JP2011033457A - Evaluation method of brittle fracture propagation stopping performance of thick steel plate - Google Patents
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本発明は、船舶、海洋構造物、低温貯蔵タンクおよび建築・土木構造物等の大型構造物に用いられる厚鋼板、特に厚みが50mm以上の厚鋼板の脆性破壊伝播停止性能の評価方法に関する。 The present invention relates to a method for evaluating brittle fracture propagation stopping performance of thick steel plates used for large structures such as ships, marine structures, low-temperature storage tanks, and construction / civil engineering structures, and particularly thick steel plates having a thickness of 50 mm or more.
前記の大型構造物においては、脆性破壊に伴う事故が経済や環境に及ぼす影響が大きく、安全性の向上が常に求められるところから、使用される鋼材に対しては、使用温度における靭性や脆性破壊伝播停止性能を有することが要求されている。 In the large structures described above, accidents associated with brittle fractures have a large impact on the economy and the environment, and since there is always a need to improve safety, the toughness and brittle fracture at the service temperature are used for the steel materials used. It is required to have propagation stop performance.
脆性破壊伝播停止性能の評価は、ESSO試験や二重引張試験に代表されるような、大型試験にて行われるのが通例である。しかし、これらの試験は大型であるため、試験を行うために多くの日数やコストを要することになり、簡便に行うことが難しい点が問題となる試験である。 The evaluation of brittle fracture propagation stop performance is usually performed in a large-scale test such as an ESSO test or a double tensile test. However, since these tests are large, many days and costs are required to perform the tests, and it is a test that is difficult to perform easily.
この問題を解決するための方法として、大型試験に代りシャルピー衝撃試験や落重試験（ＤＷＴＴ）など、比較的小型で簡易な評価方法が開発されている。この落重試験については、より安定して脆性破面から試験が進行するように、試験片の板厚方向に圧縮変形を与えた後に、プレスノッチにより試験片を作製する方法が、特許文献１にて提案されている。 As a method for solving this problem, a comparatively small and simple evaluation method such as a Charpy impact test and a drop weight test (DWTT) has been developed instead of a large test. Regarding this drop weight test, Patent Document 1 discloses a method in which a test piece is prepared by a press notch after compressive deformation is applied in the thickness direction of the test piece so that the test proceeds more stably from a brittle fracture surface. Has been proposed.
また、シャルピー衝撃試験片に代り、より効率よく脆性破面から試験を進行させる方法として、シャルピー衝撃試験片のノッチに相当する部分に溶接ビードを盛った後に深さ２mm以下のソーノッチを入れる試験片を用いることが、特許文献２に提案されている。 In addition, instead of Charpy impact test piece, as a method of proceeding from the brittle fracture surface more efficiently, a test piece in which a saw bead with a depth of 2mm or less is placed after depositing a weld bead on the part corresponding to the notch of the Charpy impact test piece Is proposed in Patent Document 2.
さらに、非特許文献１には、板厚位置により靭性に分布があることに起因して、脆性破壊伝播停止性能を表す、ESSO試験により求まるＫca値は低靭性領域の影響を強く受ける、として、各板厚位置における靭性値をその鋼板の面積平均を取った値に、さらに、板厚中央部の値を重み付けして脆性破壊伝播停止性能を評価している。その他、板厚効果を考慮した、脆性破壊伝播停止性能の簡易評価法について、板厚中心部と表層部から採取した試験片を用い、３点曲げ試験を行った結果よりＫca値を予測する方法が、特許文献３に提案されている。また、特許文献４には、特殊形状を有する変形シャルピー衝撃試験片を用いて脆性破壊伝播停止性能を評価する技術が提案されている。 Furthermore, in Non-Patent Document 1, due to the distribution of toughness depending on the plate thickness position, the Kca value obtained by the ESSO test representing brittle fracture propagation stop performance is strongly influenced by the low toughness region. The brittle fracture propagation stopping performance is evaluated by weighting the toughness value at each plate thickness position to the value obtained by taking the average of the area of the steel plate and further the value at the center portion of the plate thickness. In addition, with regard to the simple evaluation method of brittle fracture propagation stopping performance in consideration of the plate thickness effect, the Kca value is predicted from the results of a three-point bending test using test pieces taken from the plate thickness center and the surface layer. Is proposed in Patent Document 3. Patent Document 4 proposes a technique for evaluating brittle fracture propagation stopping performance using a deformed Charpy impact test piece having a special shape.
