DESC:FIELD OF THE INVENTION:
This invention relates to the field of metallurgy.

Particularly, this invention relates to the field of processes and techniques for manufacturing hardfacing alloys.

Specifically, this invention relates to a process for manufacturing improved iron-based hardfacing alloys. Specifically, this invention relates to a process of manufacturing nitrogen rich carbide dispersed austenitic matrix hardfacing alloys.

BACKGROUND OF THE INVENTION:
Hardfacing materials include a wide variety of alloys, carbides, and combinations of these materials.
Conventional Iron-based hardfacing alloys and Nickel based hardfacing alloy with Austenitic matrix show hardness in the range 41- 60HRC. The following tabulated prior art shows the prior art’s hardness range and purely austenitic matrix.

Patent no. Year Material Composition Process Hardness Claims
European patent 0265165 A2 1988 Iron based hardfacing alloy (Austenitic matrix) 0.85-1.4 % C
18-27 %Cr
Upto 6 %Mo
4-12 %Ni
5-13 %Mn
1.5-5.5 %Si
0.1-0.3 %N
0-1 %V
0-1 %Ti
0-1 %Nb
0-1 %Ta Plasma arc welding, GTA 389-476 HV
(41-46 HRC) 1. A cobalt-free, wear-resistant and anti-galling hardfacing alloy consisting essentially by weight of (said compostion); said alloy having a microstructure consisting essentially of an austenitic matrix and eutectic alloy carbides.
2. In a method for constructing a plant comprising elements exposed to an aggressive environment, ihe
improvement comprising the step of forming said elements from a wear-resistant, anti-galling cobalt-free alloy consisting essentially by weight of (said composition); wherein said alloy has a microstructure consisting essentially of austenitic matrix and eutectic alloy carbides.
European patent
EP 0659895 B1 1994 Iron based hardfacing alloy (Austenitic matrix) 1.3-2 % C
19-23 %Cr
8-11 %Mo
17-21 %Ni
6-13 %Mn
0.5 %Si Plasma arc welding (Powder) 420 HV
43 HRC 1. An internal combustion engine valve having a body, a head, and a contact surface disposed on said head adapted to periodically enter into gas-sealing engagement with a valve seat, said contact surface being formed in metal deposit welded to said valve head, the composition of said metal deposit, measured at said contact surface, consisting of said composition
U.S Patent no. 4331741 1982 Nickel Based hardfacing alloy (Austenitic matrix) 27-30% Cr 7-9.5% Mo 1-1.75% Si 1.2-1.8% C 0.75-1.3% Mn 5% Fe 4-6% W 0.05-0.5% Ti Balance Ni Plasma transferred arc welding (gas atomized powder) 44.2-46 HRC 1. A nickel-base alloy suitable for use as a hard surfacing material and characterized by good weld ability and elevated temperature wear resistance, said alloy consisting of (weight percent) about 27 to 30% chromium, about 7 to 9.5% molybdenum, about 4 to 6% tungsten, about 0.75 to 1.3% manganese, 0.05 to 0.5% titanium, 0.2 to 0.75% columbium, about 1.2 to 1.8% carbon, 1 to 1.75% silicon, iron up to about 5%, and the balance essentially nickel.
U.S Patent no. 5935350 1999 Nickel Based hardfacing alloy (Austenitic matrix) 16-22% Cr 1-7% Mo 2.5-3.7% Si 0.8-1.4% C 2-3% B 2-3.9% Fe 4.3-17% Co Balance Ni Plasma transferred arc welding (gas atomized powder) 50-60 HRC 1. A nickel based hardfacing alloy having improved wear resistance comprising at least about 40% Ni by weight, between about 4% and 18% Co by weight, between about 15% and 23% Cr by weight, between about 1% and 7% Mo by weight, and between about 2% and 3% B by weight.
2. Said alloy being in gas-atomized powder form Suitable for deposition by plasma transferred arc welding and having a hardness in the range of about 50 Rc to 60 Rc, a coefficient of friction in the range of about 0.12 to 0.13, an ASTM G-65 wear rating in the range of about 20 to 26, and an ASTM
G-77 wear rating in the range of about 0.0 to 0.074.
3. A plastic extruder Screw comprising a metallic body having Screw flights and a coating on the screw flights, Said coating having a thickness between about 0.025 in. and about 0.5 in., and Said coating further being Ni based and comprising between 4% and 18% Co by weight, between
about 15% and 23%. Cr by weight, between about 1% and 7%. Mo by weight, and between 2% and 3% B by weight.
5 United States patent no. 5958332 1999 Nickel Based hardfacing alloy (Austenitic matrix) 40-51% Cr >1% Mo >1% Si 0-0.1% C 0.05-0.5% B 2-3.9% Fe 0-1.5% Ti 0-5% Mn 0-1% Al Balance Ni Plasma transferred arc welding (gas atomized powder) 200-220 HV (before Heat treatment)
467-551 HV (after Heat treatment)(46-52 HRC) 1. A nickel-based facing alloy which, expressed in percentage by weight and apart from commonly occurring impurities, comprises from 40 to 51% Cr, from 0 to 0.1% C, less than 1.0% Si, from 0 to 5.0% Mn, less than 1.0% Mo, from 0.05 to less than 0.5% B, from 0 to 1.0% Al, from 0 to 1.5% Ti, from 0 to 0.2% Zr, from 0.5 to 3.0% Nb, an aggregate content of Co and Fe of maximum 5.0%, maxi mum 0.2% O, maximum 0.3% N and the balance Ni.
2. A cylinder member selected from the group of a valve,
a Seat portion, a piston and a cylinder liner, in an internal combustion engine, particularly a large two-stroke cross
head engine, wherein the member is provided with a welded high-temperature corrosion-resistant facing alloy being at an operating temperature at normal running of the engine, Said welded facing alloy having a hardness which has been increased by means of a precipitation hardening mechanism based on a Solid-State phase transformation, the facing alloy having a temperature of activation of the precipitation hardening mechanism that is above the operating temperature of the alloy, and the precipitation hardening mechanism acting So slowly, that the alloy Substantially has not hardened at welding on the cylinder member, but has hardened during a Subsequent heat treatment at a temperature higher than the activation temperature for the precipitation hardening mechanism.

