KR102167935B1 - Ferrite-Austenitic Steel Powder Metallurgy Method Using Femnnic Alloy Powder - Google Patents

Abstract

The present invention relates to a ferrite-austenitic steel powder metallurgy method using FeMnNiC-based alloy powder containing a high fraction of austenite through a relatively simple process when manufacturing a product using FeMnNiC-based alloy powder having nano-sized microcrystalline grains. will be. The present invention provides a ferrite-austenitic steel powder metallurgy method using FeMnNiC-based alloy powder for sintering FeMnNiC-based alloy powder having a nanocrystal size through a discharge plasma sintering method.

Description

Ferrite-Austenitic Steel Powder Metallurgy Method Using Femnnic Alloy Powder {Ferrite-Austenitic Steel Powder Metallurgy Method Using Femnnic Alloy Powder}

The present invention relates to a ferrite-austenite-based steel powder metallurgy method using FeMnNiC-based alloy powder, and more particularly, a high fraction of austenite through a relatively simple process when manufacturing a product using a nano-sized FeMnNiC-based alloy powder. It relates to a ferrite-austenitic steel powder metallurgy method using the FeMnNiC-based alloy powder containing.

Steel refers to an alloy made of iron and carbon, and generally refers to an alloy of iron having a carbon content of 0.03 to 1.7% by weight. Iron having a side carbon component of less than 2% by weight may be defined as steel. These steels have excellent formability compared to iron having a carbon content of more than 2% by weight, but their strength is low, and most of the steels have high tensile strength through heat treatment or alloying with other elements.

These high-tensile strength steels can be classified into high-tensile strength steel (HSS) and ultra-high strength steel (AHSS) according to their tensile strength, and recently UHSS, which further improved the tensile strength of AHSS, has been released and used. As a standard for classifying the high-tensile steel and ultra-high-strength steel, steels with a yield strength of 550 MPa and tensile strength exceeding 780 MPa are generally classified as ultra-high-tensile steel. .

These ultra-high-strength steels are competitively adopted by automobile manufacturers as global environmental and safety regulations are strengthened. If the existing steel plate is replaced with an ultra-high-strength steel plate, not only can the vehicle body be made lighter with the same crash stability, but also can be manufactured to have high strength even in the limited body weight limit, so many automobile manufacturers increase the use of the ultra-high-strength steel plate. There is a trend.

However, ultra-high-strength steel is manufactured by mixing various elements with steel, and because of its high tensile strength, it is difficult to post-process and requires a lot of cost for manufacturing. Therefore, when manufacturing a vehicle, it is possible to increase manufacturing cost and stability through mixing with general steel plates. At the same time satisfying

Recently, studies related to the 3rd generation AHSS are being conducted to meet this trend, and the demand reflecting this is also increasing. However, the existing AHSS has a disadvantage that the manufacturing cost is higher than that of the existing mild steel because it is manufactured through processes such as wire making-steel-casting-rolling-critical heat treatment to obtain excellent mechanical properties and composite structure.

The iron-based powder alloy is a material having excellent dimensional accuracy, high production efficiency, and excellent mechanical properties, and is used in the field of mechanical parts and automobile parts. It is used to manufacture structural parts such as control gears and shift gears of automobile engines and transmissions. Currently, iron powder alloys of 20 kg in North America and 10 kg in Europe and Japan are used as standard for mid-sized sedans, and only 6 kg in Korea. In the future, the proportion of iron powder parts is increasing to enhance automotive quality.

In Korea, Hyundai Steel is investing in iron-based powder alloys by commencing construction of an iron powder factory with an annual capacity of 25,000 tons in Dangjin Steel Works in October 2013 to mass-produce pure iron powder. In addition, POSCO also started production by establishing an iron powder plant with an annual capacity of 30,000 tons. Accordingly, interest in iron powder materials is increasing in domestic research institutes and universities as well as large research institutes, and basic studies on iron-based powder alloys are being reported.

Iron-based powder materials are expected to account for about 70% of the total powder metallurgy market in 2017. The size of auto parts, which account for about 70% of the P/M industry, is expected to increase as shown in the figure until 2020, and in the case of Asia, the growth rate in 2020 is expected to increase by more than 44.5% compared to 2014. Accordingly, major overseas companies such as Sweden, the United States, Japan, and Canada are actively developing iron-based and iron alloy powder manufacturing technology and iron-based powder densification technology.

(0001) Korean Patent Registration No. 10-0711357 (0002) Korean Patent Application Publication No. 10-2000-0015391

The present invention has been conceived to solve the above problem, and an object of the present invention is to provide a powder metallurgy method capable of increasing the content of austenite when manufacturing a product using ferrite-austenite-based FeMnNiC alloy powder having nano-sized microcrystalline grains.

