Hardfacing Alloy Research Articles

Microstructure and Tribological Properties of WC Reinforced Iron-based Hardfacing Alloy

In this paper, WC reinforced and non-reinforced iron-based hardfacing alloys were deposited by PTA welding. Influence of WC particles on the hardfacing alloy was revealed by analysing the microstructure, microhardness and wear behavior. The results show that the matrix metals of the two hardfacing alloys are similar in structure. The primary carbides (Fe, Cr)7C3 and eutectic carbides are distributed on the cryptocrystalline martensite and residual austenite. The distribution of the large WC particles in the whole hardfacing alloy are relatively uniform, compared with the non-reinforced hardfcing alloy, the WC reinforced hardfacing alloy exhibits higher microhardness and better wear resistance property.

Effect of Mo on microstructure and wear resistance of slag-free self-shielded metal-cored welding overlay

A new type of slag-free self-shielded metal-cored wire with various Mo contents has been developed to fabricate an experimental hardfacing alloy. The developed metal-cored wire exhibits an average Mo transfer coefficient of 90%. All the hardfacing alloys have a hypereutectic microstructure consisting of primary M7C3 carbide, and eutectic of M3C carbide plus martensite and residual austenite. The primary carbide fraction is about 38 vol. % in the Mo-free hardfacing alloy; it increases to about 45 vol. % in the alloy when the Mo content increases to 1.35 wt. %. No significant increase in the primary carbide fraction has been observed when the Mo content in the hardfacing alloy is increased further. The wear resistance of Mo-containing hardfacing alloys is better than the Mo-free hardfacing alloy. However, the wear resistance does not increase significantly when the Mo content in the hardfacing alloy is increased beyond 1.35 wt. %. Thermodynamic driving force calculations provide an explanation for the observed primary carbide fraction change in the hardfacing alloys as a function of Mo levels, and the fraction of primary M7C3 carbide seems to play a key role in deciding the wear performance of the hardfacing alloys.

The identification of a silicide phase and its crystallographic orientation to ferrite within a complex stainless steel

Recently, a high-hardness intermetallic phase, named π-ferrosilicide, has been identified within a stainless steel alloy intended to replace Co-based hardfacings within pressurised water reactors. The present study explores the evolution and relationship of the π-ferrosilicide and ferrite phases after a hot isostatic pressing cycle, compared to a cast π-ferrosilicide microstructure. Electron backscatter diffraction is used to identify two orientation relationships between the π-ferrosilicide and ferrite phases. Due to variant selection and growth of the interdendritic π-ferrosilicide within the gas-atomised hardfacing alloy powder, a microtexture develops within this phase with potential implications for the mechanical properties of the alloy.

Evaluation of cobalt free coatings as hardfacing material candidates in sodium-cooled fast reactor and effect of oxygen in sodium on the tribological behaviour

The feedback produced by operating Sodium-cooled Fast Reactors (SFRs) has shown the importance of material tribological properties. Where galling or adhesive wear cannot be allowed, hardfacing alloys, known to be galling-resistant coatings, are usually applied on rubbing surfaces. The most used coating is the cobalt-base alloy named Stellite 6® because of its outstanding friction and wear behaviour. Nevertheless, cobalt is an element which activates in the reactor leading to complex management of safety during reactor maintenance and mainly decommissioning. As a consequence, a collaborative work between CEA, EDF and FRAMATOME has been launched for selecting promising cobalt-free hardfacing alloys for the 600 MWe Sodium-cooled Fast breeder reactor project named ASTRID. Several nickel-base alloys have been selected from literature review then deposited by Plasma Transferred Arc or Laser Cladding on 17Cr austenitic stainless steel 316L(N) according to RCC-MRx Code (AFCEN Code). Among the numerous properties required for qualifying their use as hardfacing alloys in SFR, good corrosion behaviour and good friction and wear behaviour in sodium are essential. First results on these properties are shown in this article. Firstly, the corrosion behaviour of all coatings was evaluated through exposure tests in purified sodium for 5000 h at 400 °C. All coatings showed an acceptable corrosion behaviour in sodium. Finally, the friction and wear properties of one alloy candidate, NiCrBSi alloy, were studied in sodium in a dedicated designed facility. The influence of the oxygen concentration in sodium on the friction and wear properties was evaluated.

