JP6630191B2 - Forging steel cleanliness evaluation method - Google Patents
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本発明は、鍛鋼品の清浄度評価方法に関する。 The present invention relates to a method for evaluating cleanliness of a forged steel product.
鍛鋼品等が用いられる機械構造部材には、高い疲労強度が求められる。このような機械構造部材は、金属材料中に存在する非金属介在物が疲労破壊の起点となり易い。そのため、機械構造部材の疲労強度を向上させるために、金属材料中の非金属介在物の低減技術及び縮小技術と共に、非金属介在物の精確な評価技術が求められている。 High fatigue strength is required for a mechanical structural member using a forged steel product or the like. In such a mechanical structural member, non-metallic inclusions present in the metal material tend to be the starting points of fatigue failure. Therefore, in order to improve the fatigue strength of the mechanical structural member, a technique for accurately evaluating nonmetallic inclusions is required along with a technique for reducing and reducing nonmetallic inclusions in a metal material.
一方、最近の製鋼技術の進歩により、金属材料の清浄度は大幅に改善され、疲労強度に影響を与えるような大型非金属介在物の発生確率は非常に低くなったため、金属材料中の非金属介在物の検出が非常に困難となっている。ここで、金属材料の清浄度は非金属介在物の大きさによって判断されるため、上記非金属介在物の検出が困難となっていることにより、金属材料の清浄度の評価も困難となっている。 On the other hand, recent advances in steelmaking technology have greatly improved the cleanliness of metallic materials and greatly reduced the probability of large nonmetallic inclusions that affect fatigue strength. Inclusion detection is very difficult. Here, since the cleanliness of the metal material is determined by the size of the nonmetallic inclusions, it is difficult to detect the nonmetallic inclusions, and thus the evaluation of the cleanliness of the metal material becomes difficult. I have.
このように金属材料の清浄度の評価が困難になっていることに対して、大型非金属介在物の発生確率が低い場合でも金属材料の清浄度を評価できる方法として、極値統計法を用いる方法が提案されている（例えば特開２００１−１４１７０４号公報、特開２０００−２１４１４２号公報、特開２０１２−７３０５９号公報参照）。 As described above, it is difficult to evaluate the cleanliness of the metal material, and the extreme value statistical method is used as a method for evaluating the cleanliness of the metal material even when the probability of occurrence of large nonmetallic inclusions is low. Methods have been proposed (see, for example, JP-A-2001-141704, JP-A-2000-214142, and JP-A-2012-73059).
上記公報で提案されている極値統計法を用いる方法は、まず、検査対象の金属材料について、ｎ個の検査部位を設定し、各検査部位について非金属介在物を測定し、検査部位毎の最大非金属介在物寸法を求める。次に、上記方法は、ｎ個の検査部位で求めた各最大非金属介在物寸法に基づいて、上記金属材料中に存在する最大の非金属介在物寸法を予測する。具体的には、ｎ個の検査部位での昇順に並べた各最大非金属介在物寸法ａｊ（ｊ＝１、２、３、…、ｎ）及び基準化変数ｙｊ＝−ｌｎ［−ｌｎ｛ｊ／（ｎ＋１）｝］から作成される一次回帰式とｙｍａｘの値とから、金属材料中に存在する最大の非金属介在物寸法を予測する。なお、上記各検査部位における非金属介在物の測定は、超音波探傷や超音波疲労試験などにより行う。 In the method using the extreme value statistical method proposed in the above publication, first, for a metal material to be inspected, n inspection sites are set, nonmetallic inclusions are measured for each inspection site, and each inspection site is measured. Find the maximum non-metallic inclusion dimensions. Next, the method predicts the maximum non-metallic inclusion size present in the metal material based on each of the maximum non-metallic inclusion sizes determined at the n inspection sites. Specifically, the maximum non-metallic inclusion dimensions a j (j = 1, 2, 3,..., N) and the standardization variable y j = −ln [−ln From the primary regression equation created from {j / (n + 1)}] and the value of y max , the maximum non-metallic inclusion size existing in the metallic material is predicted. The measurement of non-metallic inclusions at each of the inspection sites is performed by ultrasonic flaw detection, ultrasonic fatigue test, or the like.
しかし、鍛鋼品においては、非金属介在物の形状が鍛造により一方向に延伸した形状に変形するため、同一介在物に対しても検査面の向きにより測定される介在物寸法が変化する。そのため、鍛鋼品の清浄度評価では、検査面の取り方によっては、予測される介在物の寸法が実際に清浄度を評価した評価面での介在物寸法と大きく乖離することがある。 However, in a forged steel product, since the shape of the nonmetallic inclusion is deformed to a shape elongated in one direction by forging, the size of the inclusion measured for the same inclusion depending on the direction of the inspection surface changes. For this reason, in the evaluation of cleanliness of a forged steel product, the size of the predicted inclusion may greatly differ from the size of the inclusion on the evaluation surface from which the cleanness was actually evaluated, depending on how the inspection surface is formed.
本発明は、上述のような事情に基づいてなされたものであり、比較的高い精度で鍛鋼品の清浄度を評価できる清浄度評価方法を提供することを目的とする。 The present invention has been made in view of the above circumstances, and has as its object to provide a cleanliness evaluation method capable of evaluating the cleanliness of a forged steel product with relatively high accuracy.
上記課題を解決するためになされた発明は、鍛鋼品内の特定の評価面における清浄度評価方法であって、ｎ個の検査面における最大非金属介在物寸法ａｉ（ｉ＝１〜ｎ）を測定する工程と、上記ｎ個の検査面の鍛伸方向に対する各角度θｉ（ｉ＝１〜ｎ）及び上記評価面の鍛伸方向に対する角度θ’を用い、各検査面の最大非金属介在物寸法ａｉを評価面での投影寸法ａ’ｉ（ｉ＝１〜ｎ）に変換する工程と、極値統計法を用い、上記評価面投影寸法ａ’ｉから評価面での推定最大非金属介在物寸法ａｍａｘを算出する工程とを備えることを特徴とする鍛鋼品の清浄度評価方法である。 The invention made in order to solve the above-mentioned problem is a method for evaluating cleanliness on a specific evaluation surface in a forged steel product, wherein a maximum nonmetallic inclusion size a i (i = 1 to n) on n inspection surfaces is provided. And the angles θ i (i = 1 to n) of the n inspection surfaces with respect to the forging direction and the angles θ ′ of the evaluation surface with respect to the forging direction are used to determine the maximum nonmetallicity of each inspection surface. A step of converting the inclusion dimension a i into a projection dimension a ′ i (i = 1 to n) on the evaluation plane, and using the extreme value statistical method to estimate the estimated maximum on the evaluation plane from the evaluation plane projection dimension a ′ i Calculating a dimension a max of the nonmetallic inclusions.
当該鍛鋼品の清浄度評価方法は、複数の検査面から得た最大非金属介在物寸法ａｉを、これらの検査面の鍛伸方向に対する角度θｉと、清浄度を評価したい評価面の鍛伸方向に対する角度θ’とを用いて、鍛鋼品内部の任意の評価面への投影寸法ａ’ｉに変換する。この評価面投影寸法ａ’ｉは、複数の検査面で測定された最大非金属介在物の寸法ａｉを、評価面で測定され得る非金属介在物の寸法にそれぞれ置き換えたものであるので、当該鍛鋼品の清浄度評価方法は、この評価面投影寸法ａ’ｉから推定最大非金属介在物寸法ａｍａｘを算出することで、評価面での清浄度を比較的高い精度で評価することができる。 The method for evaluating the cleanliness of a forged steel product includes the steps of: measuring the maximum non-metallic inclusion size a i obtained from a plurality of inspection surfaces, the angle θ i of these inspection surfaces with respect to the forging direction, and the forging of the evaluation surface to be evaluated for cleanness. Using the angle θ ′ with respect to the elongation direction, it is converted into a projection dimension a ′ i on an arbitrary evaluation surface inside the forged product. Since the evaluation plane projection dimension a ′ i is obtained by replacing the maximum non-metallic inclusion dimension a i measured on the plurality of inspection planes with the dimension of the non-metallic inclusion that can be measured on the evaluation plane, The forged steel product cleanliness evaluation method calculates the estimated maximum non-metallic inclusion size a max from the evaluation surface projected size a ′ i to evaluate the cleanliness on the evaluation surface with relatively high accuracy. it can.
