TECHNICAL FIELD
[001] Present disclosure relates in general to a field of material science and metallurgy.
Particularly, but not exclusively, the present disclosure relates to a hot rolled steel plate.
Further, embodiments of the disclosure, discloses a method of manufacturing a high hardness
hot rolled steel plates.
BACKGROUND OF THE DISCLOSURE
[002] Structural steels are one of the essential engineering materials, as such steel has been
used in multiple applications, such as, construction material, automotive steel, and load
intensive applications such as crushers, lifting excavation, mining, etc. The structural steel
generally includes properties such as high hardness with high impact load bearing capacity.
Especially, the steel for load intensive applications is generally required to have high hardness,
toughness, and reduction in weight.
[003] In certain cases, there may have been attempts made to develop the structural steel
with improved hardness behavior and wear resistance over years. Such attempts include
varying composition for alloying and develop improved hardness and tough steel. However,
such alloying may result in expensive composition for producing such steel.
[004] In certain instances, there may have been attempts to produce steel with hardness more
than 200BHN by using quenching and tempering method through a plate mill. However, such
instances may tend to provide drawbacks of a low production rate, which may subsequently
lead to a minimal economic benefit. Further, steels provided via the plate mill, may have a low
toughness microstructure, and there may be a requirement for additional processing to improve
the toughness and elongation of the produced steel.
[005] The drawbacks/difficulties/disadvantages/limitations of the conventional techniques
explained in the background section are just for exemplary purpose and the disclosure would
never limit its scope only such limitations. A person skilled in the art would understand that
this disclosure and below mentioned description may also solve other problems or overcome
the other drawbacks/disadvantages of the conventional arts which are not explicitly captured
above.
3
SUMMARY OF THE DISCLOSURE
[006] The following presents a simplified summary to provide a basic understanding of
certain aspects of a system and method to form a high hardness hot rolled steel plate. This
summary is not an extensive overview and is intended to neither identify key or critical
elements nor delineate the scope of such elements. Its purpose is to present certain concepts of
the described features in a simplified form as a prelude to the more detailed description that is
presented later.
[007] In one non-limiting embodiment, a high hardness hot rolled steel plate is disclosed.
The steel plate includes composition in weight percent including carbon (C) more than 0.11
wt.% but less than 0.119 wt.%, manganese (Mn) more than of 0.009 wt.% but less than 0.009
wt.%, silicon (Si) more than of 0.14 wt.% but less than 0.70 wt.%, phosphorous (P) more than
of 0.014 wt.% but less than 0.026 wt.%, sulphur (S) more than of 0.001 wt.% but less than
0.009 wt.%, aluminum (Al) more than of 0.009 wt.% less than 0.06 wt.%, nitrogen (N) more
than of 0.003 wt.% less than 0.02 wt.%, with additive elements including chromium (Cr),
Molybdenum (Mo), nickel (Ni) and Niobium (Nb) in combination being more than 0.3 wt.%
less than 0.9 wt.%, and balance element being iron (Fe),wherein, the high hardness hot rolled
steel plate has a hardness value more than 200 BHN and a bendability value of 2T.
[008] In an embodiment, the chromium (Cr) in the composition being more than of 0.15
wt.%, but less than 0.3 wt.%.
[009] In an embodiment, the molybdenum (Mo) in the composition being more than of 0.1
wt.%, but less than 0.21 wt.%.
[010] In an embodiment, the nickel (Ni) in the composition being more than of 0.15 wt.%,
but less than 0.3 wt.%.
[011] In an embodiment, the niobium (Nb) in the composition being more than of 0.015
wt.%, but less than 0.05 wt.%.
[012] In an embodiment, the high hardness hot rolled steel plate includes a microstructure
that includes 70% - 80% of a primary phase, and 20 - 30% of a secondary phase. The primary
phase is a bainitic phase; and the secondary phase includes a ferrite phase, a martensite phase,
carbides and at least one of: niobium carbide (NbC) precipitates or niobium carbonitride
(NbCN) precipitates.
[013] In an embodiment, the bainitic phase has a plate thickness less than 1 micron.
[014] In an embodiment, the high hardness hot rolled steel has a first thickness that is in a
range between 4.75 mm to 5.25 mm.
4
[015] In an embodiment, the bendability value of 2T corresponds to an inner radius of the
high hardness hot rolled steel plate that is formed when the high hardness hot rolled steel plate
is bent, wherein, the inner radius formed is equal to twice a thickness of the high hardness hot
rolled steel plate.
