Carbide Morphology Research Articles

Micro abrasion in Fe-Cr-C-Nb alloys samples: The role of niobium

This paper addresses to analyze the role played by Niobium (Nb) in the microstructure of Fe-Cr-C alloys being tested in micro abrasion conditions (ball abrasion test). Three alloys with differences in Cr content and one of them with 5% Nb have been prepared as weld tracks under Fe-C substrate. The resulting microstructures contain carbides embedding in a metallic matrix (MMC). Significant changes in mechanical properties are expected depending on the morphology, size and distribution of carbides. Results pointed out to an improvement in wear resistance of Fe-Cr-C-Nb alloy although it showed lower values of hardness and volume fraction of carbides in comparison to the other alloys. The coefficient of friction was also affected by Nb addition. Such results evidence the possibility of using such alloy in applications that require high performance in wear resistance as mining and agriculture equipment.

Effects of Y addition on carbide morphology and impact properties of D2 cold work die steel

In this study, heavy rare-earth Y element was added to D2 cold work die steel to improve its carbide morphology and distribution, thereby increasing its impact resistance. A comprehensive study was conducted on the morphology and distribution of carbides in D2 steel in the as-cast, as-forged, and spheroidized annealing states. After the forging process, the degree of breakage of the network distribution of the as-forged M7C3 eutectic carbide morphology in the Y-containing D2 steel increased. As the Y content increased from 0 to 0.0210 wt%, the secondary dendrite spacing of the as-cast M7C3 eutectic carbides as well as the volume fraction and average size of carbide clusters decreased from 43 μm, 16.7%, and 29 μm–31.96 μm, 14.2%, and 23 μm, respectively. After the spheroidized annealing process, the addition of Y increased the M7C3 eutectic carbide spheroidization degree. Moreover, the number of the M7C3 secondary carbides increased from 50/25 to 71/25 μm2, and Y addition increased the number of dimples in the impact fracture and proportion of high-angle grain boundaries from 79.1% to 93.4%. Finally, the longitudinal impact toughness of D2 cold work die steel increased from 103.9 to 163.2 J.

Effect of magnesium on primary carbides in GCr15 bearing steel

GCr15 bearing steel has higher carbon and chromium content, large-size primary carbides tend to be easily precipitated during the solidification, which is harmful for the performance of steel. Hence, magnesium treatment was applied to refine primary carbides and the influence of magnesium on the size, distribution and morphology of primary carbides in GCr15 bearing steel was studied in this paper. The results indicated that M3C, M3C2, and M7C3 were precipitated during the solidification of GCr15 bearing steel. When magnesium was added into the steel, the area ratio and maximum size of primary carbide were decreased with the increase of magnesium content. The refinement of primary carbides was the most obvious when the magnesium content was 27 ppm. Compared with the steel without magnesium, the area ratio and maximum size of primary carbides were reduced by 2.41 % and 11.16μm respectively. In addition, for the steel without magnesium, MnS were likely to be attached with primary carbides. Once magnesium was added, smaller and two-layer structured composite inclusions (the inner layer was Mg-Al-O, and the outer layer was MnS) were formed and provided the preferred nucleation site for primary carbides, which ultimately promoted the refinement of primary carbides.

Effect of trace niobium on the microstructure and properties of full-pearlite steel used in the high-strength hypereutectoid wire rods

The present study investigated the impact of 20–80 ppm Nb on the microstructure and properties of hypereutectoid pearlite steel. Remarkably, even trace amounts of Nb exhibited a favorable effect on the refinement of austenite grain. The addition of the Nb element resulted in a reduction of pearlite transition temperature, leading to a decrease of approximately 13% in lamellar spacing and 11% in the size of pearlite colonies. Furthermore, the dragging effect of the Nb element on the carbon atoms in hypereutectoid steel facilitated the control and refinement of network carbides. These findings offer valuable theoretical guidance for the production of ultra-high-strength wire rods. When the Nb content reached 80 ppm, it promoted the precipitation of (Ti, V)C, while simultaneously improving the morphology of square carbides. The grain refining strengthening mechanism accounted for about 70% of the overall strengthening effect observed in high carbon wire rods, with the influence of the Nb element primarily targeting grain refinement. Consequently, the incorporation of minute quantities of Nb presents a promising avenue for the development of ultra-high-strength hypereutectoid wire rods, offering significant potential for enhancing their strength properties.

