U.S. patent application number 13/976239 was filed with the patent office on 2013-10-31 for lightweight cast-iron product.
This patent application is currently assigned to ASADA KATAN CHUTETU-SYO CO., LTD.. The applicant listed for this patent is Yasushi Asada. Invention is credited to Yasushi Asada.
Application Number | 20130284320 13/976239 |
Document ID | / |
Family ID | 46382872 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130284320 |
Kind Code |
A1 |
Asada; Yasushi |
October 31, 2013 |
LIGHTWEIGHT CAST-IRON PRODUCT
Abstract
Provided is a cast-iron product that satisfies demands for both
weight reduction and strength enhancement with good balance. A
cast-ion product having an inner honeycomb structure is produced by
a process including: a decarburization step, in which a cast-iron
product made of a hypoeutectic cast iron is heated to form a
decarburized layer on the surface of the cast-iron product; an
outflow-hole formation step, in which an outflow hole penetrating
through the decarburized layer into an inner region is formed; and
a liquation step, in which the cast-iron product is heated to a
temperature lower than the melting point of the decarburized layer
and higher than the melting point of the hypoeutectic cast iron
remaining inside, while being held in such a manner that the
outflow hole is located in the lower portion thereof.
Inventors: |
Asada; Yasushi;
(Fukuchiyama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Asada; Yasushi |
Fukuchiyama-shi |
|
JP |
|
|
Assignee: |
ASADA KATAN CHUTETU-SYO CO.,
LTD.
Fukuchiyama-shi, Kyoto
JP
|
Family ID: |
46382872 |
Appl. No.: |
13/976239 |
Filed: |
December 19, 2011 |
PCT Filed: |
December 19, 2011 |
PCT NO: |
PCT/JP2011/079367 |
371 Date: |
June 26, 2013 |
Current U.S.
Class: |
148/522 ;
148/321 |
Current CPC
Class: |
C22C 2001/087 20130101;
C22C 1/08 20130101; C21D 10/00 20130101; C22C 2001/1089 20130101;
B22D 25/02 20130101; C22C 37/00 20130101 |
Class at
Publication: |
148/522 ;
148/321 |
International
Class: |
C21D 10/00 20060101
C21D010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2010 |
JP |
2010-290847 |
Claims
1. A lightweight cast-iron product comprising a shell portion
having a melting point increased by surface decarburization and a
honeycomb region inside the shell portion.
2. The cast-iron product according to claim 1, wherein a a carbon
equivalent of a composition of a cast-iron before the surface
decarburization is hypoeutectic.
3. A method for producing a lightweight cast-iron product,
comprising: a) a decarburization step, in which a cast-iron product
made of a hypoeutectic cast iron is heated to form a decarburized
layer on a surface of the cast-iron product; b) an outflow-hole
formation step, in which an outflow hole penetrating through the
decarburized layer into an inner region is formed; and c) a
liquation step, in which the cast-iron product is heated to a
temperature lower than a melting point of the decarburized layer
and higher than a melting point of the hypoeutectic cast iron
remaining inside, while being held in such a manner that the
outflow hole is located in a lower portion thereof.
Description
TECHNICAL FIELD
[0001] The present invention relates to a lightweight cast-iron
product and a method for producing the same.
BACKGROUND ART
[0002] A number of cast-iron products are currently used for the
main bodies and parts of automobiles or other mid-size to
large-size mechanical systems. As compared to plastic products,
cast-iron products are more suitable for such parts or portions
that must have high mechanical strength or heat resistance. As
compared to other kinds of metals including steels, they are more
suitable for such parts which have complex shapes or which need to
be inexpensively produced. Accordingly, cast-iron products are used
in a large number of areas where the aforementioned properties and
performance are required. However, their superiorities are
gradually undermined by plastic materials and other kinds of metals
which have achieved technical improvements in various
functionalities. Under such a situation, similar technical
improvements of cast-iron products for meeting the demands of the
times are also expected.
[0003] One of the major areas where the cast-iron products are used
is the automobile industry, where the reduction of weight has
always been a critical problem. Needless to say, there are also
other application areas in which weight reduction is regarded as an
eternal problem. To address this issue, the present inventor and
his associates have provided an epoch-making solution, i.e. the
hollow cast-iron product (Patent Document 1).
