JP6261640B2 - Ferritic stainless steel sheet and steel pipe for exhaust parts with excellent workability and manufacturing method thereof - Google Patents
Ferritic stainless steel sheet and steel pipe for exhaust parts with excellent workability and manufacturing method thereof Download PDFInfo
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Description
本発明は、特に高温強度や耐酸化性が必要な自動車の排気系部材などに使用される排気部品用として最適な加工性に優れた耐熱フェライト系ステンレス鋼板およびその製造方法に関するものであるとともに、これを素材として造管された加工性に優れたフェライト系ステンレス鋼管に関するものである。 The present invention relates to a heat-resistant ferritic stainless steel sheet excellent in workability optimal for exhaust parts used for automobile exhaust system members that require particularly high-temperature strength and oxidation resistance, and a method for producing the same, The present invention relates to a ferritic stainless steel pipe excellent in workability, which is made from this material.
自動車のエキゾーストマニホールド、コンバーター、フロントパイプおよびマフラーなどの排気系部材には、高温強度や耐酸化性が要求されるため、Ｃｒを含有した耐熱鋼が使用されている。これら排気系部材の使用環境温度は年々高温化しており、Ｃｒ、Ｍｏ、Ｎｂなどの合金添加量を増加させて高温強度や熱疲労特性などを高める必要が生じ、現状ではＳＵＳ４２９系（１４％Ｃｒ−Ｎｂ，Ｓｉ添加鋼）やＳＵＳ４４４系（１８％Ｃｒ−Ｎｂ，Ｍｏ添加鋼）が主に使用されている。一方、これらの部材は、鋼板からプレス加工されるか、鋼板を所定のサイズ（径）の鋼管に造管した後に目的の形状に成形される。そのため、部材を構成する素材鋼板および鋼管の加工性が求められる。ここで、鋼板については深絞り性が重視され、鋼管については曲げ性が重視される。特にエキゾーストマニホールドについては熱効率や軽量化の観点から、近年その形状が複雑化、多様化しており、上記のような高合金成分で通常得られる程度の絞り性や曲げ性を有する鋼板および鋼管では、加工時に割れや皺等が生じる場合が生じてきた。 High temperature strength and oxidation resistance are required for exhaust system members such as exhaust manifolds, converters, front pipes, and mufflers of automobiles, and therefore, heat-resistant steel containing Cr is used. The operating environment temperature of these exhaust system members is increasing year by year, and it is necessary to increase the amount of alloy such as Cr, Mo, Nb, etc. to increase the high temperature strength and thermal fatigue characteristics. At present, SUS429 system (14% Cr) -Nb, Si-added steel) and SUS444 series (18% Cr-Nb, Mo-added steel) are mainly used. On the other hand, these members are pressed from a steel plate or formed into a desired shape after forming the steel plate into a steel pipe having a predetermined size (diameter). Therefore, workability of the material steel plate and the steel pipe constituting the member is required. Here, the deep drawability is emphasized for the steel sheet, and the bendability is important for the steel pipe. In particular, the exhaust manifold has become more complex and diversified in recent years from the viewpoint of thermal efficiency and weight reduction, and steel plates and steel pipes having drawability and bendability that are usually obtained with the high alloy components as described above, In some cases, cracks, wrinkles, etc. occur during processing.
耐熱フェライト系ステンレス鋼板および鋼管の加工性に関する問題を解決するために、いくつかの工夫がなされてきた。特に鋼板の深絞り性については、ｒ値がその指標となり、結晶方位を制御することによって高ｒ値材を得る技術が開示されている。ここで、ｒ値とは、冷延焼鈍板から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％歪みを付与した後に（１）式および（２）式を用いて平均ｒ値（ｒm）が算出される。
ｒ＝ｌｎ（Ｗ0／Ｗ）／ｌｎ（ｔ0／ｔ） （１）
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＋２ｒ45＋ｒ90）／４ （２）
ここで、ｒ0は圧延方向のｒ値、ｒ45は圧延方向と４５°方向のｒ値、ｒ90は圧延方向と直角方向のｒ値である。
In order to solve the problems relating to the workability of the heat-resistant ferritic stainless steel sheet and the steel pipe, some contrivances have been made. In particular, with respect to the deep drawability of a steel sheet, the r value serves as an index, and a technique for obtaining a high r value material by controlling the crystal orientation is disclosed. Here, the r value is obtained by collecting a JIS No. 13 B tensile specimen from a cold-rolled annealed plate and applying a 14.4% strain in the rolling direction, the rolling direction and 45 ° direction, and the rolling direction and 90 ° direction ( The average r value (r m ) is calculated using the formulas (1) and (2).
r = ln (W 0 / W) / ln (t 0 / t) (1)
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 + 2r 45 + r 90 ) / 4 (2)
Here, 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 direction perpendicular to the rolling direction.
耐熱フェライト系ステンレス鋼板の中で、板厚が比較的厚い材料（例えば、板厚が１〜３ｍｍ程度）では、製造工程における冷延圧下率が高く付与できないことから、ｒ値向上のために種々の技術が開示されている。特許文献１には、１４〜１９％Ｃｒ、０．５〜２．０％Ｍｏ、０．３〜１．０％Ｎｂを含有するＣｒ含有耐熱鋼板において、板厚中心領域部のＸ線強度比｛１１１｝／（｛１００｝＋｛２１１｝）を２以上に規定した鋼およびその製造方法が開示されている。この製造方法は、熱延板焼鈍を９００〜１０００℃とし、その際の冷却速度を３００℃まで３０℃／ｓｅｃ以上とするもので、冷間圧延前の組織および析出物をコントロールして製品板の｛１１１｝集合組織を発達させ高ｒ値鋼板を得るものである。特許文献２および３には、９〜３５％Ｃｒ、０．１５〜０．８０％Ｎｂを含有するフェライト系ステンレス鋼板において、析出物のサイズと量ならびに板厚１／４深さにおける結晶方位を規定した鋼が開示されている。この製造方法は、製造過程において４５０〜７５０℃で２０ｈｒ以下の析出処理、あるいは７００〜８５０℃で２５ｈｒの析出処理を施すものである。また、特許文献４には１０〜２０％Ｃｒ、０．２〜２．０％Ｍｏ、０．０５〜０．６％Ｎｂ添加鋼に対して、最表層から板厚の１／４領域における｛１１１｝＋｛５５４｝と｛１００｝＋｛１１０｝の比率を規定した技術が開示されている。ここでは、熱延板焼鈍を省略し直径が３００ｍｍ以上の大径ロールを使用して冷延されることで上記組織が得られている。これらは、板厚中心領域部のみ、板厚１／４部のみあるいは表層から板厚１／４部までの結晶方位を制御するものでありｒ値を高める技術とされているが、局所的な結晶方位の制御では鋼板の成形において割れ等の不具合が生じることがあった。また、これらの素材を用いて鋼管を製造し曲げ加工した際には効果的ではなかった。
Among heat-resistant ferritic stainless steel sheets, materials with a relatively large thickness (for example, a thickness of about 1 to 3 mm) cannot be applied with a high cold rolling reduction ratio in the manufacturing process, so various improvements have been made to improve the r value. The technology is disclosed. In
特許文献５には、１３．０〜２０．０％Ｃｒ、０．１〜３．０％Ｍｏ、０．３０〜１．０％Ｎｂを含有するフェライト系ステンレス冷延鋼板および熱延鋼板において、表層からｔ／４部、ｔ／４〜ｔ／２部（ここで、ｔは板厚）の｛１１１｝方位および｛０１１｝方位の面積率を規定する加工性に優れた鋼板が開示されている。高ｒ値を得る結晶方位｛１１１｝について着目されているが、ここでも表層からｔ／４部とｔ／４〜ｔ／２における｛１１１｝方位粒の面積率がそれぞれ２０％以上と４０％以上で異なっていることから、上記のように板材成形、更には鋼管成形においては十分な加工性を示さない。 In Patent Document 5, in a ferritic stainless steel cold-rolled steel sheet and hot-rolled steel sheet containing 13.0-20.0% Cr, 0.1-3.0% Mo, 0.30-1.0% Nb, Disclosed is a steel sheet excellent in workability that defines the area ratio of the {111} orientation and {011} orientation of t / 4 part, t / 4 to t / 2 part (where t is the plate thickness) from the surface layer. Yes. Although attention is paid to the crystal orientation {111} for obtaining a high r value, the area ratio of {111} orientation grains at t / 4 part and t / 4 to t / 2 from the surface layer is 20% or more and 40%, respectively. Since they are different from each other as described above, sufficient workability is not exhibited in plate material forming and further steel pipe forming as described above.
特許文献６には、曲げ半径がフェライト系ステンレス鋼管の直径の１．２倍以下である鋼管の曲げ成形に対して、減肉抑制と部品断面形状確保を両立するステンレス鋼管が開示されている。ここでは、曲げ管用鋼板の引張強さ（５００ＭＰａ以下）、全伸び（２５％以上）、平均ｒ値（１．３以上）が規定され、厳しい曲げに対しても割れが発生しないとされている。一般的に鋼管の曲げは長手方向が圧延方向になるが、曲げ部では幅方向（鋼管の円周方向）や圧延方向と４５°方向の材料流動が生じるため、単純に平均ｒ値だけでは曲げ性が十分確保できない場合があった。曲げ性が十分確保できないとは、具体的には曲げ部の背側の減肉および腹側の増肉が過大になることである。 Patent Document 6 discloses a stainless steel pipe that achieves both a reduction in thickness and securing a cross-sectional shape of a part against bending of a steel pipe whose bending radius is 1.2 times or less the diameter of a ferritic stainless steel pipe. Here, the tensile strength (500 MPa or less), the total elongation (25% or more), and the average r value (1.3 or more) of the steel sheet for bent pipes are defined, and it is said that cracks do not occur even in severe bending. . In general, the bending direction of a steel pipe is the rolling direction, but since the material flow in the width direction (circumferential direction of the steel pipe) and the rolling direction at a 45 ° direction occurs in the bending portion, the bending is simply performed with the average r value alone. In some cases, sufficient sex could not be secured. The fact that sufficient bendability cannot be ensured specifically means that the thickness reduction on the back side and the thickness increase on the abdomen side of the bent portion becomes excessive.
