DE102016202885B4 - Selective laser sintering process - Google Patents

Abstract

A selective laser sintering method, comprising: alternately repeating a step of building up metal powder in layers, the metal powder made of a silicon-rich stainless steel containing C: less than 0.020, Si: 3.0 - 5.0, Mn: 0.5 - 1.5 , Cu: 0.8 - 1.2, Ni: 6.0 - 7.0, Cr: 10.0 - 13.0, Mo: 0.3 - 1.0, Nb: 0.30 - 1.00 in weight percent, and a balance of Fe and inevitable impurities, and a step of selectively applying a laser to the metal powder built up in layers to melt and sinter the metal powder,wherein the energy density E is calculated by the following formula 36 to 124 [J/ mm3] is E=P/v×s×t, where P is the power of the laser, v is the scanning speed of the laser, s is the scanning feed of the laser, and t is the lamination thickness of the layer of metal powder, where the particle size of the metal powder is 32 to 62 microns and wherein the method further comprises a heat treatment process having an S a step of performing a solution treatment at 1050°C for 20 minutes on a molded product molded by the selective laser sintering method and then water cooling, and a step of performing an aging treatment at 480°C for 7 hours on the molded product after the solution treatment and then air cooling.

Description

Technical area

The present invention relates to a laser sintering method that sinter a metal powder with a laser and laminates it to build a desired three-dimensional shape.

Description of the prior art

Metal powder additive manufacturing or generative manufacturing with metal powder or metal powder 3D printing is a 3D molding that does not require any casting mold, and it has been noticed as a type of rapid prototyping (RP) that quickly takes a prototype Using 3D CAD data. Recently, with the progress made in 3D printing technology, there have been factors such as an increase in the accuracy of products, an increase in the speed of manufacture, and an increase in the types of materials, and this manufacturing process is now called additive manufacturing (AM), that is is not limited to manufacturing prototypes and that can directly manufacture end products. The applications to which this method can be applied have become diverse, and it can be applied not only to molds and machine parts, but also to custom medical parts such as artificial joints and artificial crowns.

Because powder metal additive manufacturing is additive manufacturing that attaches material to a required part, it is possible to manufacture parts that have shapes that could not be made by the existing processing methods (forging, casting, cutting, etc.) such as an injection mold where any cooling channel suitable for a product shape is placed within the mold, and an aircraft component such as a fuel injector of a jet engine having a complex shape.

For example, the JP 2002 - 66 844 A a metal powder additive manufacturing that generates a variety of disk data from 3D data of an object to be processed and applies a laser beam to a copper-nickel alloy powder based on the plurality of disk data to thereby sinter and laminate each layer .

However, due to equipment manufacturer restrictions, there are few grades of material that can be molded by this process, which hinders the expansion of the applications to which this process can be applied.

the DE 100 39 143 C1 discloses a method for producing precise components by laser sintering a powder material which consists of a mixture of at least two powder elements and is characterized in that the powder mixture is formed by the main constituent iron powder and further powder alloy elements which are in elemental, pre-alloyed or partially pre-alloyed form, and that a powder alloy is created from these powder elements in the course of the laser sintering process. The following powder alloy elements are added to the iron powder, each individually or in any combination: carbon, silicon, copper, tin, nickel, molybdenum, manganese, chromium, cobalt, tungsten, vanadium, titanium, phosphorus, boron. which are used individually or in any combination, subjected to: homogenization, stress-relieving annealing, heat treatment, removal of internal imperfections and improvement of the surface quality.

From the DE 602 13 779 T2 an iron-based material for coating surfaces as well as products coated therewith is known, which comprises a bonding phase made of a corrosion-proof alloy containing at least 50% Fe, 12-30% Cr, 0-40% Ni, 0-7% Mo, 0- Contains 1% N and 6-20% Si and a maximum of 5% Mn, with all specified% being percent by weight, which Si addition the liquidus temperature, i.e. the temperature at which the bonding phase is completely melted, to a value below 1250 ° C and the material also includes hard particles based on oxides, nitrides, carbides, borides, and / or mixtures of these.

the DE 100 39 144 C1 shows a method for producing precise components by laser sintering a powder material which consists of a mixture of at least two powder elements and is characterized in that the powder mixture is formed by the main component iron powder and further powder alloy elements which are in elemental, pre-alloyed or partially pre-alloyed form, and that a powder alloy is created from these powder elements during the laser sintering process. It the following powder alloy elements are added to the iron powder, each individually or in any combination: carbon, silicon, copper, tin, nickel, molybdenum, manganese, chromium, cobalt, tungsten, vanadium, titanium, phosphorus, boron.

From the US 8 590 157 B2 a selective laser sintering process is known in which different energy densities are taken into account depending on the powder material selected.

the EP 1 352 980 A1 discloses a silicon-rich stainless steel with very good corrosion resistance with its special composition.

