Hardfacing Alloy Research Articles

Microstructure and Microhardness of 17-4PH Deposited with Co-based Alloy Hardfacing Coating

Abstract Hardfacing is widely used to improve the performance of components exposed to severe service conditions. In this paper, the surface modification was evaluated for precipitation hardening martensitic stainless steel 17-4PH deposited with Co-based alloy stellite12 by the plasma-transferred arc welding (PTAW). The microstructure and microhardness of coating and heat affected zone(HAZ) of base metal were characterized by optical microscope (OM), scanning electron scanning microscope (SEM), X-ray diffractometer and hardness tester. The results show that the interface between weld metal and base metal is favorable without pore and crack, at the same time elements diffusion is observed in the fusion area. However, as the distance from the interface increases, HAZ comprises three different microstructural zones, namely, zones of coarse overheated structures, quenching martensite and martensite, ferrite. The microhardness decreases gradually from the HAZ near interface to the base metal, except the zone of coarse overheated structures. The microhardness of the coating improves a lot and fluctuates in a definitive range, and microstructural gradient is observed including the fusion area (the planar region and the bulky dendrite in a direction perpendicular to the weld interface), the transition zone (the dendrite in a multi-direction way) and the fine grain zone near the surface in the coating (fine equiaxial structure).

Improving High‐Temperature Wear Resistance of Fe–Cr13–C Hardfacing Alloy by Nitrogen Alloying

AbstractNitrogen alloying of Fe–Cr13–C hardfacing alloy produces marked precipitation strengthening to achieve an improvement in high‐temperature wear resistance. Two hardfacing alloys of Fe–Cr13–C (with and without nitrogen) are slid on carbon steel at high‐temperature of 600°C and high load of 600 N, and wear behaviors are studied systematically. It is found that abrasive wear occurrs on the surface of the hardfacing alloy due to abrasive action of crushed oxide particles coming from the surface of carbon steel on the high temperature. The wear resistance is determined by the size and distribution of precipitates. The results show that the hardfacing alloy can obtain a great increase in hardness and a marked decrease in wear depth of grooving due to the effect of carbonitirde precipitates. The high‐temperature wear resistance of the Fe–Cr13–C hardfacing alloy is improved by nitrogen alloying, and the wear mechanism is mainly plastic deformation with minimum depth of grooving caused by the oxide particles.

The intensifying effect of carbon nanoparticles on formation of microarc coatings on aluminum alloys

It is shown that carbon nanomaterials (ultradispersed diamond-graphite batch mixture, ultradispersed diamonds) introduced into basic electrolytes cause significant intensification of the process of micro-plasma formation of ceramic coatings on aluminum alloys of different compositions, including silumins characterized by a strongly heterogeneous structure. This is primarily manifested in an increase in the coating thickness as dependent on the chemical composition of the hard-facing alloys by 1.8–2.5 times. Modification of ceramic coatings by carbon nanoparticles results in a significant increase in their microhardness and wear resistance and a simultaneous decrease in the friction coefficient

Effect of Ta on the microstructure and hardness of Stellite 6 coating deposited by low power pulse laser treatments

Stellite 6 hardfacing alloy with different Ta contents is successfully synthesized with an in situ process on low carbon ferritic steel substrate by Nd:YAG pulsed laser cladding with pre-placed Stellite 6 and Ta mixed powders. The effect of different amounts of Ta on the microstructure of the Stellite 6 hardfacing alloy is investigated using scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. With an increase in Ta content, in addition to orthorhombic Cr-rich M7C3 carbides observed in the Ta-free Stellite 6 alloy in interdendritic regions, Ta-rich M4C3.04 type carbides are formed as well as individual bulky Ta-rich MC type carbides in Chromium carbide–Cobalt solid solution eutectic area. Furthermore, the Co-rich dendrites become much finer. With further increase of Ta, hexagonal M7C3 carbides are formed at the interface of orthorhombic ones. These microstructural changes are responsible for the improvement of the hardness of the Ta modified Stellite 6 hardfacing alloy.

