JP6402913B2 - Chromium-nickel stainless steel continuous casting method - Google Patents
Chromium-nickel stainless steel continuous casting method Download PDFInfo
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本発明は、内部割れ及び表面割れを同時に抑制可能なステンレス鋼、特にCrを18質量％以上、Niを11質量％以上、及びNbを0.4 質量％以上含有するクロムニッケル系ステンレス鋼を連続鋳造する方法に関するものである。 The present invention continuously casts a stainless steel capable of simultaneously suppressing internal cracks and surface cracks, particularly chromium-nickel stainless steel containing 18 mass% or more of Cr, 11 mass% or more of Ni, and 0.4 mass% or more of Nb. It is about the method.
なお、以下の説明では、鋼の成分組成については、特に断らない限り、「％」は「質量％」を意味する。 In the following description, “%” means “mass%” unless otherwise specified.
例えば、油井管に使用される継目無鋼管や、化学プラントや発電所の熱交換器などに使用される継目無鋼管は、そのハイエンド化に合わせてクロム系からクロムニッケル系のステンレス鋼で製造する割合が増加している。このようなクロムニッケル系のステンレス鋼(以下、高合金鋼ともいう。)は、CuやNbなどの合金成分を多く含有している。 For example, seamless steel pipes used for oil well pipes, and seamless steel pipes used for heat exchangers in chemical plants and power plants are manufactured from chromium-based to nickel-nickel-based stainless steel in line with the high-end trend. The rate is increasing. Such chromium-nickel stainless steel (hereinafter also referred to as high alloy steel) contains many alloy components such as Cu and Nb.
従来、Nbを含有する高合金鋼は、表面割れや内部割れの感受性が高いので、Nbの含有量に応じて、Nbを含有しないステンレス鋼に比べて鋳造速度を遅くし、この鋳造速度を遅くした分だけ溶鋼温度を高くして鋳造していた。 Conventionally, high alloy steels containing Nb have high susceptibility to surface cracks and internal cracks, so depending on the Nb content, the casting speed is reduced compared to stainless steel not containing Nb. The molten steel temperature was raised by the amount corresponding to the casting.
しかしながら、連続鋳造時における表面割れや内部割れの発生の抑制を、鋳造速度を遅くすることで対応する場合、操業能率が低下するという問題がある。 However, when the suppression of the occurrence of surface cracks and internal cracks during continuous casting is dealt with by slowing the casting speed, there is a problem that the operation efficiency is lowered.
ところで、連続鋳造速度を遅くすることなく、鋳片のコーナー割れの発生を抑制する技術として特許文献１が、鋳片の表面割れと内部割れを共に防止する技術として特許文献２が提案されている。
By the way, Patent Document 1 is proposed as a technique for suppressing the occurrence of corner cracks in a slab without slowing the continuous casting speed, and
このうち、特許文献１は、連続鋳造時、二次冷却帯での比水量を規定することで、連続鋳造後の鋳片の圧延時におけるコーナー割れの発生を少なくする高合金鋼の連続鋳造方法である。 Among these, Patent Document 1 discloses a continuous casting method for high alloy steel that reduces the occurrence of corner cracks during rolling of a slab after continuous casting by defining a specific water amount in a secondary cooling zone during continuous casting. It is.
また、特許文献２は、鋳片の幅方向の温度偏差と鋳片表面の過冷却を抑制することで、鋳片の表面割れと内部割れを共に防止して、良質な鋳片を製造可能とするクロム系ステンレス鋼の連続鋳造方法である。
しかしながら、特許文献１で対象とする鋼種は、高合金鋼であっても、Nbの含有量は0.4 ％未満で、しかも、連続鋳造時に発生する鋳片のコーナー割れではなく、連続鋳造後の鋳片の圧延時におけるコーナー割れの抑制を目的としたものである。 However, even if the steel type targeted in Patent Document 1 is a high-alloy steel, the Nb content is less than 0.4%, and it is not a corner crack of the slab that occurs during continuous casting. The purpose is to suppress corner cracks during the rolling of the pieces.
