JP5687590B2 - Method for producing boron-containing stainless steel - Google Patents

Method for producing boron-containing stainless steel Download PDF

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JP5687590B2
JP5687590B2 JP2011211099A JP2011211099A JP5687590B2 JP 5687590 B2 JP5687590 B2 JP 5687590B2 JP 2011211099 A JP2011211099 A JP 2011211099A JP 2011211099 A JP2011211099 A JP 2011211099A JP 5687590 B2 JP5687590 B2 JP 5687590B2
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轟 秀和
秀和 轟
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Nippon Yakin Kogyo Co Ltd
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本発明は、原子力発電所の使用済み核燃料貯蔵用容器材料などに用いて好適なボロン含有ステンレス鋼の製造方法に関し、特に、ボロンを鋼中に効率よく含有させるのに有効な製造方法を提案するものである。   The present invention relates to a method for producing boron-containing stainless steel suitable for use in, for example, a spent nuclear fuel storage container material of a nuclear power plant, and in particular, proposes an effective production method for efficiently containing boron in steel. Is.

ボロン含有ステンレス鋼は、中性子吸収能が高く、耐食性にも優れることから、原子力発電所の使用済み核燃料貯蔵用容器材料やその遮薇材料などとして使用されている。このボロン含有ステンレス鋼は、金相学的に見ると、オーステナイトとボライド[(Cr、Fe)B]との共晶型合金であり、熱間での加工性が悪いという問題点がある。 Boron-containing stainless steel has high neutron absorption capability and excellent corrosion resistance, and is therefore used as a spent nuclear fuel storage container material for nuclear power plants and its barrier material. This boron-containing stainless steel is a eutectic alloy of austenite and boride [(Cr, Fe) 2 B] when viewed metallurgically, and has a problem that hot workability is poor.

そこで従来は、主としてその熱間加工性を向上させるための技術が数多く提案されている。例えば、
(1)特許文献1では、ボロン含有ステンレス鋼の熱延鋼帯を好適な熱処理を施すことによって解決する方法、
(2)特許文献2では、ボロン含有ステンレス鋼の溶湯を攪拌を行ないながら冷却し、過熱度を5℃以下、固相率が0.5以下の半凝固スラリの状態で鋳造することによって解決する方法、
(3)特許文献3では、B、C、Si、Cr、Ni、Mo、NおよびOを含有する500μm以下の窒素ガスアトマイズ粉を軟鋼製缶内に真空充填し、その後、特定の温度、圧力にてHIP処理することによりボライドの微細化を達成し、鋼板の延性や靭性、耐食性を向上させることによって熱間圧延時の耳割れをなく方法、
などの提案がある。
Thus, conventionally, many techniques for mainly improving the hot workability have been proposed. For example,
(1) In Patent Document 1, a method for solving a hot-rolled steel strip of boron-containing stainless steel by performing a suitable heat treatment,
(2) Patent Document 2 solves this problem by cooling a molten boron-containing stainless steel while stirring and casting in a semi-solid slurry with a superheat degree of 5 ° C. or less and a solid phase ratio of 0.5 or less. Method,
(3) In Patent Document 3, nitrogen gas atomized powder of 500 μm or less containing B, C, Si, Cr, Ni, Mo, N and O is vacuum-filled into a mild steel can, and then at a specific temperature and pressure. HIP treatment to achieve finer boride and improve the ductility, toughness, and corrosion resistance of the steel sheet, eliminating the ear cracks during hot rolling,
There are suggestions.

特開平5−320750号公報JP-A-5-320750 特許公開平6−328196号公報Japanese Patent Publication No. 6-328196 特許公開平6−207207号公報Japanese Patent Publication No. 6-207207

一方で、このボロンはまた、ボロン含有ステンレス鋼を製造するとき、ボロンの特性として、シリコンと同程度の酸化性をもつことから、精錬工程での脱酸処理をシリコンのみで行なおうとすると、ボロンが酸化してスラグ中に移行してしまい、目標とするボロン含有量を確保することができなくなるという別の問題点があった。この点に関しては従来、あまり注目されておらず、注目すべき従来技術というのは無いのが実情である。   On the other hand, when producing boron-containing stainless steel, this boron has the same degree of oxidation as silicon as a characteristic of boron, so when trying to perform deoxidation treatment in the refining process only with silicon, There was another problem that boron was oxidized and moved into the slag, making it impossible to secure the target boron content. Conventionally, this point has not received much attention, and there is no prior art to be noted.

