Microstructure of low-alloy cast iron with spheroidal graphite and high crack resistance

Abstract

1. The results of investigations of the resistance of cast irons with different structures and shapes of graphite inclusions to brittle failure suggest the absence of correlation between KIc and δ, and the presence of a weak correlation between σu and σo.2. The critical embrittlement temperature can be estimated qualitatively from the results of tests on the resilience of specimens with an acute notch (Charpy-type). 2. Two-stage annealing at 920°C and 720°C with subsequent heating to Ac2, holding for 15...30 min, and cooling in air to 600...500°C, and thereafter in water or oil makes it possible to fix ductile austenite, which is stable to the normal temperature, along the ferrite-grain boundaries; in this case, redistribution of Mn, Ni, Cr, Mo, Cu, Al, and Si occurs between the α- and γ-solid solutions, and the fracture toughness KIc is increased as compared with the KIc of cast iron with an initial ferritic structure. 3. An increase of up to a total of 2.0...3.5% in the extent to which ferritic cast iron with spheroidal graphite is alloyed with Ni, Cu, Cr, Mn, Mo, and Al contributes to an increase in the amount and stability of austenite, even during slow cooling in air. 4. The investigations that we conducted to determine the feasibility of increasing the resistance to brittle failure, which were conducted on compact specimens for eccentric tensioning and which were computed by methods used for steel components, make it possible to expand the range of application of low-alloy cast iron with spheroidal graphite.