Hardfacing Alloy Research Articles

TRIBALOY T-401

Abstract Tribaloy T-401 is a cobalt hardfacing alloy with smaller Laves phase particles to promote ductility and keep corrosion resistance and wear properties. This datasheet provides information on composition, microstructure, and hardness. It also includes information on high temperature performance and corrosion resistance as well as casting, forming, joining, and powder metal forms. Filing Code: CO-113. Producer or source: Deloro Stellite Company Inc.

Effect of boron addition on the cavitation erosion resistance of Fe-based hardfacing alloy

The cavitation erosion behavior of Fe–Cr–C–Si– xB ( x = 0, 0.3 and 0.6 wt.%) alloys were investigated up to 50 h by using 20 kHz vibratory cavitation erosion test equipment. The boron-added alloys showed the improved cavitation erosion resistance compared to the boron-free alloy. This improvement was attributed to that the boron addition enhanced the grain boundary strength and refined the grain size of the matrix. However, the cavitation erosion rate of the 0.6 wt.% boron specimen was higher than that of the 0.3 wt.% boron specimen. The higher erosion rate of the 0.6 wt.% boron was due to the larger carbide volume in the matrix.

Thermal sensitivity of the π - phase in Nickel-based industrial hardfacing alloy

Thermal sensitivity of the π - phase in Nickel-based industrial hardfacing alloy

The effect of boron on the wear behavior of iron-based hardfacing alloys for nuclear power plants valves

The effect of boron of Fe–Cr–C–Si alloys, replacing Stellite 6 traditionally used in nuclear power industry, on the high temperature wear resistance was characterized. Sliding wear tests of Fe–Cr–C–Si–xB (x=0.3, 0.6, 1.0 and 2.0wt%) alloys were performed in air at temperatures ranging from 300 to 725K under a contact stress of 103MPa. Low-boron alloys containing less than 0.6wt% boron showed the excellent wear resistance than any other tested alloys in an elevated temperature. The improvement was associated with the matrix hardening by promotion of the γ→α′ strain-induced martensitic transformation occurred during wear. In addition, protective oxide layers formed on the contacting surface reduced the wear loss by minimizing the direct metal-to-metal contact. However, high-boron alloys containing more than 1wt% boron showed somewhat larger amount of wear loss than low-boron alloys due to the absence of the strain-induced martensitic transformation and the presence of the brittle FeB particles connected with easy crack initiation.

Microstructure of Fe-Based Alloy Hardfacing Coating Reinforced by TiC-VC Particles

Abstract Microstructure of the Fe-based alloy hardfacing coating reinforced by TiC-VC particles was investigated by means of SEM, TEM, XRD and EPMA. The thermodynamics and effect of elements on the carbides were discussed. The result shows that TiC-VC carbides can be formed during are welding. Carbides with particle size of 2–4 μm are uniformly dispersed in the matrix. Evidently the covering components and their amount affect the microstructure and hardness of the coatings. An excellent microstructure and hardness of hardfacing coating were obtained, while the amount of graphite, FeTi and FeV was controlled within the range of 8%–10%, 15%–18% and 8%–12%, respectively.

The Cavitation Behavior of Fe-Cr-C-Si-Ni Alloys

The cavitation erosion behavior of Fe-Cr-C-Si-xNi (x = 1, 2 and 3 wt.%) alloys were investigated for 50 hours using a 20 kHz vibratory cavitation erosion test equipment. 1 wt.% Ni added Fe-based hardfacing alloy showed excellent cavitation erosion resistance, comparable to the stellite 6. Above 1 wt.% Ni, however, the erosion resistance deteriorated quickly. It is conjectured that Ni addition above 1 wt.%, which has been shown to increase the stacking fault energy (SFE), resulted in reduction of the work hardening rate during the erosion test. Therefore, the enhanced cavitation erosion resistance of the 1 wt.% Ni alloy over the 2 and 3 wt.% Ni alloys could be explained in terms of the SFE, Ms temperature and work hardening.

