KR20200040970A - Precipitation strengthenend high entropy steel and method for manufacturing the same - Google Patents

Abstract

The present invention provides precipitation-hardening high-entropy steel with excellent machinability and strength performance and a manufacturing method thereof. The high-entropy steel comprises four or more selected in an element group consisting of 35-80 atom% (excluding 35 atom%) of Fe, 5-35 atom% (excluding 5 atom%) of Ni, 5-35 atom% (excluding 5 atom%) of Mn, 5-35 atom% (excluding 5 atom%) of Co, 5-35 atom% (excluding 5 atom%) of Cr, and 5-35 atom% (excluding 5 atom%) of Cu. The high-entropy steel further comprises one or more selected in an element group defined in the following 1) and 2). And precipitate is distributed in the matrix structure. 1) 0.01-0.9% of C, 0.01-0.9% of N, and 0.01-0.9% of B 2) 0.05-10% of Ti, 0.05-10% of Zr, 0.05-10% of Mo, 0.05-10% of W, 0.05-10% of Nb, 0.05-10% of Si, 0.05-10% of V, and 0.05-10% of Al.

Description

Precipitation hardening type high-entropy steel and its manufacturing method {PRECIPITATION STRENGTHENEND HIGH ENTROPY STEEL AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a precipitation hardening type high-entropy steel that can be used in parts materials such as electromagnetic, chemical, shipbuilding, machinery, high temperature parts materials such as nuclear power, power generation parts, etc. that require extreme environment or high temperature strength, and a method for manufacturing the same.

In accordance with the rapid development of industrial technology level, a new kind of material recently referred to as a high-entropy alloy as a new alloy system to meet the complex functional needs that cannot be solved with a single metal due to the demand for various materials. Are being proposed and developed.

The high-entropy alloy is composed of multiple alloy elements in an even composition, and thus the total free energy is reduced by increasing the configuration etropy by mixing several elements rather than by forming a compound by reducing the free energy through the formation of an intermetallic compound. In other words, it does not form an intermetallic compound or an amorphous alloy between multi-component alloy elements, but rather an alloy in which a solid solution in which several alloy elements are mixed is formed.

The high entropy alloy became known through non-patent document 1. In the non-patent document 1, the multi-alloy alloy Fe ₂₀ Cr ₂₀ Mn ₂₀ Ni ₂₀ Co ₂₀ prepared in anticipation of the formation of an amorphous alloy or a complex intermetallic compound is formed of a crystalline FCC (Face Centered Cubic) solid solution unlike expected. It has become an interesting and interesting alloy.

The high-entropy alloy contains 4 or more metal components having an atomic concentration between 5 and 35 at%, and is an alloy system in which all added alloying elements act as main elements, resulting in high mixed entropy due to similar atomic fractions in the alloy. Induces and forms a solid solution of a simple structure stable at high temperature instead of an intermetallic compound or an intermediate compound.

Prior arts related to high entropy alloys include Patent Documents 1 and 2. The patent document 1 is a multi-metal component and contains 5 or more metal components containing V, Nb, Ta, Mo, Ti, and other elements with variations of ± 15 atomic% or less, and all added elements act as main elements. As an alloy system, we disclose high-entropy alloys that realize high hardness and modulus, consisting of single-phase solid solutions of face-centered cubic and / or body-centered cubic structures. However, Patent Document 1, as described above, has a difficulty in the manufacturing process due to the difference in melting point between the added heavy alloy elements and various kinds of expensive alloy elements.

On the other hand, Patent Document 2 is a ceramic phase (representatively tungsten carbide) and a multi-component high-entropy alloy powder, which relates to a high-entropy alloy that realizes high hardness produced through a powder metallurgy process, and has a face-centered cubic and / or body-centered cubic structure. It is composed of a single-phase solid solution, and is a technology that realizes excellent mechanical properties. However, as in Patent Document 2, when manufacturing an alloy using a ceramic-based material, there is a problem in that manufacturing is difficult because a high temperature process is required.

