U.S. patent application number 15/051293 was filed with the patent office on 2016-09-01 for selective laser sintering method, heat treatment method, metal powder, and shaped product.
The applicant listed for this patent is JAPAN SILICOLLOY INDUSTRY CO., LTD.. Invention is credited to Takayasu Shimizu.
Application Number | 20160251736 15/051293 |
Document ID | / |
Family ID | 56682725 |
Filed Date | 2016-09-01 |
United States Patent
Application |
20160251736 |
Kind Code |
A1 |
Shimizu; Takayasu |
September 1, 2016 |
SELECTIVE LASER SINTERING METHOD, HEAT TREATMENT METHOD, METAL
POWDER, AND SHAPED PRODUCT
Abstract
A selective laser sintering method alternately repeats a step of
forming silicon alloy A2 powder (metal powder) in layers, the
silicon alloy A2 powder made of high silicon stainless steel
containing C:less than 0.10, Si:2.0.about.9.0, Mn:0.05.about.6.0,
Cu:0.5.about.4.0, Ni:1.0.about.24.0, Cr:6.0.about.28.0,
Mo:0.2.about.4.0, Nb:0.03.about.2.0 in wt % and the balance of Fe
and inevitable impurities, and a step of selectively applying a
laser to the silicon alloy A2 powder formed in layers to melt and
sinter the silicon alloy A2 powder.
Inventors: |
Shimizu; Takayasu; (Ako-gun,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JAPAN SILICOLLOY INDUSTRY CO., LTD. |
Ako-gun |
|
JP |
|
|
Family ID: |
56682725 |
Appl. No.: |
15/051293 |
Filed: |
February 23, 2016 |
Current U.S.
Class: |
419/7 |
Current CPC
Class: |
C21D 6/005 20130101;
B22F 2998/10 20130101; B22F 3/1055 20130101; C22C 33/0285 20130101;
C21D 6/008 20130101; C22C 38/44 20130101; C22C 38/48 20130101; C21D
9/0068 20130101; C22C 38/04 20130101; C21D 6/004 20130101; Y02P
10/25 20151101; Y02P 10/295 20151101; B22F 2003/248 20130101; C22C
38/42 20130101; C21D 1/18 20130101; B22F 2999/00 20130101; C22C
38/34 20130101; B22F 2998/10 20130101; B22F 3/1055 20130101; B22F
2003/248 20130101; B22F 2999/00 20130101; B22F 2009/0824 20130101;
B22F 2201/11 20130101; B22F 2999/00 20130101; B22F 1/0011 20130101;
B22F 2009/0824 20130101 |
International
Class: |
C21D 1/18 20060101
C21D001/18; B22F 3/105 20060101 B22F003/105; C22C 38/48 20060101
C22C038/48; C21D 6/00 20060101 C21D006/00; C22C 38/42 20060101
C22C038/42; C22C 38/34 20060101 C22C038/34; C22C 38/04 20060101
C22C038/04; C21D 9/00 20060101 C21D009/00; B22F 1/00 20060101
B22F001/00; C22C 38/44 20060101 C22C038/44 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2015 |
JP |
2015-038168 |
Claims
1. A selective laser sintering method comprising: alternately
repeating a step of forming metal powder in layers, the metal
powder being made of high silicon stainless steel containing C:less
than 0.10, Si:2.0.about.9.0, Mn:0.05.about.6.0, Cu:0.5.about.4.0,
Ni:1.0.about.24.0, Cr:6.0.about.28.0, Mo:0.2.about.4.0,
Nb:0.03.about.2.0 in wt %, and a balance of Fe and inevitable
impurities; and a step of selectively applying a laser to the metal
powder formed in layers to melt and sinter the metal powder.
2. The selective laser sintering method according to claim 1,
wherein a particle size of the metal powder is 32 to 62
micrometers.
3. The selective laser sintering method according to claim 1,
wherein energy density E calculated by following equation is 31 to
124 [J/mm.sup.3] E = P v .times. s .times. t ##EQU00003## where P
is an output of the laser, v is a scanning speed of the laser, s is
a scanning pitch of the laser, and t is a lamination thickness of
one layer of the metal powder.
4. The selective laser sintering method according to claim 3,
wherein the energy density E is 36 to 124 [J/mm.sup.3].
5. The selective laser sintering method according to claim 3,
wherein the energy density E is 50 to 124 [J/mm.sup.3].
6. The selective laser sintering method according to claim 3,
wherein the energy density E is 50 to 118 [J/mm.sup.3].
