JP7775993B2 - Fe-based alloy, alloy member, product, and method for manufacturing alloy member - Google Patents

Description

The present invention relates to an Fe-based alloy, an alloy component and its products, and a method for manufacturing an alloy component.

Traditionally, tools such as punches and dies used in hot precision press working have been made of hot work tool steels with high high-temperature strength, such as SKD8 specified in JIS G 4404, and high-speed tool steels such as SKH51 specified in JIS G 4403. However, these steels have had problems such as being prone to settling, wear, breakage, cracking, and heat cracking.

For example, Patent Document 1 discloses a high-speed tool steel that contains, by mass%, 0.4 to 0.9% C, 1.0% or less Si, 1.0% or less Mn, 1.5 to 6% of one or both of W and Mo (1/2W+Mo) (however, W is 3% or less), and 0.5 to 3% of one or both of V and Nb (V+Nb), and that is characterized in that the average particle size of precipitated carbides dispersed in the matrix is 0.5 μm or less and the distribution density thereof is 80 × ¹⁰³ particles/ ^mm2 or more.

Japanese Patent Application Laid-Open No. 2004-307963

In the tool steel of Patent Document 1, coarse primary carbides are formed in the ingot due to solidification segregation during cooling during ingot-making processes such as casting or remelting of the steel ingot. The presence of these coarse primary carbides promotes the initiation and propagation of cracks, thereby reducing toughness and heat crack resistance. It is preferable that the precipitated carbides have a finely dispersed, uniform structure. To achieve such a structure, soaking at 1200-1300°C for 10-20 hours is required. However, even after soaking, the steel still requires subsequent quenching and tempering processes to obtain forging tools such as dies and punches, as well as molds. This process can sometimes result in the precipitation of coarse precipitated carbides, which may reduce toughness and heat crack resistance.

The present invention therefore aims to provide an Fe-based alloy, alloy component and its manufactured product, and a method for manufacturing the alloy component, which are expected to be less susceptible to cracking and have high toughness and heat crack resistance.

In order to achieve the above-mentioned object, a first invention is an Fe-based alloy comprising C, Cr, W, Mo, and V, with the balance being Fe and unavoidable impurity elements, and having an alloy structure including an Fe-BCC phase, wherein the Fe-BCC phase contains, in mass %, C of 3% to 7%, Cr of 2% to 6%, W of 0.5% to 4%, Mo of 0.5% to 4%, V of 0.5% to 4%, and Fe of 75% to 90%, and wherein the Fe-BCC phase has precipitated carbides, and the precipitated carbides have a circle-equivalent average particle size of 1.30 μm or less. The circle-equivalent average particle size of the precipitated carbides can be calculated by calculating the average area of precipitated carbide portions within an observation field using electron backscattered diffraction (EBSD), and then calculating the circle-equivalent diameter from the area. Furthermore, when the total area is the sum of the areas of the Fe-BCC phase, the Fe-FCC phase, and the zero solution portion , the proportion of the precipitated carbides is 0.38% or less, as calculated by dividing the area of the zero solution portion by the total area .

It is also desirable that the Fe-BCC phase accounts for 96% or more of the alloy structure in terms of area ratio.

It is also desirable that the average circle-equivalent particle size of the precipitated carbides be 0.60 μm or more.

Furthermore, it is desirable that the Fe-based alloy as a whole contains, in mass %, C of 0.1% or more and 2% or less, Cr of 2% or more and 6% or less, W of 0.5% or more and 4% or less, Mo of 0.5% or more and 4% or less, V of 0.5% or more and 4% or less, Si of 1.0% or less, Mn of 1.0% or less, Co of 4% or less, and the balance consisting of Fe and inevitable impurity elements.

It is also desirable that the alloy further contains either Si or Mn, or both, with Si being 1.0% or less and Mn being 0.1% or more and 1.0% or less, by mass.

It is desirable that the Fe-based alloy as a whole further contains 0.5% to 4% Co by mass, and that the Fe-BCC phase further contains 0.5% to 4% Co.

According to the first invention, fine precipitated carbides are dispersed in the Fe-BCC phase, making it possible to obtain an Fe-based alloy that is less susceptible to cracking and is also expected to have high toughness and heat crack resistance.

The second invention is an alloy component characterized by comprising at least a portion of the Fe-based alloy of the first invention.

The Fe-based alloy is formed on the surface of the base material of the alloy component, and it is desirable that the hardness of the surface layer be 350 HV or more.

According to the second invention, an alloy component can be obtained that is less susceptible to cracking and is also expected to have toughness and heat crack resistance.

Furthermore, by forming an alloy layer made of the Fe-based alloy according to the first invention on the surface of the base material, a component with excellent surface toughness and heat crack resistance can be obtained. Furthermore, even if a portion of the surface is damaged, for example, repair can be easily carried out by simply forming a new alloy layer on only the damaged area by buildup, resulting in an alloy component with excellent toughness and heat crack resistance.

The alloy component may have one or more of a nitride layer, a compound layer, or a ceramic coating layer on the surface of the Fe-based alloy.

In addition, greater durability can be achieved by forming a nitride layer, compound layer, or ceramic coating layer on the surface.

The third invention is a manufactured product characterized by having at least a portion thereof comprised of the alloy component of the second invention.

According to the third invention, a product can be obtained that is less prone to cracking and is also expected to have high toughness and heat crack resistance.

Particularly suitable products for this purpose are hot stamping dies, cold forging dies or cold press dies that are repaired before use.

The above Fe-based alloy components and products can be obtained by additive manufacturing using metal powder of the desired composition.

The fourth invention is a method for manufacturing an alloy part, which comprises using an alloy powder consisting of, by mass%, C from 0.1% to 2%, Cr from 2% to 6%, W from 0.5% to 4%, Mo from 0.5% to 4%, V from 0.5% to 4%, Si from 1.0% to 1.0%, Mn from 1.0% to 1.0%, Co from 4% to 1.0%, and the remainder being Fe and unavoidable impurities, spraying the alloy powder while moving it onto a substrate, irradiating the sprayed alloy powder with an electron beam or laser beam to melt and solidify it to form a solidified layer, and repeating the melting and solidification process to obtain the alloy part.

