U.S. patent application number 15/751591 was filed with the patent office on 2018-08-23 for high-hardness steel sheet, and manufacturing method thereof.
The applicant listed for this patent is POSCO. Invention is credited to Young-Roc IM, Jun-Sang JANG.
Application Number | 20180237875 15/751591 |
Document ID | / |
Family ID | 57835400 |
Filed Date | 2018-08-23 |
United States Patent
Application |
20180237875 |
Kind Code |
A1 |
IM; Young-Roc ; et
al. |
August 23, 2018 |
HIGH-HARDNESS STEEL SHEET, AND MANUFACTURING METHOD THEREOF
Abstract
The objective of one aspect of the present invention is to
provide a high-hardness steel sheet and a manufacturing method, the
high-hardness steel sheet having Brinell hardness of 500 HB or more
by setting a steel composition according to a minimum carbon
content relation (1). C (minimum carbon
(c)content).gtoreq.0.481-0.104
Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C.R. [Relation 1] (wherein
Mn, Si, Cr, Ni and Mo are a value representing the content of each
element by wt %, and C.R. is a value represent cooling rate during
cooling a hot rolled steel sheet and the unit thereof is .degree.
C./sec)
Inventors: |
IM; Young-Roc; (Pohang-si,
Gyeongsangbuk-do, KR) ; JANG; Jun-Sang; (Pohang-si,
Gyeongsangbuk-do, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POSCO |
Pohang-si, Gyeongsangbuk-do |
|
KR |
|
|
Family ID: |
57835400 |
Appl. No.: |
15/751591 |
Filed: |
August 18, 2016 |
PCT Filed: |
August 18, 2016 |
PCT NO: |
PCT/KR2016/009079 |
371 Date: |
February 9, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 38/50 20130101;
C22C 38/48 20130101; C22C 38/54 20130101; C21D 9/46 20130101; C22C
38/58 20130101; C21D 8/0226 20130101; C21D 2211/005 20130101; C21D
2211/008 20130101; C22C 38/06 20130101; C22C 38/44 20130101; C22C
38/46 20130101; C21D 8/0263 20130101; C21D 1/18 20130101; C21D 8/02
20130101; C22C 38/02 20130101; C21D 2211/002 20130101 |
International
Class: |
C21D 8/02 20060101
C21D008/02; C22C 38/58 20060101 C22C038/58; C22C 38/54 20060101
C22C038/54; C22C 38/50 20060101 C22C038/50; C22C 38/48 20060101
C22C038/48; C22C 38/46 20060101 C22C038/46; C22C 38/44 20060101
C22C038/44; C22C 38/06 20060101 C22C038/06; C22C 38/02 20060101
C22C038/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 21, 2015 |
KR |
10-2015-0117985 |
Claims
1. A high-hardness steel sheet, the steel sheet provided by cooling
a hot rolled steel sheet, comprising: carbon (C): 0.05 wt % to 0.3
wt %, silicon (Si): 0.5 wt % or less (excluding 0%), manganese
(Mn): 2.5 wt % or less (excluding 0%), chrome (Cr): 1.5 wt % or
less (excluding 0%), molybdenum (Mo): 1.0 wt % or less (excluding
0%), nickel (Ni): 1.0 wt % or less (excluding 0%), niobium (Nb):
0.1 wt % or less (excluding 0%), titanium (Ti): 0.1 wt % or less
(excluding 0%), vanadium (V): 0.1 wt % or less (excluding 0%),
boron (B): 0.01 wt % or less (excluding 0%), aluminum (Al): 0.1 wt
% or less (excluding 0%), a balance of iron (Fe) and other
unavoidable impurities; having a minimum content of carbon (C)
satisfying Relation (1); having a microstructure comprising 95 vol.
% or more of a martensite phase; and having a Brinell hardness of
500 HB or more, C (a minimum content of carbon
(C)).gtoreq.0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C.R.
[Relation 1] where Mn, Si, Cr, Ni, and Mo are values representing
the content of each element by wt %, C.R. is a value representing a
cooling rate during the cooling a hot-rolled steel sheet, and the
unit thereof is .degree. C./sec.
2. The high-hardness steel sheet of claim 1, wherein the
microstructure includes one or two of ferrite and bainite, in an
amount of less than 5.0 vol. %, as a second phase structure, other
than martensite.
