JP2842868B2 - Iron-based sintered alloy for valve seat - Google Patents

Description

Description: BACKGROUND OF THE INVENTION (Industrial Application Field) The present invention relates to an iron-based sintered alloy for a valve seat which is suitably used as a material for a valve seat as an engine part for an automobile or the like. Things. (Prior art) Valve seats, which are engine parts for automobiles, are gradually being converted from ingot materials to sintered alloy materials as the output of automobile engines is increased and gasoline, one of the fuels, is made lead-free. is there. In recent years, the thermal and mechanical loads on the valve seat tend to be further increased due to the increase in output and speed of the automobile engine and the addition of a supercharger. In order to respond to the trend of automobile engines and improve the wear resistance, high temperature strength, and oxidation resistance of valve seats, alloy elements such as Cr, Ni, Co, W, and Mo are added to the base metal. And a dispersion method in the form of a hard phase. (Problems to be Solved by the Invention) However, although the wear resistance of the material is improved by the addition of such an alloy element, there is a problem that the cost is increased. Also, there are many unclear points as to whether the addition of such an alloy element can provide a corresponding effect. (Object of the Invention) The present invention has been made in view of such conventional problems, and has a high load capable of coping with an increase in thermal and mechanical loads due to a high output and a high speed of a vehicle engine. It is an object of the present invention to provide an iron-based sintered alloy for a valve seat suitable as a high-performance valve seat material for an engine. (Means for Solving the Problems) The iron-based sintered alloy for a valve seat according to the present invention is, in terms of% by weight, Mo: 3 to 14%, Ni: 3 to 14%, and C: 0.3. ~ 1.5%
The sintering of Fe powder, which consists of the balance of Fe and impurities and uniformly dissolves Mo, has a structure in which most of Mo is uniformly dissolved in the iron matrix or uniformly distributed as an intermetallic compound on the order of several μm. Is characterized by the fact that
The Fe-Ni-C-based and Fe-Mo-C-based iron-based sintered alloys that were developed badly were further improved, and Ni and Mo were simultaneously added to Fe, and
Is characterized by having a structure in which most of the above are uniformly distributed in the iron base to further improve the wear resistance. Next, the components (% by weight) of the iron-based sintered alloy for a valve seat according to the present invention and the reasons for limiting the structure will be described. Mo: 3 to 14% Mo is an element that is effective for further improving wear resistance because most of Mo is uniformly dissolved in an iron matrix or uniformly distributed as an intermetallic compound on the order of several μm. It is. Conventionally, materials containing Mo have been used as sintered alloys for valve seats, but this Mo is mainly added as ferromolybdenum particles, and these ferromolybdenum particles have been used as hard particles to improve wear resistance. . However, when used in this way, molybdenum is difficult to diffuse into the iron base, and the periphery of the ferromolybdenum particles is strengthened, but the other parts are not strengthened. Alloying due to solid solution of molybdenum in the iron matrix, that is, strengthening of the matrix by solid solution strengthening could not be expected so much. In the present invention, in view of the problem caused by the addition as conventional ferromolybdenum particles, by forming a structure in which Mo is uniformly dissolved in an iron matrix or dispersed as an intermetallic compound of several μm order, Specifically, by using the powder created by atomizing a molten metal in which Mo is uniformly dissolved in molten iron as a raw material powder, most of Mo is uniformly dissolved in the iron matrix, This is to make the most of the effect of Mo on improving wear resistance. However, if the Mo content is less than 3%, the effect of improving the wear resistance is small, and if it exceeds 14%, the moldability during powder molding is reduced and the material becomes hard and brittle. Therefore, Mo was set in the range of 3 to 14%. As described above, in order to uniformly distribute Mo in the iron matrix, as described above, Fe-Mo-based powder in which molybdenum is uniformly distributed in iron powder, which is a main component of the raw material powder, or Fe-Mo-Ni-based powder. Must be used. However, when aiming for a high Mo and high Ni composition, it is desirable to add a part of Ni and Mo as fine metal nickel and metal molybdenum of 200 mesh or less in order to secure formability. Ni: 3-14% Ni is effective in improving the wear resistance of the alloy,
If it is less than 3%, the effect of improving the wear resistance cannot be sufficiently obtained, and if it exceeds 14%, austenite and martensite are generated in the metal structure, making it difficult to work and brittle. Absent. Therefore, the Ni content is in the range of 3 to 14%. C: 0.3-1.5% C aims at the eutectoid composition, and is inevitably determined by the amount of added Mo and the amount of Ni so as not to generate ferrite and carbide. In this case, the above Mo amount and Ni