BACKGROUND ART DOCUMENT
Patent Document
[0004] Patent Document 1: JP-B 4099535
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0005] The cast-iron product described in Patent Document 1 has
achieved significant progress in terms of weight reduction. As for
its strength, the product is adequately stronger than plastic
products. However, due to its hollow structure, the product is
often not strong enough to substitute for such parts that have
conventionally been made of cast iron.
[0006] Accordingly, the problem to be solved by the present
invention is to provide a cast-iron product which satisfies demands
for both weight reduction and strength enhancement with good
balance.
Means for Solving the Problems
[0007] The lightweight cast-iron product according to the present
invention aimed at solving the aforementioned problem includes a
shell portion having a melting point increased by surface
decarburization, and a honeycomb region inside the shell
portion.
[0008] A method for producing such a cast-iron product
includes:
[0009] a) a decarburization step, in which a cast-iron product made
of a hypoeutectic cast iron is heated to form a decarburized layer
on the surface of the cast-iron product;
[0010] b) an outflow-hole formation step, in which an outflow hole
penetrating through the decarburized layer into an inner region is
formed; and
[0011] c) a liquation step, in which the cast-iron product is
heated to a temperature lower than the melting point of the
decarburized layer and higher than the melting point of the
hypoeutectic cast iron remaining inside, while being held in such a
manner that the outflow hole is located in the lower portion
thereof.
[0012] The aforementioned "hypoeutectic cast iron" is a cast iron
having a composition whose carbon equivalent CE satisfies the
following equation (I):
2.0<CE=C %+(Si %+P %)/3<4.3 (1)
where the "%" values are in weight percent.
[0013] If CE is within this range, the melting point of the
hypoeutectic cast iron will be approximately 1147.degree. C.,
regardless of the CE value. Accordingly, it is preferable to set
the heating temperature in step c) at a value higher than that
melting point (1147.degree. C.) by up to approximately 50.degree.
C., i.e. within a range from 1147 to 1200.degree. C. As for the
carburized layer, if its carbon concentration is equal to or less
than 1%, the melting point of that portion (the carburized layer)
will be approximately 1350.degree. C.
Effect of the Invention
[0014] The previously described process according to the present
invention is basically similar to the process described in Patent
Document 1. However, a significant difference exists: The cast-iron
part according to Claim 1 of Patent Document 1 is merely described
as a "cast-iron part" and there is no specific limitation on its
material. By contrast, the present invention is limited to a
product "made of a hypoeutectic cast iron." It should also be noted
that the cast-iron part according to Claim 3 of Patent Document 1
is characterized by "having a eutectic carbon concentration." In
this respect, the invention described in Patent Document 1 is
entirely different from the method according to the present
invention.
[0015] As described previously, the present invention uses a
hypoeutectic east iron as the material. As can be understood from
the phase diagram in FIG. 1, the hypoeutectic cast iron in the
non-decarburized portion (inner region) does not completely melt in
the Equation step c); a portion of the dendrite-shaped .gamma.
phase, which has a higher melting point, remains in a lattice form.
As a result, the inner region (non-decarburized portion) will have
a honeycomb structure, unlike the cast-iron part described in
Patent Document 1 whose inner region is completely hollow.
Naturally, the honeycomb structure is somewhat inferior to the
complete hollow structure in terms of the weight-reducing effect.
However, it is adequately stronger than the hollow structure. Thus,
by the method according to the present invention, it is possible to
produce a cast-iron product which satisfies demands for both weight
reduction and strength enhancement with good balance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a phase diagram of the iron-carbon system (for
Si=0%).
[0017] FIG. 2 is an external view of a cast-iron product 1 as the
first example.
[0018] FIG. 3 is a table showing the major chemical composition of
the cast-iron product 1 of the first example.
[0019] FIG. 4 is a sectional view of the cast-iron product 1 after
a honeycomb-structure formation process.
[0020] FIG. 5 is a table showing the major chemical composition of
a cast-iron product 2 as the second example.
BEST MODE FOR CARRYING OUT THE INVENTION
[0021] Two examples of the cast-iron product according to the
present invention will be hereinafter described.
