Effect of Compositional Variation Induced by EBM Processing on Deformation Behavior and Phase Stability of Austenitic Cr-Mn-Ni TRIP Steel

Abstract

Electron beam melting (EBM) is an established powder bed-based additive manufacturing process for the fabrication of complex-shaped metallic components. For metastable austenitic Cr-Mn-Ni TRIP steel, the formation of a homogeneous fine-grained microstructure and outstanding damage tolerance have been reported. However, depending on the process parameters, a certain fraction of Mn evaporates. This can have a significant impact on deformation mechanisms as well as kinetics, as was previously shown for as-cast material. Production of chemically graded and, thus, mechanically tailored parts can allow for further advances in terms of freedom of design. The current study presents results on the characterization of the deformation and strain-hardening behavior of chemically tailored Cr-Mn-Ni TRIP steel processed by EBM. Specimens were manufactured with distinct scan strategies, resulting in varying Mn contents, and subsequently tensile tested. Microstructure evolution has been thoroughly examined. Starting from one initial powder, an appropriate scan strategy can be applied to purposefully evaporate Mn and, therefore, adjust strain hardening as well as martensite formation kinetics and ultimate tensile strength.

Microstructural and Mechanical Characterization of Square‐Celled TRIP Steel Honeycomb Structures Produced by Electron Beam Melting

“…[47][48][49] As Mn has a high impact on the γ-phase stability and the SFE of CrMnNi steels, the loss of Mn should be minimized by implementing reduced energy input and at the same time avoiding lack of fusion. [46,50] In the current study, only a slight difference of Mn mass fraction between the highest energy input (G1, 5.17 wt% Mn) and the lowest (H3, 5.46 wt% Mn) was measured. Thus, the driving force for the TRIP effect in the different structures should be comparable.…”

“…The explanation for this effect is the high vapor pressure implying a great susceptibility of Mn to evaporate during handling at elevated temperatures . As Mn has a high impact on the γ ‐phase stability and the SFE of CrMnNi steels, the loss of Mn should be minimized by implementing reduced energy input and at the same time avoiding lack of fusion . In the current study, only a slight difference of Mn mass fraction between the highest energy input (G1, 5.17 wt% Mn) and the lowest (H3, 5.46 wt% Mn) was measured.…”

“…Previous studies showed that the energy input during EBM processing influences the Mn content in the final product . The explanation for this effect is the high vapor pressure implying a great susceptibility of Mn to evaporate during handling at elevated temperatures .…”

“…Previous studies showed that the energy input during EBM processing influences the Mn content in the final product. [20,24,46] The explanation for this effect is the high vapor pressure implying a great susceptibility of Mn to evaporate during handling at elevated temperatures. [47][48][49] As Mn has a high impact on the γ-phase stability and the SFE of CrMnNi steels, the loss of Mn should be minimized by implementing reduced energy input and at the same time avoiding lack of fusion.…”

Adjustment of Mechanical Properties of Medium Manganese Steel Produced by Laser Powder Bed Fusion with a Subsequent Heat Treatment

“…They exhibit solid strength and ductility properties and, in case of the TRIP steels, additionally, a safety buffer by strain hardening in the case of a crash [ 17 ]. Despite their good mechanical properties, they have been hardly investigated in AM [ 18 , 19 , 20 ].…”