1
FORM 2
THE PATENTS ACT 1970
[39 OF 1970]
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10; rule 13]
TITLE: “A FREE CUTTING STEEL AND A METHOD OF MANUFACTURING
THEREOF”
Name and Address of the Applicant:
TATA STEEL LIMITED of Jamshedpur - 831001, Jharkhand, India.
Nationality: Indian
The following specification particularly describes the invention and the manner in which it is to
be performed.
2
TECHNICAL FIELD
Present disclosure, in general, relates to a field of metallurgy. Particularly, but not exclusively, the
present disclosure relates to steels. Further, embodiments of the present disclosure disclose a free
5 cutting steel and a method of manufacturing the free cutting steel.
BACKGROUND OF THE DISCLOSURE
Steel is an alloy of iron (Fe), carbon (C), and other alloying elements such as Phosphorous (P),
10 Sulphur (S), Manganese (Mn), Silicon (Si), etc. Because of its high tensile strength and low cost,
steel is considered as a major component in wide variety of applications. Some of the applications
of the steel may include buildings, ship building, tools, automobiles, machines, bridges, and
numerous other applications.
Generally, in manufacturing industries steel having high machinability is preferred. Typically, free
15 cutting steels are employed for manufacturing which exhibit the high machinability. Conventional
free cutting steels include additives such as lead (Pb), which improves the machinability of the
free cutting steel. Inclusion of lead (Pb) enables higher cutting speed, extended tool life, improved
chip formation and enables easy removal of swarf during machining, which results in lower energy
consumption. However, certain regulations prohibit the use of heavy metal elements including lead
20 (Pb) due to its highly toxic and health hazardous nature. Therefore, usage of lead (Pb) poses a
negative impact on the environment, which is undesired.
With advancements in technology, bismuth, tellurium have been tested as an alternative for lead.
However, in tests with high-speed steel tools and lubricant, the leaded steel showcased better
performance in terms of production rate, surface finish and chip formation. Further, in tests with
25 coated carbide tools, the steel with the alternative additives showcased low tool wear but showed
poorer chip formation than the leaded steel. Furthermore, the alternative additives such as bismuth
and tellurium are expensive when compared to lead.
Present disclosure is directed to overcome one or more limitations stated above or any other
limitations associated with the known arts.
30
3
SUMMARY OF THE DISCLOSURE
One or more shortcomings of the prior art are overcome by a free cutting steel and the method of
manufacturing as claimed and additional advantages are provided through the free cutting steel
5 and the method as claimed in the present disclosure. Additional features and advantages are
realized through the techniques of the present disclosure. Other embodiments and aspects of the
disclosure are described in detail herein and are considered a part of the claimed disclosure.
In one non-limiting embodiment of the present disclosure a free cutting steel is disclosed. The free
10 cutting steel includes an alloy composition in weight (wt%) percentage of carbon (C) at about
0.07% to about 0.09%, manganese (Mn) at about 0.5% to about 0.6%, silicon (Si) up-to 0.05%,
phosphorus (P) at about 0.04% to about 0.09%, sulphur (S) at about 0.38% to about 0.45%,
chromium (Cr) at about 0.7% to about 0.9%, nitrogen (N) up-to 60ppm, oxygen (O) up-to 0.012%,
and the balance being Iron (Fe) optionally along with incidental elements. Further, the free cutting
15 steel with said alloy composition includes ferrite and pearlite microstructure.
In an embodiment, sulphur (S) and chromium (Cr) in the alloy composition expands crystallization
temperature ensuring crystallization by monotectic reaction. Inclusion of at least one of the
chromium (Cr) and manganese (Mn) in the alloy composition forms elongated shape sulphide
20 inclusions in the ferrite and pearlite microstructure.
In an embodiment, the free cutting steel exhibits hardness of about 146 HV to about 159 HV.
In an embodiment, the microstructure of the free cutting steel is represented by, in area%, ferrite
25 microstructure in the range of about 90% to about 95% and pearlite microstructure in the range of
about 5% to about 10%.
