Alloying effect on the microstructure and mechanical properties of hot-rolled Fe-C-Mn-Si base TRIP steels (part I); Microstructure and mechanical properties

摘要

The present study is aimed at developing the highstrength, high formability low alloy steels having retained austeniteas one of the constituents. The main emphasis has been put onunderstanding the effects of processing variables and alloyingelements (Cu, Nb) on the microstructure and mechanicalproperties of hot-rolled Fe-C-Mn-Si base TRIP (TransformationInduced Plasticity) steels. Experimental results show thatmicrostructure of hot-rolled alloys consists of ferrite, bainite,martensite and retained austenite, whose volume fraction andmorphology vary depending on the hot-rolling conditions and alloycompositions. The increase in the quench-finish temperatureresults in a homogeneous distribution of fine granular particles ofretained austenite and hard second phases in a ferrite matrix andaccordingly a good combination of strength and ductility The Cu-containing alloy has been found to improve mechanical propertiesover the base alloy due to the precipitation of fine ε-Cu in ferritegrains. Nb addition increases the dynamic recrystallizationtemperature of austenite, resulting in the formation of coarse pan-caked bainite packets. Based on these results, the optimummicrostructure for a better combination of strength and ductility issuggested to be the one having granular particles of retainedaustenite and hard phase (martensite or bainite) in a fine ferrite matrix.