[0001] 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.
[0002] 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.
[0003] 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.
[0004] However the property required for the abrasion 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.
[0005] It is an object of the invention to provide an abrasion resistant steel.
[0006] 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 contributing to the enhancement
of the abrasion resistance property.
[0007] 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 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.
[0008] 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.
[0009] 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 0.35 to 0.45 wt.% in C content.
[0010] Figure 1 is a graph showing the relationship between the added quantity of titanium
and the ratio of resistance to abrasion.
[0011] 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 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] The ratio of resistance to abrasion is an index wherein the resistance to abrasion
of an abrasion resistant steel is divided 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.
[0016] The followings are the reason why the contents of the elements of the invented steel
is specified.
[0017] 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.%.
[0018] 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.
[0019] 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 effective 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.%.
[0020] 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 required to be 0.05 to 1.5 wt.%.
[0021] 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.
[0022] 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 .
[0023] 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.%.
[0024] 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 wt.%.
[0025] 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.%.
[0026] 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.%.
[0027] 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.%.
[0028] 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.%.
[0029] 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.%, the weldability
is deteriorated. Therefore the V content is determined to be 0.01 to 0.5 wt.%.
[0030] 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
[0031] Table 1 shows the chemical compositions of the samples of the invented and conventional
steel.
[0032] 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.
Table 1
Kind of Steel |
C |
Si |
Mn |
Cu |
Ni |
Cr |
Mo |
Nb |
V |
Ti |
B |
N |
A |
0.30 |
0.36 |
0.70 |
|
|
|
|
- |
|
0.09 |
- |
33 |
B |
0.28 |
0.37 |
0.73 |
- |
- |
- |
- |
- |
- |
0.37 |
- |
38 |
C |
0.29 |
0.37 |
0.74 |
- |
- |
- |
- |
- |
- |
0.98 |
- |
36 |
D |
0.29 |
0.36 |
0.71 |
- |
- |
- |
- |
- |
- |
1.41 |
- |
30 |
E |
0.28 |
0.36 |
0.71 |
0.24 |
0.29 |
- |
- |
- |
- |
0.40 |
- |
31 |
F |
0.31 |
0.33 |
0.73 |
- |
- |
1.02 |
0.23 |
- |
- |
1.08 |
10 |
32 |
G |
0.19 |
0.33 |
1.44 |
- |
- |
0.27 |
- |
- |
- |
0.65 |
9 |
22 |
H |
0.14 |
0.34 |
1.40 |
- |
- |
- |
- |
0.025 |
- |
0.40 |
- |
24 |
I |
0.32 |
0.34 |
0.72 |
- |
- |
- |
- |
- |
0.045 |
0.41 |
- |
21 |
J |
0.34 |
0.26 |
1.01 |
0.35 |
0.55 |
- |
- |
0.028 |
0.041 |
0.54 |
- |
42 |
K |
0.31 |
0.38 |
0.71 |
- |
- |
0.99 |
0.23 |
0.022 |
0.044 |
0.06 |
8 |
24 |
L |
0.29 |
0.38 |
0.70 |
- |
- |
0.99 |
0.23 |
- |
0.044 |
0.08 |
9 |
23 |
M |
0.30 |
0.36 |
0.71 |
0.25 |
- |
0.55 |
0.23 |
- |
0.045 |
0.19 |
8 |
30 |
N |
0.31 |
0.36 |
0.71 |
- |
- |
1.02 |
0.23 |
- |
0.045 |
0.38 |
8 |
31 |
O |
0.31 |
0.33 |
0.73 |
- |
0.36 |
0.63 |
0.34 |
- |
- |
1.28 |
- |
32 |
P |
0.30 |
0.30 |
0.75 |
- |
- |
- |
- |
- |
- |
0.02 |
- |
37 |
Q |
0.30 |
0.30 |
0.96 |
- |
- |
1.03 |
0.21 |
- |
0.045 |
0.01 |
11 |
47 |
R |
0.03 |
0.30 |
0.75 |
- |
- |
- |
- |
- |
- |
0.47 |
- |
37 |
Note: The values are in wt.% except B and N. The values of B and N are in ppm. |
Table 2
|
Process |
Ratio of resistance to abrasion |
Brinell Hardness(HB) |
A |
RQ |
6.5 |
474 |
B - 1 |
RQ |
8.3 |
393 |
B - 2 |
RQT(400°C) |
6.1 |
277 |
C - 1 |
DQ |
9.7 |
335 |
C - 2 |
DQT(400°C) |
6.8 |
245 |
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 |
I |
RQ |
10.1 |
451 |
J |
DQ |
8.9 |
417 |
K |
RQ |
6.4 |
503 |
L - 1 |
AR |
4.5 |
293 |
L - 2 |
DQ |
8.2 |
507 |
M - 1 |
AR |
4.7 |
286 |
M - 2 |
DQ |
9.1 |
454 |
N - 1 |
AR |
6.1 |
274 |
N - 2 |
RQ |
11.6 |
448 |
O - 1 |
AR |
7.3 |
246 |
O - 2 |
RQ |
11.1 |
275 |
P |
RQ |
4.9 |
464 |
Q - 1 |
AR |
2.8 |
326 |
Q - 2 |
RQ |
5.2 |
481 |
R |
RQ |
1.2 |
122 |
[0033] 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 O are made of the invented
steel, whereas samples from P to R are made of the steel for comparison.
[0034] The abrasion test is carried out according to ASTM G 65-85 as described before. The
measurement of the abrasion is done by the change of the weight of the sample.
[0035] 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.
[0036] 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.
[0037] 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-1, 8.3 and that 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.
[0038] This result agrees with the purpose of the invention wherein the invented steel possesses
high resistance to abrasion and low hardness.
[0039] 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.
[0040] 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.
1. An abrasion resistant steel containing from 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, apart from incidental
elements and impurities, if any; and
optionally also containing at least one 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; and optionally
also containing at least one of 0.005 to 0.5 wt.% Nb and 0.01 to 0.5 wt.% V.
2. An abrasion resistant steel containing from 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, at least one 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, and
the balance Fe, apart from incidental elements and impurities, if any.
3. An abrasion resistant steel containing 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, at least one of 0.005 to 0.5 wt.% Nb and 0.01
to 0.5 wt.% V, the balance Fe, apart from incidental elements and impurities, if any.
4. An abrasion resistant steel containing from 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, at least one 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, at
least one of 0.005 to 0.5 wt.% Nb and 0.01 to 0.5 wt.% V, and the balance Fe, apart
from incidental elements and impurities, it any.
5. A steel as claimed in any one of the preceding claims characterised in that it has
a Ti content of from 0.05 to 0.3 wt.%.
6. A steel as claimed in claim 1, 2, 3 or 4, characterised in that it has a Ti content
of from 0.3 to 1.0 wt.%.
7. A steel as claimed in claim 1, 2, 3 or 4, characterised in that it has a Ti content
of from 1.0 to 1.5 wt.%.
8. A steel as claimed in any one of claims 1 to 7, characterised in that it has a C content
of from 0.05 to 0.2 wt.%.
9. A steel as claimed in any one of claims 1 to 7, characterised in that it has a C content
of from 0.2 to 0.35 wt.%.
10. A steel as claimed in any one of claims 1 to 7, characterised in that it has a C content
of from 0.35 to 0.45 wt.%.