Note: Descriptions are shown in the official language in which they were submitted.
CA 02801708 2012-12-05
Description
[Title of the Invention]
ABRASION RESISTANT STEEL PLATE WHICH EXHIBITS EXCELLENT
WELD TOUGHNESS AND EXCELLENT DELAYED FRACTURE RESISTANCE
[Technical Field]
[0001]
The present invention relates to an abrasion resistant
steel plate or steel sheet having a plate thickness of 4 mm
or more preferably used in construction machines, industrial
machines, shipbuilding, steel pipes, civil engineering,
architecture or the like, and more particularly to an abrasion
resistant steel plate or steel sheet which exhibits excellent
toughness and excellent delayed fracture resistance of a multi
pass weld.
[Background Art]
[0002]
When a hot-rolled steel plate is employed for forming
steel structural products, machines, devices or the like in
construction machines, industrial machines, shipbuilding,
steel pipes, civil engineering, architecture or the like, there
may be a-case where the steel plates are required to possess
abrasion resistant property. Conventionally, to impart
excellent abrasion resistant property to a steel material,
hardness is increased in general, and hardness of the steel
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CA 02801708 2012-12-05
. .
material can be remarkably enhanced by forming the steel
material into the martensite single phase microstructure. The
increase of an amount of solid solution carbon is also effective
for enhancing hardness of martensite microstructure per se.
[0003]
Accordingly, the abrasion resistant steel plate
exhibits high cold cracking susceptibility so that the steel
plate exhibits inferior weld toughness in general whereby when
the abrasion resistant steel plate is used in forming the welded
steel structure, in general, the abrasion resistant steel plate
is laminated to a surface of a steel member which is brought
into contact with rock, earth and sand or the like as a liner.
For example, with respect to a vessel of a damped motor lorry,
there has been known a case where the vessel is assembled by
welding using mild steel and, thereafter, an abrasion resistant
steel plate is laminated to only a front surface of the vessel
which is brought into contact with earth and sand.
[0004]
However, in the manufacturing method in which the
abrasion resistant steel plate is laminated to the welded steel
structure after the welded steel structure is assembled, labor
for the manufacture and a manufacturing cost are increased.
Accordingly, there has been a demand for an abrasion resistant
steel plate which is excellent in weldability and weld
toughness and can be used as a strength member of the welded
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steel structure, and such an abrasion resistant steel plate
has been proposed in patent documents 1 to 5, for example.
Patent document 1 relates to an abrasion resistant steel
plate which exhibits excellent delayed fracture resistance and
a method of manufacturing the abrasion resistant steel plate.
In patent document 1, there is the description that, to improve
the delayed fracture resistance, steel which further contains
one, two or more kinds of components selected from a group
consisting of Cu, V, Ti, B and Ca in the composition of a type
containing low-Si, low-P, low-S, Cr, Mo and Nb is subjected
to direct quenching (hereinafter also referred to as DQ), and
tempering is performed when necessary.
[0005]
Patent document 2 relates to steel having high abrasion
resistant property and a method of manufacturing a steel
product. In patent document 2, there is described steel which
has the composition composed of a 0.24 to 0.3C-Ni, Cr, Mo, B
system, satisfies a parameter formula constituted of contents
of these elements, and includes martensite containing 5 to 15
volume% of austenite or martensitic structure and bainitic
structure thus enhancing abrasion resistant property. Patent
document 2 also describes that the steel having the
above-mentioned components is .cooled at a cooling rate of
1 C/sec or more at a temperature between an austenitizing
temperature and 450 C.
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[0006]
Patent document 3 relates to an abrasion resistant steel
material which exhibits excellent toughness and excellent
delayed fracture resistance and a method of manufacturing the
abrasion resistant steel material. In patent document 3,
there is described a steel material which has the composition
containing Cr, Ti, and B as indispensable components, wherein
a surface layer is formed of tempered martensite, an internal
part is formed of tempered martensite and tempered lower
bainitic structure, and an aspect ratio of prior austenite
grain diameter between the wall thickness direction and the
rolling direction is defined. Patent document 3 also
describes that the steel having the content composition is
subject to hot rolling at a temperature of 900 C or below and
at a cumulative reduction ratio of 50% or more and, thereafter,
is directly quenched and tempered.
[0007]
Patent document 4 relates to an abrasion resistant steel
material which exhibits excellent toughness and excellent
delayed fracture resistance and a method of manufacturing the
abrasion resistant steel material. In patent document 4,
there is described a steel material which has the composition
containing Cr, Ti and B as indispensable components, wherein
a surface layer is formed of martensite, and an internal part
is formed of the mixed structure of martensite and lower
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bainitic structure or lower bainitic single-phase structure,
and an elongation rate of prior austenite grains expressed by
an aspect ratio between prior austenite grain diameter at a
plate thickness center portion and prior austenite grain
diameter in the rolling direction is defined. Patent document
4 also describes that the steel having the composition is
subjected to hot rolling at a temperature of 900 C or below
and at a cumulative reduction ratio of 50% or more and,
thereafter, is directly quenched.
[0008]
Patent document 5 relates to abrasion resistant steel
which exhibits excellent weldability, excellent abrasion
resistant property and excellent corrosion resistance, and a
method of manufacturing the abrasion resistant steel. In
patent document 5, there is described steel which contains 4
to 9 mass% of Cr as an indispensable element, contains one or
two kinds of Cu and Ni and satisfies a parameter formula
-
constituted of contents of specific components. Patent
document 5 also describes that the steel having the composition
is subjected to hot rolling at a temperature of 950 C or below
and at a cumulative reduction ratio of 30% or more and,
thereafter, the steel is reheated at a temperature of Ac3 or
more and is quenched.
[Prior Art Literature]
[Patent Document]
CA 02801708 2012-12-05
[0009]
[Patent Document 1] JP-A-5-51691
[Patent Document 2] JP-A-8-295990
[Patent Document 3] JP-A-2002-115024
[Patent Document 4] JP-A-2002-80930
[Patent Document 5] JP-A-2004-162120
[Summary of the Invention]
[Task to be Solved by the Invention]
[0010]
In case of a weld joint using a steel plate having a plate
thickness of 4 mm or more, it is often the case that the weld
joint is formed by multi pass welding. However, in a weld,
a bond area formed by a preceding weld pass is reheated by
succeeding welding so that a region where toughness is
remarkably deteriorated appears. Particularly, in an
abrasion resistant steel plate, when a bond area formed by
welding for forming a first layer is reheated to a temperature
around 300 C due to succeeding welding, toughness is remarkably
deteriorated due to low-temperature tempering embrittlement.
[0011]
It is thought that low-temperature tempering
embrittlement is brought about by a synergistic action between
a morphology change of carbide in martensite and the
intergranular segregation of impurity elements or the like.
In a bond area which has coarse grain particles and contains
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a large quantity of solid solution N, the low-temperature
tempering embrittlement becomes conspicuous. It has been
pointed out that delayed fracture is liable to occur in a region
which is reheated to such a low-temperature tempering
embrittlement temperature.
