JP5047871B2 - Steel wire rod with excellent wire drawing workability and fatigue resistance - Google Patents

Steel wire rod with excellent wire drawing workability and fatigue resistance Download PDF

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JP5047871B2
JP5047871B2 JP2008112929A JP2008112929A JP5047871B2 JP 5047871 B2 JP5047871 B2 JP 5047871B2 JP 2008112929 A JP2008112929 A JP 2008112929A JP 2008112929 A JP2008112929 A JP 2008112929A JP 5047871 B2 JP5047871 B2 JP 5047871B2
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浩一 磯部
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Description

本発明は伸線加工性と耐疲労特性に優れた高清浄度鋼に関するものであり、好ましくは高張力鋼線、極細鋼線、高強度ばね(特に弁ばね)などとした時に極めて有用な高清浄度鋼に関するものである。   The present invention relates to a high cleanliness steel excellent in wire drawing workability and fatigue resistance, and is preferably a very useful high strength steel wire, ultrafine steel wire, high strength spring (particularly a valve spring), etc. It relates to clean steel.

伸線加工により0.1〜0.5mmに伸線される極細鋼線や高い疲労強度が要求されるばね用鋼材では、鋼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。これら非金属介在物は、伸線中の断線原因となり、また疲労強度を低下させる原因となるためである。こうした観点から上記のような用途に使用される鋼材には、非金属介在物を極力低減した高清浄度鋼が用いられる。   For ultra-fine steel wires drawn to 0.1 to 0.5 mm by wire drawing and spring steel materials that require high fatigue strength, it is necessary to reduce hard non-metallic inclusions present in the steel as much as possible. It is. This is because these non-metallic inclusions cause disconnection during wire drawing and cause a decrease in fatigue strength. From this point of view, high cleanliness steel in which non-metallic inclusions are reduced as much as possible is used as the steel material used for the above-described applications.

近年、排ガス低減や燃費改善を目的として自動車の軽量化や高出力化の要望が高まってきており、エンジンやサスペンション等に用いられる弁ばねや懸架ばねは、高応力設計が志向されている。そのためばね鋼は、高強度化及び細径化していく方向にあり、負荷応力は益々増大することが予想されている。このため、耐疲労特性や耐へたり性においても一段と優れた高性能のばね鋼が求められており、特に弁ばねは最も高い疲労強度が要求されている。   In recent years, there has been an increasing demand for lighter and higher-powered automobiles for the purpose of reducing exhaust gas and improving fuel efficiency, and valve springs and suspension springs used for engines, suspensions, and the like are designed for high stress. Therefore, spring steel is in the direction of increasing strength and reducing the diameter, and the load stress is expected to increase more and more. For this reason, there is a demand for a high-performance spring steel that is further excellent in fatigue resistance and sag resistance. In particular, valve springs are required to have the highest fatigue strength.

一方、タイヤコードに代表される極細鋼線についても、タイヤの軽量化を目的として高強度化が進み、最近では4000MPa級の強度を有するスチールコードが使用されるに至っている。しかし極細鋼線を高強度化するほど、伸線加工時(伸線時)に介在物を起点に断線しやすくなるため、一層の介在物が少ない伸線加工性に優れた鋼材が要求されている。   On the other hand, with respect to ultra fine steel wires typified by tire cords, the strength has been increased for the purpose of reducing the weight of tires, and steel cords having a strength of 4000 MPa class have recently been used. However, the higher the strength of ultrafine steel wire, the easier it is to break with inclusions as the starting point during wire drawing (during wire drawing). Therefore, there is a demand for steel materials with fewer wire inclusions and excellent wire drawing workability. Yes.

上述したように、これらばね鋼や極細鋼線は高強度化するにつれて非金属介在物に起因する疲労折損や断線が生じやすくなり、その主たる原因である非金属介在物の低減及び小型化の要求は一段と厳しくなっている。   As described above, as these spring steels and ultrafine steel wires become stronger, fatigue breakage and breakage due to non-metallic inclusions are likely to occur, and the main cause is the demand for reduction and miniaturization of non-metallic inclusions. Is getting tougher.

硬質の非金属介在物の低減及び小型化については、これまでに多くの技術が提案されており、例えば非特許文献1には、ばね鋼では介在物を融点が1400〜1500℃以下のCaO−Al23−SiO2系に制御すると疲労破壊の起点とならないこと、またタイヤコードではAl23等の非延性介在物を低減すればよいことなどが開示されている。また特許文献1〜2には、介在物の平均組成をSiO2:20〜60%、MnO:10〜80%、CaO:50%以下、MgO:15%以下とすれば(特許文献1の場合)、あるいは介在物の平均組成をSiO2:35〜75%、Al23:30%以下、CaO:50%以下、MgO:25%以下とすれば、伸線加工時または伸線時に介在物が砕かれ分散するため、無害化できることが記載されている。 For reducing and reducing the size of hard non-metallic inclusions, many techniques have been proposed so far. For example, in Non-Patent Document 1, inclusions in spring steel have a melting point of 1400-1500 ° C. It has been disclosed that if controlled to Al 2 O 3 —SiO 2 system, it does not become a starting point of fatigue failure, and that non-ductile inclusions such as Al 2 O 3 may be reduced in the tire cord. In Patent Documents 1 and 2, if the average composition of inclusions is SiO 2 : 20 to 60%, MnO: 10 to 80%, CaO: 50% or less, MgO: 15% or less (in the case of Patent Document 1) ), Or if the average composition of inclusions is SiO 2 : 35 to 75%, Al 2 O 3 : 30% or less, CaO: 50% or less, MgO: 25% or less, intervening during wire drawing or wire drawing It describes that it can be rendered harmless because it breaks up and disperses.

しかしながら、近年の要求特性の向上を鑑みると、さらなる高性能化が求められる。   However, in view of the recent improvement in required characteristics, higher performance is required.

なお特許文献3では、Si系脱酸剤とアルカリ金属化合物の混合物を溶鋼中に加えて、脱酸生成物の組成を、アルカリ金属を含む組成にコントロールしながら清浄鋼を製造している。これらアルカリ金属はアルミナ系やSiO2系の硬質非金属介在物の融点を下げるために使用されており、その結果、該非金属介在物を熱間圧延中に糸のように細長く引き延ばすことができ、伸線性や耐疲労特性に無害な形態にしている。なお前記アルカリ金属としては、例えばNaやLiなどが使用されているが、NaとLiは同様な効果を有する元素であるとされている。またアルカリ金属は溶鋼中にそのまま添加しても歩留まりが悪いため、脱酸剤と共に添加することを推奨しており、例えば転炉から取鍋へ出鋼した後の溶鋼処理(LF)工程初期にLiをLiFの形態で珪酸ナトリウムと共に攪拌用Ar気泡が上昇してくる位置に添加している。 In Patent Document 3, a clean steel is manufactured while adding a mixture of a Si-based deoxidizer and an alkali metal compound to molten steel and controlling the composition of the deoxidation product to a composition containing an alkali metal. These alkali metals are used to lower the melting point of alumina and SiO 2 hard nonmetallic inclusions, and as a result, the nonmetallic inclusions can be elongated like a thread during hot rolling, The form is harmless to the drawability and fatigue resistance. For example, Na or Li is used as the alkali metal, and Na and Li are considered to be elements having the same effect. Alkaline metals are recommended to be added together with a deoxidizer because the yield is poor even if it is added to molten steel as it is. For example, at the beginning of the molten steel treatment (LF) process after steel is removed from the converter to the ladle. Li is added in the form of LiF together with sodium silicate at the position where the stirring Ar bubbles rise.

また特許文献4でも、介在物の融点を低下して熱間圧延時に介在物を変形させることを目的に、アルカリ金属を溶鋼中に添加している。該アルカリ金属としては、Li、Na、Kなどが使用されているが、これらも同様な効果を有する元素であるとされている。またアルカリ金属は溶鋼中に溶解しないため、Siで希釈して使用することを推奨している。   Also in Patent Document 4, an alkali metal is added to molten steel for the purpose of lowering the melting point of inclusions and deforming the inclusions during hot rolling. As the alkali metal, Li, Na, K and the like are used, and these are also considered to be elements having the same effect. In addition, since alkali metals do not dissolve in molten steel, it is recommended to use diluted with Si.

特許文献5にも延性のある介在物とするために、SiO2が主体の介在物においてアルカリ金属の酸化物を含有させている。なおこの文献では介在物の延性向上は、上記文献3〜4に記載されているような融点低下ではなく、アルカリ金属による介在物と溶鉄との界面エネルギーの低下によるものであると説明されているが、いずれにせよアルカリ金属であるNa、K、Liは等価であると説明されている。しかもアルカリ金属は、スラグ添加で、最大で10%(スラグ中濃度)程度も添加されている。なお実際にはNaだけが使用されている。 In order to make ductile inclusions in Patent Document 5, alkali metal oxides are included in inclusions mainly composed of SiO 2 . In this document, it is explained that the ductility improvement of inclusions is not due to the melting point decrease as described in the above documents 3 to 4, but due to the decrease in interfacial energy between inclusions and molten iron due to alkali metal. However, in any case, the alkali metals Na, K, and Li are described as being equivalent. Moreover, the alkali metal is added as much as 10% (concentration in slag) by adding slag. Actually, only Na is used.

特許文献6はSi脱酸する際に、アルカリ金属酸化物を利用することを提案している。この文献においてアルカリ金属酸化物を利用するのは、取鍋スラグ中のSiO2活量を充分に低い状態にすることができ、その結果、溶鋼中の全酸素濃度を低下させることができるためであるとしている。なおこの文献においても、アルカリ金属酸化物としては、Na2O、K2O、Li2Oなどが挙げられているがこれらは同様な効果を有する元素として記載されている。この文献では前記特許文献5とは異なり実際にLiを添加しているが、具体的にはLi2Oを炭酸塩の状態でスラグに配合しており、Liの場合の濃度(スラグ中)は最大で8%程度まで達している。 Patent Document 6 proposes to use an alkali metal oxide when deoxidizing Si. The reason for using alkali metal oxide in this document is that the SiO 2 activity in the ladle slag can be made sufficiently low, and as a result, the total oxygen concentration in the molten steel can be reduced. There is. In this document, Na 2 O, K 2 O, Li 2 O and the like are listed as alkali metal oxides, but these are described as elements having similar effects. In this document, Li is actually added unlike the above-mentioned patent document 5, but specifically, Li 2 O is blended in the slag in a carbonate state, and the concentration in Li (in the slag) is It has reached up to about 8%.

特許文献7は、total−Liを0.020ppm〜20ppm(質量基準)の範囲で含有するか、或いはtotal−LiとSiをtotal−Li/Si(質量比)=1×10-6〜1000×10-6で含有させ、Li2Oに特有の結晶相の微細析出を促す効果を利用して、ガラス質状の単相の介在物中に平衡相である結晶相が微細に析出した状態で分塊圧延や熱間圧延を行い、低融点・低粘性のために延伸性に富むガラス質と結晶相とガラス相の界面には圧延時の応力が集中し、酸化物が画期的に分断されやすくなることが記載されている。 Patent Document 7 contains total-Li in the range of 0.020 ppm to 20 ppm (mass basis), or total-Li and Si in total-Li / Si (mass ratio) = 1 × 10 −6 to 1000 ×. is contained in 10 -6, by utilizing the effect of promoting the precipitation of fine specific crystalline phase Li 2 O, in a state in which the crystalline phase in equilibrium phase in inclusions glassy shaped single phase is finely precipitated Rolling and hot rolling are performed, and due to the low melting point and low viscosity, the stress during rolling is concentrated at the interface between the glassy material, which is highly stretchable, and the crystal phase and glass phase, and the oxide breaks down dramatically. It is described that it becomes easy to be done.

特公平6−74484号公報Japanese Patent Publication No. 6-74484 特公平6−74485号公報Japanese Patent Publication No. 6-74485 特開平1−319623号公報JP-A-1-319623 特開平2−15111号公報Japanese Patent Laid-Open No. 2-15111 特開2002−167647号公報JP 2002-167647 A 特開2002−194497号公報JP 2002-194497 A 特開2006−16639号公報JP 2006-16639 A 社団法人日本鉄鋼協会編集「第126・127回西山記念技術講座」、社団法人日本鉄鋼協会出版、昭和63年11月14日、第145〜165頁Edited by the Japan Iron and Steel Institute “126th and 127th Nishiyama Memorial Technology Course”, published by the Japan Iron and Steel Institute, November 14, 1988, pages 145 to 165

従来提案されている、CaO−Al23−SiO2系介在物の融点を1400〜1500℃以下の領域に介在物組成を制御した上、熱間圧延や伸線加工で介在物を延伸したり、分断する方法では、酸化物系介在物における結晶相の存在により熱間圧延時の軟質化や伸線加工時の介在物の破砕性が十分でないために、介在物の小型化は不十分となる。また、スラグにアルカリ金属酸化物(Na2O、K2O、Li2O、)を添加して、Al23やSiO2等の有害介在物を無害化する方法では、それらの添加濃度をあまり高くすると、耐火物の溶損により却って耐火物由来の外来系介在物が増加して、伸線加工性や耐疲労特性を著しく低下させる。また、上述の方法を組み合わせ、耐火物をあまり損傷させない範囲でスラグの融点を低下させても、介在物の微細化は不十分となり、その結果、耐疲労特性や伸線加工性の改善は限定されたものになる。 The inclusion composition is controlled by hot rolling or wire drawing after the melting point of the conventionally proposed CaO-Al 2 O 3 -SiO 2 inclusion has a melting point of 1400 to 1500 ° C or lower. In the method of cutting or dividing, the inclusions are not sufficiently miniaturized because the oxide phase inclusions are not sufficiently soft during hot rolling and the inclusions are not easily crushed during wire drawing. It becomes. In addition, in the method of detoxifying harmful inclusions such as Al 2 O 3 and SiO 2 by adding alkali metal oxides (Na 2 O, K 2 O, Li 2 O, etc.) to the slag, the concentration of those added If it is too high, the foreign inclusions derived from the refractory increase due to melting of the refractory, and the wire drawing workability and fatigue resistance are significantly reduced. Moreover, even if the melting point of the slag is lowered within a range that does not damage the refractory so much by combining the above-described methods, the inclusions are not sufficiently refined, and as a result, the improvement in fatigue resistance and wire drawing workability is limited. It will be done.

