JP2012184494A - Ferritic stainless steel excellent in rusting resistance - Google Patents
Ferritic stainless steel excellent in rusting resistance Download PDFInfo
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- JP2012184494A JP2012184494A JP2011050280A JP2011050280A JP2012184494A JP 2012184494 A JP2012184494 A JP 2012184494A JP 2011050280 A JP2011050280 A JP 2011050280A JP 2011050280 A JP2011050280 A JP 2011050280A JP 2012184494 A JP2012184494 A JP 2012184494A
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- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 22
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 27
- 239000010959 steel Substances 0.000 claims abstract description 27
- 239000000203 mixture Substances 0.000 claims abstract description 26
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 15
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 10
- 229910010413 TiO 2 Inorganic materials 0.000 claims description 9
- 150000001875 compounds Chemical class 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 3
- 230000015572 biosynthetic process Effects 0.000 abstract description 11
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 abstract description 7
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 abstract description 5
- 238000004519 manufacturing process Methods 0.000 abstract description 5
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 abstract description 3
- 230000014509 gene expression Effects 0.000 abstract 1
- 230000004907 flux Effects 0.000 description 9
- 238000005755 formation reaction Methods 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 9
- 238000000034 method Methods 0.000 description 9
- 238000002844 melting Methods 0.000 description 8
- 230000008018 melting Effects 0.000 description 8
- 238000006243 chemical reaction Methods 0.000 description 6
- 239000002893 slag Substances 0.000 description 5
- 238000005260 corrosion Methods 0.000 description 4
- 230000007797 corrosion Effects 0.000 description 4
- 238000010304 firing Methods 0.000 description 4
- 238000007670 refining Methods 0.000 description 4
- 238000000137 annealing Methods 0.000 description 3
- 238000005266 casting Methods 0.000 description 3
- 238000011109 contamination Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000004453 electron probe microanalysis Methods 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 229910052698 phosphorus Inorganic materials 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
- 239000000725 suspension Substances 0.000 description 3
- 238000003723 Smelting Methods 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 238000005554 pickling Methods 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 239000011819 refractory material Substances 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 238000000550 scanning electron microscopy energy dispersive X-ray spectroscopy Methods 0.000 description 2
- 229910018575 Al—Ti Inorganic materials 0.000 description 1
- 229910004261 CaF 2 Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000010309 melting process Methods 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000004071 soot Substances 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- 230000037303 wrinkles Effects 0.000 description 1
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Abstract
Description
本発明は、発銹起点となるＣａＳなど水溶性の硫化物系非金属介在物の生成を抑制したフェライト系ステンレス鋼に関するものである。 The present invention relates to a ferritic stainless steel that suppresses the formation of water-soluble sulfide-based non-metallic inclusions such as CaS, which is a starting point.
フェライト系ステンレス鋼板では、水溶性の硫化物系非金属介在物を起点とした発銹が問題となる。ＣａＳなどによる発銹を抑制する方法としては、溶製条件を適正化する方法が知られている。 In ferritic stainless steel sheets, there is a problem of starting from water-soluble sulfide-based nonmetallic inclusions. As a method of suppressing wrinkling due to CaS or the like, a method of optimizing melting conditions is known.