In view of the foregoing, it is an object of the present invention to provide a selective laser sintering process using a new type of steel.

Summary of the invention

According to a first aspect of the present invention there is provided a selective laser sintering method comprising a step of building metal powder in layers, the metal powder made of a silicon-rich stainless steel containing C: less than 0.020, Si: 3.0-5.0, Mn: 0.5 - 1.5, Cu: 0.8 - 1.2, Ni: 6.0 - 7.0, Cr: 10.0 - 13.0, Mo: 0.3 - 1.0, Nb: 0.30-1.00 in weight percent, and a balance of Fe and inevitable impurities, and a step of selectively applying a laser to the layered metal powder to melt and sinter the metal powder, alternately repeated with the energy density E. 36 to 124 [J / mm ³ ].

A particle size of the metal powder is 32 to 62 micrometers.
An energy density E is 50 to 124 [J / mm ³ ].
An energy density E is 50 to 118 [J / mm ³ ].

There is also provided a heat treatment method comprising a step of performing solution treatment on a molded product formed by the selective laser sintering method according to any one of claims 1 to 3, and a step of performing aging treatment on the molded product after the solution treatment.

According to a second aspect, there is provided a metal powder used in a selective laser sintering process that selectively applies a laser to metal powder to melt and sinter the metal powder for lamination, the metal powder being made of a silicon-rich stainless steel, containing C: less than 0.020, Si: 3.0-5.0, Mn: 0.5-1.5, Cu: 0.8-1.2, Ni: 0.8-1.2, Cr: 10 , 0 - 13.0, Mo: 0.3 - 1.0, Nb:
0.30 - 1.00 in percent by weight, and a remainder of Fe and inevitable impurities.

The particle size of the metal powder is 32 to 62 micrometers.

There is provided a molded product formed by the laser sintering method described above.

There is provided a molded product heat-treated by the heat treatment method described above.

According to the invention, a selective laser sintering process using a new type of steel is provided.

The above and other objects, features and advantages of the present invention will be more fully understood from the following detailed description and accompanying drawings, which are used for the purpose of illustration only and are therefore not to be considered as limiting the present invention.

Figure list

• 1 shows photographs of silicon alloy A2 powder.
• 2 shows a photograph of a specimen.
• 3 FIG. 13 is a graph showing a relationship between an energy density E and a relative density D. FIG.
• 4th FIG. 13 is a graph showing a relationship between a laser scanning speed v and a relative density D. FIG.
• 5 FIG. 13 is a graph showing a relationship between an energy density E and a relative density D. FIG.
• 6th FIG. 13 is a graph showing a relationship between a scan feed rate s and a relative density D. FIG.
• 7th shows photographs of the longitudinal profile of a molded product after molding.
• 8th shows photographs of the longitudinal profile of a sample after the solution treatment.
• 9 shows photographs of the longitudinal profile of a sample after the curing treatment.
• 10 Fig. 13 is a bar graph showing test results of a hardness test.
• 11th Fig. 13 is a view showing the size and shape of a tensile test specimen.
• 12th Figure 12 shows a photograph of a sample from a tensile stress test.
• 13th Fig. 13 is a bar graph showing test results of a tensile stress test.
• 14th Fig. 13 is a flow chart of a selective laser sintering process and a flow chart of a heat treatment process.

Detailed description

1. Type of steel

The applicant of the present invention has made a detailed study as to whether precipitation hardening stainless steel, which contains high levels of Si and extremely little C, can be used as a steel grade of metal powder to be used in a selective laser sintering process, and reports the test results in this specification . In the following, precipitation hardening stainless steel is referred to as “silicon alloy steel”. There are a variety of component specifications of silicon alloy steel, and silicon alloy steel A2 shown in Table 1 is selected in this forming test. Further, the silicon alloy steel A2 powder is simply called “silicon alloy A2 powder”. In the following Table 1, the components of silicon alloy steel and silicon alloy steel A2 are shown in comparison with the component specification of typical SUS630. Note that silicon alloy steel A2 is a region where three phases that are ferrite, austenite and martensite coexist. Table 1 C. Si Mn Cu Ni Cr Mo Nb Fe Silicon alloy steel <0.10 2.0∼9.0 0.05∼6.0 0.5∼4.0 1.0∼24.0 6.0∼28.0 0.2∼4.0 0.03∼2.0 rest Silicon alloy steel A2 <0.020 3.0-5.0 0.5-1.5 0.8∼1.2 6.0∼7.0 10.0∼13.0 0.3∼1.0 0.30∼1.00 rest SUS630 <0.07 <1.0 <1.0 3.00∼5.00 3.00∼5.00 15.00∼17.00 - 0.15∼0.45 rest

More specifically, silicon alloy steel is high silicon stainless steel containing C: less than 0.10, Si: 2.0-9.0, Mn: 0.05-6.0, Cu: 0.5-4.0, Ni: 1.0-24.0, Cr: 6.0-28.0, Mo: 0.2- 4.0, Nb: 0.03∼2.0 in percent by weight, and a remainder of Fe and inevitable impurities.

