JP6790989B2 - Three-dimensional morphological quantitative analysis method of pearlite tissue - Google Patents

Description

The present invention relates to a method for quantitatively analyzing a three-dimensional morphology of a pearlite structure.

Metallic materials such as steel materials (hereinafter referred to as "steel materials") contain the same type and amount of elements, but have mechanical properties such as strength, elongation, and toughness due to differences in the fine alloy structure in the materials. Chemical properties such as corrosion resistance are different. Therefore, in the development of steel materials, it is desirable to quantitatively analyze the difference in the morphology of fine alloy structures and analyze the effects together.

For example, pearlite steel is generally used as the steel material used as a material for high carbon steel wire such as steel cord, bridge steel wire, and PC steel wire. As the name implies, pearlite steel mainly has an alloy structure called pearlite structure.
This pearlite structure is a composite alloy structure separated into two phases of cementite (Fe ₃ C) and ferrite (αFe) in a steel material, and cementite and ferrite are alternately laminated in layers to form a lamella. It is an alloy structure that exists as.
In general, cementite has high strength but is brittle, and ferrite has low strength but is easy to stretch. Therefore, in the pearlite structure, it is necessary to analyze the arrangement and curvature of the cementite and ferrite forming the lamellar morphology in the steel material in order to improve the mechanical properties of the steel material. This is an important issue.

To analyze the alloy structure, for example, the pearlite structure, a test piece taken from a steel material is polished so that the observed polishing surface is almost horizontal. Then, the existence form of the cementite layer 1 and the ferrite layer 2 appearing on the polished observation polished surface is observed from the observation direction 3 by an electron microscope such as SEM as shown in FIG.
However, in ordinary microscopic observation, only planar existence information of the cementite layer 1 and the ferrite layer 2 that can be observed from the observation direction 3 can be obtained. Therefore, it is not possible to quantitatively analyze how the cementite layer 1 and the ferrite layer 2 form a lamellar morphology as a three-dimensional morphology of the pearlite structure including the depth direction of the observed polished surface. Therefore, it is not possible to grasp the relationship between the morphology of the pearlite structure and the mechanical properties, especially in the depth direction.

Until now, the method of knowing the three-dimensional morphology of a steel alloy structure such as a pearlite structure has been to repeatedly polish a test piece of a steel material and photograph a new observed polished surface that appears by polishing, and the photographed images are polished in the order of polishing. It was analyzed by superimposing it on the street. Since this requires a great deal of time and effort, research has not progressed on the influence of the existence morphology of the cementite layer 1 and the ferrite layer 2 of the pearlite structure forming the lamellar morphology on the mechanical properties of the steel material.

In recent years, a serial sectioning technique based on FIB-SEM observation has been studied as the only technique capable of evaluating a pearlite structure three-dimensionally and quantitatively (Non-Patent Document 1). This technology uses a focused ion beam (FIB) to grind a minute thickness of several hundred nm of the observed sample, and then repeatedly obtains a tissue tomographic photograph by FE-SEM to determine the internal morphology of the alloy structure of the steel material on a computer. It is intended to be reconstructed with.
This technology can reconstruct the three-dimensional form on a computer by interpolating and joining the obtained two-dimensional images on the premise that grinding at each fault is performed in parallel and accurately with a constant thickness, but it costs a huge amount of money. And because it requires machine time, it cannot be used industrially yet.

On the other hand, as shown in Non-Patent Document 2, phenomena such as voids and defects (cracks) in the material, which are not in nanometer-order fine morphology, can be evaluated by a combination of polishing and an optical microscope. Although it was possible, the lamellar morphology of the pearlite structure is inexpensive and efficient because the interlayer spacing (lamellar spacing) between the adjacent cementite layer 1 and the ferrite layer 2 is several tens of nm to about 100 nm at most, which cannot be decomposed by an optical microscope. It was difficult to evaluate.

