In additive manufacturing processes, solidification velocities are extremely high in comparison to ordinary directional solidification. Therefore, the dependencies of the primary dendrite arm spacing (PDAS) on the process parameters deviate from the dependencies predicted by standard analytical methods. In this work, we investigate the microstructure evolution and element distribution in Fe-18.9Mn and Fe-18.5Mn-Al-C alloys solidified during the selective laser melting process. A quantitative multicomponent phase-field model verified by Green-function calculations (Karma, Rappel: Phys. Rev. E, 1998, 57, 4323) and the convergence analysis is used. The resulting non-standard dependencies of the PDAS on the process parameters in a wide range of solidification velocities are compared with analytical calculations. It is shown that the numerical values of the PDAS are similar to the values predicted by the Kurz–Fisher method for the low and intermediate solidification velocities and are smaller for the solidification velocities higher than 0.03 m/s. The PDAS and the Mn distribution in a Fe-18.5Mn-Al-C alloy are compared to the experimental results and a very good agreement is found.

We combined electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA) techniques to characterize the microstructure of industrial produced complex-phase CP800 steel. First, three major constituents (ferrite, martensite and bainite) are characterized. Then, transformation-induced dislocation zones in ferrite and bainitic regions consisting of different sub-structures are quantified and segmented. A final digitalized component map including plenty of microstructural features including crystal structures, orientations and elemental distribution are successfully achieved. The precise carbon content is measured in bainite and martensite utilizing EPMA line scans, which is around 0.2 wt% and 0.4 wt%, respectively. In the bainite phase of CP800, a typical Bagaryatski orientation relationship between cementite and lath-like bainitic ferrite is revealed based on the select diffraction patterns of transmission electron microscopy measurements.

The effect of martensitic phase fraction on the cyclic stress-strain behavior of two DP steels is investigated via a micromechanical model based on a representative volume element (RVE). A dislocation density based model and a Chaboche hardening model are used to identify the isotropic and kinematic hardening behavior of constituent phases, respectively. The Chaboche parameters obtained by fitting flow curves computed from a dislocation density based model for both ferrite and martensite phases of each steel are incorporated into a Finite Element code ABAQUS to simulate the low cycle fatigue with a combined hardening behavior. Based on experimental observations reported in the literature, fatigue crack initiates in ferrite phase. A ductile damage model, therefore, is used to simulate damage initiation in ferrite. The results show that the martensite fraction has a significant influence on cyclic plastic strain accumulation during the cyclic deformation. It is also concluded that with an increase in the martensite volume fraction in DP steel, the elastic component of the total strain amplitude increases and higher fatigue strength is, subsequently, observed.

Chapter 1 Steel and Iron Based Alloys Ali Ramazani, Ali Ramazani RWTH Aachen University, Institut für Eisenhüttenkunde (IEHK), Department of Ferrous, Metallurgy, Intzestrasse 1, 52072 Aachen, GermanySearch for more papers by this authorBanu Berme, Banu Berme RWTH Aachen University, Institut für Eisenhüttenkunde (IEHK), Department of Ferrous, Metallurgy, Intzestrasse 1, 52072 Aachen, GermanySearch for more papers by this authorUlrich Prahl, Ulrich Prahl RWTH Aachen University, Institut für Eisenhüttenkunde (IEHK), Department of Ferrous, Metallurgy, Intzestrasse 1, 52072 Aachen, GermanySearch for more papers by this author Ali Ramazani, Ali Ramazani RWTH Aachen University, Institut für Eisenhüttenkunde (IEHK), Department of Ferrous, Metallurgy, Intzestrasse 1, 52072 Aachen, GermanySearch for more papers by this authorBanu Berme, Banu Berme RWTH Aachen University, Institut für Eisenhüttenkunde (IEHK), Department of Ferrous, Metallurgy, Intzestrasse 1, 52072 Aachen, GermanySearch for more papers by this authorUlrich Prahl, Ulrich Prahl RWTH Aachen University, Institut für Eisenhüttenkunde (IEHK), Department of Ferrous, Metallurgy, Intzestrasse 1, 52072 Aachen, GermanySearch for more papers by this author Book Editor(s):Dr.-Ing. Dirk Lehmhus, Dr.-Ing. Dirk Lehmhus University of Bremen, ISIS Sensorial Materials Scientific Centre, Wiener Straße 12, 28359 Bremen, GermanySearch for more papers by this authorProf. Dr.-Ing. Matthias Busse, Prof. Dr.-Ing. Matthias Busse University of Bremen, ISIS Sensorial Materials Scientific Centre and Fraunhofer IFAM, Wiener Str. 12, 28359 Bremen, GermanySearch for more papers by this authorProf. Dr.-Ing. Axel S. Herrmann, Prof. Dr.-Ing. Axel S. Herrmann University Bremen, Faserinstitut Bremen e.V., Am Biologischen Garten 2, 28359 Bremen, GermanySearch for more papers by this authorProf. Dr. Kambiz Kayvantash, Prof. Dr. Kambiz Kayvantash Cranfield University, School of Applied Sciences (SAS), Centre for Automotive Technology, Building 61, Cranfield Campus, Cranfield MK43 0AL, UK CADLM Sarl, 43 rue du Saule Trapu, 91300 Massy, FranceSearch for more papers by this author First published: 12 April 2013 https://doi.org/10.1002/9783527649846.ch1Citations: 4 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter contains sections titled: Introduction Sheet Steels Forging Steels Casting Steel References Citing Literature Structural Materials and Processes in Transportation RelatedInformation

Electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA) measurements are combined to characterize an industrial produced dual-phase steel containing some bainite fraction. High-resolution carbon mappings acquired on a field emission electron microprobe are utilized to validate and improve the identification of the constituents (ferrite, martensite, and bainite) performed by EBSD using the image quality and kernel average misorientation. The combination eliminates the ambiguity between the identification of bainite and transformation-induced dislocation zones, encountered if only the kernel average misorientation is considered. The detection of carbon in high misorientation regions confirms the presence of bainite. These results are corroborated by secondary electron images after nital etching. Limitations of this combined method due to differences between the spatial resolution of EBSD and EPMA are assessed. Moreover, a quantification procedure adapted to carbon analysis is presented and used to measure the carbon concentration in martensite and bainite on a submicrometer scale. From measurements on reference materials, this method gives an accuracy of 0.02 wt% C and a precision better than 0.05 wt% C despite unavoidable effects of hydrocarbon contamination.

The flow behavior of dual-phase (DP) steels is modeled on the finite-element method (FEM) framework on the microscale, considering the effect of the microstructure through the representative volume element (RVE) approach. Two-dimensional RVEs were created from microstructures of experimentally obtained DP steels with various ferrite grain sizes. The flow behavior of single phases was modeled through the dislocation-based work-hardening approach. The volume change during austenite-to-martensite transformation was modeled, and the resultant prestrained areas in the ferrite were considered to be the storage place of transformation-induced, geometrically necessary dislocations (GNDs). The flow curves of DP steels with varying ferrite grain sizes, but constant martensite fractions, were obtained from the literature. The flow curves of simulations that take into account the GND are in better agreement with those of experimental flow curves compared with those of predictions without consideration of the GND. The experimental results obeyed the Hall-Petch relationship between yield stress and flow stress and the simulations predicted this as well.