As in Patent Literature 1 and Patent Literature 2, high-entropy alloys using metal or ceramic alloy elements have attracted attention as new materials in the metal field because they have excellent mechanical properties. Recently, various studies have been conducted as it is known that it shows excellent properties even in extreme environment properties such as high temperature mechanical properties and low temperature mechanical properties, but most studies have high-entropy alloys composed of equal fractions that are easy to form high-entropy alloys. Since it remains at the level of evaluating mechanical properties and physical properties by manufacturing, there is insufficient research on alloy development to obtain more improved mechanical properties based on high-entropy alloys.

In addition, when the change in structural and mechanical properties due to the increase in entropy is applied to existing non-ferrous materials and steel materials, the concept of high-entropy is applied to the existing alloy system despite the possibility that new properties are induced or the existing properties are further improved. There is no research and development to improve the characteristics by applying.

United States Patent Publication US 2013/0108502 A1 United States Patent Publication US 2009/0074604 A1

 Matreial Science and Engineering A, Volumes 375-377, July 2004, page 213-218.

One aspect of the present invention is a method for developing an alloy to obtain more improved mechanical properties based on a high-entropy alloy, by introducing the concept of forming a precipitate on a high-entropy alloy base containing 35% or more of Fe in a steel material, various It is to provide a high-entropy steel excellent in workability and strength performance according to heat treatment conditions by forming a precipitate of an alloy element on a base and a method for manufacturing the same.

Specifically, it is intended to provide a high-entropy steel having improved mechanical properties by increasing the strength characteristics by forming a precipitate on a high-entropy matrix after processing, after improving the processing rate in a heat treatment condition where no precipitate is formed. .

In addition, the subject of this invention is not limited to the above-mentioned content. The subject matter of the present invention will be understood from the entire contents of the present specification, and those skilled in the art to which the present invention pertains will have no difficulty in understanding the additional subject matter of the present invention.

One aspect of the present invention,

In atomic (at)%, Fe: more than 35% 80%, Ni: more than 5% 35%, Mn: more than 5% 35%, Co: more than 5% 35%, Cr: more than 5% 35 % Or less and Cu: more than 5% and 35% or less;

It includes one or more selected from the group of elements defined in 1) and 2), respectively; And

It is a precipitation hardening type high-entropy steel in which precipitates are distributed in the matrix.

1) C: 0.01 to 0.9%, N: 0.01 to 0.9% and B: 0.01 to 0.9%

2) Ti: 0.05 to 10%, Zr: 0.05 to 10%, Mo: 0.05 to 10%, W: 0.05 to 10%, Nb: 0.05 to 10%, Si: 0.05 to 10%, V: 0.05 to 10% And Al: 0.05 to 10%

The precipitate may be at least one of Cr, Ti, Zr, Mo, W, Nb, Si or V-based carbonitride to boride, Mn-based carbonitride and (Cr, Mn) -based carbonitride.

The precipitate has an average diameter of 0.5 to 50 nm in size, and the spacing between the precipitates may be distributed to 1 to 500 nm.

Another aspect of the present invention,

 In atomic (at)%, Fe: more than 35% 80%, Ni: more than 5% 35%, Mn: more than 5% 35%, Co: more than 5% 35%, Cr: more than 5% 35 % Or less and Cu: more than 5% and 35% or less; And preparing metal materials each containing at least one selected from the group of elements defined in 1) and 2) below;

Manufacturing an alloy by melting the prepared metal material;

Homogenizing heat treatment of the prepared alloy in a temperature range of 900 to 1350 ° C;

Cooling after the homogenization heat treatment; And

After processing the cooled alloy, it is a method of manufacturing a precipitation hardening type high-entropy steel, which includes the step of cooling after a second heat treatment to maintain 0.2 to 72 hours in a temperature range of 300 to 900 ° C.

1) C: 0.01 ~ 0.9%, N: 0.01 ~ 0.9%, B: 0.01 ~ 0.9%

2) Ti: 0.05 to 10%, Zr: 0.05 to 10%, Mo: 0.05 to 10%, W: 0.05 to 10%, Nb: 0.05 to 10%, Si: 0.05 to 10%, V: 0.05 to 10% , Al: at least one of 0.05 to 10%

The homogenization heat treatment may be performed for 1 to 48 hours in a temperature range of 900 to 1350 ° C.

