TWI565811B - A steel sheet excellent in cold workability at the time of molding, and a method for manufacturing the same - Google Patents

Description

成形時之冷加工性優異之鋼板及其製造方法 Steel sheet excellent in cold workability at the time of forming and method for producing the same 發明領域 Field of invention

本發明係關於成形時之冷加工性優異之鋼板及其製造方法。 The present invention relates to a steel sheet excellent in cold workability at the time of molding and a method for producing the same.

發明背景 Background of the invention

汽車用構件、刃物及其它機械構件係經由穿孔、彎曲、加壓加工等加工步驟而製造。在其加工步驟中，為了提升產品品質、穩定化及/或降低製造成本，針對素材之碳鋼板會力求其加工性之提升。 Automobile components, blades, and other mechanical components are manufactured through processing steps such as perforation, bending, and press working. In the processing step, in order to improve product quality, stabilize and/or reduce manufacturing costs, the carbon steel plate for the material will strive to improve its processability.

一般係對碳鋼板施行冷軋延及球狀化退火而製造出一由肥粒鐵與球狀化碳化物所構成且加工性優良的軟質碳鋼板。截至目前，已有多數文獻提出用以改善碳鋼板之加工性的技術。 Generally, a carbon steel sheet is subjected to cold rolling and spheroidizing annealing to produce a soft carbon steel sheet which is composed of ferrite iron and spheroidized carbide and has excellent workability. As of now, most of the literature has proposed techniques for improving the processability of carbon steel sheets.

例如，專利文獻1中便揭示了一種精密穿孔用高碳鋼板及其製造法，該精密穿孔用高碳鋼板具有之組織含有C：0.15~0.90質量%、Si：0.40質量%以下、Mn：0.3~1.0質量%、P：0.03質量%以下、全Al：0.10質量%以下、Ti：0.01~0.05質量%、B：0.0005~0.0050質量%、N：0.01質量%以下、Cr：1.2質量%以下，且於肥粒鐵基質內分散 有平均碳化物粒徑0.4~1.0μm且碳化物球狀化率80%以上的碳化物；並且，該鋼板的缺口拉伸伸長率(notched tensile elongation)為20%以上。 For example, Patent Document 1 discloses a high carbon steel sheet for precision perforation and a method for producing the same, which has a structure containing C: 0.15 to 0.90% by mass, Si: 0.40% by mass or less, and Mn: 0.3. ~1.0% by mass, P: 0.03 mass% or less, all Al: 0.10% by mass or less, Ti: 0.01 to 0.05% by mass, B: 0.0005 to 0.0050% by mass, N: 0.01% by mass or less, and Cr: 1.2% by mass or less. And dispersed in the ferrite iron matrix A carbide having an average carbide particle diameter of 0.4 to 1.0 μm and a carbide spheroidization ratio of 80% or more; and the steel sheet has a notched tensile elongation of 20% or more.

專利文獻2中則揭示了一種加工性優異的中‧高碳鋼板及其製造法，該鋼板的特徵在於：其組織含有C：0.3~1.3質量%、Si：1.0質量%以下、Mn：0.2~1.5質量%、P：0.02質量%以下、S：0.02質量%以下，且碳化物係以肥粒鐵結晶粒界上之碳化物C_GB與肥粒鐵結晶粒內之碳化物數C_IG之間成立C_GB/C_IG≦0.8之關係的方式分散；並且，該鋼板的截面硬度為160HV以下。 Patent Document 2 discloses a medium-high carbon steel sheet excellent in workability and a method for producing the same, the steel sheet characterized in that the structure contains C: 0.3 to 1.3% by mass, Si: 1.0% by mass or less, and Mn: 0.2%. 1.5% by mass, P: 0.02% by mass or less, S: 0.02% by mass or less, and the carbide is between the carbide C _GB on the grain boundary of the ferrite grain iron and the number of carbides C _IG in the grain of the ferrite grain crystal The relationship of C _GB /C _IG ≦0.8 is dispersed, and the steel plate has a cross-sectional hardness of 160 HV or less.

專利文獻3中揭示了一種加工性優異的中‧高碳鋼板，其特徵在於：該鋼板具有之組織含有C：0.30~1.00質量%、Si：1.0質量%以下、Mn：0.2~1.5質量%、P：0.02質量%以下、S：0.02質量%以下，並且，於肥粒鐵結晶粒界上之碳化物C_GB與肥粒鐵結晶粒內之碳化物數C_IG之間成立C_GB/C_IG≦0.8之關係，同時肥粒鐵中分散有全部之碳化物內有90%以上由長軸/短軸為2以下之球狀化碳化物佔據的碳化物。 Patent Document 3 discloses a medium-high carbon steel sheet having excellent workability, wherein the steel sheet has a structure containing C: 0.30 to 1.00% by mass, Si: 1.0% by mass or less, and Mn: 0.2 to 1.5% by mass. P: 0.02 mass% or less, S: 0.02 mass% or less, and C _GB /C _IG is established between the carbide C _GB on the ferrite grain crystal grain boundary and the carbide number C _IG in the ferrite grain crystal grain. In the relationship of ≦0.8, at the same time, 90% or more of all the carbides dispersed in the ferrite iron are occupied by spheroidized carbides having a major axis/minor axis of 2 or less.

而且，在專利文獻1~3中闡述肥粒鐵粒內之碳化物所佔比率愈多，愈可提升加工性。 Further, in Patent Documents 1 to 3, the more the ratio of the carbides in the ferrite grains is, the more the workability can be improved.

此外，專利文獻4中揭示出一種FB加工性、模具壽命及FB加工後之成形加工性優異的鋼板，其特徵在於：該鋼板具有由C：0.1~0.5質量%、Si：0.5質量%以下、Mn：0.2~1.5質量%、P：0.03質量%以下、S：0.02質量%以下所 構成之組成以及以肥粒鐵及碳化物為主體的組織，並且，以S_gb={S_on/(S_on+S_in)}×100(在此，S_on：係每單位面積中所存在之碳化物中，存在於粒界上之碳化物的總佔有面積；S_in：係每單位面積中所存在之碳化物中，存在於粒內之碳化物的總佔有面積)為定義之肥粒鐵粒界碳化物量S_gb為40%以上。 Further, Patent Document 4 discloses a steel sheet excellent in FB workability, mold life, and moldability after FB processing, characterized in that the steel sheet has C: 0.1 to 0.5% by mass and Si: 0.5% by mass or less. Mn: 0.2 to 1.5% by mass, P: 0.03 mass% or less, S: 0.02 mass% or less, a composition mainly composed of ferrite iron and carbide, and S _gb = {S _on / (S _On +S _in )}×100 (here, S _on is the total occupied area of carbides present on the grain boundary in the carbides present per unit area; S _in : is present in each unit area Among the carbides, the total occupied area of the carbides present in the grains is defined as the amount of carbide grain boundary S _gb of the ferrite grains is 40% or more.

但，專利文獻1中記載之技術聚焦在肥粒鐵粒徑及碳化物之粗大化，為了達成軟質而在A_C1點以上之溫度下進行退火，但在A_C1點以上之溫度下進行退火時會於退火中析出棒狀‧板狀之碳化物。該碳化物會造成加工性降低，所以即使可降低硬度，也不利於加工性。 However, the technique described in Patent Document 1 focuses on the coarsening of the grain size of the ferrite iron and the carbide, and annealing at a temperature _equal to or higher than the point A _C1 in order to achieve softness, but annealing at a temperature _equal to or higher than the point A _C1 . Rod-shaped ‧ plate-like carbides are precipitated during annealing. This carbide causes a decrease in workability, so that even if the hardness can be lowered, workability is disadvantageous.

專利文獻2及3中記載之技術皆視析出於粒界之碳化物的低碳化物球狀化率為造成加工性惡化的原因，而不以提升粒界碳化物之球狀化率為問題。專利文獻4中記載之技術僅規定出組織因子而未研討加工性與機械特性之關係。 The techniques described in Patent Documents 2 and 3 all consider that the low carbide spheroidization rate of the carbide at the grain boundary causes deterioration in workability, and does not raise the problem of the spheroidization rate of the grain boundary carbide. The technique described in Patent Document 4 specifies only the tissue factor and does not examine the relationship between the workability and the mechanical properties.

專利文獻5中記載之技術係著眼在精密沖裁加工性與存在於肥粒鐵粒內之碳化物量及肥粒鐵粒徑的關係所做的發明。但，在專利文獻5中並未研討集合組織對於塑性異向性有何影響。 The technique described in Patent Document 5 focuses on the relationship between the precision punching workability and the amount of carbides present in the ferrite grains and the grain size of the ferrite grains. However, Patent Document 5 does not discuss how the aggregate structure affects the plastic anisotropy.

專利文獻6中係揭示出一種已抑制因軋延而發達之集合組織發達的熱軋鋼板及其製造方法。但，在專利文獻6並未研討經由軋延而發達之集合組織以外的集合組織與冷鍛造性的關係。 Patent Document 6 discloses a hot-rolled steel sheet having improved developed aggregate structure developed by rolling and a method for producing the same. However, Patent Document 6 does not discuss the relationship between the aggregate structure other than the aggregate structure developed by rolling and the cold forgeability.

專利文獻7中記載之技術係思及肥粒鐵粒內之雪明碳鐵密度對於淬火前之高碳熱軋鋼板的硬度及全伸長有極大影響所做的發明。專利文獻7中記載之熱軋鋼板的特徵在於具有由肥粒鐵及雪明碳鐵所構成之微組織且該肥粒鐵的肥粒鐵粒內之雪明碳鐵密度為0.10個/μm²以下。但，在專利文獻7並未研討集合組織對於塑性異向性有何影響。 The technique described in Patent Document 7 is an invention in which the density of the stellite carbon in the ferrite grains is greatly affected by the hardness and total elongation of the high carbon hot-rolled steel sheet before quenching. The hot-rolled steel sheet described in Patent Document 7 is characterized in that it has a microstructure composed of ferrite iron and ferritic carbon iron, and the density of the stellite carbon in the ferrite grains of the ferrite is 0.10 / μm ² the following. However, Patent Document 7 does not investigate how the aggregate structure affects the plastic anisotropy.

專利文獻8中記載之技術係思及，在具有微細組織之鋼材中，C_eq值不僅與機械特性及熔接性相關，與疲勞龜裂進展速度也有關係所做的發明。專利文獻8係揭示出藉由將C_eq值之範圍限制在0.28%~0.65%，而讓鋼材之耐疲勞特性獲得改善並同時可確保熔接性。但，在專利文獻8並未研討集合組織對於塑性異向性有何影響。 According to the technique described in Patent Document 8, in the steel material having a fine structure, the C _eq value is related not only to mechanical properties and weldability, but also to the progress rate of fatigue cracking. Patent Document 8 discloses that by limiting the range of the C _eq value to 0.28% to 0.65%, the fatigue resistance of the steel is improved and the weldability is ensured. However, Patent Document 8 does not investigate how the aggregate structure affects the plastic anisotropy.

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

專利文獻1：日本專利第4465057號公報 Patent Document 1: Japanese Patent No. 4465057

專利文獻2：日本專利第4974285號公報 Patent Document 2: Japanese Patent No. 4974285

專利文獻3：日本專利第5197076號公報 Patent Document 3: Japanese Patent No. 5197076

專利文獻4：日本專利第5194454號公報 Patent Document 4: Japanese Patent No. 5194454

專利文獻5：日本特開2007-270331號公報 Patent Document 5: Japanese Laid-Open Patent Publication No. 2007-270331

專利文獻6：日本特開2009-263718號公報 Patent Document 6: JP-A-2009-263718

專利文獻7：日本特開2015-17294號公報 Patent Document 7: JP-A-2015-17294

專利文獻8：日本特開2004-27355號公報 Patent Document 8: Japanese Patent Laid-Open Publication No. 2004-27355

發明概要 Summary of invention

本發明係有鑑於先前技術之現狀，以提升鋼板中成形時之冷加工性為課題，所以本發明目的在於提供一種解決該課題之鋼板及其製造方法。 The present invention has been made in view of the current state of the art, and it is an object of improving the cold workability at the time of forming in a steel sheet. Therefore, an object of the present invention is to provide a steel sheet and a method for producing the same.

本發明人等針對解決上述課題之手法進行精闢研討。結果發現，藉由將熱軋至退火的製造條件最佳化以控制冷加工前之鋼板組織中的碳化物之分散狀態，可使碳化物析出至肥粒鐵粒界上並同時可控制熱軋鋼板中的集合組織，進而得以提升冷加工性。 The inventors of the present invention have made intensive studies on the methods for solving the above problems. As a result, it was found that by optimizing the manufacturing conditions of hot rolling to annealing to control the dispersion state of carbides in the steel sheet structure before cold working, carbides can be precipitated onto the ferrite grain boundary and the hot rolled steel sheet can be controlled at the same time. The collection organization in the middle, in turn, can improve the cold workability.

此外，單靠個別單獨著墨熱軋條件或退火條件也很難製造出滿足上述條件之鋼板，所以吾等係在重複各式研究中發現，在熱軋‧退火步驟之一貫步驟中彼此相互協調予以最佳化便可製造出滿足上述條件之鋼板。 In addition, it is difficult to manufacture steel sheets satisfying the above conditions by individual inking hot rolling conditions or annealing conditions alone, so we have found that in the repeated studies, it is coordinated with each other in the consistent steps of the hot rolling and annealing steps. Optimization can produce steel sheets that meet the above conditions.

本發明係根據上述見解而實施，其主旨如下。 The present invention has been made based on the above findings, and the gist thereof is as follows.

(1)一種成形時之冷加工性優異之鋼板，特徵在於其成分組成以質量%計含有：C：0.10~0.40%、Si：0.01~0.30%、Mn：0.30~1.00%、P：0.0001~0.020%、S：0.0001~0.010%、及Al：0.001~0.10%，且剩餘部分由Fe及無法避免的雜質所構成；並且， (a)肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率超過1；(b)肥粒鐵粒徑為5μm以上且50μm以下；(c)按JIS Z 2254規格之r值的面內異向性｜△r｜為0.2以下；(d)維氏硬度為100HV以上且150HV以下；(e)對鋼板之結晶粒呈隨機方位分布之試料進行X射線繞射時，相對於該X射線繞射強度，鋼板於1/2板厚部分之{311}<011>方位的X射線繞射強度比為3.0以下。 (1) A steel sheet excellent in cold workability at the time of molding, characterized in that its component composition is contained in mass%: C: 0.10 to 0.40%, Si: 0.01 to 0.30%, Mn: 0.30 to 1.00%, P: 0.0001 to 0.020 %, S: 0.0001 to 0.010%, and Al: 0.001 to 0.10%, and the remainder is composed of Fe and unavoidable impurities; (a) The ratio of the number of carbides in the ferrite grain boundary to the number of carbides in the ferrite grain is more than 1; (b) the grain size of the ferrite is 5 μm or more and 50 μm or less; (c) according to JIS In-plane anisotropy of r value of Z 2254 specification | Δr| is 0.2 or less; (d) Vickers hardness is 100 HV or more and 150 HV or less; (e) X-ray is performed on a sample having a random orientation distribution of crystal grains of a steel sheet At the time of diffraction, the X-ray diffraction intensity ratio of the {311}<011> orientation of the steel sheet in the 1/2 plate thickness portion is 3.0 or less with respect to the X-ray diffraction intensity.

