U.S. patent application number 10/096422 was filed with the patent office on 2003-03-20 for nodular graphite cast iron with high strength and high toughness.
This patent application is currently assigned to AISIN SEIKI KABUSHIKI KAISHA. Invention is credited to Coderre, Francois, Enya, Yasuhiro, Ibayashi, Yoshikazu, Matukura, Masaru.
Application Number | 20030051776 10/096422 |
Document ID | / |
Family ID | 18928225 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030051776 |
Kind Code |
A1 |
Enya, Yasuhiro ; et
al. |
March 20, 2003 |
Nodular graphite cast iron with high strength and high
toughness
Abstract
A nodular graphite cast iron is provided, having a pearlite
matrix, with high strength and high toughness. The nodular graphite
cast iron consists essentially of, by weight %,: from 3.0 to 4.6%
of carbon; from 1.6 to 2.5% of silicon; from 0.2 to 0.6% of
manganese; from 0.02 to 0.05% of magnesium; from 0.0004 to 0.090%
of zirconium; at least one of tin and copper such that .alpha.
ranges from 0.01 to 0.06% where .alpha. indicates a tin conversion
amount defined by a summation of a weight % of the tin and
0.1.times.a weight % of the copper; and the balance of iron and
inevitable foreign matters.
Inventors: |
Enya, Yasuhiro; (Kariya-shi,
JP) ; Coderre, Francois; (Kariya-shi, JP) ;
Ibayashi, Yoshikazu; (Toyama-ken, JP) ; Matukura,
Masaru; (Toyama-ken, JP) |
Correspondence
Address: |
F. Lindsey Scott
Law Office of F. Lindsey Scott
Suite B
2329 Coit Road
Plano
TX
75075
US
|
Assignee: |
AISIN SEIKI KABUSHIKI
KAISHA
Kariya-shi
JP
|
Family ID: |
18928225 |
Appl. No.: |
10/096422 |
Filed: |
March 13, 2002 |
Current U.S.
Class: |
148/321 ;
420/26 |
Current CPC
Class: |
C22C 37/10 20130101;
C22C 33/08 20130101 |
Class at
Publication: |
148/321 ;
420/26 |
International
Class: |
C22C 037/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2001 |
JP |
2001-070332 |
Claims
What is claimed is:
1. A nodular graphite cast iron consisting essentially of: from 3.0
to 4.6 weight % of carbon; from 1.6 to 2.5 weight % of silicon;
from 0.2 to 0.6 weight % of manganese; from 0.02 to 0.05 weight %
of magnesium; from 0.0004 to 0.090 weight % of zirconium; at least
one of tin and copper such that the sum of a weight % of the tin
and 0.1 times a weight % of the copper ranges from 0.01 to 0.06
weight %; and a balance of iron and inevitable impurities.
2. The nodular graphite cast iron according to claim 1, wherein the
carbon is from 3.1 to 4.5 weight %.
3. The nodular graphite cast iron according to claim 1, wherein the
silicon is from 1.7 to 2.4 weight %.
4. The nodular graphite cast iron according to claim 1, wherein the
manganese is from 0.3 to 0.5 weight %.
5. The nodular graphite cast iron according to claim 1, wherein the
magnesium is from 0.03 to 0.05 weight %.
6. The nodular graphite cast iron according to claim 1, wherein the
zirconium is from 0.0005 to 0.080 weight %.
7. The nodular graphite cast iron according to claim 1, wherein the
nodular graphite cast iron is a non-heat-treated nodular graphite
cast iron.
8. The nodular graphite cast iron according to claim 1 wherein the
nodular graphite cast iron has a tensile strength of 700 MPa or
more and an impact value of 15 J/cm.sup.2 or more.
9. A method of making a nodular graphite cast iron, the method
comprising heating a melt containing carbon, silicon, manganese,
magnesium, zirconium, iron and at least one of tin and copper; and
producing the cast iron of claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is generally directed to a nodular
graphite cast iron. In particular, the present invention is
directed to a nodular graphite cast iron with high strength and
high toughness.