Experimental investigation on effect of cooling rate on carbide precipitation during solidification of high manganese steel

In order to elucidate the effect of cooling rate on the carbide formation during the solidification process of high manganese steel Mn13, the solidification process is artificially divided into two stages, namely the liquid-solid phase transition stage and solid-state cooling stage. The final Mn13 samples with different cooling rates are used to the analysis of solidification structure and carbides by high-temperature confocal microscopy (HTCLSM), optical microscopy (OM), electron backscatter diffraction (EBSD), and scanning electron microscopy (SEM). The result shows that the change of cooling rate at the liquid-solid phase transition stage has a great influence on the solidification structure and carbide precipitation. At this stage, with the increase of cooling rate from 0.2 °C/s to 5.0 °C/s, the dendrite structure is obviously refined, and the secondary dendrite arm spacing and cooling rate are satisfied with the relationship: λΠ=54.14×v−0.33. Also, the average grain size in the Mn13 sample decreases from 549 μm to 346 μm, and the aspect ratio of gains in the Mn13 sample increases from 1.7 to 2.0. Moreover, the distribution of carbide in the interdendritic regions and grain boundaries increases, and the morphology of carbide at the grain boundary change from block to dendrite. But it seems that the change of cooling rate from 1 °C/s to 5.0 °C/s at the solid-state cooling stage has a slight effect on the secondary dendrite arm spacing, the average size and aspect ratio of the grain structure and the amount and morphology of carbide precipitation at the grain boundary.

Enhanced properties of hard metal WC-Ni processed from nanostructured powders

In this study, we investigated the effects of nanostructured composite powders (WC-Ni), nickel binder content, and sintering techniques on the morphology and mechanical properties of tungsten carbide. An alternative low-temperature gas-solid reaction route with a short reaction time was employed to produce nanostructured composite powders with 5 and 15 wt% Ni. The powders were consolidated using spark plasma sintering (SPS) and conventional vacuum furnace sintering at temperatures of 1350 °C and 1450 °C. The composite powders were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and particle size measurements. The expansion/contraction of the compacted nanocomposite powders was studied through dilatometric analysis. The composite powders exhibited a uniform distribution of Ni, in both compositions. For the WC-5 wt% Ni nanocomposite powders, the average crystallite sizes for WC and Ni were 41.6 nm and 46.2 nm, respectively. While, for the WC-15 wt% Ni nanocomposite, the crystallite sizes for WC and Ni were 45.6 and 38.4 nm. The sintered composites were evaluated through XRD, SEM, measurements of density and Vickers hardness. The enhanced sinterability of the nanostructured powders enabled their consolidation into (WC-Ni) hard metal with densities approaching the theoretical relative density of 96.07 %, even with low binder content (5 wt% Ni). This is attributed to the uniform distribution of Ni and an extensive Ni-WC interface present prior to sintering. The SPS process at 1350 °C produced sintered bodies (WC-5 wt% Ni and WC-15 wt% Ni) with higher Vickers hardness (2322 HV and 1512 HV, respectively) and superior microstructural quality compared to samples produced by conventional vacuum furnace techniques. These results demonstrated that the mechanical properties of the system WC-Ni processed by SPS are superior to those obtained by vacuum furnace. Therefore, WC-Ni hard metals processed by this approach is a promising alternative to conventional hard metals (WC-Co) for a wide range of applications.

