| The effects of martensite morphology on the quasi-static and dynamic deformation behavior of dual phase steels were investigated in this study. Quasi-static and dynamic torsional tests were conducted using a torsional Kolsky bar for four steel specimens, which had different martensite morphologies and volume fractions, and then the test data were compared via microstructures, tensile properties, and fracture mode. In the intermediate quenched (IQ) steel specimens, very fine fibrous martensites were well distributed in the ferrite matrix, whereas bulk martensites were mixed with ferrite grains in the step quenched (SQ) specimens. The quasi-static torsional properties were similar to tensile properties, and in IQ-specimens, fracture occurred in a ductile mode whereas cleavage fracture were predominated in SQ-specimens. Under a dynamic loading condition, the fracture mode of SQ-specimens was changed from cleavage to ductile fracture, whereas IQ-specimens had a ductile fracture mode, irrespective of loading rate. This phenomena were analyzed using a shear lag model, phase continuity, and thermal softening effect of the martensite. |
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