また、特許文献２で対象とする鋼種は、Niを含有しないクロム系ステンレス鋼であり、防止しようとするのは、バルジングに起因する内部割れと、過冷却に起因する表面割れである。
Moreover, the steel type made into
つまり、特許文献１，２で提案された方法は、いずれもNbを0.4 ％以上含有する高合金鋼に特有の連続鋳造鋳片に発生する表面割れや内部割れの抑制についての考慮はなされていない。
In other words, none of the methods proposed in
Nbを0.4 ％以上含有する高合金鋼の連続鋳造に際し、Nbを含有しないステンレス鋼に比べて鋳造速度を遅くし、この鋳造速度を遅くした分だけ溶鋼温度を高くして鋳造する場合は、操業能率が低下するという問題がある。 In continuous casting of high alloy steel containing 0.4% or more of Nb, the casting speed is slower than that of stainless steel not containing Nb. There is a problem that efficiency decreases.
一方、特許文献１，２で提案された方法は、いずれもNbを0.4 ％以上含有する高合金鋼に特有の連続鋳造鋳片に発生する表面割れや内部割れの抑制についての考慮はなされていないという問題がある。
On the other hand, none of the methods proposed in
本発明は、上記の従来技術にあった問題に鑑みてなされたものであり、連続鋳造時の鋳造速度を低下させることなく、Nbを0.4 ％以上含有する高合金鋼に特有の連続鋳造鋳片に発生する表面割れや内部割れを同時に抑制可能な連続鋳造方法を提供することを目的としている。 The present invention has been made in view of the above-described problems of the prior art, and is a continuous cast slab unique to high alloy steels containing 0.4% or more of Nb without reducing the casting speed during continuous casting. It aims at providing the continuous casting method which can suppress the surface crack and internal crack which generate | occur | produce at the same time.
すなわち、本発明は、
Cr：18％以上、Ni：11％以上、Nb：0.4 ％以上を含有するクロムニッケル系ステンレス鋼を連続鋳造する方法において、
連続鋳造鋳片の幅方向に隣接配置したスプレーノズルから噴射するミストスプレーによる、最大流量を１００％とした最少流量の水量の比率で定義する均一冷却度が８０％以上となる二次冷却設備を使用し、
二次冷却帯通過後の鋳片の表面温度上昇量Ｔ（℃）と、凝固シェル厚比[｛（二次冷却帯出側の凝固シェル全体の厚さ／２）／鋳片厚｝×１００％]ｘが、
Ｔ＜10・ｘ
の関係を満足し、
かつ、二次冷却帯での比水量ｗ1と水量密度ｗ2が、
ｗ2＜400 ・ｗ1
の関係（但し、比水量ｗ 1 は０．３３〜０．５０の範囲）を満足する条件で二次冷却することを最も主要な特徴としている。
That is, the present invention
In a continuous casting method of chromium nickel-based stainless steel containing Cr: 18% or more, Ni: 11% or more, Nb: 0.4% or more,
Secondary cooling equipment with a uniform cooling degree of 80% or more defined by the ratio of the minimum flow rate water volume with the maximum flow rate set to 100% by mist spraying spray nozzles arranged adjacent to the width direction of the continuous cast slab use,
A secondary cooling zone surface temperature increase of the slab after passing through T (° C.), the solidified shell thickness ratio [{(secondary cooling home use side of the solidified shell of total thickness / 2) / IhenAtsu} × 100% ] x
T <10 · x
Satisfied with the relationship
And the specific water amount w 1 and the water amount density w 2 in the secondary cooling zone are
w 2 <400 ・ w 1
The secondary feature is that the secondary cooling is performed under conditions satisfying the above relationship (however, the specific water amount w 1 is in the range of 0.33 to 0.50) .
なお、比水量は、単位時間当りにおける（冷却水量／鋳片重量）で表される。また、水量密度とは、単位面積当たりの冷却水量である。 The specific water amount is expressed as (cooling water amount / slab weight) per unit time. The water density is the amount of cooling water per unit area.
すなわち、本発明では、二次冷却帯通過後の鋳片の表面温度上昇量Ｔ（℃）と、凝固シェル厚比ｘの関係が最適となるように二次冷却することで、鋳片の強度を向上して、二次冷却帯通過後に鋳片が復熱によって膨張変形することを抑制する。また、二次冷却帯での比水量ｗ1と水量密度ｗ2の関係が最適となるように二次冷却することで、鋳片幅方向における冷却むらを抑制する。 That is, in the present invention, the strength of the slab is obtained by performing secondary cooling so that the relationship between the surface temperature increase amount T (° C.) of the slab after passing the secondary cooling zone and the solidified shell thickness ratio x is optimized. To prevent the slab from expanding and deforming due to recuperation after passing through the secondary cooling zone. In addition, secondary cooling is performed so that the relationship between the specific water amount w 1 and the water density w 2 in the secondary cooling zone is optimal, thereby suppressing uneven cooling in the slab width direction.
