JP5912986B2 - Electrode material, electrode for spark plug and spark plug - Google Patents

Description

  The present invention relates to an electrode material used as a constituent material of an electrode of a spark plug (ignition plug) of an internal combustion engine, an electrode made of the electrode material, and a spark plug including the electrode. In particular, the present invention relates to an electrode material from which an electrode for a spark plug excellent in oxidation resistance at high temperatures, spark wear resistance, and sweat resistance can be obtained.

  Conventionally, spark plugs are used for ignition of internal combustion engines such as automobile gasoline engines. The spark plug typically includes a rod-shaped center electrode and a ground electrode arranged so as to face the end face of the center electrode, and performs a spark discharge between the center electrode and the ground electrode. This discharge ignites the fuel mixture gas flowing between both electrodes.

  As the electrode material, Patent Document 1 discloses a nickel alloy containing Nd.

JP 2009-016278

  In recent years, it has been desired to improve the fuel efficiency of automobiles for environmental conservation measures. In order to improve fuel consumption, for example, raising the combustion temperature in an internal combustion engine can be mentioned. However, by further increasing the combustion temperature, the spark plug electrode has a higher temperature environment than before (for example, in the conventional general automobile gasoline engine, the highest temperature reached during use (about 900 to 1000 ° C.) +100 It will be used in a high temperature environment such as about ℃. Accordingly, it is desired that the electrode of the spark plug has sufficient usable characteristics even in a higher temperature environment, specifically, oxidation resistance, spark consumption resistance, and sweat resistance.

  The electrode of the spark plug disclosed in Patent Document 1 contains Nd or Y as an additive element, and makes it difficult for internal corrosion due to oxidation to occur due to the presence of an intermetallic compound of Nd, Y and Ni, or an additive element As a result, a second element such as Ti or Si is included, and an oxide of the second element is generated on the surface layer of the electrode, thereby enhancing oxidation resistance. In addition, the resistance to sparks is increased by reducing the specific resistance by reducing the content of the second element to less than 1% by weight and improving the thermal conductivity of the electrode. However, as a result of investigations by the present inventors, it cannot be said that this electrode has sufficient oxidation resistance and spark consumption resistance for use in further high temperature environments as described above.

  In addition, an electrode made of a nickel alloy having a very high Ni content, such as the electrode of a spark plug described in Patent Document 1, causes a phenomenon of so-called sweating in which grains containing Ni are formed on the electrode surface. obtain. Patent Document 1 does not fully examine this sweating phenomenon.

  The above sweat particles are formed by reacting Ni in the matrix with elements (Ca, P, etc.) in an atmosphere such as gasoline, and the surface of the electrode, in particular, the part where spark discharge is performed on the electrode (mainly It is considered that the adhesion occurs around the surfaces of the center electrode and the ground electrode facing each other), and the melting point of the adhesion portion is partially lowered to further increase the mother phase. If such sweat particles continue to be formed, the ignition state of the engine may become unstable, or in the worst case, the sweat particles may fall off and damage the engine. As described above, in a further high temperature environment, the matrix phase is easily melted, and thus it is desired to improve the anti-perspiration property as compared with the conventional electrode.

  Accordingly, an object of the present invention is to provide an electrode material from which an electrode of a spark plug excellent in high temperature oxidation resistance, spark wear resistance and sweat resistance can be obtained. Another object of the present invention is to provide a spark plug electrode excellent in high-temperature oxidation resistance, spark consumption resistance, and sweat resistance, and a spark plug including the electrode.

  As a result of investigations by the present inventors, Y is contained in a specific range, Si and Al are contained in a relatively small amount, and Cr and Mn are contained in a small amount, thereby being resistant to high-temperature oxidation and spark consumption. And the knowledge that an electrode material excellent in sweat resistance can be obtained. The present invention is based on the above findings.

  The electrode material of the present invention is used for an electrode of a spark plug, and in mass%, at least one of Al and Si is 0.01% or more and 0.4% or less, and less than 0.5% in total, and Cr is 0.05% or more and 0.8%. Hereinafter, it is made of a nickel alloy containing 0.05% or more and 0.8% or less of Mn, 1.5% or less of Cr and Mn in total, Y of 0.3% or more and 1.0% or less, with the balance being Ni and inevitable impurities.