非金属介在物が鍛伸方向を長軸とする回転楕円体であると仮定して上記変換を行うとよい。一般に金属材料内の非金属介在物は球状であり、鍛鋼品においては鍛伸により非金属介在物は鍛伸方向を長軸とする回転楕円体となる。そのため、上記仮定を行って非金属介在物の寸法を変換することとで、精度を維持したまま、評価の手順を簡略化することができる。 The above conversion may be performed on the assumption that the nonmetallic inclusion is a spheroid whose major axis is the forging direction. In general, nonmetallic inclusions in a metal material are spherical, and in a forged steel product, the nonmetallic inclusions become spheroids whose major axis is in the forging direction by forging. Therefore, by performing the above assumption and converting the dimension of the nonmetallic inclusion, the evaluation procedure can be simplified while maintaining the accuracy.
上記変換工程が、上記最大非金属介在物寸法ａｉを鍛伸方向に対する角度が０°の基準面への一次投影寸法ａ’’ｉに一次変換する工程と、上記一次投影寸法ａ’’ｉを上記評価面投影寸法ａ’ｉに二次変換する工程とを有するとよい。このような手順で最大非金属介在物寸法ａｉを評価面投影寸法ａ’ｉに変換することで、容易かつ確実に評価面投影寸法ａ’ｉへの変換を行うことができる。 A step of converting the maximum non-metallic inclusion dimension a i into a primary projection dimension a ″ i on a reference plane having an angle of 0 ° with respect to the forging direction; and the primary projection dimension a ″ i. Is quadratic-converted into the evaluation plane projection dimension a ′ i . By converting the maximum non-metallic inclusion dimension a i into the evaluation plane projection dimension a ′ i in such a procedure, the conversion to the evaluation plane projection dimension a ′ i can be performed easily and reliably.
上記一次変換工程で、下記式（１）を用い、上記最大非金属介在物寸法ａｉを上記一次投影寸法ａ’’ｉに変換するとよい。このように基準面での既知の非金属介在物のアスペクト比γを用いて上記一次変換を行うことで、一次投影寸法ａ’’ｉを比較的容易に得ることができる。
ａ’’ｉ＝ａｉ・（γ／（ｓｉｎ２θｉ＋γ２・ｃｏｓ２θｉ）１／２）１／２ ・・・（１）
式（１）中、γは上記基準面における非金属介在物のアスペクト比である。
In the primary conversion step, the maximum non-metallic inclusion dimension a i may be converted to the primary projection dimension a ″ i using the following equation (1). By performing the primary conversion using the known aspect ratio γ of the nonmetallic inclusion on the reference plane, the primary projection dimension a ″ i can be obtained relatively easily.
a ″ i = a i · (γ / (sin 2 θ i + γ 2 · cos 2 θ i ) 1/2 ) 1/2 (1)
In equation (1), γ is the aspect ratio of the non-metallic inclusion on the reference plane.
上記二次変換工程が、下記式（２）及び式（３）を用い、上記一次投影寸法ａ’’ｉから上記基準面に投影したアスペクト比γの非金属介在物の長径ｌｉ及び短径ｓｉを算出する工程と、下記式（４）、式（５）及び評価領域における非金属介在物のアスペクト比γ’を用い、上記長径ｌｉ及び短径ｓｉからアスペクト比γ’の非金属介在物の長径ｌ’ｉ及び短径ｓ’ｉを算出する工程と、下記式（６）及び式（７）を用い、上記長径ｌ’ｉ及び短径ｓ’ｉから上記評価面に投影したアスペクト比γ’の非金属介在物の長径ｌ’’ｉ及び短径ｓ’’ｉを算出する工程と、下記式（８）を用い、上記長径ｌ’’ｉ及び短径ｓ’’ｉから上記評価面投影寸法ａ’ｉを算出する工程とを有するとよい。このように上記二次変換を行うことで、一次投影寸法ａ’’ｉから評価面投影寸法ａ’ｉを比較的容易に得ることができる。
ａ’’ｉ＝（ｌｉ・ｓｉ・π）１／２ ・・・（２）
γ＝ｌｉ／’ｉ ・・・（３）
ｌ’ｉ＝（ｓｉ ２・ｌｉ）１／３・（γ’）２／３ ・・・（４）
ｓ’ｉ＝（（ｓｉ ２・ｌｉ）／γ’）１／３ ・・・（５）
ｌ’’ｉ＝（ｓｉ ２・ｓｉｎ２θ’＋（γ’）２・ｃｏｓ２θ’）１／２ ・・・（６）
ｓ’’ｉ＝ｓ’ｉ ・・・（７）
ａ’ｉ＝（ｌ’’ｉ・ｓ’’ｉ・π）１／２ ・・・（８）
In the secondary conversion step, the major axis l i and the minor axis of the nonmetallic inclusion having an aspect ratio γ projected on the reference plane from the primary projection dimension a ″ i using the following equations (2) and (3). calculating a s i, the following equation (4), non of the formula (5) and 'used, the aspect ratio from the longer diameter l i and the minor axis s i gamma' aspect ratio gamma of the non-metallic inclusions in the evaluation region Calculating the major axis l ′ i and the minor axis s ′ i of the metal inclusion, and projecting the major axis l ′ i and the minor axis s ′ i onto the evaluation surface using the following equations (6) and (7). 'using a step of calculating a i, the following expression (8), the major axis l' and 'i and the minor axis s'' diameter l of non-metallic inclusions' aspect ratio γ was' i and the minor axis s''i from it may have a step of calculating the evaluation surface projection size a 'i. By performing the above-described secondary conversion, the evaluation plane projection dimension a ′ i can be relatively easily obtained from the primary projection dimension a ″ i .
a '' i = (l i · s i · π) 1/2 ··· (2)
γ = l i / 'i ··· (3)
l 'i = (s i 2 · l i) 1/3 · (γ') 2/3 ··· (4)
s 'i = ((s i 2 · l i) / γ') 1/3 ··· (5)
l ″ i = (s i 2 · sin 2 θ ′ + (γ ′) 2 · cos 2 θ ′) 1/2 (6)
s ″ i = s ′ i (7)
a ′ i = (l ″ i · s ″ i · π) 1/2 (8)
上記課題を解決するためになされた別の発明は、鍛鋼品内の特定の評価面における清浄度評価方法であって、鍛伸方向に対する角度が等しいｎ個の検査面における最大非金属介在物寸法ａｉ（ｉ＝１〜ｎ）を測定する工程と、極値統計法を用い、上記最大非金属介在物寸法ａｉから検査面での推定最大非金属介在物寸法ａｍａｘを算出する工程と、上記検査面の鍛伸方向に対する角度θ及び上記評価面の鍛伸方向に対する角度θ’を用い、検査面での推定最大非金属介在物寸法ａｍａｘを評価面での推定最大非金属介在物寸法ａ’ｍａｘに変換する工程とを備えることを特徴とする鍛鋼品の清浄度評価方法である。 Another invention made in order to solve the above-mentioned problem is a cleanliness evaluation method on a specific evaluation surface in a forged steel product, wherein a maximum non-metallic inclusion size on n inspection surfaces having the same angle with respect to the forging direction. measuring a i (i = 1 to n); and calculating an estimated maximum non-metallic inclusion size a max on the inspection surface from the maximum non-metallic inclusion size a i using an extreme value statistical method. Using the angle θ of the inspection surface with respect to the forging direction and the angle θ ′ of the evaluation surface with respect to the forging direction, the estimated maximum non-metallic inclusion size a max on the inspection surface is estimated as the maximum non-metallic inclusion on the evaluation surface. a forgings cleanliness evaluation method characterized by comprising the step of converting the dimensions a 'max.
