JPH0753900B2 - Heat and wear resistant iron-based sintered alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention is used as a material for parts required to have heat resistance and wear resistance at high temperatures. The present invention relates to an iron-based sintered alloy that exhibits excellent heat resistance and high-temperature wear resistance when used as a valve face, etc., and exhibits good compatibility with a small attack on the mating material.

(Prior Art) In recent years, wear of valve train members of an internal combustion engine is becoming a problem with the demand for higher speed and higher output of the internal combustion engine. The requirements for dynamic properties and durability are extremely demanding.

In general, valve seats are required to have excellent heat resistance, wear resistance, and pitting resistance in order to be hit at high speed, as well as to be compatible with valve materials, in addition to being exposed to high temperatures. .

In view of the above facts, the present inventors have filed a patent application No. 61-54150.
Filed an invention of a wear-resistant iron-based sintered alloy for sliding members of an internal combustion engine in which fine carbides and borides and / or carboborides are uniformly dispersed in the matrix structure. The iron-based sintered alloy according to the invention of Japanese Patent Application No. 61-54150 is, in order to obtain a predetermined structure, one or two of Mo and W in 5% by weight; 5 to 20%, Cr; ~ 10%, Si; 0.1-0.9
%, Mn; 0.7% or less, P; 0.05% or less, C; 0.1 to 0.8%, B; 0.
It is characterized by being composed of 5 to 2.0% and the balance 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, it is assumed that the maximum operating temperature of the valve seat is about 450 ° C. When used in an internal combustion engine for automobiles, it shows extremely excellent characteristics without any problems, but in the environment of high temperature combustion accompanying the turbocharger of diesel engine and lean combustion of gasoline engine, heat resistance and wear resistance There was still room for improvement.

As a result of various experiments and studies, the present inventors increased the C content to 0.5 to 2.0% by weight and the Mo and W contents to 7 to 25% as compared with the previous invention, By adding one or more kinds selected from rare earth elements in a total of 0.1 to 5% by weight and / or one or more kinds selected from oxides of rare earth elements in a total of 0.3 to 7% by weight, 500 ° C. The present invention has been completed by finding that a heat resistant and wear resistant material having high wear resistance and conformability even at a high temperature exceeding the above can be obtained, and confirming that it exhibits favorable characteristics as a material such as a valve seat.

[Structure of the Invention] (Means for Solving Problems) The heat-resistant and wear-resistant iron-based sintered alloy according to the first invention of the present inventors is, in weight%, either one or two of Mo and W. ; 7
~ 25%, Cr; 2-10%, Si; 0.1-0.9%, Mn; 0.7% or less,
P; 0.05% or less, C; 0.5 to 2.0%, B; 0.5 to 2.0%, the total of one or more kinds selected from rare earth elements including Sc and Y; 0.1 to 5% and / or Sc and Y are included. Sum of at least one selected from oxides of rare earth elements; 0.3 to 7
%, The balance Fe and impurities.

Further, the wear-resistant iron-based sintered alloy according to the second invention of the present inventors is one kind selected from V, Nb, Ta, Ti, Zr, Hf, Co and Ni in addition to the above composition. It is characterized by including the above total; 20% or less.

In the wear resistant iron-based sintered alloys according to the two inventions having the above-mentioned compositions, the present inventors have found that a fine and sufficient amount of carbide and fine boride and / or
Alternatively, a material in which carbon boride is uniformly dispersed and the above-mentioned rare earth element is diffused in the matrix exhibits excellent heat resistance and good wear resistance, and particularly in, for example, a valve seat and a valve face of an internal combustion engine. It has been found that when used, it exhibits excellent heat resistance and wear resistance.

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

Mo and W; Mo and W are combined with C and B together with Fe and Cr in the components to form double carbides, double borides or double carbon borides to give wear resistance, and some are solid in the matrix. It melts and strengthens the matrix and also improves heat resistance. And especially Mo
Oxide film has self-lubricating property, and the effect of containing it is great, but if it is less than 7%, the desired effect is not obtained and wear resistance becomes insufficient, and if it exceeds 25%, further improvement effect is not obtained. Since it is not recognized and it is not economical, the content of 1 type or 2 types was defined as 7 to 25% in total.

Cr; Cr forms a double carbide or double boride with Mo, W, etc. to improve wear resistance, and at the same time, forms a solid solution in the matrix to increase hardenability, and further has the effect of increasing temper hardening ability. It also has the effect of increasing the corrosion resistance of the base. But,
If the content is less than 2%, the effect is not recognized, and if the content exceeds 10%, not only there is no further improvement effect, but also the mechanical strength decreases and the aggressiveness to the mating material increases. Therefore, the content was determined to be 2 to 10%.