しかしながら、特許文献１〜３の試験片の採取方法は、試験片の大きさの面や、溶接を行った後に再度加工を行うことなどから、試験片の作製が煩雑であり必ずしも簡便な方法とは言い難い。特許文献４の技術は、試験片形状が特殊であるため、汎用性に乏しい。また、非特許文献１の板厚位置の靭性値を考慮して求めたＫca値と実際の実験結果との相関もある程度の一致は見られるものの全体としてばらつきが大きく、この方法により大型試験の代りと出来るほどには一致していないのが現状である。 However, the method for collecting the test pieces of Patent Documents 1 to 3 is a simple method that is complicated and difficult to prepare because the size of the test piece or the processing is performed again after welding. Is hard to say. The technique of Patent Document 4 is poor in versatility because the shape of the test piece is special. In addition, the correlation between the Kca value obtained in consideration of the toughness value at the plate thickness position of Non-Patent Document 1 and the actual experimental result is somewhat consistent, but the overall variation is large. The current situation is that they do not agree as much as possible.
そこで、本発明は、大型試験を行わずとも厚鋼板の脆性破壊伝播停止性能を正確に評価できる簡易な手法を提供することを目的とするものである。 Therefore, an object of the present invention is to provide a simple method capable of accurately evaluating the brittle fracture propagation stopping performance of a thick steel plate without performing a large test.
本発明者らは、上記課題の達成に向けて、厚肉材の脆性破壊伝播停止性能と、様々な小型試験との関連について鋭意検討し、以下の知見を得た。
(i)脆性亀裂伝播停止性能は、脆性亀裂の進展する方向にプレスによるノッチを入れた試験片を用いたシャルピー衝撃試験と良い相関がある。
(ii)また、板厚が50mm以上となるような極厚鋼板において、脆性破壊伝播停止性能は、ある特定の一カ所の板厚位置における材料特性によらずに、板厚方向の分散位置での材料特性を総合した特性に影響を受ける。
(iii)色々な板厚位置におけるプレスノッチシャルピー衝撃試験を行い、脆性破壊伝播停止性能との関係を調査した結果、板厚中心部および1／4部でのプレスノッチシャルピー衝撃試験の破面遷移温度を総合した結果が、脆性破壊伝播停止性能の値と最も良い相関が得られる。
In order to achieve the above-mentioned problems, the present inventors diligently investigated the relationship between the brittle fracture propagation stopping performance of a thick-walled material and various small tests, and obtained the following knowledge.
(i) The brittle crack propagation stopping performance has a good correlation with the Charpy impact test using a test piece notched by a press in the direction in which the brittle crack propagates.
(ii) Also, in an extremely thick steel sheet having a thickness of 50 mm or more, the brittle fracture propagation stop performance is not limited by the material properties at a specific one thickness position, but at a dispersed position in the thickness direction. It is influenced by the total characteristics of the materials.
(iii) Press notch Charpy impact test at various plate thickness positions and investigation of the relationship with brittle fracture propagation stop performance. As a result, the fracture surface transition of the press notch Charpy impact test at the center and 1/4 part of the plate thickness The result of combining the temperatures gives the best correlation with the brittle fracture propagation stop performance value.
