FRACTURE-BEHAVIOR OF SPHEROIDIZED HYPEREUTECTOID STEELS

A fracture model for spheroidized hypereutectoid steels is developed b ased on the concept that the stress in the ferrite matrix is the drivi ng force for crack initiation at grain boundaries within the coarse ca rbides. The ferrite matrix fracture stress, sigma(f,ferr) is calculate d 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 fr acture mechanics relation in that the fracture strength is a unique fu nction of the reciprocal of the square root of the carbide particle si ze with sigma(f,ferr) equal to zero at infinite carbide (crack) size. II is concluded that the fracture strength of the iron-iron carbide co mposite is enhanced by: (i) increasing the strength of grain boundarie s within carbides; (ii) decreasing the average carbide size, and (iii) increasing the carbide volume fraction.