Влияние микролегирования иттрием и гафнием на прочностные характеристики и морфологию карбидной фазы сплава ЖС3ДК-ВИ при замедленной кристаллизации

There are analyzed the melts of the ZhS3DK-VI alloy with different levels of strength characteristics and the factors influencing their reduction, differences in the macro and microstructure of the alloy, the effect of the crystallization rate when pouring the melt into hot and cold ceramic molds are determined. Since when casting parts, the level of properties is determined on separately cast samples, in the technology of manufacturing samples, the casting parameters of the corresponding part must be observed, and when increasing the strength characteristics due to changing technological parameters, it is imperative to consider the possibility of changing the technology of casting parts. However, for parts of complex configuration, cast from heat-resistant nickel alloys, it is often impossible to change the technology, therefore the only way to influence the properties of the material is to use microalloying with rare earth elements, for example, yttrium and hafnium. The introduction of these alloying elements in small amounts has a positive effect on factors that reduce the properties of the ZhS3DK-VI alloy, such as the unfavorable shape and topography of the carbide phase, or even slightly change the chemical composition of carbides. The article analyzes the effect of microalloying with hafnium and yttrium on the morphology and topography of the carbide phase; positive changes in the microstructure and strength characteristics at room temperature of the heat-resistant nickel alloy ZhS3DK-VI are noted. The technology of microalloying the melt has been developed to obtain satisfactory valuesof strength characteristics in tensile tests and impact toughness at room temperature. Microalloying the ZhS3DK-VI alloy with hafnium in a concentration of 0.15...0.25 % made it possible to increase the strength characteristics on samples for mechanical tests by 10…15 %, provided that the melt was drained into hot ceramic molds and slowed down. Higher concentrations of hafnium during slow crystallization lead to the formation of eutectic phases uncharacteristic for the ZhS3DK-VI alloy, requiring a decrease in the heat treatment temperature, which, accordingly, leads to a decrease in the level of long-term strength at 850 °C.

ASSESSMENT OF THE EFFECT OF CARBON ON PERFORMANCE PROPERTIES AND THE MICROSTRUCTURE OF ROLL STEEL

This paper concentrates on studying the effect of carbon on performance properties of 150KhNM roll steel grade. The introduction contains a brief literature review on the effect of the roll alloy chemistry on performance and mechanical properties of mill rolls. Besides, it demonstrates the relevance of the presented studies. The paper describes the effect of chemical elements, such as manganese, niobium, vanadium, nickel on the microstructure and mechanical properties of mill rolls. It also classifies alloying elements by their effect on polymorphic transformation temperatures and shows carbide-forming elements increasing such property. We also considered the effect of the carbide phase on hypereutectoid steel. The paper contains carbide compounds that may be formed in steels, and their classification. It describes the mechanism of the effect of the carbide phase on performance properties of steel castings. The second part of the paper presents a research procedure and briefly describes materials used for the research and laboratory and analytical equipment. The third part of the paper presents the research results. It describes the effect of carbon in a broad range on service durability of hypereutectoid roll steel in conditions of wear at room and elevated (400 ºС) temperatures. Besides, we determined the effect of carbon on the roll alloy microstructure and analyzed relations between the microstructure and performance properties of hypereutectoid roll steel. The conclusion of the paper summarizes the results and contains the references used for an analytical review.

INFLUENCE OF PRE-OXIDATION ON THE NITRIDING PROCESS OF IRON ALLOYS

The article presents the results of studying the kinetics of oxidation of Fe-Cr, Fe-Al and iron alloys at temperatures of 450–550 °C. The influence of preliminary oxidation of these alloys on the nitriding process has been studied. It has been established that alloying of Fe-Cr, Fe-Al alloys increases the amount of absorbed nitrogen, but decreases the overall depth of the nitrided layer. The duration of nitriding required to develop high hardness (over HV 1,000) depends on the composition of the solid solution. At a nitriding temperature of 520 °C, exposure is 10–15 minutes for steels of the first group, at least 3–4 h for steels of the second and third groups, and 5–6 h for steels of the fourth group. Studies have shown that the hardness of the layer is determined mainly by the composition of the solid solution; the amount and dispersion of the carbide phase have less effect. The hardness increases as a result of an increase in the hardening temperature and a decrease in the tempering temperature, which reduce the amount of the carbide phase, but increase the alloying of the solid solution. The hardness of the nitrided layer of high-speed steels P9, P18, having the same composition of the solid solution, is the same (HV 1,340) even despite the significant difference in the amount of the carbide phase. The hardness of the layer of steel 4Х5В2ФС (4Kh5V2FS), which contains more chromium in the solution, is HV 50–90 higher than the hardness of the layer on the steel 3Х2В8Ф (3Kh2V8F), which has 1.5–2 times more of the carbide phase. The behavior of steels with the same high chromium content (12 %), but different carbon content is characteristic. The hardness of the layer in steel 1Х13 (1Kh13), which has few carbides, is HV 100–180 higher than the hardness of the layer in steel Х12М (Kh12M), in which a significant portion of chromium is bound into carbides.

Production and Properties of High Entropy Carbide Based Hardmetals

Dense, high-entropy carbide cobalt-bonded hardmetals with two different compositions, namely (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co and (Ta-Ti-Nb-V-W)C-19.2 vol% Co, were successfully manufactured by gas pressure sintering (SinterHIP) at 1400 °C and 100 bar Ar pressure. The microstructure of these hardmetals consists of a rigid skeletal carbide phase embedded in a tough Co binder phase. EDS mappings showed that the high-entropy carbide phase did not decompose and that a typical hardmetal microstructure was realized. Only in the case of the (Hf-Ta-Ti-Nb-V)C-Co hardmetal was some undissolved TaC and HfO2, as well as some clustered vanadium titanium carbide phase, found, resulting in a split-up of the HEC phase into two very similar HEC phases. This resulted in a reduced hardness to fracture toughness ratio for this composition. Measurements of magnetic saturation polarization showed values between 57.5% and 70% of theoretical magnetic saturation polarization, indicating marginal dissolution of the carbide-forming metal elements in the binder phase. The hardness value HV10 for (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co was 1203 HV10 and 1432 HV10 for (Ta-Ti-Nb-V-W)C-19.2 vol% Co.

Modeling of structural transformation kinetics in steels during their heat treatment

Analysis of carbide phase growth kinetics during carburizing of steel has been made in this paper, using experimental and calculated data obtained according to the classical theory of transformations in metals and alloys.

TUNGSTEN-FREE HARD ALLOYS: MANUFACTURING METHODS, STRUCTURE AND PROPERTIES (review)

In this paper provides an overview of scientific and technical literature and developments in the field of tungsten-free hard alloys or cermet as promising materials of a new generation metalworking tools. Methods of obtaining sintered hard alloys, their structure and basic operational properties are considered The main directions of improving the properties of hard alloys are given. The results of experimental work on the production of cermet by high-speed quenching of the melt are presented. The obtained fast-quenched materials of the Fe–TiC–TiB2 system demonstrate physical and mechanical properties at the level of sintered hard alloys, but at the same time it contain 2–3 times less of the carbide phase.

Распад остаточного аустенита в стали У12 при обработке в магнитном поле

In article the analysis of influence of magnetic field on process of disintegration of austenite at release of U12 steel is carried out. The influence of the magnetic field leads to an intensification of the decay process of residual austenite and more intense isolation of the carbide phase from austenite.