TW201704501A

TW201704501A - Steel sheet and method for producing same

Info

Publication number: TW201704501A
Application number: TW105116486A
Authority: TW
Inventors: Ken Takata; Kazuo Hikida; Kengo Takeda; Motonori Hashimoto
Original assignee: Nippon Steel & Sumitomo Metal Corp
Priority date: 2015-05-26
Filing date: 2016-05-26
Publication date: 2017-02-01
Also published as: TWI612154B; KR20170138510A; KR102029566B1; MX2017014938A; EP3305930A4; WO2016190396A1; CN107614726A; CN107614726B; US20180135146A1; JPWO2016190396A1; EP3305930A1; JP6119924B1; BR112017024957A2

Abstract

This steel sheet has improved hardenability and material moldability, and has a predetermined component composition. The metal structure of the steel sheet satisfies the following conditions: the average particle size of carbides is 0.4 [mu]m to 2.0 [mu]m; the area ratio of perlite is 6% or less; B/A > 1 wherein A is the number of carbide particles in ferrite grains and B is the number of carbide particles at ferrite grain boundaries; and I1/I0 < 1 wherein I1 is the X-ray diffraction intensity of the {211}<011> orientation on a surface at a depth of 1/2 the thickness of the steel sheet and I1 is the X-ray diffraction intensity of the {100}<011> orientation. The steel sheet has a Vickers hardness of 100 HV to 150 HV.

Description

鋼板及其製造方法 Steel plate and method of manufacturing same

技術領域 Technical field

本發明有關於鋼板及其製造方法。 The present invention relates to a steel sheet and a method of manufacturing the same.

背景技術 Background technique

含有以質量%計0.1~0.7%之碳的鋼板，可作為對胚料施行壓製成形、擴孔成形、彎曲成形、沖壓成形、增厚及減厚成形、或組合該等之冷鍛等成形，以製造汽車之齒輪、離合器等驅動系零件的素材使用。因會對鋼板施行淬火回火來確保所述零件的強度，故對鋼板要求高淬火性。 A steel sheet containing 0.1% to 0.7% by mass of carbon can be used as a press forming, a reaming forming, a bending forming, a press forming, a thickening and a thickening forming, or a combination of cold forging, etc., on a billet. It is used to manufacture materials for drive system parts such as gears and clutches for automobiles. Since the steel sheet is quenched and tempered to ensure the strength of the part, the steel sheet is required to have high hardenability.

此外，對於作為前述驅動系零件之素材的鋼板，要求冷環境下之高成形性。零件成形以沖壓成形及/或增厚成形為主，零件成形中左右素材成形性之最大的因子係塑性異向性。鋼板之塑性異向性的改善需適用於鋼板之零件成形。 Further, the steel sheet which is a material of the above-described drive system component is required to have high formability in a cold environment. The forming of the parts is mainly press forming and/or thickening forming, and the factor of the greatest formability of the left and right materials in the forming of the parts is plastic anisotropy. The improvement of the plastic anisotropy of the steel sheet is required to be applied to the forming of the steel sheet.

關於所要求之淬火性與經改善塑性異向性之成形性，迄今有幾個提案，以下之專利文獻中揭示了冷鍛性及耐衝撃特性優異之鋼板。 There have been several proposals for the required formability of hardenability and improved plastic anisotropy, and the following patent documents disclose steel sheets excellent in cold forgeability and impact resistance.

例如，專利文獻1中揭示了一種機械構造用鋼，係藉由抑制浸碳熱處理之結晶粒的粗大化來提升韌性的機械構造用鋼，以質量%計，含有：C：0.10~0.30%、Si：0.05~2.0%、Mn：0.10~0.50%、P：0.030%以下、S：0.030%以下、Cr：1.80~3.00%、Al：0.005~0.050%、Nb：0.02~0.10%、N：0.0300%以下，且剩餘部分由Fe及不可避免的雜質所構成，冷加工前之組織係肥粒鐵．波來鐵組織，肥粒鐵粒徑的平均值係15μm以上。 For example, Patent Document 1 discloses a steel for machine structural use, which is a steel for machine structural use which improves the toughness by suppressing the coarsening of crystal grains by the carbon-baking heat treatment, and contains C: 0.10 to 0.30% by mass%. Si: 0.05 to 2.0%, Mn: 0.10 to 0.50%, P: 0.030% or less, S: 0.030% or less, Cr: 1.80 to 3.00%, Al: 0.005 to 0.050%, Nb: 0.02 to 0.10%, N: 0.0300 Below %, and the rest is composed of Fe and inevitable impurities, and the structure before cold working is ferrite. In the Borne iron structure, the average particle size of the ferrite iron is 15 μm or more.

專利文獻2中揭示了一種鋼，作為冷加工性與浸碳淬火性優異之鋼，含有：C：0.15~0.40%、Si：1.00%以下、Mn：0.40%以下、sol.Al：0.02%以下、N：0.006%以下、B：0.005~0.050%，且剩餘部分由Fe及不可避免的雜質所構成，且具有以肥粒鐵相與石墨相作為主體之組織。 Patent Document 2 discloses a steel which is excellent in cold workability and carbon kneading property, and contains C: 0.15 to 0.40%, Si: 1.00% or less, Mn: 0.40% or less, and sol. Al: 0.02% or less. N: 0.006% or less, B: 0.005 to 0.050%, and the remainder is composed of Fe and unavoidable impurities, and has a structure mainly composed of a ferrite-grained iron phase and a graphite phase.

專利文獻3中揭示了一種衝撃強度優異之浸碳斜齒輪用鋼材、高韌性浸碳斜齒輪、及其製造方法。 Patent Document 3 discloses a steel material for a carbon-impregnated helical gear excellent in punching strength, a high-toughness carbon-impregnated helical gear, and a method for producing the same.

專利文獻4中揭示了一種對球化退火後進行冷鍛，並於浸碳淬火回火步驟中製造之零件，具有優異之加工性，且之後的浸碳中亦可抑制結晶粒之粗大化，具優異之耐衝撃特性、耐衝撃疲勞特性的浸碳零件用鋼。 Patent Document 4 discloses a part which is subjected to cold forging after spheroidizing annealing and which is produced in a carbon-impregnated quenching and tempering step, and has excellent workability, and can also suppress coarsening of crystal grains in the subsequent carbon impregnation. Steel for carbon-impregnated parts with excellent punching resistance and crushing fatigue resistance.

專利文獻5中揭示了一種鋼，作為電漿浸碳用冷工具鋼，含有：C：0.40~0.80%、Si：0.05~1.50%、Mn：0.05~1.50%、及、V：1.8~6.0%，更含有Ni：0.10~2.50%、Cr：0.1~2.0%、及Mo：3.0%以下之1種或2種以上，且剩餘部分由Fe及不可避免的雜質所構成。 Patent Document 5 discloses a steel as a cold tool steel for plasma impregnation, comprising: C: 0.40 to 0.80%, Si: 0.05 to 1.50%, Mn: 0.05 to 1.50%, and V: 1.8 to 6.0%. Further, it contains one or more of Ni: 0.10 to 2.50%, Cr: 0.1 to 2.0%, and Mo: 3.0% or less, and the remainder is composed of Fe and unavoidable impurities.

另一方面，改善成形性、即改善塑性異向性有以下提案。 On the other hand, there are the following proposals for improving formability, that is, improving plastic anisotropy.

例如，專利文獻6中提出了於C：0.25~0.75%下規定碳化物粒徑與球化率，並規定冷軋延率與箱退火條件、熱軋延之捲取溫度、利用規定集合組織來改善面內異向性，藉此規定r值及△r。 For example, Patent Document 6 proposes to specify a carbide particle size and a spheroidization ratio at C: 0.25 to 0.75%, and to specify a cold rolling rate, a box annealing condition, a coiling temperature of a hot rolling, and a predetermined aggregate structure. Improve the in-plane anisotropy, thereby specifying the r value and Δr.

專利文獻7及8中提出了一種鋼板，藉由規定最終軋延機之軋台間的熱軋材加熱、退火條件，減少△r值，改善面內異向性。專利文獻8中提出了一種鋼板，藉於熱軋延時規定Ar3點以上之溫度下的最終軋延，並以500-630℃捲取，來降低面內異向性。 Patent Documents 7 and 8 propose a steel sheet which reduces the Δr value and improves the in-plane anisotropy by specifying the heating and annealing conditions of the hot-rolled material between the rolling stands of the final rolling mill. Patent Document 8 proposes a steel sheet which is subjected to final rolling at a temperature of not more than Ar3 by a hot rolling delay and wound at 500 to 630 ° C to reduce in-plane anisotropy.

先前技術文獻 Prior technical literature 專利文獻 Patent literature

專利文獻1：日本專利特開2013-040376號公報 Patent Document 1: Japanese Patent Laid-Open Publication No. 2013-040376

專利文獻2：日本專利特開平06-116679號公報 Patent Document 2: Japanese Patent Laid-Open No. Hei 06-116679

專利文獻3：日本專利特開平09-201644號公報 Patent Document 3: Japanese Patent Laid-Open No. 09-201644

專利文獻4：日本專利特開2006-213951號公報 Patent Document 4: Japanese Patent Laid-Open Publication No. 2006-213951

專利文獻5：日本專利特開平10-158780號公報 Patent Document 5: Japanese Patent Laid-Open No. Hei 10-158780

專利文獻6：日本專利特開2000-328172號公報 Patent Document 6: Japanese Patent Laid-Open Publication No. 2000-328172

專利文獻7：日本專利特開2001-073076號公報 Patent Document 7: Japanese Patent Laid-Open No. 2001-073076

專利文獻8：日本專利特開2001-073077號公報 Patent Document 8: Japanese Patent Laid-Open Publication No. 2001-073077

發明概要 Summary of invention

前述專利文獻中，有人提出了改善面內異向性的方法，但並未提出兼具零件所要求之強度，即淬火性的方法。 In the aforementioned patent documents, a method for improving the in-plane anisotropy has been proposed, but a method of combining the strength required for the part, that is, the hardenability, has not been proposed.

本發明有鑑於以往技術之前述情事，目的在於提供可提升淬火性與素材成形性，特別是藉由增厚等冷鍛成形後適合得到齒輪等零件之鋼板與其製造方法。 The present invention has been made in view of the above-described circumstances of the prior art, and an object of the present invention is to provide a steel sheet which can improve the hardenability and the formability of the material, and is particularly suitable for obtaining a gear or the like after cold forging by thickening or the like.

為解決前述課題，得到適合驅動系零件等素材之鋼板，可知於含有提高淬火性所需之C的鋼板中，增大肥粒鐵之粒徑，將碳化物(主要係雪明碳鐵)球化成適當之粒徑，減少波來鐵組織即可。這是因為以下理由。 In order to solve the above-mentioned problems, it is known that a steel sheet suitable for a material such as a drive component is obtained. In a steel sheet containing C required for improving hardenability, the particle size of the ferrite iron is increased, and the carbide (mainly ferritic carbon iron) ball is obtained. Turn into a suitable particle size and reduce the Borne iron structure. This is because of the following reasons.

肥粒鐵相之硬度低、延性高。因此，以肥粒鐵作為主體之組織藉由加大其粒徑，即可提高素材成形性。 The ferrite iron phase has low hardness and high ductility. Therefore, the structure in which the ferrite-grained iron is the main body can be improved by increasing the particle diameter thereof.

藉於金屬組織中適當地分散碳化物，可保持素材成形性，並賦與優異之耐磨耗性或轉動疲勞特性，故係驅動系零件中不可或缺的組織。又，鋼板中之碳化物係防止滑動之堅硬的粒子，藉於肥粒鐵晶界中存在碳化物，可防止滑動之傳播越過結晶晶界，可抑制剪切帶(shear zone)之形成，提升冷鍛性，同時亦提升鋼板之成形性。 By properly dispersing the carbides in the metal structure, the material formability can be maintained, and the excellent wear resistance or rotational fatigue characteristics are imparted, so that the structure is indispensable in the drive system parts. Further, the carbide in the steel sheet is a hard particle that prevents sliding, and the presence of carbide in the ferrite grain boundary prevents the sliding from propagating over the crystal grain boundary, thereby suppressing the formation of the shear zone and improving Cold forgeability also improves the formability of the steel sheet.

但，雪明碳鐵係硬且脆之組織，於存在與肥粒鐵為層狀組織之波來鐵的狀態時，因鋼變硬且脆，故需以球狀存在。考量到冷鍛性、或鍛造時產生之裂縫，該粒徑需於適當之範圍。 However, the stellite carbon iron is a hard and brittle structure, and when the iron and iron are in the form of a layered structure, since the steel is hard and brittle, it needs to exist in a spherical shape. Consider the cold forging property, or the crack generated during forging, which is required to be in the proper range.

然而，迄今尚未揭示可實現前述組織之製造方法。因此，本發明人等專心地研究可實現前述組織之製造方法。 However, the manufacturing method for realizing the aforementioned organization has not been disclosed so far. Therefore, the inventors of the present invention have intensively studied a manufacturing method capable of realizing the aforementioned structure.

