U.S. patent application number 10/523990 was filed with the patent office on 2005-12-01 for steel for machine structural use excellent in friability of chips.
Invention is credited to Hayaishi, Masakazu, Kano, Takashi, Siiki, Katsuaki, Yamada, Noriyuki.
Application Number | 20050265886 10/523990 |
Document ID | / |
Family ID | 31711831 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050265886 |
Kind Code |
A1 |
Hayaishi, Masakazu ; et
al. |
December 1, 2005 |
Steel for machine structural use excellent in friability of
chips
Abstract
Disclosed is a free cutting steel for machine structural use
having excellent chip-breakability. The steel consists essentially
of, by wt. %. C: 0.05-0.8%, Si: 0.01-2.5%, Mn: 0.1-3.5%, S:
0.01-0.2%, Ca or Ca+Mg; 0.0005-0.02%, Ti: 0.002-0.010% and/or Zr:
0.002-0.025%, O: 0.0005-0.010%, and the balance of impurities and
Fe. At least five MnS inclusion particles having averaged particles
sizes of 1.0 .mu.m or more exists per mm.sup.2 per 0.01% of
S-content in the steel. The steel satisfies the condition that, in
the microscopic fields, (area[.mu.m.sup.2]/aspect ratio).gtoreq.10,
and that the the area percentage of Ca-containing sulfide
inclusions containing at least 1.0 wt. % of Ca is in the range of
15-40% of the area of all the sulfide inclusions.
Inventors: |
Hayaishi, Masakazu; (Aichi,
JP) ; Kano, Takashi; (Aichi, JP) ; Yamada,
Noriyuki; (Saitama, JP) ; Siiki, Katsuaki;
(Saitama, JP) |
Correspondence
Address: |
ARENT FOX PLLC
1050 CONNECTICUT AVENUE, N.W.
SUITE 400
WASHINGTON
DC
20036
US
|
Family ID: |
31711831 |
Appl. No.: |
10/523990 |
Filed: |
February 9, 2005 |
PCT Filed: |
August 6, 2003 |
PCT NO: |
PCT/JP03/10029 |
Current U.S.
Class: |
420/87 |
Current CPC
Class: |
C21D 2261/00 20130101;
C22C 38/02 20130101; C21D 2211/004 20130101; C22C 38/14 20130101;
C21D 6/005 20130101; C22C 38/60 20130101; C22C 38/04 20130101; C22C
38/18 20130101; C22C 38/22 20130101; C22C 38/002 20130101; C21D
6/008 20130101 |
Class at
Publication: |
420/087 |
International
Class: |
C22C 038/60 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2002 |
JP |
2002232425 |
Claims
1. A steel for machine structural use having excellent
chip-breakability, comprising alloying elements necessary for a
machine structural steel except for Pb and Bi, at least five
MnS-inclusion particles having averaged particle size of 1.0 .mu.m
or more existing per mm.sup.2 per S-content 0.01%, in the
microscopic field, the condition (area [.mu.m.sup.2]/aspect
ratio).gtoreq.10 being met, the area percentage of Ca-containing
sulfide inclusion particles containing at least 1.0 wt. % of Ca
being in the range of 15-40% of the area of all the sulfide
inclusion particles, and film of sulfide inclusions being formed on
the tool surface during turning thereby to minimize curl diameter
of chips.
2. The steel for machine structural use having excellent
chip-breakability according to claim 1, wherein the steel consists
essentially of, by wt. %, C: 0.05-0.8%, Si: 0.01-2.5%, Mn:
0.1-3.5%, S: 0.01-0.2%, Ca alone or both Ca and Mg (in case of the
both, the total amount): 0.0005-0.02%, one or both of Ti:
0.002-0.010% and Zr: 0.002-0.025%, O: 0.0005-0.010%, and the
balance of inevitable impurities and Fe.
3. The steel for machine structural use having excellent
chip-breakability according to claim 2, wherein the steel further
contains, one or more of Se: up to 0.4%, Te: up to 0.2% and REM: up
to 0.05%.
4. The steel for machine structural use having excellent
chip-breakability according to one of claims 2 and 3, wherein the
steel further contains, one or more of Cr: up to 3.5%, Mo: up to
2.0%, Cu: up to 2.0%, Ni: up to 4.0% and B: 0.0005-0.01%.
5. The steel for machine structural use having excellent
chip-breakability according to one of claims 2 to 3, wherein the
steel further contains, one or both of Nb: up to 0.2% and V: up to
0.5%.
