Continuous Cooling Transformation Temperatures and Microstructures of Niobium Bearing Microalloyed Steels

摘要

Effects of niobium content and cooling rate on ferrite and bainite start temperatures (Ar3, Bs) and the microstructural features have been studied in niobium bearing ultralow carbon microalloyed steels. The Ar3 and Bs temperatures decrease as the niobium content or cooling rate is increased. The dependence of Ar3 on cooling rate is greater than that of Bs in all niobium contents.The bainitic ferrite laths become longer and narrower as the niobium content or cooling rate is increased, and the niobium also shows a tendency to decrease the polygonal ferrite grain size.