In order to overcome this limitation, Iron-based hardfacing alloys were developed in the prior art.

Commercially, Iron-based hardfacing alloys are cheaper than imported Nickel-based hardfacing alloys.

Therefore, and however, there is, firstly, a need to improve the hardness of Iron-based hardfacing alloys and, secondly, a need to provide Iron-based hardfacing alloys with hardness equivalent to Nickel-based hardfacing alloys.

In high temperature application such as a nuclear reactor, liquid Sodium is used as a coolant which is highly corrosive in nature. This tends to corrode components which come in contact with the coolant and also leads to self welding between the components. Hardfacing alloys are used to weld overlay to improve its corrosion resistance.

Furthermore, in prior art, in an austenitic matrix, the hardness is seen at a lower level at elevated temperatures; there is a need to address this problem.

Furthermore, in prior art, it was observed that Cobalt-based hardfacing alloys produce a radioactive isotope of cobalt which is a concern for safety. Also, it was observed that Nickel-based hardfacing alloys, of the prior art, showed self-welding between components which decreases the life of components

Therefore, there is a need to alleviate these problems.

OBJECTS OF THE INVENTION:
An object of the invention is to improve hardness of Iron-based hardfacing alloys.

Another object of the invention is to provide Iron-based hardfacing alloys with hardness equivalent to Nickel-based hardfacing alloys.

Yet another object of the invention is to achieve austenitic phase formation in iron-based hardfacing alloys.

SUMMARY OF THE INVENTION:
According to this invention, there is provided a process for manufacturing improved iron-based hardfacing alloys. Specifically, this invention discloses a process of manufacturing nitrogen rich carbide dispersed austenitic matrix hardfacing alloys.

