201102443 六、發明說明： 【韻^明戶斤屬技^軒々貝】 發明領域 本發明係有關於一種使用在汽車用輪胎之鋼索（steel cord)或鋸線(saw wire)等之高強度鋼線及其製造方法。詳而 言之，本發明有關於一種線徑為〇〇4〜〇4mm且強度達 4500MPa級以上之極細鋼線，其係使用鑄模並藉由冷作而 經拉線加工強化者。 本申請案係依據已於2009年6月22日在日本提出申請 之曰本專利申請案特願第2〇〇9_148〇51號來主張優先權，並 在此援用其内容。 I：先前技術】 發明背景 關於汽車所用之鋼索，基於輪胎輕量化之要求，故對 鋼線之咼張力化之需求益增。同樣地，用以精密切割藍寶 石結晶或Sic結晶等之鋸線，對高張力化之需求亦逐漸增 加。為回應這些需求，已有多項專門研朗始進行。結^ 發現，除鋼線之高張力化外，亦需確保充分之延展性。延 展性扣軚有數種，舉例言之，如\經扭轉測試直至斷裂之 扭轉-人數，或於扭轉測試中是否產生沿鋼線之長向形成之 裂痕(脫層）。Pit著鋼線之高強度化導致延展性降低成了重大 課題’因此重點在於如何加以抑制。此外並發現，高強度 鋼線經室科效(聰〜4代，數日〜數年)後有雜劣化2 現象’是以如何使良好之延展性在實質上經時效後不會降 201102443 低亦為重要課題。 一般而言，高強度鋼線係藉由將具有波來鐵組織之線 材以鑄模等進行拉線加工所製成。藉此加工，縮小波來鐵 層間距，且於肥粒鐵相中導入多量之差排，以增加抗拉強 度。近年發現，若該拉線應變非常大，將使波來鐵組織中 之雪明碳鐵細化分解。然而，因組織特別微細，故該等碳 之存在位置及存在狀態與機械性質間之關係不明，特別是 有關延展性劣化之原因方面，不明之處甚多。實際之高強 度鋼線，鋼線内之組織或局部之應變量於表面區域與中心 區域應是不盡相同，此對鋼線之特性亦有所影響。 為求極細鋼線之高強度化，必須使最終韌化處理後之 素線強度增加，或增加最終之拉線加工應變。但是，增加 最終韌化處理後之素線強度、或拉線加工應變以使極細鋼 線向強度化之方法’同樣將於強度超過450014?3時發生延 展性明顯降低之情形，故極難予以實用化。 相對於此，過去在延展性降低少之高強度化手段之研 究發展實例上，已有專利文獻1、專利文獻2及專利文獻3分 別提出業已規定C、Si、Mn、Cr等化學成分之高強度及高 延展性之極細線用向碳鋼線材。但由該等公報揭示之實施 例亦可知，鋼線之抗拉強度最大僅3500〜3600MPa，極細 鋼線之高強度化有限。 又，專利文獻4中提出一種已控制化學成分與非金屬夾 雜物組織及共析前雪明碳鐵之面積分率之高強度鋼高勒性 鋼線材。進而，專利文獻5中揭示—種用以控制鋼之化學成 201102443 分與最終矯模斷面縮率之高強度鋼高韌性極細線鋼之製造 方法。但該等技術亦無法實現抗拉強度為4500MPa以上且 具有高延展性之極細鋼線。 4卜另有研究發現鋼索之特性受到波來鐵組織内肥 粒鐵相中之碳濃度影響，因而提議藉由規定該等濃度提升 強度與延展性之平衡。以專利文獻6為例，係藉由規定鋼線 中之碳濃度’獲得良好之特性。專利文獻7係揭示一種再施 以熱處理以實現理想之碳狀態，並獲得良好特性之方法。 再如專利文獻8 ’係藉由規定鋼線中之碳濃度與層間距，獲 得良好特性。但該等專利文獻均未提及鋼線最外層（由表面 至深度2μιη之區域）之碳狀態，此乃當時之技術尚無法進行 實際測量(及控制）之故。 又’專利文獻9係就碳濃度之不均情形加以規定。進而 於專利文獻10 ’對於會影響碳濃度之不均情形之層間距差 異程度加以規定。然而，該等專利文獻係討論全體之不均， 並未規定特定部位之碳濃度。另一方面，專利文獻u所示 之鋼線及鋼線之製造方法，係藉由規定鋼線表層部與鋼線 中心部之肥粒鐵相中之C濃度比，獲得良好特性。但始終為 中心部與表層部之相對值之規定，並未規定用以作為明確指 標之絕對值。又，實際測量僅於距離表面1〇μϊη以上之内部進 仃，由表面至2μιη之區域(最外層）中之c濃度則未予以控制。 另一方面，有關鋼線最外層之殘留應力，專利文獻12 或專利文獻13中係根據疲勞性或抗縱向破裂性之觀點對殘 留應力之範圍加以規定。然而，雖然殘留壓縮應力佳，但 201102443 其數值之絕對值小，且用以取得最佳延展性與強度之平衡 之範圍未予規定。甚至未揭示與最外層之碳狀態之關係。 負起高強度極細鋼線之延展性之責任者係肥粒鐵相之 延展性。只要維持肥粒鐵相之延展性，即使在高強度之狀態 下亦可確保延展性。但若拉線加工應變增加，一般而言雪明 碳鐵將分解以致c原子於肥粒鐵相中擴散，且肥粒鐵相中之碳 濃度增加。非專利文獻1述及，冷軋鋼板中，肥粒鐵相中之碳 濃度業已増加之情形下，於抗拉測試時將產生肥粒鐵相之差 排因碳而固著之動態應變時效，並引發顯著之延展性降低。 【先行技術文獻】 【專利文獻】 【專利文獻1】日本專利公開公報特開昭第60_204865號 【專利文獻2】曰本專利公開公報特開昭第63_24〇46號 【專利文獻3】曰本專利公告公報特公平第3 _23 674號 【專利文獻4】日本專利公開公報特開平第卜⑷奶號 【專利文獻5】日本專利公開公報特開平第7_ini B號 【專利文獻6】日本專利公開公報特開平第丨丨_丨9 9 $ 8 〇號 [^c|ic7] 9 ^ ^ 2008-208450^； 【專利文獻8】日本專利公開公報特開第2__2495_ 【專利文獻9】日本專利公開公報特開第綱^篇9號 【專利文獻10】日本糊公開公_開第雛期96號 【專利文獻11】日本專利公開公_㈣湖_3難6號 【專利文獻12】日本專利公開公報特開平第Hi靡號 【專利文獻13】日本專利公_叫開第細⑽规 201102443 【非專利文獻】 【非專利文獻1】曰本金屬學會誌第45卷第9號 (1981)942〜947 【發明内容3 發明概要 發明欲解決之課題 藉由在鋼線進行拉線加工時設定非常大之拉線加工 量，雖說利用習知技術亦可謀求張力高強度化之效果，但 延展性降低之問題卻無可避免。本發明乃以上述現狀為背 景，提供一種具有4500MPa以上之高強度且延展性優異之 高強度鋼線，特別是一種高強度極細鋼線。 用以解決課題之手段 本發明為解決前述課題乃採用以下手段。 (1) 本發明之第1態樣：一種鋼線，係含有C : 0.7〜1.2 質量％、Si : 0.05〜2.0質量％&Mn : 0.2〜2.0質量％之化學 成分且殘餘部分含有Fe及不可避免之雜質者；前述鋼線具 有波來鐵組織，且前述鋼線最外層之肥粒鐵相中心部之平 均C濃度為0.2質量％以下，前述最外層之鋼線長向之殘留壓 縮應力為600MPa以上。 (2) 如上述（1)之鋼線，其可更含有Cr: 0.05〜1.0質量％、 Ni : 0.05〜1.0 質量 ％、V : 0.01 〜0.5質量％、Nb : 0.001 〜 0.1 質量％、Mo : 0.01 〜0.1 質量％&B : 0.0001 〜0.01 質量％ 等之1種以上化學成分。 (3) 如上述（1)或（2)之鋼線，其可為具有4500MPa以上抗 201102443 拉強度之高強度極細鋼線。 (4) 如上述（3)之高強度極細鋼線，其可為鋼索（steel cord) 〇 (5) 如上述（3)之高強度極細鋼線，其可為鋸線（saw wire)。 (6) 本發明之第2態樣：一種鋼線之製造方法，係用以製 造具有4500MPa以上之抗拉強度之鋼線者；該製造方法具 備下列步驟：韌化步驟，係對下述鋼線進行韌化處理而生 成波來鐵組織者，該鋼線含有C : 0.7〜1.2質量％、Si : 0.05 〜2.0質量％及Μη: 0.2〜2.0質量％等化學成分，且殘餘部 份含有Fe及不可避免之雜質；拉線步驟，係將前述鋼線最 外層之前述波來鐵組織中的肥粒鐵相中心部之平均C濃度 控制在0.2質量％以下，並將前述鋼線予以拉線者；及，賦 予殘留應力步驟，係賦予前述鋼線600MPa以上之殘留壓縮 應力。 發明效果 本發明之鋼線因具有波來鐵組織之鋼線最外層之肥粒 鐵相中心部的碳濃度受到控制，且被賦予殘留壓縮應力， 而可發揮高強度與延展性。 又，由於可提供具有充分延展性與抗拉強度之高強度 鋼線，因此可使製造物輕量化。 圖式簡單說明 第1圖所示者係對4500MPa以上之極細鋼線表面之肥 粒鐵相中心部之平均C濃度與表面殘留應力、延展性之關係 201102443 調查所得之結果。 第圖所示者係由極細鋼線之距離表面1 μπι内部區域 取出針°樣之方法+之試塊#貞出步驟。 第圖所示者係將該試塊固定於針台座上之步驟。 第2C圖所示者係業經聚焦離子束(FIB)裝置加工後之 該試塊。 第2D圖係該試塊之上部觀察圖。 第2E圖係由上觀察於該試塊進行FIB加工製得之針試 樣之圖。 第2F圖係錄針試樣之側邊觀察圖。 第3圖所示者係經三維原子微探法(3 D AP)測定所得之 C分佈與肥粒織相中”之C濃度。 【實施冷式】 用以實施發明之型態 本發月人等根據高強度鋼線之延展性之控制因素進行 各種研究分析後魏，社量塑性變形之㈣波來鐵組織 中，鋼線最外層之練鐵相中之碳（以下以C示之)濃度、與 鋼線最外層之鋼線長向上之殘留應力，對鋼線之延展性造 成強烈影響。此應係彎曲或扭轉時，鋼線最外層受到比内 部強之應力而成為破壞之起點之故。檢測最外層二殘留應 力之方法早已存在，但麟表面至2帅以内之鱗最外層 肥粒鐵相中之C濃度則無精準測量之法。此次開發了該方= 並研究與特性間之關係後發現，藉由控制鋼線最外層/之肥 粒鐵相中之C濃度在規定值以下，同時壓縮鋼線長向i之殘 201102443 留應力’並使該壓縮應力達特定值以上，將大幅改善極細 鋼線<強度與延展性之平衡。 另一方面，鋼線最外層相對於鋼線内部，受到更劇列 工’並承受摩擦發熱等所造成之激烈溫度變化。因此， 努詞線内部形成明顯不同之組織及狀態。是故，更催化雪 月叹織之分解’且最外層之肥粒鐵相中之c濃度，一般而言 呈現向於鋼線内部之肥粒鐵相中之c濃度之狀態。因鋼線最 卜層與特性有最強烈之關係，由此可知藉由控制最外屛 組織耸 θ < ’，可大致實現強度與延展性形成良好平衡之鋼線。 ^向強度鋼線一般係將具有波來鐵組織之線材以鑄模等 由於杈線加工強化而得。以前述方法製造高強度鋼線時， 之2巧拉線加工時發生高拉線應變，將產生波來鐵組織中 $明碳鐵細化分解，以致c熔入肥粒鐵相中之現象。 子微本發明人結合可測量細倾域之C局部濃度之三維原 二探法（町稱3歸)與此幼切行之自鋼線最外層取 ，針試樣製作技術’詳細探究鋼財所有地方之肥粒鐵 目之C濃度與鋼線之強度、延展性之關係。結果證明，特 別在鋼線表層敎肥粒鐵相巾之Cit度變高，或者，同樣最 外層之殘留應力於鋼線長向上拉伸或弱壓縮時，延展性明 顯降低(參照第1圖）。 ,t t % 〜α咬到鐧線最外層之碳 狀態與殘留應力均於適當範圍 田軏圍内之條件。此一認知使得此 次得以新開發出用以檢測 』綱踝取外層之C局部濃度之方 法’並百度發現鋼線最外層之碳狀態為可檢測者。 10 201102443 由該等發現並導出下列結論，為實現可確保充分延展 性之強度鋼線，必須將鋼線最外層之肥粒鐵相中心部之平 均c濃度設定為特定值以下，再將表面之鋼線長向上之殘留 應力設為達充分大小之壓縮應力。 又，本發明人等藉由各種製法製作具有45〇GMPa以上 之抗拉強度之試樣，並檢測抗拉強度及延展性與表面之波 來鐵組織之肥粒鐵相中心部之平均c濃度、表面之殘留應力 之關係。鋼線最外層之肥粒鐵相中心部之平均c濃度係藉由 3DAP測定，殘留應力係、以聰線繞射測定法檢測。抗拉強 度測定係由拉伸試驗儀進行，延展性評價之一之扭轉測試 係由扭轉測試機進行，測量直至破裂為止之扭轉次數以作 為延展性指標。 第1圖所示者係調查位於鋼線表面下1μιη之肥粒鐵相 中心部之平均c濃度及鋼線最表層之鋼線長向上之殘留應 力與、經扭轉測試直至破裂之扭轉次數所表示之延展性間 之關係所得之結果。其中，扭轉次數達20次以上之試樣以 白圈（延展性佳）表示，進而達25次以上之試樣以白四角（延 展性極佳）表示。又，未達20次之試樣則以黑三角（延展性不 佳）表不。具有45〇〇MPa以上之抗拉強度且延展性佳之鋼 線，僅於鋼線最外層之肥粒鐵相中心部之平均c濃度為 質量％以下，且殘留應力大幅壓縮至-600MPa以下時可見。 進而，延展性極佳之鋼線，則於肥粒鐵相中心部之平均c 浪度為0.1質量％以下，且殘留應力達一㈨河〜以下之強力 壓縮應力時可見。 201102443 由以上結果可知’為貫現尚強度且充分之延展性，鋼 線最外層之肥粒鐵相中心部之平均C濃度宜為〇. 2質量。/〇以 下’若為0.1質量以下更佳，且鋼線最外層之鋼線長向上 之殘留應力宜為-600MPa以下，較理想者為—700MPa以 下。平均C濃度雖愈低愈佳，但最終韌化材之波來鐵組織之 肥粒鐵相中心部碳濃度’原則上為最低之碳濃度。因此， 最外層之肥粒鐵相中心部之平均C濃度下限值亦可設定為 0.0001質量％。此外’殘留壓縮應力之最高值，原則上相當 於鋼線之屈服應力，但實質上亦可設定為-3000MPa。若外 施更大之壓縮應力將造成成本顯著增加，有違實用性。 其中，所謂鋼線最外層，係表示扣除鍍相或表面之非 均質相後、表面至深度2μηι以内之區域。又，鋼線最外層 之波來鐵組織之肥粒鐵相中心部，係指包含由肥粒鐵相之 中心面位置向兩側至肥粒鐵相寬度之1/4之距離以内之區 域(肥粒鐵相寬度一半之區域）。 基於上述發現產生之本發明之一實施型態之鋼線，係 含有0.7〜1.2質量％之c、〇.〇5〜2.0質量％2Si、0.2〜2.0質量 0/〇之Μη ’且殘餘部分含有以及不可避免之雜質者。該鋼線之 特徵在於具有業經拉線加工之波來鐵組織，且最外層之肥粒 鐵相中心部之平均C濃度為0.2質量％以下，前述鋼線最外層 之鋼線長向上之殘留壓縮應力為600MPa以上。其限定理由詳 述於後。另’下列所示「％」若未特別說明，則指「質量％」。 C· C具有增加韌化處理後之抗拉強度及提高拉線加工硬 化率之效果’並可藉更少之拉線加工應變提高抗拉強度。若 12 201102443 C含量為0.7%以下，將難以實現本發明目的所在之高強度鋼 線，反之，若超過1.2%，韌化處理時共析前雪明碳鐵將於沃 斯田鐵晶界析出’使拉線加工性劣化，並成為拉線加工中造 成斷線的原因。因此，C含量之範圍限定在0 7〜12ό/ο。201102443 VI. Description of the invention: [Rhyme ^ Ming Hu Ji Technology ^ Xuan Mubei] Field of the Invention The present invention relates to a high strength steel used for steel cords or saw wires of automobile tires Line and its manufacturing method. More specifically, the present invention relates to an ultra-fine steel wire having a wire diameter of 〇〇4 to 〇4 mm and a strength of up to 4500 MPa or more, which is molded by a mold and strengthened by a cold work. The present application claims priority based on Japanese Patent Application No. 2, No. Hei. I: Prior Art Background of the Invention Regarding the steel wire used for automobiles, the demand for the tension of the steel wire has increased due to the demand for lightweight tires. Similarly, the use of saw wires for precision cutting of sapphire crystals or Sic crystals has gradually increased the demand for high tension. In response to these needs, a number of special studies have begun. It is found that in addition to the high tension of the steel wire, it is also necessary to ensure sufficient ductility. There are several types of ductile buckles, such as, for example, twisting tests until the torsion-number of fractures, or whether cracks (delamination) are formed along the length of the steel wire during the torsion test. The high strength of the Pit steel line has led to a decrease in ductility, which has become a major issue. So the focus is on how to suppress it. In addition, it was found that the high-strength steel wire