Segregation Of Elements Research Articles

Microstructure and mechanical properties of electron beam welded joints of GH3128 and CoCrFeNi high-entropy alloy

This study addresses the research gap in the field of fusion welding for high-entropy alloys and high-temperature alloys. The microstructure and mechanical properties of CoCrFeNi/GH3128 electron beam welded joints were investigated. Influenced by solidification rate and elemental composition, differences in grain crystallization modes and morphologies were observed on both sides of the weld, accompanied by a columnar-to-equiaxed transition in the weld center. Significant fluctuations in elemental concentrations across the weld indicated elemental segregation, with distinct segregation behaviors observed for Fe, Co, Cr, Ti, Al, W, and Mo elements between columnar and dendritic grains. XRD results revealed the presence of γ, γ', FeCrNi solid solution, and various intermetallic compounds such as Ni17W3, Cr4Ni15W, and Fe3Ni2 in the weld zone. Hardness testing showed a gradual increase in microhardness from CoCrFeNi to GH3128 within the weld. Tensile testing indicated a tensile strength of 532.5 MPa and an elongation of 40.4 %, suggesting a ductile fracture mechanism for the joint. Post-tensile testing, noticeable work hardening, tensile deformation in the weld zone, grain refinement, and increased hardness were observed, highlighting the joint's enhanced strain-hardening ability. However, the corrosion resistance of the CoCrFeNi base material decreased.

Microstructural evolution and mechanical behavior of novel TiZrTaxNbMo refractory high-entropy alloys

The refractory high-entropy alloy (RHEA) with a body-centered-cubic (BCC) solid-solution structure has excellent high-temperature softening resistance, which has attracted wide interest in the field of high-temperature alloys. However, its limited room-temperature plasticity has greatly hindered its engineering application. To obtain an excellent strength-plasticity matching relationship, in this reported study, the Ta content in the high-entropy alloy (HEA) was adjusted to rectify this shortcoming. A series of TiZrTaxNbMo (x = 1.0, 0.9, 0.8, 0.7, and 0.6 at. percent, at%) RHEAs were prepared using the vacuum arc-melting technique, and the microstructure and mechanical properties of these RHEA alloys were systematically investigated. The experimental results show that the TiZrTaxNbMo RHEAs are composed of main BCC1 and minor BCC2 phases, which exhibit a dendritic structure. By reducing the Ta content, the elemental segregation caused by the non-equilibrium solidification is reduced. In terms of mechanical properties, with the decrease of Ta content, the hardness and room-temperature yield strength of the alloy decreases slightly, but the room-temperature plasticity increases significantly. The Ta0.7 alloy has the highest plasticity (34.8 %), which is about twice that of the equimolar Ta 1.0 alloy, while the yield strength remained at 1297 MPa. The excellent mechanical properties of the alloys can be attributed to solid-solution strengthening and the formation of moderate amounts of interdendritic regions. The interaction between slip bands and dislocations formed during compression of the Ta0.7 alloy decreased its work hardening. Moreover, the theoretical model of solid-solution strengthening elucidates that the calculated values of the alloy’s yield strength are consistent with that obtained experimentally.

Experimental study on the micro-mechanical parameters of Ni-based single-crystal superalloys using nanoindentation and element distribution analysis

Ni-based single-crystal superalloys are normally prepared by directional solidification. Due to different solidification sequences, Ni-based single-crystal superalloys exhibit a typical dendritic arm structure, and the element segregation in the dendritic arm can affect the high temperature mechanical properties of the alloy. Solid solution treatment has a certain extent to reduce the inter-dendritic and dendritic arm between the concentrations of the elements, thereby changing the alloy micro-nano view parameters to improve the high temperature mechanical properties of the alloy. In this study, nanoindentation experiments were carried out on the inter-dendritic and dendritic arm of the cast and solid solution samples. The micromechanical parameters were calculated. The amounts of changes in elemental concentration were discussed with the results of the energy dispersive spectroscopy and electron probe microanalysis, so as to analyse the relationship between the micromechanical parameters and the changes in elemental concentration. The results show that solid solution treatment has a significant impact on the elastic modulus, with an increase of 114.7% of the inter-dendritic region and an increase of 142.7% of the dendritic arm. However, solid solution treatment has little effect on the hardness, with no significant change in the hardness of the inter-dendritic region and an increase of 43.86% of the dendritic arm. Solid solution treatment has a more significant effect on improving the segregation behavior of Al and Co elements, with the segregation coefficients of Al and Co elements in the inter-dendritic region decreasing and increasing by 36% and 19%, and the segregation coefficients of Al and Co elements in the dendritic arm region decreasing and increasing by 29% and 34%.

