Hot Compression of Additively Manufactured Martensitic Stainless Steels
Ayda Shahriari (University of New Brunswick)
Shokat Keshavarzi (University of New Brunswick)
Foroozan Forooghi (University of New Brunswick)
Mohsen Keshavarzan (University of New Brunswick)
Amir Hadadzadeh (University of New Brunswick, University of Memphis)
Mehdi Sanjari (University of New Brunswick, Natural Resources Canada)
Hadi Pirgazi (Universiteit Gent)
Leo A.I. Kestens (Universiteit Gent, TU Delft - Mechanical Engineering)
Babak Shalchi Amirkhiz (University of New Brunswick, Natural Resources Canada)
Nana Ofori-Opoku (McMaster University)
M. A. Wells (University of Waterloo)
Mohsen Mohammadi (University of New Brunswick)
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Abstract
Understanding the hot deformation behavior of metallic components produced via additive manufacturing (AM) is crucial, especially for applications in dynamic loads and high temperatures. This research examines the hot compression behavior of a martensitic precipitated hardened stainless steel, known as CX SS, produced through laser powder bed fusion (LPBF). Microstructural evolutions were examined on two sample types—as-built and heat-treated—subjected to hot compression at a constant 1 s−1 strain rate within the temperature range of 300 °C to 650 °C. The impact of microstructural features such as cellular solidification subgrains, nanoscale NiAl precipitates, and the austenite reversion transformation on dynamic recovery (DRV) and dynamic recrystallization (DRX) as mechanisms of restoration is explored using electron backscattered diffraction (EBSD) techniques. A comparison between two sample types revealed that the presence of cellular solidification substructure in the as-built samples delays the restoration mechanism compared to heat-treated samples. Furthermore, LPBF CX specimens in the as-built state and after heat-treatment process exhibit nearly identical deformation behavior at temperatures above 450 °C. This identical deformation behavior is associated with the partial or complete destruction of cells in the as-built samples and the dissolution of NiAl particles in heat-treated ones. The dynamic softening mechanism primarily stems from DRV and partial DRX. Although discontinuous dynamic recrystallization (DDRX) was alleviated in heat-treated samples, the as-built CX SS also showed softening mechanism in form of continuous dynamic recrystallization (CDRX) accompanied by DDRX. A constitutive equation of Arrhenius model, including Zener–Hollomon parameters, evaluated strain accumulation during hot deformation, identifying regions prone to shear bands (SBs), microcracks, and voids.