Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
AN ABRASION RESISTANT STEEL
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to the field of metallurgy and
particularly relates to the field of an abrasion resistant
steel utilized in the field of construction, civil
engineering and mining.
DESCRIPTION OF THE RELATED ART
Abrasion resistant steels are utilized in the field
of construction) civil engineering and mining such as in
power shovel, bulldozer, hopper and bucket to keep the lives
of these machines or their parts. It is well known
that the steel having high hardness possesses high abrasion
resistance property. For this purpose a high
alloyed steel treated by quenching has commonly been
utilized.
Japanese Patent laid open Publication Nos. 142726 / 19
87) 169359 / 1988 and 142023 / 1989 disclose the information
about the production of the conventional abrasion
resistant steel. In these inventions the Brinell
Hardness of the steel is more than 300. The
improvements are aimed at the weldability, the toughness and
the workability in bending, and the abrasion resistance
property is realized by increasing the hardness of the
steel.
However the property required for the abrasion
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resistant steel has recently become severer and the
essential solution to higher abrasion resistance of steel
will not be obtained by simply enhancing the hardness of
steel. When the hardness of steel is significantly
enhanced, the weldability and the workability of steel are
deteriorated due to the high alloying and the cost of
producing such steels increases significantly.
Accordingly in the practical point of view the significant
increase in the hardness of abrasion resistant steel is
facing with a difficulty with respect to the workability of
the steel.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an
abrasion resistant steel.
It is an object of the invention to provide an
abrasion resistant steel having an excellent abrasion
resistance property without considerably increasing the
hardness of steel. According to the invention an
abrasion resistant steel is provided with approximately 0.05
to 0.45 wt.~ C, 0.1 to 1.0 wt.~ Si, 0.1 to 2.0 wt.~ Mn,
0.05 to 1.5 wt.~ Ti and the balance Fe as the basic elements
cotributing to the enhancement of the abrasion resistance
property.
In addition to the basic elements, at least one
element selected from the group consisting of 0.1 to 2.0
wt.~ Cu, 0.1 to 10.0 wt.~ Ni, 0.1 to 3.0 wt.~ Cr, 0.1 to 3.0
wt.~ Mo and 0.0003 to 0.01 wt.~ B may be added to enhance
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the quenching hardenability of the steel, and at least one
element selected from the group consisting of 0.005 to 0.5
wt.~ Nb, 0.01 to 0.5 wt.~ V may be added to enhance the
precipitation hardenability of the steel.
A more preferable range aiming at the economy of
the steel is 0.05 to 0.3 wt.~ in Ti content. A more
preferable range with respect to thr balance of the stable
abrasion resistance and the economy of the steel is 0.3 to
1.0 wt.~ in Ti content. A more preferable range for
stable abrasion resistance is 1.0 to 1.5 wt.~ in Ti
content.
A more preferable range aiming at the bending
workability and the weldability of the steel is 0.05 to 0.2
wt.~ in C content. A more Preferable range with
respect to the balance of the bending workability and the
weldability of the steel and the stable abrasion resistance
of the steel is 0.2 to 0.35 wt.~ in C content. A
more preferable range for stable abrasion resistance of the
steel is 0.35to 0.45 wt.~ in C content.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a graph showing the relationship between
the added quantity of titanium and the ratio of resistance
to abrasion.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The most significant characteristic of the invented
steel is effectively utilizing of very hard TiC. In
this invention it is not necessary to enhance the hardness
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of the abrasion resistant steel only by transforming the
microstructure of the steel to a martensite which is the
conventional way to enhance the abrasion resistance of
steel.
In the conventional way the purpose of the addition
of titanium to steel is to react with the nitrogen so that
the nitrogen is stabilized as TiN. As the result
boron does not react with nitrogen since there is not enough
nitrogen in the steel, and retained in the steel as a
soluble boron, which enhances the quenching
hardenability.The quantity of the addition in this case is
about 0.02 wt.~ of steel. The addition of a large
quantity of titanium to steel is limited by the oxidation of
the titanium in the steel melting stage, the clogging of
the nozzle and the reaction with the oxidation preventing
powder in the casting stage. Therefore the effect of
the addition of a large quantity of titanium is not yet
known.