7. A heat treatment method comprising: a step of performing
solution treatment on a shaped product shaped by the selective
laser sintering method according to claim 1; and a step of
performing ageing treatment on the shaped product after the
solution treatment.
8. Metal powder used in a selective laser sintering method that
selectively applies a laser to metal powder to melt and sinter the
metal powder for lamination, wherein the metal powder is made of
high silicon stainless steel containing C:less than 0.10,
Si:2.0.about.9.0, Mn:0.05.about.6.0, Cu:0.5.about.4.0,
Ni:1.0.about.24.0, Cr:6.0.about.28.0, Mo:0.2.about.4.0,
Nb:0.03.about.2.0 in wt %, and a balance of Fe and inevitable
impurities.
9. The metal powder according to claim 8, wherein a particle size
of the metal powder is 32 to 62 micrometers.
10. A shaped product shaped by the selective laser sintering method
according to claim 1.
11. A shaped product heat-treated by the heat treatment method
according to claim 7.
Description
INCORPORATION BY REFERENCE
[0001] This application is based upon and claims the benefit of
priority from Japanese patent application No. 2015-038168, filed on
Feb. 27, 2015, the disclosure of which is incorporated herein in
its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a selective laser sintering
method that sinters metal powder with a laser and laminates it to
form a desired three-dimensional shape, a heat treatment method,
metal powder, and a shaped product.
[0004] 2. Description of Related Art
[0005] Metal powder additive manufacturing is 3D shaping that does
not require any mold, and it has attracted attention as one type of
rapid prototyping (RP) that rapidly manufactures prototypes by
using 3D CAD data. Recently, with the progress made in 3D printer
technology, 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 have been added, and this processing
method is now called additive manufacturing (AM) that is not
limited to manufacturing prototypes, and that can directly
manufacture end products. The applications which this method can be
applied to have become widespread, and it can be applied not only
to molds and machine parts but also customized medical parts like
artificial joints and artificial crowns.
[0006] Because metal powder additive manufacturing is additive
manufacturing that attaches material to a necessary part, it is
possible to manufacture parts having shapes that have not been able
to be manufactured by the existing processing methods (forging,
casting, cutting etc.), such as an injection mold where an
arbitrary cooling channel suitable for a product shape is placed
inside the mold and an aerospace component like a fuel injection
nozzle of a jet engine having a complex shape.
[0007] For example, Patent Literature 1 (Japanese Unexamined Patent
Publication No. 2002-66844) discloses metal powder additive
manufacturing that creates a plurality of slice data from 3D data
of an object to be processed and applies a laser beam onto
copper-nickel alloy powder based on the plurality of slice data to
thereby sinter each layer and laminate them. However, because of
constraints of device manufacturer, there are only a few types of
materials that can be shaped by this method, which hinders widening
of the applications which this method can be applied to.
[0008] In view of the foregoing, an object of the present invention
is to provide a selective laser sintering method using a new type
of steel, a heat treatment method, metal powder, and a shaped
product.
SUMMARY OF THE INVENTION
[0009] According to a first aspect of the present invention, there
is provided a selective laser sintering method that alternately
repeats a step of forming metal powder in layers, the metal powder
being made of high silicon stainless steel containing C:less than
0.10, Si:2.0.about.9.0, Mn:0.05.about.6.0, Cu:0.5.about.4.0,
Ni:1.0.about.24.0, Cr:6.0.about.28.0, Mo:0.2.about.4.0,
Nb:0.03.about.2.0 in wt %, and a balance of Fe and inevitable
impurities, and a step of selectively applying a laser to the metal
powder formed in layers to melt and sinter the metal powder.
[0010] A particle size of the metal powder is 32 to 62
micrometers.
[0011] Energy density E is 31 to 124 [J/mm.sup.3].
[0012] Energy density E is 36 to 124 [J/mm.sup.3].
[0013] Energy density E is 50 to 124 [J/mm.sup.3].
[0014] Energy density E is 50 to 118 [J/mm.sup.3].
[0015] Also provided is a heat treatment method including a step of
performing solution treatment on a shaped product shaped by the
above-described selective laser sintering method, and a step of
performing ageing treatment on the shaped product after the
solution treatment.
