JP2002167647A - Si KILLED STEEL HAVING EXCELLENT FATIGUE STRENGTH AND ITS PRODUCTION METHOD - Google Patents
Si KILLED STEEL HAVING EXCELLENT FATIGUE STRENGTH AND ITS PRODUCTION METHODInfo
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- JP2002167647A JP2002167647A JP2000359368A JP2000359368A JP2002167647A JP 2002167647 A JP2002167647 A JP 2002167647A JP 2000359368 A JP2000359368 A JP 2000359368A JP 2000359368 A JP2000359368 A JP 2000359368A JP 2002167647 A JP2002167647 A JP 2002167647A
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Abstract
Description
【0001】[0001]
【発明の属する技術分野】本発明は、従来の鋼と比較し
て、有害な大型介在物が少なく、しかも残留した介在物
も延性のある介在物であり、かつその介在物は微細に分
散されたものであり、疲労強度に優れたSi脱酸鋼およ
びその製造方法に関する。BACKGROUND OF THE INVENTION The present invention relates to a steel according to the present invention, which has less harmful large inclusions than conventional steels, and furthermore, the remaining inclusions are ductile inclusions, and the inclusions are finely dispersed. The present invention relates to a Si deoxidized steel excellent in fatigue strength and a method for producing the same.
【0002】[0002]
【従来の技術】Si脱酸鋼は、Siが鋼材としての必要
成分であると同時に、溶鋼中での酸素との親和力が大き
く鋼を脱酸する機能を有することから、強脱酸元素を含
有しない鋼に脱酸材として広く用いられている。2. Description of the Related Art Si-deoxidized steel contains a strongly deoxidized element because Si is a necessary component as a steel material and, at the same time, has a large affinity for oxygen in molten steel and has a function of deoxidizing steel. Widely used as a deoxidizer for steel that does not.
【0003】一般にSi脱酸鋼は、鋼中のSi濃度がA
l脱酸鋼のAl濃度と比較して数倍ないし数十倍高い。
また、Si脱酸鋼は、Al脱酸鋼よりも全酸素濃度が高
くなるが、介在物組成の制御が可能であるという利点が
ある。この利点を生かして、疲労強度向上に有害な介在
物の生成を抑制することが広く行われている。[0003] In general, Si deoxidized steel has an Si concentration of A
1 It is several times to several tens times higher than the Al concentration of deoxidized steel.
In addition, Si deoxidized steel has a higher total oxygen concentration than Al deoxidized steel, but has the advantage that the inclusion composition can be controlled. Taking advantage of this advantage, it has been widely practiced to suppress the generation of inclusions harmful to the improvement of fatigue strength.
【0004】[0004]
【発明が解決しようとする課題】例えば、特公昭54−
7252号公報には、線材用高炭素Si脱酸鋼中のSi
O2 −MnO−Al2 O3 系の3元系非金属介在物を低
融点のスペサタイト領域に制御する技術が開示されてい
る。この技術は、介在物を低融点化することにより、熱
間圧延段階での介在物の伸展性を向上させ、線材加工時
の伸線性を良好にするものである。しかしながら、この
技術は全酸素濃度が高く介在物量が多いという問題があ
る。[Problems to be solved by the invention] For example,
No. 7252 discloses that Si in a high carbon Si deoxidized steel for a wire is used.
O 2 -MnO-Al 2 O 3 based techniques for controlling the ternary nonmetallic inclusions Supesataito region of the low melting point is disclosed. This technique improves the extensibility of inclusions in the hot rolling step by lowering the melting point of the inclusions and improves the drawability during wire processing. However, this technique has a problem that the total oxygen concentration is high and the amount of inclusions is large.
【0005】また、特公昭58−56021号公報に
は、線材用の高炭素Si脱酸鋼中の全酸素濃度が50重
量ppm以下、非粘性介在物インデックスが15以下、
および介在物組成が硬度の低いロードナイト質を含む複
合酸化物からなることを特徴とする清浄鋼が開示されて
いる。しかしながら、この発明でのSi脱酸鋼中の全酸
素濃度は30〜45ppmと高い水準にとどまってい
る。Japanese Patent Publication No. 58-56021 discloses that the total oxygen concentration in a high carbon Si deoxidized steel for a wire is 50 ppm by weight or less, the non-viscous inclusion index is 15 or less,
Further, a clean steel characterized in that the inclusion composition is composed of a composite oxide containing rhodonite having a low hardness is disclosed. However, the total oxygen concentration in the Si deoxidized steel according to the present invention is as high as 30 to 45 ppm.
【0006】さらに、特公平6−74484号公報に
は、介在物を無害化するという観点から介在物の長さ
(l)と幅(d)のアスペクト比(l/d)が5以下
で、組成がSiO2 :20〜60%、MnO:10〜8
0%、およびCaO:50%以下、MgO:15%以下
の介在物であることを特徴とする冷間加工性および疲労
特性に優れた高清浄鋼が提案されている。また、特公平
6−74485号公報には、同じアスペクト比で、組成
がSiO2 :35〜75%、Al2 O3 :30%以下、
CaO:50%以下、MgO:25%以下からなる介在
物であることを特徴とする冷間加工性および疲労特性に
優れた高清浄鋼が提案されている。これらは、熱間圧延
で残存している介在物であっても、その段階での形状と
組成を限定することにより、大型の有害介在物が存在す
る割合を小さくする技術と言える。しかしながら、これ
らの技術は、介在物低減には限界があり、疲労特性の向
上にも限界があった。Furthermore, Japanese Patent Publication No. 6-74484 discloses that from the viewpoint of detoxifying inclusions, the aspect ratio (l / d) of the length (l) and width (d) of the inclusion is 5 or less, composition of SiO 2: 20~60%, MnO: 10~8
A high clean steel excellent in cold workability and fatigue properties characterized by inclusions of 0%, CaO: 50% or less, and MgO: 15% or less has been proposed. Japanese Patent Publication No. 6-74485 discloses that the composition is SiO 2 : 35 to 75%, Al 2 O 3 : 30% or less at the same aspect ratio.
A highly clean steel excellent in cold workability and fatigue properties, characterized by inclusions of CaO: 50% or less and MgO: 25% or less, has been proposed. These can be said to be techniques for reducing the proportion of large harmful inclusions by limiting the shape and composition at that stage even if the inclusions remain during hot rolling. However, these techniques have a limit in reducing inclusions and a limit in improving fatigue characteristics.
【0007】特公平4−8499号公報には、介在物を
さらに延性なものとする方法として、全酸素量、非粘性
介在物インデックスを規定し、さらに介在物成分のうち
SiO2 、MnO、MgO、Al2 O3 、CaO、Ti
O2 組成を限定するとともに、さらにその他酸化物とし
てV、Ba、Zr、Naの酸化物および不可避的に混入
する酸化物を5%以下に制御した技術が提案されてい
る。この技術は、非粘性介在物組成を制御するために全
酸素濃度を15ppm以上とする必要があるため、介在
物量そのものを減じる、あるいは微細化するという機能
はない。In Japanese Patent Publication No. 4-8499, as a method for making inclusions more ductile, the total oxygen content and the non-viscous inclusion index are specified, and among the inclusion components, SiO 2 , MnO and MgO are included. , Al 2 O 3 , CaO, Ti
A technique has been proposed in which the composition of O 2 is limited and oxides of V, Ba, Zr, and Na and oxides inevitably mixed are controlled to 5% or less as other oxides. In this technique, since the total oxygen concentration needs to be 15 ppm or more in order to control the composition of the non-viscous inclusion, there is no function of reducing the amount of the inclusion itself or miniaturizing it.
【0008】特許2654099号公報には、Si脱酸
剤とアルカリ金属化合物を添加することにより、脱酸生
成物をアルカリ金属含有組成にコントロールする清浄鋼
の製造法が開示され、この方法によれば介在物にアルカ
リ金属化合物量を4〜24%含有させることにより、
7.5μm以上の大型介在物量を減少させることができ
るとしている。この大型介在物が減少する理由は、アル
カリ金属化合物によるアルミナ系およびシリカ系介在物
の延性化により圧延過程で微細化されるためである。し
かしこの方法では、脱酸生成物に起因する介在物の組成
制御が考慮されていないことから、より有害なアルミナ
系介在物そのものを減ずるものではなく、しかもこれは
安定な酸化物であるため、容易には組成変化し難く、し
たがって非延性な組成で残存するおそれがある。また、
この方法はアルカリ金属化合物を直接溶鋼に添加するの
で、アルカリ金属の蒸発やそれによる発煙といった製造
法上の問題が避けられない。Japanese Patent No. 2654099 discloses a method for producing a clean steel in which a deoxidation product is controlled to an alkali metal-containing composition by adding a Si deoxidizing agent and an alkali metal compound. By allowing the inclusion to contain 4 to 24% of the alkali metal compound,
It is stated that the amount of large inclusions of 7.5 μm or more can be reduced. The reason why the large inclusions are reduced is that the alumina-based and silica-based inclusions are made ductile by the alkali metal compound to be refined in the rolling process. However, this method does not reduce the more harmful alumina-based inclusions themselves because the composition control of inclusions caused by deoxidation products is not considered, and since this is a stable oxide, The composition is difficult to change easily, and therefore, there is a possibility that the composition may remain in a non-ductile composition. Also,
In this method, since the alkali metal compound is directly added to the molten steel, problems in the production method such as evaporation of the alkali metal and fuming due to the evaporation are inevitable.
