JP2017201049A - High-strength stainless steel sheet excellent in workability and method for manufacturing the same - Google Patents
High-strength stainless steel sheet excellent in workability and method for manufacturing the same Download PDFInfo
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Abstract
Description
本発明は、特に加工性と強度の両立が必要な自動車部品に用いられる、加工性に優れた高強度ステンレス鋼板およびその製造方法に関するもので、特に自動車、二輪車、バス、鉄道車両などの車体や足回り、ピラー、バンパー、フロントサイドメンバー等の構造用冷延鋼板およびそれらの固定金具、フランジ、クランプ、バンド等の締結部品用冷延鋼板に関わるものである。 The present invention relates to a high-strength stainless steel plate excellent in workability and a method for producing the same, particularly used for automobile parts that require both workability and strength. Particularly, the present invention relates to a vehicle body such as an automobile, a motorcycle, a bus, and a railway vehicle. The present invention relates to structural cold-rolled steel sheets such as undercarriages, pillars, bumpers, and front side members, and cold-rolled steel sheets for fastening parts such as fixtures, flanges, clamps, and bands.
近年、環境問題の観点から、自動車、二輪車、バス、鉄道車両などの輸送機器の燃費向上が必須課題になってきている。その解決手段の一つとして、車体の軽量化が積極的に推進されており、その中で高耐食鋼であるステンレス鋼の適用が検討されている。Crを含有するステンレス鋼を適用した場合、錆代低減による軽量化、塗装省略化が適用の着眼である。また、乗員の安全性確保という観点からは、衝突安全性向上が要求されるが、上記の車体軽量化との両立が必要である。衝突安全性向上の対策としては、部材を構成する鋼板の高強度化が有効であり、高強度ステンレス鋼板の適用により安全性と軽量化の両立が達成できる可能性がある。高強度材を上記構造部材に適用する際の問題点は、加工性の確保である。高強度化により加工性が低下すると、複雑形状部品への成型が困難になるためである。特に、高強度ステンレス鋼板は、穴拡げ加工時に割れが発生する問題が多く、自動車、バス、鉄道車両の構造部材で穴拡げ加工を施される場合に問題を残していた。 In recent years, from the viewpoint of environmental problems, improvement in fuel consumption of transportation equipment such as automobiles, motorcycles, buses, and railway vehicles has become an essential issue. As one of the solutions, weight reduction of the vehicle body is actively promoted, and application of stainless steel, which is a high corrosion resistance steel, is being studied. When stainless steel containing Cr is applied, weight reduction by reducing rust allowance and omission of painting are the focus of application. Further, from the viewpoint of ensuring the safety of passengers, it is required to improve the collision safety, but it is necessary to achieve both the above-mentioned weight reduction of the vehicle body. As a measure for improving the collision safety, it is effective to increase the strength of the steel plate constituting the member, and there is a possibility that both safety and light weight can be achieved by applying the high strength stainless steel plate. A problem in applying a high-strength material to the structural member is securing workability. This is because if the workability is reduced due to the increase in strength, it becomes difficult to mold into a complex shaped part. In particular, the high-strength stainless steel sheet has many problems that cause cracks during hole expansion processing, and has left a problem when it is subjected to hole expansion processing in structural members of automobiles, buses, and railway vehicles.
従来から上記構造部材用のステンレス鋼板としては、焼き入れにより高強度化するマルテンサイト系ステンレス鋼板が知られているが、延性が著しく低いため部材への加工性に問題がある。一方、オーステナイト系ステンレス鋼板としてはS304やS301が使用されている。これらは、延性に優れており、加工誘起変態を活用した高加工硬化特性が得られる。しかしながら、Niを多量に含有しコスト高であったり、環境によっては応力腐食割れが問題になり、構造材としての信頼性を落とす場合があった。 Conventionally, a martensitic stainless steel plate that is strengthened by quenching is known as the stainless steel plate for the structural member, but there is a problem in workability of the member because the ductility is extremely low. On the other hand, S304 and S301 are used as the austenitic stainless steel sheet. These are excellent in ductility, and high work hardening characteristics utilizing work-induced transformation can be obtained. However, it contains a large amount of Ni and is expensive, and depending on the environment, stress corrosion cracking becomes a problem, and the reliability as a structural material may be lowered.
このような問題の中、特許文献1には、面内異方性が小さい高延性高強度の複相組織クロム系ステンレス鋼板の製造方法が開示されている。ここでは、Cr:10〜14%含有する鋼帯に対して、熱処理条件を規定して仕上焼鈍加熱時の組織をフェライト+オーステナイト組織として冷却速度を調整することで、強度と延性の面内異方性を小さくすることが特徴である。しかしながら、上記のように構造部品として加工する際、特に穴拡げ加工においては、延性以外に深絞り性が問題になり、深絞り性の指標であるr値が低い課題があった。
Among such problems,
特許文献2には、Cr:11〜15%含有し、主相をフェライト相とし、2〜20%をマルテンサイト相とする穴拡げ性に優れ、引張強さが600MPa超とする構造用ステンレス鋼板が開示されている。ここでは、製品組織の二相化により、破断伸びが15%以上、穴拡げ率が70%以上となることが示されており、軟質なフェライト相中にマルテンサイト相を生成させることで穴拡げ加工時の割れ起点となる炭窒化物を低減することが特徴である。しかしながら、通常の製法で製品組織を二相化しただけでは、十分な穴拡げ性が得られない場合がある他、マルテンサイト自体が割れの起点となるおそれがある。また、深絞り性が不十分となる課題もあった。これは、マルテンサイトの体積分率だけでなく、その分散状態やフェライト相の結晶方位に起因する塑性異方性が影響するためである。 Patent Document 2 discloses a structural stainless steel sheet containing Cr: 11 to 15%, having a main phase of a ferrite phase, an excellent hole expansion property of 2 to 20% of a martensite phase, and a tensile strength exceeding 600 MPa. Is disclosed. Here, it is shown that the elongation at break is 15% or more and the hole expansion rate is 70% or more due to the two-phase structure of the product structure. By expanding the martensite phase in the soft ferrite phase, the hole expansion is achieved. It is characterized by reducing the carbonitride that becomes the starting point of cracking during processing. However, there is a case where sufficient hole expansibility cannot be obtained only by making the product structure into two phases by a normal manufacturing method, and martensite itself may be a starting point of cracking. There is also a problem that the deep drawability becomes insufficient. This is because not only the volume fraction of martensite but also the plastic anisotropy due to the dispersion state and the crystal orientation of the ferrite phase are affected.
特許文献3には、Cr:9〜13%を含み、フェライト相を70%以上、炭窒化物およびマルテンサイト相を30%未満含む金属組織を有し、引張強さが600〜900MPaで伸びフランジ性(穴拡げ性と同様)に優れたCr含有高強度冷延鋼板およびその製造方法が開示されている。この鋼は、特許文献2と同様にマルテンサイト相を製品に残留させて伸びフランジ性の向上を図っているが(穴拡げ性が100%以上)、上記と同様に母相のフェライト相の結晶方位によっては、単純に二相化しただけでは十分な伸びフランジ性は得られなかった。 Patent Document 3 includes Cr: 9 to 13%, has a metal structure including ferrite phase of 70% or more, carbonitride and martensite phase of less than 30%, and has an elongation flange with a tensile strength of 600 to 900 MPa. A Cr-containing high-strength cold-rolled steel sheet having excellent properties (similar to hole expandability) and a method for producing the same are disclosed. In this steel, the martensite phase remains in the product as in Patent Document 2 to improve stretch flangeability (hole expandability is 100% or more). Depending on the orientation, sufficient stretch flangeability could not be obtained by simply making it two-phased.
また、特許文献4には、Cr:7〜15%を含み、耐粒界腐食性と穴拡げ性に優れた自動車用クロム含有鋼が開示されている。ここでは、穴拡げ率を90%以上とするために、種々の成分含有量を調整しているが、組織や結晶方位の影響について規定されておらず、成分の規定だけでは穴拡げ性が著しくばらつく場合があった。また、冷延鋼板製造時の条件についても、通常のステンレス鋼等のCr含有鋼の製法を前提としているのみであり、高加工性を得るための製造条件の規定としては不十分であった。 Patent Document 4 discloses a chromium-containing steel for automobiles containing Cr: 7 to 15% and having excellent intergranular corrosion resistance and hole expansibility. Here, the content of various components is adjusted in order to make the hole expansion ratio 90% or more, but the influence of the structure and crystal orientation is not defined, and the hole expansion property is remarkably only by the definition of the components. There was a case where it varied. Further, the conditions at the time of manufacturing the cold-rolled steel sheet are only premised on the manufacturing method of the Cr-containing steel such as ordinary stainless steel, and the manufacturing conditions for obtaining high workability are insufficient.
また、特許文献5には、Cr:10〜18%を含み、フェライト−オーステナイトの二相域を呈する組成を有するステンレス鋼板の製造工程において、第一熱処理工程においてマルテンサイト相を20〜80%生成させた後、冷延後の熱処理をAc1変態点未満で熱処理することでフェライト単相組織とする延性に優れた高強度ステンレス鋼板の製造方法が開示されている。この製造方法では、製品板のフェライト相の結晶方位発達が不十分で塑性異方性が十分に発達せず、穴拡げ性が劣ることがあった。また、炭素および窒素を固着するための合金元素を添加していないため、硬質な炭窒化物が生成するおそれもある。 Patent Document 5 includes Cr: 10 to 18%, and in the manufacturing process of a stainless steel plate having a composition exhibiting a two-phase region of ferrite and austenite, 20 to 80% of martensite phase is generated in the first heat treatment step. A method for producing a high-strength stainless steel sheet having excellent ductility by forming a ferrite single phase structure by performing heat treatment after cold rolling below the A c1 transformation point is disclosed. In this manufacturing method, the crystal orientation of the ferrite phase of the product plate is not sufficiently developed, the plastic anisotropy is not sufficiently developed, and the hole expandability is sometimes inferior. Moreover, since an alloy element for fixing carbon and nitrogen is not added, hard carbonitride may be generated.