Microstructure change caused by (Cr,Fe) 23C 6 carbides in high chromium Fe–Cr–C hardfacing alloys

A series of high chromium Fe–Cr–C hardfacing alloys were produced by gas tungsten arc welding (GTAW). Chromium and graphite alloy fillers were used to deposit coatings on ASTM A36 steel substrates. These coatings were especially designed to vary the size and proportion of the (Cr,Fe) 23C 6 carbides that are present in the microstructure at room temperature. Depending on the three different graphite additions of those alloy fillers, hypoeutectic, eutectic and hypereutectic microstructures were obtained on coated surfaces. No crack formation was found on the coatings. According to the X-ray diffraction analysis and microstructure characteristics, the hypereutectic composites consist of three phases, i.e. Cr–Fe solid solution (α), (Cr,Fe) 23C 6 and trace amounts of (Cr,Fe) 7C 3. Massive (Cr,Fe) 23C 6 contain (Cr,Fe) 7C 3 in the center, and cause its high hardness value up to HRC 70. And the massive (Cr,Fe) 23C 6 are surrounded by a eutectic structure to restrain cracks from appearing. All the microstructure constituents were rationalized in terms of a ternary diagram.

Abrasive wear behaviour of laser clad and flame sprayed-melted NiCrBSi coatings

In this work, the influence of the processing conditions on the microstructure and abrasive wear behaviour of a NiCrBSi hardfacing alloy is analysed. The hardfacing alloy was applied in the form of coatings onto a mild steel substrate (Fe–0.15%C) by different techniques: laser cladding (LC) and flame spraying (FS) combined with surface flame melting (SFM). In both cases, the appropriate selection of the process parameters enabled high-quality, defect-free NiCrBSi coatings to be obtained. The microstructure of the coatings was analysed by scanning electron microscopy (SEM), with attached energy dispersive spectroscopy (EDS) microprobe, and by X-ray diffraction (XRD). Their tribological properties were evaluated by micro-scale ball cratering abrasive wear tests using different abrasives: diamond, SiC and WC. Microstructural characterisation showed that both coatings exhibit similar phases in their microstructure, but the phases present differ in morphology, size distribution and relative proportions from one coating to another. Wear tests showed that in three-body abrasive conditions, despite these microstructural differences, the wear behaviour is comparable for both coatings. Conversely, in two-body wear conditions with diamond particles as the abrasive, it was observed that the specific wear rate of the material is sensitive to microstructural changes. This fact is particularly apparent in LC coatings, in which the zones of the layers with higher proportions of very small hard particles present a lower wear resistance. These results indicate that it is important to have good microstructural control of this material, in order to obtain coatings with an optimized and homogeneous tribological behaviour.

Wear, corrosion and cracking resistance of some W- or Mo-containing Stellite hardfacing alloys

Traditional Stellite hardfacing materials are Co–Cr–W–C type of alloys. A series of new Stellite alloys are developed based on Co–Cr–Mo–C system. Immersion–corrosion test is conducted in 10% HNO 3 oxidizing acid at boiling temperature, in 10% H 2SO 4 reducing acid at 66 °C and in 5% HCl reducing acid at 40 °C to evaluate the general corrosion resistance of the Stellite alloys. The abrasive, adhesive and erosive wear resistance is investigated on these two types of Stellite alloys. Critical plastic shear strain is obtained by conducting scratch test to evaluate the resistance to cracking. The W-containing Stellite alloys have better corrosion resistance in oxidizing acid. The Mo-containing Stellite alloys exhibit unusual combination of excellent wear resistance and corrosion resistance in reducing environments. Mo-containing Stellite alloys also have adequate cracking resistance compared with the W-containing Stellite alloys.

Microstructure and properties of the TiC/Fe-based alloy hardfacing layers

TiC/Fe-based alloy hardfacing layers were obtained by shielded metal arc welding (SMAW), in which H08A bare electrode was coated with a powder mixture of ferrotitanium, rutile, graphite, calcium carbonate and calcium fluoride. TiC particles are produced by direct metallurgical reaction between ferrotitanium and graphite during welding. The particles of TiC with cubic shape are distributed evenly in the Fe-rich matrix in the hardfacing layers, the particle size is about 3–5 μ m. The microstructure and mechanical properties of the hardfacing layers are markedly affected by the amounted of the ferrotitanium and graphite in the coating of the electrode. The wear properties of the hardfacing layers are superior to the substrate AISI 1045 steel. The coefficient of friction data of the hardfacing layers do not show significant fluctuations.

