Plastic behavior of medium carbon vanadium microalloyed steel at temperatures near gamma <-> alpha transformation

Abstract

Dilatometric techniques were used to build the continuous cooling transformation (CCT) diagramfor amediumcarbonmicroalloyed steel; themicrostructure and hardnesswere determined at different cooling rates. The mechanical behavior of the steel in the austenite field and at temperatures approaching austenite to ferrite transformationwas measured by means of hot torsion tests under isothermal and continuous cooling conditions. The no recrystallization temperatures, Tnr, and start of phase transformation, Ar3, were determined under continuous cooling condition usingmeanflow stress vs. inverse of absolute temperature diagrams. Interruption of static recrys- tallization within the interpass time in the austenite field indicated that the start of vanadium carbonitride precipitation occurred under 860 C. Austenite transformation was found to start at around 710 C, a temperature similar to that measured by dilatometry, suggesting that interphase precipitation delays the transformation of deformed austenite. Pearlitewas observed at temperatures ranging from 650 C to 600 C, with the flow curves taking on a particular shape, i.e., stress rose sharply as strain was increased, reaching peak stress at low deformation, around 0.2, followed by an extensive softening region after peak stress.