例えば下記特許文献１では、ＣａＳの生成を抑制するために、鋼中のＣａ量を１０ｐｐｍ未満とすることを提案している。この方法では、酸化物の組成が高ＣaＯとなった場合には、その周囲に水溶性硫化物系非金属介在物のＣａＳが生成し発銹起点となる。しかしながら、鋼中の酸化物は精錬スラグの懸濁に起因するため、[Ｃａ]濃度を管理するのみでは不十分である。ＣａＳ生成を抑制するためには（ＣａＯ）濃度だけではなく、他の酸化物成分や鋼成分の制御が重要なことが本発明により明らかになった。
For example,
また、下記特許文献２に示されるような酸化物系非金属介在物の組成と非金属介在物中の平衡Ｓ溶解量を０．０３％以下に制御することで水溶性硫化物系非金属介在物ＣａＳの析出を抑制する方法がある。この方法は、溶製・鋳造工程における非金属介在物組成を制御することを対象としており、スラブ加熱時のＣａＳ生成などまでは考慮しておらず、発銹を完全に防止できないという問題点があった。
Further, by controlling the composition of oxide-based nonmetallic inclusions as shown in
ステンレス鋼板の発銹を低減する従来の製造方法では、前述のような非金属介在物組成を制御するために、溶製工程での脱酸剤の投入時期やスラグ精錬方法など厳しい工程管理が必要とされている。しかしながら、溶製時に生成した非金属介在物の組成によっては、その後のスラブ加熱工程において酸化物周囲に硫化物が析出・成長し、発銹の起点となる場合がある。本発明はスラブ加熱時の硫化物生成までを考慮して、非金属介在物組成を制御し、最終製品の発銹を改善することを課題とする。 In conventional manufacturing methods that reduce the occurrence of stainless steel sheet wringing, strict process management is required, such as the timing of adding a deoxidizer and the slag refining method in the melting process in order to control the composition of non-metallic inclusions as described above. It is said that. However, depending on the composition of the non-metallic inclusions produced during melting, sulfide may precipitate and grow around the oxide in the subsequent slab heating process, which may be the starting point of igniting. An object of the present invention is to control the composition of non-metallic inclusions in consideration of the formation of sulfides during slab heating and to improve the formation of the final product.
本発明者らが鋭意検討を行った結果、以下の手段によって前記課題を解決出来ることを見出し、本発明の完成に至ったものであり、その要旨とするところは特許請求の範囲に記載した通りの下記内容である。
（１）酸化物系介在物を含むフェライト系ステンレス鋼であって、該介在物はＣａＯ，及びＡｌ2Ｏ3を含有し、直径２μｍ以上の該介在物平均組成が下記（１）、（２）式を満足し、且つ鋼中のＳ濃度が質量％で０．００２％以下であることを特徴とする耐発銹性に優れたフェライト系ステンレス鋼である。
［（ＣａＯ）＋（ＭｇＯ）］／［（Ａｌ2Ｏ3）＋（ＳｉＯ2）＋（ＴｉＯ2）］≦０．５０ ・・・（１）
（ＦｅＯ）≦１．５ ・・・（２）
但し、式中の（化合物名）は、介在物中における当該化合物の含有割合（質量％）を意味する。
（２）また、前記フェライト系ステンレス鋼の成分組成が、質量％で、Ｃ：０．０７０％以下、Ｎ：０．０２０％以下、Ｓｉ：０．０５〜０．６０％、Ｍｎ：０．０４〜０．５０％、Ｐ：０．０３０％以下、Ｓ：０．０００３〜０．００２０％、Ｃｒ：１６〜２１％、Ｎｉ：０．６０％以下、Ａｌ：０．００２〜０．１４％、Ｔｉ：０．３５％以下、を含有し、残部がＦｅおよび不可避不純物からなることを特徴とする前記（１）に記載の耐発銹性に優れたフェライト系ステンレス鋼である。
As a result of intensive studies by the present inventors, it has been found that the above-mentioned problems can be solved by the following means, and the present invention has been completed. The gist of the present invention is as described in the claims. It is the following contents.
(1) Ferritic stainless steel containing oxide inclusions, which contain CaO and Al 2 O 3 , and the average composition of inclusions having a diameter of 2 μm or more has the following (1), (2 ) And a ferritic stainless steel excellent in sprinkling resistance, characterized in that the S concentration in the steel is 0.002% or less by mass.
[(CaO) + (MgO)] / [(Al 2 O 3 ) + (SiO 2 ) + (TiO 2 )] ≦ 0.50 (1)
(FeO) ≦ 1.5 (2)
However, (compound name) in the formula means the content ratio (% by mass) of the compound in the inclusion.
