JPS63109142A - Ferrous sintered alloy combining heat resistance with wear resistance - Google Patents

Abstract

PURPOSE:To obtain a ferrous sintered alloy excellent in heat resistance and wear resistance at high temp. and reduced in attack upon opposite materials, by specifying a composition consisting of Mo, W, Cr, Si, Mn, P, C, B, RE, oxides of RE, and Fe. CONSTITUTION:The ferrous sintered alloy combining heat resistance with wear resistance has a composition consisting of, by weight, 7-25% Mo and/or W, 2-10% Cr, 0.1-0.9% Si, <=0.7% Mn, <=0.05% P, 0.5-2.0% C, 0.5-2.0% B, 0.1-5%, in total, of one or more elements among RE including Sc and Y and/or 0.3-7%, in total, of one or more kinds among the oxides of RE including Sc and Y, and the balance Fe with impurities and further containing, if necessary, <=20%, in total, of one or more elements among V, Nb, Ta, Ti, Zr, Hf, Co, and Ni. This alloy is reduced in attacking opposite materials and has superior conformability.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention can be used as a material for parts that require heat resistance and wear resistance at high temperatures, such as valve seats of internal combustion engines, The present invention relates to an iron-based sintered alloy that exhibits excellent thermal properties and high-temperature wear resistance when used for valve faces, etc., and exhibits less aggressiveness to mating materials and good conformability.

(Prior Art) In recent years, with the demand for higher speeds and higher outputs for internal combustion engines, wear of valve train members of internal combustion engines has become a problem. In particular, valve seats are becoming more susceptible to sliding due to higher combustion temperatures in engines. Requirements regarding dynamic properties and durability have become extremely strict.

In general, valve seats are exposed to high temperatures and struck at high speeds, so they are required to have excellent heat resistance, wear resistance, pitting resistance, and compatibility with valve materials. .

In view of the above facts, the inventors of the present invention have applied for
In No. 150, the present invention was filed for an invention of a wear-resistant iron-based sintered alloy for sliding members of internal combustion engines, in which fine carbides, borides, and/or carborides are uniformly dispersed in a matrix structure. The iron-based sintered alloy according to the invention of Japanese Patent Application No. 61-54150 contains 1% by weight, one or both of Mo and W; 5-20% Cr;
2-10%, Si; 0.1-0.9%, Mn; 0
, 7% or less, P, 0.05% or less, C; 0.1 to 0.
Kudzu is characterized by having 8% B, 0.5 to 2.0%, and the balance consisting of Fe and impurities.

(Problems to be Solved by the Invention) However, in the iron-based sintered alloy according to the invention of Japanese Patent Application No. 61-54150, the operating temperature of the valve seat is up to 45
Since it is assumed to be at around 0°C, it exhibits excellent characteristics without any problems when used in general automobile internal combustion engines, but with the shift to turbocharging in diesel engines and lean burn in gasoline engines, etc. In a high-temperature combustion environment, there was still room for improvement in thermal properties and wear resistance.

As a result of various experiments and research, the present inventors increased the C content to 0.5 to 2.0% by weight compared to the previous invention,
The content of Mo and W is increased to 7 to 25%, a total of 0.1 to 5% by weight of one or more selected from rare earth elements, and/or one selected from oxides of rare earth elements. It was discovered that by containing the above in a total of 0.3 to 7% by weight, a heat-resistant and wear-resistant material that exhibits high wear resistance and conformability even at high temperatures exceeding 500°C can be obtained. The present invention was completed after confirming that it exhibits good characteristics.

[Structure of the Invention] (Means for Solving the Problems) The heat-resistant and wear-resistant iron-based sintered alloy according to the first invention of the present inventors contains one or two of Mo and W in weight%. , 7-25%, Cr; 2-10%, Si; 0.1-0.
9%, Mn; 0, 7% or less, P, 0.05% or less, C, 0.5-2.0%, B, 0.5-2.0%, S
A total of one or more types selected from rare earth elements containing c and Y; 0.1 to 5% and/or a total of one or more types selected from rare earth element oxides containing Sc and Y; 0. It is characterized in that it consists of 3 to 7%, the balance Fe and impurities.

