JPH076027B2 - Method for producing 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 suitable for producing an iron-based sintered alloy used as a raw material of parts requiring wear resistance. , Applied to the production of iron-based sintered alloys that exhibit excellent wear resistance and conformability when used in sliding parts subject to high surface pressure, such as rocker arms and tappets of internal combustion engines The present invention relates to a method for producing a wear-resistant iron-based sintered alloy.

(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, and particularly, a rocker arm or a sliding portion between a tappet and a camshaft. The durability requirements for are extremely stringent.

Generally, the sliding parts of the rocker arm and tappet on the camshaft are subject to high surface pressure, so they have excellent wear resistance, scuffing resistance, and pitting resistance, and are also compatible with the camshaft. Required to have.

Conventionally, the rocker arm is made of chill cast iron, and the rocker arm sliding portion is subjected to surface treatment such as Cr plating or spray coating of self-fluxing alloy (for example, new edition Automotive Engineering Handbook 12th edition 1- 54 to 1-55), or Fe-
A high-alloy high-density sintered wear-resistant material obtained by liquid-phase sintering a powder compact of a Cr-C-based high-alloy powder (for example, JP-A-57-10).
No. 8246) is used.

However, among the above, the rocker arm made of chill cast iron has a problem in terms of pitting resistance and wear resistance, and there is a problem of peeling of the plating layer in the rocker arm that has been plated with Cr, and thus spray coating has been performed. The rocker arm has problems such as scuffing and wear of the cam shaft of the mating member. Further, in the case of a rocker arm made of a Fe-Cr-C-based sintered alloy, it often shows considerably better characteristics than the rocker arm made of chill casting, Cr plating or thermal spraying, but the surface pressure is very high. In the present situation, not only does the wear resistance of oneself be insufficient, but the wear amount of the camshaft is also increased, so that the required characteristics are not satisfied.

Therefore, the present inventors aim to develop a material having not only excellent wear resistance, scuffing resistance, and pitting resistance, but also having compatibility with a mating member from the above viewpoints. As a result of carrying out various studies as above, a wear-resistant iron-based sintered alloy having the following composition was developed (Japanese Patent Application No. 61-54150).

That is, the above wear-resistant iron-based sintered alloy, in weight ratio, Mo
One or two of W and W: 5 to 20%, Cr: 2 to 10
%, Si: 0.1 to 0.9%, Mn: 0.7% or less, P: 0.05% or less, C:
0.1-0.8%, B: 0.5-2.0%, the composition consisting of the balance Fe and impurities, an iron-based sintered alloy in which fine boride or carbon boride and carbide coexist in a matrix composed of bainite or martensite. is there.

(Problems to be Solved by the Invention) This iron-based sintered alloy is obtained by molding, sintering and heat treating a mixed powder of alloy steel powder and Fe-B alloy powder. The present inventors have found that the following problems exist when alloy powder containing too much B or alloy containing a large amount of Si or Al is used.

That is, when the structure of the obtained iron-based sintered alloy was observed when B was manufactured using an Fe-B alloy powder in which the amounts of Si and Al were too large, it was found that hard precipitates were dispersed in the matrix. It has a heterogeneous structure with a dilute portion and an aggregated portion, and SiO ₂ and Al ₂ O exist at the grain boundaries.
It was found that many inclusions of ₃ existed, and there was a problem that there was a limit to improvement of mechanical strength and pitching wear and abrasive wear.

(Object of the Invention) In view of the above-mentioned conventional problems, the present invention has been made for the purpose of achieving improvement in mechanical strength and pitching wear and abrasive wear of an iron-based sintered alloy. Completed by conducting various studies on effective means for uniformly precipitating oxides and carbon borides and reducing inclusions (Al ₂ OC, SiO ₂ ) that promote brittle fracture Is.

[Structure of the Invention] (Means for Solving Problems) That is, in the method for producing a wear-resistant iron-based sintered alloy according to the present invention, the weight ratio is C: 0.1 to 2.0% and B: 0.5 to 2.5. %, And at least one selected from the boride-forming elements Mo, W, Cr, V, Nb, Ta, Co: 5.5 to 34.1% as a basic component, and other Si, Mn, Ni, etc. In producing an iron-based sintered alloy containing, Fe-B alloy powder is used as a B supply source, and the Fe-
The composition of the B alloy powder is B: 2 to 18% by weight, impurity element Si: 0.5% or less, and the same impurity element A.
l: 0.1% or less, the balance Fe and inevitable impurities are used.