[0012]
Patent documents 1 and 2 fail to describe the enhancement
of weld toughness in an abrasion resistant steel, and patent
documents 3 and 4 also define the microstructure aiming at the
enhancement of toughness of a base material. Although patent
document 5 studies weldability and abrasion resistant property
of a weld, the study does not aim at the enhancement of weld
toughness. That is, the abrasion resistant steels proposed
in patent documents 1 to 5 and the like are less than optimal
with. respect to the improvement of both weld toughness and
delayed fracture resistance of a multi pass weld.
Accordingly, it is an object of the present invention
to provide an abrasion resistant steel plate which exhibits
excellent toughness of a multi pass weld and excellent delayed
fracture resistance without inducing lowering of productivity
and the increase in a manufacturing cost.
[Means for Solving the Problem]
[0013]
To achieve the above-mentioned object, inventors of the
present invention have made extensive studies on various
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factors which decide chemical components of a steel plate, a
method of manufacturing the steel plate and the microstructure
of the steel plate so as to secure toughness of a multi pass
weld and delayed fracture resistance with respect to an
abrasion resistant steel plate, and have made following
findings.
[0014]
1. To secure excellent abrasion resistant property, it
is indispensable to form the base microstructure or the main
microstructure (also referred to as a base phase or a main
phase) of the steel plate into martensite. For this end, it
is important to strictly control the chemical composition of
the steel plate thus securing quenching property.
2. To achieve the excellent toughness of a multi pass
weld, it is necessary to suppress grain particles in a welded
heat affected zone from becoming coarse, and for this end, it
is effective to make use of a pinning effect by dispersing fine
precipitates in the steel plate. Accordingly, a control of
Ti, N is important.
3. The reduction of solid solution N in a bond area forming
an initial layer is effective for suppressing low-temperature
tempering embrittlement caused by succeeding welding. For
this end, it is important to strictly control B for fixing solid
solution N as BN.
4. To secure the excellent toughness and to suppress
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delayed fracture in a low-temperature tempering embrittlement
temperature area of the welded heat affected zone, it is
important to properly control quantities of alloy elements such
as C, Mn, Cr, Mo, P.
[0015]
The present invention has been made by further studying
the above-mentioned findings. That is, the present invention
is directed to:
1. An abrasion resistant steel plate having a composition
containing by mass% 0.20 to 0.30% C, 0.05 to 0.5% Si, 0.40 to
1.2% Mn, 0.010% or less P, 0.0018% or less S, 0.40 to 1.5% Cr,
0.05 to 1.0% Mo, 0.005 to 0.025% Nb, 0.005 to 0.03% Ti, 0.1%
or less Al, 0.0015 to 0.0060% N, 0.0003 to 0.0020% B, and Fe
and unavoidable impurities as a balance, wherein;
- hardenability index DI* expressed by a formula (1):
DI* =33.85 x (0.1xC) '5x (0.7xSi+1) x (3.33xMn+1) x (0.35xCu+1)
x (0.36xNi+1) x (2.16xCr+1) x (3xMo+1) x (1.75xV+1) x (1.5xW+1)
................................................................. (1),
wherein the respective element symbols are contents
(mass%) of the elements, is 45 or more;
- a base phase of the microstructure is formed of martensite;
- carbonitride particles of Nb and Ti having an average particle
size of 1 pm or less are present at a rate of 1000 pieces/mm2
or more;
- an average particle size of prior austenite is less than 200
pm; and
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- an average particle size of lower microstructure surrounded
by a large tilt grain boundary having a radial hook of 15 or
more is less than 70 pm.
2. The abrasion resistant steel plate described in 1,
wherein the steel composition further contains by mass% 0.05
to 1.0% W.
3. The abrasion resistant steel plate described in 1 or
2, wherein the steel composition further contains by mass% one,
two or more kinds of components selected from a group consisting
of 1.5% or less Cu, 2.0% or less Ni, and 0.1% or less V.
4. The abrasion resistant steel plate described in any
one of 1 to 3, wherein the steel composition further contains
by mass% one, two or more kinds of components selected from
a group consisting of 0.008% or less REM, 0.005% or less Ca,
and 0.005% or less Mg.
5. The abrasion resistant steel plate described in any
one of 1 to 4, wherein surface hardness of the steel plate is
400 HBW10/3000 or more in Brinell hardness.
6. The abrasion resistant steel plate described in any
one of 1 to 5, wherein hardenability index DI* is from 45 and
up to 180.
7. The abrasion resistant steel plate described in any
one of 1 to 6, wherein the steel plate satisfies a formula (2):
C+Mn / 4-Cr / 3+10P 0.47 .. (2),
wherein the respective element symbols are contents (mass%)
CA 02801708 2014-10-06
of the elements.
[Advantage of the Invention]
[0016]
According to the present invention, it is possible to
acquire the abrasion resistant steel plate having excellent
toughness and excellent delayed fracture resistance at a multi
pass weld. The present invention largely contributes to the
enhancement of manufacturing efficiency and safety at the time
of manufacturing a steel structure thus acquiring an
industrially remarkable effect.
[Brief Description of the Drawings]
[0017]
Fig. 1 is a view for explaining a T shape fillet weld
cracking test.
Fig. 2 is a view showing a position where a Charpy impact
test piece is taken from a weld.
[Mode for Carrying Out the Invention]
[0018]
The present invention defines the composition and the
microstructure.
[Composition]
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In the explanation made hereinafter, % indicates mass%.
C: 0.20 to 0.30%
C is an important element for increasing hardness of
martensite and for allowing the steel plate to secure the
excellent abrasion resistant property. It is necessary for
the steel plate to contain 0.20% or more C to acquire such
effects. On the other hand, when the content of C exceeds 0.30%,
not only weldability is deteriorated but also toughness of a
bond area of a multi pass weld is deteriorated due to
low-temperature tempering embrittlement. Accordingly,
content of C is limited to a value which falls within a range
from 0.20 to 0.30%. The content of C is preferably limited
to a value which falls within a range from 0.20 to 0.28%.
[0019]
Si: 0.05 to 1.0%
Si acts as a deoxidizing agent, and not only Si is
necessary for steel making but also Si has an effect of
increasing hardness of a steel plate by solid solution
strengthening where Si is present in steel in a solid solution
state. Further, Si has an effect of suppressing the
deterioration of toughness of a bond area of a multi pass weld
due to low-temperature tempering embrittlement. It is
necessary for the steel plate to contain 0.05% or more Si to
acquire such an effect. On the other hand, when the content
of Si exceeds 1.0%, toughness of the multi pass welded heat
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affected zone is remarkably deteriorated. Accordingly, the
content of Si is limited to a value which falls within a range
from 0.05 to 1.0%. The content of Si is preferably limited
to a value which falls within a range from 0.07 to 0.5%.
[0020]
Mn: 0.40 to 1.2%
Mn has an effect of increasing hardenability of steel,
and it is necessary for the steel plate to contain 0.40% or
more Mn to secure hardness of a base material. On the other
hand, when the content of Mn exceeds 1.2%, not only toughness,
ductility and weldability of the base material are deteriorated,
but also intergranular segregation of P is accelerated thus
accelerating the generation of delayed fracture. Accordingly,
the content of Mn is limited to a value which falls within a
range from 0.40 to 1.2%. The content of Mn is preferably
limited to a value which falls within a range from 0.40 to 1.1%.
