TW202024349A

TW202024349A - Steel sheet and manufacturing method for steel sheet

Info

Publication number: TW202024349A
Application number: TW108137478A
Authority: TW
Inventors: 林宏太郎; 岡本力; 上西朗弘; 神武孝彦
Original assignee: 日商日本製鐵股份有限公司
Priority date: 2018-10-17
Filing date: 2019-10-17
Publication date: 2020-07-01
Also published as: CN112313351A; JP6760543B1; WO2020080493A1; CN112313351B; JPWO2020080493A1

Abstract

The steel sheet contains C, Si, and sol. Al, and further contains Mn: more than 2.50% to less than 4.20% by mass, with the balance being iron and inevitable impurities. The steel sheet has, at a 1/8 thickness position from the surface, a metallographic structure comprising, by area ratio, austenite phases: 10% or greater, total of tempered martensite phases and bainite phases: 5% or greater, ferrite phases: 35% or greater, and fresh martensite phases: less than 15%, wherein the area ratio of non-recrystallized ferrite phases to the ferrite phases is 10 to 50%, CMn[gamma]/CMn[alpha], that is, a ratio between mean Mn concentration CMn[gamma] in the austenite phases and mean Mn concentration CMn[alpha] in the ferrite phases, is 1.20 or greater, and variation in the Vickers hardness at the 1/8 thickness position from the surface is 40 Hv or less.

Description

鋼板及鋼板之製造方法Steel plate and its manufacturing method

本揭示關於一種鋼板及其製造方法。This disclosure relates to a steel plate and its manufacturing method.

一般來說，若將鋼板高強度化，延伸率便會降低而會減低鋼板的成形性。因此，為了要使用高強度鋼板作為汽車車體用零件，必須提高屬相反特性之強度與成形性二者。另外，以鋼板為胚料的汽車車體用零件大多須進行彎曲加工，故對於用來作為車體用零件的高強度鋼板，係要求具有優異彎曲性。因此，鋼板之機械特性係要求具有高強度與優異成形性並且還具有優異彎曲性。Generally speaking, if the strength of the steel sheet is increased, the elongation will decrease and the formability of the steel sheet will be reduced. Therefore, in order to use high-strength steel sheets as parts for automobile bodies, it is necessary to improve both strength and formability, which are opposite characteristics. In addition, most automobile body parts using steel plates as blanks require bending processing. Therefore, high-strength steel sheets used as automobile body parts are required to have excellent bendability. Therefore, the mechanical properties of steel sheets require high strength and excellent formability as well as excellent bendability.

為了使延伸率提升、亦即使成形性提升，截至目前已提案有一種所謂的中Mn鋼，其積極添加了Mn，使鋼板中含有約5質量%的Mn，而在鋼中生成殘留沃斯田鐵(殘留γ)，並且係利用其變態誘發塑性(例如：非專利文獻1)。In order to increase the elongation and even the formability, a so-called medium Mn steel has been proposed so far, which actively adds Mn to make the steel plate contain about 5 mass% Mn, and the residual austenitic is generated in the steel. Iron (residual γ), and its deformation is used to induce plasticity (for example, Non-Patent Document 1).

另外，已提案有一種鋼板，其添加有2.60%以上且4.20%以下的Mn(專利文獻1)。由於上述鋼板亦較一般的高強度鋼含有更多Mn，故容易生成殘留沃斯田鐵，而延伸率高並顯示出優異成形性。In addition, a steel sheet has been proposed in which 2.60% or more and 4.20% or less of Mn is added (Patent Document 1). Since the above-mentioned steel sheet also contains more Mn than general high-strength steel, it is easy to generate residual austenitic iron, has a high elongation, and shows excellent formability.

先前技術文獻專利文獻專利文獻1：國際公開第2016/067623號Prior art literature Patent literature Patent Document 1: International Publication No. 2016/067623

非專利文獻非專利文獻1：古川敬、松村理，熱處理，日本，日本熱處理協會，平成9年，第37號卷，第4號，p.204Non-patent literature Non-Patent Document 1: Keikawa Furukawa, Ri Matsumura, Heat Treatment, Japan, Japan Heat Treatment Association, Heisei 9, Vol. 37, No. 4, p.204

發明概要發明欲解決之課題然而，非專利文獻1中揭示之鋼板因Mn含量多，在用於汽車車體用零件時熔接性有時會成為問題。因此，若考慮到作為汽車零件等的利用性，則期望以較少的Mn含量來提升鋼板的強度與成形性兩者。此外，專利文獻1中揭示之鋼板形成明顯的帶狀組織，故彎曲性顯示出顯著的各向異性。當彎曲稜線為軋延方向時，彎曲性尤其惡化。如上述，彎曲性的各向異性若變大，便難以製成方筒狀的零件等，不僅零件設計的自由度降低，成形零件時的產率也會降低。以下，將彎曲稜線為軋延方向時的彎曲性僅稱為彎曲性。Summary of the invention Problems to be solved by the invention However, since the steel sheet disclosed in Non-Patent Document 1 has a large Mn content, the weldability sometimes becomes a problem when it is used for automobile body parts. Therefore, considering the usability as automobile parts, etc., it is desirable to improve both the strength and formability of the steel sheet with a small Mn content. In addition, the steel plate disclosed in Patent Document 1 has a distinct band-like structure, and therefore exhibits significant anisotropy in bending properties. When the bending ridge is in the rolling direction, the bendability is particularly deteriorated. As mentioned above, if the anisotropy of the bendability increases, it becomes difficult to form a rectangular cylindrical part. Not only does the degree of freedom of part design decrease, but also the productivity when forming the part decreases. Hereinafter, the bendability when the bending ridge line is in the rolling direction is simply referred to as bendability.

從而，期望一種具有優異延伸特性、優異彎曲性及高強度之鋼板。Therefore, a steel sheet having excellent elongation characteristics, excellent bendability, and high strength is desired.

用以解決課題之手段本發明人等得知以下方式可有效確保優異延伸特性、優異彎曲性及高強度：使含有預定成分之鋼板中以面積%計含有：10%以上的沃斯田鐵相，合計5%以上的回火麻田散鐵相與變韌鐵相、及35%以上的肥粒鐵相，並將新生麻田散鐵相限制為小於15%，使未再結晶肥粒鐵相相對於肥粒鐵相的面積率為10~50%，使沃斯田鐵相之平均Mn濃度CMnγ與肥粒鐵相之平均Mn濃度CMnα之比CMnγ/CMnα為1.20以上，並且使從表面起算1/8厚度位置的維氏硬度之參差在40Hv以下。Means to solve the problem The inventors of the present invention have learned that the following methods can effectively ensure excellent elongation characteristics, excellent bending properties and high strength: a steel plate containing a predetermined composition contains: 10% or more of austenitic iron phase, and a total of 5% or more Tempering the loose iron phase and toughened iron phase, and more than 35% of the ferrous iron phase, and limit the new-born Astian scattered iron phase to less than 15%, so that the unrecrystallized ferrous iron phase is relative to the ferrous iron phase. The area ratio is 10-50%, so that the ratio of the average Mn concentration CMnγ of the austenitic iron phase CMnγ to the average Mn concentration Cmnα of the fertilizer grain iron phase CMnγ/CMnα is 1.20 or more, and the dimension of 1/8 thickness position from the surface The variation in hardness is below 40Hv.

本揭示之鋼板及其製造方法係根據上述知識見解而作成者，其主旨如下。The steel plate and its manufacturing method of this disclosure are based on the above-mentioned knowledge and knowledge, and its gist is as follows.

本揭示之主旨如下。 (1) 一種鋼板，其化學組成以質量%計為： C：大於0.15且小於0.40%、 Si：0.001且小於2.00%、 Mn：大於2.50且小於4.20%、 sol.Al：0.001且小於1.500%、 P：0.030%以下、 S：0.0050%以下、 N：小於0.050%、 O：小於0.020%、 Cr：0~0.50%、 Mo：0~2.00%、 W：0~2.00%、 Cu：0~2.00%、 Ni：0~2.00%、 Ti：0~0.300%、 Nb：0~0.300%、 V：0~0.300%、 B：0~0.010%、 Ca：0~0.010%、 Mg：0~0.010%、 Zr：0~0.010%、 REM：0~0.010%、 Sb：0~0.050%、 Sn：0~0.050%、 Bi：0~0.050%及剩餘部分：鐵及不純物，且從表面起算1/8厚度位置的金屬組織以面積率計為：沃斯田鐵相：10%以上、回火麻田散鐵相與變韌鐵相之合計：5%以上、肥粒鐵相：35%以上、及新生麻田散鐵相：小於15%；未再結晶肥粒鐵相相對於前述肥粒鐵相的面積率為10~50%；前述沃斯田鐵相之平均Mn濃度CMnγ與前述肥粒鐵相之平均Mn濃度CMnα之比CMnγ/CMnα為1.20以上；並且從表面起算1/8厚度位置的維氏硬度之參差在40Hv以下。 (2) 如(1)之鋼板，其中前述化學組成含有選自於由以下所構成群組中之1種或2種以上元素：以質量%計， Cr：0.01~0.50%、 Ti：0.005~0.300%、 Nb：0.005~0.300%、 V：0.005~0.300%及 B：0.0001~0.010%。 (3) 如(1)或(2)之鋼板，前述鋼板的表面具有熔融鍍鋅層。 (4) 如(1)或(2)之鋼板，前述鋼板的表面具有合金化熔融鍍鋅層。 (5) 一種鋼板之製造方法，包含以下步驟：對鋼施行熱軋延以製成熱軋鋼板，該熱軋延中，精整軋延溫度為1000℃以下，前述精整軋延後的放冷時間為0.8秒以上，前述放冷後的平均冷卻速度為30℃/秒以上以及捲取溫度低於300℃，並且前述鋼之化學組成以質量%計為： C：大於0.15且小於0.40%、 Si：0.001且小於2.00%、 Mn：大於2.50且小於4.20%、 sol.Al：0.001且小於1.500%、 P：0.030%以下、 S：0.0050%以下、 N：小於0.050%、 O：小於0.020%、 Cr：0~0.50%、 Mo：0~2.00%、 W：0~2.00%、 Cu：0~2.00%、 Ni：0~2.00%、 Ti：0~0.300%、 Nb：0~0.300%、 V：0~0.300%、 B：0~0.010%、 Ca：0~0.010%、 Mg：0~0.010%、 Zr：0~0.010%、 REM：0~0.010%、 Sb：0~0.050%、 Sn：0~0.050%、 Bi：0~0.050%及剩餘部分：鐵及不純物；對前述熱軋鋼板在沃斯田鐵相分率成為20~50%之溫度區下進行1小時以上的熱處理，然後施行酸洗及冷軋延，以製成冷軋鋼板；設前述冷軋延之冷軋延率為30~70%；將前述冷軋鋼板在沃斯田鐵相分率成為20~65%之溫度區下維持30秒以上，進行退火；及在前述退火之溫度維持後，冷卻至100~530℃之溫度區，並在100~530℃之溫度區下維持10~1000秒。 (6) 如(5)之鋼板之製造方法，其中前述化學組成含有選自於由以下所構成群組中之1種或2種以上元素：以質量%計， Cr：0.01~0.50%、 Ti：0.005~0.300%、 Nb：0.005~0.300%、 V：0.005~0.300%及 B：0.0001~0.010%。 (7) 如(5)或(6)之鋼板之製造方法，其中前述精整軋延後的放冷時間為1.2~4.0秒。 (8) 如(5)至(7)中任一項之鋼板之製造方法，其中於前述退火後施行熔融鍍鋅處理。 (9) 如(8)之鋼板之製造方法，其中於施行前述熔融鍍鋅處理後，在450~620℃之溫度區下施行前述熔融鍍鋅的合金化處理。The gist of this disclosure is as follows. (1) A steel plate whose chemical composition is calculated as mass %: C: greater than 0.15 and less than 0.40%, Si: 0.001 and less than 2.00%, Mn: greater than 2.50 and less than 4.20%, sol.Al: 0.001 and less than 1.500%, P: 0.030% or less, S: 0.0050% or less, N: less than 0.050%, O: less than 0.020%, Cr: 0~0.50%, Mo: 0~2.00%, W: 0~2.00%, Cu: 0~2.00%, Ni: 0~2.00%, Ti: 0~0.300%, Nb: 0~0.300%, V: 0~0.300%, B: 0~0.010%, Ca: 0~0.010%, Mg: 0~0.010%, Zr: 0~0.010%, REM: 0~0.010%, Sb: 0~0.050%, Sn: 0~0.050%, Bi: 0~0.050% and Remaining part: iron and impurities, and The area ratio of the metal structure at 1/8 thickness from the surface is: Austenitic iron phase: 10% or more, the sum of tempered Matian scattered iron phase and toughened iron phase: 5% or more, Fertilizer iron phase: 35% or more, and scattered iron phase of Xinsheng Matian: less than 15%; The area ratio of the unrecrystallized fertilizer grain iron phase relative to the aforementioned fertilizer grain iron phase is 10-50%; The ratio CMnγ/CMnα of the average Mn concentration CMnγ of the aforementioned austenitic iron phase to the average Mn concentration CMnα of the aforementioned fertilizer grain iron phase is 1.20 or more; and The variation of Vickers hardness at 1/8 thickness from the surface is below 40Hv. (2) The steel plate of (1), wherein the aforementioned chemical composition contains one or more elements selected from the group consisting of: In terms of mass %, Cr: 0.01~0.50%, Ti: 0.005~0.300%, Nb: 0.005~0.300%, V: 0.005~0.300% and B: 0.0001~0.010%. (3) Like the steel sheet of (1) or (2), the surface of the steel sheet has a hot-dip galvanizing layer. (4) Like the steel sheet of (1) or (2), the surface of the steel sheet has an alloyed hot-dip galvanized layer. (5) A method of manufacturing steel plate, including the following steps: Hot rolling is performed on the steel to produce a hot-rolled steel sheet. In this hot rolling, the finishing temperature is 1000°C or less, and the cooling time after the finishing rolling is 0.8 seconds or more. The average after cooling is The cooling rate is 30°C/sec or more and the coiling temperature is lower than 300°C, and the chemical composition of the aforementioned steel is calculated as mass%: C: greater than 0.15 and less than 0.40%, Si: 0.001 and less than 2.00%, Mn: greater than 2.50 and less than 4.20%, sol.Al: 0.001 and less than 1.500%, P: 0.030% or less, S: 0.0050% or less, N: less than 0.050%, O: less than 0.020%, Cr: 0~0.50%, Mo: 0~2.00%, W: 0~2.00%, Cu: 0~2.00%, Ni: 0~2.00%, Ti: 0~0.300%, Nb: 0~0.300%, V: 0~0.300%, B: 0~0.010%, Ca: 0~0.010%, Mg: 0~0.010%, Zr: 0~0.010%, REM: 0~0.010%, Sb: 0~0.050%, Sn: 0~0.050%, Bi: 0~0.050% and Remaining part: iron and impurities; The aforementioned hot-rolled steel sheet is heat-treated for more than 1 hour in a temperature zone where the austenitic iron phase fraction becomes 20-50%, and then pickled and cold-rolled to produce cold-rolled steel sheets; Let the cold rolling elongation rate of the aforementioned cold rolling be 30~70%; Keep the aforementioned cold-rolled steel sheet in a temperature zone where the austenitic iron phase fraction becomes 20-65% for more than 30 seconds, and then perform annealing; and After maintaining the aforementioned annealing temperature, it is cooled to a temperature zone of 100~530℃, and maintained at a temperature zone of 100~530℃ for 10~1000 seconds. (6) Such as (5) of the method for manufacturing a steel plate, wherein the aforementioned chemical composition contains one or more elements selected from the group consisting of: In terms of mass %, Cr: 0.01~0.50%, Ti: 0.005~0.300%, Nb: 0.005~0.300%, V: 0.005~0.300% and B: 0.0001~0.010%. (7) Such as (5) or (6) of the method of manufacturing steel plate, wherein the cooling time after the finishing rolling is 1.2~4.0 seconds. (8) The method for manufacturing a steel sheet according to any one of (5) to (7), wherein the hot-dip galvanizing treatment is performed after the aforementioned annealing. (9) The method for manufacturing a steel sheet as in (8), wherein after performing the hot-dip galvanizing treatment, the alloying treatment of the hot-dip galvanizing is performed at a temperature range of 450 to 620°C.

