Correlation between microstructure and mechanical properties of heat affected zones in Fe-8Mn-0.06C steel welds

This study presents the mechanical properties of Fe-8Mn-0.06C steel welds, and examines local brittle zones in the heat affected zones of these steels. The microstructure of the base metal was composed primarily of lath martensite and a small amount of retained austenite. Mn segregation was also found along the thickness direction due to the banded structure of the rolled base metal. A significant local brittle zone (coarsened grained heat affected zone) and local hardness drop zone (subcritical heat affected zone) were observed in the weld heat affected zone. The Vickers hardness distribution measured from the weld metal to the base metal and Charpy V-notch toughness results revealed that decreases in hardness and toughness were more pronounced in the coarsened grained heat affected zone than in the fine-grained heat affected zone. A decrease in hardness was noticeable in the subcritical heat affected zone. The increases in hardness and toughness in the fine-grained heat affected zone relative to that of the coarsened grained heat affected zone were expected, due to the smaller martensite packet and block sizes. Further, the noticeable decrease in mechanical properties of the subcritical heat affected zone was strongly related to the formation of the austenite.