Wear Behavior of Fe-Cr-V based Hard Facing Alloy on ASTM A105 Steel

Wear Behavior of Fe-Cr-V based Hard Facing Alloy on ASTM A105 Steel

Coating Toughness Estimation through a Laser Shock Testing in Ni-Cr-B-Si-C Coatings

In the nuclear field, efforts are made to find substitutes to cobalt hardfacing alloys since these alloys have a principal drawback, the transmutation from stable 59Co to 60Co under neutron irradiation. In case of wear, fragments could be deposed on the surface of primary circuit and thus contaminate it, causing a real issue for deconstruction.

Microstructural characterisation of Tristelle 5183 (Fe-21%Cr-10%Ni-7.5%Nb-5%Si-2%C in wt%) alloy powder produced by gas atomisation

Nitrogen gas atomised powders of the hardfacing alloy Tristelle 5183 (Fe-21%Cr-10%Ni-7%Nb-5%Si-2%C in wt%) were sieved into different particle size ranges and their microstructures have been investigated. Powder particles larger than approximately 53 μm are composed of dendritic fcc γ-Fe as the principal phase with smaller quantities of: α-Fe, an interdendritic silicide phase isostructural to Fe5Ni3Si2, and Nb(C,N). Particles <53 μm have increasing quantities of either dendritic α-Fe or cellular silicide phase with decreasing amounts of γ-Fe as the particle size decreases, along with ~5% Nb(C,N). Coarse (> 10 μm) sized Nb(C,N) particles, that are seen in all powder size fractions, pre-existed in the melt prior to atomisation, whereas micron-sized Nb(C,N) particles that are found within α-Fe, γ-Fe or silicide are the primary solidification phase. Nanoscale Nb(C,N) also formed interdendritically in the last stages of solidification. Compared with a mould cast sample, a significant difference is the suppression of M7C3 formation in all powder size ranges. The increasing quantities of α-Fe and silicide in smaller sized powder particles is consistent with increased undercooling prior to nucleation permitting metastable phase formation.

Effect of simultaneous addition of ferroniobium and ferrotitanium on properties of hardfacing

ABSTRACTThe slag-free self-shielded flux-cored wire with simultaneous addition of ferroniobium (Fe-Nb) and ferrotitanium (Fe-Ti) was developed to fabricate the iron-based hardfacing alloys. The transfer coefficients of Nb and titanium of slag-free self-shielded flux-cored wire were 91.2 and 63.8%, respectively. The changes in microstructures indicate that Nb and Ti addition shifted the carbon concentration in the remaining liquid to one corresponding to the near eutectic state owing to the formation of (Nb, Ti)C which consumed carbon. The wear loss of the hardfacing alloy with 18 wt-% Fe-Nb and 6 wt-% Fe-Ti addition was the smallest among all the alloys owing to the formation of reinforced uniform quadrangle-shaped (Nb, Ti)C carbides in the refined microstructure and the highest hardness.

Remanufacture of hot forging tools and dies using laser metal deposition with powder and a hard-facing alloy Stellite 21\xae

Additive Layer Manufacturing (ALM) processes are attracting interest in the forging industry due to their potential suitability for remanufacturing and repair of tools and dies. The ALM process known as Laser Metal Deposition with powder (LMD-p) can be used to provide a hard-facing alloy repair to hot forging tools. This is particularly important on complex tool geometries due their superior wear resistance. The Advanced Forming Research Centre (AFRC) has established a low cost standard test method to evaluate abrasive and adhesive wear on hot forging H13 tool steel dies on an industrial scale 160 kJ Schuler screw press. The bespoke tool design allows researchers to benchmark new and novel coatings, lubricants and additive layers against a known standard. Furthermore, AFRC metrology standard methods ensure repeatability and reproducibility of benchmark results. To evaluate the performance of LMD-p for remanufacturing of hot forging tools and dies, a cobalt based alloy (Stellite 21®) was selected. Stellite 21® is widely used as a hard-facing alloy as it provides excellent machinability coupled with superior wear characteristics. AFRC standard dies were coated with LMD-p Stellite 21®. The LMD-p coating was then machined to final geometry and then subjected to hot forging under AFRC standard conditions to compare to benchmark wear characteristics. Adhesive and abrasive wear was evaluated. It was shown that the Stellite 21® LMD-p additive layer performed better in both adhesive and abrasive conditions than standard H13 tools steel dies.