In order to solve the above problems, the present invention provides a ferrite-austenitic steel powder metallurgy method using FeMnNiC-based alloy powder in which FeMnNiC-based alloy powder having a nanocrystal size is sintered through a discharge plasma sintering method.

The powder metallurgy method may include 1 to 2 heating steps and 1 to 2 cooling steps.

The FeMnNiC-based alloy powder may contain 2 to 15 parts by weight of manganese (Mn), or 5 to 20 parts by weight of nickel (Ni) relative to 100 parts by weight of iron.

The FeMnNiC-based alloy powder may further contain nitrogen, cobalt, or copper.

The present invention also provides a powder metallurgy product manufactured by the above method.

The powder metallurgy product may contain 10 to 90 vol% of austenite in the total iron content.

The powder metallurgy method according to the present invention can increase the austenite content and stability even with the addition of an alloying element lower than that of the conventional metallurgical method, and it is possible to omit the heat treatment process to increase the stability of austenite. It is possible to manufacture alloy products having a phase structure.

1 is a graph showing the temperature change of the conventional AHSS manufacturing method.
2 is a graph showing the temperature change of the powder metallurgy method according to an embodiment of the present invention.
3 shows the results of an X-ray diffraction analysis test according to the content of Mn according to an embodiment of the present invention.
4 shows the results of an X-ray diffraction analysis test according to a decrease in grain size of an alloy powder according to an embodiment of the present invention.
5 shows the results of an X-ray diffraction analysis test according to the content of Ni according to an embodiment of the present invention.
6 shows the results of an X-ray diffraction analysis test according to the content of C in the Fe-Mn alloy according to an embodiment of the present invention.
7 shows the results of an X-ray diffraction analysis test according to the content of C in the Fe-Ni alloy according to an embodiment of the present invention.

Hereinafter, a preferred embodiment of the present invention will be described in detail. In describing the present invention, when it is determined that a detailed description of a related known technology may obscure the subject matter of the present invention, a detailed description thereof will be omitted. Throughout the specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components, unless otherwise stated.

The present invention is intended to illustrate specific embodiments and to be described in detail in the detailed description, since various transformations can be applied and various embodiments can be provided. However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all conversions, equivalents, or substitutes included in the spirit and scope of the present invention.

The terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present invention, terms such as include or have are intended to designate the presence of features, numbers, steps, actions, components, parts, or a combination of them described in the specification, and one or more other features, numbers, and steps. It is to be understood that it does not preclude the possibility of the presence or addition of, operations, components, parts, or combinations thereof.

The present invention relates to a ferrite-austenitic steel powder metallurgy method using FeMnNiC-based alloy powder in which FeMnNiC-based alloy powder having a nanocrystal size is sintered through a discharge plasma sintering method.

C is the most basic element for securing strength and hardenability, and may contain 0.03 to 2 parts by weight compared to 100 parts by weight of iron as used in general steel. If it is included in less than 0.03 parts by weight, the strength may be lowered below the specified value, and if it is included in more than 2 parts by weight, the hardness increases, but the elasticity may decrease, resulting in poor workability and tensile strength. There is a possibility that toughness may be deteriorated by this.

Mn is an element effective in increasing the strength, and may contain 2 to 15 parts by weight based on 100 parts by weight of iron. If it is included in less than 2 parts by weight, the strength may be lowered, and if it is included in more than 15 parts by weight, the toughness may be lowered by forming MnS by reaction with sulfur during manufacture.

Ni is an essential alloying element for securing low-temperature toughness, and it is preferable to include 5 to 20 parts by weight of iron compared to 100 parts by weight for securing low-temperature toughness. If it is included in less than 5 parts by weight, low-temperature toughness may be deteriorated, and if it is included in more than 20 parts by weight, the price of the manufactured product may increase due to the use of expensive nickel.

The FeMnNiC-based alloy powder may further contain nitrogen, cobalt, or copper.

The nitrogen (N), copper (Cu), and cobalt (Co) are elements contributing to the stabilization of residual austenite, and they act in combination with the aforementioned C, Mn, and Ni to contribute to the stabilization of austenite. However, if the content exceeds 5 parts by weight for each of N and Co, and exceeds 1 part by weight for each of Cu, there is a problem that the manufacturing cost is excessively increased. In addition, since Cu may cause brittleness during hot rolling, it is more preferable that Ni is added together when Cu is added.

The powder metallurgy method may include 1 to 2 heating steps and 1 to 2 cooling steps. Existing metallurgical methods produce products through additional heat treatment several times through hot-cold rolling after casting and forging processes (Fig. 1), but the powder metallurgy method of the present invention produces products through one sintering step. Because it is produced, it is possible to minimize additional heat treatment (Fig. 2). However, if additional physical properties are required for the product according to the present invention, it is also possible to improve the physical properties through minimal heat treatment (one time).

