| Summary: | 碩士 === 長庚大學 === 機械工程研究所 === 86 === Abstract
The microstructure and anodic polarization behavior on the surface of martensitic stainless steel （DIN 1.2316） multi-cut by WEDM is studied. For the microstructure investigation, the result shows that the intergrannular cracks on the surface of the as-quenched specimen was found after rough cutting, but the crack initiation could be avoided by tempering above 200℃. The porous recast layer created by rough cutting contains multiple phases with amorphous layer, wire electrode deposited droplets, laminar eutectoidic structure and martensite. The deposition from the wire electrode material in the recast layer was observed. On the top of the recast layer, a thin amorphous layer found contains many small deposits of wire electrode with the size less than 10nm in diameter. However, inside the recast layer larger spherical droplets (> 50 nm ) is observed. Beneath the recast is a white layer consisting of lath and twin martensite. On the other hand, high density of the spherical deposition of wire electrode about 60-100 nm in diameter and the oxide formation is found in circumference of the deposition for fine cut surface at some local areas on the surface. Auto-tempering in martensitic structure is also found by 2nd finishing cut. A lot of deposition of wire electrode material on the surface after 5th finishing cut with passive polarity was found. However, the electrode deposition zone is less than 100 nm from the top of finishing surface.
Anodic polarization behavior of WEDMed surface is studied in both sulfuric and perchloric acid solutions containing 0.2 wt% sodium chloride. On the 1st rough cutting surface, which has porous profile and the high density of deposition of wire electrode, it is shown that the highest anodic passive current density and contains secondary anodic peak on the anodic polarization in both solutions. But in sulfuric acid solution the difference of the anodic polarization on the other finishing cut surface can not be identified. On the other hand, in perchloric acid solution the difference can be observed.
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