JP2014074649A - Method for observing surface layer part of steel material and method for manufacturing steel material - Google Patents
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本発明は、鋼材の表層部の観察方法および鋼材の製造方法に関し、特に、鋼材の表層部における析出物等の第二相の三次元分布を正確に把握することができる鋼材の表層部の観察方法、およびこの観察結果に基づいて製造条件を適切に修正することができる鋼材の製造方法に関するものである。 The present invention relates to a method for observing a surface layer portion of a steel material and a method for producing a steel material, and in particular, to observe a surface layer portion of a steel material capable of accurately grasping the three-dimensional distribution of second phases such as precipitates in the surface layer portion of the steel material. The present invention relates to a method and a method for manufacturing a steel material that can appropriately correct manufacturing conditions based on the observation result.
一般に、材料の機械的性質は、組織単位の大きさ、結晶方位、組織内の欠陥、母相における第二相の分散状態など、多くの要因に支配されている。例えば、材料の強度は、組織を構成する結晶粒径の1/2乗に反比例する。また、母相内に微細に分散する析出物の粒径および量を適切に制御することにより、大きな析出強化量を得ることができる。 In general, the mechanical properties of a material are governed by many factors such as the size of a structural unit, crystal orientation, defects in the structure, and the dispersion state of the second phase in the matrix. For example, the strength of the material is inversely proportional to the 1/2 power of the crystal grain size constituting the structure. Moreover, a large precipitation strengthening amount can be obtained by appropriately controlling the particle size and amount of the precipitate finely dispersed in the matrix.
このため、従来、組織や析出物の制御により、材料の強度の向上が図られてきた。例えば、特許文献1には、利用する析出物のサイズや量を定量的に制御することにより、所望の材質を有する鋼材を製造する技術について記載されている。 For this reason, conventionally, the strength of the material has been improved by controlling the structure and precipitates. For example, Patent Document 1 describes a technique for manufacturing a steel material having a desired material by quantitatively controlling the size and amount of precipitates to be used.
ところで、材料の組織を最適に制御するためには、定常部における組織の状態のみならず、非定常部における析出物等の第二相の状態、例えば、高温で処理された鋼材の表面近傍の酸化状態や、溶接熱影響部における介在物の分布状態等を把握することが必要である。特に前者に関しては、鋼材が溶融亜鉛めっき鋼板(以下、単に「めっき鋼板」とも言い、本発明においては鋼材として溶融亜鉛めっき鋼板も含むものとする)の場合に重要である。すなわち、近年の自動車用鋼板のハイテン化に伴って、高濃度のSiが下地鋼板に添加されているが、めっき処理前の鋼板の酸化および還元処理の際に、SiもしくはSi−Mn系の酸化物等の析出物が、下地鋼板とめっき層との界面もしくはめっき層内に分散して、めっき層の合金化過程そのものや、めっき層の機械的性質にも悪影響を及ぼし、場合によっては、めっきが施されない不めっき部(めっき層中の合金相が充分に形成されていない部分やめっき層の厚さが周囲に比べ薄い部分をも含む)を形成することがある。 By the way, in order to optimally control the material structure, not only the state of the structure in the stationary part but also the state of the second phase such as precipitates in the unsteady part, for example, near the surface of the steel material treated at high temperature. It is necessary to grasp the oxidation state and the distribution state of inclusions in the weld heat affected zone. In particular, the former is important when the steel material is a hot-dip galvanized steel plate (hereinafter also referred to simply as “plated steel plate”, and in the present invention, a hot-dip galvanized steel plate is also included as a steel material). That is, with the recent increase in the strength of steel sheets for automobiles, a high concentration of Si has been added to the base steel sheet, but during the oxidation and reduction treatment of the steel sheet before plating treatment, oxidation of Si or Si-Mn series is performed. Precipitates such as deposits are dispersed at the interface between the base steel plate and the plating layer or within the plating layer, adversely affecting the alloying process itself of the plating layer and the mechanical properties of the plating layer. In some cases, an unplated portion (including a portion where the alloy phase in the plating layer is not sufficiently formed and a portion where the thickness of the plating layer is thinner than the surroundings) is formed.
こうした問題を解決するためには、めっき性の低下を抑制する下地鋼板の酸化条件および還元条件を求める必要があるが、そのためには、下地鋼板とめっき層との界面近傍の領域における析出物について、二次元的にそのサイズ、形態や量を把握するだけでは不十分であり、それらが三次元的にどのように分散しているかを把握することが不可欠である。 In order to solve such problems, it is necessary to determine the oxidation conditions and reduction conditions of the base steel sheet that suppresses the decrease in plating properties. To that end, the precipitates in the region near the interface between the base steel sheet and the plating layer are required. It is not enough to grasp the size, form and quantity in two dimensions, and it is essential to grasp how they are distributed in three dimensions.
しかしながら、特許文献1に記載の技術では、利用する析出物のサイズ、形態や、母相内での析出物の分布が均一であることを前提としたものであり、めっき鋼板の表層部のような非定常部における析出物の三次元分布を把握することができない。 However, the technique described in Patent Document 1 is based on the premise that the size and form of the precipitate to be used and the distribution of the precipitate in the matrix are uniform, like the surface layer portion of the plated steel sheet. It is impossible to grasp the three-dimensional distribution of precipitates in the unsteady part.
このように、鋼材の表層部における第二相の三次元分布を正確に把握できる方法は未だ存在せず、こうした方法の確立が希求されていた。
そこで、本発明の目的は、鋼材の表層部における第二相の三次元分布を正確に把握することができる鋼材の表層部の観察方法、およびこの観察結果に基づいて製造条件を適切に修正することができる鋼材の製造方法を提供することにある。
Thus, there is no method that can accurately grasp the three-dimensional distribution of the second phase in the surface layer portion of the steel material, and establishment of such a method has been demanded.
Therefore, an object of the present invention is to appropriately correct the manufacturing conditions based on the observation method of the surface layer portion of the steel material, which can accurately grasp the three-dimensional distribution of the second phase in the surface layer portion of the steel material, and this observation result. An object of the present invention is to provide a method for manufacturing a steel material.