[0003] 2. Discussion of the Background
[0004] In general, automotive products having a thin and
lightweight structure are desired. Because many automotive products
are formed from nodular graphite cast iron, this desire translates
into a need for nodular graphite cast iron to be strengthened,
which will allow automotive products to be made thinner and more
lightweight.
[0005] However, when conventional nodular graphite cast iron is
strengthened so that its tensile strength reaches 700 MPa, its
impulse value becomes 5 J/cm.sup.2 or less. Although this
conventional nodular graphite cast iron has high tensile strength,
its low toughness limits its use in making thin, lightweight
automotive parts.
[0006] There is a need for a nodular graphite cast iron combining
both high strength and high toughness.
SUMMARY OF THE INVENTION
[0007] A first aspect of the present invention provides a nodular
graphite cast iron consists essentially of, by weight %: 3.0 to
4.6% of carbon; 1.6 to 2.5% of silicon; 0.2 to 0.6% of manganese;
0.02 to 0.050% of magnesium; 0.0004 to 0.090% of zirconium; at
least one of tin and copper such that .alpha. ranges from 0.01 to
0.06% where .alpha. indicates a tin conversion amount defined by a
summation of a weight % of the tin and 0.1.times. a weight % of the
copper; and the balance of iron and inevitable impurities. This
nodular graphite cast iron has been found to exhibit both high
strength and high toughness. Without limiting the invention, at
present the inventors believe that the combination of high strength
and high toughness in a nodular graphite cast iron is achieved is
the following manner. When Zr, which constitutes a new treating
material to be added to graphite cast iron, is placed inside Si,
the Si, instead of the Zr, is oxidized by oxygen in an iron melt.
The Zr does not oxidize in the melt. Instead the Zr melts, mixes
with the iron melt and becomes part of the resulting graphite cast
iron. Deposits including Zr and at least one of Sn and Cu appear
evenly around each particle of the cast iron matrix. This results
in fine nodular graphite and fine matrix crystal particles around
the nodular graphite, thereby increasing the strength and toughness
of the nodular graphite cast iron. Electron probe microanalysis
(EPMA) has confirmed the formation of fine deposits including Zr
and at least one of Sn and Cu appearing evenly around each particle
of the cast iron matrix.
[0008] The above-mentioned chemical elements are included in the
inventive nodular graphite cast iron for the following reasons.
Each percentage (%) below is a weight percent.
[0009] C: If the amount of C is less than 3%, the amount of
graphite is insufficient, resulting in an increase in chill
structure in addition to poor fluidity of the molten nodular
graphite cast iron, thereby not obtaining the desired high
strength. On the other hand, if the amount of C is in excess of
4.6%, the graphite per se becomes brittle or breakable, which makes
it impossible to obtain the desired high strength. Thus, the amount
of C is 3.0-4.6%, preferably 3.0-4.5%, more preferably 3.6-3.8%.
The lower limit of the amount of C can be, for example, 3.1%, 3.2%
or 3.3%. The upper limit of the amount of C can be, for example,
4.5%, 4.4% or 4.3%.
[0010] Si: If the amount of Si is less than 1.6%, the amount of
graphite becomes insufficient, resulting in an increase in chill
structure in addition to poor fluidity of the melted graphite,
thereby not obtaining the desired high strength. On the other hand,
if the amount of Si is in excess of 2.5%, the graphite per se
becomes brittle or breakable, which makes the impact strength lower
considerably at low temperatures. In addition, the hardness of
nodular graphite cast iron decreases, and a nodular graphite cast
iron having of high strength is not obtained. Thus, the amount of
Si is 1.6-2.5%. The lower limit of the amount of Si can be, for
example, 1.7%, 1.8% or 1.9%. The upper limit of the amount of Si
can be, for example, 2.4%, 2.3% or 2.2%.
