Precipitation Behavior Of Carbides Research Articles

The influence of carbon content gradient and carbide precipitation on the microstructure evolution during carburizing-quenching-tempering of 20MnCr5 bevel gear

Due to the mechanism of microstructural transition, high-strength low-carbon alloy steel gears exhibit high strength and surface hardness after Carburizing-Quenching-Tempering (CQT) combined heat treatment, while maintaining good toughness in the core. The carbon potential gradient and the precipitation of carbides are the main factors affecting the final microstructure, yet there is a shortage of related research. To address this gap, this study developed a multi-physics coupled model considering the impact of carbon content to simulate microstructural transformation. Using finite element analysis, we simulated the microstructural evolution during the CQT heat treatment of 20MnCr5 bevel gear. By comparing the simulation results with the calculations from the commercial heat treatment software DANTE®, the accuracy of this model in predicting microstructural distribution and hardness has been validated. Furthermore, the study established a carbide precipitation kinetics model that takes into account the influence of grain size, to investigate the precipitation behavior of carbides within the matrix during the tempering stage. The cellular automaton method was applied to demonstrate the evolution process of the quenched microstructure during tempering. The study shows that during tempering, carbides primarily precipitate in areas with higher carbon content, preferentially at the boundaries of fine grains with a high density of lattice defects. As the carbon content increases, the number density of precipitates rises, while their average radius decreases. The reduction in matrix supersaturation due to carbide precipitation is one of the causes for the reduction of tooth surface hardness during tempering. The model constructed in this study provides a new perspective for understanding the laws governing material microstructural evolution and offers a solid theoretical foundation for the study of stress and deformation during the heat treatment process.

Carbide Precipitation Behavior of High‐Alloy Steel During Solidification and Cooling Process

The precipitation, growth, and transformation of carbides rich in Cr and Mo during solidification and cooling process of high‐alloy steel for cold working dies are investigated. The Fe–C pseudobinary phase diagram of high‐alloy steel is calculated by Thermo‐Calc software to ascertain the critical phase transformation temperatures. The temperatures of phase transformation during the solidification process are determined by a differential scanning calorimeter. Then the microstructure of the samples at these characteristic temperatures is observed in situ by high‐temperature confocal microscope. The results show that the characteristic temperatures for phase transformation and carbide precipitation are 1380, 1315, 1140, and 980 °C, respectively. At 1315 °C, thick rod‐like or island‐like M7C3 carbides enriched in Cr and Fe are formed. At 1140 °C, secondary M7C3, adhering to the primary eutectic M7C3, grows rapidly in a rod‐like morphology and maintains a similar composition. The secondary M6C carbides of segregated Mo elements precipitate in fan‐shaped clusters near M7C3 through the dissolution of M7C3 and the conversion of M2C. Thermodynamic calculation further indicates that the eutectic Cr7C3 precipitates at 1213 °C, and secondary Cr7C3 remains under conditions favorable for precipitation below the solidus, preceding the precipitation of secondary carbides Cr23C6 and Mo2C.

Intervention mechanism of carbide precipitation during tempering and its impact on residual stress and mechanical properties of wear-resistant steels

The production of low-stress, high-performance wear-resistant steels poses a formidable challenge in the steel industry. This article delves into the carbide precipitation behaviour of wear-resistant steel NM300TP during tempering and its subsequent impact on residual stress and mechanical properties. Our findings reveal a crucial aspect: prolonging the holding time can interfere with the precipitation behaviour of carbides, thereby altering the relaxation mechanism of residual stress and its influence on material properties. Remarkably, we discovered that substituting the formation of θ-cementites with the precipitation of ε-transition carbides can yield a steel with significantly lower residual stress while maintaining exceptional mechanical properties. Specifically, when θ-cementites precipitate, the residual stress in the wear-resistant steel diminishes by 54.23%, accompanied by a hardness measurement of 299.58 HV0.5. However, when a substantial quantity of ε-transition carbides is dispersed and precipitated, the residual stress is further diminished by 69.51%, and the hardness reaches 317.2 HV0.5. Furthermore, this precipitation of ε-transition carbides exhibits superior wear resistance compared to θ-cementites. These groundbreaking discoveries offer critical theoretical insights for the development of low-stress, high-performance wear-resistant steels, paving the way for innovative advancements in the steel industry.

