Abstract
	The influence of cold deformation after primary heat treatment, annealing after cold deformation, and influence of thermal expositions at temperatures 580, 620, and 650 °C for times from 100 to 5000 h on impact toughness and fracture mode of the P91 steel after impact failure at ambient temperature were investigated. The results were analyzed from the viewpoint of the influence of (I) cold deformation after primary heat treatment, (II) annealing after cold deformation, and (III) isothermal exposition on the impact toughness values (KCV) at ambient temperature. The highest impact toughness have the states with deformation of 20 % and annealing regardless the exposition time and temperature. The states with deformation of 29 % with or without annealing reached the KCV values of the same range. Material without deformation and annealing has the lower impact toughness than the primary state. Exposure induces decrease of impact toughness at ambient temperature regardless the samples were annealed to decrease internal strain after cold deformation. After exposition for 1000 h, the higher exposition temperature, the higher impact toughness. The impact toughness of undeformed states after 1000 h of exposition decreases with increasing exposition temperature. Cold deformation up to 30 % before exposure influenced an impact toughness (increased KCV values) in the beginning of exploitation only, where the additional secondary phases precipitation occurs. All states of the P1 steel with a thermal-deformation history were fractured by ductile transgranular fracture with dimple morphology.