[0011] Mn:Mn aids in the formation of pearlite during cooling
processes and therefore is very important in controlling the
strength of the nodular graphite cast iron. If the amount of Mn is
less than 0.2%, then segregation of sulfide in molten nodular
graphite cast iron leads to a decrease in the strength of the
nodular graphite cast iron. On the other hand, if the amount of Mn
is in excess of 0.6%, the resulting promotion of a chill structure
increases structures such as cementite and martensite in the
matrix. This causes the nodular graphite cast iron to increase in
strength and to decrease in machinability, resulting in an
impractical nodular graphite cast iron. Thus, the amount of Mn is
0.2-0.6%, preferably 0.3-0.5%, more preferably 0.3-0.4%. The lower
limit of the Mn can be, for example, 0.22% or 0.25%. The upper
limit of the Mn can be, for example, 0.45% or 0.40%.
[0012] Mg: Mg acts as a means for spheroidizing graphite. If the
amount of Mg is 0.02% or less, the resulting insufficient
spheroidization of graphite causes a stress concentration at an
in-matrix graphite deposit portion of the solidified structure,
which makes it impossible to a obtain a desired strength. On the
other hand, because Mg is very easily oxidized, if the amount of Mg
is 0.05% or above, then an in-matrix Mg-oxide is increased to make
the matrix lower in strength, which makes it impossible to obtain a
desired strength. Thus, the amount of Mg is 0.02-0.05%, preferably
0.03-0.05%, more preferably 0.035-0.045%. The lower limit of the Mg
can be, for example, 0.035%. Th upper limit of the Mg can be, for
example, 0.048%.
[0013] Zr: As previously described, Zr is observed to make the
graphite particles in nodular graphite cast iron finer and finer.
Thus, Zr increases the structure of the matrix in addition to
forming Zr-carbide. If the amount of Zr is 0.0004% or less, the
Zr-carbide formed is insufficient to reinforce the matrix and
making the graphite particles finer and finer is difficult to
realize. Thus, it is impossible to obtain a nodular graphite cast
iron which is of high strength. On the other hand, if the amount of
Zr is in excess of 0.090%, then spheroidizing of graphite is
prevented leading to a stress concentration at an in-matrix
graphite deposit portion, which makes it impossible to obtain a
desired strength. Thus, the amount of Zr is set to be
0.0004-0.090%, preferably 0.0005-0.080%, more preferably
0.0010-0.070%. The lower limit of Zr can be, for example, 0.0006%
or 0.001%. The upper limit Zr can be, for example, 0.085% or
0.075%.
[0014] .alpha.: .alpha. indicates tin conversion amount and is
defined as a summation of a weight % of Sn and 0.1.times. a weight
% of Cu. .alpha. is set to range from 0.01 to 0.06%. Sn is a
chemical element for forming a pearlite and is added in order to
reinforce the matrix. Cu is similar to Sn but is of about 1/10
inferior effect when compared to the Sn-effect, resulting in the
above-mentioned coefficient:0.1 with respect to the tin conversion
amount. If .alpha. is less than 0.01%, then it is difficult to form
pearlite sufficiently in the matrix, so that the desired strength
is not obtained. On the other hand, if .alpha. is in excess of
0.06%, the matrix is lowered considerably in strength to separate a
chill structure, resulting in that the formed nodular graphite
becomes difficult in machine. Thus, .alpha. is set to range from
0.01 to 0.06%, preferably from 0.01 to 0.05%, more preferably from
0.01 to 0.04%. The lower limit of .alpha. can be, for example,
0.015% or 0.02%. The upper limit of .alpha. can be, for example,
0.045% or 0.04%.
[0015] Sn can be used exclusively (i.e., without using Cu), and Cu
can be used exclusively (i.e., without using Sn). Of course, both
Sn and Cu can be used together. When only Sn, but not Cu, is used,
the amount of Sn is 0.01-0.06%, preferably 0.01-0.04%. When only
Cu, but not Sn, is used, the amount of Cu is 0. 1-0.6%, preferably
0.2-0.4%.