It is also preferable that the Si content be 0.1% or more and 1.0% or less, and the Mn content be 0.1% or more and 1.0% or less.

It is also preferable that the alloy powder further contains Co, and that the Co content is, by mass%, 0.5% or more and 4% or less.

It is also preferable that the obtained alloy component undergoes at least one of a quenching treatment in which the component is held at a temperature of 1000°C or higher and 1400°C or lower, followed by cooling in oil or water, and a tempering treatment in which the component is held at a temperature of 400°C or higher and 700°C or lower.

It is also preferable that the method further includes a surface treatment step in which the obtained alloy component is subjected to a surface treatment, and that the surface treatment step is a nitriding treatment or film formation by a PVD method. By performing the surface treatment step, higher durability can be obtained.

According to the fourth invention, a method for manufacturing alloy components can be obtained that are less susceptible to cracking and are also expected to have high toughness and heat crack resistance.

Furthermore, during the melting and solidifying process, it is desirable that the thickness of the solidified layer be 0.1 mm or more and 5 mm or less.

The present invention provides an Fe-based alloy, alloy component, and method for manufacturing an alloy component that is less susceptible to cracking and is expected to have high toughness and heat crack resistance.

FIG. 1 illustrates a schematic configuration of an additive manufacturing method. 10 is a photograph of the structure of a shaped body of an alloy member according to the present invention after quenching treatment. 2B is a structural photograph of the shaped body of FIG. 2A after tempering treatment. 1 is a photograph of the structure of a shaped body of an alloy member of the present invention before heat treatment. 2D is a structural photograph of the shaped body of FIG. 2C after tempering treatment. Photograph of the structure of conventional forged material after quenching and tempering treatment. FIG. 10 is a diagram showing the Vickers hardness (HV) of each molded body.

One embodiment of the present invention will be described below. First, an Fe-based alloy will be described, followed by an additive manufacturing method. Note that in the following description, % indicates mass %. Furthermore, in this specification, a numerical range expressed using "to" means a range that includes the numerical values written before and after "to" as the lower and upper limit values. Furthermore, the lower and upper limit values of a numerical range can be combined as appropriate.

<Fe-based alloy>
The Fe-based alloy of this embodiment contains C, Cr, W, Mo, and V, with the balance being Fe and unavoidable impurity elements; in other words, it is a high-speed tool steel containing C, Cr, W, Mo, V, and Fe, and has an alloy structure including an Fe-BCC phase. The Fe-BCC phase contains, in mass %, 3% to 7% C, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, and 75% to 90% Fe, and one of its features is that carbides precipitate in the Fe-BCC phase, and the circle-equivalent average particle size of the carbides is 1.3 μm or less.

(C: 3-7%)
Carbon combines with carbide-forming elements such as Cr, W, Mo, and V to form hard complex carbides, improving the wear resistance of alloy members and their products. Carbon also has the effect of strengthening the matrix by dissolving partially within the matrix. By setting the C content in the Fe-BCC phase to 3% or more, the hardness of the Fe-BCC phase can be ensured through both the strengthening of the matrix and the formation of fine carbides within the matrix grains. On the other hand, by setting the C content in the Fe-BCC phase to 7% or less, the formation of excessive carbides within the matrix grains can be suppressed, ensuring toughness.

(Cr: 2 to 6%)
Cr combines with C to form carbides, improving wear resistance and also contributing to improved hardenability. By setting the Cr content in the Fe-BCC phase to 2% or more, the amount of carbides formed within the matrix grains can be optimized, improving wear resistance and hardenability. On the other hand, by setting the Cr content in the Fe-BCC phase to 6% or less, the amount of carbides formed within the matrix grains can be prevented from becoming excessive, ensuring toughness.

(W: 0.5-4%)
W bonds with C to form carbides, contributing to improved wear resistance. It also contributes to ensuring strength in high-temperature environments, and is therefore effective in improving the wear resistance of dies used in particularly high-temperature environments. By setting the W content in the Fe-BCC phase to 0.5% or more, it dissolves in the matrix, increasing heat treatment hardness and improving wear resistance. On the other hand, by setting the W content in the Fe-BCC phase to 4% or less, it is possible to prevent excessive formation of carbides within the matrix grains and ensure toughness.

(Mo: 0.5-4%)
Mo combines with C to form carbides, improving wear resistance and also contributing to improved hardenability. By making the Mo content in the Fe-BCC phase 0.5% or more, it dissolves in the matrix grains, increasing heat treatment hardness and improving wear resistance. On the other hand, by making the Mo content in the Fe-BCC phase 4% or less, it is possible to prevent excessive formation of carbides in the matrix grains and ensure toughness.

(V: 0.5-4%)
V combines with C to form carbides, contributing to improved wear resistance and seizure resistance. By setting the V content in the Fe-BCC phase to 0.5% or more, fine carbides that are difficult to aggregate are precipitated within the matrix grains by heat treatment, increasing softening resistance in high-temperature ranges and high-temperature yield strength. In addition, the matrix crystal grains are refined, improving toughness and raising the A1 transformation point, which, combined with excellent high-temperature yield strength, improves heat crack resistance. On the other hand, by setting the V content in the Fe-BCC phase to 4% or less, it is possible to prevent excessive formation of carbides within the matrix grains and ensure toughness.

(Fe-BCC phase)
The Fe-BCC phase is generally a structure containing α-Fe and martensite formed when an Fe-based alloy is cooled from a high temperature. Here, due to the high cooling rate, the Fe-BCC phase refers to a structure containing martensite of an Fe-based alloy in which C is supersaturated in solid solution, and is hard. The Fe-BCC phase contains 3% to 7% C, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, and 75% to 90% Fe. The Fe-BCC phase can be evaluated using electron backscattering diffraction (EBSD). The evaluation method using EBSD will be described later.

