Ligang Liu
Yanshan University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Ligang Liu.
Journal of Rare Earths | 2011
Feifei Hao; Bo Liao; Da Li; Ting Dan; Xuejun Ren; Qingxiang Yang; Ligang Liu
The electrodes for hardfacing medium carbon steel with six additions of rare earth oxide were developed in this work. By means of optical microscopy and scanning electron microscopy, the microstructure, inclusion and the fractograph of the hardfacing metal were observed. Then, the effects of rare earth oxide on microstructure and inclusions in hardfacing metal were analyzed. The effectiveness of rare earth oxide as heterogeneous nuclei of δ-Fe was calculated with the misfit theory. The results showed that, the microstructure of hardfacing metal was composed of ferrite and small amount of pearlite. The microstructure was refined at first and then coarsened with the increase of rare earth oxide addition. The fractograph was changed from brittle to equiaxed dimples, then became quasi-cleavage and cleavage gradually. The calculated results showed that, the ferrite grain size could be refined because that LaAlO3 as heterogeneous nuclei of δFe was moderately effective, and the ferrite grain size was coarsened because the misfits between Ce2O3 and δFe, Ce2O2S and δFe were increased with futher increase of rare earth oxide addition.
International Journal of Minerals Metallurgy and Materials | 2009
Yuan Fang; Zhenmin Wang; Qing-xiang Yang; Yunkun Zhang; Ligang Liu; Hong-yan Hu; Yue Zhang
Abstract The temperature field of stainless steel during twin-roll strip casting was simulated by experiment and a finite element (FE) model. By comparing the measured result with the simulated values, it is found that they fit close to each other, which indicates this FE model is effective. Based on this model, the effects of roll gap ( t ) and roll radius ( R ) on solidification were simulated. The simulated results give the relationship between t or R and the position of the freezing point. The larger the t is and the smaller the R is, the closer the position of the freezing point is to the exit.
International Journal of Minerals Metallurgy and Materials | 2013
Jing Guo; Hongwei Qu; Ligang Liu; Yanliang Sun; Yue Zhang; Qingxiang Yang
A high speed steel (HSS) was studied for rollers in this work. The steel was quenched at 1150°C and tempered at 520°C. The phase structures of the steel were determined by X-ray diffraction (XRD), and the hardness of specimens was measured. The volume fraction of carbides was counted by Image-Pro Plus software. The typical microstructures were observed by field emission scanning electron microscope (FESEM). Stable and meta-stable carbides were deduced by removing the existing phases one by one in the Fe-C equilibrium calculation. It is found that the precipitated carbides are bulk-like MC, long stripe-like M2C, fishbone-like M6C, and daisy-like M7C3 during the tempering process. The stable carbides are MC and M6C, but the meta-stable ones are M2C, M7C3, and M3C.
Materials and Manufacturing Processes | 2011
Ligang Liu; Bo Liao; Da Li; Qiang Li; Yuhui Wang; Qingxiang Yang
The aim of this article is to study the internal stress evolution law of quenched specimens with complex phase transformation during the cooling process. The complex phase transformations were treated by analyzing the expansion coefficient evolution of steel 40Cr and the finite element method (FEM) was used to build the thermal–elastic–plastic simulation model based on ANSYS software. Then the internal stress fields of steel 40Cr during the quenching process were simulated. The mechanical parameters used in internal stress numerical simulation were measured by using a Gleeble-3500 thermal/mechanical simulator (DSI, Poestenkill, NY). The residual internal stress field of the oil-quenched specimen was measured by using an X-305A X-ray stress analyzer. The simulated behaviors fit well with the experimental data, which indicates that the model is practical to be used in the simulation of quenched specimens and helpful to understand the evolution of the internal stress during quenching process.