Description
TECHNICAL FIELD
[0001] The present invention concerns a steel for machine
structural use having excellent chip-breakability at machining with
cemented carbide tools. The steel for machine structural use of the
invention is characterized by configuration of sulfide inclusions
in the steel.
[0002] In the specification the term "Ca-containing sulfide
inclusion" means the inclusion of the structure formed by a core
inclusion mainly consisting of CaO, and another inclusion mainly
consisting of sulfides and surrounding the core. In regard to the
MnS inclusion the phrase "finely dispersed" means that the
inclusion particles are finer than the MnS inclusion particles in
the conventional steel, and that they are homogeneously dispersed
throughout the steel without either coagulation or concentration.
The "aspect ratio" is defined as the value given by dividing the
longest diameter by the shortest diameter of the inclusion
particles observed on the surface formed by cutting a steel sample
along the direction of rolling.
BACKGROUND TECHNOLOGY
[0003] Research for developing machine structural steel with good
machinability has been made for years, and as the results, steels
containing various machinability-improving elements have been
proposed. They are sulfur free cutting steel, tellurium free
cutting steel, calcium free cutting steel, lead free cutting steel
and sulfur-calcium free cutting steel. Of these steels, lead free
cutting steel is superb in that it has improved machinability
without substantial lowering of mechanical properties of the steel.
Recently, however, due to increasing significance of environmental
problems, free cutting steels containing no lead are often
demanded.
[0004] The technical problem common in the lead-free free cutting
steels is breakability of chips at machining. As is well known, in
the automated machining not only tool lives but also the chip
breakability is important, because lower chip breakability may
cause entangling of the chips with the tools or works, or conveying
troubles in chip conveyers, and thus, results in obstruction of
automation. With the premise that enjoying the excellent chip
breakability of lead free cutting steel is given up, it is
necessary to improve the chip breakability of the sulfur free
cutting steels or sulfur-calcium free cutting steels, which are the
majors of lead-free free cutting steels.
[0005] Efforts have been made to realize improved chip breakability
by controlling the aspect or configuration of sulfide-based
inclusion particles which bear the machinability. At present,
however, the achieved chip breakability is not satisfactory,
because the fluctuation of the improvement is significant and it is
difficult to ensured substantially constant chip breakability.
[0006] The applicants have been made research in this technical
field. Our discovery mentioned above that the structure of the
inclusion particles consisting of the core of CaO-containing
inclusion and the surrounding sulfide inclusion is useful is one of
the results of our research activities.
[0007] The recent knowledge on improving the chip breakability and
ensuring a certain level of the effect, in addition to the increase
of tool lives, by controlling the configuration of the sulfide
inclusion particles is that it is necessary to form numerous fine
sulfide inclusion particles for realizing good chip breakability.
More specifically, it is necessary to satisfy the condition that at
least five MnS inclusion particles having averaged size of 1.0
.mu.m or more exist per S-content 0.01%.
[0008] However, it was further discovered that existence of fine
sulfide inclusion particles is not sufficient and that it is
necessary to form sulfide inclusion films having a smaller friction
coefficient with the chips on the surface of the tools. The
mechanism is explained as follows. If the sulfide films of smaller
friction coefficient with the chips are formed on the surfaces of
the tools, the films give the effect of decreasing "curl diameter"
of the chips formed by machining, and as the results, the chips may
be easily broken. It is discovered that such a sulfide film may be
formed only in the cases where the Ca-containing sulfide inclusion
having specific configuration occupies a specific quantitative
range in all the sulfide inclusions.
DISCLOSURE OF THE INVENTION
[0009] The object of the invention is to provide, on the basis of
the above mentioned our discovery, a free cutting steel for machine
structural use which facilitates automation of machining by
controlling the configuration of the sulfide inclusion particles so
that the good tool lives and improved chip breakability may be
enjoyed.
[0010] The steel for machine structural use having excellent chip
breakability of the present invention which achieves the above
mentioned object is a steel containing alloying elements necessary
for a steel for machine structural use, without either Pb or Bi,
and In the steel, at least five MnS inclusion particles having
averaged particles sizes of 1.0 .mu.m or more exists per mm.sup.2
per S-content 0.01%, the condition that, in the microscopic fields,
(area[.mu.m.sup.2]/aspect ratio).gtoreq.10 is satisfied, and that
the area percentage of Ca-containing sulfide inclusion particles
containing at least 1.0 wt. % of Ca is in the range of 15-40% of
the area of all the sulfide inclusion particles.