また、特許文献6には、Cr:10〜18%を含み、冷延素材の組織を微細なラスマルテンサイト組織とすることで、冷延・焼鈍後の母相のフェライト相の集合組織を制御し、特定結晶方位を成長させる、フェライト+マルテンサイト組織となる加工性に優れた高強度ステンレス鋼板の製造方法が開示されている。しかし、この製造方法でも、平均r値が0.9〜1.2程度であり加工性はまだ不十分であった。 Patent Document 6 includes Cr: 10 to 18%, and controls the texture of the ferrite phase of the parent phase after cold rolling and annealing by making the structure of the cold rolled material into a fine lath martensite structure. And the manufacturing method of the high intensity | strength stainless steel plate excellent in the workability which becomes a ferrite + martensite structure | tissue which grows a specific crystal orientation is disclosed. However, even in this production method, the average r value is about 0.9 to 1.2, and the workability is still insufficient.
上記のように、Cr含有ステンレス鋼板において、高強度化と穴拡げ性の向上に関する検討は種々成されているが、強度と加工性を安定的に両立させることはできなかった。また、フェライト+マルテンサイトの二相鋼とした場合には、硬質なマルテンサイトと軟質なマルテンサイトの界面で欠陥が発生し、穴拡げ性が劣化することが考えられるため、フェライト単相であることが望ましい。このようなことから、本発明は従来技術の問題点を解決し、高強度でかつ加工性に優れたCr含有ステンレス鋼板およびその製造方法を提供することを目的とする。 As described above, in the Cr-containing stainless steel sheet, various studies have been made on increasing the strength and improving the hole expansibility, but it has been impossible to stably achieve both strength and workability. In addition, when a ferrite + martensite duplex steel is used, defects are generated at the interface between hard martensite and soft martensite, and the hole expandability may be deteriorated. It is desirable. In view of the above, an object of the present invention is to solve the problems of the prior art and to provide a Cr-containing stainless steel plate having high strength and excellent workability and a method for producing the same.
本発明では、従来技術であるフェライト+マルテンサイト二相化による穴拡げ性向上技術とは全く異なる思想により、フェライト単相鋼を高強度化しつつ、母相の結晶方位を制御することでr値を向上させ、穴拡げ性を向上させることを課題とするものである。 In the present invention, the r value is obtained by controlling the crystal orientation of the parent phase while increasing the strength of the ferrite single-phase steel based on a completely different idea from the conventional technique of improving hole expansion by ferrite + martensite biphasic. It is an object to improve the hole expanding property.
上記課題を解決するために、本発明者らは高温でフェライト相とオーステナイト相の二相となるCr含有ステンレス鋼の強度と加工性について金属組織的な観点から入念に研究した。そして、従来技術とは異なる観点で加工性を向上(特に深絞り性の指標となるr値および穴拡げ性)させる技術を見出した。即ち上記文献の中で、特に特許文献2と3は金属組織を二相化して穴拡げ性を向上させる技術があるが、母相であるフェライト相の変形特性に大きく依存し、二相化だけでは十分な特性が得られないことを知見した。そして、フェライト単相組織のまま高強度化し、さらに集合組織制御によりr値を同時に向上させることで、穴拡げ性を向上できることを見出した。具体的には、最終製品の金属組織制御にあたり、再結晶と相変態を同時に活用した。その結果、フェライト単相のままで、[1]組織細粒化による延性を確保しつつの高強度化と、同時に、[2]フェライト相の加工性向上に有効なフェライト相の({111}〈011〉、{211}〈011〉)の発達と、加工性を低下させる特定結晶方位({311}〈136〉)の抑制を両立して、加工性(r値と穴拡げ性)の向上を達成することができる。その際、各製造工程のフェライト相と第二相の結晶方位関係を精査し、冷延素材の組織を微細なラスマルテンサイト組織化することで、冷延・焼鈍後のフェライト相の結晶方位を制御し、加工性(r値、穴拡げ性)を向上させるものである。 In order to solve the above-mentioned problems, the present inventors have carefully studied the strength and workability of Cr-containing stainless steel that becomes a two-phase ferrite phase and austenite phase at a high temperature from the viewpoint of metallographic structure. And the technique which improves workability from the viewpoint different from a prior art (especially r value used as a parameter | index of deep drawability and hole expansibility) was discovered. That is, among the above-mentioned documents, Patent Documents 2 and 3 have a technique for improving the hole expansibility by making the metal structure into a two-phase, but greatly depends on the deformation characteristics of the ferrite phase as a parent phase, and only the two-phase is provided. Then, it was found that sufficient characteristics could not be obtained. It was also found that the hole expandability can be improved by increasing the strength while maintaining the ferrite single phase structure and further improving the r value by texture control. Specifically, recrystallization and phase transformation were used at the same time in controlling the microstructure of the final product. As a result, while maintaining the ferrite single phase, [1] high strength while ensuring ductility by refining the structure, and [2] ferrite phase ({111} effective in improving the workability of the ferrite phase) <011>, {211} <011>) and the suppression of a specific crystal orientation ({311} <136>) that lowers workability, and improves workability (r value and hole expandability) Can be achieved. At that time, by examining the crystal orientation relationship between the ferrite phase and the second phase in each manufacturing process and making the microstructure of the cold-rolled material a fine lath martensite structure, the crystal orientation of the ferrite phase after cold-rolling and annealing can be changed. It controls and improves workability (r value, hole expansibility).
上記課題を解決する本発明の要旨は、
(1) 質量%にて、C:0.001〜0.03%、N:0.001〜0.03%、Si:0.05〜3.0%、Mn:0.1〜15.0%、P:0.05%以下、S:0.01%以下、Cr:10%以上18%未満を含有し、さらにTi:0.30%以下、Nb:0.50%以下の1種または2種を含有し、TiとNbの合計が、8(C+N)〜0.75%であり、残部がFeおよび不可避的不純物からなり、γp(ガンマポテンシャル)が65〜85%であり、X線回折による板厚中心のフェライト相の結晶方位強度において、{111}<011>結晶方位強度が3.0以上、{211}<011>結晶方位強度が3.0以上、{311}〈136〉結晶方位強度および{100}<011>結晶方位強度の比({311}〈136〉結晶方位強度/{100}<011>結晶方位強度)が2.5以下であり、フェライト粒径が20μm以下、およびフェライト相面積率が90%以上であることを特徴とする加工性に優れた高強度ステンレス鋼板。なお、γpは(1)式のCastroの式を用いて評価する。
γp=420(%C)+470(%N)+23(%Ni)+9(%Cu)+7(%Mn)
−11.5(%Cr)−11.5(%Si)−12(%Mo)−23(%V)−47(%Nb)
−49(%Ti)−52(%Al)+189 (1)
なお、(%X)は、各成分Xの質量割合を示す。不可避的不純物量程度しか含有していない場合はゼロとする。
(2) さらに質量%にて、B:0.0002〜0.0030%、Al:0.030〜0.300%、Mo:0.1〜2.0%、Ni:0.1〜1.2%、Cu:0.1〜2.0%、V:0.05〜1.00%、Sn:0.005〜0.500%、W:0.005〜3.00%、Co:0.01〜0.30%、Sb:0.005〜0.500%、Ta:0.01〜0.10%、Ga:0.0002%〜0.1000%、REM:0.001〜0.200%の1種または2種以上を含有することを特徴とする(1)に記載の加工性に優れた高強度ステンレス鋼板。
(3) 平均r値が1.5以上であることを特徴とする(1)または(2)に記載の加工性に優れた高強度ステンレス鋼板。
(4) rminが1.0以上、n×(1+rmin)が0.40以上であることを特徴とする(1)〜(3)のいずれかひとつに記載の加工性に優れた高強度ステンレス鋼板。
nはn値(加工硬化指数)、rminは最小r(ランクフォード)値である。
(5) 引張強度が440MPa以上、破断伸びが20%以上、穴拡げ率が100%以上であることを特徴とする(1)〜(4)のいずれかひとつに記載の加工性に優れた高強度ステンレス鋼板。
(6) (1)または(2)に記載の成分組成のスラブを用い、熱間圧延において、スラブ加熱温度を1100〜1200℃として粗圧延を行い、仕上げ圧延を開始温度が900℃以上、終了温度が800℃以上、その差が200℃以内となるように仕上げ圧延を行い、600℃以上で巻取った後、冷間圧延し、冷間圧延後の焼鈍処理として700〜1000℃で熱処理し、熱処理後の冷却速度を1〜10℃/secとすることを特徴とする(1)〜(5)のいずれかひとつに記載の加工性に優れた高強度ステンレス鋼板の製造方法。
(7) 前記ステンレス鋼板は、自動車構造部品用として使用される(1)〜(5)のいずれかひとつに記載の加工性に優れた高強度ステンレス鋼板。
(8) 前記ステンレス鋼板は、自動車締結部品用として使用される(1)〜(5)のいずれかひとつに記載の加工性に優れた高強度ステンレス鋼板。
The gist of the present invention for solving the above problems is as follows.
(1) In mass%, C: 0.001 to 0.03%, N: 0.001 to 0.03%, Si: 0.05 to 3.0%, Mn: 0.1 to 15.0 %, P: 0.05% or less, S: 0.01% or less, Cr: 10% or more and less than 18%, Ti: 0.30% or less, Nb: 0.50% or less 2 types are included, the total of Ti and Nb is 8 (C + N) to 0.75%, the balance is made of Fe and inevitable impurities, γ p (gamma potential) is 65 to 85%, X In the crystal orientation strength of the ferrite phase at the center of the plate thickness by line diffraction, the {111} <011> crystal orientation strength is 3.0 or more, {211} <011> the crystal orientation strength is 3.0 or more, {311} <136 > The ratio of crystal orientation strength and {100} <011> crystal orientation strength ({311} <136> Orientation strength / {100} <011> crystal orientation strength) is 2.5 or less, ferrite grain size is 20 μm or less, and ferrite phase area ratio is 90% or more. Strength stainless steel sheet. Note that γ p is evaluated using the Castro equation (1).
γ p = 420 (% C) +470 (% N) +23 (% Ni) +9 (% Cu) +7 (% Mn)
-11.5 (% Cr) -11.5 (% Si) -12 (% Mo) -23 (% V) -47 (% Nb)
-49 (% Ti) -52 (% Al) +189 (1)
In addition, (% X) shows the mass ratio of each component X. Zero if it contains only inevitable impurities.
(2) Further, by mass%, B: 0.0002 to 0.0030%, Al: 0.030 to 0.300%, Mo: 0.1 to 2.0%, Ni: 0.1 to 1. 2%, Cu: 0.1 to 2.0%, V: 0.05 to 1.00%, Sn: 0.005 to 0.500%, W: 0.005 to 3.00%, Co: 0 .01-0.30%, Sb: 0.005-0.500%, Ta: 0.01-0.10%, Ga: 0.0002% -0.1000%, REM: 0.001-0. The high-strength stainless steel plate having excellent workability as described in (1), which contains 200% of one kind or two or more kinds.
