KR101531347B1 - Method for manufacturing iron-based diffusion bonding powders - Google Patents

Abstract

The present invention relates to a method of producing an iron-based diffusion bonded powder, comprising the steps of: preparing an iron-based powder having a surface oxidized by spraying molten steel; uniformly mixing the oxidized iron- Based diffusion powder to a surface of the iron-based powder while reducing the iron-based powder and the manganese oxide powder in a heat treatment furnace in a reducing atmosphere, and then crushing the diffusion-bonded powder A manufacturing method is disclosed.

Description

METHOD FOR MANUFACTURING IRON-BASED DIFFUSION BONDING POWDERS [0002]

The present invention relates to a method of manufacturing an iron-based diffusion bonded powder, and more particularly, to a method of producing an iron-based diffusion bonded powder by diffusion bonding using manganese oxide powder.

Recently, the demand for automobile parts using powder metallurgy is increasing. This is because mechanical properties are lower than that of processed parts, but precise and complex parts can be mass-produced at low cost.

Particularly, in order to manufacture sintered parts for automobiles, a sintered body which is light in weight and exhibits properties of high strength and high toughness is required.

In general, iron-based sintered parts manufactured by powder metallurgy are superior in quality and economical to those manufactured by forging or rolling. However, due to the nature of the manufacturing process, sintered products necessarily form pores in the product, and these residual pores degrade the mechanical properties of the sintered product. This is because the pores act as a stress concentration part and reduce the effective volume to receive the stress.

Therefore, in order to prevent deterioration of properties due to pores, a technique using iron-based alloy powder prepared by adding various metals has been developed in the case of iron-based sintered parts. In particular, carbon, copper, and nickel are alloying elements that are mainly added to pure iron powder, which affects the mechanical properties, moldability, and sinterability of the sintered body and is mixed at an appropriate ratio.

The carbon is the most commonly added element and is effective in increasing the strength and hardness of the sintered body and usually added in the form of graphite powder before the molding process. The powder prepared by pre-alloying the carbon has a reduced compressibility of the iron-based powder due to the strengthening effect of carbon.

Copper diffuses into the liquid phase at sintering temperature to promote sinterability and increase the hardenability of the sintered body, but it has the disadvantage of expanding during the sintering process.

Nickel is a metal used for improving tensile strength among various additive metals, and is effective when used with molybdenum, copper, etc. rather than being used alone.

However, in the case of such a metal alloy powder, the cost of the metal alloy powder is extremely high because it contains a large amount of nickel, molybdenum and the like which are expensive alloying elements.

If we look at trends in the use of auto parts in recent years, the share of raw materials in product prices is steadily increasing. In particular, because nickel is very expensive and its price is rising, the proportion of the raw material to the price of the product is continuously increasing due to the nickel alloy powder containing nickel. Therefore, iron-based alloy powder which is capable of producing an economical automobile part having excellent mechanical properties is desperately required.

Examples of the method for producing the alloy include simple mixing using a general mixer, and preliminary alloying by adding an alloy element to the molten steel state. These methods have various problems such as generation of segregation or deterioration of formability. To solve this problem, a diffusion bonded powder manufacturing method is used in which an additive metal is diffused and bonded to the surface of an iron-based powder. The diffusion bonded powder is prepared by adding a reduced iron powder, a metal powder or a metal oxide and heat-treating the powder in an oxygen-free atmosphere or a reducing atmosphere to diffuse the additive metal on the surface of the iron powder. In this case, since the reducing process for producing reduced iron powder and the heat treatment process for preparing the diffusion bonded powder are required, the price of diffusion bonded powder is usually twice as high as that of pure iron powder.

Meanwhile, high manganese steel has been developed in order to meet the demand for high strength and high ductility mechanical properties as the social demand for efficient resource utilization increases with rising raw material prices. In the case of high manganese twin-induced plasticity (TWIP) steels, deformation twin in the austenite structure during plastic deformation is generated, resulting in high work hardening, resulting in excellent strength and elongation.

Such excellent mechanical properties vary depending on the content of manganese, and contain an element such as C, Al, Si, Cr, etc. within 10%. Therefore, an appropriate proportion of alloy design is required. Since the content of high manganese is accompanied by an increase in manufacturing process load and material price, development of an alloy which reduces the content of manganese is required.

In order to solve the above problems, the present invention provides a method for producing an iron-based alloy powder using manganese which is relatively inexpensive instead of expensive additive metal such as nickel or molybdenum.

According to one or more embodiments of the present invention, there is provided a method of manufacturing a steel sheet, comprising the steps of: preparing an iron-based powder having a surface oxidized by spraying molten steel; Uniformly mixing the surface-oxidized iron-based powder and the manganese oxide powder; And reducing the iron-based powder and the manganese oxide powder in a heat treatment furnace in a reducing atmosphere to diffusion-bond the manganese oxide powder to the surface of the iron-based powder; And a step of crushing the diffusion bonded powder may be provided.