In an embodiment, the microstructure of the free cutting steel exhibits grain size in the range of
about 10 µm to about 15 µm.
30
In an embodiment, the free cutting steel is structured to have substantially large solidus
temperature resulting in large sulphide inclusions.
4
In another non-limiting embodiment of the present disclosure, a method for manufacturing a free
cutting steel is disclosed. The method includes casting a steel slab which includes an alloy
composition in weight (wt%) alloy composition in weight (wt%) percentage of carbon (C) at about
0.07% to about 0.09%, manganese (Mn) at about 0.5% to about 0.6%, silicon (Si) up-to 0.05%,
5 phosphorus (P) at about 0.04% to about 0.09%, sulphur (S) at about 0.38% to about 0.45%,
chromium (Cr) at about 0.7% to about 0.9%, nitrogen (N) up-to 60ppm, oxygen (O) up-to 0.012%,
and the balance being Iron (Fe) optionally along with incidental elements. Further, the casted steel
is cooled to ambient temperature. Furthermore, the cooled casted steel is subjected to metal
working process to form a free cutting steel. The inclusion of at least one of the chromium (Cr)
10 and manganese (Mn) in the alloy composition forms elongated shape sulphide inclusions in the
ferrite and pearlite microstructure.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In
addition to the illustrative aspects, embodiments, and features described above, further aspects,
15 embodiments, and features will become apparent by reference to the drawings and the following
detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
20 The novel features and characteristics of the disclosure are set forth in the appended claims. The
disclosure itself, however, as well as a preferred mode of use, further objectives, and advantages
thereof, will best be understood by reference to the following detailed description of an illustrative
embodiments when read in conjunction with the accompanying figures. One or more embodiments
are now described, by way of example only, with reference to the accompanying figures wherein
25 like reference numerals represent like elements and in which:
Fig. 1 is a flowchart illustrating a method for manufacturing a free cutting steel, according to an
exemplary embodiment of the present disclosure.
30 Fig. 2a illustrates optical micrographs taken from cross section and longitudinal section of a
conventional free cutting steel having lead as additive.
5
Fig. 2b illustrates a scanning electron microscope (SEM) micrograph which showcases presence
of ferrite and pearlitic structure in the conventional free cutting steel having lead as additive.
Fig. 3 illustrates optical micrographs of the free cutting steel, in accordance with an embodiment
5 of the present disclosure.
Fig. 4 illustrates a scanning electron microscope (SEM) micrograph of the free cutting steel, in
accordance with an embodiment of the present disclosure.
10 Figs. 5a and 5b are graphs illustrating the energy dispersive spectroscopy (EDS) mapped for the
free cutting steel, in accordance with an embodiment of the present disclosure.
Figs. 6a and 6b illustrates phase diagrams calculated based on chemistry of developed steel
according to present disclosure and compared with lead added free cutting steel.
15
Fig. 7 is a graph illustrating percentage of reduction in area (%RA) values which are plotted against
testing temperature during hot tensile test, in accordance with an embodiment of the present
disclosure.
20 Fig. 8a and 8b illustrates a comparison of surface finish and chip size between free cutting steel
according to present disclosure and lead added free cutting steel.
The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in
the art will readily recognize from the following description that alternative embodiments of the
25 system and method illustrated herein may be employed without departing from the principles of
the disclosure described herein.
DETAILED DESCRIPTION
30 The foregoing has broadly outlined the features and technical advantages of the present disclosure
in order that the detailed description of the disclosure that follows may be better understood.
Additional features and advantages of the disclosure will be described hereinafter which forms the
subject of the claims of the disclosure. It should be appreciated by those skilled in the art that, the
conception and specific embodiments disclosed may be readily utilized as a basis for modifying
6
other materials, products, methods, and processes for carrying out the same purposes of the present
disclosure. It should also be realized by those skilled in the art that, such equivalent method do not
depart from the scope of the disclosure as set forth in the appended claims. The novel features
which are believed to be characteristics of the disclosure, to its composition and method, together
5 with further objects and advantages will be better understood from the following description when
considered in connection with the accompanying figures. It is to be expressly understood, however,
that each of the figures is provided for the purpose of illustration and description only and is not
intended as a definition of the limits of the present disclosure.
