Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR PRODUCING CAST STEEL HAVING HIGH WEAR
RESISTANCE AND STEEL HAVING SAID CHARACTERISTICS
Field of application
The present invention relates to the field of wear-
resistant metallic materials, especially cast steels
resistant to wear by abrasion and impact for mining
applications. More particularly, the present invention
relates to a method for producing cast steel, by which
a wear-resistant steel is obtained, with predominantly
bainite microstructure and a suitable balance of
toughness and hardness for use thereof in mining
applications, such as grinding, crushing and all those
applications that require large components with high
resistance to wear by abrasion and impact. Even more
particularly, the present invention relates to a cast
steel of predominantly bainite structure, with a
suitable balance of toughness and hardness and
resistant to wear, to be used in the applications
mentioned above.
The technical problem
Various methods for producing steels for mining
applications are known in the prior art. However, the
useful life of the components obtained by these methods
is unable to meet production requirements. In
particular, the known methods do not provide steels
whose hardenability is sufficient to ensure high
hardness over the entire cross section of components of
large thickness made with this steel.
Solutions in the prior art
No methods have been identified for producing cast
steels that are able to provide an alloy with the
necessary hardenability and hardness for use thereof in
mining applications that require large components with
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high resistance to wear by abrasion and impact, such as
grinding and crushing; and with increased resistance to
wear by abrasion and impact, such as is provided by the
present invention.
In general terms, the cast steels that are usually
employed in the aforementioned mining applications may
be classified as: i) austenitic steels of the Hadfield
type; ii) low-alloy Cr-Mo steels with predominantly
pearlitic structure; and iii) low-alloy steels with low
to medium carbon content with predominantly martensitic
microstructure. None of these steels effectively solves
the aforementioned problems, as is explained in detail
hereunder.
The austenitic manganese steels of the Hadfield type,
such as those described in standard ASTM A128, are
produced by heat treatment for solution of carbides and
water quenching, obtaining a Brinell hardness in the
as-heat-treated condition of about 200 BHN. Moreover,
these cast steels possess a high capacity for hardening
by cold working, and may reach a hardness on the worked
surface of up to 450 BHN. Moreover, in view of the
increased toughness of these steels, they are mainly
used in coatings for ore crushing equipment.
However, when the mechanical stress is not sufficient
to produce high hardening by cold working, austenitic
manganese steels inevitably display low abrasive wear
resistance, greatly reducing the useful life of
components made with said steels.
For their part, low-alloy Cr-Mo steels with
predominantly pearlitic microstructure are made by a
normalizing and annealing heat treatment, reaching
Brinell hardnesses in the range 275-400 BHN. These
steels have been widely used as cladding for SAG mills
over the course of the last 30 years with acceptable
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results, without undergoing large modifications.
Despite the foregoing, owing to the global trend in the
mining industry to use ore processing equipment of
larger size, added to the ever-increasing mechanical
stress to which the components are subjected, the
"acceptable results" currently obtained with Cr-Mo
steels are inadequate. In view of this, the use of low-
alloy Cr-Mo steels with predominantly pearlitic
microstructure is limited, since it is not possible to
increase their wear resistance by increasing the
hardness, without having an adverse effect on
toughness. Consequently, the use of these alloys under
the current conditions inevitably increases the
probability of failure.
Finally, another type of steel commonly used in the
mining industry corresponds to the low-alloy steels
with low to medium carbon content with predominantly
martensitic microstructure. These steels are produced
by a heat treatment of hardening and annealing,
reaching Brinell hardnesses in the range 321-551 BHN,
depending on the specific carbon content of the alloy
and the conditions employed in heat treatment. At
present, these steels are widely used in cavities of
crushers, shovel teeth of earth-moving machinery,
discharge chutes and antiwear plates, all these
components having thicknesses typically of less than 8
inches (20.3 cm). However, since these steels do not
possess sufficient hardenability, it is not possible to
guarantee constant high hardness through the cross
section of the component, from the surface to the
center, for components with thicknesses above 6 inches
(15.2 cm). To solve the above problem, increasing the
content of carbon and of alloying elements has been
tried. However, it has been found that this route
causes a considerable decrease in toughness. Moreover,
low-alloy steels with low to medium carbon content
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require a greater cooling rate to obtain a martensitic
structure, usually employing water, oil or forced air
as the quenching medium. This not only gives rise to
higher costs of manufacture, but also hampers the
production of large components or those with complex
geometry with large changes of section.