The present invention also provides a powder metallurgy product manufactured by the above method. Powder metallurgy products can be used as mechanical parts used in engine parts, transmission parts, gear parts, etc. of automobiles and various mechanical devices.

The powder metallurgy product may contain 10 to 90 vol% of austenite in the total iron content.

Austenite is one of the microstructures of steel or cast iron, and refers to γ iron, that is, γ solid solution, in which carbon is dissolved. The crystal structure is a face-centered cubic crystal, and can be obtained when heated above the A1 transformation point (723°C). When cooling austenite, it transforms into martensite, bainite, and pearlite structures according to the difference in cooling rate. By doing so, properties such as required mechanical properties are imparted to steel or cast iron. In the case of the present invention, since the product is manufactured using the powder metallurgy method, austenite may occupy 10 to 90 vol% of the total iron content with only one sintering, and thus, it may have high tensile strength.

Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily implement the present invention. However, the present application may be implemented in various different forms and is not limited to the embodiments described herein. In the drawings, parts not related to the description are omitted in order to clearly describe the present invention.

Example

Table 1 below shows the change in the volume fraction of austenite in the sintered metal according to the amount of alloying elements such as Mn, Ni, and C added and the powder manufacturing process conditions.

Alloy composition (wt%) Milling condition (time/PCA) Austenite fraction X-ray diffraction test result Fe-4%Mn 5hr/0wt% 20% Figure 3 Fe-7%Mn 5hr/0wt% 48% Figure 3 Fe-10%Mn 5hr/0wt% 67% Figure 3 Fe-7%Mn 24hr/0wt% 66% Fig. 4 Fe-7%Mn 24hr/0.5wt% 72% Fig. 4 Fe-7%Mn 24hr/1wt% 81% Fig. 4 Fe-11%Mn 5hr/0wt% 42% Figure 5 Fe-13%Mn 5hr/0wt% 58% Figure 5 Fe-15%Mn 5hr/0wt% 80% Figure 5 Fe-11%Mn 24hr/1wt% 64% Figure 5 Fe-7%Mn-0.05%C 24hr/1wt% 84% Fig. 6 Fe-7%Mn-0.1%C 24hr/1wt% 86% Fig. 6 Fe-7%Mn-0.2%C 24hr/1wt% 89% Fig. 6 Fe-7%Mn-0.5%C 24hr/1wt% 90% Fig. 7 Fe-11%Ni-0.05%C 24hr/1wt% 70% Fig. 7 Fe-11%Ni-0.1%C 24hr/1wt% 73% Fig. 7 Fe-11%Ni-0.2%C 24hr/1wt% 76% Fig. 7 Fe-11%Ni-0.5%C 24hr/1wt% 90% Fig. 7

The volume fraction of austenite can be analyzed for the image inside the powder metallurgy sample using X-ray difraction. As shown in Table 1, as the content of Mn increases, the volume fraction of austenite increases (FIG. 3). When manufacturing powder, the size of the powder crystal can be reduced according to the milling time and the addition of a process control agent. As the grain size of the powder decreases, the volume fraction of austenite increases even with the same alloying element content (FIG. 4). In addition, as the content of Ni increases, the volume fraction of austenite increases (FIG. 5). The austenite stability increases with the addition of C. In the alloy to which the same amount of Mn and Ni are added, respectively, the volume fraction of austenite increases as the content of C increases (FIGS. 6 and 7).

As described above, specific parts of the present invention have been described in detail, and it will be apparent to those of ordinary skill in the art that these specific techniques are only preferred embodiments, and the scope of the present invention is not limited thereby. will be. Accordingly, it will be said that the substantial scope of the present invention is defined by the appended claims and their equivalents.

Claims (6)

Including the step of sintering the FeMnC-based alloy powder or FeNiC-based alloy powder having a nanocrystal size through the discharge plasma sintering method,
The FeMnC-based alloy powder is composed of 2 to 15 parts by weight of manganese and 0.03 to 2 parts by weight of carbon based on 100 parts by weight of iron, and the FeNiC-based alloy powder is composed of 5 to 20 parts by weight of nickel and 0.03 to 2 parts by weight of carbon relative to 100 parts by weight of iron. What is done,
Ferritic-austenitic steel powder metallurgy method.
The method of claim 1,
The powder metallurgy method comprises a heating step 1-2 times and a cooling step 1-2 times.
delete delete Powder metallurgy products manufactured by the method of claim 1 or 2.
The method of claim 5,
The powder metallurgy product is a powder metallurgy product, characterized in that the austenite is 10 to 90% by volume with respect to the total 100% by volume of the product.

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