(2)如前述(1)記載之成形時之冷加工性優異之鋼板，其中前述成分組成以質量%計更含有下述元素中之1種或2種以上：N：0.0001~0.010%、O：0.0001~0.020%、Cr：0.001~0.50%、Mo：0.001~0.10%、Nb：0.001~0.10%、V：0.001~0.10%、Cu：0.001~0.10%、W：0.001~0.10%、Ta：0.001~0.10%、Ni：0.001~0.10%、Sn：0.001~0.050%、Sb：0.001~0.050%、 As：0.001~0.050%、Mg：0.0001~0.050%、Ca：0.001~0.050%、Y：0.001~0.050%、Zr：0.001~0.050%、La：0.001~0.050%、及Ce：0.001~0.050%。 (2) The steel sheet which is excellent in the cold workability at the time of the molding described in the above (1), wherein the component composition further contains one or more of the following elements in terms of % by mass: N: 0.0001 to 0.010%, O: 0.0001~0.020%, Cr: 0.001~0.50%, Mo: 0.001~0.10%, Nb: 0.001~0.10%, V: 0.001~0.10%, Cu: 0.001~0.10%, W: 0.001~0.10%, Ta: 0.001 ~0.10%, Ni: 0.001~0.10%, Sn: 0.001~0.050%, Sb: 0.001~0.050%, As: 0.001 to 0.050%, Mg: 0.0001 to 0.050%, Ca: 0.001 to 0.050%, Y: 0.001 to 0.050%, Zr: 0.001 to 0.050%, La: 0.001 to 0.050%, and Ce: 0.001 to 0.050%.

(3)一種成形時之冷加工性優異之鋼板的製造方法，係製造如前述(1)或(2)記載之成形時之冷加工性優異之鋼板，該製造方法之特徵在於：將具有如前述(1)或(2)記載之成分組成的鋼片加熱並供於熱軋延，且在800℃以上且900℃以下之溫度區內結束完工熱軋，並在400℃以上且550℃以下進行捲取，再於酸洗後對該已捲取之熱軋鋼板實施保持在2種溫度區內的2階段步驟型退火；並且，在實施前述2階段步驟型退火時，(i)係在650℃以上且720℃以下之溫度區內實施保持在3小時以上且60小時以下的第1階段退火，接著在725℃以上且790℃以下之溫度區內實施保持在3小時以上且50小時以下的第2階段退火；其後，(ii)在冷卻速度1℃/小時以上且30℃/小時以下的條件下冷卻至650℃以下。 (3) A method for producing a steel sheet excellent in cold workability during molding, which is a steel sheet excellent in cold workability at the time of molding as described in the above (1) or (2), which is characterized in that it has the above ( 1) or (2) The steel sheet of the component composition is heated and supplied for hot rolling, and the hot rolling is completed in a temperature range of 800 ° C or more and 900 ° C or less, and the coil is rolled at 400 ° C or more and 550 ° C or less. Taking the hot-rolled steel sheet which has been taken up after pickling, a two-stage step type annealing which is maintained in two temperature zones is carried out; and, in carrying out the above-mentioned two-stage step type annealing, (i) is at 650 ° C In the temperature range of 720 ° C or less, the first-stage annealing is maintained for 3 hours or more and 60 hours or less, and then the temperature is maintained in the temperature range of 725 ° C or higher and 790 ° C or lower for 3 hours or longer and 50 hours or shorter. The two-stage annealing is followed by (ii) cooling to 650 ° C or lower under the conditions of a cooling rate of 1 ° C / hour or more and 30 ° C / hour or less.

(4)如(3)記載之鋼板的製造方法，其中鋼板的截面收縮率為40%以上。 (4) The method for producing a steel sheet according to (3), wherein the steel sheet has a cross-sectional shrinkage ratio of 40% or more.

根據本發明，可製造提供一成形時之冷加工性優異之鋼板。 According to the present invention, it is possible to manufacture a steel sheet which is excellent in cold workability at the time of forming.

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

本發明之成形時之冷加工性優異之鋼板(以下有時會稱「本發明鋼板」)之特徵在於其成分組成以質量%計含有：C：0.10~0.40%、Si：0.01~0.30%、Mn：0.30~1.00%、P：0.0001~0.020%、S：0.0001~0.010%、及Al：0.001~0.10%，且剩餘部分由Fe及無法避免的雜質所構成；並且，(a)肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率超過1；(b)肥粒鐵粒徑為5μm以上且50μm以下；(c)按JIS Z 2254規格之r值的面內異向性｜△r｜為0.2以下；(d)維氏硬度為100HV以上且150HV以下；(e)對鋼板之結晶粒呈隨機方位分布之試料進行X射線繞射時，相對於該X射線繞射強度，鋼板於1/2板厚部分之 {311}<011>方位的X射線繞射強度比為3.0以下。 The steel sheet excellent in cold workability at the time of molding of the present invention (hereinafter referred to as "the steel sheet of the present invention") is characterized in that its component composition contains, by mass%, C: 0.10 to 0.40%, Si: 0.01 to 0.30%, Mn. : 0.30~1.00%, P: 0.0001~0.020%, S: 0.0001~0.010%, and Al: 0.001~0.10%, and the remainder is composed of Fe and unavoidable impurities; and, (a) ferrite particles The ratio of the number of carbides in the boundary to the number of carbides in the ferrite particles exceeds 1; (b) the particle size of the ferrite is 5 μm or more and 50 μm or less; (c) the r value according to the JIS Z 2254 specification In-plane anisotropy |Δr| is 0.2 or less; (d) Vickers hardness is 100 HV or more and 150 HV or less; (e) When X-ray diffraction is performed on a sample in which crystal grains of a steel sheet are randomly distributed, X-ray diffraction intensity, steel plate in 1/2 plate thickness The X-ray diffraction intensity ratio of the {311}<011> orientation is 3.0 or less.

本發明之成形時之冷加工性優異之鋼板的製造方法(以下有時會稱「本發明製造方法」)係製造本發明鋼板者，本發明製造方法之特徵在於：將本發明鋼板之成分組成的鋼片加熱供於熱軋延，且在800℃以上且900℃以下之溫度區內結束完工熱軋，並在400℃以上且550℃以下進行捲取，再於酸洗後對該已捲取之熱軋鋼板實施保持在2種溫度區內的2階段步驟型退火；並且，在實施前述2階段步驟型退火時，(i)係在650℃以上且720℃以下之溫度區內實施保持在3小時以上且60小時以下的第1階段退火，接著在725℃以上且790℃以下之溫度區內實施保持在3小時以上且50小時以下的第2階段退火；其後，(ii)在冷卻速度1℃/小時以上且30℃/小時以下的條件下冷卻至650℃以下。 The method for producing a steel sheet excellent in cold workability at the time of molding of the present invention (hereinafter referred to as "the method for producing the present invention") is a method for producing the steel sheet of the present invention, and the method for producing the present invention is characterized by comprising the composition of the steel sheet of the present invention. The steel sheet is heated for hot rolling, and the hot rolling is completed in a temperature range of 800 ° C or more and 900 ° C or less, and coiling is performed at 400 ° C or more and 550 ° C or less, and the coiling is performed after pickling. The hot-rolled steel sheet is subjected to a two-stage step type annealing maintained in two temperature zones; and, in performing the two-stage step type annealing described above, (i) is maintained in a temperature zone of 650 ° C or more and 720 ° C or less. First-stage annealing of 3 hours or more and 60 hours or less, followed by second-stage annealing maintained in a temperature range of 725 ° C or more and 790 ° C or less for 3 hours or more and 50 hours or less; thereafter, (ii) cooling The temperature is cooled to 650 ° C or lower under the conditions of a speed of 1 ° C / hour or more and 30 ° C / hour or less.

以下說明本發明鋼板及本發明製造方法。 The steel sheet of the present invention and the method for producing the present invention will be described below.

首先說明本發明鋼板之成分組成的限定理由。至於，關於成分組成之符號%係表示質量%。 First, the reason for limiting the composition of the steel sheet of the present invention will be described. As for the symbol % of the component composition, the mass % is expressed.

C：0.10~0.40% C: 0.10~0.40%

C係在鋼中形成碳化物且有利於鋼強化及肥粒鐵粒之微細化的元素。為了抑制在冷加工產生緞紋以確保冷鍛造構件之表面美觀，必須抑制肥粒鐵粒徑粗大化，但低於0.10%時碳化物之體積率會不足而無法於退火中抑制碳化物粗大化，故將C限定為0.10%以上。且宜為0.12%以上。 C is an element which forms carbides in steel and contributes to steel strengthening and miniaturization of ferrite particles. In order to suppress the occurrence of satin in the cold working to ensure the appearance of the surface of the cold forged member, it is necessary to suppress the coarsening of the ferrite iron particle diameter, but when the content is less than 0.10%, the volume fraction of the carbide is insufficient to suppress the coarsening of the carbide during the annealing. Therefore, C is limited to 0.10% or more. And it should be 0.12% or more.

另一方面，若超過0.40%，碳化物之體積率會增加而於瞬間附加荷重時大量生成成為破壞起點之裂痕，進而降低耐衝撃特性，故將C限定為0.40%以下。且宜為0.38%以下。 On the other hand, when it exceeds 0.40%, the volume fraction of the carbide increases, and when the load is instantaneously added, a large number of cracks which are the starting point of the fracture are formed, and the punching resistance is further lowered. Therefore, C is limited to 0.40% or less. And it should be 0.38% or less.

Si：0.01~0.30% Si: 0.01~0.30%

Si係作用為去氧劑且可影響碳化物之形態的元素。為了減少肥粒鐵粒內之碳化物個數並增加肥粒鐵粒界上之碳化物個數，在2階段步驟型退火必須於退火中生成沃斯田鐵相，暫時使碳化物溶解後進行徐冷以促進碳化物析出至肥粒鐵粒界。 The Si system functions as an oxygen scavenger and can affect the form of the carbide. In order to reduce the number of carbides in the ferrite grains and increase the number of carbides on the ferrite grain boundary, the two-stage step type annealing must generate the Worthfield iron phase in the annealing, temporarily dissolving the carbides. Xu cold promotes the precipitation of carbides to the ferrite grain boundary.

在本發明鋼板中，Si愈少愈好，但若低於0.01%，製造成本便會上升，故將Si限定為0.01%以上。 In the steel sheet of the present invention, the smaller the Si, the better, but if it is less than 0.01%, the production cost increases, so Si is limited to 0.01% or more.

另一方面，若超過0.30%，肥粒鐵之延性便會降低而容易在冷加工時引發破裂，降低冷加工性，故將Si限定為0.30%以下。且宜為0.28%以下。 On the other hand, when it exceeds 0.30%, the ductility of the ferrite iron is lowered, and it is easy to cause cracking at the time of cold working, and the cold workability is lowered, so Si is limited to 0.30% or less. And it should be 0.28% or less.

Mn：0.30~1.00% Mn: 0.30~1.00%

Mn係在2階段步驟型退火中控制碳化物之形態的元素。低於0.30%時，便很難在第2階段退火後之徐冷使碳化物析出至肥粒鐵粒界，故將Mn限定為0.30%以上。且宜為0.33%以上。 Mn is an element that controls the form of carbides in a two-stage step type annealing. When the amount is less than 0.30%, it is difficult to precipitate the carbides to the ferrite core boundary after the second-stage annealing, so that Mn is limited to 0.30% or more. And it should be 0.33% or more.

另一方面，若超過1.00%，肥粒鐵之硬度便會增加而降低冷加工性，故將Mn限定為1.00%以下。且宜為0.96%以下。 On the other hand, when it exceeds 1.00%, the hardness of the ferrite iron increases and the cold workability is lowered, so Mn is limited to 1.00% or less. And it should be 0.96% or less.

P：0.0001~0.020% P: 0.0001~0.020%

P係偏析在肥粒鐵粒界用以抑制粒界碳化物形成的元素。雖然愈少愈好，但在精製步驟中若將P減低到少於0.0001%，精製成本便會大幅上升，故將P限定為0.0001%以上。且宜為0.0013%以上。 The P system segregates the elements in the ferrite grain boundary to suppress the formation of grain boundary carbides. Although the less the better, if the P is reduced to less than 0.0001% in the purification step, the purification cost is greatly increased, so P is limited to 0.0001% or more. And it is preferably 0.0013% or more.

另一方面，若超過0.020%，粒界碳化物之個數比率便會降低，進而降低冷加工性，故將P限定為0.020%以下。且宜為0.018%以下。 On the other hand, when it exceeds 0.020%, the ratio of the number of grain boundary carbides is lowered, and the cold workability is further lowered, so P is limited to 0.020% or less. And it should be 0.018% or less.

S：0.0001~0.010% S: 0.0001~0.010%

S係會形成MnS等非金屬夾雜物的元素。非金屬夾雜物於冷鍛造時會成為產生破裂的起點，故而S愈少愈好，但若減低到少於0.0001%，精製成本便會大幅上升，故將S限定在0.0001%以上。且宜為0.0012%以上。 The S system forms an element of a non-metallic inclusion such as MnS. Non-metallic inclusions are the starting point for cracking during cold forging. Therefore, the smaller the S, the better. However, if the reduction is less than 0.0001%, the purification cost will increase significantly, so S is limited to 0.0001% or more. And it is preferably 0.0012% or more.

另一方面，若超過0.010%，冷加工性便會降低，故將S限定在0.010%以下。且宜為0.007%以下。 On the other hand, when it exceeds 0.010%, cold workability will fall, and S is limited to 0.010% or less. And it should be 0.007% or less.

Al：0.001~0.10% Al: 0.001~0.10%

Al係作用為鋼之去氧劑且使肥粒鐵穩定化的元素。低於0.001%時將無法充分獲得添加效果，故將Al限定為0.001%以上。且宜為0.004%以上。 Al acts as an element of the oxygen scavenger of steel and stabilizes the ferrite iron. When the amount is less than 0.001%, the effect of addition cannot be sufficiently obtained, so Al is limited to 0.001% or more. And it should be 0.004% or more.

另一方面，若超過0.10%，粒界上之碳化物個數比率便會降低，進而降低冷加工性，故將Al限定為0.10%以下。且宜為0.08%以下。 On the other hand, when it exceeds 0.10%, the ratio of the number of carbides on the grain boundary is lowered, and the cold workability is further lowered. Therefore, Al is limited to 0.10% or less. And preferably it is 0.08% or less.

