ACIER RESISTANT A L'ABRASION, PROCEDE DE FABRICATION D'UN ACIER RESISTANT A L'ABRASION ET ARTICLES REALISES A PARTIR DE CE DERNIER

ABRASION RESISTANT STEEL, METHOD OF MANUFACTURING AN ABRASION RESISTANT STEEL AND ARTICLES MADE THEREFROM

Abrégé français

La présente invention se rapporte à un acier résistant à l'abrasion qui se compose essentiellement, en % en poids : d'une quantité de carbone comprise entre 0,20 et 0,30 %, d'une quantité de manganèse comprise entre 0,40 et 1,25 %, d'une quantité maximale de phosphore égale à 0,05 %, d'une quantité maximale de soufre égale à 0,01 %, d'une quantité de silicium comprise entre 0,20 et 0,60 %, d'une quantité de chrome comprise entre 0,50 et 1,70 %, d'une quantité de nickel comprise entre 0,20 et 2,0 %, d'une quantité de molybdène comprise entre 0,07 et 0,60 %, d'une quantité de titane comprise entre 0,022 et 0,10 %, d'une quantité de bore comprise entre 0,001 et 0,10 %, d'une quantité d'aluminium comprise entre 0,027 et 0,10 %, le reste étant du fer et des impuretés inévitables. L'acier peut être fondu et coulé sous forme de lingot d'acier ou de brame d'acier, laminé à chaud jusqu'à une épaisseur de plaque souhaitée ; austénisé à une température comprise entre 1 650 et 1 700 °F ; trempé à l'eau ; et trempé à une température comprise entre 350 et 450 °F. La tôle d'acier résultante peut présenter une dureté superficielle d'au moins 440 HBW, une dureté à mi-épaisseur égale à au moins 90 % de la dureté superficielle et une résistance dans la direction transversale à une température égale à -60 °F d'au moins 20 pieds/livres et à température ambiante d'au moins 40 pieds/livres.

Abrégé anglais

An abrasion resistant steel consisting essentially of, in weight %: 0.20-0.30% carbon, 0.40-1.25% manganese, 0.05% maximum phosphorous, 0.01% maximum sulfur, 0.20-0.60% silicon, 0.50-1.70% chromium, 0.20-2.00% nickel, 0.07-0.60% molybdenum, 0.022-0.10% titanium, 0.001-0.10% boron, 0.027-0.10% aluminum, balance iron, and incidental impurities. The steel may be melted and cast into a steel ingot or slab, hot rolled to a desired plate thickness; austenitized at 1650-1700°F; water quenched; and tempered at 350-450 °F. The resulting steel plate may have a surface hardness of at least 440 HBW, a mid-thickness hardness of at least 90% of the surface hardness, and toughness in the transverse direction at -60°F of at least 20 ft-lbs and at room temperature of at least 40 ft-lbs.

Revendications

CLAIMS:
1. An abrasion resistant steel consisting essentially of, in weight %: 0.20-
0.30%
carbon, 0.40-1.25% manganese, 0.05% maximum phosphorous, 0.01% maximum sulfur,
0.20-0.60% silicon, 0.50-1.70% chromium, 0.20-2.00% nickel, 0.07-0.60%
molybdenum,
0.022-0.10% titanium, 0.001-0.10% boron, 0.015-0.10% aluminum, balance iron,
and
incidental impurities, wherein the surface hardness is at least 440 HBW.
2. The abrasion resistant steel according to claim 1, wherein the mid-
thickness
hardness is at least 90% of the surface hardness.
3. The abrasion resistant steel according to claim 1 or 2, wherein the
microstructure is
tempered martensite.
4. The abrasion resistant steel according to any one of claims 1 to 3,
wherein the
toughness in the transverse direction at -60°F is at least 20 ft-lbs
and at room temperature is at
least 40 ft-lbs.
5. The abrasion resistant steel according to any one of claims 1 to 4,
wherein the
surface hardness is between 440-514 HBW.
6. The abrasion resistant steel according to any one of claims 1 to 5,
consisting
essentially of, in weight %: 0.22-0.26% carbon, 0.70-0.90% manganese, 0.025%
maximum
phosphorous, 0.003% maximum sulfur, 0.20-0.40% silicon, 0.80-1.00% chromium,
0.40-
0.60% nickel, 0.07-0.15% molybdenum, 0.022-0.04% titanium, 0.001-0.003% boron,
0.015-
0.06% aluminum, balance iron, and incidental impurities.
7. The abrasion resistant steel according to any one of claims 1 to 5,
consisting
essentially of, in weight %: 0.24% carbon, 0.80% manganese, 0.010% maximum
phosphorous, 0.003% maximum sulfur, 0.25% silicon, 0.90% chromium, 0.50%
nickel,
0.10% molybdenum, 0.03% titanium, 0.0015% boron, 0.035% aluminum, balance
iron, and
incidental impurities.
8. The abrasion resistant steel according to any one of claims 1 to 7,
wherein the steel
has been austenitized at 1650-1700°F, water quenched, and tempered 350-
450 °F.
8

