Carbide Size Research Articles

Quantitative assessment of microstructural damage for interior crack initiation and high cycle fatigue life modeling

Axially loaded cyclic tests of a nickel-based alloy were conducted at 550 °C, 630 °C and 650 °C and stress ratios of −1, −0.3 and 0.5 up to high cycle fatigue regime. Multiscale characterizations and quantitative analyses of microstructural damage were carried out to illustrate the physics and mechanics of interior microstructure induced fatigue strength degradation and cracking. Results showed that the fatigue strength increased with the decreases of twin spacing, the size and aspect ratio of carbide, and γ′ phase size. Twin collapse due to slip band-twin interaction was found for the first time and confirmed as a form of crack initiation process, followed by short crack growth forming facets with significant contribution from shear stress. A new mechanistic fatigue life model of interior microstructure induced cracking was established with sound agreement with experimental data. All these combined into a design-manufacturing integrated approach which are capable of ensuring the safe operation and maintenance of service structures in long-life regime.

Effect of carbide refinement on high temperature erosive wear behavior of high chromium white cast iron with different titanium and carbon additions

It is known that better erosion wear resistance of high chromium (27 wt% Cr) white cast iron (HWCI) with titanium (Ti) addition can be achieved by controlling the size of M7C3 carbides. Nevertheless, it might not be directly applicable to high temperature conditions due to the more complex factors involved, especially the hot oxidation behavior. Therefore, the effect of 0–2 wt% Ti and 3–4 wt% carbon (C) addition on the high temperature erosion wear behavior of HWCI has been investigated in this research. The results show that there are TiC and M7C3 carbides precipitated in the material matrix. The size of M7C3 carbides decreases drastically as the amount of Ti increases. On the contrary, it is effectively enlarged with the addition of higher C. In addition, there is no significant difference in hardness among all specimens due to the relatively similar carbide volume fraction (CVF). The wear resistance of HWCI is improved by increasing the amount of Ti although it has a lower value as the C content increases. It means that hardness is not an important factor in evaluating the wear characteristics of HWCI at high temperatures. The worn surfaces and cross-sections show that the smaller M7C3 carbides are more likely to undergo plastic deformation rather than being directly peeled out. In addition, the effect of hot oxidation behavior was negligible because there is only a very thin oxidation layer on the worn surface. Therefore, it can be concluded that the erosive wear behavior of the material is greatly influenced by the size of M7C3, which the material with better erosive wear resistance contains finer carbides.

Effect of Processing Routes on Physical and Mechanical Properties of Advanced Cermet System

The present research focuses on the effects of different processing routes on the physical and mechanical properties of nano Ti(CN)-based cermets with metallic binders. Tungsten carbide (WC) is added as a secondary carbide and Ni-Co is added as a metallic binder to nano Ti(CN)-based cermet processed via conventional and spark plasma sintering (SPS). A systematic comparison of the composition and sintering conditions for different cermets’ systems was carried out to design novel composition and sintering conditions. Nano TiCN powder was prepared by 30 h of ball milling. The highest density of >98.5% was achieved for the SPS-processed cermets sintered at 1200 °C and 1250 °C for 3 min at 60 MPa of pressure in comparison to the conventionally sintered cermets at 1400 °C for 1 h with a two-stage compaction process—uniaxially at 150 MPa and isostatically at 300 MPa of pressure. Comparative X-ray diffraction (XRD) analysis of the milled powders at different time intervals was performed to understand the characteristics of the as-received and milled powders. Peak broadening was observed after 5 h of ball milling, and it increased to 30 hr. Also, peak broadening and a refined carbide size was observed in the XRD and scanning electron microscope (SEM) micrographs of the SPS-processed cermet. Transmission electron microscope (TEM) analysis of the milled powder showed that its internal structure had a regular periodic arrangement of planes. SEM base scattered electron (BSE) images of all the cermets primarily showed three major microstructural phases of the core–rim–binder with black, grey, and white contrast, respectively. With the present sintering conditions, a high hardness of ~16 GPa and a fracture toughness of ~9 MPa m1/2 were obtained for SPS-processed cermets sintered at higher temperatures.

