JP2005179176A - Molten-metal-resistant member and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems that cracks and fissures are liable to occur due to repeated use when a member to be exposed to molten metal is formed of a silicon nitride and that the oxide, dust, etc., in the metal element in the molten metal are liable to stick when the silicon nitride is used as a member to be immersed with the molten metal. <P>SOLUTION: The molten-metal-resistant member comprises a silicon nitride-based sintered material having crystals of the silicon nitride and a grain boundary layer containing at least one of a metal element of ≥1,000°C in melting point, wherein the concentration of the metal silicide on the surface of the silicon nitride-based sintered material is made lower than that of the interior thereof. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is an excellent member for a molten metal comprising a silicon nitride-based sintered body that is excellent in thermal properties and mechanical properties, can suppress the mixing of impurities into the molten metal, or can suppress adhesion of the molten metal, In particular, the present invention relates to a member for molten metal, for example, a member for molten metal that can be directly immersed in a molten metal of aluminum, zinc, copper and alloys of these metals, a member for welding, for example, a nozzle for welding. Moreover, it is related with the manufacturing method of this member for molten metal.

  Conventionally, silicon nitride-based sintered bodies and sialon-based ceramics have been used as members for molten metal such as members for molten metal that are directly immersed in molten metal alloys and welding members such as welding nozzles. .

As such a member for molten metal, Patent Document 1 discloses that a sialon-based ceramic sintered body containing a Group 3 element oxide and aluminum oxide in the periodic table and having a surface layer of BN—SiO _2. consists _{-Al 2 O 3 -Y 2 O 3} , thermocouple protective tube for measuring the temperature of molten metal is described. This thermocouple protective tube is manufactured by applying BN powder and SiO ₂ powder to the surface of a molded body, which is a precursor of sialon-based ceramics, and then firing. Further, Patent Document 2 discloses a silicon nitride sintered body in which a surface layer having a surface Al concentration higher than the internal Al concentration, a member for a molten metal using the same, and a Y concentration higher than the internal concentration. A silicon nitride sintered body that is low on the surface and has a higher concentration of rare earth elements other than Y on the surface than the inside thereof, and a member for molten metal using the same are described. The member for molten metal disclosed in Patent Document 2 is manufactured by applying a powder containing a large amount of aluminum oxide or a powder containing a large amount of cerium oxide to a molded body that is a precursor of a silicon nitride sintered body, followed by firing. Has been. Further, Patent Document 3 discloses a silicon nitride material containing Mg obtained by molding and firing a mixture containing silicon nitride powder, aluminum oxide powder and magnesium oxide powder as a member for molten metal to be directly immersed in Al molten metal. It has been proposed to use a sintered body.

Such a member for molten metal is required to have high thermal shock resistance, high erosion resistance to molten metal, and to prevent impurities and dust mixed in the molten metal from being fixed, and is used as these members. As a silicon nitride-based sintered body, Patent Document 4 discloses a silicon nitride-based sintered body that contains Fe as an impurity and further suppresses variation in characteristics by adding a small amount of W. A silicon nitride sintered body in which crystal grains of at least one metal silicide of W, Mo, Cu, Mn, Fe and Nb are dispersed in a grain boundary layer is further disclosed in Patent Document 6. A silicon nitride-based sintered body is described in which a compound composed of a melting point metal—Fe—Si—O is formed in a grain boundary layer. Further, Patent Document 7 contains particles made of silicides such as W and Fe and Ti compounds (nitrides, carbonitrides, carbonitrides) in the grain boundary layer, and silicides such as W and Fe are converted into Ti compounds. A silicon nitride-based sintered body aggregated around each of the above has been proposed.
JP 63-11574 A JP-A-8-73286 JP-A-6-322457 Japanese Patent Laid-Open No. 5-148031 JP 2001-206774 A JP 2001-106576 A JP-A-11-267538

  However, the silicon nitride sintered body used as a conventional member for molten metal has various problems.

  The members for molten metal of Patent Documents 1 to 3 have a problem that when BN is applied to the surface of the member, BN is detached and mixed into the molten metal, and the quality of the metal cast using the molten metal is deteriorated. there were. When a member having a large amount of Al compound on the surface is used as a nozzle for Al welding, there is a problem that Al adheres to the nozzle and welding accuracy is lowered or the nozzle becomes unusable.

  In addition, a member containing a large amount of Mg compound in the grain boundary layer reacts with molten Mg such as Pb, Cu, Mg, Zn, Sn and Mg compound. By this reaction, for example, in the case of Al molten metal, aluminum oxide, Al, etc. There is a problem that the life of the member is shortened because the fixed object is fixed to the surface of the member.

  For this reason, it has been demanded to suppress the mixing of impurities into the molten metal or to suppress the reaction with the molten metal by a method other than those described in Patent Documents 1 to 3.

  However, the silicon nitride-based sintered bodies of Patent Documents 4 to 7 that are not provided with a layer (BN layer, Al layer, etc.) for suppressing reaction with the molten metal are used as a member for molten metal, for example, a member for molten metal. When used, the metal component (Fe, W, etc.) contained in the metal compound such as metal silicide existing in the grain boundary layer easily diffuses and moves to the grain boundary layer on the surface during firing. A large amount of the compound exists on the surface side from the inside of the member, and a concentration gradient of the metal compound is generated. Since this metal compound is more likely to cause a chemical reaction with the molten metal than silicon nitride crystals, the molten metal reacts with the metal compound on the surface side, and the metal compound becomes a large amount of impurities as an impurity in the molten metal. . As a result, there is a problem that the quality of the metal cast by the molten metal is deteriorated.

  Similarly, when used as a welding nozzle, for example, there are many metal silicides present in the grain boundary layer on the surface of the member, so that the molten metal reacts with the molten metal and adheres to the nozzle. There is a problem that the weld nozzle becomes unusable with repeated use due to the accumulated metal.

  In addition, since the silicon nitride sintered bodies of Patent Documents 5 to 7 were manufactured without premixing only a plurality of metal compounds as raw materials of metal silicide in the manufacturing process, Fe silicide is formed in the grain boundary layer. And silicide such as W silicide existed alone. When this silicon nitride sintered body is used as a member for molten metal, a large number of metal silicides exist on the surface of the member alone, and mechanical stress and thermal stress are concentrated on these metal silicides. This single metal silicide is a failure source, causing cracks between the silicon nitride crystal and the metal silicide, resulting in a decrease in mechanical strength and thermal shock resistance. It also had the problem of.

  The present invention has been devised in view of the above-mentioned problems, and improves mechanical characteristics and thermal characteristics, in particular mechanical strength and thermal shock resistance, and suppresses the incorporation of impurities into the molten metal. An object of the present invention is to provide a member for a molten metal made of a silicon nitride-based sintered body capable of suppressing adhesion of molten metal and a method for producing the member.

  The member for molten metal of the present invention comprises a silicon nitride sintered body having a silicon nitride crystal and a grain boundary layer containing a metal silicide composed of at least one metal element having a melting point of 1000 ° C. or higher. It is a member for molten metal, wherein the concentration of metal silicide on the surface of the silicon nitride sintered body is lower than the inside.

  The metal element is at least one of Fe and Cu.

  The metal silicide is contained in an amount of 0.01 to 10% by mass in terms of total Fe and Cu.

  The concentration of the metal silicide on the surface of the silicon nitride sintered body is ½ or less compared to the inside.

  The grain boundary layer contains an amorphous phase composed of Group 3 elements (RE), Al and O in the periodic table.

  The RE is at least one of Y, Er, Yb, and Lu.

The ratio of Si and RE contained in the grain boundary layer is 0.2 to 10 in terms of a molar ratio of SiO ₂ / RE ₂ O ₃ .

The ratio of Al and RE contained in the grain boundary layer is 0.2 to 5 in terms of a molar ratio of Al ₂ O ₃ / RE ₂ O ₃ .

  The silicon nitride crystal is a needle crystal, and the needle crystal has a major axis having an average diameter of 30 μm or less and a needle crystal having a minor axis of 2 μm or less.

  The metal silicide contains a first metal silicide containing at least one of Fe and Cu and a second metal silicide containing at least one of W and Mo, and the first metal silicide and the second metal The silicide is characterized by forming adjacent phases in contact with each other.

  The method for producing a member for molten metal according to the present invention is a method for producing a member for molten metal according to any one of the above, and the sintered body obtained after molding and firing a predetermined raw material powder Is immersed in an aqueous solution having a pH of 3 or less, or exposed to a gas comprising a halide.

  According to the member for a fusion resistant metal of the present invention, from a silicon nitride sintered body having a silicon nitride crystal and a grain boundary layer including a metal silicide composed of at least one metal element having a melting point of 1000 ° C. or higher. Since the concentration of the metal silicide on the surface of the silicon nitride sintered body is lower than the inside, it has excellent heat resistance and mechanical properties, and when exposed to molten metal, the molten metal is difficult to adhere and the molten metal It is possible to prevent contamination of impurities.

  In addition, by using at least one of Fe and Cu as the metal element, it is possible to suppress the occurrence of cracks in the grain boundary layer even when a large strain is generated in the entire member for molten metal due to mechanical stress or thermal stress. As a result, the molten metal member can be prevented from cracking.

  Furthermore, by containing 0.01 to 10% by mass of the metal silicide in terms of the total of Fe and Cu, the fracture toughness of the grain boundary layer can be increased even at higher temperatures. Even when applied, it is possible to prevent the molten metal member from cracking.

  When the concentration of the metal silicide on the surface of the silicon nitride sintered body is ½ or less compared to the inside, when exposed to molten metal, the molten metal is more difficult to adhere and impurities to the molten metal It can be set as the corrosion-resistant member which can further suppress mixing.

