Uniformly sized, iron-based, foreign metallic contaminant 0.028 inches deep
We performed an analysis on defects in a 304 Stainless Steel mixer. The defects were identified as a uniformly sized, iron-based, foreign metallic contaminant 0.028 inches deep, containing approximately 3% nickel and 6% chromium.
Metallurgical bonding at the defect-to-base metal interface indicates the defects became incorporated into the plate during thermo-mechanical processing. The shallow nature of the defects, along with a significantly higher hardness than the base material, should allow for defect removal and weld repair without structural damage to the vessel.
SEM images with corresponding EDS line scan data showed compositional variability at the base metal / defect interface. The line scan data also showed elemental compositions across the defect and the base metal, indicating the chromium and nickel was initially present in the contamination.
We concluded that the defects are consistent with a foreign metallic contaminant that got incorporated during hot working processing, such as would occur at the slab/plate rolling facility during rolling of these plates.
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