Thus, although in the prior art there are methods for
producing steels for mining applications, the inventors
have not detected any disclosure of a method capable of
producing a cast steel of the composition and
microstructure specified in the present invention and
which in addition offers the aforementioned advantages.
As an example, document JP 2000 328180 of Tamura Akira
et al. relates to a wear-resistant cast steel of
predominantly martensitic microstructure, to be used in
components of mills used by the cement industry,
ceramic industry, etc. Both the chemical composition
and the microstructure of this steel are substantially
different from those of the steel obtained by the
method of the present invention. The steel described in
JP 2000 328180 has a chromium content preferably in the
range 3.8-4.3% w/w. Moreover, said document teaches
that a chromium content below 3.01 w/w adversely
affects the hardenability of the steel. In contrast,
the present invention describes steels with
predominantly bainite microstructure with chromium
concentrations in the range 2.3-3.2% w/w and with
adequate hardenability and hardness in large
components.
In addition, the steel described in document JP
2000 328180 does not disclose microadditions of
titanium and zirconium, as envisaged in the present
invention. This document also does not disclose
optional additions of niobium, boron and/or rare
earths.
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Moreover, document JP 09 170017 of IIHARA Katsuyuki et
al. relates to a rolled steel of high strength and
toughness that has a predominantly bainite
microstructure. However, both the chemical composition
of this steel and the method for producing it differ
from those disclosed for the steel obtained by the
method of the present invention. As an example, the
steel described in JP 09 170017 has a higher carbon
content and a lower content of silicon and manganese
than the steel of the invention. Moreover, it has
addition of vanadium for controlling grain size.
Although the bainitic steel of high strength and
toughness described in JP 09 170017 uses microalloying
elements to obtain a fine bainite microstructure, it
has a lower content of silicon and manganese to ensure
high toughness, and accordingly it does not develop
sufficient hardness, hardenability and wear resistance
for use in conditions of abrasion and severe impact in
mining operations.
US patent 7,662,247 of HU Kaihua discloses wear-
resistant cast steels with a predominantly martensitic
microstructure that includes films of austenite for
improving toughness, and the method for producing same.
For its part, US patent 3,973,951 of SATSUMABAYASHI
Kazuyoshi et al. discloses a cast steel of high wear
resistance and toughness for use as nails, tips, blades
or other tools for excavation in construction industry
machinery.
Although both documents disclose steels with increased
toughness, the high silicon concentration in these
steels (1.40-2.05% w/w) has an adverse effect on the
manufacture of components with large thickness, since
it promotes the occurrence of phenomena of hot crackTing
during solidification of the components.
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Additionally, patents US 5,382,307 of KAGEYAMA Hideaki
et al., US 5,676,772 of KOBAYASHI Kazutaka et al. and
US 6,254,696 of UEDA Masaharu et al. describe steels
used for making railway tracks with high strength and
toughness, resistant to contact fatigue, and that are
manufactured by a process of melting, hot rolling and
normalizing in forced air. These steels differ from the
steels of the present invention in that, although they
possess high toughness, they do not have a suitable
balance of chemical composition that allows them to
obtain a high hardness that is practically constant
through the cross section in components with large
thickness, despite the fact that high contents of
manganese, silicon and/or nickel are specified.
Finally, the steel obtained by the method of the
invention also differs from other bainitic steels, such
as the carbide-free steels described in US 2010/0294401
of Gonzalo Gomez et al. and US 5,879,474 of BHADESHIA
Harshad et al. In contrast to the steel of the
invention, the carbide-free bainitic steels of these
documents have contents of manganese, silicon and/or
aluminum above 1.50% w/w for promoting the presence of
bainite and inhibiting the precipitation of cementite,
and moreover have a microstructure with high contents
of retained austenite. This retained austenite could
optionally be transformed to martensite under the
action of events with severe impact, causing phenomena
of surface fatigue with large losses of material by a
mechanism of accelerated wear known as spalling.
The present invention provides a bainitic cast steel
that overcomes all the drawbacks mentioned above, since
it possesses suitable wear resistance and a suitable
balance between toughness and hardness, and is useful
in mining applications that require large components
with high resistance to wear by abrasion and impact,
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especially those associated with crushing and grinding.
Brief description of the invention
The method and the steel of the present invention provide a
solution to the limitations described above displayed by
conventional wear-resistant steels that are used at present and
do not provide a suitable balance between high hardness,
hardenability, toughness and wear resistance in components with
large thickness, typically up to 17 inches (43.18 cm).