当該鍛鋼品の清浄度評価方法は、検査面及び評価面それぞれの鍛伸方向に対する角度を用い、複数の検査面で測定された最大非金属介在物の寸法ａｉから得た推定最大非金属介在物寸法ａｍａｘを、評価面で測定され得る非金属介在物の推定最大非金属介在物寸法ａ’ｍａｘに変換する。そのため、当該鍛鋼品の清浄度評価方法は、評価面での清浄度を比較的高い精度で評価することができる。 The method of evaluating the cleanliness of the forged steel product is based on the estimated maximum nonmetallic inclusion obtained from the dimensions ai of the maximum nonmetallic inclusions measured on a plurality of inspection surfaces, using the angles of the inspection surface and the evaluation surface with respect to the forging direction. The object size a max is converted into an estimated maximum non-metallic inclusion size a ′ max of the non-metallic inclusion that can be measured on the evaluation surface. Therefore, the method for evaluating cleanliness of a forged steel product can evaluate the cleanliness on the evaluation surface with relatively high accuracy.
なお、「非金属介在物」とは、金属材料の凝固過程において金属材料中に析出又は巻き込まれる非金属性の介在物を意味し、例えば硫化マンガン（ＭｎＳ）等の硫化物系、酸化アルミニウム（Ａｌ２Ｏ３）、二酸化ケイ素（ＳｉＯ２）等の酸化物系、窒化チタン（ＴｉＮ）等の窒化物系などの介在物である。また、「非金属介在物寸法」とは、非金属介在物の検査面又は評価面での投影面積で表される大きさを意味し、この投影面積のほか、例えば投影面積と等面積の真円の直径、投影面積の１／２乗値（√ａｒｅａ）などが含まれる。 The term “non-metallic inclusions” refers to non-metallic inclusions that are precipitated or entrained in the metal material during the solidification process of the metal material, and include, for example, sulfides such as manganese sulfide (MnS), aluminum oxide ( al 2 O 3), oxide such as silicon dioxide (SiO 2), which inclusions such as nitride such as titanium nitride (TiN). The term “non-metallic inclusion dimensions” means a size represented by a projected area of the non-metallic inclusion on the inspection surface or the evaluation surface. Includes the diameter of the circle, the 1/2 power of the projected area (√area), and the like.
以上説明したように、本発明の鍛鋼品の清浄度評価方法によれば、比較的高い精度で鍛鋼品の清浄度を評価できる。 As described above, according to the forged steel product cleanliness evaluation method of the present invention, the cleanness of a forged steel product can be evaluated with relatively high accuracy.
以下、本発明に係る鍛鋼品の清浄度評価方法の実施形態について説明する。 Hereinafter, an embodiment of a method for evaluating cleanliness of a forged steel product according to the present invention will be described.
〔第一実施形態〕
当該鍛鋼品の清浄度評価方法は、鍛鋼品内の検査面とは異なる特定の評価面の清浄度を評価する方法である。当該鍛鋼品の清浄度評価方法は、ｎ個の検査面における最大非金属介在物寸法ａｉ（ｉ＝１〜ｎ）を測定する工程（測定工程）と、上記ｎ個の検査面の鍛伸方向に対する各角度θｉ（ｉ＝１〜ｎ）及び上記評価面の鍛伸方向に対する角度θ’を用い、各検査面の最大非金属介在物寸法ａｉを評価面での投影寸法ａ’ｉ（ｉ＝１〜ｎ）に変換する工程（変換工程）と、極値統計法を用い、上記評価面投影寸法ａ’ｉから評価面での推定最大非金属介在物寸法ａｍａｘを算出する工程（算出工程）とを備える。
(First embodiment)
The cleanness evaluation method of the forged steel product is a method of evaluating the cleanness of a specific evaluation surface different from the inspection surface in the forged steel product. The method for evaluating the cleanliness of the forged steel product includes a step (measurement step) of measuring a maximum nonmetallic inclusion dimension a i (i = 1 to n) on the n inspection surfaces, and a forging / elongation of the n inspection surfaces. Using the angles θ i (i = 1 to n) with respect to the direction and the angle θ ′ of the evaluation surface with respect to the forging direction, the maximum nonmetallic inclusion size a i of each inspection surface is projected onto the evaluation surface a ′ i (I = 1 to n) (conversion step) and a step of calculating an estimated maximum non-metallic inclusion dimension a max on the evaluation plane from the evaluation plane projection dimension a ′ i using the extreme value statistical method. (Calculation step).
［測定工程］
測定工程では、検査対象の鍛鋼品にｎ個の検査面を設定し、各検査面における非金属介在物の大きさを測定する。
[Measurement process]
In the measuring step, n inspection surfaces are set on the forged steel product to be inspected, and the size of nonmetallic inclusions on each inspection surface is measured.
各検査面の鍛伸方向に対する各角度θｉ（ｉ＝１〜ｎ）は、全て同一でもよいが、評価精度の観点から異なる角度が含まれることが好ましい。この角度θｉは、鍛鋼品の中央縦断面における鍛伸方向に対する角度であり、０°以上９０°未満である。なお、鍛伸方向とは、鍛伸によって形成される鋼材の鍛流線の方向であり、上記角度θｉは、鍛鋼品の断面マクロ観察により鍛流線を観察することで計測又は決定することができる。また、形状や鍛造条件が同等であれば、鍛流線の向きもほぼ同じとなるため、清浄度評価対象とは異なるチャージ（鍛鋼品）でマクロ観察結果を採取しておくことで、鍛伸方向の計測を省略できる。 The angles θ i (i = 1 to n) of each inspection surface with respect to the forging direction may be the same, but preferably include different angles from the viewpoint of evaluation accuracy. The angle θ i is an angle with respect to the forging direction in the central longitudinal section of the forged steel product, and is 0 ° or more and less than 90 °. The forging direction is a direction of a forging line of a steel material formed by forging, and the angle θ i is measured or determined by observing the forging line by macroscopic observation of a cross section of a forged product. Can be. In addition, if the shape and forging conditions are the same, the direction of the forging line will be almost the same. Direction measurement can be omitted.
当該鍛鋼品を形成する金属材料として、鉄（Ｆｅ）、アルミニウム（Ａｌ）、チタン（Ｔｉ）、ニッケル（Ｎｉ）、銅（Ｃｕ）、亜鉛（Ｚｎ）、銀（Ａｇ）、金（Ａｕ）、これらの合金、マグネシウム（Ｍｇ）合金、クロム（Ｃｒ）合金等が挙げられる。 As a metal material forming the forged steel product, iron (Fe), aluminum (Al), titanium (Ti), nickel (Ni), copper (Cu), zinc (Zn), silver (Ag), gold (Au), These alloys, a magnesium (Mg) alloy, a chromium (Cr) alloy, and the like can be given.
上記測定工程における測定方法としては、金属材料中の非金属介在物を測定できる方法であれば特に制限はなく、超音波探傷による測定方法、超音波疲労試験による測定方法、電子顕微鏡観察による測定方法などを用いることができる。これらの中でも、基本的に非破壊検査法であり、迅速に検査できる点において超音波探傷による測定が好ましい。 The measuring method in the above measuring step is not particularly limited as long as it is a method capable of measuring nonmetallic inclusions in a metal material, and is a measuring method by ultrasonic testing, a measuring method by ultrasonic fatigue test, a measuring method by electron microscope observation. Etc. can be used. Among these, measurement by ultrasonic flaw detection is preferable because it is basically a nondestructive inspection method and can be inspected quickly.
上記測定工程では、鍛鋼品の検査領域に、非金属介在物を測定する任意のｎ個の検査面を設定する。ここで、測定工程における測定は、金属材料から検査領域を切り出して行ってもよく、金属材料から切り出しをせずに設定した検査面の領域に対して行ってもよい。 In the above measurement step, any n inspection surfaces for measuring nonmetallic inclusions are set in the inspection region of the forged steel product. Here, the measurement in the measurement step may be performed by cutting out the inspection region from the metal material, or may be performed on a region of the inspection surface set without cutting out from the metal material.