10 In the present document, the word "exemplary" is used herein to mean "serving as an example,
instance, or illustration." Any embodiment or implementation of the present subject matter
described herein as "exemplary" is not necessarily to be construed as preferred or advantageous
over other embodiments.
15 While the disclosure is susceptible to various modifications and alternative forms, specific
embodiments thereof have been shown by way of example in the drawings and will be described
in detail below. It should be understood, however that it is not intended to limit the disclosure to
the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications,
equivalents, and alternatives falling within the scope of the disclosure.
20 The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a nonexclusive inclusions, such that a method comprises a list of steps does not include only those steps
but may include steps not expressly listed or inherent to such setup or device. In other words, one
or more steps in a method proceeded by “comprises… a” does not, without more constraints,
preclude the existence of other steps.
25
Embodiments of the present disclosure discloses a free cutting steel and a method for
manufacturing or producing the free cutting steel. The conventional free cutting steels include
additives such as lead (Pb), which improves the machinability property of the free cutting steel.
However, certain regulations prohibit the use of heavy metal elements including lead (Pb) due to
30 its highly toxic and health hazardous nature. Therefore, usage of lead (Pb) poses a negative impact
on the environment, which is undesired. Accordingly, the present disclosure discloses the free
cutting steel and the method for manufacturing the free cutting steel which employ chromium as
7
additive in the alloy composition. Addition of chromium aids the free cutting steel to exhibit same
mechanical properties as of the free cutting steel, which includes lead (Pb) as additive, and without
posing any environmental hazardous.
5 In the method of manufacturing the free cutting steel, a first step may include casting the steel
comprising an alloy composition in weight (wt%) percentage of carbon (C) at about 0.07% to
about 0.09%, manganese (Mn) at about 0.5% to about 0.6%, silicon (Si) up-to 0.05%, phosphorus
(P) at about 0.04% to about 0.09%, sulphur (S) at about 0.38% to about 0.45%, chromium (Cr) at
about 0.7% to about 0.9%, nitrogen (N) up-to 60ppm, oxygen (O) up-to 0.012%, and the balance
10 being Iron (Fe) optionally along with incidental elements. Further, the method includes cooling
the casted steel to an ambient temperature. Furthermore, the method includes subjecting the casted
steel to a metal working process to form a free cutting steel.
The addition of chromium in right ratios with the manganese and sulphur may aid in substantially
15 increasing solidus temperature resulting in large sulphide inclusions. Also, the addition of
chromium may improve machinability. Further, addition of chromium may act as an additive
during machining which helps in easy cutting, better surface finish and smaller chip formation,
which are essential properties to be exhibited by the free cutting steels. Furthermore, the chromium
in the alloy composition eliminates formation of compounds prior to, during and after
20 transformation of austenite to ferrite phase. Additionally, the chromium may aid in elongated
distribution of sulphide inclusions which may enhance the surface properties of the free cutting
steel.
Henceforth, method of manufacturing the free cutting steel having chromium (Cr) of the present
25 disclosure is explained with the help of figures. However, such exemplary embodiments should
not be construed as limitations of the present disclosure since the method may be used on other
types of steels where such need arises. A person skilled in the art may envisage various such
embodiments without deviating from scope of the present disclosure.
30 Fig. 1 is a flowchart depicting a method for manufacturing the free cutting steel. In the present
disclosure, mechanical properties such as machinability, better surface finish, smaller chips
formation and microstructure of the free cutting steel may be improved. The free cutting steel may
8
be manufactured by adding chromium (Cr), aiding in improving the mechanical properties of the
free cutting steel without addition of lead (Pb), which is hazardous to environment. The method is
now described with reference to the flowchart blocks.