背景技術に記載の技術を検討したところ以下の課題が明らかになった。曲げ加工においては板厚方向に歪み分布が発生するため、前述の特許文献４のような板厚方向に限定された結晶方位制御は有効ではないとともに、造管における溶接によって溶接部の結晶方位が母材と異なることに起因することが判明した。また、特許文献５、６に記載しているような造管溶接部の曲げ性能を考えた場合、その曲げ性は溶接部の結晶方位に依存することが本発明では判明し、有効な結晶方位を溶接組織で得るためには、｛１１１｝方位の中でもより限定した結晶方位に制御する必要があることがわかった。加えて、鋼管はＥＲＷ、ＴＩＧ、レーザー等の溶接によって製管されるが、特許文献６では溶接部特性について検討されていないため、溶接線が曲げ背側に位置するような曲げ加工の際に、有用ではなかった。本発明の目的は、成分及び製造方法を規定し、鋼板および鋼管の結晶方位をより厳密に制御することで、上記の問題点を解決し、加工性に優れた排気部品用フェライト系ステンレス鋼板、鋼管を提供することにある。 Examination of the technology described in the background art revealed the following issues. In bending, strain distribution occurs in the plate thickness direction. Therefore, the crystal orientation control limited to the plate thickness direction as described in Patent Document 4 is not effective, and the crystal orientation of the welded portion is changed by welding in pipe making. It was found that it was caused by the difference from the base material. Further, when considering the bending performance of the pipe-forming weld as described in Patent Documents 5 and 6, it was found in the present invention that the bendability depends on the crystal orientation of the weld, and the effective crystal orientation It has been found that it is necessary to control the crystal orientation to be more limited among the {111} orientations in order to obtain a weld structure. In addition, although steel pipes are manufactured by welding such as ERW, TIG, and laser, Patent Document 6 does not discuss the characteristics of the welded part, so that the welding line is positioned at the bending back side during bending. Was not useful. The object of the present invention is to define the components and the production method, and more precisely control the crystal orientation of the steel sheet and the steel pipe, thereby solving the above-mentioned problems and excellent ferritability stainless steel sheet for exhaust parts, To provide a steel pipe.
上記課題を解決するために、本発明者ら耐熱フェライト系ステンレス鋼板および鋼管の加工性に関して、鋼組成、製造過程における組織、結晶方位形成についての詳細な研究を行った。更に、鋼管に対しては、特に曲げ性が重視されるが、溶接部の組織、結晶方位形成と曲げ性に関する詳細な検討を行った。 In order to solve the above-mentioned problems, the present inventors conducted detailed studies on the steel composition, the structure in the manufacturing process, and the crystal orientation formation regarding the workability of the heat-resistant ferritic stainless steel sheet and the steel pipe. Furthermore, for steel pipes, bendability is particularly important, but detailed investigations were made regarding the structure of the welded portion, crystal orientation formation, and bendability.
上記課題を解決する本発明の要旨は、
（１）鋼管の母材が、質量％にて、Ｃ：０．００１〜０．０２％、Ｓｉ：０．１〜１．５％、Ｍｎ：０．１〜１．５％、Ｐ：０．０１〜０．０４％、Ｓ：０．０００１〜０．０１％、Ｃｒ：１０〜２０％、Ｎ：０．００１〜０．０３％、ＮｂあるいはＴｉの一種以上を０．１〜０．８％含有し、残部がＦｅおよび不可避的不純物から成り、板厚全体におけるＥＢＳＰ法により測定される｛１１１｝＜１１２＞と｛１１１｝＜０１１＞方位の面積率の総和が４０％以上であり、平均ｒ値が１．５以上、４５°方向のｒ値が１．０以上であるステンレス鋼板からなり、鋼管のＹＲ（引張強度／０．２％耐力）が１．１以上、溶接された鋼管突き合わせ部の板厚全体におけるＥＢＳＰ法により測定される｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位の面積率の総和が３０％以上であることを特徴とする加工性に優れた排気部品用フェライト系ステンレス鋼管。
（２）鋼管の母材が、さらに質量％にて、Ｂ：０．０００２〜０．００５％、Ａｌ：０．００３〜０．５％、Ｃｕ：０．０１〜２．０％、Ｖ：０．０５〜１．０％、Ｍｏ：０．２〜３％、Ｎｉ：０．１〜２．０％、Ｗ：０．１〜３．０％、Ｚｒ：０．０５〜０．３０％、Ｓｎ：０．０１〜０．５０％、Ｓｂ：０．０１〜０．５０％、Ｃｏ：０．０５〜０．５０％、Ｍｇ：０．０００２〜０．０１００％、Ｃａ：０．０００１〜０．００３０％、Ｔａ：０．０１〜０．１０％、Ｇａ：０．０００２〜０．１％、ＲＥＭ：０．００１〜０．０５％の１種以上を含有することを特徴とする請求項１に記載の加工性に優れた排気部品用フェライト系ステンレス鋼管。
（３）前記鋼管が、電縫溶接鋼管であることを特徴とする（１）又は（２）に記載の加工性に優れた排気部品用フェライト系ステンレス鋼管。
（４）（１）又は（２）に鋼管の母材として記載されているステンレス鋼板を、電縫溶接にて造管する排気部品用フェライト系ステンレス鋼管の製造方法であって、鋼管のＹＲ（引張強度／０．２％耐力）が１．１以上であり、前記溶接された鋼管突き合わせ部の板厚全体におけるＥＢＳＰ法により測定される｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位の面積率の総和が３０％以上であることを特徴とする加工性に優れた排気部品用フェライト系ステンレス鋼管の製造方法。
（５）質量％にて、Ｃ：０．００１〜０．０２％、Ｓｉ：０．１〜１．５％、Ｍｎ：０．１〜１．５％、Ｐ：０．０１〜０．０４％、Ｓ：０．０００１〜０．０１％、Ｃｒ：１０〜２０％、Ｎ：０．００１〜０．０３％、Ｎｂを０．１〜０．８％含有し、残部がＦｅおよび不可避的不純物から成り、板厚全体におけるＥＢＳＰ法により測定される｛１１１｝＜１１２＞と｛１１１｝＜０１１＞方位の面積率の総和が４０％以上であり、平均ｒ値が１．５以上、４５°方向のｒ値が１．０以上であることを特徴とする加工性に優れた排気部品用フェライト系ステンレス鋼板。
（６）さらに質量％にて、Ｂ：０．０００２〜０．００５％、Ａｌ：０．００３〜０．５％、Ｃｕ：０．０１〜２．０％、Ｖ：０．０５〜１．０％、Ｍｏ：０．２〜３％、Ｎｉ：０．１〜２．０％、Ｗ：０．１〜３．０％、Ｚｒ：０．０５〜０．３０％、Ｓｎ：０．０１〜０．５０％、Ｓｂ：０．０１〜０．３０％、Ｃｏ：０．０５〜０．５０％、Ｍｇ：０．０００２〜０．０１００％、Ｃａ：０．０００１〜０．００３０％、Ｔａ：０．０１〜０．１０％、Ｇａ：０．０００２〜０．１％、ＲＥＭ：０．００１〜０．０５％の１種以上を含有することを特徴とする（５）に記載の加工性に優れた排気部品用フェライト系ステンレス鋼板。
（７）（５）または（６）に記載のステンレス鋼板を製造するに際し、熱延板焼鈍において加熱速度を２０℃／ｓｅｃ以上として９５０〜１０３０℃に加熱後、３０℃／ｓｅｃ以上の冷却速度で冷却し、圧下率８０％未満で仕上冷延した後、冷延板焼鈍温度を１０３０〜１１００℃とすることを特徴とする加工性に優れた排気部品用フェライト系ステンレス鋼板の製造方法。
（８）（５）または（６）に記載のステンレス鋼板を製造するに際し、熱延板焼鈍において加熱速度を２０℃／ｓｅｃ以上として９５０〜１０３０℃に加熱後、３０℃／ｓｅｃ以上の冷却速度で冷却し、圧下率５０％未満で冷延した後、中間焼鈍において加熱速度を２０℃／ｓｅｃとして９３０〜９８０℃に加熱、３０℃／ｓｅｃ以上の冷却速度で冷却し、圧下率７５％未満で仕上圧延した後、冷延板焼鈍温度を１０３０〜１１００℃とすることを特徴とする加工性に優れた排気部品用フェライト系ステンレス鋼板の製造方法。
（９）仕上冷延時の組織、すなわち熱延板焼鈍組織、あるいは中間焼鈍組織の表層〜ｔ／４部の結晶粒径が５０μｍ以下かつ、再結晶率が８０％以上であることを特徴とする（７）または（８）に記載の加工性に優れた排気部品用フェライト系ステンレス鋼板の製造方法。
（１０）熱延板焼鈍を省略し、直径が４００ｍｍ以上のロール径を有する圧延機を用いて４０％以上の圧下率で冷延することを特徴とする（７）または（８）に記載の加工性に優れた排気部品用フェライト系ステンレス鋼板の製造方法。
The gist of the present invention for solving the above problems is as follows.
(1) When the base material of the steel pipe is mass%, C: 0.001 to 0.02%, Si: 0.1 to 1.5%, Mn: 0.1 to 1.5%, P: 0 .01-0.04%, S: 0.0001-0.01%, Cr: 10-20%, N: 0.001-0.03%, one or more of Nb or Ti is 0.1-0. 8% content, the balance is made of Fe and inevitable impurities, and the sum of the area ratios of {111} <112> and {111} <011> directions measured by the EBSP method over the entire thickness is 40% or more. It was made of a stainless steel plate having an average r value of 1.5 or more and an r value in the 45 ° direction of 1.0 or more, and the YR (tensile strength / 0.2% proof stress) of the steel pipe was 1.1 or more. {110} <011> and {211} <011 measured by the EBSP method over the entire thickness of the steel pipe butt portion Exhaust component ferritic stainless steel having excellent workability, wherein the sum of the orientation area ratio of 30% or more.
(2) The base material of the steel pipe is further in mass%, B: 0.0002 to 0.005%, Al: 0.003 to 0.5%, Cu: 0.01 to 2.0%, V: 0.05 to 1.0%, Mo: 0.2 to 3%, Ni: 0.1 to 2.0%, W: 0.1 to 3.0%, Zr: 0.05 to 0.30% Sn: 0.01 to 0.50%, Sb: 0.01 to 0.50%, Co: 0.05 to 0.50%, Mg: 0.0002 to 0.0100%, Ca: 0.0001 -0.0030%, Ta: 0.01-0.10%, Ga: 0.0002-0.1%, REM: It contains 0.001-0.05% or more, It is characterized by the above-mentioned The ferritic stainless steel pipe for exhaust parts excellent in workability according to
(3) The ferritic stainless steel pipe for exhaust parts having excellent workability according to (1) or (2), wherein the steel pipe is an electric resistance welded steel pipe.
(4) A method for producing a ferritic stainless steel pipe for exhaust parts , in which a stainless steel plate described as a base material for a steel pipe in (1) or (2) is formed by electric resistance welding, (Tensile strength / 0.2% proof stress) is 1.1 or more, and {110} <011> and {211} <011> orientations measured by the EBSP method over the entire thickness of the welded steel pipe butt portion A method for producing a ferritic stainless steel pipe for exhaust parts excellent in workability, wherein the total area ratio is 30% or more .
(5 ) In mass%, C: 0.001 to 0.02%, Si: 0.1 to 1.5%, Mn: 0.1 to 1.5%, P: 0.01 to 0.04 %, S: 0.0001 to 0.01%, Cr: 10 to 20%, N: 0.001 to 0.03%, Nb 0.1 to 0.8%, the balance being Fe and inevitable The total of the area ratios of {111} <112> and {111} <011> orientations, which are made of impurities and measured by the EBSP method over the entire plate thickness, is 40% or more, and the average r value is 1.5 or more, 45 A ferritic stainless steel sheet for exhaust parts excellent in workability, wherein the r value in the ° direction is 1.0 or more.
