FeNbP in ultra-low carbon Nb-added steel containing high P

Precipitation of FeTIP is reported to occur in TI-added IF steels containing high P during thermomechanical processing. An ultra-low carbon (ULC) Nb-added steel ingot containing a higher P content (<0.8 wt-%) was produced via aluminothermic reduction of Fe2O3 followed by double electron beam melting (EBM). FeNbP coarse precipitates were observed in the as-cast microstructure. After soaking at 1050°C for 1 h, the plate was hot-rolled from 31 mm down to 7 mm in thickness (total reduction of 77%). During cold rolling of these hot bands we oberved embrittlement. We believe that this embrittlement can be attributed to the presence of the FeNbP precipitates. Light optical and scanning electron microscopy (SEM/EDS) were used to characterize the microstructure of this ULC steel.