U.S. patent application number 14/428336 was filed with the patent office on 2015-09-03 for method for manufacturing steel casts.
This patent application is currently assigned to F.A.R. - FONDERIE ACCIAIERIE ROIALE - SPA. The applicant listed for this patent is F.A.R. - FONDERIE ACCIAIERIE ROIALE - SPA. Invention is credited to Alberto Andreussi, Primo Andreussi, Eddy Pontelli, Enrico Veneroso.
Application Number | 20150246391 14/428336 |
Document ID | / |
Family ID | 47138118 |
Filed Date | 2015-09-03 |
United States Patent
Application |
20150246391 |
Kind Code |
A1 |
Andreussi; Alberto ; et
al. |
September 3, 2015 |
Method for Manufacturing Steel Casts
Abstract
A method for manufacturing steel casts (110), in particular but
not exclusively manganese steel, intended to obtain a wear element,
comprises at least a step (15) of making at least a reinforcement
insert (115), a step (11) of preparing a mold (111) for the cast
(110) to be manufactured, in which the reinforcement insert (115)
is positioned, and a subsequent step (12) of casting the steel
inside the mold. The reinforcement insert (115) is made by
compacting in a desired geometric shape, by means of selective
melting techniques, of an amorphous mass of hardening powder (118)
obtained by mixing powders of pure elements, or of compounds that
form carbides and/or micro-structures of great hardness.
Inventors: |
Andreussi; Alberto;
(Tricesimo, IT) ; Andreussi; Primo; (Reana del
Rojale, IT) ; Pontelli; Eddy; (Tricesimo, IT)
; Veneroso; Enrico; (Udine, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
F.A.R. - FONDERIE ACCIAIERIE ROIALE - SPA |
Reana Del Rojale |
|
IT |
|
|
Assignee: |
F.A.R. - FONDERIE ACCIAIERIE ROIALE
- SPA
Reana Del Rojale
IT
|
Family ID: |
47138118 |
Appl. No.: |
14/428336 |
Filed: |
September 4, 2013 |
PCT Filed: |
September 4, 2013 |
PCT NO: |
PCT/IB2013/001904 |
371 Date: |
March 13, 2015 |
Current U.S.
Class: |
419/5 |
Current CPC
Class: |
C22C 38/24 20130101;
B22D 19/02 20130101; B22F 3/1055 20130101; C22C 33/003 20130101;
Y02P 10/25 20151101; C22C 38/36 20130101; B22D 19/0081 20130101;
C22C 45/02 20130101; B22F 7/08 20130101; C22C 38/22 20130101; C22C
38/32 20130101 |
International
Class: |
B22D 19/02 20060101
B22D019/02; B22F 3/105 20060101 B22F003/105; B22D 19/00 20060101
B22D019/00; B22F 7/08 20060101 B22F007/08 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2012 |
IT |
UD2012A000159 |
Claims
1. Method for manufacturing steel casts, in particular but not
exclusively manganese steel, intended to obtain a wear element,
comprising at least a step of making at least a reinforcement
insert, a step of preparing a mold for the cast to be manufactured,
in which the reinforcement insert is positioned, and a subsequent
step of casting the steel inside said mold, wherein said at least
one reinforcement insert is made by compacting in a desired
geometric shape, by means of sintering techniques with a selective
and localized melting of the EBM (Electron Beam Melting) type, or
SLM (Selective Laser Melting), or other similar or comparable
techniques, an amorphous mass of hardening powder obtained by
mixing powders of pure elements, or of compounds that form carbides
and/or micro-structures of great hardness which due to the effect
of the melting generate carbides and/or micro-structures of great
hardness.
2. Method as in claim 1, wherein said step of preparing the mold
provides a sub-step of precise positioning, inside said mold, of at
least one reinforcement insert having anchoring means obtained in a
single piece with the reinforcement insert during said
manufacturing step, said anchoring means being able to allow a
desired stable positioning of said reinforcement insert inside said
mold.
3. Method as in claim 1, wherein during the step of making the
reinforcement insert, through or blind or reciprocally intersecting
channels are made, in order to promote the anchorage of said
reinforcement insert to the steel cast during said casting
step.