鍛鋼品に設定する検査面の個数ｎとしては、統計計算的に、５以上１００以下が好ましい。 The number n of the inspection surfaces set on the forged steel product is preferably 5 or more and 100 or less from a statistical calculation.
検査面を切り出して測定する場合、検査面を含む同じサイズの直方体形状の複数の検査試料を切り出すことが好ましい。このように同一形状の検査試料を切り出すことで、連続検査及び自動測定がし易くなる。 When the measurement is performed by cutting out the inspection surface, it is preferable to cut out a plurality of rectangular parallelepiped inspection samples including the inspection surface. By cutting out test samples having the same shape in this way, continuous inspection and automatic measurement can be easily performed.
検査面の面積としては、１ｍｍ２以上１００００ｍｍ２以下が好ましい。検査面積が上記下限に満たないと、検査面における非金属介在物の検出精度が低下するおそれがある。逆に、検査面積が上記上限を超えると、検査面における非金属介在物の測定が困難となるおそれがある。 The area of the inspection surface is preferably 1 mm 2 or more and 10000 mm 2 or less. If the inspection area is less than the above lower limit, the accuracy of detecting nonmetallic inclusions on the inspection surface may be reduced. Conversely, when the inspection area exceeds the upper limit, measurement of nonmetallic inclusions on the inspection surface may be difficult.
また、複数の検査面は、検査対象の鍛鋼品の外周部及び中心部のそれぞれに設定することが好ましい。これは、鋼材において、一般に中心部は最終凝固位置であり、非金属介在物の濃化溶鋼への排出及び非金属介在物の沈降量が多いため、このように中心部及び外周部を検査することによって、大型の非金属介在物の検出率を向上させることができるからである。その結果、清浄度評価の精度をより向上させることができる。 Further, it is preferable that the plurality of inspection surfaces be set at each of the outer peripheral portion and the central portion of the forged steel product to be inspected. This is because, in a steel material, the center is generally the final solidification position, and the discharge of nonmetallic inclusions into the concentrated molten steel and the settling of nonmetallic inclusions are large. Thereby, the detection rate of large nonmetallic inclusions can be improved. As a result, the accuracy of the cleanliness evaluation can be further improved.
なお、鋳造した金属材料は、一般的に微細な空洞が無数にあるため、超音波探傷法により走査する場合、上記空洞による無数の乱反射やノイズが発生し、正常に測定できないことがある。そのため、鋳造した金属材料を評価対象とし、測定工程で超音波探傷法を用いる場合、検査面の測定前に、検査面を含む金属材料を圧延又は鍛造することが好ましい。このように検査対象の金属材料を圧延又は鍛造することで、金属材料の圧着により上記空洞が消滅するので、超音波探傷法による上記検査領域の正常な測定ができる。 Incidentally, since the cast metal material generally has an infinite number of fine cavities, when scanning by the ultrasonic flaw detection method, an infinite number of irregular reflections and noises are generated by the cavities, so that normal measurement may not be possible. Therefore, when the cast metal material is to be evaluated and the ultrasonic inspection method is used in the measurement process, it is preferable to roll or forge the metal material including the inspection surface before measuring the inspection surface. By rolling or forging the metal material to be inspected as described above, the cavity disappears due to the compression of the metal material, so that the inspection area can be normally measured by the ultrasonic flaw detection method.
［変換工程］
変換工程では、上記ｎ個の検査面の鍛伸方向に対する各角度θｉ及び上記評価面の鍛伸方向に対する角度θ’を用い、測定工程で得られた各検査面の最大非金属介在物寸法ａｉを評価面での投影寸法ａ’ｉ（ｉ＝１〜ｎ）に変換する。
[Conversion process]
In the conversion process, the maximum non-metallic inclusion size of each inspection surface obtained in the measurement process is obtained by using each angle θ i of the n inspection surfaces with respect to the forging direction in the forging direction and the evaluation surface of the evaluation surface θ ′ with respect to the forging direction. a i is converted into a projection dimension a ′ i (i = 1 to n) on the evaluation plane.
図１及び図２に示すように、同一の金属介在物Ｓを測定する場合でも、鍛伸方向Ｐに対する検査面Ｉの向きにより測定される介在物寸法が変化する。そのため、本変換工程では、検査面で計測した最大非金属介在物寸法ａｉを評価面での投影寸法ａ’ｉに変換する。 As shown in FIGS. 1 and 2, even when the same metal inclusion S is measured, the measured inclusion size changes depending on the orientation of the inspection surface I with respect to the forging direction P. Therefore, in this conversion step, the maximum non-metallic inclusion size ai measured on the inspection surface is converted into a projection size a ′ i on the evaluation surface.
評価面の鍛伸方向に対する角度θ’は、上記角度θｉ同様、鍛鋼品の中央縦断面における鍛伸方向に対する角度であり、０°以上９０°未満である。また、角度θ’は、鍛鋼品の断面マクロ観察により、鍛流線を観察することで計測することができる。 Angle theta 'relative to forging direction of the evaluation plane, like the angle theta i, is the angle relative to forging direction in the central longitudinal plane of the forgings, it is less than 0 ° or 90 °. The angle θ ′ can be measured by observing a forging line by macroscopic observation of a cross section of a forged steel product.
具体的には、変換工程は、非金属介在物が鍛伸方向を長軸とする回転楕円体であると仮定することで容易に変換を行うことができる。 Specifically, the conversion step can be easily performed by assuming that the nonmetallic inclusion is a spheroid whose major axis is the forging direction.
また、本変換工程は、上記最大非金属介在物寸法ａｉを鍛伸方向に対する角度が０°の基準面への一次投影寸法ａ’’ｉに一次変換する工程（一次変換工程）と、上記一次投影寸法ａ’’ｉを上記評価面投影寸法ａ’ｉに二次変換する工程（二次変換工程）とを有する。 The conversion step includes a step (primary conversion step) of primarily converting the maximum non-metallic inclusion dimension a i into a primary projection dimension a ″ i on a reference plane having an angle of 0 ° with respect to the forging direction. 'i-the evaluation surface projection size a' primary projection size a 'and a step (secondary conversion step) for converting secondary to i.
ここで、鍛鋼品内の領域によって非金属介在物の鍛錬による変形度合いも変化するので、基準面の非金属介在物のアスペクト比γと、評価領域の非金属介在物のアスペクト比γ’とを用いることで、評価精度を高めることができる。 Here, since the degree of deformation due to forging of nonmetallic inclusions changes depending on the region within the forged steel product, the aspect ratio γ of the nonmetallic inclusions on the reference plane and the aspect ratio γ ′ of the nonmetallic inclusions on the evaluation region are determined. By using this, the evaluation accuracy can be improved.
基準面及び評価面の非金属介在物のアスペクト比は、例えばそれぞれの領域での疲労試験破断面を観察することで求めることができる。また、基準面の非金属介在物のアスペクト比は、上記観察から求めた検査面の非金属介在物のアスペクト比から算出してもよい。 The aspect ratio of the non-metallic inclusions on the reference surface and the evaluation surface can be obtained by observing the fracture surface of the fatigue test in each region, for example. Further, the aspect ratio of the non-metallic inclusion on the reference surface may be calculated from the aspect ratio of the non-metallic inclusion on the inspection surface obtained from the above observation.