9. The abrasion resistant steel according to any one of claims 1 to 8,
wherein
Cr + Mn + Mo is 1.4 weight % minimum.
10. The abrasion resistant steel according to any one of claims 1 to 8,
wherein
Ni + Si +Cr is 1.4 weight % minimum.
11. The abrasion resistant steel according to any one of claims 1 to 8,
wherein Cr + Si
is 1 weight % minimum.
12. A method for producing an abrasion resistant steel plate comprising:
a. melting and casting a steel ingot or slab consisting essentially of, in
weight %:
0.20-0.30% carbon, 0.40-1.25% manganese, 0.05% maximum phosphorous, 0.01%
maximum sulfur, 0.20-0.60% silicon, 0.50-1.70% chromium, 0.20-2.00% nickel,
0.07-0.60% molybdenum, 0.022-0.10% titanium, 0.001-0.10% boron, 0.015-0.10%
aluminum, balance iron, and incidental impurities;
b. hot rolling the ingot or slab to a desired thickness;
c. austenitizing the plate at 1650-1700°F;
d. water quenching the plate; and
e. tempering the plate at 350-450 °F,
wherein the surface hardness of the steel is at least 440 HBW.
13. The method according to claim 12, wherein during the melting and
casting step the
steel is killed, desulfurized, vacuum degassed, treated for sulfide shape
control, or a
combination thereof.
14. The method according to claim 12 or 13, wherein cross rolling is used
during the
hot rolling step.
15. The method according to any one of claims 12 to 14, wherein the
microstructure is
tempered martensite.
9

16. The method according to any one of claims 12 to 15, wherein the
toughness in the
transverse direction at -60°F is at least 20 ft-lbs and at room
temperature is at least 40 ft-lbs.
17. The method according to any one of claims 12 to 16, wherein the mid-
thickness
hardness is at least 90% of the surface hardness.
18. The method according to any one of claims 12 to 17, wherein the steel
consisting
essentially of, in weight %: 0.22-0.26% carbon, 0.70-0.90% manganese, 0.025%
maximum
phosphorous, 0.003% maximum sulfur, 0.20-0.40% silicon, 0.80-1.00% chromium,
0.40-
0.60% nickel, 0.07-0.15% molybdenum, 0.022-0.04% titanium, 0.001-0.003% boron,
0.015-
0.06% aluminum, balance iron, and incidental impurities.
19. The method according to any one of claims 12 to 17, wherein the steel
consisting
essentially of, in weight %: 0.24% carbon, 0.80% manganese, 0.010% maximum
phosphorous, 0.003% maximum sulfur, 0.25% silicon, 0.90% chromium, 0.50%
nickel,
0.10% molybdenum, 0.03% titanium, 0.0015% boron, 0.035% aluminum, balance
iron, and
incidental impurities.