(2) Moreover, the component composition of the said ferritic stainless steel is the mass%, C: 0.070% or less, N: 0.020% or less, Si: 0.05-0.60%, Mn: 0.00. 04 to 0.50%, P: 0.030% or less, S: 0.0003 to 0.0020%, Cr: 16 to 21%, Ni: 0.60% or less, Al: 0.002 to 0.14 %, Ti: 0.35% or less, and the balance is made of Fe and inevitable impurities, and is the ferritic stainless steel having excellent resistance to sprinkling as described in (1) above.
本発明のフェライト系ステンレス鋼は、スラブ加熱工程における水溶性ＣａＳなど硫化物系非金属介在物の生成が無く、発銹を大幅に抑制することを可能とするものである。 The ferritic stainless steel of the present invention does not generate sulfide-based non-metallic inclusions such as water-soluble CaS in the slab heating process, and can greatly suppress the generation of rust.
以下に本発明を詳細に説明する。なお、本発明において、特に指定しない限り、％は質量％を意味する。また、［元素名］濃度は、当該元素の含有質量％を、（化合物名）濃度は、当該化合物の含有質量％を意味する。 The present invention is described in detail below. In the present invention, unless otherwise specified,% means mass%. The [element name] concentration means the mass% of the element, and the (compound name) concentration means the mass% of the compound.
本発明者らは、溶製時の制御に加え、ステンレス鋼板となるまでの間に施される熱処理まで考慮した制御方法を見出すべく、以下の検討を行った。まず、溶製段階として、Ａｒ雰囲気の高周波溶解炉にて、Ｃ：０．００３〜０．０６５％、Ｍｎ：０．１０〜０．５０％、Ｐ：０．０１１〜０．０３０％、Ｓ：０．０００３〜０．００５０％、Ｃｒ：１６〜２１％のフェライト系ステンレス鋼となるよう原料を溶解し、Ｓｉ脱酸、Ａｌ脱酸またはＡｌ−Ｔｉ脱酸した後、フラックス（６７％ＣａＯ−２３％Ａｌ2Ｏ3−１０％ＣａＦ2）を添加することで、酸化物組成をＣａＯ−Ａｌ2Ｏ3−ＴｉＯ2−ＳｉＯ2を主に含有する酸化物に制御した。この際、脱酸元素であるＳｉ、Ａｌ、Ｔｉの濃度をそれぞれＳｉ添加量：０．１０〜０．５３％、Ａｌ添加量：０．０１〜０．０７％、Ｔｉ添加量：０．０５〜０．３０％と変化させ、また、フラックス添加量を溶鋼１ｋｇ当り０．０５〜０．１０ｋｇ、処理時間を５〜３０ｍｉｎの範囲で変えることによって、鋼中の酸化物組成を変更した。 In order to find out a control method that takes into account the heat treatment performed before becoming a stainless steel plate in addition to the control at the time of melting, the present inventors have conducted the following studies. First, as a melting stage, C: 0.003 to 0.065%, Mn: 0.10 to 0.50%, P: 0.011 to 0.030%, S in an Ar atmosphere high-frequency melting furnace : 0.0003 to 0.0050% Cr: 16 to 21% ferritic stainless steel is dissolved, and after Si deoxidation, Al deoxidation or Al-Ti deoxidation, flux (67% CaO By adding −23% Al 2 O 3 -10% CaF 2 ), the oxide composition was controlled to an oxide mainly containing CaO—Al 2 O 3 —TiO 2 —SiO 2 . At this time, the concentrations of Si, Al, and Ti, which are deoxidizing elements, are respectively set to Si addition amount: 0.10 to 0.53%, Al addition amount: 0.01 to 0.07%, and Ti addition amount: 0.05. The oxide composition in the steel was changed by changing the amount of flux to 0.05 to 0.10 kg per 1 kg of molten steel and changing the treatment time in the range of 5 to 30 min.