本発明は、上記した知見を基に更に検討を加えてなされたものであり、その要旨は次のとおりである。
（１）厚鋼板につき、その板厚の中心部および表面から板厚の１／４の位置から採取しプレスノッチを導入したシャルピー衝撃試験片を用いて、シャルピー衝撃試験を行い、試験片毎のシャルピー衝撃試験にて得られた破面遷移温度vTrs＊に基いて、脆性破壊伝播停止性能を評価することを特徴とする厚鋼板の脆性破壊伝播停止性能の評価方法。
The present invention has been made by further study based on the above-described findings, and the gist thereof is as follows.
(1) A Charpy impact test was performed on a thick steel plate using a Charpy impact test piece that was sampled from the center of the plate thickness and from the position ¼ of the plate thickness and introduced a press notch. A method for evaluating the brittle fracture propagation stop performance of a thick steel plate, characterized by evaluating the brittle fracture propagation stop performance based on the fracture surface transition temperature vTrs * obtained in the Charpy impact test.
（２）前記破面遷移温度vTrs＊に基いて、下記式（１）に従って算出されるＴｋ＊をもって、脆性破壊伝播停止性能（Ｋca値）が6000Ｎ／mm1.5となる温度を推定することを特徴とする厚鋼板の脆性破壊伝播停止性能の評価方法。
記
Ｔｋ＊＝35＋0.5×vTrs＊（C）＋0．3×vTrs＊（Q）・・・（1）
但し、
vTrs＊（C）：板厚中心部から採取したプレスノッチシャルピー衝撃試験片を用
いて実施したシャルピー衝撃試験における脆性破面率が75％となる温度。
vTrs＊（Q）：表面から板厚の１／４の位置から採取したプレスノッチシャルピー
衝撃試験片を用いて実施したシャルピー衝撃試験における脆性破面率が75％とな
る温度。
(2) Based on the fracture surface transition temperature vTrs * , the temperature at which the brittle fracture propagation stopping performance (Kca value) is 6000 N / mm 1.5 is estimated with Tk * calculated according to the following formula (1). Evaluation method of brittle fracture propagation stopping performance of thick steel plate.
Tk * = 35 + 0.5 x vTrs * (C) + 0.3 x vTrs * (Q) (1)
However,
vTrs * (C): Temperature at which the brittle fracture surface ratio is 75% in the Charpy impact test conducted using a press-notched Charpy impact specimen taken from the center of the plate thickness.
vTrs * (Q): Temperature at which the brittle fracture surface ratio is 75% in the Charpy impact test carried out using a press-notched Charpy impact test specimen taken from 1/4 of the plate thickness from the surface.
本発明によれば、特に板厚50mm以上の厚鋼板について脆性破壊伝播停止性能を評価する際に、大型の脆性亀裂伝播試験を行わずとも、通常行っているシャルピー衝撃試験と同様のサイズの試験片を用いて、簡便かつ精度良く脆性破壊伝播停止性能を評価できるため、産業上極めて有用である。 According to the present invention, when evaluating the brittle fracture propagation stoppage performance particularly for a thick steel plate having a thickness of 50 mm or more, a test having the same size as the normal Charpy impact test is performed without performing a large brittle crack propagation test. Since the piece can be used to evaluate the brittle fracture propagation stopping performance simply and accurately, it is extremely useful in the industry.
さて、前記した大型構造物に用いられる厚鋼板の脆性亀裂伝播性能は、日本溶接協会規格 WES3003 「低温用圧延鋼板判定基準」（1995）に準拠した、大型試験片を用いたESSO試験により求まるＫca値をもって評価するのが一般的である。かように、この試験方法では、大型試験体の使用を余儀なくされる点、小型の試験片を用いての試験での代替を鋭意検討した。 The brittle crack propagation performance of the thick steel plates used in the large structures described above is determined by the ESSO test using large specimens in accordance with the Japan Welding Association Standard WES3003 “Low Temperature Rolled Steel Sheet Judgment Criteria” (1995). It is common to evaluate by value. As described above, in this test method, the use of a large test specimen is unavoidable, and an alternative to a test using a small test piece has been intensively studied.