本発明では、二次冷却帯通過後の復熱によって、鋳片凝固シェルの内面に引張応力が働くことを効果的に抑制することで、Nbを0.4 ％以上含有する高合金鋼に特有の内部割れを抑制することができる。また、鋳片幅方向における冷却むらを抑制することで、Nbを0.4 ％以上含有する高合金鋼に特有の表面割れを抑制することができる。また、本発明では、鋳造速度を低下させる必要がないので、操業効率が低下することもない。 The present invention effectively suppresses the tensile stress from acting on the inner surface of the slab solidified shell due to the recuperation after passing through the secondary cooling zone, so that an internal characteristic of high alloy steel containing 0.4% or more of Nb is obtained. Cracking can be suppressed. Moreover, the surface cracking peculiar to the high alloy steel which contains Nb 0.4% or more can be suppressed by suppressing the cooling nonuniformity in the slab width direction. Further, in the present invention, since it is not necessary to reduce the casting speed, the operation efficiency is not reduced.
発明者らは、連続鋳造における内部割れ発生原因を整理すべく、連続鋳造後の鋳片から横断面マクロ組織を調査した。また、凝固計算によって、表面温度の履歴と凝固シェル厚の成長推移を求めた。その結果、内部割れの発生起点について二次冷却条件との関連性を認めたことから、二次冷却条件を見直して、Nbを0.4 ％以上含有する高合金鋼に特有の内部割れを抑制することを考えた。 The inventors investigated the cross-sectional macrostructure from the slab after continuous casting in order to sort out the causes of internal cracks in continuous casting. Moreover, the growth history of the surface temperature history and the solidified shell thickness was obtained by solidification calculation. As a result, it was confirmed that the origin of internal cracks was related to the secondary cooling conditions, so the secondary cooling conditions were reviewed to suppress internal cracks specific to high alloy steels containing 0.4% or more of Nb. Thought.
すなわち、二次冷却帯を通過した鋳片は復熱によって膨張変形する。このとき、鋳片強度が低い場合には熱応力で鋳片内部に割れが発生する。また、鋳片の幅方向の冷却能力が不均一な場合、局所的な凝固遅れ部が発生し、表面割れの発生だけでなく、内部割れの発生率もさらに上昇する。 That is, the slab passing through the secondary cooling zone is expanded and deformed by recuperation. At this time, if the strength of the slab is low, cracks occur inside the slab due to thermal stress. Further, when the cooling capacity in the width direction of the slab is not uniform, a local solidification delay portion is generated, and not only surface cracks but also internal cracks are further increased.
この鋳片の幅方向における冷却むらによって発生する表面割れを抑制するには、水量密度を低下することが望ましい。しかしながら、その一方で、水量密度の低下により凝固シェルの成長が遅れた強度が低い鋳片は熱応力で内部割れが発生しやすくなって、内部割れの感受性が高くなる。 In order to suppress surface cracks caused by uneven cooling in the width direction of the slab, it is desirable to reduce the water density. However, on the other hand, a low-strength slab in which the growth of the solidified shell is delayed due to a decrease in water density tends to cause internal cracking due to thermal stress, and the internal cracking sensitivity becomes high.
そこで、発明者らは、水量密度を増加させることなく、凝固シェルの厚みを確保できる二次冷却条件、すなわち、二次冷却帯通過後の鋳片の表面温度上昇量Ｔ（℃）と凝固シェル厚比ｘ、及び二次冷却帯での比水量ｗ1と水量密度ｗ2の関係に着目し、調査を行った。 Accordingly, the inventors have established secondary cooling conditions that can ensure the thickness of the solidified shell without increasing the water density, that is, the surface temperature increase T (° C.) of the slab after passing through the secondary cooling zone and the solidified shell. The investigation was conducted by paying attention to the relationship between the thickness ratio x and the specific water volume w 1 and the water volume density w 2 in the secondary cooling zone.