( 6 ) Further, by mass%, B: 0.0002 to 0.005%, Al: 0.003 to 0.5%, Cu: 0.01 to 2.0%, V: 0.05 to 1.%. 0%, Mo: 0.2 to 3%, Ni: 0.1 to 2.0%, W: 0.1 to 3.0%, Zr: 0.05 to 0.30%, Sn: 0.01 To 0.50%, Sb: 0.01 to 0.30%, Co: 0.05 to 0.50%, Mg: 0.0002 to 0.0100%, Ca: 0.0001 to 0.0030%, It contains at least one of Ta: 0.01 to 0.10%, Ga: 0.0002 to 0.1%, and REM: 0.001 to 0.05%. ( 5 ) Ferritic stainless steel sheet for exhaust parts with excellent workability.
( 7 ) When manufacturing the stainless steel sheet according to ( 5 ) or ( 6 ), the heating rate is set to 20 ° C / sec or more in hot-rolled sheet annealing, and after heating to 950 to 1030 ° C, the cooling rate is 30 ° C / sec or more. A method for producing a ferritic stainless steel sheet for exhaust parts excellent in workability, characterized in that after cooling at a rolling rate and finish cold rolling at a rolling reduction of less than 80%, the cold rolled sheet annealing temperature is set to 1030 to 1100 ° C.
( 8 ) When manufacturing the stainless steel sheet according to ( 5 ) or ( 6 ), the heating rate is set to 20 ° C./sec or more in hot-rolled sheet annealing, and after heating to 950 to 1030 ° C., the cooling rate is 30 ° C./sec or more. After cooling at a reduction rate of less than 50%, in intermediate annealing, heating at 930 to 980 ° C with a heating rate of 20 ° C / sec, cooling at a cooling rate of 30 ° C / sec or more, and a reduction rate of less than 75% A method for producing a ferritic stainless steel sheet for exhaust parts excellent in workability, characterized in that the cold-rolled sheet annealing temperature is set to 1030 to 1100 ° C. after finish-rolling.
( 9 ) The structure at the time of finish cold rolling, that is, the crystal grain size of the surface layer to t / 4 part of the hot-rolled sheet annealed structure or intermediate annealed structure is 50 μm or less and the recrystallization rate is 80% or more. ( 7 ) or the manufacturing method of the ferritic stainless steel plate for exhaust parts excellent in workability as described in ( 8 ).
( 10 ) The method according to ( 7 ) or ( 8 ), wherein hot-rolled sheet annealing is omitted and cold rolling is performed at a rolling reduction of 40% or more using a rolling mill having a roll diameter of 400 mm or more. Manufacturing method of ferritic stainless steel sheet for exhaust parts with excellent workability.
以上の説明から明らかなように、本発明によれば加工性に優れた耐熱フェライト系ステンレス鋼板および鋼管を特別な新規設備を必要とせず、効率的に提供することができる。 As is apparent from the above description, according to the present invention, a heat-resistant ferritic stainless steel plate and a steel pipe excellent in workability can be efficiently provided without requiring special new equipment.
以下に本発明の限定理由について説明する。
Ｃは、靭性、耐食性および耐酸化性を劣化させる他、固溶Ｃは｛１１１｝集合組織の発達を阻害するため、その含有量は少ないほど良いため、上限を０．０２％とした。但し、過度の低減は精錬コストの増加に繋がる他、溶接部の｛１１０｝＜０１１＞方位形成を阻害するため、下限を０．００１％とした。更に、製造コストと耐食性を考慮すると０．００２〜０．０１％が望ましい。
The reason for limitation of the present invention will be described below.
Since C deteriorates toughness, corrosion resistance, and oxidation resistance, and since solid solution C inhibits the development of {111} texture, the lower the content thereof, the better. Therefore, the upper limit was made 0.02%. However, excessive reduction leads to an increase in refining costs and inhibits formation of {110} <011> orientation of the weld, so the lower limit was made 0.001%. Furthermore, if considering the manufacturing cost and corrosion resistance, 0.002 to 0.01% is desirable.
Ｓｉは、脱酸元素として添加される場合がある他、耐酸化性と高温強度を向上させる元素である。Ｓｉを添加することで、鋼中の酸素量が低減し、｛１１１｝方位の発達に寄与する他、溶接部の｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位形成を促す効果があるため、０．１％以上添加する。Ｓｉを０．５％超含有すると前記集合組織の発達が顕著である。０．８％以上が更に好適である。また、一方、１．５％超のＳｉ添加により著しく硬質化し、鋼管の曲げ性が劣化するため、上限を１．５％とした。鋼板製造時の靭性や酸洗性を考慮すると、Ｓｉの上限を１．２％とするのが好ましい。０．１〜１．２％が望ましい。さらに望ましくは、０．５超、１．０％であり、０．８％〜１．２％である。 In addition to being added as a deoxidizing element, Si is an element that improves oxidation resistance and high-temperature strength. Addition of Si reduces the amount of oxygen in the steel and contributes to the development of the {111} orientation, and also has the effect of promoting the formation of {110} <011> and {211} <011> orientation in the weld. Therefore, 0.1% or more is added. When the Si content exceeds 0.5%, the development of the texture is remarkable. 0.8% or more is more preferable. On the other hand, the upper limit was made 1.5% because the addition of Si exceeding 1.5% remarkably hardens and the bendability of the steel pipe deteriorates. In consideration of toughness and pickling properties during the production of the steel sheet, the upper limit of Si is preferably 1.2%. 0.1 to 1.2% is desirable. More desirably, it is more than 0.5 and 1.0%, and is 0.8% to 1.2%.
Ｍｎは、高温においてＭｎＣｒ2Ｏ4やＭｎＯを形成し、スケール密着性を向上させる。この効果は、０．１％以上で発現することから、下限を０．１％とした。一方、Ｍｎを１．５％超含有すると、酸化増量を増加させるため異常酸化が生じ易くなる他、溶接部の｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位形成が抑制され、鋼管曲げ性の低下をもたらすことから上限を１．５％とした。鋼板製造時の靭性や酸洗性を考慮すると０．１〜１．０％が望ましい。鋼管溶接部の酸化物起因の偏平割れを考慮すると更に望ましくは０．１〜０．６％が良い。 Mn forms MnCr 2 O 4 and MnO at a high temperature and improves scale adhesion. Since this effect appears at 0.1% or more, the lower limit was made 0.1%. On the other hand, if Mn exceeds 1.5%, abnormal oxidation is likely to occur due to an increase in the amount of oxidation, and {110} <011> and {211} <011> orientation formation of the weld is suppressed, and the steel pipe bending is suppressed. Therefore, the upper limit was made 1.5%. If considering the toughness and pickling property at the time of steel plate production, 0.1 to 1.0% is desirable. In consideration of flat cracks caused by oxides in the welded portion of the steel pipe, 0.1 to 0.6% is more preferable.
Ｐは、Ｓｉ同様に固溶強化元素であるため、材質および靭性の観点からその含有量は少ないほど良く、上限を０．０４％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０．０１％とした。更に、製造コストと耐酸化性を考慮すると０．０１５〜０．０３％が望ましい。 Since P is a solid solution strengthening element like Si, its content is preferably as small as possible from the viewpoint of material and toughness, and the upper limit is made 0.04%. However, excessive reduction leads to an increase in refining costs, so the lower limit was made 0.01%. Furthermore, if considering the manufacturing cost and oxidation resistance, 0.015 to 0.03% is desirable.
Ｓは、材質、耐食性および耐酸化性の観点から少ないほど良いため、上限を０．０１％とした。特に、過度な添加はＴｉやＭｎと化合物を生成させ鋼管曲げの際に介在物起点で割れが生じる他、溶融部のメタルフローに影響して溶接部の｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位形成が抑制される。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０．０００１％とした。更に、製造コストと耐食性を考慮すると０．０００５〜０．００５０％が望ましい。 The lower the S content, the better from the viewpoint of material, corrosion resistance and oxidation resistance, so the upper limit was made 0.01%. In particular, excessive addition generates Ti and Mn and a compound, which causes cracks at the starting point of inclusions during bending of the steel pipe, and affects the metal flow of the melted part to affect {110} <011> and {211} of the welded part. <011> Orientation formation is suppressed. However, excessive reduction leads to an increase in refining costs, so the lower limit was made 0.0001%. Furthermore, if considering the manufacturing cost and corrosion resistance, 0.0005 to 0.0050% is desirable.
Ｃｒは、排気部品で最重要特性となる高温強度および耐酸化性を確保する他、溶接部の｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位形成を促す効果があるため１０％以上の添加が必要であるが、２０％超の添加は靱性劣化により製造性が悪くなる他、特に鋼管溶接部の脆性割れや曲げ性不良が生じる。よって、Ｃｒの範囲は１０〜２０％とした。鋼板製造時の熱延板靭性の観点から１０〜１８％が望ましい。更にコストの観点から、１０〜１４％未満が望ましい。 Cr has the effect of promoting the formation of {110} <011> and {211} <011> orientations in the welded part, as well as ensuring high temperature strength and oxidation resistance, which are the most important characteristics in exhaust parts, and more than 10% Although addition is necessary, addition exceeding 20% results in poor productivity due to toughness deterioration, and also causes brittle cracks and poor bendability particularly in welded steel pipes. Therefore, the Cr range is 10 to 20%. 10 to 18% is desirable from the viewpoint of hot-rolled sheet toughness during steel plate production. Furthermore, from a viewpoint of cost, less than 10 to 14% is desirable.
Ｎは、Ｃと同様に低温靭性、加工性、耐酸化性を劣化させるため、その含有量は少ないほど良いため、上限を０．０３％とした。但し、過度の低下は精錬コストの増加に繋がる他、溶接部の｛１１０｝＜０１１＞方位形成を阻害するため、下限を０．００１％とした。更に、コストおよび靭性を考慮すると０．００５〜０．０２％が望ましい。 N, like C, deteriorates low-temperature toughness, workability, and oxidation resistance. The lower the content, the better. Therefore, the upper limit was made 0.03%. However, excessive reduction leads to an increase in refining costs and inhibits the formation of {110} <011> orientation of the weld, so the lower limit was made 0.001%. Furthermore, if considering cost and toughness, 0.005 to 0.02% is desirable.
ＴｉあるいはＮｂは、一種以上をそれぞれ０．１〜０．８％含有する。これらの元素は、ＣやＮと結合して炭窒化物を形成し、製品板の｛１１１｝方位を発達させ、ｒ値の向上並びに鋼管曲げ性の向上を促進する。また、特にＮｂについては、高温域における固溶強化および析出強化能が高いため、高温強度や熱疲労特性を向上させる。これらの効果は０．１％以上から生じるため、下限を０．１％とする。一方、０．８％超の添加は、鋼板製造段階の靭性の著しい劣化をもたらすとともに、粗大な炭窒化物の形成やＬａｖｅｓ相と呼ばれる粗大な金属間化合物の形成をもたらし、集合組織の発達抑制およびｒ値の低下につながる。また、溶接部の｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位形成が抑制されるため、上限を０．８％とした。更に、溶接部の粒界腐食性、コストおよび製造性を考慮すると０．１５〜０．５５％が望ましい。 Ti or Nb contains one or more of each 0.1 to 0.8%. These elements combine with C and N to form carbonitrides, develop the {111} orientation of the product plate, and promote the improvement of the r value and the steel pipe bendability. In particular, Nb has a high solid solution strengthening and precipitation strengthening ability in a high temperature region, so that high temperature strength and thermal fatigue characteristics are improved. Since these effects occur from 0.1% or more, the lower limit is made 0.1%. On the other hand, addition of more than 0.8% leads to remarkable deterioration of toughness in the steel plate manufacturing stage, and also causes formation of coarse carbonitrides and coarse intermetallic compounds called Laves phases, thereby suppressing the development of texture. And the r value decreases. Moreover, since {110} <011> and {211} <011> orientation formation of the weld is suppressed, the upper limit was made 0.8%. Furthermore, if considering the intergranular corrosion property, cost, and manufacturability of the weld zone, 0.15 to 0.55% is desirable.