  The electrode material of the present invention is composed of a nickel alloy containing a specific element in a specific range as described above, so that it can be used for an electrode used in a higher temperature environment than a conventional electrode material. Even if it is a case, it is hard to be oxidatively corroded and consumption by a spark can be suppressed. And even if it is a case where this invention electrode material is a case where it is used for the said electrode, compared with the conventional electrode material, it is hard to produce perspiration particles and is excellent in perspiration resistance.

Hereinafter, the present invention will be described in more detail. In addition, unless otherwise indicated, content of an element shall be mass%.
[Electrode material]
(composition)
《Main component》
The electrode material of the present invention is composed of a nickel alloy containing at least one of Al and Si, Cr and Mn as additive elements in addition to Y, and a Ni content of 97% by mass or more. By using Ni as a main component, it is excellent in plastic workability, can reduce the specific resistance, and can reduce consumption due to sparks.

《Y》
Y contained in the electrode material of the present invention exists mainly as an intermetallic compound with Ni as a parent phase, and a very small part is present in a solid solution in Ni. Here, since the electrode of the spark plug is used in a high temperature environment of about 900 to 1000 ° C., the crystal grains constituting the electrode may grow and become coarse during use. On the other hand, the electrode material of the present invention can suppress the growth of crystal grains due to the so-called pinning effect of the intermetallic compound, and even if the electrode made of the electrode material is used in a high temperature environment, A fine grain state can be maintained. Therefore, even if oxygen from outside tries to enter the inside of the electrode through the crystal grain boundary, it is possible to prevent the penetration degree (depth) from becoming deep due to the long grain boundary. Accordingly, the electrode material of the present invention can reduce oxidation and corrosion particularly to the inside thereof, and is excellent in oxidation resistance. In order to obtain the effect of oxidation resistance sufficiently, it is necessary to contain 0.3% or more of Y. The more Y, the finer the crystal grains that can be maintained and the better the oxidation resistance. However, when the amount is too large, the specific resistance increases or the plastic workability decreases, resulting in an electrode having a predetermined shape. Therefore, the upper limit of Y is set to 1.0% or less. Y is less likely to occlude hydrogen than Nd. Therefore, even when heat treatment is performed in an atmosphere containing hydrogen in the manufacturing process, the electrode material of the present invention is unlikely to be hydrogen embrittled. A more preferable content of Y is 0.3% or more and 0.6% or less.

《Al, Si》
The electrode material of the present invention contains at least one element of Al and Si, thereby reducing the intrusion of oxygen into the electrode material by forming an oxide of Al or Si on the surface of the electrode material. As described above, the internal oxidation can be suppressed and the oxidation resistance can be enhanced. Further, by containing Al and Si together with Cr and Mn described later, the electrode material can improve the sweat resistance. In order to obtain such an effect sufficiently, it is necessary to contain at least one of Al and Si in an amount of 0.01% or more, and in particular, it is preferable to contain 0.1% or more, and more preferably 0.2% or more. As the amount of Al or Si increases, the above-mentioned oxide is more easily formed, and the oxidation resistance can be enhanced or the sweat resistance can be enhanced, but if the amount is too large, the formed oxide layer expands and cracks (cracks) occur. In order to enter or rupture, or the oxide layer may peel off, the upper limit of one element is 0.4% or less, and the total is less than 0.5%. Al and Si have almost the same oxidation suppression effect, but Si tends to have a slightly higher oxidation suppression effect than Al. Therefore, when the effect of suppressing oxidation is exhibited with a small amount of addition, it is more preferable to contain only Si than to contain both Al, Si and Al. The Si content is preferably 0.1% or more and 0.4% or less.