Microstructure and abrasive wear behaviour of iron base hardfacing

The influence of the composition and heat treatment of overlays on the abrasive wear resistance of iron base hardfacing alloy overlays is reported. Overlays were deposited using a shielded metal arc (SMA) welding process on structural steel using two commercial hardfacing electrodes, i.e.Fe – 6%Cr – 0.7%C (H1) and Fe – 32%Cr – 4.5%C (H2). Abrasive wear resistance of overlays in as welded and heat treated conditions was tested using a pin on disc system against a 300 grade waterproof SiC polishing paper at different normal loads (1 – 4 N) and constant sliding speed 2.0 m s-1. Optical microscopy was used to study the microstructure of overlays in as welded and heat treated conditions. SEM studies of wear surfaces were carried out to analyse wear mechanisms. It was found that the wear resistance of the high Cr – C coating is better than the low Cr – C hardfacing under identical conditions. Significant variation in hardness was noticed across the interface, indicating the effect of dilution. Hardness of the coating adjacent to the interface was found to be comparatively lower than the coating further away from the interface. Post-weld heat treatment enhanced the abrasive wear resistance.

Selection of hardfacing material for components of the Indian Prototype Fast Breeder Reactor

Nickel-base hardfacing alloys have been chosen to replace cobalt-base alloys as hardfacing material for components of the Indian Prototype Fast Breeder Reactor, for minimising the dose rate to personnel during maintenance and decommissioning, and to reduce the shielding thickness required for component handling. Induced activity, dose rate and shielding computations showed that replacing cobalt-base alloys with nickel-base alloys for hardfacing of components would result in a marked reduction in both the dose rate from the components and the thickness of lead handling flasks. Long-term ageing studies on the nickel-base hardface deposits on austenitic stainless steel showed that the hardface deposit would retain adequate hardness at the end of the components' design service-life of 40 years of exposure at 823 K.

Study on Composition-Induced Microstructural Variation in the Interface Between Co-Based Hardfacing Alloys and IN738 Ni-Based Superalloy

Alloy mixtures with varying composition of two Co-based hardfacing alloys and IN738 Ni-based super alloy were examined using differential scanning calorimetry. The microstructure of the resulting specimens was then analyzed using optical and scanning electron microscopy and energy dispersive spectroscopy. The microstructural evolution between each hardfacing alloy and the IN738 substrate was documented and the formation of topologically close-packed and/or additional carbide phases was noted. Microstructures that are undesirable for high temperature and stress applications were produced in specimens with a higher degree of mixing (from 25 to 75 wt.% of hardfacing alloy in IN738). The two hardfacing alloys produced markedly different microstructures in the alloy mixtures due to differences in elemental composition. A hardfacing process that minimizes the degree of deposit-substrate mixing will be beneficial to the performance of the coating.

The effect of cerium on the oxidation resistance of Fe -20Cr-1.7C-lSi

Co is the major contributor to the radiation build-up in nuclear power plants. Many studies have been done to develop Co-free hardfacing alloys to replace Co-based Stellite 6 which is used for valve hardfacing. The Co-free alloys should have equivalent wear resistance, cavitation erosion resistance, and oxidation resistance to Stellite 6. Recently, we developed Fe-20Cr-1.7C-lSi alloy to replace Stellite 6. The new alloy has equivalent sliding wear resistance, and cavitation erosion resistance to Stellite 6. However, the high temperature oxidation resistance of the Fe-based hardfacing alloy is not as good as much as that of Stellite 6 due to the Cr deficiency in the Fe-based hardfacing alloy matrix. Ce is known to improve oxidation resistance of Fe-based alloys at elevated temperatures due to the beneficial effects of Ce such as formation of fine oxide layers and reduction of oxide-growth stresses. Therefore, in present study, the effect of Ce on the oxidation resistance was investigated in pressurized-water at 300? under 7 MPa for 200 days in an autoclave. The concentration range of Ce was up to 0.2 wt.%. The specimens containing 0.2 wt.% Ce showed lower weight loss compared to that of the Ce-free specimen. With increasing Ce concentration, high temperature oxidation resistance of new alloy increased. The increased high temperature oxidation resistance may be due to the formation of adhesive oxide layers.

Study on the cavitation erosion behavior of Fe-based hardfacing alloys containing Mn, Ti and V for replacing Co-based Stellite 6

Stellite 6 has been used as hardfacing material of valve components in nuclear power plant industry and other applications. Stellite 6 contains more than 60 wt % Co and it was recognized that Stellite 6 used in valve hardfacing is one of the main sources of Co, which is the major contributor to build up the radiation field in nuclear power plants. Thus it is largely responsible for the occupational radiation exposure of plant maintenance personnel. Also the price of Co is expensive and highly varying. Therefore, there have been many efforts to develop Co-free hardfacing alloy We have also developed Fe-based new alloy, of which sliding wear and cavitation erosion resistance were almost equivalent to those of Stellite 6. In the present study, the effects of Mn, Ti and V on the cavitation erosion behavior of the alloy were investigated. The Fe-based new alloy containing V had similar cavitation erosion resistance to Stellite 6 but the others containing Mn and Ti were inferior to Stellite 6.