Furthermore, silicon alloy steel A2 is a stainless steel with a high silicon content, containing C: less than 0.20, Si: 3.0∼5.0, Mn: 0.05∼61.5, Cu: 0.8∼1.2, Ni: 6.0∼7.0, Cr: 10.0∼13.0, Mo: 0.3 ∼1.0, Nb: 0.03∼1.00 in percent by weight, and a remainder of Fe and inevitable impurities.

C is an element that increases the strength of steel and it is essential for typical high strength steel to contain a certain amount of C. However, it is not essential for silicon alloy steel, which contains a large amount of Si, to contain C because its strength is ensured by a special metal structure produced by Si. Instead, C is an element that lowers the toughness of silicon alloy steel and adversely affects oxidation resistance and corrosion resistance. Therefore, the content of C in silicon alloy steel is preferably as low as possible. The tolerable upper limit of the content of C in silicon alloy steel is 0.10%, and it is more preferably 0.05% or less. Further, the content of C in silicon alloy steel A2 is less than 0.020%.

Not only is Si the primary element that gives steel its strength, but it also gives it heat resistance, oxidation resistance, corrosion resistance, and softening resistance. Furthermore, Si is an element that lowers the melting point of steel in order to increase the flowability and improve its castability. If the content of Si is less than 2.0%, the improvements in the above properties are insufficient. On the other hand, since Si is a highly distant forming element, if the content thereof exceeds 9.0%, it is necessary to increase the amount of Ni or the like added in order to prevent the ferrite phase from becoming too excessive in the steel structure, which is shown in FIG high material costs would result. Therefore, the tolerable content of Si in the silicon alloy steel is 2.0% to 9.0%, and further, the tolerable content of Si in silicon alloy steel A2 is 3.0% to 5.0%.

Mn works as a deoxidizer of steel and it is also an austenite-forming element. Although Mn does not greatly affect the mechanical properties of silicon alloy steel, an Mn content of 0.05% or more is required because it contributes to densification and stabilization of the metal structure. On the other hand, if the Mn content exceeds 6.0%, the corrosion resistance lowers. Therefore, the tolerable content of Mn in silicon alloy steel is 0.05% to 6.0%, and further, the tolerable content of Mn in silicon alloy steel A2 is 0.5% to 1.5%.

Cu is a component to be added to silicon alloy steel as needed. Cu is an element that contributes to improving the corrosion resistance (especially acid resistance) and precipitation hardening of silicon alloy steel. Furthermore, Cu is an austenite-forming element and contributes to the adjustment of the balance of the metal structure. In order to achieve these effects, the content of Cu is preferably 0.5% or more. However, because the Cu content exceeding 4.0% causes a decrease in the heat ductility of steel, the upper limit of the Cu content when added to the silicon alloy steel is 4.0%. Therefore, the tolerable content of Cu in silicon alloy steel is 0.5% to 4.0%. It is more preferably 2.0% or less. Furthermore, the tolerable content of Cu in silicon alloy steel A2 is 0.8% to 1.2%.

Ni is an element that imparts corrosion resistance (particularly acid resistance), oxidation resistance and heat resistance to steel, and it is essential to substantially keep the duplex metal structure of steel in good balance with Cr, which will be described next. In order to obtain these effects, a Ni content of 1.0% or more is required. On the other hand, if the Ni content exceeds 24%, the austenite phase increases excessively, which causes the loss of not only the characteristics of the duplex stainless steel but also lowers the cost efficiency of steel. Therefore, the tolerable content of Ni in silicon alloy steel is 1.0% to 24.0%. Further, the tolerable content of Ni in silicon alloy steel A2 is 6.0% to 7.0%.

Cr is a component that ensures the basic characteristics of stainless steel, which are corrosion resistance (especially acid resistance), heat resistance, and oxidation resistance. These properties are insufficient if the Cr content is 6.0% or less. On the other hand, if the Cr content is more than 28%, the amount of Ni required to maintain the essential duplex metal structure of steel increases, so that the cost-effectiveness of steel is decreased. Therefore, the tolerable content of Cr in silicon alloy steel is 6.0% to 28%. Further, the tolerable content of Cr in silicon alloy steel A2 is 10.0% to 13.0%.