発明者らは、上記課題を解決する方途について鋭意検討した。そのために、集束イオンビーム(Focused Ion Beam,FIB)による加工と、走査電子顕微鏡(Scanning Electron Microscope,SEM)による表面観察とを組み合わせることを想到した。すなわち、FIBにより鋼材試料をナノスケールで加工することができるため、対象とする領域について非常に微細なピッチで断面を現出させることができること、また、それら微細なピッチで現出された各断面においてナノスケールで分散する析出物等の第二相の分布をSEMで観察できることから、得られた観察結果を統合することにより、鋼材の表層部における第二相の三次元分布を把握できることを見出し、本発明を完成させるに至った。 The inventors diligently studied how to solve the above problems. For this purpose, the inventors have come up with a combination of processing using a focused ion beam (FIB) and surface observation using a scanning electron microscope (SEM). In other words, since the steel material sample can be processed on the nanoscale by FIB, the cross section can be made to appear at a very fine pitch in the target region, and each cross section made to appear at the fine pitch can be made. It is found that the distribution of the second phase such as precipitates dispersed on the nanoscale in SEM can be observed by SEM, so that the three-dimensional distribution of the second phase in the surface layer of the steel material can be grasped by integrating the obtained observation results. The present invention has been completed.
すなわち、本発明の要旨構成は以下の通りである。
(1)鋼材の表層部における第二相の三次元分布を観察するに当たり、前記表層部における観察面を決定した後、集束イオンビームにより加工後の表面が前記観察面と平行になるように前記観察面を加工する処理と走査電子顕微鏡により前記加工後の観察面を観察する処理とを繰り返し行い、各観察結果を統合して前記表層部における前記第二相の三次元分布を把握することを特徴とする、鋼材の表層部の観察方法。
That is, the gist of the present invention is as follows.
(1) In observing the three-dimensional distribution of the second phase in the surface layer portion of the steel material, after determining the observation surface in the surface layer portion, the surface processed by the focused ion beam is parallel to the observation surface. The process of processing the observation surface and the process of observing the observation surface after processing by a scanning electron microscope are repeatedly performed, and each observation result is integrated to grasp the three-dimensional distribution of the second phase in the surface layer portion. A method for observing the surface layer of steel.
(2)前記鋼材は溶融亜鉛めっき鋼板であり、前記第二相は酸化物である、前記(1)に記載の方法。 (2) The method according to (1), wherein the steel material is a hot-dip galvanized steel sheet, and the second phase is an oxide.
(3)鋼材を所定の製造条件の下で製造し、次いで、前記(1)または(2)に記載の方法により前記製造した鋼材の表層部における第二相の三次元分布を把握した後、該把握した第二相の三次元分布に基づいて、前記鋼材の前記所定の製造条件を修正することを特徴とする、鋼材の製造方法。 (3) After manufacturing a steel material under predetermined manufacturing conditions, and then grasping the three-dimensional distribution of the second phase in the surface layer portion of the manufactured steel material by the method described in (1) or (2), The method for manufacturing a steel material, wherein the predetermined manufacturing condition of the steel material is corrected based on the grasped three-dimensional distribution of the second phase.
本発明の鋼材の表層部の観察方法によれば、鋼材の表層部における第二相の三次元分布を正確に把握することができる。
また、本発明の鋼材の製造方法によれば、鋼材における第二相の三次元分布を把握することができるため、製造条件を適切に修正して鋼材を製造することができる。
According to the method for observing the surface layer portion of the steel material of the present invention, it is possible to accurately grasp the three-dimensional distribution of the second phase in the surface layer portion of the steel material.
Moreover, according to the manufacturing method of the steel materials of this invention, since the three-dimensional distribution of the 2nd phase in steel materials can be grasped | ascertained, steel materials can be manufactured by correcting manufacturing conditions appropriately.
(鋼材の表層部の観察方法)
以下、図面を参照して、本発明の実施形態について詳細に説明する。図1は、本発明に係る鋼材の表層部の観察方法のフローチャートを示している。まず、ステップS1において、鋼材の表層部における観察面を決定する。本発明において対象とする鋼材は、特に亜鉛めっき鋼板であり、その表層部、すなわち、下地鋼板とめっき層の界面近傍の領域に分散する、酸化物等の析出物の三次元分布を把握する。上述のように、めっき鋼板の表層部の不めっき部は、SiもしくはSi−Mn系の酸化物が、下地鋼板とめっき層との界面もしくはめっき層内に分散することに起因するものである。そこで、例えば、めっき鋼板におけるめっき層と鋼板の界面近傍に分散する酸化物を観察対象とし、その三次元分布を調べる場合には、まず、めっき層と鋼板の界面の位置を目視や光学顕微鏡等により確認して、めっき層と鋼板の界面を含む適切な大きさの観察面を決定する。本発明では、この観察面は任意に決定することができ、例えば、めっき鋼板の板厚方向に垂直な面であってもよいし、また、めっき鋼板の深さ方向断面(すなわち、板厚方向断面)としても良い。通常、この観察面は板厚方向に対して平行な面であるが、板厚方向に対して斜めとなるような断面でもよい。この観察面は、FIBにより現出させることもできるし、適切な切断および研磨処理により現出することもできるが、加工の精度および清浄度を考慮してFIBによる加工とすることが好ましい。こうして現出した鋼材の表層部における観察面をSEMにより観察することにより、鋼材の表層部における酸化物等の第二相の三次元分布を把握する。
(Method for observing the surface layer of steel)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a flowchart of a method for observing a surface layer portion of a steel material according to the present invention. First, in step S1, an observation surface in the surface layer portion of the steel material is determined. The steel material to be used in the present invention is particularly a galvanized steel sheet, and grasps the three-dimensional distribution of precipitates such as oxides dispersed in the surface layer portion thereof, that is, in the vicinity of the interface between the base steel sheet and the plating layer. As described above, the unplated portion of the surface layer portion of the plated steel sheet is caused by the Si or Si—Mn-based oxide dispersed in the interface between the base steel sheet and the plated layer or in the plated layer. Therefore, for example, when an oxide dispersed in the vicinity of the interface between the plating layer and the steel plate in the plated steel plate is to be observed and the three-dimensional distribution is examined, first, the position of the interface between the plating layer and the steel plate is visually or optical microscope To determine an observation surface of an appropriate size including the interface between the plating layer and the steel plate. In the present invention, the observation surface can be arbitrarily determined, for example, a surface perpendicular to the plate thickness direction of the plated steel plate, or a depth direction cross section of the plated steel plate (that is, the plate thickness direction). (Cross section). Usually, this observation plane is a plane parallel to the thickness direction, but it may be a cross section that is inclined with respect to the thickness direction. Although this observation surface can be revealed by FIB or can be revealed by appropriate cutting and polishing treatment, it is preferable to perform processing by FIB in consideration of processing accuracy and cleanliness. By observing the observation surface in the surface layer portion of the steel material thus revealed by SEM, the three-dimensional distribution of the second phase such as oxide in the surface layer portion of the steel material is grasped.
