Novel formation of Ferrite in Ingot of 0Cr17Ni4Cu4Nb Stainless Steel

Abstract

The 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 the 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 the distribution and density of ferrite among zones of the surface, ½ radius, and core in neither the risers nor tails of 0Cr17Ni4Cu4Nb ingots. Additionally, fewer ferrites were found in 0Cr17Ni4Cu4Nb compared to other examined steels. The difference of ferrite formation in 0Cr17Ni4Cu4Nb elicited a debate on the traditional models explicating ferrite formation. Considering the compelling advantages in mechanical strength, plasticity, and corrosion resistance, further investigation on the unusual ferrite formation in 0Cr17Ni4Cu4Nb would help understand the mechanism to improve steel quality. In summary, we observed that ferrite formation in steel was correlated with the mushy zone temperature. The advantages of 0Crl7Ni4Cu4Nb in corrosion resistance and mechanical stability could be the result of fewer ferrites being formed and distributed in a scattered manner in the microstructure of the steel.