Phase Transformations and Microstructural Evolution: Phase Transformations in Ferrous Alloys
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Yufeng Zheng, University of North Texas; Rongpei Shi, Harbin Institute of Technology; Stoichko Antonov, University of Science and Technology Beijing; Yipeng Gao, Jilin University; Rajarshi Banerjee, University of North Texas; Yongmei Jin, Michigan Technological University
Wednesday 8:30 AM
February 26, 2020
Room: 33B
Location: San Diego Convention Ctr
Session Chair: Leslie Mushongera, University of Nevada Reno
8:30 AM
Coupled Grain Structure and Carbide Evolution during Rapid Thermal Cycling of an Fe-Cr-C Steel: Bala Radhakrishnan1; Younggil Song1; Gary Cola2; 1Oak Ridge National Laboratory; 2SFP Works, LLC
Excellent combinations of high strength and ductility have been achieved by rapid-thermal processing of low-alloy steels. The commercial Flash(TM) process produces a compositional heterogeneity in the microstructure resulting from dissolving carbides in austenite as it forms and grows at the carbide-ferrite matrix interface. The resulting on-cooling phase transformations lead to a bainite+martensite+austenite microstructure. The microstructural environment of the carbide particles during the thermal cycle is governed by their interaction with the evolving grain boundaries, resulting in intragranular or inter-granular dissolution with uniquely differing kinetics and solute profiles. We present phase field simulations of carbide and grain structure evolution in a polycrystal to capture the effect of processing parameters on the resulting patterns of heterogeneity in the microstructure prior to bainitic/martensitic transformation. Research performed at ORNL under contract DE-AC05-00OR22725 and supported by the Advanced Manufacturing Office through the HPC for Manufacturing Program at the Department of Energy.
8:50 AM
Pearlite in Multicomponent Steels: Phenomenological Steady-state Modeling: Jiayi Yan1; John Ågren1; Johan Jeppsson1; Kaisheng Wu2; 1Thermo-Calc Software AB; 2Thermo-Calc Software Inc
A steady-state model for austenite-to-pearlite transformation in multicomponent steel is presented, including Fe, C, and eight more elements. The model considers classic ingredients but also finite austenite-pearlite interfacial mobility which resolves some previous difficulties. A transition between orthopearlite and parapearlite is realized by optimizing the partitioning of substitutional alloying elements under constrained carbon equilibrium between ferrite and cementite. Solute drag effect is included to account for the bay in growth rate curves. Grain boundary nucleation rate is modeled as a function of chemical composition, driving force, and temperature, with consideration of grain boundary equilibrium segregation. Overall transformation kinetics is obtained from growth rate and grain boundary nucleation rate, assuming pearlite colonies only nucleate on austenite grain boundaries. Further theoretical and experimental work are suggested for generalization and improvements.
9:10 AM
Novel Alloy Design Strategies for High Strength Car Body Parts Manufactured by Superplastic Forming: Lukas Stemper1; Paul Oberhauser2; Peter Uggowitzer1; Stefan Pogatscher1; 1Montanuniversitaet Leoben; 2AMAG Rolling GmbH
Over the last decades the evolution of transportation and traffic has significantly challenged the automotive industry due to the negative environmental aspects coming along with these changes. Light-weight construction and increased demand on design flexibility has led to the development of new aluminum-based materials capable of replacing heavy and, therefore, unbeneficial materials and offering new possibilities towards increasing freedom of design. Progress has been made by the development of 5xxx-series aluminum alloys offering superplastic formability and, therefore, enabling the production of outer car body parts with high demands on formability and complexity. A major drawback of commonly used alloys for such forming operations is their relatively low strength in operation.This study investigates novel alloy design strategies offering increased strength without negatively affecting the superior formability. Detailed investigations on thermomechanical treatment and microstructure evolution are performed in this study.
9:30 AM
Microstructural and Mechanical Characterization of Cast Austenitic Stainless Steel Alloyed with Si: Prince Setia1; R Sarvesha1; Aditya Gokhale2; Thomas Tharrian3; T Venkateswaran3; Sudhanshu Shekhar Singh1; Shashank Shekhar1; 1Indian Institute of Technology Kanpur; 2Indian Institute of Technology Delhi; 3Indian Space Research Organization
High-silicon stainless steel, abbreviated as ‘Silicolloy’, has earned importance owing to their excellent set of properties. In this study, effect of Si content (up to 6 wt%) on the microstructure and mechanical properties of 15kh18N12C4TЮ (yu) silicon steel has been studied. Microstructural characterization was performed by using a combination of SEM, EDS and EBSD. Increasing the Si content led to change in the microstructure from ~100% austenite (γ) to 66% ferrite (α) + 34% austenite (γ). Further, SEM and EDS results confirmed the presence of (Ti,V) carbo nitride precipitates in all grades of FeSi alloy. The EBSD and nano-indentation were conducted to establish the correlation between nano-mechanical properties, such as hardness (H)/modulus (E) and orientation of grains along with the determination of mechanical properties of the individual phases. Uniaxial tensile testing and fractography were carried out to quantify the flow behavior and understand the deformation mechanism and will be discussed.
