JP5320791B2 - Center segregation evaluation method - Google Patents
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本発明は、鋼の連続鋳造鋳片および厚鋼板の内部品質を評価する一手法である中心偏析評価方法に関するものである。 The present invention relates to a central segregation evaluation method, which is one method for evaluating the internal quality of a continuous cast slab of steel and a thick steel plate.
鋼の連続鋳造鋳片（以降、単に「鋳片」ともいう）やそれらを素材とする厚鋼板（厚板）の分野においては、連続鋳造時に形成される鋳片中心部の偏析が、製品品質に大きく影響することが知られている。そこで、この中心偏析を軽減するために、数多くの技術開発が行われてきている。 In the field of continuous cast slabs of steel (hereinafter simply referred to as “slabs”) and thick steel plates (thick plates) made from them, segregation at the center of the slab formed during continuous casting is the product quality. It is known to greatly affect Therefore, many technological developments have been made to reduce this center segregation.
一方、中心偏析を評価する方法については、幾つかの方法が知られており、例えば、鋳片や厚鋼板を厚さ方向に順次スライスしていき、そのスライスして採取した切粉の成分を分析し、厚さ方向の濃度分布を得る方法（スライス法）、鋳片の縦断面からマクロプリントを採取して中心偏析領域を特定し、この中心偏析領域上の多数の分析点から、ドリルで切粉サンプルを採取し、この切粉を分析する方法（ドリル法）、鋳片の切断面を研磨して、偏析部をピクリン酸等の腐食液により腐食させてからインク等を染み込ませた後、一旦、表面のインクを拭き取り、腐食部に残ったインクをセロハン紙等に写し取り、偏析の発生状況を可視化する方法（マクロ腐食法）、また、上記腐食後に写し取ったプリントを中心偏析部の最大偏析粒径等を測定する方法（Ｈプリント法）等がある。 On the other hand, several methods are known for evaluating center segregation. For example, a slab or a thick steel plate is sequentially sliced in the thickness direction, and the components of the chips collected by slicing are obtained. Analyzing and obtaining the concentration distribution in the thickness direction (slicing method), taking a macro print from the longitudinal section of the slab to identify the center segregation region, and drilling from a number of analysis points on this center segregation region After collecting a chip sample, analyzing this chip (drill method), polishing the cut surface of the slab, corroding the segregated portion with a corrosive liquid such as picric acid, and then soaking the ink First, wipe off the ink on the surface, copy the ink remaining in the corroded area onto cellophane paper, etc., and visualize the occurrence of segregation (macro corrosion method). Measure maximum segregation particle size A method (H printing method) or the like that.
一般に、鋳片の中心偏析は、Ｃ断面、即ち、鋳造方向に垂直な断面全体についてみると、厚さ方向および幅方向で決して均一とはいえない。そのため、鋳片や厚鋼板の偏析を調べるためには全幅に亘って評価する必要がある。 In general, the center segregation of a slab is never uniform in the thickness direction and the width direction when viewed from the C cross section, that is, the entire cross section perpendicular to the casting direction. Therefore, in order to investigate the segregation of a slab or a thick steel plate, it is necessary to evaluate over the entire width.
この点から上記方法を検討すると、スライス法は、試料調整・分析に時間がかかるため、結果が出るまでに長時間を要するため、鋳片や厚鋼板等の中心偏析評価をＣ断面全体に亘って行うことは困難である。また、この方法では、スライスした切粉を分析するため、厚さ方向の平均としての分析値しか得られない。そのため、従来は、一部領域の評価にのみ用いられる程度であった。 Considering the above method from this point, the slicing method takes time to prepare and analyze the sample, so it takes a long time to obtain the result. It is difficult to do. Moreover, in this method, since the sliced chips are analyzed, only an analysis value as an average in the thickness direction can be obtained. For this reason, the conventional technique has been used only for evaluating a partial area.
また、ドリル法は、スライス法に比較して、迅速性は優れるが、切粉の採取領域がスライス法に比較し、さらに狭くなるため、全体的な評価ができないという問題があった。
一方、マクロ腐食法は、迅速性の点からは、上記２つの方法と比較すると優位である。しかし、マクロ腐食法は、目視による判定となるため、非定量的な評価となるという問題がある。また、Ｈプリント法は、定量的ではあるが、評価に熟練を要し、時間がかかり、コストが高いという問題がある。
In addition, the drill method is faster than the slicing method, but there is a problem that the whole area cannot be evaluated because the chip collection region is further narrower than the slicing method.