has a heterogeneous deterioration after the chamber effect (Song ~ 4 generations, several days to several years). The phenomenon is how to make good ductility not substantially lower after the aging period is 201102443. It is also an important issue. In general, a high-strength steel wire is produced by drawing a wire having a Borne iron structure by a mold or the like. By this, the wave-to-iron layer spacing is reduced, and a large amount of difference is introduced into the ferrite-grained iron phase to increase the tensile strength. In recent years, it has been found that if the tensile strain is very large, the stellite carbon in the Borne iron structure will be refined and decomposed. However, since the organization is extremely fine, the relationship between the existence position and the existence state of the carbon and the mechanical properties is unclear, and in particular, there are many unclear reasons for the deterioration of the ductility. For the actual high-strength steel wire, the strain or the local strain in the steel wire should be different in the surface area and the center area, which also affects the characteristics of the steel wire. In order to increase the strength of the ultra-fine steel wire, it is necessary to increase the strength of the wire after the final toughening treatment, or to increase the strain of the final wire drawing process. However, the method of increasing the strength of the plain wire after the final toughening treatment, or straining the strained wire to increase the strength of the ultra-fine steel wire, also causes a significant decrease in ductility when the strength exceeds 450014?3, so it is extremely difficult to Practical. On the other hand, in the past, in the research and development examples of the high-strength means for reducing the decrease in ductility, Patent Document 1, Patent Document 2, and Patent Document 3 have respectively proposed that the chemical compositions such as C, Si, Mn, and Cr are high. Extremely thin wires of strength and high ductility are used for carbon steel wires. However, it is also known from the examples disclosed in the publications that the tensile strength of the steel wire is at most 3,500 to 3,600 MPa, and the high strength of the ultra-fine steel wire is limited. Further, Patent Document 4 proposes a high-strength steel high-strength steel wire material having a controlled chemical composition and a non-metallic inclusion structure and an area fraction of the pre-eutectoid snow alloy. Further, Patent Document 5 discloses a method for producing a high-strength steel high-toughness ultra-fine wire which is used to control the chemical conversion of steel into a 201102443 minute and a final profile reduction ratio. However, these techniques are also unable to achieve extremely fine steel wires having a tensile strength of 4,500 MPa or more and high ductility. 4 Other studies have found that the properties of the cable are affected by the carbon concentration in the ferrite phase of the Borne iron structure. It is therefore proposed to increase the balance between strength and ductility by specifying these concentrations. Taking Patent Document 6 as an example, good characteristics are obtained by specifying the carbon concentration in the steel wire. Patent Document 7 discloses a method of further applying heat treatment to achieve a desired carbon state and obtaining good characteristics. Further, as in Patent Document 8', good characteristics are obtained by specifying the carbon concentration and the layer spacing in the steel wire. However, none of the patent documents mentions the carbon state of the outermost layer of the steel wire (the area from the surface to the depth of 2 μm), which was the actual measurement (and control) of the technology at the time. Further, Patent Document 9 specifies the unevenness of carbon concentration. Furthermore, in Patent Document 10', the difference in layer pitch which affects the unevenness of the carbon concentration is defined. However, these patent documents discuss the overall inequality and do not specify the carbon concentration of a particular part. On the other hand, the method for producing the steel wire and the steel wire shown in the patent document u obtains good characteristics by specifying the C concentration ratio in the ferrite phase of the steel wire surface layer portion and the steel wire center portion. However, the relative value of the central and surface parts is always specified and is not specified as the absolute value of the explicit indicator. Further, the actual measurement was only performed at an internal pressure of 1 〇 μϊη or more from the surface, and the concentration of c in the region (outermost layer) from the surface to 2 μm was not controlled. On the other hand, in the case of the residual stress of the outermost layer of the steel wire, in Patent Document 12 or Patent Document 13, the range of the residual stress is defined in terms of fatigue or resistance to longitudinal fracture. However, although the residual compressive stress is good, the absolute value of the value of 201102443 is small, and the range for achieving the best balance between ductility and strength is not specified. It does not even reveal the relationship with the carbon state of the outermost layer. The person responsible for the ductility of the high-strength ultra-fine steel wire is the ductility of the ferrite-iron phase. As long as the ductility of the ferrite-rich iron phase is maintained, ductility can be ensured even in a high-strength state. However, if the strain of the wire is increased, in general, the ferritic carbon iron will be decomposed so that the c atom diffuses in the ferrite phase and the carbon concentration in the ferrite phase increases. Non-Patent Document 1 mentions that in the cold-rolled steel sheet, in the case where the carbon concentration in the ferrite-grained iron phase has been increased, the dynamic strain aging of the difference between the ferrite-grain and the iron phase due to carbon is generated during the tensile test. And caused a significant decrease in ductility. [PRIOR ART DOCUMENT] [Patent Document 1] Japanese Patent Laid-Open Publication No. SHO-60-204865 [Patent Document 2] Japanese Patent Laid-Open Publication No. 63-24-46 (Patent Document 3) [Patent Document 4] Japanese Patent Laid-Open Publication No. Hei No. Hei No. Hei No. 7-ini B [Patent Document 6] Japanese Patent Laid-Open Publication No. JP-A No. Hei No. Hei. Kaiping 丨丨_丨9 9 $8 〇号 [^c|ic7] 9 ^ ^ 2008-208450^; [Patent Document 8] Japanese Patent Laid-Open Publication No. 2__2495_ [Patent Document 9] Japanese Patent Laid-Open Publication No. Japanese Patent Publication No. 9 [Patent Document 10] Japanese Patent Publication No. 96 [Patent Document 11] Japanese Patent Publication No. _ (4) Lake _3 Difficult No. 6 [Patent Document 12] Japanese Patent Laid-Open No.