二次冷却帯通過後の鋳片の表面温度上昇量Ｔ（℃）と凝固シェル厚比ｘの関係を、二次冷却設備の均一冷却度が最大４８％と８０％以上の場合について調査した。ここで、二次冷却設備の均一冷却度とは、連続鋳造鋳片の幅方向に隣接配置したスプレーノズルから噴射するミストスプレーによる、最大流量を１００％とした最少流量の水流の比率で定義する。その結果、図１（ａ）に示すように、二次冷却設備の均一冷却度が最大４８％の場合は何れの場合も内部割れが発生するが、二次冷却設備の均一冷却度が８０％以上の場合は内部割れが発生する領域と、内部割れが発生しない領域が存在することが判明した。 The relationship between the surface temperature increase T (° C.) of the slab after passing through the secondary cooling zone and the solidified shell thickness ratio x was investigated when the uniform cooling degree of the secondary cooling equipment was 48% at the maximum and 80% or more. Here, the uniform cooling degree of the secondary cooling equipment is defined as the ratio of the water flow with the minimum flow rate with the maximum flow rate being 100% by the mist spray injected from the spray nozzle arranged adjacent to the width direction of the continuous cast slab. . As a result, as shown in FIG. 1A, when the uniform cooling degree of the secondary cooling equipment is 48% at the maximum, internal cracks occur in any case, but the uniform cooling degree of the secondary cooling equipment is 80%. In the above cases, it has been found that there are regions where internal cracks occur and regions where internal cracks do not occur.
また、二次冷却帯での比水量ｗ1と水量密度ｗ2の関係を、二次冷却設備の均一冷却度が最大４８％と８０％以上の場合について調査した。その結果、図１（ｂ）に示すように、二次冷却設備の均一冷却度が最大４８％の場合は何れの場合も表面割れが発生するが、二次冷却設備の均一冷却度が８０％以上の場合は何れの場合も表面割れが発生しないことが判明した。 Moreover, the relationship between the specific water amount w 1 and the water amount density w 2 in the secondary cooling zone was investigated in the case where the uniform cooling degree of the secondary cooling equipment was 48% at the maximum and 80% or more. As a result, as shown in FIG. 1B, when the uniform cooling degree of the secondary cooling equipment is 48% at the maximum, surface cracks occur in any case, but the uniform cooling degree of the secondary cooling equipment is 80%. In the above cases, it was found that surface cracks did not occur in either case.
上記調査結果に基づき、発明者らは、二次冷却設備の均一冷却度と、二次冷却帯通過後の鋳片の表面温度上昇量Ｔ（℃）と凝固シェル厚比ｘの関係、及び二次冷却帯での比水量ｗ1と水量密度ｗ2の関係を規定することで、Nbを0.4 ％以上含有する高合金鋼に特有の連続鋳造鋳片に発生する表面割れと内部割れを同時に抑制できることを見出した。 Based on the above investigation results, the inventors have found that the degree of uniform cooling of the secondary cooling equipment, the relationship between the surface temperature rise T (° C.) of the slab after passing through the secondary cooling zone and the solidified shell thickness ratio x, and By defining the relationship between the specific water volume w 1 and the water density w 2 in the secondary cooling zone, surface cracks and internal cracks that occur in continuous cast slabs unique to high-alloy steels containing 0.4% or more of Nb are simultaneously suppressed. I found out that I can do it.
すなわち、復熱による内部割れの発生を抑制するためには、二次冷却帯を通過する間に凝固シェル厚を確保することと、二次冷却帯通過後の温度上昇量を低減することが有効である。 In other words, in order to suppress the occurrence of internal cracks due to recuperation, it is effective to secure a solidified shell thickness while passing through the secondary cooling zone and to reduce the amount of temperature rise after passing through the secondary cooling zone. It is.
以上の観点から、図１（ａ）に示すように、凝固シェル厚と温度上昇量の関係により、内部割れの発生の有無を整理できることを見出した結果、二次冷却帯通過後の鋳片の表面温度上昇量Ｔ（℃）と、凝固シェル厚比ｘが、Ｔ＜10・ｘを満たせば、内部割れの発生を抑制することが可能であるという知見を得た。 From the above viewpoint, as shown in FIG. 1 (a), as a result of finding that the presence or absence of internal cracks can be arranged by the relationship between the solidified shell thickness and the amount of temperature increase, the slab of the slab after passing through the secondary cooling zone It was found that if the surface temperature rise T (° C.) and the solidified shell thickness ratio x satisfy T <10 · x, the occurrence of internal cracks can be suppressed.
