Effect of δ ferrite on impact property of hot-rolled 12Cr-Ni steel

The effect of delta ferrite (δ) on impact property of the 12Cr-Ni steel has been studied to some degree, but controversial literatures still exist. In order to clarify the effect of delta ferrite on toughness, volume fraction, the morphology and the degree of banding were taken into consideration. Three kinds of the 12Cr-Ni steels with slightly different chemical compositions were prepared in order to change the volume fraction of delta ferrite (δ). It was seen that toughness and the microhardness of martensite increase with increasing delta ferrite volume fraction, while the Brinell hardness decreases. The microhardness of delta ferrite seems to be little changed. The cleavage fracture area decreased with increasing test temperature and delta ferrite volume fraction. Charpy V-notch fracture toughness transition curves of the steels were determined. The impact energy of as-rolled plates increased, as the microstructural banding index decreased. From the 3D morphology of the delta ferrite (δ), possible effect of connections between bands was discussed.