そこで、本発明の目的は、ボロン含有ステンレス鋼の製造に当たり、ボロンを鋼中に効率よく歩留らせることのできるボロン含有ステンレス鋼の製造方法を提案することにある。   Accordingly, an object of the present invention is to propose a method for producing boron-containing stainless steel, which can efficiently yield boron in steel when producing boron-containing stainless steel.

発明者らはまず、ボロン含有ステンレス鋼の製造に当たり、ボロンを鋼中に効率よく歩留らせる方法について究明するために、次のような実験を行なった。この実験は、高周波誘導炉で、種々の微量成分を添加したFe−19.5mass%Cr−10.3mass%Ni合金を溶解し、このときのボロン添加量と鋼中ボロン濃度との関係を調べた。実験には、20kgのマグネシア坩堝を用いた。溶解直後の酸素濃度は300ppm程度もあったので、脱酸処理を行なった。この脱酸処理は、フェロシリコン合金のみの添加、Alのみの添加、またはその両方を添加することによりCrの還元を行ない、さらに、フラックスとして生石灰と蛍石を添加して、CaO−SiO−Al−MgO−F系スラグを生成させることで脱酸するものである。その後、必要に応じてBを添加して脱酸、脱硫するに当たり、鋼中のB含有量が0.7mass%、1.0mass%、1.5mass%となるようにB源を添加して、Bの歩留りを確認することにした。 The inventors first conducted the following experiment in order to investigate a method for efficiently yielding boron in steel in producing boron-containing stainless steel. In this experiment, Fe-19.5 mass% Cr-10.3 mass% Ni alloy with various minor components added was melted in a high-frequency induction furnace, and the relationship between the boron addition amount and the boron concentration in the steel was investigated. It was. In the experiment, a 20 kg magnesia crucible was used. Since the oxygen concentration immediately after dissolution was about 300 ppm, deoxidation treatment was performed. In this deoxidation treatment, Cr is reduced by adding only a ferrosilicon alloy, adding only Al, or both. Further, quick lime and fluorite are added as a flux, and CaO—SiO 2 − is added. it is intended to deoxidation by to produce al 2 O 3 -MgO-F slag. After that, when deoxidizing and desulfurizing by adding B as necessary, B source is added so that the B content in the steel becomes 0.7 mass%, 1.0 mass%, 1.5 mass%, I decided to check the yield of B.

その結果、フェロシリコン合金で脱酸した場合は、目標に対しての歩留りは80%未満と低かった。一方で、AlあるいはAlおよびフェロシリコン合金で脱酸した場合には、歩留りが80%以上と高いことがわかった。そして、Alの添加量は0.005mass%以上が必要であることもわかった。   As a result, when deoxidizing with a ferrosilicon alloy, the yield with respect to the target was as low as less than 80%. On the other hand, it was found that the yield was as high as 80% or more when deoxidized with Al or Al and a ferrosilicon alloy. It was also found that the added amount of Al needs to be 0.005 mass% or more.

本発明は、このような実験を通じて知見した事実に基づいて開発した方法である。即ち、本発明は、鉄、クロムおよびニッケル含有原料を電気炉で溶解し、得られた溶鋼をAODおよび/またはVODにて脱炭精錬し、次いで、Al、またはAlとフェロシリコン合金を用いて脱酸することでCrの還元を行ない、その後、生石灰や蛍石を添加すると共にAlを添加してAlの含有量が0.005〜0.2mass%となるようにし、その後、0.05〜2.50mass%のボロン源を添加して、C:0.001〜0.15mass%、Si:0.1〜2mass%、Mn:0.1〜2mass%、Ni:5〜25mass%、Cr:11〜27mass%、B:0.04〜2.48mass%、Al:0.005〜0.2mass%、S:0.005mass%以下を含有し、残部がFeおよび不可避的不純物からなるボロン含有鋼を得ることを特徴とするボロン含有ステンレス鋼の製造方法である。 The present invention is a method developed based on the facts found through such experiments. That is, in the present invention, iron, chromium and nickel-containing raw materials are melted in an electric furnace, the obtained molten steel is decarburized and refined by AOD and / or VOD, and then Al or Al and a ferrosilicon alloy are used. Cr is reduced by deoxidation, and thereafter, quick lime and fluorite are added and Al is added so that the Al content becomes 0.005 to 0.2 mass%, and then 0.05 to 2. A boron source of 50 mass% is added, C: 0.001 to 0.15 mass%, Si: 0.1 to 2 mass%, Mn: 0.1 to 2 mass%, Ni: 5 to 25 mass%, Cr: 11 to 27 mass%, B: 0.04 to 2.48 mass%, Al: 0.005 to 0.2 mass%, S: 0.005 mass% or less, with the balance being Fe and inevitable impurities A method for producing boron-containing stainless steel characterized by obtaining boron-containing steel.

