OS5-1-1 Measurement of Stress in Austenitic Stainless Steel by an Indentation Method

Abstract

Compressive residual stress is introduced into various components by surface modification methods in order to mitigate stress corrosion cracking susceptibility and to improve fatigue strength. There are also some nondestructive evaluation methods of residual stress including X-ray diffraction, neutron diffraction and Barkhausen noise. However, these methods are not suitable for small areas of austenitic stainless steel because it has large grain size and nonmagnetic property. A more reliable method is therefore required to evaluate residual stress in austenitic stainless steel. Recently, much research has focused on an indentation method for the metrology of residual stress. The indentation load-depth curve and impression size obtained from the indentation process can be used to determine residual stress and various mechanical properties such as hardness, the Young's modulus, fracture toughness, yield stress and work hardening exponent of a material. However, these values affect each other and it is necessary to clarify the relations between residual stress and each mechanical property. This study investigates the possibility of separating stress and mechanical properties both experimentally and by numerical calculation using the micro indentation method. For the indentation test using a sharp indenter, it was possible to evaluate stress by comparison of the maximum depth hmax or residual depth hf obtained from the load-depth curve. Furthermore, the 2-dimensional X-ray diffraction method is examined comparatively with the indentation method.