《Cr, Mn》
One feature of the electrode material of the present invention is that it contains both Cr and Mn together with the Al and Si. As a result of investigation by the present inventors, it was found that sweat grains are hardly generated by containing Cr and Mn together with Al and Si. The reason for this is that Cr and Mn react with elements in the atmosphere such as Ca and P contained in gasoline together with Al and Si, thereby suppressing the reaction of the parent phase Ni with Ca and P, etc. This is thought to be because it is possible to reduce the adhesion of Ni and Ca to the electrode material. In particular, Cr tends to have a higher effect of suppressing the generation of sweat particles than Mn. In addition, when a large amount of Al or Si is added, although sweating can be suppressed as described above, the oxide layer is easily cracked or the oxide layer is easily peeled off. It has been found that when a small amount of Cr or Mn is contained, problems such as expansion of the oxide layer hardly occur and the sweat resistance is excellent. Furthermore, Cr and Mn also have an effect of improving oxidation resistance. From these facts, the electrode material of the present invention contains Cr and Mn. In order to sufficiently obtain the above effect, it is necessary to contain both 0.05% or more of Cr and Mn, and the higher the content of Cr and Mn, the more effective the improvement of sweat resistance. However, if there is too much Cr or Mn, the specific resistance becomes too large, so the upper limit is 0.8% or less and the total is 1.5% or less. In particular, the Cr content is preferably 0.2% to 0.8%, and the Mn content is preferably 0.1% to 0.3%. Further, it is preferable to contain about 0.2% of Mn because internal oxidation can be effectively suppressed.

  In particular, the more Cr, the higher the effect of suppressing sweating. Therefore, when Cr is contained more than Mn, the oxidation resistance can be improved and the sweat resistance can be further improved. That is, the Cr and Mn contents preferably satisfy Cr> Mn, and particularly, the Cr mass ratio Cr / Mn with respect to Mn preferably satisfies 2 or more.

  The content of the additive element in the electrode material can be adjusted to the specific range by adjusting the amount of the element added as a raw material. In addition to the above additive elements, when high temperature strength is desired, a small amount of C is allowed. However, if the amount of C is too large, the workability tends to deteriorate, so the C content is preferably 0.05% by mass or less.

[Resistivity]
The electrode material of the present invention contains a specific element in the above specific range, so that the specific resistance is small and the consumption by the spark is small. Although depending on the content of the additive element, the electrode material of the present invention can satisfy a specific resistance of 20 μΩ · cm or less at room temperature (typically 20 ° C.). The specific resistance changes mainly depending on the content of the additive element as described above, and the specific resistance tends to decrease as the content of the additional element decreases.

[Oxidation resistance]
The electrode material of the present invention can maintain a fine structure of crystal grains even when exposed to a high temperature environment for a long time. Specifically, after the electrode material is heated at 1000 ° C. for 72 hours, the average crystal grain size of the electrode material after the heating can satisfy 300 μm or less. The condition of "1000 ° C x 72 hours" is a temperature condition equivalent to the maximum temperature achieved when using a conventional general automobile gasoline engine, and the heating time is long. It is a thing. As described above, the smaller the crystal grains that make up the electrode material, even when such severe heating is performed, can suppress the intrusion of oxygen into the electrode material as described above, resulting in superior oxidation resistance. It can be evaluated that it has. Therefore, in the present invention, “average crystal grain size after heating at 1000 ° C. × 72 hours” is adopted as an index for evaluating oxidation resistance. The average crystal grain size can be changed depending on the content of the additive element. For example, an electrode material satisfying 200 μm or less, particularly 100 μm or less can be obtained.

[shape]
The electrode material of the present invention typically includes a wire formed by wire drawing. The cross-sectional shape can be various shapes such as a rectangular shape and a circular shape.

[Production method]
The electrode material of the present invention is typically obtained by melting → casting → hot rolling → cold drawing and heat treatment. Further, in order for the intermetallic compound containing Y to be present in the electrode material as described above, for example, the atmosphere during melting or casting is controlled so that the oxygen concentration becomes low.

  When the final heat treatment (softening treatment) is performed after the cold wire drawing, it is preferably performed at 700 to 1000 ° C., particularly about 800 to 950 ° C. in a non-oxidizing atmosphere (for example, a hydrogen atmosphere or a nitrogen atmosphere). By performing such a softening process, it is easy to process the electrode material into a predetermined electrode shape, or the processing distortion due to the process before the softening process can be removed, and the specific resistance of the electrode material can be reduced.