  By containing an amorphous phase composed of Group 3 elements (RE), Al and O in the periodic table in the grain boundary layer, a liquid phase is generated at a low temperature during firing, so that the crystal of silicon nitride is fine. As a result, it is possible to obtain a member for a molten metal having excellent thermal shock resistance and high mechanical strength.

  When the RE is at least one of Y, Er, Yb, and Lu, the mechanical strength can be improved even at a high temperature.

The mechanical characteristics of the member for molten metal can be further improved by setting the ratio of Si and RE contained in the grain boundary layer to 0.2 to 10 in terms of a molar ratio of SiO ₂ / RE ₂ O _3. it can. The ratio of Al and RE contained in the grain boundary layer is 0.2 to 5 in terms of the molar ratio of Al ₂ O ₃ / RE ₂ O ₃ , thereby further improving the sinterability of the member for molten metal. And the fracture toughness can be improved.

  Fracture toughness is improved by making the crystal of silicon nitride consist of needle-like crystals, the average diameter of the major axis of the needle-like crystals being 30 μm or less, and the average grain size of the minor axis of the needle-like crystals being 2 μm or less. Moreover, it can be set as the member for molten metal which improved mechanical strength.

  The metal silicide contains a first metal silicide containing at least one of Fe and Cu and a second metal silicide containing at least one of W and Mo, and the first metal silicide and the second metal By forming adjacent phases in which the silicides are in contact with each other, it is possible to suppress the concentration of mechanical stress and thermal stress on the first and second metal silicides. The impact property can be further improved.

  A method for producing a member for fusion-resistant metal according to any one of the above, wherein a predetermined raw material powder is molded and fired, and then the obtained sintered body is put into an aqueous solution having a pH of 3 or less. By using a method for manufacturing a member for molten metal that is immersed or exposes a silicon nitride sintered body to a gas comprising a halide, the concentration of the metal silicide on the surface can be reduced. It is possible to produce a member for a molten metal that is difficult to adhere to the molten metal and that can prevent impurities from being mixed into the molten metal while improving the mechanical characteristics and the thermal shock resistance.

  The present invention is described in detail below.

  The member for molten metal of the present invention comprises a silicon nitride sintered body having a silicon nitride crystal and a grain boundary layer containing a metal silicide composed of at least one metal element having a melting point of 1000 ° C. or higher. Is.

  Crystals of silicon nitride are mainly formed in a needle shape, and include β-type silicon nitride crystals or β′-sialon crystals having the same crystal structure as β-type silicon nitride.

Examples of the grain boundary layer containing a metal silicide composed of at least one metal element having a melting point of 1000 ° C. or higher include, for example, Cr, Co, Cu, Hf, Fe, Mn, Mo, Ni, Ru, Ta, Ti, W and Zr are preferable, and examples of the metal silicide composed of these metal elements include CrSi ₂ , CrSi ₂ , Cr ₃ Si ₂ , CoSi, Cu ₂ Si, HfSi ₂ , FeSi ₂ , FeSi, Fe ₃ Si, Fe _{5 Si 3, MnSi, MoSi 2} , NiSi, Ru, TaSi 2, SiTi 2, WSi 2, W 5 Si 3, WSi 3, W 2 Si 3, there is ZrSi _2. These metal silicides are composed of a metal element having a melting point of 1000 ° C. or higher, so that they are particularly strongly bonded to silicon nitride crystals and are thermodynamically stable even when exposed to molten metal. Therefore, even when a large thermal stress is applied to the member by exposure to molten metal, it is possible to further suppress the development of microcracks at the interface between the grain boundary layer containing these metal silicides and the silicon nitride crystal. To do. As a result, thermal characteristics such as thermal shock resistance can be further improved.

  Here, the member for resistance to molten metal according to the present invention is characterized in that the concentration of metal silicide on the surface is lower than the inside, and when exposed to molten metal, the metal silicide is removed on the surface of the member. The reaction between the constituent metal element and the molten metal can be suppressed, and the mechanical properties and thermal properties can be improved by the metal silicide contained in the interior. For this reason, it has excellent mechanical properties and thermal properties, and adhesion of molten metal to the surface of the member for molten metal is suppressed, and chemical reaction between the metal silicide and molten metal is suppressed. The metal component contained in the product becomes an impurity and is difficult to be released out of the system, and as a result, the impurity can hardly be mixed into the molten metal. The grain boundary layer refers to a region surrounded by silicon nitride crystals.

  Further, the silicon nitride sintered body constituting the member for resistance to molten metal according to the present invention may be one after firing or one subjected to processing such as polishing after sintering. In either case, the concentration of the metal silicide on the surface should be lower than that inside.

  The method of comparing the concentration of the metal silicide inside the surface of the molten metal member of the present invention with the case where the metal silicide contains Fe silicide and Cu silicide will be described as an example.

  For example, the comparison of the concentration of the metal silicide inside the surface of the member for resistance to molten metal and the internal metal silicide is performed as follows using a fluorescent X-ray analyzer.

First, X-rays are irradiated on the surface of the member for molten metal and the polished surface at a predetermined position, respectively, and the fluorescent X-rays (characteristic X-rays) of each element of Fe and Cu generated thereby. Intensity is measured as follows. Fluorescent X-rays (characteristic X-rays) of each element of Fe and Cu are incident on a high-resolution proportional counter, amplified by an amplification circuit such as a preamplifier, and further decomposed for each energy by a multichannel analyzer. Here, the elements (Fe, Cu) to be measured are specified, and the count number (intensity) of fluorescent X-rays counted by setting the energy window specific to these elements is output. In order to make the measurement conditions the same, the area of the sample, the intensity of X-rays to be irradiated, the time for counting fluorescent X-rays, etc. are the same. The counts of the fluorescent X-rays of the elements Fe and Cu on the surface thus measured are C _Fe1 and C _Cu1 , and the counts of the fluorescent X-rays of the elements Fe and Cu inside are C _Fe2 and C _Cu2 . To do. Furthermore, it is analyzed by an X-ray diffraction method, a micro X-ray diffraction method, a transmission electron microscope, etc., that a crystalline phase made of a metal silicide is contained inside the member for molten metal. When metal silicide is contained on the surface of the member for molten metal, it can be confirmed by analyzing the crystal phase with an X-ray diffraction method, a micro X-ray diffraction method, a transmission electron microscope or the like. The ratio of the metal silicide concentration between the surface and the interior is calculated from C _Fe1 / C _{Fe2 for Fe} silicide and C _Cu1 / C _Cu2 for Cu silicide. In the molten metal member according to the present invention, the fact that the concentration on the surface of the metal silicide is lower than the inside of the sintered body means that at least one of C _Fe1 / C _Fe2 and C _Cu1 / C _Cu2 is more than 1. It is defined as a small case. Thus, when the metal silicide includes a plurality of metal elements, when the concentration of at least one metal silicide is lower than the inside at the surface, the concentration of the metal silicide at the surface of the member for resistance to molten metal is higher than the inside. Is also defined as low. Further, the concentration of the metal silicide is 1 / n (n is an arbitrary numerical value larger than 1) compared to the inside, which is smaller one of C _Fe1 / C _Fe2 and C _Cu1 / C _Cu2. It is defined as a case of 1 / n or less. However, a case where a crystal phase composed of a metal silicide is not present on the surface of the member for molten metal is also one of the preferred embodiments of the present invention. In this case, the values of C _Fe1 / C _Fe2 and C _Cu1 / C _Cu2 are defined as zero. To do.

  Further, the inside of the member for molten metal is a portion excluding the surface of the member for molten metal and the vicinity of the surface. Specifically, the inside means that when a member for molten metal is exposed to the molten metal, the molten metal does not penetrate through the pores on the surface of the member for molten metal and does not penetrate by diffusion or the like. The inside of the member is approximately 0.2 mm or more.

  In addition, in order to control the density | concentration of the metal silicide in the surface of the member for fusion-resistant metals of this invention, although details are mentioned later in a manufacturing method, first, the silicon nitride obtained by the general method is made into a main component. After obtaining the sintered body, the concentration of the metal silicide on the surface can be reduced by immersing in an aqueous solution having a pH of 3 or less or by exposing to a gas comprising a halide. When immersed in an aqueous solution, the pH and the immersion time are changed, and the lower the pH and the longer the immersion time, the lower the concentration of metal silicide on the surface. When exposed to a gas comprising a halide, the exposure time is changed, and the longer the exposure time, the smaller the concentration of metal silicide on the surface.

  The metal element is preferably at least one of Fe and Cu.

As a result, not only has excellent mechanical and thermal properties, but also a metal silicide with high fracture toughness can be generated in the grain boundary layer, so when stress is applied to the member for molten metal, Even when a large strain is generated in the entire member for molten metal by mechanical stress or thermal stress, the occurrence of cracks in the grain boundary layer can be suppressed, and as a result, the member for molten metal can be prevented from cracking. In addition, when this molten metal member is used as a member for molten metal, metal oxides produced by the reaction of the molten metal with oxygen, etc., and sticking matters such as dust and impurities in the molten metal are fixed to the surface of the member. Can be suppressed, and the generation of desorbed substances can also be suppressed. In general, melting of a metal such as Al or Cu, or injection of a molten metal melt into a mold is performed in the air. When a metal silicide is present on the surface of the member for molten metal, the metal silicide reacts with oxygen in the air to become an oxide, for example, Fe ₂ O ₃ or CuO. These oxides tend to cause a thermite reaction with the molten Al when the molten metal is an Al molten metal, for example. This reaction formula is represented by the following formula.

