Case study of severe strip breakage in rolling mill of Thin Slab Casting and Rolling (TSCR) shop of TATA Steel, Jamshedpur

• A case of severe strip breakage during hot rolling in Thin Slab Caster and Rolling (TSCR) unit has been investigated.
• White stringer like defects and holes are observed in the vicinity of the breakage location in the strip.
• Metallurgical investigation reveals heavy amount of foreign material in form of secondary steelmaking slag at the breakage location.
• The foreign materials entrapped in slab get fully exposed during hot rolling and lead to discontinuities on the surface.
• It is understood that the heavy amount of un-deformable foreign inclusions would have caused splitting of the strip during rolling.

In this paper, a case of severe strip breakage in rolling mill of Thin Slab Casting and Rolling (TSCR) shop of TATA Steel, Jamshedpur is presented. Visual observation revealed complete splitting with material missing along the central axis of the strip. Presence of defects in form of white stringers, white patches and holes were observed along the same axis just ahead of split location. Metallurgical analysis revealed association of these defects with slag type foreign materials in the rolled strip. The entrapments of un-deformable materials like slag in slab resulted in the formation of surface discontinuities on the strip on account of differential rolling. The discontinuities manifested in form of holes at lower strip thickness in the later stands of the mill. Inhomogeneous deformation about such holes also resulted in material overlapping. In summary, the breakage of the strip was found to have a strong correlation with the presence of heavy chunk of foreign inclusions from secondary steelmaking sources.