Iron-based Hardfacing Alloys Research Articles

Development of novel carbon-free cobalt-free iron-based hardfacing alloys with a hard π-ferrosilicide phase

Recently, iron-based alloys with a π-ferrosilicide phase have emerged as potential alternatives to cobalt-based hardfacing alloys. Here, we present the development of two π-ferrosilicide containing alloys: one with a ferritic matrix and the other with a ferritic-austenitic matrix. In the as-cast condition, both alloys revealed fine Ni- and Si-rich coherent cubic shaped D03 precipitates in the BCC matrix. The π-ferrosilicide phase was found to have an orientation relationship with the ferrite phase, nucleating within ferrite matrix and from ferrite grain boundaries. In contrast to carbide-strengthened hardfacing Fe-alloys, here the dissolution of the π-ferrosilicide phase at 1200 °C enables easy thermomechanical processing of these alloys, which results in refinement of the π-ferrosilicide and additional formation of χ-phase precipitates in the ferrite. Nano-scratch tests provided evidence of a resilient silicide-ferrite interface, likely to due to it possessing some coherency. Both alloys also displayed compressive strengths approaching 2 GPa and ductility in compression of approximately 25 %. The combination of processability and attractive mechanical properties suggests that these alloys have the potential to serve as alternatives to carbide-reinforced hardfacing Fe-alloys.

Crack-free hard facing options for orifice plate used in oil refinery applications

The purpose of this study is to select a suitable tubular wire electrode as an alternative hardfacing material for Stellite 1 in the production of SS304 orifice plates used in oil refineries. It is also intended to develop an efficient deposition procedure for crack-free hardfacing. Compatible cobalt, nickel, and iron-based hardfacing alloys were selected so as to match the hardness and hot hardness properties of stellite 1. Moving heat source analysis was performed to find the heat affected zones and the thermal stress distribution during hardfacing. The significance of weld speed, bead width, and weld concentration on the weld deposition process was analysed using ANSYS, to extract an efficient deposition procedure. The hardfacing alloys were tested for stress and deformation at working temperature (up to 815 οC) to understand the performance. Seven materials were taken into consideration as options along with six parameters. The results revealed a higher longitudinal residual stress of 2000 MPa for Talonite and Tribaloy hardfacing alloys. Colmonoy 6 was found to be having the least stress value of 2186 MPa. Furthermore, the von mises stress values arrived for different conditions showed that the optimal welding condition is 5 mm/s welding speed, 3 mm radius of beam and 455 °C preheat temperature. Microstructural study revealed the dendrite growth in the surface of Colomony 6 hardfacing during solidification, which led to the improvement in mechanical properties.

Microstructure and wear resistance of in situ TiC-reinforced low-chromium iron-based hardfacing alloys

Microstructure and wear resistance of in situ TiC-reinforced low-chromium iron-based hardfacing alloys

Characterisation of the wear and friction behaviour of laser deposited cobalt and iron-based hardfacing alloys for nuclear applications

Valves and pumps in nuclear plants operate in a particularly aggressive environment of a high neutron flux, high contact loads and in superheated water up to 300 °C. Traditionally there has only been one material that can survive these conditions: cobalt based hardfacing alloys called Stellites. There is an urgent need to replace cobalt-based alloys because of the formation of cobalt-60 radioisotope, which causes radioactive exposure. In this study an iron-based hardfacing alloy, Tristelle 5183 was compared with Stellite 6. The hardfacings were manufactured via laser cladding. Wear testing was performed using a pin-on-flat configuration, with like-on-like couples, from room temperature up to 300 °C with loads of 50–500 N. The friction coefficient for the Tristelle was higher (typically 0.45) than the Stellite (typically 0.35) across all temperatures and loads. The wear rate of the Tristelle was higher than the Stellite, but the exact difference varied with both load and temperature. The specific wear rate increased with temperature, but only gradually. The operative wear mechanism was a combination of adhesive and oxidational wear, but there were significant differences found between the two alloys. For the Tristelle, the oxide became mechanically mixed with the heavily deformed surface metal. In contrast, the oxide on the Stellite was detached from the surface without any mechanical mixing. The extent of surface deformation was much greater for the Tristelle than the Stellite. The large (5–20 mm) NbC in the Tristelle fractured a considerable distance (up to 40 mm) below the worn surface and became increasingly fine as the worn surface was approached as a result of high strain deformation in the matrix. In the Stellite no carbide fracture was observed. The reasons for the marked difference in behaviour between the two alloys, each with the same mechanical properties, are discussed in detail.

