Masanobu Ohmori1, Akira Kaya2, Yasunori Harada3, Fusahito Yoshida1 and Misao Itoh1
1Department of Mechanical Engineering, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima
Tensile properties of sintered powder chromium (99.9 mass% purity) produced by a cold isostatic press (CIP) and a hot isostatic press (HIP) were preliminarily examined to find conditions favorable to the plastic working of the sintered chromium. Specimens A and B1 taken from a sintered ingot A and a half of an ingot B, respectively, were annealed at 1823 K higher than 1473 K encountered in the present HIP. Specimen B2 from the remainder of the ingot B was not heat treated.
Transition from ductile to brittle fracture occurred very sharply, i.e., in a small range of temperature, and at the higher temperature in a testing at the higher speed of deformation. Ductile-to-brittle transition temperature of the specimen B1 was lower than that of the specimen B2 suggesting that the annealing at 1823 K is effective in lowering the transition temperature. Small plastic tensile prestrain given to a specimen at a temperature slightly beyond its transition temperature considerably reduced the brittleness of the specimen. This prestraining effect is supposed to come from free dislocations generated in the prestrained specimen. At temperatures between 700 K to 1023 K, flow stress was never changed even when the strain rate was increased from 1.7×10-4 s-1 to 1.7×10-1 s-1, and the decrease of the stress with increasing temperature was small.
sintered chromium, ductile-to-brittle transition, effect of strain rate, effect of prestraining, free dislocations, tensile deformation
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