Homogeneous Segregation Research Articles

STUDY OF THE INFLUENCE OF THE Si/Mn CONTENT RATIO ON THE DENDRITIC STRUCTURE OF STEELS FOR RAILWAY AXLES

Purpose. Investigation of the effect of different total concentration and ratio of Si and Mn content on the dendritic structure and segregation inhomogeneity of cast carbon steel and its transformation after hot plastic deformation.
 Methods of research. To determine the effect of the content of Si and Mn, experimental ingots with a variable chemical composition within the grade were made for three steel grades used for the manufacture of railway axles – grade OS according to DSTU 31334, F according to AAR M 101 and EA1N according to EN 13261. To determine the dendritic structure microstructural analysis was used after etching in sodium picrate.
 Results. A comparative analysis of the microstructure of the experimental heats of steels with a variable chemical composition has been carried out. The ratio of content in steel Si and Mn in the cast state and after deformation is established. A significant effect of the total deoxidation in steel on the formation of microhardness inhomogeneity over the cross section of a carbon steel ingot and microinhomogeneity of the structure of individual sections is shown. It was found that after deformation, the central zones turned out to be the most worked out (especially for steel with a chemical composition within the EA1N grade, characterized by an increased content of Mn).
 Scientific novelty. The study of the influence of fluctuations in the content of the basic elements of carbon steel leads to the development of ideas about the formation of a dendritic structure and segregation heterogeneity in railway axle steels.
 Рractical value. Knowledge of the principles of segregation formation is necessary to determine further modes of deformation and heat treatment not only for continuously cast billets or ingots, but also for final products.

Study of Chemical Inhomogeneity in Beta-Solidifying TiAl Alloys of Various Composition

The results of original research into the structure and statistical distribution of elements alloyed into ingots from a new Russian intermetallic TiAl alloy having two variable compositions (Ti–44.5Al–2V–1Nb–1.5Zr/2.5Cr–0.1Gd, at.%) are presented. The experimental ingots having a nominal weight of 3–30 kg were obtained according to two technological schemes: 1 — triple vacuum arc remelting (VAR + VAR + VAR) with a consumable compacted electrode; 2 — VAR → VAR → single vacuum induction melting (VAR + VAR + VIM) in a cold crucible furnace. The statistical processing of the chemical analysis results was carried out using Shewhart charts. The results indicate a minimum degree of volumetric macrosegregation in the ingots and the almost complete absence of segregation inhomogeneity in Zr- and Cr-containing compositions: the maximum range of Al content over the cross section of triple-remelted ingots was no more than 0.84 at.% (0.42 wt.%), while along the height of the ingots, Al content was no more than 1.87 at.% (0.55 wt.%).

Structure, phase composition, and strength properties of single-crystal nickel alloy bearing titanium and rhenium

The fine structure, phase composition, segregation inhomogeneity, and strength properties of alloy ZhS32-VI with Ta and Re additives are studied. The thermal stability of the alloy is analyzed after temperature holds and in service.

Structure of high-temperature nickel alloy ZhS36VI for single-crystal blades of high-pressure turbines

The fine structure, phase composition, and segregation inhomogeneity of carbonless single-crystal rhenium-alloyed alloy ZhS36VI in cast and heat-treated conditions are studied. The structural and phase stability of the alloy is determined at elevated temperatures and loads.

Formation of segregation inhomogeneity in high-temperature nickel-base alloys

The process of hardening of model high-temperature nickel alloys with additives of Nb, Mo, Ti, W is studied in a range of cooling rates typical for large castings. The rules of the segregation processes and the formation of the structure are described. It is shown that despite the low volume fraction of the eutectic component its morphology and laws of formation have a considerable effect on the structural homogeneity of the alloy. Carbide, intermetallic, and carbide-intermetallic eutectics can form in the alloys depending on the cooling conditions. The diffusion processes in crystallization of the alloys are a sign of active mass exchange between the eutectic liquid and the primary solid phases.

Structural features of powder materials operating under high temperatures, stresses, and wear

It is known that parts of hot zones of metallurgical plants as well as heavily loaded pressing and forging tools operate under a high temperature, elevated mechanical stresses, the action of a steam ambient, slag, surface wear due to contact with the hot metal, etc. The possibility of providing the requisite properties by using high-temperature alloys has already been exhausted because the complexity of their composition intensifies the segregation inhomogeneity of the ingots which cannot be eliminated in the process of hot deformation and homogenizing annealing. As a rule, fracture starts under the conditions of cyclic loads on local structural defects such as accumulations of coarse particles of the eutecie γ′-phase, borides, carbides, nonmetallic inclusions. The chemical inhomogeneity and the structural defects caused by it can be removed by using methods of powder metallurgy that can provide materials with unique properties unattainable in the conventional metallurgy. The present paper is devoted to the special features of the structure of powder nickel alloys.

Phase composition and mechanical properties of a high-strength low-alloy steel 03G4N2MAF after tempering

1. Austenite is formed in low-alloy steel 03G4N2MAF quenched to martensite during tempering in the range 550–650°C. The maximum amount of austenite is observed after tempering close to the Ac1 point (670°C), and in fact at 640–660°C. 2. A homogenizing anneal at 1250–1280°C leads to a reduction in the amount of austenite formed during tempering and this is connected with a reduction in segregation inhomogeneity of the steel for manganese and carbon, which is one of the reasons for premature formation of austenite. 3. An increase in the amount of austenite formed during tempering steel 03G4N2MAF facilitates an increase in ductility and impact strength determined on Menage-type specimens. However, impact strength determined on specimens with a fatigue crack characterizing work for crack propagation decreases with increasing amounts of austenite in the steel.

Removal of microinhomogeneities in grade 4Kh12N8G8MFB (EI481) creep resistant steel by electroslag remelting

1. In grade 4Kh12N8G8MFB steel alloyed with elements exhibiting a strong tendency to carbide formation and with carbon, the basic components segregate in the interaxial space. The tendency of an alloying element to segregation is directly related to the thermodynamic interaction parameter for the element with carbon in the iron melt. 2. The segregation inhomogeneity is determined by the nature of the macrostructure. In the columnar zone the degree of segregation increases linearly with increase in the thickness of the crystallized layer. The maximum development of segregation is attained in the center of the equiaxed zone. 3. The maximum inhomogeneity in ER and OA ingots is the same irrespective of the significant difference in weight and cross section of the ingots investigated, and therefore in the larger ER ingots, because of the greater number of intermediate heatings and the significant reduction, the ER metal is more homogeneous. 4. Because of the marked interdendritic segregation, grade 4Kh12N8G8MFB steel exhibits anisotropy. The anisotropic properties of the steel are affected by two factors: the chemical inhomogeneity and the associated different degree of hardening corresponding to the axes and interaxes, and the nonuniform distribution of insoluble inclusions. Below the temperature limit of solubility of the dispersed hardening phases, inhomogeneous decomposition is of fundamental importance. During high-temperature tests the magnitude of the anisotropy is determined by the residual quantity of undissolved inclusions.