Patent Description:
Cast iron is widely used in the manufacturing of several components with complex geometry and cavities due to its good castability, low cost and excellent machinability. The most common types of cast iron are grey cast iron, vermicular cast iron and spheroidal cast iron. Currently, different technologies of surface modification are used to increase the wear and/or corrosion resistance, such as thermo-reactive diffusion treatment (TRD), laser cladding (LC), physical vapor deposition (PVD), in-situ casting heat treatment reaction, plasma jet cladding, etc. Although good results can be obtained by these technologies, there are still many problems such as limitation on coating thickness, high cost and complex equipment.

Surface modification by in-situ casting combines the technologies of casting and chemical reaction at the surface, some of them are based on the casting of the cast iron in a carbide plate with a subsequent heat treatment, another method used an in-situ solid-solid reaction between the carbide plate and the iron plate as a subsequent heat treatment or by covering the sand mold surfaces with a slurry. These in-situ techniques generate coatings with a series of excellent properties of corrosion and wear resistance, however, some of these methods require additional processes, such as heat treatment, that significantly increases the cost of the final product.

To increase the wear and/or corrosion resistance of cast iron parts without substantially increasing its price, laser cladding has been proposed as an alternative method. However, laser cladding on cast iron is a difficult and complex process because it can generate heterogeneous thermal and stress fields as result of the graphite and matrix properties, formation of pores for the carbon dioxide produced during the laser beam radiates and formation of hard and brittle phases (martensite and ledeburite) due to the high cooling rate and may lead to crack formation.

Some of these problems can in some cases be solved with the use of a preheating in the substrate, double or multilayer deposited by laser cladding. However, these methods are accompanied by considerable energy consumption, poor production efficiency, price increase, etc. Examples of the above can be found in <NPL>; <NPL>; <NPL>; and patent applications <CIT>, <CIT> and <CIT>. Therefore, there is still the need in the state of the art of a solution that solves drawbacks of the technologies currently used to increase wear and/or corrosion resistance of a cast iron part or component, in particular for components with complex geometry or to cover localized areas.

The present invention provides a method for producing a cast iron part which combines surface modification by an in-situ casting with laser directed energy deposition (L-DED). This surface modification prior to the deposition L-DED coating removes the drawbacks commonly associated with laser cladding (LC), in particular the method described herein is able to avoid brittle phase formation in the cast iron, carbide formation and the migration of chemical elements from the cast iron to the coating layer. In such a way that properties of the cast iron components such as corrosion resistance and/or wear resistance can be more effectively optimized thanks this combination of surface modification by in-situ casting with L-DED.

Thus, the instant patent application provides a method for producing a cast iron part having an increased corrosion and/or wear resistance.

The scope of the present invention is defined by independent claims <NUM> and <NUM>, and further embodiments of the invention are specified in dependent claims <NUM>-<NUM>.

The first metallic material comprised in the reactive paint obtained in stage a) of the method described herein is preferably a metallic particulate such as, for example, powder, fine chips, grainy, insert or strip of sheet, which may have a size not higher than <NUM>. Preferably, the first metallic material is powder (i.e., a metallic powder).

In some particular embodiments, the first metallic material may be powder and, preferably, powder having a particle size distribution contained in the range of <NUM> to <NUM>, more preferably of <NUM> to <NUM>, and even more preferably of <NUM> to <NUM>, wherein said particle size distribution is determined by sieving.

The first metallic material is a metal alloy comprising:.

preferably with the proviso that the amount of each one of Cr, Mo and W is lower than the sum of Cu + Al + Ni + Co + Mn.

The first metallic material is preferably an Ni-Co alloy comprising an amount of C equal to or less of <NUM> wt. %, since this alloy can provide the desired surface modification to the cast iron member without generating carbides.

In preferred embodiments of the method described herein, the first metallic material is a Ni-Co alloy comprising:.

with the proviso that the amount of Fe is lower than the sum of Ni + Co.

