TW201829791A - Steel plate having a predetermined chemical composition and excellent elongation and hole expandability - Google Patents
Steel plate having a predetermined chemical composition and excellent elongation and hole expandability Download PDFInfo
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本發明是有關一種適用於汽車零件之鋼板。The present invention relates to a steel sheet suitable for use in automotive parts.
為了抑制源自於汽車之二氧化碳廢氣的排出量,使用了高強度鋼板之汽車車體持續向輕量化發展。又,為了確保搭乘者之安全性,也多半於車體使用高強度鋼板。為了使車體朝向更輕量化發展,更進一步的強度提高是重要的。其中一方面,視車體之零件而異,而被要求有優良的成形性。例如,對骨架系供零件用之高強度鋼板,就被要求有優良的伸長性及擴孔性。In order to suppress the amount of carbon dioxide exhaust gas derived from automobiles, the automobile body using high-strength steel sheets continues to be lighter. In addition, in order to ensure the safety of the rider, most of the high-strength steel sheets are used in the vehicle body. In order to make the car body more lightweight, further strength improvement is important. On the one hand, depending on the parts of the vehicle body, it is required to have excellent formability. For example, high-strength steel sheets for parts for skeletons are required to have excellent elongation and hole expandability.
但是,強度提高與成形性提高二者兼得是困難的。However, both strength improvement and formability improvement are both difficult.
例如,專利文獻1中記載為了強度及加工性兼得,控制由肥粒鐵及麻田散鐵構成之鋼板的奈米硬度分布。專利文獻1中,就加工性之評價,亦記載有模擬了伸長凸緣成形之側向彎曲試驗。但是,並沒有有關彎曲性之記載。For example, Patent Document 1 describes controlling the nano hardness distribution of a steel sheet composed of ferrite iron and 麻田散铁 for both strength and workability. In Patent Document 1, a lateral bending test simulating the formation of an elongated flange is also described for the evaluation of workability. However, there is no record of bending.
專利文獻2中記載之鋼板是以麻田散鐵組織作為主相,強度及彎曲性雖然優異,但缺少延展性,而在壓製成形時可能發生裂痕。The steel sheet described in Patent Document 2 is a main phase of the granulated iron structure, and is excellent in strength and flexibility, but lacks ductility, and may be cracked during press forming.
延展性優良鋼板,存在有,例如,專利文獻3中記載之含有殘留沃斯田鐵之TRIP(Transformation Induced Plasticity)鋼。在TRIP鋼中,在成形時會使得鋼中存在之殘留沃斯田鐵變態成為麻田散鐵,藉此方式得到優良延展性。但是,成形時,由殘留沃斯田鐵變態而得到麻田散鐵是硬質性,容易成為龜裂之起點,也是擴孔性或彎曲性劣化的原因。 [先前技術文獻] [專利文獻]For example, the TRIP (Transformation Induced Plasticity) steel containing the residual Worth iron is described in Patent Document 3. In the TRIP steel, the residual Worstian iron present in the steel is metamorphosed into the granulated iron during the forming, whereby excellent ductility is obtained. However, at the time of molding, the vestibular iron is metamorphosed by the residual Worthite iron, which is hard, and is likely to be a starting point of cracking, and is also a cause of deterioration of hole expandability or bendability. [Prior Technical Literature] [Patent Literature]
[專利文獻1]:日本特開2011-144409號公報 [專利文獻2]:日本專利特公平7-74412號公報 [專利文獻3]:日本特開10-130776號公報[Patent Document 1] Japanese Patent Publication No. Hei 7-74412 (Patent Document 3): JP-A-H10-130776
[發明欲解決之課題] 本發明之目的係在提供一種具有高強度且可以獲得優良的伸長性及擴孔性的鋼板。 [用以解決課題之手段][Problem to be Solved by the Invention] An object of the present invention is to provide a steel sheet which has high strength and which can obtain excellent elongation and hole expandability. [Means to solve the problem]
為了解決上述課題,本發明者等進行專心研討。其結果判斷出下述情事是重要的:肥粒鐵之面積分率為30%~50%、麻田散鐵之面積分率為30%~55%、粒狀變韌鐵之面積分率為5%~20%、變韌鐵之面積分率為低於35%、殘留沃斯田鐵及波來鐵之面積分率合計在10%以下。回火麻田散鐵是被包含在麻田散鐵中。粒狀變韌鐵主要是由差排密度低之變韌肥粒鐵所構成,且幾乎不含有硬質雪明碳鐵,因此,其是比肥粒鐵更硬,比變韌鐵及麻田散鐵為柔軟。據此,粒狀變韌鐵表現出比變韌鐵及麻田散鐵鐵更為優異的性。再者,粒狀變韌鐵是比肥粒鐵硬,但比變韌鐵及麻田散鐵軟,因此,擴孔加工之際,可抑制自肥粒鐵與麻田散鐵或變韌鐵之界面發生有空隙。In order to solve the above problems, the inventors of the present invention conducted intensive studies. As a result, it is judged that the following is important: the area ratio of fertilized iron is 30% to 50%, the area of Matian iron is 30% to 55%, and the area of granular toughened iron is 5 %~20%, the area ratio of toughened iron is less than 35%, and the area ratio of residual Worthite and Borne iron is less than 10%. The tempered Ma Tian loose iron is included in the Ma Tian loose iron. Granular toughening iron is mainly composed of tough ferrite iron with low difference density and hardly contains hard ferritic carbon iron. Therefore, it is harder than fertilized iron, and is more tough than iron and granulated iron. It is soft. Accordingly, the granular toughened iron exhibits superiority to the toughened iron and the granitic iron. Furthermore, the granular toughened iron is harder than the ferrite, but softer than the toughened iron and the granulated iron. Therefore, at the time of reaming, the interface between the self-fertilized iron and the granulated iron or the toughened iron can be inhibited. There are gaps.
本案之發明者們根據這些知識見解更進行了深入的研究,因而想到以下所示之發明各種態樣。The inventors of the present invention conducted in-depth research based on these knowledge findings, and thus thought of various aspects of the invention shown below.
(1)一種鋼板,其特徵在於:其以質量%計具有以下表示之化學組成: C:0.09%~0.15%, Si:0.2%~2.5%, Al:0.01%~1.00%, Mn:1.0%~3.0%, P:0.02%以下, S:0.01%以下, N:0.007%以下, O:0.006%以下, Cr:0.00%~1.00%、 Mo:0.00%~1.00%, B:0.0000%~0.010%, Nb:0.000%~0.30%, Ti:0.000%~0.30%, Ni:0.00%~1.00%, Cu:0.00%~1.00%, V:0.000%~0.50%, Mg:0.0000%~0.04%, REM:0.0000%~0.04%,及 剩餘部分:Fe及雜質;並且 該鋼板以面積分率計具有以下表示之金屬組織: 肥粒鐵:30%~50%, 粒狀變韌鐵:5%~20%, 麻田散鐵:30%~55%, 變韌鐵:低於35%,及 殘留沃斯田鐵及波來鐵:合計在10%以下。(1) A steel sheet characterized by having the chemical composition represented by the following: C: 0.09% to 0.15%, Si: 0.2% to 2.5%, Al: 0.01% to 1.00%, Mn: 1.0% ~3.0%, P: 0.02% or less, S: 0.01% or less, N: 0.007% or less, O: 0.006% or less, Cr: 0.00% to 1.00%, Mo: 0.00% to 1.00%, B: 0.0000% to 0.010 %, Nb: 0.000%~0.30%, Ti: 0.000%~0.30%, Ni: 0.00%~1.00%, Cu: 0.00%~1.00%, V: 0.000%~0.50%, Mg: 0.0000%~0.04%, REM: 0.0000%~0.04%, and the remainder: Fe and impurities; and the steel plate has the following metal structure in terms of area fraction: ferrite iron: 30%~50%, granular toughening iron: 5%~ 20%, Ma Tian loose iron: 30% ~ 55%, toughened iron: less than 35%, and residual Worthfield iron and Borne iron: a total of less than 10%.
(2)如(1)所記載之鋼板,其特徵在於: 拉伸強度在1180MPa以上, 伸長性在10%以上,且 擴孔值在20%以上。(2) The steel sheet according to (1), which has a tensile strength of 1180 MPa or more, an elongation of 10% or more, and a hole expansion value of 20% or more.
(3)如(1)或2所記載之鋼板,其特徵在於:令厚度為t( mm) 時之VDA彎角是在「7.69t2 -38.4t+109」以上。(3) The steel sheet according to (1) or 2, wherein the VDA angle when the thickness is t ( mm ) is "7.69t 2 - 38.4t + 109" or more.
(4)如(1)~(3)中任一項所記載之鋼板,其特徵在於:於表面具有熔融鍍鋅層。(4) The steel sheet according to any one of (1) to (3) which has a hot-dip galvanized layer on the surface.
(5) 如(1)~(3)中任一項所記載之鋼板,其特徵在於:於表面具有合金化熔融鍍鋅層。(5) The steel sheet according to any one of (1) to (3) which has an alloyed hot-dip galvanized layer on the surface.
[發明效果] 依據本發明,由於在金屬組織中含有適當面積分率的粒狀變韌鐵等,故可獲得高強度,優良伸長性及擴孔性。[Effect of the Invention] According to the present invention, since a granular toughened iron or the like having an appropriate area fraction is contained in a metal structure, high strength, excellent elongation, and hole expandability can be obtained.
較佳實施例之詳細說明 以下,就本發明實施形態作說明。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described.