4. Method as in claim 1, characterized in that wherein said
sintering techniques with a selective and localized melting melt
said powders of pure elements, or of compounds that form carbides
and/or micro-structures of great hardness present inside said
hardening powderer, said melting triggering chemical reactions to
generate carbides and/or micro-structures of great hardness
uniformly and homogeneously distributed inside said reinforcement
insert and defining a homogeneous micro-structure of said
reinforcement insert.
5. Steel cast, in order to obtain a wear element, manufactured
according to a method as in claim 1, having overall a heterogeneous
micro-structure and hardness, said micro-structure and said
hardness being defined by at least a reinforcement insert
integrated into said steel cast during the casting of the steel
into a mold, wherein said reinforcement insert is obtained with
sintering techniques with a selective and localized melting
according to one or another of the techniques EBM (Electron Beam
Molding), or SLM (Selective Laser Melting), or other similar or
comparable techniques, and has a homogeneous micro-structure
comprising carbides and/or structures of great hardness.
Description
FIELD OF THE INVENTION
[0001] The present invention concerns a method for manufacturing
steel casts, advantageously but not exclusively of manganese steel,
used to obtain wear elements, and casts thus manufactured.
[0002] The wear elements are usable in all the applications where a
high resistance to wear is required, even under impulsive loads,
such as crushers, mills, grinding members, turbo-machine components
or earth moving machines.
BACKGROUND OF THE INVENTION
[0003] It is known to manufacture, by casting, steel casts to
obtain wear elements, used in a plurality of applications which
require great resistance both to abrasion and to knocks. For
example, such steels are used to make components for mills,
crushers or safes, components for excavators or tracked means or
turbo-machines etc.
[0004] In a preferential formulation the steels in question contain
up to 1.5% carbon and up to 20% manganese, and have an austenitic
structure that allows to combine great hardness with considerable
toughness. These steels also have a good tendency for
work-hardening and great ductility.
[0005] It is known to add elements that form complex carbides to
these steels, in order to form manganese steel alloys that are more
resistant to wear. Among these components the most commonly used is
chromium which, as well as raising the yield point, induces the
formation of chromium carbide in the austenitic matrix.
[0006] However, chromium carbides have the tendency to precipitate
to the grain edge, making the structure fragile and reducing the
toughness of the steel. A heat treatment is therefore necessary,
typically a solubilization annealing followed by water quenching,
which is carried out after the cooling of the steel has been
completed. The annealing and subsequent rapid cooling allow to make
the carbides migrate from the grain edge to the austenitic
matrix.
[0007] For high chromium contents, annealing does not allow to
obtain a complete solubilization of the carbides, and therefore it
is intended to modify the form of the latter, so as to make them
globular and therefore less inclined to form cracks. Furthermore,
another function of annealing and quenching is to distribute the
carbides present at the grain edge uniformly around the austenitic
grain.
[0008] Although these known steels are the best for resistance to
wear with regard to materials to be ground having considerable
toughness and abrasiveness, they also have the disadvantage that
they have low heat-conductivity. Indeed, this has limited their use
to thicknesses of not more than about 100 mm, because in products
of greater thicknesses the water quenching process entails the
creation of internal tensions such as to cause cracks. In this way,
if such thicknesses are obtained with steels containing manganese
comprised between 12% and 20%, the properties of toughness that are
typical of such steels are compromised.
[0009] It is also known that this limitation in the thicknesses can
be overcome by introducing elements, such as for example titanium,
able to give origin to hard compounds already in the liquid phase
of the alloy. The hard compounds are rarely located at the grain
edge, but remain uniformly distributed in the austenitic matrix,
even after the solubilization treatment. The steel alloys that are
obtained are therefore more resistant to abrasion and wear compared
with steels containing chromium and without titanium, especially in
the case of considerable thicknesses and particularly onerous
conditions of use.
[0010] One disadvantage of steels containing titanium is that they
confer greater resistance to wear on the whole section of an
article, even though it is necessary to have a particular
resistance only in those parts that are most stressed. This makes
the article less workable and causes a considerable increase in the
costs of working, due to the removal of chip.
[0011] Another disadvantage connected to the use of titanium and
the manufacture of an article having uniformly optimum
characteristics lies in the cost of said article, which is very
high.
