STRUCTURE AND PROPERTIES OF COMPLEX-ALLOYED HIGH-CHROMIUM CAST IRONS FOR MASSIVE COMPOSITE CASTINGS

Abstract

The article investigates the problems of structure formation and mechanical properties of massive composite castings, the working layer of which is made of high-chromium cast irons. Under slow cooling conditions and in the absence of an intermediate buffer layer, it is critical to ensure the stability of properties and the strength of the transition zone between the wear-resistant layer and the core material. To address this issue, a comprehensive analysis of 30 heats with different Cr/C ratios and microalloying systems was conducted. Regression analysis methods were applied to build mathematical models of the chemical composition's influence on hardness and strength characteristics. It has been established that the optimal balance of properties is achieved with a carbide-forming elements ratio of 5 < Cr/C < 7.5 and a chromium content of 15.0–18.0%. This prevents the precipitation of brittle primary cubic carbides and significantly reduces residual thermal stresses. It is shown that the combined effect of alloying with nickel and molybdenum inhibits the pearlitic transformation of supercooled austenite under conditions of delayed heat dissipation, while microalloying with titanium and boron promotes grain refinement and uniform distribution of the carbide phase. It was determined that to ensure satisfactory machinability and sufficient toughness of the transition zone, the ratio of carbide- to austenite-forming elements must be 1.5–2.0. The presence of a stable correlation between the hardness and strength of high-chromium cast iron is proven, which allows using the calculated transition coefficients to evaluate the properties of finished products. Based on the obtained data, an optimized chemical composition of complex-alloyed cast iron is proposed, which guarantees high operational reliability of massive composite components