＜一次変換工程＞
一次変換工程では、下記式（１）を用い、上記最大非金属介在物寸法ａｉを上記一次投影寸法ａ’’ｉに変換する。
ａ’’ｉ＝ａｉ・（γ／（ｓｉｎ２θｉ＋γ２・ｃｏｓ２θｉ）１／２）１／２ ・・・（１）
<Primary conversion process>
In the primary conversion step, the maximum non-metallic inclusion size a i is converted into the primary projection size a ″ i using the following equation (1).
a ″ i = a i · (γ / (sin 2 θ i + γ 2 · cos 2 θ i ) 1/2 ) 1/2 (1)
＜二次変換工程＞
二次変換工程は、基準面に投影したアスペクト比γの非金属介在物の長径ｌｉ及び短径ｓｉを算出する工程（第一算出工程）と、アスペクト比γ’の非金属介在物の長径ｌ’ｉ及び短径ｓ’ｉを算出する工程（第二算出工程）と、評価面に投影したアスペクト比γ’の非金属介在物の長径ｌ’’ｉ及び短径ｓ’’ｉを算出する工程（第三算出工程）と、評価面投影寸法ａ’ｉを算出する工程（第四算出工程）とを有する。
<Secondary conversion step>
The secondary conversion step, a step of calculating the major axis l i and the minor axis s i of nonmetallic inclusions having an aspect ratio gamma projected on the reference plane (first calculation step), the non-metallic inclusions of an aspect ratio gamma ' a step (second calculation step) for calculating the major axis l 'i and the minor axis s' i, a' i and the minor axis s''i' major axis l of non-metallic inclusions' aspect ratio γ projected onto the evaluation plane There is a step of calculating (third calculation step) and a step of calculating the evaluation plane projection dimension a ′ i (fourth calculation step).
（第一算出工程）
第一算出工程では、下記式（２）及び式（３）を用い、上記一次投影寸法ａ’’ｉから上記基準面に投影したアスペクト比γ’’の非金属介在物の長径ｌｉ及び短径ｓｉを算出する。
ａ’’ｉ＝（ｌｉ・ｓｉ・π）１／２ ・・・（２）
γ＝ｌｉ／ｓｉ ・・・（３）
(First calculation step)
In the first calculation step, using the following equations (2) and (3), the major axis l i and the minor axis of the non-metallic inclusion having an aspect ratio γ ″ projected onto the reference plane from the primary projection dimension a ″ i to calculate the size s i.
a '' i = (l i · s i · π) 1/2 ··· (2)
γ = l i / s i (3)
（第二算出工程）
第二算出工程では、下記式（４）、式（５）及び評価領域における非金属介在物のアスペクト比γ’を用い、上記長径ｌｉ及び短径ｓｉからアスペクト比γ’の非金属介在物の長径ｌ’ｉ及び短径ｓ’ｉを算出する。
ｌ’ｉ＝（ｓｉ ２・ｌｉ）１／３・（γ’）２／３ ・・・（４）
ｓ’ｉ＝（（ｓｉ ２・ｌｉ）／γ’）１／３ ・・・（５）
(Second calculation step)
In the second calculation step, the following equation (4), (5) and 'used, the aspect ratio γ from the major axis l i and the minor axis s i' Aspect ratio γ of nonmetallic inclusions in the evaluation region nonmetallic inclusions of The major axis l ′ i and the minor axis s ′ i are calculated.
l 'i = (s i 2 · l i) 1/3 · (γ') 2/3 ··· (4)
s 'i = ((s i 2 · l i) / γ') 1/3 ··· (5)
（第三算出工程）
第三算出工程では、下記式（６）及び式（７）を用い、上記長径ｌ’ｉ及び短径ｓ’ｉから上記評価面に投影したアスペクト比γ’の非金属介在物の長径ｌ’’ｉ及び短径ｓ’’ｉを算出する。
ｌ’’ｉ＝（ｓｉ ２・ｓｉｎ２θ’＋（γ’）２・ｃｏｓ２θ’）１／２ ・・・（６）
ｓ’’ｉ＝ｓ’ｉ ・・・（７）
(Third calculation step)
In the third calculation step, using the following equations (6) and (7), the major axis l ′ of the nonmetallic inclusion having the aspect ratio γ ′ projected onto the evaluation surface from the major axis l ′ i and minor axis s ′ i to calculate the 'i and the minor axis s'' i.
l ″ i = (s i 2 · sin 2 θ ′ + (γ ′) 2 · cos 2 θ ′) 1/2 (6)
s ″ i = s ′ i (7)
（第四算出工程）
第四算出工程では、下記式（８）を用い、上記長径ｌ’’ｉ及び短径ｓ’’ｉから上記評価面投影寸法ａ’ｉを算出する。
ａ’ｉ＝（ｌ’’ｉ・ｓ’’ｉ・π）１／２ ・・・（８）
(Fourth calculation step)
In the fourth calculating step, using the following equation (8), calculates the evaluation surface projection size a 'i from the major axis l''i and the minor axis s'' i.
a ′ i = (l ″ i · s ″ i · π) 1/2 (8)
［算出工程］
算出工程では、極値統計法を用い、変換工程で得られた上記評価面投影寸法ａ’ｉから評価面での推定最大非金属介在物寸法ａｍａｘを算出する。
[Calculation process]
In the calculation step, an estimated maximum non-metallic inclusion size a max on the evaluation plane is calculated from the evaluation plane projection dimension a ′ i obtained in the conversion step using an extreme value statistical method.
上記極値統計法としては、例えば以下の方法が使用できる。まず、評価面投影寸法ａ’ｉを昇順に並べ、この昇順に並べた評価面投影寸法ａ’ｊ（ｊ＝１〜ｎ）と、基準化変数ｙｊ＝−ｌｎ［−ｌｎ｛ｊ／（ｎ＋１）｝］とから、ｙｊを従属変数、ａｊを独立変数とする下記式（９）のｍ次回帰式を導出する。このｍ次回帰式は、一次以上の回帰式の導出ができる例えば最小二乗法や最尤法などの公知の方法を用いて導出できる。
ｙｊ＝ｆｍ（ａｊ） ・・・（９）
As the extreme value statistical method, for example, the following method can be used. First, the evaluation plane projection dimensions a ′ i are arranged in ascending order, and the evaluation plane projection dimensions a ′ j (j = 1 to n) arranged in this ascending order and a standardization variable y j = −ln [−ln ｛j / ( n + 1)｝], an m-th order regression equation of the following equation (9) is derived with y j as a dependent variable and a j as an independent variable. The m-th order regression equation can be derived using a known method such as a least square method or a maximum likelihood method that can derive a first-order or higher regression equation.
y j = f m (a j ) ··· (9)
上記導出で得られた上記式（９）のｍ次回帰式と下記式（１０）との解を求め、評価面での推定最大非金属介在物寸法ａｍａｘを算出する。
ｆｍ（ａｍａｘ）＝ｙｍａｘ ・・・（１０）
The solution of the m-order regression equation of the above equation (9) obtained by the above derivation and the following equation (10) is obtained, and the estimated maximum nonmetallic inclusion size a max on the evaluation surface is calculated.
f m (a max ) = y max (10)
上記式（９）において、ｆｍ（ａｊ）は例えばａｊ＋ｂとでき（ｂは定数）、式（１０）において、ｙｍａｘは例えばｌｎ［−ｌｎ｛Ｓｄ／（Ｓｄ＋Ｓｅ）｝］とできる。Ｓｄは、評価領域における応力負荷が加わる表面積（危険面積）であり、Ｓｅは、検査領域における応力負荷が加わる表面積（危険面積）である。 In the above equation (9), f m ( aj ) can be, for example, a j + b (b is a constant), and in equation (10), y max is, for example, ln [−ln ｛S d / (S d + S e ). ｝]. S d is the surface area of stress loading in the evaluation area is added (hazardous area), S e is the surface area (hazardous area) stress load in the examination region is applied.
なお、本算出工程において、評価面投影寸法ａ’ｉから異常値を除去した上で、最大非金属介在物寸法ａｍａｘを算出することが好ましい。これは、上記測定工程で非金属介在物以外のものが非金属介在物と判断されて非金属介在物寸法として測定される場合があるためである。例えば超音波探傷による測定において、非金属介在物でない空洞からの反射波や外からの飛び込み乱反射ノイズなどが非金属介在物として測定される場合がある。これに対し、異常値を除去することで、非金属介在物でない欠陥からのデータを省くことができる。例えば超音波探傷では、異常値と正常値との波形が異なるので、波形によって容易に異常値を除去することができる。 In this calculation step, it is preferable to calculate the maximum non-metallic inclusion size a max after removing abnormal values from the evaluation plane projection size a ′ i . This is because, in the above-described measurement step, there may be a case where something other than the nonmetallic inclusion is determined to be a nonmetallic inclusion and is measured as a nonmetallic inclusion size. For example, in the measurement by ultrasonic flaw detection, a reflected wave from a cavity that is not a non-metallic inclusion, a diving diffuse reflection noise from the outside, and the like may be measured as a non-metallic inclusion. On the other hand, by removing abnormal values, data from defects that are not non-metallic inclusions can be omitted. For example, in ultrasonic flaw detection, since abnormal values and normal values have different waveforms, abnormal values can be easily removed based on the waveform.
