Non-destructive characterization of strain induced surface hardness increase by measuring magnetic properties of AISI 304

The goal of this work is to establish a correlation between the surface integrity and magnetic properties of stainless steels like AISI 304 (X5CrNi18-10). In metastable austenitic stainless steels, a phase transformation from the austenitic to the martensitic phase can occur even at room temperature. In this work, machine hammer peening (MHP) is used to selectively introduce the activation energy required for martensite formation on discrete areas of the surface. The phase transformation is confirmed by electron back scatter diffraction (EBSD) and micrographs. A correlation between the energy input by MHP, magnetic properties, and surface hardness is established. Using this approach, characterization of the surface integrity by measuring magnetic properties can be achieved. In addition, a novel solution to code and encode information with high information density onto metastable austenitic materials is proposed.