The binder used in stage a) to obtain the reactive paint can be organic or inorganic. On the one hand, organic binders can be, for example, casting resins such as silanes, furanic or phenolic resins. On the other hand, inorganic binders can be water or alcohol base solutions comprising an inorganic precursor. Said inorganic precursor can be colloidal such as colloidal silica, or non-colloidal such as a silicate, in particular, ethyl silicate or sodium silicate.

In particular embodiments, the binder is a sodium silicate aqueous solution, more specifically a sodium silicate aqueous solution comprising of at least <NUM> wt. % of sodium silicate by weight of the solution.

The reactive paint obtained in stage a) may also comprise other additives such as surfactants, defoamers or a combination thereof and/or a solvent, in particular water or an alcohol such as methanol, ethanol or propanol. These solvents are preferred because they can be easily removed from the sand mould at least partially coated with the reactive paint in stage c) of the method (see further details below).

The reactive paint can be obtained by mixing the required amounts of first metallic material, binder and, optionally, solvent. If further additives such as surfactants and/or defoamers are present in the reactive paint, the required amounts of said additives can also mixed with the first metallic material and the binder to obtain the reactive paint.

The reactive paint obtained in stage a) of the method for producing a cast iron part or component described herein preferably comprises <NUM>-<NUM> % weight of binder and <NUM>-<NUM>% weight of first metallic material, wherein these percentages are expressed regarding the total weight amount of binder and first metallic material of the reactive paint.

In some particular embodiments, the reactive paint may have low adherence to the sand mould. More specifically, if the sand mould is highly porous, it might occur that the binder will be excessively absorbed, thus jeopardizing the deposition of the reactive paint on the sand mould surface. This might happen, for example, when the sand has a particle size higher than <NUM> and the reactive paint has lower than <NUM> wt. % of solid content.

To overcome this drawback, the method for producing a cast iron part or component described in this document may comprise an additional stage b-<NUM>), prior to stage b), wherein the sand mould is wetted prior to apply the reactive paint. This stage can be carried out by immersion of the sand mould in a water bath, preferably for at least one minute, or, alternative, by spraying water to the sand mould, so that its surface contains the required amount of water.

The reactive paint may be applied to the sand mould, optionally wetted as described in this document, by conventional means such as brush or immersion. If the sand mould has one or more cavities, the reactive paint can be applied by filling and subsequent emptying said cavities. In the method described herein, the reactive paint may be applied to all the surface of the sand mould or, alternatively, it may only be applied to one or more specific zones of the sand mould. In some particular embodiments, different reactive paints as described herein may be applied to different portions of the sand mould, thus obtaining a sand mould at least partially coated with different reactive paints.

Once the reactive paint(s) has/have been applied to either the total surface or one or more specific zones of the sand mould, the sand mould at least partially coated with reactive paint is dried in stage c) of the method described herein. This drying can be done allowing the sand mould to naturally dry at room temperature (i.e., without applying heat). For instance, the sand mould may be dried in a foundry plant environment for at least <NUM> hours. Since the evaporation of the binder and other volatile compounds such as solvents that might be present in the reactive paint(s) causes the sand mould surface to cool, the drying process can be controlled by measuring the temperature of said surface. The drying stage c) of the sand mould at least partially coated with reactive paint can be deemed to be finished when the surface of the mould achieves the same temperature than the room wherein said sand mould is being dried. Alternatively, the drying of the sand mould at least partially coated with reactive paint can be carried out at a temperature of <NUM> to <NUM> for a period of at least <NUM> hours, preferable of <NUM> to <NUM> hours.

Then, the dried sand mould at least partially coated with the reactive paint may be assembled to obtain a sand mould ready for casting in stage d) of the method for producing a cast iron part described herein.

The cast iron melt casted in stage d) of the method described herein may have the chemical composition of any known cast iron such as, in particular, a ductile iron alloy. More specifically, the cast iron may be selected from EN-GJS-<NUM>-<NUM>-LT, EN-GJS-<NUM>-<NUM>-RT, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>-LT, EN-GJS-<NUM>-<NUM>-RT, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>, EN-GJS-<NUM>-<NUM>, EN-GJL-<NUM>, EN-GJL-<NUM>, EN-GJL-<NUM>,EN-GJL-<NUM> and EN-GJL-350a.

