Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02801703 2012-12-05
t, r
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
weld toughness and excellent delayed fracture resistance.
[Background Art]
[0002]
When a hot-rolled steel plate is employed for making
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
material can be remarkably enhanced by obtaining the steel
1
CA 02801703 2012-12-05
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 obtaining 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, soil 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 has been assembled,
the labor for the manufacture and a manufacturing cost are
increased. Accordingly, there has been a demand for an
abrasion resistant steel plate which can be used as a strength
member of the welded steel structure.
Patent document 1 relates to an abrasion resistant steel
2
CA 02801703 2012-12-05
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.
[0006]
Patent document 3 relates to an abrasion resistant steel
material which exhibits excellent toughness and excellent
3
CA 02801703 2012-12-05
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
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
4
CA 02801703 2012-12-05
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 kind
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]
[0009]
[Patent Document 1] JP-A-5-51691
[Patent Document 2] JP-A-8-295990
CA 02801703 2012-12-05
[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]
The most serious problem relating to the lowering of
toughness when a steel material is welded is the deterioration
of toughness at a bond area of a fusion line. In abrasion
resistant steel having martensite structure in a quenched state,
the deterioration of toughness which is referred to as
low-temperature tempering embrittlement arises as a problem
also in a welded heat affected zone (hereinafter also referred
to as HAZ) reheated to a temperature around 300 C which is away
from the fusion line. 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.
[0011]
In a region which is reheated at a low-temperature
tempering embrittlement temperature, hydrogen which invades
a weld from a shielding gas at the time of welding and a residual
stress generated by welding heat overlap with each other so
that delayed fracture (cracks which occur in the weld are
6
CA 02801703 2012-12-05
referred to as low-temperature cracks in general) is liable
to occur and, particularly, delayed fracture is liable to occur
in an abrasion resistant steel having high strength.
Accordingly, in applying an abrasion resistant steel
plate to a strength member of a welded structure, it is
necessary to enhance toughness of the bond area and the welded
heat affected zone reheated to a temperature around 300 C which
is away from a fusion line. However, in the conventional
abrasion resistant steel plate, cold cracking susceptibility
of the weld is high and hence, to prevent cold cracks, it is
necessary to discharge hydrogen in the steel plate and to lower
a residual stress in the steel plate by performing treatments
such as preheating and post heating before and after welding.
[00121
Patent documents 1 and 2 fail to describe the enhancement
of weld toughness in the 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.
Accordingly, it is an object of the present invention
7
CA 02801703 2012-12-05
to provide an abrasion resistant steel plate which exhibits
excellent weld toughness and excellent delayed fracture
resistance without inducing lowering of productivity and the
increase in a manufacturing cost. In the present invention,
weld toughness means toughness of a welded heat affected zone,
and the excellent weld toughness means particularly that the
toughness is excellent in a bond area and a low-temperature
tempering embrittlement temperature area.
[Means for Solving the Problem]
[0013]
To achieve the above-mentioned object, inventors of the
present invention have made extensive studies on various
factors which determine chemical components of a steel plate,
a method of manufacturing the steel plate and the
microstructure of the steel plate so as to secure weld toughness
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 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 weld toughness, it is
8
CA 02801703 2015-07-30
necessary to suppress grain particles in the bond area 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.
3. To secure the excellent toughness and to suppress
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, 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 0.283% C, 0.05 to 0.5% Si, 0.40
to 1.2% Mn, 0.010% or less P, 0.0025% or less S, 0.40 to 1.5%
Cr, 0.005 to 0.025% Nb, 0.005 to 0.03% Ti, 0.1% or less Al,
0.01% or less N, excluding Mo as a component of the composition,
and Fe and unavoidable impurities as a balance; wherein:
- hardenability index DI*, expressed by a formula (1) :
DI* = 33.85 x (0.1xC) '5 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)
................................................................. (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;
9
CA 02801703 2015-07-30
- 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
- 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% one
or two of components selected from a group consisting of 0.05
to 1.0% W, and 0.0003% to 0.0030% B.
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
CA 02801703 2014-10-06
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%)
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
weld toughness and excellent delayed fracture resistance. 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.
