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A Multi-phase Field Model for Static Recrystallization of Hot Deformed Austenite in a C–Mn Steel

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Acta Metallurgica Sinica(English Letters) 2018年第2期31卷 208-215页

作者： Jun Zhang Cheng-Wu Zheng dian-zhong li School of Chemistry and Materials Science University of Science and Technology of China Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences

A multi-phase-field model has been developed to simulate the microstructure evolution and kinetics of the austenite static recrystallization（SRX） in a C–Mn steel. In this model, the bulk free energy that coupling the deformation stored energy with a special interpolation function is incorporated. Both the deformed grain topology and the deformation stored energy have been included in order to investigate the influence of pre-deformation on the subsequent austenite SRX at different hot deformation levels. Diverse scenarios of microstructure evolution show different deformation-dependent recrystallized grain sizes. The transformation kinetics is then discussed by analyzing the overall SRX fraction and the average interface velocity on the recrystallization front.

关键词： Phase-field Static recrystallization Microstructure evolution Hot deformation Mesoscopic modeling

Effect of Nb and Mo on the Microstructure, Mechanical Properties and Ductility-Dip Cracking of Ni–Cr–Fe Weld Metals

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Acta Metallurgica Sinica(English Letters) 2016年第10期29卷 928-939页

作者： Xu Zhang dian-zhong li Yi-Yi li Shan-Ping Lu Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences School of Materials Science and Engineering University of Science and Technology of China Key Laboratory of Nuclear Materials and Safety Assessment Institute of Metal Research Chinese Academy of Sciences

A series of Ni-Cr-Fe welding wires with different Nb and Mo contents were designed to investigate the effect of Nb and Mo on the rnicrostructure, mechanical properties and the ductility-dip cracking susceptibility of the weld metals by optical microscopy （OM）, scanning electron microscopy, X-ray diffraction as well as the tensile and impact tests. Results showed that large Laves phases formed and distributed along the interdendritic regions with high Nb or Mo addition. The Cr-carbide （M23C6） was suppressed to precipitate at the grain boundaries with high Nb addition. Tensile testing indicates that the ultimate strength of weld metals increases with Nb or Mo addition. However, the voids formed easily around the large Laves phases in the interdendritic area during tensile testing for the weld metal with high Mo content. It is found that the tensile fractographs of high Mo weld metals show a typical feature of interdendritic fracture. The high Nb or Mo addition, which leads to the formation of large Laves phases, exposes a great weakening effect on the impact toughness of weld metals. In addition, the ductility-dip cracking was not found by OM in the selected cross sections of weld metals with different Nb additions. High Nb addition can eliminate the ductility-dip cracking from the Ni-Cr-Fe weld metals effectively.

关键词： Nb Mo Laves phase Microstructure Mechanical properties

Hot Deformation Behavior and Processing Maps of 0.3C-15Cr-1Mo-0.5N High Nitrogen Martensitic Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2020年第5期33卷 693-704页

作者： Xin Cai Xiao-Qiang Hu Lei-Gang Zheng dian-zhong li Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences72 Wenhua RoadShenyang 110016China School of Materials Science and Engineering University of Science and Technology of China72 Wenhua RoadShenyang 110016China

Hot deformation behavior of 0.3 C-15 Cr-1 Mo-0.5 N high nitrogen martensitic stainless steel(HNMSS)was investigated in the temperature range of 1173-1473 K and at strain rates of 0.001-10 s-1 using a Gleeble 3500 thermal-mechanical *** true stress-strain curves of the studied HNMSS were measured and corrected to eliminate the effect of friction on the flow *** relationship between the flow stress and Zener-Hollomon parameter for the studied HNMSS wsa analyzed in the Arrhenius hyperbolic sine constitutive model by the law of Z=3.76×1015 sinh(0.004979σp)*** processing maps at different strains of the studied HNMSS were plotted,and its flow instability regions in hot working were also confirmed in combination with the microstructure ***,the optimal hot deformation parameters of the studied HNMSS could be suggested at T=1303-1423 K andε=5-10 s-1 or T=1273-1473 K andε=0.005-0.04 s-1.

