JPH0717923B2 - Low alloy iron powder for sintering and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a low alloy iron powder for sintering which is a raw material of a high density and high strength sintered material applied to structural machine parts and the like.

(Prior Art) Generally, there is a demand for higher strength of an iron-based sintered material that is widely used as a material for structural machine parts and the like. To meet this demand, various excellent strengthening methods such as alloying, densification and homogenization have been forcibly developed for excellent sintered materials.

For example, as a method for achieving high strength of a material by alloying (hereinafter referred to as alloying strengthening method), powders of alloying elements such as copper (Cu), nickel (Ni), manganese (Mn) and chromium (Cr) are used. A mixing method of individually mixing with iron powder, a prealloying method using a prealloyed powder in which the above-mentioned strengthening elements (Cu, Ni, Mn, Cr, etc.) are alloyed in advance are used.

In addition, as a method for strengthening the densification, the 2press-2sinter method and the sintering forging method (P / F) are used.

Further, as a homogenizing and strengthening method, a homogenizing method in which high temperature sintering is performed when sintering a sintered material is performed.

In addition to the above, strengthening measures such as a spheroidizing method for spheroidizing the pores of structural machine parts are known.

However, although all of the above-mentioned various strengthening methods bring about an effect of strengthening the sintered material, all of them have some problems.

That is, in the 2press-2sinter method and the sintering forging method (P / F), etc., which are densification strengthening methods, the structural machine is manufactured by changing or adding the manufacturing process and performing strong processing such as compression. Since high density of parts etc. has been achieved, the management process such as atmosphere control and temperature setting during strong processing is increased and the manufacturing process becomes complicated, resulting in a significant increase in manufacturing cost. Had.

In addition, the mixing method among the alloying strengthening methods has a problem that it takes a long time to sufficiently diffuse the added alloying elements into iron (Fe), and the active metals such as chromium (Cr) and manganese are involved. (Mn) and the like have a problem that if the sintering atmosphere is not strictly controlled, they will oxidize and hinder their diffusion.

Further, even in the prealloying method, the hardness of the powder is increased by the alloying and the compression moldability is deteriorated, so that the densification of structural mechanical parts and the like is prevented.

By the way, various proposals have been made in order to solve the problem of reduction in compression moldability in the above-described conventional prealloying method, for example, "Production method of low alloy powder iron" (Japanese Patent Publication No. 49-9649).
(See Japanese Patent Laid-Open Publication), it is proposed that an alloying element is attached to the surface of iron powder by a special reduction method to improve compression moldability.

(Problems to be solved by the invention) However, with the low alloy powder iron for sintering obtained by the above conventional manufacturing method, although the improvement of the compression moldability was achieved, the price of the powder itself was lower than that of the ordinary low alloy steel powder. However, there is a problem that the manufacturing cost becomes high.

In addition, the conventional low alloy iron powder does not have sufficient tensile strength in the sintered body, especially the sintered body after the heat treatment, and therefore, when the structural machine part is constructed of this sintered body, the deterioration of the part It also had the problem of causing

The present invention has been made in order to overcome the above problems in view of the above circumstances, and has excellent hardenability and compression moldability at low cost, and has high strength when machined by sintering. It is intended to provide a low alloy iron powder for sintering.

(Means for Solving the Problems) The features of the present invention for achieving the above object include molybdenum (Mo), chromium (Cr), and carbon (C) pre-alloyed with iron (Fe), And a ferro-alloy powder for sintering, in which nickel (Ni) is present in a diffused state on the surface, in a weight ratio of Mo
0.2 to 1.4%, Ni 0.5 to 4%, Cr 0.1 to 0.3%, C 0.05
% Or less, oxygen (O) 0.3% or less and unavoidable impurities 2
% Or less, and the balance consists essentially of Fe.

Further, in order to produce a low alloy iron powder for sintering having the above composition, a low alloy iron powder containing other components other than Ni is produced.
Step, second step of mixing the powder with nickel (Ni) or nickel oxide in powder, and third step of reduction treatment at 800-1050 ° C for 20 minutes or more in an inert vacuum or protective atmosphere having reducing property It is also characterized by comprising a step and a fourth step of pulverizing the reduced mixture.

