KR100330502B1 - Quantitative analysis method of microstructures of steels using mossbauer spectroscopy - Google Patents

Abstract

The present invention relates to a method for quantitatively analyzing the microstructure of steel materials using Mossbauer spectroscopy. The analysis method comprises the steps of obtaining a Mossbauer spectrum by transmitting a gamma ray emitted from a gamma ray source to a standard specimen consisting of a pure phase; Fitting the spectra using a Lorentzian function to obtain three ultrafine factor values of isomeric shift, electrical quadrupole cleavage, and magnetic dipole cleavage for each standard specimen; Transmitting gamma rays emitted from a gamma ray source to steel specimens to be analyzed to obtain a Mossbauer spectrum; And fitting the three ultrafine factor values to the spectra of the specimen using the least-squares method, so that the volume fraction of each phase present in the steel specimen from the extent that the three ultrafine factor values of each of the standard specimens contribute to the spectral fitting. It characterized in that it comprises a step of obtaining. According to the present invention, it is possible not only to qualitatively analyze the microstructure of the steel material but also to accurately and quantitatively analyze the phase fraction of each phase present in the steel material.

Description

Quantitative analysis method of microstructures of steels using mossbauer spectroscopy

The present invention relates to a method for quantitatively analyzing complex phases mixed in steel, and more particularly, to a method for quantitatively analyzing complex phases mixed in steel using Mossbauer spectroscopy.

Quantitative analysis of phases mixed in steel is required in various fields.

For example, it can be used to quantitatively analyze the heat affected zone of the steel material to identify micro histological causes causing local embrittlement. The weld heat affected zone is complicated by various factors such as the chemical composition of the steel, the welding conditions and the maximum heating temperature, and the weld heat affected zone has a local brittle zone in the welded heat affected zone. It has significantly lower fracture toughness compared to mechanical properties. Therefore, it is necessary to identify the microhistological causes that cause local embrittlement because it can cause serious problems in the stability of the steel structure.

In addition, the microstructure of rolls such as high speed steel (HSS) rolls and nickel-grain rolls can be quantitatively analyzed to determine the effects of casting and heat treatment conditions on the roll properties. . In general, rolls are cast in large sizes and do not undergo a subsequent hot working step, so that a cast structure made of coarse carbide remains intact, and only by tempering by heat treatment such as solution treatment and tempering. It is common to change to martensite. After the heat treatment, the roll is affected by many factors such as chemical composition, casting conditions, heat treatment conditions, and thus has a complex structure including various phases such as carbide, tempered martensite, austenite, and the like. Most coarse carbides are hardly affected by heat treatment, but the residual austenite formed after solution treatment reduces the hardness and abrasion resistance of the rolls. Therefore, the microstructures that vary with casting and heat treatment conditions are analyzed in detail. It is necessary to make sure that it is removed after the heat treatment.

However, in the steel material, many images such as martensite, bainite, ferrite, pearlite, austenite and carbide are mixed together depending on the composition and processing conditions of the steel, so an optical microscope and an electron microscope are used. There is a problem in that it is difficult to quantitatively accurately analyze their phase ratios by conventional methods such as using a method or X-ray analysis (X-ray analysis).

The technical problem to be solved by the present invention is to provide a method for accurately and quantitatively analyzing various phases mixed in steel using Mossbauer spectroscopy to solve the above problems.

1 is a microstructure optical micrograph of the SA 508 steel base material,

2 is a Mossbauer spectrum of SA 508 steel substrate,

3A-3G are Mossbauer spectra of A1 to A7 specimens subjected to double thermal cycles,

4A to 4G are Mossbauer spectra of B1 to B7 specimens subjected to post-weld heat treatment.

5 (a) to (g) are microstructure optical micrographs of A1 to A7 specimens subjected to double heat cycles,

6 (a) to (g) are optical microscope microstructure photographs of B1 to B7 specimens subjected to heat treatment after welding,

7 is a scanning electron micrograph (SEM) of the microstructure of the A4 specimen,

8 is a transmission electron microscope (TEM) image of the microstructure of the A4 specimen,

(A) and (b) of FIG. 9 are microstructure optical micrographs of HSS roll and Ni-grain roll, respectively,

(A) to (d) of Figure 10 is an X-ray diffraction graph of the C1 to C4 specimen of the HSS roll,

(A) to (c) of FIG. 11 are X-ray diffraction graphs of D1 to D2 specimens of Ni-grain roll,

(A) to (d) of Figure 12 is the Mossbauer spectrum of the C1 to C4 specimens of the HSS roll,

(A)-(c) of FIG. 13 are Mossbauer spectra of D1-D2 specimens of Ni-grain roll.