發明效果根據本揭示，可提供一種具有優異延伸特性、優異彎曲性及高強度之鋼板。Invention effect According to the present disclosure, it is possible to provide a steel sheet having excellent elongation characteristics, excellent bendability, and high strength.

用以實施發明之形態以下，說明本揭示鋼板之一實施形態之示例。The form used to implement the invention Hereinafter, an example of one embodiment of the steel plate of the present disclosure will be described.

1.化學組成說明將本揭示鋼板的化學組成規定成如上述的理由。以下說明中，表示各元素含量之符號「%」只要未特別說明即指質量%。就鋼板的化學組成，使用「~」來表示之數值範圍除了有使用「大於」或「小於」的情況之外，意指包含「~」之前後所記載的數值作為下限值及上限值之範圍。1. Chemical composition The reason for specifying the chemical composition of the steel sheet of the present disclosure as described above will be explained. In the following description, the symbol "%" indicating the content of each element means mass% unless otherwise specified. Regarding the chemical composition of the steel sheet, the numerical range indicated by "~" means that the numerical value described before and after "~" is included as the lower limit and upper limit, except for the case of "greater than" or "less than". The scope.

(C：大於0.15且小於0.40%) C在用以提高鋼之強度並確保沃斯田鐵相上係極為重要之元素。為了獲得充分的沃斯田鐵相，必須有大於0.15%的C含量。另一方面，若含有過多C，會變得難以維持鋼板之熔接性，因此C含量上限設為小於0.40%。C含量之下限值宜在0.20%以上，且較宜在0.25%以上。若使C含量在0.20%以上，則可更加促進沃斯田鐵相生成。而C含量之上限值宜在0.36%以下、較宜在0.32%以下，藉由使C含量之上限值為上述範圍，可更加提高鋼板的韌性。(C: greater than 0.15 and less than 0.40%) C is an extremely important element for improving the strength of steel and ensuring the iron phase of austenitic. In order to obtain sufficient austenitic iron phase, the C content must be greater than 0.15%. On the other hand, if too much C is contained, it becomes difficult to maintain the weldability of the steel sheet, so the upper limit of the C content is set to less than 0.40%. The lower limit of C content should be above 0.20%, and more preferably above 0.25%. If the C content is 0.20% or more, the formation of austenitic iron phase can be further promoted. The upper limit of the C content is preferably 0.36% or less, more preferably 0.32% or less. By setting the upper limit of the C content within the above range, the toughness of the steel sheet can be further improved.

(Si：0.001且小於2.00%) Si係一種可有效強化回火麻田散鐵相並將組織均一化以改善成形性之元素。並且，Si也具有抑制雪明碳鐵析出並促進沃斯田鐵相殘留的作用。為了獲得上述效果，必須有0.001%以上之Si含量。另一方面，若含有過多Si，會變得難以維持鋼板之鍍敷性及化學轉化處理性，因此Si含量之上限值設為小於2.00%。Si含量之下限值宜在0.005%以上、較宜在0.010%以上且更宜在0.10%以上。藉由使Si含量之下限值為上述範圍，可更加提升鋼板的延伸特性。而Si含量之上限值宜在1.90%以下，且較宜在1.80%以下。(Si: 0.001 and less than 2.00%) Si is an element that can effectively strengthen the scattered iron phase of tempered Asada and homogenize the structure to improve formability. In addition, Si also has the effect of suppressing the precipitation of snow carbon iron and promoting the residue of the austenitic iron phase. In order to obtain the above effects, a Si content of 0.001% or more is necessary. On the other hand, if too much Si is contained, it becomes difficult to maintain the plating properties and chemical conversion processability of the steel sheet, so the upper limit of the Si content is set to less than 2.00%. The lower limit of Si content should be above 0.005%, more preferably above 0.010%, and more preferably above 0.10%. By setting the lower limit of the Si content to the above range, the elongation characteristics of the steel sheet can be further improved. The upper limit of Si content should be below 1.90%, and more preferably below 1.80%.

(Mn：大於2.50且小於4.20%) Mn係可使沃斯田鐵相穩定化並提高淬火性之元素。此外，本揭示之鋼板中係使Mn在沃斯田鐵相中濃化，以使沃斯田鐵相更加穩定化。為了要在室溫下使沃斯田鐵相穩定化，必須有大於2.50%的Mn。另一方面，為了確保熔接性並使彎曲稜線為軋延方向時的彎曲性不減低，而將Mn含量上限設為小於4.20%。Mn含量之下限值宜大於3.00%，且較宜在3.50%以上。而Mn含量之上限值宜在4.10%以下，且較宜在4.00%以下。藉由使Mn含量之下限值為上述範圍，可增加穩定之沃斯田鐵相的分率，而藉由使Mn含量之上限值為上述範圍，則可使彎曲性充分發揮。(Mn: more than 2.50 and less than 4.20%) Mn is an element that stabilizes the austenitic iron phase and improves hardenability. In addition, in the steel plate of the present disclosure, Mn is concentrated in the austenitic iron phase to stabilize the austenitic iron phase more. In order to stabilize the austenitic iron phase at room temperature, there must be more than 2.50% Mn. On the other hand, in order to ensure the weldability and not reduce the bendability when the bending ridge line is in the rolling direction, the upper limit of the Mn content is made less than 4.20%. The lower limit of Mn content should be more than 3.00%, and more preferably more than 3.50%. The upper limit of Mn content should be below 4.10%, and more preferably below 4.00%. By setting the lower limit of the Mn content in the above range, the fraction of the stable austenitic iron phase can be increased, and by setting the upper limit of the Mn content in the above range, the flexibility can be fully exhibited.

(sol.Al：0.001且小於1.500%) Al為脫氧劑，必須含有0.001%以上。又，Al會擴大退火時二相區的溫度範圍，因此也具有提高材質穩定性的作用。Al含量越多則該效果變得越大，但若含有過多Al，會變得難以維持表面性狀、塗裝性及熔接性，因此sol.Al上限設為小於1.500%。sol.Al含量之下限值宜在0.005%以上、較宜在0.010%以上且更宜在0.020%以上。而sol.Al含量之上限值宜在1.200%以下，且較宜在1.000%以下。藉由使sol.Al含量之下限值及上限值為上述範圍，可使脫氧效果及提升材質穩定之效果與表面性狀、塗裝性及熔接性之平衡變得更加良好。(sol.Al: 0.001 and less than 1.500%) Al is a deoxidizer and must contain 0.001% or more. In addition, Al expands the temperature range of the two-phase region during annealing, and therefore also has the effect of improving material stability. The greater the Al content, the greater the effect, but if too much Al is contained, it becomes difficult to maintain the surface properties, paintability, and weldability, so the upper limit of sol.Al is made less than 1.500%. The lower limit of sol.Al content should be above 0.005%, more preferably above 0.010%, and more preferably above 0.020%. The upper limit of sol.Al content should be below 1.200%, and more preferably below 1.000%. By setting the lower limit and upper limit of the sol.Al content to the above range, the deoxidation effect and the effect of improving the stability of the material can be better balanced with the surface properties, paintability and weldability.

(P：0.030%以下) P為不純物，若鋼板含有過多P便會損及彎曲性。因此，P含量上限設為0.030%以下。P含量之上限值宜在0.025%以下、較宜在0.020%以下且更宜在0.015%以下。本實施形態鋼板不一定需要P，故P含量之下限值為0%。P含量之下限值可大於0%或亦可在0.001%以上，而P含量越少越好。(P: 0.030% or less) P is an impure substance. If the steel plate contains too much P, it will impair the bendability. Therefore, the upper limit of the P content is made 0.030% or less. The upper limit of P content should be below 0.025%, more preferably below 0.020% and more preferably below 0.015%. The steel sheet of this embodiment does not necessarily need P, so the lower limit of the P content is 0%. The lower limit of P content can be greater than 0% or more than 0.001%, and the lower the P content, the better.

(S：0.0050%以下) S為不純物，若鋼板含有過多S便會損及熔接性。因此，S含量上限設為0.0050%以下。S含量之上限值宜在0.0030%以下，且較宜在0.0020%以下。本實施形態之鋼板不一定需要S，故S含量之下限值為0%。S含量之下限值可設為大於0%或亦可設為0.0003%以上，而S含量越少越好。(S: 0.0050% or less) S is an impure substance. If the steel plate contains too much S, the weldability will be impaired. Therefore, the upper limit of the S content is made 0.0050% or less. The upper limit of the S content should be below 0.0030%, and more preferably below 0.0020%. The steel plate of this embodiment does not necessarily need S, so the lower limit of the S content is 0%. The lower limit of the S content can be set to be greater than 0% or can be set to be greater than 0.0003%, and the lower the S content, the better.

(N：小於0.050%) N為不純物，若鋼板含有0.050%以上之N，韌性就會減低。因此，N含量上限設為小於0.050%。N含量之上限值宜在0.010%以下，且較宜在0.006%以下。本實施形態之鋼板不一定需要N，故N含量之下限值為0%。N含量之下限值可設為大於0%或亦可設為0.001%以上，而N含量越少越好。(N: less than 0.050%) N is impure. If the steel plate contains more than 0.050% of N, the toughness will decrease. Therefore, the upper limit of the N content is set to less than 0.050%. The upper limit of N content should be below 0.010%, and more preferably below 0.006%. The steel sheet of this embodiment does not necessarily need N, so the lower limit of the N content is 0%. The lower limit of the N content can be set to be greater than 0% or 0.001% or greater, and the smaller the N content, the better.

(O：小於0.020%) O為不純物，若鋼板含有0.020%以上之O，延性就會減低。因此，O含量上限設為小於0.020%。O含量之上限值宜在0.010%以下、較宜在0.005%以下且更宜在0.003%以下。本實施形態之鋼板不一定需要O，故O含量之下限值為0%。O含量之下限值可設為大於0%或亦可設為0.001%以上，而O含量越少越好。(O: less than 0.020%) O is impure. If the steel plate contains more than 0.020% O, the ductility will be reduced. Therefore, the upper limit of the O content is set to less than 0.020%. The upper limit of O content should be below 0.010%, more preferably below 0.005% and more preferably below 0.003%. The steel sheet of this embodiment does not necessarily need O, so the lower limit of the O content is 0%. The lower limit of O content can be set to be greater than 0% or 0.001% or more, and the less O content, the better.

本實施形態之鋼板亦可更含有選自於由以下所構成群組中之1種或2種以上元素：Cr、Mo、W、Cu、Ni、Ti、Nb、V、B、Ca、Mg、Zr、REM、Sb、Sn及Bi。然而，本實施形態之鋼板亦可不含有以下元素，亦即含量之下限值亦可為0%：Cr、Mo、W、Cu、Ni、Ti、Nb、V、B、Ca、Mg、Zr、REM、Sb、Sn及Bi。The steel sheet of this embodiment may further contain one or more elements selected from the group consisting of: Cr, Mo, W, Cu, Ni, Ti, Nb, V, B, Ca, Mg, Zr, REM, Sb, Sn and Bi. However, the steel sheet of this embodiment may not contain the following elements, that is, the lower limit of the content may be 0%: Cr, Mo, W, Cu, Ni, Ti, Nb, V, B, Ca, Mg, Zr, REM, Sb, Sn and Bi.