[Spark plug electrode]
The electrode material of the present invention can be suitably used for any constituent material of the center electrode and the ground electrode provided in the spark plug. The ground electrode tends to be disposed at a position closer to the center of the combustion chamber in an internal combustion engine such as an automobile engine than the center electrode. Since the electrode material of the present invention is excellent in characteristics at a high temperature as described above, it can be suitably used particularly as a constituent material of the ground electrode. The electrode of the present invention can be produced by cutting the electrode material into an appropriate length or further forming it into a predetermined shape.

[Spark plug]
The electrode of the present invention can be suitably used as a constituent member of a spark plug used for ignition in an internal combustion engine such as an automobile engine. The spark plug of the present invention typically includes 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 above One having one end welded to the front end surface of the metal shell and the other end facing the end surface of the center electrode and a terminal metal fitting provided at the rear end of the insulator. Can be mentioned. The electrode of the present invention can be used in place of a known spark plug electrode.

  The electrode of the present invention constituted by the electrode material of the present invention and the spark plug of the present invention including the electrode are excellent in high-temperature oxidation resistance, spark consumption resistance, and sweat resistance.

FIG. 1 is an optical micrograph of an electrode material for explaining the formation state of an oxide layer.

Embodiments of the present invention will be described below.
A plurality of wires made of nickel alloy were prepared, and electrodes for spark plugs used for ignition of a general automobile gasoline engine were prepared from each wire, and the characteristics were evaluated.

  Each wire was produced as follows. Using an ordinary vacuum melting furnace, a nickel alloy melt having the composition shown in Table 1 (unit: mass%) was produced. Commercially available pure Ni (99.0 mass% or more Ni) and grains of each additive element were used as the raw material for the molten metal. In addition, the molten metal was refined to reduce and remove impurities and inclusions. The molten metal temperature was appropriately adjusted to obtain an ingot (2 tons) by vacuum casting. Sample Nos. 120 and 127 are adjusted so that the content of C (carbon) is as shown in Table 1 by adjusting the refining conditions, and the other refining conditions are such that C is not substantially contained in other samples. Adjusted. Further, the above melting and casting were carried out by controlling the atmosphere so that the oxygen concentration was lowered.

  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 having a wire diameter of 5.5 mmΦ. This rolled wire was subjected to a combination of cold wire drawing and heat treatment to obtain a cold wire material having a wire diameter of 2.5 mmΦ and a wire diameter of 4.2 mmΦ. The cold-drawn wire rod having a wire diameter of 2.5 mmΦ was subjected to a rolling process and deformed into a 1.5 mm 2.8 mm flat wire, thereby obtaining a flat wire. Final flat heat treatment (softening treatment, temperature: 800-1000 ° C, non-oxidizing atmosphere (nitrogen atmosphere or hydrogen atmosphere), using continuous softening furnace) is applied to the obtained rectangular wire and cold drawn wire with a diameter of 4.2 mmΦ. A soft material (electrode material) was obtained. Each soft material obtained is cut to an appropriate length, then molded into a predetermined shape, and a spark plug ground electrode (1.5mm 2.8mm rectangular wire used in ordinary ordinary passenger cars) is used. ), A spark plug center electrode (using a wire diameter of 4.2 mmΦ) was prepared and used as a sample.

  When the composition of the electrode of each obtained sample was examined using an ICP emission spectroscopic analyzer, it was the same as the composition shown in Table 1, and the balance was Ni and inevitable impurities. Further, the Ni content of each sample electrode was 95% by mass or more (sample Nos. 1 to 8 were 97% by mass or more Ni). The composition can be analyzed by the atomic absorption spectrophotometry method as well as the above ICP emission spectroscopic analysis method. Further, when the carbon content of the electrode of each sample was measured by the high frequency combustion infrared absorption method, it was the same as the composition shown in Table 1. In Table 1, “-(hyphen)” is less than the detection limit and indicates that it is not substantially contained. Furthermore, when each sample containing Y was examined using elemental analysis by SEM and EDX, or EPMA, it was confirmed that an intermetallic compound of Y and Ni was present.

《Specific resistance》
The specific resistance of each soft material used for the production of the electrode was measured. The results are shown in Table 2. The specific resistance (room temperature) was measured by a four-terminal method using an electrical resistance measuring device (distance between grades GL = 100 mm).