靡Hi靡号 [Patent Document 13] Japanese Patent Publication No. PCT Publication No. 201102443 [Non-Patent Document] [Non-Patent Document 1] 曰本金属学会志45:9 (1981) 942~947 [Invention Content 3 Summary of Invention Problem to be solved By setting a very large amount of wire drawing during wire drawing, it is possible to achieve the effect of high tension by using conventional techniques, but the problem of reduced ductility is inevitable. The present invention provides a high-strength steel wire having a high strength of 4,500 MPa or more and excellent ductility, in particular, a high-strength ultra-fine steel wire, in view of the above-mentioned status quo. Means for Solving the Problems In order to solve the above problems, the present invention employs the following means. (1) A first aspect of the invention: a steel wire containing a chemical composition of C: 0.7 to 1.2% by mass, Si: 0.05 to 2.0% by mass & Mn: 0.2 to 2.0% by mass, and a residual portion containing Fe and The inevitable impurity; the steel wire has a Borne iron structure, and the average C concentration of the center portion of the iron phase of the outermost layer of the steel wire is 0.2% by mass or less, and the residual compressive stress of the outermost steel wire is long. It is 600 MPa or more. (2) The steel wire according to the above (1) may further contain Cr: 0.05 to 1.0% by mass, Ni: 0.05 to 1.0% by mass, V: 0.01 to 0.5% by mass, Nb: 0.001 to 0.1% by mass, Mo: 0.01 to 0.1% by mass & B: 0.0001 to 0.01% by mass of one or more chemical components. (3) A steel wire according to the above (1) or (2), which may be a high-strength ultra-fine steel wire having a tensile strength of 4,500 MPa or more and a resistance of 201102443. (4) The high-strength ultra-fine steel wire of the above (3) may be a steel cord (5). The high-strength ultra-fine steel wire of the above (3) may be a saw wire. (6) A second aspect of the present invention: a method for producing a steel wire for manufacturing a steel wire having a tensile strength of 4,500 MPa or more; the manufacturing method comprising the following steps: a toughening step, the following steel The wire is subjected to a toughening treatment to form a Borne iron structure, and the steel wire contains chemical components such as C: 0.7 to 1.2% by mass, Si: 0.05 to 2.0% by mass, and Μη: 0.2 to 2.0% by mass, and the residual portion contains Fe. And an unavoidable impurity; the wire drawing step is to control the average C concentration of the center portion of the ferrite grain iron phase in the aforementioned Borne structure of the outermost layer of the steel wire to 0.2% by mass or less, and to pull the steel wire And, the step of imparting a residual stress is to impart a residual compressive stress of 600 MPa or more to the steel wire. EFFECT OF THE INVENTION The steel wire according to the present invention is controlled by the carbon concentration in the center portion of the iron phase of the outermost layer of the steel wire having the wave-iron structure, and is imparted with residual compressive stress to exhibit high strength and ductility. Further, since a high-strength steel wire having sufficient ductility and tensile strength can be provided, the manufactured article can be made lighter. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows the relationship between the average C concentration at the center of the ferrite phase of the ultrafine steel wire surface of 4500 MPa or more and the surface residual stress and ductility. 201102443 The results of the investigation. The figure shown in the figure is the method of taking out the needle-like sample from the inner surface of the very thin steel wire at a distance of 1 μm. The figure shown in the figure is the step of fixing the test block to the needle pedestal. The panel shown in Fig. 2C is a test piece processed by a focused ion beam (FIB) device. The 2D drawing is an observation view of the upper part of the test block. Fig. 2E is a diagram of a needle sample prepared by FIB processing of the test piece. Figure 2F is a side view of the needle sample. The figure shown in Fig. 3 is the C concentration obtained by the three-dimensional atomic micro-exploration method (3 D AP) and the C concentration in the fat grain phase. [Implementation of the cold type] According to the control factors of the ductility of high-strength steel wire, after various research and analysis, Wei, the plastic deformation of the social quantity (4) in the wave-iron structure, the carbon in the outermost layer of the steel wire in the iron phase (hereinafter referred to as C) concentration The residual stress of the steel wire with the outermost layer of the steel wire has a strong influence on the ductility of the steel wire. When bending or twisting, the outermost layer of the steel wire is subjected to a stronger internal stress and becomes the starting point of the damage. The method of detecting the residual stress of the outermost layer has existed for a long time, but there is no accurate measurement method for the C concentration in the outermost layer of ferrite in the scale of the lining to the inside of the 2 scale. This time, the research and the relationship between the research and the characteristics are developed. After the relationship, it is found that the C concentration in the iron phase of the outermost layer of the steel wire is below a predetermined value, and the stress of the steel wire is reduced to the residual value of 102102443, and the compressive stress is above a certain value. Will greatly improve the ultra-fine steel wire <strength and extension On the other hand, the outermost layer of the steel wire is subjected to more intense temperature changes caused by friction and heat, etc., relative to the inside of the steel wire. Therefore, a distinct organization and state are formed inside the wire. Therefore, it is more catalyzed by the decomposition of snow sigh woven and the concentration of c in the outermost layer of ferrite is generally in the state of the concentration of c in the ferrite phase of the steel wire. The layer has the strongest relationship with the characteristics. It can be seen that by controlling the outermost organization, θ < ', a steel wire with a good balance between strength and ductility can be roughly realized. ^The strength steel wire will generally have a wave. The wire rod of the iron structure is obtained by the strengthening of the boring line by the casting mold, etc. When the high-strength steel wire is manufactured by the above method, the high tensile strain occurs during the processing of the 2 wire drawing, and the carbon steel in the Borne iron structure is generated. The phenomenon of refinement and decomposition, so that c is melted into the iron phase of the ferrite. The inventor of the present invention combined with the three-dimensional original two-exploration method for measuring the local concentration of C in the fine dip field (the town is called 3 return) and the young cut itself The outermost layer of steel wire is taken, and the needle sample making technology' Exploring in detail the relationship between the C concentration of the fertilized iron and the strength and ductility of the steel wire in all places of steel and steel. The results show that the Cit degree of the iron-coated iron-coated towel on the surface of the steel wire becomes high, or the same outermost layer. The residual stress is significantly reduced when the steel wire is stretched upward or weakly compressed (refer to Fig. 1). tt % 〜α bite into the outermost layer of the squall line and the residual stress is in the appropriate range. The condition of this. This recognition enabled the new development of a method for detecting the local concentration of C in the outer layer, and Baidu discovered that the carbon state of the outermost layer of the steel wire is detectable. 