JPH0660370B2 - Iron-based sintered alloy for valve seats - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an iron-based sintered alloy for a valve seat of an internal combustion engine.

(With the prior art) Valve seats for internal combustion engines are being converted from ingots to sintered alloys in response to higher engine output and unleaded gasoline, which is one of the fuels.

In recent years, the thermal and mechanical load on the valve seat tends to increase further due to the increase in output and rotation of the internal combustion engine and the addition of a supercharger.

In order to improve the wear resistance, high temperature strength, and oxidation resistance of the valve seat against the trend of automobile engines, elements such as Cr, Ni, Co, W, and Mo have been used as a hard phase or alloyed base on the base. Was added by dispersion. At that time, the proportion of alloying was small and most of them were dispersed as a hard phase.

(Problems to be Solved by the Invention) For example, Mo was mainly added as ferromolybdenum particles and expected to act as hard particles. When it is used in this way, Mo is difficult to diffuse into the matrix, and the periphery of the ferro-molybdenum particles is strengthened, but other parts are not strengthened. It could not be expected to be strengthened by forming a solid solution in the base and alloying. The same applies to the other elements described above. At the same time, it was desired to improve the attackability of the opponent.

(Object of the Invention) The present invention has been made in view of such conventional problems, and is for a high-load engine capable of coping with an increase in thermal and mechanical loads due to higher output and higher rotation of the internal combustion engine. It is an object of the present invention to provide an iron-based sintered alloy for valve seats suitable as a high performance valve seat material.

(Means for Solving Problems) The iron-based sintered alloy for a valve seat according to the present invention includes: Mo: 0.3 to 14% by weight, Cu: 1 to 8% by weight, C: 0.3 to 2. A material containing 0% by weight, the balance Fe and unavoidable impurities, characterized in that most of Mo is evenly distributed in the iron matrix and a fine Cu phase is uniformly dispersed. is there.

The inventors of the present invention have already applied for a patent for the Fe-Mo-C-based material (Japanese Patent Application No. 61-305242).
It is an iron-based sintered alloy for valve seats in which wear resistance is further improved by simultaneously adding Cu and Mo to e. M
By using a material powder in which o is evenly distributed and solid-dissolved in the iron base, Mo is dispersed uniformly and the wear resistance improving effect of Mo is maximized. . At the same time, by specifying alloy components and heat treatment to precipitate a fine Cu phase as shown in FIGS. 1 and 2, the shock absorbing effect at the time of being beaten and the intervening effect of the soft phase at the time of sliding wear The purpose was to improve wear resistance and opponent attack. 1 and 2
In the figure, the fine spherical phase is a composite carbide such as (Fe, Mo) C.

Next, the reasons for limiting the components and structure of the iron-based sintered alloy for valve seats according to the present invention will be described.

If the amount of Mo is less than 3% by weight, the effect of improving wear resistance is not sufficient, and if it exceeds 14% by weight, the formability during powder molding is deteriorated and the material becomes hard and brittle, which is not preferable. Therefore, Mo must be 3 to 14% by weight. In order to evenly distribute this Mo in the matrix, the iron powder, which is the main raw material powder, uniformly distributes Mo and forms a solid solution with F.
It is necessary to use e-Mo-based powder (atomized powder). At this time, a part of Mo may be added as fine metal Mo of 325 mesh under. Thus, in the material in which Mo is uniformly distributed and solid-solved in the mother alloy, the effect of improving the wear resistance as well as the effect of improving the corrosion resistance due to the alloying of Mo are sufficiently obtained. It is a particularly effective material in engines that use fuels that produce corrosive materials as combustion products. (In leaded gasoline, a halogen compound is used as a lead scavenger, and this halogen compound decomposes during gasoline combustion to form a corrosive substance.) When the amount of Cu is 1% by weight or less, there is almost no precipitation of Cu phase, If it exceeds 8% by weight, Cu in the sintering temperature range
Since the solubility of Fe in the Fe-Mo alloy base material is exceeded, Cu is distributed in a net form from the grain boundaries of the base material powder particles, and the strength is reduced, which is not preferable. Therefore, Cu needs to be 1 to 8% by weight.

The amount of carbon is aimed at, for example, a Fe-Mo-C-based eutectoid composition, that is, it is inevitably determined as a range in which ferrite and primary carbides are not produced corresponding to the amounts of Mo and other alloying elements added. . The amount of carbon corresponding to the above Mo and Cu amount range is 0.3 to 2.0% by weight. When the carbon content is lower than the eutectoid composition, soft ferrite is produced, which is not preferable because the wear resistance is deteriorated. On the contrary, when the carbon content is high, coarse primary crystal carbides are formed, which makes it difficult to process and becomes brittle, which is preferable. Absent. Therefore, it is preferable that ferrite and carbide are not generated, but in reality, it is difficult to strictly control the amount of carbon because the amount of oxygen in the raw material powder and the atmosphere in the sintering furnace affect the amount. Generation of ferrite and carbide is allowed.