【0009】本発明は、従来の鋼と比較して、有害な大
型介在物が少なく、しかも残留した介在物も延性のある
介在物であり、かつその介在物は微細に分散されたもの
であり、疲労強度に優れたSi脱酸鋼およびその製造方
法を提供することにある。According to the present invention, as compared with conventional steel, there are fewer harmful large inclusions, and the remaining inclusions are ductile inclusions, and the inclusions are finely dispersed. Another object of the present invention is to provide a Si deoxidized steel excellent in fatigue strength and a method for producing the same.
【0010】[0010]
【課題を解決するための手段】本発明者は、有害な大型
介在物の生成を抑制する等の検討を重ねた結果、下記の
知見を得た。Means for Solving the Problems The present inventor has made the following findings as a result of repeated studies on suppressing generation of harmful large inclusions.
【0011】(A)大型介在物の生成を防ぐには、介在
物量を抑制するとともに介在物を微細に分散させること
が有効である。微細な介在物が安定であるためには、溶
鉄との界面エネルギーが低いものが望ましく、介在物中
のFeO、MnO濃度が高いものが良いと推察される。
しかしながら、介在物中でのこれらのFeO、MnO濃
度が高くなると、溶鋼中の酸素ポテンシャルが高くな
り、介在物量の増加をまねくという問題を生じる。(A) In order to prevent the formation of large inclusions, it is effective to suppress the amount of inclusions and finely disperse the inclusions. In order for the fine inclusions to be stable, those having low interface energy with molten iron are desirable, and those having high concentrations of FeO and MnO in the inclusions are presumed to be good.
However, when the concentrations of FeO and MnO in the inclusions increase, the oxygen potential in the molten steel increases, which causes a problem of increasing the amount of inclusions.
【0012】(B)延性のある介在物とするには、Si
O2 を基本組成とする必要があるので、SiO2 が主体
の介在物で、それら介在物の微細化を図るために、アル
カリ金属:R(R= Na、K、Li)の酸化物(以下、
R2 Oともいう)を含有させればよいと着想した。(B) In order to make ductile inclusions, Si
Since it is necessary to use O 2 as a basic composition, the inclusions are mainly composed of SiO 2 , and in order to reduce the size of the inclusions, an oxide of an alkali metal: R (R = Na, K, Li) (hereinafter referred to as “O”) is used. ,
R 2 O).
【0013】すなわち、SiO2 系介在物にR2 Oが含
まれている状態は、FeOやMnOが含まれている状態
に比べて溶鋼温度域で熱力学的により安定であり、溶鋼
との平衡酸素ポテンシャルが低い。一方、CaO、Al
2 O3 およびMgOと比較すると、R2 Oは溶鋼温度域
で熱力学的により不安定であるため、SiO2 系介在物
にR2 Oが含まれている状態は、SiO2 系介在物にC
aO、Al2 O3 およびMgOが含まれている状態に比
較して溶鋼との反応性が高くなるため、界面エネルギー
が低くなる。この界面エネルギーの低下効果により、R
2 Oが含まれているSiO2 系介在物は微細化が可能と
なる。この結果、介在物起因の疲労強度の低下要因が低
減され、疲労強度に優れたSi脱酸鋼が得られる。That is, the state in which R 2 O is contained in the SiO 2 -based inclusions is more thermodynamically stable in the temperature range of the molten steel than the state in which FeO or MnO is contained, and the equilibrium with the molten steel is obtained. Low oxygen potential. On the other hand, CaO, Al
Compared to 2 O 3 and MgO, for R 2 O is unstable thermodynamically more at the molten steel temperature range, the state of the SiO 2 type inclusions contain the R 2 O is the SiO 2 inclusions C
Since the reactivity with molten steel is higher than in the state containing aO, Al 2 O 3 and MgO, the interface energy is low. Due to this effect of lowering the interface energy, R
SiO 2 -based inclusions containing 2 O can be miniaturized. As a result, the cause of the decrease in fatigue strength due to inclusions is reduced, and Si-deoxidized steel excellent in fatigue strength is obtained.
【0014】(C)このような良好な介在物を含有する
Si脱酸鋼は、取鍋精錬におけるスラグ組成を適正な組
成に制御することにより得られる。本発明は、以上の知
見に基づいてなされたもので、その要旨は、下記のとお
りである。(C) The Si deoxidized steel containing such good inclusions can be obtained by controlling the slag composition in ladle refining to an appropriate composition. The present invention has been made based on the above findings, and the gist is as follows.
【0015】(1)質量%でAl:0.003%以下、
Ti:0.003%以下、Zr:0.0010%以下お
よびSi:0.05〜4.0%含有するSi脱酸鋼であ
って、かつ該Si脱酸鋼中の介在物が質量%でSi
O2 :45%以上、アルカリ金属R(R= Na、K、L
i)の酸化物(R2 O):0.5〜10%含有すること
を特徴とする疲労強度に優れたSi脱酸鋼。(1) Al: not more than 0.003% by mass%
A Si deoxidized steel containing 0.003% or less of Ti, 0.0010% or less of Zr, and 0.05 to 4.0% of Si, and the inclusions in the Si deoxidized steel are expressed in mass%. Si
O 2 : 45% or more, alkali metal R (R = Na, K, L
i oxide) (R 2 O): Excellent Si-deoxidized steel in fatigue strength, characterized in that it contains 0.5% to 10%.
【0016】(2)前記Si脱酸鋼が、更に、C:1.
2%以下、Mn:0.20〜1.50%、O:0.00
20%以下含有することを特徴とする上記(1)に記載
の疲労強度に優れたSi脱酸鋼。(2) The Si deoxidized steel further comprises C: 1.
2% or less, Mn: 0.20 to 1.50%, O: 0.00
The Si-deoxidized steel having excellent fatigue strength according to the above (1), which contains 20% or less.
【0017】(3)前記Si脱酸鋼が、更に、C:1.
2%以下、Mn:0.20〜1.50%、O:0.00
20%以下、Cr:0.05〜2.0%含有することを
特徴とする上記(1)に記載の疲労強度に優れたSi脱
酸鋼。(3) The Si deoxidized steel further comprises C: 1.
2% or less, Mn: 0.20 to 1.50%, O: 0.00
The Si-deoxidized steel having excellent fatigue strength according to the above (1), which contains 20% or less and Cr: 0.05 to 2.0%.
【0018】(4)前記Si脱酸鋼が、更に、C:0.
15%以下、Mn:0.1〜2.0%、Cr:4〜20
%、O:0.0080%以下含有することを特徴とする
上記(1)に記載の疲労強度に優れたSi脱酸鋼。(4) The above-mentioned Si deoxidized steel further contains C: 0.
15% or less, Mn: 0.1 to 2.0%, Cr: 4 to 20
%, O: 0.0080% or less, wherein the Si-deoxidized steel having excellent fatigue strength according to the above (1).
【0019】(5)上記(1)〜(4)のいずれかに記
載のSi脱酸鋼を製造する方法であって、精錬炉から取
鍋に出鋼するときにSi脱酸を行い、その後の取鍋スラ
グ精錬時のスラグ組成を質量%でCaO:20〜45
%、SiO2 :25〜60%、MgO:5〜18%、A
l2 O3 :1〜12%、MnO:0.2〜8%、アルカ
リ金属R(R= Na、K、Li)の酸化物(R2 O):
0.5〜10%とすることを特徴とする疲労強度に優れ
たSi脱酸鋼の製造方法。(5) A method for producing Si deoxidized steel according to any one of the above (1) to (4), wherein the Si is deoxidized when the steel is discharged from the refining furnace to the ladle. Ladle slag refining slag composition in mass% CaO: 20-45
%, SiO 2: 25~60%, MgO: 5~18%, A
l 2 O 3: 1~12%, MnO: 0.2~8%, alkali metal R (R = Na, K, Li) oxide (R 2 O):
A method for producing Si deoxidized steel having excellent fatigue strength, characterized in that the content is 0.5 to 10%.
【0020】[0020]
【発明の実施の形態】介在物中の(SiO2 )濃度が4
5質量%(以下、単に%で質量%を表す)以上であれ
ば、非延性で有害なAl2 O3 系介在物、MgO・Al
2 O3 系介在物およびMgO系介在物の生成確率は確実
に減少する。望ましい介在物中の(SiO2 )濃度は7
0%以上である。BEST MODE FOR CARRYING OUT THE INVENTION The (SiO 2 ) concentration in inclusions is 4
If it is 5% by mass or more (hereinafter simply expressed as% by mass), it is non-ductile and harmful Al 2 O 3 -based inclusion, MgO · Al
The generation probability of 2 O 3 -based inclusions and MgO-based inclusions is definitely reduced. The preferred inclusion (SiO 2 ) concentration is 7
0% or more.