(carbide)
Carbides containing at least one of Cr, W, Mo, and V (hereinafter also referred to as precipitated carbides) are precipitated in the Fe-BCC phase. In the Fe-BCC phase, carbide-forming elements such as Cr, W, Mo, and V combine with C (carbon) to form hard carbides, which are effective in improving wear resistance. Furthermore, C has the effect of strengthening the matrix by dissolving partially in the matrix. The phase containing precipitated carbides can be referred to as the carbide phase. The carbide phase is a region where Cr, V, Mo, and W are more concentrated than in the Fe-BCC phase and where C is abundant. The carbide phase contains, for example, 7% to 11% C, 3% to 7% Cr, 1% to 5% W, 1% to 5% Mo, 1% to 5% V, and 75% to 90% Fe.

In addition, the moderate refinement of the precipitated carbides makes them less susceptible to cracking, resulting in an Fe-based alloy with excellent toughness and heat crack resistance. Specifically, the size of the precipitated carbides is refined to an average circle-equivalent diameter of 1.30 μm or less. This is preferably 0.50 μm to 1.1 μm, and more preferably 0.60 μm to 1.1 μm. For example, when using EBSD, the average diameter can be determined from carbides that are visible at a magnification of 400x or more.

(Method for calculating the average particle diameter equivalent to a circle)
The circle-equivalent average grain size of precipitated carbides in the Fe-BCC phase can be calculated as follows: First, the phase map obtained by EBSD (e.g., RGB image, field of view: 200 × 200 μm) is divided into each color (red, green, blue), and only the precipitated carbide portions are extracted.

Specifically, the phase map obtained by EBSD is first divided into a red area (Fe-BCC phase), a blue area (mainly Fe-FCC phase), and a green area (area that is neither Fe-BCC nor Fe-FCC phase; hereafter referred to as the zero solution area). By dividing the phase map in this way, the proportion of the Fe-BCC phase and precipitated carbides in the structure can be determined. By displaying the image of the divided red area (Fe-BCC phase) in black and white, the Fe-BCC phase appears white.

The blue area (mainly Fe-FCC phase) and green area (zero solution area) are displayed in white. If the total area is the sum of the areas of the red area (Fe-BCC phase), blue area (mainly Fe-FCC phase), and zero solution area, then the value obtained by dividing the red area (Fe-BCC phase) by the total area can be rephrased as the Fe-BCC layer ratio (area ratio).

By subtracting the image of the separated blue area (mainly the Fe-FCC phase) from this inverted black-and-white image, the zero solution area can be displayed. This zero solution area is the area that is neither the Fe-BCC nor the Fe-FCC phase, and corresponds to the precipitated carbide area. Next, by calculating the average area of the precipitated carbide areas within the field of view and calculating the equivalent circle diameter of that area, the average equivalent circle diameter of the precipitated carbide within the Fe-BCC phase can be calculated.

Each structure can be evaluated using energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) associated with a scanning electron microscope (SEM).

For example, analytical conditions may be set to a scanning electron microscope acceleration voltage of 15 kV, a working distance from the objective lens to the observation surface of 10 mm, and an observation magnification of 3000x. Furthermore, elemental distribution evaluation using EDS involves obtaining elemental distribution through EDS area analysis in the same field of view of the SEM as described above. For example, when analyzing precipitated carbides, the target elements may be, for example, C, Cr, W, Mo, V, Fe, Co, and O, with Si and Mn also being possible. Fe-BCC phases can also be analyzed in the same manner as described above.

Furthermore, the higher the proportion of the Fe-BCC phase, the more uniform the metal structure becomes, and localized distortion due to external stress, for example, is less likely to occur, which is expected to have the effect of suppressing cracks. Specifically, the proportion of Fe-BCC in terms of area ratio is preferably 96% or more, more preferably 97% or more, even more preferably 98% or more, and even more preferably 99% or more.

The structure of the Fe-based alloy of this embodiment is such that the Fe-BCC phase accounts for 96% or more of the alloy structure, and fine carbides are precipitated within the Fe-BCC phase, making it difficult for cracks to occur originating from the carbides. Even if cracks do occur, they are uniformly dispersed and therefore do not propagate easily. This improves toughness and heat crack resistance.

In addition, the Fe-based alloy as a whole contains, in mass %, 0.1% to 2% C, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, 1.0% or less Si, 1.0% or less Mn, 4% or less Co, and the remainder being Fe and unavoidable impurity elements.

(C: 0.1-2%)
C combines with carbide-forming elements such as Cr, W, Mo, and V to form hard composite carbides, improving the wear resistance of alloy members and their products. C also dissolves partially in the matrix, strengthening the matrix. By setting the C content in the Fe-based alloy to 0.1% or more, the hardness of the Fe-based alloy as a whole can be ensured through the strengthening of the matrix, the formation of fine carbides within the matrix grains, and the formation of carbides at the matrix grain boundaries. On the other hand, by setting the C content in the Fe-based alloy as a whole to 2% or less, the formation of excessive carbides in the Fe-based alloy as a whole can be suppressed, ensuring the toughness of the Fe-based alloy as a whole.

(Cr: 2 to 6%)
Cr combines with C to form carbides, improving wear resistance and hardenability. By making the Cr content in the entire Fe-based alloy 2% or more, the amount of carbides formed in the entire Fe-based alloy can be optimized, improving wear resistance and hardenability. On the other hand, by making the Cr content in the entire Fe-based alloy 6% or less, the amount of carbides formed in the entire Fe-based alloy can be prevented from becoming excessive, ensuring toughness.

(W: 0.5-4%)
W combines with C to form carbides, contributing to improved wear resistance. It also contributes to ensuring strength in high-temperature environments, making it particularly effective in improving the wear resistance of dies used in high-temperature environments. By making the W content in the entire Fe-based alloy 0.5% or more, W dissolves in the matrix grains, increasing heat treatment hardness, and carbides are also formed at the matrix grain boundaries, improving wear resistance. On the other hand, by making the W content in the entire Fe-based alloy 4% or less, excessive carbide formation in the entire Fe-based alloy can be suppressed, ensuring toughness.