首先,說明本實施形態之鋼板的金屬組織。詳細係如後所述者,但本發明實施形態之鋼板是經過鋼之熱軋、冷軋、退火、回火等而被製造的。因此,鋼板之金屬組織不僅考量了鋼板之特性,也考量了其等處理中的相變態等。本實施形態之鋼板具有下述金屬組織:面積分率計,肥粒鐵:30%~50%、粒狀變韌鐵:5%~20%、麻田散鐵:30%~55%、變韌鐵:低於35%,且殘留沃斯田鐵及波來鐵:合計在10%以下。First, the metal structure of the steel sheet according to the embodiment will be described. The details are as described later, but the steel sheet according to the embodiment of the present invention is produced by hot rolling, cold rolling, annealing, tempering, or the like of steel. Therefore, the metal structure of the steel sheet not only considers the characteristics of the steel sheet, but also considers the phase transition state in the treatment. The steel sheet of the present embodiment has the following metal structure: area fraction meter, ferrite iron: 30% to 50%, granular toughened iron: 5% to 20%, 麻田散铁: 30% to 55%, toughening Iron: less than 35%, and residual Worthite and Borne: total below 10%.
(肥粒鐵:30%~50%) 肥粒鐵由於是軟質組織,故容易變形,有助於增高伸長性。肥粒鐵亦有助於由沃斯田鐵變成粒狀變韌鐵之相變態。肥粒鐵之面積分率若低於30%,則無得到足夠的拉伸性。再者,適當的粒狀變韌鐵面積分率是無法得到的。據此,肥粒鐵之面積分率是在30%以上,較佳是在35%以上。一方面,肥粒鐵面積分率若超過50%,要得到在1180MPa以上之拉伸強度是困難的。據此,肥粒鐵之面積分率是在50%以下,較佳是在45%以下。(Ferrous iron: 30%~50%) Because of its soft texture, ferrite is easy to deform and contribute to increased elongation. Fertilizer iron also contributes to the phase change of the ferrite iron into a grainy tough iron. If the area fraction of the ferrite iron is less than 30%, sufficient stretchability is not obtained. Furthermore, an appropriate granular tough iron area fraction is not available. Accordingly, the area fraction of the ferrite iron is 30% or more, preferably 35% or more. On the one hand, if the ferrite iron area fraction exceeds 50%, it is difficult to obtain a tensile strength of 1180 MPa or more. Accordingly, the area fraction of the ferrite iron is below 50%, preferably below 45%.
(粒狀變韌鐵:5%~20%) 粒狀變韌鐵主要是由約1013 m/m3 等級之差排密度低的變韌肥粒鐵所構成,且幾乎不含有硬質雪明碳鐵,因此,其是比肥粒鐵更硬,比變韌鐵為柔軟。因此,粒狀變韌鐵表現出比變韌鐵更為優異的伸長性。粒狀變韌鐵是比肥粒鐵硬,但比變韌鐵及麻田散鐵軟,因此,擴孔加工之際,可抑制自肥粒鐵與麻田散鐵之界面發生有空隙以及自肥粒鐵與變韌鐵之界面發生有空隙。粒狀變韌鐵之面積分率低於5%,就無法獲充分獲得此等效果。據此,粒狀變韌鐵之面積分率是在5%以上,較佳是在10%以上。一方面,粒狀變韌鐵之面積分率若超過20%,就無法充分獲得麻田散鐵,且得到1180MPa以上之拉伸強度則是困難的。據此,粒狀變韌鐵之面積分率是在20%以下,較佳是在15%以下。(granular toughening iron: 5%~20%) Granular toughening iron is mainly composed of tough ferrite iron with a low difference in density of about 10 13 m/m 3 and hardly contains hard snow Carbon iron, therefore, is harder than fat iron and softer than toughened iron. Therefore, the granular toughened iron exhibits superior elongation than the toughened iron. Granular toughening iron is harder than fat iron, but softer than toughened iron and granulated iron. Therefore, when reaming is processed, it can suppress the gap between the self-fertilizer iron and the granulated iron and the self-fertilizer iron and There is a gap in the interface of the toughened iron. If the area fraction of granular toughened iron is less than 5%, such effects cannot be fully obtained. Accordingly, the area fraction of the granular toughened iron is 5% or more, preferably 10% or more. On the other hand, if the area fraction of the granular toughened iron exceeds 20%, the granulated iron cannot be sufficiently obtained, and it is difficult to obtain a tensile strength of 1180 MPa or more. Accordingly, the area fraction of the granular toughened iron is 20% or less, preferably 15% or less.
(麻田散鐵:30%~55%) 麻田散鐵因差排密度高且為硬質組織,故有助於提升拉伸強度。麻田散鐵之面積分率若低於30%,就無法得到1180MPa以上之拉伸強度。據此,麻田散鐵之面積分率是在30%以上,較佳是在35%以上。一方面,麻田散鐵之面積分率若超過55%超,就無法得到足夠的伸長性。據此,麻田散鐵之面積分率是在55%以下,較佳是在50%以下。淬火狀態下麻田散鐵及回火麻田散鐵是屬於麻田散鐵。即,麻田散鐵之面積分率是淬火麻田散鐵之面積分率及回火麻田散鐵之面積分率的合計。得到回火麻田散鐵之方法並不受到限定,回火麻田散鐵可以是冷卻中自動回火所得到者,也可以是連續退火後之回火熱處理所得到者。(Ma Tian loose iron: 30% ~ 55%) Ma Tian loose iron is high in density and is hard tissue, so it helps to increase tensile strength. If the area fraction of the granulated iron is less than 30%, the tensile strength of 1180 MPa or more cannot be obtained. Accordingly, the area fraction of the granulated iron is more than 30%, preferably more than 35%. On the one hand, if the area fraction of the Ma Tian loose iron exceeds 55%, it will not be able to obtain sufficient elongation. Accordingly, the area fraction of the granulated iron is below 55%, preferably below 50%. The quarrying iron and the tempered granulated iron in the quenching state belong to the granulated iron. That is, the area fraction of the granulated iron is the sum of the area fraction of the quenched granulated iron and the area fraction of the tempered granulated iron. The method of obtaining the tempered granulated iron is not limited, and the tempered granulated iron may be obtained by automatic tempering during cooling, or may be obtained by tempering heat treatment after continuous annealing.
(變韌鐵:低於35%) 變韌鐵主要是由約1.0×1014 m/m3 之差排密度高之變韌肥粒鐵及硬質雪明碳鐵所構成,且有助於提升拉伸強度。但是,變韌鐵之面積分率若在35%以上,則比變韌鐵更能助於提高拉伸強度之麻田散鐵面積分率就不足,故要得到1180MPa以上拉伸強度是困難的。因此,變韌鐵之面積分率設在低於35%。(toughened iron: less than 35%) The toughened iron is mainly composed of toughened ferrite iron and hard swarf carbon iron with a high density of about 1.0×10 14 m/m 3 , and helps to improve Tensile Strength. However, if the area fraction of the toughened iron is 35% or more, the area fraction of the granulated iron which is more effective than the toughened iron to improve the tensile strength is insufficient, so it is difficult to obtain a tensile strength of 1180 MPa or more. Therefore, the area fraction of the toughened iron is set to be less than 35%.
(殘留沃斯田鐵及波來鐵:合計在10%以下) 殘留沃斯田鐵在變形中加工引起變態而朝向麻田散鐵變態,因而具有優異的加工硬化及高的均勻伸長性。但是,加工誘發而得之麻田散鐵會使得擴孔性明顯地劣化。波來鐵由於含有硬質雪明碳鐵,在擴孔加工之際,會變成空隙發生之起點,擴孔性劣化。特別是,殘留沃斯田鐵及波來鐵之面積分率合計若超過10%,擴孔性明顯劣化。因此,殘留沃斯田鐵及波來鐵之面積分率下設在10%以下。(Residual Worthite iron and Wolla iron: a total of 10% or less) Residual Worth iron is deformed to cause metamorphosis and metamorphosis toward the granulated iron, and thus has excellent work hardening and high uniform elongation. However, the processing-induced granulated iron can significantly deteriorate the hole expandability. Since the Bora iron contains hard ferritic carbon iron, it becomes a starting point of void generation at the time of reaming processing, and the hole expandability is deteriorated. In particular, if the total area fraction of the remaining Worthite iron and the Borne iron exceeds 10%, the hole expandability is remarkably deteriorated. Therefore, the area ratio of the remaining Worthfield iron and the Bora iron is set below 10%.
肥粒鐵、粒狀變韌鐵、麻田散鐵、變韌鐵、殘留沃斯田鐵及波來鐵之鑑別及特定出面積分率可利用,例如,電子線背散射繞射(electron back scattering diffraction:EBSD)法,X線測定,或是掃描式電子顯微鏡(scanning electron microscope:SEM)來觀察。進行SEM觀察時,例如,使用硝太(Nital)試劑或里培拉(LePera)液腐蝕試料,以1000倍~50000倍之倍率觀察平行於在軋壓方向及厚度方向之截面及/或垂直於軋壓方向之截面。鋼板之金屬組織可以由鋼材表面起算之深度為該鋼板厚度1/4左右之區域的金屬組織作為代表。例如,鋼板之厚度若為1.2mm,則可用由鋼材表面起算之深度為0.3mm左右之區域的金屬組織作為代表。Identification of ferrite iron, granular toughening iron, granulated iron, toughened iron, residual Worth iron and Borne iron, and specific area fractions, for example, electron back scattering Diffraction: EBSD) method, X-ray measurement, or scanning electron microscope (SEM). For SEM observation, for example, a sample is etched using a Nital reagent or a LePera solution, and a cross section parallel to the rolling direction and the thickness direction and/or perpendicular to the sample is observed at a magnification of 1000 to 50,000 times. The section of the rolling direction. The metal structure of the steel sheet can be represented by a metal structure in a region where the depth of the steel material is about 1/4 of the thickness of the steel sheet. For example, if the thickness of the steel sheet is 1.2 mm, a metal structure in a region having a depth of about 0.3 mm from the surface of the steel material can be used as a representative.
肥粒鐵之面積分率,例如,可使用SEM觀察得到之電子通道化對比圖像來特定出。電子通道化對比圖像是以結晶粒內結晶方位差作為對比的差來表示,電子通道化對比圖像中對比均一之部分是肥粒鐵。在此方法中,例如,由鋼材表面起算之深度為該鋼板厚度之1/8至3/8之區域作為觀察對象。The area fraction of the ferrite iron can be specified, for example, using an electronically channelized contrast image obtained by SEM observation. The electron channel contrast image is represented by the difference in the crystal orientation difference in the crystal grain as the contrast difference. The comparative uniform part in the electron channel contrast image is the ferrite iron. In this method, for example, a region from the surface of the steel material having a depth of 1/8 to 3/8 of the thickness of the steel sheet is taken as an observation object.