[016] In another non-limiting embodiment, a method for forming a high hardness hot rolled
steel plate is disclosed. The method step includes casting a steel slab with an alloying
composition of: carbon (C) more than 0.11 wt.% but less than 0.119 wt.%, manganese (Mn)
more than of 0.005 wt.% but less than 0.009 wt.%, silicon (Si) more than of 0.4 wt.% but less
than 0.7 wt.%, phosphorous (P) more than of 0.014 wt.% but less than 0.026 wt.%, sulphur (S)
more than of 0.001 wt.% but less than 0.009 wt.%, aluminium (Al) more than of 0.009 wt.%
less than 0.06 wt.%, nitrogen (N) more than of 0.003 wt.% less than 0.02 wt.%, with additive
elements including chromium (Cr), molybdenum (Mo), nickel (Ni), and niobium (Nb) in
combination being more than of 0.3 wt.% less than 0.9 wt.%, and balance element being iron
(Fe). The casted steel slab is then heated to a first temperature for a first period. Upon heating,
the steel slab may be subjected to hot rolling the steel slab to a first thickness at a second
temperature, to form a hot rolled steel plate. After hot rolling the hot rolled steel plate is cooled
at a first cooling rate. The method further includes the step of cooling the hot rolled steel plate
to a third temperature, to form a high hardness steel plate. After coiling the high hardness hot
rolled steel plate maybe cooled to the room temperature. The high hardness steel plate has a
hardness value more than 200 BHN and a bendability value of 2T.
[017] In an embodiment, the first temperature ranges from 1150°C to 1275°C, and the first
period ranges from 2 hours to 4 hours.
[018] In an embodiment, the second temperature ranges from 850℃ to 890℃, and the first
thickness ranges from 4.75 mm to 5.25 mm.
[019] In an embodiment, the first cooling rate ranges from 5°C/s to 40°C/s.
[020] In an embodiment, the third temperature ranges from 450 ℃ to 490 ℃.
[021] In an embodiment, the bendability value of 2T corresponds to an inner radius of the
high hardness hot rolled steel plate that is formed when the high hardness hot rolled steel plate
is bent, wherein, the inner radius formed is equal to twice a thickness of the high hardness hot
rolled steel plate.
[022] In an embodiment the cold working process is a cold rolling process, for reducing
thickness to the third predetermined thickness in a range of 1.3 mm to 1.5 mm.
[023] In an embodiment, the high hardness hot rolled steel plate includes a microstructure
that includes 70% - 80% of a primary phase, and 20 - 30% of a secondary phase. The primary
5
phase is a bainitic phase; and the secondary phase includes a ferrite phase, a martensite phase,
carbides and at least one of: niobium carbide (NbC) precipitates or niobium carbonitride
(NbCN) precipitates.
[024] In an embodiment, the bainitic phase has a plate thickness less than 1 micron.
[025] In another non-limiting embodiment, a method of manufacturing a high hardness steel
plate is disclosed. The method includes soaking a casted steel slab of composition in weight
percent including carbon (C) more than 0.11 wt.% but less than 0.119 wt.%, manganese (Mn)
more than of 0.005 wt.% but less than 0.009 wt.%, silicon (Si) more than of 0.4 wt.% but less
than 0.7 wt.%, phosphorous (P) more than of 0.014 wt.% but less than 0.026 wt.%, sulphur (S)
more than of 0.001 wt.% but less than 0.009 wt.%, aluminium (Al) more than of 0.009 wt.%
less than 0.06 wt.%, nitrogen (N) more than of 0.003 wt.% less than 0.02 wt.%, with additive
elements including chromium (Cr), molybdenum (Mo), nickel (Ni), and niobium (Nb) in
combination being more than of 0.3 wt.% less than 0.9 wt.%, and balance element being iron
(Fe) to a first temperature for a first period. Upon soaking the steel slab, the steel may be
subjected to hot rolling the steel slab to a first thickness at a second temperature, to form a hot
rolled steel plate. After hot rolling the hot rolled steel plate is cooled at a first cooling rate. The
method further includes the step of cooling the hot rolled steel plate to a third temperature, to
form a high hardness steel plate. After coiling the high hardness hot rolled steel plate maybe
cooled to the room temperature. The high hardness steel plate has a hardness value more than
200 BHN and a bendability value of 2T.
[026] In an embodiment, the bendability value of 2T corresponds to an inner radius of the
high hardness hot rolled steel plate that is formed when the high hardness hot rolled steel plate
is bent, wherein, the inner radius formed is equal to twice a thickness of the high hardness hot
rolled steel plate.
[027] In an embodiment, the first temperature ranges from 1150°C to 1275°C, and the first
period ranges from 2 hours to 4 hours. Further, the embodiment includes the second
temperature ranging from 850℃ to 890℃, and the third temperature ranging from 450 ℃ to
490 ℃.
[028] In an embodiment, the first thickness ranges from 4.75 mm to 5.25 mm. Further,
embodiment defines the cooling rate ranging from, and the first cooling rate ranges from 5°C/s
to 40°C/s.