(3) The high-strength stainless steel plate excellent in workability as described in (1) or (2), wherein the average r value is 1.5 or more.
(4) The high strength excellent in workability according to any one of (1) to (3), wherein r min is 1.0 or more and n × (1 + r min ) is 0.40 or more. Stainless steel sheet.
n is an n value (work hardening index), and r min is a minimum r (Rankford) value.
(5) The tensile strength is 440 MPa or more, the elongation at break is 20% or more, and the hole expansion ratio is 100% or more. The high excellent workability according to any one of (1) to (4) Strength stainless steel sheet.
(6) Using the slab having the component composition described in (1) or (2), in hot rolling, rough rolling is performed at a slab heating temperature of 1100 to 1200 ° C, and finishing rolling is started at a temperature of 900 ° C or more. Finish rolling so that the temperature is 800 ° C. or higher and the difference is within 200 ° C., winding at 600 ° C. or higher, cold rolling, and heat-treating at 700 to 1000 ° C. as an annealing treatment after cold rolling. The method for producing a high-strength stainless steel plate excellent in workability according to any one of (1) to (5), wherein a cooling rate after heat treatment is 1 to 10 ° C./sec.
(7) The said stainless steel plate is a high strength stainless steel plate excellent in workability as described in any one of (1)-(5) used for automotive structural components.
(8) The high-strength stainless steel plate excellent in workability according to any one of (1) to (5), wherein the stainless steel plate is used for automobile fastening parts.
以上の説明から明らかなように、本発明によれば特に高価な合金元素を添加せずとも、高強度で加工性に優れたCr含有鋼板を提供することができ、特に自動車、バス、鉄道等の運輸に関わる構造部材や締結部品に適用することにより、環境対策、安全性向上などに大きく寄与できる。 As is clear from the above description, according to the present invention, it is possible to provide a Cr-containing steel sheet having high strength and excellent workability without adding particularly expensive alloy elements, particularly automobiles, buses, railways, etc. By applying it to structural members and fastening parts related to transportation, it can greatly contribute to environmental measures and safety improvements.
以下に本発明の限定理由について説明する。
鋼の成分範囲について説明する。
The reason for limitation of the present invention will be described below.
The component range of steel will be described.
Cは、成形性と耐食性を劣化させる。また、Cが高いと、本発明で必要とするフェライト相の結晶方位強度(集合組織)が得られにくくなるとともに鋼中にマルテンサイトが残存してしまうため、その含有量は少ないほど良く、上限を0.03%とした。但し、過度の低減は精錬コストの増加に繋がるため、下限を0.001%とした。更に、製造コストと溶接部の粒界腐食性を考慮すると0.002〜0.02%が望ましい。 C deteriorates moldability and corrosion resistance. Further, if C is high, the crystal orientation strength (texture) of the ferrite phase required in the present invention is difficult to obtain and martensite remains in the steel. Therefore, the lower the content, the better. Was 0.03%. However, excessive reduction leads to an increase in refining costs, so the lower limit was made 0.001%. Furthermore, if considering the manufacturing cost and intergranular corrosion properties of the weld, 0.002 to 0.02% is desirable.
Nは、Cと同様に成形性と耐食性を劣化させる他、Nが高いと、本発明で必要とするフェライト相の結晶方位強度(集合組織)が得られにくくなるとともに鋼中にマルテンサイトが残存してしまうため、その含有量は少ないほど良く、上限を0.03%とした。ただし、過度の低下は精錬コストの増加に繋がるため、下限を0.001%とした。更に製造コストと加工性および耐食性を考慮すると、0.005〜0.015%が望ましい。 N deteriorates formability and corrosion resistance in the same way as C. If N is high, the crystal orientation strength (texture) of the ferrite phase required in the present invention is difficult to obtain and martensite remains in the steel. Therefore, the lower the content, the better, and the upper limit was made 0.03%. However, excessive reduction leads to an increase in refining costs, so the lower limit was made 0.001%. Furthermore, if considering the manufacturing cost, workability and corrosion resistance, 0.005 to 0.015% is desirable.
Siは、脱酸元素として添加される場合がある他、耐酸化性の向上をもたらすが、固溶強化元素であり、過度の添加は急激に延性を低下させる他、すべり系の制限により{311}を発達させるため、上限を3.0%とした。ただし、過度の低下は精錬コストの増加に繋がるため、下限を0.05%とした。更に、製造コストと耐食性を考慮すると0.1〜1.0%が望ましい。 Si is sometimes added as a deoxidizing element, and also improves oxidation resistance. However, Si is a solid solution strengthening element. Excessive addition rapidly reduces ductility, and {311 due to slip system limitations. }, The upper limit was made 3.0%. However, excessive reduction leads to an increase in refining costs, so the lower limit was made 0.05%. Furthermore, if considering the manufacturing cost and corrosion resistance, 0.1 to 1.0% is desirable.
Mnは、Ni同様、オーステナイト安定化元素であり、相変態による結晶粒微細化に有効である。また、スケール密着性の向上や異常酸化の抑制にも寄与する。この作用は0.1%以上で発現するため、下限を0.1%とした。ただし、過度に添加した場合、MnSを形成して耐食性を低下させる他、鋼中にマルテンサイトが残存してしまうため、上限を15.0%とした。更に、製造コストと耐食性を考慮すると1.0〜5.0%が望ましい。 Mn, like Ni, is an austenite stabilizing element and is effective for refining crystal grains by phase transformation. It also contributes to improved scale adhesion and suppression of abnormal oxidation. Since this effect appears at 0.1% or more, the lower limit was made 0.1%. However, when excessively added, MnS is formed to lower the corrosion resistance and martensite remains in the steel, so the upper limit was made 15.0%. Furthermore, if considering the manufacturing cost and corrosion resistance, 1.0 to 5.0% is desirable.
Pは、Si同様、固溶強化元素であるため、材質上その含有量は少ないほど良いため、上限は0.05%とした。更に、製造コストと耐食性を考慮すると0.01〜0.02%が望ましい。 Since P is a solid solution strengthening element like Si, the lower the content, the better. Therefore, the upper limit was made 0.05%. Furthermore, if considering the manufacturing cost and corrosion resistance, 0.01 to 0.02% is desirable.
Sは、耐食性を劣化させる元素であるため、上限を0.01%とした。更に、製造コストや、部品とした際の隙間腐食抑制を考慮すると0.0005〜0.0050%が望ましい。 Since S is an element that degrades corrosion resistance, the upper limit was made 0.01%. Furthermore, if considering the manufacturing cost and suppression of crevice corrosion when used as a part, 0.0005 to 0.0050% is desirable.
Crは、耐食性や耐酸化性を向上させる元素であり、排気部品環境を考慮すると異常酸化抑制の観点から10%以上が必要である。一方、Crの過度の添加は硬質化をもたらし成形性を劣化させる。また、Crはフェライト安定化元素であるため、過度に添加すると、オーステナイト相変態が起こらなくなる。さらに、コストアップの観点から、上限は18%未満とした。なお、製造コストや靭性劣化による鋼板製造時の板破断ならびに加工性を考慮すると、10.5%以上、15%未満が望ましい。 Cr is an element that improves corrosion resistance and oxidation resistance. When considering the exhaust part environment, 10% or more is necessary from the viewpoint of suppressing abnormal oxidation. On the other hand, excessive addition of Cr causes hardening and deteriorates formability. Further, since Cr is a ferrite stabilizing element, if added excessively, austenite phase transformation does not occur. Furthermore, from the viewpoint of cost increase, the upper limit was made less than 18%. In addition, when considering the sheet breakage and workability at the time of manufacturing the steel sheet due to the manufacturing cost and toughness deterioration, 10.5% or more and less than 15% are desirable.
本発明は、Ti:0.30%以下、Nb:0.50%以下の1種または2種を含有し、TiとNbの合計を8(C+N)〜0.75%の範囲とする。ここで、Ti、Nb、C、Nは、それぞれの元素の含有量(質量%)を意味する。
Tiは、C,N,Sと結合して耐食性、耐粒界腐食性、深絞り性を向上させるために添加する元素である。また、0.30%超の添加は固溶Tiにより硬質化し、靭性が劣化するため、上限を0.30%とした。更に製造コスト等を考慮すると、0.06〜0.25%が望ましい。
Nbは、Tiと同様に、C,N,Sと結合して耐食性、耐粒界腐食性、深絞り性を向上させるために添加する元素である。また、加工性の向上や高温強度の向上に加え、隙間腐食の抑制や再不動態化を促進させるため、必要に応じて添加される。ただし、過度の添加は硬質化をもたらし成形性を劣化させる他、再結晶を遅延させるため上限を0.50%とした。更に製造コスト等を考慮すると、0.05〜0.3%が望ましい。
また、TiとNbの合計が8(C+N)未満であると、過剰なC、Nが鋼中に固溶して硬化させるので、TiとNbの合計を8(C+N)以上とする。さらに、TiとNbの合計が0.75%を超えると固溶Tiや固溶Nb、および、NbとTiの炭窒化物や金属間化合物が硬質化をもたらし、靭性や成形性を劣化させるため、TiとNbの合計を0.75%以下とする。
The present invention contains one or two of Ti: 0.30% or less and Nb: 0.50% or less, and the total of Ti and Nb is in the range of 8 (C + N) to 0.75%. Here, Ti, Nb, C, and N mean content (mass%) of each element.
Ti is an element added to combine with C, N, and S to improve corrosion resistance, intergranular corrosion resistance, and deep drawability. Moreover, since addition exceeding 0.30% hardens by solute Ti and toughness deteriorates, the upper limit was made 0.30%. Furthermore, if considering the manufacturing cost, 0.06 to 0.25% is desirable.
Nb, like Ti, is an element added to combine with C, N, and S to improve corrosion resistance, intergranular corrosion resistance, and deep drawability. In addition to improving workability and high-temperature strength, it is added as necessary to suppress crevice corrosion and promote repassivation. However, excessive addition causes hardening and deteriorates moldability, and also delays recrystallization, so the upper limit was made 0.50%. Furthermore, if considering the manufacturing cost, 0.05 to 0.3% is desirable.