The present invention overcomes these drawbacks with a method
for producing steel that provides a cast steel of
predominantly bainite structure with high hardness that is
practically constant through the cross section in components
with large thickness, which translates into high resistance to
wear by abrasion and impact, maintaining a suitable balance
between its hardness and toughness.
In one aspect, the present invention provides a method for
producing cast steel having high wear resistance, with
predominantly bainite microstructure and a suitable balance of
toughness and hardness for grinding mining applications,
crushing mining applications, or mining applications that
require large components with high resistance to wear by
abrasion and impact, wherein the chemical composition of steel
used, expressed in percentage by weight, comprises at least:
- 0.30-0.40% w/w C;
- 0.50-1.30% w/w Si;
- 0.60-1.40% w/w Mn;
- 2.30-3.20% w/w Cr;
- 0.00-1.00% w/w Ni;
- 0.25-0.70% w/w Mo;
- 0.00-0.50% w/w Cu;
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- 0.00-0.10% w/w Al;
- 0.00-0.10% w/w Ti;
- 0.00-0.10% w/w Zr;
- less than 0.050% w/w P;
- less than 0.050% w/w S;
- less than 0.030% w/w N;
- the remainder is iron;
where the method comprises:
a) completely melting the steel having the aforementioned
composition;
b) normalizing heat treatment at a temperature between 950
and 1050 C, for a time of between 3 and 10 hours; followed by
cooling from the normalizing temperature to a temperature
between 500 and 80 C, at a rate in the range from 0.05 to
0.5 C./s;
c) annealing heat treatment at a temperature in the range
from 450 to 630 C, for a time of between 3 and 10 hours.
In another aspect, the present invention provides cast steel
having high wear resistance, with predominantly bainite
microstructure and a suitable balance of toughness and hardness
for grinding mining applications, crushing mining applications,
or mining applications that require large components with high
resistance to wear by abrasion and impact, produced by the
method as described herein.
One of the aims of the present invention is to provide a cast
steel whose hardenability is sufficient to ensure high
hardness over the entire cross section of components with
large thickness or components of complex geometry with large
changes of section, used in mining applications that require
large components with high resistance to wear by abrasion and
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impact, such as grinding and crushing, thus increasing the
useful life of the components.
In another aspect, the present invention provides cast steel
having high wear resistance and a suitable balance of toughness
and hardness for grinding mining applications, crushing mining
applications, or mining applications that require large
components with high resistance to wear by abrasion and impact,
comprising at least:
- 0.30-0.40% w/w C;
- 0.50-1.30% w/w Si;
- 0.60-1.40% w/w Mn;
- 2.30-3.20% w/w Cr;
- 0.00-1.00% w/w Ni;
- 0.25-0.70% w/w Mo;
- 0.00-0.50% w/w Cu;
- 0.00-0.10% w/w Al;
- 0.00-0.10% w/w Ti;
- 0.00-0.10% w/w Zr;
- less than 0.050% w/w P;
- less than 0.050% w/w S;
- less than 0.030% w/w N; and
- the remainder is iron;
and in that said steel has a predominantly bainite structure.
Brief description of the figures
For the purpose of describing the method of the present
invention with greater clarity, a detailed description of the
invention is provided below, with examples of application, which
are illustrated in the accompanying figures, where:
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= Fig. 1 is a block diagram of an embodiment of the
present invention, where the solid lines represent
the main steps of the present invention.
= Fig. 2 illustrates the typical bainite
microstructure of the steel obtained by the method
of the present invention. Reagent Nital 5%, at
400X.
= Fig. 3 corresponds to a continuous cooling diagram
(CCT, abbreviation for continuous cooling
transformation) determined for one of the steels
described in the present invention.
= Fig. 4 is a curve describing the kinetics of
precipitation of particles of second phase of a
GS-35 CrMoV 10 4 steel.
= Fig. 5 is a
curve describing the kinetics of
precipitation of particles of second phase of one
of the steels described by the invention.
= Fig. 6 is the profile of Brinell hardness
evaluated from the surface to the center of
components made from a conventional pearlitic CrMo
steel and a steel described by the invention.
= Fig. 7 is a graph showing the thermal cycle of
normalizing and annealing according to a typical
application of the present invention.
Detailed description of the invention
One of the aims of the present invention is to provide
a method for producing bainitic cast steel having high
wear resisLance and exhibiting greater hardenability
than the steels known in the prior art.
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Another aim of the present invention is to provide a
method for producing steel with high hardness over the
entire cross section of components made therewith,
especially those of large size.