本算出工程で得られた上記推定最大非金属介在物寸法ａｍａｘにより、鍛鋼品の評価対象領域での清浄度を評価することができる。 From the estimated maximum non-metallic inclusion size a max obtained in this calculation step, the cleanliness of the forged steel in the evaluation target area can be evaluated.
［利点］
当該鍛鋼品の清浄度評価方法は、複数の検査面から得た最大非金属介在物寸法ａｉを、これらの検査面の鍛伸方向に対する角度θｉと、清浄度を評価したい評価面の鍛伸方向に対する角度θ’とを用いて、評価面への投影寸法ａ’ｉに変換するので、検査面での計測値から評価面での清浄度を比較的高い精度で評価することができる。
[advantage]
The method for evaluating the cleanliness of a forged steel product includes the steps of: measuring the maximum non-metallic inclusion size a i obtained from a plurality of inspection surfaces, the angle θ i of these inspection surfaces with respect to the forging direction, and the forging of the evaluation surface to be evaluated for cleanness. The angle θ ′ with respect to the elongation direction is used to convert to the projection dimension a ′ i on the evaluation surface, so that the cleanliness on the evaluation surface can be evaluated with relatively high accuracy from the measured value on the inspection surface.
〔第二実施形態〕
当該鍛鋼品の清浄度評価方法は、鍛鋼品内の特定の評価面における清浄度評価方法である。当該鍛鋼品の清浄度評価方法は、鍛伸方向に対する角度が等しいｎ個の検査面における最大非金属介在物寸法ａｉ（ｉ＝１〜ｎ）を測定する工程（測定工程）と、極値統計法を用い、上記最大非金属介在物寸法ａｉから検査面での推定最大非金属介在物寸法ａｍａｘを算出する工程（算出工程）と、上記検査面の鍛伸方向に対する角度θ及び上記評価面の鍛伸方向に対する角度θ’を用い、検査面での推定最大非金属介在物寸法ａｍａｘを評価面での推定最大非金属介在物寸法ａ’ｍａｘに変換する工程（変換工程）とを備える。
(Second embodiment)
The cleanness evaluation method for the forged steel product is a cleanness evaluation method for a specific evaluation surface in the forged steel product. The forged steel product cleanliness evaluation method includes a step of measuring the maximum nonmetallic inclusion size a i (i = 1 to n) on n inspection surfaces having the same angle to the forging direction (measurement step), and an extreme value. A step of calculating an estimated maximum non-metallic inclusion size a max on the inspection surface from the maximum non-metallic inclusion size a i using a statistical method (calculation step); an angle θ of the inspection surface with respect to the forging / stretching direction; 'using the estimated maximum non-metallic inclusion size a max of the inspection surface estimated maximum non-metallic inclusion size a of the evaluation plane' angle θ with respect to forging direction evaluation plane step of converting the max and (conversion step) Is provided.
［測定工程］
上記測定工程は、ｎ個の検査面の鍛伸方向に対する角度を同じにする点以外は、第一実施形態の鍛鋼品の清浄度評価方法の測定工程と同じである。
[Measurement process]
The above measurement step is the same as the measurement step of the method for evaluating cleanliness of a forged steel product of the first embodiment, except that the angles of the n inspection surfaces with respect to the forging direction are the same.
［算出工程］
上記算出工程は、極値統計法を用い、上記測定工程で得た最大非金属介在物寸法ａｉから検査面での推定最大非金属介在物寸法ａｍａｘを算出する。この極値統計法は第一実施形態で説明したものが使用できる。
[Calculation process]
In the calculation step, an estimated maximum non-metallic inclusion size a max on the inspection surface is calculated from the maximum non-metallic inclusion size ai obtained in the measurement step using an extreme value statistical method. The extreme value statistical method described in the first embodiment can be used.
［変換工程］
上記変換工程は、検査面の鍛伸方向に対する角度θ及び上記評価面の鍛伸方向に対する角度θ’を用い、上記算出工程で得た検査面での推定最大非金属介在物寸法ａｍａｘを評価面での推定最大非金属介在物寸法ａ’ｍａｘに変換する。検査面での推定最大非金属介在物寸法ａｍａｘを評価面での推定最大非金属介在物寸法ａ’ｍａｘに変換する方法としては、第一実施形態の鍛鋼品の清浄度評価方法の変換工程で説明した最大非金属介在物寸法ａｉを評価面での投影寸法ａ’ｉに変換する方法が使用できる。
[Conversion process]
In the conversion step, the estimated maximum non-metallic inclusion size a max on the inspection surface obtained in the calculation step is evaluated using the angle θ of the inspection surface with respect to the forging direction and the angle θ ′ of the evaluation surface with respect to the forging direction. Is converted to the estimated maximum non-metallic inclusion size a ′ max in the plane. As a method of converting the estimated maximum non-metallic inclusion size a max in the inspection surface on the estimated maximum non-metallic inclusion size a 'max of the evaluation plane, the conversion step of forgings cleanliness evaluation method of the first embodiment The method of converting the maximum non-metallic inclusion size a i described in the above into the projection size a ′ i on the evaluation plane can be used.
［利点］
当該鍛鋼品の清浄度評価方法は、検査面及び評価面それぞれの鍛伸方向に対する角度を用い、複数の検査面で測定された最大非金属介在物の寸法ａｉから得た推定最大非金属介在物寸法ａｍａｘを、評価面で測定され得る非金属介在物の推定最大非金属介在物寸法ａ’ｍａｘに変換する。そのため、当該鍛鋼品の清浄度評価方法は、評価面での清浄度を比較的高い精度で評価することができる。
[advantage]
The method of evaluating the cleanliness of the forged steel product is based on the estimated maximum nonmetallic inclusion obtained from the dimensions ai of the maximum nonmetallic inclusions measured on a plurality of inspection surfaces, using the angles of the inspection surface and the evaluation surface with respect to the forging direction. The object size a max is converted into an estimated maximum non-metallic inclusion size a ′ max of the non-metallic inclusion that can be measured on the evaluation surface. Therefore, the method for evaluating cleanliness of a forged steel product can evaluate the cleanliness on the evaluation surface with relatively high accuracy.
〔その他の実施形態〕
なお、本発明の清浄度評価方法は、上記実施形態に限定されるものではない。
[Other embodiments]
Note that the cleanliness evaluation method of the present invention is not limited to the above embodiment.
つまり、当該鍛鋼品の清浄度評価方法においては、検査面における最大非金属介在物寸法ａｉを評価面での投影寸法ａ’ｉに変換する方法は、上記実施形態に限定されず、他の手順を用いて変換を行ってもよい。例えば、一次投影寸法ａ’’ｉを介さずに最大非金属介在物寸法ａｉを評価面での投影寸法ａ’ｉに直接変換してもよい。 That is, in the cleanness evaluation method of the forgings, a method of converting the maximum non-metallic inclusion size a i in the test surface to the projection size a 'i of the evaluation surface is not limited to the above embodiments, other The conversion may be performed using a procedure. For example, the maximum non-metallic inclusion dimension a i may be directly converted to the projection dimension a ′ i on the evaluation plane without going through the primary projection dimension a ″ i .
