Enhancement of impact toughness on warm forged microalloyed steel-38MnSiVS6

The effect of warm forging in the inter-critical temperature range between 705 and 844°C, in improving the impact toughness of an industrially important micro alloyed steel, 38MnSiVS6 was investigated. The impact properties were enhanced to as high as 148 J after warm forging in the inter critical range, as against 19 J in the steel hot rolled from 1200°C and air cooled. In addition, the strength was enhanced by about 100 MPa after warm forging. The microstructure evolution that led to the improved toughness and strength was analyzed. The significantly enhanced toughness with moderate strength enhancement in warm deformation is attributed to the increases in the ferrite content, finer ferrite grain size, finer pearlite colonies and finer interlamellar spacing. The fractography of the impact test samples in hot deformed and air-cooled condition shows poor toughness associated with cleavage facets, while the warm forged steel, showed fine dimple rupture.