阅读说明：本技术 层叠造型物及其制造方法、以及层叠造型用金属粉末 (Layered structure, method for producing same, and metal powder for layered structure ) 是由 福泽范英 坂巻功一 中野洋佑 桑原孝介 福元志保 斉藤和也 于 2018-12-17 设计创作，主要内容包括：关于包含马氏体时效钢的层叠造型物,提供一种韧性优异的层叠造型物与其制造方法、以及层叠造型用金属粉末。一种层叠造型物,其为包含含有0.1质量％～5.0质量％的Ti的马氏体时效钢的层叠造型物,并且在对所述层叠造型物的与层叠方向平行的剖面的Ti浓度的分布进行面分析时,相对于所述剖面的平均Ti浓度A,具有(1.5×A)以上的Ti浓度B的线状Ti浓化部的长度为15μm以下。另外,为一种层叠造型物的制造方法,其使用包含含有0.1质量％～5.0质量％的Ti的马氏体时效钢的金属粉末,所述层叠造型物的制造方法中,将层叠造型时的热源输出设为50W～330W,将扫描速度设为480mm/秒～3000mm/秒。而且,为一种层叠造型用金属粉末,其包含含有0.1质量％～5.0质量％的Ti的马氏体时效钢,且中数直径D50为200μm以下。(A layered shaped article comprising a maraging steel, which comprises a maraging steel containing 0.1 to 5.0 mass% of Ti, and in which, when a distribution of Ti concentration in a cross section parallel to a stacking direction of the layered shaped article is subjected to surface analysis, a linear Ti concentration section having a Ti concentration B of not less than (1.5 × A) has a length of not more than 15 [ mu ] m relative to an average Ti concentration A of the cross section, and a method for producing a layered shaped article using a metal powder comprising a maraging steel containing 0.1 to 5.0 mass% of Ti, wherein a heat source output at the time of layer formation is 50 to 330W, a scanning speed is 480 to 3000 mm/sec, and a metal powder for layer formation comprising a maraging steel containing 0.1 to 5.0 mass% of Ti has a diameter of not more than 50 μm.)

1. A layered structure comprising a maraging steel containing 0.1 to 5.0 mass% of Ti, characterized in that:

when the distribution of Ti concentration in a cross section parallel to the stacking direction of the stacked shaped article is subjected to surface analysis, the length of a linear Ti concentrated portion having a Ti concentration B of not less than (1.5 × A) is not more than 15 [ mu ] m with respect to the average Ti concentration A in the cross section.

2. A laminated shaped article according to claim 1, characterized in that: the hardness is 40 HRC-60 HRC.

3. A laminated shaped article according to claim 1 or 2, characterized in that: the maraging steel has a Co content of 0 to 20 mass%.

4. A laminated shaped article according to claim 1 or 2, characterized in that: the maraging steel comprises, in mass%, C: 0.1% or less, Ni: 14% -22%, Co: 0% -20%, Mo: 0.1-15.0%, Ti: 0.1-5.0%, Al: 3.0% or less, and the balance of Fe and impurities.

5. A method for manufacturing a layered shaped article, which forms an article by a layered shaping step that repeats an operation of laying a metal powder containing maraging steel containing 0.1 to 5.0 mass% of Ti on a surface plate and an operation of scanning the metal powder laid on the surface plate with a heat source and irradiating the metal powder, characterized in that: the heat source output when the metal powder is irradiated while scanning the heat source is set to 50W to 330W, and the scanning speed is set to 480 mm/sec to 3000 mm/sec.

6. The method of manufacturing a laminated shaped article according to claim 5, characterized in that: the article formed in the lamination molding step is further subjected to a heat treatment step including a solutionizing treatment and an aging treatment.

7. The method of manufacturing a layered molding according to claim 5 or 6, characterized in that: the maraging steel has a Co content of 0 to 20 mass%.

8. The method of manufacturing a layered molding according to claim 5 or 6, characterized in that: the maraging steel comprises, in mass%, C: 0.1% or less, Ni: 14% -22%, Co: 0% -20%, Mo: 0.1-15.0%, Ti: 0.1-5.0%, Al: 3.0% or less, and the balance of Fe and impurities.

