Advanced High Strength Steels IV: Session III
Sponsored by: TMS Structural Materials Division, TMS: Steels Committee
Program Organizers: Ana Araujo, Vesuvius USA; Mary O'Brien, Los Alamos National Laboratory; Tilmann Hickel, Bam Federal Institute For Materials Research And Testing; Amy Clarke, Los Alamos National Laboratory; Kester Clarke, Los Alamos National Laboratory; C. Tasan, Massachusetts Institute of Technology; MingXin Huang, University of Hong Kong
Wednesday 8:30 AM
February 26, 2020
Room: Balboa
Location: Marriott Marquis Hotel
Session Chair: Tilmann Hickel, Max Planck Institute; Cem Tasan, Massachusetts Institute of Technology
8:30 AM
Austenitization of a Cold-rolled Dual-phase Steel: Interaction with Recrystallization and Influence of Cementite Composition: Marc Moreno1; Julien Teixeira1; Sébastien Allain1; Carla Oberbillig2; Frédéric Bonnet2; 1Institute Jean Lamour; 2ArcelorMittal Global Research and Development
The manufacturing of DP steels includes as a crucial step the annealing of a cold-rolled ferrite-pearlite microstructure, which involves recovery/recrystallization of ferrite, globularization, enrichment, coarsening of cementite and finally austenite transformation. Present study focuses on the austenite transformation, emphasizing its interaction with the ferrite recrystallization and the influence of the chemical composition of cementite. A cold-rolled ferrite-pearlite steel is heated at 3, 30 or 100°C.s-1 in order to induce weak or strong interactions. Austenite transformation kinetics is determined in situ by synchrotron HEXRD, combined with post mortem SEM observations of the microstructure. Cementite compositions are measured by EDS in TEM.Fast and slow heating lead to banded and necklace austenite morphology respectively, due to strong or weak interaction with recrystallization. Conversely, the austenite transformation kinetics is weakly influenced by the recrystallization or the cementite composition. Thermokinetic analysis of the austenite transformation (DICTRA simulations) is sufficient to interpret the transformation kinetics.
8:50 AM
Effect of High Temperature Processes on Dual Phase Steel Manufacture: Bharath Bandi1; Joost Krevel2; Sukalpan Nandi3; Prakash Srirangam1; 1Warwick Manufacturing Group (WMG), University of Warwick; 2Tata Steel, Research and Development; 3Vellore Institute of Technology
This research work demonstrates the interplay between ferrite recrystallization, grain growth, and austenite formation processes during Dual-Phase steel manufacture of hot rolled (HR) and cold reduced steels (CR). Heat treatments were carried out at inter-critical temperatures using varying heating rates. Hardness results show that the ferrite grain growth is dominating process for both CR and HR steel at lower inter-critical temperature (715-730 0C) and lower heating rates (0.2 0C/s). With increasing heating rates (~50.5 0C/s) for the same inter-critical temperatures, ferrite grain growth became less progressive, but ferrite recrystallization and austenite formation occurred simultaneously for CR steels, while in HR steels, only austenite formation was observed. However, at higher temperatures and higher holding times (>100s) austenite formation became the dominating process for both the steels. For higher heating rates, hardness values of CR steels were found to be decreasing first and then increasing with increase in holding times.
9:10 AM
Increased Damage in Dual Phase Steels under Dynamic Strain Aging Conditions: Merve Cobanoglu1; Rasim Ertan2; Caner Simsir2; Mert Efe1; 1Middle East Technical University; 2Atilim University
Damage formation in dual phase steels is a complex process and it may be sensitive to the deformation conditions and mechanisms. In this study, the damage parameter is measured and compared under quasi-static and industrial deformation conditions (temperatures: 25 vs 200°C and strain rates: 10-3 vs 10/s) for DP590 and DP800 steels. Scanning electron microscopy, resonance frequency and damping analyzer, and ultrasonic sound velocity measurement techniques are utilized for the measurements to compare the effectiveness and validity of each technique. At a given strain, the damage values can be up to 250% higher at industrial forming conditions, under which dynamic strain aging (DSA) controls the deformation behavior. DSA results in lower formability and is the likely mechanism responsible from the abnormal damage evolution. Moreover, DSA and damage evolution are both exacerbated in DP590, highlighting the importance of microstructure, and especially ferrite content, for the deformation behavior.
9:30 AM
High-performance Full-field Crystal Plasticity with Dislocation-based Hardening and Slip System Backstress Laws: Application to Modeling Deformation of Dual-phase Steels: Adnan Eghtesad1; Marko Knezevic1; 1University of New Hampshire
This research presents a high-performance elasto-viscoplastic fast Fourier transform (EVPFFT) crystal plasticity to predict elasto-plastic, anisotropic, rate-and temperature-sensitive deformation of polycrystalline aggregates of Ferritic-Martensitic dual-phase (DP) steels subjected to large plastic strains. The solver embeds strain-path aware dislocation-based hardening and slip-system- level kinematic backstress. The model is applied to simulate the elasto-plastic deformation of several steel variants: DP 590, DP 980, DP 1180, and martensitic, MS 1700. Crystallographic textures and phase fractions of these steels are characterized using electron microscopy along with electron-backscattered diffraction. The model captures the monotonic behavior and particularities pertaining to cyclic deformation characteristics such as non-linear unloading upon the load reversal, the Bauschinger effect, and changes in hardening rate during strain reversals based on the evolution of dislocation density and crystallographic grain reorientation. In addition, it offers insights into the role of backstress and dislocation annihilation on the cyclic deformation of DP steels.