本発明は、さらに以下の元素を選択的に含有すると好ましい。 The present invention preferably further contains the following elements selectively.
Ｂは、粒界に偏析することで粒界強度を向上させ、２次加工性、低温靭性を向上させる元素であるとともに、中温域の高温強度を向上させるため必要に応じて添加する。また、溶接部の｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位形成を促す効果があるため、下限を０．０００２％とした。０．００５％超の添加によりＣｒ2Ｂ等のＢ化合物が生成し、粒界腐食性や疲労特性を劣化させる他、｛０１１｝方位粒の増加をもたらして鋼板を低ｒ値化させるため、上限を０．００５％とした。更に、溶接性や製造性を考慮すると、０．０００３〜０．００１％が望ましい。 B is an element that improves the grain boundary strength by segregating at the grain boundaries and improves the secondary workability and the low temperature toughness, and is added as necessary to improve the high temperature strength in the intermediate temperature range. Moreover, since there exists an effect which accelerates | stimulates {110} <011> and {211} <011> orientation formation of a welded part, the lower limit was made 0.0002%. B compound such as Cr 2 B is generated by adding more than 0.005%, and in addition to deteriorating intergranular corrosion properties and fatigue properties, in addition to increasing the {011} orientation grain, to lower the steel sheet r value, The upper limit was made 0.005%. Furthermore, considering weldability and manufacturability, 0.0003 to 0.001% is desirable.
Ａｌは、脱酸元素として添加される場合がある他、高温強度や耐酸化性を向上させるため、必要に応じて添加する。また、ＴｉＮやＬａｖｅｓ相の析出サイトとなり微細析出に寄与し、低温靭性の向上に寄与する。その作用は０．００３％から発現するため、下限を０．００３％とした。また、０．５％以上の添加は、伸びの低下や溶接性および表面品質の劣化をもたらす他、粗大なＡｌ酸化物形成により、低温靭性の低下をもたらす他、溶融部のメタルフローに影響して溶接部の｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位形成が抑制されるため、上限を０．５％とした。更に、精錬コストを考慮する０．０１〜０．１％が望ましい。 In addition to being added as a deoxidizing element, Al is added as necessary to improve high temperature strength and oxidation resistance. Moreover, it becomes a precipitation site of TiN or a Laves phase, contributes to fine precipitation, and contributes to improvement of low temperature toughness. Since the effect is manifested from 0.003%, the lower limit was made 0.003%. In addition, addition of 0.5% or more leads to a decrease in elongation, weldability and surface quality, as well as a decrease in low-temperature toughness due to the formation of coarse Al oxide, and also affects the metal flow in the molten part. The formation of {110} <011> and {211} <011> orientations in the weld is suppressed, so the upper limit was made 0.5%. Furthermore, 0.01 to 0.1% considering the refining cost is desirable.
Ｃｕは、耐食性を向上させるとともに、ε−Ｃｕ析出によって特に中温域での高温強度を上げる元素である他、溶接部の｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位形成を促す効果があるため、必要に応じて添加する。この効果は０．０１％以上の添加により発現することから、下限を０．０１％とした。一方、過度な添加は硬質化による靭性低下、延性低下をもたらすことから、上限を２．０％とした。更に、耐酸化性や製造性を考慮すると０．０１〜１．５％未満が望ましい。 Cu is an element that improves the corrosion resistance and increases the high-temperature strength particularly in the middle temperature region by ε-Cu precipitation, and also has the effect of promoting the formation of {110} <011> and {211} <011> orientations in the weld. Therefore, add as necessary. This effect is manifested by the addition of 0.01% or more, so the lower limit was made 0.01%. On the other hand, excessive addition causes toughness reduction and ductility reduction by hardening, so the upper limit was made 2.0%. Furthermore, if considering oxidation resistance and manufacturability, 0.01 to less than 1.5% is desirable.
Ｖは、ＣやＮと結合して耐食性や耐熱性を向上する観点から、必要に応じて０．０５％以上添加することができる。但し、１．０％超の添加により、粗大な炭窒化物が形成して靭性が低下する他、ｒ値の低下をもたらすため上限を１．０％とした。更に、製造性やコストを考慮すると、０．０５〜０．２％が望ましい。 V can be added in an amount of 0.05% or more as necessary from the viewpoint of combining with C and N to improve corrosion resistance and heat resistance. However, addition of more than 1.0% causes coarse carbonitride to form and lowers the toughness, and lowers the r value, so the upper limit was made 1.0%. Furthermore, if considering the manufacturability and cost, 0.05 to 0.2% 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。Ｍｏが３．０％を越えると著しく成形性が劣化したり、製造性が悪くなる他、｛１１１｝集合組織の発達を阻害するため、Ｍｏの上限を３．０％とした。Ｍｏ含有による上記効果は０．２％以上で発現するため、下限を０．２％とした。更に、｛１１１｝方位を先鋭に発達させることと、合金コストと生産性を考慮すると０．４〜２．０％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. If the Mo content exceeds 3.0%, the formability is remarkably deteriorated, the manufacturability is deteriorated, and the development of {111} texture is inhibited. Therefore, the upper limit of Mo is set to 3.0%. The above effect due to the Mo content is manifested at 0.2% or more, so the lower limit was made 0.2%. Furthermore, considering the sharp development of the {111} orientation and the alloy cost and productivity, 0.4 to 2.0% is desirable.
Ｎｉは、靭性と耐食性を向上させる元素であるため、必要に応じて添加する。靭性への寄与は０．１％以上で発現するため、下限を０．１％とした。一方、２．０％超の添加によりオーステナイト相が生成し、低ｒ値化する他、鋼管曲げ性が著しく劣化するため上限を２．０％とした。更に、コストを考慮すると、０．１〜０．５％が望ましい。 Ni is an element that improves toughness and corrosion resistance, so it is added as necessary. Since the contribution to toughness is manifested at 0.1% or more, the lower limit was made 0.1%. On the other hand, addition of more than 2.0% generates an austenite phase, lowers the r value, and remarkably deteriorates steel pipe bendability, so the upper limit was made 2.0%. Furthermore, if considering the cost, 0.1 to 0.5% is desirable.
Ｗは、高温強度を上げるために必要に応じて添加する元素であり、その作用は０．１％から発現するため、下限を０．１％とした。但し、過度な添加は靭性劣化や伸びの低下をもたらす。また、Ｌａｖｅｓ相が生成しすぎて｛０１１｝方位粒が生成し易くなり、ｒ値の低下をもたらすために、上限を３．０％とした。更に、製造コストと製造性を考慮すると、０．１〜２．０％が望ましい。 W is an element that is added as necessary to increase the high-temperature strength. Since its action is manifested from 0.1%, the lower limit was made 0.1%. However, excessive addition causes toughness deterioration and elongation reduction. In addition, the upper limit is set to 3.0% in order that the Laves phase is generated too much and {011} oriented grains are easily generated and the r value is lowered. Furthermore, if considering the manufacturing cost and manufacturability, 0.1 to 2.0% is desirable.
Ｚｒは、耐酸化性を向上させる元素であり、必要に応じて添加する。その作用は０．０５％以上で発現するため、下限を０．０５％とした。但し、０．３０％超の添加は、靭性や酸洗性などの製造性を著しく劣化させる他、Ｚｒと炭素および窒素の化合物が粗大化して熱延焼鈍板組織を粗粒化させて低ｒ値するため、上限を０．３０％とした。更に、製造コストを考慮すると、０．０５〜０．２０％が望ましい。 Zr is an element that improves oxidation resistance and is added as necessary. The effect is manifested at 0.05% or more, so the lower limit was made 0.05%. However, addition of more than 0.30% significantly deteriorates manufacturability such as toughness and pickling properties, and the compound of Zr, carbon, and nitrogen is coarsened to coarsen the hot-rolled annealed plate structure, resulting in low r Therefore, the upper limit was made 0.30%. Furthermore, if considering the manufacturing cost, 0.05 to 0.20% is desirable.
ＳｎおよびＳｂは、粒界に偏析して高温強度を上げるために必要に応じて添加する元素であり、その作用は０．０１％から発現するため、下限を０．０１％とした。但し、０．５０％超の添加によりＳｎ偏析、Ｓｂ偏析が生じて、溶接部の｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位形成が抑制されるとともに鋼管溶接部の低温靭性が低下するため、上限を０．５０％とした。更に、高温特性と製造コストおよび靭性を考慮すると、０．０１〜０．３０％が望ましい。 Sn and Sb are elements that are added as necessary to segregate at the grain boundaries and increase the high temperature strength. Since the action is manifested from 0.01%, the lower limit was made 0.01%. However, addition of more than 0.50% causes Sn segregation and Sb segregation, which suppresses the formation of {110} <011> and {211} <011> orientations in the weld and reduces the low temperature toughness of the steel pipe weld. Therefore, the upper limit was made 0.50%. Furthermore, if considering the high temperature characteristics, production cost and toughness, 0.01 to 0.30% is desirable.
Ｃｏは高温強度を向上させる元素であり、必要に応じて０．０５％以上添加する。但し、過度な添加は靭性や加工性を劣化させるため、上限を０．５０％とした。更に、製造コストを考慮すると、０．０５〜０．３０％が望ましい。 Co is an element that improves the high-temperature strength, and is added in an amount of 0.05% or more as necessary. However, excessive addition deteriorates toughness and workability, so the upper limit was made 0.50%. Furthermore, if considering the manufacturing cost, 0.05 to 0.30% is desirable.
Ｍｇは、溶鋼中でＡｌとともにＭｇ酸化物を形成し脱酸剤として作用する他、微細晶出したＭｇ酸化物が核となり、ＮｂやＴｉ系析出物が微細析出する。これらが熱延工程で微細析出すると、熱延工程および熱延板焼鈍工程において、微細析出物が再結晶核となり非常に微細な再結晶組織が得られ、集合組織の発達に寄与するとともに、靭性向上にも寄与する。この作用が発現するのは０．０００２％からであるため、下限を０．０００２％とした。但し、過度な添加は、耐酸化性の劣化や溶接性の低下などをもたらすため、上限を０．０１００％とした。更に、精錬コストを考慮すると、０．０００３〜０．００２０％が望ましい。 Mg forms Mg oxide together with Al in molten steel and acts as a deoxidizer, and finely crystallized Mg oxide serves as a nucleus, and Nb and Ti-based precipitates are finely precipitated. When these are finely precipitated in the hot rolling process, in the hot rolling process and hot-rolled sheet annealing process, the fine precipitates become recrystallization nuclei and a very fine recrystallized structure is obtained, contributing to the development of the texture and toughness. Contributes to improvement. Since this effect appears from 0.0002%, the lower limit was made 0.0002%. However, excessive addition causes deterioration of oxidation resistance, decrease in weldability, etc., so the upper limit was made 0.0100%. Furthermore, considering refining costs, 0.0003 to 0.0020% is desirable.