On the other hand, the macro corrosion method is superior to the above two methods in terms of rapidity. However, the macro-corrosion method has a problem of non-quantitative evaluation because it is determined visually. In addition, the H printing method is quantitative, but requires skill for evaluation, takes time, and has a high cost.
上記以外の中心偏析を評価する方法としては、特許文献１に、中心偏析部の硬さを測定し、その硬さの平均値、最大値および最大値と最小値の差のいずれか１以上の値を用いて、中心偏析を評価する簡便な方法が提案されている。
しかしながら、特許文献１の方法は、腐食によって中心偏析部の領域を特定し、その中心偏析部の硬さを測定して評価しているため、腐食作業が必要であることや、鋳片全幅を評価する場合には、偏析部のすべての硬さを測定する必要があること等から、非常に時間がかかり、迅速性に劣る。
さらに、硬さは、Ｃ等の鋳片の成分組成や組織等と関連があるため、それらが異なる場合には、直接評価することができない。そのため、様々な種類の鋳片の中心偏析を評価するには、測定条件を細かく分けて決めておかなければならないという問題があった。
However, the method of
Furthermore, since the hardness is related to the composition of the slab such as C, the structure, etc., if they are different, it cannot be directly evaluated. Therefore, in order to evaluate the center segregation of various types of slabs, there is a problem that the measurement conditions must be determined in detail.
そこで、本発明の目的は、連続鋳造鋳片や厚板等の中心偏析を、定量的かつ高精度で、しかも広い領域を迅速に評価することができる中心偏析評価方法を提案することにある。 Accordingly, an object of the present invention is to propose a center segregation evaluation method capable of quantitatively and accurately evaluating center segregation of a continuously cast slab, a thick plate, and the like, and quickly evaluating a wide area.
発明者らは、従来行なわれているスライス法やドリル法、マクロ腐食法などの問題点、即ち、広い領域における中心偏析を迅速かつ高精度で、しかも定量的に評価することが難しいという問題点を解決するため、鋭意検討を重ねた。その結果、鋳片や厚鋼板等の製品品質に影響が大きい、ある特定元素を指標元素とし、その指標元素の中心偏析部における濃度がある所定濃度以上である領域の面積と、製品品質との間に極めて強い相関があり、上記面積によって中心偏析の程度を評価できることを見出し、本発明を完成させた。 The inventors have problems such as the conventional slicing method, drilling method, and macro corrosion method, that is, it is difficult to evaluate the center segregation in a wide area quickly, with high accuracy, and quantitatively. In order to solve the problem, intensive study was repeated. As a result, the product quality and the area of the region where the concentration in the central segregation part of the index element is greater than or equal to a predetermined concentration is determined as an index element, which has a large effect on the product quality such as slabs and thick steel plates. It was found that there is a very strong correlation between them, and the degree of central segregation can be evaluated by the above area, and the present invention has been completed.
すなわち、本発明は、連続鋳造鋳片および厚鋼板の中心偏析を評価する方法であって、中心偏析部を含む領域の濃度マッピング分析をＣ断面全幅に亘って行い、指標元素の濃度が所定の閾値濃度以上である面積を求め、その面積をもって中心偏析を評価することを特徴とする中心偏析評価方法である。
That is, the present invention is a method for evaluating the center segregation of a continuous cast slab and a thick steel plate, and the concentration mapping analysis of the region including the center segregation part is performed over the entire C cross section , and the concentration of the indicator element is predetermined. The center segregation evaluation method is characterized in that an area that is equal to or higher than a threshold concentration is obtained and the center segregation is evaluated using the area.
本発明の中心偏析評価方法は、上記指標元素として、Ｎｂ，Ｍｎ，Ｃ，Ｓ，ＰおよびＴｉを用いることを特徴とする。 The center segregation evaluation method of the present invention is characterized in that Nb, Mn, C, S, P and Ti are used as the index element.
