Xianghua Liu

Asymmetric cryorolling for fabrication of nanostructural aluminum sheets.

Nanostructural Al 1050 sheets were produced using a novel method of asymmetric cryorolling under ratios of upper and down rolling velocities (RUDV) of 1.1, 1.2, 1.3, and 1.4. Sheets were rolled to about 0.17 mm from 1.5 mm. Both the strength and ductility of Al 1050 sheets increase with RUDVs. Tensile strength of Al sheets with the RUDV 1.4 is larger 22.3% of that for RUDV 1.1, which is 196 MPa. The TEM observations show the grain size is 360 nm when the RUDV is 1.1, and 211 nm for RUDV 1.4.

Dynamic Recrystallization Behavior of a Heat-resistant Martensitic Stainless Steel 403Nb during Hot Deformation

Dynamic recrystallization (DRX) behaviors of a heat-resistant martensitic stainless steel 403Nb during hot deformation have been investigated by single-pass thermo-mechanical simulative experiment at temperatures of 900–1150°C and strain rates of 0.01–1 s−1. The results show that the true stress-true strain curves of this alloy can be classified into two types, one is of dynamic recovery and the other is of dynamic recrystallization. The DRX in 403Nb alloy is easy to occur at strain rates lower than 0.5 s−1 and deformation temperatures higher than 1000°C. Using regression analysis, the stress multiplier (α) and apparent stress exponent (n) were calculated to be 0.0153 and 3.22, respectively, while the activation energy (Qd) for DRX of 403Nb was calculated to be 367.293 kJ/mol. The constitutive equation of peak stress for DRX was also obtained. Based on P-J method, the critical strain for DRX was accurately determined. The mathematical models of peak strain and kinetic equation for DRX of 403Nb steel were finally established.

Prospects for Variable Gauge Rolling:Technology,Theory and Application

Variable gauge rolling (VGR) is a new technology to produce flat products with different thicknesses (FDT). which could be used to replace conventional flat products in order to save metals and reduce structure mass. The method of VGR was introduced for investigating new problems in rolling theory of VGR, and the new formulas for calculating parameters of VGR were proposed. Besides, some results of numerical simulation by finite element method were described. As an example, the products applications of.FDT in bridge construction, ship building and auto manufacturing were presented. Finally, the prospects for VGR and FDT were discussed.

FEM Analysis of Rolling Pressure Along Strip Width in Cold Rolling Process

Using 3-D elastic-plastic FEM, the cold strip rolling process in a 4-high mill was simulated. The elastic deformation of rolls, the plastic deformation of the strip, and the pressure between the work roll and the backup roll were taken into account. The distribution of rolling pressure along the strip width was obtained. Based on the simulation results, the peak value of rolling pressure and the location of the peak were analyzed under different rolling conditions. The effects of the roll bending force and the strip width on the distribution of rolling pressure along the width direction were determined.

Numerical Simulation of Temperature Field and Thermal Stress Field of Work Roll During Hot Strip Rolling

Based on the thermal conduction equations, the threedimensional (3D) temperature field of a work roll was investigated using finite element method (FEM). The variations in the surface temperature of the work roll during hot strip rolling were described, and the thermal stress field of the work roll was also analyzed. The results showed that the highest roll surface temperature is 593 °C, and the difference between the minimum and maximum values of thermal stress of the work roll surface is 145. 7 MPa. Furthermore, the results of this analysis indicate that temperature and thermal stress are useful parameters for the investigation of roll thermal fatigue and also for improving the quality of strip during rolling.

Behavior of Transversal Crack on Slab Corner During V-H Rolling Process

The behavior of transversal cracks on the surface of the slab corner during vertical and horizontal (V-H) rolling process with flat vertical roll and groove vertical roll was simulated by explicit dynamic finite element method. The closure and growth of crack and the contact pressure on surfaces of the crack in contacting zone between slab and roll during rolling process were analyzed. The results showed that during vertical rolling process, when the groove vertical roll is used, the maximum contact pressure on surfaces of the crack is 115 MPa, and the closure of crack is stable; when the flat vertical roll is used, the maximum contact pressure on surfaces of the crack is 70 MPa, and it fluctuates greatly. During horizontal rolling process, when groove vertical roll is used, the contact pressure becomes zero which may accelerate the growth of crack; when flat vertical roll is used, there is still contact pressure. The calculated results are in good agreement with the results of test.

Crack Healing in a Low-Carbon Steel Under Hot Plastic Deformation

The behavior of internal crack healing in low-carbon steel samples undergoing hot plastic deformation was investigated using the MMS 200 thermo-mechanical simulator. The characterization of cracks after plastic deformation was analyzed using scanning electron microscopy under different heating temperatures, reduction ratios, numbers of deformation passes, strain rates, and holding time durations. It was found that the degree of crack healing increases with increasing heating temperature, reduction ratio, and holding time duration, and with decreasing number of deformation passes and strain rate.

Numerical Simulation on Carburizing and Quenching of Gear Ring

The carburizing process of the gear ring was simulated by taking into account the practical carburizing and quenching techniques of the gear ring and by solving the diffusion equation. The carbon content distribution in the carburized layer was obtained. Based on the results, the quenching process of the gear ring was then simulated using the metallic thermodynamics and FEM; it was found that the carburization remarkably affects the quenching process. Microstructures and stress distributions of the gear ring in the quenching process were simulated, and the results are confirmed by experiments.

Effects of Applied Stresses on Martensite Transformation in AISI4340 Steel

This study aims at the experimental analysis of the transformation induced plasticity (TRIP) phenomenon. Experiments are conducted in which martensite is allowed to grow under the influence of a series of externally applied stresses. The magnitude of the applied stresses is less than 67 % of the yield strength of austenite σγ(Ts). Since there is no obvious difference between the transformation plasticity under tension and the compression for the lower applied stresses, only compressive stresses are applied. The results confirm that the transformation plasticity is proportional to the applied stress if the latter does not exceed 67% of σγ(Ts). The TRIP-strain, the kinetics, and their dependence on the applied stresses are studied. The comparison between calculated results and experimental results shows that the model accurately describes the phenomenon.

Optimization and Model of Laminar Cooling Control System for Hot Strip Mills

The structure of laminar cooling control system for hot rolling was introduced and the control mode, cooling strategy, segment tracking and model recalculation were analyzed. The parameters of air/water cooling models were optimized by regressing the data gathering in situ, and satisfactory effect was obtained. The coiling temperature can be controlled within ± 15 °C.