Microestrutural Evolution of Low-Carbon Bainitic Steel Submitted to Controlled Rolling Followed Accelerated Cooling

摘要

HSLA low-carbon (0,08 percent) bainitic steel containing Nb, V, Ti e B was submitted to controlled rolling followed by accelerated cooling. The influence of the cooling rate on the nature, amount and distribution of the phases and microconstituents that were formed was evaluated by optical microscopy, scanning electron microscopy, atomic force microscopy and Vickers hardness testing. Continuous cooling transformation diagram of this steel, determined by thermal analysis of the cooling curves from deformed austenite according to the 9-pass torsion test, was used to evaluate the formation of each phase. The final microstructure contains a complex mixture of granular bainite, small islands of MA constituent, bainitic ferrite, martensite and polygonal ferrite.