9. A metal powder for laminated molding, characterized in that: the maraging steel contains 0.1-5.0 mass% of Ti, and has a median diameter D50 of 200 [ mu ] m or less.

10. The metal powder for build-up molding according to claim 9, characterized in that: the maraging steel has a Co content of 0 to 20 mass%.

11. The metal powder for build-up molding according to claim 9, characterized in that: the maraging steel comprises, in mass%, C: 0.1% or less, Ni: 14% -22%, Co: 0% -20%, Mo: 0.1-15.0%, Ti: 0.1-5.0%, Al: 3.0% or less, and the balance of Fe and impurities.

Technical Field

The present invention relates to a layered shaped article that can be used for, for example, a die, a component for a die such as an ejector pin, other tool products, a structural component, and the like, and a method for manufacturing the same. The present invention also relates to a metal powder for build-up molding that can be used for producing these build-up molded articles.

Background

Recently, the stack molding method has attracted attention as a means for easily forming a metal product (part) having a complicated shape in a near net shape (near net shape). The stack modeling method is an additive manufacturing technique (also commonly referred to as 3D printing). Further, examples of the type of the layer-by-layer molding method include: a powder spraying method in which metal powder is laminated while being melted by irradiating a heat source; or a powder bed (powder bed) method in which metal powder spread on a surface plate (stage) is melted by irradiating it with a heat source and solidified, and the metal powder is stacked.

According to the stack molding method, since a metal product having a complicated shape can be produced by largely omitting a conventional machining step, a metal material having difficult workability can be used. In addition, since the metal material having difficult workability is mainly a high-strength metal material, a metal product having a complicated shape and a long durability and life can be produced.

As a high-strength metal material, maraging steel (marking steel) is known. The maraging steel is, for example, an age-hardening type super-strong steel in which an age-hardening element such as Co, Mo, Ti, Al, or the like is added to a steel containing about 18 mass% of Ni. Further, maraging steel is also excellent in toughness, and therefore, when it is used for materials for various tools or structural parts, it is effective for improving the life of these products. Further, a layered shaped article produced by the above-described layered shaping method using maraging steel as a metal material has been proposed (patent documents 1 and 2).

Disclosure of Invention

Problems to be solved by the invention

A laminated shaped article including maraging steel can cope with a complicated product shape, and high strength and excellent toughness can be expected. However, in the case of a steel formed by a laminate molding, a sufficient toughness to the extent of the composition of the maraging steel may not be achieved.

The invention aims to: a layered structure comprising maraging steel, which has excellent toughness, and a method for producing the same. Further, a metal powder for a layered molding which can be used for producing these layered moldings is provided.

Means for solving the problems

The present invention is a layered structure comprising a maraging steel containing 0.1 to 5.0 mass% of Ti, wherein, when a distribution of Ti concentration in a cross section parallel to a stacking direction of the layered structure is subjected to surface analysis, a linear Ti concentration section having a Ti concentration B of not less than (1.5 × A) is 15 [ mu ] m or less with respect to an average Ti concentration A in the cross section, and the layered structure can have a hardness of 40 to 60 HRC.

The present invention is a method for producing a layered shaped article, which forms an article by a layered shaping step that repeats an operation of laying a metal powder containing maraging steel containing 0.1 to 5.0 mass% of Ti on a surface plate and an operation of scanning the metal powder laid on the surface plate with a heat source and irradiating the metal powder, wherein a heat source output when the metal powder is scanned with the heat source and irradiated with the heat source is set to 50 to 330W, and a scanning speed is set to 480 to 3000 mm/sec.

Further, a method of manufacturing a layered structure may be provided as follows: the article formed in the lamination molding step is further subjected to a heat treatment step including a solutionizing treatment and an aging treatment.

The present invention also provides a metal powder for a laminated molding, which comprises a maraging steel containing 0.1 to 5.0 mass% of Ti, and has a median diameter (D50) of 200 [ mu ] m or less.