The melt of the cast iron to be poured into the dried sand mould at least partially coated with reactive paint can be prepared from conventional raw materials such as pig iron, steel, soft iron, graphite, ferroalloys among others. The raw materials can be put in contact according to conventional methods which may include steps such as mixing component, melting, adjusting the alloy composition by adding further components, melt treatment and, optionally, inoculation with known inoculating materials.

The cast iron melt of stage d) of the method described herein comprises: <MAT>.

As commonly known in the art, the eutectic point occurs at a composition of <NUM> wt. % C for the iron-carbon system. Thus, the amount of C in cast iron melt according to these embodiments may be of <NUM> to <NUM> wt.

The filling of the dried, and optionally assembled, sand mould at least partially coated with reactive paint with molten cast iron as described in this document is preferably performed by pouring the cast iron melt into said sand mould following a laminar flow, more preferably a laminar flow with a Reynolds number (Re) of <NUM> to <NUM>, even more preferably of <NUM> to <NUM>. In such a way, turbulence and impact on reactive paint coated areas of the sand mould can be avoided and, therefore, the reactive paint remains on its place after the sand mould is completely filled. This laminar flow can be achieved, for example, by design of the filling system of the sand mould. The Reynolds number can be determined by a commercially available simulation software commonly known in the art such as ProCAST, Magma or QuikCAST.

After pouring, the mould filled with the iron alloy melt can be cooled in a conventional manner, thus allowing the solidification of the casting, and the sand mould removed to obtain an at least partially surface modified cast iron part or component.

During casting process, alloying elements of the first metallic material are transferred from the sand mould to the cast iron surface, thus creating in-situ a modified surface layer (also called "first surface modified layer" in this document) by using the heat content of a molten cast iron. This modified surface layer preferably presents a thickness of <NUM> to <NUM>, more preferably of <NUM> to <NUM>. This first surface layer may be present in the whole surface of the cast iron part or component or, alternative, it may be present only in specific zones of said part or components, thus providing a great versatility to the method described herein.

The first surface modified layer applied by in-situ casting has different chemical composition and microstructure than cast iron. The main differences are that it has less graphite content and other matrix phases. Unexpectedly, the inventors found that the presence of this first surface layer on the cast iron provides significant advantages when the L-DED technology is used for improving corrosion and/or wear resistance of said cast iron part or component. Thus, the combination of surface modification by in-situ casting and L-DED provided by the method described herein is able to achieve the great advantages of L-DED, while avoiding some important drawbacks of the laser cladding process such as the generation of heterogenous heating, stress fields and formation of hard and brittle phases which can lead to cracking. Furthermore, there is minimal interaction of the base cast iron with the L-DED coating material, while avoiding hardening of the cast iron.

The cast iron part obtained in stage d) of the method described herein, which comprises at least one surface portion modified with the first metallic material, optionally all its surface is modified with such first metallic material, is conditioned prior to be L-DED coated. This conditioning stage comprises cleaning by shot blasting or machining the surface of the cast iron to remove any residue from the sand mould.

Thus, depending on the final use of the cast iron part obtained by the method described herein, the cast iron part comprising at least one surface portion modified with the first metallic material obtained in stage d) is shot blasted or machined, with the proviso that the machining depth leaves a minimum modified layer thickness of <NUM>, preferably a minimum modified layer thickness of <NUM>.

The method for producing a cast iron part or component described in this document further comprises stage f), wherein at least one layer of a second metallic material is deposited on surface portions modified with the first metallic material (i.e., on the first surface modified layer), wherein said at least one layer of second metallic material is deposited by laser directed energy deposition (L-DED), and said second metallic material is selected from an anti-corrosion material, an anti-wearing material; and an anti-corrosion and anti-wearing material, and it is an iron base alloy comprising equal to or more than <NUM> wt. % of Cr + Mo + Ni. In the method described herein, one or more layers of the second metallic material can be deposited on all portions of the cast iron part wherein the first surface modified layer is present or, alternative, it can be deposited only to some of them.

