Cr Carbides Research Articles

Comparative study on the effects of Cr, V, and Mo carbides for hydrogen-embrittlement resistance of tempered martensitic steel

In this study, the ideal alloying element (among Cr, V, and Mo carbides) to enhance the resistance to hydrogen embrittlement (HE) in a tempered martensitic steel was investigated. Four types of steels were designed to contain cementites, Cr-rich M7C3 carbides, V carbides, and Mo carbides, respectively. These steels were tailored to possess a comparable tensile strength (~1.6 GPa). The HE resistances of these steels were evaluated through the slow strain rate test and cyclic corrosion test. The results showed an enhanced HE resistance, characterized by a high notch fracture strength after hydrogen charging, in the samples containing V carbides and Mo carbides. In particular, Mo carbide was regarded as the most ideal alloying element for HE resistance because of the high resistivity parameter, inhibited hydrogen penetration, and suppressed strength loss by internal hydrogen.

Microstructure and processing performance of brazed diamond drill bits with Ni–Cr + Cu–Ce composite solder

In this study, new brazed diamond drill bits and brazed samples were fabricated using Ni–Cr + Cu–Ce composite solder (i.e. Ni–Cr composite solder). The surface morphology and interfacial microstructure of the brazed samples that used Ni–Cr composite solder was characterised. The processing performance of the brazed diamond drill bits was evaluated and the surface morphology of the drill bits was analysed after conducting a drilling test. Results showed that the surface morphology of the brazed samples fabricated using Ni–Cr composite solder was better than that of its conventional counterpart using Ni–Cr alloy. Cr carbides (Cr3C2 and Cr7C3) were still obtained between the diamonds and Ni–Cr composite solder. When the amount of added Cu–Ce alloy exceeded a critical value, an increase in Cu–Ce alloy formed more brittle intermetallic compounds. The new brazed diamond drill bits with the Ni–Cr composite solder that contained 5 wt% Cu–Ce alloy achieved the longest tool life and highest drilling efficiency. The wear patterns of the aforementioned diamond drill bits were composed of grain micro fracture and macro fracture, which were the mildest wear types amongst all the drill bits.

Development of gas tungsten arc welding using current pulsing technique to preclude chromium carbide precipitation in aerospace-grade alloy 80A

Weldments were produced using gas tungsten arc welding (GTAW) and pulsed current gas tungsten arc welding (PCGTAW) techniques with ERNiCr-3 filler wire. Macro examination revealed that the resultant weldments were free from defects. A refined microstructure was observed in the weldment fabricated through PCGTAW. Scanning electron microscopy (SEM) analysis revealed secondary phases in the grain boundaries. Energy-dispersive X-ray spectroscopy (EDS) analysis revealed that microsegregation of Cr carbide precipitates was completely eradicated through PCGTAW. The microsegregation of Nb precipitates was observed in the GTA and PCGTA weldments. X-ray diffraction (XRD) analysis revealed the existence of M23C6 Cr-rich carbide and Ni8Nb phases in the GTA weldments. By contrast, in the PCGTA weldments, the Ni8Nb phase was observed. The Cr2Ti phase was observed in both the GTA and the PCGTA weldments. Tensile tests showed that the strength and ductility of the PCGTA weldments were slightly higher than those of the GTA weldments.

Development of the organization of rational schemes for the use of technogenic waste in the processes of off-treatment of steel intermediate

The results of the experimental verification of the efficiency of complex out-of-furnace treatment of low carbon steel using a test mixture based on man-made waste, which is fed partly to the melting unit at the end of the oxidation period of melting and partly by pouring under a stream of liquid metal. is the use of slag-forming materials obtained by joint heat treatment of mixtures of components containing the above mentioned oxides and carbonaceous material of vegetable origin. Their weight ratio in the initial mixture is determined by the purpose and properties of the finished product. The positive technological effects that are achieved by applying the developed method of after-treatment will in future provide favorable conditions for the effective conduct of microalloying, modification, vacuuming and stable casting of low-quality and ultra-low carbon steel. A slight decrease in the temperature of the steel intermediate in the implementation of the method is about 10 - 15 ° C, which is easily compensated for the installation of the ladle, and a slight increase in electricity consumption is compensated by the effects achieved in the processing of low-carbon steel intermediate. Obtaining a higher degree of desulfurization and deoxidation of steel, as well as reducing the contamination of Al2O3 steel and improving the ecological purity of the process can be achieved by reducing the composition of the SHS used in the first stage of processing, the amount of slag aluminothermal production of ferromanganese and complete exclusion of melting, melting weight ratios of powdered waste production of lime, aluminum-thermal slag production of ferromanganese, sludge neutralization of electrocorundum and carbide cr emnia.

