Role of Microstructural Constituents on Surface Crack Formation During Hot Rolling of Standard and Low Nickel Austenitic Stainless Steels

The effect of alloy segregation and delta (δ) ferrite contents on surface cracking of three standard (i.e. AISI 304L, AISI 310S and AISI 321) and two low nickel (i.e. LNi-1 and LNi-0.3) austenitic stainless steels (ASS) during hot rolling was investigated using optical microscopy (OM), automatic image analyzer, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and electron probe micro analyzer (EPMA). It was observed that the amount of δ-ferrite varied among different grades and also distributed heterogeneously across the width of the steel plates. In general, low nickel ASS showed higher amount of δ-ferrite compared to the standard ASS grades. The tendency to surface cracking during hot rolling gradually increased with increasing δ-ferrite content. Interestingly, carbon and nitrogen exerted maximum effect on δ-ferrite formation. The higher carbon and nitrogen content in the steel decreased δ-ferrite content. In addition, the segregation of Cu and Mn plays significant role in low nickel ASS and Ni-Cr in case of standard ASS has profound effect on surface cracking of the steel plates. A possible cause of surface crack formation/origination in steel plates during hot rolling was discussed.