Another aim of the present invention is to provide a
bainitic cast steel having high wear resistance, with a
suitable balance of toughness and hardness.
Yet another aim of the present invention is to provide
a method for producing a cast steel with a suitable
balance between chemical composition, toughness and
hardenability; and a steel with said characteristics.
Another aim of the present invention is to provide
large steel components for mining applications, such as
crushing, grinding and all those applications that
require large components with high resistance to wear
by abrasion and impact, whose useful life is greater
than that of components of the prior art; and a method
for producing said steel.
The bainitic steel with increased toughness of the
present invention has the following chemical
composition:
= 0.30-0.40% w/w C
= 0.50-1.30% w/w Si
= 0.60-1.40% w/w Mn
= 2.30-3.20% w/w Cr, more preferably 2.40-3.0% w/w
Cr
= 0.0-1.00% w/w Ni
= 0.25-0.70% w/w Mo
= 0.0-0.50% w/w Cu
= 0.0-0.10% w/w Al
= 0.0-0.10% w/w Ti
= 0.0-0.10% w/w Zr
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= Less than 0.050% w/w P
= Less than 0.050% w/w S
= Less than 0.030% w/w N
= Optionally less than 0.050% w/w Nb
= Optionally 0.0005-0.005% w/w B
= Optionally 0.015-0.080% w/w rare earths
= Residual contents of W, V, Sn, Sb, Pb and Zn less
than 0.020% w/w and the balance iron.
Unless stated otherwise, the concept "Rare earths"
preferably refers herein to commercial mixtures of
cerium and lanthanum.
Some of the basic criteria considered for limiting the
chemical composition In the range described by the
present invention were as follows:
= The carbon content is essential for determining
the hardness of steel. Carbon contents under 0.30%
w/w are insufficient to obtain hardening by solid
solution, high hardenability and hardening by
precipitation of complex carbides or carbonitrides
that guarantee practically constant hardness in
large components and high wear resistance; whereas
carbon contents above 0.40% w/w have an adverse
effect on impact toughness in bainitic-martensitic
steels.
= Silicon increases the strength of steel by solid
solution hardening of the ferritic matrix of the
bainite structures and delays the precipitation of
carbides, so that it prevents abrupt decrease of
hardness during annealing. However, silicon
contents above 1.30% w/w have an adverse effect on
the manufacture of components with large
thickness, promoting the occurrence of phenomena
of hot cracking.
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= Manganese causes a moderate increase in
hardenability of steel and refines bainite
structures. However, at contents above 1.40% w/w
it displays pronounced interdendritic chemical
segregation, especially in large components.
= Chromium is an important element that provides
strength, hardenability and hardening by
precipitation of alloyed carbides of the M7C3 and
M23C6 type. The inventors concluded that the range
previously defined for chromium will produce a
suitable balance of hardness, hardenability and
distribution of chromium-rich alloyed carbides
that ensure high wear resistance.
= Molybdenum is an important element that provides
strength, high hardenability and hardening by
precipitation of carbides of the M6C type and
carbonitrides of the M(C,N) and M2(C,N) type.
Moreover, it greatly reduces the harmful effect of
impurities that may segregate at grain boundaries,
causing embrittlement. For this reason a minimum
molybdenum content of 0.25% w/w is stipulated.
However, in view of its high cost, it is desirable
to limit its content to a maximum of 0.70% w/w.
= Nickel increases the cohesion energy of the grain
boundary, promotes the presence of bainite
structures to the detriment of pearlite and has a
synergistic effect on additions of manganese and
molybdenum. However, it also has a high cost and
its addition must be limited.
= Apart from having a deoxidizing effect, additions
of titanium and zirconium allow nitrogen to be
fixed in solid solution, control the grain size
and provide hardening by precipitation of
carbonitrides of the M(C,N) type. For its part,
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zirconium modifies the morphology of sulfide inclusions.
= Additions of rare earths, specifically mixtures of
cerium and lanthanum, have an important effect on
refinement of casting microstructure and on modification
of the morphology of sulfide inclusions in steel.
Moreover, they increase resistance to surface fatigue.
= Additions of boron greatly increase hardenability and
refine the acicular phases (bainite and martensite).
However, they may have an embrittlement effect when
combined with nitrogen and form insoluble precipitates
of BN at grain boundaries. Accordingly, the amount to be
added and the sequence must be controlled in the ranges
defined above.
