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Article Strain Hardening Behavior Characterization of Dual Phase Steels(2018) Davut, Kemal; Şimşir, Caner; Çetin, BarişThe requirements for higher passenger safety, improved fuel economy and weight reductionin automobile industry necessitates the usage of advanced high strength steel (AHSS)grades. Dual phase (DP) steels are the most widely used one among AHSS. DP steels becomeincreasingly popular, since they provide a combination of sufficient formability at room temperatureand tensile strength over 1000 MPa. The current standards for DP steels only specifiesyield and tensile strength. Steels from various producers have considerably different compositionand microstructure; however they still have the same grade name. Combined withthe inherited heterogeneous microstructure, those steels exhibit different strain hardeningbehavior. The aim of this study is to evaluate the strain hardening behavior of DP800 steels,obtained from different vendors and thus having different compositions and microstructures.The strain hardening behavior was characterized with tensile tests performed along rollingand transverse directions. The microstructure has been characterized with optical andscanning electron microscopes. The martensite fraction, grain size of ferrite and chemicalcomposition has been correlated to the strain hardening behavior. The results show thatthe steel with more micro-alloying addition has finer ferritic grain size, which cause higherinitial strain hardening rate. The steel with higher Mn and Cr has higher martensite fraction,which cause strain hardening rate to be higher at higher strain levels.Article Transformation Induced Plasticity (trip) of Sae 52100 Steel During Martensitic and Bainitic Transformations(2017) Şimşir, CanerTransformation induced plasticity (TRIP) of SAE 52100 steel during quenching is investigatedboth experimentally and theoretically. TRIP parameter (K) is determinedexperimentally for both martensitic and bainitic transformations by using the stresseddilatometry technique. A new method for extraction of for an incomplete transformationis suggested for the martensitic transformation. Theoretical calculations using wellestablishedmodels for the TRIP effect and the results from the literature are used forthe justification of the results of this work. The results for bainitic transformation isfound to be in good agreement with both the literature and theoretical calculations usingLeblond`s model. On the other hand, experimentally determined value is found to besignificantly different from the literature. Nevertheless, it is still in reasonable agreementwith the calculations using Leblond`s model.