Microstructural characterization and abrasive wear resistance of a high chromium white iron composite reinforced with in situ formed TiCx

Abstract A high chromium white iron (HCWI) composite reinforced with in situ formed 17.2 wt.% TiCx has been prepared. The in situ formed TiCx grains resulting from the decomposition of Ti3AlC2 are round and small. The presence of small TiCx grains effectively inhibited the rapid growth of M7C3 (M: Fe, Cr and other strong carbide formers) carbides, refining the microstructure of composite. High resolution TEM micrographs show that interfaces of TiCx/M7C3 and TiCx/matrix are clean, suggesting the formation of strong bonding interfaces in the composite. The wear behavior of the composite and the unreinforced HCWI material as a function of the normal load in the range of 78–123 N was investigated using dry sliding pin-on-disc wear testing against a YG8 disk under ambient conditions. The wear resistance of HCWI and TiCx/HCWI decreased with increasing load. However, the wear resistance of the TiCx/HCWI composite was over six times that of the unreinforced HCWI material even at the highest load of 123 N. The improved wear resistance of the composite should be ascribed to contributions from both the presence of smaller TiCx grains reinforcing the matrix and the refinement of the M7C3 structure. Scanning electron microscopy was used to characterize the microstructures of materials before and after wear testing.

On the role of intergranular carbides on improving the stress corrosion cracking resistance in a cold-worked alloy 600

The mitigating effect introduced by intergranular Cr carbides on the stress corrosion cracking propagation of a cold-worked Alloy 600 has been firstly examined through high-resolution 3-dimensional (3D) sequential sectioning. High-resolution transmission electron microscope (TEM) and transmission Kikuchi diffraction (TKD) are used to reveal the underlying mechanisms contributing to the mitigating effect. Previously reported mechanisms contributing to the increased stress corrosion cracking resistance are evaluated and discussed. A new mechanism based on grain boundary migration inhibition and crack path deviation is proposed.

Mechanical Spectroscopy Investigation of Point Defect-Driven Phenomena in a Cr Martensitic Steel

The paper presents and discusses results of mechanical spectroscopy (MS) tests carried out on a Cr martensitic steel. The study regards the following topics: (i) embrittlement induced by Cr segregation; (ii) interaction of hydrogen with C–Cr associates; (iii) nucleation of Cr carbides. The MS technique permitted characterising of the specific role played by point defects in the investigated phenomena: (i) Cr segregation depends on C–Cr associates distribution in as-quenched material, in particular, a slow cooling rate (~150 K/min) from austenitic field involves an unstable distribution, which leads to Cr concentration fluctuations after tempering at 973 K; (ii) hydrogen interacts with C–Cr associates, and the phenomenon hinders hydrogen attack (HA) because hydrogen atoms bound by C–Cr associates are not able to diffuse towards grain boundaries and dislocation where CH4 bubbles may nucleate, grow, and merge to form the typical HA cracks; (iii) C–Cr associates take part in the nucleation mechanism of Cr7C3 carbides, and specifically these carbides form by the aggregation of C–Cr associates with 1 Cr atom.

Effects of (W, Cr) carbide on grain refinement and mechanical properties for CoCrFeMnNi high entropy alloys

In this study, we investigated the influence of (W, Cr) carbide on the hardness and tensile properties of friction stir welds (FSWs) for CoCrFeMnNi high entropy alloys. FSW without cracks or voids were achieved for rotational speeds of 400–1000 rpm. As the rotational speed increased, the thinning of the weld thickness compared to the thickness of the base metal was increased. Specifically, an abnormal tornado-shaped region was observed in the stir zone at rotation speeds of 600 rpm and above. The tensile strength increased as the rotation speed increased from 400 to 800 rpm and decreased at a rotation speed of 1000 rpm. The abnormal region with a fine (W, Cr) carbide of 0.5 μm or less was dispersed in the grain boundaries. At a rotation speed of 800 rpm, the dispersion of fine (W, Cr) carbide was optimized to produce grain refinement and maximum tensile strength. However, at 1000 rpm, (W, Cr) carbide coarsened due to high heat input, and the number of carbide particles per unit area decreased, thereby decreasing the hardness and tensile strength.

