Primary Carbides Research Articles

Inhibiting primary carbide in steel by diffusion: A perspective of phase-field study

This study provides a potentially viable approach to manipulate the precipitation of primary carbides in molten steel by modifying the diffusion coefficient of carbon. The solidification process of a Fe-C alloy is simulated using the multi-phase-field method, and we focus on the impact of diffusion coefficient of carbon on the solute segregation and cementite precipitation. Two benefits have been revealed as the ratio of the diffusivities of carbon in solid to that in liquid is increased. A potential advantage is the reduction in the volume fraction of the residual liquid enriched with carbon during the late solidification. Furthermore, the magnitude of the chemical driving force for the phase transition of cementite precipitation will be lower. The combined influence of both factors results in an exponential decrease in the volume fraction of cementite formed at the end of solidification.

Insights into primary carbides and nanoparticles in an additively manufactured high-alloy steel

This paper reports the use of combined electron microscopy and small-angle neutron scattering (SANS) to probe into the compositional and size evolution of the primary carbides and nanoparticles (defined by a size threshold of 100 nm) in an additively manufactured high-alloy steel before and after heat treatment. The primary carbides exhibit marginal changes in their total volume fraction and size after the austenitising and tempering. However, those carbides located at the prior-austenite boundaries provide a pinning effect to impede grain growth during the austenitising. The grain size increases from 1.7 µm in the as-manufactured to 2.8 µm in the as-tempered conditions, resulting in a limited strength loss of 33–126 MPa as estimated by using the Hall-Petch relationship. Atom probe tomography, which offers atomic spatial resolution examining a sample volume of 6.6 × 105 nm3, reveals the presence of numerous V and Cr-enriched nanoparticles with sizes of 1 to 10 nm within the steel matrix after the tempering. In contrast, the complementary SANS which examines a significantly larger sample volume of 0.9 mm3 but lacking spatial resolution, provides nanoparticle size information. It reveals a radius reduction from 7.6 to 1.0 nm and a volume fraction increase from 1.6 % to 2.3 %, in the as-manufactured and as-tempered conditions, respectively. The nanoparticles induced during tempering can contribute to a strength enhancement of 691 MPa, primarily through the Orowan bypass mechanism. This suggests that the combination of limited prior-austenite grain growth and the presence of nanoparticles is the key factor responsible for the unprecedented material strength.

Multi-interface migration mechanism induced by carbide precipitation during the quenching-partitioning-tempering process in a high-carbon steel

Phase-field finite element (PFFE) modeling of the quenching-partitioning-tempering (Q-P-T) process is proposed, and the two-dimensional PFFE-QPT model considering carbide precipitation and the interface migration between martensite and austenite is used to investigate microstructural evolution and the elastic/plastic strain distribution at quenching, partitioning and tempering stages in a high-carbon steel, respectively. The simulation results of the high carbon Q-P-T steel indicate that the precipitation strengthening of carbides occurs not only because they can block the movement of dislocations, but also because they can produce high internal stress. Meanwhile, the volume fractions of different phases (including primary martensite, retained austenite, secondary martensite, and carbide) and the carbon content in retained austenite predicted by the PFFE-QPT model are slightly better than those predicted by the novel one-dimensional QPT-LE (local equilibrium) model and much closer to experimental values. The PFFE-QPT model is also used to successfully predict the volume fractions of different phases in low-carbon and medium-carbon Q-P-T steels. More importantly, the microstructural morphologies closely related to mechanical properties can be demonstrated by the PFFE-QPT model and are comparable with the experimental observation. Therefore, the PFFE-QPT model will be a more powerful tool for guiding the process and microstructure design of Q-P-T steels compared with the QPT-LE model.

Insights into refinement mechanism of primary M7C3 carbide by La2O3 via experiments and first-principles calculations

