JP6719976B2 - Electrode material and spark plug electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrode material used as an electrode material for a spark plug provided in an engine that uses alcohol fuel, and a spark plug electrode. In particular, the present invention relates to an electrode for a spark plug which is excellent in corrosion resistance in an environment where alcohol fuel is used, and is also excellent in spark wear resistance and oxidation resistance, and an electrode material suitable for the material of such an electrode.

There is a spark plug as a vehicle engine part. The spark plug typically includes a rod-shaped center electrode and a ground electrode that is arranged opposite to the end face of the center electrode in a spaced-apart state.A spark discharge is generated between the electrodes, and the spark discharge flows between the electrodes. Ignition of the fuel mixture gas to be performed. Patent Document 1 discloses a spark plug used in an engine that uses alcohol fuel. In addition, Patent Document 1 discloses a configuration in which the outer periphery of a core portion made of copper or a copper alloy is surrounded by a nickel alloy as a center electrode provided in the spark plug.

On the other hand, Patent Document 2 discloses that a spark plug electrode having excellent high-temperature oxidation resistance and corrosion resistance is made of a nickel alloy having a specific composition.

JP, 2013-055022, A JP, 2014-029002, A

It is desired that an electrode of a spark plug provided in an engine that uses alcohol fuel has excellent corrosion resistance, spark consumption resistance, and oxidation resistance. Further, there is a demand for an electrode material capable of obtaining an electrode for a spark plug which is excellent in corrosion resistance in an environment where alcohol fuel is used, and is also excellent in spark wear resistance and oxidation resistance.

Conventionally, when a spark plug electrode made of a nickel alloy is used in an engine that uses alcohol fuel, the cause of corrosion and a structure having excellent corrosion resistance have not been sufficiently studied.

Therefore, one of the objects of the present invention is to provide an electrode material from which an electrode for a spark plug having excellent corrosion resistance in an environment where alcohol fuel is used, as well as spark wear resistance and oxidation resistance can be obtained. ..

Another object of the present invention is to provide an electrode for a spark plug which is excellent in corrosion resistance in an environment where alcohol fuel is used, and is also excellent in spark consumption resistance and oxidation resistance.

The electrode material according to one aspect of the present invention is, in mass %, a total of 0.05% or more and 0.5% or less of rare earth elements, 1.1% or more and 2.5% or less of Mn, and at least one of Al and Cr. Is less than 0.01%, Si is contained in a range where Si/Mn is 0.5 or more and less than 1.1, and the balance is Ni and inevitable impurities.

INDUSTRIAL APPLICABILITY The electrode material of the present invention can form an ignition plug electrode that is excellent in corrosion resistance in an environment where alcohol fuel is used, and is also excellent in spark wear resistance and oxidation resistance.

[Description of Embodiments of the Present Invention]
The present inventors have examined the cause of corrosion and a structure having excellent corrosion resistance in the case where the electrode for a spark plug provided in an engine using alcohol fuel and the electrode material as the material thereof are made of a nickel alloy. As a result, the following findings were obtained. As a result of component analysis of the corroded electrode, elements other than the electrode constituent elements such as S (sulfur) were included. S is an element that forms a compound with Ni, and since the melting point of this compound is low (generally about 800° C. or lower), S adhering to the electrode forms a compound with Ni, locally lowering the melting point. It is considered that Ni around this compound was corroded. It is considered that elements such as S were contained in the engine oil, and it is considered that what was mixed in the combustion chamber with time was dissolved in alcohol and adhered to the electrodes and the electrodes were corroded. Therefore, an engine that uses alcohol fuel is considered to be an environment in which corrosive elements such as S may exist over time, and in order to enhance the corrosion resistance in such a usage environment, a specific element is contained in a specific range. It was found that it is preferable to use a nickel alloy. Based on the above findings, the present invention defines that the electrode material is composed of a nickel alloy having a specific composition. First, the contents of the embodiments of the present invention will be listed and described.

(1) The electrode material according to the embodiment is, in mass %, a total of rare earth elements of 0.05% or more and 0.5% or less, Mn of 1.1% or more and 2.5% or less, and at least one of Al and Cr. Is less than 0.01%, Si is contained in a range where Si/Mn is 0.5 or more and less than 1.1, and the balance is Ni and inevitable impurities. Si/Mn is the mass ratio of the Si content to the Mn content. The content of Al and Cr includes 0% by mass.

Since the above electrode material is composed of a nickel alloy with a specific composition, it has excellent corrosion resistance when used as an electrode material for a spark plug equipped in an engine that uses alcohol fuel, and also has excellent spark wear resistance and oxidation resistance. Is also excellent. The details are considered as follows.