In the case of the present invention, the maraging steel preferably contains Co in an amount of 0 to 20 mass%. Further, the maraging steel contains, for example, C: 0.1% or less, Ni: 14% -22%, Co: 0% -20%, Mo: 0.1-15.0%, Ti: 0.1-5.0%, Al: 3.0% or less, and the balance of Fe and impurities.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, the toughness of a laminated shaped article comprising maraging steel can be improved.

Drawings

Fig. 1 is a diagram showing an element mapping image (a) of Ti and an image (b) obtained by binarizing the image (a) when a cross section parallel to the stacking direction of the layered shaped article of the present invention and the comparative example was analyzed by an Electron Probe MicroAnalyzer (EPMA).

Fig. 2 is a diagram showing an element map image (a) of Ti and an image (b) obtained by binarizing the image (a) when a cross section parallel to the stacking direction of a layered shaped article after the heat treatment step of the present invention example and the comparative example is analyzed by EPMA.

Fig. 3 is a diagram showing an element map image (a) of Ti and an image (b) obtained by binarizing the image (a) when a cross section parallel to the stacking direction of the layered shaped article after the heat treatment step of the present example is analyzed by EPMA.

Detailed Description

The present invention is characterized by the following aspects: it was found that the deterioration of the toughness of the laminated structure including the maraging steel is caused by the relationship between Ti in the component composition and a special manufacturing process of the laminated structure method. Hereinafter, the respective requirements of the present invention and preferred requirements thereof will be described together.

(1) The laminated shaped article of the present invention comprises maraging steel containing 0.1 to 5.0 mass% of Ti.

In maraging steel, Ti is Ni which forms a strengthening phase in the structure after aging treatment₃Imparting Ti to maraging steelElements of strength. However, if the Ti content is too large, significant Ti segregation occurs in the structure during solidification, and the significant Ti segregation remains in the structure after aging treatment, thereby deteriorating the toughness of the maraging steel. Therefore, in the present invention, the Ti content is set to 0.1 to 5.0 mass%. Preferably 0.5 mass% or more. More preferably 1.0 mass% or more. More preferably 1.5% by mass or more. Further, it is preferably 4.0 mass% or less. More preferably 3.0 mass% or less. More preferably 2.5 mass% or less.

(2) When the laminated structure of the present invention is subjected to surface analysis of the distribution of Ti concentration in a cross section parallel to the direction of lamination, the length of a linear Ti concentrated portion having a Ti concentration B of not less than (1.5 × A) is not more than 15 [ mu ] m relative to the average Ti concentration A in the cross section.

As described above, by setting the Ti content of the maraging steel to 5.0 mass% or less, Ti segregation in the structure can be reduced, and the toughness of the maraging steel can be ensured. However, in the case of a layered product, even if the Ti content of the maraging steel is suppressed to 5.0 mass% or less, sufficient toughness may not be achieved to the extent corresponding to the composition of the components in a particular production process of the layered product.

That is, even in the maraging steel of the present invention containing 0.1 to 5.0 mass% of Ti, Ti segregation may occur in a large amount in the structure at the time of solidification, and as a result, in the case of the maraging steel obtained by the layer-by-layer forming method, the solidified structure is easily formed by being elongated in the direction of lamination. Therefore, the maraging steel is likely to have a long shape along the stacking direction at the final solidification portion where the alloying element is concentrated, and the final solidification portion where the alloying element is concentrated is segregated in a "linear shape".

Then, the article of the maraging steel of the laminated shape is subjected to the heat treatment process, i.e., the solutionizing treatment and the aging treatment, to form Ni from Ti in the structure₃As a result, Ni is formed more in the Ti-enriched segregation portion than in other portions₃And (3) Ti. And, due to the formation of Ni in large amounts₃Ti is also "linear" in shape and is therefore considered to bePromoting crack propagation during use. As a result, in the case of a laminated structure including maraging steel, it is considered that, since Ti is contained, toughness is likely to deteriorate particularly in a direction orthogonal to the laminating direction (for example, a scanning direction of a heat source).

