JP4731537B2 - Method for producing firelite sintered body - Google Patents

Description

  The present invention relates to a method for producing a firelite sintered body which can be used as a measurement sample for grasping various physical properties of a firelite phase or used as various materials.

  In the manufacturing process of steel products, an oxide film (scale) is formed on the surface, which causes the quality and performance of the product to deteriorate and the production yield to decrease. For example, if the removal of the thick primary scale formed in the heating furnace is incomplete and it is subjected to rolling with a part remaining, the scale may be broken or pushed in, and the scale material may generate scale flaws. . Further, due to the secondary scale, mechanical descaling (MD) property may be poor or plating property may be poor. Thus, the scale greatly affects the surface properties of the steel material. Therefore, in order to solve the problem caused by the scale, it is only necessary to grasp the dynamic behavior such as the scale formation behavior and the scale fracture / deformation behavior during the rolling process. In particular, in order to grasp the fracture / deformation behavior of the scale during the rolling process, it is only necessary to grasp the physical properties of the scale (for example, physical characteristics and mechanical characteristics) in a high temperature state.

By the way, the scale is usually composed of an Fe-based oxide (for example, FeO, Fe ₃ O ₄ , Fe ₂ O _3, etc.). Especially when the steel material is Si-containing steel, as a subscale, for example, Light (Fe ₂ SiO ₄ ) or the like is also formed. Therefore, to understand the physical properties of the scale at high temperatures, it is necessary to prepare such Fe-type oxide and subscale single samples and measure the physical properties such as hardness, Young's modulus (elastic constant), and linear expansion coefficient at high temperatures. It is considered good.

However, since the firelite formed as a subscale is a scale formed as a secondary when the Fe-based oxide is formed, it is extremely difficult to produce a single sample. This is because when Fe is oxidized during the rolling process, it forms relatively stable Fe-based oxides such as FeO, Fe ₃ O ₄ , and Fe ₂ O _3, but these Fe-based oxides are formed. The equilibrium oxygen pressure at this time varies depending on the temperature, but usually increases in the order of FeO, Fe ₃ O ₄ and Fe ₂ O ₃ . Therefore, Fe ₂ O ₃ is formed on the surface of the steel material having a high oxygen potential (oxygen partial pressure), and a layered scale is formed in the order of Fe ₂ O ₃ , Fe ₃ O ₄ , and FeO from the surface toward the ground iron. . Among these scales, the oxygen potential (oxygen partial pressure) is further lower than the equilibrium oxygen pressure when FeO is formed in the iron region inside the FeO layer formed at the deepest position. However, since the equilibrium oxygen pressure when SiO ₂ is formed is lower than the equilibrium oxygen pressure when FeO is formed, if Si is present in the iron region inside the FeO layer, Si is oxidized, SiO ₂ is formed. The formed SiO ₂ reacts with nearby FeO to form a composite compound, ie, firelite (Fe ₂ SiO ₄ ). The layer of the formed firelite is called a subscale. Thus, the firelite is a scale that is formed as a secondary layer as the inner layer scale when the Fe-based oxide is formed as the outer layer scale, and is a scale formed at the interface between the outer layer scale and the ground iron. For this reason, it is extremely difficult to produce a single sample having high firelite purity.

  On the other hand, since firelite is formed as an inner layer scale, it is considered that the physical properties of the entire scale including the outer layer scale (Fe-based oxide) are affected. In order to grasp the physical characteristics and mechanical characteristics), it is considered to be extremely important to grasp the physical properties (for example, physical characteristics and mechanical characteristics) of the firelite.

As a technique for evaluating the physical characteristics of firelite, Non-Patent Document 1 discloses that, in the exposed scale section, firelite (Fe ₂ SiO ₄ ) is formed by heating Si-added steel to form a scale on the surface of the steel material. It is disclosed that the Vickers hardness of the formed layer is measured at 1000 ° C. However, since this Non-Patent Document 1 does not disclose a technique for producing a single sample having high firelite purity, the mechanical properties of firelite (for example, Young's modulus and linear expansion coefficient of firelite) are measured. It is not possible.