11
CA 02801703 2012-12-05
[Mode for Carrying Out the Invention]
[0018]
The present invention defines the composition and the
microstructure.
[Composition]
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 and toughness of a low-temperature tempering region
are deteriorated. 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
12
CA 02801703 2012-12-05
state. Further, Si has an effect of suppressing the
deterioration of toughness in a tempering embrittlement area
of a welded heat affected zone. 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 welded heat 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
13
CA 02801703 2012-12-05
in a grain boundary, the segregated P becomes an initiation
point of delayed fracture, and deteriorates toughness of a
welded heat affected zone. 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
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
in the tempering embrittlement area of the welded heat affected
zone. 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.
14
CA 02801703 2012-12-05
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 within a range from 0.40 to 1.2%.
[0024]
Nb: 0.005 to 0.025%
Nb is an important element having both an effect of
improving toughness of the welded heat affected zone and an
effect of suppressing the occurrence of delayed fracture by
making the microstructure of the base material and the welded
heat affected zone finer by causing the precipitation of
carbonitride and also by fixing solid solution N. It is
necessary for the steel plate to contain 0.0050% or more Nb
to acquire such effects. On the other hand, when the content
of Nb exceeds 0.025%, coarse 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%.
[0025]
Ti: 0.005 to 0.03%
Ti has an effect of suppressing grains in the bond area
CA 02801703 2012-12-05
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%.
[0026]
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,
by forming AIN by fixing solid solution N in steel, Al has an
effect of suppressing grains in a bond area from becoming coarse
and an effect of suppressing the deterioration of toughness
and the occurrence of delayed fracture in a 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
16
CA 02801703 2012-12-05
is preferably limited to a value which falls within a range
from 0.01 to 0.07%.
[0027]
N: 0.01% or less
N forms a nitride with Nb or Ti, and has an effect of
suppressing grains of welded heat affected zone from becoming
coarse. However, when the content of N exceeds 0.01%,
toughness of a base material and weld toughness is remarkably
lowered and hence, the content of N is limited to 0.01% or less.
The content of N is preferably limited to a value which falls
within a range from 0.0010 to 0.0070%. A balance is Fe and
unavoidable impurities.
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 Mo, W, B, Cu, Ni, V, REM, Ca and Mg.
[0028]
Mo: 0.05 to 1.0%
Mo is an element effective for remarkably increasing
hardenability thus increasing hardness of a base material.
The content of Mo may preferably be 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. Accordingly, the content of
17
CA 02801703 2012-12-05
Mo is set to 1.0% or less.
[0029]
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.
[0030]
B: 0.0003 to 0.0030%
B is an element effective for remarkably increasing
hardenability with addition of a trace amount of B thus
increasing hardness of a base material. The content of B may
preferably be 0.0003% or more for acquiring such an effect.
However, when the content of B exceeds 0.0030%, B adversely
influences toughness, ductility and weld crack resistance of
the base material. Accordingly, the content of B is set to
0.0030% or less.
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.
[0031]
18
CA 02801703 2012-12-05
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.
[0032]
Ni: 2.0% or less
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.
[0033]
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.
[0034]
19
CA 02801703 2012-12-05
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
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%.
[0035]
DI* = 33.85x (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.
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
CA 02801703 2012-12-05
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 DI* 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.
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.
[0036]
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
21
CA 02801703 2012-12-05
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.
[0037]
[Microstructure]
According to the present invention, to enhance abrasion
resistant property, a base phase or a main phase of the
microstructure of a steel plate is defined to martensite. The
structure such as bainite or ferrite other than martensite
lowers abrasion 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.
[0038]
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
22
CA 02801703 2012-12-05
of these structures is less than 20%, the influence exerted
by these structures can be ignored.
Further, to secure toughness of the bond area, it is
preferable that carbonitride particles of Nb and Ti having an
average particle size of 1 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
boundary having a radial hook of 15 or more is less than 70
m.
[0039]
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.
[0040]
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
23
CA 02801703 2012-12-05
after cooling thus obtaining 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]
[0041]
Steel slabs which were prepared with various
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.
[0042]
24
CA 02801703 2012-12-05
[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.
[0043]
[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), and
absorbed energy at a test temperature of 0 C was 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
CA 02801703 2012-12-05
present invention).