Role of Cr-rich carbide precipitates in the intergranular oxidation of Ni-Cr alloys

The influence of grain boundary Cr carbides on the intergranular oxidation behavior of a Ni-16Cr alloy is considered using atomistic-to-mesoscale model and atom probe tomography. Cr carbide strongly perturbs the collective reactive dynamics of oxidizing species and alloy elements in the intergranular region. Strong attractive interactions between oxygen and carbide create a driving force for Cr and Ni accumulation in the grain boundary adjacent to the carbide, and for the depletion of Cr and Ni ahead of the oxidation front beyond the carbide. The results shed light on the mechanism of carbide-assisted protection of the alloy against grain boundary corrosion/oxidation.

Development of welding technique to suppress the microsegregation in the aerospace grade alloy 80A by conventional current pulsing technique

Alloy 80 A is prone to hot cracking during conventional arc welding process. Microsegregation of alloying element Cr lead to the formation of M23C6 carbide phase during solidification of fusion zone, and it contributes to hot cracking. The current study employs different welding techniques and filler wires to minimize the microsegregation. The weldments were fabricated by Gas Tungsten Arc Welding (GTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) techniques using filler wires 263 and ERNiCrMo-3. Scanning electron microscope (SEM) reveals the existence of secondary phase in the interdendritic region for all the weldments. Energy dispersive X-ray spectroscopy (EDS) analysis reports that PCGTAW eliminates microsegregation of Cr precipitate and suppress Nb and Mo precipitates better when compared to GTAW. X-ray Diffraction (XRD) analysis indicate the presence of M23C6 Cr and Mo-rich carbide phase in GTA weldment of 263 filler wire. Whereas in PCGTAW, NiCrCoMo phase is observed. In both GTAW and PCGTAW of ERNiCrMo-3, the intermetallic phases Ni8Nb and Cr2Ti are observed. The tensile test was conducted to assess the strength and ductility of the weldments. The results of the PCGTAW weldments have improved compared to their respective GTAW weldments.

Structure and Mechanical and Tribotechnical Properties of Iron–High-Carbon Ferrochrome Doped with Ni3B Additions

The production conditions and mechanical and tribotechnical properties of iron–high-carbon ferrochrome FKh800 materials doped with nickel boride have been studied. It is shown that Ni3B additions promote the formation of a multiphase microheterogeneous matrix-reinforced structure consisting of chromium steel and solid inclusions of complex chromium–iron carbides such as Me7C3 and Me23C6. When the doping content increases from 3.5 to 7.0 wt.%, complex Fe–Cr carbides and carboborides form, decreasing the hardness and bending strength and increasing the abrasive wear resistance of the base material from 5.0 to 12.2 km/mm. The Fe–35% FKh800 materials containing 5–7 wt.% Ni3B are found to be promising as they combine acceptable mechanical properties and improved abrasive wear resistance.

Influence of Al Addition Upon the Microstructure and Mechanical Property of Dual-Phase 9Cr-ODS Steels

With Al addition, dual-phase oxide dispersion strengthened (ODS) steels consisting of martensite and ferrite are fabricated by spark plasma sintering. It is found that Al addition has a negligible effect on martensite lath size, while the amount and size of ferrite grains are related to the Al content. M23C6 (M = Fe, Cr) carbides have been identified within the ferrite grains or along ferrite boundaries. With increasing Al concentration, more fine Y–Al–O oxide nanoparticles are formed. Upon annealing treatment, homogeneous and refined distribution of ferrite grains is obtained, which may involve the particle-stimulated nucleation of recrystallization caused by the large sized M23C6. As Al is increased from 0.05 to 0.1 wt%, the tensile strength of the annealed steel is decreased, as well as its ductility. For the annealed 9Cr-ODS steel containing 0.1 wt% Al, in tensile loading the large sized M23C6 along ferrite boundaries would facilitate the cracking along boundaries between the hard annealed ferrite and soft annealed martensite, producing the mixed fracture of dimple and intergranular fracture.

Effects of Nb and Tempering Time on Carbide Precipitation Behavior and Mechanical Properties of Cr–Mo–V Steel for Brake Discs

To improve the performance of the steel for brake discs, like mechanical properties and thermal fatigue resistance, Nb is added to the steel. In this paper, the effects of Nb and tempering time on the microstructure and mechanical properties of the steel have been studied. The investigation of precipitation behaviors is based on Thermo‐Calc software and transmission electron microscopy. The results show there is a negative linear relationship between the yield strength and the logarithm of time, and tempering time should not exceed 2 h. V‐rich M8C7 and NbC occur during austenitizing, while (Mo,V)C, M23C6, and M7C3 precipitate during tempering. (Mo,V)C has a strong strengthening effect at the early stage of tempering, but it grows faster than M8C7. With 0.025% Nb addition, the yield strength and impact energy increase simultaneously due to the refinement of martensite; the addition of 0.045% Nb promotes the tempering stability due to the suppression of precipitation and coarsening of Cr carbides and the precipitation strengthening of M8C7 and NbC, therefore, the addition of 0.025–0.045% Nb is conducive to improving the performance of the steel. Moreover, the suppression of Cr carbides with 0.045% Nb addition makes up for the damage of large NbC to toughness.