本發明鋼板在意圖提升本發明鋼板之特性的前提下，除了上述元素以外，亦可含有下述元素中之1種或2種以上：N：0.0001~0.010%、O：0.0001~0.020%、Cr： 0.001~0.50%、Mo：0.001~0.10%、Nb：0.001~0.10%、V：0.001~0.10%、Cu：0.001~0.10%、W：0.001~0.10%、Ta：0.001~0.10%、Ni：0.001~0.10%、Sn：0.001~0.050%、Sb：0.001~0.050%、As：0.001~0.050%、Mg：0.0001~0.050%、Ca：0.001~0.050%、Y：0.001~0.050%、Zr：0.001~0.050%、La：0.001~0.050%、Ce：0.001~0.050%。 The steel sheet of the present invention may contain one or more of the following elements in addition to the above elements, in addition to the above-mentioned elements: N: 0.0001 to 0.010%, O: 0.0001 to 0.020%, Cr : 0.001~0.50%, Mo: 0.001~0.10%, Nb: 0.001~0.10%, V: 0.001~0.10%, Cu: 0.001~0.10%, W: 0.001~0.10%, Ta: 0.001~0.10%, Ni: 0.001 ~0.10%, Sn: 0.001 to 0.050%, Sb: 0.001 to 0.050%, As: 0.001 to 0.050%, Mg: 0.0001 to 0.050%, Ca: 0.001 to 0.050%, Y: 0.001 to 0.050%, Zr: 0.001~ 0.050%, La: 0.001 to 0.050%, and Ce: 0.001 to 0.050%.

N：0.0001~0.010% N: 0.0001~0.010%

N係一旦多量含有便會引發肥粒鐵脆化的元素。雖然愈少愈好，但若減低到少於0.0001%，精製成本便會大幅上升，故將N限定為0.0001%以上。且宜為0.0006%以上。另一方面，若超過0.010%，肥粒鐵便會脆化，令冷鍛造性降低，故將N限定為0.010%以下。且宜為0.007%以下。 When the N system is contained in a large amount, it will cause iron embrittlement of the fat. Although the less the better, if the reduction is less than 0.0001%, the refining cost will increase significantly, so N is limited to 0.0001% or more. And it should be 0.0006% or more. On the other hand, when it exceeds 0.010%, the ferrite iron is embrittled and the cold forgeability is lowered, so N is limited to 0.010% or less. And it should be 0.007% or less.

O：0.0001~0.020% O: 0.0001~0.020%

O係一旦多量含有便會於鋼中形成粗大氧化物的元素。雖然以少量為宜，但若減低到少於0.0001%，精製成本便會大幅上升，故將O限定為0.0001%以上。且宜為0.0011%以上。另一方面，若超過0.020%，便會於鋼中生成粗大氧化物而於冷加工時成為破裂之起點，故將O限定為0.020%以下。且宜為0.017%以下。 When the O system is contained in a large amount, an element of a coarse oxide is formed in the steel. Although it is preferable to use a small amount, if it is reduced to less than 0.0001%, the refining cost will increase greatly, so O is limited to 0.0001% or more. And preferably it is 0.0011% or more. On the other hand, when it exceeds 0.020%, a coarse oxide is formed in steel and it is a starting point of cracking at the time of cold working, so O is limited to 0.020% or less. And it should be 0.017% or less.

Cr：0.001~0.50% Cr: 0.001~0.50%

Cr係可提高淬火性而有助於強度提升的元素，亦是可濃化於碳化物形成即使為沃斯田鐵相也相當穩定之碳化物的元素。低於0.001%時將無法充分獲得淬火性提升效果，故將Cr限定為0.001%以上。且宜為0.007%以上。另一方面， 若超過0.50%，碳化物可能會穩定化而於淬火時延遲碳化物的溶解，進而無法達成所需的淬火強度，故將Cr限定為0.50%以下。且宜為0.45%以下。 The Cr system is an element which enhances the hardenability and contributes to the improvement of the strength, and is an element which can be concentrated in the formation of a carbide which is stable even in the iron phase of the Vostian iron phase. When the amount is less than 0.001%, the effect of improving the hardenability cannot be sufficiently obtained, so Cr is limited to 0.001% or more. And it should be 0.007% or more. on the other hand, When it exceeds 0.50%, the carbide may be stabilized and the dissolution of the carbide may be delayed during quenching, and the desired quenching strength may not be achieved. Therefore, Cr is limited to 0.50% or less. And it should be 0.45% or less.

Mo：0.001~0.10% Mo: 0.001~0.10%

Mo與Mn同樣地係可有效控制碳化物之形態的元素。低於0.001%時將無法充分獲得添加效果，故將Mo限定為0.001%以上。且宜為0.010%以上。另一方面，若超過0.10%，r值之面內異向性便會惡化而降低冷加工性，故將Mo限定為0.10%以下。且宜為0.08%以下。 Like Mn, Mo is an element which can effectively control the form of carbide. When the amount is less than 0.001%, the effect of addition cannot be sufficiently obtained, so Mo is limited to 0.001% or more. And it should be 0.010% or more. On the other hand, when it exceeds 0.10%, the in-plane anisotropy of the r value deteriorates and the cold workability is lowered, so Mo is limited to 0.10% or less. And preferably it is 0.08% or less.

Nb：0.001~0.10% Nb: 0.001~0.10%

Nb係可有效控制碳化物之形態的元素，亦是使組織微細化而有助於提升韌性的元素。低於0.001%時將無法充分獲得添加效果，故將Nb限定為0.001%以上。且宜為0.004%以上。另一方面，若超過0.10%，便會析出多數個微細的Nb碳化物，令強度過度增強，此外，粒界碳化物之個數比率會降低，令冷鍛造性降低，故將Nb限定為0.10%以下。且宜為0.08%以下。 The Nb system is an element that can effectively control the form of carbides, and is an element that makes the structure finer and contributes to the improvement of toughness. When the amount is less than 0.001%, the effect of addition cannot be sufficiently obtained, so Nb is limited to 0.001% or more. And it should be 0.004% or more. On the other hand, if it exceeds 0.10%, a large number of fine Nb carbides are precipitated, the strength is excessively enhanced, and the ratio of the number of grain boundary carbides is lowered to lower the cold forgeability, so Nb is limited to 0.10. %the following. And preferably it is 0.08% or less.

V：0.001~0.10% V: 0.001~0.10%

V與Nb同樣地係可有效控制碳化物之形態的元素，亦是使組織微細化而有助於提升韌性的元素。低於0.001%時將無法充分獲得添加效果，故將V限定為0.001%以上。且宜為0.004%以上。另一方面，若超過0.10%，便會析出多數個微細的V碳化物，令強度過度增強，此外，粒界碳化物之個數比率會降低，令冷鍛造性降低，故將V限定為0.10%以 下。且宜為0.08%以下。 V, like Nb, is an element that can effectively control the form of carbides, and is an element that makes the structure finer and contributes to the improvement of toughness. When the amount is less than 0.001%, the effect of addition cannot be sufficiently obtained, so V is limited to 0.001% or more. And it should be 0.004% or more. On the other hand, if it exceeds 0.10%, a large number of fine V carbides are precipitated, the strength is excessively enhanced, and the ratio of the number of grain boundary carbides is lowered to lower the cold forgeability, so V is limited to 0.10. % by under. And preferably it is 0.08% or less.

Cu：0.001~0.10% Cu: 0.001~0.10%

Cu係偏析在肥粒鐵之結晶粒界，還會形成微細的析出物且有助於提升強度的元素。低於0.001%時將無法充分獲得強度提升效果，故將Cu限定為0.001%以上。且宜為0.005%以上。另一方面，若超過0.10%，便會產生紅熱脆性而降低熱軋時的生產性，故將Cu限定為0.10%以下。且宜為0.08%以下。 Cu is segregated in the grain boundary of the ferrite iron, and forms fine precipitates and contributes to the strength enhancement. When the amount is less than 0.001%, the strength improvement effect cannot be sufficiently obtained, so Cu is limited to 0.001% or more. And it should be 0.005% or more. On the other hand, when it exceeds 0.10%, red hot brittleness is generated and productivity in hot rolling is lowered, so Cu is limited to 0.10% or less. And preferably it is 0.08% or less.

W：0.001~0.10% W: 0.001~0.10%

W亦與Nb、V同樣地係可有效控制碳化物之形態的元素。低於0.001%時將無法充分獲得添加效果，故將W限定為0.001%以上。且宜為0.003%以上。另一方面，若超過0.10%，便會析出多數個微細的W碳化物，令強度過度增強，此外，粒界碳化物之個數比率會降低，令冷鍛造性降低，故將W限定為0.10%以下。且宜為0.08%以下。 W is also an element which can effectively control the form of carbides in the same manner as Nb and V. When the amount is less than 0.001%, the effect of addition cannot be sufficiently obtained, so W is limited to 0.001% or more. And it should be 0.003% or more. On the other hand, if it exceeds 0.10%, a large number of fine W carbides are precipitated, and the strength is excessively enhanced. Further, the ratio of the number of grain boundary carbides is lowered to lower the cold forgeability, so W is limited to 0.10. %the following. And preferably it is 0.08% or less.

Ta：0.001~0.10% Ta: 0.001~0.10%

Ta與Nb、V、W同樣地係可有效控制碳化物之形態的元素。低於0.001%時將無法充分獲得添加效果，故將Ta限定為0.001%以上。且宜為0.005%以上。另一方面，若超過0.10%，便會析出多數個微細的W碳化物，令強度過度增強，此外，粒界碳化物之個數比率會降低，令冷鍛造性降低，故將Ta限定為0.10%以下。且宜為0.08%以下。 Ta is an element which can effectively control the form of carbides in the same manner as Nb, V, and W. When the amount is less than 0.001%, the effect of addition cannot be sufficiently obtained, so Ta is limited to 0.001% or more. And it should be 0.005% or more. On the other hand, if it exceeds 0.10%, a large number of fine W carbides are precipitated, and the strength is excessively enhanced. Further, the ratio of the number of grain boundary carbides is lowered to lower the cold forgeability, so that Ta is limited to 0.10. %the following. And preferably it is 0.08% or less.

Ni：0.001~0.10% Ni: 0.001~0.10%

Ni係可有效提升構件韌性的元素。低於0.001%時將無 法充分獲得添加效果，故將Ni限定為0.001%以上。且宜為0.003%以上。另一方面，若超過0.10%，粒界碳化物之個數比率便會降低，令冷鍛造性降低，故將Ni限定為0.10%以下。且宜為0.08%以下。 Ni is an element that effectively enhances the toughness of components. Below 0.001% will be no Since the addition effect is sufficiently obtained by the method, Ni is limited to 0.001% or more. And it should be 0.003% or more. On the other hand, when it exceeds 0.10%, the ratio of the number of grain boundary carbides is lowered, and the cold forgeability is lowered, so Ni is limited to 0.10% or less. And preferably it is 0.08% or less.

Sn：0.001~0.050% Sn: 0.001~0.050%

Sn係從鋼原料(廢料)混入的元素。偏析於粒界且會招致粒界碳化物之個數比率降低，故而愈少愈好，但若減低到少於0.001%，精製成本便會大幅上升，故將Sn限定為0.001%以上。且宜為0.002%以上。另一方面，若超過0.050%，肥粒鐵便會脆化，令冷鍛造性降低，故將Sn限定為0.050%以下。且宜為0.040%以下。 Sn is an element mixed from a steel raw material (waste). Segregation at the grain boundary causes a decrease in the ratio of the number of grain boundary carbides. Therefore, the smaller the better, but if the reduction is less than 0.001%, the purification cost will increase significantly, so Sn is limited to 0.001% or more. And it should be 0.002% or more. On the other hand, when it exceeds 0.050%, the ferrite iron becomes brittle and the cold forgeability is lowered, so Sn is limited to 0.050% or less. And it should be 0.040% or less.

Sb：0.001~0.050% Sb: 0.001~0.050%

Sb與Sn同樣地係由鋼原料(廢料)混入的元素。偏析於粒界且會招致粒界碳化物之個數比率降低，故而愈少愈好，但若減低到少於0.001%，精製成本便會大幅上升，故將Sb設定為0.001%以上。且宜為0.002%以上。另一方面，若超過0.050%，冷鍛造性便會降低，故將Sb限定為0.050%以下。且宜為0.040%以下。 Sb is an element mixed with steel raw material (waste) like Sn. Segregation at the grain boundary causes a decrease in the ratio of the number of grain boundary carbides. Therefore, the smaller the better, but if the reduction is less than 0.001%, the purification cost will increase significantly, so Sb is set to 0.001% or more. And it should be 0.002% or more. On the other hand, when it exceeds 0.050%, cold forgeability will fall, and Sb is limited to 0.050% or less. And it should be 0.040% or less.

As：0.001~0.050% As: 0.001~0.050%

As與Sn、Sb同樣地係由鋼原料(廢料)混入的元素。偏析於粒界且會招致粒界碳化物之個數比率降低，故而愈少愈好，但若減低到少於0.001%，精製成本便會大幅上升，故將As限定為0.001%以上。且宜為0.002%以上。另一方面，若超過0.050%，粒界碳化物之個數比率便會降低，令冷鍛 造性降低，故將As限定為0.050%以下。且宜為0.040%以下。 As in the case of Sn and Sb, As is an element mixed with a steel material (waste). Segregation at the grain boundary causes a decrease in the ratio of the number of grain boundary carbides. Therefore, the smaller the better, but if the reduction is less than 0.001%, the purification cost will increase significantly, so As is limited to 0.001% or more. And it should be 0.002% or more. On the other hand, if it exceeds 0.050%, the ratio of the number of grain boundary carbides will decrease, making cold forging Since the workability is lowered, As is limited to 0.050% or less. And it should be 0.040% or less.

Mg：0.0001~0.050% Mg: 0.0001~0.050%

Mg係以微量添加便可控制硫化物之形態的元素。低於0.0001%時將無法充分獲得添加效果，故將Mg限定為0.0001%以上。且宜為0.0008%以上。另一方面，若超過0.050%，肥粒鐵便會脆化，令冷鍛造性降低，故將Mg限定為0.050%以下。且宜為0.040%以下。 The Mg system is an element which can control the form of the sulfide in a small amount. When the amount is less than 0.0001%, the effect of addition cannot be sufficiently obtained, so Mg is limited to 0.0001% or more. And it should be 0.0008% or more. On the other hand, when it exceeds 0.050%, the ferrite iron becomes brittle and the cold forgeability is lowered, so Mg is limited to 0.050% or less. And it should be 0.040% or less.

Ca：0.001~0.050% Ca: 0.001~0.050%

Ca與Mg同樣地係以微量添加便可控制硫化物之形態的元素。低於0.001%時將無法充分獲得添加效果，故將Ca限定為0.001%以上。且宜為0.003%以上。另一方面，若超過0.050%，便會生成粗大的Ca氧化物而於冷鍛造時成為產生破裂之起點，故將Ca限定為0.050%以下，且宜為0.040%以下。 In the same manner as Mg, Ca is an element which can control the form of the sulfide in a small amount. When the amount is less than 0.001%, the effect of addition cannot be sufficiently obtained, so Ca is limited to 0.001% or more. And it should be 0.003% or more. On the other hand, when it exceeds 0.050%, coarse Ca oxide is formed and the starting point of cracking occurs in cold forging, so Ca is limited to 0.050% or less, and preferably 0.040% or less.