Fe ₂ O ₃ + 2Al → Al ₂ O ₃ + 2Fe (Formula 1)
3CuO + 2Al → Al ₂ O ₃ + 3Cu (Formula 2)
Al ₂ O ₃ produced by the reactions of Formulas 1 and 2 adheres to the surface of the member for molten metal. Once Al ₂ O ₃ is fixed to the surface of the molten metal member, impurities and dust in the molten metal are more likely to be fixed on the fixed Al ₂ O ₃ . In order to suppress the sticking of the sticking matter, it is necessary to reduce the abundance of the metal silicide on the surface of the member for molten metal. The member for molten metal of the present invention contains a metal silicide capable of improving the mechanical characteristics, and is a metal silicide on the surface of the silicon nitride-based sintered body that causes adhesion of impurities such as a metal oxide. By making the concentration lower than the inside, it is possible to provide a metal melt member in which impurities in the melt are difficult to adhere while improving the mechanical characteristics. Moreover, even when the member for a molten metal of the present invention is used as a member for a molten metal other than an Al molten metal, for example, a molten metal such as Pb, Cu, Mg, Zn, Sn, etc., a fixed object is difficult to adhere.

Further, the metal silicide is preferably contained in an amount of 0.01 to 10% by mass in terms of the total of Fe and Cu, and the fracture toughness of the grain boundary layer can be increased even in a higher temperature environment. Even when stress is applied, it is possible to prevent the molten metal member from cracking. The metal _silicide, FeSi 2, _FeSi, at least one of Fe 2 Si, _Cu 2 Si is selected. In particular, it is preferable that the grain boundary layer contains Fe silicide, and the concentration of Fe silicide on the surface of the member for molten metal is lower than the concentration of Fe silicide in the sintered body.

  Further, the concentration of the metal silicide on the surface of the member for resistance to molten metal is preferably ½ or less compared to the inside, and when exposed to the molten metal, the molten metal is more difficult to adhere, Impurity contamination can be further suppressed. In particular, when the molten metal member is used as an Al molten metal member, the reactions of the above (Formula 1) and (Formula 2) can be further suppressed, so that the fixation of the fixed object can be further suppressed. In particular, the concentration of the metal silicide on the surface is more preferably 1/4 or less of the inside. In the member for molten metal, metal silicide may not be substantially present on the surface of the member for molten metal, but this member for molten metal is one of the preferred embodiments of the member for molten metal of the present invention. is there.

  In addition, in order to make the concentration of metal silicide on the surface of the member for molten metal resistant to ½ or less of the inside, details will be described later in the manufacturing method, but a sintered body mainly composed of silicon nitride. Is immersed in an aqueous solution having a pH of 2.5 or lower for 10 minutes or more, or exposed to a gas containing at least one of fluorine and chlorine for 20 minutes or more.

The grain boundary layer preferably contains an amorphous phase composed of Group 3 elements (RE), Al and O in the periodic table. As a result, the liquid phase is generated at low temperature during firing, so that the silicon nitride crystals are fine and uniform in particle size. As a result, a member for a molten metal with excellent thermal shock resistance and high mechanical strength is obtained. Can be obtained. The amorphous phase can be generated in the sintered body by, for example, adding an oxide of Group 3 element (hereinafter referred to as RE) of the periodic table and aluminum oxide powder in the manufacturing process, and then molding and firing. it can. Preferably, the molten metal member of the present invention contains 1 to 20% by mass of RE in terms of RE ₂ O ₃ and 0.1 to 10% by mass of Al in terms of Al ₂ O ₃ . The Group 3 element means at least one element selected from Sc, Y, lanthanoid elements, and actinoid elements.

  The RE is preferably at least one of Y, Er, Yb, and Lu. This tends to produce a liquid phase at a low temperature during firing and to reduce the difference between the thermal expansion coefficient of the resulting amorphous phase and the thermal expansion of the silicon nitride crystals. For this reason, not only the silicon nitride crystals are fine and uniform in particle size, but also when mechanical stress or thermal stress is applied at high temperatures, the difference in thermal expansion coefficient between silicon nitride and the grain boundary layer Generation of microcracks in the boundary layer can be suppressed. As a result, the mechanical strength at high temperature can be improved while maintaining the thermal shock resistance. Thereby, the oxidation resistance in a high-temperature oxidizing atmosphere can also be improved. When RE is Y, the evaporation of RE can be suppressed during firing than when RE is other than Y, so the material composition of the member for molten metal can be controlled with high accuracy, thereby reducing variations in mechanical properties. This is particularly preferable.

It is preferable that the grain boundary layer contains at least one of an apatite phase, a borastite phase, and a disilicate phase. Thereby, the mechanical strength of the member for molten metal can be further improved. The apatite phase is a compound represented by RE ₅ (Si ₄ ) ₃ N, the borastite phase is represented by RESiO ₂ N, and the disilicate phase is represented by RE ₂ Si ₂ O ₇ . Further, when the grain boundary layer contains an apatite phase or a borastite phase, the high temperature strength, high temperature creep resistance, and thermal shock resistance are improved. Further, when the grain boundary layer contains a disilicate phase, the oxidation resistance at high temperatures is improved.

  Moreover, it is preferable that the grain boundary layer containing RE and Al is present on the surface in a smaller amount than the inside of the member for molten metal. As a result, when the molten metal member of the present invention is used as a molten metal member, it is possible to further suppress the fixation of the fixed matter, and this grain boundary layer becomes a detachment from the molten metal member to the molten metal. It is possible to obtain a member for molten metal that is difficult to be mixed. Preferably, the amount of the grain boundary layer containing RE and Al on the surface of the molten metal member is ½ or less, particularly preferably ¼ or less of the inside.

  In order to measure the amount of the grain boundary phase on the surface of the molten metal member with respect to the amount of the grain boundary phase inside the molten metal member containing RE and Al, for example, the following is performed using a fluorescent X-ray analyzer.

The surface of the molten metal member and the polished surface of the molten metal member are each irradiated with X-rays, and the intensity of the fluorescent X-rays (characteristic X-rays) of each element of RE and Al generated thereby. Is measured as follows. Fluorescent X-rays (characteristic X-rays) of each element of RE and Al are incident on a high-resolution proportional counter, amplified by an amplifier circuit such as a preamplifier, and further decomposed for each energy by a multichannel analyzer. Here, the elements (RE, Al) to be measured are designated, and the count number (intensity) of fluorescent X-rays counted by setting the energy window specific to these elements is output. In order to make the measurement conditions the same, the area of the sample, the intensity of X-rays to be irradiated, the time for counting fluorescent X-rays, etc. are the same. The counts of the fluorescent X-rays of each element of RE and Al on the surface of the molten metal member measured in this way are C _RE1 and C _Al1 , the RE inside the molten metal member and the fluorescent X-rays of each element of Al. The count numbers are C _RE2 and C _Al2 . However, when a plurality of fluorescent X-rays of RE are detected, the total number of fluorescent X-rays of the plurality of REs is calculated as C _RE1 and C _RE2 for the surface of the molten metal member and the inside of the molten metal member, respectively. Define. The ratio of the concentration of the surface and the interior of the member for molten metal for each of _RE and Al is calculated by C _RE1 / C _{RE2 for RE} and C _Al1 / C _{Al2 for Al} . In the molten metal member of the present invention, the fact that the grain boundary layer containing RE and Al is present on the surface less than the inside of the molten metal member indicates that C _RE1 / C _RE2 and C _Al1 / C _Al2 It is defined that at least one of them is smaller than 1. However, when the grain boundary layer containing RE and Al does not exist on the surface of the member for molten metal, the values of C _RE1 / C _RE2 and C _Al1 / C _Al2 are set to zero.

The ratio of Si and RE contained in the grain boundary layer _is preferably 0.2 to 10 in molar ratio terms of SiO 2 / _RE 2 _{O 3.} Thereby, the mechanical characteristics of the member for a molten metal can be further improved. It is more preferable that the molar ratio of SiO ₂ / RE ₂ O ₃ is 0.2 to 4 in order to improve the sinterability of the molten metal member. This molar ratio can be determined as follows. Let G (mass%) be the total of the amount of oxygen (mass%) contained in RE ₂ O ₃ and Al ₂ O ₃ converted to volume% by the above method. The total oxygen content in the member for molten metal is measured with an oxygen analyzer manufactured by LECO, G (mass%) is subtracted from the total oxygen content (mass%), and the remaining oxygen content (mass%) is reduced to SiO _2. Convert to amount (mass%). The ratio of the amount of SiO ₂ (% by mass) and the content (% by mass) of RE ₂ O ₃ in terms of mass is defined as the ratio of Si to RE in terms of the molar ratio of SiO ₂ / RE ₂ O ₃ .

It is preferable that the ratio of Al and RE contained in the grain boundary layer is 0.2 to 5 in terms of a molar ratio of Al ₂ O ₃ / RE ₂ O ₃ . Thereby, the sinterability of the member for molten metal can be further improved and the fracture toughness can be improved. More preferably, it is 0.4 to ₃ in terms of a molar ratio of Al ₂ O ₃ / RE ₂ O ₃ . The molar ratio of Al to RE can be measured by ICP emission spectroscopic analysis as follows.

The content (mass%) of RE and Al in the member for molten metal is measured by ICP emission spectroscopic analysis, and this content is converted into the content (mass%) in terms of RE ₂ O ₃ and Al ₂ O ₃ To do. Further, using the content and theoretical density of RE ₂ O ₃ and Al ₂ O ₃ in terms of mass (for example, Y ₂ O ₃ is 5.02 g / cm ³ , Al ₂ O ₃ is 3.98 g / cm ³ ), The content of RE ₂ O ₃ and Al ₂ O ₃ in terms of volume% is determined.

