JPS61276949A - Manufacture of sintered parts - Google Patents

Abstract

PURPOSE:To obtain sintered parts having superior hardening characteristics during nitriding by incorporating Cr into a sintered steel having a specified composition such as a sintered Cu-C or Ni-Mo-C steel and by specifying the structure before nitriding. CONSTITUTION:A green compact consisting of, by weight, 0.5-6.0% Cr, 0.2-0.6% C, one or more among 0.3-1.5% Mn, 0.1-2.0% Mo, 0.2-2.0% Cu and 0.2-3.0% Ni and the balance Fe or further contg. 0.2-1.0% V and one or more among 0.035-0.500% S, <=0.3% Se and <=0.3% Te is prepd. The green compact is sintered in an atmosphere of an inert or reducing gas or in vacuum, and the sintered body is cooled so as to form a bainite or martensite structure. The sintered body is then ion-nitrided or soft-nitrided in a salt bath.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing i7J sintered parts with excellent nitridation hardening properties.

(Prior Art and its Problems) In recent years, sintered steel has been widely used as a constituent material for mechanical parts because of its good dimensional accuracy and low incidence of defective products.

By the way, surface nitriding hardening treatments such as gas soft nitriding, salt bath soft nitriding, and ion nitriding are heat treatment methods suitable for sintered products that require high dimensional accuracy because the processing temperature is as low as 480 to 580°C. .

However, in conventional sintered steels such as Cu-C series and Ni-Mo-C series, sufficient surface hardness was not obtained due to the nitriding.

Furthermore, it is known that nitriding a sintered product containing Cr increases its surface hardness, but the relationship between the structure before nitriding and nitriding properties is not clear, and it is difficult to ensure that the desired result is achieved. Hardness was not always achieved.

The present invention was made in view of the above-mentioned problems, and it is an object of the present invention to provide a method for manufacturing a sintered part having improved nitridation hardening properties.

(Means for Solving the Problems) As a result of various experiments and research, the present inventor found that the nitriding hardness of Cr
It has been found that in addition to depending on the components such as, it is greatly influenced by & and 11 weave before nitriding treatment. In order to obtain sufficient nitriding hardness, the structure before nitriding must be bainite or martenzai 1 to 8;11 weave.
The pearlite structure has low nitriding hardness.

In other words, in the ferrite I transformation, Cr etc. are distributed between the ferrite I- and the carbide, and Cr9j in the ferrite is
% degree decreases. For this reason, the effective amount of Cr that forms a compound with nitrogen expanded from the surface decreases, and even in a sintered body containing Cr, the surface hardness decreases.

On the other hand, in bainitic transformation, Cr etc. are not distributed between ferrite and carbide, and the Cr concentration in ferrite is high (effectively acting on nitriding).This term is almost the same in the case of martensitic transformation. .

Therefore, by sintering a green compact containing Cr, appropriately controlling the cooling rate after sintering, and nitriding the sintered body in the form of Heinai 1- or Martensai Ni-weave, it is possible to achieve a high nitriding hardness. It is IH'B.

However, in the present invention, Cr: 0.5-6.0% by weight
, C:O, 2 to 0.6% by weight, and Mn:
0.3~], 5% by weight, Mo: 0.1~2.0% by weight,
Cu: 0.2-2.0% by weight.

Ni: Sintering a powder compact containing one or more of 0.2 to 3.0% by weight and the balance consisting of Fe in an atmosphere of an inert gas or reducing gas or in a vacuum, A method for producing a sintered part, the gist of which is to perform ion nitriding treatment or salt bath nitrocarburizing treatment after cooling so that the structure of the sintered product becomes Baini I or marten suite, and the pressure A method of manufacturing using a powder containing V: 0.2 to 1.0% by weight, and further, a method of manufacturing using a powder containing V: 0.2 to 1.0% by weight, and further, a method of manufacturing using a powder containing S: 0.035 to 0°5 for both of the green compacts, respectively.
00% by weight, Se: 0.3% by weight or less, and Te: 0.3% by weight or less.

The reason why the components of the green compact used in the method of the present invention are limited as described above is as follows.

■Cr Cr is an essential element for increasing surface hardness by forming nitrides through nitriding, and also has the effect of increasing base hardness. However, if it is less than 0.5% by weight, the nitriding hardness will be low, and if it exceeds 6.0% by weight, the hardness will be small and the economy will be poor. Therefore, the content should be 0.5 to 6.0% by weight.