Y：0.001~0.050% Y: 0.001~0.050%

Y與Mg、Ca同樣地係以微量添加便可控制硫化物之形態的元素。低於0.001%時將無法充分獲得添加效果，故將Y限定為0.001%以上。且宜為0.003%以上。另一方面，若超過0.050%，便會生成粗大的Y氧化物而於冷加工時成為產生破裂之起點，故將Y限定為0.050%以下。且宜為0.035%以下。 In the same manner as Mg and Ca, Y is an element which can control the form of the sulfide in a small amount. When the amount is less than 0.001%, the effect of addition cannot be sufficiently obtained, so Y is limited to 0.001% or more. And it should be 0.003% or more. On the other hand, when it exceeds 0.050%, a coarse Y oxide is formed and a crack originates at the time of cold working, so Y is limited to 0.050% or less. And it should be 0.035% or less.

Zr：0.001~0.050% Zr: 0.001~0.050%

Zr與Mg、Ca、Y同樣地係以微量添加便可控制硫化物之形態的元素。低於0.001%時將無法充分獲得添加效果， 故將Zr限定為0.001%以上。且宜為0.004%以上。另一方面，若超過0.050%，便會生成粗大的Zr氧化物而於冷加工時成為產生破裂之起點，故將Zr限定為0.050%以下。且宜為0.045%以下。 Similarly to Mg, Ca, and Y, Zr is an element which can control the form of a sulfide in a small amount. If it is less than 0.001%, the addition effect will not be fully obtained. Therefore, Zr is limited to 0.001% or more. And it should be 0.004% or more. On the other hand, when it exceeds 0.050%, a coarse Zr oxide is formed and a crack originates at the time of cold working, so Zr is limited to 0.050% or less. And it should be 0.045% or less.

La：0.001~0.050% La: 0.001~0.050%

La係以微量添加便可控制硫化物之形態的元素，同時也是偏析於粒界而招致粒界碳化物之個數比率降低的元素。低於0.001%時將無法充分獲得形態控制效果，故將La限定為0.001%以上。且宜為0.004%以上。另一方面，若超過0.050%，粒界碳化物之個數比率會降低而令冷加工性降低，故將La限定為0.050%以下。且宜為0.045%以下。 The La system is an element which controls the form of the sulfide in a small amount, and is also an element which segregates at the grain boundary and causes a decrease in the ratio of the number of grain boundary carbides. When the amount is less than 0.001%, the form control effect cannot be sufficiently obtained, so La is limited to 0.001% or more. And it should be 0.004% or more. On the other hand, when it exceeds 0.050%, the ratio of the number of grain boundary carbides is lowered to lower the cold workability, so La is limited to 0.050% or less. And it should be 0.045% or less.

Ce：0.001~0.050% Ce: 0.001~0.050%

Ce與La同樣地係以微量添加便可控制硫化物之形態的元素，同時也是偏析於粒界而招致粒界碳化物之個數比率降低的元素。低於0.001%時將無法充分獲得形態控制效果，故將Ce限定為0.001%以上。且宜為0.004%以上。另一方面，若超過0.050%，粒界碳化物之個數比率會降低而令冷鍛造性降低，故將Ce限定為0.050%以下。且宜為0.045%以下。 In the same manner as La, Ce is an element which can control the form of a sulfide in a small amount, and is also an element which segregates at the grain boundary and causes a decrease in the ratio of the number of grain boundary carbides. When the amount is less than 0.001%, the form control effect cannot be sufficiently obtained, so Ce is limited to 0.001% or more. And it should be 0.004% or more. On the other hand, when it exceeds 0.050%, the ratio of the number of grain boundary carbides is lowered to lower the cold forgeability, so Ce is limited to 0.050% or less. And it should be 0.045% or less.

至於，本發明鋼板之成分組成的剩餘部分為Fe及無法避免的雜質。 As for the remainder of the composition of the steel sheet of the present invention, Fe and unavoidable impurities.

本發明人等發現了一新穎見解，即，本發明鋼板除了上述成分組成以外，再加上最佳的熱軋與退火結果以及下列事項，可有優異的成形時之冷加工性：(a)肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化 物個數的比率超過1；(b)肥粒鐵粒徑為5μm以上且50μm以下；(c)按JIS Z 2254規格之r值的面內異向性｜△r｜為0.2以下；(d)維氏硬度為100HV以上且150HV以下；(e)對鋼板之結晶粒呈隨機方位分布之試料進行X射線繞射時，相對於該X射線繞射強度，鋼板於1/2板厚部分之{311}<011>方位的X射線繞射強度比為3.0以下。 The present inventors have found a novel finding that the steel sheet of the present invention, in addition to the above-described compositional composition, together with the best hot rolling and annealing results and the following, can have excellent cold workability during forming: (a) fertilizer The number of carbides in the grain boundary is relative to the carbonization in the iron particles The ratio of the number of objects exceeds 1; (b) the particle size of the ferrite iron is 5 μm or more and 50 μm or less; (c) the in-plane anisotropy of the r value according to the JIS Z 2254 specification | Δr| is 0.2 or less; ) Vickers hardness is 100 HV or more and 150 HV or less; (e) When X-ray diffraction is performed on a sample in which the crystal grains of the steel sheet are randomly distributed, the steel sheet is in a 1/2 plate thickness portion with respect to the X-ray diffraction intensity. The X-ray diffraction intensity ratio of the {311}<011> orientation is 3.0 or less.

以下針對上述(a)~(e)作說明。 The following (a) to (e) will be described.

(a)肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率超過1：本發明鋼板係實質上由肥粒鐵與碳化物所構成，且肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率超過1的組織。至於，碳化物除了是屬於鐵與碳之化合物的雪明碳鐵(Fe₃C)以外，亦是將雪明碳鐵中之Fe以Mn、Cr等元素取代之化合物或合金碳化物(M₂₃C₆、M₆C、MC等，M為Fe及其它的添加金屬元素)。 (a) The ratio of the number of carbides in the iron grain boundary of the fat grain to the number of carbides in the iron grain of the fat grain exceeds 1: the steel plate of the present invention is substantially composed of ferrite iron and carbide, and the ferrite iron The ratio of the number of carbides at the grain boundary to the number of carbides in the iron particles of the ferrite is more than one. As for the carbide, in addition to the ferritic carbon iron (Fe ₃ C) which is a compound of iron and carbon, it is also a compound or alloy carbide in which Fe in ferritic carbon iron is replaced by an element such as Mn or Cr (M ₂₃ C ₆ , M ₆ C, MC, etc., M is Fe and other added metal elements).

將鋼板成形為既定的構件形狀時，會於鋼板之巨組織形成剪切帶，且在剪切帶附近會集中引發滑動變形。滑動變形會伴隨差排之增生，而在剪切帶附近形成高差排密度的區塊。伴隨賦予鋼板之應變量的增加，更促使滑動變形，增加差排密度。在冷鍛造係施行以等效應變計超過1的高度變形(high deformation)。 When the steel sheet is formed into a predetermined member shape, a shear band is formed on the giant structure of the steel sheet, and sliding deformation is concentrated in the vicinity of the shear band. The sliding deformation is accompanied by the proliferation of the poor row, and a block of high differential density is formed in the vicinity of the shear band. Along with the increase in the strain amount imparted to the steel sheet, the sliding deformation is further promoted, and the difference in density is increased. In the cold forging system, a high deformation is performed with an equivalent strain gauge exceeding one.

因此，在昔知的鋼板中無法防止伴隨差排密度增 加而產生的孔隙及/或裂痕，故而難圖冷鍛造性的提升。 Therefore, it is impossible to prevent the increase in the density of the adjacent row in the steel plate of the prior art. The resulting pores and/or cracks are difficult to improve the cold forgeability.

為了解決上述難題，抑制成形時形成剪切帶即相當有效。在微組織之觀點下，剪切帶之形成係某一結晶粒產生的滑動跨越結晶粒界而連續擴散至鄰接之結晶粒的現象。因此，為了抑制剪切帶形成就必須防止滑動跨越結晶粒界的擴散。 In order to solve the above problem, it is quite effective to suppress the formation of a shear band during forming. From the viewpoint of the microstructure, the formation of the shear band is a phenomenon in which the sliding of a certain crystal grain continuously spreads to the adjacent crystal grain across the grain grain boundary. Therefore, in order to suppress the formation of the shear band, it is necessary to prevent the diffusion of the sliding across the grain boundary.

鋼板中之碳化物係可阻礙滑動的穩固的粒子，使碳化物存在於肥粒鐵粒界可抑制剪切帶之形成，而終於得以提升冷鍛造性。 The carbide in the steel plate can block the stable particles of the sliding, so that the presence of carbides in the iron grain boundary can inhibit the formation of the shear band, and finally the cold forgeability can be improved.

根據理論及原則，冷鍛造性深受碳化物在肥粒鐵粒界的被覆率影響，因此必須以高精度才能測定該被覆率。 According to the theory and principle, the cold forgeability is deeply affected by the coverage of carbides in the iron grain boundary of the fertilizer. Therefore, the coverage must be measured with high precision.

本發明人等曾明確指出，為了在3維空間測定碳化物在肥粒鐵粒界的被覆率，需要在掃描型電子顯微鏡內進行利用FIB重複進行試樣切削與觀察之連續切片SEM(serial-sectioning SEM)觀察或3維EBSP觀察，便需要龐大的測定時間，同時技術訣竅的累積也不可欠缺。也因此本發明人等曾下結論，一般的分析手法不適用。 The present inventors have clearly pointed out that in order to measure the coverage of carbides at the ferrite grain boundary in a three-dimensional space, it is necessary to perform continuous section SEM (serial--processing of sample cutting and observation by FIB in a scanning electron microscope. Sectioning SEM) observation or 3-dimensional EBSP observation requires a large measurement time, and the accumulation of know-how is not lacking. Therefore, the inventors have concluded that the general analysis method is not applicable.

所以，在探索簡易且高精度之評估指標時，本發明人等發現，以肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率作為指標，可用來評估冷鍛造性，而肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率若超過1，便可顯著提升冷鍛造性。 Therefore, the inventors have found that the ratio of the number of carbides in the ferrite grain boundary to the number of carbides in the ferrite grain can be used as an index for the evaluation of the simple and high-precision evaluation index. Cold forgeability, and if the ratio of the number of carbides in the ferrite grain boundary to the number of carbides in the ferrite grain is more than 1, the cold forgeability can be remarkably improved.

至於，在冷加工時發生的鋼板之翹曲(buckling)、 夾入、折入皆係伴隨剪切帶形成而生之應變局佈化所產生，因此使碳化物存在於肥粒鐵粒界，可減緩剪切帶形成及應變之局佈化，進而可有效地抑制翹曲、夾入、折入發生。 As for the buckling of the steel sheet which occurs during cold working, The sandwiching and folding are caused by the strain of the shear band formed by the formation of the shear band, so that the carbide exists in the iron grain boundary of the fertilizer, which can slow the formation of the shear band and the localization of the strain, thereby being effective Inhibition of warping, pinching, and folding occurs.

結晶粒界上之碳化物的球狀化率若低於80%，應變便會局部集中至棒狀或板條之碳化物，而容易產生孔隙及/或裂痕，因此結晶粒界上之碳化物的球狀化率在80%以上為佳，較宜為90%以上。 If the spheroidization rate of the carbide on the grain boundary is less than 80%, the strain will locally concentrate to the carbide of the rod or the lath, and the pores and/or cracks are easily generated, so the carbide on the grain boundary is formed. The spheroidization rate is preferably 80% or more, and more preferably 90% or more.

肥粒鐵粒內碳化物及肥粒鐵粒界的碳化物平均粒徑若低於0.1μm，鋼板硬度便會顯著增加而降低加工性，所以碳化物平均粒徑為0.1μm以上為宜。且較宜為0.17μm以上。另一方面，碳化物平均粒徑若超過2.0μm，在冷加工時粗大碳化物便會成為起點而產生龜裂，降低冷加工性，所以碳化物平均粒徑在2.0μm以下為宜。且較宜為1.95μm以下。 If the average carbide particle size of the carbide in the ferrite grain and the iron grain boundary of the grain is less than 0.1 μm, the hardness of the steel sheet is remarkably increased to lower the workability, so that the average grain size of the carbide is preferably 0.1 μm or more. More preferably, it is 0.17 μm or more. On the other hand, when the average particle diameter of the carbide exceeds 2.0 μm, coarse carbides may become a starting point during cold working to cause cracking, and the cold workability is lowered. Therefore, the average carbide particle diameter is preferably 2.0 μm or less. And it is preferably 1.95 μm or less.

接下來說明組織之觀察方法及測定方法。 Next, the observation method and measurement method of the tissue will be described.

碳化物之觀察係以掃描型電子顯微鏡進行。在觀察之前，會先將組織觀察用試樣以砂紙進行濕式研磨及以具有1μm之平均粒子大小的鑽石研磨粒予以研磨，將觀察面完工成鏡面後，再以3%硝酸-醇溶液蝕刻組織。 The observation of the carbide was carried out by a scanning electron microscope. Before the observation, the tissue observation sample was first wet-polished with sandpaper and ground with diamond abrasive grains having an average particle size of 1 μm, and the observation surface was finished into a mirror surface, and then etched with a 3% nitric acid-alcohol solution. organization.

觀察倍率係在3000倍中選擇可辨別肥粒鐵與碳化物之倍率。並在所選倍率下在板厚1/4層之30μm×40μm的視野隨機拍攝8張影像。 The observation magnification is selected in 3000 times to distinguish the ratio of ferrite iron to carbide. Eight images were randomly taken at a selected magnification at a field of 30 μm × 40 μm with a thickness of 1/4 layer.

針對所得組織影像，利用以三谷商事股份有限公司製(Win ROOF)為表率的影像解析軟體詳細測定該等區塊 中所含之各碳化物的面積。從各碳化物之面積求出圓等效直徑(=2×√(面積/3.14))，並以其平均值作為碳化物粒徑。 For the obtained tissue images, the blocks are determined in detail using image analysis software based on Win ROOF. The area of each carbide contained in the material. A circle equivalent diameter (= 2 × √ (area / 3.14)) was obtained from the area of each carbide, and the average value thereof was used as the carbide particle diameter.

此外，碳化物之球狀化率係使碳化物近似成等面積且慣性距相等之橢圓後，計算最大長度與其直角方向之最大長度之比小於3者之比率來求算。 Further, the spheroidization rate of the carbide is obtained by approximating the ratio of the maximum length to the maximum length in the direction perpendicular to the longitudinal direction of the ellipse after the carbide is approximately equal to the same area and the inertia distance is equal to three.

至於，為了抑制雜訊所致之測定誤差的影響，粒內及粒界之碳化物中面積在0.01μm²以上之碳化物列為個數計數對象，面積在0.01μm²以下之碳化物則自評估對象除外。 As, in order to suppress the influence of the measurement noise due to the error, the area of the carbide grains and grain boundaries of the object as the counted number of 0.01μm ² or more carbides, the carbide area is 0.01μm ² or less from the Except for evaluation objects.

