INFLUENCE OF REDUCED CARBON CONTENT ON THE PROPERTIES OF ZHS3DK-VI ALLOY

Procesi littâ, 2025, Vol 1 (159), 3-10

Abstract

The effect of reduced carbon content (0.015...0.020 % С) and, accordingly, the carbide phase on the properties of ЖС3ДК-ВІ alloy with additional alloying and modification with niobium, hafnium-nickel and nickel-yttrium alloys was investigated. It was established that in the structure of test samples with reduced carbon content, carbides are practically absent, and grain boundaries are very thin. When niobium, yttrium and hafnium are introduced, carbides are formed in the form of globular particles mostly uniformly distributed in the volume of the metal. The microstructure of samples with reduced carbon content is coarsely crystalline, which is probably due to the absence of competitive phase growth during melt crystallization. Experimental variants with low carbon content have impact toughness values at the level of 90...150 J/cm², but extremely low long-term strength, probably due to the lack of carbide strengthening in the alloy. High impact toughness values are associated with the uniform distribution of the finely dispersed carbonitride phase in the structure. Complex modified (Nb+Hf+Y) samples, with a carbon content of 0.06%, showed sufficient impact toughness and long-term strength, which significantly exceeded the requirements of OST 1.90126-85. In these samples, the almost complete absence of large carbides in the bulk of the main γ-solid solution grains and the presence of small carbides of the Me₂₃C₆ type, which were released during heat treatment along the grain boundaries, prevented grain boundary slippage under conditions of high temperatures and applied load. The level of impact toughness, in this case, is provided by the release and uniform distribution of discrete and globular carbides and carbonitrides (approximately 2...3 µm in size) during the treatment of the melt  with yttrium and hafnium. The decrease in impact strength, compared to low-carbon options, is probably due to the release of double carbides of font morphology.