なお、後のステップS5において、FIBにより行うことができる観察面の加工の幅は数10μm以下であるため、一般的な切断および研磨処理によって、ある程度予め加工しておくこともできる。この場合には、蒸着等により観察部分を含む適切な大きさの領域に表面保護を施した上で、研磨によって観察面を現出させる。この前工程により、後述するステップS5における、FIBおよびSEMを用いた連続加工および観察を行う際に必要な加工処理を大幅に省略することができ、同じ加工時間でより広い領域を観察することができる。 In addition, in the subsequent step S5, since the processing width of the observation surface that can be performed by FIB is several tens of μm or less, it can be processed in advance to some extent by general cutting and polishing processing. In this case, the surface of an appropriate size including the observation portion is subjected to surface protection by vapor deposition or the like, and the observation surface is revealed by polishing. By this pre-process, the processing required when performing continuous processing and observation using FIB and SEM in step S5 described later can be largely omitted, and a wider area can be observed in the same processing time. it can.
こうして決定した観察面の近傍には、後にSEMにより観察面を確認できるように、ペンやビッカース圧痕、ケガキ等により適当な目印を付与しておく。 In the vicinity of the observation surface thus determined, an appropriate mark is given by a pen, a Vickers indentation, an inscription, or the like so that the observation surface can be confirmed later by SEM.
次に、ステップS2において、SEMの観察条件を決定する。このSEMの観察条件とは、具体的には、電子の加速電圧や、電流量、使用する検出器の種類等である。ここで決定する観察条件は、後のステップにおいてFIBにより加工される観察面を観察することを前提としたものである。すなわち、一般に行われるSEM観察では、鏡面研磨面を適当な腐食液にてエッチングし、表面に形成された微小な凹凸に基づいて組織の特定を行うが、腐食による組織の現出は、微細な酸化物等の第二相を保存することができない場合が多いため、本発明においては、一般に行われるSEM観察の条件をそのまま適用できるとは限らない。 Next, in step S2, SEM observation conditions are determined. The SEM observation conditions are specifically the acceleration voltage of electrons, the amount of current, the type of detector used, and the like. The observation conditions determined here are based on the premise that the observation surface processed by the FIB is observed in a later step. That is, in general SEM observation, the mirror-polished surface is etched with a suitable corrosive liquid, and the structure is specified based on the minute irregularities formed on the surface. In many cases, the second phase such as an oxide cannot be preserved. Therefore, in the present invention, the conditions of SEM observation generally performed cannot always be applied as they are.
一方、本発明における観察面は、FIBにより加工された表面であるため、非常に平滑であり、上記の一般的な方法により表面の凹凸から第二相の組織を特定することは困難である。しかし、SEM観察に用いられる二次電子は、(1)観察領域表面の凹凸情報に加えて、(2)原子番号情報、および(3)結晶方位情報が重畳する。そこで、本発明においては、これらの複合効果を利用して、観察面における酸化物等の第二相の存在を特定する。 On the other hand, since the observation surface in the present invention is a surface processed by FIB, it is very smooth, and it is difficult to specify the structure of the second phase from the unevenness of the surface by the above general method. However, secondary electrons used for SEM observation are superposed by (1) atomic number information and (3) crystal orientation information in addition to (1) unevenness information on the surface of the observation region. Therefore, in the present invention, the presence of the second phase such as an oxide on the observation surface is specified using these combined effects.
さらに、反射電子像を用いることにより、上記した原子番号情報および結晶方位情報を強調することもできるため、観察対象となる第二相に応じて二次電子および反射電子を使い分けることにより、第二相の特定をより容易に行うことができる。
その際、二次電子は二次電子検出器を用いて観察し、結晶方位や平均原子番号に敏感な反射電子は反射電子検出器を用いて観察する。一般に、反射電子検出器は、試料とレンズの間に挿入される場合が多くFIBによる逐次加工と両立しない場合もあるため、状況に応じて使用する。
Furthermore, since the atomic number information and the crystal orientation information described above can be emphasized by using the backscattered electron image, the secondary electrons and backscattered electrons can be used properly according to the second phase to be observed. Phase identification can be performed more easily.
At that time, secondary electrons are observed using a secondary electron detector, and reflected electrons sensitive to crystal orientation and average atomic number are observed using a reflected electron detector. In general, the backscattered electron detector is often inserted between a sample and a lens, and may not be compatible with sequential processing by FIB, and is used according to the situation.
なお、めっき鋼板の表層部の下地鋼板やめっき層中の酸化物については、反射電子を用いることなく二次電子のみにより十分に特定可能である。このようにして、FIBにより加工された、表面が非常に平滑な観察面であっても、観察条件を適正なものにすることにより第二相の組織を特定することができる。 In addition, about the base steel plate of the surface layer part of a plated steel plate, and the oxide in a plating layer, it can fully specify only by a secondary electron, without using a reflected electron. In this way, even if the surface is a very smooth observation surface processed by FIB, the structure of the second phase can be specified by making the observation conditions appropriate.
また、SEM観察では、使用する電子の加速電圧によって、取得できる観察面からの情報の深さが変化する。すなわち、加速電圧が、SEMの分解能を重視した15〜30kV程度の場合には、入射電子が観察面の下方深くまで侵入するため、観察する最表面の情報の割合が低下する。一方、加速電圧が1kV以下と低い場合には、最表面の情報は強調されるものの、分解能の低下を招きやすい。加えて、対象とする試料によっても観察に適した加速電圧は異なるため、続くステップS3において、観察対象である第二相の大きさから決定されるFIB加工ステップも考慮して、表層部に分散する第二相の三次元分布を得るための適切な加速電圧を設定する。 In SEM observation, the depth of information from the observation surface that can be obtained varies depending on the acceleration voltage of the electrons used. That is, when the accelerating voltage is about 15 to 30 kV with emphasis on the resolution of the SEM, incident electrons penetrate deeply below the observation surface, so the ratio of information on the outermost surface to be observed decreases. On the other hand, when the acceleration voltage is as low as 1 kV or less, the information on the outermost surface is emphasized, but the resolution tends to be lowered. In addition, since the accelerating voltage suitable for observation differs depending on the target sample, in the subsequent step S3, the FIB processing step determined from the size of the second phase to be observed is also taken into consideration and dispersed in the surface layer portion. Set an appropriate acceleration voltage to obtain a three-dimensional distribution of the second phase.