[0012] Methods are known, from GB-A-2098112 and GB-A-2003932, for
manufacturing wear elements reinforced by high-resistance inserts
having a heterogeneous structure defined by sintered particles in a
metal matrix. The above methods provide to make the inserts by
uniting carbides, for example tungsten or titanium carbides, in the
form of powders or granules, to metal matrixes containing alloys of
iron or cobalt using sintering techniques carried out at
temperatures above the melting temperature of the alloys.
[0013] The melting of the alloys causes the carbides to be
incorporated into the metal matrixes and possibly the sizes of the
carbides to be reduced. Afterward, the inserts thus made are
introduced into a mold and incorporated into the metal alloy that
is cast onto them.
[0014] EP-B1-0554682 describes a method for manufacturing an
element subject to wear in which one or more planar inserts,
conformed as plates, sheets or discs, are obtained by incorporating
powders of materials with high resistance to wear, in particular
carbides, for example tungsten carbides, in a metal matrix. The
reinforcement inserts described in EP-B 1-0554682 can also include
organic binders, plasticizers and hardening agents. The planar
insert is subjected to high-temperature vacuum sintering and is
then attached to a sand mold by means of pins or other anchoring
elements made of the same material.
[0015] In the three documents cited above, sintering is carried out
essentially at temperatures that come within the range of the
melting temperature of the metal matrix, and lower than the melting
temperatures of the carbides. In these documents, the purpose of
sintering is essentially to determine an interface contact, or
uniformly distributed, between the carbides and the matrix, in
order to obtain reinforcement inserts consisting of a conglomerate
of carbides immersed in the metal matrix.
[0016] The original carbides remain substantially unchanged, except
for possible variations in size.
[0017] DE-A1-4214524 describes a method for manufacturing a
wear-resistant cast that provides to insert into the mold, before
casting, a reinforcement insert made with balls of hard material,
in particular carbides, housed in seatings made in holed sheets of
steel and held in position by the same holed sheets of steel.
[0018] WO-A1-2012/004654 describes a method for manufacturing
elements subject to wear which provides to make reinforcement
inserts to be incorporated in casts of melted steel. The
reinforcement inserts comprise a porous support, like a sponge,
impregnated with a liquid mixture consisting of a binder and metal
powders containing hard elements, in particular carbides.
[0019] The use of sintering techniques as described in
GB-A-2098112, GB-A-2003932 and EP-B1-0554682 has the disadvantage
that they need long working times, enormous energy consumption and
a consequent increase in the costs of manufacturing the final cast.
This is due to the fact that, to make the inserts with these known
techniques, preliminary operations are needed to prepare a mixture,
or "green", to be sintered, and molds, in which the mixture is
subjected to sintering.
[0020] Another disadvantage of these known methods is that they are
not very flexible in terms of possible shapes of the inserts
obtainable, since the shapes are limited to planar objects or with
a simple conformation, also because of the molds as described
above.
[0021] One disadvantage of all the known methods indicated above is
connected to the micro-structural heterogeneity of the
reinforcement inserts, and consists in the consequent discontinuity
of the physical and mechanical properties, the distribution of
which is not uniform.
[0022] Purpose of the present invention is to perfect a method that
allows to obtain, by casting, casts of steel alloys, advantageously
but not exclusively manganese steel, having throughout the
toughness of manganese steel and, in localized zones, the hardness
needed to resist stresses of wear and abrasion. In particular, the
invention obtains steel casts that, throughout the localized zones,
have a homogeneous micro-structure and a uniform distribution of
the mechanical characteristics.
[0023] The Applicant has devised, tested and embodied the present
invention to overcome the shortcomings of the state of the art and
to obtain these and other purposes and advantages.
SUMMARY OF THE INVENTION
[0024] The present invention is set forth and characterized in the
independent claims, while the dependent claims describe other
characteristics of the invention or variants to the main inventive
idea.
[0025] In accordance with the above purpose, a method according to
the present invention is used for manufacturing steel casts, in
particular but not exclusively for manufacturing manganese steel
casts intended to obtain wear elements.
[0026] The method comprises at least a step of making at least a
reinforcement insert, a step of preparing a mold for the cast to be
manufactured, and a subsequent step of casting the steel inside the
mold.
