JP2018154857A - Ferritic stainless steel hot rolled steel strip and manufacturing method of steel strip - Google Patents
Ferritic stainless steel hot rolled steel strip and manufacturing method of steel strip Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 122
- 239000010959 steel Substances 0.000 title claims abstract description 122
- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 31
- 238000004519 manufacturing process Methods 0.000 title claims description 20
- 238000005096 rolling process Methods 0.000 claims abstract description 61
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 58
- 239000011159 matrix material Substances 0.000 claims abstract description 15
- 239000000758 substrate Substances 0.000 claims abstract description 8
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 6
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 5
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 5
- 238000005098 hot rolling Methods 0.000 claims description 60
- 238000000137 annealing Methods 0.000 claims description 58
- 238000000034 method Methods 0.000 claims description 22
- 239000000463 material Substances 0.000 claims description 18
- 238000010438 heat treatment Methods 0.000 claims description 17
- 230000008569 process Effects 0.000 claims description 15
- 239000002184 metal Substances 0.000 claims description 14
- 229910052751 metal Inorganic materials 0.000 claims description 14
- 150000001247 metal acetylides Chemical class 0.000 claims description 10
- 239000000203 mixture Substances 0.000 claims description 10
- 230000002093 peripheral effect Effects 0.000 claims description 9
- 239000000126 substance Substances 0.000 claims description 7
- 238000001816 cooling Methods 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 6
- 229910052782 aluminium Inorganic materials 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims description 5
- 229910052720 vanadium Inorganic materials 0.000 claims description 5
- 230000014509 gene expression Effects 0.000 claims 1
- 239000010935 stainless steel Substances 0.000 claims 1
- 238000010304 firing Methods 0.000 abstract 1
- 229910001566 austenite Inorganic materials 0.000 description 21
- 229910000734 martensite Inorganic materials 0.000 description 16
- 238000001953 recrystallisation Methods 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 11
- 239000013078 crystal Substances 0.000 description 11
- 230000009467 reduction Effects 0.000 description 9
- 238000000354 decomposition reaction Methods 0.000 description 8
- 238000007542 hardness measurement Methods 0.000 description 8
- 230000002441 reversible effect Effects 0.000 description 7
- 239000002436 steel type Substances 0.000 description 7
- 238000004804 winding Methods 0.000 description 7
- 238000012545 processing Methods 0.000 description 6
- 238000012360 testing method Methods 0.000 description 6
- 238000005097 cold rolling Methods 0.000 description 5
- 230000007797 corrosion Effects 0.000 description 5
- 238000005260 corrosion Methods 0.000 description 5
- 239000000047 product Substances 0.000 description 5
- 230000003068 static effect Effects 0.000 description 5
- 238000007545 Vickers hardness test Methods 0.000 description 4
- 238000000879 optical micrograph Methods 0.000 description 4
- 238000005554 pickling Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 230000009466 transformation Effects 0.000 description 3
- 239000002253 acid Substances 0.000 description 2
- 239000010960 cold rolled steel Substances 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 230000008520 organization Effects 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000001186 cumulative effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000013067 intermediate product Substances 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000010309 melting process Methods 0.000 description 1
- 230000002250 progressing effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
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Abstract
Description
本発明は、短時間の熱延板焼鈍を施すだけで再結晶フェライト相＋炭化物の軟質な焼鈍組織が得られるように組織調整されたフェライト系ステンレス鋼熱延鋼帯に関する。また、その熱延鋼帯およびその熱延鋼帯に由来する熱延焼鈍鋼帯の製造方法に関する。 The present invention relates to a ferritic stainless steel hot-rolled steel strip whose structure is adjusted so that a soft annealed structure of recrystallized ferrite phase and carbide can be obtained only by performing hot-rolled sheet annealing for a short time. Moreover, it is related with the manufacturing method of the hot-rolled steel strip and the hot-rolled annealed steel strip derived from the hot-rolled steel strip.
本明細書において、「熱延鋼板」とは、熱間圧延を終えて巻き取られたまま（いわゆる「ａｓ ｈｏｔ」）の組織状態を有する鋼の板材、すなわち熱間圧延後に加熱処理を受けていない鋼の板材を意味する。「熱延鋼帯」は、熱延鋼板であって、特にコイル状に巻き取られた状態、あるいはそれを通板ラインで展開した状態の板材を意味する。 In the present specification, the “hot rolled steel sheet” is a steel plate having a textured state after being hot rolled (so-called “as hot”), that is, subjected to heat treatment after hot rolling. Means no steel plate. “Hot-rolled steel strip” is a hot-rolled steel plate, and particularly means a plate material wound in a coil shape or developed through a plate line.
ＳＵＳ４３０に代表されるフェライト系ステンレス鋼板の製造においては、熱間圧延の後、バッチ式焼鈍炉により長時間の熱延板焼鈍を施すことが一般的である。フェライト系ステンレス鋼種の熱延鋼板には、通常、硬質なマルテンサイト相が混在する。加工性の良好な鋼板製品を得るためには熱延板焼鈍においてマルテンサイト相をフェライト相と炭化物に分解しておく必要がある。その分解反応には例えば７９０〜８６０℃×１〜２４ｈといった長時間の加熱保持を要する。そのような長時間焼鈍にはバッチ式の焼鈍炉が必要となる。 In the production of a ferritic stainless steel sheet represented by SUS430, it is common to perform hot-rolled sheet annealing for a long time in a batch-type annealing furnace after hot rolling. Usually, a hard martensite phase is mixed in a hot rolled steel sheet of a ferritic stainless steel type. In order to obtain a steel sheet product with good workability, it is necessary to decompose the martensite phase into a ferrite phase and a carbide in the hot-rolled sheet annealing. The decomposition reaction requires long-time heating and holding such as 790 to 860 ° C. × 1 to 24 hours. Such a long annealing requires a batch-type annealing furnace.
バッチ式焼鈍炉による長時間の熱延板焼鈍は、多大なエネルギーを消費する。また、大気雰囲気下で焼鈍した場合表面に酸化スケールが形成されるため、一般的に焼鈍後には酸洗が行われるが、バッチ式焼鈍炉で焼鈍された鋼板については、一般的な連続焼鈍酸洗設備にて酸洗のみを行う必要がある。そのため、フェライト系ステンレス鋼種は通常、オーステナイト系ステンレス鋼種に比べ、熱延焼鈍鋼板を得るまでの通板工程が１つ多くなる。さらに、大量生産においては多数のバッチ式焼鈍炉を設置するための広い敷地が必要となる。熱間圧延後の工程合理化のためには、バッチ式の長時間焼鈍を回避する製造工程の採用が望ましい。 Long-time hot-rolled sheet annealing using a batch annealing furnace consumes a great deal of energy. In addition, since an oxide scale is formed on the surface when annealed in an air atmosphere, pickling is generally performed after annealing, but for steel sheets annealed in a batch annealing furnace, a general continuous annealing acid is used. It is necessary to perform only pickling at the washing equipment. Therefore, the ferritic stainless steel type usually has one more plate-passing process until a hot-rolled annealed steel plate is obtained than the austenitic stainless steel type. Furthermore, in mass production, a large site is required for installing a large number of batch annealing furnaces. In order to rationalize the process after hot rolling, it is desirable to employ a manufacturing process that avoids batch-type long-term annealing.
一方、フェライト系ステンレス鋼種では、鋳造組織に起因する方位の近い結晶の集合組織（コロニー）が冷延鋼板にまで残留しやすく、リジングあるいはローピングと呼ばれるような冷延製品の外観・形状不良を招く場合がある。このような問題の対策としては、熱間圧延工程で鋳造組織をできるだけ破壊し、結晶方位のランダム化を図ることが有効である。例えば特許文献１には圧延機の両側に保温炉を備えたリバース式圧延機で熱間圧延を行う手法が記載されている。しかし、バッチ式焼鈍炉による熱延板焼鈍は回避できていない。 On the other hand, in ferritic stainless steel grades, crystallographic structures (colony) with close orientation due to the cast structure tend to remain on the cold-rolled steel sheet, resulting in poor appearance and shape of cold-rolled products such as ridging or roping. There is a case. As a countermeasure against such a problem, it is effective to destroy the cast structure as much as possible in the hot rolling process and to randomize the crystal orientation. For example, Patent Document 1 describes a method of performing hot rolling with a reverse rolling mill provided with a heat-retaining furnace on both sides of the rolling mill. However, hot-rolled sheet annealing using a batch annealing furnace cannot be avoided.
特許文献２〜８にはバッチ式の熱延板焼鈍を回避し得るフェライト系ステンレス鋼板の製造技術が開示されている。特許文献２、３はＡｌを比較的多量に含有する鋼種を対象とし、特許文献４は低Ｃ鋼を対象としている。特許文献５、６は粗圧延中にγ相が十分に確保できるよう成分組成に限定を課すとともに粗圧延での累積圧下率を４０％以上かつ巻取温度を６００℃以下に制限するものである。特許文献７はＴｉ、Ｍｎの含有量に応じて熱間圧延での加熱温度を設定するものである。特許文献８は粗圧延に相当する第１の熱間圧延を１０００℃超えの高温で行うものである。 Patent Documents 2 to 8 disclose manufacturing technologies for ferritic stainless steel sheets that can avoid batch-type hot-rolled sheet annealing. Patent Documents 2 and 3 target steel types containing a relatively large amount of Al, and Patent Document 4 targets low C steel. Patent Documents 5 and 6 impose a limitation on the component composition so that the γ phase can be sufficiently secured during rough rolling, and limit the cumulative rolling reduction in rough rolling to 40% or more and the coiling temperature to 600 ° C. or less. . Patent Document 7 sets the heating temperature in hot rolling according to the contents of Ti and Mn. Patent document 8 performs the 1st hot rolling equivalent to rough rolling at the high temperature exceeding 1000 degreeC.
