INSIGHTS INTO VOID NUCLEATION AND GROWTH IN A DUAL PHASE STEEL BY SMALL SCALE MECHANICAL TESTING [Keynote]

Dual phase (DP) steels are comprised of a soft ferrite matrix and hard martensite islands. They are often used in automotive applications due to their advantageous combination of high strength and good ductility. During forming, DP steels can suffer from ductile damage, i.e. the formation and growth of voids, which typically occur by interface decohesion and martensite fracture [1]. As of now, the void content of a deformed part cannot precisely be predicted and, therefore, safety factors are used to assure the required mechanical properties and component lifetime. These safety factors are opposing sustainability and light-weight design. Consequently, the DFG-funded collaborative research center TRR188 aims at a quantitative characterization, prediction and control of ductile damage during forming.
In the talk, micromechanical experiments on the plasticity and fracture of single ferrite grains and martensite islands of two nominal identical steel grades will be presented. While one steel grade exhibits a low ferrite and a high martensite strength, the other shows a significantly stronger ferrite and lower strength martensite compared to the first steel grade [2]. This results in huge differences in the void nucleation and growth characteristics of the two steel grades.
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