KR20170044235A

KR20170044235A - Manufacturing method for mixed iron powder

Info

Publication number: KR20170044235A
Application number: KR1020150143328A
Authority: KR
Inventors: 윤준철; 류현곤; 구원석
Original assignee: 현대제철 주식회사
Priority date: 2015-10-14
Filing date: 2015-10-14
Publication date: 2017-04-25

Abstract

A method for producing an iron-based mixed powder is disclosed. The method for producing an iron-based mixed powder includes the steps of: preparing an iron-based powder having an oxide layer formed on its surface by water spraying molten steel; Mixing the iron-based powder and the metal-based oxide powder to prepare a mixture; And subjecting the mixture to a reduction heat treatment to form the formed body by binding the metal oxide powder to the surface of the oxide layer formed on the iron-based powder.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for manufacturing an iron-based mixed powder,

The present invention relates to a method for producing an iron-based mixed powder. More particularly, the present invention relates to a method for producing iron-based mixed powder excellent in moldability and sinterability.

The sintered parts produced through the powder metallurgy process usually have about 3% to 10% of pores inside the sintered body due to the molding and sintering using the powder material. Since the density of the sintered body is a factor directly related to the strength, it is industrially used to improve density of 2 ~ 3% sintered body through DPDS (Double Press and Double Sintering) and HIP (Hot Isostatic Pressing) In order to increase the densification of the final part, attempts have been made to change the powder itself in the powder manufacturing process in addition to the above-described subsequent process.

BACKGROUND ART [0002] The background art relating to the present invention is disclosed in Korean Patent Publication No. 2008-0087185 (published on September 30, 2008, entitled "Iron-based Powder Composition").

According to one embodiment of the present invention, there is provided a method for producing an iron-based mixed powder excellent in molding properties and sintering properties.

According to one embodiment of the present invention, there is provided a method for producing an iron-based mixed powder excellent in economical efficiency.

One aspect of the present invention relates to a method for producing an iron-based mixed powder. In one embodiment, the method for preparing an iron-based mixed powder includes the steps of: preparing an iron-based powder having an oxide layer formed on its surface by spraying molten steel; Mixing the iron-based powder and the metal-based oxide powder to prepare a mixture; And subjecting the mixture to a reduction heat treatment to form the formed body by binding the metal oxide powder to the surface of the oxide layer formed on the iron-based powder.

In one embodiment, the iron-based powder may further include at least one of chromium (Cr), nickel (Ni), and molybdenum (Mo).

In one embodiment, the metal oxide powder may include at least one of a mill scale, a nickel (Ni) oxide, a chromium (Cr) oxide, and a molybdenum (Mo) oxide powder.

In one embodiment, the size of the iron-based powder is 80 μm to 120 μm, and the size of the metal-based oxide powder is 10 nm to 5 μm.

In one embodiment, 50 to 95% by weight of the iron-based powder and 5 to 50% by weight of the metal-based oxide powder may be included in the total weight of the mixture.

In one embodiment, the reduction heat treatment may be performed at a temperature of 600 ° C to 1,000 ° C.

In one embodiment, the reducing heat treatment may use at least one of a hydrogen gas, a nitrogen gas, an ammonia decomposition gas, or an endo gas.

The iron-based mixed powder produced by the method for producing an iron-based mixed powder of the present invention can lead to rounding, thereby increasing the contact points between the powders at the time of molding, thereby improving the molding strength, the molding density and the sintering density, The sintering property is excellent, and the manufacturing cost is low, so that the economical efficiency can be excellent.

FIG. 1 shows a method of preparing an iron-based mixed powder according to one embodiment of the present invention.
Fig. 2 (a) shows the iron-based powder of the present invention, and Fig. 2 (b) shows the metal-based oxide powder of the present invention.
3 shows an iron-based mixed powder prepared according to one embodiment of the present invention.
Fig. 4 (a) is an enlarged view of the surface of the iron-based mixed powder produced according to the embodiment of the present invention, and Fig. 4 (b) is an enlarged photograph of the surface of the iron-based powder of the comparative example according to the present invention.

Hereinafter, the present invention will be described in detail. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to be exemplary, self-explanatory, allowing for equivalent explanations of the present invention.

One aspect of the present invention relates to a method for producing an iron-based mixed powder. FIG. 1 shows a method of preparing an iron-based mixed powder according to one embodiment of the present invention. Referring to FIG. 1, the iron-based mixed powder manufacturing method includes: (S10) preparing an iron-based powder; (S20) preparing a mixture; And (S30) a reducing heat treatment step. More specifically, the iron-based mixed powder producing method comprises the steps of: water-jetting molten steel to produce an iron-based powder having an oxide layer formed on its surface; Mixing the iron-based powder and the metal-based oxide powder to prepare a mixture; And subjecting the mixture to a reduction heat treatment to form the formed body by binding the metal oxide powder to the surface of the oxide layer formed on the iron-based powder.

Hereinafter, the method for producing the iron-based mixed powder according to the present invention will be described in detail.

