JPH05320833A - High strength nitrided and sintered member excellent in wear resistant and its manufacture - Google Patents

Abstract

PURPOSE:To provide a sintered member more excellent in strength and wear resistance and suitable as the stock for valve seats and various sliding members. CONSTITUTION:A high strength nitrided and sintered member excellent in wear resistance in which, in an alloy matrix constituted of, by weight, 6 to 30% Cr and <=5% Mo and, according to circumstances, constituted of <=2% Si, <=5% Ni and <=3% C, and the balance substantial Fe, FeMo is dispersed as hard grains in the range of <=20% and CaFe2 is dispersed as lubricating components in the range of <=2%, and nitriding and sintering have been attained to the inside is prepd. In this way, the objective sintered member suitable as the stock for valve seats and various sliding members can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength nitrided sintered member having excellent wear resistance and a method for manufacturing the same, and particularly to a member required to have high strength and excellent wear resistance,
For example, the present invention relates to a high-strength nitriding sintered member having excellent wear resistance suitable for use as a material for valve seats of automobile engines and various sliding members, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A valve seat for an automobile engine is one of the members which are required to have high strength and excellent wear resistance.

This valve seat is formed into a conical ring shape so that the surface portion of the valve head portion is in close contact with the valve seat, and it is possible to satisfy the required characteristics of the valve seat portion of the cylinder head. In addition, it is used as a member separate from the cylinder head by molding it into a conical ring shape and fitting it into the cylinder head.

By the way, in recent years, due to higher engine speed of automobiles and lead-free fuel gasoline, the required characteristics for the valve seat have become more severe, and the thermal and mechanical load on the valve seat is greater. It has become a thing.

Therefore, a molten material has been conventionally used as the material for the valve seat, but in recent years, a sintered material has been used.

And, among others, an iron-based sintered alloy is used,
In some cases, elements such as Cr, Ni, W, Mo and Co were added so that the matrix can be strengthened or dispersed as a hard phase in the matrix.

[0007]

On the other hand, there is an increasing tendency for engine output to increase, such as higher engine speeds of automobiles and higher output by turbochargers, and valves having higher strength and wear resistance than before. Development of sheet material was desired.

Also, in other various sliding members,
It was still desired to improve strength and abrasion resistance.

Therefore, there has been a problem that development of a material having further improved strength and wear resistance is desired.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a sintered member having more excellent strength and wear resistance.

[0011]

A high-strength nitriding and sintering member excellent in wear resistance according to the present invention comprises Cr: 6% by weight or more and 3% or more.
0 wt% or less, Mo: 5 wt% or less, balance substantially Fe
FeM as hard particles in an alloy matrix composed of
It is characterized in that o is 20% by weight or less and CaF ₂ as a lubricating component is dispersed in a range of 2% by weight or less, and the nitriding sintering is performed to the inside. In some cases, in the alloy matrix, It is characterized by including one or more of Si: 2 wt% or less, Ni: 5 wt% or less, and C: 3 wt% or less, and is excellent in such wear resistance. The structure of the invention relating to the high-strength nitrided sintered member is used as a means for solving the above-mentioned conventional problems.

The method for producing a high-strength nitrided sintered member having excellent wear resistance according to the present invention is Cr: 6% by weight or more and 3% or more.
0 wt% or less, Mo: 5 wt% or less, balance substantially Fe
Steel alloy powder consisting of 20 and FeMo as hard particles
%, Less than 2% by weight of CaF ₂ as a lubricating component, and other suitable auxiliary components, and then molded, and the molded body is formed in a vacuum or a substantially vacuum (in a low pressure nitrogen gas of several tens Torr or less). It is characterized in that it is sintered in some cases) and is nitrided to the inside by N ₂ gas at the end stage of sintering.

A method for producing a high-strength nitrided sintered member having excellent wear resistance according to the present invention which achieves the same object is C
r: 6 wt% or more and 30 wt% or less, Mo: 5 wt% or less, the balance being a steel alloy powder consisting essentially of Fe, FeMo as hard particles of 20 wt% or less, and C as a lubricating component.
It is characterized in that it is formed by mixing aF _{2 in an amount} of 2% by weight or less and other appropriate auxiliary components, followed by molding, sintering the molded body in N ₂ gas, and nitriding the inside.