Structural Changes in Cobalt Solid-Solution Crystals Due to Milling

Abstract A detailed microstructural study was carried out using a field emission-scanning electron microscope with the aim of analysing the effect of surface work-hardening which occurs when milling the cobalt based hard facing alloy ”Stellite 12“. The strengthening was determined to be caused by the formation of two-dimensional structural defects in the cobalt solid-solution matrix. The assumption that a stress induced martensitic transformation of the crystalline areas of the cubic cobalt phase into thin hexagonal cobalt platelets occurs was confirmed by X-ray diffraction phase analysis. In addition, it was assumed that stacking faults would be formed. For the microscopic investigation, the channeling effect achieved by imaging using a conventional ring-shaped back scattered electron detector proved most useful. Because of needed high quality of polished sections, an optimised method of preparation was developed.

Non-Destructive Characterization of Nickel-Base Hardface Deposit on Austenitic Stainless Steel Through Eddy Current and Magnetic Barkhausen Techniques

Nickel-base Colmonoy (AWS ER NiCr) alloys find extensive application for hardfacing of austenitic stainless steel (SS) components in Fast Breeder Reactors. Gas Tungsten Arc deposited Colmonoy alloys suffer from significant loss in hardness and wear properties due to dilution from the austenitic SS substrate. In a multilayer deposit, dilution in first layer is highest and dilution decreases progressively in the subsequent layers. Although, both Colmonoy alloys and austenitic SS are non-magnetic, the deposit of Colmonoy on austenitic SS is ferromagnetic. The susceptibility to magnetic attraction in the hardface deposits is highest for maximum level of dilution and reduces with decreasing dilution. In the present study, Colmonoy-6 alloy co-deposited with austenitic SS filler wire, to obtain deposits with different levels of dilution, have been non-destructively evaluated by eddy current (EC) and magnetic Barkhausen (MB) techniques. The deposits were also characterized by microstructural and hardness studies. The EC parameters viz. magnitude and phase angle of the induced voltage showed an increasing trend with increasing dilution of the deposits. MB root mean square (RMS) voltage and peak height also indicated similar trend with dilution. The results produced from nondestructive tests could be correlated with hardness and microstructure of the deposits. Thus, it is possible to develop a non-destructive technique to predict hardness of the Colmonoy hardfacing alloy, which can serve as quality control tool in estimating the hardness of the hardfaced coating to ensure that dilution of the deposit by the substrate does not bring down the hardness of the deposit below the acceptable minimum values.

Effect of PTA Hardfaced Interlayer Thickness on Ballistic Performance of Shielded Metal Arc Welded Armor Steel Welds

Ballistic performance of armor steel welds is very poor due to the usage of low strength and low hardness austenitic stainless steel fillers, which are traditionally used to avoid hydrogen induced cracking. In the present investigation, an attempt has been made to study the effect of plasma transferred arc hardfaced interlayer thickness on ballistic performance of shielded metal arc welded armor steel weldments. The usefulness of austenitic stainless steel buttering layer on the armor grade quenched and tempered steel base metal was also considered in this study. Joints were fabricated using three different thickness (4, 5.5, and 7 mm) hardfaced middle layer by plasma transferred arc hardfacing process between the top and bottom layers of austenitic stainless steel using shielded metal arc welding process. Sandwiched joint, in addition with the buttering layer served the dual purpose of weld integrity and ballistic immunity due to the high hardness of hardfacing alloy and the energy absorbing capacity of soft backing weld deposits. This paper will provide some insight into the usefulness of austenitic stainless steel buttering layer on the weld integrity and plasma transferred arc hardfacing layer on ballistic performance enhancement of armor steel welds.