As described above, it is important to three-dimensionally and quantitatively evaluate the existence morphology of the cementite layer 1 and the ferrite layer 2 constituting the fine lamellar morphology of the pearlite structure of the steel material from the viewpoint of material control. Due to the difficulty, it could not be realized industrially.
Further, as shown in FIG. 1, in the fine lamella morphology, the interface (lamella interface) between the cementite layer 1 and the ferrite layer 2 is not always flat, and is generally curved to some extent. However, when the two-dimensional tomographic images of the polished surface are to be statistically aggregated and handled, the degree of this curvature should be quantitatively measured in the depth direction, including the case where the two-dimensional tomographic image is not curved and is flat. Was difficult.

Adachi.et.al, Acta Materiaria vol56 (2008) 5995-6002, "computer-aided three-dimensional visualization of twisted cementite lamellae in eutectoid steel" Owada, Kurumada, Ito, Tomoda, Adachi, Japan Society of Mechanical Engineers Kanto Branch, Precision Engineering Society, Ibaraki University Ibaraki Lecture Proceedings Vol. 21st Page. 81-82 (2013.09.06), 3D observation of crack growth and microstructure of steel materials

As described above, the characteristics of steel wire are improved by defining the three-dimensional morphology of the pearlite structure of steel wire as a starting material for wire drawing of high-strength steel wire such as steel cord, bridge steel wire, and PC steel wire. Although it is required to make a proposal for making the pearlite structure, an effective means for quantitatively analyzing the three-dimensional morphology of the pearlite structure has not been proposed.
This is because the pearlite structure has a very fine lamellar spacing of about several tens of nm, and it seems that it was difficult to quantitatively capture the fine morphology including its curvature.
Further, in order to analyze the morphology of the pearlite structure in the depth direction, it is necessary to sequentially scrape the observed polished surface, so that the same test piece cannot be reanalyzed.

An object of the present invention is to provide a three-dimensional morphological analysis method for a pearlite structure, which can quantitatively analyze the three-dimensional morphology of cementite and ferrite spreading in the depth direction by a non-destructive and simple method for a test piece. And.

In view of the above circumstances, the present inventor has completed a technique for solving the above problems by making diligent efforts.
That is, the gist of the present invention for solving the above problems is as follows.
(1) A three-dimensional morphological quantitative analysis method for the pearlite structure spreading in the depth direction of a steel material having a pearlite structure forming a lamellar morphology with a cementite layer and a ferrite layer.
The surface of the test piece collected from the steel material is polished to obtain an observation-polished surface, and the observation-polished surface is subjected to the EBSD method.
With respect to the crystal plane, (010) plane or (031) plane of the cementite layer, tilt information indicating how much the cementite layer is tilted from the observation polishing plane at each point of the observation polishing plane is acquired.
By obtaining the curvature of the crystal plane of the cementite layer from the inclination information of each point,
A method for quantitatively analyzing a three-dimensional morphology of a pearlite structure, which comprises quantitatively determining the three-dimensional morphology of the cementite layer and the ferrite layer spreading in the depth direction.
(2) The pearlite structure according to (1), wherein the crystal plane and crystal orientation of the ferrite layer that matches the crystal plane of the cementite layer are determined by the crystal orientation relationship between the cementite layer and the ferrite layer. Three-dimensional morphological quantitative analysis method.
(3) The measurement by the EBSD method is characterized in that the angle formed by the normal vector of the observed polished surface and the normal vector of the interface between the cementite layer and the ferrite layer is within 30 ° (1) or. The method for quantitatively analyzing a three-dimensional morphology of a pearlite structure according to (2).
(4) One of (1) to (3), which comprises polishing with a colloidal silica-dispersed polishing liquid for 10 minutes or more, and then electrolytically polishing for 10 minutes or more in forming the observation polishing surface. The method for quantitatively analyzing the three-dimensional morphology of the pearlite structure described in 1.

According to the present invention, one cross section is measured by an EBSD method (Electron Backscattered Diffraction), which is a simple method, including the case where the cementite layer 1 and the ferrite layer 2 spreading in the depth direction constituting the pearlite structure are flat plates. It has made it possible to analyze the three-dimensional form (lamellar form) easily and clearly.