【0021】このように介在物中の(SiO2 )濃度が
45%以上と高い介在物は、圧延長手方向に著しく延伸
した形状ではないが、オーバルな鋭角のない形状であ
り、微細である限りにおいては、疲労強度に悪影響を及
ぼしにくい。As described above, the inclusions having a high (SiO 2 ) concentration of 45% or more in the inclusions are not remarkably elongated in the longitudinal direction of the rolling, but are fine without oval acute angles. As far as possible, it does not easily affect the fatigue strength.
【0022】しかしながら、単に(SiO2 )濃度が高
い介在物が主体となった場合、これが10μm以上の幅
を有する大きなものであれば、疲労強度に悪影響を及ぼ
す可能性が高い。また、(SiO2 )濃度が高い介在物
組成に制御すること自体は、介在物径を減少させる効果
はないし、また、(SiO2 )濃度が極端に高い介在物
は熱間圧延加工での延伸効果が期待できず、10μm以
上の幅を有する介在物が圧延加工後でも存在する確率が
高い。However, in the case where only inclusions having a high (SiO 2 ) concentration are mainly used, if the inclusions are large having a width of 10 μm or more, there is a high possibility of adversely affecting the fatigue strength. Controlling the composition of the inclusions having a high (SiO 2 ) concentration has no effect of reducing the diameter of the inclusions, and inclusions having an extremely high (SiO 2 ) concentration are stretched by hot rolling. No effect can be expected, and there is a high probability that inclusions having a width of 10 μm or more exist even after rolling.
【0023】そこで、この10μm以上の幅を有するS
iO2 系介在物の生成を防ぐために、介在物を微細に分
散させる条件について、脱酸過程での溶鋼−酸化物間の
界面エネルギーから検討すると、Si脱酸鋼で一般的な
SiO2 −CaO−Al2 O 3 系介在物よりも、FeO
やMnO濃度の高い介在物の方が微細に分散させるのに
有利となる。Therefore, the S having a width of 10 μm or more is
iOTwoInclusions are finely divided to prevent the formation of system inclusions.
The conditions for dispersing, between molten steel and oxide during the deoxidation process
Considering from the interfacial energy, the general characteristics of Si deoxidized steel
SiOTwo-CaO-AlTwoO ThreeFeO rather than system inclusions
And inclusions with high MnO concentration can be finely dispersed
This is advantageous.
【0024】しかしながら、FeOやMnO濃度の高い
介在物を生成させるには、溶鋼中のSi濃度を低く抑え
る必要があり、多くのSi脱酸鋼には適用できず、また
弱脱酸になることから介在物個数はむしろ増加する。However, in order to generate inclusions having a high concentration of FeO or MnO, it is necessary to suppress the Si concentration in the molten steel to a low level. Therefore, the number of inclusions increases rather.
【0025】そこで、SiO2 系介在物に、介在物を微
細に分散させるのに有利になると考えられる強塩基性の
アルカリ金属酸化物(R2 O、R= Li、Na、K)を
含有させることを前述の通り着想した。Therefore, a strongly basic alkali metal oxide (R 2 O, R = Li, Na, K), which is considered to be advantageous for finely dispersing the inclusions, is contained in the SiO 2 -based inclusions. This was conceived as described above.
【0026】以下に、この着想を確認するために実施し
た模擬実験結果を示す。取鍋スラグ精錬を模擬すること
ができる雰囲気調整炉を用いて、種々のSi脱酸鋼を1
500〜1560℃で溶解した。The results of a simulation experiment conducted to confirm this idea will be described below. Using an atmosphere control furnace that can simulate ladle slag refining, various Si deoxidized steel
Melted at 500-1560 ° C.
【0027】溶鋼を[C]:0.70%、[Mn]:
0.25%にそれぞれ成分調整後、所定成分のスラグを
添加し、取鍋スラグ精錬を行い、溶鋼温度を1500〜
1560℃に保持した後、スラグが混入しないように炉
を傾動して得られた溶鋼を鋳造した。このようにして得
られた鋼塊(大きさ:220mmφ×500mm、質
量:150kg)を65mmφまで鍛圧し、さらに5.
5mmφまで圧延加工した。[C]: 0.70% of molten steel, [Mn]:
After adjusting each component to 0.25%, slag of a predetermined component is added, ladle slag refining is performed, and the molten steel temperature is set to 1500 to 1500.
After maintaining at 1560 ° C., the molten steel obtained by tilting the furnace so as not to mix slag was cast. The steel ingot (size: 220 mmφ × 500 mm, mass: 150 kg) thus obtained was forged to 65 mmφ.
It was rolled to 5 mmφ.
【0028】スラグの生成は、CaO−SiO2 −Mg
O−Al2 O3 −Na2 O系を基本とするフラックスを
対象溶鋼質量kgあたり15g使用して行い、スラグ中
のNa2 O濃度を8%とした。The slag is formed by CaO—SiO 2 —Mg
O-Al 2 O 3 -Na 2 O based flux was carried out with 15g used per target molten steel mass kg which is based, it was 8% of concentration of Na 2 O in the slag.
【0029】圧延加工した試料から、長手方向断面に切
断、鏡面研磨して、内在する幅1μm以上の酸化物系介
在物を調査した。調査した酸化物系介在物は、すべて単
独または硫化物と複合した形態であり、組成については
そのうちの酸化物部分をエネルギー分散型X線マイクロ
アナライザで分析した。The rolled sample was cut into a longitudinal section, mirror-polished, and an internal oxide-based inclusion having a width of 1 μm or more was examined. The investigated oxide-based inclusions were all in the form of a single compound or a complex with a sulfide, and the oxide portion of the composition was analyzed with an energy dispersive X-ray microanalyzer.
【0030】図1は、鋼中の[Al]濃度と介在物中の
(SiO2 )濃度との関係を示すグラフである。なお、
図中の●値は、観察した介在物(n= 30〜40)中の
(SiO2 )濃度の平均値を、図中のエラーバーは、観
察した介在物(n= 30〜40)中の最大値と最小値を
それぞれ示す(以下の図2〜5および8も同様)。FIG. 1 is a graph showing the relationship between the [Al] concentration in steel and the (SiO 2 ) concentration in inclusions. In addition,
The ● values in the figure indicate the average values of the (SiO 2 ) concentration in the observed inclusions (n = 30 to 40), and the error bars in the figures indicate the values in the observed inclusions (n = 30 to 40). The maximum value and the minimum value are shown (the same applies to FIGS. 2 to 5 and 8 below).
【0031】同図に示すように、鋼中の[Al]濃度が
0.003%以下で介在物中の(SiO2 )濃度が45
%以上となる。また、鋼中の[Al]濃度が0.001
%以下で介在物中の(SiO2 )濃度が70%以上とな
る。As shown in the figure, the [Al] concentration in the steel is 0.003% or less and the (SiO 2 ) concentration in the inclusion is 45%.
% Or more. [Al] concentration in steel is 0.001.
% Or less, the (SiO 2 ) concentration in the inclusion becomes 70% or more.
【0032】図2は、鋼中の[Ti]濃度と介在物中の
(SiO2 )濃度との関係を示すグラフである。同図に
示すように、鋼中の[Ti]濃度が0.003%以下で
介在物中の(SiO2 )濃度が45%以上となる。ま
た、鋼中の[Ti]濃度が0.001%以下で介在物中
の(SiO2 )濃度が70%以上となる図3は、鋼中の
[Zr]濃度と介在物中の(SiO2 )濃度との関係を
示すグラフである。FIG. 2 is a graph showing the relationship between the [Ti] concentration in steel and the (SiO 2 ) concentration in inclusions. As shown in the figure, when the [Ti] concentration in the steel is 0.003% or less, the (SiO 2 ) concentration in the inclusion becomes 45% or more. Also, Figure 3 is [Ti] concentration in the steel (SiO 2) concentration in inclusions in 0.001% or less is 70% or more, in the steel [Zr] concentration and inclusions of (SiO 2 4) is a graph showing the relationship with the concentration.
【0033】同図に示すように、鋼中の[Zr]濃度が
0.0010%以下で介在物中の(SiO2 )濃度が4
5%以上となる。また、鋼中の[Zr]濃度が0.00
02%以下で介在物中の(SiO2 )濃度が70%以上
となる次に、[Al]≦0.003%、[Ti]≦0.
003%および[Zr]≦0.0010%である鋼を使
用して、[Si]濃度を0.03%から4.4%の範囲
に調整し、そのときの加工試料中に観察される介在物中
の(SiO2 )濃度および(Na2 O濃度)を分析し
た。As shown in the figure, the [Zr] concentration in the steel is 0.0010% or less and the (SiO 2 ) concentration in the inclusion is 4%.
It becomes 5% or more. [Zr] concentration in steel is 0.00
When the content of (SiO 2 ) in the inclusions is 70% or more when the content is 02% or less, [Al] ≦ 0.003% and [Ti] ≦ 0.