Si; Si has a small deoxidizing effect with an addition amount of less than 0.1%, the oxygen content in the powder increases, and the sinterability decreases, and
Coarse plate-like M ₂ C-based carbides are likely to precipitate, and the compatibility with the mating member deteriorates. On the other hand, even if the addition amount exceeds 0.9%, the deoxidizing effect is not improved, the powder becomes round and the moldability is only reduced, so the content is set to 0.
It was set at 1 to 0.9%.

Mn; Mn has the same deoxidizing effect as Si described above, and adding it lowers the oxygen content in the powder and improves the sinterability, but if it exceeds 0.7%, the shape of the powder becomes round. The decrease in the moldability of the powder tends to cause chipping of the edge portion of the molded body, so the content of the powder even if added is determined to be 0.7% or less.

P; P is generally widely used as a sintering promoting element in the case of a wear-resistant sintered alloy, but in the case of the sintered alloy according to the present invention, the addition amount of P is 0. .
When the content exceeds 05%, the compound boride or compound carbon boride becomes coarse and its compatibility with the mating material decreases, and at the same time the compound boride or compound carbon boride precipitates in the network at the grain boundaries and the strength increases. If the content is lowered, the pitting resistance property is also reduced especially when a high surface pressure is applied. Therefore, the content is set to 0.05% or less.

C; C partly combines with carbide forming elements such as Mo, W, Cr and V to form double carbides to improve wear resistance, and the rest forms a solid solution in the matrix to give hardness and strength. , It gives the stability of the structure at high temperature, but if it is less than 0.5%, its effect is not observed, and if it exceeds 2.0%, the precipitation amount of double carbide increases and coarsening occurs, and the compatibility with the partner material decreases. Therefore, the content was determined to be 0.5 to 2.0%.

The method for adding C is as follows: vacuum-annealed Fe-Mo-
W-Cr- (V) -Si- (Mn)-(Co)-(rare earth) -C
It is necessary to add it in the form of a system atomized alloy powder. This is because if C is added alone in the form of graphite powder, it will combine with Fe-B or Fe-Cr-B added as a B source, which will be described later, to form coarse carbon boride at the time of sintering into a network along grain boundaries. In contrast to the precipitation, which increases the aggressiveness to the mating material, vacuum-annealed Fe-Mo-W-Cr-
When added in the form of (V) -Si- (Mn)-(Co)-(rare earth) -C atomized alloy powder, most of C is Mo, W, Cr, V, during vacuum annealing after atomization. Since fine double carbides are precipitated in the atomized alloy powder in association with Fe and the like, even if Fe-B or Fe-Cr-B is added, the double carbides at the grain boundaries or near the grain boundaries during the sintering are Fe. -B and Fe-Cr-
When combined with B, it only becomes a slightly larger double carbon boride than the original double carbide, and the fine double carbide in the grains remains as it is after sintering, and Fe-B or Fe-Cr-B and atomized alloy powder This is because a structure peculiar to the sintered alloy according to the present invention, which is uniformly dispersed together with fine double boride generated by decomposition and precipitation with Mo and W in the inside, can be obtained.

B; B forms a double boride together with Mo, W, Cr and Fe in the components to provide wear resistance and conformability, and partly forms a solid solution in the matrix to improve hardenability. Further, a part of the above-mentioned compound boride is combined with C to form compound boride and improve the wear resistance.

As described above, B is an essential main component for improving the wear resistance and the running-in resistance of the sintered alloy of the present invention by forming fine double boride or double carbon boride, but addition of less than 0.5% On the other hand, the effect is not recognized, on the other hand, even if it exceeds 2.0%, further improvement effect is not recognized, and rather, the coarsening of the complex boride occurs and the compatibility with the counterpart material decreases, so its content is 0.5 It was set at ~ 2.0%.

The B addition amount of the sintered alloy according to the present invention needs to be 0.5 to 2.0% as described above, but particularly excellent characteristics are that the B addition amount is between the Mo + W addition amount and the [Mo + W content is Amount (atomic weight)] / [B content (atomic weight)] = 0.8 to 1.5 is satisfied. This has an atomic ratio of 1.5
If it exceeds, the compounding amount of the compound of the present invention is small and the familiarity is reduced, and if the atomic ratio is less than 0.8, the compound of boride becomes coarse and forms a network at grain boundaries. The reason for this is that they are deposited and the compatibility with the mating material is reduced, and at the same time, the pitting resistance of oneself is reduced. The method of adding B is Fe-B
Alternatively, it is preferable to add in the form of Fe-Cr-B based alloy powder.