上述のように、フェライト系ステンレス鋼種は冷延製品においてリジングやローピングといった外観・形状不良が生じやすいという問題を有しているが、これまでに種々の対策が提案されて改善効果が得られている。しかしながら、バッチ式の熱延板焼鈍を回避しうる手法で耐リジング性の良好なフェライト系ステンレス鋼板を得るためには、成分組成に特別な限定を加えたり、熱延工程で非常に負荷の大きい高温強加工や高圧下率のプロセスを採用したりする必要があった。これらの手法は製造コストを増大させる要因となる。また、保温炉を備えたリバース式圧延機で熱間圧延を行う手法では、熱延鋼帯の長手方向において、端部付近と中央付近の組織状態に差が生じやすいという問題があった。 As mentioned above, ferritic stainless steel grades have the problem of poor appearance and shape defects such as ridging and roping in cold-rolled products, but various countermeasures have been proposed so far and improvement effects have been obtained. Yes. However, in order to obtain a ferritic stainless steel sheet with good ridging resistance by a technique that can avoid batch-type hot-rolled sheet annealing, a special limitation is imposed on the composition of components, or a very heavy load is applied in the hot-rolling process. It was necessary to employ high-temperature high-strength machining and high-pressure low-rate processes. These techniques are factors that increase manufacturing costs. Moreover, in the method of performing hot rolling with a reverse rolling mill equipped with a heat-retaining furnace, there is a problem in that a difference in the microstructure state near the end and near the center tends to occur in the longitudinal direction of the hot-rolled steel strip.
本発明は、特殊な成分限定や非常に負荷の大きい熱間圧延に頼ることなく製造される熱延鋼帯であって、酸洗のため従来の製造方法でも通板させる必要がある連続焼鈍酸洗設備にて短時間の焼鈍に供するだけで、鋼帯の長手方向いずれの場所においても、再結晶フェライト相からなる軟質なマトリックス（金属素地）中に炭化物が分布した耐リジング性の確保に有利な組織状態が得られる性質を具備するフェライト系ステンレス鋼熱延鋼帯を提供しようというものである。また、その熱延鋼帯を用いた熱延焼鈍鋼帯の製造方法を開示する。 The present invention is a hot-rolled steel strip that is manufactured without resorting to special component limitations or extremely heavy hot rolling, and is a continuous annealing acid that needs to be passed through a conventional manufacturing method for pickling. It is advantageous for securing ridging resistance in which carbides are distributed in a soft matrix (metal substrate) composed of recrystallized ferrite phase at any location in the longitudinal direction of the steel strip simply by subjecting it to annealing in a washing facility for a short time. It is an object of the present invention to provide a ferritic stainless steel hot-rolled steel strip having the property of obtaining a satisfactory structural state. Moreover, the manufacturing method of the hot-rolled annealing steel strip using the hot-rolled steel strip is disclosed.
上記目的は、質量％で、Ｃ：０.０２０〜０.１５０％、Ｓｉ：０.１０〜１.００％、Ｍｎ：０.１０〜１.００％、Ｎｉ：０.０１〜０.６０％、Ｃｒ：１１.００〜１９.００％、Ｍｏ：０〜０.５０％、Ｃｕ：０〜０.５０％、Ａｌ：０〜０.１００％、Ｃｏ：０〜０.１０％、Ｖ：０〜０.２０％、Ｂ：０〜０.０１０％、Ｎ：０.００１〜０.０５０％、残部Ｆｅおよび不可避的不純物からなる化学組成を有する熱延鋼帯であって、熱間圧延の最終パス後に巻き取られたコイルの最外周に相当する位置（後端部）、および最外周よりも内周側かつ最内周から数えて２周目よりも外周側に相当する位置（中間部）のいずれにおいても、再結晶フェライト相と未再結晶フェライト相で構成されるマトリックス（金属素地）中に炭化物が分布し、圧延方向および板厚方向に平行な断面（Ｌ断面）の平均硬さが２３０ＨＶ以上かつ最大硬さが３００ＨＶ以下である組織状態を呈する、フェライト系ステンレス鋼熱延鋼帯によって達成される。熱延鋼帯の板厚は例えば３.０〜７.０ｍｍとすることができる。 The purpose is mass%, C: 0.020 to 0.150%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, Ni: 0.01 to 0.60. %, Cr: 11.00 to 19.00%, Mo: 0 to 0.50%, Cu: 0 to 0.50%, Al: 0 to 0.100%, Co: 0 to 0.10%, V A hot-rolled steel strip having a chemical composition comprising: 0 to 0.20%, B: 0 to 0.010%, N: 0.001 to 0.050%, the balance Fe and inevitable impurities, A position (rear end portion) corresponding to the outermost periphery of the coil wound after the final pass of rolling, and a position corresponding to the outer peripheral side from the innermost side than the outermost periphery and from the innermost periphery (second end) In any of the intermediate portions), carbides are distributed in the matrix (metal substrate) composed of the recrystallized ferrite phase and the non-recrystallized ferrite phase, and the rolling direction and The average hardness of the parallel to the thickness direction cross section (L cross section) exhibits a tissue condition or more and the maximum hardness of 230HV is less than 300 HV, is achieved by a ferritic stainless steel hot rolled strip. The thickness of the hot-rolled steel strip can be set to 3.0 to 7.0 mm, for example.
ここで、Ｍｏ、Ｃｕ、Ａｌ、Ｃｏ、Ｖ、Ｂは任意含有元素である。
本発明の対象となる規格鋼種としては例えばＪＩＳ Ｇ４３０５：２０１２の表５に規定されるＳＵＳ４３０が挙げられる。
上記の炭化物は主としてＭ23Ｃ6（ＭはＣｒ等の金属元素）タイプのものである。
Here, Mo, Cu, Al, Co, V, and B are arbitrarily contained elements.
Examples of standard steel types that are the subject of the present invention include SUS430 defined in Table 5 of JIS G4305: 2012.
The above carbides are mainly of the M 23 C 6 (M is a metal element such as Cr) type.
Ｌ断面の硬さにおいて、「最大硬さが３００ＨＶ以下である」とは、ＪＩＳ Ｚ２２４４：２００９に従うマイクロビッカース硬さ試験でＨＶ０.０５（試験力Ｆ＝０.４９０３Ｎ）にてＬ断面内を測定することにより得られる測定値が、当該Ｌ断面内いずれの位置においても３００ＨＶを超えないことを意味する。
Ｌ断面の平均硬さは、ＪＩＳ Ｚ２２４４：２００９に従う低試験力ビッカース硬さ試験でＨＶ１（試験力Ｆ＝９.８０７Ｎ）にてＬ断面内に無作為に選択した２０箇所以上の位置について上記の方法で硬さを測定し、それらの測定値を平均することによって求めることができる。
Regarding the hardness of the L cross section, “the maximum hardness is 300 HV or less” means that the inside of the L cross section is measured by HV 0.05 (test force F = 0.4903N) in a micro Vickers hardness test according to JIS Z2244: 2009. This means that the measured value obtained by doing so does not exceed 300 HV at any position in the L cross section.
The average hardness of the L cross section is the above for 20 or more positions randomly selected in the L cross section with HV1 (test force F = 9.807N) in the low test force Vickers hardness test according to JIS Z2244: 2009. It can be determined by measuring the hardness with a method and averaging the measured values.
巻き取られたコイルにおいて「最内周から数えて２周目よりも外周側」とは、巻かれた鋼板の層がコイル内周側に２層以上存在している部位を意味する。例えば最内周を１層目とするとき、最内周から２層目の部分は前記の部位に該当せず、最内周から３層目の部分は前記の部位に該当する。 In the wound coil, “the outer peripheral side than the second round counted from the innermost circumference” means a portion where two or more layers of the wound steel sheet are present on the inner circumference side of the coil. For example, when the innermost circumference is the first layer, the portion of the second layer from the innermost circumference does not correspond to the above portion, and the portion of the third layer from the innermost circumference corresponds to the above portion.
上記の熱延鋼板は、８００℃以上かつ下記（２）式で定義されるＡＣ（Ａ）点（℃）未満の温度に昇温したのち常温まで冷却する熱処理に供することにより、再結晶フェライト相からなるマトリックス中に炭化物が分布し、Ｌ断面の平均硬さが２００ＨＶ以下である組織状態となる性質を有するものである。
ＡＣ（Ａ）（℃）＝−２２１Ｃ−４０Ｍｎ−８０Ｎｉ−２４７Ｎ＋６４Ｓｉ＋２０Ｃｒ＋１２４０Ａｌ＋６０２ …（２）
ここで、（２）式の元素記号の箇所には当該元素の質量％で表される含有量の値が代入される。上記の熱処理は、８００℃以上ＡＣ（Ａ）点未満の範囲に設定した温度ＴM（℃）まで昇温したのち、炉から取り出して空冷する方法で行えばよい。ＴMは材料の最高到達温度であり、鋼板の材料温度は表面温度の測定値によって表すことができる。ＴMを８２０℃以上ＡＣ（Ａ）点未満の範囲に設定するように熱処理条件を管理してもよい。
The above hot-rolled steel sheet is subjected to a heat treatment in which the temperature is raised to a temperature of 800 ° C. or higher and lower than the AC (A) point (° C.) defined by the following formula (2), and then cooled to room temperature. The carbide is distributed in the matrix made of and has a property of becoming an organization state in which the average hardness of the L cross section is 200 HV or less.