本発明は上記の様な事情に着目してなされたものであって、その目的は、伸線加工性と耐疲労特性がさらに改善された高清浄度鋼を提供することにある。   The present invention has been made paying attention to the above-described circumstances, and an object thereof is to provide a high cleanliness steel having further improved wire drawing workability and fatigue resistance characteristics.

本発明者らは、前記課題を解決するために鋭意研究を重ねた結果、B23を複合系酸化物(例えば、CaO−Al23−SiO2系複合酸化物やCaO−Al23−SiO2−MgO系複合酸化物など)に含有(固溶)させることができると、熱間圧延時に複合酸化物を著しく軟質化させ、また著しく伸線加工時の破砕性を向上でき、その結果、熱間圧延や伸線加工で上記複合酸化物が微細に分断される結果、伸線加工性や耐疲労特性を顕著に改善できることを見出した。より具体的には、鋼線材の長手方向縦断面における厚み2μm以上のSiO2−Al23−CaO系酸化物の平均組成を、SiO2:30〜60%、Al23:1〜30%、CaO:10〜50%とし、複合系酸化物の融点を1400℃以下好ましくは1350℃以下の組成に制御した上で、さらにこれらの酸化物にB23:0.1〜10%の範囲(質量基準)を含有させることにより、酸化物系介在物は微細に分散され、伸線加工性や疲労強度を顕著に向上できる。 As a result of intensive studies to solve the above problems, the present inventors have made B 2 O 3 into a complex oxide (for example, CaO—Al 2 O 3 —SiO 2 complex oxide or CaO—Al 2). O 3 When -SiO 2 -MgO-based composite oxides) may be contained (dissolved), the hot significantly soften the composite oxide at the time of rolling, also can significantly improve the friability during wiredrawing As a result, it has been found that, as a result of the above-mentioned complex oxide being finely divided by hot rolling or wire drawing, wire drawing workability and fatigue resistance can be remarkably improved. More specifically, the average composition of SiO 2 —Al 2 O 3 —CaO-based oxide having a thickness of 2 μm or more in the longitudinal cross-section of the steel wire rod is defined as SiO 2 : 30 to 60%, Al 2 O 3 : 1 30%, CaO: 10 to 50%, and the melting point of the composite oxide is controlled to a composition of 1400 ° C. or less, preferably 1350 ° C. or less, and further B 2 O 3 : 0.1 to 10 is added to these oxides. By including the range of% (based on mass), the oxide inclusions are finely dispersed, and the wire drawing workability and fatigue strength can be remarkably improved.

このような本発明に対して、非特許文献1や特許文献1〜2に開示されているような発明(CaO−Al23−SiO2系介在物の融点が1400〜1500℃以下となる領域に介在物組成を制御する発明など)では介在物はある程度は小型化されるものの、熱間圧延時の軟質化や伸線加工時の破砕性が十分でないために、小型化は不十分となっている。これらの文献では介在物組成を直接制御することを目的としている。介在物組成を直接制御するためには、スラグ精錬中に、無害なトップスラグを巻き込ませ、巻き込まれたスラグと溶鋼中の有害な脱酸生成物(特にSiO2やAl23)を合体、反応させ、無害化することが重要となる。 In contrast to the present invention, the invention disclosed in Non-Patent Document 1 and Patent Documents 1 and 2 (CaO—Al 2 O 3 —SiO 2 inclusions have a melting point of 1400 to 1500 ° C. or lower. In inventions that control the inclusion composition in the region, etc.), the inclusions are reduced in size to some extent, but because the softening during hot rolling and the crushability during wire drawing are not sufficient, miniaturization is insufficient. It has become. These documents aim to directly control the inclusion composition. In order to directly control the inclusion composition, harmless top slag is involved during slag refining, and the slag and harmful deoxidation products (especially SiO 2 and Al 2 O 3 ) in molten steel are combined. It is important to react and detoxify.

また特許文献3〜6ではアルカリ金属酸化物(Na2O、K2O、Li2O)を用いて、Al23やSiO2等の有害介在物を軟質化して変形能を向上させたり、SiO2系介在物に含有させ、溶鋼との界面エネルギーを低下して酸化物を微細化させたり、Na2O、K2O、Li2OやZrO2を用いてスラグ中のSiO2の活量を下げ、酸化物系介在物を低融点化すると共に低酸素化を図ることで疲労強度向上する方法が記載されている。 In Patent Documents 3 to 6, alkali metal oxides (Na 2 O, K 2 O, Li 2 O) are used to soften harmful inclusions such as Al 2 O 3 and SiO 2 to improve deformability. , SiO 2 inclusions to reduce the interfacial energy with molten steel to refine the oxide, or Na 2 O, K 2 O, Li 2 O or ZrO 2 to use SiO 2 in the slag. A method is described in which the fatigue strength is improved by lowering the activity, lowering the melting point of oxide inclusions and lowering the oxygen.

特許文献7は、total−Li量或いはtotal−LiとSiをtotal−Li/Si(質量比)を特定の範囲に制御することで、Li2Oに特有の結晶相の微細析出を促す効果を利用して、酸化物の分断を促進することで疲労強度や伸線加工性が改善できることが記載されている。 Patent Document 7 has an effect of promoting fine precipitation of a crystal phase peculiar to Li 2 O by controlling total-Li amount or total-Li and Si to a specific range of total-Li / Si (mass ratio). It is described that fatigue strength and wire drawing workability can be improved by utilizing and promoting oxide fragmentation.

特許文献3〜7の方法では、酸化物系介在物における結晶相の晶出防止や固溶促進が不十分であるばかりでなく、スラグ中のアルカリ金属酸化物(Na2O、K2O、Li2O)濃度をあまり高くすると、逆にスラグの融点や粘性が著しく低下し、耐火物の溶損性が著しく高くなり、このような状態で溶鋼やスラグを強撹拌すると耐火物の損傷が激しくなり、脱酸系介在物の軟質化を図ろうとしても、却って耐火物由来の外来系介在物が増加し、伸線加工性や耐疲労特性は著しく低下する。 In the methods of Patent Documents 3 to 7, not only the prevention of crystallization and the promotion of solid solution in the oxide inclusions are insufficient, but also alkali metal oxides (Na 2 O, K 2 O, If the Li 2 O) concentration is too high, the melting point and viscosity of the slag will be significantly reduced, and the refractory will be significantly damaged. If the molten steel or slag is vigorously stirred in such a state, the refractory will be damaged. Even if it becomes intense and attempts to soften the deoxidized inclusions, the foreign inclusions derived from the refractory increase on the contrary, and the wire drawing workability and fatigue resistance properties are significantly lowered.

また、上述の方法を組み合わせ、耐火物をあまり損傷させない範囲でスラグの融点を低下させても、介在物の微細化は不十分となり、その結果、耐疲労特性や伸線加工性の改善は限定されたものになる。本発明の鋼では、耐火物に由来する酸化物系介在物の増加を抑制しながら、酸化物系介在物における結晶相の晶出防止や固溶促進を効果的に図ることにより、鋼材中の酸化物系介在物の熱間加工時における変形能と伸線加工時における破砕性を顕著に高め、それにより、製品における介在物を極めて微細化できることを見出し、本発明を完成した。なお、かかる鋼は、例えば、B23の添加方法を工夫してB23の分解を極力避けて、溶鋼中の介在物へ効率よく添加することによって製造できる。 Moreover, even if the melting point of the slag is lowered within a range that does not damage the refractory so much by combining the above-described methods, the inclusions are not sufficiently refined, and as a result, the improvement in fatigue resistance and wire drawing workability is limited. It will be done. In the steel of the present invention, while suppressing the increase in oxide inclusions derived from refractories, effectively preventing the crystallization of the crystal phase and promoting solid solution in the oxide inclusions, The present inventors have found that the deformability during hot working of oxide inclusions and the crushability during wire drawing are significantly increased, thereby making it possible to make the inclusions in the product extremely fine, thereby completing the present invention. Incidentally, such a steel, for example, B 2 O 3 additive method as much as possible to avoid the decomposition of B 2 O 3 by devising a can be prepared by adding efficiently to inclusions in the molten steel.

すなわち、本発明に係る耐疲労特性又は伸線加工性に優れた高清浄度鋼は、
(1)鋼の化学成分が質量%で、C:0.45〜1.1%、Si:0.1〜3.0%、Mn:0.1〜2.0%を含み、残部はFe及び不可避的不純物からなり、不純物中のPは0.030%以下、Sは0.030%以下、Alは0.005%以下、Nは0.006%以下、O(酸素)は0.0030%以下の鋼線材であって、その長手方向縦断面における厚みが2μm以上の酸化物の平均組成が、質量%で、SiO2:30〜60%、Al23:1〜30%、CaO:10〜50%、B23:0.1〜10%を含むことを特徴とする鋼線材。
(2)鋼線材の長手方向縦断面における厚みが2μm以上の酸化物の平均組成が、さらに、質量%で、0.1〜15%のMgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23よりなる群から選択される少なくとも1種を含有する上記(1)に記載の鋼線材。
(3)鋼の化学成分が、さらに、質量%で、Cr:0.005〜1.5%、Cu:0.005〜0.5%、Ni:0.005〜1.5%、Mo:0.005〜0.5%、W:0.005〜0.5%、Co:0.005〜2.0%、B:0.0002〜0.0030%、V:0.005〜0.5%、Ti:0.005〜0.1%、Zr:0.005〜0.1%、Nb:0.005〜0.100%を1種以上含む上記(1)又は(2)に記載の鋼線材。
である。
That is, high cleanliness steel excellent in fatigue resistance or wire drawing workability according to the present invention,
(1) The chemical composition of steel is% by mass, including C: 0.45-1.1%, Si: 0.1-3.0%, Mn: 0.1-2.0%, the balance being Fe And P in the impurity is 0.030% or less, S is 0.030% or less, Al is 0.005% or less, N is 0.006% or less, and O (oxygen) is 0.0030. %, And the average composition of oxides having a thickness of 2 μm or more in the longitudinal direction in the longitudinal direction is mass%, SiO 2 : 30 to 60%, Al 2 O 3 : 1 to 30%, CaO : 10~50%, B 2 O 3 : steel wire rod, characterized in that it comprises 0.1 to 10%.
(2) The average composition of the oxide having a thickness of 2 μm or more in the longitudinal cross section in the longitudinal direction of the steel wire is 0.1% to 15% MgO, Na 2 O, K 2 O, Li 2 O by mass%. The above (1) contains at least one selected from the group consisting of ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , TiO 2 , NbO, FeO, and Fe 2 O 3. Steel wire rod.
(3) The chemical composition of the steel is further mass%, Cr: 0.005-1.5%, Cu: 0.005-0.5%, Ni: 0.005-1.5%, Mo: 0.005-0.5%, W: 0.005-0.5%, Co: 0.005-2.0%, B: 0.0002-0.0030%, V: 0.005-0. 5%, Ti: 0.005 to 0.1%, Zr: 0.005 to 0.1%, Nb: 0.005 to 0.100% or more are described in the above (1) or (2) Steel wire rod.
It is.

また、本発明に係る耐疲労特性又は伸線加工性に優れた鋼線材の製造方法については、基本プロセスとして、通常の転炉による一次精錬、転炉外での二次精錬後、連続鋳造し、熱間圧延する鋼線材の製造方法を適用することができる。この製造方法において、転炉から取鍋へ出鋼後、添加原料としてのB23を単独、あるいは他酸化物と共に、取鍋内の溶鋼へあるいは事前に添加した酸化物系フラックスへ、もしくは取鍋スラグへ添加する際、溶鋼中におけるAlを0.005%以下として、溶鋼を撹拌しながらB23を添加するとともに、溶鋼の撹拌により、B23、フラックスもしくは取鍋スラグを溶鋼へ懸濁させ、その後連続鋳造工程までの溶鋼中におけるAlを0.005%以下に制御するとともに、加えて二次精錬終了後の取鍋スラグ中のCaO/SiO2比を0.3〜2.0とする製造方法、または、転炉から取鍋へ出鋼後、B23を酸化物系フラックスに含有させて、取鍋内の溶鋼へ、もしくは取鍋スラグへ添加する際、溶鋼中におけるAlを0.005%以下として、溶鋼を撹拌しながらB23を含有させた酸化物系フラックスを添加し、溶鋼の撹拌により、B23、フラックスもしくは取鍋スラグを溶鋼へ懸濁させ、その後連続鋳造工程までの溶鋼中におけるAlを0.005%以下に制御するとともに、加えて二次精錬終了後の取鍋スラグ中のCaO/SiO2比を0.3〜2.0とする製造方法を組み合わせて適用すればよい。 In addition, regarding the method for producing a steel wire rod excellent in fatigue resistance or wire drawing workability according to the present invention, as a basic process, primary refining by a normal converter, secondary refining outside the converter, and continuous casting are performed. A method for producing a hot-rolled steel wire can be applied. In this manufacturing method, after steel is discharged from the converter to the ladle, B 2 O 3 as an additive raw material alone or with other oxides is added to the molten steel in the ladle or to an oxide flux added in advance, or When adding to the ladle slag, Al in the molten steel is 0.005% or less, and while stirring the molten steel, B 2 O 3 is added, and by stirring the molten steel, B 2 O 3 , flux or ladle slag is added. In addition to controlling the Al in the molten steel to 0.005% or less until the continuous casting process is suspended in the molten steel, in addition, the CaO / SiO 2 ratio in the ladle slag after the secondary refining is 0.3 to 2.0, or after adding steel from the converter to the ladle, adding B 2 O 3 to the oxide flux and adding it to the molten steel in the ladle or to the ladle slag, 0.001 Al in molten steel Percent or less, the addition of oxide-based flux which contains a B 2 O 3 while stirring the molten steel by stirring the molten steel, B 2 O 3, was suspended flux or ladle slag to the molten steel, then continuous casting In addition to controlling Al in molten steel up to the process to 0.005% or less, in addition, combined with a production method in which the CaO / SiO 2 ratio in the ladle slag after the secondary refining is 0.3 to 2.0 And apply.

本発明によれば耐火物由来などの酸化物系介在物の増大を抑制しながらも、熱間加工時の介在物の軟質化や伸線加工時の介在物の破砕性が向上し、製品での介在物サイズはより減少するため、高清浄度鋼の伸線加工性及び耐疲労特性を大幅に改善できる。   According to the present invention, while suppressing the increase of oxide inclusions such as those derived from refractories, the inclusions are softened during hot working and the inclusions are more easily crushed during wire drawing. Since the inclusion size is further reduced, the drawability and fatigue resistance of the high cleanliness steel can be greatly improved.