計數出存在於肥粒鐵粒界上之碳化物個數，並從總碳化物數減去肥粒鐵粒界上之碳化物數，以求出肥粒鐵粒內之碳化物數。根據測得的個數求出粒界之碳化物相對於肥粒鐵粒內之碳化物的個數比率。 The number of carbides present on the ferrite grain boundary is counted, and the number of carbides on the ferrite grain boundary is subtracted from the total number of carbides to determine the number of carbides in the ferrite grains. Based on the measured number, the ratio of the number of carbides in the grain boundary to the carbide in the ferrite grain was determined.

(b)肥粒鐵粒徑為5μm以上且50μm以下：在冷軋鋼板已退火後之組織中，使肥粒鐵粒徑在5μm以上可改善冷加工性。肥粒鐵粒徑若低於5μm，硬度會增加，且於冷加工時容易產生龜裂或裂痕，故而將肥粒鐵粒徑設定為5μm以上。且宜為7μm以上。 (b) The ferrite iron particle diameter is 5 μm or more and 50 μm or less: in the structure after the cold-rolled steel sheet has been annealed, the cold-processability can be improved by making the ferrite-grain iron particle diameter 5 μm or more. When the particle size of the ferrite iron is less than 5 μm, the hardness is increased, and cracks or cracks are likely to occur during cold working, so the particle size of the ferrite iron is set to 5 μm or more. And it is preferably 7 μm or more.

另一方面，若超過50μm，抑制滑動擴散的結晶粒界上之碳化物個數會減少而降低冷加工性，故將肥粒鐵粒徑設定為50μm以下。且宜為37μm以下。 On the other hand, when it exceeds 50 μm, the number of carbides on the crystal grain boundary which suppresses the sliding diffusion is reduced, and the cold workability is lowered. Therefore, the particle size of the ferrite iron is set to 50 μm or less. And it should be 37 μm or less.

肥粒鐵粒徑係已前述研磨方法將試樣之觀察面研磨成鏡面後，以3%硝酸-醇溶液予以蝕刻，再以光學顯微鏡或掃描型電子顯微鏡觀察觀察面之組織，於所拍攝之影 像應用線分法進行測定。 The particle size of the ferrite is the same as the grinding method. After the observation surface of the sample is polished into a mirror surface, it is etched with a 3% nitric acid-alcohol solution, and the observed surface is observed by an optical microscope or a scanning electron microscope. Shadow The measurement is performed by applying line division method.

(c)按JIS Z 2254規格之r值的面內異向性｜△r｜為0.2以下：為鋼板之塑性應變比(r值)的面內異向性｜△r｜係按JIS Z 2254規定之方法測定。從軋延方向起計0°方向、45°方向及90°方向之各方向採取試驗片進行測定，並使用所得r值(0°方向：r₀、45°方向：r₄₅、90°方向：r₉₀)以下述式算出。 (c) In-plane anisotropy of the r value according to JIS Z 2254 specification | Δr| is 0.2 or less: In-plane anisotropy of the plastic strain ratio (r value) of the steel sheet | Δr| is JIS Z 2254 Determined by the method specified. A test piece was taken from each of the 0° direction, the 45° direction, and the 90° direction from the rolling direction, and the obtained r value was used (0° direction: r ₀ , 45° direction: r ₄₅ , 90° direction: r ₉₀ ) was calculated by the following formula.

｜△r｜=(r₀-2r₄₅+r₉₀)/2 |△r|=(r ₀ -2r ₄₅ +r ₉₀ )/2

藉由將鋼板之塑性應變比(r值)的面內異向性｜△r｜設定為0.2以下，可改善冷加工性。｜△r｜一旦超過0.2，抽製加工時零件厚度及凸緣高度會不均勻，故將面內異向性｜△r｜設定為0.2以下。 By setting the in-plane anisotropy |Δr| of the plastic strain ratio (r value) of the steel sheet to 0.2 or less, the cold workability can be improved. When Δr| exceeds 0.2, the thickness of the part and the height of the flange during the drawing process are not uniform, so the in-plane anisotropy |Δr| is set to 0.2 or less.

(d)維氏硬度為100HV以上且150HV以下：將鋼板之維氏硬度設定為100HV以上且150HV以下，可改善冷加工性。維氏硬度若低於100HV，冷加工中便容易產生翹曲，故將維氏硬度設定為100HV以上。且宜為110HV以上。 (d) Vickers hardness: 100 HV or more and 150 HV or less: When the Vickers hardness of the steel sheet is set to 100 HV or more and 150 HV or less, cold workability can be improved. If the Vickers hardness is less than 100 HV, warpage is likely to occur during cold working, so the Vickers hardness is set to 100 HV or more. And it should be 110HV or more.

另一方面，維氏硬度若超過150HV，延性便會降低而容易在冷鍛造時產生內部破裂，故將維氏硬度設定為150HV以下。且宜為146HV以下。 On the other hand, if the Vickers hardness exceeds 150 HV, the ductility is lowered and internal cracking is likely to occur during cold forging, so the Vickers hardness is set to 150 HV or less. And it should be 146HV or less.

(e)對鋼板之結晶粒呈隨機方位分布之試料進行X射線繞射時，相對於該X射線繞射強度，鋼板於1/2板厚部分之{311}<011>方位的X射線繞射強度比為3.0以下：冷鍛造時，除了需抑制碳化物之形態以外，還必須確 保冷鍛造時的抽製成形性。為了提升冷鍛造時的抽製成形性，就必須改善面內異向性｜△r｜等塑性異向性。爰此，必須控制熱軋鋼板中的集合組織。集合組織之評估係採用對與熱軋鋼板1/2板厚部分之板面平行之面進行X射線繞射的解析。 (e) X-ray diffraction of the {311}<011> orientation of the steel plate in the 1/2 plate thickness portion of the X-ray diffraction intensity of the X-ray diffraction of the sample in which the crystal grain of the steel plate is randomly distributed. The injection intensity ratio is 3.0 or less: in cold forging, in addition to suppressing the form of carbide, it must be confirmed. The shape is formed during cold forging. In order to improve the formability during cold forging, it is necessary to improve the plastic anisotropy such as in-plane anisotropy |Δr|. Thus, it is necessary to control the aggregate structure in the hot rolled steel sheet. The evaluation of the collective organization is performed by analyzing the X-ray diffraction of the surface parallel to the plate surface of the 1/2 plate thickness portion of the hot rolled steel sheet.

在熱軋鋼板之一表面起至1/2板厚面為止，以與表面平行的方式進行研磨使1/2板厚面露出後，針對前述1/2板厚面利用X射線繞射進行解析。前述X射線繞射亦可使用Mo管球的X射線繞射。獲得藉反射所得之繞射方位{110}、{220}、{211}、{310}的繞射強度後，根據該等製成結晶方位分布(Orientation Distribution Function：ODF)。 After the surface of one of the hot-rolled steel sheets is 1/2 thick, the surface is parallel to the surface, and the 1/2 thick surface is exposed, and then the X-ray diffraction is analyzed for the 1/2 thick surface. . The X-ray diffraction described above can also be X-ray diffraction using a Mo bulb. After obtaining the diffraction intensities of the diffraction directions {110}, {220}, {211}, and {310} obtained by reflection, an Orientation Distribution Function (ODF) is formed according to the above.

X射線繞射強度比係以由ODF取得之前述1/2板厚面的繞射強度數據與熱軋鋼板之隨機方位的繞射強度數據來決定。具體上，係使用將測定對象之熱軋鋼板的鐵粉末燒結而成的試料或燒結前的前述粉末作為金屬組織不具備集積於特定方位的標準試料，在取得前述1/2板厚面之繞射強度數據時的相同條件下求算繞射強度。至於，得以採取作為前述標準試料的部位並無特別限定，可為熱軋鋼板的任意部位。特定方位的X射線繞射強度比係將由ODF取得之前述1/2板厚面的該特定方向之繞射強度除以前述標準試料之繞射強度後所得的數值。 The X-ray diffraction intensity ratio is determined by the diffraction intensity data of the 1/2 plate thickness surface obtained by the ODF and the diffraction intensity data of the random orientation of the hot rolled steel sheet. Specifically, a sample obtained by sintering iron powder of a hot-rolled steel sheet to be measured or a powder before sintering is used as a metal sample without a standard sample accumulated in a specific orientation, and the 1/2 plate thickness surface is obtained. The diffraction intensity is calculated under the same conditions when the intensity data is shot. The portion to be taken as the standard sample is not particularly limited, and may be any portion of the hot-rolled steel sheet. The X-ray diffraction intensity ratio of a specific orientation is a value obtained by dividing the diffraction intensity of the specific direction of the 1/2 plate thickness surface obtained by the ODF by the diffraction intensity of the aforementioned standard sample.

將前述利用ODF解析所得{311}<011>方位的X射線繞射強度比視為I1，對熱軋時之隨機集合組織而言，該I1必須為3.0以下。且宜為2.5以下。只要獲得I1為3.0以下 的隨機集合組織，便可減低塑性異向性且提升成形性。 The X-ray diffraction intensity ratio of the {311}<011> orientation obtained by the ODF analysis is regarded as I1, and the I1 must be 3.0 or less for the random assembly structure at the time of hot rolling. And it should be 2.5 or less. As long as I1 is below 3.0 The random collection of tissue can reduce plastic anisotropy and improve formability.

接下來說明本發明製造方法。 Next, the production method of the present invention will be described.

本發明製造方法的特徵在於一貫管理熱軋及退火來實施組織控管。將既定成分組成的鋼片予以連續鑄造後，將鋼片加熱供於熱軋延，且在800℃以上且900℃以下之溫度區內結束完工熱軋，並在400℃以上且550℃以下進行捲取，再於酸洗後對該已捲取之熱軋鋼板實施保持在2種溫度區內的2階段步驟型退火；並且，在實施2階段步驟型退火時，(i)係在650℃以上且720℃以下之溫度區內實施保持在3小時以上且60小時以下的第1階段退火，接著在725℃以上且790℃以下之溫度區內實施保持在3小時以上且50小時以下的第2階段退火；其後，(ii)在將冷卻速度設定為1℃/小時以上且30℃/小時以下的條件下冷卻至650℃以下；可製造成形時之冷加工性優異之鋼板。 The manufacturing method of the present invention is characterized by consistently managing hot rolling and annealing to perform tissue control. After continuously casting a steel sheet of a predetermined composition, the steel sheet is heated for hot rolling, and the hot rolling is completed in a temperature range of 800 ° C or higher and 900 ° C or lower, and is performed at 400 ° C or higher and 550 ° C or lower. After coiling, the coiled hot-rolled steel sheet is subjected to a two-stage step type annealing in two temperature zones after pickling; and, in carrying out the two-stage step type annealing, (i) is at 650 ° C In the temperature range of 720 ° C or less, the first-stage annealing is maintained for 3 hours or more and 60 hours or less, and then the temperature is maintained in the temperature range of 725 ° C or higher and 790 ° C or lower for 3 hours or longer and 50 hours or shorter. After the second-stage annealing, (ii) cooling to 650 ° C or lower under the conditions of setting the cooling rate to 1 ° C / hour or more and 30 ° C / hour or less, a steel sheet excellent in cold workability at the time of molding can be produced.

藉由上述熱軋延及退火，可將鋼板組織製成由微細波來鐵及變韌鐵所構成的組織。 By the above-described hot rolling and annealing, the steel sheet structure can be made into a structure composed of fine-wave iron and toughened iron.

以下說明步驟條件。 The step conditions are explained below.

鋼片加熱溫度：1000℃以上且1250℃以下 Steel sheet heating temperature: 1000 ° C or more and 1250 ° C or less

供給於熱軋延的鋼片加熱溫度為1000℃以上且1250℃以下為宜，且加熱時間為0.5小時以上且3小時以下為宜。 The heating temperature of the steel sheet supplied to the hot rolling 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.

加熱溫度若低於1000℃或加熱時間少於0.5小時，會無法解除在鑄造形成的微偏析或巨偏析，而於鋼材內部 殘留Si或Mn等局部濃化的區塊，降低耐衝撃特性，故而加熱溫度在1000℃以上為宜，且加熱時間在0.5小時以上為宜。 If the heating temperature is lower than 1000 ° C or the heating time is less than 0.5 hours, the microsegregation or macro segregation formed in the casting cannot be released, and inside the steel The partially concentrated portion such as Si or Mn remains, and the punching resistance is lowered. Therefore, the heating temperature is preferably 1000 ° C or higher, and the heating time is preferably 0.5 hours or longer.

另一方面，加熱溫度若超過1250℃或加熱時間超過3小時，從鋼片表層的脫碳就會很明顯，而造成在浸碳淬火前之加熱時表層的沃斯田鐵粒異常成長，降低耐衝撃特性，故而加熱溫度在1250℃以下為宜，且加熱時間在3小時以下為宜。 On the other hand, if the heating temperature exceeds 1250 ° C or the heating time exceeds 3 hours, the decarburization from the surface of the steel sheet will be obvious, and the Worthite iron particles in the surface layer will grow abnormally when heated before carbon hardening. The stamping resistance is good, so the heating temperature is preferably below 1250 ° C, and the heating time is preferably less than 3 hours.

完工熱軋溫度：800℃以上且900℃以下 Finished hot rolling temperature: 800 ° C or more and 900 ° C or less

完工熱軋係在800℃以上且900℃以下結束。完工熱軋溫度若低於800℃，鋼片的變形阻力便會增加且軋延負荷明顯上升，此外輥件的磨耗量增大而降低生產性，故將完工熱軋溫度設定為800℃以上。且宜為820℃以上。 The finished hot rolling is completed at 800 ° C or higher and 900 ° C or lower. If the finishing hot rolling temperature is lower than 800 ° C, the deformation resistance of the steel sheet will increase and the rolling load will increase remarkably. In addition, the wear amount of the roller member is increased to reduce the productivity, so the finishing hot rolling temperature is set to 800 ° C or higher. And it should be 820 ° C or more.

另一方面，完工熱軋溫度若超過900℃，在ROT(Run Out Table：輸出輥道)上通板期間會生成很厚的鏽皮而因該鏽皮於鋼板表面產生瑕疵，於冷鍛造及浸碳淬火回火後加諸衝撃荷重時該瑕疵成為起點，發生龜裂而降低耐衝撃特性，故將完工熱軋溫度設定為900℃以下。且宜為880℃以下。 On the other hand, if the finishing hot rolling temperature exceeds 900 ° C, a very thick scale will be formed during the ROT (Run Out Table), and the scale will be generated on the surface of the steel sheet for cold forging. When the carbon-impregnated tempering and tempering load are added, the crucible becomes a starting point, and cracking occurs to lower the punching resistance characteristics, so that the finishing hot rolling temperature is set to 900 ° C or lower. And it should be below 880 °C.

