球状セメンタイト綱(0.7%C)の低温での引張破壊挙動について

概要

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The relation between microcracks and transition temperatures was examined on a spheroidized 0. 7% carbon steel. The spheroidization anneal was achieved by repeated heating and cooling 'between 710 and 735℃ after being quenched in oil. The specimens were stretched to fracture a constant speed of crosshead at various temperatures. The four kinds of fracture regions divided by three transition temperatures were determined from the temperature dependence of tensile properties. At each transition temperature range, the fractured specimens were observed under an optical microscope and a scanning electron microscope. In the temperature range below the transition temperature T_C, at which fracture stress took a maximum value below the nil-ductility transition temperature T_B, microcracks were initiated at the buondary between the cementite particle and surrounding ferrite perpendicular to the direction of tension, and propagated by going around particles. In the temperature range from T_C to T_B, crack initiation occured at the cementite particles and its propagation occured by cleavage of the ferrites. In the temperature range from T_B to the ductility transition temperature T_D, microcracks initiated at ferrites by their slipping and also at cementite particles and propagated by cracking cemetite particles. Many microcracks of void type were observed above T_D.
社団法人日本材料学会の論文
1981-11-15