Therefore, in order to improve the toughness of a layered structure made of maraging steel containing Ti, it is effective to reduce the linear Ti segregation. Furthermore, it is effective to reduce the amount of linear Ni after the solution treatment and the aging treatment, which are the heat treatment steps₃And (3) Ti. That is, before the heat treatment step, the "length" of linear Ti segregation distributed in a cross section parallel to the stacking direction of the stacked shaped article is reduced (the Ti concentration in the cross section is equalized). Further, after the heat treatment step, the linear Ni distributed in the cross section parallel to the stacking direction of the stacked shaped article is reduced₃"length" of Ti (let Ni be)₃In the present invention, when the distribution of Ti concentration in a cross section parallel to the stacking direction of the stacked shaped article is subjected to surface analysis before or after the heat treatment step, the length of a linear Ti-concentrated portion having a Ti concentration B of not less than (1.5 × a) is not more than 15 μm with respect to the average Ti concentration a in the cross section, and is preferably less than 10 μm.

The "linear Ti-concentrated portion" refers to a continuous, elongated Ti-concentrated portion. In addition, when the elongated shape of the Ti concentrated portion is a straight line or a curved line, the "linear Ti concentrated portion" can be confirmed, for example, as follows: the "length of the Ti-concentrated portion" which is the length of the straight line or the curved line is a length of about 3 times or more the maximum width of the straight line or the curved line in the direction perpendicular to the longitudinal direction. The "length of the linear Ti-concentrated portion is 15 μm or less" means that the length of the continuous and elongated Ti-concentrated portion is limited to 15 μm or less. The above case also includes the case where the length is "0 μm" (that is, the case where there is no continuous and elongated Ti concentrated portion itself).

On the other hand, in the cross section parallel to the stacking direction of the layered shaped article of the present invention, there may be a point-like Ti-concentrated portion instead of the linear portion. The dot-shaped Ti concentrated portions may be Ti concentrated portions other than the "linear Ti concentrated portions". The dot-shaped Ti-concentrated portion is not likely to be a path for promoting the propagation of the crack regardless of the size because of its substantially isotropic shape, and therefore the degree of influence of deterioration of the toughness of the layered molded article is small.

In the case of the "plane analysis" of the Ti concentration distribution in the cross section for measuring the "length of the linear Ti concentration portion", for example, an EPMA (electron beam microanalyzer) may be used to first take a cross section of the layered shaped object parallel to the stacking direction from the position of the central portion of the layered shaped object, and in this case, the cross section may be confirmed to be the "cross section parallel to the stacking direction" from the specification of the layered shaped object or the stacking trace in the layered shaped object, and the EPMA analysis may be performed on a region 800 μm in length × in width 800 μm with a magnification of 100 times at positions (positions totaling 160000 points) at equal intervals with 400 points in length and width, respectively, with respect to the cross section, whereby the average Ti concentration a of the cross section may be obtained, and an element map image (fig. 1(a)) showing the distribution state of the Ti concentration portion having a Ti concentration B of not less than (1. 1.5 × a) with respect to the average Ti concentration a may be obtained, and in this case, the critical value of the Ti concentration B may be clearly processed as a threshold value of the "linear Ti concentration B" (fig. may be clearly confirmed by the EPMA analysis).

In the binarized image, the Ti concentration portion is represented by a set of pixels (black dot group) at each analysis position, and as a result, the "linear" state can be confirmed by "adjoining" each pixel in a vertical, horizontal, or oblique manner.

When the "linear Ti concentrated parts" of the present invention are confirmed in one or more than two regions extending 800 μm in the vertical direction of 800 μm ×, the phrase "the length of the linear Ti concentrated parts is 15 μm or less" in the present invention may mean that "the linear Ti concentrated parts having a length of more than 15 μm are smaller than 1.0 piece per region extending 800 μm in the vertical direction of 800 μm ×".

(3) The laminated structure of the present invention is preferably maraging steel containing Co in an amount of 0 to 20 mass%.