[0027] According to one feature of the present invention, the
reinforcement insert is made by compacting an amorphous mass of
hardening powder in a desired geometric shape. The compacting is
obtained by means of sintering techniques with a selective and
localized melting comprising one or another of the techniques
identified as EBM (Electron Beam Melting), SLM (Selective Laser
Melting), or other similar or comparable techniques. The amorphous
mass of hardening powder is obtained by mixing powders of pure
elements, or of compounds that form carbides and/or
micro-structures of great hardness, which due to the effect of the
melting generate carbides and/or micro-structures of great
hardness.
[0028] These techniques have the advantage that they allow to form
almost any geometric shape, developed in three dimensions according
to specific requirements.
[0029] The techniques described above allow to obtain complex
shapes with variable geometries, starting directly from the
amorphous mass of powder, because they are techniques of the
adaptive type and obtain localized melting of the powder only in
the zones affected by a high energy beam.
[0030] Thanks to the high energy intensity and the compacting to
which the hardening powder is subjected, they also allow to obtain
reinforcement inserts that are substantially without residual
porosity and tensions.
[0031] Making reinforcement inserts with EBM or SLM techniques or
similar also has the other advantage of obtaining a rapid and
accurate process, and also allows to obtain reinforcement inserts
starting from powders of high-melting materials, for example
tungsten, titanium, molybdenum, advantageously usable pure or
alloyed in iron alloys, which, after the chemical reactions that
are triggered due to the effect of the type of melting, give rise
to carbides or other hard micro-structures.
[0032] The method according to the present invention provides that
the mold preparation step comprises a sub-step of positioning at
least one reinforcement insert inside the mold. In order to allow a
desired stable positioning of the reinforcement insert inside the
mold, when the reinforcement insert is made, at least one appendix
is also made in a piece therewith, with the function of anchoring
the reinforcement insert to the mold.
[0033] According to a variant of the present invention, during the
making of the reinforcement insert, through or blind or
reciprocally intersecting channels are made, to promote the
anchoring of the reinforcement insert to the steel cast during the
casting step.
[0034] According to another feature of the invention, the sintering
techniques melt the powders of pure elements, or compounds that
form carbides and/or micro-structures of great hardness, triggering
chemical reactions to generate carbides and/or micro-structures of
great hardness, uniformly and homogeneously distributed inside the
reinforcement insert and defining a homogeneous micro-structure of
the latter.
[0035] The carbides make the reinforcement insert uniformly hard
and resistant to wear, and suitable to confer these properties
throughout the volume of the zones of the cast into which it is
inserted.
[0036] The present invention also concerns a steel cast, in order
to obtain a wear element, manufactured according to the method
described above. The cast has overall a heterogeneous
micro-structure and hardness, defined by at least one reinforcement
insert integrated into the steel cast during the casting of the
steel in a mold.
[0037] According to a characteristic feature of the cast, the
reinforcement insert has a homogeneous micro-structure comprising
carbides and/or structures of great hardness, and is obtained with
sintering techniques with a selective and localized melting
comprising one or the other of the following techniques: EBM
(Electron Beam Molding), SLM (Selective Laser Melting), or other
similar or comparable techniques.
[0038] The cast can comprise simple or mixed carbides, or complex
aggregations of carbides. The carbides confer, uniformly in the
zones where the insert is applied, hardness and resistance to wear
on the cast that incorporates it, and consequently on the wear
element that is made from it.
[0039] During the casting step, the reinforcement insert is partly
melted, which advantageously allows an intimate welding with the
cast steel, to confer on the cast obtained a homogeneous
macro-structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] These and other characteristics of the present invention
will become apparent from the following description of a
preferential form of embodiment, given as a non-restrictive example
with reference to the attached drawings wherein:
[0041] FIG. 1 is a schematic representation of one form of
embodiment of a method according to the present invention;
[0042] FIG. 2 is a variant of a detail of FIG. 1;
[0043] FIG. 3 shows schematically a cast according to the present
invention.
DETAILED DESCRIPTION OF ONE FORM OF EMBODIMENT
[0044] With reference to FIG. 1, a method 10 for manufacturing
steel casts 110, advantageously but not exclusively manganese
steel, according to the present invention, allows to obtain casts
110 having a heterogeneous micro-structure.
