Research On The Strength Toughness And Spring-back Mechanism Of Medium-Mn Steel

The third generation automotive medium manganese steel can ensure the impact safety of body part and the good stamping performance at the same time. The excellent properties of medium manganese steel mainly due to its fine-grained microstructure of the ferrite and metastable austenite. During the plastic deformation, the martensite is produced by the phase transformations caused by the TRIP effect, which results in a better plastic performance of the steel. However, this phase transformations also bring about complex problems of work hardening and poor precision of spring-back prediction.Aiming at these practical engineering problems, this paper investigated the basic mechanical properties, inelastic recovery and work hardening behavior as follow:? The basic mechanic parameters and tearing toughness was measured through uniaxial tension test and Kahn tear test and the influences of different directions and strain rates on the above properties are verified. And the conclusions of the tests were analyzed with the method of fracture morphology from a microscopic perspective.?The inelastic recovery behavior was studied by cyclic loading-unloading experiments. And the relationship between the elastic modulus and strain during the deformation was summarized, which could offer a reliable guidance to following simulation of spring-back.?The work hardening during the multi-pass forming process was investigated through tensile tests with different gradients of pre-stain and cyclic loading-unloading pre-strain.And the mechanic property changes were explained from the microscopic point of view with the observations through the optical microscope, TEM test and the fracture surface.?The influence of forming speed, punch stroke and pre-strain on the spring-back angle of test samples in three-point bending experiment was explored. The finite element model for the three-point bending test with variable elastic modulus was established by the subroutines of USDFLD in ABSQUS and compared with the experimental data to achieve a higher precision of spring-back prediction compared with the experimental data.