本発明の高清浄度鋼は、B23が有効利用されている。B23を複合酸化物系介在物(例えば、CaO−Al23−SiO2系複合酸化物やCaO−Al23−SiO2−MgO系複合酸化物など)に含有させると、その介在物を著しく変質させることが可能である。すなわち製鋼時にB23を上記複合酸化物系介在物に含有させ、B23含有複合酸化物系介在物(CaO−Al23−SiO2−B23系複合酸化物やCaO−Al23−SiO2−MgO−B23系複合酸化物など)を形成し、この鋼材を熱間温度に加熱すると、上記介在物は低融点化して軟質化するとともに、特にガラス質状の単相からの種々の結晶相の晶出を効果的に防止でき、あるいは上記介在物中に一旦晶出した結晶相を容易に再固溶することができ、この状態で分塊圧延や熱間圧延を行うと、結晶相を伴わない軟質化したガラス相は極めて延伸性に富み、よく伸びで分断される結果、熱間圧延によって介在物は著しく微細となる。 B 2 O 3 is effectively used in the high cleanliness steel of the present invention. When B 2 O 3 is contained in a complex oxide inclusion (for example, CaO—Al 2 O 3 —SiO 2 complex oxide or CaO—Al 2 O 3 —SiO 2 —MgO complex oxide), The inclusions can be significantly altered. That the B 2 O 3 is contained in the composite oxide inclusions during steel making, B 2 O 3 containing composite oxide inclusions (CaO-Al 2 O 3 -SiO 2 -B 2 O 3 composite oxide Ya CaO—Al 2 O 3 —SiO 2 —MgO—B 2 O 3 composite oxide etc.) and this steel material is heated to a hot temperature, the inclusions lower in melting point and soften, Crystallization of various crystal phases from the glassy single phase can be effectively prevented, or the crystal phase once crystallized in the inclusions can be easily re-dissolved, and in this state, When rolling or hot rolling is performed, the softened glass phase not accompanied by a crystal phase is extremely stretchable, and as a result of being divided by elongation, inclusions become extremely fine by hot rolling.

加えて融点の低下に伴い、伸線加工時の酸化物系介在物の破砕性も向上するため、上記熱間圧延で微細化した酸化物系介在物は更に伸線加工でも細かく破砕される結果、製品段階での酸化物系介在物のサイズは著しく減少するため、伸線加工時に酸化物系介在物起点での断線が抑制されるばかりでなく、この介在物起点での疲労破壊も抑制され耐疲労特性も顕著に改善できる。   In addition, as the melting point decreases, the oxide inclusions in the wire drawing process are also improved, so that the oxide inclusions refined by the hot rolling are further finely broken in the wire drawing process. In addition, the size of oxide inclusions at the product stage is significantly reduced, so that not only wire breakage at the origin of oxide inclusions is suppressed during wire drawing, but also fatigue failure at the origin of inclusions is suppressed. The fatigue resistance can also be remarkably improved.

種々の種類の酸化物成分の添加による酸化物系介在物の改質効果について調査した結果、なかでもB23はCaO−Al23−SiO2系複合酸化物やCaO−Al23−SiO2−MgO系複合酸化物に対して、高温からの冷却や加熱過程で極めて結晶化を抑制する効果や一旦晶出した結晶相を再加熱時に再固溶する効果が極めて大きく、さらに伸線加工時の破砕性も顕著に向上でき、それらの結果として、伸線加工性や耐疲労特性の大幅な改善に寄与することがわかった。本発明は、このような優れたB23の酸化物系介在物の改質効果を高清浄度鋼製造に適用することで、耐疲労特性と伸線加工性に極めて優れた鋼線材の提供を実現するものである。 As a result of investigating the modification effect of oxide inclusions by adding various kinds of oxide components, B 2 O 3 is a CaO—Al 2 O 3 —SiO 2 composite oxide or CaO—Al 2 O. Compared to 3- SiO 2 -MgO-based composite oxides, it has an extremely large effect of suppressing crystallization during cooling from a high temperature and heating process, and an effect of re-dissolving a crystal phase once crystallized upon reheating. It was found that the crushability during wire drawing can be remarkably improved, and as a result, it contributes to a significant improvement in wire drawing workability and fatigue resistance. In the present invention, by applying such an excellent modification effect of oxide inclusions of B 2 O 3 to the production of high cleanliness steel, it is possible to produce a steel wire material that is extremely excellent in fatigue resistance and wire drawing workability. It is to realize the provision.

酸化物系介在物の熱間加工時の変形能は酸化物の結晶化の度合いに強く依存し、介在物の融点とも関連があり、酸化物系介在物結晶質よりはガラス質の方が熱間変形能は高く、また、伸線加工時の破砕性は、酸化物系介在物の融点と相関があり、融点の低下に伴い、伸線加工時の破砕性は向上する。種々の酸化物の中でも、B23は少ない含有量でも上記複合酸化物系介在物の結晶化を効果的に抑制し、また、結晶相の再固溶促進する酸化物であり、また、融点を低下させる酸化物であるため、酸化物系介在物にB23を含有できると熱間加工温度域での変形能や伸線加工時の破砕性を効果的に増大できる。 Deformability during hot working of oxide inclusions depends strongly on the degree of crystallization of the oxide, and is related to the melting point of the inclusions. Glassy is more hot than oxide inclusion crystals. The interdeformability is high, and the friability during wire drawing correlates with the melting point of oxide inclusions, and the friability during wire drawing improves as the melting point decreases. Among various oxides, B 2 O 3 is an oxide that effectively suppresses crystallization of the complex oxide inclusions even at a small content, and promotes re-solution of the crystal phase. Since it is an oxide that lowers the melting point, if B 2 O 3 can be contained in the oxide inclusions, the deformability in the hot working temperature range and the friability during wire drawing can be effectively increased.

本発明の鋼線材中の酸化物の平均組成において、質量%でB23:0.1〜10%を含むことを特徴とする。B23含有量が少なすぎては本発明の効果を発揮することができず、多すぎると逆に伸線加工性や疲労強度が悪化する。酸化物中のB23含有量が0.1〜10質量%であれば、良好な品質を実現することができる。B23含有量が0.5質量%以上であるとより好ましい。1.0質量%以上であるとさらに好ましい。 The average composition of the oxide in the steel wire rod of the present invention is characterized by containing B 2 O 3 : 0.1 to 10% by mass. If the content of B 2 O 3 is too small, the effects of the present invention cannot be exhibited. If the content is too large, the wire drawing workability and fatigue strength are deteriorated. If the content of B 2 O 3 in the oxide is 0.1 to 10% by mass, good quality can be realized. The B 2 O 3 content is more preferably 0.5% by mass or more. More preferably, it is 1.0 mass% or more.

しかしながら、CaO−Al23−SiO2系等の複合酸化物にやみくもにB23を含有させても上記効果を得られない。その効果を得るには、請求項1のように、質量%で、SiO2:30〜60%、Al23:1〜30%、CaO:10〜50%と、CaO−Al23−SiO2系複合酸化物の組成を規定する必要がある。上記組成範囲ではCaO−Al23−SiO2系複合酸化物自体の融点がおよそ1400℃以下で、そのような組成領域であれば上記酸化物系介在物は熱間圧延で変形能が高く、また冷間加工時に破砕し易い。本発明者がB23に着目し種々検討した結果、SiO2、Al23、CaOの組成範囲が上記範囲から外れると、B23を添加し、CaO−Al23−SiO2系複合酸化物にB23を含有させても介在物の熱間加工時の変形能や冷間加工時の破砕性はいくらか改善されるものの十分には改善されない。B23を酸化物系介在物に含有させて熱間加工時の介在物の延性や冷間加工時の破砕性改善効果を得るには、CaO−Al23−SiO2系複合酸化物の組成を質量%で、SiO2:30〜60%、Al23:1〜30%、CaO:10〜50%に制御した上で、B23を所定量添加して初めて、B23の優れた酸化物系介在物の改質効果が得られることが判明した。 However, the above effect cannot be obtained even if B 2 O 3 is added to the complex oxide such as CaO—Al 2 O 3 —SiO 2 . In order to obtain the effect, as in claim 1, in mass%, SiO 2: 30~60%, Al 2 O 3: 1~30%, CaO: 10~50% and, CaO-Al 2 O 3 It is necessary to define the composition of the —SiO 2 -based composite oxide. In the above composition range, the melting point of the CaO—Al 2 O 3 —SiO 2 composite oxide itself is about 1400 ° C. or less, and in such a composition region, the oxide inclusions are highly deformable by hot rolling. Also, it is easy to crush during cold working. As a result of various investigations by the inventor paying attention to B 2 O 3, when the composition range of SiO 2 , Al 2 O 3 , and CaO is out of the above range, B 2 O 3 is added, and CaO—Al 2 O 3 — Even if B 2 O 3 is contained in the SiO 2 -based composite oxide, the deformability during hot working of inclusions and the crushability during cold working are somewhat improved, but not sufficiently improved. In order to obtain the effect of improving ductility of inclusions during hot working and crushability improvement during cold working by including B 2 O 3 in oxide inclusions, CaO—Al 2 O 3 —SiO 2 based composite oxidation in mass% composition of the object, SiO 2: 30~60%, Al 2 O 3: 1~30%, CaO: on controlled at 10-50%, the first time the B 2 O 3 is added a predetermined amount, It has been found that an excellent modification effect of oxide inclusions of B 2 O 3 can be obtained.

なお、鋼線材縦断面において厚み2μm以上の酸化物で平均組成を規定したのは、鋼線材において厚み2μm以下の介在物は疲労破壊起点や冷間伸線での断線原因となることはなく、それら疲労破壊の起点や冷間伸線での断線原因となる介在物は、厚み2μm以上の介在物であり、しかも組成との関連があるため鋼線材縦断面において厚み2μm以上の酸化物で平均組成を規定した。また、厚みが2μm未満ではEPMAや走査電子顕微鏡(SEM)等で組成を分析する際、電子線の広がりにより酸化物直下やその周囲のマトリックスからの信号も拾い、酸化物のみの組成を精度良く測定することが困難となるためである。なお、本発明でいう(鋼線材の)「長手方向縦断面」とは、線材の圧延方向に平行に、その中心線を通って切断した面をいう。さらに「鋼線材」とは、棒状に熱間圧延され、コイル状に巻かれた鋼材を指し、所謂「バーインコイル」を含む鋼製の線材である。酸化物の組成は鋳片や鋼片で測定しても構わないが、製品における伸線加工性や耐疲労特性との相関はより製品に近い段階での酸化物の組成との相関が高く、その意味では鋼線材において酸化物系介在物が所定の組成を満足することが好ましい。   In addition, the average composition was defined by oxides having a thickness of 2 μm or more in the longitudinal section of the steel wire material. The inclusions having a thickness of 2 μm or less in the steel wire material did not cause breakage at the fatigue fracture starting point or cold wire drawing, The inclusions that cause breakage at the starting point of these fatigue fractures and cold wire drawing are inclusions with a thickness of 2 μm or more, and are related to the composition. The composition was defined. When the thickness is less than 2 μm, when analyzing the composition with EPMA, scanning electron microscope (SEM), etc., the signal from the matrix directly under and around the oxide is picked up by the spread of the electron beam, and the composition of the oxide alone is accurately obtained. This is because it becomes difficult to measure. In the present invention, the “longitudinal longitudinal section” (of the steel wire) means a surface cut through the center line in parallel to the rolling direction of the wire. Furthermore, the “steel wire” refers to a steel material that has been hot rolled into a rod shape and wound in a coil shape, and is a steel wire rod that includes a so-called “burn-in coil”. The composition of the oxide may be measured with slabs or steel slabs, but the correlation with the wire drawing workability and fatigue resistance of the product has a high correlation with the oxide composition at a stage closer to the product, In that sense, it is preferable that the oxide inclusions satisfy a predetermined composition in the steel wire.

また、さらに鋼線材の長手方向縦断面における厚みが2μm以上の酸化物の平均組成において、質量%で、MgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23よりなる群から選択される少なくとも1種を、各成分毎に0.1〜15%以下の範囲で含有させることができると、よりB23の結晶化抑制や結晶相の固溶効果による熱間変形能の改善効果や伸線加工時の破砕性が向上効果が安定するため、製品の介在物サイズがより安定して減少するため、伸線加工性や耐疲労特性はより一層向上できる。 Further, in the average composition of the oxide having a thickness of 2 μm or more in the longitudinal longitudinal section of the steel wire rod, the mass percentage is MgO, Na 2 O, K 2 O, Li 2 O, ZrO 2 , MnO, Ce 2 O 3. , La 2 O 3 , Nd 2 O 3 , TiO 2 , NbO, FeO, Fe 2 O 3 , at least one selected from the group consisting of 0.1 to 15% or less for each component If this is possible, the effect of improving the hot deformability by suppressing the crystallization of B 2 O 3 and the solid solution effect of the crystal phase and the effect of improving the friability during wire drawing will become more stable. Therefore, the wire drawing workability and fatigue resistance can be further improved.

また、弁ばねでは高強度化に伴い鋼材のSi濃度は高まる傾向にあり、溶製時にSiO2リッチな酸化物が生成し易い。本酸化物は熱間変形能や冷間での破砕性も低いため、製品でのサイズも大きく耐疲労特性を著しく低下させる。このようなSiO2リッチな酸化物に対し、MgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23の添加はSiO2の活量を低下させたり、介在物に組成における低融点組成域を拡大する等の効果でSiO2リッチな介在物の生成を抑制したり、複合系酸化物と接触した際その酸化物への固溶を促進する結果、製品におけるSiO2リッチな酸化物の出現を顕著に抑制できる。但し、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La2O、Nd23、TiO2、NbO、FeO、Fe23よりなる群から選択される少なくとも1種を15%超の範囲で含有させるとスラグによる耐火物の損傷も大きくなるため、15%以下に制御する必要がある。また、MgOを15%を超えて酸化物系介在物に含有させると融点が上昇したり、結晶化が促進され、却って、熱間加工時に介在物の微細化が阻害される。 Further, in the valve spring, the Si concentration of the steel material tends to increase as the strength is increased, and an oxide rich in SiO 2 is easily generated during melting. Since this oxide has low hot deformability and cold crushability, the size of the product is large and the fatigue resistance is significantly reduced. For such oxides rich in SiO 2 , MgO, Na 2 O, K 2 O, Li 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , TiO 2 , NbO , FeO, or suppress the formation of SiO 2 rich inclusions in effects such expanding or addition of Fe 2 O 3 lowers the activity of SiO 2, a low-melting composition range in the composition in inclusions, composite As a result of promoting the solid solution to the oxide when it comes into contact with the system oxide, it is possible to remarkably suppress the appearance of SiO 2 rich oxide in the product. However, it is selected from the group consisting of Na 2 O, K 2 O, Li 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O, Nd 2 O 3 , TiO 2 , NbO, FeO, Fe 2 O 3. If at least one of these is contained in a range of more than 15%, refractory damage due to slag also increases, so it is necessary to control it to 15% or less. Further, when MgO is contained in an oxide inclusion exceeding 15%, the melting point is increased or crystallization is promoted, and on the contrary, the refinement of the inclusion is inhibited during hot working.