Impact of carbon segregation on transition carbides and cementite precipitation during tempering of low carbon steels: Experiments and modeling

Tempering of low-carbon steels (less than about 0.3 wt.% C) may differ from the traditional precipitation sequence, which includes transition carbide precipitation, retained austenite decomposition and cementite precipitation. The main difference is the partial or total absence of transition carbides. In the present work, the effect of the carbon segregation on the mitigation of the precipitation of the latter is analyzed by combining multi-scale experimental investigations with a new precipitation model accounting for the carbon heterogeneities induced by the segregation. The full precipitation sequence is considered in order to study the impact of the segregation not only on the transition carbides, but also on the cementite which forms afterwards. The experimental work includes APT characterization of carbon segregation, in-situ HEXRD experiments to reveal precipitation kinetics, and TEM observations for carbide size measurements.The here-in developed precipitation mean-field and physics-based model combines two previous ones dedicated to the nucleation and growth of transition carbides and cementite and to the segregation of carbon at dislocations. It is shown that, even after water-quench, carbon atoms are already segregated on dislocations. The mitigation of transition carbide precipitation is caused by the presence of such segregations, which decrease the driving force for the transition carbide nucleation and enhance cementite precipitation. In agreement with previous experiments, the model also demonstrates that inside a martensitic microstructure, the precipitation sequence is different between the first (formed close to Ms temperature) and the last martensite (formed at room temperature) formed upon cooling, because of the difference in dislocation density, which influences the intensity of the segregation phenomenon.

Effects of Oxygen Content on Microstructure and Creep Property of Powder Metallurgy Superalloy

The effects of oxygen content on the microstructure and creep properties of the FGH96 superalloy were investigated. When oxygen content increased from 135 ppm to 341 ppm, the prior particle boundary (PPB) rose from degree 2 to degree 3, the size of the γ′ phase on PPB enlarged from 1.07 μm to 1.27 μm, and the MC carbide size grew from 77.4 nm to 104.0 nm. Meanwhile, the steady creep rate accelerated from 4.34 × 10−3 h−1 to 1.87 × 10−2 h−1, and the creep rupture life shortened from 176 h to 94 h, the creep rupture mode transferred from intergranular and transgranular mixed fracture to along PPB fracture. During creep, the micro-twin formation and gliding will be restrained by ∑3 boundaries. FGH96 superalloy with higher oxygen content contains less ∑3 boundaries, and its micro-twins cross-slipped instead of single-direction slip in lower oxygen content superalloy. Consequently, samples with a higher oxygen content crept faster and ruptured earlier.

Effect of tempering temperature on stress corrosion resistance of a low alloy high strength steel with high vanadium content

The stress corrosion resistance of a low alloy high strength steel with high vanadium content, tempered at different temperatures, was examined by electrochemical measurements and slow strain rate tensile test under different environments. Combined with scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), the results show that three different tempering temperatures had an influence on the microstructure of this steel as well as its electrochemical behavior and stress corrosion sensitivity. With the increase of tempering temperature, the ferrite grains coarsened, the average dislocation density lowered as well as the number of vanadium carbide also decreased, though the size of vanadium carbide increased. However, the interface distortion between vanadium carbide and matrix exacerbated, resulting in the increase of the local dislocation density. Therefore, the corrosion potential and impedance decreased, meantime, the stress corrosion sensitivity aggravated.

Effect of Heat Treatment on Fatigue Performance of 316L Stainless Steel Fabricated by Laser Powder Bed Fusion

Abstract The 316L stainless steel part built by laser powder bed fusion has attracted much attention in recent years. However, current studies have not systematically revealed the influence of post-heat treatment on fatigue performance. In this study, we utilized two common heat treatment processes (450 °C anneal treatment and 1050 °C solution treatment) for 316L stainless steel and then discussed their influence on fatigue life and crack growth rate. It can be found that both the heat treatment processes led to a decrease in fatigue life. The 1050 °C solution treatment can decrease crack growth rate. This can be attributed to the increase in grain size and decline of carbide at the grain boundary. The former can lead to a longer propagation path. The latter may cause more and deeper secondary cracks along the propagation path, which exhaust more energy.