[0021]
P: 0.010% or less
When the content of P exceeds 0.010%, P is segregated
in a grain boundary, the segregated P becomes an initiation
point of delayed fracture, and deteriorates toughness of a
multi pass weld. Accordingly, an upper limit of the content
of P is set to 0.010% and it is desirable that the content of
P is set as small as possible. Since the excessive reduction
of P pushes up a refining cost and becomes economically
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disadvantageous, the content of P is desirably set to 0.002%
or more.
[0022]
S: 0.005% or less
S deteriorates low-temperature toughness and ductility
of a base material and hence, the content of S is desirably
set small with an allowable upper limit of 0.005%.
[0023]
Cr: 0.40 to 1.5%
Cr is an important alloy element in the present invention,
and has an effect of increasing hardenability of steel and also
has an effect of suppressing the deterioration of toughness
of the bond area of the multi pass weld due to low-temperature
tempering. This is because the inclusion of Cr delays the
diffusion of C in the steel plate and hence, when the steel
plate is reheated to a temperature region where the
low-temperature tempering embrittlement occurs, morphology
change of carbide in martensite can be suppressed. It is
necessary for the steel plate to contain 0.40% or more of Cr
to acquire such an effect. On the other hand, when the content
of Cr exceeds 1.5%, the effect is saturated so that not only
does it become economically disadvantageous but also
weldability is lowered. Accordingly, the content of Cr is
limited to a value which falls within a range from 0.40 to 1.5%.
The content of Cr is preferably limited to a value which falls
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within a range from 0.40 to 1.2%.
[0024]
Mo: 0.05 to 1.0%
Mo is an element effective for remarkably increasing
hardenability thus increasing hardness of a base material.
Further, Mo has an effect of suppressing the deterioration of
toughness of the bond area of the multi pass weld due to
low-temperature tempering. The content of Mo is set to 0.05%
or more for acquiring such an effect. However, when the content
of Mo exceeds 1.0%, Mo adversely influences toughness,
ductility and weld crack resistance of the base material and
hence, the content of Mo is set to 1.0% or less. Accordingly,
the content of Mo is limited to a value which falls within a
range from 0.05 to 1.0%. The content of Mo is preferably
limited to a value which falls within a range from 0.1 to 0.8%.
[0025]
Nb: 0.005 to 0.025%
Nb is an important element having both an effect of
improving toughness of the multi pass weld and an effect of
suppressing the occurrence of delayed fracture by making the
microstructure of the base material and the multi pass weld
finer by causing the precipitation of carbonitride and also
by fixing solid solution N . It is necessary for the steel plate
to contain 0.005% or more Nb to acquire such effects. On the
other hand, when the content of Nb exceeds 0.025%, coarse
CA 02801708 2012-12-05
carbonitride precipitates and there may be a case where the
coarse carbonitride becomes an initiation point of fracture.
Accordingly, the content of Nb is limited to a value which falls
within a range from 0.005 to 0.025%. The content of Nb is
preferably limited to a value which falls within a range from
0.007 to 0.023%.
[0026]
Ti: 0.005 to 0.03%
Ti has an effect of suppressing grains in the bond area
of the multi pass weld from becoming coarse by forming TiN due
to fixing of solid solution N, and also has an effect of
suppressing the deterioration of toughness and the occurrence
of delayed fracture in the low-temperature tempering
temperature region due to the decrease of solid solution N.
It is necessary for the steel plate to contain 0.005% or more
Ti to acquire such effects. On the other hand, when the content
of Ti exceeds 0.03%, TiC precipitates so that toughness of the
base material is deteriorated. Accordingly, the content of
Ti is limited to a value which falls within a range from 0.005
to 0.03%. The content of Ti is preferably limited to a value
which falls within a range from 0.007 to 0.025%.
[0027]
Al: 0.1% or less
Al acts as a deoxidizing agent and is most popularly used
in a molten steel deoxidizing process of a steel plate. Further,
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by forming AIN by fixing solid solution N in steel, Al has an
effect of suppressing grains in the bond area of the multi pass
weld from becoming coarse and an effect of suppressing the
deterioration of toughness and the occurrence of delayed
fracture in the low-temperature tempering temperature region
due to the reduction of solid solution N. On the other hand,
when the content of Al exceeds 0.1%, Al is mixed into weld metal
at the time of welding thus deteriorating toughness of weld
metal. Accordingly, the content of Al is limited to 0.1% or
less. The content of Al is preferably limited to a value which
falls within a range from 0.01 to 0.07%.
[0028]
N: 0.0015 to 0.0060%
N is bonded with Ti thus precipitating TiN, and has an
effect of contributing to the enhancement of toughness by
suppressing austenite particles from becoming coarse in HAZ.
It is necessary for the steel plate to contain 0.0015% or more
N to secure a required quantity of TiN having such an effect.
On the other hand, when the content of N exceeds 0.0060%, in
a region which is heated to a temperature at which TiN is melted
at the time of welding, a quantity of solid solution N is
increased so that the deterioration of toughness in the
low-temperature tempering temperature region becomes
conspicuous. Accordingly, the content of N is limited to a
value which falls within a range from 0.0015 to 0.0060%. The
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content of N is preferably limited to a value which falls within
a range from 0.0020 to 0.0055%.
[0029]
B: 0.0003 to 0.0020%
B is an element effective for remarkably increasing
hardenability with addition of a trace amount of B thus
increasing hardness of a base material. Further, in a region
which is heated to a temperature at which TiN is melted at the
time of welding, solid solution N is fixed as BN so that B has
an effect of suppressing the deterioration of toughness in the
low-temperature tempering temperature region due to
succeeding welding. The content of B may preferably be 0.0003%
or more for acquiring such an effect. However, when the content
of B exceeds 0.0020%, B adversely influences toughness,
ductility and weld crack resistance of the base material.
Accordingly, the content of B is set to 0.0020% or less. The
content of B is preferably limited to a value which falls within
a range from 0.0005 to 0.0018%. The balance of the steel plate
is Fe and unavoidable impurities.
[0030]
According to the present invention, to further enhance
properties of the steel plate, in addition to the
above-mentioned basic component system, the steel plate may
contain one, two or more kinds of components selected from a
group consisting of W, Cu, Ni, V, REM, Ca and Mg.
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[0031]
W: 0.05 to 1.0%
W is an element effective for remarkably increasing
hardenability thus increasing hardness of a base material.
The content of W may preferably be 0.05% or more for acquiring
such an effect. However, when the content of W exceeds 1.0%,
W adversely influences toughness, ductility and weld crack
resistance of the base material. Accordingly, the content of
W is set to 1.0% or less.
[0032]
All of Cu, Ni and V are elements which contribute to the
enhancement of strength of steel, and the steel plate may
contain proper amounts of Cu, Ni, V depending on strength which
the steel plate requires.
[0033]
Cu: 1.5% or less
Cu is an element effective for increasing hardenability
thus increasing hardness of the base material. The content of
Cu may preferably be 0.1% or more for acquiring such an effect.
However, when the content of Cu exceeds 1.5%, the effect is
saturated and Cu causes hot brittleness thus deteriorating
surface property of a steel plate. Accordingly, the content
of Cu is set to 1.5% or less.
[0034]
Ni: 2.0% or less
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Ni is an element effective for increasing hardenability
thus increasing hardness of the base material. The content of
Ni may preferably be 0.1% or more for acquiring such an effect.