殘留沃斯田鐵之面積分率可以,例如,用X線測定來特定出。在此方法中,例如,由鋼材表面起直到之該鋼板厚度之1/4為止之部分利用機械研磨及化學研磨予以除去,使用MoKα線作為特性X線。因此,利用下式,由體心立方晶格(bcc)相之(200)及(211)以及面心立方晶格(fcc)相之(200)、(220)及(311)之繞射峰積分強度比,算出殘留沃斯田鐵之面積分率。 Sγ=(I200f +I220f +I311f )/(I200b +I211b )×100 (Sγ為殘留沃斯田鐵之面積分率:I200f 、I220f 、I311f 分別表示fcc相之(200)、(220)、(311)之繞射峰強度;I200b 、I211b 分別表示bcc相之(200)、(211)之繞射峰強度。)The area fraction of the residual Worthite iron can be specified, for example, by X-ray measurement. In this method, for example, a portion from the surface of the steel material up to 1/4 of the thickness of the steel sheet is removed by mechanical polishing and chemical polishing, and a MoKα line is used as the characteristic X-ray. Therefore, using the following equation, the diffraction peaks of (200), (220), and (311) from the body-centered cubic lattice (bcc) phase (200) and (211) and the face-centered cubic lattice (fcc) phase The integral intensity ratio is used to calculate the area fraction of the residual Worthfield iron. Sγ=(I 200f +I 220f +I 311f )/(I 200b +I 211b )×100 (Sγ is the area fraction of residual Worth iron: I 200f , I 220f , I 311f respectively represent fcc phase (200 The diffraction peak intensities of (220) and (311); I 200b and I 211b represent the diffraction peak intensities of (b) and (211) of the bcc phase, respectively.
淬火麻田散鐵之面積分率可利用,例如,場致發射型掃描電子顯微鏡(field emission-scanning electron microscope:FE-SEM)觀察及X線測定來特定出。在此方法中,例如,由鋼材表面起算之深度為該鋼板厚度之1/8至3/8之區域作為觀察對象,來使用腐蝕用里培拉液。由於不能被里培拉液腐蝕之組織是淬火麻田散鐵及殘留沃斯田鐵,故藉由自不能被里培拉液腐蝕區域的面積分率減去以X線測定所特定之殘留沃斯田鐵之面積分率Sγ,就可以特定出淬火麻田散鐵之面積分率。淬火麻田散鐵之面積分率可,例如,使用SEM觀察得到的電子通道化對比圖像,來特定出。電子通道化對比圖像中,差排密度高,在粒內帶有塊體(block)、小包(packet)等下部組織之區域是淬火麻田散鐵。回火麻田散鐵之面積分率是可,例如,利用FE-SEM觀察而特定出。在此方法中,例如,由鋼材表面起算之深度為該鋼板厚度之1/8至3/8之區域作為觀察對象,使用腐蝕用硝太試劑。因此,基於雪明碳鐵之位置及其變異性,鑑別出回火麻田散鐵。回火麻田散鐵含有在麻田散鐵長條狀(lath)內部中之雪明碳鐵。麻田散鐵針與雪明碳鐵之間結晶方位之關係為2種以上,故在回火麻田散鐵中所含有之雪明碳鐵具有多個變異。基於此種雪明碳鐵之位置及變異,可鑑別回火麻田散鐵,並特定出此等之面積分率。The area fraction of the quenched granulated iron can be determined by, for example, field emission-scanning electron microscope (FE-SEM) observation and X-ray measurement. In this method, for example, a region from the surface of the steel material having a depth of 1/8 to 3/8 of the thickness of the steel sheet is used as an observation object, and a lining solution for corrosion is used. Since the structure which cannot be corroded by the Riedera liquid is the quenched granulated iron and the residual Worthite iron, the residual Worth determined by the X-ray is subtracted from the area fraction of the area which cannot be corroded by the Ribeira liquid. Tian Iron's area fraction Sγ can specify the area fraction of the quenched Ma Tian loose iron. The area fraction of the quenched granulated iron can be specified, for example, using an electron-channel contrast image obtained by SEM observation. In the electron channel contrast image, the difference in density is high, and the area of the lower structure such as a block or a packet in the grain is a quenched granulated iron. The area fraction of the tempered granulated iron is ok, for example, by FE-SEM observation. In this method, for example, a region from the surface of the steel material having a depth of 1/8 to 3/8 of the thickness of the steel sheet is used as an observation object, and a nitrate reagent for corrosion is used. Therefore, based on the location and variability of Xueming carbon iron, the tempered granulated iron was identified. The tempered granulated iron contains ferritic carbon iron in the interior of the lath of the granulated iron. There are two or more kinds of crystal orientations between the Ma Tian loose iron needle and the Xueming carbon iron. Therefore, the Xueming carbon iron contained in the tempered Ma Tian loose iron has a plurality of variations. Based on the location and variation of the ferritic carbon iron, the tempered granulated iron can be identified and the area fraction is specified.
變韌鐵是可,例如,利用FE-SEM觀察而特定出。在此方法中,例如,由鋼材表面起算之深度為該鋼板厚度之1/8至3/8之區域作為觀察對象,使用腐蝕用硝太試劑。此外,基於雪明碳鐵之位置及其變異性,鑑別出變韌鐵。變韌鐵含有上部變韌鐵與下部變韌鐵。上部變韌鐵含有位在長條狀(lath)之變韌肥粒鐵界面上之雪明碳鐵或殘留沃斯田鐵。下部變韌鐵含有位在長條狀之變韌肥粒鐵之內部的雪明碳鐵。變韌肥粒鐵與雪明碳鐵之間的結晶方位之關係為1種,因此在下部變韌鐵中含有的雪明碳鐵是具有相同的變異。基於此種雪明碳鐵之位置及變異,可鑑別變韌鐵,並特定出此等之面積分率。Toughened iron is possible, for example, by FE-SEM observation. In this method, for example, a region from the surface of the steel material having a depth of 1/8 to 3/8 of the thickness of the steel sheet is used as an observation object, and a nitrate reagent for corrosion is used. In addition, based on the location of the sulphur carbon iron and its variability, the toughened iron was identified. Toughened iron contains upper toughened iron and lower toughened iron. The upper toughened iron contains swarf carbon iron or residual Worth iron at the interface of the tough, fermented iron of the lath. The lower toughened iron contains swarf carbon iron located inside the long strip of tough ferrite. The relationship between the crystal orientation of the toughened ferrite iron and the swarf carbon iron is one, and therefore the smectite carbon iron contained in the lower toughened iron has the same variation. Based on the location and variation of the ferritic carbon iron, the toughened iron can be identified and the area fraction can be specified.
波來鐵可例如,利用光學顯微鏡觀來鑑別,因而特定出其面積分率。在此方法中,例如,由鋼材表面起算之深度為該鋼板厚度之1/8至3/8之區域作為觀察對象,使用腐蝕用硝太試劑。光學顯微鏡觀察下顯示出暗對比之區域是波來鐵。Borite can be identified, for example, by optical microscopy, and thus its area fraction is specified. In this method, for example, a region from the surface of the steel material having a depth of 1/8 to 3/8 of the thickness of the steel sheet is used as an observation object, and a nitrate reagent for corrosion is used. The area showing the dark contrast under the optical microscope observation was a Borne iron.
粒狀變韌鐵是利用習知之腐蝕法且使用掃描型電子顯微鏡之2次電子影像觀察,其要與肥粒鐵區別是困難的。本發明者經銳意檢討,其發現粒狀變韌鐵在粒內具有微小結晶方位差。因此,藉由檢測出晶粒內之微小結晶方位差,而可與肥粒鐵區別。在此,就粒狀變韌鐵之面積分率之具體的特定方法加以說明。在此方法中,例如,由鋼材表面起算之深度為該鋼板厚度之1/8至3/8之區域作為觀察對象,利用EBSD法,在該區域內之複數個處所(像素)之結晶方位以0.2μm之間隔加以測定,由其結果計算出GAM(顆粒平均錯誤方位(Grain Average Misorientation))值。在此計算中,相鄰像素間之結晶方位差在5°以上之情況,當作此等像素之間存在有晶界,計算被此等晶界所包圍之區域內相鄰像素間之結晶方位差,並求得該差之平均值。此平均值為GAM值。如此做,變韌肥粒鐵就檢測出具有微小結晶方位差。GAM值在0.5°以上之區域是屬於粒狀變韌鐵、變韌鐵、回火麻田散鐵、波來鐵或麻田散鐵中任一者。因此,由GAM值在0.5°以上區域之面積分率,減去變韌鐵、回火麻田散鐵、波來鐵及麻田散鐵之合計面積分率而得的值,就是粒狀變韌鐵之面積分率。Granular toughening iron is a secondary electron image observation using a conventional etching method using a scanning electron microscope, which is difficult to distinguish from ferrite iron. The inventors of the present invention have intensively reviewed and found that the granular toughened iron has a slight crystal orientation difference in the grains. Therefore, it can be distinguished from the ferrite iron by detecting a slight crystal orientation difference in the crystal grains. Here, a specific specific method of the area fraction of the granular toughened iron will be described. In this method, for example, a region from the surface of the steel material having a depth of 1/8 to 3/8 of the thickness of the steel sheet is used as an observation object, and the crystal orientation of a plurality of spaces (pixels) in the region is determined by the EBSD method. The interval of 0.2 μm was measured, and the result of GAM (Grain Average Misorientation) was calculated from the result. In this calculation, when the crystal orientation difference between adjacent pixels is 5° or more, there is a grain boundary between the pixels, and the crystal orientation between adjacent pixels in the region surrounded by the grain boundaries is calculated. Poor and find the average of the difference. This average is the GAM value. In doing so, the toughened ferrite iron was detected to have a slight crystal orientation difference. The region where the GAM value is 0.5° or more is any one of granular toughened iron, toughened iron, tempered granulated iron, ferritic iron or 麻田散铁. Therefore, the value obtained by subtracting the total area fraction of the toughened iron, the tempered granulated iron, the ferritic iron, and the granulated iron from the area ratio of the GAM value in the region above 0.5° is the granular toughened iron. Area fraction.
