Specimen size effect on evaluation of strength properties of 3Cr1MoV and Incoloy 800H using small punch test

Abstract

Standardization of small punch test (SPT) is being carried out, but the specimen thickness is not unified in different laboratories and specimen size effect on deformation mechanism still remains unclear. In this paper, SPT specimens with thicknesses of 100 μm–500 μm were used to investigate specimen size effect on strength properties and fracture morphology of 3Cr1MoV and Incoloy 800H. The grain sizes of two materials were 10 μm (3Cr1MoV) and 50 μm (Incoloy 800H). Yield and ultimate tensile strengths were extracted from SPT data based on a combined-scheme of finite element simulations and experiments. Fractography of specimens was studied using a scanning electron microscope. The results showed that the strength value of Incoloy 800H increased with the decrease of thickness, the size dependence of yield strengths was stronger than that of ultimate strengths, and the strength value of 3Cr1MoV was thickness independent. Fractographic investigations found that failure was caused by ductile fracture for all the specimens. A theoretical model considering geometrically necessary dislocations densities, available dislocation sources and grain sizes was proposed to explain the different mechanical responses of investigated materials to specimen thicknesses. This work clarifies the SPT specimen thickness and the grain size of studied materials should be taken into consideration before sampling.