3. The high-hardness steel sheet of claim 1, wherein Relation (1)
is derived from Relation (3), HB (Brinell
hardness)=100.4+830.5*C+86.5*Mn+28.8*Si+73.4*Cr+44.5*Ni+28.8*Mo+0.252*C.R-
. [Relation 3] where C, Mn, Si, Cr, Ni, and Mo are values
representing the content of each element by wt %, C.R. is a value
representing a cooling rate during the cooling a hot-rolled steel
sheet, and the unit thereof is .degree. C./sec.
4. The high-hardness steel sheet of claim 1, wherein the content of
carbon (C) is 0.19 wt % to 0.3 wt %.
5. The high-hardness steel sheet of claim 1, wherein the content of
silicon (Si) is 0.21 wt % to 0.5 wt %.
6. The high-hardness steel sheet of claim 1, wherein the content of
manganese is 1.4 wt % to 2.5 wt %.
7. A method of manufacturing a high-hardness steel sheet, the
method of manufacturing a steel sheet, having a microstructure
comprising 95 vol. % or more of a martensite phase and a Brinell
hardness of 500 HB or more, comprising: hot-rolling and cooling a
steel slab including carbon (C): 0.05 wt % to 0.3 wt %, silicon
(Si): 0.5 wt % or less (excluding 0%), manganese (Mn): 2.5 wt % or
less (excluding 0%), chrome (Cr): 1.5 wt % or less (excluding 0%),
molybdenum (Mo): 1.0 wt % or less (excluding 0%), nickel (Ni): 1.0
wt % or less (excluding 0%), niobium (Nb): 0.1 wt % or less
(excluding 0%), titanium (Ti): 0.1 wt % or less (excluding 0%),
vanadium (V): 0.1 wt % or less (excluding 0%), boron (B): 0.01 wt %
or less (excluding 0%), aluminum (Al): 0.1 wt % or less (excluding
0%), a balance of iron (Fe) and other unavoidable impurities, as a
hot-rolled steel sheet, wherein a minimum content of carbon (C)
satisfies Relation (1), C (a minimum content of carbon
(C)).gtoreq.0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C.R.
[Relation 1] where Mn, Si, Cr, Ni, and Mo are values representing
the content of each element by wt %, C.R. is a value representing a
cooling rate during cooling a hot-rolled steel sheet, and the unit
thereof is .degree. C./sec.
8. The method of manufacturing a high-hardness steel sheet of claim
7, wherein a cooling rate during the cooling the hot-rolled steel
sheet is 20.degree. C./sec to 150.degree. C./sec.
9. The method of manufacturing a high-hardness steel sheet of claim
7, wherein a cooling end temperature during the cooling the
hot-rolled steel sheet is the Ms point (a martensite transformation
start temperature) or below.
10. The method of manufacturing a high-hardness steel sheet of
claim 7, wherein the content of carbon (C) is 0.19% to 0.3%.
11. The method of manufacturing a high-hardness steel sheet of
claim 7, wherein the content of silicon (Si) is 0.21% to 0.5%.
12. The method of manufacturing a high-hardness steel sheet of
claim 7, wherein the content of manganese is 1.4% to 2.5%.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a high-hardness steel
sheet used in various fields and a manufacturing method
thereof.
BACKGROUND ART
[0002] A steel sheet having high hardness is excellent in terms of
wear resistance and load supporting ability, thus guaranteeing long
service life as well as durability, and is used in various
components.
[0003] In detail, in the case of wear-resistant steel, a steel
grade is defined on the basis of Brinell hardness, and steel is
manufactured to have various levels of hardness, from a Brinell
hardness (HB) grade of 350 to a HB grade of 600, according to the
related art.
[0004] Moreover, a steel sheet having high hardness also has high
strength, and thus may even be used in a field requiring a
structure having high strength, such as a collision member or a
reinforcing member. In addition, the steel sheet described above
may have good economic value in terms of lightweightness and
efficiency.
[0005] In the case of the high-hardness steel sheet described
above, a steel sheet is phase-transformed to a martensite or
bainite structure in a cooling process from an austenite
temperature range to room temperature, so high hardness and
strength, which a low temperature transformation structure has, are
generally provided.