[0016] According to a second aspect of the present invention, there
is provided metal powder used in a selective laser sintering method
of selectively applying a laser to the metal powder to melt and
sinter the metal powder for lamination, wherein the metal powder is
made of high silicon stainless steel containing C:less than 0.10,
Si:2.0.about.9.0, Mn:0.05.about.6.0, Cu:0.5.about.4.0,
Ni:1.0.about.24.0, Cr:6.0.about.28.0, Mo:0.2.about.4.0,
Nb:0.03.about.2.0 in wt %, and a balance of Fe and inevitable
impurities.
[0017] A particle size of the metal powder is 32 to 62
micrometers.
[0018] A shaped product shaped by the above-described selective
laser sintering method is provided.
[0019] A shaped product heat-treated by the above-described heat
treatment method is provided.
[0020] According to the invention, there is provided a selective
laser sintering method using a new type of steel, a heat treatment
method, metal powder, and a shaped product.
[0021] The above and other objects, features and advantages of the
present invention will become more fully understood from the
detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not to be considered as limiting the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 shows photographs of silicon alloy A2 powder.
[0023] FIG. 2 shows a photograph of a sample.
[0024] FIG. 3 shows a graph representing the relationship between
energy density E and relative density D.
[0025] FIG. 4 shows a graph representing the relationship between
laser scanning speed v and relative density D.
[0026] FIG. 5 shows a graph representing the relationship between
energy density E and relative density D.
[0027] FIG. 6 shows a graph representing the relationship between
scanning pitch s and relative density D.
[0028] FIG. 7 shows photographs of the longitudinal section of a
shaped sample after shaping.
[0029] FIG. 8 shows photographs of the longitudinal section of a
sample after solution treatment.
[0030] FIG. 9 shows photographs of the longitudinal section of a
sample after ageing treatment.
[0031] FIG. 10 shows a bar graph representing test results of a
hardness test.
[0032] FIG. 11 is a view showing the size and shape of a sample of
a tensile test.
[0033] FIG. 12 shows a photograph of a sample of a tensile
test.
[0034] FIG. 13 shows a bar graph representing test results of a
tensile test.
[0035] FIG. 14 is a flowchart of a selective laser sintering method
and a flowchart of a heat treatment method.
DETAILED DESCRIPTION
[0036] 1. Steel type
[0037] The applicant of the present invention has made a close
investigation as to whether precipitation hardening stainless steel
containing high Si and extremely low C can be employed as a steel
type of metal powder to be used in a selective laser sintering
method, and reports the investigation results in this
specification. Hereinafter, the precipitation hardening stainless
steel is referred to as "silicon alloy steel". There are a
plurality of component specifications of silicon alloy steel, and
silicon alloy steel A2 shown in the following table 1 is selected
in this shaping test. Further, powder of silicon alloy steel A2 is
simply referred to as "silicon alloy A2 powder". In the following
table 1, the component specifications of silicon alloy steel and
silicon alloy steel A2 are shown in comparison with the component
specifications of typical SUS630. Note that silicon alloy steel A2
is a region where three phases, which are ferrite, austenite and
martensite, coexist.
TABLE-US-00001 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 Bal. 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 Bal. SUS630 <0.07
<1.0 <1.0 3.00~5.00 3.00~5.00 15.00~17.00 -- 0.15~0.45
Bal.
[0038] Specifically, silicon alloy steel is high silicon stainless
steel containing C:less than 0.10, Si:2.0.about.9.0,
Mn:0.05.about.6.0, Cu:0.5.about.4.0, Ni:1.0.about.24.0,
Cr:6.0.about.28.0, Mo:0.2.about.4.0, Nb:0.03.about.2.0 in wt %, and
the balance of Fe and inevitable impurities.
[0039] Further, silicon alloy steel A2 is high silicon stainless
steel containing C:less than 0.020, Si:3.0.about.5.0,
Mn:0.5.about.1.5, Cu:0.8.about.1.2, Ni:6.0.about.7.0,
Cr:10.0.about.13.0, Mo:0.3.about.1.0, Nb:0.30.about.1.00 in wt %,
and the balance of Fe and inevitable impurities.
[0040] 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, in silicon alloy steel that contains a large
amount of Si, because its strength is ensured by a peculiar metal
structure produced by Si, it is not essential for it to contain C.
Rather, C is an element that decreases the toughness of silicon
alloy steel and adversely affects oxidation resistance and
corrosion resistance. Thus, 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%.
[0041] Si is not only the primary element that gives steel its
strength but also gives it heat resistance, oxidation resistance,
corrosion resistance and softening resistance. Further, Si is an
element that lowers the melting point of steel to increase the
flowability and improve the castability thereof. When the content
of Si is less than 2.0%, the improvement of the above properties is
insufficient. On the other hand, because Si is a strong ferrite
forming element, when 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 in the steel structure from becoming
excessive, which would result in high material costs. Thus, the
tolerable content of Si in 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%.