Effects of titanium additive on microstructure and wear performance of iron-based slag-free self-shielded flux-cored wire

In this investigation, a new slag-free type of iron-based self-shielded flux-cored wires (SSFCW) with varying titanium content was developed to fabricate experimental hardfacing alloys. The titanium can be transferred to the weld pool using magaluma powder and graphite in the wire as stronger deoxidizers. The phase composition and microstructure of the as-prepared alloys were characterized by X-ray diffraction and scanning electron microscopy. The wear behavior of SSFCW was investigated using a HT-500 pin-on-disk tribometer. The results showed that TiC was preferentially formed in the alloy. It acted as the nucleus of the primary M7(C,B)3 (M=Cr, Fe mainly) carbides; and that it decreased the amount of M7(C,B)3 when titanium was added into the wires. When 24wt.% ferrotitanium (Fe–Ti: containing 30wt.% Ti) was added, the microstructure of the alloy changed from a hypereutectic structure to a hypoeutectic one due to the formation of TiC, which consumed carbon. The addition of titanium to iron-based SSFCW improves the wear resistance of the alloy with respect to the higher hardness and refined microstructure. The wear loss of the sample with 24wt.% Fe–Ti was the smallest among all the samples.

Fe–24wt.%Cr–4.1wt.%C hardfacing alloy: Microstructure and carbide refinement mechanisms with ceria additive

The microstructure and carbide refinement mechanisms of Fe–24 wt.%Cr–4.1 wt.%C hardfacing alloys with 0 wt.%, 0.5 wt.%, 1.0 wt.%, 2 wt.%, and 4 wt.% ceria additives have been systematically investigated in this work. Optical microscopy, field emission scanning electron microscopy with energy dispersive spectrometer, and X-ray diffraction were collectively used to study the microstructure, the phase components, and the chemical formation of inclusion formed in the welding process. Wear-resistance of the alloys was comparatively studied using an abrasive wear testing machine. The structure analysis results show that the Fe–Cr–C hardfacing alloy mainly consists of martensite, retained austenite, MC carbide and M7C3 carbide. With increasing ceria additive contents, the average size of the primary M7C3 carbide decreases and reaches a most refined state in the alloy with 2 wt.% ceria additives. Comparative wear tests data shows that the wear resistance of the hardfacing alloys with ceria additives is better than that without ceria additive. In a good agreement with the carbide refinement results, the wear resistance of the alloy reaches an optimum level in the sample with 2 wt.% ceria additive. The main RE inclusion type identified with in-situ XRD analysis is RE inclusion Ce2O2S. Thermodynamics calculation confirms that this type of RE inclusion could precipitate prior to M7C3 carbides, and act as a heterogeneous nucleus for M7C3 in the welding process, which effectively provides a mechanism for significant refinement of the M7C3 carbide and improves its wear resistance.

Microstructure and properties of Fe–Cr–C hardfacing alloys reinforced with TiC–TiB2

Different amounts of TiB2 powder were added to flux cores of wear resistant hardfacing flux cored wires for the preparation of new flux cored wires. Fe–Cr–C hardfacing alloys reinforced with TiB2 were produced by arc hardfacing. The microstructure, hardness and wear resistance behaviour of the hardfacing alloys were investigated using an optical micrograph, scanning electron micrograph (SEM), X-ray diffractometer, macrohardness tester, microhardness tester and abrasive wear tester. The results showed that, among the hardfacing alloys, a new hard phase, i.e. TiC–TiB2 composite compound particles, was formed and dispersed in the primary carbides and matrix structures. The TiC–TiB2 reinforced Fe–Cr–C hardfacing alloys imparted greater hardness and better wear resistance. The presence of TiC–TiB2 hard phase particles is the main reason for the improvement in hardness and wear resistance of Fe–Cr–C hardfacing alloys.

Comparison of abrasive wear of a complex high alloy hardfacing deposit and WC–Ni based metal matrix composite

The abrasive wear of hardfacing deposits of a complex high alloy (SHS9290) and a tungsten carbide–Ni based metal matrix composite (MMC) has been compared using silica, garnet and alumina grit. In dry sand rubber wheel tests with silica abrasive and pin-on-flat tests with garnet abrasive, the SHS9290 alloy has shown a lower wear rate than the WC–Ni MMC. In comparison, in pin-on-flat tests using alumina abrasive, a higher wear rate was measured for SHS9290 alloy than the WC–Ni based MMC. The wear data has been interpreted in terms of the hardness of the constituent phases relative to the abrasives. The combination of high resistance to abrasive wear and known fracture toughness of SHS9290 alloy are optimal properties for digging picks used in ore excavation except with minerals of extreme hardness.