(Mo: 0.5-4%)
Mo combines with C to form carbides, improving wear resistance and contributing to improved hardenability. By making the Mo content in the Fe-based alloy 0.5% or more, the Mo content dissolves in the matrix grains, increasing the heat treatment hardness, and carbides are also formed at the matrix grain boundaries, improving wear resistance. On the other hand, by making the Mo content in the Fe-based alloy 4% or less, the amount of carbide formed in the Fe-based alloy as a whole can be prevented from becoming excessive, ensuring toughness.

(V: 0.5-4%)
V combines with C to form carbides, contributing to improved wear resistance and seizure resistance. By making the V content in the entire Fe-based alloy 0.5% or more, fine, non-aggregating carbides are precipitated within the matrix grains by heat treatment, increasing softening resistance in high-temperature regions and improving high-temperature yield strength. In addition, the matrix crystal grains are refined, improving toughness and raising the A1 transformation point, which, combined with excellent high-temperature yield strength, improves heat crack resistance. On the other hand, by making the V content in the entire Fe-based alloy 4% or less, it is possible to prevent excessive carbide formation in the entire Fe-based alloy and ensure toughness.

Furthermore, it is preferable that the alloy further contains either Si or Mn, or both, with Si being 0.1% to 1.0% by mass and Mn being 0.1% to 1.0% by mass. Si is expected to improve oxidation resistance. The above range is desirable in consideration of workability. Mn is expected to improve wear resistance and hardenability and reduce embrittlement. The above range is desirable in consideration of the effects of embrittlement due to quench cracking and residual γ.

(Si: 1.0% or less)
Furthermore, Si may be contained. When Si is contained in the entire Fe-based alloy, the content of Si in the entire Fe-based alloy is preferably 0.1% or more and 1.0% or less in order to improve oxidation resistance and suppress deterioration of workability.

(Mn: 1.0% or less)
Furthermore, Mn may be contained. When Mn is contained in the entire Fe-based alloy, the content of Mn in the entire Fe-based alloy is preferably 0.1% or more and 1.0% or less in order to improve wear resistance and hardenability, reduce embrittlement, and suppress embrittlement due to quench cracking and residual γ.

(Co: 4.0% or less)
In addition to the above elements, the Fe-based alloy may contain Co. In order to improve the softening resistance of the matrix and suppress a decrease in toughness in the entire Fe-based alloy, the content of Co in the entire Fe-based alloy is preferably 4.0% or less, and more preferably 0.5% or more and 4% or less.

(Inevitable impurities)
Inevitable impurities refer to trace amounts of impurities that are technically difficult to remove, such as trace elements mixed into raw materials or reactions with various components that come into contact during the manufacturing process. In the case of the alloy of this embodiment, unavoidable impurities specifically refer to, for example, Al, Cu, N, Ni, O, P, S, and Ti. Among these impurities, impurities that should be particularly limited are P, S, O, and N. In mass%, P is preferably 0.03% or less, S is preferably 0.003% or less, O is preferably 0.02% or less, and N is preferably 0.05% or less. Of course, the content of these unavoidable impurities is preferably low, and 0% is even better.

<Method of manufacturing alloy member>
The Fe-based alloy and alloy member of this embodiment can be obtained by spraying alloy powder onto a substrate while moving it, irradiating the sprayed alloy powder with an electron beam or laser beam to melt and solidify it to form a solidified layer, stacking another solidified layer on top of the solidified layer, and repeating this process. This is a so-called additive manufacturing method. Note that this specification may also be referred to as a layered manufacturing method.

(alloy powder)
Here, the alloy powder is an Fe-based alloy powder containing the above-mentioned predetermined composition of C, Cr, W, Mo, and V, with the remainder being Fe and unavoidable impurity elements. First, predetermined amounts of each element are weighed out so as to obtain an alloy having a predetermined composition range, and these are mixed to produce a raw material powder. This raw material powder is used to obtain an atomized powder. For example, the raw material powder is loaded into a crucible, high-frequency melted, and the molten alloy is dropped from a nozzle below the crucible and sprayed with high-pressure argon to produce a gas-atomized powder. This gas-atomized powder can then be classified to obtain an alloy powder.

The Fe-based alloy powder of this embodiment may be alloyed to satisfy the composition of the Fe-based alloy described above. For example, the powder may contain, by mass, 0.1% to 2% C, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, 4.0% or less Co, 1.0% or less Si, and 1.0% or less Mn, with the remainder being Fe and unavoidable impurities.

When a shaped body is produced using the Fe-based alloy powder of this embodiment, C in the alloy structure of the shaped body combines with carbide-forming elements such as Cr, W, Mo, and V to form hard complex carbides, which has the effect of improving the wear resistance of the alloy member and its products. Furthermore, C dissolves in part of the matrix of the alloy structure of the shaped body, thereby strengthening the matrix.

By setting the C content in the Fe-based alloy powder to 0.1% or more, the hardness of the alloy structure can be ensured by strengthening the matrix of the alloy structure, forming fine carbides within the matrix grains, and forming carbides at the matrix grain boundaries. On the other hand, by setting the C content in the Fe-based alloy powder to 2% or less, the formation of excessive carbides within the alloy structure can be suppressed, ensuring the toughness of the Fe-based alloy as a whole.

Cr combines with C to form carbides, improving the wear resistance of the alloy structure of the shaped body and also contributing to improved hardenability. By making the Cr content in the Fe-based alloy powder 2% or more, the amount of carbides formed in the alloy structure of the shaped body can be optimized, improving the wear resistance and hardenability of the alloy structure. On the other hand, by making the Cr content in the entire Fe-based alloy 6% or less, the amount of carbides formed in the alloy structure of the shaped body can be prevented from becoming excessive, ensuring toughness.