It is a figure which observes the observation polishing surface of the steel material test piece which has a pearlite structure. It is a schematic diagram which shows the cross section in the depth direction of the steel material test piece which has a pearlite structure. It is a schematic diagram which enlarged the cross section in the depth direction of the steel material test piece having a pearlite structure surrounded by the broken line of FIG. 2, and shows only three layers of a ferrite layer 2, a cementite layer 1, and a ferrite layer 2. It is a figure which shows the interface shape (lamella shape) in the depth direction of a cementite layer 1 and a ferrite layer 2 analyzed by this invention.

The present invention will be described below.
First, since making multiple microstructure observations leads to an increase in time and cost for evaluation, we have developed a method limited to the method of measuring only one observation and polishing surface.
The present inventor obtained the crystal orientation distribution information of at least the cementite layer 1 constituting the steel material having a pearlite structure by the EBSD method (Electron Backscattered Diffraction), and utilized that cementite and ferrite have a certain crystal face relationship. By acquiring tilt information indicating how much the crystal plane, (010) plane, or (031) plane of the cementite layer 1 is tilted from the observed polished surface at each point of the observed polished surface, the pearlite structure of the lamella morphology can be obtained. We have developed a technology to detect internal morphology. By using this technique, the spacing of the lamellar morphology of the pearlite structure, and if it is flat or curved, the morphology of the curved surface can be detected three-dimensionally and quantitatively from only the information of one cross section of the pearlite. can do.

As described above, the pearlite structure exists in the form of lamella, in which the cementite layer 1 and the ferrite layer 2 are alternately laminated in layers.
FIG. 2 is a schematic view showing a cross section in the depth direction of a steel material test piece having a pearlite structure. That is, it is a schematic view which cut out the UNKOWN plane shown in FIG. In FIG. 2, each layer of the cementite layer 1 and the ferrite layer 2 is curved.

As shown in FIG. 2, the pearlite structure is formed by an aggregate of regions called colonies shown by 5. Each of the colonies 5 has a size of about 10 to 50 μm, and inside the region of this one colony 5, the cementite layer 1 and ferrite have almost the same thickness and curvature as the surface in the depth direction. Layer 2 is formed.

Therefore, when paying attention to the morphology of the interface (lamella interface; hereinafter simply referred to as “interface”) between one adjacent cementite layer 1 and the ferrite layer 2, the curvature in the depth direction, for example, a part of this interface If the curvature of the interface near the surface surrounded by the broken line in FIG. 2 (the lamellar interface in the depth direction near the observed polished surface) can be obtained, this one interface has the same morphology as long as it belongs to at least the same colony 5. It can be estimated that it has (curvature). Similarly, for other interfaces, the existence form of the interface inside the colony 5 is estimated by measuring the curvature near the surface. By obtaining the curvature of the interface near the surface in this way, the morphology of this interface can be analyzed three-dimensionally at a depth of 10 to 50 μm belonging to the same colony 5.

Therefore, the EBSD method (Electron Backscattered Diffraction) is applied in order to obtain the curvature information of the interface near the surface. In the EBSD method, the surface of a test piece collected from a steel material is usually polished to obtain an observation-polished surface, and this observation-polished surface is analyzed non-destructively. FIG. 3 is an enlarged portion of the portion surrounded by the broken line in FIG. 2, and shows a schematic view showing only the three layers of the ferrite layer 21, the cementite layer 1, and the ferrite layer 22.

Various crystal orientation relationships between cementite and ferrite in steel materials have been reported, but usually only the following three types can be used to identify the crystal habit plane relationship at the lamellar interface of the pearlite structure.
Pitsch-Petch
[100] cem // [-311] fer, [001] cem // [131] fer, (010) cem // (-12-5) fer
Bagaryatsky
[001] cem // [-110] fer, [100] cem // [-1-11] fer, (010) cem // (112) fer
Isaichev
[100] cem // [111] fer, (031) cem // (1-10) fer

In the above, for example, [100] cem // [-311] fer means that the [100] orientation of the cementite layer 1 is parallel to the [-311] orientation of the adjacent ferrite layer 2 and is (010). ) Cem // (-12-5) fer means that the (010) plane of the cementite layer 1 is parallel to the (-12-5) plane of the adjacent ferrite layer 2. The length of the unit cell in each direction of the crystal orientation [a b c] of cementite is a direction, 0.509 nm, b direction, 0.674 nm, c direction, and 0.4502 nm.