(Reason for Limitation and Action) The present invention relates to the relationship of the contribution ratio to the compression moldability by the addition of various alloy elements, the relationship between the alloy element and the hardenability, the relationship between the alloy element and the mechanical strength characteristics of the sintered body, The present invention was invented on the basis of the knowledge obtained as a result of detailed investigation of various correlations such as the relationship between the alloying element and the mechanical strength characteristics of the sintered body by the addition method thereof.

In the low alloy iron powder for sintering and the manufacturing method thereof according to the present invention having the above characteristics, molybdenum (Mo) is added for the purpose of forming a solid solution with iron (Fe) to strengthen the powder and the sintered body. Is. However, if the weight ratio is less than 0.2%, the effect is small, and if it exceeds 1.4%, the strengthening performance is improved, but the solid solution hardening of the powder reduces the compression moldability of the powder, so it was decided to include 0.2 to 1.4%. .

Next, chromium (Cr) is added because chromium (Cr) is an element for improving the hardenability. However, if the weight ratio is less than 0.1%, the effect of improving the hardenability is not sufficiently obtained, and if it exceeds 0.3%, the powder is significantly hardened and the compression moldability is deteriorated, so the content was made 0.1 to 0.3%.

Nickel (Ni) is an element for improving heat-treatability and toughness, but if the weight ratio is less than 0.5%, no effect can be expected, and the above effect is sufficiently achieved at 4%, and further addition reduces the raw material cost. However, since Ni only deteriorates the compression moldability depending on the existing state,
This was made to exist on the surface in a diffused state.

Oxygen (O) deteriorates the compression moldability of the powder and adversely affects the formation as a sintered body, so that the weight ratio is 0.
It should be 3% or less.

Further, since carbon (C) also deteriorates the compression moldability of the powder, it is necessary to set the weight ratio to 0.05% or less.

The above are the reasons for limiting the composition of the low alloy iron powder for sintering according to the present invention, and in the method for producing the iron powder having the above composition, in the first step, molybdenum (Mo) and chromium (C
Since r) and r) are added in the form of prealloy, the strength can be improved.

Next, in the second step, nickel (Ni) or nickel oxide is mixed with the prealloy powder by powder. Here, the reason why nickel (Ni) is not prealloyed as in the first step is that when nickel (Ni) is prealloyed, the strength characteristics are not improved so much and the compression moldability is also deteriorated. Therefore, by mixing with powder, the strength and toughness are improved and the compression moldability is maintained.

Further, in the third step, the mixed powder is subjected to reduction treatment at 800 to 1050 ° C., so that oxygen (O) in the mixed powder is removed and oxidation is suppressed. Here, if the temperature is set to 800 ° C. or higher, the reduction treatment is not performed well, and if the temperature exceeds 1050 ° C., the mixed powder will be sintered, so the temperature was set to 800 to 1050 ° C.

Finally, in the fourth step, the mixture that has become a cake-like powder can be pulverized by a pulverizer to obtain a low alloy powder as a sintering material.

As described above, it is possible to provide a low-alloy iron powder for sintering which is excellent in compression moldability, heat treatment property, and toughness, and is obtained by sintering the iron powder obtained through the above process. The bonded body has excellent mechanical strength characteristics.

(Example) Hereinafter, an example of the present invention will be described in comparison with a comparative example.
In the table, the manufacturing method of the low alloy iron powder for sintering and the chemical composition of the final powder used in Examples and Comparative Examples of the present invention are described in each column.

Example 1 First, as a first step, a raw material powder is sprayed by an atomizing method to be manufactured. The composition of this raw material powder is 0.4% by weight of molybdenum (Mo) in iron (Fe). Chromium (Cr) 0.16
%, Carbon (C) 0.12% and oxygen (O) 0.5%.

Next, in the second step, the raw material powder is mixed with 1.5% by weight of nickel powder. This nickel powder is as follows. About 200 parts of nickel tetracarbonyl (Ni (CO) ₄ )
Nickel compound (nickel carbonyl) when heated to ℃
And carbon monoxide (CO). The soot-like fine powder of nickel carbonyl generated at this time is classified to have an average particle size of about 2.9 μm, and the powder is added.

Next, in the third step, heating in an atmosphere of decomposed ammonia gas (3H ₂ + N ₂ ) at 950 ° C. for 90 minutes causes oxygen (O) in the low alloy iron powder to react with hydrogen (H) for reduction. .
The reduction-treated iron powder is gradually cooled. In the third step, reduction treatment can be performed, and the nickel powder can be sufficiently diffused on the surface of the pre-alloyed powder in the first step.