10 201102443 And the following conclusions are drawn. In order to realize a steel wire which can ensure sufficient ductility, the average c concentration of the iron core phase center portion of the outermost layer of the steel wire must be set to a specific value or less, and then the steel wire length of the surface is left upward. The stress is set to a compressive stress of sufficient magnitude. Further, the inventors of the present invention produced a sample having a tensile strength of 45 〇 GMPa or more by various methods, and examined the tensile strength and ductility and the average c concentration of the center portion of the ferrite grain iron phase of the surface iron structure. The relationship between residual stress on the surface. The average c concentration of the iron-phase center of the outermost layer of the steel wire is determined by 3DAP, and the residual stress is detected by the Cong line diffraction test. The tensile strength measurement was carried out by a tensile tester, and one of the ductility evaluations was performed by a torsion tester, and the number of twists until the breakage was measured as an index of ductility. The figure shown in Fig. 1 is the average c concentration at the center of the ferrite grain iron phase at the surface of the steel wire and the residual stress of the steel wire at the outermost layer of the steel wire, and the number of twists after twisting test until rupture. The result of the relationship between the extensions. Among them, the sample having the number of twists of 20 or more is represented by a white circle (good ductility), and the sample of 25 or more times is represented by a white square (excellent ductility). Also, samples that were not 20 times were shown as black triangles (poorly ductile). A steel wire having a tensile strength of 45 〇〇 MPa or more and excellent ductility is only found in the outermost portion of the outermost layer of the steel wire, and the average c concentration is less than or equal to the mass%, and the residual stress is greatly compressed to below -600 MPa. . Further, the steel wire having excellent ductility is visible when the average c-wavelength at the center portion of the ferrite grain iron phase is 0.1% by mass or less, and the residual stress reaches a strong compressive stress of one (nine) river to below. 201102443 From the above results, it can be seen that the average C concentration of the center portion of the iron and steel phases of the outermost layer of the steel wire is preferably 质量. 2 mass. If the thickness is less than 0.1 mass, the residual stress of the steel wire of the outermost layer of the steel wire should be -600 MPa or less, preferably -700 MPa or less. The lower the average C concentration, the better, but the carbon concentration in the center of the ferrite phase of the ferrite of the toughened material is, in principle, the lowest carbon concentration. Therefore, the lower limit value of the average C concentration of the center portion of the iron phase of the outermost layer of the fat particles can also be set to 0.0001% by mass. Further, the highest value of the residual compressive stress is in principle equivalent to the yield stress of the steel wire, but may be substantially set to -3000 MPa. If a larger compressive stress is applied, the cost will increase significantly, which is against practicality. Here, the outermost layer of the steel wire is a region in which the surface is degraded to a depth of 2 μm after deducting the non-homogeneous phase of the plating phase or the surface. In addition, the center of the iron phase of the ferrite grain of the outermost layer of the steel wire is the area containing the center plane position of the ferrite grain iron phase to the sides of the ferrite grain iron phase by a quarter of the width ( The area where the ferrite grain is half the width of the iron phase). The steel wire according to one embodiment of the present invention, which is produced based on the above findings, contains 0.7 to 1.2% by mass of c, 〇.〇5 to 2.0% by mass of 2Si, 0.2 to 2.0 mass% of Μ, and the residual portion contains And the inevitable impurities. The steel wire is characterized by having a wave-like iron structure processed by a wire drawing, and an average C concentration of a center portion of the outermost layer of the ferrite grain is 0.2% by mass or less, and the residual compression of the outermost steel wire length of the steel wire is upward. The stress is 600 MPa or more. The reasons for this are detailed below. In addition, "%" shown below means "% by mass" unless otherwise specified. C·C has the effect of increasing the tensile strength after the toughening treatment and increasing the hardening rate of the wire drawing, and can increase the tensile strength by processing strain with less wire drawing. If the content of 12 201102443 C is 0.7% or less, it will be difficult to achieve the high-strength steel wire for the purpose of the present invention. On the contrary, if it exceeds 1.2%, the pre-eutectoid ferritic carbon iron will be precipitated in the Worthfield iron grain boundary during the toughening treatment. The wire drawability is deteriorated, which causes the wire breakage during the wire drawing process. Therefore, the range of the C content is limited to 0 7 to 12 ό / ο.
Si: Si係可有效使波來鐵中之肥粒鐵相強化，或使鋼脫 氧之元素。Si含量未達〇·05%時無法達到上述效果，反之， 若超過2%則容易產生對拉線加工性有害之硬質si〇2系夾雜 物。因此’ Si含量之範圍限定在0 05〜20%。 Μη : Μη不僅為脫氧、脫硫之所必須，且為可有效提升 鋼之硬化也並提咼勒化處理後之抗拉強度之元素。但Μη含 量未達0.2%時無法達到上述效果，反之，若超過2 〇%則上 述效果達到飽和’甚至韌化處理時直至波來鐵變態完成為 止之處理時間過長，以致生產力降低。因此，Μη含量之範 圍限定在0.2〜2.0%。 上述本發明之一實施型態之鋼線，根據下列理由，可 更包含Cr、Ni、V、Nb、Mo、Β中之1種以上。Si: Si is an element that effectively strengthens the ferrite phase of the ferrite or deoxidizes the steel. When the Si content is less than 5%·5%, the above effect cannot be obtained. On the other hand, if it exceeds 2%, it is likely to cause hard si〇2-based inclusions which are harmful to the wire drawability. Therefore, the range of the 'Si content is limited to 0 05 to 20%. Μη : Μη is not only necessary for deoxidation and desulfurization, but also an element which can effectively improve the hardening of steel and the tensile strength after the treatment. However, the above effect cannot be obtained when the Μη content is less than 0.2%. On the other hand, if it exceeds 2 〇%, the above effect is saturated ‘ even when the toughening treatment is completed until the wave-forming iron is completed, the treatment time is too long, so that the productivity is lowered. Therefore, the range of the Μη content is limited to 0.2 to 2.0%. The steel wire of one embodiment of the present invention may further contain one or more of Cr, Ni, V, Nb, Mo, and yttrium for the following reasons.
Cr : Cr係用以細化波來鐵之雪明碳鐵相間距並提高韌 化處理後之抗拉強度’且使拉線加工硬化率提升者。然而， Cr含量未達0.05%時前述作用之效果減少，反之，若超過 1.0 %則韌化處理時之波來鐵變態完成時間增加以致生產力 降低。因此’ Cr含量宜限縮於〇.〇5〜1.0%之範圍内。Cr : Cr is used to refine the spacing of the ferritic carbon-iron phase of the ferrite and to increase the tensile strength after the toughening treatment and to increase the wire drawing hardening rate. However, when the Cr content is less than 0.05%, the effect of the aforementioned action is reduced. On the other hand, if it exceeds 1.0%, the completion time of the wave-forming iron during the toughening treatment is increased to lower the productivity. Therefore, the 'Cr content should be limited to within the range of 〜.〇5 to 1.0%.
Ni : Ni係具有使韌化處理時生成變態之波來鐵成為拉 線加工性良好者之作用，但Ni含量未達0.5%時達不到上述 效果’即使超過1.0%亦少有與添加量相符之效果。因此， 13 201102443Ni: Ni has a function of generating a metamorphic wave during the toughening treatment, and the iron has a good workability in wire drawing. However, when the Ni content is less than 0.5%, the above effect is not obtained. Even if it exceeds 1.0%, it is rare and added. Matching effect. Therefore, 13 201102443
