Effects of additive manufacturing processes and isothermal aging on the microstructure and properties of 13-8 Mo precipitation hardening martensitic stainless steel

Abstract

The objective of this study is to evaluate the effect of AM process on the microstructure and properties of PH 13-8 Mo steel in the as-printed and aged conditions. Samples were produced by both laser powder bed fusion (L-PBF) and arc directed energy deposition (arc-DED) and characterized in both the as-printed and direct aged (530 °C, 3 h) conditions. The as-printed L-PBF sample was characterized by a nearly fully martensitic microstructure, while the as-printed arc-DED microstructure included coarser lath martensite, 2.3 vol % retained austenite, and δ-ferrite. However, the hardness of the as-printed arc-DED sample (401.0 HV1) was greater than the as-printed L-PBF (347.7 HV1), due to precipitation of β-NiAl particles in the as-printed arc-DED condition. Aging of the L-PBF sample resulted in microstructure refinement, precipitation of β-NiAl particles, and a corresponding increase in hardness to 508.3 HV1. Conversely, aging the arc-DED sample resulted in the formation of a large amount of reverted austenite (7.2 vol %), Cr23C6 particles, as well as β-NiAl particles, but was unable to remove the δ-ferrite grains. Consequently, the hardness of the aged arc-DED sample was similar to the as-printed value (428.3 HV1). It is concluded that the selection of the AM process has an important effect on the microstructure and properties of PH 13–8 Mo steel, and that a single-step direct aging heat treatment is suitable for samples produced by L-PBF but not arc-DED.

Publication Title

Additive Manufacturing

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