  Further, it is preferable that the silicon nitride crystal is a needle-like crystal, and the needle-like crystal has a major axis having an average diameter of 30 μm or less and a needle-like crystal having a minor axis of 2 μm or less. Thereby, since the acicular crystal suppresses the progress of fine cracks more effectively, it can be a member for molten metal having improved fracture toughness and improved mechanical strength. In particular, in order to further improve mechanical properties such as mechanical strength, it is preferable that the average diameter of the major axis of the needle-like crystal is 15 μm or less. This is because when the average particle size exceeds 15 μm, the fracture toughness cannot be remarkably improved, so that the mechanical strength cannot be remarkably improved.

  There are the following various methods for measuring the average grain size of silicon nitride crystals. That is, a cross-section of a molten metal member is mirror-polished, the mirror surface is taken in a SEM (scanning electron microscope) photograph, and the long diameter of the silicon nitride crystal in the SEM photograph is measured. Use this method to identify the crystal of silicon nitride and measure the major axis of the crystal, or after removing the grain boundary layer on the surface of the mirror-finished member for molten metal from the surface by etching by heat treatment or chemical etching There is a method of measuring the long diameter, and in any case, the measurement is performed by averaging a plurality of measured long diameter data.

  The grain boundary layer preferably contains at least one metal silicide of a metal element having a melting point of 1400 ° C. or higher and contains less than 20% by volume of the grain boundary layer. Thereby, the metal silicide excellent in the creep resistance at high temperature is generated in the grain boundary layer during firing performed in the process of manufacturing the member for molten metal. As a result, since deformation can be suppressed during firing in the process of manufacturing the member for molten metal, a member for molten metal with high dimensional accuracy can be obtained. When the content of the grain boundary layer is 20% by volume or more, deformation is likely to occur during the firing step, which makes it difficult to produce a member for molten metal with high dimensional accuracy, which is not preferable. Further, when the grain boundary layer exceeds 15% by volume and is less than 20% by volume, deformation cannot be significantly reduced. Further, when the grain boundary layer is less than 5% by volume, it is necessary to fire at a high temperature in order to obtain a dense member for fusion-resistant metal. Strength and wear resistance cannot be remarkably improved. For this reason, the content of the grain boundary layer is particularly preferably 5 to 15% by volume.

  In the grain boundary layer, the metal silicide contains a first metal silicide containing at least one of Fe and Cu and a second metal silicide containing at least one of W and Mo, and the first metal silicide. Preferably, the material and the second metal silicide form an adjacent phase in contact with each other.

Here, the adjacent phase only needs to be in a state in which one of the first and second metal silicides is in contact with a part thereof, whereby mechanical stress and thermal stress are applied to the first and second metal silicides. As a result, the mechanical properties and thermal shock resistance of the molten metal member can be further improved.
More preferably, one of the first and second metal silicides surrounds part or all of the other metal silicide.

  Further, the adjacent phase includes a first metal silicide, a second metal silicide, a metal element that includes the metal element that forms the first metal silicide, and a metal element that includes the metal element that forms the second metal silicide. It is preferable to have a trimetallic silicide. Since the third metal silicide is similar in crystal structure to the first and second metal silicides, not only the adjacent phase is easily formed but also the adjacent phase is thermodynamically stable. This is because, when used as a member for use at high temperatures, the adjacent phase is less likely to undergo phase transformation, and mechanical properties and thermal shock resistance at high temperatures are improved.

  Here, the structure of the adjacent phase will be specifically described with reference to FIG.

  FIG. 1 is an example of a cross section 10 of a silicon nitride sintered body constituting a member for a fusion resistant metal of the present invention. A cross section 10 is mirror-polished, and this mirror surface is observed with a scanning electron microscope (SEM). A schematic diagram is shown. The cross section 10 has a grain boundary layer 20 between the silicon nitride crystals 12, and the grain boundary layer 20 contains a first metal silicide 16, a second metal silicide 18, and a third metal silicide 22. Furthermore, an adjacent phase 14 is provided. The adjacent phase 14 includes the first metal silicide 16a and the second metal silicide 18a adjacent to each other, the first metal silicide 16b surrounding the second metal silicide 18b, and the first metal silicide. Some of the second metal silicide 18c is exposed from 16c.

  The member for molten metal having an adjacent phase is more effectively suppressed from concentrating mechanical stress and thermal stress on the first to third metal silicides, further improving mechanical characteristics and thermal characteristics, In particular, the thermal shock resistance can be further improved. That is, when a metal silicide is present adjacently, the proportion of the metal silicide increases with respect to the entire grain boundary layer. Therefore, when thermal stress is applied to the adjacent phase, the stress is concentrated, and Although mechanical stress and thermal stress are less likely to be applied to the third metal silicide, the first to third metal silicides each have a higher Young's modulus than silicon nitride even if the stress is concentrated in the adjacent phase. Since the rate of change of the thermal expansion coefficient with respect to temperature is small, it is considered that the adjacent phase suppresses the uneven distribution of thermal stress in the grain boundary layer of the member for molten metal.

Therefore, even if a fine crack occurs in the member for molten metal, the adjacent phase can suppress the progress of the silicon nitride crystal crack, and the crack and crack of the member for molten metal can be suppressed. In particular, it is preferable that the first metal element is Fe and the second metal element is W. Among the first metal silicides made of the first metal element, Fe silicide and the second metal element made of the second metal element are used. Among the two metal silicides, W silicide has an approximate crystal structure, so it is easy to form adjacent phases remarkably, and the content ratio of adjacent phases to the grain boundary layer increases, and as a result, the thermal shock resistance is further improved. Because it can.

In addition, as a preferable form of the first metal silicide, at least one selected from FeSi ₂ , FeSi, Fe ₃ Si, Fe ₅ Si ₃ , Cr ₃ Si ₂ , MnSi, and Cu ₂ Si is used. The preferred form of the second metal silicide is one selected from at least one of WSi ₂ , W ₅ Si ₃ , WSi ₃ , W ₂ Si ₃ and MoSi ₂ . Furthermore, as a preferable form of the third metal silicide, a plurality of metal components (compounds) containing Fe and W, for example, a solid solution is used. The reason why these metal silicides are selected is that, among the first to third metal silicides, these metal silicides are thermodynamically stable phases, so even when mechanical stress or thermal stress is applied. This is because the transformation hardly occurs, and there is no fear of further increase in mechanical stress and thermal stress accompanying the phase transformation.

Further, the Fe silicide of the first metal silicide is preferably selected from at least one of FeSi and FeSi ₂ , and more preferably FeSi ₂ . Moreover, it is preferable that the W silicide of the second metal silicide contains WSi ₂ .

The most preferred combination is FeSi ₂ as the first metal silicide and WSi ₂ as the second metal silicide. The reason for this is that WSi ₂ and FeSi ₂ are both thermodynamically particularly stable phases, and because their crystal structures are particularly close to each other, it is easy to form adjacent phases, thus further improving the thermal shock. It is because it can be made.

  When the third metal silicide is contained in the adjacent phase, the third metal silicide preferably contains Fe and W. This is because the third metal silicide containing Fe and W is strongly bonded to the first and second metal silicides, and as a result, the fracture toughness of the adjacent phase is improved, so that the thermal shock is a member for a molten metal. In this case, the adjacent phase suppresses the development of microcracks, so that a molten metal member having excellent thermal shock resistance can be obtained.

  The average particle size of the adjacent phase is preferably 30 μm or less, particularly preferably 1 to 5 μm. This is because if the average particle size is larger than 30 μm, the thermal shock resistance cannot be remarkably improved because the adjacent phase cannot sufficiently relax the mechanical and thermal stress. In this case, the average particle size of the adjacent phase is a value obtained by observing the sintered body by magnifying it with a scanning electron microscope (SEM) or the like, and measuring and averaging the particle sizes of a plurality of adjacent phases. It can be measured in the same manner as the average grain size of the crystals. Furthermore, the content of the adjacent phase is preferably 0.01 to 10% by volume since the thermal shock resistance and mechanical strength can be particularly improved, and particularly preferably 0.1 to 5% by volume. 0.1 to 1% by volume.

  In addition, about the 1st-3rd metal silicide, presence of an adjacent phase, and those content, it measures as follows. The presence of the first metal silicide 16, the second metal silicide 18, the third metal silicide 22, and the adjacent phase 14 shown in FIG. 1 is determined by the X-ray diffraction method, the micro X-ray diffraction method, the X-ray microanalyzer (example) : Wavelength dispersion type EPMA (Electron Probe Micro-Analyzer), TEM (transmission electron microscope), etc. In the case of using the X-ray diffraction method, it is preferable to perform measurement using an X-ray microanalyzer or TEM in combination. When analyzing by TEM, it measures after processing the member for a fusion-resistant metal into a thin piece.

  The content of the adjacent phase 14 is, for example, an X-ray microanalyzer in a section of about 500 μm × 500 μm of the mirror surface (hereinafter, the area of this part is referred to as “area A”). Is used to irradiate an electron beam and measure the type and intensity of characteristic X-rays generated from the sintered body to obtain Si, first and second metal elements (Fe, Cr, Mn, Cu, W, Mo And (1) the area of the first portion (second metal silicide 18) containing Si and rich in at least one of the second metal elements, (2) The area of the second portion (first metal silicide 16) containing Si and at least one of the first metal elements being rich; (3) containing Si and the first and second metal elements Each area (third silicide 22) to be obtained The area B of the part where at least two of the first to third parts of (1) to (3) are in contact with each other is measured, the ratio of the area B to the area A is calculated, and this ratio is the content of the adjacent phase 14 (% By volume). For the area A, the magnification at the time of measurement may be changed as appropriate so that the first to third silicides and the adjacent phase 14 can be identified. In addition, it is preferable to confirm the crystal phase contained in the adjacent phase 14 using X-ray microanalyzer and TEM together.