在ROT上的冷卻速度：10℃/秒以上且100℃/秒以下 Cooling rate on ROT: 10 ° C / sec or more and 100 ° C / sec or less

完工熱軋後在ROT上冷卻熱軋鋼板時的冷卻速度以10℃/秒以上且100℃/秒以下為宜。冷卻速度少於10℃/秒時，冷卻途中會生成很厚的鏽皮，進而無法抑制因該鏽皮而在 鋼板表面產生瑕疵的情況，故將冷卻速度設定為10℃/秒以上。且較宜為20℃/秒以上。 The cooling rate at the time of cooling the hot-rolled steel sheet on the ROT after completion of hot rolling is preferably 10 ° C / sec or more and 100 ° C / sec or less. When the cooling rate is less than 10 ° C / sec, a thick scale of scale is formed during cooling, and it is impossible to suppress the scale due to the scale. Since the surface of the steel sheet is crotched, the cooling rate is set to 10 ° C /sec or more. More preferably, it is 20 ° C / sec or more.

另一方面，冷卻速度若超過100℃/秒，從鋼板表層到內部便會在超過100℃/秒之冷卻速度下被冷卻，令鋼板之最表層部被過度冷卻而生成變韌鐵或麻田散鐵等低溫變態組織。 On the other hand, if the cooling rate exceeds 100 ° C / sec, it will be cooled from the surface of the steel sheet to the inside at a cooling rate of more than 100 ° C / sec, so that the outermost layer of the steel sheet is excessively cooled to form a toughened iron or 麻田散Low temperature metamorphic tissue such as iron.

捲取後在將已從100℃冷卻至室溫之熱軋卷料送出時，會於上述低溫變態組織產生微小裂痕，就算在後續的酸洗步驟及冷軋步驟中也很難除去該微小裂痕，而微小裂痕會在冷加工中成為起點使龜裂進展，冷加工性因而降低。所以，冷卻速度在100℃/秒以下為宜。 After the coiling, the hot rolled coil which has been cooled from 100 ° C to room temperature is sent out, and micro cracks are generated in the above-mentioned low temperature metamorphic structure, and it is difficult to remove the micro crack in the subsequent pickling step and cold rolling step. However, the micro cracks will become the starting point in the cold working to cause the crack to progress, and the cold workability is thus lowered. Therefore, the cooling rate is preferably 100 ° C / sec or less.

至於，上述冷卻速度係指完工熱軋後之熱軋鋼板通過無注水區間後，在注水區間開始接受水冷卻的時間點開始，至在ROT上被冷卻到捲取目標溫度之時間點從各注水區間的冷卻設備接收的冷卻能，而非從注水開始點起到被捲取機捲取之溫度為止的平均冷卻速度。 As for the cooling rate, the hot-rolled steel sheet after completion of hot rolling passes through the no-water injection section, and starts at the time when the water-injection section starts to receive water cooling, and starts from the time point when the ROT is cooled to the coiling target temperature. The cooling energy received by the cooling device in the interval, rather than the average cooling rate from the start of the water injection to the temperature taken up by the coiler.

捲取溫度：400℃以上且550℃以下 Coiling temperature: 400 ° C or more and 550 ° C or less

捲取溫度係設定為400℃以上且550℃以下。捲取溫度若低於400℃，捲取前尚未變態的沃斯田鐵會變態成硬質的麻田散鐵，而在送出熱軋卷料時於鋼板表層產生裂痕，降低加工性，故將捲取溫度設定為400℃以上。且宜為430℃以上。 The coiling temperature is set to 400 ° C or more and 550 ° C or less. If the coiling temperature is lower than 400 °C, the Worthite iron which has not been metamorphosed before coiling will be transformed into a hard granulated loose iron, and when the hot rolled coil is sent, cracks will be formed on the surface of the steel sheet to reduce the workability, so the coiling will be taken. The temperature is set to 400 ° C or higher. And it should be 430 ° C or more.

另一方面，捲取溫度若超過550℃，便會生成層狀間隔很大的波來鐵而形成熱穩定性高且厚度很厚的針狀 碳化物，就算於2階段步驟型退火後，針狀碳化物依舊會殘留。該針狀碳化物會作為起點於冷加工時生成龜裂，故將捲取溫度設定為550℃以下。且宜為520℃以下。 On the other hand, if the coiling temperature exceeds 550 ° C, a layer of iron having a large interval is formed to form a needle having a high thermal stability and a thick thickness. Carbide, even after the 2-stage step type annealing, the acicular carbide remains. Since the acicular carbides are used as a starting point to generate cracks during cold working, the coiling temperature is set to 550 ° C or lower. And it should be 520 ° C or less.

對以上述條件所製造之熱軋卷料於酸洗後實施保持在2種溫度區內的2階段步驟型退火。至於，第1階段退火及第2階段退火可任擇為箱型退火或連續退火。藉由2階段步驟型退火，可控制碳化物的穩定性並促進在肥粒鐵粒界的碳化物生成，同時還可提高肥粒鐵粒界上的碳化物之球狀化率。 The hot rolled coil produced under the above conditions was subjected to a two-stage step type annealing maintained in two temperature zones after pickling. As for the first-stage annealing and the second-stage annealing, it may be selected as a box annealing or a continuous annealing. By the two-stage step type annealing, the stability of the carbide can be controlled and the formation of carbides at the ferrite grain boundary can be promoted, and the spheroidization rate of the carbide on the ferrite grain boundary can be improved.

以下針對2階段步驟型退火加以說明。 The following is a description of the 2-stage step type annealing.

在A_C1點以下之溫度區內進行第1階段退火，使碳化物粗大化並同時讓合金元素濃化，而提高碳化物之熱穩定性。其後，升溫至A_C1點以上且A₃點以下之溫度區內，使組織中生成沃斯田鐵。 The first-stage annealing is performed in a temperature region below the A _C1 point to coarsen the carbides while enriching the alloying elements, thereby improving the thermal stability of the carbides. Thereafter, the temperature is raised to a temperature range of A _C1 or more and A ₃ or less to generate Worthite iron in the structure.

其後，藉由徐冷讓沃斯田鐵中變態成肥粒鐵，提高沃斯田鐵中之碳濃度。隨著徐冷進展，碳原子會吸附至殘留在沃斯田鐵中之碳化物上，碳化物與沃斯田鐵便會覆蓋肥粒鐵之粒界，最終便可形成肥粒鐵粒界上存有諸多球狀化碳化物的組織。 Later, by Xu Leng, the Worth iron was transformed into fertilized iron to increase the carbon concentration in the Worthite iron. As the cold progresses, the carbon atoms will adsorb to the carbides remaining in the Worthite iron. The carbides and the Worthite iron will cover the grain boundary of the ferrite grains, and finally the fat iron grains will be formed. The organization of many spheroidized carbides.

保持在A_C1點以上且A₃點以下之溫度區內時，殘留碳化物如果很少，便會在冷卻中生成波來鐵及棒狀碳化物、板狀碳化物。一旦生成該波來鐵及棒狀碳化物、板狀碳化物，鋼板之加工性便會顯著降低，所以在提高鋼板加工性的前提下，增加在A_C1點以上且A₃點以下之溫度區內的 殘留碳化物數便是相當重要的因素。 When it is maintained at a temperature above A _C1 and below A ₃ point, if there are few residual carbides, it will generate ferrite and rod-like carbides and platy carbides during cooling. Once the ferrite and the rod-shaped carbides and the platy carbides are formed, the workability of the steel sheet is remarkably lowered. Therefore, under the premise of improving the workability of the steel sheet, the temperature region above the A _C1 point and below the A ₃ point is increased. The number of residual carbides within is a very important factor.

藉由使用以上述熱軋條件製得的鋼板組織，可在A_C1點以下之溫度下確保碳化物的熱穩定性，故而可伺機增加在A_C1點以上且A₃點以下之溫度區內的殘留碳化物數。 By using the steel sheet structure obtained by the above hot rolling conditions, the thermal stability of the carbide can be ensured at a temperature below the A _C1 point, so that it can be opportunistically increased in the temperature range above the A _C1 point and below the A ₃ point. The number of residual carbides.

以下針對2階段步驟型退火之退火條件加以說明。 The annealing conditions for the two-stage step type annealing will be described below.

第1階段退火 Stage 1 annealing

溫度區：650℃以上且720℃以下 Temperature zone: 650 ° C or more and 720 ° C or less

保持時間：3小時以上且60小時以下 Hold time: 3 hours or more and 60 hours or less

在第1階段退火中，退火溫度係設定為650℃以上且720℃以下。第1階段退火溫度若低於650℃，碳化物之穩定度便不足，而很難在第2階段退火中使沃斯田鐵中殘存有碳化物，故而將第1階段退火溫度設定為650℃以上。且宜為670℃以上。 In the first-stage annealing, the annealing temperature is set to 650 ° C or more and 720 ° C or less. When the first-stage annealing temperature is lower than 650 ° C, the stability of the carbide is insufficient, and it is difficult to cause carbides to remain in the Worthite iron in the second-stage annealing. Therefore, the first-stage annealing temperature is set to 650 ° C or higher. And it should be above 670 °C.

另一方面，第1階段退火溫度一旦超過720℃，在提高碳化物之穩定度之前，沃斯田鐵便會生成，而變得很難控制成所需的組織變化，故將第1階段退火溫度設定為720℃以下。且宜為700℃以下。 On the other hand, once the first-stage annealing temperature exceeds 720 ° C, the Worthite iron is formed before the stability of the carbide is increased, and it becomes difficult to control the desired structural change, so the first-stage annealing is performed. The temperature is set to 720 ° C or less. And it should be below 700 °C.

第1階段之保持時間係設定為3小時以上且60小時以下。保持時間少於3小時時，碳化物之穩定化便不足而很難在第2階段退火時使碳化物殘存，故將第1階段之保持時間設定為3小時以上。另一方面，第1階段之保持時間一旦超過60小時，便無法預期碳化物的穩定度提升，此外生產性還會降低，故將第1階段之保持時間設定為60小時以下。 且宜為55小時以下。 The holding time of the first stage is set to be 3 hours or longer and 60 hours or shorter. When the holding time is less than 3 hours, the stabilization of the carbide is insufficient, and it is difficult to retain the carbide during the second-stage annealing. Therefore, the holding time in the first stage is set to 3 hours or longer. On the other hand, if the holding time of the first stage exceeds 60 hours, the stability of the carbide cannot be expected to be improved, and the productivity is also lowered. Therefore, the holding time of the first stage is set to 60 hours or less. And it should be 55 hours or less.

退火氣體環境並未限定為特定的氣體環境。例如，可任擇為氮95%以上之氮氣環境、氫95%以上之氫氣環境及大氣環境。 The annealing gas environment is not limited to a specific gas environment. For example, it may optionally be a nitrogen atmosphere having a nitrogen content of 95% or more, a hydrogen atmosphere having a hydrogen content of 95% or more, and an atmospheric environment.

第2階段退火 Stage 2 annealing

溫度區：725℃以上且790℃以下 Temperature zone: 725 ° C or more and 790 ° C or less

保持時間：3小時以上且50小時以下 Hold time: 3 hours or more and 50 hours or less

在第2階段退火中，退火溫度係設定為725℃以上且790℃以下。第2階段退火溫度若低於725℃，沃斯田鐵之生成量就很少而降低肥粒鐵粒界上之碳化物個數比率，故將第2階段退火溫度設定為725℃以上。且宜為745℃以上。 In the second-stage annealing, the annealing temperature is set to 725 ° C or more and 790 ° C or less. When the second-stage annealing temperature is lower than 725 ° C, the amount of formation of the Worthite iron is small and the ratio of the number of carbides on the iron grain boundary of the ferrite is lowered, so the second-stage annealing temperature is set to 725 ° C or higher. And it should be 745 ° C or more.

另一方面，第2階段退火溫度若超過790℃，便很難使碳化物殘存於沃斯田鐵中，進而很難控制成所需的組織變化，故將第2階段退火溫度設定為790℃以下。且宜為770℃以下。 On the other hand, if the second-stage annealing temperature exceeds 790 ° C, it is difficult to keep the carbides in the Worthite iron, and it is difficult to control the desired structural change. Therefore, the second-stage annealing temperature is set to 790 ° C or lower. And it should be below 770 °C.

第2階段之保持時間係設定為3小時以上且50小時以下。第2階段之保持時間若少於3小時，沃斯田鐵之生成量便很少，且肥粒鐵粒內之碳化物溶解不足，進而很難增加肥粒鐵粒界上之碳化物個數比率，故將第2階段之保持時間設定為3小時以上。且宜為5小時以上。 The holding time of the second stage is set to be 3 hours or longer and 50 hours or shorter. If the holding time of the second stage is less than 3 hours, the amount of iron in the Worthite iron is small, and the carbides in the ferrite grains are insufficiently dissolved, so that it is difficult to increase the number of carbides on the ferrite grain boundary. Since the ratio is set, the holding time of the second stage is set to 3 hours or more. And it should be more than 5 hours.

另一方面，第2階段之保持時間一旦超過50小時，便很難使碳化物殘存於沃斯田鐵中，故將第2階段之保持時間設定為50小時以下。且宜為46小時以下。 On the other hand, when the holding time of the second stage exceeds 50 hours, it is difficult to keep the carbides in the Vostian iron, so the holding time in the second stage is set to 50 hours or less. And it should be below 46 hours.

退火氣體環境並未設定為特定的氣體環境。例如， 可任擇為氮95%以上之氮氣環境、氫95%以上之氫氣環境及大氣環境。 The annealing gas environment is not set to a specific gas environment. E.g, Optionally, it is a nitrogen atmosphere with a nitrogen content of 95% or more, a hydrogen atmosphere with a hydrogen content of 95% or more, and an atmospheric environment.

在2階段步驟型退火結束後會將熱軋鋼板冷卻，屆時係在1℃/小時以上且30℃/小時以下之冷卻速度下冷卻至650℃。 After the completion of the two-stage step type annealing, the hot-rolled steel sheet is cooled, and then cooled to 650 ° C at a cooling rate of 1 ° C / hour or more and 30 ° C / hour or less.

冷卻至650℃以下之溫度的冷卻速度：1℃/小時以上且30℃/小時以下 Cooling rate of cooling to a temperature below 650 ° C: 1 ° C / hour or more and 30 ° C / hour or less

藉由徐冷控制組織變化的溫度區到650℃為止便足矣，故而控制冷卻至650℃之溫度區的冷卻速度即可。此外，到達650℃以下之溫度後，可不將冷卻速度控制在前述範圍內而冷卻至室溫。 It is sufficient to control the temperature range of the tissue change by chilling to 650 ° C, so that the cooling rate in the temperature zone cooled to 650 ° C can be controlled. Further, after reaching a temperature of 650 ° C or lower, the cooling rate can be controlled to the room temperature without being controlled within the above range.

為了將第2階段退火中所生成之沃斯田鐵徐冷使其變態成肥粒鐵，同時讓碳吸附至沃斯田鐵中所殘存的碳化物上，冷卻速度愈慢愈好。但，冷卻速度低於1℃/小時時，冷卻所需的時間便會增大而降低生產性，故將冷卻速度設定為1℃/小時以上。且宜為5℃/小時。 In order to cold-extrude the Worthite iron generated in the second-stage annealing to be fermented into the ferrite, and to adsorb the carbon to the remaining carbides in the Worthite iron, the cooling rate is as slow as possible. However, when the cooling rate is lower than 1 ° C / hour, the time required for cooling is increased to lower the productivity, so the cooling rate is set to 1 ° C / hour or more. And it is preferably 5 ° C / hour.