AC (A) (° C.) = − 221C−40Mn−80Ni−247N + 64Si + 20Cr + 1240Al + 602 (2)
Here, the value of the content expressed by mass% of the element is substituted for the element symbol in the formula (2). The above heat treatment may be performed by a method in which the temperature is raised to a temperature T M (° C.) set to a range of 800 ° C. or more and less than the AC (A) point, and then taken out from the furnace and air-cooled. T M is the maximum temperature reached by the material, and the material temperature of the steel sheet can be expressed by a measured value of the surface temperature. The heat treatment conditions may be managed so that T M is set to a range of 820 ° C. or more and less than the AC (A) point.
上記熱延鋼帯の製造方法として、上記化学組成を有する鋳片を１０００〜１２５０℃に加熱したのち炉から出し、粗圧延機を用いて板材とし、次いで仕上熱延機を用いて複数パスの仕上熱延を行い、仕上熱延の初パス開始から最終パス終了までの間に６５０℃以上かつ下記（１）で定義されるＡＣ点（℃）未満の温度域での滞在時間を材料の長手方向の全ての位置で３００秒以上確保して熱延鋼帯を得る工程（熱延工程）を有する、フェライト系ステンレス鋼熱延鋼帯の製造方法が提供される。
ＡＣ（℃）＝−２５０Ｃ−６６Ｍｎ−１１５Ｎｉ−１８Ｃｕ−２８０Ｎ＋７３Ｓｉ＋３５Ｃｒ＋６０Ｍｏ＋７５０Ａｌ＋３１０ …（１）
ここで、（１）式の元素記号の箇所には当該元素の質量％で表される含有量の値が代入される。
As a method for producing the hot-rolled steel strip, the slab having the above chemical composition is heated to 1000 to 1250 ° C. and then taken out of the furnace, and is made into a plate material using a rough rolling mill, and then a plurality of passes using a finishing hot-rolling machine After finishing hot rolling, the residence time in the temperature range of 650 ° C or higher and less than the AC point (° C) defined in (1) below is defined as the length of the material. There is provided a method for producing a ferritic stainless steel hot-rolled steel strip having a step (hot-rolling step) of obtaining a hot-rolled steel strip by securing 300 seconds or more at all positions in the direction.
AC (° C.) = − 250C−66Mn−115Ni−18Cu−280N + 73Si + 35Cr + 60Mo + 750Al + 310 (1)
Here, the value of the content expressed by mass% of the element is substituted for the element symbol in the formula (1).
また、その熱延鋼帯を用いた熱延焼鈍鋼帯の製造方法として、前記熱延鋼帯に、連続焼鈍炉を用いて８００℃以上かつ下記（２）式で定義されるＡＣ（Ａ）点（℃）未満に加熱する熱処理を施す工程（熱延板焼鈍工程）を有する、フェライト系ステンレス鋼熱延焼鈍鋼帯の製造方法が提供される。 Moreover, as a manufacturing method of the hot-rolled annealed steel strip using the hot-rolled steel strip, AC (A) defined by the following formula (2) at 800 ° C. or higher using a continuous annealing furnace for the hot-rolled steel strip There is provided a method for producing a ferritic stainless steel hot-rolled annealed steel strip having a step (hot-rolled plate annealing step) for performing a heat treatment to be heated to a temperature lower than the point (° C).
本発明の熱延鋼帯を用いると、バッチ式焼鈍炉による長時間の熱延板焼鈍を行うことなく、軟質で加工性に優れたフェライト系ステンレス鋼の熱延焼鈍鋼板を得ることが可能である。本発明の熱延鋼帯を製造するための熱間圧延工程においては、高温域での特段の強加工や、高圧下率の圧延パスを特に必要としない。また、鋼の成分組成に厳しい制限を加えることもなく、汎用規格鋼種であるＳＵＳ４３０を適用することができる。この熱延鋼帯を用いて得た軟質な熱延焼鈍鋼板では、結晶方位のランダム化が進行しているので、それを加工して得られる冷延製品の耐リジング性確保にも有効である。 By using the hot-rolled steel strip of the present invention, it is possible to obtain a hot rolled annealed steel sheet of ferritic stainless steel that is soft and excellent in workability without performing long-time hot-rolled sheet annealing in a batch-type annealing furnace. is there. In the hot rolling process for producing the hot-rolled steel strip of the present invention, special strong working in a high temperature region and a rolling pass at a high pressure reduction rate are not particularly required. Further, SUS430, which is a general-purpose standard steel type, can be applied without severely restricting the component composition of steel. In the soft hot-rolled annealed steel sheet obtained by using this hot-rolled steel strip, the randomization of crystal orientation is progressing, so it is also effective in securing ridging resistance of cold-rolled products obtained by processing it. .
〔化学組成〕
本発明では、フェライト系ステンレス鋼種を対象とする。以下、鋼の化学組成に関する「％」は特に断らない限り「質量％」を意味する。
[Chemical composition]
In the present invention, a ferritic stainless steel type is targeted. Hereinafter, “%” regarding the chemical composition of steel means “mass%” unless otherwise specified.
Ｃは、オーステナイト生成元素であり、熱間圧延中のフェライト結晶粒粗大化防止のために有効である。０.０２０％以上のＣ含有量を確保することが望ましい。ただし、多量のＣ含有は加工性の低下を招く。Ｃ含有量は０.１５０％以下であることが望ましく、０.１００％未満であることがより好ましい。 C is an austenite-forming element and is effective for preventing ferrite crystal grain coarsening during hot rolling. It is desirable to ensure a C content of 0.020% or more. However, if a large amount of C is contained, workability is reduced. The C content is preferably 0.150% or less, and more preferably less than 0.100%.
Ｓｉは、脱酸作用を有する元素であるが、多量に含有すると加工性、靱性の低下要因となる。一方、過度の低Ｓｉ化は精錬コストの増大に繋がる。Ｓｉ含有量は０.１０〜１.００％とする。０.２０〜０.７０％の範囲に管理してもよい。 Si is an element having a deoxidizing action, but if it is contained in a large amount, it causes a decrease in workability and toughness. On the other hand, excessively low Si leads to an increase in refining costs. The Si content is 0.10 to 1.00%. You may manage in the range of 0.20 to 0.70%.
Ｍｎは、オーステナイト生成元素であり、熱間圧延中のフェライト結晶粒粗大化防止のために有効である。０.１０％以上のＭｎ含有量を確保することが望ましく、０.２５％以上であることがより好ましい。多量のＭｎ含有は加工性、耐食性の低下を招く。Ｍｎ含有量は１.００％以下の範囲とする。 Mn is an austenite-forming element and is effective for preventing ferrite crystal grain coarsening during hot rolling. It is desirable to ensure a Mn content of 0.10% or more, and more preferably 0.25% or more. A large amount of Mn content causes deterioration of workability and corrosion resistance. The Mn content is in the range of 1.00% or less.
Ｎｉは、オーステナイト生成元素であり、熱間圧延中のフェライト結晶粒粗大化防止のために有効である。また、靱性や耐食性の向上にも有効である。Ｎｉ含有量は０.０１〜０.６０％の範囲で調整することが望ましく、０.０５〜０.３０％の範囲に管理してもよい。 Ni is an austenite-forming element and is effective for preventing ferrite crystal grain coarsening during hot rolling. It is also effective in improving toughness and corrosion resistance. The Ni content is desirably adjusted in the range of 0.01 to 0.60%, and may be controlled in the range of 0.05 to 0.30%.
Ｃｒは、耐食性の観点から１１.００％以上の含有量を確保する必要がある。ただし、多量のＣｒ含有は加工性低下、靱性低下、コスト増大を招くので、１９.００％以下の範囲に制限される。より好ましいＣｒ含有量範囲は１６.００〜１８.００％である。 From the viewpoint of corrosion resistance, Cr needs to ensure a content of 11.00% or more. However, since a large amount of Cr causes workability reduction, toughness reduction, and cost increase, it is limited to a range of 19.00% or less. A more preferable Cr content range is 16.00 to 18.00%.
Ｍｏは、Ｃｒ含有鋼の耐食性改善に有効であり、必要に応じて添加することができる。０.０１％以上のＭｏ含有量を確保することがより効果的である。過剰のＭｏ含有は加工性低下、コスト増大を招く。Ｍｏを添加する場合は０.５０％以下の範囲で行うことが望ましく、０.１５％以下の範囲に管理してもよい。 Mo is effective in improving the corrosion resistance of the Cr-containing steel, and can be added as necessary. It is more effective to secure a Mo content of 0.01% or more. Excessive Mo content causes a decrease in workability and an increase in cost. When adding Mo, it is desirable to carry out in the range of 0.50% or less, and you may manage in the range of 0.15% or less.
Ｃｕは、オーステナイト生成元素であり、熱間圧延中のフェライト結晶粒粗大化防止のために有効であることから、必要に応じて添加することができる。０.０１％以上のＣｕ含有量を確保することがより効果的である。過剰のＣｕ含有は耐食性や加工性の低下を招く。Ｃｕを添加する場合は０.５０％以下の範囲で行うことが望ましく、０.１５％以下の範囲に管理してもよい。 Cu is an austenite-forming element and is effective for preventing ferrite crystal grain coarsening during hot rolling, and therefore can be added as necessary. It is more effective to secure a Cu content of 0.01% or more. Excessive Cu content causes a decrease in corrosion resistance and workability. When adding Cu, it is desirable to carry out in the range of 0.50% or less, and you may manage in the range of 0.15% or less.