[0042] 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, a Mn content of 0.05%
or more is needed because it contributes to the densification and
stabilization of the metal structure. If, on the other hand, the Mn
content exceeds 6.0%, the corrosion resistance decreases. Thus, 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%.
[0043] Cu is a component to be added to silicon alloy steel as
needed. Cu is an element that contributes to the improvement of
corrosion resistance (particularly, acid resistance) and
precipitation hardening of silicon alloy steel. Further, Cu is an
austenite forming element and contributes to the adjustment of the
balance of the metal structure. To achieve these effects, the
content of Cu is preferably 0.5% or more. However, because the Cu
content exceeding 4.0% causes degradation of the hot workability of
steel, the upper limit of the Cu content when added to silicon
alloy steel is 4.0%. Thus, the tolerable content of Cu in silicon
alloy steel is 0.5% to 4.0%. It is more preferably 2.0% or less.
Further, the tolerable content of Cu in silicon alloy steel A2 is
0.8% to 1.2%.
[0044] Ni is an element that gives corrosion resistance
(particularly, acid resistance), oxidation resistance and heat
resistance to steel and it is essential to substantially maintain
the duplex metal structure of steel in a good balance with Cr,
which is described next. To obtain these effects, a
[0045] Ni content of 1.0% or more is required. If, on the other
hand, the Ni content exceeds 24.0%, the austenite phase excessively
increases, which causes the loss of not only the characteristics of
duplex stainless steel but also reduces the cost efficiency of
steel. Thus, 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%.
[0046] Cr is a component to ensure the basic characteristics of
stainless steel, which are corrosion resistance (particularly, acid
resistance), heat resistance and oxidation resistance. These
properties are not sufficient if the Cr content is 6.0% or less. On
the other hand, if the Cr content is more than 28.0%, the amount of
Ni, which is required to substantially maintain the duplex metal
structure of steel, increases so that the cost efficiency of steel
is reduced. Thus, the tolerable content of Cr in silicon alloy
steel is 6.0% to 28.0%. Further, the tolerable content of Cr in
silicon alloy steel A2 is 10.0% to 13.0%.
[0047] Mo increases the corrosion resistance (acid resistance) and
high-temperature strength to improve the creep resistance and
further contributes to an increase in the toughness and wear
resistance of silicon alloy steel. These effects are not sufficient
if the Mo content is 0.2% or less. Because 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
needs to be increased. Further, Mo is an expensive element. In view
of all these factors, the tolerable content of Mo in silicon alloy
steel is 0.2% to 4.0%. Further, the tolerable content of Mo in
silicon alloy steel A2 is 0.3% to 1.0%.
[0048] Nb is an element that is effective for increasing the case
depth in aging treatment without degrading the toughness of silicon
alloy steel. Further, 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. If, on the other hand, the Nb content is
more than 2.0%, the hot workability of silicon alloy steel is
degraded, and the toughness is reduced. Thus, 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%.
[0049] Silicon alloy steel including silicon alloy steel A2
contains, in addition to the above-described components, the
balance of iron (Fe) and inevitable impurities. Note that it is
preferred that the content of each of P and S, which are
impurities, be 0.04% or less.
[0050] According to the above Table 1, silicon alloy steel A2 has
higher contents of Si, Ni, Mo and Nb and lower contents of Cu and
Cr compared with SUS630, respectively.
2. Silicon alloy A2 Powder
[0051] Silicon alloy A2 powder can be manufactured by, for example,
gas atomizing. Gas atomizing is a method by which an alloy composed
of desired components is dissolved, and then the molten metal flows
out of a nozzle hole at the bottom of a tundish to produce a fine
flow of the molten metal. Then, jet fluid composed of inert gas
such as argon gas is sprayed against the flow of the molten metal
to sequentially convert the molten metal flow into powder form by
the energy of the jet fluid, and generated droplet is solidified as
it is dropping to thereby produce alloy powder. FIG. 1 shows
photographs of silicon alloy A2 powder manufactured by the gas
atomizing. In this shaping test, silicon alloy A2 powder is
classified so that the particles range in size from 32 to 62
micrometers (sieving method).
3. Selective Laser Sintering System
[0052] A selective laser sintering system used in this shaping test
is EOSINT-M280 from EOS GmbH. The specifications of this selective
laser sintering system are shown in the following table 2.