(S10) Iron-based Powder production step

The above step is a step of water-jetting molten steel to prepare an iron-based powder (black powder) having an oxide layer formed on its surface. The term " black powder " refers to black-based powder as-water atomized immediately after water injection, and may mean an iron-based powder having an oxidized layer formed on the surface of the powder.

In one embodiment, the water spray can be pulverized by injecting high-pressure water through a nozzle into a molten steel stem falling freely using a high-pressure pump. After the water jetting, the iron-based powder can be produced by dehydration and drying. Since the water and the molten steel (iron) are in direct contact with each other at a high temperature when the water is pollinated, an oxide layer is formed on the surface of the iron-based powder, and the molten steel is formed into irregular shapes and sizes in the course of separating and cooling the molten steel by the water spray.

In one embodiment, the iron-based powder is not only pure-Fe, but also iron-chromium (Fe-Cr), iron-nickel (Fe-Ni), iron-molybdenum (Fe- Fe-Cr-Mo) and iron-nickel-chromium-molybdenum (Fe-Ni-Cr-Mo).

The iron-based powder may be prepared by using pure iron or at least one metal component selected from the group consisting of chromium (Cr), nickel (Ni), and molybdenum (Mo). For example, at least one metal component of chrome (Cr), nickel (Ni), and molybdenum (Mo) may be added to the pure steel molten steel. When the above-mentioned metal component is contained, it can be dissolved in the iron-based powder to improve strength and hardness.

In one embodiment, the size of the iron-based powder may be 80 to 120 탆. In this specification, the " size " is defined to mean the maximum size of the iron-based powder. The metal oxide powder and the sintering property and the molding property at the time of forming the formed body may be excellent.

(S20) Mixture preparation step

The above step is a step of mixing the iron-based powder and the metal-based oxide powder to prepare a mixture.

The metal oxide powder may include at least one of a mill scale powder, a nickel oxide powder, a chromium oxide powder and a molybdenum oxide powder. When the metal oxide powder is used, it is excellent in economical efficiency and can be sphericalized in the reduction heat treatment by mixing with the iron-based powder, and the molding property and the sintering property of the compact can be excellent.

The mill scale powder refers to an iron oxide coating formed on a steel surface during a hot rolling or cooling operation, and contains iron oxide (FeO and Fe ₂ O ₃ ) as a main component. In one embodiment, the mill scale powder may be a cold rolled mill scale or a hot mill scale powder.

In one embodiment, the size of the metal oxide powder may be 10 nm to 5 μm. In the above-mentioned size, the metal-based oxide powder is easily located in the irregularities formed on the surface of the iron-based powder, sphering of the formed body can be achieved, and the sintering property and molding property can be excellent.

In one embodiment, 50 to 95% by weight of the iron-based powder and 5 to 50% by weight of the metal-based oxide powder may be included in the total weight of the mixture. When included in the above range, spheroidization of the molded body can be achieved, and sintering property and molding property can be excellent.

(S30) Reduction heat treatment step

In this step, the mixture is subjected to a reduction heat treatment to bond the metal oxide powder to the surface of the oxide layer formed on the iron-based powder to form a formed body.

The metal oxide powder is located on the surface irregularities of the iron-based powder (black powder) and changes in oxygen content and phase change occur in the powder through the reduction heat treatment, so that the shape of the formed body can be rounded have.

In one embodiment, the reduction heat treatment may be performed at a temperature of 600 ° C to 1,000 ° C. In the above range, the metal oxide powder is reduced to be strongly bonded to the iron-based powder irregularities, so that a round shaped body can be easily formed.

Further, on the surface of the iron-based powder formed by the water jetting, an oxide layer containing iron oxide (FeO) component is generated by reacting with oxygen contained in air and moisture. In the reduction heat treatment step, the iron oxide may be reduced to iron.

In one embodiment, the reducing heat treatment may use at least one reducing gas selected from hydrogen gas, nitrogen gas, ammonia decomposition gas and endo gas. When the reducing gas of the above kind is used, the reduction efficiency is excellent, and the compacting density and strength of the compact can be excellent.

The ammonia decomposition gas may be one obtained by pyrolyzing anhydrous ammonia under a nickel catalyst and containing hydrogen and nitrogen in a ratio of 75:25 mol%.

The endo gas (or Rx-carburizing gas) comprises 30 to 50 wt% of hydrogen (H ₂ ), 3 to 30 wt% of methane (CH ₄ ), 0.5 to 5 wt% of carbon dioxide (CO ₂ ) (H ₂ O) 0 to 0.5 wt% or less, and the balance nitrogen (N ₂ ).

Another aspect of the present invention relates to an iron-based mixed powder produced by the iron-based mixed powder production method. When the iron-based mixed powder produced through the iron-based mixed powder production method is used, the molding density and the strength of the molded body are excellent, and the density and strength of the sintered body produced after sintering the molded body can be excellent.

