JPS58217601A - Manufacture of high-strength sintered material - Google Patents

Abstract

PURPOSE:To inexpensively manufacture the sintered material excellent in mechanical properties, by mixing graphite powder in high-oxygen alloyed steel powder, subjecting the mixture to the reactions of sintering-reducing-alloying with C in the step of sintering, and then heat treating it. CONSTITUTION:Alloyed steel powder containing, by wt%, 0.4-0.7% one or two of Mn<=2.3% anc Cr<=5.5% and 0.25-1.0% O is prepared. Graphite and a selective lubricant are then added to this alloyed steel powder, to prepare a powdery mixture having C content controlled at 0.25-1.0%. Thereafter, this powdery mixture is compression-formed to obtain a compressed powdery body having compression density above 6.0g/cm<3>. This compressed powdery body is then heated at a temp. of 1,150-1,300 deg.C in an unoxidizing atmosphere such as H2 gas having a dew point below -30 deg.C for a predetermined time, to obtain a sintered body of 0.2-0.5% C and 0-0.25% O. This sintered body is then quenched in a cooling medium of cooling power above 0.16cm<-1> from the temp. range of the point Ac3- the point Ac3+100 deg.C in an unoxidizing atmosphere having a dew point below -30 deg.C and tempered, to obtain the objective high-strength sintered material.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing high-strength sintered materials, and in particular, to manufacture inexpensive materials using high oxygen alloy steel powder as raw material powder, graphite powder is used. This paper proposes a method for producing a sintered material with excellent mechanical properties by mixing to cause a sintering-reduction-C alloying reaction in the sintering process and then heat-treating.

・ Conventionally, sintered machine parts made mainly from pure iron powder had a low strength level, which limited their use.

Therefore, in order to compensate for the above drawbacks, a method was developed that uses low-alloy steel powder, which has excellent hardenability, as the main raw material, but Kn is an inexpensive alloying element that makes a significant contribution to hardenability.

Taking the case of alloyed steel powder containing Or as an example, if it is manufactured by water atomization, In and Qr react with water during atomization and preferentially oxidize, so In and Or are effective for hardenability. The amount of surface melting in the copper powder was small and the yield was poor. On the other hand, in order to restore the hardenability of this steel powder,
In in conjunction with softening annealing of copper powder.

Although it is necessary to reduce the oxide of Or, there is a drawback that a special reduction annealing furnace is required to reduce the copper powder.

Generally, when sintering is performed, the sintered density gradually increases as time passes, and the strength of the sintered body increases. In this case, since the sintered density decreases due to the reduction reaction, there is a problem that sufficient sintering strength cannot be obtained with the conventional sintering time for only sintering.

In addition, in products where the sintered body is hardened, even when heating is performed to austenitize for quenching, the sintered body is oxidized by the atmosphere, resulting in a decrease in hardenability and the characteristics of alloyed steel powder. There are also some problems in which they are not able to perform to their full potential.

In Sarabanko, the thermal conductivity of porous materials such as sintered bodies is inferior to that of dense materials of the same material, so if the cooling capacity of the quenching coolant is small, the quench hardening depth will be shallow and the mechanical There was also the problem that the properties deteriorated.

The present invention aims to overcome the various problems mentioned above in producing high-strength sintered materials, and particularly to provide an advantageous method for producing high-strength sintered materials at low cost. be. The details of the configuration will be explained below.

The features of the structure of the present invention are, firstly, that high oxygen alloy steel powder, which is easily and inexpensively produced by conventional general manufacturing equipment, is used as the raw material powder, and secondly, graphite powder is used as the high oxygen alloy steel powder. In the next sintering process, the eight reactions of sintering, reduction, and carbon alloying are carried out by mixing the two, and the resulting sintered body undergoes a series of heat treatments to create a sintered body with excellent mechanical properties. The reason lies in the fact that the materials have been manufactured.

The features of the present invention as described above are based on the following findings.

) Alloy steel powder (0,05%O-0,7%In-1%O
r -0.6%0-0.54%MnO-1.2%Or,
08) t, - Graphite powder was mixed to make a mixed powder, and a green compact with a total carbon content of 0.9% was sintered at 1150'C for 50 minutes in a reducing gas atmosphere with a dew point of -50°C. , O2 of the sintered body
As a result of analyzing the amount of Mno 10”2011, each 0.5
4%C10,084%Mn0, 0.1c'0%Qr
, aOa, and it was found that the oxides of Mn and Qr were reduced by the mixed graphite powder.