= It has been found that the appropriate use of
multicomponent master alloys that contain boron,
titanium, zirconium, rare earths and particular mixtures
thereof, together with controlled addition of these
elements, ostensibly improves the properties of cast
steels having high wear resistance for the mining
applications described in this invention.
As illustrated in Figure 1, the method of production of the
present invention provides a bainitic steel with the chemical
composition detailed above that comprises the following steps:
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1. Melting: can be carried out by any conventional method.
For example, this operation can be performed in an arc
furnace with basic or acidic refractory, or in an
induction furnace.
Melting in an arc furnace, as a normal operation
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comprises complete melting of the charge, followed
by blowing oxygen in, to produce oxidation of the
liquid metal, transfer of impurities to the slag
and decarburization of the metal to remove the
nitrogen and hydrogen in solution. Then the
operation of blocking of the liquid metal is
carried out to stop oxidation, followed by the
operation of refining and adjustment of the
chemical composition to the specified range. Next,
an operation of deoxidation is carried out using
aluminum and master alloys of titanium and/or
zirconium. Deoxidizing elements will be added in
suitable amounts so that the residual contents of
aluminum, titanium or zirconium are within the
specified range for the alloy. If addition of
boron and/or treatment with rare earths is
required, this is performed in the ladle.
For its part, melting in an induction furnace as a
normal operation comprises complete melting of the
metal charge up to a temperature not above 1700 C,
followed by adjustment of the chemical
composition; followed by addition of master alloy
of an element that is a strong nitride former -
preferably titanium - to form a slag with a high
capacity for nitrogen. Then the slag formed is
removed and next the operation of deoxidation and
discharge of the metal into a ladle is carried
out.
2. Heat treatment: the normal operation of heat
treatment applied to noncritical components
comprises normalizing and annealing.
Normalizing is performed at a temperature in the
range from 950 to 1050 C, for a holding time of
between 3 and 10 hours depending on the
characteristic thickness and geometry of the
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components to be produced. Then the components are
submitted to a cooling step from the normalizing
temperature to a temperature in the range from 500
to 80 C, more preferably between 500 and 150 C.
Cooling may be carried out either in still air or
direct or indirect forced air, or a combination of
both types of cooling, whenever the cooling rates
of the center and surface of the component are
within the range 0.050-0.50 C/s, so as to ensure
optimal phase distribution.
Immediately following normalizing, an annealing
heat treatment is carried out at a temperature in
the range 450-630 C, for a time of between 3 and
10 hours depending on the geometry of the
component and the range of hardness that is to be
reached. The annealing heat treatment has the aim
of achieving maximum possible transformation of
the austenite, annealing the acicular phases
formed and producing secondary hardening by
precipitation of alloyed carbides predominantly
rich in molybdenum.
As has been mentioned, the cast steel of predominantly
bainite structure (like that shown in Fig. 2) that is
obtained by the method of the present invention, and
that comprises the chemical composition detailed above,
has a number of advantages over other steels of the
prior art. One of these advantages is the high hardness
of the steel obtained, which is attained, among other
factors, owing to the absence of phenomena of
enlargement and coalescence of precipitates during a
normal annealing cycle, as shown in Fig. 5.
In contrast, it can be seen from Fig. 4 that the steels
of the prior art, such as CrMoV, usually exhibit an
abrupt decrease in hardness, which could promote the
occurrence of phenomena of embritt1ement during
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annealing. In particular, this figure illustrates the
kinetics of precipitation of particles of second phase
of a GS-35 CrMoV 10 4 steel, according to standard DIN
17205, which specifies hardened and annealed cast
steels for general applications. Although this steel
has a chemical composition somewhat similar to that of
the present invention, it displays rapid enlargement
and coalescence of cementite and carbonitrides of the
M2(C,N) type, affecting its hardness.
Another advantage of the present invention is that the
increased hardness is constant through the cross
section of a component of large thickness, which is not
achieved with steels of the prior art, as can be seen
in Fig. 6.
In accordance with the foregoing, the cast steel
obtained by the method of the present invention
exhibits a suitable balance of chemical composition,
toughness and hardenability to ensure complete
hardening in castings of large size, typically up to 17
inches (43.18 cm) in thickness, with Brinell hardness
preferably in the range 385-495 BHN throughout the
cross section of the component and excellent resistance
to wear by abrasion and impact.
Embodiment examples
Various tests of the method of the present invention
were carried out, using chemical compositions within
the ranges that are disclosed here.
In the following, a conventional Cr-Mo pearlitic steel,
widely used in coatings for SAG mills, is compared
against five examples of steels obtained by the method
of the present invention.
