JP4177404B2 - Si-killed steel wire rod and spring with excellent fatigue characteristics - Google Patents
Si-killed steel wire rod and spring with excellent fatigue characteristics Download PDFInfo
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Description
本発明は、疲労特性の優れたSiキルド鋼線材およびこの鋼線材から得られるばねに関するものであり、例えば高強度ばね(特に弁ばね)などとしたときに高い疲労特性が発揮でき、こうした特性が要求される自動車用エンジンの弁ばねやクラッチばね、ブレーキばね、更には懸架ばねやスチールコード等の素材として有用なものである。 The present invention relates to a Si-killed steel wire having excellent fatigue characteristics and a spring obtained from the steel wire. For example, when a high-strength spring (particularly a valve spring) is used, high fatigue characteristics can be exhibited. It is useful as a material for required automotive engine valve springs, clutch springs, brake springs, suspension springs, steel cords and the like.
最近、自動車の軽量化や高出力化の要請が高まるにつれて、エンジンやサスペンション等に使用される弁ばねや懸架ばね等においても高応力設計が指向されている。そのためこれらのばねには、負荷応力の増大に対応するため、耐疲労性や耐へたり性に優れたものが強く望まれている。とりわけ弁ばねについての疲労強度増大の要請は非常に強く、従来鋼の中でも疲労強度に優れているとされているSWOSC−V(JIS G 3566)でも対応が困難になってきている。 Recently, as demands for weight reduction and high output of automobiles increase, high stress design is directed to valve springs and suspension springs used for engines and suspensions. Therefore, in order to cope with an increase in load stress, those having excellent fatigue resistance and sag resistance are strongly desired for these springs. In particular, the demand for increasing the fatigue strength of valve springs is very strong, and SWOSC-V (JIS G 3566), which is considered to be excellent in fatigue strength among conventional steels, has become difficult to cope with.
高い疲労強度が要求されるばね用線材では、線材中に存在する硬質の非金属介在物を極力低減することが必要である。こうした観点から、上記の様な用途に用いられる鋼材としては、上記非金属介在物の存在を極力低減した高清浄鋼が用いられるのが一般的である。また、素材の高強度化が図られるにつれて、非金属介在物に起因する断線、疲労折損の危険性が高まることから、その主要因となる非金属介在物の低減・小型化の要求は一段と厳しいものとなっている。 In a spring wire that requires high fatigue strength, it is necessary to reduce hard non-metallic inclusions present in the wire as much as possible. From such a point of view, as a steel material used for the above-described applications, it is common to use highly clean steel in which the presence of the non-metallic inclusions is reduced as much as possible. In addition, as the strength of materials increases, the risk of breakage and fatigue breakage due to non-metallic inclusions increases, so the demand for reduction and downsizing of non-metallic inclusions, which are the main factor, is more severe. It has become a thing.
鋼材中における硬質の非金属介在物の低減・小型化を図るという観点から、これまでにも様々な技術が提案されている。例えば非特許文献1には、介在物をガラス質に保つことで、圧延時に介在物が微細化すること、およびCaO−Al2O3−SiO2系の成分でガラスが安定な組成に介在物が存在することが記載されている。またガラス部分の変形を促進するために、介在物の融点を下げることが有効であることが提案されている(例えば、特許文献1)。 Various techniques have been proposed so far from the viewpoint of reducing and miniaturizing hard non-metallic inclusions in steel materials. For example, Non-Patent Document 1 discloses that inclusions are kept in a glassy state so that the inclusions are refined during rolling, and the inclusions have a stable composition with a CaO—Al 2 O 3 —SiO 2 -based component. Is described. It has also been proposed that it is effective to lower the melting point of inclusions in order to promote the deformation of the glass portion (for example, Patent Document 1).
また特許文献2には、Ca,Mg,(La+Ce)の量を適切な範囲に制御しつつ鋼材の化学成分組成を適切に調整し、且つ鋼中の非金属介在物の平均的組成の構成比(SiO2,MnO,Al2O3,MgOおよびCaOの構成比)を適切な範囲とすることによって、疲労特性に優れたばね鋼が得られることが示されている。 In Patent Document 2, the chemical composition composition of the steel material is appropriately adjusted while controlling the amounts of Ca, Mg, and (La + Ce) within an appropriate range, and the composition ratio of the average composition of nonmetallic inclusions in the steel is disclosed. It has been shown that a spring steel having excellent fatigue characteristics can be obtained by adjusting (the composition ratio of SiO 2 , MnO, Al 2 O 3 , MgO and CaO) to an appropriate range.
一方、特許文献3には、C,Si,Mn,Cr等の基本成分を制御すると共に、Ca,Mg,Ba,Srのうちの1種以上を0.0005〜0.005%の範囲で含有させ、且つ非金属介在物の大きさを20μm以下とすること等によって、優れた「へたり特性」を発揮させた高強度ばね用線材が提案されている。 On the other hand, Patent Document 3 controls basic components such as C, Si, Mn, and Cr, and contains at least one of Ca, Mg, Ba, and Sr in a range of 0.0005 to 0.005%. In addition, there has been proposed a high-strength spring wire material that exhibits excellent “sag characteristics” by making the size of the nonmetallic inclusions 20 μm or less.