上記のボロン含有ステンレス鋼の製造方法において、
(1)生石灰や蛍石ならびにAl添加後のスラグ組成を、CaO−SiO−Al−MgO−F系のものとすること、
)前記鋼はさらに、Moを0.1〜3mass%を含有するものであること、
がより好ましい製造条件と言える。
In the above method for producing boron-containing stainless steel,
(1) Quick lime, fluorite, and slag composition after addition of Al shall be CaO—SiO 2 —Al 2 O 3 —MgO—F system,
( 2 ) The steel further contains 0.1 to 3 mass% of Mo,
Is a more preferable production condition.

以上説明したような構成を有する本発明によれば、熱間加工性や溶接性に優れると共に、鋼材としたときに良好な表面性状を有するボロン含有ステンレス鋼を低コストで製造することができるようになる。   According to the present invention having the configuration as described above, it is possible to produce a boron-containing stainless steel having excellent surface properties when it is made of steel while being excellent in hot workability and weldability at low cost. become.

また、本発明によれば、有価元素であるボロンの酸化ロスを招くことなく、これを高い歩留りで鋼中に含有させることができるため、ボロン含有ステンレス鋼の製造方法として優れている。   Further, according to the present invention, since it can be contained in steel with high yield without incurring oxidation loss of boron, which is a valuable element, it is excellent as a method for producing boron-containing stainless steel.

以下、ボロン含有ステンレス鋼を製造する本発明方法について説明する。
まず、電気炉にて配合原料を溶解し、引き続きAODおよび/またはVODにて、Arまたは窒素および酸素を吹精して脱炭精錬する。次いで、Al、またはAlとフェロシリコン合金とを添加して脱酸することで、スラグ相に移行した酸化Crを還元する処理を行なう。その後、生石灰や螢石を添加し、さらにAlを添加してAl含有量が0.005〜0.2mass%となるように調整する。最後にFeBなどのボロン源を所定量(0.05〜2.50mass%)添加する。本発明では、鋼中におけるBの最終的な含有量が0.04〜2.48mass%になるように調整する。
Hereinafter, the method of the present invention for producing boron-containing stainless steel will be described.
First, the compounding raw material is melted in an electric furnace, and subsequently, decarburized and refined by blowing Ar, nitrogen and oxygen in AOD and / or VOD. Next, Al or Al and a ferrosilicon alloy are added and deoxidized to perform a process of reducing Cr oxide transferred to the slag phase. Thereafter, quick lime and meteorite are added, and Al is further added to adjust the Al content to 0.005 to 0.2 mass%. Finally, a predetermined amount (0.05 to 2.50 mass%) of a boron source such as FeB is added. In the present invention, the final content of B in the steel is adjusted to be 0.04 to 2.48 mass%.

このような製造方法によれば、予め脱酸が十分に行なわれた後で、ボロンの添加を行なうので、ボロンのスラグへの移行を阻止して高い歩留り、即ち80%以上〜99%超程度まで歩留まらせることができる。なお、本発明方法において、ボロン添加前のスラグ成分は、生石灰および蛍石、必要に応じてAlを添加して、スラグ成分がCaO−SiO−Al−MgO−F系となるように調整する。なお、脱酸処理時に行なうフェロシリコンの投入に当たっては、Siの含有量が0.1mass%以上2mass%以下となるように調整することが好ましい。 According to such a manufacturing method, since boron is added after deoxidation is sufficiently performed in advance, the transfer of boron to slag is prevented, and a high yield, that is, about 80% to over 99%. Can yield up to. In the method of the present invention, the slag component before boron addition is quick lime and fluorite, and if necessary, Al is added so that the slag component becomes a CaO—SiO 2 —Al 2 O 3 —MgO—F system. Adjust to. In addition, when introducing ferrosilicon performed at the time of deoxidation treatment, it is preferable to adjust the Si content to be 0.1 mass% or more and 2 mass% or less.

