Carbide Size Research Articles

Influence of the Grain Size of Tungsten Carbide in the VK8 Anode Material on the Formation of an Alloyed Layer of Steel 35

The influence of the grain size of tungsten carbide of tungsten-cobalts hard alloy, received as anode material for the electro-spark deposition (ESD) of steel 35, on its erosion resistance, on the weight gain of the substrate material, and on the coefficient of electro-mass transfer. It is shown that in the preparation of new anode materials with different structure, density, porosity, fracture strength, and grain size of tungsten carbide, a pressing charge with additives of 0.4% Cr3C2–0.4% VC grain growth inhibitors and grinding in alcohol and argon atmosphere at a grinding time of 20 to 320 minutes was used. The results of the erosion resistance and the use of the obtained new anode materials in the ESD of steel 35 are shown. When performing kinetic studies, a number of indicators of the efficiency of the formation of the doped layer were identified, taking into account the obtained values of the of additional weight of the cathode, the time of the ESD, the specific surface area of 1 cm2, and the coefficient of electro-mass transfer at the ESD of the studied anode materials. The results of the studies of the structure, thickness, composition of the doped layer, and of the heat resistance and wear resistance of the coating are shown. It was revealed that among the created new anode materials, the best oxidation resistance of the coating after ESD with the selected processing modes were obtained using a new nanodispersed anode material WC8%Co–0.4%Cr3C2–0.4%VC, with an average grain size of 0.8 microns WC.

Effect of isothermal quenching on microstructure and hardness of GCr15 steel

Through hardness measurement and microstructure observation, the effect of isothermal quenching on the bainite transformation, the size and area fraction of carbides in GCr15 steel was studied. Results show that, at the solid solution temperature of 860 °C, as the isothermal quenching temperature increases from 200 °C to 230 °C, the bainite transformation rate in GCr15 steel increases. At the initial stage of isothermal quenching, there is relatively less bainite transformation in GCr15 steel, but the increasing rate is relatively larger. With the extension of the isothermal time, the bainite content increases, and the increasing rate gradually becomes slower. The above phenomena are related to the existence of the incubation period of bainite transformation, the driving force of bainite ferrite nucleation, and the stability of undercooled austenite. As isothermal time increases, the carbide content decreases, while the carbide size generally increases, which is related to the dissolution of some undissolved carbides due to the change of the surrounding carbon concentration and the Ostwald ripening mechanism. The hardness of GCr15 steel is obviously reduced at the stage of the first 1 h, while between 2 and 4 h the hardness decrease of GCr15 steel tends to be gentle, which is related to the increase of bainite content, the weakening of dispersion strengthening effect resulted from the increase of carbide size, and the self-inhibiting behavior of the bainite transformation.

Precipitation behavior of carbides and cryogenic toughness in heat-affected zone of high-Mn twinning-induced plasticity steel welded joint

The newly designed cryogenic high-Mn steel plates (Fe-23Mn-1.5Al-0.45C) were joined by metal inert gas (MIG) multi-pass welding process. To evaluate the inhomogeneity of microstructure and cryogenic toughness in heat-affected zone (HAZ) of welded joint, the impact samples were prepared by zonal sampling method. The microstructure features and embrittlement mechanism in HAZ of welded joint were systematically investigated. The results reveal that grains obviously grew in the coarse-grain HAZ (CGHAZ). C element segregated and nano-sized lamellar and granular (Cr, Mn) 7 C 3 carbides precipitated at the grain boundary in HAZ, and the size of precipitate carbides in CGHAZ and fine-grain HAZ (FGHAZ) was about 100 nm and 40 nm, respectively. The interface between (Cr, Mn) 7 C 3 and γ-austenite matrix in CGHAZ was incoherent with the lattice misfit of 45.13%. Higher fraction of low angle grain boundaries (LAGBs) appeared in CGHAZ (25.89%) and FGHAZ (11.99%), compared with the base metal (4.33%). Such microstructural differences can degrade the impact toughness in CGHAZ. From cryogenic Charpy impact tests, the impact toughness in different zones of the joint at each test temperature follows this sequence: base metal > fine-grain HAZ > coarse-grain HAZ > fusion line. These results can provide a fundamental understanding and guidance on the brittle failure of cryogenic high-Mn steel welded joint during service.

