JP4624691B2 - Method for producing ferritic stainless steel slab - Google Patents
Method for producing ferritic stainless steel slab Download PDFInfo
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- JP4624691B2 JP4624691B2 JP2004036527A JP2004036527A JP4624691B2 JP 4624691 B2 JP4624691 B2 JP 4624691B2 JP 2004036527 A JP2004036527 A JP 2004036527A JP 2004036527 A JP2004036527 A JP 2004036527A JP 4624691 B2 JP4624691 B2 JP 4624691B2
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- 238000004519 manufacturing process Methods 0.000 title claims description 22
- 229910001220 stainless steel Inorganic materials 0.000 title claims description 22
- 238000001816 cooling Methods 0.000 claims description 28
- 238000000034 method Methods 0.000 claims description 16
- 238000003303 reheating Methods 0.000 claims description 13
- 238000009749 continuous casting Methods 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 2
- 238000010438 heat treatment Methods 0.000 description 33
- 230000007797 corrosion Effects 0.000 description 24
- 238000005260 corrosion Methods 0.000 description 24
- 238000007670 refining Methods 0.000 description 19
- 238000005336 cracking Methods 0.000 description 16
- 230000003647 oxidation Effects 0.000 description 16
- 238000007254 oxidation reaction Methods 0.000 description 16
- 238000005266 casting Methods 0.000 description 14
- 229910000831 Steel Inorganic materials 0.000 description 12
- 239000010959 steel Substances 0.000 description 12
- 230000009467 reduction Effects 0.000 description 10
- 230000007547 defect Effects 0.000 description 9
- 230000000694 effects Effects 0.000 description 9
- 238000010583 slow cooling Methods 0.000 description 7
- 239000012071 phase Substances 0.000 description 6
- 239000002436 steel type Substances 0.000 description 6
- 239000002244 precipitate Substances 0.000 description 5
- 229910000859 α-Fe Inorganic materials 0.000 description 5
- 239000000463 material Substances 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 3
- 229910052804 chromium Inorganic materials 0.000 description 3
- 229910052758 niobium Inorganic materials 0.000 description 3
- 230000007704 transition Effects 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000001681 protective effect Effects 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000000137 annealing Methods 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000005489 elastic deformation Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000005764 inhibitory process Effects 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
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- Heat Treatment Of Steel (AREA)
Description
本発明はフェライト系ステンレス鋼連続鋳造鋳片における課題である内部割れが無くスケールロスを低減し、かつコスト，能率への阻害を最小限とする製造方法に関するものである。 The present invention relates to a production method that eliminates internal cracks, which is a problem in ferritic stainless steel continuous cast slabs, reduces scale loss, and minimizes cost and efficiency.
ＳＵＳ４３０鋼で代表されるフェライト系ステンレス鋼は高価なＮｉを大量に含まず安価であるため、自動車外装部品や建築内装品などの比較的マイルドな腐食環境で表面の美麗さを要求される用途に広く用いられている。ＳＵＳ３０４鋼で代表されるオーステナイト系ステンレス鋼に比べて一般的に耐食性が劣るため用途が限定されていたが、近年では例えば特許文献１に示されているごとく高Ｃｒ化およびＮｂ，Ｔｉ，Ｍｏ等の添加により、ＳＵＳ３０４や鋼種によってはＳＵＳ３１６と同レベルの耐銹性を持った鋼種が登場し、オーステナイト系ステンレス鋼と全く同様もしくは応力腐食割れ感受性がない利点を生かした用途に広く使用されている。 Since ferritic stainless steel represented by SUS430 steel does not contain a large amount of expensive Ni and is inexpensive, it is suitable for applications that require a beautiful surface in a relatively mild corrosive environment such as automobile exterior parts and building interior parts. Widely used. Although its corrosion resistance is generally inferior compared to austenitic stainless steel typified by SUS304 steel, its use has been limited. In recent years, for example, as shown in Patent Document 1, high Cr and Nb, Ti, Mo, etc. With the addition of SUS304 and some steel types, steel types with the same level of weather resistance as SUS316 have appeared and are widely used in applications that take advantage of the same as austenitic stainless steels or no stress corrosion cracking susceptibility. .
上記の高耐食鋼種の場合、耐食性を劣化させるＣ，Ｎを極力低減させる必要があり、これらはオーステナイト生成元素であるため低減すると全温度でオーステナイト相に変態しないオールフェライト鋼となる。フェライト系ステンレス鋼はオーステナイト系と比べ元々靱性に劣るが、オールフェライト鋼もしくはごく少量のオーステナイト相のみ生じる鋼は鋳造時に固相変態を生じないかごく少量であることから鋳片粒のサイズがｍｍ単位の非常に大きなものとなり、特に低靱性となる。それに加え、耐食性向上のために添加するＮｂ等は靱性を更に低下させる。 In the case of the above high corrosion resistance steel types, it is necessary to reduce C and N, which deteriorate the corrosion resistance, as much as possible. Since these are austenite-generating elements, all ferrite steel that does not transform into the austenite phase at all temperatures is obtained. Ferritic stainless steel is originally inferior in toughness compared to austenitic, but all ferritic steel or steel that produces only a small amount of austenitic phase has a very small amount that does not cause solid phase transformation during casting. It becomes a very large unit, and particularly has low toughness. In addition, Nb or the like added for improving corrosion resistance further reduces toughness.
この低靱性のフェライト系ステンレス鋼の場合、製造時に問題となるのが、連続鋳造による鋳片が冷却時に割れる内部割れである。これは、鋳片冷却時の外内面の温度差に起因して生じる引張残留応力により、鋳片の横断面もしくは表面と平行に生じる大きな割れであり、再加熱中に鋳片が折損する等の重大な事故の原因となる。 In the case of this low toughness ferritic stainless steel, a problem that occurs at the time of manufacture is an internal crack in which a slab formed by continuous casting cracks during cooling. This is a large crack that occurs parallel to the cross section or the surface of the slab due to the tensile residual stress caused by the temperature difference between the outer and inner surfaces during slab cooling, and the slab breaks during reheating. It may cause a serious accident.
