The Mechanical Properties of High Density Sintered Iron Sheets and Direct Observation of Their Fractured Surface

Abstract

The effect of pores on the mechanical properties of high density sintered iron sheets has been examined by means of tensile test and direct observation on the surface of the specimen during tensile test in the scanning electron microscope. As the test pieces used, the high density sintered iron sheets were prepared by direct powder rolling or by laminating the sheets. The volume fraction and the shape of pores, and the distribution of pore size were changed by sintering at 850°C for 60 min, cold-rolling within the range of 44% to 92%, and annealing at 700°C for 60 min in hydrogen.The following results were obtained. (1) In an atomized iron sheet, which was sintered and cold rolled at about 50% (total reduction) and then annealed, weakly bonded grain boundaries were observed, which seemed to be composed of pores. Then, these grain boundaries play a role on the nucleation and propagation of cracks in the iron sheet during tensile tests. (2) After laminating atomized iron powder sheets with carbonyl iron powder, these sheets were sintered, cold-rolled at about or more than 60% total reduction and annealed. In consequence, the high density was attained. The mechanical properties of these sheets depend more effectively on the elongated grain shape and average grain size than on the scattered fine pores in them.