[0016] The nodular graphite cast iron has a matrix based on
pearlite. The area ratio of the pearlite to the matrix (without
graphite) is generally 0.80-0.97, preferably 0.83-0.95%. Generally,
ferrite is formed around graphite particles to form a bull's eye
structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above and other objects, features and advantages of the
present invention will be more apparent and more readily
appreciated from the following detailed description of preferred
exemplary embodiments of the present invention, taken in connection
with the accompanying drawings, in which:
[0018] FIG. 1 shows how a spheroidizing process is performed;
[0019] FIG. 2 shows how a melted material is poured into a sand
mold using an inoculation;
[0020] FIG. 3 is a microscopic photograph (.times.100
magnification) of nodular graphite cast iron according to the
present invention;
[0021] FIG. 4 is a microscopic photograph (.times.100
magnification) of a conventional example (FCD700);
[0022] FIG. 5 is a microscopic photograph (.times.100
magnification) of another conventional example (FCD450);
[0023] FIG. 6 is a schematic of a Zr family treating material;
[0024] FIG. 7 is a front view of a tensile test piece;
[0025] FIG. 8(A) is a front view of an impact test piece;
[0026] FIG. 8(B) is a side view of the impact test piece;
[0027] FIG. 8(C) is a front view of the A-portion encircled in FIG.
8(A); and
[0028] FIGS. 9 through 11 show a variety of automotive products
formed using the nodular graphite cast iron of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0029] Embodiments of the present invention will now be described
in greater detail with reference to the attached drawings.
[0030] As a starting material, nodular graphite cast iron or a pig
iron was prepared. After adjusting the contents of ingredients such
as C, Si and S, the starting material in amount of 25 kg was put
into a high frequency melting furnace 50 and was heated up to a
temperature of 1580.degree. C. to melt. Thereafter, proper or
adequate amounts of substances such as C, Si, Mn, Sn, and Cu were
added to the melted starting material to adjust the contents. When
the added substances were fully mixed in the melted starting
material and the melted starting material attained again the
temperature of 1550.degree. C. or above, the melting furnace 50 was
brought into tilt or inclination as illustrated in FIG. 1 to pour
or tap the melted material via an outlet 50a of the melting furnace
50 into a ladle 60. At the bottom of the ladle 60 was provided a
spheroidizing material 65 of the Mg family having an average
particle diameter of 5.0-1.5 mm and a treating material 2 having an
average particle diameter of 1.0-3.0 mm. In detail, at the bottom
of the ladle 60 there was formed a chamber 61. In the chamber 61,
the spheroidizing material 65 of the Mg family was provided or
accommodated and thereon the treating material 2 of the Zr family
was provided. The chamber 61 was closed by an iron plate 68. The
reason why the treating material 2 was provided on the
spheroidizing material 65 is to make the melted material at higher
temperature to contact with the treating material 65 for the
prevention of possible heat absorption reaction upon direct contact
of the melted material with the spheroidizing material 65. It is to
be noted that the above-indicated particle diameters are exemplary
and are not limited values.
[0031] Referring to FIG. 6, there is illustrated a conceptual
structure illustration of the treating material 2. The treating
material 2 included a plurality of inner layers 10 which was formed
of Zr--Si--Fe family alloy. Each of the inner layers 10 was covered
with a first outer layer 21 formed of a Si-family alloy. The first
outer layers 21 including or accommodating therein the respective
inner layers 10 were covered with or accommodated in a second or
common outer layer 22. As a whole each of the inner layers 10 was
covered with or accommodated in an outer layer 20 which was made up
of the second outer layer 22 and the first outer layer 21.
[0032] The inner layer 10 is formed of the Zr--Si--Fe family and
contained 58% Zr, 35% Si and 7% Fe. The inner layer 10 had a
melting point of about 1600.degree. C. The inner layer 10 formed
about 13% by weight of the treating material 2. The inner layer 10
had an average particle diameter of 40-60 .mu.m (50 .mu.m).
[0033] The first outer layer 21 had a melting point of about
1414.degree. C. and was essentially Si. The first outer layer 21
formed about 47% by weight of the treating material 2. The first
outer layer 21 had an average particle diameter of 60-150 .mu.m
(100 .mu.m).