[0044]
[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 mint
(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
is less than 10 mint), and by using abrasive sands 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.
[0045]
[Delayed Fracture 1]
In a T shape fillet weld cracking test, restriction
welding was carried out on specimens each of which was assembled
26
CA 02801703 2012-12-05
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.
The welding method was shielded metal arc welding
(welding material: LB52UL (4.0 mmcD) ) , wherein a heat input was
17 kJ/cm, and welding of 3 layers and 6 passes was carried out.
After welding, the specimen was left at a room temperature for
48 hours and, thereafter, 5 pieces of weld cross-sectional
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.
[0046]
[Weld Toughness 1-1]
In a synthetic heat-affected zone test, a bond area and
a low-temperature tempering embrittlement area when one pass
CO2 gas shielded arc welding with a welding heat input of 17
kJ/cm is performed were simulated. In the simulation of the
bond area, the bond area was held at 1400 C for 1 second and
27
CA 02801703 2012-12-05
was cooled at a cooling rate of 30 C/s from 800 to 200 C. On
the other hand, in the simulation of the low-temperature
tempering embrittlement area, the low-temperature tempering
embrittlement 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 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) in the bond area and the low-temperature
tempering embrittlement area was 30 J or more was determined
as the steel plate having excellent weld toughness (within the
scope of the present invention).
[0047]
[Weld Toughness 1-2]
Further, to confirm toughness of an actual weld joint,
bead on plate welding was applied to a steel plate by shielded
metal arc welding (heat input: 17 kJ/cm, preheating: 150 C,
welding material: LB52UL (4.0=0)). A Charpy impact specimen
was sampled from a position 1 mm below a surface of the steel
28
CA 02801703 2012-12-05
plate, and a V notch Charpy impact test was carried out in
accordance with the stipulation of JIS Z 2242(1998) using a
notch location as the bond area. 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. 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
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
0 C. Further, no cracks occured 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 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 14) whose compositions were outside the scope
29
CA 02801703 2012-12-05
. 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]
[0048]
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
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
CA 02801703 2012-12-05
accordance with following manners. The acquired result is
shown in Table 6.
[0049]
[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. .
[0050]
[Base-material Toughness 2]
A V 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) , 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.
31
CA 02801703 2012-12-05
The steel plate where an average value of three absorbed
energies (also referred to as vE0) at the test temperature of
000 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).
[0051]
[Abrasion Resistant Property 2]
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 mint (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 mint),
and by using abrasive sand made of 100% Si02 as an abrasive
material.
32
CA 02801703 2012-12-05
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.
[0052]
[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.
The welding method was shielded metal arc welding
(welding material: LB52UL (4.0 mmcD) ) , 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
observation samples (bead length 200 mm 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
33
CA 02801703 2012-12-05
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.
[0053]
[Weld Toughness 2-1]
In a synthetic heat-affected zone test, a bond area and
a low-temperature tempering embrittlement area when one pass
CO2 gas shielded arc welding with a welding heat input of 17
kJ/cm is performed were simulated. In the simulation of the
bond area, the bond area was heated at 1400 C for 1 second and
was cooled at a cooling rate of 30 C/s from 800 to 200 C.
Further, in the simulation of the low-temperature tempering
embrittlement area, the low-temperature tempering
embrittlement area was heated at a temperature of 300 C for
1 second and was performed 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 V notch Charpy impact
34
CA 02801703 2012-12-05
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) in the bond area and the low-temperature
tempering embrittlement area was 30 J or more and an average
value of three absorbed energies (vE_40) in the bond area and
the low-temperature tempering embrittlement area was 27 J or
more was determined as the steel plate having excellent weld
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 in the bond area and the
low-temperature tempering embrittlement area and an average
value of three absorbed energies (vE_40) was 13 J or more in
the bond area and the low-temperature tempering embrittlement
area was determined as the steel plate having excellent weld
toughness (within the scope of the present invention).