結果，為使熱軋延後捲取後之鋼板的金屬組織，成為層狀間隔小的微細之波來鐵或細小之肥粒鐵中分散有雪明碳鐵的變韌鐵組織，而以較低溫捲取(400℃~550℃)。藉以較低溫捲取，分散於肥粒鐵中之雪明碳鐵亦變得容易球化。接著，第1階段退火中，以Ac1點下之溫度進行退火使雪明碳鐵部分球化。然後，第2階段退火中，以Ac1點與Ac3點間之溫度(即肥粒鐵與沃斯田鐵之二相域)進行退火，殘留一部分之肥粒鐵粒，並使一部分變態成沃斯田鐵。之後進行緩冷卻使殘留之肥粒鐵粒成長，並以其為核地使沃斯田鐵變態成肥粒鐵變態，藉此，可得大之肥粒鐵相並於晶界析出雪明碳鐵，發現可實現前述組織。 As a result, in order to make the metal structure of the steel sheet after the hot rolling is rolled up, a fine wave having a small layer interval is formed, and the tough iron structure of the ferritic carbon iron is dispersed in the iron or the fine ferrite iron. Low temperature coiling (400 ° C ~ 550 ° C). By taking it at a lower temperature, the smectite carbon iron dispersed in the ferrite iron also becomes easy to spheroidize. Next, in the first-stage annealing, annealing is performed at a temperature lower than the Ac1 point to partially spheroidize the sulphur carbon. Then, in the second-stage annealing, the temperature between the Ac1 point and the Ac3 point (ie, the two-phase domain of the ferrite iron and the Vostian iron) is annealed, and a part of the ferrite particles are left, and a part of the ferrite is transformed into a worth. Tian Tie. Then, the slow cooling is carried out to grow the residual ferrite particles, and the Worthite iron is transformed into a fermented iron and iron metamorphism, thereby obtaining a large ferrite iron phase and precipitating the snow-light carbon at the grain boundary. Iron, found to be able to achieve the aforementioned organization.

換言之，發現僅單一地研究熱軋條件或退火條件等將不易實現同時滿足淬火性與成形性之鋼板的製造方法，藉由以熱軋．退火步驟等所謂之一連串之步驟達成最佳化方可實現。 In other words, it has been found that only a single study of hot rolling conditions or annealing conditions, etc., which is difficult to achieve at the same time satisfying the hardenability and formability of the steel sheet by hot rolling. A so-called series of steps such as an annealing step can be achieved by optimizing the steps.

又，改善冷鍛時之沖壓成形性需降低塑性異向性，且發現調整熱軋條件對於該改善係重要。 Further, the improvement of the press formability at the time of cold forging is required to reduce the plastic anisotropy, and it has been found that the adjustment of the hot rolling conditions is important for the improvement.

本發明有鑑於該等觀察所得知識而構成，其要旨係如下述。 The present invention has been constructed in view of the knowledge gained from such observations, and the gist thereof is as follows.

(1)一種鋼板，以質量%計含有：C：0.10~0.70%、Si：0.01~0.30%、Mn：0.30~3.00%、Al：0.001~0.10%、Cr：0.010~0.50%、Mo：0.0010~0.50%、B：0.0004~0.01%、Ti： 0.001~0.10%、P：0.02%以下、S：0.01%以下、N：0.0100%以下、O：0.0200%以下、Sn：0.05%以下、Sb：0.05%以下、As：0.05%以下、Nb：0.10%以下、V：0.10%以下、Cu：0.10%以下、W：0.10%以下、Ta：0.10%以下、Ni：0.10%以下、Mg：0.05%以下、Ca：0.05%以下、Y：0.05%以下、Zr：0.05%以下、La：0.05%以下及Ce：0.05%以下，且剩餘部分係Fe及不可避免的雜質；前述鋼板之金屬組織滿足：碳化物之平均粒徑係0.4μm以上且2.0μm以下，波來鐵之面積率係6%以下，令肥粒鐵粒內之碳化物個數為A，且肥粒鐵晶界之碳化物個數為B時，B/A>1，及令前述鋼板1/2板厚部分板面的{211}<011>之X射線繞射強度為I1，且令{100}<011>之X射線繞射強度為I0時，I1/I0<1；前述鋼板之維克氏硬度係100HV以上且150HV以下。 (1) A steel sheet containing, by mass%, C: 0.10 to 0.70%, Si: 0.01 to 0.30%, Mn: 0.30 to 3.00%, Al: 0.001 to 0.10%, Cr: 0.010 to 0.50%, Mo: 0.0010 ~0.50%, B: 0.0004~0.01%, Ti: 0.001 to 0.10%, P: 0.02% or less, S: 0.01% or less, N: 0.0100% or less, O: 0.0200% or less, Sn: 0.05% or less, Sb: 0.05% or less, As: 0.05% or less, Nb: 0.10 % or less, V: 0.10% or less, Cu: 0.10% or less, W: 0.10% or less, Ta: 0.10% or less, Ni: 0.10% or less, Mg: 0.05% or less, Ca: 0.05% or less, and Y: 0.05% or less Zr: 0.05% or less, La: 0.05% or less, and Ce: 0.05% or less, and the remainder is Fe and unavoidable impurities; the metal structure of the steel sheet satisfies: the average particle diameter of the carbide is 0.4 μm or more and 2.0 μm. Hereinafter, the area ratio of the Bora iron is 6% or less, so that the number of carbides in the ferrite grains is A, and the number of carbides in the ferrite grain boundary is B, B/A>1, and The X-ray diffraction intensity of {211}<011> of the plate surface of the 1/2 plate thickness portion of the steel plate is I1, and when the X-ray diffraction intensity of {100}<011> is I0, I1/I0<1; The Vickers hardness of the steel sheet is 100 HV or more and 150 HV or less.

(2)一種鋼板之製造方法，係製造前述(1)之鋼板，該方法係將具有如前述(1)之成分組成的鋼片直接加熱或暫時冷卻後加熱，並對加熱後之鋼片施行熱軋延而製成熱軋鋼板，且該熱軋延係於820℃以上且950℃以下之溫度域中結束最終軋延；以400℃以上且550℃以下捲取前述熱軋鋼板；對捲取後之熱軋鋼板施行酸洗；以30℃/小時以上且150℃/小時以下之加熱速度將酸洗後之熱軋鋼板加熱至650℃以上且720℃以下的退火溫度後，施行保持3小時以上且60小時以下之第1階段退火；接著以1℃/小時以上且80℃/小時以下之加熱速度將熱軋鋼板加熱至725℃以上且790℃以下之退火溫度後，施行保持3小時以上且小於10小時之第2階段退火；以1℃/小時以上且100℃/小時以下之冷卻速度將退火後之熱軋鋼板冷卻至650℃。 (2) A method of producing a steel sheet according to the above (1), wherein the steel sheet having the composition of the above (1) is directly heated or temporarily cooled, and then heated, and the heated steel sheet is subjected to heating. Hot rolling is performed to form a hot-rolled steel sheet, and the hot rolling is terminated in a temperature range of 820 ° C or higher and 950 ° C or lower; the hot rolling steel sheet is taken up at 400 ° C or higher and 550 ° C or lower; The hot-rolled steel sheet is subjected to pickling; the hot-rolled steel sheet after pickling is heated to an annealing temperature of 650 ° C or higher and 720 ° C or lower at a heating rate of 30 ° C /hr or more and 150 ° C /hr or less, and then maintained. Annealing in the first stage of hours or more and 60 hours or less; then heating the hot-rolled steel sheet to an annealing temperature of 725 ° C or more and 790 ° C or less at a heating rate of 1 ° C / h or more and 80 ° C / h or less, and then maintaining for 3 hours. The second order above and less than 10 hours Segment annealing; the annealed hot-rolled steel sheet is cooled to 650 ° C at a cooling rate of 1 ° C / hour or more and 100 ° C / hour or less.

依據本發明，可提供淬火性與素材成形性優異、特別是可適宜用於藉由增厚等冷鍛成形來製得齒輪等零件之鋼板及其製造方法。 According to the present invention, it is possible to provide a steel sheet which is excellent in hardenability and material formability, and particularly suitable for use in cold forging forming by thickening or the like to obtain a gear or the like, and a method for producing the same.

用以實施發明之形態 Form for implementing the invention

以下，詳細地說明本發明。首先，說明本發明鋼板成分組成之限定理由。此處，成分之「%」係「質量%」之意。 Hereinafter, the present invention will be described in detail. First, the reasons for limiting the composition of the steel sheet of the present invention will be described. Here, the "%" of the ingredients means "% by mass".

[C：0.10~0.70%] [C: 0.10~0.70%]

C係形成碳化物，對鋼之強化及肥粒鐵粒之微細化有效之元素。為抑制冷成形時產生梨皮，確保冷成形品表面之美觀，需抑制肥粒鐵粒徑之粗大化。 The C system forms a carbide, and is an element effective for strengthening steel and miniaturizing the iron particles. In order to suppress the production of pear skin during cold forming and to ensure the appearance of the surface of the cold formed product, it is necessary to suppress the coarsening of the particle size of the ferrite.

但C小於0.10%時，碳化物之體積率不足，未能抑制退火中碳化物之粗大化，故將C設為0.10%以上。以0.14%以上為佳。另一方面，C之含量變大時，碳化物之體積率增加，於瞬間負載載重時將生成成為破壞起點之裂痕，有成形性或耐衝撃特性下降的疑慮。於儘量減少其下降時，將C設為0.40%以下。以0.38%以下為佳。 However, when C is less than 0.10%, the volume fraction of the carbide is insufficient, and the coarsening of the carbide during annealing is not suppressed, so C is made 0.10% or more. It is preferably 0.14% or more. On the other hand, when the content of C is increased, the volume fraction of the carbide is increased, and when the load is instantaneously loaded, cracks which are the starting point of the fracture are generated, and there is a fear that the formability or the impact resistance characteristics are lowered. When the drop is minimized, C is set to 0.40% or less. It is preferably 0.38% or less.

另一方面，因碳化物之體積率增加，強度上升時，疲勞特性將提升，於期望提升疲勞特性時將C設為大於 0.40%。以0.44%以上為佳。C大於0.70%時，將大量地生成成為破壞起點之裂痕，疲勞特性反而下降，故將C設為0.70%以下。以0.66%以下為佳。 On the other hand, as the volume fraction of carbide increases, the fatigue characteristics increase when the strength increases, and C is set to be larger when it is desired to improve the fatigue characteristics. 0.40%. More preferably 0.44% or more. When C is more than 0.70%, cracks which are the starting point of destruction are generated in a large amount, and the fatigue characteristics are rather lowered. Therefore, C is set to 0.70% or less. It is preferably 0.66% or less.

[Si：0.01~0.30%] [Si: 0.01~0.30%]

Si係除了作為脫氧劑作用外，將對碳化物之形態造成影響，有助於提升素材成形性的元素。為得到脫氧效果，將Si設為0.01%以上。以0.07%以上為佳。 In addition to acting as a deoxidizer, the Si system affects the form of carbides and contributes to the improvement of the formability of the material. In order to obtain a deoxidation effect, Si is made 0.01% or more. More than 0.07% is preferred.

Si大於0.30%時，因肥粒鐵之固溶強化硬度上升，延性下降，冷鍛時變得容易產生裂痕，冷鍛時之成形性與浸碳淬火回火後之耐衝撃特性下降，故將Si設為0.30%以下。以0.28%以下為佳。 When Si is more than 0.30%, the solid solution strengthening hardness of the ferrite iron increases, the ductility decreases, and cracks are likely to occur during cold forging, and the formability during cold forging and the resistance to impregnation after carbon-quenching and tempering are lowered. Si is set to 0.30% or less. It is preferably 0.28% or less.

[Mn：0.30~]3.00% [Mn: 0.30~] 3.00%

Mn係於2階段退火中控制碳化物形態的元素。小於0.30%時，因第2階段退火後的緩冷卻中不易於肥粒鐵晶界上生成碳化物，故將Mn設為0.30%以上。以0.40%以上為佳。 Mn is an element that controls the morphology of carbides in a two-stage annealing. When it is less than 0.30%, since the carbide is formed on the grain boundary of the ferrite grain in the slow cooling after the second-stage annealing, Mn is set to 0.30% or more. It is preferably 0.40% or more.

Mn大於1.00%時，浸碳淬火回火後之韌性下降，但強度提升。於極度抑制浸碳淬火回火後之韌性下降時，將Mn設為1.00%以下。以0.96%以下為佳。 When Mn is more than 1.00%, the toughness after carbon immersion quenching is lowered, but the strength is increased. When the toughness after carbon immersion quenching is extremely suppressed, Mn is set to 1.00% or less. It is preferably 0.96% or less.

於期望高強度化時將Mn設為大於1.00%。以1.10%以上為佳。Mn大於3.00%時，因浸碳淬火回火後之韌性顯著地下降，故將Mn設為3.00%以下。以2.70%以下為佳。 When Mn is desired to be high, Mn is set to be more than 1.00%. More than 1.10% is preferred. When Mn is more than 3.00%, the toughness after tempering by carbon impregnation is remarkably lowered, so Mn is set to 3.00% or less. It is preferably 2.70% or less.