[029] In an embodiment, the high hardness hot rolled steel plate includes a microstructure
that includes 70% - 80% of a primary phase, and 20 - 30% of a secondary phase. The primary
phase is a bainitic phase; and the secondary phase includes a ferrite phase, a martensite phase,
6
carbides and at least one of: niobium carbide (NbC) precipitates or niobium carbonitride
(NbCN) precipitates.
[030] In an embodiment, the bainitic phase has a plate thickness less than 1 micron.
[031] It is to be understood that the aspects and embodiments of the disclosure described
above may be used in any combination with each other. Several of the aspects and embodiments
may be combined to form a further embodiment of the disclosure.
[032] 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, embodiments, and features will become apparent by reference to the drawings
and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[033] The novel features and characteristics of the disclosure are set forth in the appended
description. 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 like reference numerals represent like
elements and in which:
[034] Figure. 1 is a flowchart illustrating a method for manufacturing a high hardness hot
rolled steel plate, according to an exemplary embodiment of the present disclosure.
[035] Figure. 2 is a graphical representation that illustrates an optical micrograph image of
the steel plate, manufactured by the method of the present disclosure, according to an
embodiment of the present disclosure.
[036] Figure. 3 is a graphical representation that illustrates a Scanning Electron Micrograph
(SEM) image of the steel plate manufactured by the method of the present disclosure, according
to an embodiment of the present disclosure.
[037] Figure. 4 is a graphical representation that illustrates an Electron Backscatter
Diffraction (EBSD) micrograph image of the steel plate manufactured by the method of the
present disclosure, according to an embodiment of the present disclosure.
[038] Figure. 5 is a graphical representation that illustrates an X-ray diffraction phase map
of the steel plate manufactured by the method of the present disclosure, according to an
embodiment of the present disclosure.
7
[039] Figure. 6 is an exemplary scenario that illustrates a three-point bending test of the
high hardness hot rolled steel plate manufactured by the method of the present disclosure,
according to an embodiment of the present disclosure.
[040] 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 methods illustrated herein may be employed without departing from the
principles of the disclosure described herein.
DETAILED DESCRIPTION
[041] Exemplary embodiments are described with reference to the accompanying drawings.
Wherever convenient, the same reference numbers are used throughout the drawings to refer
to the same or like parts. While examples and features of disclosed principles are described
herein, modifications, adaptations, and other implementations are possible without departing
from the spirit and scope of the disclosed embodiments. It is intended that the following
detailed description be considered as exemplary only, with the true scope and spirit being
indicated by the following claims. Additional illustrative embodiments are listed below.
[042] Figure. 1 is a flowchart illustrating a method for manufacturing a high hardness hot
rolled steel plate, according to an exemplary embodiment of the present disclosure. In the
present disclosure, mechanical properties of the steel plate, such as hardness, bendability,
strength, tensile strength, yield strength of the final microstructure of the steel plate may be
improved. In an embodiment, the high hardness steel plate has a hardness value more than 200
BHN and a bendability value of 2T. The method is now described with reference to blocks of
a flowchart 100. Referring to Figure. 1, the flowchart 100 may start at block 102.
[043] At block 102, a steel slab of desired alloy composition is formed by any of the
manufacturing process such as casting including, but not limited to, continuous casting process.
In an embodiment, the steel is manufactured in the form of slabs, while other forms such as
billets and blooms may also be applicable. The alloy of said steel may be prepared in at least
one of: an air-melting furnace or a vacuum furnace. In an embodiment, the steel slab may have
a composition of composition in weight percent including carbon (C) more than 0.11 wt.% but
less than 0.119 wt.%, manganese (Mn) more than of 0.005 wt.% but less than 0.009 wt.%,
silicon (Si) more than of 0.4 wt.% but less than 0.7 wt.%, phosphorous (P) more than of 0.014
wt.% but less than 0.026 wt.%, sulphur (S) more than of 0.001 wt.% but less than 0.009 wt.%,
8
aluminium (Al) more than of 0.009 wt.% less than 0.06 wt.%, nitrogen (N) more than of 0.003
wt.% less than 0.02 wt.%, with additive elements including chromium (Cr), molybdenum (Mo),
nickel (Ni), and niobium (Nb) in combination being more than of 0.3 wt.% less than 0.9 wt.%,
and balance element being iron (Fe) to a first temperature for a first period. In the illustrative
embodiment, the chromium (Cr) in the composition being more than of 0.15 wt.%, but less
than 0.3 wt.%, the molybdenum (Mo) in the composition being more than of 0.1 wt.%, but less
than 0.21 wt.%, the nickel (Ni) in the composition being more than of 0.15 wt.%, but less than
0.3 wt.%, and the niobium (Nb) in the composition being more than of 0.015 wt.%, but less
than 0.05 wt.%. Such combination of chromium (Cr), molybdenum (Mo), nickel (Ni), and
niobium (Nb) may be varied as per requirements without considering any of such elemental
proportion to be zero. In an embodiment, the steel may also include incidental elements that
may be considered as impurities being present in negligible (i.e., in untraceable proportions)
quantities which may not substantially affect final properties of the steel, whereby such
impurities may not be listed among the above-mentioned compositional elements, rather are to
be considered inherent in the casting process of the steel slab.