[0011] A typical steel containing alloy elements necessary for a
steel for machine structural use consists essentially of, by wt. %,
C: 0.05-0.8%, Si: 0.01-2.5%, Mn: 0.1-3.5%, S: 0.01-0.2%, Ca alone
or both Ca and Mg (in case of the both is used, the total amount):
0.0005-0.02%, one or both of Ti: 0.002-0.010% and Zr: 0.002-0.025%,
and O: 0.0005-0.010%, and the balance of inevitable impurities and
Fe.
THE BEST MODE FOR PRACTICING THE INVENTION
[0012] The following explains the reason for choosing the alloy
components and limiting the composition of the typical steel for
machine structural use of the invention as mentioned above.
[0013] C: 0.05-0.8%
[0014] Carbon is necessary for ensuring strength of the steel, and
a C-content less than 0.05% will not give the sufficient strength
to the steel for the machine structural use. On the other hand,
carbon increases the activity of sulfur, and, at a higher
C-content, it will be difficult to form the Ca-containing sulfide
inclusion. At the same time, a larger amount of carbon lowers the
resilience and the machinability of the steel. Thus, the upper
limit is set to 0.8%.
[0015] Si: 0.01-2.5%
[0016] Silicon is used as a deoxidizing agent at steelmaking and
becomes a component of the steel. Si is useful because it enhances
hardenability of the steel. The effect may not be expected at a
small amount less than 0.01%. Si also increases the activity of
sulfur, and a large amount of Si causes the same problem as that of
a large amount of carbon, namely, formation of Ca-containing
sulfide inclusion may be prevented. Also, a large amount of Si
damages the resilience of the steel, which results in tendency of
cracking at plastic processing. The addition amount of Si must be,
therefore, up to 2.5%.
[0017] Mn: 0.1-3.5%
[0018] Manganese is an important element for forming the sulfide.
Unless the Mn-content in the steel does not reach 0.1%, the amount
of the formed inclusion will be insufficient. Excess addition of Mn
more than 3.5% makes the steel hard and lowers the
machinability.
[0019] S: 0.01-0.2%
[0020] Sulfur is an essential element for forming the sulfides, and
added in an amount of 0.01% or more. For the purpose of achieving
the "tool life ratio" of 5 or more aimed at by the invention sulfur
of 0.01% or more is necessary. An S-content higher than 0.2% not
only damages both the resilience and the ductility of the steel but
also causes combination of S and Ca to form CaS. CaS will cause
troubles in casting due to its high melting point.
[0021] Ca alone or both Ca and Mg (in case of the both is used, the
total amount): 0.0005-0.02%
[0022] Calcium is a very important component for the present steel.
In order to have Ca contained in the sulfide inclusion it is
essential to add Ca amounting to 0.0005% or more. On the other
hand, too much addition of Ca exceeding 0.02% brings about
formation of the above mentioned high melting point CaS, which
causes troubles in casting. It is possible to replace a part of Ca
with Mg. In that case, however, It is preferable that the
Ca-content may not fall below the above mentioned lower limit,
0.0005%.
[0023] One or both of Ti: 0.002-0.010% and Zr: 0.002-0.025%
[0024] A small amount of titanium or zirconium combines with oxygen
in the steel which was deoxidized with calcium and aluminum to form
finely divided oxides. The oxide inclusion particles act as the
cores at precipitation of MnS, and are useful for the fine
dispersion of the MnS inclusion particles. It is advantageous to
use both Ti and Zr, because the fine dispersing effect on MnS will
be stronger. In order to form suitable amounts of Ti-oxide and
Zr-oxide it is necessary to control the addition amounts of Ti an
Zr to be in the above ranges, i.e., 0.002-0.010% and
0.002-0.025%.
[0025] O: 0.0005-0.010%
[0026] Oxygen is an element essential for forming oxides. Because a
large amount of CaS forms in an excessively deoxidized steel and
causes troubles in casting, at least 0.0005% of oxygen is
necessary, and 0.0015% or more is preferable. Oxygen of a content
exceeding 0.01% will give a large amount of hard oxides, and as the
results, the machinability will be damaged and formation of the
desired Ca-containing sulfide inclusion will be difficult.
[0027] Phosphor, which is inevitable as an impurity in the steel,
is harmful to the resilience, and therefore, should not be
contained in an amount exceeding 0.2%. However, P is a
component-which improves the machinability, particularly, the
properties of the finished surface. This effect may be observed at
a content of 0.001% or more.
