SOME STUDIES ON THE IMPACT BEHAVIOR OF BANDED MICROALLOYED STEEL

Microalloyed steels are used in automobile industries, offshore platfo rms and in structural applications. It is essential to establish a rel ation between service condition such as temperature, loading rate and fracture behavior of the steel. Impact study on new material is very h andy to understand the mechanical properties in a rapid and inexpensiv e way. The present investigation aims to assess impact toughness (CVN) , ductile brittle transition temperature (DBTT, 25J), and initiation d ynamic fracture toughness (J(id)) of the indigenously developed micro alloyed steel. The steel has shown banding with alternate layers of fe rrite and pearlite. The banding concentration (ferrite bands per mm) h as been altered by heat treatment. Presence of banding has given spike s and splits in impact fracture. Change in banding concentration has a ffected DBTT of the steel, upper shelf energy and the extent of splitt ing. A model of crack divider with respect to the present microstructu re has been analyzed. Banding in divider orientation improves the impa ct as well as initiation dynamic fracture toughness of the steel. The effect of temperature on splitting is also discussed. Splits in fractu red surface disappear with decreasing temperature and higher numbers o f splits yield lower toughness. Further, initiation dynamic fracture t oughness is calculated for all temperatures and correlated with impact toughness.