例えば、観察対象が酸化物であり、そのサイズが数100nm程度であれば、FIBの加工間隔は数10nm程度とすれば十分と考えられるが、この時、加速電圧が10kVを超えるような条件では、次の加工面の組織情報を含んだ観察になってしまう。このような状況は、特にエネルギーの高い反射電子像で顕著になるため注意を要する。一般に、鉄鋼材料を対象とする場合においては、サブミクロンの水平方向の分解能の確保と、10nm程度の深さ方向の分解能を両立させるために、加速電圧を10kV未満、好ましくは数kVに設定し、得られた二次電子像もしくは反射電子像により観察することが望ましい。観察対象がめっき鋼板の表層部における酸化物である場合、そのサイズは数10〜数100nm程度であるため、加速電圧を5kV程度に設定することが好ましい。 For example, if the object to be observed is an oxide and the size thereof is about several hundreds of nanometers, it is considered sufficient that the processing interval of FIB is about several tens of nanometers. However, under this condition, the acceleration voltage exceeds 10 kV. Therefore, the observation includes the structure information of the next processed surface. Such a situation is particularly noticeable in high-energy backscattered electron images. In general, in the case of steel materials, the acceleration voltage is set to less than 10 kV, preferably several kV, in order to achieve both submicron horizontal resolution and about 10 nm depth resolution. It is desirable to observe the obtained secondary electron image or reflected electron image. When the observation object is an oxide in the surface layer portion of the plated steel sheet, the size is about several tens to several hundreds of nm, and therefore the acceleration voltage is preferably set to about 5 kV.
続いて、ステップS3において、FIBによる加工条件を決定する。具体的には、観察対象とする第二相のおおよその大きさから、FIBによる観察面に垂直な方向における加工ステップを選択する。この加工ステップは、観察面をどの程度の厚み単位で加工するかを規定するものであるが、いたずらに小さい値に設定しても、上述した加速電圧との関係から、加工表面において組織の特定を正しく行うことができないばかりでなく、加工時間およびデータ処理時間が大幅に増大し、組織評価のスループットの低下を招いてしまう。発明者らが様々な材料を用いて調査した結果、着目する観察対象の平均サイズの1/10程度とすることにより、組織評価のスループットを低下させること無く、複数の深さ方向断面図から第二相の三次元分布を十分に把握することができることが分かった。例えば、観察対象が溶融亜鉛めっき鋼板の表層部における酸化物の場合、その大きさは数10〜数100nm程度であることから、加工ステップは、3nm以上100nm以下、とすることが好ましい。 Subsequently, in step S3, processing conditions by FIB are determined. Specifically, the processing step in the direction perpendicular to the observation surface by FIB is selected from the approximate size of the second phase to be observed. This processing step regulates how many thickness units the observation surface is processed, but even if it is set to a small value, it is necessary to specify the structure on the processing surface from the relationship with the acceleration voltage described above. Not only cannot be performed correctly, but also the processing time and data processing time greatly increase, leading to a decrease in the throughput of the tissue evaluation. As a result of the inventors' investigation using various materials, it is possible to obtain a plurality of depth direction sectional views from a plurality of depth direction views without reducing the throughput of the tissue evaluation by reducing the average size of the observation target of interest to about 1/10. It was found that the two-dimensional three-dimensional distribution can be fully understood. For example, when the observation target is an oxide in the surface layer portion of a hot-dip galvanized steel sheet, the size is about several tens to several hundreds of nm, and therefore, the processing step is preferably 3 nm to 100 nm.
その後、ステップS4において、ステップS2およびS3で設定したSEMおよびFIBの条件の下で、めっき鋼板の表層部における酸化物などの第二相の組織が特定できるかを評価する。この評価は、具体的には、SEMによる観察面の観察と、FIBによる観察面の加工とを1回以上、好ましくは複数回、通常は2〜3回行い、得られた画像において、第二相が特定できるか否かを評価する。その結果、第二相の認識が困難な場合や、画像に不連続性が認められる場合は、ステップS2に戻ってSEMの観察条件の見直しを行うか、あるいはステップS3においてFIBの加工条件の見直しを行う。 Thereafter, in step S4, it is evaluated whether or not a second phase structure such as an oxide in the surface layer portion of the plated steel sheet can be specified under the conditions of SEM and FIB set in steps S2 and S3. Specifically, this evaluation is performed by performing observation of the observation surface by SEM and processing of the observation surface by FIB at least once, preferably a plurality of times, usually 2 to 3 times. Evaluate whether the phase can be identified. As a result, when it is difficult to recognize the second phase or when discontinuity is recognized in the image, return to step S2 to review the observation conditions of the SEM, or review the processing conditions of the FIB in step S3. I do.
続いて、ステップS5において、こうして設定したFIBの加工条件およびSEMの観察条件の下で、FIBにより観察面を加工する処理とSEMにより加工後の観察面の観察する処理とを行い、観察面の画像を保存する。ここで、FIBによる加工は、加工後の表面が直前の観察面(前回の加工面)に対して平行となるように行う。これらの処理は、所定の回数だけ繰り返し行う。例えば、FIBによる加工ス−テップを100nmとし、FIBによる加工とSEMによる観察を100回繰り返す。これにより、10μm3程度の領域を観察することになり、この領域における第二相の三次元分布を求めることができる。 Subsequently, in step S5, the processing of processing the observation surface with FIB and the processing of observing the observation surface after processing with SEM are performed under the processing conditions of FIB and the observation conditions of SEM thus set, Save the image. Here, the processing by FIB is performed so that the surface after processing is parallel to the immediately preceding observation surface (previous processing surface). These processes are repeated a predetermined number of times. For example, the processing step by FIB is set to 100 nm, and processing by FIB and observation by SEM are repeated 100 times. Thereby, an area of about 10 μm 3 is observed, and the three-dimensional distribution of the second phase in this area can be obtained.
次に、ステップS6において、ステップS5の処理を所定の回数だけ繰り返したか否かを判定し、繰り返していない場合にはステップS5に戻り、繰り返した場合にはステップS7に進む。 Next, in step S6, it is determined whether or not the process of step S5 has been repeated a predetermined number of times. If not, the process returns to step S5, and if it has been repeated, the process proceeds to step S7.