In order to achieve the above object, the present invention comprises the steps of obtaining a Mossbauer spectrum by transmitting a gamma ray emitted from a gamma ray source to a standard specimen consisting of a pure phase; By fitting the spectra using a Lorentzian function represented by Equation 1, isomer shift, quadrupole splitting, and magnetic splitting for each of the standard specimens Obtaining three ultrafine factor values of; Transmitting gamma rays emitted from a gamma ray source to steel specimens to be analyzed to obtain a Mossbauer spectrum; And fitting the three ultrafine factor values to the spectra of the specimen using the least-squares method, so that the volume fraction of each phase present in the steel specimen from the extent that the three ultrafine factor values of each of the standard specimens contribute to the spectral fitting. It provides a method for analyzing steel materials comprising the step of obtaining.

σ = σ0 (Γa / 2) 2 / [(Ε-Ε0) 2 + (Γa / 2) 2]

In Equation 1, σ is the total absorption means area, σ ₀ is the maximum absorption means area, Γa is the gamma ray linewidth of the sample, Ε is gamma ray energy, Ε ₀ is gamma ray energy without bounce.

The gamma ray source is Co⁵⁷This is preferable because of Co⁵⁷Is cheap and has a good half-life Cos as a source of Mossbauer spectroscopy on steels⁵⁷Because it is useful.

In addition, the steel specimen to be analyzed is preferably taken from SA 508 steel welding heat affected zone, high speed steel (HSS) roll or nickel-grain roll.

Preferably, the steel specimens include ferrite, martensite austenite, and carbides, and ferrite and martensite, which are difficult to distinguish from the Mossbauer spectrum due to alloying elements located around iron atoms, are measured as a whole, and then the body core cube It is more preferable to obtain the contribution of ferrite and martensite according to the ratio of -Fe and body square-Fe.

In addition, the pure phase constituting the standard specimen is preferably any one selected from the group consisting of ferrite, martensite and carbide.

The analysis method of the steel material according to the present invention creates subspectrums for each phase from the intrinsic ultrafine factor values of the respective phases constituting the steel material, and minimizes the subspectrums from the absorption lines obtained from spectra by Mossbauer spectroscopy. It is characterized by quantitative analysis of phases in steel by fitting using square method. The principle of the present invention with respect to these features is as follows.

Mossbauer spectroscopy is an analytical method commonly used to analyze the chemical composition of steel materials. The Mossbauer effect and Doppler, which refers to the phenomenon in which the nucleus emitting gamma rays emit or absorb gamma rays without recoil. This is done by converting the energy of gamma rays using the Doppler effect. The process of Mossbauer spectroscopy is as follows.

First, gamma rays emitted from a gamma ray source are transmitted to steel specimens. When gamma rays emitted from the source reach the specimen, the nuclei in the specimen that are homologous to the source nuclei are in an energy excited state, which transitions back to a stable energy state after the half-life. In the transition process, a photon having 14.4 KeV is generated and spreads in all directions. Gamma rays that pass through the specimen are collected by a detector. When nuclear resonance occurs, the number of photons incident on the detector is reduced by that, resulting in the Mossbauer spectrum.

The Mossbauer spectrum of the steel specimen obtained by the method is the sum of the subspectrals for the various phases constituting the specimen, and the phase fraction of each phase present in the specimen is determined by the contribution of the subspectral of each phase to the spectrum of the specimen do. Therefore, in order to determine the phase percentages of the various phases constituting the steel specimen, the subspectrum of each phase in the specimen must be separated and the contribution is measured. The method of measuring the contribution by separating the subspectrum is as follows.