上記スラグの組成は、特には限定しないが、各酸化物は以下の成分範囲にすることが好ましい。CaO:40〜65mass%、SiO:2〜15mass%、Al:10〜30mass%、MgO:5〜15mass%、F:10mass%以下である。この組成にする理由は、特に脱硫を効果的に進めることができるからである。その他の成分として、FeO、MnO、Cr酸化物、S、P、Bを合計で4mass%以下含有していても、本発明の作用効果を阻害するようなことはない。 The composition of the slag is not particularly limited, but each oxide is preferably in the following component ranges. CaO: 40~65mass%, SiO 2: 2~15mass%, Al 2 O 3: 10~30mass%, MgO: 5~15mass%, F: at most 10 mass%. The reason for this composition is that desulfurization can be effectively advanced. Even if FeO, MnO, Cr oxide, S, P, and B 2 O 3 are contained in a total of 4 mass% or less as other components, the effects of the present invention are not inhibited.

前記のようなスラグ調整をした後、アルゴンガスあるいは窒素ガスを吹き込んで撹拌することにより、前記スラグを使って脱硫を進行させ、硫黄濃度をS≦0.005%に調整する。   After the slag adjustment as described above, argon gas or nitrogen gas is blown in and stirred to advance desulfurization using the slag, and the sulfur concentration is adjusted to S ≦ 0.005%.

本発明方法の実施に当って使用する精錬容器は、耐火物としてマグネシア系耐火物を内張りしたものを用いる。ただし、その耐火物を保護するために、スラグ中にマグネシア煉瓦屑を適宜添加してもよい。また、この製造方法において、AOD炉、VOD鍋あるいは取鍋の耐火物は、特に限定するものではないが、MgO−C系、A1−MgO−C系、ドロマイト系、マグクロ系から適宜選択して使用する。 The smelting vessel used for carrying out the method of the present invention uses a magnesian refractory lined as a refractory. However, in order to protect the refractory, magnesia brick waste may be added as appropriate to the slag. Further, in this manufacturing method, AOD furnace, VOD pan or refractory ladle, is not particularly limited, MgO-C-based, A1 2 O 3 -MgO-C type, dolomite, suitably from Magukuro system Select and use.

このようにして成分調整した溶鋼を、連続鋳造法または普通造塊法により鋳込む。溶鋼の過熱度は、その製造性を考慮して、連続鋳造法の場合10〜60℃、普通造塊法の場合30〜150℃とすることが好ましい。連続鋳造法の場合のタンディッシュ内および普通造塊法の場合のインゴット中は、B、Alといった溶鋼中有効成分の酸化を防止するために、Arあるいは窒素でシールすることが好ましい。その後、連続鋳造または普通造塊法により得られた鋼塊は熱間鍛造し、スラブとする。鋼板は、このようにして得られたスラブを、熱間圧延を施し、その後冷間圧延を施すことにより製造する。   The molten steel whose components have been adjusted in this way is cast by a continuous casting method or a normal ingot casting method. The superheat degree of the molten steel is preferably 10 to 60 ° C. in the case of the continuous casting method and 30 to 150 ° C. in the case of the ordinary ingot casting method in consideration of its manufacturability. In the tundish in the case of the continuous casting method and in the ingot in the case of the ordinary ingot casting method, it is preferable to seal with Ar or nitrogen in order to prevent oxidation of active components in the molten steel such as B and Al. Thereafter, the steel ingot obtained by continuous casting or ordinary ingot casting is hot forged into a slab. The steel sheet is manufactured by subjecting the slab thus obtained to hot rolling and then cold rolling.

なお、前述した本発明に係る製造方法の実施に当たっては、溶解用原料として、例えば、フェロニッケル、純ニッケル、フェロクロム、クロム、鉄屑、ステンレス屑、Fe−Ni合金屑等から適宜に選択して使用する。   In carrying out the manufacturing method according to the present invention described above, the melting raw material is appropriately selected from, for example, ferronickel, pure nickel, ferrochrome, chromium, iron scrap, stainless scrap, Fe-Ni alloy scrap, etc. use.