[0054]
[Weld Toughness 2-2]
Further, to confirm toughness of an actual weld joint,
bead on plate welding was applied to a steel plate by shielded
metal arc welding (heat input: 17 kJ/cm, preheating: 150 C,
CA 02801703 2012-12-05
=
welding material: LB52t1l, (4.0 mmcD) ) . A Charpy impact specimen
was sampled from a position 1 mm below a surface of the steel
plate, and a V notch Charpy impact test was carried out in
accordance with the stipulation of JIS Z 2242(1998) using a
notch location as the bond area. Fig. 2 shows a sampling
position of the Charpy impact specimen and the notch location.
[0055]
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 temperatures 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 bond area 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 bond area toughness (within
the scope of the present invention) .
[0056]
Table 5 shows manufacturing conditions of steel plates
36
CA 02801703 2012-12-05
used in the test, and Table 6 shows the results of the
above-mentioned respective tests. The present invention
examples (steels No. 15 to 17 (steel No. 17 having a plate
thickness of 8mm)) 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 and hence, it was confirmed that the present
invention examples exhibited excellent weld toughness.
[0057]
On the other hand, it was confirmed that although the
steel No.18 where the composition falls within the scope of
the present invention but DI* exceeds 180 exhibited favorable
results in surface hardness, abrasion resistant property,
babe-material toughness and a T shape fillet weld cracking test,
the results of a reproduced heat cycle Charpy impact test
corresponding to the low-temperature tempering embrittlement
area and an actual weld joint Charpy impact test were close
to lower limit values of targeted performances and hence, the
steel No.18 was inferior to other present invention examples
with respect to low-temperature weld toughness.
[0058]
37
CA 02801703 2012-12-05
The steel No.19 fell outside the range of the present
invention with respect to Si in composition. Accordingly,
although the steel No.19 exhibited the favorable results in
surface hardness, abrasion resistant property and
base-material toughness, toughness in the tempering
embrittlement area of the welded heat affected zone were
deteriorated and hence, the steel No.19 could not satisfy the
targeted performances with respect to a T shape fillet weld
cracking test, a synthetic heat-affected zone Charpy impact
test corresponding to the low-temperature tempering
embrittlement area and an actual weld joint Charpy impact test.
[0059]
Although the steel No.20 falls within the scope of the
present invention in composition, a value obtained by the
formula (2) exceeded 0.47. Accordingly, it was confirmed that
vE_40 is close to a lower limit of the performance of the present
invention in both a synthetic heat-affected zone Charpy impact
test and an actual weld joint Charpy impact test so that the
steel No.20 is inferior to other present invention examples.
In the description of Tables 4, 5 and 6, although the steels
No. 18 and 20 fall within the scope of the present invention
called for in claim 3 in composition, the value of DI* and the
value of the formula (2) fall outside the scope of the present
invention called for in claims 6, 7 and hence, these steels
are set as comparison examples.
38
[0060]
Table 1
No Chemical components
(mass%) ' DI. P in
.
Remarks
C Si Mn P S Al Cr Nb Ti Mo W Cu Ni V
N B REM Ca Mg formula (2)
r
1 0.237 0.30 0.91 0.008 0.0015 0.032 , 0.58 0.016 _ 0.014 30
57.3 0.35 Present invention example
2 0.215 0.20
0.49 0.009 0.0011 0.021 1.21 0.024 0.025 , 0.2114 12 , õ 87.7 0.02
Present invention example
, .