Ａｌは、Ｎを固定し高純度化に寄与し、フェライト系ステンレス鋼の加工性を改善する上で有効な元素であるため、必要に応じて添加することができる。０.０１０％以上のＡｌ含有量を確保することがより効果的である。ただし、過剰のＡｌ添加はコスト増大を招くので、Ａｌを添加する場合は０.１００％以下の含有量範囲で行うことが望ましい。 Al is an element that fixes N and contributes to high purity and is effective in improving the workability of ferritic stainless steel, and therefore can be added as necessary. It is more effective to secure an Al content of 0.010% or more. However, excessive addition of Al causes an increase in cost. Therefore, when adding Al, it is desirable that the content be within a range of 0.100% or less.
Ｂは、高温でのオーステナイト相を微細分散化する作用があるので、必要に応じて添加することができる。０.００１％以上のＢ含有量を確保することがより効果的である。多量のＢ含有は溶接高温割れを引き起こす要因となるので、Ｂを添加する場合は０.０１０％以下の含有量範囲で行うことが望ましい。 B has the effect of finely dispersing the austenite phase at a high temperature, and can be added as necessary. It is more effective to secure a B content of 0.001% or more. A large amount of B content causes welding hot cracking, so when B is added, it is desirable that the content be within a range of 0.010% or less.
Ｎは、オーステナイト生成元素であり、熱間圧延中のフェライト結晶粒粗大化防止のために有効である。０.００１％以上のＮ含有量であることが望ましい。ただし、多量のＮ含有は加工性の低下を招く。Ｎ含有量は０.０５０％以下であることが望ましく、０.０３５％以下であることがより好ましい。 N is an austenite-forming element and is effective for preventing ferrite crystal grain coarsening during hot rolling. It is desirable that the N content is 0.001% or more. However, a large amount of N causes a decrease in workability. The N content is desirably 0.050% or less, and more preferably 0.035% or less.
その他、Ｃｏを必要に応じて０.１０％以下の範囲で含有することができる。また、Ｖを必要に応じて０.２０％以下の範囲で含有することができる。 In addition, Co can be contained in the range of 0.10% or less as required. Moreover, V can be contained in the range of 0.20% or less as required.
上記以外の残部はＦｅおよび製造上不可避的に混入しうる不純物元素である。一般的なフェライト系ステンレス鋼の溶製工程で、通常の原料や、前の溶製チャージとして別鋼種（例えば、Ｎｂ含有鋼やＴｉ含有鋼）で使用した取鍋などから混入しうる程度の不純物元素は、本発明の課題を達成する上で支障はない。規格鋼種としては、例えば汎用的な鋼種であるＳＵＳ４３０（ＪＩＳ Ｇ４３０５：２０１２の表５）を採用することができる。 The remainder other than the above is Fe and an impurity element which can be inevitably mixed in the production. Impurities that can be mixed from ordinary raw materials or ladle used in other steel types (for example, Nb-containing steel or Ti-containing steel) as a previous melting charge in the melting process of general ferritic stainless steel The element does not hinder the achievement of the object of the present invention. As the standard steel type, for example, SUS430 (Table 5 of JIS G4305: 2012), which is a general-purpose steel type, can be adopted.
〔金属組織〕
本発明に従う熱延鋼帯は、いわゆるａｓ ｈｏｔの状態であるにもかかわらず、鋼帯長手方向の全長にわたってマルテンサイト相が見られず、再結晶フェライト相と未再結晶フェライト相で構成されるマトリックス（金属素地）中に炭化物が分布した組織を有する点に特徴がある。
[Metal structure]
Although the hot-rolled steel strip according to the present invention is in a so-called as hot state, a martensite phase is not seen over the entire length in the longitudinal direction of the steel strip, and is composed of a recrystallized ferrite phase and a non-recrystallized ferrite phase. It is characterized by having a structure in which carbides are distributed in a matrix (metal substrate).
熱延鋼帯中にマルテンサイト相が見られないことから、長時間の熱延板焼鈍を施すことなく、短時間の連続焼鈍にて軟質な熱延焼鈍鋼板が得られる。マルテンサイト相が見られない組織状態であることは、マイクロビッカース硬さ試験ＨＶ０.０５によって測定される圧延方向および板厚方向に平行な断面（Ｌ断面）の最大硬さが３００ＨＶ以下を満たすことによって担保される。 Since no martensite phase is observed in the hot-rolled steel strip, a soft hot-rolled annealed steel sheet can be obtained by short-time continuous annealing without performing hot-rolled sheet annealing for a long time. The fact that the martensite phase is not observed means that the maximum hardness of the cross section (L cross section) parallel to the rolling direction and the plate thickness direction measured by the micro Vickers hardness test HV 0.05 satisfies 300 HV or less. Secured by.
マトリックスのフェライト相のうち、未再結晶フェライト相は加工歪を蓄えており、再結晶フェライト相よりも硬質な部分である。加工歪を蓄えた未再結晶フェライト相が存在しているために、短時間の熱延板焼鈍にてその加工歪のエネルギーを利用した再結晶化が迅速に進行し、加工性の良好な熱延焼鈍鋼板が得られる。軟質な再結晶フェライト相と、それより硬質な未再結晶フェライト相が混在していることは、低試験力ビッカース硬さ試験ＨＶ１によって測定されるＬ断面の平均硬さが２３０ＨＶ以上を満たすことによって担保される。マトリックスに占める再結晶フェライト相の割合は面積率で例えば１０〜３０％である。 Of the ferrite phase of the matrix, the non-recrystallized ferrite phase stores processing strain and is a harder portion than the recrystallized ferrite phase. Since there is an unrecrystallized ferrite phase that stores processing strain, recrystallization using the energy of processing strain proceeds rapidly in short-time hot-rolled sheet annealing, and heat with good workability. A annealed steel sheet is obtained. The fact that the soft recrystallized ferrite phase and the harder non-recrystallized ferrite phase are mixed together means that the average hardness of the L cross section measured by the low test force Vickers hardness test HV1 satisfies 230 HV or more. Secured. The ratio of the recrystallized ferrite phase in the matrix is, for example, 10 to 30% in terms of area ratio.
発明者の検討によれば、鋼帯の長手方向全長にわたって上記のような組織状態が得られているかどうかは、熱間圧延の最終パス後に巻き取られたコイルの最外周に相当する位置（後端部）、および最外周よりも内周側かつ最内周から数えて２周目よりも外周側に相当する位置（中間部）の金属組織によって評価できることが確認された。巻き取られた熱延コイルの最外周の部分は、リバース式の仕上熱延機を用いた熱間圧延において材料温度が低下しやすい鋼帯長手方向端部付近に相当する。一方、最外周よりも内周側かつ最内周から数えて２周目よりも外周側の部分は、リバース式の仕上熱延機を用いた熱間圧延において材料温度が高く維持されやすい鋼帯長手方向中央付近と同等の組織状態を呈する。したがって、熱延鋼帯の後端部と中間部の両方において、再結晶フェライト相と未再結晶フェライト相で構成されるマトリックス（金属素地）中に炭化物が分布し、圧延方向および板厚方向に平行な断面（Ｌ断面）の平均硬さが２３０ＨＶ以上かつ最大硬さが３００ＨＶ以下である組織状態を呈していれば、その鋼帯は、長手方向すべての位置で上記の組織状態を呈していると評価することができる。 According to the inventor's study, whether or not the above-described structure state is obtained over the entire length in the longitudinal direction of the steel strip depends on the position corresponding to the outermost periphery of the coil wound after the final pass of hot rolling (rear) It was confirmed that the evaluation can be carried out by the metal structure at the end portion) and the position (intermediate portion) corresponding to the outer peripheral side from the second periphery counting from the innermost peripheral side and the innermost peripheral side. The outermost peripheral portion of the wound hot rolled coil corresponds to the vicinity of the end portion in the longitudinal direction of the steel strip where the material temperature is likely to be lowered in hot rolling using a reverse type finish hot rolling machine. On the other hand, the portion of the inner circumference side from the outermost circumference and the outer circumference side from the second inner circumference is a steel strip that is easily maintained at a high material temperature in hot rolling using a reverse finishing hot rolling machine. It exhibits a tissue state equivalent to that in the vicinity of the center in the longitudinal direction. Therefore, carbide is distributed in the matrix (metal substrate) composed of the recrystallized ferrite phase and the non-recrystallized ferrite phase in both the rear end portion and the intermediate portion of the hot-rolled steel strip, in the rolling direction and the plate thickness direction. If the average hardness of the parallel section (L section) is 230 HV or more and the maximum hardness is 300 HV or less, the steel strip exhibits the above-described structure at all positions in the longitudinal direction. Can be evaluated.
〔熱間圧延工程〕
上記の熱延鋼帯は、例えば、鋳片加熱炉、粗圧延機、リバース式の仕上熱延機、仕上熱延の各圧延パス間で鋼板を巻き取って加熱保持する炉（以下「ファーネスコイラー」と呼ぶ）、および仕上熱延機による最終パス終了後の鋼板を巻き取る巻取装置、を備える熱間圧延設備により製造することができる。以下、この設備構成にて熱延鋼帯を製造する手法を例示する。
[Hot rolling process]
The hot-rolled steel strip is, for example, a furnace (hereinafter referred to as “furnescoiler”) that winds and holds a steel plate between rolling passes of a slab heating furnace, a rough rolling mill, a reverse type finishing hot rolling mill, and a finishing hot rolling roll. And a winding device for winding the steel sheet after the final pass by the finishing hot rolling machine. Hereinafter, the method of manufacturing a hot-rolled steel strip with this equipment configuration will be exemplified.