In the embodiment of the method for producing a high-strength nitrided sintered member having excellent wear resistance according to the present invention,
In steel alloy powder, Si: 2 wt% or less, Ni: 5 wt%
Hereinafter, C: characterized in that it is configured to include one or two or more of 3% by weight or less, and relates to the above-described method for producing a high-strength nitrided sintered member having excellent wear resistance. The structure of the present invention serves as means for solving the above-mentioned conventional problems.

The high-strength nitrided sintered member having excellent wear resistance according to the present invention has the above-described component composition, and the reason will be described below.

Cr: 6% by weight or more and 30% by weight or less Cr is effective in significantly improving the wear resistance of the sintered member by forming a large amount of nitride by nitriding and sintering. The amount is 6% by weight or more so that the effect can be obtained. However, if it is added in an amount of more than 30% by weight, the formability will be poor and the density will not increase, resulting in a decrease in strength and wear resistance.
The amount is 30% by weight or less.

Mo: 5 wt% or less Mo forms a double carbide with Cr, and is effective in reducing the retained austenite and increasing the hot strength. In order to make it hard and reduce moldability, it was set to 5% by weight or less.

Si: 2% by weight or less Si is effective in lowering the oxygen content in the powder and improving the characteristics of the sintered member, so it may be added in some cases, but if too much, the powder Since it is hardened and spheroidized, the moldability is deteriorated. Therefore, even if added, the content is preferably 2% by weight or less.

Ni: 5 wt% or less Ni is effective in improving the toughness of the sintered member, so it may be added in some cases, but if it is too much, nitriding is reduced and retained austenite is increased. Therefore, even if added, it is preferably 5% by weight or less.

C: 3% by weight or less C is effective in forming carbides to increase hardness, improving wear resistance of the sintered member and increasing nitriding amount.
It may be added in some cases, but if it is too large, it becomes brittle and the toughness of the sintered member is lowered, so even if it is added, it is preferable to make it 3% by weight or less.

Hard particles (FeMo): 20% by weight or less Hard particles of FeMo are uniformly dispersed in the sintered member to improve its wear resistance, but if too large, the toughness of the sintered member is lowered. Therefore, it is dispersed in the range of 20% by weight or less.

Lubricating component (CaF ₂ ): 2% by weight or less CaF ₂ , which is a lubricating component, is evenly dispersed in the sintered member to improve its sliding characteristics, and as a result, it has excellent wear resistance. Therefore, it is added in the range of 2% by weight or less.

The high-strength nitrided sintered member having excellent wear resistance according to the present invention contains the above-mentioned alloy components such as Cr, Mo, Si, Ni and C and additional components such as FeMo and CaF ₂ and has an internal structure. The amount of nitrogen in this case is approximately 0.2% by weight at 100 Torr and 0.6 at 600 Torr, although it varies depending on the nitrogen gas pressure, temperature, time, etc. at the time of nitriding. % By weight, 800
It is 1.0 wt% in Torr.

When manufacturing such a nitrided sintered member, Cr: 6% by weight or more and 30% by weight or less, Mo: 5% by weight or less, and in some cases Si: 2% by weight or less, Ni:
5% by weight or less, C: 3% by weight or less, the balance being steel alloy powder consisting essentially of Fe, FeMo as hard particles 20% by weight or less, CaF ₂ as a lubricating component 2% by weight or less, and if necessary. After mixing with an appropriate binder and other auxiliary components and uniformly dispersing the mixture, the mixture is molded, and after appropriate dewaxing, the molded body is subjected to vacuum or substantially vacuum (for example, in a nitrogen gas of several tens Torr). Sintering, and at the end of sintering, for example, at a temperature of 800 ° C. or higher, nitrogen gas of 100 To
Pressurize to rr or 800 Torr for 5 minutes or more 1
It is heated up to about a time to nitride the inside of the molded body.

