JP4323069B2 - Valve guide material - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to wear resistance and machinability suitable for a valve guide of an internal combustion engine, in particular, the latter excellent sintered alloy.
[0002]
[Prior art]
Special cast irons such as gray cast iron and boron cast iron are sometimes used as valve guides for internal combustion engines, but in the case of cast iron, there are problems with work environment, mass productivity, price, etc., so replacement with sintered alloy Has been promoted. However, general sintered alloys have inadequate wear resistance. On the other hand, if the material is strengthened by adding alloy components, the wear resistance will reach a usable level. (Machinability) decreases. Since the valve guide is assembled to the cylinder head of the engine and the inner diameter is finished by reaming, if the valve guide material is poor in machinability, the time required for machining will be increased and the wear of the tool will be accelerated, leading to increased production efficiency. Be inhibited.
[0003]
[Problems to be solved by the invention]
Previously, the valve guide material developed by the present applicant in order to achieve both wear resistance and machinability (see Japanese Examined Patent Publication No. 55-34858) has a composition of C ... 1.5-4% by mass, Cu ... Sintered alloy of 1-5%, Sn ... 0.1-2%, P ... 0.1-0.3% and Fe balance, but wear resistance is superior to boron cast iron and machinability Although it is harder to cut than cast iron, it is superior to conventional sintered materials and has been widely used by automobile manufacturers. However, in recent years, due to changes in the environment surrounding this field, it has become more necessary than ever to improve productivity as well as improve quality, and a material with better machinability has been demanded for the valve guide material.
[0004]
[Means for Solving the Problems]
Therefore, when the improvement was attempted while based on the valve guide material according to the above-mentioned prior invention, the Fe-PC alloy phase precipitated by sintering decreased when the phosphorus content was reduced, and at the same time the free graphite increased. As a result, the machinability was improved. This invention has been made based on such findings, and one of them has a phosphorus content of 0.01 to less than 0.1% (mass%; hereinafter,% in this specification is unless otherwise specified). (All are mass%.) The main point is to limit the range to less than 4%, and the other one is less than 4% in total with pyroxene (enstatite; MgSiO ₃ ) and manganese sulfide (MnS) in conjunction with phosphorus suppression. The main point is that it has been added.
[0005]
That is, the valve guide material according to the first invention has a composition of C ... 1.5-4%, Cu ... 1-5%, Sn ... 0.1-2%, P ... 0.01-0.1% and It is a sintered alloy of the remainder of Fe, and its metal structure exhibits a state in which free graphite is dispersed in a matrix mainly composed of pearlite. According to the second invention, the alloy composition is C ... 1.5-4%, Cu ... 1-5%, Sn ... 0.1-2%, P ... 0.01-0.1%, A total of less than 4% of pyroxene and manganese sulfide and the balance of Fe exhibit a structure in which free graphite, pyroxene and manganese sulfide are dispersed in a base mainly composed of pearlite. In addition, in the bases of these alloys, the generation of Fe-PC-based alloy phases depending on the content of phosphorus, and the generation of Cu-Sn-based alloy phases in the case where the content of copper or tin is high Is recognized. Therefore, such a case is also included in the above-mentioned base mainly composed of perlite.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the sintered alloy according to the present invention, carbon is added in the form of graphite powder, and a part (generally 0.8 to 1%) is solid-solved in iron to strengthen the base, or is bonded to phosphorus and relatively A hard particulate Fe-PC-based alloy phase (steadite phase) is generated and dispersed, and the remainder remains in the state of free carbon (graphite) to act as a solid lubricant. The amount of free graphite is about 0.3% when the carbon content (total carbon content) is 1.5%, and about 1.7% when the total carbon content is 3%. When it is less than%, the wear of the valve guide due to sliding with the valve increases. For this reason, the lower limit of the carbon content is 1.5%. On the other hand, if the amount is excessive, the strength of the base material is reduced and segregation or fluidity inhibition is caused during powder molding. Therefore, the upper limit of the carbon content is 4%.
