Abstract
The kinetics of ferritic transformation and the corresponding microstructural evolution in 0.17C-3.1Mn-1.6Al-0.04Nb-0.22Mo-0.22Si medium-Mn steel during isothermal annealing was investigated in dilatometric studies. The material was subjected to thermal and thermo-mechanical treatments aimed at obtaining, by the austenite → ferrite transformation, a sufficient fraction of ferrite to stabilize the retained austenite by C and eventual Mn partitioning. The samples were isothermally held for 5 h in a temperature range from 600 to 750 °C to simulate simplified temperature conditions of an industrial coiling process following hot rolling. Some of the samples were plastically deformed at a temperature of 900 °C before isothermal holding in order to study the effect of hot deformation on the kinetics of phase transformations. After the dilatometric investigations the material was subjected to light and scanning electron microscopy to reveal relationships between the holding temperature, deformation and microstructure evolution. Hardness tests were performed to assess the mechanical behavior. A significant effect of manganese in slowing down diffusional transformations during the cooling of steel was found. The influence of austenite deformation on the kinetics of austenite to ferrite transformation was noted. The plastically deformed samples showed an accelerated start of ferritic transformation and the extension of its range. During dilatometric tests, low-range dynamic ferritic transformation was recorded, which was also confirmed by the microscopic tests.
Highlights
Medium-Mn steels containing 3–12% Mn, which show the Transformation-Induced-Plasticity effect (TRIP), are of great interest to wide-world researchers [1,2,3]
Inter-critical annealing (IA) [8,9,10] is currently the main heat treatment process, which allows the obtaining of the highest fraction of retained austenite in medium-Mn steels
It is based on the austenite reverted transformation (ART) process [11,12], which allows the producing of lath-like duplex microstructures
Summary
Medium-Mn steels containing 3–12% Mn, which show the Transformation-Induced-Plasticity effect (TRIP), are of great interest to wide-world researchers [1,2,3] Their advantage over conventional TRIP steels is the possibility of obtaining a retained austenite (RA) amount over 30% [4,5]. Inter-critical annealing (IA) [8,9,10] is currently the main heat treatment process, which allows the obtaining of the highest fraction of retained austenite in medium-Mn steels. It is based on the austenite reverted transformation (ART) process [11,12], which allows the producing of lath-like duplex microstructures. It is used both for hot-rolled [13,14,15] and cold-rolled [16,17] sheet steels
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