そこで次に、酸化物系介在物の平均組成を目標とする範囲に制御し、酸化物系介在物を効果的に熱間加工で延伸、分断し、伸線加工で破砕して、微細化するための鋼の製造方法について調査・研究を重ね、下記の知見を得た。   Therefore, next, the average composition of the oxide inclusions is controlled to a target range, and the oxide inclusions are effectively stretched and divided by hot working, and are crushed and refined by wire drawing. The following knowledge was obtained through repeated investigations and research on steel manufacturing methods.

転炉による一次精錬、転炉外での二次精錬の工程は、鋼中の不純物元素の低減に極めて有効であり、しかも、この後連続鋳造して鋼塊にすれば製造コストを比較的低く抑えることができる。この転炉による一次精錬、転炉外での二次精錬、連続鋳造の工程で鋼を製造する際に、転炉から連続鋳造の工程において、酸化物系介在物の組成はほぼ規定される。   The primary refining process using the converter and the secondary refining process outside the converter are extremely effective in reducing the impurity elements in the steel. Can be suppressed. When steel is manufactured in the steps of primary refining by the converter, secondary refining outside the converter, and continuous casting, the composition of oxide inclusions is substantially defined in the continuous casting process from the converter.

酸化物系介在物の組成を制御するには、転炉出鋼時や炉外精錬において、SiO2、Al23、CaO、B23、MgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23各成分濃度を、ほぼ目標とする酸化物組成になるよう成分調整したフラックスを添加し、溶鋼に懸濁させる方法が最も有効で、効果的な方法である。 In order to control the composition of oxide inclusions, SiO 2 , Al 2 O 3 , CaO, B 2 O 3 , MgO, Na 2 O, K 2 O, and Li are used at the time of converter steelmaking and in refining outside the furnace. 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , TiO 2 , NbO, FeO, Fe 2 O 3 Concentration of components so that the target oxide composition is almost achieved. The method of adding adjusted flux and suspending it in molten steel is the most effective and effective method.

また、酸化物系フラックス中のAl23、CaO、MgO、ZrO2、Ce23、La23、Nd23、TiO2等の強脱酸元素の酸化物成分の含有量の調整にあたっては、Al,Ca、Mg、Zr、Ce、La、Nd、Tiの各元素は脱酸力が強いため、純物質や、これらの元素を成分調整用合金鉄に含有させたり、各種化合物の形やそれら化合物に混入して溶鋼に添加すると、酸化物を形成するため、それらの生成酸化物を溶鋼中に懸濁した酸化物系介在物と結合させることにより、酸化物系介在物の組成を調整することも可能である。 The content of oxide components of strong deoxidizing elements such as Al 2 O 3 , CaO, MgO, ZrO 2 , Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , and TiO 2 in the oxide flux In the adjustment of Al, Ca, Mg, Zr, Ce, La, Nd, and Ti, each element has a strong deoxidizing power. Therefore, pure substances and alloy elements for component adjustment may contain various elements. Oxide inclusions are formed by combining these oxides with oxide inclusions suspended in molten steel to form oxides when added to molten steel in the form of compounds or mixed with these compounds. It is also possible to adjust the composition.

一方、Al,Ca,Mg,等の強脱酸元素が不可避的に成分調整用合金鉄や各種化合物から溶鋼へ混入し各種酸化物を形成する場合や、上記酸化物系介在物の組成調整用のフラックス等と耐火物が反応して、SiO2、Al23、CaO、MgO、ZrO2、TiO2等が混入する場合もあり、それらの酸化物系介在物の組成への影響を考慮して、酸化物組成調整用のフラックスの組成や添加量を調整する必要がある。 On the other hand, when a strong deoxidation element such as Al, Ca, Mg, etc. is inevitably mixed into molten steel from a component adjusting alloy iron or various compounds to form various oxides, or for the composition adjustment of the oxide inclusions Refractory materials react with the flux of SiO 2 , Al 2 O 3 , CaO, MgO, ZrO 2 , TiO 2, etc., and the influence on the composition of oxide inclusions is considered. Thus, it is necessary to adjust the composition and addition amount of the flux for adjusting the oxide composition.

酸化物系介在物中にB23を所定量含有させることは、Bが弱脱酸元素であることに起因して、B23以外のB化合物の形や合金にBを含有させて溶鋼へ単純に添加しても実現できない。高炭素鋼では溶鋼酸素濃度が低いため、B23以外のB化合物や合金に含有させて、鋼材の材質を劣化させない含有量の範囲でBを溶鋼に添加しても、Bの酸化物を生成させることは難しい。酸化物系介在物中にB23を所定量含有させる方法について種々検討し、溶鋼を撹拌しながらB23の形で添加したり、あるいは他の酸化物と一緒に溶鋼へ、あるいは事前に添加した酸化物系フラックスへ、もしくは取鍋スラグへ添加し、溶鋼の撹拌により、B23、取鍋スラグやフラックス中の他の酸化物成分と一緒に溶鋼へ懸濁させる方法や、また、溶鋼を撹拌しながらB23を含有させた酸化物系フラックスを溶鋼もしくは取鍋スラグに添加し、溶鋼の撹拌によりB23、フラックスもしくは取鍋スラグを溶鋼へ懸濁させて添加する方法がB23を酸化物系介在物に含有させるのに有効なことを見いだした。これらの方法をベースに酸化物系介在物中に効率的にB23を所定量含有させる方法についてさらに検討し、それを実現する方法を見出した。 Inclusion of a predetermined amount of B 2 O 3 in the oxide inclusion causes B to be contained in the form or alloy of a B compound other than B 2 O 3 because B is a weak deoxidizing element. Even if it is simply added to the molten steel, it cannot be realized. Since high-carbon steel has a low oxygen concentration in molten steel, it can be contained in B compounds and alloys other than B 2 O 3 , and even if B is added to the molten steel within a range that does not degrade the steel material, the oxide of B It is difficult to generate. Various studies have been made on the method of containing a predetermined amount of B 2 O 3 in oxide inclusions, and the molten steel is added in the form of B 2 O 3 with stirring, or it is added to the molten steel together with other oxides, or Add to the oxide-based flux added in advance or ladle slag and stir the molten steel together with B 2 O 3 , ladle slag and other oxide components in the flux. Also, an oxide flux containing B 2 O 3 is added to the molten steel or ladle slag while stirring the molten steel, and the B 2 O 3 flux or ladle slag is suspended in the molten steel by stirring the molten steel. It has been found that this method is effective for incorporating B 2 O 3 into oxide inclusions. Based on these methods, a method for efficiently containing a predetermined amount of B 2 O 3 in oxide inclusions was further studied, and a method for realizing the method was found.

溶鋼中に投入する金属Al量又は不可避的に合金鉄等から不純物として混入する金属Al量が多いと、溶鋼中のAlにより酸化物系介在物中のB23が還元され、酸化物系介在物中のB23を必要量確保できないため、AlによるB23の還元を抑制し、酸化物系介在物においてB23を必要量確保する条件について検討した。その結果、B23を添加する前から連続鋳造の工程まで、Al量を0.005%以下、好ましくは0.003%以下に制御することでB23の還元を抑制し、B23を必要量確保できることがわかった。ここで鋼中のAl量は、トータルAl量である。さらに、二次精錬後の時点での取鍋スラグ中のCaO/SiO2比が2を超えると、溶鋼の酸素濃度が低下したり、取鍋スラグから溶鋼へ混入するCaの影響で、酸化物系介在物中のB23が還元され介在物を改質するのに必要な量のB23が確保できなくなるため、上記CaO/SiO2比は2以下にする必要がある。一方、このCaO/SiO2比が0.3未満になると溶鋼中の酸化物系介在物の量が増加し清浄性が悪化するため、前述のCaO/SiO2比は0.3以上に制御することも必要である。また、B23を溶鋼へ直接添加する方法では、上記Al量を制限したり、CaO/SiO2比を2以下に制御することに加え、溶鋼との反応でB23は還元され易いため、B23を添加前に予め酸化物系フラックスを溶鋼に懸濁させて組成制御した上でB23を添加し、B23を懸濁した酸化物系介在物と速やかに複合化することがB23を効率的に酸化物系介在物に含有させるのに有効な方法であることも判明した。 When there is a large amount of metal Al introduced into the molten steel or an amount of metal Al inevitably mixed as an impurity from the alloy iron or the like, B 2 O 3 in the oxide inclusions is reduced by the Al in the molten steel, and the oxide type Since the necessary amount of B 2 O 3 in the inclusions could not be secured, the reduction of B 2 O 3 by Al was suppressed, and the conditions for securing the necessary amount of B 2 O 3 in the oxide inclusions were examined. As a result, before the addition of B 2 O 3 to the continuous casting process, the Al content is controlled to 0.005% or less, preferably 0.003% or less, to suppress the reduction of B 2 O 3 , It was found that the required amount of 2 O 3 can be secured. Here, the amount of Al in the steel is the total amount of Al. Furthermore, when the CaO / SiO 2 ratio in the ladle slag at the time after secondary refining exceeds 2, the oxygen concentration of the molten steel decreases or the oxides are affected by Ca mixed into the molten steel from the ladle slag. Since B 2 O 3 in the system inclusions is reduced and an amount of B 2 O 3 necessary for modifying the inclusions cannot be secured, the CaO / SiO 2 ratio needs to be 2 or less. On the other hand, when the CaO / SiO 2 ratio is less than 0.3, the amount of oxide inclusions in the molten steel increases and the cleanliness deteriorates. Therefore, the CaO / SiO 2 ratio is controlled to 0.3 or more. It is also necessary. In the method of directly adding B 2 O 3 to the molten steel, in addition to limiting the amount of Al and controlling the CaO / SiO 2 ratio to 2 or less, B 2 O 3 is reduced by reaction with the molten steel. Therefore, before adding B 2 O 3 , the oxide flux is suspended in the molten steel in advance and the composition is controlled. Then, B 2 O 3 is added, and the oxide inclusion in which B 2 O 3 is suspended. It has also been found that rapid compounding is an effective method for efficiently incorporating B 2 O 3 into oxide inclusions.

NbOもB23同様に弱脱酸生成物であり、NbOを酸化物系介在物へ所定量含有させるには、B23と同様な配慮が必要であり、種々検討した結果、B23と同様な方法、条件で添加すればNbOを酸化物系介在物へ所定量含有させることが可能なこともわかった。 NbO is also a weak deoxidation product, like B 2 O 3 , and in order to incorporate NbO into the oxide inclusions in a predetermined amount, the same consideration as B 2 O 3 is necessary. It was also found that a predetermined amount of NbO can be added to the oxide inclusions if added in the same manner and under the same conditions as 2 O 3 .

本発明は、上記の知見に基づいて完成されたものである。   The present invention has been completed based on the above findings.

本発明の高清浄度鋼は、伸線加工性や耐疲労特性に優れているため、高張力鋼線、極細鋼線、高強度ばね(特に弁ばね)などに有利に利用できる。これらの用途に本発明の高清浄度鋼を適用する場合、C:0.45〜1.1%、Si:0.1〜3.0%、Mn:0.1〜2.0%を含み、残部はFe及び不純物からなり、不純物中のPは0.030%以下、Sは0.030%以下、Alは0.005%以下、Nは0.005%以下、O(酸素)は0.0030%以下に調整するのが好ましい。   Since the high cleanliness steel of the present invention is excellent in wire drawing workability and fatigue resistance, it can be advantageously used for high-tensile steel wires, ultrafine steel wires, high-strength springs (particularly valve springs), and the like. When applying the high cleanliness steel of the present invention to these uses, C: 0.45-1.1%, Si: 0.1-3.0%, Mn: 0.1-2.0% The balance is Fe and impurities, P in the impurities is 0.030% or less, S is 0.030% or less, Al is 0.005% or less, N is 0.005% or less, and O (oxygen) is 0. It is preferable to adjust to 0030% or less.

また必要により物性向上元素として、質量%で更に、Cr:0.005〜1.50%、Cu:0.005〜0.5%、Ni:0.005〜1.5%、Mo:0.005〜0.5%、W:0.005〜0.5%、Co:0.005〜2.0%、B:0.0002〜0.0030%、V:0.005〜0.5%、Ti:0.005〜0.1%、Zr:0.005〜0.1%、Nb:0.005〜0.100%の1種以上を含有させてもよく、これら元素は単独で又は2種以上を適宜組み合わせて含有していてもよい。残部はFe及び不可避不純物であってもよい。   Further, if necessary, as an element for improving physical properties, by mass%, Cr: 0.005 to 1.50%, Cu: 0.005 to 0.5%, Ni: 0.005 to 1.5%, Mo: 0.00. 005 to 0.5%, W: 0.005 to 0.5%, Co: 0.005 to 2.0%, B: 0.0002 to 0.0030%, V: 0.005 to 0.5% , Ti: 0.005 to 0.1%, Zr: 0.005 to 0.1%, Nb: 0.005 to 0.100% may be included, and these elements may be used alone or You may contain 2 or more types in combination as appropriate. The balance may be Fe and inevitable impurities.

素材鋼の化学成分を規定する理由について説明する。   The reason for defining the chemical composition of the raw steel will be explained.