In Mossbauer spectroscopy, gamma resonant absorption lines are determined by three ultrafine factors: isomer shift, quadrupole splitting, and magnetic splitting. It has a hyperfine parameter. For example, austenite is a body-centered cube, and iron atoms have a high isotropic environment and are not magnetic. Thus, the subspectrum of austenite appears as a single absorption channel with no isomeric shift, i.e., no cleavage. On the other hand, ferrite, martensite and bainite all have an isotropic crystal structure, so quadrupole fission is not seen but exhibits magnetic fission. As such, each phase has a unique ultrafine factor value depending on the crystal structure, and the unique ultrafine factor value can be measured from the Mossbauer spectrum of each pure phase. That is, after the specimens of each of the pure phases are made, the spectra are subjected to Mossbauer spectroscopy, as described above, to obtain spectra, which have a Lorentzian shape. Therefore, the above three ultrafine factor values are determined by fitting the program based on the Lorentzian function of Equation 1 below to explain this form.

<Equation 1>

σ = σ ₀ (Γa / 2) ² / [(Ε-Ε ₀ ) ² + (Γa / 2) ² ]

In Equation 1, σ is the total absorption means area, σ ₀ is the maximum absorption means area, Γa is the gamma ray linewidth of the sample, Ε is gamma ray energy, Ε ₀ is gamma ray energy without bounce.

The three ultrafine parameters of each of these purely determined phases are used as a set to fit the spectra of steel specimens with multiple phases. That is, when the ultrafine factor value set for each phase is input to the fitting program using the least squares method, the fitting program uses the set value input to create the subspectrum of each phase and then fits the spectrum of the steel specimen. Once the fitting is complete, the contribution of the set values of each phase to the fitting of the spectrum is provided for each phase subspectral, thus quantitative phase analysis of the various phases that make up the steel specimen.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples.

<Example 1>

As Example 1 according to the present invention, Mossbauer spectroscopic analysis was performed on the weld heat affected zone of SA 508 steel which is used as a nuclear pressure vessel. The basic chemical composition of the SA 508 bristle material, the optical micrograph of the microstructure, and the conventional welding conditions are shown in Tables 1, 1, and 2, respectively.

In Table 2, * refers to submerged arc welding (Submerged Arc Welding).

Due to the complicated thermal history, the heat affected zone of the multi-layered weld has a complicated distribution of microstructures, and it is difficult to obtain a specimen of a size suitable for Mossbauer spectroscopy. Therefore, thermal cycle simulation is performed on the SA 508 steel specimen. It was. In order to perform heat cycle reproducing for the welding heat affected zone, the welding heat reproduction test conditions as shown in Table 3 were set based on Rosenthal's heat flow equation.

In Table 3, Δt _8/5 ^＊＊ represents a cooling time between 800 ° C. and 500 ° C., and in the subarea ^＊ UCGHAZ, SCRCGHAZ, ICRCGHAZ, SCRFGHAZ, ICRFGHAZ, IRHAZ, and SRHAZ, respectively, are invariant coarse thermal effects. Partial, supercritical reheating coarse heat affected zone, critical reheating coarse heat affected zone, supercritical reheating fine grain heat affected zone, critical reheating microparticle heat affected zone, critical reheating heat affected zone, subcritical reheating heat affected zone.

Thermal reproduction experiments were carried out using a metal thermal cycle simulator (Model: MTCS) purchased from Fuji Electronic Industry, which can control heating and cooling rates. Specimens subjected to double welding heat cycles are labeled A1-A7 in order of decreasing peak temperature. In addition, the specimens subjected to post-weld heat treatment for 4.5 hours at 620 ° C. for the A1-A7 specimens subjected to the double heat cycle were designated as B1-B7. A thin disk-shaped specimen of about 50 μm in thickness and 10 mm in diameter was collected from the SA 508 steel base material and the heat affected zones of the A1-A7 and B1-B7 specimens heat-treated under the above conditions. Spectroscopic analyzes of the specimens were performed using a Fast Comtec Mossbauer spectrometer (model name: MA250 / MR351) using Co ⁵⁷ as a gamma ray source, FIGS. 2, 3A-3G and 4A. -The spectra are shown in Figure 4g.