其次,就本發明實施形態的鋼板及其製造上所使用之化學組成加以說明。如上所述,本發明實施形態之鋼板是鋼胚經熱軋、冷軋及退火等而製造的。因此,鋼板及鋼胚之化學組成不僅考量了鋼板之特性,也考量了其等處理而獲得的。以下說明中,在鋼板及鋼胚所含有的各個元素之含量的單位「%」,若沒有特別指明,均是指「質量%」。本實施形態中鋼板具有下列表示之化學組成:C:0.09%~0.15%、Si:0.2%~2.5%、Al:0.01%~1.00%、Mn:1.0%~3.0%、P:0.02%以下、S:0.01%以下、N:0.007%以下、O:0.006%以下、Cr:0.00%~1.00%、Mo:0.00%~1.00%、B:0.0000%~0.010%、Nb:0.000%~0.30%、Ti:0.000%~0.30%、Ni:0.00%~1.00%、Cu:0.00%~1.00%、V:0.000%~0.50%、Mg:0.0000%~0.04%、REM:0.0000%~0.04%、及剩餘部分:Fe及雜質。雜質方面是,以礦石及廢料等的原材料中所含有者、或者在製造步驟中所含有者,來加以例示說明。Next, the steel sheet according to the embodiment of the present invention and the chemical composition used in the production thereof will be described. As described above, the steel sheet according to the embodiment of the present invention is produced by hot rolling, cold rolling, annealing, or the like. Therefore, the chemical composition of the steel sheet and the steel embryo is not only taken into consideration by the characteristics of the steel sheet, but also by the treatment thereof. In the following description, the unit "%" of the content of each element contained in the steel sheet and the steel embryo means "% by mass" unless otherwise specified. In the present embodiment, the steel sheet has the chemical composition shown below: C: 0.09% to 0.15%, Si: 0.2% to 2.5%, Al: 0.01% to 1.00%, Mn: 1.0% to 3.0%, P: 0.02% or less, S: 0.01% or less, N: 0.007% or less, O: 0.006% or less, Cr: 0.00% to 1.00%, Mo: 0.00% to 1.00%, B: 0.0000% to 0.010%, Nb: 0.000% to 0.30%, Ti: 0.000% to 0.30%, Ni: 0.00% to 1.00%, Cu: 0.00% to 1.00%, V: 0.000% to 0.50%, Mg: 0.0000% to 0.04%, REM: 0.0000% to 0.04%, and remaining Part: Fe and impurities. The impurities are exemplified by those contained in raw materials such as ore and scrap, or those included in the production steps.
(C:0.09%~0.15%) C是有助於拉伸強度增高。C含量是低於0.09%時,難以得到1180MPa以上拉伸強度。因此,C含量設在0.09%以上,較佳設在0.10%以上。一方面,C含量超過0.15%時,由於會抑制肥粒鐵之生成,無法得至足夠的伸長性。因此,C含量是在0.15%以下,較佳是在0.13%以下。(C: 0.09% to 0.15%) C is an increase in tensile strength. When the C content is less than 0.09%, it is difficult to obtain a tensile strength of 1180 MPa or more. Therefore, the C content is set to 0.09% or more, preferably 0.10% or more. On the other hand, when the C content exceeds 0.15%, sufficient elongation can not be obtained because the formation of ferrite iron is inhibited. Therefore, the C content is 0.15% or less, preferably 0.13% or less.
(Si:0.2%~2.5%) Si會抑制雪明碳鐵,助於粒狀變韌鐵之生成。粒狀變韌鐵是,多數個變韌肥粒鐵在其等界面所存在之差排回復而構成一塊的組織。因此,若在變韌肥粒鐵之界面存在有雪明碳鐵,在該處就不會生成粒狀變韌鐵。Si含量若低於0.2%時,雪明碳鐵會生成過多,就無法得到足夠的粒狀變韌鐵。因此,要將Si含量設在0.2%以上。一方面,Si含量若超過2.5%,則熱軋中易發生有鋼胚龜裂。因此,要將Si含量設在2.5%以下。(Si: 0.2%~2.5%) Si inhibits ferritic carbon iron and contributes to the formation of granular toughened iron. Granular toughening iron is a structure in which a plurality of toughened ferrite irons are returned at their interfaces to form a piece of tissue. Therefore, if there is ferritic carbon iron at the interface of the tough ferrite, no granular toughened iron will be formed there. When the Si content is less than 0.2%, ferritic carbon iron is excessively formed, and sufficient granular toughened iron cannot be obtained. Therefore, the Si content is set to be 0.2% or more. On the other hand, if the Si content exceeds 2.5%, cracks in the steel are likely to occur during hot rolling. Therefore, the Si content should be set to 2.5% or less.
(Al:0.01%~1.00%) Al會抑制雪明碳鐵,助於粒狀變韌鐵之生成。粒狀變韌鐵是,多數個變韌肥粒鐵在其等界面所存在之差排回復而構成一塊的組織。因此,若在變韌肥粒鐵之界面存在有雪明碳鐵,在該處就不會生成粒狀變韌鐵。Al亦是作為脫氧劑上可以活用的元素。Al之含量若合計在低於0.01%時,雪明碳鐵會生成過多,就無法得到足夠的粒狀變韌鐵。因此,要將Al含量設在0.01%以上。一方面,Al含量若超過1.00%,則熱軋中易發生有鋼胚龜裂。再者,因Al系之粗大夾雜物的個數密度增大,而構成擴孔性劣化之原因。因此,要將Al含量設在1.00%以下。(Al: 0.01%~1.00%) Al inhibits ferritic carbon iron and contributes to the formation of granular toughened iron. Granular toughening iron is a structure in which a plurality of toughened ferrite irons are returned at their interfaces to form a piece of tissue. Therefore, if there is ferritic carbon iron at the interface of the tough ferrite, no granular toughened iron will be formed there. Al is also an element that can be used as a deoxidizer. When the total content of Al is less than 0.01%, too much ferritic carbon iron is formed, and sufficient granular toughened iron cannot be obtained. Therefore, the Al content should be set to 0.01% or more. On the other hand, if the Al content exceeds 1.00%, cracks in the steel are likely to occur during hot rolling. Further, the number density of the coarse inclusions of the Al system is increased to cause deterioration of the hole expandability. Therefore, the Al content is set to be 1.00% or less.
(Mn:1.0%~3.0%) Mn在冷軋後後之連續退火或者鍍敷產線上的熱處理中,抑制肥粒鐵變態,有助於強度之提高。Mn含量合計低於1.0%時,肥粒鐵之面積分率就過高,難以得到1180MPa以上之拉伸強度。因此,要將Mn含量設在1.0%以上。Mn含量超過3.0%時,肥粒鐵之面積分率變得過少,而無法得到足夠之拉伸強度。因此,要將Mn含量設在3.0%以下。(Mn: 1.0% to 3.0%) In the continuous annealing after cold rolling or the heat treatment on the plating line, Mn suppresses the deformation of the ferrite and iron and contributes to the improvement of strength. When the total Mn content is less than 1.0%, the area fraction of the ferrite iron is too high, and it is difficult to obtain a tensile strength of 1180 MPa or more. Therefore, the Mn content is set to 1.0% or more. When the Mn content exceeds 3.0%, the area fraction of the ferrite iron becomes too small, and sufficient tensile strength cannot be obtained. Therefore, the Mn content is set to 3.0% or less.
(P:0.04%以下) P並非必要元素,且例如,是作為鋼中的雜質而被含有。P會使擴孔性降低,會於鋼板板厚方向之中心偏析而使韌性降低,或會使熔接部脆化。因此,P含量愈低愈好。特別是,P含量若超過0.04%,則擴孔性顯著降低。因此,P含量是在0.04%以下,較佳是在0.01%以下。再者,在P含量的降低上需要成本,且欲降低到低於0.0001%時,會使成本顯著上升。(P: 0.04% or less) P is not an essential element and is contained, for example, as an impurity in steel. P lowers the hole expandability and segregates at the center of the thickness direction of the steel sheet to lower the toughness or embrittle the welded portion. Therefore, the lower the P content, the better. In particular, when the P content exceeds 0.04%, the hole expandability is remarkably lowered. Therefore, the P content is 0.04% or less, preferably 0.01% or less. Furthermore, the cost is required to reduce the P content, and if it is to be lowered to less than 0.0001%, the cost is remarkably increased.
(S:0.01%以下) S並非必要元素,且是例如,作為鋼中的雜質而被含有。S會使熔接性降低,會使鑄造時及熱軋時之製造性降低,或者形成粗大之MnS而會使擴孔性降低。因此,S含量愈低愈好。特別是,S含量若超過0.01%,熔接性之降低,製造性之降低與擴孔性之降低皆顯著。因此,S含量是在0.01%以下,較佳是在0.005%以下。再者,在S含量的降低上需要成本,且欲降低到低於0.0001%時,會使成本顯著上升。(S: 0.01% or less) S is not an essential element and is contained, for example, as an impurity in steel. S lowers the weldability, lowers the manufacturability at the time of casting and hot rolling, or forms coarse MnS to lower the hole expandability. Therefore, the lower the S content, the better. In particular, when the S content is more than 0.01%, the weldability is lowered, and the decrease in manufacturability and the decrease in hole expandability are remarkable. Therefore, the S content is 0.01% or less, preferably 0.005% or less. Furthermore, the cost is required to reduce the S content, and if it is to be reduced to less than 0.0001%, the cost is remarkably increased.