次に、本発明に係る製造方法を適用することによって得られるボロン含有ステンレス鋼は、以下に述べるような成分組成のものとする。
C:0.001〜0.15mass%
Cは、鋼の強度を確保するために有用な成分であるから、少なくとも0.001mass%は必要である。しかし、このCの含有量が多すぎるとステンレス鋼中でCr炭化物を形成し、耐食性に寄与する有効Cr量を却って減少させてしまう。従って、C含有量は、0.001〜0.15mass%とする。
Next, the boron-containing stainless steel obtained by applying the manufacturing method according to the present invention has a component composition as described below.
C: 0.001 to 0.15 mass%
Since C is a component useful for securing the strength of steel, at least 0.001 mass% is necessary. However, if the C content is too large, Cr carbides are formed in the stainless steel, and the effective Cr amount contributing to the corrosion resistance is reduced. Therefore, the C content is set to 0.001 to 0.15 mass%.

Si:0.1〜2mass%
Siは、脱酸元素であり、溶鋼中の酸素濃度を低下させるために精錬上は少なくとも0.1mass%は必要な成分である。しかし、このSiの含有量が2mass%を超えると、熱間加工性を悪化させる。従って、Si含有量は、0.1〜2mass%とする。
Si: 0.1 to 2 mass%
Si is a deoxidizing element, and at least 0.1 mass% is a necessary component in refining in order to reduce the oxygen concentration in the molten steel. However, when the Si content exceeds 2 mass%, the hot workability is deteriorated. Therefore, the Si content is 0.1 to 2 mass%.

Mn:0.1〜2mass%
Mnは、Siと同様に脱酸元素であり精錬上必要な成分である。しかし、このMn含有量が2mass%を超えると誘導放射能の残留が多くなる。従って、Mnの含有量は0.1〜2mass%とする。
Mn: 0.1 to 2 mass%
Mn, like Si, is a deoxidizing element and a necessary component for refining. However, if the Mn content exceeds 2 mass%, the residual induced radioactivity increases. Therefore, the Mn content is 0.1 to 2 mass%.

Ni:5〜25mass%
Niは、Crとともに、ステンレス鋼としての基本的な成分であり、オーステナイト相を安定させるために必須の成分である。とりわけ、ボロン含有ステンレス鋼においてこのNiは、ボライド中にはほとんど混入せず、ボライド相に消費されないため、5mass%以上でその効果が十分に得られる。一方で、Ni含有量が25mass%を超えると、その効果が飽和するためコスト高になってしまうと共に、鋼の液相線温度の低下を招いて鋳造時に引け巣欠陥などを発生する原因となる。従って、Niの含有量は5〜25mass%とする。好ましくは7〜14mass%がよい。
Ni: 5 to 25 mass%
Ni, together with Cr, is a basic component as stainless steel, and is an essential component for stabilizing the austenite phase. In particular, in the boron-containing stainless steel, this Ni is hardly mixed in the boride and is not consumed in the boride phase, so that the effect is sufficiently obtained at 5 mass% or more. On the other hand, if the Ni content exceeds 25 mass%, the effect is saturated and the cost is increased, and the liquidus temperature of the steel is lowered, causing shrinkage defects during casting. . Therefore, the Ni content is 5 to 25 mass%. Preferably, 7 to 14 mass% is good.

Cr:11〜27mass%
Crは、Niとともにステンレス鋼の基本的な成分であり、鋼表面に耐食性を確保するために必要な不動態皮膜の形成に有効な元素である。しかし、このCrの含有量が27mass%を超えると鋼の脆化が著しくなり実用上好ましくない。従って、Crの含有量は11〜27mass%とする。好ましくは、より優れた耐食性を確保できる18mass%以上を添加する。また、脆化を抑えるには25mass%以下の範囲とする。より好ましくは17〜21mass%がよい。
Cr: 11-27 mass%
Cr is a basic component of stainless steel together with Ni, and is an effective element for forming a passive film necessary for ensuring corrosion resistance on the steel surface. However, if the Cr content exceeds 27 mass%, the steel becomes extremely brittle, which is not preferable for practical use. Therefore, the Cr content is set to 11 to 27 mass%. Preferably, 18 mass% or more that can ensure better corrosion resistance is added. Further, in order to suppress embrittlement, the range is 25 mass% or less. More preferably, 17 to 21 mass% is good.