C:0.45〜1.1%
Cは、強度を確保するのに有効な元素である。しかし、その含有量が0.45%未満の場合には、ばねやスチールコードなどの最終製品に高い強度を付与させることが困難である。一方、その含有量が1.1%を超えると熱間圧延後の冷却過程中に初析セメンタイトが生成して、伸線加工性が著しく劣化する。したがって、Cの含有量は0.45〜1.1%とするのがよい。
C: 0.45-1.1%
C is an element effective for securing strength. However, when the content is less than 0.45%, it is difficult to impart high strength to the final product such as a spring or a steel cord. On the other hand, if the content exceeds 1.1%, pro-eutectoid cementite is generated during the cooling process after hot rolling, and wire drawing workability is significantly deteriorated. Therefore, the C content is preferably 0.45 to 1.1%.

Si:0.1〜3.0%
Siは、脱酸に有効な元素であり、その含有量が0.1%未満ではその効果を発揮させることができない。一方、3.0%を超えて過剰に含有させると、パーライト中のフェライト相の延性が低下してしまう。なお、ばねにおいては、「耐へたり特性」が重要で、Siには「耐へたり特性」を高める作用もあるが、3.0%を超えて含有させてもその効果は飽和してコストが嵩むし、脱炭を助長してしまう。したがって、Si含有量は0.1〜3.0%とするのがよい。
Si: 0.1-3.0%
Si is an element effective for deoxidation, and if its content is less than 0.1%, its effect cannot be exhibited. On the other hand, if the content exceeds 3.0%, the ductility of the ferrite phase in the pearlite is lowered. In springs, “sag resistance” is important, and Si also has the effect of enhancing “sag resistance”, but even if it exceeds 3.0%, the effect is saturated and the cost is reduced. Increases and promotes decarburization. Therefore, the Si content is preferably 0.1 to 3.0%.

Mn:0.1〜2.0%
Mnは、脱酸に有効な元素であり、その含有量が0.1%未満ではこの効果を発揮させることができない。一方、2.0%を超えて過多に含有させると、偏析を生じやすくなり、偏析部へのミクロマルテンの生成により伸線加工性及び耐疲労特性が劣化してしまう。したがって、Mnの含有量は0.1〜2.0%とするのがよい。
Mn: 0.1 to 2.0%
Mn is an element effective for deoxidation, and if its content is less than 0.1%, this effect cannot be exhibited. On the other hand, if the content exceeds 2.0%, segregation is likely to occur, and the drawing workability and fatigue resistance are degraded due to the formation of micromartens in the segregated part. Therefore, the Mn content is preferably 0.1 to 2.0%.

線材の素材鋼となる鋼は、更に下記の元素を含有してもよい。   Steel used as the raw material steel for the wire may further contain the following elements.

Cr:0.005〜1.50%
Crは、既に述べた酸化物の平均組成を比較的容易に所望の範囲に調整することができることに加えて、パーライトのラメラ間隔を小さくして熱間圧延後及びパテンティング後の強度を高める作用を有する。さらに、伸線加工時における加工硬化率を高める作用も有しているので、Crの添加によって比較的低い加工率でも高い強度を得ることができる。Crには耐食性を高める作用もある。これらの効果を確実に得るには、Crは0.005%以上の含有量とすることが望ましい。しかし、1.50%を超えて含有させても前記の効果が飽和するばかりか、過剰なCr23により伸線加工性や耐疲労特性の劣化を招く場合がある。したがって、Crの含有量は、1.50%以下とするのがよい。
Cr: 0.005 to 1.50%
In addition to being able to adjust the average composition of the oxide described above to a desired range relatively easily, Cr increases the strength after hot rolling and patenting by reducing the lamella spacing of pearlite. Have Furthermore, since it has the effect | action which raises the work hardening rate at the time of a wire drawing process, high intensity | strength can be obtained even with a comparatively low processing rate by addition of Cr. Cr also has an effect of improving corrosion resistance. In order to reliably obtain these effects, it is desirable that the Cr content is 0.005% or more. However, the content exceeding 1.50% not only saturates the above effects, but excessive Cr 2 O 3 may lead to deterioration of wire drawing workability and fatigue resistance. Therefore, the Cr content is preferably 1.50% or less.

Nb:0.005〜0.100%
Nbを0.005%以上添加すれば、オーステナイト結晶粒を微細化させ、延性及び靱性を高める作用を有する。しかし、0.1%を超えて含有させても前記の効果が飽和する。したがって、Nbの含有量は、0.1%以下とするのがよい。
Nb: 0.005 to 0.100%
If Nb is added in an amount of 0.005% or more, the austenite crystal grains are refined, and the ductility and toughness are increased. However, the above effect is saturated even if the content exceeds 0.1%. Therefore, the Nb content is preferably 0.1% or less.

Cu:0.005〜0.5%
Cuを0.005%以上添加すれば、耐食性を高める効果を発揮する。この効果を確実に得るには、Cuは0.1%以上の含有量とすることが望ましい。しかし、Cuを0.5%を超えて含有させると、結晶粒界に偏析し、鋼塊の分塊圧延時や線材の熱間圧延時における割れや疵の発生が顕著になる。したがって、Cuの含有量は0.005〜0.5%とするのがよい。
Cu: 0.005-0.5%
If Cu is added by 0.005% or more, the effect of improving the corrosion resistance is exhibited. In order to reliably obtain this effect, it is desirable that the Cu content is 0.1% or more. However, when Cu is contained in excess of 0.5%, segregation occurs at the grain boundaries, and cracks and wrinkles are significantly generated during the ingot rolling of the steel ingot and the hot rolling of the wire. Therefore, the Cu content is preferably 0.005 to 0.5%.

Ni:0.005〜1.5%
Niを0.005%以上添加すれば、フェライト中に固溶してフェライトの靱性を高める作用を有する。この効果を確実に得るには、Niは0.05%以上の含有量とすることが好ましい。しかし、その含有量が1.5%を超えると、焼入れ性が高くなりすぎてマルテンサイトが生成しやすくなり伸線加工性が劣化する。したがって、Niの含有量は0.005〜1.5%とするのがよい。
Ni: 0.005-1.5%
If Ni is added in an amount of 0.005% or more, it has the effect of increasing the toughness of the ferrite by dissolving in the ferrite. In order to reliably obtain this effect, the Ni content is preferably 0.05% or more. However, if the content exceeds 1.5%, the hardenability becomes too high and martensite is easily generated, and the wire drawing workability deteriorates. Therefore, the Ni content is preferably 0.005 to 1.5%.

Mo:0.005〜0.5%
Moを0.005%以上添加すれば、熱処理で微細な炭化物として析出し強度と耐疲労特性を高める作用がある。この効果を確実に得るには、Moは0.1%以上の含有量とすることが好ましい。一方、0.5%を超えて含有させても前記の効果は飽和し、コストが嵩むばかりである。したがって、Moの含有量は0.005〜0.5%とするのがよい。
Mo: 0.005-0.5%
If 0.005% or more of Mo is added, it precipitates as fine carbides by heat treatment and has the effect of increasing strength and fatigue resistance. In order to reliably obtain this effect, the Mo content is preferably 0.1% or more. On the other hand, even if the content exceeds 0.5%, the above effect is saturated and the cost is increased. Therefore, the Mo content is preferably 0.005 to 0.5%.

W:0.005〜0.5%
Wは添加しなくてもよい。Wを0.005%以上添加すれば、Crと同様に伸線加工時の加工硬化率を顕著に高める作用がある。この効果を確実に得るには、Wは0.1%以上の含有量とすることが好ましい。しかし、その含有量が0.5%を超えると鋼の焼入れ性が高くなりすぎて、パテンティング処理が困難になる。したがって、Wの含有量は0.005〜0.5%とするのがよい。
W: 0.005-0.5%
W may not be added. Addition of 0.005% or more of W has an effect of remarkably increasing the work hardening rate at the time of wire drawing as in the case of Cr. In order to reliably obtain this effect, W is preferably set to a content of 0.1% or more. However, if its content exceeds 0.5%, the hardenability of the steel becomes too high and the patenting process becomes difficult. Therefore, the W content is preferably 0.005 to 0.5%.

Co:0.005〜2.0%
Coを0.005%以上添加すれば、初析セメンタイトの析出を抑制する効果を有する。この効果を確実に得るには、Coは0.1%以上の含有量とすることが好ましい。しかし、2.0%を超えて含有させても前記の効果は飽和し、コストが嵩むばかりである。したがって、Coの含有量は0.005〜2.0%とするのがよい。
Co: 0.005 to 2.0%
Addition of 0.005% or more of Co has an effect of suppressing precipitation of pro-eutectoid cementite. In order to reliably obtain this effect, the Co content is preferably 0.1% or more. However, even if the content exceeds 2.0%, the above effects are saturated and the cost is increased. Therefore, the Co content is preferably 0.005 to 2.0%.

B:0.0002〜0.0030%
Bを0.0002%以上添加すれば、パーライト中のセメンタイトの成長を促進させて、線材の延性を高める作用を有する。この効果を確実に得るには、Bは0.0005%以上の含有量とすることが好ましい。しかし、その含有量が0.0030%を超えると、温間や熱間での加工時に割れが生じやすくなる。したがって、Bの含有量は0.0002〜0.0030%とするのがよい。
B: 0.0002 to 0.0030%
If 0.0002% or more of B is added, it has the effect of promoting the growth of cementite in pearlite and increasing the ductility of the wire. In order to reliably obtain this effect, the B content is preferably 0.0005% or more. However, if the content exceeds 0.0030%, cracking is likely to occur during warm or hot processing. Therefore, the B content is preferably 0.0002 to 0.0030%.

V:0.005〜0.5%
Vを0.005%以上添加すれば、オーステナイト結晶粒を微細化させ、延性及び靱性を高める作用を有する。この効果を確実に得るには、Vは0.05%以上の含有量とすることが好ましい。しかし、0.5%を超えて含有させても前記の効果は飽和し、コストが嵩むばかりである。したがって、Vの含有量は0.005〜0.5%とするのがよい。
V: 0.005-0.5%
If V is added in an amount of 0.005% or more, the austenite crystal grains are refined, and the ductility and toughness are increased. To obtain this effect with certainty, it is preferable that V is 0.05% or more. However, even if the content exceeds 0.5%, the above effects are saturated and the cost is increased. Therefore, the content of V is preferably 0.005 to 0.5%.

Ti:0.005〜0.1%
Tiを0.005%以上添加すれば、オーステナイト結晶粒を微細化させ、延性及び靱性を高める作用を有する。この効果を確実に得るには、Tiは0.005%以上の含有量とすることが好ましい。しかし、0.1%を超えて含有させても前記の効果は飽和し、コストが嵩むばかりである。したがって、Tiの含有量は0.005〜0.1%とするのがよい。
Ti: 0.005 to 0.1%
Addition of 0.005% or more of Ti has the effect of refining austenite crystal grains and improving ductility and toughness. In order to obtain this effect with certainty, Ti is preferably contained in an amount of 0.005% or more. However, even if the content exceeds 0.1%, the above effects are saturated and the cost is increased. Therefore, the Ti content is preferably 0.005 to 0.1%.

Zr:0.005〜0.1%
Zrを0.005%以上添加すれば、オーステナイト結晶粒を微細化させ、延性及び靱性を高める作用を有する。しかし、0.1%を超えて含有させても前記の効果が飽和し、コストが嵩むばかりである。したがって、Zrの含有量は0.005〜0.1%とするのがよい。
Zr: 0.005 to 0.1%
If Zr is added in an amount of 0.005% or more, the austenite crystal grains are refined and the ductility and toughness are increased. However, even if the content exceeds 0.1%, the above effect is saturated and the cost is increased. Therefore, the Zr content is preferably 0.005 to 0.1%.

不純物元素としてのP、S、Al、N及びO(酸素)はその含有量を下記のとおりにするのがよい。   The contents of P, S, Al, N and O (oxygen) as impurity elements are preferably as follows.

P:0.030%以下
Pは伸線加工時における断線を誘発する。特に、その含有量が0.030%を超えると伸線加工時に断線が多くなる。したがって、不純物としてのPの含有量は0.030%以下とするのがよい。
P: 0.030% or less P induces disconnection during wire drawing. In particular, when the content exceeds 0.030%, disconnection increases during wire drawing. Therefore, the content of P as an impurity is preferably 0.030% or less.

S:0.030%以下
Sは伸線加工時における断線を誘発する。特に、その含有量が0.030%を超えると伸線加工時に断線が多くなる。したがって、不純物としてのSの含有量は0.030%以下とするのがよい。
S: 0.030% or less S induces breakage during wire drawing. In particular, when the content exceeds 0.030%, disconnection increases during wire drawing. Therefore, the content of S as an impurity is preferably 0.030% or less.

Al:0.005%以下
Alは、Al系酸化物の生成の原因となる元素で、Al系酸化物は耐疲労特性及び伸線加工性を劣化させる。特に、その含有量が0.005%を超えると耐疲労特性の劣化が大きくなる。したがって、不純物としてのAlの含有量は0.005%以下とするのがよく、0.003%以下とすれば一層よい。また、前記したように酸化物系介在物の平均組成で所定量のNbOあるいはB23を含有させるには溶鋼段階からAl含有量を0.005%以下、このましくは0.003%以下に制御する必要がある。
Al: 0.005% or less Al is an element that causes the formation of an Al-based oxide, and the Al-based oxide deteriorates fatigue resistance and wire drawing workability. In particular, when the content exceeds 0.005%, the fatigue resistance is greatly deteriorated. Therefore, the content of Al as an impurity is preferably 0.005% or less, and more preferably 0.003% or less. Further, as described above, in order to contain a predetermined amount of NbO or B 2 O 3 with an average composition of oxide inclusions, the Al content is 0.005% or less from the molten steel stage, preferably 0.003%. It is necessary to control the following.

N:0.006%以下
Nは、窒化物となる元素であり、又、歪時効によって延性及び靱性に悪影響を及ぼす。特に、その含有量が0.006%を超えると弊害が顕著になる。したがって、不純物としてのNの含有量は0.006%以下とするのがよく、0.0035%以下とすれば一層よい。
N: 0.006% or less N is an element that becomes a nitride, and has an adverse effect on ductility and toughness by strain aging. In particular, when the content exceeds 0.006%, the harmful effect becomes remarkable. Therefore, the content of N as an impurity is preferably 0.006% or less, and more preferably 0.0035% or less.

O(酸素):0.0030%以下
Oの含有量が0.0030%を超えると酸化物の数と幅が増大し、耐疲労特性が著しく劣化する。このため、不純物としてのOの含有量は0.0030%以下とするのがよく、0.0025%以下とすれば一層よい。
O (oxygen): 0.0030% or less When the content of O exceeds 0.0030%, the number and width of oxides increase, and the fatigue resistance is remarkably deteriorated. For this reason, the content of O as an impurity is preferably 0.0030% or less, and more preferably 0.0025% or less.

