Deformation and Strength of Malleable Cast Iron in the Complex Stressed State

Abstract

We analyze the experimental data on the specific features of deformation, damageability, and strength of malleable cast iron obtained in testing tubular specimens under conditions of simple loading by axial forces and internal pressure. It is shown that the degradation of the structure of the material depends on the parameters of the stressed state. New criteria required for the description of the limiting states of yield and fracture are established.Keywords: malleable cast iron, spheroidization, complex stressed state, limiting state, yield, fracture, coefficient of transverse strain, damage, loosening, dispersion of characteristics, hardness, coefficient of variation, Weibull coefficient of homogeneity.In recent years, cast irons with graphite inclusions of special shape (including malleable cast irons with flaked graphite) are extensively used in manufacturing load-bearing structural elements in various branches of machine building. The application of these materials is explained by the unique combination of physicomechanical and technological properties, which are often better than the corresponding characteristics of other metallic materials, including structural steels (see, e.g., [1,2]).The mechanical properties of cast irons depend on various factors, including the structure of the metallic base, the shape and sizes of free graphite inclusions, the chemical composition and type of modifying admixtures affecting the formation of graphite inclusions whose shape and sizes can be controlled within fairly broad limits by changing both the technology of production of the metal and the modes of thermal treatment.It is well known [3][4][5] that, in the presence of graphite inclusions, the deformation of cast irons under mechanical loading on the micro-and macrolevels is accompanied by cracking (loosening of the structure), whose intensity mainly depends on the shape and sizes of graphite inclusions. The process of cracking always affects the serviceability of the analyzed materials in structures.Numerous dependences aimed at the description of the behavior of cast irons with graphite inclusions of special shape under conditions of uniaxial loading were proposed on the basis of the accumulated experimental data (see, e.g., [1,2,6]). Unfortunately, in view of the absence of sufficient amounts of experimental data, the problem of prediction of the behavior of cast irons operating under conditions of complex stressed state is extremely complicated. Therefore, various problems of mechanical behavior of the analyzed class of materials under operating conditions of actual structural elements remain, in fact, unsolved.In what follows, we present the results of experimental investigation of the regularities of the behavior of malleable cast iron subjected to mechanical loading under conditions of complex stressed state.Malleable cast iron was produced by the long-term annealing (in the presence of nickel) of preliminarily prepared castings of hypoeutectic white iron 30 mm in diameter and 200 mm in length with the followi...