After the nitriding, it is possible to perform quenching in one step by quenching the nitrogen gas as it is, but the quenching may be performed in another step.

As another method for producing the nitrided sintered member, Cr: 6% by weight or more and 30% by weight or less, M
o: 5 wt% or less, in some cases Si: 2 wt% or less, Ni: 5 wt% or less, C: 3 wt% or less, the balance being a steel alloy powder consisting essentially of Fe, and FeM as hard particles.
20% by weight or less of o, 2% by weight or less of CaF ₂ as a lubricating component, and an auxiliary component such as an appropriate binder, if necessary, and uniformly dispersed, and then molded and appropriately dewaxed. After that, the molded body is heated at a temperature of, for example, 800 ° C. or higher and nitrogen gas is supplied at 100 Torr or 800 Torr.
The pressure is applied to about r and heating is performed for 5 minutes or more and up to about 1 hour to nitride the inside of the formed body.

After nitriding, it is possible to perform quenching in one step by quenching nitrogen gas as it is, but quenching may be performed in another step.

[0028]

In the nitrided sintered member and the method for manufacturing the same according to the present invention, a powder compact having a predetermined component composition is heated or pressurized during or after sintering in nitrogen gas to reach its interior. Since it is nitrided, an appropriate amount of Cr-based nitride, Fe-based nitride, Cr-Mo-based compound carbide, etc. are dispersed, and an appropriate amount of FeM is used as hard particles.
Since o and a proper amount of CaF ₂ as a lubricating component are dispersed, a high-strength nitrided sintered member having excellent wear resistance is obtained.

[0029]

【Example】

(Example 1) A raw material powder was prepared so that a sintered body having a composition shown in Table 1 was obtained, mixed with 0.75% by weight of zinc stearate, and then molded at a molding pressure of 6 ton / cm ² to have a diameter of 1 ton.
It was molded into 1 mm × height 10 mm.

The compact was sintered and nitrided under the conditions shown below.

Room temperature → 1200 ° C. Vacuum 10 ⁻² torr 1200 ° C. × 40 minutes 〃 1200 ° C. × 20 minutes N ₂ gas 100 torr 1200 ° C. → room temperature N ₂ gas ₂ barr As a result of this treatment, a sintered body having the characteristics shown in Table 2 was obtained. A nitriding sintered member was obtained.

[0032]

[Table 1]

[0033]

[Table 2]

As is clear from the results shown in Table 2, by carrying out the present invention, it was possible to obtain a nitrided sintered member that was nitrided only in the sintering step.

Example 2 Graphite was added to the raw material powder used in Example 1 to prepare a raw material powder so that a sintered body having the composition shown in Table 3 was obtained, and then the same conditions as in Example 1 were applied. Was molded and nitrided. As a result of this treatment, a nitrided sintered member made of a sintered body having the characteristics shown in Table 4 was obtained.

[0036]

[Table 3]

[0037]

[Table 4]

As is clear from the results shown in Table 4, by adding graphite, the residual nitrogen in the sintered body is increased, nitriding is more likely to occur, and the residual oxygen is decreased. I was able to get a unity. Also,
It was also possible to improve the strength by increasing the residual carbon (see Table 8 below).

Example 3 Graphite powder and carbonyl nickel were added to the raw material powder used in Example 1 to prepare a raw material powder so that a sintered body having the composition shown in Table 5 was obtained.
When molding and nitriding were performed under the same conditions as in Example 1, the residual nitrogen in the sintered body was about 0.1% by weight, and the effect of nitriding was not sufficiently obtained. Sintering and nitriding were performed under the conditions shown in.

Room temperature → 1200 ° C. Vacuum 10 ⁻² torr 1200 ° C. × 40 minutes 〃 1200 ° C. × 20 minutes N ₂ gas 600 torr 1200 ° C. → room temperature N ₂ gas ₂ barr As a result of this treatment, a sintered body having the characteristics shown in Table 6 was obtained. A nitriding sintered member was obtained.