[044] At block 104, the method may further include heating the steel slab to a first
temperature for a first period. As an example, the casted steel slab may be heated in a reheating
furnace. Alternatively, according to another embodiment, the slab may be hot charged and
soaked at the first temperature for the first period. In an embodiment, the first temperature may
range from 1150°C to 1275°C, and the first period may range from 2 hours to 4 hours. Heating
the casted steel slab to the first temperature for the first time may facilitate a homogenization
and a dissolution of micro-alloying elements to reach a substantially austenitic structure.
[045] At block 106, the method may further include hot rolling the heated steel slab. In an
embodiment, the heated steel slab may be subjected to hot rolling until the heated steel slab
reaches a first thickness at a second temperature and forms a hot rolled steel plate. The hot
rolling is performed to reduce the thickness of the steel slab to the first thickness. In an
embodiment, the second temperature ranges from 850℃ to 890℃, and the first thickness
ranges from 4.75 mm to 5.25 mm. In another embodiment, the reheated slab after soaking
maybe transferred to a rough deformation (also known as rough rolling) to break the cast
structure and achieve suitable thickness prior to hot rolling process. The hot rolling process
may be carried out by passing the through a pair of rolls and rolling may also be performed for
several times, based on user requirements. The hot rolling may be carried out in two stages,
i.e., above and below the Recrystallization Temperature (Tnr). The first rolling process is above
Tnr in which static recrystallization occurs, and the second rolling process is below Tnr, in
9
which dynamic recrystallization occurs. Additionally, the hot rolling process may facilitate in
refining grains and thickness while reduction occurs. In the illustrative embodiment, each of
the static recrystallization and the dynamic recrystallization are collectively part of the hot
rolling process.
[046] At block 108, the method may further include cooling the hot rolled steel place. In an
embodiment, the hot rolled steel plate may be subjected to a cooling process at a first cooling
rate. For example, the cooling process may involve setting a first cooling rate ranges from 5°C/s
to 40°C/s. The first cooling rate may be set based on a cooling medium coupled with the hot
rolled steel plate. The cooling medium may include, but not limiting to, air cooling, quenching
operation by water and oil, or a mixture of oil.
[047] At block 110, the method may further include coiling the cooled hot rolled steel plate.
In an embodiment, the hot rolled steel plate may be coiled and subsequently cooled to a third
temperature, which subjected to coiling process. In an embodiment, the third temperature may
range from 450 ℃ to 490 ℃. The coiling temperature was based on the alloy deign to achieve
suitable microstructure.
[048] At block 112, the method may further include cooling the coiled steel plate to a room
temperature. In an exemplary embodiment of the present disclosure, the steel plate maybe
cooled to a room temperature in an open environment from the third temperature. The steel
plate produced through present disclosure exhibits hardness value more than 200 BHN and a
bendability value of 2T.
[049] In an embodiment, the bendability value of 2T corresponds to an inner radius of the
high hardness hot rolled steel plate that is formed when the high hardness hot rolled steel plate
is bent, wherein, the inner radius formed is equal to twice a thickness of the high hardness hot
rolled steel plate.
[050] The order in which the method is described is not intended to be construed as a
limitation, and any number of the described method blocks can be combined in any order to
implement the method. Additionally, individual blocks may be deleted from the methods
without departing from the scope of the subject.
[051] Figure. 2 is a graphical representation that illustrates an optical micrograph image of
the steel plate, manufactured by the method of the present disclosure, according to an
embodiment of the present disclosure. Figure 2 is described in conjunction with elements from
Figure 1. With reference to Figure 2, there is shown an optical micrograph image 200 of the
high hardness hot rolled steel plate.
10
[052] In an embodiment, the high hardness hot rolled steel plate includes a microstructure
that includes 70% - 80% of a primary phase, and 20 - 30% of a secondary phase. The primary
phase may include a bainitic phase; and the secondary phase may include a ferrite phase, a
martensite phase, carbides and at least one of: niobium carbide (NbC) precipitates or niobium
carbonitride (NbCN) precipitates. The optical micrograph image 200 may confirm that the
developed steel has primarily bainite microstructure with some amount of ferrite, martensite,
and carbide.
[053] Figure. 3 is a graphical representation that illustrates a Scanning Electron Micrograph
(SEM) image of the steel plate manufactured by the method of the present disclosure, according
to an embodiment of the present disclosure. Figure 3 is described in conjunction with elements
from Figure 1 and Figure 2. With reference to Figure 3, there is shown a Scanning Electron
Micrograph (SEM) image 300 of the high hardness hot rolled steel plate.
