JP4706441B2 - Spark plug electrode material - Google Patents

Description

  The present invention relates to an electrode material for a spark plug of an internal combustion engine.

Due to the increasing demand for prevention of global warming and fossil fuel savings in recent years and the movement of various environmental regulations in line with it, exhaust gas regulations for automobiles and the like have become stricter. For this reason, the combustion temperature of internal combustion engines such as automobiles tends to increase, and ignition plugs used in internal combustion engines such as automobiles have been required to be more durable than before.
Conventionally, various Ni-based alloys have been widely used for electrode materials for spark plugs of this application because they are required to have oxidation resistance, spark wear resistance, high temperature strength, and the like. Recently, in addition to a spark plug using a Ni-based alloy single electrode, a spark plug that has improved life by joining a noble metal to the discharge portion of the electrode made of a Ni-based alloy to withstand higher temperatures, An electrode base material made of a Ni-base alloy and provided with Ag or Cu having a good thermal conductivity as a core material has been often used.

In such Ni-based alloys used for the electrode materials of various spark plugs, for example, from the viewpoint of workability, Cr is about 3% or less, and an additive element for supplementing or enhancing oxidation resistance and high-temperature strength is included. There is a proposal of a Ni-based alloy to be contained.
Specifically, a proposal to add one or more elements such as Si, Mn, Al, or the addition of Y or a rare earth element to supplement oxidation resistance in a low Cr Ni-based alloy is disclosed in JP JP 63-18033 (refer to Patent Document 1), JP-A-2-34734 (refer to Patent Document 2), JP-A-2-34735 (refer to Patent Document 3), JP-A-4-45239 (refer to Patent Document 4) JP-A-9-235637 (see Patent Document 5).

Japanese Unexamined Patent Publication No. 63-18033 JP-A-2-34734 JP-A-2-34735 JP-A-4-45239 Japanese Patent Laid-Open No. 9-235637

The above-described material that suppresses Cr to some extent is a promising material in terms of workability. However, all of the above-mentioned alloys have a low amount of Cr effective for oxidation resistance, but instead of Si, Mn, and Al as essential elements to supplement oxidation resistance, the total amount of alloy elements in Ni increases. As a result, the thermal conductivity and melting point tend to decrease.
When the amount of alloying elements to supplement oxidation resistance increases, the electrode temperature is less likely to decrease due to low thermal conductivity, resulting in exposure to high temperatures that are likely to oxidize, or melting damage due to a decrease in melting point There is a risk that spark wear, which is influenced by, tends to occur.
In addition, due to recent high performance and combustion efficiency improvement of internal combustion engines and high loads due to combustion mechanism conversion, the environment for spark plug alloys has become more severe, and the above-mentioned alloys do not always have satisfactory characteristics. It is no longer available.
In view of the above circumstances, an object of the present invention is an electrode for a spark plug having excellent oxidation resistance, spark wear resistance, and excellent manufacturability in response to higher loads and higher performance of an internal combustion engine. Is to provide materials.

  The present inventor has examined an electrode material for a spark plug, and it is necessary to increase the thermal conductivity in order to improve the oxidation resistance of the spark plug alloy, and in order to improve the spark wear resistance, the melting point must be reduced. Although it is effective to make it high, in order to solve these two necessary characteristics at the same time, a small amount of Si, a small amount of Hf and / or Re, a decrease in Mn and Al, and a rare earth The inventors have newly found out that it is effective to simultaneously add one or more elements and / or a small amount of Y to arrive at the present invention.

That is, the present invention is, in mass%, C: 0.1% or less (including 0), Si: 0.3 to 3.0%, Mn: less than 0.5% (including 0), Cr: 0.00. Less than 5% (including 0), Al: 0.3% or less (including 0), one or more of Y and rare earth elements in a total of 0.01 to 0.3%, of Hf and Re One or two of them are a total of 0.01 to 0.5%, and the balance is a spark plug electrode material made of Ni and inevitable impurities.
Further, the preferred composition of the present invention is, in mass%, C: 0.05% or less (including 0), Si: 0.5 to 1.5%, Mn: 0.2% or less (including 0), Cr: 0.3% or less (including 0), Al: 0.3% or less (including 0), one or more of Y and rare earth elements in a total of 0.01 to 0.2%, An electrode material for a spark plug in which one or two of Hf and Re are 0.01 to 0.3% in total, and the balance is Ni and inevitable impurities.