Influence of hardfacings on wear behavior of EN-42A steel in actual field conditions

ABSTRACT In agriculture, the wear significantly influences the working edges of the ploughshare blades. So any improvement in the life of the tillage tools will be of great significance. In the present work EN-42A steel, ploughshare blades were hardfaced by three different iron-based hardfacing alloys, designated as H1, H2, and H3 using manual metal arc welding technique with an aim to improve the abrasive wear behaviour of ploughshare blades. The full edge (120 mm) and half-edge (60 mm) of the ploughshare were overlaid in order to examine the influence of the overlaid area. The study reveals the bare EN-42A steel experienced maximum weight loss (103 g), indicating low abrasive wear resistance due to its soft ferritic and pearlitic structure. Hardfacings were found to be protective against abrasive wear, and H1 hardfacing has shown minimum weight loss (71 g), followed by H2 (84 g) and H3 (86 g) hardfacing. Wear rate indices (WRI) for H1, H2, and H3 hardfaced steel are found to be 1.45, 1.22, and 1.19, respectively. Better behaviour of H1 hardfacing is attributed to its high hardness, and presence of complex nanocarbides in the metal matrix. Full-edge hardfaced ploughshare blades indicated better abrasive wear resistance than the half-edge hardfaced blades.

Impact-abrasive wear of martensitic steels and complex iron-based hardfacing alloys

Highly loaded wear components in manifold applications such as sieves, crushers, etc. suffer from combined impact and abrasive wear. To gain deeper understanding of different ongoing mechanisms, four different Fe-based materials, two martensitic steels Hardox 450 and Hardox 600, and two gas metal arc welded (GMAW) hardfacings - a Fe–Cr–C based hardfacing and a complex-alloyed Fe–Cr–Nb–C–B alloy were investigated with a novel modification of a cyclic impact and abrasion test. This test rig uses quartz sand as abrasive and a plunger simulating industrial sieving applications. Pre- and post-test materials analyses were performed utilising 3D microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), microhardness and nanoindentation tests for a thorough materials analysis and the clarification of the main occurring damaging mechanisms.Results indicate a very beneficial performance of a complex-alloyed Fe–Cr–Nb–C–B alloy due to its fine-dispersed hard phases and their homogenous distribution throughout the material, which does not change much with varying deposition parameters. In comparison, higher wear rates of a hypereutectic Fe–Cr–C alloy are attributed to coarse precipitated Cr-carbides within the microstructure. At martensitic steels, mechanically mixed layer were formed in the impact-abrasion region, which decreases the wear attack to a certain extent. However, massive materials displacement and abrasive wear occurs due to the lack of hard phases and high ductility, which obstruct increased abrasive attack.

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 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.

Modeling the impact–sliding wear characteristics of rare earth additive iron-based hardfacing alloys

This paper presents a systematic study of the effect of the cerium oxide content on the mechanical, microstructural and tribological properties of iron-based alloys. The results indicate that the microstructure of the hardfaced alloys is mainly composed of austenite, MC and M7C3 carbides. The primary austenite grain size was refined at first and then coarsened with the increase of the rare earth oxide additions. Meanwhile, the hardness of the hardfacing alloy was also increased. The increased area fraction of carbides was found to be beneficial for enhanced wear resistance. A statistical regression model was developed and verified with a number of test cases in order to evaluate the adequacy of the model. The optimal amount of rare earth was found to be less than 6 wt.%; below this composition, the microstructural, mechanical and tribological properties were excellent.

