WO2009113821A2

WO2009113821A2 - Iron-based sintered body with high strength and high elongation and preparation method thereof

Info

Publication number: WO2009113821A2
Application number: PCT/KR2009/001247
Authority: WO
Inventors: 박동규; 석세훈; 김상석
Original assignee: 가야에이엠에이 주식회사
Priority date: 2008-03-12
Filing date: 2009-03-12
Publication date: 2009-09-17
Also published as: WO2009113821A3; KR20090097715A

Abstract

Disclosed is a method for preparing an iron-based sintered body, which comprises: mixing a lubricant and at least two kinds of powder to prepare a mixture; press-molding the mixture to form a molding; and pre-sintering the molding, then sintering and cooling the molding. The powder includes Cr 1.0~2.5wt%, Mo 0.1~0.8wt%, Mn 1.0~2.5wt%, C 0.1~1.1wt% and the balance of Fe and inevitable impurities, wherein Mn in the powder is present in an elemental form. Also, the sintered body has a sintering density of 7.0g/cm³ or more. In the disclosed method, the sintering is carried out at a temperature of 1150℃-1350℃ for 15-90 minutes in a reductive or neutral atmosphere which maintains a dew point of -30℃ or less. Accordingly, an iron-based sintered body with high strength and high elongation can be obtained through the method.

Description

[Correction 26.05.2009 by Rule 26] (철) Iron-based sintered body having high strength and toughness and manufacturing method thereof

The present invention relates to a sintered body made of an iron base alloy widely used in automobile parts and the like, and a manufacturing method thereof.

Small alloys manufactured by powder metallurgy are widely used as automotive parts, and the need for small alloys having high strength and toughness is increasing according to the demand for light weight and high strength of such components.

Generally, iron-based sintered alloy products manufactured by powder metallurgy are advantageous in terms of quality and cost as compared to products manufactured through a forging or rolling process. However, due to the nature of the manufacturing process of the sintered alloy product, pores are inevitably formed in the product, and the residual pores have an effect of lowering the mechanical properties of the sintered powder metallurgy product compared to a fully dense alloy such as forging. This is because the pores act as stress concentration regions, and the pores also reduce the effective volume under stress.

Therefore, in order to prevent such deterioration of properties due to pores, in the case of iron-based sintered alloys, many techniques using alloy steel powders to which nickel (Ni), chromium (Cr), molybdenum (Mo), copper (Cu), etc. are added have been developed. .

Among them, a powder mainly used to increase the tensile strength is a metal alloy powder containing 1 to 8% by weight of nickel.

Nickel is an alloying element commonly contained in the composition of iron base alloy powder in order to increase the tensile strength in powder metallurgy field, and the iron base alloy product manufactured by iron base alloy powder containing up to 8% of nickel has its tensile strength. Improves by nickel is described in US Pat. No. 6620218, "IRON POWDER COMPOSITIONS," as a prior art incorporated herein.

Nickel also promotes sintering, increases hardenability, and affects elongation, but when used with molybdenum, copper, or the like, the effect is greater.

However, such a metal alloy powder contains a large amount of expensive alloying elements nickel, molybdenum and copper, so that the price of the metal alloy powder is very expensive.

In light of recent trends in the use of automotive parts, the proportion of raw materials in product prices continues to increase. In particular, since nickel is very expensive and its unit price is rising, the proportion of raw materials to product prices continues to increase due to the metal alloy powder containing nickel.

Therefore, there is an urgent need for a small-alloy alloy that can be manufactured at low cost while having high mechanical strength and high mechanical properties.

On the other hand, as a technique using a chromium-based alloy powder has been disclosed in US Patent WO / 2005/120749 "SINTERED METAL PARTS AND METHOD FOR THE MANUFACTURING THEREOF". The prior art is considered to be incorporated herein.

However, chromium requires strict control of the sintering atmosphere due to the high affinity with chromium, as confirmed by the oxygen affinity according to the alloying elements of FIG. 1.