Effect of nano-SiC on microstructure evolution and enhanced high wear resistance mechanism of laser surface alloyed M42 high-speed steel

M42 high-speed steel is one of the main materials for preparing bimetallic band saw parts. In this paper, nano-SiC particles of different densities (0–1.00 mg/mm2) were precoated on the surface of M42 high-speed steel samples, then, the samples were prepared by laser alloying. The matching relationship between the quantity, size, and type of martensite and MxCy carbides in laser alloyed samples play a decisive role in improving wear resistance. It is found that under the optimized particle density of 0.75 mg/mm2, compared with M42 high-speed steel, the hardness was increased by 50%, the wear rate decreased by 84.7%. The matching relationship between Martensite and MxCy carbides formed by laser alloying of nano-SiC particles on the improvement of wear resistance was elucidated.

Effect of Carbides on Thermos-Plastic and Crack Initiation and Expansion of High-Carbon Chromium-Bearing Steel Castings

The bearing steel’s high-temperature brittle zone (1250 °C–1100 °C), second brittle zone (1100 °C–950 °C), and low-temperature brittle zone (800 °C–600 °C) were determined by the reduction in area and true fracture toughness. The crack sensitivity was strongest at temperatures of 1200 °C, 1000 °C, and 600 °C, respectively. Various experimental and computational methods were used to establish the phase type, microstructure, size, and mechanical properties of carbides in bearing steel. The critical conditions for crack initiation in the matrix (FCC-Fe, FCC-Fe, and BCC-Fe)/carbides (striped Fe0.875Cr0.125C, netted Fe2.36Cr0.64C, and spherical Fe5.25Cr1.75C3) were also investigated. The values for the high-temperature brittle zone, the second brittle zone, and the low-temperature brittle zone were 13.85 MPa and 8.21 × 10−3, 4.64 MPa and 6.52 × 10−3, and 17.86 MPa and 1.86 × 10−2, respectively. These were calculated using Eshelby’s theory and ABAQUS 2021 version software. The ability of the three carbides to cause crack propagation was measured quantitatively by energy diffusion: M3C > MC > M7C3. This study analyzed the mechanism of carbide precipitation on the formation of high-temperature cracks in bearing steel casting. It also provided the critical conditions for carbide/matrix interface cracks in bearing steel continuous casting, thus providing effective support for improving the quality of bearing steel casting.

Failure analysis and numerical drive structure optimization design of Cr12Mo1V1 electrical connection die

A type of Cr12Mo1V1 electric connection die occured brittle fracture after 200 times of service, and its life was much lower than the design life of the die. In this paper, the 5M1E failure analysis method was adopted, combined with the characteristics of Cr12Mo1V1 cold-work die steel, scanning electron microscopy, direct reading spectrometer, Rockwell hardness tester, metallographic microscope and other means were used to analyze and test the macro fracture morphology, material composition, mechanical properties and microstructure of Cr12Mo1V1 electric connection die. The crimping process of the die was simulated by Deform software. The results show that the material composition is not up to standard, the strength is too low, the internal eutectic carbide is not uniform, the size of carbide exceeds the standard and so on are the root causes of the short life and brittle fracture of the die. In addition, the unreasonable designs of the crack slot and round hole of the die lead to excessive stress concentration in the crimping process of the die, which is too the main reason for the brittle fracture failure of the die. In view of the above factors, the paper puts forward some measures to prolong the life of the electric connection die from the aspects of raw materials, heat treatment, forging process and die structure design.

