4th World Congress on Integrated Computational Materials Engineering (ICME 2017): Microstructure Evolution - II
Program Organizers: Paul Mason, Thermo-Calc Software Inc.; Michele Manuel, University of Florida; Alejandro Strachan, Purdue University; Ryan Glamm, Boeing Research and Technology; Georg J. Schmitz, Micress/Aachen; Amarendra Singh, IIT Kanpur; Charles Fisher, Naval Surface Warfare Center

Monday 2:00 PM
May 22, 2017
Room: Salon IV
Location: Ann Arbor Marriott Ypsilanti at Eagle Crest

2:00 PM  
Process Simulation and Experimental Investigation of Material Properties in Aluminum Resistance Spot Welds (P-51): Sainan Wu1; Bita Ghaffari2; Elizabeth Hetrick2; Mei Li2; Zhihong Jia1; Qing Liu1; 1Chongqing University; 2Ford Motor Company
    Resistance spot welding (RSW) is a key joining technique in numerous industries. Though ubiquitous in the automotive industry, the vast majority of resistance spot welding production and research have been conducted on steel. The current emphasis on lightweighting has greatly increased the interest in fully understanding the influence of the process on RSW of aluminum alloys. In the present study, a variety of experiments and simulations have been conducted to characterize the microstructure and property evolution of AA6111 RSW. In addition to the traditionally-observed heat-affected zone, the presence of a few-millimeter wide thermo-mechanically affected zone (TMAZ), which lies between the weld nugget and base metal and is notably harder than both, is established and explored. The impact of two hardening mechanisms, strain hardening induced by the compressive force from the welding electrodes and precipitation hardening, are investigated. The evidence establishes that the formation of the TMAZ is dominated by strain hardening.

2:30 PM  
Effect of Microsegregation on the Microstructural Banding in Manganese Steels - An Integrated Multiscale Approach: Himanshu Nirgudkar1; Saurabh Mangal1; Savya Sachi1; Surya Ardham1; Sagar Salunke1; Ayush Suhane1; Srimannarayana Pusuluri1; Rishabh Shukla1; Danish Khan1; Pramod Zagade1; Gautham BP1; Gerald Tennyson Peter1; 1TCS Research, Tata Consultancy Services Limited
    Microstructural banding is a major concern in wrought manganese steels, that occurs after hot rolling, in regions where austenite grain size is less than the wavelength of Mn microsegregation. The signature of microsegregation on banding and thereby on properties is a multiscale problem, which may be brought out significantly using an integrated multiscale modelling approach from casting to phase transformation at the run out table (ROT). In this study, a method is proposed to quantify microsegregation using a computational thermodynamics (CALPHAD) approach, with temperature and composition distribution as inputs from casting simulations. The microsegregation parameter along with grain size distribution from hot rolling are used as inputs for predicting phase transformation in ROT using a phase-field approach. Finite element based micromechanics approach is then used for predicting the mechanical properties of the microstructure. Structure-property relationships as a function of microsegregation and austenite grain size are obtained for an ensemble of microstructures. This established relationship of microsegregation - grain size - structure - properties will be used for predicting the locations of banding and variation of properties of a hot rolled strip through the microsegregation parameter.

2:50 PM  
Numerical Simulation of Macrosegregation in a 535 Tons Steel Ingot with a Multicomponent-Multiphase Model : Chen Kangxin1; Tu Wutao2; Shen Houfa1; 1Tsinghua University; 2SMIC Advanced Technology Research & Development (Shanghai) Corporation
    To accurately simulate the formation of macrosegregation, a major defect commonly encountered in large ingots, solidification researchers have developed various mathematical models and conducted corresponding steel ingot dissection experiments for validation. A multicomponent and multiphase solidification model was utilized to predict macrosegregation of steel ingots in this research. The model described the multi-phase flow phenomenon during solidification, with the feature of strong coupling among mass, momentum, energy, concentration conservation equations. Impact factors as thermo-solutal buoyancy flow, grains sedimentation, and shrinkage-induced flow on the macroscopic scale were taken into consideration. Besides, the interfacial solute constraint relations were derived to close the model by solving the solidification paths in the multicomponent alloy system. The phase diagrams of the multicomponent alloy system were determined by Thermal-Calc Software. Thus the impact of multicomponent on macrosegregation was considered. A finite-volume method was employed to solve the governing equations of the model. In particular, a multi-phase SIMPLEC (semi-implicit method for pressure-linked equations-consistent) algorithm was utilized to solve the velocity-pressure coupling for the specific multiphase flow system. Finally, the model was applied to simulate the macrosegregation in a 535 tons steel ingot with composition of Fe-0.24 wt.%C-1.65wt.%Cr-1.39wt.%Mo. The simulated results were compared with the experimental results. Predictions have reproduced the macrosegregation patterns in measurements. A good agreement is shown generally in quantitative comparisons between experimental results and numerical predictions of carbon, chromium and molybdenum. It is demonstrated that the multicomponent multiphase solidification model can well predict macrosegregation in steel ingots and help optimize the ingot production process.