Rare earth elements including Sc and Y and / or oxides of these rare earth elements such as La, Ce, Nd, Sm, Eu, Gd, Yb, Y and Sc are concentrated on the surface as the temperature rises, and Fe, Cr And the like form an oxide film having good heat resistance. Furthermore, it also has an effect of preventing coarsening of crystal grains during sintering and an effect of preventing coarsening of carbides, and these effects combine to contribute to improvement of wear resistance at high temperatures. However, if the total amount of rare earth elements is less than 0.1%, the desired effect is not obtained, and if it is contained in excess of 5%, no further effect is observed, and it is not economical. The above total is set to 0.1 to 5%. These rare earth elements are Fe-Mo-W-Cr- (V) -Si- (Mn)-
It may be contained in the matrix powder in the form of (Co) -rare earth-C atomized alloy, or may be added alone or separately in the form of ferroalloy. When two or more kinds are added separately, they may be added in the form of misch metal.

Further, the rare earth element may be added as an oxide, and in that case, in order to obtain the same effect, 0.3% or more in total of at least one kind of oxide is necessary, but more than 7% Even if contained, no further effect is observed. Further, in some cases, when further 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, Ni V, Nb, Ta, Ti, Zr, Hf, Co, Ni are all effective elements for increasing the toughness of the alloy.

Of these, V, Nb, Ta combine with C together with Fe and Cr to form an extremely hard double carbide, and at the same time form a double carbide or double boride in the form of a part of Mo, W substituted to form wear resistance. And partly forms a solid solution in the matrix to strengthen the matrix and enhances the temper hardening ability. Further, these V, Nb, and Ta also have the effect of preventing the coarsening of crystal grains during sintering and the coarsening of carbides. These effects are not so noticeable when the total of one or more of V, Nb, and Ta is less than 0.5%, and the wear resistance and strength are deteriorated. The effect of improvement is not recognized and it is not economical, so even if added, its content should be 0.5 to 8%.

Further, Ti, Zr, Hf, and Co are boride-forming elements, and one or more of them may be added in the range of 12% or less, if necessary. And in particular, Co not only replaces a part of Mo, W, etc. to form a double boride, but also forms a solid solution in the matrix to improve the hardness at high temperature. When it is used for valve seats, etc., it is desirable to add it.

Furthermore, Ni is used as long as the matrix does not become austenite.
May be added. This is because the addition of Ni not only improves the toughness of the matrix but also improves the corrosion resistance, and is particularly effective when applied to parts such as valve seats of diesel engines that are subject to severe hot corrosion wear. However, when the amount of Ni added increases and the matrix becomes austenitic, not only does the hardness decrease, but also the cohesiveness with the mating material increases, so even if it is added, it becomes austenitic. It is better to add it within the range not to.

However, if the amount of V, Nb, Ta, Ti, Zr, Hf, Co, Ni added is too large, the toughness and wear resistance may be reduced, so it is desirable to keep the total of these 20% or less. .

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

<Examples 1 to 10, Comparative Examples 1 to 7> As a raw material powder, vacuum-annealed grain size −100 mesh F
e-Cr-Mo-W-Si-C-Rare earth / rare earth oxide-based atomized alloy powder (V, Nb, Ta, Co added if necessary), -32
5 mesh Fe-Mo powder or pure Mo powder, -325 mesh Fe-W powder or pure W powder, -250 mesh Fe
-B alloy powder (B: 20% content), -250 mesh Fe-26
% P alloy powder, -250 mesh ferrotitanium, ferrozirconium, ferrohafnium alloy powder, -325 mesh carbonyl Ni powder, etc. are appropriately mixed so as to have the final composition shown in Table 1, and stearin is used as a lubricant. Zinc acid is added and mixed, the mixed powder is pressed at a pressure of 6 tonf / cm ² to form a green compact, and then each of the green compacts is held in vacuum at a temperature of 1150 to 1260 ° C for 60 minutes. And after sintering,
Quenching and tempering treatments were performed to produce alloys 1 to 10 of the present invention and comparative alloys 1 to 7.

<Examples 11 to 17 and Comparative Examples 8 to 12> As a raw material powder, vacuum-annealed grain size-100 mesh F
e-Cr-Mo-W-Si-C based atomized alloy powder (V, Nb, Ta, Co added if necessary), -250 mesh La, Ce, Nd,
Sm, Eu, Gd, Yb, Y, Sc powder or their misch metal or their oxide powder, -325 mesh Fe-M
o Powder or pure Mo powder, -325 mesh Fe-W powder or pure W powder, -250 mesh Fe-B alloy powder (B; 2
0% content), -250 mesh Fe-26% P alloy powder, -25
Ferro-titanium, ferro-zirconium, ferro-hafnium alloy powder of 0 mesh, Carbonyl N of -325 mesh
i powder and the like are appropriately blended so as to have the final component composition shown in Table 1, zinc stearate as a lubricant is added and mixed, and the same as in Examples 1 to 10 and Comparative Examples 1 to 7 described above. The alloy of the present invention after being molded, sintered and heat-treated under the conditions
11-17, comparative alloys 8-12 were produced.