Using steel with 003% and [Zr] ≦ 0.0010%, the [Si] concentration was adjusted in the range of 0.03% to 4.4%, and the intervening observed in the processed sample at that time. The (SiO 2 ) concentration and (Na 2 O concentration) in the product were analyzed.
【0034】図4は、鋼中の[Si]濃度と介在物中の
(SiO2 )濃度との関係を示すグラフである。なお、
図中の●は、スラグにNa2 Oを8%配合したときの試
験結果を、○はNa2 Oを無添加としたときの試験結果
を、それぞれ示す。FIG. 4 is a graph showing the relationship between the [Si] concentration in steel and the (SiO 2 ) concentration in inclusions. In addition,
In the figure, ● indicates the test result when 8% of Na 2 O was added to the slag, and ○ indicates the test result when Na 2 O was not added.
【0035】同図に示すように、スラグにNa2 Oの添
加有無に関係なく、鋼中の[Si]濃度が0.05〜
4.0%の範囲において、介在物中の(SiO2 )濃度
が45%以上となる。As shown in the figure, regardless of whether Na 2 O is added to the slag, the [Si] concentration in the steel is 0.05 to
In the range of 4.0%, the (SiO 2 ) concentration in the inclusion becomes 45% or more.
【0036】図5は、鋼中の[Si]濃度と介在物中の
(Na2 O)濃度との関係を示すグラフである。なお、
図中の●は、スラグにNa2 Oを8%配合したときの試
験結果を、□はNa2 Oを無添加としたときの試験結果
を、それぞれ示す。FIG. 5 is a graph showing the relationship between the [Si] concentration in steel and the (Na 2 O) concentration in inclusions. In addition,
In the figure, ● indicates the test results when 8% of Na 2 O was added to the slag, and □ indicates the test results when Na 2 O was not added.
【0037】同図に示すように、スラグにNa2 Oを8
%配合すると、鋼中の[Si]濃度が0.05〜4.0
%の範囲において、介在物中の(Na2 O)濃度が0.
5%以上となる。As shown in the figure, the Na 2 O in the slag 8
%, The [Si] concentration in the steel is 0.05 to 4.0.
%, The (Na 2 O) concentration in the inclusions is 0.1%.
It becomes 5% or more.
【0038】次に、[C]:0.70%、[Si]:
0.25%、[Mn]:0.50%、[Al]:0.0
004%、[Ti]:0.0004%、[Zr]:0.
0001%以下の鋼組成を有し、かつ介在物中の(Na
2 O)濃度が3.2〜3.6%を有するものについて、
SiO2 濃度が42%、54%および75%の3水準の
試料を作製し、前記の通り5.5mmφまで圧延加工し
た。Next, [C]: 0.70%, [Si]:
0.25%, [Mn]: 0.50%, [Al]: 0.0
004%, [Ti]: 0.0004%, [Zr]: 0.
0001% or less steel composition and (Na
For those 2 O) concentration has a 3.2 to 3.6 percent,
Samples with three levels of SiO 2 concentration of 42%, 54% and 75% were prepared and rolled to 5.5 mmφ as described above.
【0039】図6は、圧延方向断面における介在物の幅
の大きさとその度数分布との関係を示すグラフである。
なお、図中横軸に記載の例えば1〜2とは1〜2μm未
満を示し、2〜4とは2〜4μm未満をそれぞれ示す。FIG. 6 is a graph showing the relationship between the size of the inclusion width in the cross section in the rolling direction and its frequency distribution.
In addition, for example, 1-2 described on the horizontal axis in the drawing indicates less than 1-2 μm, and 2-4 indicates less than 2-4 μm, respectively.
【0040】同図に示すように、介在物中の(Si
O2 )濃度が42%では、Na2 Oを含有していても8
μm以上の介在物が有るのに対し、SiO2 濃度が54
%では、8μm未満となり、75%では6μm未満であ
り、介在物が微細化する。As shown in FIG.
O 2 ) at a concentration of 42%, even if Na 2 O is contained,
μm or more, while the SiO 2 concentration is
%, It is less than 8 μm, and at 75%, it is less than 6 μm, and the inclusions are finer.
【0041】同様に上記鋼組成で、介在物の組成が(S
iO2 )70%以上で、(Na2 O)濃度が0.3%、
1.8%、3.6%、9.7%の4水準の試料を作製
し、前記の通り5.5mmφまで圧延加工した。Similarly, in the above steel composition, the composition of the inclusion is (S
iO 2 ) 70% or more, (Na 2 O) concentration 0.3%,
Samples of four levels of 1.8%, 3.6% and 9.7% were prepared and rolled to 5.5 mmφ as described above.
【0042】図7は、介在物中の(Na2 O)濃度をパ
ラメータとした圧延方向断面における介在物の幅の大き
さとその度数分布との関係を示すグラフである。同図に
示すように、介在物中の(Na2 O)濃度が0.3%で
は、8μm以上の介在物が有るのに対し、(Na2 O)
濃度が1.8%では、8μm未満となり、3.6重量以
上%では6μm未満であり、介在物が微細化する。FIG. 7 is a graph showing the relationship between the width of the inclusions in the cross section in the rolling direction and the frequency distribution thereof with the (Na 2 O) concentration in the inclusions as a parameter. As shown in the figure, when the concentration of (Na 2 O) in inclusions is 0.3%, inclusions of 8 μm or more are present, while (Na 2 O)
When the concentration is 1.8%, the concentration is less than 8 μm, and when the concentration is 3.6% by weight or more, the concentration is less than 6 μm.
【0043】さらに、詳しく介在物中のアルカリ金属酸
化物の濃度について試験検討したところ、アルカリ金属
酸化物の濃度は、0.5%以上で望ましくは3%以上で
介在物を微細に分散させる効果が認められた。Furthermore, when the concentration of the alkali metal oxide in the inclusions was examined in detail, the concentration of the alkali metal oxide was 0.5% or more, preferably 3% or more, and the effect of finely dispersing the inclusions was obtained. Was observed.
【0044】しかし、その介在物を微細に分散させる効
果は約10%で飽和する。一方、アルカリ金属酸化物
は、溶鋼脱酸が生じるような還元性雰囲気下で分解しや
すくなり、その結果、介在物中に約10%を越えるアル
カリ金属酸化物を安定して維持させることは困難とな
る。However, the effect of finely dispersing the inclusions is saturated at about 10%. On the other hand, alkali metal oxides are easily decomposed in a reducing atmosphere where deoxidation of molten steel occurs, and as a result, it is difficult to stably maintain more than about 10% of alkali metal oxides in inclusions. Becomes
【0045】本発明の優れた点は、Si脱酸鋼のSiO
2 系介在物中にアルカリ金属酸化物を含有させれば、さ
まざまな鋼種に適用が可能となることである。そこで、
本発明を使用できる望ましい鋼種について以下に述べ
る。An excellent point of the present invention is that the SiO deoxidized steel is made of SiO.
If an alkali metal oxide is contained in the second inclusion, it can be applied to various steel types. Therefore,
Preferred steel types in which the present invention can be used are described below.
【0046】その一には、C:1.20%以下、Mn:
0.10%〜1.50%、およびO:0.0020%以
下の組成を基本とする高炭素Si脱酸鋼が望ましい。C
濃度の上限を1.20%とした理由は、1.20%を越
えると鋼自体が脆化し加工性が悪化するとともに、アル
カリ金属酸化物が溶鋼中の炭素によって分解しやすくな
るおそれがあるからである。One of them is that C: 1.20% or less, Mn:
High carbon Si deoxidized steel based on a composition of 0.10% to 1.50% and O: 0.0020% or less is desirable. C
The reason for setting the upper limit of the concentration to 1.20% is that if it exceeds 1.20%, the steel itself becomes brittle and the workability is deteriorated, and the alkali metal oxide may be easily decomposed by the carbon in the molten steel. It is.
【0047】下限は特に限定されるものではないが、鋼
材強度を適度に保つには0.05%以上とすることが望
ましい。Mn濃度の上限を1. 5%とした理由は、Mn
濃度が高くなるとSi−Mn複合脱酸の影響が現れ始
め、Mn濃度が1.5%を越えると介在物中のMnO濃
度が10%を越えて、介在物中のSiO2 濃度が70%
以上となることが困難となるおそれがあるからである。
下限は介在物制御の観点から特にないが、鋼材の強度等
を鑑みれば、0.20%以上とすることが望ましい。Although the lower limit is not particularly limited, it is preferable that the lower limit is 0.05% or more in order to keep the steel material strength at an appropriate level. The reason for setting the upper limit of the Mn concentration to 1.5% is that
When the concentration increases, the influence of the Si—Mn composite deoxidation starts to appear. When the Mn concentration exceeds 1.5%, the MnO concentration in the inclusions exceeds 10%, and the SiO 2 concentration in the inclusions increases to 70%.
This is because it may be difficult to achieve the above.
The lower limit is not particularly limited from the viewpoint of inclusion control, but is preferably 0.20% or more in view of the strength of the steel material and the like.