Microstructural evolution and carbides precipitation behavior and their effects on mechanical property of Nb–Ti microalloyed FB590 steel

Ferrite-bainite dual phase steels have been widely used in automobile manufacturing industry due to their high strength and excellent hole expansion performance. In this study, the effects of coiling temperature on mechanical properties and hole expansion performance of low carbon Nb–Ti micro-alloyed FB590 ferrite-bainite steel have been studied. Additionally, the microstructure evolution and carbide precipitation behavior during hot rolling and coiling processes have been investigated. The influence mechanism of microstructures and carbides on both mechanical properties and hole expansion performance has also been discussed. The results suggest that the fraction of the retained austenite and the martensite decreases gradually with increasing coiling temperatures from 450 °C to 500 °C. The main reason for the formation of martensite and retained austenite in steel CT450 coiled at 450 °C is that the coiling temperature is near the martensitic transformation temperature Ms. Increasing the coiling temperature to 500 °C which is above the Ms leads to ferritic and bainitic structure. The carbides precipitation behavior has been studied by TEM, thermodynamic and kinetics calculation. The results show that the size of the carbides increases with increasing coiling temperatures from 450 °C to 500 °C. Most of the large size carbides above 100 nm with high percent of Ti are the undissolved particles in austenite during slab heating. The medium size particles between 50 nm and 100 nm and enriched in Ti precipitate during rough rolling at higher temperature, while the particles smaller than 50 nm enriched in Nb precipitate during finish rolling and coiling processes. The strength of the steel is effectively increased by the fine carbides and martensite formed at low coiling temperature of 450 °C. With increasing coiling temperature from 450 °C to 500 °C, the steel's strength decreases from 630 MPa to 591 MPa, while the HER are improved from 76.8 % to 119.9 % due to the reduction of martensite and retained austenite. Although the strength is a little reduced due to the coarsening of carbides and reducing of the martensite, the plasticity and hole expansion performance is improved significantly with the coiling temperature of 500 °C.

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.

Carbide Precipitation and Hydrogen Trapping Behavior in Mo and V Added Tempered Martensitic Steel

Carbide Precipitation and Hydrogen Trapping Behavior in Mo and V Added Tempered Martensitic Steel

Development and Application of On‐Line Solution Annealing Process for 304 Austenitic Stainless Steel

After hot rolling, 304 austenitic stainless steel requires a solution annealing treatment to prevent intergranular corrosion and eliminate work hardening effects. Compared to traditional offline processes, on‐line solution annealing offers advantages in terms of cost and time savings. However, both recrystallization behavior and M23C6 carbide precipitation behavior are significantly influenced by the cooling process after rolling, which poses conflicting requirements. This study investigates the precipitation behavior of M23C6 carbides and the recrystallization softening behavior during the continuous cooling process of hot‐rolled samples. The kinetics equations are derived using the Scheil's additivity rule. The temperature profiles in different regions of the plate are studied using finite element analysis. A practical approach for online solution annealing is proposed and applied in industrial testing.

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 tempering temperature on the precipitation behavior of B-containing carbides and mechanical properties of heat-resistant steel

The precipitation behavior of B-containing carbides during tempering at 300–700 °C has here been studied. With an increase in the tempering temperature, the variation of mechanical properties of the heat-resistant steel was then revealed. It was found that the BN inclusion, which had been formed during solidification, disappeared and a fine (Nb,V)(C,N) precipitation was observed by SEM analysis after isothermal quenching. The carbides were acicular M7(C,B)3, with a dominant brittle fracture morphology, when the tempering temperature was lower than, or equal to, 550 °C. Also, the carbides were block M23(C,B)6, with a dominant ductile fracture morphology, when the temperature was higher than 550 °C. It was also found that the lath boundaries of the martensite and the phase boundaries of M7(C,B)3 were favorable conditions for a preferential nucleation of M23(C,B)6.

Effect of Si on δ‐Ferrite/γ‐Austenite Transformation and M23C6 Precipitation During Solidification of X10CrAlSi18 Ferritic Heat‐Resistant Stainless Steel

Herein, the δ‐ferrite/γ‐austenite transformation and the precipitation behavior of M23C6 carbides in X10CrAlSi18 ferritic heat‐resistant stainless steel (FHSS) with various Si contents at a cooling rate of 100 °C min−1 using confocal scanning laser microscopy (CSLM) are investigated. The findings reveal that γ‐austenite preferentially forms along the δ‐ferrite phase boundaries, and it progressively precipitates into the δ‐ferrite phase as the temperature decreases. The increase in the Si content reduces the δ‐ferrite/γ‐austenite transformation temperature. It also inhibits the martensite transformation in the subsequent cooling process, decreasing the volume fraction of γ‐austenite/martensite. M23C6 carbides are mostly found at the δ‐ferrite and γ‐austenite/martensite phase boundaries. Meanwhile, the nucleation of M23C6 carbides becomes more difficult as the volume fraction of γ‐austenite/martensite decreases. Furthermore, the complex solidification mechanism of the nucleus is addressed.