However, when the content of Ni exceeds 2.0%, the effect is
saturated so that it becomes economically disadvantageous.
Accordingly, the content of Ni is set to 2.0% or less.
[0035]
V: 0.1% or less
V is an element effective for increasing hardenability
thus increasing hardness of the base material. The content of
V may preferably be 0.01% or more for acquiring such an effect.
However, when the content of V exceeds 0.1%, toughness and
ductility of the base material is deteriorated. Accordingly,
the content of V is set to 0.1% or less.
[0036]
All of REM, Ca and Mg contribute to the enhancement of
toughness, and these elements are selectively added
corresponding to properties which the steel plate desires.
When REM is added, the content of REM may preferably be 0.002%
or more. On the other hand, when the content of REM exceeds
0.008%, the effect is saturated. Accordingly, an upper limit
of REM is set to 0.008%.
When Ca is added, the content of Ca may preferably be
0.0005% or more. On the other hand, when the content of Ca
exceeds 0.005%, the effect is saturated. Accordingly, an
CA 02801708 2012-12-05
upper limit of Ca is set to 0.005%.
When Mg is added, the content of Mg may preferably be
0.001% or more. On the other hand, when the content of Mg
exceeds 0.005%, the effect is saturated. Accordingly, an
upper limit of Mg is set to 0.005%.
[0037]
DI* =33.85 x (0.1xC)(3-5x (0.7xSi+1) x (3.33xMn+1) x (0.35xCu+1)
x (0.36xNi+1) x (2.16xCr+1) x (3xMo+1) x (1.75xV+1) x (1.5xW+1)
.. (1),
wherein the respective element symbols are contents (mass%)
of the elements.
This parameter: DI*(hardenability index) is defined to
form the base structure of the base material into martensite
thus imparting excellent abrasion resistant property to the
base structure within the range of the above-mentioned
composition, and a value of the parameter is set to 45 or more.
When the value of the parameter is set to less than 45, a
quenching depth from a surface layer in the plate thickness
direction becomes less than 10 mm and hence, a lifetime of the
steel plate as the abrasion resistant steel plate is shortened.
When the value of the parameter exceeds 180, the base
structure of the base material is martensite and hence, the
base structure exhibits favorable abrasion resistant property.
However, low-temperature crack property at the time of welding
and low-temperature weld toughness are deteriorated.
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Accordingly, the value of the parameter DI* is preferably set
to 180 or less. The value of the parameter DI* is more
preferably set to a value which falls within a range from 50
to 160.
[0038]
C+Mn / 4-Cr / 3+10P 0.47 .. (2),
wherein the respective element symbols are contents (mass%)
of the elements.
When the basic structure of the base material of the steel
plate is formed of martensite and has the composition which
exhibits excellent toughness in both the bond area and the
low-temperature tempering embrittlement area when welding is
performed, a value of the parameter: C+Mn/4-Cr/3+10P is set
to 0.47 or less within a range of the above-mentioned
composition. Although the base structure of the base material
is held in martensite and exhibits favorable abrasion resistant
property even when the value of the parameter exceeds 0.47,
weld toughness is remarkably deteriorated. The value of
parameter may preferably be 0.45 or less.
[0039]
[Microstructure]
According to the present invention, to enhance abrasion
resistant property, a base phase or of the microstructure of
a steel plate is defined to martensite. The structure such
as bainite or ferrite other than martensite lowers abrasion
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resistant property and hence, it is preferable not to mix such
structure into martensite as much as possible. However, when
a total area ratio of these structures is less than 10%, the
influence exerted by these structures can be ignored. Further,
when surface hardness of the steel plate is less than 400
HBW10/3000 in Brinell hardness, a lifetime of the steel plate
as abrasion resistant steel is shortened. Accordingly, it is
desirable to set the surface hardness to 400 HBW10/3000 or more
in Brinell hardness.
[0040]
In the developed steel according to the present invention,
the microstructure of the bond area is the mixed structure of
martensite and bainite. The structure such as ferrite other
than martensite and bainite lowers abrasion resistant property
and hence, it is preferable not to mix such structure as much
as possible. However, when a total area ratio of these
structures is less than 20%, the influence exerted by these
structures can be ignored.
Further, in the developed steel according to the present
invention, to secure toughness of the bond area, it is
preferable that carbonitride particles of Nb and Ti having an
average particle size of 1 p.m or less are present at a rate
of 1000 pieces/mm2 or more, an average particle size of prior
austenite is less than 200 m, and an average particle size
of lower microstructure surrounded by a large tilt grain
23
CA 02801708 2012-12-05
boundary having a radial hook of 15 or more is less than 70
rim.
[0041]
The abrasion resistant steel according to the present
invention can be manufactured under the following
manufacturing conditions. In the
explanation made
hereinafter, the indication " C" relating to temperature means
temperature at 1/2 position of a plate thickness. It is
preferable that a molten steel having the above-mentioned
composition is produced by a known molten steel producing
method, and the molten steel is formed into a raw steel material
such as a slab having a predetermined size by a continuous
casting process or an ingot-making/blooming method.
[0042]
Next, the obtained raw steel material is immediately
subjected to hot rolling without cooling or is subjected to
hot rolling following heating at a temperature of 950 to 1250 C
after cooling thus forming a steel plate having a desired plate
thickness. Immediately after hot rolling, water cooling is
performed or quenching is performed after reheating.
Thereafter, when necessary, tempering is performed at a
temperature of 300 C or below.
[Embodiment 1]
[0043]
Steel slabs which were prepared with various
24
CA 02801708 2012-12-05
compositions shown in Table 1 by way of a steel converter, ladle
refining and a continuous casting method were heated at a
temperature of 1000 to 1250 C and, thereafter, the steel slabs
were subjected to hot rolling under manufacturing conditions
shown in Table 2. Water cooling (quenching (DQ) ) was applied
to some steel plates after rolling. With respect to other steel
plates, air cooling was performed after rolling, and water
cooling (quenching (RQ) ) was performed after reheating.
On the obtained steel plates, the surface hardness
measurement, the evaluation of abrasion resistant property,
the base material toughness measurement, a T shape fillet weld
cracking test (evaluation of delayed fracture resistant
property) , a synthetic heat-affected zone test and a toughness
test of a weld of an actual weld joint were carried out in
accordance with following manners. The acquired result is
shown in Table 3.
[0044]
[Surface Hardness 1]
The surface hardness measurement was carried out on each
steel plate in accordance with the stipulation of JIS Z
2243(1998) for measuring surface hardness below a surface layer
(hardness of a surface measured after removing scales on the
surface layer) . In the
measurement, tungsten hard balls
having a diameter of 10 mm were used, and a load was set to
3000 kgf.
CA 02801708 2012-12-05
[0045]
[Base-material Toughness 1]
AV notch test specimen was sampled from each steel plate
in the direction perpendicular to the rolling direction at a
position away from a surface of the steel plate by 1/4 of a
plate thickness in accordance with the stipulation of JIS Z
2202(1998), and a Charpy impact test was carried out at three
respective temperatures with respect to each steel plate in
accordance with the stipulation of JIS Z 2242(1998), absorbed
energies at a test temperature of 0 C and -40 C were obtained,
and base-material toughness is evaluated. The test
temperature of 0 C was selected by taking the use of the steel
plate in a warm area into consideration.