<Evaluation example> Next, the alloys 1 to 17 of the present invention and the comparative alloys 1 to 12 were processed into a valve seat shape, and a wear test was performed using a valve / valve seat tester simulating an actual machine. This tester heats the valve and valve seat by combustion of propane gas while adjusting the temperature automatically, and opens and closes the valve by driving an eccentric cam to reproduce the beating wear condition of the valve and valve seat. The test conditions in this case are as shown in Table 2.

Then, the wear depth of the valve seat and the valve was measured after the above test. The results of these measurements are also shown in Table 1.

As is clear from Table 1, the test was conducted at a high temperature and the wear conditions were severe, so that as shown in Comparative Alloys 1 to 12,
Valve seats made of alloys whose composition ranges deviate from the present invention have large wear of valve seals and mating valves, and in some cases pitching occurs in the valve seats, indicating satisfactory and satisfactory characteristics. Not not.

On the other hand, in the valve seat manufactured from the alloy of the present invention, wear of the valve seat and the mating valve is small, and pitting does not occur at all in the valve seat, showing excellent characteristics.

[Effects of the Invention] As described above, the iron-based sintered alloy according to the first invention of the inventors of the present invention is, in weight%, any one of Mo and W or 2
Species; 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%, Sc and Y A total of one or more selected from rare earth elements containing 0.1 to 5% and / or a total of one or more selected from oxides of rare earth elements containing Sc and Y; 0.3 to
The iron-based sintered alloy according to the second invention has a composition of 7%, balance Fe and impurities. In addition to the above components, the iron-based sintered alloy contains V, Nb, Ta, Ti, Zr, Hf, Co and Ni. Since the total content of one or more selected from the above; 20% or less is contained, in the alloy according to any of the invention, fine double carbide and fine double boride and / or double carbon boride are contained in the matrix as hard particles. Can be uniformly dispersed, and the structure can be such that the rare earth element and / or the oxide of the rare earth element is sufficiently dispersed in the matrix, and the heat resistance and wear resistance and the compatibility with the mating material are remarkably excellent. It is an alloy. Therefore, when the alloy of the present invention is used for a material such as a valve seat of an internal combustion engine which becomes extremely high in temperature, it exhibits excellent heat and wear resistance due to a heat resistant oxide film due to rare earth and the like and the hard particles, and Is a complex boride and /
Further, it has extremely useful properties in industry, such as wear of the mating member can be improved by the excellent conformability of the double carbon boride.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Kano 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Ichiro Tanimoto 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. ( 72) Inventor Hiroyuki Endo 3-chome 3-208 Tsukushino, Abiko-shi, Chiba (72) Inventor Hiroshi Ikenoue 3-26-3-102 Tokiwadaira, Matsudo-shi, Chiba (72) Inventor Kei Ishii 3 Serigaya, Konan-ku, Yokohama-shi, Kanagawa 31- (15) (56) References JP-A-59-200743 (JP, A)

Claims (2)

[Claims] 1. In weight%, one or two of Mo and W; 7 to 25%, Cr; 2 to 10%, Si; 0.1 to 0.9%, Mn; 0.7.
% Or less, P; 0.05% or less, C; 0.5 to 2.0%, B; 0.5 to 2.0%,
Total of one or more selected from rare earth elements including Sc and Y; 0.1 to 5% and / or total of one or more selected from oxides of rare earth elements including Sc and Y;
A heat- and wear-resistant iron-based sintered alloy, characterized in that it comprises 0.3 to 7%, the balance being Fe and impurities. 2. By weight%, one or two of Mo and W; 7 to 25%, Cr; 2 to 10%, Si; 0.1 to 0.9%, Mn; 0.7.
% Or less, P; 0.05% or less, C; 0.5 to 2.0%, B; 0.5 to 2.0%,
Total of one or more selected from rare earth elements including Sc and Y; 0.1 to 5% and / or total of one or more selected from oxides of rare earth elements including Sc and Y;
0.3 to 7%, and a total of at least one selected from V, Nb, Ta, Ti, Zr, Hf, Co, and Ni; 20% or less, the balance Fe and impurities, which are heat and wear resistant Iron-based sintered alloy.