[0045] The method 10 provides that in a preparation step 11 a mold
11 is made for every cast 110, that in a subsequent casting step 12
molten manganese steel is cast inside the mold 111 and that in a
standby step the cast 110 solidifies.
[0046] During the preparation step 11, a plurality of perimeter
walls 112 are made, in this case for example with olivine sand and
binder additives, which delimit an internal cavity 113. An upper
opening 114 puts the internal cavity 113 in communication with the
outside of the mold 111 and allows the molten steel to enter into
the internal cavity 113 during the casting step 12.
[0047] The preparation step 11 comprises a sub-step 14 of
positioning at least one reinforcement insert 115 inside the
internal cavity 113 of the mold 111.
[0048] A step 15 of making the reinforcement insert 115 (FIG. 1) is
performed prior to the step 11 of preparing the mold 111, and
provides that the reinforcement insert 115 is made by sintering a
hardening powder 118.
[0049] Sintering provides an initial compacting of the hardening
powder 118, which is then at least partly melted using high density
energy, and subsequently re-solidified.
[0050] The hardening powder 118 is for example iron-based and also
contains compounds containing chromium and/or titanium, or other
elements similar to carbon, which, melting due to the high energy,
can obtain alloys with simple or mixed carbides, or complex
aggregations of carbides and/or micro-structures of great
hardness.
[0051] The hardening powder 118 can be defined, for example, by a
mixture of powders of pure elements, such as for example carbon,
tungsten, chromium, iron, or powders of iron alloys containing said
elements and others, such as for example titanium, molybdenum,
boron or vanadium.
[0052] A first formulation of the present invention provides that,
as well as iron-based powder, the hardening powder 118 comprises
the following components:
[0053] carbon in a percentage comprised between 2.5% and 3.5%;
[0054] chromium in a percentage comprised between 20% and 30%;
[0055] to which can be added, depending on the other
characteristics to be obtained, the following optional
components:
[0056] molybdenum in a percentage comprised between 0.1% and
1%;
[0057] tungsten in a percentage comprised between 0.1% and
0.5%.
[0058] A second formulation of the present invention provides that,
as well as iron-based powder, the hardening powder 118 comprises
the following components:
[0059] carbon in a percentage comprised between 0.5% and 1.0%;
[0060] chromium in a percentage comprised between 10% and 15%; to
which can be added the following optional components:
[0061] molybdenum in a percentage comprised between 0.1% and
1%;
[0062] vanadium in a percentage comprised between 0.2% and
1.5%;
[0063] boron in a percentage comprised between 0.001% and
0.015%.
[0064] According to a third formulation of the present invention,
as well as iron-based powder, the hardening powder 118 comprises
the following components:
[0065] carbon in a percentage comprised between 0.3% and 0.5%;
[0066] chromium in a percentage comprised between 4% and 5%;
[0067] molybdenum in a percentage comprised between 0.5% and
1.5%.
[0068] Other formulations of the mixtures can be obtained as simple
applications of the base lines indicated above.
[0069] The formulation of the hardening powder 118 can be
established, according to specific requirements, by selecting on
each occasion the powders of elements and/or compounds to be used,
based on the carbides and/or micro-structures of great hardness
that are to be obtained for the reinforcement insert 115.
[0070] The hardening powder 118 is treated in a sintering machine,
in which the structure and geometric shape of the reinforcement
insert 115 are defined, starting from the hardening powder 118.
[0071] To this purpose, sintering techniques with a selective and
localized melting, such as for example EBM (Electron Beam Melting),
or SLM (Selective Laser Melting), but also other techniques of the
additive type, or other techniques similar or comparable to these,
may be used.
[0072] Hereafter in the description, by way of example, we shall
refer to EBM and SLM techniques, however the following
considerations shall also apply to other similar techniques.
[0073] EBM or SLM techniques allow to obtain the desired
reinforcement insert 115 with hardening powder 118, by the
localized melting of specific areas of the latter, which is
initially in the form of a mass of amorphous powder.
[0074] The high energy density reached with EBM or SLM techniques
allows to melt and then sinter powders of high-melting materials,
such as for example titanium, tungsten and molybdenum as above.