This study is dedicated to summarize refinement mechanism of the primary M7C3 carbide by rare earth oxide La2O3. The La2O3 was added into hypereutectic Fe–27Cr–4C alloy, and its microstructure was observed and analyzed by optical microscope (OM), X-ray diffractometer (XRD) and scanning electron microscope (SEM). The lattice mismatch degrees of La2O3//M7C3 interfaces were calculated. The interface properties of La2O3//M7C3 were calculated by the first principles. The effectiveness of La2O3 as the heterogeneous nucleus of the primary M7C3 carbide in the alloy was analyzed. The results show that the primary M7C3 carbide can be refined by La2O3 in this alloy. The lattice mismatch degree between La2O3(111) plane and M7C3(0001) plane is 2.36%, which indicates that La2O3 as the heterogeneous nucleus of M7C3 is the most effective. La2O3(111) plane and M7C3(0001) plane were chosen to construct the interface models. Two surface models, such as La-termination and O1-termination on La2O3(111) plane were constructed, which converge to 26 and 21 layers, and their surface energies are 5.256 J/m2 and 2.029 J/m2, respectively. The surface model of M7C3(0001) plane converges to 17 layers, and its surface energy is 3.199 J/m2. Among La-M7C3 and O1-M7C3 interfaces, the adhesion work (16.162 J/m2) of O1-M7C3 is larger than that (1.731 J/m2) of La-M7C3. However, the interface energy (−10.910 J/m2) of O1-M7C3 is smaller than that (6.725 J/m2) of La-M7C3, which indicates that O1-M7C3 interface has the best interface bonding property and the lowest interface nucleation resistance. Therefore, La2O3 can serve as the heterogeneous nucleus of M7C3 and tends to form an O1-M7C3 heterogeneous nucleation interface.

Effect of rare earth on primary carbides in H13 die steel and their addition method: a review

Effect of rare earth on primary carbides in H13 die steel and their addition method: a review

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.

Carbide precipitation during tempering of hybrid steel 60

The effects of carbide precipitation on mechanical performance of Hybrid Steel 60, known as a novel bearing steel, have not been investigated. In this study, the austenite transformation temperatures of Hybrid Steel 60 during heating were revealed by the thermal expansion curve. The temperature and effective activation energy of the second phase precipitation were determined by the differential scanning calorimetry (DSC) curve. Different solid solution structures after austenitization were detected using various cooling rates. The solubility temperature was determined based on hardness and residual austenite content. The carbides precipitated at the peak temperature were qualitatively identified using XRD. It was discovered that the temperature points Ac1 and Ac3 of the steel were 786 °C and 864 °C, respectively. In addition, the effect of solid solution temperature on quenching hardness is minimal, while the cooling rate has a greater impact on hardness, reaching a peak at 5 °C s−1. The primary carbide phase in Hybrid Steel 60 is the M7C3 and VC. When the temperature ranges from 500 °C to 550 °C, M23C6 begins to precipitate. As a result, after tempering at 525 °C, the hardness peak value reached 566 HV.

STRUCTURE AND PROPERTIES OF REFRACTORY BIMONOCRYSTAL MICROCOMPOSITES

The features of high-gradient crystallization of refractory quasi-binary alloys have been studied. The processes of phase nucleation and their joint influence on the evolution of the formation of spatially ordered microstructures are considered. The possibility of regulating the volumetric ratio of phases by crystallization of alloys of noneutectic composition has been revealed. The results of expanding the area of compositional growth and the possibility of creating a regular quasi-eutectic microstructure without primary carbides are explained. The mechanism of post-crystallization heat treatment has been determined, leading to the purification of the matrix from interstitial impurities and embrittling carbides, the creation of perfect bi-monocrystalline materials that are thermally stable up to pre-melting temperatures with a high level of ductility and heat resistance.

Effect of Ce Addition on Inclusions and Primary Carbide Network in AISI 440C Bearing Steel

The effects of Ce on inclusions and the primary carbide network of AISI 440C bearing steel are experimentally and theoretically investigated. Adding Ce improves the cleanliness and refinement of primary carbide networks in AISI 440C bearing steel ingots. The addition of Ce substantially reduces the contents of total oxygen (T.O) and S in the steel, and MnS and Al2O3 inclusions are modified into finer Ce‐containing inclusions (Ce2O2S and Ce2O3). When Ce is added, the average equivalent diameter of the inclusions decreases from 1.82 to 1.33 μm, and the number of inclusions per unit area (mm2) increases from 59 to 105. Moreover, the addition of Ce reduces the secondary dendrite spacing from 33.82 to 24.2 μm, and the proportion of primary carbide is reduced from 22.08% to 11.17%. The 2D lattice disregistry theory confirms that Ce2O2S and Ce2O3 inclusions can be utilized as effective heterogeneous nucleation cores for γ‐Fe, thus refining the solidification microstructure and also the primary carbide. This study provides theoretical guidelines for the fabrication of domestic AISI 440C bearing steel ingots.