The method for producing a wear-resistant iron-based sintered alloy according to the present invention, as described above, in weight ratio, C: 0.1 ~ 2.0%, B: 0.5 ~ 2.5%.
And at least one selected from the boride-forming elements Mo, W, Cr, V, Nb, Ta, Co: 5.5 to 34.1% as a basic component, and other Si, Mn, Ni, etc. Although it is applied to the iron-based sintered alloy containing, the reason for limiting the component composition (% by weight) will be described below.

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 have high room temperature hardness. It has the effect of giving strength, but if it is less than 0.1%, its effect is small, 2.0%
If the content exceeds 0.2%, the precipitation amount of the double carbide increases and the coarsening occurs, and the compatibility with the counterpart material decreases, so the C content of the iron-based sintered alloy to which the present invention is applied is 0.1 to 2.0%, and more desirably.
0.1-0.8% is good.

B: B forms a complex boride with Mo, W, V, Cr, Fe in the components to give 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 forming fine double boride or double carbon boride to improve wear resistance and running-in resistance of the iron-based sintered alloy to which the present invention is applied. 0.5
%, The effect is small, while even if it exceeds 2.5%, no further improvement effect is observed, rather the coarsening of the complex boride occurs, and the compatibility with the counterpart material decreases,
The B content of the iron-based sintered alloy to which the present invention is applied is 0.5 to 2.5.
%, And more preferably 0.5 to 2.0%.

Si: If Si is less than 0.1%, the deoxidizing effect is small, the oxygen content in the powder increases, the sinterability decreases, and M ₂ C-based coarse plate-shaped carbides tend to precipitate, which makes it Familiarity decreases. On the other hand, even if the addition amount exceeds 0.9%, there is no improvement in the deoxidizing effect, the powder becomes round and the formability only decreases, so the Si content of the sintered alloy to which the present invention is applied is 0.1. It is good to set it to ~ 0.9%.

Mn: Mn has the same deoxidizing effect as Si described above, and by adding it reduces the oxygen content in the powder and improves the sinterability, but if it exceeds 0.7%, the shape of the powder becomes round. Since the moldability of the powder is lowered and chipping of the edge portion of the molded body is likely to occur, even if added, the Mn content of the iron-based sintered alloy to which the present invention is applied is preferably 0.7% or less. .

Mo and W Mo and W combine with Fe and Cr in the components to form C and B to form double carbides, double borides or double carbon borides to provide wear resistance, and some of them form a solid solution in the matrix. It has the effect of strengthening the matrix and increasing the tempering hardening ability, but if it is less than 5%, the desired effect is not obtained and the wear resistance becomes insufficient, and if it exceeds 30%, further improvement effect is recognized. Since it is not economical and is not economical, the Mo + W content of the sintered alloy to which the present invention is applied is preferably 5 to 30%.

Cr: Cr has the effect of forming double carbides and double borides 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 enhances temper hardening ability. Along with this, it also has the effect of increasing the corrosion resistance of the base, but not only if it is contained in excess of 10%, there is no further improvement effect, but also the mechanical strength decreases and the aggressiveness to the partner material increases. Therefore, its content is preferably 10% or less.

V, Nb, Ta: V, Nb, Ta combines with Fe and Cr together with C to form an extremely hard double carbide, and also forms a double carbide or double boride in a form in which a part of Mo or W is substituted. Abrasion resistance is provided, and a part of the solid solution forms a solid solution in the matrix to strengthen the matrix and enhances the temper hardening ability. 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 due to V, Nb, Ta
If it is less than 0.5%, it is not recognized so much, and wear resistance and strength are deteriorated. On the other hand, if it is added over 8%, no further improvement effect is recognized and it is not economical. The content is preferably 0.5-8%.

In addition to the above, 12% or less of a boride-forming element such as Co, Ti, Zr, or Hf may be added if necessary. In particular, when Co is not only substituted with Mo, W, etc. to form a double boride, but also forms a solid solution in the matrix to improve the red hot hardness, wear resistance during hot is required. It is particularly effective to add to.

The content of at least one selected from these boride-forming elements Mo, W, Cr, V, Nb, Ta, Co is 5.5 to 34.1.
%, More preferably 10 to 20%. That is, if it is less than 5.5%, the amount of boride and carbon boride formed is small, and the amount of solid solution in the matrix is also small, resulting in insufficient wear resistance, while if it exceeds 34.1%, the compressibility of the powder is poor. In addition, the sintered alloy becomes hard and brittle, which increases the aggressiveness to the mating material and deteriorates the machinability, which is not preferable.