TABLE-US-00002 TABLE 2 Laser output P 250~350 W Laser scanning
speed v 400~1600 mm/s Scanning pitch s 0.06~0.16 mm Lamination
thickness t 50 micrometers Laser diameter 100 micrometers
[0053] The energy density E of laser sintering is defined by the
following equation (1):
Equation 1 : E = P v .times. s .times. t ( 1 ) ##EQU00001##
4. Shaping Test
[0054] In this shaping test, the following four types of tests were
conducted to determine whether silicon alloy A2 powder can be
employed as the steel type of metal powder to be used in the
selective laser sintering method.
(1) Energy Density Test
[0055] A change in the relative density 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 scanning pitch s was varied to increase and
decrease the energy density E.
(2) Structure Observation Test
[0056] The structure along the longitudinal section of a sample
before and after solution treatment and ageing treatment was
observed.
(3) Hardness Test
[0057] The hardness of a sample before and after solution treatment
and ageing treatment was examined.
(4) Tensile Test
[0058] The maximum tensile strength of a sample before and after
solution treatment and ageing treatment was examined.
[0059] Note that a specific component of silicon alloy A2 powder
used in this shaping test was C:0.015, Si:3.45, Mn:0.96, Cu:1.12,
Ni:6.7, Cr:10.8, Mo:0.39 in wt %, and the balance of Fe and
inevitable impurities.
4.1. Energy Density Test
[0060] First, a method of calculating the relative density D is
described. 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 regarded as 0) of a sample is
calculated by the following equation (3). The relative density D of
a sample is calculated by the following equation (4). Note that, in
the following equations (2) to (4), V is the overall volume of a
sample, V' is a pore volume, p is the true density (7.61
g/cm.sup.3), pt is the density of a sample, pw 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 relative density of a sample.
Equation 2 : M in - air = V .times. .rho. t M in - water = V
.times. .rho. t - V .times. .rho. w .rho. t = M in - air M in - air
- M in - water .times. .rho. w ( 2 ) Equation 3 : .rho. t .times. V
= .rho. t .times. ( V - V ' ) + 0 .times. V ' P = V ' V .times. 100
= .rho. - .rho. t .rho. .times. 100 ( % ) ( 3 ) Equation 4 : D =
100 - P = .rho. t .rho. .times. 100 ( 4 ) ##EQU00002##
[0061] In the energy density test, a base plate was formed first,
and a cylindrical sample with a diameter of 8 millimeters and a
height of 15 millimeters was formed on the base plate as shown in
FIG. 2. Each sample stands upright in the direction of lamination.
After shaping, each sample was separated from the base plate, and
the relative density of each sample was measured. The height of
each separated sample was 12 millimeters.
[0062] The following table 3 shows test results when the laser
scanning speed v was varied. In the following table 3, "Appearance"
is a photograph of the upper end face of the shaped sample.
Further, "Shaping stopped" in the following table 3 means that
shaping was stopped because a sample was molten and could not keep
its cylindrical shape. Note that the scanning pitch s was 0.1 mm,
the thickness t of lamination was 50 micrometers, and the laser
diameter was 100 micrometers. FIG. 3 shows the relationship between
the energy density E and relative density D in the following table
3. In FIG. 3, the horizontal axis indicates the energy density E,
and the vertical axis indicates the relative density D. A result
when the laser output P was 250 [W] is indicated by an outline
rhombus, a result when the laser output P was 300 [W] is indicated
by an outline circle, and a result when the laser output P was 350
[W] is indicated by an outline triangle.
[0063] It is evident from the above Table 3 and FIG. 3 that (1) a
sample cannot be shaped in a desired shape when the energy density
E is 125 [J/mm.sup.3] or more, (2) a sample can be shaped without
any problem when the energy density E is 31 [J/mm.sup.3], (3) there
is a certain relationship between the energy density E and the
relative density D, and (4) the relative density D begins to be
saturated when the energy density E is 36 [J/mm.sup.3] or more.
From these findings, it is found that a sample in a desired shape
can be shaped without any problem when the energy density E is in
the range of 31 to 124 [J/mm.sup.3]. Further, the energy density E
is preferably in the range of 36 to 124 [J/mm.sup.3]. In this
range, a high density sample with the relative density D of 95 [%]
or more can be shaped. Further, the energy density E may be 36 to
118 [J/mm3].