【0048】O濃度の上限を0.0020%とした理由
は、疲労強度の向上には、介在物量が少ないことが望ま
しいからである。また、上記高炭素Si脱酸鋼に、Cr
を0.05〜2.0%含有させた高炭素Cr含有Si脱
酸鋼も望ましい。The reason why the upper limit of the O concentration is set to 0.0020% is that it is desirable to reduce the amount of inclusions in order to improve the fatigue strength. In addition, Cr is added to the high carbon Si deoxidized steel.
Is also desirable for high carbon Cr-containing Si deoxidized steel containing 0.05 to 2.0%.
【0049】さらに、本発明は、Si脱酸で溶製できる
フェライト系、あるいは、オーステナイト系ステンレス
鋼にも適用することができる。これらのステンレス鋼の
望ましいCr濃度は4.0〜20%である。Further, the present invention can be applied to a ferritic or austenitic stainless steel which can be produced by deoxidation of Si. The desirable Cr concentration of these stainless steels is 4.0 to 20%.
【0050】Crが含有されると、Crと酸素の親和力
が強く脱酸処理が困難となるおそれがある。脱酸が不足
した場合には介在物が多量に残留して、本技術による介
在物形態制御をもってしても、疲労強度に影響が出る可
能性があることから、全酸素濃度を0.0080%以下
にすることが望ましい。When Cr is contained, the affinity between Cr and oxygen is so strong that the deoxidizing treatment may be difficult. If the deoxidation is insufficient, a large amount of inclusions remain, and even if the inclusion morphology control according to the present technology can affect the fatigue strength, the total oxygen concentration is reduced to 0.0080%. It is desirable to make the following.
【0051】なお、Cr濃度が8.0%以上では、上記
脱酸が不足するのを回避するために、Si濃度が0.1
0%以上あることが望ましい。C濃度は、加工性と耐食
性とを両立させるために、0.15%以下が望ましい。When the Cr concentration is 8.0% or more, the Si concentration is set to 0.1% in order to avoid the shortage of deoxidation.
Desirably, it is 0% or more. The C concentration is desirably 0.15% or less in order to achieve both workability and corrosion resistance.
【0052】Mn濃度は、Si脱酸の予備脱酸機能を持
たせるために、また強度を確保するために、0.1%以
上が望ましい。一方、Si脱酸・Mn脱酸の複合脱酸効
果による介在物中のSiO2 濃度の低下を防止するため
には2.0%以下が望ましい。The Mn concentration is desirably 0.1% or more in order to provide a preliminary deoxidizing function for Si deoxidation and to secure strength. On the other hand, in order to prevent a decrease in the SiO 2 concentration in inclusions due to a combined deoxidation effect of Si deoxidation and Mn deoxidation, the content is preferably 2.0% or less.
【0053】また、Ni濃度については、特に制限はな
く、オーステナイト系ステンレス鋼としての特徴を発揮
する組成においても本発明は適用できる。さらに、本発
明は、Si脱酸鋼で溶製できるVやMoを含む高強硬度
鋼や肌焼き鋼へも適用できる。すなわち、本発明におい
ては脱酸に影響を及ぼさない合金成分、例えばVやMo
は通常の鋼成分の範囲であればその効果を発揮すること
ができる。またNi濃度についても特に制限はなく、そ
の効果を発揮することができる。The Ni concentration is not particularly limited, and the present invention can be applied to a composition exhibiting the characteristics of an austenitic stainless steel. Further, the present invention can be applied to a high-strength steel and a case hardened steel containing V and Mo which can be produced by deoxidizing steel. That is, in the present invention, alloy components that do not affect deoxidation, such as V and Mo
Can exert its effect as long as it is within the range of ordinary steel components. The Ni concentration is not particularly limited, and the effect can be exhibited.
【0054】次に、介在物組成の制御方法について述べ
る。介在物組成は、基本的には溶鋼中の脱酸元素濃度お
よびスラグ組成によって制御することができる。Next, a method for controlling the composition of inclusions will be described. The inclusion composition can be basically controlled by the deoxidizing element concentration in the molten steel and the slag composition.
【0055】スラグ組成はスラグ精錬のタイミング、添
加するフラックス組成および量、初期酸素濃度、精錬温
度にも影響されるためこれらを考慮する必要がある。S
i添加の時期については、転炉あるいは電気炉といった
製鋼炉の出鋼前あるいは出鋼硫に対しての添加が望まし
い。その理由は、脱酸初期に生成する大型介在物が浮上
・除去するためである。The slag composition is affected by the timing of slag refining, the composition and amount of flux to be added, the initial oxygen concentration, and the refining temperature. S
Regarding the timing of i addition, it is desirable to add it before tapping or in tapping sulfur of a steelmaking furnace such as a converter or an electric furnace. The reason is that large inclusions generated in the early stage of deoxidation float and are removed.
【0056】本発明で対象とするSi脱酸鋼の溶製に際
し、製鋼炉からの流出スラグを取鍋中の溶鋼から除滓を
行い、あらためて溶鋼中にフラックス添加を行う。ここ
で最も重要な点は、フラックス添加取鍋精錬におけるス
ラグ組成である。In the production of the Si deoxidized steel, which is the subject of the present invention, the slag flowing out of the steelmaking furnace is subjected to the removal of slag from the molten steel in the ladle, and flux is added to the molten steel again. The most important point here is the slag composition in the ladle refining with flux addition.
【0057】すなわち、この取鍋精錬段階において、C
aO−SiO2 −MgO−Al2 O 3 −MnO−R2 O
(R= Li、Na、K)系スラグを用いる。スラグ中の
CaOは熱的に安定なスラグを構成するための必須成分
であり、その濃度は20%以上が望ましいが、45%を
越えると、スラグ塩基度が高くなることにより、介在物
中のCaO、MgO等の塩基性成分、Al2 O3 等の中
性成分が高い濃度で安定となり、介在物中の(Si
O2 )濃度が45%未満となるおそれがあり45%以下
が望ましい。すなわち、スラグ中のCaO濃度は20〜
45%が望ましい。That is, in this ladle refining stage, C
aO-SiOTwo-MgO-AlTwoO Three-MnO-RTwoO
(R = Li, Na, K) slag is used. In the slag
CaO is an essential component for constituting a thermally stable slag
The concentration is preferably 20% or more, but 45%
Beyond that, the slag basicity increases,
Basic components such as CaO and MgO, AlTwoOThreeInside
Content becomes stable at high concentration, and (Si
OTwo) Concentration may be less than 45% and not more than 45%
Is desirable. That is, the CaO concentration in the slag is 20 to
45% is desirable.
【0058】スラグ中のSiO2 は、Si脱酸鋼を安定
に溶製するための必須成分であり、その濃度が25%未
満では、介在物中の(SiO2 )濃度が45%未満とな
るおそれがあり、60%を越えると取鍋耐火物の溶損が
生じるおそれがあるため、スラグ中のSiO2 濃度は2
5〜60%が望ましい。The SiO 2 in the slag is an essential component for stably producing the Si deoxidized steel. If the concentration is less than 25%, the (SiO 2 ) concentration in the inclusions will be less than 45%. If it exceeds 60%, the ladle refractory may be melted, so that the SiO 2 concentration in the slag is 2%.
5 to 60% is desirable.
【0059】スラグ中のMgOは製鋼炉流出スラグ、耐
火物や副原料から入る不可避的適成分で極端に低減する
ことはコスト的に困難であり、また耐火物保護の観点か
らスラグ中のMgO濃度は5%以上が望ましいが、Mg
O濃度が18%を越えると、介在物にMgO濃度が50
%を越え、非延性介在物が発生するおそれがあり、スラ
グ中のMgO濃度は18%以下が望ましい。すなわち、
スラグ中のMgO濃度は5〜18%が望ましい。The MgO in the slag is an inevitable suitable component entering from the slag flowing out of the steelmaking furnace, refractories and auxiliary materials, and it is difficult to reduce it extremely in terms of cost. Is preferably 5% or more.
When the O concentration exceeds 18%, the inclusion has a MgO concentration of 50%.
%, Non-ductile inclusions may be generated, and the MgO concentration in the slag is desirably 18% or less. That is,
The MgO concentration in the slag is preferably 5 to 18%.
【0060】スラグ中のAl2 O3 は製鋼炉流出スラ
グ、耐火物や副原料から入る不可避的適成分で極端に低
減することはコスト的に困難であり、Al2 O3 濃度が
12%を越えると介在物の(Al2 O3 )濃度が30%
を越え、非延性介在物が発生するおそれがあるため、ス
ラグ中のAl2 O3 濃度は1〜12%が望ましい。[0060] Al 2 O 3 in the slag is steelmaking furnace effluent slag, be extremely reduced by unavoidable suitable components entering from refractories and auxiliary raw material is cost difficult, 12% is the concentration of Al 2 O 3 If it exceeds, the (Al 2 O 3 ) concentration of the inclusion becomes 30%
Therefore, the concentration of Al 2 O 3 in the slag is desirably 1 to 12%, since non-ductile inclusions may be generated.