The temperature of the heat treatment furnace is in the range of 600 to 900 占 폚, and the reduction time in the heat treatment furnace is 20 to 120 minutes.

Wherein the reducing atmosphere comprises a mixed gas of hydrogen and nitrogen, and the ratio of hydrogen in the mixed gas of hydrogen and nitrogen is 30 wt% % Or more.

According to the embodiment of the present invention, it is possible to lower the price of raw materials by replacing the manganese having equivalent mechanical properties with cheaper manganese, and to perform the high-temperature heat treatment process twice to increase the productivity and to manufacture the iron- .

1 is a view illustrating a manufacturing process of a diffusion bonded powder according to an embodiment of the present invention.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims.

In general iron-based powders, an expensive metal such as nickel or molybdenum is used to maintain a low manganese content and to improve mechanical properties. However, in the embodiment of the present invention, TWIP (Twinning-Induced Plasticity) steel or Hadfield Steel A method for producing an alloy powder for sintering having high strength and high toughness properties by increasing the content of manganese used in steel products such as aluminum alloys.

In the examples according to the present invention, the irreducible iron-based powder and the metal-based oxide powder prepared through the water-drawing process and the drying process are mixed, and the reduction and diffusion process are simultaneously performed through one heat treatment to increase the productivity and manufacture the diffusion- can do.

1 is a view illustrating a process for manufacturing a diffusion bonded powder according to an embodiment of the present invention. Hereinafter, a process of manufacturing a diffusion bonded powder will be briefly described with reference to FIG.

First, iron-based powder whose surface is oxidized by water jetting and drying using pure iron molten steel is prepared (S10), and the prepared unfermented iron-based powder and manganese oxide powder are uniformly mixed (S20) (S30) for reducing and diffusion bonding in an atmospheric or non-oxidizing atmosphere, and finally, crushing (S40) and breaking apart the masses of the finally bonded powder which are clumped together at a high temperature.

At this time, in the embodiment of the present invention, the unreduced iron-based powders made of water-dispersed powder have a content of less than 0.2% by weight of carbon and less than 1.2% by weight of oxygen and an impurity content of 1.5% by weight, Metal oxide is used as the metal oxide. In the embodiment according to the present invention, manganese oxide is used.

The manganese oxide includes all compounds formed by manganese (Mn) and oxygen (O), preferably Mn ₃ O ₄ and Mn ₂ O ₃ . The Mn ₃ O ₄ can be obtained from natural sources without any additional method and is easily reduced in a reducing atmosphere to cause reaction on the iron-based surface. Mn ₂ O ₃ is Mn ₃ O ₄ produced by heating at 500 ° C. or higher, It makes the environment. On the other hand, in the case of MnO, the reduction reaction is not easy even at a high temperature of 1200 ° C, which is not suitable for use as a bonding powder.

In the embodiment according to the present invention, the content of manganese oxide may be 5 to 40 wt% when converted to metal manganese. If the content is outside the above range, austenite structure may not be formed or the impact resistance of the sintered body may be deteriorated Therefore, the content of manganese oxide in the examples according to the present invention is limited to the above range. More preferably 10 to 30% by weight.

Hereinafter, a method of manufacturing an iron-based diffusion bonded powder according to an embodiment of the present invention will be described.

First, a molten steel for producing an iron-based powder is prepared by using a converter or an electric furnace. At this time, it is possible to control the target other metallic components through the component control of the molten steel.

The pure iron powder prepared as described above may be collected, dewatered using a predetermined dewatering equipment, and dried to remove moisture mixed with the iron-based powder.

At this time, it is possible to further include a step of separating the impurities of the dried iron-based powder, and the oxidized iron-based powder having the surface is uniformly mixed with the manganese oxide powder for bonding. In this case, a general mixer such as a V-mixer or a double cone mixer can be used.

The uniformly mixed powders can be heat-treated using a conveyor belt type (Conveyor Belt Furnace). In the embodiment according to the present invention, the temperature of the heat treatment furnace is 600 to 900 ° C. and the reduction time is limited to 20 to 120 minutes.

If the temperature of the heat treatment furnace is lower than 600 ° C, the reduction and diffusion bonding reaction may take a long time and the productivity may be lowered. On the other hand, when the temperature of the heat treatment furnace is higher than 900 ° C, The temperature of the heat treatment furnace in the embodiment according to the present invention is limited to the above range since the reducing gas may not be introduced partially in the depth direction due to the plasticization.