The effect of microstructure on the oxidation and carburisation of 9Cr-1Mo steel exposed to CO2

To understand the effect of microstructure on the oxidation characteristics of 9Cr-1Mo steel, experimental material with two different starting microstructures (ferritic and martensitic) were exposed to a CO2 rich atmosphere at 600 °C and 640 °C for up to ∼7000 h.The microstructure influences the size and distribution of carbides forming within the 9Cr-1Mo steel exposed to a CO2 rich atmosphere. These differences lead to elemental segregation during carburisation and oxidation. This elemental segregation influences the oxidation characteristics of the 9Cr-1Mo steel and the morphology of the internal oxidation zone, and subsequently the spinel structure shows ghosts of the prior substrate microstructure.

Influence of carbides on the strain hardening behavior of 60Si2CrVAT spring steel treated by a Q&T process

The strain hardening behavior was studied in ultra-high strength 60Si2CrVAT spring steel subjected to quenching and tempering (Q&T) treatments via tailoring the carbides precipitated during tempering at 400–530 °C. Results showed that the strain hardening characteristic of the spring steel changed from a single-n upwardly convex (tempering temperatures below 470 °C) to a double-n downwardly convex (tempering temperatures equal to or higher than 470 °C), which is more suitable for cold coiling process. For the double-n state, the value of the strain hardening exponent(n) in the low-strain region of uniform plastic strain (n1) gradually decreased while the value of n in the high-strain region of uniform plastic strain (n2) gradually increased with tempering temperature increasing. It was attributed to the continuous decrease in initial dislocation density of matrix with tempering temperature increasing and the continuous increase in geometric necessary dislocations (GNDs) during cold deformation, which was significantly affected by the quantity, size, distribution and related microscopic characteristic parameters of carbides. The strengthening effect corresponding to the high-strain region is proportional to the value of n2 and the carbide particle size parameter (f/d).

A new approach to thermo-mechanical treatment of steel T91 by multiple upsetting-extrusion in a ferritic range

The microstructure and mechanical properties of the ferritic-martensitic steel T91 after severe plastic deformation (SPD) and subsequent thermal treatment are investigated. SPD was realized by the method of multiple “upsetting-extrusion” (MUE) in temperature range of stability of ferritic phase (750-575 °C), thermal treatment of SPD specimens was carried out at temperatures 550–730 °C during 1–100 h. It is revealed that decrease of temperature of “upsetting-extrusion” and increase of cycle number to 5 induces the decrease of mean grain size to 145 nm and increase of degree of microstructure homogeneity. At the same time microhardness increases from 1800 MPa to 2850 MPa. Composition, shape, size and density of carbide precipitates in steel after SPD and thermal treatment are determined. Obtained submicron grain ferritic microstructure with high value of microhardness is stable at exposure temperature of 550 °C. It is shown that temperature variation of thermal treatment induces the considerable change in grain size and mechanical characteristics.

Influence of Cooling Parameters on the Microstructure and Primary Carbide Precipitation in GCr15 Steel

With the high temperature confocal laser scanning microscope applied, the effect of cooling rate, temperature interval, and cooling mechanism on the solidification microstructure and primary carbide participation in GCr15 steel are investigated. The solute distribution in interdendritic segregation and participation carbide are analyzed by electron probe microanalysis. The results show that solute concentrate is low in the dendrite zone but it increases clearly in the segregation zone. The carbon concentration in the precipitation can reach 6.49%, which means the primary carbide is M3C. In the heating process, the segregation zone and carbide participation melt first before it reaches the solidus temperature. During the solidification stage, the microstructure is refined and the size of primary carbide is reduced with a higher cooling rate, but the number density of primary carbide is increased. Moreover, it is found that the microstructure is formed in the earlier solidification, before the temperature declines to 1673 K. While the primary carbide participates in the later cooling stage and the transition temperature for the primary carbide is 1503 K. In addition, the primary carbide size can be reduced with the cooling rate larger than 300 K min−1 in the subsequent cooling stage.