Investigation on collaborative regulation shape, fibrous macrostructure and microstructure of raceway groove in BG801 steel bearing ring with mounted edge

Whether the macro- and micro-structure of bearing ring forging is desired or not greatly decides the property of ring parts. An unreasonable forging design or processing easily leads to the fibrous macrostructure outcrop in the raceway damaging service life. In this study, a novel forging design method of symmetry design on raceway groove (RG) and mounted edge for ball bearing ring with mounted edge structure was proposed. Meanwhile, the height diameter ratio (HDR) of the billet was adjusted to achieve metal fibers distributed along the RG shape in both forging and parts, which was verified by experiments. Fibrous macrostructures of BG801 steel are mainly dominated by primary carbides M23C6/I-M6C and assisted by precipitated carbides II-M6C along matrix shear regions. The microstructure on the RG can be regulated by deformation temperature, in which the texture transforms from Cube to Rotated-Cube than to {332} 〈120〉, the size and content of retained austenite (RA) increase and twin substructure appear within lath martensite with temperature. By optimizing parameters HDR = 1.1 and deformation at 1050 °C, the high strength and hardness of RG were achieved that yield strength (YS), ultimate tensile strength (UTS), and hardness were 671 MPa, 1560 MPa, and 419.9 HV, respectively. The strengthening effect is not only attributed to the desired microstructure of thin film-like RA, dislocation martensite and carbides, but also fine grain strengthening of the prior austenite grain (PAG) that induces almost half of strengthen contribution.

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.

Dissolution of Large‐Sized Primary Carbides in 6Cr13 Continuous Casting Slabs during High‐Temperature Homogenization

The morphology of carbides, the distribution of alloying elements, and the dissolution of primary carbides in 6Cr13 continuous casting slabs during the high‐temperature homogenization process are studied herein. The results show that severe segregation of alloying elements exists at the center of the cast slabs, accompanied by large, interconnected primary carbides in the form of a network. Large‐sized reticulated primary carbides are difficult to completely dissolve and eliminate during homogenization treatments. Large‐sized primary carbides will dissolve along the contours and the joints between the carbides when the temperature of high‐temperature homogenization does not exceed 1250 °C and the time does not exceed 1 h. The carbides that had broken off will precipitate again along the original contour in the form of large‐sized brain‐like carbides beyond this temperature and time. In situ observation of the high‐temperature homogenization process reveals that when the slab is heated to 1200 °C, the local liquid phase starts to be generated around the carbide. Cr atoms diffuse into the matrix through the liquid–matrix interface; it will accelerate the high‐temperature homogenization process and improve the segregation of alloying elements around carbides.

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.

Microstructure and properties of hypereutectic high chromium cast iron containing nitrogen

This article investigates the effect of N content on the microstructure, mechanical properties and wear resistance of hypereutectic high chromium cast iron (HHCCI). With the increase of N content, the primary carbides are obviously refined, the austenite content increases, and the dispersed granular Cr2N precipitates. After quenching at 1000 °C, secondary carbides are precipitated from the matrix, the matrix transforms into martensite + retained austenite. With the increase of N content, the corrosion resistance of HHCCI increases, and 0.3 wt.% N HHCCI shows the best corrosion resistance. With the increase of N content, the wear resistance of HHCCI increases. The wear resistance of HHCCI with 0.15 wt.% N is the best, which is 1.57 times that of HHCCI without N.

Effect of heat treatment on microstructure and properties of bimetallic band saw blade

Quenching and tempering treatment experimentswere conducted on the bimetallic band saw blades,and theeffect of quenching and tempering processes on the microstructure and properties of the band saw blades were studied. The results indicate that with increasing quenching temperature, the solid solution strengthening effect of the tooth tip improves the quenching hardness, but the high quenching temperature leads to martensitic coarser of the tooth back, which results in a significant decrease in the hardness. Moreover, with the increase in tempering temperature, the martensite in the microstructure of the tooth tip and tooth back was transformed into tempered trootensite and sortensite, and the primary and secondary carbides in the tooth tip became coarser, which led to the reduction of tempering hardness, and the fatigue properties changed too.