(b) Graphite was mixed with the same steel powder as in (a) above, and after molding, it was heated to 1250' in a reducing gas atmosphere with a dew point of -50'C.
After sintering at C for various sintering times, dewaxing at the initial stage of sintering.

Departure 9. The sintering time during which the density decrease due to decarbonization and the density increase due to the progress of sintering are balanced, that is, the time when substantial densification that contributes to improving the strength of the sintered body begins with an O content of 0.2 to 0.5%.
As shown in Figure 1, 80
It was found that substantial densification begins in minutes or more.

(c) Graphite is mixed with the same steel powder as in (a) above, and after molding, the temperature is 1200°C1 in a reducing gas atmosphere with a dew point of -50°C.
The 9 weight 0.075% sintered body was sintered for 50 minutes at a dew point of -10.
°c, -aooC, -50°C in an Ng atmosphere at 870°C for 180 minutes and then quenched in oil.The results of analyzing the amount of the sintered body were 0.225% and 0.225%, respectively.
It was found that oxidation during heat treatment was significantly reduced below the μ point -ao'c of 185% and 0.110%.

2) Graphite was mixed with the same steel powder as in (a) above, and after molding, it was heated at 1200°C in a reducing gas atmosphere with a dew point of -60°C.
The sintered body sintered for 0 minutes had a weight of 0.24% and a weight of 0.8%.

The 0.46% and 0.58% sintered bodies were heated with N at a dew point of -50°C.

1 After heating and holding at 870'C in air flow, cooling capacity is 0.
12Cm, 0.16Cm, 0.20Cm,
After quenching in 0.25 CfM oil and then tempering, the tensile strength was measured. As shown in Figure 2, when the sintered body had a C content of 0.5% or less, the cooling capacity was 0, and when the cooling capacity was 16 Cn1-1 or more, the tensile strength was measured. It was found that strength improved rapidly.

Based on the above-mentioned knowledge, the present invention basically contains 1% by weight of Mn with an upper limit of 2.8% and Qr with an upper limit of 5.5%, with a total amount of at least 0.0%. A compacted powder is made from a mixed powder consisting of an alloy steel powder containing 4 to 7.0% and an amount of 0.25 to 1.0%, graphite powder, and a lubricant selectively added. Obtain a green compact with a density of 6.09/cr1 or higher, and store the green compact in a non-oxidizing atmosphere with a dew point of -80°C or lower at 1150~
By heating at a temperature of 1800 ° C for 80 to 180 minutes, a sintered body with C: 0.2 to 0.5% and 0: 0.25% or less is made, and this sintered body has a dew point of -80 ° C. The structure was such that the quenching and tempering process was performed in a cooling medium with a cooling capacity of 0.16 Cm-1 or more in the following non-oxidizing and aqueous atmosphere from a temperature range of AC point to AO8 point +100°C.

The reason why the main alloying element of the raw steel powder is at least one of Mn and ar is that Mn and Or are
It shows excellent performance in improving corrosion resistance, is extremely inexpensive compared to other alloying elements such as lti, MO, etc., and its oxide in steel powder can be used in mixed powder graphite within a temperature range of 1150 to 1800"C. This is because reduction is possible, and the resulting sintered parts can be made with higher strength and lower cost.The reason for limiting the amount of each alloy is as follows.

Mn: Effective in improving hardenability, but if excessive, the compressibility of the steel powder will deteriorate and the sinterability will decrease due to an increase in the amount of oxygen in the steel powder, so the upper limit should be set at 2.8%. And so.

Or: It is effective in improving hardenability and hardness, but if it is excessive, the compressibility of the steel powder decreases and the sinterability decreases due to an increase in the amount of oxygen in the copper powder. The upper limit was set at 5.6% because machinability deteriorates due to an increase in .

Furthermore, the total amount range of G, Mn, and (lr) was set to 0.4 to 7.0% in consideration of improvement in hardenability and reduction in compressibility of steel powder.

Reason for setting the amount of raw material steel powder to 0.25-1.0% &amp;
In the case of water atomized steel powder alloyed with In and/or Or, the amount is within the range of 2, which can be easily produced by reduction using conventional pure iron powder production equipment, and because it is easy to produce, copper powder can be produced at low cost. This is because it reduces the manufacturing cost of the product sintered parts.