(Cr：0~0.50%) (Mo：0~2.00%) (W：0~2.00%) (Cu：0~2.00%) (Ni：0~2.00%) Cr、Mo、W、Cu及Ni各皆非本實施形態鋼板的必要元素，故各自的含量為0%以上。但是，由於Cr、Mo、W、Cu及Ni係會提升鋼板強度的元素，故亦可含有。為了獲得提升鋼板強度之效果，鋼板亦可含有選自於由Cr、Mo、W、Cu及Ni所構成群組中之1種或2種以上元素，且可分別含有0.01%以上、0.04%以上或0.10%以上。然而，若鋼板含有過多該等元素，便容易產生熱軋時之表面傷痕，而且會有熱軋鋼板之強度變得過高而冷軋延性降低的情況。因此，選自於由Cr、Mo、W、Cu及Ni所構成群組中之1種或2種以上元素之各自含量中，Cr含量之上限值設為0.50%以下，Mo、W、Cu及Ni各自的含量上限值則設為2.00%以下。Cr含量之上限值亦可為0.45%以下、0.40%以下或0.35%以下，而Mo、W、Cu及Ni各自的含量上限值亦可為1.80%以下、1.50%以下、1.20%以下或1.00%以下。(Cr: 0~0.50%) (Mo: 0~2.00%) (W: 0~2.00%) (Cu: 0~2.00%) (Ni: 0~2.00%) Each of Cr, Mo, W, Cu, and Ni is not an essential element of the steel sheet of the present embodiment, so the content of each is 0% or more. However, since Cr, Mo, W, Cu, and Ni are elements that increase the strength of the steel sheet, they may also be contained. In order to obtain the effect of increasing the strength of the steel plate, the steel plate may also contain one or more elements selected from the group consisting of Cr, Mo, W, Cu and Ni, and may contain 0.01% or more and 0.04% or more, respectively Or more than 0.10%. However, if the steel sheet contains too much of these elements, it is easy to produce surface scars during hot rolling, and the strength of the hot rolled steel sheet may become too high and the cold rolling ductility may decrease. Therefore, in the respective contents of one or more elements selected from the group consisting of Cr, Mo, W, Cu and Ni, the upper limit of the Cr content is set to 0.50% or less, Mo, W, Cu The upper limit of each content of Ni and Ni is set to 2.00% or less. The upper limit of the Cr content can also be 0.45%, 0.40%, or 0.35%, and the upper limit of the content of Mo, W, Cu, and Ni can also be 1.80%, 1.50%, 1.20%, or 1.00% or less.

(Ti：0~0.300%) (Nb：0~0.300%) (V：0~0.300%) Ti、Nb及V並非本實施形態鋼板的必要元素，故各自的含量為0%以上。然而，Ti、Nb及V係會生成微細碳化物、氮化物或碳氮化物之元素，故可有效提升鋼板強度。因此，鋼板亦可含有選自於由Ti、Nb及V所構成群組中之1種或2種以上元素。為了獲得提升鋼板強度之效果，選自於由Ti、Nb及V所構成群組中之1種或2種以上元素各自的含量下限值宜設為0.005%以上，且較宜設為0.010%以上。另一方面，若含有過多該等元素，便會有熱軋鋼板強度過度上升而冷軋延性降低的情況。另外，針對Nb，若使Nb含量在0.300%以下，可抑制肥粒鐵相之再結晶化的延遲，而可更穩定地獲得所欲組織。因此，選自於由Ti、Nb及V所構成群組中之1種或2種以上元素各自的含量上限值設為0.300%以下，且宜設為0.250%以下，較宜設為0.200%以下。(Ti: 0~0.300%) (Nb: 0~0.300%) (V: 0~0.300%) Ti, Nb, and V are not essential elements of the steel sheet of the present embodiment, so their respective contents are 0% or more. However, Ti, Nb, and V are elements that generate fine carbides, nitrides or carbonitrides, so they can effectively increase the strength of the steel sheet. Therefore, the steel sheet may contain one or more elements selected from the group consisting of Ti, Nb, and V. In order to obtain the effect of increasing the strength of the steel sheet, the lower limit of the content of one or more elements selected from the group consisting of Ti, Nb and V should be set to 0.005% or more, and more preferably 0.010% the above. On the other hand, if these elements are contained too much, the strength of the hot-rolled steel sheet may increase excessively and the cold-rolled ductility may decrease. In addition, for Nb, if the Nb content is 0.300% or less, the delay of the recrystallization of the ferrite phase can be suppressed, and the desired structure can be obtained more stably. Therefore, the upper limit of the content of one or two or more elements selected from the group consisting of Ti, Nb and V is set to 0.300% or less, preferably 0.250% or less, more preferably 0.200% the following.

(B：0~0.010%) (Ca：0~0.010%) (Mg：0~0.010%) (Zr：0~0.010%) (REM：0~0.010%) B、Ca、Mg、Zr及REM(稀土族金屬)並非本揭示鋼板的必要元素，故各自的含量為0%以上。但B、Ca、Mg、Zr及REM可提升鋼板之局部延性及擴孔性。為了獲得該效果，選自於由B、Ca、Mg、Zr及REM所構成群組中之1種或2種以上元素各自的下限值宜設為0.0001%以上，且較宜設為0.001%以上。然而，過量的該等元素會使鋼板之成形性劣化，故該等元素各自的含量上限宜設為0.010%以下，並且選自於由B、Ca、Mg、Zr及REM所構成群組中之1種或2種以上元素之合計含量宜設為0.030%以下。(B: 0~0.010%) (Ca: 0~0.010%) (Mg: 0~0.010%) (Zr: 0~0.010%) (REM: 0~0.010%) B, Ca, Mg, Zr, and REM (rare earth metals) are not essential elements of the steel sheet of the present disclosure, so the content of each is 0% or more. However, B, Ca, Mg, Zr and REM can improve the local ductility and hole expandability of the steel plate. In order to obtain this effect, the lower limit of each of one or two or more elements selected from the group consisting of B, Ca, Mg, Zr, and REM should be set to 0.0001% or more, and more preferably to 0.001% the above. However, excessive amounts of these elements will deteriorate the formability of the steel sheet, so the upper limit of each of these elements is preferably set to 0.010% or less, and is selected from the group consisting of B, Ca, Mg, Zr and REM The total content of one or more elements should be set to 0.030% or less.

(Sb：0~0.050%) (Sn：0~0.050%) (Bi：0~0.050%) Sb、Sn及Bi並非本揭示鋼板的必要元素，故各自的含量為0%以上。然而，Sb、Sn及Bi會抑制鋼板中的Mn、Si及/或Al等易氧化元素擴散至鋼板表面形成氧化物，而可提高鋼板的表面性狀及鍍敷性。為了獲得該效果，選自於由Sb、Sn及Bi所構成群組中之1種或2種以上元素各自的含量下限值宜設為0.0005%以上，且較宜設為0.001%以上。另一方面，該等元素各自的含量若大於0.050%，該效果便會飽和，故該等元素各自的含量上限值設為0.050%以下，且宜設為0.040%以下，較宜設為0.030%以下。(Sb: 0~0.050%) (Sn: 0~0.050%) (Bi: 0~0.050%) Sb, Sn, and Bi are not essential elements of the steel sheet of the present disclosure, so their respective contents are 0% or more. However, Sb, Sn, and Bi inhibit the diffusion of easily oxidizable elements such as Mn, Si and/or Al in the steel sheet to the surface of the steel sheet to form oxides, thereby improving the surface properties and plating properties of the steel sheet. In order to obtain this effect, the lower limit of the content of each of one or two or more elements selected from the group consisting of Sb, Sn, and Bi is preferably set to 0.0005% or more, and more preferably 0.001% or more. On the other hand, if the content of each of these elements is greater than 0.050%, the effect will be saturated. Therefore, the upper limit of the content of each of these elements is set to 0.050% or less, preferably 0.040% or less, more preferably 0.030 %the following.

本實施形態鋼板在上述任意成分當中，亦可含有選自於由以下所構成群組中之1種或2種以上元素：Cr：0.01~0.50%、Ti：0.005~0.300%、Nb：0.005~0.300%、V：0.005~0.300%及B：0.0001~0.010%。The steel sheet of this embodiment may contain one or more elements selected from the group consisting of: Cr: 0.01~0.50%, Ti: 0.005~0.300%, Nb: 0.005~ 0.300%, V: 0.005~0.300% and B: 0.0001~0.010%.

又，本實施形態鋼板的化學組成之剩餘部分為鐵及不純物。不純物係從鋼原料、廢料以及/或會在製鋼過程中無法避免地混入之物，可例示在不阻礙本實施形態鋼板之特性的範圍內可容許的元素。並且，不純物係除了以上說明之成分以外的元素，且亦包含以該元素特有之作用效果並不會對本發明實施形態鋼板之特性產生影響之程度被含於該鋼板中之元素。In addition, the remainder of the chemical composition of the steel sheet of this embodiment is iron and impurities. Impurities include steel raw materials, scraps, and/or things that are unavoidably mixed in the steel making process, and can exemplify elements that are permissible within a range that does not hinder the characteristics of the steel sheet of this embodiment. In addition, the impurity is an element other than the components described above, and also includes an element contained in the steel sheet to the extent that its unique effect does not affect the characteristics of the steel sheet of the embodiment of the present invention.

2.金屬組織接下來說明本實施形態鋼板的金屬組織。2. Metal structure Next, the metal structure of the steel sheet of this embodiment will be described.

從本實施形態鋼板之表面起算1/8厚度位置(也稱為1/8t部)的金屬組織，以面積率計為：沃斯田鐵相：10%以上、回火麻田散鐵相與變韌鐵相之合計：5%以上、肥粒鐵相：35%以上、及新生麻田散鐵相：小於15%。各組織之分率會依熱處理條件而有所變化，且會對強度、延伸特性及彎曲性等鋼板的材質造成影響。The metal structure of the 1/8th thickness position (also called 1/8t part) from the surface of the steel plate of this embodiment is calculated by area ratio as follows: Austenitic iron phase: 10% or more, tempered Asada scattered iron phase and transformation The total tough iron phase: 5% or more, the fat grain iron phase: 35% or more, and the new matian scattered iron phase: less than 15%. The fraction of each structure will vary depending on the heat treatment conditions, and will affect the strength, elongation, and bendability of the steel plate material.

(鋼板之1/8t部的金屬組織中沃斯田鐵相的面積%：10%以上) 就本實施形態之鋼板，重要的係金屬組織中之沃斯田鐵相的量在預定範圍中。沃斯田鐵相係一種可利用變態誘發塑性來提高鋼板的延伸特性之組織。沃斯田鐵相可藉由伴隨拉伸變形的撐壓加工、引伸加工、延伸凸緣加工或彎曲加工而變態為麻田散鐵相，因此也有助於提升鋼板強度。為獲得該等效果，本實施形態之鋼板以面積率計，必須在金屬組織中含有10%以上之沃斯田鐵相。沃斯田鐵相之面積率宜為15%以上，且較宜為18%以上。沃斯田鐵相之面積率若在15%以上，更甚者若成為18%以上，便可兼顧強度與延伸率，後述TS×EL就會變高。沃斯田鐵相之面積率上限並未特別規定，而實質上係在30%以下。又，沃斯田鐵相之面積率係利用X射線繞射法來測定。(The area% of the austenitic iron phase in the metal structure of 1/8t of the steel plate: 10% or more) In the steel sheet of this embodiment, the amount of the austenitic iron phase in the important metal structure is within a predetermined range. Austenitic iron phase is a kind of organization that can use deformation induced plasticity to improve the elongation characteristics of steel plate. The austenitic iron phase can be transformed into the Asada scattered iron phase by pressing processing, drawing processing, extension flange processing or bending processing accompanying tensile deformation, so it also helps to increase the strength of the steel plate. In order to obtain these effects, the steel sheet of this embodiment must contain 10% or more of the austenitic iron phase in the metal structure in terms of area ratio. The area ratio of the austenitic iron phase should be over 15%, and more preferably over 18%. If the area ratio of the austenitic iron phase is more than 15%, or even more than 18%, the strength and elongation can be balanced, and the TS×EL described later will increase. The upper limit of the austenitic iron phase area ratio is not specifically specified, but is essentially below 30%. In addition, the area ratio of the austenitic iron phase is measured by the X-ray diffraction method.

(鋼板之1/8t部的金屬組織中新生麻田散鐵相的面積%：小於15%) 新生麻田散鐵相係於其組織中富含差排的硬質相，且係可有效用以獲得鋼板強度之相。惟，因其會使彎曲性明顯劣化，故新生麻田散鐵相在金屬組織中之面積率設為小於15%。特別需要彎曲性時，新生麻田散鐵相之面積率宜為10%以下且較宜為5%以下，實質上更宜為0%。(The area% of the newly formed Asada scattered iron phase in the metal structure of 1/8t of the steel plate: less than 15%) The new Asada scattered iron phase is rich in poorly arranged hard phases in its structure and can be effectively used to obtain the strength of steel plates. However, because it will significantly degrade the bendability, the area ratio of the nascent Asada scattered iron phase in the metal structure is set to be less than 15%. When flexibility is particularly required, the area ratio of the scattered iron phase of the new matian should be less than 10%, more preferably less than 5%, and substantially more preferably 0%.

(鋼板之1/8t部的金屬組織中回火麻田散鐵相與變韌鐵相之合計面積%：5%以上) 回火麻田散鐵相及變韌鐵相亦為硬質相，但係不同於上述新生麻田散鐵相之組織，其等有助於確保鋼板強度並且提升彎曲性。為了兼顧強度與彎曲性，回火麻田散鐵相與變韌鐵相在金屬組織中之合計面積率須在5%以上。當重視鋼板強度時，回火麻田散鐵相與變韌鐵相之合計面積率宜為10%以上、較宜為15%以上且更宜為20%以上。回火麻田散鐵相與變韌鐵相之合計面積率的上限並無特別限定，而實質上係在50%以下。在本實施形態鋼板的金屬組織中，大多係回火麻田散鐵相與變韌鐵相之合計面積率當中皆為回火麻田散鐵之面積率。另一方面，金屬組織中有時會含有變韌鐵相，但變韌鐵相具有與回火麻田散鐵相同樣的特徵，因此當金屬組織中含有變韌鐵相時，亦係將回火麻田散鐵相之面積率與變韌鐵相之面積率一併測定。(The total area% of tempered Asada scattered iron phase and toughened iron phase in the metal structure of 1/8t of the steel plate: 5% or more) The tempered Asada scattered iron phase and the toughened iron phase are also hard phases, but they are different from the above-mentioned newly formed Asada scattered iron phase. They help to ensure the strength of the steel plate and improve the bendability. In order to balance strength and flexibility, the total area ratio of tempered Asada scattered iron phase and toughened iron phase in the metal structure must be above 5%. When attaching importance to the strength of the steel plate, the combined area ratio of the tempered Matian scattered iron phase and the toughened iron phase should be more than 10%, more preferably more than 15%, and more preferably more than 20%. The upper limit of the total area ratio of the tempered Asada scattered iron phase and the toughened iron phase is not particularly limited, but is substantially less than 50%. In the metal structure of the steel sheet of this embodiment, most of the total area ratios of the tempered Asada scattered iron phase and the toughened iron phase are the area ratios of the tempered Asada scattered iron. On the other hand, the metal structure sometimes contains a toughened iron phase, but the toughened iron phase has the same characteristics as the tempered Asada scattered iron phase. Therefore, when the metal structure contains a toughened iron phase, it will also be tempered. The area ratio of the scattered iron phase of Matian is measured together with the area ratio of the toughened iron phase.