In addition, although iron olivine is available as a single sample of firelite, the available iron olivine is in the form of gypsum with a side of about 10 to 20 mm and is too small, so Young's modulus, linear expansion coefficient, etc. The mechanical properties of can not be measured.
Materials Science Forum Vols.522-523 (August 2006) pp.469-476

  This invention is made | formed in view of such a condition, The objective is to provide the method of manufacturing a sintered compact with high firelite purity.

  The method for producing a firelite sintered body according to the present invention that has solved the above problems includes a step of molding iron olivine powder passing through a 150-mesh sieve to obtain a molded body, and the obtained molded body The molding is performed at a pressure of 98 to 294 MPa, and the sintering is performed at 1000 to 1150 ° C. in a vacuum atmosphere of 0.13 Pa or less. Have

  As the iron olivine powder, it is preferable to use a powder obtained by pulverizing iron olivine and performing classification using a 150-mesh sieve and collecting the powder passing through the sieve. The sintering is preferably performed for 10 to 120 minutes.

  According to the present invention, a sintered body with high firelite purity can be produced by using iron olivine powder as a raw material and sintering a molded body obtained by molding the powder under appropriate conditions. If this firelite sintered body is used, the mechanical properties (for example, Young's modulus and linear expansion coefficient of firelite) of firelite can be measured.

  The inventors of the present invention have made extensive studies in order to produce a sintered body with high firelite purity. As a result, it has been found that a sintered body with high firelite purity can be produced by using iron olivine powder as a raw material and sintering a molded body obtained by molding the powder under appropriate conditions, thereby completing the present invention.

  As described in Non-Patent Document 1, if Si-added steel is heated, a scale containing firelite can be formed on the surface, and the hardness of firelite can be measured. However, in this method, since a bulk material of firelite cannot be produced, mechanical properties (for example, Young's modulus and linear expansion coefficient of firelite) cannot be measured.

Firelite (Fe ₂ SiO ₄ ) is a complex oxide formed by the reaction of FeO and SiO _{2. Even} if Si-added steel is heated to form Fe ₂ SiO ₄ , it is cooled to room temperature. On the way, there is a possibility of separation into two phases of FeO and SiO ₂ . For example, after forming the Fe ₂ SiO _4, even if an attempt is prepared frozen metastable phase of Fe ₂ SiO ₄ by increasing the cooling rate to room temperature, likely to cause a portion of two-phase separation in the middle cooling There is also.

  The firelite itself is commercially available as iron olivine, but the commercially available product is small, and a single firelite sample that is large enough to measure the mechanical properties of firelite has not been commercially available.

Therefore, the inventors have paid attention to the powder metallurgy technology, and have repeatedly studied along the line whether a firelite sintered body can be manufactured by sintering a molded body obtained by molding powder. as a result,
(1) molding iron olivine powder passing through a 150 mesh sieve to obtain a molded body;
(2) a step of obtaining a sintered body by sintering the obtained molded body,
The molding is performed at a pressure of 98 to 294 MPa, and if the sintering is performed at 1000 to 1150 ° C. in a vacuum atmosphere of 0.13 Pa or less, it is clear that a sintered body with high firelite purity can be manufactured. It became.

(1) Step of obtaining a molded body In the present invention, it is important to use iron olivine powder as a raw material. This is because a high-purity firelite sintered body can be produced by sintering a molded body obtained by molding iron olivine powder under predetermined conditions.

  Iron olivine is available from, for example, Wako Pure Chemical Industries. In addition, commercially available iron olivine usually has a gypsum shape with a side of about 10 to 20 mm and is too small to measure mechanical properties such as Young's modulus and linear expansion coefficient.

  In the present invention, a powder that passes through a 150 mesh sieve is used as the iron olivine powder. When powder that does not pass through a 150-mesh sieve is used, the powder itself is large, so that the gap between the powders becomes large when molded, and the density of the molded body decreases. Therefore, a high-density sintered body cannot be manufactured. Therefore, in this invention, the powder which passes a 150 mesh sieve is used as iron olivine powder.

  The iron olivine powder that passes through the 150 mesh sieve can be obtained by pulverizing the iron olivine, classifying it using a 150 mesh sieve, and collecting the powder that passes through the sieve.

  Iron olivine may be pulverized according to a conventional method, and may be pulverized using a mortar, ball mill, jet mill, auto mill, or the like.