That is, at the interface between the cementite layer 1 and the ferrite layer 2 in the pearlite structure, the cementite is substantially parallel to the (010) plane or the (031) plane. Therefore, it can be determined that the shape of the interface matches the (010) plane or the (031) plane with the crystal orientation relationship in the very vicinity of the interface between the cementite layer 1 and the ferrite layer 2, which can be measured from the surface by the EBSD method. ..

By the EBSD method, it is possible to obtain tilt information on the angle at which the (010) plane or the (031) plane is tilted from the observed polishing surface at each point of the cementite layer 1 to a depth of about 50 nm from the observation polishing surface. Be done.
In FIG. 3, as an example, when paying attention to the surface (010), what angles θ ₁ (010) 21, θ ₂ (010) 21, and θ ₃ (010) 21 are observed from the polished surface at each point. Shown if it is tilted.
By the EBSD method, it is possible to know at what angles θ ₁ (010) 21, θ ₂ (010) 21, and θ ₃ (010) 21 are tilted from the observation polishing surface. Therefore, as will be described later, the curvature H21 of the interface between the cementite layer 1 and the ferrite layer 21 can be obtained by accumulating a large number of such angles at each point regarding the relationship between the inclination of the (010) cem surface and the interface. be able to.
In addition, at the point directly below the point where the angles θ ₁ (010) 21, θ ₂ (010) 21, and θ ₃ (010) 21 were measured, the angle between the crystal plane (hkl) and the observed polishing surface θ ₁ (010). _{22, θ 2 (010) 22} , θ 3 (010) 22 , respectively, the angle _{θ 1 (010) 21, θ} 2 (010) 21, θ 3 (010) 21 to match the presumably confirmed (theta ₁ (010 ) 22 = θ ₁ (010) 21, θ ₂ (010) 22 = θ ₂ (010) 21, θ ₃ (010) 22 = θ ₃ (010) 21). That is, it can be inferred that the curvature H22 at the interface between the cementite layer 1 and the ferrite layer 22 is the same as the curvature H21 at the interface between the cementite layer 1 and the ferrite layer 21.

As described above, if the curvature information of the interface between the cementite layer 1 and the ferrite layer 21 is obtained from the surface to a depth of about 50 nm by the EBSD method, the depth of 10 to 50 μm in the same colony 5 in which the same morphology continues can be obtained. The curvature of the interface (lamella interface) between the cementite layer 1 and the ferrite layers 21 and 22 on both sides thereof can be analyzed three-dimensionally and quantitatively.

Further, not only the inclination information of the (010) plane or the (031) plane of the cementite layer 1 but also the crystal orientation information of the cementite layer 1 can be obtained by the EBSD method. Therefore, the crystal plane and crystal orientation of the ferrite layers 2 (21, 22) that match the crystal plane of the cementite layer 1 may also be determined based on the crystal orientation relationship that matches the cementite layer 1.

From the above Pitsch-Petch, Bagaryatsky, or Isaichev relationship, if the crystal plane of the cementite layer 1 forming the interface between the cementite layer 1 and the ferrite layer 2 is (031) cem, this cementite is according to the Isaichev relationship. It can be said that the adjacent ferrite layer 2 consistent with the layer 1 is (1-10) fer. Therefore, if the crystal plane and crystal orientation information of the cementite layer 1 are measured, the crystal plane and crystal orientation information of the ferrite layer 2 can be determined by applying the above relationship.
Therefore, when determining the plane and crystal orientation information of the ferrite layer 2, it is not always necessary to measure by the EBSD method. However, the crystal orientation relationship between the cementite layer 1 and the ferrite layer 2 may be directly measured and determined by the EBSD method. Further, the crystal orientations of the adjacent cementite layer 1 and the ferrite layer 2 may be measured by the EBSD method to determine whether the interface has a relationship of Pitsch-Petch, Bagaryatsky, or Isaichev.

