Spherical indentation method for measuring local mechanical properties of welded stainless steel at high temperature

Indentation method was employed to evaluate the local mechanical properties of welded stainless steel at a high temperature of 320 °C. The welding process often changes the mechanical properties (in particular the plastic properties), and make the material property inhomogeneous. An indentation method was proposed to effectively evaluate the stress-strain relationship (approximated by the Ludwick-type hardening law) in the welded SUS316L at 320 °C. Functional relationship between the indention response and plastic property was established using finite element method (FEM). The dimensional function was deduced based on sufficiently-deep indentation, so that it can directly estimate plastic properties up to large uni-axial strain (about 20%). Spherical indentation tests applied to welded SUS316L may enable the evaluation of the distribution of plastic properties, such as the yield stress, plastic strain and tensile strength. The properties around the welded area were estimated to be higher than the base material of SUS316L, owing to the local plastic deformation from welding-induced thermal expansion and construction. Parallel test was conducted to validate the model. The proposed indentation technique can quantitatively evaluate the local mechanical properties at high working temperature, and supply useful information on inhomogeneous property distribution in materials.