Ｃａは、脱硫元素として有効な元素であるため、含有させてもよい。この効果を得るため、Ｃａ含有量は０．０００１％以上であることが好ましい。一方、Ｃａ含有量が０．００３０％を超えると、粗大なＣａＳが生成し、靭性および耐食性を劣化させる。そのため、Ｃａ含有量は０．００３０％以下とする。なお、Ｃａ含有量は、精錬コストおよび製造性を考慮すると、０．０００３％以上であることがより好ましく、０．００２０％以下であることが好ましい。 Ca is an element effective as a desulfurization element, and therefore may be contained. In order to obtain this effect, the Ca content is preferably 0.0001% or more. On the other hand, if the Ca content exceeds 0.0030%, coarse CaS is generated, and the toughness and corrosion resistance are deteriorated. Therefore, the Ca content is 0.0030% or less. The Ca content is more preferably 0.0003% or more and preferably 0.0020% or less in consideration of refining costs and manufacturability.
Ｔａは、ＣおよびＮと結合して靭性の向上に寄与するため、含有させてもよい。前記効果を得るため、Ｔａ含有量は、０．０１％以上であることが好ましい。一方、Ｔａの含有量が０．１０％を超えると、コスト増になる他、製造性を著しく劣化させる。そのため、Ｔａの含有量は、０．１０％以下とする。なお、精錬コストおよび製造性を考慮すると、Ｔａの含有量は、０．０２％以上であることがより好ましく、０．０８％以下であることが好ましい。 Ta binds to C and N and contributes to the improvement of toughness, so Ta may be contained. In order to acquire the said effect, it is preferable that Ta content is 0.01% or more. On the other hand, if the content of Ta exceeds 0.10%, the cost is increased and the productivity is remarkably deteriorated. Therefore, the content of Ta is set to 0.10% or less. In consideration of refining costs and manufacturability, the Ta content is more preferably 0.02% or more, and preferably 0.08% or less.
Ｇａは、耐食性向上および水素脆化抑制のため、含有させてもよい。前記効果を得るため、Ｇａ含有量は０．１％以下とする。一方、硫化物および水素化物形成の観点から、Ｇａ含有量は、０．０００２％以上であることが好ましい。なお、製造性およびコストの観点、ならびに、延性および靭性の観点から、Ｇａ含有量は、０．０００５％以上であることがより好ましく、０．０２０％以下であることが好ましい。 Ga may be contained for improving corrosion resistance and suppressing hydrogen embrittlement. In order to acquire the said effect, Ga content shall be 0.1% or less. On the other hand, from the viewpoint of sulfide and hydride formation, the Ga content is preferably 0.0002% or more. In addition, from the viewpoints of manufacturability and cost, and from the viewpoints of ductility and toughness, the Ga content is more preferably 0.0005% or more, and preferably 0.020% or less.
ＲＥＭは、種々の析出物の微細化による靭性向上および耐酸化性の向上の観点から、含有させてもよい。前記効果を得るため、ＲＥＭ含有量は、０．００１％以上であることが好ましい。一方、ＲＥＭ含有量が０．０５％を超えると、鋳造性が著しく低くなり、かつ、＜０１１＞方位の発達を抑制する。そのため、ＲＥＭ含有量は０．０５％以下とする。なお、精錬コストおよび製造性を考慮すると、ＲＥＭ含有量は、０．００３％以上であることがより好ましく、０．０１％以下であることが好ましい。
ＲＥＭ（希土類元素）は、一般的な定義に従い、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。これらは単独で用いてもよいし、混合物として用いてもよい。
REM may be contained from the viewpoint of improving toughness and oxidation resistance by refining various precipitates. In order to acquire the said effect, it is preferable that REM content is 0.001% or more. On the other hand, when the REM content exceeds 0.05%, the castability is remarkably lowered and the development of the <011> orientation is suppressed. Therefore, the REM content is 0.05% or less. In consideration of refining costs and manufacturability, the REM content is more preferably 0.003% or more, and preferably 0.01% or less.
REM (rare earth element) refers to a generic name of two elements of scandium (Sc) and yttrium (Y) and 15 elements (lanthanoid) from lanthanum (La) to lutetium (Lu) according to a general definition. These may be used singly or as a mixture.
鋼板および鋼管の加工性について、特に鋼管の曲げ加工性の観点から鋼板段階の結晶方位の観点から詳細に検討した。鋼管の曲げ加工は、回転ひき曲げ等の手法によって初期の径を一定にした状態で所定の形状に曲げが成される。曲げ性が悪いものは所定の角度まで達する前に、外面部にネッキングや割れが発生する。一般にこの曲げ性は素管および素板の伸びが支配的と考えられてきたが、本発明では素材の結晶方位分布に起因するｒ値、ならびに管溶接部の結晶方位分布が大きく影響することが判明した。前述のように、鋼板の加工性については、局所的な集合組織も反映されるため、ｒ値を向上させる｛１１１｝方位の増加、ｒ値を低下させる｛１００｝方位の低減を板厚方向の特定部位で達成することにより得られる。しかしながら、本発明では特に鋼管の曲げ性を課題としており、この場合、板厚方向全体に歪み分布が生じることから、板厚方向全体の結晶方位分布を規定する。具体的には、ｒ値を向上させる｛１１１｝＜０１１＞方位と｛１１１｝＜１１２＞方位の板厚全体に占める面積率が４０％以上とする。 The workability of the steel sheet and the steel pipe was examined in detail from the viewpoint of the crystal orientation at the steel sheet stage, particularly from the viewpoint of the bending workability of the steel pipe. The bending of the steel pipe is performed into a predetermined shape with a constant initial diameter by a method such as rotary pull bending. Those having poor bendability cause necking or cracking on the outer surface before reaching a predetermined angle. In general, it has been considered that the elongation of the raw pipe and the base plate is dominant in this bendability. However, in the present invention, the r value resulting from the crystal orientation distribution of the material and the crystal orientation distribution of the pipe weld are greatly affected. found. As described above, since the local texture is also reflected in the workability of the steel sheet, the increase of the {111} orientation for improving the r value and the reduction of the {100} orientation for decreasing the r value are performed in the thickness direction. It is obtained by achieving at a specific site. However, in the present invention, the bendability of the steel pipe is particularly a problem, and in this case, since the strain distribution is generated in the entire plate thickness direction, the crystal orientation distribution in the entire plate thickness direction is defined. Specifically, the area ratio of the {111} <011> orientation and the {111} <112> orientation for improving the r value is 40% or more of the entire plate thickness.
図１に｛１１１｝＜０１１＞方位と｛１１１｝＜１１２＞方位の板厚全体に占める面積率と鋼板のｒ値ならびに鋼管の曲げ性の関係を示す。結晶方位の面積率については、種々の鋼板のＣ断面（板幅と平行な断面）について、リガク製ＳＥＭ−ＥＢＳＰ（Electron Back Scattering Pattern）装置を用いて結晶粒単位の方位を測定した。この際、測定ステップを３μｍとし、板厚１．２ｍｍについて連続的に全厚測定した後、付属の結晶方位解析ソフトで各結晶方位の比率を算出した。また、鋼板のｒ値については、前記手法により実施し、圧延方向と０°方向、４５°方向ならびに９０°方向のｒ値を求めた後に平均ｒ値を算出した。 FIG. 1 shows the relationship between the area ratio of the entire thickness of the {111} <011> orientation and {111} <112> orientation, the r value of the steel sheet, and the bendability of the steel pipe. Regarding the area ratio of the crystal orientation, the orientation of crystal grains was measured using a Rigaku SEM-EBSP (Electron Back Scattering Pattern) apparatus for C cross sections (cross sections parallel to the plate width) of various steel plates. At this time, the measurement step was set to 3 μm, and after measuring the total thickness continuously for a plate thickness of 1.2 mm, the ratio of each crystal orientation was calculated with the attached crystal orientation analysis software. Moreover, about the r value of the steel plate, it implemented by the said method, and calculated | required the average r value after calculating | requiring the r value of a rolling direction, 0 degree direction, 45 degree direction, and 90 degree direction.
更に、同鋼板からφ４２．７×１．２ｍｍ厚の電縫溶接管を製造した後、電縫溶接管の母材部が曲げ外周部となるように配置してＲ４０の９０°曲げを回転引き曲げにより行い、曲げ外周部の最小板厚を測定し、素管板厚との比率から母材部減肉率を求めた。一般的な排気部品では減肉率が２０％超になると、高温の排気ガスに曝された際に、熱疲労破壊の起点になる等信頼性が低下するため、減肉率の合格基準を２０％以下とする。 Furthermore, after manufacturing an ERW welded pipe of φ42.7 × 1.2mm thickness from the same steel plate, it is placed so that the base metal part of the ERW welded pipe becomes the bending outer peripheral part, and the 90 ° bending of R40 is rotated. It was performed by bending, the minimum plate thickness of the outer periphery of the bend was measured, and the base metal portion thickness reduction rate was determined from the ratio to the raw tube plate thickness. In general exhaust parts, if the thinning rate exceeds 20%, the reliability will decrease when exposed to high-temperature exhaust gas. % Or less.
図１（ａ）（ｂ）は横軸をいずれも｛１１１｝＜０１１＞方位と｛１１１｝＜１１２＞方位の板厚全体に占める面積率とし、図１（ａ）は縦軸が平均ｒ値、図１（ｂ）は縦軸が４５°方向のｒ値である。図１（ａ）（ｂ）いずれも、曲げ部の減肉率が●は２０％以下、○は２０％超である。 1 (a) and 1 (b), the horizontal axis represents the area ratio of the {111} <011> orientation and the {111} <112> orientation in the entire plate thickness. In FIG. 1 (a), the vertical axis represents the average r In FIG. 1B, the vertical axis represents the r value in the 45 ° direction. In each of FIGS. 1 (a) and 1 (b), the thickness reduction ratio of the bent portion is 20% or less , and ◯ is more than 20%.
図１（ａ）より、｛１１１｝＜１１２＞方位と｛１１１｝＜０１１＞方位の比率が増加すると平均ｒ値が向上し、当該方位比率を４０％以上とすることで平均ｒ値を１．５以上とすることができ、これにより鋼管曲げ加工時の減肉率を２０％以下にすることができる。 As shown in FIG. 1A, the average r value is improved when the ratio of the {111} <112> azimuth and the {111} <011> azimuth increases, and the average r value is 1 by setting the azimuth ratio to 40% or more. .5 or more, which can reduce the thinning rate during bending of the steel pipe to 20% or less.