<Oxidation resistance>
Each of the prepared samples was evaluated for oxidation resistance. The results are shown in Table 2. The oxidation resistance was determined by using a spark plug comprising the above-mentioned ground electrode made of a 1.5 mm × 2.8 mm flat soft material and a center electrode made of a soft material having a wire diameter of 4.2 mmΦ for a test engine (displacement volume). 2000cc, 6 cylinders), and a durability test was repeated for 100 hours of operation for 1 minute with the throttle fully open and 1 minute in the idle state. After the durability test, a cross-sectional photograph of the ground electrode was taken, and the thickness of the oxidized region (oxide layer) of the electrode was measured.
As shown in FIG. 1, the oxide layer is formed on the outermost surface and has a high content of additive elements and a small amount of Ni, and an inner oxide layer that is formed inside and has a large amount of Ni. And a two-layer structure. Therefore, the inner oxide layer has an average thickness from the surface of the electrode to the boundary between the inner oxide layer and the outer oxide layer, and the outer oxide layer has an average thickness from the boundary to the outermost surface of the electrode. It was measured. It can be said that the lower the degree of oxygen intrusion into the electrode, the thinner the internal oxide layer and the less internal oxidation occurs. The optical micrograph shown in FIG. 1 is an explanatory sample produced by subjecting the soft material used for producing the electrode of Sample No. 2 to heat treatment at 1000 ° C. for 72 hours.

  In addition, the oxidation resistance is determined when the total thickness of the outer oxide layer and the inner oxide layer is 200 μm or more, or due to the expansion of the oxide layer, the oxide layer is internally ruptured or cracked in the oxide layer. If it occurs remarkably, the high temperature oxidation resistance is equivalent to that of the conventional product x, the total thickness is less than 200 μm, and the internal burst or crack is slight, or the internal burst or crack is The case where there was almost none was evaluated as good, and the case where the total thickness was less than 180 μm and there was almost no internal rupture or crack was evaluated as ◎ as particularly preferable.

《Spark resistance and sweat resistance》
Each of the prepared samples was evaluated for spark wear resistance and sweat resistance. The results are shown in Table 2. For spark wear resistance and sweat resistance, a spark plug is prepared that includes the ground electrode made of the above-mentioned 1.5 mm x 2.8 mm flat soft material and the center electrode made of soft material with a wire diameter of 4.2 mmΦ. Attach the above spar plug to a severe test engine (displacement 2800cc, 6 cylinders) adjusted so that the combustion temperature is about 100 ° C higher than the normal combustion temperature (about 900-1000 ° C), and 400 hours An endurance running test (running about 60,000 km at 150 km / h) was conducted. After the endurance running test, observe the surface condition of the electrode with a magnifying glass to observe the state of sweat particles, and the gap between the center electrode and the ground electrode used for spark discharge (hereinafter referred to as spark discharge). The amount of increase in size (called the gap) (the amount of increase from the initial design value) was measured.

  The spark wear resistance was evaluated as x when the increase in the size of the spark discharge gap was 0.5 mm or more, ◯ when 0.2 mm or more and less than 0.5 mm, and ◎ when it was less than 0.2 mm. The spark discharge gap can be measured by using a gap gauge or the like.

  Sweating resistance is x when sweat particles are remarkably generated, that is, when large particles are present and the electrode is greatly swollen or sweat particles are generated entirely. The case where the unevenness of the electrode surface was large was evaluated as △, the case where the generation of sweating particles was slight, and the case where the generation of sweating particles was hardly observed were evaluated as ◎.

<Crystal grain size>
After each soft material used for the production of the above electrode was heated in an atmospheric furnace at 1000 ° C. for 72 hours, a cross-sectional photograph of each soft material after heating was taken with an optical microscope (magnification: 50 to 200 times). For the image, the average crystal grain size was calculated using the intersection method (line method). The results are shown in Table 2.