Mossbauer spectroscopy was carried out on specimens consisting solely of pure phases to determine the values of the ultrafine parameters of the phases of the SA 508 steel. Pure ferrite specimens were purchased from Fast Comtec, and pure martensite specimens were prepared by quenching the base material dissolved and solidified in an induction furnace at 1600 ° C after homogenization at 1100 ° C. A powder sample obtained by filtering the wire-containing wire rod by electrochemical extraction (2-3 V, <40 mA) in a 1% ammonium tetrachloride, 10% acetylacetone and methanol solution was used.

Mossbauer spectra were acquired using a Fast Comtec Mossbauer spectrometer (model name: MA250 / MR351) and then fitted with Fast Comtec's fitting software (product name: PCMOS II). Three ultrafine factor values were determined as shown in Table 4 below.

In Table 4, δ, Q, and H _f represent the ultrafine factor values of isomer shift, electrical quadrupole cleavage, and magnetic dipole cleavage, respectively, and bcc, bct, and fcc are body-centered cubes, body-centered cubes, It represents a face square. Each phase is divided into several sub-spectrum according to the iron atom's surroundings, so they are separated by numbers in parentheses like bct-Fe (1) and bct-Fe (2). In Table 4, Fe-M (1) and Fe-M (2) represent iron atoms having alloy elements first and second neighboring in the phase, respectively. Fe ₃ C (a) and Fe ₃ C (b) refer to two crystallographic equivalent site cementite particles in the cementite structure. One of the problems that may arise in the interpretation of the Mossbauer spectrum is that it is not easy to distinguish between pure ferrite and ferrite present in bainite and pearlite, so in the present invention, pure ferrite, bainite and perlite are all ferrite. Prescribed. Another problem is that it is difficult to distinguish the Mossbauer spectrum for ferrite and martensite when the alloying element is in the position adjacent to the iron atom. The problem was solved by analyzing the ferrite and martensite as Fe-M (M: alloying elements) as a whole, and then distinguishing each phase according to the ratio of bcc-Fe and bct-Fe.

The determined set of ultra fine values of each phase was input to the fitting software of Fast Comtec (product name: PCMOS II) and fitted to the spectra of SA 508 steel substrates, A1-A7 and B1-B7 specimens. The phase percentage was measured by integrating the subspectrals of each phase. The results of the quantitative analysis measured by the above method for SA 508 steel base material, A1-A7 specimens and B1-B7 specimens are shown in Table 5 below.

As shown in Table 5, the SA 508 steel base material may be composed of about 3% by volume of carbide and ferrite, pearlite or bainite. FIG. 3A is a Mossbauer spectrum of an A1 specimen, which is divided into several subspectrals. The fcc-Fe subspectrum is represented by residual austenite, the carbides (1) through (3) subspectrum is represented by carbide, and bct-Fe ( 1) to bct-Fe (3) subspectrum is represented by martensite, bcc-Fe subspectrum is represented by ferrite, and Fe-M (1) and Fe-M (2) subspectrum are represented by ferrite and martensite. will be. Therefore, it can be seen from the analysis results according to the present invention that most of the A1 specimens are composed of martensite, and a small amount of ferrite, austenite, and carbide are present.

FIG. 3B shows the Mossbauer spectrum of the A2 specimen, in which the amount of ferrite is increased and the amount of martensite is decreased when compared with the spectrum for the A1 specimen. The reason is that since the maximum heating temperature in the second heat cycle for the A2 specimen is 900 ° C., the cooling rate is slower than that of the A1 specimen with the highest heating temperature in the second heat cycle of 1350 ° C., thus producing bainite as well as martensite. .

5 (a)-(g) and 6 (a)-(g) are optical microscope microstructure photographs of A1-A7 specimens and B1-B7 specimens, respectively, at the highest heating temperature in the second heat cycle. The microstructure changes of the A1 and A2 specimens can be confirmed by comparing the optical microscope microstructure photograph of FIGS. 5 (a) and 5 (b).