(N:0.01%以下) N並非必要元素,且是例如,作為鋼中的雜質而被含有。N形成粗大之氮化物。粗大之氮化物會造成彎曲性及擴孔性降低,進而,使熔接時發生有氣孔。因此,N含量愈低愈好。特別是,N含量若超過0.01%,則擴孔性顯著降低,氣孔發生是顯著的。因此,N含量是在0.01%以下,較佳是在0.008%以下。在N含量的降低上需要成本,且欲降低到低於0.0005%時,會使成本顯著上升。(N: 0.01% or less) N is not an essential element and is contained, for example, as an impurity in steel. N forms a coarse nitride. The coarse nitride causes a decrease in flexibility and hole expandability, and further, pores are generated during welding. Therefore, the lower the N content, the better. In particular, when the N content exceeds 0.01%, the hole expandability is remarkably lowered, and the occurrence of pores is remarkable. Therefore, the N content is 0.01% or less, preferably 0.008% or less. Cost is required for the reduction of the N content, and if it is to be lowered to less than 0.0005%, the cost is significantly increased.
(O:0.006%以下) O並非必要元素,且是例如,作為鋼中的雜質而被含有。O形成粗大之氧化物。粗大之氧化物會造成彎曲性及擴孔性降低,進而,使熔接時發生有氣孔。因此,O含量愈低愈好。特別是,O含量若超過0.006%,則擴孔性顯著降低,氣孔發生是顯著的。因此,O含量是在0.006%以下,較佳是在0.005%以下。在O含量的降低上需要成本,且欲降低到低於0.0005%時,會使成本顯著上升。(O: 0.006% or less) O is not an essential element and is contained, for example, as an impurity in steel. O forms a coarse oxide. The coarse oxide causes a decrease in flexibility and hole expandability, and further, pores are generated during welding. Therefore, the lower the O content, the better. In particular, when the O content exceeds 0.006%, the hole expandability is remarkably lowered, and the occurrence of pores is remarkable. Therefore, the O content is 0.006% or less, preferably 0.005% or less. The cost is required to reduce the O content, and if it is to be reduced to less than 0.0005%, the cost is significantly increased.
Cr、Mo、Ni、Cu、Nb、Ti、V、B、Ca、Mg及REM非必要元素,其等是在鋼板及鋼中有限度地適當調整預定量之任意元素。Cr, Mo, Ni, Cu, Nb, Ti, V, B, Ca, Mg, and REM are unnecessary elements, and the like is a limited amount of any element that is appropriately adjusted in a steel sheet and steel.
(Cr:0.00%~1.00%、Mo:0.00%~1.00%、Ni:0.00%~1.00%、Cu:0.00%~1.00%) Cr、Mo,Ni及Cu冷軋後之退火或鍍敷之際,會抑制肥粒鐵變態,而有助於強度之增高。因此,亦可含有Cr、Mo,Ni或Cu或者其等的任意組合。為了得到足夠的此效果,較佳的是,Cr含量設在0.10%以上,Mo含量設在.0.01%以上,Ni含量設在0.05%以上,Cu含量設在0.05%以上。但是,Cr含量超過1.00%,或Mo含量是超過1.00%,或Ni含量是超過1.00%,或者Cu含量是超過1.00%時,肥粒鐵之面積分率變得過少,而無法得到足夠之伸長性。因此,Cr含量、Mo含量,Ni含量及Cu含量任一者皆被設在1.00%以下。即,較佳是符合Cr:0.10%~1.00%、Mo:0.01%~1.00%,Ni:0.05%~1.00%,或Cu:0.05%~1.00%,或者此等任意之組合。(Cr: 0.00% to 1.00%, Mo: 0.00% to 1.00%, Ni: 0.00% to 1.00%, Cu: 0.00% to 1.00%) Annealing or plating after cold rolling of Cr, Mo, Ni and Cu It will inhibit the fat and iron metamorphosis and contribute to the increase of strength. Therefore, Cr, Mo, Ni or Cu or any combination thereof may be contained. In order to obtain sufficient effect, it is preferable that the Cr content is set to 0.10% or more, the Mo content is set to 0.01% or more, the Ni content is set to 0.05% or more, and the Cu content is set to 0.05% or more. However, when the Cr content exceeds 1.00%, or the Mo content is more than 1.00%, or the Ni content is more than 1.00%, or the Cu content is more than 1.00%, the area fraction of the ferrite iron becomes too small, and sufficient elongation cannot be obtained. Sex. Therefore, any of the Cr content, the Mo content, the Ni content, and the Cu content is set to 1.00% or less. That is, it is preferably in accordance with Cr: 0.10% to 1.00%, Mo: 0.01% to 1.00%, Ni: 0.05% to 1.00%, or Cu: 0.05% to 1.00%, or any combination thereof.
(Nb:0.000%~0.30%、Ti:0.000%~0.30%、V:0.000%~0.50%) Nb,Ti及V藉由在冷軋後之退火步驟等中將沃斯田鐵細粒化來增加沃斯田鐵之晶界面積,促進肥粒鐵變態。因此,亦可含有Ni,Ti或V或者其等的任意組合。為得到足夠的此效果,較佳的是,Nb含量設在0.005%以上,Ti含量設在0.005%以上,V含量設在0.005%以上。但是,Nb含量是超過0.30%,Ti含量含量是超過0.30%,或V含量含量是超過0.50%,肥粒鐵之面積分率變得過多,而無法得到足夠之拉伸強度。因此,Nb含量設為0.30%以下,Ti含量設為0.30%以下,V含量設為0.50%以下。即,較佳是符合Nb:0.005%~0.30%,Ti:0.005%~0.30%,或V:0.005%~0.50%,或者此等任意之組合。(Nb: 0.000% to 0.30%, Ti: 0.000% to 0.30%, V: 0.000% to 0.50%) Nb, Ti and V are finely granulated by Worthite iron in an annealing step after cold rolling or the like. Increase the area of the grain boundary of the Worthfield Iron and promote the metamorphosis of the ferrite. Therefore, it is also possible to contain Ni, Ti or V or any combination thereof. In order to obtain sufficient effect, it is preferable that the Nb content is set to 0.005% or more, the Ti content is set to 0.005% or more, and the V content is set to 0.005% or more. However, the Nb content is more than 0.30%, the Ti content is more than 0.30%, or the V content is more than 0.50%, and the area fraction of the ferrite iron becomes excessive, and sufficient tensile strength cannot be obtained. Therefore, the Nb content is set to 0.30% or less, the Ti content is set to 0.30% or less, and the V content is set to 0.50% or less. That is, it is preferably in accordance with Nb: 0.005% to 0.30%, Ti: 0.005% to 0.30%, or V: 0.005% to 0.50%, or any combination thereof.
(B:0.0000%~0.010%) B是在冷軋後之退火等中在沃斯田鐵之晶界上偏析,並抑制肥粒鐵變態。因此,B亦可被包含於其中。為得到足夠的此效果,較佳的是,B含量設在0.0001%以上。但是,B含量若超過0.010%時,肥粒鐵之面積分率設得過低,而無法得到足夠的伸長性。因此,將B含量設為0.010%以下。即,較佳是B:0.0001%~0.010%來構成。(B: 0.0000% to 0.010%) B is segregated on the grain boundary of the Worthfield iron during annealing after cold rolling, and suppresses the deformation of the ferrite. Therefore, B can also be included in it. In order to obtain sufficient effect, it is preferred that the B content be set to 0.0001% or more. However, when the B content exceeds 0.010%, the area fraction of the ferrite iron is set too low, and sufficient elongation cannot be obtained. Therefore, the B content is made 0.010% or less. That is, it is preferably composed of B: 0.0001% to 0.010%.
(Ca:0.0000%~0.04%、Mg:0.0000%~0.04%、REM:0.0000%~0.04%) Ca,Mg及REM是抑制氧化物及硫化物之形態,而助於擴孔性的增高。因此,亦可含有Ca,Mg或REM或者其等的任意組合。為得到足夠的此效果,較佳的是,Ca含量、Mg含量及REM含量任一者皆在0.0005%以上。但是,Ca含量若是超過0.04%,或Mg含量若超過0.04%,或REM含量若是超過0.04%,則會形成粗大氧化物而無法得到足夠擴孔性。因此,Ca含量、Mg含量及REM含量任一者皆設在0.04%以下,較佳是設在0.01%以下。即,較佳是符合Ca:0.0005%~0.04%,Mg:0.0005%~0.04%,或REM:0.0005%~0.04%,或者此等任意之組合。(Ca: 0.0000% to 0.04%, Mg: 0.0000% to 0.04%, REM: 0.0000% to 0.04%) Ca, Mg, and REM inhibit the form of oxides and sulfides, and contribute to the increase in hole expandability. Therefore, it is also possible to contain Ca, Mg or REM or any combination thereof. In order to obtain sufficient effect, it is preferred that any of the Ca content, the Mg content, and the REM content is 0.0005% or more. However, if the Ca content exceeds 0.04%, or the Mg content exceeds 0.04%, or the REM content exceeds 0.04%, a coarse oxide is formed and sufficient hole expandability cannot be obtained. Therefore, any of the Ca content, the Mg content, and the REM content is set to 0.04% or less, preferably 0.01% or less. That is, it is preferably in accordance with Ca: 0.0005% to 0.04%, Mg: 0.0005% to 0.04%, or REM: 0.0005% to 0.04%, or any combination thereof.
REM是屬於Sc,Y及鑭系之元素合計17種元素的總稱,REM含量是此等元素合計之含量。REM是例如被包含在混合稀土金屬(mischmetal)內,REM之添加可為,例如,添加混合稀土金屬,或者添加金屬La,金屬Ce等金屬REM。REM is a generic term for a total of 17 elements belonging to the elements of Sc, Y and lanthanide, and the REM content is the total content of these elements. The REM is, for example, contained in a mixed rare earth metal (mischmetal), and the addition of the REM may be, for example, addition of a mixed rare earth metal, or addition of a metal RE such as a metal La or a metal Ce.