According to the present invention, among the elements of Co, Cr, Fe, Mn, Ni, and Cu contained in the existing high-entropy alloy, high-entropy steel comprising Fe as a main element and other four or more alloy elements ( steel), and also, by forming nano-sized precipitates in a matrix of high-entropy steel, excellent strength and ductility can be realized. Accordingly, through this, there is an advantage that more various applications of high-entropy steel, such as application as a high-temperature material such as a nuclear pressure vessel, a sheath, and a turbine blade for thermal power generation, are possible.

Figure 1 is a schematic diagram showing the microstructure of the high-entry steel of the present invention, (a) is before the second heat treatment, (b) shows the microstructure after the second heat treatment.
Figure 2 is a process flow chart showing an example of the manufacturing method of the present invention.
3 is an electron micrograph showing the microstructure of Inventive Example 1 among the examples of the present invention, and shows the microstructure in which spherical precipitates are distributed after heat treatment.
4 is a photograph of the microstructure of Inventive Example 5 among the examples of the present invention, and is a microstructure in which precipitates of needles are distributed after heat treatment.

Hereinafter, the present invention will be described.

The inventors of the present invention recently conducted research on the development of new materials that exhibit high strength and high ductility mechanical properties in order to solve problems such as stricter environmental problems such as rising prices of raw materials and greenhouse gases related to resource limitations. As a method for alloy development to obtain improved mechanical properties, the concept of high-entropy alloy was applied to steel materials. Accordingly, it was confirmed that the workability and the work hardening performance of the steel produced by forming precipitates of various alloying elements on a high-entropy steel base based on a steel material are improved. That is, carbon or nitrides are precipitated by adding carbon (C), nitrogen (N), boron (B), etc., which are nonmetallic alloy elements, to the high-entropy alloy beyond the solid solution limit, or precipitate carbonitride or boride, or Ti, Zr, Mo, W, By adding metal elements such as Nb, Si, V, and Al to form a precipitate, it is confirmed that the high-entropy steel having excellent strength and ductility can be produced and the present invention is presented.

That is, unlike the high-entropy alloy of the present invention, unlike the existing high-entropy alloy, Fe is essentially contained in alloy elements of Co, Cr, Fe, Mn, Ni, and Cu, and contains at least four other elements, but the content of Fe It is characterized by being higher than the content of other constituents added. In addition, the high-entropy steel of the present invention further includes at least one element from the C, N, B group and Ti, Zr, Mo, W, Nb, Si, V, Al group, respectively, to form a precipitation phase at the base to strengthen precipitation. It is characterized by improving processing hardening and solid solution strengthening characteristics as well as characteristics.

First, the reason for limiting the composition and content of the high-entropy steel of the present invention will be described in detail.

The high-entropy steel of the present invention, in atomic (at)%, Fe: more than 35% and 80% or less, Ni: 5% or more and 35% or less, Mn: 5% or more and 35% or less, Co: more than 5% and 35% Or less, Cr: more than 5% and less than 35% and Cu: more than 5% and more than 35%, and includes four or more selected from the group of elements; It includes one or more selected from the group of elements defined in 1) and 2), respectively; In addition, precipitates are distributed in the matrix.

1) C: 0.01 to 0.9%, N: 0.01 to 0.9% and B: 0.01 to 0.9%

2) Ti: 0.05 to 10%, Zr: 0.05 to 10%, Mo: 0.05 to 10%, W: 0.05 to 10%, Nb: 0.05 to 10%, Si: 0.05 to 10%, V: 0.05 to 10% And Al: 0.05 to 10%

In the present invention, Fe, Cr, Ni, Mn, Co, and Cu are elements constituting a high entropy alloy, and are a group of 4 cycle transition elements, and are small and suitable for forming a solid solution. The Mn and Ni are elements that promote the surface centered cubic (FCC) solid solution, Co is to refine the structure, and Cr improves corrosion resistance. The reason why the Fe content in the element is more than 35% and 80% or less is to maximize the entropy as much as possible, but to make the Fe component higher than other elements so that the base has the characteristics of steel. The reason that the Ni and Cu contents are more than 5% and 35% or less is to maximize entropy, but to make the matrix have the characteristics of FCC, and the reason why the Mn content is more than 5% and 35% or less is to maximize entropy, but the base is laminated To lower the defect energy and to have FCC characteristics, the reason why the Co content is more than 5% and less than 35% is to maximize the entropy, but to control the micronization and lamination defect energy of the tissue, and the Cr content is more than 5%, The reason it is less than 35% is to maximize entropy, but to optimize corrosion resistance.