Description

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ABRASION RESISTANT STEEL, METHOD OF MANUFACTURING AN ABRASION
RESISTANT STEEL AND ARTICLES MADE THEREFROM
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to an abrasion resistant steel and, more
specifically, to an
abrasion resistant steel haying good hardenability, good weldability, and high
toughness, and a
method of manufacturing same.
Description of Related Art
[0002] Steels used to manufacture tools used for extraction, movement, and
processing of
abrasive materials such as liners for haul truck beds, bulldozers, chutes, and
other material
handling equipment for the mining (coal, hardrock, gold, silver, and others),
timber and paper,
biomass, quarrying, and other similar industries must have high abrasion and
wear resistance as
well as high toughness to avoid fracture. Generally, abrasion resistance and
wear resistance
increase as hardness and harcienability increase while toughness often
decreases with increased
hardness and hardenability. Therefore, it is desired that steels for these
applications possess a
combination of high hardness and hardenability and good toughness.
[0003] Such steels generally include significant amounts of alloying elements
such as Cr, Ni,
Si, and Al to achieve the high hardness and hardenability in combination with
good toughness
which can make them expensive and difficult to weld.
SUMMARY OF THE INVENTION
[0004] The present invention is directed to an abrasion resistant steel, a
method for making an
abrasion resistant steel plate, and articles made therefrom. The steel of the
present invention
consists essentially of in weight %: 0.20-0.30% carbon, 0.40-1.25% manganese,
0.05%
maximum phosphorous, 0.01% maximum sulfur, 0.20-0.60% silicon, 0.50-1.70%
chromium,
0.20-2.00% nickel, 0.07-0.60% molybdenum, 0.022-0.10% titanium, 0.001-0.10%
boron, 0.027-
Ø10% aluminum, balance iron, and incidental impurities. The inventive steel
plate may have a
microstructure of tempered martensite, a surface hardness of at least 440 HBW,
a mid-thickness
hardness that is at least 90% of the surface hardness, and a toughness in the
transverse direction
at -60 F of at least 20 ft-lbs and at room temperature of at least 40 ft-lbs.
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[0005] The inventive method of making the abrasion resistant steel plate
of the invention
comprises melting and casting a steel ingot or slab of the composition
detailed above, hot
rolling the ingot or slab to a plate of the desired thickness, austenitizing
the plate at 1650-
1700 F, water quenching the plate, and tempering the plate at 350-450 F.
10005A1 The present specification discloses and claims an abrasion resistant
steel consisting
essentially of, in weight %: 0.20-0.30% carbon, 0.40-1.25% manganese, 0.05%
maximum
phosphorous, 0.01% maximum sulfur, 0.20-0.60% silicon, 0.50-1.70% chromium,
0.20-2.00%
nickel, 0.07-0.60% molybdenum, 0.022-0.10% titanium, 0.001-0.10% boron, 0.015-
0.10%
aluminum, balance iron, and incidental impurities, wherein the surface
hardness is at least 440
HBW.
[0005B] The present specification also discloses and claims a method for
producing an
abrasion resistant steel plate comprising: a. melting and casting a steel
ingot or slab consisting
essentially of, in weight %: 0.20-0.30% carbon, 0.40-1.25% manganese, 0.05%
maximum
phosphorous, 0.01% maximum sulfur, 0.20-0.60% silicon, 0.50-1.70% chromium,
0.20-2.00%
nickel, 0.07-0.60% molybdenum, 0.022-0.10% titanium, 0.001-0.10% boron, 0.015-
0.10%
aluminum, balance iron, and incidental impurities; b. hot rolling the ingot or
slab to a desired
thickness; c. austenitizing the plate at 1650-1700 F; d. water quenching the
plate; and e.
tempering the plate at 350-450 F, wherein the surface hardness of the steel is
at least 440
HBW.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0006] Fig. 1 shows Jominy hardenability curves for laboratory melted
heats of abrasion,
resistant steel and a prior art steel;
[0007] Fig. 2A shows Charpy impact energies for longitudinal samples from
laboratory
produced plates of abrasion resistant steel; and
[0008] Fig. 2B shows Charpy impact energies for transverse samples from
laboratory
produced plates of abrasion resistant steel.