(A) Mn is an element that forms a compound with S, and the melting point of the formed compound (about 1600° C.) is higher than the melting point of Ni (about 1450° C.). Moreover, Mn has a lower sulfide formation free energy than Ni. Therefore, it is considered that S and Mn easily form a compound before the corrosion element such as S and Ni form a compound, and corrosion of Ni (combination with S or the like) can be reduced. Further, since the compound of S and Mn has a high melting point and can stably exist even in a high temperature environment, it is possible to suppress corrosion around the compound (particularly Ni).
(B) Since Si is contained in a specific range as compared with Mn, although it contains a relatively large amount of Mn, it has excellent oxidation resistance. When Si is sufficiently contained as compared with Mn, an oxide film can be formed on the surface when used as an electrode of a spark plug. By the oxide film formed after this, the invasion of oxygen from the surface to the inside can be reduced and the internal oxidation can be suppressed.
(C) Since the rare earth element is contained in a specific range, the crystal can be made fine. Therefore, even if oxygen or a corrosive element from the outside tries to penetrate the inside of the electrode along the crystal grain boundary, the long grain boundary can suppress the degree of penetration (depth) from becoming deep, and internal corrosion, Internal oxidation can be suppressed.
By the above (b) and (c), internal oxidation can be suppressed, and it is easy to reduce the occurrence of cracks in the oxide film and peeling of the oxide film due to the excessive increase in thickness of the oxide film due to the progress of internal oxidation. An oxide film having an appropriate thickness can be maintained well. Therefore, the effect of suppressing internal corrosion due to the provision of the oxide film can be expected, and it is considered that excellent corrosion resistance can be maintained for a long period of time.
(D) Cr and Al, which tend to increase the specific resistance, are not contained, or even if they are contained very little, and Mn, Si, and a rare earth element are contained in a specific range, an increase in the specific resistance is suppressed, The consumption due to sparks can be reduced.
When Al is contained in a specific range, the oxidation suppressing effect can be further enhanced together with Si, and the oxidation resistance is more excellent. When Cr is contained in a specific range, the effect of suppressing internal oxidation can be further enhanced, and the oxidation resistance is more excellent.

By using the above electrode material, a spark plug electrode having excellent corrosion resistance in an environment where alcohol fuel is used, and also having excellent spark wear resistance and oxidation resistance can be obtained.

(2) As an example of the above-mentioned electrode material, a mode in which Ti is contained in an amount of 0.02% or more and 0.6% or less by mass% can be mentioned. This electrode material is, in mass%, a total of rare earth elements of 0.05% or more and 0.5% or less, Mn of 1.1% or more and 2.5% or less, and at least one of Al and Cr less than 0.01%. , Ti in the range of 0.02% to 0.6%, Si in the range of Si/Mn of 0.5 to less than 1.1, and the balance Ni and unavoidable impurities.

Since the above-described form contains Ti in a specific range, further suppression of internal oxidation and refinement of crystals can be expected.

(3) As an example of the above electrode material, there may be mentioned a form in which the rare earth element contains at least one of Y and Nd.

Among the rare earth elements, Y and Nd are more excellent in the crystal refining effect. Therefore, the above-described embodiment is enhanced in the crystal refining effect and is more excellent in corrosion resistance and oxidation resistance.

(4) As an example of the above electrode material, a mode in which C is contained in an amount of 0.005% or more and 0.05% or less by mass% can be mentioned. This electrode material is, in mass%, a total of rare earth elements of 0.05% or more and 0.5% or less, Mn of 1.1% or more and 2.5% or less, and at least one of Al and Cr less than 0.01%. , C is contained in the range of 0.005% to 0.05%, Si is contained in the range of Si/Mn of 0.5 to less than 1.1, and the balance is Ni and inevitable impurities.

The above-described form is excellent in corrosion resistance, spark wear resistance, and oxidation resistance, and also has effects such as high temperature strength and excellent workability.

(5) As an example of the above-mentioned electrode material, there is a mode in which the specific resistance of the above-mentioned electrode material at room temperature is 25 μΩ·cm or less.

The above-mentioned form has a low specific resistance and excellent spark wear resistance.

(6) As an example of the above electrode material, when the above electrode material is heated at 1100° C. for 50 hours, an average crystal grain size of the electrode material after the heating is 300 μm or less.

It can be said that the above heating conditions simulate a state of being maintained at about 1100° C. for a long time when used as an electrode of an ignition plug. In this case, it can be said that the above-described form can maintain the state in which the crystal grains are hard to grow (become coarse) and the average crystal grain size is small. Therefore, the above-described embodiment can maintain a long crystal grain boundary even when exposed to an environment of about 1100° C. for a long time when used as an electrode of a spark plug provided in an engine using alcohol fuel, and Oxygen and corrosive elements are less likely to enter the inside of the electrode along the grain boundaries, and thus have excellent corrosion resistance and oxidation resistance.

(7) As an example of the above electrode material, when the above electrode material is heated at 1100° C. for 50 hours, the thickness of the oxide film formed on the surface of the electrode material after heating is 400 μm or less. ..

