Microstructure. Fig. 2 shows the lo

Microstructure. Fig. 2 shows the low-magnification optical micrograph of longitudinal andtransverse cracks of typical roll-cast strip. It can be seen that all the cracks including longitudinal and transverse crackswere initiated from the grain boundary, but the crack propagation directionwas different. For the transverse crack, the crack propagated granularly or inter-granularly asillustrated in Figs. 2 (a) and 2 (c). While, the longitudinal crack only propagated granularly asshown in Figs. 2 (b) and 2 (d). Besides, it was observed that the grain size near the crack was largerthan the normal region of processed strip. The obvious hightemperature oxide layer on the tip ortwo-sides of the crack indicated that the cracks were hot crack.