依據本實施形態可以得到下列彎曲性:例如,1180MPa以上之拉伸強度、10%以上之伸長性、20%以上之擴孔性、令厚度為t(mm)時的VDA彎角是在「7.69t2 -38.4t+109」以上之彎曲性。即,其可以得到高強度,優異拉伸性、擴孔性、彎曲性。此一鋼板是容易成形為例如汽車之骨架零件,且可確保衝撞時之安全性。According to the present embodiment, the following bending properties can be obtained: for example, a tensile strength of 1180 MPa or more, an elongation of 10% or more, a hole expandability of 20% or more, and a VDA angle when the thickness is t (mm) is "7.69". Flexibility above t 2 -38.4t+109". That is, it can obtain high strength, excellent stretchability, hole expandability, and flexibility. This steel plate is easily formed into a skeleton part such as an automobile, and can secure safety in the event of collision.
接下來說明本發明實施形態之鋼板之製造方法。在本發明之實施形態的鋼板製造方法中,是將具有上述化學組成之鋼胚依序進行熱軋、酸洗、冷軋及退火。Next, a method of producing a steel sheet according to an embodiment of the present invention will be described. In the method for producing a steel sheet according to the embodiment of the present invention, the steel preform having the chemical composition described above is sequentially subjected to hot rolling, pickling, cold rolling, and annealing.
對先前鑄造上施行的製造方法並無特別限定。即,在由高爐或電爐等熔製之後,亦可接續進行各種二次精煉。又,亦可使用金屬廢料作為原料。There is no particular limitation on the manufacturing method previously performed on the casting. That is, after being melted by a blast furnace or an electric furnace or the like, various secondary refinings can be carried out. Also, metal scrap can be used as a raw material.
鑄造得到的鋼胚暫時地冷卻到低溫,之後,亦可再度加熱而供應至熱軋,亦可將鑄造而得之鋼胚連續地供給至熱軋。The cast steel obtained is temporarily cooled to a low temperature, and then may be heated again to be supplied to hot rolling, or the cast steel may be continuously supplied to hot rolling.
熱軋是在1100℃以上之溫度開始,在Ar3 點以上之溫度結束。冷軋則是設定軋縮率為30%以上80%以下。在退火時,保持在Ac1 點以上Ac3 點以下之最高加熱溫度達10秒以上,在其後冷卻中,自Ar3 點起直到650℃為止之冷卻速度是設在0.5℃/秒以上50℃/秒以下,自650℃起直到450℃為止之冷卻速度是設在0.5℃/秒以上5℃/秒以下。Hot rolling starts at a temperature above 1100 ° C and ends at a temperature above Ar 3 . In cold rolling, the rolling reduction ratio is set to 30% or more and 80% or less. During annealing, maintained at above Ac Ac 1:00 3:00 maximum heating temperature of less than 10 seconds, in the subsequent cooling, since the Ar 3 point of the cooling rate is provided until at least 650 ℃ 0.5 ℃ / 50 sec The cooling rate from 650 ° C to 450 ° C is set to be 0.5 ° C / sec or more and 5 ° C / sec or less.
開始熱軋之溫度若低於1100℃,則會有無法使得Fe以外元素在Fe中充分固溶,會殘存在有粗大合金碳化物,熱軋中容易引起脆化。因此,熱軋是在1100℃以上之溫度開始。開始熱軋溫度為例如,鋼胚加熱溫度。作為鋼胚者可使用,例如,連續鑄造得到的鋼胚,薄鋼胚鑄造所作製之鋼胚。鋼胚亦可在鑄造後以保持在原先1100℃以上溫度狀態下供給至熱軋設備,亦可冷卻到低於1100℃之後再加熱而供給到熱軋設備。When the temperature at which the hot rolling is started is less than 1,100 ° C, the elements other than Fe may not be sufficiently solid-solved in Fe, and coarse alloy carbides may remain therein, which may cause embrittlement during hot rolling. Therefore, hot rolling starts at a temperature of 1100 ° C or higher. The hot rolling temperature is started, for example, at a steel embryo heating temperature. As the steel slab, for example, a steel slab obtained by continuous casting and a steel slab made of a thin steel slab can be used. The steel blank may also be supplied to the hot rolling equipment after being cast at a temperature of 1100 ° C or higher, or may be cooled to less than 1100 ° C and then heated to be supplied to the hot rolling equipment.
讓熱軋終結之溫度在低於Ar3 點時,沃斯田鐵及肥粒鐵會被包含在熱軋鋼板之金屬組織中,由於沃斯田鐵與肥粒鐵之間的機械特性不同,會在有冷軋之類的熱軋後處理上變得困難。因此,熱軋在Ar3 點以上之溫度終結。熱軋在Ar3 點以上之溫度終結時,可以比較地減輕熱軋中之軋壓荷重。When the temperature at the end of hot rolling is lower than the Ar 3 point, the Worthite iron and the ferrite iron are contained in the metal structure of the hot rolled steel sheet. Due to the difference in mechanical properties between the Worthite iron and the ferrite iron, It will become difficult to perform hot rolling after cold rolling. Therefore, hot rolling is terminated at a temperature above Ar 3 point. When the hot rolling is terminated at a temperature above Ar 3 , the rolling load in hot rolling can be relatively reduced.
熱軋包含粗軋壓及最後軋壓,最後軋壓亦可將粗軋壓得到的多個鋼板經接合而成者,進行連續地軋壓。又,也可以在粗軋延板暫時捲取後,再進行最後軋延。捲取溫度設在500℃以上650℃以下。捲取溫度若超過650℃,則生產性劣化。因此,捲取溫度設在650℃以下。一方面,捲取溫度若低於500℃,熱軋鋼板之硬度過高,其後難以進行冷軋。因此,捲取溫度設在500℃以上。The hot rolling includes rough rolling and final rolling, and finally, rolling may be performed by joining a plurality of steel sheets obtained by rough rolling and continuously rolling. Further, it is also possible to perform the final rolling after the rough rolling of the rough rolling plate is temporarily taken up. The coiling temperature is set to be 500 ° C or more and 650 ° C or less. If the coiling temperature exceeds 650 ° C, the productivity is deteriorated. Therefore, the coiling temperature is set to be 650 ° C or less. On the other hand, if the coiling temperature is lower than 500 ° C, the hardness of the hot-rolled steel sheet is too high, and thereafter it is difficult to perform cold rolling. Therefore, the coiling temperature is set at 500 ° C or higher.
如此方式製得之熱軋鋼板,為了去除表面氧化物,進行酸洗。酸洗進行1次或2次。藉由酸洗,去除熱軋鋼板之表面的氧化物,以增高化成處理性及鍍敷性。The hot-rolled steel sheet obtained in this manner is pickled in order to remove surface oxides. Pickling is carried out once or twice. The oxide on the surface of the hot-rolled steel sheet is removed by pickling to increase the processability and plating properties.
要在冷軋之軋縮率低於30%的情況下,會有將冷軋鋼板的形狀保持成平坦是困難的,不能得到足夠之延展性。因此,冷軋之軋縮率設定在30%以上。一方面,冷軋之軋縮率若超過80%,軋壓荷重變得過大,冷軋變得困難。因此,冷軋之軋縮率設定在80%以上。In the case where the cold rolling reduction ratio is less than 30%, it is difficult to keep the shape of the cold rolled steel sheet flat, and sufficient ductility cannot be obtained. Therefore, the rolling reduction ratio of cold rolling is set to 30% or more. On the other hand, if the rolling reduction ratio of cold rolling exceeds 80%, the rolling load becomes too large, and cold rolling becomes difficult. Therefore, the rolling reduction ratio of cold rolling is set to 80% or more.
冷軋鋼板在連續退火產線或鍍敷產線上進行通板時之加熱速度並沒有特別的限制。The heating rate of the cold-rolled steel sheet when passing through the continuous annealing line or the plating line is not particularly limited.
退火下,藉由Ac1 點以上Ac3 點以下之最高加熱溫度保持10秒,生成沃斯田鐵。沃斯田鐵,經過後冷卻而變態成肥粒鐵、粒狀變韌鐵或麻田散鐵。若保持溫度是在低於Ac1 點,或者保持時間低於10秒時,無法生充分地形成沃斯田鐵。一方面,最高加熱溫度若超過Ac3 點,則無法得到肥粒鐵,延展性不足。因此,最高加熱溫度是在Ac1 點以上Ac3 點以下,且保持時間 是10秒以上。Annealed, by the maximum heating temperature for 3 point or less of the Ac Ac 1:00 for 10 seconds, to generate austenite. Worthite iron, after cooling, metamorphosed into fermented iron, granular tough iron or 麻田散铁. If the temperature is kept below the Ac 1 point, or the holding time is less than 10 seconds, the Worthite iron cannot be sufficiently formed. On the other hand, if the maximum heating temperature exceeds Ac 3 point, the ferrite iron cannot be obtained, and the ductility is insufficient. Therefore, the maximum heating temperature is below Ac 3 point above Ac 1 point, and the holding time is 10 seconds or more.
在由最高加熱溫度開始之冷卻中,自Ar3 點直到650℃為止之溫度域中的平均冷卻速度(第1平均冷卻速度)是設為0.5℃/秒~50℃/秒。平均冷卻速度若是低於0.5℃/秒,冷卻過程中會過度由沃斯田鐵生成肥粒鐵或波來鐵。此結果為,要確保充分麻田散鐵之面積分率變得困難,要得到1180MPa以上之拉伸強度變得困難。即使平均冷卻速度增大,雖不會有材質上問題,仍有平均冷卻速度過度升高,招致製造成本上昇,故平均冷卻速度設在50℃/秒以下。在冷卻方法中,亦可是軋壓冷卻、空氣冷卻或者水冷卻,或此等併用之任一者。In the cooling from the highest heating temperature, the average cooling rate (first average cooling rate) in the temperature range from Ar 3 to 650 ° C is set to 0.5 ° C / sec to 50 ° C / sec. If the average cooling rate is less than 0.5 ° C / sec, the ferrite iron or the Borne iron is excessively generated by the Worthite iron during the cooling process. As a result, it has become difficult to ensure sufficient area fraction of the granulated iron in the field, and it is difficult to obtain a tensile strength of 1180 MPa or more. Even if the average cooling rate is increased, there is no material problem, and the average cooling rate is excessively increased, resulting in an increase in manufacturing cost, so the average cooling rate is set to 50 ° C / sec or less. In the cooling method, it may be either roll cooling, air cooling or water cooling, or any of these.