Iron olivine powder that passes through a 150-mesh sieve is molded to obtain a molded body, but it is important that the molding load be 98 to 294 MPa (1.0 to 3.0 tonf / cm ² ). When the molding load is less than 98 MPa (1.0 tonf / cm ² ), the load becomes insufficient and a molded body cannot be formed. Accordingly, the molding load is 98 MPa (1.0 tonf / cm ² ) or more. However, when the molding load exceeds 294 MPa (3.0 tonf / cm ² ), the stress remaining in the molded body increases, and cracks occur in the sintered body in the subsequent sintering process, making it impossible to obtain a sintered body. . Accordingly, the molding load is 294 MPa (3.0 tonf / cm ² ) or less.

The type of mold used for molding is not particularly limited, and a mold or a rubber mold may be used. When a rubber mold is used, CIP molding may be performed. For example, when producing a cylindrical molded body, a neoprene rubber tube is cut to a desired length and filled with iron olivine powder as uniformly and densely as possible, and both ends of the tube are made of neoprene rubber. Stop with a stopper and seal. If this sample is CIP-molded at a hydrostatic pressure of 98 to 294 MPa (1.0 to 3.0 tonf / cm ² ), a cylindrical molded body can be produced.

  In addition, the shape of a molded object is not specifically limited, The shape of various test pieces may be sufficient, and plate shape and block shape may be sufficient.

(2) Step of obtaining a sintered body The obtained molded body is sintered to produce a sintered body. This sintering is performed in a vacuum atmosphere of 0.13 Pa (1 × 10 ⁻³ Torr) or less, It is important to perform at 1000-1150 degreeC.

By making the sintering atmosphere a vacuum atmosphere of 0.13 Pa (1 × 10 ⁻³ Torr) or less, contact with oxygen is cut off and Fe ₂ SiO ₄ is prevented from separating into two phases of FeO and SiO _2. it can. For example, in order to shut off oxygen, the sintering atmosphere may be an Ar atmosphere or an N ₂ atmosphere. However, as will be apparent from the examples described later, since only a small amount of oxygen inevitably remains in the atmosphere if the sintering atmosphere is an Ar atmosphere or an N ₂ atmosphere, Fe ₂ SiO ₄ is composed of ₂ of FeO and SiO ₂ . It separates into phases, or Fe ₂ SiO ₄ is further oxidized to form Fe ₃ O ₄ , Fe ₂ O ₃ , SiO ₂ . Accordingly, the sintering atmosphere is a vacuum atmosphere of 0.13 Pa (1 × 10 ⁻³ Torr) or less. The degree of vacuum is preferably 0.0013 Pa (1 × 10 ⁻⁵ Torr) or less.

Moreover, in this invention, it is necessary to perform sintering temperature at 1000-1150 degreeC. If the sintering temperature is less than 1000 ° C., the sintering is insufficient, the density of the sintered body cannot be increased, and the mechanical properties cannot be measured. Accordingly, the sintering temperature is set to 1000 ° C. or higher. Preferably it is 1050 degreeC or more, More preferably, it is 1100 degreeC or more. However, when the sintering temperature exceeds 1150 ° C., Fe ₂ SiO ₄ cannot be melted to form a sintered body. Accordingly, the sintering temperature is 1150 ° C. or lower. Preferably it is 1140 degrees C or less. In sintering, the rate of temperature rise until reaching the sintering temperature may be, for example, 100 to 1200 ° C./h.

  Since the sintering time is affected by the sintering temperature, it cannot be uniformly defined, and the sintering time may be performed while considering the sintering temperature so as to obtain a density at which mechanical characteristics can be measured. The sintering time may be, for example, 10 to 120 minutes. This is because if the sintering time is too short, the sintering tends to be insufficient, and if the sintering time is too long, it is economically wasteful. A more preferable lower limit of the sintering time is 15 minutes, and a more preferable upper limit is 90 minutes.

  In addition, what is necessary is just to cool in a sintering furnace when cooling to room temperature after sintering.