[0028] The free cutting steel for machine structural use may
optionally contain, in addition to the above mentioned basic
alloying components, depending on the use of the steel, one or more
of the elements of the following groups in the ranges defined
below. The following explains the roles of the optional alloying
elements and the reasons for limiting the composition ranges in the
modified embodiments of the invention.
[0029] One or more of Se: up to 0.4%, Te: up to 0.2% and REM: up to
0.05%
[0030] These elements are machinability-improving elements. The
respective upper limits, 0.4%, 0.2% and 0.05% were set in
consideration of unfavorable effect on the hot workability of the
steel and prevention of forming the fine sulfide inclusion
particles by excess addition.
[0031] One or more of Cr: up to 3.5%, Mo: up to 2.0%, Cu: up to
2.0%, Ni: up to 4.0% and B: 0.0005-0.01%
[0032] Chromium and molybdenum enhance hardenability of the steel
and addition of a suitable amount or amounts are recommended.
Excess addition will damage the hot workability of the steel and
cause cracking. With consideration of the costs of addition, the
respective upper limits are set to 3.5% for Cr and 2.0% for Mo.
Copper makes the matrix of the steel dense and heightens the
strength. Because addition of Cu in a large amount is not favorable
from the view points of both the hot workability and the
machinability, addition amount should be up to 2.0%. Though nickel
also enhances the hardenability like chromium and molybdenum, it is
unfavorable element as far as the machinability is concerned.
Taking this and the costs of addition into account, the upper limit
is set to 4.0%. Boron enhances the hardenability even at a small
amount of addition. In order to obtain this effect, boron must be
added in an amount of 0.0005% or more. Addition of B exceeding
0.01% is unfavorable due to lowered hot workability.
[0033] One or both of Nb: up to 0.2% and V: up to 0.5%
[0034] Niobium is useful for preventing coarsening of crystal
grains at high temperature. Because the effect of addition
saturates as the Nb-content increases, it is recommended to add it
in an amount up to 0.2%. Vanadium combines with carbon and nitrogen
to form the carbonitride, which makes the crystal grains fine. The
effect saturates at a content exceeding 0.5%.
[0035] The inclusions existing in the free cutting steel for
machine structural use according to the invention are as shown in
FIG. 1, the Ca-containing sulfide inclusion and MnS inclusion. The
Ca-containing sulfide inclusion has, according to EPMA analysis,
the double structure consisting of the core of oxides of calcium,
magnesium, silicon and aluminum, which are surrounded by MnS
containing CaS. In the steel according to the present invention MnS
inclusion is finely dispersed. On the other hand, in the
conventional free cutting steel, with which just machinability
improving effect by MnS is sought, MnS inclusion is, as shown in
FIG. 2, of a large form and elongated during rolling of the
steel.
[0036] The improved chip breakability characterizing the free
cutting steel for machine structural use according to the invention
is brought about, in one aspect, as mentioned above, by
disintegration of the MnS inclusion. On the premise that the amount
of the inclusion is constant, disintegration means increase of the
number of the inclusion particles. The amount of MnS inclusion in
the present steel is determined mainly by S-content, and as the
S-content varies in the range of 0.01-0.2% MnS-content also varies
with varied number of the fine inclusion particles.
[0037] In the present steel the MnS inclusion particles are finer
than MnS inclusion particles of the conventional steels. The
inclusion particles which give substantial influence on the chip
breakability are those having averaged particles size of 1.0 .mu.m
or more. The "averaged particle size" means, as defined above,
averaged value of the longest diameter and the shortest diameter at
the cross section of the particle in the microscopic fields.
[0038] Measurement on the numbers of the MnS inclusion particles
having averaged particle sizes of 1.0 .mu.m or more per unit area
(mm.sup.2) in the steels of the invention exhibiting excellent chip
breakability with different S-contents was made with an optical
microscope at a magnitude .times.400. The numbers of the inclusion
particles as shown in TABLE 1 below were obtained and it was
ascertained that the relation between the numbers of the inclusion
particles and the S-contents is nearly constant. Based on these
data it was concluded that the excellent chip breakability can be
given by ensuring five or more MnS inclusion particles per mm.sup.2
per S-content 0.01% throughout a wide range of S-content.