Failure Analysis and Magnetic Evaluation of Tertiary Superheater Tube Used in Gas-Fired Boiler

Failure analysis was carried out on a prematurely failed tertiary superheater tube used in gas-fired boiler. The analysis includes a comparative study of visual examination, chemical composition, hardness and microstructure at failed region, adjacent and far to failure as well as on fresh tube. The chemistry was found matching to the standard specification, whereas the hardness was low in failed tube compared to the fish mouth opening region and the fresh tube. Microscopic examination of failed sample revealed the presence of spheroidal carbides of Cr and Mo predominantly along the grain boundaries. The primary cause of failure is found to be localized heating. Magnetic hysteresis loop (MHL) measurements were carried out to correlate the magnetic parameters with microstructure and mechanical properties to establish a possible non-destructive evaluation (NDE) for health monitoring of the tubes. The coercivity of the MHL showed a very good correlation with microstructure and mechanical properties deterioration enabling a possible NDE technique for the health monitoring of the tubes.

Corrosion and wear resistance properties of multilayered diamond‐like carbon nanocomposite coating

Multilayered diamond‐like carbon (DLC) nanocomposite coating has been deposited on silicon and stainless steel substrates by combination of cathodic arc evaporation and magnetron sputtering. In order to make DLC coating adhered to metal substrate, a chromium interlayer has been deposited with constant bias voltage of −150 V applied to the substrate. Dense multilayered coating consists of metallic or nonmetallic and tetrahedral carbon (ta‐C) layers with total thickness of 1.44 μm. The coating has been studied for composition, morphology, surface nature, nanohardness, corrosion resistance, and tribological properties. The composition of the coating has been estimated by energy‐dispersive spectroscopy. Field‐emission scanning electron microscopy and atomic force microscopy have been used to study the surface morphology and topography. ID/IG ratio of ta‐C:N layer obtained from Raman spectroscopy is 1.2, indicating the disorder in the layer. X‐ray photoelectron spectroscopy studies of individual ta‐C:N, CrN, and Cr‐doped DLC layers confirm the presence of sp2C, sp3C, CrN, Cr2N, and carbidic carbon, and sp2C, sp3C, and Cr carbide. Nanohardness studies show the maximum penetration depth of 70 to 85 nm. Average nanohardness of the multilayered DLC coating is found to be 35 ± 2.8 GPa, and Young's modulus is 270 GPa. The coating demonstrates superior corrosion resistance with better passivation behavior in 3.5% NaCl solution, and corrosion potential is observed to move towards nobler (more positive) values. A low coefficient of friction (0.11) at different loads is observed from reciprocating wear studies. Wear volume is lower at all loads on the multilayered DLC nanocomposite coating compared to the substrate.

Wear Mechanism of Wear Resistant HVOF Thermal Spray Coating: Chromium Carbide Nickel Chrome on 304 AISI Steel

One of the common ways to overcome wear is by surface modification which is a coating process. The application of cermet of chromium (Cr carbide) in Nickel-Chromium (Ni-Cr) matrix is widely used as coating material since it provides high wear resistant. Besides, thermal spray process is widely known as the most suitable technique to produce cermet coating. In this study, chromium carbide-nickel chrome (Cr3C2- NiCr) powder is used as the feedstock. High Velocity Oxy Fuel (HVOF) thermal spraying is used to deposit the coating on mild steel substrate to study the behaviour of wear of the coating. The wear test is conducted by using TABER Linear Abrasion Wear Test machine. The wear rate of both coated and uncoated pin is measured by measuring the weight loss of the samples. The Cr3C2-NiCr coated pins have shown less weight loss than the uncoated pins. The lifetime prediction of Cr3C2-NiCr coated pins is higher than the uncoated pins at different time duration and applied loads. The results showed that the wear resistant properties of Cr3C2-NiCr coated pins are higher than the uncoated pins. Scanning Electron Microscopic (SEM) integrated with Energy-dispersive X-ray spectroscopy (EDS) are used to determine the microstructure of Cr3C2-NiCr coating. The microstructure of Cr3C2-NiCr coated pin after the wear testing showed no presence of crack and the wear track was homogenous.

