SOFTENING KINETICS DURING SUB-CRITICAL ANNEALING OF CERIUM MODIFIED STEEL

Abstract

Low carbon steel is generally alloyed with the other elements to obtain optimum mechanical properties along with high corrosion and oxidation resistance. Each alloying element has a different influence on the properties of steel. Frequently, transition elements (Nickel, Chromium, Manganese, Silicon, and Cobalt) are alloyed with steel due to some common chemical properties like high melting temperature, and large charge to radius ratio. On other hand, high affinity to oxidation of rare earth elements is generally added to the deoxidation and desulphurization of steel. Rare-earth elements have also the ability to form non-metallic inclusion with the impurities present in the steel. Merely alloying is not sufficient to achieve good properties of metallic material but apart from alloying, the processing of the material is also an important aspect. The batch annealing is an important part of the processing of material to get optimum properties. During annealing, different microstructure changes happened, like the formation of strain-free grain (recrystallization), and grain growth that leads to changes in the physical and sometimes chemical properties of the material to enhance the ductility and reduced the hardness to make it more workable. In this project, the Softening kinetics of 60% cold-rolled two Cerium (Ce) modified steel (0.6wt% Ce and 0.03wt% Ce) are named high cerium (HCe) steel and low Cerium steel (LCe) respectively, were studied during subcritical annealing with different annealing time. Optical Microscopy, scanning electron microscopy (SEM), and Electron Back-Scatter Diffraction (EBSD) were used to study the recrystallization process along with the role of different intermetallic precipitates during annealing and their effects on recrystallization kinetics of Ce modified steel. The static recrystallization behaviour of 60% cold-rolled Ce-steel for the 2-, 8- and 16-hours annealing time was studied. The microstructure of LCe steel is consist of ferrite, pearlite with a volume fraction of 6.2% and acicular ferrite. Whereas the HCe microstructure has only a ferrite phase apart from this there was cerium rich intermetallic inclusion also observed in both Cerium modified steels. These intermetallic phases influenced the recrystallization and softening process.