B:0.04〜2.48mass%
Bは、中性子吸収能のために必要不可欠な元素であり、その多くは鋼中にボライド[(Cr、Fe)2B]の形態で存在する。このBによって中性子吸収能を発現させるためには少なくとも0.04mass%含有させることが必要である。また、Bの含有量は2.48mass%以下であれば、初晶がオーステナイトとなって鋳造時に十分な強度と延性を発現し、割れを発生することがない。ただし、B含有量が、2.48mass%を超えると初晶が[(Cr、Fe)2B]なって鋳造時に割れを引き起こしたり、材料強度や耐摩耗性、加工性を低下させてしまう。従って、Bの含有量は、0.04〜2.48mass%の範囲とする。なお、中性子吸収能を十分に確保するという観点からは、0.2〜2.48mass%の範囲が好ましく、中性子吸収能と加工性の両方を考慮した場合は、0.5〜1.8mass%の範囲がより好ましい。
B: 0.04 to 2.48 mass%
B is an indispensable element for neutron absorption ability, and many of them exist in the form of boride [(Cr, Fe) 2B] in steel. In order for B to exhibit neutron absorption ability, it is necessary to contain at least 0.04 mass%. Further, if the content of B is 2.48 mass% or less, the primary crystal becomes austenite, and sufficient strength and ductility are exhibited at the time of casting, and cracks are not generated. However, if the B content exceeds 2.48 mass%, the primary crystal will be [(Cr, Fe) 2B], causing cracking during casting, and reducing the material strength, wear resistance, and workability. Therefore, the B content is in the range of 0.04 to 2.48 mass%. In addition, from the viewpoint of sufficiently securing the neutron absorption ability, the range of 0.2 to 2.48 mass% is preferable, and when considering both neutron absorption ability and workability, 0.5 to 1.8 mass is preferable. % Range is more preferred.

Al:0.005〜0.2mass%
Alは、本発明では脱酸成分として機能する成分である。このAlの含有量が、0.005mass%未満では、溶鋼の脱酸が不十分となってBの歩留りが80mass%未満となる。逆に、このAlの含有量が0.2mass%を超えると、溶接ビード上に黒点を発生することがある。従って、Alの含有量は、0.005〜0.2mass%とする。
なお、Alの添加に対する前記作用・効果を考えた場合、好ましくは0.01〜0.2mass%の範囲が適当であり、より好ましくは0.015〜0.15mass%の範囲である。
Al: 0.005-0.2 mass%
In the present invention, Al is a component that functions as a deoxidizing component. If the Al content is less than 0.005 mass%, deoxidation of the molten steel is insufficient, and the yield of B is less than 80 mass%. Conversely, if the Al content exceeds 0.2 mass%, black spots may be generated on the weld bead. Therefore, the content of Al is set to 0.005 to 0.2 mass%.
In addition, when the said effect | action and effect with respect to addition of Al are considered, Preferably the range of 0.01-0.2 mass% is suitable, More preferably, it is the range of 0.015-0.15 mass%.

S:0.005mass%以下
Sは、熱間加工性を低下させる成分であるから極力少ないことが望ましい。そのため、Sの含有量は0.005mass%以下とする。
S: 0.005 mass% or less Since S is a component that reduces hot workability, it is desirable that S be as small as possible. Therefore, the content of S is set to 0.005 mass% or less.

Mo:0.1〜3mass%
Moは、Crに比べて約3倍の耐食性付加作用を有し、耐食性の向上にきわめて有効な成分であることから必要に応じて添加する成分である。その耐食性を効果的に向上させるには、少なくとも0.1mass%以上の添加が必要である。しかし、3mass%を超えて添加した場合には脆化することやコスト高となることから好ましくない。従って、Moの含有量は0.1〜3mass%とする。
Mo: 0.1-3 mass%
Mo is a component that is added as necessary because it has an effect of adding corrosion resistance about three times that of Cr and is an extremely effective component for improving the corrosion resistance. In order to effectively improve the corrosion resistance, it is necessary to add at least 0.1 mass% or more. However, it is not preferable to add more than 3 mass% because of embrittlement and high cost. Therefore, the Mo content is set to 0.1 to 3 mass%.