In addition, Ni is used as long as the matrix does not become austenite.
May be added. This is especially effective when applied to parts with severe corrosive wear such as rocker arms and hydraulic lifters of EGR specifications for diesel engines because the addition of Ni improves the matrix's corrosion resistance. 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 does not become austenitic. It is good to add in the range.
Further, in the case of a wear-resistant sintered alloy, P is generally widely used as a sintering promoting element by adding about 0.2 to 0.8%, but in the case of the sintered alloy to which the present invention is applied, the amount of P added is If the content exceeds 0.05%, 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 form of a network at the grain boundaries and the strength increases. When the surface pressure is high, the pitting resistance characteristic is also deteriorated, so that the content is preferably 0.05% or less.

It is desirable that the wear-resistant sintered alloy to which the present invention is applied has the above composition. Next, Fe-B alloy powder is used as the B supply source when manufacturing such a sintered alloy. And the composition (weight ratio) of the Fe-B alloy powder is B: 2.
.About.18%, impurity element Si: 0.5% or less, and also impurity element Al: 0.1% or less, the balance Fe and the reason why the unavoidable impurities are used will be described.

B: B forms a complex boride with Mo, W, V, Cr, Fe in the components to provide wear resistance and conformability, and partly forms a solid solution in the matrix to improve hardenability. As described above, it is an element that functions. In the present invention, this B is Fe-
Although it is supplied in the form of B alloy powder, if the B addition amount is kept constant, the higher the B concentration, the smaller the addition amount of Fe-B alloy powder will be, but uneven distribution of the B-rich portion will occur and This causes the generation of a typical eutectic liquid phase and the coarsening of precipitated boride. On the other hand, the lower the B concentration, the larger the amount of addition of Fe-B is required. However, since the distribution of the added B is made uniform, the generation of the liquid phase occurs on average over the whole, and accordingly the boride is also finely divided. Some of them will be evenly deposited. However, since the amount of Fe-B alloy powder added is large, there is a problem that the balance alloy composition is reduced.

More specifically, when the B concentration of the Fe-B alloy powder is less than 2%, the amount of the Fe-B alloy powder added becomes too large, and accordingly, the balance of the alloy is maintained in order to maintain the overall component composition. Since the powder composition has a high concentration, the sinterability of moldability is deteriorated.
On the other hand, when the B concentration exceeds 18%, local eutectic liquid phase is generated and the boride is coarsened, so that not only the compatibility with the mating material and the wear resistance are deteriorated but also the shape of the part is changed. As a result, the dimensional accuracy of is also deteriorated. Further, since the hardness of the Fe-B alloy powder is MHV 1200 or higher, the problem of die wear during molding occurs. Therefore, the B content of the Fe-B alloy powder should be 2
-18%.

Impurity elements (Si and Al): In the production of Fe-B alloy powder, Si and Al are impurity elements that are particularly likely to be contained, and most of them are present as SiO ₂ and Al ₂ O ₃ . Then, these oxides collect as inclusions at the crystal grain boundaries by sintering, which hinders the densification due to liquid phase sintering and becomes a cause of not improving the mechanical strength.

More specifically, if the Si content exceeds 0.5%, the SiO ₂ inclusions existing in the crystal grain boundaries are increased, so that the grain boundaries are easily broken and the mechanical strength is significantly lowered. Along with that, pitching wear and abrasive wear increase, and the other party also wears. Therefore, Si is set to 0.5% or less. Also, A
When l exceeds 0.1%, Al existing at the grain boundaries is the same as Sl.
_{Since the amount of 2} O ₃ inclusions increases, grain boundary breakage easily occurs, mechanical strength is significantly reduced, and pitting resistance, wear resistance, and attack resistance deteriorate. Therefore, Al is set to 0.1% or less.

When the particle size of the Fe-B alloy powder is made fine, the distribution of the additive B is made uniform, the liquid phase is uniformly generated, and the boride is also finely precipitated and dispersed. Therefore, Fe-B
The particle size of the alloy powder is preferably 350 mesh (44 μm) or less, but industrially it may be 250 mesh (63 μm) or less. However, powders containing a large amount of coarse particles exceeding 250 mesh may coarsen precipitates and adversely affect the mechanical strength and the compatibility with the sliding mating material.

(Example) Next, the Example of this invention is shown with a comparative example.

Vacuum-annealed grain size-100 mesh F as raw material powder
e-Cr-Mo-W-Si-C based atomized alloy powder, -325
Fe-Mo powder or pure Mo powder of mesh, Fe-W powder or pure W powder of -325 mesh, B-content, Si and Al contents of impurity elements, and Fe-B having different grain sizes
Using alloy powder and appropriate blending so as to have the final component composition shown in sample materials No. 1 to 12 in Table 1, add 1.0% of higher fatty acid accra wax as a lubricant and mix, Each mixed powder was molded at a pressure of 7 tonf / cm ² , and then each green compact was sintered by holding it at a temperature of 1150 to 1250 ° C. for 60 minutes in vacuum. Then, each sintered body was subjected to quenching and tempering treatment to obtain each test material. Mn is an element usually contained in alloy steel powder.