In addition, a few percent by weight of a carbide-forming element such as Cr or V, or a matrix-strengthening element such as Co or Si may be supplementarily added, but the present invention does not precipitate Cu as a fine phase. Since it is a feature, it is necessary that the content of Ni or the like, which is an element that enhances the solubility of Cu in the master alloy and suppresses the precipitation of Cu, be 1% by weight or less.

Next, the sintering conditions will be described. Fine Cu after sintering
In order to precipitate the phase, Cu is temporarily added to Fe-M during sintering.
It is necessary to form a solid solution in the o-based master alloy. For that purpose, the solubility of Cu in the master alloy is high, about 1100 ° C.
It is preferable to sinter at the above temperature. However, if the sintering temperature is 1200 ° C. or higher, the amount of liquid phase generated from the Fe—Mo matrix phase becomes too large, and the structure becomes coarse and abnormal, which is not preferable. Therefore, the sintering temperature is 1100 to 1200 ° C.
And need to. Cooling after sintering requires that a fine Cu phase be precipitated by a subsequent heat treatment, and therefore, it is necessary to cool at a cooling rate equal to or higher than gas cooling in order to prevent Cu precipitation during cooling.

Further, tempering is performed at 400 to 600 ° C. in order to precipitate the Cu phase.

(Example) 5% by weight having a peak in the particle size of 150 to 200 mesh
325 mesh under electrolytic Cu powder and graphite powder were added to the atomized iron powder containing Mo evenly so that the final composition would be as shown in Table 3. However, No.6 Mo, C
r, Co and Ni are added as hard particles, and N
Most of o.7 Mo is a solid solution in the matrix. Furthermore, in order to improve the mold release during metal forming, a mixed powder containing 0.6% of zinc stearate as a lubricant is formed by a press at a forming pressure of 7 t / cm ^{2 and} demolded at 650 ° C. for 1 hour. After brazing, it was sintered at 1150 ° C. for 1 hour. After sintering, the furnace was cooled to 900 ° C, and the gas was cooled from 900 ° C. To precipitate finer Cu, a tempering treatment was performed at 550 ° C. for 1 hour. Outer diameter produced in this way 46 mm
A test piece having an inner diameter of 30 mm and a height of 7.5 mm was processed into a predetermined valve seat shape, and the suitability as a valve seat material was evaluated by a single wear test and a bench engine durability test.

FIG. 3 shows a schematic diagram of the single-body abrasion tester used.
By the cam 2 rotated by a drive device (not shown),
The lifted valve 3 repeats the operation of striking the valve seat 1 by the spring 5 below the valve stem 4, and the gas burner 6 is provided above the valve 3.
Is provided with a nozzle 8 that blows compressed air to the cylinder head 7 laterally, and the supply amount of propane gas supplied to the gas burner 6 and the air flow rate of the nozzle 8 are adjusted by a control device (not shown) to control the valve 3. The surface is heated and maintained at a constant temperature. Using such a wear tester, tests were conducted under the test conditions shown in Tables 1 and 2 below assuming the usage conditions of the intake valve seats, and the wear amount of the valve seats was determined from the sinking amount of the reference valve.

As shown in Tables 4 and 5, the test results show that the sintered alloy valve seat of the present invention has significantly improved wear resistance as compared with the conventional one.

(Effects of the Invention) As described above, in the valve seat iron-based sintered alloy according to the present invention, most of Mo is uniformly dissolved in the iron base, so that wear resistance is improved, and Since the fine Cu phase is uniformly dispersed, the shock absorbing effect is improved and the mating attack property is improved, and the iron-based sintered alloy for a valve seat for a high load engine can be provided.

[Brief description of drawings]

FIG. 1 is a micrograph showing the metal structure of the iron-based sintered alloy of the present invention (magnification: 400 times), FIG. 2 is a sketch showing the position of the Cu phase in FIG. 1, and FIG. FIG. In the figure: 1 ... Valve seat, 2 ... Cam, 3 ... Valve.

Claims (1)

[Claims] Claims: 1. Mo: 3-14% by weight, Cu: 1-8% by weight, C: 0.3-2.0% by weight, balance Fe and unavoidable impurities, most of Mo is iron-based. An iron-based sintered alloy for a valve seat, which has a structure in which a fine Cu phase is uniformly dispersed in a solid solution.