以下、実施例によって本発明をさらに詳細に説明するが、本発明はこれらの実施例に限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
まず、評価対象の鍛鋼品として、直径３５０ｍｍの軸系鍛鋼品を製鋼した。この軸系鍛鋼品は、図３に示すように半径方向の一方向から鍛錬することで、軸の中央部Ａが端部Ｂよりも中心軸がオフセット（偏心）するように加工されており、この中央部Ａを評価領域とした。また、この鍛錬により、中央部Ａでは鍛伸方向（鍛流線の向き）Ｐが図示するように軸方向に沿って変化している。 First, as a forged product to be evaluated, a shaft-based forged product having a diameter of 350 mm was manufactured. As shown in FIG. 3, this shaft-based forged product is worked so that the central portion A of the shaft is offset (eccentric) from the end portion B by forging from one direction in the radial direction. This central part A was used as an evaluation area. In addition, due to this forging, the forging / stretching direction (direction of the forging line) P changes along the axial direction in the central portion A as shown in the figure.
次に、この軸系鍛鋼品の端部Ｂから、鍛伸方向Ｐに対する角度が０°、９０°となる面で疲労破断する小型疲労試験片を６本ずつ、計１２本採取した。また、中央部Ａから、鍛伸方向Ｐに対する角度が６０°となる面で疲労破断する大型疲労試験片を一本採取した。これらの試験片は、破壊起点部位が鍛造前の鋼塊の１／３Ｒ位置に想到する部位になるように採取した。さらに、これらの試験片について、疲労試験において最大負荷応力から最大負荷応力の９０％の応力が加わる危険領域を検査領域又は評価領域とした。疲労試験の結果、小型疲労試験片の検査領域の表面積は６７６ｍｍ２、大型疲労試験片の評価領域の表面積は３３２０ｍｍ２であった。 Next, from the end portion B of the shaft-based forged product, a total of 12 small fatigue test pieces, each of which was subjected to fatigue fracture on a plane where the angles with respect to the forging direction P were 0 ° and 90 °, were collected. From the central part A, one large fatigue test piece that was subjected to fatigue fracture on a plane where the angle with respect to the forging direction P was 60 ° was collected. These test pieces were sampled such that the fracture starting point was located at the 1 / 3R position of the steel ingot before forging. Further, with respect to these test pieces, a risk region where a stress of 90% of the maximum load stress from the maximum load stress was applied in the fatigue test was defined as an inspection region or an evaluation region. As a result of the fatigue test, the surface area of the inspection area of the small fatigue test piece was 676 mm 2 , and the surface area of the evaluation area of the large fatigue test piece was 3320 mm 2 .
上記小型疲労試験片及び大型疲労試験片について疲労試験破断面を観察し、最大非金属介在物寸法を求めた。この小型疲労試験片における最大非金属介在物寸法について、昇順に並べた結果を表１に示す。 The fracture surface of the fatigue test was observed for the small fatigue test piece and the large fatigue test piece, and the maximum nonmetallic inclusion size was determined. Table 1 shows the results of the maximum non-metallic inclusion size in this small fatigue test piece arranged in ascending order.
一方、上記大型疲労試験片の評価面（疲労破断面）での最大介在物寸法は９８μｍ、アスペクト比γ’は１４．１であった。 On the other hand, the largest inclusion size on the evaluation surface (fatigue fracture surface) of the large fatigue test piece was 98 μm, and the aspect ratio γ ′ was 14.1.
さらに、鍛伸方向Ｐに対する角度が７５°（θ１）となる面で疲労破断する別の小型疲労試験片に対し、疲労試験破断面を観察したところ非金属介在物の平均アスペクトγ１は３．１５であった。このアスペクト比γ１を鍛伸方向Ｐに対する角度が０°となる基準面のアスペクト比γに下記式（１１）を用いて変換したところ、３．９２が得られた。なお、鍛鋼方向Ｐに対する角度が０°となる検査面（疲労破断面）を有する試験片を用いて、基準面のアスペクト比γを観察により直接求めてもよい。
γ＝（（γ１ ２−ｓｉｎ２θ１）／ｃｏｓ２θ１）１／２ ・・・（１１）
Furthermore, when the fatigue test fracture surface was observed for another small fatigue test piece that fractured on the surface where the angle with respect to the forging direction P was 75 ° (θ 1 ), the average aspect γ 1 of the nonmetallic inclusion was 3 .15. When the aspect ratio gamma 1 is an angle with respect to forging direction P was converted using the following equation (11) to gamma aspect ratio of the reference plane as the 0 °, 3.92 was obtained. Note that the aspect ratio γ of the reference plane may be directly obtained by observation using a test piece having an inspection surface (fatigue fracture surface) whose angle with respect to the forging steel direction P is 0 °.
γ = ((γ 1 2 −sin 2 θ 1 ) / cos 2 θ 1 ) 1/2 (11)
上述の鍛伸方向Ｐに対する角度が９０°となる検査面（疲労破断面）を有する小型疲労試験片の最大非金属介在物寸法を上記式（１）を用いて、基準面における一次投影寸法ａ’’ｉに変換し、さらに上記式（２）、（３）を用いて、アスペクト比γの非金属介在物の長径ｌｉ及び短径ｓｉを算出した結果を表２に示す。 The maximum non-metallic inclusion size of a small fatigue test piece having an inspection surface (fatigue fracture surface) having an angle of 90 ° with respect to the forging direction P is determined by using the above equation (1) to obtain a primary projection dimension a on a reference plane. into a '' i, further the above formula (2), Table 2 shows the result of calculating the major axis l i and the minor axis s i (3) using a non-metallic inclusions of an aspect ratio gamma.
さらに、上記式（４）、（５）を用いて、長径ｌｉ及び短径ｓｉからアスペクト比γ’の非金属介在物の長径ｌ’ｉ及び短径ｓ’ｉを算出した結果を表３に示す。 Furthermore, the table the results of the above formula (4) with (5), to calculate the i and the minor axis s' i 'major axis l of non-metallic inclusions' aspect ratio γ from the major axis l i and the minor axis s i 3 is shown.
さらに、上記式（６）、（７）を用いて、長径ｌ’ｉ及び短径ｓ’ｉからアスペクト比γ’の非金属介在物の長径ｌ’’ｉ及び短径ｓ’’ｉを算出した結果を表４に示す。 Further, the formula (6), calculates the 'i and the minor axis s'' i 'major axis l of non-metallic inclusions' (7) with a major axis l' i and the minor axis s' aspect ratio from i gamma Table 4 shows the results.
さらに、上記式（８）を用いて、長径ｌ’’ｉ及び短径ｓ’’ｉから評価面投影寸法ａ’ｉを算出した。この結果を基準化変数ｙｊ＝−ｌｎ［−ｌｎ｛ｊ／（ｎ＋１）｝］と共に表５に示す。 Furthermore, using the above equation (8) to calculate the evaluation surface projection size a 'i from the major axis l''i and the minor axis s'' i. Consequently the reference variables y j = -ln [-ln {j / (n + 1)}] are shown in Table 5 together.
最後に、得られた評価面投影寸法ａ’ｉに対し、基準化変数の近似式をｙｊ＝ａｊ＋ｂ（ｂは定数）、ｙｍａｘ＝ｌｎ［−ｌｎ｛Ｓｄ／（Ｓｄ＋Ｓｅ）｝］として極値統計法を用い、評価面での推定最大非金属介在物寸法ａｍａｘを算出したところ、ａｍａｘとして９９．８μｍが得られた。これにより、本発明により実測値９８μｍに近い評価ができることがわかる。一方で、表１の最大非金属介在物寸法を用いて極値統計法を用いた場合、鍛伸方向Ｐに対する角度が０°となる検査面の結果のみを用いると推定最大非金属介在物寸法は１２９．１μｍ、上記角度が９０°となる検査面の結果のみを用いると推定最大非金属介在物寸法は３７．４μｍとなり、実測値と大きく乖離する。 Finally, for the obtained evaluation plane projection dimension a ′ i , the approximate expression of the scaling variable is expressed as y j = aj + b (b is a constant), and y max = ln [−lnεS d / (S d + S using an extreme value statistical methods as e)}], was calculated estimated maximum non-metallic inclusion size a max of the evaluation plane, 99.8Myuemu was obtained as a max. This indicates that the present invention enables an evaluation close to the measured value of 98 μm. On the other hand, when the extreme value statistical method is used using the maximum non-metallic inclusion size in Table 1, the estimated maximum non-metallic inclusion size is determined by using only the result of the inspection surface whose angle with respect to the forging direction P is 0 °. When only the result of the inspection surface where the angle is 90 ° is 129.1 μm, the estimated maximum nonmetallic inclusion size is 37.4 μm, which is largely different from the actually measured value.