The inventors after detailed examination found that
the addition of titanium in a large quantity realizes the
improvement of steel with respect to the abrasion resistance
property.
Figure 1 is a graph showing the relationship between
the added quantity of titanium and the ratio of resistance
to abrasion. The abscissa denotes the added quantity of
titanium and the ordinate denotes the ratio of resistance
to abrasion.
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The ratio of resistance to abrasion is an index
wherein the resistance to abrasion of an abrasion resistant
steel is devided by that of a mild steel. The
resistance to abrasion is measured according to ASTM
Standard G 65-85 wherein an abrasive is introduced between
the test specimen and a rotating wheel with a chlorobutyl
rubber tire. The abrasive is a sand composed of 100
silica and of controlled size. The C content of the
test specimen is 0.3 wt.~ and the specimen is heat treated
by quenching. The Brinell Hardness is below 500.
As shown in Figure 1, the ratio of resistance to abrasion
linearly increases with the increase of the added quantity
of titanium up to 0.5 wt.~. The addition of titanium
is effective when the added quantity of titanium is 0.05
wt.~. When the added quantity is 1.5 wt.~) the ratio of
resistance to abrasion reaches about 10, which shows the
remarkable improvement in the abrasion resistance
property.
The followings are the reason why the contents of the
elements of the invented steel is specified.
C is an indispensable element in forming TiC and also
enhances the hardness of the matrix of steel.
However when C is increased too much, the weldability and
the workability are deteriorated. Therefore the
upper limit of C is determined to be 0.45 wt.~. As
for the lower limit of C the minimum quantity of C wherein
the effect of TiC is shown is 0.05 wt.~.
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A more preferable range aiming at the bending
workability and the weldability of the steel is 0.05 to 0.2
wt.~ in C content. A more preferable range with
respect to the balance of the bending workability and the
weldability of the steel and the stable abrasion resistance
of the steel is 0.2 to 0.35 wt.~ in C content. A
more preferable range for the stable abrasion resistance of
the steel is 0.35 to 0.45 wt.~ in C content.
Si is an element effective in deoxidation process of
steel making and a minimum addition of 0.1 wt.~ is
required for this purpose. Si is also an effective
element for solution hardening. However when the Si
content exceeds 1.0 wt.~, the toughness of steel is lowered
and the inclusion in steel is increased. Therefore the
Si content is determined to be 0.1 to 1.0 wt.~.
Mn is an element effecive in quenching
hardenability. At least 0.1 wt.~ is required for this
purpose. When the Mn content exceeds 2.0 wt.~, the
weldability of steel is deteriorated. Therefore the Mn
content is determined to be 0.1 to 2.0 wt.~.
In this invention Ti is one of the most important
element as is C. The addition of at least 0.05 wt.~ of Ti is
required to stably form a large quantity of TiC. When
the Ti content exceeds 1.5 wt.~, the steel possesses good
abrasion resistance property but high cost is required for
the production, also the weldability and the workability of
steel are lowered. Therefore the Ti content is
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required to be 0.05 to 1.5 wt.~.
A more preferable range aiming at the economy of the
steel is 0.05 to 0.3 wt.~ in Ti content. A more
preferable range with respect to the balance of the stable
abrasion resistance and the economy of the steel is 0.3 to
1.0 wt.~ in Ti content. A more preferable range for
stable abrasion resistance of the steel is 1.0 to 1.5
wt.~ in Ti content.