この対策として従来は、徐冷炉等により８００℃付近から１００℃付近までを徐冷する方法、鋳片の延性―脆性遷移温度が３００℃付近にあることから３００℃以下に冷却することなく再加熱する方法（特許文献１）や、３００℃になる前に再加熱し軽圧下をする方法（特許文献２）、更には３００℃になるまでに再加熱し８００〜１３００℃で１〜１０時間加熱後３００℃まで平均４０℃／ｈｒ以下で徐冷する方法（特許文献３）が開示されている。 Conventionally, as a countermeasure, a method of gradually cooling from about 800 ° C. to about 100 ° C. by using a slow cooling furnace or the like, the ductile-brittle transition temperature of the slab is near 300 ° C., and reheating without cooling to 300 ° C. The method (Patent Document 1), the method of reheating and lowering the pressure before reaching 300 ° C (Patent Document 2), and further heating to 800 ° C and heating at 800 to 1300 ° C for 1 to 10 hours A method of slow cooling to 300 ° C. at an average of 40 ° C./hr or less (Patent Document 3) is disclosed.
しかしながらこれらの方法は、上記問題を解決するには不適切であったり、他の問題を生じるものである。まず徐冷するという方法は、その速度を５℃／ｈｒ程度まで低下しても効果がなく、たとえそれ以下にすることで効果があったとしてもコスト的に不利である。３００℃以下に冷却しないという対策は、当該鋼において延性−脆性遷移温度が２００℃程度であり、従って、脆性域を一度も通らずに済ますという意味で確実かつ適切な方法ではあるが、鋳造と圧延を必ず同一タイミングで行うという製造制約の非常に大きい方法をとるのでない限り、数日〜数週間に渡って３００℃以上をキープする保定熱処理を行う必要があり、該当鋼鋳片を全て熱処理する大規模な設備を必要とするのみならず、製造工程の自由度とコストを大きく阻害する方法であると言える。軽圧下をする方法は上記の阻害を解決することは出来るが、軽圧下の設備を設置する必要がある。 However, these methods are inappropriate for solving the above-mentioned problems and cause other problems. First, the method of slow cooling is ineffective even if the rate is reduced to about 5 ° C./hr, and it is disadvantageous in terms of cost even if it is effective at lower than that. The measure of not cooling to below 300 ° C is a reliable and appropriate method in the sense that the ductile-brittle transition temperature is about 200 ° C in the steel, and therefore it is not necessary to pass through the brittle region. Unless you take a very large manufacturing constraint method that always performs rolling at the same timing, it is necessary to perform a holding heat treatment that keeps the temperature above 300 ° C for several days to several weeks. In addition to requiring large-scale equipment, it can be said that the method greatly hinders the freedom and cost of the manufacturing process. Although the method of light reduction can solve the above-mentioned obstacles, it is necessary to install equipment under light pressure.
一方、特許文献４に示される方法は、該処理を行った後は冷片に出来るため製造工程の自由度が高く、設備として必要なのは熱処理炉だけであり、熱処理時間も数時間のみのためコスト、能率の阻害も最小限度であることから、最も効果的な方法と言える。しかしながら残った問題として、８００〜１３００℃という高温の熱処理を実施するためスケールロスが無視出来ないことがある。 On the other hand, the method disclosed in Patent Document 4 has a high degree of freedom in the manufacturing process because it can be made into a cold piece after the treatment, and only a heat treatment furnace is required as equipment, and the heat treatment time is only a few hours. This is the most effective method because the inhibition of efficiency is minimal. However, as a remaining problem, since a high-temperature heat treatment of 800 to 1300 ° C. is performed, scale loss cannot be ignored.
本発明は全温度でほとんど全てがフェライト相となるため靱性が非常に低く、鋳造後の冷却時に残留応力による内部割れを生じるフェライト系ステンレス鋼連続鋳造鋳片において、設備費、製造費、製造工程の自由度への阻害を最小限度としつつ、内部割れが無く、キャビティー酸化起因欠陥を低減した製造方法を提供することを目的とするものである。 The present invention has very low toughness because almost all of it becomes a ferrite phase at all temperatures. In a ferritic stainless steel continuous cast slab that causes internal cracks due to residual stress during cooling after casting, the equipment cost, manufacturing cost, manufacturing process It is an object of the present invention to provide a manufacturing method in which there are no internal cracks and defects due to cavity oxidation are reduced while minimizing the hindrance to the degree of freedom.
本発明は上記課題を達成するための方策として、従来技術で検討されてきた鋳造後の温度パターン制御に加え、鋳片鋳造時の条件を規定することに着目し、それによりキャビティー酸化起因欠陥を抑制可能な条件を見出し具現化したものである。 The present invention pays attention to defining the conditions at the time of casting slab casting in addition to the temperature pattern control after casting, which has been studied in the prior art, as a measure for achieving the above-mentioned problems. It is a result of finding and realizing a condition that can suppress this.