Further, if the sum of Ti and Nb is less than 8 (C + N), excess C and N are dissolved in the steel and hardened, so the sum of Ti and Nb is 8 (C + N) or more. Furthermore, if the total of Ti and Nb exceeds 0.75%, solid solution Ti, solid solution Nb, and Nb and Ti carbonitrides and intermetallic compounds cause hardening and deteriorate toughness and formability. , Ti and Nb total is 0.75% or less.
本発明は、必要に応じてさらに以下の元素を含有することができる。 This invention can contain the following elements further as needed.
Bは、粒界に偏析することで製品の二次加工性を向上させる元素である。排気系部品を二次加工する際の縦割れを抑制する他、特に冬場に割れが生じないためには、0.0002%以上添加すると良い。ただし、過度の添加は加工性、耐食性の低下をもたらすため、上限を0.0030%とした。更に、精錬コストや延性低下を考慮すると、0.0003〜0.0015%が望ましい。 B is an element that improves the secondary workability of the product by segregating at the grain boundaries. In addition to suppressing vertical cracks during secondary processing of exhaust system parts, 0.0002% or more is preferably added in order to prevent cracks in winter. However, excessive addition causes a decrease in workability and corrosion resistance, so the upper limit was made 0.0030%. Furthermore, if considering the refining cost and ductility reduction, 0.0003 to 0.0015% is desirable.
Alは、脱酸元素として添加される他、酸化スケールの剥離を抑制する効果がある。この効果は0.030%以上で発現するため、下限を0.030%とした。一方、0.300%以上の添加は、伸びの低下、溶接溶け込み性および表面品質の劣化をもたらすため、上限を0.300%とした。更に、精錬コストと鋼板製造時の酸洗性を考慮すると、0.050〜0.150%が望ましい。 In addition to being added as a deoxidizing element, Al has an effect of suppressing oxide scale peeling. Since this effect is manifested at 0.030% or more, the lower limit was made 0.030%. On the other hand, addition of 0.300% or more causes a decrease in elongation, weld penetration, and surface quality deterioration, so the upper limit was made 0.300%. Furthermore, if considering the refining cost and the pickling property at the time of manufacturing the steel sheet, 0.050 to 0.150% is desirable.
Moは、耐食性を向上させる元素であり、特に隙間構造を有する場合には隙間腐食を抑制する元素である。この効果は0.1%以上で発現するため、下限を0.1%とした。また、2.0%を超えると著しく成形性が劣化する他、製造性が悪くなるため、上限を2.0%とした。合金コストと生産性を考慮すると、0.1〜0.5%が望ましい。 Mo is an element that improves the corrosion resistance, and is an element that suppresses crevice corrosion, particularly when it has a crevice structure. Since this effect appears at 0.1% or more, the lower limit was made 0.1%. Further, if it exceeds 2.0%, the moldability is remarkably deteriorated and the manufacturability is deteriorated, so the upper limit was made 2.0%. Considering the alloy cost and productivity, 0.1 to 0.5% is desirable.
Niは、オーステナイト安定化元素であり、相変態による結晶粒微細化に有効である。また、隙間腐食の抑制や再不動態化を促進させる。この作用は0.1%以上で発現するため、下限を0.1%とした。但し、過度の添加は硬質化し成形性を劣化させる他、応力腐食割れが生じやすくなるため、上限を1.2%とした。なお、原料コストを考えると0.2%〜1.0%が望ましい。さらに望ましくは上限は0.8%である、0.5%以下でもよい。 Ni is an austenite stabilizing element and is effective for refining crystal grains by phase transformation. It also promotes crevice corrosion suppression and repassivation. Since this effect appears at 0.1% or more, the lower limit was made 0.1%. However, excessive addition hardens and deteriorates moldability, and stress corrosion cracking tends to occur, so the upper limit was made 1.2%. In view of the raw material cost, 0.2% to 1.0% is desirable. More desirably, the upper limit is 0.8%, which may be 0.5% or less.
Cuは、NiやMn同様、オーステナイト安定化元素であり、相変態による結晶粒微細化に有効である。また、隙間腐食の抑制や再不動態化を促進させるため、必要に応じて添加される。この作用は0.1%以上で発現するため、下限を0.1%とした。但し、過度の添加は硬質化する他、靭性および成形性を劣化させるため、上限を2.0%とした。合金コストと生産性を考慮すると、0.15〜1.0%が好ましい。 Cu, like Ni and Mn, is an austenite stabilizing element and is effective for refining crystal grains by phase transformation. Moreover, in order to promote suppression of crevice corrosion and repassivation, it adds as needed. Since this effect appears at 0.1% or more, the lower limit was made 0.1%. However, excessive addition hardens and deteriorates toughness and moldability, so the upper limit was made 2.0%. Considering alloy cost and productivity, 0.15 to 1.0% is preferable.
Vは、隙間腐食を抑制させるため、必要に応じて添加される。この作用は、0.05%以上から発現するため、下限を0.05%とした。但し、過度の添加は、硬質化し成形性を劣化させるため、上限を1.00%とした。なお、原料コストを考慮すると、0.10〜0.50%が望ましい。 V is added as necessary to suppress crevice corrosion. Since this effect appears from 0.05% or more, the lower limit was made 0.05%. However, excessive addition hardens and deteriorates moldability, so the upper limit was made 1.00%. In consideration of the raw material cost, 0.10 to 0.50% is desirable.
Snは、耐食性と高温強度の向上に寄与するため、必要に応じて0.005%以上添加する。ただし、0.500%超の添加により鋼板製造時のスラブ割れが生じる場合が有るため、上限を0.500%とする。更に、精錬コストや製造性を考慮すると、0.003〜0.300%が望ましい。 Sn contributes to the improvement of corrosion resistance and high-temperature strength, so 0.005% or more is added as necessary. However, since addition of more than 0.500% may cause slab cracking during steel sheet manufacture, the upper limit is made 0.500%. Furthermore, if considering the refining cost and manufacturability, 0.003 to 0.300% is desirable.
Wは、耐食性と高温強度の向上に寄与するため、必要に応じて0.005%以上添加する。ただし、3.00%超の添加により硬質化し、鋼板製造時の靭性劣化やコスト増に繋がるため、上限を3.00%とする。更に、精錬コストや製造法を考慮すると、0.01〜0.10%が望ましい。 W contributes to improvement of corrosion resistance and high-temperature strength, so 0.005% or more is added as necessary. However, the upper limit is set to 3.00% because it hardens by addition of more than 3.00% and leads to toughness deterioration and cost increase at the time of manufacturing the steel sheet. Furthermore, if refining costs and manufacturing methods are taken into consideration, 0.01 to 0.10% is desirable.
Coは、高温強度の向上に寄与するため、必要に応じて0.01%以上添加する。0.30%超の添加により鋼板製造時の靭性劣化やコスト増に繋がるため、上限を0.30%とする。更に、精錬コストや製造性を考慮すると、0.01〜0.10%が望ましい。 Co contributes to improving the high-temperature strength, so 0.01% or more is added as necessary. Since addition of more than 0.30% leads to toughness deterioration and cost increase at the time of manufacturing the steel sheet, the upper limit is made 0.30%. Furthermore, if refining costs and manufacturability are taken into consideration, 0.01 to 0.10% is desirable.
Sbは、粒界に偏析して高温強度を上げる作用をなす元素である。これは、0.005%以上から発現するため、下限を0.005%とした。但し、0.500%を超えると、Sb偏析が生じて、溶接時に割れが生じるので、上限は0.500%とする。高温特性と製造コストおよび靭性を考慮すると、0.03〜0.30%が望ましい。さらに望ましくは、0.050〜0.200%である。 Sb is an element that segregates at the grain boundary to increase the high temperature strength. Since this is expressed from 0.005% or more, the lower limit was made 0.005%. However, if it exceeds 0.500%, Sb segregation occurs and cracks occur during welding, so the upper limit is made 0.500%. Considering high temperature characteristics, production cost and toughness, 0.03 to 0.30% is desirable. More desirably, it is 0.050 to 0.200%.
Taは、CやNと結合して靭性の向上に寄与するため必要に応じて0.01%以上添加する。ただし、0.10%超の添加によりコスト増になるため、上限を0.10%とする。更に、精錬コストや製造性を考慮すると、0.01〜0.08%が望ましい。 Ta is combined with C and N to contribute to the improvement of toughness, so 0.01% or more is added as necessary. However, the addition of more than 0.10% increases the cost, so the upper limit is made 0.10%. Furthermore, if considering refining costs and manufacturability, 0.01 to 0.08% is desirable.
Gaは、耐食性向上や水素脆化抑制のため、0.1000%以下で添加してもよい。硫化物や水素化物形成の観点から下限は0.0002%とする。好ましくは0.0010%以上である。 Ga may be added at 0.1000% or less for improving corrosion resistance and suppressing hydrogen embrittlement. The lower limit is made 0.0002% from the viewpoint of sulfide and hydride formation. Preferably it is 0.0010% or more.
REM(希土類元素)は、耐酸化性の向上に有効であり、必要に応じて0.001%以上添加する。また、0.200%を超えて添加してもその効果は飽和し、REMの硫化物による耐食性低下を生じるため、0.001〜0.200%で添加する。製品の加工性や製造コストを考慮すると、下限を0.002%とし、上限を0.10%とすることが望ましい。REMは、一般的な定義に従う。スカンジウム(Sc)、イットリウム(Y)の2元素と、ランタン(La)からルテチウム(Lu)までの15元素(ランタノイド)の総称を指す。単独で添加しても良いし、混合物であっても良い。 REM (rare earth element) is effective in improving oxidation resistance, and is added in an amount of 0.001% or more as necessary. Moreover, even if added over 0.200%, the effect is saturated and the corrosion resistance is lowered by sulfide of REM, so 0.001 to 0.200% is added. Considering the workability and manufacturing cost of the product, it is desirable that the lower limit is 0.002% and the upper limit is 0.10%. REM follows the general definition. It is a generic term for two elements of scandium (Sc) and yttrium (Y) and 15 elements (lanthanoid) from lanthanum (La) to lutetium (Lu). It may be added alone or as a mixture.
その他の成分について本発明では特に規定するものではないが、Hfは高温強度向上のために0.001%〜1.0%添加しても良い。また、Biを必要に応じて0.001〜0.02%含有しても構わない。なお、As、Pb等の一般的な有害な不純物元素はできるだけ低減することが望ましい。 The other components are not particularly defined in the present invention, but Hf may be added in an amount of 0.001% to 1.0% in order to improve the high temperature strength. Moreover, you may contain Bi 0.001 to 0.02% as needed. Note that it is desirable to reduce general harmful impurity elements such as As and Pb as much as possible.