Finally, in the fourth step, the cake-like powder that was heated and cooled was pulverized by a pulverizer to obtain a low alloy iron powder to be sintered.

The composition of the low alloy iron powder manufactured as described above is 0.39% by weight of molybdenum (Mo) and 0.15% of chromium (Cr). Nickel (Ni) 1.4%. Carbon (C) 0.02% and oxygen (O) 0.1
%, Balance iron (Fe).

Example 2 First, as the first step, as in Example 1, a prealloyed raw material powder was produced by the atomizing method. This composition contains 0.8% by weight of molybdenum (Mo). Chromium (Cr) 0.2
1%, carbon (C) 0.11%, oxygen (O) 0.6%, balance iron (Fe).

Next, in the second step, the weight ratio to the low alloy iron powder is
1.9% nickel oxide (NiO) powder (classified to an average particle size of 1.8 μm) was added and mixed.

Next, in a third step, the mixed powder was heated in 950 ° C. for 90 minutes in decomposed ammonia gas (3H ₂ + N ₂ ) for reduction treatment, and gradually cooled to obtain a cake-like powder.

Finally, as a fourth step, the cake-like powder was pulverized by a pulverizer to obtain a low alloy iron powder for sintering.

The chemical analysis of the low alloy iron powder produced through the above-mentioned processes showed that the composition of the powder was iron (Fe) in a weight ratio of molybdenum (Mo) 0.75%, chromium (Cr) 0.19%, nickel (N).
i) 1.4%, carbon (C) 0.02% and oxygen (O) 0.1%.

Comparative Example 1 Commercially available low alloy steel powder (atomized powder) produced by the atomization method was used for the test, and when this powder was chemically analyzed, molybdenum (Mo) 0.45% and nickel (Ni) 1.8% were obtained by weight ratio. , Manganese (Mn) 0.17%, balance iron (F)
It was found to have the composition of e). It differs from the present invention in that it contains manganese (Mn).

Comparative Example 2 By the same manufacturing method as for the low alloy iron powder according to the present invention, the alloy elements contained in the raw material powder and the alloy elements mixed were manufactured differently from those of the present application.

That is, in the first step, the low alloy iron powder is sprayed and produced by the atomizing method. The powder contained iron (Fe) containing nickel (Ni) 1.6%, carbon (C) 0.08% and oxygen (O) 0.3% by weight.

Next, in the second step, 0.4% by weight of molybdenum (Mo) powder is added to the low alloy iron powder having the above composition (average particle size 1.2 μm).
Add 0.27% medium carbon ferrochrome powder (JIS standard FC _r M3 -350 Nash powder) and mix.

Next, in the third step, the mixed powder was heated at 950 ° C. for 90 minutes in an atmosphere of decomposed ammonia gas (3H ₂ + N ₂ ) and then slowly cooled to obtain a cake-like powder.

Finally, as the fourth step, the cake-like powder was pulverized with a pulverizer to obtain a final powder.

A chemical analysis of the low alloy iron powder for sintering produced through the above-described production process was performed. As shown in the table above, iron (Fe) contained 0.4% by weight of molybdenum (Mo), chromium ( Cr) 0.17%, nickel (Ni) 1.4%, carbon (C) 0.03
%, And oxygen (O) 0.2% was confirmed to be a powder. This analysis value satisfies the content value of each element as the constituent requirement of the present invention, but the manufacturing process is completely different.

Using the low-alloy iron powder for sintering that was manufactured in each of the above manufacturing processes, test pieces were manufactured under the same manufacturing conditions in order to measure the tensile strength of these powders. The manufacturing process of the test piece will be described below.

First, the weight ratio to the low alloy iron powders of Examples and Comparative Examples
0.6% graphite powder and 0.8% zinc stearate powder for lubrication were added and mixed with a V-type mixer for 30 minutes. Using this mixed powder, a tensile test piece (JSPM standard 2-64) having a compact density of 7.0 g / cm ³ was compacted.

Then, the tensile test piece was sintered in a sintering furnace at 1200 ° C. for 40 minutes (atmosphere of decomposed ammonia gas) to produce a sintered tensile test piece. A tensile test was performed using this sintered body tensile test piece. Tensile test at normal temperature
The results are shown in the bar graphs of FIG. 1 under the conditions of 2 mm / min.