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= ,
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DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
100091 The abrasion resistant steel of the present invention consists
essentially of, in weight
Vo: 0:20-0.30% carbon, 0.40-1.25% manganese, 0.05% maximum phosphorous, 0.01%
maximum sulfur, 0.20-0.60% silicon, 0.50-1.70% chromium, 0.20-2.00% nickel,
0.07-0.60%
molybdenum, 0.022-0.10% titanium, 0.001-0.10% boron,0.027-0.10% aluminum,
balance iron,
and incidental impurities. It may more narrowly consist essentially of, in
weight %: 0.22-0.26%
carbon, 0.70-0.90% manganese, 0.025% maximum phosphorous, 0.003% maximum
sulfur,
0.20-0.40% silicon, 0.80-1.00% chromium, 0.40-0.60% nickel, 0.07-0.15%
molybdenum,
0.022-0.04% titanium, 0.001-0,003% boron,0.027-0.06% aluminum, balance iron,
and
incidental impurities. And nominally, the composition may consist essentially
of, in weight %:
0.24% carbon, 0.80% manganese, 0.010% maximum phosphorous, 0.003% maximum
sulfur,
0.25% silicon, 0.90% chromium, 0.50% nickel, 0.10% molybdenum, 0.03% titanium,
0.0015%
boron, 0.035% aluminum, balance iron, and incidental impurities.
[0010] The ranges for each alloying element have been chosen to
achieve the necessary
hardness and hardenability while maintaining good weldability. The lower limit
for each
alloying element is necessary to achieve the desired hardness and the upper
limit is necessary to
assure good weldability. In addition, Cr + Mn + Mo may equal 1.4% minimum
and/or Ni + Si +
Cr may equal 1.4% minimum, and/or Cr + Si may equal 1% minimum in order to
assure that
the necessary hardness and hardenability are achieved to provide good wear
resistance.
2a
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[0011] The steel may be melted and cast into ingots or slabs. During the
melting and casting,
the steel may be killed, desulfurized, vacuum degassed, and treated for
sulfide shape control
according to common methods known in the art. Desulfurization and/or sulfide
shape control
may be used to reduce the amount of large sulfide inclusions that can
contribute to a reduction in
toughness by acting as crack nucleation sites.
[0012] The steel may then be hot rolled into plate of 1 inch or less in
thickness. Cross-rolling
may be utilized to improve toughness in the transverse direction. The steel
plate may be held for
a minimum of 24 hours prior to heat treating to allow any hydrogen from the
melting and/or hot
rolling processes to outgas from the steel plate.
[0013] The steel plate may be austenitized at 1650-1700 F for a minimum of 30
minutes per
inch of thickness, water quenched, and then tempered at 350-450 F for a
minimum of 1 hour per
inch of thickness to form a microstructure of tempered martensite.
Austenitizing for times
exceeding 1 hour per inch of thickness may lead to grain growth and/or loss of
impact strength
and tempering times exceeding 2 hours per inch of thickness may lead to
detrimental surface
oxidation.
[0014] The resulting steel plate may have surface hardness of at least 440
HBW, a mid-
thickness hardness that is at least 90% of the surface hardness, longitudinal
yield strength of
1200 MPa or greater, longitudinal tensile strength of 1450 'MPa or greater,
and toughness in the
transverse direction at -60 F of at least 20 ft-lbs and at room temperature of
at least 40. ft-lbs.
The steel may further have surface hardness of 440-514 HBW.
[0015] Three heats (A, 13, C) of steel were melted in a 45-kg (100-1b) vacuum
induction
furnace. Each heat was top cast into iron molds to produce one ingot per heat
measuring
approximately 125 by 125 by 360 mm (5 x 5 x 14-inches). The three heats of
steel had
compositions as shown in Table 1 with heat C representing the inventive steel.
= Table!
Heat C Mn P S Cu Ni Cr Mo _ Si Ti
Al
A 0.23
0.79 0.009 0.004 0.10 0.50 0.89 0.10 0.26 0.021 0.024 0.0006 0.0062
0.23 0.71 0.008 0.004 0.10 0.51 0.90 0.10 0.25 0.020 0.012 0.0008 0.0055
0.24 0.79 0.007 0.004 0.11 0.51 0.90 0.10 0.26 0.022 0.027 0.0015 0.0078
Prior Art 0.22 0.90 0.65 1.65 0.23 0.25 0.025 0.025 0.0015
0.0080
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[0016] A 1-1/2-inch (37 mm) thick slice was sawcut from the bottom of each
ingot to provide