これまで提案されている各種従来技術では、介在物組成を低融点領域に制御して、微細化を図ることを目指すことが中心となっている。例えばCaO−Al2O3−SiO2三成分系介在物では、一般的に知られている三元系状態図において、三成分が或る組成範囲に低融点領域が存在することが知られているが、いずれかの成分が高くなるような組成では、融点が高くなって線材の疲労強度が低下することになる。こうした傾向は、MgO−Al2O3−SiO2三成分系介在物の場合であっても同様である。 Various conventional techniques that have been proposed so far center on the aim of miniaturization by controlling the inclusion composition in the low melting point region. For example, a CaO—Al 2 O 3 —SiO 2 ternary inclusion is known to have a low melting point region in a certain composition range in a ternary phase diagram generally known. However, in a composition in which any of the components is high, the melting point is high and the fatigue strength of the wire is reduced. Such a tendency is the same even in the case of MgO—Al 2 O 3 —SiO 2 ternary inclusions.
上記各種技術では、疲労特性等の特性を高めるための方向性は示されている。しかしながら、熱間加工時の加熱時間や温度においては、例えば非特許文献1に示されたような組成に制御するだけでは、必ずしも完全なガラス状態を保つことはできず、結晶が生成することがある。また、近年の更なる鋼疲労強度化のニーズに対応するためには、ガラス部の変形もより促進する必要がある。 In the various techniques described above, directions for improving characteristics such as fatigue characteristics are shown. However, in the heating time and temperature at the time of hot working, for example, it is not always possible to maintain a complete glass state by controlling the composition as shown in Non-Patent Document 1, and crystals may be generated. is there. Moreover, in order to meet the needs for further steel fatigue strength in recent years, it is necessary to further promote the deformation of the glass portion.
更に、鋼の高強度化に伴って、鋼の成分は高Si化しており、従来知られているCaO−Al2O3−SiO2系での目標組成へのピンポイント制御の難度は高くなる傾向にあり、例えば特許文献4に示されているように、トータルだけでなく、溶存成分を制御するなど、高度な制御が必要となっている。 Furthermore, as the strength of steel increases, the components of the steel increase in Si, and the difficulty of pinpoint control to the target composition in the conventionally known CaO—Al 2 O 3 —SiO 2 system increases. For example, as shown in Patent Document 4, advanced control such as controlling not only the total but also dissolved components is required.
また上記特許文献3では、Ba,Ca,Mg,Sr等の利用に言及しているが、これらの低融点化効果のみに着目し、また各々の成分の差異や複合化の効果を活用できておらず、その結果現在の高い要求に耐え得る疲労強度を実現できない技術となっている。 Moreover, in the said patent document 3, although mentioning utilization of Ba, Ca, Mg, Sr, etc., it pays attention only to these low melting-point effects, and can utilize the difference of each component, and the effect of compounding. As a result, it has become a technology that cannot realize the fatigue strength that can withstand the current high demands.
尚、非金属介在物のうち、Al2O3を多く含むものでは、低融点介在物を得ることが困難であることから、こうした線材を得るための鋼材は、Alキルド鋼ではなく、Siを用いて脱酸する所謂「Siキルド鋼」を素材とした線材が用いられるのが一般的である。
本発明はこうした状況の下になされたものであって、その目的は、介在物の全体を低融点にして変形し易くすることで、疲労特性に優れたばね等を得るためのSiキルド鋼線材、およびこうした鋼線材から得られる疲労特性に優れたばねを提供することにある。 The present invention has been made under such circumstances, the purpose of which is to make the inclusions have a low melting point and easily deform, Si-killed steel wire for obtaining a spring having excellent fatigue properties, And it is providing the spring excellent in the fatigue characteristic obtained from such a steel wire.
このような状況下において、本発明者らは、Sr,Si,Al,Mg,Caの濃度をバランス良く制御することによって、溶鋼中の介在物を適切な組成に制御し、なおかつ鋳造時にも有害な介在物の生成を防止できることを見出した。 Under such circumstances, the present inventors control the inclusions in the molten steel to an appropriate composition by controlling the concentrations of Sr, Si, Al, Mg, and Ca in a well-balanced manner, and are also harmful during casting. The present inventors have found that it is possible to prevent the formation of complex inclusions.