FIRST EXAMPLE
[0022] The first example is a bearing cap as shown in FIG. 2. Its
chemical composition was as shown in FIG. 3. As indicated in the
last field of FIG. 3, the material of the cast-iron product of the
present example (which is hereinafter called the "cast-iron product
1") has a CE value of 4.03, and therefore, is hypoeutectic.
[0023] A decarburization process was performed as follows: The
cast-iron product 1 was heated to 1060.degree. C. in an electric
furnace and maintained at that temperature for 12 hours in an
ambience of a converted gas prepared from a city gas by altering
its composition to CO/(CO+CO.sub.2)*100-75%. Following the
decarburization process, the ambient gas was replaced with N.sub.2
gas and the furnace was cooled to 500.degree. C., after which the
product was cooled in atmospheric air.
[0024] After the cast-iron product 1 was cooled to room
temperature, a hole of 3 mm in depth (outflow hole) was bored in
one portion of the product (indicated by "A" in FIG. 2) with a
drill of 4.5 mm in diameter.
[0025] Then, the cast-iron product 1 was placed in the same
electric furnace, with the outflow hole directed downward. After
the inner space of the furnace was filled with N.sub.2 gas, the
temperature was increased to 1185.degree. C. in 50 minutes and
maintained at that temperature for eight minutes. When the
cast-iron product 1 reached that temperature, the molten metal
began to flow out of the outflow hole. A few minutes later, the
outflow of the molten metal began to slow down, which was almost
stopped at the end of the eight-minute period. Then, the product in
the furnace was cooled to 500.degree. C. in the same N.sub.2
ambience, after which it was cooled in atmospheric air.
[0026] After being cooled to room temperature, the cast-iron part 1
was cut at a plane in the middle of its thickness. FIG. 4 shows the
cross section. As shown, a honeycomb structure was formed inside
the decarburized peripheral layer which had a thickness of
approximately 3 mm.
[0027] The weight of the cast-iron part 1, which was 370 gram
before the previously described process, decreased to 315 gram
after the process. The weight reduction rate was 15%.
SECOND EXAMPLE
[0028] The second example is an oil pump cover. The cast-iron
product in the present example (which is hereinafter called the
"cast-iron product 2") is a disc-shaped part of 185 mm in outer
diameter having a 45-mm-diameter hole at its center. The central
hole was surrounded by a circumferential rim with a thickness of 28
mm. The outer circumferential portion of the disc was 21 mm in
thickness. Before undergoing the process, this cast-iron product 2
weighed 3.45 kg, which was approximately nine times the weight of
the cast-iron product 1. The chemical composition of the used
material was as shown in FIG. 5. Its CE value was 4.11
(hypoeutectic).
[0029] The decarburization of the cast-iron product 2 was performed
in the same manner as the previous example. That is to say, it was
heated to 1060.degree. C. in an electric furnace and maintained at
that temperature for 12 hours in an ambience of a converted gas
prepared from a city gas by altering its composition to
CO/(CO+CO.sub.2)*100=75%. Following the decarburization process,
the ambient gas was replaced with to N.sub.2 gas and the furnace
was cooled to 500.degree. C., after which the product was cooled in
atmospheric air. In the obtained cast-iron product 2, two outflow
holes were bored in the circumferential portion with a drill of 8
mm in diameter.
[0030] Then, the cast-iron product 2 was placed in the same
electric furnace, with the outflow holes directed downward. After
the inner space of the furnace was filled with N.sub.2 gas, the
heating temperature was increased to 1190.degree. C. in 60 minutes
and maintained at that temperature for 12 minutes. Similar to the
previous example, when the cast-iron product 2 reached that
temperature, the molten metal began to flow out of the outflow
holes. The outflow was almost stopped at the end of the 12-minute
period. Then, the product in the furnace was cooled to 500.degree.
C. in the same N.sub.2 ambience, after which it was cooled in
atmospheric air.
[0031] After being cooled to room temperature, the cast-iron part 2
was cut in a radial direction, and its inner condition was visually
checked. This checking confirmed that a honeycomb structure was
formed both inside the rim surrounding the central hole and inside
the outer circumferential portion having the increased thickness.
After the hollow-structure formation process, the weight of the
cast-iron part 2 was 2.31 kg. The weight reduction rate was
33%.
* * * * *