W combines with C to form carbides, contributing to improved wear resistance of the alloy structure of the shaped body. It also contributes to ensuring strength in high-temperature environments, making it particularly effective in improving the wear resistance of molds used in high-temperature environments. By setting the W content in the Fe-based alloy powder to 0.5% or more, W dissolves within the matrix grains in the alloy structure, increasing heat treatment hardness, and carbides are also formed at the matrix grain boundaries, improving the wear resistance of the alloy structure. On the other hand, by setting the W content in the Fe-based alloy powder to 4% or less, excessive carbide formation within the alloy structure can be suppressed, ensuring toughness.

Mo combines with C to form carbides, improving the wear resistance of the alloy structure of the molded body and also contributing to improved hardenability. By setting the Mo content in the Fe-based alloy powder to 0.5% or more, the Mo dissolves in the matrix grains within the alloy structure, increasing heat treatment hardness, and carbides are also formed at the matrix grain boundaries, improving the wear resistance of the alloy structure. On the other hand, by setting the Mo content in the Fe-based alloy powder to 4% or less, excessive carbide formation within the alloy structure can be suppressed, ensuring toughness.

V combines with C to form carbides, contributing to improved wear resistance and seizure resistance of the alloy structure of the shaped body. By setting the V content in the Fe-based alloy powder to 0.5% or more, fine, non-agglomerating carbides precipitate within the matrix grains in the alloy structure upon heat treatment, increasing the softening resistance of the alloy structure at high temperatures and improving high-temperature yield strength. Furthermore, the matrix grains in the alloy structure become finer, improving toughness and raising the A1 transformation point. This, combined with excellent high-temperature yield strength, improves heat crack resistance. Meanwhile, setting the V content in the Fe-based alloy powder to 4% or less prevents excessive carbide formation within the alloy structure, ensuring toughness.

For example, an Fe-based alloy powder containing, by mass, 0.1% to 2% C, 0.1% to 1.0% Si, 0.1% to 1.0% Mn, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, and the remainder being Fe and unavoidable impurity elements can be used. It is also preferable that the powder contains either Si or Mn, or both.

If the Fe-based alloy powder contains Si, the content in the Fe-based alloy powder is preferably 0.1% to 1.0% in order to improve the oxidation resistance of the alloy structure of the shaped body and prevent a decrease in workability. If the Fe-based alloy powder contains Mn, the content in the Fe-based alloy powder is preferably 0.1% to 1.0% in order to improve the wear resistance and hardenability of the alloy structure of the shaped body, reduce embrittlement, and prevent embrittlement due to quench cracking and residual γ.

In addition to the above elements, Co can also be included. To prevent a decrease in the toughness of the alloy structure of the shaped body, the content of Co in the Fe-based alloy as a whole is preferably 4% or less. To improve the softening resistance of the matrix of the alloy structure, it is preferable to set the content to 0.5% or more.

Therefore, when Co is included, it is preferable to use an Fe-based alloy powder containing 0.1% to 2% C, 0.1% to 1.0% Si, 0.1% to 1.0% Mn, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, 0.5% to 4% Co, and the remainder being Fe and unavoidable impurity elements.

The composition of the alloy powder can be analyzed, for example, using inductively coupled plasma (ICP) optical emission spectrometry.

In one embodiment, an Fe-based composite powder is irradiated with an electron beam or laser beam to melt and solidify it to form a shape. This can be applied to either Powder Bed Fusion (PBF) or Directed Energy Deposition (DED), which are additive manufacturing methods for metal materials.

For example, the Fe-based alloy component of this embodiment can be manufactured by repeatedly performing a melting and solidifying process in which the above-mentioned Fe-based alloy powder is irradiated with a heat source such as an electron beam or laser beam to melt and solidify it and form a solidified layer, thereby stacking further solidified layers on top of the solidified layer. Furthermore, for example, the directed energy deposition method can be used to spray alloy powder onto a substrate while moving it, and then irradiate the sprayed alloy powder with an electron beam or laser beam to melt and solidify it and form a solidified layer, repeatedly repeating this melting and solidifying process, thereby stacking further solidified layers on top of the solidified layer, thereby obtaining the alloy component (shaped body) of this embodiment.

In addition, powder particle size may be adjusted by mesh sieving or airflow classification to suit the modeling method of the additive manufacturing process. For example, the modeling powder used in powder bed fusion, which uses an electron beam or laser beam, is melted by the laser beam, which serves as the heat source, but coarse powder that is difficult to melt must be removed to minimize the area affected by the heat. Furthermore, highly adhesive fine powder must also be removed to achieve optimal fluidity to ensure powder spreadability.

For example, when applying the powder bed fusion (PBF) method, it is preferable to adjust the average particle size (D50) of the alloy powder to the range of 10 to 53 μm. Furthermore, for example, metal powders used in directed energy deposition methods must be melted using a laser beam, which serves as the heat source, and coarse powder that is difficult to melt must be removed. Furthermore, fine powder must also be removed to prevent dust scattering when the powder is supplied to the heat source and to ensure fluidity that allows the powder to be easily transported. For this reason, when applying the molding powder of the present invention to directed energy deposition methods, it is preferable to adjust the D50 to the range of 53 to 106 μm. On the other hand, when using an electron beam or plasma as the heat source, it is possible to use coarser metal particles for molding, so it is preferable to set the D50 to 75 to 250 μm.

Figure 1 shows the schematic configuration of an additive manufacturing device 1 that uses a laser beam as a heat source for additive manufacturing using the directed energy deposition method. The additive manufacturing device 1 is mainly composed of a powder feed nozzle 3, a focusing lens 5, a protective lens 7, etc. Alloy powder 11 is supplied to the powder feed nozzle 3 and injected into the tip of the powder feed nozzle 3 together with argon gas. A laser beam 9 emitted from a laser oscillator (not shown) is focused by the focusing lens 5 and irradiated near the tip of the powder feed nozzle 3. A protective lens 7 is provided below the focusing lens 5.

