Xinfeng Li

Effect of shot peening on hydrogen embrittlement of high strength steel

The effect of shot peening (SP) on hydrogen embrittlement of high strength steel was investigated by electrochemical hydrogen charging, slow strain rate tensile tests, and hydrogen permeation tests. Microstructure observation, microhardness, and X-ray diffraction residual stress studies were also conducted on the steel. The results show that the shot peening specimens exhibit a higher resistance to hydrogen embrittlement in comparison with the no shot peening (NSP) specimens under the same hydrogen-charging current density. In addition, SP treatment sharply decreases the apparent hydrogen diffusivity and increases the subsurface hydrogen concentration. These findings are attributed to the changes in microstructure and compressive residual stress in the surface layer by SP. Scanning electron microscope fractographs reveal that the fracture surface of the NSP specimen exhibits the intergranular and quasi-cleavage mixed fracture modes, whereas the SP specimen shows only the quasi-cleavage fractures under the same hydrogen charging conditions, implying that the SP treatment delays the onset of intergranular fracture.

Failure Analysis and Fatigue Investigation on Titanium Tubes in a Condenser

This paper presents an analysis of condenser titanium tube leakage in nuclear power plants. Chemical compositions, mechanical properties, metallographic structures, and microscopic morphologies were analyzed. The results show that the titanium tube leakage was mainly caused by fatigue failure on the basis of the fatigue fracture features. Fatigue tests had been carried out in both air and steam environments, and the fatigue resistance of titanium tubes decreased distinctly in a steam environment. Based on the investigations, proper recommendations have been proposed to enhance the prevention of fatigue fracture of titanium tubes in condensers.