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A high speed abrasive electrical discharge machining (AEDM-HS) process has been developed to improve the performance and save the machining energy of the conventional EDM process in machining particulate reinforced metal matrix composites (MMCs). The AEDM-HS process functions under a combined action of spark erosion and direct mechanical grinding. A set of experiments was conducted and the results showed that the material removal rate (MRR) of AEDM-HS was much higher than that of EDM under the experimental conditions of this study. Moreover, the surface roughness value (Ra) measured for the AEDM-HS specimen was about six times smaller than that of the specimen machined without high speed abrasive action (i.e., EDM alone). The material removal mechanism of this novel process has been analyzed by means of single-pulse experimentation. And the relative importance of the various processing parameters on MRR was established using orthogonal analysis. The results showed that the MRR is influenced by the machining factors in the order of duty cycle > current > pulse duration. This study showed that the AEDM-HS process is superior to the EDM process for machining particulate reinforced MMCs, where a higher machining efficiency and a better surface quality can be obtained.

The X80 pipeline steel was welded with the way of submerged arc welding. The SST (slow strain test) of the welded joint samples in the air, NACE (National Association of Corrosion Engineers) solution (no H2S), NACE solution (saturated H2S) was performed to research the sensibility index of SCC (stress corrosion cracking) Iscc. The morphologies of the welded joint fractures and the fracture modes were observed with SEM (scanning electron microscope), and the fracture chemical compositions were analyzed with EDS (energy dispersive spectrometer), respectively. The fracture mechanisms of the welded joints were discussed. The results show that sensibility index of SCC in the air is not obvious, the fracture is dimple, and the mode of fracture is ductile fracture. The sensibility index of SCC in NACE solution (no H2S) is 13.21%, the stress corrosion is not obvious. The sample fracture shows quasi cleavage+dimple, and the fracture mode is toughness+brittle rupture. The sensibility index of SCC in NACE solution (saturated H2S) is 56.94%, the plastic loss is the most serious, appearing an obvious stress corrosion tendency, and there is no obvious necking phenomenon. The fracture mode is brittle fracture, and the sample fracture has a high sulfur concentration, prompting S to a aliquation of crisp crystal in the welded zone, and making its mechanical properties worsen.