【0061】スラグ中のMnOは製鋼炉流出スラグ、合
金成分の脱酸から入る不可避的成分で極端に低減するこ
とはコスト的に困難であり、MnO濃度が8%を越える
と全酸素濃度を下げることが困難となり、介在物量その
ものが増加するおそれがあるため、スラグ中のMnO濃
度は0.2〜8.0%が望ましい。MnO in the slag is an unavoidable component coming from the deoxidation of slag and alloy components flowing out of the steelmaking furnace, and it is difficult to reduce it extremely in terms of cost. If the MnO concentration exceeds 8%, the total oxygen concentration is reduced Therefore, the amount of inclusions itself may increase, so that the MnO concentration in the slag is desirably 0.2 to 8.0%.
【0062】スラグ中のR2 Oは、スラグ中に0.5%
以上含有させることが望ましいが、R2 O濃度が10%
を越えるとスラグ中であっても蒸発し易くなり、その蒸
発量が増加してダスト量が増加する等の問題が発生する
おそれがあり、スラグ中のR 2 O濃度は0.5〜10%
が望ましい。R in slagTwoO is 0.5% in slag
It is desirable to containTwoO concentration is 10%
If it exceeds, it is easy to evaporate even in slag,
Problems such as an increase in the amount of dust and the amount of dust occur
There is a possibility that R in slag TwoO concentration is 0.5-10%
Is desirable.
【0063】R2 O原料の代表例であるNa2 O原料
は、熱的に安定でコスト的にも有利な珪酸ソーダ、メタ
珪酸ソーダ、ソーダ灰、ソーダガラス等が望ましい。R
2 O原料の添加時期は特に制限はないが、スラグへの速
やかな溶解を図るため、添加フラックスとの同時添加、
または造滓後スラグへのR2 O原料の個別添加が望まし
い。The Na 2 O raw material, which is a typical example of the R 2 O raw material, is preferably sodium silicate, sodium metasilicate, soda ash, soda glass, etc., which are thermally stable and advantageous in cost. R
The timing of addition of the 2O raw material is not particularly limited. However, in order to dissolve the slag quickly, simultaneous addition with the added flux,
Alternatively, it is desirable to add the R 2 O raw material to the slag after slag making.
【0064】スラグ精錬段階におけるR2 Oの過大な蒸
発を抑制するには、溶鋼温度を低くすることが有効であ
り、スラグ精錬時の溶鋼温度を1600℃以下とするこ
とが望ましい。In order to suppress excessive evaporation of R 2 O in the slag refining stage, it is effective to lower the temperature of the molten steel, and it is desirable that the temperature of the molten steel during the slag refining be 1600 ° C. or less.
【0065】なお、CaF2 の併用は、通常、スラグの
滓化性を改善する効果が期待できるので必要に応じて使
用すればよいが、本発明の効果に影響を及ぼさないた
め、CaF2 の濃度範囲を特に限定しない。In general, the combined use of CaF 2 can be used as necessary, since the effect of improving the slag-making properties of the slag can be expected. However, since the effect of the present invention is not affected, the use of CaF 2 is not affected. The concentration range is not particularly limited.
【0066】また、不可避的成分としてスラグに含有さ
れるFeO濃度またはステンレス溶製時におけるスラグ
中のCr2 O3 濃度は、スラグからの溶鋼再酸化を防ぐ
観点から極力低いことが有効であるが、それらの合計濃
度で5%以下とすることが望ましい。It is effective that the concentration of FeO contained in the slag as an unavoidable component or the concentration of Cr 2 O 3 in the slag at the time of melting stainless steel is as low as possible from the viewpoint of preventing reoxidation of molten steel from the slag. It is desirable that the total concentration thereof be 5% or less.
【0067】次に、本発明のスラグ精錬の実施形態につ
いて、転炉( または電気炉) −取鍋精錬プロセスを模擬
した実験に沿って述べる。通常、Si脱酸鋼は、転炉あ
るいは電気炉によって所期の目的炭素濃度および温度に
なるように酸素吹精された後、取鍋へ出鋼される。出鋼
時、Fe−Si等のSi源をFe−Mn等のMn源とと
もに添加することによりSi脱酸される。Next, an embodiment of the slag refining of the present invention will be described along with an experiment simulating a converter (or electric furnace) -ladle refining process. Normally, Si deoxidized steel is subjected to oxygen blowing by a converter or an electric furnace so as to have a desired target carbon concentration and temperature, and then is discharged to a ladle. At the time of tapping, Si is deoxidized by adding a Si source such as Fe-Si together with a Mn source such as Fe-Mn.
【0068】このSi脱酸出鋼時の流出スラグを極力抑
制し、出鋼後に取鍋中の残滓を除去した後に所定組成の
フラックスを添加して造滓する。本発明は、この取鍋ス
ラグ精錬によって、Si脱酸鋼中の介在物における(S
iO2 )濃度および(R2 O)濃度を制御するものであ
り、前に述べたように本発明のRはLi、Na、Kであ
りこれらの効果は等価として扱えることから、(Na2
O)濃度を制御する方法について以下に説明する。The outflow slag during the deoxidation of Si is minimized, the residue in the ladle is removed after tapping, and a flux of a predetermined composition is added to produce the slag. According to the present invention, the ladle slag refining enables the inclusion of (S) in the inclusions in the Si deoxidized steel.
iO 2) is for controlling the concentration and (R 2 O) concentration, the R of the present invention as mentioned before Li, Na, or K from the handle these effects as an equivalent, (Na 2
O) A method for controlling the concentration will be described below.
【0069】取鍋スラグ精錬機能を模擬した溶鋼量15
kgの試験装置により、溶鋼組成としては、C:0.4
5〜0.55%、Mn:0.20〜0.30%を含むS
i未添加鋼を1520〜1560℃で溶解した。ここで
出鋼を模擬してSiおよびMn添加を行い、最終的にS
i:0.20〜0.30%およびMn:0.45〜0.
55%になるよう調整する。所定時間保持した後、種々
の組成に配合した合成スラグを添加した後、さらに所定
時間保持し、ボンブサンプラーで溶鋼から採取した試料
中の介在物組成とスラグ組成との関係を調査した。Molten steel amount 15 simulating ladle slag refining function
kg test equipment, C: 0.4 as molten steel composition
S containing 5 to 0.55%, Mn: 0.20 to 0.30%
i The non-added steel was melted at 1520 to 1560 ° C. Here, Si and Mn were added to simulate tapping, and finally S
i: 0.20 to 0.30% and Mn: 0.45 to 0.
Adjust to be 55%. After maintaining for a predetermined time, synthetic slag mixed with various compositions was added, and then further maintained for a predetermined time, and the relationship between the inclusion composition and the slag composition in a sample collected from molten steel with a bomb sampler was investigated.
【0070】スラグの基本成分としては、CaO−Si
O2 −Al2 O3 −MgO−CaF 2 として、そこにN
a2 Oはその炭酸塩の試薬で配合した。図8は、Ca
O:33〜40%、SiO2 :33〜40%、Al2 O
3 :2〜5%、MgO:12〜15%、残部にCa
F2 :2〜5と不可避的に含まれるFeO、MnOおよ
びその他不純物を含有するスラグ中のNa2 O濃度と介
在物中のNa2 O濃度との関係を示すグラフである。The basic component of the slag is CaO—Si
OTwo-AlTwoOThree-MgO-CaF TwoAs there N
aTwoO was formulated with the carbonate reagent. FIG.
O: 33-40%, SiOTwo: 33-40%, AlTwoO
Three: 2 to 5%, MgO: 12 to 15%, the balance being Ca
FTwo: FeO, MnO and unavoidably contained as 2 to 5
In slag containing iron and other impuritiesTwoO concentration and mediation
Na in substanceTwoIt is a graph which shows the relationship with O concentration.
【0071】同図に示すように、スラグ中のNa2 O濃
度の上昇とともに介在物中の(Na 2 O)濃度も上昇
し、その効果は10%で飽和する。また、この試験の
際、10%を越えて配合すると、スラグからの蒸発物が
著しく増加することが認められた。As shown in FIG.TwoO concentration
(Na) in inclusions with increasing degree TwoO) Concentration also rises
The effect saturates at 10%. In addition, this test
At this time, if it exceeds 10%, evaporation from slag will
A significant increase was observed.
【0072】このように、この取鍋スラグ精錬によっ
て、Si脱酸鋼中の介在物における(R2 O)濃度を任
意に制御することができる。As described above, the ladle slag refining can arbitrarily control the (R 2 O) concentration in the inclusions in the Si deoxidized steel.
【0073】[0073]
【実施例】80t転炉で脱炭精錬を行った後、取鍋へ出
鋼する際に、Fe−SiおよびFe−Mn等の合金鉄お
よび加炭剤を適宜添加し、Si脱酸および成分の調整を
行った。この際、後のスラグ組成制御をより効率良く行
うために、流出スラグを極力防止し、さらに、スラグド
ラッガーで除滓を行った。EXAMPLE After decarburization and refining in an 80-t converter, when steel is extracted to a ladle, ferrous alloys such as Fe-Si and Fe-Mn and a carburizing agent are appropriately added to deoxidize Si and remove components. Was adjusted. At this time, in order to more efficiently control the slag composition later, the outflow slag was prevented as much as possible, and the slag was removed with a slag dragger.
