Influence of Microstructure on the Strength and Cyclic Crack Resistance of Cast Irons

Abstract

We study the influence of microstructure of high-strength cast irons of ferritic, ferritic-pearlitic, and pearlitic classes on the characteristics of strength and cyclic crack resistance and establish the relationship between the characteristics of strength and cyclic crack resistance and the chemical composition and microstructural parameters of the matrix and graphite inclusions of high-strength cast irons. Indeed, the ultimate strength σu = 750–850 MPa, fatigue threshold ΔKth = 8–10 MPa\(\sqrt {\text{m}}\), and cyclic fracture toughness ΔKfc = 50–60 MPa\(\sqrt {\text{m}}\) are guaranteed by the pearlitic matrix and the following parameters of the graphite phase: the content of graphite fp ≈ 10%, the degree of its spheroidization of about 95%, the size of globules dgl ≈ 20–50 μm, and the distance between them λ ≈ 40–70 μm, obtained in high-strength cast irons containing (wt.%): 3.2–3.5 C, 1.9–2.5 Si, 0.35–0.4 Mn, and 0.05 Mg.