(鋼板之1/8t部的金屬組織中肥粒鐵相之面積率：35%以上) 肥粒鐵相在確保延性上係必要組織。為了確保必要的延性，金屬組織中肥粒鐵相之面積率為35%以上。金屬組織中肥粒鐵相之面積率宜為40%以上，且較宜為45%以上。金屬組織中肥粒鐵相之面積率上限並無特別限定，而實質上係在75%以下。另外，未再結晶肥粒鐵相相對於肥粒鐵相之面積率為10%以上，且宜為20%以上。藉由使未再結晶肥粒鐵相之面積率在上述範圍內，可獲得降伏點高之鋼板。另一方面，未再結晶肥粒鐵相若過多便會導致延性降低，故未再結晶肥粒鐵相之面積率上限設為50%以下。並且，未再結晶肥粒鐵相之面積率上限較宜為40%以下。(The area ratio of the ferrous iron phase in the metal structure of the 1/8t part of the steel plate: 35% or more) The ferrite phase is the necessary organization to ensure ductility. In order to ensure the necessary ductility, the area ratio of the ferrous iron phase in the metal structure is over 35%. The area ratio of the ferrous iron phase in the metal structure should be more than 40%, and more preferably more than 45%. The upper limit of the area ratio of the ferrous iron phase in the metallic structure is not particularly limited, but is substantially less than 75%. In addition, the area ratio of the non-recrystallized ferrous iron phase relative to the ferrous iron phase is 10% or more, and preferably 20% or more. By setting the area ratio of the unrecrystallized ferrous iron phase within the above range, a steel sheet with a high yield point can be obtained. On the other hand, too much unrecrystallized fertilizer grain iron phase will lead to a decrease in ductility, so the upper limit of the area ratio of the unrecrystallized fertilizer grain iron phase is set to 50% or less. In addition, the upper limit of the area ratio of the iron phase of unrecrystallized fertilizer grains is preferably less than 40%.

又，金屬組織中，除以下之相外的剩餘部分可為波來鐵與雪明碳鐵等組織：沃斯田鐵相、新生麻田散鐵相、回火麻田散鐵相(包含變韌鐵相)及肥粒鐵相。以替代方案而言，本實施形態之鋼板亦可僅由沃斯田鐵相、新生麻田散鐵相、回火麻田散鐵相、變韌鐵相及肥粒鐵相所構成。In addition, the remaining part of the metal structure except for the following phases can be pleite and snow carbon iron: austenitic iron phase, new matian scattered iron phase, tempered Matian scattered iron phase (including toughened iron Phase) and fat grain iron phase. As an alternative, the steel plate of the present embodiment can also be composed of only austenitic iron phase, newly-born Asada scattered iron phase, tempered Asada scattered iron phase, toughened iron phase, and fertile iron phase.

(CMnγ/CMnα≧1.20) 沃斯田鐵相之平均Mn濃度CMnγ與肥粒鐵相(包含未再結晶肥粒鐵相之所有肥粒鐵相)之平均Mn濃度CMnα之比CMnγ/CMnα為1.20以上，且宜為1.35以上。藉由使CMnγ/CMnα在上述範圍內，在熱處理中可充分獲得Mn分配，使Mn在原為沃斯田鐵相之處濃化，即使在短時間退火下也能獲得穩定之沃斯田鐵相，而可得到優異延性。另一方面，若CMnγ/CMnα小於1.20，則Mn分配不充分，難以在短時間退火下獲得沃斯田鐵相。另，CMnγ/CMnα之上限並無特別規定，而實質上係在1.60以下。(CMnγ/CMnα≧1.20) The ratio of the average Mn concentration CMnγ of the austenitic iron phase to the average Mn concentration CMnα of the fat iron phase (including all the fat iron phases of the unrecrystallized fat iron phase) CMnγ/CMnα is 1.20 or more, and preferably 1.35 or more . By making CMnγ/CMnα within the above range, Mn distribution can be fully obtained during heat treatment, and Mn can be concentrated at the place where the austenitic iron phase was originally, and a stable austenitic iron phase can be obtained even under short-time annealing. , And can get excellent ductility. On the other hand, if CMnγ/CMnα is less than 1.20, Mn distribution is insufficient, and it is difficult to obtain the austenitic iron phase under short-time annealing. In addition, the upper limit of CMnγ/CMnα is not specifically defined, but is substantially below 1.60.

(鋼板之1/8t部的位置的維氏硬度之參差在40Hv以下) 從鋼板表面起算1/8厚度位置的維氏硬度之參差在40Hv以下，且宜在30Hv以下。藉由將精整軋延後的冷卻條件與熱軋鋼板的熱處理條件最佳化，來抑制維氏硬度之參差，本實施形態鋼板之組織就會變得均一並可抑制帶狀組織生成，從而會提升彎曲稜線為軋延方向時的彎曲性。(The variation of Vickers hardness at the 1/8t part of the steel plate is below 40Hv) The variation of Vickers hardness at 1/8 thickness from the surface of the steel plate is below 40Hv, and preferably below 30Hv. By optimizing the cooling conditions after finishing rolling and the heat treatment conditions of the hot-rolled steel sheet to suppress the variation in Vickers hardness, the structure of the steel sheet of this embodiment becomes uniform and the formation of band-like structures is suppressed. This improves the bendability when the bending ridge is in the rolling direction.

以下，說明各測定方法。Hereinafter, each measurement method will be described.

(沃斯田鐵相之面積率的測定方法) 沃斯田鐵相之面積率係如以下方式算出。從鋼板表面的中央部(鋼板寬度方向之中點)切出試驗片，該試驗片在軋延方向之長度為25mm、在鋼板寬度方向(與軋延方向成直角的方向)上寬25mm且厚度係經退火之試樣的原有厚度。然後，對該試驗片施行化學研磨，使其厚度減少板厚的1/8份量，而獲得具有經化學研磨後的表面的試驗片。又，「與軋延方向成直角的方向」係指平行於鋼板表面且與軋延方向成直角的方向。接下來，對該試驗片表面實施3次X射線繞射分析，該X射線繞射分析係採用Co管球並將測定範圍2θ設為45~105度。藉由解析以上述方式進行而得之沃斯田鐵相分布圖，並將其等加以平均，便可獲得沃斯田鐵相之面積率。(Method of measuring the area ratio of austenitic iron phase) The area ratio of the austenitic iron phase is calculated as follows. A test piece was cut from the center of the steel sheet surface (the midpoint in the width direction of the steel sheet). The test piece had a length of 25 mm in the rolling direction, a width of 25 mm and a thickness in the width direction of the steel sheet (direction at right angles to the rolling direction). It is the original thickness of the annealed sample. Then, the test piece was chemically polished to reduce its thickness by 1/8 part of the plate thickness to obtain a test piece having a chemically polished surface. In addition, the "direction at right angles to the rolling direction" refers to a direction parallel to the surface of the steel sheet and at right angles to the rolling direction. Next, the X-ray diffraction analysis was performed three times on the surface of the test piece. The X-ray diffraction analysis system used Co tubes and the measurement range 2θ was set to 45 to 105 degrees. By analyzing the austenitic iron phase distribution map obtained in the above manner, and averaging them, the area ratio of the austenitic iron phase can be obtained.

(肥粒鐵相、回火麻田散鐵相與變韌鐵相之合計、及新生麻田散鐵相之面積率的測定方法) 肥粒鐵相、回火麻田散鐵相與變韌鐵相之合計、及新生麻田散鐵相之面積率係從利用掃描型電子顯微鏡(SEM)所行組織觀察來算出。對鋼板的L截面進行鏡面研磨，接著以3%硝太蝕劑使微觀組織露出，利用倍率5000倍的掃描型電子顯微鏡觀察從表面起算1/8位置中縱長0.1mm(板厚方向的長度)×寬0.3mm(軋延方向的長度)的範圍的微觀組織。肥粒鐵相(包含未再結晶肥粒鐵相)係被判別為灰色之基底組織，沃斯田鐵相及新生麻田散鐵相則被判別為白色組織。從沃斯田鐵相與新生麻田散鐵相之合計面積率減去藉由X射線繞射法測得之沃斯田鐵相之面積率，藉此便可算出新生麻田散鐵相之面積率。回火麻田散鐵相(包含變韌鐵相)係與新生麻田散鐵相同樣看起來呈白色，而係藉由將晶粒內可確認到下部組織者判斷為回火麻田散鐵相(包含變韌鐵相)來算出。又，L截面係指平行於軋延方向且相對於鋼板表面成垂直地裁切鋼板而成的面。本實施形態之L截面係設為以通過鋼板的寬度方向中心之方式裁切而成面。(Method for measuring the area ratio of the fat grain iron phase, tempered Matian scattered iron phase and toughened iron phase, and the area ratio of the newly formed Matian scattered iron phase) The total of the fat grain iron phase, the tempered Asada scattered iron phase and the toughened iron phase, and the area ratio of the new Asada scattered iron phase are calculated from the observation of the structure using a scanning electron microscope (SEM). The L section of the steel plate is mirror-polished, and then the microstructure is exposed with 3% nitrate etchant. Observed by a scanning electron microscope with a magnification of 5000 times, the length is 0.1 mm (the length in the thickness direction) from the surface at 1/8 position ) Microstructure in the range of 0.3 mm in width (length in the rolling direction). The fat iron phase (including the unrecrystallized fat iron phase) is judged to be the gray basal structure, and the austenitic iron phase and the newly-born Asada scattered iron phase are judged to be the white structure. The area rate of the austenitic iron phase measured by the X-ray diffraction method is subtracted from the total area rate of the austenitic iron phase and the new-born Astian scattered iron phase to calculate the area ratio of the newly-born Astian scattered iron phase. . The tempered Asada scattered iron phase (including the toughened iron phase) looks white like the new Asada scattered iron phase, and it is judged as the tempered Asada scattered iron phase (including Toughened iron phase) to calculate. In addition, the L cross section refers to a surface obtained by cutting a steel plate parallel to the rolling direction and perpendicular to the surface of the steel plate. The L cross section of the present embodiment is a surface cut so as to pass through the center in the width direction of the steel plate.

(未再結晶肥粒鐵相之面積率的測定方法) 未再結晶肥粒鐵相之面積率係藉由以下方式算出：以上述方式判別出肥粒鐵相之晶粒後，對該區域、亦即對肥粒鐵相區域進行背向散射電子繞射(EBSP)測定，並將以KAM值計在1°以上的區域判斷為未再結晶肥粒鐵相組織。從而，「未再結晶肥粒鐵相之面積率」係指未再結晶肥粒鐵相相對於肥粒鐵相之比率。(Measurement method of area ratio of iron phase of unrecrystallized fertilizer grains) The area ratio of the unrecrystallized ferrous iron phase is calculated by the following method: After the ferrous iron phase crystal grains are identified in the above manner, the area, that is, the ferrous iron phase area, is diffracted by backscattered electrons (EBSP) measurement, and judge the region above 1° in terms of KAM value as unrecrystallized ferrous iron phase structure. Therefore, the "area ratio of the unrecrystallized ferrite iron phase" refers to the ratio of the unrecrystallized ferrite iron phase to the ferrite iron phase.

(CMnγ/CMnα的測定方法) CMnγ/CMnα係利用EBSP、SEM及電子探針顯微分析儀(EPMA)來測定。如上所述，使用EBSP及SEM來鑑定沃斯田鐵相及肥粒鐵相的區域，並且在該區域中，利用EPMA測定CMnγ(沃斯田鐵相的Mn濃度)及CMnα(肥粒鐵相的Mn濃度)，算出CMnγ/CMnα。更具體地說，係針對從表面起算1/8位置中縱長50μm(板厚方向的長度)且寬50μm(軋延方向的長度)的區域，就鑑定出的任意的沃斯田鐵相(γ相)與肥粒鐵相(α相)，在各相10個晶粒分別測得Mn濃度並算出該Mn濃度的平均值，以該值作為CMnγ及CMnα，來算出CMnγ/CMnα。(Method of measuring CMnγ/CMnα) CMnγ/CMnα is measured by EBSP, SEM and Electron Probe Microanalyzer (EPMA). As mentioned above, EBSP and SEM are used to identify the regions of the austenitic iron phase and the fat iron phase, and in this area, the EPMA is used to measure CMnγ (the Mn concentration of the austenitic iron phase) and CMnα (the fat iron phase) Mn concentration) to calculate CMnγ/CMnα. More specifically, it is an austenitic iron phase identified for an area of 50 μm in length (length in the plate thickness direction) and 50 μm in width (length in the rolling direction) at 1/8 position from the surface. For the γ phase) and the ferrous iron phase (α phase), the Mn concentration is measured in 10 crystal grains in each phase, and the average value of the Mn concentration is calculated. The value is used as CMnγ and CMnα to calculate CMnγ/CMnα.

(維氏硬度之參差的測定方法) 對鋼板的L截面進行鏡面研磨，接著以3%硝太蝕劑使微觀組織露出後，測定從鋼板表面的中央部起算1/8厚度位置的維氏硬度之參差。維氏硬度之參差係將荷重設為100g，測定從表面起算1/8厚度位置的8點的維氏硬度，以其最大與最小之差作為維氏硬度之參差。惟，針對8點的維氏壓痕，鄰接之壓痕的間隔設為50~70μm。維氏硬度之測定係依據JIS2244：2009來進行。(Measurement method of variation in Vickers hardness) The L-section of the steel plate was mirror-polished, and then the microstructure was exposed with 3% nitrate. Then, the variation of the Vickers hardness at 1/8 thickness from the center of the steel plate surface was measured. The variation of Vickers hardness is that the load is set to 100g, the Vickers hardness is measured at 8 points at 1/8 thickness from the surface, and the difference between the maximum and minimum is used as the variation of the Vickers hardness. However, for the 8-point Vickers indentation, the interval between adjacent indentations is set to 50~70μm. The measurement of Vickers hardness is carried out in accordance with JIS2244:2009.