Mo increases corrosion resistance (acid resistance) and high temperature strength to improve creep resistance, and also contributes to increases in toughness and wear resistance of silicon alloy steel. These effects are not sufficient if the Mo content is 0.2% or less. Since Mo is a ferrite-forming element, if its content in silicon alloy steel becomes higher, the amount of an austenite-forming element (Ni, Cu, Mn) added thereto must be increased. Furthermore, Mo is an expensive element. With all these factors in mind, the tolerable level is Mo in silicon alloy steel 0.2% to 4.0%. Further, the tolerable content of Mo in silicon alloy steel A2 is 0.3% to 1.0%.

Nb is an element effective for increasing the hardening depth in the age hardening treatment without lowering the toughness of silicon alloy steel. Furthermore, Nb improves the intergranular corrosion resistance and weldability, and also improves the strength of the silicon alloy steel. These effects are significant when the Nb content is 0.03% or more. On the other hand, if the Nb content is more than 2.0%, the heat ductility of silicon alloy steel is lowered and the toughness is lowered. Therefore, the tolerable content of Nb in silicon alloy steel is 0.03% to 2.0%, and more preferably 0.1% to 2.0%. Further, the tolerable content of Nb in silicon alloy steel A2 is 0.30% to 1.00%.

Silicon alloy steel including silicon alloy steel A2 contains the remainder of iron (Fe) and inevitable impurities in addition to the components described above. Note that it is preferable that the content of each of P and S which are impurities is 0.04% or less.

According to Table 1 described above, silicon alloy steel A2 has higher contents of Si, Ni, Mo and Nb and lower contents of Cu and Cr, respectively, compared to SUS630.

2. Silicon alloy A2 powder

For example, silicon alloy A2 powder can be produced by gas atomization. Gas atomization is a process by which an alloy composed of desired components is dissolved and then the molten metal flows out of a nozzle bore at the bottom of a tundish to create a thin flow of the molten metal. Then, a jet flow of an inert gas such as argon is sprayed against the flow of the molten metal to gradually convert the flow of molten metal into a powder form by the energy of the jet flow, and a generated droplet is solidified when it drips to thereby Generate alloy powder. 1 Fig. 10 shows photographs of silicon alloy A2 powder produced by the gas atomization. In this shaping test, the silicon alloy A2 powder is classified so that the particles vary in size between 32 and 62 micrometers (sieving method).

3. Selective laser sintering system

A selective laser sintering system that is used in this shaping test is EOSINT-M280 from EOS GmbH. The specifications of this selective laser sintering system are shown in Table 2 below. Table 2: Laser power P 250-350W Laser scanning speed v 400∼1600mm / s Scanning feed s 0.06 ~ 0. 16mm Lamination thickness t 50 microns Laser diameter 100 microns

The energy density E of the laser sintering system is defined by the following equation (1):
Equation 1: $$\mathrm{E.}=\frac{\mathrm{P.}}{v\times s\times t}$$

4. Shaping test

In this molding test, the following four kinds of tests were carried out to determine whether silicon alloy A2 powder can be used as the steel type of metal powder to be used in the selective laser sintering method.

(1) Energy density test

A change in the specific gravity of a sample when the energy density E was varied was examined. To be specific, the laser scanning speed v was varied to increase and decrease the energy density E, and then the scan feed rate s was varied to increase and decrease the energy density E.

(2) Structure observation test

The structure along the longitudinal profile of a sample before and after the solution treatment and aging treatment was observed.

(3) endurance test

The hardness of a sample before and after the solution treatment and aging treatment was examined.

(4) tensile stress test

The maximum tensile strength of a sample before and after the solution treatment and aging treatment was examined.

Note that a specific component of the silicon alloy A2 powder used in this molding test has C: 0.015, Si: 3.45, Mn: 0.96, Cu: 1.12, Ni: 6.7, Cr: 10.8, Mo: 0.39% by weight and the balance of Fe and inevitable impurities.

4.1 Energy density test

Gleichung 3: $$\begin{array}{l}{\rho }_t\times V={\rho }_t\times \left(V-V\text{'}\right)+0\times V\text{'}\\ P=\frac{V\text{'}}{V}\times 100=\frac{\rho -{\rho }_t}{\rho }\times 100\left(\%\right)\end{array}$$

Gleichung 4: $$D=100-P=\frac{{\rho }_t}{\rho }\times 100$$

First, a method of calculating the specific gravity D will be described. More specifically, the density of a sample (Archimedes method) is calculated by the following equation (2). The porosity P (note that the density of a pore is considered to be 0) of a sample is calculated using the following equation (3). The relative density D of a sample is calculated using the following equation (4). Note that in the following equations (2) to (4), V is a total volume of a sample, V 'is a pore volume, ρ is the true density (7.61g / cm ³ ), pt is the density of a sample, pw is the Is the density of water, Min-Air is the weight of a sample in air, Min-Water is the weight of a sample in water, P is the porosity of a sample, and D is the specific gravity of a sample.
Equation 2: $$\begin{array}{l}{\mathrm{M.}}_{in-\mathrm{L.}uft}=V\times {\rho }_t\\ {\mathrm{M.}}_{in-\mathrm{W.}asser}=V\times {\rho }_t-V\times {\rho }_w\\ {\rho }_t=\frac{{\mathrm{M.}}_{in-\mathrm{L.}uft}}{{\mathrm{M.}}_{in-\mathrm{L.}uft}-{\mathrm{M.}}_{in-\mathrm{W.}asser}}\times {\rho }_w\end{array}$$