03/02197 Hydrogenation of coals from the Yerkovetsk field to obtain liquid fuel: Maloletnev, A. S. et al. Khimiya Tverdogo Topliva, 2002, (6), 40–50. (In Russian)

The wear characteristics of a cobalt-base hardfacing alloy and SUJ2 (ASTM 52100) steel were studied under conditions of unlubricated sliding wear. The maximum specific wear rates were obtained under a sliding velocity of 0.25 m s−1 for cobalt-base alloy SF12 and SF20 specimens. From X-ray diffraction the wear debris was found to be composed of the iron oxide α-Fe2O3 and the spinel-type oxides NiCr2O4 and CoFe2O4 formed by oxidative wear and α-Fe formed by mechanical wear. The quantity of oxide on the wear surface of SUJ2 steel was considerably greater with a velocity of 3.0 m s−1 than with a velocity of 0.25 m s−1. Transfer of iron from the SUJ2 steel specimen to the friction surface of the cobalt hardfaced specimen was readily observed at a velocity of 0.25 m s−1.

Crack propagation in a hard-faced AISI type 304 stainless steel

This work presents the results of a study on crack propagation in AISI type 304 stainless steel pipe coated with a wear-resistant (hard-facing) alloy. This layer was applied by electric arc welding directly to the pipe. After the alloy solidifies, cracks are generated. Most of them start at the surface of the hard-facing alloy and grow towards the steel. The objective of this work was to analyze the crack propagation into the stainless steel by means of thermal cycling. For this, four samples were obtained from a pipe. The samples were subjected to 40 thermal cycles. Heating was achieved in an electric resistance furnace up to 700 °C, the samples were held at this temperature for 5 min and were cool down outside the furnace to 300 °C. Three samples were cooled in air and the last one in water. One of the samples underwent an aging treatment for 168 h at 750 °C previous to the cycling. All the samples were metallographically inspected before and after thermal cycling by light optical microscopy. Microhardness testing was carried out on all the samples.

Distribution of strong carbide forming elements in hard facing weld metal

Carbides and the matrix microstructure in high carbon hard facing weld metals reinforced with strong carbide forming elements were investigated by means of electron probe microanalysis (EPMA), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The thermodynamics and the effect on the matrix of the formation of carbides were discussed. It was revealed that Nb, Ti, and V strongly influenced the distribution and existing state of carbon, induced obvious depletion of carbon in the matrix, and precipitation of carbides. However, when only V was alloyed as the carbide forming element, carbides were scarce and distributed along the grain boundary, and the hard facing metalwas easily hardened. The hard facing alloy reinforced with Nb, V, and Ti can form finely dispersed carbides and low carbon martensite matrix.

Laser Cladding of Austenitic Stainless Steel with Hardfacing Alloy Nickel Base

A nickel base alloy Colmonoy 6 was chosen as a candidate material for hard facing many components in the prototype fast breeder reactor. This alloy offers outstanding wear resistance and high hardness at elevated temperatures. Previous research using the gas tungsten arc welding process revealed that the hardness of the deposit is influenced by the dilution from the base metal up to a deposit thickness as high as 2.5 mm. The present study aims to control the level of dilution in the hard face deposits by carrying out deposition using a low heat input laser cladding process. The samples were characterised by macroscopic and metallographic examination, and microhardness measurements, SEM - EDAX and XRD analysis were used to determine their properties. The study demonstrated that by controlling laser cladding parameters, thin deposits with a low level of dilution can be laid on austenitic stainless steel substrate. Cracking of the deposit was minimised by controlling the heating and cooling rates.

Study on the cavitation erosion behavior of hardfacing alloys for nuclear power industry

The cavitation erosion behavior of wear resistant hardfacing alloys for nuclear power industry Co-base Stellite 6 and new Fe-base alloy was investigated using 20 kHz vibratory cavitation erosion test equipment. Although the crack was initiated at the carbide-matrix interfaces, the matrix hardened by strain-induced phase transformation from austenite to martensite effectively repressed the crack propagation. The cumulative weight loss of new Fe-base alloy was about 2.40 mg/cm 2 after exposing to cavitation for 150 h and the cavitation erosion characteristic was similar to that of Stellite 6 on the whole range. The improved cavitation erosion resistance of new Fe-base alloy was due to the matrix hardening by the strain-induced phase transformation and to the small volume fraction of the carbide-matrix interface acting as crack initiation sites.