The effect of Hafnium on the microstructure and tensile property in a Ni-based superalloy

The effects of Hafnium on the microstructure and tensile property of a Ni-based superalloy after solution heat treatment and long-term thermal exposure were investigated with field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD). The results revealed reveal that Hf intensified intensifies the element segregation and promoted promotes the precipitation of MC carbide and honeycomb-like Ni5Hf phase in the as-cast alloy. The solid solution strengthening and second phase (MC) strengthening effects are both enhanced in the alloy doping 0.5 wt% Hf after solution heat treatment. Therefore, the tensile yield strength at 700 °C of the alloy with 0.5 wt% Hf is higher than that in the Hf-free alloy. Otherwise, a large amount of the low melting point Ni5Hf phases appear in the alloy with 0.8 wt% Hf. Ni5Hf phase is prone to become the crack initiation, which decreases diminishes the yield strength in the alloy with 0.8 wt% Hf. The addition of 0.5 wt% Hf can inhibit the formation of needle-like δ phase at grain boundary due to the decrease of grain boundary energy and diffusion rate at grain boundary. Therefore, the 700 °C tensile strength and ductility increase simultaneously in the alloy with 0.5 wt% Hf after thermal exposure at 700 °C.

Influence of Al addition on microstructure and electrochemical behaviour of CrMnFeCoNi high-entropy alloy

To develop new corrosion-resistant materials for structural applications, CrMnFeCoNiAlx high-entropy alloys (HEAs) are produced via semi-industrial induction casting. The study aimed to investigate the influence of Al content (x = 0–0.3) on both microstructure evolution and corrosion properties of the alloys. X-ray diffraction and scanning electron microscopy (SEM) analysis revealed that all the alloys exhibited a single-phase face-centered cubic structure, with dendritic (Fe, Co, Cr-rich) and interdendritic (Mn, Ni, Al-rich) regions distinguished by elemental segregations. Furthermore, the incorporation of Al atoms into the solid solution led to an increase in the lattice parameter, indicating alloy strengthening. The corrosion resistance of the CrMnFeCoNiAlx alloy improved with higher Al addition. Electrochemical polarisation tests demonstrated a slight increase in the corrosion potential (Ecorr) and a significant decrease in the corrosion current density (icorr) upon Al addition. Additionally, slower kinetics for pit nucleation (higher E'corr) were observed, particularly notable for x = 0.3. Analysis of the corroded surfaces revealed a mixed degradation mechanism, involving pitting corrosion and selective dissolution of the interdendritic zone, which decreased as the Al content of the HEA increased. These findings underscore the effectiveness of Al addition in not only enhancing the mechanical properties of the Cantor alloy through solid solution strengthening, but also improving its corrosion resistance.

Investigation on the diffusion mechanism of Ga element and regulation of the V-shaped bandgap in CIGS thin films based on magnetron sputtering with a quaternary target

Gradient bandgap engineering has been acknowledged as an effective approach for improving the efficiency of CIGS solar cells. However, an effective method for achieving gradient bandgap engineering in quaternary sputtered CIGS films has not yet been identified.This is due to the uniform and singular nature of the quaternary target composition, as well as the complex kinetic mechanisms that result in the rearrangement of film elements (particularly Ga) during the annealing process. In this study, a grain boundary migration-driven diffusion mechanism for the Ga element in CIGS thin films was established to address the presented issue. The segregation of Ga element is believed to be caused by the flow velocity field generated from the migration of grain boundaries, and the distribution of Ga element can be precisely calculated using the mass transport equation. By modulating the V-shaped bandgap, a notable enhancement in open-circuit voltage (Voc) was achieved, with an increase from 0.405 V to 0.515 V, leading to an effectively improvement of solar cell's efficiency. By comparing and analyzing the actual performance parameters of the solar cells and the simulated results, we conclude that the increase in Voc is due to the alteration in bandgap structure. This study presents a novel approach to bandgap engineering in quaternary sputtered CIGS films through the quantitative calculation of Ga element distribution.

