Chemical Composition Of Carbides Research Articles

REGULARITIES OF INFLUENCE OF CHEMICAL COMPOSITION ON MORPHOLOGYAND TYPE OF CARBIDES IN NICKEL-BASED SUPERALLOY

Purpose. It consists in optimizing the chemical composition and morphology of carbides of the welded nickel-based superalloy by changing the chemical composition, which allows to increase the performance properties of body parts by improving the shape and size of the carbide component.
 Methods of research Process modeling was performed by CALPHAD method. The initial data were the chemical compositions of model alloys with different concentrations of carbide-forming elements. The result of the calculation was the chemical compositions of carbides released in the respective systems. The experimental values were processed by the method of least squares to obtain correlation dependences of the "parameter-property" type and to establish mathematical equations of regression models that optimally describe these dependences.
 Results. Regularities of influence of chemical composition of metal on morphology and type of carbides are established. It is shown that depending on the introduced chemical elements in the system, the types of carbides and their chemical composition can change, which leads to a reduction of crack formation processes in the material. It is shown that the change in the composition of the material affects the shape, size and composition of the primary carbides.
 Scientific novelty. The established dependences of the multicomponent system Ni-22,5Cr-19Co-1,9Al-3,7Ti-2W-1,4Ta-1Nb-0,15C allow to determine the chemical composition of carbides by the chemical composition of the alloy. This makes it possible to change the types of carbides, their composition and morphology, thereby improving the mechanical properties of the material, first of all the fatigue and heat-resistant characteristics.
 Practical value. An effective solution for establishing the structural-phase state of nickel-based superalloys by optimizing their chemical composition, which allowed to improve the performance properties of the material. The established dependences can be used in optimizing the composition of industrial nickel-based superalloys and in the development of new compositions.

CONTROL OF THE PROCESSES OF PHASE FORMATION OF CARBIDE COMPONENTS IN NICKEL-BASED SUPERALLOYS

The mathematical dependences of thermodynamic processes of precipitation of carbide phases are determined, and a practical study of the structure and distribution of chemical elements is carried out. Regularities were established for the effect of the chemical composition of the alloy on the morphology and type of carbides. It is shown that, depending on the introduced chemical elements in the system, the types of carbides and their chemical composition can change, which leads to a decrease in the processes of crack formation in the material. The established dependencies for the multicomponent system Ni-22.5Cr-19Co-1.9Al-3.7Ti-2W-1.4Ta-1Nb-0.15C make it possible to determine the chemical composition of carbides from the chemical composition of the alloy. The evaluation of the results obtained by the calculation method and experimental data was carried out, the analysis of the results gave good convergence and can be recommended for industrial use.

Prediction carbides composition in nickel-based superalloys directional crystallization

Objective. To study the specifics of the distribution of alloying elements in the carbides of the multicomponent system Ni-5Cr-9Co-6Al-1Ti-11.7W-1.1Mo-1.6Nb-0.15C by directional crystallization, using the calculated method of CALPHAD prediction. Research methods. To find regularities and calculate the distribution of alloying elements in the alloy, the latest CALPHAD method was chosen, and modeling of thermodynamic processes of phase crystallization was performed. The obtained results. The results of thermodynamic calculations of the chemical composition of carbides are given in the form of mathematical dependences. The equation of the influence of alloying elements on the dissolution (release) temperature of carbides is obtained. It is shown that the obtained dependences are closely correlated with the thermodynamic processes occurring in the system. Scientific novelty. It is shown that with increasing total concentration of carbide-forming elements, the chemical composition of carbides becomes more complicated. The titanium content of more than 2% leads to an increase in the temperature of the carbide liquidus, and at 4.5 % topologically densely packed phases is formed. When the concentration of molybdenum in the alloy is more than 4%, the probability of precipitating topologically close-packed phases in the structure increases markedly, which negatively affects the mechanical properties and heat resistance. Practical value. Based on an integrated approach for multicomponent heat-resistant nickel-based alloys, new regression models were obtained that allow adequately predict the chemical composition of carbides by the chemical composition of the alloy, which allowed to solve the problem of calculated prediction of carbide composition by chemical composition of the alloy.