本発明の要旨とするところは以下の通りである。
（１）質量％にて、
Ｃ：０．００１〜０．０７％
Ｓｉ：０．０１〜１．０％
Ｍｎ：０．０１〜２．０％
Ｐ：０．０１〜０．０５％
Ｓ：０．０００１〜０．０１％
Ｃｒ：１１〜２５％
Ｎｉ：０．０１〜０．７％
Ａｌ：０．０００５〜０．１％
Ｎ：０．００１〜０．０５％
Ｎｂ：０．００１〜０．８％
を含有し、
残部がＦｅおよび不可避的不純物からなり、かつ１式で示されるγｐｏｔ．が−５０以上２０以下を満足するフェライト系ステンレス鋼鋳片の製造方法において、
前記フェライト系ステンレス鋼を連続鋳造し、
連続鋳造時における１２００〜９００℃の温度域の平均冷却速度を０．２５℃／秒以上に制御し、
続いて少なくとも２００℃以上温度を確保して再加熱炉に装入し、
続いて６５０〜１０００℃の温度範囲で１〜１０時間再加熱する。フェライト系ステンレス鋼鋳片の製造方法。
γｐｏｔ．＝４２０Ｃ＋４７０Ｎ＋２３Ｎｉ＋９Ｃｕ＋７Ｍｎ−１１．５Ｃｒ−
１１．５Ｓｉ−１２Ｍｏ−４７Ｎｂ−５２Ａｌ＋１８９ １式
（２）さらに、質量％にて、
Ｍｏ：０．３〜５．０％
Ｃｕ：０．３〜１．０％
の１種以上含有することを特徴とする請求項１に記載のフェライト系ステンレス鋼鋳片の製造方法。
（３）（１）又は（２）に記載の再加熱後の再加熱温度から５００℃以下までの平均冷却速度が５℃／ｈｒ以上４０℃／ｈｒ以下であることを特徴とするフェライト系ステンレス鋼鋳片の製造方法。
The gist of the present invention is as follows.
(1) In mass%,
C: 0.001 to 0.07%
Si: 0.01 to 1.0%
Mn: 0.01 to 2.0%
P: 0.01-0.05%
S: 0.0001 to 0.01%
Cr: 11-25%
Ni: 0.01 to 0.7%
Al: 0.0005 to 0.1%
N: 0.001 to 0.05%
Nb: 0.001 to 0.8%
Containing
The balance consists of Fe and inevitable impurities, and γpot. In the method for producing a ferritic stainless steel slab satisfying -50 or more and 20 or less,
Continuous casting of the ferritic stainless steel,
The average cooling rate in the temperature range of 1200 to 900 ° C. during continuous casting is controlled to 0.25 ° C./second or more,
Subsequently, ensure a temperature of at least 200 ° C. and insert it into a reheating furnace,
Subsequently, reheating is performed in a temperature range of 650 to 1000 ° C. for 1 to 10 hours. Manufacturing method for ferritic stainless steel slabs.
γpot. = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-
11.5Si-12Mo-47Nb-52Al + 189 Formula 1 (2) Further, in mass%,
Mo: 0.3-5.0%
Cu: 0.3 to 1.0%
The method for producing a ferritic stainless steel slab according to claim 1, wherein the ferritic stainless steel slab is contained.
(3) Ferritic stainless steel characterized in that the average cooling rate from the reheating temperature after reheating according to (1) or (2) to 500 ° C. or less is 5 ° C./hr or more and 40 ° C./hr or less. Steel slab manufacturing method.
本発明によると、全温度でオーステナイト相が生じないかもしくは極少量で残りがフェライト相となるため靱性が非常に低く、鋳造後の冷却時に残留応力による内部割れを生じるようなフェライト系ステンレス鋼連続鋳造鋳片において、設備費、製造費、製造工程の自由度への阻害を最小限度にした上で、内部割れの防止と、キャビティー酸化起因欠陥の低減を両立する事が出来、効率的に高品質の鋼材を製造することが可能となる。 According to the present invention, the austenite phase does not occur at all temperatures, or the remainder becomes a ferrite phase in a very small amount, so the toughness is very low, and a continuous ferritic stainless steel that causes internal cracks due to residual stress during cooling after casting. For cast slabs, it is possible to achieve both the prevention of internal cracking and the reduction of defects caused by cavity oxidation while minimizing the hindrance to equipment costs, manufacturing costs, and freedom of manufacturing processes. It becomes possible to manufacture high-quality steel materials.
以下、発明を詳細に説明する。 Hereinafter, the invention will be described in detail.
当該鋼の内部割れは、前述の通り、鋳片冷却時の外内面の温度差に起因して生じる引張残留応力による脆性割れであるが、割れの起点は粒界等に析出する粗大炭窒化物である。従って、内部割れを低減するには残留応力を低減するか粗大炭窒化物の形態を変更することが有効と言える。 As described above, the internal crack of the steel is a brittle crack due to the tensile residual stress caused by the temperature difference between the outer and inner surfaces when the slab is cooled, but the starting point of the crack is coarse carbonitride that precipitates at grain boundaries, etc. It is. Therefore, it can be said that it is effective to reduce the residual stress or change the form of the coarse carbonitride to reduce the internal crack.
そのうち炭窒化物の形態を制御することについては、前述の特許文献４では後熱処理によって形態制御をしているが、鋳造後の冷却によって析出する際に微細化するのが最も効果的であるにも関わらずこれまで検討されたことは無かった。 Of these, regarding the control of the form of carbonitride, in the above-mentioned Patent Document 4, the form is controlled by post-heat treatment, but it is most effective to make it finer when precipitated by cooling after casting. Nevertheless, it has never been studied.
そこで発明者らは、鋳造後炭窒化物が析出する温度域を急冷することで炭窒化物を微細析出させ、割れ感受性を低める事を考え実験を行った結果、必要な後熱処理温度を低減出来、前述の高温酸化による鋳片キャビティー酸化欠陥を抑制できることを見出し本発明に至ったものである。 Therefore, the inventors conducted an experiment considering that carbonitride is finely precipitated by quenching the temperature range in which carbonitride precipitates after casting, thereby reducing the susceptibility to cracking. The present inventors have found that the above-described slab cavity oxidation defects due to high-temperature oxidation can be suppressed, and have led to the present invention.