In at least an embodiment, this invention teaches a process for manufacturing improved iron-based hardfacing alloys, said process comprising the steps of:
- deriving an austenitic matrix alloy having composition Fe-20Cr-2C-18Ni-2Mn-4Si-2Ti-1B [STEP 1a, STEP 1b];
- deriving an iron-based alloy with nickel percentage in the range of 16 - 18 wt%;
- mechanically alloying [STEP 3], by milling, premixed ferroalloy powders, under nitrogen atmosphere, in a range of 50 - 150 µm, having ball-to-powder (BPR) ratio of 10:1 (by wt.), in order to obtain Iron-based hardfacing alloy powder; and
- laser cladding [STEP 4] said milled powder (150-200 gms) in order to obtain laser cladded Iron-based hardfacing alloy weld overlay;

In at least an embodiment, said step of mechanically alloying [STEP 3] being carried out in an attritor mill having a stainless-steel vial of 1 kg at 400 rpm for 3 hours.

In at least an embodiment, said powders [STEP 3] being selected from a group of powders consisting of Ferro Chromium (FeCr), Ferro Manganese (FeMn), Ferro Titanium (FeTi), Ferro Boron (FeB), Nickel (Ni), Silicon (Si), Carbon (C), and Iron (Fe).

In at least an embodiment, said step of laser cladding [STEP 4] comprising:
- cladding on a 10 mm thick 50*50 mm SS 316 plate;
- pulsing with a 4000W pulsed CO2 laser system with a laser power of 2000-2200W;
- providing scanning speed of 25-35 mm/s;
- obtaining cladding thickness per layer of 1-1.5 mm; and
- continuously blowing Argon gas to prevent oxidation.

In at least an embodiment, said laser cladded Iron based hardfacing alloy weld overlay having hardness range between 63HRC to 65HRC.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:
FIGURE 1 illustrates a flow chart of the process of achieving the Iron-based hardfacing alloy of this invention; and
FIGURE 2 showing microstructure of the laser cladded weld overlay, interface and substrate;
FIGURE 3A illustrates this invention’s Iron based hardfacing alloy when compared (in terms of Chemical composition, Particle size range (µm), Optical microstructure analysis, Matrix, Micro Hardness (HRC)) with FIGURE 3B which illustrate’s prior art’s nickel based hardfacing alloy;
FIGURE 3C illustrates this invention’s Iron based hardfacing alloy when compared (in terms of Carbide volume fraction (by ImageJ software), Sliding Wear analysis SEM microstructure of the weld overlay and interface)) with FIGURE 3D which illustrate’s prior art’s nickel based hardfacing alloy;
FIGURE 3E illustrates this invention’s Iron based hardfacing alloy when compared (in terms of SEM microstructure of the weld overlay and interface)) with FIGURE 3F which illustrate’s prior art’s nickel based hardfacing alloy;
FIGURE 4 illustrates microhardness comparison of Iron based and Nickel based hardfacing alloy across the cross section; and
FIGURE 5 illustrates Sliding wear analysis- COF vs. time.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a process for manufacturing improved iron-based hardfacing alloys. Specifically, this invention discloses a process of manufacturing nitrogen rich carbide dispersed austenitic matrix hardfacing alloys.

FIGURE 1 illustrates a flow chart of the process of achieving the Iron-based hardfacing alloy of this invention.

In at least an embodiment, of this invention, an austenitic matrix alloy having composition Fe-20Cr-2C-18Ni-2Mn-4Si-2Ti-1B is derived [STEP 1a, STEP 1b].
In at least an embodiment, of this invention, there is taught a step of deriving an iron-based alloy with nickel percentage in the range of 16-18 wt%, compared to commercially available nickel-based alloys with 60-70 wt% with equivalent properties; since the ratio of nickel, which is an expensive commodity, it drastically reduced, it contributes to INVENTIVE STEP, therein.
Primarily, premixed ferroalloy powders (50-150 µm) [STEP 2] are mechanically alloyed [STEP 3] in an attritor mill, which is carried out in a stainless-steel vial of 1 kg at 400 rpm for 3 hours. Hardened steel balls with ball to powder (BPR) ratio of 10:1 (by wt.) are maintained. The attritor ball milling process is carried out under nitrogen atmosphere. Purification unit was used to maintain the purity of the gas.
List of powders used:
Sr. no Raw material powder % Specification
1 Ferro Chromium (FeCr) C Cr Fe
0.0009 70 Bal
2 Ferro Manganese (FeMn) C Mn Fe
0.07 77 Bal
3 Ferro Titanium (FeTi) C Ti Fe
0.0009 35 Bal
4 Ferro Boron C B Fe
(FeB) 0.0026 15 Bal
5 Nickel (Ni) C Ni Fe
0.08 99.5 0.01
6 Silicon (Si) 98.5 Purity
7 Carbon
8 Iron (Fe) 99.5 Purity