In addition, the test materials Nos. 13 to 18 in Table 1 are F as alloy steel powder.
e-Mo-Cr-Si-C-Ni system (No.13, 14) and F
e-Mo-Cr-Si-VC-Nb system (No.15, 16)
And Fe-Mo-W-Cr-Si-VC-Co-Nb system (No.17, 18) were vacuum-annealed with a grain size of -100, respectively.
The case where the atomized powder of the mesh is used is shown, and the respective test materials are manufactured in the same manner as the above-mentioned added raw material powder and manufacturing conditions.

Next, the mechanical properties of each test material (No. 1 to 18) were examined, and the wear amount of the rocker arm itself and the wear amount of the mating material cam when attached to the sliding part of the rocker arm were as follows. It was measured under the wear test conditions using an actual engine.

In other words, in the actual engine test, each test material was used for the sliding part of the rocker arm with built-in lash justifier and the camshaft, and each was incorporated into a 4-cylinder OHC gasoline engine, and the camshaft; chill casting, engine speed; 6
50rpm, oil; 10,000km running waste oil for gasoline, operating time;
A wear test was performed under the same conditions as in actual market driving for 600 hours and other conditions, and the wear amount at the sliding portion of the rocker arm and the wear amount of the cam as the mating material were measured.

Table 1 shows the results of these tests.

In the test materials Nos. 1 to 12 shown in Table 1, the B content of the Fe-B alloy powder and the bending strength are correlated, and particularly, the test material No. 1
As is clear from ~ 6, when the amount of B is too large, the bending strength shows a considerably low value. In addition, there is a correlation in the relationship between the B content of the Fe-B alloy powder and the sum of the wear amounts of the rocker arm and the cam of the mating member, and when the B content is high, the wear tends to be large. Furthermore, the sample materials No. 7-12
This is a comparison of the Si and Al contents with the B content of the Fe-B alloy powder kept constant. The smaller the Si and Al content of the impurity elements, the greater the bending strength and the less the amount of wear. Is shown. These facts are supported by the results of observing the microstructure of each test material and the distribution state of elements by electron microscope, and the samples containing a small amount of B in Fe-B alloy powder and the amounts of Si and Al that are impurity elements In Example 1, the hard precipitates were uniformly dispersed, and the number of lumpy inclusions of SiO ₂ and Al ₂ O ₃ was extremely small.

Next, sample materials Nos. 13 to 18 show examples in which the composition of the alloy steel is different, and the composition of the Fe-B alloy powder is compared with the conventional composition and the composition of the present invention.

The tendency is the same as that described above, and it is clear that the amount of wear is about 40% smaller than that in the case of using the conventional Fe-B alloy powder.

[Effects of the Invention] As described above, according to the method for producing a wear-resistant iron-based sintered alloy according to the present invention, an element containing C and B in the components of the sintered alloy and forming carbides and borides. Sintered alloys containing alloys, especially C: 0.1-2.0% by weight, B:
0.5-2.5%, the boride forming elements Mo, W, Cr, V, Nb, Ta,
In producing an iron-based sintered alloy containing at least one selected from Co: 5.5 to 34.1% as a basic component, B
Fe-B alloy powder is used as a supply source, and the components of the Fe-B alloy powder are B: 2 to 18% in weight ratio, and Si: 0.
5% or less and Al: 0.1% or less, which is also an impurity element, the balance Fe and unavoidable impurities are used, so that the B-rich portion is unevenly distributed and a local eutectic liquid phase is generated. It is possible to prevent the coarsening of precipitated borides and to make the structure dense and uniform and to reduce the inclusion of SiO ₂ and Al ₂ O ₃ in the grain boundaries. Therefore, it is possible to make the mechanical strength extremely excellent, and it is possible to significantly reduce the wear caused by brittle fracture as the mechanical strength is improved. And is a very effective method especially in the manufacture of valve train mechanism members for internal combustion engines.

 ─────────────────────────────────────────────────── ─── 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-61-44152 (JP, A)

Claims (1)

[Claims] 1. A weight ratio of C: 0.1 to 2.0% and B: 0.5 to 2.5.
%, At least one selected from Mo, W, Cr, V, Nb, Ta and Co which are boride forming elements: 5.5 to 34.1%, when manufacturing an iron-based sintered alloy containing as a basic component. , Fe-B alloy powder is used as the B supply source, and the component of the Fe-B alloy powder is
By weight, B: 2-18%, impurity element Si: 0.5% or less, and also impurity element Al: 0.1% or less, balance
A method for producing a wear-resistant iron-based sintered alloy, which comprises using Fe and inevitable impurities.