The effect of nickel on the carbide precipitation behavior in Cr–Mo–V hot-working die steel

The addition of small amount of nickel to hot-working die steel has been found to be beneficial for hardenability and toughness. In this paper, the addition of nickel to Cr–Mo–V hot-working die steel was studied to improve hardenability, and the inherent mechanism of enhancing toughness was further explored. The research results indicate that nickel as a non-carbide-forming element does not alter the type and total amount of carbide precipitation at equilibrium, but it can dissolve into the matrix and form substitutional lattice distortions with Fe atoms, promoting the dispersion of secondary carbides during the tempering process. This mechanism can reduce intergranular precipitation and inhibit grain boundary embrittlement, thereby improving toughness. However, it can also accelerate the precipitation, aggregation, and growth of secondary carbides during prolonged tempering, which deteriorates the high-temperature anti-softening properties of die steels. The role of Ni has been revealed through thermodynamic and kinetic calculations. The results show that Ni significantly enhances the diffusion coefficient of Cr atoms in the face centered cubic (fcc) Fe matrix during tempering and also improves the phase transition driving force of various precipitates. This work provides new insights into the mechanism of Ni in hot-working die steels, and can provide guidance for designing novel hot-working die steel.

Precipitation behavior of hexagonal carbides in a C containing intermetallic γ-TiAl based alloy

Intermetallic γ-TiAl based alloys are currently used as structural materials in high-temperature applications such as turbocharger wheels, valves and turbine blades. Adding C yields solid solution and precipitation hardening of the TiAl alloys, which raises their service temperature. Within this work, the effect of C on the TNM alloying system is analyzed by complementary differential scanning calorimetry measurements and selected heat treatments in conjunction with detailed electron microscopy analysis. This allowed the determination of the transition temperatures and revealed the precipitation onset of hexagonal Ti2AlC carbides between 1450 °C and 1475 °C. The precipitation kinetics of the carbides were further investigated by laser scanning confocal microscopy and revealed a preferred and steady growth in the length direction. Further, orientation relationships between the TiAl phases and the carbides from Blackburn and Burgers type could be determined by electron back-scatter diffraction. The results of this study provide a better understanding of the effect of C addition on the TNM alloy and thus enable further improvement of the alloying design process.

Effect of cooling medium on the κ carbide precipitation behavior, microstructure and impact properties of FeMnAlC low-density steel

The effect of four different cooling mediums, namely ice brine, water, oil, and air on the κ carbide precipitation behavior, microstructure, and impact properties of FeMnAlC low-density steel is thoroughly investigated by using OM (Optical Microscope), SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope), XRD (X-Ray Diffraction), VSM (Vibrating Sample Magnetometer), Rockwell hardness tester and in conjunction with low-temperature impact experiments. The results indicate that after cooling with different mediums, the austenite structure exhibits a mixed crystalline phenomenon and has a significant presence of twins. The average grain size of austenite increases as the cooling rate decreases, with the largest size observed in air-cooled conditions. Concurrently, the volume fraction and size of intragranular κ carbides gradually increase with a decreasing cooling rate. This phenomenon contributes to an increase in Rockwell hardness, with the highest value recorded in the air-cooled state at 36.8 HRC. Furthermore, the impact toughness initially increases and then decreases as the cooling rate decreases. Notably, water cooling demonstrates the highest impact energy at 68 J. The formation of intergranular κ carbides in oil and air-cooled conditions is identified as the primary reason for the decline in impact toughness.

Influence of band microstructure on carbide precipitation behavior and toughness of 1 GPa-grade ultra-heavy gauge low-alloy steel

Influence of band microstructure on carbide precipitation behavior and toughness of 1 GPa-grade ultra-heavy gauge low-alloy steel

Effect of nitrogen content on the precipitation and growth behavior of eutectic carbides M7C3 in electroslag remelted 7Cr13 steel

The effect of nitrogen content on the type, distribution, morphology, precipitation, composition, growth and aggregation behavior of eutectic carbides in 7Cr13 steel ingots were studied. The results show that the eutectic carbide type (all M7C3) and composition do not change when the nitrogen content in the 7Cr13 steel varies from 0.043% to 0.164%. The increase of N content in the steel refines the eutectic carbides, but the heterogeneous nucleation effect of (Ti,V)N particles increases the number density of eutectic carbides precipitated. As the N content increases, the eutectic carbide area fraction at the edge of the ingot gradually increased. However, the area fraction of carbides first decreases and then increases at other locations in the ingot. Eutectic carbides in steel consist of aggregates of carbide particles of different morphologies and orientations. The higher supersaturation of Cr atoms at the beginning of carbide precipitation in high-N steels will favor the formation of brain-like carbides. The morphology of the eutectic carbide changes from blocky-fibrous (closely linked to the blocky carbide) - spherical to brain-like as the N content increases from 0.043% to 0.164%. The refinement of secondary dendrites and the inhibition of eutectic carbides precipitation by nitrogen make the space for eutectic carbide growth smaller with increasing nitrogen content in the steel, which reduces the precipitation of fibrous carbides (independent existence) that serve as a bridge between different carbides in low-nitrogen steels. This allows the network carbide structure to gradually disappear and promotes the uniform distribution of carbides.

