Bizarreness of Ferrite Formation in Ingot of 0Cr17Ni4Cu4Nb Stainless Steel

Ferrite body is the origin of crack and corrosion initiation of steels. Distribution and density of ferrite in seven steel ingots were examined by light optical microscopy and computational modeling in the study to explore the correlation of ferrite formation to chemical composition and mushy zone temperature in ingot forming. The central segregation phenomenon in ferrite distribution was observed in all the examined steel specimens except 0Cr17Ni4Cu4Nb stainless steel. No significant difference was found in distribution and density of ferrite amongst zones of the surface, ½ radius and core in neither riser nor tail of 0Cr17Ni4Cu4Nb ingot. Additionally, fewer ferrite was found in 0Cr17Ni4Cu4Nb compared to other examined steels. The bizarreness of ferrite formation observed in 0Cr17Ni4Cu4Nb elicited a debate on the traditional concepts explicating ferrite formation. Considering the compelling advantage in the mechanical strength, plasticity and corrosion resistance, further investigation on the unusual ferrite forming occurrence in 0Cr17Ni4Cu4Nb would help develop steels with improved quality. In summary, we observed that ferrite formation was correlated to mushy zone temperature, Cr:Fe and Cu:Fe ratios. We originally assume that Fe, the major component of steel could play an unrecognized role via proportion to other chemical components in ferrite formation.