[0034] The second outer layer 22 was the outermost layer, had a
melting point of about 1220.degree. C., and was formed of a Fe--Si
alloy. The second outer layer 22 contained about 56% Si and about
42% Fe. The second outer layer 22 formed about 40 weight % of the
treating material 2.
[0035] As described above, it was possible to make the melted
material spheriodized by tapping the melted material at higher
temperature into the ladle 60 in which was previously provided the
Mg-family spheroidizing material 65 and the Zr-family treating
material 2. After the spheroidizing process, as shown in FIG. 2,
the ladle 60 was tilted to tap the melted material accommodated
therein into a sand mold 80 for a Y-block (JIS-G5502 B-type test
piece). After solidification in the sand mold 80, inventive members
(No. 1-No. 11) were obtained as test pieces.
[0036] At this stage, it should be noted that the above-mentioned
Zr-including treating material 2 provided remarkable advantages. In
general, when a treating material which includes Zr is put into
molten iron, the Zr, which has a higher melting point than iron, is
oxidized starting with the surface of the Zr. The oxidized surface
of the Zr is believe to prevent Zr from spreading into the molten
iron. However, with the above-described and newly provided treating
material 2, before the inner layer 10 whose main portion is Zr is
contacted with the molten iron the first outer layer 21 and second
outer layer 22 are subject to contact with the molten iron. As a
result, Si contained in the first outer layer 21 and the second
outer layer 22 is bonded to oxygen in the molten iron to produce
silicon oxide and consume the oxygen in the molten iron. When the
inner layer 10 whose main portion is Zr is finally brought into
contact with the molten iron, the amount of the oxygen in the
molten iron near the treating material 2 is very small and Zr
oxidation is minimized. This results in rapid dispersion of the Zr
into the molten iron. It should be emphasized that the treating
material 2 as detailed above is not disclosed in any conventional
or known documents such as Japanese Patent Publication No. Sho.
63(1983)-483 and Japanese Patent Laid-open Print No. Hei.
10(1994)-237528.
[0037] The pouring of molten material into the sand mold described
above was performed in such a manner that the molten material was
kept at a temperature of 1410.degree. C. or above and was added
with an inoculation such as ferrosilicon. In such case, the pouring
the molten material into the sand mold 80 was initiated within 8
minute after completion of the spheroidizing process in order to
restrict a fading effect.
1TABLE 1 Piece Composition (weight %) No. C Si Mn Mg Sn Cu Zr Fe 1
3.00 1.60 0.20 0.030 0.010 0.250 0.0005 Bal. 2 3.21 2.50 0.50 0.040
0.015 0.300 0.0080 Bal. 3 3.53 2.39 0.39 0.043 0.040 0.195 0.0502
Bal. 4 3.80 2.00 0.20 0.040 0.025 0.200 0.0700 Bal. 5 4.02 2.30
0.45 0.045 0.045 0.000 0.0804 Bal. 6 4.56 2.33 0.32 0.038 0.040
0.051 0.0253 Bal. 7 3.00 2.30 0.30 0.036 0.043 0.000 0.0450 Bal. 8
3.70 2.42 0.37 0.038 0.030 0.180 0.0500 Bal. 9 3.50 2.39 0.39 0.043
0.040 0.100 0.0310 Bal. 10 3.80 2.10 0.20 0.040 0.025 0.250 0.0300
Bal. 11 3.11 2.30 0.45 0.045 0.040 0.005 0.0604 Bal. CP. 1 2.50
2.60 0.35 0.038 0.070 0.100 0.0300 Bal. CP. 2 3.80 1.50 0.20 0.100
0.000 0.200 0.1000 Bal. CV. 1 FCD700 CV. 2 FCD450 Notes CP. 1:
Comparative Example 1 CP. 2: Comparative Example 2 CV. 1:
Conventional Example 1 CV. 2: Conventional Example 2
[0038] TABLE 1 indicates compositions of inventive materials (No.
