کلیدواژهها
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inclusion, crystallographic texture, electron backscatter diffraction, energy dispersive spectroscopy, kernel average misorientation
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چکیده
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In this study, the surface and cross section of an as-received API X70 pipeline steel was studied by SEM and EDS
techniques in order to categorize the shape and morphology of inclusions. Then, an electrochemical hydrogen
charging using a mixed solution of 0.2 M sulfuric acid and 3 g/l ammonium thiocyanate has been utilized to create
hydrogen cracks in X70 steel. After hydrogen charging experiments, the cross section of this steel has been accurately
checked by SEM in order to find out hydrogen cracks. The region of hydrogen cracks was investigated by
SEM and EBSD techniques to predict the role of different microstructural parameters involving hydrogen induced
cracking (HIC) phenomenon. The results showed that inclusions were randomly distributed in the cross section of
tested specimens. Moreover, different types of inclusions in as-received X70 steel were found. However, only
inclusions which were hard, brittle and incoherent with the metal matrix, such as manganese sulfide and carbonitride
precipitates, were recognized to be harmful to HIC phenomenon. Moreover, HIC cracks propagate dominantly
in transgraular manner through differently oriented grains with no clear preferential trend. Moreover, a
different type of HIC crack with about 15-20 degrees of deviation from the rolling direction was found and studied
by EBSD technique and role of micro-texture parameters on HIC was discussed.
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