Effect of hot isostatic pressing on the microstructure and mechanical properties of Udimet 720Li alloy formed by laser melting deposition

In this paper, the effect of hot isostatic pressing (HIP) treatment on defects, microstructure, precipitated phases and mechanical properties of Udimet 720Li alloy formed by laser melting deposition (LMD) was investigated. The results showed that the internal microcracks of Udimet 720Li alloy formed by LMD were completely eliminated after HIP treatment, but a few small pores still existed, and the density of the sample were improved from 97.06 % to 99.97 %. Partial recrystallisation occurred in the as-deposited sample. After HIP treatment almost complete recrystallisation occurred, and the grain morphology changed from epitaxially grown columnar grains to equiaxed grains with a decreasement in grain size. After HIP treatment, the MC carbides in the sample were changed from granular to large-sized lumps. For the sample with hot isostatic pressing and heat treatment (HIP + HT), a large number of carbides dissolution, the carbides morphology became granular diffusely distributed in the grain. Meanwhile, the HIP treatment eliminated the γ/γ′ eutectic phases present due to solute segregation, and a large number of secondary γ′ phases were uniformly precipitated within the grain. After the HIP + HT treatment, the average size of the secondary γ′ phase decreased from 283.4 nm to 266.3 nm, and the quantity was significantly enhanced. The HIP treatment reduced the mechanical properties of Udimet 720Li alloy, the microhardness decreased from 480 HV to 404 HV and the tensile strength decreased from 1258 MPa to 1234 MPa, which was mainly related to the decrease in the number of γ′ phases and the increase in the size of carbides. After HIP + HT treatment, the room temperature tensile properties of the samples were enhanced (σUTS = 1394 MPa, σYS = 702 MPa, εf = 18.33 %), which was mainly attributed to the precipitation of more small-sized secondary γ′ phases by heat treatment.

Effect of microstructure on sag resistance of ultra-high strength spring steel evaluated by hysteresis loop

Sag refers to the reduction in the free height of coil springs during actual usage, hence sag resistance is one of the crucial properties of spring steel and its improvement is essential for prolonging the service life of springs. However, limited research has been conducted on the effect of microstructure on sag resistance in recent years. This study aims to investigate the relationship between microstructure and sag resistance in 65SiCrV6 spring steel. The steel was quenched from various temperatures to obtain microstructures with varying sub-block size, and tempered at different temperatures to obtain microstructures with distinct tempered carbides morphology. The microstructures were characterized and the sag resistance was evaluated by hysteresis loop effect formed during cyclic tensile test. The results revealed that smaller sub-block sizes of martensite and higher proportions of high-angle grain boundary (HAGB) are beneficial for improving sag resistance. Incoherent granular cementite precipitated in the tempered microstructure improves sag resistance by enhancing interactions with dislocations, and coarsened cementite does not reduce the sag resistance due to the generation of back stress in heterogeneous microstructure. The hysteresis loop effect resulting from heterostructure as well as interactions between dislocations and tempered carbides increases with rising tempering temperature until it reaches a saturation state. This study highlights the importance of optimizing the microstructure with both small sub-block size and incoherent cementite precipitation through appropriate heat treatment process to enhance sag resistance, meanwhile provides valuable insights into understanding the micromechanism of sag resistance in spring steel.

Effect of melt temperature on the quasi-equilibrium solidification of K465 Ni-based superalloy

The solidification process of Ni-based superalloy K465 was examined using DTA and X-ray diffraction. The impact of melt structure on solidification process and the morphology of MC carbide and γ′-phase was analyzed. It was observed that an increase in melt peak temperature led to a significant decrease in precipitation temperature for carbides, but only a slight increase in the formation temperature of matrix and eutectic microstructure. The X-ray diffraction results showed that some ordered structures were detected in the sample with melt peak temperature of 1450 °C and 1500 °C, but not in the sample with melt peak temperature of 1360 °C. Furthermore, the ordered structure displayed similar crystalline features with M6C carbide. As the melt peak temperature increased, the carbides changed from block type to script type morphology. This phenomenon was likely caused by the formation of ordered structures at high temperatures. However, the microstructure of γ matrix and γ′ precipitates remained unaffected by the melt peak temperature.

