Carbide Precipitation Research Articles

Aging-Induced Microstructural and Property Changes in Direct Laser Energy Deposited NiCrFeSiBC Hardfacing Alloy Bushes

Abstract Wear resistant NiCrFeSiBC hardfacing alloy bushes for fast breeder reactor applications are fabricated through direct laser energy deposition (DLED) using CO2 laser with optimized parameters for laser power (2.5 kW), scan speed (4.2 mm/s), powder feed rate (4 g/min) and 60% of track to track overlap. DLED bushes have significantly different microstructure than weld deposited ones. As-deposited bushes have predominantly uniform fine dendritic solidification structure of γ-Ni + Ni3B, γ-Ni + Ni3B + Cr3C2 and Ni-B-Si eutectics with low volume fractions of Cr-rich borides and carbides. Microstructural heterogeneity is observed only in layer overlap regions characterized by coarsening of carbides that resulted in lower hardness (625 ± 11 HV0.1) compared to layer interiors (740 ± 19 HV0.1). Effect of aging at 550 °C on the microstructure and properties of the bushes is investigated using experimental and thermo-kinetic simulation techniques. Microstructure of the bushes remains stable without significant coarsening of the γ-Ni + Ni3B eutectic structures even after heat treatment for 4000 h. However, precipitation and coarsening behavior of Cr7C3 and Cr23C6 carbides are affected by aging which is reflected in the variation in hardness. Hardness of the bushes increases up to 100 h of aging due to the precipitation of fine Cr-rich carbides, and with increase in the duration of aging, carbides coarsen thereby reducing the hardness. Based on the study, it is concluded that direct laser energy deposited bushes may have better stability with respect to microstructure and properties at service temperatures.

Carbon Partitioning and Carbide Precipitation During Quenching and Partitioning Process of 12%Cr Martensitic Stainless Steel

Carbon Partitioning and Carbide Precipitation During Quenching and Partitioning Process of 12%Cr Martensitic Stainless Steel

Effect of precipitates on martensite formation and shape memory effect of FeMnSi-based shape memory alloys fabricated by laser powder bed fusion

The initial and evolving microstructure during the tensile test of two Fe-17Mn-5Si-10Cr-4Ni shape memory alloys, with and without V, C and fabricated by laser powder bed fusion are investigated and compared via electron backscattered diffraction, transmission electron microscopy and in-situ neutron diffraction. Tensile samples are fabricated from the two alloys in order to analyze their thermo-mechanical properties. The addition of V and C leads to the formation of a high area density of fine precipitates, mainly carbides, after heat treatment. The chemistry modifications caused by carbide precipitation cause a decrease in the stacking fault energy (SFE), promoting the formation of wider stacking faults and higher volume fractions of martensite phase under loading, which affect the pseudo-elastic properties and deformation behavior of the material. The carbide-containing alloy shows higher strength, work-hardening capability and pseudo-elasticity compared to the carbide-free alloy. However, the shape memory effect is reduced in the former. The present work sheds light on the crucial role of alloy composition, precipitation and SFE in shaping the mechanical and shape memory properties of Fe-based shape memory alloys. The findings hold potential implications for the design and optimization of materials for specific engineering applications, where either enhanced pseudoelasticity or shape memory effect is desired.

Carbide precipitation in a Ni-based superalloy fabricated by DED and cast after long-term thermal exposure

Carbide precipitation in a Ni-based superalloy fabricated by DED and cast after long-term thermal exposure

High-temperature-driven degradation analysis and modelling of an industrial gas turbine applicable γ/β NiCoCrAlYRe coating– Part II: Diffusion modelling and experimental validation under isothermal conditions