关键词： High nitrogen martensitic stainless steel(HNMSS) Hot deformation Processing map Microstructure

Micro-scale Cellular Automaton Modeling of Interface Evolution During Reaustenitization from Pearlite Structure in Steels

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Acta Metallurgica Sinica(English Letters) 2018年第7期31卷 713-722页

作者： Gang Shen Cheng-Wu Zheng Jian-Feng Gu dian-zhong li Institute of Materials Modification and Modelling School of Materials Science and Engineering Shanghai Jiao Tong University Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Materials Genome Initiative Center Shanghai Jiao Tong University Shanghai Key Laboratory of Materials Laser Processing and Modification Shanghai Jiao Tong University

A modified cellular automaton model is developed to depict the interface evolution inside the cementite plus ferrite lamellar microstructures during the reaustenitization of a pearlite steel. In this model, migrations of both the austenite- ferrite and austenite-cementite interfaces coupled with the carbon diffusion and redistribution are integrated. The capil- laxity effect derived from local interface curvatures is also carefully considered by involving the concentration given by the phase diagram modified by the Gibbs-Thomson effect. This allows the interface evolution from a transient state to a steady state under different annealing conditions and various interlamellar spacings to be simulated. The proposed cellular automaton approach could be readily used to describe the kinetics of austenite formation from the lamellar pearlites and virtually reveal the kinematics of the moving interfaces from the microstructural aspect.

关键词： Austenite formation Lamellar pearlite Interface evolution Cellular automaton Microstructural modeling

Microstructural Depictions of Austenite Dynamic Recrystallization in a Low-Carbon Steel:A Cellular Automaton Model

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Acta Metallurgica Sinica(English Letters) 2016年第12期29卷 1127-1135页

作者： Xuan Ma Cheng-Wu Zheng Xing-Guo Zhang dian-zhong li School of Materials Science and Engineering Dalian University of Technology Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences College of Physical Science and Technology Shenyang Normal University

A mesoscopic cellular automaton model that takes into account grain deformation during hot deformation has been developed to quantitatively depict the microstructural evolution of the austenite dynamic recrystallization （DRX） in a low-carbon steel. Both the grain deformation and the concept of DRX cycle are introduced, allowing accurate depictions of the grain structures, the overall microstructural properties and the flow stress evolutions that involving in the austenite DRX. The simulation results are compared with the experimental results and the predictions by the macroscopic DRX model and are found to be in good agreement.

关键词： Dynamic recrystallization Austenite DRX cycle Cellular automaton Mesoscopic modeling

Effect of Intergranular Precipitation on the Internal Oxidation Behavior of Cr–Mn–N Austenitic Stainless Steels

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Acta Metallurgica Sinica(English Letters) 2015年第8期28卷 1008-1014页

作者： Lei-Gang Zheng Xiao-Qiang Hu Xiu-Hong Kang dian-zhong li Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences

The effect of intergranular precipitation on the internal oxidation behavior of Cr–Mn–N austenitic steels at 1000 °C in dry air atmosphere was investigated using scanning electron microscope, transmission electron microscope, and X-ray diffraction analysis. The results show that intergranular M23C6 carbide morphologies play an important role on the internal oxidation behavior of Cr–Mn–N steels. During the period of the oxidation, both discontinuous chain-shaped and continuous film-shaped intergranular M23C6 carbides precipitated along the grain boundaries. Internal oxides of silica preferentially intruded into the matrix along grain boundaries with discontinuous M23C6 carbide particles, while silica was obviously restricted at the interfaces between the external scale and matrix on the occasion of continuous film-shaped M23C6 carbides. It is seemed that reasonable microstructure could improve the oxidation resistance of Cr–Mn–N steels.

关键词： M23C6 precipitation Internal oxidation Cr–Mn–N austenitic steel

Numerical simulation and control of welding distortion for double floor structure of high speed train

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Acta Mechanica Sinica 2014年第6期30卷 849-859页

作者： Wen-Chao Dong Shan-Ping Lu Hao Lu dian-zhong li li-Jian Rong Yi-Yi li Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences CSR Qingdao Sifang Co. Ltd.