  Thus, the molten metal member of the present invention has high mechanical strength and excellent thermal shock resistance, so that it does not break or crack even when subjected to a thermal cycle, and further adheres to the molten metal. Therefore, it is also suitable for use as a nozzle member for welding exposed to molten metal, containers used to cast molten metal, ladle, heater tube, stalk, die casting sleeve, welded sleeve, thermocouple protection tube it can. In particular, it can be suitably used as a member for molten Al.

  Next, the manufacturing method of the member for molten metal of this invention is demonstrated.

  The method for producing a member for resistance to molten metal according to the present invention comprises forming a raw material powder and firing it, then immersing the obtained sintered body in an aqueous solution having a pH of 3 or less, or exposing to a gas comprising a halide. is there.

  Thereby, the density | concentration of the metal silicide of the surface of the member for a fusion-resistant metal can be made lower than an inside. This makes it possible to produce a molten metal member that is less likely to adhere to the molten metal while suppressing mechanical properties and thermal shock resistance, and that can prevent impurities from being mixed into the molten metal.

  Furthermore, the manufacturing method of the member for molten metal of this invention is demonstrated concretely.

  First, a known production method, for example, a raw material production step of producing a raw material powder by mixing silicon nitride powder and a metal compound composed of at least one metal element (excluding Si) having a melting point of 1000 ° C. or higher, A molding step for producing a molded body composed of the raw material powder and the organic binder, and a degreased body is produced by degreasing the organic binder in an atmosphere substantially composed of nitrogen gas, argon gas, or a mixed gas thereof. A sintered body is produced by a manufacturing method having a degreasing step for performing and a firing step for firing the degreased body in a non-oxidizing atmosphere containing nitrogen gas. This sintered body is a silicon nitride-based sintered body mainly composed of β-type silicon nitride crystal or β′-sialon crystal having the same crystal structure as β-type silicon nitride. Moreover, it is preferable that the metal element mentioned above is chosen as at least 1 metal element among melting | fusing point of 1000 degreeC or more.

  Next, an immersion process in which the obtained sintered body is immersed in an aqueous solution having a pH of 3 or less, or an exposure process in which the sintered body is exposed to a gas composed of a halide.

In the dipping process, the metal silicide present on the surface of the sintered body is reacted with an aqueous solution having a pH of 3 or less to remove at least a part thereof from the surface of the sintered body. Examples of the aqueous solution having a pH of 3 or lower include aqueous solutions of HCl, HNO ₃ , H ₂ SO ₄ , HF, H ₂ O ₂ , and HClO ₄ and aqueous solutions obtained by mixing at least two of them. Among the aqueous solutions, HCl aqueous solution alone or mixed acid aqueous solution as HNO ₃ + H ₂ SO ₄ , HF + HNO ₃ + H ₂ SO ₄ , HF + H ₂ O ₂ , HF + HNO ₃ , HNO ₃ + HF, HNO ₃ + HF + H ₂ SO ₄ , HNO ₃ + HF It is preferable to use any aqueous solution of HNO ₃ + HF + HClO ₄ . By immersing the sintered body in the aqueous solution, the metal silicide is removed from the surface of the sintered body. Among the aqueous solutions, an aqueous HCl solution that can improve economy and safety in the manufacturing process is particularly preferable. Even when the aqueous solution having a pH of 3 or less used in the dipping step is, for example, only HCl (not including water), the metal silicide on the surface of the sintered body can be removed in the dipping step. The reason why water is contained in the aqueous solution having a pH of 3 or less used in the dipping process is to improve the economy and safety in the production process. The time for exposing the sintered body to an aqueous solution having a pH of 3 or less is preferably 5 minutes or more.

In the exposure step, the sintered body is exposed to a halide. As the halide, a gas composed of fluoride is preferable. In particular, ClF ₃ , CF ₂ Cl ₂ , CFCl ₃ , CF ₃ Cl, CF ₄ , A gas containing any of NF ₃ , SF ₆ , SiF ₄ , BF ₃ , PF ₃ , and PF ₅ is preferable. Thereby, the metal silicide contained in the surface of the sintered body is removed. In particular, metal silicides containing W and Mo as metal silicides can be efficiently removed. More preferably, an air stream of these halides is formed, and the sintered body is exposed to the air stream for 1 minute or more.

  The reason why the immersion step or the exposure step is selected as a method for reducing the metal silicide on the surface of the sintered body will be described. There are many methods for reducing the metal silicide on the surface of the silicon nitride-based sintered body, and among these, it is preferable to use the immersion step and the exposure step. As another method for removing the metal silicide present on the surface of the silicon nitride sintered body, for example, sodium oxide and the sintered silicon nitride sintered body may be any one of Au, Fe, Ni, Ag, and Zr. There is a method of heating to about 500 ° C. in a metal container made of such. However, this method has a problem that the container is easily eroded, a problem that a metal component contained in the container is fixed to the silicon nitride sintered body, a problem that the sodium oxide used is fixed to the silicon nitride sintered body, and the like. There is. For this reason, this method cannot be used as a method of removing metal silicide from the surface of a silicon nitride-based sintered body for use as a member for molten metal.

  Further, in order to control the concentration of the metal silicide on the surface to ½ or less compared to the inside, for example, an aqueous solution having a pH of 2.5 or less is used as the aqueous solution, and the sintered body is immersed in this solution for 10 minutes or more. Or exposed to a gas containing at least one of fluorine and chlorine for 20 minutes or more.

  Furthermore, when using at least one metal compound of Fe and Cu as a metal compound composed of at least one metal element (excluding Si) having a melting point of 1000 ° C. or higher, Fe silicide, Cu is used in the sintered body. By controlling the content of Fe and Cu so that the silicide is contained in an amount of 0.01 to 10% by mass in terms of the total of Fe and Cu, the fracture toughness of the grain boundary layer can be increased even at higher temperatures. In addition, even when a thermal stress is applied at a higher temperature, it is possible to produce a member for molten metal that is difficult to break.

Further, by adding an oxide (RE ₂ O ₃ ) of group 3 element (RE) of the periodic table and aluminum oxide to the raw material powder, a liquid phase is generated at a low temperature in the firing step, and the grain boundary layer Can contain an amorphous phase composed of RE, Al and O. As a result, it is possible to manufacture a molten metal member having a fine silicon nitride crystal, uniform particle size, excellent thermal shock resistance, and high mechanical strength. In addition, in order to make the silicon nitride crystals fine and uniform throughout the sintered body by uniformly dispersing the amorphous phase in the grain boundary layer, it is the highest in the firing step. After passing through the temperature, it is preferable that the rate of temperature decrease to 800 ° C. is greater than 100 ° C./hour.

Furthermore, by using at least one of _{Y 2 O 3, Er 2 O} 3, Yb 2 O 3, Lu 2 O 3 as the _RE 2 _{O 3,} with improved mechanical strength and oxidation resistance at high temperatures A member for molten metal can be manufactured. Furthermore, in the firing step, the rate of temperature decrease is set to be greater than 200 ° C./hour, so that the ratio of Si and RE contained in the grain boundary layer is 0.2 to 10 in terms of the molar ratio of SiO ₂ / RE ₂ O _3. Therefore, it is possible to manufacture a molten metal member having further improved mechanical characteristics.

Further, RE ₂ O ₃ and aluminum oxide should be added to the raw material powder so that the ratio of Al to RE in the sintered body is 0.2 to 5 in terms of molar ratio of Al ₂ O ₃ / RE ₂ O _3. Therefore, the amorphous phase can be uniformly formed over the entire grain boundary layer, and uneven distribution of the amorphous phase can be suppressed, so that the sinterability is improved and the fracture toughness is improved. Can be manufactured.

Further, by setting the specific surface area of the degreased body to 1 to 30 m ² / g, the silicon nitride crystals contained in the sintered body are made of needle-like crystals, and the average diameter of the major axis of the needle-like crystals is 30 μm or less. The average particle diameter of the minor axis of the acicular crystal can be 2 μm or less. As a result, it is possible to produce a molten metal member having improved fracture toughness and further improved mechanical strength.

  Further, it is preferable to control the content of the grain boundary layer contained in the sintered body to be less than 20% by volume by controlling the content of the compound other than silicon nitride contained in the raw material powder, Therefore, it is possible to manufacture a molten metal member with high dimensional accuracy.

  In addition, it is preferable to continuously perform the degreasing step, the nitriding step, and the firing step in the same furnace because the manufacturing cost of the silicon nitride sintered body is particularly reduced.

  Here, the manufacturing method for obtaining the member for molten metal which contains an adjacent phase in a grain boundary layer is demonstrated.

  The member for molten metal having an adjacent phase is prepared by adding at least one of Fe, Cr, Mn and Cu having an average particle diameter of 0.1 to 20 μm in advance to Si powder or a mixed powder of Si powder and silicon nitride powder. The raw material powder obtained by mixing the compound of the metal element with a premixed powder obtained by wet-mixing and drying at least one second metal element compound of W and Mo having an average particle diameter of 0.1 to 30 μm A raw material manufacturing step, a molding step of manufacturing a molded body composed of the raw material powder and an organic binder, and the organic binder in an atmosphere substantially composed of nitrogen gas, argon gas, or a mixed gas thereof. A degreasing process for producing a degreased body by degreasing, a nitriding step for substantially converting the degreased body into a nitride in a nitrogen gas atmosphere, and firing the nitride in a non-oxidizing atmosphere containing nitrogen gas Sintered body A firing step of immersing the sintered body, an immersion step of immersing the sintered body in an aqueous solution having a pH of 3 or less, or an exposure step of exposing to a gas comprising a halide. In this production method, the process of incorporating an adjacent phase into the grain boundary layer of the sintered body obtained in the firing step is as follows.