3:10 PM  
Validation of CAFE Model with Experimental Macroscopic Grain Structures in a 36-ton Steel Ingot: Jing'an Yang1; Zhenhu Duan2; Baicheng Liu1; Houfa Shen1; 1Tsinghua University; 2Lishui University
    In order to recognize macroscopic grain structures evolution within large heavy casting, a 36-ton steel ingot has been experimentally investigated. Fourteen thermocouples have been used to record temperature variations during solidification of the ingot to ensure a reliable simulation of temperature field. Half of the longitudinal section has been etched to obtain as-cast macrostructure. Fine equiaxed grains are found in the ingot periphery, then slender columnar grains next to them, finally widely spread coarse equiaxed grains in the ingot center. Besides, several etched bands are detected which may be A-segregation channels. Then, simulation of macroscopic grain structure is processed by a three dimensional Cellular Automaton Finite Element(CAFE) module of ProCAST software. The nucleation algorithm is based on an instantaneous nucleation model considering a Guassian distribution of nucleation sites proposed by Rappaz. Besides, the growth algorithm is based on the growth of an octahedron bounded by (111) faces and the growth kinetics law is given by the model of Kurz et al. The microscopic CA and macroscopic FE calculation is weak coupled where the temperature of each cell is simply interpolated from the temperature of the FE nodes using a unique solidification path at the macroscopic scale. Simulation parameters of CAFE about Guassian nucleation and growth kinetics have been adjusted so that the macroscopic grain structures correlate with the as-cast macrostructure experiment.

3:30 PM Break

3:50 PM  
Integrated Approach for Modelling of Precipitate Evolution and Grain Growth in Steel Slabs: Saurabh Mangal1; Himanshu Nirgudkar1; Savya Sachi1; Gerald Tennyson1; 1TRDDC, TCS Research, Tata Consultancy Services, Pune, INDIA
    Micro-alloying elements such as Nb, V and Ti are added in steels to pin grain boundaries through precipitation and solute drag effect. Formation and dissolution of precipitates in casting and reheating, significantly impact further downstream operations. In this study, an integrated multiscale approach to capture the precipitation kinetics of vanadium carbonitrides V(C,N) during casting and reheating is proposed. The formation of precipitates depend on localized variation in composition due to microsegregation and dendrite arm spacing. Evolution of V(C,N) is predicted using temperature and composition distribution as input from macroscale casting simulations. The subsequent dissolution during reheating is modelled based on temperature evolution in the reheating furnace and is coupled to a cellular automata (CA) model simultaneously which takes inputs from CALPHAD calculations and predicts grain size evolution taking into account the grain boundary pinning effect due the presence of V(C,N). Precipitate evolution and dissolution for various processing parameters such as casting speed, superheat, reheating temperature and time are studied.

4:10 PM  
Analysis of Localized Plastic Strain in Heterogeneous Cast Iron Microstructures using 3D Finite Element Simulations: Kent Salomonsson1; Jakob Olofsson1; 1Jonkoping University
    The design and production of light structures in cast iron with high static and fatigue performance is of major interest in e.g. the automotive area. Since the casting process inevitably leads to heterogeneous solidification conditions and variations in microstructural features and material properties, the effects on multiple scale levels needs to be considered in the determination of the local fatigue performance. In the current work, microstructural features of different cast irons are captured by use of micro X-ray tomography, and 3D finite element models generated. The details of the 3D microstructure differ from the commonly used 2D representations in that the actual geometry is captured and that there is not a need to compensate for 3D-effects. The first objective with the present study is to try and highlight certain aspects at the micro scale that might be the underlying cause of fatigue crack initiation, and ultimately crack propagation, under fatigue loading for cast iron alloys. An approach is implemented using cohesive elements to enable crack propagation in the microstructure simulations, and the simulation results are compared to 2D observations using Digital Image Correlation (DIC). The second objective is to incorporate the gained knowledge about the microstructural behaviour into multi-scale simulations at a structural length scale, including the local damage level obtained in the heterogeneous structure subjected to fatigue load.