In a two-part research, the degradation process of a commercially utilised NiCoCrAlYRe coating on an IN738LC substrate was both simulated and experimentally validated. The first part of the study delved into the microstructural characteristics of the overlay coating system and analysed the oxidation and interdiffusion mechanisms. This second part extends the analysis to simulations of the coating degradation at temperatures of 900 °C and 1000 °C.The interdiffusion between the substrate and coating was modelled utilising thermodynamic and kinetic mobility data, while the oxidation aspect was addressed using two different established models from Whittle and Meier et al., along with an adapted approach specifically tailored for MCrAlY overlay coatings devised in this research. The simulation results were validated experimentally for up to 7000 h, with the degradation state evaluated based on the depletion of β-NiAl in the coating.Good agreement was found between simulated and experimental data. The initial coating and substrate microstructures were sufficiently predicted based on thermodynamic data, and the simulations closely matched the observed degradation pattern. The most precise alignment between simulated and experimental β-NiAl depletion was achieved with the newly proposed oxidation modelling approach for MCrAlY systems. While more optimisation is required to accurately predict the precipitation of chromium phases and carbides and to account for interdiffusion-obstructing effects, particularly at 1000 °C, the results demonstrate the potential of thermodynamic-kinetic modelling for estimating the lifespan of MCrAlY systems under diffusion-driven degradation conditions.

Investigation of Microstructure and Hot Crack Formation Mechanisms in the Heat-Affected Zone of GTAW-Repaired Cast K4002 Nickel-Based Superalloy with HGH3113 Filler Metal

Surface forming employing the gas tungsten arc welding (GTAW) with the HGH3113 filler metal was developed to repair gas-turbine investment castings composed of the non-weldable cast Ni-based superalloy K4002. This study mainly investigated the microstructure evolutions, fracture modes of the as-cast and repaired specimen, as well as the formation mechanisms of hot cracks. The results showed that as-cast K4002 alloy had millimeter-sized grains and various phases and solidified as follows: L → L1+γ1 → L2+γ1+(γ2+MC(1))eut →γ1+(γ2+MC(1))eut+(γ3+γ'1)eut+MC(2) → γ1+(γ2+MC(1))eut+(γ3+γ'1)eut+MC(2)+γ'2. The phase transformations of repaired specimens were intricate. The cladding layer (CL) was constituted of columnar dendrites of varying dimensions, as well as the precipitated carbide particles and flocculent structures within the interdendrites. In the heat-affected zone (HAZ), the reprecipitated granular carbides coexisted with the initial blocky carbides, and the sizes and morphologies of the γ' phase were also significantly different. Compared with the as-cast condition, the volume fractions of the γ/γ' eutectic, MC carbide, and initial γ' exhibited a decrease from 14.7% to 9.7%, 2.5% to 2.0%, and 62.1% to 43.1%, respectively. The tensile strength after repair reduced slightly, but the ductility improved significantly. What’s more, liquation cracking, strain-age cracking (SAC), and ductility-dip cracking (DDC) all occurred in the HAZ. There was a partially melted zone (PMZ) between the CL and HAZ. The PMZ contained reprecipitated γ/γ' eutectics and fine carbides, and both liquation cracks and SAC arose from this region. The intergranular liquid film solidified through two modes (liquid film migration and normal solidification), which led to insufficient wetting of the grain boundaries, forming the liquation crack. Both SAC and DDC eventuated under great stress due to the reduction of grain boundary ductility. These two kinds of cracks were identified by the type of precipitated phases around the cracks. Moreover, high-angle grain boundaries decreased the susceptibility of liquation crack but intensified the DDC sensitivity.

Проблеми зварювання високомарганцевих сталей

The sensitivity of high-manganese steels to deformation and heat treatment leads to problems with their welding. They consist in the tendency to crack formation in the zone of thermal influence during rapid heating and cooling. They are also characterized by sensitivity to overheating, which is expressed in the possibility of the carbides precipitation and structure heterogenization. Tendency to cold-hardening due to welding stress can also cause micro- and macro-defects and reduce the quality and reliability of the welded joint. The work represents analysis of the modern global experience of high-manganese steels welding in various ways and with the use of various materials. The importance of maintaining the homogeneity of the chemical composition between the weld metal and the base material is shown in order to prevent the formation of martensite due to an austenite stability decrease. While welding dissimilar steels, the release of harmful carbides can occur, so such joints should be preheated with controlled cooling. Welding of high-manganese austenitic steels is not recommended to be performed with a consumable electrode made of stainless austenitic steel due to the formation of significant structural and phase heterogeneity, eutectics and cracks that can pass from the welding zone through heat affected zone to the base metal. As a result of the research analysis, it was established that the welding of high-manganese steels is best performed with electrodes with a chemical composition that is close to the materials being welded. Before welding, it is recommended to reduce the level of residual stress and cold hardening by heat treatment. Welding should be carried out under the conditions of minimizing the thermal load on the material, which is achieved by low-current and short-seam welding, as well as by preheating the metal. For welding thin parts from high-manganese steels, laser welding can be used. For larger thicknesses, welding with a fusible electrode in an environment of shielding gases (MIG\MAG) and argon arc welding with a non-fusible electrode (TIG) is applicable.