It can be said that the above heating conditions simulate a state of being maintained at about 1100° C. for a long time when used as an electrode of an ignition plug. In this case, the above-described embodiment has an oxide film having an appropriate thickness without being too thick, and it can be said that the oxide film is unlikely to be cracked or the oxide film is difficult to peel off. Therefore, the above-described embodiment has excellent oxidation resistance and also has good corrosion resistance due to the provision of the oxide film.

(8) The spark plug electrode according to the embodiment is made of any one of the electrode materials (1) to (7).

The above-mentioned spark plug electrode is composed of an electrode material having the above-mentioned specific composition, and therefore has excellent corrosion resistance when used as an ignition part of an engine using alcohol fuel, as well as spark consumption resistance and oxidation resistance. Is also excellent.

[Details of the embodiment of the present invention]
Hereinafter, the electrode material, the spark plug electrode, and the spark plug according to the embodiment of the present invention will be sequentially described in detail. Unless otherwise specified, the content of elements is mass %.

-Electrode Material-Composition The electrode material of the embodiment contains a rare earth element, Mn, and Si as essential addition elements, and the balance is Ni and a nickel alloy that is an unavoidable impurity. In addition to the above-mentioned essential additional elements, at least one element of Ti, Al, and Cr or C can be included. When Al and Cr are contained, the content is made extremely small as described later.

By using Ni as the main component, specifically, by setting the Ni content to 90% or more, 95% or more, and 96% or more, the plastic workability is excellent and the specific resistance is small (the conductivity is high. ), excellent spark wear resistance when used as an electrode of a spark plug. The larger the amount of Ni, the more the specific resistance can be reduced, and the larger the content of the additional element, the higher the corrosion resistance and the oxidation resistance.

...Rare earth element A rare earth element exists mainly as an intermetallic compound. The electrode material of the embodiment suppresses crystal growth by the so-called pinning effect of this intermetallic compound and has a fine crystal structure. By refining the crystal and maintaining it, intrusion of corrosive elements and oxygen into the interior can be reduced, and internal corrosion and internal oxidation can be suppressed. A part of the rare earth element is allowed to exist as a solid solution in Ni, but it is preferable that the rare earth element exists as an intermetallic compound as described above, because the miniaturization effect is sufficiently obtained.

Of the 17 kinds of elements belonging to Group 3 of the periodic table, which are rare earth elements, it is possible to adopt a form containing only one kind of element or a form containing plural kinds of elements. In particular, it is preferable to contain at least one of Y (yttrium) and Nd (neodymium). This is because it is more excellent in the effect of refining the crystal.

As the content of the rare earth element (the total content in the case of containing a plurality of kinds of elements; the same applies to the following in this section) is more likely to make the crystal finer, the content of the rare earth element is set to 0.05% or more. Considering the improvement of the crystal refining effect, the content of the rare earth element is preferably 0.06% or more, more preferably 0.08% or more. If the content of the rare earth element is small to a certain extent, (1) it is difficult to increase the specific resistance, thermal deterioration of the electrode due to the increase in the specific resistance is suppressed, and the spark wear resistance is excellent, (2) the deterioration of plastic workability is suppressed. Therefore, the content of the rare earth element is set to 0.5% or less in order to produce the effect that the electrode having a predetermined shape is easily processed and the manufacturability of the electrode is excellent. Considering good spark consumption resistance, plastic workability, etc., the content of the rare earth element is preferably 0.45% or less, more preferably 0.4% or less, and 0.3% or less.

...Mn (manganese)
Mn is an element having an effect of improving corrosion resistance. Specifically, it is an element that forms a compound with a corrosive element such as S and has a lower melting point than Ni. When used as an electrode of a spark plug, at a high temperature, Mn combines with the above-mentioned corrosive elements before Ni and suppresses corrosion of Ni (combination with corrosive elements). A compound such as MnS containing Mn and a corrosive element such as S has a higher melting point than Ni and can stably exist even in a high temperature environment. As a result, Ni existing around the compound such as MnS becomes difficult to melt, and thus corrosion of Ni can be suppressed.

The higher the Mn content, the easier the formation of a compound with the above-mentioned corrosion element and the higher corrosion resistance. Therefore, the Mn content is 1.1% or more. Considering the improvement of corrosion resistance, the Mn content is preferably 1.2% or more, more preferably 1.3% or more, and 1.5% or more. If the amount of Mn is too large, the specific resistance increases and the spark wear resistance decreases. Further, although the internal oxidation can be suppressed when the Mn amount is large, the oxide film is easily peeled off when the Mn amount is too large, and the oxidation resistance is deteriorated due to the peeling of the oxide film. Therefore, the Mn amount is set to 2.5% or less. Considering suppression of increase in specific resistance and suppression of decrease in oxidation resistance, the amount of Mn is preferably 2.2% or less, more preferably 2.1% or less.