この溶鋼を鋳造した後、鋼片中における大きさが最大径で２μｍ以上の介在物を２０個選んで、その組成および形態をＥＰＭＡおよびＳＥＭ−ＥＤＸによって調査した。ここで、介在物の最大径を限定した理由は、最大径２μｍ未満の微細な介在物が発銹の起点にはなり難いためである。また、この鋼片を圧延した薄鋼板から試験片を採取し、この試験片について、塩水噴霧試験−ＪＩＳ−Ｚ−２３７１（以下、ＳＳＴ）を実施した。 After casting this molten steel, 20 inclusions having a maximum diameter of 2 μm or more in the steel slab were selected, and their compositions and forms were investigated by EPMA and SEM-EDX. Here, the reason why the maximum diameter of inclusions is limited is that fine inclusions having a maximum diameter of less than 2 μm are unlikely to be the starting point of the generation. Moreover, the test piece was extract | collected from the thin steel plate which rolled this steel piece, and the salt spray test-JIS-Z-2371 (henceforth, SST) was implemented about this test piece.
さらに、ＳＳＴ試験を行った試験片および鋼片に対して、ステンレス鋼製造段階を模擬するための熱処理（１２００℃×１ｈｒ→空冷）を施し、その試験片についても、介在物組成および形態をＥＰＭＡおよびＳＥＭ−ＥＤＸにて調査して発銹と酸化物組成との関係を評価した。なお、酸化物組成はＣａＯ−ＳｉＯ2−Ａｌ2Ｏ3−ＭｇＯ−ＴｉＯ2−Ｃｒ2Ｏ3−ＦｅＯ系で分析し、以下では１００％に換算した濃度を用いている。なお、ＭｇＯは耐火物からの混入に起因し、Ｃｒ2Ｏ3やＦｅＯは脱酸レベルやフラックス処理時間、量に応じて微量に含有されるものである。 Furthermore, heat treatment (1200 ° C. × 1 hr → air cooling) for simulating the stainless steel production stage was performed on the test pieces and steel pieces subjected to the SST test, and the inclusion composition and form were also changed to EPMA. And SEM-EDX was used to evaluate the relationship between rusting and oxide composition. The oxide composition was analyzed in a CaO—SiO 2 —Al 2 O 3 —MgO—TiO 2 —Cr 2 O 3 —FeO system, and the concentration converted to 100% is used below. Incidentally, MgO is caused by contamination from the refractory, Cr 2 O 3 and FeO are those deoxidation levels and flux treatment time, it is contained in trace amounts in accordance with the amount.
図１に、鋼片および熱処理後の介在物のＥＰＭＡ測定結果を示す。一部の鋼片においては、熱処理後にＣａＯ−Ａｌ2Ｏ3主体の介在物の周囲にＣａＳが析出している様子が確認できた。また、酸化物中にＣａＳの析出している鋼片から得られた薄鋼板では、ＳＳＴ発銹量が多く、しかも酸化物の周囲のＣａＳを起点として錆が生成していることが判明した。以上のような分析結果などから得られた本発明の知見によると、酸化物周囲におけるＣａＳ生成反応は、
（ＣａＯ）＋[Ｓ]→（ＣａＳ）＋[Ｏ] ・・・・・ （Ａ）
のように考えられ、介在物組成以外に鋼中の[Ｓ]濃度の影響が挙げられる。つまり、従来知見のような（ＣａＯ）濃度の制御だけでは課題を解決することは出来ず、[Ｓ]濃度を低減することが非常に重要であることを見出した。
FIG. 1 shows the EPMA measurement results of the steel slab and the inclusions after heat treatment. In some steel pieces, it was confirmed that CaS was precipitated around inclusions mainly composed of CaO—Al 2 O 3 after heat treatment. Further, it was found that the thin steel plate obtained from the steel piece in which CaS is precipitated in the oxide has a large amount of SST cracking and rust is generated starting from CaS around the oxide. According to the knowledge of the present invention obtained from the analysis results as described above, the CaS generation reaction around the oxide is
(CaO) + [S] → (CaS) + [O] (A)
In addition to the inclusion composition, the influence of the [S] concentration in the steel can be mentioned. That is, it has been found that the problem cannot be solved only by controlling the (CaO) concentration as in the conventional knowledge, and it is very important to reduce the [S] concentration.