1TABLE 1 Number of MnS Inclusion Particles in Steel Number of
Number of MnS S-content MnS Inclusion Inclusion Particles in the
Steel Particles Per S-content 0.01% 0.01% 5.4/mm.sup.2 5.4/mm.sup.2
0.03% 16.2/mm.sup.2 5.4/mm.sup.2 0.062% 32.0/mm.sup.2 5.2/mm.sup.2
0.125% 32.0/mm.sup.2 6.2/mm.sup.2
[0039] The condition that the area percentage of Ca-containing
sulfide inclusions containing at least 1.0 wt. % of Ca and
satisfying the formula (area[.mu.m.sup.2]/aspect ratio).gtoreq.10
occupies 15-40% of the area of all the sulfide inclusion
particles:
[0040] In order that the inclusion have the above explained double
structure it is necessary that the Ca-containing sulfide inclusion
contains at least 1.0 wt. % of Ca. From another point of view, the
inclusion particles of the Ca-content of 1.0 wt. % or more (in
other words, the content of CaO, which is the typical one of the
oxide inclusions, is corresponding to S-content) are useful
inclusion and their configuration is the subject of controlling in
this invention. The inclusion particles satisfying the formula
(area[.mu.m.sup.2]/aspect ratio).gtoreq.10 are, in short,
relatively large and not so elongated ones.
[0041] Significance of the Ca-containing sulfide inclusion
particles which are of relatively large size and not so elongated
can be seen from the graph of FIG. 3, The graph was prepared by
plotting the relation between the aspect ratio and the area
occupied by the inclusion particles. The straight inclined line
indicates (area[.mu.m.sup.2]/aspect ratio)=10.
[0042] Also, significance of the fact that the Ca-containing
sulfide inclusion particles containing at least 1.0 wt. % of Ca and
satisfying the formula (area[.mu.m.sup.2]/aspect ratio).gtoreq.10
occupies 15-40% of the area of all the sulfide inclusions for the
improved chip breakability can be understood from the graph of FIG.
4. The graph was prepared by plotting the relation between the area
percentage of the Ca-containing inclusion particles and the chip
breakability indices, which are explained later in reference to the
working examples described below, particularly, those of S45C
containing 0.045-0.055% of sulfur. Comparison is made with the
conventional sulfur free cutting steels containing the same amounts
of S. It is seen that tip breakability exceeding that of the
conventional steel is obtained in the range of area percentage of
15-40%.
[0043] Based on the interpretation of the above facts from a
different point of view it is pointed out that, in case where the
area percentage of the Ca-containing sulfide inclusion does not
amount to 15%, MnS-component in the inclusion which adheres to and
lubricates the surface of the tools will be dominating. Though the
melting point of MnS is low, the stability of the lubricating film
is so low that the film will not endure and the chip breakability
is not improved. On the other hand, at such an excess amount of the
Ca-containing inclusion as more than 40%, the relative amount of
MnS in all the sulfide inclusions will be low, and it will be
difficult to ensure the above mentioned premise that at least five
MnS inclusion having averaged particle size of 1.0 .mu.m or more
exist per S-content 0.1%.
[0044] The reason why the present free cutting steel for machine
structural use exhibits excellent chip breakability is considered
to attribute to the mechanism that, at turning in machining, the
sulfide inclusion forms a melted film on the surface of the tool to
minimize the curl diameter of the chips. The melted film of the
sulfide inclusion exhibits so high lubricating effect that it may
be useful for minimizing the curl diameter.
EXAMPLES
[0045] The following explained the testing methods carried out in
the working examples and the control examples. Measurement of the
number of MnS inclusion particles is done as explained above, and
the other tests were carried out as noted below.
[0046] [Area Percentage of Ca-containing Sulfide Inclusion
Particles]
[0047] Microscopic photos (magnitude .times.200) are taken and all
the sulfide inclusion particles are classified by EPMA analysis
into two, the simple sulfide inclusion and the Ca-containing
sulfide inclusion of the double structure. Calculation is made to
determine the area percentage occupied by the double structure
inclusion particles.
[0048] [Lubricating Film]
[0049] The test pieces were subjected to machining by turning with
cemented carbide tools. Whether the melted inclusion forms a film
to cover the surface of the tool and whether the formed film is
stable is observed. Also, the chemical composition of the film was
determined by EPMA analysis.
[0050] [Chip Breakability]
[0051] Chips formed by turning under the conditions below were
recovered and points "0" to "4" depending on the length of the
chips were assigned thereto. The respective sums of the points of
each 30 samples were recorded as the "Chip Breakability Index".
[0052] Cutting Speed: 150 m/min.