また、表面割れの発生は鋳片の幅方向に生じる冷却能率の不均一さによって助長されることから、水量密度を増加させることなく、鋳片の冷却に必要な比水量を確保することが要求される。 In addition, the occurrence of surface cracks is promoted by the non-uniformity of the cooling efficiency that occurs in the width direction of the slab, so it is necessary to ensure the specific water amount necessary for cooling the slab without increasing the water density. Is done.
以上の観点から、図１（ｂ）に示すように、水量密度ｗ2と比水量ｗ1の関係より表面割れの発生の有無を整理できることを見出した結果、ｗ2＜400 ・ｗ1を満たせば、表面割れの発生を抑制することが可能であるという知見を得た。 In view of the above, as shown in FIG. 1 (b), the results were found to be organized occurrence of surface cracks than relationship water density w 2 and specific amount of water w 1, satisfy the w 2 <400 · w 1 As a result, it was found that the occurrence of surface cracks can be suppressed.
本発明は、発明者らが調査した上記知見に基づいてなされたものであり、
Cr：18％以上、Ni：11％以上、Nb：0.4 ％以上を含有するクロムニッケル系ステンレス鋼を連続鋳造する方法において、
連続鋳造鋳片の幅方向に隣接配置したスプレーノズルから噴射するミストスプレーによる、最大流量を１００％とした最少流量の水量の比率で定義する均一冷却度が８０％以上となる二次冷却設備を使用し、
二次冷却帯通過後の鋳片の表面温度上昇量Ｔ（℃）と、凝固シェル厚比[｛（二次冷却帯出側の凝固シェル全体の厚さ／２）／鋳片厚｝×１００％]ｘが、
Ｔ＜10・ｘ
の関係を満足し、
かつ、二次冷却帯での比水量ｗ1（リットル／kg・steel）と水量密度ｗ2（リットル／min／m2）が、
ｗ2＜400 ・ｗ1
の関係（但し、比水量ｗ 1 は０．３３〜０．５０の範囲）を満足する条件で二次冷却することを最も主要な特徴としている。
The present invention has been made based on the above findings investigated by the inventors,
In a continuous casting method of chromium nickel-based stainless steel containing Cr: 18% or more, Ni: 11% or more, Nb: 0.4% or more,
Secondary cooling equipment with a uniform cooling degree of 80% or more defined by the ratio of the minimum flow rate water volume with the maximum flow rate set to 100% by mist spraying spray nozzles arranged adjacent to the width direction of the continuous cast slab use,
A secondary cooling zone surface temperature increase of the slab after passing through T (° C.), the solidified shell thickness ratio [{(secondary cooling home use side of the solidified shell of total thickness / 2) / IhenAtsu} × 100% ] x
T <10 · x
Satisfied with the relationship
In addition, the specific water amount w 1 (liter / kg · steel) and the water density w 2 (liter / min / m 2 ) in the secondary cooling zone are
w 2 <400 ・ w 1
The secondary feature is that the secondary cooling is performed under conditions satisfying the above relationship (however, the specific water amount w 1 is in the range of 0.33 to 0.50) .
本発明において、Cr：18％以上、Ni：11％以上、Nb：0.4 ％以上を含有するクロムニッケル系ステンレス鋼を対象とするのは、Nbを0.4 ％以上を含有する、Cr：18％以上、Ni：11％以上含有するクロムニッケル系ステンレス鋼を、Nbの含有量が0.4 ％未満のステンレス鋼と同様の条件で連続鋳造した場合に、特有の表面割れや内部割れが発生するからである。 In the present invention, chromium nickel-based stainless steel containing Cr: 18% or more, Ni: 11% or more, and Nb: 0.4% or more is intended to contain Nb 0.4% or more, Cr: 18% or more , Ni: 11% or more chromium-nickel stainless steel, when surface casting the same conditions as stainless steel with Nb content less than 0.4%, unique surface cracks and internal cracks will occur .
また、本発明において、前記均一冷却度が８０％以上となる二次冷却設備を使用するのは、図１に示した調査結果、及びその他の調査結果によれば、前記均一冷却度が８０％以上でないと、二次冷却帯通過後の鋳片の表面温度上昇量Ｔ（℃）と凝固シェル厚比ｘの関係、二次冷却帯での比水量ｗ1と水量密度ｗ2の関係をどのように変化させても内面割れ、表面割れが発生しない領域が存在しないからである。 Further, in the present invention, the secondary cooling equipment having the uniform cooling degree of 80% or more is used according to the investigation result shown in FIG. 1 and the other investigation results. If not, what is the relationship between the surface temperature increase T (° C.) of the slab after passing through the secondary cooling zone and the solidified shell thickness ratio x, and the relationship between the specific water amount w 1 and the water density w 2 in the secondary cooling zone? This is because there is no region in which internal cracks and surface cracks do not occur even when such changes are made.