On the other hand, cementite is not a cubic crystal (cubic structure) but a rectangular parallelepiped (cuboidal structure) and has anisotropy, so that it is easy to determine the crystal orientation. Therefore, the crystal orientation distribution information of the cementite layer 1 is measured by the EBSD method.

Further, in the measurement by the EBSD method, when the angle between the observation polished surface and the lamella interface exceeds 30 °, the crystal orientation distribution information of cementite is drowned out by that of ferrite and it becomes difficult to detect. The angle formed by the vector and the normal vector at the interface between the cementite layer 1 and the ferrite layer 2 is preferably within 30 °.

Next, the sample preparation conditions for forming the observation polishing surface will be described.
In forming the observation polishing surface, it is preferable to polish for 10 minutes or more with a polishing liquid in which colloidal silica is dispersed. By continuing polishing for 10 minutes or more, it is possible to eliminate the strain in the vicinity of the observed polishing surface, which causes noise during measurement by the EBSD method.

The silica particles in the dispersion liquid of the colloidal silica dispersion are preferably 0.5 μm or less as usual. Further, it is preferable that the polishing pressure is as usual at a reduction pressure of 5 g / cm ² or less and a pressure such that polishing scratches disappear.

Further, it is preferable to polish with a colloidal silica-dispersed polishing solution for 10 minutes or more, and then electropolish for 10 minutes or more.

In the measurement by the EBSD method, the signal strength due to secondary electrons tends to be lower in cementite than in ferrite. Therefore, the ferrite layer 2 is slightly eluted by electrolytic polishing to lower the height on the observation polishing surface, and the cementite layer 1 is projected. When the cementite layer 1 is projected, the signal strength is increased and the accuracy of crystal orientation distribution information and the like is improved. For that purpose, it is preferable that the time of electrolytic polishing is 10 minutes or more. The time for electropolishing is preferably 120 minutes or less. If the electrolysis time is too long, the cementite layer 1 will be projected too much, and when collecting EBSD data, a shadow may be formed by the protruding portion and the accuracy of the information may be lowered. The preferred height of the protrusion, that is, the height difference between the cementite layer 1 and the ferrite layer 2, is 5 to 30 nm.

According to the method of the present invention as described above, the three-dimensional morphology of the pearlite structure can be estimated only by the measurement from the surface by the EBSD method.
As the steel material having a pearlite structure to which the present invention is applied, since the main structure is a pearlite structure, high carbon steel wires such as steel cords, bridge steel wires, and PC steel wires manufactured by strong wire drawing are preferable. ..

An example will be described as an example of the case where the distribution of the orientation of the lamella interface is parallel to the cementite (010) cem.
The crystal orientation analysis of the cementite layer 1 and the ferrite layer 2 constituting the lamellar morphology of the pearlite structure according to the present invention can be performed by, for example, the following method. However, the following method merely describes the detailed procedure as a uniform state, and does not limit the content of the present invention. According to the uniform state of the present invention, the observation steel test piece is cut out while sufficiently suppressing the heat flow to the test piece steel while supplying sufficient water with a wet cutter, and then wet-polished with fine-grained emery paper in stages. Then, wrapping (buffing) with 3 μm diamond paste and 1 μm diamond paste, and finally polishing with 0.05 μm colloidal silica dispersion for about 10 minutes, and then performing electrolytic polishing to make the observed polished surface a mirror surface. Finish.

Observation and analysis were performed by SEM (scanning electron microscope). Using a general-purpose SEM such as JEOL FE-SEM (JEOL-7100F), secondary electron image observation was performed at an acceleration voltage of 10 kV and an operating distance of 5.5 mm. For the crystal orientation distribution information, an EBSD device installed in the SEM was used. For EBSD measurement, use a TSL digiview-IV CCD camera with an acceleration voltage of 15 kV, an irradiation current of 3.5 × ^10-7 A, and an objective diaphragm diameter of 70 μm, and the observation polishing surface is tilted by 70 ° with respect to the electron beam incident direction. The EBSD pattern was acquired. In pattern identification, ferrite (cubic crystal) and cementite (orthorhombic crystal) were selected from the attached database. Data acquisition was performed in a region of 6 × 12 μm with a step size of 0.1 μm. Preferably, the step size is 0.04 μm.
The concept of three-dimensional morphological quantitative analysis of lamella morphology will be described in more detail. Normally, the three-dimensional interface morphology cannot be directly viewed unless it is actually cut out by a FIB (focused ion beam) or the like.