In this invention, in addition to the above basic
elements) at least one element selected from the group
consisting of Cu, Ni, Cr, Mo and B may be added to enhance
the quenching hardenability and at least one element
selected from the group consisting of Nb and V may be
added to enhance the precipitation hardening
Cu is an element for enhancing the quenching
hardenability and effective in controlling the hardness of
steel. When the Cu content is below 0.1 wt.~, the effect
is not sufficient. When the Cu content exceeds 2.0 wt.~,
the hot workability is lowered and the production cost is
increased. Therefore the Cu content is determined to be
0.1 to 2.0 wt.~.
Ni is an element which enhances the quenching
hardenability and the low temperature toughness. When
the Ni content is below 0.1 wt.~, the effect is not
sufficient. When the Ni content exceeds 10.0 wt.~,
the production cost is increased significantly.
Therefore the Ni content is determined to be 0.1 to 10.0
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wt.~.
Cr is an element which enhances the quenching
hardenability. When the Cr content is below 0.1
wt.~, the effect is not sufficient. When the Cr
content exceeds 3.0 wt.~, the weldability is deteriorated)
and the production cost is increased. Therefore the
Cr content is determined to be 0.1 to 3.0 wt.~.
Mo is an element which enhances the quenching
hardenability. When the Mo content is below 0.1
wt.~, the effect is not sufficient. When the Mo
content exceeds 3.0 wt.~, the weldability is deteriorated,
and the production cost is increased. Therefore the
Mo content is determined to be 0.1 to 3.0 wt.~.
B is an element which enhances the quenching
hardenability by the addition to steel even by a small
amount. When the B content is below 0.0003 wt.~ , the
effect is not sufficient. When the B content exceeds 0.01
wt.~, the weldability is deteriorated, and the quenching
hardenability is also deteriorated. Therefore the B
content is determined to be 0.0003 to 0.01 wt.~.
Nb is an element effective in the precipitation
hardening and can control the hardness of steel according
to the purpose of steel. When the Nb content is below
0.005 wt.~, the effect is not sufficient. When the Nb
content exceeds 0.5 wt.~) the weldability is
deteriorated. Therefore the Nb content is determined to
be 0.005 to 0.5 wt.~.
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V is an element effective in the precipitation
hardening and can control the hardness of steel according to
the purpose of steel. When the V content is below 0.01
wt.~, the effect is not sufficient. When the V
content exceeds 0.5 wt.°6, the weldability is deteriorated.
Therefore the V content is determined to be 0.01 to 0.5
wt. ~.
In this invention no specification is required as for
the method of working the steel and as for the method of
heat treating of the steel. The invention may not be
inoperable by heat treatments such as quenching, annealing)
aging and stress relief annealing.
EXAMPLE
Table 1 shows the chemical compositions of the
samples of the invented and conventional steel.
Samples from A to 0 are made of the invented steel,
whereas samples from P to R are made of the steel for
comparison. The chemical composition of the samples
from P to R varies with respect to Ti and other alloying
elements. The chemical compositions of the samples P
and Q are within the same range with those of the invented
steel except that of Ti. The chemical composition of
the sample R is within the same range of the invented steel
with respect to Ti, but out of the range with respect to C.
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Table 1
Kind
of C Si Mn Cu Ni Cr Mo Nb V Ti B N
Steel
A 0.300.36 0.70- - - - - ~ - 0.09 - 33
B 0.280.37 0.73- - - - - - 0.37 - 38
C 0.290.37 0.74- - - - - - 0.98 - 36
D 0.290.36 0.71- - - - - - 1.41 - 30
E 0.280.36 0.710.24 0.29- - - - 0.40 - 31
F 0.310.33 0.73- - 1.02 0.23 - - 1.08 10 32
G 0.190.33 1.44- - 0.27 - - - 0.65 9 22
H 0.140.34 1.40- - - - 0.025 - 0.40 - 24
I 0.320.34 0.72- - - - - 0.045 0.41 - 21
,J 0.340.26 1.010.35 0.55- - 0.028 0.041 0.54 - 42
K 0.310.38 0.71- - 0.99 0.23 0.022 0.044 0.06 8 24
L 0.290.38 0.70- - 0.99 0.23 - 0.044 0.08 9 23
M 0.300.36 0.?10.25 - 0.55 0.23 - 0.045 0.19 8 30
N 0.310.36 0.71- - 1.02 0.23 - 0.045 0.38 8 31
0 0.310.33 0.73- 0.360.63 0.34 - - 1.28 - 32
P 0.300.30 0.75- - - - - - 0.02 - 37
Q 0.300.30 0.96- - 1.03 0.21 - 0.045 0.01 11 47
R 0.030.30 0.75- - - - - - 0.47 - 37
Note: The values are in wt.% except B and N. The values of B and N are in ppm.