1-No. 11). In TABLE 1, "Bal." indicates the substantial remaining
amount. As apparent from TABLE 1, each of the inventive materials
consists essentially of, by weight %, from 3.0 to 4.6% of carbon;
from 1.6 to 2.5% of silicon; from 0.2 to 0.6% of manganese; from
0.02 to 0.05% of magnesium; from 0.0004 to 0.090% of zirconium; at
least one of tin and cooper such that .alpha. ranges from 0.01 to
0.06% where .alpha. indicates a tin conversion amount defined by
the summation of a weight % of the tin and 0.1.times. a weight % of
the cooper; and the balance comprising an iron and inevitable
foreign matters. Amounts of S and P as the foreign matters were
0.02% or less and 0.1% or less, respectively, by weight %.
[0039] In a manner similar to the above-described process, each of
comparative examples 1 and 2 was obtained in the form of a non-heat
treated nodular graphite cast iron. The comparative example 1 was
produced similar to each of the inventive materials except that an
amount of Sn was set to be slightly larger than that in the
inventive material. The comparative example 2 was produced similar
to each of the inventive materials except that amounts of Mg and Zr
were set to be slightly larger than those in the inventive
material.
[0040] In addition, a conventional example 1 of non-heat treated
type high strengthened nodular graphite cast iron, available as
FCD700 (JIS G 5502), was produced. Another conventional example 2,
available as FCD450, was similarly produced. FCD450 consists of, by
weight %, carbon in amount of 2.5% or above, silicon in amount of
2.7% or less, manganese in amount of 0.4% or less, magnesium in
amount of 0.09%, phosphorus in amount of 0.08% or less and sulfur
in amount of 0.02% or less. FCD700 is similar to FCD450 in
composition except for the addition of a very small amount of tin.
FCD700 does not contain additional zirconium.
[0041] FIG. 3 illustrates the microstructure of the inventive
material (No. 2) when observed by a light microscope
(magnification: .times.100). As FIG. 3 illustrates, the nodular
graphite was found to be very, very fine and its particle number
was very, very large. In addition, a ferrite was produced around
the nodular graphite, forming a so-called bull's eye structure. It
is natural to conclude that when the nodular graphite cast iron has
a fine microstructure, the crystal particle of the matrix can be
very, very minute from the view point of metallography, to the
point that determining the size of the crystal particle of a
pearlite structure is difficult by light microscopy.
[0042] FIG. 4 illustrates the microstructure of the conventional
example 1, i.e., the non heat-treated high strengthened cast iron
FCD700 (JIS 65503), when observed by a light microscope
(magnification=X100). Obviously, the nodular graphite shown in FIG.
4 is relatively large and smaller in number when compared to the
nodular graphite in FIG. 3. In addition, despite of formation of a
so-called bull's eye structure, i.e., ferrite formation around the
nodular graphite, the ratio of the ferrite around the nodular
graphite is small when compared to that in FIG. 3.
[0043] FIG. 5 illustrates the microstructure of the conventional
example 2, i.e., the non heat-treated high strengthened cast iron
FCD450, when observed by a light microscope (magnification:
.times.100). The matrix regions of the FCD450 were mostly ferrite.
The nodular graphite is relatively large and smaller in number as
shown in FIG. 5.
[0044] TABLE 2 below provides results of tests showing
characteristics of the inventive material (No.2) and the
conventional example 2. The inventive material (No.2) has a
spheroidizing ratio of as high as 85.8%, like the FCD450, and its
graphite number is 134 particles per mm.sup.2, which is
considerably larger than that of the FCD450. In other words, the
number of graphite particles in the inventive material is 1.6 times
(.apprxeq.134/82) that of the FCD450 (with 82 particles per
mm.sup.2). The inventive material (No. 2) has a graphite particle
diameter of 41.7 .mu.m, which is considerably smaller than the 66.2
.mu.m particle diameter of the FCD450. Thus, in the inventive
material (No. 2) very finite nodular graphite and an increase
particle number are found.