In addition to the above composition, at least one of B, Ti, Nb, and Zr is 0.015% or less for B, 0.50% or less for Ti, and 1.0% or less for Nb. It is preferable to further add about 0.20% or less.
In addition, the above-described spark plug electrode material of the present invention preferably has a thermal conductivity of 35 W / (m · K) or more at room temperature, and more preferably the melting point of the spark plug electrode material during the temperature rising process is It is good that it is 1420 ° C. or higher.
In the present application, “one or more of Y and rare earth elements” means at least one or more selected from the group of elements that combine Y and rare earth elements.

  According to the present invention, it is possible to provide an electrode material for a spark plug that has excellent thermal conductivity, good oxidation resistance, and good spark wear resistance, and is easy to process. Therefore, it is extremely effective industrially.

As described above, the important features of the present invention are that Mn, Cr, Al are kept low, a small amount of Si is essential, and a small amount of Hf and / or Re is added, and then one or more rare earth elements and / or By adding Y, the thermal conductivity is prevented from lowering and the melting point is prevented from lowering.
According to the inventor's study, by increasing the thermal conductivity, the material temperature can be lowered during use as a spark plug, and as a result, the oxidation resistance can be improved. Further, by preventing the melting point from being lowered, it is possible to make it difficult to cause spark wear during use as a spark plug.

The reason for limitation of each element prescribed | regulated by this invention below is demonstrated.
C is preferable to be low in order to improve the workability, and if it exceeds 0.1%, the hardness after annealing increases and the cold workability decreases, so it is limited to 0.1% or less. The desirable range of C is 0.05% or less, and may be 0% (below the additive-free level).
Si is an element that is very effective for improving oxidation resistance, but it is an element that lowers thermal conductivity and melting point. Therefore, in order to obtain good oxidation resistance, the range that does not greatly reduce thermal conductivity and melting point. Add it positively. If the amount is less than 0.3%, the effect of improving the oxidation resistance is small. On the other hand, if the amount exceeds 3.0%, the melting point and the thermal conductivity are greatly reduced. Therefore, Si is 0.3 to 3.0%. It was. More preferably, Si is 0.5 to 1.5%.
Mn is also an element that improves oxidation resistance, while it is an element that lowers thermal conductivity and melting point. When Si is contained to some extent as in the present invention, it is necessary to keep Mn low in order to ensure high thermal conductivity and melting point. Addition of 0.5% or more increases the melting point, so Mn is less than 0.5%. More preferably, Mn is 0.2% or less, and may be 0% (no additive level or less).

While Cr is an element that improves oxidation resistance, it lowers thermal conductivity and degrades workability. Therefore, when Si is contained to some extent, Cr is kept low to ensure high thermal conductivity. There is a need. When 0.5% or more is added, the thermal conductivity decreases greatly, so Cr is made less than 0.5%.
In the present invention, the oxidation resistance deficiency due to the Cr content being suppressed to less than 0.5% is reduced by adding a small amount of Si, a small amount of Hf and Re, or a small amount of Y and rare earth elements. It supplements by adding 1 type, or 2 or more types. The desirable range of Cr is 0.3% or less, and it may be 0% (below the additive-free level).
Al is an element that enhances oxidation resistance, while it is an element that greatly reduces thermal conductivity. When Si is contained to some extent as in the present invention, Al must be kept low. When Al is added in an amount of more than 0.5%, the thermal conductivity is greatly reduced. Therefore, Al is set to 0.3% or less here. Preferably, it is 0.1% or less, and it may be 0% (no additive level or less).