【0074】その後あらためて造滓のためのフラックス
を添加し、所要の組成を有するスラグを形成せしめた。
フラックスとしては、製鋼で一般に用いられる生石灰
(CaO源)、珪砂(SiO2 源)、ドロマイト(Mg
OおよびCaO源)、蛍石(CaF2 )等を適宜添加し
た。Thereafter, a flux for slag was added again to form a slag having a required composition.
Examples of the flux include quick lime (CaO source), silica sand (SiO 2 source), dolomite (Mg
O and CaO sources), fluorite (CaF 2 ) and the like were added as appropriate.
【0075】また、Al2 O3 、FeOおよびMnO成
分は、残存スラグ、耐火物および脱酸生成物に由来し上
記スラグ中に混入した。ここで、スラグ中へのR2 O源
としては、Li2 O、Na2 OおよびK2 Oがほぼ等価
な機能を有していることから、製鋼プロセスで利用しや
すく工業的規模の入手が可能なNa2 Oを含有する珪酸
ソーダを用いた。スラグ量は、溶鋼質量トン当たり約1
5kgとなるようにした。この取鍋精錬時の温度は、1
500℃〜1600℃の範囲であった。The Al 2 O 3 , FeO and MnO components were derived from residual slag, refractories and deoxidized products and were mixed into the slag. Here, as the R 2 O source in the slag, since Li 2 O, Na 2 O and K 2 O have almost equivalent functions, they can be easily used in the steelmaking process and can be obtained on an industrial scale. Sodium silicate containing possible Na 2 O was used. The amount of slag is about 1 per ton of molten steel.
The weight was adjusted to 5 kg. The temperature during this ladle refining is 1
The range was from 500C to 1600C.
【0076】上記条件下のスラグ精錬を約10分間以上
実施した後、スラグが均一になった状態でスラグを採取
し組成を調べた。スラグ精錬をさらに約5分間以上実施
した後、常法にしたがい連続鋳造を行い、得られた鋳片
を常法にしたがい圧延を施し、5.5mmφの線材を得
た。線材の長手方向断面に観察される介在物を無作為に
20個以上選び、その組成をエネルギー分散型のX線マ
イクロアナライザーで調べ、その平均値を比較した。After performing slag refining under the above conditions for about 10 minutes or more, slag was sampled in a state where the slag was uniform, and the composition was examined. After slag refining was further performed for about 5 minutes or more, continuous casting was performed according to a conventional method, and the obtained slab was rolled according to a conventional method to obtain a 5.5 mmφ wire. Twenty or more inclusions observed in the longitudinal section of the wire were randomly selected, their compositions were examined with an energy dispersive X-ray microanalyzer, and their average values were compared.
【0077】上記の方法により種々の組成を有する鋼材
を製造し、これらの圧延試料を用いて回転曲げ疲労試験
(107 回回転曲げ試験)を行った。各試料は、鋼種ご
とに焼き入れ焼き戻し等の同じ熱処理を施した。疲労強
度の評価は、温度は20〜25℃、湿度50〜60%の
条件下試験を行った。[0077] By the above method to produce a steel having various compositions were rotating bending fatigue test using these rolling samples (rotary bending test 10 7 times). Each sample was subjected to the same heat treatment such as quenching and tempering for each steel type. For the evaluation of the fatigue strength, a test was performed under the conditions of a temperature of 20 to 25 ° C. and a humidity of 50 to 60%.
【0078】(実施例1)表1に高炭素Si脱酸鋼の化
学組成および介在物の化学組成と疲労強度との関係を示
す。Example 1 Table 1 shows the relationship between the chemical composition of high carbon Si deoxidized steel, the chemical composition of inclusions, and fatigue strength.
【0079】[0079]
【表1】 [Table 1]
【0080】表1に示すように、高炭素Si脱酸鋼の化
学組成がAl≦0.003%、Ti≦0.003%およ
びZr≦0.0010%でSiが0.05〜4.0%
で、かつ介在物中のSiO2 濃度が45%以上、Na2
O濃度が0.5〜10%である試料No. 1〜5 の本発明
例は疲労強度が1023MPa以上と大きな値が得られ
たが、No.6〜10の比較例は疲労強度が780MPa以下
と比較的に小さな値しかえられなかった。As shown in Table 1, when the chemical composition of the high carbon Si deoxidized steel is Al ≦ 0.003%, Ti ≦ 0.003% and Zr ≦ 0.0010%, the content of Si is 0.05 to 4.0. %
And the SiO 2 concentration in the inclusions is 45% or more and Na 2
The samples of the present invention of sample Nos. 1 to 5 having an O concentration of 0.5 to 10% had a large fatigue strength of 1023 MPa or more, whereas the comparative examples of Nos. 6 to 10 had a fatigue strength of 780 MPa or less. And only a relatively small value was obtained.
【0081】(実施例2)表2に高炭素Cr含有Si脱
酸鋼の化学組成および介在物の化学組成と疲労強度との
関係を示す。Example 2 Table 2 shows the relationship between the chemical composition of high carbon Cr-containing Si deoxidized steel, the chemical composition of inclusions, and the fatigue strength.
【0082】[0082]
【表2】 [Table 2]
【0083】表2に示すように、高炭素Cr含有Si脱
酸鋼の化学組成がAl≦0.003%、Ti≦0.00
3%およびZr≦0.0010%でSiが0.05〜
4.0%で、かつ介在物中のSiO2 濃度が45%以
上、Na2 O濃度が0.5〜10%である試料No.11 〜
15の本発明例は疲労強度が1224MPa以上と大きな
値が得られたが、No.16 〜20の比較例は疲労強度が10
40MPa以下と比較的に小さな値しかえられなかっ
た。As shown in Table 2, the chemical composition of the high carbon Cr-containing Si deoxidized steel was such that Al ≦ 0.003% and Ti ≦ 0.003%.
3% and Zr ≦ 0.0010%, Si is 0.05 to
Sample No. 11 to 4.0%, in which the SiO 2 concentration in the inclusions is 45% or more and the Na 2 O concentration is 0.5 to 10%
The fifteen examples of the present invention had a large fatigue strength of 1224 MPa or more, while the comparative examples of Nos. 16 to 20 had a fatigue strength of 10
A relatively small value of 40 MPa or less was obtained.
【0084】(実施例3)表3に中炭素Cr、Mo含有
Si脱酸鋼の化学組成および介在物の化学組成と疲労強
度との関係を示す。Example 3 Table 3 shows the relationship between the chemical composition of medium carbon Cr and Mo-containing Si deoxidized steel, the chemical composition of inclusions, and the fatigue strength.
【0085】[0085]
【表3】 [Table 3]
【0086】表3に示すように、中炭素Cr、Mo含有
Si脱酸鋼の化学組成がAl≦0.003%、Ti≦
0.003%およびZr≦0.0010%でSiが0.
05〜4.0%で、かつ介在物中のSiO2 濃度が45
%以上、Na2 O濃度が0.5〜10%である試料No.2
1 〜25の本発明例は疲労強度が628MPa以上と大き
な値が得られたが、No.26 〜30の比較例は疲労強度が5
08MPa以下と比較的に小さな値しかえられなかっ
た。As shown in Table 3, the chemical composition of the medium carbon Cr and Mo containing Si deoxidized steel was such that Al ≦ 0.003%, Ti ≦
0.003% and Zr.ltoreq.0.0010% when Si is 0.1%.
And the SiO 2 concentration in the inclusions is 45 to 4.0%.
% Or more, and the Na 2 O concentration is 0.5 to 10%.
In the present invention examples 1 to 25, the fatigue strength was as large as 628 MPa or more, whereas in the comparative examples No. 26 to 30, the fatigue strength was 5
A relatively small value of 08 MPa or less was obtained.
【0087】(実施例4)表4に中炭素Cr、Mo、N
i含有Si脱酸鋼の化学組成および介在物の化学組成と
疲労強度との関係を示す。Example 4 Table 4 shows that medium carbon Cr, Mo, N
4 shows the relationship between the chemical composition of i-containing Si deoxidized steel, the chemical composition of inclusions, and fatigue strength.
【0088】[0088]
【表4】 [Table 4]
【0089】表4に示すように、同脱酸鋼の化学組成が
Al≦0.003%、Ti≦0.003%およびZr≦
0.0010%でSiが0.05〜4.0%で、かつ介
在物中のSiO2 濃度が45%以上、Na2 O濃度が
0.5〜10%である試料No.31 〜35の本発明例は疲労
強度が609MPa以上と大きな値が得られたが、No.3
6 〜40の比較例は疲労強度が508MPa以下と比較的
に小さな値しかえられなかった。As shown in Table 4, the chemical composition of the deoxidized steel was as follows: Al ≦ 0.003%, Ti ≦ 0.003%, and Zr ≦
Si is at 0.05 to 4.0 percent by 0.0010%, and SiO 2 concentration in inclusions at least 45%, Na 2 O concentration of the sample No.31 to 35 are 0.5% to 10% In the example of the present invention, the fatigue strength was as large as 609 MPa or more.