一般論としては、酸化物の複合化による低融点化は考え得ることである。しかしながら、鋼中介在物として制御できる限られた成分によって、Siキルド鋼の介在物融点を低下させ、しかもガラスを安定に保つことは容易ではなく、具体的な手段はこれまで実現できていなかった。これに対して、本発明者らは、Sr,Si,Al,Mg,Caを最適なバランスで制御することでそれを実現したのである。特に、従来類似と考えられていたSr,Ca,Mgのなかでも、Sr,(Mg+Ca)を夫々制御すること、およびいずれも含有させることが重要である。なおかつ、SiO2系のガラスの安定性に対して複雑な影響を発現するAlを適切に制御することによって、著しく疲労強度を向上させることが可能となったのである。 In general, it is conceivable to lower the melting point by combining oxides. However, due to the limited components that can be controlled as inclusions in steel, it is not easy to lower the melting point of inclusions in Si killed steel and keep the glass stable, and no concrete means has been realized so far. . In contrast, the present inventors have realized this by controlling Sr, Si, Al, Mg, and Ca with an optimal balance. In particular, it is important to control Sr, (Mg + Ca), and to contain them, among Sr, Ca and Mg, which have been conventionally considered similar. In addition, the fatigue strength can be remarkably improved by appropriately controlling Al that has a complicated influence on the stability of the SiO 2 glass.
即ち、上記目的を達成し得た本発明のSiキルド鋼線材とは、Sr:0.02〜20ppm(「質量ppm」の意味、以下同じ)、Al:1〜30ppmおよびSi:0.2〜4%(「質量%」の意味、以下同じ)を夫々含有する他、Mgおよび/またはCaを合計で0.5〜30ppmの範囲で含むものである点に要旨を有するものである。 That is, the Si-killed steel wire rod of the present invention that has achieved the above-mentioned object is Sr: 0.02 to 20 ppm (meaning “mass ppm”, the same applies hereinafter), Al: 1 to 30 ppm, and Si: 0.2 to In addition to containing 4% (meaning “mass%”, the same shall apply hereinafter), it also includes Mg and / or Ca in a total range of 0.5 to 30 ppm.
上記の各種Siキルド鋼線材においては、Liを0.03〜20ppmの範囲で含むものも好ましい実施形態である。 In said various Si killed steel wire, what contains Li in the range of 0.03-20 ppm is also preferable embodiment.
本発明のSiキルド鋼線材の化学成分組成については、「ばね」として用いられるものであれば特に限定されるものではないが、好ましいものとして、例えば、C:1.2%以下(0%を含まない)、Mn:0.1〜2.0%、を夫々含む鋼材が挙げられる。また、こうした鋼材においては、更に、Cr,Ni,V,Nb,Mo,W,Cu,Ti,Coおよび希土類元素よりなる群から選択される1種以上を含むものであってもよい。これらを含有させるときの好ましい含有量は、各々の元素によって異なるが、Cr:0.5〜3%、Ni:0.5%以下、V:0.5%以下、Nb:0.1%以下、Mo:0.5%以下、W:0.5%以下、Cu:0.1%以下、Ti:0.1%以下、Co:0.5%以下である。また介在物粘性を下げ、より効果を発揮する元素としてREMを0.05%以下程度添加しても良い。 The chemical composition of the Si-killed steel wire rod of the present invention is not particularly limited as long as it is used as a “spring”. For example, C: 1.2% or less (0%) Steel materials containing Mn: 0.1 to 2.0%. Such steel materials may further contain one or more selected from the group consisting of Cr, Ni, V, Nb, Mo, W, Cu, Ti, Co, and rare earth elements. The preferable content when these are contained varies depending on each element, but Cr: 0.5 to 3%, Ni: 0.5% or less, V: 0.5% or less, Nb: 0.1% or less Mo: 0.5% or less, W: 0.5% or less, Cu: 0.1% or less, Ti: 0.1% or less, Co: 0.5% or less. Moreover, you may add about 0.05% or less of REM as an element which lowers the viscosity of inclusions and exhibits more effect.
上記成分の他(残部)は、基本的にFeおよび不可避不純物である。尚、介在物に大きな影響を与えない成分(例えば、B,Pb,Bi等)は鋼特性向上のために加えても、本発明の効果を発揮するものである。 Other than the above components (remainder) are basically Fe and inevitable impurities. In addition, even if components that do not significantly affect the inclusions (for example, B, Pb, Bi, etc.) are added to improve the steel properties, the effects of the present invention are exhibited.
上記のようなSiキルド鋼線材を用いて、ばねに成形することによって、疲労強度の優れたばねが実現できる。 A spring having excellent fatigue strength can be realized by forming the spring using the Si-killed steel wire as described above.
本発明は以上の様に構成されており、Srを含有させつつ化学成分組成を適切に調整することによって、介在物の全体を低融点化して変形し易くすると共に、熱延前や熱延中の加熱時に相分離してもSiO2が生成しにくいものとでき、疲労特性に優れたばねを得るためのSiキルド鋼線材が実現できた。 The present invention is configured as described above, and by appropriately adjusting the chemical component composition while containing Sr, the entire inclusions have a low melting point and are easily deformed, and before hot rolling or during hot rolling. Even when the phase was separated during heating, SiO 2 was hardly generated, and a Si-killed steel wire for obtaining a spring having excellent fatigue characteristics could be realized.