また、酸化物組成についても数多く調査し、酸化物組成とＣａＳの析出状態および発銹状況から検討を重ねた結果、（ＣａＯ），（ＭｇＯ）濃度が高いほど、また（Ａｌ2Ｏ3）、（ＳｉＯ2）、（Ｔｉ2Ｏ3）濃度が低いほど、さらに微量成分である（ＦｅＯ）濃度が高いほど酸化物の周囲にＣａＳが析出し、発銹の起点となることが判明した。（ＭｇＯ）濃度は耐火物の溶損に起因して混入し、（ＣａＯ）と同様に塩基性であるため（Ａ）式の反応に大きく寄与すると考えられる。一方、（Ａｌ2Ｏ3）、（ＳｉＯ2）、（ＴｉＯ2）は（ＣａＯ）や（ＭｇＯ）と異なり、塩基性ではなく、また後述する液相介在物の生成を抑制するために、（Ａ）式の反応の進行を起こりにくくすると考えられる Moreover, as a result of investigating many oxide compositions, and repeating examination from the oxide composition, the precipitation state of CaS, and the state of mist generation, the higher the (CaO), (MgO) concentration, the more (Al 2 O 3 ), It was found that the lower the (SiO 2 ) and (Ti 2 O 3 ) concentration and the higher the (FeO) concentration as a trace component, the more CaS precipitates around the oxide and becomes the starting point of igniting. It is considered that the (MgO) concentration is mixed due to the melting loss of the refractory, and as basic as (CaO), it contributes greatly to the reaction of the formula (A). On the other hand, (Al 2 O 3 ), (SiO 2 ), and (TiO 2 ) are not basic, unlike (CaO) and (MgO), and in order to suppress the formation of liquid phase inclusions described later, A) It is thought that the progress of the reaction of the formula hardly occurs
図２に介在物中の［（ＣａＯ）+（ＭｇＯ）］／[（Ａｌ2Ｏ3）＋（ＳｉＯ2）＋（ＴｉＯ2）]（以下、Ｘ値）とＳＳＴ発銹個数の関係を示す。Ｘ値が０．５０以下において、発銹を抑えることができることが分かった。Ｘ値が大きい場合には（Ａ）式の左辺の（ＣａＯ）、（ＭｇＯ）が相対的に高いことに相当し、ＣａＳ生成反応が促進されると考えられる。なお、Ｘ値の制御は、式を構成する各化合物量を調整することによって行うが、これらの含有量は脱酸元素やフラックスとして意図的に添加する以外にも溶鋼中に懸濁するスラグの量、耐火物からの混入、溶製・鋳造工程における介在物の浮上分離除去量、など、使用している設備や操業条件で異なってくる要因が大きく影響する。したがって、これら設備・操業要因を考慮して脱酸元素やフラックスの添加量、処理時間を適宜調整することで制御することができる。 FIG. 2 shows the relationship between [(CaO) + (MgO)] / [(Al 2 O 3 ) + (SiO 2 ) + (TiO 2 )] (hereinafter referred to as X value) in the inclusion and the number of SST occurrences. . It was found that wrinkles can be suppressed when the X value is 0.50 or less. When the X value is large, this corresponds to relatively high (CaO) and (MgO) on the left side of the formula (A), and it is considered that the CaS formation reaction is promoted. The X value is controlled by adjusting the amount of each compound constituting the formula, but these contents are not limited to deoxidation elements or fluxes but are added to the slag suspended in the molten steel. Factors that vary depending on the equipment and operating conditions used, such as the amount, contamination from refractories, and the amount of floating separation and removal of inclusions in the smelting / casting process, are greatly affected. Therefore, it can be controlled by appropriately adjusting the addition amount of deoxidizing element and flux and the processing time in consideration of these equipment / operation factors.