[0064] Further, the energy density E is more preferably in the
range of 50 to 124 [J/mm.sup.3]. In this range, a high density
sample with the relative density D of approximately 98 [%] or more
can be shaped. Further, the energy density E may be 50 to 118
[J/mm.sup.3].
[0065] FIG. 4 shows the relationship between the laser scanning
speed v and the relative density D in the above table 3. In FIG. 4,
the horizontal axis indicates the laser scanning speed v, and the
vertical axis indicates the relative density D. A result when the
laser output P was 250 [W] is indicated by an outline rhombus, a
result when the laser output P was 300 [W] is indicated by an
outline circle, and a result when the laser output P was 350 [W] is
indicated by an outline triangle. It is evident from the above
Table 3 and FIGS. 3 and 4 that the highest relative density D is
obtained when the laser output P is 300 or 350 [W] and the laser
scanning speed v is 800 [mm/s].
[0066] The following table 4 shows test results when the scanning
pitch s was varied. In the following table 4, "Appearance" is a
photograph of the upper end face of the shaped sample. Further,
"Shaping stopped" in the following table 4 means that shaping was
stopped because a sample was molten and could not keep its
cylindrical shape. Note that the laser scanning speed v was 800
[mm/s], the thickness t of lamination was 50 micrometers, and the
laser diameter was 100 micrometers. FIG. 5 shows the relationship
between the energy density E and the relative density D in the
following table 4. In FIG. 5, the horizontal axis indicates the
energy density E, and the vertical axis indicates the relative
density D. A result when the laser output P was 300 [W] is
indicated by an outline rhombus, and a result when the laser output
P was 350 [W] is indicated by an outline circle.
[0067] It is evident from the above Table 4 and FIG. 5 that (1) a
sample cannot be shaped in a desired shape when the energy density
E is 125 [J/mm.sup.3] or more, (2) a sample can be shaped without
any problem when the energy density E is 47 [J/mm.sup.3], and (3)
there is a certain relationship between the energy density E and
the relative density D. From these findings, it is found that a
sample in a desired shape can be shaped without any problem when
the energy density E is in the range of 47 to 124 [J/mm.sup.3].
Note that the graph of FIG. 5 is substantially similar to the graph
of FIG. 3.
[0068] FIG. 6 shows the relationship between the scanning pitch s
and the relative density D in the above table 4. In FIG. 6, the
horizontal axis indicates the scanning pitch s, and the vertical
axis indicates the relative density D. A result when the laser
output P was 300 [W] is indicated by an outline rhombus, and a
result when the laser output P was 350 [W] is indicated by an
outline circle.
[0069] It is evident from the above Table 4 and FIGS. 5 and 6 that
the highest relative density D is obtained when the laser output P
is 300 [W] and the scanning pitch s is 0.08 [mm].
[0070] Further, taking the above Tables 3 and 4 and FIGS. 3 to 6
into consideration as a whole, the energy density E is most
dominantly involved in the relative density D. Accordingly, it can
be stated that, to obtain a desired relative density D, it is
important to manage the energy density E with particular
attention.
4.2. Structure Observation Test
[0071] In this structure observation test, a structure observation
was conducted on a shaped sample before any treatment, a sample
after solution treatment, and a sample after solution treatment and
ageing treatment to examine a change in the structure before and
after solution treatment and ageing treatment. The purpose of the
structure observation test is to see whether or not there is a
difference between microstructure in the diameter direction and
that in the height direction and to see whether three phases,
ferrite, austenite and martensite, coexist. The conditions of the
test were as follows.
[0072] Object to be tested: an object to be observed was a sample
shaped with the selective laser sintering system at the laser
output P of 300 [W], the laser scanning speed v of 800 [mm/s], and
the scanning pitch s of 0.08 [mm]. The size of the sample and the
procedure of shaping were the same as those in the energy density
test described above.
[0073] Test method: a sample was cut using a fine cutter to obtain
a longitudinal section thereof, and the longitudinal section was
filed with resin. Next, the longitudinal section was ground
sequentially using carbon Mac papers #80, #220, #600, #1200 and
#2000. Then, the longitudinal section was burnished sequentially
using diamond paste with a size of 3 micrometers and 1 micrometer.
After that, the sample was immersed in marble liquid to etch the
longitudinal section. Then, the structure of the longitudinal
section was observed using an optical microscope (with a
magnification of 50 to 100).
[0074] Solution treatment conditions: the sample began to be heated
starting at a room temperature, maintained at 1050.degree. C. for
20 minutes, and then water-cooled.