The second metallic material deposited on the first surface modified layer by L-DED in stage f) of the method described herein is selected from an anti-corrosion material, an anti-wearing material; and an anti-corrosion and anti-wearing material and, therefore, it is characterized by increasing corrosion resistance and/or wear resistance of cast iron. Those materials are broadly known in the art and, therefore, the skilled person may select them without undue burden.

Said second metallic material can be metallic powder or metallic wire.

A material can be considered an anti-corrosion material, if it is capable of generating a passive layer or very low corrosion weight loss under a given environment. This environment dependence gives a wide range of anti-corrosion materials that might be used. For example, high Cu alloys, such as Bronze are appropriate for marine environments, stainless steels with an amount of Cr equal or higher than <NUM> wt. % cover a wide range of applications, nickel alloys (Ni content equal or higher than <NUM> wt. %) and cobalt alloys (Co content equal or higher than <NUM> wt. %) are widely used in high chloride content media and high temperature corrosion.

A material can be considered an anti-wearing material if its hardness is equal or higher than <NUM> HRC (standard hardness Rockwell-C) and it has a hard phase (carbide, nitride and/or oxide) dispersion content equal or higher than <NUM> % in volume.

The combination of the two above gives anti-wear plus anti-corrosion materials. High Entrophy Alloys are a special case of anti-corrosion + anti-wear, since they fulfil both targets despite not having hard phase dispersions.

The second metallic material deposited by L-DED in stage f) is an iron base alloy such as tool steels or stainless steels. More specifically, the second metallic material is an iron base alloy comprising equal to or more than <NUM> wt. % of Cr + Mo + Ni.

In more particular embodiment, the second metallic material deposited by L-DED in stage f) is a stainless-steel alloy comprising:.

More specifically, said second metallic material is a <NUM>-Si powder, preferably with a particle size distribution contained in the range of <NUM> to <NUM>, preferably of <NUM> to <NUM> (determined by sieving), and the following chemical composition Cr <NUM> wt. %, Ni <NUM> wt. %, Mo <NUM> wt. %, Si <NUM> wt. %, Mn <NUM> wt. %, C equal to or less than <NUM> wt. %, less than <NUM> wt. % of each other element, wherein the total amount of unspecified elements is equal to or less than <NUM> wt. %, and iron as balance.

The L-DED may be carried out by conventional means known by in the art. In particular said process may be carried out at a laser powder of <NUM> to <NUM> W and/or with a spot diameter of <NUM> to <NUM>.

The present specification also refers to a cast iron part or component obtained or obtainable by the method described herein. Said cast iron part or component is characterized by comprising a first modified surface layer in at least some portions of its surface and, additionally, one or more second layers deposited over this first modified surface layer, wherein the first and the second layers has different composition and microstructure, as well as different physical, tribological, electrochemical and chemical properties.

Besides that, this cast iron part or component advantageously may have better properties of wear resistance and/or corrosion resistance than cast iron since the first modified surface layer is able to avoid the cracking problems in the surface. In particular embodiments, the cast iron part or component obtained or obtainable by the method described herein can achieve corrosion resistance and wear resistance equivalent to those achieved by wrought materials. More specifically, the wear resistance may comply with the requirements of AISI H13 grade, whereas the corrosion resistance may comply with the requirements of 5A duplex grade (ASTM A890/ A <NUM>).

A reactive paint was obtained by mixing <NUM> wt. % of a Ni-Co alloy powder with <NUM> wt. % of a sodium silicate aqueous solution (<NUM> % w/w of sodium silicate), wherein these percentage are expressed regarding the total weight amount of binder and first metallic material of the reactive paint.

The Ni-Co alloy (first metallic material) was a powder with a particle size distribution in the range of <NUM> to <NUM> (by sieving), and chemical composition:
<NUM> wt. % Ni, <NUM> wt. % Co, <NUM> wt. % C, <NUM> wt. % Cr, <NUM> wt. % Mo, <NUM> wt. % Al, <NUM> wt. % Ta, <NUM> wt. % Ti, equal to or less than <NUM> wt. % of each other unspecified element, wherein the total amount of unspecified elements is equal to or less than <NUM> wt.