material for as-cast Jominy hardenability specimens. The slices were
normalized at 1650 F (900
C) and one standard ASTM A255 Jominy specimen was machined from each slice.
The Jominy
specimens were austenitized at 1650 F (900 C) and end-quenched. The Jominy
hardenability
curves for the three laboratory heats are presented in Fig. 1. Compared to
prior art abrasion
resistant steel, the inventive steel has higher initial hardness and less
hardenability as intended.
It can be seen that the three laboratory heats exhibit different degrees of
hardenability. This is
because heats A and B contain only 0.0006 and 0.0008 10B, respectively, as
compared to heat C
which has 0.0015 %B.
[0017] The balance of the ingots were conditioned, then reheated at 2250 F
(1230 C) in an
electric furnace with a protective nitrogen atmosphere. The ingots from heats
A and B were
rolled to 3/8 inch (9.6 mm) thick plates and the ingot from heat C was rolled
to a 3/4 inch
(19mm) thick plate.
[0018] The plates were then heat treated to simulate mill processing. They
were austenitized
at a temperature of 1650 F (900 C) for 30 minutes/inch of thickness followed
by water
quenching by agitating in cold water. The plates were then tempered at 400 F
(205 C) for 30
minutes/inch of thickness and air cooled.
[0019] Brinell hardness (HBW) measurements were made on both surfaces of the
three plates.
Round 0.350-inch (9 min) tensile specimens were machined from plate C in both
the longitudinal
and the transverse directions. Flat tensile specimens were machined from
plates A and B and
tested in the longitudinal direction. All tests were performed in duplicate.
[0020] Charpy V-notch specimens were machined in both the longitudinal and
transverse
, directions. For plates A and B, the thickness of the Charpy specimens was
7.5 mm, while full
size 10.0 mm specimens were machined from plate C. The Charpy transition
curves were
measured by testing triplicate specimens at r60, -40, 0,40, 72, and 212 F (51,
-40, 18, 4, 22,
and 100 C).
[0021] The hardness of the three plates is presented in Table 2. Hardness
values on opposite
surfaces of each plate were the same. Plates A and B failed to achieve the
targeted 440 HBW
minimum hardness. However, plate C, having the inventive composition, achieved
an average
hardness of 460 HBW, which is well above the desired value of 440 HBW minimum.
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Table 2
Plate Plate
Thickness Thickness Average
(mm) (in.) HBW Values HBW
Plate A 9.6 3/8 440, 440, 442 441
Plate B 9.6 3/8 .428,435, 438 434
Plate C 19 3/4 456, 460, 460, 460, 461,462 460
[0022] The tensile properties of the three plates are presented in Table 3.
Plates A and B
exhibited essentially the same tensile properties. The longitudinal yield
strength of plate C is the
same as the thinner plates at about 1210 MPa (176 ksi). However, consistent
with the higher
hardness of plate C, its tensile strength is about 100 MPa (15 ksi) higher.
The yield strength of
plate C is higher in the transverse orientation than the longitudinal
orientation while the tensile
strength in both directions is approximately the same. Although plates A and B
have higher
elongations than plate C which is expected based on their lower hardness, the
reduction of area
value of plate C is higher than plates A and B, indicating reasonable tensile
ductility for the
inventive steel.
Table 3
Yield Strength Tensile Strength Elongation
RA
Direction MPa ksi MPa ksi
Plate A L 1223 177.6 1496 217.2 15.7 43.0
Plate B L 1214 176.2 1488 216.0 16.3 41.3
Plate C L 1210 175.7 1584 229.9 8.7 45.0
Plate C T 1330 193.1 1600 232.2 9.3 54.3
[0023] The Charpy impact test results are presented in Table 4 and in Figs. 2A
and 2B. To
compare the thinner plate, A and B, values to the values for plate C, the
"Full-size Equivalent"
absorbed energy values were calculated as recommended by ASTM A370 by dividing
the
measured energies from the 7.5 mm thick specimens by 0.75. Both the raw data
and the "Full-
size Equivalent" values are presented in -Figure 2. Consistent with the high
hardness of the
steels, the Charpy specimens exhibit low percent shear at all test
temperatures. The full-size
equivalent data for the three plates have essentially the same values in the
longitudinal