（鋳片加熱）
熱延工程に供する鋳片としては連続鋳造スラブを適用することが好適である。鋳片を鋳片加熱炉に装入して１０００〜１２５０℃に加熱する。鋳片加熱の温度が低すぎると熱間変形抵抗が過大となりやすく、温度が高すぎるとエネルギーコストや耐火物の維持コストなどの面で不利となる。鋳片の加熱保持時間（上記温度範囲での均熱時間）は例えば５０〜１６０分とすればよい。なお、鋳片の厚さは例えば２００〜２５０ｍｍである。
(Slab heating)
It is preferable to apply a continuous casting slab as the slab to be subjected to the hot rolling process. The slab is charged into a slab heating furnace and heated to 1000 to 1250 ° C. If the slab heating temperature is too low, the hot deformation resistance tends to be excessive, and if the temperature is too high, it is disadvantageous in terms of energy costs and refractory maintenance costs. The heating and holding time of the slab (soaking time in the above temperature range) may be, for example, 50 to 160 minutes. The thickness of the slab is, for example, 200 to 250 mm.
（粗圧延）
加熱後の鋳片を炉から出し、粗圧延機を用いて板厚を減じ、例えば板厚２０〜３０ｍｍ程度の板材（中間製品）を得る。粗圧延での圧延は５〜７パス程度で行えばよい。粗圧延最終パスの圧延温度（その圧延パスに供する直前の板材の表面温度）が８５０℃を超え１０００℃以下となるように各パスのタイミングを管理することがより効果的である。
(Rough rolling)
The heated slab is taken out from the furnace, and the plate thickness is reduced using a roughing mill to obtain a plate material (intermediate product) having a plate thickness of about 20 to 30 mm, for example. The rolling in rough rolling may be performed in about 5 to 7 passes. It is more effective to manage the timing of each pass so that the rolling temperature of the final rough rolling pass (surface temperature of the plate immediately before being used for the rolling pass) exceeds 850 ° C. and is 1000 ° C. or less.
（仕上熱延）
ＳＵＳ４３０に代表されるフェライト系ステンレス鋼は、高温域にフェライト＋オーステナイト２相温度域を有する。従来一般的な熱延工程では、オーステナイト相が冷却過程でマルテンサイト相に変態するので、通常、熱延鋼板はフェライト相＋マルテンサイト相の組織となる。また、仕上圧延を連続式圧延機（タンデムミル）で行う従来一般的な生産手法では、数秒で仕上圧延が終わってしまうのでフェライト相の再結晶が進行せず、圧延後の伸長した組織である未再結晶フェライト相となる。これらのことから従来一般的な熱延工程で製造された熱延鋼板は未再結晶フェライト相＋マルテンサイト相を有している。そのような組織状態から軟質な焼鈍組織を得るためには、マルテンサイト相を「再結晶フェライト相＋炭化物」に分解する必要があるが、この分解反応には１時間以上の長時間の焼鈍が必要なため、バッチ式焼鈍炉を用いて焼鈍する必要があった。
(Finish hot rolling)
Ferritic stainless steel represented by SUS430 has a ferrite + austenite two-phase temperature range in a high temperature range. In the conventional general hot rolling process, the austenite phase transforms into a martensite phase during the cooling process, and thus the hot rolled steel sheet usually has a structure of ferrite phase + martensite phase. In addition, in the conventional general production method in which finish rolling is performed by a continuous rolling mill (tandem mill), the finish rolling is completed in a few seconds, so recrystallization of the ferrite phase does not proceed, and the structure is elongated after rolling. It becomes a non-recrystallized ferrite phase. From these facts, a hot-rolled steel sheet produced by a conventional general hot-rolling process has an unrecrystallized ferrite phase + martensitic phase. In order to obtain a soft annealed structure from such a structural state, it is necessary to decompose the martensite phase into “recrystallized ferrite phase + carbide”, but this decomposition reaction requires a long annealing time of 1 hour or more. Since it was necessary, it was necessary to perform annealing using a batch annealing furnace.
本発明では仕上熱延工程にて比較的短時間で進行する、オーステナイト相からの直接的な「フェライト相＋炭化物」への分解反応を効率よく進行させることで、熱延鋼板の時点でフェライト相の組織にすることが可能となる。オーステナイト相からのフェライト相＋炭化物への分解反応は、仕上圧延の初パス開始から最終パス終了までの過程において、ＡＣ点より低温かつ６５０℃以上の温度域での滞在時間を、鋼板長手方向の全長にわたって、３００秒以上確保することが極めて効果的であることがわかった。ＡＣ点はオーステナイト相が形成し始める温度であり、本発明の対象鋼種では下記（１）式により表される。
ＡＣ（℃）＝−２５０Ｃ−６６Ｍｎ−１１５Ｎｉ−１８Ｃｕ−２８０Ｎ＋７３Ｓｉ＋３５Ｃｒ＋６０Ｍｏ＋７５０Ａｌ＋３１０ …（１）
ここで、（１）式の元素記号の箇所には当該元素の質量％で表される含有量の値が代入される。
In the present invention, the ferrite phase at the time of the hot-rolled steel sheet is efficiently advanced by proceeding the decomposition reaction from the austenite phase directly into the “ferrite phase + carbide”, which proceeds in a relatively short time in the finish hot rolling process. It becomes possible to be an organization. The decomposition reaction from the austenite phase to the ferrite phase and carbides takes place in the longitudinal direction of the steel sheet in the process from the start of the first pass of finish rolling to the end of the final pass. It was found that securing 300 seconds or more over the entire length is extremely effective. The AC point is a temperature at which the austenite phase starts to form, and is represented by the following formula (1) in the target steel type of the present invention.
AC (° C.) = − 250C−66Mn−115Ni−18Cu−280N + 73Si + 35Cr + 60Mo + 750Al + 310 (1)
Here, the value of the content expressed by mass% of the element is substituted for the element symbol in the formula (1).
ＡＣ点より低温での滞在時間を十分に確保することにより、フェライト相からオーステナイト相への変態を抑制しオーステナイト相からフェライト相への変態を十分に進行させることでオーステナイト相からのフェライト相＋炭化物への分解反応が進行し、上述した組織状態を実現することができる。最終パス温度が６５０℃を下回るような条件ではオーステナイト相からのフェライト相＋炭化物への分解反応が進行しづらくなる。また、最終パス温度がＡＣ点以上であったり、ＡＣ点より低温での滞在時間が３００秒未満であったりする条件では、オーステナイト相からのフェライト相＋炭化物への分解反応が不十分で熱延鋼板にマルテンサイト相が残留する組織状態となりやすい。 By ensuring a sufficient residence time at a temperature lower than the AC point, the transformation from the ferrite phase to the austenite phase is suppressed, and the transformation from the austenite phase to the ferrite phase is sufficiently advanced, so that the ferrite phase + carbide from the austenite phase The decomposition reaction proceeds to the above-described tissue state. Under the condition that the final pass temperature is lower than 650 ° C., the decomposition reaction from the austenite phase to the ferrite phase + carbide hardly proceeds. Moreover, under the condition that the final pass temperature is higher than the AC point or the stay time at a temperature lower than the AC point is less than 300 seconds, the decomposition reaction from the austenite phase to the ferrite phase + carbide is insufficient and hot rolling is performed. It tends to be in a structure state in which the martensite phase remains on the steel plate.
一般的にフェライト系ステンレス鋼では動的再結晶が起こりにくい。そのため、再結晶化を進行させるには、静的再結晶の促進を重視する必要がある。しかし、熱延工程の仕上圧延を連続式圧延機（タンデムミル）で行う従来一般的な生産手法では、数秒で圧延が終わってしまうので、静的再結晶はほとんど起こらない。その結果、鋳造組織に起因する方位の近い結晶の集合組織（コロニー）が熱延工程で分解されず、後の冷延工程でも残留するため、冷延鋼板表面にリジングが発生する。 In general, dynamic recrystallization hardly occurs in ferritic stainless steel. Therefore, in order to proceed with recrystallization, it is necessary to emphasize the promotion of static recrystallization. However, in the conventional general production method in which the finish rolling in the hot rolling process is performed by a continuous rolling mill (tandem mill), since the rolling is completed in a few seconds, static recrystallization hardly occurs. As a result, a crystal texture (colony) having a close orientation due to the cast structure is not decomposed in the hot rolling process and remains in the subsequent cold rolling process, so that ridging occurs on the surface of the cold rolled steel sheet.
本発明に従う熱延鋼板はリバース式の仕上熱延機を用いて、圧延パス間で鋼板を炉中に巻き取って加熱することで、圧下時に導入された歪のエネルギーを活用した静的再結晶を進行させ、圧延によって破壊されたコロニーの結晶方位のランダム化を進行させる。保持する温度はフェライト相の再結晶が効率良く進行する８００℃以上が最も効率がよいが上述のようにオーステナイト相への変態が進行してしまうため、温度はＡＣ点以下に制限される。ただし、ＡＣ点より低温かつ６５０℃以上の温度域での滞在時間を、鋼帯長手方向の全長にわたって、３００秒以上確保する条件下でも結晶方位のランダム化が十分に進行していることがわかった。静的再結晶を繰り返し再結晶組織となったフェライト相は最終パスにて再び圧延され伸長した未再結晶組織となるが、最終パス後の温度は７００℃以下まで低下しているため再結晶は一部表面しか進行せず、本発明に従う熱延鋼板は再結晶フェライト相と未再結晶フェライト相の金属組織を有する。 The hot-rolled steel sheet according to the present invention uses a reverse type finish hot-rolling machine to wind the steel sheet in a furnace between rolling passes and heat it, thereby utilizing static recrystallization utilizing the energy of strain introduced during rolling And randomizing the crystal orientation of the colonies destroyed by rolling. The temperature to be maintained is best at 800 ° C. or higher at which recrystallization of the ferrite phase proceeds efficiently, but since the transformation to the austenite phase proceeds as described above, the temperature is limited to the AC point or lower. However, it is understood that the randomization of crystal orientation is sufficiently advanced even under the condition that the residence time in the temperature range lower than the AC point and higher than 650 ° C. is ensured over 300 seconds over the entire length in the longitudinal direction of the steel strip. It was. The ferrite phase that has been recrystallized after repeated static recrystallization becomes an unrecrystallized structure that has been rolled and elongated again in the final pass, but since the temperature after the final pass has decreased to 700 ° C. or lower, Only a part of the surface proceeds, and the hot-rolled steel sheet according to the present invention has a metal structure of a recrystallized ferrite phase and a non-recrystallized ferrite phase.