The tests were performed in the operating conditions
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presented in Tables 1 and 2. Table 3 shows the chemical
compositions used in each case, expressed in % w/w.
Finally, Table 4 shows the phase distribution and
hardnesses obtained in the heat treatment conditions
applied, whose cooling rate corresponds to that
typically encountered in components of large thickness.
Fig. 7 shows a diagram of the thermal cycle used in
this example, where segment (a) describes the step of
heating the components to the normalizing temperature.
Segment (b) shows a holding time at the normalizing
temperature for 4 hours. For its part, segment (c)
represents the step of cooling in air from normalizing
to a temperature of 200 C, at an average cooling rate
as indicated in Table 2. Segment (e) shows a holding
time at the annealing temperature of 5 hours.
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0
2
,,
g;
r8 Table 1: Operational data of the step of
melting and casting
Parameter CrMo pearlitic
Example 1, Example 2, Example 3, Example 4, Example 5,
steel Invention
Invention Invention Invention Invention
Type of melting
induction induction induction
arc furnace arc furnace
arc furnace
furnace
furnace furnace furnace
Casting
1520 C 1530 C 1530 C
1530 C 1530 C 1530 C
temperature
Table 2: Operational data of the thermal cycle applied
5
_______________________________________________________________________________
___________________________________
CrMo pearlitic Example 1, Example 2, Example 3, Example 4, Example 5,
Parameter
steel Invention Invention
Invention Invention Invention
Normalizing temperature 950 C 970 C 970 C
970 C 970 C 970 C
_
Holding time 4 h 4 h
4 h 4 h 4 h 4 h
Average cooling rate 0.10 C/s 0.10 C/s 0.10
C/s 0.10 C/s 0.10 C/s 0.10 C/s
_
Annealing temperature 570 C 570 C 570 C
570 C 570 C 570 C
_
_______________________________________________________________________________
___________________________________________
Annealing time 5 h 5 h
5 h 5 h 5 h 5 h
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0
2
m
m
m
to
m
m
N,
. Table 3: Chemical composition of steels
expressed in % w/w
N,
m
CrMo pearlitic Example 1,
Example 2, Example 3, Example 4, Example 5,
Element
steel Invention
Invention Invention Invention Invention
C 0.60 0.36 0.35
0.38 0.34 0.33
Si 0.70 0.90 1.0
0.80 1.0 1.0
Mn 0.90 1.20 0.85
1.10 1.30 1.20
Cr 2.20 2.70 2.50
2.80 2.60 3.0
Ni 0.0 0.40 0.30
0.30 0.0 0.30
Mo 0.40 0.50 0.45
0.55 0.40 0.45
Cu 0.10 0.0 0.10
0.10 0.0 0.0
Al 0.035 0.02 0.015
0.015 0.020 0.015 __
Ti 0.0 0.030 0.020
0.020 0.030 0.0
Zr 0.02 0.010 0.025
0.020 0.015 0.035
Nb 0.0 0.0 0.0
0.020 0.015 0.020
N 0.011 0.010 0.012
0.013 0.010 0.012
B 0.0 0.0 0.0010
0.0010 0.0010 0.0
WO 2014/022944 - 19 -
PCT/C1L2013/000047
to
r8 Table 4: Microstructure and Brinell hardness developed by the
method of the present invention
Resultant microstructure
Alloy
Brinell hardness
% pearlite % bainite
% martensite
CrMo pearlitic steel 67.6 32.4
349
Example 1, Invention 3.60 83.20
13.70 476
Example 2, Invention 5.60 86.60
5.70 466
Example 3, Invention 3.10 77.40
19.20 491
Example 4, Invention 3.0 67.60
29.10 468
Example 5, Invention 4.2 84.5
11.2 468
CA 02886286 2015-03-26 2014/022944 - 20 -
PCT/0L2013/000047
As can be seen, in all cases the method of the present
invention provides a cast steel with predominantly
bainite structure and with higher Brinell hardness.
As can be seen in Fig. 6, the profile of Brinell
hardness evaluated from the surface of the component
toward its interior, to a depth of 13 inches (33.0 cm),
remains practically constant. In contrast, the Cr-Mo
pearlitic steel shows a considerable decrease in
hardness through its cross section.
The foregoing description deals with the aims and
advantages of the present invention. It must be
understood that various embodiments of this invention
may be implemented and that all the subject matter
disclosed here must be interpreted as being for
purposes of illustration and is not limiting in any
way.