In maraging steel, Co is an element having an effect of improving the strength and toughness of the product. In this respect, the layered structure of the present invention may contain Co as an optional element. Preferably 0.1 mass% or more. More preferably 0.2 mass% or more. More preferably 0.3% by mass or more.

On the other hand, Co is an expensive element. If the amount is too large, the element deteriorates toughness as the hardness of the layered structure increases. Therefore, even when Co is contained, the upper limit is preferably set to 20 mass%. Further, as described above, the layered structure of the present invention has improved toughness by suppressing the linear Ti-enriched portion in the structure. Therefore, in the present invention, the content of Co, which is an element for improving toughness, can be limited to be low in the above-described aspect. Preferably, the content is limited to 15 mass% or less. More preferably, it is limited to 10% by mass or less, and still more preferably, it is limited to 5% by mass or less.

(4) The layered shaped article of the present invention preferably contains C: 0.1% or less, Ni: 14% -22%, Co: 0% -20%, Mo: 0.1-15.0%, Ti: 0.1-5.0%, Al: 3.0% or less, and the balance of Fe and impurities.

C: 0.1% by mass or less

C is generally an element limited to obtain a high-toughness low-carbon martensite (martensite) structure, which is a characteristic of maraging steel. Therefore, in the present invention, C is preferably limited to 0.1 mass% or less. More preferably, the content is limited to 0.08% by mass or less, and still more preferably, 0.05% by mass or less.

Ni: 14 to 22 mass%

Ni is a basic element necessary for forming an intermetallic compound with Ti, Mo, or the like to contribute to strength improvement and achieve maraging steel. Therefore, the Ni content is preferably 14 mass% or more. More preferably 15% by mass or more, and still more preferably 16% by mass or more.

However, if Ni is too large, the austenite (austenite) structure is stabilized, and the martensite structure is hardly formed. Therefore, the Ni content is preferably 22 mass% or less. More preferably 20% by mass or less, and still more preferably 19% by mass or less.

Mo: 0.1 to 15.0 mass%

Mo is an element having the following effects: ni as an intermetallic compound is formed during aging treatment₃Mo enhances the strength of the maraging steel by precipitation strengthening or solution strengthening the metal structure. Therefore, the content of Mo is preferably 0.1 mass% or more. More preferably 0.5% by mass or more, and still more preferably 1.0% by mass or more.

However, if Mo is too large, a coarse intermetallic compound is formed with Fe, and the toughness of the maraging steel is lowered. Therefore, the content of Mo is preferably 15.0 mass% or less. More preferably 10.0% by mass or less, and still more preferably 5.0% by mass or less.

Al: 3.0 mass% or less

Al is an element that can be used as a deoxidizer in the melting process of a maraging steel material. Further, when Al in the maraging steel after melting is too large, non-metallic inclusions in the metal structure increase, and the toughness of the maraging steel decreases. Therefore, the content of Al is preferably 3.0 mass% or less. More preferably 1.0% by mass or less, and still more preferably 0.5% by mass or less.

Further, when Al is contained in the maraging steel, Al and Ni form an intermetallic compound, and the metal structure is precipitation-strengthened. Therefore, when Al is contained, the content of Al may be 0.01 mass% or more. More preferably 0.03 mass% or more, and still more preferably 0.05 mass% or more.

In the maraging steel of the present invention, a composition that selectively contains the element species and contains Fe and impurities in the remainder may be a basic composition.

(5) The layered shaped article of the present invention can be produced, for example, by a method for producing a layered shaped article by a layered shaping step of repeating an operation of spreading a metal powder containing maraging steel containing 0.1 to 5.0 mass% of Ti on a surface plate and an operation of scanning the metal powder spread on the surface plate with a heat source and irradiating the metal powder, wherein the heat source output when the metal powder is scanned with the heat source and irradiated is set to 50 to 330W, and the scanning speed is set to 480 to 3000 mm/sec.