Dilution effects in laser cladding of Ni–Cr–B–Si–C hardfacing alloys

Ni–Cr–B–Si–C coatings were deposited by laser cladding and effects of additional iron (Fe) as a result of dilution from the steel substrate were investigated. It was found that for Fe contents of up to around 25wt%, chromium borides with higher Fe fractions could form but further increase of the Fe content to over 40wt% entirely suppressed the precipitation of primary Cr borides. Similarly, the Ni–Si–B eutectics were diminished as dilution increased. By reducing the amount of chromium borides and Ni–Si–B eutectics, excessive iron contents degraded the hardness of Ni–Cr–B–Si–C coatings from 800 to 500 HV. These findings can be used to explain the role of dilution in evolution of microstructure and properties of Ni–Cr–B–Si–C coatings and to tune the processing parameters to obtain the desirable deposits.

Mapping the micro-abrasion resistance of a Ni-based coating deposited by PTA on gray cast iron

Micro-scale abrasion was used to characterize abrasion resistance of a nickel-based hardfacing alloy deposited by Plasma Transferred Arc on gray cast iron using silica as abrasive agent. In order to investigate the occurrence of different abrasion mechanisms, several test conditions were used, namely: different silica abrasive contents and a range of normal loads and test durations. A scanning electron microscope (SEM) was used to study the morphologies of the spherical cup-shaped depressions induced by different test conditions. The results are discussed in terms of the effect of the dominant wear mechanisms on the abrasion resistance and the influence of the test conditions on the mechanism transition. The wear results lead to the conclusion that the specific wear rate essentially depends on the wear mechanisms (rolling or grooving) involved and not on the tests conditions employed, since these do not produce changes in the wear mechanism.

Advanced chromium carbide-based hardfacings

Ceramic metal composite powders are widely used in thermal spray technologies; however, application of such hardphases in cladding systems has not been strongly developed yet. In the present study, two different hardfacings produced by the plasma transferred arc (PTA) process were analysed and compared to reveal differences between NiCrBSi coatings reinforced with standard chromium carbide and chromium-based cermet powders. The coatings were produced from a mixture of hardphases (Cr3C2 or Cr3C2–Ni) and nickel based powder with a ratio of 40/60vol.%. The coatings' thickness was set to 2–2.5mm on an austenite substrate. Hardfacings were characterised in terms of their microstructures, mechanical properties and impact–abrasion wear resistance at room and elevated temperatures. The manufactured Cr3C2–Ni reinforced hardfacing alloy has shown promising microstructural features with a low level of carbide dissolution and high temperature wear performance.

Effect of dilution and cooling rate on microstructure and magnetic properties of Ni base hardfacing alloy deposited on austenitic stainless steel

Nickel base Colmonoy 6 alloy finds application in hardfacing of various components made of austenitic stainless steel used in fast reactors. Gas tungsten arc deposited Colmonoy suffers from significant loss in hardness and wear properties due to dilution from the substrate. Magnetic property of the deposit is also influenced by dilution, and variation in magnetic parameters with dilution can be employed for non-destructive assessment of hardness in the hardfaced coating of the finished components. During hardfacing deposition, cooling rate may vary with deposition technique and process parameters. Development of a procedure for measurement of hardness of hardface deposit, irrespective of cooling rate, can prove to be useful for practical application. In the present study, the effect of cooling rate on microstructure, hardness and magnetic parameters of the Ni–Cr–B–Si hardface deposits is evaluated, and for coating cooled at different cooling rates, good prediction of hardness from its magnetic property could be obtained.