Abrasive wear behavior of Nb-containing hypoeutectic Fe–Cr–C hardfacing alloy under the dry-sand/rubber-wheel system

AbastractDry sand/rubber wheel test with different normal loads (70 N, 190 N) and rubber wheel rotational speeds (100 rpm, 130 rpm, 160 rpm, 190 rpm, 220 rpm) was carried out on Nb-containing hypoeutectic Fe–Cr–C hardfacing alloy. The change of alloy wear behavior with wear conditions was investigated. The results showed that increasingly-severe wear condition deteriorated the uniformity of macro wear scar. The wear behavior change of two regions on the wear scar affected the overall wear loss variation. When abrasives driven by rubber wheel were gradually fed into the immediate-contact position between rubber wheel and alloy surface, a fully-worn region was left on the alloy surface. Afterwards, abrasives continued to be driven by rubber wheel away from the immediate-contact position and tended to leave a weakly-worn region that can impede the increase in wear loss. The wear mechanism of the fully-worn region was the dendritic austenitic micro-cutting and, the spalling of NbC and eutectic-carbides. The weakly-worn region, however, mainly showed a mechanism of slight cutting/ploughing along wear direction. Under the 70 N load, abrasives driven by increasing rotational speed performed severer abrasion to make the wear scar mainly consist of the fully-worn region, which resulted in a relatively uniform macro wear scar and the constant increase in wear loss. Under the 190 N load, differently, the increasing rotational speed significantly intensified the work-hardening of the fully-worn region and the fragmentation of abrasives, which was advantageous for improving the wear-resistance of austenitic matrix and developing the area of weakly-worn region. Therefore, as the rotational speed increased, the alloy wear loss showed a trend of first stepping up and then decreasing.

Effect of different carbides on the wear resistance of Fe-based hardfacing alloys

Hardfacing plates are being used in raw material conveying system of an integrated steel plants to mitigate the wear of chutes and hoppers. Four Fe-based commercial hardfacing alloys were studied in this work. To prepare test samples, mild steel base plates was used. In hardfaced plates, mild steel backing provides the weldability, formability, and ductility whereas the hard weld deposit provides the required wear resistance. This investigation aims to correlate microstructural, tribological and hardness properties of hardfacing plate samples with varying chemical composition. Microstructural characterization involved the morphological study and elemental analysis of different types of carbides through EDS, hardness evaluation mainly involved measurement of bulk hardness and micro-hardness, whereas tribological studies involved pin-on-disc wear test. Higher hardness doesn't always mean higher wear resistance. Presence of alloying elements resists the material removal by abrasive action and increases the wear resistance.

Optimisation of cutting parameters for machining of newly developed Co-free hard-faced nuclear reactor components

ABSTRACT The components of nuclear reactor require wear and corrosion resistance properties at elevated temperatures. In the nuclear industry, the use of cobalt-based alloys is eliminated because of the induced radioactivity in the reactor environment. Hence, Nickel-based Tribaloy 700 hard-facing alloys have been chosen for many reactor components. Due to the non-availability of cast Tribaloy 700, an alternative method was evaluated by depositing the hard-facing Tribaloy 700 on a SS rod with subsequent machining to obtain the desired properties. Tribaloy 700 is basically a Nickel base alloy and the hardness of the deposited weld metal is 58–65 HRC. In this regard, various cutting tools are available for normal machining, like high speed steel, coated carbide and cubic boron nitride inserts tools. Among these, which tool to be used for easy machining of Tribaloy 700 is evaluated by the optimisation of cutting parameters using the Taguchi method.

Interface relation between CeO2/TiC in hypereutectic Fe-Cr-C-Ti-CeO2 hardfacing alloy

Abstract The lattice misfit of the different CeO2/TiC planes was calculated by Bramfitt two-dimensional lattice misfit degree theory. Then, the interface relation of CeO2(100)/TiC(111) was calculated by first principles, and the possibility of CeO2 as the heterogeneous nucleus of TiC was analyzed as well. Hypereutectic Fe-Cr-C-Ti-CeO2 hardfacing alloy was prepared in this paper, and its microstructure was observed by Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The calculated results show that the lattice misfit between CeO2 (100) and TiC (111) is 6.09%, which indicates that it is moderately effective for the CeO2 as the TiC heterogeneous nucleus. Four interfaces exist between CeO2 and TiC, which are Ce-C, Ce-Ti, O-C, and O-Ti ones. The interface adhesive works of Ce-C and Ce-Ti interfaces are small, and their interface energies are large, which indicates that they are extremely unstable and easy to decompose. However, the interface adhesive works of O-C and O-Ti interfaces are large, and their interface energies are small, which indicates that the two interfaces are thermodynamic stable. In addition, The O-C interface consists of covalent and metallic bonds, meanwhile the O-Ti interface consists of covalent, ionic and metallic bonds. Therefore, CeO2 can be as the heterogeneous nucleus of TiC. The experimental results show that CeO2 exists in TiC, which proves that CeO2 can be as the heterogeneous nucleus of TiC, then refines TiC.