Microstructure Evolution and Tensile Properties of Cold-Rolled and Annealed Fe-30Mn-0.14C-7Cr-0.26Ni Steel

The carbide precipitation, microstructure evolution, and tensile properties of Fe-30Mn-0.14C-7Cr-0.26Ni (in wt pct) steel after cold rolling to 95 pct reduction followed by annealing at temperatures ranging from 600 °C to 900 °C for 1 hour were investigated. The results show that, when the annealing temperature is increased from 600 °C to 900 °C, the grain size increases from 0.65 ± 0.30 to 5.75 ± 3.87 μm. When the annealing temperature is 600 °C, Cr23C6 carbides begin to precipitate. When the annealing temperature is increased from 600 °C to 800 °C, the average size of carbides increases from 39 to 69 nm. When the annealing temperature is increased to 900 °C, no carbides are produced due to the increased solubility of C in the austenite matrix. Ultrafine grains (~ 0.8 ± 0.58 μm) with a large amount of nanoscale carbides (~ 53 ± 21.8 nm) were obtained after annealing at 700 °C, resulting in a good combination of yield strength (679 MPa) and total elongation (38.4 pct). The fraction of deformation twins within the samples under different tensile strains was calculated, and it was revealed that grain refinement can seriously inhibit the generation of deformation twins. In addition, it has been found that grain refinement strengthening, precipitation strengthening, and dislocation strengthening have significant effects on yield strength, while the effects of solution strengthening and lattice friction are relatively weaker.

Influence of Al addition on the microstructure and mechanical properties of Zr-containing 9Cr-ODS steel

Abstract Two oxide dispersion strengthened (ODS) steels with compositions of 9Cr-ODS (9Cr-ODS) and 9Cr-3Al-ODS (9Cr-ODS-Al) were fabricated by hot isostatic pressing (HIP). The microstructures and precipitates of the ODS samples were characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results showed that the addition of Al could reduce the precipitation of coarse M23C6 and optimized the size of carbides in ODS steels. Furthermore, it was found that the mean size of nanoparticles in 9Cr-ODS-Al is larger than that in 9Cr-ODS due to the formation of large-size Y–Al–O nanoparticles with Al addition. The tensile test results indicated that the addition of Al slightly decreased the strength of ODS steels, but substantially increased the ductility.

Effects of W and Ce micro addition in filler metal on microstructure and creep strength of Cr35Ni45NbM alloy weld joint

The effect of the filler metal chemical composition on the performance of Cr35Ni45NbM alloy weld joint is studied in this paper. The Cr35Ni45NbM alloy weld joints with two type filler metals are produced through manual gas tungsten arc welding (GTAW) process. The number of carbide in weld metal is more than that of base metal, and the size of carbide is smaller. The carbide size in the fusion zone of the weld joint with addition Ce and W elements in filler metal is smaller than that without Ce and W elements. The micro addition of W and Ce in filler metal could improve the high temperature creep strength of weld joint, and has no evident effect on the tensile properties at room temperature. After high temperature creep test, the creep test specimens break at fusion zone, which indicates that the weak part of the weld joint is the fusion zone during service. In the creep process, the cracks first nucleate at the interface between carbide and γ matrix, and then propagate along the carbide, finally the weld joint fractures along the dendrite boundary.