また、本発明の中心偏析評価方法は、濃度マッピング分析を、ＥＰＭＡ、発光分光分析およびＳＥＭ−ＥＤＸのいずれかを用いて行うことを特徴とする。 The center segregation evaluation method of the present invention is characterized in that concentration mapping analysis is performed using any one of EPMA, emission spectroscopic analysis, and SEM-EDX.
本発明によれば、連続鋳造鋳片や厚鋼板の中心部の偏析を、定量的かつ高精度で、しかも広い領域を迅速に測定することができるので、中心偏析の評価を正確かつ迅速に行うことができ、ひいては、連続鋳造鋳片や厚鋼板等の品質向上に大いに寄与することが可能となる。 According to the present invention, the segregation of the central portion of a continuous cast slab or a thick steel plate can be measured quantitatively and with high accuracy, and a wide area can be quickly measured. As a result, it is possible to greatly contribute to the quality improvement of continuous cast slabs and thick steel plates.
本発明は、連続鋳造鋳片および厚鋼板の中心偏析を評価するに際して、ある特定の元素を指標元素として用い、その指標元素の中心偏析部を含む領域における濃度を分析して濃度マッピングを作成する濃度マッピング分析をＣ断面全幅に亘って行い、その指標元素の濃度がある所定の濃度以上である面積を求め、その面積の大きさから中心偏析の程度を評価し、製品の品質を判定しようとする方法である。
In the present invention, when evaluating the center segregation of continuously cast slabs and thick steel plates, a specific element is used as an indicator element, and the concentration in the region including the center segregation portion of the indicator element is analyzed to create a concentration mapping. Concentration mapping analysis is performed over the entire width of the C section , the area where the concentration of the indicator element is equal to or greater than a predetermined concentration is determined, the degree of central segregation is evaluated from the size of the area, and the product quality is determined. It is a method to do.
ここで、上記指標とする元素としては、鋳片や厚鋼板等の製品品質に影響が大きい元素を用いることが好ましく、Ｎｂ，Ｍｎ，Ｃ，Ｓ，ＰおよびＴｉ等を用いることができる。例えば、Ｎｂを添加したラインパイプ用素材では、析出したＮｂＣの個数や量が、水素誘起割れ（Ｈｙｄｒｏｇｅｎ Ｉｎｄｕｃｅｄ Ｃｒａｃｋｉｎｇ：ＨＩＣ）に影響することが知られていることから、Ｎｂを指標元素として好適に用いることができる。また、ＭｎＳは、割れの起点になり、やはり水素誘起割れ（ＨＩＣ）に影響を及ぼすことから、ＭｎやＳも指標元素として好適に用いることができる。ただし、Ｓは、数ｍａｓｓｐｐｍまで低減されている場合には、指標元素として用いるのは難しい。その他に用いることができる元素としては、ＳｉやＣｒ，Ｎｉ，Ｍｏ，Ｃｕ等がある。 Here, it is preferable to use an element having a large influence on the product quality such as a slab or a thick steel plate as the index element, and Nb, Mn, C, S, P, Ti, or the like can be used. For example, in a line pipe material to which Nb is added, it is known that the number and amount of precipitated NbC affects hydrogen induced cracking (HIC), so Nb is preferably used as an indicator element. Can be used. Further, since MnS becomes a starting point of cracking and also affects hydrogen induced cracking (HIC), Mn and S can also be suitably used as an indicator element. However, when S is reduced to several mass ppm, it is difficult to use S as an indicator element. Other elements that can be used include Si, Cr, Ni, Mo, and Cu.
また、上記指標元素の濃化領域の面積を求める際に用いる閾値は、指標として用いる元素や鋼の成分組成、マッピングの画素数の大きさによっても変動するので、予め、実験等を行い、最適化するのが好ましい。例えば、鋳片と厚鋼板では、中心偏析の厚さ方向の幅が異なる。そのため、鋳片のマッピング画素数で厚鋼板を測定すると、画素数が大きくなり過ぎるため偏析を検出できない。そこで、鋳片に対しては１００μｍ角、厚鋼板に対しては１０μｍ角のように、中心偏析の厚さ方向の幅を考慮したマッピング画素数を採用する。その後、閾値レベルを調整して、品質と最もよい相関が得られる閾値を決定するのが好ましい。 In addition, the threshold value used when determining the area of the concentration region of the index element varies depending on the element used as the index, the composition of steel, and the size of the number of mapping pixels. Is preferable. For example, the width in the thickness direction of the center segregation differs between the slab and the thick steel plate. Therefore, if a thick steel plate is measured with the number of mapping pixels of a slab, segregation cannot be detected because the number of pixels becomes too large. Therefore, the number of mapping pixels in consideration of the width in the thickness direction of the center segregation is employed, such as 100 μm square for the cast slab and 10 μm square for the thick steel plate. Thereafter, the threshold level is preferably adjusted to determine the threshold that provides the best correlation with quality.
