Critical Evaluation of Spherical Indentation Stress-Strain Protocols for the Estimation of the Yield Strengths of Steels

Abstract

Accelerated development of advanced metals and alloys requires validated relationships between the high throughput indentation measurements and standardized tensile test protocols. The main objective of this paper is to critically evaluate the quantitative relationships between the yield strengths measured in standard tensile tests and the indentation yield strengths obtained from the recently developed spherical indentation stress-strain protocols for a broad range of steels with varying properties and microstructures. The tensile yield strengths for the tested steels varied from 300 to 1400 MPa, providing the broadest experimental evaluation to date for the spherical indentation stress-strain protocols. Standardized tension tests, standardized hardness measurements, and the recently developed spherical microindentation stress-strain protocols were employed on all the steels included in this study. The indentation stress-strain protocols provide a suitably normalized characterization of the material’s intrinsic mechanical response, when compared to standardized hardness measurements. It was found that the yield strengths estimated using the spherical indentation stress-strain protocols were within a 10% error. Furthermore, it was found that the tensile strengths estimated from the conventional hardness measurements exhibited higher error compared to those estimated from the spherical indentation stress-strain protocols. Spherical indentation stress-strain protocols were able to predict tensile yield strengths. The role of sample thickness on the indentation measurements was specifically investigated and quantified, resulting in specific recommendation for the minimum sample size for the indentation measurements.