JP2004218046A - Surface-treating method for cast iron article, and cast iron article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a high-quality surface-treated cast iron article which need not to be rustproofed by densifying the oxide film formed on the surface of the article by inhibiting the formation of a dispersion in the oxide film and inhibiting violent oxidation. <P>SOLUTION: An electric furnace 1 equipped with a furnace chamber 2 in which a cast article S is held and an electric heater 4 that heats the inside of the chamber 2 is used. The article S is held in the chamber 2, the inside of the chamber 2 is filled with inert gas, and the article S is heat-treated at a temperature of 700 to 930°C at the chamber 2 in an oxygen concentration of 0.1 to 5%, desirably, 0.5 to 1.5%, for 5 to 30 min, desirably, 12 to 15 min. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface treatment method for a cast iron product that provides an oxide film to a produced cast iron product, and a cast iron product having an oxide film formed thereon.
[0002]
[Prior art]
Conventionally, as a method for surface treatment of cast iron products, for example, so-called kiln firing, charcoal is arranged around a cast iron product, and this is heated to about 800 ° C. to 1000 ° C. to form an oxide film on the surface of the cast iron product. (See Non-Patent Document 1).
Conventionally, for example, there is a surface treatment method using an electric furnace. In this method, the temperature can be controlled, and the surface treatment is completed easily and in a short time.
[0003]
[Non-patent document 1]
Traditional crafts series "Nanbu Tekki" Akira Horie, first published in June 2000, published by Rikkensha [0004]
[Problems to be solved by the invention]
By the way, in such a conventional surface treatment method of cast iron products, in the former method of charcoal treatment, adjustment of the amount of charcoal and the amount of air is complicated, and the treatment temperature and the atmosphere gas concentration depend on the amount of charcoal and the amount of air. There is a problem that the oxide film on the surface of the cast iron product varies due to irregularities around the product, and a uniform product cannot be obtained. There is also a problem that the processing time becomes long.
In the latter method using an electric furnace, since a high concentration of oxygen exists around the cast iron product, an oxidation reaction occurs rapidly on the surface of the cast iron product. For this reason, there was a problem that rust prevention treatment was separately required, and the number of steps was increased.
[0005]
The present invention has been made in view of the above-described problems, and to prevent the oxide film from having a variation, to suppress the rapid oxidation, and to make the oxide film formed on the surface of the cast iron product dense, An object of the present invention is to provide a surface treatment method of a cast iron product capable of producing a high quality product that does not require rust prevention treatment, and a cast iron product having a dense oxide film.
[0006]
[Means to solve the problem]
In order to achieve such an object, the surface treatment method of a cast iron product of the present invention uses a furnace chamber in which the cast iron product is stored and an electric furnace equipped with an electric heater for heating the furnace chamber. In the surface treatment method for a cast iron product which is housed in a furnace chamber and heat-treated, the furnace chamber is filled with an inert gas, heat-treated at an oxygen concentration of 0.1 to 5%, and then cooled in the air. It has a configuration.
[0007]
Here, the cast iron product is ordinary cast iron or spheroidal graphite cast iron, for example, having the following components.
C 2.5-4.0%
Si 0.5-3.0%
Mn 0.4-1.0%
P 0.03-0.8%
S 0.05-0.12%
[0008]
Further, the cast iron product is obtained by injecting a melted product into a mold such as a sand mold, and then removing the mold and performing some finishing such as sand removal and deburring. The present invention performs the above-described heat treatment on such a cast iron product. The heat treatment of the present invention is a treatment different from annealing performed for the purpose of stress reduction or quenching for the purpose of hardening. Although a heat treatment technique performed in an inert gas has been conventionally used, this technique is for the purpose of changing the internal structure, and is different from the technique of performing surface treatment by controlling oxygen of the present invention.
[0009]
According to the configuration of the present invention, since the furnace chamber is filled with the inert gas and the heat treatment is performed with the oxygen concentration set to 0.1 to 5%, the rapid oxidation reaction can be suppressed, and the surface of the cast iron product can be suppressed. In this way, a dense oxide film can be uniformly formed. The oxide film is mainly composed of hematite (hematite Fe ₂ O ₃ ) and magnetite (magnetite Fe ₃ O ₄ ). That is, since the electric furnace is used, the processing temperature can be easily set, the temperature around the cast iron product can be made uniform, and the oxide film on the surface of the cast iron product can be uniformly generated without variation over the entire surface. In addition, since the furnace chamber is filled with an inert gas and the heat treatment is performed with the oxygen concentration set to 0.1 to 5%, the oxygen concentration in the electric furnace is reduced uniformly, so that the surface of the cast iron product is densely oxidized. A coating can be produced. As a result, the quality of the cast iron product can be improved, and the processing time can be reduced.