[Al：0.001~0.10%] [Al: 0.001~0.10%]

Al係作為脫氧劑作用並穩定化肥粒鐵之元素。小於 0.001%時，因未能充分地得到添加效果，故將Al設為0.001%以上。以0.004%以上為佳。 Al acts as a deoxidizer and stabilizes the elements of ferrite. Less than When 0.001%, the addition effect was not sufficiently obtained, so Al was made 0.001% or more. More preferably 0.004% or more.

另一方面，Al大於0.10%時，肥粒鐵晶界之碳化物個數減少，成形性下降，故將Al設為0.10%以下。以0.09%以下為佳。 On the other hand, when Al is more than 0.10%, the number of carbides in the ferrite grain boundary is reduced, and the formability is lowered. Therefore, Al is made 0.10% or less. It is preferably 0.09% or less.

[Cr：0.010~0.50%] [Cr:0.010~0.50%]

Cr係有助於熱處理時碳化物之穩定化的元素。小於0.010%時，浸碳時將不易殘留碳化物，導致表層之沃斯田鐵粒徑粗大化，強度下降，故將Cr設為0.010%以上。以0.050%以上為佳。 Cr is an element that contributes to the stabilization of carbides during heat treatment. When the amount is less than 0.010%, carbides are less likely to remain during carbon immersion, and the Worstian iron particle size in the surface layer is coarsened and the strength is lowered. Therefore, Cr is set to 0.010% or more. It is preferably 0.050% or more.

另一方面，Cr大於0.50%時，碳化物中之Cr濃化量增加，2階段退火中生成的沃斯田鐵相中殘留有大量微細之碳化物，又，緩冷卻後肥粒鐵粒內存在有碳化物，導致硬度增加與肥粒鐵晶界碳化物之個數減少，成形性下降，故將Cr設為0.50%以下。以0.40%以下為佳。 On the other hand, when Cr is more than 0.50%, the amount of Cr concentration in the carbide increases, and a large amount of fine carbide remains in the iron phase of the Worth field formed in the two-stage annealing, and, in the ferrite grain after cooling, The presence of carbides causes an increase in hardness and a decrease in the number of carbides at the ferrite grain boundary, and the formability is lowered. Therefore, Cr is set to 0.50% or less. It is preferably 0.40% or less.

[Mo：0.001~0.50%] [Mo: 0.001~0.50%]

Mo與Mn、Cr相同，係有助於控制碳化物之形態的元素。小於0.001%時因未能充分地得到添加效果，故將Mo設為0.001%以上。以0.005%以上為佳。 Mo, like Mn and Cr, is an element that helps control the morphology of the carbide. When the amount is less than 0.001%, the effect of addition is not sufficiently obtained, so Mo is made 0.001% or more. More preferably 0.005% or more.

另一方面，大於0.50%時，因碳化物中之Mo濃化，沃斯田鐵相中穩定之碳化物亦增加，故緩冷卻後於肥粒鐵粒內亦存在碳化物，導致硬度增加與肥粒鐵晶界碳化物之個數減少，素材成形性下降，故將Mo設為0.50%以下。以0.40%以下為佳。 On the other hand, when it is more than 0.50%, due to the concentration of Mo in the carbide, the stable carbide in the iron phase of the Worthfield also increases, so that carbides are also present in the ferrite grains after the slow cooling, resulting in an increase in hardness and The number of carbides in the ferrite grain boundary is reduced, and the formability of the material is lowered. Therefore, Mo is set to 0.50% or less. It is preferably 0.40% or less.

[B：0.0004~0.01%] [B: 0.0004~0.01%]

B係提高淬火性，甚至是提高韌性之元素。本發明鋼板中因需所需之淬火性，故添加0.0004~0.01%。小於0.0004%時，因為能得到添加效果，故將B設為0.0004%以上。以0.0010%以上為佳。 B series improves hardenability and even enhances toughness. In the steel sheet of the present invention, 0.004 to 0.01% is added because of the required hardenability. When it is less than 0.0004%, since the effect of addition can be obtained, B is made 0.0004% or more. More preferably 0.0010% or more.

另一方面，大於0.01%時，因鋼製造時生成將成為內部缺陷等瑕疵之原因的粗大之B化物，故將B設為0.01%以下。以0.007%以下為佳。 On the other hand, when it is more than 0.01%, since a coarse B compound which causes a flaw such as an internal defect is generated at the time of steel production, B is made 0.01% or less. It is preferably 0.007% or less.

[Ti：0.001~0.10%] [Ti: 0.001~0.10%]

Ti係形成氮化物，有助於結晶粒之微細化，並具有可有效地發揮添加B之效果的作用之元素。小於0.001%時，因未能得到添加效果，故將Ti設為0.001%以上。以0.010%以上為佳。 Ti forms a nitride, contributes to the refinement of crystal grains, and has an effect of effectively exhibiting the effect of adding B. When the amount is less than 0.001%, Ti is not more than 0.001% because the effect of addition is not obtained. It is preferably 0.010% or more.

另一方面，大於0.10%時，因生成粗大之Ti氮化物，素材成形性下降，故將Ti設為0.10%以下。以0.07%以下為佳。 On the other hand, when it is more than 0.10%, since the coarse Ti nitride is formed, the material formability is lowered, so Ti is made 0.10% or less. It is preferably 0.07% or less.

以下元素係雜質，需控制在固定量以下。 The following elements are impurities and need to be controlled below a fixed amount.

[P：0.02%以下] [P: 0.02% or less]

P係於肥粒鐵晶界偏析，具抑制肥粒鐵晶界碳化物生成的作用之元素。故，P以越少越佳。P含量亦可為0，但欲減少至小於0.0001%時，因精煉步成本大幅增加，故實質之下限係0.0001~0.0013%。 P is segregated at the grain boundary of the ferrite grain, and has an action of suppressing the formation of carbides at the iron grain boundary of the ferrite. Therefore, P is as small as possible. The P content may also be 0, but if it is to be reduced to less than 0.0001%, since the refining step cost is greatly increased, the substantial lower limit is 0.0001 to 0.0013%.

P大於0.02%時，將抑制肥粒鐵晶界碳化物之生成，碳化物之個數減少，素材成形性下降，故將P設為0.02% 以下。以0.01%以下為佳。 When P is more than 0.02%, the formation of carbides at the ferrite grain boundary is suppressed, the number of carbides is reduced, and the formability of the material is lowered, so P is set to 0.02%. the following. It is preferably 0.01% or less.

[S：0.01%以下] [S: 0.01% or less]

S係形成MnS等非金屬夾雜物之雜質元素。非金屬夾雜物因於冷鍛時將成為裂痕之起點，故S以越少越佳。S含量亦可為0，但減少至小於0.0001%時，因精煉成本大幅地增加，故實質之下限係0.0001~0.0012%。 S forms an impurity element of a non-metallic inclusion such as MnS. Non-metallic inclusions will become the starting point of cracks during cold forging, so S is preferably as small as possible. The S content may be 0, but when it is reduced to less than 0.0001%, since the refining cost is greatly increased, the substantial lower limit is 0.0001 to 0.0012%.

S大於0.01%時，將生成非金屬夾雜物，素材成形性下降，故將S設為0.01%以下。以0.009%以下為佳。 When S is more than 0.01%, non-metallic inclusions are formed, and the formability of the material is lowered. Therefore, S is made 0.01% or less. It is preferably 0.009% or less.

[N：0.02%以下] [N: 0.02% or less]

N係大量存在時將使肥粒鐵脆化之元素。因此，N以越少越佳。N含量亦可為0，但減少至小於0.0001%時，因精煉成本大幅地增加，故實質之下限係0.0001~0.0006%。 An element that will embrittle iron in the presence of a large amount of N. Therefore, N is as small as possible. The N content may be 0, but when it is reduced to less than 0.0001%, since the refining cost is greatly increased, the substantial lower limit is 0.0001 to 0.0006%.

N大於0.02%時，因肥粒鐵脆化，素材成形性下降，故將N設為0.02%以下。以0.017%以下為佳。 When N is more than 0.02%, since the ferrite is embrittled and the material formability is lowered, N is made 0.02% or less. It is preferably 0.017% or less.

本發明鋼板含有C：0.10~0.40%、Mn：0.30~1.00%時，為抑制肥粒鐵脆化，故將N設為0.01%以下。以0.007%以下為佳。 When the steel sheet of the present invention contains C: 0.10 to 0.40% and Mn: 0.30 to 1.00%, in order to suppress iron embrittlement of the fertilizer, N is made 0.01% or less. It is preferably 0.007% or less.

[O：0.02%以下] [O: 0.02% or less]

O係大量存在時將促進粗大之氧化物形成的元素。因此，O以越少越佳，但減少至小於0.0001%時，因精煉成本大幅地增加，故設為0.0001%以上。以0.0011%以上為佳。 An element that promotes the formation of coarse oxides when O is present in a large amount. Therefore, O is preferably as small as possible, but when it is reduced to less than 0.0001%, since the refining cost is greatly increased, it is made 0.0001% or more. More preferably, it is 0.0011% or more.

另一方面，，大於0.020%時，鋼中將生成粗大之氧化物，該氧化物將成為冷鍛時裂痕之起點，素材成形性下降，故將O設為0.02%以下。以0.01%以下為佳。 On the other hand, when it is more than 0.020%, a coarse oxide is formed in the steel, and this oxide becomes a starting point of cracks during cold forging, and the formability of the material is lowered. Therefore, O is made 0.02% or less. It is preferably 0.01% or less.

[Sn：0.05%以下] [Sn: 0.05% or less]

Sn係自鋼原料不可避免地混入之元素。因此，Sn以越少越佳。S含量亦可為0，但減少至小於0.001%時，因精煉成本大幅地增加，故實質之下限係0.001~0.002%。 Sn is an element that is inevitably mixed from a steel material. Therefore, the Sn is as small as possible. The S content may be 0, but when it is reduced to less than 0.001%, since the refining cost is greatly increased, the substantial lower limit is 0.001 to 0.002%.

另一方面，大於0.05%時，因肥粒鐵脆化，素材成形性下降，故將Sn設為0.05%以下。以0.04%以下為佳。 On the other hand, when it is more than 0.05%, since the ferrite is embrittled and the material formability is lowered, Sn is made 0.05% or less. It is preferably 0.04% or less.

[Sb：0.05%以下] [Sb: 0.05% or less]

Sb與Sn相同，係自鋼原料不可避免地混入後，於晶界偏析，減少肥粒鐵晶界之碳化物個數的元素。因此，Sb以越少越佳。Sb含量亦可為0，減少至小於0.001%時，因精煉成本大幅地增加，故實質之下限係0.001~0.002%。 Sb is the same as Sn, and is an element which segregates at the grain boundary after the steel raw material is inevitably mixed, and reduces the number of carbides in the ferrite grain boundary. Therefore, the Sb is as small as possible. The Sb content may be 0. When the amount is reduced to less than 0.001%, since the refining cost is greatly increased, the lower limit of the substance is 0.001 to 0.002%.

另一方面，大於0.050%時，因Sb於肥粒鐵晶界偏析，肥粒鐵晶界之碳化物個數減少，素材成形性下降，故將Sb設為0.050%以下。以0.04%以下為佳。 On the other hand, when it is more than 0.050%, Sb is segregated at the ferrite grain boundary, and the number of carbides in the ferrite grain boundary is reduced, and the material formability is lowered. Therefore, Sb is set to 0.050% or less. It is preferably 0.04% or less.

[As：0.05%以下] [As: 0.05% or less]

As與Sn、Sb相同，係自鋼原料不可避免地混入，並於肥粒鐵晶界偏析之元素。因此，As以越少越佳。As含量亦可為0，但減少至小於0.001%時，因精煉成本大幅地增加，故實質之下限係0.001~0.002%。 As is the same as Sn and Sb, and is an element that is inevitably mixed from the steel material and segregated at the ferrite grain boundary. Therefore, As is as small as possible. The As content may be 0, but when it is reduced to less than 0.001%, since the refining cost is greatly increased, the lower limit of the essence is 0.001 to 0.002%.

另一方面，大於0.05%時，因As於肥粒鐵晶界偏析，肥粒鐵晶界之碳化物個數減少，素材成形性下降，故將As設為0.050%以下。以0.04%以下為佳。 On the other hand, when it is more than 0.05%, As is segregated at the grain boundary of the ferrite grain, the number of carbides in the grain boundary of the ferrite grain is reduced, and the formability of the material is lowered, so As is set to 0.050% or less. It is preferably 0.04% or less.

本發明鋼板以前述元素作為基本元素，更以提升鋼板之冷鍛性為目的，亦可含有以下元素。以下元素因非用以得到本發明效果所必需，故含量亦可為0。 The steel sheet of the present invention has the above-mentioned elements as a basic element, and is intended to enhance the cold forgeability of the steel sheet, and may also contain the following elements. The following elements are not It is necessary to obtain the effects of the present invention, so the content may be zero.