本発明の鋼板は、上記の成分範囲内でγpを65%以上になるように調整する。γpが低すぎると、フェライト−オーステナイト変態に高温での加熱が必要となり、本発明で必要とするフェライト相の結晶方位強度(集合組織)が得られにくくなるとともに結晶粒を微細化することが難しくなるので、65%以上とした。また、γpが高すぎると鋼中にマルテンサイト生成が避けられず、フェライト相を主体とした鋼板ではなくなるため、85%以下とした。さらに、材質と結晶粒径の両立を考慮すると、γpが72%以上、80%以下が望ましい。γpは(1)式のCastroの式を用いて評価する。
γp=420(%C)+470(%N)+23(%Ni)+9(%Cu)+7(%Mn)
−11.5(%Cr)−11.5(%Si)−12(%Mo)−23(%V)−47(%Nb)
−49(%Ti)−52(%Al)+189 (1)
なお、(%X)は、各成分Xの質量割合を示す。不可避的不純物量程度しか含有していない場合はゼロとする。
In the steel sheet of the present invention, γ p is adjusted to 65% or more within the above-described component range. If γ p is too low, it is necessary to heat the ferrite-austenite transformation at a high temperature, which makes it difficult to obtain the crystal orientation strength (texture) of the ferrite phase required in the present invention and to refine the crystal grains. Since it becomes difficult, it was made 65% or more. Further, if γ p is too high, martensite formation is unavoidable in the steel, and the steel sheet is not made mainly of a ferrite phase. Furthermore, considering the balance between the material and the crystal grain size, γ p is preferably 72% or more and 80% or less. γ p is evaluated using the Castro equation (1).
γ p = 420 (% C) +470 (% N) +23 (% Ni) +9 (% Cu) +7 (% Mn)
-11.5 (% Cr) -11.5 (% Si) -12 (% Mo) -23 (% V) -47 (% Nb)
-49 (% Ti) -52 (% Al) +189 (1)
In addition, (% X) shows the mass ratio of each component X. Zero if it contains only inevitable impurities.
次に集合組織と加工性(r値、n値、穴拡げ性)の関係について説明する。 Next, the relationship between texture and workability (r value, n value, hole expandability) will be described.
本発明においては、母相のフェライト相の結晶方位が加工性に極めて重要であり、かつ鋼板の板厚方向の平均的な結晶方位分布がr値向上に寄与し、構造材の基本的な成型性の一つである穴拡げ性向上に有益に作用することを見出した。図1に鋼A(0.005%C−0.43%Si−1.85%Mn−0.022%P−0.0010%S−0.23%Ni−11.0%Cr−0.79%Cu−0.05%Al−0.011%N、γp=77)と鋼B(0.005%C−0.42%Si−0.66%Mn−0.021%P−0.0004%S−0.16%Ni−10.9%Cr−0.07%Al−0.009%N、γp=59)の結晶方位分布とr値を示す。鋼Aは熱延後に冷延(板厚1mm)・焼鈍(A:800℃×60sec)したものである。一方、鋼Bは熱延後に冷延(板厚1mm)・焼鈍(900℃×60sec)したものである。
In the present invention, the crystal orientation of the ferrite phase of the parent phase is extremely important for workability, and the average crystal orientation distribution in the thickness direction of the steel sheet contributes to the improvement of the r value, and the basic molding of the structural material It has been found that it has a beneficial effect on improving the hole expandability, which is one of the characteristics. FIG. 1 shows steel A (0.005% C-0.43% Si-1.85% Mn-0.022% P-0.0010% S-0.23% Ni-11.0% Cr-0. 79% Cu-0.05% Al-0.011% N, γ p = 77) and steel B (0.005% C-0.42% Si-0.66% Mn-0.021% P-0 .0004% S-0.16% Ni-10.9% Cr-0.07% Al-0.009% N, γ p = 59). Steel A is cold-rolled (plate thickness: 1 mm) and annealed (A: 800 ° C. × 60 sec) after hot rolling. On the other hand, steel B is cold-rolled (
ここで、集合組織の測定は、X線回折装置(理学電気興業株式会社製)を使用し、Moの−Kα線を用いて、板厚中心領域(機械研磨と電解研磨の組み合わせで中心領域を現出)の(200)、(110)、(211)正極点図を得、これらのデータから、球面調和関数を用いてODF(orientation distribution function)を得た。 Here, the texture is measured using an X-ray diffractometer (manufactured by Rigaku Denki Kogyo Co., Ltd.), and using the Mo-Kα ray, the central region of the plate thickness (combination of mechanical polishing and electrolytic polishing) (200), (110), (211) positive pole figure of the present) was obtained, and ODF (orientation distribution function) was obtained from these data using spherical harmonics.
図1は上記鋼Aと鋼Bの結晶方位の強度分布を等高線で示したものであり、{111}<011>はr値を向上させ、{211}<011>については、{111}<011>よりもr値は低い結晶方位であるが、45°方向のr値を増加させる方位であり、3.0以上と強い。{311}<136>はr値を低減させ、{100}<011>については、r値への影響は小さいが、相変態により{311}〈136〉の生成が抑制されたことにより生じた結晶方位である。この鋼Aは、{111}〈011〉強度が3.0以上、{211}<011>強度が3.0以上と強く、{311}〈136〉結晶方位強度と{100}<011>結晶方位強度の比({311}〈136〉結晶方位強度/{100}<011>結晶方位強度)が2.5以下であり、平均r値が1.9と高い。一方、鋼Bの結晶方位強度は鋼Aと異なるため、平均r値が1.4と低い。平均r値は1.5以上であれば、構造部材として満足な加工性を有することから、X線回折による全板厚の結晶方位強度において、フェライト相の{111}<011>強度が3.0以上、{311}〈136〉結晶方位強度と{100}<011>結晶方位強度の比が2.5以下とする。この条件を満たす集合組織とすることで、平均r値が1.5以上となる高加工性ステンレス鋼板を提供することができる。 FIG. 1 shows the strength distribution of the crystal orientations of the steel A and the steel B with contour lines. {111} <011> improves the r value, and {211} <011> has {111} < Although the r value is lower than 011>, it is an orientation that increases the r value in the 45 ° direction and is as strong as 3.0 or more. {311} <136> reduces the r value, and {100} <011> has a small effect on the r value, but is caused by the suppression of the production of {311} <136> by the phase transformation. The crystal orientation. This steel A has a strong {111} <011> strength of 3.0 or more and a {211} <011> strength of 3.0 or more, a {311} <136> crystal orientation strength and a {100} <011> crystal. The ratio of orientation strength ({311} <136> crystal orientation strength / {100} <011> crystal orientation strength) is 2.5 or less, and the average r value is as high as 1.9. On the other hand, since the crystal orientation strength of steel B is different from that of steel A, the average r value is as low as 1.4. If the average r value is 1.5 or more, it has satisfactory processability as a structural member. Therefore, the {111} <011> strength of the ferrite phase is 3. 0 or more, and the ratio of {311} <136> crystal orientation strength to {100} <011> crystal orientation strength is 2.5 or less. By setting the texture satisfying this condition, it is possible to provide a high workability stainless steel sheet having an average r value of 1.5 or more.
即ち本発明は、X線回折による板厚中心のフェライト相の結晶方位強度において、{111}<011>結晶方位強度が3.0以上、{211}<011>結晶方位強度が3.0以上、{311}〈136〉結晶方位強度および{100}<011>結晶方位強度の比({311}〈136〉結晶方位強度/{100}<011>結晶方位強度)が2.5以下と規定する。 That is, according to the present invention, in the crystal orientation strength of the ferrite phase at the center of the plate thickness by X-ray diffraction, the {111} <011> crystal orientation strength is 3.0 or more, and the {211} <011> crystal orientation strength is 3.0 or more. , {311} <136> crystal orientation strength and {100} <011> crystal orientation strength ratio ({311} <136> crystal orientation strength / {100} <011> crystal orientation strength) is defined as 2.5 or less. To do.
平均r値の評価は、製品板からJIS13号B引張試験片を採取して、圧延方向、圧延方向と45°方向、圧延方向と90°方向に14.4%歪を付与した後に(2)式および(3)式を用いて算出した。
r=ln(W0/W)/ln(t0/t) (2)
ここで、W0は引張前の板幅、Wは引張後の板幅、t0は引張前の板厚、tは引張後の板厚である。
rm=(r0+r45+r90)/4 (3)
ここで、rmは平均r値、r0は圧延方向のr値、r45は圧延方向と45°方向のr値、r90は圧延方向と90°方向のr値である。
また、最小r値(rmin)とは、r0、r45、r90のうち最も値が小さいr値である。
The average r value was evaluated by taking a JIS13B tensile test piece from the product plate and applying a 14.4% strain in the rolling direction, the rolling direction and 45 ° direction, and the rolling direction and 90 ° direction (2). It calculated using Formula (3) and Formula (3).
r = ln (W 0 / W) / ln (t 0 / t) (2)
Here, W 0 is the plate width before tension, W is the plate width after tension, t 0 is the plate thickness before tension, and t is the plate thickness after tension.
r m = (r 0 + r 45 + r 90 ) / 4 (3)
Here, r m is the average r value, r 0 is the r value in the rolling direction, r 45 is the r value in the rolling direction and the 45 ° direction, and r 90 is the r value in the rolling direction and the 90 ° direction.
The minimum r value (r min ) is the r value having the smallest value among r 0 , r 45 , and r 90 .
n値、すなわち加工硬化指数の評価は、製品板からJIS13号B引張試験片を採取して、JIS Z 2253に従い応力歪曲線を得た後、%塑性ひずみが5%と15%の試験力(N)を求め、(4)式を用いて算出した。
穴拡げ性の評価は、JIS Z 2256に準拠し、φ10mmの打ち抜き穴に60°の円錐ポンチを押し込んで少しずつ穴を拡げ、穴に亀裂が入った時点でポンチを停止し、穴径の変化から穴拡げ率λを(5)式を用いて求めた。
λ=100×(D−D0)/D0 (5)
ここで、Dは穴拡げ試験後の穴径で、D0は穴拡げ前の穴径である。
The hole expandability is evaluated in accordance with JIS Z 2256. A 60 ° conical punch is pushed into a punched hole of φ10mm to gradually expand the hole, and when the hole cracks, the punch is stopped and the hole diameter changes. From this, the hole expansion rate λ was obtained using the equation (5).
