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℃ 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℃. Using regression analysis, the stress multiplier （a） 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.
On the basis of the finite difference method, the factors affecting the temperature distribution along the thickness of plate during cooling process were analyzed, which include transformation heat, coefficient of heat conduction, specific heat, carbon content, cooling time, plate thickness, and unit of water flow volume. To ensure the homogenous temperature distribution along the thickness of plate, some cooling strategies, such as interval cooling, stepped cooling, and unsymmetrical cooling of upper and lower surfaces, were applied online. The online results showed that the cooling strategies can improve the temperature homogeneity greatly and the finite difference method can correctly simulate the cooling process.
CAI Xiao-hui ZHANG Dian-hua LIU Xiang-hua WANG Guo-dong
In order to meet the severe requirements of market and reduce production costs of high quality steels,advanced run-out table cooling based on ultra fast cooling(UFC) and laminar cooling(LC) was proposed and applied to industrial production.Cooling mechanism of UFC and LC was introduced first,and then the control system and control models were described.By using UFC and LC,low-cost Q345B strips had been produced in a large scale,and industrial trials of producing low-cost dual phase strips were completed successfully.Application results show that the ultra fast cooling is uniform along the strip width and length,and does not affect the flatness of strips.The run-out table cooling system runs stably with a high precision,and makes it possible for the user to develop more high quality steels with low costs.
Dimensions of one kind of stainless steel plate before finish rolling were obtained through analysis of the rough rolling processes by finite element method and updated geometrical method. The FE models of finish rolling process with a front edge roll were built, and influences of the edge rolling reduction on the stress change in the plate edge during finish rolling were analyzed. The results show that when the edge rolling reduction is increased from 0 mm to 2 mm, the compressive stress in plate corner clearly increases in edge rolling process, and the zone of tensile stress during whole rolling decreases; when the edge rolling reduction is increased from 2 mm to 5 ram, the compressive stress in the plate corner seldom changes, and the compressive stress decreases after the horizontal rolling.
YU Hai-liang LIU Xiang-hua CHEN Li-qing LI Chang-sheng ZHI Ying LI Xin-wen
A coupled thermo-mechanical model containing metal flow and temperature field for calculating temperature variation has been developed on fourteen-pass hot continuous rolling of round rod for Inconel 718 alloy using 3D elastic-plastic finite element method （FEM）. The temperature of characteristic analysis points in the intermediate cross-section of the workpiece has been simulated at initial temperature ranging from 960 to 1000 ℃ and initial velocity in range of 0.15-0.55 m·s^-1. Based on finite element analysis and microstructural observation in cylindrical hot compression experiments, the appropriate hot continuous rolling technologies have been designed for rod products with different diameters. For a real rolling practice, the simulated surface temperature was examined and is in good agreement with the measured one.
Fengli SUILiqing CHENXianghua LIULintao WANGWei LI