[0053] Feed: 0.025-0.200 mm/rotation
[0054] Depth: 0.3-1.0 mm
[0055] Tool: DNMG150480-MA
[0056] The cases where the chip breakability indices of the working
examples are superior to those of the conventional sulfur free
cutting steels containing the corresponding amounts of sulfur are
marked "good", and the oases where the data of the examples are
equal or inferior to those of the controls, "no good".
Example 1
[0057] The present invention was applied to S45C steels. The
prepared steels were cast into ingots, and from the ingots test
pieces in the form of round rods of diameter 72 mm were taken, and
subjected to the tests. The alloy compositions and the test results
are shown in TABLE 2 (working examples) and TABLE 3 (control
examples).
Example 2
[0058] In regard to S15C free cutting steel preparation of the
steels and the cutting tests were carried out as done in Example 1.
The alloy compositions and the test results are shown in TABLE 4
(working examples) and TABLE 5 (control examples).
Example 3
[0059] In regard to S55C free cutting steel preparation of the
steels and the cutting tests were carried out as done in Example 1.
The alloy compositions and the test results are shown in TABLE 6
(working examples) and TABLE 7 (control examples).
Example 4
[0060] In regard to SCR415 free cutting steel preparation of the
steels and the cutting tests were carried out as done in Example 1.
The alloy compositions and the test results are shown in TABLE 8
(working examples) and TABLE 9 (control examples).
Example 5
[0061] In regard to SCM440 free cutting steel preparation of the
steels and the cutting tests were carried out as done in Example 1.
The alloy compositions and the test results are shown in TABLE 10
(working examples) and TABLE 11 (control examples).
[0062] In the TABLES below the following terms have the following
meanings.
[0063] Sulfide Area Percentage:
[0064] the area in the microscopic fields occupied by the sulfide
inclusion particles containing 1 wt. % or more of Ca out of the
area of all the sulfide inclusion particles.
[0065] Number of MnS Inclusion Particles;
[0066] the numbers of MnS inclusion particles having averaged
particle sizes of 1.0 .mu.m or more per S-content 0.01% (unit:
particles/mm.sup.2).
[0067] Film Formation:
[0068] observation as to whether film of melted sulfide inclusion
is formed to cover the surface of the tools "Yes" indicates
formation of sulfide film, "no", formation of oxide film and "-",
no film formation.
[0069] Chip Breakability:
[0070] comparison of the chip breakability indices of the working
examples mentioned above with those of the sulfur free cutting
steels of the equal S-contents. "Good" means superior results, and
"no good", equal or inferior results.
2TABLE 2 S45C Series Examples Sulfide Film Chip Area Forma- Break-
No. C Si Mn S Ca/Mg Ti/Zr O others % Number tion ability 1 0.45
0.21 0.65 0.018 Ca: 0.0019 Ti: 0.0051 0.0012 -- 34 5.3 yes good 2
0.43 0.23 0.81 0.054 Ca: 0.0023 Ti: 0.0051 0.0032 Cu: 0.42 28 7.4
yes good 3 0.46 0.32 0.93 0.068 Ca: 0.0025 Ti: 0.0077 0.0043 -- 24
8.2 yes good 4 0.45 0.18 0.71 0.121 Ca: 0.0058 Ti: 0.0033 0.0052 --
16 9.3 yes good Mg: 0.0012 5 0.45 0.27 0.84 0.039 Ca: 0.0036 Ti:
0.0032 0.0012 Te: 0.03 38 5.8 yes good Mg: 0.0008 6 0.44 0.86 0.66