Structure and surface properties of stable austenitic steel subjected to liquid carburizing at lowered temperature

The paper studies the structure, chemical and phase composition, microhardness, and surface roughness of heat-resistant chromium–nickel (in wt %: 24.27 Cr and 18.81 Ni) austenitic steel subjected to liquid carburizing at a temperature of 780°С. It is established that the microstructure of the carburized layer predominately consists of carbon-rich austenite (γ-phase), chromium carbide Cr7C3, and cementite Fe3C. It is revealed that carbides precipitate both at boundaries and inside the austenite grains; as we move away from the steel surface, the amount and dispersity of intragranular carbides decreases. It is also established that liquid carburizing leads to an increase in the microhardness of steel surface from 200 to 590 HV0.0025. The total depth of hardening is approximately 200 μm, and the hardened layer is gradient-wise. The surface of the carburized steel is characterized by large surface roughness (Ra = 2.40 μm and Rz = 17.60 μm), compared to the electropolished surface of specimens before carburizing (Ra = 0.17 μm and Rz = 1.80 μm), which is caused by several factors, including, e.g., oxidation of the surface.

Pre-deformation induced precipitation of alloy carbides and its effect on residual stress

The plasticity generated by carbide precipitation during tempering can relax the residual stress. For low-carbon micro alloyed steel 700L. The plastic behavior resulting from carbide precipitation leads to low stress relaxation. And it is prone to plate shape problems such as warping and edge waves. How to enhance carbide precipitation to relax stress has always been the goal pursued by researchers. In this paper, I discussed the effect of carbide precipitation on stress relaxation by applying pre-deformation to intervene the precipitation law of carbides. It is found that pre-deformation can interfere with the precipitation behavior of carbides during tempering, which in turn affects the relaxation degree of residual stress. Applying pre-deformation can inhibit the precipitation of cementite, improve the dispersion degree and precipitation size of alloy carbides, and improve the relaxation degree of residual stress in the tempering process. With the increase of deformation, the precipitation of cementite during tempering is inhibited, the precipitation of cementite decreases, the precipitation of alloy carbides increases and distributes more dispersed, and the size of alloy carbides decreases from 11.4 nm to 8.6 nm. After pre-deformation tempering, the residual stress is greatly relaxed, up to 85.09%.

Effect of tempering temperature on the microstructure and mechanical properties of Q125 shale gas casing steel

Abstract This study investigates the effects of tempering temperature on the microstructure and mechanical properties of Q125 grade shale gas casing steel using experimental methods such as optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results show that during the tempering process at 500–560°C, the morphology of the quenched laths gradually disappeared and the microstructure gradually recovered. Carbides precipitate from lamellar structures and gradually transform into short rod-like and fine dispersed spherical shapes, mainly distributed along the prior austenite grain boundaries (PAGB) and lath boundaries, accompanied by a decrease in dislocation density. At a tempering temperature of 530°C, the steel exhibited optimum overall mechanical properties, with a tensile strength of 961 MPa, yield strength of 921 MPa, and impact energy of 138.9 J. Within the tempering range of 500–560°C, the macroscopic tensile fracture surfaces exhibited obvious necking and delamination, with a microscopic morphology characterized by dimples accompanied by secondary cracks and tearing ridges. Both the initiation and propagation zones of the impact fracture surfaces exhibited dimple features, indicating good ductility. Microcracks and micropores observed in the longitudinal section of the tensile fracture are distributed along the PAGB or lath boundaries, with carbides located at the interfaces, reducing the interfacial energy.