Dry sliding adhesive wear characteristics of Fe-based hardfacing alloys with different CeO2 additives – A statistical analysis

In the present investigation, four different rare earth (RE) additive iron-based hardfacing alloys were prepared by the shielded metal arc welding process with pre-placement technique. The objective was to examine the effect of dry sliding wear parameters and to develop a statistical regression model using full factorial approach. A regression equation was developed and validated with a number of test cases. The morphology of worn surfaces and corresponding wear debris was studied in order to examine the wear mechanism using SEM. The RE additive alloys exhibited a significant improvement in macrohardness and wear resistance. The microstructure was refined at first and then coarsened with the increase of RE additions. The optimal amount of RE was found to be 4wt%.

In situ X-ray diffraction analysis of strain-induced transformations in Fe- and Co-base hardfacing alloys

A cobalt-base alloy and an iron-base hardfacing alloy were characterized by in situ diffraction during tensile testing at room and elevated temperatures. Both alloys showed a transition temperature above which a stress-induced martensite transformation disappears. This transition temperature is high (700–825 °C) for the cobalt-base alloy and low (

Influence of tungsten on microstructure and wear resistance of iron base hardfacing alloy

A series of iron based hardfacing alloys with varying tungsten contents were fabricated using slag free self-shielded flux cored wire, and the effects of tungsten addition on microstructure and wear performance were investigated. The experimental results showed that the iron base tungsten free hardfacing alloy has a typical hypereutectic microstructure, which consists of primary hexagonal M7(C, B)3 carbides and eutectic long bar-like M3(C, B) carbides in the austenite and martensite matrix. The addition of tungsten increases the size of primary hexagonal M7(C, B)3 carbides and promotes the formation of martensite, as well as changes the morphology of eutectic carbides. It was found that the eutectic carbides change from the long bar-like shape to the scattered web shape with the increase in tungsten content to 9 wt-%, and subsequently change to the plate shape with further increasing the tungsten content to 12 wt-%. For the all tungsten containing hardfacing alloys, tungsten exists in both the carbides and matrix uniformly. Results also showed that the wear loss of the sample with 9 wt-% tungsten was the smallest among all the samples owing to the higher hardness and reinforced microstructure.

Comparative behaviour of cobalt and iron base hardfacing alloys

This paper aims to compare the behaviour of cobalt and iron base hardfacing alloys on hot forging dies under temper, shock and wear. Tempering resistance, shocking behaviour and wear resistance were investigated using a tubular furnace, press and pin on disc tribometer respectively. The results showed that the thermal stability of commercial iron base hardfacing alloy (named RMD248) is good below 550°C but poor in the case of higher temperature, whereas the cobalt base hardfacing alloy presents superior tempering resistance. The cobalt base hardfacing alloy possesses excellent shock hardening properties at all the experimental temperatures, but RMD248 does not, especially at high temperature (600°C). Compared with the hardfacing layer produced by RMD248, the cobalt base hardfacing layer produces high wear resistance at 600°C and high temperature oxidation resistance at 600°C for 100 h.

Behaviour of iron-based hardfacing alloys under abrasion and impact

Iron-based hardfacing alloys are widely used to protect machinery equipment exposed either to pure abrasion or to a combination of abrasion and impact. The specific wear behaviour of a welding alloy under these conditions depends on its chemical composition, the microstructure obtained after welding and finally the welding technology used to apply them respectively the parameter settings which strongly influence, for example, dilution with the base material or formation of metallurgically precipitated hard phases. The main objective of this study was to evaluate the wear behaviour for pure abrasion and for combined wear of iron-based alloys which are typically applied by gas metal arc welding (GMAW). A new complex Fe–Cr–W–Mo–Nb alloy with high boron content was set into comparison with lower alloyed materials on basis Fe–Cr–B–C, a synthetic multiphase alloy on iron base with around 50 wt.% tungsten carbides and a crack free martensitic Fe–Cr–C alloy containing finely precipitated Niobium carbides. Besides these a conventional hypereutectic Fe–Cr–Nb–C alloy was integrated in the program serving as standard which is already well described in literature. In order to simulate real field conditions on a lab scale, tests were performed with a standard ASTM G65 dry-sand rubber-wheel tester (3-body abrasion). A specially designed impeller-tumbler apparatus enabled investigation of impact abrasion wear tests (combined impact and abrasion wear). The evaluation of wear behaviour was supported by micro- and macrostructural investigations and by hardness tests.