なお、上記した成分以外は、主にFeおよび不可避的不純物で構成される残余成分である。   In addition, the components other than those described above are residual components mainly composed of Fe and inevitable impurities.

この実施例は、容量:60トンの電気炉によって、フェロニッケルや純ニッケル、フェロクロム、鉄屑、ステンレス屑、Fe−Ni合金屑などの中から選択した原料を溶解し、その後、AODおよび/またはVODにて脱炭精錬し、その後、Al、またはAlとFe−Si合金を添加して脱酸することでスラグ中に移行したCrの還元を行ない、次いで、Cr還元後の溶鋼中に生石灰、螢石を添加して、CaO−SiO−Al−MgO−F系スラグを形成させると共に、Alを添加して脱酸、脱硫を行ない、その後、最終的にFeBを添加して所定量のB濃度になるように調節した例である。このようにして溶製した溶鋼を連続鋳造機にて鋳造してスラブを得た後、熱間圧延に続き冷間圧延して板厚5mmのB含有ステンレス鋼板を得た。このようにして得られた冷延鋼板について、以下の評価試験を行ったので、その結果を説明する。 In this example, a raw material selected from ferronickel, pure nickel, ferrochrome, iron scrap, stainless steel scrap, Fe-Ni alloy scrap, etc. is melted by an electric furnace having a capacity of 60 tons, and then AOD and / or Decarburizing and refining with VOD, and then reducing Al transferred to slag by adding Al or Al and Fe-Si alloy and deoxidizing, then, quick lime in molten steel after Cr reduction, A meteorite is added to form a CaO—SiO 2 —Al 2 O 3 —MgO—F slag, and Al is added to perform deoxidation and desulfurization, and finally FeB is added. In this example, the B concentration is adjusted so as to be a fixed amount. The molten steel thus melted was cast with a continuous casting machine to obtain a slab, followed by hot rolling and cold rolling to obtain a B-containing stainless steel plate having a thickness of 5 mm. Since the following evaluation tests were performed on the cold-rolled steel sheet thus obtained, the results will be described.

a.化学成分:得られたB含有ステンレス鋼板から切り出したサンプルについて、酸素、窒素は酸素窒素同時分析装置にて、炭素および硫黄については、炭素硫黄同時分析装置にて分析した。その他の元素については、蛍光X線分析装置を用いて分析した。
b.スラグ組成:取鍋から採取したスラグを粉砕し、圧粉して蛍光X線分析装置を用いて分析した。分析値の合計は100mass%を下回るが、残部としてBやCr酸化物、FeO、P、Sなどを含有している。
c.溶接性:Al濃度が高くなってしまったチャージのみ評価した。電流120A、溶接速度200mm/分の条件でTIG溶接し、ビード上の黒点の有無を目視により評価した。黒点が発生したものは、溶接性が悪いと評価した。
a. Chemical component: About the sample cut out from the obtained B containing stainless steel plate, oxygen and nitrogen were analyzed with the oxygen-nitrogen simultaneous analyzer, and carbon and sulfur were analyzed with the carbon-sulfur simultaneous analyzer. Other elements were analyzed using a fluorescent X-ray analyzer.
b. Slag composition: Slag collected from a ladle was pulverized, compacted, and analyzed using a fluorescent X-ray analyzer. The total analysis value is less than 100 mass%, but contains B 2 O 3 , Cr oxide, FeO, P, S, etc. as the balance.
c. Weldability: Only the charge where the Al concentration became high was evaluated. TIG welding was performed at a current of 120 A and a welding speed of 200 mm / min, and the presence or absence of black spots on the beads was visually evaluated. Those with black spots were evaluated as having poor weldability.

この実施例の結果を表1、表2に示す。これらの表に示すとおり、発明例(No.1〜15)は、ボロンの歩留りが80%以上で84.2〜99.1%と高く、かつスラグの組成も合計で96.6%以上と高く、ボロンの酸化ロスも少なかった。   The results of this example are shown in Tables 1 and 2. As shown in these tables, the inventive examples (Nos. 1 to 15) have a boron yield of 80% or higher and as high as 84.2 to 99.1%, and the composition of the slag is 96.6% or higher in total. The oxidation loss of boron was low.

