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Damage mechanisms of ultrahigh strength steels in bending application to a trip steel

In order to optimize their metallurgical quality, the present study aims at understanding damage mechanisms involved in bending of Ultra High Strength Steels (UHSSs). It focuses on a TRansformation Induced Plasticity (TRIP)-aided steel. This work is based on three complementary approaches: first, instrumented V-bending and stretch bending tests that are usually performed to compare the bending behaviour of various steels, then, metallographic observations carried out to investigate damage initiation and finally, simulation of bending tests by finite element methods. Three-point-bending and stretch bending tests involve different crack initiation areas. Metallographic observations performed on V-bent specimens show crack initiation just below the outer surface, whereas in a stretch bending test, the crack clearly initiates from the central segregation (if any). V-bending tests were modelled with a finite element simulation approach to assess the stress and strain fields by comparison with experimental results. Modelling of stretch bending is currently in progress.