J.J. Chen

Bio: J.J. Chen is an academic researcher from National Taiwan Ocean University. The author has contributed to research in topics: Paris' law & Crack closure. The author has an hindex of 1, co-authored 1 publications receiving 25 citations.

Microstructure and mechanical properties of annealed SUS 304H austenitic stainless steel with copper

Abstract: An experimental investigation into the effect of Cu on the mechanical properties of 0 and 3 wt.% Cu added SUS 304H austenitic stainless steel upon annealing at 700 °C for up to 100 h was conducted. Optical microscopy reveals grain coarsening in both the alloys upon annealing. Observations by transmission electron microscopy revealed the precipitation of nanometer-sized spherical Cu particles distributed within the austenitic grains and the presence of carbides at the dislocations. Both the yield and ultimate tensile strengths of the alloys were found to remain invariant with annealing. Tensile ductility and the threshold stress intensity factor range for fatigue crack growth for 3 wt.% Cu added alloy increase with annealing. These are attributed to the grain coarsening with annealing. In all, the addition of Cu to SUS 304H does not affect the mechanical performance adversely while improving creep resistance.

Effect of microstructure on hydrogen embrittlement of various stainless steels

Abstract: This work investigated the effect of microstructure on the susceptibility of 304L (metastable), 310S (stable) austenitic and 410 martensitic stainless steels (SSs) to hydrogen embrittlement (HE). Slow-displacement-rate notched tensile tests were performed at various combinations of temperature (25 and 80 °C) and environment (air and H 2 ) to evaluate the relative HE susceptibility of these alloys. At 25 °C, the untempered 410 SS was the specimen most susceptible to HE among the investigated specimens, whereas the 310S and tempered 410 specimens exhibited low HE susceptibility. The formation of strain-induced α′-martensite in a localized region in front of the notch tip was the main cause for the high HE susceptibility of the 304L SS tested at 25 °C. In general, the HE susceptibility was reduced to various degrees for specimens tested at 80 °C. A significantly lower susceptibility to HE was observed for the 304L specimen at 80 °C due to the suppressed formation of α′-martensite in the highly strained region.

Numerical simulation of the effects of residual stress on the concentration of hydrogen around a crack tip

Abstract: For this study we used finite element analysis to show how the residual stress affects the hydrogen concentration around a crack tip in a plastically deformable material after a fatigue process. Following a 9 cycle fatigue process, hydrogen diffusion analysis was carried out at the highest applied fatigue stress. This showed hydrogen invading the crack surface and diffusing into the material. The concentration of hydrogen was higher close to the crack tip and its behavior was largely affected by the residual stress in the material. Tensile residual stress accelerated the hydrogen invasion and increased its concentration, while compressive residual stress simulated as the stress induced by peening clearly suppressed them. This is due to the affect the residual stress has on the hydrostatic stress around the crack tip which is a dominant factor in the hydrogen diffusion behavior. Peening, which is a surface treatment used to introduce compressive residual stress to enhance the mechanical properties of a material, such as its resistance to stress corrosion cracking and its fatigue strength, may, therefore, suppress the embrittlement caused by hydrogen.