The amount of C corresponding to the amount is 0.3 to 1.5%. When the amount of C is less than the eutectoid composition, ferrite is generated and the wear resistance is deteriorated, which is not preferable. On the contrary, when the amount of C is more than the eutectoid composition, carbides are formed, making it difficult to process and brittle. Is not preferred. Therefore, it is preferable that the carbon content be in a range that does not generate ferrite and carbides. However, it is actually difficult to precisely control the carbon content because it is affected by the oxygen content of the raw material powder and the atmosphere of the sintering furnace. , Slightly, eg 5
Ferrite and carbide compositions up to volume% are acceptable. (Example) An iron powder in which 5 wt% molybdenum having a particle size having a peak at 150 to 200 mesh, which is formed by atomizing a molten metal in which Mo is dissolved in molten iron uniformly, is uniformly dissolved in iron.
0 Add a mesh-under metal nickel powder, graphite powder and metal molybdenum powder so as to have the compositions of Nos. 5 to 9 in Table 2, respectively, and further lubricate the mold to improve mold release. A powder mixture containing 0.6% by weight of zinc stearate as an agent is prepared, and each mixture is pressed to 7 tons.
After molding at a molding pressure of / cm ² , each compact was dewaxed at 650 ° C for 1 hour, then fired and sintered at 1200 ° C for 1 hour, and then furnace cooled to 900 ° C. Then, a test piece (valve seat) having an outer diameter of 46 mm, an inner diameter of 30 mm, and a height of 7.5 mm was produced by gas cooling from 900 ° C. Then, for each test piece, after the hardness was subjected to heat treatment so that H _R B95 before and after processed into a predetermined size was evaluated properly as valve seat material by performing a simple abrasion test. This evaluation was performed under the conditions shown in Table 1, assuming the use conditions of the exhaust-side valve seat. The results of this evaluation test are also shown in Table 2. (Comparative Example) For comparison, a Fe-Mo-C-based sintered alloy (No. 1), Fe
-Ni-C based sintered alloy (No.2,3), comparative sintered alloy of the present invention having small amount of Mo and Ni, Fe-5% Mo-5% Ni sintered with addition of Mo in the form of ferromolybdenum Binders (No. 10) were prepared, and test pieces were prepared in the same manner as in the above Examples, and the suitability as a valve seat material was evaluated under the conditions shown in Table 1. These results are also shown in Table 2. As is clear from the results shown in Table 2, the material of the present invention (N
o.5 to 9), the conventional comparative material (N
It is clear that the mesh resistance is further improved as compared with the valve seats composed of o.1 to 3), and the comparative material (No. 4) having a small amount of Mo and Ni does not have good wear resistance. It was recognized that. In addition, it was confirmed that the material of the present invention (No. 5) had considerably the same abrasion resistance as the comparative material (No. 10) in which Mo was added in the form of ferromolybdenum, although it had the same components. As described above, the iron-based sintered alloy for a valve seat according to the present invention is Mo: 3 to 14% and Ni: 3 to 14% by weight.
%, C: contains 0.3-1.5%, the balance consists of Fe and impurities, and most of Mo is uniformly dissolved in the iron matrix by sintering of Fe powder that uniformly dissolves Mo, or in the order of several μm. Since it has a structure that is uniformly distributed as an intermetallic compound, it is an iron-based sintered alloy with remarkably excellent wear resistance. An extremely excellent effect is obtained that the iron-based sintered alloy for a valve seat is suitable as a high-performance valve seat material for a high-load engine that can cope with an increase in mechanical load.

Continuation of front page    (72) Inventor Ichiro Tanimoto               2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Sun               Industrial Motor Co., Ltd. (72) Inventor Akiyoshi Ishibashi               810 Kumagaya, Kumagaya City, Saitama Prefecture (72) Inventor Kazutoshi Takemura               3167 Kamino, Kumagaya City, Saitama Prefecture                (56) References JP-A-53-86605 (JP, A)                 JP-A-49-96912 (JP, A)

Claims (1)

(57) [Claims] By weight, Mo: 3-14%, Ni: 3-14%, C: 0.3-1.5%
The main feature of Mo is that it has a solid solution strengthened matrix structure in which most of Mo is uniformly dissolved in the iron matrix by sintering of Fe powder that is composed of the balance of Fe and impurities and uniformly dissolves Mo. Iron-based sintered alloy for valve seats. 2. The iron-based sintered alloy for a valve seat according to claim 1, wherein the Fe powder that uniformly dissolves Mo is an atomized powder of a molten metal in which Mo is uniformly dissolved in molten iron.