熱間圧延時の変形比の大きい線材では、介在物は熱間圧延時に延伸分断させて微細化することが有用であることは知られている。本発明者らは、こうした情況の下で、凝固後の加熱、熱間圧延による介在物形態の変化をも考慮して、ばねの疲労特性を向上させるための個々の介在物の組成と形態について、様々な角度から検討した。その結果、Sr,Al,Si,Mg,Caの濃度を適切に制御することで、酸化物系介在物の熱延時の変形が著しく促進されて微細化され易くなることを見出した。 It is known that in a wire rod having a large deformation ratio at the time of hot rolling, it is useful to make the inclusions fine by stretching and cutting at the time of hot rolling. Under these circumstances, the present inventors considered the composition and form of individual inclusions for improving the fatigue characteristics of the spring, taking into account changes in the form of inclusions due to heating after solidification and hot rolling. Considered from various angles. As a result, it has been found that by appropriately controlling the concentrations of Sr, Al, Si, Mg, and Ca, deformation during hot rolling of the oxide inclusions is significantly promoted and is easily refined.
従来においても、Sr,Mg,Ca等のアルカリ土類金属元素の微量添加がばねの特性向上に有効であることは知られているが(例えば、前記特許文献3)、どの成分であっても微量添加しさえすれば良いというわけではなく、これらをバランス良く含有させることによって、Siキルド鋼線材の疲労特性が格段に向上し得ることが判明したのである。例えば、CaO−Al2O3−SiO2三成分系介在物では、一般的に知られている三元系状態図において、三成分が或る組成範囲に低融点領域が存在することが知られているが、いずれかの成分が高くなるような組成では、介在物の融点が却って高くなって、線材の疲労特性が低下することになる。これに対して、Sr,Al,Si,Mg,Caの濃度を適切に制御することによって、上記三成分系介在物中の何れの成分も高くなり過ぎず、またいずれかの成分がない場合と比べてより変形し易い介在物となるものと考えられる。 Conventionally, it is known that addition of trace amounts of alkaline earth metal elements such as Sr, Mg, and Ca is effective in improving the spring characteristics (for example, Patent Document 3). It is not necessary to add a trace amount, and it has been found that the fatigue characteristics of Si-killed steel wire can be remarkably improved by containing them in a balanced manner. For example, a CaO—Al 2 O 3 —SiO 2 ternary inclusion is known to have a low melting point region in a certain composition range in a ternary phase diagram generally known. However, in a composition in which any of the components is high, the melting point of the inclusions is increased and the fatigue properties of the wire are lowered. On the other hand, by appropriately controlling the concentrations of Sr, Al, Si, Mg, and Ca, none of the components in the ternary inclusions become too high, and there is no component. It is considered that the inclusions are more easily deformed than those.
本発明のSiキルド鋼線材は、上記の如くSr,Al,Si,Mg,Ca等の成分をバランスよく含有させることを特徴とするものであるが、これらの成分の範囲限定理由は次の通りである。 The Si killed steel wire rod of the present invention is characterized by containing components such as Sr, Al, Si, Mg, and Ca in a balanced manner as described above. The reasons for limiting the ranges of these components are as follows. It is.
[Sr:0.03〜20ppm]
Srは、介在物を複合化して低融点化するためになくてはならない成分である。介在物中にSrOを含有させると、ガラスの安定性はあまり低下させずに、低融点化させる効果がある。また、Si濃度の高い鋼中に酸素との結合力の強いSrを含有させることで、凝固時に、著しくSiO2濃度の高い介在物が生成しても、ある程度の融点に保つ効果がある。これらの効果を発現するためには、最低でも0.03ppmのSrが必要である。好ましくは0.2ppm以上含有させるのが良い。一方、Sr濃度が高くなり過ぎると、介在物のほかの成分(Mg,Ca,Al,Si,Mn等)の濃度を下げ、最も融点が低くなる組成に制御できなくなる。従って、Sr濃度は20ppm以下とする必要があり、好ましくは8ppm以下とするのが良い。
[Sr: 0.03 to 20 ppm]
Sr is a component that is indispensable for complexing inclusions to lower the melting point. Inclusion of SrO in the inclusions has the effect of lowering the melting point without significantly reducing the stability of the glass. Further, by containing Sr having a strong binding force with oxygen in steel having a high Si concentration, there is an effect of maintaining a certain melting point even when inclusions having a remarkably high SiO 2 concentration are formed during solidification. In order to exhibit these effects, 0.03 ppm of Sr is required at the minimum. Preferably it is 0.2 ppm or more. On the other hand, if the Sr concentration becomes too high, the concentration of other components (Mg, Ca, Al, Si, Mn, etc.) of inclusions is lowered, and it becomes impossible to control the composition to have the lowest melting point. Therefore, the Sr concentration needs to be 20 ppm or less, preferably 8 ppm or less.