Nl含量宜限縮於0.05〜1.0%之範圍内。 V · V係具有細化波來鐵之雪明碳鐵相間距並提高韌化 處理時之抗拉強度之效果，但V含量未達0.01%時該效果不 足’反之若超過〇 5%則效果達到飽和。因此，V含量宜限 縮於0.01〜0.5%之範圍内。The Nl content is preferably limited to a range of 0.05 to 1.0%. The V · V system has the effect of refining the spacing of the ferritic carbon-iron phase of the wave and improving the tensile strength during the toughening treatment, but the effect is insufficient when the V content is less than 0.01%. Saturated. Therefore, the V content should be limited to a range of 0.01 to 0.5%.
Nb : Nb與V同樣具有細化雪明碳鐵相間距並提高韌化 處理時之抗拉強度之效果’但^^含量未達〇 〇〇1%時該效果 不足’反之若超過〇·1%則效果達到飽和。因此，Nb含量宜 限縮於0.001〜0.1%之範圍内。Nb: Nb and V have the same effect of refining the spacing of the stellite carbon-iron phase and improving the tensile strength during the toughening treatment. 'But the effect is less than 1% when the content of ^^ is less than '1, if it exceeds 〇·1 % The effect is saturated. Therefore, the Nb content is preferably limited to the range of 0.001 to 0.1%.
Mo : Mo與V同樣具有細化雪明碳鐵相間距並提高韌化 處理時之抗拉強度之效果，但Mo含量未達0.01%時該效果 不足’反之若超過0.1%則效果達到飽和。因此，M〇含量宜 限縮於0.01〜0.1%之範圍内。 B : B係具有使N形成BN後固定，並防止n造成時效劣 化之作用效果，為充分發揮該效果，須使鋼材中之B含量達 到0.0001%以上。反之，鋼材中之B含量即使超過〇〇1%， 效果亦已達飽和，添加更多B只會拉高製造成本，並不合 宜。基於該理由，本發明使鋼材中含有6時，B含量宜限縮 於0.0001〜0.1%之範圍内。 其他元素並無特殊限定，但作為雜質之元素，含量範 圍宜設定為P . 0.015%以下、S : 0.015〇/〇以下、N : 0.007% 以下。又，A1若超過0.005%，容易生成鋼中之夾雜物中最 硬之Al2〇3系夾雜物，並成為拉線加工或絞線加工時造成斷 線之原因，故理想之範圍在0.005%以下。 14 201102443 又，除上述元素外’亦可含有因製程等而無可避免地 混入之雜質，但以盡可能不混入雜質為宜。 為將業經大量塑性變形之極細線之拉線波來鐵組織 中’鋼線最外層之肥粒鐵相中心部之平均C濃度控制在0.2 質量％以下並且賦予足量之殘留壓縮應力，以最終韌化處 理後之製程中分別由下列A群組、B群組、C群組各採用一 個製法最為有效。假如採用3個製法，卻集中於一個群組， 而非採用全部群組之製法時，有時反使特性降低。由全部 群組採用製法，ϋ由某一群組再採用一個製法，亦無法達到 更佳效果。此係由於在同一群組之製法，基本上具有類似之 效果’另-方面，若增加不同之製法’則有消除效果之可能 !生。因此宜如前所述，由每個群組各採用一個製法。 (八群組製法） 1.於最終段加幻:域歧札轉，理想料複數次。 重要製法之-之表皮輕乾拉線，係以與一般拉線之斷 面縮率〇〇%以上）相較特別小之斷面縮率進行拉線之方 该斷面縮率宜為1%以上6%以下，若為以以上5%以下 工佳。斷面縮率未達1%時，難以於鋼線之表層全體進行加 殘留過大，無法触理想之表面 單粒鐵r之c濃度。該表皮輥軋拉線可以 進行r獨知’錄線同時 程序，理，目者斷面辦以〜斷表皮輥札 力，鋼線表面外施壓縮之殘留應 可使表面之層狀構造更平均。藉由該表面之適當 S3 15 201102443 碳之效果，易於減 明碳鐵分解。 殘留壓縮應力施加與去除固著於差排之 低碳之局部固溶量，並抑制最外層之雪 A2 :於拉線加工後進行珠擊。 珠擊係一以特定壓力、特定時間、特 将疋大小之球形珠粒 衝擊鋼線全體’並僅於鋼線之表面區_成加卫層或應變層 之方法。珠擊之進行，舉例言之，於空氣投射式且空氣壓力曰4 〜5xl05Pa之狀態下，時間宜為5〜10秒，珠粒球形宜為1〇〜 ΙΟΟμιη。如此方可有效於鋼線之表面全體進行足量之衝擊。 於拉線加工後進行珠擊，藉以於鋼線表面賦予壓縮之 殘留應力，同時使表面之層狀構造更為平均。藉由該表面 之適當殘留壓縮應力施加與去除固著於差排之碳之效果， 將減低碳之局部固溶量，並抑制最外層之雪明碳鐵分解。 (Β群組製法） Β1 :最終段之拉線速度設為2〇〇m/分以下，理想者以 5〇m/分以下之低速進行拉線。 藉由進行低速拉線，可降低摩擦或塑性變形所產生之 加工發熱量，從而抑制波來鐵組織中之雪明碳鐵分解並可 減少於肥粒鐵相中擴散之碳量。 B2 :於拉線加工層間進行溫度4〇〜40〇°C之加熱處理 0.5秒〜5分鐘，若以1〇〇〜3〇〇〇c之溫度進行1秒〜3分鐘更佳。 拉線加工之線溫係瞬間上升並立即下降。除此之外， 藉由於拉線加工層間施以適當溫度之加熱處理，可使拉線 加工中因雪明碳鐵分解而熔入肥粒鐵相中所形成之過飽和 之碳，經層間之加熱處理後由肥粒鐵相排出，使肥粒鐵相 16 201102443 之c濃度降低’同時消除不需要之點缺陷（空位等）或差 卜因此’可回復延展性並進行高應變量之加工，亦 粒鐵相間距之細化。惟，該處is並接减加工層間全數 施做，施行於特定層間方為有敦。 B3:包含表皮觀軋之最終段及之前之拉線程序中，係 使用接近角為8〜12。且動摩擦係數為q丨，理想者為 下之鑄模。 藉由使用接近角小、且動摩擦係數小之鑄模，抑制执 線加工時之轉發熱，並抑制因最外層之溫度上升使雪明 碳鐵分解而造成肥粒鐵相巾之⑶度增加。此須於接近最終 段之程序使用方為有效。 、 (C群組製法） C1 :拉線加工後，保持60〜30(rc之加熱〇丨分至24小 時，以180〜260°c進行20秒〜15分鐘更佳。 藉由拉線加工中或加工後之時效，使因雪明碳鐵分解 而熔入肥粒鐵相中所形成之過飽和碳排出，且使肥粒鐵相 中之碳濃度降低。惟，該溫度過高時，將形成球狀雪明碳 鐵或過渡碳化物，若過低則效果甚小。故須依鋼材種類、 拉線條件設定在適當溫度。 C2 .於最終段前3段以外之拉線加工中加入丨次高達 20〇/〇以上之斷面縮率之程序，理想者為複數次。 藉由加入1次尚達20%以上之斷面縮率之程序，理想者 為複數次，可使拉線應變均勻深入内部，而非集中於表面。 此須於最終段前3段之前進行方為有效。 17 201102443 鋼線中之肥粒鐵相中之c濃度，可藉由三維原子微探法 (3DAP)正確測量。然而，以往無法測量鋼線最外層之拉線 波來鐵組織中之肥粒鐵相中之C濃度。因開發出利用聚焦離 子束(FIB)裝置由鋼線表面擷出小片，並藉Fm將之加工製 成針試樣之技術後，故可精確測定最外層之碳濃度。 須注意固溶C濃度有時因肥粒鐵相中位置之差異而顯 示不同之數值。雪明碳鐵分解且c：於肥粒鐵相中擴散時，一般 而言，位於肥粒鐵相/雪明碳鐵相之界面位置之c濃度較高， 於肥粒鐵相中心位置則數值最小。本實施型態中，由肥粒鐵 相之中心面位置向兩側至肥粒鐵相寬度之1/4之距離以内之 區域(肥粒鐵相寬度一半之區域)之平均c濃度係有所規定。 藉由3DAP之分析，可測量包含肥粒鐵相/雪明碳鐵相之 界面之肥粒鐵相中之C濃度，因此由測量數據在欲檢測之區域 選擇特定大小之盒子並擷出，可計算盒子内之c原子與全原子 之比率，並以原子％求出肥粒鐵相中之c濃度。將求出數值乘 以12/56可轉換成質量％。針對複數肥粒鐵相中心部進行此項 測篁並求取平均值，作為肥粒鐵相中心部之平均c濃度。 舉例言之，第2A圖〜第2F圖所示者係用以測量距離鋼 線表面Ιμηι内部之肥粒鐵相中心部c濃度之針試樣製作方 法，第3圖顯示利用製成之針試樣以3DAP測出之C分佈與肥 粒鐵相中心部之C濃度。 為製作距離鋼線表面Ιμηι内部之區域之針試樣，以第 2Α圖所示為例，由鋼線表面區域，以ΠΒ擷出一側含有鋼線 表面之棒狀試塊。利用如鎢等蒸鍍（氣相沈積），將該試塊如 18 201102443 第2B圖所示固定於針台座上。將該試棟如第沈圖所示，以 FIB加工形成前端部變細之狀態。第2D圖係由上部觀察加工 後之試塊之圖示，可看出係形成前㈣包含鱗表面之棒 狀。繼之，由上部照射環狀之射束，藉以將前端部加工成 針狀。第2F圖係由側邊觀察依前述方法製成之針試樣之圖 示。針前端位置乃如第2E圖所示，製作成相當於距離鋼線 表面㈣内部之狀態。藉由利用上述針試樣製作技術，可 製成鋼線最外層之針試樣。 又，第3圖中，顏色濃之部分表示c濃度高，顏色淡之 部分表示C濃度低。因此，顏色濃之帶狀區域表示業經拉線 加工之雪明碳鐵相’其等之間顏色較淡之區域表示業經拉 線加工之肥粒鐵相。肥粒鐵相中亦顯示出c已固溶之狀態。 如圖所示，由肥粒鐵相中心位置擷出盒子，將該盒^子 所含之C原子數除以盒子中之全原子數，可估算肥粒鐵:中 心部之碳濃度。本财，C濃度係G.18#4%。練鐵相中 心部係位於兩個雪明碳鐵相之中間部，相當於由肥粒鐵相 之t心面位置向兩側至肥粒鐵相寬度之丨/4之距離以内之 區域(肥粒鐵相寬度一半之區域）。 肥粒鐵相之寬度隨加工量或取樣地方而未必一定，亦 有狹窄部分在1Gnm以下之區域1於盒子位置包含有雪明 碳鐵區域，則比肥粒鐵相中真正之c濃度高。因此，欲分析 之盒子位置視為肥粒鐵相中心部，且盒子寬度為肥粒鐵相 寬度之_。又，平均c濃度之估算係5個以上，理相者為 _以上不同肥粒鐵相中心、部之c濃度測定值之平均數。 19 201102443 鋼線最外層之殘留應力，舉例言之，係可藉由X射線繞 射測定法精準測量。特別是，可使用可測量局部區域之微 小區域X射線繞射儀並以德拜環擬合法進行更正確之測 定。該方法係一將鋼線之晶粒反射擬合成德拜環，並由德 拜環之歪斜變形檢測殘留應力之大小與方向之方法。由又 射線之穿透深度將決定包含表面之深度區域。例如X射線源 為Cr時，可得表面數之深度之估計值。又，檢測鋼線表 面之殘留應力之方法另有一隨時熔解法（海恩法）。該方法係 藉由測量欲檢側之最外層熔化前後之鋼線長度之差異，檢 測鋼線長向上之殘留應力。該等方法均可精準求出組構發 達之高強度鋼線之殘留應力。 實施例 以下藉由實施例更具體說明本發明之可實施性及效果。 將具有表1所示化學組成之供試體以熱軋形成預定線 徑後，利用鉛浴進行韌化處理、拉線加工，試做成抗拉強 度達4500MPa以上、線徑0.04〜0.40mm之由具有黃銅電鍵 之拉線波來鐵組織構成之兩強度極細線鋼。黃銅電鑛係於 最終韌化處理後之酸洗後實施。 表2顯示極細鋼線之拉線加工真應變、製造方法、線 徑、鋼線最外層之肥粒鐵相中心部之平均C濃度、鋼線最外 層之殘留應力、抗拉強度、及扭轉測試中直至破裂為止之 扭轉次數。表2中，以表示前述内容之記號表示製造方法。 杻轉測試係以試片兩端線控1〇〇倍之夾台間距加以固定，並 檢測直至破裂為止之扭轉次數。抗拉強度為4500MPa以上 20 201102443 且扭轉次數達20次以上者評為延展性佳，25次以上者評為 延展性極佳。鋼線最外層之肥粒鐵相中之C濃度，係利用前 述方法以3DAP測量表面1 μιη位置，鋼線最外層之鋼線長向 上之殘留應力係藉由前述德拜環擬合法測量。殘留應力為 負時表示壓縮應力，若為正則表示拉伸應力。 【表1】 鋼 化學成分(重量％) 種 C Si Μη Ρ S A1 N Cr Ni V Nb Mo B A 1.16 0.19 0.33 0.008 0.007 0.001 0.0031 — — — 一 — — B 0.85 1.63 0.42 0.011 0.005 0.002 0.0035 0.32 C 0.88 0.26 0.40 0.009 0.008 0.003 0.0039 — — — 0.005 0.03 — D 1.01 0.15 0.27 0.007 0.009 0.001 0.0028 0.25 — 0.11 — — — E 0.78 1.78 0.38 0.008 0.006 0.002 0.0033 0.19 — — — — 0.0018 F 0.88 0.33 1.46 0.005 0.007 0.001 0.0035 0.22 0.33 — 0.028 一 — G 0.69 0.28 0.50 0.007 0.006 0.002 0.0028 Η 0.90 2.40 0.39 0.008 0.008 0,003 0.0030 0.0030 I 1.23 0.35 0.45 0.010 0.0010 0.003 0.0042 — — — 0.004 — — 【表2】 測 試 No. 材料 製造條件 極細鋼線之特性 鋼種 韌化材 之強度 (MPa) 拉線 加工 真應力 製造方法 線徑 (mm) 最外層之肥粒 鐵相中心部 之平均C濃度 (質量％) 殘留 應力 (MPa) 抗拉 強度 (MPa) 扭轉 次數 (次） 備註 1 A 1520 4.46 A1+B1+C1 0.17 0.07 1040 4520 27 本發明例 2 B 1480 4.61 A1+B2+C2 0.16 0.04 -700 4530 26 本發明例 3 C 1460 4.73 A1+B3+C1 0.15 0.14 -1080 4550 22 本發明例 4 D 1500 4.61 A1+B2+C2 0.16 0.18 -940 4510 23 本發明例 5 E 1450 4.73 A2+B3+C2 0.15 0_]0 -850 4600 24 本發明例 6 F 1460 4.87 A2+B1+C1 0.14 0.12 -620 4620 20 本發明例 7 G 1450 5.02 A1+B1+C1 0.13 0.60 -650 4500 17 比較例 8 H 1510 4.48 A2+B3+C2 0.18 0.18 -620 4520 19 比較例 9 I 1550 4.15 A1+B3+C1 0.20 0.13 -720 4620 14 比較例 10 A 1500 4.61 A1+C2 0.16 0.32 -1200 4550 19 比較例 11 B 1480 4.61 A1+B3+C1+C2 0.16 0.21 •740 4560 14 比較例 12 B 1480 4.87 A2 0.14 0.26 -900 4630 16 比較例 13 C 1460 4.61 A2 十 B2 0.16 0.42 -650 4510 18 比較例 21 201102443 14 D 1530 4.48 A1+A2+B3+C1 0.17 0.15 -450 4630 16 比較例 15 C 1460 4.87 B1+C1 0.14 0.05 210 4530 15 比較例 16 E 1450 4.73 B1+B2+C1 0.16 0.09 820 4600 18 比較例 17 E 1380 4.73 A1+A2+B3 0.15 0.25 -350 4500 19 比較例 18 F 1460 4.87 — 0.14 0.50 -170 4730 8 比較例 19 A 1500 4.61 B2+C1 0.16 0.35 -60 4620 19 比較例 20 D 1500 1 4.37 C2 0.18 0.36 540 4540 14 比較例 表2中測試No.l〜6係本發明例，其他為比較例。如該 表所見’本發明例之抗拉強度均為4500MPa以上，且最外 層之肥粒鐵相中心部之平均C濃度為0.2質量％以下，殘留應 力為-600MPa以下（殘留壓縮應力為6〇〇MPa以上）。如此一 來’即可實現扭轉次數高並具有充分延展性之極細鋼線。 特別是測試No.l〜2之扭轉次數達25次以上，延展性極佳。 反之’測試No.7〜20係比較例，且抗拉強度達4500MPa 以上，但扭轉次數不足。 Νο·7〜9係鋼線成分在本發明之範圍外之比較例。No.7 因鋼線之C量過少’且提高拉線應變量’故肥粒鐵相中心部 之C濃度達規定值以上’以致延展性降低。又，ν〇·8係鋼線 之Si量，Νο·9係C量高於本發明之範圍之比較例。該等比較 例係殘留應力及肥粒鐵相中心部之c濃度在規定範圍内，但 延展性降低。 又，Νο.10〜13係鋼線成分與殘留應力在本發明之範園 内’但最外層之肥粒鐵相中心部之C濃度在規定值以上之比 較例。該等比較例呈延展性降低之狀態^ N〇 14〜16係鋼線 成分與肥粒鐵相中心部之C濃度在本發明之範圍内，但殘留 應力在範圍外之比較例。該等比較例呈延展性降低之狀 態。