On the other hand, when it is cut out and observed at a very shallow angle with respect to the lamella orientation, it is observed from a direction close to perpendicular to the lamella interface. It is possible to measure the angle (tilt). Within a depth of about 5 or 1 colonies in the pearlite structure from the observed polished surface, the same lamellar morphology (alignent) as the observed polished surface (polished surface) is considered to be crystallographically repeated. It is possible to three-dimensionally and quantitatively estimate the orientation and shape of the lamella in the vicinity from only the information on the polished surface. More specifically, in order to obtain a clear cementite EBSD pattern, lamella oriented at a very shallow angle within 30 ° as the normal angle between the observed polished surface and the lamella interface was observed.

The inventor's diligent research has revealed that the orientation distribution of the lamella interface is consistent with the orientation of cementite (031) cem or (010) cem. If it matches the orientation of (010) cem, it is possible to plot the spatial distribution of cementite (010) cem on a graph to obtain an approximate function and to regard the slope as the curvature of the lamella interface. Specifically, as shown in FIG. 4, it is possible to obtain the shape (curvature, slope) of the lamella orientation in the depth direction by integrating the approximation function of the distribution representing the slope with the distance.
In FIG. 3, the plane orientation relationship between the ferrite / cementite interface (the crystal orientation relationship between the cementite layer 1 and the ferrite layer 2) is the relationship of Pitsch-Petch [(-12-5) fer // (010) cem]. Is illustrated on the premise of. Normally, such an interface morphology shown in the figure cannot be directly viewed unless it is actually cut out by a FIB or the like. However, due to the improvement of EBSD skills, it has become possible to obtain the crystal orientation distribution of cementite and the crystal orientation relationship between the cementite layer and the ferrite layer. Therefore, the lamella morphology (alignment) of the observed polished surface (polished surface) is crystallographic. For the first time, it has become possible to estimate the orientation and shape of the lamella three-dimensionally and quantitatively from only the information on the polished surface of one observation.

From the above idea, it is possible to know the distribution of the "tilt" of the ferrite / cementite interface with respect to the observed polished surface. By the EBSD method, the most commonly used inverse pole (IPF) map for displaying the crystal orientation distribution was created. The reverse pole (IPF) map can display the orientation of the lamella interface by gradation.

In order to further quantitatively evaluate the degree of inclination of the ferrite / cementite interface, the magnitude of the projection of the (010) cem unit vector along the A-axis and C-axis of the cementite crystal lattice was sampled and shown in the drawing. The slope and curvature of the lamella interface seen from parallel directions were quantitatively analyzed by differential geometry.