2 TABLE 2 Conventional Inventive Example 2 Material No. 2 Graphite
number 82 134 (particles/mm.sup.2) Graphite particle diameter 66.2
41.7 (.mu.m) Splieroidizing ratio % 86.9 85.8 Pearlite ratio % 13
66
[0045] Each of the inventive materials (No. 1-No. 11) was machined
to produce a tensile test piece (FIG. 7) and a Charpy impact test
piece (JIS Z2202 No. 3) as shown in FIG. 8. With respect to the
tensile test piece and the Charpy impact test piece of each of the
inventive materials (No. 1-No. 11), tensile and Charpy impact test
were conducted. In addition, cutting tests were performed.
[0046] The cutting tests were performed to evaluate cutting
properties with regard to each of the comparative examples 1 and 2,
the conventional examples 1 and 2, and the inventive materials (No.
1-No. 6) which were not heat-treated or were in an as-cast state.
These tests were conducted to verify an easy-to-machine property of
each inventive material pursuant to the following cutting
conditions with usage of generally or commercially available
carbide cutting tools. Each of the resulting flank wear (V.sub.B)
was detected and listed in TABLE 3 as a cutting evaluation
result.
[0047] Test conditions
[0048] material to be cut: 110 mm (outer diameter)
[0049] cutting speed: 150 m/min
[0050] feed: 0.15 min/rev
[0051] width of cut: 0.3 mm
[0052] cutting oil: aqueous cutting oil (Chemi-cool SR-1)
[0053] cutting length: 10000 m
3TABLE 3 Tensile Strength Charpy Impact Test Piece No. (MPa) Value
(J/cm.sup.2) Flank Wear (mm) 1 702.4 15.0 0.29 2 707.6 17.7 0.28 3
738.1 16.4 0.35 4 724.7 16.5 0.33 5 716.3 17.3 0.28 6 704.8 18.2
0.36 7 702.4 15.4 -- 8 732.2 15.7 -- 9 709.1 15.3 -- 10 705.7 15.4
-- 11 704.3 17.3 -- CP. 1 802.8 2.0 0.42 CP. 2 661.2 17.6 0.28 CV.
1 732.5 3.2 0.39 CV. 2 482.7 19.0 0.26 Notes: CP. 1: Comparative
Example 1 CP. 2: Comparative Example 2 CV. 1: Conventional Example
1 CV. 2: Conventional Example 2
[0054] As TABLE 3 represents, each of the inventive materials (No.
1-No. 11) is of 700 MPa or above in tensile strength and is of 15.0
J/cm.sup.2 or above in Charpy impact value. These results show that
the inventive nodular graphite cast irons have both high strength
and high toughness. In particular, the inventive material No. 2 has
a tensile strength of 700 MPa or above and a Charpy impact value of
17.0 J/cm.sup.2 or above. The inventive material No. 3 has a
tensile strength of 730 MPa or above and a Charpy impact value of
16.0 J/cm.sup.2 or above. The invented material No. 4 has a tensile
strength of 720 MPa or above and a Charpy impact value of 16.0
J/cm.sup.2 or above. The invented material No. 5 has a tensile
strength of 710 MPa or above and a Charpy impact value of 17.0
J/cm.sup.2 or above. The invented material No. 6 has a tensile
strength of 700 MPa or above and a Charpy impact value of 18.0
j/cm.sup.2 or above.
[0055] In addition, according to TABLE 3, the inventive material
No. 7 has a tensile strength of 700 MPa or above and a Charpy
impact value of 15.0 J/cm.sup.2 or above. The invented material No.
8 has a tensile strength of 730 MPa or above and a Charpy impact
value of 15.0 J/cm.sup.2 or above. The invented material No. 9 has
a tensile strength of 700 MPa or above and a Charpy impact value of
15.0 J/cm.sup.2 or above. The invented material No. 10 has a
tensile strength of 700 MPa or above and a Charpy impact value of
15.0 j/cm.sup.2 or above. The invented material. No. 11 has a
tensile strength of 700 MPa or above and a Charpy impact value of
17.0 J/cm.sup.2 or above.
[0056] Though the comparative example 1, i.e., the nodular graphite
cast iron in which a slightly smaller amount of C and a slightly
larger amount of Sn were contained, is indicative of an excellent
tensile strength of as high as 800 MPa or above, it is indicative
of poor toughness due to the fact that the Charpy impact value was
as low as of 2 j/cm.sup.2. On the other hand, though the
comparative example 2, i.e., the nodular graphite cast iron in
which a slightly larger amount of Si was contained, is indicative
of an excellent toughness due to the fact that the Charpy impact
value is about 17 J/cm.sup.2, it is indicative of poor tensile
strength of about 660 MPa.