一方、比較例(No.16〜21、ただし、19を除く)では、Alを添加せずに脱酸したので、ボロンの歩留りが70.0〜72.9と低く、スラグ組成も合計が96%未満でボロンが酸化ロスしていることが見てとれた。さらに、脱酸が不十分なため、S≧0.005mass%と高く熱延工程で、耳割れが発生したり、表面欠陥が発生し、また、溶接時に黒点を発生して問題となった。なお、No.19は逆に、Alを高濃度に添加した例であるが、ボロンの歩留りやS濃度は問題がなかったものの、製品で溶接時に黒点が発生し品質不良を起こしてしまった。   On the other hand, in the comparative examples (No. 16 to 21, except 19), since deoxidation was performed without adding Al, the yield of boron was as low as 70.0 to 72.9, and the total slag composition was 96. It can be seen that boron is oxidatively lost at less than%. Furthermore, since the deoxidation was insufficient, S ≧ 0.005 mass%, which was high in the hot rolling process, an ear crack was generated, surface defects were generated, and black spots were generated during welding, which became a problem. In addition, No. In contrast, No. 19 is an example in which Al is added at a high concentration. However, although there was no problem in the yield of boron and the S concentration, black spots were generated in the product during welding, resulting in poor quality.

本発明に係るB含有ステンレス鋼の製造方法は、主に原子力発電所の使用済み核燃料の貯蔵容器用材料やその遮蔽材料として使用されるステンレス鋼の製造技術であるが、熱間加工性が求められるような二相ステンレス鋼やNi基合金などの分野における代替材料の製造技術としても有効である。   The method for producing B-containing stainless steel according to the present invention is a technique for producing stainless steel mainly used as a material for a storage container of spent nuclear fuel in a nuclear power plant or a shielding material thereof, but requires hot workability. It is also effective as a manufacturing technique for alternative materials in the fields such as duplex stainless steel and Ni-base alloy.

Claims (3)

鉄、クロムおよびニッケル含有原料を電気炉で溶解し、得られた溶鋼をAODおよび/またはVODにて脱炭精錬し、次いで、Al、またはAlとフェロシリコン合金を用いて脱酸することでCrの還元を行ない、その後、生石灰や蛍石を添加すると共にAlを添加してAlの含有量が0.005〜0.2mass%となるようにし、その後、0.05〜2.50mass%のボロン源を添加して、C:0.001〜0.15mass%、Si:0.1〜2mass%、Mn:0.1〜2mass%、Ni:5〜25mass%、Cr:11〜27mass%、B:0.04〜2.48mass%、Al:0.005〜0.2mass%、S:0.005mass%以下を含有し、残部がFeおよび不可避的不純物からなるボロン含有鋼を得ることを特徴とするボロン含有ステンレス鋼の製造方法。 The raw material containing iron, chromium and nickel is melted in an electric furnace, and the obtained molten steel is decarburized and refined by AOD and / or VOD, and then deoxidized using Al or Al and a ferrosilicon alloy to obtain Cr. Then, quick lime or fluorite is added and Al is added so that the Al content is 0.005 to 0.2 mass%, and then boron is 0.05 to 2.50 mass%. C: 0.001 to 0.15 mass%, Si: 0.1 to 2 mass%, Mn: 0.1 to 2 mass%, Ni: 5 to 25 mass%, Cr: 11 to 27 mass%, B : Boron-containing steel containing 0.04 to 2.48 mass%, Al: 0.005 to 0.2 mass%, S: 0.005 mass% or less, the balance being Fe and inevitable impurities A process for producing boron-containing stainless steel. 生石灰や蛍石ならびにAl添加後のスラグ組成を、CaO−SiO−Al−MgO−F系のものとすることを特徴とする請求項1に記載のボロン含有ステンレス鋼の製造方法。 The slag composition of quicklime and fluorite and Al after addition, CaO-SiO 2 -Al 2 O 3 production method of the boron-containing stainless steel of claim 1, characterized in that as the -MgO-F system. 前記鋼はさらに、Moを0.1〜3mass%を含有するものであることを特徴とする請求項1に記載のボロン含有ステンレス鋼の製造方法。 The method for producing a boron-containing stainless steel according to claim 1, wherein the steel further contains 0.1 to 3 mass% of Mo.
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