On surface carbides in low-temperature carburized austenitic stainless steels

Surface carbides are occasionally found at the surface of austenitic stainless steels subjected to low-temperature carburizing surface treatments which are intended to induce an interstitially supersaturated surface layer. The crystallographic nature and chemical composition of the carbides can have a significant influence on the surface properties, especially on the corrosion resistance of the steel. However, their phase identification and chemical characterization via conventional methods (e.g. X-ray diffraction) is difficult due to their complex structure and metastable nature. In this paper, a combined metallographic and electron microscopic approach is applied to characterize the morphology and chemical composition of surface carbides found on AISI 304L and SS2343 after the same Kolsterising® treatment. Exclusively M5C2, also known as Hägg or χ-carbide was found at the surface of 304L, preferentially oriented along (111) deformation bands. In SS2343, however, χ-carbide coexisted with M7C3 (or ω-carbides) and M23C6. The carbides had preferential orientation relationships with the matrix, suggesting a carbide evolution during carburizing. All the carbides show elemental partitioning, with Cr enrichment and Ni depletion. A microstructure development sequence regarding precipitation and growth of surface carbides is proposed in this paper.

Wear Resistance of Knives Made of DI37-VI (11Kh4V2MF3S2-VI) Steel During Cutting with Addition of An Abrasive Material

A method of heat treatment of DI37-VI steel exhibiting precipitation hardening is developed with due allowance for the steel microstructure and with determining the chemical composition of carbides and the matrix after each operation. In the case of low-temperature tempering, the mechanical properties of steel are found to be little different from its properties obtained by means of multiple high-temperature tempering (ageing); in the latter case, however, the wear resistance of steel in the case of cutting of steel bars is 1.5 times higher. It is demonstrated that the wear resistance of steel is significantly affected by the chemical composition of carbides and the matrix.

The Effect of Vanadium on Morphology and Chemical Composition of Carbides in High Alloyed Chromium–Molybdenum Steels

Despite of the permanent progress of technique and finding of the new, modern materials that successfully replace metals, steel continues to play an important role in the technical practice. The tendency is to discover the new alloys with better mechanical and technological characteristics, compared to conventional and standard types of steels. High-alloyed Cr–Mo steel, with a high content of Vanadium is the new type of wear resistant material, with high hardness and satisfactory impact and fracture toughness. During the solidification process Vanadium, as a strong carbide forming element, creates a network of M7C3 type carbide grains around the metal matrix, while in the matrix, the finely dispersed V6C5 type carbides are formed. In this paper, the chemical composition and morphology have been studied of carbides and the other phases present in the metal matrix in 1.4 wt % C, 12 wt % Cr, 1.0 wt % Mo steels with additions up to 3.0 wt % V. Experimental results indicate that Vanadium affects the solidification process in high Chromium steel. Vanadium is distributed between eutectic M7C3 carbide and the matrix, but its content in carbides is considerably higher. Vanadium changed the microstructure parameters of phases present in the structure of alloys, including volume fraction, size and morphology.

Effect of Ni alloying on the microstructural evolution and mechanical properties of two duplex light-weight steels during different annealing temperatures: Experiment and phase-field simulation

This paper presents a study of two lightweight steels, Fe-15Mn-10Al-0.8C-5Ni and Fe-15Mn-10Al-0.8C (in wt.%) where strength is dependent upon the microstructure of 2nd phase precipitates. We investigate the effects of annealing temperature from 500 °C to 1050 °C on the precipitation of ordered phases size and morphology through phase-field modelling and experimental studies based on laboratory scale annealing and characterization. The chemical composition of carbides and B2 compounds as a function of isothermal annealing temperature and the matrix within which they formed are elucidated in this study. It is found that nano-sized disk-shaped B2 particles form at higher annealing temperatures (e.g. 900 °C and 1050 °C). The simulation results on carbides demonstrated the effects of energetic competition between interfacial energy and elastic strain energy on the morphological evolution of carbides. In addition to that, different ordering behaviours observed depending on the Ni content into the steel. The results demonstrate processing route designed through the phase-field simulations led to a better combination of strength and ductility. The tensile testing results indicate an increase in the strength and elongation when B2 precipitate morphology changes from micro-size faceted shape to nano-size disk-like particles.