In additive manufacturing, alloy powder 11 is supplied onto a base plate 17 while the powder supply nozzle 3 is moved relative to the base plate 17 (direction A in the figure). A laser beam 9 focused by a focusing lens 5 is irradiated onto the supplied alloy powder 11, forming a molten pool of the alloy powder 11, which then solidifies to form a shaped body 15 (Fe-based alloy). This process is repeated using a program file created using CAD-CAM software to stack shaped bodies 15 on the base plate 17, thereby forming a three-dimensional alloy part that contains at least a portion of an Fe-based alloy.

In the directed energy deposition method, a three-dimensional additive manufacturing device is used to rapidly melt the surface of a base material such as a base plate, a shaped body, or a mold by irradiating it with a laser, and then raw material powder is supplied into the molten pool that results, where it is rapidly cooled and solidified. This series of processes is repeated to create a shaped body. The shaped body formed on the base plate is the Fe-based alloy component of this embodiment. In the case of mold repair, a manufactured product can also be obtained. Additive manufacturing conditions are determined appropriately taking into account the particle size and composition of the raw material powder, the size, shape, and characteristics of the shaped body, production efficiency, etc., but for the alloy of this embodiment, they can be selected, for example, from the following ranges.

The thickness of each layer during additive manufacturing is, for example, 0.1 mm to 1.0 mm, preferably 0.4 to 0.8 mm. The thickness of the first layer of Fe-based alloy formed on the surface of the base plate is 0.1 mm to 1 mm. The thickness of the entire layer from the interface with the base material to the surface of the Fe-based alloy is preferably 0.1 mm to 5 mm to prevent peeling of the Fe-based alloy from the base material and cracking of the Fe-based alloy itself. Here, the dilution layer refers to a layer that dissolves with the base material when the Fe-based alloy is molded, resulting in a mixture of the compositions of both the base material and the first layer of Fe-based alloy.

Next, the laser beam diameter is preferably about 3 mm at the irradiation position. The laser output is preferably 1500 to 2500 W. The laser scanning speed is preferably 200 to 2000 mm/min, and more preferably 500 to 1000 mm/min. The powder supply rate is preferably 10 to 20 g/min.

The energy density (heat source energy density: J/mm) input by laser irradiation to melt the raw material powder is preferably 90 to 300 J/mm, and more preferably 180 to 240 J/mm. If the energy density is too low, the defect rate will increase and the supplied powder will be difficult to melt, making it difficult to maintain the shape of the molded object. On the other hand, if the energy density is too high, the base plate or the molded object itself will melt over a wide area centered on the laser irradiation position, again making it difficult to maintain the shape of the molded object. Energy density E (J/mm) can be calculated using the laser output P (W) and laser scanning speed v (mm/min) as E = P/v x 60.

(Heat treatment)
The Fe-based alloy of this embodiment may be subjected to a quenching treatment after shaping to improve hardness, or, if costs and the like are within an acceptable range, an additional tempering treatment may be performed to remove quenching stress and improve toughness. Regarding heat treatment conditions, in the case of quenching, for example, the holding temperature may be 1000 to 1400°C, more preferably 1100 to 1300°C, and even more preferably 1150 to 1280°C. The holding time may be 0.1 to 5 hours, more preferably 0.1 to 2 hours. Cooling can be performed in oil or water, but cooling in oil is more preferable to prevent distortion and quench cracking. Quenching and cooling may also be performed using a salt bath.

When tempering, the material should be held at 400°C to 700°C, preferably 560°C to 580°C. The holding time should be 1 to 10 hours, more preferably 2 to 6 hours. Cooling is preferably by air cooling.

Carbide precipitates when carbon (C) dissolves or diffuses into the Fe-BCC phase and combines with carbide-forming elements such as Fe, W, Mo, and V. Therefore, by performing heat treatment that facilitates carbon dissolution and diffusion within the Fe-BCC phase, carbide precipitates within the Fe-BCC phase and is appropriately refined.

For example, quenching promotes the decomposition of carbides present in the formed body and facilitates the diffusion of carbon that bonds with carbide-forming elements such as Fe, W, Mo, and V into the Fe-BCC phase, making it easier for precipitated carbides to form. Therefore, alloys that have been quenched have a higher proportion of precipitated carbides than alloys that have not been quenched. It can also be assumed that the diffusion of carbon disperses the precipitated carbides, reducing the average circle-equivalent particle size of the precipitated carbides.

(Hardness)
The hardness of the surface layer of the Fe-based alloy or alloy member of this embodiment can be evaluated by Vickers hardness HV (hereinafter referred to as hardness), and is desirably 350 HV or more, preferably 500 HV or more. For example, the hardness can be measured by setting the indentation load of a Vickers indenter to 0.5 kg and the dwell time during indentation to 10 seconds, and determining the hardness from the length of the diagonal line of the indentation formed on the measurement surface by indentation of the indenter.

The method may further include a surface treatment process in which the obtained alloy component is subjected to a surface treatment. The surface treatment process may involve, for example, nitriding or forming a film on the surface layer of the Fe-based alloy using a PVD method, such as a nitride layer, a compound layer, or a ceramic coating layer. These surface treatment processes can form a coating on the surface layer of the Fe-based alloy that is harder than Fe-based alloys formed by additive manufacturing, thereby further strengthening the surface of the alloy component obtained by additive manufacturing and improving its wear resistance.

<Product>
The manufactured product having at least a part of the alloy member thus obtained is not particularly limited, but is particularly suitable for, for example, a hot stamping die, a cold forging die, and a cold pressing die. In this case, even if a part of the surface of the die is damaged, the damaged part can be easily repaired by forming an alloy layer of the present invention by buildup only on the damaged part. In this case, the die repaired with the Fe-based alloy according to this embodiment is less susceptible to cracking and has excellent toughness and heat crack resistance.