[054] In an embodiment, the high hardness hot rolled steel plate includes a microstructure
that includes 70% - 80% of a primary phase, and 20 - 30% of a secondary phase. The primary
phase may include a bainitic phase; and the secondary phase may include a ferrite phase, a
martensite phase, carbides and at least one of: niobium carbide (NbC) precipitates or niobium
carbonitride (NbCN) precipitates. The Scanning Electron Micrograph (SEM) image 300 may
show a very fine structure and a bainite plate thickness below submicron size (such as <1
micron), imparting the high hardness, while ensuring reduced carbide content ensures
bendability and high toughness.
[055] In an exemplary embodiment of the present disclosure, the high hardness steel plate
constitutes bainite phase with essentially very fine plate thickness. In an embodiment, the
bainitic phase has a plate thickness less than 1 micron. Further, the composition of martensite
as a secondary phase is beneficial to the steel plate as it improves the hardness, however, the
ductility decreased. To get beneficial effect martensite should be tempered and finer size. The
constituent carbides as a high temperature product may form <10% of the total microstructure.
The carbide constituents are undesirable as it degrades the mechanical properties of the steel
plate. However, minor addition of Nb is helpful in enhancing the hardness through formation
of niobium carbide (NbC) precipitates and niobium carbonitride (NbCN) precipitates.
[056] Following portions of the present disclosure, provides details about the proportion of
each element in a composition of the steel plate and their role in enhancing properties.
[057] Carbon (C: more than 0.11 wt.%, but less than 0.119 wt.%): More preferably, the
carbon may have a composition of 0.11 wt.%. The carbon in this compositional range is
required for desired strengthening, and proportion of phase fractions. Carbon plays important
11
role to affect coiling temperature as well as mechanical properties. Further, the carbon plays
important role in weldability. Preferable carbon content should be kept below 0.15% to achieve
desired strength and elongation and weldability, therefore, C is suggested to be restricted below
0.16% and preferably below 0.12 wt%.
[058] Manganese (Mn: more than of 0.005 wt.% but less than 0.009 wt.%, is used in the
steel slab. More preferably, the manganese may have a composition of 0.005 wt%. Manganese
imparts strength to the steel along with reducing overall weight.
[059] Silicon (Si: more than of 0.4 wt.% but less than 0.7 wt.%): Silicon is a ferrite stabilizer
and strengthening element. Silicon when added given range yields carbide precipitation during
bainite or martensite transformation during constant temperature holding / coiling and facilitate
mechanical properties improvement. However, higher amount of silicon addition is not
desirable due to varieties of unwanted scale formation during hot rolling and subsequent
cooling. The scale formation may lead to a bad surface and reduce a coat-ability. Hence, the
silicon is suggested to be restricted below 0.7 wt%.
[060] Phosphorus (P: more than of 0.014 wt.% but less than 0.026 wt.%): Phosphorus is
considered detrimental in steel. Therefore, the phosphorous should be in an amount that may
be restricted to 0.026% maximum or preferably 0.03% or less.
[061] Sulphur (S: more than of 0.001 wt.% but less than 0.009 wt.%): Similar to phosphorus,
sulphur is also considered detrimental. Hence, the sulphur content to be kept as low as possible,
preferably below 0.014 wt%. More preferably, the sulphur content may be suggested to be
below 0.01 wt% to minimize number of inclusions, which is potential sites for premature
failure during forming operations.
[062] Aluminium (Al: more than of 0.009 wt., % less than 0.06 wt.%): Aluminium is an
essential element for deoxidation. However, the amount should be kept below the defined value
to avoid detrimental effects.
[063] Nitrogen (N: more than of 0.003 wt.% less than 0.02 wt.%): Nitrogen is decremental
for the present disclosed steel plate.
[064] Molybdenum (Mo: more than of 0.1 wt.%, but less than 0.21 wt.%): Molybdenum is
added to enhance the hardenability in steel, thereby favors easy formation of bainite. Due to
enhancing to excess hardenability, softer ferrite and relatively harder pearlite phase formation
could be suppressed during bainitic reaction. As molybdenum is costly, its amount is suggested
to be restricted below 0.21 wt% to make the steel economical and taking processing advantage
during hot rolling.
12
[065] Chromium (Cr: more than of 0.15 wt.%, but less than 0.3 wt.%): Chromium acts very
much similar manner to molybdenum, avoids formation of polygonal ferrite and pearlite.
However, chromium could be harmful if added more than 0.3 wt.%, due to the ability to form
various kind of carbides, and less economical.
[066] Nickel (Ni: more than of 0.15 wt.%, but less than 0.3 wt.%): Ni is added to improve
impact toughness.