5 At block 101, an alloy including an alloy composition in weight (wt%) percentage of carbon (C)
at about 0.07% to about 0.09%, manganese (Mn) at about 0.5% to about 0.6%, silicon (Si) up-to
0.05%, phosphorus (P) at about 0.04% to about 0.09%, sulphur (S) at about 0.38% to about 0.45%,
chromium (Cr) at about 0.7% to about 0.9%, nitrogen (N) up-to 60ppm, oxygen (O) up-to 0.012%,
and the balance being Iron (Fe) optionally along with incidental elements, may be casted. As an
10 example, liquid alloy with the above-mentioned composition and range of alloying elements may
be continuously casted into a steel billets. In an embodiment, the steel billet may be are smaller
billet. The alloying elements may be melted to liquid form in at least one of but not limited to an
electric arc furnace. In an embodiment, the electric arc furnace may be employed to melt the
alloying elements which may aid in controlling the composition of sulphur (S).
15
At block 102 and as seen in Fig. 1, the method may include cooling the casted steel to an ambient
temperature. In an embodiment, the ambient temperature may be a temperature equal to a room
temperature. Further, the casted steel may be subjected to cooling by without any external coolers
or may be subjected to cooling with the aid of external coolers.
20
At block 103, the method may include subjecting the steel billets obtained by the casting process
to a metal working process to produce the free cutting steel. In an embodiment, the metal working
process may be including but not limited to wire rolling..
25 The free cutting steel, formed by the method of the present disclosure may include ferrite and
pearlite microstructure. The microstructure of the free cutting steel may be represented by, in
area%, ferrite microstructure in the range of about 90% to about 95% and pearlite microstructure
in the range of about 5% to about 10%. Further, the microstructure of the free cutting steel may
exhibit grain size in the range of about 10 µm to about 15 µm. In an embodiment, the free cutting
30 steel may exhibit ferrite grain boundaries after a shaping process which may be formed due to the
inclusion of chromium (Cr). Further, the free cutting steel formed by the method of the present
disclosure may exhibit hardness in the range of about 146HV to about 159HV.
9
In an embodiment, the controlled addition of manganese (Mn) and chromium (Cr) may improve
machinability by increasing the size of sulfide inclusions. The controlled addition of manganese
(Mn) and Chromium (Cr) may lead to elongated shape of the sulphide inclusions in the ferrite and
5 pearlite microstructure of the free cutting steel. The elongated shape of sulphide inclusions may
be achieved by addition of the chromium (Cr) in the alloy composition which may substantially
increase the solidus temperature. That is the time for conversion of liquid steel to solid may be
substantially increased.
10 Fig. 2a illustrates optical micrographs taken from a cross section and a longitudinal section of a
conventional free cutting steel having lead as the additive. The micrographs showcases elongated
inclusion in the microstructure when taken from the longitudinal section and a circular inclusion
when taken from the cross section. The conventional free cutting steel having lead as the additive
includes a grain size in the range of 10-18 microns with hardness in the range of 107-112HV.
15 Furthermore, referring to Fig. 2b which illustrates a scanning electron microscope (SEM)
micrograph which showcases presence of ferrite and pearlitic structure in the conventional free
cutting steel having lead as the additive.
Referring to Figs. 3 and 4, which illustrates optical micrographs of the free cutting steel having
20 the composition of the present disclosure. The free cutting steel of the present disclosure includes
chromium (Cr) which may be employed as additive element to enhance the machinability. The
controlled addition of chromium (Cr) and manganese (Mn) provides elongated sulphide inclusions
which may be viewed in longitudinal section and circular shape in the cross-sectional microstructure. The hardness of the free cutting steel achieved may be in the range of about 146HV to
25 about 159HV which is greater than the hardness of the conventional free cutting steel having lead
as the additive. Further, the scanning electron microscope (SEM) micrograph as seen in Fig. 4,
showcases the presence of pearlite in the microstructure of the steel.