接著，說明本實施形態之鋼板之機械特性。Next, the mechanical properties of the steel sheet of this embodiment will be explained.

(拉伸強度、延伸率) 本實施形態鋼板的拉伸強度(TS)宜在980MPa以上，更宜在1180MPa以上。這係為了在使用鋼板作為汽車胚料時，透過高強度化來減少板厚以有助於輕量化。另外，由於會將本實施形態鋼板供於壓製成形，故理想的係延伸率(EL)亦優異，例如延伸率(EL)為20%以上，較佳係在22%以上。本實施形態鋼板的TS×EL宜在24000MPa・%以上、較宜在26000MPa・%以上且更宜在28000MPa・%以上。並且，本實施形態鋼板，其彎曲稜線為軋延方向時的彎曲性亦優異。(Tensile strength, elongation) The tensile strength (TS) of the steel sheet of this embodiment is preferably 980 MPa or more, more preferably 1180 MPa or more. This is to reduce the plate thickness by increasing the strength when the steel plate is used as the car blank, thereby contributing to weight reduction. In addition, since the steel sheet of this embodiment is used for press forming, the ideal elongation (EL) is also excellent. For example, the elongation (EL) is 20% or more, preferably 22% or more. The TS×EL of the steel plate of this embodiment should be 24000MPa·% or more, more preferably 26000MPa·% or more, and more preferably 28000MPa·% or more. In addition, the steel sheet of the present embodiment is also excellent in bendability when the bending ridge line is in the rolling direction.

本揭示之鋼板可用於各種用途，尤其適合用於側樑等汽車的結構零件用途上且亦有助於汽車輕量化，故其在產業上的貢獻極為顯著。The steel plate of the present disclosure can be used for various purposes, and is particularly suitable for use in structural parts of automobiles such as side beams, and also contributes to the weight reduction of automobiles, so its contribution to the industry is extremely significant.

3.製造方法說明本實施形態之鋼板之製造方法。又，於以下使用「~」來表示之數值範圍除了有使用「大於」或「小於」的情況之外，意指包含「~」之前後所記載的數值作為下限值及上限值之範圍。3. Manufacturing method The method of manufacturing the steel plate of this embodiment will be described. In addition, the numerical range indicated by "~" in the following, except for the use of "greater than" or "less than", means the range that includes the numerical value described before and after "~" as the lower limit and upper limit .

本實施形態鋼板係以以下方式製出：以常規方法熔煉具有上述化學組成的鋼並進行鑄造而製出扁胚或鋼塊後，將其加熱並施行熱軋延，然後在肥粒鐵/沃斯田鐵的二相區下對所得熱軋鋼板進行熱處理，並於酸洗後以30~70%的冷軋延率進行冷軋延，接著在肥粒鐵/沃斯田鐵的二相區下施行短時間退火後，冷卻至100~530℃並在該溫度下維持而製出，該熱軋延中，精整軋延溫度為1000℃以下，精整軋延後的放冷時間為0.8秒以上，放冷後的平均冷卻速度為30℃/秒以上以及捲取溫度低於300℃。The steel plate of this embodiment is produced in the following manner: after smelting and casting the steel with the above chemical composition in a conventional method to produce a flat billet or steel block, it is heated and hot rolled, and then it is heated and hot rolled. The hot-rolled steel sheet is heat-treated under the two-phase zone of Sita iron, and then cold rolled at a cold rolling rate of 30 to 70% after pickling, and then in the two-phase zone of fat grain iron/austrian iron After annealing for a short period of time, it is made by cooling to 100~530℃ and maintaining at this temperature. During the hot rolling, the finishing temperature is below 1000℃, and the cooling time after finishing rolling is 0.8 Seconds or more, the average cooling rate after cooling is 30°C/sec or more and the coiling temperature is less than 300°C.

熱軋延只要在一般的連續熱軋延產線中進行即可。對熱軋延後之熱軋鋼板的熱處理，可用箱式退火爐(BAF)等分批式爐或連續退火爐等隧道爐來進行。冷軋延亦只要在一般的連續冷軋延產線中進行即可。本揭示之方法中，可使用連續退火產線來進行退火，故生產性非常優異。Hot rolling can be carried out in a general continuous hot rolling production line. The heat treatment of the hot-rolled steel sheet after hot rolling can be carried out in batch furnaces such as box annealing furnaces (BAF) or tunnel furnaces such as continuous annealing furnaces. Cold rolling can also be carried out in a general continuous cold rolling production line. In the method of this disclosure, a continuous annealing line can be used for annealing, so the productivity is very excellent.

為了獲得本揭示鋼板的金屬組織，宜於以下所示範圍內施行下述條件，特別係熱軋條件、對熱軋延後之熱軋鋼板的熱處理條件、冷軋延條件、退火條件及冷卻條件。In order to obtain the metal structure of the steel sheet of the present disclosure, it is advisable to implement the following conditions within the range shown below, especially hot rolling conditions, heat treatment conditions for hot rolled steel sheets after hot rolling, cold rolling conditions, annealing conditions and cooling conditions .

本實施形態之鋼板只要具有上述化學組成，則鋼液可為以一般的高爐法熔煉而成者，亦可為像以電爐法製成之鋼這類於原材料含有大量廢料者。而扁胚可為以一般的連續鑄造製程製出者，亦可為以薄扁胚鑄造而製出者。As long as the steel sheet of the present embodiment has the above-mentioned chemical composition, the molten steel may be melted by a general blast furnace method, or may be a steel made by an electric furnace method that contains a large amount of scrap in raw materials. The flat blank can be produced by a general continuous casting process, or can be produced by casting a thin flat blank.

加熱上述扁胚或鋼塊並進行熱軋延，以製得熱軋鋼板。供於熱軋延之鋼材的溫度宜設為1100~1300℃。藉由使供於熱軋延之鋼材的溫度在1100℃以上，可使熱軋延時之變形阻力變得更小。另一方面，藉由使供於熱軋延之鋼材的溫度在1300℃以下，可抑制因氧化皮損失(scale loss)增加所造成的產率降低。本案說明書中，溫度係指扁胚或鋼材表面的中央部之表面溫度。The flat blank or steel block is heated and hot rolled to obtain a hot rolled steel sheet. The temperature of the hot rolled steel should be 1100~1300℃. By making the temperature of the steel for hot rolling above 1100°C, the deformation resistance of the hot rolling delay can be made smaller. On the other hand, by setting the temperature of the steel material for hot rolling to below 1300°C, it is possible to suppress the decrease in the yield due to the increase in scale loss. In the specification of this case, the temperature refers to the surface temperature of the center part of the flat blank or steel surface.

在熱軋延前維持於上述較佳溫度範圍即1100~1300℃之溫度區的時間並無特別規定，而為了提升韌性，宜設為30分鐘以上，更宜設為1小時以上。另外，為了抑制過度之氧化皮損失，宜設為10小時以下，設為5小時以下更佳。又，當進行直送軋延或直接軋延時，亦可不施行加熱處理而直接供於熱軋延。The time to maintain the temperature range of 1100 to 1300°C, which is the above-mentioned preferred temperature range, before hot rolling is not particularly specified, but in order to improve the toughness, it is preferably set to 30 minutes or more, more preferably 1 hour or more. In addition, in order to suppress excessive scale loss, it is preferably 10 hours or less, more preferably 5 hours or less. In addition, when direct-feed rolling or direct-rolling is delayed, it may be directly applied to hot-rolling without heating.

(精整軋延及捲取：在1000℃以下進行精整軋延，於精整軋延後放冷0.8秒以上，於放冷後以30℃/秒以上的平均冷卻速度進行冷卻以及在低於300℃下捲取) 於熱軋延中會進行精整軋延。開始精整軋延之溫度設為1000℃以下，並且在1000℃以下進行精整軋延。若開始精整軋延之溫度設為高於1000℃，便無法防止熱軋狀態下之組織粗大化，除了後續之組織控制會變得困難之外，還難以抑制因晶界氧化所造成的鋼板表面性狀之劣化。並且，開始精整軋延之溫度宜為750℃以上。藉由使開始精整軋延之溫度在750℃以上，可使軋延時之變形阻力變小，而能輕易控制組織。(Finishing rolling and coiling: Finishing rolling is carried out below 1000°C, cooling is carried out for 0.8 seconds or more after finishing rolling, and cooling is carried out at an average cooling rate of 30°C/s or more after cooling. Coiling at 300℃) Finishing rolling will be carried out during hot rolling. The temperature at which the finishing rolling is started is set to 1000°C or lower, and the finishing rolling is performed at 1000°C or lower. If the temperature at the start of the finishing rolling is set to higher than 1000°C, the coarsening of the structure in the hot rolled state cannot be prevented. In addition to the difficulty of subsequent structure control, it is also difficult to suppress the steel sheet caused by grain boundary oxidation. Deterioration of surface properties. In addition, the temperature at which the finishing rolling starts is preferably 750°C or higher. By making the temperature at the beginning of the finishing rolling above 750°C, the deformation resistance during the rolling delay can be reduced, and the structure can be easily controlled.

於精整軋延後進行放冷0.8秒以上。一般從組織微細化的觀點看來，係認為在精整軋延後馬上急速冷卻為佳。然而，在如本實施形態鋼板這種含有大於2.50%的Mn之鋼板中，會因Mn偏析造成再結晶延遲，而導致剛精整軋延後的沃斯田鐵粒徑變得不均一。或者，肥粒鐵不會均勻地生成，而在熱軋鋼板的熱處理時並且在冷軋鋼板的退火時變得容易生成帶狀組織。因此，藉由於精整軋延後放冷0.8秒以上，可抑制帶狀組織形成，維氏硬度之參差就會在40Hv以下。放冷時間的上限宜少於6.0秒。當放冷時間為6.0秒以上時，抑制帶狀組織形成的效果會達飽和。After finishing rolling, let it cool for 0.8 seconds or more. In general, from the viewpoint of the refinement of the structure, it is considered that it is better to cool down immediately after finishing rolling. However, in a steel sheet containing more than 2.50% of Mn, such as the steel sheet of the present embodiment, recrystallization is delayed due to Mn segregation, and the grain size of the austenitic iron immediately after finishing rolling becomes non-uniform. Alternatively, the ferrous iron is not uniformly generated, but it becomes easy to form a band-like structure during the heat treatment of the hot-rolled steel sheet and during the annealing of the cold-rolled steel sheet. Therefore, by cooling for more than 0.8 seconds after finishing rolling, the formation of band-like structure can be suppressed, and the variation of Vickers hardness will be below 40Hv. The upper limit of the cooling time should be less than 6.0 seconds. When the cooling time is 6.0 seconds or more, the effect of suppressing the formation of the band structure will be saturated.

宜於精整軋延後進行1.2~4.0秒的放冷。透過使放冷時間在前述範圍內，沃斯田鐵晶粒會變得更均一，從而退火後的鋼板組織會變得更均一，維氏硬度之參差就會在30Hv以下。放冷時間亦可為1.5秒以上、1.8秒以上、2.0秒以上、2.2秒以上或2.5秒以上。並且，放冷時間亦可為3.8秒以下、3.5秒以下、3.2秒以下或3.0秒以下。It is suitable to cool down for 1.2~4.0 seconds after finishing rolling. By keeping the cooling time within the aforementioned range, the austenitic iron grains will become more uniform, and the structure of the annealed steel sheet will become more uniform, and the variation of Vickers hardness will be below 30Hv. The cooling time can also be 1.5 seconds or more, 1.8 seconds or more, 2.0 seconds or more, 2.2 seconds or more, or 2.5 seconds or more. In addition, the cooling time may be 3.8 seconds or less, 3.5 seconds or less, 3.2 seconds or less, or 3.0 seconds or less.

於上述放冷後以30℃/秒以上的平均冷卻速度進行冷卻。平均冷卻速度若小於30℃/秒，在麻田散鐵變態中便會於熱軋板的團塊境界及舊沃斯田鐵晶界不均勻地生成雪明碳鐵，因此維氏硬度之參差會大於40Hv。平均冷卻速度的上限宜為500℃/秒以下。平均冷卻速度越快越好，只要在500℃/秒以下便不易發生冷卻不均，冷軋延性就不易降低。After leaving to cool as described above, cooling is performed at an average cooling rate of 30°C/sec or more. If the average cooling rate is less than 30°C/sec, in the deformation of Matian loose iron, Xueming carbon iron will be formed unevenly at the agglomerate boundary of the hot-rolled plate and the grain boundary of the old austenitic iron, so the variation of Vickers hardness will be greater than 40Hv . The upper limit of the average cooling rate is preferably 500°C/sec or less. The faster the average cooling rate is, the better, as long as the temperature is below 500°C/sec, uneven cooling will not easily occur, and cold rolling ductility will not easily decrease.

於進行精整軋延後，進行冷卻並且在低於300℃的溫度下進行捲取。若在300℃以上的溫度下進行捲取，便無法將熱軋鋼板的組織製成全麻田散鐵組織，而於熱軋鋼板的熱處理及冷軋鋼板的退火步驟中，分別難以有效產生Mn分配與沃斯田鐵逆變態。After finishing rolling, cooling is performed and coiling is performed at a temperature lower than 300°C. If coiling is performed at a temperature above 300°C, the structure of the hot-rolled steel sheet cannot be made into a full-marine scattered iron structure. In the heat treatment of the hot-rolled steel sheet and the annealing step of the cold-rolled steel sheet, it is difficult to effectively produce Mn distribution. Inverted state with austenitic iron.

