ERİŞİR Ersoy University of Kocaeli

Spoluautoři GÜMÜŞ Serap, BILIR Oğuz Gürkan

Multi-phase microstructure gain importance increasingly in new generation steels. Dual phase (DP) steels can be produced by the quenching from a temperature in intercritical temperatures in the phase region of austenite and ferrite. The final microstructure is composed of martensite and ferrite. Microstructure before the annealing at intercritical temperature can include martensite, ferrite, pearlite or austenite. The initial microstructure affects the final morphology strongly and the annealing temperature affects the amount of ferrite and martensite phases. Thus, the mechanical properties of dual phase steel depend on the morphology and phase distribution. In the intermediate quenching method, the initial microstructure is fully martensitic and final microstructure is fine and randomly scattered at former martensite boundaries in a ferritic matrix. Morphology of ferritic matrix can be acicular ferrite. There are some difficulties in selecting the correct etching solutions to obtain a sharply different contrast for the microstructure like this. On this study, hot rolled medium carbon steel was employed and intermediate quenching method was applied and microstructure showed randomly distributed martensite laths in acicular ferritic matrix. On the other hand, not only martensite and ferrite but also retained austenite, bainite, pearlite were observed. There are difficulties in distinguishing the different phases. The work presented here demonstrates the effect of the different etchings on the microstructural contrast. Nital and La Pera solutions were applied and light microscope, scanning electron microscope and microhardness tests were carried out observing the microstructures. The La Pera etchant was more effective to distinguish the martensite and ferrite. On the other hand, distinguishing the bainite, retained austenite and pearlite from martensite, same etchant was not favorable.

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