To obtain a shaped body with the desired composition, the raw materials for each element shown in Table 1 were weighed out in predetermined amounts, mixed, and loaded into a crucible. The raw materials were then melted using high-frequency induction in a vacuum, and the molten alloy was dropped from a nozzle below the crucible and sprayed with high-pressure argon to produce gas-atomized powder. This gas-atomized powder was then classified to obtain Fe-based alloy powder with a particle size of 53 to 106 μm. The composition of the resulting Fe-based alloy powder is shown in Table 1, and its particle size distribution in Table 2.

Next, using a directed energy deposition 3D additive manufacturing device (LASERTEC65 3D Hybrid manufactured by DMG Mori Seiki Co., Ltd.), raw material powder was supplied to a molten pool formed by laser irradiation on a base plate, where it was rapidly melted and rapidly solidified to produce a shaped object measuring 3 mm in width, 80 mm in length, and approximately 10 mm in height. The additive manufacturing conditions were as follows: Maraging steel (YAG300 manufactured by Proterial Co., Ltd. (YAG is a registered trademark of Proterial Co., Ltd.)) was used for the base plate.

・ Layer thickness when additive manufacturing: 0.47 mm
・Laser beam diameter: approx. 3 mm
Laser output: 2400W
Laser scanning speed: 600 mm/s
Energy density: 240 J/mm

The shaped bodies evaluated were those that had undergone heat treatment and those that had not. The shaped body that had undergone only quenching was designated F1, the shaped body that had undergone quenching and tempering was designated F2, the shaped body that had not undergone heat treatment was designated F3, and the shaped body that had undergone only tempering was designated F4. The quenching treatment involved holding the body at 1200°C for 0.5 hours, followed by cooling in oil. The tempering treatment involved holding the body at 560°C for 4 hours, followed by air cooling.

First, the molded bodies F1 and F2 were observed and evaluated using an SEM. Test specimens for evaluation were prepared by cutting a portion of the molded body into small pieces and embedding them in resin, then polishing the cut surface of the embedded molded body to a mirror finish. Observation was performed at a magnification of 3000x. Eight elements were analyzed: C, Co, Cr, Fe, Mo, V, W, and O.

Figures 2A to 2E show examples of acquired SEM images. Figure 2A is an SEM image of a shaped body F1 that underwent only quenching as a heat treatment, and Figure 2B is an SEM image of a shaped body F2 that underwent quenching and tempering. Figure 2C is an SEM image of a shaped body F3 that did not undergo heat treatment (no heat treatment), Figure 2D is an SEM image of a shaped body F4 that underwent only tempering, and Figure 2E is an SEM image of a forged material F0 (powder sintered, forged, and then heat-treated (quenching and tempering)) made using a conventional powder metallurgy method, which is an alloy of the same composition.

Referring to Figures 2A to 2E, the structure indicated by the gray shades can be seen. A phase map was obtained using the method described above, and elemental analysis was then performed within the field of view. Here, the area of the field of view (also referred to as the field of view area) was 200 μm x 200 μm.

Table 3 shows the compositions of the Fe-BCC phase and carbides of F2, which was quenched and tempered. The Fe-BCC phase was analyzed at the position A in FIG. 2B, and the precipitated carbides (sometimes simply referred to as carbides) were analyzed at the position B in FIG. 2B. Table 4 also shows the results of an analysis of the Fe-BCC phase of F3, which was not heat-treated (no heat treatment), at the position C in FIG. 2C.
For F0, the Fe-BCC phase was analyzed at the position D in FIG. 2E, and the carbides were analyzed at the position E in FIG. 2E. The results are shown in Table 5.

As shown in Table 3, for F2, both the Fe-BCC phase and the carbides contained primarily Fe. The C, Cr, W, Mo, V, and Co contents in the Fe-BCC phase were 5.0% C, 4.2% Cr, 1.8% W, 2.1% Mo, 1.1% V, 1.3% Co, and 84.5% Fe, with the C being within the ranges of 3%-7%, 2%-6%, W 0.5%-4%, Mo 0.5%-4%, V 0.5%-4%, and Fe 75%-90%. The carbides contained 8.9% C, 4.8% Cr, 2.5% W, 3.3% Mo, 2.5% V, and 78.1% Fe. Furthermore, the electron diffraction pattern generated upon electron beam irradiation was measured by EBSD, and it was found that the Fe-BCC phase had a BCC structure.

As shown in Table 4, for F3, the C, Cr, W, Mo, V, and Co contents in the Fe-BCC phase were 4.9% C, 4.2% Cr, 1.9% W, 2.2% Mo, 1.2% V, 1.3% Co, and 84.5% Fe, with C falling within the ranges of 3% to 7%, 2% to 6%, W 0.5% to 4%, Mo 0.5% to 4%, V 0.5% to 4%, and Fe 75% to 90%. Carbides could not be analyzed because the area they occupied was small and below the resolution of the analytical equipment. One of the reasons why carbides did not precipitate in F3 is thought to be that the absence of heat treatment made it difficult for carbides to be decomposed and for C to dissolve and diffuse into the Fe-BCC phase, resulting in a shortage of C to bond with carbide-forming elements such as Cr, W, Mo, and V, making it difficult for carbides to be formed.

Next, the circle-equivalent average particle size of precipitated carbides within the Fe-BCC phase was calculated. Table 6 shows the ratio of the Fe-BCC phase and precipitated carbides, as well as the circle-equivalent average particle size of precipitated carbides within the Fe-BCC phase, for F1 to F4 and F0.

As shown in Table 6, the proportion of the Fe-BCC phase was 96.0% or more for all of F1 to F4, 99.4% for F1, which was subjected to only quenching treatment, 99.5% for F2, which was subjected to both quenching and tempering treatment, 99.8% for F3, which was not subjected to quenching or tempering treatment (no heat treatment), and 99.9% for F4, which was subjected to only tempering treatment.

Furthermore, the proportion of precipitated carbides in the formed bodies F1 to F4 was 0.27% for F1 and 0.38% for F2, confirming that the precipitated carbides were moderately precipitated within the Fe-BCC phase. On the other hand, the proportions were 0.012% for F3 and 0.009% for F4, confirming that the proportion of precipitated carbides within the Fe-BCC phase was lower than that of F1 and F2.