A sand mould was used with rectangular shape. The sand mould component was wetted by immersion in a bath with water for a period of <NUM> minute. After, the wetted sand mould is painted with the reactive paint by filling in all bottom side of the mould. Then, that sand mould partially coated with the reactive paint (i.e., coated in its bottom side) was dried during a day in a foundry plant environment.

On the other hand, a melt of the ductile iron alloy was prepared from conventional raw materials such as pig iron, steel, soft iron, graphite, ferroalloys, among others. The raw materials were put in contact according to conventional methods. The melt obtained had the following chemical composition (percentages expressed by weight with respect to the total weight of the ductile iron alloy):.

The cast iron melt at a temperature of <NUM> was poured to the partially coated sand mould following a laminar flow having a Reynolds number (Re) of <NUM>, to avoid a direct flow over the layer of reactive paint. The solidification of the casting and subsequent cooling in the mould was carried out in a conventional manner. During that process, alloying elements of the reactive paint such as Ni, Cr, Mo and Co were transferred to cast iron surface. The result was an in-situ modified surface layer which presented a thickness of <NUM> to <NUM>.

Then, cast components or part were removed from the mould. The modified surface was conditioned by cleaning by shot blasting or machining before L-DED was carried out.

For the L-DED process was used a metallic particulate powder (second metallic material) with the following composition:
<NUM>-Si powder with particle size distribution in the range of <NUM> to <NUM> (by sieving), and chemical composition; Cr <NUM> wt. %, Ni <NUM> wt. %, Mo <NUM> wt. %, Si <NUM> wt. %, Mn <NUM> wt. %, C equal to or less than <NUM> wt. %, and other less than <NUM> wt. %; wherein the total amount of unspecified elements is equal to or less than <NUM> wt. %, and iron as balance.

Then, L-DED process was carried out on the cast iron components which have been modified by reaction with the reactive paint. In particular, one layer of the second metallic material was deposited on the first modified surface layer previously applied by in-situ casting. This deposition was carried out following a conventional L-DED process, at a laser powder of <NUM> W and a spot diameter of <NUM>.

Claim 1:
A method for producing a cast iron part, wherein the method combines surface modification by an in-situ casting with laser directed energy deposition (L-DED) and comprises the following stages:
a) obtaining a reactive paint comprising at least one first metallic material and at least one binder, wherein the first metallic material is a metal alloy comprising:
equal to or more than <NUM> wt. % of Cu + Al + Ni + Co + Mn,
equal to or less than <NUM> wt. % of C,
equal to or less than <NUM> wt. % of Cr,
equal to or less than <NUM> wt. % of Mo,
equal to or less than <NUM> wt. % of Ta,
equal to or less than <NUM> wt. % of Si,
equal to or less than <NUM> wt. % of Nb,
equal to or less than <NUM> wt. % of V,
equal to or less than <NUM> wt. % of W,
equal to or less than <NUM> wt. % of each other unspecified element, wherein the total amount of unspecified elements is equal to or less than <NUM> wt. %, and
Fe as balance;
b) applying the reactive paint to a sand mould to obtain a sand mould at least partially coated with reactive paint;
c) drying the sand mould at least partially coated with reactive paint;
d) casting a cast iron melt comprising <MAT>
<NUM> to <NUM> wt. % of Si,
equal to or less than <NUM> wt. % of Cu,
<NUM> to <NUM> wt. % of Mn, and
iron as balance;
wherein this stage comprises:
pouring the cast iron melt into the dried sand mould at least partially coated with reactive paint, and
cooling the poured cast iron melt to obtain a cast iron part comprising at least one surface portion modified with the first metallic material;
e) conditioning the cast iron part obtained in stage d) by shot blasting or machining the surfaces of the cast iron to remove any residue from the sand mould, with the proviso that it leaves a minimum modified layer thickness of <NUM>; and
f) depositing at least one layer of a second metallic material on at least one of the surface portions modified with the first metallic material, wherein said at least one layer of the second metallic material is deposited by laser directed energy deposition (L-DED), and said second metallic material is selected from an anti-corrosion material, an anti-wearing material, and an anti-corrosion and anti-wearing material; and it is an iron base alloy comprising equal to or more than <NUM> wt. % of Cr + Mo + Ni.