Effect of Heat Treatment on the Corrosion Behavior of Weld-Deposited Chromium Carbide-Based Hardfacing Alloys

The effects of heat treatment on the microstructure and corrosion behavior of chromium carbide-based hardfacing alloys deposited via gas metal arc welding were investigated. The hardfacing alloy, high chromium white iron (HCWI), containing 27 wt% Cr and 4.8 wt% C, was heat treated at 650 °C and 950 °C for six hours followed by natural cooling to room temperature. Microstructural characterization revealed that heat treatment promoted the transformation of austenite to ferrite and increased carbide precipitation. X-ray diffraction analysis identified the primary carbides as Cr7C3, which remained stable during heat treatment. Electrochemical corrosion testing in artificial seawater, including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), demonstrated progressively improved corrosion resistance with heat treatment temperature. Both techniques confirmed that the specimen treated at 950 °C exhibited superior corrosion resistance compared to the 650 °C treatment and as-deposited condition, with the specimen treated at 950 °C exhibiting the highest charge transfer resistance (4711 Ω·cm2) compared to the 650 °C treatment (2608 Ω·cm2) and as-deposited condition (374.6 Ω·cm2). The enhanced corrosion resistance was attributed to the increased carbide precipitation and optimization of the matrix composition. While heat treatment at both temperatures improved corrosion performance, the 950 °C treatment yielded superior results, suggesting this could be an optimal temperature for enhancing the corrosion resistance of chromium carbide-based hardfacing alloys.

Hydrogen Content Dependence of the Contribution of Dislocation-slip Stability and Carbide Precipitation Morphology to the Hydrogen Embrittlement Property of High-strength Martensitic Steels

Hydrogen Content Dependence of the Contribution of Dislocation-slip Stability and Carbide Precipitation Morphology to the Hydrogen Embrittlement Property of High-strength Martensitic Steels

Tailoring the microstructure and mechanical properties of laser metal deposited Hastelloy X superalloy via heat treatment and subsequent hot plastic deformation

The laser metal deposition technology, characterized by its inherent rapid cooling rate and high thermal gradient, poses significant challenges in fabricating large-scale, complex thin-walled Hastelloy X components that necessitate precise dimensional accuracy and structural integrity. To tackle this issue, a novel compound forming process is proposed, wherein a near-net-shaped preform is produced using laser metal deposition technology, followed by shape and properties regulation through the hot metal gas forming process. This investigation systematically explores the hot formability, pre-deformed microstructure and properties of Hastelloy X superalloy sheets fabricated through laser metal deposition, aiming to identify optimized process parameters and to validate the feasibility of this advanced forming process. Results indicate that: (1) The laser metal deposited Hastelloy X superalloy, subjected to solution and aging heat treatments, demonstrates remarkable microstructural integrity and exceptional hot formability, attributed to its pronounced overall crystalline texture and minimal dislocation density. (2) The optimal processing domain was established within a temperature range of 900 °C to 1000 °C and a strain rate of 0.001 s−1, as derived from hot processing maps based on dynamic material model. (3) Pre-deformation at 950 °C facilitates uniform and stable precipitation of nanoscale M23C6 carbides and the formation of a high-density dislocation network, significantly enhancing strength. Overall, through appropriate heat treatment and subsequent hot plastic deformation, the microstructure of Hastelloy X superalloy was optimized, yielding exceptional mechanical properties at both room and elevated temperatures. The feasibility of forming laser metal deposited preforms using the hot metal gas forming process was confirmed, laying a foundation for the future application of this innovative process. The methodologies and insights derived from this research are particularly relevant to the fabrication of large-sized, complex thin-walled components, especially within demanding aerospace applications and next-generation transportation systems.