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Table 2.
Process Ratio of Brinell
resistance toHardness(HB)
A RQ 6.5 474
B - RQ 8.3 393
.. 1 ...R Q.T ~ 4 ........ ..............
. .. 0 0.C '~.... .~....... Z.7 7 ........
.
:
2
...
C - 1 DQ 9.7 335
...D Q.T ~ 4 ........6 ..............
0 0'C '~.... . a '..... 2.4 5........
D RQ 9.3 242
E RQ 8.6 390
F RQ 9.1 321
G RQ 4.7 302
H DQ 3.4 253
z RQ 10.1 451
J' DQ 8.9 417
K RQ 6.4 503
L - 1 AR 4.5 293
..........DQ........................a .............5.~7........
. .......
M 1 AR 4.7 Z86
- 2............. Q ........9 .............4.5
..M ............... .~........ 4........
..
..
N - 1 AR 6.1 274
..N..~... ...........RQ....................i.i .............448........
... . 6.......
O - 1 AR 7.3 246
.. .~............... ~ ...... ~.1......... .. 2
O ............... . ........ 7 5"......
.
P RQ 4.9 464
..........~ ~.........................Z.:..............3
Q - 2 RQ $........ ~ 2 6.,......
~ 5. 2 481
RQ 1.2 122
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Table 2 shows the process of making the samples, the
ratio of the resistance to abrasion and the Brinell
Hardness of the samples. Samples from A to 0 are made of the
invented steel, whereas samples from P to R are made of the
steel for comparison.
The abrasion test is carried out according to ASTM G
65-85 as decribed before. The measurement of the
abrasion is done by the change of the weight of the sample.
As described before the ratio of resistance to
abrasion is the ratio of the weight change of the specimen
made of the invented steel versus that of the specimen made
of a mild steel.
The processes in the table are classified as follows
AR, as rolled; RQ) as quenched after heated to 900 °C
following the rolling and air-cooling; RQT) as tempered at
the temperature shown in the parenthesis after RQ treatment;
DQ, as directly quenched after finish rolled at 880 °C
following the heating of the slab at 1150 °C ; DQT) as
tempered at the temperature shown in the parenthesis
following DQ. The thickness of the sample is 15 mm. The
kind of steel in Table 1 corresponds with those in Table 2.
The steel for comparison P corresponds with the
invented steel A, B-1 and D and the Ti content is below the
range of the invented steel. Examining the ratio of
the resistance to abrasion, it is found that the ratio is
4.9 in the steel for comparison P, whereas the ratio of the
invented steel A is 6.5) that of the steel B-l, 8.3 and that
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of the steel D, 9.3. This is to say that the ratio of the
invented steel can be enhanced twice as much as that of the
steel for comparison which is a conventional abrasion
resistant steel. Moreover the hardness of the invented
steel is lower than those of the steel for comparison.
This result agrees with the purpose of the invention
wherein the invented steel possesses high resistance to
abrasion and low hardness.
The steel for comparison Q corresponds with the
invented steel L and N. The ratios of the resistance to
abrasion in both L and N are higher than that of Q.
The steel for comparison R corresponds with the
invented steel B-1. The C content of the steel for
comparison R is below the range of the invented steel.
Since the C content of the steel R is so low that the
ratio of the resistance to abrasion is significantly lower
than that of B-1.
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