Further, as seen in Figs. 5a and 5b, an energy dispersive spectroscopy (EDS) has been mapped
30 for free cutting steel of the present disclosure. From the energy dispersive spectroscopy (EDS),
manganese (Mn), chromium (Cr) and sulphur (S) has been confirmed to be present in the
inclusions [as seen in Fig. 5a]. Furthermore, the energy dispersive spectroscopy (EDS) showcased
10
that chromium (Cr) has been also traced in some of the inclusions [as seen in Fig. 5b]. Further, it
is confirmed that, there is no formation of grain boundary segregation, because of the presence of
chromium (Cr) in the alloy composition.
5 Referring now to Fig. 6a and 6b, which illustrates a phase diagram calculated based on the
chemistry of the free cutting steel manufactured according to the present disclosure and
conventional free cutting steel having lead as the additive. FIG. 6a illustrates phase diagram of
the free cutting steel according to the present disclosure and FIG.6b illustrates phase diagram of
free cutting steel having lead as the additive. From FIG.6a it can be noted that the crystallization
10 temperature range is only expanded by “chromium (Cr) and sulphur (S) increment”. The
calculated phase diagram of the free cutting steel of present disclosure in comparison with the
calculated result of the conventional lead added free cutting steel can be seen in Fig. 6a and 6b.
The crystallization temperature range for sulphide inclusions in conventional lead added free
cutting steel was calculated as 18°C. In contrast, the temperature range of the free cutting steel of
15 present disclosure expanded by more than six times, to 119°C.
Following portions of the present disclosure, provides details about the role of proportion of each
element in the composition of the free cutting steel.
20 Carbon (C) may be used in the range of about 0.07wt% to about 0.09wt%, which may provide the
appropriate hardness to the free cutting steel. Further, variation of the carbon beyond the specified
range in the composition, may lead to difficulty in machining the free cutting steel.
Manganese (Mn) may be used in the range of about 0.5wt% to about 0.6wt%, chromium in the
25 range of about 0.7wt% to about 0.9wt% and Sulphur (S) may be used in the range of about
0.38wt% to 0.45wt%. The ratio of composition of the manganese, chromium and sulphur provides
may be required to achieve the desired sulphide inclusions of elongated shape and results in
smaller chip formation during machining of the free cutting steel.
30 Further, the free cutting steel may include silicon (Si) up-to 0.05%, phosphorus (P) at about 0.04%
to about 0.09%, nitrogen (N) up-to 60ppm and oxygen (O) up-to 0.012%, which are required to
manufacture steel. Table 1 provided below illustrates a range of elements in the alloy composition
of the free cutting steel with chromium (Cr) and conventional lead added free cutting steel.
11
Name/wt% C Mn Si P S Cr N O Pb Cost/ton
(Rs)
Conventional lead
added steel 0.15 Max
0.85 -
1.15
0.05
Max
0.040 -
0.090
0.26 -
0.35 -
0.006
max
0.012
max
0.15 -
0.35 Costly
Cr added free
cutting steel
0.07-
0.09 0.5-0.6
0.05
max
0.040 -
0.06
0.38-
0.45
0.7-
0.9
0.006
max
0.012
max NIL Economical
Table 1
5 Exemplary Experimental analysis:
Further embodiments of the present disclosure will be now described with experiments conducted
to compare the conventional free cutting steel having lead as the additive with the free cutting steel
manufactured by the method and composition as disclosed in the present disclosure.
10
Machinability test:
Machinability tests has been performed with the conventional free cutting steel having lead as the
additive and the free cutting steel having chromium (Cr). All the machinability parameters, such
15 as surface finish, chip size and tool wear has been captured and compared with the results of the
conventional free cutting steel having lead as the additive. The tool wear data has been measured
after cutting and have been recorded as showcased in the Table 2, below. From the table 2, it is
evident that, the tool wear of the free cutting steel having chromium (Cr) is measured to be
comparable and similar to the conventional free cutting steel having lead as the additive. Further,
20 the surface finish of both the steels have been captured and chips formed during machining of the
the free cutting steel having chromium (Cr) and the conventional free cutting steel having lead as
the additive have been collected for comparison, which showcased that the surface finish and the
chips formation of the free cutting steel having chromium (Cr) is similar to the conventional leaded
free cutting steel, where the nature of chips were curly in shape and were easily broken into small
25 sizes. Fig.8 illustrates a comparison of surface finish and chip size between free cutting free cutting
steel according to present disclosure and lead added free cutting steel. Fig. 8a illustrates
comparison of surface finish between free cutting steel according to present disclosure [depicted
12
as I] and lead added free cutting steel [depicted as L]. Fig. 8b illustrates comparison of chip size
between free cutting steel according to present disclosure [depicted as I] and lead added free
cutting steel [depicted as L].
