Cavitation erosion damage behaviors in the coolant of electroless nickel plated diesel engine cylinder liners were investigated. In the case of electroless nickel coating, pitting damage was locally induced by cavitation erosion attacks. The pitting damage was promoted as galvanic corrosion accompanied it. Continued cavitation erosion attacks led to the plastic deformation, fatigue, and failure of electroless nickel coating. Consequently, local pitting damage to electroless nickel coating showed a tendency to progress in the depth direction so that the surface damage depth developed greatly.

In the present study, a high strength steel for offshore wind turbine tower substructure was submitted to tensile load using slow strain rate technique to evaluate fracture characteristics of the steel with application of electrochemical potentials ranging from free corrosion potential to-1.2 V in natural seawater. The results of the study revealed that the fracture characteristics of the steel changed drastically with different applied potentials. The failure time ratio was 0.5 or less in the potential range of-1.0 V to-1.20 V due to hydrogen evolution. The fractured surface after the slow strain rate test indicated that the brittle fracture tendency was prevalent in the potential region corresponding to the hydrogen embrittlement. It is concluded that cathodic overprotection exceeding-1.2 V may lead to brittle fracture of the offshore steel structure.

Thermal aging was conducted at 650 • C until 1,000 h under the atmospheric environment to evaluate the degradation characteristics of microstructure and mechanical properties of 9Cr-1MoVNb steel. The analysis of the microstructure and carbide of aged specimens was conducted by scanning electron microscopy and energy dispersive X-ray spectroscopy. The mechanical properties were evaluated by tensile and Vickers hardness tests. In addition, fractured tensile specimens were characterized by using scanning electron microscopy and energy dispersive X-ray spectroscopy to observe the changes in fracture mode with aging time. As a result, loss of martensite lath, coarsening of M23C6 carbide, and precipitation of Laves phase were observed after aging for 100 h. Degradation leads to deterioration in mechanical properties due to the effect of the nucleation and coarsening of Cr-rich M23C6 carbide. However, the change in fracture mode was more affected by the Laves phase (Fe2Mo) than the M23C6.

This study investigated the effect of temperature and time on the sensitization behavior of alloy 600. A doubleloop electrochemical potentiokinetic reactivation test was conducted to evaluate the degree of sensitization (DOS) in 0.1 M H2SO4 + 0.001 M potassium thiocyanate solution. The microstructure and surface damages of the aged specimens were characterized by optical microscope, scanning electron microscope, and energy dispersive X-ray spectroscopy. As a result of the experiment, the sensitization behavior was significantly influenced by the expansion of the Cr-depleted zone and Cr-diffusion rate depending on the aging temperature. In particular, the alloy 600 aged for 300 h or longer at 650 • C represented a very low DOS value of 3% or less, and its resistance against intergranular corrosion greatly improved.