[Al:1〜30ppm]
Alは、Siキルド鋼の介在物組成を低融点化する効果がある。また、介在物中のCaOなどの濃度が高くなったときにガラス化を制御する効果もある。更に、Alは、Ca,Sr等と比べて鋼中に溶存しやすい成分であり、凝固時に著しくSiO2濃度の高い介在物が生成するのを抑制する効果が高い。これらの効果を発揮するためには、1ppm以上含有させる必要がある。しかしながら、Al含有量が高くなると、凝固時に純粋なAl2O3が生成する危険があるため、30ppm以下とする必要がある。尚、介在物の融点を最も下げる最適な組成に制御するためには、20ppm以下とすることが好ましい。
[Al: 1 to 30 ppm]
Al has the effect of lowering the melting point of the inclusion composition of Si killed steel. In addition, there is an effect of controlling vitrification when the concentration of CaO or the like in the inclusion is increased. Furthermore, Al is a component that is more easily dissolved in steel than Ca, Sr, and the like, and has a high effect of suppressing the formation of inclusions with a significantly high SiO 2 concentration during solidification. In order to exert these effects, it is necessary to contain 1 ppm or more. However, if the Al content is high, there is a risk that pure Al 2 O 3 is generated during solidification, so it is necessary to set it to 30 ppm or less. In addition, in order to control to the optimal composition which lowers the melting | fusing point of an inclusion most, it is preferable to set it as 20 ppm or less.
[Si:0.2〜4%]
Siは、Siキルド鋼の製鋼時における主たる脱酸剤であり、本発明の線材を得るための必須の元素である。また高強度化にも寄与し、本発明の疲労特性向上効果が顕著にあらわれる点からも重要な元素である。更には、軟化抵抗を高め耐へたり性を向上させるのにも有用な元素である。こうした効果を発揮させるためには、Si含有量は0.2%以上(好ましくは2%以上)とする。しかしながら、Si含有量が過剰になると、凝固中に純粋なSiO2が生成する可能性があり、表面脱炭や表面疵が増加するため疲労特性が却って低下することになる。こうしたことから、Siは4%以下、好ましくは3%以下とする。
[Si: 0.2-4%]
Si is a main deoxidizer during the production of Si killed steel, and is an essential element for obtaining the wire of the present invention. It is also an important element in that it contributes to higher strength and the remarkable effect of improving the fatigue characteristics of the present invention. Further, it is an element useful for increasing softening resistance and improving sag resistance. In order to exert such effects, the Si content is 0.2% or more (preferably 2% or more). However, if the Si content is excessive, pure SiO 2 may be generated during solidification, and surface decarburization and surface flaws increase, so that the fatigue characteristics are deteriorated. For these reasons, Si is made 4% or less, preferably 3% or less.
[Mgおよび/またはCa:合計で0.5〜30ppm]
MgやCaは、介在物を最適な複合組成にし、低融点化するために必須の成分である。Ba単独、Mg単独、Ca単独、Al単独を含有させれば、高融点の介在物となる。従って、いずれかは必ず含有させる必要がある。また、MgやCaは酸素との親和力が強く、純粋なSiO2がまれに生成した場合に、それらを複合組成に改質しやすいという効果もある。これらの効果を発揮させるためには、MgやCa(Mg、Ca単独または併用)の含有量(併用する場合は合計含有量)は、0.5ppm以上とする必要がある。尚、好ましくは各元素を少なくとも0.1ppm以上(但し、合計含有量は0.5ppm以上)含有させて併用するのが良い。しかしながら、これらの元素が過剰になると、介在物中の他の成分の濃度が低くなり、最適な低融点組成が保てなくなる。従って、その上限は30ppm(好ましくは、20ppm以下)とする。
[Mg and / or Ca: 0.5 to 30 ppm in total]
Mg and Ca are indispensable components for making inclusions into an optimal composite composition and lowering the melting point. If Ba alone, Mg alone, Ca alone, or Al alone is contained, inclusions with a high melting point are obtained. Therefore, any of them must be contained. In addition, Mg and Ca have a strong affinity for oxygen, and when pure SiO 2 is rarely produced, there is an effect that they can be easily modified into a composite composition. In order to exert these effects, the content of Mg and Ca (Mg, Ca alone or in combination) (the total content when used in combination) needs to be 0.5 ppm or more. Preferably, each element is used in combination by containing at least 0.1 ppm or more (however, the total content is 0.5 ppm or more). However, when these elements become excessive, the concentration of other components in the inclusions becomes low, and an optimum low melting point composition cannot be maintained. Therefore, the upper limit is 30 ppm (preferably 20 ppm or less).
