Fracture behavior of spheroidized hypereutectoid steels

Abstract

A fracture model for spheroidized hypereutectoid steels is developed based on the concept that the stress in the ferrite matrix is the driving force for crack initiation at grain boundaries within the coarse carbides. The ferrite matrix fracture stress, δ_f,ferr is calculated by averaging the ferrite stress using upper and lower bound concepts, and by utilizing the fracture strength of the carbide. The analyses and results indicate that the fracture behavior follows a classical fracture mechanics relation in that the fracture strength is a unique function of the reciprocal of the square root of the carbide particle size with δ_f,ferr equal to zero at infinite carbide (crack) size. It is concluded that the fracture strength of the iron-iron carbide composite is enhanced by: (i) increasing the strength of grain boundaries within carbides; (ii) decreasing the average carbide size, and (iii) increasing the carbide volume fraction.