Effect of Si content on the microstructure and mechanical properties of 9Cr-ferritic/martensitic steels

9Cr-F/M−xSi (x = 0–1.0 wt%) steels were fabricated through vacuum induction melting technique and processed by hot forging, hot rolling, normalizing and tempering, subsequently. Their microstructure and mechanical properties were characterized using OM, SEM, TEM, Vickers hardness tester and tensile tester. The steel has a typical ferrite/martensitic structure, with M23C6 and MX phases precipitated at the martensite lath boundary or in the lath. With Si content increasing, the average ultimate tensile strength (UTS) and hardness of 9Cr-F/M−xSi increase simultaneously from 678 MPa and 235 HV for 9Cr-F/M−0Si steel to 788 MPa and 265 HV for 9Cr-F/M−1.0Si steel, respectively, while the total elongation kept almost constant at 22.5%. The main strengthening mechanism is the solid solution strengthening due to silicon addition and the change in the carbide precipitation behavior caused no remarkable hardening contribution. These results can provide a reference for the composition design of structural materials for nuclear reactors.

Effects of Cr Carbides Formation on the High Temperature Creep Property of Alloy 690 for Steam Generator Tube Material

The creep properties of Alloy 690, used as a steam generator tube material in nuclear power plants, were evaluated at 650°C, 750°C, and 850°C. The parameters of creep life prediction models were derived using the Larson-Miller (LM), Manson-Haferd (MH), and Orr-Sherby-Dorn (OSD) models, to use as mechanical properties under a virtual severe accident condition like station black out (SBO). The yield strength (YS) and creep property of Alloy 690 were compared with those of Alloy 600, and the effects of the precipitation behavior of Cr carbides on creep properties were analyzed. The YS of Alloy 600 decreased rapidly above the temperature of 750°C, but the YS of Alloy 690 decreased linearly up to the temperature of 850°C because of the formation of M23C6 carbides. The creep stress exponent (n) of Alloy 690 was between 5 and 6, and this indicated that dislocation creep was the major creep mechanism at the test temperatures. The results of creep tests were well matched with the LM, MH, and OSD models for Alloy 690, and there were no significant differences in accuracy between the models. The stress-rupture test results of Alloy 600 and Alloy 690 using the LM model showed that the decrease in creep strength with rupture time of Alloy 690 was steeper than that of Alloy 600 at high temperatures. This indicated that Alloy 690 was more susceptible to creep degradation under longterm creep conditions. The precipitation of Cr carbides in Alloy 690 increased YS, benefitting creep properties for short-term creep. However, the Cr carbides coarsened significantly under loading conditions at high temperature, and this deteriorated the creep properties for long-term creep.

Mo, V複合添加焼戻しマルテンサイト鋼の炭化物析出と水素トラップ挙動

Mo, V複合添加焼戻しマルテンサイト鋼の炭化物析出と水素トラップ挙動

Effect of twin-related boundaries distribution on carbide precipitation and intergranular corrosion behavior in nuclear-grade higher carbon austenitic stainless steel

Based on different character distribution of twin-related boundaries (Σ3n, 1 ≤ n ≤ 3) introduced by special thermomechanical processing, the effect on carbide precipitation and the resulting intergranular corrosion (IGC) behavior was investigated in depth in nuclear-grade 316H stainless steel. It was worked out that the Σ3 twin boundaries with single distribution was difficult to suppress the IGC percolation along random high-angle grain boundaries, while the interconnected Σ3 twin boundaries could fully block the percolation channel and thus greatly improve the IGC resistance. Among which, the precipitation of M23C6 carbides at different boundaries plays key role to affect their ability of resisting IGC attack.

Precipitation Behavior of Carbides and Its Effect on the Microstructure and Mechanical Properties of 15CrNi3MoV Steel

In this study, quenching and tempering were employed to achieve the optimal match of strength and toughness of the high-strength low-alloy (HSLA) 15CrNi3MoV steel. The effect of the tempering temperature on the microstructure evolution and the carbides precipitation of the steel was also investigated using scanning electron microscopy (SEM), a X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The results showed that after tempering at different temperatures, the microstructure of 15CrNi3MoV steel was tempered martensite. During the tempering process, the M3C carbides precipitated on the ferrite matrix, the needle-like carbides accumulated and grew into a short rodlike shape or a granular shape with the increase of the tempering temperature. Subsequently, the strength and hardness of the steel showed a downward trend, and the elongation and the low temperature impact toughness showed an upward trend. The tensile strength and yield strength of the steel tempered at 650 °C decreased dramatically compared with the steel tempered at 550 °C, while the elongation increased rapidly. Considering the influence of the microstructure and the carbides and the demand for mechanical properties, the optimal tempering temperature is about 600 °C.