...Si (silicon)
Si is an element having a high oxidation suppressing effect. By containing Si, an oxide (oxide film) containing Si can be generated afterwards on the surface of the electrode when the spark plug is used as an electrode. This oxide film can reduce the invasion of oxygen into the electrode and suppress internal oxidation. By suppressing internal oxidation, it is possible to generate a dense and highly adherent oxide film and prevent it from becoming excessively thick, and by suppressing the occurrence of cracks, ruptures, and peeling due to thickening (porous), oxidation of an appropriate thickness The membrane can be maintained. This oxide film is also expected to contribute to the suppression of corrosion by reducing the penetration of corrosive elements into the electrode.

Here, as described above, although the oxide film is easily peeled off when the Mn amount is large, it is considered that when the Si amount is adjusted with respect to the Mn amount, Si functions like a wedge just below the oxide film. It was found that the peeling can be suppressed and good oxidation resistance can be obtained. Therefore, in the electrode material of the embodiment, the amount of Si is set to a specific range as compared with the amount of Mn. Specifically, the amount of Si is set to a range in which the mass ratio Si/Mn of the content of Si to the content of Mn satisfies 0.5 or more and less than 1.1. If the mass ratio Si/Mn is less than 0.5, the amount of Si is relatively small, and the effect of improving the oxidation resistance due to Si becomes insufficient, so that an oxide film is not sufficiently formed or peeling easily occurs. Therefore, it becomes difficult to maintain the oxide film. When the mass ratio Si/Mn is 1.1 or more, peeling of the oxide film due to excess Si occurs, and it becomes difficult to maintain the oxide film. Considering good corrosion resistance and formation and maintenance of a healthy oxide film, the mass ratio Si/Mn can be 0.51 or more and 1.09 or less, and further 0.52 or more and 1.08 or less. It is considered that the rare earth element also functions as a wedge just below the oxide film.

Specific Si amount is, for example, 0.9% or more and 2.0% or less, and further 1.0% or more and 1.5% or less. The larger the amount of Si, the easier it is to obtain an oxidation suppressing effect by forming an oxide film or suppressing peeling. The smaller the amount of Si, the more the increase in specific resistance can be reduced, and the more excellent the spark wear resistance is. Further, the oxide film is unlikely to be a porous thick film, cracking and peeling due to thickening can be suppressed, and an oxide film having an appropriate thickness can be more easily maintained.

...Al (aluminum)
Al is an element having a high oxidation suppressing effect, and if Al is also contained together with Si, the oxidation suppressing effect can be further enhanced. If the amount of Al is too large, damage and increase in resistivity due to the thickening of the oxide film described above are caused. Therefore, when Al is contained, the amount of Al is set to less than 0.01%, preferably 0.008% or less, and more preferably 0.005% or less. Since the electrode material of the embodiment uses Si, which has a higher oxidation suppressing effect than Al, as an essential element, it does not contain Al (Al content is 0%).

...Cr (chrome)
Cr has excellent resistance to corrosive elements and is also effective in suppressing internal oxidation. If the amount of Cr is too large, the specific resistance increases and the spark wear resistance decreases. Therefore, when Cr is contained, the Cr content is set to less than 0.01%, preferably 0.008% or less, and more preferably 0.005% or less. Since the electrode material of the embodiment essentially requires Mn having a high corrosion inhibiting effect and Si having a high oxidation inhibiting effect, it does not contain Cr (the Cr content is 0%).

...Ti (titanium)
Ti has an effect of refining crystals and contributes to suppression of internal corrosion and internal oxidation. The larger the amount of Ti, the easier it is to obtain a crystal refining effect, and the larger the amount of Ti, the more the resistivity increases, resulting in a decrease in spark wear resistance. Therefore, when Ti is contained, the Ti amount is preferably 0.02% or more and 0.6% or less. The larger the amount of Ti, the easier it is to obtain a crystal refining effect, and the amount of Ti is preferably 0.03% or more, more preferably 0.05% or more. Considering suppression of increase in specific resistance, the Ti amount is preferably 0.4% or less, more preferably 0.3% or less.

...Other elements B (boron) can be contained in excess of 0% and 0.05% or less, and further 0.001% or more and 0.02% or less. In this case, the hot workability is excellent, and the electrode material of the embodiment and the spark plug electrode of the embodiment are easily manufactured.
When C (carbon) is contained in the range of 0.005% or more and 0.05% or less, it is preferable because the high temperature strength can be increased while ensuring the workability. The C content is preferably 0.01% or more and 0.04% or less, and more preferably 0.015% or more and 0.03% or less.