  If the firelite sintered body thus obtained is used, the hardness of firelite can be measured, the Young's modulus and the linear expansion coefficient can be measured, and the mechanical properties of firelite can be examined. By examining the mechanical properties of firelite in detail, it becomes possible to grasp the scale fracture and deformation behavior during the rolling process.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

[Experiment 1]
Commercially available massive iron olivine (FAYALITE reagent manufactured by Wako Pure Chemical Industries, Ltd.) was pulverized in a mortar and classified using a 150 mesh sieve to obtain iron olivine powder that passed through the sieve. The obtained iron olivine powder was charged into a cylindrical mold (φ10 mm × 10 mm) and a square mold (55 mm × 55 mm × 8 mm ^t ), respectively, and molded by applying pressure. The molding pressure is 49 MPa (0.5 tonf / cm ² ), 98 MPa (1.0 tonf / cm ² ), 196 MPa (2.0 tonf / cm ² ), 294 MPa (3.0 tonf / cm ² ), or 392 MPa (4.0 tonf). / Cm ² ). As a result, when the pressure at the time of molding is 49 MPa (0.5 ton / cm ² ), the molded body is taken out from the mold regardless of whether it is a cylindrical mold or a square mold. Collapsed.

On the other hand, when the pressure during molding is 98 MPa (1.0 tonf / cm ² ) or more, the molding taken out from the mold can be performed using either a cylindrical mold or a square mold. The body did not collapse and it was confirmed that a stable molded body was formed.

Next, the molded body taken out from the mold was sintered by heating at 1130 ° C. for 1 hour in a vacuum atmosphere of 0.13 Pa or lower (1 × 10 ⁻³ Torr or lower) to obtain a sintered body. In the sintering, the temperature rising rate when the temperature was raised to 1130 ° C. was 100 ° C./h, and the cooling after sintering at 1130 ° C. for 1 hour was performed by allowing to cool in a sintering furnace. As a result of visual observation of the obtained sintered body, cracks were generated in the sintered body obtained at a molding pressure of 392 MPa (4.0 tonf / cm ² ). The collapse of the body was also confirmed visually.

On the other hand, generation of cracks was not observed in the sintered body obtained at a molding pressure of 98 to 294 MPa (1.0 to 3.0 tonf / cm ² ), and a good sintered body could be produced. Was confirmed visually.

[Experiment 2]
Commercially available lump iron olivine (FAYALITE reagent manufactured by Wako Pure Chemical Industries) is pulverized in a mortar and classified into the following four types of powders using 16 mesh, 35 mesh, 80 mesh, and 150 mesh sieves. did.
Powder A: Powder that passed through a 16 mesh screen but remained on a 35 mesh screen.
Powder B: Powder that passed through a 35 mesh screen but remained on an 80 mesh screen.
Powder C: Powder that passed through an 80 mesh screen but remained on a 150 mesh screen.
Powder D: Powder that passed through a 150 mesh sieve.

The obtained iron olivine powders (powder A to D) were respectively charged into square molds (55 mm × 55 mm × 8 mm ^t ) and molded under a pressure of 147 MPa (1.5 tonf / cm ² ). As a result, it was confirmed that none of the molded bodies taken out from the mold was disintegrated and a stable molded body was formed.

Next, the molded body taken out from the mold was sintered under the same conditions as in Experiment 1 to obtain a sintered body. As a result of visual observation of the obtained sintered body, generation of cracks was not recognized, and a good sintered body could be produced. The obtained sintered body was subjected to XRD (X-ray diffraction) measurement under the same conditions as in Experiment 3 described later, and the oxide species constituting the sintered body were examined. As a result, only the diffraction peak derived from Fe ₂ SiO ₄ among the oxide species was detected from the sintered body, and it was confirmed that a firelite (Fe ₂ SiO ₄ ) sintered body was obtained.

Next, the bulk density (apparent density) of the obtained firelite sintered body was measured by Archimedes method. The value calculated by (apparent density of firelite sintered body) ÷ (true density of firelite) was taken as the sintered density of the sintered body. The true density of firelite is 3.4 g / cm ³ . Table 1 below shows the particle size of the powder used and the calculated sintered density.

  As is apparent from Table 1, when a powder (powder D) that has passed through a 150-mesh sieve, that is, a powder having a small particle diameter, the sintering density can be increased to 95% or more, and high-density sintering is achieved. You can get a body. On the other hand, if powders (powder A to C) that do not pass through a 150-mesh sieve, that is, powders having a large particle size, the sintered density cannot be 95% or more.