In addition, in the present invention, in addition to the above-mentioned main components, Nb, V, and O can be added as subcomponents in order to obtain a sintered material that is excellent in hardenability, corrosion resistance, high-temperature strength, and machinability. B, Ou, Ni.

All of the alloying elements in the steel powder have an oxide of 1150~
It is possible to reduce the mixed powder graphite G with a trowel within a temperature range of 1300°C, and it has the characteristic that it can work with Mn and/or Or to further improve the properties of sintered parts.

Regarding the above-mentioned selected components to be included in the alloy steel powder of the present invention, the alloy amount range is limited for the following reasons due to the effects that appear when they are added to the steel powder.

Nb: It is effective in making crystal grains finer and improving strength, but if it is less than 0.01%, the effect is small, and if it is in excess, hardenability and machinability will decrease, so 0.01 to 1%. .0%.

■...0.25% or less improves hardenability, and 0.8% or less improves hardenability.
% or more, it is effective in making crystal grains finer and improving strength, but if it is less than 0.01%, the effect is small, and if it is in excess, hardenability decreases, so it was set at 0.01 to 8.5%. .

B: It is effective in improving hardenability, but if it is less than 0.001%, the effect is small, and if it is excessive, the toughness decreases, so it was set to 0.001 to 0.6%.

CU...Effective in improving strength and corrosion resistance, but 0.1
% or less, the effect is small, and if it is excessive, the compressibility and toughness of the copper powder decreases, so it was set at 0.1 to 8.0%.

N soil: It is effective in improving hardenability, corrosion resistance, and a property, but if it is less than 0.1%, the effect is small, and if it is excessive, the economical efficiency and compressibility of the copper powder will decrease. 1-5.0
%.

CO... is effective in improving high-temperature strength, but if it is less than 0.1%, the effect is small, and if it is excessive, the economical efficiency and compressibility of the steel powder will decrease. did.

MO...It is effective in improving hardenability in conjunction with In and (Hr), but if it is less than 0.1%, the effect is small, and if it is in excess, it will affect economic efficiency, compressibility of copper powder, and machinability. was set at 0.1 to 7.0%.

Sn: Effective in improving machinability and corrosion resistance, but 0.
If it is less than 1%, the effect will be small, and if it is excessive, the economical efficiency and compressibility of the copper powder will decrease, so it was set to 0.1 to 8.0%.

W...Effective alone or in combination with Qr and V to improve high temperature strength, hardness, and hardenability, but if it is less than 0.1%, the effect is small, and if it is in excess, it will affect the economy and copper powder. Since compressibility and machinability decrease, the content was set at 0.1 to 8.0%.

P: Effective in improving machinability and corrosion resistance, but 0.0
If it is less than 4%, the effect will be small, and if it is excessive, the compressibility and toughness of the steel powder will decrease, so it was set to 0.04 to 0.8%.

S: is effective in improving stiffness, but if it is 0.04% or less, the effect is small, and if it is excessive, the toughness decreases, so it was set to 0.04 to 0.8%.

In addition to the above-mentioned examples, the raw material steel powder naturally contains impurities and Fe, which are unavoidable.In addition, in a preferred example, O: 0.2% from the viewpoint of compressibility and formation as an alloy steel powder.
Below, On 1.0% or less, S Sat2 0.1% or less,
Al: 0.01% or less; Ti: o, o1% or less. Among these elements, Q, Si
.

When the content of both Al and Ti exceeds a limited value, nonmetallic inclusions in the sintered body increase, and the hardenability of the product sintered part decreases rapidly, resulting in loss of mechanical properties.

On the condition that 70% or more of the above-mentioned steel powder is mixed, the balance is non-ferrous metal powder 9 alloy powder and non-metal powder in order to supplementally improve the characteristics of the raw steel powder.

It is also possible to mix and use any one or more of the alloy powders other than the alloy steel powder. The reason why the proportion of the raw material steel powder is set at 70% or more is that if it is less than 70%, the characteristics of the raw material steel powder itself will be lost from the mixed powder, and the hardenability 1 mechanical properties of the sintered body will be impaired. .

Further, if necessary, a lubricant is further added to obtain a mixed powder.