なお、本発明のうちでも、特に、ばね及びスチールコードの用途に好適な素材鋼の化学成分は次に示すものである。   In the present invention, the chemical components of the material steel that are particularly suitable for the use of springs and steel cords are as follows.

ばねの用途に対しては、鋼の化学組成が質量%で、C:0.45〜0.70%、Si:0.1〜2.5%、Mn:0.1〜1.0%を含み、更に選択的に、Cr:0.01〜1.5%、Nb:0.005〜0.100%、Cu:0.005〜0.5%、Ni:0.005〜1.5%、Mo:0.005〜0.5%、W:0.005〜0.5%、Co:0.005〜1.0%、B:0.0002〜0.0030%、V:0.005〜0.5%、Ti:0.005〜0.1%、Zr:0.005〜0.1%のいずれかを含有し、残部はFe及び不可避不純物からなり、不純物中のPは0.030%以下、Sは0.030%以下、Alは0.01%以下、Nは0.006%以下、Oは0.0030%以下のものがよい。   For spring applications, the steel has a chemical composition of mass%, C: 0.45-0.70%, Si: 0.1-2.5%, Mn: 0.1-1.0%. In addition, Cr: 0.01-1.5%, Nb: 0.005-0.100%, Cu: 0.005-0.5%, Ni: 0.005-1.5% , Mo: 0.005-0.5%, W: 0.005-0.5%, Co: 0.005-1.0%, B: 0.0002-0.0030%, V: 0.005 -0.5%, Ti: 0.005 to 0.1%, Zr: 0.005 to 0.1%, and the balance consists of Fe and inevitable impurities, and P in the impurities is 0.00. 030% or less, S is 0.030% or less, Al is 0.01% or less, N is 0.006% or less, and O is 0.0030% or less.

上記した鋼の化学成分の場合、熱処理後のばねに容易に1600MPa以上の引張強度を付与できる。   In the case of the above chemical components of steel, a tensile strength of 1600 MPa or more can be easily imparted to the spring after heat treatment.

スチールコードの用途に対しては、鋼の化学成分が質量%で、C:0.60〜1.1%、Si:0.1〜1.0%、Mn:0.1〜0.7%を含み、更に選択的に、Cr:0.01〜1.5%、Nb:0.005〜0.100%、Cu:0.005〜0.5%、Ni:0.005〜1.5%、Mo:0.005〜0.2%、W:0.005〜0.5%、Co:0.005〜2.0%、B:0.0002〜0.0030%、V:0.005〜0.5%、Ti:0.005〜0.1%、Zr:0.005〜0.1%以下のいずれかを含有し、残部はFe及び不可避不純物からなり、不純物中のPは0.030%以下、Sは0.030%以下、Alは0.005%以下、Nは0.006%以下、Oは0.0030%以下のものがよい。   For steel cord applications, the chemical composition of steel is mass%, C: 0.60 to 1.1%, Si: 0.1 to 1.0%, Mn: 0.1 to 0.7% And, optionally, Cr: 0.01 to 1.5%, Nb: 0.005 to 0.100%, Cu: 0.005 to 0.5%, Ni: 0.005 to 1.5 %, Mo: 0.005-0.2%, W: 0.005-0.5%, Co: 0.005-2.0%, B: 0.0002-0.0030%, V: 0.00. 005 to 0.5%, Ti: 0.005 to 0.1%, Zr: 0.005 to 0.1% or less, the balance is composed of Fe and inevitable impurities, P in the impurity is 0.030% or less, S is 0.030% or less, Al is 0.005% or less, N is 0.006% or less, and O is 0.0030% or less.

上記した鋼の化学成分の場合、直径で0.15〜0.35mmまで湿式伸線された鋼線に3200MPa以上の大きな引張強度を付与できる。   In the case of the above-described chemical components of steel, a large tensile strength of 3200 MPa or more can be imparted to a steel wire wet-drawn to a diameter of 0.15 to 0.35 mm.

前記した耐疲労特性及び伸線加工性に優れた線材の素材鋼となる鋼の具体的な製造方法は特に限定する必要はない。しかし、鋼の溶製方法及び鋳造方法によって鋼の化学成分、特に不純物の含有量が変化するし、鋳造方法によって鋼塊の製造コストも変化する。このため、本発明においては、線材の素材鋼となる鋼の製造方法、なかでも溶製方法及び鋳造方法を下記のとおりするのが好ましい。なお、ここでいう「鋼塊」とはJIS用語として規定されているように「鋳片」を含むものである。   There is no need to specifically limit the specific method for producing the steel used as the raw material steel for the wire rod having excellent fatigue resistance and wire drawing workability. However, the content of chemical components, particularly impurities, varies depending on the steel melting method and casting method, and the production cost of the steel ingot varies depending on the casting method. For this reason, in this invention, it is preferable to perform the manufacturing method of the steel used as the raw material steel of a wire, especially the melting method and the casting method as follows. Here, the “steel ingot” includes “slab” as defined in JIS terms.

○鋼の精錬と鋳造の工程
転炉精錬、転炉外での二次精錬の工程は、鋼中の不純物元素の低減に極めて有効であるため高い清浄性を有する鋼の製造に適しており、更に、連続鋳造して鋼塊にすることで製造コストを比較的低く抑えることができる。したがって、鋼線材の素材鋼となる鋼は、転炉による一次精錬、転炉外での二次精錬、連続鋳造の工程を順に経て鋼塊にするのがよい。「二次精錬」とは、既に述べたように、ガスバブリングやアーク式加熱方式などを有する取鍋精錬法、真空処理装置を使用する精錬法といった「清浄化のための転炉外での精錬法」で通常「炉外精錬」と称されるもので、具体的にはLF、RH、ASEA−SKF,VOD,AOD,CAS、インジェクション機能付き精錬装置等を指す。
○ Steel refining and casting processes Converter refining and secondary refining processes outside the converter are extremely effective in reducing impurity elements in steel and are suitable for the production of highly clean steel. Furthermore, manufacturing costs can be kept relatively low by continuously casting into steel ingots. Therefore, the steel used as the steel material for the steel wire is preferably made into a steel ingot through the steps of primary refining by a converter, secondary refining outside the converter, and continuous casting. “Secondary refining” means, as already mentioned, “smelting ladle refining method with gas bubbling and arc heating method”, refining method using vacuum processing equipment, etc. The “method” is generally referred to as “outside furnace refining”, and specifically refers to LF, RH, ASEA-SKF, VOD, AOD, CAS, a refining apparatus with an injection function, and the like.

転炉による一次精錬、転炉外での二次精錬、連続鋳造の工程をこの順に経て、しかも既に述べたB23の添加方法やAl量の制御及び取鍋スラグの最終CaO/SiO2比を適正に制御すれば、目標とする酸化物系介在物の組成が比較的容易に得られる。 Through the steps of primary refining by the converter, secondary refining outside the converter, and continuous casting in this order, the addition method of B 2 O 3 and the control of the Al amount and the final CaO / SiO 2 of the ladle slag are already described. If the ratio is controlled appropriately, the target composition of oxide inclusions can be obtained relatively easily.

前述した様に、溶鋼中に投入する金属Al量又は不可避的に合金鉄等から不純物として混入する金属Al量が多いと、溶鋼中のAlにより酸化物系介在物中のB23が還元されるため、B23を添加する前から連続鋳造の工程まで、Al量を0.005%以下、好ましくは0.003%以下に制御することでB23の還元を抑制する。さらに、二次精錬後の時点での取鍋スラグ中のCaO/SiO2比が2を超えると、溶鋼の酸素濃度が低下したり、取鍋スラグから溶鋼へ混入するCaの影響で、酸化物系介在物中のB23が還元され介在物を改質するのに必要な量のB23が確保できなくなるため、CaO/SiO2比は2以下にする必要がある。また、B23を溶鋼へ直接添加する方法では、上記Al量を制限したり、CaO/SiO2比を2以下に制御すること加え、溶鋼との反応でB23は還元され易いため、B23を添加前に予め酸化物系フラックスを溶鋼に懸濁させて組成制御した上でB23を添加し、B23を懸濁した酸化物系介在物と速やかに複合化することがB23を効率的に酸化物系介在物に含有させるのに有効な方法である。 As described above, when the amount of metal Al introduced into molten steel or the amount of metal Al inevitably mixed as an impurity from alloy iron or the like is large, B 2 O 3 in oxide inclusions is reduced by Al in molten steel. Therefore, from the time before adding B 2 O 3 to the continuous casting step, the reduction of B 2 O 3 is suppressed by controlling the Al content to 0.005% or less, preferably 0.003% or less. Furthermore, when the CaO / SiO 2 ratio in the ladle slag at the time after secondary refining exceeds 2, the oxygen concentration of the molten steel decreases or the oxides are affected by Ca mixed into the molten steel from the ladle slag. Since B 2 O 3 in the system inclusions is reduced and an amount of B 2 O 3 necessary for modifying the inclusions cannot be secured, the CaO / SiO 2 ratio needs to be 2 or less. Further, in the method of directly adding B 2 O 3 to molten steel, B 2 O 3 is easily reduced by reaction with molten steel in addition to limiting the amount of Al and controlling the CaO / SiO 2 ratio to 2 or less. Therefore, before adding B 2 O 3 , the oxide flux is suspended in the molten steel in advance and the composition is controlled, and then B 2 O 3 is added to quickly oxidize inclusions in which B 2 O 3 is suspended. It is an effective method for efficiently incorporating B 2 O 3 into oxide inclusions.

また、高い清浄性を有する素材鋼を安定して製造するために、二次精錬終了後の取鍋スラグ中のCaO/SiO2比を0.3以上であることが好ましく、0.6以上であれば一層好ましい。更に、0.8以上であれば極めて好ましい。 Further, in order to stably produce a raw steel having high cleanliness, the CaO / SiO 2 ratio in the ladle slag after the completion of secondary refining is preferably 0.3 or more, and 0.6 or more It is more preferable if it exists. Furthermore, it is very preferable if it is 0.8 or more.

二次精錬終了後の取鍋スラグ中の最終CaO/SiO2比を制御するためには、精錬の各段階においてCaO/SiO2比を変化させないで一定の値にしてもよいし、低い値から、又は、高い値から適宜調整して最終CaO/SiO2比を最終目標範囲になるようにしてもよい。なお、最終CaO/SiO2比は、溶鋼に添加するフラックスを適正に選択したり添加する石灰やCaC2量を調整することで制御できる。 In order to control the final CaO / SiO 2 ratio in the ladle slag after the completion of secondary refining, the CaO / SiO 2 ratio may be kept constant without changing the CaO / SiO 2 ratio at each stage of refining. Alternatively, the final CaO / SiO 2 ratio may be adjusted to a final target range by appropriately adjusting from a high value. The final CaO / SiO 2 ratio can be controlled by appropriately selecting the flux to be added to the molten steel and adjusting the amount of lime and CaC 2 to be added.

○熱間圧延による線材の製造
上記項に記した精錬と鋳造の工程を経て製造された鋼を線材にするための熱間圧延方法は特に規定する必要はなく、例えば、通常行われている線材の熱間圧延方法でよい。
○ Manufacture of wire rod by hot rolling The hot rolling method for making the steel manufactured through the refining and casting process described in the above section into a wire rod does not need to be specified. The hot rolling method may be used.

○線材の冷間加工、最終の熱処理、めっき処理及び湿式伸線
熱間圧延して得られた鋼線材の冷間加工は、穴ダイスを用いた伸線加工、ローラダイスを用いた伸線加工、所謂「2ロール圧延機」、「3ロール圧延機」や「4ロール圧延機」を用いた冷間圧延加工など通常の冷間加工方法で行えばよい。「最終の熱処理」である最終パテンティング処理も、例えば、通常行われているパテンティング処理でよい。次の湿式伸線の過程における引き抜き抵抗の低減や、スチールコード用途におけるようなゴムとの密着性を高めることなどを目的に施されるめっき処理も特別なものである必要はなく、通常のブラスめっき、Cuめっき、Niめっきなどでよい。更に、湿式伸線加工も通常行われているものでよい。
○ Cold working of wire rods, final heat treatment, plating treatment and wet wire drawing Cold working of steel wires obtained by hot rolling is performed using a hole die or a wire die. What is necessary is just to perform by normal cold working methods, such as cold rolling using what is called a "2 roll rolling mill", a "3 roll rolling mill", or a "4 roll rolling mill". The final patenting process, which is the “final heat treatment”, may be, for example, a commonly performed patenting process. There is no need for a special plating process to reduce the pull-out resistance in the next wet wire drawing process or to improve the adhesion to rubber as in steel cord applications. Plating, Cu plating, Ni plating, etc. may be used. Further, wet wire drawing may be performed normally.

なお、鋼線材を冷間加工し、最終の熱処理、めっき処理及び湿式伸線加工を施して製造された極細鋼線は、この後所定の最終製品へと加工されることもある。例えば、その極細鋼線を更に撚り加工で複数本撚り合わせて撚鋼線とすることでスチールコードが成形される。   In addition, the ultrafine steel wire manufactured by cold-working a steel wire material and performing final heat treatment, plating treatment, and wet wire drawing may be processed into a predetermined final product thereafter. For example, a steel cord is formed by further twisting a plurality of the ultrafine steel wires into a twisted steel wire.

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包含される。   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.

(実施例1)
表2に示す化学組成を有するスチールコードの素材鋼である鋼A1〜A18及びB1〜B22を、転炉による一次精錬、炉外精錬による二次精錬、連続鋳造のプロセスで製造した。すなわち、270トン転炉で溶製し、出鋼時にSi、Mnで脱酸してからLFを用いて「炉外精錬」して成分(化学組成)の調整と清浄化処理を施し、連続鋳造して鋳片とした。なお、表2には、鋼線材の長手方向縦断面における厚みが2μm以上の酸化物の平均組成を調査した結果とB23の添加形態、B23を添加する前から連鋳工程までにおける溶鋼中の最高Al%、最終工程である連鋳工程での取鍋スラグのCaO/SiO2比と伸線試験での断線回数及び断線原因となった介在物の種類及び最大厚み(破断面上での長径で定義)も併せて示した。
Example 1
Steels A1 to A18 and B1 to B22, which are steel materials of steel cords having the chemical composition shown in Table 2, were manufactured by a process of primary refining by a converter, secondary refining by out-of-furnace refining, and continuous casting. In other words, it is melted in a 270-ton converter, deoxidized with Si and Mn at the time of steel extraction, and then “outside furnace refining” using LF to adjust the components (chemical composition) and perform a cleaning process. And made a slab. In Table 2, continuous casting step from before the addition mode of addition of the results the thickness in the longitudinal direction longitudinal section of the steel wire rod were investigated average composition of the above oxide 2μm and B 2 O 3, the B 2 O 3 The maximum Al% in molten steel, the CaO / SiO 2 ratio of ladle slag in the final casting process, the number of breaks in the wire drawing test, the type of inclusions that caused the break, and the maximum thickness (breakage) It is also shown together (defined by the major axis on the cross section).