另一方面，冷卻速度若超過30℃/小時，沃斯田鐵便會變態成波來鐵，而增加鋼板硬度，降低冷鍛造性，此外浸碳淬火回火後的耐衝撃特性也會降低，故將冷卻速度設定為30℃/小時以下。且宜為26℃/小時以下。 On the other hand, if the cooling rate exceeds 30 ° C / hour, the Worthite iron will be transformed into a wave of iron, which increases the hardness of the steel plate, reduces the cold forgeability, and also reduces the impact resistance characteristics after carbon tempering and tempering. Therefore, the cooling rate is set to 30 ° C / hour or less. And it should be 26 ° C / hour or less.

此外，根據本發明製造方法，可製造下述成形時之冷加工性優異之鋼板：成分組成以質量%計含有C：0.10~0.40%、Si：0.01~0.30%、Mn：0.30~1.00%、P：0.0001~0.020%、S：0.0001~0.010%、Al：0.001~0.10%，且剩 餘部分由Fe及無法避免的雜質所構成；金屬組織實質上為肥粒鐵與球狀化碳化物之組織，其中：(a)肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率超過1；(b)肥粒鐵粒徑為5μm以上且50μm以下；(c)按JIS Z 2254規格之r值的面內異向性｜△r｜為0.2以下；(d)維氏硬度為100HV以上且150HV以下，且截面收縮率為40%以上，並且，對鋼板之結晶粒呈隨機方位分布之試料進行X射線繞射時，相對於該X射線繞射強度，鋼板於1/2板厚部分之{311}<011>方位的X射線繞射強度比為3.0以下。 Further, according to the production method of the present invention, it is possible to produce a steel sheet excellent in cold workability at the time of molding, wherein the component composition contains, by mass%, C: 0.10 to 0.40%, Si: 0.01 to 0.30%, and Mn: 0.30 to 1.00%, P. : 0.0001~0.020%, S: 0.0001~0.010%, Al: 0.001~0.10%, and left The remainder consists of Fe and unavoidable impurities; the metal structure is essentially the structure of ferrite iron and spheroidized carbide, wherein: (a) the number of carbides in the iron grain boundary of the fat grain is relative to the iron grain of the grain The ratio of the number of carbides in the inside exceeds 1; (b) the particle size of the ferrite iron is 5 μm or more and 50 μm or less; (c) the in-plane anisotropy of the r value according to the JIS Z 2254 specification | Δr| is 0.2 or less (d) Vickers hardness is 100 HV or more and 150 HV or less, and the cross-sectional shrinkage ratio is 40% or more, and when X-ray diffraction is performed on a sample in which the crystal grain of the steel sheet has a random orientation distribution, the X-ray diffraction is performed with respect to the X-ray diffraction. Intensity, the X-ray diffraction intensity ratio of the {311}<011> orientation of the steel sheet in the 1/2 plate thickness portion is 3.0 or less.

至於，截面收縮率係以下述式(1)為定義。該值愈大表示局部變形能愈高，鋼板之加工性會隨著式(1)之值增大而增高。 As for the cross-sectional shrinkage ratio, it is defined by the following formula (1). The larger the value, the higher the local deformation energy, and the workability of the steel sheet increases as the value of the formula (1) increases.

截面收縮率(%)=100-(拉伸破斷時的截面積/初始截面積)×100…式(1) Section shrinkage ratio (%) = 100 - (cross-sectional area at the time of tensile fracture / initial cross-sectional area) × 100... Formula (1)

以上，本案發明的特徵在於可藉由軋延控制及軋延後的熱處理成為碳化物(即雪明碳鐵)均勻分散的組織，進而可消去結晶的異向性。所以，本案發明可使鋼板於1/2板厚部分之{311}<011>方位的隨機強度比成為3.0以下。 As described above, the present invention is characterized in that it is possible to form a structure in which carbides (i.e., stellite) are uniformly dispersed by rolling control and heat treatment after rolling, and the anisotropy of crystals can be eliminated. Therefore, in the present invention, the random strength ratio of the {311}<011> orientation of the steel sheet to the 1/2 plate thickness portion can be made 3.0 or less.

實施例 Example

接下來針對實施例加以說明，惟，實施例之水準僅為用以確認本發明之可實施性及效果所採用的條件一例，且本發明不受該一條件例限定。本發明可在不脫離本發明主旨且可達成本發明目的之前提下，採用各種條件。 The examples are described below, but the level of the examples is merely an example of the conditions used to confirm the applicability and effects of the present invention, and the present invention is not limited by the conditions. The present invention may be practiced without departing from the spirit and scope of the invention.

(實施例1) (Example 1)

為了查驗熱軋條件的影響，在表2所示條件下將表1所示成分組成之連續鑄造鑄片(鋼塊)熱軋延，製造出板厚3.0mm的熱軋卷料。至於，表1之「備註」欄中記載為「開發鋼」的鋼種具有包含在本發明之鋼板組成範圍內的組成。此外，表1之「備註」欄中記載為「比較鋼」的鋼種係具有本發明之鋼板組成範圍外之組成者，且於不滿足本發明之鋼板組成條件的成分下畫有底線。 In order to examine the influence of the hot rolling conditions, a continuous casting slab (steel block) having the composition shown in Table 1 was hot rolled under the conditions shown in Table 2 to produce a hot rolled coil having a thickness of 3.0 mm. The steel grade described in the "Remarks" column of Table 1 as "developed steel" has a composition included in the composition range of the steel sheet of the present invention. In addition, the steel type described as "Comparative Steel" in the "Remarks" column of Table 1 has a composition outside the steel sheet composition range of the present invention, and a bottom line is drawn under the component that does not satisfy the steel sheet composition condition of the present invention.

將熱軋卷料酸洗並將熱軋卷料裝入箱型退火爐內，將環境氣體控制成95%氫-5%氮後，從室溫加熱至705℃並保持36小時，使熱軋卷料內之溫度分布均勻，其後再加熱至760℃，並進一步在760℃下保持10小時後，在10℃/小時之冷卻速度下冷卻至650℃，然後爐冷至室溫，製作出特性評估用試樣。至於，試樣之組織係以前述方法測定。 The hot rolled coil is pickled and the hot rolled coil is placed in a box annealing furnace, and the ambient gas is controlled to 95% hydrogen to 5% nitrogen, and then heated from room temperature to 705 ° C for 36 hours to be hot rolled. The temperature distribution in the coil was uniform, and then heated to 760 ° C, and further maintained at 760 ° C for 10 hours, cooled to 650 ° C at a cooling rate of 10 ° C / hour, and then cooled to room temperature to produce Sample for evaluation of characteristics. As for the tissue of the sample, it was measured by the aforementioned method.

[表1] [Table 1]

[表2] [Table 2]

冷加工性係使用附缺口之拉伸試驗與r值之面內異向性來評估。附缺口之拉伸試驗係從板厚3mm之退火原材採取附缺口之拉伸試驗片，沿軋延方向進行拉伸試驗以測定截面收縮率，評估局部的變形能。截面收縮率為40%以上時係評點為「優」。 Cold workability was evaluated using a tensile test with a notch and an in-plane anisotropy of the r value. The tensile test with a notch was carried out by taking a tensile test piece with a notch from an annealed material having a thickness of 3 mm, and performing a tensile test in the rolling direction to measure the cross-sectional shrinkage rate, and to evaluate the local deformation energy. When the cross-sectional shrinkage rate is 40% or more, the evaluation point is "excellent".

此外，r值之面內異向性係在板厚3mm之退火原材按JIS Z 2254規格之r值的面內異向性｜△r｜為0.2以下時，評點為「優」。 In addition, the in-plane anisotropy of the r value is "excellent" when the in-plane anisotropy |Δr| of the r-value of the JIS Z 2254 specification is 0.2 or less in the annealed material having a thickness of 3 mm.

為了測定{311}<011>之X射線繞射強度比(I1)，從各試樣之板厚中央進行利用Mo管球的X射線繞射，進行ODF解析。並根據ODF解析所得結果測定前述I1。 In order to measure the X-ray diffraction intensity ratio (I1) of {311} <011>, X-ray diffraction using a Mo bulb was performed from the center of the thickness of each sample, and ODF analysis was performed. The above I1 was determined based on the results obtained by ODF analysis.

表2中針對所製造出之試樣分別顯示碳化物徑長、肥粒鐵粒徑、維氏硬度、肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率、截面收縮率、{311}<011>之X射線繞射強度比及面內異向性的測定結果。表2之試樣中，於備註欄標示「發明鋼」者係滿足本發明之鋼板主要條件者，於備註欄標示「比較鋼」者係不滿足本發明之鋼板主要條件者。表2中，在不滿足本發明之鋼板主要條件的測定結果及不滿足本發明之鋼板製造方法之主要條件的製造條件下畫有底線。 Table 2 shows the carbide diameter, the ferrite iron particle size, the Vickers hardness, the number of carbides in the ferrite grain boundary, and the number of carbides in the ferrite grain, respectively. The ratio of the ratio, the cross-sectional shrinkage ratio, the X-ray diffraction intensity ratio of {311}<011>, and the in-plane anisotropy. Among the samples in Table 2, those who indicated "inventive steel" in the remark column were the main conditions for the steel sheet of the present invention, and those who indicated "comparative steel" in the remark column were not satisfied with the main conditions of the steel sheet of the present invention. In Table 2, the bottom line is drawn under the measurement conditions which do not satisfy the main conditions of the steel sheet of the present invention and the manufacturing conditions which do not satisfy the main conditions of the steel sheet manufacturing method of the present invention.

如表2所示，發明鋼之B-1、C-1、G-1、H-1、J-1、L-1、P-1、Q-1、S-1、U-1、W-1、X-1、Y-1、Z-1、AA-1、AB-1、AD-1皆為肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率超過1，且維氏硬度為150HV以下。此外，前述發明鋼的截面收縮率皆超過40%，且r值之面內異向性｜△r｜皆為0.2以下，故冷加工性優異。又，前述發明鋼均確認未在鋼板表面生成鏽皮瑕疵，故該等鋼很適合使用於冷加工。 As shown in Table 2, the steels of the invention B-1, C-1, G-1, H-1, J-1, L-1, P-1, Q-1, S-1, U-1, W -1, X-1, Y-1, Z-1, AA-1, AB-1, AD-1 are the number of carbides in the ferrite grain boundary and the number of carbides in the ferrite grain. The ratio is more than 1, and the Vickers hardness is 150 HV or less. Further, in the steel of the invention, the cross-sectional shrinkage ratio is more than 40%, and the in-plane anisotropy |Δr| of the r value is 0.2 or less, so that the cold workability is excellent. Further, all of the above-mentioned inventive steels were confirmed to have no scale defects on the surface of the steel sheet, and therefore these steels are very suitable for use in cold working.

相對於此，比較鋼A-1因為Al之含有率高且A₃點 降低，所以完工熱軋中之再結晶受阻，使｜△r｜惡化，冷加工性低。比較鋼I-1係Mo與Cr很高，完工熱軋中之再結晶受阻，且｜△r｜惡化。比較鋼K-1及N-1係S或Mn之含有率高，於鋼中形成有粗大的MnS，故冷加工性低。比較鋼M-1因為Si之含有率高，硬度增加，所以冷加工性很低。此外，比較鋼M-1還因為A₃點上升，所以完工熱軋中之再結晶受阻，且｜△r｜惡化。 In contrast, the comparative steels A-1 because of a high content of Al and A ₃ point reduction, the recrystallization completion of hot rolling is blocked, so that | △ r | deteriorating cold workability is low. The comparative steel I-1 series Mo and Cr were high, recrystallization in the finish hot rolling was hindered, and |Δr| deteriorated. Comparative steel K-1 and N-1 series S or Mn have a high content rate, and coarse MnS is formed in the steel, so cold workability is low. Compared with steel M-1, since the content of Si is high and the hardness is increased, the cold workability is low. Further, since the comparative steel M-1 was also raised by the A ₃ point, the recrystallization in the completion hot rolling was hindered, and |Δr| deteriorated.

比較鋼O-1因為C很高，碳化物之體積率增加，多量生成成為破壞起點之裂痕且截面收縮率低，所以冷加工性很低。比較鋼D-1係熱軋之完工溫度低，且生產性降低。比較鋼F-1係熱軋之完工溫度高，且於鋼板表面生成鏽皮瑕疵。 Comparing steel O-1, since C is high, the volume fraction of carbide increases, and a large amount of cracks are formed as break points of the fracture origin and the cross-sectional shrinkage rate is low, so cold workability is low. The comparison of the steel D-1 series hot rolling has a low completion temperature and a decrease in productivity. The comparison of the steel F-1 series hot rolling has a high completion temperature and the formation of scale skin on the surface of the steel sheet.

比較鋼R-1與AC-1係熱軋之捲取溫度低，變韌鐵或麻田散鐵等低溫變態組織變多而脆化，於熱軋卷料送出時破裂頻發，生產性降低。比較鋼E-1及T-1係因為熱軋之捲取溫度高，在熱軋組織中生成層狀間隔很厚的波來鐵及熱穩定性高的針狀粗大碳化物，該碳化物在2階段步驟型退火後依舊殘留在鋼板中，所以截面收縮率變低，且冷加工性低。 Compared with the hot rolling of R-1 and AC-1, the coiling temperature of the steel is low, and the low temperature metamorphic structure such as toughened iron or granulated iron is more and more brittle, and the hot rolling coil is frequently ruptured and the productivity is lowered. Comparing steels E-1 and T-1, because of the high coiling temperature of hot rolling, the formation of a thick layer of intercalated iron and a highly thermally stable needle-like coarse carbide in the hot-rolled structure. After the two-stage step type annealing remains in the steel sheet, the cross-sectional shrinkage rate is low and the cold workability is low.

接著，為了查驗退火條件之影響，將表1之成分組成的鋼片(slab)在1240℃下加熱1.8小時後供給於熱軋延，並在890℃下結束完工熱軋後，於ROT上在45℃/秒之冷卻速度下冷卻至520℃，並在510℃下捲取，製造出板厚3.0mm的熱軋卷料，然後在表3所示條件下製作出板厚3.0mm的熱 軋板退火試樣。 Next, in order to examine the influence of the annealing conditions, the steel sheet (slab) of the composition of Table 1 was heated at 1240 ° C for 1.8 hours, and then supplied to the hot rolling, and after finishing the hot rolling at 890 ° C, on the ROT. After cooling to 520 ° C at a cooling rate of 45 ° C / sec, and coiling at 510 ° C, a hot rolled coil having a thickness of 3.0 mm was produced, and then a heat of 3.0 mm was produced under the conditions shown in Table 3. Rolled sheet annealed samples.

針對所製得之各個前述試樣分別以與表2之各發明鋼及各比較鋼相同的方法測定碳化物徑長、肥粒鐵粒徑、維氏硬度、肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率、截面收縮率、{311}<011>之X射線繞射強度比及面內異向性。並將其結果顯示於表3。 For each of the obtained samples, the carbide diameter, the ferrite iron particle diameter, the Vickers hardness, and the carbide grain of the ferrite grain boundary were measured in the same manner as the respective invention steels of Table 2 and the comparative steels. The ratio of the number to the number of carbides in the ferrite grains, the cross-sectional shrinkage ratio, the X-ray diffraction intensity ratio of {311}<011>, and the in-plane anisotropy. The results are shown in Table 3.