In addition, in the case of chromium-based alloy powder, since the moldability is very low, it is difficult for the molded body to have a high density, and the content of pores is increased, so that it is very difficult to realize high strength as a whole.

In addition, U.S. Pat.No., 7329380, "METHOD OF CONTROLLING THE DIMENSIONAL CHANGE WHEN SINTERING AN IRON-BASED POWDER MIXTURE", has been disclosed as a technique using a powder containing a large amount of molybdenum and copper. The prior art is considered to be incorporated herein. In the case of molybdenum, the problem of low moldability can be solved. However, it is difficult to improve the strength with molybdenum alone. Therefore, even if molybdenum is added more than 1.0%, the strength is lowered. have.

In order to overcome this disadvantage, Fe-Mn-Si-based mother alloy or master alloy is used to make EP 0,097,737B1 "Powder metallurgy process for producing parts having high strength and hardness from Si-Mn or Si-Mn -C alloyed steel "has been disclosed. The prior art is considered to be incorporated herein. When the sintering using the master alloy as described above can reduce the oxygen affinity of the components, it is difficult to produce an alloy having a uniform structure.

In order to solve the above problems, the present invention is to provide a method for producing an iron-based sintered body having a low cost, high strength and high toughness using manganese and an iron-based sintered body having a tensile strength of 1100MPa or more and a hardness of HRC 25 or more.

In particular, the present invention allows manganese to be added as a powder in elemental form to the mixture before press molding so that manganese can be uniformly distributed in the alloy and is prevented from being oxidized during sintering. By controlling the sintering atmosphere, it is possible to obtain an iron-based sintered body having high strength and high toughness.

As a result, it is possible to provide an iron base alloy containing manganese having strength and toughness superior to that of the iron base alloy containing expensive nickel.

In order to solve the above problems, the present invention, after mixing at least two or more kinds of powders and lubricants to form a mixture, the mixture is press-molded to form a molded body, and then after the pre-sintering the molded body after the main sintering In the method for producing an iron-based sintered body by cooling: The powder is composed of Cr 1.0 ~ 2.5wt%, Mo 0.1 ~ 0.8wt%, Mn 1.0 ~ 2.5wt%, C 0.1 ~ 1.1wt% and the balance Fe and other unavoidable impurities Mn in the powder is present as an elemental powder; The molded body has a molding density of at least 7.0 g / cm ³ ; The main sintering is sintering for 15 minutes to 90 minutes at a temperature of 1150 ℃ to 1350 ℃ in a reducing or neutral protective atmosphere in which the dew point below -30 ℃ is maintained; It is characterized by.

In the above, Cr, Mo, and Fe in the powder is present as an alloy powder of Fe-Cr-Mo, C in the powder is preferably present as a graphite powder.

In the above, the elemental Mn powder preferably has an average particle size of 10 μm to 20 μm.

In another aspect of the present invention, in the iron-based sintered body consisting of Cr 1.0 ~ 2.5wt%, Mo 0.1 ~ 0.8wt%, Mn 1.0 ~ 2.5wt%, C 0.1 ~ 1.1wt% and the balance Fe and other unavoidable impurities, 1100Mpa It provides an iron-based sintered body having a high strength and high toughness, characterized in that the tensile strength and HRC 25 or more.

According to the present invention as described above, it is possible to provide a method for producing an iron-based sintered body having low cost, high strength and high toughness using manganese, and an iron-based sintered body containing manganese having a tensile strength of 1100 MPa or more and a hardness of HRC 25 or more.

In particular, the present invention allows manganese to be added as a powder in elemental form to the mixture before press molding so that manganese can be uniformly distributed in the alloy and is prevented from being oxidized during sintering. By controlling the sintering atmosphere, an iron-based sintered body having high strength and high toughness can be obtained.

1 is an oxygen affinity according to the alloying elements.

2 is a hardenability index according to the alloying elements.

3 is a change in the toughness of the sintered body according to the alloying element addition amount.

Hereinafter, the configuration and operation according to an embodiment of the present invention will be described in detail.