The above-mentioned mixed powder is then compression-molded to form a green compact.The reason why the compacted powder density after compression-molding is set to 6.09/cr1 or more is to sufficiently promote sintering and obtain sufficient strength. This is in order to obtain a sufficient amount of heat and to maintain a sufficiently high cooling rate during quenching.

If the density is too low, even if the cooling capacity of the coolant is increased, sufficient rapid cooling will not be possible and a sufficient hardening depth will not be obtained. The above-mentioned lubricant is used in the form of a mixture of raw material steel powder and graphite powder in advance, if necessary, when the mixture is compression-molded in a mold.

Next, the compacted powder is sintered to form a sintered body.
This is because in a temperature range lower than 1150°C, the progress of sintering and the reduction of the alloyed 2m compound of mixed graphite are insufficient, and sufficient hardenability and strength cannot be obtained.
This is because a temperature higher than C lowers the economical efficiency and causes large dimensional changes during sintering, making it impractical.

In addition, the reason why the sintering atmosphere was set to be a non-oxidizing atmosphere with a dew point of -30°C or less was because of the oxidation of the steel powder during heating.
) This is to suppress the oxidation of In, Or, Nb, V, and B, and prevent a decrease in the hardenability of the sintered body.

Note that the non-oxidizing atmosphere refers to an atmosphere having one or more of reducing, inert, and carburizing properties. However, from the viewpoint of promoting sintering, an atmosphere containing 8% or more of H3 is desirable.

The reason why the sintering time was set to 80 to 180 minutes is that
If the time is shorter than 1 minute, sintering will not proceed sufficiently in the practical compact C lid range, the sintered compact will not be substantially densified, and reduction will also be insufficient, resulting in insufficient strength and hardenability. This is because they cannot be obtained. Further, if the time is longer than 180 minutes, the economical efficiency decreases and the dimensional change during sintering increases, making it impractical.

The amount of C in the sintered body produced through sintering is 0.2 to 0.5%,
03iO, the reason for keeping it below 25% is that the amount of O is 0.
．． If it is less than 2%, the strength and hardness will be insufficient due to the small amount of O in the quenched martensite, and if it is more than 0.5%, the tensile length will be improved by increasing the cooling ability of the coolant during quenching. This is because the effect is small. In other words, in a sintered body with a large amount of zero, elements with a strong tendency to form carbides, such as the main alloy components In and Qr and the subcomponents Nb and V, have a strong interaction with C in the sintered body. This is because coarse carbides are easily formed, and even if the cooling capacity during hardening is increased, the effect of improving hardenability is small.

Next, the sintered body is heat-treated to form a predetermined sintered part. AO of
8 The reason why the temperature range is 0-100'C higher than the transformation point is that at temperatures above the dew point -ao'c, Mn and Or are solidly dissolved in the copper powder due to the heating atmosphere.

Nb, V, Bno! This is because Ac8 is rapidly lost as an oxide and the hardenability of the sintered body becomes insufficient.
This is because at temperatures lower than the transformation point, austenitization is insufficient and strength decreases due to the appearance of ferrite phase.
This is because a temperature higher than the transformation point by 100'C or more is undesirable because it increases the amount of retained austenite after quenching due to stabilization of austenite and coarsens the crystal grains, resulting in a decrease in strength.

In addition, the cooling capacity of the coolant used in this quenching process is reduced to 0.
．． The reason for this is that below 0.16 cm, the cooling rate is slow, and the low carbon/low alloy steel sintered body of the present invention has a lower heat resistance than a dense material with the same roughness. This is because sufficient hardening depth and hardness cannot be obtained even with quenching due to low conductivity.After quenching, the sintered body is finally tempered to become the final product.

Next, the present invention will be explained by comparing examples with comparative examples.

Example raw material steel powder green density 6.859/cd Heating atmosphere during sintering H4 + dew point -50°C sintering conditions
1200℃×150 minutes Sintered body O amount 0
．． 041% Sintered body C content 0.87% Heating atmosphere during quenching N, 111 points -50°C quenching conditions 810°C x 80 minutes cooling capacity after holding 6.2
Quenching in oil of cm"1 Tempering conditions: 170"C In addition to the prevention of oxidation of the sintered body and the quenching effect with a large cooling capacity, the sintered body becomes substantially denser due to the extension of the sintering time, and the hardenability is further restored due to the enhanced reduction. A high tensile strength of 110 kg/yrd or more was obtained.