The method for producing a layered shaped article is based on, in particular, a previously known powder bed method. For example, the method of forming an article includes a lamination molding step of repeatedly performing an operation of locally melting and solidifying a predetermined metal powder by applying the metal powder spread on a surface plate and scanning the metal powder spread on the surface plate with a heat source while irradiating the metal powder, and the lamination molding step is performed above the heat source in a scanning direction. The heat source may utilize, for example, a laser or an electron beam.

Further, by using a metal powder containing maraging steel containing 0.1 to 5.0 mass% of Ti as the predetermined metal powder and adjusting the conditions at the time of irradiation of the heat source to the following specific conditions, it is possible to suppress linear Ti concentrated portions (Ti segregation) in the formed article and improve the toughness of the layered shaped article.

First, if the output of the heat source is too high, the molten portion of the metal in the process of irradiating the heat source becomes deep, and strong segregation occurs during solidification, and as a result, a long "linear Ti-concentrated portion" is easily formed. However, if the output of the heat source is too low, the metal powder cannot be sufficiently melted, and many voids due to gaps in the metal powder are formed in the solidified shaped object. Therefore, the output of the heat source is preferably 50 to 330W. More preferably 100W or more. More preferably 150W or more, still more preferably 200W or more, and particularly preferably 250W or more.

Next, if the scanning speed of the heat source is too high, the metal powder does not obtain sufficient heat, and therefore the metal powder is not sufficiently melted, and as a result, many of the above-described voids are easily formed in the solidified molded article. However, if the scanning speed of the heat source is too slow, the molten portion of the metal in the process of irradiating the heat source becomes deep, and as a result, a long "linear Ti-concentrated portion" is easily formed. If the scanning speed of the heat source is too slow, excessive heat is applied to the metal powder, the flow of molten metal becomes vigorous, and air is entrained into the molten metal, so that air bubbles are likely to be mixed into the solidified shaped article. Therefore, the scanning speed is preferably 480 mm/sec to 3000 mm/sec. More preferably 500 mm/sec or more. More preferably 800 mm/sec or more. Further, it is more preferably 2000 mm/sec or less. More preferably 1500 mm/sec or less.

In the method of manufacturing a layered structure, the scanning pitch may be set to 0.02mm to 0.20 mm. The scan pitch is a distance (distance between the center positions of light beams) between adjacent light beam irradiation positions with respect to a heat source for scanning. If the scanning pitch is too large, it becomes difficult to melt the metal powder spread over the entire surface when the heat source is irradiated, and this may cause formation of voids in the solidified shaped object. When the scanning pitch is excessively reduced, the molten portion of the metal in the process of irradiating the heat source is deepened, and a long "linear Ti-concentrated portion" is easily formed. Therefore, the scanning pitch is preferably set to 0.02mm to 0.20 mm. More preferably 0.05mm or more. Further, it is more preferably 0.15mm or less.

Further, if the lamination thickness per scan is too large, heat is not easily conducted to the entire metal powder spread when the heat source is irradiated, and the metal powder is not sufficiently melted. The "thickness of the stack per scan" means "the thickness of each metal powder layer" which is fully spread in the stack molding. If the lamination thickness per scan is too small, the number of laminations until the predetermined size of the laminated shaped object is obtained increases, and the time required for the lamination shaping step increases. Therefore, the thickness of the laminate layer for each scan is preferably 10 μm to 200 μm. More preferably 20 μm or more. More preferably 30 μm or more. Further, it is more preferably 100 μm or less. More preferably 80 μm or less, and still more preferably 60 μm or less.

The atmosphere in the lamination molding step may be, for example, an inert atmosphere such as argon or nitrogen. In addition, the atmosphere may be reduced in pressure (including vacuum). In particular, when the heat source uses an electron beam, it is preferable that the atmosphere during molding is a reduced pressure atmosphere (including vacuum).