  First, by wet mixing as described above, the first and second metal element compounds are uniformly dispersed in the premixed powder without uneven distribution, and the particles made of the first and second metal element compounds are dried to dry the particles. Preliminary powders fixed together are prepared. As a result, the premixed powder is one in which the compounds of the first and second metal elements are uniformly dispersed and the particles are fixed to each other. In order to achieve this uniform dispersion and fixation, at least one of water, isopropyl alcohol, ethanol, and methanol is suitable as a solvent used for wet mixing. It is more preferable to include water in the solvent because the particles of the first and second metal element compounds can be firmly fixed to each other during the drying process.

  Next, by mixing the above-mentioned premixed powder with Si powder or a mixed powder of Si powder and silicon nitride powder, the particles of the first and second metal element compounds are fixed to each other and uniformly dispersed. The raw material powder in which the mixed powder is dispersed in the mixed powder can be produced.

  Then, during the nitriding step, the first metal element compound, the second metal element compound, the first and second metal element compounds each react with the Si component, and the first metal silicide precursor, A second metal silicide precursor and a third metal silicide precursor are formed, and an adjacent phase precursor in which at least two of the precursors are in contact with each other is formed. Here, the first to third metal silicide precursors and the adjacent phase precursors indicate substances which are amorphous or partially not crystallized. In the nitriding step, the adjacent phase precursor is formed because the particles made of the compound of the first metal element and the particles made of the compound of the second metal element are fixed to each other in the raw material powder. This is because the particles fixed to each other are nitrided while adjoining. The reason why the Si powder is contained in the raw material powder is to promote the reaction between the first and second metal elements and Si in the nitriding step to form the adjacent phase precursor. If the raw material powder does not contain Si powder, the reaction between the first and second metal elements and Si is not promoted, so that a nitride containing the adjacent phase precursor cannot be obtained.

  The adjacent phase precursor contained in such a nitride is crystallized in the firing step to become an adjacent phase. Even when the contents of the first and second metal elements in the molten metal member are the same, the content of the adjacent phase can be controlled by controlling the temperature and holding time of the nitriding step.

  According to the method for manufacturing a member for resistance to molten metal of the present invention, an adjacent phase containing a third metal silicide can be formed without using a compound containing both the first and second metal elements in the premixed powder. Can do. The formation mechanism of this adjacent phase is considered as follows, for example. That is, when the particles composed of the first and second metal element compounds are nitrided while adjoining each other, either the first metal silicide precursor or the second metal silicide precursor is dissolved in the other. An adjacent phase precursor is formed in which the solid solution is adjacent to one of the first and second metal silicide precursors. This adjacent phase precursor is an adjacent phase in which the third metal silicide and the first or second metal silicide are adjacent in the firing step.

As described above, a powder having an average particle size of 0.1 to 20 μm made of the compound of the first metal element and a powder having an average particle size of 0.1 to 30 μm made of the compound of the second metal element are used. This is because the formation of the above-mentioned adjacent phase precursor in the nitriding step is promoted by setting the particle size range, and the proportion of the first to third metal silicides that contributes to the formation of the adjacent phase. This is thought to be because it can be increased. This ratio can be increased as the powders are mixed more uniformly in the above-described powder mixing step. In addition, it is preferable that the specific surface area of premixed powder exists in the range of 3-30 m < ² > / g. The reason for this is to promote the nitriding in the nitriding step and increase the ratio of at least two of the first metal silicide, the second metal silicide and the third metal silicide contributing to the formation of the adjacent phase. Because you can.

  When both Si powder and silicon nitride powder are used as starting materials, the mass ratio of Si powder to silicon nitride powder (mass of Si powder) / (total of mass of Si powder and silicon nitride powder) is 0. It is preferably 4 to 0.95. If this ratio is less than 0.4, the first to third metal silicide precursors and adjacent phase precursors may not be easily generated, and the dimensional accuracy of the resulting molten metal member is increased. It becomes impossible to control to accuracy. If this ratio is greater than 0.95, when nitriding a degreased body having a large thickness, the nitriding time is increased and the manufacturing cost increases, which is not preferable.

  The reason why the molded body made of the mixed powder and the organic binder is prepared is to increase the density of the molded body and reduce the variation in density in the molded body. Thereby, since sintering of the nitride proceeds uniformly over the entire member for molten metal during firing, mechanical strength and thermal shock resistance can be improved.

  Degreasing the organic binder in an atmosphere consisting essentially of nitrogen gas, argon gas, or a mixed gas thereof to produce a degreased body is achieved by reducing the carbon contained in the degreased body and reducing the sinterability. This is because it can be improved. Further, the above degreasing is performed by placing the molded body in a furnace.

  Nitriding starts from the Si powder on the surface of the molded body in the nitriding step, and the nitriding of the Si powder existing inside the molded body proceeds with time. Therefore, there is a state in which the amount of Si inside is larger than that of the surface of the molded body during or after the first nitriding step. In order to completely nitride the molded body from this state, it is necessary to perform nitriding at a high temperature (second nitriding step) after nitriding at a low temperature (first nitriding step).

  In particular, the abundance (content) of the adjacent phase can be controlled by controlling the temperature of the second nitriding step. That is, by setting the temperature of the second nitriding step to 1200 ° C. or more and less than 1400 ° C., the molten metal member can contain 0.1 to 5% by volume of the adjacent phase. When the temperature of the second nitriding step is 1100 ° C. or more and less than 1200 ° C., or 1400 ° C. or more and 1500 ° C. or less, the adjacent phase can be contained only less than 0.1% by volume. It is not preferable because an excellent member for molten metal cannot be produced.

  In order to improve mechanical properties by densifying the member for molten metal, it is preferable that the maximum temperature in the firing step is 1600 ° C. or higher. By firing at 1600 ° C. or higher, a dense member for molten metal having a relative density of 97% or higher can be produced, and the mechanical properties can be improved. In order to suppress the decrease in mechanical strength by suppressing abnormal grain growth of silicon nitride crystals, the upper limit of the maximum firing temperature is preferably set to 1850 ° C.

  Next, in order for the first metal silicide to be an adjacent phase formed so as to surround the second metal silicide or the third metal silicide, the first metal element is more than the second metal element. In the powder mixing step, the first metal element is contained in a total of 0.2 to 10% by mass, and the second metal element is contained in a total of 0.1 to 3% by mass in the member for molten metal. The addition amount of the metal element compound and the second metal element compound is controlled.

  In this nitriding step, an adjacent phase precursor formed so that the first metal silicide precursor surrounds the second metal silicide precursor or the third metal silicide precursor is generated in the nitriding step. is there. When the first and second metal elements are mixed as impurities during the manufacturing process, the contents of the first and second metal elements may be controlled by removing the impurities. Specifically, for example, when the metal Fe component is mixed in the raw material powder due to wear of the machine used in the powder mixing step, after the powder mixing step, a magnetic field is applied to the powder to adsorb the Fe component, By removing, the content of Fe finally contained in the member for molten metal can be controlled.

  Further, by setting the average particle size of the powder composed of the first metal element compound to 1 to 20 μm and the average particle size of the powder composed of the second metal element compound to 0.1 to 5 μm, the surrounding first metal Since the content of silicide can be increased, it is possible to produce a molten metal member having further excellent mechanical properties.

More preferably, by setting the average particle size of the Si powder as a starting material to 2 to 50 μm and the specific surface area of the degreased body to ² to 30 m ² / g, the silicon nitride crystals contained in the member for molten metal The average particle diameter of the major axis is controlled to 15 μm or less. If the average particle size of the Si powder is less than 2 μm, a large amount of heat is generated due to the rapid nitridation reaction of the Si powder during the nitriding process, so that the temperature of the nitride rapidly increases, and large silicon nitride crystals are formed in the nitriding process. As a result, the silicon nitride crystal grows abnormally in the baking process, so that the average grain size may exceed 15 μm. Further, when the average particle diameter of the Si powder exceeds 50 μm, large Si particles are nitrided in the nitriding process to generate large silicon nitride crystals, and the large silicon nitride crystals further grow abnormally in the firing process. The particle size may exceed 15 μm. By setting the specific surface area of the degreased body to ² to 30 m ² / g, it is possible to suppress a large amount of heat generation due to the rapid nitriding reaction of the Si powder in the nitriding step, and even when large silicon nitride crystals are generated in the nitriding step. Since the grain growth of the silicon nitride crystal is suppressed during firing, it becomes possible to control the average grain size of the major axis of the silicon nitride body crystal to 15 μm or less.

  Next, in order to make the second metal silicide a member for a molten metal containing an adjacent phase formed so as to surround the first metal silicide or the third metal silicide, the second metal element More than the first metal element, and 0.01 to 2% by mass of the first metal element and 1 to 10% by mass of the second metal element in the member for molten metal, The addition amount of the first metal element compound and the second metal element compound in the powder mixing step is controlled.

  By this manufacturing method, the adjacent phase precursor formed so that the second metal silicide precursor may surround the first metal silicide precursor or the third metal silicide precursor may be generated in the nitriding step. . When the first and second metal elements are mixed as impurities during the manufacturing process, the contents of the first and second metal elements are controlled by removing the impurities in the same manner as described above.

  In addition, by setting the average particle size of the powder made of the first metal element compound to 0.1 to 5 μm and the average particle size of the powder made of the second metal element compound to 1 to 30 μm, the surrounding second metal Since the content of silicide can be increased, it is possible to manufacture a member for a molten metal having further excellent thermal shock resistance.