[067] Niobium (Nb: more than of 0.015 wt.%, but less than 0.05 wt.%): Niobium is added
to increase the strength of the steel by various mechanism such as grain refinement,
precipitation. Nb addition also useful to have larger amount of retained austenite in the
microstructure. In certain cases, Nb should be added carefully and optimized to take advantage
of economic advantage as Nb is costly. Therefore, Nb level should be below 0.05% or more
preferably, below 0.04%.
EXAMPLES
[068] Embodiments of the present disclosure will now be described with an example of a
particular composition of the steel. Experiments have been carried out for a specific
composition of the steel formed by using method of the present disclosure. The composition of
the steel for which the tests are carried out is as shown in below Table 1. Compositions
C Mn Si P S Al N Cr Mo Ni Nb
BHN
Bendability
1 0.11 0.005 0.4 0.02 0.006 0.009 0.006 0.25 0.15 0.22 0.026 220 2T
2 0.112 0.006 0.5 0.02 0.006 0.02 0.006 0.25 0.15 0.2 0.026 218 2T
3 0.116 0.007 0.6 0.02 0.006 0.015 0.006 0.25 0.15 0.21 0.025 215 2T
TABLE 1
[069] Described composition of steel was processed by the method of the present disclosure
to obtain a high hardness steel plate as described through the Figure. 1.
13
[070] The test samples were then carved out from the hot rolled plates. The test samples
were subjected to testing for determining mechanical properties of high hardness steel plate.
As an example, the test samples were subjected to a hardness testing. Hardness is recorded
employing Brinell hardness testing equipment. The results show excellent hardness over 200
BHN. The maximum and minimum hardness value obtained were 220 BHN and 215 BHN
respectively ensuring the improved homogeneity in the steel plates as tabulated in Table. 1.
[071] Further, the samples were subjected to Optical microscopy and Scanning Electron
Micrograph (SEM) analysis. Figures. 2 and 3 illustrate images of the microstructure of the steel
plate subjected to Optical and Scanning Electron Micrograph (SEM) analysis. The optical
micrograph [as shown in Figure 2] confirms that the developed steel has primarily bainite
microstructure with some amount of ferrite, martensite, and carbide. The scanning electron
micrograph [as shown in Figures. 3] reveals the very fine structure and bainite plate thickness
well below submicron size, imparting the high hardness, while ensuring reduced carbide
content ensures bendability and high toughness.
[072] Further, the test samples were subjected to Electron back scatter diffraction (EBSD)
to view an electron back scattered micrograph 400 (shown in Figure. 4). Electron back scattered
micrograph 400 may be further corroborated well with the optical and scanning electron
microstructure and indicating presence of bainite, martensite in the microstructure [as shown
in Figure 4]. Electron back scatter diffraction (EBSD) also confirms absence any retained
austenite in the structure. The fineness of bainite determine the strength and toughness of the
steel. The thickness of bainitic plates was found below submicron size.
[073] Further, the test samples were subjected to X-ray diffraction. Diffraction experiments
were carried out to view an X-ray diffraction image 500 (shown in Figure. 5). The X-ray
diffraction image 500 may be analyzed to ensure a presence of body center cubic (BCC) phase
and absence of austenite in the microstructure. This confirms that the steel plate according to
the present disclosure developed has mainly the bcc structure comprising primarily bainite
along with some amount ferrite, martensite, and carbide.
[074] Thus, the steel plate manufactured through present disclosure, has 70% - 80% of a
bainitic phase, and 20 - 30% of mix of ferrite phase, martensite phase, carbides. The steel plate
may facilitate an improved loading, wear and tear resistance, good bendability, coat-ability,
castability and forming capabilities.
[075] Further, the test samples were subjected to a bendability test. The bendability of the
plate was determined by bend test, where the plate is subjected to three point bending test (600)
as shown in Figure 6. The test samples of the high hardness hot rolled steel plate has a first
14
edge (602), a second edge (604), and a mid-section (606), wherein the mid-section (606) is
configured to be disposed on a mandrel (608), and the high hardness hot rolled steel plate is
configured to bend over the mandrel (608) until the first edge (602) touches the second edge
(604). The mandrel (608) is disposed at an axis being parallel to a surface of the high hardness
hot rolled steel plate (610). Results from the bend test have been tabulated in Table. 1. may
show the bendability test results performed on steel plates obtained by the method of the present
disclosure, confirms that the high hardness hot rolled steel plate (610) manufactured through
present disclosure satisfy 2T.
[076] In an embodiment of the present disclosure, the bendability value of 2T corresponds
to an inner radius of the high hardness hot rolled steel plate that is formed when the high
hardness hot rolled steel plate is bent, wherein, the inner radius formed is equal to twice a
thickness of the high hardness hot rolled steel plate.