■CC C has the effect of increasing base hardness by forming carbides. However, if it is less than 0.2% by weight, the hardness will be low due to the small amount of carbides, and if it exceeds 0.6% by weight, the nitriding property will be significantly reduced. Therefore, the content should be 0.2 to 0.6% by weight.

(2) Mn\Mo, Cu, Ni These elements all have the effect of increasing the hardness of the base material, and together with Cr, are important components for obtaining a predetermined hardness. Therefore, the addition of Type 1 plate-7 is essential.

That is, Mn has the effect of increasing hardenability and base hardness, but if it is less than 0.3% by weight, the effect is small, and even if it exceeds 1.5% by weight, the rate of increase in the effect is small. few. Therefore, the content should be 0.3 to 1.5% by weight.

Next, since Mo has the effect of delaying the barley 1 precipitation nose, adding Mo makes it easier to obtain a bainite structure. Moreover, Mo also has the effect of increasing base hardness. However, if it is less than 0.1% of double stars, the effect is small, and
Even if it exceeds 2.0% by weight, the rate of increase in the effect is small. Therefore, the content should be 0.1 to 2.0% by weight.

Cu has the effect of increasing the hardness of the matrix, but 0
．． If it is less than 2% by weight, the effect will be small, and if it exceeds 2.0% by weight, the toughness will decrease.

Therefore, the content should be 0.2 to 2.0% by weight.

Ni has the effect of increasing base hardness and improving toughness, but if it is less than 0.2% by weight, the effect is small, and if it exceeds 3.0% by weight, there is no significant improvement. Economic efficiency is also bad. Therefore, the content should be 0.2 to 3.0% by weight.

■■ Like Cr, V forms nitrides, increases surface hardness, and has the effect of improving base hardness. However, 0
．． If it is less than 20%, the nitriding hardness is less likely to be 1-, and
Even if it exceeds 1.0% by weight, the improvement effect is small. Therefore, the content should be 0.2 to 1.0% by weight.

■S, Se, and 1゛e These elements all have a remarkable effect of improving the machinability of sintered steel products in the presence of Mn and with a reduced oxygen content. In order to realize the product, it is essential to add 1.

In other words, S is an extremely inexpensive component that improves the machinability of sintered copper products, and its effect is already observed at a content of 0.035% by weight, so the lower limit of the S content should be set at 0. It was set at .035%. On the other hand, S content is 0.500%
Since the powder properties deteriorate if the content exceeds 0.035 to 0.500%. Note that within this range, nitriding properties are not inhibited.

Next, like S, Se and Te also have the effect of improving the machinability of sintered steel products, and this effect has been confirmed even in high-strength products and even in very small amounts, such as traces. However, the content is 0.3% by weight each.
If the content of Se and Te exceeds 0.3% by weight, the powder properties will deteriorate.
below.

Te: determined to be 0.3% by weight or less. In addition, Se.

If Te is also within this range, nitriding properties will not be inhibited.

In addition, it is preferable that the composition of such a green compact is a pre-alloyed steel powder, excluding C, since a uniform structure can be obtained. However, pure iron powder contains Fe-Cr.

It is also possible to mix and mold Fe-Mn, Cu, Mo, Ni powder, etc. Furthermore, since C significantly inhibits compressibility, graphite is generally used in alloyed steel powder.

Next, the green compact is sintered, and the sintering is performed using CC
An atmosphere in which Mn and V do not oxidize, for example, an H2 gas atmosphere,
This is carried out in an ammonia decomposition gas atmosphere, a N2 gas atmosphere, etc., or in a vacuum. CCM in an endothermic metamorphic gas atmosphere
It cannot be applied because n and V are oxidized.

The sintering temperature and time vary depending on the shape, size, etc. of the green compact, but are generally carried out at 1100 to 1300°C for 10 to 60 minutes.

The cooling rate after the sintering process is selected to be a rate at which a bainite or martensitic structure is obtained.

For example, 0.6%C-0,7%Mn-1,0%Cr-0
, 2% Mo steel, a bainitic structure can be obtained by cooling at 10°C/m1n (average cooling rate from Ac3 to 500°C) or higher.

The final step of nitriding treatment includes ion nitriding, salt bath soft nitriding, and gas soft nitriding, and the first two treatments are suitable for sintered products. That is, in the case of gas nitrocarburizing, NH, gas, or endothermic modified gas enters into the pores, and nitriding progresses not only to the surface but also to the inside, causing significant hardening to the inside.