[表3] [table 3]

如表3所示，發明鋼之B-2、C-2、D-2、F-2、G-2、L-2、P-2、R-2、S-2、U-2、W-2、X-2、AA-2、AD-2皆係肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率超過1，且維氏硬度為150HV以下。此外，前述發明鋼皆係截面收縮率超過40%且r值的面內異向性｜△r｜為 0.2以下，所以冷加工性優異。 As shown in Table 3, the steels of the invention B-2, C-2, D-2, F-2, G-2, L-2, P-2, R-2, S-2, U-2, W -2, X-2, AA-2, and AD-2 are all based on the ratio of the number of carbides in the iron grain boundary to the number of carbides in the iron particles in the ferrite, and the Vickers hardness is 150 HV or less. . Further, the aforementioned invention steels have an in-plane anisotropy |Δr| of a cross-sectional shrinkage ratio exceeding 40% and an r value. 0.2 or less, it is excellent in cold workability.

相對於此，比較鋼A-2因為Al之含有率高，且A₃點降低，所以完工熱軋中之再結晶受阻，｜△r｜惡化，且冷加工性很低。比較鋼I-2係Mo與Cr很高，完工熱軋中之再結晶受阻，且｜△r｜惡化。比較鋼K-2及N-2係S或Mn之含有率很高，於鋼中形成粗大的MnS且冷加工性降低。比較鋼M-2係Si之含有率很高，硬度增加且冷加工性降低。此外，比較鋼M-2還因為A₃點降低，所以完工熱軋中之再結晶受阻，｜△r｜惡化且冷加工性很低。 In contrast, the comparative steels A-2 because of a high content of Al, and A ₃ point reduction, the recrystallization completion of hot rolling is blocked, | △ r | worsened, and the cold workability is low. The comparative steel I-2 system Mo and Cr were high, recrystallization in the finish hot rolling was hindered, and |Δr| deteriorated. The content ratio of the steel K-2 and the N-2 system S or Mn is high, and coarse MnS is formed in the steel and the cold workability is lowered. The content of Si in the comparative steel M-2 system is high, the hardness is increased, and the cold workability is lowered. Further, in comparison with steel M-2, since the A ₃ point is lowered, recrystallization in the finish hot rolling is hindered, |Δr| is deteriorated and cold workability is low.

比較鋼O-2因為C很高，碳化物之體積率增加，多量生成成為破壞起點之裂痕且截面收縮率低，所以冷加工性很低。 Comparing steel O-2, since C is high, the volume fraction of carbide increases, and a large amount of cracks are formed as a starting point of breakage and a low cross-sectional shrinkage rate, so cold workability is low.

比較鋼AC-2係在2階段步驟型之箱型退火時，第1階段退火之退火溫度很低，Ac1溫度以下之碳化物的粗大化處理不足且碳化物之熱穩定度不夠充分，造成第2階段退火時殘存的碳化物減少，而無法在徐冷後之組織抑制波來鐵變態，且截面收縮率低，所以冷加工性很低。 When the comparative steel AC-2 system is subjected to the box annealing of the two-stage step type, the annealing temperature of the first stage annealing is very low, the coarsening treatment of the carbide below the Ac1 temperature is insufficient, and the thermal stability of the carbide is insufficient, resulting in the first In the two-stage annealing, the amount of carbide remaining is reduced, and the structure after the cold cooling cannot suppress the wave-induced iron metamorphism, and the cross-sectional shrinkage rate is low, so the cold workability is low.

比較鋼T-2係因為在2階段步驟型之箱型退火時，第1階段退火之退火溫度很高，於退火中生成沃斯田鐵，無法提高碳化物之穩定度，造成第2階段退火時殘存的碳化物減少，而無法在徐冷後之組織抑制波來鐵變態，且截面收縮率低，所以冷間鍛加工性很低。 Comparing the steel T-2 system, because the annealing temperature of the first-stage annealing is high in the 2-stage step type box annealing, the Worthite iron is formed during the annealing, and the stability of the carbide cannot be improved, resulting in the second-stage annealing. When the residual carbide is reduced, it is impossible to suppress the wave-induced iron metamorphosis in the structure after the cold, and the cross-sectional shrinkage rate is low, so the cold forging processability is low.

比較鋼Q-2係在2階段步驟型退火時，第1階段退火的保持時間很短，Ac1溫度以下之碳化物的粗大化處理不 足，且碳化物之熱穩定度不夠充分，造成第2階段退火時殘存的碳化物減少，而無法在徐冷後之組織抑制波來鐵變態，且截面收縮率低，所以冷加工性很低。比較鋼AB-2係在2階段步驟型之箱型退火時，第1階段退火之保持時間很長，故生產性很低。 When the comparative steel Q-2 system is subjected to the two-stage step type annealing, the holding time of the first stage annealing is short, and the coarsening treatment of the carbide below the Ac1 temperature is not The foot and the thermal stability of the carbide are insufficient, resulting in a decrease in the amount of carbide remaining during the second-stage annealing, and it is impossible to suppress the wave-induced iron metamorphism in the structure after the cold cooling, and the cross-sectional shrinkage rate is low, so the cold workability is low. When the comparative steel AB-2 system is subjected to the box-type annealing of the two-stage step type, the holding time of the first-stage annealing is long, so the productivity is low.

比較鋼Z-2係在2階段步驟型之箱型退火時，第2階段退火時的退火溫度很低，沃斯田鐵之生成量很少而無法增加粒界的碳化物個數比率，故冷加工性很低。比較鋼J-2係在2階段步驟型退火時，第2階段退火時的退火溫度很高，促進碳化物溶解，減少殘存之碳化物，而無法在徐冷後之組織抑制波來鐵變態，維氏硬度太高且截面收縮率低，故而冷鍛加工性低。 When the comparative steel Z-2 system is subjected to the box-type annealing in the two-stage step type, the annealing temperature in the second-stage annealing is very low, and the amount of formation of the Worthite iron is small, and the number of carbides in the grain boundary cannot be increased, so Cold workability is very low. When the comparative steel J-2 system is subjected to the two-stage step type annealing, the annealing temperature in the second stage annealing is high, the carbide dissolution is promoted, and the remaining carbides are reduced, and the structure of the wave after the cold is not suppressed. The Vickers hardness is too high and the cross-sectional shrinkage rate is low, so the cold forging processability is low.

比較鋼H-2係在2階段步驟型退火時，第2階段退火時的退火溫度低，沃斯田鐵之生成量很少而無法增加粒界的碳化物個數比率，故冷加工性低。比較鋼Y-2係在2階段步驟型退火時，第2階段退火時的保持時間很長，促進碳化物溶解，減少殘存之碳化物，而無法在徐冷後之組織抑制波來鐵變態且截面收縮率低，所以冷鍛加工性低。比較鋼E-2係在2階段步驟型退火時從第2階段退火到650℃的冷卻速度太速，於冷卻時引發波來鐵變態，維氏硬度太高且截面收縮率低，所以冷加工性低。 When the comparative steel H-2 system is subjected to the two-stage step type annealing, the annealing temperature in the second-stage annealing is low, and the amount of formation of the Worthite iron is small, and the ratio of the number of carbides at the grain boundary cannot be increased, so the cold workability is low. When the comparative steel Y-2 system is subjected to the two-stage step type annealing, the holding time in the second stage annealing is long, the carbide dissolution is promoted, and the remaining carbides are reduced, and the structure of the wave after the cold cooling cannot be suppressed. Since the cross-sectional shrinkage rate is low, the cold forging processability is low. Compared with the steel E-2 system, the cooling rate from the second stage annealing to 650 °C is too fast in the two-stage step type annealing, and the wave iron transformation is caused during cooling. The Vickers hardness is too high and the section shrinkage rate is low, so cold workability low.

比較鋼A-1、D-1、I-1、M-1、A-2及I-2皆係{311}<011>之X射線繞射強度比超過3.0。該等比較鋼的面內異向性｜△r｜超過0.2，所以冷加工性低。如此一來，便可藉 由對與熱軋鋼板1/2板厚部分之板面平行之面進行X射線繞射之解析，於冷加工前判定出作為冷加工對象之熱軋鋼板的面內異向性｜△r｜等塑性異向性的程度或冷加工性之優劣。 The comparative steels A-1, D-1, I-1, M-1, A-2, and I-2 are all X311 ray diffraction intensity ratios of {311}<011> exceeding 3.0. Since the in-plane anisotropy |Δr| of these comparative steels exceeds 0.2, cold workability is low. In this way, you can borrow The X-ray diffraction is performed on the surface parallel to the plate surface of the 1/2 plate thickness portion of the hot-rolled steel sheet, and the in-plane anisotropy of the hot-rolled steel sheet to be cold-worked is determined before the cold working. The degree of anisotropy or the cold workability.

產業上之可利用性 Industrial availability

如前述，根據本發明，可提供製造成形時之冷加工性優異之鋼板。本發明之鋼板係適合作為經過穿孔、彎曲、加壓加工等加工步驟而製造之汽車用構件、刃物及其它機械構件之素材的鋼板，因此本發明於產業上之可利用性相當高。 As described above, according to the present invention, it is possible to provide a steel sheet excellent in cold workability at the time of molding. The steel sheet according to the present invention is suitable as a steel sheet of a member for an automobile, a blade, and other mechanical members which are produced by a processing step such as punching, bending, or press working. Therefore, the present invention is highly industrially usable.

Claims (4)

一種成形時之冷加工性優異之鋼板，特徵在於其成分組成以質量%計含有：C：0.10~0.40%、Si：0.01~0.30%、Mn：0.30~1.00%、P：0.0001~0.020%、S：0.0001~0.010%、及Al：0.001~0.10%，且剩餘部分由Fe及無法避免的雜質所構成；並且，(a)肥粒鐵粒界之碳化物個數相對於肥粒鐵粒內之碳化物個數的比率超過1；(b)肥粒鐵粒徑為5μm以上且50μm以下；(c)按JIS Z 2254規格之r值的面內異向性｜△r｜為0.2以下；(d)維氏硬度為100HV以上且150HV以下；(e)對鋼板之結晶粒呈隨機方位分布之試料進行X射線繞射時，相對於該X射線繞射強度，鋼板於1/2板厚部分之{311}<011>方位的X射線繞射強度比為3.0以下。 A steel sheet excellent in cold workability at the time of molding, characterized in that its component composition is contained in mass%: C: 0.10 to 0.40%, Si: 0.01 to 0.30%, Mn: 0.30 to 1.00%, P: 0.0001 to 0.020%, S : 0.0001 to 0.010%, and Al: 0.001 to 0.10%, and the remainder is composed of Fe and unavoidable impurities; and (a) the number of carbides in the iron grain boundary of the fat grain is relative to that in the ferrite grain The ratio of the number of carbides exceeds 1; (b) the particle size of the ferrite is 5 μm or more and 50 μm or less; (c) the in-plane anisotropy of the r value according to JIS Z 2254 is Δr| is 0.2 or less; d) Vickers hardness is 100 HV or more and 150 HV or less; (e) When X-ray diffraction is performed on a sample in which the crystal grains of the steel sheet are randomly distributed, the steel sheet is in the 1/2 plate thickness portion with respect to the X-ray diffraction intensity. The X-ray diffraction intensity ratio of the {311}<011> orientation is 3.0 or less. 如請求項1之成形時之冷加工性優異之鋼板，其中前述成分組成以質量%計更含有下述元素中之1種或2種以上： N：0.0001~0.010%、O：0.0001~0.020%、Cr：0.001~0.50%、Mo：0.001~0.10%、Nb：0.001~0.10%、V：0.001~0.10%、Cu：0.001~0.10%、W：0.001~0.10%、Ta：0.001~0.10%、Ni：0.001~0.10%、Sn：0.001~0.050%、Sb：0.001~0.050%、As：0.001~0.050%、Mg：0.0001~0.050%、Ca：0.001~0.050%、Y：0.001~0.050%、Zr：0.001~0.050%、La：0.001~0.050%、及Ce：0.001~0.050%。 The steel sheet which is excellent in cold workability at the time of the formation of the request item 1, wherein the component composition further contains one or more of the following elements in mass %: N: 0.0001 to 0.010%, O: 0.0001 to 0.020%, Cr: 0.001 to 0.50%, Mo: 0.001 to 0.10%, Nb: 0.001 to 0.10%, V: 0.001 to 0.10%, Cu: 0.001 to 0.10%, W : 0.001 to 0.10%, Ta: 0.001 to 0.10%, Ni: 0.001 to 0.10%, Sn: 0.001 to 0.050%, Sb: 0.001 to 0.050%, As: 0.001 to 0.050%, Mg: 0.0001 to 0.050%, Ca: 0.001 to 0.050%, Y: 0.001 to 0.050%, Zr: 0.001 to 0.050%, La: 0.001 to 0.050%, and Ce: 0.001 to 0.050%. 一種成形時之冷加工性優異之鋼板的製造方法，係製造如請求項1或2之成形時之冷加工性優異之鋼板，該製造方法之特徵在於：將具有如請求項1或2之成分組成的鋼片加熱並供於熱軋延，且在800℃以上且900℃以下之溫度區內結束 完工熱軋，並在400℃以上且550℃以下進行捲取，再於酸洗後對該已捲取之熱軋鋼板實施保持在2種溫度區內的2階段步驟型退火；並且，在實施前述2階段步驟型退火時，(i)係在650℃以上且720℃以下之溫度區內實施保持在3小時以上且60小時以下的第1階段退火，接著在725℃以上且790℃以下之溫度區內實施保持在3小時以上且50小時以下的第2階段退火；其後，(ii)在冷卻速度1℃/小時以上且30℃/小時以下的條件下冷卻至650℃。 A method for producing a steel sheet excellent in cold workability at the time of molding, which is a steel sheet excellent in cold workability at the time of molding of claim 1 or 2, which is characterized in that it has a composition as claimed in claim 1 or 2. The steel sheet is heated and supplied for hot rolling, and ends in a temperature range of 800 ° C or higher and 900 ° C or lower. Finishing hot rolling, and coiling at 400 ° C or more and 550 ° C or less, and then performing the 2-stage step type annealing of the coiled hot-rolled steel sheet in the two temperature zones after pickling; and In the two-stage step type annealing, (i) is performed in a temperature range of 650 ° C or more and 720 ° C or less in a first-stage annealing maintained for 3 hours or more and 60 hours or less, followed by 725 ° C or more and 790 ° C or less. The second temperature annealing is maintained in the temperature zone for 3 hours or more and 50 hours or less; thereafter, (ii) cooling to 650 ° C under the conditions of a cooling rate of 1 ° C / hour or more and 30 ° C / hour or less. 如請求項3之鋼板的製造方法，其中鋼板的截面收縮率為40%以上。 The method for producing a steel sheet according to claim 3, wherein the steel sheet has a cross-sectional shrinkage ratio of 40% or more.