Observation of inclusions and intra-granular ferrite evolutions at the HAZ of low-carbon steel with different thermal histories

Abstract

This study investigated the formation and growth of intra-granular ferrite with inclusions (TiN, MnS) in the heat-affected zone (HAZ) of a welding joint in low-carbon steels. The relationship between the cooling rate and the density and size of inclusions was analyzed. An orientation relationship akin to the Baker–Nutting relationship was identified between TiN and ferrite, while the orientation relationship between MnS and ferrite approximated the Kurdjumov–Sachs relationship. At low cooling rates, in the absence of nucleation support from TiN and MnS inclusions, the microstructure in the HAZ comprised Widmanstätten ferrite. Additionally, the shape, size, and density of primary ferrites and Widmanstätten ferrite in steels were influenced by sulfur content.

Keywords

• intra-granular ferrite
• bainite
• inclusion
• transmission electron microscopy (TEM)
• orientation relationship