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 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.

Measurement of the threshold galling stress of hardfacing alloys

Galling is a severe type of wear that occurs when relative motion exists between contacting surfaces with extensive local adhesion. The ASTM button-on-block test method for galling resistance of a material couple requires a large number of specimens and an apparatus with very high load capacity for testing at a range of different loads to find the threshold galling stress. In contrast, the galling test method of sliding two crossed cylinders over each other has the advantages of determining the galling resistance by using a small number of samples and utilizing a standard metallurgical/mechanical test apparatus. In this study, the crossed cylinder method is used to test cobalt- and iron-based hardfacing alloys with very high threshold galling stresses. How to measure or calculate the threshold galling stress in the crossed cylinder method is also studied.

Some observations of the influence of δ-ferrite content on the hardness, galling resistance, and fracture toughness of selected commercially available iron-based hardfacing alloys

Iron-based weld hardfacing deposits are used to provide a wear-resistant surface for a structural base material. Iron-based hardfacing alloys that are resistant to corrosion in oxygenated aqueous environments contain high levels of chromium and carbon, which results in a dendritic microstructure with a high volume fraction of interdendrite carbides which provide the needed wear resistance. The ferrite content of the dendrites depends on the nickel content and base composition of the iron-based hardfacing alloy. The amount of ferrite in the dendrites is shown to have a significant influence on the hardness and galling wear resistance, as determined using ASTM G98 methods. Fracture-toughness (K IC) testing in accordance with ASTM E399 methods was used to quantify the damage tolerance of various iron-based hardfacing alloys. Fractographic and microstructure examinations were used to determine the influence of microstructure on the wear resistance and fracture toughness of the iron-based hardfacing alloys. A crack-bridging toughening model was shown to describe the influence of ferrite content on the fracture toughness. A higher ferrite content in the dendrites of an iron-based hardfacing alloy reduces the tendency for plastic stretching and necking of the dendrites, which results in improved wear resistance, high hardness, and lower fracture-toughness values. A NOREM 02 hardfacing alloy has the most-optimum ferrite content, which results in the most-desired balance of galling resistance and high K IC values.

The effect of manganese on the strain-induced martensitic transformation and high temperature wear resistance of Fe–20Cr–1C–1Si hardfacing alloy

Sliding wear tests of Fe–20Cr–1C–1Si– xMn alloys with x varying from 0 to 25 wt% were performed in air at temperatures of 25–450°C under a contact stress of 103 MPa. During wear at 25°C, low-Mn alloys containing less than 5 wt% Mn and high-Mn alloys containing more than 10 wt% Mn exhibited the γ→α ′ and γ→ε strain-induced martensitic transformations, respectively. As the test temperature increased, low-Mn alloys showed a wear transition from mild oxidative wear to galling at a temperature between 350°C and 400°C due to the absence of γ→α ′ strain-induced martensitic transformation. In the case of high-Mn alloys, the mild oxidative wear was maintained until 450°C, which was the highest test temperature in this study, with the formation of strain-induced ε martensite. It was considered that the γ→ε strain-induced martensitic transformation could be more beneficial to the high temperature wear resistance of iron-base hardfacing alloy than the γ→α ′ strain-induced martensitic transformation due to the higher M d temperature.

Corrosion Resistance and Electrochemical Potentiokinetic Reactivation Testing of Some Iron-Based Hardfacing Alloys

Abstract Hard facing alloys were weld-deposited on a base material to provide a wear-resistant surface. Commercially available iron-based hardfacing alloys were evaluated for replacement of cobalt-...