[0010]
The oxygen concentration is set to 0.5 to 1.5% as required. A dense oxide film can be more reliably formed on the surface of the cast iron product.
Further, the temperature in the furnace chamber is set to 700 ° C. to 930 ° C. as necessary. By setting the temperature in the furnace chamber to 700 ° C. to 930 ° C., a dense oxide film can be more reliably formed on the surface of the cast iron product.
In this case, it is effective to set the heat treatment time to 5 to 30 minutes, desirably, to set the heat treatment time to 12 to 15 minutes. A dense oxide film can be more reliably formed on the surface of the cast iron product, and an oxide film having an optimum thickness can be obtained. The heat treatment time is empirically less than 5 minutes, the thickness of the oxide film is not enough, and if it exceeds 30 minutes, the oxide film becomes too thick and the oxide film peels off, so that 12 to 15 minutes is effective. Within this range, and an optimum oxide film thickness can be obtained.
[0011]
Further, a cast iron product of the present invention for achieving the above object is a cast iron product having an oxide film formed on the surface by the above-described surface treatment method. Since a dense oxide film is uniformly formed on the surface of the cast iron product, the quality of the cast iron product is improved. In addition, since a dense oxide film is formed, rust prevention treatment can be made unnecessary, so that the number of man-hours can be reduced and a cast iron product can be manufactured at low cost.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a surface treatment method for a cast iron product according to an embodiment of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, the surface treatment method for a cast iron product according to this embodiment performs the surface treatment using an electric furnace. Examples of the cast iron products include various products cast in a sand mold or the like, for example, iron kettles, iron pots, wind chimes, and the like.
[0013]
FIG. 1 shows an electric furnace 1 used in the surface treatment method for a cast iron product of the present invention. The electric furnace 1 includes a furnace chamber 2 in which a cast iron product S is stored, and an electric heater 4 for heating the inside of the furnace chamber 2. Reference numeral 3 denotes a boat on which the cast iron product S is placed, and reference numeral 7 denotes an exhaust port having a diameter of about 40 mm for exhausting and sucking the furnace chamber 2.
[0014]
An electric heater 4 for heating the inside of the furnace chamber 2 is controlled by an electric heater control unit 5. The electric heater control unit 5 includes a temperature sensor 6 for measuring the temperature of the furnace chamber 2 and a furnace chamber processing temperature setting means (not shown). The set processing temperature and the temperature sensor set by the furnace chamber processing temperature setting means are provided. The temperature is compared with the temperature detected in step 6, and if the detected temperature is equal to or higher than the set processing temperature, the electric heater 4 is turned off so that the furnace chamber 2 is not heated, and the detected temperature is higher than the set processing temperature. When the temperature is low, a control function of turning on the electric heater 4 to heat the furnace chamber 2 is provided. By the synergistic effect of the electric heater control unit 5 and the tightness of the furnace chamber 2, the temperature distribution in the furnace chamber 2 can be made uniform and the processing temperature in the furnace chamber 2 can be set arbitrarily. Here, the inside of the furnace chamber 2 is controlled at 700 ° C. to 930 ° C.
[0015]
The electric furnace 1 includes an inert gas supply unit 10 that supplies an inert gas from the inert gas supply port 9 to the furnace chamber 2. As the inert gas, for example, an appropriate gas such as nitrogen (N ₂ ) and argon (Ar) is used.
The inert gas supply unit 10 includes a flow control valve 11 for adjusting the flow rate of the inert gas, an opening / closing valve 12, and a pressure control valve 13 for adjusting the pressure. A predetermined flow rate of the inert gas can be supplied from the source 14 into the furnace chamber 2.
[0016]
Further, an inert gas control unit 15 that controls the opening and closing of the opening and closing valve 12 to control the supply of the inert gas is provided. The inert gas control unit 15 includes an oxygen concentration sensor 16 for detecting the oxygen concentration of the atmosphere in the furnace chamber 2 and an oxygen concentration setting means (not shown) for setting the oxygen concentration of the atmosphere in the furnace chamber 2. By comparing the oxygen concentration detected by the oxygen concentration sensor 16 with the set oxygen concentration set by the oxygen concentration setting means of the inert gas control unit 15, if the detected oxygen concentration is higher than the set oxygen concentration, the opening / closing valve 12 is opened. A control function is provided in which the inert gas is supplied to the furnace chamber 2 and if the detected oxygen concentration is the same or lower than the set oxygen concentration, the on-off valve 12 is closed and the inert gas is not supplied to the furnace chamber 2. .