しかしながら、平均ｒ値が１．５以上でも減肉率が２０％超になる場合があり、ｒ値の異方性を詳細に調べた結果、４５°方向のｒ値が減肉率に大きく影響し、これを１．０以上とする必要があることが判明した。鋼管の曲げ加工時に曲げ外周部は板厚減少が生じるが、曲げ部の材料流入は素材鋼板の圧延方向に対して４５°方向に材料が流入することが本検討で明らかとなった。４５°方向のｒ値が１．０以上と高い場合には減肉部に４５°方向から材料流入が生じ易く、減肉が抑制されると考えられる。図１（ｂ）から明らかなように、｛１１１｝＜１１２＞方位と｛１１１｝＜０１１＞方位比率を４０％以上とすることにより４５°方向のｒ値を１．０以上とすることができ、鋼管曲げ加工時の減肉率も２０％以下となっている。平均ｒ値を１．５以上とするとともに、４５°方向ｒ値についても確実に１．０以上とするための製造方法については、後に詳述する。 However, even if the average r value is 1.5 or more, the thinning rate may exceed 20%. As a result of examining the anisotropy of the r value in detail, the r value in the 45 ° direction greatly affects the thinning rate. It has been found that this needs to be 1.0 or more. Although the thickness of the outer periphery of the bent portion is reduced during bending of the steel pipe, it has been clarified in this study that the material flows into the bent portion in the direction of 45 ° with respect to the rolling direction of the raw steel plate. When the r value in the 45 ° direction is as high as 1.0 or more, it is considered that material inflow easily occurs from the 45 ° direction in the thinned portion, and the thinning is suppressed. As is clear from FIG. 1B, the r value in the 45 ° direction can be set to 1.0 or more by setting the {111} <112> orientation and the {111} <011> orientation ratio to 40% or more. The thickness reduction rate at the time of steel pipe bending is also 20% or less. A manufacturing method for setting the average r value to 1.5 or more and ensuring that the 45 ° direction r value is 1.0 or more will be described in detail later.
ステンレス鋼板を電縫鋼管等の鋼管に２次成形する場合、ロール成形等によって歪みが付与され、加工硬化する。過度に加工硬化すると、鋼管の曲げ性が劣化するが、従来知見としては鋼管の伸び（破断伸び）が重視されていた。しかしながら、本発明では、鋼管の引張強度と０．２％耐力の比率であるＹＲが極めて重要であることを知見した。図２に同一成分で種々の製法により製造した電縫鋼管に対して引張試験と曲げ試験を行い、鋼管のＹＲと曲げ部の最大減肉率について調べた結果を示す。ここで引張試験はＪＩＳ１１号試験片を使用し、鋼管長手方向に引張試験を行い、０．２％耐力と引張強度を求め、鋼管のＹＲ（引張強度／０．２％耐力）を算出した。鋼管のＹＲが１．１以上である鋼管は厳しい曲げ加工においても最大減肉率が２０％未満となり良好な曲げ性を示す。これは、曲げ加工時の加工硬化が影響しており、ＹＲが高い方が曲げ変形が厳しい鋼管外面部において均一な変形が生じ、局部変形が生じ難いことが減肉率の低減に寄与すると考えられる。 When a stainless steel plate is secondarily formed into a steel pipe such as an electric resistance steel pipe, distortion is imparted by work such as roll forming and the work is hardened. When the work hardening is excessive, the bendability of the steel pipe deteriorates. However, as a conventional knowledge, the elongation (breaking elongation) of the steel pipe has been regarded as important. However, in the present invention, it has been found that YR, which is the ratio between the tensile strength of steel pipe and the 0.2% proof stress, is extremely important. FIG. 2 shows the results of conducting a tensile test and a bending test on ERW steel pipes manufactured by various manufacturing methods using the same components, and examining the YR of the steel pipe and the maximum thickness reduction rate of the bent portion. Here, the tensile test used a JIS No. 11 test piece, the tensile test was performed in the longitudinal direction of the steel pipe, the 0.2% yield strength and the tensile strength were obtained, and the YR (tensile strength / 0.2% yield strength) of the steel pipe was calculated. A steel pipe having a YR of 1.1 or more in the steel pipe exhibits a good bendability with a maximum thickness reduction of less than 20% even in severe bending. This is because work hardening at the time of bending influences, and a higher YR is considered to contribute to a reduction in the thinning ratio because uniform deformation occurs at the outer surface of the steel pipe where bending deformation is severe and local deformation is less likely to occur. It is done.
以上より、本発明においては素材の全厚における｛１１１｝＜１１２＞と｛１１１｝＜０１１＞の面積率を４０％以上とすることにより、鋼板の平均ｒ値が１．５以上、４５°方向のｒ値を１．０以上とすることができ、さらに加えて鋼管のＹＲを１．１以上とすることによって、鋼管の曲げ加工において曲げ外周部の減肉率を２０％以下とすることができ、優れた加工性を有する排気部品用フェライト系ステンレス鋼管を得ることが可能となる。 From the above, in the present invention, by setting the area ratio of {111} <112> and {111} <011> in the total thickness of the material to 40% or more, the average r value of the steel sheet is 1.5 or more and 45 °. The r value in the direction can be set to 1.0 or more, and in addition, the YR of the steel pipe is set to 1.1 or more, so that the thickness reduction ratio of the bending outer peripheral portion is set to 20% or less in the bending process of the steel pipe. It is possible to obtain a ferritic stainless steel pipe for exhaust parts having excellent workability.
以上記載した技術は、曲げ加工時の曲げ外周部が母材になる場合について、曲げ外周部の減肉を防止するための技術である。一方、部品加工に際しては溶接部が曲げ外周部になる場合もある。その際には、溶接部の結晶方位が曲げ性の支配要因となる。本発明では溶接部、特に電縫溶接部の結晶方位分布と曲げ性についての検討を行い新たな知見を得た。電縫溶接時には成形加工され突き合わされた板端部が高周波誘導加熱により局部的に加熱され、その後アップセット量の調整により加圧され接合される。ここで突き合わせ部では高温で加圧されるため、素材の結晶方位は変化し、｛１１０｝＜０１１＞方位と｛２１１｝＜０１１＞方位が主体となる。｛１１０｝方位は０°方向（鋼管長手方向）のｒ値を向上させるが４５°方向と９０°方向（鋼管周方向）のｒ値を低下させる。一方、｛２１１｝＜０１１＞方位は、０°方向（鋼管長手方向）と９０°方向（鋼管周方向）のｒ値を低下させるが、４５°方向のｒ値を向上させる。 The technique described above is a technique for preventing the thinning of the bending outer peripheral portion when the bending outer peripheral portion at the time of bending is a base material. On the other hand, the welded part may be a bent outer peripheral part during parts processing. In that case, the crystal orientation of the weld becomes the dominant factor of bendability. In the present invention, the crystal orientation distribution and the bendability of the welded portion, particularly the ERW welded portion, were studied and new knowledge was obtained. At the time of ERW welding, the plate ends formed and abutted are locally heated by high frequency induction heating, and then pressed and joined by adjusting the upset amount. Here, since the butt portion is pressurized at a high temperature, the crystal orientation of the material changes, and the {110} <011> orientation and the {211} <011> orientation are mainly used. The {110} orientation improves the r value in the 0 ° direction (steel pipe longitudinal direction) but decreases the r value in the 45 ° direction and 90 ° direction (steel pipe circumferential direction). On the other hand, the {211} <011> orientation decreases the r value in the 0 ° direction (steel pipe longitudinal direction) and the 90 ° direction (steel pipe circumferential direction), but improves the r value in the 45 ° direction.
溶接された鋼管突き合わせ部の板厚全体における｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位比率の総和を種々変化させて鋼管を製造し、鋼管突き合わせ部を曲げ外周部として、曲げ加工時の減肉率評価を行った。結果を図３に示す。これより、溶接された鋼管突き合わせ部の板厚全体における｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位比率の総和が３０％以上である場合、突き合わせ部が曲げ外周部に位置したとしても、曲げ外周部の減肉率が２０％未満になり優れた曲げ性を示す。なお、鋼管突き合わせ部とは、溶接突き合わせからＨＡＺ部までを指す。 The steel pipe is manufactured by changing the sum of the orientation ratios of {110} <011> and {211} <011> in the entire thickness of the welded steel pipe butt portion, and the steel pipe butt portion is used as a bending outer peripheral portion during bending. The thickness reduction rate was evaluated. The results are shown in FIG. From this, even if the sum of the {110} <011> and {211} <011> orientation ratios in the entire plate thickness of the welded steel pipe butt portion is 30% or more, even if the butt portion is positioned on the outer periphery of the bend The thinning rate of the outer periphery of the bend is less than 20% and exhibits excellent bendability. In addition, a steel pipe butt | matching part points out from welding butt | matching to a HAZ part.
鋼管の曲げは主として０°方向（鋼管長手方向）に変形が進行するが、｛１１０｝＜０１１＞の存在により０°方向（鋼管長手方向）の板厚減少が抑制される。また、本発明では種々の曲げ実験と解析を行った結果、曲げ時には鋼管外面の減肉箇所に対して４５°方向からの塑性流動が生じることを見出した。即ち、４５°方向のｒ値が高い場合に最減肉部の板厚減少を抑制する効果があり、｛２１１｝＜０１１＞方位の存在は、曲げ性改善に有効であることを知見した。 In the bending of the steel pipe, deformation mainly proceeds in the 0 ° direction (longitudinal direction of the steel pipe), but the presence of {110} <011> suppresses a decrease in the thickness in the 0 ° direction (longitudinal direction of the steel pipe). Moreover, as a result of performing various bending experiments and analyzes in the present invention, it has been found that a plastic flow from a 45 ° direction occurs with respect to the thinned portion of the outer surface of the steel pipe during bending. That is, it has been found that when the r value in the 45 ° direction is high, there is an effect of suppressing the reduction in the thickness of the thinnest portion, and the presence of the {211} <011> orientation is effective in improving the bendability.
尚、溶接管の製造における溶接方法は、電縫溶接以外にレーザー溶接やＴＩＧ溶接が知られているが、レーザー溶接やＴＩＧ溶接では溶接部に粗大な柱状晶組織が形成され、｛１１０｝＜０１１＞と｛２１１｝＜０１１＞結晶方位は発達しないため、これら方位比率の総和を３０％以上とすることは難しい。それに対して、電縫溶接であれば、これら方位比率の総和を３０％以上とすることができる。従って、本発明の鋼管製造の際の溶接方法は電縫溶接が望ましい。また、電縫溶接条件については溶接欠陥が生じない範囲で選択すれば良いが、アップセット量が過小であると溶接部のメタルフローが小さく、｛１１０｝＜０１１＞と｛２１１｝＜０１１＞結晶方位が発達しないことがあるため、アップセット量が１．５ｍｍ以上になるようにスクイズ量や溶接入熱を調整することが望ましい。
In addition, laser welding and TIG welding are known as welding methods in the production of welded pipes, but in laser welding and TIG welding, a coarse columnar crystal structure is formed in the welded portion, and {110} < Since 011> and {211} <011> crystal orientation does not develop, it is difficult to make the sum of these
本発明では、上記の集合組織や材質の他に製造方法に関して、熱延板焼鈍条件、冷延条件および冷延板焼鈍条件の影響について、以下の検討を行った。 In the present invention, in addition to the textures and materials described above, the following investigations were performed on the effects of hot-rolled sheet annealing conditions, cold-rolled sheet conditions, and cold-rolled sheet annealing conditions on the manufacturing method.