[0007]
Copper and tin are usually added in the form of copper-tin alloy powder having a tin content of about 5 to 20%, or in the form of adding a necessary amount of simple powder. Both accelerate the progress of sintering and strengthen the base by solid solution, while part remains as a Cu-Sn alloy phase to improve sliding characteristics and machinability. Such an effect occurs when the content of copper is 1% or more and tin is 0.1% or more. However, if added in excess, the dimensional stability of the product is impaired due to expansion during sintering. Since it causes embrittlement of the material, the respective contents are limited to copper ... 1 to 5% and tin ... 0.1 to 2%.
[0008]
Phosphorus is added in the form of Fe-P alloy powder or Cu-P alloy powder. Depending on the phosphorus content, the steadite phase produced increases, the rigidity of the substrate increases and the wear resistance improves, but the machinability decreases. Therefore, since the object of the present invention is to improve machinability as compared with the prior invention material, the phosphorus content is less than the prior invention material and less than 0.1% (however, 0.01%). Increases free graphite and improves machinability. As the amount of phosphorus decreases, wear resistance decreases, but it is still far superior to gray cast iron.
[0009]
The pyroclasticite in the second invention is a magnesium metasilicate mineral, which is orthorhombic and cleaved, and acts as a solid lubricant like free graphite and further improves machinability. The same applies to manganese sulfide, but it also has the effect of improving the wear resistance of the substrate. Although both are added as powders, the use of campsite and manganese sulfide (preferably 20 to 30% of campsite) can further improve the wear resistance and machinability while maintaining the balance.
[0010]
Although these solid lubricants including free graphite are dispersed in the matrix and exhibit a solid lubricating effect, the material strength decreases as the content (dispersion) increases. In the case of the present invention, if the content exceeds 4%, the material strength necessary for the valve guide material cannot be maintained, so the total amount of the solid lubricant (free graphite, pyroxene and manganese sulfide) is made 4% or less. This means that, for example, when the total carbon content is 1.5% and the free graphite content is 0.7%, the pyroxene and manganese sulfide can be incorporated up to a maximum of 3.3%. The mixing, forming, and sintering of the raw material powder are in accordance with the usual method of powder metallurgy, but the sintering atmosphere is preferably a reducing or carburizing atmosphere. If the sintering temperature is too high, free graphite disappears, so 980-1100 A temperature of about ° C is suitable.
[0011]
(Example 1) First, as raw material powder, carbon is natural graphite powder, tin is Cu-10% Sn alloy powder, phosphorus is Fe-20% P alloy powder, iron is reduced iron powder, and zinc stearate as a powder lubricant. Prepared. Next, these are blended in predetermined proportions, and the total composition is fixed at 2%, uniformly 2% for carbon and 1% for copper (thus 0.11% for tin) and 5% (0.55% for tin). And phosphorus produced the mixed powder (reduced iron powder remainder) which was changed to 0.01 to 0.3%. In each mixed powder, the amount of zinc stearate added is uniformly 0.75%.
[0012]
Next, each mixed powder is molded into a predetermined shape at a molding pressure of 490 MPa, and sintered in a reducing gas atmosphere at 1000 ° C. for 60 minutes to obtain a large number of cylindrical samples having a length of 40 mm, an outer diameter of 12 mm, and an inner diameter of 7.4 mm. Produced. The alloy structure of each sample (sintered material) is a pearlite structure with a dense base, and is dotted with reddish Cu-Sn alloy particles. In the sample having a high phosphorus content, many white-white Fe-PC-based alloy phases (steadite phases) are scattered, but in the sample having a low phosphorus content, it is decreased. . In addition, when the amount of free graphite of the sample having a large phosphorus content (0.3%) and the sample having a small amount (0.03%) was measured and compared from the insoluble residue obtained by dissolving the chips of each sample in an acid, In the latter sample, free graphite is increased by about 0.2 to 0.3%.