No.17〜20係最外層之肥粒鐵相中心部之c濃度與殘留應 22 201102443 力均於範圍外之比較例。該等比較例呈延展性降低之狀態。 產業之可利用性 藉由本發明，可提供具有充分延展性之高強度鋼線， 因此對產業上之貢獻非常大。 【圖式簡單說明】 第1圖所示者係對4500MPa以上之極細鋼線表面之肥 粒鐵相中心部之平均C濃度與表面殘留應力、延展性之關係 調查所得之結果。 第2 A圖所示者係由極細鋼線之距離表面1 μιη内部區域 取出針試樣之方法中之試塊擷出步驟。 第2Β圖所示者係將該試塊固定於針台座上之步驟。 第2C圖所示者係業經聚焦離子束(FIB)裝置加工後之 該試塊。 第2D圖係該試塊之上部觀察圖。 第2E圖係由上觀察於該試塊進行ΠΒ加工製得之針試 樣之圖。 第2F圖係該針試樣之側邊觀察圖。 第3圖所示者係經三維原子微探法（3DAP)測定所得之 C分佈與肥粒鐵相中心部之C濃度。 【主要元件符號說明】 (無） [S1 23Mo: Mo has the same effect of refining the spacing of the stellite carbon-iron phase and increasing the tensile strength at the time of toughening treatment, but the effect is insufficient when the Mo content is less than 0.01%. On the other hand, if it exceeds 0.1%, the effect is saturated. Therefore, the M〇 content should be limited to a range of 0.01 to 0.1%. B: The B system has an effect of fixing N after forming BN, and prevents the aging effect from being deteriorated by n. To fully exert this effect, the B content in the steel material must be made 0.0001% or more. On the other hand, if the B content in the steel exceeds 〇〇1%, the effect is saturated, and adding more B will only increase the manufacturing cost, which is not appropriate. For this reason, in the case where the steel material is contained in the present invention, the B content is preferably limited to the range of 0.0001 to 0.1%. The other elements are not particularly limited, but as an impurity element, the content range should be set to P. 0.015% or less, S: 0.015 〇/〇 or less, and N: 0.007% or less. Moreover, when A1 exceeds 0.005%, it is easy to form the hardest Al2〇3 type inclusion in the inclusions in the steel, and it is a cause of disconnection during wire drawing or stranding, so the range is preferably 0.005% or less. . 14 201102443 In addition to the above-mentioned elements, it is also possible to contain impurities which are inevitably mixed by a process or the like, but it is preferable to avoid impurities as much as possible. In order to reduce the average C concentration of the center of the iron phase of the outermost layer of the steel wire in the iron wire structure of the ultrafine wire which is subjected to a large amount of plastic deformation, it is controlled to 0.2 mass% or less and a sufficient amount of residual compressive stress is applied to finally In the process after the toughening process, the following A group, B group, and C group are respectively most effective in adopting one method. If three methods are used, but they are concentrated in one group instead of using the whole group, sometimes the characteristics are reduced. The adoption of the method by all groups, and the adoption of a system by a group, can not achieve better results. This is because the system in the same group basically has a similar effect. In addition, if the method of adding different methods is added, there is a possibility of eliminating the effect. Therefore, as mentioned above, one method is adopted for each group. (Eight group system) 1. In the final stage, add magic: the domain is turned and turned, ideally counted several times. The important method of the method - the skin light and dry cable, is to reduce the cross-sectional shrinkage of the general cable, which is more than 5%, and the cable is less than 1%. Above 6% or less, if it is more than 5%, it is better. When the reduction ratio of the section is less than 1%, it is difficult to increase the residual concentration of the single-grain iron r on the surface of the steel wire. The skin rolling line can be re-known to the 'recording line simultaneous program, rational, the target section to do ~ broken skin roller Zhali, steel wire surface external compression should be able to make the layered structure of the surface more even . It is easy to reduce the decomposition of carbon and iron by the effect of the appropriate S3 15 201102443 carbon on the surface. The residual compressive stress applies and removes the local solid solution amount of the low carbon fixed to the poor row, and suppresses the outermost layer of snow A2: performing a bead shot after the wire drawing process. The bead is a method of impacting the entire steel wire with a specific pressure, a specific time, and a spherical bead of a specific size, and only the surface area of the steel wire into a protective layer or a strained layer. For example, in the state of air projection and air pressure 曰4 ～5×10 5 Pa, the time should be 5 to 10 seconds, and the spherical shape of the beads should be 1 〇~ ΙΟΟμιη. In this way, it is effective to carry out a sufficient impact on the entire surface of the steel wire. After the wire drawing process, a bead shot is performed to impart a residual stress to the surface of the steel wire while making the layered structure of the surface more uniform. By applying and removing the carbon fixed to the poor row by the appropriate residual compressive stress on the surface, the local solid solution amount of carbon is reduced, and the decomposition of the outermost stellite is suppressed. (ΒGroup method) Β1: The drawing speed of the final stage is set to 2〇〇m/min or less, and the ideal one is to pull the wire at a low speed of 5〇m/min or less. By performing low-speed wire drawing, the heat generated by friction or plastic deformation can be reduced, thereby suppressing the decomposition of stellite in the iron-iron structure and reducing the amount of carbon diffused in the iron phase of the fertilizer. B2: The heat treatment is carried out at a temperature of 4 Torr to 40 Torr °C for 0.5 seconds to 5 minutes, and it is preferably carried out at a temperature of 1 Torr to 3 Torr for 1 second to 3 minutes. The line temperature of the wire drawing process rises instantaneously and immediately drops. In addition, by applying heat treatment at an appropriate temperature between the processing layers of the wire, the supersaturated carbon formed by the decomposition of the ferritic carbon iron into the ferrite phase in the wire drawing process can be heated by the interlayer. After treatment, it is discharged from the ferrite grain iron phase, which reduces the concentration of the ferrite grain iron phase 16 201102443' while eliminating the unnecessary point defects (vacancies, etc.) or the difference, so it can restore the ductility and process the high strain. Refinement of the grain iron phase spacing. However, the is is the same as the processing layer, and the implementation is performed in a specific layer. B3: In the final stage of the epidermis rolling and the previous drawing procedure, the approach angle is 8~12. And the dynamic friction coefficient is q丨, and the ideal one is the lower mold. By using a mold having a small approach angle and a small dynamic friction coefficient, the heat transfer during the wire processing is suppressed, and the (3) degree of the ferrite iron phase towel is suppressed by decomposing the ferritic carbon iron due to the temperature rise of the outermost layer. This shall be valid for use by the program near the final stage. , (C group method) C1: After the wire is processed, keep 60~30 (the heating of rc is 24 hours, and it is better to do it at 180~260°C for 20 seconds~15 minutes. Or the aging after processing, the supersaturated carbon formed by the decomposition of the ferritic carbon iron into the ferrite iron phase is discharged, and the carbon concentration in the ferrite iron phase is lowered. However, when the temperature is too high, it will be formed. If the spherical stellite carbon iron or transitional carbide is too low, the effect is very small. Therefore, it must be set to the appropriate temperature according to the type of steel and the wire drawing condition. C2. Adding 丨 times to the wire drawing processing other than the first 3 segments of the final section The procedure for the reduction of the section height of up to 20 〇 / , is ideal for multiple times. By adding a procedure of reducing the section ratio of more than 20%, the ideal one is multiple times, and the strain of the cable can be made uniform. Go deep inside, not focus on the surface. This must be done before the first 3 paragraphs of the final paragraph. 