The Effect of Laser Power on the Microstructure and Wear Resistance of a Ni3Al-Based Alloy Cladding Layer Deposited via Laser Cladding

A coating prepared via laser cladding has the advantages of a high-density reinforced layer, a low matrix dilution rate, and combination with matrix metallurgy. In this study, Ni3Al-based alloy cladding layers with Cr7C3 were prepared via laser cladding, and the corresponding microstructures and wear resistance were studied in detail. The results show that the Ni3Al-based cladding layer prepared using laser cladding technology had good metallurgical bonding with the matrix, and there were no pores, cracks, or other defects on the surface. The microstructures of the laser cladding layer were mainly γ′-Ni3Al, β′-NiAl, and in situ C7C3. As the laser power increased, the heat input increased, resulting in an increase in the dilution rate. Simultaneously, the carbide size in the laser cladding layer increased. With the increase in laser power, the hardness of the laser cladding layer of the Ni3Al-based alloy decreased, and the wear resistance of the laser cladding layer first strengthened and then weakened. When the laser power increased to 2.0 kW, the wear rate of the laser cladding layer decreased to 0.480 × 10−5 mm3/N·m. When the laser power increased to 2.4 kW, the wear rate of the laser cladding layer increased to 0.961 × 10−5 mm3/N·m, which was twice the rate at 2.0 kW. This could be attributed to small Cr7C3 particles, which could not effectively separate the wear pairs, resulting in more serious adhesive wear. Large Cr7C3 particles caused the surface of cast iron material with lower hardness to be damaged, which suffered more serious particle wear. The generation of short rod-shaped carbides should be avoided because, in the process of friction and wear, carbides with these shapes are easy to break, thus leading to crack initiation.

Intermediate temperature embrittlement and Portevin-Le Châtelier effect of Inconel 625 alloy caused by carbides

The phenomena of intermediate temperature embrittlement (ITE) and Portevin-Le Châtelier (PLC) effect are common in nickel-based superalloys, which seriously restrict the machinability and serviceability of the alloys. The ITE and PLC effect of Inconel 625 alloy caused by carbides and hot ductility were studied by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscopy (TEM), and Gleeble 3500 thermal simulation equipment. The results show that hot ductility has a strong dependence on temperatures of Inconel 625 alloy. During the heating process, ductility initially decreases at 600 ℃ and reaches a minimum at 800 ℃ as the temperature increases, which was due to the formation of microcracks. Dynamic recrystallization can be observed at 900 ℃, and then ductility begins to drop until 1212 ℃ due to material melting. Meanwhile, the variation trend of the cooling process is consistent with the heating process. ITE exists in both the heating process and the cooling process, occurring at 600–900 ℃ and 600–1000 ℃ respectively of Inconel 625 alloy. The microcracks caused by the precipitation of carbides (NbC, (Nb, Ti)C, and M23C6) at grain boundaries led to the formation of ITE. The size, shape, distribution position, and type of carbides have different degrees of influence on the formation of microcracks. In addition, the serrated flow was observed throughout the test temperature range of Inconel 625 alloy. With the increase of the temperature, the type and amplitude of the serration changed, which is caused by the interaction between carbides (solute atoms) and dislocations.

The Effect of Niobium Addition on the Operational and Metallurgical Behavior of Fe-Cr-C Hardfacing Deposited by Shielded Metal Arc Welding

Hardfacing is commonly used in parts recovery and in obtaining surfaces with improved properties. Within this field, it is important to analyze the effect of alloying elements on the properties of the deposited layers. One of the critical parameters affecting alloying performances in SMAW is improper arc length. This article examines the effect of the addition of niobium in different quantities (0, 2, 4, 6, and 8% by weight) to the electrode coating in Fe-Cr-C shielded metal arc welding (SMAW), with short and long arc lengths, on the operational process efficiency, dilution, arc energy, microstructure, and microhardness of the deposited layers. A decrease in operational process efficiency and dilution was found with increases in niobium content. On the other hand, it was found that adding niobium leads to a refinement in chromium carbide sizes, directly affecting the hardness of the obtained deposits. There is a direct relationship between the arc energy, with both short and long arc lengths, leading to a tendency to decrease the dilution in the obtained hardfacing.