9:50 AM
Effect of Pre-straining on High Cycle Fatigue and Fatigue Crack Propagation Behaviors of CP (Complex Phase) Steel: Su-Min Kim1; Taejin Song2; Hyokyung Sung1; Jehyun Lee3; Sangshik Kim1; 1Gyeongsang National University; 2POSCO/Technical Research Laboratories; 3Changwon National University
CP (complex phase) steel for automobile application requires good fatigue resistance, as well as high strength. Since Fatigue behavior of steel can vary with metal forming process, fatigue behavior of CP steel with different pre-straining levels of 0, 5 and 9 % were examined in this study. Despite continuous increase in tensile strength with pre-straining from 0 to 9 %, the resistance to high cycle fatigue (HCF) decreased with increasing level of pre-straining from 0 to 5% and then increase with 9% pre-straining. The EBSD and TEM analyses suggested that such an abnormal trend was possibly related to the change in dislocation structure during fatigue loading. Unlike HCF behavior, the fatigue crack propagation (FCP) rates of CP steel tended to decrease slightly with increasing pre-straining from 0 to 9 %. Rather complex trend in HCF and FCP behaviors of CP steel were discussed based on detailed micrographic and fractographic observations.
10:10 AM Break
10:30 AM
Examination of Cementite+Austenite+Ferrite Multiphase Steel Produced by ART Annealing: Oguz Gurkan Bilir1; Ersoy Erisir1; Kemal Davut2; 1Kocaeli Univ; 2Atilim University, Metal Forming Centre of Excellence, Golbası, Ankara, Turkey
Austenitization of medium Mn steels between A1 and A3 temperature with martensitic microstructure is called as Austenite Reversion Transformation (ART) annealing. Steels that ART annealing is applied are promising for future applications with yielding a good balance of strength, toughness, energy absorption and forming properties thanks to having ferrite+austenite duplex microstructure. In this study, a new alloy (0.24%C-4.24%Mn-1.0%Si) is developed to study having a ferrite+austenite+cementite by applying ART annealing. ThermoCalc, DICTRA and Baehr dilatometer is used to decide the heat treatment strategy. SEM, XRD and EBSD are employed for characterization of microconstituents. Mechanical properties are revealed by sub-size mechanical testing. It resulted that having a wider gap between A1b and A1e temperature is an important factor for achieving ferrite+austenite+cementite. It was also concluded that using an ART annealing temperature higher than A1e lowers the possibility of enhancing austenite stability due to having lesser Mn content in Austenite.
10:50 AM
Process Design and Genetic Optimization of HSLA Steels Using Mean-field and Multi-phase Field Modeling: Maria-Ioanna Tzini1; Gregory Haidemenopoulos1; 1University of Thessaly
The optimization of the thermomechanical control process of HSLA steels remains a challenging problem in pipeline industrial applications. Controlling the microstructural evolution during multipass hot-rolling and identifying the effect of processing parameters on the microstructure is the key to process design. In the present study, a mean-field model integrated with a Kampmann-Wagner numerical precipitation model was developed for the description of static recrystallization kinetics of austenite and the strain induced precipitation kinetics of niobium carbonitrides after the multipass hot-rolling of HSLA plates. By applying specific process design criteria, the optimum processing variables such as the reduction per pass and interpass times are derived using genetic algorithms and multi-phase field modeling coupled with CALPHAD tools. The ability to describe and control the degree of microstructural homogeneity and its dependence on the processing parameters constitutes this method an effective integrated computational tool for materials process design.
11:10 AM
Mechanisms of Embrittlement and Recovery in Cast HY-80 High-strength Low-alloy Steel: Matthew Draper1; Sreeramamurthy Ankem2; 1US Navy; 2University of Maryland
HY steels were designed as a solid solution strengthened grade for both high yield strength and high impact toughness in structural applications for Naval vessels. Both lower cost and higher reliability treatments have been studied via developing an improved understanding of the structural evolution and corresponding changes in mechanical behavior for the alloy. Metallographic along with computational work supports a conclusion that temper embrittlement and subsequent recovery in the HY system cannot be solely explained by the segregation of phosphorus and other embrittling elements to grain boundaries. Rather it is shown for the first time that alloy carbides play a key role in embrittlement for this system. In addition, a novel treatment has been developed to reduce hydrogen aging times by up to 90% in industrial manufacture. Ongoing work is employing models built for the nucleation, dissolution, and coarsening of carbides to develop next-generation HY steels.
11:30 AM Cancelled
In-situ Observation of the Peritectic Reaction and Transformation in a Commercial HSLA Steel: Tao Liu1; Dengfu Chen1; Songyuan Ai1; Pingmei Tang1; Mujun Long1; Jie Yang1; 1Chongqing University
In this work, the precipitation and dissolution behavior of coarse TiN inclusions in the titanium microalloyed casting slab was in situ investigated by using the high temperature confocal scanning laser microscope (HTCSLM) and theoretical kinetics analysis. The theoretical results show that the coarse TiN inclusions precipitate in the mushy zone. Meanwhile, the precipitation of TiN inclusions was verified by combining HTCLSM observation and the scanning electron microscope (SEM) analysis. During the reheating process, it was found that the dissolution of coarse TiN inclusions observed by HTCLSM was relate to the size of the inclusions. The larger the size is, the greater the dissolution rate is. Under HTCSLM, it was found that TiN inclusions melted and formed the liquid inclusion at the temperature which was more than 1410 ºC on the surface of sample. The local dissolution rate of coarse TiN inclusion was related to the heating rate.