17 201102443 The concentration of c in the ferrite phase of the steel wire can be correctly determined by the three-dimensional atomic micro-exploration method (3DAP) Measurement. However, in the past, it was impossible to measure the iron phase of the ferrite in the outermost layer of the steel wire. The C concentration has been developed by using a focused ion beam (FIB) device to extract small pieces from the surface of the steel wire and process it into a needle sample by Fm, so that the carbon concentration of the outermost layer can be accurately determined. The solid solution C concentration sometimes shows different values due to the difference in the position of the ferrite grain iron phase. The snowy carbon iron decomposes and c: when diffused in the ferrite iron phase, generally, it is located in the ferrite iron phase/snow The concentration of c in the interface position of the carbon-iron phase is higher, and the value is the smallest in the center position of the iron phase of the ferrite. In this embodiment, the center plane position of the ferrite grain iron phase is from 1 to the width of the ferrite grain iron phase. The average c concentration of the area within the distance of 4 (the area of the iron phase of the fat grain is half) is specified. By the analysis of 3DAP, the ferrite iron containing the interface of the ferrite iron phase/snow carbon iron phase can be measured. The C concentration in the phase, so the box of the specific size is selected and measured by the measurement data in the area to be detected, and the ratio of the c atom to the total atom in the box can be calculated, and the atomic % is determined by the atomic %. Concentration. Multiply the calculated value by 12/56 to convert it to mass%. The center of the iron phase performs this measurement and obtains the average value as the average c concentration of the center portion of the ferrite grain iron phase. For example, the figures shown in Fig. 2A to Fig. 2F are used to measure the distance of the steel wire surface Ιμηι A method for producing a needle sample having a concentration of the center of the iron phase in the center of the ferrite phase, and a graph showing the C concentration measured by 3DAP and the C concentration at the center of the ferrite grain phase using the prepared needle sample. A needle sample in the area of the inner surface of the line Ιμηι is taken as an example in the second drawing, and the rod-shaped test piece containing the surface of the steel wire on the side of the steel wire is used as the surface area of the steel wire. The phase deposition is fixed to the needle pedestal as shown in Fig. 2B of Fig. 2 201102443. The test ridge is formed by FIB processing to form a state in which the front end portion is tapered as shown in the first plan view. The 2D image is an illustration of the test block after the upper portion is observed from the upper portion, and it can be seen that the front portion (4) is formed into a rod shape including a scale surface. Then, the annular beam is irradiated from the upper portion, whereby the front end portion is processed into a needle shape. Fig. 2F is a view showing a needle sample prepared by the above method from the side. The needle tip end position is formed to correspond to the inside of the steel wire surface (4) as shown in Fig. 2E. By using the above needle sample making technique, a needle sample of the outermost layer of the steel wire can be obtained. Further, in Fig. 3, the portion where the color is concentrated indicates that the c concentration is high, and the portion where the color is light indicates that the C concentration is low. Therefore, the banded area of the color indicates the stellite carbon-iron phase which has been processed by the drawing, and the area where the color is lighter between the areas indicates the ferrite-grained iron phase which has been subjected to the drawing process. The iron phase of the fat grain also shows that c is in a solid solution state. As shown in the figure, the box is extracted from the center of the iron phase of the fat grain, and the number of C atoms contained in the box is divided by the total number of atoms in the box to estimate the carbon concentration of the iron in the center of the ferrite. This fiscal, C concentration is G.18#4%. The center of the tempered iron phase is located in the middle of the two swarf carbon-iron phases, which is equivalent to the area within the distance from the t-plane position of the ferrite-grained iron phase to the 铁/4 of the width of the ferrite-grain phase. The area where the granular iron phase is half the width). The width of the ferrite phase is not necessarily the same as the amount of processing or sampling. There is also a narrow portion below 1Gnm. The area containing the ferritic carbon iron in the box position is higher than the true c concentration in the ferrite phase. Therefore, the position of the box to be analyzed is regarded as the center of the iron phase of the fat grain, and the width of the box is the width of the iron phase of the fat grain. Further, the average c-concentration is estimated to be five or more, and the rationale is the average of the measured values of the c-concentration of the center of the different ferrite phases. 19 201102443 The residual stress of the outermost layer of the steel wire, for example, can be accurately measured by X-ray diffraction measurement. In particular, a micro-area X-ray diffractometer that measures the local area can be used and a more accurate measurement can be made by the Debye fitting method. The method is a method for fitting the grain reflection of a steel wire into a Debye ring and detecting the magnitude and direction of the residual stress by the skew deformation of the Debye ring. The depth of penetration of the ray will determine the depth region containing the surface. For example, when the X-ray source is Cr, an estimate of the depth of the surface number can be obtained. Further, the method of detecting the residual stress on the surface of the steel wire has a further melting method (Hain method). The method detects the residual stress in the length of the steel wire by measuring the difference in length of the steel wire before and after melting of the outermost layer on the side to be inspected. These methods can accurately determine the residual stress of the high-strength steel wire developed by the structure. EXAMPLES Hereinafter, the applicability and effects of the present invention will be more specifically described by way of examples. The test piece having the chemical composition shown in Table 1 was formed into a predetermined wire diameter by hot rolling, and then subjected to a toughening treatment and a wire drawing process using a lead bath, and the tensile strength