Influence of aluminium on retained austenite stabilization during thermomechanical treatment of low-alloyed TRIP steel

Abstract

TRIP steels are multiphase steels. At present, they find their use primarily in the automotive industry, where they are most frequently utilized for manufacturing body panels. The thin-walled hollow semi-products obtained by thermomechanical treatment could represent new possible applications. In standard TRIP steels cementite precipitation during bainitic transformation and retained austenite stabilization are carried out mainly through silicon alloying. Silicon at higher concentrations causes problems with surface quality in some applications. One of the alloying elements being taken into consideration for silicon replacement is aluminium, whose addition not only restricts carbide and pearlite formation during bainitic transformation, but also increases formation of acicular ferrite. A lower value of solid solution hardening and the increase of the Ms temperature represent the disadvantages of aluminium addition. Thermomechanical treatment with various parameters of bainitic transformation was investigated on the 0.26C-1.5Mn-1.3Al steel with the aim of determining how aluminium affects structure development, retained austenite stabilization and mechanical properties. Experimentally achieved structures were analyzed by means of light and confocal microscopy. The fraction of ferrite and retained austenite as well as the size of ferritic grains were determined via image analysis.