まず、シャルピー衝撃試験による代替を検討したところ、大型試験の代りになるほどの一致を得るに至らなかった。次に、試験片の条件について更なる実験を繰り返したところ、切り欠きによるノッチではなくプレスによるノッチを導入したシャルピー衝撃試験片を用いた場合に、シャルピー衝撃試験結果が、脆性亀裂伝播性能試験の結果と良い相関を示すことが判明した。そこで、プレスノッチを導入したシャルピー衝撃試験片（本発明では、単に「プレスノッチシャルピー衝撃試験片」とも称する）によるシャルピー衝撃試験を様々な条件で行ったところ、厚鋼板の板厚中心部および1／4厚み部分からそれぞれ採取したプレスノッチシャルピー衝撃試験片による破面遷移温度を総合した結果が、脆性破壊伝播停止性能の値と最も良い相関が得られることを見出すに至った。 First of all, when the alternative by the Charpy impact test was examined, it was not possible to obtain a consensus enough to replace the large test. Next, when further experiments were repeated on the test piece conditions, the Charpy impact test result was obtained in the case of the brittle crack propagation performance test when using a Charpy impact test piece in which a press notch was introduced instead of a notch notch. It was found to show a good correlation with the results. Therefore, when a Charpy impact test using a Charpy impact test piece (in the present invention, simply referred to as a “press notch Charpy impact test piece”) into which a press notch was introduced was performed under various conditions. / 4 The results obtained by combining the fracture surface transition temperatures obtained by press-notch Charpy impact test specimens collected from the thickness parts, respectively, have been found to have the best correlation with the brittle fracture propagation stop performance value.
従って、本発明では、厚鋼板の板厚の中心および表面から板厚の１／４の位置から採取し、これにプレスノッチを導入したシャルピー衝撃試験片を用いてシャルピー衝撃試験を行い、得られた破面遷移温度vTrs＊に基いて、脆性破壊伝播停止性能を評価することとした。 Therefore, in the present invention, a Charpy impact test is performed by using a Charpy impact test piece obtained by sampling from the center of the thickness of the thick steel plate and a position 1/4 of the thickness from the surface, and introducing a press notch into this. Based on the fracture surface transition temperature vTrs * , we decided to evaluate the brittle fracture propagation stop performance.
なお、プレスノッチは、以下のように導入することが好ましい。すなわち、試験片方向を考慮したうえで、試験片を採取すべき素材を分割・切断し、さらに、外形仕上げ加工を施して得られた直方体状の小鋼片に対して、切り欠き部を刃型で圧入し、例えば、図１に示す、深さ２mm、角度45度の２mmＶ切欠き試験片を作製すればよい。ここで、得られる衝撃試験結果から、脆性破壊発生特性の影響を排除する目的で、試験後のプレスノッチシャルピー衝撃試験片を観察し、脆性亀裂から破壊が発生していない試験片は脆性亀裂伝播停止性能の評価をしていないとみなし、試験結果には反映しないものとする。なぜなら、脆性亀裂から破壊が発生している試験片のみを用いた衝撃試験の結果は、脆性破壊発生特性の影響を排除し、本発明が対象とする脆性破壊伝播停止性能のみの優劣を反映したものになるからである。 The press notch is preferably introduced as follows. In other words, taking into account the direction of the test piece, the material from which the test piece is to be collected is divided and cut, and further, the notch is cut into a rectangular parallelepiped small steel piece obtained by finishing the outer shape. For example, a 2 mm V-notched test piece having a depth of 2 mm and an angle of 45 degrees shown in FIG. Here, for the purpose of eliminating the influence of the brittle fracture occurrence characteristics from the obtained impact test results, press-notch Charpy impact test specimens after the test were observed, and test specimens where no fracture occurred from brittle cracks It is assumed that the stop performance has not been evaluated and will not be reflected in the test results. This is because the result of the impact test using only the test piece in which the fracture has occurred from the brittle crack excludes the influence of the brittle fracture occurrence characteristic and reflects the superiority or inferiority of the brittle fracture propagation stop performance targeted by the present invention. Because it becomes a thing.