[Experiment 3]
Commercially available massive iron olivine (FAYALITE reagent manufactured by Wako Pure Chemical Industries, Ltd.) was pulverized in a mortar and classified using a 150 mesh sieve to obtain iron olivine powder that passed through the sieve. The obtained powder was charged into a cylindrical mold (φ10 mm × 10 mm) and molded by applying a pressure of 147 MPa (1.5 tonf / cm ² ).

  The molded body taken out from the mold was sintered by heating in the atmosphere shown in Table 2 below at the temperature shown in Table 2 below for the time shown in Table 2 below to obtain a sintered body.

In Table 2, the sintering atmosphere of “vacuum” means that sintering was performed at a pressure of 0.13 Pa (1 × 10 ⁻³ Torr) or less. The sintering atmosphere “Ar” means that sintering was performed in an atmospheric pressure Ar gas atmosphere. The sintering atmosphere “N ₂ ” means that the sintering was performed in a normal pressure N ₂ gas atmosphere. The “atmosphere” as the sintering atmosphere means that the sintering was performed in an atmospheric atmosphere at normal pressure.

In sintering, the rate of temperature increase when the temperature was raised to the sintering temperature shown in Table 2 below was 100 ° C./h, and cooling after sintering was performed by allowing to cool in a sintering furnace. The obtained sintered body was measured by XRD (X-ray diffraction), and the oxide species constituting the sintered body were examined. The detected oxide species for each sintered body are shown in Table 2 below. In Table 2, “◯” means that the diffraction peak was detected to such an extent that the oxide species can be identified, and “−” means that no diffraction peak was detected to the extent that the oxide species could be identified. . In the sintered body used in this experiment, Fe ₂ O ₃ , Fe ₃ O ₄ , SiO ₂ , and Fe ₂ SiO ₄ oxide species were detected, but other oxide species were not detected.

It can be considered as follows from Table 2 below. No. From the sintered bodies of ₂ to 6 and 9, only diffraction peaks derived from Fe ₂ SiO ₄ among the oxide species were detected, and a firelite (Fe ₂ SiO ₄ ) sintered body was obtained.

No. Reference numeral 1 is a reference example, and only a diffraction peak derived from Fe ₂ SiO ₄ among the oxide species is detected from the sintered body, and a firelite (Fe ₂ SiO ₄ ) sintered body is obtained. Since the time was somewhat short, the sintering was insufficient, and the strength of the sintered body was slightly lowered and could not be used as a test piece for measuring mechanical properties.

No. From the sintered body of No. 7, only diffraction peaks derived from Fe ₂ SiO ₄ among the oxide species were detected, and a firelite (Fe ₂ SiO ₄ ) sintered body was obtained, but the sintering temperature was too high. For this reason, a part was melted, resulting in deformation, and could not be used as a test piece for measuring mechanical properties.

On the other hand, no. In addition to the diffraction peaks derived from Fe ₂ SiO ₄ among the oxide species, diffraction peaks derived from other oxide species were also detected from the sintered bodies of 8, 10 to 13. From the peak intensity ratio, the purity of firelite (Fe ₂ SiO ₄ ) was low. In addition, No. No. 8 was deformed as a result of partial melting because the sintering temperature was too high, and could not be used as a test piece for measuring mechanical properties.

No. shown in Table 2. The XRD chart of the sintered body of No. 5 is shown in FIG. The XRD chart of 14 sintered bodies is shown in FIG. As is apparent from FIG. In the sintered body of No. 5, only the diffraction peak derived from Fe ₂ SiO ₄ was confirmed.

On the other hand, as is apparent from FIG. In the sintered body of No. 14, a diffraction peak derived from Fe ₂ SiO ₄ was not detected, and in addition to a relatively strong diffraction peak derived from Fe ₂ O ₃ , a diffraction peak derived from Fe ₃ O ₄ and SiO ₂ A derived diffraction peak was also observed.