ここでB23は単独あるいはCaOと一緒にもしくは予め目標とする介在物組成にほぼ一致する組成に調整した酸化物系フラックスにB23を含有させて、溶鋼あるいは取鍋スラグへ添加した。また、介在物へMgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23を含有させる場合は、それらを介在物として目標とする組成割合に調整したフラックスを溶鋼もしくは取鍋スラグへ添加し、その後ガスバブリングで上記フラックスもしくは上記フラックスを添加した取鍋スラグを溶鋼へ懸濁させることで介在物に含有させ介在物の組成を制御した。また転炉スラグの取鍋への流出量が多いと、取鍋スラグの組成がバラツキ、その結果介在物の組成もバラツクため、転炉で湯残しを実施し、転炉スラグの流出を極力抑えた。フラックスの組成の1例を表1に示す。表1にA2として組成を示したフラックスは、後述する表2の本発明鋼であるA2を溶製する際に用いた。フラックス量は全ての実施例で溶鋼t当たり20kg一定で添加した。 Here B 2 O 3 is contain a B 2 O 3 in the oxide-based flux was adjusted to approximately match composition inclusions Composition alone or or advance the target with CaO, added to the molten steel or ladle slag did. Further, the inclusions include MgO, Na 2 O, K 2 O, Li 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , TiO 2 , NbO, FeO, Fe 2 O 3. , The flux adjusted to the target composition ratio as inclusions is added to the molten steel or ladle slag, and then the ladle slag added with the flux or the flux is suspended in the molten steel by gas bubbling. The composition of inclusions was controlled by inclusion. Also, if there is a large amount of converter slag outflow to the ladle, the composition of the ladle slag will vary, and as a result, the composition of inclusions will also vary, so hot water is left in the converter to minimize the outflow of the converter slag as much as possible. It was. An example of the composition of the flux is shown in Table 1. The flux whose composition was shown as A2 in Table 1 was used when melting A2 which is the steel of the present invention in Table 2 described later. The flux amount was constant at 20 kg per molten steel t in all examples.

Figure 0005047871
Figure 0005047871

前述した様に、溶鋼中に投入する金属Al量又は不可避的に合金鉄等から不純物として混入する金属Al量が多いと、溶鋼中のAlにより酸化物系介在物中のB23が還元されるため、溶鋼中に投入する金属Al量又は不可避的に合金鉄等から不純物として混入する金属Al量を低減、管理し、B23を添加する前から連続鋳造の工程まで、溶鋼中のAl量を0.005%以下に制御した。加えて、2次精錬終了後のCaO/SiO2比は、溶鋼に添加するフラックスの組成を適正に選択すると共に、石灰やCaC2等を添加するなどして、本実施例では2次精錬終了後のCaO/SiO2比を0.8〜1.2の範囲で制御した。 As described above, when the amount of metal Al introduced into molten steel or the amount of metal Al inevitably mixed as an impurity from alloy iron or the like is large, B 2 O 3 in oxide inclusions is reduced by Al in molten steel. Therefore, the amount of metal Al introduced into the molten steel or the amount of metal Al inevitably mixed as an impurity from the alloy iron or the like is reduced and managed, and before adding B 2 O 3 to the continuous casting process, in the molten steel The amount of Al was controlled to 0.005% or less. In addition, the CaO / SiO 2 ratio after the completion of the secondary refining is appropriately selected as the composition of the flux to be added to the molten steel and the addition of lime, CaC 2 or the like in this embodiment. The subsequent CaO / SiO 2 ratio was controlled in the range of 0.8 to 1.2.

上記の連続鋳造した各鋼を、通常の方法で圧延温度及び冷却速度を調整しながら直径5.5mmの線材に熱間圧延した。この熱間圧延後の線材を用いて、伸線加工試験を行い、伸線加工性を評価した。本試験では、熱間圧延された線材(直径5.5mm)を直径2.5mmまで1次伸線し、熱処理(空気パテンティング)した後、2次伸線して直径0.8mmとした。引き続いて熱処理(鉛パテンティング)およびブラスめっきを施した後、直径0.15mmまで湿式伸線し、鋼線10トン当りの断線回数に換算して伸線加工性を評価した。   Each continuously cast steel was hot-rolled into a wire having a diameter of 5.5 mm while adjusting the rolling temperature and the cooling rate by a usual method. Using the wire after hot rolling, a wire drawing test was performed to evaluate the wire drawing workability. In this test, a hot-rolled wire (diameter: 5.5 mm) was first drawn to a diameter of 2.5 mm, heat-treated (air patenting), and then secondarily drawn to a diameter of 0.8 mm. Subsequently, after heat treatment (lead patenting) and brass plating, wet drawing was performed to a diameter of 0.15 mm, and wire drawing workability was evaluated in terms of the number of wire breaks per 10 tons of steel wire.

また、本試験では、圧延した直径5.5mmの線材からミクロサンプルを切り出し、長手方向縦断面でトータル2000mm2の視野範囲内の厚みで2μm以上の酸化物系介在物を対象に、その組成をSEMまたはEPMAで分析し、その測定結果に基づき各酸化物成分の平均含有量を求めた。上記方法で調査した酸化物系介在物の平均組成を表2に示した。また、上記伸線加工試験において、介在物が原因で破断したものの断面をSEMで観察し、断面に現れた介在物の厚みを測定し、最大の厚み(破断面上での長径で定義)を求めるとともに、破断面に現れた介在物の組成をSEMまたはEPMAによって調べた。 In addition, in this test, a micro sample was cut out from a rolled wire having a diameter of 5.5 mm, and the composition was measured for oxide inclusions having a thickness within a visual field range of 2000 mm 2 in the longitudinal direction and a total thickness of 2 μm or more. Analysis was performed with SEM or EPMA, and the average content of each oxide component was determined based on the measurement results. The average composition of oxide inclusions investigated by the above method is shown in Table 2. In the wire drawing test, the cross section of the fracture due to inclusions was observed with an SEM, the thickness of the inclusions appearing on the cross section was measured, and the maximum thickness (defined by the major axis on the fracture surface) was determined. At the same time, the composition of inclusions appearing on the fracture surface was examined by SEM or EPMA.

表2のA1〜A20が本発明例である。これより、鋼線材の長手方向縦断面において厚みで2μm以上の酸化物系介在物における各酸化物成分の平均含有量が本発明の請求項1及び請求項2に記載の範囲にあると、断線回数及び破断面に出現する介在物の厚みも大幅に減少し、介在物の微細化によって伸線加工性の大幅な向上が図れる。また、伸線破断回数や破断原因となる介在物の厚みに、B23の平均含有量が大きく影響しており、特にB23の平均含有量を適正に制御することで伸線加工性を大きく改善できることが判る。 A1 to A20 in Table 2 are examples of the present invention. From this, when the average content of each oxide component in the oxide inclusions having a thickness of 2 μm or more in the longitudinal longitudinal cross section of the steel wire is in the range according to claim 1 and claim 2 of the present invention, the wire breaks. The number of inclusions and the thickness of inclusions appearing on the fracture surface are also greatly reduced, and wire drawing workability can be greatly improved by making the inclusions finer. In addition, the average content of B 2 O 3 greatly affects the number of wire breaks and the thickness of inclusions that cause breakage. In particular, the wire is drawn by properly controlling the average content of B 2 O 3. It can be seen that the workability can be greatly improved.

表1のA2に示すフラックス成分と表2のA2に示す介在物平均組成を対比すると、投入したフラックス成分に近似した介在物成分が得られていることがわかる。   When the flux component indicated by A2 in Table 1 is compared with the inclusion average composition indicated by A2 in Table 2, it can be seen that an inclusion component approximate to the input flux component is obtained.

さらに表2で、A1〜A13及びA15〜A20はMgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23よりなる群からなる酸化物が1種以上含有される請求項2に記載の発明鋼である。表2よりB23を4%以上含有するケースで、MgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23を適正量含有していないA14と、それらを含有するA2〜A13及びA15〜A20を比較すると後者の方が、伸線加工での断線回数や破断面の最大介在物厚みは低位であり、MgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23を適正量含有させることで伸線加工性をより安定して改善できることも判る。しかしながら、これらの酸化物成分も比較鋼B9〜B19のように過剰に含有される場合は耐火物の溶損による耐火物由来の介在物の増加または酸化物の熱間変形能や冷間加工における破砕性の低下に起因して、介在物の微細化が不十分となり、却って、伸線加工性は劣化する。 Furthermore, in Table 2, A1 to A13 and A15 to A20 are MgO, Na 2 O, K 2 O, Li 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , TiO 2 , The invention steel according to claim 2, wherein at least one oxide composed of a group consisting of NbO, FeO and Fe 2 O 3 is contained. From Table 2, it is a case containing 4% or more of B 2 O 3 , MgO, Na 2 O, K 2 O, Li 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , When comparing A14 not containing appropriate amounts of TiO 2 , NbO, FeO, Fe 2 O 3 with A2 to A13 and A15 to A20 containing them, the latter is more likely to cause wire breakage and fracture surface The maximum inclusion thickness is low, MgO, Na 2 O, K 2 O, Li 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , TiO 2 , NbO, FeO. It can also be seen that the wire drawing workability can be improved more stably by containing an appropriate amount of Fe 2 O 3 . However, when these oxide components are also contained excessively as in comparative steels B9 to B19, the increase in inclusions from the refractory due to refractory erosion or the hot deformability of the oxide and cold working Due to the decrease in crushability, the inclusions are not sufficiently refined, and the wire drawing processability is deteriorated.

表2のB1〜B22が比較例である。ここにおいて、A1、A2、A3の本発明鋼とほぼ同様な組成を有し、酸化物の平均組成が本発明の範囲から外れた比較鋼がB1〜B9とB20〜B22である。また、B20〜B22はAl量や取鍋スラグのCaO/SiO2比がこれら請求項範囲から外れたために、B23の含有量等介在物組成が目標範囲から外れている。さらに表2で、A1〜A13及びA15〜A18の各発明鋼と同様な組成を有し、上記酸化物系介在物の平均組成でMgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23の各酸化物成分のうち、いずれかを過剰に含有する場合の比較鋼がB9〜B19である。 B1 to B22 in Table 2 are comparative examples. Here, comparative steels having the same composition as the steels of the present invention of A1, A2 and A3 and having an average oxide composition outside the scope of the present invention are B1 to B9 and B20 to B22. Further, in B20 to B22, since the Al amount and the CaO / SiO 2 ratio of the ladle slag are out of these claims, the inclusion composition such as the content of B 2 O 3 is out of the target range. Further in Table 2, A1-A13 and has a composition similar to the invention steel A15~A18, the MgO in the average composition of oxide inclusions, Na 2 O, K 2 O , Li 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , TiO 2 , NbO, FeO, and Fe 2 O 3 , the comparative steel in the case where any one of them is excessively contained is B9 ~ B19.

表2のB2,B10〜B13の鋼では特定の酸化物成分の含有量が過剰なことに起因して、取鍋スラグによる耐火物の溶損が激しくなり、耐火物由来の介在物の増加によって断線回数が増大するなど、伸線加工性の劣化が認められた。   In the steels of B2, B10 to B13 in Table 2, due to the excessive content of specific oxide components, the refractory melts due to ladle slag becomes violent, and the increase in inclusions from the refractory Degradation of wire drawing workability was observed, such as an increase in the number of wire breaks.

Figure 0005047871
Figure 0005047871
Figure 0005047871
Figure 0005047871

(実施例2)
実施例1と同様、表3に示す化学組成を有する弁ばねの素材鋼である鋼C1〜C20及びD1〜D22を、転炉による一次精錬、LF法による二次精錬、連続鋳造のプロセスで製造した。本実施例でもフラックス添加量は溶鋼t当たり20kg一定で添加した。本実施例においても270トン転炉で溶製し、出鋼時にSi、Mnで脱酸してからLFを用いて「炉外精錬」して成分(化学組成)の調整と清浄化処理を施し、連続鋳造して鋳片とした。なお、表3には、鋼線材の長手方向縦断面における厚みが2μm以上の酸化物の平均組成を調査した結果とB23の添加形態、B23を添加する前から連鋳工程までにおける溶鋼中の最高Al%、最終工程である連鋳工程での取鍋スラグのCaO/SiO2比と耐疲労特性を評価した中村式回転曲げ試験での介在部物起因の折損率と破断原因となった介在物の種類及び最大厚み(破断面上での長径で定義)も併せて示した。
(Example 2)
As in Example 1, steels C1 to C20 and D1 to D22, which are material steels for valve springs having the chemical composition shown in Table 3, are manufactured by a primary refining process using a converter, a secondary refining process using an LF method, and a continuous casting process. did. Also in this example, the amount of flux added was constant at 20 kg per molten steel t. Also in this example, it was melted in a 270-ton converter, deoxidized with Si and Mn at the time of steel extraction, and then “external refining” using LF to adjust the component (chemical composition) and perform the cleaning process. The slab was continuously cast. In Table 3, continuous casting step from before the addition mode of addition of the results the thickness in the longitudinal direction longitudinal section of the steel wire rod were investigated average composition of the above oxide 2μm and B 2 O 3, the B 2 O 3 Breakage rate and fracture due to inclusions in Nakamura-type rotary bending test in which the highest Al% in molten steel and the CaO / SiO 2 ratio and fatigue resistance of ladle slag in the final continuous casting process were evaluated The type of inclusions and the maximum thickness (defined by the major axis on the fracture surface) were also shown.