Cutting condition Conventional steel Cr added free cutting steel
Cutting Speed= 70m /min
Feed=0.1mm/rev
Depth of Cutting: 0.5 mm
Length of each cut: 100 mm
Tool: HSS (side tool), Machine used: NH22
(HMT)
0.025
0.037
0.025
0.015
5 Table 2
Hot tensile test:
The ductility is measured by calculating percentage of reduction in area (%RA) of cross-section
of the specimen at the position of fracture after the tensile test. If the cross-sectional area at fracture
10 is small, %RA will be more. This means ductility is better and the material can sustain more
amount of deformation. However, if the decrease in cross sectional area is small, then %RA
becomes less and hence the ductility is low. So, the material can sustain less deformation before
the formation of cracks. The ductility of steel generally varies with temperature, and there is a
temperature range (relevant to casting temperatures) in which the ductility becomes very low.
15 Thus, if the steel is deformed at a temperature in this range, there is a possibility of crack formation.
The hot ductility test has been performed by employing a Gleeble machine. Both the conventional
free cutting steel having lead as the additive and the free cutting steel having chromium (Cr) were
subjected to hot ductility test. The hot ductility test involves reheating the steel to a solutionizing
temperature followed by cooling. Then, a tensile testing is carried out when a test temperature is
20 achieved.
The samples for hot tensile are cut into smaller pieces from the forged samples and specimens of
cylindrical shape were machined from these pieces of the steel forged samples. In order to measure
the temperature during the hot tensile tests at Gleeble machine, Pt-Pt/Rh thermocouple was spot
13
welded at the center of the specimens. The tensile testing of both the conventional free cutting
steel having lead as the additive and the free cutting steel having chromium (Cr) [also referred to
as specimen] at different temperatures in the range of 750–1250°C has been carried out. The
maximum temperature of 1350°C has been chosen in order to ensure larger grain size and
5 dissolution of all precipitates. The cooling is continued to test temperature at which the hot tensile
tests of the specimens were carried out. The crosshead speed maintained has been 1.25 mm/min,
which is equivalent to strain rate of 0.002083333, approximately assuming the deformation in the
tensile test is concentrated over a length of 10 mm around the center of the specimen. The strain
rate experienced by surface of the steel has been calculated using the following mathematical
10 relationships.
ɛ = t/2R, where ɛ is surface strain due to bending, t is thickness of the steel and R is bending radius.
ɛ* = ɛ(V/L), where ɛ* is the strain rate, V is the casting speed and L is the gauge length, which is
assumed to be equal to thickness of the steel.
15
In the experiment, the diameters of the specimens before and after the test (at the position of the
fracture) has been measured. The ductility is measured in terms of reduction in area (%RA). For
fractography study, samples have been cut from the fractured specimens and then the fracture
surfaces has been observed in a scanning electron microscope.
20
Referring now to Fig. 7, which illustrates the %RA values which are plotted against testing
temperature during hot tensile test conducted using the Gleeble machine.
The hot ductility curves which have been generated by plotting %RA against different test
25 temperatures for both the conventional free cutting steel having lead as the additive and the free
cutting steel having chromium (Cr) are shown in Fig. 7. A ductility channel is observed for both
the steels in the curves. The position and the width of the channels are varying for both the
conventional free cutting steel having lead as the additive and the free cutting steel having
chromium (Cr). As a comparison, the free cutting steel having chromium (Cr), has a maximum
30 %RA value at the temperature range of 850-950°C, although it has lower Mn/S ratio. The higher
%RA value is recorded to be better than the conventional free cutting steel having lead as the
additive, which indicates the better hot ductility behavior of the free cutting steel having chromium
14
(Cr). Further, higher side of the hot ductility (%RA) value will be taken as consideration for
straightening and below this value, straightening is not advised. Hence, the free cutting steel
having chromium (Cr) is less prone to cracking during casting and rolling than the conventional
free cutting steel having lead as the additive.