Effect of Heat Treatment on Microstructure and Mechanical Properties of 2.25Cr–1Mo Steel

AbstractThe effect of heat treatment on microstructure and mechanical properties of a ferritic heat‐resistant steel, 2.25Cr–1Mo, was investigated. The characteristics of carbides, i.e., size, morphology, distribution, and composition, in different stages of heat treatment were examined by using transmission electron microscopy (TEM) and energy dispersive X‐ray (EDX). As the heat treatment proceeded from normalizing and tempering (NT, the delivery state), simulated post‐welding heat treatment (PWHT), to step cooling (SC), the carbides evolved from M3C, Mo2C to M7C3, M23C6. The uniformly dispersed carbides, e.g., Mo2C, M7C3, and M23C6, are responsible for the excellent mechanical properties and creep resistance of the steel. The result demonstrates that the coarsening of carbides deteriorates impact toughness and the morphology, crystal structure, and chemical composition of carbides are also important influencing factors.

Changes in chemical composition of carbides in 2·25Cr–1Mo power plant steel

Changes in chemical composition of carbides in 2·25Cr–1Mo power plant steel

Changes in chemical composition of carbides in 2·25Cr–1Mo power plant steel

It is found that the carbide chemistry changes at a slower rate in a mixed microstructure of bainite and allotriomorphic ferrite when compared with carbides in a fully bainitic microstructure. These results are expected intuitively and confirmed theoretically.MST/1896

Changes in chemical composition of carbides in 2·25Cr–1Mo power plant steel

The microstructure of a power plant steel changes during elevated temperature service. These changes in effect provide a built in time–temperature recorder which can be used in remanent life assessments. Hence, extensive studies have been undertaken of cementite composition changes as a function of time and temperature in a 2·25Cr–1Mo steel with a fully bainitic microstructure. The results are interpreted theoretically using a model for the enrichment of carbides as a function of heat treatment and steel chemistry. The results confirm the validity of the model, although further work is needed to predict the onset of alloy carbide formation at the expense of cementite.MST/1895

Changes in chemical composition of carbides in 2·25Cr–1Mo power plant steel

The microstructure of a power plant steel changes during elevated temperature service. These changes in effect provide a built in time–temperature recorder which can be used in remanent life assessments. Hence, extensive studies have been undertaken of cementite composition changes as a function of time and temperature in a 2·25Cr–1Mo steel with a fully bainitic microstructure. The results are interpreted theoretically using a model for the enrichment of carbides as a function of heat treatment and steel chemistry. The results confirm the validity of the model, although further work is needed to predict the onset of alloy carbide formation at the expense of cementite.MST/1895

Unusual Chemical Composition of Carbides in Rapidly Solidified High Speed Steels

ABSTRACTStudies of the elemental composition of carbide phases formed by rapid solidification of a Mo-base high speed steel (M7) have yielded an intriguing finding. Micro-analysis of the extracted carbides (M2C, M23C6 and MC) showea that these were unusually rich in refractory elements with values of Mo in the range 46-53 wt.%, corresponding values for Fe and Cr were low (6-12 wt.% Cr and 1.5-13 wt% Fe). This was in marked contrast with analyses of MC, M6C, M7C3 and M23C6 in the ‘unglazed’ material where Fe and Cr were major constituents. A distinctive feature was M23C6 in the rapidly solidified material which contained large amounts of Mo and W and very little Cr. It is proposed that this phase, initially formed as M6C, underwent solid-state transformation.

Effect of milling in various media on the composition and some properties of niobium carbide

Comminution of carbides in various media which do not prevent the well-developed surfaces of their particles from coming into contact with water and oxygen leads to surface oxidation of these particles. This is reflected in the chemical composition of carbides, which almost continually changes during sintering in the usual temperature range, right up to 2200‡C, and in the densification kinetics and properties of carbide-base materials. Because of the instability of oxycarbides of the Group V metals in a vacuum at these temperatures, with the carbides “MevC” (NbC and TaC) the surface oxidation experienced by their particles during milling in certain dispersing media may have an activating effect on the sintering process and shift the composition of the carbides toward the lower limits of their homogeneity ranges.