• Esderts, Alfons
• Masendorf, Rainer
• Medhurst, Tim

Abstract

TRIP steels (TRansformation Induced Plasticity) possess a higher forming potential than steels of comparable strength due to the forming induced transformation of remaining austenite into martensite. This property makes TRIP steels very well suited for ligh weight formed thin metal sheet structures. A reliable estimation of the structures' fatigue life requires material data which descibres the behaviour of the used material. Differences in three lots of nominally identical TRIP steels (TRIP700 or RAK40/70) from various manufacturers already show in their tensile test characteristics. The cyclic stress-strain curve and the strain S-N-curves also differ considerably. The reliability of the fatigue life estimation is strongly influenced by the choice of the "correct" characteristic material data. Previous forming of the material also shows strongly different influences on the material behaviour under oscillating loads. The material was pre-stretched in one axis previous to the tests. Whereas the stress-strain curve and the strain S-N-curve for one TRIP steel are dependant of the amount of pre-stretch, the stress-strain curve of another TRIP steel shows an increase with increasing amounts of pre-stretch. further research shall find the interrelationship of easy to determine data such as tensile tests and the cyclic data. Also the influence of preceding ageing on the phase transformation udring the formation of martensite out of austenite must be taken into account.

Topics

• impedance spectroscopy
• phase
• strength
• steel
• stress-strain curve
• fatigue
• forming
• aging
• plasticity