Analysis of Cold Forming Surface Crack of High-Strength Low-Alloyed Steel Produced by TSCR Process

Surface cracking is commonly observed during cold forming or bending of hot-rolled (HR) strips. The present study is an investigation to ascertain the root cause of such defects mostly manifested in the subsurface of thick gauge strips. SEM-EDS analysis revealed the debris entrapped in these cracks to be enriched with iron oxides. Since surface cracks with entrapment of iron oxides are hardly observed in HR strip coils produced by thin slab casting and rolling (TSCR); a combination of literature review and extensive characterization was carried out to understand the reasons for entrapment of iron oxides in the observed subsurface cracks. The key inference drawn from this study is that the subsurface cracks with entrapped iron oxides originate during the solidification stage at the caster such as longitudinal facial crack (LFC) and groove formation on slab surface due to caster process and machine condition, respectively. Hence, this article presents detailed metallurgical investigation of a surface crack generated during 90 degrees bending operation of 10 mm thick steel plate of IS5986: ISH500LA standard grade with an objective to suggest countermeasure for the same.