5
It should be understood that the experiments are carried out for particular compositions of the free
cutting steel and the results brought out in the optical micrographs, graph, tables should not be
construed as a limitation to the present disclosure as it could be varied based on composition and
testing techniques and methods.
10
In an embodiment, the inclusion of Chromium (Cr) in the free cutting steel does not lead to harmful
effects to the environment. Further, Chromium (Cr) is abundantly available and is economical.
In an embodiment, the free cutting steel having chromium (Cr) remains in solid solution during
15 hot rolling of the steel which is suitable for manufacturing.
In an embodiment, the free cutting steel having chromium (Cr) may be significantly less costly
compared to the conventional free cutting steel having lead additive.
20 In an embodiment, the free cutting steel having chromium (Cr) includes the required hot-ductility
property to avoid cracking during casting and hot-rolling. In an embodiment, the composition and
method described aid in reducing the amount of additive elements to minimize alloy cost.
It should be imperative that the composition and the method and any other elements described in
25 the above detailed description should not be considered as a limitation with respect to the figures.
Rather, variation to such composition and the method should be considered within the scope of
the detailed description.
Equivalents:
With respect to the use of substantially any plural and/or singular terms herein, those having skill
30 in the art can translate from the plural to the singular and/or from the singular to the plural as is
appropriate to the context and/or application. The various singular/plural permutations may be
expressly set forth herein for sake of clarity.
15
It will be understood by those within the art that, in general, terms used herein, and especially in
the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms
(e.g., the term “including” should be interpreted as “including but not limited to,” the term
“having” should be interpreted as “having at least,” the term “includes” should be interpreted as
5 “includes but is not limited to,” etc.). It will be further understood by those within the art that if a
specific number of an introduced claim recitation is intended, such an intent will be explicitly
recited in the claim, and in the absence of such recitation no such intent is present. For example,
as an aid to understanding, the following appended claims may contain usage of the introductory
phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such
10 phrases should not be construed to imply that the introduction of a claim recitation by the indefinite
articles “a” or “an” limits any particular claim containing such introduced claim recitation to
inventions containing only one such recitation, even when the same claim includes the introductory
phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or
“an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true
15 for the use of definite articles used to introduce claim recitations. In addition, even if a specific
number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize
that such recitation should typically be interpreted to mean at least the recited number (e.g., the
bare recitation of “two recitations,” without other modifiers, typically means at least two
recitations, or two or more recitations). Furthermore, in those instances where a convention
20 analogous to “at least one of A, B, and C, etc.” is used, in general such a process intended in the
sense one having skill in the art would understand the convention (e.g., “a method having at least
one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C
alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In
those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general
25 such a process is intended in the sense one having skill in the art would understand the convention
(e.g., “a method having at least one of A, B, or C” would include but not be limited to method that
have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A,
B, and C together, etc.). It will be further understood by those within the art that virtually any
disjunctive word and/or phrase presenting two or more alternative terms, whether in the
30 description, claims, or drawings, should be understood to contemplate the possibilities of including
16
one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be
understood to include the possibilities of “A” or “B” or “A and B.”
In addition, where features or aspects of the disclosure are described in terms of Markush groups,
those skilled in the art will recognize that the disclosure is also thereby described in terms of any
5 individual member or subgroup of members of the Markush group.
While various aspects and embodiments have been disclosed herein, other aspects and
embodiments will be apparent to those skilled in the art. The various aspects and embodiments
disclosed herein are for purposes of illustration and are not intended to be limiting, with the true
scope being indicated by the following claims.