[Nb：0.10%以下] [Nb: 0.10% or less]

Nb係有效控制碳化物形態之元素，又，可微細化組織有助於提升韌性之元素。為得添加效果，Nb以設為0.001%以上為佳。較佳者是0.002%以上。 The Nb system effectively controls the elements of the carbide form, and the microstructure can be refined to help improve the toughness. In order to add an effect, Nb is preferably set to 0.001% or more. Preferably, it is 0.002% or more.

另一方面，大於0.10%時，將大量地生成微細之Nb碳化物，強度過度地上升，且因肥粒鐵晶界之碳化物個數減少，素材成形性下降，故將Nb設為0.10%以下。以0.09%以下為佳。 On the other hand, when it is more than 0.10%, fine Nb carbides are formed in a large amount, the strength is excessively increased, and the number of carbides at the grain boundary of the ferrite grains is decreased, and the formability of the material is lowered. Therefore, Nb is set to 0.10%. the following. It is preferably 0.09% or less.

[V：0.10%以下] [V: 0.10% or less]

V亦與Nb相同，係有效控制碳化物形態之元素，又，可微細化組織，有助於提升韌性之元素。為得添加效果，以將V設為0.001%以上為佳。較佳者是0.004%以上。 V is also the same as Nb. It is an element that effectively controls the form of carbides. It also refines the structure and helps to improve the elements of toughness. In order to add an effect, it is preferable to set V to 0.001% or more. Preferably it is 0.004% or more.

另一方面，大於0.10%時，將大量地生成微細之V碳化物，強度過度地上升，且因肥粒鐵晶界之碳化物個數減少，素材成形性下降，故將V設為0.10%以下。以0.09%以下為佳。 On the other hand, when it is more than 0.10%, fine V carbides are formed in a large amount, the strength is excessively increased, and the number of carbides in the ferrite grain boundary is decreased, and the material formability is lowered, so V is set to 0.10%. the following. It is preferably 0.09% or less.

[Cu：0.10%以下] [Cu: 0.10% or less]

Cu係於肥粒鐵晶界偏析之元素，又，係形成微細之析出物，有助於提升強度的元素。為得到提升強度效果，以將Cu設為0.001%以上為佳。較佳者是0.008%以上。 Cu is an element that segregates at the grain boundary of the ferrite grain, and is an element that forms fine precipitates and contributes to strength. In order to obtain the effect of improving the strength, it is preferable to set Cu to 0.001% or more. Preferably, it is 0.008% or more.

另一方面，大於0.10%時對肥粒鐵晶界之偏析將導致赤熱脆性，因熱軋延之生產性下降，故將Cu設為0.10%以下。以0.09%以下為佳。 On the other hand, when it is more than 0.10%, the segregation of the ferrite grain boundary causes red hot brittleness, and the productivity of the hot rolling is lowered, so Cu is made 0.10% or less. It is preferably 0.09% or less.

[W：0.10%以下] [W: 0.10% or less]

W亦與Nb、V相同，係有效控制碳化物形態之元素。為得到添加效果，以將W設為0.001%以上為佳。較佳者是0.003%以上。 W is also the same as Nb and V, and is an element that effectively controls the morphology of carbides. In order to obtain an effect of addition, it is preferable to set W to 0.001% or more. Preferably, it is 0.003% or more.

另一方面，大於0.10%時，將大量地生成微細枝W碳化物，強度過度地上升強度過度地上升，且因肥粒鐵晶界之碳化物個數減少，素材成形性下降，故將W設為0.10%以下。以0.08%以下為佳。 On the other hand, when it is more than 0.10%, fine-grained W carbides are formed in a large amount, and the strength is excessively increased, the strength is excessively increased, and the number of carbides at the grain boundary of the ferrite grains is decreased, and the formability of the material is lowered, so W Set to 0.10% or less. It is preferably 0.08% or less.

[Ta：0.001~0.10%] [Ta: 0.001~0.10%]

Ta亦與Nb、V、W相同，係有效控制碳化物形態之元素。為得到添加效果，以將Ta設為0.001%以上為佳。較佳者是0.007%以上。 Ta is also the same as Nb, V, and W, and is an element that effectively controls the morphology of carbides. In order to obtain an effect of addition, it is preferable to set Ta to 0.001% or more. Preferably, it is 0.007% or more.

另一方面，大於0.10%時將大量地生成微細之W碳化物，強度過度地上升，且因肥粒鐵晶界之碳化物個數減少，素材成形性下降，故將Ta設為0.100%以下。以0.09%以下為佳。 On the other hand, when it is more than 0.10%, fine W carbide is formed in a large amount, the strength is excessively increased, and the number of carbides in the ferrite grain boundary is reduced, and the material formability is lowered. Therefore, Ta is made 0.100% or less. . It is preferably 0.09% or less.

[Ni：0.10%以下] [Ni: 0.10% or less]

Ni係有效提升成形品之耐衝撃特性的元素。為得到添加效果，以將Ni設為0.001%以上為佳。較佳者是0.002%以上。 Ni is an element that effectively enhances the punching resistance of a molded article. In order to obtain an effect of addition, it is preferable to set Ni to 0.001% or more. Preferably, it is 0.002% or more.

另一方面，大於0.10%時因肥粒鐵晶界之碳化物個數減少，素材成形性下降，故將Ni設為0.10%以下。以0.09%以下為佳。 On the other hand, when it is more than 0.10%, the number of carbides at the grain boundary of the ferrite grains is decreased, and the formability of the material is lowered. Therefore, Ni is made 0.10% or less. It is preferably 0.09% or less.

[Mg：0.05%以下] [Mg: 0.05% or less]

Mg係添加微量即可控制硫化物形態之元素。為得到添加效果，以將Mg設為0.0001%以上為佳。較佳者是0.0008%以上。 The addition of a trace amount of Mg to control the element of the sulfide form. In order to obtain an effect of addition, it is preferable to set Mg to 0.0001% or more. Preferably, it is 0.0008% or more.

另一方面，大於0.05%時，因肥粒鐵脆化，素材成形性下降，故將Mg設為0.05%以下。以0.04%以下為佳。 On the other hand, when it is more than 0.05%, since the ferrite is embrittled and the material formability is lowered, Mg is made 0.05% or less. It is preferably 0.04% or less.

[Ca：0.05%以下] [Ca: 0.05% or less]

Ca與Mg相同，係添加微量即可控制硫化物形態之元素。為得到添加效果，以將Ca設為0.001%以上為佳。較佳者是0.003%以上。 Ca is the same as Mg, and it is an element that controls the form of sulfide by adding a trace amount. In order to obtain an effect of addition, it is preferable to set Ca to 0.001% or more. Preferably, it is 0.003% or more.

另一方面，大於0.05%時將生成粗大之Ca氧化物，冷鍛時成為裂痕之起點，即素材成形性下降，故將Ca設為0.05%以下。以0.04%以下為佳。 On the other hand, when it is more than 0.05%, coarse Ca oxide is formed, and when cold forging is used as a starting point of cracks, that is, material formability is lowered, Ca is made 0.05% or less. It is preferably 0.04% or less.

[Y：0.05%以下] [Y: 0.05% or less]

Y與Mg、Ca相同，係添加微量即可控制硫化物形態之元素。為得到添加效果，以將Y設為0.001%以上為佳。較佳者是0.003%以上。 Y is the same as Mg and Ca, and is added to a small amount to control the element of the sulfide form. In order to obtain an effect of addition, it is preferable to set Y to 0.001% or more. Preferably, it is 0.003% or more.

另一方面，大於0.05%將生成粗大之Y氧化物，冷鍛時成為裂痕之起點，即素材成形性下降，故將Y設為0.05%以下。以0.03%以下為佳。 On the other hand, when it is more than 0.05%, a coarse Y oxide is formed, and when cold forging becomes a starting point of cracks, that is, material formability is lowered, Y is made 0.05% or less. It is preferably 0.03% or less.

[Zr：0.05%以下] [Zr: 0.05% or less]

Zr與Mg、Ca、Y相同，係添加微量即可控制硫化物形態之元素。為得到添加效果，以將Zr設為0.001%以上為佳。較佳者是0.004%以上。 Zr is the same as Mg, Ca, and Y, and is added to a small amount to control the element of the sulfide form. In order to obtain an effect of addition, it is preferable to set Zr to 0.001% or more. Preferably it is 0.004% or more.

另一方面，大於0.05%時將生成粗大之Zr氧化物，冷鍛時成為裂痕之起點，即素材成形性下降，故將Zr設為0.05%以下。以0.04%以下為佳。 On the other hand, when it is more than 0.05%, coarse Zr oxide will be formed. When cold forging is the starting point of the crack, that is, the material formability is lowered, so Zr is set to 0.05% or less. It is preferably 0.04% or less.

[La：0.05%以下] [La: 0.05% or less]

La係添加微量即可控制硫化物形態之元素，又係於肥粒鐵晶界偏析，減少肥粒鐵晶界之碳化物個數的元素。為得到硫化物之形態控制效果，以將La設為0.001%以上為佳。較佳者是0.003%以上。 The La system can control the element of the sulfide form by adding a trace amount, and is also an element which segregates at the grain boundary of the ferrite grain and reduces the number of carbides in the iron grain boundary of the grain. In order to obtain the form control effect of the sulfide, it is preferable to set La to 0.001% or more. Preferably, it is 0.003% or more.

另一方面，大於0.05%時，因La會於肥粒鐵晶界偏析，肥粒鐵晶界之碳化物個數減少，素材成形性下降，故將La設為0.05%以下。以0.04%以下為佳。 On the other hand, when it is more than 0.05%, La is segregated at the ferrite grain boundary, and the number of carbides in the ferrite grain boundary is reduced, and the material formability is lowered. Therefore, La is set to 0.05% or less. It is preferably 0.04% or less.

[Ce：0.05%以下] [Ce: 0.05% or less]

Ce與La相同，係添加微量即可控制硫化物形態之元素，亦係於肥粒鐵晶界偏析，減少肥粒鐵晶界之碳化物個數的元素的元素。為得到形態控制效果，以將Ce設為0.001%以上為佳。較佳者是0.003%以上。 Ce, like La, is an element that controls the form of sulfides by adding a trace amount, and is also an element that segregates at the grain boundary of the ferrite grain and reduces the number of carbides in the grain boundary of the ferrite grain. In order to obtain a form control effect, it is preferable to set Ce to 0.001% or more. Preferably, it is 0.003% or more.

另一方面，大於0.05%時，因Ce於肥粒鐵晶界偏析，肥粒鐵晶界之碳化物個數減少，素材成形性下降，故將Ce設為050%以下。以設為0.04%以下為佳。 On the other hand, when it is more than 0.05%, since Ce is segregated at the ferrite grain boundary, the number of carbides in the ferrite grain boundary is reduced, and the material formability is lowered, so Ce is set to 050% or less. It is preferably set to 0.04% or less.

成分組成之剩餘部分係Fe及不可避免的雜質。 The remainder of the composition of the composition is Fe and unavoidable impurities.

接著，說明本發明之鋼板組織。 Next, the steel sheet structure of the present invention will be described.

本發明鋼板之組織實質上係肥粒鐵與碳化物所構成的組織。碳化物除了鐵與碳之化合物的雪明碳鐵(Fe₃C)以外，亦為經Mn、Cr等合金元素取代雪明碳鐵中之Fe原子的化合物、或合金碳化物(M₂₃C₆、M₆C、MC等[添加有M： Fe及其他合金之金屬元素])。 The structure of the steel sheet of the present invention is essentially a structure composed of ferrite iron and carbide. In addition to ferritic carbon iron (Fe ₃ C) of iron and carbon compounds, carbides are compounds that replace Fe atoms in swarf carbon iron with alloying elements such as Mn and Cr, or alloy carbides (M ₂₃ C ₆ , M ₆ C, MC, etc. [addition of metal elements of M: Fe and other alloys]).

於將鋼板成形成預定之形狀時，於鋼板之巨觀組織中形成剪切帶，於剪切帶之附近集中產生滑動變形。滑動變形隨著差排之增殖，於剪切帶之附近形成差排密度高之區域。隨著賦與鋼板之應變量增加，促進滑動變形，差排密度增加。 When the steel sheet is formed into a predetermined shape, a shear band is formed in the giant structure of the steel sheet, and sliding deformation is concentrated in the vicinity of the shear band. The sliding deformation grows in the vicinity of the shear band to form a region having a high difference in density. As the strain amount imparted to the steel sheet increases, the sliding deformation is promoted, and the difference in density is increased.

冷鍛中施行等效應變大於1之強加工。因此，以往之鋼板中未能防止隨著差排密度增加所產生之孔隙及/或裂痕，以往之鋼板中不易提升冷鍛性。為解決該課題，抑制成形時之剪切帶的形成係有效的。 In cold forging, the equivalent strain is more than 1 strong processing. Therefore, in the conventional steel sheets, it has not been possible to prevent voids and/or cracks which are generated as the difference in density is increased. In the conventional steel sheets, it is difficult to improve the cold forgeability. In order to solve this problem, it is effective to suppress the formation of a shear band at the time of molding.