Typically, the premixing process is cost effective than atomized processes of the prior art, which is used to develop the other nickel based alloys

In at least an embodiment, of this invention, the milled powder (150-200 gms) is then laser cladded [STEP 4] on a 10 mm thick 50*50 mm SS 316 plate by laser cladding process. A 4000W pulsed CO2 laser system was used and laser power of 2000-2200W is chosen for cladding. The scanning speed was 25-35 mm/s. The cladding thickness per layer is 1-1.5 mm and Argon gas is continuously blown on the samples' surfaces to prevent oxidation. The hardfacing thickness of 1-2 mm is cladded. After the cladding, the specimen is machined by wire cutting for further characterization [STEP 5].

In at least an embodiment, of this invention, the microstructure of the milled powder and the cladded surface were examined using optical microscope, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffractometer (XRD). Images were captured, at the interface of the cladded region, and the substrate to study the grain structure and carbide formation along the grain boundaries. The sample was polished and etched with reagent (10ml HCl + 10ml HNO + 10ml H2O). Further, Carbide volume fraction (CVF) was calculated from the mean of three different areas by ImageJ software. About 40% CVF was observed in the matrix.

FIGURE 2 showing microstructure of the laser cladded weld overlay, interface and substrate.

Hardness was measured on the weld overlay surface. Microhardness measurements were conducted four times on the specimen of each test and average valve was taken by a Vickers Micro indentation hardness tester under a load of 500 gf for 10 sec of dwell time.

Moreover, the given iron-based hardfacing alloy is developed with readily available ferro alloys powders. The alloy is primarily premixed and mechanically alloyed in nitrogen-based atmosphere.

The following observations, and inferences, were made in respect of this invention’s Iron-based hardfacing allows:
1. Hardness range – 63-65HRC;
2. Additional precipitation of Nitrides due to nitrogen enrichment at room temperature mechanical alloying process;
3. Austenitic Phase formation for high temperature application;
4. Around 40% dispersion precipitation in the matrix primarily consists of carbides and nitrides;
5. Low dilution due to laser cladding process.

In contrast, in prior art, hardness achieved in regard to Iron-based hardfacing alloys is in the range of 41-60 HRC. Welding techniques used, in prior arts, work exhibited high dilution, due to usage of filler rods or wires. In most of prior art, austenitic phase formation was not observed.

The TECHNICAL ADVANCEMENT of this invention lies in the following:
The Iron-based hardfacing alloy developed has an average hardness of 64 HRC which is better than the prior art Iron-based hardfacing alloy. The said hardness in the range of 63-65 HRC is also at par with the existing Nickel-based hardfacing alloys which are used in Nuclear reactor applications, but without the problems of self-welding.
Austenitic hardfacing alloys, with nitrogen enrichment, is possible even at room temperature mechanical alloying with ball to powder ratio of 10:1 (by wt. %).
In an austenitic matrix, the hardness, of the Iron-based hardfacing alloys, according to this invention, is seen to have obtained hardness in range of 63-65 HRC.
Iron based hardfacing alloys, according to this invention, show none of the above problems and are free from Cobalt.

FIGURE 3A illustrates this invention’s Iron based hardfacing alloy when compared (in terms of Chemical composition, Particle size range (µm), Optical microstructure analysis, Matrix, Micro Hardness (HRC)) with FIGURE 3B which illustrate’s prior art’s nickel based hardfacing alloy.