(熱軋鋼板的熱處理：在沃斯田鐵相分率成為20~50%之溫度區下維持1小時以上) 對所得熱軋鋼板在肥粒鐵/沃斯田鐵的二相區下且於沃斯田鐵相分率成為20~50%之溫度區下進行1小時以上的熱處理。藉由在鋼板的高於Ac1且低於Ac3的二相區之溫度範圍內，於沃斯田鐵相分率成為20~50%之溫度範圍內進行熱處理，便可將Mn分配至沃斯田鐵相，使沃斯田鐵相穩定化，從而可獲得高延性。反之，若於沃斯田鐵相分率小於20%或大於50%之溫度下進行熱處理，則難以使沃斯田鐵相穩定化。而熱處理若進行不到1小時，也難以使沃斯田鐵相穩定化。透過在沃斯田鐵相分率成為20~50%之溫度下進行熱處理1小時以上，退火後之鋼板以面積率計會含有10%以上的沃斯田鐵相，而可提高CMnγ/CMnα。沃斯田鐵相分率成為20~50%之溫度範圍可藉由以下方式求算：依鋼板成分的不同，於離線之預備實驗中從室溫起以0.5℃/秒之加熱速度加熱，根據加熱中的體積變化來測定沃斯田鐵相分率。為了促進沃斯田鐵相穩定化，熱處理的維持時間的下限宜為3小時以上，更宜為4小時以上。為了更加促進沃斯田鐵相穩定化，可將熱處理時的沃斯田鐵相分率設為25%以上或30%以上，亦可設為45%以下或40%以下。熱處理的維持時間的上限從生產性的觀點來看，宜在10小時以內，更宜在8小時以內。此外，熱處理的氣體環境並無特別限定，譬如可為大氣環境、非活性氣體環境或含H₂ 等之還原氣體環境中之任一者。(Heat treatment of hot-rolled steel sheet: Maintain for more than 1 hour in the temperature zone where the austenitic iron phase fraction becomes 20 to 50%) Heat treatment for more than 1 hour in a temperature zone where the austenitic iron phase fraction becomes 20-50%. By performing heat treatment in the temperature range of the two-phase zone higher than Ac1 and lower than Ac3 of the steel plate, and the austenitic iron phase fraction becomes 20~50%, Mn can be distributed to the austenitic The iron phase stabilizes the austenitic iron phase to obtain high ductility. Conversely, if the heat treatment is performed at a temperature where the austenitic iron phase fraction is less than 20% or more than 50%, it is difficult to stabilize the austenitic iron phase. However, if the heat treatment is performed for less than 1 hour, it is difficult to stabilize the austenitic iron phase. By performing heat treatment at a temperature where the austenitic iron phase fraction becomes 20-50% for more than 1 hour, the annealed steel sheet will contain more than 10% austenitic iron phase in terms of area ratio, which can increase CMnγ/CMnα. The temperature range where the austenitic iron phase fraction becomes 20~50% can be calculated by the following method: Depending on the composition of the steel plate, in the off-line preliminary experiment, heating from room temperature at a heating rate of 0.5°C/sec. The volume change during heating is used to determine the austenitic iron phase fraction. In order to promote the stabilization of the austenitic iron phase, the lower limit of the maintenance time of the heat treatment is preferably 3 hours or more, more preferably 4 hours or more. In order to further promote the stabilization of the austenitic iron phase, the austenitic iron phase fraction during the heat treatment can be set to 25% or more or 30% or more, or 45% or less or 40% or less. From the viewpoint of productivity, the upper limit of the maintenance time of the heat treatment is preferably within 10 hours, and more preferably within 8 hours. In addition, the gas environment for the heat treatment is not particularly limited. For example, it may be any of an atmospheric environment, an inert gas environment, or a reducing gas environment containing H ₂ .

在沃斯田鐵相分率成為20~50%之溫度範圍下進行熱處理後，進行冷卻。藉此，可維持在熱處理中獲得的Mn分配狀態。After heat treatment in a temperature range where the austenitic iron phase fraction becomes 20-50%, cooling is performed. Thereby, the Mn distribution state obtained in the heat treatment can be maintained.

熱軋鋼板在以常規方法施行酸洗後，會以30~70%的軋縮率(冷軋延率)進行冷軋延，製成冷軋鋼板。若將冷軋延的軋縮率設為小於30%，再結晶會變得不均勻，而不會均勻地生成沃斯田鐵相，導致退火後鋼板的維氏硬度之參差變大。另外，若將軋縮率設為大於70%，冷軋延時變得容易發生斷裂。冷軋延的軋縮率下限值宜為40%以上。冷軋延的軋縮率上限值則宜為60%以下。After the hot-rolled steel sheet is pickled in a conventional method, it is cold-rolled at a reduction ratio (cold-rolled elongation rate) of 30 to 70% to produce a cold-rolled steel sheet. If the reduction ratio of cold rolling is set to less than 30%, recrystallization will become non-uniform, and the austenitic iron phase will not be uniformly generated, resulting in large variations in the Vickers hardness of the steel sheet after annealing. In addition, if the rolling reduction ratio is more than 70%, fractures tend to occur after a delay in cold rolling. The lower limit of cold rolling reduction ratio is preferably 40% or more. The upper limit of the cold rolling reduction ratio is preferably 60% or less.

若於冷軋延前且在酸洗之前或之後，進行大於0且至5%左右的輕度軋延來修正形狀，在確保平坦的觀點上為有利，故適宜。又，藉由在酸洗前進行輕度軋延，可提升酸洗性，促進除去表面濃化元素，而有提升化學轉化處理性及鍍敷處理性之效果。Before cold rolling and before or after pickling, light rolling of more than 0 to about 5% is performed to correct the shape, which is advantageous from the viewpoint of ensuring flatness, and is therefore suitable. In addition, by performing light rolling before pickling, pickling properties can be improved, the removal of concentrated elements on the surface can be promoted, and the chemical conversion processability and plating processability can be improved.

(冷軋鋼板之退火：在沃斯田鐵相分率成為20~65%之溫度區下維持30秒以上) 將所得冷軋鋼板在肥粒鐵/沃斯田鐵的二相區下且於沃斯田鐵相分率成為20~65%之溫度區下維持30秒以上、較佳係維持1分鐘以上來進行退火。由於在上述熱軋鋼板的熱處理中已完成Mn分配，Mn會在熱處理中原為沃斯田鐵相之處濃化，故該處即使在短時間退火下也容易立刻變為沃斯田鐵相，而可獲得穩定之沃斯田鐵相，以短時間的退火處理便可獲得優異延性。另一方面，該退火中，若在沃斯田鐵相分率小於20%之溫度下進行熱處理，則無法充分獲得沃斯田鐵相，而若在大於65%之溫度下進行熱處理，便無法充分生成肥粒鐵相，並且會變得容易從沃斯田鐵相變態為麻田散鐵相。另外，退火時間若少於30秒，再結晶就不會充分進行。退火時間之上限並無特別規定，從生產性之觀點看來宜少於15分鐘，在5分鐘以下更佳。為了獲得所欲金屬組織，可將退火時的沃斯田鐵相分率設為25%以上或30%以上，亦可設為60%以下、55%以下、50%以下或40%以下。而較佳係在沃斯田鐵相分率成為25~40%之溫度區下退火。另外，退火氣體環境可為大氣環境、非活性氣體環境或含H₂ 等之還原氣體環境中之任一者。(Annealing of cold-rolled steel sheet: Maintain for more than 30 seconds in the temperature zone where the austenitic iron phase fraction becomes 20~65%) Put the obtained cold-rolled steel sheet under the two-phase zone of fat grain iron/austenitic iron and The austenitic iron phase fraction is maintained at a temperature zone of 20-65% for more than 30 seconds, preferably for more than 1 minute for annealing. Since the Mn distribution has been completed in the heat treatment of the hot-rolled steel sheet, Mn will be concentrated in the austenitic iron phase during the heat treatment, so even if it is annealed for a short time, it will easily become austenitic iron phase immediately. A stable austenitic iron phase can be obtained, and excellent ductility can be obtained with a short annealing treatment. On the other hand, in this annealing, if the austenitic iron phase fraction is heat-treated at a temperature of less than 20%, the austenitic iron phase cannot be sufficiently obtained, and if the heat treatment is performed at a temperature greater than 65%, the austenitic iron phase cannot be obtained. The fat-grained iron phase is fully formed, and it becomes easy to transform from the austenitic iron phase to the Asada scattered iron phase. In addition, if the annealing time is less than 30 seconds, recrystallization will not proceed sufficiently. The upper limit of the annealing time is not specifically defined. From the viewpoint of productivity, it is preferably less than 15 minutes, and more preferably less than 5 minutes. In order to obtain the desired metal structure, the austenitic iron phase fraction during annealing can be set to 25% or more or 30% or more, or 60% or less, 55% or less, 50% or less or 40% or less. It is better to anneal in a temperature region where the austenitic iron phase fraction becomes 25-40%. In addition, the annealing gas environment may be any of an atmospheric environment, an inert gas environment, or a reducing gas environment containing H ₂ or the like.

冷軋延前之熱處理的溫度與冷軋延後之退火的溫度之差，換算成沃斯田鐵相分率之差宜相當於15%以下，更宜相當於10%以下。冷軋延前之熱處理的溫度與冷軋延後之退火的溫度，不論何者為高皆可。藉由使冷軋延前之熱處理的溫度與冷軋延後之退火的溫度之差在上述範圍內，可使冷軋延前之熱處理的沃斯田鐵相分率與冷軋延後之退火的沃斯田鐵相分率相近，故於冷軋延後之退火中，可使沃斯田鐵相僅生成於Mn濃化之處。冷軋延前之熱處理的溫度及冷軋延後之退火的溫度，係熱處理曲線中實質上的最高溫度。The difference between the heat treatment temperature before cold rolling and the annealing temperature after cold rolling, when converted into austenitic iron phase fraction, should be equivalent to less than 15%, more preferably less than 10%. The heat treatment temperature before cold rolling and the annealing temperature after cold rolling can be higher. By making the difference between the heat treatment temperature before cold rolling and the annealing temperature after cold rolling within the above range, the austenitic iron phase fraction of the heat treatment before cold rolling and annealing after cold rolling can be made The austenitic iron phase fraction is similar, so in the annealing after cold rolling, the austenitic iron phase can be formed only where Mn is concentrated. The heat treatment temperature before cold rolling and the annealing temperature after cold rolling are the substantially highest temperature in the heat treatment curve.

(退火後的冷卻條件：冷卻至100~530℃的溫度區為止，並在100~530℃的溫度區下維持10~1000秒) 在退火之溫度維持後，將冷軋鋼板冷卻至100~530℃的溫度區為止。(Cooling conditions after annealing: cooling to the temperature zone of 100~530℃, and maintaining the temperature zone of 100~530℃ for 10~1000 seconds) After the annealing temperature is maintained, the cold-rolled steel sheet is cooled to a temperature range of 100~530℃.

停止冷卻之溫度高於530℃時，因難以將麻田散鐵相回火或難以生成變韌鐵相，結果變得容易在金屬組織中產生新生麻田散鐵相，導致退火後鋼板的彎曲性降低。另外，停止冷卻之溫度低於100℃時，變得容易產生麻田散鐵變態所伴隨之應變，而難以維持鋼板的平坦性，並且會妨礙提升連續退火產線的效率。When the cooling stop temperature is higher than 530°C, it is difficult to temper the Asada scattered iron phase or form a toughened iron phase. As a result, it becomes easy to produce a new Asada scattered iron phase in the metal structure, resulting in a decrease in the bendability of the steel sheet after annealing. . In addition, when the temperature at which the cooling is stopped is lower than 100°C, strain accompanying the deformation of Asada bulk iron becomes easy to occur, which makes it difficult to maintain the flatness of the steel sheet and hinders the improvement of the efficiency of the continuous annealing line.

退火後的平均冷卻速度宜為2~2000℃/秒。退火後的平均冷卻速度為2℃/秒以上時，可更抑制肥粒鐵相過度粗大化。另外，平均冷卻速度為2000℃/秒以下時，冷卻停止後之鋼板溫度分布容易變得更均一，而可充分維持鋼板的平坦性。The average cooling rate after annealing should be 2~2000°C/sec. When the average cooling rate after annealing is 2°C/sec or more, the excessive coarsening of the ferrite phase can be further suppressed. In addition, when the average cooling rate is 2000°C/sec or less, the temperature distribution of the steel sheet after cooling is stopped is likely to become more uniform, and the flatness of the steel sheet can be sufficiently maintained.

冷卻至100~530℃的溫度區為止後，在100~530℃的溫度區下維持10~1000秒。在100~530℃的溫度區下的維持時間少於10秒時，往沃斯田鐵相之C分配變得難以進行，而難以使金屬組織中穩定生成沃斯田鐵相。並且，因難以將麻田散鐵相回火或難以生成變韌鐵相，結果變得容易在金屬組織中產生新生麻田散鐵相，導致退火後鋼板的延伸率與彎曲性容易降低。在100~530℃的溫度區下的維持時間宜為30秒以上。另一方面，上述維持時間超過1000秒時，上述作用所帶來的效果便達飽和，而招致連續退火產線的生產性降低。因此，在100~530℃的溫度區下的維持時間設為1000秒以下，且宜為300秒以下。維持溫度只要係在100~530℃的範圍內則亦可為與停止冷卻之溫度相異的溫度，而維持溫度與停止冷卻之溫度的溫度差宜在50℃以內，較佳係實質上為0℃。After cooling to the temperature zone of 100 to 530°C, maintain it in the temperature zone of 100 to 530°C for 10 to 1000 seconds. When the maintenance time in the temperature range of 100 to 530°C is less than 10 seconds, the C distribution to the austenitic iron phase becomes difficult, and it is difficult to stably form the austenitic iron phase in the metal structure. In addition, it is difficult to temper the Asada iron phase or to produce a toughened iron phase, and as a result, it becomes easy to generate a new Asada iron phase in the metal structure, and the elongation and bendability of the steel sheet after annealing are likely to decrease. The maintenance time in the temperature zone of 100~530℃ should be more than 30 seconds. On the other hand, when the above-mentioned holding time exceeds 1000 seconds, the effect of the above-mentioned action will be saturated, and the productivity of the continuous annealing line will decrease. Therefore, the maintenance time in the temperature range of 100 to 530°C is set to 1000 seconds or less, and preferably 300 seconds or less. The maintenance temperature may be a temperature different from the temperature at which cooling is stopped as long as it is within the range of 100 to 530°C. The temperature difference between the maintenance temperature and the temperature at which cooling is stopped should preferably be within 50°C, preferably substantially 0 ℃.