The steel plate where an average of three absorbed
energies (also referred to as vE0) at the test temperature of
0 C was 30 J or more was determined as the steel plate having
excellent base-material toughness (within the scope of the
present invention).
[0046]
[Abrasion Resistant Property 1]
With respect to abrasion resistant property, a rubber
wheel abrasion test was carried out on each steel plate in
accordance with the stipulation of ASTM G65. The test was
carried out by using specimens each having a size of 10 mmt
(t: plate thickness) x 75 mmw (w: width) x 20 mmL (L: length)
26
CA 02801708 2012-12-05
(t(plate thickness) x 75 mmw x 20 mmL when the plate thickness
is less than 10 mmt), and by using abrasive sand made of 100%
Si02 as an abrasive material.
A weight of the specimen was measured before and after
the test, and wear of the specimen was measured. The test
result was evaluated based on an abrasion resistance rate:
(wear of soft steel plate)/(wear of each steel plate) using
the wear of soft steel plate (SS400) as the reference (1.0).
This means that the larger the abrasion resistance rate, the
more excellent the abrasion resistant property becomes, and
with respect to the scope of the present invention, the steel
plate which exhibited the abrasion resistance rate of 4.0 or
more was determined excellent.
[0047]
[Delayed Fracture 1]
In a T shape fillet weld cracking test, restriction
welding was carried out on specimens each of which was assembled
in a T shape as shown in Fig. 1 by shielded metal arc welding
and, thereafter, test welding was carried out at a room
temperature (25 Cx humidity 60%) or after preheating to 100 C.
The welding method was shielded metal arc welding
(welding material: LB52UL (4.0 mm(D) ) , wherein a heat input was
17 kJ/cm, and welding of 3 layers and 6 passes was carried out.
After the test, the specimen was left at a room temperature
for 48 hours and, thereafter, 5 pieces of weld cross-sectional
27
CA 02801708 2012-12-05
observation samples (bead length 200 mm being equally divided
by 5) were sampled from the test plate, and the presence or
non-presence of occurrence of cracks in a welded heat affected
zone was investigated by a projector and an optical microscope.
In both the specimens prepared without preheating and the
specimens prepared with preheating at a temperature of 100 C,
in 5 respective sampled cross-sectional samples, the samples
where the occurrence of cracks in the welded heat affected zone
was not found at all were evaluated as being excellent in
delayed fracture resistance.
[0048]
[Weld Toughness 1-1]
In a synthetic heat-affected zone test, the
low-temperature tempering of the bond area when two pass CO2
gas shielded arc welding with a welding heat input of 17 kJ/cm
is performed was simulated. A heat cycle is applied to the
bond area in such a manner that the bond area in first pass
welding (initial pass) was held at a temperature of 1400 C for
1 second and was cooled at a cooling rate of 30 C/s from 900
to 200 C, and next, as the low-temperature tempering by second
pass welding (succeeding welding), the bond area was held at
a temperature of 300 C for 1 second and was cooled at a cooling
rate of 5 C/s from 300 to 100 C.
A square bar test specimen sampled in the rolling
direction was subjected to the above-mentioned heat cycle by
28
CA 02801708 2012-12-05
a high-frequency induction heating device and, thereafter, a
V notch Charpy impact test was carried out in accordance with
the stipulation of JIS Z 2242(1998) . The V notch Charpy impact
test was carried out with respect to three specimens for each
steel plate while setting a test temperature at 0 C.
The steel plate where an average value of three absorbed
energies (vE0) was 30 J or more was determined as the steel
plate having excellent HAZ toughness (within the scope of the
present invention) .
With respect to the steel plates having a plate thickness
of less than 10 mm, V notch Charpy specimens having a sub size
(5 mm x 10 mm) were sampled and were subjected to a Charpy impact
test. The steel plate where an average value of three absorbed
energies (vE0) was 15 J or more was determined as the steel
plate having excellent HAZ toughness (within the scope of the
present invention) .
[0049]
[Weld Toughness 1-2]
Further, to confirm toughness of an actual weld joint,
a multi-pass weld joint (V-shape groove) was prepared by
shielded metal arc welding (heat input: 17 kJ/cm, preheating:
150 C, interpass temperature: 150 C, welding material: LB52UL
(4.0 mmia) ) ) .
A Charpy impact specimen was sampled from the weld joint
at a position 1 mm below a surface of the weld joint, and a
29
CA 02801708 2012-12-05
notch location was the V-shape groove and is set at a bond on
a groove side perpendicular to the surface of the steel plate.
A V notch Charpy impact test was carried out in accordance with
the stipulation of JIS Z 2242(1998) using the specimens sampled
in this manner. Fig. 2 shows a sampling position of the Charpy
impact specimen and the notch location.
The V notch Charpy impact test of the actual weld joint
was carried out using three specimens while setting the test
temperature at 0 C. The steel plate where an average value of
three absorbed energies (vE0) is 30 J or more was determined
as the steel plate having excellent toughness at a multi pass
weld (within the scope of the present invention) .
With respect to the steel plates having a plate thickness
of less than 10 mm, V notch Charpy specimens having a sub size
(5 mm x 10 mm) were sampled and were subjected to a Charpy impact
test. The steel plate where an average value of three absorbed
energies (vE0) was 15 J or more was determined as the steel
plate having excellent bond area toughness (within the scope
of the present invention) .
Table 2 shows manufacturing conditions of steel plates
used in the test, and Table 3 shows the results of the
above-mentioned respective tests. The present invention
examples (steels No. 1 to 5) had the surface hardness of 400
HBW10/3000 or more, exhibited excellent abrasion resistant
property, and had base-material toughness of 30 J or more at
CA 02801708 2012-12-05
0 C. Further, no cracks occurred in the T shape fillet weld
cracking test, and the present invention examples had excellent
toughness also with respect to the synthetic heat-affected zone
test and the actual weld joint toughness and hence, it was
cOnfirmed that the present invention examples exhibited
excellent weld toughness.
On the other hand, with respect to comparison examples
(steels No. 6 to 19) whose compositions were outside the scope
of the present invention, it was confirmed that the comparison
examples could not satisfy targeted performances with respect
to any one or a plurality of properties and tests among surface
hardness, abrasion resistant property, the T shape fillet weld
cracking test, base-material toughness, the reproduced heat
cycle Charpy impact test, the Charpy impact test of the actual
weld joint.
[Embodiment 2]
[0050]
Steel slabs which were prepared with various
compositions shown in Table 4 by way of a steel converter, ladle
refining and a continuous casting method were heated at a
temperature of 1000 to 1250 C and, thereafter, the steel slabs
were subjected to hot rolling under manufacturing conditions
shown in Table 5. Water cooling (quenching (DQ) ) is applied
to some steel plates immediately after rolling. With respect
to other steel plates, air cooling was applied to other steel
31
CA 02801708 2012-12-05
plates after rolling, and water cooling (quenching (RQ)) was
performed after reheating.
On the obtained steel plates, the surface hardness
measurement, the evaluation of abrasion resistant property,
the base material toughness measurement, a T shape fillet weld
cracking test (evaluation of delayed fracture resistant
property), a synthetic heat-affected zone test and a toughness
test of a weld of an actual weld joint were carried out in
accordance with following manners. The acquired result is
shown in Table 6.