-Structure The electrode material of the embodiment can maintain a fine crystal state even when it is held at about 1100°C for a long time by being composed of the above-mentioned specific composition. Specifically, the average crystal grain size after heating the electrode material of the embodiment at 1100° C. for 50 hours satisfies 300 μm or less. The electrode of the spark plug made of such an electrode material can suppress the intrusion of corrosive elements and oxygen into the inside, and is excellent in corrosion resistance and oxidation resistance. The average crystal grain size can be set to 290 μm or less, further 280 μm or less and 270 μm or less depending on the content of the above-mentioned additional element. The smaller the average crystal grain size, the longer the crystal grain boundary, and it is difficult for oxygen and corrosive elements from the outside to penetrate inside the electrode along the crystal grain boundary, so it is easy to suppress internal corrosion and internal oxidation, and a lower limit is set. Absent. Details of the heating conditions will be described in the oxidation test described later.

.. Specific resistance The electrode material of the embodiment has a small specific resistance because it is composed of the specific composition described above. For example, the specific resistance at room temperature (typically about 20° C.) may be 25 μΩ·cm or less. The specific resistance typically changes depending on the content of the additional element, and tends to decrease as the content decreases. Depending on the composition, the specific resistance can satisfy 22 μΩ·cm or less, and further 20 μΩ·cm or less. The lower the specific resistance, the more excellent the spark wear resistance tends to be, and the lower limit is not set. The smaller the content of the additional element and the closer to pure nickel, the smaller the specific resistance, but the poorer the corrosion resistance and the oxidation resistance.

.. State of Forming Oxide Film The electrode material of the embodiment may have an oxide film having a specific thickness when it is held at about 1100° C. for a long time because it is composed of the specific composition described above. Specifically, the thickness of the oxide film formed on the surface of the electrode material after heating the electrode material of the embodiment at 1100° C. for 50 hours is 400 μm or less. It can be said that such an oxide film is not too thick, cracks and peeling are unlikely to occur, and that it is easy to maintain a healthy state. When the electrode material of the embodiment is used as an electrode of a spark plug provided in an engine using alcohol fuel, an oxide film having such an appropriate thickness can be formed and can be well maintained. In addition to excellent corrosion resistance, this oxide film also provides excellent corrosion resistance. The thickness of the oxide film can be set to 390 μm or less, further 380 μm or less and 370 μm or less, depending on the content of the above-mentioned additional element. Note that this oxide film typically has a two-layer structure of an internal oxide layer and a surface oxide layer as shown in a test example described later, and the total thickness thereof is 400 μm or less. Details of the heating conditions will be described in the oxidation test described later.

-Shape As a typical shape of the electrode material of the embodiment, there is a wire rod that has been plastically processed including wire drawing. The cross-sectional shape includes various shapes such as a rectangular shape and a circular shape. The cross-sectional size and wire diameter can be selected as appropriate. For example, a rectangular wire having a rectangular cross section has a thickness of about 1 mm to 3 mm, a width of about 2 mm to 4 mm, and a circular wire having a circular cross section has a wire diameter of about 2 mm to 6 mm.

-Method of Manufacturing Electrode Material The electrode material of the embodiment can be typically manufactured by the steps of melting-casting-hot rolling-cold wire drawing and heat treatment. When the atmosphere during melting or casting is an atmosphere having a lower oxygen concentration than the air atmosphere, for example, a low oxygen atmosphere with an oxygen concentration of 10% by volume or less, oxidation of rare earth elements is suppressed, and rare earth element-containing intermetallics are suppressed. The compound is fully present in the electrode material.

When the final heat treatment is performed after cold drawing, the workability is improved by softening, the electrode material can be easily processed into a predetermined electrode shape, and the working strain introduced during plastic working such as wire drawing is removed to obtain a specific resistance. Can be reduced. The conditions of the final heat treatment include a heating temperature of 700° C. or higher and 1000° C. or lower, preferably 800° C. or higher and 950° C. or lower, and a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include an atmosphere having a low oxygen concentration (for example, an oxygen concentration of 10% by volume or less) such as a hydrogen atmosphere or a nitrogen atmosphere, or an atmosphere containing substantially no oxygen.

The shape of the wire rod can be changed by rolling after cold drawing. For example, the circular cross section can be changed to a rectangular cross section. The final heat treatment described above can be performed after rolling.

In addition, an electrode material having an oxide film in advance can be used. In this case, a heat treatment (oxidation treatment) for forming an oxide film is performed after the above-mentioned cold drawing, rolling, or final heat treatment. The conditions of the oxidation treatment include a heating temperature of 800° C. or more and 1100° C. or less, preferably 900° C. or more and 1000° C. or less in batch processing, and an atmosphere includes an atmosphere containing oxygen such as an air atmosphere. The oxidation treatment can be a continuous treatment using an electric heating furnace or an atmosphere furnace.

-Ignition plug electrode The ignition plug electrode of the embodiment is made of the electrode material of the above-described embodiment and is used as an ignition component provided in an engine that uses alcohol fuel. The spark plug electrode of the embodiment can be used as a center electrode, a ground electrode, or both. The spark plug electrode of the embodiment can be manufactured by cutting the electrode material of the above-described embodiment into an appropriate length, or further forming the cut material into a predetermined shape. In addition, an electrode having an oxide film can be formed by performing the above-mentioned oxidation treatment. The spark plug electrode of the embodiment substantially maintains the characteristics and properties of the electrode material of the above-described embodiment such as the composition, structure, and specific resistance.