10 Referral Numerals:
Reference Number Description
101-103 Flow chart blocks
101 Casting stage
102 Cooling stage
103 Metal working stage
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We Claim:
1. A free cutting steel, comprising:
an alloy composition in weight (wt%) percentage of:
5 carbon (C) at about 0.07% to about 0.09%,
manganese (Mn) at about 0.5% to about 0.6%,
silicon (Si) up-to 0.05%,
phosphorus (P) at about 0.04% to about 0.09%,
sulphur (S) at about 0.38% to about 0.45%,
10 chromium (Cr) at about 0.7% to about 0.9%,
nitrogen (N) up-to 60ppm,
oxygen (O) up-to 0.012%, and
the balance being Iron (Fe) optionally along with incidental elements;
wherein, the free cutting steel comprises ferrite and pearlite microstructure.
15 2. The free cutting steel as claimed in claim 1, wherein the sulphur (S) and chromium (Cr) in
the alloy composition expands crystallization temperature ensuing crystallization by
monotectic reaction.
3. The free cutting steel as claimed in claim 1, wherein inclusion of at least one of the
20 chromium (Cr) and manganese (Mn) in the alloy composition forms elongated shape
sulphide inclusions in the ferrite and pearlite microstructure.
4. The free cutting steel as claimed in claim 1, wherein the free cutting steel exhibits hardness
of about 146 HV to about 159 HV.
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5. The free cutting steel as claimed in claim 1, wherein the microstructure of the free cutting
steel is represented by, in area%, ferrite microstructure in the range of about 90% to about
95% and pearlite microstructure in the range of about 5% to about 10%.
30 6. The free cutting steel as claimed in claim 1, wherein the microstructure of the free cutting
steel exhibits grain size in the range of about 10 µm to about 15 µm.
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7. The free cutting steel as claimed in claim 1, wherein the free cutting steel is structured to
have substantially large solidus temperature resulting in large sulphide inclusions
8. A method for manufacturing a free cutting steel, the method comprising:
5 casting a steel slab, comprising an alloy composition in weight percentage (wt%) of:
carbon (C) at about 0.07% to about 0.09%,
manganese (Mn) at about 0.5% to about 0.6%,
silicon (Si) up-to 0.05%,
phosphorus (P) at about 0.04% to about 0.09%,
10 sulphur (S) at about 0.38% to about 0.45%,
chromium (Cr) at about 0.7% to about 0.9%,
nitrogen (N) up-to 60ppm,
oxygen (O) up-to 0.012%, and
the balance being Iron (Fe) optionally along with incidental elements;
15 cooling, the casted steel to ambient temperature; and
subjecting the casted steel to a metal working process to from a free cutting steel;
wherein, the free cutting steel comprises ferrite and pearlite microstructure
wherein inclusion of at least one of the chromium (Cr) and manganese (Mn) in the
alloy composition forms elongated shape sulphide inclusions in the ferrite and
20 pearlite microstructure.
9. The method as claimed in claim 8, wherein the sulphur (S) and chromium (Cr) in the alloy
composition expands crystallization temperature ensuing crystallization by monotectic
reaction.
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10. The method as claimed in claim 8, wherein the metal working process is a wire rolling
process.
11. The method as claimed in claim 8, wherein the microstructure of the free cutting steel is
30 represented by, in area%, ferrite microstructure in the range of about 90% to about 95%
and pearlite microstructure in the range of about 5% to about 10%.
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12. The method as claimed in claim 8, wherein the free cutting steel exhibits hardness of about
146 HV to about 159 HV.
13. The method as claimed in claim 8, wherein the free cutting steel exhibits hardness of about
5 124 HV to about 135 HV.
14. The method as claimed in claim 8, wherein the microstructure of the free cutting steel
exhibits grain size in the range of about 10 µm to about 15 µm.
10 15. A wire rod comprising a free cutting steel as claimed in claim 1.
16. Machinability property was evaluated in terms of
a) tool wear (0.015-0.025 mm),
15 b) Chip size: similar to standard product AISI12L14,
c) Surface finish: as good as AISI12L14 grade.