  Hf and Re are elements that need to be added because they can improve oxidation resistance and high-temperature strength while maintaining high thermal conductivity with a very small amount of addition. In order to obtain the effects described above, it is desirable to contain 0.01% or more of one or two of Hf and Re. However, Hf and Re are expensive elements, and if the total exceeds 0.5%, the material becomes expensive, which is not preferable, and addition of a large amount leads to a decrease in melting point. 1 type or 2 types of Hf and Re were 0.01 to 0.5% in total. The upper limit with preferable Hf and Re is 0.3% by 1 type or 2 types.

  Y and rare earth elements are elements that contribute to the improvement of oxidation resistance when added in a very small amount. When added together with an oxidation resistance improving element such as Si, the effect is great, so one or more elements are added. Here, the rare earth element (REM) refers to a lanthanoid element such as La, Ce, Nd, and Pr. If it is less than 0.01%, the effect of improving oxidation resistance is small, and depending on the product design, if added over 0.3%, the hot workability and weldability are lowered. The total amount of seeds or two or more kinds was set to 0.01 to 0.3%. In addition, the upper limit with preferable Y and rare earth elements is 0.2% or less. Moreover, a preferable upper limit when importance is attached to hot workability and weldability is 0.1%.

In the present invention, the following range of elements can be added to the Ni-base alloy electrode material.
First, B, Ti, Nb, and Zr are used as grain boundary strengthening elements to increase strength at high temperatures, ductility, and resistance to grain boundary oxidation. Therefore, B: 0.015% or less, Ti: 0.50% as necessary. Hereinafter, Nb: 1.0% or less and Zr: 0.20% or less can be added alone or in combination of two or more.
Further, Ca and Mg are deoxidation and desulfurization elements, which increase the cleanliness of the alloy and improve the ductility at high temperature. May be added.
Note that main elements that may remain as unavoidable impurities are P, S, N, O, and the like. These are preferably as low as possible, but if P ≦ 0.03%, S ≦ 0.03%, N ≦ 0.05%, O ≦ 0.01%, the basic characteristics of the spark plug electrode material are particularly large. This range is acceptable because it is thought to have no effect.

Next, the thermal conductivity and melting start temperature defined in the present invention will be described.
The thermal conductivity is one of the important characteristics that influence the temperature drop of the heated spark plug electrode and influence the temperature reached by the tip portion, and is preferably higher.
Since thermal conductivity tends to decrease as the number of alloy elements increases, it is necessary to suppress the amount of alloy elements added in order to maintain high thermal conductivity. On the other hand, in order to improve the oxidation resistance, it is desirable to add a lot of alloy elements having an effect of improving the oxidation resistance.
Therefore, in order to maintain high thermal conductivity while ensuring good oxidation resistance, elements that are effective in oxidation resistance while suppressing the total amount of alloy elements as specified in the component range of the present invention. It is necessary to select appropriately and to select an alloy element that does not easily lower the thermal conductivity.
By increasing the thermal conductivity, the temperature of the spark plug electrode is lowered, which is advantageous for oxidation. The thermal conductivity can be adjusted to 35 W / (m · K) or more, which is effective for lowering the temperature of the spark plug electrode, by selecting an effective alloy element within the prescribed range of the alloy components. it can. Furthermore, it is desirable to adjust to 40 W / (m · K) or more by selecting an appropriate alloy element.

The melting point is one of important characteristics affecting the spark wear resistance of the spark plug electrode, and a higher one is desirable. Since the melting point tends to decrease as the number of alloy elements increases, it is necessary to suppress the amount of alloy element added in order to maintain the melting point high. On the other hand, in order to improve the oxidation resistance, it is desirable to add a lot of alloy elements having an effect of improving the oxidation resistance.
Therefore, in order to maintain a high melting point while ensuring good oxidation resistance, the elements having an effect on oxidation resistance can be appropriately selected while suppressing the total amount of alloy elements as defined in the component range of the present invention. It is necessary to select an alloy element that does not easily lower the melting point.
The melting point can be adjusted to 1420 ° C. or more, which is effective in improving the spark wear resistance of the spark plug electrode, by selecting an effective alloy element within the specified range of the alloy components.