一方残留応力は、冷却時に表層と中心の温度差がある場合、熱収縮の不均一が起きることから生じるものである。連続鋳造の場合、凝固時の冷却で十分大きな引張応力が発生するため、上述のような炭窒化物の微細化を図って割れ感受性を高めても割れ防止出来ず、どちらにしても除去工程を加える必要はある。そのためには鋳片をある一定の条件で熱処理すればよい。一定温度以上の熱処理により材料にクリープ現象が生じ残留応力が消失するためである。これに要する温度は材料がクリープする温度以上であり、時間については鋳片全体が一定温度になってさえいれば極短時間で終了する。従って、析出物の形態制御に要するような高温長時間は要しない。 On the other hand, the residual stress is caused by uneven heat shrinkage when there is a temperature difference between the surface layer and the center during cooling. In the case of continuous casting, a sufficiently large tensile stress is generated by cooling during solidification, so cracking cannot be prevented even if the carbonitrides as described above are refined to increase cracking susceptibility. There is a need to add. For this purpose, the slab may be heat-treated under certain conditions. This is because the heat treatment at a certain temperature or more causes a creep phenomenon in the material and the residual stress disappears. The temperature required for this is equal to or higher than the temperature at which the material creeps, and the process is completed in a very short time as long as the entire slab is at a constant temperature. Therefore, a high temperature and a long time required for controlling the form of the precipitate are not required.
一方、熱処理による酸化状況については、実験を行ったところ、通常の燃焼雰囲気熱処理の場合、１０００℃超で急速に酸化量が増え、１０００℃以下における酸化量は比較的少量であることが判明した。これは１０００℃以下の場合Ｃｒリッチスケールが保護被膜の役割を果たし、酸化は一定以上あまり進まないのに対し、１０００℃超ではこの保護効果が消失するためである。 On the other hand, as for the oxidation state by heat treatment, an experiment was conducted, and it was found that in the case of normal combustion atmosphere heat treatment, the oxidation amount rapidly increased above 1000 ° C., and the oxidation amount at 1000 ° C. or less was relatively small. . This is because Cr-rich scale plays the role of a protective film when the temperature is 1000 ° C. or lower, and oxidation does not proceed much more than a certain level, whereas this protective effect disappears when the temperature exceeds 1000 ° C.
以下に本発明の製造方法について工程順を追って説明する。 Hereinafter, the manufacturing method of the present invention will be described in the order of steps.
まず、当該鋼の鋳片を鋳造すると、固溶したＣとＮが１２００〜９００℃の温度域でＮｂまたはＣｒの炭窒化物となって析出する。この析出温度域を平均０．２５℃／秒以上の冷却速度で冷却することにより炭窒化物を微細析出させる。ここで、鋳片温度は鋳片表面温度を意味する。 First, when the steel slab is cast, solid solution C and N are precipitated as carbonitrides of Nb or Cr in a temperature range of 1200 to 900 ° C. By cooling this precipitation temperature range at a cooling rate of 0.25 ° C./second or more on average, carbonitrides are finely precipitated. Here, the slab temperature means the slab surface temperature.
次に脆性域となり割れが発生する２００℃以下にすることなく加熱炉に挿入する。この際の冷却速度、加熱炉における昇温速度については特に規定はない。なぜなら、炭窒化物は既に析出しており、残留応力については以降の熱処理で消失出来る上、２００℃以上の場合になっている限り高応力でも割れを生じないためである。 Next, it inserts into a heating furnace, without making it 200 degreeC or less which becomes a brittle region and a crack generate | occur | produces. There are no particular restrictions on the cooling rate and the heating rate in the heating furnace. This is because carbonitride has already precipitated, and the residual stress can be eliminated by subsequent heat treatment, and cracking does not occur even at high stress as long as the temperature is 200 ° C. or higher.
更に成分に応じた適正温度、時間で熱処理を行う。これは熱処理以前に発生した残留応力をクリープ効果によって消失させるためである。酸化によるスケールロス、中心キャビティー酸化起因欠陥を抑制するため必要以上の高温では熱処理を行わないことが望ましい。 Further, heat treatment is performed at an appropriate temperature and time according to the components. This is because the residual stress generated before the heat treatment is eliminated by the creep effect. In order to suppress scale loss due to oxidation and defects due to central cavity oxidation, it is desirable not to perform heat treatment at a higher temperature than necessary.
再加熱処理が完了した後、冷片とするまでの冷却については、それによって生じる残留応力がさほど大きくはないため必須ではないが、出来る限り低減するためには再加熱温度から５００℃までの平均冷却速度を４０℃／ｈｒ以下の徐冷をし冷片とすればよい。 After the reheating process is completed, the cooling to the cold piece is not essential because the residual stress generated thereby is not so large, but in order to reduce as much as possible, the average from the reheating temperature to 500 ° C What is necessary is just to anneal at a cooling rate of 40 ° C./hr or less to form a cold piece.
この結果、鋳片を常温まで冷却しても割れを起こすことは無くなる。 As a result, no cracking occurs even when the slab is cooled to room temperature.
次に本発明の構成要件の限定理由を示す。 Next, the reasons for limiting the constituent requirements of the present invention will be described.
Ｃは、加工性と耐食性を劣化させるため、その含有量は少ないほど良いが、過度の低下は精錬コストの増加に繋がるため、０．００１〜０．０７％とした。更に、経済性と特性を考慮すると０．００２〜０．０５％が望ましい。 Since C deteriorates workability and corrosion resistance, the smaller the content, the better. However, excessive reduction leads to an increase in refining cost, so 0.001 to 0.07% was set. Furthermore, if considering economy and characteristics, 0.002 to 0.05% is desirable.