スラブを出発材として所定の板厚に熱延された熱延板は、熱延板焼鈍が施される。冷延焼鈍後に｛１１１｝＜０１１＞方位と｛１１１｝＜１１２＞の面積率が４０％を超える結晶方位を得るためには、熱延板焼鈍条件が重要となる。ＮｂやＭｏ等の合金元素が多量に添加される鋼では、炭窒化物の他にＬａｖｅｓ相と呼ばれるＦｅ，Ｎｂ，Ｍｏを主体とする金属間化合物が加熱段階で生成する。加熱中にこれらが多量に析出すると、再結晶が遅延して再結晶集合組織の発達が遅れてしまう。これを防止するためには、熱延板焼鈍において加熱速度を２０℃／ｓｅｃ以上として９５０〜１０３０℃に加熱後、３０℃／ｓｅｃ以上の冷却速度で冷却する。析出物および再結晶組織等を考慮すると、熱延板焼鈍における加熱温度は９５０以上１０００℃以下、加熱速度は３０℃／ｓｅｃ以上、冷却速度は３５℃／ｓｅｃ以上が望ましい。さらに望ましい加熱温度は、９８０℃超、１０００℃未満である。 A hot-rolled sheet that has been hot-rolled to a predetermined thickness using a slab as a starting material is subjected to hot-rolled sheet annealing. In order to obtain a crystal orientation in which the area ratio of {111} <011> and {111} <112> exceeds 40% after cold rolling annealing, the hot rolled sheet annealing conditions are important. In steel to which a large amount of alloy elements such as Nb and Mo are added, an intermetallic compound mainly composed of Fe, Nb, and Mo called a Laves phase is generated in the heating stage in addition to carbonitride. If a large amount of these precipitates during heating, the recrystallization is delayed and the development of the recrystallized texture is delayed. In order to prevent this, the heating rate is set to 20 ° C./sec or more in the hot-rolled sheet annealing, and after heating to 950 to 1030 ° C., cooling is performed at a cooling rate of 30 ° C./sec or more. Considering precipitates, recrystallized structure, etc., the heating temperature in hot-rolled sheet annealing is preferably 950 to 1000 ° C., the heating rate is 30 ° C./sec or more, and the cooling rate is 35 ° C./sec or more. A more desirable heating temperature is more than 980 ° C. and less than 1000 ° C.
冷間圧延途中に中間焼鈍を行わずに１回の冷延工程で製造するフェライト系ステンレス鋼板（以下、１回の冷延工程を「仕上冷延」ともいう。）において、ｒ値を向上されるためには、通常であれば冷延工程における圧下率を高くすることが常識的な技術であるが、本発明では４５°方向のｒ値を１．０以上とするため圧下率を８０％未満とする。更に、冷延後の焼鈍に際しては、加熱温度を１０３０〜１１００℃として、再結晶を促進して加工性を向上させる集合組織の発達を促す。再結晶集合組織の発達や加工肌荒れ等を考慮すると、仕上冷延圧下率は６０〜８０％未満、焼鈍温度は１０４０〜１０７０℃が望ましい。 In a ferritic stainless steel sheet manufactured in a single cold rolling step without intermediate annealing during cold rolling (hereinafter, one cold rolling step is also referred to as “finish cold rolling”), the r value is improved. In order to achieve this, it is common knowledge to increase the rolling reduction in the cold rolling process, but in the present invention, the r value in the 45 ° direction is set to 1.0 or more so that the rolling reduction is 80%. Less than. Furthermore, during annealing after cold rolling, the heating temperature is set to 1030 to 1100 ° C. to promote the development of a texture that promotes recrystallization and improves workability. In consideration of the development of recrystallized texture, rough processing, etc., the finish cold rolling reduction is preferably 60 to less than 80%, and the annealing temperature is preferably 1040 to 1070 ° C.
生産性を考慮すると前述のように１回の冷延工程で製造することが望ましいが、本発明では中間焼鈍を付与する２回冷延工程で製造しても構わない。この際、熱延板焼鈍条件や最終の冷延板焼鈍条件は前述の１回冷延工程の場合と同じである。中間焼鈍を付与する前の１回目（前段）冷延工程においては圧下率を５０％未満、中間焼鈍後の２回目（後段）冷延工程（仕上冷延）の圧下率は７５％未満とする。これは過度に冷延圧下率を高くすると４５°方向のｒ値が低下するためであり、望ましくは、１回目（前段）冷延工程においては圧下率を３０〜５０％未満、中間焼鈍後の２回目（後段）の仕上冷延工程の圧下率は６０〜７５％未満とする。また、本発明では中間焼鈍における加熱速度を２０℃／ｓｅｃ以上、加熱温度を９３０〜９８０℃、冷却速度を３０℃／ｓｅｃ以上と規定する。加熱速度と冷却速度については、熱延板焼鈍における技術と同じであり、焼鈍時の靭性や鋼板形状を考慮すると加熱速度は３０℃／ｓｅｃ以上、冷却速度は３５℃／ｓｅｃ以上が望ましい。また、加熱温度については、本発明が対象とする耐熱フェライト系ステンレス鋼の場合、通常１０００℃以上で焼鈍されるが、ｒ値向上のために中間焼鈍段階で微細組織を得るとともに、集合組織発達に寄与する析出物を粗大に残留させるために、低温焼鈍とする。加熱の安定性や鋼板形状および酸洗性等を考慮すると、９３０〜９５０℃が望ましい。 In view of productivity, it is desirable to manufacture in a single cold rolling process as described above, but in the present invention, it may be manufactured in a two cold rolling process that provides intermediate annealing. Under the present circumstances, the hot-rolled sheet annealing conditions and the final cold-rolled sheet annealing conditions are the same as the case of the above-mentioned 1st cold rolling process. The rolling reduction is less than 50% in the first (previous) cold rolling process before applying the intermediate annealing, and the rolling reduction in the second (following) cold rolling process (finishing cold rolling) after the intermediate annealing is less than 75%. . This is because when the cold rolling reduction ratio is excessively increased, the r value in the 45 ° direction decreases. Desirably, in the first (previous stage) cold rolling process, the rolling reduction ratio is less than 30 to 50%, after the intermediate annealing. The rolling reduction of the second (second stage) finish cold rolling step is 60 to less than 75%. In the present invention, the heating rate in the intermediate annealing is defined as 20 ° C./sec or more, the heating temperature is defined as 930 to 980 ° C., and the cooling rate is defined as 30 ° C./sec or more. About a heating rate and a cooling rate, it is the same as the technique in hot-rolled sheet annealing, and when considering the toughness and steel plate shape at the time of annealing, a heating rate is 30 ° C./sec or more, and a cooling rate is preferably 35 ° C./sec or more. As for the heating temperature, in the case of the heat-resistant ferritic stainless steel targeted by the present invention, it is usually annealed at 1000 ° C. or higher, but a microstructure is obtained at the intermediate annealing stage to improve the r value, and the texture is developed. In order to leave coarse precipitates that contribute to the heat treatment, low-temperature annealing is performed. Considering the stability of heating, the shape of the steel plate and the pickling property, 930 to 950 ° C. is desirable.
本発明では、前述のように、素材の全厚にわたって｛１１１｝＜１１２＞と｛１１１｝＜０１１＞の面積率が４０％を超える組織を得ることが必要である。そのためには、本発明に規定する成分組成の鋼板を用いるとともに、仕上冷延の際の剪断変形を抑制することが必須であるとの知見を得た。そして、そのためには仕上冷延前の組織、すなわち熱延板焼鈍組織、あるいは中間焼鈍組織の表層〜ｔ／４部の再結晶率が８０％以上かつ、結晶粒径が５０μｍ以下であることが重要であると判明した。通常、冷延の際には板表層に近い部分ほどロールから受ける剪断応力により剪断変形が導入される。この剪断変形した剪断帯と呼ばれる部分からはランダム方位の再結晶粒が生成されるため、｛１１１｝＜０１１＞方位と｛１１１｝＜１１２＞方位の面積率は低下する。剪断帯の導入を抑制するには再結晶組織の微細化が有効である。本発明では表層〜ｔ／４の組織を８０％以上再結晶させつつ、その再結晶粒を５０μｍ以下とした組織に対し、前述の製造条件で製造することで、｛１１１｝＜０１１＞方位と｛１１１｝＜１１２＞方位の面積率が４０％以上となるとの知見を得た。望ましくは表層〜ｔ／４の再結晶率９０％以上、結晶粒径４０μｍ以下である。また、上記本発明の熱延板焼鈍条件、冷延中間焼鈍条件を用いて焼鈍を行うことにより、表層〜ｔ／４の組織を８０％以上再結晶させつつ、その再結晶粒を５０μｍ以下とすることができる。 In the present invention, as described above, it is necessary to obtain a structure in which the area ratio of {111} <112> and {111} <011> exceeds 40% over the entire thickness of the material. For that purpose, while using the steel plate of the component composition prescribed | regulated to this invention, the knowledge that it was essential to suppress the shear deformation in the case of finish cold rolling was acquired. For that purpose, the recrystallization rate of the surface layer to t / 4 part of the structure before the finish cold rolling, that is, the hot-rolled sheet annealing structure or the intermediate annealing structure is 80% or more and the crystal grain size is 50 μm or less. It turned out to be important. Usually, in the case of cold rolling, shear deformation is introduced by the shear stress received from the roll in the portion closer to the surface of the plate. Since recrystallized grains with random orientation are generated from the portion called sheared shear band, the area ratios of {111} <011> orientation and {111} <112> orientation are lowered. Refinement of the recrystallized structure is effective for suppressing the introduction of the shear band. In the present invention, the structure of the surface layer to t / 4 is recrystallized by 80% or more, and the structure having the recrystallized grains of 50 μm or less is manufactured under the above-described manufacturing conditions, thereby obtaining the {111} <011> orientation. The knowledge that the area ratio of {111} <112> orientation is 40% or more was obtained. Desirably, the recrystallization rate of the surface layer to t / 4 is 90% or more and the crystal grain size is 40 μm or less. In addition, by performing annealing using the hot rolled sheet annealing conditions and cold rolling intermediate annealing conditions of the present invention, the recrystallized grains are 50 μm or less while recrystallizing the structure of the surface layer to t / 4 by 80% or more. can do.
本発明ではさらに、熱延板焼鈍を省略することも剪断変形の抑制に効果が大きいとの知見を得ている。これは、熱延板焼鈍を省略し敢えて再結晶させないことで、軟質な再結晶組織への剪断帯導入を抑制するためである。ただし、硬質な熱延まま組織であってもステンレスへの圧延に利用される直径１００ｍｍ程度の通常の径のロールによる圧延では、剪断変形の抑制は不十分である。これは、熱延まま材に対し、直径４００ｍｍ以上のロール径を有する圧延機を用いて４０％以上の圧下率で冷延することで解決可能である。 Furthermore, in the present invention, it has been found that omission of hot-rolled sheet annealing is also effective in suppressing shear deformation. This is in order to suppress the introduction of the shear band into the soft recrystallized structure by omitting the hot-rolled sheet annealing and not recrystallizing it. However, even with a hard hot rolled structure, rolling with a roll having a normal diameter of about 100 mm used for rolling into stainless steel does not sufficiently suppress shear deformation. This can be solved by cold rolling at a rolling reduction of 40% or more using a rolling mill having a roll diameter of 400 mm or more with respect to the hot-rolled material.