In general, a method for producing a sintered body by metal powder comprises the steps of uniformly mixing two or more powders and lubricants to form a mixture, forming a molded body by pressing the mixture to form a molded body, the pre-sintering of the molded body After sintering, it is cooled to obtain a sintered body. In addition, in order to increase the mechanical properties of the sintered body thus obtained, heat treatment may be involved.

Hereinafter, a description of a general method for manufacturing a sintered body will be omitted as much as possible, and the following will mainly describe specific or significant points in an embodiment of the present invention.

(1) Mixture Formation Step

In powder metallurgy, the formation of the mixture is appropriately mixing two or more powders and a lubricant.

The composition of two or more powders is composed of Cr 1.0 ~ 2.5wt%, Mo 0.1 ~ 0.8wt%, Mn 1.0 ~ 2.5wt%, C 0.1 ~ 1.1wt% and the balance Fe and other unavoidable impurities, and the lubricant is powder metallurgy It is understood that any lubricants commonly used in the art can be applied as appropriate.

The method of forming the mixture may be used a conventional mixing method for sintering, and the specific matters are the ratio of the components constituting the mixture, the particle size of manganese, the form of manganese and the like.

Cr, Mo, and Fe may each be added to the mixture as a powder in elemental form, but are preferably added as pre-alloy powders of Fe—Cr—Mo in order to prevent oxidation of Cr. The alloy powder of Fe-Cr-Mo preferably has an average particle size of 45 μm to 150 μm.

Chromium (Cr) provides excellent crush strength and hardness in the final sintered body. In order to provide adequate strength to the sintered body, chromium should contain at least 1.0 wt% or more, preferably 1.5 wt% or more. When the chromium content is 2.5 wt% or more, the compressibility of the powder is remarkably reduced, which is not only a problem in forming, but also the brittleness of the sintered body after sintering, thereby reducing the strength. Therefore, the content of chromium may vary between 1.0 and 2.5 wt%.

Molybdenum (Mo) provides excellent hardenability in the final sintered body.

The content of molybdenum is to be present between 0.1 and 0.8% by weight. When the content of molybdenum is less than 0.1%, the effect of addition is insignificant, and the addition amount increases the hardenability, but the compressibility of the powder is lowered and the amount of molybdenum should be limited to within 0.8% by weight because molybdenum is an expensive metal over nickel.

Manganese (Mn) is an elemental powder, i.e., manganese powder, in which manganese flakes are broken into particles having an average particle size of 10 µm to 20 µm, and are added to the mixture, and preferably in a weight ratio of 1.0% or more and 2.5% or less. Manganese powder in the above and below elemental form means manganese powder consisting of pure manganese, not manganese in a compound or alloy form. Of course, even in the case of pure manganese powder, inevitable impurities may be added.

Manganese has an additive effect similar to that of nickel and has a higher hardenability than nickel (see the hardenability index according to the alloying elements of FIG. 2). When the molded body of the mixture containing manganese is sintered at a high temperature of 1150 ° C. or higher, the melting point of the alloy powder is lowered and the diffusibility of the alloy powder is improved, which helps to improve the sinterability. If the content of manganese is 1.0wt% or less by weight ratio, the effect of addition is drastically reduced, and when it is 2.5% or more by weight ratio, dimensional stability and toughness are reduced, and also high oxidation is likely to cause a problem that the tensile strength of the sintered body is reduced.

On the other hand, nickel, in contrast to manganese, has a slow diffusion rate with iron and a difference in diffusion rate, resulting in a nickel-rich phase in which nickel is not diffused or Kirkendall pores. Done. In the case of nickel, in order to reduce such a problem, use fine nickel of 10 μm or less, or prepare an alloy powder.

In the case of manganese, the size of manganese added to reduce such non-uniformity of tissue should be adjusted. According to the research of the inventors, the added manganese is completely alloyed at a sintering temperature of 1150 ° C. or more when added to a particle size of 150 mesh or less. However, when the particle size is larger than 150 mesh, the manganese rich phase exists. Therefore, the average particle size of manganese added is limited to 20 μm or less. In addition, if the particle size is too small, the flow of the powder is bad during molding and easily oxidized during sintering, so the amount of powder having a size of 10 μm or less needs to be limited to 15% or less. Use of manganese powder of this size can reduce tissue non-uniformity.