Ｓｉは、脱酸元素であるため精錬中に添加されるが、１．０％を超えると加工性が劣化し、０．０１％未満では精錬コストの増加につながる。従って、Ｓｉの範囲は０．０１〜１．０％とした。更に、材質特性を考慮すると０．１〜０．６％が望ましい。 Since Si is a deoxidizing element, it is added during refining. However, if it exceeds 1.0%, workability deteriorates, and if it is less than 0.01%, refining costs increase. Therefore, the range of Si is set to 0.01 to 1.0%. Furthermore, if considering material properties, 0.1 to 0.6% is desirable.
Ｍｎは、加工性と耐食性を劣化させるため、その含有量は少ないほど良いが、過度の低下は精錬コストの増加に繋がると共に、Ｓｉ同様脱酸効果を有することから、０．０１〜２．０％とした。更に、経済性と特性を考慮すると０．１〜０．５％が望ましい。 Since Mn deteriorates workability and corrosion resistance, its content is preferably as small as possible. However, excessive reduction leads to an increase in refining costs and has a deoxidation effect similar to Si. %. Furthermore, if considering the economy and characteristics, 0.1 to 0.5% is desirable.
Ｐは、加工性と耐食性を劣化させるため、その含有量は少ないほど良いが、過度の低下は精錬コストの増加に繋がるため、０．０１〜０．０５％とした。更に、経済性と特性を考慮すると０．０２〜０．０４％望ましい。 P decreases the workability and corrosion resistance, so its content is preferably as small as possible. However, excessive reduction leads to an increase in refining costs, so 0.01 to 0.05% was made. Furthermore, if considering economy and characteristics, 0.02 to 0.04% is desirable.
Ｓは、Ｐと同様で含有量が少ないほど良いが、過度の低下は精錬コストの増加に繋がる。従って、Ｓの範囲は０．０００１〜０．０１％とした。更に、経済性と特性を考慮すると０．０００５〜０．００５％が望ましい。 S is the same as P, and the smaller the content, the better. However, excessive reduction leads to an increase in refining costs. Therefore, the range of S is set to 0.0001 to 0.01%. Furthermore, if considering economy and characteristics, 0.0005 to 0.005% is desirable.
Ｃｒは、耐食性確保のために１１％以上の添加が必要であるが、２５％超の添加により靱性の劣化が生じ、本発明の方法を持ってしても内部割れを抑えることが出来ない。従って、Ｃｒの範囲は１１〜２５％とした。更に、耐食性と加工性の確保という観点では１２〜２０％が望ましい。 Cr needs to be added in an amount of 11% or more in order to ensure corrosion resistance. However, the addition of more than 25% causes toughness deterioration, and internal cracking cannot be suppressed even with the method of the present invention. Therefore, the Cr range is 11-25%. Furthermore, 12 to 20% is desirable from the viewpoint of ensuring corrosion resistance and workability.
Ｎｉは、高価であること、耐応力腐食割れ性を劣化させることから、その含有量は少ないほど良いが、過度の低下は精錬コストの増加に繋がるため、０．０１〜０．７％とした。更に、経済性と特性を考慮すると０．０１〜０．５％が望ましい。 Since Ni is expensive and deteriorates the stress corrosion cracking resistance, its content is preferably as small as possible. However, excessive reduction leads to an increase in refining costs, so 0.01 to 0.7% is set. . Furthermore, if considering the economy and characteristics, 0.01 to 0.5% is desirable.
Ａｌは、脱酸元素であるため精錬中に添加されるが、０．１％を超えると加工性が劣化し、０．０００５％未満では精錬コストの増加につながる。従って、Ａｌの範囲は０．０００５〜０．１％とした。更に、経済性と特性を考慮すると０．００１〜０．０７％が望ましい。 Since Al is a deoxidizing element, it is added during refining. However, if it exceeds 0.1%, workability deteriorates, and if it is less than 0.0005%, refining costs increase. Therefore, the Al range is set to 0.0005 to 0.1%. Furthermore, if considering economy and characteristics, 0.001 to 0.07% is desirable.
Ｎは、Ｃと同様に加工性と耐食性を劣化させるため、その含有量は少ないほど良いが、過度の低下は精錬コストの増加に繋がるため、０．００１〜０．０５％とした。更に、経済性と特性を考慮すると０．００５〜０．０２％が望ましい。 N, like C, deteriorates workability and corrosion resistance, so its content is preferably as small as possible. However, excessive reduction leads to an increase in refining costs, so 0.001 to 0.05% was set. Furthermore, if considering economy and characteristics, 0.005 to 0.02% is desirable.
Ｎｂは、Ｃ，Ｎと析出物を形成し、固溶Ｃ，Ｎを低減し、耐食性を向上させる作用が有るが、過度の添加は激しく靱性低下を生じるため、０．００１〜０．８％とした。更に経済性と特性を考慮すると０．００１〜０．５％が望ましい。 Nb has the effect of forming precipitates with C and N, reducing the solid solution C and N, and improving the corrosion resistance. However, excessive addition causes severe toughness reduction, so 0.001 to 0.8% It was. Furthermore, if considering economy and characteristics, 0.001 to 0.5% is desirable.
Ｍｏ，Ｃｕは必要に応じて添加する。 Mo and Cu are added as necessary.
Ｍｏは、耐食性を向上させる効果があるが、その効果は０．３％以上からで、５．０％を超えると加工性の低下につながる。従って、Ｍｏの望ましい範囲は０．３〜５．０％とした。更に、経済性と耐食性を考慮すると０．５〜２．５％がより望ましい。 Mo has an effect of improving the corrosion resistance, but the effect is from 0.3% or more, and if it exceeds 5.0%, the workability is lowered. Therefore, the desirable range of Mo is set to 0.3 to 5.0%. Furthermore, if considering economy and corrosion resistance, 0.5 to 2.5% is more desirable.