3 0.283 0.14 0.61 0.005 0.0009 0.038 0.78 0.021 0.009 0.10 0.15 0.12
61 23 64.3 0.23 Present invention example
4 0.223 0.41 1.14 0.007 0.0016 0.044 0.44 0.008, 0.019 0.04 27 5
32 65.1 , 0.43 Present invention example
0.254 0.26 0.55 0.004 0.0008 0.028 0.49 0.012 0.011 0.10 0.05 62
22 19 51.9 0.27 Present invention example
6 0.16 0.32 1.05 0.008 0.0021 0.031 0.59 0.020 0.019 0.18 45 10
82.5 0.31 Comparison example
7 0.321 0.40 0.51 0.007 ' 0.0014 0.025 0.71 , 0.015 0.012 0.15 , 0.21
0.18 28 r , 20 , 74.3 0.28 , Comparison example
8 0.263 0.19 1.43 0.007 0.0007 0.040 0.43 0.019 0.010 0.08 0.05 38 36
50 93.2 0.55 Comparison example
9 0.274 0.24 0.95 0.013 0.0022 0.030 ' 0.71 0.020 0.011 0.06
0.21 35 14 80.9 0.40 Comparison example
,
0.226 0.43 0.87 0.008 0.0014 0.023 0.14 0.015 0.007 0.23 ' ' 59
11 ' 20 56.8 0.48 , Comparison example
11 0.241 0.30 1.05 0.006 0.0023 0.042 0.60 aocn 0.014 0.11 0.03 31
7 91.9 0.36 Comparison example
12 0.230 ' 0.27 0.69 ' 0.005 ' 0.0010 ' 0.028 1.01 0.039' 0.008
0.05 0.41 53 ' ' ' 84.5 0.12 Comparison
example n
13 0.255 0.21 0.77 0.009 0.0014 , 0.031 0.47 0.018 , 0.001 0.14
31 8 63.2 0.38 Comparison example
14 0.284 0.13 0.46 0.007 0.0013 0.051 0.51 0.021 0.010 55
33.1 0.30 Comparison example o
iv
Note 1: Underlined values being outside the scope of the present invention
co
o
Note 2: Contents of N, B, REM, Ca, Mg indicated by ppm in chemical components
H
-A
W Note 3: 131* = 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) o
u.)
Note 4: P in formula (2): left side of formula (2) =C+Mn/4-Cr/3+10P
Respective element symbols being contents (mass%)
iv
o
H
IV
I
H
IV
ol
=
Ui
[0061]
Table 2
Steel Raw material Plate Hot rolling
Heat treatment Remarks
No. thickness thickness Heating Hot
rolling finish Cooling method Heating Cooling method
temperature temperature
temperature
(mm) (mm) ( ( C ) ( (C ) ( (C
)
=
Present
1 200 air water 12 1150 900 900
invention
cooling
cooling
example
Present
2 200 32 1050 880 air 900
water invention
cooling
cooling
example
-
Present
n
3 200 25 1200 920 air 930
water invention 0
cooling
cooling 1\)
co
example
0
H
,I. .
Present
c)
0
u.)
4 200 25 1150 890 water no heat
invention
. cooling treatment
I.)
example
0
H
.
N
200 20 1150 900 water cooling 200
air cooling Present invention example1
H
_
N
6 200 25 1150 900 air cooling 900
water cooling Comparison example 1
0
in
7 200 20 1150 900 water cooling no
heat treatment Comparison example
8 250 32 1200 950 j air cooling 900
water cooling Comparison example
_
9 180 20 1100 880 air cooling 930
water cooling Comparison example
_
300 25 1150 920 water cooling no heat treatment
f Comparison example
11 200 32 1050 870 air cooling 900
water cooling Comparison example
12 250 16 1200 900 water cooling no
heat treatment Comparison example
13 200 12 1150 860 air cooling 930
water cooling Comparison example
14 250 25 1150 900 air cooling 900
water cooling Comparison example
Note: Underlined values being outside the scope of the present invention
a
[0062]
Table 3
Steel Surface Abrasion resistant Base material T shape 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 Corresponding to Toughness of
1013000 resistance rate 100 C to bond
area low-temperature tempering weld joint
embrittlement region
(J) (presence or (presence or
vE0(J) vE0(J) vE0(J)
non-presence of non-presence of
cracks) cracks)
1 442 4.7 68 no cracks no cracks 60
48 119 Present invention example
2 410 4.2 95 no cracks no cracks 83
70 151 Present invention example
3 519 5.6 42 no cracks no cracks 39
33 77 Present invention example
_
4 428 4.5 85 no cracks no cracks 76
66 128 Present invention example n
_
490 5.0 57 no cracks no cracks 50 47
94 Present invention example o
iv
co
o
,4. 6 328 3.0 168 no cracks no cracks 140
155 182 Comparison example H
-A
7 59.8 6.0 14 cracks occurred cracks occurred
6 5 23 Comparison example u.)