Further, in order to measure the tensile strength of the above-described sintered body tensile test piece after heat treatment, the sintered body was quenched and tempered.
For quenching, a vacuum heat treatment was used. After heating at 880 ° C for 30 minutes, oil quenching was performed, and for tempering, heating was performed at 180 ° C for 60 minutes in the atmosphere. The tensile test pieces after the heat treatment were subjected to a tensile test at the same rate as described above, that is, at a normal temperature at a tensile rate of 2 mm / min, and the results are shown in the bar graphs of FIG.

The results of the tensile strength test conducted as described above will be described.

First, the tensile strength in the sintered body shown in FIG. 1, the embodiment 1 in 62kgf / mm ^2, Example 2 shows respectively the measured values of ^{65kgf / mm 2, 47kgf / mm} 2 Comparative Example 1, Comparative The performance was outstanding compared to 50 kgf / mm ² in Example 2. Example 2 is 3 kg / more than Example 1.
The strength of mm ² is molybdenum (M
This is because it contains nearly double.

Next, the tensile strength after heat treatment will be described with reference to FIG. Example 1 is a test piece formed by using a low-alloy iron powder according to the present invention is 137kgf / mm ^2, Example 2 showed a high tensile strength both as 142kgf / mm ^2, in Comparative Example 1 103kgf / mm ² , Comparative Example 2
It can be seen that the performance is better than that of 98 kgf / mm ² . Here, the measured value of Example 2 is also superior, because nickel (Ni), which is an element excellent in heat treatability and toughness, is mixed in a slightly large amount in addition to the above-mentioned reason. .

(Effects of the Invention) As described above, the low alloy iron powder for sintering and the manufacturing method thereof according to the present invention have the following effects.

By weight ratio, molybdenum (Mo) 0.2 to 1.4%, nickel (N
j) 0.5 to 4%, chromium (Cr) 0.1 to 0.3%, carbon (C) 0.
05% or less, oxygen (O) 0.3% or less and inevitable impurities 2
% Or less, and the remainder is a low alloy iron powder for sintering which consists essentially of iron (Fe). Moreover, in this alloy iron powder, molybdenum (Mo), chromium (Cr) and carbon (C) are pre-alloyed. Since it is contained and nickel (Ni) is present on the surface in a diffused state, it exhibits good compression moldability and excellent hardenability when producing a sintered body, and the strength and toughness of the obtained sintered body. Is significantly improved. Further, in the method of the present invention, the nickel powder is mixed with the prealloyed iron powder and the reduction treatment is performed under predetermined conditions, so that the diffusion of nickel to the surface is sufficient and the low alloyed iron powder for sintering is stabilized. Can be obtained. Further, since the reinforcing metal element, which is too expensive in terms of raw material cost, is not used and the manufacturing method is carefully devised, there is a thing that contributes to cost reduction.

[Brief description of drawings]

FIG. 1 and FIG. 2 are for explaining the mechanical strength characteristics of the low alloy iron powder for sintering and the manufacturing method thereof according to the present invention,
FIG. 1 is a characteristic diagram showing the tensile strength of a sintered body tensile test piece manufactured by the low alloy iron powder according to the present invention, and FIG. 2 is a tensile strength after heat treatment of the sintered body tensile test piece. FIG.

Claims (2)

[Claims] 1. A low sintering powder which contains molybdenum (Mo), chromium (Cr) and carbon (C) pre-alloyed with iron (Fe) and has nickel (Ni) present on the surface in a diffused state. Alloyed iron powder with a weight ratio of 0.2-1.4% Mo and 0.5-4 Ni.
%, Cr 0.1-0.3%, C 0.05% or less, oxygen (O) 0.3%
A low-alloy iron powder for sintering, containing the following and unavoidable impurities in an amount of 2% or less, and the balance substantially consisting of Fe. 2. A weight ratio of Mo is 0.2 to 1.4% and Ni is 0.5 to 4
%, Cr 0.1-0.3%, C 0.05% or less, O 0.3% or less and unavoidable impurities 2% or less, respectively, and the balance is substantially
A method for producing a low alloy iron powder for sintering comprising Fe, comprising a first step of producing a low alloy iron powder containing other components except Ni, and mixing the powder with Ni or a Ni oxide. For sintering, which comprises a second step of: reducing the mixed powder at 800 to 1,050 ° C. for 20 minutes or more; and a fourth step of pulverizing the reduced product again. Method for producing low alloy iron powder.