On the other hand, the C, N, and B forms Fe, Mn, and Cr in the high-entropy steel, among others, carbide and nitride, and precipitates on the high-entropy steel base to strengthen the base and improve the work hardening ability. When the content of the C, N, and B is 0.01 to 0.9%, respectively, if these elements are less than 0.01%, the precipitation hardening capacity is too small, and if it exceeds 0.9%, the workability is deteriorated and brittleness appears. You can.

In addition, the Ti, Zr, Mo, W, Nb, Si, V, and Al have a large difference in atomic radius from Fe, Cr, Ni, Mn, Co, and Cu, which are the main elements constituting a high-entropy steel base, and a difference in valence, etc. Because it is large, it has low solubility in the high-entropy steel base, and precipitates or carbon / nitride can be precipitated to strengthen the base. When the contents of Ti, Zr, Mo, W, Nb, Si, V, and Al are 0.05 to 10%, the precipitation hardening effect is too small at less than 0.05%, whereas when it exceeds 10%, the ratio of precipitates is too high. It is because it becomes large and deteriorates the workability, which may cause brittleness.

Hereinafter, the high-entropy steel microstructure of the present invention will be described in detail.

1 is a schematic diagram schematically showing the microstructure of the high-entropy alloy of the present invention, (a) is not employed in the matrix structure (matrix) that is a solid solution of a single phase before the second heat treatment in the process of manufacturing the high-entropy alloy of the present invention It shows the form (second phase) in which some metal components are not distributed, and (b) shows that the precipitates are evenly distributed throughout the matrix through secondary heat treatment.

In the present invention, the precipitate may be at least one of Cr, Ti, Zr, Mo, W, Nb, Si or V-based carbonitride to boride, Mn-based carbonitride and (Cr, Mn) -based carbonitride. Specifically, the precipitate is Cr, Ti, Zr, Mo, W, Nb, Si, and carbides containing V, nitrides to borides, carbides to nitrides containing Mn (hereinafter referred to as Mn-based carbonitrides) and Cr and It may be a carbide to nitride containing Mn (hereinafter, (Cr, Mn) -based carbonitride). The high-entropy steel of the present invention can obtain a high-entropy steel excellent in strength and ductility by depositing the above precipitate on the main matrix structure as described above.

On the other hand, in the present invention, the precipitates are precipitated at the base to prevent dislocation movement or to prevent dislocation due to defects in dislocation to increase dislocation density, thereby improving strength. It is preferable that the average diameter of the precipitate is 0.5 to 50 nm, and the spacing between the precipitates is distributed at 1 to 500 nm.

Next, the method of manufacturing the high-entropy steel of the present invention will be described in detail.

The method of manufacturing a high-entropy steel of the present invention comprises the steps of preparing a metal material having the above compositional components; Manufacturing an alloy by melting the prepared metal material; Homogenizing heat treatment of the prepared alloy in a temperature range of 900 to 1350 ° C; Cooling after the homogenization heat treatment; And after processing the cooled alloy, cooling after a second heat treatment to maintain 0.2 to 72 hours in a temperature range of 300 to 900 ° C.

Figure 2 is a process flow chart showing an example of the manufacturing method of the present invention.

As shown in Fig. 2, a metal material having the above-mentioned composition component is prepared and then melted.

In the present invention, the melting process is for alloying the manufactured metal material, and the method is not particularly limited, and a general method commonly performed in the technical field to which the present invention pertains can be used. For example, it can be produced from the alloy through casting, arc melting, powder metallurgy, spray casting, spray coating, spray coating, 3D-printing, and the like.

Subsequently, in the present invention, the alloy prepared by melting is subjected to homogenization heat treatment. Since a high entropy alloy contains various elements, homogenization heat treatment is performed to induce sufficient diffusion. The homogenization heat treatment is preferably maintained for 1 to 48 hours in a temperature range of 900 to 1350 ° C.

And in the present invention, cooling is performed after the homogenization heat treatment. Since the cooling method is not particularly limited, it can be performed by a method such as water cooling, oil cooling, or air cooling. Through the cooling process, some metal components that are not employed in the matrix structure in the microstructure may be uniformly distributed.

