Austenite Formation in Plain Low-Carbon Steels

Abstract

In this study, austenite formation from hot-rolled (HR) and cold-rolled (CR) ferrite-pearlite structures in a plain low-carbon steel was investigated using dilation data and microstructural analysis. Different stages of microstructural evolution during heating of the HR and CR samples were investigated. These stages include austenite formation from pearlite colonies, ferrite-to-austenite transformation, and final carbide dissolution. In the CR samples, recrystallization of deformed ferrite and spheroidization of pearlite lamellae before transformation were evident at low heating rates. An increase in heating rate resulted in a delay in spheroidization of cementite lamellae and in recrystallization of ferrite grains in the CR steel. Furthermore, a morphological transition is observed during austenitization in both HR and CR samples with increasing heating rate. In HR samples, a change from blocky austenite grains to a fine network of these grains along ferrite grain boundaries occurs. In the CR samples, austenite formation changes from a random spatial distribution to a banded morphology.

Formation of Ultrafine Grained Dual Phase Steels through Rapid Heating

“…The volume fraction of austenite was determined via analyzing the dilatometric data employing the lever rule, details of which can be found elsewhere. 21) All microstructures were analyzed in the transverse plane of the rolled sheet, i.e. the through thickness plane perpendicular to the rolling direction.…”

Effect of heating rate on ferrite recrystallization and austenite formation of cold-roll dual phase steel

“…Mohanty et al [16] reported that higher heating rate results in relatively larger volume fraction of austenite in the range of lower intercritical temperatures. Azizi-Alizamini et al [17] investigated the austenite formation of hot-rolled and cold-rolled ferrite-pearlite structures. They showed that a delay in spheroidization of cementite lamellae and recrystallization of ferrite grains in the cold-rolled steel with increasing heating rates from 1°C/s to 900°C/s.…”

Grain-refining ability of ultra-rapid annealing for low-carbon steel: severe plastic deformation

“…It should be noted that the transformation of austenite to pearlite during cooling was accelerated by the small size of the austenite grains. 12,23,24 URA with a heating rate of 600°C/s up to 730°C does not show a homogeneous grain refinement. This microstructure ( Figure 5) consists of two-sized grains of 10 μm and 2 μm.…”

“…URA shifts the start temperature of recrystallization to higher values near and above Ac 1 . 3,[7][8][9][10][11][12][13][14][15] So, in the intercritical temperature range, recrystallization and phase transformation proceed concurrently and with a mutual "interaction". The intensity of the interaction depends of the amount of stored energy and determines the final microstructure of the steel.…”