以上説明したように、当該清浄度評価方法は、比較的高い精度で鍛鋼品の清浄度を評価できるので、クランクシャフトのような高い疲労強度が求められる鍛鋼品の清浄度を保証できる。 As described above, since the cleanliness evaluation method can evaluate the cleanliness of a forged steel product with relatively high accuracy, the cleanliness of a forged steel product such as a crankshaft that requires high fatigue strength can be guaranteed.
Ａ 中央部
Ｂ 端部
Ｉ 検査面
Ｐ 鍛伸方向
Ｓ 非金属介在物
A Central part B Edge part I Inspection surface P Forging direction S Non-metallic inclusion
Claims (6)
ｎ個の検査面における最大非金属介在物寸法ａｉ（ｉ＝１〜ｎ）を測定する工程と、
上記ｎ個の検査面の鍛伸方向に対する各角度θｉ（ｉ＝１〜ｎ）及び上記評価面の鍛伸方向に対する角度θ’を用い、各検査面の最大非金属介在物寸法ａｉを評価面での投影寸法ａ’ｉ（ｉ＝１〜ｎ）に変換する工程と、
極値統計法を用い、上記評価面投影寸法ａ’ｉから評価面での推定最大非金属介在物寸法ａｍａｘを算出する工程と
を備えることを特徴とする鍛鋼品の清浄度評価方法。 A cleanness evaluation method for a specific evaluation surface in a forged steel product,
measuring the maximum non-metallic inclusion dimensions a i (i = 1 to n) on the n inspection surfaces;
Using the angles θ i (i = 1 to n) of the n inspection surfaces with respect to the forging direction and the angles θ ′ of the evaluation surfaces with respect to the forging direction, the maximum non-metallic inclusion size a i of each inspection surface is determined. Converting into a projection dimension a ′ i (i = 1 to n) on the evaluation surface;
Calculating the estimated maximum non-metallic inclusion size a max on the evaluation surface from the evaluation surface projection size a ′ i using an extreme value statistical method.
上記最大非金属介在物寸法ａｉを鍛伸方向に対する角度が０°の基準面への一次投影寸法ａ’’ｉに一次変換する工程と、
上記一次投影寸法ａ’’ｉを上記評価面投影寸法ａ’ｉに二次変換する工程と
を有する請求項２に記載の鍛鋼品の清浄度評価方法。 The conversion step is
A step of linearly converting the maximum non-metallic inclusion dimension a i into a primary projection dimension a ″ i on a reference plane having an angle of 0 ° with respect to the forging direction;
3. The method for evaluating cleanliness of a forged steel product according to claim 2, further comprising a step of quadratic converting the primary projection dimension a ″ i into the evaluation plane projection dimension a ′ i .
ａ’’ｉ＝ａｉ・（γ／（ｓｉｎ２θｉ＋γ２・ｃｏｓ２θｉ）１／２）１／２ ・・・（１）し、
式（１）中、γは上記基準面における非金属介在物のアスペクト比である。 Above primary conversion process, using the following equation (1), the maximum non-metallic inclusion size a i cleanliness evaluation method of forgings according to claim 3, converted into the primary projection size a '' i.
a ″ i = a i · (γ / (sin 2 θ i + γ 2 · cos 2 θ i ) 1/2 ) 1/2 (1)
In equation (1), γ is the aspect ratio of the non-metallic inclusion on the reference plane.
下記式（２）及び式（３）を用い、上記一次投影寸法ａ’’ｉから上記基準面に投影したアスペクト比γの非金属介在物の長径ｌｉ及び短径ｓｉを算出する工程と、
下記式（４）、式（５）及び評価領域における非金属介在物のアスペクト比γ’を用い、上記長径ｌｉ及び短径ｓｉからアスペクト比γ’の非金属介在物の長径ｌ’ｉ及び短径ｓ’ｉを算出する工程と、
下記式（６）及び式（７）を用い、上記長径ｌ’ｉ及び短径ｓ’ｉから上記評価面に投影したアスペクト比γ’の非金属介在物の長径ｌ’’ｉ及び短径ｓ’’ｉを算出する工程と、
下記式（８）を用い、上記長径ｌ’’ｉ及び短径ｓ’’ｉから上記評価面投影寸法ａ’ｉを算出する工程と
を有する請求項３又は請求項４に記載の鍛鋼品の清浄度評価方法。
ａ’’ｉ＝（ｌｉ・ｓｉ・π）１／２ ・・・（２）
γ＝ｌｉ／ｓｉ ・・・（３）
ｌ’ｉ＝（ｓｉ ２・ｌｉ）１／３・（γ’）２／３ ・・・（４）
ｓ’ｉ＝（（ｓｉ ２・ｌｉ）／γ’）１／３ ・・・（５）
ｌ’’ｉ＝（ｓｉ ２・ｓｉｎ２θ’＋（γ’）２・ｃｏｓ２θ’）１／２ ・・・（６）
ｓ’’ｉ＝ｓ’ｉ ・・・（７）
ａ’ｉ＝（ｌ’’ｉ・ｓ’’ｉ・π）１／２ ・・・（８） The secondary conversion step,
Using the following equation (2) and (3), a step of calculating the major axis l i and the minor axis s i of the primary projection size a '' non-metallic inclusions of an aspect ratio γ that is projected on the reference surface from the i ,
Formula (4), (5) and 'used, the aspect ratio γ from the major axis l i and the minor axis s i' Aspect ratio of nonmetallic inclusions γ in the evaluation region major axis l 'i nonmetallic inclusions And calculating the minor axis s ′ i ;
Using the following equation (6) and (7), the longer diameter l 'i and the minor axis s'' diameter l of non-metallic inclusions' aspect ratio γ projected onto the evaluation plane from i 'i and the minor axis s '' calculating i ;
Using the following equation (8), from the major axis l '' i and the minor axis s''i of the forgings according to claim 3 or claim 4 and a step of calculating the evaluation surface projection size a' i Cleanliness evaluation method.
a '' i = (l i · s i · π) 1/2 ··· (2)
γ = l i / s i (3)
l 'i = (s i 2 · l i) 1/3 · (γ') 2/3 ··· (4)
s 'i = ((s i 2 · l i) / γ') 1/3 ··· (5)
l ″ i = (s i 2 · sin 2 θ ′ + (γ ′) 2 · cos 2 θ ′) 1/2 (6)
s'' i = s' i (7)
a ′ i = (l ″ i · s ″ i · π) 1/2 (8)
鍛伸方向に対する角度が等しいｎ個の検査面における最大非金属介在物寸法ａｉ（ｉ＝１〜ｎ）を測定する工程と、
極値統計法を用い、上記最大非金属介在物寸法ａｉから検査面での推定最大非金属介在物寸法ａｍａｘを算出する工程と、
上記検査面の鍛伸方向に対する角度θ及び上記評価面の鍛伸方向に対する角度θ’を用い、検査面での推定最大非金属介在物寸法ａｍａｘを評価面での推定最大非金属介在物寸法ａ’ｍａｘに変換する工程と
を備えることを特徴とする鍛鋼品の清浄度評価方法。 A cleanness evaluation method for a specific evaluation surface in a forged steel product,
Measuring the maximum nonmetallic inclusion dimensions a i (i = 1 to n) on n inspection surfaces having the same angle with respect to the forging direction;
Calculating an estimated maximum non-metallic inclusion size a max on the inspection surface from the maximum non-metallic inclusion size a i using an extreme value statistical method;
Using the angle θ of the inspection surface with respect to the forging direction and the angle θ ′ of the evaluation surface with respect to the forging direction, the estimated maximum non-metallic inclusion size a max on the inspection surface is estimated as the maximum non-metallic inclusion size on the evaluation surface. cleanliness evaluation method of forgings, characterized in that it comprises a step of converting the a 'max.
Priority Applications (1)
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