Effect of Ta addition on primary MC carbide in Ti-Nb-Mo-W-alloyed superalloy

The effect of Ta addition on characterization of primary MC carbides with regard to their morphology, composition, and size in Ti-Nb-Mo-W-alloyed Ni-based superalloy were investigated. Several tools including automated scanning electron microscopy as well as electrolytic etching technology were used for broad characterization of carbides including three-dimensional morphology. The addition of Ta significantly influences the composition and morphology of primary MC carbides. Large dendrite (Ti,Nb,W,Mo)C carbides were changed to smaller (Ta,Ti,Nb)C carbides. The hardness of both MC primary carbides and the matrix were increased. MC carbides in the studied superalloys were developed dendrite in three-dimensional morphology, which was much larger than that in two-dimensional morphology. The formation mechanism of carbides was clarified by thermodynamic calculation.

Influence of prior austenite grain size on martensite-austenite islands morphology and decomposition characteristics during two-step tempering in Mn-Ni-Mo steel

Martensite-austenite (M/A) islands are typical in the quenched microstructure of Mn-Ni-Mo steel, frequently utilized for fabricating reactor pressure vessels (RPV). These islands can decompose into harmful long rod-shaped Fe3C carbides during tempering above 600°C, quantifying the negative effect of M/A island decomposition on mechanical properties and indicating a potential issue in RPV fabrication. To address this issue, the present study investigates a two-step tempering process on three different prior austenite grain size (PAGS) specimens (5 µm, 47 µm, and 119 µm). The effect of PAGS on M/A island decomposition characteristics during sub-600°C tempering and their impact on precipitated carbide morphology is investigated. A preliminary pre-tempering treatment at 200°C, 350°C, and 500°C for 2 hours was followed by a 3-hour final tempering step at 650°C. The findings revealed unique temperature-dependent decomposition characteristics of M/A islands. For example, at 200°C, partial M/A island decomposition took place, resulting in long rod-shaped carbides during final tempering. Meanwhile, the 350°C pre-tempering specimen revealed aggregated carbide precipitates of varying sizes in former M/A island locations. In contrast, the 500°C pre-tempering specimen showed coarse globular carbides and the absence of carbide precipitate clustering. This result can be attributed to the decrease in surface energy associated with the carbide-matrix interface as size increases. After tempering, all specimens produced three types of precipitates: rod-shaped Fe3C carbides, rhombus-shaped Mn7C3, and globular-shaped Mn23C6 carbides. The formation of long rod-shaped carbides during M/A island decomposition reduces the critical cleavage stress for micro-crack initiation, jeopardizing steel mechanical properties. Aggregated carbides cause the simultaneous formation of numerous micro-voids in close proximity, which eventually merge to form a large crack, resulting in material failure. When compared to other pre-tempered and directly tempered specimens, pre-tempering at 500°C produced the most favorable microstructure in terms of impact properties.

Thermal strengthening of seamless steel pipes grades 13KhFA for oil and gas industry

The present study focuses on grade 13KhFА steel alloyed with chromium and vanadium for the production of seamless pipes. The pipes were subjected to heat treatment throughout their body and along their entire length. They were fed individually into the furnace, end-to-end, consecutively. The heat treatment furnace was fueled by natural gas. Cooling of the pipes from the quenching temperature was achieved using water in a jet cooling multi-hole device (sprayer). This was followed by high self-tempering due to the heat retained after exiting the quenching furnace. Following quenching and high tempering, the structure of the 13KhFА steel on the surface of the pipe consisted of a mixture of ferrite and carbides with a granular carbide morphology (tempered sorbite). This structure enhances the corrosion resistance of the steel and provides an optimal combination of strength and toughness. The hardening temperature for seamless pipes made of 13KhFА steel was set within the range of 915–920 °C, while the tempering temperature was maintained at 720–730 °C. This careful selection of quenching and tempering temperatures within the specified limits makes it possible to obtain an improved structure of the 13KhFА steel. Keywords: pipe steel; thermal hardening; economically alloyed steel; regulatory standards; corrosion resistance.