In addition to the above composition, the wear-resistant iron-based sintered alloy according to the second invention of the present inventors contains V and Nb.

It is characterized by containing a total of 20% or less of one or more selected from Ta, Ti, Zr, Hf, Go, and N1 (7).

In the wear-resistant iron-based sintered alloys according to the two inventions having the above-mentioned compositions, the inventors of the present invention have found that, in particular, the matrix structure contains fine and sufficient amounts of carbides, fine borides, and/or fine borides.
Alternatively, materials in which carborides are uniformly dispersed and the above-mentioned rare earth elements are diffused in the matrix exhibit excellent heat resistance and good wear resistance, and are particularly useful for, for example, valve seats and valve faces of internal combustion engines. It was found that when used, it exhibits excellent heat resistance and wear resistance.

The present invention has been made based on the above findings, and the reason why the component composition (weight %) is limited as described above will be explained below.

Mo and W: Mo and W combine with C and B together with Fe and Cr in the components to form double carbides, complex borides, or double carbides, providing wear resistance, and some of them are solidified in the matrilas. Melts to strengthen the matrix and also improves heat resistance. In particular, the oxide film of Mo has self-lubricating properties, and its inclusion has a great effect, but if it is less than 7%, the desired effect cannot be obtained and the wear resistance is insufficient, and if it is contained in an amount exceeding 25%, it becomes even more effective. Since no improvement effect was observed and it was not economical, the content was determined to be 7 to 25% in total of one or two types.

Cr; Cr forms double carbides and complex borides together with Mo, W, etc. to improve wear resistance, and at the same time, dissolves solidly in the matrix to increase hardenability and further improves temper hardening ability. It has the effect of increasing the corrosion resistance of the base. However, the effect is not observed at less than 2%, and 1
If the content exceeds 0%, not only will there be no further improvement effect, but the mechanical strength will decrease and the aggressiveness to the mating material will increase, so the content should be set at 2 to 10%. Established.

Si: If Si is added in an amount less than 0.1%, the deoxidizing effect is small, the oxygen content in the powder increases, sinterability decreases, and M2C-based coarse plate-shaped carbides are likely to precipitate. Therefore, the compatibility with the mating member decreases. On the other hand, the amount added is 0.
If the content exceeds 9%, there is no improvement in the deoxidizing effect, and the powder becomes round and the moldability is reduced, so the content was set at 0.1 to 0.9%.

Mn: Like the aforementioned Si, Mn has a deoxidizing effect, and adding it lowers the oxygen content in the powder and improves sinterability, but if it exceeds 0.7%, the shape of the powder becomes round. As a result, the moldability of the powder decreases, making it more likely to cause cracks on the edges of the compact, so the content, if added at all, was set at 0.7% or less.

P; In the case of wear-resistant sintered alloys, P is generally added as a sintering accelerating element in an amount of about 0.2 to 0.8%, but in the case of the sintered alloys of the present invention, P is When the amount added exceeds 0.05%, the complex boride or the carbide boride becomes coarse and the compatibility with the mating material decreases, and the complex boride or the carbide boride forms a network at the grain boundaries. The content is set at 0.05% or less because the precipitation reduces the strength, which also reduces the pitting resistance, especially when high surface pressure is applied.

C: A part of C combines with carbide-forming elements such as Mo, W, Cr, and V to form double carbides to improve wear resistance,
The remainder dissolves in the matrix, giving hardness and strength, and stability to the structure at high temperatures; however, if it is less than 0.5%, this effect is not observed, and if it exceeds 2.0%, double carbides precipitate. The content is set at 0.5 to 2.0% because the amount increases and coarsening occurs, and the compatibility with the mating material decreases.