0.044 Ca: 0.0023 Ti: 0.0045 0.0023 Se: 0.051 37 5.3 yes good 7 0.46
0.19 0.70 0.054 Ca: 0.0026 Ti: 0.0062 0.0017 -- 24 8.2 yes good 8
0.47 0.25 0.87 0.046 Ca: 0.0017 Zr: 0.0043 0.0022 -- 29 6.7 yes
good 9 0.45 0.20 0.93 0.121 Ca: 0.0021 Ti: 0.0044 0.0032 REM: 0.02
23 5.3 yes good
[0071]
3TABLE 3 S45C Series Controls Sulfide Film Chip Area Forma- Break-
No. C Si Mn S Ca/Mg Ti/Zr O others % Number tion ability 1 0.44
0.33 0.73 0.019 Ca: 0.0004 Ti: 0.0043 0.0031 -- 12 4.2 no no good 2
0.46 0.21 0.84 0.061 Ca: 0.0015 Ti: 0.0056 0.0019 Cu: 0.37 21 3.8
no no good 3 0.45 0.22 0.88 0.071 Ca: 0.0044 Ti: 0.0035 0.0043 --
20 4.2 no no good 4 0.43 0.25 0.75 0.132 Ca: 0.0023 Ti: 0.0061
0.0009 -- 8 6.6 -- no good Mg: 0.0009 5 0.45 0.23 0.80 0.036 Ca:
0.0033 Ti: 0.0023 0.0025 Te: 0.05 45 3.2 yes no good Mg: 0.0012 6
0.45 0.19 0.91 0.041 Ca: 0.00l8 Ti: 0.0069 0.0031 Se: 0.082 47 2.9
yes no good 7 0.45 0.88 0.63 0.051 Ca: 0.0022 Zr: 0.0085 0.0067 --
13 3.9 no no good 8 0.44 0.18 0.88 0.030 Ca: 0.0016 Zr: 0.0045
0.0023 Te: 0.03 51 2.8 no no good Mg: 0.0021 9 0.47 0.19 0.84 0.051
Ca: 0.0022 Ti: 0.0041 0.0008 -- 14 4.7 yes no good 10 0.46 0.18
0.89 0.132 Ca: 0.0024 Ti: 0.0016 0.0012 REM: 0.06 12 3.1 yes no
good
[0072]
4TABLE 4 S15C Series Examples Film Chip Sulfide Forma- Break- No. C
Si Mn S Ca/Mg Ti/Zr O others Area % Number tion ability 1 0.14 0.22
0.51 0.022 Ca: 0.0013 Ti: 0.0033 0.0014 -- 25 6.1 yes good 2 0.16
0.19 0.59 0.081 Ca: 0.0023 Ti: 0.0072 0.0033 V: 0.08 31 5.6 yes
good Mg: 0.0008 3 0.15 0.31 0.82 0.019 Ca: 0.0028 Ti: 0.0054 0.0012
B: 0.0010 29 6.2 yes good Zr: 0.0023
[0073]
5TABLE 5 S15C Series Controls Sulfide Film Chip Area Forma- Break-
No. C Si Mn S Ca/Mg Ti/Zr O others % Number tion ability 1 0.15
0.30 0.60 0.041 Ca: 0.0036 Ti: 0.0039 0.0035 -- 12 6.1 no no good 2
0.15 0.19 0.99 0.028 Ca: 0.0018 Ti: 0.0124 0.0022 V: 0.08 21 5.6 no
no good Mg: 0.0012 3 0.14 0.24 0.49 0.093 Ca: 0.0008 Ti: 0.0038
0.0009 B: 0.0018 8 6.2 -- no good Zr: 0.0056
[0074]
6TABLE 6 S55C Series Examples Film Chip Sulfide Forma- Break- No. C
Si Mn S Ca/Mg Ti/Zr O others Area % Number tion ability 1 0.57 0.31
0.91 0.018 Ca: 0.0026 Ti: 0.0045 0.0038 -- 34 5.4 yes good 2 0.54
0.18 0.87 0.044 Ca: 0.0025 Ti: 0.0062 0.0025 -- 23 7.3 yes good Mg:
0.0009 3 0.55 0.19 0.88 0.023 Ca: 0.0019 Ti: 0.0058 0.0017 Ni: 1.23
21 7.8 yes good Zr: 0.0052
[0075]
7TABLE 7 S55C Series Controls Sulfide Film Chip Area Forma- Break-
No. C Si Mn S Ca/Mg Ti/Zr O others % Number tion abilitv 1 0.55
0.22 1.04 0.024 Ca: 0.0033 Ti: 0.0033 0.0046 -- 11 4.9 no no good 2
0.56 0.26 0.89 0.054 Ca: 0.0028 Ti: 0.0072 0.0013 -- 24 4.0 no no
good Mg: 0.0006 3 0.55 0.19 0.94 0.021 Ca: 0.0011 Ti: 0.0063 0.0011
Ni: 2.23 6 5.3 -- no good Zr: 0.0037
[0076]
8TABLE 8 SCR415 Series Examples Sulfide Film Chip Area Forma-
Break- No. C Si Mn S Ca/Mg Ti/Zr O others % Number tion ability 1
0.17 0.12 0.68 0.036 Ca: 0.0022 Ti: 0.0053 0.0031 Cr: 1.89 34 5.3
yes good 2 0.15 0.21 0.71 0.048 Ca: 0.0027 Ti: 0.0045 0.0035 Cr:
1.12 29 6.0 yes good Mg: 0.00079 Nb: 0.039 3 0.16 0.15 0.56 0.096
Ca: 0.0019 Ti: 0.0032 0.0018 Cr: 1.54 19 7.7 yes good Zr:
0.0033
[0077]
9TABLE 9 SCR415C Series Controls Sulfide Film Chip Area Forma-
Break- No. C Si Mn S Ca/Mg Ti/Zr O others % Number tion ability 1