Effects of niobium and molybdenum addition on microstructural characteristics and wear properties of 14 wt%Cr white cast irons

White cast iron (WCIs) alloys were developed by adding Nb, Mo, and a combination of both (∼3 wt% Nb, ∼3 wt% Mo, ∼1 wt% Mo-2 wt% Nb) through melting and casting. The objective was to analyze the microstructural characteristics of the alloys, as well as the impact of reinforcing carbides on their mechanical and tribological properties. The alloy containing the highest percentage of niobium exhibited a refined microstructure, tending towards a eutectic structure, unlike the Mo-containing materials with totally hypoeutectic microstructures. The microstructural characteristics of the alloys and morphology of niobium carbides, as well as the percentage of M7C3 eutectic carbides produced were affected by the varying percentages of Nb and the Mo–Nb combination. Moreover, thermodynamic simulations revealed that the NbC carbide precipitated before the M7C3 eutectic carbides, austenite dendrites, and the MC (composed mainly of Nb containing bound Mo) carbide resulting from the Mo–Nb combination. The alloys containing Mo had similar bulk hardness values, while the alloy with the highest percentage of Nb showed a higher bulk hardness value. This was attributed to the effect of Nb on microstructure refinement and on the production of M7C3 eutectic carbides from the alloy. Although there were different reinforcing carbides (NbC, MC and M2C), the differences in microstructural characteristics had no noticeable influence on the Charpy impact energy. Micro-scale abrasive wear test (conducted with SiC abrasive slurry) demonstrated that the reinforcing carbides MC and mainly NbC had a beneficial effect in blocking and preventing the progression of continuous micro-cuttings and formation of grooves. The M7C3 and M2C carbides were less effective at protecting the matrix against the high-hardness SiC abrasive.

Microstructures and mechanical properties of TA1 sintered samples prepared by injection molding using water-soluble binder

A water-soluble binder was used to obtain TA1 sintered samples prepared by injection molding. The effects of the sintering temperature on the microstructures and mechanical properties of the sintered samples were analyzed. A relative density of >91% is achieved. Some residual carbon and oxygen remain in the sintered samples, affecting the mechanical properties. The tensile strength and elongation of the sample sintered at 1,300 °C are the highest: 592 MPa and 12.95%, respectively. Detailed electron microscopic analysis was performed to identify the morphology and nature of the resultant titanium carbides and oxides.

Morphology evolution of P-Ti3AlC carbides and their influence on creep properties in a crept Ti-45Al-5Nb-0.75C alloy

In this study, the influence of the Ti3AlC carbide morphology on the creep properties, the interaction between carbides and dislocations during creep deformation as well as the influence of external stress on carbide morphology evolution were investigated in a Ti-45Al-5Nb-0.75C alloy. The results show that the best creep properties are obtained after annealing at 800 °C for 336 h. This is probably due to the splitting of the carbides into conglomerates of sub-particles, which provides an increased number of interfacial area and interfaces to hinder dislocation glide. After prolonged annealing for 1054 h at 800 °C, although the carbide splitting still existed, the matrix grains coarsened and the lamellar structure was decomposed, which counteracted the positive effect of carbide splitting and led to a reduction in the creep resistance. By comparing the carbide morphology evolution after creep and after annealing alone, it can be concluded that the external stress does not significantly affect the morphology evolution. During creep at 800 °C the Ti3AlC carbides obviously interact with dislocations, and the majority of them were identified to be ½<110] ordinary dislocations. The glide of these dislocations was strongly hindered, and thus the creep properties of the alloy can be improved by carbide precipitation.