Meanwhile, even when manganese is added in the form of a powder of a prealloy of ferro-manganese (Fe-Mn) or Fe-Mn-Si, the overall nonuniformity can be reduced, but microscopic nonuniformity is difficult to avoid.

When manganese is added to the mixture as an elemental powder, it is necessary to properly control the sintering atmosphere in order to prevent the manganese from being oxidized by the affinity with oxygen during sintering.

Manganese is preferably added in an amount ratio of 1.0% or more and 2.5% or less. The change in the elongation of the final prepared sintered body according to the amount of manganese added is shown in FIG. 3.

In FIG. 3, test piece 1 is an iron-based small alloy (Fe-4wt% Ni-1.5wt% Cu-0.5wt% Mo-0.3wt% C) containing nickel, and test piece 2 (Fe-1.5wt% Cr-0.2wt%). Mo-1.0wt% Mn-0.3wt% C), 3 (Fe-1.5wt% Cr-0.2wt% Mo-1.5wt% Mn-0.3wt% C), 4 (Fe-1.5wt% Cr-0.2wt% Mo-2.0wt% Mn-0.3wt% C), 5 (Fe1.5wt% Cr-0.2wt% Mo-2.5wt% Mn-0.3wt% C) have Mn content of 1.0%, 1.5%, 2.0%, It is a 2.5% iron base alloy.

The toughness test measured the displacement until the test piece failed while increasing the crush strength.

As confirmed in FIG. 3, the

test pieces

2 and 3 have better toughness than the test piece 1, and the

test pieces

4 and 5 have a greater pressure-reducing strength than the test piece 1.

Carbon (C) is added as graphite powder, and the amount of carbon added is 0.1 to 1.1% by weight.

The amount of carbon added is preferably 0.1 wt or more because the amount of carbon added affects the tensile strength, and when toughness is required, a composition of about 0.3 wt% is preferable as in a conventional powder alloy material. Of course, in the case of a material having a composition of about 0.3 wt% C, when toughness and abrasion resistance are required together, surface treatment such as carburization is required.

In addition, the carbon content is 0.6 ~ 0.7wt% when a simple high strength material is required. In this case, the wear resistance is excellent and some toughness is retained.

When carbon is 0.7 wt% or more and 1.1 wt%, it is mainly used when a high wear resistance is required regardless of the toughness of the material. If the carbon content is 1.1 wt% or more, brittleness is increased, so its use is limited.

Other unavoidable impurities may include Cu, Sn, P, Si, and S in an amount of 0.1 wt% or less.

Lubricants are added to facilitate molding, and conventional powder metallurgy lubricants are sufficient to be used. The lubricant is later removed from the preliminary results. A representative example of a lubricant is stearic acid. Stearic acid may usually be added in an amount of about 0.5 wt% to 1.0 wt% based on the total weight of the powder.

In the case of chromium and molybdenum as described above, the alloy powder of Fe-Cr-Mo is added, and manganese and carbon are added to the alloy powder of Fe-Cr-Mo before the mixing process together with a lubricant added to facilitate molding. After mixing, mix evenly to form a mixture.

(2) molding body forming step

The mixture of the metal alloy powders obtained by the above mixing is molded at a pressure of 400 to 700 MPa or more to prepare a molded body having a molding density of 7.1 to 7.15 g / cm ³ . Since the molding density of the molded article is directly related to the tensile strength and the like, it depends on the required tensile strength, but in order to have a strength of 1100 MPa or more, it is preferable to have a molding density of at least 7.1 g / cm ³ .

(3) sintering step

The sintering step can be divided into the main sintering and the pre-sintering for removing the lubricant, but the pre-sintering is naturally solved in the process of raising the temperature in the sintering furnace for the main sintering, and thus cannot be regarded as the core of the present invention.