was determined to be 4500 MPa or more and the wire diameter was 0.04 to 0.40 mm. A two-strength ultra-fine wire steel composed of a wire structure having a brass electric wave. The brass electric ore system is applied after pickling after the final toughening treatment. Table 2 shows the true strain of the wire drawing process of the ultra-fine steel wire, the manufacturing method, the wire diameter, the average C concentration of the iron-phase center portion of the outermost layer of the steel wire, the residual stress of the outermost layer of the steel wire, the tensile strength, and the torsion test. The number of twists until the rupture. In Table 2, the manufacturing method is indicated by the symbol indicating the foregoing. The twirling test was performed by fixing the distance between the two ends of the test piece by 1 〇〇, and detecting the number of twists until the rupture. Tensile strength is 4,500 MPa or more 20 201102443 and the number of twists is more than 20 times, the ductility is good, and those of 25 or more are rated as excellent ductility. The C concentration in the iron phase of the outermost layer of the steel wire is measured by the above method using 3DAP to measure the surface position of 1 μm, and the residual stress in the longitudinal direction of the steel wire of the outermost layer of the steel wire is measured by the aforementioned Debye fitting method. When the residual stress is negative, it indicates compressive stress, and if it is positive, it indicates tensile stress. [Table 1] Steel chemical composition (% by weight) Species C Si Μ Ρ S A1 N Cr Ni V Nb Mo BA 1.16 0.19 0.33 0.008 0.007 0.001 0.0031 — — — One — — B 0.85 1.63 0.42 0.011 0.005 0.002 0.0035 0.32 C 0.88 0.26 0.40 0.009 0.008 0.003 0.0039 — — — 0.005 0.03 — D 1.01 0.15 0.27 0.007 0.009 0.001 0.0028 0.25 — 0.11 — — — E 0.78 1.78 0.38 0.008 0.006 0.002 0.0033 0.19 — — — — 0.0018 F 0.88 0.33 1.46 0.005 0.007 0.001 0.0035 0.22 0.33 — 0.028 一— G 0.69 0.28 0.50 0.007 0.006 0.002 0.0028 Η 0.90 2.40 0.39 0.008 0.008 0,003 0.0030 0.0030 I 1.23 0.35 0.45 0.010 0.0010 0.003 0.0042 — — — 0.004 — — [Table 2] Test No. Material manufacturing conditions Characteristics of extremely fine steel wire Toughness (MPa) Tensile processing True stress manufacturing method Wire diameter (mm) Average C concentration (% by mass) of the outermost part of the iron phase of the ferrite phase Residual stress (MPa) Tensile strength (MPa) Number of twists (times) Remark 1 A 1520 4.46 A1+B1+C1 0.17 0.07 1040 4520 27 Inventive Example 2 B 1480 4.61 A1+B2+C2 0.16 0.04 -700 4530 26 Inventive Example 3 C 1460 4.73 A1+B3+C1 0.15 0.14 -1080 4550 22 Inventive Example 4 D 1500 4.61 A1+B2+C2 0.16 0.18 -940 4510 23 Inventive Example 5 E 1450 4.73 A2+B3+C2 0.15 0_]0 -850 4600 24 Inventive Example 6 F 1460 4.87 A2+B1+C1 0.14 0.12 -620 4620 20 Inventive Example 7 G 1450 5.02 A1+B1+C1 0.13 0.60 -650 4500 17 Comparative Example 8 H 1510 4.48 A2+B3+C2 0.18 0.18 -620 4520 19 Comparative Example 9 I 1550 4.15 A1+B3+C1 0.20 0.13 -720 4620 14 Comparative Example 10 A 1500 4.61 A1+C2 0.16 0.32 - 1200 4550 19 Comparative Example 11 B 1480 4.61 A1 + B3 + C1 + C2 0.16 0.21 • 740 4560 14 Comparative Example 12 B 1480 4.87 A2 0.14 0.26 - 900 4630 16 Comparative Example 13 C 1460 4.61 A2 Ten B2 0.16 0.42 - 650 4510 18 Comparative Example 21 201102443 14 D 1530 4.48 A1+A2+B3+C1 0.17 0.15 -450 4630 16 Comparative Example 15 C 1460 4.87 B1+C1 0.14 0.05 210 4530 15 Comparative Example 16 E 1450 4.73 B1+B2+C1 0.16 0.09 820 4600 18 Comparative Example 17 E 1380 4.73 A1+A2+B3 0.15 0.25 -350 4500 19 Comparative Example 18 F 1460 4.87 — 0.14 0.50 -170 4730 8 Comparative Example 19 A 1 500 4.61 B2+C1 0.16 0.35 -60 4620 19 Comparative Example 20 D 1500 1 4.37 C2 0.18 0.36 540 4540 14 Comparative Example Test Nos. 1 to 6 in Table 2 are examples of the present invention, and others are comparative examples. As seen in the table, the tensile strength of the present invention is 4,500 MPa or more, and the average C concentration of the center portion of the outermost ferrite phase is 0.2% by mass or less, and the residual stress is -600 MPa or less (the residual compressive stress is 6 〇). 〇 MPa or more). In this way, a very fine steel wire with a high number of twists and sufficient ductility can be realized. In particular, the number of twists of the test No. 1 to 2 was 25 or more, and the ductility was excellent. On the other hand, Test Nos. 7 to 20 are comparative examples, and the tensile strength is 4,500 MPa or more, but the number of twists is insufficient. A comparative example in which the steel wire component of the Νο·7 to 9 is outside the scope of the present invention. In No. 7, since the amount of C in the steel wire is too small' and the strain amount of the wire is increased, the C concentration in the center portion of the iron phase of the fat grain reaches a predetermined value or more, so that the ductility is lowered. Further, the amount of Si in the ν〇·8 series steel wire, and the comparative example in which the amount of C in the Νο·9 series is higher than the range of the present invention. In these comparative examples, the residual stress and the c concentration in the center portion of the ferrite grain iron phase are within a predetermined range, but the ductility is lowered. Further, the composition of the steel wire and the residual stress of the Νο. 10 to 13 are in the range of the present invention, but the C concentration of the center portion of the iron phase of the outermost layer of the fertilizer is a predetermined value or more. These comparative examples showed a state in which the ductility was lowered, and the C concentration of the N 〇 14 to 16 steel wire component and the center portion of the ferrite grain iron phase was within the range of the present invention, but the residual stress was out of the range. These comparative examples showed a state of reduced ductility. No. 17~20 is the outermost layer of the iron phase in the center of the iron phase of the fat phase and the residual should be 22 201102443 force is outside the range of comparison examples. These comparative examples showed a state in which the ductility was lowered. INDUSTRIAL APPLICABILITY According to the present invention, a high-strength steel wire having sufficient ductility can be provided, and thus the industrial contribution is very large. [Simple description of the drawings] The results shown in Fig. 1 are the results of investigations on the relationship between the average C concentration at the center of the ferrite phase of the ultrafine steel wire surface of 4500 MPa or more and the surface residual stress and ductility. The figure shown in Fig. 2A is a test block extraction step in which the needle sample is taken out from the inner region of the ultrafine steel wire at a distance of 1 μm. The figure shown in Fig. 2 is a step of fixing the test piece to the needle pedestal. The panel shown in Fig. 2C is a test piece processed by a focused ion beam (FIB) device. The 2D drawing is an observation view of the upper part of the test block. Fig. 2E is a view of a needle sample obtained by observing the test piece for the boring process. Fig. 2F is a side view of the needle sample. The figure shown in Fig. 3 is the C distribution obtained by the three-dimensional atomic micro-exploration method (3DAP) and the C concentration in the center portion of the ferrite grain iron phase. [Main component symbol description] (none) [S1 23