Analysis and prevention of vertical cracking phenomena during deep drawing of hot-rolled SG295 steel strips

Abstract

Microscopic examination and microstructural analysis of vertical cracking phenomena in deep-drawn cups of hot-rolled SG295 steel strips were carried out in this study. Microvoids initiated preferentially at grain-boundary carbides were observed to form intergranular cracks. These grain-boundary carbides were identified as (Fe,Mn)(3)C carbides. The morphology of carbides was varied with processing variables, e.g., killing method and coiling temperature. In the Al-killed steels, the carbide shape tends to change from film type to bulk type, which may be beneficial to elongation and consequently formability. In addition, as the coiling temperature increased, the amount of banded pearlite structures and bulk-type carbides increased. These findings suggest that the deep drawability can be improved by modifying the carbide morphology in the microstructures.