[0041]

[Table 5]

[0042]

[Table 6]

As is clear from the results shown in Table 6, a nitrided sintered body was easily obtained, and a sintered body having further improved strength was obtained. From this result, it was confirmed that in order to obtain a high-strength sintered body by adding Ni, it is necessary to increase the pressure of N ₂ gas in the nitriding treatment.

(Evaluation example) Each of the sintered bodies obtained in Examples 1 to 3, as a comparative example, a sintered body having the same alloy composition as that of Example 1 but not subjected to the nitriding treatment, and the working material. The alloy composition shown in Table 7 is vacuum sintered at 1160 ° C. for 60 minutes → hot forging → vacuum sintering at 1160 ° C. × 60 minutes → N ₂ gas at ₂ barr and the sintered body is 650 ° C.
When the tensile strength and the amount of wear of each sintered body were measured by subjecting to the aging treatment, the results shown in Table 8 were obtained.

[0045]

[Table 7]

[0046]

[Table 8]

As is clear from the results shown in Table 8, each of the sintered bodies obtained according to the examples of the present invention is a sintered body superior in strength and wear resistance to the current material. It was confirmed that it was possible to obtain a sintered body having excellent characteristics in this way.

[0048]

The nitrided sintered member according to the present invention is made of Cr:
6 wt% or more and 30 wt% or less, Mo: 5 wt% or less, with the balance being FeMo as hard particles and 20 wt% or less in an alloy matrix consisting essentially of Fe, and C as a lubricating component.
Since aF ₂ is dispersed within a range of 2% by weight or less and the nitriding and sintering is performed to the inside, an appropriate amount of Cr-based nitride, Fe-based nitride, Cr-Mo-based composite carbide, etc. are dispersed. In addition, a suitable amount of FeMo as hard particles and an appropriate amount of CaF ₂ as a lubricating component are dispersed, so that it is a high-strength nitrided sintered member having excellent wear resistance, and strength and wear resistance. It has a great effect that it is suitable as a material for valve seats and various sliding members that are required to be excellent in And, a significant effect that a nitrided sintered member excellent in wear resistance is manufactured is brought about.

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[Procedure amendment]

[Submission date] July 7, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 5

[Correction method] Change

[Correction content]

Claims (5)

[Claims] 1. Cr: 6% by weight or more and 30% by weight or less, M
o: 5 wt% or less, the balance being FeMo as hard particles in an amount of 20 wt% or less and CaF ₂ as a lubricating component of 2 wt% or less in an alloy matrix consisting essentially of Fe, and nitriding and sintering to the inside. A high-strength nitrided sintered member having excellent wear resistance, which is characterized by 2. Si: 2% by weight in the alloy matrix
The high-strength nitrided sintered member having excellent wear resistance according to claim 1, which contains Ni: 5 wt% or less and C: 3 wt% or less. 3. Cr: 6% by weight or more and 30% by weight or less, M
o: 5% by weight or less, the balance being steel alloy powder consisting essentially of Fe, 20% by weight or less of FeMo as hard particles, and 2% by weight or less of CaF ₂ as a lubricating component, and then molded to obtain a molded body. A method for producing a high-strength nitrided sintered member having excellent wear resistance, which comprises sintering in a vacuum or in a substantially vacuum, and nitriding the inside by N ₂ gas at the end stage of sintering. 4. Cr: 6% by weight or more and 30% by weight or less, M
o: 5% by weight or less, the balance being steel alloy powder consisting essentially of Fe, 20% by weight or less of FeMo as hard particles, and 2% by weight or less of CaF ₂ as a lubricating component, and then molded to obtain a molded body. A method for producing a high-strength nitrided sintered member having excellent wear resistance, which comprises sintering in N ₂ gas and nitriding the inside. 5. A steel alloy powder containing Si: 2% by weight or less,
Ni: 5 wt% or less, C: 3 wt% or less is included.
Alternatively, the method for producing a high-strength nitrided sintered member having excellent wear resistance as described in 5 above.