Improvement of Corrosion Resistance of Maraging Steel Manufactured by Selective Laser Melting Through Intercritical Heat Treatment

Abstract

Selective laser melting allows the layerwise fabrication of bespoke designs, creating new prospects in applications and properties compared to conventional methods. Like other ultra-high-strength steels, maraging steels offer a high toughness/strength ratio. However, additively prepared maraging steels’ lower ductility and strain-hardening limit their commercial adaptability. Studies exist that show superior mechanical performance is attainable through martensite-to-austenite reversion. However, their impact on corrosion properties is not well understood. In the present study, maraging steel specimens were tempered close to austenite forming temperatures to investigate the reversed austenite effect on maraging steels’ pitting behavior. X-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy were used to characterize selective laser melting samples’ microstructure. To characterize and analyze the pitting performance, potentiodynamic polarization and open-circuit potential were performed in a 3.5 wt% NaCl solution. The intercritical heat-treatment within α’ + γ range of 720°C shows that reversed austenite precipitated mainly along the martensite laths boundaries. The local Ni enrichment as a result of intermetallic particles’ dissolution enables the nucleation of reversed austenite. As a result, the 720°C-tempered specimen exhibits a higher pitting potential, lower corrosion current density, and lower corrosion rate than the as-printed, aged, and homogenized (without reversed austenite) specimens. This study shows that the reversed austenite enhances the pitting resistance of maraging steels.