In addition, when the heat treatment in the embodiment of the present invention is performed for less than 20 minutes, the reduction and diffusion bonding may not be sufficiently performed, and if it exceeds 120 minutes, no additional advantage is generated. Is limited to the above range.

In the reducing atmosphere in the embodiment according to the present invention, a mixed gas of hydrogen and nitrogen can be used, and the ratio of hydrogen in the mixed gas of hydrogen and nitrogen is 30 wt% or more. If the hydrogen ratio is less than 30%, the trapping of nitrogen may occur due to an excessive amount of nitrogen atmosphere, which may reduce the physical properties of the powder. Therefore, the reducing atmosphere gas in the embodiment of the present invention has a hydrogen ratio of 30 %.

The oxygen concentration in the furnace during the heat treatment is maintained at 10 ppm or less to prevent oxidation of the powder at a high temperature, and the iron-based powder mass obtained through the heat treatment at a high temperature is supplied to a general mill Diffusion bonded powders clumped through a crusher are separated from each other to prepare an iron - based diffusion bonded powder.

As described above, according to the embodiment of the present invention, the reduction process and the bonding process are simultaneously performed by a single heat treatment instead of the conventional method of manufacturing the diffusion bonded powder by performing the heat treatment for reducing heat treatment and the heat treatment for bonding, .

Hereinafter, results of measurement of apparent density, flow, molding strength, tensile strength and dispersity of additive powder for evaluating the characteristics of the high manganese iron-based diffusion bonded powder produced by the examples according to the present invention will be described.

The iron-based diffusion bonded powder was prepared by the above-mentioned production method, and the content of manganese in the iron-based powder was 13 wt%. The reduction and diffusion bonding was performed at 850 ℃ for 60min. At this time, the heat treatment atmosphere was 1: 1 ratio of hydrogen to nitrogen and the oxygen concentration in the furnace was kept below 10ppm. For the comparison of the physical properties, a mixture of reduced iron and manganese powders were prepared. Table 1 shows the contents of the pure iron powder (A), the simple mixed powder (B) and the diffusion bonded powder (C) prepared by the examples according to the present invention.

division Chemical composition (% by weight) C O N S P Si Mn Cr Cu Ni Al A 0.008 0.125 0.0052 0.02 0.008 0.009 0.13 0.08 0.12 0.07 0.12 B 0.006 0.11 0.0048 0.018 0.01 0.009 13.4 0.07 0.12 0.07 0.12 C 0.008 0.124 0.0051 0.02 0.008 0.009 12.7 0.08 0.12 0.07 0.12

10 parts of a tensile strength specimen for measuring the tensile strength according to ASTM E8 was prepared at a pressure of 600 MPa after mixing 0.6 wt% of a commercial lubricant ZS1000F in the powder, To prepare a sintered body. At this time, the atmosphere of the sintering furnace was 1: 3 ratio of hydrogen to nitrogen. The results of the sintering characteristics are shown in Table 2 below.

division Maximum tensile strength (MPa) Yield strength (MPa) Elongation (% in 25.4 mm) A 266 ± 30 170 ± 30 3.2 ± 0.4 B 870 ± 50 592 ± 60 32 ± 6 C 1157 ± 15 674 ± 10 37 ± 1

As a result of analysis of sintering characteristics, it was confirmed that the strength and elongation of the pure manganese powder mixed with the pure iron powder and the diffusion bonded powder were increased compared with the pure iron powder (A).

This is similar to that of conventional manganese containing high manganese content. In addition, the strength and elongation of the sintered body of the C powder prepared by the diffusion bonding were higher than those of the sintered body of the simple mixed B powder. Such a deviation was caused by the segregation of the simple mixed powder, The results are shown in Fig.

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (5)

Water-spraying molten steel to produce an iron-based powder whose surface is oxidized;
Uniformly mixing the surface-oxidized iron-based powder and the manganese oxide powder;
And reducing the iron-based powder and the manganese oxide powder in a heat treatment furnace in a reducing atmosphere to diffusion-bond the manganese oxide powder to the surface of the iron-based powder; And
And breaking the diffusion bonded powder,
When the manganese oxide powder is converted to manganese metal, it is 5 to 40 wt%
And a step of diffusively bonding the manganese oxide powder to the surface of the iron-based powder while reducing the iron-based powder and the manganese oxide powder in a heat treatment furnace in a reducing atmosphere,
Wherein the heat treatment is carried out at a temperature range of 600 to 900 占 폚 for 20 to 120 minutes. delete delete delete The method according to claim 1,
Wherein the reducing atmosphere is composed of a mixed gas of hydrogen and nitrogen, and the ratio of hydrogen in the mixed gas of hydrogen and nitrogen is 30 wt% or more.

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