発明者らが調査した結果、上記本発明は、Cr：20％以上、Ni：20％以上、Nb：0.4 ％以上含有するクロムニッケル系ステンレス鋼の連続鋳造にも効果的であった。 As a result of investigation by the inventors, the present invention was also effective for continuous casting of chromium nickel-based stainless steel containing Cr: 20% or more, Ni: 20% or more, and Nb: 0.4% or more.
以下、本発明の効果を確認するために行った実験結果について説明する。
下記表１に記載の成分組成の高合金鋼を、垂直型連続鋳造機を使用して380mm／分、450mm／分、510mm／分の鋳造速度で厚み280mm×幅600mmの角鋳片を連続鋳造した。
Hereinafter, the results of experiments conducted to confirm the effects of the present invention will be described.
Using a vertical continuous casting machine, high-alloy steels with the composition shown in Table 1 below are continuously casted at 380 mm / min, 450 mm / min, 510 mm / min. did.
下記表２，３に記載の比較例１〜４は、鋳型直下の二次冷却を、図５（ａ）の紙面左側に示す、メニスカスから0.70m 〜0.73m の範囲を水冷却、メニスカスから0.73m 〜1.89m の範囲をミスト冷却（エアー圧力：0.2MPa）によって行った。このミスト冷却は、図３（ａ）に示した形状の、図３（ｂ）に示す流量分布（前記均一冷却度：最大48％）のノズルを使用して行った。 In Comparative Examples 1 to 4 described in Tables 2 and 3 below, secondary cooling just below the mold is shown on the left side of the sheet of FIG. 5 (a), with water cooling in the range of 0.70m to 0.73m from the meniscus, and 0.73m from the meniscus. The range of m to 1.89 m was performed by mist cooling (air pressure: 0.2 MPa). This mist cooling was performed using a nozzle having a flow rate distribution (the uniform cooling degree: 48% at the maximum) shown in FIG. 3B having the shape shown in FIG.
また、下記表２，３に記載の比較例５，６は、鋳型直下の二次冷却を、図５（ａ）の紙面左側に示す、メニスカスから0.70m 〜0.73m の範囲を水冷却、メニスカスから0.73m 〜3.86m の範囲をミスト冷却（エアー圧力：0.2MPa）によって行った。このミスト冷却は、図３（ａ）に示した形状の、図３（ｂ）に示す流量分布（前記均一冷却度：最大48％）のノズルを使用して行った。 In Comparative Examples 5 and 6 shown in Tables 2 and 3 below, secondary cooling just below the mold is shown on the left side of the sheet of FIG. 5A. Water cooling is performed in the range of 0.70 m to 0.73 m from the meniscus. The range from 0.73 m to 3.86 m was performed by mist cooling (air pressure: 0.2 MPa). This mist cooling was performed using a nozzle having a flow rate distribution (the uniform cooling degree: 48% at the maximum) shown in FIG. 3B having the shape shown in FIG.
また、下記表２，３に記載の比較例７，８は、鋳型直下の二次冷却を、図５（ａ）の紙面右側に示す、メニスカスから0.70m 〜0.73 m の範囲を水冷却、メニスカスから0.73m 〜1.89m の範囲をミスト冷却（エアー圧力：0.1MPa）によって行った。このミスト冷却は、図２（ａ）に示した形状の、図２（ｂ）に示す流量分布（前記均一冷却度：８０％以上）のノズルを使用して行った。 In Comparative Examples 7 and 8 shown in Tables 2 and 3 below, secondary cooling just below the mold is shown on the right side of the sheet of FIG. 5A. Water cooling is performed in the range from 0.70 m to 0.73 m from the meniscus. The range from 0.73 m to 1.89 m was performed by mist cooling (air pressure: 0.1 MPa). This mist cooling was performed using a nozzle having a flow rate distribution (the degree of uniform cooling: 80% or more) shown in FIG. 2B and having the shape shown in FIG.
