S. Gholami Shiri - Department of materials science and engineering, school of engineering, Shiraz University, Shiraz, Iran
Y. Palizdar - Nanotechnology and Advanced Materials Department, Materials and Energy Research Center, Karaj, Iran
A. Jenabali Jahromi - Department of materials science and engineering, school of engineering, Shiraz University, Shiraz, Iran
F. de Monlevade - Department of Metallurgical and Materials Engineering, Polytechnic School, University of São Paulo, São Paulo, Brazil

The relation between microstructure and the fracture mechanisms of δ-TRIP steel with different Nb-content has been investigated using complementary methods of light microscopy, SEM, EDS, EBSD, X-ray phase analysis and tensile test. The results revealed a close dependency between the presences of constitutive phases i.e. ferrite, bainite, retained austenite and martensite and the mode and characteristics of fracture. All samples revealed almost different fractography pattern which could be associated to the effect of Nb microalloying element. The different fractography patterns were consisted of dimple rupture, riverside and Wallner lines pattern. The proportion of the cleavage fracture in comparison of dimple rapture increased by increasing the Nb-content due to the increase of primary martensite in the microstructure.

δ-TRIP steel, High Al steel, Fracture mode, Fractography, Nb-microalloyed