[0075] Ageing treatment conditions: the sample began to be heated
starting at a room temperature, maintained at 480.degree. C. for 7
hours, and then air-cooled.
[0076] FIG. 7 shows photographs of the longitudinal section of a
shaped sample before solution treatment and solution treatment. As
shown in FIG. 7, the microstructure (laminated structure) similar
to thermal spraying is seen all over the longitudinal section.
Further, the coexistence of three phases, which are ferrite,
austenite and martensite, is found. Further, it is seen that the
proportion of martensite slightly differs between the inward and
the outward of the longitudinal section.
[0077] FIG. 8 shows photographs of the longitudinal section of a
sample after solution treatment. As shown in FIG. 8, martensite is
substantially all over the longitudinal section, and a slight
amount of residual austenite is seen. The laminated structure has
disappeared, and the sample has a substantially uniform metal
structure.
[0078] FIG. 9 shows photographs of the longitudinal section of a
sample after solution treatment and ageing treatment. As shown in
FIG. 8, the residual austenite has substantially disappeared.
4.3. Hardness Test
[0079] A hardness test was conducted on a shaped sample before any
treatment, a sample after solution treatment, and a sample after
solution treatment and ageing treatment to examine a change in the
hardness before and after solution treatment and ageing treatment.
The conditions of the test were as follows.
[0080] Object to be tested: an object to be tested was the
longitudinal section of a chuck of a sample, which is an object to
be tested by a tensile test described later.
[0081] Test conditions: a low-load Vickers hardness test was
conducted. A test force was 0.3 kgf, a loading time was 4.0
seconds, a retention time was 15.0 seconds, a unloading time was
4.0 seconds, an approach speed was 60 micrometers per second, and
the number of tests was 8 to 12 for each sample.
[0082] FIG. 10 shows test results. In FIG. 10, "shaped" indicates a
shaped sample before any treatment, "solution" indicates a sample
after solution treatment, and "ageing" indicates a sample after
solution treatment and ageing treatment. The vertical axis
indicates Vickers hardness HV. In FIG. 10, measurement results are
represented by box plots, and the average is represented by a bar
chart. For reference, the catalogue values of a casted product of
silicon alloy steel A2 are represented by horizontal bands.
"Catalogue value (solution)" is the catalogue value of a casted
product of silicon alloy steel A2 after solution treatment.
"Catalogue value (ageing)" is the catalogue value of a casted
product of silicon alloy steel A2 after solution treatment and
ageing treatment.
[0083] It is obvious from FIG. 10 that a sample shaped with silicon
alloy A2 powder has substantially the same Vickers hardness as a
casted product of silicon alloy steel A2. Note that maraging steel
after ageing treatment has Vickers hardness of HV513. Thus, it can
be stated that a sample that has been shaped with silicon alloy A2
powder and undergone solution treatment and ageing treatment has
the Vickers hardness that substantially equals that of maraging
steel after ageing treatment.
4.4. Tensile Test
[0084] A tensile test was conducted on a shaped sample before any
treatment and a sample after heat treatment to examine the maximum
tensile strength of each sample.
[0085] Object to be tested: an object to be observed was a sample
shaped with the selective laser sintering system at the laser
output P of 300 [W], the laser scanning speed v of 800 [mm/s], and
the scanning pitch s of 0.08 [mm].
[0086] 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 cutting is performed
after the solution treatment, and then ageing treatment is
performed after that treatment. "Vertical" indicates a sample
shaped in an orientation that stands in the direction of
lamination, and "horizontal" indicates a sample shaped in an
orientation that is orthogonal to the direction of lamination.
[0087] Sample shape: As shown in FIGS. 11 and 12.
[0088] Solution treatment conditions: the sample began to be heated
starting at a room temperature, maintained at 1050.degree. C. for
20 minutes, and then water-cooled.
[0089] Ageing treatment conditions: the sample began to be heated
starting at a room temperature, maintained at 480.degree. C. for 7
hours, and then air-cooled.