続いて、ステップS7において、ステップS5において得られた各観察結果を統合して、表層部における第二相の三次元分布を把握する。この段階で、所定の枚数の観察面の画像が得られている。例えば、上記した加工ステップ:100nm、繰り返し回数:100回の場合には、100枚の画像が得られている。ここでは、これらの画像を統合して、表層部における第二相の三次元分布を得る。これは、適切なソフトウェア(例えばVisage Imaging社製Amira 5等)を用いて行うことができ、各観察面における第二相組織の二次元的な分布を三次元的に可視化することができる。その際、必要に応じて、画像間の位置ずれの補正やコントラストの調整を自動あるいは手動で行うことができる。 Subsequently, in step S7, the observation results obtained in step S5 are integrated to grasp the three-dimensional distribution of the second phase in the surface layer portion. At this stage, a predetermined number of images of the observation surface are obtained. For example, when the processing step is 100 nm and the number of repetitions is 100, 100 images are obtained. Here, these images are integrated to obtain a three-dimensional distribution of the second phase in the surface layer portion. This can be performed using appropriate software (for example, Amira 5 manufactured by Visage Imaging), and the two-dimensional distribution of the second phase structure on each observation surface can be visualized three-dimensionally. At that time, if necessary, correction of misalignment between images and adjustment of contrast can be performed automatically or manually.
こうして最終的に得られた、観察領域における第二相の三次元分布から、第二相組織の平均サイズや体積分率、さらに、任意の第二相間の距離等の定量的な情報を得ることができ、適宜鋼材の製造方法の製造条件に反映させることができる。 Obtaining quantitative information, such as the average size and volume fraction of the second phase tissue, and the distance between any second phases, from the three-dimensional distribution of the second phase in the observation region, finally obtained in this way And can be appropriately reflected in the manufacturing conditions of the manufacturing method of the steel material.
こうして、本発明により、鋼材の表層部における第二相の三次元分布を正確に把握することができる。 Thus, according to the present invention, the three-dimensional distribution of the second phase in the surface layer portion of the steel material can be accurately grasped.
(鋼材の製造方法)
以上の本発明の鋼材の表層部の観察方法により、所定の製造条件の下で製造した鋼材の表層部における第二相の三次元分布を把握し、該把握した第二相の三次元分布に基づいて、鋼材の製造条件を適切に修正することにより、所望の性質を有する鋼材を製造することができる。
(Method for manufacturing steel materials)
By the method for observing the surface layer portion of the steel material of the present invention as described above, the three-dimensional distribution of the second phase in the surface layer portion of the steel material manufactured under predetermined manufacturing conditions is grasped, and the grasped second-phase three-dimensional distribution is obtained. Based on this, the steel material which has a desired property can be manufactured by correct | amending the manufacturing conditions of steel materials appropriately.
図2に、本発明の鋼材の製造方法のフローチャートを示す。まず、ステップS11において、所定の製造条件の下で鋼材を製造した後、上述した本発明の鋼材の表層部の観察方法により、表層部における第二相の三次元分布を把握する。具体的には、ステップS12〜S18において、図1に示したステップS1〜S7と同じ処理を行う。その後、ステップS19において、ステップS12〜18において得られた表層部における第二相の三次元分布に基づいて、ステップS11における所定の製造条件を修正する。 In FIG. 2, the flowchart of the manufacturing method of the steel materials of this invention is shown. First, in step S11, after manufacturing a steel material under a predetermined manufacturing condition, the three-dimensional distribution of the second phase in the surface layer part is grasped by the method for observing the surface layer part of the steel material of the present invention described above. Specifically, in steps S12 to S18, the same processing as steps S1 to S7 shown in FIG. 1 is performed. Thereafter, in step S19, the predetermined manufacturing condition in step S11 is corrected based on the three-dimensional distribution of the second phase in the surface layer portion obtained in steps S12 to S18.
鋼材における第二相の組織が材料特性に及ぼす影響は種々存在する。上述のように、この第二相の三次元分布の把握は、とりわけ、鋼材がめっき鋼板の場合、下地鋼板の酸化および還元処理の際の条件設定において肝要である。つまり、めっき層において、鋼板との界面近傍の酸化物の三次元分布を観察して、めっき性に悪影響を与える膜状酸化物が分布している場合には、酸化強化処理時の酸素ポテンシャルを高めて内部酸化を促進し、さらに鋼表面でのSiの酸化抑制を行なうことにより製造条件を適正化できる。また、内部酸化物が多すぎて機械特性に悪影響が懸念される場合には、酸化強化処理時の酸素ポテンシャルを低減すればよい。 There are various effects of the structure of the second phase in steel on the material properties. As described above, grasping the three-dimensional distribution of the second phase is important in setting conditions in the oxidation and reduction treatment of the base steel plate, particularly when the steel material is a plated steel plate. In other words, in the plating layer, when the three-dimensional distribution of oxides near the interface with the steel sheet is observed, and when film-like oxides that adversely affect the plating properties are distributed, the oxygen potential during the oxidation strengthening treatment is reduced. The production conditions can be optimized by increasing the internal oxidation and further suppressing the oxidation of Si on the steel surface. Further, when there is a concern about the adverse effect on the mechanical characteristics due to too much internal oxide, the oxygen potential during the oxidation strengthening process may be reduced.
具体的な判定基準としては、観察した領域のめっき層(合金層)における内部酸化物の体積率(%)、さらに、各酸化物のアスペクト比を求め、アスペクト比が5以上のものを膜状酸化物とした時のその発生頻度((膜状酸化物の数/全酸化物の数)×100(%))を指標とすることができる。 As specific judgment criteria, the volume ratio (%) of the internal oxide in the plating layer (alloy layer) in the observed region and the aspect ratio of each oxide are obtained. The frequency of occurrence of oxides ((number of film-like oxides / number of total oxides) × 100 (%)) can be used as an index.
発明者らが鋭意検討した結果、通常の亜鉛めっき鋼板では、鋼とめっき層との界面近傍、好ましくは界面より5〜10μmの範囲のめっき層部分における内部酸化物の体積率が2.8%以下、膜状酸化物の発生頻度が18%以下の時に不めっきなどが発生せず十分な厚みのめっき層を有し、機械特性の高いめっき鋼板が得られることが分かった。
ただし、これらの指標は亜鉛めっき鋼板に対するものであり、めっきの種類が異なる場合や、観察対象がめっき鋼板ではなく、厚鋼板溶接部の溶接熱影響部における析出物の状態から溶接強度を評価したい等の場合には、適宜予備実験を行ない、酸化物の三次元分布状態がどのような範囲が適正か決定し、本発明を適用することができる。
As a result of intensive studies by the inventors, in a normal galvanized steel sheet, the volume ratio of the internal oxide in the vicinity of the interface between the steel and the plated layer, preferably in the plated layer portion in the range of 5 to 10 μm from the interface, is 2.8%. In the following, it was found that when the occurrence frequency of the film-like oxide is 18% or less, non-plating or the like does not occur and a plated steel sheet having a sufficient thickness and having high mechanical properties can be obtained.
