Pancakes Research Paper

3. RESULTS AND DISCUSSION
Typical photograph of pancakes of all the three lightweight steels based on Fe-7Al are shown in Fig. 1. All the three steel pancakes exhibit excellent surface finish. It is seen that the yield of the pancake is greater than 99% (Table 1). Radiography of all the pancakes indicated that they were sound and free from internal defects such as cracks and porosity. The nominal composition and chemical analysis of the pancakes of three steels is given in Table 2. The macrostructure of all the three steel pancakes are shown in Fig. 2. It is clear from the figure that in all the three steel pancakes columnar grains are seen running almost parallel to ingot axis indicating directional solidification. During the non-consumable

5. The SEM EDAX analysis of matrix and particles as well EPMA line scan of hot rolled and annealed pancakes of all the three steels are shown in Fig, 6 to 9. The back scattered images of SEM revealed the presence of bright particles in Steel 2 and dark particles in Steel 3, whereas no such phase was observed in Steel 1 (Fig 5). These particles are distributed uniformly throughout the matrix in Steel 2 and 3. SEM, EDAX analysis revealed no obvious presence of Zr in the matrix of Steel 2 (Fig. 6c) and Ti in the matrix of Steel 3 (Fig.8c). The bright particles in Steel 2 and dark particles in Steel 3 were confirmed to be rich in Zr and Ti respectively (Figs 6b and 8b). EPMA line scan of bright particles in Steel 2 and dark particles in Steel 3 also indicates that, they are rich in Zr and Ti respectively (Figs 7 and 9). The chemical analysis of Steel 2 and 3 shows presence of 0.37Zr and 0.09B in Steel 2 and 0.34Ti and 0.14B in Steel 2 (Table 2) respectively. Based on the above facts, dark particles present in Steel 2 and bright particles in Steel 3 may probably be identified as zirconium diboride (ZrB2) and titanium diboride (TiB2) respectively. These ZrB2 and TiB2 particles were not observed in optical micrographs as the size of precipitates is too small to be resolved by optical microscope. The XRD traces using of (a) Fe-7Al steel, (b)

It can be observed from the table that the hardness of Steel 2 and 3 are marginally higher than the hardness values of the base steel (Steel 1) (Table 4). Table 4 also summarizes the room temperature tensile properties of hot rolled and annealed pancakes. The engineering and true stress-strain curves of all the three lightweight steels based on Fe-7Al are presented in Fig 11. It can be seen from the Table 4 and Fig 11 that the marginal improvement in tensile strength was observed by addition of ZrB2 and TiB2 to the lightweight steels based on Fe-7Al. Addition of both ZrB2 and TiB2 resulted in significant improvement in room temperature ductility. Addition of ZrB2 has resulted in about 63% improvement in room temperature ductility, whereas addition of TiB2 has resulted in about 100 % improvement in room temperature ductility. The steel containing TiB2 also exhibits higher uniform elongation as compared to the steel containing ZrB2. This improvement in room temperature ductility may be attributed to significant reduction in the grain size (Table 3). Addition of ZrB2 and TiB2 resulted in improvement in strain hardening exponent (n). This is reflected in their low yield ratio (Table 4). The yield ratio increases with addition of ZrB2 and