由650℃至450℃之平均冷卻速度(第2平均冷卻速度)設在0.5℃/秒~5℃/秒,可生成適當之面積分率的粒狀變韌鐵。如上所述粒狀,變韌鐵是,多數個變韌肥粒鐵在其等界面所存在之差排回復而構成一塊的組織。如此的差排回復在650℃以下之溫度範圍可使其發生。但是,在此溫度範圍中的冷卻速度超過5℃/秒時,就無法使差排充分地回復,而有粒狀變韌鐵之面積分率不足之情事。因此,宜將此一溫度範圍中的平均冷卻速度設在5℃/秒以下。一方面,若此溫度域中的冷卻速度是低於0.5℃/秒,粒狀變韌鐵及變韌鐵之面積分率就變得過多,得到拉伸強度在1180MPa以上是必要之麻田散鐵變得困難。因此,宜將此一溫度範圍中的平均冷卻速度設在0.5℃/秒以上。冷卻方法亦可是連續冷卻、傾斜冷卻或等溫保持或者此等之併用。The average cooling rate (second average cooling rate) from 650 ° C to 450 ° C is set at 0.5 ° C / sec to 5 ° C / sec, and a granular toughened iron having an appropriate area fraction can be produced. As described above, the granular, toughened iron is a structure in which a plurality of toughened ferrite irons are returned at their interfaces to form a piece of tissue. Such a differential recovery can occur in a temperature range below 650 °C. However, when the cooling rate in this temperature range exceeds 5 ° C / sec, the difference row cannot be sufficiently recovered, and the area fraction of the granular toughened iron is insufficient. Therefore, it is preferable to set the average cooling rate in this temperature range to 5 ° C / sec or less. On the one hand, if the cooling rate in this temperature range is less than 0.5 ° C / sec, the area fraction of the granular toughened iron and the toughened iron becomes too large, and it is necessary to obtain a tensile strength of 1180 MPa or more. It has become difficult. Therefore, it is preferable to set the average cooling rate in this temperature range to 0.5 ° C / sec or more. The cooling method may also be continuous cooling, slant cooling or isothermal holding or the like.
如此一來便可製造本發明實施形態之鋼板。In this way, the steel sheet according to the embodiment of the present invention can be produced.
鋼板上亦可進行電氣鍍敷處理、蒸著鍍敷處理等鍍敷處理,更甚者,其亦可在鍍敷處理後進行合金化處理。鋼板亦可進行有機皮膜形成、薄膜積層、有機鹽類/無機鹽類處理、無鉻處理等之表面處理。The steel sheet may be subjected to a plating treatment such as an electric plating treatment or a vapor deposition treatment, and more preferably, it may be alloyed after the plating treatment. The steel sheet may be subjected to surface treatment such as organic film formation, film lamination, organic salt/inorganic salt treatment, or chromium-free treatment.
在鋼板上進行作為鍍敷處理之熔融鍍鋅處理之情況下,例如,加熱或冷卻鋼板之溫度至其為下述溫度,並使鋼板通板鋅鍍敷浴,該溫度是一比鋅鍍敷浴之溫度更低40℃溫度以上之溫度且比鋅鍍敷浴之溫度更高50℃之溫度以下之溫度。藉由熔融鍍鋅處理,就可得到於表面具有熔融鍍鋅層之鋼板,即熔融鍍鋅鋼板。熔融鍍鋅層具有,例如,Fe:7質量%以上15質量%以下,及剩餘部分:Zn、Al及雜質表示之化學組成。In the case of performing a hot-dip galvanizing treatment as a plating treatment on a steel sheet, for example, heating or cooling the temperature of the steel sheet to a temperature at which the steel sheet is passed through a zinc plating bath, the temperature is a ratio of zinc plating The temperature of the bath is lower than the temperature above 40 ° C and is higher than the temperature of the zinc plating bath by a temperature of 50 ° C or less. By hot-dip galvanizing, a steel sheet having a hot-dip galvanized layer on the surface, that is, a hot-dip galvanized steel sheet can be obtained. The hot-dip galvanized layer has, for example, Fe: 7 mass% or more and 15 mass% or less, and the remainder: chemical composition represented by Zn, Al, and impurities.
熔融鍍鋅處理後進行合金化處理時,例如,加熱熔融鍍鋅鋼板至460℃以上600℃以下之溫度。此溫度若低於460℃,則合金化不足。此溫度若超過600℃超,則有合金化過多,耐蝕性劣化。藉由合金化處理,可得到於表面具有合金化熔融鍍鋅層之鋼板,即合金化熔融鍍鋅鋼板。When the alloying treatment is performed after the hot-dip galvanizing treatment, for example, the hot-dip galvanized steel sheet is heated to a temperature of 460 ° C or higher and 600 ° C or lower. If the temperature is lower than 460 ° C, the alloying is insufficient. If the temperature exceeds 600 ° C, the alloying is excessive and the corrosion resistance is deteriorated. By alloying, a steel sheet having an alloyed hot-dip galvanized layer on the surface, that is, an alloyed hot-dip galvanized steel sheet can be obtained.
再者,上述實施形態均僅是用於表示實施本發明時的具體化之例,並非透過其等而用以限定地解釋本發明之技術性範圍者。亦即,本發明只要沒有脫離其技術思想或其主要特徵的情形,均可以用各種形式實施。It is to be understood that the above-described embodiments are merely illustrative of the specific embodiments of the invention, and are not intended to limit the technical scope of the invention. That is, the present invention can be implemented in various forms as long as it does not deviate from the technical idea or its main features.
[實施例] 接下來說明本發明之實施例。實施例之條件係用以確認本發明之可實施性及效果所採用的一條件例,本發明不受此一條件例限定。只要能在不脫離本發明之宗旨下達成本發明之目的,本發明為可以採用各種條件而形成者。[Embodiment] Next, an embodiment of the present invention will be described. The conditions of the examples are a conditional example used to confirm the practicability and effects of the present invention, and the present invention is not limited by such a condition. The present invention can be formed by various conditions as long as the object of the present invention can be achieved without departing from the gist of the present invention.
(第1試驗) 在第1試驗中,製造具有表1~表2所示之化學組成的鋼胚,熱軋此等鋼胚而得到熱軋鋼板。表1~表2中的空白欄位表示該元素之含量低於檢測極限,剩餘部分是Fe及雜質。表2中的底線則表示該數值在超出本發明的範圍外。(First Test) In the first test, steel slabs having chemical compositions shown in Tables 1 to 2 were produced, and the steel slabs were hot rolled to obtain hot rolled steel sheets. The blank fields in Tables 1 to 2 indicate that the content of the element is below the detection limit, and the remainder is Fe and impurities. The bottom line in Table 2 indicates that the value is outside the scope of the present invention.
[表1] [Table 1]
[表2] [Table 2]
其後,進行熱軋鋼板之酸洗、冷軋及退火而得到鋼板。熱軋、冷軋及退火之條件顯示於表3~表7。表3~表7中的底線則表示該數值落在超出本發明的範圍之外。Thereafter, pickling, cold rolling, and annealing of the hot rolled steel sheet are performed to obtain a steel sheet. The conditions of hot rolling, cold rolling and annealing are shown in Tables 3 to 7. The bottom line in Tables 3 to 7 indicates that the value falls outside the scope of the present invention.
[表3] [table 3]
[表4] [Table 4]
[表5] [table 5]
[表6] [Table 6]
[表7] [Table 7]
其後,測定各鋼板中肥粒鐵之面積分率fF、麻田散鐵之面積分率fM、粒狀變韌鐵之面積分率fGB、變韌鐵之面積分率fB、波來鐵之面積分率fP及殘留沃斯田鐵之面積分率fR-γ。這些結果顯示於表8~表12中。與此等結果相關之表8~表12中的底線則表示該數值在超出本發明的範圍外。Thereafter, the area fraction fF of the ferrite iron in each steel sheet, the area fraction fM of the granulated iron, the area fraction fGB of the granular toughened iron, the area fraction fB of the toughened iron, and the area of the ferritic iron were measured. The fractional rate fP and the area fraction of residual Worthite iron are fR-γ. These results are shown in Tables 8 to 12. The bottom line in Tables 8 to 12 associated with these results indicates that the value is outside the scope of the present invention.
因此,進行各鋼板之拉伸試驗、擴孔試驗及彎曲試驗。在拉伸試驗中,自鋼板採取與軋壓方向呈直角之日本工業規格JIS5號試驗片,依據JISZ2242測定拉伸強度TS及全伸長率EL。擴孔試驗則依據JISZ2256之記載測定擴孔率λ。彎曲試驗中,依據德國汽車工業會(Verband der Automobilindustrie:VDA)之規格238-100之規定進行試驗,測定VDA彎角α。這些結果顯示於表8~表12中。與此等結果相關之表8~表12中的底線則表示該數值在超出所期望的範圍外。在此所期望之範圍是、TS為1180MPa以上、EL為10%以上、λ為20%以上、VDA彎角α為基準值α0 以上(令厚度為t(mm)時,α0 =7.69t2 -38.4t+109)。Therefore, the tensile test, the hole expansion test, and the bending test of each steel plate were performed. In the tensile test, a Japanese Industrial Standard JIS No. 5 test piece was taken from the steel sheet at a right angle to the rolling direction, and the tensile strength TS and the total elongation EL were measured in accordance with JIS Z2242. In the hole expansion test, the hole expansion ratio λ was measured in accordance with the description of JIS Z2256. In the bending test, the test was carried out in accordance with the specifications of 238-100 of the Verbin der Automobilindustrie (VDA), and the VDA angle α was measured. These results are shown in Tables 8 to 12. The bottom line in Tables 8 to 12 associated with these results indicates that the value is outside the desired range. The range expected here is that TS is 1180 MPa or more, EL is 10% or more, λ is 20% or more, and VDA bending angle α is a reference value α 0 or more (when thickness is t (mm), α 0 = 7.69 t 2 -38.4t+109).