Addressing the strength-corrosion tradeoff in 316 L stainless steel by introducing cellular ferrite via directed energy deposition

Typical cellular structure composed of high-density dislocation tangle can lead to high strength in directed energy deposition 316 L stainless steel, but with reduced corrosion resistance in acid solution due to accompanied element segregation. Herein, a unique cellular structure consisting of a ferrite phase is manufactured to address the strength-corrosion tradeoff via a direct energy deposition process. The relationship between strength and microstructural features, such as grain type, ferrite phases, and dislocations, as well as the relationships between corrosion resistance and these microstructural characteristics, are identified. Cellular ferrite retains the beneficial effect of the cellular structure on increasing strength and changes the material from a pure austenitic phase to an austenite-ferrite biphasic structure. The ferrite phase has a lower corrosion potential, which promotes the rapid formation of Cr- and Mo-rich corrosion product layers. It can avoid the unfavorable effects of element segregation and suppress the corrosion rate in acid solution. This study shows that directed energy deposition has the potential to customize the microstructure through a printing process that introduces a cellular ferrite phase to improve its corrosion resistance in acidic solutions as well as its strength and ductility.

Triplex steel powder design to avoid hot cracking in laser-powder bed fusion using computational thermodynamics

High manganese steels offer exceptional combinations of high strength and ductility, resulting in weight reduction when utilized in structural applications. Nevertheless, the conventional manufacturing routes of these steels is hindered by many production problems. Additive Manufacturing (AM) has emerged as a reliable solution to fabricate thin or complex shape compounds using these steel grades. Indeed, several studies have demonstrated the success to fabricate high manganese twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) steels by laser-powder bed fusion (L-PBF). However, a recent study on a high manganese triplex steel composition has revealed the occurrence of both hot cracking and micro segregation during rapid solidification in L-PBF, highlighting potential processability issues of this family of high alloy steels. In this study, the hot cracking susceptibility of different triplex steels is evaluated, focusing on the impact of the composition on the solidification paths and final microstructures. A Computer Coupling of Phase Diagrams and Thermochemistry (CALPHAD) approach is employed to predict alloy-dependent hot cracking susceptibility so as to establish guidelines for preventing hot cracking and provide insights into alloy design for AM. Microstructural observations are used to determine the accuracy of CALPHAD predictions in terms of elemental segregation, phase formation and hot cracking susceptibility. To this end, scanning transmission electron microscopy is used to evaluate elemental segregation at grain boundaries, while the local distribution of phases and their relative amount is measured by electron backscattered and X-ray diffraction, respectively. Hot cracking susceptibility is experimentally evaluated by measuring the length of cracks (when present) in the cross section of printed specimens.

Phase transformation and strengthening of the gas-atomized FeCoCrNiMo0.5Al1.3 high-entropy alloy powder during annealing

Phase evolution and strengthening of the FeNiCoCrMo0.5Al1.3 powder alloy produced via inert gas atomization and annealed in the temperature interval of 300–800 °C have been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and microhardness testing. It was found that annealing at 300–600 °C leads to an increase of the element segregations between the several solid solutions with a rise of the lattice misfit (ε) to 1.5 % and microhardness growth to 1070 HV. It was assumed that elastic stress caused by the element partitioning is the main strengthening mechanism: microhardness rises linearly with misfit rise with dHV/dε = 43400 MPa. Sigma arises after the maximum elastic deformation (in 1.5 %) was reached. Formation of the dispersed coherent sigma phase in the annealing interval 600–800 °C results in the microhardness rise. Oxidation that began at 800 °C in 27 h is accompanied with FCC formation due to a depletion of the B2 in Al caused by Al2O3 formation. Estimation of the activation energy of the initial stage of the solid solution decomposition gives a very low value in 0.65eV, apparently caused by the high concentration of quenched vacancies. The activation energy of sigma formation approximately coincides with the activation energy of self-diffusion in BCC metals (about 2.60 eV).

