In this study we investigate the microstructure and the corrosion performance of an 18Ni 300 maraging steel after prepared by selective laser melting (SLM) technique and the effects of by aging. The rolling manufactured 18 Ni 300 maraging steel followed by aging acts as a comparison. The SLM specimens showed fine microstructures with homogeneous cellular and column dendrites, which resulted in relative uniform corrosion, while the conventionally rolled specimens displayed a typical lath martensite microstructure. The aging treatment accelerated corrosion rate possibly due to the galvanic corrosion between intermetallic precipitates Ni3(Ti, Mo) and martensite matrix, as well as the corrosion of Ni and Co which diffuses into matrix. The formation of un-melted particles made of (Al, Ti)O during the SLM process are deleterious to the corrosion resistance as they lead to localized attack. The long term immersion makes for the accumulation of thick and corrosion product layer which prevents further dissolution of metal substrate by preventing oxygen and ion species from contacting metals.

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