The method of adding C is as follows: vacuum annealed Fe-Mo
-W-Cr-(V)-3i-(Mn)-(Co
)-(Rare Earth)-C-based atomized alloy powder must be added. This is because when C is added alone in the form of graphite powder, it combines with Fe-B or Fe-Cr-B added as a B source, which will be described later, and forms a network of coarse carborides along grain boundaries during sintering. Fe-Mo-W-Cr-(V)-S i- subjected to vacuum annealing
When added in the form of (Mn)-(Co)-(rare earth)-C-based atomized alloy powder, most of the C becomes Mo, W, and Cr during vacuum annealing after atomization.

Fe-B and Fe-C combine with V, Fe, etc. and precipitate in the atomized alloy powder as fine double carbides.
Even if r-B is added, during sintering, the double carbide at the grain boundary or near the grain boundary will combine with Fe-B or Fe-Cr-B to form a double carbide that is slightly larger than the original double carbide. However, the fine double carbides within the grains remain as they are after sintering, and the F
Mo in e-B, Fe-Cr-B and atomized alloy powder
This is because a unique structure of the sintered alloy according to the present invention is obtained, which is uniformly dispersed together with fine complex borides generated by decomposition and precipitation between the sintered alloy and W.

B; B forms a complex boride together with Mo, W, (r, and F6 in the components) to provide wear resistance and compatibility, and a portion is dissolved in the matrix to improve hardenability. Further, a part of the complex boride is also combined with C to form a complex boride, thereby improving wear resistance.

As described above, B is a major component essential for forming fine complex borides or carbonized borides to improve the wear resistance and conformability resistance of the sintered alloy of the present invention, but B is less than 0.5%. No effect was observed with the addition of more than 2.0%, while no further improvement was observed with the addition of more than 2.0%, which instead resulted in coarsening of the complex boride and reduced compatibility with the mating material. The content was determined to be 0.5 to 2.0%.

As mentioned above, the amount of B added in the sintered alloy according to the present invention needs to be 0.5 to 2.0%, but particularly excellent properties are shown when the amount of B added is equal to the amount of M o + W added. Between,
This is when the relationship of [Mo+W content (atomic weight)]/[B content (atomic weight)]=0.8 to 1.5 is satisfied. This is because when the above atomic ratio exceeds 1.5, the amount of complex boride produced is small and the compatibility, which is a characteristic of the alloy of the present invention, is reduced, and when the above atomic ratio is less than 0.8, complex boride is formed. This is because the particles become coarser and precipitate at the grain boundaries in the form of a network, resulting in a decrease in compatibility with the mating material and at the same time a decrease in pitting resistance of itself.

The method of adding B is Fe-B or Fe-Cr.
It is preferable to add it in the form of -B alloy powder.

Rare earth elements and/or oxides thereof including Sc and Y, Ce, Nd, Sm, Eu, Gd, Yb.

Rare earth elements such as Y and Sc concentrate on the surface as the temperature rises, and together with Fe, Cr, etc., form an oxide film with good heat resistance. Furthermore, it has the effect of preventing the coarsening of crystal grains and the coarsening of carbides during sintering, and these effects together contribute to improved wear resistance at high temperatures. However, if the total amount of rare earth elements is less than 0.1%, the desired effect cannot be obtained, and even if it is contained in more than 5%, no further effect is observed, and it is not economical, so the content is 1
The total content of all species and above was set at 0.1 to 5%. These rare earth elements are Fe-Mo-W-Cr-(V)-3i-
(Mn) (Co)-Rare earth--It may be contained in the matrix powder in the form of an atomized alloy, or it may be added separately or separately in the form of a ferroalloy, or when two or more types are added separately. may be added in the form of Mitsushmetal.

Furthermore, the above-mentioned rare earth elements may be added as oxides, and in that case, in order to obtain the same effect, the total amount of one or more oxides is required to be 0.3% or more, but 7%
Even if the content exceeds 100%, no further effect will be observed, and in some cases, when even higher high-temperature wear resistance is required, the rare earth element and the oxide of the rare earth element may be added at the same time.

V, Nb, Ta, Ti, Zr, Hf, Co, NiV,
N b , T a , T i ,
2: r, Hf, Co.