[0013]
Next, the machinability and wear resistance of each sample thus obtained were tested. Machinability is a sample containing 5% copper and 0.3% phosphorous corresponding to the material of the prior invention. The time required for reaming the inner diameter of the sample and cutting 10 mm in the axial direction is obtained. Comparison was made in terms of an index of 100. Therefore, the smaller the index is, the easier it is to cut and the shorter the processing time, that is, the better the machinability. In addition, the wear resistance is determined by finishing each sample to the specified shape and dimensions of the valve guide and mounting it on the engine simulation test device, and sliding it back and forth for a specified time with a valve loaded with a radial load in the heated state. The difference in the inner diameter of the sample was determined as the amount of wear and compared.
[0014]
The drawing is a graph of these data, FIG. 1 shows the relationship between phosphorus content and machinability, and FIG. 2 shows the relationship between phosphorus content and wear resistance. From this graph, it can be understood that the influence of copper is superior as the amount of copper increases in both machinability and wear resistance regardless of the phosphorus content in the copper content range of 1 to 5%. Next, with regard to the influence of phosphorus, as the phosphorus content is reduced from 0.3%, the machinability improves almost linearly, and this tendency continues even if the conventional lower limit of 0.1% is cut off. ing. Therefore, sufficient significance is recognized for stopping the phosphorus content below 0.1% in order to improve machinability. As for wear resistance, the amount of wear is slightly increased as a result of the suppression of phosphorus compared to the material of the previous invention. It is in a range that is possible, and is far superior to the wear amount of 170 μm of gray cast iron valve guides under the same test conditions.
[0015]
(Example 2) The raw material powder prepared in Example 1 is used, natural graphite powder is 2%, Cu-10% Sn alloy powder is 5%, Fe-20% P alloy powder is 0.25%, and fire-fighting A mixed powder was prepared by adding 0.8% pyroxene powder, 0.2% manganese sulfide powder, and 0.75% zinc stearate to the remaining reduced iron powder. Its total composition is C ... 2%, Cu ... 4.5%, Sn ... 0.5%, P ... 0.05% (in addition to pyrite, manganese sulfide, and iron balance). For comparison, a mixed powder was prepared by omitting the pyroclastic powder and manganese sulfide powder from the above composition.
[0016]
Next, these two types of mixed powders were molded and sintered under the same conditions as in Example 1, and the machinability and wear resistance of the obtained samples were tested. As a result, the former data containing pyroxene and manganese sulfide had a machinability index of 23 and a wear amount of 50 μm, whereas in the latter case, the machinability index of 25 and the wear amount of 55 μm. The former is better in both machinability and wear resistance. Looking at the structure of both samples, in the former case, free graphite, pyroxene and manganese sulfide are dispersed as lubricants in the base, whereas in the latter, only free graphite is present. The difference is considered to have caused the difference in characteristics.
[0017]
【The invention's effect】
The valve guide material according to the present invention has a machinability that is higher than that of the prior art while maintaining wear resistance that is not significantly different from that of the prior art. Therefore, the present invention is extremely useful when the workability of the valve guide material is particularly emphasized in view of working conditions in the assembly process of the engine, compatibility with the machine tool used, and various other relationships.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the phosphorus content of a sample and machinability.
FIG. 2 is a graph showing the relationship between the phosphorus content of a sample and the wear resistance.

Claims (3)

When the alloy composition is C ... 1.5-4% by mass, Cu ... 1-5%, Sn ... 0.1-2%, P ... 0.01-0.1% and Fe balance, A sintered valve guide material characterized by exhibiting a structure in which free graphite is dispersed in a main base. Alloy composition by mass ratio: C ... 1.5-4%, Cu ... 1-5%, Sn ... 0.1-2%, P ... 0.01-less than 0.1%, of pyroxene and manganese sulfide A sintered valve guide material characterized by exhibiting a structure in which free graphite, dolomite and manganese sulfide are dispersed in a base mainly composed of pearlite, with a total of less than 4% and the balance of Fe. The sintered valve guide material according to claim 2, wherein the total amount of free graphite, dolomite and manganese sulfide dispersed in the matrix is 4% or less.

Images