図３に介在物中の（ＦｅＯ）濃度とＳＳＴ発銹個数の関係を示す。なお、ここでは［（ＣａＯ）+（ＭｇＯ）］／[（Ａｌ2Ｏ3）＋（ＳｉＯ2）＋（ＴｉＯ2）]の値は０．４０〜０．５０のものを選んでいる。（ＦｅＯ）濃度が１．５％を越えるとＣａＳ生成が促進され、発銹しやすくなることが分かった。（ＦｅＯ）濃度が高い場合には、熱処理時において介在物中にＣａＯ−Ａｌ2Ｏ3−ＦｅＯ系の液相が存在するため、（Ａ）式の反応が容易に起こると考えられる。なお、（ＦｅＯ）濃度は脱酸元素が多い場合やフラックス量、処理時間が多い場合に低い傾向にあることが本発明で分かった。（ＦｅＯ）の制御についても、上記介在物中の（ＣａＯ）等の制御同様、設備や操業要因を考慮し、脱酸元素やフラックスの添加量、処理時間を適宜調整することで適正な範囲にすることができる。 FIG. 3 shows the relationship between the (FeO) concentration in inclusions and the number of SST generations. Here, the value of [(CaO) + (MgO)] / [(Al 2 O 3 ) + (SiO 2 ) + (TiO 2 )] is selected from 0.40 to 0.50. It has been found that when the (FeO) concentration exceeds 1.5%, CaS generation is promoted, and it becomes easy to start soot. When the (FeO) concentration is high, a CaO—Al 2 O 3 —FeO-based liquid phase is present in the inclusions during the heat treatment, and therefore the reaction of the formula (A) is considered to occur easily. It has been found in the present invention that the (FeO) concentration tends to be low when the amount of deoxidizing element is large or when the amount of flux and the treatment time are large. Regarding the control of (FeO), in the same manner as the control of (CaO) and the like in the inclusions, considering the equipment and operating factors, the addition amount of deoxidizing element and flux and the processing time are appropriately adjusted to within an appropriate range. can do.
図４に鋼中のＳ濃度とＳＳＴ発銹個数の関係を示す。ここでは、Ｘ値が０．４０〜０．５０、且つ（ＦｅＯ）濃度が１．５％以下のものを選んでいる。Ｓ濃度が０．００２％を越えると、前述のように（Ａ）式の反応によるＣａＳ生成量が多くなり、発銹が顕著になることが分かった。 FIG. 4 shows the relationship between the S concentration in steel and the number of SST firing. Here, an X value of 0.40 to 0.50 and a (FeO) concentration of 1.5% or less are selected. It has been found that when the S concentration exceeds 0.002%, the amount of CaS produced by the reaction of the formula (A) increases as described above, and sooting becomes remarkable.
以上のように、本発明は脱酸による介在物組成制御と鋼中Ｓ量の制御を行うことで、発銹が抑制できることを見出したものである。したがって、一般的に製造されている全てのフェライト系ステンレス鋼に適用可能なものである。その範囲としては、例えばＣ：０．０７０％以下、Ｎ：０．０２０％以下、Ｍｎ：０．０４〜０．５０％、Ｐ：０．０３０％以下、Ｓ：０．０００３〜０．００２０％、Ｃｒ：１６〜２１％、Ｎｉ：０．６０％以下が挙げられる。なお、下限を規定してない成分の好ましい範囲は、後述の表１に示す本発明例における下限値以上とする。また、記載した以外の元素については、脱酸元素やフラックス、スラグからの懸濁や、耐火物からの混入などで含まれる不可避不純物である。以下に本発明で用いられる脱酸に関わる各元素の添加量について説明する。 As described above, the present invention has been found that the formation of cracks can be suppressed by controlling the inclusion composition control by deoxidation and the control of the amount of S in steel. Therefore, it is applicable to all ferritic stainless steels that are generally manufactured. As the range, for example, C: 0.070% or less, N: 0.020% or less, Mn: 0.04-0.50%, P: 0.030% or less, S: 0.0003-0.0020 %, Cr: 16 to 21%, Ni: 0.60% or less. In addition, the preferable range of the component which does not prescribe | regulate a minimum shall be more than the lower limit in the example of this invention shown in Table 1 mentioned later. In addition, elements other than those described are unavoidable impurities contained due to deoxidation elements, flux, suspension from slag, contamination from refractories, and the like. The amount of each element involved in deoxidation used in the present invention will be described below.