於上述在100~530℃的溫度區下的維持後，宜將鋼板冷卻至80℃以下，較佳係冷卻至室溫為止。After the above-mentioned maintenance in the temperature range of 100 to 530°C, the steel plate is preferably cooled to below 80°C, preferably to room temperature.

上述退火後之冷卻在不對鋼板進行鍍敷時，宜直接進行至80℃以下，更宜直接進行至室溫為止。另外，當要對鋼板進行鍍敷時，可依以下方式製造。The above-mentioned cooling after annealing should be carried out directly to below 80°C, more preferably carried out directly to room temperature when the steel sheet is not plated. In addition, when the steel plate is to be plated, it can be manufactured in the following manner.

於鋼板表面施行熔融鍍鋅來製造熔融鍍鋅鋼板時，係在上述退火後將冷軋鋼板冷卻至100~530℃的溫度區為止，並且在100~530℃的溫度區下維持10~1000秒後，升溫至430~500℃的溫度，接著將冷軋鋼板浸漬於熔融鋅之鍍浴中，進行熔融鍍鋅處理。鍍浴的條件只要設定在一般範圍內即可。鍍敷處理後則冷卻至室溫即可。When hot-dip galvanizing is applied to the surface of the steel sheet to produce a hot-dip galvanized steel sheet, the cold-rolled steel sheet is cooled to a temperature range of 100 to 530°C after the above annealing, and maintained in the temperature range of 100 to 530°C for 10 to 1000 seconds After that, the temperature is raised to a temperature of 430 to 500°C, and then the cold-rolled steel sheet is immersed in a molten zinc plating bath for hot-dip galvanizing. The conditions of the plating bath may be set within the general range. After the plating treatment, just cool to room temperature.

於鋼板表面施行合金化熔融鍍鋅來製造合金化熔融鍍鋅鋼板時，係在對鋼板施行熔融鍍鋅處理後，於將鋼板冷卻至室溫為止前，在450~620℃之溫度下進行熔融鍍鋅之合金化處理。合金化處理條件設定在一般範圍內即可。When alloying hot-dip galvanizing is applied to the surface of the steel sheet to produce an alloyed hot-dip galvanizing steel sheet, the steel sheet is melted at a temperature of 450 to 620°C before cooling the steel sheet to room temperature after hot-dip galvanizing is applied to the steel sheet. Galvanized alloying treatment. The alloying treatment conditions can be set within the general range.

對於退火後之鋼板或鍍敷後之鋼板，亦可進行平整軋延。所述平整軋延的軋縮率宜為0且小於5.0%(亦即，也包含不進行平整軋延的情況)。進行平整軋延時的軋縮率則為大於0且小於5.0%。For the annealed steel plate or the plated steel plate, it can also be flat rolled. The reduction ratio of the skin-pass rolling is preferably 0 and less than 5.0% (that is, the case where the skin-pass rolling is not performed is also included). The rolling reduction rate after the delay of the leveling rolling is greater than 0 and less than 5.0%.

藉由如以上方式製造鋼板，便可製得本實施形態之鋼板。實施例By manufacturing the steel plate as described above, the steel plate of this embodiment can be manufactured. Example

參照示例更具體地說明本揭示之鋼板。惟，以下示例為本揭示之鋼板及其製造方法之示例，本揭示之鋼板及其製造方法並不限於以下示例之態樣。The steel plate of the present disclosure will be explained more specifically with reference to examples. However, the following example is an example of the steel plate and the manufacturing method thereof of the present disclosure, and the steel plate and the manufacturing method thereof of the present disclosure are not limited to the following examples.

1.製造評估用鋼板熔煉具有表1所示化學成分之鋼，製得厚30mm的扁胚。1. Manufacturing of steel plates for evaluation The steel with the chemical composition shown in Table 1 was smelted to obtain a flat embryo with a thickness of 30 mm.

[表1]

[Table 1]

在表2所示開始精整軋延之溫度、放冷時間、平均冷卻速度及捲取溫度下將所得扁胚進行熱軋延，製出厚2.6mm之熱軋鋼板。對所得熱軋鋼板，以成為表2所示沃斯田鐵相分率的溫度及維持時間進行熱處理，接著進行酸洗，再以表2所示冷軋延率施行冷軋延，製出冷軋鋼板。熱軋鋼板的熱處理係在氮98%及氫2%之還原氣體環境中進行。未記載有熱處理的沃斯田鐵相分率及維持時間之示例，係指在熱軋延後不進行熱處理而在捲取後直接進行了冷軋延之示例。The obtained flat blanks were hot-rolled at the starting temperature, cooling time, average cooling rate and coiling temperature shown in Table 2 to produce hot-rolled steel sheets with a thickness of 2.6 mm. The obtained hot-rolled steel sheet was heat-treated at a temperature and holding time to achieve the austenitic iron phase fraction shown in Table 2, followed by pickling, and then subjected to cold rolling at the cold rolling elongation rate shown in Table 2 to produce cold Rolled steel plate. The heat treatment of the hot-rolled steel sheet is carried out in a reducing atmosphere of 98% nitrogen and 2% hydrogen. Examples of austenitic iron phase fraction and maintenance time that are not described with heat treatment refer to an example where heat treatment is not performed after hot rolling and cold rolling is performed directly after coiling.

[表2]

[Table 2]

對所得冷軋鋼板，以成為表3所示沃斯田鐵相分率的溫度及維持時間進行退火。冷軋鋼板之退火係在氮98%及氫2%之還原氣體環境中進行。熱軋鋼板的熱處理溫度與冷軋鋼板的退火溫度，係相當於表3所示沃斯田鐵相分率差之溫度差。在退火之溫度維持後，以表3所示冷卻停止溫度、冷卻停止後之維持溫度及維持時間之條件來冷卻鋼板。退火之溫度維持後的平均冷卻速度設為100℃/秒。未記載有冷卻停止溫度、冷卻停止後之維持溫度及維持時間之數值之示例，係指於退火後之冷卻中，在100~530℃之溫度區下不停止冷卻及不進行維持，而在退火後直接冷卻至室溫為止之例。The obtained cold-rolled steel sheet was annealed at a temperature and a holding time to achieve the austenitic iron phase fraction shown in Table 3. The annealing of cold-rolled steel sheets is carried out in a reducing atmosphere of 98% nitrogen and 2% hydrogen. The heat treatment temperature of the hot-rolled steel sheet and the annealing temperature of the cold-rolled steel sheet are equivalent to the temperature difference of the austenitic iron phase fraction shown in Table 3. After the annealing temperature is maintained, the steel sheet is cooled under the conditions of the cooling stop temperature, the maintenance temperature after the cooling stop, and the maintenance time shown in Table 3. The average cooling rate after maintaining the annealing temperature was set to 100°C/sec. Examples that do not record the values of the cooling stop temperature, the maintenance temperature after the cooling stop, and the maintenance time mean that during the cooling after annealing, the cooling is not stopped or maintained in the temperature range of 100 to 530 ℃, but during annealing After cooling directly to room temperature.

[表3]

[table 3]

針對一部分的退火冷軋鋼板，在進行了退火後，以表3中記載的冷卻停止溫度、維持溫度及維持時間進行冷卻及維持，接著升溫至460℃，將冷軋鋼板在該溫度下維持10秒後，將其於460℃的熔融鋅之鍍浴中浸漬2秒，進行了熔融鍍鋅處理。鍍浴的條件與以往相同。當不施行後述合金化處理時，在熔融鍍鋅處理後以平均冷卻速度10℃/秒冷卻至室溫。For some of the annealed cold-rolled steel sheets, after annealing, they were cooled and maintained at the cooling stop temperature, maintenance temperature, and maintenance time described in Table 3, and then the temperature was increased to 460°C, and the cold-rolled steel sheet was maintained at this temperature for 10 Seconds later, it was immersed in a molten zinc plating bath at 460°C for 2 seconds to perform a hot dip galvanizing treatment. The conditions of the plating bath are the same as before. When the alloying treatment described later is not performed, it is cooled to room temperature at an average cooling rate of 10°C/sec after the hot-dip galvanizing treatment.

針對一部分的退火冷軋鋼板，在進行了熔融鍍鋅處理後，不冷卻至室溫而以10℃/秒加熱至500℃並在500℃下維持5秒，進行合金化處理，然後以平均冷卻速度10℃/秒冷卻至室溫。For some annealed cold-rolled steel sheets, after hot-dip galvanizing, they are heated to 500°C at 10°C/sec and maintained at 500°C for 5 seconds without cooling to room temperature, then alloyed, and then cooled evenly. Cool down to room temperature at a rate of 10°C/sec.

對以上述方式製得之退火冷軋鋼板施行軋縮率0.5%之平整軋延，製作出各示例之鋼板。The annealed cold-rolled steel sheet produced in the above-mentioned manner was subjected to flat rolling with a reduction ratio of 0.5% to produce steel sheets of each example.

2. 評估方法針對以表2及表3所示條件製出之各示例退火冷軋鋼板，實施X射線繞射測定、微觀組織觀察、拉伸試驗及彎曲試驗，並評估了肥粒鐵相(α)、沃斯田鐵相(γ)、回火麻田散鐵相(T.M)(包含變韌鐵相)、新生麻田散鐵相(F.M)、及未再結晶肥粒鐵相(未再結晶α)相對於肥粒鐵相的面積率、CMnγ/CMnα、及維氏硬度之參差ΔHv。各評估方法係如上述實施形態之記載。又，針對各示例退火冷軋鋼板，如以下所記載，評估了拉伸強度(TS)、延伸率(EL)、TS×EL及彎曲性(Rmin)。2. Evaluation method For each sample annealed cold-rolled steel sheet produced under the conditions shown in Table 2 and Table 3, X-ray diffraction measurement, microstructure observation, tensile test, and bending test were carried out, and the ferrite phase (α) and the ferrite phase were evaluated. Sita iron phase (γ), tempered matian scattered iron phase (TM) (including toughened iron phase), new matian scattered iron phase (FM), and unrecrystallized fertilizer grain iron phase (unrecrystallized α) The area ratio of the fertilizer grain iron phase, CMnγ/CMnα, and the variation ΔHv of Vickers hardness. Each evaluation method is as described in the above embodiment. In addition, for each example annealed cold-rolled steel sheet, the tensile strength (TS), elongation (EL), TS×EL, and bendability (Rmin) were evaluated as described below.

(機械性質之試驗方法) 從與鋼板之軋延方向成直角的方向採取JIS5號拉伸試驗片後，進行拉伸試驗及延伸試驗，測定了拉伸強度(TS)及延伸率(EL)。拉伸試驗係使用有JIS5號拉伸試驗片且以JIS-Z2241：2011所規定的方法來進行。延伸試驗則使用有平行部長度為50mm的JIS5號試驗片且以JIS-Z2241：2011所規定的方法來進行。(Test method of mechanical properties) After taking a JIS No. 5 tensile test piece from a direction perpendicular to the rolling direction of the steel sheet, a tensile test and an elongation test were performed, and the tensile strength (TS) and elongation (EL) were measured. The tensile test was performed by the method specified in JIS-Z2241:2011 using a JIS No. 5 tensile test piece. The extension test was performed using a JIS No. 5 test piece with a parallel portion length of 50 mm and the method specified in JIS-Z2241:2011.

彎曲性(Rmin)係進行彎曲試驗來評估。彎曲試驗係以彎曲稜線成為軋延方向之方式從鋼板表面的中央部採取試驗片，該試驗片係寬度為15mm(成為彎曲稜線之方向)、長度為50mm(軋延直角之方向)且係經退火之試樣的原有厚度(板厚方向)者，然後以前端角度90度且前端R為板厚的2.5倍之V型衝頭將該試驗片壓入V型凹塊。然後，觀察彎曲稜線，於稜線無破裂時評為彎曲性「良好」。於稜線有破裂時評為彎曲性「不良」。並且，關於在以2.5倍之V型衝頭壓入V型凹塊時並無破裂之鋼板，以前端R為板厚的1.5倍之V型衝頭將另一個試驗片壓入V型凹塊。然後，觀察彎曲稜線，於稜線無破裂時評為彎曲性「更良好」。Flexibility (Rmin) is evaluated by conducting a bending test. The bending test is to take a test piece from the center of the surface of the steel sheet so that the bending ridge becomes the rolling direction. The test piece has a width of 15 mm (the direction of the bending ridge), a length of 50 mm (the direction of the rolling right angle) and The original thickness of the annealed sample (in the direction of plate thickness), and then press the test piece into the V-shaped concave block with a V-shaped punch with a front end angle of 90 degrees and a front end R of 2.5 times the plate thickness. Then, the bending ridgeline was observed, and when the ridgeline was not broken, the bending property was evaluated as "good". When the ridgeline is broken, it is rated as "bad" in bending. In addition, regarding the steel plate that did not break when pressed into the V-shaped block with a 2.5-fold V-shaped punch, press the other test piece into the V-shaped block with a V-shaped punch with the tip R being 1.5 times the thickness of the plate. . Then, the bending ridgeline was observed, and when the ridgeline was not broken, it was judged that the bending property was "better".

3. 評估結果於表4列示以表2及表3所示條件製出之鋼板的評估結果。在本發明例中，獲得了顯示出980MPa以上的TS、24000MPa・%以上的TS×EL及「良好」的Rmin之鋼板。3. Evaluation results Table 4 lists the evaluation results of the steel plates produced under the conditions shown in Table 2 and Table 3. In the example of the present invention, a steel sheet showing a TS of 980 MPa or more, a TS×EL of 24,000 MPa·% or more, and a "good" Rmin was obtained.

[表4]

[Table 4]

示例編號1~3、6、7、9、10、13~15、17、20~22、27、30、32及33係依據預定製造方法製出，故獲得了所欲金屬組織且具有優異特性(強度及延伸特性(TS×EL之值)、以及彎曲性)。The sample numbers 1~3, 6, 7, 9, 10, 13~15, 17, 20~22, 27, 30, 32 and 33 are made according to the predetermined manufacturing method, so the desired metal structure is obtained and has excellent characteristics (Strength and elongation characteristics (TS×EL value), and flexibility).