[0006] However, in the prior art, various components and process
control methods are used to obtain the required hardness according
to a component, but a criteria for unified hardness acquisition is
not provided.
DISCLOSURE
Technical Problem
[0007] An aspect of the present disclosure may provide a
high-hardness steel sheet having a Brinell hardness of 500 HB or
more in which a steel composition is set using a minimum carbon
content relation for obtaining a Brinell hardness of 500 HB or
more.
[0008] Another aspect of the present disclosure may provide a
method of manufacturing a high-hardness steel sheet having a
Brinell hardness of 500 HB or more by setting a steel composition
according to a minimum carbon content relation for obtaining a
Brinell hardness of 500 HB or more.
Technical Solution
[0009] According to an aspect of the present disclosure, a
high-hardness steel sheet having a Brinell hardness of 500 HB or
more, the steel sheet manufactured by including cooling of a hot
rolled steel sheet, includes carbon (C): 0.05 wt % to 0.3 wt %,
silicon (Si): 0.5 wt % or less (excluding 0%), manganese (Mn): 2.5
wt % or less (excluding 0%), chrome (Cr): 1.5 wt % or less
(excluding 0%), molybdenum (Mo): 1.0 wt % or less (excluding 0%),
nickel (Ni): 1.0 wt % or less (excluding 0%), niobium (Nb): 0.1 wt
% or less (excluding 0%), titanium (Ti): 0.1 wt % or less
(excluding 0%), vanadium (V): 0.1 wt % or less (excluding 0%),
boron (B): 0.01 wt % or less (excluding 0%), aluminum (Al): 0.1 wt
% or less (excluding 0%), a balance of iron (Fe) and other
unavoidable impurities; has a minimum content of carbon (C)
satisfying Relation (1); and has a microstructure including 95 vol.
% or more of a martensite phase.
C (a minimum content of carbon
(C)).gtoreq.0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C.R.
[Relation 1]
[0010] Here, Mn, Si, Cr, Ni, and Mo are values representing the
content of each element by wt %, C.R. is a value representing a
cooling rate during cooling of a hot-rolled steel sheet, and the
unit thereof is .degree. C./sec.
[0011] According to another aspect of the present disclosure, a
method of manufacturing a high-hardness steel sheet, the method of
manufacturing a steel sheet, having a microstructure including 95
vol. % or more of a martensite phase and a Brinell hardness of 500
HB or more, includes hot-rolling and cooling a steel slab including
carbon (C): 0.05 wt % to 0.3 wt %, silicon (Si): 0.5 wt % or less
(excluding 0%), manganese (Mn): 2.5 wt % or less (excluding 0%),
chrome (Cr): 1.5 wt % or less (excluding 0%), molybdenum (Mo): 1.0
wt % or less (excluding 0%), nickel (Ni): 1.0 wt % or less
(excluding 0%), niobium (Nb): 0.1 wt % or less (excluding 0%),
titanium (Ti): 0.1 wt % or less (excluding 0%), vanadium (V): 0.1
wt % or less (excluding 0%), boron (B): 0.01 wt % or less
(excluding 0%), aluminum (Al): 0.1 wt % or less (excluding 0%), a
balance of iron (Fe) and other unavoidable impurities, as a
hot-rolled steel sheet, wherein a minimum content of carbon (C)
satisfies Relation (1).
C (a minimum content of carbon
(C)).gtoreq.0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C.R.
[Relation 1]
[0012] Here, Mn, Si, Cr, Ni, and Mo are values representing the
content of each element by wt %, C.R. is a value representing a
cooling rate during cooling of a hot-rolled steel sheet, and the
unit thereof is .degree. C./sec.
Advantageous Effects
[0013] According to an exemplary embodiment in the present
disclosure, in order to manufacture a steel sheet including a
microstructure having 95 vol. % or more of a martensite phase and
Brinell hardness of 500 HB or more, a component of a more
economical and unified steel sheet may be designed.
Best Mode for Invention
[0014] The prior art related to a high-hardness steel sheet has
proposed various components and process control methods in order to
obtain a level of hardness required, according to the components,
but fails to provide a component criteria for unified hardness
acquisition.