λ = 100 × (D−D 0 ) / D 0 (5)
Here, D is the hole diameter after the hole expansion test, and D 0 is the hole diameter before the hole expansion.
本発明が対象とする自動車構造部品に用いられる鋼板には、440MPa以上の高強度を有するとともに、高い平均r値に加え高い穴拡げ性が求められる。本発明は前述のように、フェライト主体の組織として、[1]組織細粒化による延性を確保しつつの高強度化と、同時に、[2]フェライト相の加工性向上に有効なフェライト相の集合組織を実現して、加工性(r値と穴拡げ性)の向上を達成するものである。 The steel plate used for the automotive structural component targeted by the present invention is required to have high strength of 440 MPa or more and high hole expansibility in addition to a high average r value. In the present invention, as described above, as a structure mainly composed of ferrite, [1] high strength while ensuring ductility by refining the structure, and [2] ferrite phase effective for improving workability of the ferrite phase. A texture is realized to improve workability (r value and hole expandability).
穴拡げ率が100%以上であれば、自動車構造部品用鋼材として満足な加工性を有する。図2に示すように、穴拡げ性はn値および最小r値(rmin)と相関関係に有り、n×(1+rmin)が0.40以上の条件を満たす材質とすることで、自動車構造部品用鋼材に適する穴拡げ率100%以上となる高加工性ステンレス鋼板を提供することができる。図2において、穴拡げ率が100%以上を□、それ以外を黒四角としている。さらに望ましくは、n×(1+rmin)が0.45以上である。最小r値が1.0以上であれば、n×(1+rmin)を0.40以上とすることができる。 If the hole expansion ratio is 100% or more, it has satisfactory workability as a steel material for automobile structural parts. As shown in FIG. 2, the hole expansibility correlates with the n value and the minimum r value (r min ), and the vehicle structure is such that n × (1 + r min ) satisfies the condition of 0.40 or more. It is possible to provide a high-workability stainless steel plate having a hole expansion rate of 100% or more suitable for steel for parts. In FIG. 2, the hole expansion rate is 100% or more, and the others are black squares. More desirably, n × (1 + r min ) is 0.45 or more. If the minimum r value is 1.0 or more, n × (1 + r min ) can be set to 0.40 or more.
次に、結晶組織および高温強度について説明する。 Next, the crystal structure and the high temperature strength will be described.
この際の組織形態については、上記のようにフェライト主体となる組織である必要がある。本発明におけるフェライト主体組織とは、フェライト相率(面積率)が90%以上となる組織である。望ましくは、95%以上である。さらに望ましくはフェライト相率100%の単相組織である。フェライト相率の測定は、EBSD(Electron Back Scattering Diffraction)および画像解析より測定した。マルテンサイト生成量は、TSL社OIM(Orientation Imaging Microscopy)解析ソフトを用いてフェライト相とマルテンサイトの分率を定量的に測定した。フェライト相率が90%未満となると、r値が不良または測定不能となるとともに穴拡げ率が不良となる。 The structure form at this time needs to be a structure mainly composed of ferrite as described above. The ferrite main structure in the present invention is a structure having a ferrite phase ratio (area ratio) of 90% or more. Desirably, it is 95% or more. A single-phase structure with a ferrite phase ratio of 100% is more desirable. The ferrite phase ratio was measured by EBSD (Electron Back Scattering Diffraction) and image analysis. The amount of martensite produced was determined quantitatively by measuring the fraction of ferrite phase and martensite using TSL OIM (Orientation Imaging Microscopy) analysis software. If the ferrite phase ratio is less than 90%, the r value becomes poor or unmeasurable and the hole expansion rate becomes poor.
このとき、フェライトの結晶粒径は20μm以下とする。図3に示すように、フェライト組織であっても、結晶粒径を20μm以下とすることにより、引張強度が高強度部材として一般的に要求される強度レベルである440MPa以上となる高強度ステンレス鋼板を提供することができる。更に望ましくは、結晶粒径10μm以下である。図3において、強度が440MPa以上を○、それ以外を●としている。結晶粒径は平均結晶粒径である。フェライトの結晶粒径は、EBSD法により測定した。粒径の測定条件は、測定倍率1000倍で0.3〜0.6μmステップの条件とし、得られたデータをOIM解析ソフトにより方位差15°以上を粒界として一つの粒界を設定し円相当径を算出した。得られた円相当径を算術平均によって求めた値を結晶粒径とした。 At this time, the crystal grain size of the ferrite is 20 μm or less. As shown in FIG. 3, a high-strength stainless steel plate having a tensile strength of 440 MPa or more, which is a generally required strength level as a high-strength member, even if it is a ferrite structure by setting the crystal grain size to 20 μm or less. Can be provided. More desirably, the crystal grain size is 10 μm or less. In FIG. 3, the strength is 440 MPa or more, and the others are ●. The crystal grain size is an average crystal grain size. The crystal grain size of ferrite was measured by the EBSD method. The measurement condition of the particle diameter is a condition of 0.3 to 0.6 μm step at a measurement magnification of 1000 times, and the obtained data is set to one circle boundary with an orientation difference of 15 ° or more by OIM analysis software. The equivalent diameter was calculated. The value obtained by arithmetic average of the obtained equivalent circle diameter was defined as the crystal grain size.
また、引張破断伸びも穴拡げ性に対して重要であるが、20%以上の破断伸びで十分な穴拡げ性が得られ、高強度構造部材としての加工も可能であることから、好ましくは破断伸びを20%以上とする。さらに望ましくは25%以上である。 In addition, the tensile elongation at break is also important for hole expansibility. However, since sufficient hole expansibility is obtained at a break elongation of 20% or more, and processing as a high-strength structural member is possible, it is preferable to break Elongation is 20% or more. More desirably, it is 25% or more.
本発明は、前記本発明の成分を含有するとともに、上述のように、本発明の集合組織およびフェライト粒径が20μm以下、かつフェライト相面積率が90%以上の結晶組織を有することにより、平均r値が1.5以上、n×(1+rmin)が0.40以上とでき、引張強度が440MPa以上、破断伸びが20%以上、穴拡げ率が100%以上の加工性と高温強度を有するステンレス鋼板を実現することができる。 The present invention contains the above-described components of the present invention and, as described above, has a texture of the present invention and a crystal structure having a ferrite grain size of 20 μm or less and a ferrite phase area ratio of 90% or more. r value is 1.5 or more, n × (1 + r min ) is 0.40 or more, tensile strength is 440 MPa or more, elongation at break is 20% or more, hole expansion rate is 100% or more, and has high workability and high temperature strength. Stainless steel sheet can be realized.
次に製造方法について説明する。 Next, a manufacturing method will be described.
前述の本発明の成分組成を有するスラブを鋳造する。鋳造されたスラブは、1100〜1200℃で加熱される。冷延・焼鈍板の集合組織発達の観点からは、熱延板にはラスマルテンサイト量が多い程良く、生成量としては80%超が望ましい。また、加熱温度が低すぎるとスケール生成が少なくなり圧延ロールと鋼材の焼き付きにより表面品質が低下するため、下限温度を1100℃とした。炉の性能、経済性の観点から、スラブ加熱温度は1100〜1200℃とした。更に生産性や表面疵を考慮すると、1120℃〜1160℃が望ましい。 A slab having the above-described component composition of the present invention is cast. The cast slab is heated at 1100 to 1200 ° C. From the viewpoint of the development of the texture of the cold-rolled / annealed sheet, the hot-rolled sheet should have a larger amount of lath martensite, and the generated amount is preferably over 80%. Further, if the heating temperature is too low, scale generation is reduced and the surface quality is deteriorated due to seizure of the rolling roll and the steel material, so the lower limit temperature is set to 1100 ° C. From the viewpoint of furnace performance and economy, the slab heating temperature was set to 1100 to 1200 ° C. Furthermore, considering productivity and surface wrinkles, 1120 ° C. to 1160 ° C. is desirable.
スラブ加熱後、熱間圧延工程では、複数パスの粗圧延が施され、複数スタンドからなる仕上圧延が一方向に施される。粗圧延後、高速で仕上圧延が施され、コイル状に巻き取られる。本発明では、巻取り時に微細組織を得るために、粗圧延温度(上記スラブ加熱温度)と、巻取温度を規定する。製造時の割れや破断を防ぐためには、熱延板の組織を微細組織にすることが重要である。また、組織微細化させた熱延板を冷延することで、{111}〈011〉結晶方位と{211}〈011〉結晶方位を発達させつつ、{311}〈136〉方位の発達を抑制し、{311}〈136〉と{100}〈011〉結晶方位の比を2.5以下にすることが可能となる。ただし、巻取温度が低すぎると巻取時に再結晶と相変態が生じないため、仕上圧延は高温かつ高速で行う必要が有る。そこで、仕上げ圧延温度を開始温度が900℃以上、終了温度が800℃以上、その差が200℃以内となるように行う。また、巻取温度も600℃以上で行うものとする。これにより、後述の冷延板焼鈍条件と相まって、鋼板の結晶粒径と引張強度を本発明範囲内とすることができる。本発明では、熱延板厚さは適宜選択すれば良いが、巻取形状、板厚精度、表面性状を考慮すると、2〜15mm程度が望ましい。 After the slab heating, in the hot rolling process, multiple passes of rough rolling are performed, and finish rolling consisting of a plurality of stands is performed in one direction. After rough rolling, finish rolling is performed at a high speed and the coil is wound up. In the present invention, in order to obtain a fine structure during winding, the rough rolling temperature (the slab heating temperature) and the winding temperature are defined. In order to prevent cracks and breaks during production, it is important to make the structure of the hot-rolled sheet a fine structure. Further, by cold-rolling a hot-rolled sheet having a refined structure, the development of the {311} <136> orientation is suppressed while the {111} <011> crystal orientation and the {211} <011> crystal orientation are developed. In addition, the ratio of the {311} <136> and {100} <011> crystal orientations can be made 2.5 or less. However, if the winding temperature is too low, recrystallization and phase transformation do not occur during winding, and thus finishing rolling must be performed at a high temperature and at a high speed. Therefore, the finish rolling temperature is set such that the start temperature is 900 ° C. or higher, the end temperature is 800 ° C. or higher, and the difference is within 200 ° C. In addition, the coiling temperature is 600 ° C. or higher. Thereby, the crystal grain size and tensile strength of the steel sheet can be within the scope of the present invention in combination with the cold-rolled sheet annealing conditions described later. In the present invention, the hot-rolled plate thickness may be selected as appropriate, but about 2 to 15 mm is desirable in consideration of the winding shape, plate thickness accuracy, and surface properties.