Ni is an element effective in increasing the toughness of the alloy.

Among these, V, Nb, and Ta are combined with Fe and Cr.
It combines with Mo to form an extremely hard double carbide.
, forming double carbides and complex borides in the form of partial substitution of W to provide wear resistance, and some of them are solid dissolved in the matrix to strengthen the matrix and increase tempering hardenability. There is.

Further, these V, Nb, and Ta have the effect of preventing coarsening of crystal grains during sintering and also preventing coarsening of carbides. These effects are not so noticeable when the total content of one or more of V, Nb, and Ta is less than 0.5%, resulting in a decrease in wear resistance and strength. Since no further improvement effect is observed and it is not economical, even if it is added, it is preferable to limit its content to 0.5 to 8%.

Furthermore, Ti, Zr, Hf, and Co are boride-forming elements, and one or more of these may be added in an amount of 12% or less as necessary.In particular, Co is a boride-forming element, and Co is a boride-forming element. In addition to forming a complex boride by substituting with
It is desirable to add it when used for valve seats of engines equipped with turbochargers.

Furthermore, N as long as the matrix does not become austenitized
It is also possible to add Ni because adding Ni not only improves the toughness of the matrix but also improves the corrosion resistance, and it is suitable for application to parts that are subject to severe high-temperature corrosion wear such as diesel engine valve seats. is particularly effective.

However, if the amount of Ni added increases and the matrix becomes austenite, not only will the hardness decrease, but also the adhesion with the mating material will increase.
Even if it is added, it is preferable to add it within a range that does not cause austenitization.

However, V, Nb, Ta, Ti, Zr, Hf.

If the amounts of Co and Ni added are too large, the toughness and wear resistance may deteriorate, so it is desirable that the total amount of these is 20% or less.

(Example) Hereinafter, examples of the heat-resistant and wear-resistant iron-based sintered alloy according to the present invention will be described in comparison with comparative examples.

<Examples 1 to 10. Comparative Examples 1 to 7> Particle size -100 mesh subjected to vacuum annealing as raw material powder,
Fe-Cr-Mo-W-Si-C-rare earth/rare earth oxide-based atomized alloy powder (V, Nb, T
a, Co also added), -325 mesh F e -M
o powder or pure Mo powder.

-325 mesh Fe-W powder or pure W powder, -
250 mesh Fe-8 alloy powder (B: 20% content)
, -250 mesh (7) Fe 2652 alloy powder,
-250 mesh ferrotitanium.

Ferrozirconium, ferrohafnium alloy powder, -
325 mesh carbonyl Ni powder, etc. were appropriately blended so as to have the final component composition shown in Table 1, and zinc stearate was added as a lubricant and mixed, and this mixed powder was mixed with 6 to
The powder bodies are formed by pressing at a pressure of nf/cm2, and then each of the green bodies is held in a vacuum at a temperature of 1150 to 1260°C for 60 minutes to sinter, and then subjected to quenching and tempering treatment. Inventive alloys 1-10 and comparative alloys 1-7 were produced.

<Examples 11 to 17. Comparative Examples 8 to 12> Particle size -100 mesh Fe-Cr- subjected to vacuum annealing as raw material powder
Mo-W-Si-C atomized alloy powder (V, Nb, Ta as necessary).

CO also added), -250 mesh La, Ce.

Powders of Nd, Sm, Eu, Gd, Yb, Y, Sc, metals or oxides thereof, -325 mesh Fe-Mo powder or pure Mo powder, -325 mesh Fe-” wV powder or pure W powder, -250 mesh Fe-8 alloy powder (B, 20% content).

-250 mesh Fe-26%P alloy powder.

-250 mesh ferrotitanium, ferrozirconium, ferrohafnium alloy powders, -325 mesh carbonyl Ni powder, etc. were appropriately blended to give the final composition shown in Table 1, and zinc stearate was added as a lubricant. The alloys 11 to 17 of the present invention were mixed and then molded, sintered and heat treated under the same conditions as in Examples 1 to 10 and Comparative Examples 1 to 7. Comparative alloys 8-12 were produced.