[0015] Therefore, the present inventors have conducted studies and
experiments on the conditions of component design for securing a
required level of hardness, when a microstructure of a steel sheet
is formed to have 95 vol. % or more of a martensite structure in
order to secure a high level of hardness and strength, and the
present invention has been completed on the basis of the results
thereof.
[0016] In other words, one of the main technical features of the
present invention is to provide the conditions of a component
design for securing a required level of hardness when a
microstructure of a steel sheet is formed as 95 vol. % or more of a
martensite structure in order to secure high hardness and strength,
and thus, more economically manufacturing a microstructure
including 95 vol. % or more of a martensite phase and a steel sheet
having a Brinell hardness of 500 HB or more, and obtaining unified
hardness.
[0017] Hereinafter, a steel sheet according to a preferred aspect
of the present invention will be described.
[0018] Carbon (C): 0.05 wt % to 0.3 wt % (hereinafter, referred to
as "%")
[0019] The content of carbon (C) may be 0.05% to 0.3%.
[0020] When the content of carbon is less than 0.05%, it may be
difficult for martensitic transformation from an austenite region
to occur during cooling. When the content of carbon exceeds 0.3%,
it may be difficult to ensure stability of a component due to
increased brittleness of steel.
[0021] The content of carbon (C) may be 0.19 wt % to 0.3%.
[0022] Silicon (Si): 0.5% or less (excluding 0%)
[0023] The content of silicon (Si) may be 0.5% or less (excluding
0%).
[0024] Silicon is a preferred alloying element in applications in
which hardness is used, because silicon increases the wear
resistance of steel. However, when an amount of Si is excessive,
surface properties and plating properties of the steel become poor,
and a complete austenitization may not be performed during
reheating.
[0025] The content of silicon (Si) may be 0.21% to 0.5%. The
content of silicon (Si) may be 0.253% to 0.34%.
[0026] Manganese (Mn): 2.5% or less (excluding 0%) and Chrome (Cr):
1.5% or less (excluding 0%)
[0027] Manganese (Mn) and chrome (Cr) are elements significantly
lowering martensite transformation temperatures, and manganese and
chrome are elements, which may be used economically as low-cost
elements, since manganese and chrome have an effect of reducing a
transformation temperature less than that of carbon, among elements
generally added to steel.
[0028] An upper limit of the manganese content is preferably
limited to 2.5%, and an upper limit of the chromium content is
preferably limited to 1.5%.
[0029] When the contents of manganese and chrome are excessively
high, austenite may remain at room temperature, so 95 vol. % or
more of a martensitic structure, a targeted amount, may not be
obtained.
[0030] The content of manganese may be 1.4% to 2.5%. The content of
manganese may be 2.1% to 2.5%.
[0031] Molybdenum (Mo): 1.0% or less (excluding 0%) and Nickel
(Ni): 1.0% or less (excluding 0%)
[0032] Molybdenum (Mo) and nickel (Ni) are elements lowering a
martensite transformation start temperature.
[0033] However, a degree of lowering a martensite transformation
start temperature is smaller than those of Mn and Cr. Due to being
relatively expensive elements, an upper limit of an addition amount
of each of these elements is preferably limited to 1.0%.
[0034] Niobium (Nb): 0.1% or less (excluding 0%) and Titanium (Ti):
0.1% or less (excluding 0%),
[0035] Each of niobium (Nb) and titanium (Ti) may be added in an
amount of 0.1% or less (excluding 0%), and may have an effect of
improving the impact characteristics of a steel sheet through
austenite grain refinement. However, the excessive addition of Nb
and Ti may cause coarsening of Nb carbonitride, fixing grain
boundaries, so a crystal grain refinement effect may be lost. Thus,
an upper limit of each of Nb and Ti is preferably limited to
0.1%.
[0036] On the other hand, when B is added, Ti may be essentially
added to protect B from N. Titanium (Ti) first reacts with carbon
or nitrogen in steel, so TiC or TiN is formed. Thus, an addition
effect of boron (B) may be increased. In this case, the content of
titanium (Ti) may satisfy Relation 2 depending on stoichiometry,
with respect to an amount of nitrogen in steel.