次に、前記シャルピー衝撃試験にて得られた破面遷移温度vTrs＊に基づいて脆性破壊伝播停止性能を評価する際の具体例を、詳しく説明する。
まず、一例として、脆性破壊伝播停止性能Ｋca値が6000Ｎ／mm1.5となる温度の推定をもって脆性破壊伝播停止性能を評価する場合について、以下に説明する。
ここで、Ｋca値が6000Ｎ／mm1.5となる特性温度に着目したのは、次のような理由による。すなわち、最近の研究成果として、板厚75mm以下の鋼板の場合、−10℃におけるＫca値が6000Ｎ／mm1.5以上であれば、−10℃において脆性亀裂が停止することが確認された。そこで、本発明においては、プレスノッチを形成したシャルピー衝撃試験片を用いてシャルピー衝撃試験を行って得られた破面遷移温度vTrs＊から、Ｋca値が6000Ｎ／mm1.5となる温度を求め、それが、基準である−10℃より高いか低いかによって、脆性破壊伝播停止性能を評価することとしたものである。
Next, a specific example for evaluating brittle fracture propagation stop performance based on the fracture surface transition temperature vTrs * obtained in the Charpy impact test will be described in detail.
First, as an example, the case where the brittle fracture propagation stop performance is evaluated by estimating the temperature at which the brittle fracture propagation stop performance Kca value is 6000 N / mm 1.5 will be described below.
The reason for paying attention to the characteristic temperature at which the Kca value is 6000 N / mm 1.5 is as follows. That is, as a recent research result, it was confirmed that in the case of a steel sheet having a plate thickness of 75 mm or less, if the Kca value at −10 ° C. is 6000 N / mm 1.5 or more, the brittle crack stops at −10 ° C. Therefore, in the present invention, the temperature at which the Kca value is 6000 N / mm 1.5 is obtained from the fracture surface transition temperature vTrs * obtained by performing the Charpy impact test using the Charpy impact test piece in which the press notch is formed. However, the brittle fracture propagation stoppage performance is evaluated depending on whether it is higher or lower than the standard −10 ° C.
すなわち、厚鋼板、中でも板厚が50mm以上の厚鋼板に対して、その板厚の中心部および表面から板厚の１／４の位置からシャルピー衝撃試験片を採取し、この試験片にプレスノッチを導入してから、種々の試験温度にてシャルピー衝撃試験を行う。
なお、プレスノッチの導入方向としては、亀裂の伝播する方向に採取すべきであるため、ESSO試験におけるノッチ方向に、具体的には圧延方向もしくは圧延幅方向に入れるものとする。このプレスノッチシャルピー衝撃試験の結果より、各試験片によるシャルピー衝撃試験において、脆性破面率が75％となった時の温度を破面遷移温度（vTrs＊）とし、各試験片によるvTrs＊を、板厚中心部および板厚1／4においてそれぞれ求めて、その値を下記（１）式に代入することによってＴｋ＊を求める。ここで求まるＴｋ＊は、ESSO試験により測定される、脆性破壊伝播停止性能Ｋca値が6000Ｎ／mm1.5となる特性温度Ｔｋ（6000）と極めて良好な相関を示し、従って、前記の如く算出したＴｋ＊をもって、脆性破壊伝播停止性能の評価が可能になる。
記
Ｔｋ＊＝35＋0.5×vTrs＊（C）＋0.3×vTrs＊（Q）・・・（1）
但し、
vTrs＊（C）：板厚中心部から採取したプレスノッチシャルピー衝撃試験片を用い
て実施したシャルピー衝撃試験における脆性破面率が75％となる温度。
vTrs＊（Q）：表面から板厚の１／４の位置から採取したプレスノッチシャルピー
衝撃試験片を用いて実施したシャルピー衝撃試験における脆性破面率が75％とな
る温度。
That is, for a thick steel plate, especially a thick steel plate having a thickness of 50 mm or more, a Charpy impact test piece was taken from the center of the plate thickness and a position 1/4 of the plate thickness from the surface. Then, Charpy impact test is performed at various test temperatures.