[0051]
[Surface Hardness 2]
The surface hardness measurement was carried out in
accordance with the stipulation of JIS Z 2243(1998) thus
measuring surface hardness below a surface layer (hardness of
a surface measured after removing scales on the surface layer) .
In the measurement, tungsten hard balls having a diameter of
mm were used, and a load was set to 3000 kgf.
[0052]
[Base-material Toughness 2]
AV notch test specimen was sampled from each steel plate
in the direction perpendicular to the rolling direction at a
position away from a surface of the steel plate by 1/4 of a
plate thickness in accordance with the stipulation of JIS Z
2202(1998), and a Charpy impact test was carried out at three
32
CA 02801708 2012-12-05
respective temperatures with respect to each steel plate in
accordance with the stipulation of JIS Z 2242(1998), and
absorbed energy at test temperatures of 0 C and -40 C were
obtained, and base-material toughness was evaluated. The test
temperature of 0 C was selected by taking the use of the steel
plate in a warm region into consideration, and the test
temperature of -40 C was selected by taking the use of the steel
plate in a cold region into consideration.
The steel plate where an average value of three absorbed
energies (also referred to as vE0) at the test temperature of
0 C was 30 J or more and an average value of three absorbed
energies (also referred to as vE_40) at the test temperature
of -40 C was 27 J or more was determined as the steel plate
having excellent base-material toughness (within the scope of
the present invention). With respect to the steel plates
having a plate thickness of less than 10 mm, V notch Charpy
specimens having a sub size (5 mm x 10 mm) were sampled and
were subjected to a Charpy impact test. The steel plate where
an average value of three absorbed energies (vE0) was 15 J or
more and an average value of three absorbed energies (vE_40)
was 13 J or more was determined as the steel plate having
excellent base-material toughness (within the scope of the
present invention).
[0053]
[Abrasion Resistant Property 2]
33
CA 02801708 2012-12-05
With respect to abrasion resistant property, a rubber
wheel abrasion test was carried out in accordance with the
stipulation of ASTM G65. The test was carried out by using
a specimen having a size of 10 mmt (t: plate thickness) x 75
mmw (w: width) x 20 mmL (L: length) (t (plate thickness) x 75
mmw x 20 mmL when the plate thickness was less than 10 mmt),
and by using abrasive sand made of 100% Si02 as an abrasive
material.
A weight of the specimen was measured before and after
the test and wear of the specimen was measured . The test result
was evaluated based on an abrasion resistance rate: (wear of
soft steel plate)/(wear of each steel plate) using wear of soft
steel plate (SS400) as the reference (1.0). This means that
the larger the abrasion resistance rate, the more excellent
the abrasion resistant property becomes, and with respect to
the scope of the present invention, the steel plate which
exhibits the abrasion resistance rate of 4.0 or more was
determined excellent.
[0054]
[Delayed Fracture 2]
In a T shape fillet weld cracking test, restriction
welding was carried out on a specimen which was assembled in
a T shape as shown in Fig. 1 by shielded metal arc welding and,
thereafter, test welding was carried out at a room temperature
(25 C x humidity 60%) or after preheating to 100 C.
34
CA 02801708 2012-12-05
The welding method was shielded metal arc welding
(welding material: LB52UL (4.0 mmoD) ), wherein a welding heat
input was 17 kJ/cm, and welding of 3 layers and 6 passes was
carried out. After the test, the specimen was left at a room
temperature for 48 hours and, thereafter, 5 pieces of weld
cross-sectional observation samples (bead length 200 =being
equally divided by 5) were sampled from a test plate, and the
presence or non-presence of occurrence of cracks in a welded
heat affected zone was investigated by a projector and an
optical microscope. In both the specimens prepared without
preheating and the specimens prepared with preheating at a
temperature of 100 C, among 5 respective sampled
cross-sectional samples, the samples where the occurrence of
cracks in the welded heat affected zone was not found at all
were evaluated as being excellent in delayed fracture
resistance.
[0055]
[Weld Toughness 2-1]
In a synthetic heat-affected zone test, the
low-temperature tempering of the bond area of the welded heat
affected zone when two layer CO2 gas shielded arc welding with
a welding heat input of 17 kJ/cm is performed was simulated.
A heat cycle is applied to the bond area in such a manner that
the bond portion in first pass welding (initial pass) was held
at a temperature of 1400 C for 1 second and was cooled at a
CA 02801708 2012-12-05
cooling rate of 30 C/s from 800 to 200 C, and next, as the
low-temperature tempering by second pass welding (succeeding
welding), the bond area was held at a temperature of 300 C for
1 second and was cooled at a cooling rate of 5 C/s from 300
to 100 C.
A square bar test specimen sampled in the rolling
direction was subjected to the above-mentioned heat cycle by
a high-frequency induction heating device and, thereafter, a
V notch Charpy impact test was carried out in accordance with
the stipulation of JIS Z 2242(1998). The Charpy impact test
was carried out with respect to three specimens for each steel
plate while setting test temperatures at 0 C and -40 C at
respective temperatures.
The steel plate where an average value of three absorbed
energies (vE0) was 30 J or more and an average value of three
absorbed energies (vE_40) was 27 J or more was determined as
the steel plate having excellent HAZ toughness (within the
scope of the present invention).
With respect to the steel plates having a plate thickness
of less than 10 mm, V notch Charpy specimens having a sub size
(5 mmx 10 mm) were sampled and were subjected to a Charpy impact
test. The steel plate where an average value of three absorbed
energies (vE0) was 15 J or more and an average value of three
absorbed energies (vE_40) was 13 J or more was determined as
the steel plate having excellent HAZ toughness (within the
36
CA 02801708 2012-12-05
scope of the present invention) .
[0056]
[Weld Toughness 2-2]
Further, to confirm toughness of an actual weld joint,
a multi-pass weld joint (V-shape groove) was prepared by
shielded metal arc welding (heat input: 17 kJ/cm, preheating:
150 C, interpass temperature: 150 C, welding material: LB52UL
(4.0 mmcb ) ) .
A Charpy impact specimen was sampled from the weld joint
at a position 1 mm below a surface of the weld joint, and a
notch location was the V-shape groove and is set at a bond on
a groove side perpendicular to the surface of the steel plate.
A V notch Charpy impact test was carried out in accordance with
the stipulation of JIS Z 2242(1998) using the specimens sampled
in this manner. Fig. 2 shows a sampling position of the Charpy
impact specimen and the notch location.
The V notch Charpy impact test of the actual weld joint
was carried out using three specimens for each test temperature
while setting the test temperature at 0 C and -40 C. The steel
plate where an average value of three absorbed energies (vE0)
is 30 J or more and an average value of three absorbed energies
(vE_40) is 27 J or more was determined as the steel plate having
excellent multi pass weld toughness (within the scope of the
present invention) .
With respect to the steel plates having a plate thickness
37
CA 02801708 2012-12-05
of less than 10 mm, V notch Charpy specimens having a sub size
(5 mmx 10 mm) were sampled and were subjected to a Charpy impact
test. The steel plate where an average value of three absorbed
energies (vE0) was 15 J or more and an average value of three
absorbed energies (vE_40) was 13 J or more was determined as
the steel plate having excellent multi pass weld toughness
(within the scope of the present invention).