熱延終了後、熱延板焼鈍は行わずに下記の冷間圧延と冷延板焼鈍を行う。熱延板焼鈍を省略することにより、後述の冷延板焼鈍条件と相まって、結晶粒径を本発明範囲内とするとともに、鋼板の集合組織を本発明の好ましい組織とすることができる。 After the hot rolling is completed, the following cold rolling and cold rolling sheet annealing are performed without performing hot rolling sheet annealing. By omitting the hot-rolled sheet annealing, the crystal grain size is within the range of the present invention in combination with the cold-rolled sheet annealing conditions described later, and the texture of the steel sheet can be a preferable structure of the present invention.
冷延板焼鈍後の組織を得るためは、フェライト+オーステナイト二相域で焼鈍する必要がある。このとき、過度に高温で焼鈍すると、鋼中にマルテンサイトが生成し延性が低下する。また、冷延板の{111}結晶方位も相変態してしまい、製品板の{111}結晶方位が弱くなる。そこで、上限温度を1000℃とした。また、加熱温度が低すぎると、再結晶が十分に起こらず、冷延加工組織が鋼中に残存し、加工性(r値および穴拡げ性)が低下してしまう。よって、熱処理温度を700〜1000℃とした。さらに望ましくは750〜900℃である。また、焼鈍温度が本発明範囲内であっても、冷却速度が速過ぎるとマルテンサイトが生成してしまい、フェライト面積率が低減してr値及び穴拡げ性が低下する。また、冷却速度が遅過ぎるとフェライト結晶粒が成長し20μm以上に粗大化してしまう。そのため、焼鈍後の冷却速度は上限を10℃/sec以下、下限を1℃/sec以上とする。基本的に空冷するのが望ましいが、水冷してもフェライト単相組織となる場合には水冷してもよい。 In order to obtain the structure after cold-rolled sheet annealing, it is necessary to anneal in the ferrite + austenite two-phase region. At this time, if the annealing is performed at an excessively high temperature, martensite is generated in the steel and the ductility is lowered. Further, the {111} crystal orientation of the cold-rolled plate also undergoes phase transformation, and the {111} crystal orientation of the product plate becomes weak. Therefore, the upper limit temperature was set to 1000 ° C. On the other hand, if the heating temperature is too low, recrystallization does not occur sufficiently, the cold-rolled texture remains in the steel, and the workability (r value and hole expandability) decreases. Therefore, the heat treatment temperature was set to 700 to 1000 ° C. More desirably, the temperature is 750 to 900 ° C. Even if the annealing temperature is within the range of the present invention, if the cooling rate is too high, martensite is generated, the ferrite area ratio is reduced, and the r value and the hole expandability are lowered. If the cooling rate is too slow, ferrite crystal grains grow and become coarser to 20 μm or more. Therefore, the upper limit of the cooling rate after annealing is 10 ° C./sec or less and the lower limit is 1 ° C./sec or more. Basically, it is desirable to cool by air, but if it becomes a ferrite single phase structure even if cooled by water, it may be cooled by water.
本発明のように、製品板で集合組織を発達させ、高r値、高穴拡げ特性を得るためには、途中工程にて再結晶と、相変態(フェライト相→オーステナイト相→フェライト相)を同時にさせることが重要であることを見出した。本発明では、熱間圧延板焼鈍を施さずに酸洗処理し、冷間圧延工程に冷間圧延素材として供する。これは、通常の製法とは異なる(通常は熱間圧延板焼鈍を施す)ものである。通常の製造方法では、フェライト単相域で熱間圧延板焼鈍を施して、整粒再結晶組織を得る方法が一般的である。これに対して本発明では、熱延板焼鈍を行わないので、熱延工程で生成したマルテンサイト組織が残存したまま冷延し、冷延後焼鈍することで、r値が向上する。なお、十分に微細なマルテンサイトが生成される場合には熱延板焼鈍を行ってもよい。本発明の鋼を、熱延中あるいは高温熱延板焼鈍中にオーステナイト域に加熱すると、冷却中にマルテンサイト変態を起こすが、本発明の成分系ではラス状の極めて微細な組織であるため、その後の冷延・焼鈍時に微細組織の結晶粒界近傍から{111}方位が発達し易いためと考えられる。{111}方位粒はBCC結晶構造を有するフェライト鋼のr値を向上させる結晶方位であるが、一般的には、硬質なマルテンサイトと軟質なフェライト相の二相組織を冷延すると、硬質なマルテンサイト相によりフェライト相に不均一変形が導入され、{111}方位結晶粒は生成し難い。しかしながら、本発明の成分系においてはラスマルテンサイト組織の形態が極めて細かいことから冷延板焼鈍時の変態・再結晶時に細かいラスマルテンサイトから{111}結晶方位を有するフェライトが発達する作用が発現すると考えられる。この集合組織の発現性は、マルテンサイト相とフェライト相の硬度差にもよる可能性があり、本発明の成分系では両相の硬度バランスが適正であるためと考えられる。また、この冷延後の焼鈍時に、フェライト+オーステナイト二相域で焼鈍することにより、相変態しやすい{100}〈011〉を相変態させつつ、相変態しにくい〈111〉方位粒を再結晶させる。加工された{100}〈011〉は、再結晶した場合r値を大きく低下させる{311}〈136〉再結晶粒を生成させるが、オーステナイト相に変態させることでこの再結晶粒の生成を抑制することが可能となる。また、この相変態した{100}〈011〉は、冷却時に方位記憶効果によりもとの{100}〈011〉近傍の方位を持ったフェライト相あるいはマルテンサイト相へと変態する。この方位記憶効果を起こすにはMn添加による強度上昇が重要であるため、本発明の成分系が適正であると考えられる。また、相変態させずに残存させた{111}方位粒は、焼鈍中に{111}方位粒へと再結晶する。以上より、非常に{111}方位が発達しつつ、{311}〈136〉の形成を抑制した高加工性鋼を得ることができる。 As in the present invention, in order to develop a texture in the product plate and obtain a high r value and high hole expansion characteristics, recrystallization and phase transformation (ferrite phase → austenite phase → ferrite phase) are performed in the middle process. I found it important to do it at the same time. In this invention, it pickles without performing hot-rolled sheet annealing, and uses for a cold-rolling process as a cold-rolling raw material. This is different from a normal manufacturing method (usually hot-rolled sheet annealing is performed). In a normal manufacturing method, a method of obtaining a sized recrystallized structure by performing hot rolling plate annealing in a ferrite single phase region is general. On the other hand, in this invention, since hot-rolled sheet annealing is not performed, r value improves by carrying out cold rolling with the martensite structure | tissue produced | generated at the hot rolling process remaining, and annealing after cold rolling. In addition, when sufficiently fine martensite is generated, hot-rolled sheet annealing may be performed. When the steel of the present invention is heated in the austenite region during hot rolling or high-temperature hot-rolled sheet annealing, it causes martensitic transformation during cooling, but in the component system of the present invention, it is a lath-like extremely fine structure, This is probably because the {111} orientation easily develops from the vicinity of the grain boundary of the fine structure during the subsequent cold rolling and annealing. The {111} -oriented grains are crystal orientations that improve the r-value of ferritic steel having a BCC crystal structure. Generally, however, when a two-phase structure of hard martensite and soft ferrite phase is cold rolled, The martensite phase introduces non-uniform deformation in the ferrite phase, and {111} oriented grains are difficult to generate. However, in the component system of the present invention, since the morphology of the lath martensite structure is extremely fine, the effect of developing ferrite having {111} crystal orientation from fine lath martensite during transformation and recrystallization during cold-rolled sheet annealing is manifested. I think that. The expression of this texture may depend on the hardness difference between the martensite phase and the ferrite phase, and it is considered that the hardness balance of both phases is appropriate in the component system of the present invention. Further, during annealing after cold rolling, by annealing in the ferrite + austenite two-phase region, {111} oriented grains that are difficult to undergo phase transformation are recrystallized while {100} <011>, which tends to undergo phase transformation, are recrystallized. Let The processed {100} <011> produces {311} <136> recrystallized grains that greatly reduce the r value when recrystallized, but suppresses the formation of these recrystallized grains by transforming to an austenite phase. It becomes possible to do. Further, the phase transformed {100} <011> transforms into a ferrite phase or a martensite phase having an orientation in the vicinity of the original {100} <011> due to the orientation memory effect during cooling. In order to bring about this azimuth memory effect, it is considered that the component system of the present invention is appropriate because the increase in strength due to the addition of Mn is important. Further, the {111} oriented grains remaining without undergoing phase transformation are recrystallized into {111} oriented grains during annealing. From the above, it is possible to obtain a high workability steel in which the {111} orientation is developed and the formation of {311} <136> is suppressed.
以上のように、本発明で規定する成分組成のスラブを用い、熱間圧延において、スラブ加熱温度を1100〜1200℃として粗圧延を行い、仕上げ圧延を開始温度が900℃以上、終了温度が800℃以上、その差が200℃以内となるように仕上げ圧延を行い、600℃以上で巻取った後、冷間圧延し、冷間圧延後の焼鈍処理として700〜1000℃で熱処理し、熱処理後の冷却速度を1〜10℃/secとすることにより、本発明で規定するフェライト相の結晶方位強度(集合組織)を実現するとともに、フェライト粒径が20μm以下、フェライト相面積率が90%以上の鋼板とすることができ、引張強度が440MPa以上、破断伸びが20%以上、穴拡げ率が100%以上の品質を実現することができる。また、rminが1.0以上、フェライト相面積率が90%以上かつ、平均r値が1.5以上とすることができる。 As described above, using a slab having a component composition defined in the present invention, in hot rolling, rough rolling is performed at a slab heating temperature of 1100 to 1200 ° C., and finish rolling is started at a temperature of 900 ° C. or higher and an end temperature of 800 ° C. After finishing rolling so that the difference is within 200 ° C., winding at 600 ° C. or more, cold rolling, heat treatment at 700-1000 ° C. as an annealing treatment after cold rolling, and after heat treatment The cooling rate of 1 to 10 ° C./sec realizes the crystal orientation strength (aggregate structure) of the ferrite phase defined in the present invention, the ferrite grain size is 20 μm or less, and the ferrite phase area ratio is 90% or more. The quality of the tensile strength is 440 MPa or more, the breaking elongation is 20% or more, and the hole expansion rate is 100% or more. Further, the rmin can be 1.0 or more, the ferrite phase area ratio can be 90% or more, and the average r value can be 1.5 or more.