Ｓｉは、脱酸元素として有用であり、耐食性にも有効な元素である。しかし、多すぎると加工性が低下するために、０．０５〜０．６０％とする。好ましくは０．１０〜０．５０％である。また、ＳｉはＴｉとの相互作用が大きく、溶鋼中のＴｉの活量を大きくする効果があるために、Ｔｉ添加の有効活用も考慮して添加量が選択される。 Si is useful as a deoxidizing element and is also an element effective for corrosion resistance. However, since processability will fall when there is too much, it is made 0.05 to 0.60%. Preferably it is 0.10 to 0.50%. Further, since Si has a large interaction with Ti and has an effect of increasing the activity of Ti in the molten steel, the addition amount is selected in consideration of effective utilization of Ti addition.
Ａｌは、強力な脱酸元素として有用な元素である。しかしながら、過剰に添加すると製造時に表面疵を生じやすくなる。このため、０．００２〜０．１４％とする。望ましくは、０．０１〜０．０７％である。 Al is an element useful as a powerful deoxidizing element. However, excessive addition tends to cause surface defects during production. For this reason, it is set to 0.002 to 0.14%. Desirably, it is 0.01 to 0.07%.
Ｔｉは、フェライト系ステンレス鋼におけるＣ，Ｎ安定化のため添加されるが、脱酸にも寄与する。したがって、必要に応じて添加する。しかしながら多すぎると、製造時に表面疵を生じやすくなり、耐食性および溶接部の強度を下げる為、上限を０．３５％とする。望ましい範囲は、０．０５〜０．３０％である。 Ti is added to stabilize C and N in ferritic stainless steel, but also contributes to deoxidation. Therefore, it adds as needed. However, if the amount is too large, surface flaws are likely to occur during production, and the upper limit is set to 0.35% in order to reduce corrosion resistance and weld strength. A desirable range is 0.05 to 0.30%.
Ｃａを添加しない場合も、精錬スラグの懸濁に起因したＣａＯ主体の介在物が生成し、温度降下に伴う脱酸反応によりＣａＯ−Ａｌ2Ｏ3−ＳｉＯ2−ＴｉＯ2主体の介在物が形成される。[Ｃａ]濃度が０．００１％未満でも上記のような介在物が主体になり、脱硫などの溶製条件や二次精錬における介在物除去などの影響も大きく受ける。 Even when Ca is not added, inclusions mainly composed of CaO due to suspension of the refining slag are generated, and inclusions mainly composed of CaO—Al 2 O 3 —SiO 2 —TiO 2 are formed by the deoxidation reaction accompanying the temperature drop. Is done. Even if the [Ca] concentration is less than 0.001%, the inclusions as described above are mainly used, and are greatly affected by melting conditions such as desulfurization and inclusion removal in secondary refining.
以上のように介在物組成を制御した本発明のフェライト系ステンレス鋼は、前述のＳＳＴ試験において、発銹個数が２０個／１００ｃｍ2未満と著しく耐発銹性に優れたものとなる。好ましくは１０個／１００ｃｍ2以下であり、更に好ましくは５個／１００ｃｍ2以下である。 As described above, the ferritic stainless steel of the present invention, in which the inclusion composition is controlled, has a remarkably excellent resistance to spattering, with the number of sprung being less than 20/100 cm 2 in the SST test described above. The number is preferably 10 pieces / 100 cm 2 or less, and more preferably 5 pieces / 100 cm 2 or less.