本発明のSiキルド鋼線材においては、上記各成分をバランスよく含有させることによって、疲労特性が向上したものとなるが、必要によってLiを含有させることも有用である。Liは介在物中の結晶を微細にする効果があり、ガラスを安定でなおかつ低融点に制御した本発明鋼において、万が一結晶が生成した場合にも、結晶を粗大にしない効果がある。従って、Liを含有させることも有用である。こうした作用を発揮させるためには、Liは0.2〜20ppm含有させることが好ましいが、0.03ppm程度の添加によっても、多少の効果は発揮すると考えられ、低濃度の添加によって少なくとも悪影響を及ぼさないと推定される。 In the Si killed steel wire rod of the present invention, the fatigue characteristics are improved by containing each of the above components in a balanced manner, but it is also useful to contain Li if necessary. Li has the effect of making the crystals in the inclusions finer, and in the steel of the present invention in which the glass is stable and controlled to have a low melting point, it has the effect of preventing the crystals from becoming coarse even if crystals are produced. Therefore, it is also useful to contain Li. In order to exert such an effect, it is preferable to contain Li in an amount of 0.2 to 20 ppm. However, it is considered that some effects are exhibited even by addition of about 0.03 ppm, and at least an adverse effect is exerted by addition of a low concentration. Presumed not.
本発明では、ばねの素材として有用なSiキルド鋼線材を想定してなされたものであり、その鋼種については特に限定するものではないが、Mnは鋼の脱酸に寄与する元素であり、また焼入れ性を高めて強度向上に寄与する。こうした観点からMnは0.1%以上含むものであることが好ましい。但し、Mn含有量が過剰になると、靭性、延性が悪くなるので2%以下とすべきである。 In the present invention, Si killed steel wire useful as a spring material is assumed, and the steel type is not particularly limited, but Mn is an element contributing to deoxidation of steel, Increases hardenability and contributes to strength improvement. From such a viewpoint, it is preferable that Mn is contained by 0.1% or more. However, if the Mn content is excessive, the toughness and ductility deteriorate, so it should be 2% or less.
ばね用鋼としての基本成分であるC含有量については、1.2%以下であることが好ましい。C含有量が1.2%を超えると、鋼材が脆化し、実用的でなくなる。 About C content which is a basic component as spring steel, it is preferable that it is 1.2% or less. If the C content exceeds 1.2%, the steel material becomes brittle and becomes impractical.
上記基本成分の他は、Feおよび不可避不純物(例えば0.02%以下のS,0.02%以下のP等)であるが、必要によってCr,Ni,V,Nb,Mo,W,Cu,Ti,Coおよび希土類元素(REM)よりなる群から選択される1種以上を含むものであってもよい。これらを含有させるときの好ましい含有量は、各々の元素によって異なるが、Cr:0.5〜3%、Ni:0.5%以下、V:0.5%以下、Nb:0.1%以下、Mo:0.5%以下、W:0.5%以下、Cu:0.1%以下、Ti:0.1%以下、Co:0.5%以下、REM:0.05%以下である。 In addition to the above basic components, Fe and inevitable impurities (for example, S of 0.02% or less, P of 0.02% or less, etc.), Cr, Ni, V, Nb, Mo, W, Cu, One or more selected from the group consisting of Ti, Co, and rare earth elements (REM) may be included. The preferable content when these are contained varies depending on each element, but Cr: 0.5 to 3%, Ni: 0.5% or less, V: 0.5% or less, Nb: 0.1% or less Mo: 0.5% or less, W: 0.5% or less, Cu: 0.1% or less, Ti: 0.1% or less, Co: 0.5% or less, REM: 0.05% or less .
上記のように化学成分を適切に調整したSiキルド鋼線材を用いてばね成形することによって、疲労特性に優れたばねが実現できる。 As described above, a spring having excellent fatigue characteristics can be realized by forming a spring using a Si-killed steel wire whose chemical composition is appropriately adjusted.
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも勿論可能であり、それらはいずれも本発明の技術的範囲に含まれるものである。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.
実験は、実機(または実験室レベル)で実施した。すなわち、実機では転炉で溶製した溶鋼を取鍋に出鋼し(実験室では、転炉から出鋼される溶鋼を模擬した500kgの溶鋼を溶製し)、各種フラックスを添加して成分調整、電極加熱、およびアルゴンバブリングを実施し、溶鋼処理(スラグ精錬)を実施した。また他の成分を調整した後、Ca,Mg,Ce,Ba,Liなどを必要に応じて溶鋼処理中に添加し、5分以上保持した。得られた鋼塊を鍛造および熱間圧延して直径:8.0mmの線材とした。 The experiment was performed on a real machine (or laboratory level). That is, in the actual machine, the molten steel melted in the converter is put into a ladle (in the laboratory, 500 kg of molten steel simulating the molten steel discharged from the converter is melted), and various fluxes are added to the components. Adjustment, electrode heating, and argon bubbling were performed, and molten steel treatment (slag refining) was performed. Moreover, after adjusting other components, Ca, Mg, Ce, Ba, Li, etc. were added during the molten steel treatment as needed and held for 5 minutes or longer. The obtained steel ingot was forged and hot-rolled to obtain a wire having a diameter of 8.0 mm.