Microstructure evolution during laser direct energy deposition of a novel Fe-Cr-Ni-W-B hardfacing coating

The paper presents a detailed study on the microstructure evolution and cracking tendency of a novel Fe-Cr-Ni-Mo-W-B hard facing alloy deposited on a carbon steel substrate using blown powder directed energy deposition technique. CALPHAD approach was used to understand the phase equilibrium in the system and to optimize the volume fraction of the hard facing precipitates. The preliminary deposits showed extensive cracking in the hard facing deposit, which was attributed to solidification cracking. To evaluate the cracking tendency of the alloy solidification sequence of the current alloy was evaluated using a Scheil Gulliver simulation and contrasted with the solidification sequence of the commercially available alloys. The simulations showed that the alloy used in this current study showed a primary FCC mode of solidification as opposed to a primary BCC mode of solidification in the commercial alloys. Crack free deposits were then fabricated by preheating the substrate to 400 °C thereby reducing the thermal strains. The segregation of the elements and phase fractions calculated using the THERMOCALC's® TCFE8 data base were then compared with the experimentally measured phase fractions and compositions. Both the simulations and the experimental work showed that the as solidified microstructure consists of a (Cr,Fe)2B phase in a FCC matrix. However, while CALPHAD is able to capture the phase fractions of the various phases during build fabrication, the partitioning behavior of W is not accurately captured. In this work we have developed a novel alloy and demonstrate that crack free deposits can be obtained with this new alloy with a hardness close to 600 VHN (55 HRC).

Effect of TiN on microstructure and wear resistance of Fe–Cr–C hardfacing alloy: experimental research and first-principles calculation

Fe–Cr–C coatings with and without TiN additive were developed by harden-surface welding. The effect of TiN on the wear resistance and microstructure of the surfacing layer in the surfacing layer were discussed. Analyze the refining mechanism of TiN on primary M7C3 with first-principles calculation. The Rockwell hardness tester was used to examine the hardness of the surfacing layer. Abrasive wear was test by wet grinding wheel wear tester. X ray diffractometer (XRD), scanning electron microscope (SEM), energy spectrum analyzer (EDS), Transmission electron microscope (TEM) and other equipment were used for testing and analysis. The results show that in the hardfacing layer containing TiN, the primary M7C3 was significantly smaller than that without TiN. As the TiN content increases, the hardness and wear resistance of the surfacing layer increase accordingly. The thermodynamic and kinetic calculations show that the two-dimensional misfit of TiN/M7C3 is 8.43%, and TiN can be used as a heterogeneous nucleus for primary M7C3. Based on the experimental study, the interfacial energy of Fe3Cr4C3 (0001)/TiN (111) was calculated by first-principles calculations. The interfacial energies of Fe3Cr4C3 (0001)/TiN (111) were lower than those of nucleation in iron-based melts. It indicates that TiN can be used as the heterogeneous nucleation base of primary M7C3, which is consistent with the experimental analysis.

Investigations on the Characteristics of Thermally Sprayed NiCrBSi Coatings Fused by Flame and Inductive Processing

Ni-based materials are some of the most used hardfacing alloys to improve wear and corrosion resistance for parts functioning under severe conditions. For the current study, a NiCrBSi self-fluxing alloy powder with particle size in range of 45-106 μm was employed as feedstock material and deposited onto a steel substrate material using the oxyacetylene thermal spraying process. The as-sprayed components have been subsequently subjected to thermal post-processing in order to increase the adhesion to the substrate and to reduce the inherent porosity of the coatings. Consequently, two types of heating sources were chosen. One of them was the neutral oxyacetylene flame and the second one was based on high frequency currents. The aim of this work was to study the influence of the heat source type of the post treatment on the final characteristics of the coatings. Evaluation of the morphology and microstructure of the developed coatings was performed after the remelting process by means of scanning electron microscopy. Hardness tests were carried out in cross-section complying with the ASTM E384 standard. In both cases, after fusing, the microstructure was refined, with a drastic decrease in porosity. Evaluation of the hardness distribution along the coating cross-section revealed similar values of microhardness.