In the case of main sintering the molded product prepared as described above, in the case of the metal alloy powder added with chromium and manganese, the oxidation incidence is high, so that the appropriate sintering conditions should be adjusted.

To this end, the molded article prepared as described above is subjected to 10 minutes to 60 minutes at a temperature of 450 ° C to 900 ° C in a reducing or neutral protective atmosphere in which a dew point of -30 ° C or lower (preferably -40 ° C to -60 ° C) is maintained. After presintering and main sintering at a temperature of 1150 ° C to 1350 ° C for 15 minutes to 90 minutes, cooling is performed at a cooling rate of 0.5 to 6.0 ° C / s to obtain a final sintered body. Presintering conditions vary depending on the amount and type of lubricant. It is understood that the presintering is naturally performed in the process of raising the temperature of the sintering furnace for the main sintering, so that the process conditions of the presintering may be appropriately modified by those skilled in the art.

In the above protective atmosphere, oxidation of chromium and manganese is prevented by using a mixed atmosphere in which nitrogen and hydrogen are properly mixed. Usually used atmosphere is a nitrogen atmosphere containing 0 to 95% hydrogen by volume ratio.

The dew point should also be kept below -30 ° C to prevent oxidation.

The protective atmosphere usually maintains a mixed atmosphere of nitrogen and hydrogen in a volume ratio of 90:10 to 80:20 for economical considerations and to maintain a low dew point. Another reason for the high use of nitrogen is conventionally liquid liquefied nitrogen, which has been disadvantageous in that the dew point gradually increases due to several exposures in the air during the transfer from the gas supplier to the consumer at high pressure. As the purification technology to obtain high-purity nitrogen by directly separating and purifying with molecular sieves has been developed, it is possible to supply nitrogen with high purity in a dew point of -75 ° C or lower from the nitrogen generator to the line to facilitate the atmosphere control. to be. By mixing a small amount of hydrogen having reducibility with such high purity nitrogen and keeping the dew point below -30 ° C, sintering of manganese powder which is difficult to control becomes possible.

Iron-based small alloys sintered by this process have a density of 0.10 to 0.20 g / cm ³ higher than the molding density, and have a tensile strength of 1100 MPa or more and a hardness of HRC 25 or more at a sintered density of 7.1 to 7.15 g / cm ³ or more. .

The iron-based sintered body manufactured according to the present embodiment has characteristics of high strength and high toughness having excellent strength and hardness, that is, tensile strength of 1100 MPa or more and hardness of HRC 25 or more.

Experimental Example 1

Experimental Example 1 was used by mixing a variety of materials as shown in Table 1, 0.8 wt% stearic acid was added to the total weight of the powder as a lubricant. The figures in Table 1 are based on weight ratio.

Table 1

division	Material composition ratio
division	Fe-1.5wt% Cr-0.2wt% Mo	Fe-3wt% Cr-0.5wt% Mo	Mn	C
Material
1	99.5	-	0.2	0.3
Material 2	99.4	-	0.3	0.3
Material 3	99.2	-	0.5	0.3
Material 4	98.7	-	1.0	0.3
Material 5	98.2	-	1.5	0.3
Material 6	97.7	-	2.0	0.3
Material 7	97.2	-	2.5	0.3
Material 8	96.7	-	3.0	0.3
Material 9	-	99.5	0.2	0.3
Material 10	-	99.4	0.3	0.3
Material 11	-	99.2	0.5	0.3
Material 12	-	98.7	1.0	0.3
Material 13	-	98.2	1.5	0.3
Material 14	-	97.7	2.0	0.3
Material 15	-	97.2	2.5	0.3
Material 16	-	96.7	3.0	0.3
Material 17	49.75	49.75	0.2	0.3
Material 18	49.7	49.7	0.3	0.3
Material 19	49.6	49.6	0.5	0.3
Material 20	49.35	49.35	1.0	0.3
Material 21	49.1	49.1	1.5	0.3
Material 22	48.85	48.85	2.0	0.3
Material 23	48.6	48.6	2.5	0.3
Material 24	48.35	48.35	3.0	0.3

As confirmed in Table 1, the materials 1 to 8 were made of Fe-1.5wt% Cr-0.2wt% Mo alloy powder, and the manganese powder of elemental form was 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 were added at a weight ratio and the graphite powder was added at 0.3%.

