Aging Behaviour of a 12.2Cr-10Ni-1Mo-1Ti-0.6Al Precipitation-Hardening Stainless Steel Manufactured via Laser Powder Bed Fusion

Alessandro Morri; Mattia Zanni; Lorella Ceschini; Alessandro Fortunato; Massimo Pellizzari

doi:10.3390/met13091552

Metals (Sep 2023)

Aging Behaviour of a 12.2Cr-10Ni-1Mo-1Ti-0.6Al Precipitation-Hardening Stainless Steel Manufactured via Laser Powder Bed Fusion

Alessandro Morri,
Mattia Zanni,
Lorella Ceschini,
Alessandro Fortunato,
Massimo Pellizzari

Affiliations

Alessandro Morri: Department of Industrial Engineering (DIN), Alma Mater Studiorum—University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
Mattia Zanni: Department of Industrial Engineering (DIN), Alma Mater Studiorum—University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
Lorella Ceschini: Department of Industrial Engineering (DIN), Alma Mater Studiorum—University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
Alessandro Fortunato: Department of Industrial Engineering (DIN), Alma Mater Studiorum—University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
Massimo Pellizzari: Department of Industrial Engineering, University of Trento, Via Sommarive 9, 38123 Trento, Italy

DOI: https://doi.org/10.3390/met13091552
Journal volume & issue: Vol. 13, no. 9
p. 1552

Abstract

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The combination of precipitation-hardening stainless steels (PH-SS) and laser powder bed fusion (LPBF) enables the manufacturing of tools for plastic injection moulding with optimised geometry and conformal cooling channels, with potential benefits in terms of productivity, part quality, and tool duration. Moreover, the suitability of LPBF-manufactured PH-SS in the as-built (AB) condition to be age-hardened through a direct aging (DA) treatment enables a great heat treatment simplification with respect to the traditional solution annealing and aging treatment (SA). However, plastic injection moulding tools experience severe thermal cycles during their service, which can lead to over-aging of PH-SS and thus shorten tool life. Therefore, proper thermal stability is required to ensure adequate tool life and reliability. The aim of the present work is to investigate the aging and over-aging behaviour of a commercially available PH-SS (AMPO M789) manufactured by LPBF in the AB condition and after a solution-annealing treatment in order to evaluate the effect of the heat treatment condition on the microstructure and the aging and over-aging response, aiming at assessing its feasibility for plastic injection moulding applications. The AB microstructure features melt pool borders, oriented martensite grains, and a cellular solidification sub-structure, and was retained during aging and over-aging. On the other hand, a homogeneous and isotropic martensite structure was present after solution annealing and quenching, with no melt pool borders, cellular structure, or oriented grains. The results indicate no significant difference between AB and solution-annealed and quenched specimens in terms of aging and over-aging behaviour and peak hardness (in the range 580–600 HV), despite the considerably different microstructures. Over-aging was attributed to both the coarsening of strengthening precipitates and martensite-to-austenite reversion (up to ~11 vol.%) upon prolonged exposure to high temperature. Based on the results, guidelines to aid the selection of the most suitable heat treatment procedure are proposed.

Published in Metals

ISSN: 2075-4701 (Online)
Publisher: MDPI AG
Country of publisher: Switzerland
LCC subjects: Technology: Mining engineering. Metallurgy
Website: http://www.mdpi.com/journal/metals

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