また、濃度マッピング分析に用いる分析機器としては、ＥＰＭＡや発光分光分析装置およびＳＥＭ−ＥＤＸ等、マッピング分析できるものであれば、いずれでも用いることができる。中でも、ＥＰＭＡは、迅速性に優れる点から好適である。 Moreover, as an analytical instrument used for the concentration mapping analysis, any apparatus capable of mapping analysis, such as EPMA, an emission spectroscopic analyzer, and SEM-EDX, can be used. Among these, EPMA is preferable because it is excellent in rapidity.
本発明に係る中心偏析評価方法を、Ｃ：０．４０〜０．４７ｍａｓｓ％、Ｓｉ：０．３ｍａｓｓ％、Ｍｎ：１．１ｍａｓｓ％、Ｐ：０．００５ｍａｓｓ％、Ｓ：０．０００６ｍａｓｓ％、Ｃｕ：０．１７ｍａｓｓ％、Ｎｉ：０．１０ｍａｓｓ％、Ｍｏ：０．０８ｍａｓｓ％、Ｎｂ：０．０３７ｍａｓｓ％、Ｖ：０．０２３ｍａｓｓ％、Ｔｉ：０．０１０ｍａｓｓ％、Ａｌ：０．０３ｍａｓｓ％、Ｃａ：０．００２５ｍａｓｓ％、Ｎ：０．００４ｍａｓｓ％の成分組成を有するＡＰＩ規格Ｘ６０級のラインパイプ用厚鋼板（板厚：１９ｍｍ×幅：３２００ｍｍ）に適用し、中心偏析とＨＩＣとの関係を調査した。 The center segregation evaluation method according to the present invention was performed using C: 0.40 to 0.47 mass%, Si: 0.3 mass%, Mn: 1.1 mass%, P: 0.005 mass%, S: 0.0006 mass%, Cu. : 0.17 mass%, Ni: 0.10 mass%, Mo: 0.08 mass%, Nb: 0.037 mass%, V: 0.023 mass%, Ti: 0.010 mass%, Al: 0.03 mass%, Ca: Applied to API standard X60 grade thick steel plate for line pipes (component thickness: 19 mm x width: 3200 mm) having a component composition of 0.0025 mass%, N: 0.004 mass%, and investigated the relationship between center segregation and HIC. .
中心偏析測定用およびＨＩＣ試験用の試験片は、素材用の厚鋼板から、図１に示したように、中心偏析測定用とＨＩＣ試験用の２つの試験片が長手方向で対となるように採取した。なお、各試験片の寸法は、中心偏析測定用が、幅方向：４０ｍｍ×長さ方向：１０ｍｍ×板厚、ＨＩＣ試験用は、幅方向：２０ｍｍ×長さ方向：１００ｍｍ×板厚とした。
＜中心偏析＞
上記位置から採取した中心偏析測定用試験片のＣ断面を研磨し、板厚中心部の中心偏析部を含む厚さ方向：２ｍｍ×幅方向：４０ｍｍの領域について、偏析指標元素としてＮｂを選択し、ＥＰＭＡを用いてマッピング分析を行った。なお、ＥＰＭＡ分析は、加速電圧：２５ｋＶ、照射電流：５μＡ、ビーム径：２０μｍ、積算時間：１０ｍｓｅｃの条件で、Ｎｂの蛍光Ｘ線強度を測定し、この強度を予め標準試料で求めておいた検量線を用いて濃度（ｍａｓｓ％）に換算し、Ｎｂが０．４ｍａｓｓ％以上に偏析している領域の面積を測定した。分析に要した時間は、１試料当たり１．５時間であった。
＜ＨＩＣ試験＞
上記位置から採取したＨＩＣ試験片を用いて、ＮＡＣＥ ＴＭ０２８４−９６規格に準じてＨＩＣ試験を行い、割れ面積率（ＣＡＲ（％））を測定した。
As shown in FIG. 1, the test pieces for the center segregation measurement and the HIC test are made from the steel plate for the raw material so that the two test pieces for the center segregation measurement and the HIC test are paired in the longitudinal direction. Collected. In addition, the dimension of each test piece was set to the width direction: 40 mm x length direction: 10 mm x plate thickness for the center segregation measurement, and the width direction: 20 mm x length direction: 100 mm x plate thickness for the HIC test.
