Defects and Properties of Cast Metals: Cast Iron & Steel
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Solidification Committee
Program Organizers: Lang Yuan, University of South Carolina; Brian Thomas, Colorado School of Mines; Peter Lee, University College London; Mark Jolly, Cranfield University; Alex Plotkowski, Oak Ridge National Laboratory; Charles Monroe, University of Alabama Tuscaloosa

Wednesday 8:30 AM
February 26, 2020
Room: 17B
Location: San Diego Convention Ctr

Session Chair: Charles Monroe, The University of Alabama at Birmingham

8:30 AM
In-situ Synchrotron Examination of the Evolution and Transition of Nodular, Compacted and Laminar Graphite During Solidification of Cast Iron: Chaoling Xu¹; Mohammed Azeem²; Tim Wigger³; Tito Andriollo¹; Samuel Clark⁴; Zhixuan Gong²; Zhixuan Gong³; Robert Atwood⁵; Peter Lee³; Niels Tiedje¹; ¹Technical University of Denmark; ²University of Leicester; ³University College London; ⁴University College, London; ⁵Diamond Light Source
    In cast iron, graphite particles nucleate and grow simultaneously with the austenite matrix during solidification. The alloy composition and cooling rate are pivotal parameters controlling morphology and distribution of the graphite phase, and thus the resultant mechanical properties of the material. In-situ time resolved synchrotron tomography was used to dynamically capture the evolution of three different morphologies of graphite during solidification: nodular, compacted and laminar graphite. By running various thermal cycles, the precipitation kinetics and the transitions between different graphite morphologies were quantitatively evaluated for the first time. With ex-situ cyclic heating experiments, computed tomography, SEM and energy-dispersive X-ray spectroscopy, a correlation between formation of different graphite types and changes in chemical composition and cooling rates is established. These results provide invaluable data for the validation and development of predictive numerical models and give insights for the further understanding of solidification kinetics and design of advanced cast iron alloys.

8:50 AM
The 3D Correlation of Si Segregation to Nodules Size, Nodules Spatial Distribution and Local Mechanical Strain in Ductile Cast Iron: Chaoling Xu¹; Tito Andriollo¹; Yubin Zhang¹; Fengxiang Lin²; Juan-Carlos Hernando²; Jesper Hattel¹; Niels Tiedje¹; ¹Technical University of Denmark; ²Jönköping University
    Alloying elements such as Si, Mn and Mo are frequently added to ductile cast iron (DCI) for the improvement of mechanical properties. Additionally, the segregation of these elements is strongly affected by the chronology of formation of the graphite nodules and of metallic matrix during solidification. For the first time, computed tomography, energy-dispersive X-ray spectroscopy (EDS) and digital volume correlation were used to quantitatively investigate the correlation of Si segregation to the size and spatial distribution of the nodules as well as to the 3D mechanical strain pattern arising during tensile loading. Furthermore, immersion color etching sensitive to Si segregation was employed to generate 2D Si segregation maps to support the outcome of the EDS analysis. The results provide fundamental knowledge about the mechanism and chronology of microstructure formation in 3D space and shed light on how the segregation can affect the mechanical response of DCI at the microstructural level.

9:10 AM
Influence of Composition on the Solidification and Weldability of Cast Austenitic Stainless Steels: Sean Orzolek¹; John DuPont¹; ¹Lehigh University
    Austenitic stainless steels such as 0.4C-25Cr-35Ni-1Nb, HP-Nb alloys are commonly used in high temperature applications above 850°C and exhibit superior creep properties due to chromium and niobium carbide precipitation strengthening. However, the high carbide content increases the susceptibility to hot cracking during welding and riser removal. The microstructure is a result of the solidification conditions and composition of the alloy, however, limited studies have focused on the solidification of HP-Nb alloys. Therefore, the objective of this study is to improve the understanding of the solidification in the C-Cr-Nb-γ pseudo-quaternary system in order to improve the weldability of HP-Nb alloys. In this study, a systematic matrix of 30 alloys are evaluated in order to determine the influence of composition on the solidification path and resultant microstructure. High temperature mechanical testing using a GleebleŠ is used to relate the composition and microstructure to the weldability and susceptibility to hot cracking during fabrication.