**1. Introduction**

The steel industry is playing an important role in providing about 45% of the raw material to the automotive sector [1]. The advancement in the steel parts used in an automobile is inevitable to competitively improve the strength to weight ratio, fuel economy, and crash safety of cars. Researchers have studied various multi-phase steels to increase the ultimate tensile strength (UTS) and percentage elongation of steels using different thermo-mechanical methods and phase combinations [2,3].

The ever-increasing demand for lightweight materials for the mobility sector has promoted the utilization of the multi-phase phenomenon in steel [4]. For instance, quenched and partitioned (Q&P) steels have shown a UTS up to 1.4 GPa with a uniform elongation of up to 20% [5]. This remarkable combination is desirable during steel formation into sheets and during individual component making with application-based mechanical strength capabilities. Small-sized hard phase inclusions added into the soft ferrite matrix during steel making act as reinforcement participants [6–8]. The common inclusions in the ferrite matrix—i.e., alumina (Al2O3), cementite (Fe3C), manganese sulfide (MnS), and pyrite (Fe2S)—are very small in size,

**Citation:** Qayyum, F.; Umar, M.; Elagin, V.; Kirschner, M.; Hoffmann, F.; Guk, S.; Prahl, U. Influence of Non-Metallic Inclusions on Local Deformation and Damage Behavior of Modified 16MnCrS5 Steel. *Crystals* **2022**, *12*, 281. https://doi.org/ 10.3390/cryst12020281

Academic Editor: Mingyi Zheng

Received: 31 January 2022 Accepted: 15 February 2022 Published: 18 February 2022

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in the micron range [9–11]. Alloy steel thus formed with this microstructure, called gear steel, has good machinability and improved hardenability [12,13]. Post-carburizing-quenching casehardened parts are used in an automobile where a core tensile strength of 800–1100 MPa is needed. Their good wear resistance and low-temperature impact toughness make them usable for piston bolts, camshaft levers, gears, worms, seals, and other sleeve parts [14].

The particle size, distribution, and morphology have a grea<sup>t</sup> effect on the overall mechanical properties of these steels [15,16]. MnS with better plasticity and major inclusions in desulphurized alloy steels affects the mechanical anisotropy after being rolled into elongated strips [6]. The deoxidation of the molten steel produces Al2O3; being hard, it can act to initiate microcracks and as a propagation source during the application of a load on the component [17]. Moreover, Al2O3 can also cause excessive wear of the tool during the machining of the component. Therefore, understanding, controlling, and utilizing the limiting effects of these two inclusions can assist in the material forming processes and producing application-based materials [18–20].

A crystal plasticity-based microstructural approach for investigating material behavior is comparatively more accurate than empirical and phenomenological studies [21–23]. The large-scale crystal plasticity finite element method (CPFEM), with multiple calculation points in a single orientation, can evaluate the average mechanical response of a polycrystalline material. An added advantage of this type of modeling and simulation is the analysis of the local stress and strain behavior to mitigate the concentrations and prolong the global elongation process [24,25].

Although large-scale CPFEM methods are considered important for the true behavior recognition of multi-phase materials, the literature has limited results that can be applied satisfactorily to the mass production of parts [26–31]. Recently, DP steel (martensite in a ferrite matrix) has been studied using the relaxed grain cluster homogenization technique using the Düsseldorf Advanced Material Simulation Kit (DAMASK) [32–34]. The results gave an interesting insight into microstructural evolution during the deformation of heterogeneous multi-phase materials. However, there is still a need for extensive study based on individual phase constituents in the steel matrix to reach a point where industrially required process maps can be generated and utilized for microstructurally informed material production.

This study is a unique combination of various techniques to evaluate the micromechanical response of polycrystalline multi-phase material. Industrially produced modified 16MnCrS5 with alumina, pyrite, and cementite as precipitate phase particles spread all over the ferrite matrix has been used as a starting material. An EBSD map has been generated, and in situ tensile deformation has been performed while recording the local material state at various global stress values. A crystal plasticity-based numerical simulation model built on finite strain theory has been used to study slip-based plastic deformation in a ferrite matrix. The correlation of simulation results with the experimental obtained local material behavior is studied and presented.

The manuscript has been categorized so that Section 1 presents the introduction and background of the study. Section 2 has very brief information about the experimental procedures. The modeling technique with the current numerical simulation procedure with boundary conditions is mentioned in Section 3, while the results are detailed in Section 4. Finally, Section 5 gives a complete discussion of the results compared to the already published literature, while the study's conclusions are presented in Section 6.