ここでもB23は単独あるいはCaOと一緒にもしくは予め目標とする介在物組成にほぼ一致する組成に調整した酸化物系フラックスにB23を含有させて、溶鋼あるいは取鍋スラグへ添加した。介在物組成の各酸化物成分の含有量制御は実施例1と同様の方法で行い、各酸化物成分は介在物としての目標とする組成割合に含有量を調整したフラックスを溶鋼もしくは取鍋スラグへ添加し、その後ガスバブリングで上記フラックスもしくは上記フラックスを添加した取鍋スラグを溶鋼へ懸濁させることで介在物に含有させ、介在物の組成を制御した。また転炉スラグの取鍋への流出量抑制するため、転炉での湯残しも実施した。フラックスの組成の1例を表1に示す。表1にC2として組成を示したフラックスは、後述する表3の本発明鋼であるC2を溶製する際に用いた。 Again B 2 O 3 is contain a B 2 O 3 in the oxide-based flux was adjusted to approximately match composition inclusions Composition alone or or advance the target with CaO, added to the molten steel or ladle slag did. The content control of each oxide component of the inclusion composition is performed in the same manner as in Example 1, and each oxide component is made of molten steel or ladle slag with the content adjusted to the target composition ratio as an inclusion. After that, the above-mentioned flux or ladle slag added with the above-mentioned flux was suspended in molten steel by gas bubbling, and contained in inclusions to control the composition of the inclusions. Moreover, in order to suppress the outflow amount of the converter slag to the ladle, hot water was left in the converter. An example of the composition of the flux is shown in Table 1. The flux whose composition was shown as C2 in Table 1 was used when melting C2 which is the steel of the present invention in Table 3 described later.

本実施例においても、溶鋼中のAlにより酸化物系介在物中のB23が還元することを防止するため、溶鋼中に投入する金属Al量又は不可避的に合金鉄等から不純物として混入する金属Al量を低減、管理し、B23を添加する前から連続鋳造の工程まで、Al量を0.005%以下に制御した。加えて、2次精錬終了後のCaO/SiO2比は、溶鋼に添加するフラックスの組成を適正に選択すると共に、石灰やCaC2等を添加するなどして、本実施例では2次精錬終了後のCaO/SiO2比を0.8〜1.2の範囲で制御した。 Also in this example, in order to prevent B 2 O 3 in oxide inclusions from being reduced by Al in the molten steel, the amount of metal Al introduced into the molten steel or inevitably mixed as an impurity from alloy iron or the like The amount of Al metal to be reduced was reduced and managed, and the Al amount was controlled to 0.005% or less from before adding B 2 O 3 until the continuous casting step. In addition, the CaO / SiO 2 ratio after the completion of the secondary refining is appropriately selected as the composition of the flux to be added to the molten steel and the addition of lime, CaC 2 or the like in this embodiment. The subsequent CaO / SiO 2 ratio was controlled in the range of 0.8 to 1.2.

上記の連続鋳造した各鋼を、通常の方法で圧延温度及び冷却速度を調整しながら直径5.5mmの線材に熱間圧延した。この熱間圧延後の線材を用いて、疲労強度試験を行い耐疲労特性を評価した。本試験では、各熱延鋼線材(直径5.5mm)について、皮削り(SV)→低温焼鈍(LA)→冷間線引加工(直径4.8mm)→オイルテンパー[油焼入れと鉛浴(約450℃)焼戻し連続工程]→簡易歪取焼鈍(ブルーイング:約400℃)→ショットピーニング→歪取焼鈍を行った後、試験材として直径4.8mm×650mmのワイヤを採取し、中村式回転曲げ試験機を用いて、公称応力940MPa、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、下記式により折損率を求めた。
折損率(%)=[介在物折損本数/(介在物折損+所定回数に達し中止した本数)]×100
Each continuously cast steel was hot-rolled into a wire having a diameter of 5.5 mm while adjusting the rolling temperature and the cooling rate by a usual method. Using the hot-rolled wire, a fatigue strength test was performed to evaluate fatigue resistance. In this test, for each hot-rolled steel wire (diameter 5.5 mm), skin cutting (SV) → low temperature annealing (LA) → cold drawing (diameter 4.8 mm) → oil temper [oil quenching and lead bath ( (Approx. 450 ° C.) Continuous tempering process] → Simple strain relief annealing (Bluing: about 400 ° C.) → Shot peening → Strain relief annealing, then a wire with a diameter of 4.8 mm × 650 mm is taken as a test material. Using a rotary bending tester, the test was performed with a nominal stress of 940 MPa, a rotation speed: 4000 to 5000 rpm, and a number of cancellations: 2 × 10 7 times. And the breakage rate was calculated | required by the following formula about what the inclusion broke among the fracture | ruptured things.
Breakage rate (%) = [inclusion breakage number / (inclusion breakage + number of breaks after reaching a predetermined number of times)] × 100

また、上記疲労強度試験において、介在物が原因で破断したものの断面をSEMで観察し、断面に現れた介在物の厚みを測定して最大厚みを求めるとともに、破断面に出現した介在物の組成をSEMまたはEPMAによって調べた。   Further, in the fatigue strength test, the cross section of the fracture due to the inclusion was observed with an SEM, the thickness of the inclusion that appeared on the cross section was measured to obtain the maximum thickness, and the composition of the inclusion that appeared on the fracture surface Were examined by SEM or EPMA.

また、本試験では、圧延した直径5.5mmの線材からミクロサンプルを切り出し、長手方向縦断面でトータル2000mm2の視野範囲内の厚みで2μm以上の酸化物系介在物を対象に、その組成をSEMまたはEPMAで分析し、その測定結果に基づき各酸化物成分の平均含有量を求めた。上記方法で調査した酸化物系介在物の平均組成も表3に示した。 In addition, in this test, a micro sample was cut out from a rolled wire having a diameter of 5.5 mm, and the composition was measured for oxide inclusions having a thickness within a visual field range of 2000 mm 2 in the longitudinal direction and a total thickness of 2 μm or more. Analysis was performed with SEM or EPMA, and the average content of each oxide component was determined based on the measurement results. The average composition of oxide inclusions investigated by the above method is also shown in Table 3.

表3のC1〜C20が本発明例である。表3より鋼線材の長手方向縦断面において厚みで2μm以上の酸化物系介在物における各酸化物成分の平均含有量が本発明の請求項1及び請求項2に記載の範囲にあると、介在物起因の折損率は及び破断面に出現する介在物の厚みも大幅に減少し、介在物の微細化によって耐疲労特性の大幅な向上が図れる。また、介在物起因の折損率や破断原因となる介在物の厚みに、B23の平均含有量が大きく影響し、特にB23の平均含有量を適正に制御することで耐疲労特性も大きく改善できることが判る。 C1 to C20 in Table 3 are examples of the present invention. According to Table 3, when the average content of each oxide component in the oxide inclusions having a thickness of 2 μm or more in the longitudinal cross-section in the longitudinal direction of the steel wire is within the range described in claim 1 and claim 2 of the present invention, The breakage rate due to objects and the thickness of inclusions appearing on the fracture surface are also greatly reduced, and the fatigue resistance can be greatly improved by making the inclusions finer. In addition, the average content of B 2 O 3 greatly affects the breakage rate due to inclusions and the thickness of inclusions that cause breakage. In particular, fatigue resistance is achieved by appropriately controlling the average content of B 2 O 3. It can be seen that the characteristics can be greatly improved.

表1のC2に示すフラックス成分と表3のC2に示す介在物平均組成を対比すると、投入したフラックス成分に近似した介在物成分が得られていることがわかる。   When the flux component shown in C2 of Table 1 and the inclusion average composition shown in C2 of Table 3 are compared, it can be seen that an inclusion component approximate to the input flux component is obtained.

さらに表3で、C1〜C13及びC15〜C20はMgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23よりなる群からなる酸化物が1種以上含有される本発明鋼である。表3よりB23を4%以上含有するケースで、MgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23を適正量含有していないC14と、それらを含有するC2〜C13及びC15〜C20を比較すると後者の方が、中村式回転曲げ試験での介在物起因の折損率や破断面の最大介在物厚みは低位にあり、MgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23を適正量含有させると耐疲労特性をより安定して改善できることも判る。しかしながら、これらの酸化物成分も比較鋼D9〜D19のように過剰に含有される場合は耐火物の溶損による耐火物由来の介在物の増加または酸化物の熱間変形能や破砕性の低下に起因して、介在物の微細化が不十分となり、却って、耐疲労特性も劣化する。 Further in Table 3, C1 to C13 and C15~C20 is MgO, Na 2 O, K 2 O, Li 2 O, ZrO 2, MnO, Ce 2 O 3, La 2 O 3, Nd 2 O 3, TiO 2, The steel according to the present invention contains at least one oxide composed of NbO, FeO and Fe 2 O 3 . From Table 3, in the case of containing 4% or more of B 2 O 3 , MgO, Na 2 O, K 2 O, Li 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , Comparing C14 that does not contain proper amounts of TiO 2 , NbO, FeO, Fe 2 O 3 and C2-C13 and C15-C20 containing them, the latter is due to inclusions in the Nakamura rotary bending test And the maximum inclusion thickness of the fracture surface is low, MgO, Na 2 O, K 2 O, Li 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , It can also be seen that the fatigue resistance can be improved more stably by containing appropriate amounts of TiO 2 , NbO, FeO, and Fe 2 O 3 . However, when these oxide components are also contained excessively as in comparative steels D9 to D19, an increase in inclusions derived from the refractory due to refractory melting or a decrease in hot deformability and crushability of the oxide As a result, the inclusions are not sufficiently refined, and the fatigue resistance is also deteriorated.

表3のD1〜D22が比較例である。ここにおいてはC1、C2、C3の本発明鋼とほぼ同様な組成を有し、酸化物の平均組成が本発明の範囲から外れた比較鋼がD1〜D9とD20〜D22である。また、D20〜D22はAl量と取鍋スラグのCaO/SiO2比がこれら適正な範囲から外れたために、B23の含有量等介在物組成が目標範囲から外れている。さらに表3で、C1〜C13及びC15〜C18の各発明鋼と同様な組成を有し、上記酸化物系介在物の平均組成でMgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23を過剰に含有する場合の比較鋼がD9〜D19である。 D1 to D22 in Table 3 are comparative examples. Here, comparative steels having the same composition as the steels of the present invention of C1, C2, and C3 and having an average oxide composition outside the scope of the present invention are D1 to D9 and D20 to D22. Further, in D20 to D22, since the Al amount and the CaO / SiO 2 ratio of the ladle slag deviate from these proper ranges, the inclusion composition such as the content of B 2 O 3 deviates from the target range. Further in Table 3, C1 to C13 and have the same composition as the invention steel C15 -C18, the MgO in the average composition of oxide inclusions, Na 2 O, K 2 O , Li 2 O, ZrO 2 , MnO, Ce 2 O 3 , La 2 O 3 , Nd 2 O 3 , TiO 2 , NbO, FeO, and Fe 2 O 3 are comparative steels D9 to D19.

表3のD2,D10〜D13の鋼では特性の酸化物成分の含有量が過剰なことに起因して、取鍋スラグによる耐火物の溶損が激しくなり、耐火物由来の介在物が増加して介在物起因の折損率が増大するなど耐疲労特性の劣化が認められた。   In steels of D2, D10 to D13 in Table 3, due to the excessive content of the oxide component of the characteristics, the refractory melts due to ladle slag becomes severe, and inclusions derived from the refractory increase. As a result, deterioration of fatigue resistance was observed, such as an increase in breakage due to inclusions.

Figure 0005047871
Figure 0005047871
Figure 0005047871
Figure 0005047871

Claims (3)

鋼の化学成分が質量%で、C:0.45〜1.1%、Si:0.1〜3.0%、Mn:0.1〜2.0%を含み、残部はFe及び不可避的不純物からなり、不純物中のPは0.030%以下、Sは0.030%以下、Alは0.005%以下、Nは0.006%以下、O(酸素)は0.0030%以下の鋼線材であって、その長手方向縦断面における厚みが2μm以上の酸化物の平均組成が、質量%で、SiO2:30〜60%、Al23:1〜30%、CaO:10〜50%、B23:0.1〜10%を含むことを特徴とする鋼線材。 The chemical composition of steel is% by mass, including C: 0.45-1.1%, Si: 0.1-3.0%, Mn: 0.1-2.0%, the balance being Fe and inevitable Composed of impurities, P in the impurities is 0.030% or less, S is 0.030% or less, Al is 0.005% or less, N is 0.006% or less, and O (oxygen) is 0.0030% or less. The average composition of oxides having a thickness of 2 μm or more in the longitudinal direction in the longitudinal direction of the steel wire is mass%, SiO 2 : 30 to 60%, Al 2 O 3 : 1 to 30%, CaO: 10 A steel wire material containing 50% and B 2 O 3 : 0.1 to 10%. 鋼線材の長手方向縦断面における厚みが2μm以上の酸化物の平均組成が、さらに、質量%で、0.1〜15%のMgO、Na2O、K2O、Li2O、ZrO2、MnO、Ce23、La23、Nd23、TiO2、NbO、FeO、Fe23よりなる群から選択される少なくとも1種以上を含有する請求項1に記載の鋼線材。 The average composition of the oxide having a thickness of 2 μm or more in the longitudinal cross-section of the steel wire is 0.1% to 15% by weight of MgO, Na 2 O, K 2 O, Li 2 O, ZrO 2 , MnO, Ce 2 O 3, La 2 O 3, Nd 2 O 3, TiO 2, NbO, FeO, steel wire rod according to claim 1 containing at least one element selected from the group consisting of Fe 2 O 3 . 鋼の化学成分が、さらに、質量%で、Cr:0.005〜1.5%、Cu:0.005〜0.5%、Ni:0.005〜1.5%、Mo:0.005〜0.5%、W:0.005〜0.5%、Co:0.005〜2.0%、B:0.0002〜0.0030%、V:0.005〜0.5%、Ti:0.005〜0.1%、Zr:0.005〜0.1%、Nb:0.005〜0.100%を1種以上含む請求項1または2に記載の鋼線材。   Further, the chemical composition of the steel is, by mass, Cr: 0.005-1.5%, Cu: 0.005-0.5%, Ni: 0.005-1.5%, Mo: 0.005 -0.5%, W: 0.005-0.5%, Co: 0.005-2.0%, B: 0.0002-0.0030%, V: 0.005-0.5%, The steel wire rod according to claim 1 or 2, comprising at least one of Ti: 0.005-0.1%, Zr: 0.005-0.1%, and Nb: 0.005-0.100%.
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