[表8] [Table 8]
[表9] [Table 9]
[表10] [Table 10]
[表11] [Table 11]
[表12] [Table 12]
如表8~表10所示者,本發明範圍內之試料,可以得到高強度,優異伸長性及擴孔性。As shown in Tables 8 to 10, the samples within the scope of the present invention can obtain high strength, excellent elongation, and hole expandability.
試料編號71由於C含量過低,故拉伸強度是低的。試料編號72中由於C含量過高,擴孔率是低的。試料編號73中,由於Si由於含量過低,拉伸強度是低的。試料編號74中,由於Si含量過高,拉伸強度是低的。試料編號75中,由於Mn含量過低,拉伸強度及擴孔率是低的。試料編號76中,由於Mn含量過高,擴孔率及VDA彎角是低的。試料編號77中,由於P含量過高,拉伸強度、伸長性、擴孔率及VDA彎角是低的。試料編號78中,由於S含量過高,拉伸強度及擴孔率是低的。試料編號79中,由於Al含量過低,拉伸強度、伸長性及擴孔率是低的。試料編號80中,由於Al含量過高,拉伸強度、伸長性、擴孔率及VDA彎角是低的。試料編號81中,由於N含量過高,擴孔率是低的。試料編號82中,由於O含量過高,擴孔率及VDA彎角是低的。Sample No. 71 has a low tensile strength because the C content is too low. In sample No. 72, since the C content was too high, the hole expansion ratio was low. In sample No. 73, since Si was too low in content, the tensile strength was low. In sample No. 74, since the Si content was too high, the tensile strength was low. In sample No. 75, since the Mn content was too low, the tensile strength and the hole expansion ratio were low. In sample No. 76, since the Mn content was too high, the hole expansion ratio and the VDA angle were low. In sample No. 77, since the P content was too high, tensile strength, elongation, hole expansion ratio, and VDA angle were low. In sample No. 78, since the S content was too high, the tensile strength and the hole expansion ratio were low. In sample No. 79, since the Al content was too low, tensile strength, elongation, and hole expansion ratio were low. In sample No. 80, since the Al content was too high, tensile strength, elongation, hole expansion ratio, and VDA angle were low. In sample No. 81, since the N content was too high, the hole expansion ratio was low. In sample No. 82, since the O content was too high, the hole expansion ratio and the VDA angle were low.
試料編號83中,由於Cr含量過高,擴孔率是低的。試料編號84中,由於Mo含量過高,擴孔率是低的。試料編號85中,由於Ni含量過高,擴孔率是低的。試料編號86中,由於Cu含量過高,拉伸強度及擴孔率是低的。試料編號87中,由於Nb含量過高,拉伸強度及擴孔率是低的。試料編號88中,由於Ti含量過高,拉伸強度、伸長性、擴孔率及VDA彎角是低的。試料編號89中,由於V含量過高,擴孔率及VDA彎角是低的。試料編號90中,由於B含量過高,拉伸強度、伸長性、擴孔率及VDA彎角是低的。試料編號91中,由於Ca含量過高,伸長性、擴孔率及VDA彎角是低的。試料編號92中,由於Mg含量過高,拉伸強度、擴孔率及びVDA彎角是低的。試料編號93中,由於REM含量過高,伸長性、擴孔率及VDA彎角是低的。In sample No. 83, since the Cr content was too high, the hole expansion ratio was low. In sample No. 84, since the Mo content was too high, the hole expansion ratio was low. In sample No. 85, since the Ni content was too high, the hole expansion ratio was low. In sample No. 86, since the Cu content was too high, the tensile strength and the hole expansion ratio were low. In sample No. 87, since the Nb content was too high, the tensile strength and the hole expansion ratio were low. In sample No. 88, since the Ti content was too high, tensile strength, elongation, hole expansion ratio, and VDA angle were low. In sample No. 89, since the V content was too high, the hole expansion ratio and the VDA angle were low. In sample No. 90, since the B content was too high, tensile strength, elongation, hole expansion ratio, and VDA angle were low. In sample No. 91, since the Ca content was too high, the elongation, the hole expansion ratio, and the VDA angle were low. In sample No. 92, since the Mg content was too high, the tensile strength, the hole expansion ratio, and the びVDA angle were low. In sample No. 93, since the REM content was too high, the elongation, the hole expansion ratio, and the VDA angle were low.
試料編號94中,鋼胚加熱溫度過低,熱軋中會發生有不欲之龜裂,其後無法進行通板。試料編號95中,由於精加工軋壓之終結溫度過低、熱軋之途中會有形狀惡化,其後無法進行通板。試料編號96中,由於捲取溫度過度,熱軋鋼板變得過硬,其後無法進行冷軋。試料編號97中,由於捲取溫度過高,且麻田散鐵面積分率不足,伸長性、擴孔率及VDA彎角是低的。試料編號98中,由於冷軋軋縮率過低,冷軋途中形狀會惡化,其後無法進行冷軋。試料編號99中,由於冷軋軋縮率過高,軋壓荷重變過大,其後無法進行冷軋。試料編號100中,由於退火之最高加熱溫度過高,肥粒鐵之面積分率不足,且變韌鐵之面積分率過多,故伸長性是低的。試料編號101中,由於退火之最高加熱溫度過低,肥粒鐵及波來鐵之面積分率是過多,麻田散鐵及粒狀變韌鐵之面積分率是不足,故拉伸強度及擴孔率是低的。試料編號102中,由於最高加熱溫度之保持時間過短,肥粒鐵及波來鐵之面積分率過高,麻田散鐵及粒狀變韌鐵之面積分率不足,故拉伸強度、擴孔率及VDA彎角是低的。試料編號103中,由於最高加熱溫度之保持時間過短,波來鐵之面積分率是過多,粒狀變韌鐵之面積分率是不足,拉伸強度是低的。試料編號104中,第1之平均冷卻速度是過低、肥粒鐵之面積分率是過高,麻田散鐵之面積分率不足,故拉伸強度是低的。試料編號105中,由於第1之平均冷卻速度是過高、肥粒鐵之面積分率不足,粒狀變韌鐵及波來鐵之面積分率過高,故拉伸強度及VDA彎角是低的。試料編號106中,由於第2之平均冷卻速度是過度的,麻田散鐵之面積分率不足,故拉伸強度、擴孔率及VDA彎角是低的。試料編號107中,由於第2之平均冷卻速度是過低、麻田散鐵及粒狀變韌鐵之面積分率不足、變韌鐵之面積分率是過高,拉伸強度及VDA彎角是低的。試料編號108中,由於第2之平均冷卻速度是過高,麻田散鐵及粒狀變韌鐵之面積分率不足,且變韌鐵之面積分率是過高,故拉伸強度、擴孔率及VDA彎角是低的。In sample No. 94, the steel embryo heating temperature was too low, and undesired cracking occurred during hot rolling, and the through-plate could not be performed thereafter. In sample No. 95, since the finishing temperature of the finishing rolling was too low and the shape was deteriorated during the hot rolling, the through-plate could not be performed thereafter. In sample No. 96, since the coiling temperature was excessive, the hot-rolled steel sheet became too hard, and thereafter cold rolling could not be performed. In sample No. 97, since the coiling temperature was too high and the area fraction of the granulated iron was insufficient, the elongation, the hole expansion ratio, and the VDA angle were low. In sample No. 98, since the cold rolling reduction ratio was too low, the shape was deteriorated during cold rolling, and thereafter cold rolling could not be performed. In sample No. 99, since the cold rolling reduction ratio was too high, the rolling load was excessively increased, and thereafter cold rolling could not be performed. In sample No. 100, since the maximum heating temperature of the annealing was too high, the area fraction of the ferrite iron was insufficient, and the area fraction of the toughened iron was too large, so the elongation was low. In sample No. 101, since the maximum heating temperature of annealing is too low, the area fraction of ferrite iron and ferritic iron is too much, and the area fraction of granulated iron and granular toughened iron is insufficient, so tensile strength and expansion The porosity is low. In sample No. 102, since the holding time of the highest heating temperature is too short, the area fraction of the ferrite iron and the ferrite is too high, and the area fraction of the granulated iron and the granular toughened iron is insufficient, so the tensile strength and expansion The porosity and VDA angle are low. In sample No. 103, since the holding time of the highest heating temperature was too short, the area fraction of the ferrite was excessive, the area fraction of the granular toughened iron was insufficient, and the tensile strength was low. In sample No. 104, the first average cooling rate was too low, the area fraction of the ferrite iron was too high, and the area fraction of the granulated iron was insufficient, so the tensile strength was low. In sample No. 105, since the first average cooling rate is too high, the area fraction of the ferrite iron is insufficient, and the area fraction of the granular toughened iron and the ferrite is too high, the tensile strength and the VDA angle are low. In sample No. 106, since the second average cooling rate was excessive, the area fraction of the granulated iron was insufficient, so the tensile strength, the hole expansion ratio, and the VDA angle were low. In sample No. 107, since the second average cooling rate is too low, the area fraction of the granulated iron and the granular toughened iron is insufficient, and the area fraction of the toughened iron is too high, the tensile strength and the VDA angle are low. In sample No. 108, since the second average cooling rate is too high, the area fraction of the granulated iron and the granular toughened iron is insufficient, and the area fraction of the toughened iron is too high, so the tensile strength and the reaming are performed. The rate and VDA corner are low.
產業上之可利用性 本發明可利用於例如與汽車零件好適之鋼板相關連的產業。Industrial Applicability The present invention can be utilized, for example, in an industry associated with steel sheets suitable for automobile parts.
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