The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD ***,the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based on Weld Planner *** effects of welding sequence,clamping configuration and reverse deformation on welding distortion of floor structure were examined *** results indicate that the established elastic FEM model for floor structure is reliable for predicting the distribution of welding distortion in view of the good agreement between the calculated results and the measured distortion for real double floor *** with the welding sequence,the clamping configuration and the reverse deformation have a significant influence on the welding distortion of floor *** the case of30 mm reverse deformation,the maximum deformation can be reduced about 70%in comparison to an actual welding process.

关键词： Welding distortion Double floor welded structure High speed train Numerical simulation

Effect of strain rate on plastic deformation bonding behavior of Ni-based superalloys

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Journal of Materials Science & Technology 2020年第5期40卷 54-63页

作者： Jian Yang Zhang Bin Xu Naeem ul Haq Tariq Ming Yue Sun dian zhong li Yi Yi li Key Laboratory of Nuclear Materials and Safety Assessment Institute of Metal ResearchChinese Academy of SciencesShenyang110016China School of Materials Science and Engineering University of Science and Technology of ChinaShenyang110016China Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang110016China Department of Metallurgy and Materials Engineering Pakistan Institute of Engineering and Applied SciencesNiloreIslamabadPakistan

Plastic deformation bonding(PDB)has emerged as a promising solid state bonding technique with limited risk of phase transformations and residual thermal stresses in the *** this study,the PDB behavior of IN718 superalloy was systematically investigated by performing a series of isothermal compression tests at various processing *** was revealed that,with increasing PDB strain rate at 1000?C,different extents of dynamic recrystallization(DRX)occur in the bonding area of IN718 *** extent of DRX,average size of DRXed grains,and a newly proposed"interfacial bonding ratio(?Bonding)"parameter(to quantify the bond quality)were initially reduced with increase in the strain rate up to 0.1 s-1 and later increased at further higher strain *** backscattered diffraction(EBSD)and transmission electron microscopy(TEM)based interfacial microstructure analyses indicated that the quality of the bonded joints is closely related with the development of fine DRXed grains at the bonding interface with the increasing strain,which promotes adiabatic temperature *** was revealed that the initial bulging and subsequent migration of the original interfacial grain boundary(IGB)were the main mechanisms promoting DRX in the well bonded IN718 superalloy ***,the mechanical properties of the bonded joints were not only controlled by the recrystallized microstructure but also depended upon the Bonding parameter of the joints.

关键词： Inconel 718 superalloy Isothermal compression bonding Dynamic recrystallization Grain boundary Subgrain Strain rate

Modeling motion and growth of multiple dendrites during solidification based on vector-valued phase field and two-phase flow models

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Journal of Materials Science & Technology 2020年第23期58卷 171-187页

作者： Jian-kun Ren Yun Chen Yan-fei Cao Ming-yue Sun Bin Xu dian-zhong li Key Laboratory of Nuclear Materials and Safety Assessment Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China

Movement and growth of dendrites are common phenomena during *** numerically investigate these phenomena,two-phase flow model is employed to formulate the FSI(fluid-structure interaction)problem during dendritic *** this model,solid is assumed to have huge viscosity to maintain its own shape and an exponential expression is constructed to describe variable viscosity across s-l(solid-liquid)*** an effective preconditioner for saddle point structure,we build a N-S(Navier-Stokes)solver robust to tremendous viscosity ratio(as large as 10^(10))between solid and *** solidification is computed by vector-valued phase field model,which is computationally convenient to handle contact between *** of dendrites are updated by solving advection *** change due to dendrite's rotation has been considered as *** is accelerated by two-level time stepping scheme,adaptive mesh refinement,and parallel *** and growth of a single dendrite and multiple dendrites in Al-Cu alloy were simulated,showing the availability of the provided model to handle anisotropic growth,motion and impingement of *** study lays foundation to simulate solidification coupled with deformation in the future.

关键词： Phase field Solidification Two-phase flow Dendrite's motion Variable viscosity