Influence of tempered microstructures on the transformation behaviour of cold deformed and intercritically annealed medium carbon low alloy steel

Abstract

This research is focused on understanding the role of microstructural variables and processing parameters in obtaining optimised dual phase structures in medium carbon low alloy steels. Tempered Martensite structures produced at 300, 500, and 650 °C, were cold rolled to varied degrees ranging from 20 to 80% deformation. Intercritical annealing was then performed at 740, 760, and 780 °C for various time duration ranging from 60 seconds to 60 minutes before quenching in water. The transformation behaviour was studied with the aid of optical microscopy and hardness curves. From the results, it is observed that microstructural condition, deformation, and intercritical temperatures influenced the chronological order of the competing stress relaxation and decomposition phase reactions which interfered with the rate of the expected α → γ transformation. The three unique transformation trends observed are systematically analyzed. It was also observed that the 300 and 500 °C tempered initial microstructures were unsuitable for the production of dual structures with optimized strength characteristics.

Ferrite recrystallisation and intercritical annealing of cold-rolled low alloy medium carbon steel

“…There are few reports on the intercritical annealing of medium carbon steels [17][18][19][20][21][22][23][24]. Alaneme [17] studied the effect of tempered martensite microstructures on the transformation behaviour of cold deformed and intercritically annealed medium carbon low alloy steel with 0.3 wt-% C. Recovery processes, primary recrystallisation, intense spheroidisation, ferrite to austenite transformation, and grain growth were identified by hardness test.…”

“…There are few reports on the intercritical annealing of medium carbon steels [17][18][19][20][21][22][23][24]. Alaneme [17] studied the effect of tempered martensite microstructures on the transformation behaviour of cold deformed and intercritically annealed medium carbon low alloy steel with 0.3 wt-% C. Recovery processes, primary recrystallisation, intense spheroidisation, ferrite to austenite transformation, and grain growth were identified by hardness test. Using thermodynamics calculations and dilatometry, Erişir, and Bilir [18] investigated the phase transformations during quenching of a dualphase (DP) steel with 0.368 wt-% C, where the effects of chemical composition and grain size were taken into account.…”

“…Cold rolling and recrystallisation of intercritically annealed medium carbon steels has received less attention [17]. It should be noted that for low carbon steels, refining the pre-intercritical annealing microstructure has been shown to be very effective in the enhancement of the properties, especially via heat treatment [25][26][27][28][29][30], cold rolling followed by subcritical annealing [31,32], and intercritical annealing of cold-rolled sheet [33][34][35][36][37][38].…”