Subsequently, in the present invention, the cooled alloy is processed. In the present invention, methods such as forging, extrusion, rolling, and drawing may be used as the processing method. Various deformation defects can be introduced into the cooled alloy material by such processing.

Subsequently, in the present invention, secondary heat treatment is performed to create a microstructure in which precipitates are simultaneously present in the cooled single-phase solid solution matrix structure.

The secondary heat treatment is a process for uniformly depositing elements that exceed the solid-solution limit or elements that are thermodynamically unstable or metastable in an alloy matrix in which components are uniformly distributed, in the form of a single element or an intermetallic compound.

At this time, in the present invention, it is preferable to perform a secondary heat treatment that is maintained for 0.2 to 72 hours in a temperature range of 300 to 900 ° C.

Thereafter, the secondary heat-treated alloy is cooled, and cooling at this time may use a conventional cooling method such as water cooling, oil cooling, air cooling, and furnace cooling.

Hereinafter, the present invention will be described in detail through examples.

(Example)

A metal material having a composition (at%) of Table 1 below was prepared, and arc melted in a vacuum atmosphere to prepare high-entropy alloys, respectively. Subsequently, the produced alloy was cooled after performing homogenization heat treatment at 1250 ° C. for 24 hours. And after the homogenization treatment, the cooled alloy was subjected to a rolling processing process, and then heat-treated at 450 ° C. for 3 hours to form a precipitate.

Then, for each of the high-entropy steel (Comparative Example 1-3, Inventive Example 1-12) prepared as described above, a plate having a thickness of 1 mm was formed, a tensile test was performed, and the mechanical properties were evaluated, and the results were shown in Table 1 below. Shown.

division alloy Precipitate The tensile strength
(MPa) Yield strength
(MPa) Elongation
(%) Comparative Example 1 Co ₂₀ Cr ₂₀ Fe ₂₀ Mn ₂₀ Ni ₂₀ - 620 480 40 Comparative Example 2 Fe ₂₅ Ni ₂₅ Co ₂₅ Cr ₂₅ - 1000 870 35 Comparative Example 3 Fe ₂₀ Mn ₂₀ Ni ₂₀ Co ₂₀ Cr ₂₀ - 760 640 15 Inventive Example 1 Fe ₆₀ Cr _19.5 Co ₁₀ Mn ₁₀ C _0.5 Spherical precipitate (0.5-50 nm) 875 728 24 Inventive Example 2 Fe ₆₀ Cr _19.5 Co ₁₀ Mn ₁₀ N _0.5 Spherical precipitate (0.5-50 nm) 900 712 18 Inventive Example 3 Fe ₆₀ Cr _19.5 Co ₁₀ Mn ₁₀ B _0.5 Needle shape (0.5-50nm) 915 765 17 Inventive Example 4 Fe ₆₀ Cr ₁₅ Ni ₁₀ Mn ₁₀ Ti _4.5 C _0.5 Needle precipitate (0.5-50 nm) 1065 915 25 Inventive Example 5 Fe ₆₀ Co ₁₅ Ni ₁₀ Mn ₁₀ W _4.5 C _0.5 Needle precipitate (0.5-50 nm) 1095 952 26 Inventive Example 6 Fe ₆₀ Cr ₁₅ Ni ₁₀ Mn ₁₀ Mo _4.5 C _0.5 Needle precipitate (0.5-50 nm) 1080 926 24 Inventive Example 7 Fe ₆₀ Ni ₁₅ Co ₁₀ Mn ₁₀ V _4.5 C _0.5 Needle precipitate (0.5-50 nm) 1073 930 23 Inventive Example 8 Fe ₆₀ Cr ₁₅ Co ₁₀ Mn ₁₀ Nb _4.5 C _0.5 Needle precipitate (0.5-50 nm) 1091 934 25 Inventive Example 9 Fe ₆₀ Cr ₁₅ Co ₁₀ Ni ₁₀ Zr _4.5 C _0.5 Needle precipitate (0.5-50 nm) 1058 923 24 Inventive Example 10 Fe ₆₀ Ni ₁₅ Co ₁₀ Mn ₁₀ Cu _4.5 N _0.5 Spherical precipitate (0.5-50 nm) 983 840 21 Inventive Example 11 Fe ₆₀ Cr ₁₅ Co ₁₀ Mn ₁₀ Al _4.5 N _0.5 Spherical precipitate (0.5-50 nm) 1020 874 25 Inventive Example 12 Fe ₆₀ Mn ₁₅ Co ₁₀ Cr ₁₀ Si _4.5 B _0.5 Needle precipitate (0.5-50 nm) 994 848 22