前記比較例１〜８は、鋼種Ａを連続鋳造したもので、比較例１，３，５，７は380 mm／分の速度で、また比較例２，４，６，８は510 mm／分の速度で連続鋳造した。 In Comparative Examples 1 to 8, steel type A was continuously cast, Comparative Examples 1, 3, 5, and 7 were at a speed of 380 mm / min, and Comparative Examples 2, 4, 6, and 8 were 510 mm / min. Continuous casting at a speed of
一方、下記表２，３に記載の発明例１，２は、図５（ａ）の紙面右側に示す、メニスカスから0.70m 〜0.73 m の範囲は水冷却、メニスカスから0.73m 〜3.86m の範囲はミスト冷却（エアー圧力：0.1MPa）によって二次冷却した。このミスト冷却は、図２（ａ）に示した形状の、図２（ｂ）に示す流量分布（前記均一冷却度：８０％以上）のノズルを使用して行った。このうち、鋼種Ａを連続鋳造した発明例１は510 mm／分で、鋼種Ｂを連続鋳造した発明例２は450 mm／分の速度で連続鋳造した。 On the other hand, Invention Examples 1 and 2 shown in Tables 2 and 3 below show water cooling in the range from 0.70 m to 0.73 m from the meniscus, and from 0.73 m to 3.86 m from the meniscus, as shown on the right side of FIG. Was cooled by mist cooling (air pressure: 0.1 MPa). This mist cooling was performed using a nozzle having a flow rate distribution (the degree of uniform cooling: 80% or more) shown in FIG. 2B and having the shape shown in FIG. Among them, Invention Example 1 in which Steel Type A was continuously cast was 510 mm / min, and Invention Example 2 in which Steel Type B was continuously cast was continuously cast at a speed of 450 mm / min.
比較例１〜８、及び発明例１，２の、二次冷却条件及び鋳造結果を下記表２，３に示す。なお、下記表３中の内部割れは、連続鋳造後の鋳片を100 mm間隔で３断面作成し、その横断面マクロ組織を調査して内部に割れの発生がないものを〇、内部に割れの発生があったものを×とした。また、表面割れは前記鋳片の全面をショットブラストした後浸透探傷試験を行い、割れが見つかった場合を×、見つからなかった場合を○とした。 The secondary cooling conditions and casting results of Comparative Examples 1 to 8 and Invention Examples 1 and 2 are shown in Tables 2 and 3 below. In addition, the internal cracks in Table 3 below indicate that the slabs after continuous casting were made into three sections at 100 mm intervals, and the cross-sectional macrostructure was investigated to indicate that there were no internal cracks. The occurrence of x was marked with x. Further, surface cracking was performed by shot blasting the entire surface of the slab and then performing a penetrant flaw detection test.
比較例１〜８では、図３（ａ）に示すノズルを使用して二次冷却しているので、図４（ａ）に示すように、連続鋳造鋳片の幅方向において局所的な温度むらが発生する。さらに、比較例１〜４，７，８では、図５（ａ）の紙面左側のメニスカスからの距離に示すように、二次冷却帯の長さがメニスカスから1.89m の位置までであるため、図５（ｂ）に破線で示した計算表面温度にみるように、二次冷却帯通過後の鋳片の表面温度上昇量Ｔ（℃）が大きい。 In Comparative Examples 1 to 8, since the secondary cooling is performed using the nozzle shown in FIG. 3A, as shown in FIG. 4A, local temperature unevenness in the width direction of the continuous cast slab. Will occur. Furthermore, in Comparative Examples 1-4, 7, and 8, as shown in the distance from the meniscus on the left side of FIG. 5 (a), the length of the secondary cooling zone is 1.89 m from the meniscus. As seen from the calculated surface temperature indicated by the broken line in FIG. 5B, the surface temperature increase T (° C.) of the slab after passing through the secondary cooling zone is large.
このような二次冷却設備を用いて連続鋳造した場合、二次冷却帯での比水量ｗ1と水量密度ｗ2がｗ2＜400 ・ｗ1、二次冷却帯通過後の鋳片の表面温度上昇量Ｔと凝固シェル厚比ｘがＴ＜10・ｘの関係の何れか一方でも満たしていない場合は勿論（比較例１〜４，７，８）、前記両関係を共に満たしても、表面割れ及び内部割れが共に発生した（比較例５，６）。 When continuous casting is performed using such secondary cooling equipment, the specific water volume w 1 and water density w 2 in the secondary cooling zone is w 2 <400 · w 1 , the surface of the slab after passing through the secondary cooling zone Of course, when the temperature rise amount T and the solidified shell thickness ratio x do not satisfy any one of the relations of T <10 · x (Comparative Examples 1-4, 7, 8), Both surface cracks and internal cracks occurred (Comparative Examples 5 and 6).