  The reason is considered as follows. That is, when the average particle size of the powder composed of the second metal element compound is controlled to 1 to 30 μm, the second metal silicide becomes large crystals and is dispersed in the grain boundary layer at a high temperature during the firing step. Further, when the average particle diameter of the powder composed of the compound of the first metal element is controlled to 0.1 to 5 μm, the first metal element or the first metal which is extremely smaller than the second metal silicide at a high temperature during the firing step. Then, a liquid phase or metal silicide containing the second metal element is generated in the grain boundary layer. Furthermore, since the first metal silicide or the third metal silicide is crystallized while adjacent to the large second metal silicide crystal in the cooling process in the firing step, the second metal silicide is converted into the first metal silicide. The content of the adjacent phase formed so as to surround the material or the third metal silicide increases.

  The average particle diameter of the particles constituting the compound of the first and second metal elements can be determined by measuring the particle diameter of each particle by, for example, SEM photographs and averaging these particle diameters.

  Moreover, since the concentration of the metal silicide (at least one of the first to third metal silicides) on the surface of the molten metal member obtained by the dipping process or the exposure process is low, the mechanical characteristics and the heat resistance It becomes the member for molten metal which can suppress the adhering of a fixed substance and mixing of the detachment | desorption substance into a molten metal, improving impact property.

  In addition, as described above, when the member for molten metal according to the present invention is used as a member for molten metal that is exposed to molten metal, it is difficult for a fixed object to adhere to the molten metal member. However, the molten metal member is less likely to adhere to the fixed metal member than the conventional molten metal member, but when used as a molten metal member such as a stalk for Al molten metal, for example, the fixed object is slightly fixed. The fixed matter fixed in this way can be removed by immersion in the immersion step or exposure in the exposure step. The member for molten metal from which the solid matter has been removed in this way is originally a metal silicide concentration on the surface lower than the inside, so that it becomes a member for molten metal of the present invention and is suitably used as a member for molten metal repeatedly. can do.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

  First, as shown in Table 1, a stalk, which is a member for molten metal, was produced from a silicon nitride sintered body having various grain boundary layers, and a thermal shock test was performed.

Metal compound powders (powder 1 and powder 2) shown in Table 1, high-purity silicon nitride (Si ₃ N ₄ ) powder (average particle size 1 μm, α conversion 90%) as raw material powder, high-purity Si powder (average A mixed powder was prepared by mixing a Y ₂ O ₃ powder having a particle diameter of ₃ μm, an average particle diameter of 1 μm, and an Al ₂ O ₃ powder having an average particle diameter of 0.7 μm. At this time, the powder 1 and the powder 2 which are metal compound powders are wet pulverized using water, the average particle size of the powder after the wet pulverization is set to 0.8 to 1 μm, and then dried to prepare a premixed powder. After the production, a sample that had undergone a premixing step for producing a premixed powder and a raw material powder was also produced. The obtained mixed powder, ethanol, and silicon nitride grinding media were put into a barrel mill and mixed. Thereafter, polyvinyl alcohol (PVA) was added and mixed as an organic binder to the obtained slurry, and granulated with a spray dryer. The obtained granulated powder was degreased by obtaining a plurality of cylindrical shaped bodies having an outer diameter of 180 mm, an inner diameter of 157 mm, and a length of about 1205 mm, and holding the shaped body at 600 ° C. for 3 hours in a nitrogen atmosphere. In Table 1, the content of the metal compound powder is converted into a metal element, and the mass ratio of the Si powder is converted into Si ₃ N ₄ . Moreover, it was 10-15 m < ² > / g when the specific surface area of the degreased body was measured by the BET method.

The obtained degreased body was placed in a carbon mortar whose surface was covered with sintered silicon crystal particles of silicon nitride, and the nitrogen-containing partial pressure of 150 kPa consisting essentially of nitrogen was at 1050 ° C. for 20 hours. Nitriding is carried out by sequentially holding at 1250 ° C. for 10 hours, and further heating and holding for 3 hours at 1500 ° C. in a nitrogen partial pressure of 120 kPa, 10 hours at 1770 ° C., and 3 hours at 1800 ° C. in a nitrogen partial pressure of 200 kPa. Then, the temperature was lowered at 200 ° C./hour and fired to obtain a sintered body made of a β-type silicon nitride sintered body. The produced sintered body was surface-treated using the dipping process or the exposure process shown in Table 1 to obtain a cylindrical stalk (outer diameter 150 mm, inner diameter 130 mm, length 1000 m) which is a member for molten metal of the present invention. . The dipping process was a method of dipping in a hydrochloric acid aqueous solution having a pH shown in Table 1 for a predetermined time, washing with water, and drying. In the exposure step, the sample was placed in a chamber, and the sample was exposed for a predetermined time while flowing a CF ₄ gas into the chamber, followed by washing with water and drying.

  The following evaluation was performed using Stoke, which is a sample of the present invention produced as described above.

  First, the crystal phase of the grain boundary layer in the sample was examined, and when the metal boundary was contained in the grain boundary layer, this crystal structure was identified. That is, a sample was processed using an ion thinning device manufactured by Technology-Linda, a lattice image by electron beam diffraction of the grain boundary layer was observed using a transmission electron microscope JEM2010F manufactured by JEOL, and the lattice image was analyzed. When a plurality of metal silicides were contained in one sample, the crystal structure of the metal silicide contained most was identified.

  Moreover, the density | concentration of the metal silicide of the surface which mirror-polished the surface of the sample and the inside of the sample was measured as follows using the X-ray microanalyzer (JEOL Co., Ltd. JXA-8600M).

The intensity of fluorescent X-rays (characteristic X-rays) of metal elements (E _M ) such as Fe and Cu generated by irradiating the sample surface and the mirror-polished surface of the sample respectively with X-rays as follows: Measured. Fluorescent X-rays (characteristic X-rays) of each metal element (E _M ) were incident on a high-resolution proportional counter, amplified by an amplifier circuit such as a preamplifier, and further decomposed for each energy by a multichannel analyzer. Here, the elements (Fe, Cu, etc.) to be measured were designated, and the count number (intensity) of fluorescent X-rays counted by setting the energy window specific to these elements was output. In order to make the measurement conditions the same, the area of the sample, the intensity of the irradiated X-ray, the time for counting the fluorescent X-rays, and the like were the same. The count number of the fluorescent X-rays of each metal element on the sample surface measured in this way is, for example, C _Fe1 and C _Cu1 for Fe and Cu, and the count number of fluorescent X-rays of each element of Fe and Cu inside the sintered body is C. _Fe2 and _CCu2 were used. The ratio of the concentration of the metal silicide inside and on the surface of the sintered body was calculated by C _Fe1 / C _Fe2 for Fe silicide and C _Cu1 / C _Cu2 for Cu silicide, for example. The ratio between the surface and the interior was similarly determined for other metal silicides. When the metal silicide contains a plurality of metal elements, the concentration of the metal silicide on the sintered body surface is lower than the inside of the sintered body when the concentration of at least one metal silicide is lower than the inside on the surface. did. Further, the concentration of the metal silicide is 1 / n (n is an arbitrary numerical value larger than 1) compared to the inside, for example, the smaller one of C _Fe1 / C _Fe2 and C _Cu1 / C _Cu2 Was 1 / n or less.

  The particle diameter of silicon nitride was determined by measuring and averaging the long diameters of particles in an arbitrary 200 μm × 200 μm region of the mirror-polished sintered body cross section.

  Moreover, after putting the stalk of a sample into a thermostat and hold | maintaining at 25 degreeC, it injected into each Al molten metal of 700 degreeC and 800 degreeC, and gave the thermal shock, and confirmed the presence or absence of the stalk crack or the crack.

  In addition, while immersing the obtained stalks in the molten aluminum (the molten liquid surface and the stalk length direction are perpendicular), the molten aluminum is cast into the casting mold provided on the upper part of the stalk through the inner circumference of the stalk. After casting 1000 times, the inner circumference of the stalk was observed. Before starting casting, the stalk of each sample was gradually heated to 200 to 300 ° C., and then a casting test was performed.

  Further, a test piece according to JIS R1601 was cut out from the sample, and the bending strength (average of 7 pieces) was measured by a 4-point bending test. Moreover, the fracture toughness value was measured by the SEPB (single edge pre-cracked beam) method. Moreover, the presence or absence of the adjacent phase of each sample was measured as follows. The sample cross-section is mirror-polished, and an area of about 500 μm × 500 μm of the mirror surface (“area A”) is irradiated with an electron beam using an X-ray microanalyzer to measure the type and intensity of characteristic X-rays generated from the sample. Thus, the strength of each element of Si, the first and second metal elements (Fe, W) is mapped, and (1) the first portion containing Si and rich in the second metal element W The area of (W silicide), (2) The area of the second portion (Fe silicide) containing Si and rich in Fe, (3) The portion containing Si, Fe and W metal elements The area of (third silicide) is obtained, the area B of the part where at least two of the first to third parts (1) to (3) are in contact with each other is measured, and the ratio of the area B to the area A is determined. This ratio was calculated as the content (volume%) of the adjacent phase.

  The results are shown in Tables 1 and 2.

In the stalk (sample Nos. 1 to 16) which is a sample of the present invention, the concentration ratio between the surface and the inside of the metal silicide in the grain boundary layer is 0.7 or less, the average particle size is 23 μm or less, and the bending strength is The fracture toughness value was as high as 550 MPa or more and 5.5 MPa · m ^1/2, and no cracks or cracks occurred even when charged in a 700 ° C. molten Al. In particular, a sample containing either Fe silicide or Cu silicide was not cracked or cracked even when it was put into an 800 ° C. molten Al. Moreover, although the fixed matter was formed with a thickness of 10 to 25 mm, it could still be used sufficiently as stalk. The thickness of the fixed material was smaller as the concentration ratio of the metal silicide was lower. In addition, the sample containing the adjacent phase had a particularly high bending strength of 840 MPa or more and a fracture toughness value of 6.5 MPa · m ^1/2 or more. Although not shown in the table, an amorphous phase containing RE, Al, and O was present in the grain boundary layers of all the samples of the present invention.