示例編號4在熱軋延後之熱處理的沃斯田鐵相分率低，無法獲得所欲金屬組織，故無法獲得充分的強度及延伸特性(TS×EL之值)。示例編號5含有過多P，故無法獲得充分的彎曲性。示例編號8在退火時的沃斯田鐵相分率低，無法獲得所欲金屬組織，故無法獲得充分的強度及延伸特性(TS×EL之值)。示例編號11的冷軋延率低，無法抑制維氏硬度之參差，從而無法獲得充分的彎曲性。示例編號12的Mn含量不足，無法獲得所欲金屬組織，故無法獲得充分的強度及延伸特性(TS×EL之值)。示例編號16的捲取溫度高，CMnγ/CMnα之值變得不充分，從而無法獲得充分的強度及延伸特性(TS×EL之值)。示例編號18並無進行退火後之冷卻，故無法獲得所欲金屬組織並且無法獲得充分的彎曲性。示例編號19在退火時的沃斯田鐵相分率高，無法獲得所欲金屬組織，並且無法獲得充分的強度及延伸特性(TS×EL之值)、以及充分的彎曲性。示例編號23在熱軋延後放冷後的平均冷卻速度低，無法抑制維氏硬度之參差，從而無法獲得充分的彎曲性。示例編號24在退火後之冷卻中的維持時間短，無法獲得所欲金屬組織，從而無法獲得充分的強度及延伸特性(TS×EL之值)、以及充分的彎曲性。示例編號25在退火後之冷卻停止溫度及維持溫度高，無法獲得所欲金屬組織並且無法獲得充分的彎曲性。示例編號26的C含量不足，無法獲得所欲金屬組織，從而無法獲得充分的強度及延伸特性(TS×EL之值)。示例編號28在熱軋延後之熱處理的沃斯田鐵相分率高，無法獲得所欲金屬組織並且CMnγ/CMnα之值不充分，而無法獲得充分的強度及延伸特性(TS×EL之值)。示例編號29在熱軋延後之熱處理中的維持時間短，無法獲得所欲金屬組織並且CMnγ/CMnα之值不充分，而無法獲得充分的強度及延伸特性(TS×EL之值)。示例編號31在退火中的維持時間短，無法獲得所欲金屬組織，而無法獲得充分的強度及延伸特性(TS×EL之值)。示例編號34在熱軋延後的放冷時間短，無法抑制維氏硬度之參差，從而無法獲得充分的彎曲性。示例編號35含有過多Mn，故無法獲得充分的彎曲性。示例編號36並無進行熱軋延後之熱處理，故無法獲得充分的強度及延伸特性(TS×EL之值)。In Example No. 4, the austenitic iron phase fraction of the heat treatment after the hot rolling extension is low, and the desired metal structure cannot be obtained, so sufficient strength and elongation characteristics (TS×EL value) cannot be obtained. Sample No. 5 contains too much P, so sufficient flexibility cannot be obtained. In Example No. 8, the austenitic iron phase fraction during annealing was low, and the desired metal structure could not be obtained, so sufficient strength and elongation characteristics (TS×EL value) could not be obtained. The cold rolling of Example No. 11 has a low elongation rate and cannot suppress the variation in Vickers hardness, so that sufficient bendability cannot be obtained. The Mn content of Example No. 12 is insufficient, and the desired metal structure cannot be obtained, so sufficient strength and elongation characteristics (TS×EL value) cannot be obtained. The coiling temperature of Example No. 16 is high, and the value of CMnγ/CMnα becomes insufficient, so that sufficient strength and elongation characteristics (TS×EL value) cannot be obtained. Sample No. 18 does not perform cooling after annealing, so the desired metal structure cannot be obtained and sufficient bendability cannot be obtained. In Example No. 19, the austenitic phase fraction during annealing was high, the desired metal structure could not be obtained, and sufficient strength and elongation characteristics (TS×EL value) and sufficient bendability could not be obtained. In Example No. 23, the average cooling rate after being left to cool after the hot rolling is low, the variation in Vickers hardness cannot be suppressed, and sufficient bendability cannot be obtained. Example No. 24 has a short maintenance time in cooling after annealing, and the desired metal structure cannot be obtained, and thus sufficient strength and elongation characteristics (TS×EL value) and sufficient flexibility cannot be obtained. In Example No. 25, the cooling stop temperature and maintenance temperature after annealing are high, and the desired metal structure cannot be obtained and sufficient bendability cannot be obtained. The C content of Example No. 26 was insufficient, and the desired metal structure could not be obtained, and thus sufficient strength and elongation characteristics (TS×EL value) could not be obtained. Example No. 28 The austenitic iron phase fraction of the heat treatment after the hot rolling extension is high, the desired metal structure cannot be obtained, and the value of CMnγ/CMnα is insufficient, and sufficient strength and elongation characteristics (TS×EL value) cannot be obtained ). In Example No. 29, the maintenance time in the heat treatment after hot rolling is short, the desired metal structure cannot be obtained, and the value of CMnγ/CMnα is insufficient, and sufficient strength and elongation characteristics (TS×EL value) cannot be obtained. Example No. 31 has a short maintenance time during annealing, and the desired metal structure cannot be obtained, and sufficient strength and elongation characteristics (TS×EL value) cannot be obtained. Sample No. 34 had a short cooling time after hot rolling, and could not suppress the variation in Vickers hardness, so that sufficient bendability could not be obtained. Sample No. 35 contained too much Mn, so sufficient bendability could not be obtained. Sample No. 36 did not perform the heat treatment after hot rolling, so sufficient strength and elongation characteristics (TS×EL value) could not be obtained.

Claims

一種鋼板，其化學組成以質量%計為： C：大於0.15且小於0.40%、 Si：0.001且小於2.00%、 Mn：大於2.50且小於4.20%、 sol.Al：0.001且小於1.500%、 P：0.030%以下、 S：0.0050%以下、 N：小於0.050%、 O：小於0.020%、 Cr：0~0.50%、 Mo：0~2.00%、 W：0~2.00%、 Cu：0~2.00%、 Ni：0~2.00%、 Ti：0~0.300%、 Nb：0~0.300%、 V：0~0.300%、 B：0~0.010%、 Ca：0~0.010%、 Mg：0~0.010%、 Zr：0~0.010%、 REM：0~0.010%、 Sb：0~0.050%、 Sn：0~0.050%、 Bi：0~0.050%及剩餘部分：鐵及不純物，且從表面起算1/8厚度位置的金屬組織以面積率計為：沃斯田鐵相：10%以上、回火麻田散鐵相與變韌鐵相之合計：5%以上、肥粒鐵相：35%以上、及新生麻田散鐵相：小於15%；未再結晶肥粒鐵相相對於前述肥粒鐵相的面積率為10~50%；前述沃斯田鐵相之平均Mn濃度CMnγ與前述肥粒鐵相之平均Mn濃度CMnα之比CMnγ/CMnα為1.20以上；並且從表面起算1/8厚度位置的維氏硬度之參差在40Hv以下。A steel plate whose chemical composition is calculated as mass %: C: greater than 0.15 and less than 0.40%, Si: 0.001 and less than 2.00%, Mn: greater than 2.50 and less than 4.20%, sol.Al: 0.001 and less than 1.500%, P: 0.030% or less, S: 0.0050% or less, N: less than 0.050%, O: less than 0.020%, Cr: 0~0.50%, Mo: 0~2.00%, W: 0~2.00%, Cu: 0~2.00%, Ni: 0~2.00%, Ti: 0~0.300%, Nb: 0~0.300%, V: 0~0.300%, B: 0~0.010%, Ca: 0~0.010%, Mg: 0~0.010%, Zr: 0~0.010%, REM: 0~0.010%, Sb: 0~0.050%, Sn: 0~0.050%, Bi: 0~0.050% and Remaining part: iron and impurities, and The area ratio of the metal structure at 1/8 thickness from the surface is: Austenitic iron phase: 10% or more, the sum of tempered Matian scattered iron phase and toughened iron phase: 5% or more, Fertilizer iron phase: 35% or more, and scattered iron phase of Xinsheng Matian: less than 15%; The area ratio of the unrecrystallized fertilizer grain iron phase relative to the aforementioned fertilizer grain iron phase is 10-50%; The ratio CMnγ/CMnα of the average Mn concentration CMnγ of the aforementioned austenitic iron phase to the average Mn concentration CMnα of the aforementioned fertilizer grain iron phase is 1.20 or more; and The variation of Vickers hardness at 1/8 thickness from the surface is below 40Hv.

如請求項1之鋼板，其中前述化學組成含有選自於由以下所構成群組中之1種或2種以上元素：以質量%計， Cr：0.01~0.50%、 Ti：0.005~0.300%、 Nb：0.005~0.300%、 V：0.005~0.300%及 B：0.0001~0.010%。The steel plate of claim 1, wherein the aforementioned chemical composition contains one or more elements selected from the group consisting of: In terms of mass %, Cr: 0.01~0.50%, Ti: 0.005~0.300%, Nb: 0.005~0.300%, V: 0.005~0.300% and B: 0.0001~0.010%.

如請求項1或2之鋼板，前述鋼板的表面具有熔融鍍鋅層。For the steel sheet of claim 1 or 2, the surface of the steel sheet has a hot-dip galvanized layer.

如請求項1或2之鋼板，前述鋼板的表面具有合金化熔融鍍鋅層。For the steel sheet of claim 1 or 2, the surface of the aforementioned steel sheet has an alloyed hot-dip galvanized layer.

一種鋼板之製造方法，包含以下步驟：對鋼施行熱軋延以製成熱軋鋼板，該熱軋延中，精整軋延溫度為1000℃以下，前述精整軋延後的放冷時間為0.8秒以上，前述放冷後的平均冷卻速度為30℃/秒以上以及捲取溫度低於300℃，並且前述鋼之化學組成以質量%計為： C：大於0.15且小於0.40%、 Si：0.001且小於2.00%、 Mn：大於2.50且小於4.20%、 sol.Al：0.001且小於1.500%、 P：0.030%以下、 S：0.0050%以下、 N：小於0.050%、 O：小於0.020%、 Cr：0~0.50%、 Mo：0~2.00%、 W：0~2.00%、 Cu：0~2.00%、 Ni：0~2.00%、 Ti：0~0.300%、 Nb：0~0.300%、 V：0~0.300%、 B：0~0.010%、 Ca：0~0.010%、 Mg：0~0.010%、 Zr：0~0.010%、 REM：0~0.010%、 Sb：0~0.050%、 Sn：0~0.050%、 Bi：0~0.050%及剩餘部分：鐵及不純物；對前述熱軋鋼板在沃斯田鐵相分率成為20~50%之溫度區下進行1小時以上的熱處理，然後施行酸洗及冷軋延，以製成冷軋鋼板；設前述冷軋延之冷軋延率為30~70%；將前述冷軋鋼板在沃斯田鐵相分率成為20~65%之溫度區下維持30秒以上，進行退火；及在前述退火之溫度維持後，冷卻至100~530℃之溫度區，並在100~530℃之溫度區下維持10~1000秒。A method of manufacturing steel plate, including the following steps: Hot rolling is performed on the steel to produce a hot-rolled steel sheet. In this hot rolling, the finishing temperature is 1000°C or less, and the cooling time after the finishing rolling is 0.8 seconds or more. The average after cooling is The cooling rate is 30°C/sec or more and the coiling temperature is lower than 300°C, and the chemical composition of the aforementioned steel is calculated as mass%: C: greater than 0.15 and less than 0.40%, Si: 0.001 and less than 2.00%, Mn: greater than 2.50 and less than 4.20%, sol.Al: 0.001 and less than 1.500%, P: 0.030% or less, S: 0.0050% or less, N: less than 0.050%, O: less than 0.020%, Cr: 0~0.50%, Mo: 0~2.00%, W: 0~2.00%, Cu: 0~2.00%, Ni: 0~2.00%, Ti: 0~0.300%, Nb: 0~0.300%, V: 0~0.300%, B: 0~0.010%, Ca: 0~0.010%, Mg: 0~0.010%, Zr: 0~0.010%, REM: 0~0.010%, Sb: 0~0.050%, Sn: 0~0.050%, Bi: 0~0.050% and Remaining part: iron and impurities; The aforementioned hot-rolled steel sheet is heat-treated for more than 1 hour in a temperature zone where the austenitic iron phase fraction becomes 20-50%, and then pickled and cold-rolled to produce cold-rolled steel sheets; Let the cold rolling elongation rate of the aforementioned cold rolling be 30~70%; Keep the aforementioned cold-rolled steel sheet in a temperature zone where the austenitic iron phase fraction becomes 20-65% for more than 30 seconds, and then perform annealing; and After maintaining the aforementioned annealing temperature, it is cooled to a temperature zone of 100~530℃, and maintained at a temperature zone of 100~530℃ for 10~1000 seconds.

如請求項5之鋼板之製造方法，其中前述化學組成含有選自於由以下所構成群組中之1種或2種以上元素：以質量%計， Cr：0.01~0.50%、 Ti：0.005~0.300%、 Nb：0.005~0.300%、 V：0.005~0.300%及 B：0.0001~0.010%。Such as the method for manufacturing a steel plate of claim 5, wherein the aforementioned chemical composition contains one or more elements selected from the group consisting of: In terms of mass %, Cr: 0.01~0.50%, Ti: 0.005~0.300%, Nb: 0.005~0.300%, V: 0.005~0.300% and B: 0.0001~0.010%.

如請求項5或6之鋼板之製造方法，其中前述精整軋延後的放冷時間為1.2~4.0秒。Such as claim 5 or 6 of the method for manufacturing a steel plate, wherein the cooling time after the aforementioned finishing rolling delay is 1.2 to 4.0 seconds.

如請求項5至7中任一項之鋼板之製造方法，其中於前述退火後施行熔融鍍鋅處理。The method for manufacturing a steel sheet according to any one of claims 5 to 7, wherein hot-dip galvanizing is performed after the aforementioned annealing.

如請求項8之鋼板之製造方法，其中於施行前述熔融鍍鋅處理後，在450~620℃之溫度區下施行前述熔融鍍鋅的合金化處理。The method for manufacturing a steel sheet according to claim 8, wherein after performing the hot-dip galvanizing treatment, the alloying treatment of the hot-dip galvanizing is performed in a temperature range of 450 to 620°C.