ACOUSTIC EMISSION OF SENSITIZED 304 STAINLESS STEEL WITH SIMULTANEOUS HYDROGEN CHARGING

The tensile deformation of as-received (non-heat treated) 304 stainless steel is known to produce low levels of measurable acoustic emission (AE), which only occur at failure. It is also known that cathodic charging of sensitized 304 stainless steel results in deleterious effects on the mechanical properties, and changes the AE behavior. Tensile deformation of the test sample with simultaneous charging decreases the maximum tensile load (MTL) and failure strain accompanied by a large increase in AE, observed only close to failure. Anomalous behavior occurs when the deformation is stopped after reaching the MTL and held at constant crosshead displacement. With charging maintained throughout the test, the load will decrease to zero with time, producing copious amounts of AE as failure is approached. Without charging until after the MTL is reached, the machine stoppage produces no anomalous behavior either in load or AE. These behaviors are rationalized in terms of grain boundary separation via hydrogen accumulation.