なお、鋼板の製造方法について、本発明で規定した以外の条件については適宜選択すれば良い。例えば、熱延条件や熱延板厚、製品板厚、冷延板焼鈍雰囲気、冷延におけるパススケジュールや冷延率、ロール径についても特別な設備を必要とせず、既設設備を効率的に使用すれば良い。また、冷延・焼鈍後に調質圧延やテンションレベラーを付与しても構わない。 In addition, about the manufacturing method of a steel plate, what is necessary is just to select suitably about conditions other than prescribe | regulated by this invention. For example, no special equipment is required for hot rolling conditions, hot rolled sheet thickness, product sheet thickness, cold rolled sheet annealing atmosphere, pass schedule, cold rolled rate, roll diameter in cold rolling, and existing equipment is used efficiently Just do it. Further, temper rolling or tension leveler may be applied after cold rolling and annealing.
上記本発明のステンレス鋼板は、自動車構造部品用、あるいは自動車締結部品用として使用すると好適である。自動車構造部品用、自動車締結部品用のステンレス鋼板に要求される高強度と良好な加工性を具備しているからである。ここで、自動車構造部品としては例えばサスペンションやシャシー、アーム、メンバーを挙げることができる。また、自動車締結部品としては例えばフランジやブラケットを挙げることができる。 The stainless steel plate of the present invention is preferably used for automobile structural parts or automobile fastening parts. This is because it has high strength and good workability required for stainless steel plates for automobile structural parts and automobile fastening parts. Here, examples of the automobile structural component include a suspension, a chassis, an arm, and a member. Further, examples of the automobile fastening part include a flange and a bracket.
表1に示す成分組成の鋼を溶製してスラブに鋳造した。鋳造したスラブを表2に示す条件で熱間圧延して5mm厚の熱延コイルとした。その後、熱延コイルの焼鈍を行わずに酸洗した。表2の比較例B2のみは熱延板焼鈍を行っている。その後、1mm厚まで冷間圧延し、表2に示す条件で焼鈍・酸洗を施して製品板とした。このようにして得られた製品板に対して、引張試験(引張強度、破断伸び)、r値・n値測定、穴拡げ試験、集合組織評価を行った。結果を表3に示す。試験条件は前述のとおりとした。表3の集合組織に関する「311/100」欄には、{311}〈136〉結晶方位強度および{100}<011>結晶方位強度の比({311}〈136〉結晶方位強度/{100}<011>結晶方位強度)を記載している。 Steels having the composition shown in Table 1 were melted and cast into slabs. The cast slab was hot-rolled under the conditions shown in Table 2 to obtain a hot rolled coil having a thickness of 5 mm. Thereafter, pickling was performed without annealing the hot-rolled coil. Only Comparative Example B2 in Table 2 is subjected to hot-rolled sheet annealing. Then, it cold-rolled to 1 mm thickness, annealed and pickled on the conditions shown in Table 2, and was set as the product board. The product plate thus obtained was subjected to a tensile test (tensile strength, elongation at break), r-value / n-value measurement, hole expansion test, and texture evaluation. The results are shown in Table 3. The test conditions were as described above. In the column “311/100” regarding the texture in Table 3, the ratio of {311} <136> crystal orientation strength and {100} <011> crystal orientation strength ({311} <136> crystal orientation strength / {100} <011> crystal orientation strength).
表1の鋼No.1〜23、表2、表3のA1〜A23が本発明例である。この結果から明らかなように、本発明で規定する成分組成を有する鋼を本発明方法にて製造した場合、本発明で規定するフェライト相の結晶方位強度(集合組織)を実現するとともに、フェライト粒径が20μm以下、フェライト相面積率が90%以上、平均r値が1.5以上、最低r値が1.0以上、n×(1+rmin)が0.40以上となり、その結果、引張強度が440MPa以上、破断伸びが20%以上、穴拡げ率が100%以上と、加工性に優れている。 Steel No. 1 in Table 1 A1 to A23 in Tables 1 to 23, Table 2 and Table 3 are examples of the present invention. As is apparent from the results, when the steel having the component composition defined in the present invention is produced by the method of the present invention, the crystal orientation strength (texture) of the ferrite phase defined in the present invention is realized, and the ferrite grains The diameter is 20 μm or less, the ferrite phase area ratio is 90% or more, the average r value is 1.5 or more, the minimum r value is 1.0 or more, and n × (1 + r min ) is 0.40 or more. Is 440 MPa or more, the elongation at break is 20% or more, and the hole expansion rate is 100% or more.
表1の鋼No.24〜36、表2、表3のB1〜B20が比較例である。
B1は冷延板焼鈍温度が高すぎるため、フェライト面積率が不足するとともに、{211}<011>結晶方位強度が低く、r値が測定不能かつ加工性が不良であった。B7、B8はγpが低すぎ、集合組織が本発明範囲を外れ、平均r値が未達であった。B11はCが高すぎ、B12はNが高すぎ、集合組織が本発明範囲を外れ、加工性が不良であった。
Steel No. 1 in Table 1 24 to 36, B1 to B20 in Tables 2 and 3 are comparative examples.
Since B1 has an excessively cold-rolled sheet annealing temperature, the ferrite area ratio is insufficient, and {211} <011> crystal orientation strength is low, r value cannot be measured, and workability is poor. In B7 and B8, γ p was too low, the texture was out of the range of the present invention, and the average r value was not achieved. In B11, C was too high, and in B12, N was too high.
B2は熱延板焼鈍を行い、B4は巻取温度が低く、B5は冷延板焼鈍後の冷却速度が遅く、いずれも結晶粒径が20μmを超え、引張強度が未達であった。また、B7、B8はγpが低すぎ、B10はCrが高すぎ、いずれも結晶粒径が20μmを超え、引張強度が未達であった。 B2 was subjected to hot-rolled sheet annealing, B4 had a low coiling temperature, B5 had a slow cooling rate after cold-rolled sheet annealing, and the crystal grain size exceeded 20 μm, and the tensile strength was not achieved. Further, γ p was too low for B7 and B8, Cr was too high for B10, both had a crystal grain size exceeding 20 μm, and the tensile strength was not achieved.
B3は冷延板焼鈍温度が低く、B14はNb含有量が高め外れであるとともに熱延仕上げ圧延温度差が大きく、鋼板に未再結晶があり、いずれも加工性が不良であった。B6は冷延板焼鈍後の冷却速度が速すぎ、B9はγpが高すぎ、B11はCが高すぎ、B12はNが高すぎ、B13はTi、Nbが低すぎ、いずれもフェライト面積率が不足するとともに、平均r値、最低r値、n×(1+rmin)が未達あるいは測定不能であり、加工性が不良であった。B15〜B17は、それぞれCu、Si、Niのいずれかの成分が高すぎ、加工性が不良であった。 B3 had a low cold-rolled sheet annealing temperature, B14 had a high Nb content and was off, had a large hot-rolling finish rolling temperature difference, had unrecrystallized steel sheets, and all had poor workability. B6 has a too slow cooling rate after cold-rolled sheet annealing, B9 has too high γ p , B11 has too high C, B12 has too high N, B13 has too low Ti and Nb, both of which are ferrite area ratios In addition, the average r value, minimum r value, and n × (1 + r min ) did not reach or could not be measured, and the workability was poor. In B15 to B17, any one of Cu, Si, and Ni was too high, and the workability was poor.
Claims (8)
X線回折による板厚中心のフェライト相の結晶方位強度において、{111}<011>結晶方位強度が3.0以上、{211}<011>結晶方位強度が3.0以上、{311}〈136〉結晶方位強度および{100}<011>結晶方位強度の比({311}〈136〉結晶方位強度/{100}<011>結晶方位強度)が2.5以下であり、
フェライト粒径が20μm以下、フェライト相面積率が90%以上であることを特徴とする加工性に優れた高強度ステンレス鋼板。
なお、γpは(1)式のCastroの式を用いて評価する。
γp=420(%C)+470(%N)+23(%Ni)+9(%Cu)+7(%Mn)
−11.5(%Cr)−11.5(%Si)−12(%Mo)−23(%V)−47(%Nb)
−49(%Ti)−52(%Al)+189 (1)
なお、(%X)は、各成分Xの質量割合を示す。不可避的不純物量程度しか含有していない場合はゼロとする。 In mass%, C: 0.001 to 0.03%, N: 0.001 to 0.03%, Si: 0.05 to 3.0%, Mn: 0.1 to 15.0%, P : 0.05% or less, S: 0.01% or less, Cr: 10% or more and less than 18%, Ti: 0.30% or less, Nb: 0.50% or less And the total of Ti and Nb is 8 (C + N) to 0.75%, the balance is made of Fe and inevitable impurities, and γ p (gamma potential) is 65 to 85%,
In the crystal orientation strength of the ferrite phase at the center of the plate thickness by X-ray diffraction, {111} <011> crystal orientation strength is 3.0 or more, {211} <011> crystal orientation strength is 3.0 or more, {311} <136> crystal orientation strength and ratio of {100} <011> crystal orientation strength ({311} <136> crystal orientation strength / {100} <011> crystal orientation strength) is 2.5 or less,
A high-strength stainless steel plate excellent in workability characterized by having a ferrite particle size of 20 μm or less and a ferrite phase area ratio of 90% or more.
Note that γ p is evaluated using the Castro equation (1).
γ p = 420 (% C) +470 (% N) +23 (% Ni) +9 (% Cu) +7 (% Mn)
-11.5 (% Cr) -11.5 (% Si) -12 (% Mo) -23 (% V) -47 (% Nb)
-49 (% Ti) -52 (% Al) +189 (1)
In addition, (% X) shows the mass ratio of each component X. Zero if it contains only inevitable impurities.
なお、nはn値(加工硬化指数)、rminは最小r(ランクフォード)値である。 The high-strength stainless steel plate with excellent workability according to any one of claims 1 to 3, wherein r min is 1.0 or more and nx (1 + r min ) is 0.40 or more. .
Here, n is an n value (work hardening index), and r min is a minimum r (Rankford) value.
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