Equation 3: $$\begin{array}{l}{\rho }_t\times V={\rho }_t\times \left(V-V\text{'}\right)+0\times V\text{'}\\ \mathrm{P.}=\frac{V\text{'}}{V}\times 100=\frac{\rho -{\rho }_t}{\rho }\times 100\left(\%\right)\end{array}$$

Equation 4: $$\mathrm{D.}=100-\mathrm{P.}=\frac{{\rho }_t}{\rho }\times 100$$

In the energy density test, a base plate was first formed, and a cylindrical sample 8 millimeters in diameter and 15 millimeters in height was built on the base plate as in FIG 2 will be shown. Each sample stands upright in the direction of lamination. After molding, each sample was separated from the base plate, and the specific gravity of each sample was measured. The height of each separated sample was 12 millimeters.

The following Table 3 shows test results when the laser scanning speed v was varied. In Table 3 below, “Appearance” is a photograph of the upper end face of the molded sample. Further, “molding stopped” in the following Table 3 means that molding was stopped because a sample was melted and could not maintain its cylindrical shape. Note that the scan advance was 0.1 mm, the lamination thickness t was 50 micrometers, and the laser diameter was 100 micrometers.

300 relative Dichte D % · 98.83 98.95 98.67 98.82 97.25 95.87 Energie dichte E J/mm³ 150 100 75 60 50 43 38 Aussehen Formgeben gestoppt

350 relative Dichte D % · 98.59 98.98 98.56 97.98 98.03 97.31 Energie dichte E J/mm³ 175 118 88 70 58 50 44 Aussehen Formgeben gestoppt

3 shows the relationship between the energy density E and the relative density D in the following table 3. In 3 the horizontal axis indicates the energy density E, and the vertical axis indicates the relative density D. A result when the laser power P was 250 W is indicated by a diamond outline, a result when the laser power P was 300 W is indicated by a circular outline, and a result when the laser power P was 350 W is indicated by a triangular outline specified. Table 3 Laser scanning speed v mm / s 400 600 800 1000 1200 1400 1600 Laser power is PW 250 relative density D% · 98.85 98.72 98.87 97.51 95.32 91.28 Energy density EJ / mm ³ 125 83 63 50 42 36 31 Look Shaping stopped

300 relative density D% · 98.83 98.95 98.67 98.82 97.25 95.87 Energy density EJ / mm ³ 150 100 75 60 50 43 38 Look Shaping stopped

350 relative density D% · 98.59 98.98 98.56 97.98 98.03 97.31 Energy density EJ / mm ³ 175 118 88 70 58 50 44 Look Shaping stopped

From Table 3 and above 3 It is apparent that (1) a sample cannot be molded into a desired shape when the energy density E is 125 [J / mm ³ ] or more, (2) a sample cannot be molded without a problem when the energy density E is E 31 [J / mm ³ ], (3) there is some relationship between the energy density E and the relative density D, and (4) the relative density starts to be saturated when the energy density E is 36 [J / mm ³ ] or more. From these findings, it is found that a sample can be easily molded into a desired shape when the energy density E is in a range from 31 to 124 [J / mm ³ ].

Furthermore, the energy density E is preferably in the range from 36 to 124 [J / mm ³ ]. In this range, a high-density sample with the relative density D of 95 [%] or more can be molded. Furthermore, the energy density E can be 36 to 118 [J / mm ³ ].

Furthermore, the energy density E is more preferably in the range of 50 to 124 [J / mm ³ ]. In this range, a high-density sample with the relative density D of approximately 98 [%] or more can be molded. Furthermore, the energy density E can be 50 to 118 [J / mm ³ ].

4th shows the relationship between the laser scanning speed v and the specific gravity D in the above Table 3. In 4th the horizontal axis indicates the laser scanning speed v and the vertical axis indicates the relative density D. A result when the laser power P was 250 W is indicated by a diamond outline, a result when the laser power P was 300 W is indicated by a circular outline, and a result when the laser power P was 350 W is indicated by a triangular outline specified.

From Table 3 above and the 3 and 4th It is apparent that the highest relative density D is obtained when the laser power P is 300 or 350 [W] and the laser scanning speed v is 800 [mm / s].