[0057]
Table 5 shows manufacturing conditions of steel plates
used in the test, and Table 6 shows the results of the
above-mentioned respective tests. The present invention
examples (steels No. 20 to 22 (steel No. 22 having a plate
thickness of 8 mm)) had the surface hardness of 400 HBW10/3000
or more, exhibited excellent abrasion resistant property, and
had base-material toughness of 30 J or more at 0 C and
base-material toughness of 27 J or more at -40 C. Further, no
cracks occurred in the T shape fillet weld cracking test, and
the present invention examples also had excellent toughness
with respect to the synthetic heat-affected zone test and the
actual weld joint and hence, it was confirmed that the present
invention examples exhibited excellent multi pass weld
toughness.
[0058]
On the other hand, it was confirmed that although the
steel No.23 where the composition falls within the scope of
38
CA 02801708 2012-12-05
the present invention but DI* exceeds 180 exhibited favorable
results in surface hardness, abrasion resistant property and
base-material toughness, the results of a T shape fillet weld
cracking test, a synthetic heat-affected zone test and an
actual weld joint toughness were close to lower limit values
of targeted performances and hence, the steel No.23 was
inferior to other present invention examples. With respect
to the composition of the steel No.24, the content of Si falls
outside the scope of the present invention. Accordingly,
although steel No.24 exhibited favorable results in surface
hardness, abrasion resistant property and base-material
toughness, steel No.24 could not satisfy targeted performances
in a T shape fillet weld cracking test, a synthetic
heat-affected zone test and an actual weld joint toughness.
[0059]
Although the composition of the steel No. 25 fell within
the scope of the present invention, the value of a parameter
C+Mn/4-Cr/3+10P on a left side of the formula (2) exceeded 0 . 47 .
Accordingly, the result of the synthetic heat-affected zone
test and the actual weld joint toughness were close to lower
limits of the targeted performances and hence, steel No. 25
was inferior to other present invention examples. In the
description of Tables 4, 5 and 6, although the steel No. 23
falls within the scope of the present invention called for in
claim 3 in composition, the value of DI* falls outside the scope
39
CA 02801708 2012-12-05
of the present invention called for in claim 6 and hence, the
steel No. 23 is set as the comparison example. Although the
steel No. 25 falls within the scope of the present invention
called for in claim 1 in composition, the steel No. 25 does
not satisfy the formula (2) and falls outside the scope of the
present invention called for in claim 7 and hence, the steel
No. 25 is set as the comparison example.
[0060]
Table 1
Composition (mass%) Formula
No.
DI* Remarks
C Si Mn P s Al
Cr Mo Nb Ti W Cu Ni V N B REM Ca Mg (2)
,
1 0.241 0.29 0.75 0.007 0.0014 0.031
0.48 0.11 0.016 0.014 34 8 59.9 0.34 Present
invention example
2 0.215 0.12 0.46 , 0.008 0.0012 0.023
0.67 0.35 0.023 0.025 0.08 56 5 21 76.5 0.19
Present invention example
3 0.279 0.10 0.62 0.004 0.0010 0.037 , 1.01
0.09 0.021 0.009 0.13 0.15 0.12 24 17 _ 16
98.3 0.14 Present invention example
4 0.221 0.47 1.05 0.009 0.0015 0.047
0.52 0.18 _. 0.007 0.018 0.04 44 10 53 105.2 0.40
Present invention example
0.251 0.16 0.41 0.005 0.0009 0.026 0.43 0.42
0.013 0.011 0.12 0.05 54 9 78.9 0.26 Present
invention example
_
6 0.178 0.25 0.94 0.007 0.0019 0.031
0.59 0.18 0.020 0.019 45 10 18 76.8 0.29
Comparison example
_
.
7 0.329 0.38 0.53 0.006 0.0012 0.026 0.47 0.21
0.018 0.015 0.22 0.20 27 15 81.5 0.36
Comparison example n
_
_
8 0.260 0.15 1.47 0.005 0.0010 0.039
0.44 0.08 0.012 0.012 0.04 38 8 50 92.0
0.53 Comparison example 0
iv
9 0.273 0.29 0.84 0.015 0.0021 0.025 0.53
0.17 0.020 0.015 0.07 0.11 40 10 27 95.1
0.46 Comparison example c'2,
0.217 0.45 0.79 0.008 0.0012 0.028 0.18 0.31
0.018 0.008 0.05 23 12 69.4 _ 0.43
Comparison example 83
&z. _
_ co
1---i 11 0.238 0.27 0.65 0.006 0.0009 0.044 0.95
0.03 0.021 0.020 0.32 _ 56 9 22 72.9 0.14
Comparison example "
.
_ o
12 0.254 0.38 0.57 0.007 0.0011 0.031 0.71 0.28
0.001 0.015 0.04 40 10 98.7 0.23 Comparison
example r)`
13 0.228 0.24 0.64 0.008 0.0012 0.037 1.01 0.11
0.039 0.021 0.41 57 16 90.8 0.13 Comparison
example 11)`
14 0.264 0.15 0.59 0.006 0.0010 0.030 0.77 0.34
0.021 0.001 0.04 37 9 39 103.7 0.21
Comparison example
0.271 0.23 1.04 0.008 0.0009 0.027 0.43 0.22
0.011 0.033 , 31 8 , , 92.5 0.47 Comparison
example
16 0.229 0.17 0.61 0.004 0.0010 _ 0.033 0.82
0.30 0.018 0.017 // 12 91.5 0.15 Comparison
example
17 0.245 0.23 0.80 0.007 0.0011 0.025 0.63 0.12
0.012 0.015 0.10 0.03 68 11 20 87.6 0.31
Comparison example
18 0.230 0.38 0.96 0.005 0.0019 0.047 0.55
0.21 0.009 0.021 31 / 97.3 0.34 Comparison
example
_
19 0.286 0.12 0.45 0.009 0.0012 0.045 0.47
0.10 0.017 0.011 53 8 19 40.6 0.33 Comparison
example
- -
Note 1: Underlined values being outside the scope of the present invention
Note 2: Contents of N, B, REM, Ca, Mg indicated by ppm in chemical components
Note 3: DI* = 33.85 x (0.1xC)" x (0.7xSi+1) x (3.33xMn+1) x (0.35xCu+1) x
(0.36xNi+1) x (2.16xCr+1) x (3xMo+1) x (1.75xV+1) x (1.5xW+1)
Note 4: Formula (2) = C+Mn/4-Cr/3-Mo/6+10P
Respective element symbols being contents (mass%)
,
[ 0 0 61 ]
Table 2
Steel No. Raw material Plate Hot rolling
Heat treatment Remarks
thickness thickness Heating Hot rolling finish Cooling
method Heating temperature Cooling method
temperature temperature
(mm) . (mm) ( C) ( C) (
C)
1 200 12 1150 890 air cooling 900
water cooling Present invention example
2 200 25 1080 900 air cooling 930
water cooling Present invention example
3 200 32 1150 910 air cooling 900
water cooling Present invention example
4 200 j 25 1200 880 j water cooling
no heat treatment Present invention example
200 16 1100 900 j water cooling 200
air cooling Present invention example