仕上熱延のパス回数は例えば５〜９パス程度とすることができる。仕上熱延後の板厚は例えば３.０〜７.０ｍｍの範囲で設定すればよい。仕上熱延機によるトータル圧延率は、粗圧延終了後の板厚および熱延鋼板の目標板厚に応じて設定されるが、７０％以上のトータル圧延率とすることが圧下・加熱保持サイクルを十分繰り返すうえで有利である。トータル圧延率の上限については使用する設備の能力によって制約を受けるが、通常は９０％以下の範囲で設定すればよい。 The number of finishing hot rolling passes can be, for example, about 5 to 9 passes. What is necessary is just to set the board thickness after finishing hot rolling in the range of 3.0-7.0 mm, for example. The total rolling rate by the finishing hot rolling machine is set according to the plate thickness after the rough rolling and the target plate thickness of the hot rolled steel plate, but the total rolling rate of 70% or more should be reduced / heated holding cycle. It is advantageous to repeat enough. The upper limit of the total rolling rate is limited by the capacity of the equipment to be used, but is usually set within a range of 90% or less.
仕上熱延機を用いた各圧延パスの圧下率は１０〜３５％の範囲で設定することが好ましい。圧下率を１０％以上とすることで歪の導入効果が高まる。圧下率が３５％を超える圧延パスは設備へ過剰な負担を与えやすい。設備へ与える負荷をできるだけ軽減し、かつ効率的に静的再結晶を進行させる手法として、各パスでの圧下率の平均値（平均圧下率）を２５％未満に抑えたパススケジュールを採用することがより効果的である。 The rolling reduction of each rolling pass using a finishing hot rolling machine is preferably set in the range of 10 to 35%. The effect of introducing strain is enhanced by setting the rolling reduction to 10% or more. A rolling pass with a rolling reduction exceeding 35% tends to place an excessive burden on the equipment. Adopting a pass schedule in which the average value of the rolling reduction (average rolling reduction) at each pass is suppressed to less than 25% as a method to reduce the load on the equipment as much as possible and to promote static recrystallization efficiently. Is more effective.
仕上熱延の最終パスを終えた鋼板は、巻取装置で巻き取り、そのまま常温大気中で放冷すればよい。巻取温度は６００℃未満とすることが好ましく、５７０℃未満とすることがより好ましい。巻取温度が高いと、巻取後の放冷中に、仕上熱延の最終パスで導入した歪が解放されやすくなり、加工歪の蓄積量が減少する。その場合、次工程で行う短時間の熱延板焼鈍で歪エネルギーを積極的に利用して未再結晶フェライト相を迅速に再結晶化することが難しくなる。既に加工歪の解放は停止しているため、巻取温度を過度に低下させる必要はない。通常、４００℃以上の温度で巻き取ればよい。 The steel plate that has finished the final pass of finishing hot rolling may be wound by a winding device and allowed to cool in the normal temperature atmosphere as it is. The coiling temperature is preferably less than 600 ° C, and more preferably less than 570 ° C. When the winding temperature is high, the strain introduced in the final pass of the finish hot rolling is easily released during the cooling after winding, and the accumulated amount of processing strain is reduced. In that case, it becomes difficult to rapidly recrystallize the non-recrystallized ferrite phase by positively utilizing strain energy by short-time hot-rolled sheet annealing performed in the next step. Since the release of the processing strain has already stopped, it is not necessary to excessively lower the winding temperature. Usually, the winding may be performed at a temperature of 400 ° C. or higher.
〔熱延板焼鈍工程〕
上記のようにして得られたフェライト系ステンレス鋼熱延鋼帯は再結晶フェライト相と未再結晶フェライト相の金属組織を有するため、短時間の熱延板焼鈍を施すことによって、加工性が良好な軟質の熱延焼鈍鋼板とすることができる。この焼鈍には一般的な連続焼鈍酸洗設備を利用することができる。
[Hot rolled sheet annealing process]
Since the ferritic stainless steel hot-rolled steel strip obtained as described above has a metal structure of recrystallized ferrite phase and non-recrystallized ferrite phase, workability is good by performing short-time hot-rolled sheet annealing. And a soft hot-rolled annealed steel sheet. For this annealing, general continuous annealing pickling equipment can be used.
熱延板焼鈍温度は、最高到達温度ＴMが８００℃以上かつ下記（２）式で定義されるＡＣ（Ａ）点（℃）未満となる条件で行う。
ＡＣ（Ａ）（℃）＝−２２１Ｃ−４０Ｍｎ−８０Ｎｉ−２４７Ｎ＋６４Ｓｉ＋２０Ｃｒ＋１２４０Ａｌ＋６０２ …（２）
ここで、（２）式の元素記号の箇所には当該元素の質量％で表される含有量の値が代入される。
The hot-rolled sheet annealing temperature is performed under the condition that the maximum temperature T M is 800 ° C. or more and less than the AC (A) point (° C.) defined by the following equation (2).
AC (A) (° C.) = − 221C−40Mn−80Ni−247N + 64Si + 20Cr + 1240Al + 602 (2)
Here, the value of the content expressed by mass% of the element is substituted for the element symbol in the formula (2).
ＳＵＳ４３０に代表されるフェライト系ステンレス鋼は、高温域にオーステナイト＋フェライト２相温度域を有する。オーステナイト相が安定に存在しない低温域から昇温して行く場合、長時間保持したときに２相が共存する温度であっても、短時間の保持では２相が共存するには至らない（すなわちオーステナイト相が形成されない）ことがある。保持時間が短いほど実際にオーステナイト相が形成し始める温度は高くなる傾向にある。また、上述の熱間圧延工程では、スラブは例えば１０００℃以上の高温で十分に加熱を受けることによって、Ｃが鋼中に完全に固溶している組織状態となる。これに対し熱延板焼鈍工程では、Ｃが炭化物として存在している低温域からの昇温となるので、フェライト相がオーステナイト相に変態するには炭化物中のＣが鋼中に拡散して固溶する必要がある。このようなことから、炭化物が存在する低温域から昇温して最高到達温度ＴMに達したのち降温させる短時間の熱延板焼鈍工程においては、オーステナイト相が形成し始める温度はＡＣ点より高い温度となる。このときの、熱延板焼鈍（Ａｎｎｅａｌｉｎｇ）における、オーステナイト相が形成し始める温度をＡＣ（Ａ）点とする。最高到達温度ＴMがＡＣ（Ａ）点以上になると、オーステナイト相が形成され、その後の冷却過程でマルテンサイト相に変態して残留する。最高到達温度ＴMが８００℃を下回ると短時間での再結晶化が十分に果たせない場合がある。ＴMは８２０℃以上とすることがより好ましい。連続焼鈍炉での熱延板焼鈍における焼鈍時間に関しては特にこだわる必要はない。連続焼鈍炉の仕様にもよるが、通常、材料温度が８００℃以上ＴM以下、より好ましくは８２０℃以上ＴM以下の範囲内に保持される時間が０〜６０秒の範囲で実施すれば十分である。 Ferritic stainless steel represented by SUS430 has an austenite + ferrite two-phase temperature range in a high temperature range. When the temperature is raised from a low temperature range where the austenite phase does not exist stably, even if the temperature is such that the two phases coexist when held for a long time, the two phases do not coexist when held for a short time (ie, Austenite phase may not be formed). The shorter the holding time, the higher the temperature at which the austenite phase actually starts to form. Moreover, in the above-mentioned hot rolling process, the slab is sufficiently heated at a high temperature of, for example, 1000 ° C., so that C is completely in a solid solution in the steel. On the other hand, in the hot-rolled sheet annealing process, the temperature rises from a low temperature region where C exists as a carbide. Therefore, in order to transform the ferrite phase into the austenite phase, C in the carbide diffuses into the steel and solidifies. It is necessary to melt. For this reason, in a short hot-rolled sheet annealing process in which the temperature is raised from a low temperature region where carbides are present and reaches the maximum temperature T M and then the temperature is lowered, the temperature at which the austenite phase begins to form is higher than the AC point. High temperature. At this time, the temperature at which the austenite phase starts to be formed in hot-rolled sheet annealing (Annealing) is defined as an AC (A) point. When the maximum temperature T M becomes equal to or higher than the AC (A) point, an austenite phase is formed, and in the subsequent cooling process, it transforms into a martensite phase and remains. When the maximum temperature T M is lower than 800 ° C., recrystallization in a short time may not be sufficiently achieved. T M is more preferably 820 ° C. or higher. There is no need to pay particular attention to the annealing time in hot-rolled sheet annealing in a continuous annealing furnace. Although it depends on the specifications of the continuous annealing furnace, the material temperature is usually 800 ° C. or higher and T M or lower, more preferably 820 ° C. or higher and T M or lower in a range of 0 to 60 seconds. It is enough.