An Experimental Study on the Effect of Microstructure on Wear Behavior of Fe-Cr-C Hardfacing Alloys

Hardfacing is a low cost method of depositing wear resistant surfaces on metal components to extend service life. The prime requirement of a metal is to have good resistance to wear, corrosion and high temperature. A study has been carried out to investigate the relationship between abrasive wear resistance and microstructure of Fe-Cr-C hardfacing alloy. Two different commercial hardfacing electrodes were employed to investigate the effect of the microstructure. Results indicate that as hardness increases, the loss of wear decreases. Electrode-I has less wear as compared to electrode-II as the percentage of chromium, carbon and silicon is more in electrode-I. The abrasion tests were carried out in a dry sand-rubber wheel abrasion machine according to the procedure A of ASTM G65 standard. The factors such as, arc current, arc voltage, welding speed, electrode stick-out and preheat temperature, predominantly influence the weld quality.

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.

Microstructure and Wear Characteristics of Fe-Based Hard-Facing Alloy Claddings Formed by Gas Tungsten Arc Welding

The current investigation discusses the effect of Mn and Si contents on the microstructure and abrasive wear characteristic in Fe-based hard-facing alloy. A series of Fe-based hard-facing alloys are successfully fabricated onto the S45C steel by gas tungsten arc welding (GTAW). Results reveal that microstructure contains great amounts of martensite phases and moderate amounts of austenite phases. Si element added into Fe-based hard-facing alloy can not obviously affect the properties of the claddings, such as martensite phase, hardness, and abrasive wear resistance. Nevertheless, Mn element added into Fe-based hard-facing alloy can efficiently affect the martensite phase, hardness, and abrasive wear resistance of the claddings. The martensite contents decreases with the increasing of Mn contents in the cladding layers. The hardness increases as the Mn contents decreases, because the martensite contents increases. The abrasive wear resistance is not only related to the hardness of the cladding layer but the martensite contents of the cladding layer. The abrasive wear resistance is an inverse proportion to Mn contents of the cladding layers. Especially, the cladding layers containing 1.4Si-0.3Mn has the highest hardness of HRC 60.1 and the lowest wear loss of 0.37g.

Effect of cerium on abrasive wear behaviour of hardfacing alloy

Hardfacing alloys with different amounts of ceria were prepared by self-shielded flux cored arc welding. The abrasion tests were carried out using the dry sand-rubber wheel machine according to JB/T 7705-1995 standard. The hardness of hardfacing deposits was measured by means of HR-150AL Rockwell hardness test and the fracture toughness was measured by the indentation method. Microstructure characterization and surface analysis were made using optical microscopy, scanning electron microscopy (SEM) and energy spectrum analysis. The results showed that the wear resistance was determined by the size and distribution of the carbides, as well as by the matrix microstructure. The main wear mechanisms observed at the surfaces included micro-cutting and micro-ploughing of the matrix. The addition of ceria improved the hardness and fracture toughness of hardfacing deposits, which would increase the resistance to plastic deformation and scratch, thus the wear resistance of hardfacing alloys was improved.

Study of Carbonitride Precipitates in the Fe-Cr-Mn-N Hardfacing Alloy

The Fe-Cr-Mn-N hardfacing alloy was deposited on a low carbon steel substrate by the weld hardfacing technique. Ti and Nb as the most effective nitrogen-fixing elements were added in the hardfacing alloy. Carbonitride precipitates were systematically studied by canning electron microscopy and electron probe microanalyser. The thermodynamics and the effect on the matrix of the formation of carbonitride were also discussed. It was found that carbonitride precipitates were complex carbonitride of Ti and Nb distributing on grain boundary and matrix of the hardfacing alloy. In as-welded condition, primary carbonitride particles were readily precipitated from the hardfacing alloy with large size and morphology as they were formed already during solidification. In heat-treated condition, a large number of secondary carbonitrides can precipitate-out with very fine size and make a great secondary hardening effect on the matrix. As a result, precipitation of carbonitride in the hardfacing alloy can prevent the formation of chromium-rich phase on grain boundaries and increase the wear resistance of the hardfacing alloy. Keywords: carbonitride precipitate, hardfacing alloy, deposit, thermodynamics