Quantitative analysis of geometric shape was performed by the following procedure. First, in the regions to be evaluated on the observation polishing surface shown in FIG. 4 (A), area-1 and area-2, the cementite crystal lattice A axis (axis parallel to the cementite a direction) direction and the C axis (axis parallel to the cementite a direction) of each measurement point ( The direction is determined by averaging the directions (axis parallel to the cementite c direction), and the axes x _A and x _C projected on the observation polishing surface are set. The position and orientation information of (010) cem (unit normal vector e _{N of the} cementite B axis (axis parallel to the cementite b direction) plane) along the axes x _A and x _C is picked up. Next, the unit vectors e _NxA and e _NxC , which are the projections of the unit normal vector e _N picked up in the axes x _A and x _C directions (the axes x _A and x _C direction components of the unit normal vector e _N ) are collected. , _x a _{-e NXa,} plotted on x _{C -e NXC} coordinates, determine the linear approximation. _{x A -e NxA, x C -e} NxC slope of the straight line of the approximation on the coordinate plane (rate of change) i.e. - (∂e _NxA / ∂x _A) and (∂e _NxC / ∂x _C) is cementite It shows the curvature in the direction along the A-axis and C-axis of the crystal lattice (unit is 1 / μm). As a result, the Gaussian curvature K = k _A × k _C and the mean curvature H = (k _A + k _C ) / 2 are quantitatively calculated from the calculated curvatures k _A and k _C in the two directions, and H, k _A , and k. You can get a point of _C. The calculated value of the curvature _{k A} along the A axis in the area-1 0.066 / μm (axial _{x A} direction of the radius of curvature _R A _15.2μm), the curvature _{k C} is -0.0085 along the C axis / Μm (radius of curvature _RC 118 μm in the axis x _C direction), in area-2, the curvature k _A along the A axis is 0.0347 / μm (radius of curvature _RA 28.8 μm in the axis x _A direction), C curvature _{k C} along the axis was 0.0337 / [mu] m (the curvature in the axial _{x C} direction radius _R C _29.7μm).

From this calculation result, it can be seen that the lamellae in the region illustrated in FIG. 4 (A) as a whole are greatly depressed toward the other side of the drawing as they go in the upper right direction on the drawing. It was also found that area-1 and area-2 have slightly different irregularities. The calculation results are shown in FIGS. 4 (B) and 4 (C). In area-1, it is convex upward in the axis x _A direction and slightly downward in the axis x _C direction, whereas in area-2, it is convex upward in both the axis x _A direction and the axis x _C direction. ing. The apparent "bending" of the lamella appearing on the observed polished surface is significantly opposite in the areas 1 and 2, which corresponds to the fact that this subtle unevenness at the lamella interface is in the opposite direction. .. From the viewpoint of differential geometry, it can be said that the morphological class of lamella belongs to the saddle type (saddle type) in area-1 and the Concave type (bowl type) in area-2.

According to the present invention, the lamellar morphology of the pearlite structure can be evaluated three-dimensionally and quantitatively while the test piece is not destroyed by the measurement by the EBSD method from the observation polishing surface. In particular, it provides a means to clarify the structure of the steel wire and the chemical composition to realize it, which is necessary for producing high-strength and high-ductility steel wire in which the pearlite structure is the main structure. The above effect is enormous.

1 ... cementite layer, 2, 21, 22 ... ferrite layer, 3 ... observation direction, 4 ... measurable depth, 5 ... colony

Claims (4)

It is a three-dimensional morphological quantitative analysis method of the pearlite structure spreading in the depth direction of a steel material having a pearlite structure constituting a lamellar morphology by a cementite layer and a ferrite layer.
The surface of the test piece collected from the steel material is polished to obtain an observation-polished surface, and the observation-polished surface is subjected to the EBSD method.
With respect to the crystal plane, (010) plane or (031) plane of the cementite layer, tilt information indicating how much the cementite layer is tilted from the observation polishing plane at each point of the observation polishing plane is acquired.
By obtaining the curvature of the crystal plane of the cementite layer from the inclination information of each point,
A method for quantitatively analyzing a three-dimensional morphology of a pearlite structure, which comprises quantitatively determining the three-dimensional morphology of the cementite layer and the ferrite layer spreading in the depth direction. The three-dimensional pearlite structure according to claim 1, wherein the crystal plane and crystal orientation of the ferrite layer that matches the crystal plane of the cementite layer are determined by the crystal orientation relationship between the cementite layer and the ferrite layer. Morphological quantitative analysis method. The measurement by the EBSD method is characterized in that the angle formed by the normal vector of the observed polished surface and the normal vector of the interface between the cementite layer and the ferrite layer is within 30 °, according to claim 1 or 2. A method for quantitatively analyzing a three-dimensional morphology of a pearlite structure according to. The method according to any one of claims 1 to 3, wherein in forming the observation polishing surface, polishing is performed with a colloidal silica-dispersed polishing liquid for 10 minutes or more, and then electrolytic polishing is performed for 10 minutes or more. A method for quantitatively analyzing three-dimensional morphology of pearlite structure.

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