However, these indicators are for galvanized steel sheets. When the type of plating is different, or the observation object is not a plated steel sheet, we want to evaluate the weld strength from the state of precipitates in the welded heat affected zone of the thick steel plate welded part. In such a case, a preliminary experiment is appropriately performed to determine what range is appropriate for the three-dimensional distribution state of the oxide, and the present invention can be applied.
上述しためっき鋼板における指標についての技術的意義について以下に説明する。
鋼板めっきの際には、鋼板をめっきする前に鋼板の酸化強化処理を行い、その後に還元雰囲気で焼鈍を行い表面の鉄を還元してめっきが付きやすくするのが通例である。この酸化強化処理の際に、SiやMnの酸化物が形成されるが、酸素ポテンシャルが十分に高くない場合、Siが酸化される前にSiが鋼板表面に移動して鋼板表面にて酸化される結果、酸化物が鋼板表面で膜状になって鋼板表面を覆ってしまい、還元焼鈍後も鋼板表面に残存して、めっき性を悪化させることになる。ここで、めっき性を悪化させるとは、めっきが付着しにくいだけでなく、その後の合金化処理で合金化が進みにくく、めっき層の十分な厚みが得られなくなることも意味する。
The technical significance of the indicators in the above-described plated steel sheet will be described below.
In the case of steel plate plating, it is usual to perform oxidation strengthening treatment of the steel plate before plating the steel plate, and thereafter anneal in a reducing atmosphere to reduce the iron on the surface to facilitate the plating. During this oxidation strengthening treatment, oxides of Si and Mn are formed. If the oxygen potential is not sufficiently high, Si moves to the steel plate surface and is oxidized on the steel plate surface before Si is oxidized. As a result, the oxide forms a film on the surface of the steel plate and covers the surface of the steel plate, and remains on the surface of the steel plate even after reduction annealing, thereby degrading the plateability. Here, the deterioration of the plating property means not only that the plating does not easily adhere, but also that the alloying is difficult to proceed in the subsequent alloying treatment, and a sufficient thickness of the plating layer cannot be obtained.
一方、酸化強化処理の際に、酸素ポテンシャルが高過ぎると、酸化物となるSiの量が多くなり、かつ、鋼板表面に移動するよりも速く鋼板内部において酸化される結果、鋼板表面での膜状酸化物は生成しないものの、鋼板表面近くで多量の酸化物が生成され、酸化物の体積率が高くなる。その後施されるめっき過程での合金化処理により鋼板表面のFeが合金化するため、鋼板表面近くに存在する酸化物がめっき層内部に多量に取り込まれる結果となり、めっき鋼板を加工した際に、めっきの損傷を発生しやすくする。 On the other hand, if the oxygen potential is too high during the oxidation strengthening treatment, the amount of Si that becomes oxide increases, and the film on the steel sheet surface is oxidized faster than moving to the steel sheet surface. Although no oxide is produced, a large amount of oxide is produced near the surface of the steel sheet, and the volume ratio of the oxide is increased. Since Fe on the surface of the steel sheet is alloyed by the alloying treatment in the plating process to be applied thereafter, a large amount of oxide existing near the surface of the steel sheet is taken into the plating layer, and when the plated steel sheet is processed, Facilitates plating damage.
これらに対して、本発明による酸化物の三次元分布の把握を行うことにより、第二相である酸化物の量および分布形態を把握できるため、上記のような不良の種類を予想することができ、ひいては、製造されためっき鋼板の状態を観察することにより、より良好なめっき条件を設定することができる。 On the other hand, by grasping the three-dimensional distribution of the oxide according to the present invention, the amount and distribution form of the oxide that is the second phase can be grasped. In addition, by observing the state of the manufactured plated steel sheet, better plating conditions can be set.
つまり、めっき鋼板の鋼板とめっき層の界面近傍のめっき層を観察して膜状酸化物が鋼界面付近に多い場合は、酸化強化時の酸素ポテンシャルを高めて内部酸化物形成を促進する。また、めっき前の還元焼鈍時の温度を低下させ、鋼表面でのSiの酸化を抑制する。一方、めっき層内の内部酸化物の体積率が高い場合には、酸化強化時の酸素ポテンシャルを低める方向に調整すればよい。 That is, when the plating layer in the vicinity of the interface between the steel sheet and the plating layer of the plated steel sheet is observed and there are many film-like oxides in the vicinity of the steel interface, the oxygen potential at the time of oxidation strengthening is increased to promote the formation of internal oxides. Moreover, the temperature at the time of the reductive annealing before plating is lowered, and the oxidation of Si on the steel surface is suppressed. On the other hand, when the volume ratio of the internal oxide in the plating layer is high, the oxygen potential at the time of oxidative strengthening may be adjusted in the direction of decreasing.
その際、酸素ポテンシャルを高めるには、例えば酸化強化時の酸素分圧を高め、一方、酸素ポテンシャルを低めるには、酸化強化時の酸素分圧を低くすればよい。 At this time, in order to increase the oxygen potential, for example, the oxygen partial pressure at the time of strengthening the oxidation is increased.
このように、上述した本発明の方法により、第二相の三次元分布が得られて初めて製造条件の適正化を行うことができる。こうして、不めっき部がなく、めっき層の厚みも充分に確保され、機械特性も確保できるめっき鋼板を製造することが可能になる。 As described above, the manufacturing conditions can be optimized only after the above-described method of the present invention provides the three-dimensional distribution of the second phase. In this way, it is possible to produce a plated steel sheet that has no unplated portion, a sufficient thickness of the plated layer, and mechanical characteristics.