これに対して、鋼種Ａを連続鋳造した発明例１は、図４（ｂ）に示すような局所的な温度むらの無い、図２（ａ）に示すノズルを使用するのと共に二次冷却帯の長さをメニスカスから3.86m の位置まで延長し、かつ、前記ｗ2＜400 ・ｗ1及びＴ＜10・ｘの関係を共に満たしているので、内部割れ、表面割れの発生が共に認められなかった。 On the other hand, the invention example 1 which continuously casts the steel type A uses the nozzle shown in FIG. 2 (a) without the local temperature unevenness as shown in FIG. 4 (b) and the secondary cooling zone. Is extended from the meniscus to a position of 3.86 m, and both the relations w 2 <400 · w 1 and T <10 · x are satisfied, so both internal cracks and surface cracks are observed. There wasn't.
また、Crを20％以上、Niを20％以上、Nbを0.4 ％以上含有する鋼種Ｂを連続鋳造した発明例２も、発明例１と同様、内部割れ、表面割れの発生が共に認められなかった。 Inventive Example 2 in which steel type B containing 20% or more of Cr, 20% or more of Ni, and 0.4% or more of Nb is continuously cast, as in Inventive Example 1, shows no occurrence of internal cracks and surface cracks. It was.
一方、発明例１，２と同じ二次冷却設備を使用し、前記ｗ2＜400 ・ｗ1の関係を満たしているものの、前記Ｔ＜10・ｘの関係を満たしていない比較例７，８は、表面割れは生じなかったが、内部割れの発生が見られた。 On the other hand, Comparative Examples 7 and 8 using the same secondary cooling equipment as Invention Examples 1 and 2 and satisfying the relationship of w 2 <400 · w 1 but not satisfying the relationship of T <10 · x No surface cracks occurred, but internal cracks were observed.
本発明は上記した例に限らないことは勿論であり、請求項に記載の技術的思想の範疇であれば、適宜実施の形態を変更しても良いことは言うまでもない。 Needless to say, the present invention is not limited to the above-described examples, and the embodiments may be appropriately changed within the scope of the technical idea described in the claims.
Claims (2)
連続鋳造鋳片の幅方向に隣接配置したスプレーノズルから噴射するミストスプレーによる、最大流量を１００％とした最少流量の水量の比率で定義する均一冷却度が８０％以上となる二次冷却設備を使用し、
二次冷却帯通過後の鋳片の表面温度上昇量Ｔ（℃）と、凝固シェル厚比[｛（二次冷却帯出側の凝固シェル全体の厚さ／２）／鋳片厚｝×１００％]ｘが、
Ｔ＜10・ｘ
の関係を満足し、
かつ、二次冷却帯での比水量ｗ1（リットル／kg・steel）と水量密度ｗ2（リットル／min／m2）が、
ｗ2＜400 ・ｗ1
の関係（但し、比水量ｗ 1 は０．３３〜０．５０の範囲）を満足する条件で二次冷却することを特徴とするクロムニッケル系ステンレス鋼の連続鋳造方法。 In a method of continuously casting chromium nickel-based stainless steel containing, by mass%, Cr: 18% or more, Ni: 11% or more, Nb: 0.4% or more,
Secondary cooling equipment with a uniform cooling degree of 80% or more defined by the ratio of the minimum flow rate water volume with the maximum flow rate set to 100% by mist spraying spray nozzles arranged adjacent to the width direction of the continuous cast slab use,
A secondary cooling zone surface temperature increase of the slab after passing through T (° C.), the solidified shell thickness ratio [{(secondary cooling home use side of the solidified shell of total thickness / 2) / IhenAtsu} × 100% ] x
T <10 · x
Satisfied with the relationship
In addition, the specific water amount w 1 (liter / kg · steel) and the water density w 2 (liter / min / m 2 ) in the secondary cooling zone are
w 2 <400 ・ w 1
A continuous casting method of chromium-nickel stainless steel, wherein the secondary cooling is performed under a condition satisfying the above relationship (however, the specific water amount w 1 is in the range of 0.33 to 0.50) .
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