Effect of heat treatment on microstructure and corrosion behavior of 17-4 PH stainless steel fabricated via metal material extrusion additive manufacturing

초록

This study investigates the effect of H900 heat treatment on the microstructure and corrosion behavior of 17-4 PH stainless steel fabricated via metal material extrusion (MEX) additive manufacturing. Samples were produced through the MEX process, and the as-sintered condition was compared against specimens subjected to a standard H900 heat treatment. Corrosion properties were systematically evaluated using cyclic potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5 wt% NaCl solution, coupled with multi-scale microstructural characterization. The as-sintered samples exhibited approximately 2.6 % porosity and oxide inclusions, along with Cu segregation at delta-Fe/martensite phase boundary, and 10-20 nm Cu-rich precipitates (CRPs). While heat treatment did not significantly alter the defect fraction, it refined the martensitic grain structure, eliminated Cu segregation, promoted additional NbC precipitation, and modified the CRPs into finer, coherent particles. Consequently, the H900 specimen demonstrated superior corrosion resistance, evidenced by an increase in the corrosion potential by approximately +0.04 V and the breakdown potential by approximately +0.13 V. Post-corrosion analysis revealed that pores and oxide inclusions acted as primary sites for pitting corrosion. The enhanced corrosion resistance of the H900 specimen is attributed to the formation of a denser, more stable passive film, resulting from microstructural homogenization, grain refinement, and the elimination of a Cr-depleted zone beneath the film. These findings confirm that heat treatment is critical for optimizing the performance of MEX-fabricated 17-4 PH steel.

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