Evaluation of the Mechanical Properties of Precipitation-Hardened Martensitic Steel 17-4PH using Small and Shear Punch Testing

Abstract

Small punch and shear punch tests are promising techniques that have the potential to be used as tools to monitor in-service components and maximize the amount of information that can be obtained from limited in situ material. These tests consist of punching into a thin disk-shaped specimen, using either a flat (shear) or hemispherical-shaped (small) punch and recording the load-displacement data. To use these data in engineering design, it is necessary to convert them into conventional mechanical properties (i.e. tensile yield and ultimate tensile strength). In this paper, the suitability of using these small-scale punch methods to provide such meaningful uniaxial tensile data is investigated. A precipitation-hardened martensitic steel, 17–4PH (heat treated to different temperatures to give a wide range of mechanical properties) has been selected. Uniaxial tensile properties for the material in a range of conditions have been determined from hardness data and attempts have been made to correlate punch test data to uniaxial tensile test data. In this study, linear correlations have been proposed that will allow tensile properties to be estimated using punch data from both test types. It has, however, been shown that the shear punch test may provide more meaningful data when uniaxial data is limited, for example during alloy development or when investigating ex-service material. This will likely be particularly applicable when considering highly embrittled materials, where early fracture of a small punch test specimen may occur.