In contrast, in ion nitriding, glow discharge occurs only on the surface of the sintered product, so nitriding progresses from the surface. In addition, in the case of salt bath nitrocarburizing, the salt bath enters the pores, but since the bath is not stirred within the pores, nitriding hardly progresses inside and surface hardening occurs.

The processing temperature and processing time vary depending on the required surface hardness and hardness depth, but are generally 480 to 580°C, 1
, 0 to 30 hours.

(Example) A green compact (density 7゜0g/cJ) made by manufacturing steel powder with ingredients not shown in Table 1 below using the oil amalization method and adding graphite to it.
was prepared and heated at 1130°C x 30 in ammonia decomposition gas.
Sintered for minutes. The cooling rate after sintering was 15°C/min (only M3 was cooled at 5°C/min). Further, ion nitriding treatment was performed for nitriding. This processing condition is 550'
cx4hC pressure crab 8TorCN2:Hz =7:3
Met.

In addition, in Table 1 below, numbers 1 to 4 are manufactured by the conventional method, and numbers 5 to 26 are manufactured by the method of the present invention.

In addition, FIG. 1 shows No. ], No., 3. in Table 1. N
This shows the hardness distribution of 0.9.

As is clear from Table 1 and FIG. 1, the sintered parts manufactured by the force method of the present invention have excellent nitridation hardening properties.

(Effects of the Invention) As explained above, according to the method of the present invention, sintered parts with excellent nitriding hardening properties can be manufactured, and this invention is of great industrial benefit. It is.

[Brief explanation of the drawing]

The drawings show sintered parts manufactured by conventional methods (11 +, 1.N
. 3) and the sintered parts manufactured by the method of the present invention (No. 9)
) is a comparison diagram of hardness distribution. Patent applicant Sumitomo Metal Industries Co., Ltd.
6 silver (msu)

Claims (4)

[Claims] (1), Cr: 0.5-6.0% by weight, C: 0.2-0
．． 6% by weight, Mn: 0.3-1.5% by weight, Mo: 0.1-2.0% by weight, Cu: 0.2-2
．． 0% by weight, Ni: 0.2 to 3.0% by weight, and the balance is Fe in an atmosphere of an inert gas or reducing gas or in a vacuum. A method for producing a sintered part, which comprises sintering the product, cooling it so that the structure of the sintered product becomes bainite or martensite, and then subjecting it to ion nitriding treatment or salt bath soft nitriding treatment. (2), Cr: 0.5-6.0% by weight, C: 0.2-0
．． 6% by weight, V: 0.2-1.0% by weight, Mn: 0.3-1.5% by weight, Mo: 0.1-2.
0% by weight, Cu: 0.2-2.0% by weight, Ni: 0.2
A green compact containing one or more of ~3.0% by weight and the balance consisting of Fe is sintered in an inert gas or reducing gas atmosphere or in vacuum, and the sintered product is A method for producing a sintered part, which comprises cooling the structure to become bainite or martensite, and then subjecting it to ion nitriding or salt bath soft nitriding. (3), Cr: 0.5-6.0% by weight, C: 0.2-0
．． 6% by weight, Mn: 0.3-1.5% by weight, Mo: 0.1-2.0% by weight, Cu: 0.2-2
．． 0% by weight, Ni: 0.2 to 3.0% by weight, and S: 0.035 to 0.500% by weight, S
A green compact containing one or more of e: 0.3% by weight or less, Te: 0.3% by weight or less, and the balance consisting of Fe, in an atmosphere of an inert gas or reducing gas, or in a vacuum. 1. A method for producing a sintered part, which comprises sintering the product, cooling it so that the structure of the sintered product becomes bainite or martensite, and then subjecting it to ion nitriding treatment or salt bath soft nitriding treatment. (4), Cr: 0.5-6.0% by weight, C: 0.2-0
．． 6% by weight, V: 0.2-1.0% by weight, Mn: 0.3-1.5% by weight, Mo: 0.1-2.
0% by weight, Cu: 0.2-2.0% by weight, Ni: 0.2
-3.0% by weight, and S: 0.0
35 to 0.500% by weight, Se: 0.3% by weight or less, T
e: A green compact containing one or more of 0.3% by weight or less and the balance consisting of Fe is sintered in an atmosphere of an inert gas or reducing gas or in a vacuum, and the sintering A method for manufacturing a sintered part, which comprises cooling the part so that its structure becomes bainite or martensite, and then subjecting it to ion nitriding or salt bath soft nitriding.