Microstructural effects on impact-sliding wear mechanisms in D2 steels: The roles of matrix hardness and carbide characteristics

This study investigates the wear micromechanisms of D2 steels under impact-sliding conditions, offering insights into their performance when used in applications such as trimming dies for high-strength steel sheets where they undergo plastic deformation and chipping. Two D2 steel samples, both with a bulk hardness of 59.7 HRC but different matrix hardnesses and carbide distributions, are tested by using an impact-sliding wear test rig at Hertzian contact pressures exceeding 2 GPa. The sample with a softer matrix exhibits wear primarily through delamination caused by plastic deformation. This initiates cracks at the matrix/primary carbide interface, leading to material loss in the form of large chips. In contrast, the steel with a harder matrix shows reduced wear due to its resistance to plastic deformation. Initially, wear occurs through the fracture of primary carbides. However, with prolonged loading, the matrix begins to soften, adopting a wear mechanism similar to the D2 steel with softer matrix. Notably, smaller primary carbides are associated with improved wear resistance by limiting the initiation sites for cracks, especially at the matrix/primary carbide interface. This understanding enables the selection and design of heat treatments to optimize D2 steel microstructure, thus improving resistance to impact-sliding wear damages observed in processes like trimming.

Effect of heat treatment on microstructure and wear properties of laser additively manufactured 316 L stainless steel/Co-Cr-W alloy part using directed energy deposition method

The directed energy deposition additive manufacturing was applied to fabricate hard Co-Cr-W layers on the 316 L stainless steel substrate. The effect of different heat treatment cycles was investigated. The primary microstructure of deposited layers contained a cobalt matrix with interdendritic eutectic carbides mainly M7C3, M23C6, and M6C. Most of the primary carbides were dissolved in the matrix after the solution treatment at 1250 °C for 1 h. The aging treatment promoted the precipitation of (W/Co)6C carbides. The hard carbides caused the third-body wear and increased the wear volume loss of specimens. The solution & double aging treatment provided the optimum combination of hardness and wear resistance due to the best distribution of W/Co carbide. The wear volume loss after heat treatment was decreased from about 6.6 mm3 to 2.8 mm3 compared to the as-deposited specimen. The proposed solution & double aging heat treatment improved wear resistance by 50%.

Surface crack analysis of 8Cr4Mo4V steel based on Crystal/Phase microstructure model by grinding

Metal polycrystalline materials tend to be homogeneous and isotropic at the macroscopic level, which leads it difficult to visually characterize the sprouting and expansion of cracks by traditional grinding simulation. In this study, the Johnson–Cook constitutive model was used for the finite element method (FEM) based on grinding characteristics with a high strain rate and large plastic deformation. The models are focused on the actual microstructure distribution, one of them contains grains and grain boundaries, and another contains phase organization (martensite and acicular martensite) and carbides. The study pinpoints the changes in microstructure under different grinding parameters during the grinding process and the influences on the formation of microscopic cracks. Ultimately, it was found that the shedding of large primary carbide is a critical factor for inducing surface cracks. The uncoordinated deformation between brittle carbides with the other phases is the main cause of carbide shedding. Therefore, this article visualized shows the influence of grinding parameters on surface cracks from the perspective of microstructure modeling, which is of great significance in guiding practical processing.

Effect of Carbon and Cooling Rate on the Structure of Hypereutectic High Chromium Cast Iron in the Cast State and after Heat Treatment

The article presents experimental data on the changes in the structural parameters and properties of castings from high-chromium cast iron G-X300CrMo27-1 depending on the carbon content, which ranged from 2.8 to 4.5 wt. %. Castings were obtained under cooling conditions with two cooling rates—0.083–0.117 °C/s and 4.67–5 °C/s. Changes in the structure and properties of these castings after destabilizing annealing and subcritical heat treatment were assessed. Changes in carbon concentration and cooling rate in the crystallization interval have a significant effect on the sizes of primary carbides (Cr, Fe)7C3, and on the fraction of eutectic carbides. The microprobe analysis results indicating the effects of cooling rate on the composition of phases in cast iron castings with carbon contents of 4.2 wt. % are presented. The offset value of the crystallization onset temperature and eutectic point with an increase in the cast iron melt cooling rate from 0.083 to 0.83 °C/s is shown. The changes found in the properties of castings with increases in carbon concentration and cooling rate cannot be unambiguously explained by the transformation of the structure of primary and eutectic carbides and changes in the elemental composition of phases. The composition and condition of the matrix has a significant effect on the hardness, bending strength and abrasion resistance of castings. It is suggested that internal stresses arising in primary and eutectic carbides affect the properties of castings in the cast and heat-treated state.

Development and characterization of a cast steel reinforced with primary carbides for high strength and severe wear applications

Development and characterization of a cast steel reinforced with primary carbides for high strength and severe wear applications