すなわち、素材の全厚にわたって｛１１１｝＜０１１＞方位と｛１１１｝＜１１２＞の面積率が４０％を超える組織を得るには、熱延板焼鈍、中間焼鈍によって仕上圧延に供する際の表層〜ｔ／４の再結晶組織を微細化する方法か、熱延板焼鈍の省略と、４００ｍｍ以上の大径ロールによる冷延の二つを組み合わせた方法のどちらかで製造することが有効である。 That is, in order to obtain a structure in which the area ratio of {111} <011> orientation and {111} <112> exceeds 40% over the entire thickness of the raw material, the surface layer when subjected to finish rolling by hot-rolled sheet annealing and intermediate annealing It is effective to produce by either a method of refining a recrystallized structure of ˜t / 4, or a method of combining the omission of hot-rolled sheet annealing and the cold rolling with a large diameter roll of 400 mm or more. .
上記本発明の鋼板を用いて本発明の排気部品用フェライト系ステンレス鋼管を製造するに際しては、電縫溶接によって造管すると好ましい。本発明の成分を含有する鋼板を用いて電縫溶接によって造管することにより、鋼管のＹＲを１．１以上とすることができる。また、本発明の成分を含有する鋼板を用いて、本発明の熱延・冷延条件で鋼板を製造し、さらに電縫溶接によって造管することにより、溶接された鋼管突き合わせ部の板厚全体における｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位比率の総和を３０％以上とすることができる。 When producing the ferritic stainless steel pipe for exhaust parts of the present invention using the steel sheet of the present invention, it is preferable that the pipe is formed by electric resistance welding. YR of a steel pipe can be made 1.1 or more by making a pipe by electric resistance welding using a steel sheet containing the component of the present invention. Further, by using the steel sheet containing the component of the present invention, the steel sheet is manufactured under the hot rolling / cold rolling conditions of the present invention, and further piped by electric resistance welding, so that the entire thickness of the welded steel pipe butt portion is obtained. The sum of the {110} <011> and {211} <011> orientation ratios can be 30% or more.
なお、スラブ厚さ、熱延板厚などは適宜設計すれば良い。また、冷間圧延においては、圧下率、ロール粗度、ロール径、圧延油、圧延パス回数、圧延速度、圧延温度などは適宜選択すれば良い。焼鈍は、必要であれば水素ガスあるいは窒素ガスなどの無酸化雰囲気で焼鈍する光輝焼鈍でも大気中で焼鈍しても構わない。更に、焼鈍後に調質圧延や形状矯正のためのテンションレベラー工程を通板しても構わない。 In addition, what is necessary is just to design slab thickness, hot-rolled sheet thickness, etc. suitably. In cold rolling, the rolling reduction, roll roughness, roll diameter, rolling oil, number of rolling passes, rolling speed, rolling temperature, etc. may be appropriately selected. The annealing may be bright annealing, which is performed in a non-oxidizing atmosphere such as hydrogen gas or nitrogen gas, if necessary, or in the air. Further, a tension leveler process for temper rolling and shape correction may be passed after annealing.
表１−１、表１−２に示す成分組成の鋼を溶製しスラブに鋳造し、スラブを熱間圧延して、５．０ｍｍ厚の熱延板とした。その後、熱延板を連続焼鈍処理した後、酸洗し、中間焼鈍なしで１．２ｍｍ厚まで冷間圧延し、連続焼鈍−酸洗を施して製品板とした。熱延板焼鈍における加熱温度は９５０〜１０００℃未満、加熱速度は３０℃／ｓｅｃ以上、冷却速度は３５℃／ｓｅｃ以上とした。また、冷延板焼鈍温度は、１０５０℃とした。このようにして得られた冷延焼鈍板に対して、先述したｒ値測定ならびに結晶方位強度測定を行った。また、これら鋼板を素材として電縫溶接管（φ４２．７）を製造し、先述した引張試験を行って鋼管のＹＲを評価するとともに、溶接部の結晶方位強度測定を行った。 Steels having the component compositions shown in Table 1-1 and Table 1-2 were melted and cast into slabs, and the slabs were hot-rolled to form 5.0 mm thick hot rolled sheets. Thereafter, the hot-rolled sheet was subjected to continuous annealing treatment, then pickled, cold-rolled to 1.2 mm without intermediate annealing, and subjected to continuous annealing-pickling to obtain a product plate. The heating temperature in hot-rolled sheet annealing was 950 to less than 1000 ° C., the heating rate was 30 ° C./sec or more, and the cooling rate was 35 ° C./sec or more. The cold-rolled sheet annealing temperature was 1050 ° C. The r value measurement and the crystal orientation strength measurement described above were performed on the cold-rolled annealed plate thus obtained. Moreover, an electric resistance welded pipe (φ42.7) was manufactured using these steel sheets as raw materials, and the tensile test described above was performed to evaluate the YR of the steel pipe, and the crystal orientation strength of the weld was measured.
更に、Ｒ４０の９０°曲げを回転引き曲げにより行い、曲げ外周部の最小板厚を測定し、素管板厚との比率から最大減肉率を求めた。なお、曲げ試験の際には溶接線は横に来るようにし、腹と背が母材となるようにした場合と、溶接線が背に来るようにし、背が溶接部腹が母材になるようにした場合について曲げ性を評価した。この時、二つの場合の実験においてどちらも最大限肉率が２０％以下となれば合格（○）、いずれか又は両方が２０％超となれば不合格（×）とした。 Further, 90 ° bending of R40 was performed by rotational pulling, the minimum plate thickness of the outer periphery of the bend was measured, and the maximum thickness reduction rate was obtained from the ratio with the raw tube plate thickness. In the bending test, the weld line should be sideways, and the belly and back should be the base metal, and the weld line should be back, and the back should be the base of the weld. The bendability was evaluated in the case of doing so. At this time, in the experiment of two cases, in both cases, if the maximum meat ratio was 20% or less, it was determined to be acceptable (◯), and if either or both exceeded 20%, it was determined to be unacceptable (x).
上述のように、表１−１、１−２に示したものの製造方法は、いずれも本発明の好適な方法を用いている。そして、本発明で規定する成分組成を有する鋼（表１−１の鋼Ｎｏ．Ａ１〜Ａ１９）は、成分含有量か本発明から外れる比較例（表１−２の鋼Ｎｏ．Ｂ１〜Ｂ２０）に比べて板厚全体における｛１１１｝＜１１２＞と｛１１１｝＜０１１＞方位比率の総和が４０％以上と高いため、平均ｒ値が１．５以上、４５°方向のｒ値が１．０以上であり、加工性に優れている。また、鋼管のＹＲ（引張強度／０．２％耐力）が１．１以上、溶接部の板厚全体における｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位比率の総和が３０％以上であるため、鋼管の曲げ性評価結果がいずれも「○」となり、回転引き曲げ時の最大減肉率が２０％以下と加工性に優れた鋼管が得られている。 As described above, all of the manufacturing methods shown in Tables 1-1 and 1-2 use the preferred method of the present invention. And the steel which has a component composition prescribed | regulated by this invention (steel No.A1-A19 of Table 1-1) is a comparative example (steel No.B1-B20 of Table 1-2) from which component content or this invention remove | deviates. The total sum of the {111} <112> and {111} <011> azimuth ratios in the entire plate thickness is as high as 40% or more, so the average r value is 1.5 or more and the r value in the 45 ° direction is 1. It is 0 or more and is excellent in workability. Further, the YR (tensile strength / 0.2% proof stress) of the steel pipe is 1.1 or more, and the sum of the {110} <011> and {211} <011> orientation ratios in the entire thickness of the welded portion is 30% or more. Therefore, the evaluation results of the bendability of the steel pipe are all “◯”, and a steel pipe excellent in workability with a maximum thickness reduction rate of 20% or less at the time of rotary drawing is obtained.
表２−１の鋼Ｎｏ．に記載された鋼Ｎｏ．の鋼板成分を表１−１から選択し、表２−１、表２−２に記載するように製造条件を種々変化させた場合の特性を示す。なお、表２−２のＮｏ．２４はＴＩＧ溶接管（φ４２．７）、それ以外は電縫溶接管（ＥＲＷ）（φ４２．７）である。鋼板と鋼管の品質評価方法は上記表１に示す場合と同様である。 Steel No. in Table 2-1. Steel No. described in The steel plate components are selected from Table 1-1, and the characteristics are shown when the production conditions are variously changed as described in Table 2-1 and Table 2-2. In addition, No. of Table 2-2. Reference numeral 24 denotes a TIG welded pipe (φ42.7), and the others are electric resistance welded pipes (ERW) (φ42.7). The quality evaluation method of the steel plate and the steel pipe is the same as that shown in Table 1 above.
表２−１、表２−２に示す本発明例は、いずれも成分含有量及び製造方法が本発明範囲内であり、鋼板の品質、鋼管の品質ともに良好な結果が得られた。それに対して本発明で規定される製造条件から外れる比較例の場合、鋼板又は鋼管の溶接部における結晶方位強度の和が本発明外となり、鋼管曲げ加工時の減肉率が大きくなる。 In the examples of the present invention shown in Tables 2-1 and 2-2, the content of components and the production method are within the scope of the present invention, and good results were obtained for both the quality of the steel sheet and the quality of the steel pipe. On the other hand, in the case of the comparative example deviating from the manufacturing conditions defined in the present invention, the sum of the crystal orientation strengths in the welded portion of the steel plate or the steel pipe is out of the present invention, and the thinning rate at the time of bending the steel pipe increases.
Claims (10)
鋼管のＹＲ（引張強度／０．２％耐力）が１．１以上、溶接された鋼管突き合わせ部の板厚全体におけるＥＢＳＰ法により測定される｛１１０｝＜０１１＞と｛２１１｝＜０１１＞方位の面積率の総和が３０％以上であることを特徴とする加工性に優れた排気部品用フェライト系ステンレス鋼管。 When the base material of the steel pipe is mass%, C: 0.001 to 0.02%, Si: 0.1 to 1.5%, Mn: 0.1 to 1.5%, P: 0.01 to 0.04%, S: 0.0001 to 0.01%, Cr: 10 to 20%, N: 0.001 to 0.03%, 0.1 to 0.8% of one or more of Nb or Ti The balance is composed of Fe and inevitable impurities, and the sum of the area ratios of {111} <112> and {111} <011> orientations measured by the EBSP method over the entire plate thickness is 40% or more, and the average r It consists of a stainless steel plate having a value of 1.5 or more and an r value in the 45 ° direction of 1.0 or more,
{110} <011> and {211} <011> orientations measured by the EBSP method over the entire plate thickness of the welded steel pipe butt, where the YR (tensile strength / 0.2% proof stress) of the steel pipe is 1.1 or more A ferritic stainless steel pipe for exhaust parts excellent in workability, characterized by having a total area ratio of 30% or more.
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| JP7009278B2 (en) * | 2018-03-26 | 2022-02-10 | 日鉄ステンレス株式会社 | Ferritic stainless steel sheets with excellent heat resistance and exhaust parts and their manufacturing methods |
| JP6986135B2 (en) * | 2018-03-30 | 2021-12-22 | 日鉄ステンレス株式会社 | Ferritic stainless steel sheets, their manufacturing methods, and ferritic stainless steel members |
| JP7178791B2 (en) * | 2018-03-30 | 2022-11-28 | 日鉄ステンレス株式会社 | Steel plates for ferritic stainless steel pipes |
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| CN113684424B (en) * | 2021-08-27 | 2022-06-14 | 华能国际电力股份有限公司 | NIAL strengthened ferritic heat-resistant steel and preparation method thereof |
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