Insights into Engineering Super-Duplex Stainless-Steel Microstructures: Composition Alterations and Processing...

Area of Science:

• Materials Science
• Additive Manufacturing
• Metallurgy

Background:

• Super Duplex Stainless Steel (SDSS) requires specific microstructures for optimal performance.
• Laser Powder Bed Fusion (LPBF) processing of SDSS often results in a predominantly ferritic phase, necessitating post-processing heat treatments.
• Developing in situ methods to control austenite formation during LPBF is crucial for efficient manufacturing.

Purpose of the Study:

• To investigate in situ techniques for enhancing austenite formation in LPBF-processed SDSS.
• To evaluate the effectiveness of layer remelting, increased layer thickness, and compositional modification.
• To eliminate the need for post-process heat treatments in LPBF-manufactured SDSS.

Main Methods:

• Investigated in situ methodologies: layer remelting, increased layer thickness (40 to 80 μm), and 50/50 weight ratio blending of SDSS with SS316L powder.
• Conducted microstructural characterization using techniques such as scanning electron microscopy.
• Performed macro-hardness testing and nanoindentation to assess mechanical properties of austenite and ferrite phases.

Main Results:

• Layer remelting and increased layer thickness did not significantly increase austenite content; microstructures remained largely ferritic.
• Blending SDSS with SS316L powder successfully promoted a significant increase in austenite, forming a duplex microstructure.
• The duplex microstructure exhibited reduced macro-hardness compared to ferritic structures, attributed to compositional changes and reduced solid-solution strengthening.

Conclusions:

• Thermal strategies (layer remelting, increased thickness) are insufficient for achieving desired phase balance in LPBF-processed SDSS.
• Compositional tuning via powder blending is an effective in situ method to promote favorable duplex microstructures in LPBF-processed SDSS.
• Achieving optimal austenite-ferrite balance in LPBF-SDSS can be accomplished through powder metallurgy approaches, bypassing post-processing.