Laser Powder Bed Fusion of GH4099 Superalloy: Parameter Optimization and Effect of Heat Treatment on Microstructure and Mechanical Properties

Ni-Cr-Co-W superalloy (GH4099) can be used to manufacture high-temperature structural components of aero-engine combustion chambers for long-term service below 900 °C. This study provides a comprehensive evaluation of the GH4099 superalloy fabricated using the laser powder bed fusion (LPBF) technique, focusing on the optimization of processing parameters and a systematic investigation of the microstructural evolution and mechanical properties of the as-deposited and heat-treated samples. An optimal parameter combination was established using the response surface method (RSM) design and the variance method. The as-deposited GH4099 alloy is primarily composed of columnar crystals grown epitaxially and M23C6 carbides without the generation of the γ′-phase. After solution treatment, recrystallization and grain growth occurred, with the alloy remaining as large, irregularly shaped polygonal columnar crystals. The aging process precipitated substantial γ′-phase, which internally existed as a mixture of equiaxed and columnar crystals. LPBF-GH4099 superalloy exhibited a maximum room-temperature tensile strength of 1137.80 MPa and a high-temperature tensile strength of 780 MPa at 800 ℃. Various strengthening mechanisms were observed in the as-deposited and heat-treated samples. The most significant grain boundary strengthening effect was observed in the deposit state, while solution strengthening was primarily due to the segregation of elements, such as Mo, W, and Cr, in the γ matrix. Precipitation strengthening, predominantly due to the γ′-phase, emerged as the main strengthening mechanism for the GH4099 superalloy post-aging treatment. This study presents significant insights into the LPBF-GH4099 alloy and provides a solid foundation for future studies and practical applications in this field.

Analysis and control of surface cracks in a B-bearing continuous casting blooms

Abstract In this work, normal manufacture of a B-bearing steel was hampered by cracks in steel. In order to control these cracks, the formation mechanism has been examined through a comprehensive analysis of crack morphology, element segregation, high temperature mechanical properties, and precipitates. The high-temperature thermoplastic capabilities of the steel were found to be reduced by boron nitride particles precipitated at grain boundary. This led to the formation of a brittle zone in the straightening zone of the continuous casting process, which in turn caused cracks. Based on the formation mechanism of these cracks, the cracks were successfully controlled by adding an appropriate amount of Ti element to the steel and reducing the charging temperature of the heating furnace.

Effect of Electromagnetic Power on the Microstructure and Properties of 2219 Aluminum Alloy in Electromagnetic Continuous Casting Technology

Electromagnetic continuous casting technology serves as a significant means for enhancing the casting performance of 2219 aluminum alloy. Investigating the influence of electromagnetic field variations on the solidification process is crucial for studying the microstructure and mechanical properties of electromagnetic cast billets. Through experimental research, variations in the microstructure and mechanical properties were examined for ordinary direct chill casting, as well as three different electromagnetic power casting ingots. The COMSOL software (COMSOL Multiphysics 6.0) was utilized to simulate the temperature and flow field, enabling an explanation of the resulting performance changes. The results showed the effect on electromagnetic continuous casting technology by the electromagnetic field generated by the Lorentz force and melt stirring, improving the melt flow and temperature distribution so that the melt center and the edge of the melt forcible convection were enhanced, thus realizing the tissue refinement, mechanical properties, and Cu element segregation of the improvement. With an increase in electromagnetic power, the distribution of the temperature field was more homogeneous, the segregation phenomenon was more alleviated, and the improvement in mechanical properties was more significant. The optimal microstructure and mechanical properties were achieved at a power of 20.0 kW, with a 74.7% improvement in grain refinement in the center and a tensile strength increase of 30.8%. Additionally, significant improvements were observed in segregation phenomena.

Evolution of Laves phase related to tensile properties in cast ATI 718Plus under pulsed electric current

The Laves phase will seriously deteriorate the subsequent hot working and welding performance of cast ATI 718Plus. In traditional homogenization annealing, two-stage treatment is used to prevent the formation of harmful eutectic structures due to the initial melting of the low-melting point Laves phase. This has several obvious disadvantages including high processing temperature, long processing time and complicated operation. Electrical pulsed treatment, as a new efficient, feasible and energy-saving green means, has rapidly achieved the dissolution of Laves phase. The increase in diffusion rate of Nb element in Ni matrix by pulsed electric current is due to the enhancement of defect migration and vacancy defect density, leading to a significant enhancement in the diffusion kinetics and accelerating the dissolution of Laves phase. Laves phase dissolution process under the pulsed electric current is from the aggregated state accompanied by dense needle like η phase to the discrete state accompanied by sparse needle like η phase, finally forming a single long strip and being dissolved into an intermittent state until it disappears. In all, using pulsed electric current instead of traditional heat treatment for annealing cast ingots has the potential to achieve one-step homogenization, completely dissolving the Laves phase while eliminating element segregation.