Ｃｕも耐食性を向上させる効果があるが、その効果は０．３％以上からで、１．０％を超えると加工性、耐応力腐食割れ性の低下につながる。従って、Ｃｕの望ましい範囲は０．３〜１．０％とした。更に、特性を考慮すると０．３〜０．７％がより望ましい。 Cu also has an effect of improving the corrosion resistance, but the effect is from 0.3% or more, and if it exceeds 1.0%, the workability and the stress corrosion cracking resistance are reduced. Therefore, the desirable range of Cu is set to 0.3 to 1.0%. Furthermore, if considering the characteristics, 0.3 to 0.7% is more desirable.
更に、本発明で示す残留応力低減工程を必要とするのは、フェライト系ステンレス鋼の中で特に低靱性である、鋳造から室温まで全温度でフェライトとなるか、あるいは極少量のオーステナイト相しか生じない鋼種である。これ以外の鋼種は鋳造後せいぜい炉内徐冷をすることで内部割れを防止できる。 Furthermore, the residual stress reduction step shown in the present invention requires ferrite, which is particularly low toughness among ferritic stainless steels, or becomes a ferrite at all temperatures from casting to room temperature, or only a very small amount of austenite phase is generated. There is no steel grade. For other steel types, internal cracking can be prevented by slow cooling in the furnace after casting.
どの成分系の鋼種が該工程を必要とするかは式１で計算出来るγｐｏｔ．で判断でき、この式の値が２０以下となる成分系の鋼種について本発明の処理が必要となる。 Which component steel type requires this step can be calculated by γpot. Therefore, the processing of the present invention is required for the component steel types in which the value of this equation is 20 or less.
一方、γｐｏｔ．が−６０未満の場合、本発明の処理を持ってしても内部割れを生じるほど靱性が低下する。従って、γｐｏｔ．の範囲は−６０以上２０以下とする。
γｐｏｔ．＝４２０Ｃ＋４７０Ｎ＋２３Ｎｉ＋９Ｃｕ＋７Ｍｎ−１１．５Ｃｒ
−１１．５Ｓｉ−１２Ｍｏ−４７Ｎｂ−５２Ａｌ＋１８９・・・式１
なお、式１において、各元素記号はその元素の含有量（質量％）を表す。
On the other hand, γpot. Is less than −60, the toughness decreases as internal cracks occur even with the treatment of the present invention. Therefore, γpot. The range is from -60 to 20 inclusive.
γpot. = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr
-11.5Si-12Mo-47Nb-52Al + 189 ... Formula 1
In Formula 1, each element symbol represents the content (mass%) of the element.
次に、鋳造時の冷却速度については、１２００から９００℃までの間を平均０．２５℃／秒以上とする。この温度範囲はＮｂまたはＣｒの炭窒化物が析出する温度であり、この間を０．２５℃／秒以上で冷却すると析出する炭窒化物が微細化し、割れ感受性を低めることが出来る。 Next, regarding the cooling rate at the time of casting, between 1200 and 900 degreeC is made into an average 0.25 degreeC / second or more. This temperature range is a temperature at which Nb or Cr carbonitride precipitates, and if this interval is cooled at 0.25 ° C./second or more, the precipitated carbonitride becomes finer and crack susceptibility can be reduced.
加熱炉に挿入するまでの最低温度を２００℃としたのは、２００℃より低温にすると延性領域から脆性領域に遷移しこの時点で割れが発生するためである。 The reason why the minimum temperature until insertion into the heating furnace is 200 ° C. is that if the temperature is lower than 200 ° C., the transition from the ductile region to the brittle region occurs, and cracks occur at this point.
加熱温度については、６５０℃未満ではクリープ現象が事実上全く起きず、残留応力を低減出来ないため、１０００℃を超えると急速に酸化が進みキャビティー酸化起因欠陥が生じるため６５０℃以上１０００℃以下とした。 When the heating temperature is less than 650 ° C., the creep phenomenon does not occur at all and the residual stress cannot be reduced. Therefore, when the temperature exceeds 1000 ° C., oxidation proceeds rapidly and defects due to cavity oxidation occur, resulting in 650 ° C. or more and 1000 ° C. or less. It was.
加熱時間については１時間未満では鋳片中心部の温度が上がりきらず残留応力の低減に至らないため、１０時間を超えても効果が飽和しコストの悪化、スケール量の増加を招くだけなので１時間以上１０時間以下とした。 If the heating time is less than 1 hour, the temperature at the center of the slab does not rise and the residual stress is not reduced. If the heating time exceeds 10 hours, the effect is saturated and the cost is deteriorated and the scale amount is increased. More than 10 hours.
熱処理後の冷却速度については、平均４０℃／ｈｒを超えると、冷却時に再度残留応力が発生し、内部割れの原因となる可能性があるため平均４０℃／ｈｒ以下とした。また、平均５℃／ｈｒ未満では残留応力の低下効果はほとんど無いが徐冷時間が非常に長くなり能率の低下を招くことから平均５℃／ｈｒ以上とした。５００℃未満では熱収縮が塑性変形ではなく弾性変形となり残留応力が増加しないため、上記冷却速度の限定は５００℃までとした。但し、当該規定を外すことによる残留応力の増加は比較的少ないので必須事項ではない。 Regarding the cooling rate after the heat treatment, if the average exceeds 40 ° C./hr, residual stress is generated again during cooling, which may cause internal cracking, so the average is 40 ° C./hr or less. On the other hand, if the average is less than 5 ° C./hr, there is almost no effect of lowering the residual stress, but the annealing time becomes very long and the efficiency is lowered, so the average is set to 5 ° C./hr or more. If the temperature is less than 500 ° C., the heat shrinkage is not plastic deformation but elastic deformation and the residual stress does not increase. Therefore, the cooling rate is limited to 500 ° C. However, the increase in residual stress due to the removal of this rule is not essential since it is relatively small.