Materials 9 to 16 were made of Fe-3.0wt% Cr-0.5wt% Mo alloy powder as the known powder, and the manganese powder in elemental form was 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, It was added in the weight ratio of 2.5 and 3.0, and 0.3% of graphite powder was added.

Material 17 to Material 24 were made of Fe-1.5wt% Cr-0.2wt% Mo alloy powder and Fe-3.0wt% Cr-0.5wt% Mo alloy powder as known powders. It was added at a weight ratio of 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0, respectively, and the graphite powder was added to 0.3%.

These materials were mixed in a Dubucon mixer for 40 minutes and press-molded in a cylindrical form at a pressure of 700 MPa in a mechanical press, then the dew point was kept below -40 ° C. in a mixed atmosphere of nitrogen and hydrogen between 90:10 and 80:20. Sintering was carried out at 1250 ° C. for 40 minutes in one state, followed by cooling to prepare a sintered body. The sintered compacts of the iron-based small alloys thus obtained were examined for the rolling strength, hardness, tensile strength, density, and appearance, and the results shown in Table 2 were obtained.

TABLE 2

division	Physical Properties of Sintered Body				Exterior
division	Rolling strength (MPa)	Hardness (HRC)	Tensile Strength (MPa)	Density (g / cm 3)	Exterior
Material 1	1013	19.8	990	7.25	Good
Material
2	1096	20.9	1000	7.25	Good
Material
3	1184	21.4	1010	7.25	Good
Material
4	1692	25.9	1150	7.25	Good
Material
5	1713	29.8	1220	7.25	Good
Material 6	1870	31.5	1240	7.25	Good
Material 7	1647	31.9	1280	7.25	Good
Material 8	1395	31.1	1150	7.25	Good
Material 9	1098	20.9	1010	7.25	Good
Material
10	1147	22	1030	7.25	Good
Material 11	1259	22.8	1090	7.25	Good
Material
12	1683	27.5	1230	7.25	Good
Material 13	1777	30.3	1250	7.25	Good
Material 14	1846	32.8	1300	7.25	Good
Material 15	2007	34.2	1340	7.25	Good
Material 16	1475	26.4	1190	7.25	Good
Material 17	1072	20.2	1000	7.25	Good
Material 18	1123	21.5	1010	7.25	Good
Material
19	1192	22.3	1030	7.25	Good
Material
20	1662	26.8	1210	7.25	Good
Material 21	1722	30.1	1230	7.25	Good
Material 22	1826	31.7	1290	7.25	Good
Material 23	1899	32.5	1310	7.25	Good
Material
24	1454	35.7	1170	7.25	Good

As can be seen from Table 2, the

materials

4, 5, 6, 7, 12, 13, 14, 15, 20, 21, 22, and 23, all of which have a manganese content of 1.0% to 2.5% under the same sintering conditions, have been subjected to rolling strength. Since it has the performance of 1662 MPa or more, tensile strength of 1150 MPa or more, and hardness of HRC 25.9 or more, it can be confirmed that it has a tensile strength of 1100 MPa or more and hardness of HRC 25 or more.

On the other hand, in case of

materials

1, 2, 3, 9, 10, 11, 17, 18, and 19 having a manganese content of less than 1.0%, the compressive strength, hardness, and tensile strength all decreased drastically. In case of 8, 16, and 24, the hardness was similar or slightly decreased or increased as compared with 2.5% manganese, but the compressive strength and tensile strength decreased drastically.

As such, the sintered body of the iron base alloy composed of Cr 1.0-2.5wt%, Mo 0.1-0.8wt%, Mn 1.0-2.5wt%, C 0.1-1.1wt% and the balance Fe and other unavoidable impurities has very good rolling strength and tensile strength. It was confirmed to have strength and hardness.

