Mechanical characteristics of spheroidal graphite cast irons containing Ni and Mn with mixed ferrite and bainitic ferrite microstructure

This study aims to clarify the influence of additive elements of Ni and Mn on tensile and impact properties of three kinds of spheroidal graphite cast irons (SG irons), which are as cast, annealed and austempered samples. Spheroidal graphite cast irons with Ni (0-4.5 mass-%) and Mn (0-0.5 mass-%) melted by a high frequency induction furnace and cast into a Y block CO2 mould with 30 mm in thickness. From the viewpoint of heat treatment, tensile strength and hardness of SG irons become larger in the order of ferritised<as cast<austempered ones. Matrix structures of SG irons, which are conducted to austempering treatment from alpha and gamma mixture range, consists of bainitic ferrite with high toughness. Austempered SG iron with 3% Ni in 0.1% Mn series is found to become higher tensile strength compound with elongation and toughness of 901 MPa, 17% and 915 kJ m(-2).