0.15 0.09 0.73 0.034 Ca: 0.0012 Ti: 0.0004 0.0046 Cr: 1.93 10 4.5
no no good 2 0.14 0.18 0.81 0.045 Ca: 0.0009 Ti: 0.0082 0.0028 Cr:
1.21 12 4.4 no no good Hg: 0.0011 Nb: 0.033 3 0.16 0.14 0.54 0.089
Ca: 0.0022 Ti: 0.0029 0.0008 Cr: 1.88 11 6.2 -- no good Zr:
0.0025
[0078]
10TABLE 10 SCM440 Series Examples Sulfide Film Chip Area Forma-
Break- No. C Si Mn S Ca/Mg Ti/Zr O others % Number tion ability 1
0.40 0.24 0.63 0.037 Ca: 0.0024 Ti: 0.0042 0.0023 Cr: 1.25 34 5.5
yes good Mo: 0.14 2 0.39 0.32 0.53 0.061 Ca: 0.0017 Ti: 0.0056
0.0041 Cr: 2.01 23 6.5 yes good Mg: 0.0006 Mo: 0.23 Ni: 0.23 3 0.42
0.19 0.98 0.014 Ca: 0.0026 Ti: 0.0061 0.0011 Cr: 1.45 24 6.8 yes
good Zr: 0.0034 Mo: 0.54
[0079]
11TABLE 11 SCM440 Series Controls Sulfide Film Chip Area Forma-
Break- No. C Si Mn S Ca/Mg Ti/Zr O others % Number tion ability 1
0.44 0.26 0.68 0.041 Ca: 0.014 Ti: 0.0023 0.0024 Cr: 1.32 9 4.5 no
no good Mo: 0.16 2 0.38 0.33 0.49 0.058 Ca: 0.0031 Ti: 0.0018
0.0039 Cr: 1.96 6 3.8 no no good Mg: 0.0014 Mo: 0.25 Ni: 0.34 3
0.41 0.21 1.02 0.016 Ca: 0.0024 Ti: 0.0023 0.0032 Cr: 1.88 12 4.8
-- no good Zr: 0.0021 Mo: 0.49
INDUSTRIAL APPLICABILITY
[0080] The steel for machine structural use having good chip
breakability according to the present invention has the same
machinability as that of the previously disclosed free cutting
steel. Namely, because the present steel also contains the
inclusion giving high machinability, i.e., the Ca-containing
sulfide inclusion particles of the double structure, at machining,
particularly, at turning with cemented carbide tools, the targeted
increase of the tool life ratio (the ratio of tool life of the
present free cutting steel to the tool life of the conventional
sulfur free cutting steel containing equal amounts of sulfur) to
five times is easily achieved.
[0081] Furthermore, the present invention, by choosing the
requisite that the Ca-containing sulfide inclusion particles of the
specific configuration is In the range of 15-40% of all the sulfide
inclusions, improved the chip breakability so remarkably that the
possible entanglement of the chips to the tools and works does not
occur, and thus, eliminated the troubles in transfer of the chips
on chip conveyers. The bottleneck for automation of machining for
manufacturing machine parts was solved by the present invention,
and therefore, contribution by the invention to decrease of the
manufacturing costs of various machine parts, particularly, parts
for automobiles is remarkable.
BRIEF EXPLANATION OF THE DRAWINGS
[0082] FIG. 1 is a microscopic photo illustrating the structure of
the inclusion in the free cutting steel for machine structural use
according to the invention;
[0083] FIG. 2 is a microscopic photo illustrating the structure of
the inclusion in the conventional sulfur free cutting steel;
[0084] FIG. 3 is a graph prepared by plotting the relation between
the aspect ratio and the area occupied by the Ca-containing sulfide
inclusion particles and MnS inclusion particles in the free cutting
steels for machine structural use; and
[0085] FIG. 4 is a graph prepared by plotting the relation between
the area percentage of the Ca-containing sulfide inclusion
particles and the chip breakability indices of the free cutting
steels for machine structural use.
* * * * *