Effect of MnS inclusion and crystallographic texture on anisotropy in Charpy impact toughness of low carbon ferritic steel

The combined effect of microstructure and crystallographic texture on the anisotropy in Charpy impact toughness has been studied in two hot-rolled low-carbon steel plates having different sulphur contents: 0.03 wt% S in high-sulphur, HS, steel and 0.01 wt% S in low-sulphur, LS, steel. Sub-size Charpy impact specimens were prepared from the rolled plates along 0 degrees, 30 degrees, 60 degrees and 90 degrees to the rolling direction and tested over the temperature range of +40 degrees C to -196 degrees C. Microstructure, inclusions and crystallographic texture have been characterized on the plane parallel to the fracture plane of each sample. The variation in upper shelf energy (USE) was more severe (similar to 69%) in HS steel due to the presence of coarse and elongated MnS inclusions. Crystallographic texture, especially, higher fraction of alpha- to gamma-fibre texture and stronger cube texture resulted in stronger variation in ductile to brittle transition temperature (DBTT) in LS steel (by similar to 26 degrees C). Increase in the fraction of {001} planes of the crystals on the fracture plane of the sample increased the DBTT by helping the cleavage crack propagation. On the other hand, increase in the fraction of {110} planes of the crystals on the shear planes (inclined at 45 degrees to fracture plane) increased the USE by promoting the plastic deformation. (C) 2015 Elsevier B.V. All rights reserved.