Comparative example Raw material steel powder, green powder density, heating atmosphere during sintering, sintering conditions,
The amount of sintered body O and the amount of sintered body C were the same as those used in Example 1.

Heating atmosphere during quenching: N, 111 points -10°C Quenching conditions: 810°C x 80 minutes cooling capacity 0.1
cm-" Quenching and tempering conditions in oil 170°C x 90 minutes, then cooling in the air Tensile strength 67.8 to 9/ad In the above comparative example, the tensile strength was 67.81C9/-, Although the sintered body was sufficiently densified and reduced by the long sintering time, the tensile strength was only about half that of the example due to oxidation during quenching and slow cooling rate.

As explained above, in the present invention, by mixing graphite powder with inexpensive alloy steel powder having a high O content and sintering it, the sintered body becomes sufficiently low in oxygen and hardenability is restored. Moreover, by optimizing the combination of sintering conditions and heat treatment conditions, the following effects can be expected.

(1) Manufactured at low cost. In other words, it becomes possible to use high-oxygen alloy steel, reducing the cost of sintered parts.

(g) By simply changing the sintered body manufacturing conditions and appropriately selecting the heat treatment conditions, high-strength sintered parts that could not be obtained by conventional methods can be obtained, and the cost performance of the sintered parts can be improved.

(8) Since no special equipment is required for heat treatment, the manufacturing cost of sintered parts is reduced.

[Brief explanation of the drawing]

Figure 1 is a graph showing that the densification of the sintered body depends on the amount of C in the sintered body, and Figure 2 shows that tensile strength is improved by increasing the cooling capacity of the coolant during quenching. It is a graph.

Claims (1)

[Claims] L in weight% with an upper limit of 2.8% and 6.5
Alloy steel powder containing at least one of them in a total amount of 0.64 to 7.0% per Qr with an upper limit of % and an O content of 0.25 to 1.0%, graphite powder and From a mixed powder consisting of a selectively added lubricant, the green density is 6.09/cr! Obtain the above green compact, and store the green compact in a non-oxidizing atmosphere with a dew point of -30°C or lower for 11
By heating at a temperature of 50 to 1300°C for 80 to 180 minutes, O: O-2 to 0.5%, ○: 0.25%
The following sintered body is used, and this sintered body is used in a non-oxidizing atmosphere with a dew point of -80°C or less, from a temperature range of AC8 points to AC8 points +100"C, using a cooling medium with a cooling capacity of 0.16CI11-" or more. A method for producing a high-strength sintered material characterized by tempering after quenching. & The mixed powder is 70% by weight or more of alloy steel powder, a lubricant selectively used with graphite powder, and non-ferrous metal powder 1 alloy powder,
The manufacturing method according to claim 1, which comprises one or more types selected from non-metal powders and other alloy steel powders. & Mn up to 2.8% and 5.5% by weight
%, and contains at least one of them in a total amount of 0.4 to 7.0%, and
: 0.01~1.0%, V:0.01~L
5%, E: 0.001-0.5%, Qu: 0
．． 1-8.0%, N soil: 0.1-5.0%
, CO; 0.1~10.0%, MO: 0.1~
7.0%, sn: 0.1-3.0%, W: 0
．． 1 to 8.0%, P: 0.04 to 0.8%, and S: 0.04 to 0.8%, and the O content is 0. .25~
A green compact with a powder density of 6, Og/cff1 or more is obtained from a mixture of graphite powder and a lubricant selectively added to alloy steel powder adjusted to 1.0%. On 0.2-0.5% by heating the green compact at a temperature of 1150-1300°C for 30-180 minutes in a non-oxidizing atmosphere with a dew point of -30°C or less. 0: A sintered body of 0.25% or less, and the sintered body is heated to AC8 to AC8 in a non-oxidizing atmosphere with a dew point of -80°C or less.
Cooling capacity 0.16cm from the temperature range of point +100℃
A method for producing a high-strength sintered material, characterized by quenching in the above-mentioned coolant and then tempering. Table Mixed powder is 70% by weight or more of alloy steel powder, lubricant selectively used with graphite powder, and non-ferrous metal powder 2 alloy powder,
9. The manufacturing method according to claim 8, which comprises one or more types selected from non-metallic powder and other alloyed steel powder.