In addition, since it should extract to the direction which a crack propagates as an introduction direction of a press notch, it shall put in the notch direction in an ESSO test, specifically, a rolling direction or a rolling width direction. The results of this press-notch Charpy impact test, the Charpy impact test according to the test piece, the temperature at which brittle fracture rate becomes 75% and fracture appearance transition temperature (vTrs *), the vTrs * by each test piece Then, Tk * is obtained by obtaining the thickness center part and the thickness 1/4, respectively, and substituting the values into the following equation (1). The Tk * obtained here shows a very good correlation with the characteristic temperature Tk (6000) at which the brittle fracture propagation stop performance Kca value measured by the ESSO test is 6000 N / mm 1.5 . Therefore, the Tk calculated as described above is obtained. * Enables evaluation of brittle fracture propagation stop performance.
Tk * = 35 + 0.5 x vTrs * (C) + 0.3 x vTrs * (Q) (1)
However,
vTrs * (C): Temperature at which the brittle fracture surface ratio in a Charpy impact test conducted using a press-notched Charpy impact test specimen taken from the center of the plate thickness is 75%.
vTrs * (Q): Temperature at which the brittle fracture surface ratio is 75% in the Charpy impact test carried out using a press-notched Charpy impact test specimen taken from 1/4 of the plate thickness from the surface.
ここで、上記した式（１）は、種々の試験片について板厚中心部のvTrs＊および板厚1／4部のvTrs＊を測定するとともに、これら試験片と共通の試験体について特性温度Ｔｋ（6000）を測定し、これらの測定結果を整理し、板厚中心部のvTrs＊および板厚1／4のvTrs＊と特性温度Ｔｋ（6000）との相関を実験的に求めたものである。 Here, the above-mentioned equation (1) is adapted to measure the vTrs * of vTrs * and thickness 1/4 parts of the thickness center portion for the various specimens, the characteristic temperature on a common specimen with these test pieces Tk (6000) was measured, to organize these measurements is the correlation between the thickness center portion vTrs * and thickness 1/4 vTrs * and characteristic temperature Tk (6000) that determined experimentally .
また、遷移温度vTrs＊を脆性破面率が75％となる温度としたのは、本発明では、プレスノッチ加工を行う事により発生した脆性亀裂が、停止し始める試験温度を求めることが目的であるので、脆性亀裂が鋼板の特性により停止したと認識できる破面率として75%を採用した。 In addition, the transition temperature vTrs * is set to a temperature at which the brittle fracture surface ratio is 75%, in the present invention, for the purpose of obtaining a test temperature at which a brittle crack generated by press notching starts to stop. Therefore, 75% was adopted as the fracture surface ratio at which it can be recognized that brittle cracks stopped due to the properties of the steel sheet.
上記した評価手法以外にも、たとえば、脆性破壊伝播停止性能（Ｋca値）が4000Ｎ／mm1.5や8000Ｎ／mm1.5など、6000Ｎ／mm1.5以外の値をとる場合についても、適用可能であり、それぞれ実験結果から相関式を導くことによって、上記と同様の評価が可能となる。 Besides evaluation method described above also, for example, brittle fracture propagation stop performance (Kca value) and 4000 N / mm 1.5 or 8000 N / mm 1.5, a case where a value other than 6000 N / mm 1.5 is also applicable, respectively Evaluation similar to the above can be performed by deriving the correlation equation from the experimental results.