  As shown in Table 2, sample Nos. 1 to 8 including electrodes manufactured from an electrode material (soft material in this case) containing at least one of Y, Al and Si, Cr and Mn in a specific range are high temperatures. However, it turns out that it is excellent in oxidation resistance. Specifically, in Sample Nos. 1 to 8, an oxide layer having substantially the same thickness is present both on the surface side and inside of the electrode, and the internal oxide layer is not extremely thick. One reason for this is thought to be that internal oxidation could be suppressed by containing a small amount of Al and Si and containing appropriate amounts of Cr and Mn. In particular, among samples No. 1 to 8, samples containing a large amount of Cr tend to have a higher effect of suppressing internal oxidation, and samples containing Si tend to have better oxidation resistance than Al. I understand that. Samples Nos. 1 to 8 were able to maintain a fine structure of crystal grains even when exposed to high temperatures, and from this, it is considered that they could have excellent oxidation resistance.

  Furthermore, since all of sample Nos. 1 to 8 have a specific resistance as small as 20 μΩ · cm or less, it can be seen that consumption due to sparks is small. One reason for this is thought to be because Al and Si are not excessively contained. Samples Nos. 1 to 8 are all excellent in sweat resistance, and among them, samples containing a large amount of Cr and satisfying Cr / Mn of 2 or more tend to be particularly excellent in sweat resistance. I understand. One of the reasons is that by containing Cr and Mn, it was possible to suppress the formation of a low melting point compound between the element in the atmosphere of the use environment and Ni of the parent phase of the electrode. it is conceivable that.

  On the other hand, it can be seen that Sample Nos. 100 and 120 to 127 that do not contain the specific element in a specific range are inferior in sweat resistance. Also, among samples No. 100 and 120-127, even samples with good sweat resistance have high specific resistance, inferior spark resistance, and cracks in the oxide layer, resulting in inferior oxidation resistance. I understand that. That is, an electrode for a spark plug that does not contain the above-mentioned specific element in a specific range has a good balance of high-temperature oxidation resistance, spark consumption resistance, and sweat resistance when used in a higher temperature environment than before. It can be said that it is difficult to obtain.

  As described above, the electrode for a spark plug produced from an electrode material containing at least one of Y, Al and Si, Cr and Mn in a specific range is excellent in high temperature oxidation resistance, spark consumption resistance, and sweat resistance. Therefore, it is expected that it can be sufficiently used even in an environment where the temperature is higher than before (for example, an ultra-high temperature environment of about + 100 ° C.). In addition, the oxide layer is less likely to expand due to oxidation, and the oxide layer is not easily ruptured or cracked due to the expansion. In addition, the specific resistance is low, the consumption due to sparks is small, and sweat particles are generated. Because it is difficult, it is expected to have a long life.

  The above-described embodiment can be appropriately changed without departing from the gist of the present invention, and is not limited to the above-described configuration. For example, the composition, shape, size, etc. of the electrode material can be changed as appropriate. Further, the composition can be made different between the ground electrode and the center electrode.

  The electrode material of the present invention can be suitably used as a constituent material of an electrode for a spark plug of an internal combustion engine such as an automobile engine. The electrode of the present invention can be suitably used for the components of the spark plug. Moreover, the spark plug of the present invention can be suitably used for the ignition member of the internal combustion engine.

Claims (8)

An electrode material used for an electrode of a spark plug,
% By mass
At least one of Al and Si is 0.01% or more and 0.4% or less, and less than 0.5% in total;
Cr is 0.05% or more and 0.8% or less, Mn is 0.05% or more and 0.8% or less, and Cr and Mn are 1.5% or less in total.
An electrode material comprising Y in an amount of 0.3% to 1.0%, the balance being Ni and inevitable impurities. % By mass
Cr content is 0.2% to 0.8%,
2. The electrode material according to claim 1, wherein the Mn content is 0.1% or more and 0.3% or less. The content of Cr and Mn satisfies Cr> Mn,
3. The electrode material according to claim 1, wherein a mass ratio Cr / Mn of Cr to Mn satisfies 2 or more.   4. The electrode material according to claim 2, wherein the content of Si is 0.1% to 0.4% by mass.   5. The electrode material according to claim 1, wherein the electrode material has a specific resistance at room temperature of 20 μΩ · cm or less.   6. The electrode material according to claim 1, wherein after heating the electrode material at 1000 ° C. for 72 hours, an average crystal grain size of the heated electrode material is 300 μm or less.   A spark plug electrode comprising the electrode material according to any one of claims 1 to 6.   8. A spark plug comprising the spark plug electrode according to claim 7.

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