350 relative Dichte D % · 99.6 98.98 98.76 98.62 98.59 Energie dichte E J/mm³ 146 109 88 73 63 55 Aussehen Formgeben gestoppt

The following table 4 shows test results when the scan feed rate s was varied. In Table 4 below, “Appearance” is a photograph of the upper end face of the molded sample. Further, “molding stopped” in the following Table 4 means that molding was stopped because a sample was melted and could not maintain its cylindrical shape. Note that the laser scanning speed v was 800 [mm / s], the lamination thickness t was 50 micrometers, and the laser diameter was 100 micrometers. 5 shows the relationship between the energy density E and the relative density D in the following table 4. In 5 the horizontal axis indicates the energy density E, and the vertical axis indicates the relative density D. A result when the laser power was P 300 [W] is indicated by means of a diamond outline, and a result when the laser power was P 350 [W] is indicated by means of a circular outline. Table 4 Scan feed s mm 0.06 0.08 0.10 0.12 0.14 0.16 Laser power is PW 300 relative density D% · 99.32 98.95 98.96 99.17 98.7 Energy density EJ / mm ³ 125 94 75 63 54 47 Look Shaping stopped

350 relative density D% · 99.6 98.98 98.76 98.62 98.59 Energy density EJ / mm ³ 146 109 88 73 63 55 Look Shaping stopped

From Table 4 and above 5 It is apparent that (1) a sample cannot be molded into a desired shape when the energy density E is 125 [J / mm ³ ] or more, (2) a sample cannot be molded without a problem when the energy density E is E 47 [J / mm ³ ], and (3) there is some relationship between the energy density E and the relative density D. From these findings, it is found that a sample can be easily molded into a desired shape when the Energy density E is in the range of 47 to 124 [J / mm ³ ]. Note that the graph looks like 5 essentially similar to the graph 3 is.

6th shows the relationship between the scan feed rate s and the specific gravity D in the following table 4. In 6th the horizontal axis indicates the scan feed rate s and the vertical axis indicates the relative density D. A result when the laser power was P 300 [W] is indicated by means of a diamond outline, and a result when the laser power was P 350 [W] is indicated by means of a circular outline.

From Table 4 above and the 5 and 6th It is apparent that the highest relative density D is obtained when the laser power P is 300 [W] and the scan feed rate s is 0.08 [mm].

Furthermore, the above Tables 3 and 4 and the 3 until 6th Considering as a whole, the energy density E is most dominantly involved in the relative density D. Accordingly, in order to obtain a desired relative energy density D, it can be said that it is important to manage the energy density E with particular attention.

4.2 Structure observation test

In this structure observation test, structure observation was carried out on a shaped sample before any treatment, a sample after solution heat treatment, and a sample after solution heat treatment and aging treatment to examine a change in structure before and after the solution heat treatment and aging treatment. The purpose of the structure observation test is to see whether or not there is a difference between the microstructure in the diameter direction and in the height direction, and to see whether three phases of ferrite, austenite, and martensite coexist. The conditions of the test were as follows.

Object to be tested: an object to be observed was a sample formed with the selective laser sintering system at the laser power P of 300 [W], the laser scanning speed v of 800 [mm / s], and the scanning feed rate s of 0.08 [mm]. The size of the sample and the molding procedure were the same as those in the energy density test described above.

Test method: a sample was cut using a thin cutter to obtain a longitudinal profile thereof, and the longitudinal profile was filled with a resin. Next, the longitudinal profile was sanded in sequence using sandpaper (“carbon Mac papers”) # 80, # 220, # 600, # 1200 and # 2000. Then, the longitudinal profile was polished in turn using a diamond paste having a size of 3 micrometers and 1 micrometer. The sample was then immersed in a marble liquid in order to etch the longitudinal profile. Then, the structure of the longitudinal profile was observed using an optical microscope (with a magnification of 50 to 100).

Solution heat treatment conditions: The sample was started to be heated, starting at room temperature, kept at 1050 ° C for 20 minutes, and then water-cooled.

Curing treatment conditions: the sample was started to be heated, starting at room temperature, held at 480 ° for 7 hours, and then air-cooled.

7th shows photographs of the longitudinal profile of a shaped sample before solution heat treatment and solution heat treatment. Like in the 7th is shown, the microstructure (laminated structure), similar to thermal spraying, can be seen over the entire longitudinal profile. Further, the coexistence of the three phases, which are ferrite, austenite and martensite, is found. It can also be seen that the ratio of martensite differs slightly between the inside and the outside of the longitudinal profile.

8th shows photographs of the longitudinal profile of a sample after the solution treatment. Like in the 8th As shown, martensite is essentially throughout the length and a small amount of residual austenite is seen. The laminated structure has disappeared and the sample has a substantially uniform metal structure.