Effect of Hot Rolling on Microstructural Evolution and Wear Behaviors of G20CrNi2MoA Bearing Steel

Hot rolling can improve the mechanical properties after heat treatment by improving the microstructure. The effect of hot rolling (HR) deformation on the microstructural transformation of G20CrNi2MoA bearing steel in the subsequent CQT (carburizing-quenching and tempering) and RQT (reheating-quenching and tempering) processes was studied. The results indicate that the austenite grain size decreased by 20% after 45% hot rolling reduction, and the number of large-angle grain boundaries increased due to the recovery and recrystallization induced by hot deformation. The refinement effect of hot deformation on austenite grains was retained after dual austenitizing, and the large-angle grain boundaries and massive dislocation in the grains caused by hot deformation promoted the diffusion of carbon atoms during carburization, resulting in a higher surface carbon concentration. The refined grains and higher carbon concentration affected the volume fraction and size of undissolved carbides in RQT specimens. When the initial hot rolling reduction reached 45%, the average particle size of carbides decreased by 40%, and the area volume fraction increased by 37%. The Vickers hardness increased, but the friction coefficient and wear rate were significantly reduced with the increase in the initial hot rolling reduction. The main reasons for the improved wear resistance were fine grains, superior carbide distribution and high hardness.

Effect of cooling rate on carbides in directionally solidified nickel-based single crystal superalloy: X-ray tomography and U-net CNN quantification

X-ray computed microtomography (X-CT) and U-net convolutional neural network (U-net CNN) were used to characterize and segment the three-dimensional structure of MC and M23C6 carbides. The volume fraction of MC and M23C6 carbides, the percentage of MC carbides in all carbides, and the size of MC carbides were statistically analyzed. We found that the MC carbides were mainly distributed at the interface between γ dendrites and the interdendritic γ’ phase. The M23C6 carbide grows from the MC carbide to the interdendritic region. Combing with the finite element simulation of the directional solidification process, it was shown that the cooling rate had a significant influence on the carbide growth of superalloys. The faster the cooling rate, the smaller the MC carbides volume percentage and size, the larger the M23C6 carbides volume percentage, and the faster carbides growth. Based on the simulation results and thermodynamic calculations, we developed the relationship between the carbon addition, cooling rate, and volume fraction of carbides by regression models. The results show that the volume fraction of carbides in nickel-based single crystal superalloys increases linearly with the increase of carbon content and gradually increases with the rise of cooling rates.

Production of TiC – Co and TiC – NiCr Composite Powders and Study of Their Interaction with a Target under Cold Spray Conditions

In the first part of the paper, the effect of mechanical treatment of particles of reacting Ti + C + Me (Me = NiCr or Co) mixtures on the process of self-propagating high-temperature synthesis (SHS) is investigated. It is shown that as a result of SH-synthesis in the free burning mode, a metal-ceramic sinter of high porosity is formed, which is easily destroyed by mechanical action. An increase in the volume fraction of the metal binder (NiCr or Co) leads to a redistribution of the sizes of carbides towards smaller values.In the second part of the paper, the results of cold spraying nickel-chromium alloy particles and cermet particles of the TiC – NiCr composition on an aluminum substrate are presented. Produced NiCr coatings have a high porosity (up to 10 %) and a layered structure with clearly defined contours of individual deformed particles (splats). Due to the high hardness and low plasticity of metal – ceramic particles of the TiC – NiCr composition, during their interaction with the surface of aluminum substrate, continuous coating cannot be produced, only individual adhered particles are observed. With prolonged exposure to the flow of such particles, erosion of the substrate takes place.

Effect of precipitates on the cryogenic fracture toughness of 9%Ni steel flux cored arc weld

The microstructure and fracture toughness of 9%Ni steel flux cored arc welds with different heat input were investigated. CTOD results showed that the fracture toughness of the weld decreased with the increasing amount of precipitates at room temperature and at cryogenic temperature. Micro-regional force and deformation (MRFD) of the weld was investigated by finite element analysis. Precipitates have a significant impact on MRFD. In the stretching process, high stress concentration and local plastic deformation occurred around precipitates, which decreased crack propagation resistance in interdendritic region. The increment of precipitate amount enhanced the stress concentration and local plastic deformation. The effect of rod-shaped Laves phase on MRFD is much higher than globular-shaped carbide. For Laves phase, the maximum local plastic strain and peak stress has close relationship with its aspect ratio and its angle between long-axis direction and load-direction. The size of carbide has little influence on MRFD. Due to the high local plastic deformation and peak stress, microcracks formed at interdendritic region near precipitates during stretching at cryogenic temperature.