As shown in Table 1, in the case of Inventive Example 1-12 that satisfies the composition of the present invention and includes a precipitate in a matrix, superior strength and ductility compared to Comparative Example 1-3 can be secured in a balanced manner. Can be confirmed. Particularly, in Comparative Examples 1-3, no particular precipitate was observed, but it can be confirmed that in the invention examples of the present invention, a needle-shaped or spherical-shaped precipitate was formed, and excellent strength and ductility can be secured.

On the other hand, FIG. 3 is a photograph of the microstructure of Example 1 of the present invention. In FIG. 3, after the secondary heat treatment, it can be confirmed that spherical carbides are formed to hinder the movement of dislocations to strengthen the matrix.

4 is a photograph of the microstructure of Example 5 of the present invention, after the second heat treatment, it can be seen that the precipitates formed on the needles are evenly dispersed, thereby preventing the movement of dislocations within the matrix to strengthen the matrix.

As described above, in the detailed description of the present invention, the preferred embodiments of the present invention have been described, but those skilled in the art to which the present invention pertains have various modifications within the limits that do not depart from the scope of the present invention. Of course it is possible. Therefore, the scope of rights of the present invention should not be limited to the described embodiments, but should be defined by the equivalents as well as the claims described below.

Claims (5)

In atomic (at)%, Fe: more than 35% 80%, Ni: more than 5% 35%, Mn: more than 5% 35%, Co: more than 5% 35%, Cr: more than 5% 35 % Or less and Cu: more than 5% and 35% or less;
It includes one or more selected from the group of elements defined in 1) and 2), respectively; And
Precipitation hardening type high-entropy steel in which precipitates are distributed in the matrix.
1) C: 0.01 to 0.9%, N: 0.01 to 0.9% and B: 0.01 to 0.9%
2) Ti: 0.05-10%, Zr: 0.05-10%, Mo: 0.05-10%, W: 0.05-10%, Nb: 0.05-10%, Si: 0.05-10%, V: 0.05-10% And Al: 0.05 to 10%
The method according to claim 1, wherein the precipitate is at least one of Cr, Ti, Zr, Mo, W, Nb, Si or V-based carbonitride to boride, Mn-based carbonitride and (Cr, Mn) -based carbonitride. Precipitation hardening type high entropy steel
The precipitation hardening type high-entropy steel according to claim 1, wherein the precipitate has an average diameter of 0.5 to 50 nm, and an interval between the precipitates is distributed at 1 to 500 nm.
In atomic (at)%, Fe: more than 35% 80%, Ni: more than 5% 35%, Mn: more than 5% 35%, Co: more than 5% 35%, Cr: more than 5% 35 % Or less and Cu: more than 5% and 35% or less; And preparing metal materials each containing at least one selected from the group of elements defined in 1) and 2) below;
Manufacturing an alloy by melting the prepared metal material;
Homogenizing heat treatment of the prepared alloy in a temperature range of 900 to 1350 ° C;
Cooling after the homogenization heat treatment; And
After processing the cooled alloy, a method of manufacturing a precipitation hardening type high-entropy steel comprising the step of cooling after the second heat treatment to maintain 0.2 to 72 hours in the temperature range of 300 ~ 900 ℃.
1) C: 0.01 ~ 0.9%, N: 0.01 ~ 0.9%, B: 0.01 ~ 0.9%
2) Ti: 0.05-10%, Zr: 0.05-10%, Mo: 0.05-10%, W: 0.05-10%, Nb: 0.05-10%, Si: 0.05-10%, V: 0.05-10% , Al: at least one of 0.05 to 10%
The method of claim 4, wherein the homogenization heat treatment is performed for 1 to 48 hours in a temperature range of 900 to 1350 ° C.

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