(Experiment 2)

In Experimental Example 2, a low chromium alloy powder of Fe-1.5 wt% Cr-0.2 wt% Mo was used as a reference weight of 100, and 2.0 wt% manganese powder and 0.3 wt% graphite powder were mixed. As the lubricant, 0.8 wt% of stearic acid was added to the total weight of the powder and used. These materials were mixed in a Dubucon mixer for 40 minutes, press-molded in a cylindrical form at a pressure of 700 MPa in a mechanical press, and then sintered at 1250 ° C. for 40 minutes in a mixed atmosphere of 90:10 to 80:20 nitrogen and hydrogen. After cooling, a sintered body was produced. At this time, sintering was performed while changing the dew point in the sintering furnace from -10 ° C to -60 ° C for each of the same materials, so that the characteristics of the sintered body according to the change of the dew point could be known.

The sintered body of the iron-based small alloy obtained as described above was tested for the rolling strength, toughness, hardness, tensile strength, appearance, and the like, and the results shown in Table 3 were obtained. The toughness test measured the displacement (mm) until the test piece broke while increasing the crush strength.

TABLE 3

dew point	Rolling strength (MPa)	Deformation amount (mm)	Hardness (HRC)	Tensile Strength (MPa)	Exterior
-10 to -20	778	0.6	33.2	520	Bad
-20 to -30	211	0.7	34.6	640	Bad
-30 to -40	1861	1.4	31.4	1298	Good
-40 to -50	1865	1.5	31.3	1299	Good
-50 to -60	1870	1.5	31.5	1300	Good

As shown in Table 3, the sintered body sintered by maintaining the dew point at -30 ° C or less was found to have excellent mechanical properties, that is, a crushing strength of at least 1861 MPa, a hardness of at least 31.3 HRC, a tensile strength of at least 1298 MPa, and excellent toughness. When maintained at -30 ° C or higher, the ring strength, toughness, tensile strength, and appearance were poor. Therefore, it is very important to maintain the dew point at -30 ° C or lower, preferably -40 ° C or lower during sintering.

The above embodiments are merely preferred embodiments of the present invention, and the technical idea of the present invention may be variously modified or adjusted by those skilled in the art. Such modifications and adjustments fall within the scope of the present invention if they use the technical idea of the present invention.

According to the present invention, automobile parts requiring high strength and high hardness can be manufactured at low cost.

Claims

In the method for producing an iron-based sintered body by mixing at least two or more powders and lubricants to form a mixture, the mixture is press-molded to form a molded body, and then the molded body is pre-sintered and then cooled to produce an iron-based sintered body:

The powder is composed of Cr 1.0 ~ 2.5wt%, Mo 0.1 ~ 0.8wt%, Mn 1.0 ~ 2.5wt%, C 0.1 ~ 1.1wt% and the balance Fe and other unavoidable impurities, where Mn is an elemental powder Exists as;

The molded body has a molding density of at least 7.1 g / cm 3 ;

The main sintering is a sintering for 15 minutes to 90 minutes at a temperature of 1150 ℃ to 1350 ℃ in a reducing or neutral protective atmosphere in which the dew point below -30 ℃ is maintained;

Method for producing an iron-based sintered body having high strength and high toughness, characterized in that.
The method of claim 1,

Cr, Mo, and Fe in the powder is present as an alloy powder of Fe-Cr-Mo, C in the powder is a method for producing an iron-based sintered body having high strength and high toughness, characterized in that present as a graphite powder.
The method according to claim 1 or 2,

The method of producing an iron-based sintered body having high strength and high toughness, characterized in that the Mn powder of the element form has an average particle size of 10μm ~ 20μm.
It consists of Cr 1.0 ~ 2.5wt%, Mo 0.1 ~ 0.8wt%, Mn 1.0 ~ 2.5wt%, C 0.1 ~ 1.1wt% and the balance Fe and other unavoidable impurities, having tensile strength of 1100Mpa or more and hardness of HRC 25 or more Iron-based sintered body having high strength and high toughness, characterized in that.