[077] It should be understood that the experiments are carried out for particular
compositions of the high hardness steel plate and the results brought out in the previous
paragraphs are for the composition shown in Table 1. However, this composition should not
be construed as a limitation to the present disclosure as it could be extended to other
compositions of the high hardness steel plate, as well. Further, the method parameters
considered in Table 1 also cannot be construed as limitation, since the other parameters
considered within the claimed range also result in the high hardness steel plate, which exhibits
the enhanced properties as depicted in Table 1.
[078] The high hardness steel plate of the present disclosure may be used any application
including but not limiting to load intensive, fatigue prone applications, such as crushing and
other applications.
[079] 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 form the subject of the description of the disclosure. It should also be realized
by those skilled in the art that such equivalent methods do not depart from the scope of the
disclosure. The novel features which are believed to be characteristic of the disclosure, as to
method of manufacturing and the steel plate, together 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.
15
[080] 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.
[081] While the disclosure is susceptible to various modifications and alternative forms,
specific embodiment thereof has 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 specific forms, but on the contrary, the disclosure is to cover all modifications,
equivalents, and alternative falling within the spirit and the scope of the disclosure.
[082] The terms “comprises”, “comprising”, or any other variations thereof, are intended to
cover a non-exclusive inclusion, such that a method that comprises a list of acts does not
include only those acts but may include other acts not expressly listed or inherent to such
method. In other words, one or more acts in a method proceeded by “comprises… a” does not,
without more constraints, preclude the existence of other acts or additional acts in the method.
[083] Henceforth, the present disclosure is explained with the help of figures for a method
of manufacturing a high hardness steel plate. 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.
EQUIVALENTS
[084] With respect to the use of substantially any plural and/or singular terms herein, those
having skill 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.
[085] 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 "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
16
usage of the introductory phrases "at least one" and "one or more" to introduce claim
recitations. However, the use of such 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 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 analogous to
"at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense
one having skill in the art would understand the convention (e.g., "a system 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 such a construction is intended in the sense one having skill in the art would
understand the convention (e.g., "a system having at least one of A, B, or 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.). 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 description, claims, or drawings, should be understood to
contemplate the possibilities of including 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."
[086] 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 and spirit being indicated by the following claims.
17
REFERENCE NUMBERALS
Referral Numerals Description
102-112 Flowchart blocks
102 Casting stage
104 Heating stage
106 Hot rolling process
108 Cooling process
110 Coiling Stage
112 Cooling Stage
202 Three point bending test
204 First Edge
206 Second Edge
208 Mid-section Edge
210 Mandrel
212 High hardness hot rolled steel
plate
18
We Claim:
1. A high hardness hot rolled steel plate, comprising:
a composition of:
Carbon (C) more than 0.11 wt.% but less than 0.119 wt.%,
Manganese (Mn) more than of 0.005 wt.% but less than 0.009 wt.%,
Silicon (Si) more than of 0.4 wt.% but less than 0.7 wt.%,
Phosphorous (P) more than of 0.014 wt.% but less than 0.026 wt.%,
Sulphur (S) more than of 0.001 wt.% but less than 0.009 wt.%,
Aluminium (Al) more than of 0.009 wt.% less than 0.06 wt.%,
Nitrogen (N) more than of 0.003 wt.% less than 0.02 wt.%,
with additive elements including Chromium (Cr), Molybdenum (Mo),
Nickel (Ni) and Niobium (Nb) in combination being more than 0.3 wt.%
less than 0.9 wt.%, and balance element being Iron (Fe),
wherein, the high hardness hot rolled steel plate has a hardness value more than 200
BHN and a bendability value of 2T.
2. The high hardness hot rolled steel plate as claimed in claim 1, wherein the Chromium
(Cr) in the composition being more than of 0.15 wt.%, but less than 0.3 wt.%.
3. The high hardness hot rolled steel plate as claimed in claim 1, wherein the Molybdenum
(Mo) in the composition being more than of 0.1 wt.%, but less than 0.21 wt.%.
4. The high hardness hot rolled steel plate as claimed in claim 1, wherein the Nickel (Ni)
in the composition being more than of 0.15 wt.%, but less than 0.3 wt.%.
5. The high hardness hot rolled steel plate as claimed in claim 1, wherein the Niobium
(Nb) in the composition being more than of 0.015 wt.%, but less than 0.05 wt.%.
6. The high hardness hot rolled steel plate as claimed in claim 1, comprising a
microstructure that comprises: 70% - 80% of a primary phase, and 20 - 30% of a
secondary phase.
7. The high hardness hot rolled steel plate as claimed in claim 6, wherein the primary
phase is a bainitic phase; and the secondary phase comprising: a ferrite phase, a
19
martensite phase, carbides and at least one of: niobium carbide (NbC) precipitates or
niobium carbonitride (NbCN) precipitates.
8. The high hardness hot rolled steel plate as claimed in claim 7, wherein the bainitic phase
has a plate thickness less than 1 micron.