板厚50mm以上の数種類の厚鋼板について、板厚の1／4部および板厚中心部よりノッチ加工を行っていないシャルピー衝撃試験片素材を採取し、硬鋼で作製された刃型を用いて該試験片素材にプレスノッチを導入し、以降の衝撃試験に供した。種々の温度にてシャルピー衝撃試験を行い、脆性破面率が75％となる温度vTrs＊を求めた。なお、プレスノッチシャルピー衝撃試験は、試験後のプレスノッチシャルピー衝撃試験片を観察し、脆性亀裂から破壊が発生していない試験片は脆性亀裂伝播停止性能の評価をしていないものとみなして除外し、各試験温度において脆性亀裂から破壊が発生した試験５回の平均値をとった。その後、上記した（１）式に破面遷移温度の値を代入し、温度Ｔｋ＊を求めた。
一方、同じ数種類の厚鋼板に対して、プレスノッチシャルピー衝撃試験と併せて、大型の脆性亀裂伝播試験として、図２に示す大型試験片を用いて、ESSO試験を行い、Ｋca値が6000Ｎ／mm1.5となる温度Ｔｋ6000を求めた。
かくして得られたＴｋ＊及びＴｋ6000について表１に示す。
For several types of thick steel plates with a thickness of 50 mm or more, samples of Charpy impact test specimens that were not notched from 1/4 part of the plate thickness and the center of the plate thickness were collected and used with a blade type made of hard steel. A press notch was introduced into the specimen material and subjected to the subsequent impact test. A Charpy impact test was performed at various temperatures, and a temperature vTrs * at which the brittle fracture surface ratio was 75% was determined. In the press notch Charpy impact test, press notch Charpy impact test specimens after the test were observed, and test specimens that did not break due to brittle cracks were considered not evaluated for brittle crack propagation stop performance. The average value of five tests in which fracture occurred from the brittle cracks at each test temperature was taken. Thereafter, the value of the fracture surface transition temperature was substituted into the above equation (1) to obtain the temperature Tk * .
On the other hand, an ESSO test was performed on the same several types of thick steel plates together with the press notch Charpy impact test and a large brittle crack propagation test using the large test piece shown in FIG. 2, and the Kca value was 6000 N / mm. A temperature Tk6000 of 1.5 was determined.
Table 1 shows Tk * and Tk6000 thus obtained.
次に、表１に示した結果について、横軸に上記（１）式から得られたＴｋ＊を、縦軸にESSO試験により得られたＴｋ6000を、それぞれプロットしたグラフを、図３に示す。同図から、Ｔｋ＊とＴｋ6000との間には良い相関関係が得られ、本発明による脆性亀裂伝播停止性能の評価方法の有用性が確認された。 Next, for the results shown in Table 1, a graph plotting Tk * obtained from the above equation (1) on the horizontal axis and Tk6000 obtained by the ESSO test on the vertical axis is shown in FIG. From this figure, a good correlation was obtained between Tk * and Tk6000, confirming the usefulness of the evaluation method for brittle crack propagation stopping performance according to the present invention.
Claims (2)
記
Ｔｋ＊＝35＋0.5×vTrs＊（C）＋0．3×vTrs＊（Q）・・・（1）
但し、
vTrs＊（C）：板厚中心部から採取したプレスノッチシャルピー衝撃試験片を用
いて実施したシャルピー衝撃試験における脆性破面率が75％となる温度。
vTrs＊（Q）：表面から板厚の１／４の位置から採取したプレスノッチシャルピー
衝撃試験片を用いて実施したシャルピー衝撃試験における脆性破面率が75％とな
る温度。 Based on the fracture surface transition temperature vTrs * , the temperature at which the brittle fracture propagation stop performance (Kca value) is 6000 N / mm 1.5 is estimated from Tk * calculated according to the following formula (1). Evaluation method of brittle fracture propagation stop performance of steel sheet.
Tk * = 35 + 0.5 x vTrs * (C) + 0.3 x vTrs * (Q) (1)
However,
vTrs * (C): Temperature at which the brittle fracture surface ratio is 75% in the Charpy impact test conducted using a press-notched Charpy impact specimen taken from the center of the plate thickness.
vTrs * (Q): Temperature at which the brittle fracture surface ratio is 75% in the Charpy impact test carried out using a press-notched Charpy impact test specimen taken from 1/4 of the plate thickness from the surface.
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