Investigation of the formation mechanism between β-NiAl and C14-Laves phases in laser additive manufacturing of nickel-based superalloy

The microstructure of laser additively manufactured nickel-based superalloy was analyzed using multi-scale characterization. The phase composition of the as-deposited sample was determined. The formation mechanisms of β-NiAl and C14-Laves phases were studied in depth. The crystallographic orientation relationship between the β-NiAl and C14-Laves phases was elucidated. The formation of the β-NiAl phase exacerbates the elemental segregation at the interface, leading to the generation of micro-strain and dislocations that provide nucleation sites for the C14-Laves phase. In addition, the effect of solidification rate on the precipitation of precipitated phases from the alloy was excluded. The present work contributes to understanding the precipitation behavior of β-NiAl and C14-Laves phases in nickel-based superalloys.

Microstructure, Mechanical Properties, and Lead–Bismuth Eutectic Corrosion Behaviors of FeCrAlY-Al2O3 Nanoceramic Composite Coatings

Seven FeCrAlY-Al2O3 nanoceramic composite coatings are deposited on F/M steel via plasma spraying and laser remelting. A systematic investigation is conducted to examine the dependence of microstructure, mechanical properties, and lead–bismuth eutectic (LBE) corrosion resistance on the nano-Al2O3 addition and different Cr and Al contents. With the increase in Al content in FeCrAlY, gradual refinement of the coating grains occurs. The addition of nano-Al2O3 promotes the elemental segregation and precipitation of the second phase. The nano-Al2O3 notably enhances the mechanical properties of the coatings that are primarily attributed to second-phase and fine-grain strengthening. After LBE corrosion tests, intergranular corrosion morphology could be observed, where the contents of Cr and Al significantly influence the corrosion behavior of the coatings at varying temperatures.

Microstructure evolution and mechanical properties of new Co-free maraging steel produced by wire arc additive manufacturing

In this work, P-MIG is used as additive process, a new low-cost Co-free maraging steel wire is used as raw material to additive manufacturing block component, and the microstructure and mechanical properties of the component is investigated. The microstructure of the component is composed of martensite and austenite, and the closer to the bottom, the more serious the elemental segregation and the more austenite content. From the top to the bottom the high-angle grain boundaries increase and the grain size decrease, the difference of the heat dissipation condition and the thermal cycle are the reasons for this phenomenon. The texture of austenite is mainly Cube texture, and the texture of martensite is Rotated Cube texture and Goss texture. The tensile strength of XD, YD, ZD three directions is 1172 ± 15 MPa, 1021 ± 7 MPa, 1139 ± 16 MPa, respectively, impact toughness is 64.7 ± 1.6 J/cm2, 51.1 ± 5.6 J/cm2, 51.4 ± 3.1 J/cm2, respectively, TRIP effect occurs in the process of tensile, the main mode of fracture in tensile and impact is toughness fracture. The microhardness decreases gradually from bottom to top, which is due to the short-lived aging strengthening by thermal cycle, the change of grain size and GND density. The results of the work reveal the successful application of the new low-cost Co-free maraging steel wire in WAAM and provide an important reference for the adjustment of additive process, subsequent heat treatment and the adjustment of wire composition.

Synergic investigation of microstructure, precipitation, and micro-segregation on Inconel 825 weldments: A comparative study between GTAW and EBW

Inconel 825, a Ni–Fe–Cr alloy highly regarded for its exceptional corrosion resistance and high-temperature strength. This investigation studies the effect of heat input, precipitation, and micro segregation of Inconel 825 weldments and compares the effectiveness of two welding techniques: gas tungsten arc welding (GTAW) and electron beam welding (EBW). The findings indicate that increasing heat input generally enhances weldment quality by reducing the lack of penetration. However excessive heat input in GTAW leads to root cracking and solidification cracking; while EBW demonstrates better control over undercut and maintains consistent weld quality even at higher heat inputs. Both GTAW and EBW samples exhibit dendritic grain morphologies with distinctive grain boundaries. Precipitates, such as Al4C3 and TiN, are observed in both processes, contributing to improved mechanical properties. While GTAW weldments show some degree of segregation for Mo, Cu, Ti, and Al, EBW weldments demonstrate negligible segregation for major alloying elements but micro-segregation of Ti and Al. EBW weldments additionally showcase higher average hardness, superior tensile strength, and ductility compared to GTAW weldments. This can be attributed to lower heat input, faster cooling rates, and a reduced rate of elemental segregation. Fractographic analysis reveals the presence of voids and micro-voids, indicating a ductile mode of failure for both GTAW and EBW samples. These void characteristics vary based on the heat input and microstructural features.