この熱延板焼鈍においては、熱延鋼板中に存在する未再結晶フェライト相に蓄えられていた歪エネルギーを利用して再結晶が進行する。熱間圧延においてオーステナイト相からフェライト相と炭化物への分解は完結し、コロニーは十分に分解されているため、連続焼鈍炉を用いた短時間の焼鈍によってマトリックスは結晶方位のランダム化の進んだ再結晶フェライト相となる。
このようにして、再結晶フェライト相からなるマトリックス中に炭化物が分布し、板厚方向に平行な断面（Ｌ断面）の平均硬さが２００ＨＶ以下である組織状態を呈する熱延焼鈍鋼板が得られる。
In this hot-rolled sheet annealing, recrystallization proceeds using the strain energy stored in the non-recrystallized ferrite phase present in the hot-rolled steel sheet. In hot rolling, the decomposition of the austenite phase to the ferrite phase and carbide has been completed, and the colonies have been sufficiently decomposed, so that the matrix has been recrystallized with randomized crystal orientation by short-time annealing using a continuous annealing furnace. It becomes a crystalline ferrite phase.
In this way, a hot-rolled annealed steel sheet is obtained in which a carbide is distributed in a matrix composed of a recrystallized ferrite phase, and an average hardness of a cross section (L cross section) parallel to the thickness direction is 200 HV or less. .
〔冷間圧延・焼鈍工程〕
上記の熱延焼鈍鋼板は一般的なフェライト系ステンレス鋼冷延焼鈍鋼板の製造ラインにより冷延焼鈍鋼板とすることができる。バッチ式焼鈍炉による長時間の熱延板焼鈍を省略しているにもかかわらず、冷間圧延→焼鈍の工程を１回行うだけで、耐リジング性に優れた冷延焼鈍鋼板の製品材が得られる。目標板厚に応じて冷間圧延→焼鈍の工程を複数回行うことができる。最終焼鈍前の冷間圧延率は例えば３０〜９０％とすることができ、焼鈍温度は例えば８００〜９００℃とすることができる。最終的な冷延焼鈍鋼板の板厚は例えば０.３〜４.０ｍｍの範囲で調整すればよい。
[Cold rolling and annealing process]
The hot-rolled annealed steel sheet can be a cold-rolled annealed steel sheet using a general ferritic stainless steel cold-rolled annealed steel sheet production line. Despite the omission of long-time hot-rolled sheet annealing in a batch-type annealing furnace, the product of cold-rolled annealed steel sheets with excellent ridging resistance can be obtained by performing only one process of cold rolling → annealing. can get. The process of cold rolling → annealing can be performed a plurality of times according to the target plate thickness. The cold rolling rate before final annealing can be set to 30 to 90%, for example, and the annealing temperature can be set to 800 to 900 ° C., for example. What is necessary is just to adjust the plate | board thickness of the final cold-rolled annealing steel plate in the range of 0.3-4.0 mm, for example.
表１に示すＳＵＳ４３０系の鋼を溶製し、連続鋳造スラブを得た。 SUS430 steel shown in Table 1 was melted to obtain a continuous cast slab.
連続鋳造スラブをスラブ加熱炉で加熱した後、炉から出し、粗圧延および仕上熱延を施し、巻き取ることにより熱延鋼板とした。粗圧延に供する際の連続鋳造スラブの板厚は約２００ｍｍである。鋳片（連続鋳造スラブ）の加熱は、１０５０℃、均熱１時間とした。粗圧延は合計５パスの圧下で行い、板厚２０ｍｍの粗圧延材を得た。この粗圧延材を仕上熱延設備に搬送し、仕上熱延に供した。 After the continuous cast slab was heated in the slab heating furnace, it was taken out of the furnace, subjected to rough rolling and finish hot rolling, and wound to obtain a hot rolled steel sheet. The thickness of the continuous cast slab when subjected to rough rolling is about 200 mm. The slab (continuous casting slab) was heated at 1050 ° C. for 1 hour. Rough rolling was carried out under a total of 5 passes to obtain a rough rolled material having a plate thickness of 20 mm. This rough rolled material was conveyed to a finishing hot rolling facility and subjected to finishing hot rolling.
仕上熱延機はリバース式であり、ミルの両側に各圧延パス間で鋼板を巻き取って加熱保持する炉（ファーネスコイラー）を備えている。仕上熱延の総パス数は７パスとし、各パス間でファーネスコイラーによる加熱処理を行った。圧延時の材料温度は、ワークロールに噛み込まれる直前の鋼板表面温度を測定することによって求めた。仕上熱延の最終パス終了後の板厚は３.５〜４.０ｍｍであり、鋼帯の全長が５７０℃未満の温度域で巻き取られるように、最終パス終了後の冷却速度を調整した。 The finishing hot rolling machine is of a reverse type, and is equipped with a furnace (furnace coiler) that winds and holds a steel plate between each rolling pass on both sides of the mill. The total number of passes for finishing hot rolling was 7 passes, and a heat treatment by a furnace coiler was performed between each pass. The material temperature at the time of rolling was calculated | required by measuring the steel plate surface temperature just before biting into a work roll. The plate thickness after the final pass of finish hot rolling is 3.5 to 4.0 mm, and the cooling rate after the final pass is adjusted so that the entire length of the steel strip is wound in a temperature range of less than 570 ° C. .
仕上熱延では、圧延時の通板速度（圧延速度）を調整することにより、「実施例」および「比較例」の２通りのヒートパターンにて圧延を行った。ファーネスコイラーの設定温度（炉温）はいずれも８３０℃とした。 In the finish hot rolling, rolling was performed with two heat patterns of “Example” and “Comparative Example” by adjusting the sheeting speed (rolling speed) during rolling. The set temperature (furnace temperature) of the furnace coiler was 830 ° C.
図１に、初パス開始からの経過時間と、各パスでの材料温度の関係を示す。図１（ａ）は奇数パスで鋼帯の後端部となり、偶数パスで鋼帯の先端部となる部位について、各パス圧延温度のプロットを結んだものである。図１（ｂ）は鋼帯の長手方向中央の部位について、各パス圧延温度のプロットを結んだものである。鋼帯の長手方向端部は、後端部となるパスと先端部となるパスの間でのファーネスコイラー収容時間が短いので、鋼帯の長手方向中央部に比べて仕上熱延中の温度低下が大きくなりやすい。一般的には、圧延速度を速くするほど最終パス終了までの所要時間が短くなるので、生産性の観点からは有利となる。しかし、圧延速度が大きくなるほど、鋼帯長手方向の両端部と中央部の圧延温度に開きが生じやすくなる。ここでは、鋼帯長手方向の端部では図１（ａ）に示される通り、実施例、比較例とも、仕上熱延の初パス開始から最終パス終了までの間で６５０℃以上かつＡＣ点（実施例：８０７℃、比較例：７９３℃）未満の温度域での滞在時間を３００秒以上確保することができている。一方、鋼帯長手方向の中央部では図１（ｂ）に示される通り、圧延速度を比較例よりも遅くコントロールした実施例においてのみ、初パス開始から最終パス終了までの間で６５０℃以上かつＡＣ点（℃）未満の温度域での滞在時間を３００秒以上確保することが可能であった。 FIG. 1 shows the relationship between the elapsed time from the start of the first pass and the material temperature in each pass. FIG. 1A shows a plot of each pass rolling temperature for a portion that becomes the rear end portion of the steel strip in the odd-numbered pass and the tip portion of the steel strip in the even-numbered pass. FIG.1 (b) connects the plot of each pass rolling temperature about the center part of the longitudinal direction of a steel strip. The steel coil longitudinal end has a shorter furnace coiler storage time between the rear end and the front end pass, so the temperature drop during finish hot rolling is lower than the longitudinal center of the steel strip. Tends to grow. In general, the higher the rolling speed, the shorter the time required to complete the final pass, which is advantageous from the viewpoint of productivity. However, as the rolling speed increases, the rolling temperature at both ends and the center in the longitudinal direction of the steel strip is likely to be widened. Here, at the end in the longitudinal direction of the steel strip, as shown in FIG. 1 (a), both the example and the comparative example are 650 ° C. or higher and AC point ( (Example: 807 ° C., comparative example: 793 ° C.) The residence time in the temperature range below 300 seconds can be secured. On the other hand, as shown in FIG. 1 (b), at the central portion in the longitudinal direction of the steel strip, only in an example in which the rolling speed was controlled slower than that of the comparative example, 650 ° C. or more between the start of the first pass and the end of the final pass. It was possible to secure a stay time of 300 seconds or more in a temperature range below the AC point (° C.).
得られた熱延コイルについて、最終パスでの「後端部」に相当するコイルの最外周の位置、および鋼帯長手方向の「中央部」に相当する位置からサンプルを採取し、Ｌ断面の組織観察およびＬ断面内の硬さ測定を行った。上記の「中央部」は、「最外周よりも内周側かつ最内周から数えて２周目よりも外周側」の要件を満たす部位である。 About the obtained hot-rolled coil, a sample was taken from the position of the outermost circumference of the coil corresponding to the “rear end” in the final pass and the position corresponding to the “center” in the longitudinal direction of the steel strip. Structure observation and hardness measurement in the L cross section were performed. The above-mentioned “central part” is a part that satisfies the requirements of “inner peripheral side from the outermost periphery and outer peripheral side from the second periphery counted from the innermost periphery”.
