Based on the nonlinear FE platform ABAQUS, an elastic plastic 3D-FE model of 0Cr21Ni6Mn9N stainless steel tube was established to simulate the whole process, and its reliability was validated by experiment. Using the model, the effect of bending speed on forming quality was studied and the influence laws of bending speed on wrinkling wave ratio, wall thinning, cross section deformation and springback angle were revealed. The results show that the wrinkling wave ratio and springback angle decrease with the increasing of bending speed, while the effect of bending speed on wall thinning and cross section deformation are not significant. The maximum cross section deformation degree presents in the vicinity of the bending angle 30° along the bending direction and its position is almost unchanged with the variation of bending speed.

The dynamic recrystallization (DRX) behavior in the isothermal hot compression of AISI 52100 steel was analyzed by using the phenomenological-based cellular automaton (CA) algorithm. The developed CA model was coded into DEFORM platform, which is a Finite Element Method (FEM)-based software for simulation of material deformation process. The developed CA-model can thus predict the nucleation and growth kinetics of dynamically recrystallized grains of the testing material in hot working process. Furthermore, the effects of the deformation temperature, true strain and strain rate on the microstructural evolution of the testing material were physically studied by using Gleeble-1500 thermo-mechanical simulator and the developed CA-model was verified by the experimental results. Through simulation and experiment, it is found that the results predicted by the CA-model have a good agreement with the experimental ones.

Hot compression tests of Ti40 alloy was carried out on a GLEEBLE 3500 thermo- mechanical simulator at the deformation temperatures of 950~1100°C, the strain rates of 0.01~0.1s-1 and the height reductions from 20% to 60%. The true stress/true strain curves were obtained through the tests. Through physical experiment and FEM-based microstructure modelings, the dynamic recrystallizaiton (DRX) behavior of the alloy is extensively explored. The results show that increasing true strain, raising deformation temperature and reducing strain rate are contribute to the DRX of the Ti40 alloy. The simulation results agree well with the experiment results, which prove the accuracy of the microstructure evolution models for predicting the DRX process during hot compression.

In order to reveal the effect laws of boosting velocity on forming quality of tube bending. A three dimensional (3D) elastic plastic finite element (FE) model of whole process of high-strength TA18 tubes in numerical control (NC) bending was established based on the FE code of ABAQUS, and its reliability was validated by using the experimental results in literature. Then, the effect laws of boosting velocity on deformation behaviors of high-strength TA18 tubes in NC bending were explored with respect to multiple defects such as wall thinning, wall thickening, cross section deformation and springback. The results show that wall thinning ratio decreases with the increasing of boosting velocity; wall thickening ratio increases with the increasing of boosting velocity; cross section deformation ratio decreases with the increasing of boosting velocity; springback decreases slightly with the increasing of boosting velocity.

The effect of tempering temperature on the microstructures and mechanical properties of a microalloy low carbon bainitic steel was investigated by microscopic analysis and testing of mechanical properties. The results show that the microstructures of the tested steel primarily consists of lath bainite, granular bainite, quasipolygonal ferrite and little acicular ferrite at different tempering temperatures. With the tempering temperature increasing, the proportion of lath bainitie decreases, while the volume of granular bainite and quasipolygonal ferrite increases. At the tempering temperatures of 550-650°C and tempering time of 1 hour, the steel was mostly composed of granular bainite, quasipolygonal ferrite and a little lath bainite, which a good combination of strength and toughness can be obtained.