The layered structure of the present invention can be produced, for example, by a method for producing a layered structure, the method comprising: a step of spreading metal powder of maraging steel having a median diameter D50 (50% particle diameter of cumulative particle size distribution on a volume basis) of 200 [ mu ] m or less and containing 0.1 to 5.0 mass% of Ti in a layered manner; and a step of forming a solidified layer by successively melting and solidifying the spread metal powder by a scanning heat source, wherein the step of spreading the metal powder in layers and the step of forming the solidified layer are repeated to form a plurality of layer-shaped solidified layers.

It is preferable that the metal powder is uniformly spread by setting D50 of the metal powder to 200 μm or less. More preferably 100 μm or less, still more preferably 75 μm or less, and still more preferably 50 μm or less. The lower limit is preferably 10 μm, for example, in terms of the difficulty in scattering the metal powder during irradiation of the scanning heat source. More preferably 20 μm.

The scanning heat source may still utilize a laser or electron beam. Further, it is preferable that the diameter of the scanning heat source is larger than the diameter of D50 of the metal powder, so that the collection of the metal powder can be melted uniformly. In this case, the diameter of the scanning heat source may be specified by, for example, the width of the focal point of the heat source.

(6) Preferably, the article formed in the lamination molding step is further subjected to a heat treatment step including a solutionizing treatment and an aging treatment.

Maraging steel is generally used as a product after being subjected to solutionizing treatment and aging treatment. By performing the solutionizing treatment, high toughness due to the low-carbon martensite structure can be obtained. Further, by performing the aging treatment after that, various intermetallic compounds can be precipitated in the structure, and for example, the hardness can be adjusted to 40HRC to 60HRC, and more excellent high strength and high toughness can be obtained. Preferably 42HRC or higher. Further, it is preferably 55HRC or less, more preferably 50HRC or less, and further preferably 48HRC or less. In the case of the laminated shaped article including maraging steel of the present invention, the solution treatment is more preferable for eliminating the Ti concentrated portion (Ti segregation) formed in the structure in the lamination shaping step.

The solution treatment temperature is preferably 800 ℃ or higher. More preferably 830 ℃ or higher. Further, it is preferably 900 ℃ or higher, more preferably 950 ℃ or higher, and particularly preferably 1000 ℃ or higher. By increasing the solution treatment temperature, the effect of eliminating Ti segregation is improved. However, if the solution treatment temperature is too high, the prior austenite grains are coarsened, and thus the strength and toughness of the layered structure are reduced. Therefore, the solution treatment temperature is preferably 1200 ℃ or lower. More preferably 1100 ℃ or lower, and still more preferably 1050 ℃ or lower.

The solution treatment time (holding time at the solution treatment temperature) is preferably 10 minutes or more. More preferably 30 minutes or longer, and still more preferably 45 minutes or longer. By prolonging the solution treatment time, the effect of eliminating Ti segregation is improved. However, if the solution treatment time is too long, the prior austenite grain size becomes coarse. Therefore, the solution treatment time is preferably 120 minutes or less. More preferably 100 minutes or less, and still more preferably 80 minutes or less.

The aging treatment temperature is preferably 400 ℃ or higher. More preferably 450 ℃ or higher, still more preferably 500 ℃ or higher, and still more preferably 550 ℃ or higher. By increasing the ageing temperature, Ni₃The strength-improving effect by Ti precipitation is improved. However, if the aging treatment temperature is too high, the intermetallic compound is coarsened, and the strength corresponding to the precipitation amount of the intermetallic compound is not sufficiently obtained. Therefore, the aging treatment temperature is preferably 700 ℃ or lower. More preferably 650 ℃ or lower, still more preferably 640 ℃ or lower, and still more preferably 630 ℃ or lower. The temperature may be 600 ℃ or lower.

The aging treatment time (the maintaining time at the aging treatment temperature) is preferably 60 minutes or more. More preferably 100 minutes or longer, and still more preferably 150 minutes or longer. By extending the aging treatment time, the amount of intermetallic compound formed increases. However, if the aging treatment time is too long, the intermetallic compound becomes coarse, and the strength is lowered. Therefore, the aging treatment time is preferably 600 minutes or less. More preferably 400 minutes or less, and still more preferably 200 minutes or less.