Numerical Simulation of Reversed Austenite Evolution during Intercritical Tempering of Low-Carbon Martensitic Stainless Steel.

Since the formation of reversed austenite during critical tempering treatment is an important factor affecting the mechanical properties of 13Cr4Ni martensitic stainless steel, a detailed study of the content and morphology of reversed austenite in heat treatment is needed. In this study, the variation curves of a reversed austenite volume fraction with holding time at different tempering temperatures were measured by in situ X-ray diffraction (XRD), and the reversed austenite and carbides of each process were evaluated by transmission electron microscopy (TEM). The austenite content shows a parabolic change with the increase in the tempering temperature; the maximum can reach a peak of about 6.8% at 610 °C, and drops to 0% at 660 °C. It also shows a parabolic change with the extension of the holding time, reaching a maximum of about 9.2% at 5 h of holding time, and a decreasing trend at 10 h of holding time, about 6.8%. The results show that the precipitation of carbides in the microstructure causes elemental segregation at grain boundaries and inside, which is one of the main factors affecting the thermal stability of reversed austenite formation. The kinetic process of reversed austenite during the tempering process was simulated using the JMAK model and the KM model, which can describe the trend of reversed austenite content during the tempering process. Combining the two models, a mathematical model for the room-temperature reversed austenite content under different processes was obtained, and this can predict the room-temperature austenite content.

Arc deposition oxide-modified H13 steel: Investigating the structure of oxygen-containing second-phase particles and their influence on the microstructure

The challenge associated with depositing high-strength steel using the arc deposition method lies in the propensity for hardened microstructures to form during the deposition process. This hardened microstructure can lead to a decrease in material toughness and potentially cause cold cracks. Fortunately, oxide metallurgy technology is expected to address this issue. Specifically, nano oxides can refine the grain and induce the formation of intracrystalline ferrite, thereby enhancing steel's toughness. To gain a deeper understanding of this process, a study was conducted on the morphology and structure of oxygen-containing second-phase particles generated in parts made from H13 steel wire modified with Al2O3, TiO2, and SiO2. Additionally, the impact of these oxygen-containing second-phase particles on microstructure transformation was investigated. The following conclusions were drawn from the study: (1) The arc's high temperature causes complex reactions among the oxides in the molten pool, ultimately resulting in the formation of oxygen-containing second-phase particles with a unique core-shell structure. The size and composition of these particles vary within the interdendritic and intradendritic regions due to element segregation. (2) Through in-situ observations, this study discovered that oxygen-containing second-phase particles promote the nucleation of high-temperature ferrite and austenite. This promotes grain refinement and induces the formation of intracrystalline ferrite, which positively impacts material toughness. (3) The driving force for ferrite phase transformation induced by oxygen-containing second-phase particles may stem from the Mn-depleted zone surrounding the particles and the low mismatch between the VC outer layer of the particles and the ferrite.

Effect of Cu addition on the precipitation behavior of M2C carbides in maraging steel

In this study, two Ferrium S53 steels with and without 1.5% Cu were prepared. The microscopic morphology and structure of these steels during aging treatment were analyzed by transmission electron microscopy (TEM). The average equivalent spherical radius (Rv), volume fraction (ϕv), and number density (Nv) of Cu-rich precipitates and M2C carbides during aging treatment were analyzed by atom probe tomography (APT), and the spatial distribution, interfacial elemental segregation, and one-dimensional concentration profiles of the two types precipitates were also characterized. Based on the distribution of elements, 5%Cu and 9% (C + Mo) isoconcentration surfaces were selected to obtain Cu-rich precipitates and M2C carbides, respectively. The results demonstrate that the Cu-rich precipitates formed before the M2C carbides. The segregation of Cr and Mo elements at the phase interface due to the nucleation and growth of Cu-rich precipitates can promote the formation of the M2C carbides. The two types of precipitates display adjacent distribution relationship in steel. The number density of M2C carbides in steel contain 1.5%Cu can be greatly increased when the Cu-rich precipitates serving as nucleation particles. The formation of needle-like M2C carbides inhibited the coarsening of Cu-rich precipitates. More dispersive and fine M2C carbides were obtained in the steel.