FIGURE 3C illustrates this invention’s Iron based hardfacing alloy when compared (in terms of Carbide volume fraction (by ImageJ software), Sliding Wear analysis SEM microstructure of the weld overlay and interface)) with FIGURE 3D which illustrate’s prior art’s nickel based hardfacing alloy.

FIGURE 3E illustrates this invention’s Iron based hardfacing alloy when compared (in terms of SEM microstructure of the weld overlay And interface)) with FIGURE 3F which illustrate’s prior art’s nickel based hardfacing alloy.

FIGURE 4 illustrates microhardness comparison of Iron based and Nickel based hardfacing alloy across the cross section.

FIGURE 5 illustrates Sliding wear analysis- COF vs. time.

It was observed that the Iron based hardfacing alloy, in accordance with this invention, was compared with prior-art, commercially available, Nickel based alloy. The results showed that properties of the Iron based alloy, of this current invention, are similar (or superior in certain applications) to Nickel based alloys. Along with technical specification, the abundance of Iron makes it an efficient choice in terms of availability and in terms of finances. Therefore, it can be concluded that this can be used as a replacement to prior art alloys. Following is the list of some applications where the Iron based hardfacing alloy powder can be used.
1. Fast breeder nuclear reactor;
2. Automotive engine components;
3. Equipment used in agriculture, quarrying, mining, Screw conveyers, mineral conveying equipment, vertical crushers, and extractor fans, grinding mills;
4. Transmission shaft, rolls, Cams, raceways, press and transport screws;
5. Anti-corrosion coating, valve seats, pump bodies and rotors, hydraulic rams, hot rolling mills, static brakes for railway.

According to non-limiting exemplary embodiments, FIGURES 6A, 6B, 6C, 6D, 6E illustrate Iron-based hardfacing alloy of this invention as a comparison with FIGURES 7A, 7B, 7C, 7D, 7E which illustrate Nickel-based hardfacing alloys of this invention.

While this detailed description has disclosed certain specific embodiments for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. ,CLAIMS:WE CLAIM,

1. A process for manufacturing improved iron-based hardfacing alloys, said process comprising the steps of:
- deriving an austenitic matrix alloy having composition Fe-20Cr-2C-18Ni-2Mn-4Si-2Ti-1B [STEP 1a, STEP 1b];
- deriving an iron-based alloy with nickel percentage in the range of 16 - 18 wt%;
- mechanically alloying [STEP 3], by milling, premixed ferroalloy powders, under nitrogen atmosphere, in a range of 50 - 150 µm, having ball-to-powder (BPR) ratio of 10:1 (by wt.), in order to obtain Iron-based hardfacing alloy powder; and
- laser cladding [STEP 4] said milled powder (150-200 gms) in order to obtain laser cladded Iron-based hardfacing alloy weld overlay;

2. The process as claimed in claim 1 wherein, said step of mechanically alloying [STEP 3] being carried out in an attritor mill having a stainless-steel vial of 1 kg at 400 rpm for 3 hours.

3. The process as claimed in claim 1 wherein, said powders [STEP 3] being selected from a group of powders consisting of Ferro Chromium (FeCr), Ferro Manganese (FeMn), Ferro Titanium (FeTi), Ferro Boron (FeB), Nickel (Ni), Silicon (Si), Carbon (C), and Iron (Fe).

4. The process as claimed in claim 1 wherein, said step of laser cladding [STEP 4] comprising:
- cladding on a 10 mm thick 50*50 mm SS 316 plate;
- pulsing with a 4000W pulsed CO2 laser system with a laser power of 2000-2200W;
- providing scanning speed of 25-35 mm/s;
- obtaining cladding thickness per layer of 1-1.5 mm; and
- continuously blowing Argon gas to prevent oxidation.

5. The process as claimed in claim 1 wherein, said laser cladded Iron based hardfacing alloy weld overlay having hardness range between 63HRC to 65HRC.

Dated this 31st day of December, 2022

CHIRAG TANNA
of INK IDÉE
APPLICANT’S PATENT AGENT
REGN. NO. IN/PA – 1785