Ti (wt %)>N(wt %).times.3.42 [Relation 2]
[0037] Vanadium (V): 0.1% or less (excluding 0%)
[0038] Vanadium (V) may be added in an amount of 0.1% or less
(excluding 0%), and may serve to prevent precipitation hardening
through the formation of fine V carbides and the deterioration of
physical properties of a welded portion.
[0039] When an addition amount of V is excessive, the effect
described above may be reduced due to the coarsening of a carbide,
so that an upper limit of the content of V is preferably limited to
0.1%.
[0040] Boron (B): 0.01% or less (excluding 0%)
[0041] Boron (B) may be added in an amount of 0.01% or less
(excluding 0%), and B is an element significantly increasing
hardenability of steel by inhibiting nucleation of ferrite and
pearlite. Even when a thickness of steel is great, utilization
thereof is significant.
[0042] In the present invention, a final microstructure may be
provided as 95 vol. % or more of martensite. A manufacturing method
thereof is not particularly limited, so B may be added to secure
hardenability as required. However, when the content of B is
excessively added, B may rather act as a nucleation site on ferrite
or pearlite to deteriorate hardenability, so an upper limit of the
content of B is preferably limited to 0.01%.
[0043] Aluminum (Al): 0.1% or less (excluding 0%)
[0044] Aluminum (Al) is added for deoxidization and grain
refinement, and the content of Al is preferably limited to 0.1% or
less (excluding 0%).
[0045] The remainder excluding elements described above include
iron (Fe) and other unavoidable impurities.
[0046] In the present invention, a minimum content of carbon (C)
may satisfy Relation (1).
C (a minimum content of carbon
(C)).gtoreq.0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C.R.
[Relation 1]
[0047] Here, Mn, Si, Cr, Ni, and Mo are values representing the
content of each element by wt %, C.R. is a value representing a
cooling rate during cooling of a hot-rolled steel sheet, and the
unit thereof is .degree. C./sec.
[0048] Relation (1) represents a minimum content of a carbon (C)
for obtaining a Brinell hardness of 500 HB or more from a
composition of silicon (Si), manganese (Mn), chrome (Cr),
molybdenum (Mo), nickel (Ni), and chrome (Cr).
[0049] Even when the content of carbon (C) satisfies 0.05 wt % to
0.3 wt %, in a case in which Relation (1) is not satisfied, a
Brinell hardness of 500 HB or more may not be obtained.
[0050] Relation (1) may be designed using, for example, Relation
(3).
HB (Brinell
hardness)=100.4+830.5*C+86.5*Mn+28.8*Si+73.4*Cr+44.5*Ni+28.8*Mo+0.252*C.R-
. [Relation 3]
[0051] Here, C, Mn, Si, Cr, Ni, and Mo are values representing the
content of each element by wt %, C.R. is a value representing a
cooling rate during cooling of a hot-rolled steel sheet, and the
unit thereof is .degree. C./sec.
[0052] Relation (1) with respect to a minimum carbon content for
HB.gtoreq.500 may be derived from Relation (3).
[0053] Moreover, by using Relation (3) within a steel sheet
component range of the present invention, proper alloying element
design conditions to obtain any required level of hardness of 350
HB or more may be derived.
[0054] A microstructure of a steel sheet according to the present
invention may include 95 vol. % or more of a martensite phase. When
a fraction of the martensite phase is less than 95 vol. %, it may
be difficult to secure targeted strength and hardness.
[0055] The microstructure of a steel sheet according to the present
invention may include one or two of ferrite and bainite, in an
amount of less than 5.0 vol. %, as a second phase structure, other
than martensite.
[0056] The steel sheet according to the present invention may have
Brinell hardness of 500 HB or more.
[0057] Hereinafter, a method of manufacturing a steel sheet
according to another preferred aspect of the present invention will
be described.