本発明の実施例を以下に記す。表１に記す成分組成のフェライト系ステンレス鋼を前述のように脱酸元素、フラックス添加量と処理時間を変更して介在物組成を種々変化させながら、Ａｒ雰囲気の高周波溶解炉で溶製、鋳造した。これを熱間圧延、熱延板焼鈍・酸洗、冷延、冷延板焼鈍・酸洗を実施し、１．０ｍｍの冷延板を作製した。なお冷延板焼鈍の温度は、各々の鋼材の再結晶温度に基づき９５０〜１０５０℃の間で調整した。
この冷延板について、上述した方法で２μｍ以上の介在物の組成を調査した。また、塩水噴霧試験−ＪＩＳ−Ｚ−２３７１に準拠して、５％ＮａＣｌ溶液を用いて、３５℃−４時間の連続噴霧試験を行った。 About this cold-rolled board, the composition of the inclusion of 2 micrometers or more was investigated by the method mentioned above. Moreover, based on the salt spray test-JIS-Z-2371, the continuous spray test of 35 degreeC-4 hours was done using the 5% NaCl solution.
本発明鋼であるＮｏ.１〜１０の鋼ではＳＳＴ発銹個数が３個／１００ｃｍ2以下であり、非常に優れた耐食性を示した。一方、本発明の範囲を外れたＮｏ.１１〜１８ではＳＳＴ発銹個数が２０個／１００ｃｍ2以上と多く、耐食性
に劣ることから本発明の効果が確認された。
In the steels of Nos. 1 to 10 which are the steels of the present invention, the number of SST firing was 3/100 cm 2 or less, and very excellent corrosion resistance was exhibited. On the other hand, in No. 11-18 which was outside the scope of the present invention, the number of SST firing was as large as 20/100 cm < 2 > or more, and the corrosion resistance was poor, so the effects of the present invention were confirmed.
Claims (2)
Ｘ＝［（ＣａＯ）＋（ＭｇＯ）］／［（Ａｌ2Ｏ3）＋（ＳｉＯ2）＋（ＴｉＯ2）］≦０．５０ ・・・（１）
（ＦｅＯ）≦１．５ ・・・（２）
但し、式中の（化合物名）は、介在物中における当該化合物の含有割合（質量％）を意味する。 Ferritic stainless steel containing oxide inclusions, which contain CaO and Al 2 O 3 , and the average composition with a maximum diameter of 2 μm or more satisfies the following formulas (1) and (2) And ferritic stainless steel excellent in sprinkling resistance, characterized in that the S concentration in the steel is 0.002% or less by mass.
X = [(CaO) + (MgO)] / [(Al 2 O 3 ) + (SiO 2 ) + (TiO 2 )] ≦ 0.50 (1)
(FeO) ≦ 1.5 (2)
However, (compound name) in the formula means the content ratio (% by mass) of the compound in the inclusion.
Ｃ：０．０７０％以下、
Ｎ：０．０２０％以下、
Ｓｉ：０．０５〜０．６０％、
Ｍｎ：０．０４〜０．５０％、
Ｐ：０．０３０％以下、
Ｓ：０．０００３〜０．００２０％、
Ｃｒ：１６〜２１％、
Ｎｉ：０．６０％以下、
Ａｌ：０．００２〜０．１４％、
Ｔｉ：０．３５％以下、を含有し、残部がＦｅおよび不可避不純物からなることを特徴とする請求項１に記載の耐発銹性に優れたフェライト系ステンレス鋼。
The component composition of the ferritic stainless steel is mass%,
C: 0.070% or less,
N: 0.020% or less,
Si: 0.05 to 0.60%,
Mn: 0.04 to 0.50%
P: 0.030% or less,
S: 0.0003 to 0.0020%,
Cr: 16-21%,
Ni: 0.60% or less,
Al: 0.002 to 0.14%,
2. The ferritic stainless steel having excellent resistance to spattering according to claim 1, comprising: Ti: 0.35% or less, with the balance being Fe and inevitable impurities.
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| CN107541681A (en) * | 2016-06-23 | 2018-01-05 | Posco公司 | The ferrite-group stainless steel of the excellent in low temperature toughness of welding point |
| JP2019112672A (en) * | 2017-12-22 | 2019-07-11 | 日鉄ステンレス株式会社 | Ferritic stainless steel excellent in rust resistance |
| KR20230018458A (en) | 2020-06-02 | 2023-02-07 | 닛테츠 스테인레스 가부시키가이샤 | ferritic stainless steel |
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