Effect of Alloying and Microalloying Elements on Carbides of High-Speed Steel: An Overview

In high-speed steel, carbides are essential phase constituents, which have a direct impact on engineering performance and qualities of high-speed steel. The formation, morphology, and distribution of carbides are dictated by alloying elements. In this paper, various types of carbides in high-speed steel are presented. The effects of different alloying elements such as C, W, Mo, Cr, and V on the formation of carbides in high-speed steel are discussed. Research progresses on carbide improvement by microalloying elements such as N, B, Mg, and rare earth (RE) elements are reviewed. It is reported that Cr promotes the precipitation of M2C, N enhances the formation of fibrous M2C, Mg effectively shatters the large-size carbide grid, Nb refines granular carbide MC, and rare earth elements encourage the formation of M6C, resulting in irregular M2C lamellae. The incorporation of microalloying elements improves the distribution and size of carbides and also refines the solidification structure of high-speed steel.

Influence of magnesium treatment on inclusions and primary carbides in As-cast H13 die steel

In this study, the inclusions and primary carbides in H13 hot-work tool steel were investigated, both with and without magnesium treatment, utilizing various analytical techniques such as optical microscope (OM), scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and quantitative analysis methods. Furthermore, the experimental results were compared with the calculations obtained from Thermo-Calc software. The results revealed that as we move from the edge to the center of the steel, the equivalent diame-ter of inclusions increased. However, upon adding magnesium to the steel, the size of inclusions decreased, while the number of inclusions per unit area increased. The primary carbides found in H13 steel consisted of vanadium-rich MC carbides and molybdenum-chromium-rich M2C carbides. The addition of magnesium had a significant impact on the size of these primary carbides. The presence of MgAl2O4 particles acted as heterogeneous nuclei, providing nucleation sites that induced smaller sizes and more uniform distribution of primary carbides. Furthermore, it was observed that the banded segregation in the annealed microstructure became more uniform after magnesium treatment, leading to an improvement in the banded segregation.

Effect of destability time on microstructure and properties of hypoeutectic high chromium cast iron.

The present work investigated the effect of destabilization time on the mechanical properties and microstructure evolution of high chromium cast iron, and scanning electron microscopy and electron probe microanalysis techniques were employed. The results show that the hardness of hypoeutectic high chromium cast iron is related to the size and volume fraction of secondary carbides precipitated from the matrix. The hardness of the alloy continues to rise due to the continuous increase of the volume fraction of the secondary carbide at the initial stage of destabilization. The alloy reaches its peak hardness value at 950 °C and 1000 °C for 1 hour holding time. The solid solubility of carbon and alloying elements in the matrix increases as the holding time extends, resulting in a large number of carbides redissolved into the matrix, making the hardness of the alloy decrease; the hardness of the alloy at 14 h is less than that at 10 min. Under 1050 °C, the size and density of the secondary carbide increase significantly; extending the holding time will lead to the continuous reduction of the carbide rod that provides strength, thus, the hardness curve shows a downward trend.

Influence of microstructure on slurry erosion resistance of medium carbon high silicon steels

The present study compares slurry erosion resistance of austempered and tempered medium carbon high silicon steels. A 0.62C-1.91Si-0.85Mn-0.23Cr steel was subjected to austempering at 300, 350 and 400 °C for 10 min to develop a microstructure comprising of bainite and retained austenite. With the increase in the austempering temperature, the mechanical stability of retained austenite decreased, and the size of bainitic ferrite laths increased. As a result, strain hardening ability and toughness of the steels decreased with austempering temperature. Another set of steel with the same composition was quenched and tempered at 300, 450 and 550 °C for 60 min. An increase in the tempering temperature led to an increase in the size and fraction of carbides and a decrease in the mean free path and dislocation density. Strain hardening ability and toughness of tempered steels was substantially small than austempered steels. Both the austempered and tempered steels were subjected to slurry erosion. Austempered steels exhibited higher slurry erosion resistance as compared to tempered steels. Slurry erosion resistance of austempered steels has been noted to depend on the mechanical stability of retained austenite and the size of bainitic ferrite laths. Due to the difference in the extent of deformation-induced transformation of retained austenite into martensite in the steels austempered at different temperatures, number of mobile dislocations generated (to accommodate the dilatation due to transformation) in bainitic ferrite laths differed. A large number of mobile dislocations in the specimens austempered at 300 °C blunted the propagating crack and delayed the material loss during erosion. The erosion resistance of tempered steels was observed to decrease with an increase in tempering temperature. A large fraction of coarse carbides led to the formation of many decohesion sites in steels tempered at 450 and 550 °C. Further, a small number of mobile dislocations present per unit volume in the steels tempered at high temperatures could not resist the propagation of cracks nucleated from the decohesion sites leading to a high erosion rate in these steels.