由微觀組織之觀點來看，可將剪切帶之形成理解成於某一結晶粒產生之滑動超越結晶晶界連續地傳播至相鄰之結晶粒的現象。藉此，為抑制剪切帶之形成，需防止越過結晶晶界之滑動的傳播。 From the viewpoint of microstructure, the formation of the shear band can be understood as a phenomenon in which the sliding of a certain crystal grain continuously propagates beyond the crystal grain boundary to the adjacent crystal grain. Thereby, in order to suppress the formation of the shear band, it is necessary to prevent the spread of the sliding across the crystal grain boundary.

鋼板中之碳化物係防止滑動之堅固粒子，藉使碳化物存在於肥粒鐵晶界，可防止超越結晶晶界之滑動的傳播，抑制剪切帶之形成，提升冷鍛性。同時，亦提升鋼板之成形性。 The carbide in the steel sheet is a strong particle that prevents slippage, and the carbide is present at the grain boundary of the ferrite grain, thereby preventing the propagation of the slip beyond the grain boundary, suppressing the formation of the shear band, and improving the cold forgeability. At the same time, the formability of the steel sheet is also improved.

鋼板之成形性與對結晶粒內之應變的蓄積(差排之蓄積)極為相關，只要可阻止結晶晶界中相鄰結晶晶界間應變的傳輸，結晶粒內之應變量即增加。結果，增加加工硬化率，改善成形性。 The formability of the steel sheet is extremely dependent on the accumulation of strain in the crystal grains (accumulation of the difference), and the strain amount in the crystal grains is increased as long as the transmission of strain between adjacent crystal grain boundaries in the crystal grain boundary can be prevented. As a result, the work hardening rate is increased and the formability is improved.

為得如此之效果，需於金屬組織中分散有適當大小之碳化物。因此，將碳化物之平均粒徑設為0.4μm以上且 2.0μm以下。碳化物之平均粒徑小於0.4μm時，鋼板之硬度將顯著地增加，冷鍛性下降。較佳者是0.6μm以上。 In order to achieve such an effect, it is necessary to disperse an appropriately sized carbide in the metal structure. Therefore, the average particle diameter of the carbide is set to 0.4 μm or more and 2.0 μm or less. When the average particle diameter of the carbide is less than 0.4 μm, the hardness of the steel sheet is remarkably increased, and the cold forgeability is lowered. Preferably, it is 0.6 μm or more.

另一方面，碳化物之平均粒徑大於2.0μm時，於冷成形時碳化物將成為龜裂之起點。較佳者是1.95μm以下。 On the other hand, when the average particle diameter of the carbide is more than 2.0 μm, the carbide becomes a starting point of cracking during cold forming. Preferably, it is 1.95 μm or less.

又，鐵之碳化物即雪明碳鐵係硬且脆之組織，於以與肥粒鐵之層狀組織的波來鐵之狀態存在時，鋼將變硬且脆。因此，需儘量減少波來鐵，本發明之鋼板中以面積率計設為6%以下。 Further, the iron carbide, that is, the hard and brittle structure of the stellite carbon iron, is hard and brittle when it exists in the form of a ferrite with a layered structure of the ferrite iron. Therefore, it is necessary to minimize the amount of the iron, and the steel sheet of the present invention is set to have an area ratio of 6% or less.

波來鐵因具有特有之層狀組織，故可藉由SEM、光學顯微鏡觀察判別。藉由算出任意截面中之層狀組織區域，可求得波來鐵的面積率。 Because of its unique layered structure, the Borne iron can be discerned by SEM and optical microscopy. The area ratio of the Borne iron can be obtained by calculating the layered structure region in an arbitrary cross section.

依據理論及原則，可知冷鍛性強烈受到肥粒鐵晶界碳化物之被覆率影響，可求得其高精度之測量。但，3維空間中肥粒鐵晶界碳化物之被覆率的測量需於掃描型電子顯微鏡內以FIB反覆進行試樣切削與觀察的連續切片SEM觀察、或3維EBSP觀察，需要龐大的測量時間與技術知識之累積。 According to the theory and principle, it is known that the cold forgeability is strongly influenced by the coverage of carbides at the ferrite grain boundary, and the measurement of high precision can be obtained. However, the measurement of the coverage of the ferrite grain boundary carbide in the 3-dimensional space requires continuous SEM observation or 3-dimensional EBSP observation of the sample cutting and observation by FIB in a scanning electron microscope, which requires a large measurement. The accumulation of time and technical knowledge.

本發明人將前述觀察方法視為非一般之分析方法而不採用，探索更簡易且精度高之評價指標。結果發現，只要以肥粒鐵晶界的碳化物個數：B相對於肥粒鐵粒內之碳化物個數：A之比率：B/A作為指標，即可定量地評價冷鍛性及成形性；及，比率：B/A大於1時，即可顯著地提升冷鍛性、或沖壓．增厚之成形性。 The present inventors regarded the above observation method as a non-general analysis method and did not employ it, and explored an evaluation index which is simpler and more accurate. As a result, it was found that the cold forging property and the forming can be quantitatively evaluated as long as the number of carbides in the ferrite grain boundary: B is proportional to the number of carbides in the ferrite grain: A ratio: B/A as an index. And; ratio: when B/A is greater than 1, the cold forgeability or stamping can be significantly improved. Thickness formability.

因鋼板冷鍛時產生之翹曲、夾入、折入均由剪切帶之形成帶所帶來的應變之局部化所導致，藉於肥粒鐵晶界存在碳化物，緩和剪切帶之形成及應變之局部化，即可抑制翹曲、夾入、折入的產生。 The warpage, clamping, and folding caused by cold forging of the steel plate are all cut by The localization of the strain caused by the formation of the belt causes the formation of the shear band and the localization of the strain by the presence of carbides in the ferrite grain boundary, thereby suppressing warpage, pinching, and folding. produce.

碳化物之觀察係以掃描型電子顯微鏡進行。觀察之前，先利用剛砂紙之濕式研磨及藉以具1μm之平均粒子尺寸的鑽石研磨粒研磨組織觀察用之試樣，將觀察面作成鏡面後，於3%硝酸-醇溶液中蝕刻組織。將觀察倍率設為3000倍，隨機地拍攝8張板厚1/4層中30μm×40μm之視野。 The observation of the carbide was carried out by a scanning electron microscope. Before the observation, the sample for observation of the structure was polished by wet grinding using a sandpaper and diamond abrasive grains having an average particle size of 1 μm, and the observation surface was mirror-finished, and then the structure was etched in a 3% nitric acid-alcohol solution. The observation magnification was set to 3000 times, and a field of view of 30 μm × 40 μm in 1/4 layer of 8 sheet thicknesses was randomly taken.

藉由影像解析軟體(三谷商事股份有限公司製Win ROOF)，對所得之組織影像詳細地測量該解析區域中所含的碳化物面積。由碳化物之面積求得圓等效直徑(=2×√(面積/3.14))，並將其平均值作為碳化物粒徑。再者，為抑制噴頭造成的測量誤差變大，將面積0.01μm²以下之碳化物排除在評價對象之外。 The area of the carbide contained in the analysis region was measured in detail by the image analysis software (Win ROOF manufactured by Sangu Trading Co., Ltd.). A circle equivalent diameter (= 2 × √ (area / 3.14)) was obtained from the area of the carbide, and the average value thereof was defined as the carbide particle diameter. Further, in order to suppress the measurement error caused by the head, the carbide having an area of 0.01 μm ² or less is excluded from the evaluation target.

計算肥粒鐵晶界中存在之碳化物的個數，自總碳化物數減去肥粒鐵晶界上之碳化物數，算出肥粒鐵粒內的碳化物個數。依據計算與算出之碳化物個數，算出肥粒鐵晶界的碳化物個數：B相對於肥粒鐵粒內之碳化物個數：A之比率：B/A。 Calculate the number of carbides present in the grain boundary of the ferrite grain, subtract the number of carbides on the grain boundary of the ferrite grain from the total number of carbides, and calculate the number of carbides in the iron grain of the grain. Based on the calculated and calculated number of carbides, the number of carbides in the ferrite grain boundary is calculated: B is relative to the number of carbides in the ferrite grains: A ratio: B/A.

退火後之鋼板組織中，由提升冷鍛性之點來看，肥粒鐵粒徑以3μm以上且50μm以下為佳。肥粒鐵粒徑小於3μm時，硬度增加，冷鍛時變得容易產生龜裂或裂痕，故肥粒鐵粒徑以3μm以上為佳。較佳者是5μm以上。 In the steel sheet structure after annealing, from the viewpoint of improving the cold forgeability, the particle size of the ferrite iron is preferably 3 μm or more and 50 μm or less. When the particle size of the ferrite iron is less than 3 μm, the hardness increases, and cracks or cracks are likely to occur during cold forging. Therefore, the particle size of the ferrite iron is preferably 3 μm or more. Preferably, it is 5 μm or more.

肥粒鐵粒徑大於50μm時，因抑制滑動傳播之結晶晶界的碳化物個數減少，冷鍛性下降，故肥粒鐵粒徑以50μm以下為佳。較佳者是40μm以下。 When the particle size of ferrite is more than 50μm, the knot of sliding propagation is suppressed. The number of carbides in the crystal grain boundary is reduced, and the cold forgeability is lowered. Therefore, the particle size of the ferrite particles is preferably 50 μm or less. Preferably, it is 40 μm or less.

以前述順序將試料面之觀察面研磨成鏡面後，以光學顯微鏡或掃描型電子顯微鏡觀察經3%硝酸-醇溶液蝕刻之組織，並對拍攝下來之影像使用線分法即可測量肥粒鐵粒徑。 After the observation surface of the sample surface is polished into a mirror surface in the above-described order, the tissue etched by the 3% nitric acid-alcohol solution is observed by an optical microscope or a scanning electron microscope, and the image of the photographed image can be measured by the line division method. Particle size.

冷鍛時除了控制碳化物之形態，亦需冷鍛時之沖壓成形性。 In the cold forging, in addition to controlling the form of the carbide, the press formability in cold forging is also required.

為提升冷鍛時之沖壓成形性，則須改善塑性異向性。因此，需控制熱軋鋼板之集合組織。集合組織之評價係於與熱軋鋼板之1/2板厚部分的板面平行之面以X射線繞射進行。X射線繞射中使用利用Mo管球之X射線。 In order to improve the press formability during cold forging, the plastic anisotropy must be improved. Therefore, it is necessary to control the aggregate structure of the hot rolled steel sheet. The evaluation of the aggregate structure was carried out by X-ray diffraction on a plane parallel to the plate surface of the 1/2 plate thickness portion of the hot rolled steel sheet. X-rays using Mo bulbs are used in X-ray diffraction.

藉由反射得到繞射方位{110}、{220}、{211}、{310}之繞射強度，並以該等為基準作成ODF。ODF之作成係使用鐵之隨機方位的前述繞射強度數據。此處，將{211}<011>之X射線繞射強度設為I1、{100}<011>之X射線繞射強度設為I0。該I1/I0小於1係熱軋時隨機集合組織中顯現必要之再結晶之意。若能得到隨機集合組織，則可降低塑性異向性，使成形性提升。 The diffraction intensities of the diffraction directions {110}, {220}, {211}, and {310} are obtained by reflection, and ODF is created based on these. The ODF works by using the aforementioned diffraction intensity data of the random orientation of iron. Here, the X-ray diffraction intensity of the X-ray diffraction intensity of {211}<011> is I1 and {100}<011> is set to I0. This I1/I0 is smaller than the meaning of recrystallization which is necessary in the random aggregate structure at the time of hot rolling. If a random assembly structure is obtained, the plastic anisotropy can be lowered and the formability can be improved.

藉將鋼板之維克氏硬度設為100HV以上且150HV以下(C：0.10~0.40%、Mn：0.01~0.30%時)、或100HV以上且170HV以下，可改善冷鍛時之成形性。維克氏硬度小於100HV時，因容易於冷鍛時之成形中產生翹曲，成形品之形狀精度下降，故將維克氏硬度設為100HV以上。以 110HV以上為佳。 When the Vickers hardness of the steel sheet is 100 HV or more and 150 HV or less (C: 0.10 to 0.40%, Mn: 0.01 to 0.30%), or 100 HV or more and 170 HV or less, the formability at the time of cold forging can be improved. When the Vickers hardness is less than 100 HV, warpage is likely to occur during molding during cold forging, and the shape accuracy of the molded article is lowered. Therefore, the Vickers hardness is set to 100 HV or more. Take Above 110HV is preferred.

維克氏硬度大於170HV時延性下降，增厚等之壓縮變形中變得容易產生朝面外的翹曲，又，冷鍛時變得容易產生內部裂痕，導致耐衝撃特性惡化，故將維克氏硬度設為170HV以下。為確實地確保延性與耐衝撃特性，維克氏硬度以設為150HV以下為佳。較佳者是140HV以下。 When the Vickers hardness is greater than 170 HV, the ductility is lowered, and in the compression deformation such as thickening, warpage to the outside is likely to occur, and in the cold forging, internal cracks are likely to occur, and the punching resistance is deteriorated, so that Vickers is deteriorated. The hardness is set to 170 HV or less. In order to reliably ensure ductility and impact resistance, the Vickers hardness is preferably set to 150 HV or less. Preferably, it is 140 HV or less.