On the other hand, as a comparative example, when a metal compound composed of a metal element having a metal silicide with a lower surface concentration than the inside but having a melting point of less than 1000 ° C. is used, no metal silicide is present (sample No. 17 to 19, 20-22) had a bending strength of 650 MPa or less and a fracture toughness of 4.8 MPa · m ^1/2 or less. Further, it was found that because the fixed matter having a thickness of 40 to 65 mm was fixed, the inside of the stalk was almost blocked by the fixed matter, and as a result, it was impossible to repeatedly use it as stalk. Moreover, in the thermal shock test performed by throwing in Al molten metal, all the samples cracked or the crack generate | occur | produced.

An iron oxide (Fe ₂ O ₃ ) powder having an average particle size of 0.4 μm and a WO ₃ powder having an average particle size of 0.6 μm are mixed so that the mass conversion ratio of Fe and W is 3: 1, and the same as in Example 1. A premixed powder was prepared. The same silicon nitride powder and Si powder as in Example 1 are mixed with this premixed powder, and iron oxide powder, WO ₃ powder, silicon nitride powder, and Si powder (in terms of Si ₃ N ₄ ) are each 1.5% by mass. 0.5% by mass, 10% by mass, 70% by mass (subtotal 82% by mass) were used as base compositions.

Next, a total of 18 masses of a powder composed of an oxide of a Group 3 element (RE ₂ O ₃ ) having an average particle diameter of 0.5 μm, an Al ₂ O ₃ powder having an average particle diameter of ₃ μm, and an SiO ₂ powder having an average particle diameter of 2 μm. The total amount (100% by mass in total) was mixed in ethanol, and granulated, molded, and degreased in the same manner as in Example 1 to produce a degreased body. The obtained defatted body was placed in a silicon nitride-based mortar, and in a nitrogen partial pressure of 150 kPa consisting essentially of nitrogen, 1050 ° C for 20 hours, 1120 ° C for 10 hours, 1170 ° C for hours, 1300 ° C. Sequentially held at each step for 3 hours (the temperature was raised at a rate of temperature increase of 25 ° C./hour between each step), and after nitriding Si into Si ₃ N ₄ with an α conversion rate of 90% or more, the temperature was further raised to 120 kPa. 3 hours at 1500 ° C. in a nitrogen partial pressure, 10 hours at 1770 ° C., 3 hours at 1800 ° C. in a nitrogen partial pressure of 200 kPa, followed by lowering the temperature at a cooling rate of 200 ° C./hour and firing. Obtained. The obtained sintered body was immersed in an aqueous hydrochloric acid solution having a pH of 1.5 for 60 minutes, washed with water, and dried to produce stalk, which is a sample of the present invention.

  In the same manner as in Example 1, a test piece was cut out from the obtained sample, and bending strength and fracture toughness were measured. Further, the bending strength at 1000 ° C. was measured.

The contents of RE ₂ O ₃ and Al ₂ O ₃ were quantitatively analyzed by ICP emission spectroscopic analysis of the RE content and Al content, and further converted into RE ₂ O ₃ and Al ₂ O ₃ (the RE thus converted). The total content of ₂ O ₃ and Al ₂ O ₃ is G). The SiO ₂ content is the remainder obtained by measuring the total oxygen content with an oxygen analyzer manufactured by LECO and excluding the oxygen content contained in the total G of RE ₂ O ₃ and Al ₂ O ₃ from the total oxygen content. The amount of oxygen was calculated in terms of SiO ₂ .

  Further, the presence or absence of an adjacent phase was examined in the same manner as in Example 1.

The results are shown in Table 3. All samples contained an adjacent phase. Further, the strength at room temperature was 780 MPa or more, the bending strength at 1000 ° C. was 690 MPa or more, and the fracture toughness value was 6 MPa · m ^1/2 or more. In particular, as RE, samples using Y, Er, Yb, and Lu have a bending strength at room temperature of 830 MPa or more, a bending strength at 1000 ° C. of 800 MPa or more, and a fracture toughness value of 6.5 MPa · m ^1/2 or more. Especially excellent.

Fe ₂ O ₃ powder (average particle size 1 μm) and WO ₃ powder (average particle size 1 μm) were pre-pulverized with water and dried to prepare a pre-mixed powder having an average particle size of 0.6 μm. Here, the ratio of Fe ₂ O ₃ powder and WO ₃ powder was 10:70 in terms of mass ratio converted to Fe and W. In addition, silicon nitride powder (average particle size 1 μm, pregelatinization rate 90%, Fe impurity content 200 ppm) and Si powder (average particle size 3 μm, Fe impurity content 300 ppm) were prepared. Using the obtained premixed powder, Fe ₂ O ₃ powder, WO ₃ powder, silicon nitride powder, and Si powder were each in a mass ratio of 10: 70: 1: 1 (the mass ratio of the iron oxide powder was converted to Fe, WO ₃ powder mass ratio of W in terms, the mass ratio of Si powder for the powder 100 parts by mass were weighed mass ratio) in the _Si 3 _{N 4} basis, _Y 2 _{O 3} powder having an average particle diameter of 0.5μm to 15 7 parts by weight of Al ₂ O ₃ powder having an average particle diameter of 0.7 μm and 1 part by weight of SiO ₂ powder having an average particle diameter of 2 μm were added, mixed and granulated. Using the obtained granulated body, a cylindrical shaped body having a length of 200 mm, an outer diameter of 150 mm, and an inner diameter of 130 mm was produced at a molding pressure of 80 MPa. The obtained molded body was degreased in the same manner as in Example 1, and nitrided and fired in the same manner as in Example 1. The molded body was placed in a furnace and fired in a state where the cylindrical concentric shaft of the molded body lay down.

The obtained sintered body was immersed in an aqueous hydrochloric acid solution having a pH of 2 for 60 minutes, washed with water and dried in the same manner as in Example 1 to prepare stalks. This stalk could be used for molten Al. These samples have a shape in which the radial direction is crushed by their own weight, and the deformation rate (%) is obtained by 100 × {(maximum outer diameter portion) − (minimum outer diameter portion)} / (maximum outer diameter portion). It was. Further, the obtained sample cross-section is mirror-polished, and the area of the grain boundary layer portion is measured by excluding silicon nitride crystals from an arbitrary 200 μm × 200 μm (area 40000 μm ² ) region of the mirror surface. The area ratio of the grain boundary layer was determined by dividing the area of the layer portion by 40000 μm ² , and this area ratio was multiplied by 100 to obtain the content (volume%) of the grain boundary layer.

As shown in Table 4, the sample having a grain boundary layer content exceeding 20% by volume tended to have an extremely large deformation rate, but the sample having a grain boundary layer content of 20% by volume or less had a deformation rate. Was confirmed to be small.

It is a schematic diagram of the SEM photograph of the member for fusion-resistant metals of this invention.

Explanation of symbols

10: Cross section of member for molten metal 12: Crystal of silicon nitride 14: Adjacent phases 16, 16a, 16b, 16c: First metal silicide 18, 18a, 18b, 18c: Second metal silicide 20: Grain boundary layer 22: Third metal silicide

Claims (11)

A member for a fusion-resistant metal comprising a silicon nitride sintered body having a crystal of silicon nitride and a grain boundary layer containing a metal silicide composed of at least one metal element having a melting point of 1000 ° C. or higher, A member for a fusion resistant metal, characterized in that the concentration of metal silicide on the surface of the silicon nitride sintered body is lower than the inside. The member for molten metal according to claim 1, wherein the metal element is at least one of Fe and Cu. The member for molten metal according to claim 2, wherein the metal silicide is contained in an amount of 0.01 to 10% by mass in terms of total Fe and Cu. The member for a fusion resistant metal according to any one of claims 1 to 3, wherein a concentration of the metal silicide on the surface of the silicon nitride sintered body is ½ or less compared to the inside. The member for molten metal according to any one of claims 1 to 4, wherein the grain boundary layer contains an amorphous phase composed of Group 3 elements (RE), Al and O in the periodic table. The molten metal member according to claim 5, wherein the RE is at least one of Y, Er, Yb, and Lu. The resistance ratio according to claim 1, wherein the ratio of Si and RE contained in the grain boundary layer is 0.2 to 10 in terms of a molar ratio of SiO ₂ / RE ₂ O _3. Molten metal parts. According to claim 1, wherein the ratio of Al and RE contained in the grain boundary _layer, characterized in that a 0.2 to 5 molar ratio in terms of _{Al 2 O 3 / RE 2 O} 3 A member for anti-melting metal. 2. The silicon nitride crystal is a needle crystal, wherein the needle crystal has a major axis having an average diameter of 30 μm or less and a needle crystal having a minor axis of 2 μm or less. The member for molten metal according to any one of -8. The metal silicide contains a first metal silicide made of a metal element containing at least one of Fe and Cu, and a second metal silicide made of a metal element containing at least one of W and Mo, The member for molten metal according to any one of claims 1 to 9, wherein the first metal silicide and the second metal silicide form an adjacent phase in contact with each other. It is a manufacturing method of the member for fusion-resistant metals in any one of Claims 1-10, Comprising: After shape | molding and baking a predetermined | prescribed raw material powder, the obtained sintered compact is immersed in aqueous solution below pH3? Or a method for producing a member for a molten metal which is exposed to a gas comprising a halide.

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