Effect of C content on the microstructure and properties of in-situ synthesized TiC particles reinforced Ti composites

Titanium matrix composites (TMCs) have garnered substantial attention from researchers owing to their outstanding properties. Nonetheless, the strength and ductility of TMCs hardly co-exist and often show a trade-off between each other. In this study, we employ an ultra-thin graphite powder sheet as the carbon source and employ Ti/C composites with varying carbon contents, prepared via a layer-stacked laminated sintering method, to ensure a comprehensive in-situ reaction and uniform reinforcement distribution. With increasing carbon content, noticeable alterations occur in the size, concentration, and morphology of the titanium carbide (TiC) particles. The increase of TiC particle content is found to boost the ultimate tensile strength of the composite. However, this improvement comes at the expense of reduced elongation. Notably, as the carbon content reaches 1.81 wt%, the yield strength and ultimate tensile strength of the composites soar to 354.4 MPa and 575.4 MPa, respectively. These values represent a remarkable increase of 75.4% and 65.0% compared to pure titanium, while maintaining an acceptable elongation of 6.45%. This study unveils a promising approach for significantly enhancing the mechanical properties of titanium alloys.

New insight into the relationship between the C-Cr ratio and carbides, mechanical property of cold working die steel

An new insight into the relationship between the C-Cr Ratio and carbides, mechanical property Cr Alloyed of cold working die Steel were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), rockwell hardness and impact toughness tests. The ‘C-Cr ratio’ and ‘Cr equivalent E Cr ‘ parameters were introduced to characterize the carbide characteristics and mechanical properties. The results show that the precipitation temperature of M7C3 eutectic carbides grows linearly with E Cr when the E Cr value is less than about 22, and the precipitation temperature increases significantly when the E Cr value exceeds 22, and the growth curve takes a plateau turn. The precipitation temperature of MC carbides decreases approximately linearly with E Cr value, and the precipitation of MC eutectic carbides will be completely suppressed when the E Cr value exceeds 19. The content of eutectic carbides in the as-cast organization is more, the shape is more complex and the size is larger. The ratio of Cr and Fe content in the composition of M7C3 eutectic carbides is linearly related to the Cr-C ratio; the content of carbides in the steel after forging and the E Cr value are basically linear. The average particle size and the average length of longitudinal carbides after forging are basically proportional to the E Cr value. The average particle size of longitudinal carbides after forging is greater than 4 μm and the E Cr value are basically linear; when the Cr content is greater than 4%, the quenching peak hardness of steel and the C/Cr have a good linear relationship; as the E Cr value gradually increases, the impact toughness of steel gradually decreases. These results are important not only for understanding the strengthening mechanisms of die steel, but also for the composition design and carbide control of cold working die steel.

New insights into the formation mechanism of the multicomponent carbides (Nb, M)C (M = Ti, Cr and Mn)

Combining first-principles calculations and classical nucleation theory, the results of elemental doping on the structure, electrons and stability of niobium carbides are investigated. Ti, Cr and Mn doping altered the physical characteristics of the carbides, resulting in lower mismatch strains and interfacial energies between the carbide and the substrate. Elemental doping reduced the critical nucleation size of carbides and contributed to the promotion of carbide nucleation. However, excessive doping with Cr and Mn increases the formation energy of carbides and unfavorable to carbide stabilization. Therefore, Cr and Mn are involved in the early elemental aggregation of carbides, while Ti and Nb are the main carbide-forming elements. The nano-precipitated phases of various compositions produced in niobium microalloyed steel were experimentally validated utilizing transmission electron microscopy (TEM) and three-dimensional atom probe tomography (3D-APT). The carbides primarily composed of Nb, Ti and C elements, with the presence of Cr and Mn in the core region leading to the formation of a core-shell structure, which is consistent with theoretical calculations.