The following examples further illustrate the present invention.
A 10 kg steel ingot was produced by vacuum melting, and after homogenization heat treatment, hot working was performed to confirm hot workability, and a 30 mm square bar was produced. Moreover, a part was cold-worked and workability was confirmed. The chemical composition is shown in Table 1. Note that REM may be added as a mixture of rare earth elements, but this time La and Ce were added in combination.
Sample No. 1 to 10 are the alloys of the present invention, Sample No. Reference numerals 21 to 23 are comparative alloys. These alloys were further annealed at 800 ° C. for 1 h, and then used as samples for the following tests.
Table 2 shows the results of measuring the hardness, thermal conductivity, melting point, increase after oxidation resistance test, and amount of scale peeling after annealing of the samples obtained. In addition, the oxidation resistance test was performed by exposing the sample to air at 800, 900, and 1000 ° C. for 100 hours. Moreover, thermal conductivity shows the value in 25 degreeC and 900 degreeC.

Sample No. which is an alloy of the present invention. Nos. 1 to 10 all have high thermal conductivity at 25 ° C., show values of 35 W / (m · K) or higher, and maintain a high melting point of 1420 ° C. or higher. Moreover, it has low hardness and good cold workability. Oxidation increase is also stable and low, indicating good oxidation resistance.
On the other hand, Sample No. No. in which Si was higher than the specified amount of the present invention and Re and Hf were not added. No. 21 has a melting point lower than 1420 ° C., and it is considered that sufficient spark wear resistance cannot be obtained. Sample No. No. in which Cr and Al are higher than the specified amount of the present invention and Re and Hf are not added. No. 22 has a thermal conductivity at 25 ° C. lower than 35 W / (m · K) and a large amount of oxide scale peeling, and when used for a spark plug electrode, the temperature rises greatly and oxidation is likely to occur. Conceivable.
In addition, Sample No. to which none of Y, rare earth elements, Hf, and Re was added was used. Although No. 23 has a high thermal conductivity and a high melting point, it is considered that the amount of increase in oxidation and the amount of exfoliation scale at high temperatures, particularly 900 and 1000 ° C., are large, and the oxidation resistance necessary for the spark plug electrode material cannot be obtained sufficiently.

Since the present invention is excellent in characteristics such as high thermal conductivity, melting point, good oxidation resistance and workability required for the electrode material for spark plugs, good oxidation resistance and spark wear resistance are required. It can be applied to an electrode for a spark plug of an internal combustion engine.

Claims (5)

  In mass%, C: 0.1% or less (including 0), Si: 0.3 to 3.0%, Mn: less than 0.5% (including 0), Cr: less than 0.5% (0 Al): 0.3% or less (including 0), one or more of Y and rare earth elements in a total of 0.01 to 0.3%, one or two of Hf and Re A spark plug electrode material comprising 0.01 to 0.5% in total, the balance being made of Ni and inevitable impurities.   C: 0.05% or less (including 0), Si: 0.5 to 1.5%, Mn: 0.2% or less (including 0), Cr: 0.3% or less (0) Al): 0.3% or less (including 0), one or more of Y and rare earth elements in total 0.01 to 0.2%, one or two of Hf and Re A spark plug electrode material comprising 0.01 to 0.3% in total, the balance being made of Ni and inevitable impurities.   At least one of B, Ti, Nb, and Zr is 0.015% or less for B, 0.50% or less for Ti, 1.0% or less for Nb, and 0.20% or less for Zr The spark plug electrode material according to claim 1, further added in a step.   4. The electrode material for a spark plug according to claim 1, wherein the thermal conductivity at room temperature is 35 W / (m · K) or more. 5. Melting | fusing point is 1420 degreeC or more, The electrode material for spark plugs as described in any one of Claims 1-4 characterized by the above-mentioned.