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orientation as well as in the transverse orientation, although the transverse
absorbed energies are,
as expected, somewhat lower than the longitudinal.
[0024] Although the invention has been described in detail for the purpose of
illustration based
on what is currently considered to be the most practical and preferred
embodiments, it is to be
understood that such detail is solely for that purpose and that the invention
is not limited to the
disclosed embodiments, but, on the contrary, is intended to cover
modifications and equivalent
arrangements that are within the spirit and scope of the appended claims.
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Table 4
Temp. LIT Energy (ft.-lbs) Lat. Expansion (inches)
(T) 1 2 3 Avg. 1.000 2.000 3.000 Avg. Shear
60 L 19 21 21 20 0.015 0.015 0.015 0.015
20
-
T 17 18 19 18 0.013 0.014 0.015 0.014 20
L 22 24 26 24 0.016 0.017 0.012 0.015 20
-40 -
T 12 18 20 17 0.012 0.013 0.014 0.013 20
L 19 22 21 21 0.016 0.017 0.018 0.017 20
o - A T 18 19 19 19 0.014 0.015 0.015 0.015
20
40 L 26 27 28 27 0.014 0.016 0.017 0.016
20
T 20 21 22 21 0.015 0.016 0.018 0.016 20
72 L 27 30 31 29 0.025 0.032 0.033 0.030
20
T 20 22 22 21 0.017 0.020 0.020 0.019 20
212 L 31 32 32 32 0.021 0.022 0.022 0.022
T 22 22 22 22 0.011 0.012 0.012 0.012
60 L 20 23 23 22 0.016 0.016 0.017. 0.016
20
-
T 16 16 16 16 0.014 0.014 0.015 0.014 10
40 L 24 26 27 26 0.016 0.017 0.017 0.017
20
-
T 17 18 19 18 0.009 0.013 0.015 0.012 20
L 28 29 30 29 0.018 0.019 0.019 0.019 20
T 20 20 21 20 0.014 0.015 0.015 0.015 20
40 L 31 32 32 32 0.018 0.020 0.020 0.019
30
T 20 21 21 21 0.013 0.014 0.016 0.014 20
L 32 32 34 33 0.022 0.022 0.026 0.023 20
72 -
T 22 22 23 22 0.022 0.023 0.023 0.023 20
212 L 34 36 37 36 0.021 0.023 0.024 0.023
T 23 23 25 24 0.013 0.013 0.013 0.013
60 - L 29 31 31 30 0.018 0.019 0.021 0.019 30
-
T 20 21 22 21 0.014 0.015 0.017 0.015 20
40 - L 30 32 32 31 0.016 0.017 0.018. 0.017 30
-
T 22 23 23 23 0.011 0.015 0.016 0.014 20
0
L 33 35 35 34 0.014 0.016 0.018 0.016 20
-
T 24,25 26 25 0.014 0.014 0.016 0.015 20
40 L 37 37 37 37 0.016 0.016 0.013 0.015
30
T 25 26 26 26 0.015 0.016 0.020 0.017 20
72
L 36 38 40 38 0.017 0.020 0.022 0.020 20
-
T 25 26 27 26 0.017 0.017,,,0.020 0.018 20
212
L 42 42 43 42 0.016 0.016 0.018 0.017
-
T 27 28 29 28 0.012 0.014 0.014 0.013
7

Dessin représentatif