[0057] The conventional example 1 or FCD700 was, though it was
indicative of excellent tensile strength of as high as 730 MPa or
above, poor in toughness due to the fact that the Charpy impact
value was 3 j/cm.sup.2. The conventional example 2 or FCD450 was,
though it is indicative of excellent toughness due to the fact the
Charpy impact value was as high as about 19 j/cm.sup.2, indicative
of poor tensile strength which is as low as about 480 MPa.
[0058] Even though each of the inventive materials has a relatively
high area ratio of pearlite (area ratio: 76-93%), the inventive
materials were excellent in cutting properties. The flank wear was
restricted and was similar to the flank wear (0.26 mm) of the
conventional example 2, which is ferrite where most matrixes were
low in hardness. In other words, the flank wear was near the flank
wear of ferrite family nodular graphite cast iron, such as the
comparative example 2 or the conventional example 2, each of which
was of low tensile strength of 670 MPa or less despite being
excellent in Charpy impact value. It can be thought that the
excellent cutting property of each of the inventive materials was
due to very finite nodular graphite and an increased graphite
particle number. As can be easily understood from the above test
results, each of the inventive materials was of high strength, high
toughness, and excellent cutting property, even though it was not
heat-treated and was in an as-cast state.
[0059] In detail, in view of the above test results, each of the
inventive materials (No. 1-No. 11) was found to have a toughness or
intensity against impulse equivalent or similar to that of the
conventional example 1, which was ferrite family FCD 450, though
each inventive material was found to have a structure that was
equivalent or similar to pearlite family FCD700 from the view point
of metallography. In addition, each inventive material was found to
be excellent in an easy-to-cut property like the conventional
FCD450. Thus, each of the inventive materials makes it possible to
produce long-sought lightweight cast iron products, such as
remarkably lightweight automotive parts, at lower costs. Of course,
other than automotive parts, the inventive materials can be used
for producing general purpose mechanical parts.
[0060] FIG. 9 illustrates a disc brake caliper 100 formed of a
nodular graphite cast iron according to the present invention. FIG.
10 illustrates a brake cylinder 110 for braking a disc 105 and a
mounting member 120 for supporting the brake cylinder 110, each of
the brake cylinder 110 and the mounting member 120 being formed of
a nodular graphite cast iron according to the present invention.
FIG. 11 depicts a suspension arm 200 formed of a nodular graphite
cast iron according to the present invention. The above-mentioned
caliper 100, brake cylinder 110, mounting member 120, and
suspension arm 200 can be of high strength and high toughness while
maintaining an excellent easy-to-cut property, when they are formed
of a nodular graphite cast iron according to the present invention,
resulting in making each of the members thinner, thereby making it
possible to make each of the members extremely lightweight. Thus,
each of the resulting members or automotive products can contribute
as much as possible to improving the fuel economy of an automotive
vehicle.
[0061] The present invention is capable of providing a nodular
graphite cast iron having high strength and high toughness.
Particularly, its tensile strength can attain 700 MPa or above and
its impact value can attain 15 J/cm.sup.2 or above. These features
can be attained even when the nodular graphite cast iron is in a
untreated state, particularly in a non-heat-treated state. In
addition, the nodular graphite cast iron is easy to cut.
[0062] The disclosure of the priority document, Japanese Patent
Application No. 2001-070332, filed Mar. 13, 2001, is incorporated
by reference herein in its entirety.
[0063] The invention has thus been shown and description with
reference to specific embodiments, however, it should be understood
that the invention is in no way limited to the details of the
illustrates structures but changes and modifications may be made
without departing from the scope of the appended claims.
* * * * *