接著，說明本發明鋼板之製造方法。 Next, a method of producing the steel sheet of the present invention will be described.

本發明製造方法之基本思想係使用前述成分組成之鋼片，一貫地管理熱軋條件與退火條件地進行鋼板組織的控制。 The basic idea of the manufacturing method of the present invention is to control the steel sheet structure by continuously managing the hot rolling conditions and the annealing conditions using the steel sheets having the above-described composition.

首先，連續鑄造具所需成分組成之熔鋼作成鋼片，並將該鋼片用於熱軋延。連續鑄造後之鑄片可直接用於熱軋延、或暫時冷卻後加熱，再用於熱軋延。 First, a molten steel having a desired composition is continuously cast into a steel sheet, and the steel sheet is used for hot rolling. The cast piece after continuous casting can be directly used for hot rolling, or temporarily cooled, and then used for hot rolling.

於將鋼片暫時冷卻後加熱，再用於熱軋延時，加熱溫度以1000℃以上且1250℃以下為佳，加熱時間以0.5小時以上且3小時以下為佳。於將連續鑄造後之鋼片直接用於熱軋延時，用於熱軋延之鋼片的溫度以設為1000℃以上且1250℃為佳。 After the steel sheet is temporarily cooled and heated, it is used for the hot rolling delay, and the heating temperature is preferably 1000 ° C or more and 1250 ° C or less, and the heating time is preferably 0.5 hours or more and 3 hours or less. The steel sheet after continuous casting is directly used for the hot rolling delay, and the temperature of the steel sheet for hot rolling is preferably set to 1000 ° C or more and 1250 ° C.

鋼片溫度或鋼片加熱溫度大於1250℃、或鋼片加熱時間大於3小時時，自鋼片表層之脫碳變得顯著，浸碳淬火前之加熱時鋼板表層之沃斯田鐵粒異常地成長，耐衝撃性下降。因此，鋼片溫度或鋼片加熱溫度以1250℃以下為佳，加熱時間以3小時以下為佳。較佳者是1200℃以下、2.5小時以下。 When the steel sheet temperature or the heating temperature of the steel sheet is greater than 1250 ° C, or the heating time of the steel sheet is more than 3 hours, the decarburization from the surface layer of the steel sheet becomes remarkable, and the Worthite iron particles on the surface of the steel sheet are abnormally heated when the carbon is quenched and quenched. Growth and resistance to decline. Therefore, the steel sheet temperature or the sheet heating temperature is preferably 1250 ° C or less, and the heating time is preferably 3 hours or less. Preferably, it is 1200 ° C or less and 2.5 hours or less.

鋼片溫度或鋼片加熱溫度小於1000℃時、或加熱時間小於0.5小時時，未能消除鑄造中生成之微觀偏析或巨觀或巨觀偏析，鋼片內部殘留局部地濃化有Si或Mn等合金元素的區域，耐衝撃性下降。因此，鋼片溫度或鋼片加熱溫度以1000℃以上為佳，加熱時間以0.5小時以上為佳。較佳者是1050℃以上、1小時以上。 When the temperature of the steel sheet or the heating temperature of the steel sheet is less than 1000 ° C, or the heating time is less than 0.5 hours, the microsegregation or macroscopic or giant segregation generated in the casting cannot be eliminated, and the inside of the steel sheet is partially concentrated with Si or Mn. In areas where alloying elements are present, the resistance to bluntness is reduced. Therefore, the steel sheet temperature or the sheet heating temperature is preferably 1000 ° C or more, and the heating time is preferably 0.5 hours or more. Preferably, it is 1050 ° C or more and 1 hour or more.

熱軋延之最終軋延係於820℃以上、較佳為以900℃以上且950℃以下之溫度域中結束。最終軋延溫度小於820℃時，鋼板之變形阻力增加，軋延負載顯著地上升，又，軋滾磨耗量增加，生產性下降，且未充分地進行用以改善塑性異向性所需之再結晶化，故將最終軋延溫度設為820℃以上。由促進再結晶之點來看，以900℃以上為佳。 The final rolling of the hot rolling is terminated at a temperature of 820 ° C or higher, preferably 900 ° C or higher and 950 ° C or lower. When the final rolling temperature is less than 820 ° C, the deformation resistance of the steel sheet increases, the rolling load increases remarkably, and the rolling wear increases, the productivity decreases, and the necessary improvement for plastic anisotropy is not sufficiently performed. Since the crystallization is carried out, the final rolling temperature is set to 820 ° C or higher. From the viewpoint of promoting recrystallization, it is preferably 900 ° C or more.

最終軋延溫度大於950℃時，通過ROT(Run Out Table：輸送台)時將生成厚之鏽皮，因該鏽皮於鋼板表面產生瑕疵，於冷鍛及浸碳淬火回火後施加衝撃載重時，將容易以瑕疵為起點產生龜裂，故鋼板之耐衝撃性下降。因此，將最終熱軋溫度設為950℃以下。以920℃以下為佳。 When the final rolling temperature is greater than 950 ° C, thick rust will be formed when passing the ROT (Run Out Table), because the rust will produce bismuth on the surface of the steel sheet, and the burrow load will be applied after cold forging and carbon tempering and tempering. At the time, it is easy to generate cracks from the starting point of the crucible, so the resistance of the steel sheet is lowered. Therefore, the final hot rolling temperature is set to 950 ° C or lower. It is preferably 920 ° C or less.

於ROT上冷卻最終軋延後之熱軋鋼板時，冷卻速度以10℃/秒以上且100℃/秒以下為佳。冷卻速度小於10℃/秒時，將於冷卻途中生成厚之鏽皮，未能抑制因該鏽皮產生之瑕疵，耐衝撃性下降，故冷卻速度以10℃/秒以上為佳。較佳者是15℃/秒以上。 When the hot rolled steel sheet after the final rolling is cooled on the ROT, the cooling rate is preferably 10 ° C / sec or more and 100 ° C / sec or less. When the cooling rate is less than 10 ° C / sec, thick scale is formed during cooling, and the rust due to the scale is not suppressed, and the blister resistance is lowered. Therefore, the cooling rate is preferably 10 ° C /sec or more. Preferably it is 15 ° C / sec or more.

於鋼板表層至內部以大於100℃/秒之冷卻速度冷卻時，最表層部將過剩地冷卻，產生變韌鐵或麻田散鐵等低溫變態組織。捲取後於取出冷卻至100℃~室溫之熱軋鋼板線圈時，於低溫變態組織產生微小裂痕。該微小裂痕不易於酸洗及冷軋中去除。 When the surface of the steel sheet is cooled to a temperature of more than 100 ° C / sec, the outermost layer will be excessively cooled to produce toughened iron or granulated iron. Such as low temperature metamorphic tissue. After the coiling, the hot-rolled steel sheet coil cooled to 100 ° C to room temperature was taken out, and micro cracks were generated in the low temperature metamorphic structure. The microcracks are not easily removed by pickling and cold rolling.

此外，於冷鍛及浸碳淬火回火後施加衝撃載重時，因以微小裂痕為起點之龜裂加劇，故耐衝撃性下降。因此，為抑制鋼板之最表層部產生變韌鐵或麻田散鐵等低溫變態組織，冷卻速度以100℃/秒以下為佳。較佳者是90℃/秒以下。 In addition, when the punching load is applied after cold forging and carbon immersion quenching, the crack resistance is increased due to the micro crack, and the punching resistance is lowered. Therefore, in order to suppress the formation of a low-temperature metamorphic structure such as toughened iron or granulated iron in the outermost layer of the steel sheet, the cooling rate is preferably 100 ° C / sec or less. Preferably, it is 90 ° C / sec or less.

再者，前述冷卻速度係指於最終軋延後之熱軋鋼板通過無注水區間後，自於注水區間接受水冷卻時至捲取之目標溫度於ROT上冷卻時，自各注水區間之冷卻設備接受的冷卻能，並非指自開始注水點至藉由捲取機捲取之溫度的平均冷卻速度。 In addition, the cooling rate refers to the cooling equipment received from each water injection section after the hot rolling steel sheet after the final rolling passes through the water injection section, when the water is cooled from the water injection section until the target temperature of the coil is cooled on the ROT. The cooling energy does not refer to the average cooling rate from the start of the water injection point to the temperature taken up by the coiler.

將捲取溫度設為400℃以上且550℃以下。此係較一般之捲取溫度低的溫度，特別是C含量高時通常不會進行之條件。藉於該溫度範圍捲取以上述條件製造之熱軋鋼板，可將鋼板組織作為於微細之肥粒鐵中分散有碳化物的變韌鐵組織。 The coiling temperature is set to 400 ° C or more and 550 ° C or less. This is a temperature which is lower than the usual coiling temperature, especially when the C content is high. By winding the hot-rolled steel sheet produced under the above conditions in this temperature range, the steel sheet structure can be used as a toughened iron structure in which carbides are dispersed in the fine ferrite iron.

捲取溫度小於400℃時，捲取前係未變態之沃斯田鐵將變態成硬之麻田散鐵，於取出熱軋鋼板線圈時因熱軋鋼板之表層產生裂痕，耐衝撃性下降。 When the coiling temperature is less than 400 ° C, the Worthite iron which is not metamorphosed before the coiling will be transformed into a hard ramie loose iron. When the coil of the hot rolled steel sheet is taken out, cracks are formed on the surface layer of the hot rolled steel sheet, and the punching resistance is lowered.

此外，自沃斯田鐵再結晶成肥粒鐵時，因再結晶驅動力小，故再結晶肥粒鐵粒之方位強烈受到沃斯田鐵粒方位的影響，集合組織不易隨機化。因此，將捲取溫度設為400℃以上。以430℃以上為佳。 In addition, when the ferrite iron is recrystallized into ferrite iron, the orientation of the recrystallized iron particles is strongly influenced by the orientation of the iron particles in the Vostian, and the aggregate structure is not easily randomized. Therefore, the coiling temperature is set It is above 400 °C. It is preferably 430 ° C or higher.

捲取溫度大於550℃時，將生成層狀間隔大之波來鐵，形成熱穩定性高之厚的針狀碳化物。該針狀碳化物於2階段退火後仍殘留。鋼板之冷鍛等成形時，將以該針狀碳化物為起點生成龜裂。 When the coiling temperature is more than 550 ° C, iron having a large interlayer interval is formed to form thick needle-shaped carbide having high thermal stability. The acicular carbide remains after the 2-stage annealing. When forming a cold forging or the like of a steel sheet, cracks are generated starting from the acicular carbide.

又，自沃斯田鐵之肥粒鐵的再結晶時，反之，再結晶驅動力變得過大，此時，亦成為強力依存於沃斯田鐵粒方位之再結晶肥粒鐵粒，集合組織未隨機化。因此，將捲取溫度設為550℃以下。以520℃以下為佳。 In addition, the recrystallization of the ferrite iron from the Worthite iron, on the other hand, the recrystallization driving force becomes too large, and at this time, it becomes a recrystallized ferrite iron particle strongly depending on the orientation of the Worthite iron grain, and the assembly organization Not randomized. Therefore, the coiling temperature is set to 550 ° C or lower. It is preferably 520 ° C or less.

取出熱軋鋼板線圈並施行酸洗後，施行於2個溫度域中保持的2階段型退火(2階段退火)。藉於熱軋鋼板施行2階段退火，可控制碳化物之穩定性，促進肥粒鐵晶界中碳化物的生成。 After taking out the coil of the hot-rolled steel sheet and performing pickling, a two-stage type annealing (two-stage annealing) maintained in two temperature domains was performed. By performing two-stage annealing on the hot-rolled steel sheet, the stability of the carbide can be controlled, and the formation of carbides in the ferrite grain boundary is promoted.

退火處理前對酸洗後之鋼板施行冷軋延時，因肥粒鐵粒微細化，故鋼板不易變得軟質化。因此，本發明中，以於退火前施行冷軋延為不佳，以酸洗後未進行冷軋延而施行退火處理為佳。 Before the annealing treatment, the steel sheet after pickling is subjected to cold rolling delay, and the steel sheet is not easily softened due to the fine grain of the ferrite particles. Therefore, in the present invention, it is preferred to perform cold rolling before annealing, and it is preferred to carry out annealing after pickling without cold rolling.

第1階段之退火係於650~720℃、且以於Ac1點以下之溫度域中進行為佳。藉由該退火，使碳化物粗大化，且使部分球化的同時，可使合金元素於碳化物中濃化，提高碳化物之熱穩定性。 The first-stage annealing is performed at 650 to 720 ° C and preferably in the temperature range of Ac1 or lower. By this annealing, the carbide is coarsened and the partial spheroidization is performed, and the alloying element can be concentrated in the carbide to improve the thermal stability of the carbide.