[0090] Testing machine: INSTRON MODEL 4206
[0091] Tension speed: 1 mm/min
Detection of Strain: Strain Gauge Was Used
[0092] FIG. 13 shows test results. In FIG. 13, the lower bar on the
left side of each bar pair in the graph is the one not subjected to
the heat treatment, and the higher bar on the right side is the one
subjected to the heat treatment. "Catalogue value (ageing)" is the
catalogue value of a casted product of silicon alloy steel A2 after
solution treatment and ageing treatment. It is obvious from FIG. 13
that the orientation of each sample with respect to the direction
of lamination does not substantially affect the maximum tensile
strength and that the sample after heat treatment has substantially
the same maximum tensile strength as that of a casted product of
silicon alloy steel A2 after heat treatment. Note that maraging
steel after ageing treatment has the maximum tensile strength of
1890 MPa. Thus, it can be stated that a sample that has been shaped
with silicon alloy A2 powder and undergone heat treatment has the
maximum tensile strength that substantially equals that of maraging
steel after ageing treatment.
[0093] According to the test results described above, it was
concluded that (1) silicon alloy A2 can be employed as metal powder
to be used in the selective laser sintering method, (2) a shaped
product produced by selective laser sintering using silicon alloy
steel A2 has substantially the same mechanical quality as that of a
casted product of silicon alloy steel A2, and (3) a shaped product
produced by selective laser sintering using silicon alloy steel A2
can properly serve as a replacement for a commercially available
maraging steel.
[0094] Finally, a shaping method using silicon alloy A2 powder is
described hereinafter referring to FIG. 14.
[0095] First, 2D CAD data (slice data) is created by slicing 3D CAD
data of a shaped product (S90). Next, the selective laser sintering
system forms silicon alloy A2 powder in layers (S100). Then, the
selective laser sintering system selectively applies a laser to the
silicon alloy A2 powder to make it molten and sintered in a desired
shape (S110). After that, the selective laser sintering system
determines whether a shaped product has been completed (S120), and
when it determines that the shaped product has not been completed
(No in S120), the selective laser sintering system returns the
process to S100. On the other hand, when it determines that the
shaped product has been completed (Yes in S120), the selective
laser sintering system ends the shaping. Then, solution treatment
is performed on the shaped product at a specified temperature for a
specified period of time (S130). Further, ageing treatment is
performed on the shaped product after the solution treatment at a
specified temperature for a specified period of time (S140). A
shaped product that is comparable to maraging steel after heat
treatment is thereby obtained.
[0096] The above-described embodiment has the following
features.
[0097] A selective laser sintering method alternately repeats
(S120) a step (S100) of forming silicon alloy A2 powder (metal
powder) in layers, the silicon alloy A2 powder made of high silicon
stainless steel containing C:less than 0.10, Si:2.0.about.9.0,
Mn:0.05.about.6.0, Cu:0.5.about.4.0, Ni:1.0.about.24.0,
Cr:6.0.about.28.0, Mo:0.2.about.4.0, Nb:0.03.about.2.0 in wt %, and
the balance of Fe and inevitable impurities, and a step (S110) of
selectively applying a laser to the silicon alloy A2 powder formed
in layers to melt and sinter the silicon alloy A2 powder.
[0098] It is preferred that the particle size of silicon alloy A2
powder be 32 to 62 micrometers.
[0099] In the above-described selective laser sintering method, the
energy density E is 31 to 124 [J/mm.sup.3].
[0100] It is preferred that the energy density E be 36 to 124
[J/mm.sup.3].
[0101] It is more preferred that the energy density E be 50 to 124
[J/mm.sup.3].
[0102] It is further preferred that the energy density E be 50 to
118 [J/mm.sup.3].
[0103] The lower limit of the energy density E is any 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 any 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.
[0104] A heat treatment method includes a step (S130) of performing
solution treatment on a shaped product shaped by the
above-described selective laser sintering method and a step (S140)
of performing ageing treatment on the shaped product after the
solution treatment.
[0105] Also provided is metal powder that is used in a selective
laser sintering method that selectively applies a laser to metal
powder to melt and sinter the metal powder for lamination, wherein
the metal powder is made of high silicon stainless steel containing
C:less than 0.10, Si:2.0.about.9.0, Mn:0.05.about.6.0,
Cu:0.5.about.4.0, Ni:1.0.about.24.0, Cr:6.0.about.28.0,
Mo:0.2.about.4.0, Nb:0.03.about.2.0 in wt %, and the balance of Fe
and inevitable impurities.
[0106] The particle size of the metal powder is 32 to 62
micrometers.
[0107] Further, a shaped product shaped by the above-described
selective laser sintering method is provided.
[0108] Furthermore, a shaped product heat-treated by the
above-described heat treatment method is provided.
[0109] From the invention thus described, it will be obvious that
the embodiments of the invention may 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 as would be
obvious to one skilled in the art are intended for inclusion within
the scope of the following claims.
* * * * *