Evaluation example> Next, the above-mentioned present invention alloys 1 to 17 and comparative alloys 1 to 1
2 into a valve seat shape to create a valve that imitates the actual machine.
A wear test was conducted using a valve seat tester. This testing machine automatically adjusts the temperature, heats the valve and valve seat by burning propane gas, and opens and closes the valve by driving an eccentric cam to reproduce the wear and tear of the valve and valve seat. The test conditions in this case are as shown in Table 2.

In Table 2, the wear depth of the valve seat and valve was measured after the above test. These measurement results are also shown in Table 1.

As is clear from Table 1, the test was conducted at high temperatures and the grinding Jt conditions were severe, so alloys with compositions outside the range of the present invention, as shown in Comparative Alloys 1 to 12, were manufactured. Regarding the valve seat, the wear force of the valve seat and the mating valve is large, and pitching has occurred in some valve seats, and the valve seat does not exhibit satisfactory characteristics.

On the other hand, the valve seat manufactured from the alloy of the present invention shows excellent characteristics, with little wear on the valve seat and the mating valve, and no pitting at all in the valve seat.

[Effects of the Invention] As described above, the iron-based sintered alloy according to the first invention of the present inventors contains one or two of Mo and W in weight%.
Seed; 7-25%, Cr; 2-10%, Si; 0.1-0
．． 9%, Mn; 0.7% or less, P; 0.05% or less, C
; Total of one or more rare earth elements including O, S ~ 2.0%, B, 0.5 ~ 2.0%, Sc and Y; 0.1 ~ 5% and/or Sc and A total of one or more types selected from oxides of rare earth elements containing Y;
0.3 to 7%, the balance being Fe and impurities, and the iron-based sintered alloy according to the second invention has, in addition to the above components, (1).

Since the total content of one or more types selected from Nb, Ta, Ti, Zr, Hf, Co, and Ni is 20% or less, the alloys according to any of the inventions do not contain microscopic hard particles in the matrix. The complex carbide, complex boride, and/or double carbide boride are uniformly dispersed, and the rare earth element and/or rare earth element oxide is sufficiently dispersed in the matrix. %l weave, and is an alloy with extremely excellent heat resistance, abrasion resistance, and compatibility with mating materials. Therefore, when the alloy of the present invention is used, for example, as a material for a valve seat of an internal combustion engine that is exposed to considerably high temperatures, it exhibits excellent heat and wear resistance due to the heat-resistant oxide film caused by rare earth elements and the hard particles, and further It has extremely useful industrial properties, such as being able to improve the wear of mating parts due to the excellent compatibility of the complex boride and/or the carbonated boride.

Claims (2)

[Claims] (1) Any one or two of Mo and W in weight%
Seed; 7-25%, Cr; 2-10%, Si; 0.1-0
．． 9%, Mn; 0.7% or less, P; 0.05% or less, C
; 0.5-2.0%, B; 0.5-2.0%, a total of one or more kinds selected from rare earth elements including Sc and Y; 0.1-5% and/or Sc and A total of one or more types selected from oxides of rare earth elements containing Y;
A heat-resistant and wear-resistant iron-based sintered alloy characterized by comprising 0.3 to 7%, the balance being Fe and impurities. (2) Any one or two of Mo and W in weight%
Seed; 7-25%, Cr; 2-10%, Si; 0.1-0
．． 9%, Mn; 0.7% or less, P; 0.05% or less, C
; 0.5-2.0%, B; 0.5-2.0%, a total of one or more kinds selected from rare earth elements including Sc and Y; 0.1-5% and/or Sc and A total of one or more types selected from oxides of rare earth elements containing Y;
0.3-7%, and V, Nb, Ta, Ti, Zr, H
Total of one or more selected from f, Co, and Ni; 2
A heat-resistant and wear-resistant iron-based sintered alloy characterized by comprising 0% or less, the balance being Fe and impurities.