9:50 AM Break
10:10 AM
Rapid Solidification of Austenitic Stainless Steels by Splat Quenching: Sydney Morales1; Zachary Hasenbusch1; Luke Brewer1; Laurentiu Nastac1; Andrew Deal2; Ben Brown2; 1University of Alabama Tuscaloosa; 2Kansas City National Security Campus
This presentation will discuss the observed phase transformations and microstructural evolution that accompany rapid solidification of austenitic stainless steels by splat quenching. Splat quenching is a method that is comparable in cooling rates to fusion-based additive manufacturing but with greater control over the solidification process. This talk will describe the changes in solidification behavior for five different chemistries of 316L stainless steel with intentional variation of Cr/Ni equivalences. The starting alloys were produced via arc melting. Splat quenching is used to reach cooling rates in the range of 105-106 C/s. Electron microprobe analysis (EPMA) and electron backscatter diffraction (EBSD) will be used to determine changes in primary solidification phase and to key solidification parameters at these extremely high cooling rates. This work was funded by the Department of Energy’s Kansas City National Security Campus which is operated and managed by Honeywell Federal Manufacturing Technologies, LLC under contract number DE-NA0002839.
10:30 AM
Analysis by Dilatometry and Nanoindentation in an Experimental Medium-carbon Steel during the Martensite Isothermal Tempering: Eliuth Barrera-Villatoro1; Octavio Vázquez-Gómez1; Perla Díaz-Villaseñor1; Alexis Gallegos-Perez1; Héctor Vergara-Hernández1; Bernardo Campillo-Illanes2; 1Tecnológico Nacional de México / I.T. Morelia; 2Universidad Nacional Autónoma de México
The isothermal tempering treatment of martensite was studied in an experimental medium-carbon steel alloyed with Cr-Mo-V by differential dilatometry and nanoindentation. The martensite decomposition stages were determined under continuous heating conditions at a rate of 35 °C min-1 until reaching a temperature of 1000 °C. Through the critical transformation points associated with the stages of precipitation, dissolution and phase transformation, a temperature close to 462 °C (precipitation temperature of Cr Mo V carbides) was selected and isothermal treatments were carried out at different times: 15, 30, 60 and 120 minutes in an inert argon atmosphere. Subsequently, a nanoindentation analysis was carried out to determine the nanohardness of the present phases, correlating it with the composition of the hard phases through a microanalysis by X-ray energy dispersion spectrometry.
10:50 AM
Formation of Retained Delta-ferrite and Martensite in the Coarse Grained Heat-affected Zone of P91 Heat-resistant Steel: Yang Shen1; Cong Wang1; 1Northeastern University
P91 steel, also known as creep strength-enhanced ferritic heat-resistant steel, has been extensively employed in thermal power generation applications, where welding is necessitated in the manufacturing process. Delta-ferrite is often retained in the heat-affected zone adjacent to the weld fusion line, which plays a role in the mechanical properties of final product. In the present work, phase transformation and microstructural evolution behaviors of the coarse grained heat-affected zone have been systematically studied by a high-temperature confocal scanning laser microscope (CSLM). In situ CSLM observation shows that delta-ferrite to austenite to martensite transition commences at 1468.6 K and 578.7 K, respectively. On cooling, austenite initiates from the triple point of the delta-ferrite grain boundaries with a trihedral shape, while not all of the delta-ferrite transforms back to austenite, 2~5 pct is retained. Subsequently, the rapid growth of martensite lath is almost instantaneous, with an average rate of 1051.16 μm/s.
11:10 AM
Divergent Pearlite Growth in Fe-Mn-C Steel: Leslie Mushongera1; P.G. Gideon Kubendran2; Britta Nestler2; 1University of Nevada, Reno; 2Karlsruhe Institute of Technology
A literature review on the mechanisms of eutectoid transformation in ternary steels reveals that the subject remains fascinating, with many unresolved issues and disparate observations. Cooperative growth of pearlitic lamellae and the factors that engender transition to divergent eutectoid are the areas where stipulated bridging between theory and experiments is yet to be established. We use a grand-chemical potential model that uses thermodynamic information from the CALPHAD database to explore the conditions that stimulate fascinating morphological transitions as the eutectoid transformation proceeds in Fe-Mn-C steel. To begin with, the numerically simulated growth kinetics are compared to DICTRA sharp-interface calculations, in the parameter space of interest. The validated model is used to investigate the influence of different processing and boundary conditions on the microstructural evolution. Meaningful insights on the mechanisms of eutectoid transformation are derived based on synergies established between computational and experimental micrographs.