<Center segregation>
The C section of the center segregation measurement specimen collected from the above position is polished, and Nb is selected as the segregation index element for the thickness direction: 2 mm × width direction: 40 mm region including the center segregation portion at the center of the plate thickness. Mapping analysis was performed using EPMA. In EPMA analysis, the fluorescent X-ray intensity of Nb was measured under the conditions of accelerating voltage: 25 kV, irradiation current: 5 μA, beam diameter: 20 μm, integration time: 10 msec, and this intensity was previously obtained from a standard sample. It converted into the density | concentration (mass%) using the analytical curve, and the area of the area | region which Nb segregated to 0.4 mass% or more was measured. The time required for the analysis was 1.5 hours per sample.
<HIC test>
An HIC test was performed according to the NACE TM0284-96 standard using the HIC test piece collected from the above position, and the crack area ratio (CAR (%)) was measured.
図２は、板幅方向位置が同じ位置での中心偏析測定結果（Ｎｂ：０．４ｍａｓｓ％以上の面積）とＨＩＣ試験結果（ＣＡＲ）とを対応させて示したものである。この図から、Ｎｂの偏析とＣＡＲとは相関があり、Ｎｂ：０．４ｍａｓｓ％以上の面積が７５００μｍ２以上になると、ＨＩＣが発生するようになることが見て取れる。
以上の結果から、本発明による中心偏析評価方法は、製品の内部品質や耐水素誘起割れ（ＨＩＣ）性等の特性を定量的に精度よくかつ迅速に評価するのに有効な手段であることがわかった。
FIG. 2 shows the center segregation measurement result (Nb: area of 0.4 mass% or more) and the HIC test result (CAR) at the same position in the plate width direction. From this figure, it can be seen that there is a correlation between the segregation of Nb and CAR, and that HIC is generated when the area of Nb: 0.4 mass% or more becomes 7500 μm 2 or more.
From the above results, the center segregation evaluation method according to the present invention is an effective means for quantitatively and accurately evaluating characteristics such as internal quality and resistance to hydrogen induced cracking (HIC) of products. all right.
本発明の中心偏析評価技術は、鋳片や厚鋼板に限定されるものではなく、各種の鋼板や金属板の偏析評価にも適用することができる。 The center segregation evaluation technique of the present invention is not limited to cast slabs and thick steel plates, but can also be applied to segregation evaluation of various steel plates and metal plates.
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| JP5910195B2 (en) * | 2012-03-14 | 2016-04-27 | Ｊｆｅスチール株式会社 | Method for evaluating HIC resistance of steel material and method for producing high strength thick steel plate for line pipe using the same |
| CN102768129A (en) * | 2012-07-10 | 2012-11-07 | 莱芜钢铁集团有限公司 | Casting blank ingredient segregation sampling method and detecting method |
| JP6043217B2 (en) * | 2013-03-08 | 2016-12-14 | 株式会社神戸製鋼所 | How to change the destination by judging the quality of the sour steel slab |
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| JPS57142551A (en) * | 1981-02-27 | 1982-09-03 | Nippon Steel Corp | Determination of foreign matter in metal |
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| JPH069733B2 (en) * | 1986-07-11 | 1994-02-09 | 新日本製鐵株式会社 | Judgment method of steel slab excellent in hydrogen-induced cracking resistance |
| JPH01145558A (en) * | 1987-12-01 | 1989-06-07 | Kawasaki Steel Corp | Adjusting method of analytical sample of light element by electron beam probe x-ray analysis |
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