[Experiment 4]
Commercially available massive iron olivine (FAYALITE reagent manufactured by Wako Pure Chemical Industries, Ltd.) was pulverized in a mortar and classified using a 150 mesh sieve to obtain iron olivine powder that passed through the sieve. The obtained powder was charged into a square mold (55 mm × 55 mm × 8 mm ^t ) and molded by applying a pressure of 147 MPa (1.5 tonf / cm ² ). As a result, it was confirmed that none of the molded bodies taken out from the mold was disintegrated and a stable molded body was formed.

Next, the molded body taken out from the mold was sintered under the same conditions as in Experiment 1 to obtain a sintered body. As a result of visual observation of the obtained sintered body, generation of cracks was not recognized, and a good sintered body could be produced. The obtained sintered body was subjected to XRD (X-ray diffraction) measurement under the same conditions as in Experiment 3, and the oxide species constituting the sintered body were examined. As a result, only the diffraction peak derived from Fe ₂ SiO ₄ among the oxide species was detected from the sintered body, and it was found that a firelite (Fe ₂ SiO ₄ ) sintered body was obtained.

  The hardness (Vickers hardness) of the obtained sintered body was measured at room temperature or 1000 ° C. For the hardness measurement, an MQ type high temperature micro hardness tester manufactured by Nippon Optical Co., Ltd. was used, and the measurement was performed according to JIS Z 2244.

  As a comparison object, using a test material in which 0.11% by mass of C and 1.5% by mass of Si are contained, and the balance is made of steel and inevitable impurities, which are cut into a size of 10 mm × 20 mm × 3 mm, This sample was heated at 1000 ° C. for 30 minutes in an oxygen atmosphere to prepare a comparative sample whose surface was oxidized. A scale having a thickness of about 400 μm was generated in the comparative sample.

A cross section of the sample for comparison was processed to expose the cross section of the scale, and the hardness (Vickers hardness) measurement was performed at room temperature or 1000 ° C. at a portion where Fe ₂ SiO ₄ was formed in a layered form. The measurement results are shown in Table 3 below.

From Table 3 below, it can be considered as follows. Whether measured at room temperature or 1000 ° C., the hardness of the firelite sintered body is almost the same as the hardness of the portion where Fe ₂ SiO ₄ is formed in a layered manner in the scale generated in the comparative sample. It was value. Therefore, from the result of hardness measurement, it can be seen that the obtained firelite sintered body has a high density and is composed of high purity firelite.

[Experiment 5]
A firelite sintered body obtained in the same manner as in Experiment 4 was machined to a size of 3.5 mm × 3.5 mm × 20 mm to obtain a specimen. About the obtained specimen, the linear expansion coefficient from room temperature to 1000 degreeC was measured using the thermomechanical analysis (TMA) apparatus, and the thermal expansion coefficient was computed. The result of the calculated thermal expansion coefficient is shown in FIG. Further, as reference data, a Fe ₂ O ₃ sintered body was prepared, and the coefficient of thermal expansion was calculated by measuring the linear expansion coefficient by the same method, and the result is shown in FIG. In FIG. 3, the result of the firelite sintered body is indicated as “●: Fe ₂ SiO ₄ ”, and the result of the Fe ₂ O ₃ sintered body is indicated as “◯: Fe ₂ O ₃ ”.

As is apparent from FIG. 3, it is recognized that there is a difference in the temperature change of the linear expansion coefficient between the firelite sintered body and the Fe ₂ O ₃ sintered body, and the thermal expansion coefficients of these materials are different from each other. Was confirmed.

FIG. 5 is an XRD chart of a sintered body obtained in 5. FIG. 14 is an XRD chart of the sintered body obtained in FIG. FIG. 3 is a graph showing the result of calculating the thermal expansion coefficient.

Claims (3)

Molding iron olivine powder passing through a 150 mesh sieve to obtain a molded body;
Sintering the resulting molded body to obtain a sintered body,
The molding is performed at a pressure of 98 to 294 MPa,
The said sintering is performed at 1000-1150 degreeC by the vacuum atmosphere of 0.13 Pa or less, The manufacturing method of the firelite sintered compact characterized by the above-mentioned.   The manufacturing method according to claim 1, wherein the iron olivine powder is obtained by pulverizing iron olivine, classifying using a 150-mesh sieve, and collecting powder passing through the sieve.   The said sintering is a manufacturing method of Claim 1 or 2 performed in 10 to 120 minutes.

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