_
iv
o
8 501 5.1 42 cracks occurred cracks occurred
35 32 70 Comparison example H
iv
_
1
9 522 5.4 37 cracks occurred cracks occurred
28 8 40 Comparison example H
N
oI
435 4.6 66 no cracks no cracks 46 15
29 Comparison example co
11 456 4.7 25 cracks occurred cracks occurred
20 11 32 Comparison example
_
12 432 4.5 21 no cracks no cracks 17
9 21 Comparison example
13. 486 4.8 23 no cracks no cracks 14
10 19 Comparison example
_
.
14 369 3.5 42 no cracks no cracks 43
47 65 Comparison example
,
¨
Note: Underlined values being outside the scope of the present invention
[0063]
Table 4
Chemical components
(mass%)
No.
DI* Formula (2) Remarks
C Si Mn P S Al Cr Nb Ti Mo W Cu Ni V N B REM Ca Mg
15 0.209 0.32 0.73 0.006 0.0018 0.032
1.05 0.023 0.017 0.17 31 12 101.4 0.10 Present invention example
16 0.227 0.27 0.63 0.005 0.0020 0.025
1.31 0.014 0.012 0.29 0.44 0.21 0.04 27 10 15 178.7 0.00
Present invention example
17 0.216 0.18 0.60 0.007 0.0025 0.017
0.60 0.023 0.028 0.12 0.05 30 57.0 0.24 Present invention example
18 0.245 0.37 0.52 0.007 0.0018 0.038
1.09 0.017 0.011 0.57 0.24 0.14 30 12 21 188.6 0.08 Comparison
example
19 0.276 0.03 0.93 0.009 0.0027 0.051 0.47 0.023 0.016 0.04 30
50.7 0.44 Comparison example
_
20 0.290 0.27 1.08 0.009 0.0021 0.034 0.51 0.011 0.009 0.14 0.10 25
72.0 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 ppm in chemical components
Note 3: Dl* = 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+10P
co
Respective element symbols being contents (mass%)
0
0
ol
=
[0064]
Table 5
Steel Raw material Plate
No. thickness thickness Hot rolling
Heat treatment Remarks
Heating Hot rolling finish 1
Heating
Cooling method
Cooling method
temperature temperature 1 temperature
(mm) (mm) ( C) ( C) 1 (
C)
15 250 40 1150 900 1 air cooling
900 water cooling Present invention example
16 300 60 1120 880 1 air cooling
870 1 water cooling Present invention example
17 200 8 1150 830 1 air cooling
900 water cooling Present invention example
18 250 32 1100 870 1 air cooling
900 water cooling Comparison example
19 250 25 1100 900 1 water cooling
no heat treatment Comparison example
20 300 40 1150 900 1 air cooling
900 water cooling Comparison example
Note: Underlined values being outside the scope of the present invention
0
0
1.)
co
0
H
CA)
0
La
IV
0
H
IV
I
H
IV
I
0
Ui
[ 0 0 6 5 ]
Table 6
Steel Surface Abrasion resistant Base material T shape weld cracking
test Synthetic heat-affected zone test Shielded metal arc Remarks
No. hardness property toughness
welding
HBW Abrasion vE0 vE-40 No preheating
Preheating to Corresponding to . Corresponding to Toughness of
weld
10/3000 resistance rate 100 C bond area
low-temperature joint
tempering
embrittlement region
GO (J) (presence or (presence or
vE0(J) vE-40(J) vE0(J) vE-40(J) vE0(J) vE-40(J)
non-presence of non-presence of
.
cracks) cracks)
15 411 4.2 83 66 no cracks no cracks 90 61
72 46 133 105 Present invention example
,
-
16 435 4.7 70 49 no cracks no cracks 65 40
59 38 83 50 Present invention example
17 415 4.3 48 33 no cracks no cracks 43 28
38 30 65 39 Present invention example
n
-
18 482 4.7 50 36 no cracks no cracks 36 28
30 27 35 27 Comparison example o
I\)
-
co
19 528 5.5 35 24 cracks occurred I cracks occurred 31
23 21 j 9 28 14 Comparison example
o
H
-
20 546 5.8 38 34 no cracks I no cracks 33
28 30 27 35 27 Comparison example o
u.)
Note: Underlined values being outside the scope of the present invention
iv
o
H
IV
I
H
IV
oi
to
