Influence of Cementite Volume Fraction on Mechanical Properties and Fracture Toughness in Spheroidized Cementite Steel : Study on Fracture Behavior of Particulate-Reinforced Composite

Spheroidized cementite steel which consists of ferrite matrix and cementite particles is regarded as a kind of particulate-reinforced metal composite. Uniaxial tensile and fracture toughness tests were conducted on three kinds of spheroidized cementite steels. In the uniaxial tensile test, yield and fracture stresses increase and ductility decreases with an increase in cementite volume fraction. The fracture process is described in terms of the growth and coalescence of voids nucleated from cementite particles. Quantitative examination shows that the damage is accumulated mainly by the void growth for the material with a low volume fraction of comentite and by the void nucleation for a high volume fraction of cementite. Fracture toughness decreases with an increase in the cementite volume fraction. A crack is initiated by the growth and coalescence of voids except in the material with a high content of cementite particles, which shows a mixed fracture process combining the void coalescence type and the cleavage type. It is suggested from the present results that a new approach which takes account of the damage process is necessary for characterizing the performance of particulate-reinforced composites.