The circle-equivalent average particle size of precipitated carbides was 1.08 μm for F1 and F2, confirming refinement. Furthermore, it was 0.58 μm for F3 and 0.50 μm for F4, confirming refinement of precipitated carbides for F3 and F4 as well.

The reason why the proportion of precipitated carbides in F1 and F2 is larger than that in F3 and F4 is presumably due to differences in the amount of precipitated carbides depending on whether or not heat treatment was performed. The absence of quenching in F3 and F4 likely makes it difficult for carbides to decompose, or for C to dissolve or diffuse into the Fe-BCC phase, resulting in a lack of C to bond with carbide-forming elements such as Cr, W, Mo, and V contained in the Fe-based alloy, making it difficult for carbides to form. Therefore, it is believed that the difficulty in forming carbides in F3 and F4 is the reason for the smaller proportion of precipitated carbides and the smaller average circle-equivalent particle size of precipitated carbides.

Furthermore, when comparing F0 with F1 and F2, F1 and F2, which were produced using additive manufacturing methods like those used in this example, have a faster cooling rate relative to the precipitation rate of precipitated carbides, because the alloy powder melts and then quickly cools and solidifies. This faster cooling rate shortens the holding time in the temperature range where precipitated carbides can form, which is thought to be one of the reasons why the amount of carbides formed inside the alloy (shaped body) before heat treatment is smaller than that of F0.

As described above, the circular equivalent average particle size of the precipitated carbides in the formed bodies F1 to F4 is small, and the fineness of the precipitated carbides makes them less susceptible to cracking, resulting in an Fe-based alloy with excellent toughness and heat crack resistance. Furthermore, the circular equivalent average particle size of the precipitated carbides in formed bodies F1 and F2 in particular is 1.08 μm, and the moderate fineness of the precipitated carbides makes them an Fe-based alloy with excellent wear resistance. Furthermore, while the proportion of the Fe-BCC phase in the forged material F0 is 95.7%, the proportion of the Fe-BCC phase in formed bodies F1 to F4 is over 99%, resulting in a more uniform structure. Therefore, for example, it can be expected that localized distortion due to external stress is less likely to occur, making them less susceptible to cracking.

[Hardness]
The hardness of the resulting molded body was measured using a Vickers hardness tester. Measurements were made at five points, and the average value was calculated. The results are shown in Table 7, and a comparison with the forged material is shown in Figure 3.

As shown in Table 7, the hardness of the shaped body F1, which was subjected to only quenching treatment, was 600 HV, and the hardness of the shaped body F2, which was subjected to quenching and tempering treatment, was 578 HV. The hardness of the shaped body F3, which was not subjected to heat treatment (no heat treatment), was 409 HV, and the hardness of the shaped body F4, which was subjected to only tempering treatment, was 408 HV. From this, it was confirmed that if it is desired to improve wear resistance, it is preferable to harden the shaped body, as with shaped bodies F1 and F2.

As mentioned above, the shaped body F1, which underwent only quenching, the shaped body F2, which underwent quenching and tempering, the shaped body F3, which was not heat-treated (no heat treatment), and the shaped body F4, which underwent only tempering, have a homogeneous structure due to the proportion of Fe-BCC phase of 99% or more, as shown in Table 6. Therefore, it can be expected that cracks will not occur because localized distortion due to external stress, for example, will not occur easily. Furthermore, as shown in Table 6, the shaped body F1, which underwent only quenching, and the shaped body F2, which underwent quenching and tempering, have a moderately fine circle-equivalent average particle size of 1.08 μm for precipitated carbides, which will be less likely to crack and will be expected to have excellent toughness, heat crack resistance, and wear resistance.

1...additive manufacturing apparatus 3...powder supply nozzle 5...focusing lens 7...protective lens 9...laser beam 11...alloy powder 13...molten pool 15...shaped body 17...base plate 50...Fe-BCC phase 52...fine precipitates

Claims (9)

including C, Cr, W, Mo and V;
In mass%,
C is 0.1% or more and 2% or less,
Cr is 2% or more and 6% or less,
W is 0.5% or more and 4% or less,
Mo is 0.5% or more and 4% or less,
V is 0.5% or more and 4% or less,
Si is 1.0% or less,
containing 1.0% or less of Mn, 4% or less of Co, and the balance being Fe and inevitable impurity elements;
having an alloy structure including an Fe-BCC phase,
The alloy has precipitated carbides precipitated in the Fe-BCC phase,
The precipitated carbides have an equivalent circle average particle size of 1.30 μm or less,
When the total area is the sum of the areas of the Fe-BCC phase, the Fe-FCC phase, and the zero solution portion,
The proportion of the precipitated carbides is 0.38% or less in terms of an area ratio obtained by dividing the area of the zero solution portion by the total area ,
The Fe-BCC phase accounts for 96% or more of the alloy structure in terms of area ratio. The Fe-based alloy according to claim 1, characterized in that the average circle-equivalent grain size of the precipitated carbides is 0.60 μm or more. An Fe-based alloy according to claim 1 or 2, characterized in that, by mass%, Si is 0.1% or more and 1.0% or less, and Mn is 0.1% or more and 1.0% or less. The Fe-based alloy according to claim 1, characterized in that the Co content is, by mass%, 0.5% to 4%. An alloy member characterized by comprising, at least in part, the Fe-based alloy described in claim 1. The alloy member according to claim 5, characterized in that the hardness of the Fe-based alloy is 350 HV or more. The alloy member according to claim 5 or 6, characterized in that the outermost layer of the Fe-based alloy is provided with one or more of a nitride layer, a compound layer, or a ceramic coating layer. A manufactured product comprising, at least in part, the alloy member described in claim 7. 9. The article of manufacture according to claim 8, which is a warm forging die, a die casting die, a hot stamping die, a cold forging die or a cold pressing die.