A comparative assessment of iron and cobalt-based hard-facing alloy deformation using HR-EBSD and HR-DIC

Three iron-based alloys (Nitronic 60, Tristelle 5183 and RR2450) and a cobalt alloy (Stellite 6) are studied using bend-testing to induce progressive straining and both high resolution DIC and EBSD are utilized to provide quantitative characterization of the deformation mechanisms. The roles of austenite, ferrite and carbide/silicide phases are investigated, together with how each contributes to slip activation and localisation, GND development and hardening through to particle pull-out and fracture. The observed mechanisms are discussed in the context of galling performance.The results suggest that a distribution of fine precipitates, both intra-granular and at grain/phase boundaries, promote more homogeneous and distributed slip, and the development of distributed higher densities of GNDs. The latter promotes hardening which in turn also facilitates homogeneity of deformation and potentially better galling resistance. A uniform size of fine precipitates is also helpful; large silicides lead to particle fracture and pull-out, likely highly damaging under conditions of sliding contact and galling.

Research on Microstructure and Wear Resistance of Fe-Based Hardfacing Layer Using Plasma Surfacing Technology

In order to enhance the wear resistance of material surface, the hardfacing alloy is usually deposited on its surface by using plasma surfacing technology (PST). The technology has the advantages of the low dilution rate, small deformation, smooth welding path, food metallurgical combination, and no major defects. In this paper, a Fe-based alloy coating had been prepared by PST, and the structure and properties of surfacing layer had been studied. The results showed that the hardness of surfacing layer was significantly greater than that of the substrate. And the coating layer had a snowflake-like structure. Its Lorraine hardness was up to about 60HRC, and the friction coefficient was about half of the 65Mn after quenching. With the increase of the material hardness, the coating layer has excellent abrasion resistance.

Enhanced wear resistance of Stellite 12 by Mo addition and LSM

ABSTRACTAiming at additional improvements in the properties of Stellite 12 PTA hardfacing alloy deposited on 4140 steel substrate, the authors have adopted a dual approach. During PTA deposition Stellite 12 hardfacing powder was alloyed with 10 wt-% Mo, followed by laser surface melting (LSM). Addition of 10 wt-% Mo, led to an increase in the volume fraction of Co and W-rich complex carbides. Later on LSM executed on the PTA led to the development of unique microstructure near the surface, characterised by the segregation of hard Cr-rich carbides. The resultant layers were subjected to mechanical characterisation, at room temperature, e.g. hardness and wear resistance. It was concluded that combining both approaches i.e. addition of Mo during the hardfacing process followed by LSM of deposited layer gave additional improvements in mechanical properties owing to evolution of a unique carbide structure.

Analysis of Film Formation in High Chromium White Iron Hardfacing Alloys in Alkaline Solution using EIS and SIMS

A popular hardfacing alloy consisting of high chromium white iron (HCWI) was deposited on low carbon steel using shielded metal arc welding. The wear-resistant alloys are not only used in applications requiring wear resistance but also used in applications involving fluids of a range of pH values. It is well known that chromium containing alloys have good corrosion resistance due to the presence of passive film. In this study for understanding the film formation on carbides and eutectic austenite matrix, HCWI alloy were exposed to potentials (0.157 V vs. SCE and 0.758 V vs. SCE) derived from potentiodynamic studies in highly alkaline solution of pH 14, simulating Bayer refining process in alumina industry. Electrochemical impedance spectroscopy (EIS) technique was used to analyse the impedance of films. The thickness and the composition of film properties at various potentials were investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS). At potential 0.157 V versus SCE, chromium carbide had a thick layer of oxide film consisting of mainly FeO with minor amounts of CrO. The eutectic austenite matrix consisted of a much denser and slightly thinner film of FeO. It is proposed in this study that for the formation of an oxide film on carbides, the carbides would have to dissociate on the surface. This dissociation of carbides may likely render the hardfacing alloy less effective in wear-resistant applications. The results were explained through superimposing the Pourbaix diagram of chromium carbides and iron (Fe).