AOD and / or VOD, lime, fluorite, and ferrosilicon alloy are added and CaO / SiO 2 ratio: less than 2-5, MgO: 3-15%, Al 2 O 3 : less than 5% A CaO—SiO 2 —MgO—Al 2 O 3 —F-based slag composed of C: 0.1% or less, Si: 0.2 to 1%, Mn: 0.2 to 2%, S: 0.00. 005% or less, Ni: 3-15%, Cr: 13-20%, Al: less than 0.005%, Mg: 0.0001-0.01%, Ca: 0.0001-0.01%, O: 0.0005 to 0.01%, the balance being Fe and inevitable impurities Method for producing stainless steel and adjusting the less molten steel.
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