得られた、各線材について、鋼中のSrおよびLiの含有量を下記の方法で測定すると共に、弁ばねを模擬した回転曲げ疲労試験による評価試験を行った。 About each obtained wire, while measuring content of Sr and Li in steel with the following method, the evaluation test by the rotation bending fatigue test which simulated the valve spring was done.
[鋼中のSrおよびLiの含有量]
1)含有量が0.2ppm(mg/kg)以上の場合(定量下限値が0.2ppm)
対象となる線材から試料0.5gを採取してビーカーに取り、純水、塩酸および硝酸を加えて加熱分解した。放冷後、100mL(ミリリットル)のメスフラスコに移し入れ、測定溶液とした。この測定溶液を純水で希釈し、ICP質量分析装置(型式 SPQ8000:セイコーインスツルメント社製)を用い、SrおよびLiを定量分析した。
[Contents of Sr and Li in Steel]
1) When the content is 0.2 ppm (mg / kg) or more (lower limit of determination is 0.2 ppm)
A 0.5 g sample was taken from the target wire, taken into a beaker, and heated and decomposed by adding pure water, hydrochloric acid and nitric acid. After standing to cool, it was transferred to a 100 mL (milliliter) volumetric flask to prepare a measurement solution. This measurement solution was diluted with pure water, and Sr and Li were quantitatively analyzed using an ICP mass spectrometer (model SPQ8000: manufactured by Seiko Instruments Inc.).
2)含有量が0.2ppm(mg/kg)未満の場合(定量下限値が0.03ppm)
対象となる線材から試料0.5gを採取してビーカーに取り、純水、塩酸および硝酸を加えて加水分解を行った。その後塩酸を加えて酸濃度を調整し、メチルイソブチルケトン(MIBK)を加えて振とうし、鉄分をMIBK相に抽出した。静置後、水相のみを取り出し、100mLのメスフラスコに移し入れ、測定溶液とした。この測定溶液を純水で希釈し、ICP質量分析装置(型式 SPQ8000:セイコーインスツルメント社製)を用い、上記の条件でSrおよびLiを定量分析した。
2) When the content is less than 0.2 ppm (mg / kg) (lower limit of determination is 0.03 ppm)
A 0.5 g sample was collected from the target wire and taken in a beaker, and hydrolyzed by adding pure water, hydrochloric acid and nitric acid. Thereafter, hydrochloric acid was added to adjust the acid concentration, methyl isobutyl ketone (MIBK) was added and shaken, and iron was extracted into the MIBK phase. After standing, only the aqueous phase was taken out and transferred to a 100 mL volumetric flask to obtain a measurement solution. This measurement solution was diluted with pure water, and Sr and Li were quantitatively analyzed under the above conditions using an ICP mass spectrometer (model SPQ8000: manufactured by Seiko Instruments Inc.).
[疲労強度試験(破断率)]
各熱間圧延線材(直径:8.0mm)について、皮削り(直径:7.4mm)→パテンティング→冷間線引き加工(直径:4mm)→オイルテンパー[油焼入れと鉛浴(約450℃)焼戻し連続工程]にて直径4.0mm×650mmのワイヤを作製した。得られたワイヤについて、歪取焼鈍相当処理(400℃)→ショットピーニング→低温焼鈍200℃を行った後、中村式回転曲げ試験機を用いて、公称応力908MPa、回転数:4000〜5000rpm、中止回数:2×107回で試験を行った。そして、破断したもののうち介在物折損したものについて、下記式により破断率を求めた。
破断率(%)=[介在物折損本数/(介在物折損本数+所定回数に達し中止した本数)]×100
[Fatigue strength test (breaking rate)]
For each hot-rolled wire (diameter: 8.0 mm), shaving (diameter: 7.4 mm) → patenting → cold drawing (diameter: 4 mm) → oil temper [oil quenching and lead bath (about 450 ° C.) A wire having a diameter of 4.0 mm × 650 mm was produced in the continuous tempering step]. The obtained wire was subjected to strain relief annealing treatment (400 ° C.) → shot peening → low temperature annealing 200 ° C., and then using a Nakamura rotary bending tester, nominal stress of 908 MPa, rotation speed: 4000 to 5000 rpm, discontinued Number of times: The test was conducted at 2 × 10 7 times. And the fracture | rupture rate was calculated | required by the following formula about what the inclusion broke among the fracture | ruptured things.
Breaking rate (%) = [number of inclusions broken / (number of inclusions broken + number of broken inclusions reached a predetermined number of times)] × 100
これらの結果を、各線材の化学成分組成と共に、下記表1に示す。尚、SrおよびLi以外の元素については、下記の方法によって測定した。
C:燃焼赤外線吸収法
Si,Mn,Ni,Cr,VおよびTi:ICP発光分光分析法
Al,Mg,ZrおよびREM:ICP質量分析法
Ca:フレームレス原子吸光分析法
O:不活性ガス融解法
These results are shown in Table 1 below together with the chemical composition of each wire. In addition, about elements other than Sr and Li, it measured by the following method.
