## 1 Introduction
While the two main authoritative reviews published in 2017 [4] and 2021 [3] on low-density steels have concluded that these alloys are very promising for automotive, structural, and cryogenic applications, they pointed out that they have hardly been used in the aforementioned applications because of several reasons, including low elastic modulus, processing problems associated with high Al and Mn content, and the limited experimental results on formability, weldability, and coatability. Despite this, the authors of this work have considered the low elastic modulus and light weight of low-density steels as attractive properties for biomedical applications. Additionally, the amenability to conventional processing techniques and cheap manufacturing costs would validate the exploration of low-density steels as alternative bio-implant materials. Therefore, by building on the findings of [PERSON] et al. [5], we hypothesized that some grades of Cr-bearing low-density steels could be promising for orthopedic implant applications. This served as the basis for studying Fe-30.9 Mn-4.9 Al-4.5 Cr-0.4C and Fe-21.3 Mn-7.6 Al-4.3 Cr-1C low-density stainless steels. The use of stainless steels in the biomedical industry is not a new concept; it was first used in the 1920s, and its success paved the way for treating human bone fractures [6; 7]. Some common metallic biomaterials of preference are AISI 316L stainless steels, Co-Cr alloys, and Ti-6 Al-4V alloys [8]. The limitations of these common orthopedic implant alloys include the high cost and toxicity of Co-Cr and Ti-6 Al-4V alloys and the high density of AISI 316L stainless steels (8.03 g/cm\({}^{3}\)) compared to the density of human cortical bone (0.96 to 1.9 g/cm\({}^{3}\)) [9]. Low-density stainless steels considered in this study may replace expensive titanium alloys, and highly dense 316L stainless steel should have good corrosion resistance. Consequently, a preliminary corrosion investigation was conducted on different compositions of as-cast low-density stainless steels immersed in simulated body fluids (0.9 wt% NaCl and Hanks Balanced Salt Solution). Their corrosion rates were compared with AISI 316L stainless steel exposed to the same solutions. The as-cast low-density stainless steels had a dendritic structure with carbides forming at the inter-dendritic region of the austenite matrix [10]. The results show that the two alloys of focus in this study have a lower corrosion rate than commercial-grade AISI 316L stainless steel in simulated body fluids. However, they were still susceptible to pitting corrosion, localized in the interdendritic region of as-cast low-density stainless steels (see Supplementary Figure S1). [PERSON] et al. [11] also reported pitting corrosion in their austenitic Fe-Mn-Al-Cr-C steels in NaCl and NaOH solutions. However, the composition and microstructure of their alloys differ from those presented in this study. Prior to corrosion studies, their alloys were subjected to thermal treatment so that their starting microstructure had an equiaxed morphology. In addition to uniform corrosion, uniformly distributed pits were seen in the alloys owing to the dissolution of Fe and Mn. Their findings differ from ours in that pitting corrosion occurred preferentially at the carbide-austenite interface and the interdendritic regions. Therefore, we envisaged that the corrosion performance of the two low-density stainless steels, Fe-30.9 Mn-4.9 Al-4.5 Cr-0.4C and Fe-21.3 Mn-7.6 Al-4.3 Cr-1C, could be enhanced further if the as-cast dendritic structure is broken down using thermomechanical processing techniques. [PERSON] [3] reported that microstructural control is necessary for property optimization in Fe-Mn-Al-C alloys. However, as the response of Fe-30.9 Mn-4.9 Al-4.5 Cr-0.4C and Fe-21.3 Mn-7.6 Al-4.3 Cr-1C alloys to deformation parameters has not been previously reported, it is important to understand their hot working behavior.