6 200 25 1150 900 j air cooling 900
water cooling Comparison example n
7 200 20 1150 890 water cooling
no heat treatment Comparison example 0
iv
8 250 32 1200 930 air cooling 910
water cooling Comparison example co
0
H
9 200 25 1100 900 air cooling 900
water cooling Comparison example
0
az,
co
r,...) 10 300 20 1150 920 water
cooling no heat treatment Comparison example
iv
0
11 250 16 1150 880 air cooling 900
water cooling Comparison example H
IV
12 300 32 1050 870 air cooling 900
water cooling Comparison example HI
iv
1
13 200 16 1200 900 water cooling
no heat treatment Comparison example 0
in
14 250 25 1150 860 air cooling 930
water cooling Comparison example
250 1 25 1150 890 air cooling 900
water cooling Comparison example
16 300 30 1050 870 air cooling 930
water cooling Comparison example
17 250 20 1150 900 water cooling
no heat treatment Comparison example
18 300 I 32 1100 900 air cooling 900
water cooling Comparison example
19 250 . 25 1150 900 air cooling 900
j water cooling Comparison example
Note 1: Underlined values being outside the scope of the present invention
=
[0062]
Table 3
Steel Surface Abrasion resistant Base material T shape fillet
weld cracking test Synthetic heat-affected zone test Shielded metal
Remarks
No. hardness property toughness
arc welding
HBW Abrasion vE0 No preheating Preheating
to Corresponding to multi pass weld Toughness of
10/3000 resistance rate100 C (bonding + low-temperature multi
pass weld
,
tempering)
GO (Presence or (Presence or vE0(J) vE0(J)
non-presence of non-presence of
cracks) cracks)
_
1 462 4.8 77 no cracks
no cracks 57 92 Present invention example
2 410 4.3 102 no cracks
I no cracks 71 121 Present invention example
3 526 5.5 44 no cracks
no cracks 38 60 Present invention example
4 428 4.2 90 no cracks
no cracks 71 112 Present invention example _
, _
470 4.9 60 no cracks no cracks
44 73 Present invention example
_
6 342 3.6 153 no cracks I
no cracks , 112 159 Comparison example
n
_
7 609 6.5 18 cracks occurred cracks occurred
5 22 Com.arison exam.le 0
8 493 5.2 44 cracks occurred cracks occurred
16 34 Comparison example iv
co
9 531 5.5 35 cracks occurred cracks occurred
13 29 Com.arison exam.le 0
H,
,.1,. 10 427 w 4.3 70 no cracks
no cracks 19 39 Comparison example
11 441 4.6 59 no cracks
no cracks 17 35 Comparison example co
_
iv
12 457 4.9 23 cracks occurred I cracks occurred
15 31 Com.arison exam.le 0
13 448 4.5 27 no cracks
no cracks 13 27 Comparison example H
IV
I
14 505 5.318 no cracks
no cracks 8 18 Comparison example H
_
_ iv
506 5.3 10 cracks occurred cracks occurred 5
15 Com.arison exam ale 1
0
16 433 4.6 40 no cracks
no cracks 14 29 Comparison example in
_
17 469 4.9 11 cracks occurred cracks occurred
6 20 Corn . arison exam.le
18 451 4.7 50 cracks occurred cracks occurred
19 35 Comparison example
_
19 . 372 3.7 47 no cracks
, no cracks 33 61 Comparison example
Note 1: Underlined values being outside the scope of the present invention
[0063]
Table 4
Composition
(mass%)
No.
DI* Formula (2) Remarks
C Si Mn P S Al Cr Mo Nb Ti W Cu Ni V N B REM Ca Mg
20 0.214 0.35 0.59 0.007 0.0018 0.031 1.05 0.17 0.019 0.014 0.04 41
10 96.5 0.05 Present invention example
21 0.227 0.12 0.70 0.005 0.0015 0.020 0.96 0.48 0.023 0.017 0.25 0.24
0.04 30 12 174.6 0.05 Present invention example
22 0.251 0.22 0.62 0.006 0.0011 0.035 0.68 0.15 0.017 0.012 29 7
67.9 0.21 Present invention example
23 0.265 0.39 1.02 0.009 0.0021 0.022 0.71 0.21 0.015 0.011 0.52 0.42
0.05 27 11 188.5 0.34 Comparison example
24 0.282 0.0/ 0.89 0.008 0.0025 0.035 0.49 0.14 0.024 0.018 0.12 37 14
40 78.3 0.40 . Comparison example
25 0.278 0.35 1.12 0.009 0.0021 0.031 0.45 0.12 0.020 0.015 40 10
89.1 0.48 Comparison example
Note 1: Underlined values being outside the scope of the present invention
Note 2: Contents of N, B, REM, Ca, Mg indicated by mass ppm in chemical
components co
Note 3: DI* = 33.85 x (0.1xC)" x (0.7xSi+1) x (3.33xMn+1) x (0.35xCu+1) x
(0.36xNi+1) x (2.16xCr+1) x (3xMo+1) x (1.75xV+1) x (1.5xW+1)
Note 4: P in formula (2): C+Mn/4-Cr/3-Mo/6+10P
co
Respective element symbols being contents (mass%)
0
ol
[0064]
Table 5
-
Steel Raw material i Plate Hot rolling
Heat treatment Remarks
No. thickness i thickness
Heating Hot rolling finish Cooling
method Heating temperature 1 Cooling method
temperature temperature
i
(mm) (mm) ( C) ( C) ( C)
20 300 45 1150 900 air cooling 900
water cooling Present invention example
21 300 60 1100 880 air cooling 870
water cooling Present invention example
22 200 8 1150 820 air cooling 900
water cooling Present invention example
23 250 32 1100 870 air cooling 900
I water cooling Comparison example n
I
0
24 250 25 1100 900 water cooling no heat
treatment comparison example iv
co
0
H
300 40 1150 900 air cooling 900
water cooling comparison example
0
cri co
Note 1: Underlined values being outside the scope of the present invention
iv
0
H
IV
I
H
IV
I
0
Ui
[0065]
Table 6
Steel Surface Abrasion
Base material T shape fillet weld cracking Synthetic heat-
affected zone test Shielded metal arc Remarks
No. hardness resistant property toughness
test welding
HBW Abrasion
vE0 vE-40 No preheatingl Preheating to Corresponding to
multi pass weld Toughness of multi
10/3000 resistance rate : 100 C (bonding +
low-temperature pass weld
tempering)
(J) (J) presence or presence or
vE0(J) vE-40(J) vE0(J) vE-40(J)
non-presence non-presence
of cracks of cracks
20 412 4.3 96 74 no cracks no cracks 69
40 110 72 Present invention example
21 436 4.5 71 50 no cracks no cracks 59
40 83 50 Present invention example
22 473 5.0 40 32 no cracks no cracks 35
28 50 31 Present invention example n
0
23 499 5.3 32 32 no cracks no cracks 30
27 40 27 Comparison example iv
co
0
H
-.3
,c.. 24 530 5.5 32 30 cracks cracks 20
8 50 15 Comparison example 0
cr, occurred occurred
co
25 524 5.4 33 32 no cracks no cracks 31
27 46 27 Comparison example iv
0
H
IV
Note 1: Underlined values being outside the scope of the present invention
1
H
IV
I
0
Ui
,