[0017]
Due to the synergistic effect of the control of the inert gas control unit 15 and the hermeticity of the furnace chamber 2, the atmosphere gas in the furnace chamber 2 can be kept uniform. Here, the inert gas control unit 15 controls the oxygen concentration to 0.1 to 5%, preferably 0.5 to 1.5%. In the furnace chamber 2, gas in the furnace chamber 2 that cannot be accommodated in the furnace chamber 2 due to expansion of a gas due to supply of an inert gas or heating of the furnace chamber 2 is exhausted from an exhaust port 7. Further, the hermetic chamber 2 is improved in hermeticity so that gas cannot enter and exit from portions other than the exhaust port 7.
[0018]
Therefore, when the surface treatment of the cast iron product according to this embodiment is performed, the following is performed.
The cast iron product S here is manufactured, for example, according to the process shown in FIG. A sand mold (upper mold, lower mold) is formed in advance (1-1). When a core is used, for example, a core is formed by a shell mold method (1-2). The core is placed on the lower mold, and the upper mold is covered, and a mold is assembled (1-3).
[0019]
Then, a raw material (for example, 3.6% of C, 2.2% of Si) is dissolved at, for example, 1450 ° C. (1-4), and this is poured into a mold (1-5). When the raw material is cured, the upper die and the lower die are separated to take out the cast iron product S (1-6). Then, the molding sand is removed, deburring is performed, and if necessary, polished and finished (1-7). Quality inspection of dimensions and the like is also performed (1-8).
[0020]
Next, as shown in FIG. 3, a surface treatment according to the embodiment is performed.
First, as shown in FIG. 1, an electric furnace 1 is used, a cast iron product S is placed on a boat 3, the boat 3 is housed in a furnace chamber 2, and a furnace is provided to prevent gas from entering and exiting from portions other than the exhaust port 7. Chamber 2 is sealed. Next, the temperature of the furnace chamber 2 is set to 700 ° C. to 930 ° C. by the temperature setting means of the electric heater control unit 5, and the oxygen concentration in the furnace chamber 2 is set by the oxygen concentration setting means of the inert gas control unit 15. Is set to be 0.1 to 5%, preferably 0.5 to 1.5%. Then, the electric heater 4 for heating the inside of the furnace chamber 2 is turned on, and the heat treatment of the cast iron product S is performed (2-1). After the set processing temperature is reached, heating is performed for 5 to 30 minutes. When the heat treatment time is 12 to 15 minutes, a more optimal oxide film thickness can be obtained.
[0021]
In this process, the inert gas control unit 15 compares the oxygen concentration detected by the oxygen concentration sensor 16 with the set oxygen concentration set by the oxygen concentration setting means of the inert gas control unit 15, and calculates If the detected oxygen concentration is high, the on-off valve 12 is opened to supply the inert gas to the furnace chamber 2. If the detected oxygen concentration is the same or lower than the set oxygen concentration, the on-off valve 12 is closed to remove the inert gas. Stop supply. Therefore, a rapid oxidation reaction is suppressed, and a dense oxide film is generated on the surface of the cast iron product S.
[0022]
Thereafter, the cast iron product S placed on the boat 3 is taken out together with the boat 3 and allowed to cool in the air (2-2). In this manner, the surface treatment of the cast iron product S can be performed at a predetermined processing temperature in an atmosphere gas having a low oxygen concentration. Therefore, a dense oxide film is formed on the surface of the cast iron product S, which does not require rust prevention treatment. As the oxide film, a film of mainly hematite (hematite Fe ₂ O ₃ ) and magnetite (magnetite Fe ₃ O ₄ ) is formed.
Then, quality inspection for film formation is performed (2-3), and if necessary, coloring is performed (2-4) to obtain a product.
[0023]
【Example】
Next, examples of the present invention will be described together with comparative examples.