-Ignition plug The above-described ignition plug including the electrode for the ignition plug can be used as an ignition component of an engine using alcohol fuel, typically an engine of an automobile. The spark plug is typically an insulator, a metal shell that holds the insulator, a center electrode that is held in the insulator and partially protrudes from the tip of the insulator, and the metal shell. One end of the ground electrode is welded to the surface on the front end side, and the other end is provided with a ground electrode provided so as to face the end surface of the center electrode, and a terminal fitting provided at the rear end of the insulator. The alcohol fuel is a fuel containing only alcohol or a mixed fuel containing alcohol and gasoline.

-Main effects of the embodiment The electrode material of the embodiment is composed of a specific composition, and in particular, by including Mn in a specific range, it is possible to suppress corrosion due to a corrosive element such as S. In addition, the electrode material of the embodiment can maintain a fine crystal structure well by containing a rare earth element in a specific range, and can contain an appropriate oxide film by containing Si in a specific range in comparison with the amount of Mn. Can be favorably formed and maintained. This oxide film can also be expected to reduce the penetration of corrosive elements into the interior. In addition, the electrode material of the embodiment has a small specific resistance because it has a specific composition. From these facts, the electrode material of the embodiment is excellent in corrosion resistance in an environment where alcohol fuel is used, and is also excellent in spark wear resistance and oxidation resistance. Details of these effects will be described in Test Example 1.

The spark plug electrode of the embodiment is composed of the electrode material of the above embodiment, and when used as an ignition part of an engine using alcohol fuel, it has excellent corrosion resistance, sparks wear resistance, and oxidation resistance. Is also excellent.

[Test Example 1]
A plurality of electrode materials made of nickel alloy were prepared and their characteristics were evaluated.

The electrode material (wire material) was produced as follows.
Using a normal vacuum melting furnace, a molten nickel alloy having the composition shown in Table 1 was prepared. The unit of composition is% by mass. "Si/Mn" is a mass ratio, and "impurities" are inevitable impurities.
As the raw material of the molten metal, commercially available pure Ni (99.0 mass% or more Ni) and grains of each additive element were used. The molten metal was refined to reduce and remove impurities and inclusions. Further, the refining condition was adjusted so that the C content was 0.05% by mass or less. The atmosphere was controlled so that the oxygen concentration would be low, melting was performed, the melt temperature was appropriately adjusted, and vacuum casting was performed to obtain an ingot.

The obtained ingot was reheated and forged to obtain a billet of about 150 mm square. This billet was hot-rolled to obtain a rolled wire rod having a wire diameter of 5.5 mmφ. This rolled wire rod was subjected to a combination of cold wire drawing and heat treatment to obtain a cold wire rod. Here, a round wire having a wire diameter of 2.5 mmφ and a round wire having a wire diameter of 4.2 mmφ were manufactured. A round wire having a wire diameter of 2.5 mmφ was further rolled and deformed into a rectangular cross section to obtain a rectangular wire of 1.5 mm×2.8 mm. A final heat treatment was applied to each of the rectangular wire and the round wire having a wire diameter of 4.2 mmφ to obtain a soft material. This soft material is used as a sample of electrode material.
The final heat treatment was carried out by continuous treatment with a heating temperature selected from 800° C. or higher and 1000° C. or lower and a non-oxidizing atmosphere (nitrogen atmosphere or hydrogen atmosphere).

<Composition>
When the composition of the electrode material (soft material) of each sample was examined by using an inductively coupled plasma (ICP) emission spectroscopy analyzer, it was the same as the composition shown in Table 1, and the additive elements shown in Table 1 and the balance Ni And inevitable impurities. Sample No. The Ni content of 1-1 to 1-7 is 96 mass% or more. In Table 1, “0 (zero)” is below the detection limit and indicates that the substance is not substantially contained. The composition can be analyzed by an atomic absorption spectrophotometric method as well as an ICP emission spectral analysis method.

<Organization>
The electrode material (soft material) of each sample was observed by a scanning electron microscope (SEM) to perform elemental analysis by energy dispersive X-ray analysis (EDX), or examined by using an electron beam microanalyzer (EPMA). However, it was confirmed that an intermetallic compound of a rare earth element and Ni was present.

<Specific resistance>
The specific resistance (μΩ·cm) of the electrode material (soft material) of each sample was measured. The results are shown in Table 2. The specific resistance (room temperature) was measured by a DC four-terminal method using an electric resistance measuring device (gage length GL=100 mm).

<Spark resistance>
The above-mentioned specific resistance (room temperature) of 25 μΩ·cm or less was evaluated as A because it was excellent in spark wear resistance, and a resistivity of more than 25 μΩ·cm was evaluated as C because it was inferior in spark wear resistance. The evaluation results are shown in Table 2.