FIG. 3D is a Mossbauer spectrum of A4 specimens with the first and second highest heating temperatures of 900 ° C. A4 specimens consist mainly of 71% by volume of ferrite and 22% by volume of martensite (Table 5). In order to clarify the shape more clearly, a scanning electron microscope and a transmission electron microscope were used. 7 is a scanning electron micrograph of the A4 specimen, in which there are isolated irregularly shaped tissues as indicated by the arrow in addition to the fine bainite tissue. Fig. 8 is a transmission electron microscope image of this tissue, which is mostly composed of lath martensite, and it is observed that a small amount of austenite remains in the lath martensite. Such a structure is also called an M-A structure because martensite and a small amount of austenite coexist as a martensite island (martensite island) that is commonly seen in the weld heat affected zone. The amount of M-A tissue of the A4 specimen measured approximately by the scanning micrograph is about 20% by volume, which is consistent with the results of the Mossbauer analysis according to the present invention. As the amount of the M-A tissue increases, the amount of austenite also reaches 5%.

Specimen A3 shows a spectrum similar to that of specimen A1 (Fig. 3c), and the Mossbauer spectrum of the A5 specimen with the highest heating temperature of 900 ° C. for the first heat cycle and 700 ° C. for the second heat cycle (Fig. 3e). It is similar to the spectrum of A4 specimen, but the volume fraction of martensite and austenite is slightly reduced compared to A4 specimen.

In the heat cycle, the maximum heating temperature is below the temperature A ₁ A6 and A7 specimen spectrum (Fig. 3f, Figure 3g) of martensite was the sub-spectrum is not observed it can be seen that consists of only the sub-spectrum of ferrite and carbide.

As shown in FIGS. 4A-4G, no martensite subspectrum was observed in all specimens of B1-B7, only a large amount of ferrite and a small amount of residual austenite subspectrum. From the above results, it can be seen that the martensite present in the A1-A7 specimens was decomposed into tempered martensite by the post-welding heat treatment effect.

<Example 2>

As Example 2 according to the present invention, Mossbauer spectroscopic analysis was performed on HSS rolls and Ni-grain rolls, which are typical rolls used for rolling steel, and X-ray diffraction analysis was also used for Mossbauer spectroscopic analysis. .

Table 6 shows the basic chemical composition of HSS rolls and Ni-grain rolls.

Chemical composition C Si Mn Cr Ni Mo P S V W Fe HSS Roll (wt%) 2.0 0.75 0.35 6.5 1.0 3.0 0.003 0.002 5.0 1.5 balance Ni-grain roll (wt%) 3.3 0.8 0.6 1.8 4.5 0.3 0.003 0.002 - - balance

HSS rolls and Ni-grain rolls were cast respectively, and roll specimens taken from the shell portion, which is the outer portion of the cast roll, were polished and then etched with 3% nital solution. Optical micrographs of the etched specimens are shown in FIGS. 9A and 9B, respectively.

The cast HSS roll was solution cooled at 1050 ° C. for air cooling and tempered twice at 540 ° C. for 1 hour to collect specimens at each step. The purpose of the double tempering is to remove residual austenite by primary tempering and to convert martensite formed upon cooling by secondary tempering to tempered martensite. Ni-grain rolls were subjected to stress relief heat treatment at 450 ° C. for 15 minutes and 30 minutes without solution treatment after casting to obtain specimens at each step.

Here, the heat treatment time of the rolls is set based on the heat treatment time of the actual large roll.

10 (a) to 10 (d) show the specimen C1 in the cast state of the HSS roll, the specimen C2 after the solution treatment, the specimen C1 after the primary tempering, and the specimen C2 after the secondary tempering, respectively. X-ray diffraction graph for Fig. 11, (a) to (c) are each the specimen (D1) in the cast state of the Ni-grain roll, the specimen (D2) after 15 minutes stress relief heat treatment and An X-ray diffraction graph of the specimen (D3) after 30 minutes of stress relief heat treatment is shown.

During HSS roll casting (C1 specimen), bcc-Fe and some carbides appear (FIG. 10 (a)). bcc-Fe is a major component of martensite, and carbides are assumed to be Fe ₅ C ₂ and Mo ₂ C / VC. Here, Mo ₂ C / VC is because their lattice constants are so similar that it is impossible to separate and can not exclude the possibility of their coexistence. After casting the HSS roll and cooling the solution (C2) after solution treatment at 1050 ° C. (FIG. 10 (b)), martensite, carbides (Mo ₂ C / VC and (Cr, Fe) ₇ C ₃ / Cr ₇ with assumed to C ₃₎ when a retained austenite peak did not exist in the cast state. Referring to (c) and (d) of FIG. 10, after the first tempering (C3 specimen) and the second tempering (C4 specimen), the peak intensities corresponding to carbides do not change significantly, but the peak of residual austenite does not appear. Did.