The comparative examples 6 to 40 had relatively small values of the fatigue strength of 508 MPa or less.
【0090】(実施例5)表5に低炭素Cr系ステンレ
スSi脱酸鋼の化学組成および介在物の化学組成と疲労
強度との関係を示す。Example 5 Table 5 shows the relationship between the chemical composition of low carbon Cr-based stainless steel deoxidized steel, the chemical composition of inclusions, and fatigue strength.
【0091】[0091]
【表5】 [Table 5]
【0092】表5に示すように、同脱酸鋼の化学組成が
Al≦0.003%、Ti≦0.003%およびZr≦
0.0010%でSiが0.05〜4.0%で、かつ介
在物中のSiO2 濃度が45%以上、Na2 O濃度が
0.5〜10%である試料No.41 〜45の本発明例は疲労
強度が330MPa以上と大きな値が得られたが、No.3
6 〜40の比較例は疲労強度が311MPa以下と比較的
に小さな値しかえられなかった。As shown in Table 5, the chemical composition of the deoxidized steel was as follows: Al ≦ 0.003%, Ti ≦ 0.003%, and Zr ≦
Si is at 0.05 to 4.0 percent by 0.0010%, and SiO 2 concentration in inclusions at least 45%, Na 2 O concentration of the sample No.41 to 45 are 0.5% to 10% In the example of the present invention, the fatigue strength was as high as 330 MPa or more, but No. 3
The comparative examples 6 to 40 had a relatively small fatigue strength of 311 MPa or less.
【0093】(実施例6)表6に低炭素Cr−Ni系ス
テンレスSi脱酸鋼の化学組成および介在物の化学組成
と疲労強度との関係を示す。Example 6 Table 6 shows the chemical composition of low carbon Cr-Ni stainless steel Si deoxidized steel and the relationship between the chemical composition of inclusions and fatigue strength.
【0094】[0094]
【表6】 [Table 6]
【0095】表6に示すように、同脱酸鋼の化学組成が
Al≦0.003%、Ti≦0.003%およびZr≦
0.0010%でSiが0.05〜4.0%で、かつ介
在物中のSiO2 濃度が45%以上、Na2 O濃度が
0.5〜10%である試料No.51 〜55の本発明例は疲労
強度が356MPa以上と大きな値が得られたが、No.5
6 〜60の比較例は疲労強度が311MPa以下と比較的
に小さな値しかえられなかった。As shown in Table 6, the chemical composition of the deoxidized steel was as follows: Al ≦ 0.003%, Ti ≦ 0.003%, and Zr ≦
Si is at 0.05 to 4.0 percent by 0.0010%, and SiO 2 concentration in inclusions at least 45%, Na 2 O concentration of the sample No.51 to 55 are 0.5% to 10% In the example of the present invention, the fatigue strength was as large as 356 MPa or more.
Comparative Examples 6 to 60 had relatively small values of fatigue strength of 311 MPa or less.
【0096】[0096]
【発明の効果】本発明のSi脱酸鋼は、従来の鋼と比較
して、有害な大型介在物が少なく、しかも残留した介在
物も延性のある介在物であり、かつその介在物は微細に
分散されたものであり、今までにない疲労強度に優れた
鋼種である。The Si deoxidized steel of the present invention has less harmful large inclusions than conventional steels, and the remaining inclusions are ductile inclusions, and the inclusions are fine. It is a type of steel that has an unprecedented fatigue strength.
【図1】鋼中の[Al]濃度と介在物中の(SiO2 )
濃度との関係を示すグラフである。FIG. 1 [Al] concentration in steel and (SiO 2 ) in inclusions
It is a graph which shows the relationship with a density.
【図2】鋼中の[Ti]濃度と介在物中の(SiO2 )
濃度との関係を示すグラフである。FIG. 2 [Ti] concentration in steel and (SiO 2 ) in inclusions
It is a graph which shows the relationship with a density.
【図3】鋼中の[Zr]濃度と介在物中の(SiO2 )
濃度との関係を示すグラフである。FIG. 3 [Zr] concentration in steel and (SiO 2 ) in inclusions
It is a graph which shows the relationship with a density.
【図4】鋼中の[Si]濃度と介在物中の(SiO2 )
濃度との関係を示すグラフである。FIG. 4 [Si] concentration in steel and (SiO 2 ) in inclusions
It is a graph which shows the relationship with a density.
【図5】鋼中の[Si]濃度と介在物中の(Na2 O)
濃度との関係を示すグラフである。FIG. 5: [Si] concentration in steel and (Na 2 O) in inclusions
It is a graph which shows the relationship with a density.
【図6】圧延方向断面における介在物の幅の大きさとそ
の度数分布との関係を示すグラフである。FIG. 6 is a graph showing the relationship between the width of inclusions in the cross section in the rolling direction and the frequency distribution thereof.
【図7】介在物中の(Na2 O)濃度をパラメータとし
た圧延方向断面における介在物の幅の大きさとその度数
分布との関係を示すグラフである。FIG. 7 is a graph showing the relationship between the width of inclusions in the cross section in the rolling direction and the frequency distribution thereof, using the (Na 2 O) concentration in the inclusions as a parameter.
【図8】CaO:33〜40%、SiO2 :33〜40
%、Al2 O3 :2〜5%、MgO:12〜15%、残
部にCaF2 :2〜5と不可避的に含まれるFeO、M
nOおよびその他不純物を含有するスラグ中のNa2 O
濃度と介在物中のNa2O濃度との関係を示すグラフで
ある。FIG. 8: CaO: 33 to 40%, SiO 2 : 33 to 40
%, Al 2 O 3 : 2 to 5%, MgO: 12 to 15%, and the balance CaF 2 : 2 to 5 FeO and M inevitably contained.
Na 2 O in slag containing nO and other impurities
It is a graph showing the relationship between the concentration and the concentration of Na 2 O inclusions.
Claims (5)
i:0.003%以下、Zr:0.0010%以下およ
びSi:0.05〜4.0%含有するSi脱酸鋼であっ
て、かつ該Si脱酸鋼中の介在物が質量%でSiO2 :
45%以上、アルカリ金属R(R= Na、K、Li)の
酸化物(R2 O):0.5〜10%含有することを特徴
とする疲労強度に優れたSi脱酸鋼。1. Al in mass%: 0.003% or less, T
i: a Si-deoxidized steel containing 0.003% or less, Zr: 0.0010% or less, and Si: 0.05 to 4.0%, and the inclusions in the Si-deoxidized steel are represented by mass%. SiO 2 :
45% or more, oxides of alkali metal R (R = Na, K, Li) (R 2 O): 0.5~10% containing Si deoxidized steel with excellent fatigue strength, characterized by.
以下、Mn:0.20〜1.50%、O:0.0020
%以下含有することを特徴とする請求項1に記載の疲労
強度に優れたSi脱酸鋼。2. The Si deoxidized steel further comprises C: 1.2%
Hereinafter, Mn: 0.20 to 1.50%, O: 0.0020
The Si deoxidized steel having excellent fatigue strength according to claim 1, wherein the content thereof is not more than%.
以下、Mn:0.20〜1.50%、O:0.0020
%以下、Cr:0.05〜2.0%含有することを特徴
とする請求項1に記載の疲労強度に優れたSi脱酸鋼。3. The Si deoxidized steel further comprises C: 1.2%
Hereinafter, Mn: 0.20 to 1.50%, O: 0.0020
% Or less, Cr: 0.05 to 2.0%, Si deoxidized steel excellent in fatigue strength according to claim 1 characterized by the above-mentioned.
%以下、Mn:0.1〜2.0%、Cr:4〜20%、
O:0.0080%以下含有することを特徴とする請求
項1に記載の疲労強度に優れたSi脱酸鋼。4. The Si deoxidized steel further comprises C: 0.15
% Or less, Mn: 0.1 to 2.0%, Cr: 4 to 20%,
The Si-deoxidized steel excellent in fatigue strength according to claim 1, wherein O: 0.0080% or less is contained.
酸鋼を製造する方法であって、精錬炉から取鍋に出鋼す
るときにSi脱酸を行い、その後の取鍋スラグ精錬時の
スラグ組成を質量%でCaO:20〜45%、Si
O2 :25〜60%、MgO:5〜18%、Al
2 O3 :1〜12%、MnO:0.2〜8%、アルカリ
金属R(R= Na、K、Li)の酸化物(R2 O):
0.5〜10%とすることを特徴とする疲労強度に優れ
たSi脱酸鋼の製造方法。5. A method for producing a Si deoxidized steel according to claim 1, wherein when the steel is discharged from a refining furnace to a ladle, the Si deoxidation is performed, and then the ladle slag is produced. The slag composition at the time of refining is CaO: 20 to 45% by mass%, Si
O 2 : 25 to 60%, MgO: 5 to 18%, Al
2 O 3 : 1 to 12%, MnO: 0.2 to 8%, oxide (R 2 O) of alkali metal R (R = Na, K, Li):
A method for producing Si deoxidized steel having excellent fatigue strength, characterized in that the content is 0.5 to 10%.
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