<Oxidation resistance>
The electrode material (soft material) of each sample was heated, the thickness of the oxide film was examined, and the oxidation resistance was evaluated. Here, the following oxidation test was performed, and the thickness of the oxide film after this test was examined.
(Oxidation test)
The operation of putting in an atmospheric furnace heated to 1100° C., heating for 1 hour, taking out of the atmospheric furnace, air-cooling for 30 minutes, and heating again for 1 hour is repeated until the total heating time reaches 50 hours.

After the above oxidation test, the cross section of the sample was observed with an optical microscope (magnification: 50 to 200 times), and the thickness of the oxide film formed on the surface of the sample was measured using this microscope observation image (photograph). .. Each of the samples prepared in this test has a two-layered oxide film. Specifically, the oxide film of each sample includes a surface oxide layer that constitutes the outermost surface of the oxide film and its vicinity, and an internal oxide layer located inside the surface oxide layer. The surface oxide layer tends to have a large content of additional elements and a low content of Ni, and the inner oxide layer tends to have a high content of Ni.

In this test, the respective thickness (μm) and total thickness (μm) of the inner oxide layer and the surface oxide layer were measured. Further, when the total thickness of both oxide layers is 400 μm or less, it is B as excellent in oxidation resistance, and when 350 μm or less is extremely excellent in oxidation resistance, A, and the oxide film is peeled off is resistant to oxidation. It was evaluated as C because it was inferior to. The results are shown in Table 2.

As the thickness of the internal oxide layer, the average thickness from the boundary between the base material region composed of a nickel alloy and the internal oxide layer to the boundary between the internal oxide layer and the surface oxide layer was measured. As the thickness of the surface oxide layer, the average thickness from the boundary between both oxide layers to the outermost surface of the oxide film was measured. The average thickness can be easily obtained by performing image processing or the like on the microscope observation image (see Patent Document 2).

<Average grain size>
The average crystal grain size (μm) of the electrode material of each sample after the above-mentioned oxidation test (1100° C.×50 hours) was examined. The results are shown in Table 2. Here, the cross section of the sample is observed with an optical microscope (magnification is 50 to 200 times), and the average crystal grain size is calculated for this microscope observation image (photograph) by using the intersecting line method (line method). did.

<Corrosion resistance>
The corrosion resistance of the produced electrode material (soft material) of each sample was examined. Here, the following corrosion resistance test, in which the sample was covered with a corrosive agent and heated and held, was performed, and the corrosion state after this test was evaluated.
(Corrosion resistance test)
-Corrosion agent Powder of calcium sulfate:graphite = 80:20 in mass ratio Here, a salt (calcium sulfate) containing S (sulfur) as a corrosion element was used. However, when only a salt containing a corrosive element was used, it was excessively corroded. Therefore, a corrosive state was adjusted by adding a reducing agent such as graphite (carbon).
-Heat treatment conditions: 850°C x 4 hours, using heating furnace Here, each sample was placed in a heating furnace in a state of being covered with powder of a corrosive agent, and kept for a predetermined time.
-Evaluation of Corrosion After the lapse of the predetermined holding time (4 hours) described above, each sample was washed with water and then a cross section polisher (CP) cross section was taken to examine the degree of decrease in the cross sectional area. Here, the following reduction amount (%) of the cross-sectional area was obtained and evaluated in three levels. Table 2 shows the reduction amount (%) and the evaluation result.
Reduction amount of cross-sectional area (%)={(cross-sectional area before corrosion resistance test−cross-sectional area after corrosion resistance test)/cross-sectional area before corrosion resistance test)}×100
Reduction amount is 10% or less = very excellent corrosion resistance: A
Reduction amount is more than 10% and 20% or less = excellent corrosion resistance: B
Reduction amount is over 20% = poor corrosion resistance: C

The values shown in Table 2 are the resistivity, the thickness of the oxide film (total thickness), and the average crystal grain size of the measurement results of the round wire soft material and the rectangular wire soft material used as the electrode materials of each sample. Shows the results for soft materials with large values, and shows the evaluation results and the values for soft materials with large reductions in corrosion resistance. Table 2 also shows the results of comprehensive evaluation of corrosion resistance, spark consumption resistance, and oxidation resistance. The overall evaluation is A when all the three evaluations are A, B when at least one of the three evaluations is B, and C when at least one of the three evaluations is C. To do.

