Effect of Coiling Temperature on Kinetics of Austenite Formation in Cold Rolled Advanced High Strength Steels

Abstract

A systematic experimental investigation was conducted using lab processed low carbon 0.08C-2.0Mn-Cr-Mo steel microalloyed with Ti/Nb to evaluate the influence of initial hot-rolled microstructures on the kinetics of austenite formation and decomposition after cold-rolling and subsequent annealing. Coiling temperature as a major hot rolling parameter was used to obtain different types of hot-rolled microstructures. Dilatometer and continuous annealing simulator were employed for austenite formation studies and annealing simulations, respectively. It was found that the coiling temperature affects the processes occurring during heat treatment in continuous annealing lines of full hard material: ferrite recrystallization, austenite formation during continuous heating and austenite decomposition during cooling. A decrease in coiling temperature accelerates the recrystallization of ferrite and nucleation of austenite, which results in formation of refined ferrite-martensite structure. The effect of initial hot rolled structure on final mechanical properties after continuous annealing was also investigated.

Development of Desirable Fine Ferrite Grain Size and Random Second Phase Dual-Phase Steel Microstructures Using Composition and/or Processing Modifications

“…Therefore, a lower martensite volume fraction in the higher cold reduction samples for the slow heating rate conditions can be attributed to the stability of spheroidized cementite particles. This stability of spheroidized cementite particles and its associated sluggish austenite formation kinetics are well-reported in the literature [22,23]. However, due to lesser available time during faster heating rates, a higher amount of fragmented cementite particles is expected to be present during the recrystallisation process.…”