Journal of Rare Earths | 2006
Qingxiang Yang; Xuejun Ren; Ligang Liu; Da Li; Haifeng Dong; Bo Liao
Abstract The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure and modified inclusion in hardfacing metal with rare earth (RE) oxide were analyzed. The results show that, the hardfacing crack is initiated from the coarse dendritic crystal grain boundary, inclusions and coarse austenite grain boundary in the HAZ and propagated by the residual stress existing in the center of the hardfacing metal and HAZ. The primary columnar grain structure can be refined by adding RE oxide in the coating of the electrode. The inclusion in the hardfacing metal can be modified as well. Meanwhile, if the martensite transformation temperature is decreased, the largest value of the residual tensile stress in the dangerous region can be reduced.
Metals and Materials International | 2017
Jing Guo; Ligang Liu; Yunli Feng; Sha Liu; Xuejun Ren; Qingxiang Yang
In this work, the morphology and structures of the eutectic and secondary carbides in a new high chromium Fe-12Cr-2.5Mo-1.5W-3V-1.25C designed for cold-rolling work roll were systematically studied. The precipitated carbides inside the grains and along the grain boundaries were investigated with optical microscope, scanning electron microscopy with energy dispersive spectroscopy, transmission electron microscopy and X-Ray diffraction. Selected area diffraction patterns have been successfully used to identify the crystal formation and lattice constants of the carbides with different alloying elements. The results show that the eutectic carbides precipitated contain MC and M2C distributed along the grain boundaries with dendrite feature. The composition and crystal structure analysis shows that the eutectic MC carbides contain VC and WC with a cubic and hexagonal crystal lattice structures respectively, while the eutectic M2C carbides predominantly contain V2C and Mo2C with orthorhombic and hexagonal crystal lattices respectively. The secondary carbides contain MC, M2C, M7C3 formed along the grain boundaries and their sizes are much larger than the eutectic carbides ones. The secondary M23C6 is much small (0.3-0.5μm) and is distributed dispersively inside the grain. Similar to the eutectic carbides, the secondary carbides also contain VC, WC, V2C, and Mo2C. M7C3 is hexagonal (Fe,Cr)7C3, while M23C6 is indexed to be in a cubic crystal form.
Mechanics of Advanced Materials and Structures | 2015
Yuhui Wang; Qingfeng Wang; Ligang Liu; Wenwen Xu
The fracture mode in different M-A constituents containing multiphase steels under impact load was examined considering their microstructural and micromechanical aspects. The results showed that a ductile fracture develops in the fine-grained bainitic ferrite/M-A multiphase by microvoids initiation and coalescence, while cleavage develops in the coarse-grained polygonal ferrite/M-A multiphase by microcracks initiation and propagation, due to their diversities in morphologies of microstructural components and microhardness difference between phases.
Materials and Manufacturing Processes | 2012
Ligang Liu; Guozhu Xie; Yuhui Wang; Juefei Chu; Qingfeng Wang
In this work, a numerical simulation model was built to study the temperature rise on plate surface after laminar cooling based on finite element method (FEM) for optimizing the accelerated cooling processes of hot-rolled Q345E steel plates with thickness ≥40 mm. The effects of the cooling intensity and final cooling temperatures on the temperature rise after laminar cooling and the internal cooling rates were studied. The accelerated cooling processes of four typical thickness plates were optimized. The mechanical properties of the plates with thickness of 40 mm produced by the optimized processes proposed in this work were excellent.
International Journal of Minerals Metallurgy and Materials | 2014
Jing Guo; Yuanyuan Liu; Ligang Liu; Yue Zhang; Qingxiang Yang
This study first investigated cracks on the surface of an actual steel strip. Formulating the Anand model in ANSYS software, we then simulated the stress field in the molten pool of type 304 stainless steel during the twin-roll casting process. Parameters affecting the stress distribution in the molten pool were analyzed in detail and optimized. After twin-roll casting, a large number of transgranular and intergranular cracks resided on the surface of the thin steel strip, and followed a tortuous path. In the molten pool, stress was enhanced at the exit and at the roller contact positions. The stress at the exit decreased with increasing casting speed and pouring temperature. To ensure high quality of the fabricated strips, the casting speed and pouring temperature should be controlled above 0.7 m/s and 1520°C, respectively.
Materials & Design | 2009
Da Li; Ligang Liu; Yunkun Zhang; Chunlei Ye; Xuejun Ren; Yulin Yang; Qingxiang Yang