(鋼No.1〜8)
種々の製造方法に従って、溶融亜鉛めっき鋼板を製造した。すなわち、まず、めっき鋼板の下地鋼板として、表1に示した成分を有し、残りはFeと不可避的不純物からなる、1.5%Si−2.0%Mnを主要組成とする厚さ1.0mmの高強度鋼板を用意した。この下地鋼板に対して、溶融亜鉛めっき工程前の熱処理条件を変化させてめっき鋼板を製造した。具体的には、表2に示した、酸素強化処理時の燃焼ガス内の酸素分圧、還元焼鈍温度を変更した8つの条件の下で熱処理を行ってめっき鋼板を製造した(鋼No.1〜8)。
(Steel No. 1-8)
Hot-dip galvanized steel sheets were manufactured according to various manufacturing methods. That is, first, as the base steel plate of the plated steel plate, the thickness 1 having the components shown in Table 1 and the remainder consisting of Fe and unavoidable impurities and having a main composition of 1.5% Si-2.0% Mn. A 0.0 mm high-strength steel sheet was prepared. A plated steel sheet was manufactured by changing the heat treatment conditions before the hot dip galvanizing process for the base steel sheet. Specifically, the plated steel sheet was manufactured by performing heat treatment under eight conditions shown in Table 2 in which the oxygen partial pressure in the combustion gas during the oxygen strengthening treatment and the reduction annealing temperature were changed (Steel No. 1). ~ 8).
こうして製造された鋼No.1〜8のめっき鋼板の鋼板上に形成されるめっき層の構造を評価した。そのために、評価用の試料として、各めっき鋼板の板幅方向の中央部で表面から厚み1/4の深さ部分までを10mm角で採取したものを用い、この試料をFIB装置に導入した後、任意の場所でFIBの粗加工ビームにより鋼板板厚方向に平行な断面を作製し観察面を決定した。 Steel No. manufactured in this way. The structure of the plating layer formed on the steel plate of 1-8 plated steel plates was evaluated. Therefore, as a sample for evaluation, a sample obtained by sampling a 10 mm square from the surface to a depth part of a thickness of 1/4 at the center in the plate width direction of each plated steel sheet was used, and this sample was introduced into the FIB apparatus. A cross section parallel to the thickness direction of the steel plate was produced by a FIB rough machining beam at an arbitrary location, and the observation surface was determined.
次いで、SEMの観察条件の決定を行い、加速電圧5kV、倍率5000倍の条件の下で二次電子像観察を行った。得られた画像を図3に示す。この図から明らかなように、下地鋼板とめっき層界面付近からめっき層内部にわたる広い領域に、粒子状もしくは線状の特徴的コントラストが認められた。これらの微細構造をX線分析により評価したところ、SiもしくはSiとMnとを含む酸化物であることが判明した。また、酸化物の大きさは、線状形態の最小幅が100nm程度であった。このように、通常の二次電子像で、第二相である酸化物の微細構造が十分特定できることを確認できたため、加速電圧:5kVでSEM観察を行い、加工ステップ:50nmでFIBによる加工を行った。これらのSEMによる観察およびFIBによる加工処理を断面方向に80回繰り返し、特に重要な下地鋼板とめっき層界面付近を含む、高さ:約8μm、幅:約10μm、奥行き:約4μmの領域に対して観察を行い、総数80枚の画像を取得した。これらの画像の一部を図4に示す。 Next, SEM observation conditions were determined, and secondary electron image observation was performed under conditions of an acceleration voltage of 5 kV and a magnification of 5000 times. The obtained image is shown in FIG. As is apparent from this figure, a particulate or linear characteristic contrast was observed in a wide region extending from the vicinity of the interface between the base steel plate and the plating layer to the inside of the plating layer. When these fine structures were evaluated by X-ray analysis, they were found to be Si or an oxide containing Si and Mn. The minimum width of the linear shape of the oxide was about 100 nm. Thus, since it was confirmed that the fine structure of the oxide that is the second phase could be sufficiently specified by a normal secondary electron image, SEM observation was performed at an acceleration voltage of 5 kV, and processing by FIB was performed at a processing step of 50 nm. went. These SEM observations and FIB processing are repeated 80 times in the cross-sectional direction, especially for the area of height: about 8 μm, width: about 10 μm, depth: about 4 μm, including the area near the interface between the underlying steel plate and the plating layer. And a total of 80 images were acquired. Some of these images are shown in FIG.
こうして得られた画像を、専用画像処理ソフト(Visage Imaging社製Amira 5)により、上記領域における酸化物の分布を三次元的に描画した。各試料につき、これらの、一定体積内における酸化物の三次元的分散状態や体積率等を求めた。
具体的には、観察した領域のめっき層における内部酸化物の体積率(%)を求めた。また、酸化物の分布がめっき層全体にほぼ一様に分布しているか、鋼界面から1μmの部分に特に多く分布しているかを調べた。さらに、各酸化物のアスペクト比を求めアスペクト比が5以上のものを膜状酸化物として、その発生頻度((膜状酸化物の数/全酸化物の数)×100(%))を調べた。
また、観察した領域のめっき層における内部酸化物の体積率が2.8%超えの場合を「曲げ加工性不良」、膜状酸化物の頻度が18%超えの場合を「めっきがつきにくい」として、実際の評価を予測した。
さらに、めっき鋼板の実際の評価としては、めっきのつきやすさとして合金化処理後の合金層厚み、および加工性としてJIS Z 2248に準拠して45°曲げ加工を実施した時の稜線部におけるめっき損傷数を測定した。合金層厚みは断面のSEM観察により任意の場所20箇所で測定しその平均とした。めっき層厚みが6μm以上、45°曲げ加工時のめっき損傷数が10箇所未満の場合を適合鋼板と判定した。得られた結果を表2に示す。また、例として、鋼No.3における酸化物の三次元分布を図5に示す。この図において、直方体フレームの内部にある着色した部分が酸化物である。また、直方体の上面はめっき鋼板のめっき層の上面(表面)にあたるが、FIB加工を行うにあたり、めっき層表面に保護蒸着層を形成している。
The image obtained in this manner was three-dimensionally drawn with a dedicated image processing software (Amira 5 manufactured by Visage Imaging) for the oxide distribution in the region. For each sample, the three-dimensional dispersion state and volume ratio of these oxides in a certain volume were determined.
Specifically, the volume fraction (%) of the internal oxide in the plating layer in the observed region was determined. In addition, it was examined whether the oxide distribution was almost uniformly distributed over the entire plating layer, or whether the oxide distribution was particularly large in a portion of 1 μm from the steel interface. Further, the aspect ratio of each oxide was determined, and those having an aspect ratio of 5 or more were used as film oxides, and the occurrence frequency ((number of film oxides / total number of oxides) × 100 (%)) was examined.