9. The high hardness hot rolled steel plate as claimed in claim 1, wherein the high hardness
hot rolled steel has a first thickness that is in a range between 4.75 mm to 5.25 mm.
10. The high hardness hot rolled steel plate as claimed in claim 1, wherein the bendability
value of 2T corresponds to an inner radius of the high hardness hot rolled steel plate
that is formed when the high hardness hot rolled steel plate is bent, wherein, the inner
radius formed is equal to twice a thickness of the high hardness hot rolled steel plate.
11. A method for forming a high hardness hot rolled steel plate, comprising:
casting a steel slab with an alloying composition of:
Carbon (C) more than 0.11 wt.% but less than 0.119 wt.%,
Manganese (Mn) more than of 0.005 wt.% but less than 0.009 wt.%,
Silicon (Si) more than of 0.4 wt.% but less than 0.7 wt.%,
Phosphorous (P) more than of 0.014 wt.% but less than 0.026 wt.%,
Sulphur (S) more than of 0.001 wt.% but less than 0.009 wt.%,
Aluminium (Al) more than of 0.009 wt.% less than 0.06 wt.%,
Nitrogen (N) more than of 0.003 wt.% less than 0.02 wt.%,
with additive elements including Chromium (Cr), Molybdenum (Mo),
Nickel (Ni), and Niobium (Nb) in combination being more than of 0.3 wt.% less
than 0.9 wt.%, and balance element being Iron (Fe);
heating the steel slab to a first temperature for a first period;
hot rolling the steel slab to a first thickness at a second temperature, to form a
hot rolled steel plate;
cooling the hot rolled steel plate at a first cooling rate;
coiling the hot rolled steel plate to a third temperature, to form the high hardness
hot rolled steel plate; and
cooling the high hardness hot rolled steel plate to a room temperature,
20
wherein, the high hardness hot rolled steel plate has a hardness value
more than 200 BHN and a bendability value of 2T.
12. The method as claimed in claim 11, wherein the first temperature ranges from 1150°C
to 1275°C, and the first period ranges from 2 hours to 4 hours.
13. The method as claimed in claim 11, wherein the second temperature ranges from 850℃
to 890℃, and the first thickness ranges from 4.75 mm to 5.25 mm.
14. The method as claimed in claim 11, wherein the first cooling rate ranges from 5°C/s to
40°C/s.
15. The method as claimed in claim 11, wherein the third temperature ranges from 450 ℃
to 490 ℃.
16. The method as claimed in claim 11, wherein the bendability value of 2T corresponds to
an inner radius of the high hardness hot rolled steel plate that is formed when the high
hardness hot rolled steel plate is bent, wherein, the inner radius formed is equal to twice
a thickness of the high hardness hot rolled steel plate.
17. A method for forming a high hardness hot rolled steel plate, comprising:
soaking a steel slab casted with alloying composition of:
Carbon (C) more than 0.11 wt.% but less than 0.119 wt.%,
Manganese (Mn) more than of 0.005 wt.% but less than 0.009 wt.%,
Silicon (Si) more than of 0.4 wt.% but less than 0.7 wt.%,
Phosphorous (P) more than of 0.014 wt.% but less than 0.026 wt.%,
Sulphur (S) more than of 0.001 wt.% but less than 0.009 wt.%,
Aluminium (Al) more than of 0.009 wt.% less than 0.06 wt.%,
Nitrogen (N) more than of 0.003 wt.% less than 0.02 wt.%,
with additive elements including Chromium (Cr), Molybdenum (Mo),
Nickel (Ni), and Niobium (Nb) in combination being more than of 0.3 wt.% less
than 0.9 wt.%, and balance elements being Iron (Fe),
wherein the steel slab is soaked to a first temperature for a first period;
21
hot rolling the steel slab to a first thickness at a second temperature, to form a
hot rolled steel plate;
cooling the hot rolled steel plate at a first cooling rate;
coiling the hot rolled steel plate to a third temperature, to form the high hardness
hot rolled steel plate; and
cooling the high hardness hot rolled steel plate to a room temperature,
wherein, the high hardness hot rolled steel plate has a hardness value
more than 200 BHN and a bendability value of 2T.
18. The method as claimed in claim 17, wherein the bendability value of 2T corresponds to
an inner radius of the high hardness hot rolled steel plate that is formed when the high
hardness hot rolled steel plate is bent, wherein, the inner radius formed is equal to twice
a thickness of the high hardness hot rolled steel plate.
19. The method as claimed in claim 17, wherein,
the first temperature ranges from 1150°C to 1275°C, and the first period ranges
from 2 hours to 4 hours,
the second temperature ranges from 850℃ to 890℃, and
the third temperature ranges from 450 ℃ to 490 ℃.
20. The method as claimed in claim 17, wherein,
the first thickness ranges from 4.75 mm to 5.25 mm, and
the first cooling rate ranges from 5 °C/s to 40 °C/s.