[Example]
The surface treatment method of the cast iron product S according to the embodiment uses nitrogen (N ₂ ) 99.5% as an inert gas to be supplied to the furnace chamber 2, and sets the processing temperature in the furnace chamber 2 to 880 ° C. and the furnace chamber 2. The oxygen concentration of the internal atmosphere was set to 3%, and the processing time was set to 12 minutes. The surface of the cast iron product S according to the example has an excellent structure in which the oxide film is dense and dense, as can be seen from the micrograph of the example shown in FIG.
[0024]
[Comparative example]
The surface treatment method of the cast iron product S according to the comparative example uses the atmosphere in the furnace chamber 2 as it is without supplying an inert gas, sets the processing temperature in the furnace chamber 2 to 880 ° C., and reduces the processing time. It is 12 minutes. As can be seen from the micrograph of the comparative example shown in FIG. 5, the surface of the cast iron product S according to the comparative example has a structure in which the oxide film is granular and cracks easily occur.
[0025]
In the examples, X-ray diffraction analysis of the surface was performed. FIG. 6 shows the results. It can be seen that a coating of hematite (Hematite Fe ₂ O ₃ ) and magnetite (magnetite Fe ₃ O ₄ ) was formed.
[0026]
In the electric furnace described in the above embodiment, the method of adjusting the amount of oxygen is not limited to the above method, and may be appropriately set, for example, by mixing and supplying a predetermined amount to an inert gas. You may.
[0027]
【The invention's effect】
As described above, according to the present invention, since the electric furnace is used, the processing temperature can be easily set and the temperature around the cast iron product can be made uniform, and the oxide film on the surface of the cast iron product varies over the entire surface. And can be produced uniformly. In addition, since the furnace chamber is filled with an inert gas and the heat treatment is performed with the oxygen concentration set to 0.1 to 5%, the oxygen concentration in the electric furnace is reduced uniformly, so that the surface of the cast iron product is densely oxidized. A coating can be produced. As a result, the quality of the cast iron product can be improved, and the processing time can be reduced. Moreover, since a dense oxide film is formed, rust prevention treatment can be made unnecessary, so that the number of steps can be reduced and a cast iron product can be manufactured at low cost. Further, in the case of performing rust prevention treatment, a further rust prevention effect can be expected due to a synergistic effect with a dense oxide film.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an electric furnace used in a method for treating a surface of a cast iron product according to an embodiment of the present invention.
FIG. 2 is a view showing a process of manufacturing a cast iron product used in the method for treating a surface of a cast iron product according to the embodiment of the present invention.
FIG. 3 is a process chart showing a method for surface treatment of a cast iron product according to an embodiment of the present invention.
FIG. 4 is a photomicrograph (magnification: 1000 ×) showing an oxide film on the surface of a cast iron product manufactured by the surface treatment method for a cast iron product according to the example of the present invention.
FIG. 5 is a photomicrograph (magnification: 1000 ×) showing an oxide film on the surface of a cast iron product manufactured by the surface treatment method for a cast iron product according to the comparative example.
FIG. 6 is a table showing the results of X-ray diffraction analysis of an oxide film on the surface of a cast iron product manufactured by the surface treatment method for a cast iron product according to the example of the present invention.
[Explanation of symbols]
S Cast iron product 1 Electric furnace 2 Furnace room 3 Boat 4 Electric heater 5 Electric heater control unit 6 Temperature sensor 7 Exhaust port 9 Inert gas supply port 10 Inert gas supply unit 11 Flow control valve 12 Open / close valve 13 Pressure control valve 14 Non Active gas supply source 15 Inert gas control unit 16 Oxygen concentration sensor

Claims (6)

A method for treating a surface of a cast iron product, comprising: using a furnace chamber in which a cast iron product is stored and an electric furnace including an electric heater for heating the furnace chamber, storing the cast iron product in the furnace chamber and performing heat treatment.
A surface treatment method for a cast iron product, wherein the furnace chamber is filled with an inert gas, the oxygen concentration is set to 0.1 to 5%, heat treatment is performed, and then the mixture is allowed to cool in the air. 2. The method according to claim 1, wherein the oxygen concentration is 0.5 to 1.5%. The surface treatment method for a cast iron product according to claim 1 or 2, wherein the temperature in the furnace chamber is set to 700C to 930C. The surface treatment method for a cast iron product according to claim 3, wherein the heat treatment time is 5 to 30 minutes. 5. The surface treatment method for a cast iron product according to claim 4, wherein the heat treatment time is 12 to 15 minutes. A cast iron product having an oxide film formed on the surface by the surface treatment method according to any one of claims 1 to 5.

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