Papers by Author: Yan Dong Liu

Abstract: Ultra-rapid annealing (URA) experiments were carried out to study the effect of heating rate on the recrystallization kinetics, grain size and Bake-hardening (BH) properties of Ultra-low carbon Bake Hardening Steel annealing with different heating rates followed by gas cooling (about 100°C/s) with variation of soaking times. It was shown that the degree of grain refinement is controlled by the parameters of heating rates and soaking time of the Ultra-rapid annealing cycles. For the steels investigated, the final grain size decreases with increasing heating rate and increases with increasing soaking time. The effects of dislocation density, varied by means of non-temper rolling reduction and a temper rolling reduction of 1% on the Bake-hardening properties were investigated within an aging temperature of 170°C for 20 min.

Abstract: In this paper, the welding microstructure of Ferritic Stainless Steel sheet with different Ti, Nb elements were studied. The experiment results shows that the addition of alloying element Ti +Nb stabilization steel causes the precipitation of Nb(CN) and TiN. This can reduce the C content, so the temperature of Ac1 increases, then it would be difficult to get martensite. Due to Martensite is harmful for toughness, so Ti+Nb elements are in need.

Abstract: An experimental study of the microstructural and texture evolution attending recrystallization of Nb-Ti stabilized ferritic stainless steel is presented. Two specimens with different Nb-Ti compositions, TCS345 and B4003, have been selected for comparison. The result shows that, after annealing at 750 °C for 5min, the major orientation in the TCS345 specimen locates at {111}, microstructures presents an equiaxed grain morphology, whereas the texture in the B4003 is not typical recrystallization texture and remains weak, indicating recrystallization occur preferentially to the TCS345 sheet. And after continuous annealing at 850°C for 5 min, the texture in TCS345 remains stronger than in the B4003, indicating that the additional amount of Nb-Ti acts to significantly hinder the recrystallization process.

Abstract: NiMnCoIn alloys are new-type magnetic shape memory alloys (MSMAs) in which a reversible magnetic-field-induced phase transformation was observed. They are ideal candidates of materials used in actuators and sensors. The polycrystalline NiMnCoIn alloys are generally brittle so that they can not be easily deformed into the shape applicable to actuators and sensors until now. In the present paper, the influence of hot deformation on the microstructure of Ni₄₅Co₅ Mn_36.7In_13.3 alloy was studied. The experimental results showed that second phase was observed after deformation at high temperature between 800~900 °C and at strain rate lower than 4×10^-3s^-1. The content of Co of second phase was higher than the matrix alloy, while the content of In was lower than the matrix alloy. It was determined by TEM measurements as γ phase with fcc structure which was popular in NiFeGa and NiMnGaCo alloys. It is possible to improve the ductility of Ni₄₅Co₅Mn_36.7In_13.3 alloy by control of amount and distribution of γ phase by hot deformation.

Abstract: In this study, the effect of different compositions of the stabilized elements of Nb-Ti for cold rollling textures and the recrytalization textures of B4003M has been investigated. Cold rolling texture at 80% reduction displayed by the Nb-Ti added specimen is the weakest of all. When annealing at 900°C for 10 min, the recrystalli -zation textures displayed by the Nb-added, Ti-added, Nb-Ti-added and Nb-Ti-free alloys are compared. Results show that: {111} recrystallization texture in Nb-added alloy is the strongest, whereas it in the Nb-Ti-free alloy is the lowest. The mutual effect of Nd and Ti on refining the grain size is more obvious than the single element effect, while Nd is more effective than Ti.

Abstract: In recent years, there has been an increasing interest in magnetic shape memory alloys (MSMAs) due to their unique ability to produce very large output strains and rapid response frequency. NiMnCoIn is a new-type MSMAs in which a reversible magnetic-field-induced phase transformation is observed. The microstructural evolution in the process of dynamic recrystallization in polycrystalline Ni45Co5Mn36.7In13.3 was studied in the present paper. The experimental results showed that the high deformation temperature and slow strain rate were necessary to achieve perfect dynamic-recrystallizing microstructure in Ni45Co5Mn36.7In13.3 alloy. Precipitates with two sizes were observed. The content of Co in precipitates was higher than that in the matrix alloy, while the content of In was lower than that in the matrix alloy.

Abstract: The magnetic shape-memory alloy NiCoMnIn shows, in monocrystalline form, a large reversible magnetic-field-induced strain (MFIS). But it is difficult to achieve the properties in polycrystalline NiCoMnIn alloys. The technique of powder metallurgical preparation of NiCoMnIn foam was studied to improve the properties of polycrystalline NiCoMnIn alloys in the present paper. We introduced a processing route including choosing appropriate space-holding fillers, sintering NiCoMnIn alloy and the filling agent with appropriate grain size. The sintering temperature and time and the optimum volume fraction of the filling agent were determined by analysis of the structure of sintered bulk foams.

Abstract: In this paper, the torsional texture evolution of pearlitic steel wire is simulated by Full Constrains (FC) Taylor model. The simulation results indicate that a simple shear deformation can not explain the experiments results of torsion texture. Bring in additional rigid body rotation and rational shear deformation can emersion the torsion texture very well. The different deformation styles are imposed to the FC Taylor, a group of parameters is given to explain the torsion texture evolution.

Abstract: In this paper, the texture and micro-orientation of FSS (Ferritic Stainless Steel) during hot rolling, cold rolling and annealing were studied by using x-rays and EBSD technology. The results shown that as cast ingot of FSS was compose of random orientations equiaxed grains and <001>∥ND columnar grains; after hot rolling, the preferred orientation of <001>∥ND columnar grains of as cast ingot obtained inherits, the fiber texture was obvious stronger than that of equiaxed grains; during cold rolling, the initial <001>∥ND columnar grains turn to  fiber texture,  fiber texture can not be found.

Abstract: High-energy synchrotron diffraction offers great potential for experimental study of recrystallization kinetics. A fine experimental design to study the recrystallization mechanism of Interstitial Free (IF) steel was implemented in this work. In-situ annealing process of cold-rolled IF steel with 80% reduction was observed using high-energy X-ray diffraction. Results show that, the diffraction intensity of {001}<110> and {112}<110> belong to α-fiber texture component decreased with the annealing temperature increased while {111}<110> did nearly not change and {111}<112> increased; the FMTH decreasing and d-space changing with annealing temperature increasing indicated that the residual stress relaxed completely during recovery.