Enhanced ultra-high temperature creep resistance originating from preferred microstructures of W-Re-HfC alloys

W-Re-HfC alloys have been extensively applied in the field of high-temperature structural parts. To ensure high temperature reliability, it is essential to enhance creep resistance ability. In this study, the microstructures of forged W-Re-HfC alloys were adjusted using different heat treatment processes. The corresponding tensile creep properties were also measured at 2000 °C with 40 MPa. Furthermore, a possible creep fracture mechanism was also explored. The forged W-Re-HfC sample annealed for 2 h exhibited the best creep performances with a steady-state creep rate of 3.28 × 10−6 and a creep life of 5.6 h. Generally, a larger grain size indicates a lower steady-state creep rate; however, the precipitation of carbides at the grain boundaries (GBs) deteriorates the bonding strength of interfaces, thus reversing the former trend. The dominant creep mechanism is diffusion creep, in which the voids nucleate perpendicular to the GBs, grow and connect into cracks, ultimately leading to fractures.

Effect of heat treatment on the microstructure of additive manufactured Ni-based hardfacing alloy deposits on stainless steel

Ni based (NiCrFeSiBC) hardfacing alloy was deposited on 304 L SS build plate by laser rapid manufacturing (LRM) process. As-deposited specimen showed nearly a precipitate free zone at the interface, grain boundary (GB) precipitation in stainless steel up to 10 µm, thin dilution layer (∼60 µm) followed by formation of zones with distinct microstructure, microhardness and microchemistry in the deposit. To investigate the effect of thermal exposure on the interface microstructure, deposits were heat treated in the temperature range of 823-1123 K for 5-100 h. Up to 923 K, structure of the LRM deposits resembled that of as-deposited specimen. A planar interface region devoid of precipitates was present even after thermal exposure up to 923 K. With further increase in the temperature, formation of CrB precipitates with globular morphology was observed along the deposit/build plate interface with simultaneous increase in hardness. Thermal exposures beyond 923 K promoted coarsening of M7C3 and Cr2B precipitates. Diffusion of carbon and boron from the deposit to the build plate promoted the grain boundary precipitation of chromium carbides up to a maximum distance of ∼1000 µm for the highest temperature of 1123 K.

The Effect of TiC-TiB2 Dual-Phase Nanoparticles on the Microstructure and Mechanical Properties of Cast Ni-Fe-Based Superalloys.

TiC-TiB2 dual-phase nanoparticles were added into a Ni-Fe-based cast superalloy and their effects on the microstructure and mechanical properties were compared to those of a Ni-Fe-based superalloy with the addition of TiC nanoparticles. The addition of TiC nanoparticles led to the precipitation of a higher volume fraction of carbides. Compared to the addition of TiC, the addition of TiC-TiB2 nanoparticles not only led to the precipitation of carbides but also promoted the formation of flaky borides and a reduction in the precipitation of the Laves phase. The strengthening effect of TiC-TiB2 nanoparticles on the mechanical properties of Ni-Fe-based superalloys was stronger than that of TiC nanoparticles due to more secondary γ' precipitates. This study provides valuable insights for selecting ceramic nanoparticles to increase the mechanical properties of cast Ni-Fe-based superalloys.

Advances in Heat Treatment and Microstructural Optimization of Hadfield Steel for Enhanced Wear Resistance

Objective: This study aims to explore the impact of heat treatment processes on carbide formation in Hadfield steel, focusing on optimizing its microstructure and mechanical properties for industrial applications that require high wear resistance. Theoretical Framework: The research is grounded in theories of metallurgical transformation and work hardening, particularly in relation to the metastable austenitic structure of Hadfield steel, which transforms into martensite under impact. This transformation mechanism, alongside alloy composition and heat treatment, shapes the steel’s resistance to wear and mechanical strength. Method: A systematic literature review was conducted, encompassing 11 relevant studies on Hadfield steel from four scientific databases: Taylor & Francis, Springer, Wiley, and ScienceDirect. The selected studies were analyzed using the PRISMA methodology to evaluate the influence of heat treatments—such as austenitization, quenching, and tempering—on carbide formation and microstructure. Results and Discussion: Findings reveal that specific heat treatments significantly enhance Hadfield steel’s wear resistance and strength. The influence of processes like austenitization on carbide dissolution and rapid cooling to avoid carbide precipitation has proven critical for the steel’s toughness. This discussion aligns the observed improvements with theoretical predictions and identifies challenges in carbide control for enhanced performance. Research Implications: The study provides practical insights for industries utilizing Hadfield steel in high-wear environments, such as mining and transportation, and proposes further research into innovative heat treatment strategies. Originality/Value: This study contributes novel perspectives on the optimization of Hadfield steel's heat treatment processes, potentially informing advanced manufacturing techniques to improve the steel’s durability and economic value in key industrial applications.