9 shows photographs of the longitudinal profile of a sample after solution heat treatment and hardening treatment. As in 8th shown, the remaining austenite has essentially disappeared.

4.3 Endurance test

A hardness test was carried out on a molded sample before any treatment, a sample after solution heat treatment, and a sample after solution heat treatment and aging treatment to examine a change in hardness before and after the solution treatment and aging treatment. The conditions of the test were as follows.

Object to be tested: an object to be tested was the longitudinal profile of a chuck of a probe, which is an object to be tested by a tensile stress test which will be described later.

Test conditions: a light load Vickers hardness test was carried out. A test force was 0.3 kgf, a load time was 4.0 seconds, and a retention time was 15.0 seconds, and a release time was 4.0 seconds, an approach speed was 60 micrometers per second, and a number of tests was 8 to 12 for each sample.

10 shows test results. In 10 "Shaped" indicates a shaped sample before any treatment, "Solution" indicates a sample after a solution heat treatment, and "Curing" indicates a sample after a solution heat treatment and age hardening treatment. The vertical axis indicates the Vickers hardness HV. In 10 measurement results are shown by box graphics and the mean value is shown by a bar graph. For reference, the catalog values of a cast product made of silicon alloy steel A2 are represented by horizontal bands. "Catalog value (solution)" is the catalog value of a cast product of silicon alloy steel A2 after solution treatment. "Catalog value (hardening)" is the catalog value of a cast product of silicon alloy steel A2 after solution heat treatment and age hardening treatment.

Out 10 It is apparent that a sample molded with silicon alloy steel A2 powder has substantially the same Vickers hardness as a molded product of silicon alloy steel A2. Note that martensitic hardening steel has a Vickers hardness HV of 513 after the hardening treatment. Therefore, it can be said that a sample molded with silicon alloy A2 powder and subjected to solution heat treatment and age hardening treatment has Vickers hardness substantially the same as that of martensitic steel after age hardening treatment.

4.4 Tensile test

A tensile test was carried out on a molded sample before any treatment and a sample after heat treatment to examine the maximum tensile strength of each sample.

Object to be tested: an object to be observed was a sample formed with the selective laser sintering system at the laser power P of 300 [W], the laser scanning speed v of 800 [mm / s], and the scanning feed rate s of 0.08 [mm].

Number of samples: 24 in total: 4 round bars (vertical, with no heat treatment), 4 round bars (vertical, with heat treatment), 4 round bars (horizontal, with no heat treatment), 4 round bars (horizontal, with heat treatment), 4 Test bar shapes (with no heat treatment) and 4 test bar shapes (with heat treatment). Note that “with heat treatment” means that the sample is cut after the solution heat treatment, and then the hardening treatment is carried out after this treatment. “Vertical” indicates a sample shaped in an orientation that is perpendicular to the lamination direction, and “horizontal” indicates a sample that is shaped in an orientation that is perpendicular to the lamination direction.

Sample shape: As in the 11th and 12th will be shown.

Solution heat treatment conditions: The sample was started to be heated, starting at room temperature, held at 1050 ° C for 20 minutes, and then water-cooled.

Curing treatment conditions: the sample was started to be heated, starting at room temperature, held at 480 ° for 7 hours, and then air-cooled.
Test machine: INSTRON MODEL 4206
Tension speed: 1mm / min
Detection of exposure: an exposure meter was used.

13th shows test results. In the 13th the lower bar on the left of each pair of bars in the graph is the one that is not being subjected to the heat treatment, and the higher bar on the right is the one that is being subjected to the heat treatment. "Catalog value (hardening)" is the catalog value of a cast product of silicon alloy steel A2 after solution heat treatment and age hardening treatment. Out 13th It is apparent that the orientation of each sample with respect to the lamination direction does not significantly affect the maximum tensile strength and that the sample after heat treatment has substantially the same maximum tensile strength as that of a cast product of silicon alloy steel A2 after heat treatment. Note that hardened martensitic steel has the maximum tensile strength of 1890 MPa after the aging treatment. Therefore, it can be said that a sample molded with silicon alloy A2 powder and subjected to heat treatment has the maximum tensile strength substantially the same as that of martensitic steel after the aging treatment.

From the test results described above, it was concluded that (1) silicon alloy A2 can be used as metal powder to be used in the selective laser sintering method, (2) a molded product formed by selective laser sintering using silicon alloy steel A2 has substantially the same mechanical quality such as that of a cast product of silicon alloy steel A2, and (3) a molded product produced by selective laser sintering using silicon alloy steel A2 can suitably serve as a substitute for a commercially available martensitic steel.

Finally, a molding method using silicon alloy A2 powder will be described below with reference to FIG 14th .