Laser cladding of Metco 1040® (Fe-V-Mn-C) on Hadfield steel: Effect of processing parameters on microstructure and wear resistance

Hardfacing of Ni and Co-based alloys has been widely applied to extend the lifespan of components that operating under severe conditions. The recent development of computational tools, such as Scorpeta from Oerlikon Metco, has allowed the design of alloys with customized properties. Metco 1040® (Fe-V-Mn-C) is a novel hardfacing alloy designed by the Scorpeta process to improve the abrasion and impact resistance of manganese steel substrates. However, few authors have addressed its wear performance. Therefore, the purpose of this study was to evaluate the effect of the processing parameters on the microstructure and wear resistance of the Metco 1040® alloy deposited by laser cladding on Hadfield steel. Single beads were deposited on Hadfield steel substrates according to a full factorial design of experiment (DOE), in which the laser power and deposition scanning speed were varied with 3 levels (32). Using some selected parameters, areas were covered by depositing parallel beads with an overlap of 30%, aimed at assessing the wear resistance through the “pin on drum” test. On applying the response surface method, it was found that the observed effects of the processing parameters (laser power and scanning speed) on the bead geometry (height, width and dilution) corroborate the current literature. For a given scanning speed, the higher the laser power the larger the carbide size and interdendritic spacing will be. The deposition parameters had no significant effect on the hardness or wear resistance of the coatings. However, the coating performance was significantly higher than that of Hadfield steel substrate. The findings reported herein suggest that the Metco 1040 alloy can be used to extend the lifespan of components of Hadfield steel.

Scanning Electron Microscopy versus Transmission Electron Microscopy for Material Characterization: A Comparative Study on High-Strength Steels.

The microstructures of quenched and tempered steels have been traditionally explored by transmission electron microscopy (TEM) rather than scanning electron microscopy (SEM) since TEM offers the high resolution necessary to image the structural details that control the mechanical properties. However, scanning electron microscopes, apart from providing larger area coverage, are commonly available and cheaper to purchase and operate compared to TEM and have evolved considerably in terms of resolution. This work presents detailed comparison of the microstructure characterization of quenched and tempered high-strength steels with TEM and SEM electron channeling contrast techniques. For both techniques, similar conclusions were made in terms of large-scale distribution of martensite lath and plates and nanoscale observation of nanotwins and dislocation structures. These observations were completed with electron backscatter diffraction to assess the martensite size distribution and the retained austenite area fraction. Precipitation was characterized using secondary imaging in the SEM, and a deep learning method was used for image segmentation. In this way, carbide size, shape, and distribution were quantitatively measured down to a few nanometers and compared well with the TEM-based measurements. These encouraging results are intended to help the material science community develop characterization techniques at lower cost and higher statistical significance.

Effect of Hardening and Tempering on the Microstructure and Mechanical Properties of the Tapered-Forged Leaf Spring Steel

The sharp side of a steel axe is often broken. This part is usually forged into a tapered shape until the front edge is thin and sharp. The purpose of this study was to determine the effect of tempering on the structure and hardness of a steel axe made of AISI 5160 leaf spring steel which has undergone a forging and hardening process. The as-received samples were obtained from a commercial market after undergoing a forging process to reduce their thickness from 10 mm to 5.5 mm in the base part and 1 mm in the front edge part. The hardening process was carried out by heating the samples at a temperature of 850 °C followed by rapid cooling in an isorapid oil. The samples were then tempered with tempering temperatures of 300 °C, 350 °C, and 400 °C. The hardness of the tempered samples was evaluated using a Vickers microhardness tester in three different locations; the base, the middle, and the front edge of the tapered samples. To analyze the property change, the microstructure of the tempered samples was observed using SEM and EDS. The result showed that the hardness of the samples decreased with the increase in tempering temperature. The hardness of the front edge was higher than that of the middle and base part of the tempered samples. The faster cooling rate inside the thinner part was responsible for the higher hardness. The microstructure showed that the martensitic structure that emerged after the hardening process turned into fine tempered martensitic and secondary carbides. The size and amount of carbides increased with increasing tempering temperature

