Cyclic Crack Resistance of Grey and High-Strength Cast Irons with Increased Phosphorus Content

Abstract

We investigated the influence of phosphorus (0.02–0.76%) on the microstructure, short-term strength, cyclic crack resistance characteristics, and micromechanism of fatigue fracture of grey and high-strength cast irons. It was established that the low cyclic crack resistance of grey and high-strength cast irons with increased phosphorus contents (0.7–0.8%) is caused by the propagation of a fatigue crack via intergranular cleavage, initiated by a discontinuous or continuous network of precipitates of the ternary fine-grained phosphide eutectic along boundaries of ferrite grains. We showed that, from the viewpoint of cyclic crack resistance, it is admissible to alloy cast irons of the ferritic and ferritic–pearlitic class with phosphorus up to 0.3% when the phosphide eutectic forms in amounts of 3–5% for grey cast irons and 4–7% for high-strength cast irons without significant decrease in their resistance to brittle fracture.