Research on the Diffusion of Ti-Based Stabilizer through Flux Coated GTAW to Reduce Carbide Precipitation in SS304 Weldment

Sensitization is a major problem, which leads to intergranular corrosion in stainless steel weldments due to precipitation of Chromium (Cr) carbides. Thus, Cr depleted from heat affected zone (HAZ) results in intergranular corrosion causes failure of structure. In the present research work an attempt has been made by the diffusion of titanium based stabilizer into HAZ during welding of SS 304 by gas tungsten arc welding (GTAW). The Ti powder (< 20µm size) has been used and coated on v-joint before welding in optimized coating thickness. This process is termed as flux coated gas tungsten arc welding (FC-GTAW). The surface microstructure, surface morphology and surface chemistry have been analyzed by Microscope, Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive Spectroscopy (EDS). The EDS results along with SEM revealed that Ti has been diffused up to 2mm from the fusion boundary. The EDS line scan has confirmed the depth of Ti diffusion. Intergranular corrosion resistance is evaluated by DLEPR test, as a result of this test the sample coated with flux shows better corrosion resistance. The result indicates that FCGTAW is novel technique for reducing the formation of Cr carbides thus enhancing the corrosion resistance of stainless steel.

Evolution of microstructures and mechanical properties during solution treatment of a Ti–V–Mo-containing high‑manganese cryogenic steel

The effect of solution treatment on the microstructure and mechanical properties of a high‑manganese (Mn) twin-induced plastic (TWIP) cryogenic steel that was alloyed from elemental titanium (Ti), vanadium (V) and molybdenum (Mo) was investigated by a variety of techniques such as microstructural characterization, room tensile testing and −196°C impact testing. The austenite grain size grew slowly with an increase of the solutionizing temperature (ST). The relatively weak effect of the ST on the austenite grain size is attributed to the superior thermal stability and coarsening resistance of the (Ti, V, Mo)C precipitate, which hindered austenite grain growth. An increase in ST improved the low-temperature toughness (LTT) significantly and decreased the strain hardening rate (SHR), but had no significant effect on the yield strength. The Hall–Petch strengthening coefficient for yield strength was small, and was estimated to be 153MPaμm0.5. Undissolved large-sized chromium (Cr) carbide can deteriorate the LTT significantly. Because of its excellent mechanical properties, high-Mn steel that was alloyed by elemental Ti, V and Mo can be used to manufacture storage tanks for liquefied natural gas.

Hot wire-assisted gas metal arc welding of hypereutectic FeCrC hardfacing alloys: Microstructure and wear properties

The deposition welding of hypereutectic FeCrC hardfacing alloys requires low dilution rates in order to ensure the specified chemical composition and thus the precipitation of primary M7C3 (M=Fe, Cr) carbides, which affect the abrasive wear resistance of the hardfacing. Because dilution is critical in determining the above mentioned criteria during surfacing, the development of deposition welding processes with reduced thermal impact and hence reduced dilution of the base material is a main focus of current research. For the purpose of improving the processing properties of gas metal arc welding (GMAW) in hardfacing applications, the potential of an additional hot wire (HW-GMAW) was investigated. The application of a hot wire enabled the independent adjustment of the deposition and dilution rates. Furthermore, the dilution and microstructural properties could be adjusted independently of the deposition rate. HW-GMAW enabled hypereutectic solidification in the first layer, even at very high deposition rates of 9kg/h. In this manner, a primary M7C3 carbide content reaching 17% by area (A%) was achieved in the first layer. In comparison to single-layer GMAW overlays the wear properties were improved.

The Effect of Temperature on the Chromizing Process for Ferritic-Martensitic Steel

The formation of protective Cr2O3 layer was usually retarded in the high temperature steam oxidation of boiler tube materials. This condition makes the oxidation rate higher than that in dry condition. Therefore in this work, chromizing process is introduced to diffuse chromium on the surface of boiler steel so that it can act as a reservoir for the formation of Cr2O3 layer. The chromizing process was conducted on T91 steel by exposing it into alumina crucible. The crucible was exposed at different temperature (600°C-1050°C) under argon environment in the crucible that contains the chromizing mixture powder of masteralloy Cr, activator NH4Cl and filler Al2O3. It was found that Cr diffusion was happened at higher temperature and it formed Cr carbide on the surface. It also clarified that this chromizing process can prevent the retardation of Cr2O3 layer.