Textural, Microstructural and Chemical Characterization of Ferritic Stainless Steel Affected by the Gold Dust Defect.

Area of Science:

• Materials Science
• Surface Science
• Metallurgy

Background:

• The gold dust defect (GDD) degrades the appearance of ferritic stainless steels (FSS).
• Previous studies suggest a link between GDD, intergranular corrosion, and the beneficial effect of aluminum addition.
• The precise nature and origin of GDD remain unclear.

Purpose of the Study:

• To elucidate the nature and origin of the gold dust defect in ferritic stainless steels.
• To investigate the microstructural, textural, and chemical characteristics associated with GDD.
• To understand the role of aluminum in mitigating GDD.

Main Methods:

• Detailed electron backscatter diffraction (EBSD) analyses.
• Advanced monochromated electron energy-loss spectroscopy (EELS).
• Machine learning analyses for data interpretation.

Main Results:

• GDD is associated with significant textural, chemical, and microstructural heterogeneities.
• Affected surfaces exhibit an α-fibre texture, indicative of poorly recrystallized FSS.
• Cracks separating elongated grains are enriched in chromium oxides and MnCr2O4 spinel.
• GDD samples have a heterogeneous passive layer, unlike the continuous layer on unaffected samples.
• Aluminum addition improves passive layer quality and GDD resistance.

Conclusions:

• GDD originates from heterogeneities in texture, microstructure, and chemistry.
• The formation of cracks and an unstable passive layer are key factors in GDD.
• Aluminum enhances the passive layer, providing improved resistance to the gold dust defect.