次に実施例を示す。フェライト系ステンレス鋼連続鋳造鋳片を鋳造した後、種々の条件で熱処理を行い冷片とし、再び加熱して熱間圧延を行い線材を製造した。内部割れの有無については鋳片を冷片とした時点で一部を切り出し断面を観察することにより評価し、内部割れのあった鋳片の本数から発生率を算出した。内部キャビティー酸化起因欠陥は線材の一部を切り出し断面を観察することにより評価し、線材の本数から発生率を算出した。供試鋼の成分を表１、冷片にするまでの熱処理条件および評価結果を表２に示す。鋳造後の冷却速度は鋳片表面温度を実測することにより求めた。 Next, examples will be described. After casting a ferritic stainless steel continuous cast slab, heat treatment was performed under various conditions to form a cold slab, and heated again to perform hot rolling to produce a wire. The presence or absence of internal cracks was evaluated by cutting out a portion when the slab was made into a cold piece and observing the cross section, and the occurrence rate was calculated from the number of slabs with internal cracks. Internal cavity oxidation-induced defects were evaluated by cutting out part of the wire and observing the cross section, and the occurrence rate was calculated from the number of wires. Table 1 shows the components of the test steel, and Table 2 shows the heat treatment conditions and evaluation results until the specimens are made into cold pieces. The cooling rate after casting was determined by actually measuring the slab surface temperature.
表１のＮｏ．１、２は本発明請求項１の実施例、３〜５は本発明請求項２の実施例である。 No. in Table 1 1 and 2 are embodiments of claim 1 of the present invention, and 3 to 5 are embodiments of claim 2 of the present invention.
Ｎｏ．６〜２７は請求項１の比較例である。Ｎｏ．６はＣが低すぎるため精錬コストが増大し、Ｎｏ．７は高すぎるため加工性、耐食性が劣化する。Ｎｏ．８はＳｉが低すぎるため精錬コストが増大し、Ｎｏ．９は高すぎるため加工性が劣化する。Ｎｏ．１０はＭｎが低すぎるため精錬コストが増大し、Ｎｏ．１１は高すぎるため加工性、耐食性が劣化する。Ｎｏ．１２はＰが低すぎるため精錬コストが増大し、Ｎｏ．１３は高すぎるため加工性、耐食性が劣化する。Ｎｏ．１４はＳが低すぎるため精錬コストが増大し、Ｎｏ．１５は高すぎるため加工性、耐食性が劣化する。Ｎｏ．１６はＣｒが低すぎるため耐食性が不良であり、Ｎｏ．１７は高すぎるため靱性が劣化する。Ｎｏ．１８はＮｉが低すぎるため精錬コストが増大し、Ｎｏ．１９は高すぎるため原料コストが増大し、また耐応力腐食割れ性が劣化する。Ｎｏ．２０はＡｌが低すぎるため精錬コストが増大し、Ｎｏ．２１は高すぎるため加工性が劣化する。Ｎｏ．２２はＮが低すぎるため精錬コストが増大し、Ｎｏ．２３は高すぎるため加工性、耐食性が劣化する。Ｎｏ．２４はＮｂが低すぎるため精錬コストが増大し、Ｎｏ．２５は高すぎるため靱性が劣化する。 No. 6 to 27 are comparative examples of claim 1. No. In No. 6, C is too low, so the refining cost increases. Since 7 is too high, workability and corrosion resistance deteriorate. No. In No. 8, since Si is too low, the refining cost increases. Since 9 is too high, workability deteriorates. No. No. 10 has a too low Mn, so the refining cost increases. Since 11 is too high, workability and corrosion resistance deteriorate. No. No. 12 has too low P, so the refining cost increases. Since 13 is too high, workability and corrosion resistance deteriorate. No. No. 14 has a refining cost increased because S is too low. Since 15 is too high, workability and corrosion resistance deteriorate. No. No. 16 has poor corrosion resistance because Cr is too low. Since No. 17 is too high, toughness deteriorates. No. No. 18 has a refining cost increased because Ni is too low. Since 19 is too high, the raw material cost increases, and the stress corrosion cracking resistance deteriorates. No. In No. 20, since Al is too low, the refining cost increases. Since 21 is too high, workability deteriorates. No. No. 22 has a refining cost increased because N is too low. Since 23 is too high, workability and corrosion resistance deteriorate. No. No. 24 has a low refining cost because Nb is too low. Since 25 is too high, toughness deteriorates.
Ｎｏ．２６はγ．ｐｏｔ値が低すぎるため靱性が不良であり、Ｎｏ．２７は高いことから本発明のような再熱処理を行わずに徐冷のみで内部割れを生じないため除外される。 No. 26 is γ. Since the pot value is too low, the toughness is poor. Since No. 27 is high, it is excluded because it does not cause internal cracking only by slow cooling without reheating as in the present invention.
次に表２については、Ｎｏ．Ａ〜Ｅが本発明例である。加熱パターンを所定のものとすることによって、内部割れ、内部キャビティー酸化起因欠陥どちらも無いものを製造することが可能である。 Next, with respect to Table 2, no. A to E are examples of the present invention. By setting the heating pattern to a predetermined one, it is possible to manufacture one having neither internal cracks nor internal cavity oxidation defects.
Ｎｏ．Ｆ〜Ｎは比較例である。Ｎｏ．Ｆは鋳造後１２００〜９００℃の平均冷却速度が０．２５℃／秒未満の場合であるが、その後に８００℃加熱処理を行っても内部割れを生じた。Ｎｏ．Ｉのように高温加熱をすれば内部割れは防止できるが、内部キャビティー酸化起因欠陥を生じる。Ｎｏ．Ｇは加熱炉装入前に２００℃未満に温度が低下しているため、Ｎｏ．Ｈは加熱温度が６５０℃未満のため、Ｎｏ．Ｊは加熱時間が１時間未満のため、何れも内部割れを生じた。Ｎｏ．Ｉは加熱時間が１０時間超のため内部キャビティー酸化起因欠陥を生じた。 No. F to N are comparative examples. No. F is a case where the average cooling rate of 1200 to 900 ° C. after casting is less than 0.25 ° C./second, but internal cracking occurred even when heat treatment was performed at 800 ° C. thereafter. No. Internal cracking can be prevented by heating at a high temperature as in I, but defects due to internal cavity oxidation occur. No. G has a temperature lower than 200 ° C. before charging the heating furnace. H has a heating temperature of less than 650 ° C. Since J had a heating time of less than 1 hour, all of them had internal cracks. No. I caused defects due to internal cavity oxidation because the heating time exceeded 10 hours.