C: Combustion infrared absorption method Si, Mn, Ni, Cr, V and Ti: ICP emission spectroscopy Al, Mg, Zr and REM: ICP mass spectrometry Ca: Flameless atomic absorption analysis O: Inert gas melting method
これらの結果から、次のように考察できる。試験No.1〜3,5,6,9,10,13,18〜27のものでは、化学成分組成が適切であり、介在物組成も適切な範囲に制御されたものとなり、良好な疲労強度が得られていることが分かる。 From these results, it can be considered as follows. Test No. In the case of 1 to 3, 5, 6, 9, 10, 13, 18 to 27, the chemical component composition is appropriate, and the inclusion composition is also controlled within an appropriate range, and good fatigue strength is obtained. I understand that
これに対して、試験No.4,7,8,11,12,14〜17のものでは、化学成分組成が適切な範囲を外れ、介在物組成が適切な範囲に制御されたものとなっていないので、疲労試験結果が良くない。 In contrast, test no. In the case of 4, 7, 8, 11, 12, 14-17, the chemical composition composition is outside the appropriate range, and the inclusion composition is not controlled within the appropriate range, so the fatigue test result is good. Absent.
試験No.4、7では、Sr,CaおよびMgは適切に制御されているが、Al濃度が高かったり低かったりして破断率が高くなっている。 Test No. In Nos. 4 and 7, Sr, Ca and Mg are appropriately controlled, but the Al concentration is high or low, and the fracture rate is high.
試験No.8,11,12では、Sr濃度が高かったり低かったりして破断率が高くなっている。 Test No. In 8, 11 and 12, the Sr concentration is high or low, and the breaking rate is high.
試験No.14,16では、SrおよびAl濃度は適切であるが、CaやMgの濃度が低く破断率が高くなっている。 Test No. 14 and 16, the Sr and Al concentrations are appropriate, but the Ca and Mg concentrations are low and the fracture rate is high.
試験No.15,17では、SrおよびAl濃度は適切であるが、CaやMgの濃度が高過ぎて破断率が高くなっている。尚、試験No.18は、Li濃度が好ましい上限を外れているものであるが、試験No.19のものと比べて効果が飽和している。 Test No. In 15 and 17, the Sr and Al concentrations are appropriate, but the Ca and Mg concentrations are too high and the fracture rate is high. Test No. No. 18 shows that the Li concentration is outside the preferred upper limit. The effect is saturated compared to 19 items.
このように、Sr,Ca,MgおよびAlのすべてを適切に制御することが必要であることが分かる。 Thus, it can be seen that it is necessary to appropriately control all of Sr, Ca, Mg and Al.
Claims (4)
A spring obtained from the Si-killed steel wire rod according to any one of claims 1 to 3.
Priority Applications (11)
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JP2006356310A JP4177404B2 (en) | 2006-12-28 | 2006-12-28 | Si-killed steel wire rod and spring with excellent fatigue characteristics |
KR1020117015446A KR101146889B1 (en) | 2006-12-28 | 2007-12-03 | Si KILLED STEEL WIRE MATERIAL HAVING EXCELLENT FATIGUE PROPERTY AND SPRING |
EP07832956A EP2123784B1 (en) | 2006-12-28 | 2007-12-03 | Si KILLED STEEL WIRE MATERIAL HAVING EXCELLENT FATIGUE PROPERTY AND SPRING |
CN 201010569514 CN101982555B (en) | 2006-12-28 | 2007-12-03 | Si killed steel wire material having excellent fatigue property and spring |
EP11008115A EP2410069B1 (en) | 2006-12-28 | 2007-12-03 | Si-killed steel wire rod and spring excellent in fatigue properties |
CNA2007800453391A CN101553587A (en) | 2006-12-28 | 2007-12-03 | Si killed steel wire material having excellent fatigue property and spring |
US12/520,993 US9062361B2 (en) | 2006-12-28 | 2007-12-03 | Si-killed steel wire rod and spring excellent in fatigue properties |
PCT/JP2007/073336 WO2008081673A1 (en) | 2006-12-28 | 2007-12-03 | Si KILLED STEEL WIRE MATERIAL HAVING EXCELLENT FATIGUE PROPERTY AND SPRING |
BRPI0720475A BRPI0720475B1 (en) | 2006-12-28 | 2007-12-03 | self-contained steel wire rod with excellent fatigue and spring properties obtained from it |
BR122016000461A BR122016000461B1 (en) | 2006-12-28 | 2007-12-03 | self-contained steel wire rod with excellent fatigue and spring properties obtained from it |
KR1020097012832A KR101108334B1 (en) | 2006-12-28 | 2007-12-03 | Si KILLED STEEL WIRE MATERIAL HAVING EXCELLENT FATIGUE PROPERTY AND SPRING |
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