第1階段之退火中，至退火溫度之加熱速度(以下稱作「第1階段加熱速度」)設為30℃/小時以上且150℃/小時以下。第1階段加熱速度小於30℃/小時時，因升溫需要時間，生產性下降，故將第1階段加熱速度設為3℃/小時以上。以10℃/小時以上為佳。 In the first-stage annealing, the heating rate to the annealing temperature (hereinafter referred to as "first-stage heating rate") is 30 ° C / hour or more and 150 ° C / hour or less. When the heating speed of the first stage is less than 30 ° C / hour, it is required for temperature rise. Since the productivity is lowered in time, the heating rate in the first stage is set to 3 ° C / hour or more. It is preferably 10 ° C / hour or more.

另一方面，第1階段加熱速度大於150℃/小時時，熱軋鋼板線圈中外周部與內部之溫度差增加，因熱膨脹差產生摩擦或燒附，於鋼板表面形成凹凸。冷鍛等成形時，產生以該凹凸為起點的龜裂，導致冷鍛性下降、成形性及浸碳淬火回火後之耐衝撃性下降，故將第1階段加熱速度設為150℃/小時以下。以130℃/小時以下為佳。 On the other hand, when the first-stage heating rate is more than 150 ° C / hour, the temperature difference between the outer peripheral portion and the inner portion of the coil of the hot-rolled steel sheet increases, and friction or burn-off occurs due to the difference in thermal expansion, and irregularities are formed on the surface of the steel sheet. In the case of cold forging or the like, cracks originating from the unevenness are generated, and the cold forgeability is lowered, and the moldability and the punching resistance after the carbon-impregnated quenching are lowered. Therefore, the first-stage heating rate is set to 150 ° C / hour. the following. It is preferably 130 ° C / hour or less.

將第1階段退火的退火溫度(以下稱作「第1階段退火溫度」)設為650℃以上且720℃以下。第1階段退火溫度小於650℃時，碳化物之穩定化並不充分，第2階段退火時將不易於沃斯田鐵中殘留碳化物。因此，將第1階段退火溫度設為650℃以上。以670℃以上為佳。 The annealing temperature of the first-stage annealing (hereinafter referred to as "first-stage annealing temperature") is 650 ° C or more and 720 ° C or less. When the first-stage annealing temperature is less than 650 ° C, the stabilization of the carbide is not sufficient, and in the second-stage annealing, the carbide remains in the Worthite iron. Therefore, the first-stage annealing temperature is set to 650 ° C or higher. It is preferably 670 ° C or higher.

另一方面，第1階段退火溫度大於720℃時，於碳化物之穩定度上升前生成沃斯田鐵，而未能控制前述之組織變化，故將第1階段退火溫度設為720℃以下。以700℃以下為佳。 On the other hand, when the first-stage annealing temperature is more than 720 ° C, the Worthite iron is formed before the stability of the carbide is increased, and the above-described structural change is not controlled. Therefore, the first-stage annealing temperature is 720 ° C or lower. It is preferably 700 ° C or less.

將第1階段退火的退火時間(以下稱作「第1階段之保持時間」)設為3小時以上且60小時以下。第1階段退火時間小於3小時時，碳化物之穩定化並不充分，第2階段退火時將不易於沃斯田鐵中殘留碳化物。因此，將第1階段退火時間設為3小時以上。以5小時以上為佳。 The annealing time of the first-stage annealing (hereinafter referred to as "the holding time of the first stage") is set to 3 hours or more and 60 hours or less. When the first-stage annealing time is less than 3 hours, the stabilization of the carbide is not sufficient, and in the second-stage annealing, the carbide remains in the Worthite iron. Therefore, the first-stage annealing time is set to 3 hours or longer. More than 5 hours is preferred.

另一方面，第1階段退火時間大於60小時時，未能更加提升碳化物之穩定化，此外將導致生產性下降，故將第1階段退火時間設為60小時以下。以55小時以下為佳。 On the other hand, when the first-stage annealing time is longer than 60 hours, the stabilization of the carbide is not further improved, and the productivity is lowered, so that productivity is lowered. The first annealing time was set to 60 hours or less. It is preferably 55 hours or less.

之後，升溫至725~790℃、較佳為升溫至Ac1點以上且A3點以下之溫度域，使組織中生成沃斯田鐵。此時，微細之肥粒鐵粒內的碳化物將於沃斯田鐵中熔解，但經第1階段退火粗大化之碳化物將殘留於沃斯田鐵中。 Thereafter, the temperature is raised to 725 to 790 ° C, preferably to a temperature range of Ac1 or more and A3 or less, to form Worthite iron in the structure. At this time, the carbides in the fine ferrite grains will be melted in the Worthite iron, but the carbides which have been coarsened by the first stage annealing will remain in the Vostian iron.

未進行該第2階段退火而冷卻時，肥粒鐵粒徑並未變大，未能得到理想之組織。 When the second-stage annealing was not performed and the cooling was performed, the particle size of the ferrite iron did not become large, and an ideal structure could not be obtained.

至第2階段退火之退火溫度的加熱速度(以下稱作「第2階段加熱速度」)設為1℃/小時以上且80℃/小時以下。第2階段退火時，將自肥粒鐵晶界生成沃斯田鐵並成長。此時，藉由減緩至退火溫度之加熱速度，將抑制沃斯田鐵之核生成，於退火後之緩冷卻所形成的組織中，可提高碳化物之晶界被覆率。 The heating rate of the annealing temperature to the second-stage annealing (hereinafter referred to as "second-stage heating rate") is set to 1 ° C / hour or more and 80 ° C / hour or less. In the second-stage annealing, the Worthite iron is formed from the ferrite grain boundary and grows. At this time, by slowing down the heating rate to the annealing temperature, the formation of the nucleus of the Worthite iron is suppressed, and the grain boundary coverage of the carbide can be improved in the structure formed by the slow cooling after the annealing.

因此，第2階段加熱速度以慢為佳，但小於1℃/小時時，因升溫需要時間，生產性下降，故將第2階段加熱速度設為1℃/小時以上。以10℃/小時以上為佳。 Therefore, the second-stage heating rate is preferably slow, but when it is less than 1 ° C / hour, the time required for the temperature rise is lowered, and the productivity is lowered. Therefore, the second-stage heating rate is set to 1 ° C / hour or more. It is preferably 10 ° C / hour or more.

第2階段加熱速度大於80℃/小時時，熱軋鋼板線圈中外周部與內部之溫度差增加，因變態導致大之熱膨脹差而產生摩擦瑕疵或燒附，於鋼板表面形成凹凸。冷鍛時，產生以該凹凸為起點的龜裂，導致冷鍛性與成形性下降，又，浸碳淬火回火後之耐衝撃性亦下降，故將第2階段加熱速度設為80℃/小時以下。以70℃/小時以下為佳。 When the second-stage heating rate is more than 80 ° C / hour, the temperature difference between the outer peripheral portion and the inner portion of the coil of the hot-rolled steel sheet increases, and a large thermal expansion difference causes a frictional entanglement or burning, and irregularities are formed on the surface of the steel sheet. In cold forging, cracks originating from the unevenness are generated, resulting in a decrease in cold forgeability and formability, and also a decrease in the impact resistance after carbon-baking quenching and tempering. Therefore, the second-stage heating rate is set to 80 ° C / Less than an hour. It is preferably 70 ° C / hour or less.

將第2階段退火的退火溫度(以下稱作「第2階段退火溫度」)設為725℃以上且790℃以下。第2階段退火溫度小於725℃時，沃斯田鐵之生成量變少，第2階段退火後的冷卻後，肥粒鐵晶界之碳化物個數減少，又，肥粒鐵粒徑變小。因此，將第2階段退火溫度設為725℃以上。以735℃以上為佳。 The annealing temperature of the second-stage annealing (hereinafter referred to as "second-stage annealing temperature") is 725 ° C or more and 790 ° C or less. Phase 2 annealing temperature When the degree is less than 725 ° C, the amount of formation of Worthite iron is small, and after cooling in the second stage of annealing, the number of carbides in the ferrite grain boundary is reduced, and the particle size of the ferrite grain is reduced. Therefore, the second-stage annealing temperature is set to 725 ° C or higher. It is preferably 735 ° C or higher.

另一方面，第2階段退火溫度大於790℃時，不易於沃斯田鐵中殘留碳化物，不易控制前述之組織變化，故將第2階段退火溫度設為790℃以下。以770℃以下為佳。 On the other hand, when the second-stage annealing temperature is more than 790 ° C, it is not easy to retain carbides in the Worthite iron, and it is difficult to control the above-described structural change. Therefore, the second-stage annealing temperature is set to 790 ° C or lower. It is preferably 770 ° C or less.

將第2階段退火的退火時間(第2階段退火時間)設為3小時以上且小於10小時。第2階段退火時間小於3小時時，沃斯田鐵量的生成量少，且未充分地進行肥粒鐵粒內之碳化物的熔解，不易增加肥粒鐵晶界之碳化物的個數，又，肥粒鐵粒徑變小。因此，將第2階段退火時間設為3小時以上。以5小時以上為佳。 The annealing time (second-stage annealing time) of the second-stage annealing is set to 3 hours or more and less than 10 hours. When the second-stage annealing time is less than 3 hours, the amount of iron content in the Vostian is small, and the carbides in the ferrite grains are not sufficiently melted, and it is difficult to increase the number of carbides in the ferrite grain boundary. The particle size of the ferrite is reduced. Therefore, the second-stage annealing time is set to 3 hours or longer. More than 5 hours is preferred.

另一方面，第2階段退火時間大於10小時時，不易於沃斯田鐵中殘留碳化物，又，製造成本亦增加，故將第2階段退火時間設為小於10小時。以8小時以下為佳。 On the other hand, when the second-stage annealing time is more than 10 hours, the carbide remains in the Worthite iron, and the manufacturing cost also increases. Therefore, the second-stage annealing time is set to be less than 10 hours. It is preferably 8 hours or less.

2段退火後，將鋼板以1℃/小時以上且100℃/小時以下之冷卻速度冷卻至650℃。 After the second-stage annealing, the steel sheet was cooled to 650 ° C at a cooling rate of 1 ° C / hour or more and 100 ° C / hour or less.

藉由緩冷卻，緩冷卻第2階段退火中生成之沃斯田鐵，藉此變態成肥粒鐵，且碳原子吸著於沃斯田鐵中殘留之碳化物，碳化物與沃斯田鐵覆蓋肥粒鐵晶界，最終可成為於肥粒鐵晶界大量存在碳化物的組織。 By slow cooling, the Worthite iron formed in the second-stage annealing is slowly cooled, thereby metamorphosing into ferrite iron, and the carbon atoms adsorb the residual carbides in the Worthite iron, and the carbide and the Worthite iron cover fertilizer The granular iron grain boundary can eventually become a structure in which a large amount of carbide exists in the ferrite grain boundary.

為此，冷卻速度以慢為佳，但小於1℃/小時時，因冷卻所需之時間增加，生產性下降，故將冷卻速度設為1℃/ 小時以上。以10℃/小時以上為佳。 For this reason, the cooling rate is preferably slow, but when it is less than 1 ° C / hour, the time required for cooling increases, and the productivity is lowered, so the cooling rate is set to 1 ° C / More than an hour. It is preferably 10 ° C / hour or more.

另一方面，冷卻速度大於100℃/小時時，沃斯田鐵將變態成波來鐵，鋼板之硬度增加，冷鍛性下降，又，因浸碳淬火回火後之耐衝撃性下降，故將冷卻速度設為100℃/小時以下。以80℃/小時以下為佳。 On the other hand, when the cooling rate is greater than 100 ° C / hour, the Worthite iron will be transformed into a wave of iron, the hardness of the steel plate increases, the cold forgeability decreases, and the resistance to impregnation due to carbon tempering and tempering decreases. The cooling rate was set to 100 ° C / hour or less. It is preferably 80 ° C / hour or less.

此外，將冷卻至650℃之鋼板冷卻至室溫。並未限定此時之冷卻速度。 Further, the steel sheet cooled to 650 ° C was cooled to room temperature. The cooling rate at this time is not limited.

並未特別限定2階段退火之氣體環境為特定之氣體環境。可為例如95%以上氮氣環境、95%以上氫氣環境或大氣氣體環境之任一種氣體環境。 The gas environment of the two-stage annealing is not particularly limited to a specific gas environment. It may be, for example, any of a gaseous environment of 95% or more of a nitrogen atmosphere, 95% or more of a hydrogen atmosphere, or an atmospheric gas atmosphere.

如以上說明，只要依據一貫地管理本發明之熱軋條件與退火條件，進行鋼板之組織控制的製造方法，即可製造組合有沖壓、增厚成形之冷鍛時的成形性優異，且提升浸碳淬火回火後之耐衝撃性所需之淬火性的鋼板。 As described above, the production method for controlling the structure of the steel sheet can be performed by continuously controlling the hot rolling conditions and the annealing conditions of the present invention, and the moldability in the cold forging combined with the press forming and the thick forming can be improved, and the immersion is improved. A hardened steel plate required for the impact resistance after carbon quenching and tempering.