First, 2D CAD data (disk data) are generated by slicing 3D CAD data of a molded product (S90). Next, the selective laser sintering process builds up silicon alloy A2 powder in layers (S100). Then, the selective laser sintering system selectively applies a laser to the silicon alloy A2 powder to melt it and sinter it into a desired shape (S110). Thereafter, the selective laser sintering system determines whether a molded product has been completed (S120), and when it is determined that the molded product has not been completed (No in S120), the selective laser sintering system returns in the process to S100. On the other hand, when it is determined that the molded product has been completed (Yes in S120), the laser sintering system ends the molding. Then, solution heat treatment is performed on the molded product at a specified temperature for a specified period of time (S130). Further, curing treatment is performed on the molded product after the solution treatment treatment at a specified temperature for a specified period of time (S140). Thereby, a molded product comparable to a martensitic hardening steel after heat treatment is obtained.

The embodiment described above has the following features.

A selective laser sintering method alternately repeats (S120) a step (S100) of building silicon alloy A2 powder in layers made of silicon-rich stainless steel containing C: less than 0.10, Si: 2.0-9.0, Mn: 0.05-6.0, Cu: 0.5-4.0, Ni: 1.0-24.0, Cr: 6.0-28.0, Mo: 0.2-4.0, Nb: 0.03∼2.0 in percent by weight, and the remainder of Fe and inevitable impurities, and a step (S110 ) Selectively applying a laser to the silicon alloy A2 powder formed in layers to melt and sinter the silicon alloy A2 powder.

It is preferred that the particle size of the silicon alloy A2 powder be 32 to 62 micrometers.

In the laser sintering process described above, the energy density E is 31 to 124 [J / mm ³ ].

It is preferred that the energy density E be 36 to 124 [J / mm ³ ].

It is more preferable that the energy density E is 50 to 124 [J / mm ³ ].

It is further preferred that the energy density E is 50 to 118 [J / mm ³ ].

The lower limit of the energy density E is one of 31, 36, 38, 42, 43, 44, 47, 50, 54, 55, 58, 60, 63, 70, 73, 75, 83, 88, 94, 100, 109 and 118, and the upper limit of the energy density E is one of 36, 38, 42, 43, 44, 47, 50, 54, 55, 58, 60, 63, 70, 73, 75, 83, 88, 94, 100 , 109, 118 and 124.

A heat treatment method comprises a step (S130) of performing solution treatment on a molded product formed by the above-described laser sintering method, and a step (S140) of performing aging treatment after the solution treatment.

There is also provided a metal powder used in a selective laser sintering process that selectively applies a laser to metal powder to melt and sinter the metal powder for lamination, the metal powder being made of a silicon-rich stainless steel containing C: less than 0.10 , Si: 2.0∼9.0, Mn: 0.05∼6.0, Cu: 0.5∼4.0, Ni: 1.0∼24.0, Cr: 6.0∼28.0, Mo: 0.2∼4.0, Nb: 0.03∼2.0 in percent by weight, and the rest of Fe and inevitable impurities.

The particle size of the metal powder is 32 to 62 micrometers.

Further, a molded product formed by the above-described laser sintering method is provided.

Further, a molded product heat-treated by the above-described heat treatment method is provided.

From the invention described it is evident that the embodiments of the invention can be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are, as would be apparent to one skilled in the art, intended to be included within the scope of the following claims.

Claims (3)

A selective laser sintering process, comprising: alternately repeating a step of building metal powder in layers, the metal powder made of a silicon-rich stainless steel containing C: less than 0.020, Si: 3.0-5.0, Mn: 0.5-1, 5, Cu: 0.8 - 1.2, Ni: 6.0 - 7.0, Cr: 10.0 - 13.0, Mo: 0.3 - 1.0, Nb: 0.30 - 1, 00 in percent by weight, and a balance of Fe and inevitable impurities, and a step of selectively applying a laser to the layered metal powder to melt and sinter the metal powder, the energy density E being calculated by the following formula 36 to 124 [ J / mm ³ ] $$\text{E.}=\mathrm{P.}/\text{v}\times \text{s}\times \text{t},$$

where P is the power of the laser, v is the scanning speed of the laser, s is the scanning feed rate of the laser, and t is the lamination thickness of the layer of metal powder, the particle size of the metal powder being 32 to 62 micrometers, and the method further comprising a heat treatment process comprising a step of performing a solution treatment at 1,050 ° C for 20 minutes on a molded product formed by the selective laser sintering method and then water cooling and a step of performing a curing treatment at 480 ° C for 7 hours on the molded product after the solution treatment and subsequent air cooling. The selective laser sintering process according to Claim 1 , the energy density E being 50 to 124 [J / mm ³ ]. The selective laser sintering process according to Claim 1 , the energy density E being 50 to 118 [J / mm ³ ].

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