Role of carbides on hot deformation behavior and dynamic recrystallization of hard-deformed superalloy U720Li

Cracks are easy to occur during cogging of U720Li ingots due to the high deformation resistance and poor hot ductility. In this paper, the low-carbon alloy (0.014 wt% C) and high-carbon alloy (0.071 wt% C) ingots were fully homogenized. The effect of carbides on hot deformation behavior and dynamic recrystallization (DRX) of as-homogenized U720Li alloy was investigated with aim of providing some guidance for improving hot working performance of such hard-deformed superalloys. It has been found that the blocky MC carbide is the major form of carbon in both alloys. Compared with low-carbon alloy, the size, number density and area fraction of MC carbides in high-carbon alloy are much greater, but those of γ′ are similar. The existence of more MC carbides leads to finer initial grains in the high-carbon alloy. During compression deformation of both alloys at 1060 °C, intergranular cracking occurred preferentially along initial grain boundaries (GBs), but cracking of the high-carbon alloy occurred at larger strains than that of low-carbon alloy. Before the occurrence of cracking, the yield and flow stress of high-carbon alloy were obviously lower than those of low-carbon alloy. An interesting phenomenon was discovered that the DRX always occurred preferentially around the MC carbides. Based on this phenomenon and electron backscatter diffraction analysis, the MC carbides were assumed to act as nucleation sites during initiation of DRX by a particle stimulated dynamic recrystallization mechanism. In addition, initial GBs are also preferential sites for DRX initiation. The greater size and number density of MC carbides and finer initial grains significantly increased the stored energy and nucleation sites, which distinctly promoted DRX in the high-carbon alloy. The faster DRX is the major contributor in reducing deformation resistance and cracking of the high-carbon alloy.

High-temperature abrasion resistance and wear mechanisms of chilled high-chromium cast irons

Hard and highly wear resistant chilled cast irons are of high interest in heavy industries like mining and steel production to achieve durable and sustainable wear protection. In this work a comprehensive view on abrasion mechanisms and the change in microstructure of these materials at elevated temperatures is targeted. Therefore, two different types of commercially available chilled high-chromium white cast irons were chosen. Detailed material characterization and hot hardness tests up to 1000°C were performed to get a first indication of temperature stability. For analysis of abrasive behaviour dry sand/steel wheel testing up to 700°C was conducted. A major part of the work was a thorough examination of the wear tracks and the influence on the microstructure. In the investigated materials chromium carbides Cr(Fe)7C3 and Mo-rich precipitations are present; the size and stoichiometry depend on the chemical composition. According to the differences in carbide size and type and the respective matrix composition, the hardness and abrasive behaviour changes, especially at higher temperatures. Incorporation of SiC abrasive in the wear zone leads to an in-situ wear protection, which was especially effective at 300°C increasing material’s wear resistance compared to room temperature (RT). At higher temperatures up to 700°C it was possible to compensate the hardness loss of the cast iron materials.

Effect of melting rate on microsegregation and primary MC carbides in M2 high-speed steel during electroslag remelting

Large-size primary MC carbides can significantly reduce the performance of M2 high-speed steel. To better control the morphology and size of primary MC carbides, the effect of melting rate on microsegregation and primary MC carbides of M2 steel during electroslag remelting was investigated. When the melting rate is decreased from 2 kg·min−1 to 0.8 kg·min−1, the columnar dendrites are gradually coarsened, and the extent of segregation of Mo and V is alleviated, while the segregation of Cr becomes severe. At 2 kg·min−1, the number of primary MC carbides per unit area with the sizes in the range of 2 µm to 6 µm accounts for about 75% of all MC carbides, while the carbides are mainly concentrated on the size larger than 8 µm at 0.8 kg·min−1. Thermodynamic calculations based on the Clyne-Kurz (simplified to C-K) model shows that MC carbide can be precipitated in the final solidification stage and a smaller secondary dendrite arm spacing caused by higher melting rate (2 kg·min−1 in this experiment) facilitates the refinement of primary MC carbides.