[0058] In a method of manufacturing a steel sheet according to
another preferred aspect of the present invention, after a steel
slab including carbon (C): 0.05 wt % to 0.3 wt %, silicon (Si): 0.5
wt % or less (excluding 0%), manganese (Mn): 2.5 wt % or less
(excluding 0%), chrome (Cr): 1.5 wt % or less (excluding 0%),
molybdenum (Mo): 1.0 wt % or less (excluding 0%), nickel (Ni): 1.0
wt % or less (excluding 0%), niobium (Nb): 0.1 wt % or less
(excluding 0%), titanium (Ti): 0.1 wt % or less (excluding 0%),
vanadium (V): 0.1 wt % or less (excluding 0%), boron (B): 0.01 wt %
or less (excluding 0%), aluminum (Al): 0.1 wt % or less (excluding
0%), a balance of iron (Fe) and other unavoidable impurities is
hot-rolled as a hot-rolled steel sheet, the hot-rolled steel sheet
is cooled, so a steel sheet having a martensite phase including 95
vol. % or more of a microstructure and 500 HB or more of Brinell
hardness is manufactured.
[0059] A minimum content of carbon (C) in the steel slab satisfies
Relation (1).
C (a minimum content of carbon
(C)).gtoreq.0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C.R.
[Relation 1]
[0060] Here, Mn, Si, Cr, Ni, and Mo are values representing the
content of each element by wt %, C.R. is a value representing a
cooling rate during cooling of a hot-rolled steel sheet, and the
unit thereof is .degree. C./sec.
[0061] Before the steel slab is hot-rolled as a hot-rolled steel
sheet, a steel slab may be reheated.
[0062] Conditions for reheating a slab are not particularly
limited, and the conditions are sufficient as long as
homogenization is allowed.
[0063] A slab reheating temperature is preferably 1100.degree. C.
to 1300.degree. C.
[0064] The hot-rolling conditions are preferably not limited, and a
hot finish rolling temperature is sufficient as long as
austenitization is allowed.
[0065] The hot finish rolling temperature may be, for example,
870.degree. C. to 930.degree. C., and whole hot-rolling may be
performed within a temperature range of 1150.degree. C. to a hot
finish rolling temperature, after extraction from a heating
furnace.
[0066] A cooling rate during cooling the hot-rolled steel sheet is
not preferably limited while a cooling rate allows 95 vol. % or
more of a martensite phase to be obtained. For example, the cooling
rate is 20.degree. C./sec or more, and preferably, 20.degree.
C./sec to 150.degree. C./sec.
[0067] A cooling end temperature during cooling the hot-rolled
steel sheet is the Ms point (a martensite transformation start
temperature) or below, and is not particularly limited as long as a
cooling end temperature allows 95 vol. % or more of a martensite
phase to be obtained.
Mode for Invention
[0068] Hereinafter, the present disclosure will be described in
greater detail with reference to examples. The examples are only
for illustrating the present invention, and the present invention
is not limited thereto.
EXAMPLE
[0069] An experiment was conducted using 17 types of steel A to Q
having the compositions (unit: wt %) illustrated in Table 1.
[0070] The compositions of steels of Table 1 satisfy a composition
range of the present invention.
[0071] After a steel sheet having the steel composition of Table 1
while having a thickness of 30 mm and a width of 200 mm was
manufactured, the steel sheet was reheated for 180 minutes at
1200.degree. C. Next, the steel sheet, having been reheated, was
hot-rolled in a hot finish temperature range of 900.degree. C., and
a hot-rolled steel sheet having a thickness of 3.0 mm was
manufactured. Thereafter, the steel sheet was cooled to 200.degree.
C. at a cooling rate of Table 2.
[0072] Brinell hardness (HB) and a microstructure of the hot-rolled
steel sheet manufactured as described above were measured, and
results thereof are illustrated in Table 2.
[0073] A second phase structure of Table 2 indicates a second phase
structure, other than martensite. Moreover, a structure other than
a second phase structure is martensite, and 100% martensite is
referred to as 100% M.
[0074] In the second phase structure described above, F indicates
ferrite, B indicates bainite, and M indicates martensite.
[0075] Moreover, in Table 2, a required carbon content obtained by
Relation (1), an actual carbon content, and a difference between
the actual content and the required carbon content are
illustrated.