In addition, when the volume ratio of the internal oxide in the plating layer in the observed region exceeds 2.8%, “bending workability is poor”, and when the frequency of the film-like oxide exceeds 18%, “plating is difficult”. As predicted the actual evaluation.
Furthermore, as an actual evaluation of the plated steel sheet, the plating at the ridge line when 45 ° bending is performed according to JIS Z 2248 as the alloy layer thickness after alloying treatment as the ease of plating and the workability The number of damage was measured. The alloy layer thickness was measured at 20 arbitrary locations by SEM observation of the cross section, and was averaged. A case where the plating layer thickness was 6 μm or more and the number of plating damages during 45 ° bending was less than 10 was determined as a suitable steel plate. The obtained results are shown in Table 2. As an example, steel No. 3 shows the three-dimensional distribution of the oxide in No. 3. In this figure, the colored portion inside the rectangular parallelepiped frame is an oxide. Further, the upper surface of the rectangular parallelepiped corresponds to the upper surface (surface) of the plated layer of the plated steel sheet, but when performing the FIB processing, a protective vapor deposition layer is formed on the surface of the plated layer.
鋼No.1および2においては、膜状酸化物の発生頻度が高く、めっきがつきにくいことが予測されたが、実際に合金層の厚みも薄く不適合と判断された。
一方、鋼No.7および8では、内部酸化物は一様に分布しているが、その体積率が高く曲げ加工性が不良と予測されたが、実際に、曲げ加工後のクラック数が多く不適合と判断された。
また、鋼No.3〜6においては、膜状酸化物の発生頻度や内部酸化物の状態が適正範囲内であり、めっきのつきやすさ、曲げ加工性とも良好であると予測されたが、実際の評価結果も良好であった。
さらに、鋼No.1および2よりも酸化強化時の酸素ポテンシャルが高く、還元焼鈍時の温度が低い鋼No.3〜6においては、鋼No.1および2ほど膜状酸化物の発生頻度が高くなく、めっきのつきやすさ(合金層厚み)も良好であった。また、鋼No.3〜6は、鋼No.7および8よりも酸化強化時の酸素ポテンシャルが低く、鋼No.7および8ほど内部酸化物の体積率が高くなく、曲げ加工特性も良好なものであった。
以上より、製造されためっき鋼板のめっき層中の酸化物の三次元分布状態を調べることにより、めっき鋼板としての実際の特性を予測することが可能なこと、また、ある製造条件において膜状酸化物の発生頻度が高い場合には、酸素ポテンシャルを高く、還元焼鈍時の温度を低くすれば適正条件を見出せること、また、内部酸化物の体積率が高い場合には、酸化強化時の酸素ポテンシャルを低くすることにより適正条件を見出せることが分かった。
Steel No. In 1 and 2, it was predicted that the occurrence of film-like oxide was high and plating was difficult to occur, but the thickness of the alloy layer was actually too thin and judged to be incompatible.
On the other hand, Steel No. In 7 and 8, the internal oxide was uniformly distributed, but its volume fraction was high and bending workability was predicted to be poor, but in fact, the number of cracks after bending was large and was judged to be incompatible. .
Steel No. In 3-6, the occurrence frequency of the film-like oxide and the state of the internal oxide were within the appropriate ranges, and it was predicted that the ease of plating and bending workability were good, but the actual evaluation results were also It was good.
Furthermore, steel no. Steel No. 1 has a higher oxygen potential during oxidation strengthening than that of 1 and 2 and a lower temperature during reduction annealing. In Nos. 3-6, Steel No. The occurrence frequency of film-like oxide was not so high as in 1 and 2, and the ease of plating (alloy layer thickness) was also good. Steel No. 3-6 are steel No.3. The oxygen potential during oxidative strengthening is lower than that of steels 7 and 8, and steel no. The volume ratio of the internal oxide was not as high as 7 and 8, and the bending properties were also good.
From the above, it is possible to predict the actual characteristics of the plated steel sheet by examining the three-dimensional distribution state of the oxide in the plated layer of the manufactured plated steel sheet, and film oxidation under certain manufacturing conditions When the frequency of occurrence is high, the oxygen potential can be increased and the temperature during reduction annealing can be decreased to find an appropriate condition. When the volume fraction of the internal oxide is high, the oxygen potential during oxidation strengthening can be found. It was found that the proper condition can be found by lowering the value of.
(比較例)
上記実施例で製造しためっき鋼板(鋼No.1、3および7)、それぞれに対して、上記実施例と同様の方法でSEM観察サンプルを1つずつ作製し、それぞれに対して、特に重要な下地鋼板とめっき層界面付近を含む、高さ:約8μm、幅:約10μmの領域についてSEM観察を行なった。ただし、一つのサンプルに対してSEM観察は1回として、SEM観察で得られる二次元画像において、酸化物の面積率、およびアスペクト比が5以上のものを膜状酸化物として、その発生頻度((膜状酸化物の数/全酸化物の数)×100(%))を評価した。得られた結果を表3に示す。
表3に示すように、内部酸化物の面積率および膜状酸化物の発生頻度と実際のめっき鋼板の評価とは全く相関がなく、また、製造条件との相関もない。このように、二次元観察から実際のめっき鋼板の評価の予測、条件の適性化を行なうことは困難であることが分かった。
(Comparative example)
For each of the plated steel plates (steel Nos. 1, 3 and 7) produced in the above examples, one SEM observation sample was prepared in the same manner as in the above examples, and each sample was particularly important. SEM observation was performed on a region having a height of about 8 μm and a width of about 10 μm, including the vicinity of the interface between the base steel plate and the plating layer. However, SEM observation is performed once for one sample. In a two-dimensional image obtained by SEM observation, an oxide having an area ratio of 5 or more and an aspect ratio of 5 or more is used as a film-like oxide, and its occurrence frequency ( (Number of film-like oxides / number of total oxides) × 100 (%)) was evaluated. The obtained results are shown in Table 3.
As shown in Table 3, there is no correlation between the area ratio of the internal oxide and the occurrence frequency of the film-like oxide and the actual evaluation of the plated steel sheet, and there is no correlation with the manufacturing conditions. As described above, it has been found that it is difficult to predict the evaluation of the actual plated steel sheet and to optimize the conditions from the two-dimensional observation.
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JP2018044926A (en) * | 2016-09-16 | 2018-03-22 | 東芝メモリ株式会社 | Composition analysis method and composition analysis system |
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