Relationship between hardness and flow stress in uniaxial compression is investigated for porous sintered metals. Hardness is defined here as the applied load divided by the surface area of the indentation. When the semi-angle α of the pyramidal indenter is 68 deg, i.e., the Vickers hardness indenter, the ratio of the hardness to the flow stress decreases with decreasing relative density ρ However, when α is 45 deg, the ratio is 2.7 regardless of the value of ρ. The ratio of the Brinell hardness to the flow stress decreases with decreasing ρ when the diameter ratio d/D of the impression to the spherical indenter is 0.4. When d/D is 0.8, the ratio is nearly constant regardless of ρ. The flow stress of sintered metals can, therefore, be estimated from the hardness measured by the pyramidal indenter with the semiangle of 45 deg or from the Brinell hardness at a diameter ratio of 0.8.

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