Ｎｏ．Ｌは加熱後の平均冷却速度が５℃／ｈｒ未満であり、特性上は問題ないが徐冷炉取出まで数日を要し能率が非常に低下する。Ｎｏ．Ｍは加熱後の平均冷却速度が４０℃／ｈｒ超のため、Ｎｏ．Ｎは徐冷終了温度が５００℃超となり、その後が空冷となるため、極少量ではあるが内部割れを生じるため、内部割れを一切生じさせないためには回避すべきである。 No. L has an average cooling rate after heating of less than 5 ° C./hr, and there is no problem in characteristics, but it takes several days to take out the slow cooling furnace, and the efficiency is very low. No. M has an average cooling rate after heating exceeding 40 ° C./hr. N has a slow cooling end temperature of over 500 ° C. and then air cooling, so that although it is a very small amount, an internal crack is generated. Therefore, N should be avoided to prevent any internal crack.
Claims (3)
Ｃ：０．００１〜０．０７％
Ｓｉ：０．０１〜１．０％
Ｍｎ：０．０１〜２．０％
Ｐ：０．０１〜０．０５％
Ｓ：０．０００１〜０．０１％
Ｃｒ：１１〜２５％
Ｎｉ：０．０１〜０．７％
Ａｌ：０．０００５〜０．１％
Ｎ：０．００１〜０．０５％
Ｎｂ：０．００１〜０．８％
を含有し、
残部がＦｅおよび不可避的不純物からなり、かつ１式で示されるγｐｏｔ．が−６０以上２０以下を満足するフェライト系ステンレス鋼鋳片の製造方法において、
前記フェライト系ステンレス鋼を連続鋳造し、
連続鋳造時における１２００〜９００℃の温度域の平均冷却速度を０．２５℃／秒以上に制御し、
続いて少なくとも２００℃以上温度を確保して再加熱炉に装入し、
続いて６５０〜１０００℃の温度範囲で１〜１０時間再加熱することを特徴とする、
フェライト系ステンレス鋼鋳片の製造方法。
γｐｏｔ．＝４２０Ｃ＋４７０Ｎ＋２３Ｎｉ＋９Ｃｕ＋７Ｍｎ−１１．５Ｃｒ−
１１．５Ｓｉ−１２Ｍｏ−４７Ｎｂ−５２Ａｌ＋１８９≦２０ １式 In mass%
C: 0.001 to 0.07%
Si: 0.01 to 1.0%
Mn: 0.01 to 2.0%
P: 0.01-0.05%
S: 0.0001 to 0.01%
Cr: 11-25%
Ni: 0.01 to 0.7%
Al: 0.0005 to 0.1%
N: 0.001 to 0.05%
Nb: 0.001 to 0.8%
Containing
The balance consists of Fe and inevitable impurities, and γpot. In the method for producing a ferritic stainless steel slab satisfying -60 or more and 20 or less,
Continuous casting of the ferritic stainless steel,
The average cooling rate in the temperature range of 1200 to 900 ° C. during continuous casting is controlled to 0.25 ° C./second or more,
Subsequently, ensure a temperature of at least 200 ° C. and insert it into a reheating furnace,
Subsequently, it is reheated in a temperature range of 650 to 1000 ° C. for 1 to 10 hours,
Manufacturing method for ferritic stainless steel slabs.
γpot. = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-
11.5Si-12Mo-47Nb-52Al + 189 ≦ 20 1 set
Ｍｏ：０．３〜５．０％
Ｃｕ：０．３〜１．０％
の１種以上含有することを特徴とする請求項１に記載のフェライト系ステンレス鋼鋳片の製造方法。 Furthermore, in mass%,
Mo: 0.3-5.0%
Cu: 0.3 to 1.0%
The method for producing a ferritic stainless steel slab according to claim 1, wherein the ferritic stainless steel slab is contained.
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5913053A (en) * | 1982-07-09 | 1984-01-23 | Nippon Steel Corp | Stainless steel with superior corrosion resistance, workability and weldability |
| JPS602628A (en) * | 1983-06-18 | 1985-01-08 | Nippon Steel Corp | Method for cooling continuously cast billet of ferritic stainless steel containing niobium |
| JPH0687054A (en) * | 1992-09-08 | 1994-03-29 | Kawasaki Steel Corp | Production of stainless steel cast slab |
| JP2001234243A (en) * | 2000-02-18 | 2001-08-28 | Sumitomo Metal Ind Ltd | Heating method for slab small in scale loss |
-
2004
- 2004-02-13 JP JP2004036527A patent/JP4624691B2/en not_active Expired - Lifetime
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5913053A (en) * | 1982-07-09 | 1984-01-23 | Nippon Steel Corp | Stainless steel with superior corrosion resistance, workability and weldability |
| JPS602628A (en) * | 1983-06-18 | 1985-01-08 | Nippon Steel Corp | Method for cooling continuously cast billet of ferritic stainless steel containing niobium |
| JPH0687054A (en) * | 1992-09-08 | 1994-03-29 | Kawasaki Steel Corp | Production of stainless steel cast slab |
| JP2001234243A (en) * | 2000-02-18 | 2001-08-28 | Sumitomo Metal Ind Ltd | Heating method for slab small in scale loss |
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