Referring to (a) of FIG. 11, peaks of martensite, cementite (Fe ₃ C), and austenite appear in the Ni-grain roll specimen (D1) in the cast state, and FIGS. 11 (b) and (c) As shown in Fig. 2, the peak size of austenite was only slightly reduced even after the stress relief heat treatment (D1 and D2 specimens).

The same HSS roll (C1-C4) specimen and Ni-grain roll specimen (D1-D3) used in the X-ray diffraction analysis were prepared in a thin disk shape having a thickness of 50 µm and a diameter of 10 mm, followed by Mossbauer spectroscopy. 12 (a)-(d) and 13 (a)-(d), respectively, and the peak positions of the sub-spectrums represented by the respective phases present in the sample are indicated at the upper end of each spectrum. Here, Fe-M (1) and Fe-M (2) appear in ferrite and martensite, and alloy elements (M) are the first neighboring site and the second neighboring site ( Points to the location of the subspectral that appears when in the 2nd neighboring site.

For the Mossbauer spectroscopy of this example, three ultrafine factor values (see Table 4) and the same Mossbauer spectrometer measured in Example 1 were used. In the analysis of Mossbauer spectroscopic absorption line, ferrite and martensite alone phase and the ferrite mixed with carbide in tempered martensite are difficult to distinguish, so they were all considered ferrite. In addition, it is difficult to distinguish the absorption line between carbide and austenite when alloying elements are close to the iron atoms, and then the carbide and austenite were analyzed by referring to the X-ray diffraction analysis test results. In examining the results of X-ray diffraction analysis, BCC-Fe, Fe-M (1) and Fe-M (2) should be regarded as constituents of the tempered martensite structure. As mentioned in the X-ray diffraction analysis, complex carbides of various kinds of Fe and alloying elements are present in the specimen, and among the carbides, the magnetic ones (carbide (I) in FIGS. 12 and 13) are magnetic elements. It should be regarded as a carbide containing Fe as the main component (Fe ₅ C 2 or Fe ₃ C), and other carbides having no magnetic properties should be regarded as complex carbides containing nonmagnetic alloying elements.

The fraction of each phase obtained by integrating the resonance absorption area of the subspectrum is shown in Table 7 below.

Types of Psalms Percent fraction (% by volume) Ferrite and / or martensite Austenite Carbide ^*** Pure ^* Fe-M ^** Total amount HSS Roll C1 43 35 78 0 22 C2 30 43 73 8 19 C3 40 40 80 0 20 C4 41 41 82 0 18 Ni-grain roll D1 17 20 37 7 56 D2 14 20 34 6 60 D3 15 21 36 3 61

In Table 7, Pure ^* is the Fe fraction containing no alloying elements in the nearest and secondary adjacent position in the bcc or bct structure, Fe-M ^** is the secondary adjacent to the nearest position in the bcc or bct structure The Fe fraction containing the alloying element at the position, carbide ^*** refers to all carbides containing Fe ₃ C cementite.

Referring to Table 7, it can be seen that the cast HSS roll specimen (C1) is composed of about 20% carbide and about 80% ferrite (or martensite). Cooling after the solution treatment (C2) reduces the martensite (or ferrite) to 73%, producing about 8% of retained austenite, while the carbide remains almost unchanged at 19%. After tempering (C3 and C4) all residual austenite was decomposed into tempered martensite (or ferrite) and no longer present.