TABLE-US-00001 TABLE 1 Steel C Si Mn Cr Mo Ni Al Ti Nb V B A 0.081
0.298 1.85 0.498 0.101 0.008 0.03 0.006 0.032 0.006 0.0002 B 0.121
0.351 2.11 0.313 0.798 0.012 0.032 0.025 0.023 0.005 0.0017 C 0.195
0.354 2.01 0.297 0.006 0.812 0.031 0.029 0.025 0.003 0.0016 D 0.152
0.248 1.49 0.296 0.008 0.011 0.033 0.03 0.056 0.005 0.003 E 0.242
0.432 1.72 0.411 0.312 0.013 0.036 0.03 0.003 0.006 0.0033 F 0.148
0.243 1.48 0.607 0.012 0.005 0.034 0.029 0.004 0.004 0.0032 G 0.148
0.24 1.48 0.3 0.007 0.007 0.035 0.098 0.005 0.005 0.0033 H 0.297
0.253 1.51 0.3 0.211 0.006 0.035 0.03 0.007 0.002 0.0016 I 0.212
0.25 1.49 1.1 0.203 0.008 0.035 0.03 0.022 0.098 0.0029 J 0.2 0.249
1.47 0.3 0.011 0.021 0.03 0.029 0.005 0.003 0.0029 K 0.252 0.254
2.31 0.125 0.012 0.015 0.033 0.03 0.032 0.005 0.0028 L 0.198 0.243
1.49 0.297 0.015 0.023 0.034 0.03 0.008 0.004 0.0031 M 0.199 0.254
1.47 1.12 0.012 0.015 0.033 0.03 0.032 0.005 0.0028 N 0.2 0.207
1.47 0.3 0.011 0.014 0.034 0.098 0.045 0.002 0.0025 O 0.26 0.297
2.11 0.02 0.101 0.005 0.027 0.007 0.022 0.011 0.0003 P 0.27 0.212
1.51 0.52 0.112 0.012 0.021 0.005 0.023 0.012 0.0020 Q 0.232 0.491
1.78 0.298 0.005 0.003 0.026 0.021 0.015 0.055 0.0018
TABLE-US-00002 TABLE 2 Required Actual carbon content carbon
Cooling (wt. %, content Brinell Second Ms rate Relation 1) (wt. %)
hardness phase Classification Steel (.degree. C.) (.degree. C./sec)
{circle around (1)} {circle around (2)} {circle around (2)} -
{circle around (1)} (HB) structure Comparative A 432 100 0.200
0.081 -0.119 395 F8%, B11% Example 1 Comparative B 401 50 0.178
0.121 -0.057 445 F2%, B3% Example 2 Inventive C 381 50 0.174 0.195
0.021 519 B3% Example 1 Comparative D 433 50 0.275 0.152 -0.123 404
F1%. B4% Example 3 Inventive E 387 35 0.229 0.242 0.013 505 F1%,
B3% Example2 Inventive E 379 70 0.218 0.242 0.024 523 100% M
Example3 Comparative F 425 50 0.249 0.148 -0.101 405 B4% Example 4
Comparative G 434 20 0.286 0.148 -0.138 364 F6%, B7% Example 5
Inventive H 380 50 0.266 0.297 0.031 531 B3% Example4 Inventive I
379 35 0.202 0.212 0.010 511 100% M Example5 Comparative J 411 35
0.281 0.2 -0.081 437 F2%, 82% Example 6 Inventive K 372 100 0.190
0.252 0.062 551 100% M Example6 Comparative L 417 35 0.279 0.198
-0.081 440 F2%, B2% Example 7 Comparative M 394 20 0.213 0.199
-0.014 491 F1%, B3% Example 8 Comparative N 417 70 0.272 0.2 -0.072
448 B4% Example 9 Inventive O 377 80 0.222 0.26 0.038 527 B3%
Example7 Inventive P 386 50 0.251 0.27 0.019 510 B2% Example8
Inventive Q 396 100 0.222 0.232 0.010 502 B3% Example9
[0076] As illustrated in Table 2, according to the present
invention, in the case of Inventive Examples 1 through 9, in which
an actual carbon content is larger than a required carbon content,
it is confirmed that a Brinell hardness (HB) value is 500 HB or
more.
[0077] On the other hand, in the case of Comparative Examples 1
through 9, in which an actual carbon content is smaller than a
required carbon content, it is confirmed that a value of Brinell
hardness is less than 500 HB.
[0078] While exemplary embodiments have been shown and described
above, it will be apparent to those skilled in the art that
modifications and variations could be made without departing from
the scope of the present invention as defined by the appended
claims.
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