Effect of aging treatment on the microstructure and tribological properties of a new maraging steel manufactured by laser directed energy deposition

A new maraging steel (NMS) with high Mo element was successfully prepared by laser directional energy deposition(L-DED). Due to the rapid cooling rate, the alloy had sufficient precipitation strengthening potential and did not require solid solution treatment prior to aging. The effects of aging temperatures (450 degrees C, 490 degrees C, 530 degrees C and 570 degrees C) on the microstructure evolution and wear resistance of L-DED NMS were systematically studied. The results showed that the as-built samples contained martensite matrix with trace amount of austenite phase, and the fine cell structure ensured the overall strength of the as-built samples. During the aging treatment, the volume fraction of austenite gradually increased due to the reversal of martensite to austenite. Aging treatment leaded to the formation of Laves-Fe2Mo intermetallic phase, and the Laves-Fe2Mo particles maintain their strength at a high level through Orowan mechanism. The optimum aging condition in this work was 530 degrees C for 5 h, at which the average microhardness was reached to 813 HV0.5, the wear rate was only 7.66 x 10-5 mm3/ (N m), and the wear pattern was mainly abrasive wear and slight adhesive wear. Higher or lower aging temperature led to the decrease of hardness and wear resistance of L-DED NMS, which was primarily due to the change of phase composition and microstructure of L-DED NMS. In addition, the stress distribution after aging treatment was more uniform, which ensured the strength and dimensional stability of the sample.