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

Example

The pure steel molten steel was water sprayed to prepare an iron-based powder having an oxide layer on its surface and a size of 90 to 100 mu m. As the metal oxide powder, a cold rolled pickled scale having a size of 0.2 to 5 탆 including iron oxide (FeO, Fe ₂ O ₃ ) was prepared. Next, 80 wt% of the iron-based powder and 20 wt% of the metal oxide powder were uniformly mixed to prepare a mixture, the mixture was introduced into a reduction furnace, and subjected to reduction heat treatment in a hydrogen atmosphere at 700 ° C to form a compact, Iron mixed powder was prepared.

Comparative Example

An iron-based powder was prepared in the same manner as in the above example, except that the metal-based oxide powder was not mixed.

Fig. 2 (a) shows the iron-based powder of the present invention, and Fig. 2 (b) shows the metal-based oxide powder of the present invention. 3 shows the iron-based mixed powder prepared according to the embodiment. 2 (a), 2 (b) and 3, the iron-based mixed powder is obtained by mixing fine iron (Fe) powder reduced from the metal oxide powder (cold- Black powder), it was found that the shape was improved by bringing roundness of the powder shape as a whole while bonding at the reducing heat treatment.

Molding properties (molding density and molding strength) were evaluated for the above Examples and Comparative Examples at a pressure of 400 MPa, and the sintering sinterability (molding strength and molding strength) of Examples and Comparative Examples was measured at 1130 캜 and hydrogen atmosphere for 30 minutes Sintering density and sintering strength) were evaluated. The results are shown in Table 1 below.

Referring to Table 1, when the comparative example was reduced under the same conditions, and 0.8% of lubricant (zinc stearate (Zn-st)) was mixed and molded at a pressure of 400 MPa, the molding density was 6.51 g / , And in the case of the example, the molding density was 6.74 g / cm 3 and the result was about 3.5%.

As shown in Fig. 3, on the surface of the improved powder, the fine iron powder reduced from the cold-rolled sheath scale was located in the irregularities of the powder sprayed in the form of a sponge, and it was found that the molding density was improved by filling the empty space formed in the molding there was. In addition, as the molding density was improved as described above, the molding strength was also increased to 6.21 MPa in the comparative example and increased by about 30% in the case of the embodiment, to 8.10 MPa. This is because the contact point of the particles of cold rolled pickle scale iron powder in the sponge form distributed in the irregularities of the iron powder was increased during the molding process to increase the bonding strength.

In the comparative example, the sintered density was only 6.75 g / cm 3, while the iron-based mixed powder of the example was increased by about 4% at 7.03 g / cm 3.

4 (a) is an enlarged view of a surface of an iron-based mixed powder produced according to an embodiment of the present invention, and FIG. 4 (b) is an enlarged view of the surface of an iron-based powder of a comparative example according to the present invention. Referring to FIGS. 4 (a) and 4 (b), it can be seen that the surface of the iron-based mixed powder of the above embodiment has fewer surface pores than the iron-based powder of the comparative example. As a result of evaluating the sintering strength (tensile strength) of the sintered body, the tensile strength of the comparative example was 167.8 MPa, while in the case of the embodiment, it was 191.9 MPa, which was improved by 14%. This is because the density of the heat-treated molded body is increased, so that the contact strength against the force of fracture in the tensile strength test is high.

The results of Table 1 indicate that when the iron-based powder is used singly, the spheroidization of the powder is required for high density and high strength, but the molding strength is lowered. The iron-based powder is mixed with the fine metal oxide Based powder is bound to the irregularities on the surface of the iron-based powder to reduce the roundness of the iron-based powder, and when the oxide powder is present in the form of a sponge, the contact points between the powders So that the molding strength can be increased and the molding density and sintering density can be improved.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

Water spraying molten steel to produce an iron-based powder having an oxide layer formed on its surface;
Mixing the iron-based powder and the metal-based oxide powder to prepare a mixture; And
And subjecting the mixture to a reduction heat treatment to form a formed body by binding the metal oxide powder to the surface of the oxide layer formed on the iron-based powder.

The method according to claim 1,
Wherein the iron-based powder further comprises at least one of chromium (Cr), nickel (Ni), and molybdenum (Mo).

The method according to claim 1,
Wherein the metal-based oxide powder comprises at least one of a mill scale, nickel (Ni) oxide, chromium (Cr) oxide and molybdenum (Mo) oxide powder.

The method according to claim 1,
Wherein the size of the iron-based powder is 80 탆 to 120 탆, and the size of the metal-based oxide powder is 10 nm to 5 탆.

The method according to claim 1,
Wherein 50 to 95% by weight of the iron-based powder and 5 to 50% by weight of the metal-based oxide powder are contained in the total weight of the mixture.

The method according to claim 1,
Wherein the reducing heat treatment is performed at a temperature of 600 ° C to 1,000 ° C.

The method according to claim 1,
Wherein the reducing heat treatment uses at least one reducing gas selected from hydrogen gas, nitrogen gas, ammonia decomposition gas and endo gas.