實施例 Example

接著，說明本發明之實施例，但實施例中之條件係用以確認本發明之可實施性及效果所使用的條件之一例，本發明並未受該一條件例所限定。只要不脫離本發明之要旨，可達成本發明目的的話，即可使用各種條件來達成本發明。 Next, the examples of the present invention will be described, but the conditions in the examples are examples for confirming the conditions of use and effects of the present invention, and the present invention is not limited by the conditions. The present invention can be achieved using various conditions without departing from the gist of the present invention.

(實施例1) (Example 1)

以1240℃加熱表1及表2(接續表1)所示之成分組成的連續鑄造鑄片(鋼片)1.8小時加熱後進行熱軋延，於920℃之最終熱軋後，於ROT上以45℃/秒之冷卻速度冷卻至530℃，再以520℃捲取，製造板厚5.2mm的熱軋鋼板線圈。 The continuous casting slab (steel sheet) composed of the components shown in Table 1 and Table 2 (continued in Table 1) was heated at 1240 ° C for 1.8 hours, and then hot rolled, after final hot rolling at 920 ° C, on ROT. Cool down to 530 ° C at 45 ° C / sec, then The coil of hot-rolled steel sheet having a thickness of 5.2 mm was produced by winding at 520 °C.

取出熱軋鋼板線圈，施行酸洗後，裝入箱型退火爐，將退火氣體環境控制在95%氫-5%氮後，以100℃/小時之加熱速度自室溫加熱至705℃，並於710℃中保持24小時，均一化熱軋鋼板線圈內之溫度分布。 The hot-rolled steel coil is taken out, pickled, and then placed in a box-type annealing furnace, and the annealing gas atmosphere is controlled to 95% hydrogen-5% nitrogen, and then heated from room temperature to 705 ° C at a heating rate of 100 ° C / hour. The temperature distribution in the coil of the hot rolled steel sheet was uniformed by maintaining at 710 ° C for 24 hours.

接著，以5℃/小時之加熱速度加熱至740℃，再於740℃保持5小時後，以10℃/小時之冷卻速度冷卻至650℃，之後，爐內冷卻至室溫，製作評價特性用之試料。以前述方法觀察試料組織，並測量肥粒鐵粒徑、及碳化物之個數。 Then, it was heated to 740 ° C at a heating rate of 5 ° C / hour, and further maintained at 740 ° C for 5 hours, and then cooled to 650 ° C at a cooling rate of 10 ° C / hour, and then cooled to room temperature in the furnace to prepare evaluation characteristics. Samples. The sample structure was observed by the aforementioned method, and the particle size of the ferrite grain and the number of carbides were measured.

於表3顯示表1及表2所示之鋼板的肥粒鐵粒徑(μm)、平均碳化物粒徑(μm)、波來鐵面積率(%)、維克氏硬度(HV)、晶界碳化物數/粒內碳化物數、X射線強度比：I1/I0、r值之異向性指數|△r|、臨界冷卻速度(℃/秒)。若I1/I0為1以上，則未能充分地進行熱軋延之再結晶化，鋼板之塑性異向性變大。再者，r值之異向性指數|△r|係於沖壓試驗中求出。 Table 3 shows the ferrite iron particle size (μm), average carbide particle size (μm), wave iron area ratio (%), Vickers hardness (HV), and crystal grains of the steel sheets shown in Tables 1 and 2. Boundary carbide number / intragranular carbide number, X-ray intensity ratio: I1/I0, anisotropy index of r value | Δr|, critical cooling rate (°C / sec). When I1/I0 is 1 or more, recrystallization of the hot rolling is not sufficiently performed, and the plastic anisotropy of the steel sheet becomes large. Furthermore, the anisotropy index of r value |Δr| was determined in a press test.

一般而言，由與板面平行且3方向之r值所得的異向性指數|△r|大於0.2時，沖壓成形性下降。因此，為確保優異之成形性，要求|△r|小於2。 In general, when the anisotropy index |Δr| obtained by the r value parallel to the plate surface and the three directions is larger than 0.2, the press formability is lowered. Therefore, in order to ensure excellent formability, |Δr| is required to be less than 2.

藉由作成CCT線圖求出臨界冷卻速度。若以較求出之臨界冷卻速度慢的冷卻速度冷卻熱軋鋼板時，成形成零件後之淬火時的淬火性變差，形成波來鐵組織，未能得到充分之強度。因此，降低臨界冷卻速度係用以得到高淬火強度所必需。只要臨界冷卻速度為280℃/秒即可判斷淬火性提升。 The critical cooling rate was determined by creating a CCT line graph. If you want When the hot-rolled steel sheet is cooled at a cooling rate at which the critical cooling rate is slow, the hardenability at the time of quenching after forming the part is deteriorated, and a ferrite structure is formed, and sufficient strength is not obtained. Therefore, lowering the critical cooling rate is necessary to obtain high quenching strength. As long as the critical cooling rate is 280 ° C / sec, the improvement in hardenability can be judged.

表3所示之發明例中，因平均碳化物粒徑為0.4~2.0μm、波來鐵面積率為6%以下、晶界碳化物數/粒內碳化物數大於1、I1/I0小於1，故維克氏硬度於100HV以上且170HV以下之範圍內，|△r|小於0.2。使用有比較鋼板之比較例中，維克氏硬度大於150，晶界碳化物數/粒內碳化物數小於1。未添加B之比較鋼板(表1及2中，No.15)中，臨界冷卻速度大於280℃/秒，淬火性下降。 In the invention examples shown in Table 3, the average carbide particle diameter is 0.4 to 2.0 μm, the bronze iron area ratio is 6% or less, the grain boundary carbide number/the intragranular carbide number is greater than 1, and I1/I0 is less than 1. Therefore, the Vickers hardness is in the range of 100 HV or more and 170 HV or less, and |Δr| is less than 0.2. In the comparative example using the comparative steel sheet, the Vickers hardness was more than 150, and the number of grain boundary carbides/number of intragranular carbides was less than 1. In the comparative steel sheet to which B was not added (No. 15 in Tables 1 and 2), the critical cooling rate was more than 280 ° C / sec, and the hardenability was lowered.

(實施例2) (Example 2)

對發明鋼板之No.1~5、No.16~19、No.31、No.33、及No.35等12鋼種，使用本發明規定之條件範圍外之條件的製造方法。於表4顯示該製造條件，於表5顯示以表4所示之製造條件製造之鋼板的肥粒鐵粒徑(μm)、維克氏硬度(HV)、晶界碳化物數/粒內碳化物數、x射線強度比：I1/I0、r值之異向性指數|△r|、及臨界冷卻速度(℃/秒)。 For the 12 steel grades of No. 1 to No. 5, No. 16 to No. 31, No. 31, No. 33, and No. 35 of the invention steel sheet, a production method outside the conditions specified in the present invention is used. Table 4 shows the production conditions, and Table 5 shows the ferrite iron particle diameter (μm), Vickers hardness (HV), grain boundary carbide number/intraparticle carbonization of the steel sheet produced under the production conditions shown in Table 4. Number of objects, x-ray intensity ratio: I1/I0, anisotropy index of r value | Δr|, and critical cooling rate (°C/sec).

將熱軋延之最終軋延溫度或捲溫度設為本發明規定之條件範圍外的溫度，將導致再結晶化之下降，對集合組織之隨機化造成很大的影響，結果，可知|△r|之值上升。又，將退火條件設為本發明規定之條件範圍外的條件時，晶界碳化物數/晶界碳化物數成為1以下，可知碳化物之分布狀態大幅地變化。 Setting the final rolling temperature or the coil temperature of the hot rolling to a temperature outside the range specified by the present invention causes a decrease in recrystallization and greatly affects the randomization of the aggregated structure. As a result, it is known that |Δr |The value of the increase. When the annealing conditions are the conditions outside the range of the conditions specified in the present invention, the number of grain boundary carbides/the number of grain boundary carbides becomes 1 or less, and it is understood that the state of distribution of the carbides largely changes.

產業上之可利用性 Industrial availability

如前述，依據本發明，可提供淬火性與素材成形性優異之鋼板及其製造方法。本發明之鋼板適用於藉由增厚等冷鍛成形後得到齒輪等零件。因此，本發明於鋼板製造及利用產業中之可利用性高。 As described above, according to the present invention, it is possible to provide a steel sheet excellent in hardenability and material formability and a method for producing the same. The steel sheet of the present invention is suitable for obtaining a gear or the like after cold forging by thickening or the like. Therefore, the present invention has high availability in the steel sheet manufacturing and utilization industry.

Claims

一種鋼板，以質量%計含有：C：0.10~0.70%、Si：0.01~0.30%、Mn：0.30~3.00%、Al：0.001~0.10%、Cr：0.010~0.50%、Mo：0.0010~0.50%、B：0.0004~0.01%、Ti：0.001~0.10%、P：0.02%以下、S：0.01%以下、N：0.0200%以下、O：0.0200%以下、Sn：0.05%以下、Sb：0.05%以下、As：0.05%以下、Nb：0.10%以下、V：0.10%以下、Cu：0.10%以下、W：0.10%以下、Ta：0.10%以下、Ni：0.10%以下、 Mg：0.05%以下、Ca：0.05%以下、Y：0.05%以下、Zr：0.05%以下、La：0.05%以下、及Ce：0.05%以下，且剩餘部分係Fe及不可避免的雜質；前述鋼板之特徵在於其金屬組織滿足：碳化物之平均粒徑係0.4μm以上且2.0μm以下，波來鐵之面積率係6%以下，肥粒鐵晶界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率大於1，及令前述鋼板1/2板厚部分板面的{211}<011>之X射線繞射強度為I1，且{100}<011>之X射線繞射強度為I0時，I1/I0<1；前述鋼板之維克氏硬度係100HV以上且150HV以下。 A steel sheet containing, by mass%, C: 0.10 to 0.70%, Si: 0.01 to 0.30%, Mn: 0.30 to 3.00%, Al: 0.001 to 0.10%, Cr: 0.010 to 0.50%, Mo: 0.0010 to 0.50% B: 0.0004 to 0.01%, Ti: 0.001 to 0.10%, P: 0.02% or less, S: 0.01% or less, N: 0.0200% or less, O: 0.0200% or less, Sn: 0.05% or less, and Sb: 0.05% or less , As: 0.05% or less, Nb: 0.10% or less, V: 0.10% or less, Cu: 0.10% or less, W: 0.10% or less, Ta: 0.10% or less, and Ni: 0.10% or less. Mg: 0.05% or less, Ca: 0.05% or less, Y: 0.05% or less, Zr: 0.05% or less, La: 0.05% or less, and Ce: 0.05% or less, and the remainder is Fe and unavoidable impurities; The metal structure is characterized in that the average particle diameter of the carbide is 0.4 μm or more and 2.0 μm or less, and the area ratio of the ferrite is 6% or less, and the number of carbides in the ferrite grain boundary is relative to the ferrite. The ratio of the number of carbides in the inside is greater than 1, and the X-ray diffraction intensity of {211}<011> of the plate surface of the 1/2 plate thickness portion of the steel plate is I1, and the X-ray diffraction of {100}<011> When the incident intensity is I0, I1/I0<1; and the Vickers hardness of the steel sheet is 100 HV or more and 150 HV or less.

一種鋼板之製造方法，係製造請求項1之鋼板，該方法之特徵在於：對具有如請求項1之成分組成的鋼片施行熱軋延而製成熱軋鋼板，且該熱軋延係於820℃以上且950℃以下之溫度域中結束最終軋延；以400℃以上且550℃以下捲取前述熱軋鋼板；對捲取後之熱軋鋼板施行酸洗；以30℃/小時以上且150℃/小時以下之加熱速度將酸洗後之熱軋鋼板加熱至650℃以上且720℃以下的退火溫度後，施行保持3小時以上且60小時以下之第1階段退火；接著，以1℃/小時以上且80℃/小時以下之加熱速度將熱軋鋼板加熱至725℃以上且790℃以下之退火溫度後，施行保持3小時以上且小於10小時之第2階段退火；以1℃/小時以上且100℃/小時以下之冷卻速度將退火後之熱軋鋼板冷卻至650℃。 A method for producing a steel sheet according to claim 1, wherein the steel sheet having the composition of claim 1 is subjected to hot rolling to form a hot rolled steel sheet, and the hot rolling is carried out Final rolling is completed in a temperature range of 820 ° C or higher and 950 ° C or lower; the hot-rolled steel sheet is taken up at 400 ° C or higher and 550 ° C or lower; and the hot-rolled steel sheet after coiling is subjected to pickling; The hot-rolled steel sheet after pickling is heated to an annealing temperature of 650 ° C or higher and 720 ° C or lower at a heating rate of 30 ° C / hour or more and 150 ° C / hour or less, and then subjected to the first stage of maintaining for 3 hours or more and 60 hours or less. Annealing; then, heating the hot-rolled steel sheet to an annealing temperature of 725 ° C or higher and 790 ° C or lower at a heating rate of 1 ° C / hour or more and 80 ° C / hour or less, and then performing the second stage of maintaining for 3 hours or more and less than 10 hours Annealing; the annealed hot-rolled steel sheet is cooled to 650 ° C at a cooling rate of 1 ° C / hour or more and 100 ° C / hour or less.