As shown in Table 2, the sample No. composed of a specific composition containing a rare earth element, Mn, Si, and appropriately Al, Cr, Ti in a specific range. It can be seen that 1-1 to 1-7 are not easily corroded when exposed to a use environment in which a corrosive element such as S (sulfur) may exist, and have excellent corrosion resistance. Specifically, the sample No. In Nos. 1-1 to 1-7, the corrosion resistance evaluations are A and B, and the above-mentioned reduction amount is small. In particular, the sample No. 1-1 to 1-7 and sample No. Looking at 1-103 and 1-104, it can be seen that when the Mn amount is about 2% by mass or more, the above-described reduction amount tends to be small, and the corrosion resistance is superior. The sample Mo. It can also be seen that 1-101 and 1-102 have a large amount of the above reduction and are inferior in corrosion resistance. From this result, it can be said that by setting the amount of Mn within a specific range, corrosion elements such as S (sulfur) may be present and the corrosion resistance is excellent in a use environment such as an automobile engine using alcohol fuel.

In addition, the sample No. It is understood that 1-1 to 1-7 have an oxide film having an appropriate thickness when exposed to a high temperature environment such as 1100° C., and have excellent oxidation resistance. Specifically, the sample No. In Nos. 1-1 to 1-7, the total thickness of the oxide film is 400 μm or less, and they are maintained soundly without peeling.

Sample No. One of the reasons why 1-1 to 1-7 are excellent in oxidation resistance is that Si is contained in a specific range with respect to the amount of Mn. This means that the sample No. 1-1 to 1-7, and sample No. It is supported by comparing and referring to 1-103 and 1-104. Sample No. with Si/Mn of 0.5 or more and less than 1.1. 1-1 to 1-7 have a healthy oxide film. Sample No. having Si/Mn of less than 0.5. 1-104, 1.1 or more sample No. In Nos. 1-103, the oxide film was peeled off and the oxidation resistance was poor. Sample No. Sample No. 1-104 has a large amount of Mn and is excellent in corrosion resistance, but the amount of Si is too small to maintain an oxide film. It is considered that 1-103 could not maintain the oxide film because the amount of Si was too large. Sample No. Although 1/102 had Si/Mn of 1.1 or more, it is considered that the oxide film could be maintained because the Mn amount was very small, but the Mn amount was too small and the corrosion resistance was poor.

Sample No. As another reason why 1-1 to 1-7 are excellent in corrosion resistance and oxidation resistance, it is considered that the rare earth elements can be uniformly dispersed and present and the crystal grains can be made fine. This means that the sample No. containing the rare earth element was used. Sample Nos. 1 to 1-7 in which the average crystal grain size does not include a rare earth element. This is supported by the fact that it is smaller than 1-103 and 1-104. In this test, the sample No. The average crystal grain size of 1-1 to 1-7 is 300 μm or less, and further 260 μm or less.

Further, the sample No. Each of 1-1 to 1-7 has a small specific resistance of 25 μΩ·cm or less, and it is understood that the spark wear resistance is excellent. Sample No. Although 1-103 has a large amount of Mn and is excellent in corrosion resistance, it is inferior in oxidation resistance as described above, and also has high specific resistance and inferior spark wear resistance.

From the above test results, an electrode material composed of a specific composition containing rare earth elements, Mn, Si, and appropriately Al, Cr, Ti in a specific range is used as a material for an ignition plug electrode provided in an engine using alcohol fuel. It was confirmed to be suitable. Further, the spark plug electrode made of this electrode material and the spark plug including the spark plug electrode are expected to have excellent corrosion resistance in an environment where alcohol fuel is used.

The present invention is not limited to these exemplifications, but is defined by the scope of the claims, and is intended to include meanings equivalent to the scope of the claims and all modifications within the scope. For example, the electrode material and the composition, shape, size, etc. of the electrode shown in Test Example 1 can be changed as appropriate. The composition can be made different between the ground electrode and the center electrode.

INDUSTRIAL APPLICABILITY The electrode material of the present invention can be used as a material for an electrode provided in an ignition plug of an automobile engine such as a four-wheeled vehicle or a two-wheeled vehicle. The spark plug electrode of the present invention can be used as a component of the spark plug. The spark plug of the present invention can be used for ignition parts such as the above engine.

Claims (6)

In mass %,
0.05% or more and 0.5% or less in total of rare earth elements,
Mn is 1.1% or more and 2.5% or less,
Less than 0.01% of at least one of Al and Cr,
Ti is 0.02% or more and 0.6% or less,
C is 0.005% or more and 0.05% or less,
The Si, Si / Mn is contained in a range satisfying 0.5 and 1.1, the remainder Ri Do Ni and incidental impurities, electrode material used for the electrode for the spark plug. The electrode material according to claim 1, wherein the rare earth element contains at least one of Y and Nd. Electrode material according to claim 1 or claim 2 specific resistance at room temperature of the electrode material is less than 25μΩ · cm. The electrode material according to any one of claims 1 to 3 , wherein when the electrode material is heated at 1100°C for 50 hours, the average crystal grain size of the heated electrode material is 300 µm or less. Upon heating the electrode material 1100 ° C. × 50 hours, according to any one of claims 4 thickness of the oxide film formed on the surface of the electrode material after the heating of claims 1 is 400μm or less Electrode material. An electrode for a spark plug, which is made of the electrode material according to any one of claims 1 to 5 .