Chromite Pellet Prereduction by Methane‐Containing Gas: Influence Factors and Consolidation Mechanism

Prereduction process of chromite is an effective method for saving energy and reducing emissions during ferrochrome alloy production. This study investigates the factors affecting the reduction and strength levels of chromite pellets reduced in a CH4–H2 atmosphere. Thermodynamic calculations indicate that carbon from methane pyrolysis is highly active, and chromium oxide can be converted to metal chromium and carbide at lower temperature of 1100 °C. The experimental results show that extending the reduction time can increase the pellet metallization rate without sacrificing strength at 1100 °C in 10% CH4. As the reaction progressed, the carbon from methane cracking diffused into the pellet through the metallic iron, creating observable diffusion channels. Continuous methane input further facilitates this mechanism, leading to iron carbide precipitation and ultimately compromising the pellet strength. The consolidation mechanism of pellets in CH4–H2 = 10:90 atmosphere is analyzed using X‐ray diffraction, scanning electron microscopy‐energy dispersive X‐ray spectroscopy, and chemical analysis. The consolidation process of the pellets can be divided into four stages—namely, liquid phase formation, phase transition, strengthening, and carbonization stages.

Multiple Preheating Processes for Suppressing Liquefaction Cracks in IN738LC Superalloy Fabricated by Electron Beam Powder Bed Fusion (EB-PBF).

In additive manufacturing, controlling hot cracking in non-weldable nickel-based superalloys poses a significant challenge for forming complex components. This study introduces a multiple preheating process for the forming surface in electron beam powder bed fusion (EB-PBF), employing a dual-band infrared surface temperature measurement technique instead of the conventional base plate thermocouple method. This new approach reduces the temperature drop during forming, decreasing surface cooling by 28.6% compared to traditional methods. Additionally, the precipitation of carbides and borides is reduced by 38.5% and 80.1%, respectively, lowering the sensitivity to liquefaction cracking. This technique enables crack-free forming at a lower powder bed preheating temperature (1000 °C), thereby improving the powder recycling rate by minimizing powder sintering. Microstructural analysis confirms that this method reduces low-melting eutectic formation and alleviates liquefaction cracking at high-angle grain boundaries caused by thermal cycling. Consequently, crack-free IN738 specimens with high-temperature durability were successfully achieved, providing a promising approach for the EB-PBF fabrication of crack-resistant IN738 components.

Hierarchical microstructure design to tune the mechanical and corrosion behaviors of a marine structural steel

Marine structural steel with notable strength and ductility is considered as one of the promising construction materials for various offshore applications. However, the harsh marine environment causes a series of issues, e.g., deteriorating ductility and impact toughness, degrading corrosion resistance and inducing stress corrosion cracking. In this work, we propose a novel approach to address these issues by introducing heterogeneous structure and tailoring carbide precipitation in a step quenched and tempered marine structural steel. The step quenched and tempered process not only leads to a heterogeneous structure containing ferrite and tempered martensite zones but also obtains abundant nanoscale VC carbides, resulting in M23C6 refinement. This heterogeneity triggers additional strengthening and strain hardening mechanisms, thereby enhancing strength and ductility. Furthermore, the heterostructure and M23C6 refinement effectively inhibit the microcrack initiation and the formation of galvanic cells during Charpy impact test and electrochemical experiment, respectively, thus improving impact toughness and stress corrosion cracking resistance. This study proposes a hierarchical microstructure design to developing high-performance marine structural steel, which offers an effective avenue for addressing the conflicts between mechanical performance and corrosion resistance.