Morphology and Distribution of Primary Carbides in Forged Cr-Ni-Mo-V/Nb Steel.

This study aims to investigate in situ the three-dimensional (3D) morphology and distribution of primary carbides (PCs) in electro-slag remelting (ESR) forged 30Cr3Ni3Mo2V steel. A facile non-aqueous electrolytic etching method was applied to prepare 3D PCs on the matrix. The morphology, composition, and element concentrations of PCs were characterized using a combination of optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and electron back-scattered diffusion (EBSD). The precipitation, type, and composition of PCs in the same steel were also simulated using Thermo-Calc software Version 2015a. The results indicate that PC is rich in Nb, which is a potential heterogeneous nucleating agent. Both the size and number of PCs increase from the edge to the center of the ingot. The large-sized PCs present three dominant types of morphology, which vary in different regions, i.e., a bulky type dominates in the edge region, a lamellar type dominates in the middle region, and a stripy type dominates in the core region. The results of EBSD analysis show that the orientation of PCs with different morphologies is different and that more nanosized V-rich type carbides are precipitated on the matrix. The thermodynamic calculations show that MC precipitates from the liquid phase when the solid phase fraction is greater than 0.985 and that the MC-type carbides are rich in Nb, which agrees well with the experimental results.

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.

A correlation between carbide morphology and wear resistance of a chromium based hard facing plate

A correlation between carbide morphology and wear resistance of a chromium based hard facing plate

Precipitation, Growth, and Aggregation Behavior of Primary Carbides during Continuous Casting of 6Cr13 Slabs

The types, distribution, morphology, orientation, growth, and aggregation mechanism of primary carbides in the continuous casting slab of 6Cr13 high‐carbon martensitic stainless steel are investigated. In the results, it is shown that M7C3 carbides precipitate from the liquid steel at the end of solidification. The area fraction of primary carbides in the slab thickness direction shows an overall decreasing trend from the center to the edge. And, the closer to the center region, the greater the difference in carbide distribution due to the presence of spot segregation defects. At 1/8 thickness and edges in the slab, the fast cooling rate and fine dendrites make the carbide morphology to be a small‐sized brain like that aggregates a large number of spherical carbides. At 1/4 thickness in the slab, blocky, fibrous, and spherical carbides precipitate successively and eventually aggregate together. At 3/8 thickness and center in the slab, the cooling rate is slower and spot segregation defects are randomly distributed in this region. The carbide morphology is mostly small‐sized brain like in the non‐spot segregation region. However, the alloying elements are highly supersaturated and the carbides can grow sufficiently to form less oriented, large‐sized brain‐like carbide in the spot segregation region.

Effect of Pre-Added HfO2 Inclusions on Carbide Morphology and Deformation Behavior in DZ125 Nickel-Based Superalloy

Inclusions are important phases affecting material properties in complicated ways. In this paper, a quantitative study of the addition of HfO2 inclusions to DZ125 nickel-based superalloys was performed. Experimental results showed that the introduction of HfO2 inclusions caused a loss of strength and ductility. The carbide morphology also changed significantly from skeletal-shaped to block-shaped, resulting in a remarkable discrepancy in the fracture behavior under quasi-in-situ tensile testing. The SEM dynamic observations showed that cracks were initiated from the skeletal carbides and almost failed to propagate into the matrix. In contrast, the damage behavior of block-shaped carbides also involved internal cracking but with a tendency to form interconnected microcracks during propagation. A crystal plasticity finite element model (CPFEM) method was further developed to study the stress/strain behavior during the deformation process, considering the crystal orientations and microstructure morphologies from the EBSD data. Those elastoplastic parameters were determined through nanoindentation experiments. Simulation results verified that blocky carbides produced a pronounced strain concentration at the interface of the carbides and matrix, thereby increasing the tendency of crack formation. This paper provides a fundamental understanding of the role of inclusions in material recycling applications.