[0075] Following melting, the elements or compounds that make up
the hardening powder 118 join together to make alloys. The
compounds made due to the melting are the result of chemical
reactions triggered by the high energy administered locally and
which follow the laws of aggregation according to Gibbs' free
energy. These compounds are essentially hard and made up of
aggregations of carbides, simple or mixed, and/or micro-structures
of great hardness, for example martensitic.
[0076] Since the EBM or SLM techniques allow to obtain carbides as
indicated above, it is not necessary--and indeed it may even be
disadvantageous--to use a hardening powder 118 containing already
formed carbides.
[0077] The primary function of sintering by means of EBM or SLM is
therefore to determine the micro-structure of the reinforcement
insert 115, triggering chemical reactions starting from the base
components.
[0078] This advantageously allows to obtain a hard micro-structure
and at the same time homogeneous inside the whole reinforcement
insert 115.
[0079] Obtaining the reinforcement insert 115 is controlled and
managed by a control unit that cooperates with a melting device to
obtain the desired geometric shapes.
[0080] The sintering techniques described above advantageously
allow to make reinforcement inserts 115 of any geometric shape,
developed in the three spatial dimensions according to the specific
requirements of the cast 110 to be obtained. In fact, since they
are additive techniques, they allow to obtain, quickly and
precisely, quite complex and difficult three-dimensional
geometrical developments that are even impossible to obtain using
chip-removal operations, or by molding, or using traditional
sintering techniques.
[0081] In fact, according to the invention, the reinforcement
inserts 115 can have internal channels, intersecting or not, in
which the melted steel can penetrate during the casting step 12, to
create a better and more stable connection between the
reinforcement insert 115 and molten steel.
[0082] FIG. 2 shows, by way of example, a variant of the
reinforcement insert 115, in this case shaped as a flat spiral.
[0083] Other spatial forms of reinforcement insert 115 can be made,
according to the point-by-point requirements of the final
product.
[0084] During the positioning sub-step 14 of the reinforcement
insert 115, an anchoring operation is also carried out, during
which it is anchored at least to one of the perimeter walls 112 of
the mold 111. To this purpose, the reinforcement insert 115
comprises, at its ends, one or more appendixes 120, which function
as anchoring means and which are inserted inside the corresponding
perimeter walls 112.
[0085] This stratagem allows the reinforcement insert 115 to remain
in the correct position also during the subsequent casting step 12,
during which it is completely incorporated in the manganese steel
matrix that is cast into the mold 111.
[0086] FIG. 3 shows an example of a cast 110 showing the
incorporated position of the reinforcement insert 115.
[0087] By controlling the sintering process, the use of EBM or SLM
techniques allows to obtain reinforcement inserts 115 which are not
only micro-structurally homogeneous but also substantially without
residual porosity and tensions, and therefore advantageously
compact and resistant.
[0088] Furthermore, the reinforcement inserts 115 thus obtained do
not need heat treatments after they have been made, and therefore
can be put into the mold 111 immediately after sintering.
[0089] During the casting step 12, depending on the components,
each reinforcement insert 115 can be subjected to partial melting
which, during the subsequent solidification, allows to obtain a
cast 110 that is macro-structurally homogeneous, due to the welding
of the cast steel and the melted part of the reinforcement insert
115.
[0090] The cast 110 obtained maintains a generally heterogeneous
micro-structure, which has a greater hardness in correspondence
with the zones concerned with the reinforcement insert 115, which
is uniformly distributed in them and constant, that is, without
point-by-point variations.
[0091] The reinforcement insert 115 can be analyzed using
microscopic analysis, whether optical or, better, electronic, by
scanning or transmission.
[0092] Once the solidification of the cast 110 is terminated, after
the stand-by step 13, subsequent heat treatments allow, for example
by inducing martensitic transformations inside the cast 110, to
confer more hardness on the zones that have the reinforcement
inserts 115.
[0093] It is clear that modifications and/or additions of parts may
be made to the method 10 and cast 110 as described heretofore,
without departing from the field and scope of the present
invention.
[0094] It is also clear that, although the present invention has
been described with reference to some specific examples, a person
of skill in the art shall certainly be able to achieve many other
equivalent forms of cast 110, having the characteristics as set
forth in the claims and hence all coming within the field of
protection defined thereby.
* * * * *