Noteworthy is the change in the sub-spectrum (Fe-M (1) and Fe-M (2)) when alloy elements are present in adjacent positions. As shown by the arrows in Figs. 12A to 12D, the ratios of the bcc-Fe peak and the Fe-M peak are in solution when the details of both ends of the spectrum (near ± 5 mm / s of the x-axis relative speed) are shown. It turns out that it became about 3: 4 by the process (FIG. 12 (b)), and changes to about 1: 1 by tempering. This means that many alloying elements are dissolved in the bcc (or bct) structure by solution treatment at 1050 ° C. to contribute to the formation of the Fe-M peak, but decompose from the bcc structure by tempering. In particular, since the spectra after the first tempering (C3 specimen) (FIG. 12 (c)) and after the second tempering (C4 specimen) (FIG. 12 (d)) show little difference, such decomposition is easy with the first tempering alone. You can see it happening.

On the other hand, the alloying elements escaped from the bcc structure is believed to form their own carbide. The reason for this determination is that the tempering does not increase the intensity of the sub-spectrum corresponding to the composite carbides (carbide (2) and carbide (3)). Among the major alloying elements contained in these specimens, the Cr, Ni, and V contents were lower than the solubility in iron at the tempering temperature of 540 ° C., and the Mo and W contents were higher than the solubility, so they escaped by tempering to form carbides. The element to be made would be mainly a carbide of Mo and W. However, considering that the content of W (1.5 wt%, see Table 6) is small, most of the precipitated carbide is estimated to be Mo ₂ C, which is the result of X-ray diffraction analysis (Fig. 10 (c)-(d Also matches)).

Referring to Table 7 for Ni-grain rolls, as in the X-ray diffraction analysis results, the Mossbauer spectra of all Ni-grain rolls (Figs. 13 (a)-(c) are ferrite (or martensite), austenite It is composed of the sub-spectrum of carbide, and it can be seen that only the relative fraction is different from the case of HSS roll.

Compared with the optical micrograph of FIG. 9, 55-60% of cementite is present in all Ni-grain roll specimens (D1-D4), and the amount of such cementite is determined by the X-ray diffraction pattern (see FIG. Almost quantitatively can also be confirmed by a)-(c)). In the cast specimen (D1), the austenite fraction is about 7%, and after the 14-minute stress relief treatment (D2 specimen) at 450 ° C, the austenite fraction is lowered to about 6% and after 30-minute treatment (D3 specimen). have.

As described above, by using the Mossbauer spectroscopy, not only can the steel microstructure be qualitatively analyzed, but also the phase fraction of each phase present in the steel can be accurately and quantitatively analyzed. It can be used in various ways for research on tissues.

Claims (8)

a) transmitting a gamma ray emitted from a gamma ray source to a standard specimen consisting of a pure phase to obtain a Mossbauer spectrum; b) isomer shift, quadrupole splitting and magnetic splitting for each of the standard specimens by fitting the spectra using a Lorentzian function represented by Equation 1 below. Obtaining three ultrafine factor values of; <Equation 1> σ = σ ₀ (Γa / 2) ² / [(Ε-Ε ₀ ) ² + (Γa / 2) ² ] In Equation 1, σ is the total absorption means area, σ ₀ is the maximum absorption means area, Γa is the gamma ray linewidth of the sample, Ε is gamma ray energy, Ε ₀ is gamma ray energy without bounce. c) transmitting gamma rays emitted from the gamma ray source to the steel specimen to be analyzed to obtain a Mossbauer spectrum; And d) fitting the three ultrafine values to the spectra of the specimen using the least squares method, so that the volume of each phase present in the steel specimen from the extent to which the three ultrafine values of each of the standard specimens contribute to the spectral fitting Analytical method of the steel material comprising the step of obtaining a fraction. The method of claim 1, wherein the gamma ray source is Co ⁵⁷ . The method of claim 1, wherein the steel specimen to be analyzed is taken from the SA 508 steel weld heat affected zone. The method of claim 1, wherein the steel specimen to be analyzed is a high speed steel (HSS) roll. The method of claim 1, wherein the steel specimen to be analyzed is nickel-grain roll. The method of claim 1, wherein the steel specimen to be analyzed comprises ferrite, martensite, austenite and carbides. The ferrite according to claim 6, wherein the contribution of ferrite and martensite, which is difficult to distinguish the Mossbauer spectrum due to the alloying element, is measured around the iron atom. And how to obtain the contribution of martensite. The method of claim 1, wherein the pure phase constituting the standard specimen is any one selected from the group consisting of ferrite, martensite and carbide.