図２に、比較例の熱延鋼帯におけるＬ断面の光学顕微鏡写真およびＨＶ０.０５にて硬さ測定を行った結果を例示する。図３に、実施例の熱延鋼帯におけるＬ断面の光学顕微鏡写真およびＨＶ０.０５にて硬さ測定を行った結果を例示する。いずれも（ａ）は長手方向後端部、（ｂ）は長手方向中央部である。図２および図３の硬さ測定は、最大硬さ測定のため、マイクロビッカース硬度計にてＨＶ０.０５で各相に照準を合わせて測定し、図中の値はバラツキ範囲と平均値を示してある。ここで、αは再結晶フェライト相、Ｍはマルテンサイト相を意味する。その他、平均硬さ測定のため、ビッカース硬度計にてＨＶ１で無作為に選択した２０箇所以上の位置について硬さを測定した。 In FIG. 2, the result of having performed hardness measurement by the optical micrograph of the L cross section in the hot-rolled steel strip of a comparative example, and HV0.05 is illustrated. In FIG. 3, the result of having performed hardness measurement by the optical micrograph of the L cross section in the hot-rolled steel strip of an Example, and HV0.05 is illustrated. In either case, (a) is the longitudinal rear end, and (b) is the longitudinal center. The hardness measurements in FIGS. 2 and 3 are measured with a micro Vickers hardness tester aiming at each phase at HV 0.05 for maximum hardness measurement, and the values in the figures show the variation range and average value. It is. Here, α means a recrystallized ferrite phase and M means a martensite phase. In addition, in order to measure the average hardness, the hardness was measured at 20 or more positions randomly selected with HV1 using a Vickers hardness tester.
組織観察および硬さ測定の結果、比較例の熱延鋼帯では、長手方向中央部の金属組織にマルテンサイト相が認められ、その最大硬さは３００ＨＶを超えていた。これに対し、実施例の熱延鋼帯は、鋼帯長手方向後端部、中央部ともにマルテンサイト相は観察されず、Ｌ断面硬さは、長手方向後端部で平均硬さ２３６ＨＶ、最大硬さ２５４ＨＶであり、長手方向中央部で平均硬さ２４７ＨＶ、最大硬さ２５１ＨＶであった。実施例の熱延鋼帯は鋼帯全長にわたって再結晶フェライト相と未再結晶フェライト相で構成されるマトリックス（金属素地）中に炭化物が分布した組織状態を呈すると認められる。 As a result of the structure observation and the hardness measurement, in the hot rolled steel strip of the comparative example, a martensite phase was observed in the metal structure in the central portion in the longitudinal direction, and the maximum hardness exceeded 300 HV. On the other hand, in the hot-rolled steel strip of the example, the martensite phase is not observed in the longitudinal end portion and the central portion of the longitudinal direction of the steel strip, and the L section hardness is an average hardness of 236 HV, the maximum at the longitudinal end portion. The hardness was 254 HV, and the average hardness was 247 HV and the maximum hardness was 251 HV at the center in the longitudinal direction. It is recognized that the hot-rolled steel strip of the example exhibits a structure state in which carbides are distributed in a matrix (metal base) composed of a recrystallized ferrite phase and an unrecrystallized ferrite phase over the entire length of the steel strip.
熱延鋼帯から採取した上記サンプルを用いて、ＡＣ（Ａ）点未満である８５０℃まで昇温したのち、すぐに炉から出して空冷にて冷却する熱処理を施した。その結果、Ｌ断面の平均硬さは、比較例では鋼帯長手方向中央部で１７１ＨＶ、後端部で１６８ＨＶであり、実施例では鋼帯長手方向中央部で１７４ＨＶ、後端部で１７３ＨＶであった。この焼鈍後の金属組織を観察すると、実施例の鋼帯にはマルテンサイト相は認められなかった。しかし、比較例の鋼帯には、長手方向中央部に図２と同様のマルテンサイト相の存在が認められた。したがって、「鋼帯の長手方向いずれの場所においても、再結晶フェライト相からなる軟質なマトリックス（金属素地）中に炭化物が分布した組織状態を実現する」という本発明の課題は、実施例では達成されたが、比較例では達成されなかった。 Using the sample taken from the hot-rolled steel strip, the temperature was raised to 850 ° C., which is less than the AC (A) point, and then immediately subjected to heat treatment that was removed from the furnace and cooled by air cooling. As a result, the average hardness of the L cross section was 171 HV at the central portion in the steel strip longitudinal direction and 168 HV at the rear end portion in the comparative example, and 174 HV at the central portion in the longitudinal direction of the steel strip in the example, and 173 HV at the rear end portion. It was. When the metal structure after the annealing was observed, no martensite phase was observed in the steel strip of the example. However, in the steel strip of the comparative example, the presence of the same martensitic phase as in FIG. Therefore, the object of the present invention “achieving a microstructure in which carbides are distributed in a soft matrix (metal substrate) made of a recrystallized ferrite phase at any location in the longitudinal direction of the steel strip” is achieved in the embodiments. However, it was not achieved in the comparative example.
Claims (6)
ＡＣ（Ａ）（℃）＝−２２１Ｃ−４０Ｍｎ−８０Ｎｉ−２４７Ｎ＋６４Ｓｉ＋２０Ｃｒ＋１２４０Ａｌ＋６０２ …（２）
ここで、（２）式の元素記号の箇所には当該元素の質量％で表される含有量の値が代入される。 By heating to 800 ° C. or higher and lower than the AC (A) point (° C.) defined by the following formula (2), and then cooling to room temperature, carbides are contained in the matrix composed of the recrystallized ferrite phase. The ferritic stainless steel hot-rolled steel strip according to any one of claims 1 to 3, wherein the ferritic stainless steel hot-rolled steel strip has a property of being distributed and having a structure state in which an average hardness of an L cross section is 200 HV or less.
AC (A) (° C.) = − 221C−40Mn−80Ni−247N + 64Si + 20Cr + 1240Al + 602 (2)
Here, the value of the content expressed by mass% of the element is substituted for the element symbol in the formula (2).
ＡＣ（℃）＝−２５０Ｃ−６６Ｍｎ−１１５Ｎｉ−１８Ｃｕ−２８０Ｎ＋７３Ｓｉ＋３５Ｃｒ＋６０Ｍｏ＋７５０Ａｌ＋３１０ …（１）
ここで、（１）式の元素記号の箇所には当該元素の質量％で表される含有量の値が代入される。 In mass%, C: 0.020 to 0.150%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, Ni: 0.01 to 0.60%, Cr: 11.0 to 19.00%, Mo: 0 to 0.50%, Cu: 0 to 0.50%, Al: 0 to 0.100%, Co: 0 to 0.10%, V: 0 to 0 .20%, B: 0 to 0.010%, N: 0.001 to 0.050%, a slab having a chemical composition composed of the balance Fe and inevitable impurities is heated to 1000 to 1250 ° C. and then taken out of the furnace. , Using a rough rolling mill to obtain a plate material, and then performing a finishing hot rolling of a plurality of passes using a finishing hot rolling machine, and at least 650 ° C. between the start of the first pass of finishing hot rolling and the end of the final pass (1) A hot rolled steel strip is obtained by securing a residence time in a temperature range below the AC point (° C) defined by ≥300 seconds at all positions in the longitudinal direction of the material. Method for producing a preparative stainless steel hot rolled strip.
AC (° C.) = − 250C−66Mn−115Ni−18Cu−280N + 73Si + 35Cr + 60Mo + 750Al + 310 (1)
Here, the value of the content expressed by mass% of the element is substituted for the element symbol in the formula (1).
前記熱延鋼帯に、連続焼鈍炉を用いて８００℃以上かつ下記（２）式で定義されるＡＣ（Ａ）点（℃）未満に加熱する熱処理を施す工程（熱延板焼鈍工程）、
を有する、フェライト系ステンレス鋼熱延焼鈍鋼帯の製造方法。
ＡＣ（℃）＝−２５０Ｃ−６６Ｍｎ−１１５Ｎｉ−１８Ｃｕ−２８０Ｎ＋７３Ｓｉ＋３５Ｃｒ＋６０Ｍｏ＋７５０Ａｌ＋３１０ …（１）
ＡＣ（Ａ）（℃）＝−２２１Ｃ−４０Ｍｎ−８０Ｎｉ−２４７Ｎ＋６４Ｓｉ＋２０Ｃｒ＋１２４０Ａｌ＋６０２ …（２）
ここで、（１）式および（２）式の元素記号の箇所には当該元素の質量％で表される含有量の値が代入される。 In mass%, C: 0.020 to 0.150%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.00%, Ni: 0.01 to 0.60%, Cr: 11.0 to 19.00%, Mo: 0 to 0.50%, Cu: 0 to 0.50%, Al: 0 to 0.100%, Co: 0 to 0.10%, V: 0 to 0 .20%, B: 0 to 0.010%, N: 0.001 to 0.050%, a slab having a chemical composition composed of the balance Fe and inevitable impurities is heated to 1000 to 1250 ° C. and then taken out of the furnace. , Using a rough rolling mill to obtain a plate material, and then performing a finishing hot rolling of a plurality of passes using a finishing hot rolling machine, and at least 650 ° C. between the start of the first pass of finishing hot rolling and the end of the final pass (1) A process for obtaining a hot-rolled steel strip by securing a residence time in a temperature range below the AC point (° C.) defined by the above in all positions in the longitudinal direction of the material for 300 seconds or longer (heat Process),
A step of applying heat treatment to the hot-rolled steel strip using a continuous annealing furnace to heat to 800 ° C or higher and less than the AC (A) point (° C) defined by the following formula (2) (hot-rolled plate annealing step),
A method for producing a ferritic stainless steel hot-rolled annealed steel strip.
AC (° C.) = − 250C−66Mn−115Ni−18Cu−280N + 73Si + 35Cr + 60Mo + 750Al + 310 (1)
AC (A) (° C.) = − 221C−40Mn−80Ni−247N + 64Si + 20Cr + 1240Al + 602 (2)
Here, the value of the content expressed by mass% of the element is substituted for the element symbol in the expressions (1) and (2).
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